Rubber bloom inhibitor and rubber composition

Abstract

This invention relates to a rubber bloom inhibitor capable of suppressing bloom in vulcanization accelerators and vulcanization accelerators in vulcanization rubber compositions, and to a vulcanization rubber composition using the rubber bloom inhibitor. [Solution] [1] A rubber bloom inhibitor, which is an amorphous polyester having a softening point of 95°C or higher and is for use with at least one rubber selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber; and [2] A vulcanized rubber composition comprising a rubber component, a rubber bloom inhibitor, a vulcanization accelerator, and a vulcanization accelerator aid, wherein the rubber component is at least one selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber, and the rubber bloom inhibitor is an amorphous polyester having a softening point of 95°C or higher.

Description

[Technical Field]

[0001] This invention relates to a bloom inhibitor for rubber and a rubber composition. [Background technology]

[0002] Rubber is an amorphous, soft polymeric substance, primarily composed of organic polymers such as natural and synthetic rubber, and is a material with a high elastic limit and low elastic modulus (elastic rubber). Taking advantage of these properties, rubber compositions containing rubber are used in various fields, including tires, sealants, and vibration isolation / damping materials. In rubber compositions, techniques have been proposed to incorporate additives such as polyester to take advantage of the properties of rubber and to meet various required physical properties.

[0003] For example, Patent Document 1 discloses a tire sidewall rubber composition comprising a natural or synthetic rubber polymer and a polyester resin containing maleic anhydride or a copolymer of maleic acid and a linear or branched polyol, in order to suppress the deterioration of the aesthetic appearance of the rubber surface due to a degradation inhibitor. Furthermore, Patent Document 2 discloses an electrophotographic charging member characterized by containing acrylonitrile butadiene rubber or epichlorohydrin rubber and a polyester polymer plasticizer with a molecular weight of 500 to 1000, in order to provide a charging member that is hard enough to allow uniform contact with the photoreceptor, does not bleed, and does not have uneven charging. Furthermore, Patent Document 3 discloses an antistatic polymer composition characterized by comprising a composition comprising a compound (A) having a specific structure and one or more compounds (B) selected from alkali metal salts and alkaline earth metal salts, in order to solve the problems of bleeding and inability to freely color rubber or plastics in a method for preventing static electricity from forming, and one or more polymers (C) selected from polymers of rubber, polyolefin, polystyrene, ethylene-vinyl acetate copolymer, chlorine-containing vinyl resin, polyamide, polyacetal, polyester, polyurethane, ABS resin, polycarbonate, ethylene-acrylic acid ester copolymer resin, and thermosetting resin. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2016-504464 [Patent Document 2] Japanese Patent Publication No. 2000-162850 [Patent Document 3] Japanese Patent Application Publication No. 10-182988 [Overview of the project] [Problems that the invention aims to solve]

[0005] When the compositions described in Patent Documents 1 to 3 were used as vulcanized rubber compositions, the bloom of these vulcanizing agents, vulcanization accelerators, and vulcanization accelerators could not be sufficiently suppressed, indicating room for improvement in bloom suppression. The present invention relates to a rubber bloom inhibitor capable of suppressing bloom in vulcanization accelerators and vulcanization accelerators in vulcanization rubber compositions, and to a vulcanization rubber composition using the rubber bloom inhibitor. [Means for solving the problem]

[0006] The inventors have found that the above problem can be solved by using amorphous polyester having a softening point of 95°C or higher as a rubber bloom inhibitor for specific types of rubber. The present invention relates to the following [1]~[2]. [1] A rubber bloom inhibitor, which is an amorphous polyester having a softening point of 95°C or higher, and is for use with at least one rubber selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber. [2] A vulcanizable rubber composition comprising a rubber component, a rubber bloom inhibitor, a vulcanization accelerator, and a vulcanization accelerator auxiliary, wherein the rubber component is at least one selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber, and the rubber bloom inhibitor is an amorphous polyester having a softening point of 95°C or higher. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a rubber bloom inhibitor that can suppress bloom of vulcanization accelerators and vulcanization accelerators in vulcanized rubber compositions, and a vulcanized rubber composition using the rubber bloom inhibitor. [Modes for carrying out the invention]

[0008] [Rubber bloom inhibitor] The rubber bloom inhibitor of the present invention is an amorphous polyester (hereinafter also simply referred to as "amorphous polyester") having a softening point of 95°C or higher, and is for use with at least one type of rubber selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber.

[0009] The rubber bloom inhibitor of the present invention, when used in a vulcanized rubber composition containing rubber components, can suppress the bloom of vulcanization accelerators and vulcanization accelerator aids. The reason for this is not entirely clear, but it is thought to be as follows. Typically, vulcanization accelerators and vulcanization accelerators have low solubility in rubber components below the vulcanization molding temperature. Therefore, vulcanization accelerators and vulcanization accelerators could sometimes cause blooming, regardless of the type of rubber component. Furthermore, polyester resins with a softening point below 95°C have high molecular mobility, so even when used as a bloom inhibitor for rubber, the polyester resin itself bleeds, making it impossible to sufficiently suppress the bloom of vulcanization accelerators and vulcanization accelerators. In particular, with polyesters that have a low softening point and become liquid at room temperature (25°C), the bloom of the polyester resin itself becomes significant, making it difficult to suppress the bloom of vulcanization accelerators and vulcanization accelerators. On the other hand, because the rubber bloom inhibitor of the present invention is an amorphous polyester, it can retain the vulcanization accelerator and vulcanization accelerator through interaction with these agents. Furthermore, since the amorphous polyester, which is the rubber bloom inhibitor of the present invention, has a softening point of 95°C or higher, its molecular mobility is low under room temperature conditions, which are the main usage environment for vulcanized rubber compositions, and therefore it can remain in the vulcanized rubber composition. Based on the above, it is believed that the rubber bloom inhibitor of the present invention can remain in the vulcanized rubber composition while retaining the vulcanization accelerator and vulcanization accelerator aid, and therefore can suppress the bloom of the vulcanization accelerator and vulcanization accelerator aid.

