Acrylic rubber composition and rubber molded product

Abstract

To provide an acrylic rubber composition capable of eliminating problems of mold contamination and mold corrosion, while easy for mold removal or high-speed molding, and excellent in sealability, durability, etc., and also to provide a rubber molding using the same.SOLUTION: An acrylic rubber composition includes a component (A) as a principal component and components (B) to (D): (A) an acrylic rubber not including a halogen-based component; (B) a carbon black having a BET specific surface area of 15 to 100 m2 / g; (C) a plasticizer with a molecular weight of 400 to 3500; and (D) a cross-linking agent selected from a polyvalent primary amine compound and an organic peroxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to an acrylic rubber composition and a rubber molded article using the same. [Background technology]

[0002] Acrylic rubber possesses water resistance, heat resistance above 150°C, and oil resistance, and is also less expensive than fluororubber. Therefore, it is widely used as a material for sealing components such as oil seals, gaskets, and O-rings. Furthermore, due to the aforementioned characteristics, it is advantageously used as a material for sealing components around automobile engines and the like.

[0003] Incidentally, in recent years, with the increasing electronification of automobiles, the demand for sealing materials around these electronic components has been on the rise. Because these sealing materials require complex and precise shapes, the molds used to mold these sealing materials also need to have complex and precise shapes in order to reproduce those shapes. Since the aforementioned molds are very expensive, there is a need to use rubber compositions as the forming material for the sealing members that do not contaminate or corrode the molds. Furthermore, when using a mold of the shape described above, problems arise such as difficulty in demolding the sealing member and difficulty in high-speed molding. Therefore, there is a need for a rubber composition that can solve these problems.

[0004] Considering typical acrylic rubber compositions, for example, epoxy crosslinked acrylic rubber compositions (using epoxy monomers as the crosslinking monomers for acrylic rubber) have a slow crosslinking rate and are therefore unsuitable for high-speed molding. Chlorine-based acrylic rubber compositions (using activated chlorine monomers as the crosslinking monomers for acrylic rubber) generate substances that corrode molds, such as hydrochloric acid, resulting in enormous mold maintenance costs. Furthermore, acrylic rubber compositions are generally known for their strong adhesiveness and poor release properties.

[0005] In this context, the use of acrylic rubber compositions that improve mold release properties, for example, by containing processing aids such as stearic acid and graphite is being considered (Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-214674 [Patent Document 2] International Publication No. 2019 / 087788 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the acrylic rubber composition described in Patent Document 1 has a low tensile elongation, which makes it prone to breakage during demolding when molded into complex shapes. Therefore, the acrylic rubber composition described in Patent Document 1 has not yet solved the problems of difficulty in demolding and difficulty in high-speed molding.

[0008] Furthermore, the acrylic rubber composition described in Patent Document 1 has the problem of being prone to breakage under high compression due to its low tensile elongation, as mentioned above. Moreover, in rubber molded products used in fields such as automobiles, there is a growing demand for maintenance-free products, so products exhibiting high durability (low compression set, heat aging resistance, etc.) are required. Furthermore, epoxy-crosslinked acrylic rubber compositions and chlorine-based acrylic rubber compositions have poor compression set characteristics, making them unsuitable for applications requiring high durability.

[0009] On the other hand, Patent Document 2 discloses an ethylene acrylate rubber composition that, after molding and crosslinking, possesses a good balance of oil resistance, heat resistance, and hydrolysis resistance. This composition contains ethylene acrylate rubber, a plasticizer with an SP value of 7 or higher, and a crosslinking agent selected from aliphatic polyvalent primary amines and their derivatives, in specific proportions. However, this rubber composition has not been sufficiently studied to overcome problems such as mold contamination and corrosion, or damage during demolding. Furthermore, in its examples, it contains a large amount of silica with many active groups, which is thought to result in poor release properties, indicating that there is still room for improvement.

[0010] This invention has been made in view of these circumstances, and aims to provide an acrylic rubber composition and a rubber molded product using the same that eliminates the problems of mold contamination and mold corrosion, facilitates demolding and high-speed molding, and has excellent sealing properties and durability. [Means for solving the problem]

[0011] To solve the aforementioned problems, the inventors diligently researched acrylic rubber compositions. In the course of this research, the inventors considered using a polyvalent primary amine compound or an organic peroxide as a crosslinking agent, and using an acrylic rubber that does not contain halogen components as the polymer, in order to eliminate the problem of mold corrosion and to obtain excellent crosslinking rate and compression set characteristics. They also considered improving mold release properties and tensile elongation by using plasticizers and the like. However, based on the above considerations, various experiments were conducted and problems arose such as excessive bleeding of plasticizers, release agents, etc., contaminating the mold. Therefore, by using a plasticizer with a molecular weight within a specific range and adding carbon black with a BET specific surface area within a specific range to the rubber composition, it was discovered that the bleeding of plasticizers, etc., could be suppressed to an optimal state depending on the BET specific surface area range. Furthermore, it was found that by including the carbon black, it is possible to obtain a rubber molded product with low contamination and high release properties, as well as increased strength and durability, leading to the present invention.

