Process for the preparation of rubber compositions

Abstract

[Problem] To provide a production method of a rubber composition, which is excellent in productivity, and which can obtain a rubber molded product in which defects such as bubbles, scratches, and residual of compounding agents caused by poor dispersion are significantly reduced. [Means] A production method of a rubber composition, which has a wet pulverization process of obtaining a paste-like mixture by adding a plasticizer to at least one powder material selected from the group consisting of a vulcanizing agent and a vulcanization accelerator and performing a wet pulverization treatment, and a mixing process of mixing at least a rubber and the paste-like mixture to obtain a rubber composition.

Description

Technical Field

[0001] This invention relates to a method for preparing a rubber composition. Furthermore, it relates to a method for preparing a rubber molded article obtained by vulcanizing the rubber composition. Background Technology

[0002] Among the compounding agents such as vulcanization accelerators added to rubber compositions, some vulcanization accelerators are known to have high agglomeration properties. When such vulcanization accelerators with high agglomeration properties are mixed with rubber, poor dispersion occurs, resulting in defects such as compounding agent residue in the molded rubber product. In Patent Document 1, as a method to improve such poor dispersion, a method for preparing a vulcanization accelerator is described, which involves adding a plasticizer to a guanidine compound and then melting and gelatinizing the guanidine. It is claimed that this method can completely prevent problems caused by poor dispersion of the vulcanization accelerator in the mixing and molding processes.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2002-309040 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] However, in Patent Document 1, there are problems with productivity because the compound is melted at a high temperature above its melting point, and it is not applicable to compounding agents that are difficult to melt. Therefore, a method for preparing a rubber composition that can solve such technical problems is sought.

[0008] The present invention was made to solve the above-mentioned technical problems, and its purpose is to provide a method for preparing a rubber composition with excellent productivity, wherein the preparation method can obtain rubber molded articles with significantly reduced defects such as bubbles, scratches and compounding agent residues caused by poor dispersion.

[0009] Technical means to solve technical problems

[0010] The above-mentioned technical problem is solved by providing a method for preparing a rubber composition, characterized in that the method comprises: a wet pulverizing step of adding a plasticizer to at least one powder material selected from the group consisting of a vulcanizing agent and a vulcanization accelerator and performing wet pulverizing treatment to obtain a paste-like mixture; and a mixing step of at least mixing rubber and the above-mentioned paste-like mixture to obtain a rubber composition.

[0011] At this time, the ratio of the powder material to the plasticizer in the paste mixture is suitably 1:0.5 to 1:20. A suitable embodiment is to use 0.1 to 100 parts by weight of the paste mixture relative to 100 parts by weight of the rubber. The rubber is suitably selected from at least one of the group consisting of chloroprene rubber (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), ethylene propylene rubber (EPDM), acrylic rubber (ACM), ethylene acrylate rubber (AEM), and fluororubber (FKM); the vulcanizing agent is suitably selected from at least one of the group consisting of sulfur and amine vulcanizing agents; the vulcanization accelerator is suitably selected from at least one of the group consisting of thiuram vulcanization accelerators, guanidine vulcanization accelerators, dithiocarbamate vulcanization accelerators, and thiazole vulcanization accelerators. The maximum particle size of the particles contained in the above paste mixture is preferably less than 80 μm, and the average particle size of the particles contained in the above paste mixture is preferably 0.1 μm to 30 μm.

[0012] In the above-described mixing process, it is suitable to further add a second plasticizer and continue mixing. A suitable method for preparing a rubber molded article includes a vulcanization process for vulcanizing the rubber composition obtained in the above-described mixing process. It is also suitable to have the rubber molded article as a sealing component.

[0013] Beneficial effects

[0014] According to the present invention, a method for preparing a rubber composition with excellent productivity can be provided, which can obtain rubber molded articles with significantly reduced defects such as bubbles, scratches, and compounding agent residues caused by poor dispersion. Detailed Implementation

[0015] The present invention relates to a method for preparing a rubber composition, the method comprising: a wet pulverizing step (hereinafter sometimes referred to as the "wet pulverizing step") by adding a plasticizer (hereinafter sometimes referred to as the "first plasticizer") to at least one powder material selected from the group consisting of a vulcanizing agent and a vulcanization accelerator and performing wet pulverizing treatment to obtain a paste-like mixture; and a mixing step (hereinafter sometimes referred to as the "mixing step") by mixing at least the rubber and the above-mentioned paste-like mixture to obtain the rubber composition.

