Rubber composition and crosslinked rubber molded articles

Abstract

To provide a rubber composition which yields a crosslinked rubber molding having good flexibility and excellent repulsion performance.SOLUTION: A rubber composition contains (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and (d) an organic sulfur compound. The organic sulfur compound (d) contains (d1) a compound represented by formula (1) and / or (d2) a compound represented by formula (2). [In the formulae (1) and (2), R1 and R2 may be the same or different and each represents an alkyl group, an aryl group, an aralkyl group, an alkoxy group, an alkylthio group, a perfluoroalkyl group, an amino group, a carboxy group, a hydrogen atom, or a halogen atom; and R1 and R2 may be bonded to each other to form a cyclic structure.]SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to rubber compositions, and more particularly to rubber compositions that can yield crosslinked rubber molded articles that have good flexibility and excellent rebound performance. [Background technology]

[0002] One way to increase the distance of a golf ball during a driver shot is to use a highly resilient material. By using a highly resilient material, the initial velocity of the golf ball increases, resulting in a greater flight distance. Examples of highly resilient materials include rubber compositions that form the core and resin compositions that form the intermediate layer or cover.

[0003] As an example of a golf ball with enhanced rebound performance, Patent Document 1 describes a golf ball in which at least a part of the golf ball's constituent components is formed from a rubber composition containing (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and (d) an organic sulfur compound, wherein the organic sulfur compound is a derivative of thiophenols or diphenyl sulfide and has substituents with high electron-withdrawing properties (see Patent Document 1 (Claim 1)). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-125345 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Various rubber compositions with enhanced resilience have been proposed, but there was still room for improvement in resilience performance. This disclosure is made in view of the above circumstances and aims to provide a rubber composition that yields a crosslinked rubber molded article with good flexibility and excellent resilience performance. [Means for solving the problem]

[0006] The rubber composition of the present disclosure that has solved the above problems contains (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and (d) an organic sulfur compound, and is characterized in that the (d) organic sulfur compound contains (d1) a compound represented by formula (1) and / or (d2) a compound represented by formula (2).

[0007]

Chemical formula

Advantages of the Invention

[0008] When the rubber composition of the present disclosure is used, a crosslinked rubber molded body having good flexibility and excellent resilience performance can be obtained.

Brief Description of the Drawings

[0009] [Figure 1] It is a diagram showing the relationship between the resilience coefficient and the compression deformation amount of the crosslinked rubber composition.

Mode for Carrying Out the Invention

[0010] [Rubber Composition] The rubber composition of the present disclosure is characterized by containing (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and (d) an organic sulfur compound.

[0011] (d) Organic Sulfur Compound The (d) organic sulfur compound used in the present disclosure will be described. The (d) organic sulfur compound contains (d1) a compound represented by formula (1) and / or (d2) a compound represented by formula (2). The (d) organic sulfur compound may be used alone or in combination of two or more. By blending the compound represented by the (d1) formula (1) and / or the compound represented by the (d2) formula (2) into the rubber composition, the crosslinking reaction can be promoted and dense crosslinks can be formed, and the resilience can be improved without impairing the flexibility of the crosslinked molded body. Note that the compound represented by the (d1) formula (1) and the compound represented by the (d2) formula (2) are tautomers.

[0012] [Chemical Formula] [In formula (1) and (2), R 1 and R 2 each independently represents an alkyl group having 1 or more carbon atoms, an aryl group having 6 or more carbon atoms, an aralkyl group having 6 or more carbon atoms, an alkoxy group having 1 or more carbon atoms, an alkylthio group having 1 or more carbon atoms, a perfluoroalkyl group having 1 or more carbon atoms, an amino group, a carboxy group, a hydrogen atom or a halogen atom. R 1 and R 2They may be combined with each other to form a cyclic structure. In this case, the ring member atoms may contain at least one selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom, and the ring member atoms may have a substituent. The substituent of the ring member atom is at least one selected from the group consisting of an alkyl group having 1 or more carbon atoms, an aryl group having 6 or more carbon atoms, an aralkyl group having 6 or more carbon atoms, an alkoxy group having 1 or more carbon atoms, an alkylthio group having 1 or more carbon atoms, a perfluoroalkyl group having 1 or more carbon atoms, an amino group, a carboxy group, and a halogen atom.