[0010] Whether a resin is crystalline or amorphous is determined by its crystallinity index. The crystallinity index is defined as the ratio of the softening point of the resin to the maximum endothermic peak temperature (softening point (°C) / maximum endothermic peak temperature (°C)) in the measurement method described in the examples below. A crystalline resin is one in which the crystallinity index is 0.6 or higher and 1.4 or lower. An amorphous resin is one in which no endothermic peak is observed, or if observed, the crystallinity index is less than 0.6 or greater than 1.4. The crystallinity index can be appropriately adjusted depending on the type and ratio of raw material monomers, as well as manufacturing conditions such as reaction temperature, reaction time, and cooling rate.

[0011] The present invention's rubber bloom inhibitor can be used in vulcanized rubber compositions containing various rubber components. As the rubber component, from the viewpoint of suppressing the blooming of the vulcanization accelerator and the vulcanization accelerator aid in the vulcanized rubber composition, it is preferably at least one selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber, and more preferably ethylene propylene diene rubber.

[0012] <An amorphous polyester having a softening point of 95 °C or higher> The anti-blooming agent for rubber of the present invention is an amorphous polyester having a softening point of 95 °C or higher. Since the molecular mobility is low under normal temperature, which is the main use environment of the vulcanized rubber composition, due to the softening point being 95 °C or higher, it can remain in the vulcanized rubber composition and suppress the blooming of the vulcanization accelerator and the vulcanization accelerator aid. In the present invention, from the viewpoint of suppressing the blooming of the vulcanization accelerator and the vulcanization accelerator aid in the vulcanized rubber composition, the softening point of the amorphous polyester is 95 °C or higher, preferably 100 °C or higher, more preferably 105 °C or higher, even more preferably 110 °C or higher, even more preferably 120 °C or higher, and from the viewpoint of kneading and processability, it is preferably 165 °C or lower, more preferably 160 °C or lower, even more preferably 155 °C or lower.

[0013] In the anti-blooming agent for rubber of the present invention, from the viewpoint of suppressing the blooming of the vulcanization accelerator and the vulcanization accelerator aid in the vulcanized rubber composition, the amorphous polyester is preferably a polycondensation of a dicarboxylic acid and a diol.

[0014] (Dicarboxylic acid) As the dicarboxylic acid, from the viewpoint of suppressing the blooming of the vulcanization accelerator and the vulcanization accelerator aid in the vulcanized rubber composition, it is preferably at least one selected from the group consisting of aromatic dicarboxylic acids and aliphatic dicarboxylic acids, and more preferably aromatic dicarboxylic acids. In the present invention, the dicarboxylic acid includes not only the free acid but also anhydrides that decompose during the reaction to generate acids and alkyl esters having 1 to 3 carbon atoms. However, the carbon atoms of the alkyl group in the alkyl ester part are not included in the carbon atoms of the dicarboxylic acid.

[0015] As the aromatic dicarboxylic acid, from the viewpoint of suppressing the blooming of the vulcanization accelerator and the vulcanization accelerator assistant of the vulcanized rubber composition, it is preferably at least one selected from the group consisting of terephthalic acid, isophthalic acid, 2,5-furandicarboxylic acid, and 2,6-naphthalenedicarboxylic acid, more preferably at least one selected from the group consisting of terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, still more preferably at least one selected from the group consisting of terephthalic acid and isophthalic acid, and even more preferably terephthalic acid and isophthalic acid.

[0016] As the aliphatic dicarboxylic acid, from the viewpoint of suppressing the blooming of the vulcanization accelerator and the vulcanization accelerator assistant of the vulcanized rubber composition, it is preferably at least one selected from the group consisting of malonic acid, succinic acid, adipic acid, fumaric acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, and hexadecanedioic acid, and more preferably adipic acid.

[0017] In the blooming inhibitor for rubber of the present invention, it is preferable that the amorphous polyester further has a sulfo group. When the amorphous polyester has a sulfo group, the hydrophilic-hydrophobic property changes, and it can effectively interact with the vulcanization accelerator and the vulcanization accelerator assistant in the rubber composition. Therefore, the blooming of the vulcanization accelerator and the vulcanization accelerator assistant of the vulcanized rubber composition is more suppressed.

