Rubber composition, tire, and rubber product

Abstract

The purpose of the present invention is to provide a rubber composition that, when used in a tire, exhibits excellent crack propagation resistance after undergoing thermal degradation while having good durability.　The present invention is characterized by comprising a rubber component containing a natural rubber and / or a synthetic isoprene rubber, a syndiotactic 1,2-polybutadiene, sulfur, and a vulcanization accelerator, and is characterized in that the syndiotactic 1,2-polybutadiene has a crystal amount of 7-40 J / g and a number average molecular weight of 3.0×104 or more, and the content mass ratio (sulfur / vulcanization accelerator) of the sulfur to the vulcanization accelerator is less than 1.

Description

Rubber composition, tire and rubber product

[0001] The present invention relates to a rubber composition, a tire, and a rubber product.

[0002] Generally, high durability is required for rubber compositions used in the manufacture of rubber articles such as tires, conveyor belts, vibration-proof rubber, and seismic isolation rubber. However, diene-based rubbers such as butadiene rubber (BR) and styrene-butadiene rubber (SBR), which have been frequently used in the rubber industry, have a problem in that they are insufficient in resistance to cracks caused by ozone, deterioration over time, etc., i.e., insufficient in crack growth resistance. Under these circumstances, various rubber components and rubber compositions have been developed.

[0003] For the purpose of improving the durability of a rubber composition, a technique of compounding syndiotactic 1,2-polybutadiene (hereinafter abbreviated as "sPB") is known, as disclosed in, for example, Patent Document 1. However, the technique of Patent Document 1 does not provide sufficient crack growth resistance after thermal degradation of the rubber composition (crack growth resistance after thermal degradation), and further improvement has been desired.

[0004] Japanese Patent Application Publication No. 8-85303

[0005] Therefore, an object of the present invention is to provide a rubber composition having good durability and excellent crack propagation resistance after heat degradation, and a tire and a rubber product having good durability and excellent crack propagation resistance after heat degradation.

[0006] As a result of extensive investigations aimed at solving the above problems, the present inventors came up with the idea that a rubber composition containing a rubber component containing natural rubber and / or synthetic isoprene rubber and syndiotactic 1,2-polybutadiene can improve durability, such as crack growth resistance, of the rubber composition by applying the concept of a double network to the rubber composition. Furthermore, as a result of further extensive research, the present inventors discovered that by setting the sulfur and vulcanization accelerator in a specific ratio, crosslinking of sPB is promoted, thereby suppressing changes due to thermal degradation and improving crack growth resistance during thermal degradation, which led to the completion of the present invention.

[0007] The gist of the present invention for solving the above problems is as follows: [1] A rubber component containing natural rubber and / or synthetic isoprene rubber, syndiotactic 1,2-polybutadiene, sulfur, and a vulcanization accelerator, wherein the syndiotactic 1,2-polybutadiene has a crystallinity of 7 to 40 J / g and a number average molecular weight of 3.0 × 10 4 A rubber composition as described above, characterized in that the content mass ratio of the sulfur to the vulcanization accelerator (sulfur / vulcanization accelerator) is less than 1. By having the above configuration, it is possible to improve crack propagation resistance after thermal degradation while maintaining good durability.

[0008] [2] A tire characterized by using the rubber composition of the present invention. By having the above-mentioned constitution, it is possible to improve crack propagation resistance after thermal degradation while having good durability.

[0009] [3] A rubber product selected from the group consisting of a rubber crawler, a seismic isolation rubber, and a hose, characterized in that the rubber composition of the present invention is used. By having the above configuration, the rubber product can have good durability and improved crack growth resistance after thermal degradation.

[0010] According to the present invention, it is possible to provide a rubber composition having good durability and excellent crack propagation resistance after heat aging. Also, according to the present invention, it is possible to provide a tire and a rubber product having good durability and excellent crack propagation resistance after heat aging.

[0011] An embodiment of the rubber composition and tire of the present invention will be described below by way of example. The compounds described in this specification may be derived in part or entirely from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0012] <Rubber composition> A rubber composition comprising a rubber component containing natural rubber and / or synthetic isoprene rubber, syndiotactic 1,2-polybutadiene, sulfur, and a vulcanization accelerator, wherein the syndiotactic 1,2-polybutadiene has a crystallinity of 7 to 40 J / g and a number average molecular weight of 3.0 x 10 4 and the mass ratio of the sulfur to the vulcanization accelerator (sulfur / vulcanization accelerator) is less than 1.

[0013] The rubber composition of the present invention preferably forms, after vulcanization, a so-called double network structure in which syndiotactic 1,2-polybutadiene (sPB) forms a mesh-like three-dimensional network within a rubber component matrix of natural rubber or synthetic isoprene rubber. The sPB is a crystalline polymer, and its crystals undergo sacrificial fracture under high strain, thereby providing an input energy dissipation effect. Furthermore, the sPB is compatible with natural rubber or synthetic isoprene rubber, allowing the sPB to be partially immobilized within a rubber component containing natural rubber or synthetic isoprene rubber, thereby forming a three-dimensional network (double network) consisting of sPB crystalline portions and rubber component / sPB compatible portions in the vulcanized rubber. This double network structure provides a high energy dissipation effect due to the sPB crystalline portions and flexibility due to the rubber component / sPB compatible portions, allowing the rubber composition of the present invention to achieve good durability and excellent crack propagation resistance. Furthermore, the rubber composition of the present invention further contains a heterocyclic compound having a six-membered aromatic heterocycle, which promotes co-crosslinking of the sPB and the sPB with natural rubber and suppresses changes due to thermal degradation, thereby improving crack propagation resistance after thermal degradation.

