Rubber composition for heavy-duty tires

Abstract

Provided is a rubber composition for heavy-duty tires which comprises: a conjugated diene polymer having a glass transition temperature (Tg) of -60°C or lower and having a functional group capable of interacting with silica; and silica.

Description

Rubber composition for heavy duty tires

[0001] The present invention relates to a rubber composition for heavy load tires, which can give a cross-linked rubber product having low heat buildup, excellent abrasion resistance and chipping resistance, and which can be suitably used for heavy load tires.

[0002] Heavy-duty tires used for trucks, buses, etc. are required to have excellent abrasion resistance and chipping resistance, which contributes to a long tire life. Meanwhile, in recent years, there has been an increasing demand for low heat buildup (low fuel consumption) due to environmental and resource issues. In order to impart low heat buildup to heavy-duty tires, the incorporation of silica into rubber compositions for heavy-duty tires has been considered, but this approach has the problem of reducing abrasion resistance.

[0003] For example, Patent Document 1 discloses a rubber composition containing 100 parts by mass of a rubber component consisting of 55 to 70% by mass of natural rubber and 30 to 45% by mass of butadiene rubber, and a rubber composition having a CTAB adsorption specific surface area of ​​180 to 300 m 2 / g silica, and a nitrogen adsorption specific surface area of ​​110 to 150 m 2 The paper discloses a rubber composition for heavy-duty tires, characterized in that it contains 3 to 10 parts by mass of carbon black with a silica content of 1000 ppm / g and a silane coupling agent having a sulfide bond in an amount of 6 to 15% by mass of the amount of silica.

[0004] Japanese Patent Application Laid-Open No. 2019-056068

[0005] In recent years, there has been an increasing demand for low heat buildup, abrasion resistance, and chipping resistance in heavy-duty tires, but the technology of Patent Document 1 was unable to meet the high demands for low heat buildup, abrasion resistance, and chipping resistance. Therefore, from the perspective of suitable use in heavy-duty tire applications, further improvements in low heat buildup, abrasion resistance, and chipping resistance were required.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber composition for a heavy load tire that can give a cross-linked rubber product that is excellent in low heat buildup, abrasion resistance, and chipping resistance.

[0007] As a result of intensive research into achieving the above object, the present inventors have found that the above object can be achieved by using a conjugated diene polymer having a glass transition temperature (Tg) of −60° C. or lower and having a functional group capable of interacting with silica, and by compounding silica into this rubber composition, thereby completing the present invention.

[0008] That is, according to the present invention, there is provided a rubber composition for a heavy load tire, which contains silica and a conjugated diene polymer having a glass transition temperature (Tg) of −60° C. or lower and having a functional group capable of interacting with silica.

[0009] In the rubber composition for a heavy load tire of the present invention, it is preferable that the vinyl bond content in the conjugated diene monomer units constituting the conjugated diene polymer is 5 to 40% by weight. In the rubber composition for a heavy load tire of the present invention, it is preferable that the nitrogen adsorption specific surface area of ​​the silica measured by the BET method is 30 to 500 m ２ / g. In the rubber composition for a heavy load tire of the present invention, the content of the silica is preferably 10 to 200 parts by weight per 100 parts by weight of the rubber component containing the conjugated diene polymer. The rubber composition for a heavy load tire of the present invention preferably further contains carbon black. In this case, the nitrogen adsorption specific surface area of ​​the carbon black measured by the BET method is preferably 30 m ２ / g or more. It is more preferable that the content of the carbon black is 10 to 200 parts by weight relative to 100 parts by weight of the rubber component containing the conjugated diene polymer. In the rubber composition for a heavy load tire of the present invention, the content of the conjugated diene polymer is preferably 10 to 80% by weight relative to 100% by weight of the total rubber component. It is preferable that the rubber composition for a heavy load tire of the present invention further contains natural rubber, and the content of the natural rubber is preferably 10 to 80% by weight relative to 100% by weight of the total rubber component. In the rubber composition for a heavy load tire of the present invention, the functional group capable of interacting with silica in the conjugated diene polymer is Si-OR ａ (In the formula, R ａis a hydrogen atom or a hydrocarbyl group which may have a substituent. The rubber composition for a heavy load tire of the present invention preferably further contains a silane coupling agent. The rubber composition for a heavy load tire of the present invention preferably further contains a crosslinking agent.

[0010] According to the present invention, there is also provided a cross-linked rubber product obtained by cross-linking the rubber composition for heavy load tires according to the present invention. Furthermore, according to the present invention, there is provided a heavy load tire comprising the cross-linked rubber product of the present invention.

[0011] According to the present invention, it is possible to provide a rubber composition for a heavy-duty tire which can give a cross-linked rubber product having low heat buildup, excellent abrasion resistance and chipping resistance.

[0012] The rubber composition for a heavy-duty tire of the present invention contains a conjugated diene polymer having a glass transition temperature (Tg) of −60° C. or lower and having a functional group capable of interacting with silica, and silica.

[0013] <Conjugated Diene Polymer> The conjugated diene polymer used in the present invention is a polymer having a glass transition temperature (Tg) of −60° C. or lower and having a functional group capable of interacting with silica. In the present invention, a conjugated diene polymer having a glass transition temperature (Tg) of −60° C. or lower and having a functional group capable of interacting with silica, as described below, is used, and by combining this with silica, the obtained cross-linked rubber product can be made to have excellent low heat buildup, abrasion resistance, and chipping resistance.

[0014] The conjugated diene polymer used in the present invention, which has a glass transition temperature (Tg) of −60° C. or lower and has a functional group capable of interacting with silica (hereinafter referred to as “conjugated diene polymer” as appropriate), is composed mainly of conjugated diene monomer units and has a functional group capable of interacting with silica.

[0015] The content of conjugated diene monomer units in all monomer units constituting the conjugated diene polymer used in the present invention is preferably 90% by weight or more, more preferably 95% by weight or more, even more preferably 99% by weight or more, and particularly preferably 99.7% by weight or more. By setting the content of conjugated diene monomer units within the above range, it is possible to achieve low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product at even higher levels.

[0016] The conjugated diene compound for forming the conjugated diene monomer unit is not particularly limited, but examples thereof include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene. Among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. These conjugated diene compounds may be used alone or in combination of two or more.

[0017] The conjugated diene polymer used in the present invention preferably contains, as the conjugated diene monomer unit, a 1,3-butadiene unit, and more preferably contains a 1,3-butadiene unit and an isoprene unit.

[0018] When the conjugated diene polymer used in the present invention contains 1,3-butadiene units and isoprene units, the ratio of the content of 1,3-butadiene units to the content of isoprene units in all the monomer units constituting the conjugated diene polymer is not particularly limited, but is preferably 0.001 to 0.2, more preferably 0.005 to 0.1, and particularly preferably 0.01 to 0.05, expressed as (weight proportion of isoprene units) / (weight proportion of 1,3-butadiene units). By setting the ratio of the content of 1,3-butadiene units to the content of isoprene units within the above range, the obtained cross-linked rubber product can simultaneously achieve even higher levels of low heat buildup, abrasion resistance, and chipping resistance.

[0019] The conjugated diene polymer used in the present invention may also contain other monomer units in addition to the conjugated diene monomer units. Examples of other monomers constituting such other monomer units include aromatic vinyl monomers such as styrene, methylstyrene, ethylstyrene, t-butylstyrene, α-methylstyrene, α-methyl-p-methylstyrene, chlorostyrene, bromostyrene, methoxystyrene, dimethylaminomethylstyrene, dimethylaminoethylstyrene, diethylaminomethylstyrene, diethylaminoethylstyrene, cyanoethylstyrene, and vinylnaphthalene; chain olefin compounds such as ethylene, propylene, and 1-butene; cyclic olefin compounds such as cyclopentene and 2-norbornene; and non-conjugated diene compounds such as 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, dicyclopentadiene, and 5-ethylidene-2-norbornene. Among these, aromatic vinyl monomers are preferred, and styrene is more preferred. These other monomers may be used singly or in combination of two or more.

[0020] The content of other monomer units in all monomer units constituting the conjugated diene polymer used in the present invention is preferably 10% by weight or less, more preferably 5% by weight or less, even more preferably 1% by weight or less, and particularly preferably 0.3% by weight or less.

[0021] When the conjugated diene polymer used in the present invention contains other monomer units, the lower limit of the content of the other monomer units in all the monomer units constituting the conjugated diene polymer used in the present invention is not particularly limited, but may be, for example, 0.01% by weight or more, and the upper limit of the content of the conjugated diene monomer units is not particularly limited, but may be, for example, 99.99% by weight or less. By setting the content of each monomer unit within the above range, it is possible to achieve low heat buildup, abrasion resistance, and chipping resistance of the obtained cross-linked rubber product at even higher levels.

[0022] Furthermore, the conjugated diene polymer used in the present invention has a glass transition temperature (Tg) of -60°C or lower. The glass transition temperature (Tg) is not particularly limited, but is preferably -100 to -67°C, more preferably -97 to -74°C, even more preferably -95 to -81°C, and particularly preferably -93 to -88°C. By setting the glass transition temperature (Tg) within the above range, it is possible to achieve low heat buildup, abrasion resistance, and chipping resistance at even higher levels in the obtained cross-linked rubber product. Methods for setting the glass transition temperature (Tg) of the conjugated diene polymer within the above range include, but are not particularly limited to, a method of adjusting the vinyl bond content in the conjugated diene monomer units constituting the conjugated diene polymer, and a method of adjusting the weight average molecular weight of the conjugated diene polymer.

[0023] The vinyl bond content in the conjugated diene monomer units constituting the conjugated diene polymer used in the present invention is preferably 5 to 40% by weight, more preferably 7 to 33% by weight, even more preferably 9 to 25% by weight, particularly preferably 11 to 20% by weight, and most preferably 12 to 15% by weight. By setting the vinyl bond content within the above range, it is possible to achieve even higher levels of low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product.

[0024] The conjugated diene polymer used in the present invention is preferably one polymerized using a polymerization initiator containing an organic alkali metal compound as a main catalyst, more preferably one polymerized using an organic monolithium compound as the polymerization initiator, and even more preferably one polymerized using n-butyllithium as the polymerization initiator. By using a conjugated diene polymer polymerized using the above-mentioned polymerization initiator, the obtained cross-linked rubber product can achieve low heat buildup, abrasion resistance, and chipping resistance at even higher levels.

[0025] The conjugated diene polymer used in the present invention has a functional group capable of interacting with silica within the polymer. The functional group capable of interacting with silica is a functional group capable of forming a covalent bond between the functional group and the silica surface, or a functional group capable of forming an intermolecular force weaker than a covalent bond (for example, an ion-dipole interaction, a dipole-dipole interaction, a hydrogen bond, a van der Waals force, etc.). Such a functional group capable of interacting with silica is not particularly limited, but examples thereof include a nitrogen atom-containing functional group, a silicon atom-containing functional group, and an oxygen atom-containing functional group. Among these, a silicon atom-containing functional group is preferred from the viewpoint of a strong interaction with silica, and a Si-OR ａ (R ａ is a hydrogen atom or a hydrocarbyl group which may have a substituent).

