JP7552078B2 - Acrylic rubber sheet with excellent workability - Google Patents

Description

The present invention relates to an acrylic rubber sheet, a method for manufacturing an acrylic rubber sheet, an acrylic rubber veil, a rubber mixture, and a cross-linked rubber product, and more specifically to an acrylic rubber sheet having excellent workability, processability, and strength properties and a method for manufacturing the same, an acrylic rubber veil formed by laminating the acrylic rubber sheet, a rubber mixture formed by mixing the acrylic rubber sheet or the acrylic rubber veil and a method for manufacturing the same, and a cross-linked rubber product formed by cross-linking the same.

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

This type of acrylic rubber is usually produced by emulsion polymerizing the monomer mixture that makes up the acrylic rubber, coagulating the resulting emulsion polymerization liquid by adding a coagulant, and then drying the water-containing crumbs obtained by the coagulation to produce the product in the form of crumbs, sheets, or veils.

For example, Patent Document 1 (JP Patent Publication 1-225512 A) discloses a method for producing sheet-shaped acrylic rubber using a twin-screw extruder dryer consisting of a feed barrel, a dehydration barrel, a standard barrel, a vent barrel, and a vacuum barrel, in which nitrile rubber (NBR) crumbs with a moisture content of about 50% are fed to the feed barrel, and after most of the moisture is removed in the dehydration barrel, the remaining moisture and evaporated vapors are sucked and removed in the vacuum barrel, and the rubber is continuously extruded in a strip shape through a breaker plate and a die section. It also discloses that rubber crumbs such as acrylic rubber are used as the rubber crumbs to be applied. However, Patent Document 1 does not disclose an acrylic rubber sheet with excellent processability.

On the other hand, for veil-like acrylic rubber, for example, Patent Document 2 (International Publication No. 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 water and sodium lauryl sulfate as emulsifiers and polyethylene glycol monostearate, 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 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 generate a crumb slurry. The crumb slurry is then washed once with water and passed through a 100-mesh wire net to capture only the solid content, and the crumb-like acrylic rubber is recovered. According to this method, the obtained hydrous crumb is dehydrated by centrifugation or the like, dried at 50 to 120°C by a band dryer or the like, introduced into a baler, compressed, and commercialized. However, this method generates a large amount of semi-solidified, water-containing crumbs during the coagulation reaction, which causes problems such as a large amount of them adhering to the coagulation tank, and even when the sticky crumbs are dried and baled, they are difficult to process.

Regarding the gel content of acrylic rubber, for example, Patent Document 3 (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, emulsifiers sodium lauryl sulfate and polyoxyethylene nonylphenyl ether, sodium carbonate, and boric acid are added and adjusted to 75°C, then t-butyl hydroperoxide, Rongalite, disodium ethylenediaminetetraacetate, and ferrous sulfate are added (pH 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 (pH 7) is salted out using an aqueous sodium sulfate solution, washed with water, and dried to obtain acrylic rubber. However, acrylic rubbers that are mainly composed of (meth)acrylic acid esters have problems with handling (workability), such as decomposing in the neutral to alkaline range and having poor storage stability, and acrylic rubbers that are emulsion polymerized at a pH from neutral to alkaline have problems with poor mechanical strength due to the loss of reactive groups (crosslinking points) such as carboxyl groups, epoxy groups, and chlorine atoms.

In addition, Patent Document 4 (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 THF (tetrahydrofuran) insoluble portion of the acrylic rubber used in the technology is 80% by weight or less, preferably 5 to 80% by weight, and preferably exists as much as possible within the range of 70% or less, and that the extrusion property deteriorates when the gel content is less than 5%. It is also stated 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, there is an emerging demand for a rubber that has a high level of balance between workability, processability, and strength properties.

Japanese Patent Application Publication No. 1-225512 International Publication No. 2018/116828 Patent No. 3599962 International Publication No. 2018/143101

The present invention has been made in consideration of these circumstances, and aims to provide an acrylic rubber sheet that is excellent in workability, processability and strength characteristics, a manufacturing method thereof, an acrylic rubber veil formed by laminating the acrylic rubber sheet, a rubber mixture containing the acrylic rubber sheet or the acrylic rubber veil, and a rubber cross-linked product thereof.

As a result of intensive research conducted in consideration of the above problems, the inventors have found that an acrylic rubber sheet made of an acrylic rubber having a specific molecular weight and reactive groups, and having a specific amount of gel insoluble in methyl ethyl ketone, has excellent workability, processability and strength properties. The inventors have also found that the workability, processability and strength properties are further improved when the weight average molecular weight and pH are specific.

The inventors have also discovered that an acrylic rubber sheet with excellent workability, processability and strength properties can be produced by emulsion-polymerizing and coagulating a monomer component containing a (meth)acrylic acid ester and a reactive group-containing monomer, and then extruding the resulting water-containing crumbs, which are then dried to a specific moisture content using a specific screw-type extruder, into a sheet-like dry rubber.

The inventors have also discovered that, when the polymerization conversion rate of emulsion polymerization is increased in order to improve the strength properties of acrylic rubber having reactive groups, the amount of gel insoluble in methyl ethyl ketone increases rapidly, resulting in poor processability. However, by drying the washed water-containing crumbs in a screw-type extruder until they are essentially free of water (a specific water content) and then melt-kneading them, the rapidly increased amount of gel insoluble in methyl ethyl ketone disappears, and an acrylic rubber sheet with excellent workability, processability, and strength properties can be produced without reducing the reactive groups.

The inventors further discovered that the amount and behavior of the gel in the acrylic rubber sheet differs completely depending on the type of solvent used; for example, there is no correlation between the amount of gel in the tetrahydrofuran-insoluble portion of the acrylic rubber sheet and the amount of gel in the methyl ethyl ketone-insoluble portion, and that the properties that the gel imparts to the acrylic rubber sheet are also different.

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

Thus, according to the present invention, an acrylic rubber sheet is provided that is made of an acrylic rubber having a reactive group and a weight average molecular weight (Mw) of 100,000 to 5,000,000, and has a gel content of 5% by weight or less of methyl ethyl ketone insoluble matter.

In the acrylic rubber sheet of the present invention, it is preferable that the acrylic rubber content in the acrylic rubber sheet is 95% by weight or more.

In the acrylic rubber sheet of the present invention, it is preferable that the ash content is 1% by weight or less.

In the acrylic rubber sheet of the present invention, it is preferable that the content (total amount) of at least one element selected from the group consisting of sodium, sulfur, calcium, magnesium, and phosphorus in the ash is 50% by weight or more.

In the acrylic rubber sheet of the present invention, it is preferable that the acrylic rubber sheet is a melt-kneaded sheet.

In the acrylic rubber sheet of the present invention, it is preferable that the weight average molecular weight (Mw) is in the range of 1,000,000 to 5,000,000.

In the acrylic rubber sheet of the present invention, it is preferable that the ratio (Mz/Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of the acrylic rubber is 1.3 or more.

In the acrylic rubber sheet of the present invention, it is 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 0.8 or more.

In the acrylic rubber sheet of the present invention, it is preferable that the pH is 6 or less.

In the acrylic rubber sheet of the present invention, it is preferable that the Mooney viscosity (ML1+4, 100°C) of the acrylic rubber sheet is in the range of 10 to 150.

