JP7686979B2 - Acrylic rubber with excellent Banbury processability, storage stability and water resistance - Google Patents

Description

The present invention relates to an acrylic rubber and a manufacturing method thereof, a rubber composition, and a cross-linked rubber product, and more specifically, to an acrylic rubber having excellent Banbury processability, storage stability, and water resistance and a manufacturing method thereof, a cross-linkable rubber composition containing the acrylic rubber, and a cross-linked rubber product obtained by cross-linking the acrylic rubber.

Acrylic rubber is a polymer whose main component is acrylic ester, and is generally known for its excellent heat resistance, oil resistance, and ozone resistance, and is widely used in fields such as automobiles.

For example, Patent Document 1 (JP Patent Publication 1999-12427 A) describes a monomer component containing 100 parts of ethyl acrylate, butyl acrylate, methoxyethyl acrylate, acrylonitrile, and a monomer that introduces a carbon-carbon double bond into the side chain, such as allyl methacrylate or cyclopentenyloxyethyl acrylate, 4 parts of sodium lauryl sulfate, 0.25 parts of p-menthane hydroperoxide as an organic radical generator, 0.01 parts of ferrous sulfate, 0.025 parts of sodium ethylenediaminetetraacetate, sodium formaldehyde sulfonate, and 10 parts of ethyl acrylate. The paper discloses an acrylic rubber and crosslinked composition that has excellent extrusion processability and scorch properties, which is obtained by adding 0.04 parts of dimethyl sulfoxylate and 0.01 to 0.05 parts of t-dodecyl mercaptan as a chain transfer agent to a nitrogen-substituted autoclave, reacting at a reaction temperature of 30°C until the conversion rate of the monomer mixture reaches 100%, coagulating the resulting latex by adding it to a 0.25% aqueous calcium chloride solution, thoroughly washing the coagulated product with water, drying at about 90°C for 3 hours, and crosslinking with an organic peroxide such as 1,3-bis(t-butylperoxyisopropyl)benzene. However, the acrylic rubber obtained by this method has problems such as insufficient Banbury processability and roll processability, and poor storage stability, compression set resistance, water resistance, and strength properties.

In addition, Patent Document 2 (JP Patent Publication 5-86137A) discloses a method for producing acrylic rubber in which polymerization is initiated with an organic radical generator and a chain transfer agent is added to a monomer emulsion and continuously administered. Specifically, one-fifth of a mixture of a monomer mixture containing 2-(cyanoethoxy)ethyl acrylate, ethyl acrylate, n-butyl acrylate, and crosslinkable monomers such as vinyl chloroacetate and allyl glycidyl ether and an appropriate amount of n-dodecyl mercaptan is mixed and stirred with one-half of 1 part by weight of polyoxyethylene lauryl ether, 4 parts by weight of sodium lauryl sulfate, 0.7 parts by weight of disodium hydrogen phosphate, and 0.3 parts by weight of sodium dihydrogen phosphate to form an emulsion, which is then cooled to 15°C and then mixed with sodium ethylenediaminetetraacetate. 0.005 parts by weight of thorium iron (II), 0.02 parts by weight of tetrasodium ethylenediaminetetraacetate, 0.02 parts by weight of Rongalite, and 0.02 parts by weight of sodium hydrosulfite are added, and a 0.2% by weight aqueous solution of tert-butyl hydroperoxide, an organic radical generator, is dropped at a rate of 1.5 parts per hour to start polymerization. While maintaining the temperature at 15°C, an emulsion consisting of a mixture of the remaining monomers and n-dodecyl mercaptan and an aqueous solution of an emulsifier is dropped over 3 hours to carry out the polymerization reaction until the monomer conversion rate reaches 96 to 99%. It is also described that the obtained copolymer latex is put into an aqueous calcium chloride solution at 85°C to isolate the copolymer, which is thoroughly washed and then dried to obtain the desired copolymer rubber, which is then crosslinked with sulfur. However, the acrylic rubber obtained by this method has problems such as insufficient Banbury processability and roll processability, and also poor storage stability, water resistance, and strength properties.

In addition, Patent Document 3 (International Publication No. WO 2019/188709) discloses a method for producing acrylic rubber by feeding monomer components consisting of ethyl acrylate, butyl acrylate, methoxyethyl acrylate, and monobutyl fumarate, water, and sodium lauryl sulfate, repeatedly degassing under reduced pressure and replacing with nitrogen, and then adding sodium aldehyde sulfoxylate and cumene hydroperoxide, an organic radical generator, to initiate emulsion polymerization at normal pressure and temperature, and continuing the emulsion polymerization until the polymerization conversion rate reaches 95% by weight. The resulting mixture is then coagulated with an aqueous calcium chloride solution and dehydrated and dried in an extrusion dryer having a screw. However, the acrylic rubber obtained by this method has problems such as poor Banbury processability, roll processability, storage stability, and water resistance.

Furthermore, Patent Document 4 (International Publication No. WO 2018/117037) discloses a method for producing acrylic rubber by adding monomer components consisting of ethyl acrylate and mono-n-butyl fumarate, water, and sodium dodecyl sulfate, and then performing vacuum degassing and nitrogen replacement three times to thoroughly remove oxygen, and then adding organic radical generators azobis(isobutyronitrile) and ethyl-2-methyl-2-phenyltellanylpropionate to initiate a polymerization reaction at normal pressure and a temperature of 50 degrees, and performing polymerization until a polymerization conversion rate of 89% is reached. The resulting product is then coagulated with a calcium chloride solution, washed with water, and dried. However, the acrylic rubber obtained by this method has problems such as poor Banbury processability, roll processability, storage stability, and water resistance.

On the other hand, as a method for producing acrylic rubber using an inorganic radical generator, for example, Patent Document 5 (JP 2019-119772 A) describes a method for preparing a monomer emulsion from monomer components consisting of ethyl acrylate, butyl acrylate, methoxyethyl acrylate, and monobutyl maleate using pure water and emulsifiers such as sodium lauryl sulfate and polyoxyethylene dodecyl ether, and then pouring a portion of the monomer emulsion into a polymerization reaction tank and cooling it to 12°C under a nitrogen gas flow, and then adding the remaining monomer emulsion, ferrous sulfate, sodium ascorbate, and inorganic The method disclosed is to continuously drop an aqueous solution of potassium persulfate as a radical generator over a period of 3 hours, continue emulsion polymerization for 1 hour while maintaining the temperature at 23°C until the polymerization conversion reaches 97% by weight, and then continuously add sodium sulfate to obtain hydrous crumbs, which are solidified and filtered off, washed with water 4 times, acid washed once, and pure water once, and then continuously produce sheet-shaped acrylic rubber in an extrusion dryer with a screw, and crosslink with an aliphatic polyamine compound such as hexamethylenediamine carbamate. However, the sheet-shaped acrylic rubber obtained by this method has problems such as poor storage stability and poor water resistance of the crosslinked product.

Patent document 6 (JP Patent Publication 1-135811) discloses a method in which 1/4 of a monomer mixture consisting of monomer components consisting of ethyl acrylate, caprolactone-added acrylic ester, cyanoethyl acrylate, and vinyl chloroacetate, and n-dodecyl mercaptan as a chain transfer agent, is emulsified with sodium lauryl sulfate, polyethylene glycol nonylphenyl ether, and distilled water, sodium sulfite and ammonium persulfate as an inorganic radical generator are added to initiate polymerization, the remaining monomer mixture and a 2% aqueous solution of ammonium persulfate are added dropwise for 2 hours while maintaining the temperature at 60°C, and polymerization is continued for another 2 hours after the addition, resulting in a latex with a polymerization conversion rate of 96 to 99%, which is then poured into an aqueous sodium chloride solution at 80°C to coagulate, thoroughly washed with water, and dried to produce an acrylic rubber, which is then crosslinked with sulfur. However, the acrylic rubber obtained by this method has problems such as insufficient Banbury processability and poor storage stability and water resistance.

Patent Document 7 (JP-A-62-64809) discloses a sulfur-vulcanizable acrylic rubber which is a copolymer having a monomer composition consisting of 50 to 99.9% by weight of at least one compound selected from acrylic acid alkyl esters and acrylic acid alkoxyalkyl esters, 0.1 to 20% by weight of a dihydrodicyclopentenyl group-containing ester of an unsaturated carboxylic acid, and 0 to 20% by weight of at least one other monovinyl-, monovinylidene-, and monovinylene-based unsaturated compound, and which has a number average molecular weight (Mn) of 200,000 to 1,200,000 calculated as polystyrene using tetrahydrofuran as a developing solvent, and a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 10 or less. As a specific example, there is disclosed an acrylic rubber having a number average molecular weight (Mn) of 530,000 to 1,150,000, a weight average molecular weight (Mw) of 3,540,000 to 6,260,000, and a ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 4.7 to 8, which is obtained by adding varying amounts of monomer components including ethyl acrylate and radical crosslinkable dihydrodicyclopentenyl acrylate, sodium lauryl sulfate as an emulsifier, potassium persulfate as an inorganic radical generator, and octyl thioglycolate and t-dodecyl mercaptan as molecular weight regulators. In addition, when the amount of the chain transfer agent is small, the number average molecular weight (Mw) is large at 5 million, and the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is narrow at 1.4, and when the amount of the chain transfer agent is large, the number average molecular weight (Mn) is small at 200,000, and the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is extremely wide at 17. However, the acrylic rubber obtained by this method has a problem that Banbury processability and roll processability are insufficient, and in the crosslinking reaction, after adding sulfur as a crosslinking agent and a vulcanization accelerator and kneading with a roll, long crosslinking is required at 170°C for 15 minutes in a vulcanization press of 100 kg/ ^cm2 and further at 175°C for 4 hours in a gear oven, and further, the obtained crosslinked product has problems such as poor water resistance, compression set resistance and strength properties, and poor changes in physical properties after thermal degradation.

Japanese Patent Application Publication No. 11-12427 JP 2019-119772 A International Publication No. 2019/188709 International Publication No. 2018/117037 JP 2019-119772 A Japanese Unexamined Patent Publication No. 1-135811 Japanese Unexamined Patent Publication No. 62-64809

The present invention has been made in consideration of the current state of the prior art, and aims to provide an acrylic rubber that is excellent in Banbury processability, storage stability, and water resistance, a method for producing the same, a crosslinkable rubber composition that contains the acrylic rubber, and a crosslinked rubber product obtained by crosslinking the same.

As a result of intensive research conducted in consideration of the above problems, the inventors have discovered that an acrylic rubber that contains a specific amount of reactive groups that react with a crosslinking agent, etc., and has specific gel amount, pH, ash content, ash component content, and specific gravity of a specific solvent-insoluble portion, has excellent and highly balanced Banbury processability, storage stability, and water resistance.

The inventors have also found that the amount of gel in the acrylic rubber, particularly the amount of gel that is insoluble in the specific solvent, has a large effect on Banbury processability. The amount of insoluble (gel) in the specific solvent of the acrylic rubber is generated during emulsion polymerization of the acrylic rubber, and increases rapidly, particularly when the polymerization conversion rate is increased in an attempt to improve strength properties, making it difficult to control during polymerization. However, the presence of a chain transfer agent at the end of the emulsion polymerization can improve this to some extent, and the inventors have found that the rapidly increasing amount of gel that is insoluble in the specific solvent disappears when the water-containing crumbs generated by solidification are melt-kneaded and dried in a screw-type twin-screw extrusion dryer in a state that is substantially free of water (water content less than 1% by weight), making it possible to produce an acrylic rubber with significantly better Banbury processability.

The inventors have also found that the storage stability is greatly affected by the specific gravity of the acrylic rubber. Although the specific gravity of the acrylic rubber itself is high, it entraps air during production. In particular, acrylic rubbers having reactive groups such as carboxyl groups, epoxy groups, or chlorine atoms are sticky and have a high affinity with air, making it difficult to remove air once it has been entrapped. However, they have found that by baling the rubber in a high-pressure baler, the specific gravity can be increased even slightly, improving the storage stability, and that by extruding sheet-like acrylic rubber that does not contain air using a screw-type twin-screw extrusion dryer under reduced pressure, it is possible to produce acrylic rubber that contains almost no air, has a high specific gravity, and has significantly better storage stability. The inventors have also found that the storage stability of acrylic rubber is greatly affected by the pH of the acrylic rubber, and that the storage stability can be improved by lowering the pH.

The inventors have also discovered that the amount of ash and ash components in acrylic rubber have a large effect on water resistance. The amount of ash in acrylic rubber is difficult to reduce due to the manufacturing method that uses a large amount of emulsifiers and coagulants, but they have discovered that the water-containing crumbs produced by a specific coagulation method have significantly higher washing efficiency with hot water and ash removal rate during spin-drying, making it possible to reduce the amount of ash in acrylic rubber by a large margin and significantly improve water resistance.

The inventors have also discovered that when the reactive group is a carboxyl group, epoxy group, or chlorine atom that reacts with a crosslinking agent, or is an ionic reactive group, and in particular when the reactive group content in the acrylic rubber is within a specific range, the acrylic rubber is excellent in Banbury processability, storage stability, and water resistance, and is also highly excellent in compression set resistance and strength properties, making it suitable.

The inventors have also discovered that the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is related to the roll processability of acrylic rubber, and have found that in particular, when the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is within a specific range, the rubber has excellent Banbury processability, storage stability and water resistance as well as excellent roll processability, making it suitable. The present inventors have also discovered that an acrylic rubber having a specific ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) and excellent roll processability, Banbury processability, storage stability and water resistance can be produced by emulsifying a specific monomer component with water and an emulsifier, initiating emulsion polymerization in the presence of a redox catalyst consisting of an inorganic radical generator such as potassium persulfate and a reducing agent, and not adding a chain transfer agent at the beginning but adding it batchwise during the polymerization to carry out emulsion polymerization, coagulating the resulting emulsion polymerization under specific conditions, washing the water-containing crumbs produced by the coagulation reaction with warm water, and drying the water-containing crumbs after washing after dehydrating them, thereby allowing the high molecular weight components and low molecular weight components of the acrylic rubber to coexist and giving a wide molecular weight distribution and an ash content of the specific components.

The researchers also discovered that by melting, kneading, and drying acrylic rubber under high-share conditions using a specific extrusion dryer, they could widen the ratio (Mw/Mn) of weight-average molecular weight (Mw) to number-average molecular weight (Mn) without decreasing the weight-average molecular weight (Mw), thereby achieving a high level of balance between the roll processability and strength properties of the acrylic rubber.

The inventors have also discovered that acrylic rubber containing acrylic acid esters and methacrylic acid esters is excellent in Banbury processability, storage stability, and water resistance, as well as heat resistance. In particular, they have discovered that the heat resistance effect is highly enhanced by including a methacrylic acid ester with a specific carbon number.

Based on these findings, the inventors have completed the present invention.

Thus, according to the present invention, there is provided an acrylic rubber that has reactive groups and is made of an acrylic rubber with a reactive group content of 0.001 to 5% by weight, has a gel content of methyl ethyl ketone insoluble matter of 50% by weight or less, a pH of 6 or less, an ash content of 0.4% by weight or less, a total content of magnesium, phosphorus, calcium, sodium and sulfur in the ash of 50% by weight or more, and a specific gravity of 0.8 or more.

In the acrylic rubber of the present invention, it is preferable that the ash content is 0.15% by weight or less.

In the acrylic rubber of the present invention, it is preferable that the lower limit of the ash content is 0.0001% by weight or more.

In the acrylic rubber of the present invention, it is preferable that the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber is in the range of 1.1 to 8.

In the acrylic rubber of the present invention, it is preferable that the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber is 3.4 or more.

In the acrylic rubber of the present invention, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber is preferably in the range of 3.7 to 6.5.

In the acrylic rubber of the present invention, it is preferable that the weight average molecular weight (Mw) of the acrylic rubber is 1,000,000 or more.

In the acrylic rubber of the present invention, it is preferable that the acrylic rubber is composed of bonding units (A) derived from a (meth)acrylic acid ester, bonding units (B) derived from a reactive group-containing monomer, and, as necessary, bonding units (C) derived from other monomers.

In the acrylic rubber of the present invention, it is preferable that the (meth)acrylic acid ester-derived bond unit (A) is at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters.

In the acrylic rubber of the present invention, it is preferable that the (meth)acrylic acid ester-derived bonding unit (A) is composed of an acrylic acid ester-derived bonding unit (A1) and a methacrylic acid ester-derived bonding unit (A2).

In the acrylic rubber of the present invention, the reactive group is preferably an ionically reactive group.

In the acrylic rubber of the present invention, the reactive group is preferably at least one type of reactive group selected from the group consisting of a carboxyl group, an epoxy group, and a chlorine atom.

The acrylic rubber of the present invention is preferably in the form of a sheet or a veil.

In the present invention, the present invention also includes an emulsion polymerization step of emulsifying an acrylic rubber monomer component containing a reactive group-containing monomer with water and an emulsifier, and then initiating polymerization in the presence of a redox catalyst consisting of a radical generator and a reducing agent to obtain an emulsion polymerization liquid;
a coagulation step in which the obtained emulsion polymerization liquid is added to a coagulation liquid having a coagulant concentration of 1% by weight or more while being stirred, and coagulated to produce water-containing crumbs;
A washing step of washing the generated hydrous crumbs with warm water;
A dehydration step of dehydrating the washed wet crumbs to a moisture content of 1 to 40% by weight;
drying the dehydrated wet crumbs to less than 1% by weight;
A method for producing an acrylic rubber is provided, comprising:

In the method for producing acrylic rubber of the present invention, it is preferable to bale the dried rubber.

In the method for producing acrylic rubber of the present invention, it is preferable that the radical generator is an inorganic radical generator.

In the method for producing acrylic rubber of the present invention, it is preferable to add the chain transfer agent batchwise during the emulsion polymerization.

In the method for producing acrylic rubber of the present invention, it is preferable that the drying of the water-containing crumb is carried out using a screw-type twin-screw extrusion dryer.

In the method for producing acrylic rubber of the present invention, the dehydration and drying steps are preferably carried out by using a screw-type twin-screw extruder dryer having a dehydration barrel with a dehydration slit, a drying barrel under reduced pressure, and a die at the tip, in which the hydrous crumbs after washing are dehydrated to a moisture content of 1 to 40% by weight in the dehydration barrel, then dried to less than 1% by weight in the drying barrel, and the sheet-like dried rubber is extruded through the die.

In the method for producing acrylic rubber of the present invention, it is preferable to laminate the extruded sheet-like dried rubber to form a bale.

In the method for producing acrylic rubber of the present invention, it is preferable that the acrylic rubber monomer component contains an acrylic acid ester and a methacrylic acid ester.

The present invention also provides a rubber composition comprising a rubber component containing the acrylic rubber, a filler, and a crosslinking agent.

The present invention also provides a method for producing a rubber composition in which the acrylic rubber and a filler are mixed together, and then a crosslinking agent is mixed into the rubber composition.

The present invention also provides a cross-linked rubber product obtained by cross-linking the above rubber composition.

The present invention provides an acrylic rubber having excellent Banbury processability, storage stability and water resistance, an efficient method for producing the same, a rubber composition containing the acrylic rubber, and a cross-linked rubber product obtained by cross-linking the acrylic rubber.

FIG. 1 is a diagram illustrating an example of an acrylic rubber production system according to an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of the screw-type extruder of FIG. 1. FIG. 2 is a diagram showing the configuration of a transportable cooling device used as the cooling device in FIG. 1 .

The acrylic rubber of the present invention is characterized in that it is made of an acrylic rubber that has reactive groups and has a reactive group content of 0.001 to 5% by weight, has a gel content of methyl ethyl ketone insoluble matter of 50% by weight or less, a pH of 6 or less, an ash content of 0.4% by weight or less, a total content of magnesium, phosphorus, calcium, sodium and sulfur in the ash of 50% by weight or more, and a specific gravity of 0.8 or more.

<Reactive Group>
The acrylic rubber of the present invention is characterized by having a reactive group. The reactive group is not particularly limited as long as it is a reactive group that reacts with a crosslinking agent, etc., but for example, when it is at least one reactive group selected from the group consisting of a carboxyl group, an epoxy group, and a chlorine atom, or an ion-reactive group that participates in an ionic reaction, preferably an epoxy group or a carboxyl group, and particularly preferably a carboxyl group, it is suitable because it can highly improve the short-time crosslinkability and the compression set resistance and water resistance of the crosslinked product.

The reactive group content of the acrylic rubber of the present invention is preferably in the range of 0.001 to 5% by weight, preferably 0.01 to 3% by weight, more preferably 0.05 to 1% by weight, and particularly preferably 0.1 to 0.5% by weight, in terms of the weight ratio of the reactive groups themselves, because this range provides a high level of balance in terms of processability and crosslinkability, as well as properties such as strength, compression set resistance, oil resistance, cold resistance, and water resistance when crosslinked.

The acrylic rubber having a reactive group of the present invention may be one in which a reactive group, preferably at least one reactive group selected from the group consisting of a carboxyl group, an epoxy group, and a chlorine atom, or an ionic reactive group, has been introduced into the acrylic rubber by a post-reaction, but an acrylic rubber copolymerized with a monomer containing a reactive group is preferred.

<Monomer component>
The monomer component of the acrylic rubber of the present invention is not particularly limited as long as it is a monomer that has the above-mentioned reactive group and constitutes a normal acrylic rubber, but is preferably an acrylic rubber monomer component containing a reactive group-containing monomer, more preferably a monomer composed of a (meth)acrylic acid ester (a), a reactive group-containing monomer (b), and other copolymerizable monomers (c) as required. In the present invention, the term "(meth)acrylic acid ester" is used as a general term for esters of acrylic acid and/or methacrylic acid.

When the (meth)acrylic acid ester (a) is at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, the weather resistance, heat resistance, and oil resistance of the acrylic rubber are highly balanced, making this preferable.

The (meth)acrylic acid alkyl ester is not particularly limited, but typically, a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 12 carbon atoms, preferably a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 8 carbon atoms, and more preferably a (meth)acrylic acid alkyl ester having an alkyl group with 2 to 6 carbon atoms is used.

Specific examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. Of these, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred, with ethyl acrylate and n-butyl acrylate being more preferred.

The (meth)acrylic acid alkoxyalkyl ester is not particularly limited, but typically an (meth)acrylic acid alkoxyalkyl ester having an alkoxyalkyl group of 2 to 12, preferably an (meth)acrylic acid alkoxyalkyl ester having an alkoxyalkyl group of 2 to 8, and more preferably an (meth)acrylic acid alkoxyalkyl ester having an alkoxyalkyl group of 2 to 6 carbon atoms is used.

Specific examples of (meth)acrylic acid alkoxyalkyl esters include methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, methoxybutyl (meth)acrylate, ethoxymethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, etc. Among these, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, etc. are preferred, and methoxyethyl acrylate, ethoxyethyl acrylate, etc. are more preferred.

At least one (meth)acrylic acid ester selected from the group consisting of these (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters is used alone or in combination of two or more. When the proportion of this in the total monomer components is usually in the range of 50 to 99.99% by weight, preferably 62 to 99.95% by weight, more preferably 74 to 99.9% by weight, 80 to 99.5% by weight, or 87 to 99% by weight, the weather resistance, heat resistance, and oil resistance of the acrylic rubber are highly excellent and suitable.

When the (meth)acrylic acid ester (a) is composed of an acrylic acid ester (a1) and a methacrylic acid ester (a2), the heat resistance of the acrylic rubber is remarkably excellent, making this preferable.

The alkyl acrylate (a1) is not particularly limited, but examples thereof include alkyl acrylates having an alkyl group with 1 to 12 carbon atoms, preferably alkyl acrylates having an alkyl group with 1 to 8 carbon atoms, and more preferably alkyl acrylates having an alkyl group with 2 to 6 carbon atoms.

Specific examples of acrylic acid alkyl esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. Methyl acrylate, ethyl acrylate, isopropyl acrylate, and n-butyl acrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred.

There are no particular limitations on the alkoxyalkyl acrylate ester, but examples include alkoxyalkyl acrylate esters having an alkoxyalkyl group with 2 to 12 carbon atoms, preferably alkoxyalkyl acrylate esters having an alkoxyalkyl group with 2 to 8 carbon atoms, and more preferably alkoxyalkyl acrylate esters having an alkoxyalkyl group with 2 to 6 carbon atoms.