[0026] R ａ Examples of the hydrocarbyl group forming the formula (I) include an alkyl group, a cycloalkyl group, an alkenyl group, an aryl group, and an aralkyl group, with an alkyl group having 1 to 6 carbon atoms being preferred. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a butyl group, a pentyl group, and a hexyl group, with a methyl group and an ethyl group being more preferred, and a methyl group being particularly preferred. When the hydrocarbyl group has a substituent, examples thereof include a hydrocarbyl group having a hydrocarbyloxy group as the substituent, and examples of the hydrocarbyl group having a hydrocarbyloxy group as the substituent include alkoxyalkyl groups such as a methoxymethyl group, an ethoxymethyl group, and a methoxyethyl group; and an aryloxyalkyl group such as a phenoxymethyl group.

[0027] The method for introducing a functional group capable of interacting with silica into the conjugated diene polymer used in the present invention is not particularly limited, but examples thereof include a method in which, when producing a conjugated diene polymer, a monomer containing a conjugated diene compound is polymerized to obtain a conjugated diene polymer chain having an active end, and then the conjugated diene polymer chain having the active end is reacted with a modifier having a functional group capable of interacting with silica.

[0028] The weight average molecular weight (Mw) of the conjugated diene polymer used in the present invention is preferably 150,000 to 3,000,000, more preferably 250,000 to 1,000,000, even more preferably 350,000 to 700,000, especially preferably 400,000 to 550,000, particularly preferably 430,000 to 500,000, and most preferably 450,000 to 480,000. By setting the weight average molecular weight (Mw) of the conjugated diene polymer within the above range, it becomes easier to compound silica into the conjugated diene polymer, the processability of the rubber composition can be further improved, and further, the low heat buildup, abrasion resistance, and chipping resistance of the obtained cross-linked rubber can be simultaneously achieved at even higher levels.

[0029] The molecular weight distribution of the conjugated diene polymer used in the present invention, represented by the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is preferably 1.1 to 3.5, more preferably 1.2 to 3.0, even more preferably 1.3 to 2.5, and particularly preferably 1.4 to 2.0. By adjusting the molecular weight distribution (Mw / Mn) of the conjugated diene polymer used in the present invention to fall within the above range, the obtained cross-linked rubber product can simultaneously achieve low heat buildup, abrasion resistance, and chipping resistance at even higher levels. The weight average molecular weight (Mw) and number average molecular weight (Mn) can be determined as values ​​measured by gel permeation chromatography in terms of polystyrene.

[0030] The Mooney viscosity (ML1+4, 100°C) of the conjugated diene polymer used in the present invention is preferably 20 to 100, more preferably 35 to 90, even more preferably 45 to 80, particularly preferably 50 to 70, and most preferably 55 to 65. When the conjugated diene polymer is used as an oil-extended rubber, it is preferable that the Mooney viscosity of the oil-extended rubber be in the above-mentioned range.

[0031] The content of the conjugated diene polymer having a glass transition temperature (Tg) of -60°C or lower and having a functional group capable of interacting with silica in the rubber composition for heavy load tires of the present invention is not particularly limited, but is preferably 10 to 80% by weight, more preferably 12 to 60% by weight, and even more preferably 15 to 40% by weight, based on 100% by weight of the total rubber components contained in the rubber composition for heavy load tires of the present invention. By setting the content of the conjugated diene polymer within the above range, it is possible to achieve low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product at even higher levels.

[0032] <Method for Producing Conjugated Diene Polymer> The method for producing the conjugated diene polymer used in the present invention is not particularly limited, but a method for producing a conjugated diene polymer comprising: a polymerization step of polymerizing a monomer containing a conjugated diene compound in an inert solvent using a polymerization initiator to obtain a conjugated diene polymer chain having an active end; and a modification step of reacting the conjugated diene polymer chain having an active end obtained in the polymerization step with a modifier having a functional group capable of interacting with silica.

[0033] (Polymerization Step) As the monomer containing a conjugated diene compound used in the polymerization step, those mentioned above can be used.

[0034] The inert solvent used in the polymerization is not particularly limited as long as it is one that is commonly used in solution polymerization and does not inhibit the polymerization reaction. Specific examples of the inert solvent include chain aliphatic hydrocarbons such as butane, pentane, hexane, and heptane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and ether compounds such as tetrahydrofuran and diethyl ether. These inert solvents may be used alone or in combination of two or more. The amount of the inert solvent used is not particularly limited, but is an amount that results in a monomer concentration of, for example, 1 to 50% by weight, preferably 10 to 40% by weight.

[0035] The polymerization initiator used in the polymerization is not particularly limited as long as it can polymerize a monomer containing a conjugated diene compound to give a conjugated diene polymer chain having an active terminal. Specific examples include polymerization initiators using an organic alkali metal compound, an organic alkaline earth metal compound, or a lanthanum series metal compound as a main catalyst. Examples of organic alkali metal compounds include organic monolithium compounds such as n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; organic polyvalent lithium compounds such as dilithiomethane, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, 1,3,5-trillithiobenzene, and 1,3,5-tris(lithiomethyl)benzene; organic sodium compounds such as sodium naphthalene; and organic potassium compounds such as potassium naphthalene. Examples of organic alkaline earth metal compounds include di-n-butylmagnesium, di-n-hexylmagnesium, diethoxycalcium, calcium distearate, di-t-butoxystrontium, diethoxybarium, diisopropoxybarium, diethylmercaptobarium, di-t-butoxybarium, diphenoxybarium, diethylaminobarium, barium distearate, diketylbarium, etc. Examples of polymerization initiators using a lanthanum series metal compound as the main catalyst include polymerization initiators using a lanthanum series metal salt, such as lanthanum, cerium, praseodymium, neodymium, samarium, or gadolinium, as the main catalyst, which is composed of a lanthanum series metal salt formed from a carboxylic acid and a phosphorus-containing organic acid, etc., together with a co-catalyst such as an alkylaluminum compound, an organoaluminum hydride compound, or an organoaluminum halide compound. Among these polymerization initiators, organic monolithium compounds and organic polyvalent lithium compounds are preferably used, organic monolithium compounds are more preferably used, and n-butyllithium is particularly preferably used.

[0036] The organic alkali metal compound may be used as an organic alkali metal amide compound by reacting it in advance with a secondary amine compound such as dibutylamine, dihexylamine, dibenzylamine, pyrrolidine, piperidine, hexamethyleneimine, or heptamethyleneimine. These polymerization initiators may be used alone or in combination of two or more.

[0037] The amount of the polymerization initiator used may be determined depending on the molecular weight of the target conjugated diene polymer chain, but is usually in the range of 1 to 50 mmol, preferably 1.5 to 20 mmol, more preferably 2 to 15 mmol per 1000 g of monomer.

[0038] The polymerization temperature is usually in the range of −80 to +150° C., preferably 0 to 100° C., and more preferably 30 to 90° C. The polymerization may be carried out in any manner, such as a batch system or a continuous system.

[0039] Furthermore, in the polymerization step, when polymerizing a monomer containing a conjugated diene compound, it is preferable to carry out the polymerization in the presence of a polar compound. Specifically, by using preferably 0.01 to 1.2 mol, more preferably 0.1 to 1.1 mol, and even more preferably 0.1 to 1.0 mol of the polar compound per mol of the polymerization initiator and carrying out the polymerization in the presence of such a polar compound, the vinyl bond content in the conjugated diene monomer unit moiety contained in the conjugated diene polymer chain obtained in the polymerization step can be suitably adjusted to within the above-mentioned range.

[0040] The method of polymerization in the presence of a polar compound is not particularly limited, but examples thereof include a method of adding a polar compound to an inert solvent used in polymerization and then carrying out polymerization. Specific examples of polar compounds include ether compounds such as dibutyl ether, tetrahydrofuran, and 2,2-di(tetrahydrofuryl)propane; tertiary amines such as tetramethylethylenediamine; alkali metal alkoxides; and phosphine compounds. Among these, ether compounds and tertiary amines are preferred, with tertiary amines being more preferred, and tetramethylethylenediamine being particularly preferred. These polar compounds may be used alone or in combination of two or more.

[0041] The weight average molecular weight (Mw) of the conjugated diene polymer chain having an active end obtained in the polymerization step is not particularly limited, but is preferably 150,000 to 3,000,000, more preferably 170,000 to 2,000,000, even more preferably 200,000 to 1,500,000, particularly preferably 350,000 to 650,000, and most preferably 380,000 to 520,000, as a value measured by gel permeation chromatography in terms of polystyrene. By setting the weight average molecular weight (Mw) of the conjugated diene polymer chain having an active end within the above range, the low heat buildup, abrasion resistance, and chipping resistance of the obtained cross-linked rubber can be simultaneously achieved at even higher levels.

[0042] Furthermore, the molecular weight distribution, which is expressed as the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the conjugated diene polymer chain having an active end obtained in the polymerization step, is not particularly limited, but is preferably 1.1 to 3.5, more preferably 1.2 to 3.0, and even more preferably 1.3 to 2.5. When the molecular weight distribution (Mw / Mn) of the conjugated diene polymer chain having an active end is within the above range, the production of the conjugated diene polymer becomes easy.

[0043] In the present invention, from the viewpoint of achieving even higher levels of low heat buildup, abrasion resistance, and chipping resistance in the cross-linked rubber product obtained, the polymerization step may be the following step.

[0044] That is, the method preferably comprises the steps of: polymerizing isoprene, or a monomer containing isoprene and an aromatic vinyl compound, in an inert solvent using a polymerization initiator to form a polymer block (A) having an active end containing 80 to 100% by weight of isoprene monomer units and 0 to 20% by weight of aromatic vinyl monomer units; and mixing the polymer block (A) having an active end obtained above with a monomer containing 1,3-butadiene and continuing the polymerization reaction to form a polymer block (B) containing 1,3-butadiene monomer units in a continuous manner with the polymer block (A), thereby obtaining a conjugated diene polymer chain having an active end.

[0045] By employing such a process, the conjugated diene polymer chain having an active end obtained by the polymerization process can be one that includes a polymer block (A) containing 80 to 100% by weight of isoprene monomer units and 0 to 20% by weight of aromatic vinyl monomer units and a polymer block (B) containing 1,3-butadiene monomer units, formed in a continuous manner. Such an embodiment will be described below.

[0046] [Polymer Block (A)] The polymer block (A) in the conjugated diene polymer chain according to one embodiment of the present invention may contain 80 to 100% by weight of isoprene monomer units and 0 to 20% by weight of aromatic vinyl monomer units, preferably 85 to 97% by weight of isoprene monomer units and 3 to 15% by weight of aromatic vinyl monomer units, and more preferably 89 to 95% by weight of isoprene monomer units and 5 to 11% by weight of aromatic vinyl monomer units. When the content ratio of isoprene monomer units and aromatic vinyl monomer units is within the above range, the affinity between the conjugated diene polymer and silica can be further increased, thereby enabling the obtained cross-linked rubber product to simultaneously achieve low heat buildup, abrasion resistance, and chipping resistance at even higher levels.

[0047] The aromatic vinyl compound used to form the aromatic vinyl monomer units contained in the polymer block (A) may be the same as the aromatic vinyl compounds described above, and among these, styrene is preferred. These aromatic vinyl compounds may be used alone or in combination of two or more.

