Rubber composition and crosslinked rubber molded product

Abstract

To provide a rubber composition which contains an organic sulfur compound and gives a molding having high hardness.SOLUTION: The rubber composition contains (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, (d) a benzothiazole derivative, and (e) an organic sulfur compound. The benzothiazole derivative (d) is preferably a compound represented by formula (1-1), (1-2), (2-1) or (2-2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a rubber composition, and more particularly to a rubber composition that contains an organic sulfur compound and requires a short time for crosslinking. [Background technology]

[0002] As a material for forming the core of a golf ball, a rubber composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator is widely used because of its good resilience.

[0003] For example, Patent Document 1 describes a golf ball containing a composition including an unsaturated polymer, a crosslinking agent, a peptizer which is a non-metallic salt of an organic sulfur compound, and an accelerator selected from the group consisting of 2-mercaptobenzothiazole and salts of 2-mercaptobenzothiazole (see Patent Document 1 (claims 1, 7, and 11)).

[0004] Patent Document 2 describes a golf ball containing a composition that includes an unsaturated polymer, a crosslinking agent, a mastication accelerator, and a vulcanization accelerator, wherein the vulcanization accelerator is selected from the group consisting of 2-mercaptobenzothiazole and a salt of 2-mercaptobenzothiazole (see Patent Document 2 (Claims 1 and 25)). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-000647 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-000657 Summary of the Invention [Problem to be solved by the invention]

[0006] Although various rubber compositions have been proposed, rubber compositions containing organic sulfur compounds have the problem of requiring a long time for crosslinking. Furthermore, in rubber compositions containing organic sulfur compounds, crosslinking is not efficiently performed, so a large amount of co-crosslinking agent is required to increase the hardness of the cured product. The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a rubber composition containing an organic sulfur compound that can give molded articles with high hardness. [Means for solving the problem]

[0007] The rubber composition of the present disclosure, which has been able to solve the above problems, contains (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, (d) a benzothiazole derivative, and (e) an organic sulfur compound, and is characterized in that the (d) benzothiazole derivative is a compound represented by formula (1) and / or a compound represented by formula (2).

[0008] [ka] [R 1 represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group having 4 to 14 carbon atoms, or a metal atom. R 2 ~R 5 are the same or different and represent an electron-withdrawing group or a hydrogen atom. 3 ~R 5 At least one of is an electron-withdrawing group. [Effects of the Invention]

[0009] According to the present disclosure, a rubber composition containing an organic sulfur compound can be obtained that can give a molded product with high hardness. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a graph showing the relationship between the crosslinking time and torque of a rubber composition. [Figure 2]FIG. 2 is a graph showing the relationship between the crosslinking time and torque of a rubber composition. [Figure 3] FIG. 2 is a graph showing the relationship between the crosslinking time and torque of a rubber composition. [Figure 4] FIG. 2 is a graph showing the relationship between the crosslinking time and torque of a rubber composition. [Figure 5] FIG. 2 is a graph showing the relationship between the amount of co-crosslinking agent in a rubber composition and slab hardness. [Figure 6] FIG. 2 is a graph showing the relationship between the slab hardness and the rebound resilience of a rubber composition. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Rubber composition] The rubber composition of the present disclosure contains (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, (d) a benzothiazole derivative, and (e) an organic sulfur compound, and the (d) benzothiazole derivative is a compound represented by formula (1) and / or a compound represented by formula (2).

[0012] The rubber composition of the present disclosure can efficiently form crosslinks by blending a specific (d) benzothiazole derivative, thereby shortening the time required for crosslinking. Furthermore, because crosslinks can be efficiently formed, molded articles with high hardness can be obtained even with a small blend amount of (b) co-crosslinking agent.

[0013] The raw materials used in the rubber composition will be described below.

[0014] (a) Base rubber The base rubber (a) can be natural rubber and / or synthetic rubber. Examples of the synthetic rubber include diene rubbers such as polybutadiene rubber (BR), polyisoprene rubber (IR), styrene polybutadiene rubber (SBR), chloroprene rubber (CR), butyl rubber (IIR), and acrylonitrile butadiene rubber (NBR); and non-diene rubbers such as ethylene propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), urethane rubber, silicone rubber, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, fluororubber, and chlorosulfonated polyethylene rubber. These may be used alone or in combination of two or more.

[0015] The (a) base rubber preferably contains natural rubber and / or diene rubber. The total content of natural rubber and / or diene rubber in the (a) base rubber is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. It is also preferable that the (a) base rubber contains only natural rubber and / or diene rubber.

[0016] The base rubber (a) preferably contains polybutadiene rubber. High-cis polybutadiene, which has cis-1,4-bonds advantageous for resilience, is particularly suitable, with a content of 40% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more. The content of high-cis polybutadiene in the base rubber (a) is preferably 50% by mass or more, more preferably 70% by mass or more.

[0017] The high-cis polybutadiene preferably has a 1,2-vinyl bond content of 2.0% by mass or less, more preferably 1.7% by mass or less, and even more preferably 1.5% by mass or less. If the 1,2-vinyl bond content is too high, the resilience may decrease.

[0018] The high-cis polybutadiene is preferably synthesized using a rare earth element catalyst, and in particular, the use of a neodymium-based catalyst using a neodymium compound, which is a lanthanum series rare earth element compound, is preferred because it can produce polybutadiene rubber having a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds with excellent polymerization activity.