[0013] The above-mentioned R 1 and R 2 Examples of the alkyl group having 1 or more carbon atoms represented by include a linear alkyl group, a branched alkyl group, and a cyclic alkyl group. The number of carbon atoms of the alkyl group is preferably 1 or more, preferably 18 or less, and more preferably 12 or less. Examples of the linear alkyl group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, etc. Examples of the branched alkyl group include an isopropyl group, an isobutyl group, an s-butyl group, a t-butyl group, an isopentyl group, etc. Examples of the cyclic alkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, etc.

[0014] The above-mentioned R 1 and R 2 The number of carbon atoms of the aryl group having 6 or more carbon atoms represented by is preferably 18 or less, and more preferably 14 or less. Examples of the aryl group include a phenyl group, a naphthyl group, etc.

[0015] The above-mentioned R 1 and R 2 The number of carbon atoms of the aralkyl group having 6 or more carbon atoms represented by is preferably 20 or less, and more preferably 14 or less. Examples of the aralkyl group include a benzyl group, a phenylethyl group, a phenylpropyl group, a phenylbutyl group, an α-cumyl group, a 1-phenylethyl group, etc.

[0016] The above-mentioned R1 , R 2 The number of carbon atoms in the alkoxy group having 1 or more carbon atoms, represented by , is preferably 18 or less, and more preferably 12 or less. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, and the like.

[0017] The aforementioned R 1 , R 2 The number of carbon atoms in the alkylthio group having one or more carbon atoms represented by is preferably 18 or less, and more preferably 12 or less. Examples of the alkylthio group include methylthio group, ethylthio group, propylthio group, butylthio group, pentylthio group, and the like.

[0018] The aforementioned R 1 , R 2 The number of carbon atoms in the perfluoroalkyl group having one or more carbon atoms, represented by , is preferably 18 or less, and more preferably 12 or less. Examples of the perfluoroalkyl group include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, and the like.

[0019] The aforementioned R 1 , R 2 Examples of halogen atoms represented by this formula include fluorine, chlorine, bromine, and iodine atoms.

[0020] The aforementioned R 1 and R 2 The cyclic structure formed by the bonding of these elements is preferably a 5-membered to 7-membered ring. The cyclic structure may be either an aromatic ring or a non-aromatic ring.

[0021] The compound represented by formula (1) in (d1) is preferably the compound represented by formula (11). Also, the compound represented by formula (2) in (d2) is preferably the compound represented by formula (21).

[0022] [ka] [In formulas (11) and (21), R 11 ~R 14Each of these terms, either identical or distinct, represents an alkyl group having 1 or more carbon atoms, an aryl group having 6 or more carbon atoms, an aralkyl group having 6 or more carbon atoms, an alkoxy group having 1 or more carbon atoms, an alkylthio group having 1 or more carbon atoms, a perfluoroalkyl group having 1 or more carbon atoms, an amino group, a carboxyl group, a hydrogen atom, or a halogen atom.

[0023] R in equations (11) and (21) 11 ~R 14 The alkyl group having 1 or more carbon atoms, the aryl group having 6 or more carbon atoms, the aralkyl group having 6 or more carbon atoms, the alkoxy group having 1 or more carbon atoms, the alkylthio group having 1 or more carbon atoms, and the perfluoroalkyl group having 1 or more carbon atoms represented by formula (1) and (2) are R 1 , R 2 Examples include the following:

[0024] In equations (11) and (21) above, R 11 ~R 14 Preferably, at least one selected from the group consisting of C1-C12 alkyl groups, C1-C12 perfluoroalkyl groups, halogen atoms, and hydrogen atoms.

[0025] As the compound represented by formula (1) (d1), compounds represented by formulas (11-1) to (11-12) are particularly preferred.

[0026] [ka]

[0027] As for the compound represented by formula (d2) (2), compounds represented by formulas (21-1) to (21-12) are particularly preferred.

[0028] [ka]

[0029] The total content of the compound represented by formula (1) (d1) and the compound represented by formula (2) (d2) is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and even more preferably 15 parts by mass or less, per 100 parts by mass of the base rubber (a). If the total content is 0.01 parts by mass or more, the resilience is further improved, and if it is 20 parts by mass or less, the flexibility is further improved.

[0030] The following describes other raw materials used in rubber compositions.

[0031] (a) Base rubber As the base rubber (a) above, natural rubber and / or synthetic rubber can be used. Examples of synthetic rubbers 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 individually or in combination of two or more types.