[0048] The polymer block (A) preferably consists of only isoprene monomer units, or isoprene monomer units and aromatic vinyl monomer units, but may contain other monomer units in addition to the isoprene monomer units or isoprene monomer units and aromatic vinyl monomer units, as desired. Examples of other compounds that can be used to form the other monomer units include conjugated diene compounds other than isoprene, such as 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene; α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids or acid anhydrides such as acrylic acid, methacrylic acid, and maleic anhydride; unsaturated carboxylic acid esters such as methyl methacrylate, ethyl acrylate, and butyl acrylate; and non-conjugated dienes such as 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, dicyclopentadiene, and 5-ethylidene-2-norbornene. Among these, 1,3-butadiene is preferred. These other monomers can be used alone or in combination of two or more. The content of other monomer units in the polymer block (A) is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 6% by weight or less.

[0049] In the present invention, the polymer block (A) in the conjugated diene polymer chain is formed by polymerizing a monomer containing isoprene or a monomer containing isoprene and an aromatic vinyl compound in an inert solvent using a polymerization initiator. The formed polymer block (A) has an active terminal.

[0050] The inert solvent used in the polymerization of isoprene or a monomer containing isoprene and an aromatic vinyl compound to form polymer block (A) may be the same as the inert solvent described above. The amount of the inert solvent used is such that the monomer concentration is preferably 1 to 80% by weight, more preferably 10 to 50% by weight.

[0051] The polymerization initiator used to form the polymer block (A) is not particularly limited as long as it can polymerize isoprene or a monomer containing isoprene and an aromatic vinyl compound to give a polymer chain having an active terminal. Specific examples of the polymerization initiator include the same initiators as those described above.

[0052] The amount of the polymerization initiator used may be determined depending on the target molecular weight, but is preferably in the range of 4 to 250 mmol, more preferably 6 to 200 mmol, and particularly preferably 10 to 70 mmol, per 100 g of isoprene or a monomer containing isoprene and an aromatic vinyl compound.

[0053] The polymerization temperature when polymerizing isoprene or a monomer containing isoprene and an aromatic vinyl compound is preferably in the range of −80 to +150° C., more preferably 0 to 100° C., and even more preferably 20 to 90° C. The polymerization method may be any method, such as a batch method or a continuous method. Various bonding methods may be used, such as a block type, a tapered type, or a random type.

[0054] Furthermore, when forming the polymer block (A), it is preferable to polymerize isoprene or a monomer containing isoprene and an aromatic vinyl compound in the presence of a polar compound. Specifically, the polar compound is preferably used in an amount of 0.01 to 100 mol, more preferably 0.03 to 30 mol, and even more preferably 0.05 to 1 mol, per mol of the polymerization initiator. By carrying out the polymerization in the presence of such a polar compound, the vinyl bond content of the isoprene monomer unit moiety in the polymer block (A) can be suitably adjusted. The vinyl bond in the isoprene monomer unit moiety may be either a 1,2-vinyl bond or a 3,4-vinyl bond.

[0055] The method for polymerizing isoprene or a monomer containing isoprene and an aromatic vinyl compound in the presence of a polar compound is not particularly limited, but examples thereof include a method in which a polar compound is added to an inert solvent used for polymerization, and the like. The polar compound may be the same as the polar compounds described above.

[0056] The vinyl bond content in the isoprene monomer units in polymer block (A) is preferably 1 to 90% by weight, more preferably 2 to 50% by weight, even more preferably 3 to 30% by weight, particularly preferably 4 to 20% by weight, and most preferably 5 to 10% by weight. By setting the vinyl bond content in the isoprene monomer units within the above range, the low heat buildup properties of the obtained cross-linked rubber product can be further improved. In this specification, the vinyl bond content in the isoprene monomer units refers to the proportion of the total amount of isoprene monomer units having a 1,2-structure and isoprene monomer units having a 3,4-structure in the isoprene monomer units.

[0057] The weight average molecular weight (Mw) of the polymer block (A), expressed as a polystyrene equivalent value measured by gel permeation chromatography, is preferably 500 to 15,000, more preferably 1,000 to 12,000, and particularly preferably 1,500 to 10,000. By setting the weight average molecular weight of the polymer block (A) within the above range, the obtained cross-linked rubber product can simultaneously achieve even higher levels of low heat buildup, abrasion resistance, and chipping resistance.

[0058] The molecular weight distribution of the polymer block (A), which is expressed as the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is preferably 1.0 to 1.5, and more preferably 1.0 to 1.3. When the molecular weight distribution value (Mw / Mn) of the polymer block (A) is within the above range, the production of the conjugated diene polymer becomes easier.

[0059] [Polymer Block (B)] The polymer block (B) in the conjugated diene polymer chain according to one embodiment of the present invention preferably contains 95% by weight or more of 1,3-butadiene monomer units, more preferably 99% by weight or more of 1,3-butadiene monomer units, and even more preferably 100% by weight of 1,3-butadiene monomer units. By setting the content of 1,3-butadiene monomer units within the above range, it is possible to achieve even higher levels of low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product.

[0060] The polymer block (B) may contain other monomer units in addition to the 1,3-butadiene monomer units, if desired. The other monomers used to constitute the other monomer units can be the same compounds (excluding 1,3-butadiene) exemplified for the polymer block (A) described above. Furthermore, isoprene can also be used as the other monomer in the polymer block (B). The content of the other monomer units in the polymer block (B) is preferably 5% by weight or less, more preferably 1% by weight or less.

[0061] In one embodiment of the present invention, polymer block (B) in the conjugated diene polymer chain is formed continuously with polymer block (A) by mixing polymer block (A) having the above-mentioned active terminal with a monomer containing 1,3-butadiene and continuing the polymerization reaction. The formed polymer block (B) has an active terminal. Meanwhile, the active terminal disappears from polymer block (A).

[0062] The inert solvent used in the polymerization of the polymer block (A) with the monomer containing 1,3-butadiene to form the polymer block (B) is not particularly limited, and the same inert solvents as those described above can be used.

[0063] The amount of polymer block (A) having an active end used in forming polymer block (B) may be determined depending on the target molecular weight, but is preferably in the range of 0.1 to 5 mmol, more preferably 0.15 to 2 mmol, and even more preferably 0.2 to 1.5 mmol per 100 g of the monomer containing 1,3-butadiene.

[0064] The method for mixing the polymer block (A) with the monomer containing 1,3-butadiene is not particularly limited, and the polymer block (A) having an active end may be added to a solution of the monomer containing 1,3-butadiene, or the monomer containing 1,3-butadiene may be added to a solution of the polymer block (A) having an active end. From the viewpoint of controlling the polymerization, the method of adding the polymer block (A) having an active end to a solution of the monomer containing 1,3-butadiene is preferred.

[0065] The polymerization temperature when polymerizing a monomer containing 1,3-butadiene is preferably in the range of −80 to +150° C., more preferably 0 to 100° C., and even more preferably 20 to 90° C. As the polymerization mode, any mode such as a batch mode or a continuous mode can be adopted.

[0066] In one embodiment of the present invention, similarly to the formation of polymer block (A), when forming polymer block (B), it is preferable to polymerize a monomer containing 1,3-butadiene in the presence of a polar compound. Specifically, by using preferably 0.01 to 0.50 mol, more preferably 0.05 to 0.40 mol, and even more preferably 0.08 to 0.35 mol of the polar compound per mol of the polymerization initiator and conducting the polymerization in the presence of such a polar compound, the vinyl bond content of the 1,3-butadiene monomer unit moiety in polymer block (B) can be suitably adjusted, and as a result, the vinyl bond content of the conjugated diene monomer unit moiety contained in the finally obtained conjugated diene polymer can be suitably adjusted to the above-mentioned range.

[0067] The method for polymerizing a monomer containing 1,3-butadiene in the presence of a polar compound is not particularly limited, and examples include a method in which a polar compound is added to an inert solvent used for polymerization and then polymerization is carried out. In this case, the polar compound may be added so that the sum of the amount of polar compound added during the formation of polymer block (A) and the amount of polar compound newly added falls within the above-mentioned range. Therefore, if a polar compound is added during the formation of polymer block (A) in an amount sufficient to adjust the vinyl bond content of the 1,3-butadiene monomer unit moiety in polymer block (B), it is not necessary to add a new polar compound. Furthermore, the same polar compounds as those described above can be used as the polar compound.

[0068] In this manner, a conjugated diene polymer chain having an active end, which includes polymer block (A) and polymer block (B), can be obtained. In one embodiment of the present invention, from the viewpoint of productivity, the conjugated diene polymer chain having an active end is preferably composed of polymer block (A)-polymer block (B), and the terminal of polymer block (B) is the active terminal. However, the conjugated diene polymer chain may have a plurality of polymer blocks (A) or may have other polymer blocks. For example, a conjugated diene polymer chain having an active end may be exemplified by a polymer block (A)-polymer block (B)-polymer block (A). In this case, the active terminal is formed at the terminal of polymer block (A) formed subsequent to polymer block (B). When polymer block (A) is formed on the active terminal side of the conjugated diene polymer chain, the amount of isoprene used is preferably 10 to 100 mol, more preferably 15 to 70 mol, and particularly preferably 20 to 35 mol, per mol of the polymerization initiator used in the initial polymerization reaction (the polymerization reaction to form the first polymer block (A)).

[0069] The weight ratio of polymer block (A) to polymer block (B) in the conjugated diene polymer chain having an active end obtained in one embodiment of the present invention (when a plurality of polymer blocks (A) and polymer blocks (B) are present, the weight ratio is based on the total weight of the respective polymer blocks) is (weight of polymer block (A)) / (weight of polymer block (B)), and is preferably 0.001 to 0.2, more preferably 0.005 to 0.1, and particularly preferably 0.01 to 0.05. By setting the weight ratio of polymer block (A) to polymer block (B) within the above range, the obtained cross-linked rubber product can simultaneously achieve even higher levels of low heat buildup, abrasion resistance, and chipping resistance.

[0070] (Modification Step) Next, in the modification step, the conjugated diene polymer chain having an active end obtained in the above polymerization step is reacted with a modifier having a functional group capable of interacting with silica.

[0071] The modifying agent having a functional group capable of interacting with silica, used in the modification step, is not particularly limited, and may be any compound capable of reacting with the conjugated diene polymer chain having an active end obtained in the polymerization step described above, and having a functional group capable of interacting with silica. The functional group capable of interacting with silica is not particularly limited, and examples thereof include a nitrogen atom-containing functional group, a silicon atom-containing functional group, and an oxygen atom-containing functional group. Among these, a silicon atom-containing functional group is preferred from the viewpoint of high interaction with silica, and Si-OR ａ (R ａ is a hydrogen atom or a hydrocarbyl group which may have a substituent).

[0072] In the present invention, a siloxane compound can be suitably used as a modifier having a functional group capable of interacting with silica. Such a siloxane compound is not particularly limited as long as it has a structure represented by (-Si-O-Si-), but is preferably an organosiloxane having an organic group in addition to the structure represented by (-Si-O-Si-), and more preferably a polyorganosiloxane represented by the following general formula (1):

[0073] In general formula (1), R １ ~R ８ represents an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, which may be the same or different. １ and X ４ is any group selected from the group consisting of an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, and an epoxy group-containing group having 4 to 12 carbon atoms, and these may be the same or different. ２ is an alkoxy group having 1 to 5 carbon atoms or a group having 4 to 12 carbon atoms containing an epoxy group, and ２ They may be the same or different from each other. ３ is a group containing 2 to 20 repeating alkylene glycol units, and X ３When there are a plurality of m, they may be the same or different. m is an integer of 1 to 200, n is an integer of 0 to 200, k is an integer of 0 to 200, and m+n+k is 1 or more.

