JP7610358B2 - Acrylic rubber veil with excellent workability and water resistance - Google Patents

Description

The present invention relates to an acrylic rubber veil and a method for producing the same, a rubber mixture and a method for producing the same, and a cross-linked rubber product. More specifically, the present invention relates to an acrylic rubber veil that has excellent processability and water resistance and a method for producing the same, a rubber mixture that contains the acrylic rubber veil and a method for producing the same, and a cross-linked rubber product obtained by cross-linking the rubber mixture.

Acrylic rubber is a polymer whose main component is acrylic ester, and is generally known as a rubber with excellent heat resistance, oil resistance, and ozone resistance, and is widely used in the automotive industry. Such acrylic rubber is usually produced by emulsion polymerizing the monomer components that make up the acrylic rubber, contacting the resulting emulsion polymerization liquid with a coagulant, and drying the resulting water-containing crumbs, which are then baled and manufactured into products.

Regarding acrylic rubber, for example, Patent Document 1 (JP 2006-328239 A) discloses a method for producing a rubber polymer comprising the steps of: obtaining a crumb slurry containing a crumb-like rubber polymer by contacting a polymer latex with a coagulation liquid; crushing the crumb-like rubber polymer contained in the crumb slurry with a mixer equipped with a stirring and crushing function having a stirring power of 1 kW/m3 or more; removing water from the crumb slurry containing the crushed crumb-like rubber polymer to obtain a crumb-like rubber polymer; and heating and drying the crumb-like rubber polymer from which the water has been removed. It is described that the dried crumbs are introduced in a baler in the form of flakes and compressed into bales. It is also described that it is preferable to adjust the maximum width of the crumbs to about 3 to 20 mm when crushing with a mixer equipped with a stirring and crushing function. The rubber polymer used here is specifically an unsaturated nitrile-conjugated diene copolymer latex obtained by emulsion polymerization, and it has also been shown to be applicable to copolymers composed only of acrylates, such as ethyl acrylate/n-butyl acrylate copolymer and ethyl acrylate/n-butyl acrylate/2-methoxyethyl acrylate copolymer. However, acrylic rubber composed only of acrylates has the problem of being inferior in crosslinked rubber properties such as heat resistance and compression set resistance.

As an example of an acrylic rubber having reactive groups and excellent heat resistance and compression set resistance, Patent Document 2 (International Publication WO 2018/116828) discloses a method in which monomer components consisting of ethyl acrylate, n-butyl acrylate, and mono-n-butyl fumarate are emulsified with sodium lauryl sulfate as an emulsifier, polyethylene glycol monostearate, and water, and the resulting acrylic rubber latex is emulsion-polymerized in the presence of a polymerization initiator until a polymerization conversion rate of 95% is reached. The resulting acrylic rubber latex is then added to an aqueous solution of magnesium sulfate and a polymer flocculant, dimethylamine-ammonia-epichlorohydrin polycondensate, and stirred at 85°C to produce a crumb slurry. The crumb slurry is then washed once with water and then passed through a 100-mesh wire mesh in its entirety to capture only the solids and recover the crumb-like acrylic rubber. According to this method, the obtained hydrous crumb is dehydrated by centrifugation or the like, dried at 50 to 120°C using a band dryer or the like, and then introduced into a baler where it is compressed and baled. However, this method has problems such as the generation of a large amount of semi-coagulated hydrous crumb in the coagulation reaction, which adheres to the coagulation tank in large quantities, and the inability to sufficiently remove the coagulant and emulsifier by washing. Even if bales are produced, they have poor water resistance and are poorly processable in a Banbury machine or the like, requiring long mixing times.

In addition, Patent Document 3 (International Publication No. WO 2018/079783) discloses a method for producing an acrylic rubber having excellent water resistance (volume change after immersion in distilled water at 80°C for 70 hours) with little residual emulsifier or coagulant by emulsifying monomer components consisting of ethyl acrylate, n-butyl acrylate, and mono-n-butyl fumarate using pure water and an emulsifier consisting of sodium lauryl sulfate and polyoxyethylene dodecyl ether, emulsion polymerization in the presence of a polymerization initiator to a polymerization conversion rate of 95% by weight to obtain an emulsion polymerization liquid, continuously adding sodium sulfate to produce hydrous crumbs, and then washing the hydrous crumbs four times with industrial water, washing once with an acid at pH 3, and washing once with pure water, and then drying the resulting hydrous crumbs at 110°C for one hour in a hot air dryer. However, there is no mention of using the obtained acrylic rubber in a veil shape, and there is a problem in that handling sticky acrylic rubber in a crumb shape is poor in workability and storage stability. Furthermore, the resulting acrylic rubber has poor processability and is required to have high water resistance in harsher environments.

Regarding the gel content of acrylic rubber, for example, Patent Document 4 (JP Patent No. 3599962) discloses an acrylic rubber composition having an acetone-insoluble gel fraction of 5% or less by weight, obtained by copolymerizing 95-99.9% by weight of alkyl acrylate or alkoxyalkyl acrylate with 0.1-5% by weight of a polymerizable monomer having two or more radically reactive unsaturated groups with different reactivity in the presence of a radical polymerization initiator, a reinforcing filler, and an organic peroxide-based vulcanizing agent, and excellent extrusion processability such as extrusion speed, die swell, and surface texture. The acrylic rubber used here, which has a very small gel fraction, is obtained by adjusting the polymerization liquid to pH 6-8 with sodium bicarbonate or the like, as opposed to the acrylic rubber with a high gel fraction (60%) obtained in a polymerization liquid in the normal acidic range (pH 4 before polymerization, pH 3.4 after polymerization). Specifically, water, sodium lauryl sulfate and polyoxyethylene nonylphenyl ether as emulsifiers, sodium carbonate, and boric acid are charged and adjusted to 75°C, then t-butyl hydroperoxide, Rongalite, disodium ethylenediaminetetraacetate, and ferrous sulfate are added (pH at this time is 7.1), and then the monomer components of ethyl acrylate and allyl methacrylate are added dropwise to carry out emulsion polymerization, and the resulting emulsion with a pH of 7 is salted out using an aqueous sodium sulfate solution, washed with water, and dried to obtain acrylic rubber. However, the acrylic rubber obtained by this method has problems with handling, such as decomposition in the neutral to alkaline range, poor storage stability, and poor water resistance.

In addition, Patent Document 5 (International Publication WO 2018/143101) discloses a technology for improving the extrusion moldability, particularly the discharge amount, discharge length, and surface texture, of a rubber composition containing a reinforcing agent and a crosslinking agent, by emulsion polymerization of a (meth)acrylic acid ester and an ion-crosslinking monomer, using an acrylic rubber having a complex viscosity at 100°C ([η]100°C) of 3,500 Pa·s or less and a ratio ([η]100°C/[η]60°C) of the complex viscosity at 60°C ([η]60°C) to the complex viscosity at 100°C ([η]100°C) of 0.8 or less. The technology discloses that the gel content of the tetrahydrofuran-insoluble portion of the acrylic rubber used in this technology is 80% by weight or less, preferably 5 to 80% by weight, but preferably as much as possible within the range of 70% by weight or less, and that the extrusion property deteriorates when the gel content is less than 5%. The patent also describes that the weight-average molecular weight (Mw) of the acrylic rubber used is 200,000 to 1,000,000, and that if the weight-average molecular weight (Mw) exceeds 1,000,000, the viscoelasticity of the acrylic rubber becomes too high, which is undesirable. However, the patent document does not describe a method for improving the water resistance of the acrylic rubber or the kneading processability in a Banbury mixer, or forming the acrylic rubber into a sheet or veil shape.

On the other hand, regarding the production of sheet-shaped acrylic rubber, for example, Patent Document 6 (JP Patent Publication 1-225512 A) discloses a method in which a twin-screw extruder dryer consisting of a feed barrel, a dehydration barrel, a standard barrel, a vent barrel, and a vacuum barrel is used to supply nitrile rubber (NBR) crumbs with a moisture content of about 50% to the feed barrel, and after most of the moisture is dehydrated in the dehydration barrel, the remaining moisture and evaporated gas are removed by suction in the vacuum barrel, and the crumbs are continuously extruded in a strip shape through a breaker plate and a die, and it is described that acrylic rubber crumbs are used as the rubber crumbs to be applied. However, the same patent document does not disclose the use of such acrylic rubber sheets to form bales.

JP 2006-328239 A International Publication No. 2018/116828 International Publication No. 2018/079783 Patent No. 3599962 International Publication No. 2018/143101 Japanese Patent Application Publication No. 1-225512

The present invention has been made in consideration of the above circumstances, and aims to provide an acrylic rubber veil that has excellent processability and water resistance when kneaded using a Banbury mixer or the like, a method for producing the same, a rubber mixture containing the acrylic rubber veil, a method for producing the same, and a cross-linked rubber product thereof.

As a result of intensive research conducted in light of the above problems, the inventors have discovered that an acrylic rubber veil made of an acrylic rubber whose main component is a (meth)acrylic acid ester, in which the ash content, the amount of specific elements in the ash, and the amount of gel in a specific solvent are specified, has excellent kneading processability in a Banbury mixer and the like, and excellent water resistance.

The inventors have also discovered that by specifying the amount of reactive groups in the acrylic rubber constituting the acrylic rubber veil and by specifying the pH, complex viscosity at a specific temperature, specific gravity, and water content of the acrylic rubber veil, the processability and water resistance of the acrylic rubber veil can be further improved and the handleability as an acrylic rubber veil can be significantly improved.

The inventors have also discovered that such acrylic rubber bales can be easily produced by adding an emulsion polymerization liquid obtained by emulsion-polymerizing a monomer component mainly composed of (meth)acrylic acid ester to a stirred coagulation liquid to produce water-containing crumbs, washing the water-containing crumbs after washing with warm water, melting and drying the washed water-containing crumbs to a specific water content using a screw-type dissolving machine, and extruding the dried rubber into a bale.

The inventors have also discovered that the water resistance is significantly improved by providing a dehydration process in which water is squeezed out of the washed, water-containing crumbs, and that the handleability of the acrylic rubber veil is significantly improved and processability is also enhanced by including a reactive group-containing monomer in the monotonic component, increasing the polymerization conversion rate of the emulsion polymerization to a specific level, and forming the dried rubber extruded from the screw-type extruder into a sheet shape.

The inventors further discovered that it is difficult to control the amount of gel of the specific solvent insoluble portion of acrylic rubber during production, and that when an attempt is made to increase the polymerization conversion rate and the molecular weight of the acrylic rubber to improve the handleability of the acrylic rubber bale, the amount of gel of the specific solvent insoluble portion increases rapidly, worsening the processability of the acrylic rubber bale, but this rapidly increasing gel of the specific solvent insoluble portion disappears when the water-containing crumb is dried in a screw-type extruder until it is substantially free of water (specific water content) and melt-kneaded, and that it is difficult to dry acrylic rubber, which has a low specific heat, to a specific water content in a screw-type extruder, but that by raising the temperature of the water-containing crumb to a specific level or higher, the amount of gel of the specific solvent insoluble portion in the obtained acrylic rubber bale can be reliably reduced and the processability can be significantly improved, and that the amount of gel in the acrylic rubber bale varies completely depending on the solvent used, and for example, the amount of gel of acetone, tetrahydrofuran, and methyl ethyl ketone insoluble portions is not correlated and the properties imparted to the acrylic rubber bale are completely different.