Specific examples of alkoxyalkyl acrylates include methoxymethyl acrylate, methoxyethyl acrylate, methoxypropyl acrylate, methoxybutyl acrylate, ethoxymethyl acrylate, ethoxyethyl acrylate, propoxyethyl acrylate, butoxyethyl acrylate, etc. Among these, methoxyethyl acrylate, ethoxyethyl acrylate, ethoxymethyl acrylate, methoxymethyl acrylate, etc. are preferred, and methoxyethyl acrylate and ethoxyethyl acrylate are more preferred.

These bonding units (A1) derived from acrylic acid ester (a1) can be used alone or in combination of two or more kinds, and the amount of bonding units (A1) in the acrylic rubber is usually in the range of 10 to 98.9% by weight, preferably 32 to 97.7% by weight, more preferably 50 to 96.5% by weight, and particularly preferably 62 to 94% by weight. If the amount of bonding units (A1) in the acrylic rubber is too small, the weather resistance, heat resistance, and oil resistance may decrease, and if it is too large, the strength properties and compression set resistance may decrease, which is not preferable.

There are no particular limitations on the methacrylic acid ester (a2), and suitable examples include at least one methacrylic acid ester selected from the group consisting of methacrylic acid alkyl esters and methacrylic acid alkyl esters, with methacrylic acid alkyl esters being particularly preferred.

Examples of methacrylic acid alkyl esters include methacrylic acid alkyl esters having an alkyl group with 1 to 14 carbon atoms, preferably methacrylic acid alkyl esters having an alkyl group with 2 to 8 carbon atoms, and more preferably methacrylic acid alkyl esters having an alkyl group with 2 to 6 carbon atoms.

Specific examples of methacrylic acid alkyl esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, octyl methacrylate, dodecyl methacrylate, isotridecyl methacrylate, etc., with ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, octyl methacrylate, and more preferably ethyl methacrylate and n-butyl methacrylate.

Examples of alkoxyalkyl methacrylate esters include alkoxyalkyl methacrylate esters having an alkoxyalkyl group with 2 to 14 carbon atoms, preferably alkoxyalkyl methacrylate esters having an alkoxyalkyl group with 2 to 8 carbon atoms, and more preferably alkoxyalkyl methacrylate esters having an alkoxyalkyl group with 2 to 6 carbon atoms.

Specific examples of alkoxyalkyl methacrylates include methoxymethyl methacrylate, methoxyethyl methacrylate, methoxypropyl methacrylate, methoxybutyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, propoxyethyl methacrylate, butoxyethyl methacrylate, etc. Among these, methoxyethyl methacrylate, ethoxyethyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, etc. are preferred, and methoxyethyl methacrylate and ethoxyethyl methacrylate are more preferred.

These bond units (A2) derived from methacrylic acid ester (a2) can be used alone or in combination of two or more types, and the bond amount in the acrylic rubber is usually in the range of 1 to 50% by weight, preferably 2 to 40% by weight, more preferably 3 to 30% by weight, and particularly preferably 5 to 25% by weight.

These (meth)acrylic acid esters (a) may be used alone or in combination of two or more. When the proportion of these in the total monomer components is usually in the range of 50 to 99.99% by weight, preferably 62 to 99.95% by weight, more preferably 74 to 99.9% by weight, 80 to 99.5% by weight, or 87 to 99% by weight, the weather resistance, heat resistance, and oil resistance of the acrylic rubber are highly excellent and are suitable.

The reactive group-containing monomer (b) is not particularly limited, but examples thereof include monomers having at least one functional group selected from the group consisting of a carboxyl group, an epoxy group, and a halogen group, and is preferably a monomer having an ionically reactive reactive group, more preferably a monomer having a carboxyl group, a monomer having an epoxy group, and a monomer having a chlorine atom, and particularly preferably a monomer having a carboxyl group or a monomer having an epoxy group.

There are no particular limitations on the monomer having a carboxyl group, but ethylenically unsaturated carboxylic acids can be suitably used. Examples of ethylenically unsaturated carboxylic acids include ethylenically unsaturated monocarboxylic acids, ethylenically unsaturated dicarboxylic acids, and ethylenically unsaturated dicarboxylic acid monoesters. Among these, ethylenically unsaturated dicarboxylic acid monoesters are preferred because they can further improve the compression set resistance of the resulting acrylic rubber.

There are no particular limitations on the ethylenically unsaturated monocarboxylic acid, but ethylenically unsaturated monocarboxylic acids having 3 to 12 carbon atoms are preferred, such as acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, and cinnamic acid.

There are no particular limitations on the ethylenically unsaturated dicarboxylic acid, but ethylenically unsaturated dicarboxylic acids having 4 to 12 carbon atoms are preferred, such as butenedioic acids such as fumaric acid and maleic acid, itaconic acid, and citraconic acid. Ethylenically unsaturated dicarboxylic acids also include those that exist as anhydrides.

There are no particular limitations on the ethylenically unsaturated dicarboxylic acid monoester, but it is usually an ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms and an alkyl monoester having 1 to 12 carbon atoms, preferably an ethylenically unsaturated dicarboxylic acid having 4 to 6 carbon atoms and an alkyl monoester having 2 to 8 carbon atoms, and more preferably an alkyl monoester having 2 to 6 carbon atoms of butenedioic acid having 4 carbon atoms.

Specific examples of ethylenically unsaturated dicarboxylic acid monoesters include monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, mono-n-butyl maleate, monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclohexenyl fumarate, monocyclopentyl maleate, and monocyclohexyl maleate, and other butenedioic acid monoalkyl esters; monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, and monocyclohexyl itaconate, and other itaconic acid monoalkyl esters; and the like, with mono-n-butyl fumarate and mono-n-butyl maleate being preferred, and mono-n-butyl fumarate being particularly preferred.

Examples of monomers having an epoxy group include epoxy group-containing (meth)acrylic acid esters such as glycidyl (meth)acrylate; epoxy group-containing vinyl ethers such as allyl glycidyl ether and vinyl glycidyl ether; and the like. Note that "(meth)acrylic acid" here is used as a general term for acrylic acid and/or methacrylic acid, and the same applies below.

Examples of monomers having a halogen group include unsaturated alcohol esters of halogen-containing saturated carboxylic acids, (meth)acrylic acid haloalkyl esters, (meth)acrylic acid haloacyloxyalkyl esters, (meth)acrylic acid (haloacetylcarbamoyloxy)alkyl esters, halogen-containing unsaturated ethers, halogen-containing unsaturated ketones, halomethyl group-containing aromatic vinyl compounds, halogen-containing unsaturated amides, and haloacetyl group-containing unsaturated monomers, with these chlorine atom-containing monomers being particularly preferred.

Examples of unsaturated alcohol esters of halogen-containing saturated carboxylic acids include vinyl chloroacetate, vinyl 2-chloropropionate, and allyl chloroacetate. Examples of (meth)acrylic acid haloalkyl esters include chloromethyl (meth)acrylate, 1-chloroethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 1,2-dichloroethyl (meth)acrylate, 2-chloropropyl (meth)acrylate, 3-chloropropyl (meth)acrylate, and 2,3-dichloropropyl (meth)acrylate. Examples of (meth)acrylic acid haloacyloxyalkyl esters include 2-(chloroacetoxy)ethyl (meth)acrylate, 2-(chloroacetoxy)propyl (meth)acrylate, 3-(chloroacetoxy)propyl (meth)acrylate, and 3-(hydroxychloroacetoxy)propyl (meth)acrylate. Examples of (meth)acrylic acid (haloacetylcarbamoyloxy) alkyl esters include 2-(chloroacetylcarbamoyloxy) ethyl (meth) acrylate and 3-(chloroacetylcarbamoyloxy) propyl (meth) acrylate. Examples of halogen-containing unsaturated ethers include chloromethyl vinyl ether, 2-chloroethyl vinyl ether, 3-chloropropyl vinyl ether, 2-chloroethyl allyl ether, and 3-chloropropyl allyl ether. Examples of halogen-containing unsaturated ketones include 2-chloroethyl vinyl ketone, 3-chloropropyl vinyl ketone, and 2-chloroethyl allyl ketone. Examples of halomethyl group-containing aromatic vinyl compounds include p-chloromethylstyrene, m-chloromethylstyrene, o-chloromethylstyrene, and p-chloromethyl-α-methylstyrene. Examples of halogen-containing unsaturated amides include N-chloromethyl(meth)acrylamide. Examples of haloacetyl group-containing unsaturated monomers include 3-(hydroxychloroacetoxy)propyl allyl ether and p-vinylbenzyl chloroacetic acid ester.

These reactive group-containing monomers (b) may be used alone or in combination of two or more, and their proportion in the total monomer components is usually in the range of 0.1 to 10% by weight, preferably 0.3 to 8% by weight, more preferably 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight.

The other monomer (c) is not particularly limited as long as it is other than the above monomers (a) and (b) and is copolymerizable with them, and examples thereof include aromatic vinyl, ethylenically unsaturated nitrile, acrylamide monomer, other olefin monomer, etc. Examples of aromatic vinyl include styrene, α-methylstyrene, divinylbenzene, etc. Examples of ethylenically unsaturated nitrile include acrylonitrile, methacrylonitrile, etc. Examples of acrylamide monomers include acrylamide, methacrylamide, etc. Examples of other olefin monomers include ethylene, propylene, vinyl acetate, ethyl vinyl ether, butyl vinyl ether, etc.

These other monomers (c) may be used alone or in combination of two or more, and their proportion in the total monomer components is usually in the range of 0 to 30% by weight, preferably 0 to 20% by weight, more preferably 0 to 15% by weight, and particularly preferably 0 to 10% by weight.

<Acrylic rubber>
The acrylic rubber of the present invention is not particularly limited as long as it has a reactive group, but preferably comprises the above-mentioned (meth)acrylic acid ester (a)-derived bonding units (A), the reactive group-containing monomer (b)-derived bonding units (B), and, if necessary, the other monomer (c)-derived bonding units (C), and the respective proportions of the bonding units (A) are in the range of usually 10 to 98.9% by weight, preferably 32 to 97.7% by weight, more preferably 50 to 96.5% by weight, and particularly preferably 62 to 94% by weight. , the bonding unit (B) is usually 1 to 50% by weight, preferably 2 to 40% by weight, more preferably 3 to 30% by weight, and particularly preferably 5 to 25% by weight, the bonding unit (B) is usually 0.1 to 10% by weight, preferably 0.3 to 8% by weight, more preferably 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight, and the bonding unit (C) is usually 0 to 30% by weight, preferably 0 to 20% by weight, more preferably 0 to 15% by weight, and particularly preferably 0 to 10% by weight. That is, the acrylic rubber of the present invention is a copolymer containing the above-mentioned bonding units in the above-mentioned specific weight ratios and containing the bonding units in such a way that the total of the bonding units is 100% by weight, and when the bonding units of the monomers in the acrylic rubber are in these ranges, the acrylic rubber is crosslinked, which is preferable because it can achieve a high balance of heat resistance, water resistance, and compression set resistance. In the present invention, the heat resistance of the acrylic rubber can be highly improved when the bonding units (A) derived from the acrylic ester (a1) are in the range of usually 10 to 98.9% by weight, preferably 32 to 97.7% by weight, more preferably 50 to 96.5% by weight, and particularly preferably 62 to 94% by weight, the bonding units (A2) derived from the methacrylic ester (a2) are in the range of usually 1 to 50% by weight, preferably 2 to 40% by weight, more preferably 3 to 30% by weight, and particularly preferably 5 to 25% by weight, and the bonding units (B) are in the range of usually 0.1 to 10% by weight, preferably 0.3 to 8% by weight, more preferably 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight.

The weight average molecular weight (Mw) of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but is usually 1 million or more, preferably 1.1 million or more, more preferably 1.2 million or more, particularly preferably 1.5 million or more, and most preferably 1.6 million or more. If the weight average molecular weight (Mw) of the acrylic rubber of the present invention is excessively small, the strength characteristics and compression set resistance characteristics are inferior, which is undesirable. The weight average molecular weight (Mw) of the acrylic rubber of the present invention is also preferably in the range of usually 1 million to 3.5 million, preferably 1.2 million to 3 million, more preferably 1.3 million to 3 million, particularly preferably 1.5 million to 2.5 million, and most preferably 1.9 million to 2.1 million, in which case the roll processability, strength characteristics, and compression set resistance characteristics of the acrylic rubber are highly balanced and suitable.

The weight average molecular weight (Mw) of the acrylic rubber of the present invention is also suitable in the range of 1,000,000 to 5,000,000 (1 million to 5 million), preferably 1,100,000 to 4,000,000 (1.1 million to 4 million), more preferably 1,150,000 to 3,000,000 (1.15 million to 3 million), and most preferably 1,200,000 to 2,500,000 (1.2 million to 2.5 million), because this provides a high level of balance between the processability, strength properties, and compression set resistance properties of the acrylic rubber when mixed.

The number average molecular weight (Mn) of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but the roll processability, strength properties, and compression set resistance of the acrylic rubber are highly balanced and suitable when it is in the range of usually 100,000 to 500,000, preferably 200,000 to 480,000, more preferably 250,000 to 450,000, particularly preferably 300,000 to 400,000, and most preferably 350,000 to 400,000.

The z-average molecular weight (Mz) of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but when it is in the range of usually 1.5 million to 6 million, preferably 2 million to 5 million, more preferably 2.5 million to 4.5 million, and particularly preferably 3 million to 4 million, the roll processability, strength properties, and compression set resistance properties of the acrylic rubber are highly balanced and are suitable.

The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the present invention is not particularly limited, but is usually suitable when it is in the range of 1.1 to 8, preferably 1.2 to 7, and more preferably 1.4 to 6, since this provides a high level of balance between the processability, strength properties, and compression set resistance properties of the acrylic rubber.

The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber of the present invention is not particularly limited, but is usually 3.4 or more, preferably 3.5 or more, more preferably 3.6 or more, and particularly preferably 3.7 or more. If the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber of the present invention is too small, the roll processability is poor. The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber of the present invention is also preferably in the range of usually 3.7 to 6.5, preferably 3.8 to 6.2, more preferably 4 to 6, particularly preferably 4, 5 to 5.7, and most preferably 4.7 to 5.5, which is suitable for achieving a high balance between roll processability, strength properties when crosslinked, and compression set resistance.

The ratio (Mz/Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but is usually suitable when it is in the range of 1.3 to 3, preferably 1.4 to 2.7, more preferably 1.5 to 2.5, particularly preferably 1.8 to 2, and most preferably 1.8 to 1.95, since this provides a high level of balance between the processability and strength properties of the acrylic rubber and reduces changes in physical properties during storage.

There are no particular limitations on the molecular weight (Mn, Mw, Mz) and molecular weight distribution (Mw/Mn, Mz/Mw) of the acrylic rubber that constitutes the acrylic rubber veil of the present invention, but it is preferable to use the absolute molecular weight (Mn, Mw, Mz) and absolute molecular weight distribution (Mw/Mn, Mz/Mw) by the GPC-MALS method, as this allows each characteristic to be determined more accurately.

The measurement solvent for the GPC-MALS method for measuring the molecular weight (Mn, Mw, Mz) and molecular weight distribution (Mw/Mn, Mz/Mw) of the acrylic rubber constituting the acrylic rubber veil of the present invention is not particularly limited as long as it can dissolve and measure the acrylic rubber veil of the present invention, but dimethylformamide-based solvents are preferred. The dimethylformamide-based solvent used is not particularly limited as long as it is mainly composed of dimethylformamide, but 100% dimethylformamide or dimethylformamide with a polar substance added can be used. The proportion of dimethylformamide in the dimethylformamide-based solvent is 90% by weight or more, preferably 95% by weight or more, and more preferably 97% by weight or more. The compound to be added to dimethylformamide is not particularly limited, but in the present invention, a solution in which dimethylformamide is added with lithium chloride at a concentration of 0.05 mol/L and 37% concentrated hydrochloric acid at a concentration of 0.01% is particularly preferred.

When the gel content of the methyl ethyl ketone insoluble matter in the acrylic rubber of the present invention is 50% by weight or less, preferably 30% by weight or less, more preferably 15% by weight or less, particularly preferably 10% by weight or less, and most preferably 5% by weight or less, the processability during kneading in a Banbury or the like is highly improved, which is suitable.

The pH of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but the storage stability of the acrylic rubber is highly improved when the pH is generally 6 or less, preferably 2 to 6, more preferably 2.5 to 5.5, and most preferably in the range of 3 to 5.

The ash content of the acrylic rubber of the present invention is 0.4% by weight or less, preferably 0.3% by weight or less, more preferably 0.2% by weight or less, even more preferably 0.18% by weight or less, particularly preferably 0.15% by weight or less, and most preferably 0.13% by weight or less. When it is in this range, the water resistance, strength properties, and processability of the acrylic rubber are highly balanced and suitable.

The lower limit of the ash content of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but it is usually preferred that the ash content is 0.0001% by weight or more, preferably 0.0005% by weight or more, more preferably 0.001% by weight or more, even more preferably 0.003% by weight or more, particularly preferably 0.005% by weight or more, and most preferably 0.01% by weight or more, since this reduces the metal adhesion of the rubber and provides excellent workability.

When the acrylic rubber of the present invention has a high balance of water resistance, strength properties, processability and workability, the ash content is usually in the range of 0.0001 to 0.4% by weight, preferably 0.0005 to 0.3% by weight, more preferably 0.001 to 0.2% by weight, even more preferably 0.003 to 0.18% by weight, particularly preferably 0.005 to 0.15% by weight, and most preferably 0.01 to 0.13% by weight.

When the total amount of sodium, magnesium, calcium, phosphorus and sulfur in the ash of the acrylic rubber of the present invention is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more, the water resistance of the acrylic rubber is highly improved, metal adhesion is reduced, and workability is excellent, which is preferable.

The total amount of magnesium and phosphorus in the ash of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but it is usually preferable for the acrylic rubber to have a high balance of water resistance, strength properties, and processability, reduced metal adhesion, and excellent workability when it is at least 30% by weight, preferably at least 50% by weight, more preferably at least 70% by weight, particularly preferably at least 80% by weight, and most preferably at least 90% by weight.

The amount of magnesium in the ash of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but is usually 10% by weight or more, preferably 15 to 60% by weight, more preferably 20 to 50% by weight, particularly preferably 25 to 45% by weight, and most preferably 30 to 40% by weight.

The amount of phosphorus in the ash of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but is usually 10% by weight or more, preferably 20 to 90% by weight, more preferably 30 to 80% by weight, particularly preferably 40 to 70% by weight, and most preferably 50 to 60% by weight.

The ratio of magnesium to phosphorus ([Mg]/[P]) in the ash of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but when the ratio is in the range of usually 0.4 to 2.5, preferably 0.45 to 1.2, more preferably 0.45 to 1, particularly preferably 0.5 to 0.8, and most preferably 0.55 to 0.7 by weight, the water resistance, strength properties, and processability of the acrylic rubber are highly balanced and suitable.

Here, the ash content in acrylic rubber is mainly derived from the emulsifier used when emulsifying the monomer components and carrying out emulsion polymerization, and the coagulant used when coagulating the emulsion polymerization liquid, but the total ash content and the magnesium and phosphorus content in the ash vary depending not only on the conditions of the emulsion polymerization process and the coagulation process, but also on the conditions of each subsequent process.

The specific gravity of the acrylic rubber of the present invention is not particularly limited, but is usually 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more, particularly preferably 0.95 or more, and most preferably 1 or more, which is suitable since it contains almost no air and has excellent storage stability. The specific gravity of the acrylic rubber of the present invention is also usually in the range of 0.7 to 1.6, preferably 0.8 to 1.5, more preferably 0.9 to 1.4, particularly preferably 0.95 to 1.3, and most preferably 1.0 to 1.2, which is suitable since it provides a high balance of productivity, storage stability, and the stability of the crosslinking properties of the crosslinked product.

The glass transition temperature (Tg) of the acrylic rubber of the present invention may be appropriately selected depending on the intended use of the acrylic rubber, but is usually excellent in processability and cold resistance when it is 20°C or less, preferably 10°C or less, and more preferably 0°C or less. The lower limit of the glass transition temperature (Tg) of the acrylic rubber is not particularly limited, but is usually -80°C or more, preferably -60°C or more, and more preferably -40°C or more. By setting the glass transition temperature at or above the lower limit, it is possible to obtain excellent oil resistance and heat resistance, and by setting it at or below the upper limit, it is possible to obtain excellent processability, crosslinkability, and cold resistance.

The complex viscosity of the acrylic rubber of the present invention at 60°C ([η]60°C) is not particularly limited and may be appropriately selected depending on the intended use, but it is usually excellent in processability, oil resistance, and shape retention when it is in the range of 15,000 [Pa·s] or less, preferably 1,000 to 10,000 [Pa·s], more preferably 2,000 to 5,000 [Pa·s], particularly preferably 2,500 to 4,000 [Pa·s], and most preferably 2,500 to 3,000 [Pa·s].

The complex viscosity of the acrylic rubber of the present invention at 100°C ([η]100°C) is not particularly limited and may be appropriately selected depending on the intended use, but it is usually in the range of 1,500 to 6,000 [Pa·s], preferably 2,000 to 5,000 [Pa·s], more preferably 2,300 to 4,000 [Pa·s], particularly preferably 2,500 to 3,500 [Pa·s], and most preferably 2,500 to 3,000 [Pa·s], which provides excellent processability, oil resistance, and shape retention.

The ratio ([η]100°C/[η]60°C) of the complex viscosity at 100°C ([η]100°C) of the acrylic rubber of the present invention to the complex viscosity at 60°C ([η]60°C) is not particularly limited and may be appropriately selected depending on the intended use, but is usually 0.5 or more, preferably 0.6 or more, more preferably 0.7 or more, particularly preferably 0.8 or more, and most preferably 0.83 or more. The ratio ([η]100°C/[η]60°C) of the complex viscosity at 100°C ([η]100°C) to the complex viscosity at 60°C ([η]60°C) of the acrylic rubber of the present invention is also preferably in the range of 0.5 to 0.99, preferably 0.6 to 0.98, more preferably 0.7 to 0.97, particularly preferably 0.8 to 0.96, and most preferably 0.85 to 0.95, in which case processability, oil resistance, and shape retention are highly balanced and suitable.

The water content of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but when it is generally less than 1% by weight, preferably 0.8% by weight or less, and more preferably 0.6% by weight or less, the vulcanization characteristics of the acrylic rubber are optimized and properties such as heat resistance and strand-like water resistance are highly improved, making this an ideal range.

The Mooney viscosity (ML1+4, 100°C) of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but the processability and strength properties of the acrylic rubber are highly balanced and are suitable when it is usually in the range of 10 to 150, preferably 20 to 100, and more preferably 25 to 70.

The shape of the acrylic rubber of the present invention is not particularly limited and may be appropriately selected depending on the intended use. For example, it may be in the form of powder, crumb, strand, sheet, or veil, but is preferably in the form of a sheet or veil, which is excellent in workability and storage stability.

When the acrylic rubber of the present invention is in the form of a sheet, the thickness is not particularly limited and is appropriately selected depending on the intended use, but is usually in the range of 1 to 40 mm, preferably 2 to 35 mm, more preferably 3 to 30 mm, and most preferably 5 to 25 mm, which is suitable for achieving a high balance of workability, storage stability, and productivity. The width of the sheet-like acrylic rubber of the present invention is appropriately selected depending on the intended use, but is particularly suitable for excellent handleability when it is usually in the range of 300 to 1200 mm, preferably 400 to 1000 mm, and more preferably 500 to 800 mm. The length of the sheet-like acrylic rubber of the present invention is not particularly limited, but is particularly suitable for excellent handleability when it is usually in the range of 300 to 1200 mm, preferably 400 to 1000 mm, and more preferably 500 to 800 mm.