According to the present invention, there is provided a method for producing an acrylic rubber sheet, which includes an emulsion polymerization step in which a monomer component containing a (meth)acrylic acid ester and a reactive group-containing monomer is emulsified with water and an emulsifier, and emulsion-polymerized in the presence of a polymerization catalyst to obtain an emulsion polymerization liquid; a coagulation step in which the obtained emulsion polymerization liquid is brought into contact with a coagulation liquid to produce hydrous crumbs; a washing step in which the produced hydrous crumbs are washed; and a dehydration, drying, and molding step in which the washed hydrous crumbs are dehydrated to a moisture content of 1 to 40% by weight in the dehydration barrel using a screw-type extruder having a dehydration barrel with a dehydration slit, a drying barrel under reduced pressure, and a die at the tip, and then dried in the drying barrel to a moisture content of less than 1% by weight, and a sheet-like dried rubber is extruded from the die.

According to the present invention, an acrylic rubber veil is provided, which is formed by laminating the acrylic rubber sheets.

The present invention further provides a rubber mixture obtained by mixing the acrylic rubber sheet or the acrylic rubber veil with a reinforcing agent and a crosslinking agent.

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

The present invention provides an acrylic rubber sheet that is excellent in workability, processability and strength properties, a method for producing the same, an acrylic rubber veil formed by laminating the acrylic rubber sheet, a rubber mixture formed by mixing the acrylic rubber sheet or the acrylic rubber veil, and a cross-linked rubber product formed by cross-linking the same.

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

The acrylic rubber sheet of the present invention is characterized by being made of an acrylic rubber having reactive groups and a weight average molecular weight (Mw) of 100,000 to 5,000,000, and having a gel content of 5% by weight or less.

<Monomer component>
The acrylic rubber sheet of the present invention comprises an acrylic rubber having a reactive group.

The reactive group is not particularly limited and is appropriately selected depending on the purpose of use, but is preferably at least one functional group selected from the group consisting of carboxyl group, epoxy group, and halogen group, more preferably at least one functional group selected from the group consisting of carboxyl group, epoxy group, and chlorine atom, particularly preferably epoxy group, carboxyl group, and most preferably carboxyl group, which is suitable for highly improving the crosslinked properties of the acrylic rubber sheet. In addition, the reactive group is preferably an ion-reactive group such as a carboxyl group or epoxy group, which is particularly suitable for improving water resistance. The acrylic rubber having such a reactive group may be one in which the reactive group is introduced into the acrylic rubber by a post-reaction, but is preferably one in which a reactive group-containing monomer is copolymerized.

The acrylic rubber constituting the acrylic rubber sheet of the present invention preferably contains a (meth)acrylic acid ester, and more preferably contains at least one (meth)acrylic acid ester selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters. In the present invention, the term "(meth)acrylic acid ester" is used as a general term for esters of acrylic acid and/or methacrylic acid.

Specific examples of preferred acrylic rubbers having reactive groups include those that are composed of at least one (meth)acrylic ester selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, a reactive group-containing monomer, and other copolymerizable monomers as necessary.

There are no particular limitations on the (meth)acrylic acid alkyl ester, but it 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 (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.

There are no particular limitations on the (meth)acrylic acid alkoxyalkyl ester, but it 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 with 2 to 6 carbon atoms.

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

At least one (meth)acrylic acid ester selected from the group consisting of these (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters is used alone or in combination of two or more, 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 particular 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, 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, a monomer having a carboxyl group or an epoxy group is particularly preferred, and a monomer having a carboxyl group is most preferred.

There are no particular limitations on the monomer having a carboxyl group, but ethylenically unsaturated carboxylic acids can be suitably used. Examples of ethylenically unsaturated carboxylic acids include ethylenically unsaturated monocarboxylic acids, ethylenically unsaturated dicarboxylic acids, and ethylenically unsaturated dicarboxylic acid monoesters. Among these, ethylenically unsaturated dicarboxylic acid monoesters are particularly preferred because they can further improve the compression set resistance properties when the acrylic rubber is made into a rubber cross-linked product.

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

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

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

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

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

These reactive group-containing monomers may be 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.

Other monomers that may be used as necessary are not particularly limited as 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 sheet of the present invention is characterized by having a reactive group.

The amount of reactive groups contained may be appropriately selected depending on the intended use, but a weight ratio of the reactive groups themselves of usually 0.001 to 5% by weight, preferably 0.01 to 3% by weight, more preferably 0.05 to 1% by weight, and particularly preferably 0.1 to 0.5% by weight is suitable for achieving a high level of balance in properties such as processability, strength, resistance to compression set, oil resistance, cold resistance, and water resistance.

Specific examples of the acrylic rubber constituting the acrylic rubber sheet of the present invention include at least one (meth)acrylic ester selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, a reactive group-containing monomer, and, as necessary, other copolymerizable monomers. The proportions of each in the acrylic rubber are as follows: the bonding units derived from at least one (meth)acrylic ester selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters are usually in the range of 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; the bonding units derived from the reactive group-containing monomer are usually in the range of 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 the bonding units derived from other monomers are usually in the range of 0 to 30% by weight, preferably 0 to 20% by weight, more preferably 0 to 15% by weight, and particularly preferably 0 to 10% by weight. By setting the bonding units derived from these monomers in the acrylic rubber within this range, the object of the present invention can be achieved to a high degree, and when the acrylic rubber sheet is crosslinked, the water resistance and compression set resistance properties are significantly improved, which is preferable.

The weight average molecular weight (Mw) of the acrylic rubber constituting the acrylic rubber sheet of the present invention is an absolute molecular weight measured by GPC-MALS, and is preferably in the range of 100,000 to 5,000,000, preferably 500,000 to 4,000,000, more preferably 700,000 to 3,000,000, and most preferably 1,000,000 to 2,500,000. This is suitable because it provides a high level of balance between workability, processability, strength properties, and compression set resistance during mixing of the acrylic rubber sheet.

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 sheet of the present invention is not particularly limited, but when the absolute molecular weight distribution focused on the polymer 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 workability, processability, and strength characteristics of the acrylic rubber sheet 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 sheet of the present invention is not particularly 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 lower limit, it is possible to achieve superior oil resistance and heat resistance, and by setting it below the upper limit, it is possible to achieve superior cold resistance and processability.

The content of acrylic rubber in the acrylic rubber sheet of the present invention is appropriately selected depending on the intended use, but is usually 90% by weight or more, preferably 95% by weight or more, more preferably 97% by weight or more, and particularly preferably 98% by weight or more.

<Acrylic rubber sheet>
The acrylic rubber sheet of the present invention is characterized in that it is made of the above-mentioned acrylic rubber and has a specific amount of gel insoluble in methyl ethyl ketone.

The thickness of the acrylic rubber sheet of the present invention is not particularly limited, but is usually in the range of 1 to 40 mm, preferably 2 to 35 mm, more preferably 3 to 30 mm, and most preferably 5 to 25 mm, which is suitable for achieving a high balance of workability, storage stability, and productivity. In particular, when the productivity is significantly improved to produce an inexpensive acrylic rubber sheet, the thickness 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 acrylic rubber sheet of the present invention is appropriately selected 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, which is particularly suitable for excellent workability.

The length of the acrylic rubber sheet of the present invention is not particularly limited, 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, which is particularly suitable for excellent workability.