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

Thus, according to the present invention, there is provided an acrylic rubber veil having a rectangular parallelepiped shape, which is obtained by emulsion polymerization and which comprises an acrylic rubber containing structural units having groups derived from a (meth)acrylic acid ester as main structural units and having at least one reactive group selected from the group consisting of a carboxyl group, an epoxy group and a halogen group, said acrylic rubber having an ash content of 0.0001 to 0.3 % by weight as measured by JIS K6288 Method A , a total content of at least one element selected from the group consisting of sodium, sulfur, calcium, magnesium and phosphorus in said ash content of 50% by weight or more, and a gel content of methyl ethyl ketone insoluble matter of 50% by weight or less.

In the acrylic rubber veil of the present invention, it is preferable that the ash content is 0.2% by weight or less.

In the acrylic rubber veil of the present invention, the acrylic rubber preferably contains sodium and sulfur in the ash content .
In the acrylic rubber veil of the present invention, the reactive group content of the acrylic rubber is preferably 0.001 to 5% by weight .

In the acrylic rubber veil of the present invention, the weight average molecular weight (Mw) of the acrylic rubber is preferably in the range of 1,000,000 to 5,000,000.

In the acrylic rubber veil of the present invention, it is preferable that the amount of gel insoluble in methyl ethyl ketone is 30% by weight or less.

In the acrylic rubber veil of the present invention, it is further preferable that the amount of gel insoluble in methyl ethyl ketone is 20% by weight or less.

In the acrylic rubber veil of the present invention, the total amount of sodium and sulfur in the ash is preferably 80% by weight or more based on the total ash content .

In the acrylic rubber veil of the present invention, the ratio of sodium to sulfur in the ash ([Na]/[S]) is preferably in the range of 0.75 to 0.95 by weight.

In the acrylic rubber veil of the present invention, the pH is preferably 2 to 6 .

In the acrylic rubber veil of the present invention, it is preferable that the complex viscosity at 100°C ([η]100°C) is 1,500 to 6,000 Pa·s, and 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) is 0.5 to 0.99. Here, the complex viscosity is measured 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.), determining the complex viscosity η at each temperature, and of the dynamic viscoelasticity described above, the dynamic viscoelasticity at 60°C is defined as the complex viscosity [η]60°C, and the dynamic viscoelasticity at 100°C is defined as the complex viscosity [η]100°C.
In the acrylic rubber veil of the present invention, it is more preferable that 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) is 0.83 or more.

In the acrylic rubber veil of the present invention, the specific gravity measured in accordance with JIS K6268 Crosslinked Rubber - Density Measurement Method A is preferably in the range of 0.7 to 1.5, and the water content is preferably less than 1% by weight.

In the acrylic rubber veil of the present invention, the acrylic rubber is preferably one which has been emulsion-polymerized using a sulfate ester salt as an emulsifier.
In the acrylic rubber veil of the present invention, the acrylic rubber is preferably polymerized with an organic peroxide or an inorganic peroxide.
The acrylic rubber veil of the present invention is an acrylic rubber veil according to any one of claims 1 to 16, wherein the acrylic rubber is polymerized at a polymerization conversion rate of 80% by weight or more.
In the acrylic rubber veil of the present invention, the acrylic rubber is preferably one obtained by coagulating an emulsion-polymerized polymerization solution with a sodium salt coagulant to produce hydrous crumbs, which are then dehydrated and dried.
In the acrylic rubber veil of the present invention, it is preferable that the acrylic rubber is produced from the above-mentioned hydrous crumbs, in which the proportion of crumbs that pass through a JIS sieve with a mesh size of 6.7 mm but do not pass through a JIS sieve with a mesh size of 710 μm is 20% by weight or more.
In the acrylic rubber veil of the present invention, the acrylic rubber is preferably obtained by washing the above-mentioned water-containing crumb with warm water of 40° C. or higher and then drying.
In the acrylic rubber veil of the present invention, the drying is preferably carried out by melt kneading.
In the acrylic rubber veil of the present invention, it is preferable that the melt kneading is carried out in a state where the water content is less than 1% by weight .
In the acrylic rubber veil of the present invention, the drying is preferably carried out in a screw-type extruder.
In the acrylic rubber veil of the present invention, it is preferable that after the drying, it is cooled at a cooling rate of 50° C./hr or more.

The present invention also provides a method for producing an acrylic rubber bale, which includes an emulsion polymerization step of emulsifying a monomer component mainly composed of a (meth)acrylic acid ester and a monomer component having at least one reactive group selected from the group consisting of a carboxyl group, an epoxy group, and a halogen group, with water and an emulsifier, and emulsion-polymerizing the resulting emulsion polymerization liquid in the presence of a polymerization catalyst; a coagulation step of adding the resulting emulsion polymerization liquid to a stirred coagulation liquid to produce water-containing crumbs; a washing step of washing the produced water-containing crumbs with warm water of 40°C or higher ; a drying step of dehydrating and drying the washed water-containing crumbs using a screw-type extruder and extruding them as dried rubber having a water content of less than 1% by weight; and a baling step of forming the extruded dried rubber into rectangular bales .
In the method for producing an acrylic rubber veil of the present invention, it is preferable to produce the above-mentioned acrylic rubber veil.

In the method for producing an acrylic rubber veil of the present invention, the emulsifier or coagulant preferably contains at least one element selected from the group consisting of sodium, sulfur, calcium, magnesium and phosphorus .

In the method for producing an acrylic rubber veil of the present invention, it is preferable that the polymerization conversion rate of the emulsion polymerization is 90% by weight or more.

In the method for producing an acrylic rubber bale of the present invention, the temperature of the wet crumb fed into the screw-type extruder is preferably 40 to 100° C. In addition, it is preferable to provide a dehydration step for squeezing out the water from the wet crumb.

Furthermore, in the method for producing an acrylic rubber veil of the present invention, it is preferable that the dehydration of the hydrous crumb is carried out to a moisture content of 1 to 40% by weight.

In the method for producing an acrylic rubber veil of the present invention, it is further preferable that the water content after dehydration is in the range of 5 to 35% by weight.

In the method for producing an acrylic rubber veil of the present invention, it is preferable that the degree of vacuum in the drying barrel of the screw-type extruder is in the range of 1 to 50 kPa and the drying temperature is in the range of 100 to 250°C.

In the method for producing an acrylic rubber veil of the present invention, it is preferable that the moisture content of the water-containing crumb in the die section of the screw-type extruder is less than 1% by weight.

In the method for producing an acrylic rubber veil of the present invention, it is preferable that the resin pressure at the die of the screw-type extruder is in the range of 0.1 to 10 MPa.

In the method for producing an acrylic rubber veil of the present invention, it is preferable that the ratio (Q/N) of the extrusion rate (Q) to the rotation speed (N) of the screw-type extruder is in the range of 2 to 10.

In the method for producing an acrylic rubber veil of the present invention, it is preferable that the dried rubber is in the form of a sheet.

According to the present invention, there is also provided a rubber mixture obtained by mixing the acrylic rubber veil with a filler and a crosslinking agent.
In the rubber mixture according to the invention, the filler is preferably a reinforcing filler.
In the rubber mixture according to the invention, the filler is preferably carbon black.
In the rubber mixture according to the invention, the filler is preferably silica.
In the rubber mixture of the present invention, the crosslinking agent is preferably a polyamine compound, an ammonium carboxylate, a metal dithiocarbamate or a triazine thiol compound.
It is preferable that an antioxidant is further mixed into the rubber mixture of the present invention.
In the rubber mixture of the present invention, the antioxidant is preferably an amine-based antioxidant.
Furthermore, according to the present invention, there is provided a method for producing a rubber mixture, which comprises mixing the acrylic rubber veil with a filler , a crosslinking agent, and if necessary, an antioxidant in a mixer, and further, a method for producing a rubber mixture, which comprises mixing the acrylic rubber veil with a filler and if necessary, an antioxidant, and then mixing a crosslinking agent.

According to the present invention, there is further provided a cross-linked rubber product obtained by cross-linking the above rubber mixture.
In the cross-linked rubber product of the present invention, the cross-linking preferably includes a primary cross-linking and a secondary cross-linking.
According to the present invention, there is further provided a method for producing a cross-linked rubber product, which comprises subjecting the above-mentioned rubber mixture to primary cross-linking and then secondary cross-linking.

According to the present invention, there are provided an acrylic rubber veil having excellent processability and water resistance and a method for producing the same, a rubber mixture containing the acrylic rubber veil and a method for producing the same, and a cross-linked rubber product obtained by cross-linking the acrylic rubber veil and a method for producing the same .

FIG. 1 is a diagram illustrating an example of an acrylic rubber production system used to produce an acrylic rubber veil according to one 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 veil of the present invention is made of an acrylic rubber whose main component is a (meth)acrylic acid ester, has an ash content of 0.3% by weight or less, contains at least one element selected from sodium, sulfur, calcium, magnesium and phosphorus in the ash content in total of 50% by weight or more, and has a gel content of 50% by weight or less of methyl ethyl ketone insoluble matter.

<Monomer component>
The acrylic rubber constituting the acrylic rubber veil of the present invention is mainly composed of (meth)acrylic acid ester. The ratio of (meth)acrylic acid ester in the acrylic rubber is appropriately selected depending on the purpose of use, but is usually 50% by weight or more, preferably 70% by weight or more, and more preferably 80% by weight or more. In the present invention, "(meth)acrylic acid ester" is a general term for esters of acrylic acid and/or methacrylic acid.

The acrylic rubber constituting the acrylic rubber veil of the present invention contains at least one (meth)acrylic ester selected from (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, and is suitable because it can highly improve the crosslinking properties of the acrylic rubber veil.

The acrylic rubber constituting the acrylic rubber veil of the present invention is preferably one that contains a reactive group-containing monomer, as this can highly improve heat resistance, compression set resistance, and other properties.

Specific preferred examples of the acrylic rubber constituting the acrylic rubber veil of the present invention include those that consist of at least one (meth)acrylic acid ester selected from (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, a reactive group-containing monomer, and other copolymerizable monomers as necessary.

The (meth)acrylic acid alkyl ester is not limited, but is usually 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.

Specific examples of such (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, with ethyl (meth)acrylate and n-butyl (meth)acrylate being preferred, and ethyl acrylate and n-butyl acrylate being more preferred.

The (meth)acrylic acid alkoxyalkyl ester is not limited, but is usually 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.

Specific examples of such (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 these (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters is used alone or in combination of two or more, and the proportion in the acrylic rubber is usually 50 to 99.99% by weight, preferably 70 to 99.9% by weight, more preferably 80 to 99.5% by weight, and most preferably 87 to 99% by weight. If the amount of (meth)acrylic acid ester in the monomer component is excessively small, the weather resistance, heat resistance, and oil resistance of the resulting acrylic rubber may decrease, which is not preferable.

There are no limitations on the reactive group-containing monomer, and it is appropriately selected depending on the intended use, but a monomer having at least one functional group selected from the group consisting of a carboxyl group, an epoxy group, and a halogen group is preferred, and a monomer having at least one functional group selected from the group consisting of a carboxyl group, an epoxy group, and a chlorine atom is more preferred.

The monomer having a carboxyl group is not limited, but an ethylenically unsaturated carboxylic acid can be suitably used. Examples of the ethylenically unsaturated carboxylic acid include ethylenically unsaturated monocarboxylic acids, ethylenically unsaturated dicarboxylic acids, and ethylenically unsaturated dicarboxylic acid monoesters. Among these, ethylenically unsaturated dicarboxylic acid monoesters are particularly preferred because they can further improve the compression set resistance properties when the acrylic rubber is cross-linked into a rubber.