[0019] The high-cis polybutadiene preferably has a molecular weight distribution Mw / Mn (Mw: weight-average molecular weight, Mn: number-average molecular weight) of 2.0 or more, more preferably 2.2 or more, even more preferably 2.4 or more, and most preferably 2.6 or more, and preferably 6.0 or less, more preferably 5.0 or less, even more preferably 4.0 or less, and most preferably 3.4 or less. If the molecular weight distribution (Mw / Mn) of the high-cis polybutadiene is too small, workability may decrease, while if it is too large, resilience may decrease. The molecular weight distribution was measured by gel permeation chromatography (manufactured by Tosoh Corporation, "HLC-8120GPC") using a differential refractometer as a detector, a column: GMHHXL (manufactured by Tosoh Corporation), a column temperature: 40°C, and a mobile phase: tetrahydrofuran, and calculated as a value converted into a standard polystyrene.

[0020] The high-cis polybutadiene has a Mooney viscosity (ML 1+4 (100°C)) is preferably 30 or more, more preferably 32 or more, even more preferably 35 or more, and is preferably 140 or less, more preferably 120 or less, even more preferably 100 or less, and most preferably 80 or less. 1+4 (100°C)) is a value measured in accordance with JIS K6300 using an L rotor, with a preheating time of 1 minute, rotor rotation time of 4 minutes, and at 100°C.

[0021] (b) Co-crosslinking agent The (b) co-crosslinking agent has the effect of crosslinking rubber molecules by graft polymerizing with the base rubber molecular chain. As the (b) co-crosslinking agent, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof is preferred, and a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is more preferred. The α,β-unsaturated carboxylic acid used as the (b) co-crosslinking agent preferably has 3 to 8 carbon atoms, more preferably 3 to 6 carbon atoms, and even more preferably 3 or 4 carbon atoms. The α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof may be used alone or in combination of two or more types.

[0022] Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid. When the rubber composition contains only an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, the rubber composition preferably further contains (f) a metal compound. This is because by neutralizing the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the rubber composition with a metal compound, substantially the same effects as when a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used as a co-crosslinking agent can be obtained.

[0023] Examples of metals constituting the metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include monovalent metal ions such as sodium, potassium, and lithium; divalent metal ions such as magnesium, calcium, zinc, barium, and cadmium; trivalent metal ions such as aluminum; and other ions such as tin and zirconium. The metal components can be used alone or in combination. Among these, divalent metals such as magnesium, calcium, zinc, barium, and cadmium are preferred as the metal component. This is because the use of a divalent metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms facilitates the formation of metal crosslinks between rubber molecules. In particular, the divalent metal salt is preferably a zinc salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and more preferably zinc acrylate, because it enhances the resilience of the resulting golf ball. When an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and its metal salt are used in combination as a co-crosslinking agent, a metal compound (f) may be used as an optional component.

[0024] When the metal is a divalent or trivalent metal, (b) the metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms may contain, as the carboxylic acid component, a carboxylic acid other than the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Examples of the other carboxylic acid include saturated carboxylic acids such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid, and unsaturated carboxylic acids such as palmitoleic acid, oleic acid, linoleic acid, linolenic acid, and arachidonic acid.

[0025] The content of the (b) co-crosslinking agent is preferably more than 18 parts by mass, more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, particularly preferably 27 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 35 parts by mass or less, per 100 parts by mass of the (a) base rubber. If the content of the (b) co-crosslinking agent is more than 18 parts by mass, a small amount of the (c) crosslinking initiator can be used to impart appropriate hardness to a member formed from the rubber composition. On the other hand, if the content of the (b) co-crosslinking agent is 50 parts by mass or less, the member formed from the rubber composition will not be too hard.

[0026] (c) Crosslinking initiator The (c) crosslinking initiator is blended to crosslink the (a) base rubber component. An organic peroxide is suitable as the (c) crosslinking initiator. Specific examples of the organic peroxide include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. These organic peroxides may be used alone or in combination of two or more. Among these, dicumyl peroxide is preferably used.

[0027] The one-minute half-life temperature of the (c) crosslinking initiator is preferably 120°C or higher, more preferably 140°C or higher, and even more preferably 150°C or higher, and is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower.

[0028] The content of the (c) crosslinking initiator is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 0.7 parts by mass or more, and is preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, even more preferably 2.0 parts by mass or less, and particularly preferably 0.9 parts by mass or less, per 100 parts by mass of the (a) base rubber. If the content is 0.2 parts by mass or more, the crosslinked rubber molded article formed from the rubber composition will not be too soft and will have good resilience, and if it is 5.0 parts by mass or less, the crosslinked rubber molded article formed from the rubber composition will have appropriate hardness and will have good resilience and durability.

[0029] (d) Benzothiazole derivatives The (d) benzothiazole derivative used in the present disclosure will now be described. Examples of the (d) benzothiazole derivative include compounds represented by formula (1) and formula (2). By incorporating these (d) benzothiazole derivatives, crosslinks can be formed efficiently, and the time required for crosslinking can be shortened. Furthermore, because crosslinks can be formed efficiently, molded products with high hardness can be obtained even with a small amount of (b) co-crosslinking agent incorporated.