When the acrylic rubber of the present invention is in the form of a veil, there is no particular limitation on the size and it is selected appropriately depending on the intended use, but it is appropriate that the width is usually in the range of 100 to 800 mm, preferably 200 to 500 mm, and more preferably 250 to 450 mm, the length is usually in the range of 300 to 1,200 mm, preferably 400 to 1,000 mm, and more preferably 500 to 800 mm, and the height (thickness) is usually in the range of 50 to 500 mm, preferably 100 to 300 mm, and more preferably 150 to 250 mm. In addition, there is no limitation on the shape of the veil-shaped acrylic rubber of the present invention and it is selected appropriately depending on the intended use of the acrylic rubber veil, but in many cases a rectangular parallelepiped is suitable.

<Method of manufacturing acrylic rubber>
The method for producing the acrylic rubber is not particularly limited, but may be, for example, an emulsion polymerization step of emulsifying an acrylic rubber monomer component containing a reactive group-containing monomer with water and an emulsifier, and then initiating polymerization in the presence of a redox catalyst consisting of a radical generator and a reducing agent to obtain an emulsion polymerization liquid;
a coagulation step in which the obtained emulsion polymerization liquid is added to a coagulation liquid having a coagulant concentration of 1% by weight or more while being stirred, and coagulated to produce water-containing crumbs;
A washing step of washing the generated hydrous crumbs with warm water;
A dehydration step of dehydrating the washed wet crumbs to a moisture content of 1 to 40% by weight;
drying the dehydrated wet crumbs to less than 1% by weight;
The acrylic rubber can be easily produced by a method for producing an acrylic rubber comprising the steps of:

The acrylic rubber monomer components containing reactive group-containing monomers used in the present invention are the same as the examples and preferred ranges of the monomer components already described. The amounts of the monomer components used are also as already described, and in the emulsion polymerization, each monomer may be appropriately selected so as to obtain the above-mentioned composition of the acrylic rubber of the present invention.

(emulsifier)
The emulsifier used in the present invention is not particularly limited, but examples thereof include anionic emulsifiers, cationic emulsifiers, and nonionic emulsifiers, with anionic emulsifiers being preferred.

The anionic emulsifier is not particularly limited, and examples thereof include salts of fatty acids such as myristic acid, palmitic acid, oleic acid, and linolenic acid; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate; sulfate salts such as sodium lauryl sulfate, and phosphate salts such as polyoxyalkylene alkyl ether phosphate salts; and alkyl sulfosuccinates. Among these anionic emulsifiers, phosphate salts and sulfate salts are preferred, phosphate salts are particularly preferred, and divalent phosphate salts are most preferred.

The divalent phosphate ester salt is not particularly limited as long as it can be used as an emulsifier in an emulsion polymerization reaction, but examples include alkyloxy polyoxyalkylene phosphate ester salts, alkylphenyloxy polyoxyalkylene phosphate ester salts, etc., and among these, metal salts of these are preferred, alkali metal salts of these are more preferred, and sodium salts of these are most preferred.

Examples of the alkyloxy polyoxyalkylene phosphate ester salts include alkyloxy polyoxyethylene phosphate ester salts and alkyloxy polyoxypropylene phosphate ester salts, and among these, alkyloxy polyoxyethylene phosphate ester salts are preferred.

Specific examples of alkyloxypolyoxyethylene phosphate salts include octyloxydioxyethylene phosphate, octyloxytrioxyethylene phosphate, octyloxytetraoxyethylene phosphate, decyloxytetraoxyethylene phosphate, dodecyloxytetraoxyethylene phosphate, tridecyloxytetraoxyethylene phosphate, tetradecyloxytetraoxyethylene phosphate, hexadecyloxytetraoxyethylene phosphate, octadecyloxytetraoxyethylene phosphate, octyloxypentaoxyethylene phosphate, decyloxypentaoxyethylene phosphate, dodecyloxypentaoxyethylene phosphate, tridecyloxypentaoxyethylene phosphate, tetradecyloxypentaoxyethylene phosphate, hexadecyloxypentaoxyethylene phosphate, octyloxypentaoxyethylene phosphate, decyloxypentaoxyethylene phosphate, dodecyloxypentaoxyethylene phosphate, tridecyloxypentaoxyethylene phosphate, tetradecyloxypentaoxyethylene phosphate, hexadecyloxypentaoxyethylene phosphate, octadecyloxypentaoxyethylene phosphate, Examples of the metal salts include tridecyloxyhexaoxyethylene phosphate, octyloxyhexaoxyethylene phosphate, decyloxyhexaoxyethylene phosphate, dodecyloxyhexaoxyethylene phosphate, tridecyloxyhexaoxyethylene phosphate, tetradecyloxyhexaoxyethylene phosphate, hexadecyloxyhexaoxyethylene phosphate, octadecyloxyhexaoxyethylene phosphate, octyloxyoctaoxyethylene phosphate, decyloxyoctaoxyethylene phosphate, dodecyloxyoctaoxyethylene phosphate, tridecyloxyoctaoxyethylene phosphate, tetradecyloxyoctaoxyethylene phosphate, hexadecyloxyoctaoxyethylene phosphate, and octadecyloxyoctaoxyethylene phosphate. Among these, the alkali metal salts, particularly the sodium salts, are preferred.

Specific examples of alkyloxypolyoxypropylene phosphate salts include octyloxydioxypropylene phosphate, octyloxytrioxypropylene phosphate, octyloxytetraoxypropylene phosphate, decyloxytetraoxypropylene phosphate, dodecyloxytetraoxypropylene phosphate, tridecyloxytetraoxypropylene phosphate, tetradecyloxytetraoxypropylene phosphate, hexadecyloxytetraoxypropylene phosphate, octadecyloxytetraoxypropylene phosphate, octyloxypentaoxypropylene phosphate, decyloxypentaoxypropylene phosphate, dodecyloxypentaoxypropylene phosphate, tridecyloxypentaoxypropylene phosphate, tetradecyloxypentaoxypropylene phosphate, hexadecyloxypentaoxypropylene phosphate, octyloxypentaoxypropylene phosphate, decyloxypentaoxypropylene phosphate, dodecyloxypentaoxypropylene phosphate, tridecyloxypentaoxypropylene phosphate, tetradecyloxypentaoxypropylene phosphate, hexadecyloxypentaoxypropylene phosphate, octadecyloxypentaoxypropylene phosphate, and octyloxypentaoxypropylene phosphate. Examples of the phosphate ester include octyloxyhexaoxypropylene phosphate, octyloxyhexaoxypropylene phosphate, decyloxyhexaoxypropylene phosphate, dodecyloxyhexaoxypropylene phosphate, tridecyloxyhexaoxypropylene phosphate, tetradecyloxyhexaoxypropylene phosphate, hexadecyloxyhexaoxypropylene phosphate, octadecyloxyhexaoxypropylene phosphate, octyloxyoctaoxypropylene phosphate, decyloxyoctaoxypropylene phosphate, dodecyloxyoctaoxypropylene phosphate, tridecyloxyoctaoxyethylene phosphate, tetradecyloxyoctaoxypropylene phosphate, hexadecyloxyoctaoxypropylene phosphate, octadecyloxyoctaoxypropylene phosphate, and metal salts thereof. Among these, alkali metal salts thereof, particularly sodium salts, are preferred.

Specific examples of alkylphenyloxy polyoxyalkylene phosphate ester salts include alkylphenyloxy polyoxyethylene phosphate ester salts and alkylphenyloxy polyoxypropylene phosphate ester salts, and among these, alkylphenyloxy polyoxyethylene phosphate ester salts are preferred.

Specific examples of alkylphenyloxypolyoxyethylene phosphate salts include methyloxytetraoxyethylene phosphate, ethylphenyloxytetraoxyethylene phosphate, butylphenyloxytetraoxyethylene phosphate, hexylphenyloxytetraoxyethylene phosphate, nonylphenyloxytetraoxyethylene phosphate, dodecylphenyloxytetraoxyethylene phosphate, octadecyloxytetraoxyethylene phosphate, methylphenyloxypentaoxyethylene phosphate, ethylphenyloxypentaoxyethylene phosphate, butylphenyloxypentaoxyethylene phosphate, hexylphenyloxypentaoxyethylene phosphate, nonylphenyloxypentaoxyethylene phosphate, dodecylphenyloxypentaoxyethylene phosphate, Examples of suitable metal salts include hexaoxyethylene phosphate, methylphenyloxyhexaoxyethylene phosphate, ethylphenyloxyhexaoxyethylene phosphate, butylphenyloxyhexaoxyethylene phosphate, hexylphenyloxyhexaoxyethylene phosphate, nonylphenyloxyhexaoxyethylene phosphate, dodecylphenyloxyhexaoxyethylene phosphate, methylphenyloxyhexaoxyethylene phosphate, ethylphenyloxyoctaoxyethylene phosphate, butylphenyloxyoctaoxyethylene phosphate, hexylphenyloxyoctaoxyethylene phosphate, nonylphenyloxyoctaoxyethylene phosphate, and dodecylphenyloxyoctaoxyethylene phosphate. Among these, the alkali metal salts, particularly the sodium salts, are preferred.

Specific examples of alkylphenyloxypolyoxypropylene phosphate salts include methylphenyloxytetraoxypropylene phosphate, ethylphenyloxytetraoxypropylene phosphate, butylphenyloxytetraoxypropylene phosphate, hexylphenyloxytetraoxypropylene phosphate, nonylphenyloxytetraoxypropylene phosphate, dodecylphenyloxytetraoxypropylene phosphate, methylphenyloxypentaoxypropylene phosphate, ethylphenyloxypentaoxypropylene phosphate, butylphenyloxypentaoxypropylene phosphate, hexylphenyloxypentaoxypropylene phosphate, nonylphenyloxypentaoxypropylene phosphate, dodecylphenyloxypentaoxypropylene phosphate, methyl Examples of the metal salts include phenyloxyhexaoxypropylene phosphate, ethylphenyloxyhexaoxypropylene phosphate, butylphenyloxyhexaoxypropylene phosphate, hexylphenyloxyhexaoxypropylene phosphate, nonylphenyloxyhexaoxypropylene phosphate, dodecylphenyloxyhexaoxypropylene phosphate, methylphenyloxyoctaoxypropylene phosphate, ethylphenyloxyoctaoxypropylene phosphate, butylphenyloxyoctaoxypropylene phosphate, hexylphenyloxyoctaoxyethylene phosphate, nonylphenyloxyoctaoxypropylene phosphate, and dodecylphenyloxyoctaoxypropylene phosphate. Among these, the alkali metal salts, particularly the sodium salts, are preferred.

As the phosphate salt, a monovalent phosphate salt such as a sodium di(alkyloxypolyoxyalkylene) phosphate salt can be used alone or in combination with a divalent phosphate salt.
Examples of sulfate salts include sodium lauryl sulfate, potassium lauryl sulfate, ammonium lauryl sulfate, sodium myristyl sulfate, sodium polyoxyethylene alkyl sulfate, and sodium polyoxyethylene alkylaryl sulfate, with sodium lauryl sulfate being preferred.

Examples of cationic emulsifiers include alkyltrimethylammonium chloride, dialkylammonium chloride, and benzylammonium chloride.

Examples of nonionic emulsifiers include polyoxyalkylene fatty acid esters such as polyoxyethylene stearic acid ester; polyoxyalkylene alkyl ethers such as polyoxyethylene dodecyl ether; polyoxyalkylene alkylphenol ethers such as polyoxyethylene nonylphenyl ether; polyoxyethylene sorbitan alkyl esters, etc., with polyoxyalkylene alkyl ethers and polyoxyalkylene alkylphenol ethers being preferred, and polyoxyethylene alkyl ethers and polyoxyethylene alkylphenol ethers being more preferred.

These emulsifiers can be used alone or in combination of two or more. The amount used is usually 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 1 to 3 parts by weight, per 100 parts by weight of the monomer component.

The method (mixing method) for mixing the monomer component, water, and emulsifier may be a conventional method, such as stirring the monomer, emulsifier, and water using a stirrer such as a homogenizer or a disk turbine. The amount of water used is usually 1 to 1,000 parts by weight, preferably 5 to 500 parts by weight, more preferably 4 to 300 parts by weight, particularly preferably 3 to 150 parts by weight, and most preferably 20 to 80 parts by weight, per 100 parts by weight of the monomer component.

(Radical Generator)
The polymerization catalyst used in the present invention is characterized by using a redox catalyst consisting of a radical generator and a reducing agent. The radical generator is not particularly limited and may be an organic radical generator, an inorganic radical generator, or the like, depending on the intended use, but it is particularly preferable to use an inorganic radical generator, since it can highly improve the processability of the acrylic rubber produced in rolls, etc.

There are no particular limitations on the organic radical generator, so long as it is one that is commonly used in emulsion polymerization, and examples of such an agent include organic peroxides and azo compounds.

There are no particular limitations on the organic peroxides as long as they are known to be used in emulsion polymerization, and examples thereof include 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, 1-di-(t-hexylperoxy)cyclohexane, 1,1-di-(t-butylperoxy)cyclohexane, 4,4-di-(t-butylperoxy)n-butyl valerate, 2,2-di-(t-butylperoxy)butane, t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramenthane hydroperoxide, benzoyl peroxide, and 1,1,3,3-tetramethylphenyl hydroperoxide. tetraethylbutyl hydroperoxide, t-butylcumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, diisobutyryl peroxide, di(3,5,5-trimethylhexanoyl)peroxide, dilauroyl peroxide, disuccinic acid peroxide, dibenzoyl peroxide, di(3-methylbenzoyl)peroxide, benzoyl(3-methylbenzoyl)peroxide, diisobutyryl peroxydicarbonate, di-n-propyl peroxydicarbonate, di (2-ethylhexyl)peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutylperoxyneodecanate, t-hexylperoxypivalate, t-butylperoxyneodecanate, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate, t-hexylperoxy-2-ethylhexanate, t-butylperoxy-3,5,5-trimethylhexanate, t-hexylperoxy -oxyisopropyl monocarbonate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, t-hexylperoxybenzoate, t-butylperoxybenzoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, etc., among which diisopropylbenzene hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, benzoyl peroxide, etc. are preferred.

Examples of azo compounds include azobisisoptylonitrile, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis[2-(2-imidazolin-2-yl)propane, 2,2'-azobis(propane-2-carboxamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropanamide], 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}, 2,2'-azobis(1-imino-1-pyrrolidino-2-methylpropane), and 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propanamide}.

There are no particular limitations on the inorganic radical generator, so long as it is one that is commonly used in emulsion polymerization. Examples include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, and hydrogen peroxide. Among these, persulfates are preferred, potassium persulfate and ammonium persulfate are more preferred, and potassium persulfate is particularly preferred.

These radical generators can be used alone or in combination of two or more kinds, and the amount used is usually in the range of 0.0001 to 5 parts by weight, preferably 0.0005 to 1 part by weight, more preferably 0.001 to 0.25 parts by weight, particularly preferably 0.01 to 0.21 parts by weight, and most preferably 0.1 to 0.2 parts by weight, per 100 parts by weight of the monomer component.

(Reducing Agent)
The reducing agent used in the present invention is not particularly limited as long as it is one that is usually used in emulsion polymerization, but it is preferable to use at least two types of reducing agents, and a combination of a metal ion compound in a reduced state and another reducing agent is suitable.

The reduced metal ion compound is not particularly limited, but examples include ferrous sulfate, sodium iron hexamethylenediaminetetraacetate, and cuprous naphthenate, with ferrous sulfate being preferred. These reduced metal ion compounds can be used alone or in combination of two or more, and the amount used is usually in the range of 0.000001 to 0.01 parts by weight, preferably 0.00001 to 0.001 parts by weight, and more preferably 0.00005 to 0.0005 parts by weight, per 100 parts by weight of the monomer component.

Examples of reducing agents other than metal ion compounds in a reduced state include, but are not limited to, ascorbic acid or a salt thereof such as ascorbic acid, sodium ascorbate, potassium ascorbate, etc.; erythorbic acid or a salt thereof such as erythorbic acid, sodium erythorbate, potassium erythorbate, etc.; sulfinates such as sodium hydroxymethanesulfinate, etc.; sulfites such as sodium sulfite, potassium sulfite, sodium hydrogensulfite, aldehyde sodium hydrogensulfite, potassium hydrogensulfite, etc.; pyrosulfites such as sodium pyrosulfite, potassium pyrosulfite, sodium hydrogensulfite, potassium pyrosulfite, etc.; thiosulfates such as sodium thiosulfate, potassium thiosulfate, etc.; phosphorous acid or a salt thereof such as sodium phosphite, potassium phosphite, sodium hydrogen phosphite, potassium hydrogen phosphite, etc.; pyrophosphorous acid or a salt thereof such as pyrophosphorous acid, sodium pyrophosphite, potassium pyrophosphite, sodium hydrogen pyrophosphite, potassium hydrogen pyrophosphite, etc.; sodium formaldehyde sulfoxylate, etc. Among these, ascorbic acid or its salts, sodium formaldehyde sulfoxylate, etc. are preferred, and ascorbic acid or its salts are particularly preferred.

These reducing agents other than metal ion compounds in a reduced state can be used alone or in combination of two or more kinds, and the amount used is usually in the range of 0.001 to 1 part by weight, preferably 0.005 to 0.5 parts by weight, and more preferably 0.01 to 0.1 parts by weight, per 100 parts by weight of the monomer component.

A preferred combination of a metal ion compound in a reduced state and another reducing agent is a combination of ferrous sulfate and ascorbic acid or a salt thereof and/or sodium formaldehyde sulfoxylate, more preferably a combination of ferrous sulfate and an ascorbate and/or sodium formaldehyde sulfoxylate, and most preferably a combination of ferrous sulfate and an ascorbate. In this case, the amount of ferrous sulfate used is usually in the range of 0.000001 to 0.01 parts by weight, preferably 0.00001 to 0.001 parts by weight, and more preferably 0.00005 to 0.0005 parts by weight, per 100 parts by weight of the monomer component, and the amount of ascorbic acid or a salt thereof and/or sodium formaldehyde sulfoxylate used is usually in the range of 0.001 to 1 part by weight, preferably 0.005 to 0.5 parts by weight, and more preferably 0.01 to 0.1 parts by weight, per 100 parts by weight of both components.

The amount of water used in the emulsion polymerization reaction may be the same as that used when emulsifying the monomer components, but it is usually adjusted to be in the range of 10 to 1,000 parts by weight, preferably 50 to 500 parts by weight, more preferably 80 to 400 parts by weight, and most preferably 100 to 300 parts by weight, per 100 parts by weight of the monomer components used in the polymerization.

The emulsion polymerization reaction may be carried out in the usual manner, and may be a batch, semi-batch, or continuous system. The polymerization temperature and polymerization time are not particularly limited and may be appropriately selected depending on the type of polymerization initiator used. The polymerization time is usually 0.5 to 100 hours, and preferably 1 to 10 hours.

The emulsion polymerization reaction is an exothermic reaction, and if not controlled, the temperature will rise and the polymerization reaction can be shortened. However, in the present invention, the emulsion polymerization reaction temperature is usually controlled to 35°C or less, preferably 0 to 35°C, more preferably 5 to 30°C, and particularly preferably 10 to 25°C, which is suitable for achieving a high level of balance between the strength properties of the acrylic rubber produced and the processability during kneading with a Banbury mix, etc.

(Post-addition of chain transfer agent)
The present invention is characterized in that the chain transfer agent is not added at the initial stage, but is added batchwise during the polymerization, and by doing so, an acrylic rubber in which high molecular weight components and low molecular weight components are separated can be produced, and the strength properties of the acrylic rubber produced and the processability during kneading with a roll or the like are highly balanced, which is preferable.

The chain transfer agent used is not particularly limited as long as it is one that is usually used in emulsion polymerization, and for example, a mercaptan compound can be suitably used.
As the mercaptan compound, an alkyl mercaptan compound having usually 2 to 20 carbon atoms, preferably an alkyl mercaptan compound having 5 to 15 carbon atoms, more preferably an alkyl mercaptan compound having 6 to 14 carbon atoms can be used.

The alkyl mercaptan compound may be any of n-alkyl mercaptan compounds, sec-alkyl mercaptan compounds, and t-alkyl mercaptan compounds, but n-alkyl mercaptan compounds and t-alkyl mercaptan compounds are preferred, and n-alkyl mercaptan compounds are even more preferred, as they are more stable in their effect as a chain transfer agent and can highly improve the processability of the acrylic rubber produced in rolls, etc.

Specific examples of alkyl mercaptan compounds include n-pentyl mercaptan, n-hexyl mercaptan, n-heptyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, n-tridecane mercaptan, n-tetradecyl mercaptan, n-hexadecyl mercaptan, n-octadecyl mercaptan, sec-pentyl mercaptan, sec-hexyl mercaptan, sec-heptyl mercaptan, sec-octyl mercaptan, sec-decyl mercaptan, sec-dodecyl mercaptan, sec-tridecane mercaptan, and sec-tetradecyl mercaptan. Examples of suitable mercaptans include decyl mercaptan, sec-hexadecyl mercaptan, sec-octadecyl mercaptan, t-pentyl mercaptan, t-hexyl mercaptan, t-heptyl mercaptan, t-octyl mercaptan, t-decyl mercaptan, t-dodecyl mercaptan, n-tridecane mercaptan, t-tetradecyl mercaptan, t-hexadecyl mercaptan, and t-octadecyl mercaptan. Preferred are n-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan, and more preferably n-octyl mercaptan and n-dodecyl mercaptan.

These chain transfer agents can be used alone or in combination of two or more. The amount of chain transfer agent used is not particularly limited, but when the amount is in the range of usually 0.0001 to 1 part by weight, preferably 0.0005 to 0.5 parts by weight, more preferably 0.001 to 0.5 parts by weight, particularly preferably 0.005 to 0.1 parts by weight, and most preferably 0.01 to 0.06 parts by weight, per 100 parts by weight of the monomer component, the strength properties and roll processability of the produced acrylic rubber are highly balanced and suitable.

The present invention is characterized in that the chain transfer agent is not added at the beginning of the polymerization, but is added batchwise during the polymerization, which is advantageous in that it produces high molecular weight and low molecular weight components of the acrylic rubber produced, and the molecular weight distribution is within a specific range, allowing for a high level of balance between strength properties and processability for rolling, etc.

There are no particular limitations on the number of times the chain transfer agent is added in batches, and it is selected appropriately depending on the intended use. However, it is usually preferable to add the chain transfer agent 1 to 5 times, preferably 2 to 4 times, more preferably 2 to 3 times, and particularly preferably 2 times, in order to obtain a high level of balance between the strength properties of the acrylic rubber produced and the processability of the roll, etc.

There are no particular limitations on the timing of batchwise post-addition of the chain transfer agent, and it is selected appropriately depending on the purpose of use. However, it is usually preferable to add the agent at least 20 minutes after the start of polymerization, preferably at least 30 minutes, more preferably 30 to 200 minutes, particularly preferably 35 to 150 minutes, and most preferably 40 to 120 minutes after the start of polymerization, in order to achieve a high level of balance between the strength properties of the acrylic rubber produced and its processability in rolling, etc.

There are no particular limitations on the amount of chain transfer agent added at one time, and it is selected appropriately depending on the intended use, but a range of usually 0.00005 to 0.5 parts by weight, preferably 0.0001 to 0.1 parts by weight, more preferably 0.0005 to 0.05 parts by weight, particularly preferably 0.001 to 0.03 parts by weight, and most preferably 0.002 to 0.02 parts by weight, per 100 parts by weight of the monomer component, is suitable in order to achieve a high level of balance between the strength properties and roll processability of the acrylic rubber produced.

After the chain transfer agent is added, the polymerization reaction is usually continued for at least 30 minutes, preferably at least 45 minutes, and more preferably at least 1 hour, although there are no particular limitations, and then the reaction can be terminated.

(Post-addition of reducing agent)
In the present invention, the reducing agent for the redox catalyst can be added later during the polymerization, which is preferable because it allows the strength properties and processability for rolls and the like of the acrylic rubber to be produced to be well balanced.

The reducing agent added later during the polymerization is the same as the examples and preferred ranges of the reducing agent described above. In the present invention, ascorbic acid or a salt thereof is preferred as the reducing agent added later.

