rubber composition

Abstract

To provide a rubber composition having improved tensile strength at break (TB) and elongation at break (EB).SOLUTION: There is provided a rubber composition which comprises a polymer (A) having a conjugated diene unit, a compound (B) having at least two hydroxyl groups and a crosslinking agent (C), wherein the compound (B) having at least two hydroxyl groups, in which at least two hydroxyl groups in the compound are bonded to adjacent carbon atoms, has a functional group containing a sulfur atom, the content of the compound (B) having at least two hydroxyl groups is 3.5 pts.mass or more based on 100 pts.mass of the polymer (A) and the content of the crosslinking agent (C) is 0.1 to 5 pts.mass based on 100 pts.mass of the polymer (A).SELECTED DRAWING: None

Description

【Technical Field】 【0001】 The present invention relates to a rubber composition. 【Background Art】 【0002】 Conventionally, rubber products such as tires have been crosslinked (vulcanized) with sulfur to sufficiently secure physical properties such as tensile strength at break (TB) and elongation at break (EB) as durability indices, thereby improving durability. On the other hand, from the viewpoints of environmental problems and resource conservation, technologies for recycling used vulcanized rubber products have been studied. For example, in Patent Document 1 below, after decomposing vulcanized rubber by a lipid peroxidation reaction, the decomposed rubber component is dissolved in an organic solvent, and lipids are removed by reprecipitating the rubber component in alcohol to which an alkali has been added, and a method for recovering the rubber component is disclosed. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2011-153272 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 As described above, conventionally, various rubber products have been manufactured by crosslinking (vulcanizing) rubber components (polymers) with sulfur, and various recycling technologies have also been studied. However, vulcanized rubber crosslinked (vulcanized) only with sulfur is difficult to recycle, and the technology described in Patent Document 1 above has a large number of steps. In addition, the conventional rubber composition obtained by crosslinking a rubber component with sulfur has room for improvement in physical properties such as tensile strength at break (TB) and elongation at break (EB) in the first place. 【0005】 Therefore, an object of the present invention is to solve the problems of the above-described conventional technologies and provide a rubber composition with improved tensile strength at break (TB) and elongation at break (EB). [Means for solving the problem] 【0006】 The gist of the present invention, which solves the above problems, is as follows. 【0007】 The rubber composition of the present invention, A polymer (A) containing conjugated diene units, A compound (B) having at least two hydroxyl groups, A rubber composition comprising a crosslinking agent (C), The compound (B) having at least two hydroxyl groups is such that at least two hydroxyl groups in the compound are bonded to adjacent carbon atoms, and further has a functional group containing a sulfur atom. The content of the compound (B) having at least two hydroxyl groups is 3.5 parts by mass or more per 100 parts by mass of the polymer (A), The crosslinking agent (C) is characterized in that the content is 0.1 to 5 parts by mass per 100 parts by mass of the polymer (A). The rubber composition of the present invention exhibits improved tensile strength (TB) and elongation (EB) at break. 【0008】 In a preferred example of the rubber composition of the present invention, the conjugated diene units of the polymer (A) include at least one selected from the group consisting of isoprene units and butadiene units. In this case, the tensile strength at break (TB) and elongation at break (EB) of the rubber composition are further improved. 【0009】 In another preferred example of the rubber composition of the present invention, the mass ratio (B / C) of the compound having at least two hydroxyl groups (B) to the crosslinking agent (C) is 2 or more. In this case, the tensile strength (TB) and elongation (EB) at break of the rubber composition are further improved. 【0010】 In the rubber composition of the present invention, it is preferable that the compound (B) having at least two hydroxyl groups has a thiol group as a functional group containing the sulfur atom. In this case, the compound (B) having hydroxyl groups becomes easier to further add to the polymer (A) containing conjugated diene units. 