[0030] [ka] [R 1 represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group having 4 to 14 carbon atoms, or a metal atom. R 2 ~R 5 are the same or different and represent an electron-withdrawing group or a hydrogen atom. 3 ~R 5 At least one of is an electron-withdrawing group.

[0031] R in formula (1) or formula (2) 1 Examples of the alkyl group having 1 to 8 carbon atoms represented by the formula (I) include a linear alkyl group, a branched alkyl group, and a cyclic alkyl group. The alkyl group preferably has 1 or more carbon atoms, and 6 or less, and more preferably 4 or less carbon atoms. Examples of the linear alkyl group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, and an n-pentyl group. Examples of the branched alkyl group include an isopropyl group, an isobutyl group, a s-butyl group, a t-butyl group, and an isopentyl group. Examples of the cyclic alkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group.

[0032] R 1 The number of carbon atoms in the aryl group having 4 to 14 carbon atoms, represented by the following formula, is preferably 12 or less, and more preferably 10 or less. Examples of the aryl group include a phenyl group and a naphthyl group.

[0033] R 1 Examples of the metal atom represented by the formula include sodium, potassium, lithium, magnesium, calcium, zinc, barium, and cadmium.

[0034] R 1 is preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, more preferably a hydrogen atom.

[0035] R 2 ~R 5 The electron-withdrawing group represented by the formula (I) is a substituent that has a greater ability to attract electrons from the carbon atom to which it is bonded than a hydrogen atom. 2 ~R 5 Examples of the electron-withdrawing group represented by the formula (I) include a halogen group, a perfluoroalkyl group, a halogenated alkyl group, an alkylcarbonyl group, an alkoxycarbonyl group, a pentafluorosulfanyl group (-SF5), a nitro group (-NO2), a cyano group (-CN), a carboxy group (-COOH), an aldehyde group (-CHO), a sulfanyl group (-SH), a sulfo group (-SOH), an alkylsulfonyl group, an alkoxysulfonyl group, and a perfluoroalkylsulfonyl group.

[0036] Examples of the halogen group include a fluoro group (-F), a chloro group (-Cl), and a bromo group (-Br). Examples of the perfluoroalkyl group include a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), and a heptafluoropropyl group (-C3F7). Examples of the halogenated alkyl group include a trichloromethyl group (-CCl3) and a monochloromethyl group (-CH2Cl). Examples of the alkylcarbonyl group include an acetyl group (-COCH3) and a propionyl group (-COC2H5). Examples of the alkoxycarbonyl group include a methoxycarbonyl group (-COOCH3) and an ethoxycarbonyl group (-COOC2H5). Examples of the alkylsulfonyl group include a methylsulfonyl group (-SO2CH3) and an ethylsulfonyl group (-SO2C2H5). Examples of the alkoxysulfonyl group include a methoxysulfonyl group (-SO2OCH3) and an ethoxysulfonyl group (-SO2OC2H5). Examples of the perfluoroalkylsulfonyl group include a trifluoromethylsulfonyl group (-SO2CF3) and a pentafluoroethylsulfonyl group (-SO2C2F5).

[0037] R 2 ~R 5 The electron-withdrawing group represented by the formula (I) is preferably one selected from the group consisting of a halogen group, a perfluoroalkyl group, and a pentafluorosulfanyl group.

[0038] The (d) benzothiazole derivative is preferably a compound represented by formula (1-1), (1-2), (2-1) or (2-2). If the electron-withdrawing group is located at the 5th or 6th position, crosslinking is further promoted, resulting in a molded product with high hardness.

[0039] [ka] [In formulas (1-1) and (2-1), R 3 represents an electron-withdrawing group. In formulas (1-2) and (2-2), R 4 represents an electron-withdrawing group.]

[0040] R in the formula (1-1), (1-2), (2-1) or (2-2) 3 , R 4 The electron-withdrawing group represented by the formula (1) and (2) includes R 3 , R 4 In the formula (1-1), (1-2), (2-1) or (2-2), R 3 , R 4 The electron-withdrawing group represented by the formula (I) is preferably one selected from the group consisting of a halogen group, a perfluoroalkyl group, and a pentafluorosulfanyl group.

[0041] The amount of the (d) benzothiazole derivative is preferably 0.01 part by mass or more, more preferably 0.1 part by mass or more, and even more preferably 0.5 part by mass or more, per 100 parts by mass of the (a) base rubber, and is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less. If the amount of the (d) benzothiazole derivative is 0.01 part by mass or more, the resilience is further improved, and if it is 20 parts by mass or less, the flexibility is further improved.

[0042] (e) Organic sulfur compounds The (e) organic sulfur compound does not include the (d) benzothiazole derivative. Examples of the (e) organic sulfur compound include at least one compound selected from the group consisting of thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles, and metal salts thereof. The (e) organic sulfur compound is preferably an organic sulfur compound having a thiol group (-SH) or a metal salt thereof, and more preferably a thiophenol, a thionaphthol, or a metal salt thereof.

[0043] Examples of thiols include thiophenols and thionaphthols. Examples of the thiophenols include thiophenol; thiophenols substituted with a fluoro group, such as 4-fluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, and pentafluorothiophenol; 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, and pentachlorothiophenol. Thiophenols substituted with a chloro group such as thiophenol; thiophenols substituted with a bromo group such as 4-bromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, and pentabromothiophenol; thiophenols substituted with an iodo group such as 4-iodothiophenol, 2,5-diiodothiophenol, 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, and pentaiodothiophenol; or metal salts thereof. Zinc salts are preferred as the metal salt.