[0016] As can be seen from the comparison between the examples and comparative examples described later, in the comparative example where rubber is compounded using powders of vulcanizing agents or vulcanization accelerators, the defect rate (%) caused by poor dispersion is above a certain level, and defects such as bubbles, scratches, and compounding agent residues are observed in the obtained rubber molded articles. In contrast, in the example using a wet milling process, the defect rate (%) caused by poor dispersion is 0%, and no defects such as bubbles, scratches, or compounding agent residues are observed in the obtained rubber molded articles. That is, it is clearly shown that by using a wet milling process in which a plasticizer is added to at least one powder material selected from the group consisting of vulcanizing agents and vulcanization accelerators and wet milling is performed to obtain a paste mixture, the dispersibility becomes good in the compounding process of compounding rubber and the above-mentioned paste mixture to obtain a rubber composition, and rubber molded articles with significantly reduced defects such as bubbles, scratches, and compounding agent residues caused by poor dispersion can be provided. Thus, it can be seen that by employing a wet pulverization process, even when the melting point of the aforementioned powder material is very high, a productive paste-like mixture can be obtained without melting the powder material. Therefore, this invention is of great significance. Furthermore, in this specification, "bubbles, scratches, and compounding agent residues" are caused by at least one compounding agent selected from the group consisting of vulcanizing agents and vulcanization accelerators.

[0017] The powder material used in this invention is selected from at least one of the groups consisting of vulcanizing agents and vulcanization accelerators. While the vulcanizing agent used in this invention is not particularly limited, it is preferably selected from at least one of the groups consisting of sulfur and amine vulcanizing agents such as hexamethylenediamine carbamate (HMDC). The vulcanization accelerator used in this invention is not particularly limited, examples include thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide; guanidine-based vulcanization accelerators such as 1,3-di-o-tolylguanidine; dithiocarbamate-based vulcanization accelerators such as zinc dibutyldithiocarbamate; and thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole. Preferably, the vulcanization accelerator is selected from at least one of the groups consisting of thiuram-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and thiazole-based vulcanization accelerators. As the powder material used in wet milling processing, it is suitable to have only a vulcanizing agent as the embodiment, wherein hexamethylenediamine carbamate (HMDC) is suitably used.

[0018] The plasticizer used in this invention is not particularly limited to any plasticizer incorporated into rubber, and examples include phthalic acid derivatives such as dioctyl phthalate; adipic acid derivatives such as dioctyl adipate; sebacic acid derivatives such as dibutyl sebacate; trimellitic acid derivatives such as trimethyl trimellitate; polyester derivatives such as adipic acid polyesters and phthalic acid polyesters; polyether esters such as phthalate ether esters and adipate ether esters; phosphoric acid derivatives such as trioctyl phosphate; and petroleum hydrocarbons. These plasticizers can be used alone or in combination of two or more. It is suitable to use at least one plasticizer selected from the group consisting of phthalic acid derivatives, adipic acid derivatives, polyester derivatives, polyether esters, and phosphoric acid derivatives.

[0019] In the wet milling process of the present invention, a paste-like mixture is obtained by adding the plasticizer to the powder material and performing wet milling treatment. Known wet milling equipment such as ball mills, bead mills, pulverizers, and spray mills can be used as the apparatus for wet milling treatment. Preferably, the mixing ratio (mass ratio) of the powder material to the plasticizer is 1:0.5 to 1:20. More preferably, the mixing ratio is 1:1 to 1:18, and even more preferably, 1:1.5 to 1:15.

[0020] In this invention, a suitable embodiment is one in which the maximum particle size of the particles contained in the above-mentioned paste mixture is 80 μm or less. When the maximum particle size exceeds 80 μm, defects such as bubbles, scratches, and compounding agent residues may occur in the resulting rubber molded article due to poor dispersion; a maximum particle size is more preferably 70 μm or less, further preferably 40 μm or less, and particularly preferably 30 μm or less. The maximum particle size of the particles contained in the above-mentioned paste mixture is typically 3 μm or more. The maximum particle size in this specification is a value obtained by reading the maximum value of the maximum particle size in a particle size distribution based on volume.