【0011】 Here, it is preferable that the compound (B) having at least two hydroxyl groups is thioglycerol. In this case, the compound (B) having hydroxyl groups is particularly easy to add to the polymer (A) containing conjugated diene units. 【0012】 In the rubber composition of the present invention, the polymer (A) preferably has a vinyl bond content of 10 to 60% by mass. In this case, the compound (B) having at least two hydroxyl groups is more easily added to the polymer (A). 【0013】 In another preferred example of the rubber composition of the present invention, the crosslinking agent (C) contains at least sulfur. In this case, the tensile strength (TB) and elongation (EB) at break of the rubber composition are further improved. [Effects of the Invention] 【0014】 According to the present invention, it is possible to provide a rubber composition with improved tensile strength at break (TB) and elongation at break (EB). [Modes for carrying out the invention] 【0015】 The rubber composition of the present invention will be described in detail below, based on its embodiments. 【0016】 <Rubber composition> The rubber composition of the present invention comprises a polymer (A) containing conjugated diene units, a compound (B) having at least two hydroxyl groups, and a crosslinking agent (C). The rubber composition of the present invention is characterized in that the compound (B) having at least two hydroxyl groups is bonded to adjacent carbon atoms and further has a functional group containing a sulfur atom, the content of the compound (B) having at least two hydroxyl groups is 3.5 parts by mass or more per 100 parts by mass of the polymer (A), and the content of the crosslinking agent (C) is 0.1 to 5 parts by mass per 100 parts by mass of the polymer (A). 【0017】 In the rubber composition of the present invention, a compound (B) having at least two hydroxyl groups is added to a polymer (A) having a functional group containing a sulfur atom and containing a conjugated diene unit. The compound (B) having hydroxyl groups added to the polymer (A) then forms hydrogen bonds via its hydroxyl groups. Here, in the compound (B) having at least two hydroxyl groups, at least two hydroxyl groups in the compound are bonded to adjacent carbon atoms, that is, at least two hydroxyl groups are located in close proximity. Therefore, the hydroxyl groups of the compound (B) having hydroxyl groups added to one polymer (A) and the hydroxyl groups of the compound (B) having hydroxyl groups added to another polymer (A) form multiple hydrogen bonds in close proximity, resulting in strong hydrogen bonding. Furthermore, by having a content of 3.5 parts by mass or more of the compound (B) having hydroxyl groups per 100 parts by mass of polymer (A), the amount of compound (B) having hydroxyl groups added to the polymer (A) increases, leading to the formation of more hydrogen bonds and stronger crosslinking by hydrogen bonding. Furthermore, since the rubber composition of the present invention contains a crosslinking agent (C), the crosslinked rubber composition will contain both hydrogen-bonded crosslinks and crosslinked structures caused by the crosslinking agent (C). Here, when the content of the crosslinking agent (C) is 0.1 parts by mass or more per 100 parts by mass of polymer (A), the crosslinked structures caused by the crosslinking agent (C) are sufficiently formed, and when the content of the crosslinking agent (C) is 5 parts by mass or less per 100 parts by mass of polymer (A), appropriate extensibility can be achieved. Therefore, in the rubber composition of the present invention, polymer (A) can be crosslinked with higher strength compared to conventional rubber compositions using only sulfur crosslinking, and the tensile strength at break (TB) and elongation at break (EB) can be improved. Therefore, the rubber composition of the present invention has higher tensile strength at break (TB) and elongation at break (EB) compared to conventional rubber compositions formed solely by sulfur crosslinking. 【0018】 In addition, in the rubber composition of the present invention, the hydrogen bond can be easily dissociated. Also, the content of the crosslinking agent (C) is 5 parts by mass or less with respect to 100 parts by mass of the polymer (A), and the crosslinked structure caused by the crosslinking agent (C) does not exist excessively. Therefore, the rubber composition of the present invention is easier to recycle than a rubber composition crosslinked only by sulfur crosslinking. 