[0044] Examples of the thionaphthols (naphthalene thiols) include 2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol, 2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol, 2-bromo-1-thionaphthol, 1-fluoro-2-thionaphthol, 2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol, 2-cyano-1-thionaphthol, 1-acetyl-2-thionaphthol, 2-acetyl-1-thionaphthol, and metal salts thereof, with 2-thionaphthol and 1-thionaphthol being preferred. The metal salt is preferably a divalent metal salt, more preferably a zinc salt. Specific examples of the metal salt include the zinc salt of 1-thionaphthol and the zinc salt of 2-thionaphthol.

[0045] Polysulfides are organic sulfur compounds having polysulfide bonds, such as disulfides, trisulfides, and tetrasulfides. Diphenyl polysulfides are preferred as the polysulfides.

[0046] Diphenyl polysulfides include, in addition to diphenyl disulfide, bis(4-fluorophenyl) disulfide, bis(2,5-difluorophenyl) disulfide, bis(2,6-difluorophenyl) disulfide, bis(2,4,5-trifluorophenyl) disulfide, bis(2,4,5,6-tetrafluorophenyl) disulfide, bis(pentafluorophenyl) disulfide, bis(4-chloro ... Bis(2,5-dichlorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,4,5-trichlorophenyl) disulfide, bis(2,4,5,6-tetrachlorophenyl) disulfide, bis(pentachlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, bis(2,6-dibromophenyl) disulfide, bis(2,4,5-tribromophenyl) disulfide phenyl) disulfide, bis(2,4,5,6-tetrabromophenyl) disulfide, bis(pentabromophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(2,5-diiodophenyl) disulfide, bis(2,6-diiodophenyl) disulfide, bis(2,4,5-triiodophenyl) disulfide, bis(2,4,5,6-tetraiodophenyl) disulfide, bis(pentaiodophenyl) disulfide diphenyl disulfides substituted with a halogen group, such as bis(4-methylphenyl) disulfide, bis(2,4,5-trimethylphenyl) disulfide, bis(pentamethylphenyl) disulfide, bis(4-t-butylphenyl) disulfide, bis(2,4,5-tri-t-butylphenyl) disulfide, and bis(penta-t-butylphenyl) disulfide; and diphenyl disulfides substituted with an alkyl group, such as bis(4-methylphenyl) disulfide, bis(2,4,5-tri-t-butylphenyl) disulfide, and bis(penta-t-butylphenyl) disulfide.

[0047] Examples of thiurams include thiuram monosulfides such as tetramethylthiuram monosulfide, thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide, and thiuram tetrasulfides such as dipentamethylenethiuram tetrasulfide. Examples of thiocarboxylic acids include naphthalene thiocarboxylic acid. Examples of dithiocarboxylic acids include naphthalene dithiocarboxylic acid. Examples of sulfenamides include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and Nt-butyl-2-benzothiazole sulfenamide.

[0048] (e) The organic sulfur compounds can be used alone or in combination. (e) The organic sulfur compounds are preferably thiophenols and / or metal salts thereof, thionaphthols and / or metal salts thereof, diphenyl disulfides, and thiuram disulfides, and more preferably 2,4-dichlorothiophenol, 2,6-difluorothiophenol, 2,6-dichlorothiophenol, 2,6-dibromothiophenol, 2,6-diiodothiophenol, 2,4,5-trichlorothiophenol, pentachlorothiophenol, 1-thionaphthol, 2-thionaphthol, diphenyl disulfide, bis(2,6-difluorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide, bis(2,6-dibromophenyl)disulfide, bis(2,6-diiodophenyl)disulfide, bis(pentabromophenyl)disulfide, and metal salts thereof.

[0049] The content of the (e) organic sulfur compound is preferably at least 0.05 parts by mass, more preferably at least 0.1 parts by mass, and preferably at most 5.0 parts by mass, more preferably at most 2.0 parts by mass, per 100 parts by mass of the (a) base rubber. If the content of the (e) organic sulfur compound is less than 0.05 parts by mass, the effect of adding the (e) organic sulfur compound may not be obtained, and the resilience of the crosslinked rubber molded article may not be improved. If the content of the (e) organic sulfur compound is more than 5.0 parts by mass, the compressive deformation of the resulting crosslinked rubber molded article may increase, resulting in a decrease in resilience.

[0050] (f) Metal compounds The rubber composition may further contain (f) a metal compound. The (f) metal compound is preferably one capable of neutralizing (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the rubber composition. Examples of the (f) metal compound include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, and copper hydroxide; metal oxides such as magnesium oxide, calcium oxide, zinc oxide, and copper oxide; and metal carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. The (f) metal compound is preferably a divalent metal compound, and more preferably a zinc compound. This is because the divalent metal compound reacts with the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form a metal crosslink. Furthermore, the use of a zinc compound allows for the production of a crosslinked rubber molded product with high resilience. The (f) metal compound may be used alone or in combination of two or more. The content of the (f) metal compound may be appropriately adjusted.