[0018] 〔Dicarboxylic acid having a sulfo group〕 When the amorphous polyester has a sulfo group, the dicarboxylic acid preferably further includes a dicarboxylic acid having a sulfo group in addition to the above aromatic dicarboxylic acid and aliphatic dicarboxylic acid. As the dicarboxylic acid having a sulfo group, from the viewpoint of suppressing the blooming of the vulcanization accelerator and the vulcanization accelerator assistant of the vulcanized rubber composition, an aromatic dicarboxylic acid having a sulfo group is preferable. The aromatic dicarboxylic acid having a sulfo group is preferably at least one selected from the group consisting of sulfophthalic acid and sulfonaphthalenedicarboxylic acid, more preferably at least one selected from the group consisting of sulfophthalic acid, even more preferably at least one selected from the group consisting of sulfisophthalic acid and sulfoterephthalic acid, and even more preferably 5-sulfisophthalic acid.

[0019] The sulfo group of a dicarboxylic acid having a sulfo group is preferably a sulfo group represented as -SO3M (where M represents a counterion to a sulfonic acid base) from the viewpoint of the ease of polycondensation reaction during the production of amorphous polyester resins. The M in the sulfo group represented by -SO3M is preferably at least one selected from the group consisting of metal ions and ammonium ions, more preferably a metal ion, even more preferably at least one selected from the group consisting of alkali metal ions and alkaline earth metal ions, even more preferably an alkali metal ion, and even more preferably a sodium ion.

[0020] In the rubber bloom inhibitor of the present invention, the total content of aromatic dicarboxylic acids and aliphatic dicarboxylic acids in the dicarboxylic acid is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass, from the viewpoint of bloom inhibition of vulcanization accelerators and vulcanization accelerators in vulcanized rubber compositions.

[0021] In the rubber bloom inhibitor of the present invention, the content of aromatic dicarboxylic acid in the dicarboxylic acid is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0022] In the rubber bloom inhibitor of the present invention, the content of aliphatic dicarboxylic acid in the dicarboxylic acid is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and even more preferably 25% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0023] Furthermore, in the rubber bloom inhibitor of the present invention, when the amorphous polyester has a sulfo group, the content of the dicarboxylic acid having a sulfo group in the dicarboxylic acid is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0024] (Diol) In the rubber bloom inhibitor of the present invention, the diol can be an aliphatic diol, an aromatic diol, or the like, from the viewpoint of bloom inhibition of vulcanization accelerators and vulcanization accelerators in vulcanized rubber compositions, and is preferably an aliphatic diol from the viewpoint of availability as a raw material for amorphous polyester.

[0025] The number of carbon atoms in the diol is preferably 2 or more, more preferably 30 or less, more preferably 25 or less, even more preferably 20 or less, even more preferably 15 or less, and even more preferably 10 or less, from the viewpoint of suppressing bloom in the vulcanization accelerator and vulcanization accelerator auxiliary of the vulcanization rubber composition.

[0026] As for the aliphatic diol, from the viewpoint of suppressing bloom in vulcanization accelerators and vulcanization accelerators in vulcanized rubber compositions, at least one is preferably selected from the group consisting of chain-type diols and cyclic diols.

[0027] The chain-type diol is preferably at least one selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, and polypropylene glycol, more preferably at least one selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol, and triethylene glycol, and even more preferably at least one selected from the group consisting of ethylene glycol and 1,3-propanediol.

[0028] As for the cyclic diol, from the viewpoint of suppressing bloom in vulcanization accelerators and vulcanization accelerators of vulcanization rubber compositions, it is preferable to select at least one from the group consisting of 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, isosorbide, bisphenoxyethanol fluorene, bisphenol fluorene, biscrezooxyethanol fluorene, and biscresol fluorene, and more preferably at least one from the group consisting of 1,4-cyclohexanedimethanol and isosorbide, and even more preferably 1,4-cyclohexanedimethanol.

[0029] Among the above, the aliphatic diol is preferably at least one selected from the group consisting of chain-type diols and cyclic diols, from the viewpoint of suppressing bloom in vulcanization accelerators and vulcanization accelerators of vulcanization rubber compositions, more preferably at least one selected from the group consisting of ethylene glycol, 1,3-propanediol and 1,4-cyclohexanedimethanol, and even more preferably ethylene glycol.

[0030] In the rubber bloom inhibitor of the present invention, the content of aliphatic diol in the diol is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass, from the viewpoint of bloom suppression of vulcanization accelerators and vulcanization accelerators in vulcanized rubber compositions.

[0031] In the rubber bloom inhibitor of the present invention, the content of the chain-type diol in the diol is preferably 35% by mass or more, more preferably 40% by mass or more, even more preferably 60% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass, from the viewpoint of bloom suppression of vulcanization accelerators and vulcanization accelerators of vulcanized rubber compositions.

[0032] In the rubber bloom inhibitor of the present invention, the content of cyclic diol in the diol is preferably 45% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, and preferably 65% ​​by mass or less, more preferably 63% by mass or less, and even more preferably 60% by mass or less, from the viewpoint of bloom inhibition of vulcanization accelerators and vulcanization accelerators of vulcanized rubber compositions.

[0033] (Manufacturing of amorphous polyester) In the rubber bloom inhibitor of the present invention, amorphous polyester can be produced by known methods. For example, the polycondensation reaction between a dicarboxylic acid and a diol can be carried out in an inert gas atmosphere, preferably at a temperature of 150°C to 260°C, in the presence of an esterification catalyst, esterification co-catalyst, polymerization inhibitor, etc., as needed.

