Acrylic rubber sheet with excellent roll processability and Banbury processability

Abstract

Provided is an acrylic rubber sheet having excellent roll processability and Banbury processability. The acrylic rubber sheet according to the present invention has an ionic reactive group. The ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight average molecular weight (Mw) found in the absolute molecular weight distribution obtained by GPC-MALS is 1.8 or greater, and the gel content is 30 wt% or less.

Description

[Technical Field]

[0001] The present invention relates to an acrylic rubber sheet, a manufacturing method thereof, an acrylic rubber veil, a rubber mixture, and a cross-linked rubber product, and more specifically to an acrylic rubber sheet that is excellent in roll processability and Banbury processability and also in cross-linkability, strength properties, and compression set resistance, 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 cross-linked rubber product formed by cross-linking it. [Background technology]

[0002] Acrylic rubber is a polymer whose main component is acrylic ester, and is generally known as a rubber with excellent heat resistance, oil resistance, and ozone resistance, and is widely used in the automotive field and other fields.

[0003] For example, Patent Document 1 (International Publication No. WO 2019 / 188709) discloses a method for producing acrylic rubber by charging monomer components consisting of ethyl acrylate, butyl acrylate, methoxyethyl acrylate, and monobutyl fumarate, water, and sodium lauryl sulfate, repeatedly degassing under reduced pressure and purging with nitrogen, and then adding sodium aldehyde sulfoxylate and the organic radical generator cumene hydroperoxide to initiate emulsion polymerization at normal pressure and temperature. The emulsion polymerization is continued until a polymerization conversion rate of 95% by weight is reached, followed by coagulation with an aqueous calcium chloride solution, filtration through a wire mesh, and dehydration and drying in an extrusion dryer with a screw. However, the acrylic rubber obtained by this method suffers from extremely poor roll processability and Banbury processability, as well as poor storage stability and water resistance. Patent Document 1 also does not disclose the formation of the resulting acrylic rubber into sheets.

[0004] Patent Document 2 (JP 1-135811 A) discloses a method for producing acrylic rubber and crosslinking it with sulfur by emulsifying one-quarter of a monomer mixture consisting of ethyl acrylate, caprolactone-added acrylic ester, cyanoethyl acrylate, and vinyl chloroacetate monomer components with n-dodecyl mercaptan as a chain transfer agent with sodium lauryl sulfate, polyethylene glycol nonylphenyl ether, and distilled water, adding sodium sulfite and ammonium persulfate as an inorganic radical generator to initiate polymerization, adding the remaining monomer mixture and a 2% aqueous solution of ammonium persulfate dropwise over two hours while maintaining the temperature at 60°C, and continuing polymerization for another two hours after the dropwise addition. The resulting latex, with a polymerization conversion of 96-99%, is poured into an aqueous sodium chloride solution at 80°C, coagulated, thoroughly washed with water, and dried to produce acrylic rubber. However, the acrylic rubber obtained by this method has problems such as insufficient roll processability and Banbury processability, as well as poor storage stability and poor strength and water resistance of the crosslinked product.

[0005] Patent Document 3 (JP 2018-168343 A) discloses a method for producing an acrylic rubber by preparing a monomer emulsion containing monomer components consisting of ethyl acrylate, butyl acrylate, and monobutyl fumarate, purified water, sodium lauryl sulfate, polyethylene glycol monostearate, and n-dodecyl mercaptan as a chain transfer agent. Subsequently, a portion of the monomer emulsion and purified water are charged into a polymerization reactor and cooled to 12°C. After this, the remaining monomer emulsion, ferrous sulfate, sodium ascorbate, and potassium persulfate as an inorganic radical generator are continuously added dropwise over 2.5 hours. The temperature is then maintained at 23°C and the reaction is continued for 1 hour. After this, industrial water is added and the temperature is raised to 85°C. Sodium sulfate is then continuously added at 85°C to coagulate the crumbs, resulting in hydrous crumbs. The crumbs are then washed with purified water three times and dried in a hot air dryer to produce an acrylic rubber, which is then crosslinked with 2,2-bis[4-(4-aminophenoxy)phenyl]propane. However, although the acrylic rubber obtained by this method has excellent stress relaxation properties and extrusion processability, it has problems in that it is insufficient in roll processability, Banbury processability, and storage stability, and the strength properties and water resistance of the crosslinked product are poor.

[0006] Patent Document 4 (JP 9-143229 A) discloses a method in which a monomer mixture consisting of ethyl acrylate, a special acrylate, and vinyl monochloroacetate, the emulsifier sodium lauryl sulfate, n-octyl mercaptan as a chain transfer agent, and water are added to a reaction vessel, and after nitrogen substitution, ammonium hydrogen sulfite and sodium persulfate as an inorganic radical generator are added to initiate the polymerization reaction, which is copolymerized at 55°C for 3 hours with a reaction conversion rate of 93-96% to produce acrylic rubber, which is then crosslinked with sulfur. However, the acrylic rubber obtained by this method has problems such as insufficient Banbury processability and poor strength properties and water resistance of the crosslinked product.

[0007] Patent Document 5 (JP 62-64809 A) discloses an acrylic rubber that is excellent in processability, compression set, and tensile strength and that can be sulfur vulcanized, and is characterized by a copolymer having a monomer composition consisting of 50 to 99.9% by weight of at least one compound selected from acrylic acid alkyl esters and acrylic acid alkoxyalkyl esters, 0.1 to 20% by weight of a dihydrodicyclopentenyl group-containing ester of an unsaturated carboxylic acid having a radical reactive group, and 0 to 20% by weight of at least one other monovinyl-, monovinylidene-, and monovinylene-based unsaturated compound, and that has a number average molecular weight (Mn) of 200,000 to 1,200,000 calculated as polystyrene using tetrahydrofuran as a developing solvent, and a ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 10 or less. It also states that the number average molecular weight (Mn) should be 200,000 to 1,000,000, preferably 200,000 to 1,000,000, and that if Mn is less than 200,000, the physical properties and processability of the vulcanized product will be poor, and if it exceeds 1,200,000, the processability will be poor. It also states that if the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (Mw / Mn) exceeds 10, the compression set will increase, which is undesirable. As a specific example, a manufacturing method is disclosed in which monomer components including ethyl acrylate and radically crosslinkable dihydrodicyclopentenyl acrylate, an emulsifier sodium lauryl sulfate, an inorganic radical generator potassium persulfate, and molecular weight regulators octyl thioglycolate or t-dodecyl mercaptan are added in varying amounts to polymerize an acrylic rubber having a number average molecular weight (Mn) of 530,000 to 1,150,000, a weight average molecular weight (Mw) of 3,540,000 to 6,260,000, and a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (Mw / Mn) of 4.7 to 8, and then coagulate the resulting acrylic rubber in an aqueous calcium chloride solution, thoroughly wash with water, and directly dry. Furthermore, when the amount of chain transfer agent is small, the number average molecular weight (Mw) of the resulting acrylic rubber is as large as 5 million and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is as narrow as 1.4, while when the amount of chain transfer agent is large, the number average molecular weight (Mn) is as small as 200,000 and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is as extremely wide as 17, as shown in the examples and comparative examples.However, the acrylic rubber obtained by this method is inferior in compression set resistance and storage stability, and because it contains radical reactive groups, even if a suitable molecular weight distribution (Mw / Mn) is obtained by polymerization using a radical generator, the molecular weight (Mw, Mn) becomes too large and complex, resulting in insufficient Banbury processability and roll processability. Furthermore, the acrylic rubber obtained by this method is subjected to a crosslinking reaction in which sulfur and a vulcanization accelerator are added as crosslinking agents, and the rubber is kneaded with a roll at 100 kg / cm. 2 However, there were problems with this method, such as the need for a long crosslinking time, which required 15 minutes at 170°C in a vulcanizing press and then 4 hours at 175°C in a gear oven, and the resulting crosslinked product also had poor compression set resistance, water resistance, and strength, and was also poor in terms of changes in physical properties after thermal degradation.

[0008] On the other hand, with regard to acrylic rubber to be made into sheets, for example, Patent Document 6 (JP 2019-119772 A) describes a method of preparing a monomer emulsion from monomer components consisting of ethyl acrylate, butyl acrylate, methoxyethyl acrylate, and monobutyl maleate using pure water and emulsifiers sodium lauryl sulfate and polyoxyethylene dodecyl ether, and then charging a portion of the monomer emulsion into a polymerization reactor and cooling it to 12°C under a nitrogen gas flow, followed by adding the remaining monomer emulsion, ferrous sulfate, sodium ascorbate, and inorganic radical generating agent. The method disclosed involves continuously adding dropwise an aqueous solution of potassium persulfate as an emulsion polymerization agent over a period of three hours, subsequently maintaining the temperature at 23°C and continuing emulsion polymerization for one hour until the polymerization conversion reaches 97% by weight, at which point the temperature is raised to 85°C and sodium sulfate is continuously added to coagulate and filter to obtain hydrous crumbs, which are then washed four times with water, once with acid, and once with pure water, after which an acrylic rubber sheet is continuously produced in an extruder dryer equipped with a screw, and the resulting crosslinked acrylic rubber is crosslinked with an aliphatic polyamine compound such as hexamethylenediamine carbamate. However, the sheet-form acrylic rubber obtained by this method has problems of poor roll processability and storage stability, and the crosslinked product has poor water resistance.

[0009] Regarding the gel content of acrylic rubber, for example, Patent Document 7 (Japanese Patent No. 3599962) discloses an acrylic rubber composition with excellent extrusion processability, such as extrusion speed, die swell, and surface texture, which is 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 of different reactivity in the presence of a radical polymerization initiator. The acrylic rubber composition is composed of a reinforcing filler and an organic peroxide-based vulcanizing agent, and has a gel fraction (acetone-insoluble matter) of 5% by weight or less. The acrylic rubber composition has a very low gel fraction, and is obtained by adjusting the pH of the polymerization solution to 6-8 using sodium bicarbonate or the like, compared to the high-gel-fraction (60%) acrylic rubber obtained in a polymerization solution with a normal acidic pH (pH 4 before polymerization, pH 3.4 after polymerization). Specifically, water, emulsifiers sodium lauryl sulfate and polyoxyethylene nonylphenyl ether, sodium carbonate, and boric acid were charged and adjusted to 75°C, followed by the addition of organic radical generators t-butyl hydroperoxide, Rongalit, disodium ethylenediaminetetraacetate, and ferrous sulfate (pH 7.1 at this point). Ethyl acrylate and allyl methacrylate monomer components were then added dropwise for emulsion polymerization, and the resulting emulsion (pH 7) was salted out using an aqueous sodium sulfate solution, washed with water, and dried to yield acrylic rubber. However, acrylic rubber, whose main component is (meth)acrylate ester, decomposes in the neutral to alkaline range, and while its processability has been improved, it suffers from problems of poor storage stability and strength, as well as poor roll processability, Banbury processability, crosslinkability, and compression set resistance.

[0010] Furthermore, Patent Document 8 (International Publication No. WO 2018 / 143101) discloses a technology for improving the extrusion moldability, particularly the extrusion volume, extrusion length, and surface finish, of a rubber composition containing a reinforcing agent and a crosslinking agent, by emulsion polymerization of a (meth)acrylic acid ester and an ionically crosslinkable monomer to produce 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 also discloses that the acrylic rubber used in this technology has a gel content (THF (tetrahydrofuran) insoluble matter) of 80% by weight or less, preferably 5 to 80% by weight, and preferably as high as possible within the range of 70% or less. It also discloses that extrusion properties deteriorate when the gel content is less than 5%. It also states 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 no description of methods for improving roll processability or Banbury processability. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2019 / 188709 Brochure [Patent Document 2] Japanese Patent Application Publication No. 1-135811 [Patent Document 3] Japanese Patent Application Publication No. 2018-168343 [Patent Document 4] Japanese Patent Application Publication No. 9-143229 [Patent Document 5] Japanese Patent Application Publication No. 62-64809 [Patent Document 6] Japanese Patent Application Publication No. 2019-119772 [Patent Document 7] Patent No. 3599962 [Patent Document 8] International Publication No. 2018 / 143101 Brochure Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in view of the current state of the prior art, and has as its object to provide an acrylic rubber sheet which is excellent in both roll processability and Banbury processability, and which is also excellent in short-time crosslinkability, strength properties and compression set resistance, a method for producing the same, 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 cross-linked rubber product formed by cross-linking the same. [Means for solving the problem]

[0013] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that an acrylic rubber sheet containing ion-reactive groups and having an increased ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw), with emphasis on the absolute molecular weight and the high molecular weight component of the absolute molecular weight distribution measured by a GPC-MALS method, and having a gel content within a specific range, can provide an acrylic rubber sheet with excellent roll processability and Banbury processability, as well as extremely excellent short-time crosslinkability, strength properties, and compression set resistance.

[0014] The present inventors have found that an acrylic rubber sheet made of acrylic rubber that has ion-reactive groups that can react with crosslinking agents, such as carboxyl groups, epoxy groups, and chlorine atoms, and that has a large ratio (Mz / Mw) between the z-average molecular weight (Mz) and the weight-average molecular weight (Mw) in the absolute molecular weight distribution, with emphasis on the high molecular weight region measured by the GPC-MALS method, has excellent short-time crosslinkability, strength properties, and compression set resistance.

[0015] The present inventors have also discovered that in GPC measurement of such acrylic rubber which has ion-reactive groups and a large absolute molecular weight distribution with emphasis on the polymer region, tetrahydrofuran, which is used in GPC measurement of the above-mentioned conventional radical-reactive acrylic rubber obtained by copolymerizing ethyl acrylate with dihydrodicyclopentenyl acrylate or the like, is insufficient to dissolve the rubber, and it is not possible to measure each molecular weight and molecular weight distribution clearly and with good reproducibility. However, by using a specific solvent with a higher SP value than tetrahydrofuran as a developing solvent, it is possible to dissolve the rubber clearly and measure with good reproducibility, and moreover, by specifying the respective characteristic values, it is possible to achieve a high level of balance between the roll processability, Banbury processability, crosslinkability, strength properties and compression set resistance properties of the acrylic rubber sheet.

[0016] The inventors have found that the roll processability of acrylic rubber sheets can be improved without impairing strength properties by increasing the ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw), focusing on the high-molecular-weight component of the absolute molecular weight distribution measured by GPC-MALS. The inventors have also found that the z-average molecular weight (Mz) to weight-average molecular weight (Mw) ratio (Mz / Mw) can be increased by adding a chain transfer agent batchwise during polymerization rather than initially, preferably by adding a reducing agent later. The inventors have also found that the roll processability improves with increasing the ratio (Mw / Mn) of the weight-average molecular weight (Mw) to number-average molecular weight (Mn) of the absolute molecular weight distribution measured by GPC-MALS. They have also found that this can be achieved by adding a chain transfer agent batchwise during polymerization, more preferably by kneading and drying the water-containing crumbs at a high shear in a twin-screw extruder.

[0017] The inventors have also found that the lower the gel content of the acrylic rubber sheet, the better the Banbury processability of the acrylic rubber sheet. The gel content of the acrylic rubber sheet, preferably the gel content of methyl ethyl ketone-insoluble matter, is generated during the polymerization reaction of the acrylic rubber, and increases rapidly and becomes difficult to control, particularly when the polymerization conversion rate is increased to improve strength properties. However, they have found that this can be suppressed to some extent by emulsion polymerization in the presence of a chain transfer agent in the latter half of the polymerization reaction, and that the rapidly increased gel content of methyl ethyl ketone-insoluble matter disappears when the acrylic rubber is melt-kneaded and extruded and dried in a screw-type twin-screw extruder in a substantially water-free state (water content less than 1% by weight), thereby significantly improving the Banbury processability of the acrylic rubber sheet without impairing its strength properties.

[0018] The inventors have also discovered that specifying the ash content and the amounts of components in the ash in an acrylic rubber sheet results in excellent roll processability, Banbury processability, short-time crosslinking, strength properties, and compression set resistance, as well as excellent water resistance. While it is difficult to reduce the ash content of acrylic rubber emulsion-polymerized using large amounts of emulsifiers and coagulants, they have found that a specific coagulation method significantly improves the efficiency of washing the water-containing crumbs with hot water and the ash removal efficiency during dehydration, dramatically reducing the ash content in the resulting acrylic rubber sheet and significantly improving water resistance. They have also found that specifying the ash components in the ash significantly improves water resistance and workability. The inventors have also discovered that using a specific emulsifier in the emulsion polymerization of acrylic rubber, or a specific coagulant in the coagulation of the emulsion polymerization liquid, results in excellent water resistance of the acrylic rubber sheet and significantly improved mold releasability.

[0019] The inventors have also discovered that by increasing the specific gravity of an acrylic rubber sheet or by controlling the pH within a specific range, the sheet exhibits excellent roll processability, Banbury processability, crosslinkability, strength properties, and compression set resistance, as well as excellent storage stability. In particular, the inventors have discovered that an acrylic rubber sheet with a high specific gravity contains no air, thereby significantly improving the storage stability of the acrylic rubber sheet. Conventional acrylic rubber sheets contain a large amount of air when the water-containing crumbs produced in the coagulation process are dried, which deteriorates the sheet's storage stability. However, the inventors have discovered that by directly drying the water-containing crumbs and compressing the resulting dried rubber using a high-pressure baler or similar device, the specific gravity of the molded product can be slightly increased, thereby improving the sheet's storage stability. Preferably, the water-containing crumbs produced in the coagulation process are dried in a specific extrusion dryer in an air-free state, and the resulting dried rubber is then extruded into a sheet, thereby producing an acrylic rubber sheet with significantly improved storage stability.

[0020] The present inventors have also found that by increasing the cooling rate after drying, it is possible to significantly improve the Mooney scorch stability of the acrylic rubber sheet without impairing its properties such as roll processability, Banbury processability, water resistance, strength properties, and compression set resistance.

[0021] The present inventors have also found that by controlling the monomer composition of the acrylic rubber, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), the number average molecular weight (Mn), the weight average molecular weight (Mw), the complex viscosity at 60°C ([η]60°C), and the ratio ([η]100°C / [η]60°C) of the complex viscosity at 100°C ([η]100°C) to the complex viscosity at 60°C ([η]60°C), respectively, within specific ranges, the roll processability, Banbury processability, crosslinkability, strength properties, and compression set resistance properties are further highly improved, and that by using a polyvalent organic compound as a crosslinking agent, the short-term crosslinkability and the properties of the obtained cross-linked rubber product are further greatly improved.

[0022] The present inventors have also discovered that an acrylic rubber sheet can be obtained that has a wide molecular weight distribution with an emphasis on the high molecular weight region, a small amount of gel, and excellent roll processability, Banbury processability, crosslinkability, strength properties, and compression set resistance by emulsifying specific monomer components with water and an emulsifier, then initiating emulsion polymerization in the presence of a redox catalyst composed of an inorganic radical generator such as potassium persulfate and a reducing agent, adding a chain transfer agent batchwise during the polymerization without adding it initially, and dehydrating, drying, and molding the water-containing crumbs produced by coagulation using a specific screw-type extruder dryer.

[0023] The present inventors have further found that by melt-kneading and drying acrylic rubber under high-shear conditions using a specific extrusion dryer, it is possible to produce an acrylic rubber sheet with further improved roll processability, Banbury processability, short-time crosslinkability, strength properties, and compression set resistance properties.

[0024] The present inventors have also found that by laminating acrylic rubber sheets that are excellent in roll processability, Banbury processability, short-time crosslinking ability, strength properties, and compression set resistance, as well as in storage stability and water resistance, it is possible to easily produce an acrylic rubber veil that is excellent in operability, storage stability, roll processability, Banbury processability, short-time crosslinking ability, water resistance, strength properties, and compression set resistance.

[0025] The present inventors have further discovered that in a rubber mixture containing the acrylic rubber sheet or acrylic rubber veil of the present invention, a filler, and a crosslinking agent, the incorporation of carbon black or silica as a filler results in excellent roll processability, Banbury processability, and short-time crosslinking, and the crosslinked product has excellent water resistance, strength, and compression set resistance. The present inventors have also discovered that the crosslinking agent is preferably an organic compound, a polyvalent compound, or an ionic crosslinking compound, and that a polyvalent ionic organic compound having multiple ion-reactive groups that react with the ion-reactive groups of the acrylic rubber veil, such as amine groups, epoxy groups, carboxyl groups, or thiol groups, results in excellent roll processability, Banbury processability, and short-time crosslinking, and the crosslinked product has excellent water resistance, strength, and compression set resistance.

[0026] Based on these findings, the present inventors have completed the present invention.

[0027] Thus, the present invention provides an acrylic rubber sheet having an ion-reactive group, a ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) in the absolute molecular weight distribution measured by the GPC-MALS method of 1.8 or more, and a gel content of 30% by weight or less.

[0028] In the acrylic rubber sheet of the present invention, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the absolute molecular weight distribution measured by the GPC-MALS method is preferably 3.5 or more. In the acrylic rubber sheet of the present invention, the number average molecular weight (Mn) of the absolute molecular weight measured by the GPC-MALS method is preferably in the range of 100,000 to 500,000.

[0029] In the acrylic rubber sheet of the present invention, the weight average molecular weight (Mw) of the absolute molecular weight measured by the GPC-MALS method is preferably in the range of 1,000,000 to 3,500,000. In the acrylic rubber sheet of the present invention, the measurement solvent in the GPC-MALS method is preferably a dimethylformamide-based solvent.

[0030] In the acrylic rubber sheet of the present invention, the gel content is preferably 15% by weight or less. In the acrylic rubber sheet of the present invention, the gel content is preferably the amount insoluble in methyl ethyl ketone.

[0031] In the acrylic rubber sheet of the present invention, it is preferable that the acrylic rubber comprises bonding units derived from at least one (meth)acrylic acid ester selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, bonding units derived from an ion-reactive group-containing monomer, and bonding units derived from other monomers. In the acrylic rubber sheet of the present invention, the ash content is preferably 1% by weight or less.

[0032] In the acrylic rubber sheet of the present invention, the total amount of sodium, magnesium, calcium, phosphorus, and sulfur in the ash is preferably 50% by weight or more. In the acrylic rubber sheet of the present invention, the complex viscosity at 60° C. ([η]60° C.) is preferably 15,000 [Pa·s] or less.

[0033] In the acrylic rubber sheet of the present invention, 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 preferably 0.8 or more. In the acrylic rubber sheet of the present invention, the pH is preferably in the range of 3-6.