[0051] When the (f) metal compound is blended, the ratio of the number of moles M2 of the (d) benzothiazole derivative to the product of the number of moles M1 of the (f) metal compound and the valence of the contained metal (M2 / (M1 × valence)) is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.04 or more, and is preferably 1.0 or less, more preferably 0.5 or less, even more preferably 0.1 or less.

[0052] (g) Carboxylic acid and / or its salt The rubber composition may contain (g) a carboxylic acid and / or a salt thereof. By containing the (g) carboxylic acid and / or a salt thereof, the hardness distribution of the resulting crosslinked rubber molded article can be controlled. Examples of the (g) carboxylic acid and / or a salt thereof include aliphatic carboxylic acids, aliphatic carboxylic acid salts, aromatic carboxylic acids, and aromatic carboxylic acid salts. The (g) carboxylic acid and / or a salt thereof can be used alone or as a mixture of two or more. Note that the (g) carboxylic acid and / or a salt thereof does not include the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof used as the (b) co-crosslinking agent.

[0053] The aliphatic carboxylic acid may be either a saturated aliphatic carboxylic acid (hereinafter, sometimes referred to as a "saturated fatty acid") or an unsaturated aliphatic carboxylic acid (hereinafter, sometimes referred to as an "unsaturated fatty acid"). The aliphatic carboxylic acid may have a branched structure or a cyclic structure. The saturated fatty acid preferably has 6 or more carbon atoms, and 24 or less, more preferably 18 or less, and even more preferably 13 or less. The unsaturated fatty acid preferably has 6 or more carbon atoms, more preferably 7 or more, and even more preferably 8 or more, and preferably 24 or less, more preferably 18 or less, and even more preferably 13 or less.

[0054] Examples of the aromatic carboxylic acid include those having a benzene ring in the molecule and those having a heteroaromatic ring in the molecule. The aromatic carboxylic acids may be used alone or in combination of two or more. Examples of the carboxylic acid having a benzene ring include aromatic carboxylic acids in which a carboxyl group is directly bonded to the benzene ring, aromatic-aliphatic carboxylic acids in which an aliphatic carboxylic acid is bonded to the benzene ring, polynuclear aromatic carboxylic acids in which a carboxyl group is directly bonded to a condensed benzene ring, and polynuclear aromatic-aliphatic carboxylic acids in which an aliphatic carboxylic acid is bonded to a condensed benzene ring. Examples of the carboxylic acid having a heteroaromatic ring include those in which a carboxyl group is directly bonded to a heteroaromatic ring.

[0055] The aliphatic carboxylate or aromatic carboxylate salt can be a salt of the above-mentioned aliphatic carboxylic acid or aromatic carboxylic acid. Examples of the cationic components of these salts include metal ions, ammonium ions, and organic cations. The cationic components can be used alone or as a mixture of two or more. Examples of metal ions include monovalent metal ions such as sodium, potassium, lithium, and silver; divalent metal ions such as magnesium, calcium, zinc, barium, cadmium, copper, cobalt, nickel, and manganese; trivalent metal ions such as aluminum and iron; and other ions such as tin, zirconium, and titanium. Among these, divalent metal ions are preferred, with magnesium, zinc, and calcium being more preferred.

[0056] The organic cation is a cation having a carbon chain. The organic cation is not particularly limited, and examples thereof include organic ammonium ions. Examples of the organic ammonium ions include primary ammonium ions such as stearyl ammonium ion, hexyl ammonium ion, octyl ammonium ion, and 2-ethylhexyl ammonium ion; secondary ammonium ions such as dodecyl (lauryl) ammonium ion and octadecyl (stearyl) ammonium ion; tertiary ammonium ions such as trioctyl ammonium ion; and quaternary ammonium ions such as dioctyl dimethyl ammonium ion and distearyl dimethyl ammonium ion. These organic cations may be used alone or in combination of two or more.

[0057] The aliphatic carboxylic acids and / or their salts include saturated fatty acids and / or their salts, and unsaturated fatty acids and / or their salts. The saturated fatty acids and / or their salts are preferred, with caprylic acid (octanoic acid), pelargonic acid (nonanoic acid), capric acid (decanoic acid), lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, or their potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, and cobalt salts being preferred. The unsaturated fatty acids and / or their salts are preferred, with palmitoleic acid, oleic acid, linoleic acid, or arachidonic acid, or their potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, and cobalt salts being preferred.

[0058] Particularly preferred examples of the aromatic carboxylic acid and / or its salt include benzoic acid, butylbenzoic acid, anisic acid (methoxybenzoic acid), dimethoxybenzoic acid, trimethoxybenzoic acid, dimethylaminobenzoic acid, chlorobenzoic acid, dichlorobenzoic acid, trichlorobenzoic acid, acetoxybenzoic acid, biphenylcarboxylic acid, naphthalenecarboxylic acid, anthracenecarboxylic acid, furancarboxylic acid, and thenoic acid, as well as potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, and cobalt salts thereof.

[0059] The content of the (g) carboxylic acid and / or its salt is, for example, 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 (a) base rubber, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

[0060] Other ingredients The rubber composition may contain additives such as pigments, fillers for adjusting the weight, antioxidants, peptizers, softeners, etc. as needed. The rubber composition may also contain rubber powder obtained by pulverizing the core of a golf ball or scraps generated during the production of the core.