[0074] In the polyorganosiloxane represented by the general formula (1), R １ ~R ８ , X １ and X ４ Examples of alkyl groups having 1 to 6 carbon atoms that can constitute the above include methyl, ethyl, n-propyl, isopropyl, butyl, pentyl, hexyl, and cyclohexyl groups. Examples of aryl groups having 6 to 12 carbon atoms include phenyl and methylphenyl groups. Among these, methyl and ethyl groups are preferred from the viewpoint of ease of production of the polyorganosiloxane itself.

[0075] In addition, in the polyorganosiloxane represented by the general formula (1), X １ , X ２ and X ４ Examples of the alkoxy group having 1 to 5 carbon atoms that can constitute the above include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, and a butoxy group. Among these, from the viewpoint of ease of production of the polyorganosiloxane itself, a methoxy group and an ethoxy group are preferred.

[0076] Furthermore, in the polyorganosiloxane represented by the general formula (1), X １ , X ２ and X ４ Examples of the epoxy group-containing group having 4 to 12 carbon atoms that can constitute the above formula include groups represented by the following general formula (2): ３ -Z ４ -E ２ (2) In general formula (2), Z ３ is an alkylene group or an alkylarylene group having 1 to 10 carbon atoms, and Z ４ is a methylene group, a sulfur atom, or an oxygen atom, and E ２ is a hydrocarbon group having 2 to 10 carbon atoms and having an epoxy group.

[0077] The group represented by formula (2) includes Z ４ is preferably an oxygen atom, and Z ４ is an oxygen atom, and E ２ is more preferably a glycidyl group, and Z ３ is an alkylene group having 1 to 3 carbon atoms, and Z ４ is an oxygen atom, and E ２ is a glycidyl group is particularly preferred.

[0078] In addition, in the polyorganosiloxane represented by the general formula (1), X １ and X ４ Among the above, X is preferably a group containing an epoxy group and having 4 to 12 carbon atoms, or an alkyl group having 1 to 6 carbon atoms. ２ Among the above, an epoxy group-containing group having 4 to 12 carbon atoms is preferred as X. １ and X ４ is an alkyl group having 1 to 6 carbon atoms, and X ２ is more preferably a group containing an epoxy group and having 4 to 12 carbon atoms.

[0079] In addition, in the polyorganosiloxane represented by the general formula (1), X ３ That is, the group containing 2 to 20 repeating units of alkylene glycol is preferably a group represented by the following general formula (3):

[0080] In the general formula (3), t is an integer of 2 to 20, and X ５ is an alkylene group or alkylarylene group having 2 to 10 carbon atoms, and R ９ is a hydrogen atom or a methyl group, and X ６ is an alkoxy group or an aryloxy group having 1 to 10 carbon atoms. Among these, t is an integer of 2 to 8, and X ５ is an alkylene group having 3 carbon atoms, and R ９ is a hydrogen atom, and X ６ is preferably a methoxy group.

[0081] In the polyorganosiloxane represented by general formula (1), m is an integer of 1 to 200, preferably an integer of 20 to 150, and more preferably an integer of 30 to 120. When m is 1 or more, it is easy to set the coupling rate of the resulting conjugated diene polymer within the preferred range described below, and as a result, the resulting cross-linked rubber product can achieve low heat buildup, abrasion resistance, and chipping resistance at even higher levels. Furthermore, when m is 200 or less, the polyorganosiloxane represented by general formula (1) itself is easier to produce, and its viscosity does not become too high, making it easier to handle.

[0082] In the polyorganosiloxane represented by the general formula (1), n ​​is an integer of 0 to 200, preferably an integer of 0 to 150, more preferably an integer of 0 to 120. k is an integer of 0 to 200, preferably an integer of 0 to 150, more preferably an integer of 0 to 130. The total number of m, n, and k is 1 or more, preferably 3 to 400, more preferably 20 to 300, and particularly preferably 30 to 250. When the total number of m, n, and k is 1 or more, the reaction between the polyorganosiloxane represented by the general formula (1) and the conjugated diene polymer chain having an active terminal proceeds easily. Furthermore, when the total number of m, n, and k is 400 or less, the polyorganosiloxane represented by the general formula (1) itself is easily produced, and its viscosity does not become too high, making it easy to handle.

[0083] The amount of the siloxane compound used in the modification step, calculated as the number of repeating units of (—Si—O—) in the siloxane compound, relative to 1 mole of the polymerization initiator used in the polymerization step described above, is preferably 0.1 moles or more, more preferably 0.2 moles or more, even more preferably 0.5 moles or more, particularly preferably 1.0 moles or more, more preferably 1.1 moles or more, and is preferably 10 moles or less, more preferably 5 moles or less, even more preferably 2.5 moles or less, and particularly preferably 2 moles or less. By setting the amount of the siloxane compound within the above range, it is possible to achieve even higher levels of low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product.

[0084] In particular, it is particularly preferable to use the siloxane compound in an amount of 1 mole or more, calculated as the number of repeating units of (—Si—O—), per mole of the polymerization initiator, since substantially all of the active ends of the conjugated diene polymer chain having active ends obtained by the polymerization step can be reacted with the siloxane compound. That is, the alkyl metal group, i.e., —R － M ＋ (R is a hydrocarbon group forming a polymer chain terminal, and M is an alkali metal atom, alkaline earth metal atom, or lanthanide metal atom) can be made to substantially not remain.

[0085] The method for reacting the siloxane compound with the conjugated diene polymer chain having an active terminal is not particularly limited, but examples include a method in which they are mixed in a solvent in which each is soluble. Examples of the solvent used in this reaction include those exemplified as inert solvents used in the polymerization step described above. In this case, a simple and preferred method is to add the siloxane compound to the polymerization solution used in the polymerization to obtain the conjugated diene polymer chain having an active terminal. In this case, the siloxane compound is preferably dissolved in an inert solvent and added to the polymerization system, and the solution concentration is preferably in the range of 1 to 50 wt %. The reaction temperature is not particularly limited, but is usually 0 to 120°C. The reaction time is also not particularly limited, but is usually 1 minute to 1 hour.

[0086] The timing of adding the siloxane compound to the solution containing the conjugated diene polymer chains having active ends is not particularly limited, but it is desirable to add the siloxane compound to the solution when the polymerization reaction is not complete and the solution containing the conjugated diene polymer chains having active ends also contains a monomer, more specifically, when the solution containing the conjugated diene polymer chains having active ends contains 100 ppm or more, more preferably 300 to 50,000 ppm of a monomer. Adding the siloxane compound in this manner makes it possible to suppress side reactions between the conjugated diene polymer chains having active ends and impurities contained in the polymerization system, thereby enabling good control of the reaction.

[0087] In the modification step, a siloxane compound as a modifier is reacted with the active terminal of the conjugated diene polymer chain having an active terminal obtained in the polymerization step described above, and the active terminal of the conjugated diene polymer chain reacts with a silicon atom in the siloxane structure. Alternatively, a part of the active terminal of the conjugated diene polymer chain is converted to an alkoxy group or an epoxy group (X essentially contained in the general formula (1)) in the side chain of the polyorganosiloxane represented by the general formula (1). ２ In the modification step, a siloxane-modified structure is introduced into the conjugated diene polymer chain by such a reaction, and thereby a functional group capable of interacting with silica can be introduced into the conjugated diene polymer.

[0088] Specifically, the active end of the conjugated diene polymer chain reacts with the silicon atom in the siloxane structure, and a new bond is formed between the silicon atom in the siloxane structure and the active end of the conjugated diene polymer chain, and a modified structure by siloxane is introduced at the end of the conjugated diene polymer chain, and at the same time, a reaction residue, such as -O, is formed between the oxygen atom in the siloxane structure and the metal atom that formed the active end of the conjugated diene polymer chain. － M ＋ (wherein M is an alkali metal atom, an alkaline earth metal atom, or a lanthanide metal atom) is thought to be formed.

[0089] Alternatively, when a polyorganosiloxane represented by the above general formula (1) is used as the siloxane compound, the active end of the conjugated diene polymer chain reacts with the epoxy group on the side chain of the polyorganosiloxane, causing the ring-opening of the epoxy group, and forming a new bond between the carbon atom at the ring-opened portion of the epoxy group and the active end of the conjugated diene polymer chain, and a siloxane structure is introduced at the end of the conjugated diene polymer chain, and at the same time, a reaction residue is formed between the oxygen atom in the epoxy group and the metal atom that formed the active end of the conjugated diene polymer chain, such as -O － M ＋ Alternatively, the active end of the conjugated diene polymer chain reacts with the alkoxy group on the side chain of the polyorganosiloxane, resulting in the elimination of the alkoxy group, and the conjugated diene polymer chain forms a new bond between the silicon atom in the siloxane structure and the active end of the conjugated diene polymer chain, thereby introducing a siloxane structure into the end of the conjugated diene polymer chain.

[0090] In particular, by using 1 mole or more of the siloxane compound in terms of the number of repeating units of (-Si-O-) per mole of the polymerization initiator in the modification step, it is possible to introduce a modified structure by siloxane into almost all of the conjugated diene polymer chains having active ends obtained by the polymerization step. Therefore, the alkyl metal group, i.e., -R － M ＋ It is possible to make the state such that almost all of the -O as a reactive residue does not remain. － M ＋ Thus, a group represented by the following formula is formed.

[0091] In the present invention, a compound having a protected primary amino group and an alkoxysilyl group can be used as a modifying agent having a functional group capable of interacting with silica, such as N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, 1-trimethylsilyl-2,2-dimethoxy-1-aza-2-silacyclopentane, N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminoethyltrimethoxysilane, N,N-bis(trimethylsilyl)aminoethyltriethoxysilane, N,N-bis(trimethylsilyl)aminoethylmethyldimethoxysilane, and N,N-bis(trimethylsilyl)aminoethylmethyldiethoxysilane.

[0092] Furthermore, in the present invention, a polyfunctional compound having two or more epoxy groups and one or more nitrogen-containing groups in the molecule can be used as a modifier having a functional group capable of interacting with silica. More preferably, a polyfunctional compound represented by the following general formula (4) is used: In the above general formula (4), R １０ and R １１ is a hydrocarbon group having 1 to 10 carbon atoms or a hydrocarbon group having 1 to 10 carbon atoms and an ether structure and / or a tertiary amine, R １２ and R １３ is hydrogen, a hydrocarbon group having 1 to 20 carbon atoms or a hydrocarbon group having 1 to 20 carbon atoms and an ether and / or a tertiary amine; R １４ is a hydrocarbon group having 1 to 20 carbon atoms or a hydrocarbon group having 1 to 20 carbon atoms and having at least one group selected from the group consisting of an ether structure, a tertiary amine, an epoxy, a carbonyl, and a halogen; and s is 1 to 6.