[0014] (Rubber Component) The rubber composition of the present invention contains natural rubber (NR) and / or synthetic isoprene rubber (IR) as the rubber component. By including at least one of natural rubber and synthetic isoprene rubber in the rubber component, a double network due to the sPB described above is formed in the rubber composition after vulcanization, thereby improving durability and crack propagation resistance after thermal aging. Here, natural rubber (NR) and synthetic isoprene rubber (IR) have isoprene as the monomer and are primarily composed of a cis-1,4-polyisoprene structure. Natural rubber may be derived from rubber trees or other plant resources. The isoprene monomer used to synthesize synthetic isoprene rubber can be derived from petroleum or biomass.

[0015] In the rubber composition of the present invention, the ratio of natural rubber and synthetic isoprene rubber in the rubber component can be 100%, but other types of rubber can also be contained. Examples of other types of rubber include diene rubbers such as butadiene rubber (BR), styrene-butadiene rubber (SBR), and chloroprene rubber (CR). Among these, it is preferable to contain at least the butadiene rubber from the viewpoint of suppressing the amount of sulfur distributed in the natural rubber and reducing the amount of polysulfide bonds to further suppress deterioration. The butadiene rubber is a polybutadiene with a low vinyl content so as not to inhibit the reaction between the complex dry compound and sPB.

[0016] The total content of natural rubber (NR) and / or synthetic isoprene rubber (IR) in the rubber component is preferably 40% by mass or more, and more preferably 50% by mass or more, because this facilitates the formation of a double network with the above-mentioned sPB and allows for better crack propagation resistance after thermal degradation.

[0017] (Syndiotactic 1,2-polybutadiene) The rubber composition of the present invention has a crystal amount of 7 to 40 J / g and a number average molecular weight of 3.0×10 4The rubber composition contains the above-mentioned syndiotactic 1,2-polybutadiene (sPB). By including this sPB together with the natural rubber and / or synthetic isoprene rubber, the above-mentioned double network can be formed in the rubber composition after vulcanization, and the rubber composition can have good durability and improve crack propagation resistance after thermal aging.

[0018] The crystalline amount of the syndiotactic 1,2-polybutadiene is 7 to 40 J / g. By setting the crystalline amount of the sPB to 7 J / g or more, the double network described above can be more reliably formed in the rubber composition after vulcanization, improving the durability of the rubber composition after vulcanization and the crack propagation resistance after thermal aging. From the same perspective, the crystalline amount of the sPB is preferably 15 J / g or more, and more preferably 17 J / g or more. On the other hand, if the crystalline amount of the sPB is too large, the melting point of the sPB may become too high, making it difficult to achieve the vulcanization temperature required to form a double network. If the crystalline amount is too large, the crystals may act as fracture nuclei, resulting in a tendency for the elongation at break of the rubber to decrease. From this perspective, the crystalline amount of the sPB is set to 40 J / g, preferably 36 J / g or less, and more preferably 31 J / g or less. The crystalline amount of the sPB refers to the heat of fusion and is an index indicating the percentage of sPB that has crystallized. It can be derived from the melting peak measured with a differential scanning calorimeter.

[0019] The number average molecular weight of the syndiotactic 1,2-polybutadiene is preferably 3.0×10 from the viewpoint of more reliably forming the double network in the rubber composition after vulcanization and improving durability after vulcanization. 4 From the same viewpoint, the number average molecular weight of the sPB must be 5.0×10 or more. 4 That's it, 6.5 x 10 4 That's it, 8.0 x 10 4 That's it, 10.0 x 10 4 That's it, 11.0 x 10 4 That's it, 12.0 x 10 4 That's it, 13.0 x 10 4 That's it, 14.0 x 10 4 That's it, 15.0 x 10 4 That's it, 16.0 x 10 4That's it, 17.0 x 10 4 That's 17.9 x 10 4 That's it, 18.0 x 10 4 That's it, 19.0 x 10 4 That's it, 20.0 x 10 4 On the other hand, the number average molecular weight of the sPB can be set to 50.0 × 10 or more from the viewpoint of preventing deterioration in crack propagation resistance after thermal degradation and in ride comfort when applied to a tire. 4 From the same viewpoint, the number average molecular weight of the sPB is preferably 40.0×10 or less. 4 Below, 39.0 x 10 4 Below, 38.0 x 10 4 Below, 37.0 x 10 4 Below, 36.0 x 10 4 Below, 35.0 x 10 4 Below, 34.7 x 10 4 Below, 34.0 x 10 4 Below, 33.0 x 10 4 Below, 32.0 x 10 4 Below, 31.0 x 10 4 Below, 30.0 x 10 4 It can be as follows:

[0020] The syndiotactic 1,2-polybutadiene preferably has an amount of 1,2-bonds in the sPB (amount of 1,2-bonds in the microstructure of the sPB) of 80% by mass or more, more preferably 85% by mass or more. This is because the double network described above can be more reliably formed in the rubber composition after vulcanization, improving durability and crack propagation resistance after aging. From the same perspective, the amount of 1,2-bonds in the sPB can also be 90% by mass or more, 91% by mass or more, 92% by mass or more, 93% by mass or more, 94% by mass or more, or 95% by mass or more. In the present invention, the amount of 1,2-bonds in the sPB is １ H and １３ It can be determined by C nuclear magnetic resonance (NMR) analysis.

