Rubber composition and crosslinked rubber molded article

Abstract

To provide a rubber composition that can give a crosslinked rubber molding having excellent flexibility and excellent resilience.SOLUTION: A rubber composition contains (a) base rubber, (b) a co-crosslinker, (c) a crosslinking initiator, and (d) a salt of a benzothiazole derivative. The (d) benzothiazole derivative salt is a compound represented by formula (1), and the Mulliken charge of a sulfur atom S2 constituting a thiocarbonyl group is -0.190 or more. [In formula (1), R1-R4 each denote an electron-withdrawing group or an H atom. n is an integer of 1-4].SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition, and more particularly to a rubber composition which can give a crosslinked rubber molded article having excellent resilience. [Background technology]

[0002] As a method for increasing the flight distance of a golf ball in a driver shot, for example, there is a method of using a core with high resilience. By increasing the resilience of the core, the initial velocity of the golf ball increases, and the flight distance of the golf ball increases. Here, generally, a base rubber, a co-crosslinking agent, and a crosslinking initiator are blended into the rubber composition. It is also known to further blend a vulcanization accelerator into the rubber composition.

[0003] For example, Patent Document 1 describes a golf ball containing a composition including an unsaturated polymer, a crosslinking agent, and 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 including an unsaturated polymer, a crosslinking agent, a mastication accelerator, and a vulcanization accelerator, the vulcanization accelerator being selected from the group consisting of 2-mercaptobenzothiazole and salts of 2-mercaptobenzothiazole (see Patent Document 2 (Claims 1 and 25)). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-000647 A [Patent Document 2] JP 2005-000657 A Summary of the Invention [Problem to be solved by the invention]

[0006] Although various rubber compositions with enhanced resilience have been proposed, there has still been room for improvement in the resilience performance. The present invention has been made in view of the above circumstances, and an object thereof is to provide a rubber composition capable of obtaining a crosslinked rubber molded body having good flexibility and excellent resilience performance.

Means for Solving the Problems

[0007] The rubber composition of the present invention that has been able to solve the above problems contains (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and (d) a salt of a benzothiazole derivative, wherein the salt of the (d) benzothiazole derivative is a compound represented by the formula (1), and the sulfur atom S 2 constituting the thiocarbonyl group has a Mulliken charge of -0.190 or more.

[0008]

Chemical Formula

Effects of the Invention

[0009] By using the rubber composition of the present invention, a crosslinked rubber molded body having good flexibility and excellent resilience performance can be obtained.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] [Rubber composition] The rubber composition of the present invention contains (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and (d) a salt of a benzothiazole derivative, and the salt of the (d) benzothiazole derivative is a compound represented by the following formula (1), and the sulfur atom S 2 constituting the thiocarbonyl group has a Mulliken charge of -0.190 or more.

[0012] (d) Salt of benzothiazole derivative The salt of the (d) benzothiazole derivative used in the present invention will be described. The salt of the (d) benzothiazole derivative is a compound represented by the formula (1), and the sulfur atom S 2 constituting the thiocarbonyl group has a Mulliken charge of -0.190 or more. The salt of the (d) benzothiazole derivative may be used alone or in combination of two or more. By blending the salt of the (d) benzothiazole derivative 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.

[0013] [Chemical formula] [In formula (1), R 1 ~R 4 are the same or different and represent an electron-withdrawing group or a hydrogen atom. S 1 and S 2 represent sulfur atoms. X represents a cation component. n is an integer from 1 to 4. When n is 2 or more, at least one of R 1 ~R 4 bonded to the same benzene ring is an electron-withdrawing group.]