[0021] In this invention, an average particle size of 0.1 μm to 30 μm in the above-mentioned paste mixture is a suitable embodiment. When the average particle size is less than 0.1 μm, the preparation of the paste mixture may take time; the average particle size is more preferably 0.5 μm or more, further preferably 1 μm or more, and particularly preferably 1.5 μm or more. On the other hand, when the average particle size exceeds 30 μm, defects such as bubbles, scratches, and compounding agent residues caused by poor dispersion may occur in the obtained rubber molded article; the average particle size is more preferably 20 μm or less, further preferably 15 μm or less, and particularly preferably 12 μm or less. The average particle size in this specification is the particle size when the cumulative value of the volume reference reaches 50%, determined based on the particle size distribution on a volume reference basis.

[0022] In this invention, after the aforementioned wet pulverization step, a mixing step is performed to at least mix the rubber and the aforementioned paste mixture to obtain a rubber composition. The rubber used in the mixing step is not particularly limited, and examples include chloroprene rubber (CR); nitrile butadiene rubber (NBR) and hydrogenated nitrile butadiene rubber (HNBR); ethylene propylene rubber (EPDM); acrylic rubber (ACM) and ethylene acrylate rubber (AEM); and fluororubber (FKM). Preferably, the rubber is selected from at least one of the group consisting of chloroprene rubber (CR), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), ethylene propylene rubber (EPDM), acrylic rubber (ACM), ethylene acrylate rubber (AEM), and fluororubber (FKM); more preferably, it is selected from at least one of the group consisting of nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), acrylic rubber (ACM), and ethylene acrylate rubber (AEM).

[0023] There are no particular limitations on chloroprene rubber (CR), as long as it is a rubber with 2-chloro-1,3-butadiene as the main component. 2-chloro-1,3-butadiene can be polymerized alone or copolymerized with other monomers. Suitable monomers include methyl acrylate, ethyl acrylate, butyl acrylate, methoxyethyl acrylate, and other acrylates.

[0024] The nitrile rubber is not particularly limited, and copolymers of acrylonitrile and 1,3-butadiene can be used. Optionally, the residual double bonds in the polymerized 1,3-butadiene units are hydrogenated. Unhydrogenated nitrile rubber (NBR) and hydrogenated nitrile rubber (HNBR) can be suitably used. The content of acrylonitrile units in the nitrile rubber is preferably 15-50% by mass. Structural units from other copolymerizable monomers may also be included, provided that this does not impair the effects of the invention, but typically their content is 10% by mass or less, suitably 5% by mass or less.

[0025] Ethylene propylene diene monomer (EPDM) is not particularly limited, and copolymers of ethylene, propylene, and diene compounds can be used. Examples of diene compounds included in EPDM include ethylidene norbornene (ENB), 1,4-hexadiene, and dicyclopentadiene. Structural units from other copolymerizable monomers may also be included, provided that they do not impair the effects of the invention, but typically their content is 10% by mass or less, suitably 5% by mass or less.

[0026] The type of acrylic rubber is not particularly limited, as long as it is a rubber with acrylate as its main component. Suitable acrylates include methyl acrylate, ethyl acrylate, butyl acrylate, and methoxyethyl acrylate. Examples of monomers that copolymerize with acrylates include acrylonitrile and ethylene. Specifically, suitable acrylic rubber (ACM) is made by copolymerizing two or more acrylates selected from methyl acrylate, ethyl acrylate, butyl acrylate, and methoxyethyl acrylate with a crosslinking monomer; or ethylene acrylic rubber (AEM) is made by copolymerizing methyl acrylate, ethylene, and a crosslinking monomer. As AEM, DuPont's "VAMAC" (registered trademark) and the like can be obtained. Structural units from other copolymerizable monomers may be included as long as they do not impair the spirit of the present invention, but their content is usually 10% by mass or less, preferably 5% by mass or less.