The amount of reducing agent added later during polymerization is not particularly limited and may be appropriately selected depending on the intended use, but when the amount is in the range of usually 0.0001 to 1 part by weight, preferably 0.0005 to 0.5 parts by weight, more preferably 0.001 to 0.5 parts by weight, particularly preferably 0.005 to 0.1 parts by weight, and most preferably 0.01 to 0.05 parts by weight, per 100 parts by weight of the monomer component, this is suitable as it provides excellent productivity in acrylic rubber production and also provides a high level of balance between the strength properties and processability of the acrylic rubber produced.

The reducing agent added during polymerization may be added either continuously or batchwise, but is preferably added batchwise. There is no particular limit to the number of times the reducing agent is added batchwise during polymerization, but it is usually added 1 to 5 times, preferably 1 to 3 times, and more preferably 1 to 2 times.

When the reducing agent added at the beginning or during the polymerization is ascorbic acid or a salt thereof, the ratio of the amount of ascorbic acid or a salt thereof added at the beginning to the amount of ascorbic acid or a salt thereof added later is not particularly limited, but a weight ratio of "initial addition ascorbic acid or a salt thereof"/"batchwise later addition ascorbic acid or a salt thereof" in the range of usually 1/9 to 8/2, preferably 2/8 to 6/4, and more preferably 3/7 to 5/5 is suitable because it provides excellent productivity in acrylic rubber production and a high level of balance between the strength properties and processability of the acrylic rubber produced.

There are no particular limitations on the timing of post-addition of the reducing agent, and it is selected appropriately depending on the intended use, but it is usually more than 1 hour after the start of polymerization, preferably 1 to 3 hours, and more preferably 1.5 to 2.5 hours, which is suitable for achieving excellent productivity in acrylic rubber production and a high level of balance between the strength properties of the acrylic rubber produced and the workability of rolls, etc.

There are no particular limitations on the amount of reducing agent added at one time, and it is selected appropriately depending on the intended use, but it is usually suitable to add 0.00005 to 0.5 parts by weight, preferably 0.0001 to 0.1 parts by weight, more preferably 0.0005 to 0.05 parts by weight, and particularly preferably 0.001 to 0.03 parts by weight, per 100 parts by weight of the monomer component, as this provides a high level of balance between the strength properties of the acrylic rubber produced and its processability in rolling and the like.

After the addition of the reducing agent, the polymerization reaction is usually continued for at least 30 minutes, preferably at least 45 minutes, and more preferably at least 1 hour, although there are no particular limitations, and then the reaction can be terminated.

The polymerization conversion rate of the emulsion polymerization reaction is not particularly limited, but is usually 90% by weight or more, and preferably 95% by weight or more. The acrylic rubber produced in this manner has excellent strength characteristics and is suitable for use without any monomer odor. A polymerization terminator may be used to terminate the polymerization.

(solidification process)
The method for coagulating after emulsion polymerization is characterized in that the emulsion polymerization liquid obtained by the above emulsion polymerization is added to a stirring coagulation liquid having a coagulant concentration of 1% by weight or more, and coagulated to produce hydrous crumbs.

There are no particular limitations on the solids concentration of the emulsion polymerization liquid used in the coagulation reaction, but it is usually adjusted to a range of 5 to 50% by weight, preferably 10 to 45% by weight, and more preferably 20 to 40% by weight.

The coagulant used in the coagulation liquid is not particularly limited, but a metal salt is usually used. Examples of metal salts include alkali metals, Group 2 metal salts of the periodic table, and other metal salts, and are preferably alkali metal salts and Group 2 metal salts of the periodic table, more preferably Group 2 metal salts of the periodic table, and particularly preferably magnesium salts.

Examples of alkali metal salts include sodium salts such as sodium chloride, sodium nitrate, and sodium sulfate; potassium salts such as potassium chloride, potassium nitrate, and potassium sulfate; and lithium salts such as lithium chloride, lithium nitrate, and lithium sulfate. Of these, sodium salts are preferred, with sodium chloride and sodium sulfate being particularly preferred.

Examples of salts of metals in Group 2 of the periodic table include magnesium chloride, calcium chloride, magnesium nitrate, calcium nitrate, magnesium sulfate, and calcium sulfate, with calcium chloride and magnesium sulfate being preferred.

Other metal salts include, for example, zinc chloride, titanium chloride, manganese chloride, iron chloride, cobalt chloride, nickel chloride, aluminum chloride, tin chloride, zinc nitrate, titanium nitrate, manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, aluminum nitrate, tin nitrate, zinc sulfate, titanium sulfate, manganese sulfate, iron sulfate, cobalt sulfate, nickel sulfate, aluminum sulfate, and tin sulfate.

These coagulants can be used alone or in combination of two or more, and the amount used is usually in the range of 0.01 to 100 parts by weight, preferably 0.1 to 50 parts by weight, and more preferably 1 to 30 parts by weight, per 100 parts by weight of the monomer component. When the coagulant is in this range, it is preferable because it can sufficiently coagulate the acrylic rubber while highly improving the compression set resistance and water resistance when the acrylic rubber is crosslinked.

There are no particular limitations on the coagulant concentration of the coagulation liquid used, but it is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, and particularly preferably 1.5% by weight or more. The coagulant concentration of the coagulation liquid is also usually in the range of 0.1 to 20% by weight, preferably 0.5 to 15% by weight, more preferably 1 to 10% by weight, and particularly preferably 1.5 to 5% by weight, which is suitable for concentrating the particle size of the generated hydrous crumbs uniformly in a specific region.

There are no particular limitations on the temperature of the coagulation liquid, but a temperature of 40°C or higher, preferably 40 to 90°C, and more preferably 50 to 80°C, is generally preferred to produce uniform hydrous crumbs.

The stirring speed (rotation speed) of the coagulation liquid being stirred, that is, the rotation speed of the stirring blade of the stirring device, is not particularly limited, but is usually 100 rpm or more, preferably 200 rpm or more, more preferably 200 to 1000 rpm, particularly preferably 300 to 900 rpm, and most preferably in the range of 400 to 800 rpm.

A rotation speed that provides a certain degree of vigorous stirring is preferable because it allows the generated hydrous crumbs to be small and uniform in particle size. By setting the rotation speed above the lower limit, it is possible to prevent crumbs with excessively large and small particle sizes from being generated, and by setting the rotation speed below the upper limit, it is possible to more easily control the coagulation reaction.

The peripheral speed of the stirred coagulation liquid, i.e., the speed of the outer periphery of the stirring blade of the stirring device, is not particularly limited, but stirring vigorously to a certain extent is preferable because it makes the particle size of the water-containing crumbs small and uniform, and is usually 0.5 m/s or more, preferably 1 m/s or more, more preferably 1.5 m/s or more, particularly preferably 2 m/s or more, and most preferably 2.5 m/s or more. On the other hand, the upper limit of the peripheral speed is not particularly limited, but it is preferable that it is usually 50 m/s or less, preferably 30 m/s or less, more preferably 25 m/s or less, and most preferably 20 m/s or less, because this makes it easier to control the coagulation reaction.

By setting the above conditions for the coagulation reaction (addition method, solids concentration of the emulsion polymerization liquid, concentration and temperature of the coagulation liquid, rotation speed and peripheral speed when stirring the coagulation liquid, etc.) within a specific range, the shape and diameter of the water-containing crumbs produced are uniform and concentrated, and the removal of the emulsifier and coagulant during washing and dehydration is significantly improved, resulting in highly improved water resistance and storage stability of the acrylic rubber produced, which is advantageous.

(Washing process)
The washing step in the method for producing acrylic rubber of the present invention is characterized in that the water-containing crumbs produced in the coagulation reaction are washed with warm water.

The washing method is not particularly limited, and can be carried out, for example, by mixing the generated water-containing crumbs with a large amount of warm water.

The amount of warm water added for washing is not particularly limited, but it is suitable to use an amount of water per wash of usually 50 parts by weight or more, preferably 50 to 15,000 parts by weight, more preferably 100 to 10,000 parts by weight, and even more preferably 500 to 5,000 parts by weight, per 100 parts by weight of the monomer component, since this effectively reduces the amount of ash in the acrylic rubber.

The temperature of the hot water used is not particularly limited, but is usually 40°C or higher, preferably 40 to 100°C, and more preferably 50 to 90°C, and is particularly optimal when the temperature is 60 to 80°C, as this significantly improves the cleaning efficiency. By using water at a temperature above the lower limit mentioned above, the emulsifier and coagulant are released from the water-containing crumbs, further improving the cleaning efficiency.

There are no particular limitations on the cleaning time, but it is usually in the range of 1 to 120 minutes, preferably 2 to 60 minutes, and more preferably 3 to 30 minutes.

There are no particular limitations on the number of washings (water washings), and it is usually 1 to 10 times, preferably 1 to 5 times, and more preferably 2 to 3 times. From the viewpoint of reducing the amount of residual coagulant in the final acrylic rubber, it is desirable to wash with water more frequently, but the number of water washings can be significantly reduced by setting the shape and diameter of the wet crumbs within a specific range as described above, and/or by setting the washing temperature within the above range.

(Dehydration process)
The dehydration step in the method for producing acrylic rubber of the present invention is a step of dehydrating the above-mentioned washed water-containing crumbs.

There are no particular limitations on the method for dehydrating the hydrous crumbs, so long as it is a method that can squeeze out the water from the hydrous crumbs, and this can usually be done using a dehydrator or the like. This is advantageous because it reduces the amount of ash from the emulsifier and coagulant contained in the hydrous crumbs that could not be removed in the washing process, and significantly improves the water resistance of the acrylic rubber.

The dehydrator is not particularly limited, and for example, a centrifuge, squeezer, screw-type extruder, etc. can be used, but a screw-type extruder is particularly suitable because it can significantly reduce the moisture content of the water-containing crumb. In a centrifuge, etc., sticky acrylic rubber can usually only be dehydrated to about 45 to 55% by weight because the acrylic rubber adheres to the wall surface and between the slits. In contrast, a screw-type extruder is suitable because it has a mechanism that forcibly squeezes out the moisture.

The moisture content of the dehydrated hydrous crumb is not limited, but is usually in the range of 1 to 50% by weight, preferably 1 to 40% by weight, more preferably 10 to 40% by weight, and more preferably 15 to 35% by weight. By setting the moisture content after dehydration to above the lower limit above, the dehydration time can be shortened and deterioration of the acrylic rubber can be suppressed, while by setting it below the upper limit above, the ash content can be sufficiently reduced.

(drying process)
The drying step in the method for producing acrylic rubber of the present invention is a step of drying the dehydrated water-containing crumbs to a moisture content of less than 1% by weight.

The method for drying the dehydrated hydrous crumbs is not particularly limited, but for example, the dehydrated hydrous crumbs can be dried directly, and preferably, a screw-type twin-screw extrusion dryer can be used. There are no particular limitations on the screw-type twin-screw extrusion dryer used, as long as it is an extrusion dryer with two screws. In the present invention, it is particularly preferable to use a screw-type twin-screw extrusion dryer with two screws to dry the hydrous crumbs under high-shear conditions, since this allows for a high level of balance between the roll processability, Banbury processability, and strength properties of the acrylic rubber obtained.

The maximum torque of the screw-type twin-screw extrusion dryer used in the present invention is not particularly limited, but is usually 20 N·m or more, preferably 25 N·m or more, more preferably 30 N·m or more, particularly preferably 35 N·m or more, and most preferably 40 N·m or more. The maximum torque of the screw-type twin-screw extrusion dryer used in the present invention is also preferably in the range of usually 25 to 125 N·m, preferably 30 to 100 N·m, more preferably 35 to 75 N·m, and particularly preferably 40 to 60 N·m, because this allows the roll processability, Banbury processability, and strength properties of the acrylic rubber produced to be highly balanced.

The specific power of the screw-type twin-screw extruder used in the present invention is not particularly limited, but is usually in the range of 0.1 to 0.25 [kW·h/kg] or more, preferably 0.13 to 0.23 [kW·h/kg], and more preferably 0.15 to 0.2 [kW·h/kg], which provides a highly balanced and suitable range for the roll processability, Banbury processability, and strength properties of the resulting acrylic rubber.

The specific power of the screw-type twin-screw extruder used in the present invention is not particularly limited, but is usually in the range of 0.2 to 0.6 [A·h/kg/] or more, preferably 0.25 to 0.55 [A·h/kg/], and more preferably 0.35 to 0.5 [A·h/kg/], which is suitable for achieving a high level of balance between the roll processability, Banbury processability, and strength properties of the resulting acrylic rubber.

The shear rate of the screw-type twin-screw extruder used in the present invention is not particularly limited, but when it is in the range of usually 40 to 150 [1/s] or more, preferably 45 to 125 [1/s], and more preferably 50 to 100 [1/s], the storage stability, roll processability, Banbury processability, and strength properties of the resulting acrylic rubber are highly balanced and suitable.

The shear viscosity of the acrylic rubber in the screw-type twin-screw extruder used in the present invention is not particularly limited, but when it is in the range of usually 4000 to 8000 [Pa·s] or less, preferably 4500 to 7500 [Pa·s], and more preferably 5000 to 7000 [Pa·s], the storage stability, roll processability, Banbury processability, and strength properties of the obtained acrylic rubber are highly balanced and suitable.

The dried rubber obtained above can be baled. Baling of the dried rubber can be done according to conventional methods, for example, by putting the dried rubber into a baler and compressing it. The compression pressure is appropriately selected depending on the intended use, but is usually in the range of 0.1 to 15 MPa, preferably 0.5 to 10 MPa, and more preferably 1 to 5 MPa. The compression time is not particularly limited, but is usually in the range of 1 to 60 seconds, preferably 5 to 30 seconds, and more preferably 10 to 20 seconds.

The thus obtained acrylic rubber of the present invention has excellent roll processability, strength properties and water resistance, and can be used in various applications. The shape of the acrylic rubber of the present invention is not particularly limited and is selected according to the intended use, and examples thereof include powder, crumb, strand, sheet, veil, etc., with the sheet and veil being preferred because of their excellent workability and storage stability.
(Method for manufacturing sheet or veil acrylic rubber)

The method for producing the sheet-like or veil-like acrylic rubber of the present invention is not particularly limited, but the sheet-like acrylic rubber can be easily produced by dehydrating the above-mentioned washed water-containing crumbs in the dehydrating barrel using a screw-type twin-screw extruder dryer having a dehydration slit, a drying barrel under reduced pressure, and a die at the tip, dehydrating the water-containing crumbs to a moisture content of 1 to 40% by weight, drying the crumbs in the drying barrel to a moisture content of less than 1% by weight, and extruding the sheet-like dried rubber from the die. Also, the extruded sheet-like dried rubber can be stacked to form a bale, whereby the veil-like acrylic rubber can be easily produced.

In the present invention, it is preferable that the hydrous crumbs supplied to the screw-type twin-screw extrusion dryer are those from which free water has been removed (drained) after washing.

In the present invention, it is preferable to provide a draining step in which free water is separated from the washed wet crumbs using a drainer in order to increase the dewatering efficiency.

Any known draining machine can be used without any particular limitations, such as wire mesh, screen, electric sifter, etc., with wire mesh and screen being preferred.

There are no particular limitations on the opening size of the drainer, but it is usually suitable for efficient draining with minimal loss of water-containing crumb when it is in the range of 0.01 to 5 mm, preferably 0.1 to 1 mm, and more preferably 0.2 to 0.6 mm.

The moisture content of the hydrous crumbs after draining, i.e., the moisture content of the hydrous crumbs fed into the dehydration and drying process, is not particularly limited, but is usually in the range of 50 to 80% by weight, preferably 50 to 70% by weight, and more preferably 50 to 60% by weight.

The temperature of the hydrous crumbs after draining, i.e., the temperature of the hydrous crumbs fed into the dehydration and drying process, is not particularly limited, but is usually 40°C or higher, preferably 40 to 100°C, more preferably 50 to 90°C, particularly preferably 55 to 85°C, and most preferably in the range of 60 to 80°C. This is suitable for efficiently dehydrating and drying hydrous crumbs such as the acrylic rubber of the present invention, which has a high specific heat of 1.5 to 2.5 KJ/kg·K and is difficult to raise the temperature of, using a screw-type twin-screw extruder.

Dehydration of crumbs (dehydration barrel section)
The dehydration of the hydrous crumb is carried out in a dehydration barrel having a dehydration slit. The opening of the dehydration slit may be appropriately selected depending on the conditions of use, but when it is in the range of usually 0.01 to 5 mm, preferably 0.1 to 1 mm, more preferably 0.2 to 0.6 mm, the loss of hydrous crumb is small and the hydrous crumb can be efficiently dehydrated.

The number of dehydration barrels in a screw-type twin-screw extrusion dryer is not particularly limited, but it is usually preferable to have more than one, preferably 2 to 10, and more preferably 3 to 6, in order to efficiently dehydrate the sticky acrylic rubber.

Water is removed from the wet crumb in the dewatering barrel in two ways: through the dewatering slit in liquid form (wastewater) or in vapor form (exhaust steam). In this invention, we distinguish between the two by defining wastewater as dewatering and exhaust steam as pre-drying.

When dehydrating the hydrous crumbs, the water discharged from the dehydration slit may be in either liquid (wastewater) or vapor (exhaust steam) state, but when using a screw-type twin-screw dryer equipped with multiple dehydration barrels, a combination of drainage and exhaust steam is preferable because it allows for efficient dehydration of the viscous acrylic rubber. The choice of drainage type dehydration barrel or exhaust steam type dehydration barrel for a screw-type twin-screw extrusion dryer equipped with three or more dehydration barrels can be made appropriately depending on the intended use, but the number of drainage type barrels is increased when the ash content in the acrylic rubber produced is generally reduced, and the number of exhaust steam type barrels is increased when the moisture content is reduced.

The set temperature of the dehydration barrel is selected appropriately depending on the monomer composition, ash content, water content, and operating conditions of the acrylic rubber, but is usually in the range of 60 to 150°C, preferably 70 to 140°C, and more preferably 80 to 130°C. The set temperature of the dehydration barrel for dehydration in a wastewater state is usually in the range of 60 to 120°C, preferably 70 to 110°C, and more preferably 80 to 100°C. The set temperature of the dehydration barrel for dehydration in an exhaust steam state is usually in the range of 100 to 150°C, preferably 105 to 140°C, and more preferably 110 to 130°C.

There are no particular limitations on the moisture content after dehydration in drainage dehydration, which squeezes out moisture from the hydrous crumbs, but a moisture content of 1 to 40% by weight, preferably 5 to 40% by weight, more preferably 5 to 35% by weight, and particularly preferably 10 to 35% by weight, is suitable as it provides a high level of balance between productivity and ash removal efficiency.

When dehydrating viscous acrylic rubber that has reactive groups using a centrifuge or similar machine, the acrylic rubber adheres to the dehydration slits and is barely dehydrated (water content is up to about 45-55% by weight). However, in this invention, by using a screw-type twin-screw extrusion dryer that has a dehydration slit and is forcibly squeezed by a screw, it is possible to reduce the water content to this extent.

When a drainage type dehydration barrel and a steam exhaust type dehydration barrel are used, the moisture content after drainage in the drainage type dehydration barrel is usually 5 to 40% by weight, preferably 10 to 40% by weight, and more preferably 15 to 35% by weight, and the moisture content after preliminary drying in the steam exhaust type dehydration barrel is usually 1 to 30% by weight, preferably 3 to 20% by weight, and more preferably 5 to 15% by weight.

By setting the moisture content after dehydration to above the lower limit, the dehydration time can be shortened and deterioration of the acrylic rubber can be suppressed, while by setting it below the upper limit, the ash content can be sufficiently reduced.

Drying of moist crumbs (drying barrel section)
The method is characterized in that the drying of the water-containing crumbs after the dehydration is carried out in a drying barrel under reduced pressure. By drying the acrylic rubber under reduced pressure, the drying efficiency of the tacky acrylic rubber having reactive groups can be increased, and the air contained in the acrylic rubber can be removed, thereby producing an acrylic rubber having a high specific gravity and excellent storage stability, which is preferable.

The degree of vacuum in the drying barrel may be selected as appropriate, but a pressure of 1 to 50 kPa, preferably 2 to 30 kPa, and more preferably 3 to 20 kPa is usually suitable for efficient drying of the water-containing crumbs. By setting the degree of vacuum in the drying barrel within this range, the acrylic rubber can be dried excellently and the air contained within the dried rubber can be removed, resulting in an increase in the specific gravity of the acrylic rubber produced and a significant improvement in storage stability, making this suitable.

The set temperature of the drying barrel may be selected as appropriate, but a temperature in the range of usually 100 to 250°C, preferably 110 to 200°C, and more preferably 120 to 180°C is suitable because it allows efficient drying without discoloration or deterioration of the acrylic rubber and reduces the amount of methyl ethyl ketone insolubles in the sheet or veil-like acrylic rubber (gel amount of methyl ethyl ketone insolubles).

The number of drying barrels in a screw-type twin-screw extrusion dryer is not particularly limited, but is usually more than one, preferably 2 to 10, and more preferably 3 to 8. When there are multiple drying barrels, the degree of vacuum may be similar for all drying barrels or may be different. When there are multiple drying barrels, the set temperature may be similar for all drying barrels or may be different, but it is preferable to make the temperature of the discharge section (closer to the die) higher than the temperature of the introduction section (closer to the dehydration barrel) in order to increase the drying efficiency.

The moisture content of the dried rubber after drying is usually less than 1% by weight, preferably 0.8% by weight or less, and more preferably 0.6% by weight or less. In the present invention, it is particularly preferable to melt extrude the dried rubber in a screw-type twin-screw extruder at this moisture content (a state in which almost all water has been removed) in order to reduce the amount of methyl ethyl ketone insolubles in the sheet- or veil-shaped acrylic rubber.

In the present invention, the shear rate in the drying barrel of the screw-type twin-screw extruder dryer when the acrylic rubber is substantially free of water is not particularly limited, but a shear rate of 10 [1/s] or more, preferably 10 to 400 [1/s], and more preferably 50 to 250 [1/s] is usually preferred because it provides a highly balanced storage stability, roll processability, Banbury processability, strength properties, and compression set resistance properties of the sheet- or veil-like acrylic rubber obtained.

The shear viscosity of the acrylic rubber in the screw-type twin-screw extruder used in the present invention, particularly in the drying barrel, is not particularly limited, but is usually 12,000 [Pa·s] or less, preferably 1,000 to 12,000 [Pa·s], more preferably 2,000 to 10,000 [Pa·s], particularly preferably 3,000 to 7,000 [Pa·s], and most preferably 4,000 to 6,000 [Pa·s], which is suitable for providing a highly balanced storage stability, roll processability, Banbury processability, and strength properties of the sheet- or veil-like acrylic rubber obtained.

Drying rubber (die section)
The dried rubber dehydrated and dried in the screw section of the dehydration barrel and the drying barrel is sent to a screw-free straightening die section. A breaker plate or a wire net may or may not be provided between the screw section and the die section.

The dried rubber to be extruded is preferably extruded in sheet form using a roughly rectangular die shape, which results in less air entrapment, a higher specific gravity, and excellent storage stability.

The resin pressure in the die section is not particularly limited, but is usually in the range of 0.1 to 10 MPa, preferably 0.5 to 5 MPa, and more preferably 1 to 3 MPa, which is suitable for reducing air entrapment in the sheet or veil-like acrylic rubber (high specific gravity) and providing excellent productivity.

Screw-type twin-screw extrusion dryer and operating conditions The screw length (L) of the screw-type twin-screw extrusion dryer used may be appropriately selected depending on the purpose of use, but is usually in the range of 3,000 to 15,000 mm, preferably 4,000 to 10,000 mm, and more preferably 4,500 to 8,000 mm.

The screw diameter (D) of the screw-type twin-screw extruder used may be selected appropriately depending on the intended use, but is usually in the range of 50 to 250 mm, preferably 100 to 200 mm, and more preferably 120 to 160 mm.

The ratio (L/D) of the screw length (L) to the screw diameter (D) of the screw-type twin-screw extruder dryer used is not particularly limited, but is usually in the range of 10 to 100, preferably 20 to 80, and more preferably 30 to 60, which is suitable for reducing the moisture content to less than 1% by weight without causing a decrease in the molecular weight of the dried rubber or burning.