[0021] Furthermore, the syndiotactic 1,2-polybutadiene preferably has a syndiotacticity of 60% or more, more preferably 65% ​​or more, in the 1,2-bonds of the sPB. This is because the double network described above can be more reliably formed in the rubber composition after vulcanization, and durability and crack propagation resistance after aging can be further improved. From the same viewpoint, the syndiotacticity in the 1,2-bonds of the sPB can be 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 100%. In the present invention, the syndiotacticity in the 1,2-bonds of the sPB is １ H and １３ It can be determined by C nuclear magnetic resonance (NMR) analysis.

[0022] The syndiotactic 1,2-polybutadiene may be a copolymer in which, in addition to 1,3-butadiene, a small amount of a conjugated diene such as 1,3-pentadiene or 1-pentyl-1,3-butadiene is copolymerized, or may be a homopolymer of 1,3-butadiene. When the sPB contains units derived from a conjugated diene other than 1,3-butadiene, in one embodiment, the proportion of units derived from 1,3-butadiene in all repeating units of the sPB can be 80% or more, 85% or more, 90% or more, 95% or more, 98% or more, or 99% or more.

[0023] Furthermore, the melting point of the syndiotactic 1,2-polybutadiene is not particularly limited, but is preferably 100 to 160°C from the viewpoint of further improving the durability of the rubber composition. By setting the melting point of the sPB to 160°C or less, crystallization of the sPB is facilitated during vulcanization of the rubber composition, and the double network described above can be more reliably formed in the vulcanized rubber composition. On the other hand, by setting the melting point of the sPB to 100°C or higher, deterioration in the heat resistance and strength of the vulcanized rubber can be suppressed. From the same viewpoint, the melting point of the sPB can be set to 110°C or higher, or 120°C or higher.

[0024] The content of the syndiotactic 1,2-polybutadiene in the rubber composition of the present invention is not particularly limited and can be appropriately changed depending on the required performance. For example, from the viewpoint of further improving fuel economy, durability, and crack propagation resistance after thermal aging when the rubber composition is applied to a tire, the content of the sPB is preferably 1 to 50 parts by mass per 100 parts by mass of the rubber component. When the content of the sPB is 1 part by mass or more per 100 parts by mass of the rubber component, the energy dissipation effect is enhanced, resulting in better durability and crack propagation resistance after thermal aging. From the same viewpoint, the content of the sPB can be 5 parts by mass or more, or 10 parts by mass or more, per 100 parts by mass of the rubber component. On the other hand, when the content of the sPB is 50 parts by mass or less per 100 parts by mass of the rubber component, deterioration of fuel economy can be suppressed. From the same viewpoint, the content of the sPB can also be 40 parts by mass or less, or 30 parts by mass or less, per 100 parts by mass of the rubber component.

[0025] The method for obtaining the sPB is not particularly limited, and the sPB can be produced by hand or commercially available products can be used. For example, the sPB can be obtained by polymerizing 1,3-butadiene monomer in an organic solvent containing an aliphatic solvent using an iron-based catalyst composition, a chromium-based catalyst composition, a cobalt-based catalyst composition, or the like. Specifically, it can be prepared by the polymerization methods described in JP 2006-063183 A, JP 2000-119324 A, JP 2004-528410 A, JP 2005-518467 A, JP 2005-527641 A, JP 2009-108330 A, JP 7-25212 A, JP 6-306207 A, JP 6-199103 A, JP 6-92108 A, JP 6-87975 A, etc. Among these catalyst compositions, the sPB having a crystallinity of 7 to 40 J / g and a number average molecular weight of 6.5 × 10 4 The iron-based catalyst composition is preferably used in order to more reliably control the temperature within the above range.

[0026] Examples of the iron-based catalyst composition include a catalyst composition comprising a mixture of (a) an iron-containing compound, (b) an α-acylphosphonic acid diester, and (c) an organoaluminum compound; a catalyst composition comprising a mixture of (a) an iron-containing compound, (b) an α-acylphosphonic acid diester, (c) an organoaluminum compound, and another organometallic compound or a Lewis base; and a catalyst composition comprising (a) an iron-containing compound, (b) a dihydrocarbyl hydrogen phosphite, and (c) an organoaluminum compound. The iron-containing compound (a) is not particularly limited, but suitable examples include iron carboxylate, organic iron phosphate, organic iron phosphonate, organic iron phosphinate, iron carbamate, iron dithiocarbamate, iron xanthate, iron α-diketonate, iron alkoxide or aryloxide, and organic iron compounds. Among these compounds, compounds having an sPB crystallinity of 7 to 40 J / g and a number-average molecular weight of 6.5 × 10 are also suitable. 4 From the viewpoint of more reliably controlling the content within the above range, it is more preferable that the iron-based catalyst composition contains iron(III) tris(2-ethylhexanoate), bis(2-ethylhexyl) phosphite, triisobutylaluminum, tri-n-butylaluminum, and tri-n-octylaluminum.