[0034] Examples of esterification catalysts include tin catalysts, titanium catalysts, antimony trioxide, zinc acetate, and metal compounds such as germanium dioxide. However, from the viewpoint of esterification reaction efficiency, tin compounds such as dibutyltin oxide and tin(II) 2-ethylhexanoate, and titanium compounds such as titanium tetrabutoxide and titanium diisopropylate bis(triethanolamine) are preferred. The amount of esterification catalyst used is preferably 0.01 parts by mass or more and 1.0 part by mass or less, and more preferably 0.03 parts by mass or more and 0.5 parts by mass or less, per 100 parts by mass of the total amount of dicarboxylic acid and diol.

[0035] Preferred esterification co-catalysts include pyrogallol compounds and sodium acetate. Examples of pyrogallol compounds include pyrogallol, gallic acid, gallic acid esters, benzophenone derivatives, and catechin derivatives, but gallic acid is preferred from the viewpoint of reactivity. The amount of esterification co-catalyst used is preferably 0.001 parts by mass or more and 0.5 parts by mass or less, and more preferably 0.01 parts by mass or more and 0.1 parts by mass or less, per 100 parts by mass of the total amount of alcohol and carboxylic acid components. Examples of polymerization inhibitors include tert-butylcatechol. The amount of polymerization inhibitor used is preferably 0.001 parts by mass or more and 0.5 parts by mass or less, and more preferably 0.01 parts by mass or more and 0.1 parts by mass or less, per 100 parts by mass of the total amount of alcohol and carboxylic acid components.

[0036] [Vulcanized rubber composition] The vulcanizable rubber composition of the present invention comprises a rubber component, a rubber bloom inhibitor, a vulcanization accelerator, and a vulcanization accelerator auxiliary, wherein the rubber component is at least one selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber, and the rubber bloom inhibitor is an amorphous polyester having a softening point of 95°C or higher. The rubber bloom inhibitor in the vulcanized rubber composition of the present invention is the same as the rubber bloom inhibitor of the present invention described above. That is, the vulcanized rubber composition of the present invention comprises a rubber component, the rubber bloom inhibitor described above, a vulcanization accelerator, and a vulcanization accelerator aid. The vulcanized rubber composition of the present invention, having the above-described structure, can suppress blooming of the vulcanization accelerator and vulcanization accelerator aid.

[0037] <Rubber components> The rubber component in the vulcanized rubber composition of the present invention is at least one selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber. Since the vulcanized rubber composition of the present invention is formulated by blending the rubber bloom inhibitor of the present invention with the rubber component, it can suppress the bloom of the vulcanization accelerator and vulcanization accelerator auxiliary contained in the vulcanized rubber composition. Among the above, ethylene propylene diene rubber is preferred as the rubber component in the vulcanized rubber composition of the present invention.

[0038] <Rubber bloom inhibitor> The vulcanized rubber composition of the present invention comprises a rubber bloom inhibitor, wherein the rubber bloom inhibitor is an amorphous polyester having a softening point of 95°C or higher. The rubber bloom inhibitor in the vulcanized rubber composition of the present invention is the same as the rubber bloom inhibitor of the present invention described above. That is, the vulcanized rubber composition of the present invention contains the rubber bloom inhibitor of the present invention. Since the vulcanized rubber composition of the present invention contains the rubber bloom inhibitor of the present invention, it can suppress the bloom of vulcanization accelerators and vulcanization accelerators. In the vulcanized rubber composition of the present invention, the amorphous polyester of the rubber bloom inhibitor preferably has a sulfo group, similar to the rubber bloom inhibitor of the present invention.

[0039] In the vulcanized rubber composition of the present invention, the amount of rubber bloom inhibitor blended is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 6 parts by mass or more, and even more preferably 8 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of suppressing bloom of the vulcanization accelerator and vulcanization accelerator auxiliary.

[0040] <Sulfurizing agent> In the vulcanized rubber composition of the present invention, the vulcanizing agent is preferably sulfur from the viewpoint of efficiently promoting vulcanization. Examples of sulfur commonly used in the rubber industry include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur.

[0041] In the vulcanized rubber composition of the present invention, the amount of vulcanizing agent blended is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of efficiently promoting vulcanization, and preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1.5 parts by mass or less, from the viewpoint of suppressing bloom.

[0042] <Vulcanization promoter> In the vulcanized rubber composition of the present invention, the vulcanization accelerator preferably comprises at least one selected from the group consisting of thiazole-based vulcanization accelerators, sulfenamide-based vulcanization accelerators, thiram-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, thiourea-based vulcanization accelerators, and guanidine-based vulcanization accelerators, from the viewpoint of efficiently promoting vulcanization in the unvulcanized rubber composition and suppressing bloom of the vulcanization accelerator and vulcanization accelerator. More preferably comprises at least one selected from the group consisting of thiazole-based vulcanization accelerators, sulfenamide-based vulcanization accelerators, thiram-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators, and even more preferably comprises at least one selected from the group consisting of thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators.

[0043] The thiazole-based vulcanization accelerator is preferably at least one selected from the group consisting of 2-mercaptobenzothiazole, dibenzothiazole disulfide, zinc salt of mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, 2-(morpholinodithio)benzothiazole, and (2,4-dinitrodiphenylthio)benzothiazole, and more preferably 2-mercaptobenzothiazole.