[0034] The acrylic rubber sheet of the present invention is preferably a melt-kneaded sheet. In the acrylic rubber sheet of the present invention, the acrylic rubber content in the acrylic rubber sheet is preferably 90% by weight or more.

[0035] The acrylic rubber sheet of the present invention is preferably obtained by emulsion polymerization using a phosphate ester salt or a sulfate ester salt as an emulsifier, and is preferably obtained by coagulating the emulsion-polymerized polymerization liquid using an alkali metal salt or a Group 2 metal salt of the periodic table as a coagulant, and then drying the solidified liquid.

[0036] The acrylic rubber sheet of the present invention is preferably one that has been melt-kneaded and dried after solidification, and the melt-kneading and drying are preferably carried out in a substantially moisture-free state and under reduced pressure. Furthermore, the acrylic rubber sheet of the present invention is preferably one that has been cooled at a cooling rate of 40°C / hr or more after the melt-kneading and drying.

[0037] The present invention also provides a method for producing an acrylic rubber sheet, which includes the following steps: a step of emulsifying an acrylic rubber monomer component containing an ion-reactive group-containing monomer with water and an emulsifier; an emulsion polymerization step of initiating a polymerization reaction in the presence of a redox catalyst containing an inorganic radical generator and a reducing agent and continuing the polymerization by post-adding a chain transfer agent batchwise during the polymerization to obtain an emulsion polymerization liquid; a coagulation step of coagulating the obtained emulsion polymerization liquid with a coagulation liquid to produce water-containing crumbs; a washing step of washing the produced water-containing crumbs; a step of dehydrating the washed water-containing crumbs in the dehydration barrel using a screw-type twin-screw extrusion dryer having a dehydration slit, a drying barrel under reduced pressure, and a die at the tip, to a water content of 1 to 40% by weight; a drying step of drying in the drying barrel to a water content of less than 1% by weight; and a molding step of extruding the dried rubber sheet through the die.

[0038] The method for producing an acrylic rubber sheet of the present invention is preferably a method for producing the above-mentioned acrylic rubber sheet. In the method for producing an acrylic rubber sheet of the present invention, the maximum torque of the screw-type twin-screw extruder dryer is preferably 25 N·m or more. In the method for producing an acrylic rubber sheet of the present invention, it is preferable that the reducing agent is added later.

[0039] In the method for producing an acrylic rubber sheet of the present invention, it is preferable to carry out emulsion polymerization using a phosphate ester salt or a sulfate ester salt as an emulsifier in the emulsion polymerization step. In the method for producing an acrylic rubber sheet of the present invention, it is preferable to coagulate the polymerization liquid produced in the emulsion polymerization step using an alkali metal salt or a Group 2 metal salt of the periodic table as a coagulant, and then dry it. In the method for producing an acrylic rubber sheet of the present invention, it is preferable to add the polymerization liquid produced in the emulsion polymerization step to an aqueous solution containing a coagulant containing an alkali metal salt or a Group 2 metal salt of the periodic table, and to coagulate the mixture by stirring.

[0040] In the method for producing an acrylic rubber sheet of the present invention, it is preferable that the polymer liquid produced in the emulsion polymerization step is brought into contact with a coagulant to be coagulated, and then melt-kneaded and dried. In the method for producing an acrylic rubber sheet of the present invention, the melt-kneading and drying are preferably carried out in a state that is substantially free of moisture. In the method for producing an acrylic rubber sheet of the present invention, the melt-kneading and drying are preferably carried out under reduced pressure.

[0041] In the method for producing an acrylic rubber sheet of the present invention, it is preferable to cool the acrylic rubber after melt-kneading and drying at a cooling rate of 40° C. / hr or more.

[0042] The present invention also provides an acrylic rubber veil formed by laminating the above acrylic rubber sheets. In the acrylic rubber bale of the present invention, when the amount of gel in the acrylic rubber bale is arbitrarily sampled at multiple points and the variation is measured, it is preferable that all of the values ​​measured for the samples fall within the range of (average value ±5) weight %. In the acrylic rubber veil of the present invention, the multiple sampling is preferably 20-point sampling. The acrylic rubber veil of the present invention preferably has a specific gravity of 0.8 or more.

[0043] The present invention also provides a rubber mixture comprising the above-mentioned acrylic rubber sheet and / or acrylic rubber veil, a filler, and a crosslinking agent.

[0044] In the rubber mixture of the present invention, the filler is preferably a reinforcing filler. Also, in the rubber mixture of the present invention, the filler is preferably a carbon black. Also, in the rubber mixture of the present invention, the filler is preferably a silica.

[0045] In the rubber mixture of the present invention, the crosslinking agent is preferably an organic crosslinking agent. Also, in the rubber mixture of the present invention, the crosslinking agent is preferably a polyvalent compound. Also, in the rubber mixture of the present invention, the crosslinking agent is preferably an ionically crosslinkable compound. Also, in the rubber mixture of the present invention, the crosslinking agent is preferably an ionically crosslinkable organic compound. Also, in the rubber mixture of the present invention, the crosslinking agent is preferably a polyvalent ionic organic compound.

[0046] In the rubber mixture of the present invention, the ion of the ion-crosslinking compound, ion-crosslinking organic compound or polyvalent ionic organic compound serving as the crosslinking agent is preferably at least one ion-reactive group selected from the group consisting of an amino group, an epoxy group, a carboxyl group and a thiol group.

[0047] In the rubber mixture of the present invention, the crosslinking agent is preferably at least one polyvalent ion compound selected from the group consisting of polyvalent amine compounds, polyvalent epoxy compounds, polyvalent carboxylic acid compounds, and polyvalent thiol compounds.

[0048] In the rubber mixture of the present invention, the content of the crosslinking agent is preferably in the range of 0.001 to 20 parts by weight per 100 parts by weight of the rubber component.

[0049] The rubber mixture of the present invention preferably further contains an antioxidant, and the antioxidant is preferably an amine-based antioxidant.

[0050] The present invention also provides a method for producing a rubber mixture, which comprises mixing a rubber component containing the acrylic rubber sheet or the acrylic rubber veil, a filler, and, if necessary, an antioxidant, and then mixing a crosslinking agent therein.

[0051] The present invention further provides a cross-linked rubber product obtained by cross-linking the above rubber mixture. In the cross-linked rubber product of the present invention, it is preferable that the cross-linking of the rubber mixture is carried out after molding. Furthermore, in the cross-linked rubber product of the present invention, it is preferable that the cross-linking of the rubber mixture is carried out by primary cross-linking and secondary cross-linking. [Effects of the Invention]

[0052] According to the present invention, there are provided an acrylic rubber sheet that is highly excellent in roll processability, Banbury processability, short-time crosslinkability, strength properties, and compression set resistance properties, an efficient method for producing the same, an acrylic rubber veil formed by laminating the acrylic rubber sheet, a high-quality rubber mixture formed by mixing the acrylic rubber sheet or the acrylic rubber veil, and a cross-linked rubber product obtained by cross-linking the same. [Brief explanation of the drawings]

[0053] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of an acrylic rubber production system used to produce an acrylic rubber sheet and an acrylic rubber bale according to one embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the configuration of the screw extruder of FIG. 1. [Figure 3] FIG. 2 is a diagram showing the configuration of a transportable cooling device used as the cooling device in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0054] The acrylic rubber sheet of the present invention is characterized by comprising an acrylic rubber having ion-reactive groups, a ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) in the absolute molecular weight distribution measured by the GPC-MALS method, of 1.8 or more, and a gel content of 30% by weight or less. Here, the term "GPC-MALS method" refers to the following: GPC (gel permeation chromatography) is a type of liquid chromatography that separates molecules based on differences in molecular size. This method incorporates a multi-angle laser light scattering photometer (MALS) and a differential refractometer (RI) into the GPC apparatus. The light scattering intensity and refractive index difference of a molecular chain solution that has been size-fractionated by the GPC apparatus are measured over the melting time, allowing the molecular weight of the solute and its content to be calculated sequentially, ultimately determining the absolute molecular weight distribution and absolute average molecular weight of the polymeric substance.

[0055] <Ion-reactive group> The acrylic rubber sheet of the present invention is characterized by having an ion-reactive group. The ion-reactive group is not particularly limited as long as it is a functional group that undergoes an ion reaction, but is preferably at least one functional group selected from the group consisting of a carboxyl group, an epoxy group, and a chlorine atom, more preferably an epoxy group or a carboxyl group, and particularly preferably a carboxyl group.

[0056] The ion-reactive group content of the acrylic rubber sheet of the present invention is not particularly limited and may be selected appropriately depending on the intended use, but when the weight ratio of the ion-reactive groups themselves is in the range of usually 0.001 to 5 wt %, preferably 0.01 to 3 wt %, more preferably 0.05 to 1 wt %, and particularly preferably 0.1 to 0.5 wt %, it is suitable because it provides a high level of balance in processability and crosslinkability, as well as in the properties of the crosslinked product, such as strength, compression set resistance, oil resistance, cold resistance, and water resistance.

[0057] The acrylic rubber sheet having an ion-reactive group of the present invention may be an acrylic rubber into which an ion-reactive group has been introduced by a post-reaction, but is preferably made of an acrylic rubber copolymerized with a monomer containing an ion-reactive group.

[0058] <Monomer component> The monomer component of the acrylic rubber constituting the acrylic rubber sheet of the present invention is not particularly limited as long as it is a monomer constituting a normal acrylic rubber, but is preferably an acrylic rubber monomer component containing an ion-reactive group-containing monomer, more preferably at least one (meth)acrylic acid ester selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, the ion-reactive group-containing monomer, and, as necessary, other copolymerizable monomers. In the present invention, "(meth)acrylic acid ester" is used as a general term for esters of acrylic acid and / or methacrylic acid.

[0059] The (meth)acrylic acid alkyl ester is not particularly limited, but typically, a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 12 carbon atoms, preferably a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 8 carbon atoms, and more preferably a (meth)acrylic acid alkyl ester having an alkyl group with 2 to 6 carbon atoms is used.

[0060] Specific examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. Of these, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred.

[0061] The (meth)acrylic acid alkoxyalkyl ester is not particularly limited, but typically an (meth)acrylic acid alkoxyalkyl ester having an alkoxyalkyl group of 2 to 12, preferably an (meth)acrylic acid alkoxyalkyl ester having an alkoxyalkyl group of 2 to 8, more preferably an (meth)acrylic acid alkoxyalkyl ester having an alkoxyalkyl group of 2 to 6 carbon atoms is used.

[0062] 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 and ethoxyethyl acrylate are more preferred.

[0063] 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 may be used either alone or in combination of two or more. When the proportion of this ester in the total monomer components is generally in the range of 50 to 99.99% by weight, preferably 62 to 99.95% by weight, more preferably 74 to 99.9% by weight, particularly preferably 80 to 99.5% by weight, and most preferably 87 to 99% by weight, the acrylic rubber sheet will be suitably excellent in weather resistance, heat resistance, and oil resistance.

[0064] The ion-reactive group-containing monomer is not particularly limited as long as it has a functional group involved in an ionic reaction, and may be appropriately selected depending on the intended use. Usually, it includes a monomer having at least one functional group selected from the group consisting of a carboxyl group, an epoxy group, and a chlorine atom. Preferably, it is a monomer having a carboxyl group and an epoxy group, and more preferably, it is a monomer having a carboxyl group, which can highly improve the short-term crosslinkability and the compression set resistance and water resistance of the crosslinked product.

[0065] The monomer having a carboxyl group is not particularly limited, but an ethylenically unsaturated carboxylic acid can be suitably used. Examples of the ethylenically unsaturated carboxylic acid include an ethylenically unsaturated monocarboxylic acid, an ethylenically unsaturated dicarboxylic acid, and an ethylenically unsaturated dicarboxylic acid monoester. Among these, an ethylenically unsaturated dicarboxylic acid monoester is particularly preferred because it can further improve the compression set resistance when the acrylic rubber sheet is made into a rubber cross-linked product.

[0066] The ethylenically unsaturated monocarboxylic acid is not particularly limited, but is preferably an ethylenically unsaturated monocarboxylic acid having 3 to 12 carbon atoms, such as acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, and cinnamic acid.

[0067] The ethylenically unsaturated dicarboxylic acid is not particularly limited, but is preferably an ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms, and examples thereof include butenedioic acids such as fumaric acid and maleic acid, itaconic acid, citraconic acid, etc. The ethylenically unsaturated dicarboxylic acid also includes those that exist as an anhydride.

[0068] The ethylenically unsaturated dicarboxylic acid monoester is not particularly limited, but typically includes an ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms and an alkyl monoester having 1 to 12 carbon atoms, preferably an ethylenically unsaturated dicarboxylic acid having 4 to 6 carbon atoms and an alkyl monoester having 2 to 8 carbon atoms, and more preferably an alkyl monoester having 2 to 6 carbon atoms of butenedioic acid having 4 carbon atoms.

[0069] Specific examples of the ethylenically unsaturated dicarboxylic acid monoester include butenedioic acid monoalkyl esters such as 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 itaconic acid monoalkyl esters such as monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, and monocyclohexyl itaconate; and among these, mono-n-butyl fumarate and mono-n-butyl maleate are preferred, with mono-n-butyl fumarate being particularly preferred.

[0070] Examples of the monomer 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.

[0071] The monomer having a chlorine atom is not particularly limited, and examples thereof include unsaturated alcohol esters of chlorine atom-containing saturated carboxylic acids, (meth)acrylic acid chloroalkyl esters, (meth)acrylic acid chloroacyloxyalkyl esters, (meth)acrylic acid (chloroacetylcarbamoyloxy)alkyl esters, chlorine atom-containing unsaturated ethers, chlorine atom-containing unsaturated ketones, chloromethyl group-containing aromatic vinyl compounds, chlorine atom-containing unsaturated amides, and chloroacetyl group-containing unsaturated monomers.

[0072] Specific examples of unsaturated alcohol esters of chlorine-containing saturated carboxylic acids include vinyl chloroacetate, vinyl 2-chloropropionate, and allyl chloroacetate. Specific examples of (meth)acrylic acid chloroalkyl esters include chloromethyl (meth)acrylate, 1-chloroethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 1,2-dichloroethyl (meth)acrylate, 2-chloropropyl (meth)acrylate, 3-chloropropyl (meth)acrylate, and 2,3-dichloropropyl (meth)acrylate. Specific examples of (meth)acrylic acid chloroacyloxyalkyl 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 (chloroacetylcarbamoyloxy) alkyl esters include 2-(chloroacetylcarbamoyloxy)ethyl (meth)acrylate and 3-(chloroacetylcarbamoyloxy)propyl (meth)acrylate. Specific examples of chlorine atom-containing unsaturated ethers include chloromethyl vinyl ether, 2-chloroethyl vinyl ether, 3-chloropropyl vinyl ether, 2-chloroethyl allyl ether, and 3-chloropropyl allyl ether. Specific examples of chlorine atom-containing unsaturated ketones include 2-chloroethyl vinyl ketone, 3-chloropropyl vinyl ketone, and 2-chloroethyl allyl ketone. Specific examples of chloromethyl group-containing aromatic vinyl compounds include p-chloromethylstyrene, m-chloromethylstyrene, o-chloromethylstyrene, and p-chloromethyl-α-methylstyrene. Specific examples of chlorine atom-containing unsaturated amides include N-chloromethyl(meth)acrylamide. Specific examples of the chloroacetyl group-containing unsaturated monomer include 3-(hydroxychloroacetoxy)propyl allyl ether and p-vinylbenzyl chloroacetate.

[0073] These ion-reactive group-containing monomers may be used alone or in combination of two or more, and the proportion of these in the total monomer components is usually in the range of 0.01 to 10% by weight, preferably 0.05 to 8% by weight, more preferably 0.1 to 6% by weight, particularly preferably 0.5 to 5% by weight, and most preferably 1 to 3% by weight.

[0074] Monomers other than those mentioned above (abbreviated as "other monomers" in the present invention) that can be used together with the above-mentioned monomers as needed are not particularly limited as long as they are copolymerizable with the above-mentioned monomers, and examples thereof include aromatic vinyls such as styrene, α-methylstyrene, and divinylbenzene; ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile; acrylamide-based monomers such as acrylamide and methacrylamide; and olefin-based monomers such as ethylene, propylene, vinyl acetate, ethyl vinyl ether, and butyl vinyl ether.

[0075] These other monomers may be used alone or in combination of two or more, and the proportion of these other monomers in the total monomer components is usually kept within the range of 0 to 40% by weight, preferably 0 to 30% by weight, more preferably 0 to 20% by weight, particularly preferably 0 to 15% by weight, and most preferably 0 to 10% by weight.

[0076] <Acrylic rubber> The acrylic rubber constituting the acrylic rubber sheet of the present invention has the above-mentioned ion-reactive group, and preferably comprises bonding units from at least one (meth)acrylic acid ester selected from the group consisting of the above-mentioned (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, an ion-reactive group-containing monomer, and other monomers contained as necessary, and the proportion of each in the acrylic rubber is usually 50 to 99.9%. The content of the bonding units derived from the ion-reactive group-containing monomer is usually 0.01 to 10% by weight, preferably 0.05 to 8% by weight, more preferably 0.1 to 6% by weight, particularly preferably 0.5 to 5% by weight, and most preferably 1 to 3% by weight, and the content of the bonding units derived from other monomers is usually 0 to 40% by weight, preferably 0 to 30% by weight, more preferably 0 to 20% by weight, particularly preferably 0 to 15% by weight, and most preferably 0 to 10% by weight. When the monomer composition of the acrylic rubber is within this range, the acrylic rubber sheet is suitably provided with a highly balanced range of properties such as short-term crosslinkability, compression set resistance, weather resistance, heat resistance, and oil resistance.

[0077] The measurement solvent for the GPC-MALS method used to measure the absolute molecular weight and absolute molecular weight distribution of the acrylic rubber constituting the acrylic rubber sheet of the present invention is not particularly limited as long as it can dissolve and measure the acrylic rubber sheet of the present invention, but dimethylformamide-based solvents are preferred. The dimethylformamide-based solvent used is not particularly limited as long as it is primarily composed of dimethylformamide, but is preferably 100% dimethylformamide or a dimethylformamide-based solvent with a dimethylformamide content of 90 wt%, preferably 95 wt%, and more preferably 97 wt% or higher. The compound added to dimethylformamide is not particularly limited, but in the present invention, a solution in which dimethylformamide is added with 0.05 mol / L of lithium chloride and 0.01% of 37% concentrated hydrochloric acid at concentrations of 0.05 mol / L and 0.01% is particularly preferred.

[0078] The number average molecular weight (Mn) of the acrylic rubber constituting the acrylic rubber sheet of the present invention is not particularly limited, but when the absolute molecular weight measured by the GPC-MALS method is in the range of usually 100,000 to 500,000 (100,000 to 500,000), preferably 200,000 to 480,000, more preferably 250,000 to 450,000, particularly preferably 300,000 to 400,000, and most preferably 350,000 to 400,000, the roll processability, strength properties, and compression set resistance of the acrylic rubber sheet are well balanced, making it suitable.

[0079] There are no particular limitations on the weight-average molecular weight (Mw) of the acrylic rubber constituting the acrylic rubber sheet of the present invention, and it may be selected appropriately depending on the intended use. However, when the absolute molecular weight measured by the GPC-MALS method is in the range of usually 1,000,000 to 3,500,000 (1,000,000 to 3,500,000), preferably 1,200,000 to 3,000,000, more preferably 1,300,000 to 3,000,000, particularly preferably 1,500,000 to 2,500,000, and most preferably 1,900,000 to 2,100,000, the acrylic rubber sheet will have a high level of balance in terms of roll processability, strength properties, and compression set resistance.

[0080] There are no particular limitations on the z-average molecular weight (Mz) of the acrylic rubber constituting the acrylic rubber sheet of the present invention, and it may be selected appropriately depending on the intended use. However, when the absolute molecular weight, with emphasis on the high molecular weight region measured by the GPC-MALS method, is in the range of usually 1,500,000 to 6,000,000 (1.5 million to 6 million), preferably 2,000,000 to 5,000,000, more preferably 2,500,000 to 4,500,000, and particularly preferably 3,000,000 to 4,000,000, the acrylic rubber sheet will have a highly balanced z-average molecular weight, suitable for achieving a high level of balance in terms of roll processability, Banbury processability, strength properties, and compression set resistance.

[0081] The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the acrylic rubber constituting the acrylic rubber sheet of the present invention is not particularly limited, but is usually 3 or more, preferably 3.4 or more, more preferably 3.5 or more, particularly preferably 3.6 or more, and most preferably 3.7 or more, in terms of absolute molecular weight distribution measured by GPC-MALS. An excessively small ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the acrylic rubber is undesirably poor in roll processability. The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the acrylic rubber constituting the acrylic rubber sheet of the present invention is also preferably in the range of usually 3.7 to 6.5, preferably 3.8 to 6.2, more preferably 4 to 6, particularly preferably 4, 5 to 5.7, and most preferably 4.7 to 5.5, because this provides a high level of balance between the roll processability of the acrylic rubber sheet and the strength and compression set resistance properties after crosslinking.

[0082] 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, expressed as an absolute molecular weight distribution with emphasis on the high molecular weight region measured by the GPC-MALS method, is preferably 1.8 or more, more preferably in the range of 1.8 to 2.4, and even more preferably 1.8 to 2, which is suitable because the roll processability and Banbury processability can be highly improved without impairing the strength properties of the acrylic rubber sheet.

[0083] The glass transition temperature (Tg) of the acrylic rubber constituting the acrylic rubber sheet of the present invention may be selected appropriately depending on the intended use of the acrylic rubber, but is generally excellent in processability and cold resistance when it is 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 generally -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, excellent oil resistance and heat resistance can be achieved, and by setting it at or below the upper limit, excellent processability, crosslinkability, and cold resistance can be achieved.

[0084] <Acrylic rubber sheet> The acrylic rubber sheet of the present invention is characterized by having the ion-reactive group, preferably made of the acrylic rubber described above, and having a specific gel content. The gel content of the acrylic rubber sheet of the present invention is not particularly limited and may be selected appropriately depending on the intended use, but a methyl ethyl ketone insoluble content of 30% by weight or less, preferably 20% by weight or less, more preferably 15% by weight or less, particularly preferably 10% by weight or less, and most preferably 5% by weight or less is preferred, as this highly improves processability during Banbury kneading, etc. The acrylic rubber sheet of the present invention is also preferred when the water-containing crumbs produced in the coagulation reaction are melt-kneaded and dried in a screw-type twin-screw extruder in a state where most of the water has been removed (water content less than 1% by weight), as this highly balances Banbury processability and strength properties.