[0027] An example of the chromium-based catalyst composition is a three-component catalyst system comprising (a) a chromium-containing compound, (b) an alkylaluminum hydride compound, and (c) a hydrogen phosphite. Various chromium-containing compounds can be used as component (a) of the chromium-based catalyst composition of the present invention. Generally, it is advantageous to use a chromium-containing compound soluble in a hydrocarbon solvent such as an aromatic hydrocarbon, an aliphatic hydrocarbon, or an alicyclic hydrocarbon. However, it is also possible for an insoluble chromium-containing compound simply dispersed in the polymerization medium to generate catalytically active species. Therefore, no limitations should be placed on the chromium-containing compound in order to ensure solubility. Examples of chromium in (a) the chromium-containing compound include, but are not limited to, chromium carboxylates, chromium β-diketonates, chromium alkoxides or aryloxides, chromium halides, pseudochromium halides, and organic chromium compounds.

[0028] Examples of the cobalt-based catalyst composition include a catalyst system comprising soluble cobalt, such as cobalt octoate, cobalt 1-naphthate, or cobalt benzoate, an organoaluminum compound, such as trimethylaluminum, triethylaluminum, tributylaluminum, or triphenylaluminum, and carbon disulfide.

[0029] As commercially available sPB products, for example, the JSR RB (registered trademark) series such as JSR RB (registered trademark) 810, 820, 830, and 840 from JSR Corporation can also be used.

[0030] (Heterocyclic Compound) The rubber composition of the present invention preferably contains, in addition to the above-described rubber component and syndiotactic 1,2-polybutadiene, a heterocyclic compound having a six-membered aromatic heterocycle. The inclusion of the heterocyclic compound promotes crosslinking of the sPB during vulcanization, enabling the network density to be maintained high, thereby suppressing changes in physical properties such as crack propagation resistance due to thermal degradation.

[0031] Here, the heterocyclic compound may be any compound having a six-membered aromatic heterocycle. For example, the heterocyclic compound may be a heterocyclic compound having at least one heterocycle selected from the group consisting of a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring. The pyridine ring, the pyrimidine ring, the pyridazine ring, the pyrazine ring, the triazine ring, and the tetrazine ring have multiple nitrogen atoms in the ring, and are highly reactive with the sPB, and easily promote crosslinking by attracting zinc to the sPB.

[0032] Among the above, the heterocyclic compound preferably has a triazine ring or a tetrazine ring, because the heterocyclic compound has high reactivity with the sPB and facilitates crosslinking, resulting in superior crack propagation resistance after thermal degradation.

[0033] Here, it is more preferable that a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring of the compound having a triazine ring or a tetrazine ring, and it is even more preferable that two pyridyl groups or two pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring. When a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring, a crosslinked structure with higher strength can be formed. Furthermore, when two pyridyl groups or two pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring, a crosslinked structure with even higher strength can be formed. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred. Furthermore, the pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0034] The heterocyclic compound is represented by the following general formula (1): [In the formula, X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group, and Y １ and Y ２ are each independently a single bond or a divalent hydrocarbon group. The compound represented by the general formula (1) is more likely to form crosslinks by coordinate bonds and can form a crosslinked structure with even greater strength, thereby achieving better crack propagation resistance after thermal degradation.

[0035] In the above general formula (1), X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group. １ and X ２ is preferably a pyridyl group. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred. The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0036] In the above general formula (1), Y １ and Y ２are each independently a single bond or a divalent hydrocarbon group. Here, examples of the divalent hydrocarbon group include an alkylene group, an alkenylene group, and an arylene group. More specifically, examples of the alkylene group include a methylene group, an ethylene group, a trimethylene group, and a tetramethylene group. Examples of the alkenylene group include a vinylene group, a propenylene group, and a butenylene group. Examples of the arylene group include a phenylene group, a tolylene group, and a naphthylene group. From the viewpoint of ease of synthesis, Y １ and Y ２ is preferably a single bond (i.e., X is not attached to the tetrazine ring). １ and X ２ is preferably directly bonded).

[0037] Here, X in the general formula (1) １ and X ２ is a pyridyl group, and Y １ and Y ２ is preferably a single bond. In this case, the compound of formula (1) is easily available, and is particularly likely to form a complex with the metal salt (C), and the bond dissociation energy is particularly likely to be high, making it possible to form a crosslinked structure with even higher strength.

[0038] The compounds represented by the general formula (1) include 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, 3,6-di(3-pyridyl)-1,2,4,5-tetrazine, 3,6-di(4-pyridyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylmethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylethyl)-1,2,4,5-tetrazine, 3-(2-pyridyl)-1,2,4,5-tetrazine, lysylmethyl)-6-(2-pyridylethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(4-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(5-pyrimidinyl)-1,2,4,5-tetrazine, and the like. Among these, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is preferred.

[0039] The content of the heterocyclic compound in the rubber composition of the present invention is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of the rubber component. When the content of the heterocyclic compound is 0.01 part by mass or more per 100 parts by mass of the rubber component, crack propagation resistance after thermal aging can be more reliably improved. Furthermore, when the content of the heterocyclic compound is 5 parts by mass or less per 100 parts by mass of the rubber component, a crosslinked rubber with sufficient elastomeric properties is easily obtained.

[0040] (Sulfur, Vulcanization Accelerator) The rubber composition of the present invention contains sulfur and a vulcanization accelerator in addition to the above-described rubber component, syndiotactic 1,2-polybutadiene, and heterocyclic compound. During vulcanization, a structure in which syndiotactic 1,2-polybutadiene (sPB) forms a mesh-like three-dimensional network, a so-called double network structure, can be formed in a rubber component matrix containing the above-described natural rubber or synthetic isoprene rubber.