[0044] Examples of sulfenamide-based vulcanization accelerators include at least one selected from the group consisting of N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, N-(tert-butyl)-2-benzothiazole sulfenamide, and N,N-dicyclohexyl-2-benzothiazole sulfenamide.

[0045] Preferably, the thiram-based vulcanization accelerator is at least one selected from the group consisting of tetramethylthiram disulfide, dipentamethylenethiram tetrasulfide, tetramethylthiram monosulfide, tetraethylthiram disulfide, tetrabutylthiram disulfide, and tetrabenzylthiram disulfide, and more preferably at least one selected from the group consisting of tetramethylthiram disulfide and dipentamethylenethiram tetrasulfide.

[0046] The dithiocarbamate-based vulcanization accelerator is preferably at least one selected from the group consisting of zinc dibutyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, zinc dibenzyldithiocarbamate, sodium dibutyldithiocarbamate, copper dimethyldithiocarbamate, and tellurium diethyldithiocarbamate, and more preferably zinc dibutyldithiocarbamate.

[0047] Examples of guanidine-based vulcanization accelerators include at least one selected from the group consisting of diphenylguanidine, di-o-tolylguanidine, o-tolylguanidine, and di-o-tolylguanidine salts of dicatecholborate.

[0048] Examples of thiourea-based vulcanization accelerators include at least one selected from the group consisting of N,N'-diphenylthiourea, trimethylthiourea, N,N'-diethylthiourea, dibutylthiourea, dilaurylthiourea, and ethylenethiourea (2-mercaptoimidazoline).

[0049] In the vulcanized rubber composition of the present invention, the amount of vulcanization accelerator added is preferably 0.1 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of efficiently promoting vulcanization in the unvulcanized rubber composition, and preferably 6 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 4 parts by mass or less, from the viewpoint of suppressing bloom of the vulcanization accelerator.

[0050] <Vulcanization accelerator> The vulcanized rubber composition of the present invention contains a vulcanization accelerator. The vulcanization accelerator is added to efficiently promote vulcanization when vulcanizing an unvulcanized rubber composition. In the vulcanized rubber composition of the present invention, the vulcanization accelerator is the residue remaining in the vulcanized rubber composition after the unvulcanized rubber composition has been vulcanized.

[0051] In the vulcanized rubber composition of the present invention, the vulcanization accelerator comprises at least one selected from the group consisting of fatty acids, fatty acid metal salts, and metal oxides, from the viewpoint of efficiently promoting vulcanization in the unvulcanized rubber composition, and more preferably comprises at least one selected from the group consisting of fatty acids and metal oxides.

[0052] The fatty acid is preferably at least one selected from the group consisting of stearic acid, lauric acid, oleic acid, linoleic acid, and palmitic acid, and more preferably stearic acid.

[0053] The fatty acid metal salt is preferably at least one selected from the group consisting of zinc laurate, zinc stearate, calcium stearate, and barium stearate, and more preferably zinc stearate. The metal oxide is preferably at least one selected from the group consisting of zinc oxide, magnesium oxide, lead oxide, trilead tetroxide, iron oxide, titanium dioxide, calcium oxide, and hydrotalcite, and is more preferably zinc oxide.

[0054] Among these, the vulcanization accelerator preferably includes at least one selected from the group consisting of stearic acid, zinc oxide, and zinc stearate, from the viewpoint of efficiently promoting vulcanization in the unvulcanized rubber composition and suppressing bloom of the vulcanization accelerator, and more preferably includes stearic acid and zinc oxide.

[0055] In the vulcanized rubber composition of the present invention, the amount of vulcanization accelerator added is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of efficiently promoting vulcanization in the unvulcanized rubber composition, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, from the viewpoint of suppressing bloom of the vulcanization accelerator.

[0056] <Other ingredients> In addition to the above components, the vulcanized rubber composition of the present invention may optionally contain various additives commonly used in the rubber industry, to the extent that they do not impair the objectives of the present invention. Other additives include, for example, fillers, silane coupling agents, antioxidants, scorch inhibitors, softeners, and process oils.

[0057] (Filler) From the viewpoint of improving the physical properties of the vulcanized rubber composition, such as abrasion resistance and elastic modulus, the vulcanized rubber composition of the present invention preferably further contains a filler. There are no particular restrictions on the filler, but it is preferably an inorganic filler, and more preferably at least one selected from the group consisting of carbon black, silica, and calcium carbonate.

[0058] There are no particular restrictions on the carbon black used, and examples include carbon blacks of high, medium, or low structure grades such as SAF, ISAF, IISAF, N339, HAF, FEF, GPF, and SRF, as well as carbon and silica dual-phase fillers in which silica is supported on the surface of the carbon black. The DBP absorption of carbon black (measured according to ASTM D2414-65T) is preferably 70 cm³. 3 / 100g or more, more preferably 80cm 3 / 100g or more, more preferably 90cm 3 It is 100g or more. Furthermore, the nitrogen adsorption specific surface area of ​​carbon black (N2AS, measured in accordance with JIS K 6217-2:2017) is preferably 10 m². 2 / g or more, more preferably 20m 2 / g or more, more preferably 30m 2 It is 1 / g or more.

[0059] There are no particular restrictions on the type of silica used, but examples include wet silica, dry silica, and colloidal silica.

[0060] There are no particular restrictions on the calcium carbonate used, but light calcium carbonate is preferred.