[0014] The sulfur atom S 2The Mulliken charge is -0.190 or more, preferably -0.185 or more, more preferably -0.180 or more, preferably 0 or less, more preferably -0.01 or less, and even more preferably -0.05 or less. When the Mulliken charge is -0.190 or more, high repellency is exhibited. The Mulliken charge of the sulfur atom can be controlled by the type and position of the substituent. Also, by substituting hydrogen on the benzene ring with a plurality of electron-withdrawing groups, the charge on the sulfur of the thiocarbonyl group can be increased. In formula (1), when n is 2 or more, a plurality of sulfur atoms S 2 means that at least one sulfur atom S 2 as long as the Mulliken charge is within the above range, and it is preferable that the Mulliken charges of all sulfur atoms S 2 are within the above range.

[0015] The sulfur atom S constituting the thiocarbonyl group 2 The Mulliken charge of is obtained by performing a structure optimization calculation and a vibrational frequency calculation using Gaussian09 (manufactured by Gaussian, a quantum chemistry calculation program) under the conditions of the functional: B3LYP and the basis function: 6-31G(d), and obtaining the Mulliken charge of the sulfur atom S 2 constituting the thiocarbonyl group in the obtained optimized structure.

[0016] The R 1 ~R 4 The electron-withdrawing group represented by is a substituent that has a greater ability to attract electrons from the carbon atom to which it is bonded than a hydrogen atom. Examples of the electron-withdrawing group represented by R 1 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 sulfonic acid group (-SO3H), an alkylsulfonyl group, an alkoxysulfonyl group, a perfluoroalkylsulfonyl group, and the like.

[0017] Examples of the halogen group include a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), etc. Examples of the perfluoroalkyl group include a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), a heptafluoropropyl group (-C3F7), etc. Examples of the halogenated alkyl group include a trichloromethyl group (-CCl3), a monochloromethyl group (-CH2Cl), etc. Examples of the alkylcarbonyl group include an acetyl group (-COCH3), a propionyl group (-COC2H5), etc. Examples of the alkoxycarbonyl group include a methoxycarbonyl group (-COOCH3), an ethoxycarbonyl group (-COOC2H5), etc. Examples of the alkylsulfonyl group include a methylsulfonyl group (-SO2CH3), an ethylsulfonyl group (-SO2C2H5), etc. Examples of the alkoxysulfonyl group include a methoxysulfonyl group (-SO2OCH3), an ethoxysulfonyl group (-SO2OC2H5), etc. Examples of the perfluoroalkylsulfonyl group include a trifluoromethylsulfonyl group (-SO2CF3), a pentafluoroethylsulfonyl group (-SO2C2F5), etc.

[0018] The R 1 ~R 4 The electron-withdrawing group represented by is preferably selected from the group consisting of a halogen group, a perfluoroalkyl group, and a pentafluorosulfanyl group.

[0019] The salt of the (d) benzothiazole derivative is preferably a compound represented by the formula (2). When the position of the electron-withdrawing group represented by the R 1 is the 5-position, the electronic effect on the thiocarbonyl group is greater than that at other substitution positions.

[0020]

Chemical formula

[0021] Examples of the electron-withdrawing group represented by R 1 in formula (2) include the electron-withdrawing group represented by R 1 in formula (1). Examples of the electron-withdrawing group represented by R 1 in formula (2) are preferably one selected from the group consisting of a halogen group, a perfluoroalkyl group, and a pentafluorosulfanyl group.

[0022] As the benzothiazole derivative constituting the salt of the (d) benzothiazole derivative, compounds represented by formula (2-1) to formula (2-12) are particularly preferred.

[0023] [Chemical formula]

[0024] Examples of the cationic component represented by X in formula (1) or formula (2) include metal ions; organic cations such as organic ammonium ions and organic phosphonium ions.

[0025] Examples of the 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. As the cationic component, divalent metal ions are preferred, and zinc ions, magnesium ions, and calcium ions are more preferred.