[0041] In the present invention, the mass ratio of the sulfur to the vulcanization accelerator (sulfur / vulcanization accelerator) is less than 1. When the mass ratio of the sulfur to the vulcanization accelerator is less than 1 (sulfur / vulcanization accelerator<1), the amount of polysulfide contained in the co-crosslinking between the natural rubber and the sPB can be reduced, resulting in improved crack propagation resistance after thermal degradation. From the same viewpoint, the mass ratio of the sulfur to the vulcanization accelerator is more preferably less than 0.9, more preferably less than 0.8, more preferably less than 0.7, more preferably less than 0.6, and even more preferably less than 0.5 (sulfur / vulcanization accelerator<0.5).

[0042] Examples of the sulfur include sulfur (powdered sulfur, etc.), morpholine disulfide, and sulfur-containing crosslinking agents such as polymeric polysulfides.

[0043] The sulfur content is not particularly limited, but from the viewpoint of further improving crack propagation resistance, it is preferably 0.4 to 1.5 parts by mass, and more preferably 0.5 to 1.1 parts by mass, per 100 parts by mass of the rubber component. When the sulfur content is 0.4 part by mass or more per 100 parts by mass of the rubber component, the formation of the double network described above can be more reliably carried out, and when it is 1.5 parts by mass or less per 100 parts by mass of the rubber component, deterioration of crack propagation resistance due to hardening after vulcanization can be suppressed.

[0044] The vulcanization accelerator is not particularly limited and can be appropriately selected depending on the required performance. Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, guanidine vulcanization accelerators, thiourea vulcanization accelerators, thiuram vulcanization accelerators, dithiocarbamine vulcanization accelerators, and xanthogenate vulcanization accelerators.

[0045] The content of the vulcanization accelerator is not particularly limited, but from the viewpoint of further improving crack growth resistance, it is preferably 0.8 to 2.5 parts by mass, and more preferably 1 to 2 parts by mass, per 100 parts by mass of the rubber component. When the content of the vulcanization accelerator is 0.8 part by mass or more per 100 parts by mass of the rubber component, deterioration of crack growth resistance due to hardening after vulcanization can be suppressed, and when the content is 2.5 parts by mass or less per 100 parts by mass of the rubber component, deterioration of initial performance can be suppressed.

[0046] In addition, in the rubber composition of the present invention, the mass ratio of the syndiotactic 1,2-polybutadiene (sPb) to the vulcanization accelerator (sPB / vulcanization accelerator) is preferably 5 to 50. When the mass ratio of the syndiotactic 1,2-polybutadiene (sPB) to the vulcanization accelerator is 5 to 50, crosslinking of the sPB is further promoted, and crack propagation resistance after thermal degradation can be further improved.

[0047] (Filler) The rubber composition of the present invention preferably further contains a filler in addition to the above-described rubber component, syndiotactic 1,2-polybutadiene, heterocyclic compound, sulfur, and vulcanization accelerator. By including the filler, the durability and crack propagation resistance of the rubber composition can be simultaneously achieved at higher levels.

[0048] The filler is not particularly limited, and examples include carbon black, silica, aluminum hydroxide, clay, alumina, talc, mica, kaolin, glass balloons, glass beads, calcium carbonate, magnesium carbonate, magnesium hydroxide, magnesium oxide, titanium oxide, potassium titanate, and barium sulfate. Among these, it is preferable to include at least carbon black. These fillers may be used alone or in combination. For example, carbon black may be the only filler. The content of the filler is preferably 10 to 160 parts by mass, more preferably 15 to 140 parts by mass, even more preferably 15 to 120 parts by mass, and particularly preferably 20 to 120 parts by mass, per 100 parts by mass of the rubber component. The content of the filler may be 45 to 55 parts.

[0049] The carbon black is not particularly limited, and examples thereof include SAF, ISAF, IISAF, N339, HAF, FEF, and GPF grade carbon black. The nitrogen adsorption specific surface area (N2SA, measured in accordance with JIS K 6217-2:2001) of the carbon black is 20 to 160 m 2 / g, and more preferably 25 to 160m 2 / g, more preferably 25 to 150m 2 / g, particularly preferably 30 to 150m 2 / g. The dibutyl phthalate oil absorption (DBP, measured in accordance with JIS K 6217-4:2008) of the carbon black is preferably 40 to 160 ml / 100 g, more preferably 40 to 150 ml / 100 g, even more preferably 50 to 150 ml / 100 g, still more preferably 60 to 150 ml / 100 g, and particularly preferably 60 to 140 ml / 100 g. One type of carbon black may be used, or two or more types may be used in combination.

[0050] Furthermore, from the viewpoint of enhancing the reinforcing properties of the rubber composition, the amount of carbon black is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and particularly preferably 30 parts by mass or more, per 100 parts by mass of the rubber component. On the other hand, from the viewpoint of suppressing deterioration of low heat buildup, the amount of carbon black is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, per 100 parts by mass of the rubber component.

[0051] Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these, wet silica is preferred. The BET specific surface area of ​​the wet silica (measured according to ISO 5794 / 1) is 40 to 350 m. 2 / g. Silica with a BET specific surface area in this range has the advantage of being able to provide both rubber reinforcement and dispersibility in the rubber component. From this perspective, it is preferable that the BET specific surface area is 80 to 300 m 2 / g is more preferable. As such silica, commercially available products such as "Nipsil AQ" and "Nipsil KQ" manufactured by Tosoh Silica Corporation and "Ultrasil VN3" manufactured by Evonik can be used. One type of silica may be used, or two or more types may be used in combination. It is also possible to use a formulation containing carbon black as the filler but not containing silica. In this case, it is preferable because low heat buildup can be further improved.