[0027] The type of fluororubber (FKM) is not particularly limited, and examples include copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP); copolymers of VDF and trichlorofluoroethylene (CTFE); copolymers of VDF, HFP, and tetrafluoroethylene (TFE); copolymers of TFE and propylene; copolymers of TFE and fluorinated vinyl ethers; and copolymers of hydrocarbon diene monomers and fluorinated monomers. Ternary fluororubbers, which are copolymers of VDF, HFP, and tetrafluoroethylene (TFE), are suitably used. Structural units from other copolymerizable monomers may be included, provided that this does not impair the effects of the invention, but typically their content is 10% by mass or less, suitably 5% by mass or less.

[0028] In the above-described mixing process, it is suitable to incorporate 0.1 to 100 parts by weight of the above-described paste mixture relative to 100 parts by weight of the rubber. When the amount is less than 0.1 parts by weight, the performance of the vulcanizing agent or vulcanization accelerator may not be realized; more preferably, it is 0.2 parts by weight or more, further preferably 0.5 parts by weight or more, and particularly preferably 0.8 parts by weight or more. On the other hand, when the amount exceeds 100 parts by weight, vulcanization may be accelerated; more preferably, it is 80 parts by weight or less, further preferably 60 parts by weight or less, and particularly preferably 40 parts by weight or less.

[0029] In the above-described mixing process, the method for mixing the rubber and the paste mixture is not particularly limited, and can be performed using rollers, kneaders, Banbury mixers, Intermix mixers, extruders, etc. The temperature of the rubber composition during mixing is preferably set to 20–170°C.

[0030] In the above-described mixing process, incorporating fillers such as white fillers and carbon black is a suitable implementation method. The white filler used in this invention is not particularly limited, and silica, clay, calcium carbonate, diatomaceous earth, wollastonite, etc., can be used. The carbon black used in this invention is not particularly limited, and FEF, SRF, SAF, ISAF, HAF, MAF, GPF, FT, MT, etc., can be used. The amount of white filler or carbon black incorporated is preferably 1 to 200 parts by weight relative to 100 parts by weight of the rubber, more preferably 10 to 90 parts by weight.

[0031] In the above-described mixing process, it is a suitable implementation to further add a second plasticizer for mixing. The total amount of the first and second plasticizers is preferably 1 to 100 parts by weight relative to 100 parts by weight of the rubber. The second plasticizer may be the same as or different from the first plasticizer used in the above-described wet milling process. Furthermore, in this embodiment, the amount of plasticizer required relative to 100 parts by weight of the rubber is mixed in two separate steps as the first and second plasticizers. However, a paste-like mixture can also be obtained by adding the required amount of plasticizer to the powder material and performing wet milling in the above-described wet milling process. In this case, the second plasticizer may not be added in the above-described mixing process.

[0032] In the above-mentioned mixing process, as long as it does not impair the effect of the present invention, various compounding agents commonly used in rubber compositions, such as vulcanizing aids, anti-aging agents, processing aids, acid absorbers, colorants, and fillers, may be included.

[0033] By subjecting the rubber composition obtained in the above-mentioned mixing process to a vulcanization process, a suitable rubber molded article can be obtained. In the vulcanization process, the rubber composition is molded into the desired shape, and a cross-linking reaction (vulcanization) is carried out by heating. Examples of molding methods for the rubber composition include injection molding and compression molding. The cross-linking temperature is typically 100–250°C. The cross-linking time is typically 0.5 minutes to 24 hours. Further heating can be used for secondary cross-linking.

[0034] The rubber molded product obtained in this invention is preferably a sealing component. Suitable sealing components include packing, seals, gaskets, O-rings, and diaphragms. Specifically, examples of seals include bearing seals and oil seals; examples of gaskets include intake manifold gaskets and cylinder head cover gaskets.

[0035] Example

[0036] The raw materials used in Example 1 and Comparative Example 1 are shown below.

[0037] [raw material]

[0038] • Nitrile butadiene rubber (NBR): "Nipol 1042" manufactured by Zeon Corporation of Japan.

[0039] • Carbon black: Seat 3 (HAF) manufactured by Tokai Carbon Co., Ltd.

[0040] • Plasticizer: "DOP" manufactured by ADEKA Co., Ltd.