[0026] Examples of the organic ammonium ion include primary ammonium ions such as stearyl ammonium ion, hexyl ammonium ion, octyl ammonium ion, 2-ethylhexyl ammonium ion; secondary ammonium ions such as dodecyl (lauryl) ammonium ion, octadecyl (stearyl) ammonium ion; tertiary ammonium ions such as trioctyl ammonium ion; and quaternary ammonium ions such as dioctyldimethyl ammonium ion, distearyldimethyl ammonium ion.

[0027] Examples of the organic phosphonium ion include tetraethyl phosphonium, triethylbenzyl phosphonium, tetrabutyl phosphonium, tetraoctyl phosphonium, trimethyldecyl phosphonium, trimethyldodecyl phosphonium, trimethylhexadecyl phosphonium, trimethyloctadecyl phosphonium, tributylmethyl phosphonium, tributyldodecyl phosphonium, tributyloctadecyl phosphonium, trioctylethyl phosphonium, and the like.

[0028] The content of the salt of the (d) benzothiazole derivative is preferably 0.01 part by mass or more, more preferably 0.1 part by mass or more, still more preferably 0.5 part by mass or more, and preferably 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less, based on 100 parts by mass of the (a) base rubber. When the content of the (d) benzothiazole derivative is 0.01 part by mass or more, the resilience is further improved, and when it is 20 parts by mass or less, the flexibility becomes better.

[0029] Hereinafter, other raw materials used in the rubber composition will be described.

[0030] (a) Base rubber As the above-mentioned (a) base rubber, natural rubber and / or synthetic rubber can be used. Examples of the synthetic rubber include diene rubbers such as polybutadiene rubber (BR), polyisoprene rubber (IR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR); 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, chlorosulfonated polyethylene rubber, etc. These can be used alone or in combination of two or more.

[0031] The above-mentioned (a) base rubber preferably contains natural rubber and / or diene rubber. The total content of natural rubber and / or diene rubber in the above-mentioned (a) base rubber is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more. It is also preferable that the above-mentioned (a) base rubber contains only natural rubber and / or diene rubber.

[0032] The above-mentioned (a) base rubber preferably contains polybutadiene rubber. In particular, high-cis polybutadiene having a cis-1,4 bond content of 40% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more, which is advantageous for resilience, is suitable. The content of high-cis polybutadiene in the above-mentioned (a) base rubber is preferably 50% by mass or more, and more preferably 70% by mass or more.

[0033] 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 still more preferably 1.5% by mass or less. If the content of the 1,2-vinyl bond is too high, the resilience may decrease.

[0034] The above high-cis polybutadiene is preferably synthesized using a rare-earth element-based catalyst. In particular, the use of a neodymium-based catalyst using a neodymium compound, which is a lanthanum-series rare-earth element compound, is preferable because a polybutadiene rubber with a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds can be obtained with excellent polymerization activity.

[0035] As for the above high-cis polybutadiene, the molecular weight distribution Mw / Mn (Mw: weight-average molecular weight, Mn: number-average molecular weight) is preferably 2.0 or more, more preferably 2.2 or more, still 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, still 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, the workability will decrease, and if it is too large, the resilience may decrease. The molecular weight distribution is measured by gel permeation chromatography (manufactured by Tosoh Corporation, "HLC-8120GPC") using a differential refractometer as a detector, column: GMHHXL (manufactured by Tosoh Corporation), column temperature: 40 °C, mobile phase: tetrahydrofuran, and is a value calculated as a standard polystyrene conversion value.

[0036] The above high-cis polybutadiene has a Mooney viscosity (ML 1+4 (100 °C)) that is preferably 30 or more, more preferably 32 or more, still more preferably 35 or more, and preferably 140 or less, more preferably 120 or less, still more preferably 100 or less, and most preferably 80 or less. The Mooney viscosity (ML 1+4 (100 °C)) referred to in the present invention is a 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 a temperature of 100 °C.