[0012] However, the gist of the present invention is as follows: [1] to [9]. [1] An acrylic rubber composition comprising component (A) below as the main component and containing components (B) to (D) below. (A) Acrylic rubber that does not contain halogen-based components. (B) BET specific surface area of ​​15-100 m 2 Carbon black at / g (C) Plasticizers with a molecular weight of 400 to 3500. (D) A crosslinking agent selected from polyvalent primary amine compounds or organic peroxides. [2] The acrylic rubber composition according to [1], wherein the component (C) is a plasticizer that satisfies the requirements of (α) below. (α)|The SP value of the plasticizer is -9.5| which is 2.0 or less. [3] The acrylic rubber composition according to [1] or [2], wherein the (C) component is an ester-based plasticizer. [4] The acrylic rubber composition according to any one of [1] to [3], further comprising the following component (E). (E) A release agent with an HLB value of 6.0 or less or 9.0 or more. [5] The acrylic rubber composition according to [4], wherein component (E) is at least one selected from the group consisting of aliphatic amines, fatty acid amides, metal soaps, and soaps. [6] The content of silica contained in the acrylic rubber composition is 15% by mass or less of the total filler contained in the acrylic rubber composition. The acrylic rubber composition according to any one of [1] to [5]. [7] The acrylic rubber composition according to any one of [1] to [6], which is an acrylic rubber composition for a seal member. [8] A rubber molded product comprising a crosslinked product of the acrylic rubber composition according to any one of [1] to [6]. [9] The rubber molded product according to [8], which is a seal member.

Advantages of the Invention

[0013] In the present invention, the acrylic rubber composition contains no halogen-based component, is mainly composed of acrylic rubber, and contains carbon black (B) having a BET specific surface area of 15 to 100 m 2 / g, a plasticizer (C) having a molecular weight of 400 to 3500, and a crosslinking agent (D) selected from polyvalent primary amine compounds or organic peroxides. Therefore, the problems of mold contamination and mold corrosion can be solved, and demolding and high-speed molding become easier. Furthermore, excellent performance such as sealing performance and durability can be obtained. From this, the acrylic rubber composition can exhibit particularly excellent performance as a forming material for rubber molded products that require complex and precise shapes, such as seal members around automobile engines and electronic components.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram of an evaluation sample used in the examples.

Modes for Carrying Out the Invention

[0015] Next, embodiments of the present invention will be described in detail. However, the present invention is not limited to this embodiment.

[0016] An acrylic rubber composition (hereinafter referred to as "this rubber composition") which is one embodiment of the present invention, has component (A) as its main component and contains components (B) to (D) below. Here, "main component" refers to a component that greatly affects the properties of this rubber composition, and usually, component (A) below accounts for 40% by mass or more of the entire rubber composition, preferably 40 to 80% by mass of the entire rubber composition, and more preferably 40 to 75% by mass of the entire rubber composition. (A) Acrylic rubber that does not contain halogen-based components. (B) BET specific surface area of ​​15-100 m 2 Carbon black at / g (C) Plasticizers with a molecular weight of 400 to 3500. (D) A crosslinking agent selected from polyvalent primary amine compounds or organic peroxides.

[0017] Next, we will describe each component that makes up this rubber composition.

[0018] 《Specific type of rubber (A)》 The polymer component of this rubber composition is a specific type of rubber (A), namely an acrylic rubber that does not contain halogenated components. The acrylic rubber is a copolymer containing acrylic acid esters, such as acrylic acid ester copolymer (ACM), acrylic acid ester-ethylene copolymer (AEM), and ethylene-vinyl carboxylate-acrylic acid ester copolymer. These are used individually or in combination as the polymer component of this rubber composition. It is desirable that the polymer component of this rubber composition does not contain any polymer components other than those mentioned above. Here, "free of halogen-based components" means that the acrylic rubber molecules do not contain halogens (F, Cl, Br, I). In particular, it means that the acrylic rubber was synthesized without using halogen-based components (for example, activated chlorine-based crosslinking monomers such as 2-chloroethyl vinyl ether and vinyl chloroacetate) as crosslinking monomers during synthesis, as described below. Furthermore, by using acrylic rubber that does not contain halogen-based components, this rubber composition eliminates the problem of mold corrosion and provides good sealing performance.