[0032] 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.

[0033] The (a) base rubber preferably contains polybutadiene rubber. In particular, high-cis polybutadiene having 40% or more, preferably 80% or more, and more preferably 90% or more, cis-1,4-bonds advantageous for rebound is preferred. The content of high-cis polybutadiene in the (a) base rubber is preferably 50% or more by mass, more preferably 70% or more by mass, and it is also preferable that the (a) base rubber contains only high-cis polybutadiene.

[0034] 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.

[0035] The high-cis polybutadiene is preferably synthesized using a rare earth element catalyst, and in particular, the use of a neodymium catalyst using a neodymium compound, which is a lanthanum series rare earth element compound, is preferable because it allows for the production of polybutadiene rubber with a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds with excellent polymerization activity.

[0036] 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 higher, more preferably 2.2 or higher, even more preferably 2.4 or higher, most preferably 2.6 or higher, preferably 6.0 or lower, more preferably 5.0 or lower, even more preferably 4.0 or lower, and most preferably 3.4 or lower. If the molecular weight distribution (Mw / Mn) of the high-cis polybutadiene is too low, workability will decrease, and if it is too high, resilience may decrease. The molecular weight distribution was measured using gel permeation chromatography (Tosoh Corporation, "HLC-8120GPC") with a differential refractometer as the detector, under the conditions of column: GMHHXL (Tosoh Corporation), column temperature: 40°C, mobile phase: tetrahydrofuran, and the value was calculated as a standard polystyrene equivalent.

[0037] The aforementioned high-cis polybutadiene has a Mooney viscosity (ML). 1+4 The Mooney viscosity (ML) (at 100°C) is preferably 30 or higher, more preferably 32 or higher, even more preferably 35 or higher, preferably 140 or lower, more preferably 120 or lower, even more preferably 100 or lower, and most preferably 80 or lower. 1+4 (100℃)) refers to the value measured in accordance with JIS K6300, using an L rotor, with a preheating time of 1 minute, a rotor rotation time of 4 minutes, and under conditions of 100℃.

[0038] (b) Cocrossant The (b) cocrosslinking agent has the effect of crosslinking rubber molecules by graft polymerization onto the base rubber molecular chains. The (b) cocrosslinking agent is preferably an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or its metal salt. The number of carbon atoms of the α,β-unsaturated carboxylic acid used as the (b) cocrosslinking agent is preferably 3 to 8, more preferably 3 to 6, and even more preferably 3 or 4. The α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or its metal salt may be used alone or in combination of two or more types.

[0039] Examples of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid. When the rubber composition contains only α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms as a co-crosslinking agent, it is preferable that the rubber composition further contains (e) a metal compound. This is because neutralizing the α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms in the rubber composition with a metal compound provides substantially the same effect as when a metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used as a co-crosslinking agent.

[0040] Examples of metals that constitute the metal salts of α,β-unsaturated carboxylic acids 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 individually or as a mixture of two or more. Among these, divalent metals such as magnesium, calcium, zinc, barium, and cadmium are preferred as the metal components. This is because using divalent metal salts of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms makes it easier for metal crosslinking to occur between rubber molecules. In particular, as the divalent metal salt, zinc salt of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms is preferred, and zinc acrylate is more preferred, because it increases the rebound properties of the resulting golf ball. When using α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms and their metal salts in combination as co-crosslinking agents, (e) metal compounds may be used as optional components.

[0041] If 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 other carboxylic acids other than α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms as the carboxylic acid component. Examples of other carboxylic acids 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.

[0042] (b) The co-crosslinking agent content is preferably 15 parts by mass or more, more preferably 18 parts by mass or more, even more preferably 20 parts by mass or more, 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 (a) base rubber. If the co-crosslinking agent content is 15 parts by mass or more, the member formed from the rubber composition can be made to an appropriate hardness with a small amount of (c) crosslinking initiator, and the resilience of the crosslinked rubber molded article is further improved. On the other hand, if the co-crosslinking agent content is 50 parts by mass or less, the member formed from the rubber composition will not become too hard.

[0043] (c) Crosslinking initiator The (c) crosslinking initiator is formulated to crosslink the (a) base rubber component. Organic peroxides are preferred as the (c) crosslinking initiator. Specifically, examples of organic peroxides 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 individually or in combination of two or more. Among these, dicumyl peroxide is preferred.