[0093] In the present invention, a compound having a silyl group substituted with two or more alkoxy groups and one or more nitrogen atoms can be used as a modifying agent having a functional group capable of interacting with silica. Examples of such compounds include a compound represented by the following general formula (5), or a hydrocarbyloxysilane having a cyclic amino group containing two or more nitrogen atoms represented by the following general formula (6), as well as other hydrocarbyloxysilanes and cyclic azasilanes containing functional groups such as cyclic amines, acyclic amines, imines, and isocyanates. (In the above general formula (5), R １５ , R １６ are each independently an alkyl group having 1 to 20 carbon atoms or an aryl group, and R １７ is an alkylene group having 1 to 20 carbon atoms, and R １８ , R １９ are hydrocarbon groups having 1 to 6 carbon atoms, which may be the same or different, and form a ring structure of 5 or more members together with two adjacent Ns; R ２０ is a hydrocarbon group having 1 to 20 carbon atoms or a tri-substituted silyl group, and u is an integer of 2 or 3. (In the above general formula (6), R １５ ~R ２０ , u has the same meaning as in the general formula (5), and R ２１ is a hydrocarbon group having 1 to 20 carbon atoms or an organic substituted silyl group.

[0094] Furthermore, in the present invention, a silane-sulfide compound represented by the following general formula (7) can be used as a modifying agent having a functional group capable of interacting with silica. (R ２２ O) ｘ (R ２３ ) ｙ Si-R ２４ -S-SiR ２５ (7) (In the above general formula (7), Si is silicon, S is sulfur, O is oxygen, x is an integer selected from 1, 2 and 3, y is an integer selected from 0, 1 and 2, and x + y = 3. R ２２ , R ２３ , R ２５ are the same or different alkyl groups having 1 to 16 carbon atoms, and R２４ is an aryl group, an alkylaryl group, or an alkyl group having 1 to 16 carbon atoms.

[0095] In the present invention, a reactive polysiloxane compound represented by the following general formula (8) can be used as the siloxane compound having a functional group capable of interacting with silica: １ -CH ２ CH ２ -Si(R ２６ ) (R ２７ )-{O-Si(R ２６ ) (R ２７ ) ｚ -CH ２ CH ２ -Y １ (8) In the above general formula (8), Y １ (X ７ ) ａ (R ２８ ) ｂ Si-, where X ７ is a halogen, and R ２８ is a lower alkyl group having 20 or less carbon atoms. ２６ , R ２７ is a lower alkyl group having 20 or less carbon atoms, a is 2 or 3, b is 0 or 1, a+b=3, and z is 1 to 50,000.

[0096] In the present invention, an amide compound may be used as the terminal modifying agent. For example, N-substituted cyclic amides such as N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, and N-methyl-ε-caprolactam; N-substituted cyclic ureas such as 1,3-dimethylethyleneurea and 1,3-diethyl-2-imidazolidinone; N-substituted aminoketones such as 4,4′-bis(dimethylamino)benzophenone and 4,4′-bis(diethylamino)benzophenone; diphenylmethane diisocyanate and 2,4-tolylene Examples of suitable vinyl compounds include aromatic isocyanates such as diisocyanates; N,N-disubstituted aminoalkyl methacrylamides such as N,N-dimethylaminopropyl methacrylamide; N-substituted aminoaldehydes such as 4-N,N-dimethylaminobenzaldehyde; N-substituted carbodiimides such as dicyclohexylcarbodiimide; Schiff bases such as N-ethylethylideneimine and N-methylbenzylideneimine; and pyridyl group-containing vinyl compounds such as 4-vinylpyridine.

[0097] Furthermore, when the modification is carried out using a siloxane compound as a modifying agent having a functional group capable of interacting with silica, it is preferable to further react the conjugated diene polymer chain that has been reacted with the siloxane compound with a compound represented by the following general formula (9):

[0098] In general formula (9), R ２９ is a hydrocarbyl group, A １ is a group capable of reacting with an alkyl metal group as the active end of a conjugated diene polymer chain having an active end, or with a reaction residue formed by the reaction of a conjugated diene polymer chain having an active end with a siloxane compound, and A ２ is a group containing a nitrogen atom, p is an integer of 0 to 2, q is an integer of 1 to 3, r is an integer of 1 to 3, and p+q+r=4.

[0099] Here, the compound represented by the general formula (9) has an alkyl metal group, i.e., —R － M ＋or -O as a reaction residue by reaction with a siloxane compound － M ＋ (-O － M ＋ The amount of the siloxane compound used is 1 mole or more calculated as the number of repeating units of (—Si—O—) per mole of the polymerization initiator, and the ... － M ＋ When the compound represented by the general formula (9) is made into a state in which substantially no groups represented by the general formula (9) remain, almost all of the compound represented by the general formula (9) is converted into a reaction residue represented by the group —O － M ＋ This allows a modified structure by the compound represented by general formula (9) to be appropriately introduced into the conjugated diene polymer chain via a structure derived from a siloxane compound. This allows the obtained cross-linked rubber to simultaneously achieve low heat buildup, abrasion resistance, and chipping resistance at even higher levels.

[0100] In the compound represented by general formula (9), R ２９ is a hydrocarbyl group, and examples thereof include alkyl groups, cycloalkyl groups, alkenyl groups, aryl groups, and aralkyl groups, with an alkyl group having 1 to 6 carbon atoms being preferred. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a butyl group, a pentyl group, and a hexyl group, with a methyl group and an ethyl group being more preferred, and a methyl group being particularly preferred.

[0101] In the compound represented by the general formula (9), A in the general formula (9) １ represents an alkyl metal group (i.e., —R － M ＋ ), or a reaction residue (typically, —O － M ＋ is a group capable of reacting with a group represented by —OR ３０(R ３０ is preferably a group represented by a hydrogen atom or a hydrocarbyl group. ３０ Examples of hydrocarbyl groups that can constitute the above include alkyl groups, cycloalkyl groups, alkenyl groups, aryl groups, and aralkyl groups, but from the viewpoint of reactivity with the alkyl metal group or reaction residue, alkyl groups having 1 to 6 carbon atoms are preferred. Examples of alkyl groups having 1 to 6 carbon atoms include methyl groups, ethyl groups, n-propyl groups, isopropyl groups, butyl groups, pentyl groups, and hexyl groups, and of these, methyl groups and ethyl groups are more preferred.

[0102] In the compound represented by the general formula (9), A in the general formula (9) ２ is a group containing a nitrogen atom, and is not particularly limited as long as it is a group containing a nitrogen atom, but is preferably an organic group having a nitrogen atom, and examples thereof include a 3-aminopropyl group, a 4-aminobutyl group, a 3-(2-aminoethylamino)propyl group, a 2-dimethylaminoethyl group, a 3-dimethylaminopropyl group, a 3-diethylaminopropyl group, a 3-dipropylaminopropyl group, a 3-dibutylaminopropyl group, a 3-phenylmethylaminopropyl group, a 3-(4-methylpiperazinyl)propyl group, an N,N-bis(trimethylsilyl)aminopropyl group, an N,N-bis(triethylsilyl)aminopropyl group, and an N,N',N'-tris(trimethylsilyl)-N-(2-aminoethyl)-3-aminopropyl group. Among these, from the viewpoint of achieving a higher level of low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product, preferred are groups containing a primary amino group having an active hydrogen atom and / or a secondary amino group having an active hydrogen atom, such as a 3-aminopropyl group, a 4-aminobutyl group, or a 3-(2-aminoethylamino)propyl group. Note that an "active hydrogen atom" refers to a hydrogen atom bonded to an atom other than a carbon atom, and preferably has a bond energy lower than that of the carbon-hydrogen bond in a polymethylene chain.

[0103] In the compound represented by general formula (9), p is an integer of 0 to 2, q is an integer of 1 to 3, r is an integer of 1 to 3, and p+q+r=4. From the viewpoint of reactivity with the alkyl metal group as the active end of the conjugated diene polymer chain having an active end, or with the reaction residue generated by the reaction of the conjugated diene polymer chain having an active end with the siloxane compound, preferably, p is an integer of 0 to 1, q is an integer of 2 to 3, and r is an integer of 1 to 2, and more preferably, p=0, q=3, and r=1. When p is 2, two R groups are contained in one molecule of the compound represented by general formula (9), and ２９ Similarly, when q is 2 or 3, a plurality of A groups contained in one molecule of the compound represented by the general formula (9) may be the same or different from each other. １ The groups represented by may be the same or different from each other, and when r is 2 or 3, a plurality of A ２ The groups represented by the formula (I) may be the same or different from each other.

[0104] Specific examples of the compound represented by general formula (9) are not particularly limited, but include, for example, A ２ is a group containing a primary amino group having an active hydrogen atom and / or a secondary amino group having an active hydrogen atom, such as 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyldimethylethoxysilane, 3-aminopropylmethyldiethoxysilane, and 3-aminopropyltriethoxysilane. ２ compounds having a 3-aminopropyl group; A such as 4-aminobutyldimethylmethoxysilane, 4-aminobutylmethyldimethoxysilane, 4-aminobutyltrimethoxysilane, 4-aminobutyldimethylethoxysilane, 4-aminobutylmethyldiethoxysilane, and 4-aminobutyltriethoxysilane; ２compounds having a 4-aminobutyl group; A such as 3-(2-aminoethylamino)propyldimethylmethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propyldimethylethoxysilane, 3-(2-aminoethylamino)propylmethyldiethoxysilane, and 3-(2-aminoethylamino)propyltriethoxysilane; ２ Examples thereof include compounds having a 3-(2-aminoethylamino)propyl group;

[0105] In addition, A in the general formula (9) ２ is a group other than a group containing a primary amino group having an active hydrogen atom and / or a secondary amino group having an active hydrogen atom, such as 3-dimethylaminopropyltrimethoxysilane, 3-dimethylaminopropylmethyldimethoxysilane, 3-dimethylaminopropyldimethylmethoxysilane, 3-dimethylaminopropyltriethoxysilane, 3-dimethylaminopropylmethyldiethoxysilane, and 3-dimethylaminopropyldimethylethoxysilane. ２ compounds having a 3-dimethylaminopropyl group; A such as 3-diethylaminopropyltrimethoxysilane, 3-diethylaminopropylmethyldimethoxysilane, 3-diethylaminopropyldimethylmethoxysilane, 3-diethylaminopropyltriethoxysilane, 3-diethylaminopropylmethyldiethoxysilane, and 3-diethylaminopropyldimethylethoxysilane; ２ compounds having a 3-diethylaminopropyl group; A such as 3-dipropylaminopropyltrimethoxysilane, 3-dipropylaminopropylmethyldimethoxysilane, 3-dipropylaminopropyldimethylmethoxysilane, 3-dipropylaminopropyltriethoxysilane, 3-dipropylaminopropylmethyldiethoxysilane, and 3-dipropylaminopropyldimethylethoxysilane; ２compounds having a 3-dipropylaminopropyl group; A such as 3-dibutylaminopropyltrimethoxysilane, 3-dibutylaminopropylmethyldimethoxysilane, 3-dibutylaminopropyldimethylmethoxysilane, 3-dibutylaminopropyltriethoxysilane, 3-dibutylaminopropylmethyldiethoxysilane, and 3-dibutylaminopropyldimethylethoxysilane; ２ compounds having a 3-dibutylaminopropyl group; A such as 3-phenylmethylaminopropyltrimethoxysilane, 3-phenylmethylaminopropylmethyldimethoxysilane, 3-phenylmethylaminopropyldimethylmethoxysilane, 3-phenylmethylaminopropyltriethoxysilane, 3-phenylmethylaminopropylmethyldiethoxysilane, and 3-phenylmethylaminopropyldimethylethoxysilane; ２ compounds having a 3-phenylmethylaminopropyl group; A such as 3-(4-methylpiperazinyl)propyltrimethoxysilane, 3-(4-methylpiperazinyl)propylmethyldimethoxysilane, 3-(4-methylpiperazinyl)propyldimethylmethoxysilane, 3-(4-methylpiperazinyl)propyltriethoxysilane, 3-(4-methylpiperazinyl)propylmethyldiethoxysilane, and 3-(4-methylpiperazinyl)propyldimethylethoxysilane; ２ a compound having a 3-(4-methylpiperazinyl)propyl group as the aryl group;

[0106] A such as N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, and N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane ２compounds having an N,N-bis(trimethylsilyl)aminopropyl group; A such as N,N-bis(triethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropyltriethoxysilane, N,N-bis(triethylsilyl)aminopropylmethyldimethoxysilane, and N,N-bis(triethylsilyl)aminopropylmethyldiethoxysilane; ２ compounds having an N,N-bis(triethylsilyl)aminopropyl group; N,N',N'-tris(trimethylsilyl)-N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N,N',N'-tris(trimethylsilyl)-N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N,N',N'-tris(trimethylsilyl)-N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and N,N',N'-tris(trimethylsilyl)-N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane; ２ Examples thereof include compounds having an N,N',N'-tris(trimethylsilyl)-N-(2-aminoethyl)-3-aminopropyl group;

[0107] The amount of the compound represented by general formula (9) used is not particularly limited, but is preferably 0.1 to 5 mol, more preferably 0.2 to 2 mol, and even more preferably 0.4 to 1.5 mol, relative to 1 mol of the polymerization initiator used in the polymerization step. By using the compound represented by general formula (9) in the above range, it is possible to achieve low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product at even higher levels.