The ethylenically unsaturated monocarboxylic acid is not limited, but is preferably an ethylenically unsaturated monocarboxylic acid having 3 to 12 carbon atoms, such as acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, and cinnamic acid.

The ethylenically unsaturated dicarboxylic acid is not limited, but is preferably an ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms, such as butenedioic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, etc. Ethylenically unsaturated dicarboxylic acids also include those that exist as anhydrides.

The ethylenically unsaturated dicarboxylic acid monoester is not limited, but 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 such 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 among these, mono-n-butyl fumarate and mono-n-butyl maleate are preferred, with 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.

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.

Specific examples of the unsaturated alcohol esters of the halogen-containing saturated carboxylic acids include vinyl chloroacetate, vinyl 2-chloropropionate, and allyl chloroacetate. Specific 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. Specific 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. Specific 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. Specific examples of halogen-containing unsaturated ketones include 2-chloroethyl vinyl ketone, 3-chloropropyl vinyl ketone, and 2-chloroethyl allyl ketone. Specific examples of halomethyl group-containing aromatic vinyl compounds include p-chloromethylstyrene, m-chloromethylstyrene, o-chloromethylstyrene, and p-chloromethyl-α-methylstyrene. Specific examples of halogen-containing unsaturated amides include N-chloromethyl(meth)acrylamide. Specific examples of haloacetyl group-containing unsaturated monomers include 3-(hydroxychloroacetoxy)propyl allyl ether and p-vinylbenzyl chloroacetic acid ester.

These reactive group-containing monomers are used alone or in combination of two or more, and their proportion in the acrylic rubber is usually 0.01 to 20% by weight, preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, and most preferably 1 to 3% by weight.

There are no particular limitations on other monomers (hereinafter referred to as "other monomers") that may be used as necessary, so long as they are copolymerizable with the above-mentioned monomers, and examples thereof include aromatic vinyls, ethylenically unsaturated nitriles, acrylamide monomers, other olefin monomers, and the like. Examples of aromatic vinyls include styrene, α-methylstyrene, and divinylbenzene. Examples of ethylenically unsaturated nitriles include acrylonitrile and methacrylonitrile. Examples of acrylamide monomers include acrylamide and methacrylamide. Examples of other olefin monomers include ethylene, propylene, vinyl acetate, ethyl vinyl ether, and butyl vinyl ether.

These other monomers may be used alone or in combination of two or more, and their proportion in the acrylic rubber is usually in the range of 0 to 30% by weight, preferably 0 to 20% by weight, more preferably 0 to 15 parts by weight, and most preferably 0 to 10 parts by weight.

<Acrylic rubber>
The acrylic rubber constituting the acrylic rubber veil of the present invention preferably has a reactive group in the polymer.

The reactive group is not particularly limited and may be appropriately selected depending on the intended use, but is preferably at least one functional group selected from the group consisting of carboxyl groups, epoxy groups, and halogen groups, more preferably at least one functional group selected from the group consisting of carboxyl groups, epoxy groups, and chlorine atoms, which is suitable for highly improving the crosslinking properties of the acrylic rubber veil. The acrylic rubber having such reactive groups may be one in which reactive groups are added to the acrylic rubber by a post-reaction, but is preferably one in which a reactive group-containing monomer is copolymerized.

The content of reactive groups in acrylic rubber (polymer) may be appropriately selected depending on the intended use, but when the weight ratio of the reactive groups themselves is usually 0.001 or more, preferably 0.001 to 5 wt%, more preferably 0.01 to 3 wt%, particularly preferably 0.05 to 1 wt%, and most preferably in the range of 0.1 to 0.5 wt%, it is suitable as it provides a high level of balance in properties such as processability, strength properties, resistance to compression set, oil resistance, cold resistance, and water resistance.

Specific examples of the acrylic rubber constituting the acrylic rubber veil of the present invention include at least one (meth)acrylic ester selected from (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, a reactive monomer, and other copolymerizable monomers contained as necessary, and the proportions of each in the acrylic rubber are usually 50 to 99.99% by weight, preferably 70 to 99.9% by weight, more preferably 80 to 99.5% by weight, and particularly preferably 87 to 99% by weight, for at least one (meth)acrylic ester selected from (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, respectively; usually 0.01 to 20% by weight, preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight, and 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, for the other monomers. By setting the content of these monomers in the acrylic rubber within the above ranges, the object of the present invention can be achieved to a high degree, and the water resistance and compression set resistance properties are significantly improved when the acrylic rubber veil is crosslinked, which is preferable.

The weight average molecular weight (Mw) of the acrylic rubber constituting the acrylic rubber veil of the present invention is not limited, but when the absolute molecular weight measured by GPC-MALS is usually in the range of 100,000 to 5,000,000, preferably 500,000 to 5,000,000, more preferably 1,000,000 to 5,000,000, particularly preferably 1,100,000 to 3,500,000, and most preferably 1,200,000 to 2,500,000, the processability, strength properties, and compression set resistance properties of the acrylic rubber veil when mixed are highly balanced and are suitable.

The ratio (Mz/Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of the acrylic rubber constituting the acrylic rubber veil of the present invention is not limited, but when the absolute molecular weight distribution, with emphasis on the high molecular weight region measured by GPC-MALS, is usually 1.3 or more, preferably 1.4 to 5, and more preferably in the range of 1.5 to 2, the processability and strength characteristics of the acrylic rubber veil are highly balanced and changes in physical properties during storage can be mitigated, which is preferable.

The glass transition temperature (Tg) of the acrylic rubber constituting the acrylic rubber veil of the present invention is not limited, but is usually 20°C or lower, preferably 10°C or lower, and more preferably 0°C or lower. The lower limit of the glass transition temperature (Tg) of the acrylic rubber is not particularly limited, but is usually -80°C or higher, preferably -60°C or higher, and more preferably -40°C or higher. By setting the glass transition temperature at or above the above lower limit, it is possible to achieve superior oil resistance and heat resistance, and by setting it below the above upper limit, it is possible to achieve superior cold resistance and processability.

The content of acrylic rubber in the acrylic rubber veil of the present invention is appropriately selected depending on the purpose of use, but is usually 95% by weight or more, preferably 97% by weight or more, and more preferably 98% by weight or more. The content of acrylic rubber in the acrylic rubber veil of the present invention is approximately the same as the total amount of acrylic rubber veil minus the amount of ash that was not completely removed by the emulsifier and coagulant used in the production.

<Acrylic rubber veil>
The acrylic rubber veil of the present invention is characterized in that it is made of the above-mentioned acrylic rubber, and that the ash content, ash component content, and gel content contained therein are all within specific ranges. The ash content in the acrylic rubber veil is measured in accordance with JIS K6228 Method A, and the main components are residues of the emulsifier used in emulsifying the monomer components and emulsion polymerizing them in the production of the acrylic rubber, and the coagulant used in coagulating the emulsion polymerization liquid.

The size of the acrylic rubber veil of the present invention is not limited, 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 is usually in the range of 50 to 500 mm, preferably 100 to 300 mm, and more preferably 150 to 250 mm. The shape of the acrylic rubber veil of the present invention is also not limited and may be appropriately selected depending on the intended use of the acrylic rubber veil, but in many cases a rectangular parallelepiped is suitable.

The acrylic rubber veil of the present invention has excellent storage stability and water resistance when the ash content is 0.3% by weight or less, preferably 0.25% by weight or less, more preferably 0.2% by weight or less, particularly preferably 0.15% by weight or less, and most preferably 0.12% by weight or less.

The lower limit of the ash content in the acrylic rubber veil of the present invention is not limited, but is usually 0.0001% by weight or more, preferably 0.0005% by weight or more, more preferably 0.001% by weight or more, particularly preferably 0.005% by weight or more, and most preferably 0.01% by weight or more, which is suitable for suppressing metal adhesion and providing excellent workability. For example, the preferred range of ash content for achieving a high level of balance between the water resistance and metal adhesion of the acrylic rubber veil can be said to be 0.0001 to 0.15% by weight.

The ash content at which the storage stability, water resistance, and workability of the acrylic rubber veil of the present invention are well balanced is usually in the range of 0.0001 to 0.3% by weight, preferably 0.0005 to 0.25% by weight, more preferably 0.001 to 0.25% by weight, particularly preferably 0.005 to 0.15% by weight, and most preferably 0.01 to 0.12% by weight.

The acrylic rubber veil of the present invention has an ash content of at least one element selected from sodium, sulfur, calcium, magnesium, and phosphorus of at least 30% by weight in total. When the total content of these elements is 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 80% by weight or more, the acrylic rubber veil has excellent storage stability and water resistance.

In particular, the total amount of sodium and sulfur in the ash of the acrylic rubber veil of the present invention is not particularly limited, but is usually 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 80% by weight or more, and is therefore highly suitable for achieving outstanding storage stability and water resistance.

The ratio of sodium to sulfur in the ash of the acrylic rubber veil of the present invention ([Na]/[S]) is not particularly limited, but when the ratio is in the range of weight ratio, usually 0.4 to 2.5, preferably 0.6 to 1, more preferably 0.7 to 0.98, particularly preferably 0.75 to 0.95, and most preferably 0.8 to 0.9, the water resistance is highly excellent and the acrylic rubber veil is suitable.

The gel content of the acrylic rubber veil of the present invention is 50% by weight or less, in terms of the insoluble matter in methyl ethyl ketone, preferably 30% by weight or less, more preferably 20% by weight or less, particularly preferably 10% by weight or less, and most preferably 5% by weight or less. A gel content within this range is preferable because it provides highly improved processability during kneading with a Banbury mix, etc.

The moisture content of the acrylic rubber veil of the present invention is not limited, 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 are optimized and the properties such as heat resistance and water resistance are highly excellent and suitable.

The specific gravity of the acrylic rubber veil of the present invention is not limited, but is usually in the range of 0.7 to 1.5, preferably 0.8 to 1.4, more preferably 0.9 to 1.3, particularly preferably 0.95 to 1.25, and most preferably 1.0 to 1.2, and is therefore suitable for achieving excellent storage stability.

The pH of the acrylic rubber veil of the present invention is not limited, but is usually 6 or less, preferably 2 to 6, more preferably 2.5 to 5.5, and particularly preferably 3 to 5, and is therefore suitable as it provides highly improved storage stability.

The complex viscosity of the acrylic rubber veil of the present invention at 60°C ([η]60°C) is not limited, but is usually 15,000 Pa·s or less, preferably 2,000 to 10,000 Pa·s, more preferably 2,500 to 7,000 Pa·s, and most preferably 2,700 to 5,500 Pa·s, which is suitable for excellent processability, oil resistance, and shape retention. The complex viscosity at 100°C ([η]100°C) is usually 1,500 to 6,000 Pa·s, preferably 2,000 to 5,000 Pa·s, more preferably 2,500 to 4,000 Pa·s, and most preferably 2,500 to 3,500 Pa·s, which is suitable for 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) to the complex viscosity at 60°C ([η]60°C) of the acrylic rubber veil of the present invention is not limited, 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. In addition, when 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) is usually in the range of 0.5 to 0.99, preferably 0.5 to 0.98, more preferably 0.6 to 0.95, and most preferably 0.75 to 0.93, the processability, oil resistance, and shape retention are highly balanced and suitable.

The Mooney viscosity (ML1+4, 100°C) of the acrylic rubber veil is not limited, but is usually in the range of 10 to 150, preferably 20 to 100, and more preferably 25 to 70, which provides a high level of balance between processability and strength properties.