[0044] 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, 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 become 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 an appropriate hardness and will have good resilience and durability.

[0045] (d) Other organosulfur compounds The rubber composition may further contain (d3) other organic sulfur compounds different from the compound represented by formula (1) and (d2) formula (2). Examples of other organic sulfur compounds include at least one compound selected from the group consisting of thiophenols, thionaphthols, polysulfides, thirams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles, and metal salts thereof. (d3) Thiophenols, thionaphthols, or metal salts thereof are preferred as other organic sulfur compounds.

[0046] Examples of the thiophenols include thiophenols; 4-fluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, pentafluorothiophenol, and other thiophenols substituted with fluoro groups; 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, pentachlorothiophenone Thiophenols substituted with chloro groups such as 4-bromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, pentabromothiophenol, etc. Thiophenols substituted with iodine groups such as 4-iodothiophenol, 2,5-diiodothiophenol, 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, pentaiodothiophenol, etc., or metal salts thereof. Zinc salts are preferred as the metal salts.

[0047] Examples of the thionaphthols (naphthalenchiols) 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, or metal salts thereof, with 2-thionaphthol, 1-thionaphthol, or metal salts thereof being preferred. The metal salt is preferably a divalent metal salt, more preferably a zinc salt. Specific examples of the metal salt include, for example, zinc salt of 1-thionaphthol and zinc salt of 2-thionaphthol.

[0048] Polysulfides are organosulfur compounds having polysulfide bonds, and examples include disulfides, trisulfides, and tetrasulfides. Diphenyl polysulfides are preferred as the polysulfides.

[0049] Diphenyl polysulfides include diphenyl disulfide, as well as 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-chlorophenyl) disulfide, and bis(4-chlorophenyl) disulfide. 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 Examples include diphenyl disulfides substituted with halogen groups such as; diphenyl disulfides substituted with alkyl groups 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 so on.

[0050] Examples of thiuram compounds 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 naphthalenthiocarboxylic acid. Examples of dithiocarboxylic acids include naphthalenedithiocarboxylic acid. Examples of sulfenamides include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and Nt-butyl-2-benzothiazole sulfenamide.

[0051] (d3) Other organosulfur compounds may be used individually or in combination of two or more. (d3) Preferred other organosulfur compounds include thiophenols and / or their metal salts, thionaphthols and / or their metal salts, 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, and bis(pentabromophenyl) disulfide.

[0052] (d) The total content of the organic sulfur compounds is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and even more preferably 15 parts by mass or less, per 100 parts by mass of the base rubber (a). If the content of the organic sulfur compounds (d) is less than 0.01 parts by mass, the effect of adding the organic sulfur compounds (d) may not be obtained, and the resilience of the crosslinked rubber molded article may not improve. Also, if the content of the organic sulfur compounds (d) exceeds 20 parts by mass, the amount of compression deformation of the resulting crosslinked rubber molded article may increase, and the resilience may decrease.

[0053] (e) Metal compounds When the rubber composition used in this disclosure contains only α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms as a co-crosslinking agent, the rubber composition preferably contains (e) a metal compound. The (e) metal compound is not particularly limited as long as it can neutralize (b) α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms in the rubber composition. Examples of the (e) 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 carbon oxides such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. The (e) metal compound is preferably a divalent metal compound, and more preferably a zinc compound. This is because divalent metal compounds react with α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms to form metal crosslinks. Furthermore, by using a zinc compound, a crosslinked rubber molded article with high resilience can be obtained. The (e) metal compound may be used alone or two or more may be used in combination. (e) The content of the metal compound may be adjusted as appropriate depending on the desired degree of neutralization of the (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms.

[0054] (f) Carboxylic acids and / or salts thereof The rubber composition may contain (f) carboxylic acids and / or salts thereof. By including the (f) carboxylic acids and / or salts thereof, the hardness distribution of the resulting crosslinked rubber molded article can be controlled. Examples of the (f) carboxylic acids and / or salts thereof include aliphatic carboxylic acids, aliphatic carboxylate salts, aromatic carboxylic acids, and aromatic carboxylate salts. The (f) carboxylic acids and / or salts may be used alone or as a mixture of two or more. Note that the (f) carboxylic acids and / or salts thereof do not include α,β-unsaturated carboxylic acids and / or metal salts thereof having 3 to 8 carbon atoms, which are used as the (b) cocrosslinking agent.