【0019】 --Polymer (A)-- The rubber composition of the present invention contains a polymer (A) containing a conjugated diene unit. The polymer (A) containing the conjugated diene unit is a rubber component of the rubber composition of the present invention. Note that the rubber composition of the present invention may contain only the polymer (A) whose rubber component contains a conjugated diene unit, or may further contain other rubber components. 【0020】 The conjugated diene unit is a monomer unit derived from a conjugated diene compound. The conjugated diene compound as a monomer preferably has 4 to 8 carbon atoms. Specific examples of such a conjugated diene compound include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and the like. And the conjugated diene compound as a monomer preferably contains 1,3-butadiene and / or isoprene from the viewpoint of good elastomeric properties. The proportion of the conjugated diene unit in the polymer (A) is not particularly limited, and is preferably 0.1 mol% or more, more preferably 1 mol% or more, still more preferably 50 mol% or more, and may be 100 mol%. 【0021】 The conjugated diene unit of the polymer (A) preferably contains at least one selected from the group consisting of an isoprene unit and a butadiene unit. When the polymer (A) contains an isoprene unit and / or butadiene, the tensile strength at break (TB) and elongation at break (EB) of the rubber composition are further improved. 【0022】 The polymer (A) may contain units derived from other monomers copolymerizable with the conjugated diene compound. Examples of such units derived from other monomers include olefin units and aromatic vinyl units. The proportion of units derived from other monomers in polymer (A) is not particularly limited and may be 0 mol%, but in one embodiment, it is preferably 1 mol% or more, and preferably 50 mol% or less. 【0023】 The aforementioned olefin unit is a monomer unit derived from an olefin compound. The olefin compound used as a monomer preferably has 2 to 10 carbon atoms. Specific examples of such olefin compounds include α-olefins such as ethylene, propylene, 1-pentene, 1-hexene, 1-heptene, and 1-octene, and heteroatom-substituted alkene compounds such as vinyl pivalate, 1-phenylthioethene, and N-vinylpyrrolidone. 【0024】 The aforementioned aromatic vinyl unit is a monomer unit derived from an aromatic vinyl compound. The aromatic vinyl compound refers to an aromatic compound substituted with at least one vinyl group. The aromatic vinyl compound as a monomer preferably has 8 to 10 carbon atoms. Specific examples of such aromatic vinyl compounds include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene. 【0025】 Examples of polymers (A) containing the aforementioned conjugated diene units include natural rubber (NR) and synthetic diene rubbers. Examples of synthetic diene rubbers include synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), styrene-isoprene rubber (SIR), chloroprene rubber (CR), ethylene-butadiene copolymer, and ethylene-styrene-butadiene copolymer. Polymer (A) may be used alone or in combination of two or more types. 【0026】 The polymer (A) preferably has a vinyl bond content of 10 to 60% by mass, and more preferably 20 to 50% by mass. When the vinyl bond content of polymer (A) is 20 to 50% by mass, the compound (B) having at least two hydroxyl groups, described later, becomes easier to add to polymer (A). Here, the amount of vinyl bonds in polymer (A) refers to the proportion of vinyl-bonded conjugated diene units in the entire polymer (A). Other examples of vinyl bonds include 3,4-vinyl bonds and 1,2-vinyl bonds. In this specification, the amount of vinyl bond in polymer (A) is 1 It is determined from the integral ratio of the H-NMR spectrum. 【0027】 The polymer (A) preferably has a weight-average molecular weight (Mw) of 300 to 1,000,000, and more preferably 1,000 to 1,000,000. When the weight-average molecular weight (Mw) is 1,000 or more, the tensile strength at break (TB) and elongation at break (EB) are improved, and when the weight-average molecular weight (Mw) is 1,000,000 or less, the processability is improved. In this specification, the weight-average molecular weight (Mw) of polymer (A) is determined by gel permeation chromatography (GPC) using polystyrene as the standard substance. 