[0041] • Processing aid: Stearic acid manufactured by Jey Plus Co., Ltd.

[0042] • Zinc oxide (lead oxide): "ZINCA#20" manufactured by Sakai Chemical Industry Co., Ltd.

[0043] • Vulcanizing agent: "Micronized sulfur powder 500 mesh" manufactured by Hosoi Chemical Industry.

[0044] • Vulcanization accelerator: "ACCEL PZ" zinc dimethyl dithiocarbamate manufactured by Kawaguchi Chemical Industry Co., Ltd.

[0045] Example 1

[0046] 0.5 parts by weight of plasticizer and 0.5 parts by weight of vulcanizing agent powder (average particle size: 50 μm, maximum particle size: 175 μm) were added to a wet milling apparatus and wet milled at room temperature for 1 hour to obtain a paste mixture. When the particle size distribution of the particles in the paste mixture was measured using a particle size distribution measuring device "LA-950" manufactured by Horiba Manufacturing Co., Ltd., the average particle size was 15 μm and the maximum particle size was 70 μm. Relative to 100 parts by weight of nitrile rubber (NBR), 1 part by weight of the above paste mixture, 65 parts by weight of carbon black, 14.5 parts by weight of plasticizer, 1 part by weight of processing aid, 5 parts by weight of zinc oxide, and 0.3 parts by weight of vulcanization accelerator were mixed together at 70°C using open rollers to produce unvulcanized rubber green preforms (gom raw). Gaskets were obtained by vulcanizing the unvulcanized rubber preform at 170°C for 10 minutes using an injection molding machine. The gaskets were observed under a magnifying glass, and the defect rate (%) caused by poor dispersion was calculated. The defect rate (%) caused by poor dispersion is expressed as the proportion of the number of identified defects (bubbles, scratches, compounding agent residues) relative to the number of molded parts. The results are summarized in Table 1.

[0047] Comparative Example 1

[0048] Instead of the paste mixture obtained in Example 1, 0.5 parts by weight of vulcanizing agent powder (average particle size: 50 μm, maximum particle size: 175 μm), 65 parts by weight of carbon black, 15 parts by weight of plasticizer, 1 part by weight of processing aid, 5 parts by weight of zinc oxide, and 0.3 parts by weight of vulcanization accelerator were mixed together at 70°C using open rollers, relative to 100 parts by weight of nitrile rubber (NBR). Gaskets as molded products were obtained in the same manner as in Example 1. As in Example 1, the obtained gaskets were observed with a magnifying glass, and the defect rate (%) due to poor dispersion was calculated. The results are summarized in Table 1.

[0049] [Table 1]

[0050] Nitrile butadiene rubber (NBR) (parts by weight) 100 100 carbon black (parts by weight) 65 65 plasticizers (parts by weight) 14.5 15 Processing aids (parts by weight) 1 1 Zinc oxide (parts by weight) 5 5 sulfur (parts by weight) － 0.5 vulcanization accelerator (parts by weight) 0.3 0.3 Paste mixture (parts by weight) 1 － total (parts by weight) 186.8 186.8 Defect rate caused by poor dispersion (％) 0 2

[0051] The raw materials used in Example 2 and Comparative Example 2 are shown below.

[0052] [raw material]

[0053] • Acrylic rubber (ACM): "AR12" manufactured by Zeon Corporation of Japan.

[0054] • Carbon black: Seat 3 (HAF) manufactured by Tokai Carbon Co., Ltd.

[0055] • Plasticizer: "Adek Siasor RS1000" manufactured by ADEKA Co., Ltd.

[0056] • Processing aid a: Stearic acid manufactured by Nippon Yusen Co., Ltd.

[0057] ·Processing aid b: "Niptronix G8205" manufactured by NI Chemical Co., Ltd.

[0058] ・Anti-aging agent: "Naruto 445" manufactured by Shiraishi Calcutta Co., Ltd.

[0059] • Vulcanization accelerator: "Nocuser DT" 1,3-di-o-tolylguanidine manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

[0060] • Vulcanizing agent: "DiakNo.1" hexamethylene diamine carbamate (HMDC) manufactured by Kemaz Co., Ltd.