The rotation speed (N) of the screw-type twin-screw extrusion dryer used may be appropriately selected depending on the various conditions, but a rotation speed of 10 to 1000 rpm, preferably 50 to 750 rpm, more preferably 100 to 500 rpm, and most preferably 120 to 300 rpm is suitable for efficiently reducing the water content and methyl ethyl ketone insoluble content of the sheet or veil-like acrylic rubber.

The throughput (Q) of the screw-type twin-screw extruder used is not particularly limited, but is usually in the range of 100 to 1,500 kg/hr, preferably 300 to 1,200 kg/hr, more preferably 400 to 1,000 kg/hr, and most preferably 500 to 800 kg/hr.

The ratio (Q/N) of the output (Q) to the rotation speed (N) of the screw-type twin-screw extruder dryer used is not particularly limited, but is usually in the range of 2 to 10, preferably 3 to 8, and more preferably 4 to 6.

The maximum torque of the screw-type twin-screw extrusion dryer used is not particularly limited, but is usually 30 N·m or more, preferably 35 N·m or more, and more preferably 40 N·m or more. The maximum torque of the screw-type twin-screw extrusion dryer used in the present invention is also preferably in the range of usually 30 to 100 N·m, preferably 35 to 75 N·m, and more preferably 40 to 60 N·m, since the roll processability, Banbury processability, and strength properties of the sheet-like or veil-like acrylic rubber produced can be highly balanced. In the present invention, the use of an extrusion dryer having twin screws is preferable because it enables dehydration, drying, and molding under high shear conditions.

There are no particular limitations on the specific power of the screw-type twin-screw extruder used, but a power range of 0.1 to 0.25 [kW·h/kg] or more, preferably 0.13 to 0.23 [kW·h/kg], and more preferably 0.15 to 0.2 [kW·h/kg], is usually preferable because it provides a high level of balance between the roll processability, Banbury processability, and strength properties of the sheet or veil-like acrylic rubber obtained.

There are no particular limitations on the specific power of the screw-type twin-screw extruder used, but a power in the range of 0.2 to 0.6 [A·h/kg/] or more, preferably 0.25 to 0.55 [A·h/kg/], and more preferably 0.35 to 0.5 [A·h/kg/], is usually preferable because it provides a high level of balance between the roll processability, Banbury processability, and strength properties of the resulting sheet or veil-like acrylic rubber.

The shear rate of the screw-type twin-screw extruder used is not particularly limited, but is usually in the range of 40 to 150 [1/s] or more, preferably 45 to 125 [1/s], and more preferably 50 to 100 [1/s], which is suitable for achieving a high level of balance in the storage stability, roll processability, Banbury processability, and strength properties of the sheet- or veil-like acrylic rubber obtained.

There are no particular limitations on the shear viscosity of the acrylic rubber in the screw-type twin-screw extruder dryer used, but when it is in the range of usually 4,000 to 8,000 [Pa·s] or less, preferably 4,500 to 7,500 [Pa·s], and more preferably 5,000 to 7,000 [Pa·s], the storage stability, roll processability, Banbury processability, and strength properties of the sheet- or veil-like acrylic rubber obtained are highly balanced and suitable.

Dry rubber sheet The dry rubber extruded from the screw-type twin-screw extrusion dryer is in the form of a sheet, which is preferable because it does not trap air and can increase the specific gravity, resulting in highly improved storage stability. The dry rubber sheet extruded from the screw-type twin-screw extrusion dryer is usually cooled and cut to be used as sheet acrylic rubber.

There are no particular limitations on the thickness of the sheet-like dry rubber extruded from the screw-type twin-screw extruder, but a thickness in the range of usually 1 to 40 mm, preferably 2 to 35 mm, more preferably 3 to 30 mm, and most preferably 5 to 25 mm is suitable for excellent workability and productivity. In particular, when the thermal conductivity of the sheet-like dry rubber is as low as 0.15 to 0.35 W/mK and the cooling efficiency is increased to significantly improve productivity, the thickness of the sheet-like dry rubber is usually in the range of 1 to 30 mm, preferably 2 to 25 mm, more preferably 3 to 15 mm, and particularly preferably 4 to 12 mm.

The width of the sheet-like dried rubber extruded from the screw-type twin-screw extruder is selected appropriately depending on the intended use, but is usually in the range of 300 to 1200 mm, preferably 400 to 1000 mm, and more preferably 500 to 800 mm.

The temperature of the dried rubber extruded from the screw-type twin-screw extruder is not particularly limited, but is usually in the range of 100 to 200°C, preferably 110 to 180°C, and more preferably 120 to 160°C.

There are no particular limitations on the moisture content of the dried rubber extruded from the screw-type twin-screw extruder, but it is usually less than 1% by weight, preferably 0.8% by weight or less, and more preferably 0.6% by weight or less.

The complex viscosity at 100°C ([η]100°C) of the sheet-like dried rubber extruded from the screw-type twin-screw extruder is not particularly limited, but is usually in the range of 1500 to 6000 [Pa·s], preferably 2000 to 5000 [Pa·s], more preferably 2500 to 4000 [Pa·s], and most preferably 2500 to 3500 [Pa·s], which is suitable for achieving a high balance between extrudability as a sheet and shape retention. In other words, by setting it at or above the lower limit, the extrudability can be made superior, and by setting it at or below the upper limit, deformation or breakage of the sheet-like dried rubber can be suppressed.

The dried rubber sheet extruded from the screw-type twin-screw extruder can be folded and used as is, but it is usually cut into pieces for use.

There are no particular limitations on how the dry rubber sheet is cut, but since the acrylic rubber of the present invention has strong adhesion, it is preferable to cool the dry rubber sheet before cutting in order to cut it continuously without entraining air.

There are no particular limitations on the cutting temperature of the dry rubber sheet, but a temperature of 60°C or less, preferably 55°C or less, and more preferably 50°C or less, is usually preferred as it provides a good balance between cuttability and productivity.

The complex viscosity of the dry rubber sheet at 60°C ([η] 60°C) is not particularly limited, but is usually 15,000 [Pa·s] or less, preferably 2000 to 10,000 [Pa·s], more preferably 2500 to 7000 [Pa·s], and most preferably 2700 to 5500 [Pa·s], which allows cutting without entraining air and allows continuous cutting.

The ratio ([η]100°C/[η]60°C) of the complex viscosity of the dry rubber sheet at 100°C ([η]100°C) to the complex viscosity at 60°C ([η]60°C) is not particularly limited and may be appropriately selected depending on the intended use, but is usually 0.5 or more, preferably 0.6 or more, more preferably 0.7 or more, particularly preferably 0.8 or more, and most preferably 0.85 or more. When the upper limit is usually 0.98 or less, preferably 0.97 or less, more preferably 0.96 or less, particularly preferably 0.95 or less, and most preferably 0.93 or less, air entrapment is reduced and cutting and productivity are well balanced, making this suitable.

There are no particular limitations on the cooling method for the dried rubber sheet, and it may be left at room temperature, but since the thermal conductivity of the dried rubber sheet is very low at 0.15 to 0.35 W/mK, forced cooling such as air cooling with ventilation or cooling, water spraying, or immersion in water is preferred to increase productivity, with air cooling with ventilation or cooling being particularly suitable.

In the air-cooling method for sheet-like dry rubber, for example, the sheet-like dry rubber is extruded from a screw-type extruder onto a conveyor such as a belt conveyor, and is conveyed and cooled while being blown with cold air. The temperature of the cold air is not particularly limited, but is usually in the range of 0 to 25°C, preferably 5 to 25°C, and more preferably 10 to 20°C. The length to be cooled is not particularly limited, but is usually in the range of 5 to 500 m, preferably 10 to 200 m, and more preferably 20 to 100 m. The cooling rate of the sheet-like dry rubber is not particularly limited, but is usually 50°C/hr or more, more preferably 100°C/hr or more, and more preferably 150°C/hr or more, which is particularly easy to cut and is therefore suitable.

There are no particular limitations on the cut length of the dry rubber sheet, and it is selected appropriately depending on the intended use, but it is usually in the range of 100 to 800 mm, preferably 200 to 500 mm, and more preferably 250 to 450 mm.

The sheet-like acrylic rubber thus obtained is superior in operability to crumb-like acrylic rubber, and is also superior in roll processability, crosslinkability, strength properties and compression set resistance properties as well as in storage stability, Banbury processability and water resistance, and can be used as is or after being laminated to form a bale.
Lamination Step The method for producing the veil-like acrylic rubber of the present invention is not particularly limited, but it is preferable to obtain a veil-like acrylic rubber having excellent storage stability with less air entrapment by laminating the above-mentioned sheet-like acrylic rubber.

The lamination temperature of the sheet-like acrylic rubber is not particularly limited, but is usually 30°C or higher, preferably 35°C or higher, and more preferably 40°C or higher, which allows air entrapped during lamination to escape. The number of layers may be appropriately selected depending on the size or weight of the veil-like acrylic rubber. The veil-like acrylic rubber of the present invention is integrated by the weight of the laminated sheet-like acrylic rubber.

The veil-like acrylic rubber of the present invention thus obtained is superior in operability to crumb-like acrylic rubber, and is excellent in roll processability, crosslinkability, strength properties, and compression set resistance, as well as in storage stability, Banbury processability, and water resistance. The veil-like acrylic rubber can be used as is, or the required amount can be cut and fed into a mixer such as a Banbury or roll.

<Rubber Composition>
The rubber composition of the present invention is characterized by comprising a rubber component containing the acrylic rubber, a filler, and a crosslinking agent.

As the rubber component that is the main component of the rubber composition of the present invention, the acrylic rubber of the present invention may be used alone, or, if necessary, the acrylic rubber of the present invention may be used in combination with other rubber components. The content of the acrylic rubber of the present invention in the rubber component may be selected according to the intended use, and is, for example, usually 30% by weight or more, preferably 50% by weight or more, and more preferably 70% by weight or more.

Other rubber components that can be combined with the acrylic rubber of the present invention are not particularly limited, and examples include natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, silicone rubber, fluororubber, olefin-based elastomers, styrene-based elastomers, vinyl chloride-based elastomers, polyester-based elastomers, polyamide-based elastomers, polyurethane-based elastomers, and polysiloxane-based elastomers.

These other rubber components may be used alone or in combination of two or more. The shape of these other rubber components may be any of crumb, strand, veil, sheet, powder, etc. The content of the other rubber components in the entire rubber component is appropriately selected within a range that does not impair the effects of the present invention, and is, for example, usually 70% by weight or less, preferably 50% by weight or less, and more preferably 30% by weight or less.

The filler contained in the rubber composition is not particularly limited, but examples include reinforcing fillers and non-reinforcing fillers, with reinforcing fillers being preferred.

Examples of reinforcing fillers include carbon blacks such as furnace black, acetylene black, thermal black, channel black, and graphite; silicas such as wet silica, dry silica, and colloidal silica; and the like. Examples of non-reinforcing fillers include quartz powder, diatomaceous earth, zinc oxide, basic magnesium carbonate, activated calcium carbonate, magnesium silicate, aluminum silicate, titanium dioxide, talc, aluminum sulfate, calcium sulfate, and barium sulfate.

These fillers can be used alone or in combination of two or more. The amount of filler is appropriately selected within a range that does not impair the effects of the present invention, and is usually in the range of 1 to 200 parts by weight, preferably 10 to 150 parts by weight, and more preferably 20 to 100 parts by weight, per 100 parts by weight of the rubber component.

There are no particular limitations on the crosslinking agent used in the rubber composition, and any conventionally known crosslinking agent may be selected depending on the intended use. Examples of such agents include inorganic crosslinking agents such as sulfur compounds and organic crosslinking agents, with organic crosslinking agents being preferred.

The organic crosslinking agent is not particularly limited, but an ionically crosslinkable organic compound is preferred, and a polyvalent ion organic compound is particularly preferred. The "ion" of the ionically crosslinkable or polyvalent ion is one that reacts ionically with the ionically reactive group of the ionically reactive group-containing monomer of the acrylic rubber, and is not particularly limited, but examples thereof include an amine group, an epoxy group, a carboxyl group, and a thiol group.

Specific examples of polyvalent ion organic compounds include polyvalent amine compounds, polyvalent epoxy compounds, polyvalent carboxylic acid compounds, and polyvalent thiol compounds, of which polyvalent amine compounds and polyvalent thiol compounds are preferred, and polyvalent amine compounds are more preferred.

Examples of polyamine compounds include aliphatic polyamine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicinnamylidene-1,6-hexanediamine; and aromatic polyamine compounds such as 4,4'-methylenedianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-(m-phenylenediisopropylidene)dianiline, 4,4'-(p-phenylenediisopropylidene)dianiline, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, and 1,3,5-benzenetriamine. Among these, hexamethylenediamine carbamate, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, etc. are preferred. As the polyamine compound, carbonates of these compounds can also be preferably used. These polyamine compounds are particularly preferably used in combination with carboxyl group-containing acrylic rubber or epoxy group-containing acrylic rubber.

As the polyvalent thiol compound, a triazine thiol compound is preferably used, such as 6-trimercapto-s-triazine, 2-anilino-4,6-dithiol-s-triazine, 1-dibutylamino-3,5-dimercaptotriazine, 2-dibutylamino-4,6-dithiol-s-triazine, 1-phenylamino-3,5-dimercaptotriazine, 2,4,6-trimercapto-1,3,5-triazine, and 1-hexylamino-3,5-dimercaptotriazine. These triazine thiol compounds are particularly suitable for use in combination with chlorine atom-containing acrylic rubber.

Other polyvalent organic compounds include polycarboxylic acid compounds such as tetradecanedioic acid, and metal dithiocarbamate salts such as zinc dimethyldithiocarbamate. These other polyvalent organic compounds are particularly suitable for use in combination with epoxy group-containing acrylic rubber.

These crosslinking agents can be used alone or in combination of two or more, and the amount is usually 0.001 to 20 parts by weight, preferably 0.1 to 10 parts by weight, and more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the rubber component. By setting the amount of crosslinking agent within this range, it is possible to obtain excellent mechanical strength as a crosslinked rubber product while maintaining sufficient rubber elasticity, which is preferable.

The rubber composition of the present invention may contain an antioxidant as necessary. The type of antioxidant is not particularly limited, but examples include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butylphenol, butylhydroxyanisole, 2,6-di-t-butyl-α-dimethylamino-p-cresol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, styrenated phenol, 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), 4,4'-methylene Others such as bis(2,6-di-t-butylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), 2,4-bis[(octylthio)methyl]-6-methylphenol, 2,2'-thiobis-(4-methyl-6-t-butylphenol), 4,4'-thiobis-(6-t-butyl-o-cresol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol phenol-based antioxidants such as tris(nonylphenyl)phosphite, diphenylisodecylphosphite, and tetraphenyldipropylene glycol diphosphite; sulfur ester-based antioxidants such as dilauryl thiodipropionate; phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamido)-diphenylamine, and 4,4'-(α,α-dimethylbenzyl)diphenylamine. Examples of such antioxidants include amine-based antioxidants such as amine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensates; imidazole-based antioxidants such as 2-mercaptobenzimidazole; quinoline-based antioxidants such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline; and hydroquinone-based antioxidants such as 2,5-di-(t-amyl)hydroquinone. Among these, amine-based antioxidants are particularly preferred.

These antioxidants can be used alone or in combination of two or more. The amount of antioxidant is in the range of 0.01 to 15 parts by weight, preferably 0.1 to 10 parts by weight, and more preferably 1 to 5 parts by weight, per 100 parts by weight of the rubber component.

The rubber composition of the present invention contains the above-mentioned acrylic rubber-containing rubber component, a filler, and a crosslinking agent as essential components, and, if necessary, an anti-aging agent. If necessary, other additives commonly used in the relevant technical field, such as crosslinking aids, crosslinking accelerators, crosslinking retarders, silane coupling agents, plasticizers, processing aids, lubricants, pigments, colorants, antistatic agents, and foaming agents, can be optionally blended. These other additives can be used alone or in combination of two or more, and the blending amounts are appropriately selected within a range that does not impair the effects of the present invention.

The method for producing the rubber composition of the present invention includes mixing the rubber component containing the acrylic rubber of the present invention, the filler, the crosslinking agent, and the antioxidant and other compounding ingredients that may be contained as necessary. Any means conventionally used in the rubber processing field, such as an open roll, a Banbury mixer, or various kneaders, may be used for mixing. The mixing procedure for each component may be the usual procedure used in the rubber processing field. For example, it is preferable to thoroughly mix the components that are difficult to react or decompose by heat, and then mix the crosslinking agent, which is a component that reacts or decomposes by heat, for a short period of time at a temperature at which no reaction or decomposition occurs.

<Rubber cross-linked product>
The cross-linked rubber product of the present invention is obtained by cross-linking the above-mentioned rubber composition.

The cross-linked rubber product of the present invention can be produced by using the rubber composition of the present invention, molding the rubber composition into a desired shape using a molding machine such as an extruder, an injection molding machine, a compressor, or a roll, and then heating the composition to cause a cross-linking reaction and fix the shape as a cross-linked rubber product. In this case, the cross-linking may be carried out after molding in advance, or may be carried out simultaneously with molding. The molding temperature is usually 10 to 200°C, preferably 25 to 150°C. The cross-linking temperature is usually 100 to 250°C, preferably 130 to 220°C, more preferably 150 to 200°C, and the cross-linking time is usually 0.1 minutes to 10 hours, preferably 1 minute to 5 hours. The heating method may be appropriately selected from methods used for cross-linking rubber, such as press heating, steam heating, oven heating, and hot air heating.

The cross-linked rubber product of the present invention may be further heated to carry out secondary cross-linking depending on the shape, size, etc. of the cross-linked rubber product. The secondary cross-linking time varies depending on the heating method, cross-linking temperature, shape, etc., but is preferably carried out for 1 to 48 hours. The heating method and heating temperature may be appropriately selected.

The cross-linked rubber of the present invention has excellent compression set resistance and water resistance while maintaining basic rubber properties such as tensile strength, elongation, and hardness.

The cross-linked rubber of the present invention, taking advantage of the above-mentioned properties, is suitably used for, for example, sealing materials such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing seals, mechanical seals, wellhead seals, seals for electrical and electronic equipment, and seals for air compressors; various gaskets such as rocker cover gaskets attached to the joint between a cylinder block and a cylinder head, oil pan gaskets attached to the joint between an oil pan and a cylinder head or a transmission case, gaskets for fuel cell separators attached between a pair of housings that sandwich a unit cell having a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for the top cover of hard disk drives; cushioning materials, vibration-proofing materials; wire coating materials; industrial belts; tubes and hoses; sheets; etc.

The cross-linked rubber product of the present invention is also suitable for use as extrusion molded products and mold cross-linked products for automotive applications, such as fuel hoses, filler neck hoses, vent hoses, paper hoses, fuel oil hoses for fuel tanks such as oil hoses, air hoses such as turbo air hoses and mission control hoses, radiator hoses, heater hoses, brake hoses, and air conditioner hoses.

<Apparatus configuration used in the production of acrylic rubber>
Next, the configuration of the equipment used in the production of acrylic rubber according to one embodiment of the present invention will be described. Fig. 1 is a diagram showing an example of an acrylic rubber production system having an equipment configuration used in the production of acrylic rubber according to one embodiment of the present invention. For example, the acrylic rubber production system 1 shown in Fig. 1 can be used to produce acrylic rubber according to the present invention.

The acrylic rubber manufacturing system 1 shown in FIG. 1 is composed of an emulsion polymerization reactor (not shown), a coagulation device 3, a washing device 4, a drainer 43, and a screw-type twin-screw extrusion dryer.

The emulsion polymerization reactor is configured to carry out the treatment related to the emulsion polymerization process described above. Although not shown in FIG. 1, this emulsion polymerization reactor has, for example, a polymerization reaction tank, a temperature control unit for controlling the reaction temperature, and a stirring device equipped with a motor and a stirring blade. In the emulsion polymerization reactor, the monomer components for forming the acrylic rubber are mixed with water and an emulsifier, and emulsified while being appropriately stirred with a stirrer, and the emulsion polymerization reaction is started in the presence of a redox catalyst consisting of an inorganic radical generator and a reducing agent, and a chain transfer agent is added in batches during the polymerization to obtain an emulsion polymerization liquid. The emulsion polymerization reactor may be any of a batch type, a semi-batch type, or a continuous type, and may be any of a tank type reactor and a tubular type reactor.

The solidification device 3 shown in FIG. 1 is configured to perform the process related to the solidification step described above. As shown in FIG. 1, the solidification device 3 has, for example, a stirring tank 30, a heating unit 31 that heats the inside of the stirring tank 30, a temperature control unit (not shown) that controls the temperature inside the stirring tank 30, a stirring device 34 equipped with a motor 32 and agitating blades 33, and a drive control unit (not shown) that controls the number of rotations and the rotation speed of the agitating blades 33. In the solidification device 3, the emulsion polymerization liquid obtained in the emulsion polymerization reactor can be brought into contact with the coagulation liquid and solidified to produce water-containing crumbs.

In the coagulation device 3, for example, the emulsion polymerization liquid is brought into contact with the coagulation liquid by adding the emulsion polymerization liquid to the coagulation liquid that is being stirred. That is, the stirring tank 30 of the coagulation device 3 is filled with coagulation liquid, and the emulsion polymerization liquid is added to and brought into contact with the coagulation liquid to coagulate the emulsion polymerization liquid, thereby generating water-containing crumbs.

The heating unit 31 of the solidification device 3 is configured to heat the solidification liquid filled in the stirring tank 30. The temperature control unit of the solidification device 3 is configured to control the temperature inside the stirring tank 30 by controlling the heating operation by the heating unit 31 while monitoring the temperature inside the stirring tank 30 measured by a thermometer. The temperature of the solidification liquid inside the stirring tank 30 is controlled by the temperature control unit to be normally 40°C or higher, preferably in the range of 40 to 90°C, and more preferably 50 to 80°C.

The agitator 34 of the solidification device 3 is configured to agitate the solidification liquid filled in the agitation tank 30. Specifically, the agitator 34 is equipped with a motor 32 that generates rotational power, and an agitator blade 33 that extends in a direction perpendicular to the rotation axis of the motor 32. The agitator blade 33 can cause the solidification liquid filled in the agitation tank 30 to flow by rotating around the rotation axis due to the rotational power of the motor 32. There are no particular limitations on the shape, size, or number of the agitator blades 33.

The drive control unit of the solidification device 3 is configured to control the rotation drive of the motor 32 of the stirring device 34 to set the number of rotations and the rotation speed of the stirring blade 33 of the stirring device 34 to a predetermined value. The rotation of the stirring blade 33 is controlled by the drive control unit so that the stirring speed of the solidification liquid is, for example, usually 100 rpm or more, preferably 200 to 1000 rpm, more preferably 300 to 900 rpm, and particularly preferably 400 to 800 rpm. The rotation of the stirring blade 33 is controlled by the drive control unit so that the peripheral speed of the solidification liquid is usually 0.5 m/s or more, preferably 1 m/s or more, more preferably 1.5 m/s or more, particularly preferably 2 m/s or more, and most preferably 2.5 m/s or more. Furthermore, the rotation of the stirring blade 33 is controlled by the drive control unit so that the upper limit of the peripheral speed of the solidification liquid is usually 50 m/s or less, preferably 30 m/s or less, more preferably 25 m/s or less, and most preferably 20 m/s or less.

The cleaning device 4 shown in FIG. 1 is configured to perform the treatment related to the above-mentioned cleaning process. As shown in FIG. 1, the cleaning device 4 has, for example, a cleaning tank 40, a heating unit 41 that heats the inside of the cleaning tank 40, and a temperature control unit (not shown) that controls the temperature inside the cleaning tank 40. In the cleaning device 4, the amount of ash in the final acrylic rubber can be effectively reduced by mixing the water-containing crumbs generated in the solidification device 3 with a large amount of water and cleaning it.

The heating unit 41 of the cleaning device 4 is configured to heat the inside of the cleaning tank 40. The temperature control unit of the cleaning device 4 is configured to control the temperature inside the cleaning tank 40 by controlling the heating operation of the heating unit 41 while monitoring the temperature inside the cleaning tank 40 measured by a thermometer. As described above, the temperature of the cleaning water in the cleaning tank 40 is usually controlled to be in the range of 40°C or higher, preferably 40 to 100°C, more preferably 50 to 90°C, and most preferably 60 to 80°C.