[0052] Furthermore, when silica is used as the filler, it is preferable that the rubber composition before vulcanization further contains a silane coupling agent such as bis(3-triethoxysilylpropyl) polysulfide, bis(3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl benzothiazyl tetrasulfide, etc. The amount of the silane coupling agent in the rubber composition before vulcanization varies depending on the type of silane coupling agent, etc., but is preferably selected in the range of 2 to 20 parts by mass per 100 parts by mass of the silica.

[0053] (Other Components) In addition to the above-mentioned components, the rubber composition of the present invention may contain other components commonly used in the rubber industry, depending on the required performance. Examples of the other components that may be contained in the rubber composition before vulcanization include vulcanization retarders, antioxidants, reinforcing agents, softeners, vulcanization aids, colorants, flame retardants, lubricants, foaming agents, plasticizers, processing aids, antioxidants, scorch inhibitors, ultraviolet inhibitors, antistatic agents, color inhibitors, and oils. These may be used alone or in combination of two or more.

[0054] The method for preparing the rubber composition before vulcanization is not particularly limited, and any known method can be used. For example, the rubber composition can be obtained by adding the respective compounding components simultaneously or in any order and kneading them using a kneader such as a Banbury mixer, a roll, or an internal mixer.

[0055] <Method for Producing Vulcanized Rubber Composition> The method for producing the vulcanized rubber composition of the present invention is not particularly limited. For example, from the viewpoint of reliably forming the double network described above in the vulcanized rubber composition, a production method can be used that includes the steps of: kneading the syndiotactic 1,2-polybutadiene and rubber components such as natural rubber and / or synthetic isoprene rubber (during kneading in the masterbatch kneading stage) at a temperature 10 to 100°C higher than the melting point of the sPB, and kneading the components; and vulcanizing the resulting unvulcanized rubber composition at a temperature equal to or higher than the melting point of the sPB.

[0056] In the production method, the temperature during kneading with the rubber component is limited because the sPB can be made compatible with the rubber component by kneading at a temperature that is 10 to 100°C higher, preferably 10 to 50°C higher, and more preferably 12 to 50°C higher than the melting point of the sPB.

[0057] Furthermore, in the subsequent production method, it is believed that vulcanization at a temperature equal to or higher than the melting point of the sPB is important in order to form the double network described above. By vulcanizing the resulting unvulcanized rubber composition at a temperature equal to or higher than the melting point of the sPB, the sPB becomes semi-compatible with the rubber component and is fixed as a network within the rubber component, thereby forming the double network described above in the vulcanized rubber composition. However, this does not mean that a double network is not formed at all when vulcanized at a temperature below the melting point of the sPB. Even when vulcanized at a temperature below the melting point of the sPB, a portion of the sPB dissolves and a double network can be formed at least partially. For example, it is believed that a double network can be formed at least partially even at a temperature 15°C below the melting point and above. As a result, the resulting vulcanized rubber composition exhibits excellent crack propagation resistance without impairing low heat buildup.

[0058] The method for confirming the formation of the double network in the vulcanized rubber composition is not particularly limited. For example, the formation of a double network can be confirmed by confirming that the sPB forms a co-continuous network structure in the matrix polymer, natural rubber and / or isoprene rubber, from a phase image obtained by atomic force microscopy (AFM).

[0059] In the above-mentioned production method, when the sPB and the rubber component are kneaded (during the masterbatch kneading stage), the kneading temperature can reach a temperature 10°C higher than the melting point of the sPB, thereby more reliably making the sPB compatible with the natural rubber and / or synthetic isoprene rubber. On the other hand, when the sPB and the rubber component are kneaded (during the masterbatch kneading stage), the kneading temperature can be set to a temperature not higher than 100°C, preferably not higher than 50°C, than the melting point of the sPB, thereby effectively preventing thermal degradation of the rubber component and the sPB, thereby contributing to improving the cut resistance of the resulting vulcanized rubber composition. The sPB and the rubber component can be kneaded using a kneading machine such as a Banbury mixer, roll, or internal mixer.

[0060] The temperature during kneading in the production method refers to the temperature of the masterbatch at the time when the masterbatch of the unvulcanized rubber composition is discharged from the kneading device, and specifically refers to the temperature measured with a temperature sensor or the like during masterbatch kneading, where the internal temperature of the masterbatch is measured immediately after being discharged from the kneading device. However, if the kneading device has a means for measuring the temperature of the unvulcanized rubber composition, the temperature of the masterbatch at the time of discharge may also be measured. Here, the masterbatch refers to the rubber composition obtained in the stage of kneading the rubber component and the sPB at a kneading stage in which a crosslinking agent and a vulcanization accelerator are not blended.

[0061] The vulcanization temperature in the production method is preferably equal to or higher than the melting point of the sPB, because if the vulcanization temperature is equal to or higher than the melting point of the sPB, the sPB in the rubber component is thermodynamically less likely to assume a crystalline domain structure, thereby more reliably forming the double network described above.