【0028】 --A compound (B) having at least two hydroxyl groups-- The rubber composition of the present invention comprises a compound (B) having at least two hydroxyl groups (hereinafter sometimes simply referred to as "hydroxyl group compound (B)"). The hydroxyl group compound (B) has a functional group containing a sulfur atom and can be added to the polymer (A) containing the conjugated diene units described above. Furthermore, the hydroxyl group compound (B) added to the polymer (A) forms hydrogen bonds via the hydroxyl groups. 【0029】 Examples of the sulfur atom-containing functional groups include thiol groups (also called "mercapto groups") and sulfide groups (also called "thioether groups"), with thiol groups being preferred. When the compound (B) having the hydroxyl group has a thiol group as a sulfur atom-containing functional group, it becomes easier to further add it to the polymer (A) containing the conjugated diene unit. 【0030】 The compound (B) having at least two hydroxyl groups has at least two hydroxyl groups bonded to adjacent carbon atoms. That is, the compound (B) having hydroxyl groups is a vicinal diol having a functional group containing a sulfur atom. Because at least two hydroxyl groups are bonded to adjacent carbon atoms, the hydroxyl groups of the compound (B) having hydroxyl groups attached to one polymer (A) and the hydroxyl groups of the compound (B) having hydroxyl groups attached to the other polymer (A) can form multiple hydrogen bonds in close proximity, thereby improving the strength of the crosslinked structure through hydrogen bonding via hydroxyl groups. Furthermore, compound (B) having a hydroxyl group includes a site where multiple carbon atoms are directly bonded, and at least two of the hydroxyl groups have oxygen atoms in the hydroxyl group bonded to carbon atoms (carbon atoms in the site where multiple carbon atoms are directly bonded), and it can also be said that the number of carbon atoms between the oxygen atom in one hydroxyl group and the oxygen atom in another hydroxyl group is 2, or that it has a vicinal hydroxyl group. 【0031】 Examples of the compound (B) having a hydroxyl group include 1-mercapto-1,2-ethanediol, 3-mercapto-1,2-propanediol (also called "thioglycerol" or "α-thioglycerol"), 2-mercapto-1,2-propanediol, 1-mercapto-1,2-propanediol, 3-mercapto-2-methyl-1,2-propanediol, 3-mercapto-2-ethyl-1,2-propanediol, 1-mercapto-2-methyl-1,2-propanediol, and 1-mercapto-2-ethyl-1,2-propanediol. Among these, thioglycerol is preferred. When the compound (B) having a hydroxyl group is thioglycerol, it is particularly easy to add it to the polymer (A) containing the conjugated diene unit. 【0032】 The content of the hydroxyl group-containing compound (B) is 3.5 parts by mass or more per 100 parts by mass of the polymer (A). When the content of the hydroxyl group-containing compound (B) is 3.5 parts by mass or more per 100 parts by mass of the polymer (A), the amount of hydroxyl group-containing compound (B) added to the polymer (A) increases, more hydrogen bonds are formed, stronger hydrogen bond crosslinking can be formed, and the tensile strength (TB) and elongation at break (EB) of the rubber composition are improved. From the viewpoint of the tensile strength (TB) and elongation at break (EB) of the rubber composition, the content of the hydroxyl group-containing compound (B) is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 6 parts by mass or more per 100 parts by mass of the polymer (A), and from the viewpoint of the elongation characteristics and elongation at break (EB) of the rubber composition, it is even more preferably 10 parts by mass or less. 【0033】 --Crosslinking agent (C)-- The rubber composition of the present invention contains a crosslinking agent (C). By containing the crosslinking agent (C) together with the hydroxyl group-containing compound (B), the rubber composition after crosslinking will contain both crosslinks due to hydrogen bonding and crosslinks due to the crosslinking agent (C). 【0034】 The content of the crosslinking agent (C) is 0.1 to 5 parts by mass per 100 parts by mass of the polymer (A). When the content of the crosslinking agent (C) is 0.1 parts by mass or more per 100 parts by mass of the polymer (A), a sufficiently crosslinked structure due to the crosslinking agent (C) is formed, improving the tensile strength (TB) and elongation at break (EB) of the rubber composition. When the content of the crosslinking agent (C) is 5 parts by mass or less per 100 parts by mass of the polymer (A), the rubber composition can have appropriate extensibility, improving the elongation at break (EB). From the viewpoint of the tensile strength (TB) and elongation at break (EB) of the rubber composition, the content of the crosslinking agent (C) is preferably 0.5 parts by mass or more per 100 parts by mass of the polymer (A), and from the viewpoint of the elongation characteristics and elongation at break (EB) of the rubber composition, it is more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less. 