<Method of manufacturing acrylic rubber veil>
The acrylic rubber veil can be easily produced by the production method of the present invention, which includes the following steps:
(a) an emulsion polymerization step of emulsifying a monomer component mainly composed of a (meth)acrylic acid ester with water and an emulsifier, and emulsion-polymerizing the resulting emulsion in the presence of a polymerization catalyst to obtain an emulsion polymerization liquid;
(b) a coagulation step in which the obtained emulsion polymerization liquid is added to a stirred coagulation liquid to produce water-containing crumbs;
(c) a washing step of washing the resulting hydrous crumbs with warm water;
(d) a drying step in which the washed wet crumb is dried to a water content of less than 1% by weight by extruding a dried rubber using a screw-type extruder;
and (e) a baling step of baling the extruded dry rubber.

(Emulsion polymerization process)
The emulsion polymerization step in the method for producing an acrylic rubber veil of the present invention is characterized in that the above-mentioned monomer components are emulsified with water and an emulsifier, and then emulsion-polymerized in the presence of a polymerization catalyst to obtain an emulsion polymerization liquid.

The emulsifier used in the emulsion polymerization step is not limited and may be any of the usual methods, but examples include anionic emulsifiers, cationic emulsifiers, and nonionic emulsifiers. Among these, anionic emulsifiers and nonionic emulsifiers are preferred, anionic emulsifiers are particularly preferred, and sulfuric acid-based emulsifiers are most preferred.

The anionic emulsifier is not limited and any commonly used one can be used, but examples include fatty acid-based emulsifiers, sulfonic acid-based emulsifiers, sulfosuccinic acid-based emulsifiers, sulfuric acid-based emulsifiers, and phosphoric acid-based emulsifiers, and is preferably a sulfuric acid-based emulsifier.

Examples of fatty acid emulsifiers include sodium octanoate, sodium decanoate, sodium laurate, sodium myristate, sodium palmitate, and sodium stearate.

Examples of sulfonic acid emulsifiers include sodium hexanesulfonate, sodium octane sulfonate, sodium decane sulfonate, sodium toluenesulfonate, sodium cumene sulfonate, sodium octylbenzenesulfonate, sodium dodecylbenzenesulfonate, ammonium dodecylbenzenesulfonate, sodium naphthalenesulfonate, sodium alkylnaphthalenesulfonate, and sodium alkyldiphenyletherdisulfonate.

Examples of sulfosuccinic acid emulsifiers include sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate.

As the sulfate emulsifier, sulfate ester salts can be suitably used. Suitable sulfate ester salts include, for example, sodium lauryl sulfate, ammonium lauryl sulfate, sodium myristyl sulfate, sodium laureth sulfate, sodium polyoxyethylene alkyl sulfate, and sodium polyoxyethylene alkylaryl sulfate, with sodium lauryl sulfate being particularly preferred.

Examples of phosphoric acid emulsifiers include sodium lauryl phosphate, potassium lauryl phosphate, and sodium polyoxyalkylene alkyl ether phosphate.

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. Among these, polyoxyalkylene alkyl ethers and polyoxyalkylene alkylphenol ethers are preferred, and polyoxyethylene alkyl ethers and polyoxyethylene alkylphenol ethers are 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 monomer components, water, and emulsifier may be mixed in the usual manner, such as by stirring the monomers, emulsifier, and water using a stirrer such as a homogenizer or a disk turbine. The amount of water used is usually 10 to 750 parts by weight, preferably 50 to 500 parts by weight, and more preferably 100 to 400 parts by weight, per 100 parts by weight of the monomer components.

The polymerization catalyst used in the emulsion polymerization step may be one that is typically used in emulsion polymerization, but for example, a redox catalyst consisting of a radical generator and a reducing agent can be used.

Examples of radical generators include peroxides and azo compounds, with peroxides being preferred. As peroxides, inorganic peroxides and organic peroxides can be used.

Examples of inorganic peroxides include sodium persulfate, potassium persulfate, hydrogen peroxide, and ammonium persulfate. Among these, potassium persulfate, hydrogen peroxide, and ammonium persulfate are preferred, with potassium persulfate being particularly preferred.

Examples of organic peroxides 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, 1,1,3,3-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)peroxide peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanate, t-hexyl peroxypivalate, t-butyl peroxyneodecanate, t-hexyl peroxypivalate, t-butyl peroxypivalate, 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-hexylperoxyisopropanate Examples of peroxypropane monocarbonate include t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, t-hexylperoxybenzoate, t-butylperoxybenzoate, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane. Among these, diisopropylbenzene hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, and benzoyl peroxide 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}.

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, and more preferably 0.001 to 0.5 parts by weight, per 100 parts by weight of the monomer component.

The reducing agent can be any agent that is used in a redox catalyst for emulsion polymerization, but in the present invention, it is particularly preferable to use at least two types of reducing agents in combination. For example, a combination of a metal ion compound in a reduced state and another reducing agent is suitable as the at least two types of reducing agents.

Examples of reduced metal ion compounds 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 ascorbic acid or its salts, such as ascorbic acid, sodium ascorbate, and potassium ascorbate; erythorbic acid or its salts, such as erythorbic acid, sodium erythorbate, and potassium erythorbate; sulfinates, such as sodium hydroxymethanesulfinate; sulfites, such as sodium sulfite, potassium sulfite, sodium hydrogensulfite, aldehyde sodium hydrogensulfite, and potassium hydrogensulfite; pyrosulfites, such as sodium pyrosulfite, potassium pyrosulfite, sodium hydrogensulfite, and potassium pyrosulfite; thiosulfates, such as sodium thiosulfate and potassium thiosulfate; phosphorous acid, sodium phosphite, potassium phosphite, sodium hydrogen phosphite, and potassium hydrogen phosphite, or phosphorous acid or its salts, such as pyrophosphorous acid, sodium pyrophosphite, potassium pyrophosphite, sodium hydrogen phosphite, and potassium hydrogen phosphite; pyrophosphorous acid or its salts, such as pyrophosphorous acid, sodium pyrophosphite, potassium pyrophosphite, sodium hydrogen pyrophosphite, and potassium hydrogen pyrophosphite; sodium formaldehyde sulfoxylate. 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 the reduced metal ion compounds can be used alone or in combination of two or more. The amount used is usually 0.001 to 1 part by weight, preferably 0.005 to 0.5 parts by weight, and more preferably 0.01 to 0.3 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 0.3 parts by weight, per 100 parts by weight of the monomer component.

The amount of water used in the emulsion polymerization reaction may be the amount used during the emulsification of the monomer components, but 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 temperature is usually in the range of 0 to 100°C, preferably 5 to 80°C, and more preferably 10 to 50°C, and the polymerization time is usually 0.5 to 100 hours, and preferably 1 to 10 hours.

The polymerization conversion rate of the emulsion polymerization reaction is not limited, but is usually 80% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more, which is suitable because the strength characteristics of the acrylic rubber veil produced are excellent and there is no monomer odor. A polymerization terminator may be used to stop the polymerization.

(Solidification process)
The coagulation step in the method for producing an acrylic rubber sheet of the present invention is characterized in that the obtained emulsion polymerization liquid is added to a stirred coagulation liquid (aqueous solution containing a coagulant) to generate water-containing crumbs.

The solids concentration of the emulsion polymerization liquid used in the coagulation step is not limited, but is usually adjusted to the 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 step is not limited, but is usually a metal salt. 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 alkali metal salts, and particularly preferably sodium salts.

Examples of alkali metal salts used as coagulants 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. In the present invention, among these, sodium salts such as sodium chloride and sodium sulfate are preferred, with 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 kinds, 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 veil is crosslinked.

The coagulant concentration in the coagulation liquid is 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 because it allows the particle size of the resulting hydrous crumbs to be concentrated uniformly in a specific region.

The temperature of the coagulation liquid is not limited, but is usually 40°C or higher, preferably 40 to 90°C, and more preferably in the range of 50 to 80°C, which is suitable for producing uniform hydrous crumbs.

The stirring speed (rotation speed) of the coagulation liquid being stirred is expressed by the rotation speed of the stirring blade of the stirring device installed in the coagulation bath, and is usually 100 rpm or more, preferably 200 to 1,000 rpm, more preferably 300 to 900 rpm, and particularly preferably in the range of 400 to 800 rpm.

The rotation speed of the coagulation liquid is preferably such that the coagulation liquid is stirred vigorously to some extent, since this allows the hydrous crumbs to be small and uniform in particle size. By setting the rotation speed at or above the lower limit above, it is possible to prevent crumbs with excessively large or small particle size from being generated, while by setting the rotation speed at or below the upper limit above, it becomes easier to control the coagulation reaction.

The peripheral speed of the stirred coagulation liquid is expressed by the linear speed of the outer circumference of the stirring blade of the stirring device, and it is preferable to stir the coagulation liquid vigorously to a certain extent, since this makes it possible to produce small and uniform hydrous crumb particle sizes, 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 limited, but 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, which is preferable since it makes it easier to control the coagulation reaction.

By setting the above conditions for the coagulation reaction in the coagulation step (contact 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 generated are uniform and concentrated, and the removal of the emulsifier and coagulant during washing and dehydration is significantly improved, which is preferable.

The thus-obtained hydrous crumbs preferably satisfy all of the following conditions (a) to (e) when sieved using a JIS classification sieve. The JIS sieve complies with the provisions of the Japanese Industrial Standards (JIS Z 8801-1).
(a) the proportion of water-containing crumbs that do not pass through a JIS sieve having an opening of 9.5 mm is 10% by weight or less;
(b) the proportion of water-containing crumbs that pass through a JIS sieve with a mesh size of 9.5 mm but do not pass through a JIS sieve with a mesh size of 6.7 mm is 30% by weight or less;
(c) The proportion of water-containing crumbs that pass through a JIS sieve with an opening of 6.7 mm but do not pass through a JIS sieve with an opening of 710 μm is 20% by weight or more;
(d) the proportion of moist crumbs that pass through a JIS sieve with a mesh size of 710 μm but not a JIS sieve with a mesh size of 425 μm is 30% by weight or less, and (e) the proportion of moist crumbs that pass through a JIS sieve with a mesh size of 425 μm is 10% by weight or less.

When the proportion of the generated hydrous crumbs that do not pass through a JIS sieve with a mesh size of 9.5 mm (a) is 10% by weight or less, preferably 5% by weight or less, and more preferably 1% by weight or less, the washing efficiency of the emulsifier and coagulant can be significantly improved, which is suitable.

When the proportion of (b) the water-containing crumbs that pass through a JIS sieve with a mesh size of 9.5 mm but not a JIS sieve with a mesh size of 6.7 mm is 30% by weight or less, preferably 20% by weight or less, and more preferably 5% by weight or less, among the water-containing crumbs produced, the washing efficiency of the emulsifier and coagulant can be significantly improved, which is suitable.

When the proportion of the generated hydrous crumbs that pass through a JIS sieve with a mesh size of 6.7 mm (c) but do not pass through a JIS sieve with a mesh size of 710 μm is 20% by weight or more, preferably 40% by weight or more, more preferably 70% by weight or more, and most preferably 80% by weight or more, the washing efficiency of the emulsifier and coagulant can be significantly improved, which is suitable.

When the proportion of the generated hydrous crumbs that pass through a JIS sieve with a mesh size of 710 μm but not a JIS sieve with a mesh size of 425 μm (d) is 30% by weight or less, preferably 20% by weight or less, and more preferably 15% by weight or less, the washing efficiency of the emulsifier and coagulant is significantly improved and the productivity is also high, which is preferable.