[0055] The aliphatic carboxylic acid may be either a saturated aliphatic carboxylic acid (hereinafter sometimes referred to as "saturated fatty acid") or an unsaturated aliphatic carboxylic acid (hereinafter sometimes referred to as "unsaturated fatty acid"). The aliphatic carboxylic acid may also have a branched structure or a cyclic structure. The number of carbon atoms in the saturated fatty acid is preferably 6 or more, preferably 24 or less, more preferably 18 or less, and even more preferably 13 or less. The number of carbon atoms in the unsaturated fatty acid is preferably 6 or more, more preferably 7 or more, even more preferably 8 or more, preferably 24 or less, more preferably 18 or less, and even more preferably 13 or less.

[0056] Examples of aromatic carboxylic acids 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 carboxylic acids having a benzene ring include aromatic carboxylic acids in which a carboxyl group is directly bonded to a benzene ring, aromatic-aliphatic carboxylic acids in which an aliphatic carboxylic acid is bonded to a 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 carboxylic acids having a heteroaromatic ring include those in which a carboxyl group is directly bonded to a heteroaromatic ring.

[0057] As the aliphatic carboxylate salt or aromatic carboxylate salt, the above-mentioned salts of aliphatic carboxylic acids or aromatic carboxylic acids can be used. Examples of 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, and magnesium, zinc, and calcium are more preferred.

[0058] The aforementioned organic cation is a cation having a carbon chain. The aforementioned organic cation is not particularly limited, and examples include organic ammonium ions. Examples of the aforementioned organic ammonium ions include primary ammonium ions such as stearylammonium ion, hexylammonium ion, octylammonium ion, and 2-ethylhexylammonium ion; secondary ammonium ions such as dodecyl(lauryl)ammonium ion and octadecyl(stearyl)ammonium ion; tertiary ammonium ions such as trioctylammonium ion; and quaternary ammonium ions such as dioctyldimethylammonium ion and distearyldimethylammonium ion. These organic cations may be used individually or in combination of two or more.

[0059] Examples of the aliphatic carboxylic acid and / or its salt include saturated fatty acids and / or their salts, and unsaturated fatty acids and / or their salts. Saturated fatty acids and / or their salts are preferred, and caprylic acid (octanoic acid), pelargonic acid (nonanoic acid), capric acid (decanoic acid), lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, or potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, and cobalt salts thereof are preferred. Examples of the unsaturated fatty acid and / or its salt include palmitoleic acid, oleic acid, linoleic acid, or arachidonic acid, or potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, and cobalt salts thereof are preferred.

[0060] The aromatic carboxylic acids and / or their salts are particularly preferably 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, or thenoylic acid, or their potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, or cobalt salts.

[0061] The content of (f) carboxylic acid and / or its salt is, for example, preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, 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, per 100 parts by mass of (a) base rubber.

[0062] Other ingredients The rubber composition may optionally contain additives such as pigments, fillers for weight adjustment, antioxidants, descaling agents, and softeners. The rubber composition may also contain rubber powder obtained by crushing golf ball cores or scraps generated during core production.

[0063] Examples of pigments that can be incorporated into the rubber composition include white pigments, blue pigments, and purple pigments. Titanium dioxide is preferably used as the white pigment. While the type of titanium dioxide is not particularly limited, rutile type is preferred due to its good opacity. The titanium dioxide content is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, preferably 8 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the base rubber.

[0064] It is also a preferred embodiment that the rubber composition contains a white pigment and a blue pigment. The blue pigment is added to make the white appear more vivid, and examples include ultramarine, cobalt blue, and phthalocyanine blue. Examples of the purple pigment include anthraquinone violet, dioxazine violet, and methyl violet.

[0065] The fillers used in the rubber composition are weight adjusters added to adjust the mass of the resulting crosslinked rubber molded article, and may be added as needed. Examples of such fillers include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder.

[0066] The content of the anti-aging agent is preferably 0.1 parts by mass or more and 1 part by mass or less per 100 parts by mass of the base rubber (a). Furthermore, the content of the deconjugating agent is preferably 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base rubber (a).

[0067] Preparation of rubber composition The rubber composition used in this disclosure is obtained by mixing and kneading (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, (d) an organosulfur compound, and, if necessary, other additives. The kneading method is not particularly limited and may be carried out using known kneaders such as kneading rolls, Banbury mixers, and kneaders.