[0108] The timing of adding the compound represented by general formula (9) to the solution containing the conjugated diene polymer chains is not particularly limited, as long as it is after the addition of the siloxane compound. For example, the compound represented by general formula (9) can be added to a solution in which the polymerization reaction is not yet complete and the solution containing the conjugated diene polymer chains also contains a monomer, more specifically, when the solution containing the conjugated diene polymer chains contains 100 ppm or more, more preferably 300 to 50,000 ppm of monomer. By adding the compound represented by general formula (9) at such a timing, it is possible to suppress side reactions between the conjugated diene polymer chains and impurities contained in the polymerization system, thereby enabling good control of the reaction. Alternatively, by adding water or an alcohol such as methanol to the solution containing the conjugated diene polymer chains before or after the addition of the compound represented by general formula (9), it is possible to prevent the formation of -O as a reaction residue formed by the reaction with the siloxane compound. － M ＋ The modification reaction may be carried out in a state in which the group represented by formula (9) is hydrolyzed and converted into a hydroxyl group. When the compound represented by formula (9) is added to a solution containing a conjugated diene polymer chain, the compound represented by formula (9) may be added after being dissolved in an inert solvent, or may be added directly without being dissolved in an inert solvent. The reaction temperature and reaction time may be the same as those in the case of carrying out a reaction using a siloxane compound.

[0109] After reacting the compound represented by general formula (9), a known polymerization terminator or the like is added, if necessary, to inactivate the reaction system, and then, if desired, an antioxidant such as a phenolic stabilizer, a phosphorus-based stabilizer, or a sulfur-based stabilizer, a crumb-forming agent, or a scale inhibitor is added to the reaction solution, and then the polymerization solvent is separated from the reaction solution by direct drying or steam stripping, etc., to recover the conjugated diene polymer. Note that, before separating the polymerization solvent from the reaction solution, an extender oil may be mixed with the polymerization solution, and the conjugated diene polymer may be recovered as an oil-extended rubber.

[0110] Examples of extender oils used when recovering a conjugated diene polymer as an oil-extended rubber include paraffinic, aromatic, and naphthenic petroleum-based softeners, vegetable-based softeners, and fatty acids. When a petroleum-based softener is used, it is preferable that the content of polycyclic aromatics extracted by the IP346 method (a testing method of the Institute of Petroleum in the UK) is less than 3%. When an extender oil is used, the amount used is preferably 1 to 100 parts by weight, more preferably 2 to 60 parts by weight, and even more preferably 3 to 50 parts by weight, per 100 parts by weight of the conjugated diene polymer.

[0111] In the above, the cases where a siloxane compound and a compound represented by general formula (9) are used as the modifying agent having a functional group capable of interacting with silica have been mainly exemplified. However, the modifying agent having a functional group capable of interacting with silica is not particularly limited as long as it is a compound capable of reacting with the active end of the conjugated diene polymer chain having an active end obtained in the polymerization step described above and has a functional group capable of interacting with silica.

[0112] As a method for introducing a functional group capable of interacting with silica into a conjugated diene polymer, instead of or in addition to the method of reacting a conjugated diene polymer chain having an active end obtained in the polymerization step with a modifier having a functional group capable of interacting with silica, it is also possible to select a method of introducing a functional group capable of interacting with silica in the polymerization step. Specifically, in the polymerization step, the functional group capable of interacting with silica can be introduced by copolymerizing a compound that is reactive with the monomer used in the polymerization step and has a functional group capable of interacting with silica. The functional group capable of interacting with silica is not particularly limited, but examples include nitrogen-atom-containing functional groups, silicon-atom-containing functional groups, and oxygen-atom-containing functional groups. Among these, silicon-atom-containing functional groups are preferred from the viewpoint of their high interaction with silica.

[0113] Examples of the silicon atom-containing modifier used in the polymerization step include (dimethylamino)dimethylvinylsilane, (ethylmethylamino)dimethylvinylsilane, (diethylamino)dimethylvinylsilane, (ethyl-n-propylamino)dimethylvinylsilane, (ethylisopropylamino)dimethylvinylsilane, (di-n-propylamino)dimethylvinylsilane, (diisopropylamino)dimethylvinylsilane, (n-butyl-n-propylamino)dimethylvinylsilane, (di-n-butylamino)dimethylvinylsilane, (dimethylamino)diethylvinylsilane, (ethylmethylamino)diethylvinylsilane, (diethylamino)diethylvinylsilane, (ethyl-n-propylamino)diethylvinylsilane, (ethylisopropylamino)diethylvinylsilane, (di-n-propylamino)diethylvinylsilane, (diisopropylamino)diethylvinylsilane, (n-butyl-n-propylamino)diethylvinylsilane, (di-n-butylamino)diethylvinylsilane, (dimethylamino)dipropylvinylsilane, (ethylmethylamino)dipropylvinylsilane, (diethylamino)dipropylvinylsilane, (ethyl-n-propylamino)dipropylvinylsilane, (ethylisopropylamino)dipropylvinylsilane, (di-n-propylamino)dipropylvinylsilane, (diisopropylamino)dipropylvinylsilane, (n-butyl-n-propylamino)dipropylvinylsilane, (di-n-butylamino)dipropylvinylsilane, (dimethylamino)dibutylvinylsilane, (ethylmethylamino)dibutylvinylsilane, (diethylamino)dibutylvinylsilane, (ethyl-n-propylamino)dibutylvinylsilane, (ethylisopropylamino)dibutylvinylsilane, (di-n-propylamino)dibutylvinylsilane, (diisopropylamino)dibutylvinylsilane, (n-butyl-n-propylamino)dibutylvinylsilane, (di-n-butylamino)dibutylvinylsilane,{di(trimethylsilyl)amino}dimethylvinylsilane, di{(t-butyldimethylsilyl)amino}dimethylvinylsilane, {di(trimethylsilyl)amino}diethylvinylsilane, di{(t-butyldimethylsilyl)amino}diethylvinylsilane, bis(dimethylamino)methylvinylsilane, bis(ethylmethylamino)methylvinylsilane, bis(diethylamino)methylvinylsilane, bis(ethyl-n-propylamino)methylvinylsilane, bis(ethylisopropylamino)methylvinylsilane, bis(di-n-propylamino)methylvinylsilane, bis(diisopropylamino)methylvinylsilane, bis(n-butyl-n-propylamino)methylvinylsilane, bis(di-n-butylamino)methylvinylsilane, bis(dimethylamino)ethylvinylsilane, bis(ethylmethylamino)ethylvinylsilane, bis(diethylamino)ethylvinylsilane, bis(ethyl-n-propylamino)ethylvinylsilane, bis(ethylisopropylamino)ethylvinylsilane, bis(di-n-propylamino)ethylvinylsilane, bis(diisopropylamino)ethylvinylsilane, bis(n-butyl-n-propylamino)ethylvinylsilane, bis(di-n-butylamino)ethylvinylsilane, bis(dimethylamino)propylvinylsilane, bis(ethylmethylamino)propylvinylsilane, bis(diethylamino)propylvinylsilane, bis(ethyl-n-propylamino)propylvinylsilane, bis(ethylisopropylamino)propylvinylsilane, bis(di-n-propylamino)propylvinylsilane, bis(diisopropylamino)propylvinylsilane, bis(n-butyl-n-propylamino)propylvinylsilane, bis(di-n-butylamino)propylvinylsilane,Examples of the vinylsilane include bis(dimethylamino)butylvinylsilane, bis(ethylmethylamino)butylvinylsilane, bis(diethylamino)butylvinylsilane, bis(ethyl-n-propylamino)butylvinylsilane, bis(ethylisopropylamino)butylvinylsilane, bis(di-n-propylamino)butylvinylsilane, bis(diisopropylamino)butylvinylsilane, bis(n-butyl-n-propylamino)butylvinylsilane, bis(di-n-butylamino)butylvinylsilane, bis{di(trimethylsilyl)amino}methylvinylsilane, bis{(t-butyldimethylsilyl)amino}methylvinylsilane, bis{di(trimethylsilyl)amino}ethylvinylsilane, bis{(t-butyldimethylsilyl)amino}ethylvinylsilane, tri(dimethylamino)vinylsilane, tri(ethylmethylamino)vinylsilane, tri(diethylamino)vinylsilane, tri(ethylpropylamino)vinylsilane, tri(dipropylamino)vinylsilane, and tri(butylpropylamino)vinylsilane.

[0114] The compound having a functional group capable of interacting with silica used in the polymerization step may be any one or more selected from the group consisting of 4,4'-vinylidenebis(n,n-dimethylaniline), 3-(2-pyrrolidinoethyl)styrene, 4-(2-pyrrolidinoethyl)styrene, and (3-(2-pyrrolidino-1-methylethyl)-alpha-methylstyrene.

[0115] In the present invention, before the conjugated diene polymer chain having an active end is reacted with a modifying agent having a functional group capable of interacting with silica, such as a siloxane compound, a part of the active end of the conjugated diene polymer chain having an active end may be coupled or modified by adding a conventionally used coupling agent or modifying agent to the polymerization system within a range that does not impair the effects of the present invention.

[0116] The coupling ratio of the conjugated diene polymer used in the present invention is not particularly limited, but is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and particularly preferably 30 to 70% by weight. By setting the coupling ratio within the above range, the low heat buildup, abrasion resistance, and chipping resistance of the resulting cross-linked rubber can be simultaneously achieved at even higher levels. The coupling ratio is the weight fraction, relative to the total weight of the finally obtained conjugated diene polymer, of polymer molecules having a molecular weight 1.8 times or more the peak top molecular weight of the conjugated diene polymer chain having an active end before reaction with a siloxane compound, a compound represented by general formula (9), or other modifier having a functional group capable of interacting with silica, and a coupling agent or other modifier used as needed. The molecular weight is measured as a polystyrene-equivalent molecular weight by gel permeation chromatography.