[0019] The AEM is obtained by copolymerizing one or more (meth)acrylic monomers with ethylene monomer. The ACM is obtained by copolymerizing one or more (meth)acrylic monomers with ethylene monomer either without or to an extent that does not affect the properties (i.e., with less than 5% by mass). The ethylene-vinyl carboxylate-acrylic ester copolymer is obtained by copolymerizing one or more (meth)acrylic monomers, one or more vinyl carboxylate monomers, and ethylene monomer. In the present invention, (meth)acrylic monomer means acrylic monomer or methacrylic monomer.

[0020] Examples of the (meth)acrylic monomers mentioned above include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethyl (meth)acrylate, which can be used alone or in combination of two or more.

[0021] As the vinyl carboxylate monomer, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, etc., can be used individually or in combination of two or more.

[0022] Furthermore, the acrylic rubber has the monomer composition described above and is copolymerized with a crosslinking monomer by known methods such as emulsion polymerization, suspension polymerization, solution polymerization, and bulk polymerization. As for the type of crosslinking monomer, as mentioned earlier, a crosslinking monomer that does not contain halogenated components is used. Examples of such crosslinking monomers include carboxyl monomers such as acrylic acid, methacrylic acid, crotonic acid, 2-pentenoic acid, maleic acid, fumaric acid, itaconic acid, monoalkyl maleic acid, monoalkyl fumaric acid, and monoalkyl itaconic acid, and epoxy monomers such as glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and methallyl glycidyl ether. Among these, carboxyl monomers are preferred from the viewpoint of improving high-speed moldability. With such carboxyl monomers, the acrylic rubber acquires a carboxyl group. These crosslinking monomers can then be copolymerized in a ratio of 0.1 to 15% by mass of the polymer.

[0023] 《Specific Carbon Black (B)》 As mentioned earlier, the carbon black (B) used in this rubber composition has a BET specific surface area of ​​15 to 100 m², in order to suppress the bleeding of plasticizers and other substances to an optimal state. 2 Carbon black with a specific density of / g is used. From the above viewpoint, the BET specific surface area of ​​the carbon black (B) is preferably 15 to 90 m². 2 The range is / g, more preferably 15-80m 2 It is within the range of / g. In other words, if the BET specific surface area is too large, the bleed suppression effect of plasticizers and the like becomes too strong, and conversely, if the BET specific surface area is too small, the desired bleed suppression effect of plasticizers and the like cannot be obtained. Here, the BET specific surface area of ​​the carbon black (B) can be measured, for example, by degassing the sample at 200°C for 15 minutes, and then using a mixed gas (N2: 70%, He: 30%) as the adsorbed gas, with a BET specific surface area measuring device (Microdata Corporation, 4232-II). In addition, it is desirable that the carbon black used in this rubber composition does not contain carbon black other than the specific carbon black (B).

[0024] Also, from the viewpoints of strength and durability, the DBP oil absorption of the carbon black (B) is preferably in the range of 40 to 165 cm 3 / 100 g. Here, the DBP oil absorption of the carbon black (B) is the value measured according to JIS K 6217-4.

[0025] And, from the viewpoint of obtaining excellent durability (low compression set, heat aging resistance, etc.), the value of the BET specific surface area (m 2 / g) × DBP oil absorption (cm 3 / 100 g) of the carbon black (B) is preferably in the range of 500 to 13000, and more preferably in the range of �50 to 10000.

[0026] The grade of the carbon black (B) is not particularly limited, but preferably carbon black of FT grade, SRF grade, SRF-HS grade, GPF grade, GPF-HS grade, GPF-LS grade, FEF grade, FEF-HS grade, FEF-LS grade, MAF grade, MAF-HS grade, MAF-LS grade, HAF grade, HAF-HS grade, HAF-LS grade, LI-HAF grade, N351 grade, N339 grade, IISAF-HS grade can be mentioned. Among them, carbon black of FT grade, SRF grade, SRF-HS grade, GPF grade, GPF-HS grade, GPF-LS grade, FEF grade, FEF-HS grade, FEF-LS grade, MAF grade, MAF-HS grade, MAF-LS grade, HAF grade, HAF-HS grade, HAF-LS grade, LI-HAF grade, N351 grade is more preferable.