[0037] (b) Co-crosslinking agent The above-mentioned (b) co-crosslinking agent has the effect of crosslinking rubber molecules by graft polymerization onto the base rubber molecular chains. As the above-mentioned (b) co-crosslinking agent, α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms and / or their metal salts are preferred. The number of carbon atoms of the α,β-unsaturated carboxylic acid used as the above-mentioned (b) co-crosslinking agent is preferably 3 to 8, more preferably 3 to 6, and even more preferably 3 or 4. Note that the α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms and / or their metal salts may be used alone or in combination of two or more.

[0038] Examples of the α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid, etc. When the rubber composition contains only the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as the co-crosslinking agent, the rubber composition further contains (e) a metal compound as an essential component. This is because by neutralizing the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the rubber composition with the metal compound, an effect substantially the same as when using the metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as the co-crosslinking agent can be obtained.

[0039] As the metal constituting the metal salt of α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, there are 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 component can be used alone or as a mixture of two or more. Among these, as the metal component, divalent metal ions such as magnesium, calcium, zinc, barium, and cadmium are preferred. This is because when using the divalent metal salt of α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, metal crosslinking is likely to occur between rubber molecules. In particular, as the divalent metal salt, a zinc salt of α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is preferred because the resilience of the resulting golf ball is high, and more preferably zinc acrylate. In addition, when using α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and its metal salt in combination as a co-crosslinking agent, a (e) metal compound may be used as an optional component.

[0040] When the metal is a divalent or trivalent metal, the (b) metal salt of α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms may contain, as the carboxylic acid component, other carboxylic acids other than α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Examples of the 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.

[0041] (b) The content of the co-crosslinking agent is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 25 parts by mass or more, particularly preferably 27 parts by mass or more, preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and still more preferably 35 parts by mass or less with respect to 100 parts by mass of the (a) base rubber. If the content of the (b) co-crosslinking agent is 15 parts by mass or more, a member formed from the rubber composition with a small amount of the (c) crosslinking initiator can have an appropriate hardness, and the resilience of the crosslinked rubber molded article is further improved. 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 does not become too hard.

[0042] (c) Crosslinking initiator The (c) crosslinking initiator is compounded to crosslink the (a) base rubber component. As the (c) crosslinking initiator, an organic peroxide is suitable. Specifically, examples of the organic peroxide include organic peroxides such as 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.

[0043] 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, still more preferably 0.7 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, still more preferably 2.0 parts by mass or less, and particularly preferably 0.9 parts by mass or less with respect to 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 does not become too soft and has good resilience. If it is 5.0 parts by mass or less, the crosslinked rubber molded article formed from the rubber composition has an appropriate hardness and good resilience and durability.

[0044] (e) Metal compound When the rubber composition used in the present invention contains only an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, it is preferable that the rubber composition further contains (e) a metal compound. The (e) metal compound is not particularly limited as long as it can neutralize (b) an α,β-unsaturated carboxylic acid 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 carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. Preferred as the (e) metal compound is a divalent metal compound, and more preferably a zinc compound. This is because the divalent metal compound reacts with an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form a metal crosslink. Further, 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 in combination of two or more. The content of the (e) metal compound may be appropriately adjusted according to the desired degree of neutralization of (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and (d) an unsaturated aliphatic carboxylic acid.

[0045] (f) Organic sulfur compound The rubber composition may further contain (f) an organic sulfur compound. The (f) organic sulfur compound does not include the salt of the (d) benzothiazole derivative. Examples of the (f) organic sulfur compound include at least one compound selected from the group consisting of thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamate salts, thiazoles, and metal salts thereof. Preferred as the (f) organic sulfur compound is an organic sulfur compound having a thiol group (-SH) or a metal salt thereof, and thiophenols, thionaphthols, or metal salts thereof are preferred.

[0046] Examples of the 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; thiophenols substituted with a chloro group such as 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 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. As the metal salt, a zinc salt is preferable.