[0085] The ash content of the acrylic rubber sheet of the present invention is not particularly limited and may be selected appropriately depending on the intended use, 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. When the ash content is within this range, a high level of balance between water resistance, strength properties, and processability is achieved, which is suitable.

[0086] There is no particular limitation on the lower limit of the ash content of the acrylic rubber sheet of the present invention, and it may be selected appropriately depending on the intended use. However, an ash content of typically 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 is suitable, as this reduces adhesion of the rubber to metal and improves workability.

[0087] When the acrylic rubber sheet of the present invention has a high balance of water resistance, strength properties, processability, and workability, the ash content is usually in the range of 0.0001 to 0.5% by weight, preferably 0.0005 to 0.3% by weight, more preferably 0.001 to 0.2% by weight, particularly preferably 0.005 to 0.15% by weight, and most preferably 0.01 to 0.13% by weight.

[0088] The total amount of sodium, magnesium, calcium, phosphorus, and sulfur in the ash of the acrylic rubber sheet of the present invention is not particularly limited and may be selected appropriately depending on the intended use, but the water resistance of the acrylic rubber sheet is highly improved when the total amount is usually 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more. Furthermore, when the total amount of sodium, magnesium, calcium, phosphorus, and sulfur in the ash of the acrylic rubber sheet of the present invention is within this range, metal adhesion is reduced and workability is excellent, making it preferable.

[0089] The total amount of magnesium and phosphorus in the ash of the acrylic rubber sheet of the present invention is not particularly limited and may be selected appropriately depending on the intended use, but when it is usually 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more, the acrylic rubber sheet has a high balance of water resistance, strength properties, and processability, which is preferred. Furthermore, when the total amount of magnesium and phosphorus in the ash of the acrylic rubber sheet of the present invention is within this range, metal adhesion is reduced and workability is excellent, which is preferred.

[0090] The amount of magnesium in the ash of the acrylic rubber sheet of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but is usually 10% by weight or more, preferably 15 to 60% by weight, more preferably 20 to 50% by weight, particularly preferably 25 to 45% by weight, and most preferably 30 to 40% by weight. The amount of phosphorus in the ash of the acrylic rubber sheet of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but is usually 10% by weight or more, preferably 20 to 90% by weight, more preferably 30 to 80% by weight, particularly preferably 40 to 70% by weight, and most preferably 50 to 60% by weight.

[0091] The ratio of magnesium to phosphorus in the ash of the acrylic rubber sheet of the present invention ([Mg] / [P]) is not particularly limited and may be selected appropriately depending on the intended use, but when the ratio is in the range of usually 0.4 to 2.5, preferably 0.45 to 1.2, more preferably 0.45 to 1, particularly preferably 0.5 to 0.8, and most preferably 0.55 to 0.7 by weight, the acrylic rubber sheet will have a highly balanced water resistance, strength properties, and processability, and is therefore suitable.

[0092] Here, the ash content in the acrylic rubber sheet is derived mainly from the emulsifier used when the monomer components are emulsified and then emulsion polymerized, and the coagulant used when the emulsion polymerization liquid is coagulated. However, the total ash content and the magnesium and phosphorus contents in the ash vary depending not only on the conditions of the emulsion polymerization step and the coagulation step, but also on the conditions of each subsequent step.

[0093] The acrylic rubber sheet of the present invention is suitable when an anionic emulsifier, cationic emulsifier, or nonionic emulsifier, preferably an anionic emulsifier, more preferably a phosphate ester salt or a sulfate ester salt, is used as an emulsifier during emulsion polymerization, as described below, because this can highly improve not only water resistance and strength properties but also mold releasability and processability. The water resistance of an acrylic rubber sheet is uniquely correlated with the ash content in the acrylic rubber and the total amount of sodium, magnesium, calcium, phosphorus, and sulfur in the ash, but the use of the above emulsifiers is suitable because it can further highly balance the water resistance, strength properties, mold releasability, and processability of the acrylic rubber sheet.

[0094] The acrylic rubber sheet of the present invention is suitable when a metal salt, preferably an alkali metal salt or a Group 2 metal salt of the periodic table, is used as a coagulant, as described below, because it can highly improve not only water resistance and strength properties but also mold releasability and processability. The water resistance of an acrylic rubber sheet is uniquely correlated with the ash content in the acrylic rubber and the total amount of sodium, magnesium, calcium, phosphorus, and sulfur in the ash, but when the above coagulants are used, the acrylic rubber sheet is suitable because it has an even higher balance of water resistance, strength properties, mold releasability, and processability.

[0095] The complex viscosity at 60°C ([η]60°C) of the acrylic rubber sheet of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but excellent processability, oil resistance, and shape retention are obtained when the complex viscosity is typically 15,000 [Pa·s] or less, preferably 1,000 to 10,000 [Pa·s], more preferably 2,000 to 5,000 [Pa·s], particularly preferably 2,500 to 4,000 [Pa·s], and most preferably 2,500 to 3,000 [Pa·s].

[0096] The complex viscosity at 100°C ([η]100°C) of the acrylic rubber sheet of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but excellent processability, oil resistance, and shape retention are obtained when the complex viscosity is typically in the range of 1,500 to 6,000 [Pa·s], preferably 2,000 to 5,000 [Pa·s], more preferably 2,300 to 4,000 [Pa·s], particularly preferably 2,500 to 3,500 [Pa·s], and most preferably 2,500 to 3,000 [Pa·s].

[0097] 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 and may be selected appropriately depending on the intended use, but is usually 0.5 or more, preferably 0.6 or more, more preferably 0.7 or more, particularly preferably 0.8 or more, and most preferably 0.83 or more. The ratio ([η]100°C / [η]60°C) of the complex viscosity at 100°C ([η]100°C) to the complex viscosity at 60°C ([η]60°C) of the acrylic rubber sheet of the present invention is also preferably in the range of 0.5 to 0.99, preferably 0.6 to 0.98, more preferably 0.7 to 0.97, particularly preferably 0.8 to 0.96, and most preferably 0.85 to 0.95, which provides a high level of balance between processability, oil resistance, and shape retention.

[0098] There are no particular limitations on the water content of the acrylic rubber sheet of the present invention, and it is selected appropriately depending on the intended use. However, when the water content is generally less than 1% by weight, preferably 0.8% by weight or less, and more preferably 0.6% by weight or less, the vulcanization characteristics of the acrylic rubber sheet are optimized and properties such as heat resistance and water resistance are highly improved, which is preferable.

[0099] The pH of the acrylic rubber sheet of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but the storage stability of the acrylic rubber sheet is highly improved when the pH is generally 6 or less, preferably in the range of 3 to 6, and more preferably in the range of 3 to 5.

[0100] The Mooney viscosity (ML1+4, 100°C) of the acrylic rubber sheet of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but when it is usually in the range of 10 to 150, preferably 20 to 100, and more preferably 25 to 70, the processability and strength properties of the acrylic rubber sheet are well balanced and it is suitable.

[0101] The specific gravity of the acrylic rubber sheet of the present invention is not particularly limited, but is generally 0.7 or higher, preferably 0.8 or higher, more preferably 0.9 or higher, particularly preferably 0.95 or higher, and most preferably 1 or higher, which is suitable for achieving excellent storage stability with almost no air trapped within. Furthermore, the specific gravity of the acrylic rubber sheet of the present invention is generally within the range of 0.7 to 1.6, preferably 0.8 to 1.5, more preferably 0.9 to 1.4, particularly preferably 0.95 to 1.3, and most preferably 1.0 to 1.2, which is suitable for achieving a high balance of productivity, storage stability, and the stability of the crosslinking properties of the crosslinked product. An excessively low specific gravity of the acrylic rubber sheet indicates a large amount of air trapped within the acrylic rubber sheet, which is undesirable because it significantly affects storage stability, including oxidation degradation. The specific gravity of the acrylic rubber sheet of the present invention is calculated by dividing the mass by the volume including voids, i.e., by dividing the mass measured in air by the buoyancy, and is usually measured in accordance with JIS K6268 Crosslinked Rubber - Density Measurement Method A.

[0102] The acrylic rubber sheet of the present invention is not particularly limited as long as it is in a sheet form, but when it is a melt-kneaded sheet, it is possible to reduce the gel content of methyl ethyl ketone-insoluble matter and increase the specific gravity measured by JIS K6268A method, and is therefore preferably excellent in Banbury processability and storage stability.

[0103] The acrylic rubber sheet of the present invention, when melt-kneaded and dried, exhibits a highly balanced combination of storage stability, roll processability, Banbury processability, crosslinkability, water resistance, strength, and compression set resistance. The acrylic rubber sheet is preferably produced by melt-kneading and drying the water-containing crumbs produced in the solidification reaction in a state where almost all of the water has been removed (water content less than 1% by weight) using a screw-type twin-screw extruder, resulting in a highly balanced combination of Banbury processability and strength. The acrylic rubber sheet is also preferably produced by drying the water-containing crumbs produced in the solidification reaction under reduced pressure, or by melt-kneading and drying them under reduced pressure using a screw-type twin-screw extruder, resulting in a particularly excellent and highly balanced combination of storage stability, roll processability, and strength.

[0104] The thickness of the acrylic rubber sheet of the present invention is not particularly limited and may be appropriately selected depending on the intended use, but a thickness in the range of usually 1 to 40 mm, preferably 2 to 35 mm, more preferably 3 to 30 mm, and most preferably 5 to 25 mm is suitable, as it provides a high balance of workability, storage stability, and productivity.

[0105] The width of the acrylic rubber sheet of the present invention is appropriately selected depending on the intended use, but is generally in the range of 300 to 1200 mm, preferably 400 to 1000 mm, and more preferably 500 to 800 mm, which is particularly suitable for ease of handling.

[0106] The length of the acrylic rubber sheet of the present invention is not particularly limited, but is usually in the range of 300 to 1200 mm, preferably 400 to 1000 mm, and more preferably 500 to 800 mm, which is particularly suitable for ease of handling.

[0107] <Method of manufacturing acrylic rubber sheet> The method for producing the acrylic rubber sheet is not particularly limited, but the acrylic rubber sheet can be efficiently produced by a method including: a step of emulsifying an acrylic rubber monomer component containing an ion-reactive group-containing monomer with water and an emulsifier; an emulsion polymerization step of initiating a polymerization reaction in the presence of a redox catalyst containing an inorganic radical generator and a reducing agent, and continuing the polymerization by post-adding a chain transfer agent batchwise during the polymerization to obtain an emulsion polymerization liquid; a coagulation step of coagulating the obtained emulsion polymerization liquid with a coagulation liquid to produce water-containing crumbs; a washing step of washing the produced water-containing crumbs; a step of dehydrating the washed water-containing crumbs in a dehydration barrel using a screw-type twin-screw extrusion dryer having a dehydration slit, a drying barrel under reduced pressure, and a die at the tip; a drying step of drying in the drying barrel to a water content of less than 1% by weight; and a molding step of extruding the dried rubber sheet through a die.

[0108] (monomer component) The monomer component containing the ion-reactive group-containing monomer used in the present invention is not particularly limited, but preferably comprises at least one (meth)acrylic acid ester selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, the ion-reactive group-containing monomer, and other copolymerizable monomers as needed, and these are the same as the examples and preferred ranges of the monomer component already described. The amounts of the monomer components used are also as already described, and in emulsion polymerization, the respective monomers may be appropriately selected so as to obtain the above-mentioned composition of the acrylic rubber constituting the acrylic rubber sheet of the present invention.

[0109] (emulsifier) The emulsifier used in the present invention is not particularly limited, but examples thereof include anionic emulsifiers, cationic emulsifiers, and nonionic emulsifiers, with anionic emulsifiers being preferred.

[0110] 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; sulfates such as sodium lauryl sulfate; phosphates such as polyoxyalkylene alkyl ether phosphates; and alkyl sulfosuccinates. Among these anionic emulsifiers, phosphates and sulfates are preferred, with phosphates being particularly preferred, and divalent phosphates being most preferred, as these are suitable for achieving a high level of balance between the water resistance, strength, mold releasability, and processability of the resulting acrylic rubber sheet. Furthermore, these phosphates and sulfates are preferably alkali metal salts of phosphates and sulfates, more preferably sodium salts of phosphates and sulfates, as these are suitable for achieving a high level of balance between the water resistance, strength, mold releasability, and processability of the resulting acrylic rubber sheet.

[0111] The divalent phosphate salt is not particularly limited as long as it can be used as an emulsifier in an emulsion polymerization reaction, and examples thereof include alkyloxypolyoxyalkylene phosphate salts, alkylphenyloxypolyoxyalkylene phosphate salts, etc., and among these, metal salts of these are preferred, alkali metal salts of these are more preferred, and sodium salts of these are most preferred.

[0112] Examples of the alkyloxy polyoxyalkylene phosphate salts include alkyloxy polyoxyethylene phosphate salts and alkyloxy polyoxypropylene phosphate salts, and among these, alkyloxy polyoxyethylene phosphate salts are preferred.

[0113] Specific examples of alkyloxypolyoxyethylene phosphate ester salts include octyloxydioxyethylene phosphate ester, octyloxytrioxyethylene phosphate ester, octyloxytetraoxyethylene phosphate ester, decyloxytetraoxyethylene phosphate ester, dodecyloxytetraoxyethylene phosphate ester, tridecyloxytetraoxyethylene phosphate ester, tetradecyloxytetraoxyethylene phosphate ester, hexadecyloxytetraoxyethylene phosphate ester, octadecyloxytetraoxyethylene phosphate ester, octyloxypentaoxyethylene phosphate ester, decyloxypentaoxyethylene phosphate ester, dodecyloxypentaoxyethylene phosphate ester, tridecyloxypentaoxyethylene phosphate ester, tetradecyloxypentaoxyethylene phosphate ester, hexadecyloxypentaoxyethylene phosphate ester, octyloxypentaoxyethylene phosphate ester, and metal salts of hexaoxyethylene phosphate, octyloxyhexaoxyethylene phosphate, decyloxyhexaoxyethylene phosphate, dodecyloxyhexaoxyethylene phosphate, tridecyloxyhexaoxyethylene phosphate, tetradecyloxyhexaoxyethylene phosphate, hexadecyloxyhexaoxyethylene phosphate, octadecyloxyhexaoxyethylene phosphate, octyloxyoctaoxyethylene phosphate, decyloxyoctaoxyethylene phosphate, dodecyloxyoctaoxyethylene phosphate, tridecyloxyoctaoxyethylene phosphate, tetradecyloxyoctaoxyethylene phosphate, hexadecyloxyoctaoxyethylene phosphate, and octadecyloxyoctaoxyethylene phosphate. Among these, alkali metal salts thereof, particularly sodium salts, are preferred.

[0114] Specific examples of alkyloxypolyoxypropylene phosphate salts include octyloxydioxypropylene phosphate, octyloxytrioxypropylene phosphate, octyloxytetraoxypropylene phosphate, decyloxytetraoxypropylene phosphate, dodecyloxytetraoxypropylene phosphate, tridecyloxytetraoxypropylene phosphate, tetradecyloxytetraoxypropylene phosphate, hexadecyloxytetraoxypropylene phosphate, octadecyloxytetraoxypropylene phosphate, octyloxypentaoxypropylene phosphate, decyloxypentaoxypropylene phosphate, dodecyloxypentaoxypropylene phosphate, tridecyloxypentaoxypropylene phosphate, tetradecyloxypentaoxypropylene phosphate, hexadecyloxypentaoxypropylene phosphate, octyloxypentaoxypropylene phosphate, decyloxypentaoxypropylene phosphate, dodecyloxypentaoxypropylene phosphate, tridecyloxypentaoxypropylene phosphate, tetradecyloxypentaoxypropylene phosphate, hexadecyloxypentaoxypropylene phosphate, octadecyloxypentaoxypropylene phosphate, Examples of the octadecyloxypropylene phosphate include octyloxyhexaoxypropylene phosphate, octyloxyhexaoxypropylene phosphate, decyloxyhexaoxypropylene phosphate, dodecyloxyhexaoxypropylene phosphate, tridecyloxyhexaoxypropylene phosphate, tetradecyloxyhexaoxypropylene phosphate, hexadecyloxyhexaoxypropylene phosphate, octadecyloxyhexaoxypropylene phosphate, octyloxyoctaoxypropylene phosphate, decyloxyoctaoxypropylene phosphate, dodecyloxyoctaoxypropylene phosphate, tridecyloxyoctaoxyethylene phosphate, tetradecyloxyoctaoxypropylene phosphate, hexadecyloxyoctaoxypropylene phosphate, octadecyloxyoctaoxypropylene phosphate, and metal salts thereof. Among these, alkali metal salts, particularly sodium salts thereof, are preferred.

[0115] Specific examples of the alkylphenyloxy polyoxyalkylene phosphate salts include alkylphenyloxy polyoxyethylene phosphate salts and alkylphenyloxy polyoxypropylene phosphate salts, and among these, alkylphenyloxy polyoxyethylene phosphate salts are preferred.

[0116] Specific examples of alkylphenyloxypolyoxyethylene phosphate ester salts include methyloxytetraoxyethylene phosphate ester, ethylphenyloxytetraoxyethylene phosphate ester, butylphenyloxytetraoxyethylene phosphate ester, hexylphenyloxytetraoxyethylene phosphate ester, nonylphenyloxytetraoxyethylene phosphate ester, dodecylphenyloxytetraoxyethylene phosphate ester, octadecyloxytetraoxyethylene phosphate ester, methylphenyloxypentaoxyethylene phosphate ester, ethylphenyloxypentaoxyethylene phosphate ester, butylphenyloxypentaoxyethylene phosphate ester, hexylphenyloxypentaoxyethylene phosphate ester, nonylphenyloxypentaoxyethylene phosphate ester, dodecylphenyloxypentaoxyethylene phosphate ester, and metal salts thereof, such as hexaoxyethylene phosphate, methylphenyloxyhexaoxyethylene phosphate, ethylphenyloxyhexaoxyethylene phosphate, butylphenyloxyhexaoxyethylene phosphate, hexylphenyloxyhexaoxyethylene phosphate, nonylphenyloxyhexaoxyethylene phosphate, dodecylphenyloxyhexaoxyethylene phosphate, methylphenyloxyhexaoxyethylene phosphate, ethylphenyloxyoctaoxyethylene phosphate, butylphenyloxyoctaoxyethylene phosphate, hexylphenyloxyoctaoxyethylene phosphate, nonylphenyloxyoctaoxyethylene phosphate, and dodecylphenyloxyoctaoxyethylene phosphate. Among these, alkali metal salts thereof, particularly sodium salts, are preferred.

[0117] Specific examples of alkylphenyloxypolyoxypropylene phosphate salts include methylphenyloxytetraoxypropylene phosphate, ethylphenyloxytetraoxypropylene phosphate, butylphenyloxytetraoxypropylene phosphate, hexylphenyloxytetraoxypropylene phosphate, nonylphenyloxytetraoxypropylene phosphate, dodecylphenyloxytetraoxypropylene phosphate, methylphenyloxypentaoxypropylene phosphate, ethylphenyloxypentaoxypropylene phosphate, butylphenyloxypentaoxypropylene phosphate, hexylphenyloxypentaoxypropylene phosphate, nonylphenyloxypentaoxypropylene phosphate, dodecylphenyloxypentaoxypropylene phosphate, methyl Examples of suitable phosphates include metal salts of phenyloxyhexaoxypropylene phosphate, ethylphenyloxyhexaoxypropylene phosphate, butylphenyloxyhexaoxypropylene phosphate, hexylphenyloxyhexaoxypropylene phosphate, nonylphenyloxyhexaoxypropylene phosphate, dodecylphenyloxyhexaoxypropylene phosphate, methylphenyloxyoctaoxypropylene phosphate, ethylphenyloxyoctaoxypropylene phosphate, butylphenyloxyoctaoxypropylene phosphate, hexylphenyloxyoctaoxyethylene phosphate, nonylphenyloxyoctaoxypropylene phosphate, and dodecylphenyloxyoctaoxypropylene phosphate. Among these, alkali metal salts thereof, particularly sodium salts, are preferred.

[0118] As the phosphate ester salt, a monovalent phosphate ester salt such as a sodium di(alkyloxypolyoxyalkylene) phosphate ester salt can be used alone or in combination with a divalent phosphate ester salt.

[0119] Examples of sulfate salts include sodium lauryl sulfate, potassium lauryl sulfate, ammonium lauryl sulfate, sodium myristyl sulfate, sodium polyoxyethylene alkyl sulfate, and sodium polyoxyethylene alkylaryl sulfate, with sodium lauryl sulfate being preferred.

[0120] Examples of cationic emulsifiers include alkyltrimethylammonium chloride, dialkylammonium chloride, and benzylammonium chloride.

[0121] Examples of nonionic emulsifiers include polyoxyalkylene fatty acid esters such as polyoxyethylene stearate ester; polyoxyalkylene alkyl ethers such as polyoxyethylene dodecyl ether; polyoxyalkylene alkylphenol ethers such as polyoxyethylene nonylphenyl ether; and polyoxyethylene sorbitan alkyl esters. Polyoxyalkylene alkyl ethers and polyoxyalkylene alkylphenol ethers are preferred, and polyoxyethylene alkyl ethers and polyoxyethylene alkylphenol ethers are more preferred.

[0122] These emulsifiers can be used alone or in combination of two or more, and the amount used is usually in the range of 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.

[0123] The method (mixing system) for mixing the monomer component, water, and emulsifier may be conventional, for example, a method in which the monomer, emulsifier, and water are stirred using a stirrer such as a homogenizer or a disk turbine. The amount of water used is usually 1 to 1,000 parts by weight, preferably 5 to 500 parts by weight, more preferably 4 to 300 parts by weight, particularly preferably 3 to 150 parts by weight, and most preferably 20 to 80 parts by weight, per 100 parts by weight of the monomer component.

[0124] (inorganic radical generator) The polymerization catalyst used in the present invention is characterized by using a redox catalyst consisting of an inorganic radical generator and a reducing agent. In particular, the use of an inorganic radical generator is advantageous because it can widen the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic rubber, thereby highly improving the processability of the produced acrylic rubber sheet in rolls, etc.

[0125] The inorganic radical generator is not particularly limited as long as it is one that is commonly used in emulsion polymerization, and examples thereof include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, and hydrogen peroxide. Among these, persulfates are preferred, potassium persulfate and ammonium persulfate are more preferred, and potassium persulfate is particularly preferred.