[0027] From the viewpoint of obtaining excellent durability etc. without impairing the sealing property, the blending amount of the carbon black (B) is preferably 15 to 100 parts by mass, more preferably in the range of 20 to 95 parts by mass, and still more preferably in the range of 25 to 90 parts by mass with respect to 100 parts by mass of the specific rubber (A). Furthermore, from the same viewpoint as described above, it is preferable that 85% by mass or more of the total filler contained in the rubber composition is carbon black (B), and more preferably that 90% by mass or more is carbon black (B). Particularly preferable is that the filler contained in the rubber composition consists solely of carbon black (B).

[0028] 《Specific plasticizers (C)》 As mentioned earlier, a plasticizer (C) with a molecular weight of 400 to 3500 is used in this rubber composition to improve release properties, tensile elongation, etc., and to resolve the problem of breakage during demolding. Similarly, a plasticizer (C) with a molecular weight of 400 to 3000 is preferred, a plasticizer with a molecular weight of 500 to 3000 is more preferred, and a plasticizer with a molecular weight of 500 to 2500 is even more preferred. If the molecular weight is too high, the plasticizer will bleed too much, worsening the release properties. Conversely, if the molecular weight is too low, the plasticizer will bleed too much, worsening not only the release properties but also the heat resistance, oil resistance, and compression set. Note that for plasticizers (C), the molecular weights shown are the mass-average molecular weight (Mw) values ​​for those with high values ​​(the same applies to those used in the examples described later). Here, the mass-average molecular weight (Mw) is the mass-average molecular weight converted to standard polystyrene molecular weight, and was measured using a high-performance liquid chromatograph (Waters, "Waters 2695 (main unit)" and "Waters 2414 (detector)") with a column: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10⁻¹⁶). 7 Separation range: 100~2×10 7 The measurement is performed by using three tubes in series (theoretical plate count: 10,000 stages / tube, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm). Furthermore, it is desirable that the amount of plasticizers other than the specified plasticizer (C) used in this rubber composition be 4 parts by mass or less.

[0029] Furthermore, the plasticizer (C) is preferably a plasticizer that satisfies the requirements of (α) below, so as to maintain oil resistance while suppressing its bleeding to an optimal state. (α)|The SP value of the plasticizer is -9.5| which is 2.0 or less. From a similar viewpoint, the aforementioned SP value of the plasticizer -9.5 is more preferably 1.7 or less, and even more preferably 1.4 or less. Here, the SP value mentioned above is also called the solubility parameter and is an indicator of the polarity of a substance (cal / cm³). 3 ) 1 / 2 Therefore, it can be calculated using the following formula (1).

[0030]

number

[0031] Furthermore, as the plasticizer (C), various plasticizers exhibiting the specific molecular weight can be used. Specifically, examples include ester-based plasticizers (polyester-based plasticizers, polyether-based plasticizers, adipic acid-based plasticizers, adipic acid-ether-based plasticizers, phosphate-based plasticizers, phosphate-ether-based plasticizers, sebacate-based plasticizers, sebacate-ether-based plasticizers, alkyl sulfonic acid-based plasticizers, phthalate-based plasticizers, terephthalate-based plasticizers, trimellitate-based plasticizers, pyromellitic acid-based plasticizers), alkyl ether-based plasticizers, polyoxyethylene ether-based plasticizers, epoxidized vegetable oil-based plasticizers, silicone oils, hydrogenated hydrocarbon-based plasticizers, etc., exhibiting the specific molecular weight. These can be used alone or in combination of two or more. In particular, because of its better compatibility with acrylic rubber polymers, it is preferable that the plasticizer (C) contains an ester-based plasticizer, more preferably 50% by mass or more of the plasticizer (C) is an ester-based plasticizer, and even more preferably 70% by mass or more of the plasticizer (C) is an ester-based plasticizer. Among the ester-based plasticizers, polyester-based plasticizers, adipic acid ether ester-based plasticizers, polyether ester-based plasticizers, pyromellitic acid ester-based plasticizers, adipic acid ester-based plasticizers, etc.

[0032] Furthermore, from the viewpoint of improving release properties, tensile elongation, etc., the amount of plasticizer (C) blended is preferably 5 to 30 parts by mass, more preferably 5 to 25 parts by mass, and even more preferably 5 to 20 parts by mass, per 100 parts by mass of the specific rubber (A).

[0033] 《Specific crosslinking agents (D)》 As mentioned above, the crosslinking agent (D) used in this rubber composition is selected from polyvalent primary amine compounds or organic peroxides to resolve the problem of mold corrosion and to provide a crosslinking system with excellent crosslinking rate and compression set. In this case, if the specific rubber (A) has a carboxyl group as a crosslinking group and a polyvalent primary amine compound is used as the crosslinking agent, then less outgassing occurs during crosslinking, which can lead to even lower mold contamination.