When the proportion of the generated hydrous crumbs that pass through a JIS sieve (e) with a mesh size of 425 μm is 10% by weight or less, preferably 5% by weight or less, and more preferably 1% by weight or less, the washing efficiency of the emulsifier and coagulant is significantly improved, and the productivity is also high, which is preferable.

In the present invention, the washing efficiency of the emulsifier and coagulant is improved, and it is preferable when the ratio of (f) the water-containing crumbs that pass through a JIS sieve with a mesh size of 6.7 mm but do not pass through a JIS sieve with a mesh size of 4.75 mm is usually 40% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less.

In the present invention, it is also preferable that the ratio of the generated hydrous crumbs (g) that pass through a JIS sieve with a mesh size of 4.75 mm but do not pass through a JIS sieve with a mesh size of 710 μm is usually 40% by weight or more, preferably 60% by weight or more, and more preferably 80% by weight or more, since this significantly improves the removal efficiency of the emulsifier and coagulant during washing and dehydration.

In the present invention, it is further preferable that the ratio of (h) the hydrous crumbs that pass through a JIS sieve with a mesh size of 3.35 mm but do not pass through a JIS sieve with a mesh size of 710 μm among the hydrous crumbs produced is usually 20% by weight or more, preferably 40% by weight or more, more preferably 50% by weight or more, particularly preferably 60% by weight or more, and most preferably 70% by weight or more, since this significantly improves the removal efficiency of the emulsifier and coagulant during washing and dehydration.

(Washing process)
The washing step in the method for producing an acrylic rubber veil of the present invention is a step of washing the water-containing crumbs produced as described above with warm water.

The washing method can be done according to the usual method, for example, by mixing the produced hydrous crumbs with a large amount of warm water.

The amount of warm water used for washing is not particularly limited, but it is suitable to effectively reduce the ash content in the acrylic rubber when the amount per wash is 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 particularly preferably 150 to 5,000 parts by weight, per 100 parts by weight of the monomer component.

The temperature of the hot water used for washing is not limited, but is usually 40°C or higher, preferably 40 to 100°C, more preferably 50 to 90°C, and most preferably 60 to 80°C, which is suitable for significantly improving washing efficiency.

By keeping the temperature of the hot water during washing at or above the lower limit temperature, the emulsifier and coagulant are released from the water-containing crumbs, further improving washing efficiency.

The cleaning time is not limited, but is usually in the range of 1 to 120 minutes, preferably 2 to 60 minutes, and more preferably 3 to 30 minutes.

The number of washings is not particularly limited, and is usually 1 to 10 times, preferably multiple 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 washings can be significantly reduced by specifying the shape and diameter of the wet crumbs and/or setting the washing temperature within the above range.

(Dehydration process)
In the method for producing an acrylic rubber veil of the present invention, it is preferable to provide a dehydration step, prior to the drying step, in which water is squeezed out of the hydrous crumbs after washing using a dehydrator or the like. This reduces the amount of ash that could not be removed in the washing step, and dramatically improves the water resistance of the acrylic rubber veil.

The dehydrator used in this process is not particularly limited, and may be, for example, a centrifuge, a squeezer, or a screw-type extruder. However, a screw-type extruder is particularly suitable as it can significantly reduce the moisture content of the water-containing crumb. In a centrifuge or the like, sticky acrylic rubber can usually only be dehydrated to about 45-55% by weight, as the acrylic rubber adheres to the wall and between the slits. In contrast, a screw-type extruder is suitable as it has a mechanism for forcibly squeezing 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 an acrylic rubber bale of the present invention is a step of drying the hydrous crumbs obtained after the washing step and preferably after further dehydration, for example, by using a screw-type extruder to extrude a dried rubber having a moisture content of less than 1% by weight.

The temperature of the hydrous crumbs fed into the screw extruder is not 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 60 to 80°C. When the hydrous crumbs are fed into the screw extruder at this temperature range, it is preferable because the hydrous crumbs, which have a large specific heat of 1.5 to 2.5 KJ/kg·K and are difficult to raise in temperature, such as the acrylic rubber of the present invention, can be reliably dried in the screw extruder. In particular, in the present invention, the hydrous crumbs are dried and melt-kneaded in the screw extruder until they are substantially free of water (water content after dehydration, which will be described later), which is important in the production of acrylic rubber, since it eliminates the gel content of the methyl ethyl ketone insolubles that rapidly increases when the polymerization conversion rate of emulsion polymerization is increased.

The drying temperature (set temperature) in the screw extruder is selected appropriately, but it is usually between 100 and 250°C, preferably between 110 and 200°C, and more preferably between 120 and 180°C, which is suitable because it allows efficient drying without discoloration or deterioration of the acrylic rubber and reduces the amount of gel in the acrylic rubber veil that is insoluble in methyl ethyl ketone.

The shape of the dried rubber extruded from the screw-type extruder is not limited, and examples include crumbs, powder, rods, and sheets. Among these, a sheet shape is preferable because it produces an acrylic rubber bale that does not entrap air during molding (it has a high specific gravity) and has excellent storage stability. The moisture content of the dried rubber is less than 1% by weight, preferably 0.8% by weight or less, and more preferably 0.6% by weight or less.

(Baling process)
The baling step in the method for producing an acrylic rubber bale of the present invention is a step for baling the obtained dry rubber having a moisture content of less than 1% by weight.

The dried rubber can be baled in the usual manner. For example, an acrylic rubber bale can be produced by placing the dried rubber in a baler and compressing it. The compression pressure is selected appropriately 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 limited, but is usually in the range of 1 to 60 seconds, preferably 5 to 30 seconds, and more preferably 10 to 20 seconds.

In the present invention, dry rubber sheets can also be made into bales by laminating them together. Baling by laminating dry rubber sheets is easy to produce, and produces bales with fewer air bubbles (high specific gravity), making the resulting acrylic rubber bales ideal for storage stability.

(Dehydration, drying and baling process using a screw-type extruder)
In the present invention, the dehydration step and the drying step are preferably carried out continuously using a screw-type extruder equipped with a dehydration barrel having a dehydration slit, a drying barrel for drying under reduced pressure, and a die at the tip, and it is also preferable to carry out a baling step thereafter. An embodiment of this is shown below.

In the method for producing an acrylic rubber bale of the present invention, it is preferable to provide a draining step in which free water is separated from the hydrous crumbs after washing with a draining machine before transferring from the washing step to the dehydration and drying steps, in order to improve the efficiency of dehydration and drying.

Any known draining machine can be used without limitation, such as wire mesh, screen, electric sifter, etc., but wire mesh and screen are preferably used.

There are no limitations on the mesh size of the drainer, but it is usually suitable to have an opening size of 0.01 to 5 mm, preferably 0.1 to 1 mm, and more preferably 0.2 to 0.6 mm, since this allows for efficient draining with minimal loss of water-containing crumb.

The moisture content of the hydrous crumbs after draining, i.e., the moisture content of the hydrous crumbs fed into the dehydration, drying and molding process, is not 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, drying and molding process, is not limited, but is usually 40°C or higher, preferably 40 to 95°C, more preferably 50 to 90°C, particularly preferably 55 to 85°C, and most preferably in the range of 60 to 80°C.

Dehydration and drying in the dehydration barrel The dehydration of the hydrous crumb is carried out in a dehydration barrel having a dehydration slit provided in the screw-type extruder. The opening of the dehydration slit may be appropriately selected depending on the conditions of use, but it is usually 0.1 to 1 mm, preferably 0.2 to 0.6 mm, which is suitable because it reduces the loss of hydrous crumb and enables efficient dehydration of the hydrous crumb.

The number of dehydration barrels in a screw-type extruder is not 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 viscous acrylic rubber.

Water can be removed from the wet crumb in the dewatering barrel in two ways: in liquid form (wastewater) through the dewatering slit, or in vapor form (exhaust steam). In this invention, however, drainage is distinguished as dewatering, and exhaust steam is distinguished as preliminary drying.

When dehydration is performed using a screw-type extruder equipped with multiple dehydration barrels, a combination of drainage and exhaust steam is preferable because it allows efficient drainage (dehydration) of the viscous acrylic rubber and a reduction in its moisture content. Whether each barrel of a screw-type extruder equipped with three or more dehydration barrels is to be a drainage type dehydration barrel or an exhaust steam type dehydration barrel can be selected appropriately according to the purpose of use. Normally, to reduce the amount of ash in the acrylic rubber produced, the number of drainage type dehydration barrels is increased; for example, when there are three dehydration barrels, two drainage type dehydration barrels are selected, and when there are four dehydration barrels, three drainage type dehydration barrels are selected appropriately.

The set temperature of the dehydration barrel is selected appropriately depending on the type of acrylic rubber, the ash content, the moisture content, the operating conditions, etc., 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 a drainage type dehydration barrel that performs dehydration in a drainage state is usually in the range of 60 to 120°C, preferably 70 to 110°C, and more preferably 80 to 100°C, and the set temperature of an exhaust steam type dehydration barrel that performs drying 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.

The moisture content after dehydration in a drainage dehydration barrel, which squeezes out moisture from the hydrous crumb, is not limited, but is usually 1 to 45% by weight, preferably 1 to 40% by weight, more preferably 5 to 35% by weight, and particularly preferably 10 to 35% by weight, which provides a high level of balance between productivity and ash removal efficiency.

When dehydrating sticky acrylic rubber using a centrifuge or similar machine, the acrylic rubber adheres to the dehydration slits and is barely dehydrated, resulting in a water content reduction of only about 45-55% by weight. On the other hand, in the present invention, a screw-type extruder that has a dehydration slit and is forcibly squeezed by a screw is used, making it possible to reduce the water content to the above range.

When a drainage type dehydration barrel and a steam exhaust type dehydration barrel are used, the moisture content after dehydration in the drainage type dehydration barrel is usually 5 to 45% by weight, preferably 10 to 40% by weight, and more preferably 15 to 35% by weight, and the moisture content after pre-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 keeping the moisture content after dehydration at or above the lower limit above, the dehydration time can be shortened and deterioration of the acrylic rubber can be suppressed, while by keeping it below the upper limit above, the ash content can be sufficiently reduced.

Drying in the drying barrel section The moist crumbs that have been dehydrated and dried in the dehydrating barrel section are further dried in the drying barrel section under reduced pressure.

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 efficiently drying the hydrous crumbs.

The set temperature of the drying barrel may be selected as appropriate, but a temperature in the range of 100 to 250°C, preferably 110 to 200°C, and more preferably 120 to 180°C is usually suitable to efficiently dry the acrylic rubber without causing scorching or deterioration, and to reduce the amount of gel of the acrylic rubber that is insoluble in methyl ethyl ketone.

The number of drying barrels in a screw-type extruder is not limited, but is usually multiple, 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 part (closer to the die) higher than the temperature of the introduction part (closer to the dehydration barrel) because this increases 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, the above-mentioned water content is melted and kneaded in a drying barrel in a state that is substantially free of water, and this is advantageous because the gel content of the methyl ethyl ketone insoluble matter that rapidly increased during emulsion polymerization disappears, dramatically improving the processability of the acrylic rubber veil when kneaded in a Banbury process, etc.

Shape of acrylic rubber (die part)
The acrylic rubber dehydrated and dried in the screw sections of the dehydrating barrel and the drying barrel is sent to a screw-free straightening die section provided at the tip of the screw extruder. A breaker plate or a wire mesh may or may not be provided between the screw section and the die section.

The acrylic rubber extruded from the die of a screw-type extruder can be in a variety of shapes, including granular powder, pellets, columns, rods, and sheets, depending on the shape of the die nozzle. However, using a roughly rectangular die shape to extrude into a sheet is preferable, as it results in less air being entrained during extrusion and produces a dried rubber with a high specific gravity and excellent storage stability.