【0035】 The mass ratio (B / C) of the hydroxyl group-containing compound (B) to the crosslinking agent (C) is preferably 2 or more, more preferably 4 or more, preferably 20 or less, and even more preferably 10 or less. When the mass ratio (B / C) of the hydroxyl group-containing compound (B) to the crosslinking agent (C) is 2 or more, the tensile strength (TB) and elongation (EB) at break of the rubber composition are further improved. Furthermore, when the mass ratio (B / C) of the hydroxyl group-containing compound (B) to the crosslinking agent (C) is 20 or less, a rubber that is resistant to degradation is produced. 【0036】 Examples of the crosslinking agent (C) include sulfur and peroxides. Examples of peroxides include organic peroxides, specifically tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide, di-tert-hexyl peroxide, diisopropylbenzene hydroperoxide, tert-butylcumyl peroxide, di(2-tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, perbenzoic acid, benzoyl peroxide, 1,1-bis(1,1-dimethylethylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, Examples include 1,1-bis(tert-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-hexylperoxy)cyclohexane, 2,2-bis(4,4-di-(tert-butylperoxy)cyclohexyl)propane, n-butyl-4,4-di-(tert-butylperoxy)valerate, tert-butylperoxylaurate, tert-butylperoxy-2-ethylhexanate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyacetate, cyclohexanone peroxide, acetylacetone peroxide, diisopropylperoxydicarbonate, and di(4-tert-butylcyclohexyl)peroxydicarbonate. Here, when sulfur is used as the crosslinking agent (C), a sulfur crosslink is formed, and when a peroxide is used as the crosslinking agent (C), a crosslink structure (such as a CC bond) caused by the peroxide is formed. 【0037】 The crosslinking agent (C) preferably contains at least sulfur, more preferably 50% by mass or more of sulfur, and may be entirely sulfur. When the crosslinking agent (C) contains at least sulfur, sulfur crosslinks are formed as a crosslinked structure due to the crosslinking agent (C), further improving the tensile strength at break (TB) and elongation at break (EB) of the rubber composition. 【0038】 --Other rubber components-- As described above, the rubber composition of the present invention contains a polymer (A) containing the conjugated diene units as a rubber component, but may further contain other rubber components. Examples of such other rubber components include non-diene rubbers. Examples of non-diene rubbers include silicone rubber, fluororubber, urethane rubber, and the like. Furthermore, the rubber component of the rubber composition preferably contains 10% by mass or more of polymer (A) containing the conjugated diene units, and may contain 100% by mass of polymer (A) containing the conjugated diene units. 【0039】 --Metal ions of elements from groups 3-12 of the periodic table-- The rubber composition of the present invention may further contain metal ions of elements from groups 3 to 12 of the periodic table. When such metal ions are included, the hydroxyl groups of compound (B) having hydroxyl groups complex with the metal ions of elements from groups 3 to 12 of the periodic table, thereby crosslinking the polymer (A) with greater strength than hydrogen bonding, and further improving the tensile strength at break (TB) and elongation at break (EB) of the rubber composition. 【0040】 Examples of elements in Group 3 of the periodic table include scandium and yttrium. Other elements in Group 4 of the periodic table include titanium and zirconium. Other elements in Group 5 of the periodic table include vanadium and niobium. Other elements in Group 6 of the periodic table include chromium, molybdenum, and tungsten. Other elements in Group 7 of the periodic table include manganese and rhenium. Other elements in Group 8 of the periodic table include iron, ruthenium, and osmium. Other elements in Group 9 of the periodic table include cobalt, rhodium, and iridium. Other elements in Group 10 of the periodic table include nickel, palladium, and platinum. Other elements in Group 11 of the periodic table include copper and silver. Other elements in Group 12 of the periodic table include zinc, among others. Metal ions of elements in groups 3-12 of the periodic table tend to form strong bonds with hydroxyl groups. Furthermore, regarding metal ions of elements in groups 3-12 of the periodic table, the valency of the ions is not particularly limited and can take on any valency that each element can possess. 