[0034] The aforementioned polyvalent primary amine compounds refer to compounds having multiple primary amines in a single molecule, and their derivatives. Examples of such polyvalent primary amine compounds include hexamethylenediamine, hexamethylenediamine carbamate, hexamethylenediamine-cinnamaldehyde adduct, hexamethylenediamine dibenzoate salt, tetraethylenepentamine, pentaethylenehexamine, 4,4'-methylenedianiline, 4,4'-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 4,4'-methylenebiscyclohexylamine, 4,4'-methylenebiscyclohexylamine-cinnamaldehyde adduct, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, diethylenetriamine, and triethylenetetramine. These can be used individually or in combination of two or more.

[0035] Furthermore, examples of the organic peroxides include 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, 1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)octane, n-butyl-4,4-bis(t-butylperoxy)butane, and n-butyl-4,4- Peroxyketals such as s(t-butylperoxy)valerate, dialkylperoxides such as di-t-butylperoxide, dicumylperoxide, t-butylcumylperoxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, α,α'-bis(t-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexine-3, acetylperoxide, isobutylyl Diacyl peroxides such as peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, m-trioyl peroxide, and t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxylaurate, t-butyl peroxybenzoate, and di-t-butyl peroxide. Examples include peroxyesters such as oxyisophthalate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxymaleic acid, t-butylperoxyisopropyl carbonate, and cumylperoxyoctate, as well as hydroperoxides such as t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, and 1,1,3,3-tetramethylbutylperoxide. These can be used individually or in combination of two or more.

[0036] Furthermore, when a polyvalent primary amine compound is used as the crosslinking agent (D), the amount blended is preferably 0.2 to 5 parts by mass, more preferably 0.25 to 4 parts by mass, and even more preferably 0.3 to 2.5 parts by mass, per 100 parts by mass of the specific rubber (A), from the viewpoint of obtaining good crosslinking properties.

[0037] Furthermore, when an organic peroxide is used as the crosslinking agent (D), the amount blended is preferably 0.2 to 10 parts by mass, more preferably 0.5 to 7.5 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the specific rubber (A), from the viewpoint of obtaining good crosslinking properties. Furthermore, if a 100% pure raw material is not used as the organic peroxide, the mixture is formulated so that the ratio converted to the raw material falls within the aforementioned range.

[0038] 《Specific mold release agent (E)》 This rubber composition may contain, if necessary, a specific release agent (E), i.e., a release agent with an HLB value of 6.0 or less or 9.0 or more. When the HLB value of the release agent is within this range, it is a value that is appropriately far from the HLB values ​​of the polar monomers constituting the acrylic rubber polymer (typical HLB values ​​of polar monomers are methyl acrylate: 0.75, ethyl acrylate: 0.60, butyl acrylate: 0.43, methoxyethyl acrylate: 0.67, vinyl acetate: 0.75), thus contributing to improved release properties. Furthermore, from the above viewpoint, the HLB value of the release agent (E) is preferably 1.0 to 6.0 or less or 10.0 to 20.0, more preferably 1.5 to 6.0 or less or 11.0 to 19.0. Here, HLB stands for Hydrophilic-Lipophile Balance, which is an indicator of whether something is hydrophilic or lipophilic. A smaller HLB value indicates stronger lipophilicity. In this invention, the HLB value is calculated using the inorganic and organic values ​​used in the organic conceptual diagram, according to the following formula (2). HLB = 10 × inorganic value / organic value ……(2)

[0039] Examples of the mold release agent (E) include aliphatic amines, fatty acid amides, metal soaps, soaps, organosiloxanes, polyethers, glycols, glycerin compounds, alkanolamides, etc., which can be used alone or in combination of two or more. Among these, aliphatic amines, fatty acid amides, metal soaps, and soaps are preferred because they exhibit excellent mold release properties through interaction with carbon black and have little adverse effect on compression set. Furthermore, it is more preferable, from the viewpoint of release properties, that the metal soap or soap contains a metal element with an electronegativity of 1.0 or less. Here, "metal element with an electronegativity of 1.0 or less" means Li, Na, K, Ca, Ba, etc.

[0040] Examples of the aliphatic amines mentioned above include laurylamine, cetylamine, myristylamine, palmitylamine, stearylamine, oleylamine, behenylamine, dilaurylamine, dimystilamine, dicetylamine, distearylamine, dioleylamine, dioctadecylamine, dibehenylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dimethyloleylamine, dimethyloctadecylamine, dilaurylmethylamine, dimyristylmethylamine, dipalmitylmethylamine, distearylmethylamine, dioleylmethylamine, and dioctadecylmethylamine.