[0061] Example 2

[0062] Two parts by mass of plasticizer and 0.5 parts by mass of vulcanizing agent powder (average particle size: 50 μm, maximum particle size: 500 μm) were added to a wet pulverizing apparatus and wet pulverized at room temperature for 1 hour to obtain a paste mixture. The particle size distribution of the particles in the paste mixture was measured using a particle size distribution measuring device, "LA-950," manufactured by Horiba Manufacturing Co., Ltd., and the average particle size was 3 μm, with a maximum particle size of 25 μm. Relative to 100 parts by mass of acrylic rubber (ACM), 2.5 parts by mass of the above paste mixture, 60 parts by mass of carbon black, 8 parts by mass of plasticizer, 1 part by mass each of processing aid a and processing aid b, 1 part by mass of anti-aging agent, and 2.0 parts by mass of vulcanization accelerator were mixed together at 70°C using open rollers to prepare an unvulcanized rubber preform. The unvulcanized rubber preform was vulcanized at 170°C for 10 minutes using an injection molding machine to obtain a gasket as a molded product. Similar to Example 1, the gaskets were observed using a magnifying glass, and the defect rate (%) caused by poor dispersion was calculated. The results are summarized in Table 2.

[0063] Comparative Example 2

[0064] Instead of the paste mixture obtained in Example 2, 0.5 parts by weight of vulcanizing agent powder (average particle size: 50 μm, maximum particle size: 500 μm), 60 parts by weight of carbon black, 10 parts by weight of plasticizer, 1 part by weight each of processing aid a and processing aid b, 1 part by weight of anti-aging agent, and 2.0 parts by weight of vulcanization accelerator were mixed together at 70°C using open rollers, relative to 100 parts by weight of acrylic rubber (ACM). Otherwise, gaskets as molded products were obtained in the same manner as in Example 2. As in Example 1, the obtained gaskets were observed with a magnifying glass, and the defect rate (%) caused by poor dispersion was calculated. The results are summarized in Table 2.

[0065] [Table 2]

[0066] Acrylic rubber (ACM) (parts by weight) 100 100 carbon black (parts by weight) 60 60 plasticizers (parts by weight) 8 10 Processing aid a (parts by weight) 1 1 Processing aid b (parts by weight) 1 1 Anti-aging agents (parts by weight) 1 1 vulcanization accelerator (parts by weight) 2 2 vulcanizing agent (parts by weight) － 0.5 Paste mixture (parts by weight) 2.5 － total (parts by weight) 175.5 175.5 Defect rate caused by poor dispersion (％) 0 5

[0067] The raw materials used in Example 3 and Comparative Example 3 are shown below.

[0068] [raw material]

[0069] • Acrylic rubber (ACM): "AR51" manufactured by Zeon Corporation of Japan.

[0070] • Carbon black: Seat 3 (HAF) manufactured by Tokai Carbon Co., Ltd.

[0071] • Plasticizer: "Adek Siasor RS1000" manufactured by ADEKA Co., Ltd.

[0072] • Processing aid a: Stearic acid manufactured by Nippon Yusen Co., Ltd.

[0073] ·Processing aid b: "Niptronix G8205" manufactured by NI Chemical Co., Ltd.

[0074] ・Anti-aging agent: "Naruto 445" manufactured by Shiraishi Calcutta Co., Ltd.

[0075] • Vulcanization accelerator a: "Nocuser PZ" zinc dimethyl dithiocarbamate manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

[0076] • Vulcanization accelerator b: "Nocuser TTFE" dimethyl dithiocarbamate manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

[0077] ・Vulcanizing agent: "Fruit E / C" manufactured by Laroksu Co., Ltd. N-phenyl-N-(trichloromethylthiophenyl) Benzene sulfonamide (N-Fructamine-N-(Toluene sulfonamide))