The resin pressure in the die section is not 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 minimizing air entrapment and for excellent productivity.

Screw-type extruder and operating conditions The screw length (L) of the screw-type extruder used in the present invention 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 extruder 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 extruder is not limited, but is usually suitable when it is in the range of 10 to 100, preferably 20 to 80, more preferably 30 to 60, and particularly preferably 40 to 50, since this allows the moisture content to be reduced to less than 1% by weight without causing a decrease in the molecular weight of the dried rubber or discoloration.

In the present invention, the rotation speed (N) of the screw-type extruder may be appropriately selected depending on various conditions, but it is usually suitable to set the rotation speed to 10 to 1,000 rpm, preferably 50 to 750 rpm, more preferably 100 to 500 rpm, and most preferably 120 to 300 rpm, since this efficiently reduces the water content of the acrylic rubber and the amount of gel that is insoluble in methyl ethyl ketone.

The extrusion rate (Q) of the screw extruder is not 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 extrusion rate (Q) to the rotation speed (N) of the screw-type extruder in the present invention is not limited, but is usually in the range of 2 to 10, preferably 3 to 8, and more preferably 4 to 6, which provides a high level of balance between the quality, including the strength properties, of the resulting acrylic rubber sheet and the manufacturing productivity.

Dried Rubber As described above, the shape of the dried rubber extruded from the screw-type extruder is not limited, and can be, for example, in the form of crumbs, powder, pellets, rods, sheets, etc., with the sheet shape being particularly preferred.

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

The moisture content of the dry rubber extruded from the screw extruder is less than 1% by weight, preferably 0.8% by weight or less, and more preferably 0.6% by weight or less.

Baling process The baling process after the dehydration and drying process using a screw extruder is a process of baling the extruded dry rubber. Baling of the dry rubber may be performed according to a conventional method, for example, the dry rubber may be put into a baler and compressed to produce the rubber. The compression pressure of the baler may be 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 temperature is not limited, but is usually in the range of 10 to 80°C, preferably 20 to 60°C, and more preferably 30 to 60°C. The compression time may be appropriately selected depending on the intended use, but is usually in the range of 1 to 100 seconds, preferably 2 to 50 seconds, and more preferably 5 to 25 seconds.

In the present invention, it is preferable to extrude sheet-like dried rubber from a screw-type extruder in the dehydration and drying process, cut it as necessary, and stack it to form a bale. Forming a bale by stacking sheet-like dried rubber is easy to produce, and furthermore, it produces a bale with few air bubbles (high specific gravity), which is preferable because of its excellent storage stability.

The following shows how dry rubber sheets are extruded from a screw extruder and then stacked to form a bale.

There are no particular limitations on the thickness of the sheet-like dry rubber extruded from the screw-type 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 dry rubber extruded from the screw extruder is selected appropriately depending on the intended use, but is usually in the range of 300 to 1,200 mm, preferably 400 to 1,000 mm, and more preferably 500 to 800 mm.

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

The complex viscosity at 100°C ([η]100°C) of the sheet-like dry rubber extruded from the screw-type extruder is not limited, but is usually in the range of 1,500 to 6,000 Pa·s, preferably 2,000 to 5,000 Pa·s, more preferably 2,500 to 4,000 Pa·s, and most preferably 2,500 to 3,500 Pa·s, which is suitable for achieving a high balance between extrudability as a sheet and shape retention. In other words, by setting the complex viscosity ([η]100°C) to be equal to or higher than the lower limit above, the sheet-like dry rubber can be made to have excellent extrudability, and by setting it to be equal to or lower than the upper limit above, deformation or breakage of the sheet-like dry rubber can be suppressed.

In the present invention, the dry rubber sheet extruded from the screw extruder is cut to an appropriate size, and then multiple cut dry rubber sheets are stacked and integrated to form a bale. This method is suitable because it entraps only a small amount of air and the resulting acrylic rubber bale has excellent storage stability.

There are no particular limitations on the method for cutting the sheet-like dry rubber, but since the acrylic rubber in the acrylic rubber veil of the present invention is highly adhesive, it is preferable to cool the sheet-like dry rubber before cutting in order to cut it continuously without entraining air. There are no limitations on the cutting temperature for the sheet-like dry rubber, but a temperature of usually 60°C or less, preferably 55°C or less, and more preferably 50°C or less, is suitable as it provides a high balance between cuttability and productivity.

The complex viscosity of the dry rubber sheet at 60°C ([η]60°C) is not limited, but is usually 15,000 Pa·s or less, preferably 2,000 to 10,000 Pa·s, more preferably 2,500 to 7,000 Pa·s, and most preferably 2,700 to 5,500 Pa·s, which is suitable for cutting continuously without entraining air.

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 limited, but is usually 0.5 or more, preferably 0.5 to 0.98, more preferably 0.6 to 0.95, and most preferably 0.75 to 0.93, which is suitable for minimizing air entrapment and achieving a high balance between cutting and productivity.

There are no particular limitations on the cooling method for the dried rubber sheet, and it may be left to cool 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, a method can be adopted in which sheet-like dry rubber is extruded from a screw-type extruder onto a conveyor such as a belt conveyor, and then conveyed and cooled while being blown with cold air. The temperature of the cold air is not 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 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 cutting length of the dry rubber sheet, and it may be selected appropriately according to the size of the acrylic rubber bale to be produced, but it is usually in the range of 100 to 800 mm, preferably 200 to 500 mm, and more preferably 250 to 450 mm.

After cutting, the dry rubber sheets are stacked to form bales. There are no limitations on the lamination temperature of the dry rubber sheets, but a temperature of 30°C or higher, preferably 35°C or higher, and more preferably 40°C or higher, is usually suitable to allow air trapped during lamination to escape. The number of layers can be appropriately selected depending on the size or weight of the acrylic rubber bale.

The acrylic rubber veil of the present invention thus obtained is easier to handle and has better storage stability than crumb-like acrylic rubber. When producing a rubber mixture using the acrylic rubber veil, the acrylic rubber veil can be put into a mixer such as a Banbury mixer or roll, either as is or after cutting into the required amount.

<Rubber mixture>
The rubber mixture of the present invention is characterized by being obtained by mixing the above-mentioned acrylic rubber veil with a filler and a crosslinking agent.

The fillers to be added to the rubber mixture are not limited, but include, for example, reinforcing fillers and non-reinforcing fillers, with reinforcing fillers being preferred.

Examples of such 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 kinds, and although there are no particular limitations on the amount of filler, it 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 acrylic rubber veil.

The crosslinking agent to be contained in the rubber mixture may be appropriately selected according to the type of reactive group contained in the acrylic rubber constituting the acrylic rubber veil and the application, but is not limited as long as it can crosslink the acrylic rubber veil. For example, conventionally known crosslinking agents such as polyamine compounds such as diamine compounds and carbonates thereof; sulfur compounds; sulfur donors; triazine thiol compounds; polyepoxy compounds; organic ammonium carboxylate salts; organic peroxides; polycarboxylic acids; quaternary onium salts; imidazole compounds; isocyanuric acid compounds; organic peroxides; and triazine compounds can be used. Among these, polyamine compounds, ammonium carboxylate salts, metal dithiocarbamate salts, and triazine thiol compounds are preferred, and hexamethylenediamine carbamate, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, ammonium benzoate, and 2,4,6-trimercapto-1,3,5-triazine are particularly preferred.

When the acrylic rubber veil used is composed of a carboxyl group-containing acrylic rubber, it is preferable to use a polyamine compound and/or its carbonate as a crosslinking agent. Specific examples of such polyvalent amine compounds include aliphatic polyvalent amine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicinnamylidene-1,6-hexanediamine; and aromatic polyvalent amine 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.

When the acrylic rubber veil used is composed of an epoxy group-containing acrylic rubber, the crosslinking agent may be an aliphatic polyamine compound such as hexamethylenediamine, hexamethylenediamine carbamate, or the like, or a carbonate salt thereof; an aromatic polyamine compound such as 4,4'-methylenedianiline; an ammonium carboxylate salt such as ammonium benzoate, ammonium adipate, or the like; a metal dithiocarbamate salt such as zinc dimethyldithiocarbamate; a polycarboxylic acid such as tetradecanedioic acid; a quaternary onium salt such as cetyltrimethylammonium bromide; an imidazole compound such as 2-methylimidazole; an isocyanuric acid compound such as ammonium isocyanurate; and the like. Among these, ammonium carboxylate salts and metal dithiocarbamate salts are preferred, and ammonium benzoate is more preferred.

When the acrylic rubber veil used is composed of a halogen-containing acrylic rubber, it is preferable to use sulfur, a sulfur donor, or a triazine thiol compound as a crosslinking agent. Examples of sulfur donors include dipentamethylene thiuram hexasulfide and triethyl thiuram disulfide. Examples of triazine compounds include 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. Among these, 2,4,6-trimercapto-1,3,5-triazine is preferred.

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 acrylic rubber veil. By using a crosslinking agent in 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 mixture of the present invention may contain other rubber components in addition to the above-mentioned acrylic rubber veil, if necessary.

Other rubber components that may be used as needed 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. The shape of the other rubber components is not limited, and may be, for example, powder, crumb, sheet, or veil-like.

These other rubber components can be used alone or in combination of two or more. The amount of these other rubber components used is appropriately selected within a range that does not impair the effects of the present invention.

The rubber mixture of the present invention may be compounded with an anti-aging agent as necessary. Examples of anti-aging agents include, but are not limited to, 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'-methylenebis( 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 and other phenols. Phenolic antioxidants; phosphorous ester antioxidants such as tris(nonylphenyl)phosphite, diphenylisodecylphosphite, and tetraphenyldipropylene glycol diphosphite; sulfur ester antioxidants such as dilauryl thiodipropionate; phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamido)-diphenylamine, 4,4'-(α,α-dimethylbenzyl)diphenylamine, Examples of such antioxidants include amine-based antioxidants such as butyl aldehyde, 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, and the amount to be added 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 acrylic rubber veil.

The rubber mixture of the present invention contains the acrylic rubber veil of the present invention, a filler, a crosslinking agent, and, if necessary, other rubber components and anti-aging agents, and may further contain, 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. These other additives may be used alone or in combination of two or more, and the amount of each additive is appropriately selected within a range that does not impair the effects of the present invention.

<Method of manufacturing rubber mixture>
The method for producing the rubber mixture of the present invention includes a method in which the acrylic rubber veil of the present invention is mixed with a filler, a crosslinking agent, and other compounding ingredients that may be contained as necessary, and any means conventionally used in the field of rubber processing can be used for mixing, such as an open roll, a Banbury mixer, various kneaders, etc. That is, the acrylic rubber veil can be directly mixed with the filler, the crosslinking agent, etc., using these mixers, and preferably mixed by direct kneading.

In this case, the acrylic rubber veil of the present invention may be used as is, or may be divided (cut, etc.) before use.

The mixing procedure for each component is not limited, but for example, a two-stage mixing is preferred in which components that do not easily react or decompose when heated are thoroughly mixed, and then components that easily react or decompose when heated, such as crosslinking agents, are mixed for a short time at a temperature at which they will not react or decompose. Specifically, it is preferred to mix the acrylic rubber veil and filler in the first stage, and then mix the crosslinking agent in the second stage. Other rubber components and antioxidants are usually mixed in the first stage, the crosslinking accelerator in the second stage, and other compounding ingredients can be selected as appropriate.

The Mooney viscosity (ML1+4,100°C; compound Mooney) of the rubber mixture of the present invention thus obtained is not limited, but is usually in the range of 10 to 150, preferably 20 to 100, and more preferably 25 to 80.