When the gel content of the acrylic rubber sheet of the present invention is 5% by weight or less, preferably 4% by weight or less, in terms of the content insoluble in methyl ethyl ketone, the processability is highly improved and is suitable. The gel content, which is the content insoluble in methyl ethyl ketone in the acrylic rubber sheet, is related to the processability during kneading in a Banbury mixer, etc., but the characteristics of the gel content differ depending on the solvent used, and there is no correlation with the amount of gel insoluble in THF (tetrahydrofuran).

The specific gravity of the acrylic rubber sheet of the present invention is not particularly limited, but is usually 0.7 or more, 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 highly suitable for excellent storage stability.

There are no particular limitations on the pH of the acrylic rubber sheet of the present invention, but a pH of typically 6 or less, preferably 2 to 6, more preferably 2.5 to 5.5, and particularly preferably 3 to 5, is suitable since it provides highly improved storage stability.

The water content of the acrylic rubber sheet of the present invention is not particularly 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 crosslinking characteristics are optimized and the properties such as heat resistance and water resistance are highly excellent and suitable.

The ash content of the acrylic rubber sheet of the present invention is not particularly limited, but is usually 1% by weight or less, preferably 0.5% by weight or less, more preferably 0.3% by weight or less, particularly preferably 0.2% by weight or less, and most preferably 0.15% by weight or less, which is suitable for excellent storage stability and water resistance.

The lower limit of the ash content of the acrylic rubber sheet of the present invention is not particularly 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 preferable because it suppresses metal adhesion and provides excellent workability.

The ash content when the storage stability, water resistance, and workability of the acrylic rubber sheet of the present invention are highly balanced is usually in the range of 0.0001 to 1 weight percent, preferably 0.0005 to 0.5 weight percent, more preferably 0.001 to 0.3 weight percent, particularly preferably 0.005 to 0.2 weight percent, and most preferably 0.01 to 0.15 weight percent.

The content of at least one element selected from the group consisting of sodium, sulfur, calcium, magnesium and phosphorus in the ash of the acrylic rubber sheet of the present invention is not particularly limited, but when the content is at least 30% by weight, preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 80% by weight or more, relative to the total ash content, the storage stability and water resistance are highly excellent and suitable.

The total amount of sodium and sulfur in the ash of the acrylic rubber sheet of the present invention is not particularly limited, but when the total amount of sodium and sulfur 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 storage stability and water resistance are highly excellent and suitable.

The ratio of sodium to sulfur in the ash of the acrylic rubber sheet of the present invention ([Na]/[S]) is not particularly limited by weight, but is usually 0.4 to 2.5, preferably 0.6 to 2, preferably 0.8 to 1.7, and more preferably 1 to 1.5, and is therefore suitable for achieving high water resistance.

The total amount of magnesium and phosphorus in the ash of the acrylic rubber sheet of the present invention is not particularly limited, but when the total amount of ash 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, the storage stability and water resistance are highly excellent and suitable.

The ratio of magnesium to phosphorus ([Mg]/[P]) in the ash of the acrylic rubber sheet of the present invention is not particularly limited by weight, but is usually 0.4 to 2.5, preferably 0.4 to 1.3, more preferably 0.4 to 1, particularly preferably 0.45 to 0.75, and most preferably 0.5 to 0.7, which is suitable for achieving excellent storage stability and water resistance.

The complex viscosity of the acrylic rubber sheet of the present invention at 60°C ([η]60°C) is not particularly limited, but is usually excellent in processability, oil resistance, and shape retention when it is in the range of 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.

The complex viscosity of the acrylic rubber sheet of the present invention at 100°C ([η]100°C) is not particularly limited, but is usually excellent in processability, oil resistance, and shape retention and is suitable when it is 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.

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 sheet of the present invention is not particularly 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 0.6 to 0.98, more preferably 0.75 to 0.95, particularly preferably 0.8 to 0.94, and most preferably 0.83 to 0.93, the processability, oil resistance, and shape retention are highly balanced and are suitable.

The Mooney viscosity (ML1+4, 100°C) of the acrylic rubber sheet of the present invention is not particularly limited, but is usually suitable for achieving a high balance of processability and strength properties when it is in the range of 10 to 150, preferably 20 to 100, and more preferably 25 to 70.

The type of acrylic rubber sheet of the present invention is not particularly limited, but examples include blown sheets produced by a hollow molding method, cast sheets produced by a solution casting method, and melt-kneaded sheets produced by a melt extrusion method. Among these, melt-kneaded sheets are preferred in that they can maximize the effects of workability, processability, and storage stability.

<Method of manufacturing acrylic rubber sheet>
The method for producing the acrylic rubber sheet of the present invention is not particularly limited, but may, for example, include an emulsion polymerization step of emulsifying a monomer component containing a (meth)acrylic acid ester and a reactive group-containing monomer with water and an emulsifier, and emulsion-polymerizing the monomer component in the presence of a polymerization catalyst to obtain an emulsion polymerization liquid;
a coagulation step in which the obtained emulsion polymerization liquid is contacted with a coagulation liquid to produce water-containing crumbs;
A washing step of washing the produced hydrous crumbs;
The acrylic rubber sheet of the present invention can be easily produced by including a dehydration, drying and molding process in which the washed wet crumbs are dehydrated in the dehydration barrel using a dehydration barrel having a dehydration slit, a drying barrel under reduced pressure, and a screw-type extruder having a die at the tip thereof to a moisture content of 1 to 40% by weight, and then dried in the drying barrel to a moisture content of less than 1% by weight, and a sheet-like dried rubber is extruded through the die.

(Emulsion polymerization process)
The emulsion polymerization step in the method for producing an acrylic rubber sheet of the present invention is characterized in that a monomer component containing a (meth)acrylic acid ester and a reactive group-containing monomer is emulsified with water and an emulsifier, emulsion-polymerized in the presence of a polymerization catalyst, the resulting emulsion polymerization liquid is emulsified with water and an emulsifier, and emulsion-polymerized in the presence of a polymerization catalyst to obtain an emulsion polymerization liquid.

The monomer components used are the same as those described above, and the amount used may be appropriately selected so as to obtain the monomer composition of the acrylic rubber constituting the acrylic rubber sheet, and is usually an amount equivalent to the monomer composition of the acrylic rubber constituting the acrylic rubber sheet.

The emulsifier to be used is not particularly limited, but examples include anionic emulsifiers, cationic emulsifiers, and nonionic emulsifiers. Preferably, the emulsifier contains an anionic emulsifier, more preferably, the emulsifier contains a sulfate ester salt or a phosphate ester salt, and most preferably, the emulsifier contains a phosphate ester salt.

The anionic emulsifier is not particularly limited, and examples thereof include salts of fatty acids such as myristic acid, palmitic acid, oleic acid, and linolenic acid; alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate; sulfate salts such as sodium lauryl sulfate, and phosphate salts such as polyoxyalkylene alkyl ether phosphate salts; and alkylsulfosuccinates. Among these anionic emulsifiers, phosphate salts and sulfate salts are preferred, and phosphate salts are particularly preferred. These anionic emulsifiers can be used alone or in combination of two or more.

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

Nonionic emulsifiers are not particularly limited, but examples include polyoxyalkylene fatty acid esters such as polyoxyethylene stearic acid ester; polyoxyalkylene alkyl ethers such as polyoxyethylene dodecyl ether; polyoxyalkylene alkylphenol ethers such as polyoxyethylene nonylphenyl ether; polyoxyethylene sorbitan alkyl esters, etc., with polyoxyalkylene alkyl ethers and polyoxyalkylene alkylphenol ethers being preferred, and polyoxyethylene alkyl ethers and polyoxyethylene alkylphenol ethers being more preferred.