[0061] In the vulcanized rubber composition of the present invention, the amount of filler added is preferably 60 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 150 parts by mass or more, and even more preferably 180 parts by mass or more, per 100 parts by mass of the rubber component, and preferably 300 parts by mass or less, more preferably 280 parts by mass or less, even more preferably 250 parts by mass or less, and even more preferably 220 parts by mass or less, from the viewpoint of improving the physical properties of the vulcanized rubber composition such as abrasion resistance and elastic modulus.

[0062] (Process oil) From the viewpoint of improving the physical properties of the vulcanized rubber composition, such as abrasion resistance and elastic modulus, the vulcanized rubber composition of the present invention preferably further contains process oil. There are no particular restrictions on the process oil, but paraffinic process oils are preferred.

[0063] In the vulcanized rubber composition of the present invention, the amount of process oil blended is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 80 parts by mass or more, and preferably 150 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 120 parts by mass or less, from the viewpoint of improving the physical properties of the vulcanized rubber composition such as abrasion resistance and elastic modulus.

[0064] <Applications, etc.> Because the vulcanized rubber molded article of the present invention has the above-described structure, bloom of the vulcanization accelerator and vulcanization accelerator auxiliary can be suppressed. Therefore, the vulcanized rubber molded article of the present invention can be suitably used as a rubber molded article such as various rubber belts, various sealing materials, vibration isolation and damping materials, and shoe soles.

[0065] [Method for manufacturing vulcanized rubber composition] The vulcanized rubber composition of the present invention can be obtained by kneading the above-mentioned rubber components, a rubber bloom inhibitor, a vulcanizing agent, a vulcanization accelerator, a vulcanization accelerator aid, and other components as needed to obtain an unvulcanized rubber composition, and then vulcanizing the unvulcanized rubber composition.

[0066] As for the method of mixing, it is preferable to mix using a mixing machine. Examples of mixing machines include Banbury mixers, roll mixers, and intensive mixers. The mixing temperature is preferably 80°C or higher, more preferably 90°C or higher, and preferably 160°C or lower, more preferably 150°C or lower, from the viewpoint of improving the dispersibility of each component in the unvulcanized rubber composition and suppressing bloom in the vulcanized rubber composition.

[0067] In the manufacturing method of the present invention, the unvulcanized rubber composition is more preferably obtained by step 1, in which rubber components, a rubber bloom inhibitor, a vulcanization accelerator, and other components as needed are kneaded together, followed by step 2, in which sulfur and a vulcanization accelerator are further added to the kneaded mixture and then kneaded together, from the viewpoint of improving the dispersibility of each component in the unvulcanized rubber composition and suppressing bloom of the vulcanized rubber composition. In the manufacturing method of the present invention, when an unvulcanized rubber composition is obtained through steps 1 and 2, the kneading temperature in step 1 is preferably 120°C or higher, more preferably 130°C or higher, and preferably 160°C or lower, more preferably 150°C or lower, from the viewpoint of improving the dispersibility of each component in the unvulcanized rubber composition. Similarly, the kneading temperature in step 2 is preferably 80°C or higher, more preferably 90°C or higher, and preferably 120°C or lower, more preferably 110°C or lower, from the viewpoint of preventing the vulcanization reaction from proceeding during kneading.

[0068] In the manufacturing method of the present invention, the amount of each component blended in the unvulcanized rubber composition is the same as the amount of each component blended in the vulcanized rubber component described above.

[0069] In the manufacturing method of the present invention, the vulcanized rubber composition can be obtained by molding the above-mentioned unvulcanized rubber composition into a desired shape by a known method and then heating or heating and pressurizing it. The temperature during heating or heating and pressurizing (i.e., the vulcanization temperature) is preferably 140°C or higher, more preferably 150°C or higher, and preferably 200°C or lower, more preferably 180°C or lower. [Examples]

[0070] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way by these examples. Each property value was measured and evaluated by the following method.

[0071] <Measurement> (Softening points of amorphous and crystalline polyesters) Using a flow tester "CFT-500D" (manufactured by Shimadzu Corporation), 1 g of sample was heated at a heating rate of 6°C / min while a load of 1.96 MPa was applied by a plunger, and the sample was extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. The amount of plunger descent of the flow tester was plotted against temperature, and the temperature at which half of the sample flowed out was defined as the softening point.

[0072] (Crystallization index of amorphous polyester and crystalline polyester) Using a differential scanning calorimeter "Q100" (manufactured by T.A. Instruments Japan Co., Ltd.), 0.02 g of the sample was weighed into an aluminum pan and cooled to 0°C at a cooling rate of 10°C / min. The temperature was then maintained for 1 minute, and then the temperature was increased to 180°C at a heating rate of 10°C / min, and the amount of heat was measured. Among the observed endothermic peaks, the temperature of the peak with the largest peak area was defined as the maximum endothermic peak temperature (1), and the crystallinity index was determined by (softening point (°C)) / (maximum endothermic peak temperature (1) (°C)). Samples with a crystallinity index between 0.6 and 1.4 were judged to be crystalline, while samples without an endothermic peak, or those with a crystallinity index below 0.6 or above 1.4 if an endothermic peak was observed, were judged to be amorphous.