[0041] Examples of aliphatic amides as described above include monostearate, monomyristic acid, monooleic acid, behenamide, monoerucic acid, ethylenebisstearate, and ethylenebisoleamide.

[0042] Furthermore, examples of the aforementioned metal soaps include calcium laurate, calcium myristate, calcium palmitate, calcium stearate, calcium oleate, calcium behenate, calcium montana, lithium laurate, lithium myristate, lithium palmitate, lithium stearate, lithium oleate, lithium behenate, lithium montana, barium laurate, barium myristate, barium palmitate, barium stearate, barium oleate, barium behenate, barium montana, aluminum laurate, aluminum myristate, aluminum palmitate, aluminum stearate, aluminum oleate, aluminum behenate, aluminum montana, zinc laurate, zinc myristate, zinc palmitate, zinc stearate, zinc oleate, zinc behenate, zinc montana, magnesium laurate, magnesium myristate, magnesium palmitate, magnesium stearate, magnesium oleate, magnesium behenate, magnesium montana, and the like.

[0043] Examples of soaps like those mentioned above include sodium laurate, sodium myristate, sodium palmitate, sodium stearate, sodium oleate, sodium behenate, sodium montana, potassium laurate, potassium myristate, potassium palmitate, potassium stearate, potassium oleate, potassium behenate, and potassium montana.

[0044] Furthermore, from the viewpoint of obtaining good release properties without causing problems such as mold contamination due to release agent bleeding, the amount of the release agent (E) to be blended is preferably 0.1 to 8 parts by mass, more preferably 0.3 to 7 parts by mass, and even more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the specific rubber (A).

[0045] Other materials In addition to the aforementioned materials, this rubber composition may contain crosslinking aids, co-crosslinking agents, processing aids, antioxidants, flame retardants, and the like, as appropriate. Furthermore, as with the acrylic rubber composition disclosed in Japanese Patent Publication No. 2019-214674, incorporating graphite can lead to problems such as reduced tensile elongation and increased susceptibility to breakage during demolding. Therefore, it is preferable that this rubber composition does not contain graphite. Furthermore, if the rubber composition contains a large amount of silica, which has many active groups, the release properties will deteriorate. Therefore, it is preferable to limit its use to a small amount as a carrier for crosslinking agents and processing aids. Specifically, it is preferable to keep the silica content to 15% by mass or less of the total filler, and more preferably to 10% by mass or less.

[0046] Examples of the aforementioned crosslinking aids include guanidine, 1,3-di-o-tolylguanidine, 1,3-diphenylguanidine, di-o-tolylguanidine salts, diazabicycloundecene, diazabicyclononene, bismaleimide, and triallyl isocyanurate (TAIC). These can be used individually or in combination of two or more.

[0047] Furthermore, the amount of the crosslinking aid added is preferably 0.1 to 6 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the specific rubber (A).

[0048] Examples of the aforementioned cocrosslinking agents include sulfur-containing compounds, polyfunctional monomers, maleimide compounds, and quinone compounds. These can be used individually or in combination of two or more.

[0049] Furthermore, the amount of the co-crosslinking agent is preferably 0.1 to 6 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the specific rubber (A).

[0050] Examples of the aforementioned processing aids include fatty acids such as stearic acid, fatty acid esters, paraffin oil, waxes, aliphatic alcohols, and polyoxyethylene stearyl ether phosphate. These can be used individually or in combination of two or more.

[0051] Furthermore, the amount of the processing aid added is preferably 0.1 to 8 parts by mass, and more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the specific rubber (A).

[0052] Examples of the aforementioned antioxidants include amine-based antioxidants such as 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, phenol-based antioxidants, and benzimidazole-based antioxidants. These can be used individually or in combination of two or more.

[0053] Furthermore, the amount of the anti-aging agent blended is preferably 0.1 to 6 parts by mass, and more preferably 0.2 to 4 parts by mass, per 100 parts by mass of the specific rubber (A).

[0054] Examples of the aforementioned flame retardants include halogen-based flame retardants, phosphorus-based flame retardants, hydroxide-based flame retardants, and the like. These can be used individually or in combination of two or more.

[0055] This rubber composition can be prepared, for example, by blending the aforementioned specific rubber (A), specific carbon black (B), and further blending the aforementioned specific plasticizer (C), specific crosslinking agent (D), and other specific release agents (E), etc., and then kneading them using a kneader such as a roll, kneader, or Banbury mixer. The rubber composition obtained in this manner can be crosslinked into a predetermined shape using a mold (primary crosslinking at 150-200°C for 60-10 minutes, and secondary crosslinking at 150-180°C for 60-240 minutes) to produce the desired rubber molded product. This rubber composition does not corrode molds because it uses rubber that does not contain halogen components. Furthermore, because the amount of plasticizer and release agent bleed in this rubber composition is appropriately adjusted, the mold release properties do not deteriorate even after long-term mold use. As a result, using this rubber composition reduces mold corrosion and contamination, thereby lowering mold-related costs. Moreover, this rubber composition does not adhere to molds or jigs (jigs used during secondary crosslinking) as much as during crosslinking, and the rubber has high tensile elongation, so even complex shapes can be demolded and molded without damage. In addition, rubber molded products made from crosslinked products of this rubber composition also exhibit effects such as reduced adhesion between products.