[0061] Examples of pigments that can be compounded into the rubber composition include white pigments, blue pigments, and purple pigments. Titanium oxide is preferably used as the white pigment. The type of titanium oxide is not particularly limited, but rutile-type titanium oxide is preferably used because of its good hiding power. The content of titanium oxide is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and preferably 8 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of (a) base rubber.

[0062] In another preferred embodiment, the rubber composition contains a white pigment and a blue pigment. The blue pigment is blended to make the white color appear more vivid, and examples of the blue pigment include ultramarine, cobalt blue, and phthalocyanine blue. Examples of the purple pigment include anthraquinone violet, dioxazine violet, and methyl violet.

[0063] The filler used in the rubber composition is blended as a weight adjuster to adjust the mass of the resulting crosslinked rubber molded product, and may be blended as needed. Examples of the filler include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder.

[0064] The content of the antioxidant is preferably 0.1 part by weight to 1 part by weight per 100 parts by weight of the (a) base rubber, and the content of the peptizing agent is preferably 0.1 part by weight to 5 parts by weight per 100 parts by weight of the (a) base rubber.

[0065] Preparation of Rubber Composition The rubber composition used in the present disclosure is obtained by mixing and kneading (a) base rubber, (b) co-crosslinking agent, (c) crosslinking initiator, (d) benzothiazole derivative, (e) organic sulfur compound, and, if necessary, other additives, etc. The kneading method is not particularly limited, and may be performed using a known kneading machine such as a kneading roll, a Banbury mixer, or a kneader.

[0066] The molar ratio ((d) / (c)) of the molar amount of the (c) crosslinking initiator to the molar amount of the (d) benzothiazole derivative in the rubber composition is preferably 0.5 or more, more preferably 1.0 or more, and even more preferably 1.5 or more, and is preferably 10 or less, more preferably 7 or less, and even more preferably 5 or less. If the molar ratio ((d) / (c)) is 0.5 or more, the hardness of the obtained crosslinked rubber is further improved, and if it is 10 or less, the physical properties of the obtained crosslinked rubber are good.

[0067] The mass ratio ((d) / (e)) of the (d) benzothiazole derivative to the (e) organic sulfur compound in the rubber composition is preferably 0.5 or more, more preferably 1 or more, and even more preferably 1.5 or more, and is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less. When the mass ratio ((d) / (e)) is 0.5 or more, crosslinking proceeds efficiently, and when it is 10 or less, the physical properties of the resulting crosslinked rubber are good.

[0068] Rubber composition properties The rubber composition preferably has a ratio {(T2-T1) / (X-18)} of 0.3 or more, more preferably 0.35 or more, even more preferably 0.4 or more, and particularly preferably 0.5 or more, where X is the amount (parts by mass) of (b) co-crosslinking agent added per 100 parts by mass of (a) base rubber, T1 is the torque (N m) 10 seconds after the start of a crosslinking test of the rubber composition at 170°C, and T2 is the torque (N m) 60 seconds after the start of the test. When the ratio {(T2-T1) / (X-18)} is 0.3 or more, crosslinking can be efficiently formed.

[0069] The difference (T2-T1) is preferably 2.5 or more, more preferably 3 or more, and even more preferably 4 or more, and is preferably 20 or less, more preferably 17 or less, and even more preferably 15 or less.

[0070] The slab hardness of the rubber composition is preferably 60 or more, more preferably 65 or more, and even more preferably 70 or more, in Shore C hardness, and is preferably 100 or less, more preferably 95 or less, and even more preferably 90 or less.

[0071] [Crosslinked rubber molded body] The crosslinked rubber molded article of the present disclosure is characterized by being formed from the rubber composition. The crosslinked rubber molded article can be obtained by molding the kneaded rubber composition in a mold. The molding temperature is preferably 120°C or higher, more preferably 150°C or higher, and preferably 250°C or lower. The molding pressure is preferably 2.9 MPa to 11.8 MPa. The molding time is preferably 10 minutes to 60 minutes.

[0072] Applications of the crosslinked rubber molded article include sporting goods such as golf balls, tennis balls, grips, etc.; industrial goods such as hoses, belts, mats, etc.; shoe soles, tires, resin additives, vibration-proof rubber, fenders, etc. Examples of the golf ball include those having components formed from the rubber composition. [Example]

[0073] The present disclosure will be described in detail below using examples, but the present disclosure is not limited to the following examples, and all modifications and embodiments that do not deviate from the spirit of the present disclosure are included within the scope of the present disclosure.

[0074] [Evaluation method] (1) Cross-linking test After sampling an appropriate amount of each rubber composition, the vulcanization curve was measured at 170°C using a vulcanization tester (Curastometer Model 7, manufactured by JSR Trading Co., Ltd.). According to "9. Die vulcanization test method A" in "Method for determining vulcanization characteristics using a vibration vulcanization tester" of JIS K6300-2 (2001), a low-amplitude sinusoidal vibration was applied to the rubber test piece from the lower die, but not enough to break it, and the torque transmitted from the test piece to the upper die was measured from undervulcanization to overvulcanization. The measurement conditions were a torsional vibration frequency of 100 vibrations per minute, an amplitude angle of 1°, and a measurement time of 30 minutes.