[0073] (Melting points of amorphous and crystalline polyesters) Using a differential scanning calorimeter "Q100" (manufactured by T.A. Instruments Japan Co., Ltd.), 0.02 g of the sample was weighed into an aluminum pan, heated to 200°C, and then cooled to 0°C at a rate of 10°C / min. The sample was then heated again at a rate of 10°C / min, and the amount of heat was measured. Among the observed endothermic peaks, the temperature of the peak with the largest peak area was defined as the maximum endothermic peak temperature (2). In the case of crystalline resins, this peak temperature was defined as the melting point. In addition, the melting point was not measured for amorphous polyester.

[0074] <Preparation of bloom inhibitor for rubber (polyester)> Example 1-1 (Preparation of amorphous polyester 1) The raw materials listed in Table 1 were placed in a 2L separable flask (equipped with a K-tube, stirrer, and nitrogen inlet tube). Under a nitrogen atmosphere, the surface temperature of the mantle heater was raised from 160°C to 240°C while stirring, and the transesterification reaction was carried out by stirring at that temperature for 6.5 hours. Subsequently, the surface temperature of the mantle heater was increased from 240°C to 260°C, and the reaction was carried out for 1.5 hours under a reduced pressure from atmospheric pressure to 1.5 kPa. Subsequently, the pressure was reduced from 1.5 kPa to 1.0 kPa, and the reaction was carried out for 6 hours. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to atmospheric pressure to obtain amorphous polyester 1.

[0075] Example 1-2 (Preparation of amorphous polyester 2) The raw materials listed in Table 1 were placed in a 2L separable flask (equipped with a K-tube, stirrer, and nitrogen inlet tube). Under a nitrogen atmosphere, the surface temperature of the mantle heater was raised from 160°C to 220°C while stirring, and the transesterification reaction was carried out by stirring at that temperature for 6.5 hours. Subsequently, the surface temperature of the mantle heater was increased from 220°C to 240°C, and the reaction was carried out for 1.5 hours under a reduced pressure from atmospheric pressure to 8.5 kPa. Subsequently, the pressure was reduced from 8.5 kPa to 1.3 kPa, and the reaction was carried out for 6.5 hours. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to atmospheric pressure to obtain amorphous polyester 2.

[0076] Comparative Example 1-1 (Preparation of Crystalline Polyester 1) The raw materials listed in Table 1, excluding the reaction catalyst, were placed in a 2L four-necked flask (equipped with a nitrogen inlet tube, dehydration tube, stirrer, and thermocouple). The surface temperature of the mantle heater was raised to 149°C while stirring under a nitrogen atmosphere and maintained at that temperature for 1 hour. Subsequently, the temperature was increased at 10°C / hour until 200°C was reached. Then, 6g of tin(II) di(2-ethylhexanoate) was added as a reaction catalyst, and the mixture was held for 1 hour. Subsequently, the pressure in the flask was reduced, and the reaction was carried out at 8 kPa to obtain crystalline polyester 1.

[0077] Comparative Example 1-2 (Preparation of Crystalline Polyester 2) The raw materials listed in Table 1, excluding the reaction catalyst, were placed in a 2L four-necked flask (equipped with a nitrogen inlet tube, dehydration tube, stirrer, and thermocouple). The surface temperature of the mantle heater was raised to 140°C while stirring under a nitrogen atmosphere and maintained at that temperature for 1 hour. Subsequently, the temperature was increased at 10°C / hour until 200°C was reached. Then, 6g of tin(II) di(2-ethylhexanoate) was added as a reaction catalyst, and the mixture was held for 1 hour. Subsequently, the pressure in the flask was reduced, and the reaction was carried out at 8 kPa to obtain crystalline polyester 2.

[0078] [Table 1]

[0079] The following applies to each of the raw materials listed in Table 1. (Dicarboxylic acid) [Aromatic dicarboxylic acid] • DMT: Dimethyl terephthalate • DMI: Dimethyl isophthalate [Aliphatic dicarboxylic acids] • DMA: Dimethyl adipate • DDA: Dodecane dioxide [Dicarboxylic acids containing a sulfo group] • SID: Dimethyl sodium 5-sulfisophthalate (Diol) [Chain diols] • EG: Ethylene glycol • 1,3-PD:1,3-propanediol [Cyclic diol] • 1,4-CHDM: 1,4-cyclohexanedimethanol (Reaction catalyst) [Esterification catalyst] • Ti(OBu)4: Titanium tetrabutoxide [Esterification catalyst] • AcONa: Sodium acetate

[0080] <Preparation of vulcanized rubber composition> Examples 2-1 to 2-5, and Comparative Examples 2-1 to 2-4 The components, excluding the vulcanization accelerator and sulfur, were mixed using a Banbury mixer at a maximum temperature of 150°C for 5 minutes, according to the formulation shown in Table 2. Next, a vulcanization accelerator and sulfur were added, and the mixture was kneaded at a maximum temperature of 100°C for 2 minutes to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was heated at 160°C for 20 minutes to obtain a 2 mm thick sheet-like vulcanized rubber composition.