[0056] This rubber composition can be used, for example, as a material for sealing components such as oil seals, gaskets, and O-rings, as well as for hoses, oil deflectors, and building materials. In particular, it is preferable to use it as a material for sealing components because of its excellent sealing properties, durability, and oil resistance. Furthermore, this rubber composition exhibits particularly excellent performance as a forming material for rubber molded products that require complex and precise shapes, such as sealing components around automobile engines and electronic components.

[0057] Furthermore, the rubber molded product made from the crosslinked material of this rubber composition preferably exhibits a tensile elongation of 200% or more, and more preferably 250% or more, when subjected to a tensile test at a tensile speed of 500 mm / min in accordance with JIS K 6251.

[0058] Furthermore, the rubber molded product made from the crosslinked material of this rubber composition preferably has a compression set of less than 30% and more preferably less than 26% after being left to stand at 150°C for 72 hours, in accordance with JIS K 6262. [Examples]

[0059] Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples unless it exceeds the essence of the invention.

[0060] First, prior to the examples and comparative examples, the following materials were prepared. The numerical values ​​(measured values, etc.) shown for each material were obtained according to the criteria explained earlier.

[0061] [polymer] The polymers shown in Table 1 below were prepared.

[0062] [Table 1]

[0063] [Carbon Black] The carbon black shown in Table 2 below was prepared.

[0064] [Table 2]

[0065] [Plasticizer] The plasticizers shown in Table 3 below were prepared.

[0066] [Table 3]

[0067] [Crosslinking agent] The crosslinking agents shown in Table 4 below were prepared.

[0068] [Table 4]

[0069] [Release agent] The release agents shown in Table 5 below were prepared.

[0070] [Table 5]

[0071] [Crosslinking agent] The crosslinking agents shown in Table 6 below were prepared.

[0072] [Table 6]

[0073] [Anti-aging agent] Nonflex DCD (amine-based antioxidant), manufactured by Seiko Chemical Industries, Ltd.

[0074] [Processing aid] Camellia stearic acid (stearic acid), manufactured by NOF Corporation.

[0075] [Examples 1-12, Comparative Examples 1-7] The aforementioned components were blended in the proportions shown in Tables 7 and 8 below, and an acrylic rubber composition was prepared by kneading using a Banbury mixer and an open roll.

[0076] The acrylic rubber compositions of the examples and comparative examples obtained in this manner were evaluated for their respective properties according to the following criteria. These results are shown in Tables 7 and 8 below.

[0077] <Mold corrosion and release properties> The obtained rubber composition was crosslinked by holding it at 180°C for 10 minutes using a transfer molding die that produces a crosslinked rubber (sample) with a roughly cylindrical shape and dimensions as shown in Figure 1, and then the crosslinked rubber (sample) was demolded. This series of operations was repeated. After performing the above operation 1000 times (1000 shots) and again 2000 times (2000 shots), the state of mold corrosion and release properties were evaluated according to the following criteria. (Mold corrosion) ○: No corrosion. ×: Corrosion present. (Mold releasability) ◎: Can be demolded without stress. ○: It tucks slightly, but can be demolded without any problems. △: Tuck the mold significantly when demolding. ×: The sample was damaged during demolding, and rubber remained in the mold.

[0078] <Tensile stretch> The obtained rubber composition was crosslinked by holding it at 160°C for 45 minutes using a predetermined mold to produce a sheet measuring 120 mm × 120 mm × 2 mm thick. Furthermore, as a secondary crosslinking step, the resulting crosslinked rubber sample was heated in an oven at 160°C for 180 minutes. The sheet obtained in this manner was punched out into a JIS No. 5 dumbbell shape in accordance with JIS K 6251 to prepare a tensile evaluation sample. Then, in accordance with JIS K 6251, a tensile test was performed on the tensile evaluation sample at a tensile speed of 500 mm / min, and the tensile elongation (%) at the time of fracture was measured. In this test, the tensile elongation required for the present invention is 200% or more.