[0126] These inorganic radical generators can be used alone or in combination of two or more kinds, and the amount used is usually in the range of 0.0001 to 5 parts by weight, preferably 0.0005 to 1 part by weight, more preferably 0.001 to 0.25 parts by weight, particularly preferably 0.01 to 0.21 parts by weight, and most preferably 0.1 to 0.2 parts by weight, per 100 parts by weight of the monomer component.

[0127] (reducing agent) The reducing agent used in the present invention is not particularly limited as long as it is one that is normally used in emulsion polymerization, but it is preferable to use at least two types of reducing agents, and it is suitable to combine a metal ion compound in a reduced state with another reducing agent, since this allows the acrylic rubber sheet to have an even higher balance between the Banbury processability, roll processability and strength properties.

[0128] The reduced metal ion compound is not particularly limited, but examples thereof 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 typically 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.

[0129] The reducing agent other than a metal ion compound in a reduced state used in the present invention is not particularly limited, and examples thereof include ascorbic acid or a salt thereof such as ascorbic acid, sodium ascorbate, potassium ascorbate, etc.; erythorbic acid or a salt thereof such as erythorbic acid, sodium erythorbate, potassium erythorbate, etc.; sulfinates such as sodium hydroxymethanesulfinate; sulfites such as sodium sulfite, potassium sulfite, sodium hydrogensulfite, aldehyde sodium hydrogensulfite, potassium hydrogensulfite; pyrosulfites such as sodium pyrosulfite, potassium pyrosulfite, sodium hydrogensulfite, potassium 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, potassium hydrogen phosphite; pyrophosphorous acid or a salt thereof such as pyrophosphorous acid, sodium pyrophosphite, potassium pyrophosphite, sodium hydrogen pyrophosphite, potassium hydrogen pyrophosphite, etc.; sodium formaldehyde sulfoxylate, etc. Among these, ascorbic acid or its salts, sodium formaldehyde sulfoxylate, etc. are preferred, and ascorbic acid or its salts are particularly preferred.

[0130] These reducing agents other than 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 0.001 to 1 part by weight, preferably 0.005 to 0.5 parts by weight, and more preferably 0.01 to 0.1 part by weight, per 100 parts by weight of the monomer component.

[0131] A preferred combination of a reduced metal ion compound and another reducing agent is ferrous sulfate and ascorbic acid or a salt thereof and / or sodium formaldehyde sulfoxylate, more preferably ferrous sulfate and ascorbic acid or a salt thereof. In this case, the amount of ferrous sulfate used is typically 0.000001 to 0.01 part by weight, preferably 0.00001 to 0.001 part by weight, and more preferably 0.00005 to 0.0005 part by weight, per 100 parts by weight of the monomer component. The amount of ascorbic acid or a salt thereof and / or sodium formaldehyde sulfoxylate used is typically 0.001 to 1 part by weight, preferably 0.005 to 0.5 parts by weight, and more preferably 0.01 to 0.1 part by weight, per 100 parts by weight of both components.

[0132] The amount of water used in the emulsion polymerization reaction may be the same as the amount used in emulsifying the monomer components, but is adjusted to be in the range of usually 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.

[0133] The emulsion polymerization reaction may be carried out in a conventional manner, and may be carried out in a batch, semi-batch, or continuous manner. The polymerization temperature and polymerization time are not particularly limited and can be appropriately selected depending on the type of polymerization initiator used, etc. The polymerization time is usually 0.5 to 100 hours, and preferably 1 to 10 hours.

[0134] The emulsion polymerization reaction is an exothermic reaction, and if not controlled, the temperature will rise and the polymerization reaction may be shortened. However, in the present invention, controlling the emulsion polymerization reaction temperature to typically 35°C or lower, preferably 0 to 35°C, more preferably 5 to 30°C, and particularly preferably 10 to 25°C, is suitable because it achieves a high level of balance between the strength properties of the acrylic rubber sheet to be produced and the processability during kneading using a Banbury mixer or the like.

[0135] (Post-addition of chain transfer agent) The present invention is characterized in that the chain transfer agent is not added at the initial stage but is added batchwise during the polymerization, and by doing so, an acrylic rubber in which high molecular weight components and low molecular weight components are separated can be produced, and the strength properties of the acrylic rubber sheet produced and the processability during kneading with a roll or the like are highly balanced, which is preferable.

[0136] The chain transfer agent to be used is not particularly limited as long as it is one that is commonly used in emulsion polymerization, and for example, a mercaptan compound can be suitably used. As the mercaptan compound, an alkyl mercaptan compound having usually 2 to 20 carbon atoms, preferably an alkyl mercaptan compound having 5 to 15 carbon atoms, more preferably an alkyl mercaptan compound having 6 to 14 carbon atoms can be used.

[0137] The alkyl mercaptan compound may be any of an n-alkyl mercaptan compound, a sec-alkyl mercaptan compound, and a t-alkyl mercaptan compound, but an n-alkyl mercaptan compound or a t-alkyl mercaptan compound is preferred, and an n-alkyl mercaptan compound is more preferred, as this allows the chain transfer agent effect to be stably exerted and highly improves the processability of the produced acrylic rubber, such as for rolls.

[0138] Specific examples of alkyl mercaptan compounds include n-pentyl mercaptan, n-hexyl mercaptan, n-heptyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, n-tridecane mercaptan, n-tetradecyl mercaptan, n-hexadecyl mercaptan, n-octadecyl mercaptan, sec-pentyl mercaptan, sec-hexyl mercaptan, sec-heptyl mercaptan, sec-octyl mercaptan, sec-decyl mercaptan, sec-dodecyl mercaptan, sec-tridecane mercaptan, and sec-tetradecyl mercaptan. Examples of the mercaptan include decyl mercaptan, sec-hexadecyl mercaptan, sec-octadecyl mercaptan, t-pentyl mercaptan, t-hexyl mercaptan, t-heptyl mercaptan, t-octyl mercaptan, t-decyl mercaptan, t-dodecyl mercaptan, n-tridecane mercaptan, t-tetradecyl mercaptan, t-hexadecyl mercaptan, and t-octadecyl mercaptan. Preferred are n-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan, and more preferred are n-octyl mercaptan and n-dodecyl mercaptan.

[0139] These chain transfer agents may be used alone or in combination of two or more. The amount of chain transfer agent used is not particularly limited, but when the amount is in the range of usually 0.0001 to 1 part by weight, preferably 0.0005 to 0.5 parts by weight, more preferably 0.001 to 0.5 parts by weight, particularly preferably 0.005 to 0.1 parts by weight, and most preferably 0.01 to 0.06 parts by weight, relative to 100 parts by weight of the monomer component, the strength properties and roll processability of the acrylic rubber sheet to be produced are well balanced, making it suitable.

[0140] The present invention is characterized in that the chain transfer agent is not added at the initial stage of polymerization but is added batchwise during the polymerization, and this is advantageous because the acrylic rubber produced contains high molecular weight components and low molecular weight components, and the molecular weight distribution is within a specific range, allowing for a high level of balance between the strength properties of the acrylic rubber sheet and the processability for rolls, etc.

[0141] The number of batchwise post-additions of the chain transfer agent is not particularly limited and is appropriately selected depending on the intended use, but is generally 1 to 5 times, preferably 2 to 4 times, more preferably 2 to 3 times, and particularly preferably 2 times, which is suitable because it allows the strength properties of the acrylic rubber sheet to be produced to be well balanced with the processability of a roll or the like.

[0142] There are no particular limitations on the timing for starting the batchwise post-addition of the chain transfer agent, and the timing is appropriately selected depending on the intended use. However, a timing within the range of usually 20 minutes or more after the start of polymerization, preferably 30 minutes or more after the start of polymerization, more preferably 30 to 200 minutes, particularly preferably 35 to 150 minutes, and most preferably 40 to 120 minutes after the start of polymerization is suitable, as this allows for a high level of balance between the strength properties of the acrylic rubber sheet to be produced and the processability of rolls, etc.

[0143] The amount of chain transfer agent added each time in batchwise post-addition is not particularly limited and is selected appropriately depending on the intended use, but an amount in the range of usually 0.00005 to 0.5 parts by weight, preferably 0.0001 to 0.1 parts by weight, more preferably 0.0005 to 0.05 parts by weight, particularly preferably 0.001 to 0.03 parts by weight, and most preferably 0.002 to 0.02 parts by weight, per 100 parts by weight of the monomer component, is suitable because it allows the strength properties and roll processability of the acrylic rubber sheet to be produced to be well balanced.

[0144] After the addition of the chain transfer agent, the polymerization reaction is continued for usually 30 minutes or more, preferably 45 minutes or more, more preferably 1 hour or more, without any particular limitation, and then can be terminated.

[0145] (Post-addition of reducing agent) In the present invention, the reducing agent for the redox catalyst can be added later during the polymerization, which is advantageous because it allows the strength properties of the acrylic rubber sheet to be produced to be well balanced with the processability for rolling and the like.

[0146] The reducing agent added later during the polymerization has the same examples and preferred ranges as those of the reducing agent described above. In the present invention, ascorbic acid or a salt thereof is preferred as the reducing agent added later.

[0147] The amount of reducing agent added later during polymerization is not particularly limited and may be selected appropriately depending on the intended use, but an amount in the range of usually 0.0001 to 1 part by weight, preferably 0.0005 to 0.5 parts by weight, more preferably 0.001 to 0.5 parts by weight, particularly preferably 0.005 to 0.1 parts by weight, and most preferably 0.01 to 0.05 parts by weight, per 100 parts by weight of the monomer components is suitable, as this provides excellent productivity in acrylic rubber production and a high level of balance between the strength properties and processability of the acrylic rubber sheet produced.

[0148] The reducing agent added during polymerization may be added either continuously or batchwise, but is preferably added batchwise. When the reducing agent is added batchwise during polymerization, the number of times is not particularly limited, but is usually 1 to 5 times, preferably 1 to 3 times, and more preferably 1 to 2 times.

[0149] When the reducing agent added at the beginning of polymerization or during polymerization is ascorbic acid or a salt thereof, the ratio of the amount of ascorbic acid or a salt thereof added at the beginning to the amount of ascorbic acid or a salt thereof added later is not particularly limited, but a weight ratio of "initially added ascorbic acid or a salt thereof" / "batchwise later added ascorbic acid or a salt thereof" within the range of usually 1 / 9 to 8 / 2, preferably 2 / 8 to 6 / 4, and more preferably 3 / 7 to 5 / 5 is suitable, as this provides excellent productivity in acrylic rubber production and a high level of balance between the strength properties and processability of the acrylic rubber sheet produced.

[0150] There are no particular limitations on the timing of post-addition of the reducing agent, and it is selected appropriately depending on the intended use. However, a time within the range of usually 1 hour or more after the start of polymerization, preferably 1 to 3 hours, and more preferably 1.5 to 2.5 hours after the start of polymerization, is suitable because it provides excellent productivity in acrylic rubber production and also achieves a high level of balance between the strength properties of the acrylic rubber sheet produced and the processability of rolls, etc.

[0151] The amount of reducing agent added each time in batchwise post-addition is not particularly limited and is selected appropriately depending on the intended use, but an amount in the range of usually 0.00005 to 0.5 parts by weight, preferably 0.0001 to 0.1 parts by weight, more preferably 0.0005 to 0.05 parts by weight, and particularly preferably 0.001 to 0.03 parts by weight, per 100 parts by weight of the monomer component is suitable, as this allows for a high level of balance between the strength properties of the acrylic rubber sheet to be produced and its processability in rolls, etc.

[0152] The procedure after the addition of the reducing agent is not particularly limited, but the polymerization reaction can be terminated after the polymerization reaction is continued for usually 30 minutes or more, preferably 45 minutes or more, and more preferably 1 hour or more.

[0153] The polymerization conversion rate of the emulsion polymerization reaction is 90% by weight or more, preferably 95% by weight or more, and the acrylic rubber sheet produced in this manner has excellent strength characteristics and is free of monomer odor, making it suitable. A polymerization terminator may be used to terminate the polymerization.

[0154] (solidification process) The coagulation step in the method for producing an acrylic rubber sheet of the present invention is a step in which the emulsion polymerization liquid after emulsion polymerization is coagulated with a coagulation liquid to produce water-containing crumbs.

[0155] The solid content of the emulsion polymerization liquid used in this coagulation reaction is not particularly limited, but is usually adjusted to within the range of 5 to 50% by weight, preferably 10 to 45% by weight, and more preferably 20 to 40% by weight.

[0156] The coagulant for the coagulation liquid used is not particularly limited, but a metal salt is usually used. Examples of the metal salt include alkali metals, Group 2 metal salts of the periodic table, and other metal salts, and alkali metal salts and Group 2 metal salts of the periodic table are preferred, more preferably Group 2 metal salts of the periodic table, and particularly preferably magnesium salts, which are suitable for achieving a high level of balance between the water resistance, strength properties, mold releasability, and processability of the resulting acrylic rubber sheet.

[0157] 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, and sodium chloride and sodium sulfate are particularly preferred.

[0158] Examples of the salt of a metal of 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.

[0159] Examples of other metal salts include 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.

[0160] 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.

[0161] The coagulation liquid used is usually an aqueous solution, and the coagulant concentration of the aqueous solution 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 region.

[0162] The temperature of the coagulation liquid is not particularly limited, but when it is generally 40°C or higher, preferably in the range of 40 to 90°C, more preferably 50 to 80°C, uniform water-containing crumbs are preferably produced.

[0163] The method for coagulating the emulsion heavy liquid with the coagulating liquid is not particularly limited, and any method may be used, such as adding the coagulating liquid to the emulsion polymerization liquid, adding the coagulating liquid to the emulsion polymerization liquid while it is being stirred, adding the emulsion polymerization liquid to the coagulating liquid, or adding the emulsion polymerization liquid to the coagulating liquid while it is being stirred. However, the method of adding the emulsion polymerization liquid to the coagulating liquid while it is being stirred is preferred because it provides excellent efficiency in washing and dehydrating the water-containing crumbs that are generated and can significantly improve the water resistance and storage stability of the resulting acrylic rubber sheet.

[0164] The stirring speed (rotation speed) of the stirred coagulation liquid, i.e., the rotation speed of the stirring blades of the stirring device, is not particularly limited, but is usually 100 rpm or more, preferably 200 rpm or more, more preferably 200 to 1000 rpm, particularly preferably 300 to 900 rpm, and most preferably in the range of 400 to 800 rpm.

[0165] A rotation speed that provides a certain degree of vigorous stirring is preferable, as it allows the resulting 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 produced, and by setting the rotation speed below the upper limit, it is possible to more easily control the coagulation reaction.

[0166] 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 to a certain extent is preferred because the particle size of the generated hydrous crumbs can be made 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 is usually 50 m / s or less, preferably 30 m / s or less, more preferably 25 m / s or less, and most preferably 20 m / s or less, which makes it easier to control the coagulation reaction.

[0167] By setting the above-mentioned conditions for the coagulation reaction (contact method, solids concentration of the emulsion polymerization liquid, concentration and temperature of the coagulation liquid, rotation speed and peripheral speed during stirring of the coagulation liquid, etc.) within specific ranges, the shape and diameter of the generated water-containing crumbs become uniform and the crumbs are concentrated, and removal of the emulsifier and coagulant during washing and dehydration is significantly improved, which results in highly improved water resistance and storage stability of the produced acrylic rubber sheet, and is therefore advantageous.

[0168] (Cleaning process) The washing step in the method for producing an acrylic rubber sheet of the present invention is a step of washing away the water-containing crumbs produced in the coagulation reaction.

[0169] The washing method is not particularly limited, and for example, the produced water-containing crumbs can be mixed with a large amount of water.

[0170] The amount of water added for washing is not particularly limited, but it is suitable that the amount of water added per washing 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 even more preferably 500 to 5,000 parts by weight, per 100 parts by weight of the monomer component, since this can effectively reduce the ash content in the acrylic rubber sheet.

[0171] The temperature of the water used is not particularly limited, 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 is particularly optimal at 60 to 80° C., as this significantly improves the cleaning efficiency. By using water at a temperature above the above-mentioned lower limit, the emulsifier and coagulant are released from the water-containing crumbs, further improving the cleaning efficiency.

[0172] The washing time is not particularly limited, but is usually in the range of 1 to 120 minutes, preferably 2 to 60 minutes, and more preferably 3 to 30 minutes.

[0173] The number of washings (water washings) is not particularly limited either, and is usually 1 to 10 times, preferably 1 to 5 times, and more preferably 2 to 3 times. From the viewpoint of reducing the amount of coagulant remaining in the finally obtained acrylic rubber sheet, it is desirable to wash with water more frequently, but the number of water washings can be significantly reduced by setting the shape and diameter of the water-containing crumbs within specific ranges and / or setting the washing temperature within the above ranges, as described above.

[0174] (Draining process) In the present invention, it is preferable to provide a draining step in which free water is separated from the washed wet crumbs using a drainer in order to increase the dewatering efficiency.

[0175] Any known drainer can be used without any particular limitation, and examples thereof include wire mesh, screens, and electric sieves, with wire mesh and screens being preferred.

[0176] There are no particular limitations on the mesh size of the drainer, but a mesh size in the range of usually 0.01 to 5 mm, preferably 0.1 to 1 mm, more preferably 0.2 to 0.6 mm is suitable as it minimizes loss of water-containing crumb and allows efficient draining.

[0177] The moisture content of the drained wet crumbs, i.e., the moisture content of the wet 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.

[0178] The temperature of the hydrous crumbs after draining, i.e., the temperature of the hydrous crumbs fed into the dehydration, drying, and molding steps, 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, and is suitable for efficiently dehydrating and drying hydrous crumbs, which have a high specific heat of 1.5 to 2.5 KJ / kg K and are difficult to raise in temperature, such as the acrylic rubber constituting the acrylic rubber sheet of the present invention, using a screw-type twin-screw extruder.

[0179] (Dehydration, drying, molding process) The dehydrating, drying and molding steps in the method for producing an acrylic rubber sheet of the present invention are steps in which the above-mentioned washed, and preferably drained, water-containing crumbs are dehydrated in the dehydrating barrel using a screw-type twin-screw extruder dryer 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 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.

[0180] (Dehydration of wet crumbs in dehydration barrels) The dehydration of the hydrous crumbs is carried out in a dehydration barrel in a screw-type twin-screw extruder dryer having a dehydration slit. The opening of the dehydration slit may be selected appropriately depending on the conditions of use, but is usually in the range of 0.01 to 5 mm, preferably 0.1 to 1 mm, more preferably 0.2 to 0.6 mm, which is suitable for minimizing hydrous crumb loss and enabling efficient dehydration of the hydrous crumbs.

[0181] The number of dehydration barrels in the screw-type twin-screw extrusion dryer is not particularly limited, but it is generally suitable to have more than one, preferably 2 to 10, and more preferably 3 to 6, in order to efficiently dehydrate the sticky acrylic rubber.

[0182] There are two ways to remove water from the wet crumb in the dehydration barrel: in liquid form (wastewater) through the dehydration slit, and in vapor form (exhaust steam). In this invention, we distinguish between the two by defining wastewater as dehydration and exhaust steam as pre-drying.

[0183] The water discharged from the dewatering slit during dehydration of the hydrous crumbs may be in either a liquid state (wastewater) or a vapor state (exhaust steam), but when a screw-type twin-screw extruder dryer equipped with multiple dehydration barrels is used, a combination of wastewater and exhaust steam is preferred because this allows for efficient dehydration of the adhesive acrylic rubber. The choice of drainage-type dehydration barrel or exhaust steam-type dehydration barrel in a screw-type twin-screw extruder dryer equipped with three or more dehydration barrels can be made appropriately depending on the intended use, but typically, more drainage-type barrels are used to reduce the ash content in the acrylic rubber sheet being produced, and more exhaust steam-type barrels are used to reduce the moisture content.

[0184] The set temperature of the dehydration barrel is appropriately selected depending on the monomer composition, ash content, water content, and operating conditions of the acrylic rubber, but is usually in the range of 60 to 150°C, preferably 70 to 140°C, and more preferably 80 to 130°C. The set temperature of the dehydration barrel for dehydration in a wastewater state is usually 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 100 to 150°C, preferably 105 to 140°C, and more preferably 110 to 130°C.

[0185] The moisture content after dehydration in the drainage dehydration method in which moisture is squeezed out of the hydrous crumb is not particularly limited, but a moisture content of 1 to 40% by weight, preferably 5 to 40% by weight, more preferably 5 to 35% by weight, and particularly preferably 10 to 35% by weight, is suitable because it provides a high balance between productivity and ash removal efficiency.

[0186] When dehydrating adhesive acrylic rubber having reactive groups using a centrifuge or the like, the acrylic rubber adheres to the dehydration slits and is barely dehydrated (water content reaches approximately 45 to 55% by weight). However, in the present invention, by using a screw-type twin-screw extrusion dryer that has a dehydration slit and is forcibly squeezed by a screw, it is possible to reduce the water content to this extent.

[0187] When a drainage type dehydration barrel and a steam exhaust type dehydration barrel are provided, the moisture content of the hydrous crumb after drainage in the drainage type dehydration barrel is usually 5 to 40% by weight, preferably 10 to 40% by weight, more preferably 15 to 35% by weight, and the moisture content after pre-drying in the steam exhaust type dehydration barrel is usually 1 to 30% by weight, preferably 3 to 20% by weight, more preferably 5 to 15% by weight.

[0188] By setting the water content after dehydration to the lower limit or more, the dehydration time can be shortened and deterioration of the acrylic rubber can be suppressed, and by setting it to the upper limit or less, the ash content can be sufficiently reduced.

[0189] (Drying of moist crumbs in the drying barrel) The dehydrated hydrous crumb is preferably dried under reduced pressure in a screw-type twin-screw extruder having a drying barrel. Drying the acrylic rubber under reduced pressure increases the production efficiency of the drying process and also removes the air contained in the acrylic rubber, making it possible to produce an acrylic rubber bale with a high specific gravity and excellent storage stability. In the present invention, the storage stability can be highly improved by melting the acrylic rubber under reduced pressure and extruding and drying it. The storage stability of an acrylic rubber sheet is largely correlated with the specific gravity of the acrylic rubber sheet and can be controlled. However, when a high specific gravity is required for high storage stability, it can be controlled by the degree of vacuum reduction during extrusion drying.