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

The monomer components, water, and emulsifier can 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.

There are no particular limitations on the polymerization catalyst used, so long as it is one that is commonly used in emulsion polymerization. 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.

There are no particular limitations on the organic peroxides as long as they are known to be used in emulsion polymerization, and examples thereof include 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, 1-di-(t-hexylperoxy)cyclohexane, 1,1-di-(t-butylperoxy)cyclohexane, 4,4-di-(t-butylperoxy)n-butyl valerate, 2,2-di-(t-butylperoxy)butane, t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramenthane hydroperoxide, benzoyl peroxide, and 1,1,3,3-tetramethylphenyl hydroperoxide. tetraethylbutyl hydroperoxide, t-butylcumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, diisobutyryl peroxide, di(3,5,5-trimethylhexanoyl)peroxide, dilauroyl peroxide, disuccinic acid peroxide, dibenzoyl peroxide, di(3-methylbenzoyl)peroxide, benzoyl(3-methylbenzoyl)peroxide, diisobutyryl peroxydicarbonate, di-n-propyl peroxydicarbonate, di (2-ethylhexyl)peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutylperoxyneodecanate, t-hexylperoxypivalate, t-butylperoxyneodecanate, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate, t-hexylperoxy-2-ethylhexanate, t-butylperoxy-3,5,5-trimethylhexanate, t-hexylperoxy Examples of such peroxyisopropyl monocarbonate include oxyisopropyl monocarbonate, 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. Of 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 types, 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 reducing agent that is used in redox catalysts for emulsion polymerization, but in the present invention, it is particularly preferable to use at least two reducing agents. For example, a combination of a metal ion compound in a reduced state and another reducing agent is suitable as the at least two reducing agents.

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

The reducing agent other than the metal ion compounds in the reduced state is not particularly limited, but examples thereof 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 hydrogen sulfite, sodium aldehyde hydrogen sulfite, and potassium hydrogen sulfite; Examples of suitable sulfuric acids include pyrosulfites such as sodium pyrosulfite, potassium pyrosulfite, sodium hydrogen pyrosulfite, and potassium hydrogen pyrosulfite; thiosulfates such as sodium thiosulfate and potassium thiosulfate; phosphorous acid or a salt thereof such as phosphorous acid, sodium phosphite, potassium phosphite, sodium hydrogen phosphite, and potassium hydrogen phosphite; pyrophosphorous acid or a salt thereof such as pyrophosphorous acid, sodium pyrophosphite, potassium pyrophosphite, sodium hydrogen pyrophosphite, and potassium hydrogen pyrophosphite; sodium formaldehyde sulfoxylate, etc. Among these, ascorbic acid or a salt thereof, sodium formaldehyde sulfoxylate, etc. are preferred, and ascorbic acid or a salt thereof is particularly preferred.

These reducing agents other than metal ion compounds in a reduced state can be used alone or in combination of two or more kinds, and the amount used is usually in the range of 0.001 to 1 part by weight, preferably 0.005 to 0.5 parts by weight, and more preferably 0.01 to 0.3 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 ferrous sulfate and ascorbic acid or a salt thereof and/or sodium formaldehyde sulfoxylate, more preferably ferrous sulfate and an ascorbate and/or sodium formaldehyde sulfoxylate, and most preferably 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, relative to 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, relative to 100 parts by weight of the monomer component.

The amount of water used in the emulsion polymerization reaction may be only that 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 a conventional 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 particularly limited, but when it is usually 80% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more, the acrylic rubber sheet produced has excellent strength characteristics and is free of monomer odor, which is suitable. 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 a step in which the above-obtained emulsion polymerization liquid is brought into contact with a coagulation liquid to produce water-containing crumbs.

The solids concentration of the emulsion polymerization liquid used in the coagulation step is not particularly 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 is not particularly limited, but a metal salt is usually used. Examples of metal salts include alkali metals, Group 2 metal salts of the periodic table, and other metal salts. Of these, alkali metal salts and Group 2 metal salts of the periodic table are preferred, and Group 2 metal salts of the periodic table are more preferred, with magnesium salts being particularly preferred.

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

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

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

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

The coagulant concentration of the coagulation liquid used 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 for concentrating the particle size of the resulting hydrous crumbs uniformly in a specific area.

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

There are no particular limitations on the contact between the emulsion polymerization liquid and the coagulation liquid, but for example, either the method of adding the emulsion polymerization liquid to the stirred coagulation liquid or the method of adding the coagulation liquid to the stirred emulsion polymerization liquid may be used. However, the method of adding the emulsion polymerization liquid to the stirred coagulation liquid is preferable because it can uniformly concentrate the shape and diameter of the water-containing crumbs that are generated, and can significantly improve the washing efficiency of the emulsifier and coagulation agent.

The stirring speed (rotation speed) of the coagulation liquid being stirred, that is, the rotation speed of the stirring blade of the stirring device, is not particularly limited, but is usually 100 rpm or more, preferably 200 to 1,000 rpm, more preferably 300 to 900 rpm, and particularly preferably in the range of 400 to 800 rpm.

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

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

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

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

The washing method is not particularly limited and may be any conventional method, for example, by mixing the resulting hydrous crumbs with a large amount of water.

The amount of water used is not particularly limited, but it is suitable to effectively reduce the ash content in the acrylic rubber when the amount of water used 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.

There are no particular limitations on the temperature of the water used for washing, but it is preferable to use warm water, which is usually 40°C or higher, preferably 40 to 100°C, more preferably 50 to 90°C, and most preferably 60 to 80°C, as this significantly increases the washing efficiency.

By keeping the temperature of the cleaning water above the lower limit, the emulsifier and coagulant are released from the water-containing crumbs, improving cleaning efficiency.

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

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 water-containing crumbs and/or setting the washing temperature within the above range.

(Dehydration, drying, molding process)
In the dehydration, drying and molding process in the method for producing an acrylic rubber sheet of the present invention, the above-mentioned washed water-containing crumbs are extruded using a dehydration barrel having a dehydration slit, a drying barrel under reduced pressure, and a screw-type extruder having a die at the tip. The rubber is then dehydrated in a dehydrating barrel to a moisture content of 1 to 40% by weight, and then dried in a drying barrel to a moisture content of less than 1% by weight, and the sheet-like dried rubber is extruded through a die.

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

In the method for producing an acrylic rubber sheet of the present invention, it is preferable to provide a draining step in which free water is separated from the water-containing crumbs after washing with a draining machine after the above-mentioned water-washing step and before the dehydrating and drying steps, in order to increase the dehydration efficiency.

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

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

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

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

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

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

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

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

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

There are no particular limitations on the moisture content after dehydration in drainage dehydration, which squeezes out moisture from the hydrous crumbs, but a moisture content of 1 to 45% by weight, preferably 1 to 40% by weight, more preferably 5 to 35% by weight, and particularly preferably 10 to 35% by weight, is suitable as it provides a high level of balance between productivity and ash removal efficiency.

When dehydrating sticky acrylic rubber using a centrifuge or similar machine, the acrylic rubber adheres to the dehydration slits and is barely dehydrated (water content reaches approximately 45-55% by weight). However, in this invention, by using a screw-type extruder that has a dehydration slit and is forcibly squeezed by a screw, it is possible to reduce the water content to this extent.