<Rubber cross-linked product>
The cross-linked rubber product of the present invention is obtained by cross-linking the above-mentioned rubber mixture. The cross-linked rubber product of the present invention can be produced by using the rubber mixture of the present invention, molding it into a desired shape using a molding machine such as an extruder, an injection molding machine, a compressor, or a roll, heating it to cause a cross-linking reaction, and fixing the shape as a cross-linked rubber product. In this case, cross-linking may be performed after molding in advance, or 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. As the heating method, a method used for cross-linking rubber, such as press heating, steam heating, oven heating, and hot air heating, may be appropriately selected.

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 time for secondary cross-linking 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 water resistance while maintaining basic rubber properties such as tensile strength, elongation, and hardness.

Taking advantage of the excellent properties described above, the cross-linked rubber of the present invention is suitably used for sealing materials such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing sheaths, 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 covering materials; industrial belts; tubes and hoses; sheets; etc.

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

<Apparatus configuration used in the production of acrylic rubber veils>
Next, the configuration of the equipment used in the production of the acrylic rubber veil 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 the acrylic rubber veil 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 the 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 draining machine 43, a screw-type extruder 5, a cooling device 6, and a baling device 7.

The emulsion polymerization reactor is configured to carry out the treatment related to the emulsion polymerization step described above. Although not shown in FIG. 1, the 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, emulsified while being appropriately stirred with a stirrer, and emulsion polymerized in the presence of a polymerization catalyst to obtain an emulsion polymerization liquid. The emulsion polymerization reactor may be of any of a batch type, semi-batch type, or continuous type, and may be either a tank type reactor or 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 for heating the inside of the stirring tank 30, a temperature control unit (not shown) for controlling 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) for controlling 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 is brought into contact with the coagulation liquid as a coagulant 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 coagulation liquid to the aqueous magnesium salt solution 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 1,000 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 solidifying 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 water-containing crumbs generated in the solidification device 3 are mixed with a large amount of water and washed, thereby effectively reducing the amount of ash in the acrylic rubber veil finally obtained.

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 extruder 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 extruder 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 hydrous crumbs are supplied to the screw-type extruder 5, the temperature of the hydrous 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 hydrous crumbs when supplied to the screw-type extruder 5 can be maintained at 60°C or higher, or the hydrous 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 extruder 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 extruder 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 extruder 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 extruder 5 is configured to mold the dried rubber obtained through the dehydration and drying processes into a predetermined shape and discharge it. Specifically, the screw-type extruder 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 extruder 5 that has a molding function for molding the wet crumbs.

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

The screw-type extruder 5 shown in FIG. 2 is a twin-screw extrusion dryer having a pair of screws (not shown) in a barrel unit 51. The screw-type extruder 5 has a drive unit 50 that drives and rotates the pair of screws in the barrel unit 51. The drive unit 50 is attached to the upstream end (left end in FIG. 2) of the barrel unit 51. The screw-type extruder 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 extruder 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 extruder 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 disposed 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 is molded into various shapes, such as granular, columnar, round rod, and sheet, depending on the nozzle shape of the die 59. For example, the acrylic rubber can be extruded into a sheet by making the outlet of the die 59 approximately rectangular. A breaker plate or wire mesh may or may not be provided between the screw and the die 59.

The screw-type extruder 5 according to this embodiment extrudes the water-containing crumbs of the raw acrylic rubber into a sheet-like dried rubber in the following manner.

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 as a sheet of dried rubber.

Here is an example of the operating conditions for the screw-type extruder 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 1,000 rpm. From the viewpoint of efficiently reducing the water content and gel content of the acrylic rubber veil, 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 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 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 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 granular, columnar, round bar, and sheet, depending on the nozzle shape of the die 59. Below, referring to FIG. 3, a conveying cooling device 60 that cools the sheet-shaped dried rubber 10 formed into a sheet will be described 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. There are no particular limitations on the weight or shape of the acrylic rubber bales produced by the baling device 7, but for example, an approximately rectangular parallelepiped acrylic rubber bale 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 an acrylic rubber bale.

In addition, when the sheet-like dried rubber 10 is produced by the screw-type extruder 5, an acrylic rubber bale in which the sheet-like dried rubber 10 is laminated may be produced. 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, for example, 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, an acrylic rubber bale in which the cut sheet-like dried rubber 16 is laminated can be produced.

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

The present invention will be described in more detail below with reference to examples and comparative examples. In each example, "parts," "%," and "ratio" 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 H-NMR, and the remaining activity of reactive groups in the acrylic rubber and the content of each reactive group were confirmed by the following test 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 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 veil was measured by the following method.
(1) The amount of carboxyl groups was calculated by dissolving the acrylic rubber veil in acetone and performing potentiometric titration with a potassium hydroxide solution.
(2) The amount of epoxy groups was calculated by dissolving the acrylic rubber base 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 an acrylic rubber veil 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 veil was measured in accordance with JIS K6228 Method A.

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

[Gel amount]
The gel content (%) of the acrylic rubber veil is the amount of the insoluble matter in methyl ethyl ketone, and was determined by the following method.
Approximately 0.2 g of acrylic rubber bale was weighed out (X g), immersed in 100 ml of methyl ethyl ketone and allowed to stand at room temperature for 24 hours, after which the components insoluble in methyl ethyl ketone were 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, and the dried solid content (Y g) was weighed and calculated according to the following formula.
Gel amount (%)=100×(X−Y)/X

[specific gravity]
The specific gravity of the acrylic rubber veil was measured in accordance with JIS K6268 crosslinked rubber - density measurement, method A.

[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).

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

[Moisture content]
The water content (%) of the acrylic rubber veil was measured in accordance with JIS K6238-1: Oven A (volatile matter measurement) method.

[Molecular weight and molecular weight distribution]
The weight average molecular weight (Mw) and molecular weight distribution (Mz/Mw) of the acrylic rubber are absolute molecular weight and absolute molecular weight distribution measured by the GPC-MALS method using a solution in which lithium chloride was added to dimethylformamide at a concentration of 0.05 mol/L and 37% concentrated hydrochloric acid was added at a concentration of 0.01% as a solvent. Specifically, a multi-angle laser light scattering photometer (MALS) and a differential refractometer (RI) were 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 were measured over the elution time, thereby sequentially calculating and determining 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, and the mixture was gently stirred at room temperature (dissolution was visually confirmed), followed by filtration using a 0.5 μm filter.

[Complex viscosity]
The complex viscosity η of the acrylic rubber veil 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 values of η(100°C)/η(60°C) and η(60°C)/η(100°C) were calculated.

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

[Processability evaluation]
The processability of the rubber samples was evaluated by measuring the time until the rubber sample was integrated in the first stage and showed the maximum torque value after adding compounding ingredient A of the rubber mixture compounding shown in Table 1 and then measuring the BIT (Black Incorporation Time), and the result was evaluated as an index with Comparative Example 1 set to 100 (the smaller the index, the better the processability).

[Water resistance evaluation]
The water resistance of the rubber sample was evaluated by an immersion test in accordance with JIS K6258, in which the crosslinked rubber sample was immersed in distilled water at a temperature of 85° C. for 100 hours, and the volume change rate before and after immersion was calculated according to the following formula, with Comparative Example 1 being set as an index of 100 (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

[Example 1]
A mixing vessel equipped with a homomixer was charged with 46 parts of pure water, 48.5 parts of ethyl acrylate, 29 parts of n-butyl acrylate, 21 parts of methoxyethyl acrylate, 1.5 parts of vinyl chloroacetate, and, as emulsifiers, 0.709 parts of sodium lauryl sulfate and 1.82 parts of polyoxyethylene dodecyl ether (molecular weight 1500), and the mixture was stirred to obtain a monomer emulsion.

Next, 170 parts of pure water and 3 parts of the monomer emulsion obtained by emulsion polymerization were added to a polymerization reaction tank equipped with a thermometer and a stirrer, and cooled to 12°C under a nitrogen stream. 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.

In a coagulation bath equipped with a thermometer and agitator, the emulsion polymerization liquid obtained above was heated to 80°C and continuously added to a 2% aqueous sodium sulfate solution (coagulation liquid) that was heated to 80°C and vigorously stirred (600 rpm: peripheral speed 3.1 m/s) to coagulate the polymer, which was then filtered to obtain hydrous crumbs.

Next, 194 parts of hot water (70°C) was added to the coagulation bath and stirred for 15 minutes, after which the water was drained off, and 194 parts of hot water (70°C) was added again and stirred for 15 minutes to wash the wet crumbs. The washed wet crumbs (wet crumb temperature 65°C) were fed to a screw-type extruder, dehydrated and dried, and extruded into a sheet-like dry rubber with a width of 300 mm and a thickness of 10 mm. Furthermore, 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 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 and second dehydration barrels discharge water, and the third dehydration barrel discharges steam. The operating conditions of the screw-type extruder were as follows:

Water Content:
Moisture content of wet crumbs after draining in the second dewatering barrel: 20%
Moisture content of the wet crumb after steaming in the third dewatering barrel is 10%
Moisture content of the wet crumbs after drying in the fifth drying barrel: 0.4%
Rubber Temperature:
Temperature of the wet crumbs fed into the first feed barrel: 65° C.
Temperature of rubber discharged from the screw extruder: 140°C
Dehydration barrel temperature setting:
First dehydration barrel: 90°C
Second dehydration barrel: 100° 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:
Diameter of the screw in the barrel unit (D): 132 mm
Total length of the screw in the barrel unit (L): 4620 mm
・L/D: 35
・Rotation speed of the screw in the barrel unit: 135 rpm
・Rubber extrusion rate from die: 700 kg/hr
・Die resin pressure: 2 MPa

The extruded sheet-like dried rubber was cooled to 50°C and then cut with a cutter, and stacked to obtain 20 parts (20 kg) before the temperature dropped below 40°C to obtain acrylic rubber veil (A). The reactive group content, ash content, ash component content, specific gravity, gel content, glass transition temperature (Tg), pH, water content, molecular weight, molecular weight distribution, complex viscosity, and Mooney viscosity (ML1+4, 100°C) of the obtained acrylic rubber veil (A) were measured and shown in Table 2. The value of "water content after dehydration (drainage) (%)" shown in the dehydration process column in Table 2 is the water content of the water-containing crumb immediately after drainage in the drainage type dehydration barrel (immediately before the exhaust steam type dehydration barrel).

Next, 100 parts of the acrylic rubber veil (A) and compounding agent A of "Compound 1" shown in Table 1 were added using a Banbury mixer and mixed at 50°C for 5 minutes. At this time, the processability of the acrylic rubber veil was evaluated, and the results are shown in Table 2. Furthermore, the resulting mixture was transferred to a roll at 50°C, and compounding agent B of "Compound 1" was added and mixed to obtain a rubber mixture.

The obtained rubber mixture 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 further 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 a water resistance test, with the results shown in Table 2.

[Example 2]
The monomer components were changed to 98.5 parts of ethyl acrylate and 1.5 parts of vinyl chloroacetate, the temperature of the first dehydration barrel of the screw extruder was changed to 100°C, the temperature of the second dehydration barrel to 120°C, and drainage was carried out only in the first dehydration barrel, and the water content of the water-containing crumb after drainage in the first dehydration barrel was changed to 30%. The same procedure as in Example 1 was carried out, and an acrylic rubber veil (B) was obtained and its properties were evaluated. 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 43 parts of ethyl acrylate, 25 parts of n-butyl acrylate, 26 parts of methoxyethyl acrylate, 2 parts of acrylonitrile, and 4 parts of allyl glycidyl ether, and an acrylic rubber veil (C) was obtained and its properties were evaluated (the compounding agent was replaced with "Compound 2"). 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 4.5 parts of ethyl acrylate, 64.5 parts of n-butyl acrylate, 39.5 parts of methoxyethyl acrylate, and 1.5 parts of mono n-butyl fumarate, and an acrylic rubber veil (D) was obtained and its properties were evaluated (the compounding agent was changed to "Compound 3"). The results are shown in Table 2.