The hydrous crumb washed in the washing device 4 is supplied to a screw-type twin-screw extrusion dryer 5 which performs a dehydration process and a drying process. At this time, it is preferable that the hydrous crumb after washing is supplied to the screw-type twin-screw extrusion dryer 5 through a drainer 43 capable of separating free water. For example, a wire mesh, a screen, an electric sieve, etc. can be used as the drainer 43.

When the washed wet crumbs are supplied to the screw-type twin-screw extrusion dryer 5, the temperature of the wet crumbs is preferably 40°C or higher, more preferably 60°C or higher. For example, the temperature of the water used for washing in the washing device 4 may be set to 60°C or higher (e.g., 70°C) so that the temperature of the wet crumbs when supplied to the screw-type twin-screw extrusion dryer 5 can be maintained at 60°C or higher, or the wet crumbs may be heated to a temperature of 40°C or higher, preferably 60°C or higher, when transported from the washing device 4 to the screw-type twin-screw extrusion dryer 5. This makes it possible to effectively perform the subsequent dehydration and drying processes, and significantly reduce the moisture content of the finally obtained dried rubber.

The screw-type twin-screw extrusion dryer 5 shown in FIG. 1 is configured to perform the processes related to the dehydration process and drying process described above. Although the screw-type twin-screw extrusion dryer 5 is shown in FIG. 1 as a suitable example, a centrifuge or squeezer may be used as a dehydrator that performs the process related to the dehydration process, and a hot air dryer, reduced pressure dryer, expander dryer, kneader dryer, etc. may be used as a dryer that performs the process related to the drying process.

The screw-type twin-screw extrusion dryer 5 is configured to mold the dried rubber obtained through the dehydration process and the drying process into a predetermined shape and discharge it. Specifically, the screw-type twin-screw extrusion dryer 5 is equipped with a dehydration barrel section 53 that functions as a dehydrator for dehydrating the wet crumbs washed in the washing device 4, and a drying barrel section 54 that functions as a dryer for drying the wet crumbs, and is further configured to be equipped with a die 59 downstream of the screw-type twin-screw extrusion dryer 5 that has a molding function for molding the wet crumbs.

The configuration of the screw-type twin-screw extrusion dryer 5 will be described below with reference to FIG. 2. FIG. 2 shows the configuration of a specific example suitable for the screw-type twin-screw extrusion dryer 5 shown in FIG. 1. This screw-type twin-screw extrusion dryer 5 can suitably carry out the above-mentioned dehydration and drying process.

The screw-type twin-screw extrusion dryer 5 shown in FIG. 2 is a twin-screw extrusion dryer equipped with a pair of screws (not shown) in a barrel unit 51. The screw-type twin-screw extrusion dryer 5 has a drive unit 50 that rotates and drives the pair of screws in the barrel unit 51. This configuration is suitable for drying the acrylic rubber by applying a high shear. The drive unit 50 is attached to the upstream end (left end in FIG. 2) of the barrel unit 51. The screw-type twin-screw extrusion dryer 5 also has a die 59 at the downstream end (right end in FIG. 2) of the barrel unit 51.

The barrel unit 51 has, from the upstream side to the downstream side (from left to right in Figure 2), a supply barrel section 52, a dehydration barrel section 53, and a drying barrel section 54.

The supply barrel section 52 is composed of two supply barrels, namely, a first supply barrel 52a and a second supply barrel 52b.

The dehydration barrel section 53 is composed of three dehydration barrels, namely, a first dehydration barrel 53a, a second dehydration barrel 53b, and a third dehydration barrel 53c.

The drying barrel section 54 is composed of eight drying barrels, namely, a first drying barrel 54a, a second drying barrel 54b, a third drying barrel 54c, a fourth drying barrel 54d, a fifth drying barrel 54e, a sixth drying barrel 54f, a seventh drying barrel 54g, and an eighth drying barrel 54h.

In this way, the barrel unit 51 is composed of 13 divided barrels 52a-52b, 53a-53c, 54a-54h connected from the upstream side to the downstream side.

The screw-type twin-screw extrusion dryer 5 also has heating means (not shown) for individually heating each of the barrels 52a to 52b, 53a to 53c, and 54a to 54h to heat the water-containing crumbs in each of the barrels 52a to 52b, 53a to 53c, and 54a to 54h to a predetermined temperature. The number of heating means corresponds to each of the barrels 52a to 52b, 53a to 53c, and 54a to 54h. As such a heating means, for example, a configuration in which high-temperature steam is supplied from a steam supply means to a steam circulation jacket formed in each of the barrels 52a to 52b, 53a to 53c, and 54a to 54h is adopted, but is not limited thereto. The screw-type twin-screw extrusion dryer 5 also has temperature control means (not shown) for controlling the set temperature of each heating means corresponding to each of the barrels 52a to 52b, 53a to 53c, and 54a to 54h.

The number of supply barrels, dewatering barrels, and drying barrels constituting each barrel section 52, 53, and 54 in the barrel unit 51 is not limited to the embodiment shown in FIG. 2, but can be set according to the moisture content of the acrylic rubber hydrous crumbs to be dried, etc.

For example, the number of supply barrels installed in the supply barrel section 52 is, for example, 1 to 3. The number of dehydration barrels installed in the dehydration barrel section 53 is, for example, preferably 2 to 10, and more preferably 3 to 6, since this allows for efficient dehydration of the hydrated crumbs of sticky acrylic rubber. The number of drying barrels installed in the drying barrel section 54 is, for example, preferably 2 to 10, and more preferably 3 to 8.

The pair of screws in the barrel unit 51 are rotated by a driving means such as a motor stored in the drive unit 50. The pair of screws extend from the upstream side to the downstream side in the barrel unit 51, and are rotated so that the wet crumb supplied to the supply barrel section 52 can be mixed and transported downstream. The pair of screws is preferably a twin-shaft intermeshing type in which the peaks and valleys are intermeshed with each other, which can increase the dewatering and drying efficiency of the wet crumb.

The rotation directions of the pair of screws may be the same or different, but from the standpoint of self-cleaning performance, it is preferable that they rotate in the same direction. There are no particular limitations on the screw shape of the pair of screws, and they may have any shape required for each barrel portion 52, 53, 54.

The supply barrel section 52 is an area in which the wet crumbs are supplied into the barrel unit 51. The first supply barrel 52a of the supply barrel section 52 has a feed port 55 that supplies the wet crumbs into the barrel unit 51.

The dehydration barrel section 53 is the area where liquid (serum water) containing coagulants and other substances is separated and discharged from the water-containing crumbs.

The first to third dewatering barrels 53a to 53c that make up the dewatering barrel section 53 each have a dewatering slit 56a, 56b, 56c that discharges moisture from the wet crumb to the outside. Each of the dewatering barrels 53a to 53c has multiple dewatering slits 56a, 56b, 56c.

The slit width, i.e., the mesh size, of each dewatering slit 56a, 56b, 56c may be appropriately selected according to the conditions of use, and is usually set to 0.01 to 5 mm. In order to minimize loss of water-containing crumb and to enable efficient dewatering of the water-containing crumb, it is preferably set to 0.1 to 1 mm, and more preferably 0.2 to 0.6 mm.

The water is removed from the water-containing crumb in each of the dehydration barrels 53a to 53c of the dehydration barrel section 53 in two ways: in liquid form through the respective dehydration slits 56a, 56b, 56c, or in vapor form. In the dehydration barrel section 53 of this embodiment, the case where the water is removed in liquid form is defined as drainage, and the case where the water is removed in vapor form is defined as exhaust steam.

In the dehydration barrel section 53, the combination of drainage and exhaust steam is suitable because it can efficiently reduce the moisture content of the viscous acrylic rubber. In the dehydration barrel section 53, which of the first to third dehydration barrels 53a to 53c is used for drainage or steam exhaust can be set appropriately according to the purpose of use, but when the amount of ash in the acrylic rubber produced is usually reduced, it is better to increase the number of dehydration barrels for drainage. In that case, for example, as shown in FIG. 2, drainage is performed in the first and second dehydration barrels 53a and 53b on the upstream side, and steam exhaust is performed in the third dehydration barrel 53c on the downstream side. In addition, for example, when the dehydration barrel section 53 has four dehydration barrels, it is possible to consider an embodiment in which drainage is performed in three upstream dehydration barrels and steam exhaust is performed in one downstream dehydration barrel. On the other hand, when the moisture content is reduced, it is better to increase the number of dehydration barrels for steam exhaust.

As described above in the dehydration and drying process, the set temperature of the dehydration barrel section 53 is usually in the range of 60 to 150°C, preferably 70 to 140°C, and more preferably 80 to 130°C. The set temperature of the dehydration barrel for dehydration in a drained state is usually in the range of 60 to 120°C, preferably 70 to 110°C, and more preferably 80 to 100°C. The set temperature of the dehydration barrel for dehydration in an exhausted steam state is usually in the range of 100 to 150°C, preferably 105 to 140°C, and more preferably 110 to 130°C.

The drying barrel section 54 is an area where the dehydrated hydrous crumbs are dried under reduced pressure. Of the first to eighth drying barrels 54a to 54h that make up the drying barrel section 54, the second drying barrel 54b, the fourth drying barrel 54d, the sixth drying barrel 54f, and the eighth drying barrel 54h each have a vent port 58a, 58b, 58c, and 58d for degassing. Each of the vent ports 58a, 58b, 58c, and 58d is connected to a vent pipe (not shown).

A vacuum pump (not shown) is connected to the end of each vent pipe, and the pressure inside the drying barrel section 54 is reduced to a predetermined level by the operation of the vacuum pump. The screw-type extruder 5 has a pressure control means (not shown) that controls the operation of the vacuum pumps to control the degree of reduced pressure inside the drying barrel section 54.

The degree of reduced pressure in the drying barrel section 54 may be selected as appropriate, but as mentioned above, it is usually set to 1 to 50 kPa, preferably 2 to 30 kPa, and more preferably 3 to 20 kPa.

The temperature set in the drying barrel section 54 may be selected as appropriate, but as mentioned above, it is usually set to 100 to 250°C, preferably 110 to 200°C, and more preferably 120 to 180°C.

The set temperatures of the drying barrels 54a-54h that make up the drying barrel section 54 may be similar or different, but it is preferable to set the temperature on the downstream side (die 59 side) higher than the temperature on the upstream side (dehydration barrel section 53 side) because this improves drying efficiency.

The die 59 is a metal mold placed at the downstream end of the barrel unit 51, and has an outlet of a predetermined nozzle shape. The acrylic rubber dried in the drying barrel section 54 passes through the outlet of the die 59 and is extruded into a shape that corresponds to the predetermined nozzle shape. The acrylic rubber that passes through the die 59 can be molded into various shapes, such as granular, columnar, round rod, and sheet, depending on the nozzle shape of the die 59, but in the present invention, it is molded into a sheet. A breaker plate or wire mesh may or may not be provided between the screw and the die 59.

The hydrous crumbs of acrylic rubber obtained through the washing process are fed from the feed port 55 to the feed barrel section 52. The hydrous crumbs fed to the feed barrel section 52 are sent from the feed barrel section 52 to the dehydration barrel section 53 by the rotation of a pair of screws in the barrel unit 51. In the dehydration barrel section 53, the hydrous crumbs are dehydrated by draining water contained in the hydrous crumbs and exhausting steam from the dehydration slits 56a, 56b, and 56c provided in the first to third dehydration barrels 53a to 53c, as described above.

The hydrous crumbs dehydrated in the dehydration barrel section 53 are sent to the drying barrel section 54 by the rotation of a pair of screws in the barrel unit 51. The hydrous crumbs sent to the drying barrel section 54 are plasticized and mixed to become a melt, and are transported downstream while generating heat and increasing in temperature. The water contained in the acrylic rubber melt then evaporates, and the water (steam) is discharged to the outside through vent pipes (not shown) connected to each of the vent ports 58a, 58b, 58c, and 58d.

As described above, by passing through the drying barrel section 54, the water-containing crumb is dried and becomes a molten acrylic rubber, which is then fed to the die 59 by the rotation of a pair of screws in the barrel unit 51 and extruded from the die 59.

Here is an example of the operating conditions for the screw-type twin-screw extrusion dryer 5 according to this embodiment.

The rotation speed (N) of the pair of screws in the barrel unit 51 may be appropriately selected depending on various conditions, and is usually set to 10 to 1000 rpm. From the viewpoint of efficiently reducing the water content and methyl ethyl ketone insoluble content of the acrylic rubber, it is preferably set to 50 to 750 rpm, more preferably 100 to 500 rpm, and most preferably 120 to 300 rpm.

The extrusion rate (Q) of the acrylic rubber is not particularly limited, but is usually 100 to 1500 kg/hr, preferably 300 to 1200 kg/hr, more preferably 400 to 1000 kg/hr, and most preferably 500 to 800 kg/hr.

The ratio (Q/N) of the acrylic rubber extrusion rate (Q) to the screw rotation speed (N) is not particularly limited, but is usually 1 to 20, preferably 2 to 10, more preferably 3 to 8, and particularly preferably 4 to 6.

The maximum torque in the barrel unit 51 is not particularly limited, but is usually in the range of 30 to 100 N·m, preferably 35 to 75 N·m, and more preferably 40 to 60 N·m.

There are no particular limitations on the specific power within the barrel unit 51, but it is usually in the range of 0.1 to 0.25 [kW·h/kg] or more, preferably 0.13 to 0.23 [kW·h/kg], and more preferably 0.15 to 0.2 [kW·h/kg].

The specific power in the barrel unit 51 is not particularly limited, but is usually in the range of 0.2 to 0.6 [A·h/kg] or more, preferably 0.25 to 0.55 [A·h/kg], and more preferably 0.35 to 0.5 [A·h/kg].

The shear rate in the barrel unit 51 is not particularly limited, but is usually in the range of 40 to 150 [1/s] or more, preferably 45 to 125 [1/s], and more preferably 50 to 100 [1/s].

The shear viscosity of the acrylic rubber in the barrel unit 51 is not particularly limited, but is usually in the range of 4000 to 8000 [Pa·s] or less, preferably 4500 to 7500 [Pa·s], and more preferably 5000 to 7000 [Pa·s].

The cooling device 6 shown in FIG. 1 is configured to cool the dried rubber obtained through the dehydration process using a dehydrator and the drying process using a dryer. As a cooling method using the cooling device 6, various methods can be adopted, including an air-cooling method using blowing air or air conditioning, a water-spraying method in which water is sprayed, and an immersion method in which the rubber is immersed in water. The dried rubber may also be cooled by leaving it at room temperature.

As described above, the dried rubber discharged from the screw-type extruder 5 is extruded into various shapes, such as granules, columns, round rods, and sheets, depending on the nozzle shape of the die 59, but in the present invention, it is molded into a sheet. Below, with reference to Figure 3, we will explain a conveying type cooling device 60 that cools the sheet-shaped dried rubber 10 molded into a sheet as an example of the cooling device 6.

Figure 3 shows the configuration of a conveying type cooling device 60 suitable for the cooling device 6 shown in Figure 1. The conveying type cooling device 60 shown in Figure 3 is configured to cool the sheet-like dry rubber 10 discharged from the discharge port of the die 59 of the screw-type extruder 5 by air cooling while conveying it. By using this conveying type cooling device 60, the sheet-like dry rubber discharged from the screw-type extruder 5 can be appropriately cooled.

The conveying cooling device 60 shown in FIG. 3 is used, for example, by directly connecting it to the die 59 of the screw-type extruder 5 shown in FIG. 2 or by installing it near the die 59.

The conveying cooling device 60 has a conveyor 61 that conveys the sheet-like dried rubber 10 discharged from the die 59 of the screw-type extruder 5 in the direction of arrow A in FIG. 3, and a cooling means 65 that blows cold air onto the sheet-like dried rubber 10 on the conveyor 61.

The conveyor 61 has rollers 62, 63 and a conveyor belt 64 that is wound around the rollers 62, 63 and on which the sheet-like dried rubber 10 is placed. The conveyor 61 is configured to continuously transport the sheet-like dried rubber 10 discharged from the die 59 of the screw-type extruder 5 onto the conveyor belt 64 downstream (to the right in FIG. 3).

The cooling means 65 is not particularly limited, but may be configured to blow cooling air sent from a cooling air generating means (not shown) onto the surface of the sheet-like dried rubber 10 on the conveyor belt 64.

The length L1 of the conveyor 61 and cooling means 65 of the transport-type cooling device 60 (the length of the part where cooling air can be blown) is not particularly limited, but is, for example, 10 to 100 m, and preferably 20 to 50 m. The transport speed of the sheet-like dried rubber 10 in the transport-type cooling device 60 may be appropriately adjusted depending on the length L1 of the conveyor 61 and cooling means 65, the discharge speed of the sheet-like dried rubber 10 discharged from the die 59 of the screw-type extruder 5, the target cooling speed and cooling time, etc., and is, for example, 10 to 100 m/hr, and more preferably 15 to 70 m/hr.

According to the conveying type cooling device 60 shown in FIG. 3, the sheet-like dry rubber 10 discharged from the die 59 of the screw-type extruder 5 is conveyed by a conveyor 61 while cooling air is blown from a cooling means 65 onto the sheet-like dry rubber 10, thereby cooling the sheet-like dry rubber 10.

The transportable cooling device 60 is not limited to a configuration having one conveyor 61 and one cooling means 65 as shown in FIG. 3, but may have two or more conveyors 61 and two or more corresponding cooling means 65. In that case, the total length of each of the two or more conveyors 61 and the cooling means 65 may be within the above range.

The baling device 7 shown in FIG. 1 is configured to process the dried rubber extruded from the screw-type extruder 5 and cooled in the cooling device 6 to produce a bale, which is a block. As described above, the screw-type extruder 5 is capable of extruding the dried rubber into various shapes, such as granules, columns, round bars, and sheets, and the baling device 7 is configured to bales the dried rubber thus formed into various shapes. The weight and shape of the baled acrylic rubber produced by the baling device 7 are not particularly limited, but for example, a roughly rectangular shaped baled acrylic rubber weighing about 20 kg is produced.

The baling device 7 may, for example, be equipped with a baler, and the cooled, dried rubber may be compressed by the baler to produce baled acrylic rubber.

In addition, when the sheet-like dried rubber 10 is produced by the screw-type extruder 5, a bale-like acrylic rubber may be produced by stacking the sheet-like dried rubber 10. For example, a cutting mechanism for cutting the sheet-like dried rubber 10 may be provided in the baling device 7 arranged downstream of the conveying cooling device 60 shown in FIG. 3. Specifically, the cutting mechanism of the baling device 7 is configured to continuously cut the cooled sheet-like dried rubber 10 at predetermined intervals and process it into cut sheet-like dried rubber 16 of a predetermined size. By stacking multiple cut sheet-like dried rubber 16 cut to a predetermined size by the cutting mechanism, a bale-like acrylic rubber in which the cut sheet-like dried rubber 16 is stacked can be produced.

When manufacturing a veil-shaped acrylic rubber laminated with cut-sheet-shaped dry rubber 16, it is preferable to laminate the cut-sheet-shaped dry rubber 16 at, for example, 40°C or higher. By laminating the cut-sheet-shaped dry rubber 16 at 40°C or higher, good air release is achieved through further cooling and compression due to its own weight.

The present invention will be described in more detail below with reference to examples and comparative examples. In each example, "parts," "%," and "ratios" are by weight unless otherwise specified. Various physical properties were evaluated according to the following methods.

[Monomer composition]
Regarding the monomer composition of the acrylic rubber, the monomer composition of each monomer unit in the acrylic rubber was confirmed by ^1H -NMR, and the remaining activity of reactive groups in the acrylic rubber and the content of each reactive group were confirmed by the following method. The content ratio of each monomer unit in the acrylic rubber was calculated from the amount of each monomer used in the polymerization reaction and the polymerization conversion rate. Specifically, the polymerization reaction was an emulsion polymerization reaction, and the polymerization conversion rate was approximately 100%, with no unreacted monomers being confirmed, so the content ratio of each monomer unit in the rubber was set to be the same as the amount of each monomer used.

[Reactive group content]
The content of reactive groups in the acrylic rubber was measured by the following method.
(1) The amount of carboxyl groups was calculated by dissolving a sample (acrylic rubber) in acetone and performing potentiometric titration with a potassium hydroxide solution.
(2) The amount of epoxy groups was calculated by dissolving a sample in methyl ethyl ketone, adding a specified amount of hydrochloric acid to react with the epoxy groups, and titrating the amount of residual hydrochloric acid with potassium hydroxide.
(3) The amount of chlorine was calculated by completely burning the sample in a combustion flask, absorbing the chlorine generated in water, and titrating it with silver nitrate.

[Ash content]
The ash content (%) in the acrylic rubber was measured in accordance with JIS K6228 Method A.

[Ash content]
The amount (ppm) of each component in the acrylic rubber ash was measured by pressing the ash sampled during the above ash content measurement onto a titration filter paper of Φ20 mm and subjecting it to XRF measurement using ZSX Primus (manufactured by Rigaku Corporation).

[Molecular weight and molecular weight distribution]
The molecular weight (Mw, Mn, Mz) and molecular weight distribution (Mw/Mn and Mz/Mw) of the acrylic rubber are absolute molecular weight and absolute molecular weight distribution measured by a GPC-MALS method using a solution in which lithium chloride was added at a concentration of 0.05 mol/L and 37% concentrated hydrochloric acid was added at a concentration of 0.01% to dimethylformamide as a solvent.

The gel permeation chromatography multi-angle light scattering photometer is composed of a pump (LC-20ADOpt, Shimadzu Corporation), a differential refractometer (Optilab rEX, Wyatt Technology Corporation) and a multi-angle light scattering detector (DAWN HELEOS, Wyatt Technology Corporation). Specifically, a multi-angle laser light scattering photometer (MALS) and a differential refractometer (RI) are incorporated into a GPC (Gel Permeation Chromatography) device, and the light scattering intensity and refractive index difference of the molecular chain solution size-fractionated by the GPC device are measured over the elution time, thereby sequentially calculating the molecular weight of the solute and its content. The measurement conditions and method using the GPC device are as follows.

Column: 2 TSKgel α-M (φ7.8 mm × 30 cm, Tosoh Corporation)
Column temperature: 40°C
Flow rate: 0.8ml/mm
Sample preparation: 5 ml of solvent was added to 10 mg of sample (acrylic rubber), and the mixture was gently stirred at room temperature (dissolution was visually confirmed).Then, the mixture was filtered using a 0.5 μm filter.

[Glass transition temperature (Tg)]
The glass transition temperature (Tg) of the acrylic rubber was measured using a differential scanning calorimeter (DSC, product name "X-DSC7000", manufactured by Hitachi High-Tech Science Corporation).

[Methyl ethyl ketone insoluble matter (gel amount)]
The methyl ethyl ketone insoluble content (%) of the acrylic rubber is the amount of insoluble content (gel) in methyl ethyl ketone, and was determined by the following method.

Approximately 0.2 g of acrylic rubber was weighed out (X g), immersed in 100 ml of methyl ethyl ketone, and allowed to stand at room temperature for 24 hours. After that, the insoluble matter in methyl ethyl ketone was filtered off using an 80 mesh wire screen. The filtrate, i.e., the filtrate in which only the rubber components soluble in methyl ethyl ketone were dissolved, was evaporated, dried, and solidified. The dried solid content (Y g) was weighed and calculated according to the following formula.
Methyl ethyl ketone insoluble content (%) = 100 x (X - Y) / X
[specific gravity]
The specific gravity of the acrylic rubber was measured in accordance with JIS K6268 (1998): Crosslinked rubber - Density measurement, Method A.

[Water content]
The water content (%) was measured in accordance with JIS K6238-1: Oven A (volatile matter measurement) method.

[pH]
The pH was measured with a pH electrode after dissolving 6 g (±0.05 g) of acrylic rubber in 100 g of tetrahydrofuran and adding 2.0 ml of distilled water to confirm complete dissolution.