[0190] The degree of vacuum in the drying barrel may be selected as appropriate, but a pressure of usually 1 to 50 kPa, preferably 2 to 30 kPa, and more preferably 3 to 20 kPa is suitable, as this allows the water-containing crumb to be dried efficiently and the air in the acrylic rubber to be removed, thereby significantly improving the storage stability of the acrylic rubber bale.

[0191] The set temperature of the drying barrel may be selected as appropriate, but is generally suitable within the range of 100 to 250°C, preferably 110 to 200°C, and more preferably 120 to 180°C, since this allows for efficient drying without discoloration or deterioration of the acrylic rubber and reduces the amount of gel in the acrylic rubber sheet.

[0192] The number of drying barrels in a screw-type twin-screw extruder is not particularly limited, but is usually multiple, preferably 2 to 10, and more preferably 3 to 8. When multiple drying barrels are used, the degree of reduced pressure may be similar for all drying barrels or may be different. When multiple drying barrels are used, the set temperatures may be similar for all drying barrels or may be different, but it is preferable to make the temperature of the discharge section (closer to the die) higher than the temperature of the introduction section (closer to the dehydration barrel) in order to improve drying efficiency.

[0193] 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-knead and extrude the dried rubber at this moisture content (a state in which almost all water has been removed) in a screw-type twin-screw extruder, since this reduces the amount of gel in the methyl ethyl ketone-insoluble portion of the acrylic rubber sheet. In the present invention, an acrylic rubber sheet melt-kneaded or melt-kneaded and dried in a screw-type twin-screw extruder is preferable because it has a high balance between strength properties and Banbury processability. Note that, in the present invention, "melt-kneading" or "melt-kneading and drying" means that the acrylic rubber is kneaded (mixed) in a molten state in a screw-type twin-screw extruder or extruded in a molten state and dried at that stage, or that the acrylic rubber is kneaded in a molten (plasticized) state in a screw-type twin-screw extruder and then extruded and dried.

[0194] In the present invention, the shear rate applied to the acrylic rubber in the drying barrel of the screw-type twin-screw extruder dryer in a state where the acrylic rubber is substantially free of water is not particularly limited, but is usually 10 [1 / s] or more, preferably 10 to 400 [1 / s], and more preferably 50 to 250 [1 / s], and this is preferred because the storage stability, roll processability, Banbury processability, strength properties, and compression set resistance of the obtained acrylic rubber sheet are well balanced. There are no particular limitations on the shear viscosity of the acrylic rubber inside the screw-type twin-screw extruder dryer used in the present invention, particularly in the drying barrel, but when it is in the range of usually 12,000 [Pa·s] or less, preferably 1,000 to 12,000 [Pa·s], more preferably 2,000 to 10,000 [Pa·s], particularly preferably 3,000 to 7,000 [Pa·s], and most preferably 4,000 to 6,000 [Pa·s], the storage stability, roll processability, Banbury processability, and strength properties of the resulting acrylic rubber sheet are highly balanced and are therefore suitable.

[0195] (Extrusion of dry rubber from the die) The dried rubber dehydrated and dried in the screw sections of the dehydration barrel and drying barrel is sent to a screw-less straightening die section, from which it is extruded into the desired shape. A breaker plate or wire mesh may or may not be provided between the screw section and the die section.

[0196] The dried rubber to be extruded is preferably extruded in the form of a sheet using a die having a substantially rectangular shape, which results in a dried rubber with a high specific gravity and excellent storage stability with less air entrapment. It is particularly important that the acrylic rubber that has been melt-kneaded without containing air in the die section is extruded in the form of a sheet without containing air.

[0197] The resin pressure in the die section is not particularly limited, but is usually set 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 because it reduces air entrapment in the acrylic rubber sheet (high specific gravity) and provides excellent productivity. Screw-type twin-screw extrusion dryer and operating conditions

[0198] The screw length (L) of the screw-type twin-screw extruder used may be appropriately selected depending on the purpose of use, but is usually in the range of 3000 to 15000 mm, preferably 4000 to 10000 mm, and more preferably 4500 to 8000 mm.

[0199] The screw diameter (D) of the screw-type twin-screw extruder used may be appropriately selected depending on the purpose of use, but is usually in the range of 50 to 250 mm, preferably 100 to 200 mm, more preferably 120 to 160 mm.

[0200] The ratio (L / D) of the screw length (L) to the screw diameter (D) of the screw-type twin-screw extruder dryer used is not particularly limited, but is usually in the range of 10 to 100, preferably 20 to 80, and more preferably 30 to 60, which is suitable because the moisture content can be reduced to less than 1% by weight without causing a decrease in the molecular weight of the dried rubber or burning.

[0201] The rotation speed (N) of the screw-type twin-screw extruder used may be selected appropriately depending on various conditions, but a rotation speed of typically 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 because it allows the water content and gel content of the acrylic rubber sheet to be efficiently reduced.

[0202] The extrusion rate (Q) of the screw-type twin-screw extruder used is not particularly limited, but is usually in the range of 100 to 1,500 kg / hr, preferably 300 to 1,200 kg / hr, more preferably 400 to 1,000 kg / hr, and most preferably 500 to 800 kg / hr.

[0203] The ratio (Q / N) of the extrusion rate (Q) to the rotation speed (N) of the screw-type twin-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.

[0204] In the present invention, it is particularly preferable to use a screw-type twin-screw extruder dryer having two screws to dry the water-containing crumb under high shear conditions, since this allows the acrylic rubber sheet obtained to have a high level of balance between roll processability, Banbury processability, and strength properties.

[0205] The maximum torque of the screw-type twin-screw extruder used is not particularly limited, but is usually 25 N m or more, preferably 30 N m or more, more preferably 35 N m or more, and particularly preferably 40 N m or more. The maximum torque of the screw-type twin-screw extruder used in the present invention is also preferably in the range of usually 25 to 125 N m, preferably 30 to 100 N m, more preferably 35 to 75 N m, and particularly preferably 40 to 60 N m, because this allows for a high level of balance between the roll processability, Banbury processability, and strength properties of the acrylic rubber sheet produced.

[0206] There are no particular limitations on the specific power of the screw-type twin-screw extruder dryer used, but when the specific power is in the range of usually 0.1 to 0.25 [kw·h / kg] or more, preferably 0.13 to 0.23 [kw·h / kg], and more preferably 0.15 to 0.2 [kw·h / kg], the roll processability, Banbury processability, and strength properties of the resulting acrylic rubber sheet are well balanced, making this suitable.

[0207] There are no particular limitations on the specific power of the screw-type twin-screw extruder dryer used, but when the specific power is in the range of usually 0.2 to 0.6 [A·h / kg] or more, preferably 0.25 to 0.55 [A·h / kg], and more preferably 0.35 to 0.5 [A·h / kg], the roll processability, Banbury processability, and strength properties of the resulting acrylic rubber sheet are well balanced, making this suitable.

[0208] There are no particular limitations on the shear rate of the screw-type twin-screw extruder used, but when the shear rate is in the range of usually 40 to 150 [1 / s] or more, preferably 45 to 125 [1 / s], and more preferably 50 to 100 [1 / s], the storage stability, roll processability, Banbury processability, and strength properties of the resulting acrylic rubber sheet are well balanced, which is suitable.

[0209] There are no particular limitations on the shear viscosity of the acrylic rubber in the screw-type twin-screw extruder dryer used, but when it is in the range of usually 4000 to 8000 [Pa·s] or less, preferably 4500 to 7500 [Pa·s], and more preferably 5000 to 7000 [Pa·s], the storage stability, roll processability, Banbury processability, and strength properties of the resulting acrylic rubber sheet are well balanced, making it suitable.

[0210] (Dry rubber sheet) The dried rubber extruded from the screw-type twin-screw extruder is in the form of a sheet, which is advantageous because it does not trap air and can increase the specific gravity, thereby highly improving storage stability. The dried rubber sheet extruded from the screw-type twin-screw extruder is usually cooled and cut to be used as an acrylic rubber sheet.

[0211] The thickness of the dry rubber sheet extruded from the screw-type twin-screw extruder is not particularly limited, but 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, since the thermal conductivity of the dry rubber sheet is as low as 0.15 to 0.35 W / mK, the thickness of the dry rubber sheet, in order to significantly improve productivity by increasing cooling efficiency, is usually 1 to 30 mm, preferably 2 to 25 mm, more preferably 3 to 15 mm, and particularly preferably 4 to 12 mm.

[0212] The width of the sheet-like dried rubber extruded from the screw-type twin-screw extruder is appropriately selected depending on the intended use, but is usually in the range of 300 to 1200 mm, preferably 400 to 1000 mm, and more preferably 500 to 800 mm.

[0213] The temperature of the dried rubber extruded from the screw-type twin-screw extruder is not particularly limited, but is usually in the range of 100 to 200°C, preferably 110 to 180°C, and more preferably 120 to 160°C.

[0214] The moisture content of the dried rubber extruded from the screw-type twin-screw extruder is not particularly limited, but is usually less than 1% by weight, preferably 0.8% by weight or less, and more preferably 0.6% by weight or less.

[0215] The complex viscosity at 100°C ([η]100°C) of the dry rubber sheet extruded from the screw-type twin-screw extruder is not particularly limited, but is usually 1500 to 6000 [Pa·s], preferably 2000 to 5000 [Pa·s], more preferably 2500 to 4000 [Pa·s], and most preferably 2500 to 3500 [Pa·s], which provides a high level of balance between extrudability and shape retention as a sheet. That is, by setting the viscosity at or above the lower limit, excellent extrudability can be achieved, and by setting the viscosity at or below the upper limit, deformation and breakage of the dry rubber sheet can be suppressed.

[0216] The dried rubber sheet extruded from the screw-type twin-screw extruder may be folded as is and used, but it is usually cut into pieces before use.

[0217] There are no particular limitations on the cutting of the sheet-like dry rubber, but since the acrylic rubber of the present invention has strong adhesiveness, it is preferable to cool the sheet-like dry rubber before cutting in order to cut it continuously without entraining air.

[0218] There is no particular limitation on the cutting temperature of the dry rubber sheet, but a temperature of usually 60°C or less, preferably 55°C or less, more preferably 50°C or less is suitable as it provides a high balance between cuttability and productivity.

[0219] The complex viscosity of the dry rubber sheet at 60°C ([η]60°C) is not particularly limited, but is usually 15,000 or less, preferably 2000 to 10,000 [Pa·s], more preferably 2500 to 7000 [Pa·s], and most preferably 2700 to 5500 [Pa·s], which allows continuous cutting without entraining air.

[0220] The ratio ([η]100°C / [η]60°C) of the complex viscosity of the dry rubber sheet at 100°C ([η]100°C) to the complex viscosity at 60°C ([η]60°C) is not particularly limited and may be selected appropriately depending on the intended use, but is usually 0.5 or more, preferably 0.6 or more, more preferably 0.7 or more, particularly preferably 0.8 or more, and most preferably 0.85 or more. When the upper limit is usually 0.98 or less, preferably 0.97 or less, more preferably 0.96 or less, particularly preferably 0.95 or less, and most preferably 0.93 or less, air entrapment is reduced and a high balance between cutting and productivity is achieved, which is suitable.

[0221] The cooling method for the dried rubber sheet is not particularly limited, and it may be left at room temperature. However, 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 using ventilation or air conditioning, water spraying, or immersion in water is preferred to increase productivity, and air cooling using ventilation or air conditioning is particularly preferred.

[0222] In the air-cooling method for sheet-form dry rubber, for example, sheet-form dry rubber is extruded from a screw extruder onto a conveyer such as a belt conveyor, and then 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 of the cooling 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.

[0223] The cooling rate of the dry rubber sheet is not particularly limited, but is usually 40°C / hr or more, preferably 50°C / hr or more, more preferably 100°C / hr or more, and particularly preferably 150°C / hr or more, because cutting is easy and storage stability is improved without entraining air in the molded product. In the present invention, the scorch stability of the rubber composition is remarkably excellent when the cooling rate of the dry rubber sheet is usually 40°C / hr or more, preferably 50°C / hr or more, more preferably 100°C / hr or more, and particularly preferably 150°C / hr or more.

[0224] The cut length of the dry rubber sheet is not particularly limited and is appropriately selected depending on the intended use, but is usually in the range of 100 to 800 mm, preferably 200 to 500 mm, and more preferably 250 to 450 mm.

[0225] The acrylic rubber sheet thus obtained is superior in operability to crumb-like acrylic rubber, and is also excellent in roll processability, strength properties and compression set resistance, as well as in storage stability, Banbury processability, crosslinkability and water resistance, and can be used as is or after being laminated and formed into a bale.

[0226] <Acrylic rubber veil> The acrylic rubber veil of the present invention is formed by laminating the above-mentioned acrylic rubber sheets. The acrylic rubber veil of the present invention has the same ion-reactive group amount, characteristic values ​​of the constituent acrylic rubber, ash content, ash component amount (total amount of sodium, magnesium, calcium, phosphorus, and sulfur, total amount of magnesium and phosphorus, magnesium content, or phosphorus content), ash component ratio, 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), gel content, water content, pH, and Mooney viscosity (ML1+4, 100°C) as those exemplified and in the preferred ranges for the acrylic rubber sheet.

[0227] The value of the gel content within the acrylic rubber bale of the present invention, measured by randomly sampling multiple points, is not particularly limited. Here, "a method of measuring the gel content by randomly sampling multiple points" refers to, for example, a method of randomly sampling 20 points within a large bale and measuring the gel content variation. This is a unique effect in the method of the present application (melt-kneaded materials); in bales that are not melt-kneaded, the gel content within the bale may vary and fall outside this range. In the present invention, the value is preferably within the range of (average value ±5) wt.% for all 20 points, and preferably within the range of (average value ±3) wt.% for all 20 points, indicating no processability variation and stable physical properties of the rubber mixture and cross-linked rubber. When the gel content of an acrylic rubber veil is measured at 20 random points, all 20 values ​​falling within a range of the average value ±5 means that the gel content at all 20 measured points falls within a range of (average value -5) to (average value +5) weight percent. For example, if the average value of the measured gel content is 20 weight percent, all 20 measured values ​​fall within a range of 15 to 25 weight percent.

[0228] The specific gravity of the acrylic rubber veil of the present invention is not particularly limited, but is generally 0.7 or higher, preferably 0.8 or higher, more preferably 0.9 or higher, particularly preferably 0.95 or higher, and most preferably 1 or higher, which is suitable for containing almost no air and providing excellent storage stability. The specific gravity of the acrylic rubber sheet of the present invention is also generally within the range of 0.7 to 1.6, preferably 0.8 to 1.5, more preferably 0.9 to 1.4, particularly preferably 0.95 to 1.3, and most preferably 1.0 to 1.2, which is suitable for achieving a high balance of productivity, storage stability, and the stability of the crosslinking properties of the crosslinked product.

[0229] The size of the acrylic rubber veil of the present invention is not particularly limited and can be selected appropriately depending on the intended use, but it is appropriate that the width is usually 100 to 800 mm, preferably 200 to 500 mm, and more preferably 250 to 450 mm, the length is usually 300 to 1,200 mm, preferably 400 to 1,000 mm, and more preferably 500 to 800 mm, and the height (thickness) is usually 50 to 500 mm, preferably 100 to 300 mm, and more preferably 150 to 250 mm. The shape of the acrylic rubber veil of the present invention is also not limited and can be selected appropriately depending on the intended use of the acrylic rubber veil, but in many cases a rectangular parallelepiped is suitable.

[0230] The method for producing the acrylic rubber bale of the present invention is not particularly limited, but it is preferable to laminate the above-mentioned acrylic rubber sheets to obtain an acrylic rubber bale with little air entrapment and excellent storage stability.

[0231] The lamination temperature for the acrylic rubber sheets is not particularly limited, but is usually 30°C or higher, preferably 35°C or higher, and more preferably 40°C or higher, so that air entrapped during lamination can be released. The number of layers may be appropriately selected depending on the size or weight of the acrylic rubber veil. The acrylic rubber veil of the present invention is integrated by the weight of the laminated acrylic rubber sheets.

[0232] The acrylic rubber bale of the present invention thus obtained is superior in operability to crumb-like acrylic rubber, and is excellent in roll processability, strength properties and compression set resistance, as well as in storage stability, Banbury processability, crosslinkability and water resistance. The acrylic rubber bale can be used as is, or by cutting the required amount and putting it into a mixer such as a Banbury mixer or roll mixer.

[0233] <Rubber mixture> The rubber mixture of the present invention is characterized by containing the acrylic rubber sheet and / or acrylic rubber veil, a filler, and a crosslinking agent.

[0234] The filler contained in the rubber mixture is not particularly limited, and examples thereof include reinforcing fillers and non-reinforcing fillers. Reinforcing fillers are preferred, as they provide the rubber mixture with excellent roll processability, Banbury processability and short-time crosslinking properties, and the crosslinked product with excellent water resistance, strength properties and compression set resistance.

[0235] 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; etc. 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.

[0236] These fillers can be used alone or in combination of two or more. The amount of filler added is selected appropriately 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 and / or acrylic rubber veil of the present invention.

[0237] The crosslinking agent used in the rubber mixture is not particularly limited, and conventionally known crosslinking agents can be selected depending on the intended use, such as inorganic crosslinking agents such as sulfur compounds and organic crosslinking agents, with organic crosslinking agents being preferred. The crosslinking agent may be either a polyvalent compound or a monovalent compound, with polyvalent compounds having two or more reactivities being preferred. The crosslinking agent may further be either an ionically crosslinkable compound or a radically crosslinkable compound, with ionically crosslinkable compounds being preferred.

[0238] The organic crosslinking agent is not particularly limited, but an ionically crosslinkable organic compound is preferred, and a polyvalent ion organic compound is particularly preferred. When the crosslinking agent is a polyvalent ion organic compound (polyvalent ion crosslinkable compound), the rubber mixture exhibits excellent roll processability, Banbury processability, and short-time crosslinking, and the crosslinked product exhibits excellent water resistance, strength properties, and compression set resistance, making it particularly suitable. The "ion" in ionically crosslinkable or polyvalent ion refers to an ionically reactive ion, and is not particularly limited as long as it ionically reacts with the ionically reactive group of the ionically reactive group-containing monomer of the acrylic rubber. Preferred examples include ionically crosslinkable organic compounds having ionically reactive groups such as amine groups, epoxy groups, carboxyl groups, and thiol groups.

[0239] Specific examples of polyvalent ion organic compounds include polyvalent amine compounds, polyvalent epoxy compounds, polyvalent carboxylic acid compounds, and polyvalent thiol compounds, and polyvalent amine compounds and polyvalent thiol compounds are preferred, and polyvalent amine compounds are more preferred.

[0240] Examples of polyvalent amine compounds include aliphatic polyvalent amine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicinnamylidene-1,6-hexanediamine; and aromatic polyvalent amine compounds such as 4,4'-methylenedianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-(m-phenylenediisopropylidene)dianiline, 4,4'-(p-phenylenediisopropylidene)dianiline, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, and 1,3,5-benzenetriamine. Among these, hexamethylenediamine carbamate, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, etc. are preferred. Carbonates of these compounds can also be used as polyamine compounds. These polyamine compounds are particularly suitable for use in combination with carboxyl group-containing acrylic rubber sheets or acrylic rubber veils, or epoxy group-containing acrylic rubber sheets or acrylic rubber veils.

[0241] As the polyvalent thiol compound, a triazine thiol compound is preferably used, such as 6-trimercapto-s-triazine, 2-anilino-4,6-dithiol-s-triazine, 1-dibutylamino-3,5-dimercaptotriazine, 2-dibutylamino-4,6-dithiol-s-triazine, 1-phenylamino-3,5-dimercaptotriazine, 2,4,6-trimercapto-1,3,5-triazine, 1-hexylamino-3,5-dimercaptotriazine, etc. These triazine thiol compounds are particularly suitable for use in combination with a chlorine atom-containing acrylic rubber sheet or acrylic rubber veil.

[0242] Examples of other polyvalent organic compounds include polycarboxylic acid compounds such as tetradecanedioic acid, and metal dithiocarbamate salts such as zinc dimethyldithiocarbamate. These other polyvalent organic compounds are particularly suitable for use in combination with an epoxy group-containing acrylic rubber sheet or acrylic rubber veil.

[0243] These crosslinking agents can be used alone or in combination of two or more, and the blending 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 and / or acrylic rubber veil of the present invention. By blending the crosslinking agent in this range, it is possible to obtain excellent mechanical strength as a crosslinked rubber product while ensuring sufficient rubber elasticity, which is preferable.

[0244] The rubber mixture of the present invention may contain an antioxidant if necessary. The type of antioxidant is not particularly limited, but examples thereof include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butylphenol, butylhydroxyanisole, 2,6-di-t-butyl-α-dimethylamino-p-cresol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, styrenated phenol, 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), 4,4'-methylene Others such as bis(2,6-di-t-butylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), 2,4-bis[(octylthio)methyl]-6-methylphenol, 2,2'-thiobis-(4-methyl-6-t-butylphenol), 4,4'-thiobis-(6-t-butyl-o-cresol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol Phenolic antioxidants; phosphite ester antioxidants such as tris(nonylphenyl)phosphite, diphenyl isodecyl phosphite, and tetraphenyldipropylene glycol diphosphite; sulfur ester antioxidants such as dilauryl thiodipropionate; phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamido)-diphenylamine, and 4,4'-(α,α-dimethylbenzyl)diphenylamine. Examples of antioxidants include amine-based antioxidants such as amine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensates; imidazole-based antioxidants such as 2-mercaptobenzimidazole; quinoline-based antioxidants such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline; and hydroquinone-based antioxidants such as 2,5-di-(t-amyl)hydroquinone. Among these, amine-based antioxidants are particularly preferred.

[0245] These antioxidants can be used alone or in combination of two or more, and the amount to be added is in the range of 0.01 to 15 parts by weight, preferably 0.1 to 10 parts by weight, and more preferably 1 to 5 parts by weight, per 100 parts by weight of the acrylic rubber sheet and / or acrylic rubber veil of the present invention.

[0246] As the rubber component that is the main component of the rubber mixture of the present invention, the acrylic rubber sheet or acrylic rubber veil of the present invention may be used alone, or, if necessary, the acrylic rubber sheet and / or acrylic rubber veil of the present invention may be used in combination with other rubber components.

[0247] There are no particular limitations on the other rubber components that can be combined with the acrylic rubber sheet or acrylic rubber veil of the present invention, and examples thereof include natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, silicone rubber, fluororubber, olefin-based elastomers, styrene-based elastomers, vinyl chloride-based elastomers, polyester-based elastomers, polyamide-based elastomers, polyurethane-based elastomers, and polysiloxane-based elastomers.