[0117] The coupling agent used as needed in the present invention is not particularly limited, but for example, a metal halide compound can be used. Specific examples include silicon tetrachloride, hexachlorodisilane, bis(trichlorosilyl)methane, 1,2-bis(trichlorosilyl)ethane, 1,3-bis(trichlorosilyl)propane, 1,4-bis(trichlorosilyl)butane, 1,5-bis(trichlorosilyl)pentane, and 1,6-bis(trichlorosilyl)hexane. Among these, hexachlorodisilane, 1,2-bis(trichlorosilyl)ethane, and 1,6-bis(trichlorosilyl)hexane are particularly preferred. Additionally, tin tetrachloride can also be used.

[0118] <Silica> The rubber composition for heavy-duty tires of the present invention contains silica in addition to the above-mentioned conjugated diene polymer having a glass transition temperature (Tg) of −60° C. or lower and having a functional group capable of interacting with silica.

[0119] The silica used in the present invention is not particularly limited, but examples thereof include dry-process white carbon, wet-process white carbon, colloidal silica, and precipitated silica. Carbon-silica dual-phase fillers, in which silica is supported on the surface of carbon black, may also be used. Among these, wet-process white carbon, primarily composed of hydrated silicic acid, is preferred. These may be used alone or in combination of two or more.

[0120] The silica preferably has a nitrogen adsorption specific surface area measured by the BET method of 30 to 500 m ２ / g, more preferably 50 to 400m ２ / g, more preferably 140 to 250 m ２ / g, particularly preferably 180 to 240 m ２ / g. By using silica having a specific surface area within the above range, it is possible to achieve low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product at even higher levels. The pH of the silica is preferably less than 7, and more preferably 5 to 6.9. The nitrogen adsorption specific surface area can be measured by the BET method in accordance with ASTM D3037-81.

[0121] The amount of silica compounded in the rubber composition for heavy load tires of the present invention is preferably 10 to 200 parts by weight, more preferably 15 to 100 parts by weight, still more preferably 20 to 50 parts by weight, and particularly preferably 22 to 40 parts by weight, per 100 parts by weight of the rubber component in the rubber composition for heavy load tires. By setting the amount of silica compounded within the above range, it is possible to improve the dispersion of silica during production, while simultaneously achieving even higher levels of low heat buildup, abrasion resistance, and chipping resistance in the obtained cross-linked rubber product.

[0122] <Carbon Black> The rubber composition for heavy-duty tires of the present invention preferably further contains carbon black in addition to the above-mentioned conjugated diene polymer having a glass transition temperature (Tg) of −50° C. or lower and having a functional group capable of interacting with silica, and silica. By further containing carbon black, the obtained cross-linked rubber product can be made even more excellent in abrasion resistance.

[0123] Examples of carbon black include furnace black, acetylene black, thermal black, channel black, graphite, etc. Among these, it is preferable to use furnace black, and specific examples thereof include SAF, ISAF, ISAF-HS, ISAF-LS, IISAF-HS, HAF, HAF-HS, HAF-LS, etc. These can be used alone or in combination of two or more.

[0124] The carbon black preferably has a nitrogen adsorption specific surface area of ​​30 m as measured by the BET method. ２ / g or more, more preferably 30 to 170m ２ / g, more preferably 70 to 160 m ２ / g, particularly preferably 110 to 150m ２ / g. By using carbon black having a specific surface area within the above range, the abrasion resistance of the obtained cross-linked rubber product can be further improved. The nitrogen adsorption specific surface area can be measured by the BET method in accordance with JIS K-6217.

[0125] The carbon black preferably has a DBP absorption measured by Method A of 60 to 160 cm ３ / 100g, more preferably 85 to 150cm ３ / 100g, more preferably 110 to 145cm ３ / 100g. By using carbon black having a DBP absorption amount within the above range, the abrasion resistance of the obtained cross-linked rubber product can be further improved. The DBP absorption amount can be measured by Method A in accordance with JIS Z-8091.

[0126] The carbon black has an iodine adsorption capacity of preferably 25 to 170 mg / g, more preferably 70 to 160 mg / g, and even more preferably 110 to 150 mg / g. By using carbon black having an iodine adsorption capacity within the above range, the abrasion resistance of the obtained cross-linked rubber product can be further improved. The iodine adsorption capacity can be measured in accordance with JIS Z-8091.

[0127] The amount of carbon black blended in the rubber composition for heavy load tires of the present invention is preferably 10 to 200 parts by weight, more preferably 15 to 100 parts by weight, still more preferably 20 to 50 parts by weight, and particularly preferably 22 to 40 parts by weight, per 100 parts by weight of the rubber component in the rubber composition for heavy load tires. By setting the blending amount of carbon black within the above range, the abrasion resistance of the obtained cross-linked rubber product can be more appropriately improved.

[0128] <Natural Rubber> The rubber composition for heavy-duty tires of the present invention preferably further contains natural rubber as a rubber component in addition to the conjugated diene polymer having a glass transition temperature (Tg) of −50° C. or lower and having a functional group capable of interacting with silica. In addition to ordinary natural rubber, modified natural rubbers such as epoxidized natural rubber into which epoxy groups have been introduced and hydrogenated natural rubber can be used as the natural rubber, and these may be used in combination. By including natural rubber, the chipping resistance of the resulting cross-linked rubber can be further improved.

[0129] The content of natural rubber in the rubber composition for heavy load tires of the present invention is preferably 10 to 80% by weight, more preferably 30 to 70% by weight, even more preferably 40 to 60% by weight, and particularly preferably 45 to 55% by weight, based on 100% by weight of all rubber components contained in the rubber composition for heavy load tires of the present invention. By blending natural rubber in the above-mentioned proportions, the chipping resistance of the obtained cross-linked rubber can be more appropriately improved.

[0130] <Other Rubbers> The rubber composition for heavy load tires of the present invention may contain, as a rubber component, in addition to the above-mentioned conjugated diene polymer having a glass transition temperature (Tg) of −60° C. or lower and having a functional group capable of interacting with silica, and natural rubber used as needed, other rubbers other than these.

[0131] Examples of such other rubbers include polybutadiene rubber (which may be high cis-BR or low cis-BR, or may be polybutadiene rubber containing crystalline fibers made of 1,2-polybutadiene polymer), polyisoprene rubber, emulsion-polymerized styrene-butadiene copolymer rubber, solution-polymerized styrene-butadiene copolymer rubber, styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, acrylonitrile-styrene-butadiene copolymer rubber, cyclic olefin ring-opening polymers, and hydrogenated conjugated diene polymers, all of which have a glass transition temperature (Tg) of −60° C. or lower and are not conjugated diene polymers having functional groups capable of interacting with silica. These rubbers may be used alone or in combination of two or more.

[0132] When these other rubbers are compounded, the content thereof is preferably 10 to 80% by weight, more preferably 20 to 60% by weight, and even more preferably 25 to 40% by weight, in terms of the content ratio of all rubber components contained in the rubber composition for heavy load tires of the present invention.

[0133] Among other rubbers, styrene-butadiene copolymer rubber is preferred, and terminal-modified styrene-butadiene copolymer is more preferred, from the viewpoint that the obtained cross-linked rubber can achieve low heat buildup, abrasion resistance, and chipping resistance at even higher levels. As the styrene-butadiene copolymer rubber, for example, one having a styrene unit content of preferably 5 to 50% by weight, more preferably 10 to 30% by weight, and a butadiene unit content of preferably 50 to 95% by weight, more preferably 70 to 90% by weight can be used.

[0134] Furthermore, a silane coupling agent may be further blended into the rubber composition for heavy-duty tires of the present invention from the viewpoint of further improving low heat buildup. The silane coupling agent is not particularly limited, and various silane coupling agents can be used, but in the present invention, sulfide-based, mercapto-based, protected mercapto-based (for example, those having a carbonylthio group), thiocyanate-based, vinyl-based, amino-based, methacrylate-based, glycidoxy-based, nitro-based, epoxy-based, or chloro-based silane coupling agents can be suitably used. Specific examples of silane coupling agents include bis(3-(triethoxysilyl)propyl)disulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-(triethoxysilyl)propyl)tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-[ ethoxybis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silyl]-1-propanethiol, 3-octanoylthio-1-propyl-triethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, γ-trimethoxysilylpropylbenzothiazyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-thiocyanatopropyl triethoxysilane, vinyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, 3-trimethoxysilylpropyl methacrylate monosulfide, γ-glycidoxypropyltriethoxysilane, 3-nitropropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 3-chloropropyltrimethoxysilane. Other examples that can be used include NXT-Z100, NXT-Z30, NXT-Z45, NXT-Z60, NXT-Z45, and NXT manufactured by Momentive Performance Materials, and Si69, Si75, and VP Si363 manufactured by Evonik. These silane coupling agents can be used alone or in combination of two or more. One or more of these silane coupling agents may be oligomerized in advance and used in the oligomerized state.The amount of the silane coupling agent to be added is preferably 0.1 to 30 parts by weight, more preferably 1 to 15 parts by weight, per 100 parts by weight of silica.

[0135] Furthermore, the rubber composition for heavy-duty tires of the present invention preferably further contains a crosslinking agent. Examples of crosslinking agents include sulfur, sulfur halides, organic peroxides, quinone dioximes, organic polyamine compounds, and alkylphenol resins having methylol groups. Among these, sulfur is preferably used. The amount of crosslinking agent blended is preferably 0.1 to 15 parts by weight, more preferably 0.5 to 5 parts by weight, and particularly preferably 1 to 4 parts by weight, per 100 parts by weight of the rubber component in the rubber composition for heavy-duty tires.

[0136] Furthermore, in addition to the above-mentioned components, the rubber composition for heavy-duty tires of the present invention may contain, in accordance with a conventional method, necessary amounts of compounding agents such as a crosslinking accelerator, a crosslinking activator, an antioxidant, a filler (excluding the above-mentioned silica and carbon black), an activator, a process oil, a plasticizer, a lubricant, a tackifier, a compatibilizer, and a surfactant.

[0137] When sulfur or a sulfur-containing compound is used as the crosslinking agent, it is preferable to use a crosslinking accelerator and a crosslinking activator in combination. Examples of crosslinking accelerators include sulfenamide-based crosslinking accelerators; guanidine-based crosslinking accelerators; thiourea-based crosslinking accelerators; thiazole-based crosslinking accelerators; thiuram-based crosslinking accelerators; dithiocarbamic acid-based crosslinking accelerators; and xanthogenic acid-based crosslinking accelerators. Among these, those containing sulfenamide-based crosslinking accelerators are preferred. These crosslinking accelerators may be used alone or in combination of two or more. The amount of crosslinking accelerator blended is preferably 0.1 to 15 parts by weight, more preferably 0.5 to 5 parts by weight, and particularly preferably 1 to 4 parts by weight, per 100 parts by weight of the rubber component in the rubber composition for heavy-duty tires.

[0138] Examples of crosslinking activators include higher fatty acids such as stearic acid; zinc oxide; and the like. These crosslinking activators are used either alone or in combination of two or more. The amount of crosslinking activator blended is preferably 0.05 to 20 parts by weight, and particularly preferably 0.5 to 15 parts by weight, per 100 parts by weight of the rubber component in the rubber composition for heavy load tires.