When a drainage type dehydration barrel and a steam exhaust type dehydration barrel are used, the moisture content after drainage in the drainage type dehydration barrel is usually 5 to 45% by weight, preferably 10 to 40% by weight, and more preferably 15 to 35% by weight, and the moisture content after preliminary drying in the steam exhaust type dehydration barrel is usually 1 to 30% by weight, preferably 3 to 20% by weight, and more preferably 5 to 15% by weight.

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

Drying of moist crumbs (drying barrel section)
The drying of the water-containing crumbs after the dehydration is carried out in a drying barrel 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 suitable for efficient drying of the wet 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 discoloration or deterioration, and to reduce the amount of gel in the acrylic rubber sheet that is insoluble in methyl ethyl ketone.

The number of drying barrels in a screw-type extruder is not particularly 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) in order to increase the drying efficiency.

The moisture content of the dried rubber after drying is usually less than 1% by weight, preferably 0.8% by weight or less, and more preferably 0.6% by weight or less. In the present invention, it is particularly preferable to melt extrude the dried rubber at this moisture content (with almost all water removed) in a screw-type extruder, as this reduces the amount of gel in the methyl ethyl ketone-insoluble portion of the acrylic rubber sheet.

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

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

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

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

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

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

The rotation speed (N) of the screw-type extruder used may be selected appropriately depending on various conditions, but a rotation speed of 10 to 1,000 rpm, preferably 50 to 750 rpm, more preferably 100 to 500 rpm, and most preferably 120 to 300 rpm is suitable for efficiently reducing the water content of the acrylic rubber and the amount of gel insoluble in methyl ethyl ketone.

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

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

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

There are no particular limitations on the thickness of the sheet-like dry rubber extruded from the screw-type extruder, but it is usually 1 to 40 mm, preferably 2 to 35 mm, more preferably 3 to 30 mm, and most preferably 5 to 25 mm, which is suitable for 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 after-effect is increased to significantly improve productivity, the thickness of the sheet-like dry rubber is usually 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 dried rubber extruded from the screw extruder is not particularly limited, but is usually in the range of 100 to 200°C, preferably 110 to 180°C, and more preferably 120 to 160°C.

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

The complex viscosity at 100°C ([η]100°C) of the sheet-like dry rubber extruded from the screw-type extruder is not particularly 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 value at or above the lower limit, the sheet-like dry rubber can be made to have excellent extrudability, and by setting the value at or below the upper limit, deformation or breakage of the sheet-like dry rubber can be suppressed.

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

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

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

The complex viscosity of the dry rubber sheet at 60°C ([η]60°C) is not particularly limited, but is usually 15,000 Pa·s or less, preferably 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 allows for continuous cutting 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 particularly limited, but is usually 0.5 or more, preferably 0.6 to 0.98, more preferably 0.75 to 0.95, particularly preferably 0.8 to 0.94, and most preferably 0.83 to 0.93, which is suitable for reducing 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 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-form dry rubber, for example, the sheet-form dry rubber is extruded from a screw-type extruder onto a conveyor such as a belt conveyor, and is conveyed and cooled while being blown with cold air. The temperature of the cold air is not particularly limited, but is usually in the range of 0 to 25°C, preferably 5 to 25°C, and more preferably 10 to 20°C. The length to be cooled is not particularly limited, but is usually in the range of 5 to 500 m, preferably 10 to 200 m, and more preferably 20 to 100 m. The cooling rate of the sheet-form dry rubber is not particularly limited, but is usually 50°C/hr or more, more preferably 100°C/hr or more, and more preferably 150°C/hr or more, which is particularly easy to cut and is therefore suitable.

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

The acrylic rubber sheet thus obtained is superior in operability (workability), processability, and strength properties compared to crumb-like acrylic rubber, and also has excellent water resistance and storage stability, and can be used as is or laminated to form a bale.

<Acrylic rubber veil>
The acrylic rubber veil of the present invention is characterized in that it is formed by laminating the above-mentioned acrylic rubber sheets. The number of laminations is appropriately selected depending on the size or weight of the acrylic rubber veil.

The size of the acrylic rubber veil of the present invention is not particularly limited, but 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 characteristic values of the reactive group content, water content, ash content, amount and ratio of components in the ash, specific gravity, gel content, pH, complex viscosity at 60°C ([η]60°C), complex viscosity at 100°C ([η]100°C), ratio of complex viscosity at 100°C ([η]100°C) to complex viscosity at 60°C ([η]60°C) ([η]100°C/[η]60°C), and Mooney viscosity (ML1+4, 100°C) of the acrylic rubber veil of the present invention are the same as the respective characteristic values of the acrylic rubber sheet.

The method for producing the acrylic rubber veil of the present invention is not particularly limited, but it can be easily produced by cooling the dried rubber sheet extruded from the screw-type extruder, cutting it, and then laminating it.

There is no particular limit to the lamination temperature of the dry rubber sheet, 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 entrapped during lamination to escape. The number of layers may be appropriately selected depending on the size or weight of the acrylic rubber veil. In the acrylic rubber veil of the present invention, the acrylic rubber sheets are fused together by their own weight to form an integrated unit.

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

<Rubber mixture>
The rubber mixture of the present invention is characterized in that it is obtained by mixing the acrylic rubber sheet or acrylic rubber veil with a filler and a crosslinking agent.

There are no particular limitations on the filler, but examples include reinforcing fillers and non-reinforcing fillers, with reinforcing fillers being preferred.

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

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

The crosslinking agent may be appropriately selected according to the type of reactive group contained in the acrylic rubber constituting the acrylic rubber sheet or acrylic rubber veil and the intended use, but is not particularly limited as long as it can crosslink the acrylic rubber sheet or 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 may 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 sheet or acrylic rubber veil used is composed of a carboxyl group-containing acrylic rubber, it is preferable to use a polyamine compound and its carbonate as a crosslinking agent. Examples of the polyvalent amine compound 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 sheet or 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 or ammonium adipate; 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 sheet or 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 sheet or acrylic rubber veil. By setting the amount of crosslinking agent within this range, it is possible to obtain excellent mechanical strength as a crosslinked rubber product while maintaining sufficient rubber elasticity, which is preferable.

The rubber mixture of the present invention can contain other rubber components other than the acrylic rubber sheet or acrylic rubber veil as 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, polysiloxane-based elastomers, etc. The shape of the other rubber components is not particularly limited, and may be, for example, crumb-like, sheet-like, veil-like, etc.

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 the anti-aging agent 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 of each 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 sheet or acrylic rubber veil.

The rubber mixture of the present invention contains the acrylic rubber sheet or acrylic rubber veil of the present invention, a filler, a crosslinking agent, and other rubber components and anti-aging agents as necessary, and can further contain other additives commonly used in the relevant technical field as necessary, such as crosslinking assistants, crosslinking accelerators, crosslinking retarders, silane coupling agents, plasticizers, processing aids, lubricants, pigments, colorants, antistatic agents, and foaming agents. These other additives can 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.

The method for producing the rubber mixture is not particularly limited, and examples thereof include a method in which the filler, crosslinking agent, and other rubber components that may be contained as necessary, antioxidants, and other compounding agents are mixed with an acrylic rubber sheet or acrylic rubber veil. Any means conventionally used in the rubber processing field, such as an open roll, a Banbury mixer, or various kneaders, can be used for mixing. In other words, the acrylic rubber sheet or acrylic rubber veil can be directly mixed with the filler, crosslinking agent, etc., preferably by direct kneading, using these mixers.