[0081] <Rating> (Bloom resistance) A 2cm x 7cm test piece was cut from a sheet of vulcanized rubber composition and left to stand at 70°C and 90RH for 3 days. The surface of the test specimens after standing was measured using a laser microscope (Lasertec Corporation, OPTELICS HYBRID+ L7) at 20x magnification and a height resolution of 0.05 μm, and the arithmetic mean roughness (Ra) was calculated. A smaller relative value of the arithmetic mean roughness (Ra) indicates superior bloom suppression and bloom resistance of the vulcanization accelerator and vulcanization accelerator auxiliary. An arithmetic mean roughness (Ra) of 0.170 μm or less is within the practical range, preferably 0.150 μm or less, and more preferably 0.130 μm or less.

[0082] [Table 2]

[0083] The details of each component in Table 2 are as follows: (Rubber component) • EPDM: Ethylene propylene diene rubber (oil-extracted EPDM), manufactured by ENEOS Material Co., Ltd., product name: EP96 (contains 50 parts by mass of oil per 100 parts by mass of polymer, ENB (5-ethylidene-2-norbornene) content: 5.8% by mass, ethylene content: 66% by mass) (Rubber bloom inhibitor) · Amorphous polyester 1: Amorphous polyester 1 obtained in Example 1-1 • Amorphous polyester 2: Amorphous polyester 2 obtained in Examples 1-2 (Other polyester) • Crystalline polyester 1: Crystalline polyester 1 obtained in Comparative Example 1-1 • Crystalline polyester 2: Crystalline polyester 2 obtained in Comparative Examples 1-2 (Vulcanizing agent) • Sulfur: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Product name: Sulfur (for chemical use) (Vulcanization accelerator) • TMTD: Thiuram-based vulcanization accelerator, manufactured by Tokyo Chemical Industry Co., Ltd., tetramethylthiuram disulfide • DPTT: Thiuram-based vulcanization accelerator, manufactured by Fujifilm Wako Chemical Co., Ltd., dipentamethylenethuram tetrasulfide • ZDBC: Dithiocarbamate-based vulcanization accelerator, manufactured by Tokyo Chemical Industry Co., Ltd., zinc dibutyldithiocarbamate. • MBT: Thiazole-based vulcanization accelerator, manufactured by Tokyo Chemical Industry Co., Ltd., 2-mercaptobenzothiazole (Vulcanization accelerator) • Zinc oxide: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Product name: Zinc Oxide (Grade 1) • Stearic acid: Manufactured by Kao Corporation, product name: Lunac S-70V (Filler) · Carbon black: manufactured by Tokai Carbon Co., Ltd., product name: Seast SO (DBP absorption: 115 cm 3 / 100 g, nitrogen adsorption specific surface area: 42 m 2 / g) · Calcium carbonate: light calcium carbonate, manufactured by白石Calcium Co., Ltd., product name: Silver W (BET specific surface area: 5.0 m 2 / g) (Process oil) · Paraffinic process oil: manufactured by Nippon Sun Oil Co., Ltd., product name: SUNPAR2280

[0084] From Table 2, it is confirmed that the vulcanized rubber compositions of Examples 2-1 to 2-5 using the amorphous polyester with a softening point of 95°C or higher, which is the bloom inhibitor for rubber of the present invention, are superior in bloom resistance to the vulcanized rubber composition of Comparative Example 2-1 that does not contain a bloom inhibitor for rubber, and Comparative Examples 2-2 to 2-4 using the crystalline polyester of Comparative Example 1-1 or 1-2. Also, even in the case of a vulcanized rubber composition using nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, or natural rubber as the rubber component instead of EPDM in Examples 2-1 to 2-5, and using an amorphous polyester with a softening point of 95°C or higher as the bloom inhibitor for rubber, it is considered to be excellent in bloom resistance.

Claims

1. It is an amorphous polyester with a softening point of 95°C or higher. A rubber bloom inhibitor for at least one type of rubber selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber.

2. The rubber bloom inhibitor according to claim 1, wherein the amorphous polyester has a sulfo group.

3. It contains rubber components, rubber bloom inhibitors, vulcanization accelerators, and vulcanization accelerators, The rubber component is at least one selected from the group consisting of nitrile rubber, ethylene propylene diene rubber, isoprene rubber, chloroprene rubber, butyl rubber, and natural rubber. A vulcanized rubber composition in which the rubber bloom inhibitor is an amorphous polyester having a softening point of 95°C or higher.

4. The vulcanized rubber composition according to claim 3, wherein the amorphous polyester of the rubber bloom inhibitor has a sulfo group.

5. The vulcanized rubber composition according to claim 3, wherein the amount of the rubber bloom inhibitor blended is 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the rubber component.

6. The vulcanized rubber composition according to claim 3, wherein the vulcanization accelerator comprises at least one selected from the group consisting of thiazole-based vulcanization accelerators, sulfenamide-based vulcanization accelerators, thiram-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, thiourea-based vulcanization accelerators, and guanidine-based vulcanization accelerators.

7. The vulcanized rubber composition according to claim 3, wherein the amount of the vulcanization accelerator is 0.1 parts by mass or more and 6 parts by mass or less per 100 parts by mass of the rubber component.

8. The rubber composition according to claim 3, wherein the vulcanization accelerator comprises at least one selected from the group consisting of fatty acids, fatty acid metal salts, and metal oxides.

9. The vulcanized rubber composition according to claim 3, wherein the vulcanization accelerator comprises at least one selected from the group consisting of stearic acid, zinc oxide, and zinc stearate.

10. The vulcanized rubber composition according to claim 3, wherein the amount of the vulcanization accelerator is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber component.

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