[0075] (2) Slab hardness (Shore C) A sheet approximately 2 mm thick was prepared by heat press molding (170°C, 20 minutes), and the test specimen was stored at a temperature of 23±2°C and a relative humidity of 50±5% for 12 hours or more. Three or more sheets were stacked to avoid interference from the measurement substrate, and the hardness was measured using an automatic hardness tester (DigiTest II, manufactured by H. Burleith). A Shore C detector was used.

[0076] (3) Lubke's rebound resilience (%) The impact resilience test was performed in accordance with JIS K6255 (2013). A sheet approximately 2 mm thick was prepared by hot press molding (170°C, 20 minutes). Six 28 mm diameter circular pieces were punched out from the sheet and stacked to prepare cylindrical test specimens approximately 12 mm thick and 28 mm in diameter. These test specimens were stored at a temperature of 23±2°C and a relative humidity of 50±5% for at least 12 hours. The impact resilience of the prepared test specimens was measured using a Lübke impact resilience tester (manufactured by Ueshima Seisakusho Co., Ltd.). The flat surface of the stacked test specimens was supported by a mechanical fixation method. The measurement conditions were a temperature of 23°C, a relative humidity of 50%, a striking end diameter of 12.50±0.05 mm, a striking mass of 0.35±0.01 kg, and a striking velocity of 1.4±0.01 m / s.

[0077] [Preparation of Rubber Composition] Rubber compositions were prepared by kneading the rubber compositions having the formulations shown in Tables 1 and 2 with a kneading roll. The obtained rubber compositions were evaluated.

[0078] [Table 1]

[0079] [Table 2]

[0080] The raw materials used in Tables 1 and 2 are as follows: BR: "BR730" (high cis polybutadiene rubber (cis-1,4-bond content = 96 mass%, 1,2-vinyl bond content = 1.3 mass%, Mooney viscosity (ML 1+4 (100℃)=55, molecular weight distribution (Mw / Mn)=3)) ZN-DA90S: Zinc acrylate (containing 10% zinc stearate by mass), manufactured by Nisshoku Techno Fine Chemical Co., Ltd. ZnO: "Ginrei R" (zinc oxide) manufactured by Toho Zinc Co., Ltd. PCTP-Zn: Pentachlorothiophenol zinc salt, manufactured by Fujifilm Wako Chemical Co., Ltd. 5Cl-MBT: 5-chloro-2-mercaptobenzothiazole, manufactured by Tokyo Chemical Industry Co., Ltd. 5F-MBT: Combi-Blocks, 5-fluoro-2-mercaptobenzothiazole 5CF3-MBT: AA Blocks, 5-trifluoromethyl-2-mercaptobenzothiazole 6F-MBT:BLD Pharmatech, 6-fluoro-2-mercaptobenzothiazole 4Me-MBT: Fluorochem Ltd., 4-methyl-2-mercaptobenzothiazole 5Me-MBT: 5-methyl-2-mercaptobenzothiazole, manufactured by Cool pharm Ltd. 4Cl-MBT: 4-chloro-2-mercaptobenzothiazole, manufactured by Fluorochem Ltd. DCP: NOF Corporation, "Percumyl (registered trademark) D" (dicumyl peroxide)

[0081] The slab hardness and Lupke rebound resilience of the crosslinked rubber obtained from the rubber composition are shown in Tables 1 and 2. Figures 1 to 4 show the relationship between the crosslinking time and torque in the crosslinking test. FIG. 5 shows the relationship between the co-crosslinking agent content of a rubber composition and the slab hardness, and FIG. 6 shows the relationship between the slab hardness and the rebound resilience of a rubber composition. The dashed lines in FIG. 5 are linear approximation curves for rubber compositions No. 10 to 13. As shown in FIG. 5, when the types of raw materials contained in a rubber composition are the same, the slab hardness tends to increase as the co-crosslinking agent content increases. Therefore, it can be said that the higher the hardness at the same co-crosslinking agent content, the greater the hardness-improving effect of (d) the benzothiazole derivative. Furthermore, as shown in FIG. 6, the higher the slab hardness of a rubber composition, the lower the rebound resilience. Therefore, it can be said that the higher the rebound resilience at the same slab hardness, the better the rebound resilience of the rubber composition.

[0082] Rubber compositions Nos. 1 to 8 contain a compound represented by formula (1) or (2) as a (d) benzothiazole derivative, and an (e) organic sulfur compound. Rubber composition No. 9 contains neither a (d) benzothiazole derivative nor an (e) organic sulfur compound. Rubber compositions Nos. 10 to 13 contain an (e) organic sulfur compound but do not contain a (d) benzothiazole derivative. Rubber compositions Nos. 14 to 19 contain a benzothiazole compound other than the benzothiazole derivative represented by formula (1) or (2).

[0083] As shown in Figure 5, when comparing slab hardness when the blending amount of co-crosslinking agent is the same, the compositions containing (d) benzothiazole derivative (Nos. 1 to 8) have higher slab hardness than the compositions not containing (d) benzothiazole derivative (Nos. 10 to 13), regardless of the blending amount of co-crosslinking agent. Furthermore, when comparing rubber compositions Nos. 1 to 8 with rubber composition No. 9, rubber compositions Nos. 1 to 8 also have improved rebound resilience compared to rubber composition No. 9. Furthermore, these rubber compositions Nos. 1 to 8 have a ratio {(T2-T1) / (X-18)} of 0.3 or more, and the crosslinking rate is also increased.