[0079] <Compression set at 150℃ for 72 hours> In accordance with JIS K 6262, the obtained rubber composition was crosslinked by holding it at 160°C for 45 minutes using a predetermined mold to produce a circular crosslinked rubber sample with a diameter of 29 mm and a thickness of 12.5 mm. Furthermore, as a secondary crosslinking, the finished crosslinked rubber sample was heated in an oven at 160°C for 180 minutes. The compression set evaluation samples obtained in this manner were left to stand at 150°C for 72 hours while compressed to 25% in accordance with JIS K 6262, and the compression set (%) was measured. In this test, the compression set required for the present invention is less than 30%.

[0080] [Table 7]

[0081] [Table 8]

[0082] The results shown in Tables 7 and 8 indicate that the rubber composition of the example does not cause mold corrosion and exhibits excellent release properties even after 2000 shots of mold molding using a special transfer molding die. Furthermore, because the crosslinked rubber of the example has high tensile elongation, it does not break during demolding even when molded into complex shapes, and the compression set after compression at 150°C for 72 hours is small, suggesting that it will exhibit excellent sealing performance.

[0083] In contrast, the rubber compositions of Comparative Example 1 and Comparative Example 6 contained no plasticizers and resulted in poor release properties. In particular, the rubber composition of Comparative Example 6 had low tensile elongation and even worse release properties. The rubber composition of Comparative Example 2 used a plasticizer with too low a molecular weight, resulting in poor compression set after compression at 150°C for 72 hours and poor release properties. The rubber composition of Comparative Example 3 used a plasticizer with too high a molecular weight and resulted in poor release properties. The rubber composition of Comparative Example 4 used carbon black with a large BET specific surface area, resulting in poor compression set after compression at 150°C for 72 hours and poor release properties. The rubber composition of Comparative Example 5 used carbon black with a small BET specific surface area and resulted in poor release properties after 2000 shots of mold molding. The rubber composition of Comparative Example 7 suffered from problems with mold corrosion and release properties because its polymer, ACM, contains chlorine groups. Furthermore, it exhibited inferior compression set after compression at 150°C for 72 hours. [Industrial applicability]

[0084] The acrylic rubber composition of the present invention can be used as a material for sealing members such as oil seals, gaskets, and O-rings, as well as for hoses, oil deflectors, and building materials. In particular, it is preferable to use it as a material for sealing members because of its excellent sealing properties, durability, and oil resistance. Furthermore, this rubber composition can exhibit particularly excellent performance as a forming material for rubber molded products that require complex and precise shapes, such as sealing members around automobile engines and electronic components.

Claims

1. An acrylic rubber composition for sealing members used in mold molding, comprising the following components (A) to (D), wherein component (A) is present in an amount of 40% by mass or more of the entire acrylic rubber composition for sealing members, and the amount of component (B) is 20 to 90 parts by mass per 100 parts by mass of component (A), and which does not contain halogen-based components, polymer components other than acrylic rubber (except plasticizers with a molecular weight of 400 to 3500), and does not contain graphite. (A) An acrylic rubber comprising at least one of an acrylic ester-ethylene copolymer and an ethylene-vinyl carboxylate-acrylic ester copolymer, which does not contain halogen-based components. (B) BET specific surface area of ​​15-29 m² ２ Carbon black at a concentration of / g. (C) A plasticizer having a molecular weight of 400 to 3500, comprising one or more plasticizers selected from the group consisting of polyester plasticizers, adipic acid ether plasticizers, polyether ester plasticizers, pyromellitic acid ester plasticizers, adipic acid ester plasticizers, and silicone oils. (D) A crosslinking agent selected from polyvalent primary amine compounds or organic peroxides.

2. The acrylic rubber composition for a sealing member for mold molding according to claim 1, wherein the (C) component is a plasticizer that satisfies the requirements of (α) below. (α) |The SP value of the plasticizer -9.5| is 2.0 or less.

3. The acrylic rubber composition for sealing members for mold molding according to claim 1 or 2, further containing the following component (E). (E) A release agent whose HLB value is 6.0 or less or 9.0 or more.

4. The acrylic rubber composition for sealing members for mold molding according to claim 3, wherein the (E) component is at least one selected from the group consisting of aliphatic amines, fatty acid amides, metal soaps, and soaps.

5. The acrylic rubber composition for sealing members for mold molding according to any one of claims 1 to 4, wherein the silica content in the acrylic rubber composition for sealing members for mold molding is 15% by mass or less of the total filler content in the acrylic rubber composition for sealing members for mold molding.

6. A rubber molded article comprising a crosslinked acrylic rubber composition for sealing members for mold molding according to any one of claims 1 to 5.

7. A rubber molded product according to claim 6, which is a sealing member.

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