[0062] The temperature during vulcanization in the above-mentioned production method refers to the maximum temperature reached as the vulcanization progresses from the start of vulcanization (usually the set temperature of the vulcanization device). The vulcanization in the above-mentioned production method can be carried out using a known vulcanization system, and may be a sulfur vulcanization system or a non-sulfur vulcanization system.

[0063] Furthermore, the vulcanized rubber composition forms the double network described above, improving durability, and preferably the modulus value at 25% elongation (M25), the modulus value at 300% elongation (M300), and the modulus value at 400% elongation (M400) satisfy the following relational expressions (A) and (B): M400-M300≦5.80 (A) M25*M300 / (M400-M300) ２ >0.39 ... (B)

[0064] Whether or not the above-mentioned double network structure has been formed can be difficult to determine simply by observing the composition or structure of the vulcanized rubber composition. Therefore, when a vulcanized rubber composition contains natural rubber and / or synthetic isoprene rubber and sPB and satisfies the relationship (A) and (B), it becomes possible to determine whether a double network structure has been formed. This is because, when a crystalline material such as sPB is contained in the structure, M25 (MPa) tends to increase. Furthermore, when a portion of the sPB is compatible with the rubber component, it inhibits the elongation crystallinity of the rubber component, resulting in a slow rise in stress in the high strain region (300% or more), and the value of M400 (MPa) - M300 (MPa) becomes smaller. As a result, when a double network structure has been formed in the vulcanized rubber composition, M25 * M300 / (M400 - M300) ２ This is because the value of M25 / (M400-M300) increases. As a result, the vulcanized rubber composition contains a rubber component consisting of natural rubber and / or synthetic isoprene rubber and sPB, and satisfies the relational expressions (A) and (B), thereby improving durability such as cut resistance without causing a deterioration in low heat buildup. From the same viewpoint, it is also preferable that the vulcanized rubber composition satisfies the following relational expression (C): M25 / (M400-M300) ２ >0.04...(C)

[0065] <Tire> The tire according to the present invention is a tire using the rubber composition of the present invention described above, which allows the tire of the present invention to have excellent durability and crack growth resistance after heat degradation.

[0066] The part of the tire in which the rubber composition of the present invention is used is not particularly limited. For example, the rubber composition can be suitably used in parts requiring high durability, such as the tread and sidewall. When used in a tire tread, the entire tread rubber can be the vulcanized rubber composition of the present invention. Furthermore, at least the part of the tread that comes into contact with the road surface can be made of the vulcanized rubber composition of the present invention.

[0067] <Rubber Product> The rubber product according to the present invention is a rubber product selected from the group consisting of a rubber crawler, a seismic isolation rubber, and a hose, and is characterized by using the rubber composition according to the present invention described above. As a result, the tire of the present invention can have excellent durability and crack growth resistance after heat degradation.

[0068] In one embodiment, when the rubber product of the present invention is a rubber crawler, the rubber crawler comprises steel cords, an intermediate rubber layer covering the steel cords, a core bar disposed on the intermediate rubber layer, and a main rubber layer surrounding the intermediate rubber layer and the core bar, and further has a plurality of lugs on the contact surface side of the main rubber layer. Here, the rubber composition of the present invention may be used in any part of the rubber crawler, but is preferably used in the main rubber layer, particularly the lugs, due to its excellent durability.

[0069] When the rubber product of the present invention is a seismic isolation rubber, in one embodiment, the seismic isolation rubber comprises a laminate in which soft layers and hard layers are alternately laminated, and a plug press-fitted into a hollow portion formed in the center of the laminate. In one embodiment, the above-described rubber composition of the present invention can be used for at least one of the soft layer and the plug.

[0070] When the rubber product of the present invention is a hose, in one embodiment, the hose comprises at least an inner rubber layer disposed on the radially inner side of the hose and an outer rubber layer disposed on the radially outer side of the hose, and in one embodiment, the above-described rubber composition of the present invention can be used in at least one of the inner rubber layer and the outer rubber layer.

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0072] [Examples 1-2, Comparative Examples 1-4] Rubber composition samples were produced using a conventional Banbury mixer with the formulations shown in Table 1. Note that the values ​​for vulcanization accelerator B were rounded to one decimal place and are reported to one decimal place. Each rubber composition sample was then subjected to a vulcanization treatment at 120°C for 180 minutes to produce a vulcanized rubber composition sample.

[0073] <Evaluation> The crack propagation resistance of each sample of the vulcanized rubber composition obtained was evaluated by the following method. The results are shown in Table 2.

[0074] (1) Crack propagation resistance (without thermal degradation) For each sample of vulcanized rubber composition, a 6 mm wide dumbbell-shaped test piece was cut with a 0.5 mm cut in the width direction of the test piece. Using a tensile testing machine (manufactured by Shimadzu Corporation), repeated fatigue (stress) was applied to the test piece in the longitudinal direction within a strain range of 50% to 160% at an ambient temperature of 80°C, and the number of times until the test piece broke was measured. The evaluation was expressed as an index, with the number of times for Comparative Example 1 being set to 100. A larger value indicates a larger number of repetitions until breakage and better crack propagation resistance.