【0041】 The metal ion is preferably selected from metal ions of elements in groups 7 to 12 of the periodic table. When the metal ion is a metal ion of an element in groups 7 to 12 of the periodic table, the bond with the hydroxyl group tends to become stronger, and a higher strength crosslink can be formed. 【0042】 The metal ions are preferably selected from metal ions of elements in the fourth and fifth periods of the periodic table. Metal ions of elements in the fourth and fifth periods of the periodic table have high coordination ability to hydroxyl groups, which improves the bond dissociation energy between the metal ions and hydroxyl groups, further improving the tensile strength (TB) and elongation (EB) at break of the rubber composition. 【0043】 The aforementioned metal ion is preferably at least one selected from the group consisting of iron ions, copper ions, and zinc ions. Iron ions, copper ions, and zinc ions tend to bond particularly strongly with hydroxyl groups, and can form a stronger cross-linked structure. The valency of the iron ion is divalent (Fe 2+ ) or trivalent (Fe 3+ ) is preferable. 【0044】 Preferably, the metal ions are complexed with the hydroxyl groups of the hydroxyl group-containing compound (B) by adding a metal salt to the rubber composition. The form of the added metal salt is not particularly limited and may be, for example, a hydrate. The amount of metal salt added is preferably in the range of 1 to 30 parts by mass, more preferably in the range of 1 to 15 parts by mass, even more preferably in the range of 1 to 10 parts by mass, and particularly preferably in the range of 1 to 5 parts by mass, per 100 parts by mass of the polymer (A) containing the conjugated diene units. 【0045】 Examples of the aforementioned metal salts include metal halides, metal sulfates, metal nitrates, etc., with metal halides being preferred among these. Metal halides are easy to handle and can form high-strength crosslinks more easily. 【0046】 Furthermore, examples of metal halides include metal fluorides, metal chlorides, metal bromides, and metal iodides, and among these, metal chlorides are preferred. Metal chlorides are easy to handle and can form high-strength crosslinks more easily. 【0047】 Furthermore, it is preferable that the metal salt is something other than a metal oxide, a metal carbonate, or a fatty acid metal salt. Metal salts other than metal oxides, metal carbonates, and fatty acid metal salts are more likely to further coordinate with the hydroxyl group (more likely to complex). 【0048】 Examples of the aforementioned metal salts include FeCl2, FeCl2·4H2O, FeCl3, FeCl3·6H2O, CuCl2, CuCl2·2H2O, and ZnCl2. Furthermore, the metal salt may be used individually or in combination of two or more types. 【0049】 --others-- The rubber composition of the present invention may contain, in addition to the polymer (A) described above, a compound having a hydroxyl group (B), a crosslinking agent (C), other rubber components, and metal ions (metal salts) of elements from groups 3 to 12 of the periodic table, as well as compounding agents commonly used in the rubber industry, such as fillers (carbon black, silica, etc.), softeners, waxes, stearic acid, antioxidants, silane coupling agents, zinc oxide, vulcanization accelerators, etc., selected as appropriate within a range that does not impair the purpose of the present invention. Commercially available products can be suitably used as these compounding agents. 【0050】 Examples of the wax include paraffin wax and microcrystalline wax. The content of the wax is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the polymer (A). 【0051】 The stearic acid content is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, and more preferably 0.5 to 4 parts by mass, per 100 parts by mass of polymer (A). 【0052】 Examples of the aforementioned antioxidants include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), and N,N'-diphenyl-p-phenylenediamine (DPPD). The content of the antioxidant is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the polymer (A). 【0053】 The content of the zinc oxide is not particularly limited, but is preferably in the range of 0.1 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the polymer (A). 【0054】 Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators. The content of the vulcanization accelerator is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, and more preferably in the range of 0.2 to 3 parts by mass, per 100 parts by mass of the polymer (A). 