[0068] [Cross-linked rubber molded product] The crosslinked rubber molded article of this 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.

[0069] Applications of the cross-linked rubber molded articles include sports equipment such as golf balls, tennis balls, and grips; industrial products such as hoses, belts, and mats; and shoe soles, tires, resin additives, vibration-damping rubber, and fenders. The golf balls mentioned above include those having components formed from the rubber composition.

[0070] [Golf balls] This disclosure includes a golf ball having components formed from the rubber composition. In a preferred embodiment of the golf ball of this disclosure, the golf ball has a core and at least one cover covering the core, wherein at least a portion of the core is formed from the rubber composition. The golf ball will be described below.

[0071] core The core of the golf ball can be obtained by mixing and kneading the aforementioned rubber composition and molding it in a mold. The conditions for this process are not particularly limited, but are usually 130°C to 200°C and a pressure of 2.9 MPa to 11.8 MPa for 10 to 60 minutes. For example, it is preferable to heat the rubber composition for the golf ball at 130°C to 200°C for 10 to 60 minutes.

[0072] The core is preferably spherical in shape. The core can be either a single-layer or multi-layer structure, but a single-layer structure is preferred. This is because a single-layer core eliminates energy loss at the interface of the multi-layer structure during impact, resulting in improved resilience.

[0073] The diameter of the core is preferably 34.8 mm or more, preferably 42.2 mm or less, more preferably 41.8 mm or less, even more preferably 41.2 mm or less, and most preferably 40.8 mm or less. If the diameter of the core is 34.8 mm or more, the thickness of the cover will not become too thick, resulting in better rebound properties. On the other hand, if the diameter of the core is 42.2 mm or less, the cover will not become too thin, allowing the cover to function better.

[0074] For the core with a diameter of 34.8 mm to 42.2 mm, the amount of compressive deformation (the amount the core shrinks in the compression direction) from an initial load of 98 N to a final load of 1275 N is preferably 2.0 mm or more, more preferably 2.3 mm or more, even more preferably 2.5 mm or more, preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.3 mm or less. If the amount of compressive deformation is 2.0 mm or more, the feel of hitting the ball will be better, and if it is 5.0 mm or less, the rebound performance will be better.

[0075] cover The cover of the golf ball is formed from a cover composition containing a resin component. Examples of the resin component include ionomer resin, thermoplastic polyurethane elastomer sold by BASF Japan Ltd. under the trade name "Elastran®", thermoplastic polyamide elastomer sold by Arkema Inc. under the trade name "Pebax®", thermoplastic polyester elastomer sold by Toray DuPont Ltd. under the trade name "Hytrel®", and thermoplastic styrene elastomer sold by Mitsubishi Chemical Corporation under the trade name "Tefablock".

[0076] In addition to the resin components described above, the cover composition may also contain pigment components such as white pigments (e.g., titanium dioxide), blue pigments, and red pigments, weight adjusters such as zinc oxide, calcium carbonate, and barium sulfate, dispersants, antioxidants, ultraviolet absorbers, light stabilizers, fluorescent materials, or fluorescent whitening agents, to the extent that they do not impair the performance of the cover.

[0077] Examples of methods for forming the golf ball cover include forming a hollow shell from the cover composition and then compression molding the core with multiple shells (preferably forming a hollow half-shell from the cover composition and then compression molding the core with two half-shells), or directly injection molding the cover composition onto the core.

[0078] The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less. If the cover thickness is 4.0 mm or less, the rebound and feel of the resulting golf ball will be better. The thickness of the cover is preferably 0.3 mm or more, more preferably 0.4 mm or more, and even more preferably 0.5 mm or more. If the cover thickness is less than 0.3 mm, the durability and abrasion resistance of the cover may decrease. In the case of multiple cover layers, it is preferable that the total thickness of the multiple cover layers is within the above range.

[0079] Examples of the aforementioned golf balls include a two-piece golf ball consisting of a core and a single-layer cover disposed to cover the core, and a multi-piece golf ball (including a three-piece golf ball) having a core and two or more layers of cover disposed to cover the core.