[Complex viscosity]
The complex viscosity η was measured at each temperature by measuring the temperature dispersion (40 to 120°C) at a strain of 473% and 1 Hz using a dynamic viscoelasticity measuring device "Rubber Process Analyzer RPA-2000" (manufactured by Alpha Technology Co., Ltd.). Here, the dynamic viscoelasticity at 60°C of the above-mentioned dynamic viscoelasticity was taken as the complex viscosity η (60°C), and the dynamic viscoelasticity at 100°C was taken as the complex viscosity η (100°C), and the ratio η (100°C) / η (60°C) was calculated.

[Mooney Viscosity (ML1+4, 100°C)]
The Mooney viscosity (ML1+4, 100° C.) was measured in accordance with the physical testing method for uncrosslinked rubber of JIS K6300.

[Crosslinkability]
The crosslinkability of the rubber sample was evaluated by calculating the rate of change between the breaking strength of the cross-linked rubber product subjected to secondary cross-linking for 2 hours and the breaking strength of the cross-linked rubber product subjected to secondary cross-linking for 4 hours ((breaking strength of the cross-linked rubber product cross-linked for 4 hours/breaking strength of the cross-linked rubber product cross-linked for 2 hours)×100) and by the following criteria.
◎: The rate of change in breaking strength is less than 10%. ×: The rate of change in breaking strength is 10% or more.

[Roll processability]
The roll processability of the rubber sample was evaluated by observing the roll winding property and the state of the rubber when the rubber sample was roll-kneaded, and was evaluated according to the following criteria.
◎: The rubber composition is easy to knead, easily wraps around the roll, and does not separate from the roll, and the surface of the rubber composition after kneading is smooth. ◯: The rubber composition is easy to knead, easily wraps around the roll, and does not separate from the roll, and some unevenness is observed on the surface of the rubber composition after kneading. □: The rubber composition is easy to knead, has excellent roll-winding properties, and has a somewhat uneven surface after kneading. △: The rubber composition is easy to knead, has somewhat poor roll-winding properties, and has a somewhat rough surface after kneading. ×: Kneading is stressed, and roll-winding properties are poor.

[Banbury processability 1]
The Banbury processability 1 of the rubber sample was evaluated by measuring the time until the rubber mixture in the first stage was integrated and showed the maximum torque value, that is, the black incorporation time (BIT), after the rubber sample was charged into a Banbury mixer heated to 50° C. and masticated for 1 minute, and then compounding ingredient A of the rubber composition compounding shown in Table 1 was charged. Comparative Example 1 was set as an index of 100 (the smaller the index, the better the processability).
[Banbury processability 2]
The Banbury processability 2 of the rubber sample was evaluated by feeding the rubber sample into a Banbury mixer heated to 50° C. and masticating for 1 minute, then feeding compounding ingredient A of the rubber composition formulation shown in Table 1, and measuring the time until the rubber mixture in the first stage was integrated and showed the maximum torque value, i.e., BIT (Black Incorporation Time), and evaluating the processability as an index with Comparative Example 2 set to 100 (the smaller the index, the better the processability).

[Storage stability evaluation 1]
The storage stability 1 of the rubber sample was evaluated by placing the rubber mixture of the rubber sample in a constant temperature and humidity chamber at 45°C x 80% RH for 7 days, and using the rubber sample before and after the test as a rubber composition, a crosslinking test was performed at 180°C for 10 minutes using a rubber vulcanization tester (Moving Die Rheometer MDR; manufactured by Alpha Technology Co., Ltd.), and the rate of change in crosslink density, which is the difference between the maximum torque (MH) and the minimum torque (ML) (MH-ML), was calculated and evaluated with an index of 100 for Comparative Example 1 (the smaller the index, the better the storage stability).
[Storage stability evaluation 2]
The storage stability 2 of the rubber sample was evaluated by placing the rubber sample in a thermo-hygrostat (SH-222 manufactured by ESPEC Corporation) at 45°C x 80% RH, calculating the rate of change in water content before and after a 7-day test, and using an index based on 100 for Comparative Example 2 (the smaller the index, the better the storage stability).

[Water resistance evaluation 1]
The water resistance 1 of the rubber sample was evaluated by performing an immersion test in accordance with JIS K6258 by immersing a crosslinked rubber sample in distilled water at a temperature of 85° C. for 100 hours, calculating the volume change rate before and after immersion according to the following formula, and using an index based on 100 for Comparative Example 1 (the smaller the index, the better the water resistance).
Volume change rate before and after immersion (%)=((volume of test piece after immersion−volume of test piece before immersion)/volume of test piece before immersion)×100
[Water resistance evaluation 2]
The water resistance 2 of the rubber samples was evaluated by performing the wetting test in the same manner as above, calculating the volume change rate before and after wetting, and evaluating the water resistance 2 with Comparative Example 2 set as an index of 100 (the smaller the index, the better the water resistance).

[Compression set resistance]
The compression set resistance of the rubber sample was evaluated according to JIS K6262 by measuring the compression set rate after leaving the cross-linked rubber sample at 175° C. for 90 hours in a state where the rubber sample was compressed by 25% and the compression set rate was measured according to the following criteria.
⊚: Compression set rate is less than 15%. ×: Compression set rate is 15% or more.

[Heat resistance evaluation]
The heat resistance of the rubber sample was evaluated by carrying out a heating test in which the cross-linked rubber sample was left to stand at 175°C for 250 hours, and the tensile strength of the cross-linked rubber sample before and after the test was measured in accordance with JIS K6251 and the hardness was measured in accordance with JIS K6253. The change in elongation at break and the change in hardness were evaluated according to the following criteria.
The change in elongation at break was evaluated as "◎" when the rate of change in elongation at break was 20% or less, and as "×" when the rate of change in elongation at break exceeded 20%. The change in hardness was evaluated as "◎" when the rate of change in hardness was 20 points or less, and as "×" when the rate of change in hardness exceeded 20 points.

[Normal state physical property evaluation]
The normal state physical properties of the rubber samples were evaluated according to the following criteria by measuring the breaking strength, 100% tensile stress and breaking elongation of the cross-linked rubber samples in accordance with JIS K6251.
(1) The breaking strength was evaluated as follows: 10 MPa or more was indicated as ⊚, and less than 10 MPa was indicated as x.
(2) The 100% tensile stress was evaluated as ⊚ when it was 5 MPa or more, and x when it was less than 5 MPa.
(3) The breaking elongation was evaluated as ⊚ when it was 150% or more, and x when it was less than 150%.

[Example 1]
A mixing vessel equipped with a homomixer was charged with 46 parts of pure water, 63.25 parts of ethyl acrylate, 17 parts of n-butyl acrylate, 7 parts of methoxyethyl acrylate, 11 parts of butyl methacrylate, and 1.75 parts of monoethyl fumarate as monomer components, and 1.8 parts of octyloxydioxyethylene phosphate sodium salt as an emulsifier, and the mixture was stirred to obtain a monomer emulsion.

170 parts of pure water and 3 parts of the monomer emulsion obtained above were added to a polymerization reaction tank equipped with a thermometer and a stirrer, and cooled to 12°C under a nitrogen stream. Next, the remainder of the monomer emulsion, 0.00033 parts of ferrous sulfate, 0.264 parts of sodium ascorbate, and 0.22 parts of potassium persulfate were continuously dropped into the polymerization reaction tank over a period of 3 hours. Thereafter, the reaction was continued while maintaining the temperature inside the polymerization reaction tank at 23°C, and when it was confirmed that the polymerization conversion rate had reached approximately 100%, hydroquinone was added as a polymerization terminator to terminate the polymerization reaction, and an emulsion polymerization liquid was obtained.

Then, in a coagulation tank equipped with a thermometer and agitator, the emulsion polymerization liquid obtained above was heated to 80°C and continuously added to 350 parts of a 2% aqueous magnesium sulfate solution (coagulation liquid using magnesium sulfate as a coagulant) that was vigorously stirred at a stirring blade rotation speed of 600 rpm (circumferential speed of 3.1 m/s) and heated to 80°C, to coagulate the polymer, thereby obtaining a coagulated slurry containing acrylic rubber crumbs as the coagulation product and water. The crumbs were filtered out of the resulting slurry, while the water was drained from the coagulation layer to obtain a water-containing crumb.

194 parts of warm water (70°C) was added to the coagulation tank containing the filtered out wet crumbs, and the wet crumbs were washed by stirring for 15 minutes, after which the water was drained off, and 194 parts of warm water (70°C) was added again and stirred for 15 minutes to wash the wet crumbs (total number of washings: 2). The washed wet crumbs (crumb temperature 65°C) were fed to a screw-type extruder, dehydrated, dried and molded to extrude a sheet-like dry rubber (sheet-like acrylic rubber molding) with a width of 300 mm and a thickness of 10 mm. The sheet-like dry rubber was then cooled at a cooling temperature of 200°C/hr using a conveying cooling device directly connected to the screw-type extruder.

The screw-type extruder used in this Example 1 is composed of one supply barrel, three dehydration barrels (first to third dehydration barrels), and five drying barrels (first to fifth drying barrels). The first dehydration barrel discharges water, and the second and third dehydration barrels discharge steam. The operating conditions of the screw-type extruder were as follows:

Moisture content Moisture content of wet crumb after draining in the first dewatering barrel: 20%
Moisture content of the wet crumb after steaming in the third dewatering barrel: 10%
Moisture content of the wet crumbs after drying in the fifth drying barrel: 0.4%
Rubber temperature Temperature of the water-containing crumb fed to the feed barrel: 65°C
Temperature of rubber discharged from the screw extruder: 140°C
Set temperature for each barrel:
First dehydration barrel: 100° C.
Second dehydration barrel: 120° C.
Third dehydration barrel: 120°C
First drying barrel: 120° C.
Second drying barrel: 130° C.
Third drying barrel: 140° C.
Fourth drying barrel: 160° C.
Fifth drying barrel: 180° C.
Operating conditions:
Screw diameter (D): 132 mm
・Total length of screw (L): 4620 mm
・L/D: 35
Screw rotation speed: 135 rpm
・Decompression degree of drying barrel: 10 kPa
・Rubber extrusion rate from die: 700 kg/hr
Resin pressure in the die: 2 MPa

The sheet-like dry rubber extruded from the screw-type extruder was cooled to 50°C and then cut with a cutter to obtain sheet-like dry rubber.

Next, before the temperature of the sheet-like dried rubber dropped below 40°C, several cut sheets of the sheet-like dried rubber were stacked to obtain 20 parts (20 kg) of acrylic rubber (A) in the form of a veil. The reactive group content, gel amount, specific gravity, ash content, glass transition temperature (Tg), pH, water content, weight average molecular weight, and Mooney viscosity (ML1+4, 100°C) of the obtained acrylic rubber (A) were measured, and the results are shown in Table 2.

Next, 100 parts of acrylic rubber (A) and compounding agent A of "mixture 1" described in Table 1 were added to a Banbury mixer and mixed for 5 minutes at 50°C (first stage mixing). The BIT at this time was measured to evaluate the Banbury processability 1 of the acrylic rubber (A), and the results are shown in Table 2.

Furthermore, each mixture obtained in the first stage mixing was transferred to a roll at 50°C, and compounding agent B of "Compound 1" was added and mixed (second stage mixing) to obtain a rubber composition. A crosslinking test was performed on the rubber composition using acrylic rubber (A) before and after the storage stability test to measure the change in crosslink density (MH-ML), and the results (storage stability 1) are shown in Table 2.

The rubber composition thus obtained was placed in a mold measuring 15 cm in length, 15 cm in width, and 0.2 cm in depth, and pressed at 180°C for 10 minutes while applying a pressure of 10 MPa to cause primary crosslinking. The resulting primary crosslinked product was then heated in a gear oven at 180°C for 2 hours to cause secondary crosslinking, yielding a sheet-like crosslinked rubber product. A test piece measuring 3 cm x 2 cm x 0.2 cm was then cut from the resulting sheet-like crosslinked rubber product and subjected to a water resistance evaluation 1, heat resistance evaluation, and normal state physical property evaluation, with the results shown in Table 2.

[Example 2]
The same procedure as in Example 1 was carried out except that the monomer components were changed to 4.5 parts of ethyl acrylate, 53.5 parts of n-butyl acrylate, 29.5 parts of methoxyethyl acrylate, 11 parts of hexyl methacrylate, and 1.5 parts of monoethyl fumarate, and an acrylic rubber (B) was obtained and its properties were evaluated (the compounding agent was changed to "Compound 2"). The results are shown in Table 2.

[Example 3]
The same procedure as in Example 2 was carried out except that the monomer components were changed to 48.6 parts of ethyl acrylate, 39 parts of n-butyl acrylate, 11 parts of butyl methacrylate, and 1.4 parts of monoethyl fumarate, to obtain an acrylic rubber (C), and the properties thereof were evaluated. The results are shown in Table 2.

[Example 4]
The same procedure as in Example 2 was carried out except that the monomer components were changed to 42.3 parts of ethyl acrylate, 45.3 parts of n-butyl acrylate, 11 parts of butyl methacrylate, and 1.4 parts of monoethyl fumarate, to obtain an acrylic rubber (D), and the properties thereof were evaluated. The results are shown in Table 2.

[Example 5]
The procedure was carried out in the same manner as in Example 4, except that the water content of the water-containing crumb after dehydration in a screw-type extruder (the water content of the water-containing crumb after drainage before preliminary drying with exhaust steam) was set to 30%. An acrylic rubber (E) was obtained and its properties were evaluated. The results are shown in Table 2.

[Comparative Example 1]
In a polymerization reaction tank equipped with a thermometer and a stirrer, 200 parts of pure water, 42.3 parts of ethyl acrylate, 45.3 parts of n-butyl acrylate, 11 parts of butyl methacrylate, and 1.4 parts of monoethyl fumarate as monomer components, 2.5 parts of octyloxydioxyethylene phosphate ester, and 0.5 parts of polyoxyethylene dodecyl ether as emulsifiers were charged under nitrogen gas flow, 0.1 parts of potassium persulfate, and 0.1 parts of sodium ascorbate were charged, and then 0.1 parts of potassium persulfate and 0.1 parts of sodium ascorbate were added to start the reaction. The reaction was continued at room temperature, and it was confirmed that the polymerization conversion rate reached approximately 100%, and hydroquinone was added as a polymerization terminator to terminate the polymerization reaction, and an emulsion polymerization liquid was obtained.

Next, a 0.4% aqueous sodium sulfate solution (coagulation liquid using sodium sulfate as a coagulant) was added to the emulsion polymerization liquid, which was being stirred at a stirring blade rotation speed of 100 rpm (circumferential speed of 0.5 m/s), to coagulate the polymer, obtaining a coagulated slurry containing acrylic rubber crumbs and water, which were the coagulated product. The crumbs were filtered out of the resulting slurry, while the water was drained from the coagulated layer, obtaining a water-containing crumb.

194 parts of water at 25°C was added to the coagulation tank containing the filtered out water-containing crumbs, and the mixture was stirred for 15 minutes to wash the water-containing crumbs, after which the water was drained and the water-containing crumbs were washed (washed once). The washed water-containing crumbs were dried in a hot air dryer to obtain crumb-like acrylic rubber (F) with a water content of 0.4% by weight. The reactive group content, gel amount, specific gravity, ash content, glass transition temperature (Tg), pH, water content, weight average molecular weight, and Mooney viscosity (ML1+4, 100°C) of this acrylic rubber (F) were measured, and the results are shown in Table 2.

Next, 100 parts of acrylic rubber (F) and compounding agent A of "Compound 2" listed in Table 1 were added to a Banbury mixer and mixed at 50°C for 5 minutes (first stage mixing). The BIT at this time was measured to evaluate Banbury processability 1 of acrylic rubber (F), and the results are shown in Table 2. Furthermore, each mixture obtained in the first stage mixing was transferred to a roll at 50°C, and compounding agent B of "Compound 2" was added and mixed (second stage mixing) to obtain a rubber composition. A crosslinking test was performed on the rubber composition using acrylic rubber (F) before and after the storage stability test, and the change in crosslink density (MH-ML) was measured, and the results (storage stability 1) are shown in Table 2.

The obtained rubber composition was placed in a mold measuring 15 cm in length, 15 cm in width, and 0.2 cm in depth, and pressed at 180°C for 10 minutes while applying a pressure of 10 MPa to cause primary crosslinking. The obtained primary crosslinked product was then heated in a gear oven at 180°C for 2 hours to cause secondary crosslinking, thereby obtaining a sheet-like crosslinked rubber product. A test piece measuring 3 cm x 2 cm x 0.2 cm was then cut from the obtained sheet-like crosslinked rubber product and subjected to water resistance evaluation 1, heat resistance evaluation, and normal state physical property evaluation, with the results shown in Table 2.

From Table 2, it can be seen that the acrylic rubbers (A) to (E) of the present invention, which are made of acrylic rubbers having reactive groups and a reactive group content of 0.001 to 5% by weight, have a gel content of 50% or less by weight of methyl ethyl ketone insoluble matter, a pH of 6 or less, an ash content of 0.4% or less by weight, a total content of magnesium, phosphorus, calcium, sodium and sulfur in the ash of 50% or more by weight, and a specific gravity of 0.8 or more, have excellent Banbury processability, water resistance and storage stability, and are also excellent in normal state physical properties including heat resistance and strength characteristics (Examples 1 to 5).

From Table 2, it can be seen that the acrylic rubbers (A) to (F) of the examples and comparative examples have carboxyl groups, have a large weight average molecular weight (Mw), and contain bonding units (A1) derived from acrylic acid esters, bonding units (A2) derived from methacrylic acid esters, and bonding units (B) derived from reactive group-containing monomers, and therefore have significantly superior normal state physical properties including heat resistance and strength characteristics (Examples 1 to 5 and Comparative Example 1). However, it can be seen that the acrylic rubber (F) is inferior in Banbury processability, water resistance, and storage stability (Comparative Example 1).

From Table 2, it can be seen that the processability (BIT) of acrylic rubber in a Banbury mixer correlates with the amount of gel in the acrylic rubber that is insoluble in methyl ethyl ketone, and that in order to reduce the amount of gel, it is important to melt and rotate the acrylic rubber in a state in which it is substantially free of moisture in the fifth drying barrel section (water content is less than 1% by weight). On the other hand, it is not preferable to hold the acrylic rubber in the screw-type extruder for a long time, as this causes molecular cutting and burning, which deteriorates the properties of the acrylic rubber, such as its normal physical properties including its strength properties, its heat resistance, and its storage stability. As can be seen from Table 2, in order to quickly make the drying barrel section substantially free of moisture, the challenge is how to efficiently dehydrate the dehydration barrel section, and this was cleared in this case by adjusting the temperature and degree of vacuum of each barrel section. In addition, in order to prevent deterioration of the acrylic rubber that is melt-rotated in a state in which it is substantially free of moisture in the drying barrel section and to reduce the moisture content and gel amount of the acrylic rubber, it was important to set the extrusion amount Q of the screw-type extruder or the ratio of the extrusion amount Q to the rotation speed N (Q/N) within a specific range.

From Table 2, it can be seen that the acrylic rubbers (A) to (E) of the present invention have significantly superior water resistance (comparison between Examples 1 to 5 and Comparative Example 1). Also, from Table 2, it can be seen that the water resistance is significantly improved by adding the emulsion polymerization liquid to a thick coagulation liquid that is being vigorously stirred and performing the coagulation reaction, using warm water for washing, and performing dehydration (squeezing out water from the water-containing crumbs) (comparison between Examples 1 to 5 and Comparative Example 1). In particular, although not shown in Table 2, by adding the emulsion polymerization liquid to a thick coagulation liquid that is being vigorously stirred and performing the coagulation reaction, it is possible to generate water-containing crumbs concentrated in a small particle size range of 710 μm to 4.75 mm, which significantly improves the washing efficiency with warm water and the removal efficiency during dehydration, significantly reduces the ash content in the acrylic rubber, and improves water resistance (comparison between Examples 1 to 5 and Comparative Example 1).

From Table 2, it can be seen that the acrylic rubbers (A) to (E) of the present invention have a high specific gravity and are acrylic rubber molded bodies that do not contain air, and therefore have highly improved strength properties, processability, and storage stability (Comparison between Examples 1 to 5 and Comparative Example 1). Acrylic rubber (F) is obtained by directly drying the generated water-containing crumbs after washing. Acrylic rubbers that have reactive groups such as carboxyl groups are sticky and difficult to remove air from, resulting in a low specific gravity. However, the acrylic rubbers (A) to (E) of the present invention are dried under reduced pressure using a screw-type twin-screw extrusion dryer, the resin pressure in the die is adjusted to extrude a sheet-like dry rubber that contains almost no air, and the extruded sheet-like dry rubber is cut and laminated at a specific temperature to eliminate air entrapment and to facilitate air removal, resulting in an almost air-free (high specific gravity) state, and therefore have significantly better storage stability (Examples 1 to 5 and Comparative Example 1).

[Example 6]
As shown in Table 4-1, 46 parts of pure water, 4.5 parts of ethyl acrylate, 64.5 parts of n-butyl acrylate, 29.5 parts of methoxyethyl acrylate, and 1.5 parts of mono-n-butyl fumarate as monomer components, and 1.8 parts of octyloxydioxyethylene phosphate sodium salt as an emulsifier were charged into a mixing vessel equipped with a homomixer and stirred to obtain a monomer emulsion.

170 parts of pure water and 3 parts of the monomer emulsion obtained above were added to a polymerization reaction tank equipped with a thermometer and a stirrer, and after cooling to 12°C under a nitrogen stream, 0.00033 parts of ferrous sulfate, 0.02 parts of sodium ascorbate, and 0.2 parts of potassium persulfate as an inorganic radical generator were added to start the polymerization reaction. The temperature inside the polymerization reaction tank was kept at 23°C, and the remaining monomer emulsion was continuously added dropwise over a period of 3 hours. 50 minutes after the start of the reaction, 0.0072 parts of n-dodecyl mercaptan, 100 minutes after the start of the reaction, 0.0036 parts of n-dodecyl mercaptan, and 120 minutes after the start of the reaction, 0.4 parts of sodium L-ascorbate were added to continue the polymerization reaction, and when the polymerization conversion rate reached approximately 100%, hydroquinone was added as a polymerization terminator to stop the polymerization reaction, and an emulsion polymerization liquid was obtained.

Then, in a coagulation tank equipped with a thermometer and agitator, the emulsion polymerization liquid obtained above was heated to 80°C and continuously added to 350 parts of a 2% aqueous magnesium sulfate solution (coagulation liquid using magnesium sulfate as a coagulant) that was heated to 80°C and vigorously stirred at a stirring blade rotation speed of 600 rpm (circumferential speed of 3.1 m/s) to coagulate the polymer, obtaining a coagulated slurry containing acrylic rubber crumbs as the coagulated product and water. The crumbs were filtered out of the resulting slurry, while the water was drained from the coagulation layer to obtain a water-containing crumb.

194 parts of warm water (70°C) was added to the coagulation tank containing the filtered out wet crumbs, and the wet crumbs were washed by stirring for 15 minutes, after which the water was drained off, and 194 parts of warm water (70°C) was added again and stirred for 15 minutes to wash the wet crumbs (total number of washings: 2). The washed wet crumbs (wet crumb temperature 65°C) were fed to a screw-type twin-screw extrusion dryer 15, where they were dehydrated and dried to extrude a sheet-like dry rubber 300 mm wide and 10 mm thick. Next, the sheet-like dry rubber was cooled at a cooling rate of 200°C/hr using a conveying cooling device directly connected to the screw-type twin-screw extrusion dryer 15.