[0047] Examples of the thionaphthols (naphthalenethiols) 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. Among them, 2-thionaphthol, 1-thionaphthol, or metal salts thereof are 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 organic sulfur compounds having a polysulfide bond, and examples thereof include disulfides, trisulfides, and tetrasulfides. Among the polysulfides, diphenylpolysulfides are preferred.

[0049] Examples of 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-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, 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 and other diphenyl disulfides substituted with halogen groups; 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, bis(penta-t-butylphenyl) disulfide and other diphenyl disulfides substituted with alkyl groups; and the like.

[0050] 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 naphthalenethiocarboxylic acid. Examples of dithiocarboxylic acids include naphthalenedithiocarboxylic acid. Examples of sulfenamides include N-cyclohexyl-2-benzothiazolesulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide, and N-t-butyl-2-benzothiazolesulfenamide.

[0051] (f) The organic sulfur compound(s) can be used alone or in admixture of two or more. (f) Preferred organic sulfur compounds are thiophenols and / or their metal salts, thionaphthols and / or their metal salts, diphenyldisulfides, and thiuram disulfides. More preferred are 2,4-dichlorothiophenol, 2,6-difluorothiophenol, 2,6-dichlorothiophenol, 2,6-dibromothiophenol, 2,6-diiodothiophenol, 2,4,5-trichlorothiophenol, pentachlorothiophenol, 1-thionaphthol, 2-thionaphthol, diphenyldisulfide, 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] (f) The content of the organic sulfur compound is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, based on 100 parts by mass of the (a) base rubber, and is preferably 5.0 parts by mass or less, more preferably 2.0 parts by mass or less. When 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 body may not be improved. Further, when the content of the (e) organic sulfur compound exceeds 5.0 parts by mass, the compression deformation amount of the obtained crosslinked rubber molded body may increase, and the resilience may decrease.

[0053] (g) Carboxylic acid and / or its salt The rubber composition may contain (g) carboxylic acid and / or its salt. By containing the (g) carboxylic acid and / or its salt, the hardness distribution of the obtained crosslinked rubber molded body can be controlled. Examples of the (g) carboxylic acid and / or its salt include aliphatic carboxylic acids, aliphatic carboxylates, aromatic carboxylic acids, and aromatic carboxylates. The (g) carboxylic acid and / or salt can also be used alone or as a mixture of two or more. Note that the (g) carboxylic acid and / or its salt does not include the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or its metal salt used as the (b) co-crosslinking agent.

[0054] 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 have a branched structure or a cyclic structure. The number of carbon atoms of the saturated fatty acid is preferably 6 or more, preferably 24 or less, more preferably 18 or less, and still more preferably 13 or less. The number of carbon atoms of the unsaturated fatty acid is preferably 6 or more, more preferably 7 or more, still more preferably 8 or more, and preferably 24 or less, more preferably 18 or less, and still more preferably 13 or less.

[0055] 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 acid 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 the heteroaromatic ring.

[0056] As the aliphatic carboxylate or aromatic carboxylate, the above-described salts of the aliphatic carboxylic acid or aromatic carboxylic acid can be used. Examples of the cation component of these salts include metal ions, ammonium ions, and organic cations. The cation component can also be used alone or as a mixture of two or more. Examples of the 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 as the metal ions, and magnesium, zinc, and calcium are more preferred.

[0057] 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, 2-ethylhexyl ammonium ion; secondary ammonium ions such as dodecyl (lauryl) ammonium ion, octadecyl (stearyl) ammonium ion; tertiary ammonium ions such as trioctyl ammonium ion; and quaternary ammonium ions such as dioctyldimethyl ammonium ion, distearyldimethyl ammonium ion. These organic cations may be used alone or in combination of two or more.

[0058] 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. The 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 their potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, cobalt salts are preferred. Examples of the unsaturated fatty acids and / or their salts include 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, cobalt salts.