In this case, the acrylic rubber sheet or acrylic rubber veil may be used as is or after being divided (cut, etc.).

There are no particular limitations on the mixing procedure for each component, but two-stage mixing is preferred, in which, for example, components that do not easily react or decompose when heated are thoroughly mixed, and then components that do easily react or decompose when heated, such as crosslinking agents, are mixed for a short time at a temperature at which they do not react or decompose. Specifically, it is preferred to mix the acrylic rubber sheet or acrylic rubber veil and filler in the first stage, and then mix the crosslinking agent in the second stage. Other rubber components and anti-aging agents are usually mixed in the first stage, the crosslinking accelerator in the second stage, and other compounding agents 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 particularly 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 molding the rubber mixture of the present invention into a desired shape using a molding machine such as an extruder, injection molding machine, compressor, or roll, and then heating to cause a cross-linking reaction and fix 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, and more preferably 150 to 200°C, and the cross-linking time is usually 0.1 minutes to 10 hours, preferably 1 minute to 5 hours. The heating method may be appropriately selected from methods used for cross-linking rubber, such as press heating, steam heating, oven heating, and hot air heating.

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

The cross-linked rubber of the present invention is suitably used, for example, as 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-proof materials; wire coating materials; industrial belts; tubes and hoses; sheets; etc.

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

<Apparatus configuration used for manufacturing acrylic rubber sheet>
Next, the configuration of the equipment used in the production of the acrylic rubber sheet 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 sheet 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 sheet 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, this emulsion polymerization reactor has, for example, a polymerization reaction tank, a temperature control unit for controlling the reaction temperature, and a stirring device equipped with a motor and a stirring blade. In the emulsion polymerization reactor, the monomer components for forming the acrylic rubber are mixed with water and an emulsifier, 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 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 that heats the inside of the stirring tank 30, a temperature control unit (not shown) that controls the temperature inside the stirring tank 30, a stirring device 34 equipped with a motor 32 and agitating blades 33, and a drive control unit (not shown) that controls the number of rotations and the rotation speed of the agitating blades 33. In the solidification device 3, the emulsion polymerization liquid obtained in the emulsion polymerization reactor can be brought into contact with the coagulation liquid and solidified to produce water-containing crumbs.

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

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

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

The drive control unit of the solidification device 3 is configured to control the rotation drive of the motor 32 of the stirring device 34 to set the number of rotations and the rotation speed of the stirring blade 33 of the stirring device 34 to a predetermined value. The rotation of the stirring blade 33 is controlled by the drive control unit so that the stirring speed of the solidification liquid is, for example, usually 100 rpm or more, preferably 200 to 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 process related to the cleaning step described above. As shown in FIG. 1, the cleaning device 4 has, for example, a cleaning tank 40, a heating unit 41 that heats the inside of the cleaning tank 40, and a temperature control unit (not shown) that controls the temperature inside the cleaning tank 40. In the cleaning device 4, the amount of ash in the final acrylic rubber sheet can be effectively reduced by mixing the water-containing crumbs generated in the solidification device 3 with a large amount of water and cleaning them.

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. Note that while 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 type 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.

In each of the dehydration barrels 53a to 53c of the dehydration barrel section 53, moisture is removed from the hydrous crumbs in liquid form through the respective dehydration slits 56a, 56b, 56c, or in vapor form. In the dehydration barrel section 53 of this embodiment, when moisture is removed in liquid form, it is defined as drainage, and when moisture is removed in vapor form, it is defined as exhaust steam, and these are distinguished.

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. Also, for example, when the dehydration barrel section 53 has four dehydration barrels, it is possible to consider an embodiment in which drainage is performed in three upstream dehydration barrels and steam exhaust is performed in one downstream dehydration barrel. On the other hand, when the moisture content is reduced, it is better to increase the number of dehydration barrels for steam exhaust.

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

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

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

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

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

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

The die 59 is a metal mold placed at the downstream end of the barrel unit 51, and has an outlet of a predetermined nozzle shape. The acrylic rubber dried in the drying barrel section 54 passes through the outlet of the die 59 and is extruded into a shape that corresponds to the predetermined nozzle shape. In the present invention, the shape of the acrylic rubber passing through the die 59 can be extruded into a sheet shape by making the nozzle shape 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 sheet, 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.

Below, with reference to FIG. 3, we will explain a conveyor-type cooling device 60 that cools a sheet-shaped dry rubber 10 that has been molded into a sheet shape, as an example of a 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 single block. 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 shaped acrylic rubber bale weighing about 20 kg is produced.

The sheet-like dried rubber 10 produced by the screw-type extruder 5 may be laminated to produce an acrylic rubber bale. For example, a cutting mechanism for cutting the sheet-like dried rubber 10 may be provided in the baling device 7 arranged downstream of the conveying cooling device 60 shown in FIG. 3. Specifically, the cutting mechanism of the baling device 7 is configured to continuously cut the cooled sheet-like dried rubber 10 at predetermined intervals to 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 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 its own weight.

The present invention will be described in more detail below with reference to examples and comparative examples. Note that "parts," "%," and "ratios" in each example are by weight unless otherwise specified.

Various physical properties were evaluated according to the following methods.

[Monomer composition]
Regarding the monomer composition in the acrylic rubber, the monomer configuration 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 methods.

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 found, so the content ratio of each monomer unit was set to the same as the amount of each monomer used.

[Reactive group content]
The content of reactive groups in the acrylic rubber sheet or acrylic rubber veil was measured by the following method.
(1) The amount of carboxyl groups was calculated by dissolving an acrylic rubber sheet or acrylic rubber veil in acetone and performing potentiometric titration with a potassium hydroxide solution.
(2) The amount of epoxy groups was calculated by dissolving an acrylic rubber sheet or acrylic rubber veil 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 sheet or 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 sheet or acrylic rubber veil was measured in accordance with JIS K6228 Method A.

[Ash content]
The amount (ppm) of each component in the acrylic rubber sheet or 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 sheet or acrylic rubber veil is the amount of insoluble matter in methyl ethyl ketone, and was determined by the following method.

Approximately 0.2 g of the acrylic rubber sheet or acrylic rubber veil was weighed out (X g), immersed in 100 ml of methyl ethyl ketone and allowed to stand at room temperature for 24 hours, and then 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 dry solids (Y g) were weighed and calculated according to the following formula.
Gel amount (%)=100×(X−Y)/X

[specific gravity]
The specific gravity of the acrylic rubber sheet or 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 sheet or acrylic rubber veil was measured with a pH electrode after dissolving 6 g (±0.05 g) of acrylic rubber veil 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 sheet or 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%. 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 sheet or 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.

[Workability evaluation]
The workability of the rubber samples was evaluated based on the following criteria with respect to the workability in weight measurement during the production of the rubber mixture.
◎: Easy to measure. 〇: Sticky and sticks to some extent, but can be measured. ×: Sticks to the measuring device and is very viscous and difficult to handle.

[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).

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

[Example 1]
A mixing vessel equipped with a homomixer was charged with 46 parts of pure water, 74.5 parts of ethyl acrylate, 17 parts of n-butyl acrylate, 7 parts of methoxyethyl acrylate, 1.5 parts of mono-n-butyl fumarate, and 1.8 parts of octyloxydioxyethylene phosphate sodium salt as an emulsifier, and the mixture was stirred to obtain a monomer emulsion.