[0078] Example 3

[0079] 2.5 parts by weight of plasticizer and 2.5 parts by weight of vulcanization accelerator a powder (average particle size: 40 μm, maximum particle size: 300 μm) were added to a wet milling apparatus and wet milled at room temperature for 1 hour to obtain a paste mixture. When the particle size distribution of the particles in the above paste mixture was measured using a particle size distribution measuring device "LA-950" manufactured by Horiba Manufacturing Co., Ltd., the average particle size was 20 μm and the maximum particle size was 70 μm. Relative to 100 parts by weight of acrylic rubber (ACM), 5 parts by weight of the above paste mixture, 50 parts by weight of carbon black, 12.5 parts by weight of plasticizer, 1 part by weight each of processing aid a and processing aid b, 2 parts by weight of anti-aging agent, 0.5 parts by weight of vulcanization accelerator b, and 0.5 parts by weight of vulcanizing agent were mixed together at 70°C using open rollers to produce unvulcanized rubber green preforms. The uncured rubber preform was vulcanized at 170°C for 10 minutes using an injection molding machine to obtain a gasket as the molded product. Similar to Example 1, the obtained gasket was observed using a magnifying glass, and the defect rate (%) caused by poor dispersion was calculated. The results are summarized in Table 3.

[0080] Comparative Example 3

[0081] Instead of the paste mixture obtained in Example 3, 2.5 parts by weight of vulcanization accelerator a powder (average particle size: 40 μm, maximum particle size: 300 μm), 50 parts by weight of carbon black, 15 parts by weight of plasticizer, 1 part by weight each of processing aid a and processing aid b, 2 parts by weight of anti-aging agent, 0.5 parts by weight of vulcanization accelerator b, and 0.5 parts by weight of vulcanizing agent were mixed together at 70°C using open rollers, relative to 100 parts by weight of acrylic rubber (ACM). Gaskets as molded products were obtained in the same manner as in Example 3. As in Example 1, the obtained gaskets were observed with a magnifying glass, and the defect rate (%) caused by poor dispersion was calculated. The results are summarized in Table 3.

[0082] [Table 3]

[0083] Acrylic rubber (ACM) (parts by weight) 100 100 carbon black (parts by weight) 50 50 plasticizers (parts by weight) 12.5 15 Processing aid a (parts by weight) 1 1 Processing aid b (parts by weight) 1 1 Anti-aging agents (parts by weight) 2 2 Vulcanization accelerator a (parts by weight) － 2.5 vulcanization accelerator b (parts by weight) 0.5 0.5 vulcanizing agent (parts by weight) 0.5 0.5 Paste mixture (parts by weight) 5 － total (parts by weight) 172.5 172.5 Defect rate caused by poor dispersion (％) 0 4

Claims

1. A method for preparing a rubber composition, characterized in that, The method for preparing the rubber composition includes: a wet pulverizing step of adding a plasticizer selected from at least one of the groups consisting of phthalic acid, adipic acid, sebacic acid, trimellitic acid, polyester, polyether ester and phosphoric acid to a powdered vulcanizing agent and performing wet pulverizing treatment to obtain a paste-like mixture, wherein the maximum particle size of the particles contained in the paste-like mixture is less than 70 μm and the average particle size of the particles contained in the paste-like mixture is 0.1 μm to 30 μm; as well as The mixing process involves at least the mixing of rubber and the paste mixture to obtain a rubber composition.

2. The method for preparing the rubber composition according to claim 1, wherein, The ratio of the powder material to the plasticizer in the paste mixture is 1:0.5 to 1:

20.

3. The method for preparing the rubber composition according to claim 1 or 2, wherein, The paste mixture is prepared in proportion to 0.1 to 100 parts by weight of the rubber.

4. The method for preparing the rubber composition according to claim 1 or 2, wherein, The rubber is selected from at least one of the group consisting of chloroprene rubber (CR), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), ethylene propylene rubber (EPDM), acrylic rubber (ACM), ethylene acrylic rubber (AEM), and fluororubber (FKM). The vulcanizing agent is at least one selected from the group consisting of sulfur and amine vulcanizing agents.

5. The method for preparing the rubber composition according to claim 1 or 2, wherein, In the mixing process, a second plasticizer is further added and mixed.

6. A method for preparing a rubber molded article, characterized in that, The method for preparing the rubber molded article includes a vulcanization step in which the rubber composition obtained in the mixing step is vulcanized, as described in any one of claims 1-5.

7. The method for preparing a rubber molded article as described in claim 6, wherein, The rubber molded part is a sealing component.