[0248] These other rubber components can be used alone or in combination of two or more. The shape of these other rubber components may be any of crumb, strand, veil, sheet, powder, etc. The amount of the other rubber components used is appropriately selected within a range that does not impair the effects of the present invention, and is, for example, usually 70 parts by weight or less, preferably 50 parts by weight or less, more preferably 30 parts by weight or less, particularly preferably 20 parts by weight or less, and most preferably 10 parts by weight or less, per 100 parts by weight of the acrylic rubber sheet and / or acrylic rubber bale of the present invention.

[0249] The rubber mixture of the present invention contains the above-mentioned acrylic rubber sheet of the present invention and / or the acrylic rubber veil of the present invention, a filler, and a crosslinking agent as essential components, and optionally contains an antioxidant and other rubber components, and may further contain, as necessary, other additives commonly used in the technical field, such as crosslinking aids, crosslinking accelerators, crosslinking retarders, silane coupling agents, plasticizers, processing aids, lubricants, pigments, colorants, antistatic agents, foaming agents, etc. These other additives may be used alone or in combination of two or more, and the amounts added are selected appropriately within a range that does not impair the effects of the present invention.

[0250] Examples of methods for producing the rubber mixture of the present invention include a method of mixing the acrylic rubber sheet and / or acrylic rubber veil of the present invention, a filler, a crosslinking agent, an antioxidant that can be contained as needed, other rubber components, and other compounding ingredients, and any means conventionally used in the rubber processing field can be used for mixing, such as an open roll, a Banbury mixer, various kneaders, etc. The mixing procedure for each component may be a normal procedure used in the rubber processing field, and for example, it is preferable to thoroughly mix components that are resistant to reaction or decomposition by heat, and then mix components that are resistant to reaction or decomposition by heat, such as the crosslinking agent, for a short period of time at a temperature that will not cause reaction or decomposition.

[0251] <Rubber cross-linked products> The cross-linked rubber of the present invention is obtained by cross-linking the above rubber mixture.

[0252] 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 carried out 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 minute to 10 hours, preferably 1 minute to 5 hours. The heating method may be appropriately selected from methods commonly used for cross-linking rubber, such as press heating, steam heating, oven heating, and hot air heating.

[0253] The cross-linked rubber product of the present invention may be further heated to carry out secondary cross-linking depending on the shape, size, etc. of the cross-linked rubber product. The secondary cross-linking time varies depending on the heating method, cross-linking temperature, shape, etc., but is preferably carried out for 1 to 48 hours. The heating method and heating temperature may be selected appropriately.

[0254] The cross-linked rubber of the present invention has excellent compression set resistance and water resistance while maintaining basic rubber properties such as tensile strength, elongation, and hardness.

[0255] Taking advantage of the above-mentioned properties, the cross-linked rubber product of the present invention can be suitably used, for example, as sealing materials such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing seals, mechanical seals, wellhead seals, seals for electric and electronic equipment, and seals for air compressors; various gaskets such as rocker cover gaskets attached to the connecting portion between a cylinder block and a cylinder head, oil pan gaskets attached to the connecting portion between an oil pan and a cylinder head or a transmission case, gaskets for fuel cell separators attached between a pair of housings sandwiching a unit cell having a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for the top covers of hard disk drives; cushioning materials, vibration-proofing materials; wire coating materials; industrial belts; tubes and hoses; sheets; and the like.

[0256] The cross-linked rubber product of the present invention can also be suitably used as extrusion molded articles and mold cross-linked articles for automotive applications, for example, various hoses such as fuel oil hoses for fuel tanks, such as fuel hoses, filler neck hoses, vent hoses, paper hoses and oil hoses, air hoses, such as turbo air hoses and mission control hoses, radiator hoses, heater hoses, brake hoses and air conditioner hoses.

[0257] <Device configuration used to manufacture acrylic rubber sheets> Next, the configuration of the equipment used to manufacture the acrylic rubber sheet and acrylic rubber bale according to one embodiment of the present invention will be described. Fig. 1 is a diagram schematically showing an example of an acrylic rubber manufacturing system having the configuration of the equipment used to manufacture the acrylic rubber sheet and acrylic rubber bale according to one embodiment of the present invention. For example, the acrylic rubber manufacturing system 1 shown in Fig. 1 can be used to manufacture the acrylic rubber sheet and acrylic rubber bale according to the present invention.

[0258] The acrylic rubber production system 1 shown in FIG. 1 is composed of an emulsion polymerization reactor, a coagulation device 3, a washing device 4, a drainer 43, and a screw-type twin-screw extrusion dryer, none of which are shown.

[0259] The emulsion polymerization reactor is configured to perform the treatment related to the emulsion polymerization step described above. Although not shown in FIG. 1 , this emulsion polymerization reactor includes, for example, a polymerization reaction tank, a temperature control unit for controlling the reaction temperature, and a stirring device equipped with a motor and stirring blades. In the emulsion polymerization reactor, the monomer components for forming the acrylic rubber are mixed with water and an emulsifier and emulsified while being appropriately stirred with a stirrer. The emulsion polymerization reaction is initiated in the presence of a redox catalyst consisting of an inorganic radical generator and a reducing agent, and a chain transfer agent is added batchwise during the polymerization to obtain an emulsion polymerization liquid. The emulsion polymerization reactor may be a batch, semi-batch, or continuous reactor, and may be either a tank reactor or a tubular reactor.

[0260] The coagulation device 3 shown in Fig. 1 is configured to perform the treatment related to the coagulation step described above. As schematically shown in Fig. 1, the coagulation device 3 includes, 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 stirring blades 33, and a drive control unit (not shown) that controls the number of rotations and rotation speed of the stirring blades 33. In the coagulation device 3, the emulsion polymerization liquid obtained in the emulsion polymerization reactor can be brought into contact with a coagulation liquid and coagulated to produce water-containing crumbs.

[0261] 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 being stirred. That is, the stirring tank 30 of the coagulation device 3 is filled with the 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 producing water-containing crumbs.

[0262] 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 heating operation of the heating unit 31 while monitoring the temperature inside the stirring tank 30 measured by a thermometer, thereby controlling the temperature inside the stirring tank 30. 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.

[0263] The agitator 34 of the solidification device 3 is configured to agitate the coagulation liquid filled in the agitation tank 30. Specifically, the agitator 34 includes 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 rotates around the rotation axis by the rotational power of the motor 32 within the coagulation liquid filled in the agitation tank 30, thereby causing the coagulation liquid to flow. The shape, size, and number of the agitator blades 33 to be installed are not particularly limited.

[0264] The drive control unit of the solidification device 3 is configured to control the rotational drive of the motor 32 of the agitator 34 to set the rotation number and rotation speed of the agitator blade 33 of the agitator 34 to a predetermined value. The drive control unit controls the rotation of the agitator blade 33 so that the agitation speed of the solidification liquid is, for example, typically 100 rpm or higher, preferably 200 to 1000 rpm, more preferably 300 to 900 rpm, and particularly preferably 400 to 800 rpm. The drive control unit controls the rotation of the agitator blade 33 so that the peripheral speed of the solidification liquid is typically 0.5 m / s or higher, preferably 1 m / s or higher, more preferably 1.5 m / s or higher, particularly preferably 2 m / s or higher, and most preferably 2.5 m / s or higher. Furthermore, the drive control unit controls the rotation of the agitator blade 33 so that the upper limit of the peripheral speed of the solidification liquid is typically 50 m / s or lower, preferably 30 m / s or lower, more preferably 25 m / s or lower, and most preferably 20 m / s or lower.

[0265] Washing apparatus 4 shown in Fig. 1 is configured to perform the treatment related to the above-described washing step. As schematically shown in Fig. 1, washing apparatus 4 has, for example, washing tank 40, heating unit 41 that heats the interior of washing tank 40, and a temperature control unit (not shown) that controls the temperature inside washing tank 40. In washing apparatus 4, the water-containing crumbs generated in solidification apparatus 3 are mixed with a large amount of water and washed, thereby making it possible to effectively reduce the amount of ash in the finally obtained acrylic rubber sheet or acrylic rubber veil.

[0266] 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 heating operation of the heating unit 41 while monitoring the temperature inside the cleaning tank 40 measured by a thermometer, thereby controlling the temperature inside the cleaning tank 40. As described above, the temperature of the cleaning water inside the cleaning tank 40 is controlled to be usually 40°C or higher, preferably in the range of 40 to 100°C, more preferably 50 to 90°C, and most preferably 60 to 80°C.

[0267] The water-containing crumbs washed in the washing device 4 are supplied to a screw-type twin-screw extruder dryer 5, which performs a dehydration step and a drying step. At this time, the washed water-containing crumbs are preferably supplied to the screw-type twin-screw extruder dryer 5 through a drainer 43 capable of separating free water. The drainer 43 may be, for example, a wire mesh, a screen, or an electric sieve.

[0268] Furthermore, when the washed wet crumbs are supplied to the screw twin-screw extruder 5, the temperature of the wet crumbs is preferably 40°C or higher, more preferably 60°C or higher. For example, the temperature of the water used for washing in the washing device 4 may be set to 60°C or higher (e.g., 70°C), so that the temperature of the wet crumbs when supplied to the screw twin-screw extruder 5 can be maintained at 60°C or higher, or the wet crumbs may be heated to a temperature of 40°C or higher, preferably 60°C or higher, when transported from the washing device 4 to the screw twin-screw extruder 5. This makes it possible to effectively perform the subsequent dehydration and drying steps, and significantly reduce the moisture content of the finally obtained dried rubber.

[0269] The screw twin-screw extruder dryer 5 shown in Fig. 1 is configured to perform the treatments related to the dehydration step and drying step described above. Although the screw twin-screw extruder dryer 5 is shown in Fig. 1 as a suitable example, a centrifuge or squeezer may also be used as a dehydrator that performs the treatment related to the dehydration step, and a hot air dryer, reduced pressure dryer, expander dryer, kneader dryer, etc. may also be used as a dryer that performs the treatment related to the drying step.

[0270] The screw twin-screw extrusion dryer 5 is configured to mold the dried rubber obtained through the dehydration process and the drying process into a predetermined shape and discharge it. Specifically, the screw twin-screw extrusion dryer 5 is equipped with a dehydration barrel section 53 that functions as a dehydrator for dehydrating the water-containing crumbs washed in the washing device 4, and a drying barrel section 54 that functions as a dryer for drying the water-containing crumbs, and is further equipped with a die 59 downstream of the screw twin-screw extrusion dryer 5 that has a molding function for molding the water-containing crumbs.

[0271] The configuration of the screw twin-screw extruder 5 will be described below with reference to Fig. 2. Fig. 2 shows the configuration of a specific example suitable for the screw twin-screw extruder 5 shown in Fig. 1. This screw twin-screw extruder 5 can suitably carry out the above-mentioned dehydration and drying process.

[0272] The screw-type twin-screw extruder 5 shown in FIG. 2 is a twin-screw extruder dryer equipped with a pair of screws (not shown) in a barrel unit 51. The screw-type twin-screw extruder dryer 5 has a drive unit 50 that rotates and drives the pair of screws in the barrel unit 51. This configuration is suitable for drying by applying a high shear to the acrylic rubber. The drive unit 50 is attached to the upstream end (left end in FIG. 2) of the barrel unit 51. The screw-type twin-screw extruder dryer 5 also has a die 59 at the downstream end (right end in FIG. 2) of the barrel unit 51.

[0273] The barrel unit 51 has a supply barrel section 52, a dehydration barrel section 53, and a drying barrel section 54, from the upstream side to the downstream side (from the left side to the right side in FIG. 2).

[0274] The supply barrel section 52 is made up of two supply barrels, that is, a first supply barrel 52a and a second supply barrel 52b.

[0275] The dehydration barrel section 53 is made up of three dehydration barrels, namely, a first dehydration barrel 53a, a second dehydration barrel 53b, and a third dehydration barrel 53c.

[0276] 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.

[0277] In this way, the barrel unit 51 is configured by connecting 13 divided barrels 52a to 52b, 53a to 53c, and 54a to 54h from the upstream side to the downstream side.

[0278] The screw-type twin-screw extruder 5 also includes heating means (not shown) that individually heat each of the barrels 52a-52b, 53a-53c, and 54a-54h to heat the water-containing crumb in each of the barrels 52a-52b, 53a-53c, and 54a-54h to a predetermined temperature. The number of heating means corresponds to the number of barrels 52a-52b, 53a-53c, and 54a-54h. Examples of such heating means include, but are not limited to, a steam supply means that supplies high-temperature steam to a steam distribution jacket formed in each of the barrels 52a-52b, 53a-53c, and 54a-54h. The screw-type twin-screw extruder 5 also includes temperature control means (not shown) that control the set temperature of each heating means corresponding to each of the barrels 52a-52b, 53a-53c, and 54a-54h.

[0279] The number of supply barrels, dewatering barrels, and drying barrels that respectively constitute each of barrel portions 52, 53, and 54 in barrel unit 51 is not limited to the embodiment shown in FIG. 2, and can be set to a number that depends on factors such as the moisture content of the water-containing acrylic rubber crumbs to be dried.

[0280] For example, the number of supply barrels installed in supply barrel section 52 is, for example, 1 to 3. The number of dehydration barrels installed in 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 water-containing crumbs of sticky acrylic rubber. The number of drying barrels installed in drying barrel section 54 is, for example, preferably 2 to 10, and more preferably 3 to 8.

[0281] The pair of screws in the barrel unit 51 are driven to rotate by a driving means such as a motor housed in the drive unit 50. The pair of screws extend from the upstream side to the downstream side within the barrel unit 51, and by being driven to rotate, the wet crumb supplied to the supply barrel section 52 can be mixed and transported downstream. The pair of screws are preferably of a twin-screw intermeshing type in which the crests and troughs of the screws are intermeshed with each other, which can improve the dewatering efficiency and drying efficiency of the wet crumb.

[0282] The pair of screws may rotate in the same direction or in opposite directions, but from the viewpoint of self-cleaning performance, a type in which they rotate in the same direction is preferred. The screw shape of the pair of screws is not particularly limited as long as it has a shape required for each of barrel portions 52, 53, and 54.

[0283] The supply barrel section 52 is a region for supplying the wet crumbs into the barrel unit 51. The first supply barrel 52a of the supply barrel section 52 has a feed port 55 for supplying the wet crumbs into the barrel unit 51.

[0284] The dewatering barrel section 53 is a region where a liquid (serum water) containing a coagulant and the like is separated from the water-containing crumbs and discharged.

[0285] The first to third dewatering barrels 53a to 53c constituting the dewatering barrel section 53 each have dewatering slits 56a, 56b, and 56c for discharging moisture from the wet crumbs to the outside. A plurality of dewatering slits 56a, 56b, and 56c are formed in each of the dewatering barrels 53a to 53c.

[0286] The slit width, i.e., opening, of each dewatering slit 56a, 56b, 56c may be selected appropriately depending on the conditions of use, and is typically 0.01 to 5 mm. In order to minimize loss of water-containing crumb and enable efficient dewatering of the water-containing crumb, the slit width is preferably 0.1 to 1 mm, and more preferably 0.2 to 0.6 mm.

[0287] There are two ways to remove water from the wet crumb in each of the dewatering barrels 53a to 53c of the dewatering barrel section 53: removal in liquid form from the respective dewatering slits 56a, 56b, 56c, and removal in vapor form. In the dewatering barrel section 53 of this embodiment, removal of water in liquid form is defined as drainage, and removal of water in vapor form is defined as exhaust steam, to distinguish between the two.

[0288] In the dehydration barrel section 53, a combination of drainage and steam discharge is preferable because it can efficiently reduce the moisture content of the adhesive 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 discharge can be appropriately selected depending on the intended use. However, to reduce the ash content of the acrylic rubber produced, it is generally recommended to increase the number of dehydration barrels used for drainage. In this case, as shown in FIG. 2, for example, drainage is performed in the first and second upstream dehydration barrels 53a and 53b, and steam discharge is performed in the third downstream dehydration barrel 53c. Furthermore, if the dehydration barrel section 53 has four dehydration barrels, for example, drainage can be performed in the three upstream dehydration barrels and steam discharge in the one downstream dehydration barrel. On the other hand, to reduce the moisture content, it is recommended to increase the number of dehydration barrels used for steam discharge.

[0289] As described above in the dehydration / 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.

[0290] The drying barrel section 54 is a region where the dehydrated wet 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 vent ports 58a, 58b, 58c, and 58d for degassing. Vent pipes (not shown) are connected to the vent ports 58a, 58b, 58c, and 58d, respectively.

[0291] A vacuum pump (not shown) is connected to the end of each vent pipe, and operation of these vacuum pumps reduces the pressure inside the drying barrel section 54 to a predetermined level. The screw extruder 5 has pressure control means (not shown) that controls the operation of these vacuum pumps to control the degree of pressure reduction inside the drying barrel section 54.

[0292] The degree of reduced pressure in the drying barrel section 54 may be selected as appropriate, but as described above, it is usually set to 1 to 50 kPa, preferably 2 to 30 kPa, and more preferably 3 to 20 kPa.

[0293] The temperature set in the drying barrel section 54 may be selected as appropriate, but as described above, it is usually set to 100 to 250°C, preferably 110 to 200°C, and more preferably 120 to 180°C.

[0294] In each of the drying barrels 54a to 54h that make up the drying barrel section 54, the set temperatures within all of the drying barrels 54a to 54h 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), as this improves drying efficiency.

[0295] The die 59 is a mold placed at the downstream end of the barrel unit 51 and has a discharge opening of a predetermined nozzle shape. The acrylic rubber dried in the drying barrel section 54 passes through the discharge opening of the die 59 and is extruded into a shape that corresponds to the predetermined nozzle shape. The acrylic rubber that passes through the die 59 can be molded into various shapes such as granules, columns, rods, and sheets depending on the nozzle shape of the die 59, but in the present invention, it is molded into a sheet. A breaker plate or wire mesh may or may not be provided between the screw and the die 59.

[0296] The hydrous crumbs of acrylic rubber obtained through the washing step are supplied to the supply barrel section 52 from the feed port 55. The hydrous crumbs supplied to the supply barrel section 52 are transferred from the supply barrel section 52 to the dehydration barrel section 53 by the rotation of the pair of screws in the barrel unit 51. In the dehydration barrel section 53, the water contained in the hydrous crumbs is drained and steam is exhausted from the dehydration slits 56a, 56b, 56c provided in the first to third dehydration barrels 53a to 53c, respectively, as described above, and the hydrous crumbs are dehydrated.

[0297] The water-containing crumbs dewatered in the dewatering 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 water-containing crumbs sent to the drying barrel section 54 are plasticized and mixed to form a melt, and are transported downstream while generating heat and increasing in temperature. The water contained in this acrylic rubber melt then vaporizes, and the water (vapor) is discharged to the outside through vent pipes (not shown) connected to each of the vent ports 58a, 58b, 58c, and 58d.

[0298] As described above, by passing through the drying barrel section 54, the water-containing crumb is dried and becomes a melted acrylic rubber, and the acrylic rubber is supplied to the die 59 by the rotation of a pair of screws in the barrel unit 51 and extruded from the die 59.

[0299] Here, an example of the operating conditions of the screw-type twin-screw extruding dryer 5 according to this embodiment will be given.

[0300] The rotation speed (N) of the pair of screws in the barrel unit 51 may be appropriately selected depending on various conditions, and is normally set to 10 to 1000 rpm. From the viewpoint of efficiently reducing the water content and methyl ethyl ketone insoluble content of the acrylic rubber, the rotation speed is preferably 50 to 750 rpm, more preferably 100 to 500 rpm, and most preferably 120 to 300 rpm.

[0301] The extrusion rate (Q) of the acrylic rubber is not particularly limited, but is usually 100 to 1500 kg / hr, preferably 300 to 1200 kg / hr, more preferably 400 to 1000 kg / hr, and most preferably 500 to 800 kg / hr.

[0302] The ratio (Q / N) of the extrusion rate (Q) of the acrylic rubber 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.

[0303] The maximum torque in barrel unit 51 is not particularly limited, but is usually in the range of 30 to 100 N·m, preferably 35 to 75 N·m, and more preferably 40 to 60 N·m.

[0304] The specific power within barrel unit 51 is not particularly limited, but is usually in the range of 0.1 to 0.25 [kw·h / kg] or more, preferably 0.13 to 0.23 [kw·h / kg], and more preferably 0.15 to 0.2 [kw·h / kg].

[0305] The specific power within barrel unit 51 is not particularly limited, but is usually in the range of 0.2 to 0.6 [A·h / kg] or more, preferably 0.25 to 0.55 [A·h / kg], and more preferably 0.35 to 0.5 [A·h / kg].

[0306] The shear rate in barrel unit 51 is not particularly limited, but is usually in the range of 40 to 150 [1 / s] or more, preferably 45 to 125 [1 / s], and more preferably 50 to 100 [1 / s].

[0307] The shear viscosity of the acrylic rubber in the barrel unit 51 is not particularly limited, but is usually in the range of 4000 to 8000 [Pa·s], preferably 4500 to 7500 [Pa·s], and more preferably 5000 to 7000 [Pa·s].

[0308] 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 a fan or air conditioner, a water-spraying method in which water is sprayed, and an immersion method in which the dried rubber is immersed in water. The dried rubber may also be cooled by leaving it at room temperature.

[0309] As described above, the dried rubber discharged from the screw extruder 5 is extruded and molded into various shapes such as granules, columns, rods, and sheets depending on the nozzle shape of the die 59, but in the present invention, it is molded into a sheet. Hereinafter, with reference to Figure 3, a conveying cooling device 60 that cools the dried rubber sheet 10 molded into a sheet will be described as an example of the cooling device 6.

[0310] Fig. 3 shows the configuration of a conveying-type cooling device 60 suitable for use as the cooling device 6 shown in Fig. 1. The conveying-type cooling device 60 shown in Fig. 3 is configured to cool the dry rubber sheet 10 discharged from the discharge port of the die 59 of the screw extruder 5 by air cooling while conveying the dry rubber sheet 10. By using this conveying-type cooling device 60, the dry rubber sheet discharged from the screw extruder 5 can be suitably cooled.

[0311] The conveying cooling device 60 shown in FIG. 3 is used by being directly connected to the die 59 of the screw-type extruder 5 shown in FIG.

[0312] The conveying type 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 Figure 3, and a cooling means 65 that blows cold air onto the sheet-like dried rubber 10 on the conveyor 61.