[0080] The diameter of the golf ball is preferably 40 mm to 45 mm. From the viewpoint of meeting the standards of the United States Golf Association (USGA), a diameter of 42.67 mm or more is particularly preferred. From the viewpoint of suppressing air resistance, a diameter of 44 mm or less is more preferred, and 42.80 mm or less is particularly preferred. The mass of the golf ball is preferably 40 g to 50 g. From the viewpoint of obtaining a large inertia, a mass of 44 g or more is more preferred, and 45.00 g or more is particularly preferred. From the viewpoint of meeting the standards of the USGA, a mass of 45.93 g or less is particularly preferred. [Examples]

[0081] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to the examples below, and any modifications and modes of implementation that do not depart from the spirit of the present disclosure are included within the scope of the present disclosure.

[0082] [Evaluation Method] (1) Compression deformation amount (mm) The amount of deformation in the compressive direction (the amount the spherical molded body shrinks in the compressive direction) was measured from when an initial load of 98N was applied to a spherical molded body until a final load of 1275N was applied.

[0083] (2) Coefficient of restitution A 198.4g metal cylinder was impacted onto each spherical molded body at a speed of 40 m / s. The velocities of the cylinder and the spherical molded body were measured before and after the impact, and the coefficient of restitution of each spherical molded body was calculated from their respective velocities and masses. Twelve measurements were taken for each spherical molded body, and the average value was used as the coefficient of restitution for each spherical molded body.

[0084] [Fabrication of spherical molded bodies] A rubber composition with the formulation shown in Table 1 was kneaded using a kneading roll, and then heated and pressed at 170°C for 20 minutes in upper and lower molds having hemispherical cavities to obtain a spherical molded body with a diameter of 40.86 mm.

[0085] [Table 1] BR: JSR Corporation, "BR730" (High-cis polybutadiene rubber (cis-1,4-bond content = 96% by mass, 1,2-vinyl bond content = 1.3% by mass, Mooney viscosity (ML)) 1+4 (100℃)=55, molecular weight distribution (Mw / Mn)=3)) ZN-DA90S: Manufactured by Nichishoku Techno Fine Chemical Co., Ltd., zinc acrylate (containing 10% by mass of zinc stearate) ZnO: "Ginrei R" (zinc oxide), manufactured by Toho Zinc Co., Ltd. PCTP-Zn: Pentachlorothiophenol zinc salt, manufactured by Fujifilm Wako Chemical Co., Ltd. 6-Methyl-2-mercaptobenzoxazole: Manufactured by Tokyo Chemical Industry Co., Ltd. 5-Chloro-2-mercaptobenzoxazole: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. 7-Chloro-2-mercaptobenzoxazole: Manufactured by Sigma-Aldrich. 6-(trifluoromethyl)-2-mercaptobenzoxazole: Manufactured by Key Organics. DCP: Manufactured by NOF Corporation, "Parkmyl® D" (Dicumyl Peroxide)

[0086] Table 1 shows the compressive deformation and coefficient of restitution for each spherical molded body. Figure 1 shows the relationship between the compressive deformation and coefficient of restitution for each spherical molded body. As shown in Figure 1, when the raw materials contained in the rubber composition are the same, the higher the co-crosslinking agent content, the higher the rebound performance and the lower the compressive deformation tends to be. Therefore, the more the straight line connecting the plots of spherical molded bodies made from the same raw materials is located in the upper right of the graph, the more flexible and superior the rebound performance can be said to be.

[0087] Spherical molded bodies No. 1 to 3 are formed from a rubber composition that does not contain (d1) the compound represented by formula (1) and (d2) the compound represented by formula (2) as (d) organic sulfur compounds. Spherical molded bodies No. 4 to 11 are formed from a rubber composition that contains (d1) the compound represented by formula (1) and / or (d2) the compound represented by formula (2) as (d) organic sulfur compounds. As shown in Figure 1, when compared at a similar amount of compression deformation, these spherical molded bodies No. 4 to 11 have superior rebound performance compared to spherical molded bodies No. 1 to 3. Therefore, spherical molded bodies No. 4 to 11 can be made into spherical molded bodies with excellent rebound performance while maintaining flexibility.

[0088] The present disclosure (1) is a rubber composition comprising (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and (d) an organosulfur compound, wherein the (d) organosulfur compound comprises (d1) a compound represented by formula (1) and / or (d2) a compound represented by formula (2).