【0055】 --Method for manufacturing rubber composition-- The method for producing the rubber composition is not particularly limited, but for example, it can be produced by mixing the polymer (A), the compound having a hydroxyl group (B), and the crosslinking agent (C) described above with various components selected as needed, and then kneading, heating, extruding, etc. Furthermore, the obtained rubber composition can be crosslinked to produce crosslinked rubber. 【0056】 There are no particular restrictions on the mixing conditions, and various conditions such as the input volume of the mixing device, the rotation speed of the rotor, the ram pressure, as well as the mixing temperature, mixing time, and the type of mixing device can be appropriately selected according to the purpose. Examples of mixing devices include Banbury mixers, intermixes, kneaders, and rolls, which are commonly used for mixing rubber compositions. 【0057】 There are no particular restrictions on the heat treatment conditions, and various conditions such as heat treatment temperature, heat treatment time, and heat treatment equipment can be appropriately selected according to the purpose. Examples of such heat treatment equipment include heat treatment roll machines commonly used for heat treatment of rubber compositions. 【0058】 There are no particular restrictions on the extrusion conditions, and various conditions such as extrusion time, extrusion speed, extrusion equipment, and extrusion temperature can be appropriately selected according to the purpose. Examples of extrusion equipment include extruders typically used for extruding rubber compositions. The extrusion temperature can be determined as appropriate. 【0059】 There are no particular restrictions on the apparatus, method, and conditions for performing the aforementioned crosslinking, and they can be appropriately selected according to the purpose. Examples of apparatus for performing crosslinking include molding vulcanizers using molds, which are typically used for vulcanizing rubber compositions. As for the conditions for crosslinking, the temperature is, for example, around 100 to 190°C. 【0060】 For example, in the first stage of mixing, a polymer (A), a compound having a hydroxyl group (B), and various components selected as appropriate as needed may be combined and mixed to form a mixture containing a modified polymer in which the compound having a hydroxyl group (B) is bonded to the polymer (A). In the second and subsequent stages of mixing, a crosslinking agent (C) and various components selected as appropriate as needed may be combined and mixed to produce a rubber composition. Furthermore, after molding the rubber composition into a desired shape, it can be crosslinked to form a crosslinked rubber having a crosslinked structure due to hydrogen bonding and a crosslinked structure due to the crosslinking agent (C). 【0061】 Alternatively, for example, a modified polymer may be prepared in advance by bonding a hydroxyl group-containing compound (B) to a polymer (A). In the first stage of mixing, the pre-prepared modified polymer and an arbitrary compounding agent may be mixed. In the second and subsequent stages of mixing, a crosslinking agent (C) and various components selected as appropriate as needed may be added and mixed to produce a rubber composition. Furthermore, after molding the rubber composition into a desired shape, a crosslinked rubber having a crosslinked structure due to hydrogen bonding and a crosslinked structure due to the crosslinking agent (C) can be formed. 【0062】 --Applications-- The rubber composition of the present invention can be used in various rubber products. Examples of rubber products include tires, rubber tracks, and seismic isolation rubber. [Examples] 【0063】 The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples. 【0064】 <Polymer Analysis> The amount of styrene and vinyl bound to the polymer is measured by the following method. 【0065】 (1) Amount of bound styrene 100 mg of the polymer sample is dissolved in 100 mL of chloroform to prepare the measurement sample. The amount of bound styrene (mass%) relative to 100 mass% of the sample is determined by measuring the amount of ultraviolet absorption at the phenyl group of styrene (around 254 nm). A Shimadzu UV-2450 spectrophotometer is used as the measuring instrument. 