[0313] The conveyor 61 has rollers 62 and 63, and a conveyor belt 64 that is wound around the rollers 62 and 63 and on which the sheet-like dry rubber 10 is placed. The conveyor 61 is configured to continuously transport the sheet-like dry 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).

[0314] The cooling means 65 is not particularly limited, but may be, for example, a means 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.

[0315] The length L1 of the conveyor 61 and cooling means 65 of the transportable cooling device 60 (the length of the portion 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 dry rubber sheet 10 in the transportable cooling device 60 may be adjusted appropriately depending on the length L1 of the conveyor 61 and cooling means 65, the discharge speed of the dry rubber sheet 10 discharged from the die 59 of the screw extruder 5, the target cooling speed and cooling time, and the like, but is, for example, 10 to 100 m / hr, and more preferably 15 to 70 m / hr.

[0316] According to the conveying type cooling device 60 shown in Figure 3, the sheet-like dry rubber 10 discharged from the die 59 of the screw-type extruder 5 is transported on a conveyor 61, and cooling air is blown onto the sheet-like dry rubber 10 from a cooling means 65, thereby cooling the sheet-like dry rubber 10.

[0317] 3, the transportable cooling device 60 is not particularly limited to a configuration including one conveyor 61 and one cooling means 65, but may be configured to include 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 cooling means 65 may be within the above range.

[0318] The baling device 7 shown in Figure 1 is configured to process dried rubber extruded from the screw extruder 5 and cooled in the cooler 6 to produce bales, which are single blocks. As described above, the screw extruder 5 is capable of extruding dried rubber into various shapes, such as granules, columns, rods, and sheets, and the baling device 7 is configured to bale the dried rubber molded into these various shapes. There are no particular restrictions on the weight or shape of the acrylic rubber bales produced by the baling device 7, but for example, approximately rectangular parallelepiped acrylic rubber bales weighing approximately 20 kg are produced.

[0319] The baling device 7 may include, for example, a baler, and may produce acrylic rubber bales by compressing the cooled, dried rubber with the baler.

[0320] Furthermore, when dry rubber sheet 10 is produced using screw extruder 5, an acrylic rubber bale may be produced in which the dry rubber sheet 10 is layered. For example, a cutting mechanism for cutting the dry rubber sheet 10 may be provided in baling device 7, which is located downstream of conveyor-type cooling device 60 shown in FIG. 3. Specifically, the cutting mechanism of baling device 7 is configured, for example, to continuously cut cooled dry rubber sheet 10 at predetermined intervals to process it into cut dry rubber sheets 16 of a predetermined size. A plurality of cut dry rubber sheets 16 cut to a predetermined size by the cutting mechanism are layered to produce an acrylic rubber bale in which the cut dry rubber sheets 16 are layered.

[0321] When producing a veil-shaped acrylic rubber laminated with cut sheet-shaped dry rubber 16, it is preferable to laminate the cut sheet-shaped dry rubber 16 at a temperature of, for example, 40° C. or higher. By laminating the cut sheet-shaped dry rubber 16 at a temperature of 40° C. or higher, good air release is achieved by further cooling and compression due to its own weight. [Example]

[0322] The present invention will be described in more detail below with reference to examples and comparative examples. In each example, "parts," "%," and "ratio" are by weight unless otherwise specified. Various physical properties were evaluated according to the following methods.

[0323] [Monomer composition] Regarding the monomer composition of acrylic rubber, the monomer composition of each monomer unit in acrylic rubber is 1 The remaining activity of reactive groups in the acrylic rubber was confirmed by H-NMR, and the content of each reactive group was confirmed by the following method. The content ratio of each monomer unit in the acrylic rubber was calculated from the amount of each monomer used in the polymerization reaction and the polymerization conversion rate. Specifically, the polymerization reaction was an emulsion polymerization reaction, and the polymerization conversion rate was approximately 100%, with no unreacted monomers detected, so the content ratio of each monomer unit in the rubber was set to be the same as the amount of each monomer used.

[0324] [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 a rubber sample in acetone and performing potentiometric titration with a potassium hydroxide solution. (2) The amount of epoxy groups was calculated by dissolving the rubber sample in methyl ethyl ketone, adding a specified amount of hydrochloric acid to react with the epoxy groups, and titrating the amount of residual hydrochloric acid with potassium hydroxide. (3) The amount of chlorine was calculated by completely burning a rubber sample in a combustion flask, absorbing the generated chlorine into water, and titrating it with silver nitrate.

[0325] [Ash content] The ash content (%) in the acrylic rubber sheet or acrylic rubber bale was measured in accordance with JIS K6228 Method A.

[0326] [Ash content] The amount (ppm) of each component in the acrylic rubber sheet or acrylic rubber bale ash was measured by XRF using ZSX Primus (manufactured by Rigaku Co., Ltd.) after pressing the ash sampled during the above ash content measurement onto a 20 mm diameter titration filter paper.

[0327] [Molecular weight and molecular weight distribution] The molecular weights (Mw, Mn, Mz) and molecular weight distributions (Mw / Mn and Mz / Mw) of acrylic rubber are absolute molecular weights and absolute molecular weight distributions measured by the GPC-MALS method using a solution of dimethylformamide as the solvent to which lithium chloride was added at a concentration of 0.05 mol / L and 37% concentrated hydrochloric acid was added at a concentration of 0.01%. The gel permeation chromatography multi-angle light scattering photometer used in this experiment consisted of a pump (LC-20ADOpt, Shimadzu Corporation), a differential refractometer (Optilab rEX, Wyatt Technology) as the detector, and a multi-angle light scattering detector (DAWN HELEOS, Wyatt Technology). Specifically, a multi-angle laser light scattering photometer (MALS) and a differential refractometer (RI) were incorporated into the GPC (Gel Permeation Chromatography) apparatus. The light scattering intensity and refractive index difference of the molecular chain solution separated by size in the GPC apparatus were measured over time to sequentially calculate the molecular weight and content of the solute. The measurement conditions and method for the GPC were as follows: Column: Two TSKgel α-M columns (φ7.8 mm x 30 cm, manufactured by Tosoh Corporation) Column temperature: 40℃ Flow rate: 0.8ml / mm Sample preparation: 5 ml of solvent was added to 10 mg of sample (acrylic rubber sheet or acrylic rubber veil), and the mixture was gently stirred at room temperature (dissolution was visually confirmed), followed by filtration using a 0.5 μm filter.

[0328] [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).

[0329] [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 acrylic rubber sheet or acrylic rubber bale was weighed (X g), immersed in 100 ml of methyl ethyl ketone, and left to stand at room temperature for 24 hours. After that, the insoluble matter in methyl ethyl ketone was filtered off using an 80-mesh wire netting. The filtrate, in other words, the filtrate containing only the rubber components soluble in methyl ethyl ketone, was evaporated, dried, and solidified. The dry solid content (Y g) was then weighed and calculated using the following formula. Methyl ethyl ketone insoluble content (%) = 100 x (XY) / X

[0330] [specific gravity] The specific gravity of the acrylic rubber sheet or acrylic rubber veil was measured in accordance with Method A of JIS K6268 Crosslinked Rubber - Density Measurement. The measurement value obtained by the following measurement method is density, and the density of water is 1 Mg / m 3 The specific gravity is calculated as follows. Specifically, the specific gravity of a rubber sample determined in accordance with JIS K6268 Cross-linked Rubber - Density Measurement, Method A, is calculated by dividing the mass by the volume including the voids in the rubber sample, and is calculated by dividing the density of the rubber sample measured in accordance with JIS K6268 Cross-linked Rubber - Density Measurement, Method A, by the density of water (if the density of a rubber sample is divided by the density of water, the numerical value remains the same but the unit is lost). More specifically, the specific gravity of a rubber sample can be calculated according to the following procedure. (1) A 2.5g test piece is cut out from a rubber sample that has been left to stand at standard temperature (23°C ± 2°C) for at least 3 hours, and suspended from the hook of an analytical balance with an accuracy of 1 mg using a thin nylon thread with a mass of less than 0.010g so that the bottom of the test piece is 25mm above the distributing pan of the analytical balance. The mass (m1) of the test piece is measured twice in the air to the nearest mg. (2) Next, place a 250 cm 3Fill a cubic meter beaker with distilled water that has been boiled and then cooled to the standard temperature, immerse the test piece in it, remove any air bubbles adhering to the surface of the test piece, observe the movement of the balance pointer for several seconds, and confirm that the pointer gradually stops touching due to convection, then measure the mass (m2) of the test piece in the water twice in mg. (3) Also, the density of the test piece is 1 Mg / m 3 If the test specimen is less than this (if the test specimen floats in water), attach a weight to the test specimen and measure the mass of the weight in water (m3) and the mass of the test specimen and weight (m4) twice in mg units. (4) The specific gravity of the rubber sample was calculated by the density (Mg / m) according to the following formula using the average values ​​of m1, m2, m3, and m4 measured above. 3 ) and multiply the calculated density by the density of water (1.00 Mg / m 3 ) to find the answer. (Density of rubber sample without weight) Density=m1 / (m1-m2) (Density of rubber sample when weight is used) Density=m1 / (m1+m3-m4)

[0331] [Water content] The water content (%) was measured in accordance with JIS K6238-1: Oven A (volatile content measurement) method.

[0332] [pH] The pH was measured with a pH electrode after dissolving 6 g (±0.05 g) of acrylic rubber sheet or acrylic rubber veil in 100 g of tetrahydrofuran, adding 2.0 ml of distilled water, and confirming complete dissolution.

[0333] [Complex viscosity] The complex viscosity η was determined by measuring the temperature dispersion (40 to 120°C) at 1 Hz and 473% strain using a dynamic viscoelasticity measuring device, Rubber Process Analyzer RPA-2000 (manufactured by Alpha Technology Co., Ltd.). Here, the dynamic viscoelasticity at 60°C was taken as the complex viscosity η(60°C) and the dynamic viscoelasticity at 100°C as the complex viscosity η(100°C), and the ratio η(100°C) / η(60°C) was calculated.

[0334] [Mooney viscosity (ML1+4, 100℃)] The Mooney viscosity (ML1+4, 100°C) was measured in accordance with the physical testing method for uncrosslinked rubber of JIS K6300.

[0335] [Evaluation of gel amount variation] The variation in gel amount of the rubber sample was evaluated by measuring the gel amount at 20 points arbitrarily selected from 20 parts (20 kg) of the rubber sample and evaluating it based on the following criteria. ◎: The average gel amount of the 20 measured points was calculated, and all 20 measured points were within the range of the average value ±3. ○: The average gel amount of the 20 measured points was calculated, and all 20 measured points were within the range of the average value ±5 (even one of the 20 measured points would be outside the range of the average value ±3, but all 20 points were within the range of the average value ±5) ×: The average value of the gel amounts at 20 measured points was calculated, and even one of the 20 measured points was outside the range of the average value ±5.

[0336] [Crosslinkability] The crosslinkability of the rubber sample was evaluated by calculating the rate of change between the breaking strength of the cross-linked rubber product after 2 hours of secondary crosslinking and the breaking strength of the cross-linked rubber product after 4 hours of secondary crosslinking ((breaking strength of the cross-linked rubber product after 4 hours of crosslinking / breaking strength of the cross-linked rubber product after 2 hours of crosslinking) × 100) and evaluating it according to the following criteria. ◎: Breaking strength change rate is less than 10% ×: Breaking strength change rate is 10% or more

[0337] [Roll processability] The roll processability of the rubber sample was evaluated by observing the roll wrapping property and the state of the rubber when the rubber sample was roll-kneaded, and was evaluated according to the following criteria. ◎: Easy to knead, easily wraps around the roll and does not separate from the roll, and the surface of the rubber composition after kneading is smooth ◯: The rubber composition was easy to knead, easily wrapped around the roll, and did not separate from the roll. Slight unevenness was observed on part of the surface of the kneaded rubber composition. □: Easy to knead, excellent roll wrapping, and the surface of the rubber composition after kneading is somewhat uneven △: Easy to knead, slightly poor roll wrapping, and rough surface of the rubber composition after kneading ×: Load is applied to kneading and roll wrapping is poor

[0338] [Banbury processability] The Banbury processability of the rubber sample was evaluated by adding the rubber sample to a Banbury mixer heated to 50°C and masticating for 1 minute. Then, compounding ingredient A of the rubber mixture formulation shown in Table 1 was added, and the time until the rubber mixture in the first stage was integrated and showed the maximum torque value, i.e., the Black Incorporation Time (BIT), was measured and evaluated using an index with Comparative Example 2 set to 100 (the smaller the index, the better the processability).

[0339] [Storage stability evaluation] The storage stability of the rubber samples was evaluated by placing the rubber samples in a constant temperature and humidity chamber (SH-222 manufactured by ESPEC) at 45°C x 80% RH, calculating the rate of change in water content before and after a 7-day test, and using an index based on 100 for Comparative Example 2 (the smaller the index, the better the storage stability).

[0340] [Water resistance evaluation] The water resistance of the rubber sample was evaluated by an immersion test in accordance with JIS K6258, in which a cross-linked rubber sample was immersed in distilled water at a temperature of 85°C for 100 hours, and the volume change rate before and after immersion was calculated according to the following formula, and evaluated using an index where Comparative Example 2 is set to 100 (the smaller the index, the better the water resistance). Volume change rate before and after immersion (%) = ((volume of test piece after immersion - volume of test piece before immersion) / volume of test piece before immersion) × 100

[0341] [Compression set resistance] The compression set resistance of the rubber sample was evaluated according to JIS K6262 by measuring the compression set rate after the cross-linked rubber sample was compressed by 25% and left at 175°C for 90 hours, and then evaluated according to the following criteria. ◎: Compression set rate is less than 15% ×: Compression set rate is 15% or more

[0342] [Normal state physical property evaluation] The normal 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 rated as ⊚, and less than 10 MPa is rated 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%.

[0343] [Evaluation of processing stability by suppressing Mooney scorch] The cooling rate of a sheet-shaped acrylic rubber extruded from a screw-type twin-screw extruder described in Japanese Patent No. 6683189 and the Mooney scorch stability of the acrylic rubber composition were evaluated.

[0344] [Example 1] As shown in Table 2-1, 46 parts of pure water, 74.5 parts of ethyl acrylate, 17 parts of n-butyl acrylate, 7 parts of methoxyethyl acrylate, and 1.5 parts of mono-n-butyl fumarate as monomer components, and 1.8 parts of tridecyloxyhexaoxyethylene phosphate sodium salt as an emulsifier were charged into a mixing vessel equipped with a homomixer and stirred to obtain a monomer emulsion.

[0345] A polymerization reactor equipped with a thermometer and a stirrer was charged with 170 parts of pure water and 3 parts of the monomer emulsion obtained above, cooled to 12°C under a nitrogen stream, and then charged with 0.00033 parts of ferrous sulfate, 0.02 parts of sodium ascorbate, and 0.21 parts of an inorganic radical generator, potassium persulfate, to initiate the polymerization reaction. The temperature in the polymerization reactor was maintained at 23°C, and the remaining monomer emulsion was continuously added dropwise over 3 hours. 50 minutes after the start of the reaction, 0.017 parts of n-dodecyl mercaptan, 100 minutes after, and 120 minutes after, 0.017 parts of n-dodecyl mercaptan and 0.4 parts of sodium L-ascorbate were added to continue the polymerization reaction. When the polymerization conversion reached approximately 100%, hydroquinone was added as a polymerization terminator to terminate the polymerization reaction, yielding a polymerization emulsion.

[0346] Next, in a coagulation tank equipped with a thermometer and a stirrer, the emulsion polymerization liquid obtained above was heated to 80°C and continuously added to 350 parts of a 2% aqueous magnesium sulfate solution (coagulation liquid using magnesium sulfate as a coagulant) heated to 80°C and vigorously stirred at a stirring blade rotation speed of 600 rpm (circumferential speed of 3.1 m / s) of the stirrer, thereby coagulating the polymer and obtaining a coagulated slurry containing acrylic rubber crumbs as the coagulated product and water. The crumbs were filtered out from the obtained slurry, and water-containing crumbs were obtained by draining the water from the coagulated layer.

[0347] 194 parts of hot water (70°C) was added to the coagulation tank containing the filtered wet crumbs and stirred for 15 minutes to wash the wet crumbs. The water was then drained, and 194 parts of hot water (70°C) was added again and stirred for 15 minutes to wash the wet crumbs (a total of two washes). The washed wet crumbs (wet crumb temperature 65°C) were fed to a screw-type twin-screw extruder 15, where they were dehydrated and dried, and a dry rubber sheet 300 mm wide and 10 mm thick was extruded. Next, the dry rubber sheet was cooled at a cooling rate of 200°C / hr using a conveying extrusion device directly connected to the screw-type twin-screw extruder 15, to obtain an acrylic rubber sheet (A). The acrylic rubber sheet (A) was measured for reactive group content, ash content, ash component content, gel content, pH, specific gravity, glass transition temperature (Tg), water content, molecular weight, molecular weight distribution, and complex viscosity at 100°C and 60°C, and the results are shown in Table 2-2. In addition, the acrylic rubber sheet (A) was tested for gel content variation and storage stability to determine the rate of change in water content, and the results are shown in Table 2-2.

[0348] The screw-type twin-screw extruder used in Example 1 was composed of one feed barrel, three dehydration barrels (first to third dehydration barrels), and five drying barrels (first to fifth drying barrels). The first dehydration barrel discharges water, and the second and third dehydration barrels discharge steam. The operating conditions for the screw-type twin-screw extruder were as follows. Table 2-1 shows the water content after dehydration (drainage), maximum torque, specific power, specific power, shear rate, and shear viscosity of the screw-type twin-screw extruder.

[0349] Water content: Moisture content of the wet crumb after draining in the first dewatering barrel: 20% Moisture content of wet crumb after steaming in the third dehydration barrel: 10% Moisture content of wet crumb after drying in the fifth drying barrel: 0.4% Rubber Temperature: Temperature of wet crumbs fed into the feeding barrel: 65℃ Temperature of rubber discharged from the screw-type twin-screw extruder: 140℃ Set temperature for each barrel: First dehydration barrel: 100℃ Second dehydration barrel: 120℃ Third dehydration barrel: 120℃ First drying barrel: 120℃ Second drying barrel: 130℃ Third drying barrel: 140℃ Fourth drying barrel: 160℃ Fifth drying barrel: 180℃ Operating conditions: Screw diameter (D): 132mm Total length of screw (L): 4620mm Length / Distance: 35 Screw speed: 135 rpm Drying barrel vacuum level: 10kPa Rubber extrusion rate from die: 700 kg / hr Resin pressure in the die: 2MPa Maximum torque in screw-type twin-screw extruder: 15 N·m

[0350] The extruded dry rubber sheet was cooled to 50°C, cut with a cutter, and laminated to 20 parts (20 kg) before the temperature dropped below 40°C to obtain acrylic rubber bale (A). The reactive group content, ash content, ash component content, gel content, pH, specific gravity, glass transition temperature (Tg), water content, molecular weight, molecular weight distribution, and complex viscosity at 100°C and 60°C of the obtained acrylic rubber bale (A) were measured. The gel content variation and storage stability of the acrylic rubber bale (A) were also measured to determine the rate of change in water content.

[0351] Next, 100 parts of the acrylic rubber sheet (A) and compounding ingredient A of "Compound 1" shown in Table 1 were added to a Banbury mixer and mixed for 5 minutes at 50°C (first-stage mixing). The BIT at this stage was measured to evaluate the Banbury processability of the acrylic rubber, and the results are shown in Table 2-2.

[0352] Next, the resulting mixture was transferred to a roll at 50°C, and compounding ingredient B of "Compound 1" was compounded and mixed (second-stage mixing) to obtain a rubber mixture. The roll processability at this stage was evaluated, and the results are shown in Table 2-2.

[0353] [Table 1]

[0354] The resulting 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 effect primary crosslinking. The resulting primary crosslinked product was then heated in a gear oven at 180°C for 2 hours to effect secondary crosslinking, thereby obtaining a sheet-like crosslinked rubber product. Test pieces measuring 3 cm x 2 cm x 0.2 cm were then cut from the resulting sheet-like crosslinked rubber product to evaluate water resistance, compression set resistance, and normal state physical properties. Furthermore, the normal state physical properties of the sheet-like crosslinked rubber product, which had been subjected to secondary crosslinking for an additional 2 hours, were measured to evaluate crosslinkability. The results are shown in Table 2-2.

[0355] [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 1.8 parts of nonylphenyloxyhexaoxyethylene phosphate sodium salt, to obtain an acrylic rubber sheet (B) and an acrylic rubber veil (B), and the properties of these were evaluated. The results for the acrylic rubber sheet (B) are shown in Table 2-2.

[0356] [Example 3] The same procedure as in Example 1 was repeated, except that the amount of potassium persulfate was changed to 0.2 parts and the post-addition of n-dodecyl mercaptan was changed to two times: 0.0072 parts after 50 minutes and 0.0036 parts after 100 minutes. An acrylic rubber sheet (C) and an acrylic rubber veil (C) were obtained and their properties were evaluated. The results for the acrylic rubber sheet (C) are shown in Table 2-2.

[0357] [Example 4] The same procedure as in Example 3 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 1.8 parts of octyloxyhexaoxyethylene phosphate sodium salt, to obtain an acrylic rubber sheet (D) and an acrylic rubber veil (D), and the properties of the acrylic rubber sheet (D) were evaluated. The results for the acrylic rubber sheet (D) are shown in Table 2-2.

[0358] [Example 5] The same procedures as in Example 1 were carried out, except that the monomer components were changed to 28 parts ethyl acrylate, 38 parts n-butyl acrylate, 27 parts methoxyethyl acrylate, 5 parts acrylonitrile, and 2 parts allyl glycidyl ether, and the maximum torque of the screw-type twin-screw extruder was changed to 45 N m. 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 2"). The results for the acrylic rubber sheet (E) are shown in Table 2-2.

[0359] [Example 6] The same procedure as in Example 5 was carried out except that the monomer components were changed to 48.5 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.5 parts of mono-n-butyl fumarate, and an acrylic rubber sheet (F) and an acrylic rubber veil (F) were obtained and their properties were evaluated (the compounding agent was changed to "Compound 1"). The results for the acrylic rubber sheet (F) are shown in Table 2-2.

[0360] [Example 7] The same procedure as in Example 5 was carried out except that the monomer components were changed to 48.25 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.75 parts of mono-n-butyl fumarate, and an acrylic rubber sheet (G) and an acrylic rubber veil (G) were obtained and their properties were evaluated (the compounding agent was changed to "Compound 3"). The results for the acrylic rubber sheet (G) are shown in Table 2-2.