[0084] Comparing rubber composition No. 11 with rubber composition No. 9, rubber composition No. 11 containing (e) an organic sulfur compound has a higher rebound resilience than rubber composition No. 9, but its hardness is lower. Among the compositions containing other benzothiazole compounds (Nos. 14 to 19), those containing 4Me-MBT or 4Cl-MBT had lower slab hardness than the compositions not containing (d) benzothiazole derivatives (Nos. 10 to 13), regardless of the amount of co-crosslinking agent. Furthermore, the slab hardness of the compositions containing 5Me-MBT was increased when the amount of co-crosslinking agent was 28 parts by mass, but decreased when the amount was 25 parts by mass.

[0085] The present disclosure (1) is a rubber composition comprising (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, (d) a benzothiazole derivative, and (e) an organic sulfur compound, wherein the (d) benzothiazole derivative is a compound represented by formula (1) and / or a compound represented by formula (2).

[0086] [ka] [R 1 represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group having 4 to 14 carbon atoms, or a metal atom. R 2 ~R 5 are the same or different and represent an electron-withdrawing group or a hydrogen atom. 3 ~R 5 At least one of is an electron-withdrawing group.

[0087] The present disclosure (2) is the rubber composition according to the present disclosure (1), wherein the content of the (d) benzothiazole derivative is 0.01 to 20 parts by mass per 100 parts by mass of the (a) base rubber.

[0088] The present disclosure (3) is the rubber composition according to the present disclosure (1) or (2), in which the (e) organic sulfur compound is at least one compound selected from the group consisting of thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles, and metal salts thereof.

[0089] The present disclosure (4) is the rubber composition according to any one of the present disclosures (1) to (3), wherein the mass ratio ((d) / (e)) of the (d) benzothiazole derivative to the (e) organic sulfur compound is 0.5 to 10.

[0090] The present disclosure (5) is a rubber composition according to any one of the present disclosures (1) to (4), in which the (b) co-crosslinking agent is an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof.

[0091] The present disclosure (6) is the rubber composition according to any one of the present disclosures (1) to (5), wherein the content of the (b) co-crosslinking agent is more than 18 parts by mass and not more than 50 parts by mass per 100 parts by mass of the (a) base rubber.

[0092] The present disclosure (7) is a rubber composition according to any one of the present disclosures (1) to (6), wherein X is the amount (parts by mass) of the (b) co-crosslinking agent added relative to 100 parts by mass of the (a) base rubber in the rubber composition, T1 is the torque (N m) 10 seconds after the start of measurement when a crosslinking test is performed on the rubber composition at 170°C, and T2 is the torque (N m) 60 seconds after the start of measurement, and these satisfy the relationship {(T2-T1) / (X-18)}≧0.3.

[0093] The present disclosure (8) is a crosslinked rubber molded article formed from the rubber composition according to any one of the present disclosures (1) to (7).

[0094] The present disclosure (9) is a golf ball characterized by having a component formed from the rubber composition according to any one of the present disclosures (1) to (7). [Industrial Applicability]

[0095] The rubber composition of the present disclosure can be used to form crosslinks in a short time and to obtain crosslinked rubber molded articles with high hardness. Therefore, the rubber composition of the present disclosure can be used in sports goods such as golf balls, tennis balls, and grips; industrial goods such as hoses, belts, and mats; shoe soles, tires, resin additives, vibration-proof rubber, and fenders.

Claims

1. (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, (d) a benzothiazole derivative, and (e) an organic sulfur compound, A rubber composition, wherein the (d) benzothiazole derivative is a compound represented by formula (1) and / or a compound represented by formula (2). 【Chemical 1】 [R 1 represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 14 carbon atoms, or a metal atom. R 2 ~R 5 are the same or different and represent an electron-withdrawing group or a hydrogen atom, and at least one of R 3 and R 4 is an electron-withdrawing group.

2. 2. The rubber composition according to claim 1, wherein the content of the (d) benzothiazole derivative is 0.01 to 20 parts by weight per 100 parts by weight of the (a) base rubber.

3. 3. The rubber composition according to claim 1, wherein the (e) organic sulfur compound is at least one compound selected from the group consisting of thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles, and metal salts thereof.

4. The rubber composition according to any one of claims 1 to 3, wherein a mass ratio ((d) / (e)) of the (d) benzothiazole derivative to the (e) organic sulfur compound is 0.5 to 10.

5. 5. The rubber composition according to claim 1, wherein the co-crosslinking agent (b) is an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof.

6. The rubber composition according to any one of claims 1 to 5, wherein the amount of the (b) co-crosslinking agent is more than 18 parts by mass and not more than 50 parts by mass per 100 parts by mass of the (a) base rubber.

7. 7. The rubber composition according to claim 1, wherein X is the amount (parts by mass) of the co-crosslinking agent (b) added relative to 100 parts by mass of the base rubber (a) in the rubber composition, T1 is the torque (N m) 10 seconds after the start of measurement when a crosslinking test is performed on the rubber composition at 170°C, and T2 is the torque (N m) 60 seconds after the start of measurement, these satisfy the relationship {(T2-T1) / (X-18)}≧0.

3.

8. A crosslinked rubber molded article formed from the rubber composition according to any one of claims 1 to 7.

9. A golf ball having a component formed from the rubber composition according to any one of claims 1 to 7.

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