[0089] [ka] [In formulas (1) and (2), R 1 and R 2 Each of these represents, either identical or distinct, an alkyl group having 1 or more carbon atoms, an aryl group having 6 or more carbon atoms, an aralkyl group having 6 or more carbon atoms, an alkoxy group having 1 or more carbon atoms, an alkylthio group having 1 or more carbon atoms, a perfluoroalkyl group having 1 or more carbon atoms, an amino group, a carboxyl group, a hydrogen atom, or a halogen atom. 1 and R 2The ring members may be bonded to each other to form a cyclic structure, in which case the ring member atoms may contain at least one selected from the group consisting of oxygen atoms, nitrogen atoms, and sulfur atoms, and the ring member atoms may have substituents. The substituents on the ring member atoms are at least one selected from the group consisting of alkyl groups having 1 or more carbon atoms, aryl groups having 6 or more carbon atoms, aralkyl groups having 6 or more carbon atoms, alkoxy groups having 1 or more carbon atoms, alkylthio groups having 1 or more carbon atoms, perfluoroalkyl groups having 1 or more carbon atoms, amino groups, carboxyl groups, and halogen atoms.

[0090] This disclosure (2) states that in formulas (1) and (2), R 1 and R 2 The rubber composition according to disclosure (1) is characterized in that the members are bonded to each other to form a ring structure, and the ring structure is a 5-7 membered ring.

[0091] Disclosure (3) is a rubber composition according to Disclosure (1) or (2), wherein the compound represented by (d1) formula (1) is the compound represented by formula (11), and the compound represented by (d2) formula (2) is the compound represented by formula (21).

[0092] [ka] [In formulas (11) and (21), R 11 ~R 14 Each of these terms, either identical or distinct, represents an alkyl group having 1 or more carbon atoms, an aryl group having 6 or more carbon atoms, an aralkyl group having 6 or more carbon atoms, an alkoxy group having 1 or more carbon atoms, an alkylthio group having 1 or more carbon atoms, a perfluoroalkyl group having 1 or more carbon atoms, an amino group, a carboxyl group, a hydrogen atom, or a halogen atom.

[0093] Disclosure (4) is a rubber composition according to any one of Disclosures (1) to (3), wherein the total content of the compound represented by (d1) formula (1) and the compound represented by (d2) formula (2) is 0.01 parts by mass to 20 parts by mass per 100 parts by mass of the base rubber (a).

[0094] Disclosure (5) is a rubber composition according to any one of Disclosures (1) to (4), wherein the content of the cocrosslinking agent (b) is 15 to 50 parts by mass per 100 parts by mass of the base rubber (a).

[0095] Disclosure (6) is a crosslinked rubber molded article characterized by being formed from a rubber composition described in any of Disclosures (1) to (5).

[0096] Disclosure (7) is a golf ball characterized by having a component formed from a rubber composition described in any of Disclosures (1) to (5). [Industrial applicability]

[0097] Using the rubber composition disclosed herein, a crosslinked rubber molded article with excellent rebound performance can be obtained. Therefore, the rubber composition disclosed herein can be used in sports equipment such as golf balls, tennis balls, and grips; industrial products such as hoses, belts, and mats; shoe soles, tires, resin additives, vibration-damping rubber, fenders, and the like.

Claims

1. (a) base rubber, (b) co-crosslinking agent, (c) crosslinking initiator, and (d) organosulfur compound, The (b) cocrosslinking agent is a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. A rubber composition characterized in that the (d) organic sulfur compound contains (d1) a compound represented by formula (11) and / or (d2) a compound represented by formula (21). 【Chemistry 1】 [In formulas (11) and (21), R11 to R14 are the same or different and each represents an alkyl group having 1 or more carbon atoms, an aryl group having 6 or more carbon atoms, an aralkyl group having 6 or more carbon atoms, an alkoxy group having 1 or more carbon atoms, an alkylthio group having 1 or more carbon atoms, a perfluoroalkyl group having 1 or more carbon atoms, an amino group, a carboxyl group, a hydrogen atom, or a halogen atom.]

2. The rubber composition according to claim 1, wherein the total content of the compound represented by formula (11) (d1) and the compound represented by formula (21) (d2) is 0.01 parts by mass to 20 parts by mass per 100 parts by mass of the base rubber (a).

3. The rubber composition according to claim 1 or 2, wherein the content of the co-crosslinking agent (b) is 15 to 50 parts by mass per 100 parts by mass of the base rubber (a).

4. A crosslinked rubber molded article characterized by being formed from the rubber composition described in any one of Claims 1 to 3.

5. A golf ball characterized by having a component formed from the rubber composition described in any one of Claims 1 to 3.

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