[0361] [Example 8] The same procedures as in Example 3 were carried out, except that the monomer components were changed to 28 parts ethyl acrylate, 38 parts n-butyl acrylate, 27 parts methoxyethyl acrylate, 5 parts acrylonitrile, and 2 parts allyl glycidyl ether, and the maximum torque of the screw-type twin-screw extruder was changed to 45 N m. An acrylic rubber sheet (H) and an acrylic rubber veil (H) were obtained, and their properties were evaluated (the compounding ingredients were changed to "Compound 2"). The results for the acrylic rubber sheet (H) are shown in Table 2-2.

[0362] [Example 9] The same procedure as in Example 8 was carried out except that the monomer components were changed to 48.5 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.5 parts of mono-n-butyl fumarate, and an acrylic rubber sheet (I) and an acrylic rubber veil (I) were obtained and their properties were evaluated (the compounding agent was changed to "Compound 1"). The results for the acrylic rubber sheet (I) are shown in Table 2-2.

[0363] [Example 10] The same procedure as in Example 8 was carried out except that the monomer components were changed to 48.25 parts of ethyl acrylate, 50 parts of n-butyl acrylate, and 1.75 parts of mono-n-butyl fumarate, and an acrylic rubber sheet (J) and an acrylic rubber veil (J) were obtained and their properties were evaluated (the compounding agent was changed to "Compound 3"). The results for the acrylic rubber sheet (J) are shown in Table 2-2.

[0364] [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, and 1.3 parts of vinyl chloroacetate as monomer components, and 1.8 parts of tridecyloxyhexaoxyethylene phosphate sodium salt as an emulsifier, and the mixture was stirred to obtain a monomer emulsion.

[0365] 170 parts of pure water and 3 parts of the monomer emulsion obtained above were charged into a polymerization reactor equipped with a thermometer and a stirrer, and after cooling to 12°C under a nitrogen stream, 0.00033 parts of ferrous sulfate, 0.02 parts of sodium ascorbate, and 0.22 parts of potassium persulfate were added to initiate the polymerization reaction. The temperature inside the polymerization reactor was kept at 23°C, and the remainder of the monomer emulsion was continuously added dropwise over 3 hours. When the polymerization conversion rate reached approximately 100%, hydroquinone was added as a polymerization terminator to terminate the polymerization reaction, and an emulsion polymerization liquid was obtained.

[0366] Next, the emulsion polymerization liquid was heated to 80°C, and while stirring at a stirring impeller speed of 100 rpm (circumferential speed of 0.5 m / s), a 0.7% magnesium sulfate aqueous solution (coagulation liquid using magnesium sulfate as a coagulant) was added to coagulate the polymer, yielding a coagulated slurry containing acrylic rubber crumbs and water. The crumbs were filtered from the resulting slurry, and the water was drained from the coagulated layer to obtain wet crumbs. 194 parts of warm water (70°C) was added to the coagulation tank containing the filtered wet crumbs and stirred for 15 minutes to wash the wet crumbs, after which the water was drained. Another 194 parts of warm water (70°C) was added and stirred for 15 minutes to wash the wet crumbs (a total of two washes). The washed wet crumbs were dried to a moisture content of 0.4% using a hot air dryer at 160°C to obtain crumb-like acrylic rubber (K). The properties of the resulting crumb-like acrylic rubber (K) were evaluated and are shown in Table 2-2.

[0367] Comparative Example 2 The emulsifier was changed to 0.709 parts sodium lauryl sulfate and 1.82 parts polyoxyethylene dodecyl ether, the coagulation liquid was changed to 0.7% aqueous sodium sulfate, and the washing method was changed as follows: 194 parts of industrial water was added to 100 parts of the hydrous crumbs after the coagulation reaction, and the mixture was stirred in a coagulation tank at 25°C for 5 minutes. The hydrous crumbs were then washed four times by draining the water from the coagulation tank. Next, 194 parts of a pH 3 sulfuric acid solution was added and stirred at 25°C for 5 minutes. The water was then drained from the coagulation tank and acid washed once. Finally, 194 parts of pure water was added and washed once. Crumb-like acrylic rubber (L) was obtained by the same procedure as in Comparative Example 1. The properties of the obtained crumb-like acrylic rubber (L) were evaluated, and the results are shown in Table 2-2.

[0368] [Table 2-1]

[0369] [Table 2-2]

[0370] Tables 2-1 and 2-2 show that the acrylic rubber sheets (A) to (J) of the present invention, which have ion-reactive groups and are made of an acrylic rubber having a ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) in the absolute molecular weight distribution measured by the GPC-MALS method of 1.8 or more, and which have a gel content of 30% by weight or less, are excellent in terms of gel content variation, processability in both roll processability and Banbury processability, crosslinkability, compression set resistance, and normal state physical properties including strength properties, and further are remarkably excellent in storage stability and water resistance (Examples 1 to 10).

[0371] Table 2-2 also shows that the acrylic rubber sheets (A) to (J) and crumb-like acrylic rubbers (K) to (L) produced under the conditions of the present examples and comparative examples contain ion-reactive groups such as carboxyl groups, epoxy groups, and chlorine atoms, and also have relatively large absolute molecular weights (Mn, Mw, Mz) measured by GPC-MALS. Therefore, they are excellent in short-term crosslinkability and normal-state physical properties, including compression set resistance and strength (Examples 1 to 10 and Comparative Examples 1 and 2). However, the crumb-like acrylic rubbers (K) to (L) are poor in gel content variation and processability, both roll processability and Banbury processability, and are also poor in storage stability and water resistance (Comparative Examples 1 and 2).

[0372] It can be seen that the present invention achieves improved roll processability without impairing strength properties by increasing the ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw), which is a molecular weight distribution with an emphasis on the high molecular weight component (comparison between Examples 1 to 10 and Comparative Examples 1 and 2). Furthermore, with regard to roll processability, it is preferable that the ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), which is a molecular weight distribution in the low molecular weight region, is 3 or more, and it can be seen that the roll processability can be further improved by further widening the Mw / Mn (comparison between Examples 1 to 4 and Examples 5 to 10).

[0373] Tables 2-1 and 2-2 show that acrylic rubber sheets with a high balance of strength and roll processability can be produced by adding a small amount of inorganic radical generator and batchwise adding a chain transfer agent (n-dodecyl mercaptan) later (Examples 1-10). This is presumably because reducing the amount of inorganic radical generator, extending a single polymer chain, and batchwise adding a chain transfer agent (n-dodecyl mercaptan) combines high-molecular-weight and low-molecular-weight components, thereby increasing the Mz / Mw ratio, which emphasizes the high-molecular-weight region, and improving roll processability without sacrificing strength. It also shows that drying the hydrous crumbs using a screw-type twin-screw extruder under high shear conditions (maximum torque 46 N m) broadens the Mw / Mn ratio, further improving roll processability (comparison of Examples 1-4 and Examples 5-10). Although not shown in the data, it has been confirmed that the molecular weight and molecular weight distribution of crumb-like acrylic rubbers (K) to (L) directly dried with hot air at 160°C remain almost unchanged when dried in a screw-type twin-screw extruder under low shear conditions (maximum torque 15 N m). Furthermore, although not shown in Table 2-2, in the examples of this application, the reducing agent sodium ascorbate was added 120 minutes after the start of polymerization, which facilitates the production of high-molecular-weight components in the acrylic rubber and achieves an excellent balance between strength and roll processability.

[0374] Table 2-2 shows that the acrylic rubber sheets (A) to (J) of the present invention, which have an extremely small amount of gel of methyl ethyl ketone insoluble matter, are superior in Banbury processability (comparison between Examples 1 to 10 and Comparative Examples 1 and 2). In these Examples and Comparative Examples, emulsion polymerization is performed to nearly 100% polymerization conversion to improve strength properties. However, the amount of gel of methyl ethyl ketone insoluble matter increases rapidly as the polymerization conversion rate increases, resulting in poor Banbury processability. However, in the present invention, by drying to a substantially water-free state (water content less than 1% by weight) using a screw-type twin-screw extruder dryer and then melt-kneading, the rapidly increased amount of gel of methyl ethyl ketone insoluble matter is eliminated, achieving a high level of balance between strength properties and Banbury processability. Furthermore, because most of the gel of methyl ethyl ketone insoluble matter is eliminated in the screw-type twin-screw extruder dryer, there is almost no variation in the gel amount, resulting in stable Banbury processability and crosslinking properties. Furthermore, although the examples of the present application only show overwhelmingly excellent data, it has been confirmed that the BIT (Black Incorporation Time), which is an index of Banbury processability, and the gel content of methyl ethyl ketone-insoluble matter are on a line with a very high correlation coefficient, and for example, it has been confirmed that the gel content of methyl ethyl ketone-insoluble matter of a crumb-like acrylic rubber obtained by washing water-containing crumbs in the same manner as in Example 1 and then directly drying the same manner as in Comparative Example 1 was 23% by weight and the Banbury processability index was approximately 36. On the other hand, it has been confirmed that the gel content of methyl ethyl ketone-insoluble matter of an acrylic rubber sheet produced by dehydrating, drying, and molding water-containing crumbs in the same manner as in Comparative Example 1 using a screw-type twin-screw extruder dryer under the same conditions as in Example 1 was reduced to 3.4% by weight and the Banbury processability index was improved to approximately 24. In other words, methods that can reduce the amount of gel insoluble in methyl ethyl ketone in acrylic rubber sheets or crumb-like acrylic rubber include adding a chain transfer agent in the latter half of the emulsion polymerization of acrylic rubber, and washing the water-containing crumbs produced in the solidification process, melting and kneading them in a screw-type twin-screw extruder dryer in a state that is essentially free of moisture (water content less than 1% by weight), and then extruding and drying them, but the latter method was overwhelmingly superior.

[0375] Table 2-2 also shows that the acrylic rubber sheets (A) to (J) of the present invention are excellent in gel content uniformity, roll processability and Banbury processability, crosslinkability, compression set resistance, and strength, as well as in storage stability (Examples 1 to 10). The acrylic rubber sheets (A) to (J) of the present invention have a high specific gravity, i.e., do not entrap air, resulting in excellent storage stability. In the present invention, to prevent air entrapment in the acrylic rubber sheet, the air contained in the acrylic rubber is removed under reduced pressure in the drying barrel of a screw-type twin-screw extruder, and the acrylic rubber is melt-kneaded in a substantially moisture-free state, followed by rectification in the die section, and the resin pressure in the die section is limited to extrude the sheet-shaped dried rubber. The sheet-shaped dried rubber is then cut and laminated at a specific temperature, thereby increasing the specific gravity and significantly improving storage stability (Comparison between Examples 1 to 10 and Comparative Examples 1 and 2). Furthermore, the pH of the acrylic rubber sheets of the present invention is in a specific range of 3 to 6, which also contributes to storage stability (Comparison between Examples 1 to 10 and Comparative Example 2).

[0376] Table 2-2 also shows that the acrylic rubber sheets (A) to (J) of the present invention are excellent in gel content variation, both roll processability and Banbury processability, crosslinkability, compression set resistance, and strength, as well as in water resistance (Examples 1 to 10). Table 2-2 also shows that the total amount of phosphorus, magnesium, sodium, calcium, and sulfur in the ash of the acrylic rubber sheets (A) to (J) of the present invention and the acrylic rubbers (K) to (L) of the comparative examples all exceed 90% by weight, and the acrylic rubber veils are excellent in properties such as water resistance and mold releasability. It is also clear that water resistance improves particularly as the proportions of phosphorus and magnesium in the ash increase (comparison between Examples 1 to 10 and Comparative Example 1).

[0377] As shown in Table 2-2, the water resistance of acrylic rubber is also significantly affected by the ash content. It can be seen that the ash content in the acrylic rubber sheets (A) to (J) of the present invention can be significantly reduced by using a high coagulant concentration, vigorously stirring the coagulation solution and adding an emulsion-polymerized emulsion solution to the coagulation solution to carry out the coagulation reaction, washing with warm water, and dehydrating and then drying the water-containing crumbs (comparison between Examples 1 to 10 and Comparative Examples 1 and 2). Furthermore, the water resistance of acrylic rubber can be significantly improved by increasing the phosphorus and magnesium content in the ash and specifying the ratio of phosphorus to magnesium (comparison between Examples 1 to 10 and Comparative Example 1 and Comparative Example 2). Here, the coagulation reaction in the vigorously stirred coagulation liquid is carried out by adding the emulsion polymerization liquid to the coagulation liquid that is being very vigorously stirred at a peripheral speed of 1 m / s or more. For this reason, although not shown in the examples of this application, the water-containing crumbs produced by the coagulation method performed in this example are mostly concentrated into small particle sizes of 710 μm to 4.75 mm, and it is presumed that this significantly improves the efficiency of washing with warm water and the efficiency of ash removal by dehydration, thereby improving the water resistance of the acrylic rubber sheet of the present invention. The evaluation of each property of the acrylic rubber veils (A) to (J) of the present invention was the same as that of the corresponding acrylic rubber sheets (A) to (J) of the present invention, although not shown in Table 2-2.

[0378] For the acrylic rubber compositions containing the acrylic rubber sheets (A) to (J) of Examples 1 to 10, the Mooney scorch time t5 (minutes) at a temperature of 125°C was measured in accordance with JIS K 6300 using the method for evaluating processing stability by Mooney scorch inhibition described above, and the Mooney scorch storage stability was evaluated according to the following criteria. As a result, all of them were given a good result of "A". ◎: Mooney scorch time t5 exceeds 2.0 minutes 〇: Mooney scouring time t5 is 1.5 to 2.0 minutes ×: Mooney scorch time t5 is less than 1.5 minutes For these acrylic rubber sheets (A) to (J), the cooling rate of the dried rubber sheet extruded from the screw-type twin-screw extruder was as fast as about 200°C / hr, similar to Example 1, and all were 40°C / hr or higher.

[0379] [Mold releasability] The rubber compositions of the acrylic rubber sheets (A) to (J) obtained in Examples 1 to 10 were pressed into a 10 mmφ×200 mm mold, crosslinked at a mold temperature of 165°C for 2 minutes, and then the crosslinked rubber products were removed and evaluated for mold releasability according to the following criteria. All of the acrylic rubber sheets (A) to (J) were evaluated as good, with a rating of "◎". ◎: Easily released from the mold with no residue 〇: It can be easily released from the mold, but a small amount of mold residue is visible. △: It can be easily released from the mold, but there is a small amount of mold residue ×: Difficult to remove from the mold [Explanation of symbols]

[0380] 1. Acrylic rubber manufacturing system 3 Coagulation device 4 Cleaning equipment 5-screw extruder 6 Cooling device 7 Baling equipment

Claims

1. An acrylic rubber sheet having an ion-reactive group, in which the ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) in the absolute molecular weight distribution measured by a GPC-MALS method is 1.8 or more, and the gel content is 30% by weight or less.

2. 2. The acrylic rubber sheet according to claim 1, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the absolute molecular weight distribution measured by a GPC-MALS method is 3.5 or more.

3. 3. The acrylic rubber sheet according to claim 1, wherein the number average molecular weight (Mn) of the absolute molecular weight measured by GPC-MALS method is in the range of 100,000 to 500,000.

4. The acrylic rubber sheet according to any one of claims 1 to 3, wherein the weight average molecular weight (Mw) of the absolute molecular weight measured by a GPC-MALS method is in the range of 1,000,000 to 3,500,000.

5. The acrylic rubber sheet according to any one of claims 1 to 4, wherein a measurement solvent used in the GPC-MALS method is a dimethylformamide-based solvent.

6. The acrylic rubber sheet according to any one of claims 1 to 5, wherein the gel content is 15% by weight or less.

7. The acrylic rubber sheet according to any one of claims 1 to 6, wherein the gel content is a methyl ethyl ketone insoluble content.

8. The acrylic rubber sheet according to any one of claims 1 to 7, wherein the acrylic rubber comprises bonding units derived from at least one (meth)acrylic acid ester selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, bonding units derived from an ion-reactive group-containing monomer, and bonding units derived from other monomers.

9. The acrylic rubber sheet according to any one of claims 1 to 8, wherein the ash content is 1% by weight or less.

10. 10. The acrylic rubber sheet according to claim 1, wherein the total amount of sodium, magnesium, calcium, phosphorus, and sulfur in the ash is 50% by weight or more.

11. The acrylic rubber sheet according to any one of claims 1 to 10, having a complex viscosity at 60 ° C ([η] 60 ° C) of 15,000 [Pa s] or less.

12. The acrylic rubber sheet according to any one of claims 1 to 11, wherein 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.

13. The acrylic rubber sheet according to any one of claims 1 to 12, which has a pH in the range of 3 to 6.

14. The acrylic rubber sheet according to any one of claims 1 to 13, which is a melt-kneaded sheet.

15. The acrylic rubber sheet according to any one of claims 1 to 14, wherein the acrylic rubber content in the acrylic rubber sheet is 90% by weight or more.

16. a step of emulsifying an acrylic rubber monomer component containing an ion-reactive group-containing monomer with water and an emulsifier; an emulsion polymerization step in which a polymerization reaction is initiated in the presence of a redox catalyst containing an inorganic radical generator and a reducing agent, and a chain transfer agent is added batchwise during the polymerization to continue the polymerization, thereby obtaining an emulsion polymerization liquid; a coagulation step of coagulating the obtained emulsion polymerization liquid with a coagulation liquid to produce water-containing crumbs; A washing step of washing the produced water-containing crumbs; A step of dehydrating the washed water-containing crumbs in a dehydration barrel using a screw-type twin-screw extruder dryer having a dehydration slit, a drying barrel under reduced pressure, and a die at the tip, to a moisture content of 1 to 40% by weight; drying in a drying barrel to less than 1% by weight; a molding step of extruding the sheet-like dried rubber through a die; A method for producing an acrylic rubber sheet, comprising:

17. The method for producing an acrylic rubber sheet according to claim 16, which produces the acrylic rubber sheet according to any one of claims 1 to 15.

18. The method for producing an acrylic rubber sheet according to claim 16 or 17, wherein the screw-type twin-screw extruder has a maximum torque of 25 N·m or more.

19. The method for producing an acrylic rubber sheet according to any one of claims 16 to 18, wherein the reducing agent is added later.

20. The method for producing an acrylic rubber sheet according to any one of claims 16 to 19, wherein the emulsion polymerization is carried out using a phosphate ester salt or a sulfate ester salt as an emulsifier in the emulsion polymerization step.

21. The method for producing an acrylic rubber sheet according to any one of claims 16 to 20, wherein the polymerization liquid produced in the emulsion polymerization step is coagulated using an alkali metal salt or a Group 2 metal salt of the periodic table as a coagulant, and then dried.

22. The method for producing an acrylic rubber sheet according to claim 21, wherein the polymerization liquid produced in the emulsion polymerization step is coagulated by adding the polymerization liquid to an aqueous solution containing a coagulant containing an alkali metal salt or a Group 2 metal salt of the periodic table, and stirring the solution.

23. The method for producing an acrylic rubber sheet according to any one of claims 16 to 22, wherein the polymerization liquid produced in the emulsion polymerization step is brought into contact with a coagulant to be coagulated, and then melt-kneaded and dried.

24. The method for producing an acrylic rubber sheet according to claim 23, wherein the melt-kneading and drying are carried out with a water content of less than 1% by weight.

25. The method for producing an acrylic rubber sheet according to claim 23 or 24, wherein the melt-kneading and drying are carried out under reduced pressure.

26. The method for producing an acrylic rubber sheet according to any one of claims 23 to 25, wherein the acrylic rubber after melt-kneading and drying is cooled at a cooling rate of 40°C / hr or more.

27. An acrylic rubber veil obtained by laminating the acrylic rubber sheet according to any one of claims 1 to 15.

28. The acrylic rubber bale according to claim 27, wherein when the gel content within the acrylic rubber bale is randomly sampled at 20 points and the variation is measured, all of the values ​​measured for the samples fall within the range of (average value ±5) weight %.

29. 29. The acrylic rubber veil according to claim 27 or 28, having a specific gravity of 0.8 or more.

30. A rubber mixture comprising the acrylic rubber sheet according to any one of claims 1 to 15 and / or the acrylic rubber veil according to any one of claims 27 to 29, a filler, and a crosslinking agent.

31. 31. A rubber mixture according to claim 30, wherein the filler is a reinforcing filler.

32. 31. The rubber mixture of claim 30, wherein the filler is furnace black, acetylene black, thermal black, or graphite.

33. 31. The rubber mix of claim 30, wherein the filler is wet processed silica, dry processed silica, or colloidal silica.

34. A rubber mixture according to any one of claims 30 to 33, wherein the crosslinking agent is an organic crosslinking agent.

35. A rubber mixture according to any one of claims 30 to 34, wherein the crosslinking agent is a polyhydric compound.

36. A rubber mixture according to any one of claims 30 to 35, wherein the crosslinking agent is an ionically crosslinking compound.

37. 37. The rubber mix of claim 36, wherein the crosslinking agent is an ionically crosslinkable organic compound.

38. 38. A rubber mixture according to claim 36 or 37, wherein the crosslinking agent is a polyvalent ionic organic compound.

39. The rubber mixture according to any one of claims 36 to 38, wherein the ion of the ion-crosslinking compound, ion-crosslinking organic compound, or polyvalent ionic organic compound serving as the crosslinking agent is at least one ion-reactive group selected from the group consisting of an amino group, an epoxy group, a carboxyl group, and a thiol group.

40. 39. The rubber mixture of claim 38, wherein the crosslinking agent is at least one polyvalent ion compound selected from the group consisting of polyamine compounds, polyepoxy compounds, polycarboxylic acid compounds, and polythiol compounds.

41. The rubber mixture according to any one of claims 30 to 40, wherein the content of the crosslinking agent is in the range of 0.001 to 20 parts by weight per 100 parts by weight of the rubber component.

42. 42. The rubber mixture according to any one of claims 30 to 41, further comprising an antioxidant.

43. 43. The rubber mix of claim 42, wherein the antioxidant is an amine-based antioxidant.

44. A method for producing a rubber mixture, comprising mixing a rubber component containing the acrylic rubber sheet according to any one of claims 1 to 15 or the acrylic rubber veil according to any one of claims 27 to 29, a filler, and optionally an antioxidant, and then mixing a crosslinking agent.

45. A cross-linked rubber product in which the rubber mixture according to any one of claims 30 to 43 is in a cross-linked state.

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