The screw-type twin-screw extrusion dryer used in this Example 1 is composed of one supply barrel, three dehydration barrels (first to third dehydration barrels), and five drying barrels (first to fifth drying barrels). The first dehydration barrel discharges water, and the second and third dehydration barrels discharge steam. The operating conditions of the screw-type twin-screw extrusion dryer were as follows:

Water content:
Moisture content of wet crumbs after draining in the first dewatering barrel: 20%
Moisture content of the wet crumb after steaming in the third dewatering barrel: 10%
Moisture content of the wet crumbs after drying in the fifth drying barrel: 0.4%
Rubber Temperature:
Temperature of the wet crumbs fed to the feed barrel: 65°C
Temperature of rubber discharged from the screw-type twin-screw extrusion dryer: 140°C
Set temperature for each barrel:
First dehydration barrel: 100° C.
Second dehydration barrel: 120° C.
Third dehydration barrel: 120°C
First drying barrel: 120° C.
Second drying barrel: 130° C.
Third drying barrel: 140° C.
Fourth drying barrel: 160° C.
Fifth drying barrel: 180° C.
Operating conditions:
Screw diameter (D): 132 mm
・Total length of screw (L): 4620 mm
・L/D: 35
Screw rotation speed: 135 rpm
・Decompression degree of drying barrel: 10 kPa
・Rubber extrusion rate from die: 700 kg/hr
Resin pressure in the die: 2 MPa
Maximum torque in screw-type twin-screw extrusion dryer: 15 Nm

The extruded sheet-like dried rubber was cooled to 50°C, cut with a cutter, and laminated to 20 parts (20 kg) before the temperature dropped below 40°C to obtain a veil-like acrylic rubber (G). The reactive group content, ash content, ash component content, methyl ethyl ketone insoluble content (gel content), pH, specific gravity, glass transition temperature (Tg), water content, molecular weight, molecular weight distribution, and complex viscosity at 100°C and 60°C of the obtained acrylic rubber (G) were measured and shown in Table 4-2. In addition, storage stability test 2 of acrylic rubber (G) was performed to determine the rate of change in water content, and the results are shown in Table 4-2.

Next, 100 parts of the acrylic rubber (G) and compounding agent A of "blending 3" shown in Table 3 were added using a Banbury mixer and mixed for 5 minutes at 50°C (first stage mixing). The BIT at this time was measured to evaluate the Banbury processability 2 of the acrylic rubber, and the results are shown in Table 4-2.
Next, the obtained mixture was transferred to a roll at 50° C., and compounding ingredient B of "Compound 3" was compounded and mixed (second stage mixing) to obtain a rubber composition. The roll processability at this stage was evaluated, and the results are shown in Table 4-2.

The obtained rubber composition was placed in a mold 15 cm long, 15 cm wide, and 0.2 cm deep, and pressed at 180°C for 10 minutes while applying a pressure of 10 MPa to cause primary crosslinking. The obtained primary crosslinked product was then heated in a gear oven at 180°C for 2 hours to cause secondary crosslinking, thereby obtaining a sheet-like crosslinked rubber product. A test piece measuring 3 cm x 2 cm x 0.2 cm was then cut from the obtained sheet-like crosslinked rubber product to evaluate water resistance 2, compression set resistance, and normal state physical properties. In addition, the normal state physical properties of the sheet-like crosslinked rubber product that had been subjected to secondary crosslinking for an additional 2 hours were measured to evaluate the crosslinking property. The results are shown in Table 4-2.

[Example 7]
The same procedure as in Example 6 was carried out except that the emulsifier was changed to 1.8 parts of nonylphenyloxyhexaoxyethylene phosphate sodium salt, the amount of the inorganic radical generator potassium persulfate was changed to 0.21 parts, and the amount of the chain transfer agent n-dodecyl mercaptan added later was changed to 0.017 parts after 50 minutes, 0.017 parts after 100 minutes, and 0.017 parts after 120 minutes, to obtain an acrylic rubber (H), and the properties thereof were evaluated. The results are shown in Table 4-2.

[Example 8]
The monomer components were changed to 48.25 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.75 parts of mono n-butyl fumarate, the emulsifier was changed to 1.8 parts of tridecyloxyhexaoxyethylene phosphate sodium salt, and the water-containing crumbs after washing were dried to a water content of 0.4% using a hot air dryer at 160°C to obtain crumb-like acrylic rubber, which was then filled into a baler measuring 300 x 650 x 300 mm and pressed at a pressure of 3 MPa for 25 seconds to obtain baled acrylic rubber. The acrylic rubber (I) was obtained in the same manner as in Example 6. The properties of the acrylic rubber (I) were evaluated (the compounding agent was changed to "Compound 4"), and the results are shown in Table 4-2.

[Example 9]
The same procedure as in Example 8 was carried out except that the monomer components were changed to 28 parts of ethyl acrylate, 38 parts of n-butyl acrylate, 27 parts of methoxyethyl acrylate, 5 parts of acrylonitrile, and 2 parts of allyl glycidyl ether, and an acrylic rubber (J) was obtained and each property was evaluated (the compounding agent was changed to "Compound 5"). The results are shown in Table 4-2.

[Example 10]
The same procedure as in Example 8 was carried out except that the monomer components were changed to 42.2 parts of ethyl acrylate, 35 parts of n-butyl acrylate, 20 parts of methoxyethyl acrylate, 1.5 parts of acrylonitrile, and 1.3 parts of vinyl chloroacetate, and an acrylic rubber (K) was obtained and each characteristic was evaluated (the compounding agent was changed to "Compound 5"). The results are shown in Table 4-2.

[Example 11]
The monomer components were changed to 48.25 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.75 parts of mono n-butyl fumarate, the emulsifier was changed to 1.8 parts of tridecyloxyhexaoxyethylene phosphate sodium salt, and the water-containing crumbs after washing were dried to a water content of 0.4% using a hot air dryer at 160°C to obtain crumb-like acrylic rubber, which was then filled into a baler measuring 300 x 650 x 300 mm and pressed at a pressure of 3 MPa for 25 seconds to obtain baled acrylic rubber. The acrylic rubber (L) was obtained in the same manner as in Example 7. The properties of the acrylic rubber (L) were evaluated (the compounding agent was changed to "Compound 4"), and the results are shown in Table 4-2.

[Example 12]
The same procedure as in Example 11 was carried out except that the monomer components were changed to 28 parts of ethyl acrylate, 38 parts of n-butyl acrylate, 27 parts of methoxyethyl acrylate, 5 parts of acrylonitrile, and 2 parts of allyl glycidyl ether, and an acrylic rubber (M) was obtained and each property was evaluated (the compounding agent was changed to "Compound 5"). The results are shown in Table 4-2.

[Example 13]
The same procedure as in Example 12 was carried out except that the monomer components were changed to 42.2 parts of ethyl acrylate, 35 parts of n-butyl acrylate, 20 parts of methoxyethyl acrylate, 1.5 parts of acrylonitrile, and 1.3 parts of vinyl chloroacetate, and an acrylic rubber (N) was obtained and each characteristic was evaluated (the compounding agent was changed to "Compound 6"). The results are shown in Table 4-2.

[Example 14]
The same procedure as in Example 13 was carried out except that the amount of potassium persulfate as the inorganic radical generator was changed to 0.22 parts, and 0.025 parts of n-dodecyl mercaptan as the chain transfer agent was added continuously to the monomer emulsion and not added later, to obtain an acrylic rubber (O), and the properties thereof were evaluated. The results are shown in Table 4-2.

[Comparative Example 2]
The same procedures as in Example 14 were carried out except that no chain transfer agent was added, the coagulation reaction was carried out by adding a 0.7% aqueous magnesium sulfate solution to the stirred emulsion polymerization liquid (stirring speed 100 rpm, peripheral speed 0.5 m/s) after emulsion polymerization and crumb-like acrylic rubber was obtained without baling with a baler, and an acrylic rubber (P) was obtained and each of its properties was evaluated. The results are shown in Table 4-2.

[Comparative Example 3]
The emulsifier was changed to 0.709 parts of sodium lauryl sulfate and 1.82 parts of polyoxyethylene dodecyl ether, the coagulation reaction was carried out by adding sodium sulfate to the stirred emulsion polymerization liquid after emulsion polymerization (stirring speed 100 rpm, peripheral speed 0.5 m/s), the water-containing crumbs were washed by adding 194 parts of industrial water and stirred in the coagulation tank at 25°C for 5 minutes, and then the operation of draining water from the coagulation tank was carried out twice, and crumb-like acrylic rubber was obtained without baling with a baler, and the same procedures as in Example 14 were carried out to obtain an acrylic rubber (Q), and each of the properties was evaluated. The results are shown in Table 4-2.

From Tables 4-1 and 4-2, it can be seen that the acrylic rubbers (G) to (O) of the present invention, which are made of acrylic rubbers having reactive groups and a reactive group content of 0.001 to 5% by weight, have a gel content of 50% or less by weight of methyl ethyl ketone insoluble matter, a pH of 6 or less, an ash content of 0.4% or less by weight, a total content of magnesium, phosphorus, calcium, sodium and sulfur in the ash of 50% or more by weight, and a specific gravity of 0.8 or more, are excellent in Banbury processability, storage stability and water resistance, and further have significantly excellent normal state physical properties including roll processability, crosslinkability, compression set resistance and strength properties (Examples 6 to 14).

From Table 4-2, it can be seen that the acrylic rubbers (G) to (Q) produced under the conditions of the present application and the comparative examples have ion reactive groups or reactive groups of either carboxyl groups, epoxy groups or chlorine atoms, and have excellent normal state physical properties including crosslinkability, compression set resistance and strength properties due to their large weight average molecular weight (Mw) (Examples 6 to 14 and Comparative Examples 2 to 3). However, the acrylic rubbers (P) to (Q) are inferior in roll processability, Banbury processability, water resistance and storage stability (Comparative Example 2), and are also inferior in water resistance and storage stability (Comparative Example 3).

From Table 4-2, it can be seen that the Banbury processability of acrylic rubber correlates with the amount of gel in the methyl ethyl ketone insolubles, and that the smaller the amount of methyl ethyl ketone insolubles, the better the Banbury processability (comparison between Examples 6-14 and Comparative Example 2). The amount of methyl ethyl ketone insolubles in acrylic rubber can be reduced by emulsion polymerization in the presence of a chain transfer agent (Examples 8-13 and Comparative Example 3). In particular, since the amount of methyl ethyl ketone insolubles increases rapidly at the end of the polymerization reaction where the polymerization conversion rate is increased to improve strength properties, it can be seen that the generation of methyl ethyl ketone insolubles can be suppressed in Examples 8-13, in which the chain transfer agent is added later at the end of the polymerization reaction. The amount of methyl ethyl ketone insolubles in acrylic rubber is further significantly reduced by drying the water-containing crumbs with a screw-type twin-screw extrusion dryer, greatly improving the Banbury processability of the produced acrylic rubber (comparison between Examples 6-7 and Examples 8-13). Although not shown in this example, it has been confirmed that the amount of methyl ethyl ketone insoluble matter that rapidly increased during emulsion polymerization without the addition of a chain transfer agent (Comparative Example 2) disappears when melt-kneaded in a substantially moisture-free state (moisture content less than 1% by weight) in a screw-type twin-screw extrusion dryer, and the Banbury processability of the acrylic rubber can be significantly improved.

Table 4-2 also shows that the storage stability of acrylic rubber is closely related to the specific gravity of the acrylic rubber, and that when the specific gravity is high, the acrylic rubber does not trap air and has excellent storage stability (comparison with Examples 6-7, Examples 8-14, and Comparative Examples 2-3). Acrylic rubber with a high specific gravity can be obtained by compressing crumb-like acrylic rubber with a baler to form a bale (Examples 8-14), or more preferably by extruding it into a sheet-like material containing almost no air using a screw-type twin-screw extrusion dryer, layering it, and forming it into a bale (Examples 6-7). The lower the ash content, the more preferable the storage stability of acrylic rubber (Examples 6-14). A pH of 6 or less also contributes to the storage stability of acrylic rubber.

From Table 4-2, it can be seen that the acrylic rubbers (G) to (O) of the present invention are overwhelmingly superior in terms of water resistance (comparison between Examples 6 to 14 and Comparative Examples 2 to 3). From Table 4-2, it can also be seen that the acrylic rubbers (G) to (O) with such significantly superior water resistance can be produced by adding the coagulation liquid to the stirred coagulation liquid rather than adding the coagulation liquid to the emulsion polymerization liquid in the coagulation process of the emulsion polymerization liquid obtained by continuously or batchwise post-adding a chain transfer agent using an inorganic radical generator, and carrying out the coagulation reaction, and more preferably by vigorously stirring the coagulation liquid (stirring speed 600 rpm/circumferential speed 3.1 m/s) and increasing the coagulation agent concentration in the stirred coagulation liquid (comparison between Examples 6 to 14 and Comparative Example 2). Although no data is shown in the examples of this application, this coagulation reaction produces hydrous crumbs with diameters ranging from 710 μm to 4.75 mm, which dramatically improves the efficiency of removing emulsifiers and coagulants during the hot water washing and dehydration processes, reducing the ash content in the acrylic rubber and significantly improving water resistance.

Table 4-2 shows that, with regard to water resistance, carboxyl and epoxy groups are superior to chlorine atoms among reactive groups (comparison of Examples 8-9 and 11-12 with Examples 10 and 13).

From Table 4-2, it can be seen that, in terms of water resistance, acrylic rubbers (G) to (H), which were dehydrated (water squeezed out) before drying the wet crumbs, had a significantly reduced ash content and improved water resistance (comparison between Examples 6 to 7 and Examples 8 to 14). In addition, looking at the amount of components in the ash of acrylic rubbers (G) to (H), most of them are phosphorus (P) and magnesium (Mg), which is presumably because the sodium phosphate salt of the emulsifier is salt-exchanged with the magnesium sulfate of the coagulant and exists within the wet crumbs as magnesium phosphate, and cannot be fully removed in the washing process, but can be reduced by dehydrating (squeezing out). It can also be seen that components in the ash of acrylic rubbers that contain a lot of phosphorus and magnesium do not deteriorate water resistance (comparison between Examples 6 to 14 and Comparative Examples 2 and 3).

From Table 4-2, it can be seen that the molecular weight distribution, i.e., the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), plays a major role in roll processability, and the wider the molecular weight distribution, the better the roll processability (comparison between Examples 6-14 and Comparative Examples 3 and 2). Also, in order to achieve a high level of balance between strength properties and roll processability, it was important that the weight average molecular weight (Mw) was high and the molecular weight distribution (the ratio (Mz/Mw) of the z-average molecular weight (Mz) to the weight average molecular weight (Mw)) was high, with an emphasis on the high molecular weight region.

From Tables 4-1 and 4-2, it can be seen that an acrylic rubber having excellent strength characteristics and excellent roll processability, a large weight average molecular weight (Mw) and a wide Mw/Mn range can be produced by using a specific amount of an inorganic radical generator and a chain transfer agent, particularly n-dodecyl mercaptan (Examples 6 to 14). From Table 4-2, it can also be seen that the roll processability can be further improved without impairing the strength characteristics by reducing the amount of inorganic radical generator used and adding n-dodecyl mercaptan batchwise later rather than adding it initially (Example 14) compared to adding n-dodecyl mercaptan continuously (Example 6 to 13). This is because the length of one polymer chain is extended by reducing the amount of inorganic radical generator and not adding the chain transfer agent initially, and although there are no clear two peaks in the GPC chart, the strength characteristics and roll processability are highly balanced by producing a balanced high molecular weight component and a balanced low molecular weight component, increasing Mw and widening Mw/Mn. In addition, in order to efficiently expand Mw/Mn, the number of batch post-additions of the chain transfer agent has a greater effect than the amount of batch post-addition, and the Mw/Mn is wider when the number of batch post-additions is two than three (comparison of Examples 8-10 and Examples 11-13), but the spread of Mw/Mn is somewhat limited when the chain transfer agent is added continuously (Example 14). In addition, although not shown in Table 4-2, in the examples of the present application, the reducing agent sodium ascorbate is added 120 minutes after the start of polymerization, which makes it easier to produce high molecular weight components of the acrylic rubber and increases the effect of expanding Mw/Mn when the chain transfer agent is added later. On the other hand, although not shown in Table 4-1, when polymerization is performed using an organic radical generator, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) does not expand, and roll processability is poor, which is not preferable.

[Example 15]
As shown in Table 5-1, the same procedure as in Example 7 was carried out except that the monomer components were changed to 74.5 parts of ethyl acrylate, 17 parts of n-butyl acrylate, 7 parts of methoxyethyl acrylate, and 1.5 parts of mono n-butyl fumarate, and the emulsifier was changed to 1.8 parts of tridecyloxyhexaoxyethylene phosphate sodium salt, to obtain an acrylic rubber (R), and the properties were evaluated, and the results are shown in Table 5-2. Table 5-1 also shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extrusion dryer.

[Example 16]
The same procedure as in Example 6 was repeated except that the monomer components were changed to 74.5 parts of ethyl acrylate, 17 parts of n-butyl acrylate, 7 parts of methoxyethyl acrylate, and 1.5 parts of mono n-butyl fumarate, and the emulsifier was changed to tridecyloxyhexaoxyethylene phosphate sodium salt, to obtain an acrylic rubber (S), and the properties were evaluated, and the results are shown in Table 5-2. Table 5-1 also shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extrusion dryer.

[Example 17]
The same procedure as in Example 15 was carried out except that the monomer components were changed to 28 parts of ethyl acrylate, 38 parts of n-butyl acrylate, 27 parts of methoxyethyl acrylate, 5 parts of acrylonitrile, and 2 parts of allyl glycidyl ether, and the operating conditions of the screw-type twin-screw extrusion dryer were changed to high share (maximum torque 45 Nm), and an acrylic rubber (T) was obtained and each property (the compounding agent was changed to "Compound 5") was evaluated, and the results are shown in Table 5-2. Table 5-1 also shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extrusion dryer.

[Example 18]
The same procedure as in Example 17 was carried out except that the monomer components were changed to 48.5 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.5 parts of mono n-butyl fumarate, and an acrylic rubber (U) was obtained and its properties (the compounding agent was changed to "Compound 3") were evaluated, and the results are shown in Table 5-2. Table 5-1 also shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extrusion dryer.

[Example 19]
The same procedure as in Example 17 was carried out except that the monomer components were changed to 48.25 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.75 parts of n-butyl fumarate, to obtain an acrylic rubber (V), and the properties thereof (the compounding agent was changed to "Compound 4") were evaluated, and the results are shown in Table 5-2. Table 5-1 also shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extrusion dryer.

[Example 20]
The same procedure as in Example 16 was carried out except that the monomer components were changed to 28 parts of ethyl acrylate, 38 parts of n-butyl acrylate, 27 parts of methoxyethyl acrylate, 5 parts of acrylonitrile, and 2 parts of allyl glycidyl ether, and the operating conditions of the screw-type twin-screw extrusion dryer were changed to high share (maximum torque 45 Nm), and an acrylic rubber (X) was obtained and each property (the compounding agent was changed to "Compound 5") was evaluated, and the results are shown in Table 5-2. Table 5-1 also shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extrusion dryer.

[Example 21]
The same procedure as in Example 20 was carried out except that the monomer components were changed to 48.5 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.5 parts of mono n-butyl fumarate, and an acrylic rubber (Y) was obtained and its properties (the compounding agent was changed to "Compound 3") were evaluated, and the results are shown in Table 5-2. Table 5-1 also shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extrusion dryer.

[Example 22]
The same procedure as in Example 20 was carried out except that the monomer components were changed to 48.25 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.75 parts of mono n-butyl fumarate, and an acrylic rubber (Z) was obtained and its properties (the compounding agent was changed to "Compound 4") were evaluated, and the results are shown in Table 5-2. Table 5-1 also shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extrusion dryer.

From Table 5-2, it can be seen that the acrylic rubbers (T) to (Z) of the present invention are excellent in normal state physical properties including Banbury processability, water resistance, storage stability, crosslinkability, compression set resistance and strength properties, and also have significantly improved roll processability (comparison of Examples 17 to 22 with Examples 15 to 16). This is because the acrylic rubber consisting of high molecular weight and low molecular weight components emulsion-polymerized with the post-addition of a chain transfer agent is dried at high shear using a screw-type twin-screw extrusion dryer, resulting in an acrylic rubber with a balanced molecular weight and molecular weight distribution, which significantly improves roll processability.

1 Acrylic rubber manufacturing system 3 Solidification device 4 Cleaning device 5 Screw-type extruder 6 Cooling device 7 Baling device

Claims (20)

The acrylic rubber has at least one reactive group selected from the group consisting of a carboxyl group, an epoxy group, and a chlorine atom, or an ion-reactive group exhibiting ion reactivity as a reactive group, and has a reactive group content of 0.001 to 5% by weight, the acrylic rubber having a gel content of 30% by weight or less of methyl ethyl ketone insoluble matter, a pH of 2 to 6, an ash content of 0.09 to 0.4% by weight, with the total content of magnesium, phosphorus, calcium, sodium and sulfur in the ash being 50% by weight or more, and a specific gravity of 0.8 or more as measured by JIS K6268 Crosslinked Rubber - Density Measurement Method A , and the acrylic rubber is composed of 10 to 98.9% by weight of bonding units (A) derived from a (meth)acrylic acid ester, 0.1 to 10% by weight of bonding units (B) derived from a reactive group-containing monomer, and 0 to 30% by weight of bonding units (C) derived from other monomers . The acrylic rubber according to claim 1, wherein the ash content is 0.15% by weight or less. The acrylic rubber according to claim 1 or 2, wherein the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber is in the range of 1.1 to 8. The acrylic rubber according to any one of claims 1 to 3, wherein the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber is 3.4 or more. The acrylic rubber according to any one of claims 1 to 4, wherein the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber is in the range of 3.7 to 6.5. The acrylic rubber according to any one of claims 1 to 5, wherein the weight average molecular weight (Mw) of the acrylic rubber is 1,000,000 or more. The acrylic rubber according to claim 1 , wherein the (meth)acrylic acid ester-derived bonding unit (A) is at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters. The acrylic rubber according to claim 1 , wherein the (meth)acrylic acid ester-derived bonding units (A) comprise an acrylic acid ester-derived bonding unit (A1) and a methacrylic acid ester-derived bonding unit (A2). The acrylic rubber according to any one of claims 1 to 8 , which is in the form of a sheet or a veil. an emulsion polymerization step of emulsifying an acrylic rubber monomer component containing a reactive group-containing monomer with water and an emulsifier, and then initiating polymerization in the presence of a redox catalyst consisting of a radical generator and a reducing agent to obtain an emulsion polymerization liquid;
a coagulation step in which the obtained emulsion polymerization liquid is added to a coagulation liquid having a coagulant concentration of 1% by weight or more while being stirred, and coagulated to produce water-containing crumbs;
A washing step of washing the generated hydrous crumbs with warm water of 60°C or higher;
A dehydration step of dehydrating the washed wet crumbs to a moisture content of 1 to 40% by weight;
drying the dehydrated wet crumbs to a moisture content of less than 1% by weight;
The method for producing an acrylic rubber according to any one of claims 1 to 9 , comprising: The method for producing an acrylic rubber according to claim 10 , further comprising baling the dried rubber. The method for producing an acrylic rubber according to claim 10 or 11 , wherein the radical generator is an inorganic radical generator. The method for producing an acrylic rubber according to any one of claims 10 to 12 , wherein the chain transfer agent is added batchwise during the emulsion polymerization. The method for producing an acrylic rubber according to any one of claims 10 to 13 , wherein the water-containing crumb is dried using a screw-type twin-screw extruder dryer. The method for producing an acrylic rubber according to any one of claims 10 to 14, wherein the dehydration and drying steps are carried out by using a screw-type twin-screw extruder dryer having a dehydration barrel having a dehydration slit, a drying barrel under reduced pressure, and a die at the tip thereof, dehydrating the washed hydrous crumbs in the dehydration barrel until the moisture content is 1 to 40% by weight, and then drying the hydrous crumbs in the drying barrel until the moisture content is less than 1 % by weight, and extruding a sheet-like dried rubber through a die. The method for producing an acrylic rubber according to claim 15 , wherein the extruded dry rubber sheets are laminated to form a bale. The method for producing an acrylic rubber according to any one of claims 10 to 16 , wherein the acrylic rubber monomer component contains an acrylic acid ester and a methacrylic acid ester. A rubber composition comprising a rubber component containing the acrylic rubber according to any one of claims 1 to 9 , a filler, and a crosslinking agent. A method for producing a rubber composition, comprising mixing the acrylic rubber according to any one of claims 1 to 9 with a filler, and then mixing a crosslinking agent therewith. A cross-linked rubber product obtained by cross-linking the rubber composition according to claim 18 .

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