【0066】 (2) Amount of vinyl binding The amount of vinyl bonds in the polymer (the amount of 1,2-vinyl bonds) 1 It is determined from the integral ratio in the 1H-NMR spectrum [JEOL Alpha 400MHz NMR spectrometer, in CDCl3]. 【0067】 <Manufacturing of rubber compositions> Rubber compositions were manufactured by kneading according to the formulations shown in Tables 1 and 2. The kneading process was carried out in two stages: the first stage at 110°C for 3 minutes, and the second stage at 80°C for 1 minute and 30 seconds. The tensile strength at break (TB) and elongation at break (EB) of the obtained rubber compositions were measured using the following methods. The results are shown in Tables 1 and 2. 【0068】 (3) Measurement method for TB and EB Dumbbell-shaped test specimens conforming to JIS No. 7 were prepared from the rubber composition, and tensile tests were performed at room temperature (23°C) in accordance with JIS K6251 to measure the tensile strength at break (TB) and elongation at break (EB). In Table 1, the tensile strength at break (TB) and elongation at break (EB) of Comparative Example 1 are expressed as exponents, with the TB set to 100. Similarly, in Table 2, the tensile strength at break (TB) and elongation at break (EB) of Comparative Example 2 are expressed as exponents, with the TB set to 100. A larger exponent value indicates a greater tensile strength at break (TB) and elongation at break (EB). 【0069】 [Table 1] 【0070】 [Table 2] 【0071】 *1 Styrene-butadiene rubber: Bound styrene content = 10% by mass, vinyl bond content = 44% by mass, synthetic product *2 α-thioglycerol: Manufactured by Tokyo Chemical Industry Co., Ltd. *3 Stearic acid: Manufactured by Kao Corporation, product name "Lunac S-70V" *4 Zinc oxide: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. *5 Vulcanization accelerator DPG: 1,3-diphenylguanidine, manufactured by Sumitomo Chemical Co., Ltd., trade name "Soxinol D" *6 Vulcanization accelerator CBS: N-cyclohexyl-2-benzothiazolyl sulfenamide, manufactured by Sanshin Chemical Industry Co., Ltd., trade name "Sunceller CM-G" *7 Vulcanization accelerator DM: Di-2-benzothiazolyl disulfide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noxellar DM-P" *8 Sulfur: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. *9 Butadiene rubber: Manufactured by Asahi Kasei Corporation, product name "Toughden (registered trademark) 2000R" *10 Wax: Manufactured by Seiko Chemical Co., Ltd., product name "Suntight A" *11 Anti-aging agent 6PPD: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 6C" 【0072】 Tables 1 and 2 show that the rubber compositions of Examples 1 and 2 according to the present invention exhibit improved tensile strength at break (TB) and elongation at break (EB) compared to general sulfur-crosslinked rubber compositions (Comparative Examples 1 and 2). [Industrial applicability] 【0073】 The rubber composition of the present invention can be used in various rubber products such as tires, rubber tracks, and seismic isolation rubber.

Claims

[Claim 1] A polymer (A) containing conjugated diene units, A compound (B) having at least two hydroxyl groups, A rubber composition comprising a crosslinking agent (C), The compound (B) having at least two hydroxyl groups has at least two hydroxyl groups bonded to adjacent carbon atoms, and further has a functional group containing a sulfur atom, and the compound (B) having at least two hydroxyl groups has a thiol group as the functional group containing the sulfur atom, The content of the compound (B) having at least two hydroxyl groups is 6 parts by mass or more per 100 parts by mass of the polymer (A), A rubber composition characterized in that the amount of the crosslinking agent (C) is 0.1 to 5 parts by mass per 100 parts by mass of the polymer (A). [Claim 2] The rubber composition according to claim 1, wherein the conjugated diene units of the polymer (A) include at least one selected from the group consisting of isoprene units and butadiene units. [Claim 3] The rubber composition according to claim 1 or 2, wherein the mass ratio (B / C) of the compound (B) having at least two hydroxyl groups to the crosslinking agent (C) is 2 or more. [Claim 4] The rubber composition according to any one of claims 1 to 3, wherein the compound (B) having at least two hydroxyl groups is thioglycerol. [Claim 5] The rubber composition according to any one of claims 1 to 4, wherein the polymer (A) has a vinyl bond content of 10 to 50% by mass. [Claim 6] The rubber composition according to any one of claims 1 to 5, wherein the crosslinking agent (C) contains at least sulfur.

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