[0059] Examples of the aromatic carboxylic acid and / or its salt include benzoic acid, butyl benzoic 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 tenoyl 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 content of the carboxylic acid (g) and / or its salt is preferably 1 part by mass or more, more preferably 2 parts by mass or more, still more preferably 3 parts by mass or more, and preferably 30 parts by mass or less, more preferably 20 parts by mass or less, still more preferably 15 parts by mass or less, based on 100 parts by mass of the base rubber (a).

[0061] (Other components) The rubber composition may contain additives such as pigments, fillers for weight adjustment, antioxidants, peptizers, and softeners, as needed. Further, the rubber composition may contain a golf ball core or rubber powder obtained by pulverizing the end material generated during core production.

[0062] Examples of the pigment incorporated into the rubber composition include white pigments, blue pigments, and purple pigments. As the white pigment, it is preferable to use titanium oxide. The type of titanium oxide is not particularly limited, but the rutile type is preferably used because of its good hiding power. Further, the content of titanium oxide is preferably 0.5 part 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, based on 100 parts by mass of the base rubber (a).

[0063] It is also a preferred embodiment that the rubber composition contains a white pigment and a blue pigment. The blue pigment is blended to make the white color appear vivid, and examples thereof include ultramarine blue, cobalt blue, phthalocyanine blue, and the like. Further, examples of the purple pigment include anthraquinone violet, dioxazine violet, methyl violet, and the like.

[0064] The filler used in the rubber composition is blended as a weight regulator for adjusting the mass of the obtained crosslinked rubber molded body, and it may be blended as necessary. Examples of the filler include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder.

[0065] The content of the anti-aging agent is preferably 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the base rubber (a). Further, the content of the peptizer is preferably 0.1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the base rubber (a).

[0066] Preparation of Rubber Composition The rubber composition used in the present invention is obtained by mixing and kneading (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, (d) a salt of a benzothiazole derivative, and, if necessary, other additives. The kneading method is not particularly limited, and for example, it may be carried out using a known kneader such as a kneading roll, a Banbury mixer, or a kneader.

[0067] [Crosslinked Rubber Molded Body] The crosslinked rubber molded body of the present invention is characterized by being formed from the rubber composition. The crosslinked rubber molded body 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. Also, the pressure during molding is preferably 2.9 MPa to 11.8 MPa. The molding time is preferably 10 minutes to 60 minutes.

[0068] Examples of the uses of the crosslinked rubber molded article include 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, fenders, and the like. Examples of the golf ball include those having a constituent member formed from the rubber composition.

Examples

[0069] Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples, and modifications and embodiments within the scope not departing from the gist of the present invention are all included in the scope of the present invention.

[0070] [Evaluation method] (1) Compression deformation amount (mm) The deformation amount in the compression direction (the amount by which the spherical molded body shrinks in the compression direction) from the state where an initial load of 98 N was applied to the spherical molded body until a final load of 1275 N was applied was measured.

[0071] (2) Rebound coefficient A 198.4 g metal cylinder was made to collide with each spherical molded body at a speed of 40 m / s, and the speeds of the cylinder and the spherical molded body before and after the collision were measured. The rebound coefficient of each spherical molded body was calculated from the respective speeds and masses. The measurement was performed 12 times for each spherical molded body, and the average value was taken as the rebound coefficient of each spherical molded body.

[0072] [Preparation of salt of benzothiazole derivative] The salt of the benzothiazole derivative was synthesized using a commercially available benzothiazole derivative with reference to the production method of the zinc salt of 2-mercaptobenzothiazole described in JP-A-50-012081. Specifically, the benzothiazole derivative was reacted with an equivalent amount of a metal oxide or metal hydroxide in an inert organic solvent in the presence of an acid. The following benzothiazole derivatives were used. 5Me-MBT: Manufactured by Cool pharm LtD., 5-methyl-2-mercaptobenzothiazole 4Me-MBT: Manufactured by Fluorochem Ltd., 4-methyl-2-mercaptobenzothiazole 5Cl-MBT: Manufactured by Tokyo Chemical Industry Co., Ltd., 5-chloro-2-mercaptobenzothiazole 5F-MBT: Manufactured by Combi-Blocks, 5-fluoro-2-mercaptobenzothiazole 5CF3-MBT: Manufactured by AA Blocks, 5-trifluoromethyl-2-mercaptobenzothiazole 5Br-MBT: Manufactured by Aldrich, 5-bromo-2-mercaptobenzothiazole