Next, 170 parts of pure water and 3 parts of the monomer emulsion obtained above were added to a polymerization reaction tank equipped with a thermometer and a stirrer, and cooled to 12°C under a nitrogen stream. Next, the remainder of the monomer emulsion, 0.00033 parts of ferrous sulfate, 0.264 parts of sodium ascorbate, and 0.22 parts of potassium persulfate were continuously dropped into the polymerization reaction tank over a period of 3 hours. Thereafter, the reaction was continued while maintaining the temperature inside the polymerization reaction 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 tank equipped with a thermometer and agitator, the emulsion polymerization liquid containing the antioxidant was heated to 80°C and continuously added to a 2% aqueous magnesium sulfate solution (coagulation liquid) that had been 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 warm water (70°C) was added to the coagulation tank and stirred for 15 minutes, after which the water was drained off, and 194 parts of warm water (70°C) was added again and stirred for 15 minutes to wash the wet crumbs. 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. Next, the sheet-like dry rubber was cooled at a cooling rate of 200°C/hr using a conveying cooling device directly connected to the screw-type 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: 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
Set temperature for each barrel:
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 to obtain an acrylic rubber sheet (A). The reactive group content, ash content, ash component content, specific gravity, gel content, glass transition temperature (Tg), pH, antioxidant content, water content, molecular weight, molecular weight distribution and complex viscosity of the obtained acrylic rubber sheet (A) were measured and the results are shown in Table 2. In addition, the workability of the acrylic rubber sheet (A) was evaluated and the results are shown in Table 2.

Next, the acrylic rubber sheets (A) were laminated to 20 parts (20 kg) before the temperature of the sheets fell below 40°C to obtain an acrylic rubber veil (A). The reactive group content, ash content, ash component content, specific gravity, gel content, glass transition temperature (Tg), pH, antioxidant content, water content, molecular weight, molecular weight distribution, and complex viscosity of the obtained acrylic rubber veil (A) were measured.

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

Then, the resulting mixture was transferred to a roll at 50°C, and compounding ingredient B of "Compound 1" in Table 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 to evaluate its normal physical properties, and the results are shown in Table 2.

[Example 2]
The same procedure as in Example 1 was repeated except that the monomer components were changed to 4.5 parts of ethyl acrylate, 64.5 parts of n-butyl acrylate, 29.5 parts of methoxyethyl acrylate, and 1.5 parts of mono n-butyl fumarate, and the emulsifier was changed to nonylphenyloxyhexaoxyethylene phosphate sodium salt, to obtain an acrylic rubber sheet (B) and an acrylic rubber veil (B), and the properties of each were evaluated. The results for the acrylic rubber sheet (B) are shown in Table 2.

[Example 3]
The same procedure as in Example 1 was carried out except that the monomer components were changed to 48.25 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.75 parts of mono n-butyl fumarate, and the emulsifier was changed to tridecyloxyhexaoxyethylene phosphate sodium salt, to obtain an acrylic rubber sheet (C) and an acrylic rubber veil (C), and the properties of each were evaluated (the compounding ingredients were changed to "Compound 2"). The results for the acrylic rubber sheet (C) are shown in Table 2.

[Example 4]
The temperature of the first dehydration barrel of the screw extruder was changed to 100° C., the temperature of the second dehydration barrel was changed to 120° C., and drainage was performed only in the first dehydration barrel, and the moisture content of the water-containing crumb after drainage in the first dehydration barrel was changed to 30%. The same procedure as in Example 3 was carried out to obtain an acrylic rubber sheet (D) and an acrylic rubber veil (D), and the properties were evaluated. The results for the acrylic rubber sheet (D) are shown in Table 2.

[Example 5]
The same procedure as in Example 4 was carried out except that the monomer components were changed to 28 parts of ethyl acrylate, 38 parts of n-butyl acrylate, 27 parts of methoxyethyl acrylate, 5 parts of acrylonitrile, and 2 parts of allyl glycidyl ether, and an acrylic rubber sheet (E) and an acrylic rubber veil (E) were obtained and their properties were evaluated (the compounding ingredients were changed to "Compound 3"). The results for the acrylic rubber sheet (E) are shown in Table 2.

[Example 6]
The same procedure as in Example 4 was carried out except that the monomer components were changed to 42.5 parts of ethyl acrylate, 35 parts of n-butyl acrylate, 20 parts of methoxyethyl acrylate, 1.5 parts of acrylonitrile, and 1.3 parts of vinyl chloroacetate, and an acrylic rubber sheet (F) and an acrylic rubber veil (F) were obtained and their properties were evaluated (the compounding ingredients were changed to "Compound 4"). The results for the acrylic rubber sheet (F) are shown in Table 2.

[Comparative Example 1]
A mixing vessel equipped with a homomixer was charged with 46 parts of pure water, 42.2 parts of ethyl acrylate, 35 parts of n-butyl acrylate, 20 parts of methoxyethyl acrylate, 1.5 parts of acrylonitrile, 1.3 parts of vinyl chloroacetate, 0.709 parts of sodium lauryl sulfate as an emulsifier, 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 above were added to a polymerization reaction tank equipped with a thermometer and a stirrer, and cooled to 12°C under a nitrogen stream. Next, the remainder of the monomer emulsion, 0.00033 parts of ferrous sulfate, 0.264 parts of sodium ascorbate, and 0.22 parts of potassium persulfate were continuously dropped into the polymerization reaction tank over a period of 3 hours. Thereafter, the reaction was continued while maintaining the temperature inside the polymerization reaction 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.

Next, the emulsion polymerization liquid to which the antioxidant was added was heated to 80°C, and then a 0.7% aqueous sodium sulfate solution (coagulation liquid) was continuously added to the emulsion polymerization liquid (rotation speed 100 rpm, peripheral speed 0.5 m/s) to coagulate the polymer, which was then filtered to obtain hydrous crumbs. 194 parts of industrial water was added to 100 parts of the obtained hydrous crumbs, and the mixture was stirred at 15°C for 5 minutes, after which the hydrous crumbs were washed four times by draining the water from the coagulation tank, and then 194 parts of an aqueous sulfuric acid solution with a pH of 3 was added and stirred at 15°C for 5 minutes, after which the water was drained from the coagulation tank and acid washed once, and then 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 crumb-like 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 shown in Table 2.

From Table 2, it can be seen that the acrylic rubber sheets (A) to (F) of the present invention, which are made of acrylic rubber having reactive groups and a weight average molecular weight (Mw) of 100,000 to 5,000,000 and have a gel content of 5% by weight or less of methyl ethyl ketone insoluble matter, are remarkably superior in workability, processability, and normal physical properties (strength characteristics) (comparison between Examples 1 to 6 and Comparative Example 1).

In terms of strength characteristics (normal physical properties), the acrylic rubber sheets (A) to (F) and the crumb-like acrylic rubber (G) manufactured under the conditions of the present examples and comparative examples all have weight-average molecular weights (Mw) of absolute molecular weights measured by GPC-MALS that far exceed 100,000, and furthermore, the ratio (Mz/Mw) of the z-average molecular weight (Mz) and weight-average molecular weight (Mw) of the absolute molecular weight distribution that emphasizes the high molecular weight region measured by GPC-MALS far exceeds 1.3, indicating that the normal physical properties, including breaking strength, are excellent (Examples 1 to 6 and Comparative Example 1). However, it is clear that the crumb-like acrylic rubber (G) has excellent strength characteristics, but insufficient workability and processability (Comparative Example 1).