[Example 5]
The same procedure as in Example 2 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, to obtain an acrylic rubber veil (E), and the properties thereof were evaluated. The results are shown in Table 2.

[Comparative Example 1]
A 0.7% aqueous sodium sulfate solution was added directly to the emulsion polymerization liquid (rotation speed 100 rpm, peripheral speed 0.5 m/s) subjected to emulsion polymerization in the same manner as in Example 5 to generate hydrous crumbs, 194 parts of industrial water were added to 100 parts of the generated hydrous crumbs, and the mixture was stirred in a coagulation tank at 25°C for 5 minutes, after which the hydrous crumbs were washed 4 times by draining the water from the coagulation tank, 194 parts of an aqueous sulfuric acid solution of pH 3 was added and stirred at 25°C for 5 minutes, after which the water was drained from the coagulation tank and acid washed once, 194 parts of pure water was added and pure water washed once, and then the mixture was dried in a hot air dryer at 160°C to obtain an acrylic rubber (F) with a water content of 0.4% by weight. The properties of the obtained crumb-like acrylic rubber (F) were evaluated and shown in Table 2.

[Reference Example 1]
The washing step was carried out in the same manner as in Example 5, and the washed water-containing crumbs were dried in a hot air dryer at 160° C. to obtain an acrylic rubber (G) with a water content of 0.4% by weight. The properties of the obtained crumb-like acrylic rubber (G) were evaluated and are shown in Table 2.

From Table 2, it can be seen that acrylic rubber veils (A) to (E) containing the (meth)acrylic acid ester of the present invention as the main component, having an ash content of 0.3% by weight or less, a total content of at least one element selected from sodium, sulfur, calcium, magnesium and phosphorus in the ash of 50% by weight or more, and a gel content of methyl ethyl ketone insoluble matter of 50% by weight or less, have significantly superior processability and water resistance (comparison of Examples 1 to 5 with Comparative Example 1).

Also, Table 2 shows that when a coagulation liquid is added to the emulsion polymerization liquid in the coagulation reaction to generate hydrous crumbs, the ash content does not decrease and the water resistance of the acrylic rubber veil is insufficient, even if the washing process involves four water washes, one acid wash, and one pure water wash (Comparative Example 1). On the other hand, when a coagulation reaction involves adding the emulsion polymerization liquid to a vigorously stirred high-concentration coagulation liquid to generate hydrous crumbs, the ash content decreases and water resistance improves with just two washes with warm water (Reference Example 1).

In addition, looking at the relationship between the amount of sodium (Na) and the amount of sulfur (S) in the ash in Table 2, it can be seen that the total amount of sodium (Na) and sulfur (S) (Na+S) remains the same when the coagulation method and washing method are performed according to Reference Example 1, but the amount of sodium (Na) is reduced and the Na/S ratio is smaller compared to Comparative Example 1. This is presumably because the coagulant used (sodium sulfate: _Na2SO4 : high _Na ratio) is almost completely removed by performing the coagulation and washing method of Reference Example 1, but the sodium (Na) and sulfur ( _S ) derived from the emulsifier (sodium _lauryl sulfate: _NaC12H25SO4 ) are present in the hydrous crumbs and cannot be fully removed by washing.

Also, from Table 2, it can be seen that the method of Reference Example 1 improves water resistance, but does not improve processability much.

In contrast, by carrying out the coagulation reaction in the same manner as in Reference Example 1, washing twice with warm water, and then dehydrating and drying using a screw-type extruder until the moisture content is less than 1% by weight, the ash content and the amount of gel insoluble in methyl ethyl ketone in the acrylic rubber veils of Examples 1 to 5 are significantly reduced, and the water resistance and processability of the acrylic rubber veils are significantly improved (comparison of Examples 1 to 5 with Comparative Example 1 and Reference Example 1).

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

Claims (39)

An acrylic rubber veil having a rectangular parallelepiped shape, which is composed of an acrylic rubber obtained by emulsion polymerization, the main constituent unit of which is a group derived from a (meth)acrylic acid ester, and which contains constituent units having at least one reactive group selected from the group consisting of a carboxyl group, an epoxy group, and a halogen group, the acrylic rubber having an ash content of 0.0001 to 0.25 % by weight as measured by JIS K6288 Method A, the ash containing at least one element selected from the group consisting of sodium, sulfur, calcium, magnesium, and phosphorus being 50% by weight or more in total relative to the total ash content, and the acrylic rubber having a gel content of methyl ethyl ketone insolubles being 10 % by weight or less. The acrylic rubber veil according to claim 1, having an ash content of 0.2% by weight or less. The acrylic rubber veil according to claim 1 or 2, which contains sodium and sulfur in the ash. The acrylic rubber veil according to any one of claims 1 to 3, wherein the reactive group content of the acrylic rubber is 0.001 to 5% by weight. The acrylic rubber veil according to any one of claims 1 to 4, wherein the weight average molecular weight (Mw) of the acrylic rubber is in the range of 1,000,000 to 5,000,000. 6. The acrylic rubber veil according to any one of claims 1 to 5, wherein the amount of gel insoluble in methyl ethyl ketone is 5 % by weight or less. 7. The acrylic rubber veil according to any one of claims 1 to 6, wherein the amount of gel insoluble in methyl ethyl ketone is 3.4 % by weight or less. An acrylic rubber veil according to any one of claims 1 to 7, in which the total amount of sodium and sulfur in the ash is 80% by weight or more based on the total ash content. An acrylic rubber veil according to any one of claims 1 to 8, in which the ratio of sodium to sulfur in the ash ([Na]/[S]) is in the range of 0.75 to 0.95 by weight. The acrylic rubber veil according to any one of claims 1 to 9, having a pH of 2 to 6. The acrylic rubber veil according to any one of claims 1 to 10, wherein the complex viscosity at 100°C ([η]100°C) is 1,500 to 6,000 Pa·s, and 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) is 0.5 to 0.99. (Here, the complex viscosity is measured by measuring the temperature dispersion (40 to 120°C) at 473% strain and 1 Hz using a dynamic viscoelasticity measuring device "Rubber Process Analyzer RPA-2000" (manufactured by Alpha Technology Co., Ltd.), and determining the complex viscosity η at each temperature. Among the dynamic viscoelasticity described above, the dynamic viscoelasticity at 60°C is defined as the complex viscosity [η]60°C, and the dynamic viscoelasticity at 100°C is defined as the complex viscosity [η]100°C.) The acrylic rubber veil according to claim 11, in which 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) is 0.83 or more. The acrylic rubber veil according to any one of claims 1 to 12, which has a specific gravity measured in accordance with JIS K6268 Crosslinked Rubber - Density Measurement Method A, in the range of 0.7 to 1.5. The acrylic rubber veil according to any one of claims 1 to 13, having a water content of less than 1% by weight. an emulsion polymerization step of emulsifying a monomer component mainly composed of a (meth)acrylic acid ester and a monomer component having at least one reactive group selected from the group consisting of a carboxyl group, an epoxy group, and a halogen group, with water and an emulsifier, and emulsion-polymerizing the resulting emulsion in the presence of a polymerization catalyst to obtain an emulsion polymerization liquid;
a coagulation step in which the obtained emulsion polymerization liquid is added to a stirred aqueous solution containing a coagulant to produce water-containing crumbs;
A washing step of washing the generated hydrous crumbs with warm water of 40°C or higher;
A drying step in which the washed wet crumb is dehydrated and dried using a screw-type extruder, and extruded as a dry rubber dried to a moisture content of less than 1% by weight;
and a baling step of forming the extruded dry rubber into a rectangular bale. The method for producing an acrylic rubber veil according to claim 15 , which produces the acrylic rubber veil according to any one of claims 1 to 14 . 17. The method for producing an acrylic rubber veil according to claim 15 or 16, wherein the emulsifier contains at least one element selected from the group consisting of sodium, sulfur and phosphorus, and/or the coagulant contains at least one element selected from the group consisting of sodium, sulfur, calcium and magnesium. The method for producing an acrylic rubber veil according to any one of claims 15 to 17 , wherein the polymerization conversion rate of the emulsion polymerization is 90% by weight or more. The method for producing an acrylic rubber veil according to any one of claims 15 to 18 , wherein the temperature of the water-containing crumb fed into the screw-type extruder is 40 to 100°C. The method for producing an acrylic rubber veil according to any one of claims 15 to 19, further comprising a dehydration step of squeezing out water from the water-containing crumb. The method for producing an acrylic rubber veil according to claim 20 , wherein the hydrous crumb is dehydrated to a moisture content of 1 to 40% by weight. The method for producing an acrylic rubber veil according to claim 21 , wherein the water content after dehydration is in the range of 5 to 35% by weight. The method for producing an acrylic rubber veil according to any one of claims 15 to 22 , wherein the degree of vacuum in the drying barrel of the screw-type extruder is in the range of 1 to 50 kPa, and the drying temperature is in the range of 100 to 250°C. The method for producing an acrylic rubber veil according to any one of claims 15 to 23 , wherein the moisture content of the moisture-containing crumb at the die portion of the screw-type extruder is less than 1% by weight. The method for producing an acrylic rubber veil according to any one of claims 15 to 24 , wherein the resin pressure at the die portion of the screw-type extruder is in the range of 0.1 to 10 MPa. The method for producing an acrylic rubber veil according to any one of claims 15 to 25 , wherein the ratio (Q/N) of the extrusion rate (Q) to the rotation speed (N) of the screw-type extruder is in the range of 2 to 10. The method for producing an acrylic rubber veil according to any one of claims 15 to 26 , wherein the dried rubber is in the form of a sheet. A rubber mixture obtained by mixing the acrylic rubber veil according to any one of claims 1 to 14 with a filler and a crosslinking agent. 29. A rubber mixture according to claim 28 , wherein the filler is a reinforcing filler. 29. The rubber mixture of claim 28 , wherein the filler is carbon black. 29. A rubber mix according to claim 28 , wherein the filler is silica. 32. A rubber mixture according to claim 28, wherein the crosslinking agent is a polyamine compound, an ammonium carboxylate, a metal dithiocarbamate or a triazine thiol compound. The rubber mixture according to any one of claims 28 to 32 , further comprising an antioxidant. 34. The rubber mixture of claim 33 , wherein the antioxidant is an amine-based antioxidant. A method for producing a rubber mixture, comprising mixing the acrylic rubber veil according to any one of claims 1 to 14 with a filler, a crosslinking agent and, if necessary, an antioxidant in a mixer. A method for producing a rubber mixture, comprising mixing the acrylic rubber veil according to any one of claims 1 to 14 , a filler, and, if necessary, an antioxidant, and then mixing a crosslinking agent. A cross-linked rubber product obtained by cross-linking the rubber mixture according to any one of claims 28 to 34 . The cross-linked rubber product according to claim 37 , wherein the cross-linking is a primary cross-linking and a secondary cross-linking. A method for producing a cross-linked rubber product, which comprises subjecting the rubber mixture according to any one of claims 28 to 34 to a primary cross-link and then a secondary cross-linking.

Images