[0075] (2) Crack Growth Resistance (with Heat Aging) Each vulcanized rubber composition sample was subjected to heat aging treatment in an air atmosphere at 100°C for 24 hours or at 125°C for 18 hours. Then, for each sample after heat aging treatment, a 0.5 mm incision was made in the width direction of a 6 mm-wide dumbbell-shaped test piece. Using a tensile testing machine (Shimadzu Corporation), the test piece was subjected to repeated fatigue (stress) in the longitudinal direction at an ambient temperature of 80°C within a strain range of 50% to 160%, and the number of cycles required until the test piece broke was measured. The evaluation was expressed as an index, with the number of cycles for Comparative Example 1 being set to 100. A higher value indicates a higher number of cycles required until breakage and better crack growth resistance.

[0076]

[0077] * 1 NR: Natural rubber "RSS # 3" * 2 ZnO: Zinc oxide * 3 sPB: Syndiotactic 1,2-polybutadiene, ENEOS Material Corporation "JSRRB (registered trademark) 830" * 4 CB: HAF grade carbon black, Asahi Carbon Co., Ltd. "Asahi # 70" * 5 Heterocyclic compound: 3,6-di (2-pyridyl) -1,2,4,5-tetrazine, Otsuka Chemical Co., Ltd. "DS-01T" * 6 Vulcanization accelerator A: N-t-butyl-2-benzothiazole sulfenamide, Sanshin Chemical Industry Co., Ltd. "Suncerer NS-G" * 5 Vulcanization accelerator B: Tetrakis (2-ethylhexyl) thiuram disulfide (Ouchi Shinko Chemical Industry Co., Ltd. "Noccela TOT-N") and silica mixture

[0078] Table 1 shows that, in the sulfur-rich crosslinking systems, Comparative Example 2, which added sPB, and Comparative Example 3, which added both sPB and a heterocyclic compound, showed a significant deterioration in crack propagation resistance, especially under severe thermal degradation conditions (125°C, 18 hours). Furthermore, Comparative Example 4, which used a highly heat-resistant, accelerator-rich crosslinking system, showed poor crack propagation resistance, especially when unaged. On the other hand, Example 1, which used a highly heat-resistant, accelerator-rich crosslinking system and added sPB, maintained performance almost equivalent to that of Comparative Example 1 when unaged, while exhibiting high crack propagation resistance under thermally aged conditions. Furthermore, Example 2, which further added a heterocyclic compound to the formulation of Example 1, showed a further improvement in crack propagation resistance, especially under severe thermal degradation conditions (125°C, 18 hours). As a result, in a highly heat-resistant accelerator-rich crosslinking system, by using sPB, which can improve crack growth resistance, it is possible to achieve both crack growth resistance when new and after thermal degradation.Furthermore, it is thought that by adding a heterocyclic compound, the crosslinking of sPB can be promoted and changes due to thermal degradation can be suppressed, thereby further improving crack growth resistance.

[0079] According to the present invention, a rubber composition having good durability and excellent crack propagation resistance after heat degradation can be provided. Also, according to the present invention, a tire and a rubber product having good durability and excellent crack propagation resistance after heat degradation can be provided.

Claims

1. A rubber composition comprising a rubber component containing natural rubber and / or synthetic isoprene rubber, syndiotactic 1,2-polybutadiene, sulfur, and a vulcanization accelerator, wherein the syndiotactic 1,2-polybutadiene has a crystallinity of 7 to 40 J / g and a number average molecular weight of 3.0 x 10 4 or more, wherein the mass ratio of the sulfur to the vulcanization accelerator (sulfur / vulcanization accelerator) is less than 1.

2. The syndiotactic 1,2-polybutadiene has a number average molecular weight of 5.0 × 10 4 ~5.00×10 5 The rubber composition according to claim 1, wherein 3. The rubber composition according to claim 1 or 2, wherein the syndiotactic 1,2-polybutadiene has a crystallinity of 15 to 60%.

4. The rubber composition according to claim 1 or 2, wherein the melting point of the syndiotactic 1,2-polybutadiene is 100 to 160°C.

5. The rubber composition according to claim 1 or 2, wherein the syndiotactic 1,2-polybutadiene has a 1,2-bond content of 80% by mass or more.

6. The rubber composition according to claim 1 or 2, wherein the syndiotactic 1,2-polybutadiene has a syndiotacticity in 1,2-bonds of 60% or more.

7. The rubber composition according to claim 1 or 2, wherein the content of said syndiotactic 1,2-polybutadiene is 1 to 50 parts by mass per 100 parts by mass of said rubber component.

8. The rubber composition according to claim 1 or 2, further comprising a filler.

9. The rubber composition according to claim 1 or 2, further comprising a heterocyclic compound having a six-membered aromatic heterocycle.

10. The rubber composition according to claim 9, wherein the heterocyclic compound has at least one heterocyclic ring selected from the group consisting of a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring.

11. The rubber composition according to claim 10, wherein the heterocyclic compound has a triazine ring or a tetrazine ring.

12. The heterocyclic compound (B) is represented by the following general formula (1): [In the formula, X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group, and Y １ and Y ２ and each independently represents a single bond or a divalent hydrocarbon group.

13. The rubber composition according to claim 1 or 2, wherein the content of the heterocyclic compound is 0.01 to 5 parts by mass per 100 parts by mass of the rubber component.

14. A rubber composition according to claim 1 or 2, characterized in that the mass ratio of the sulfur to the vulcanization accelerator (sulfur / vulcanization accelerator) is less than 0.

5.

15. A tire characterized by using the rubber composition according to claim 1 or 2.

16. A rubber product selected from the group consisting of rubber crawlers, seismic isolation rubber, and hoses, characterized in that the rubber product uses the rubber composition according to claim 1 or 2.

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