[0073] [Preparation of spherical shaped bodies] The rubber composition with the formulation shown in Table 1 was kneaded by a kneading roll and heat-pressed at 170 °C for 20 minutes in an upper and lower mold having a hemispherical cavity to obtain a spherical shaped body with a diameter of 40.86 mm.

[0074]

Table 1

[0075] Table 1 shows the compression deformation amount and resilience coefficient of each spherical molded body. Also, FIG. 1 shows the relationship between the compression deformation amount and the resilience coefficient of each spherical molded body. As shown in FIG. 1, when the raw materials contained in the rubber composition are the same, the higher the content of the co-crosslinking agent, the higher the resilience performance, and the smaller the compression deformation amount tends to be. Therefore, it can be said that the higher the flexibility and the better the resilience performance of the spherical molded bodies made from the same raw materials, the higher the position of the straight line connecting the plots of the spherical molded bodies on the upper right of the graph.

[0076] Spherical molded bodies No. 1 to 8 are compounds represented by formula (1), and the sulfur atom S in formula (1) 2 is a salt of a benzothiazole derivative in which the Mulliken charge of each is -0.190 or more. These spherical formed bodies are more flexible and have better resilience performance than the other spherical molded bodies No. 9 to 16.

Industrial Applicability

[0077] By using the rubber composition of the present invention, a crosslinked rubber molded body excellent in resilience performance can be obtained. Therefore, the rubber composition of the present invention can be used for sports goods such as golf balls, tennis balls, and grips; industrial goods such as hoses, belts, and mats; shoe soles, tires, resin additives, anti-vibration rubbers, fenders, etc.

Claims

1. (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and (d) a salt of a benzothiazole derivative, and The salt of the (d) benzothiazole derivative is a compound represented by the formula (1), and the sulfur atom S 2 constituting the thiocarbonyl group has a Mulliken charge of -0.190 or more, and the rubber composition is characterized by this. 【Chemical 1】 [In formula (1), R 1 ~R 4 represents, identically or differently, an electron-withdrawing group or a hydrogen atom. S 1 and S 2 represent a sulfur atom. X represents zinc. n is 2. When n is 2, at least one of R 1 ~R 4 bonded to the same benzene ring is an electron-withdrawing group. ]

2. The above-mentioned R 1 to R 4 The rubber composition according to claim 1, wherein the electron-withdrawing group represented by is selected from the group consisting of a halogen group, a perfluoroalkyl group, and a pentafluorosulfanyl group.

3. The rubber composition according to claim 1 or 2, wherein the salt of the (d) benzothiazole derivative is a compound represented by formula (2). [Chemical 2] [In formula (2), R 1 represents an electron-withdrawing group. S 1 and S 2 represent sulfur atoms. X represents zinc. n is 2.]

4. The rubber composition according to any one of claims 1 to 3, wherein the content of the salt of the (d) benzothiazole derivative is 0.01 part by mass to 20 parts by mass with respect to 100 parts by mass of the (a) base rubber.

5. The rubber composition according to any one of claims 1 to 4, wherein the content of the (b) co-crosslinking agent is 15 parts by mass to 50 parts by mass with respect to 100 parts by mass of the (a) base rubber.

6. A crosslinked rubber molded article characterized by being formed from the rubber composition according to any one of claims 1 to 5.

7. A golf ball characterized by having a constituent member formed from the rubber composition according to any one of claims 1 to 5.

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