In terms of workability, the acrylic rubber sheets (A) to (F) of the present invention are easy to handle and do not lose their shape, and are far superior in workability to the crumb-like acrylic rubber (G), which is highly viscous and sticks to itself, making it difficult to handle (comparison of Examples 1 to 6 and Comparative Example 1).

In terms of processability, in this invention, the polymerization conversion rate of the emulsion polymerization is increased to improve strength properties. However, as the polymerization conversion rate is increased, the amount of gel that is insoluble in methyl ethyl ketone increases rapidly, worsening the processability of the acrylic rubber. However, by drying the material to a state where there is essentially no moisture (water content less than 1%) and then melt-kneading it in the screw-type extruder, the rapidly increasing amount of gel disappears, and it is found that the processability and strength properties of the acrylic rubber veil are highly balanced (comparison of Examples 1 to 6 with Comparative Example 1).

In terms of strength properties, the acrylic rubber sheets (A) to (F) produced by the present invention have a sufficient reactive group content, and the reactive groups are not lost during polymerization, etc., so that the normal strength properties are excellent (Examples 1 to 6).

As water resistance is not an issue of this application, it is not shown here, but the acrylic rubber veils (A) to (F) of this invention were excellent in terms of functionality, processability and strength properties, and also had outstanding water resistance. In this application, in order to improve processability, which is one of the issues of this application, the amount of gel insoluble in methyl ethyl ketone that had increased during emulsion polymerization for high molecular weight was eliminated by melt kneading in a screw extruder in a state that was substantially free of moisture. However, since it is difficult to reduce the water content of acrylic rubber, which has reactive groups with large specific heat, in a short screw extruder, the coagulation method was changed to create a crumb shape that makes it easier to reduce the water content, the washing method was changed to reduce impurities, and a dehydration process was provided in the screw extruder to dry efficiently, and it was found that the acrylic rubber sheet obtained in this way had outstanding water resistance.

Table 2 also shows that the "specific gravity" is significantly different between the acrylic rubber veils (A) to (F) of the present invention and the crumb-like acrylic rubber (G). This (specific gravity) could not be easily increased by the coagulation method and hot air drying method for producing the crumb-like acrylic rubber (G). However, it has been discovered that an air-free acrylic rubber veil with a high specific gravity can be obtained by extruding the sheet-like dry rubber from which the gel content of the methyl ethyl ketone insolubles has disappeared using the screw-type extruder and by examining the conditions for cutting and laminating the sheet-like dry rubber. The effect of this high specific gravity and no longer containing air is not shown because it is different from the problem of the present application, but the storage stability is highly improved, and as a result, the acrylic rubber veils (A) to (F) of the present invention have excellent workability, processability, and strength properties, as well as excellent water resistance and storage stability.

From Table 2, it can be seen that the acrylic rubber sheets (A) to (F) of the present invention, whose reactive group amount, specific gravity, gel amount, glass transition temperature (Tg), pH, water content, weight average molecular weight (Mw), ratio of z-average molecular weight (Mz) to weight average molecular weight (Mw) (Mz/Mw), complex viscosity at 100°C η (100°C), complex viscosity at 60°C η (60°C), and ratio of complex viscosity at 100°C and 60°C (η100°C/η60°C) are within specific ranges, have excellent workability, processability, and normal physical properties (strength characteristics) (Examples 1 to 6).

[Comparative Example 2]
Crumb-like acrylic rubber (H) was obtained in the same manner as in Comparative Example 1, except that the emulsifier was changed to 1.8 parts of sodium tridecyloxyhexaoxyethylene phosphate and the coagulant was changed to magnesium sulfate. The ash content of the crumb-like acrylic rubber (H) was measured to be much more than 1%, and it was found that the ash content was not sufficiently removed by washing alone when a phosphate salt was used as an emulsifier and magnesium sulfate was used as a coagulant. The workability, processability and normal physical properties of the crumb-like acrylic rubber (H) were evaluated as follows: workability x, processability 100, breaking strength ◎, 100% stress ◎, and breaking elongation ◎. Although the normal physical properties including strength properties were excellent, the workability and processability were insufficient. In addition, the water resistance was evaluated to be more than twice as poor as that of Comparative Example 1. On the other hand, it was found that the acrylic rubber veils (A) to (F) of the present invention produce hydrous crumb from which the ash can be easily removed by washing and dehydration by using a specific coagulation method, a specific coagulant concentration, and a fast stirring speed, and that by washing with warm water and then dehydrating, the ash content is significantly reduced and water resistance is improved.

Reference Signs List 1 Acrylic rubber manufacturing system 3 Coagulation device 4 Cleaning device 5 Screw-type extruder 6 Cooling device 7 Baling device

Claims (14)

An acrylic rubber sheet made of acrylic rubber having reactive groups and a weight average molecular weight (Mw) of 100,000 to 5,000,000, with a gel content of methyl ethyl ketone insoluble matter of 5% by weight or less. The acrylic rubber sheet according to claim 1, wherein the acrylic rubber content in the acrylic rubber sheet is 95% by weight or more. The acrylic rubber sheet according to claim 1 or 2, wherein the ash content is 1% by weight or less. An acrylic rubber sheet according to any one of claims 1 to 3, in which the content (total amount) of at least one element selected from the group consisting of sodium, sulfur, calcium, magnesium and phosphorus in the ash is 50% by weight or more. The acrylic rubber sheet according to any one of claims 1 to 4, wherein the acrylic rubber sheet is a melt-kneaded sheet. The acrylic rubber sheet according to any one of claims 1 to 5, wherein the weight average molecular weight (Mw) is in the range of 1,000,000 to 5,000,000. The acrylic rubber sheet according to any one of claims 1 to 6, wherein the ratio (Mz/Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of the acrylic rubber is 1.3 or more. The acrylic rubber sheet according to any one of claims 1 to 7, 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 0.8 or more. 8. The acrylic rubber sheet according to claim 2, 4, 5 or 7, which has a pH of 6 or less. The acrylic rubber sheet according to any one of claims 1 to 9, wherein the Mooney viscosity (ML1+4, 100°C) of the acrylic rubber sheet is in the range of 10 to 150. an emulsion polymerization step of emulsifying a monomer component containing a (meth)acrylic acid ester and a reactive group-containing monomer 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 contacted with a coagulation liquid to produce water-containing crumbs;
A washing step of washing the produced hydrous crumbs;
The method for producing an acrylic rubber sheet includes a dehydrating, drying and molding step of dehydrating the washed wet crumbs in the dehydrating barrel using a screw-type extruder having a dehydrating slit, a drying barrel under reduced pressure, and a die at the tip thereof to a moisture content of 1 to 40% by weight, and then drying the crumbs in the drying barrel to a moisture content of less than 1% by weight, and extruding a sheet-like dried rubber through the die. An acrylic rubber veil formed by laminating the acrylic rubber sheets according to any one of claims 1 to 10. A rubber mixture obtained by mixing a reinforcing agent and a crosslinking agent with the acrylic rubber sheet according to any one of claims 1 to 10 or the acrylic rubber veil according to claim 12. A cross-linked rubber product obtained by cross-linking the rubber mixture according to claim 13.