[0139] Examples of antioxidants include discoloration aging stabilizers with anti-fatigue and anti-ozone properties, such as N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD), N-1,4-dimethylpentyl-N'-phenyl-p-phenylenediamine (7PPD), and N,N'-bis-(1,4-dimethylpentyl)-p-phenylenediamine (77PD); discoloration aging stabilizers with fatigue protection but no anti-ozone properties, such as phenyl-α-naphthylamine (PAN); discoloration aging stabilizers with low anti-fatigue properties and no anti-ozone properties, such as octylated diphenylamine (ODPA); and non-discoloration aging stabilizers with fatigue protection and good thermal protection properties, such as styrenated phenol (SPH). These antioxidants may be used alone or in combination of two or more. The amount of antioxidant to be added is preferably 0.1 to 15 parts by weight, more preferably 0.5 to 10 parts by weight, and particularly preferably 1 to 5 parts by weight, per 100 parts by weight of the rubber component in the rubber composition for heavy-duty tires.

[0140] Furthermore, the rubber composition for heavy load tires of the present invention may contain a resin in addition to the rubber component. By incorporating a resin, it is possible to impart tackiness to the rubber composition for heavy load tires and to increase the dispersibility of silica in the rubber composition for heavy load tires. As a result, an improved balance of chipping resistance, low heat buildup, and abrasion resistance can be expected for the resulting cross-linked rubber. Furthermore, similar to the effect of a plasticizer, it is also possible to improve the processability of the rubber composition for heavy load tires. Examples of resins include C5 petroleum resins, C5 / C9 petroleum resins, C9 petroleum resins, dicyclopentadiene resins, terpene resins, terpene phenol resins, aromatic-modified terpene resins, alkylphenol-acetylene resins, rosin resins, rosin ester resins, indene resins, C9 resins containing indene, α-methylstyrene-indene copolymer resins, coumarone-indene resins, farnesene resins, and polylimonene resins. These resins may be modified or hydrogenated. These resins may be used alone or in combination of two or more. The amount of the resin to be compounded is preferably 25 parts by weight or less per 100 parts by weight of the rubber component in the rubber composition for heavy load tires.

[0141] To obtain the rubber composition for heavy-duty tires of the present invention, the components may be kneaded according to conventional methods. For example, the components used as needed, excluding thermally unstable components such as crosslinking agents and crosslinking accelerators, are kneaded with the above-described conjugated diene polymer and silica, and then the kneaded mixture is mixed with thermally unstable components such as crosslinking agents and crosslinking accelerators to obtain the desired composition. The kneading temperature for the components excluding thermally unstable components, the above-described conjugated diene polymer, and silica is preferably 80 to 200°C, more preferably 120 to 180°C, and the kneading time is preferably 30 seconds to 30 minutes. The kneaded mixture is then mixed with the thermally unstable components after cooling to typically 100°C or below, preferably 80°C or below.

[0142] <Rubber Cross-Linked Product> The rubber cross-linked product of the present invention is obtained by cross-linking the above-described rubber composition for heavy load tires of the present invention.

[0143] The crosslinking method for crosslinking the rubber composition for heavy load tires of the present invention is not particularly limited, and may be selected depending on the shape, size, etc. of the crosslinked rubber. The rubber composition for heavy load tires may be filled into a mold and heated to crosslink simultaneously with molding, or a rubber composition for heavy load tires that has been molded in advance may be heated and crosslinked. The crosslinking temperature is preferably 100 to 200°C, more preferably 130 to 190°C, and the crosslinking time is preferably 1 minute to 24 hours, more preferably 2 minutes to 12 hours, and even more preferably 3 minutes to 6 hours.

[0144] Depending on the shape, size, etc. of the cross-linked rubber, the surface may be cross-linked but the interior may not be sufficiently cross-linked, so secondary cross-linking may be carried out by further heating.

[0145] The heating method may be appropriately selected from common methods used for crosslinking rubber, such as press heating, steam heating, oven heating, and hot air heating.

[0146] The cross-linked rubber product of the present invention is obtained using the rubber composition for heavy-duty tires of the present invention described above, and therefore has excellent low heat buildup, abrasion resistance, and chipping resistance. Therefore, the cross-linked rubber product of the present invention is suitable for various tire applications, particularly for heavy-duty tires to be mounted on trucks (including tractors and trailers), buses, construction vehicles (for example, dump trucks and graders), and the like. Furthermore, the cross-linked rubber product of the present invention can be used in various tire portions such as the tread portion, carcass portion, sidewall portion, and bead portion of such tires, but is particularly suitable for use in the tread portion. Furthermore, it is also suitable for use in the tread portion of retread tires in which worn or deteriorated tread portions are replaced.

[0147] The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples. In the following, "parts" are by weight unless otherwise specified. Various tests and evaluations were carried out according to the following methods.

[0148] [Weight-average molecular weight, molecular weight distribution, and coupling rate] The weight-average molecular weight (Mw), molecular weight distribution (Mw / Mn), and coupling rate were determined based on a chart obtained by gel permeation chromatography (GPC) based on the molecular weight converted to polystyrene. Specific measurement conditions for gel permeation chromatography were as follows: Measuring instrument: High-performance liquid chromatograph (manufactured by Tosoh Corporation, trade name "HLC-8320") Column: Two polystyrene columns manufactured by Tosoh Corporation, trade name "GMH-HR-H", were connected in series. Detector: Differential refractometer Eluent: Tetrahydrofuran Column temperature: 40°C. The coupling rate was determined as the area ratio of the peak portion having a peak top molecular weight 1.8 times or more of the peak top molecular weight indicated by the smallest molecular weight peak to the total elution area in the elution curve obtained by gel permeation chromatography under the above conditions.

[0149] [Vinyl bond content] The vinyl bond content is １ Measured by H-NMR.

[0150] [Mooney Viscosity (ML(1+4)100°C)] Measured using a Mooney viscometer (manufactured by Shimadzu Corporation) in accordance with JIS K6300-1 (2013).

[0151] [Glass transition temperature (Tg)] Measurement was performed in a helium atmosphere (gas flow rate: 20.0 mL / min) using a differential scanning calorimeter (manufactured by PerkinElmer, product name "DSC8500") according to JIS K6240 (2011). The peak top temperature of the differential curve of the obtained DSC curve was determined as the glass transition temperature (Tg).

[0152] [Low Heat Build-Up Property of Cross-Linked Rubber Product] The low heat build-up property of the cross-linked rubber product was evaluated by measuring the tan δ value at 60°C under conditions of a dynamic strain of 2.5% and 10 Hz using an ARES-G2 manufactured by TA Instruments, using a test piece having a length of 50 mm, a width of 12.7 mm and a thickness of 2 mm. The low heat build-up property was determined as an index, with the measured value of Comparative Example 1 being set at 100. The larger this index, the more excellent the low heat build-up property.

[0153] [Abrasion Resistance of Cross-Linked Rubber Product] The abrasion resistance of the cross-linked rubber product was evaluated by measuring a test piece having an outer diameter of 50 mm, an inner diameter of 15 mm, and a thickness of 10 mm using an FPS abrasion tester (manufactured by Ueshima Seisakusho Co., Ltd.) at a load of 10 N and a slip ratio of 15%. The abrasion resistance was calculated as an index, with the measured value of Comparative Example 1 being set at 100. The higher this index, the more excellent the abrasion resistance.

[0154] [Chipping Resistance] Regarding the low heat buildup of the cross-linked rubber, a tensile test was carried out in accordance with JIS K6301 using a test piece having a length of 50 mm, a width of 12.7 mm and a thickness of 2 mm, and the elongation at break was measured. The chipping resistance was calculated as an index, with the measured value of Comparative Example 1 being set at 100. The larger this index, the better the chipping resistance.

[0155] Production Example 1 (Production of Polymer Block (A) Having Active Ends) 218.1 parts of cyclohexane, 7.5 parts of styrene, and 0.3 parts of tetramethylethylenediamine were placed in a nitrogen-purged vessel, and the internal temperature of the vessel was adjusted to 50°C. Next, 1.64 parts of n-butyllithium was added, followed by the addition of 92.5 parts of isoprene over 80 minutes. The mixture was then allowed to react for 15 minutes, yielding a solution containing a polymer block (A) having active ends. The polymer block (A) having active ends in the resulting solution had a weight average molecular weight (Mw) of 6,500, a molecular weight distribution (Mw / Mn) of 1.10, a styrene unit content of 7.5% by weight, an isoprene unit content of 92.5% by weight, and a vinyl bond content of 7.0%.

[0156] (Production of Terminally Modified Polybutadiene Rubber (P1)) In a nitrogen atmosphere, 596.5 parts of cyclohexane and 50.0 parts of 1,3-butadiene were charged into an autoclave equipped with a stirrer, and then 9.0 parts of the solution containing the polymer block (A) having an active terminal obtained in Production Example 1 (2.7 parts as the amount of polymer block (A) having an active terminal) was added, and polymerization was initiated at 50 ° C. 30 minutes after the start of polymerization, 50.0 parts of 1,3-butadiene was continuously added over 50 minutes, and the mixture was stirred for an additional 20 minutes. The maximum temperature during the polymerization reaction was 75 ° C. After confirming that the polymerization conversion rate was in the range of 95% to 100%, 0.015 parts of 1,6-bis(trichlorosilyl)hexane was added and the mixture was allowed to react for 10 minutes. Thereafter, 0.18 parts of a polyorganosiloxane represented by the following formula (10), which is in the form of a 40% concentration xylene solution, was added and the mixture was allowed to react for 10 minutes. Further, 0.18 parts of polyorganosiloxane represented by the following formula (10) in the state of a 40% concentration xylene solution was added and allowed to react for 20 minutes. Next, 0.18 parts of 3-(2-aminoethylamino)propyltrimethoxysilane in the state of a 50% concentration xylene solution was added and allowed to react for 15 minutes. Thereafter, as a polymerization terminator, an amount of methanol equivalent to twice the molar amount of n-butyllithium used was added to obtain a polymer solution containing terminally modified polybutadiene rubber (P1). Then, to this polymer solution, 0.20 parts of Irganox 1520L (manufactured by BASF) and Irganox 1076 (manufactured by BASF) were added as antioxidants, each per 100 parts of the polymer component contained in the polymer solution. Next, the solvent was removed by steam stripping, and a solid terminally modified polybutadiene rubber (P1) was obtained by hot air drying. The weight average molecular weight, coupling ratio, vinyl bond content, Mooney viscosity, and glass transition temperature of the obtained terminal-modified polybutadiene rubber (P1) were measured. The results are shown in Table 1.

[0157] The obtained terminally modified polybutadiene rubber (P1) has, at the polymer chain end, a polyorganosiloxane represented by the following formula (10) and a modified structure with 3-(2-aminoethylamino)propyltrimethoxysilane (Si—OH structure, Si—OCH３ The structure was the same as in Production Examples 2 to 4 described below.

[0158]

[0159] [Production Example 2] (Production of Terminally Modified Polybutadiene Rubber (P2)) A solid terminally modified polybutadiene rubber (P2) was obtained in the same manner as in Production Example 1, except that 0.019 parts of tetramethylethylenediamine was added before the start of polymerization in the production of the terminally modified polybutadiene rubber (P1) in Production Example 1. The obtained terminally modified polybutadiene rubber (P2) was measured in the same manner as in Production Example 1, and the results are shown in Table 1.

[0160] [Production Example 3] (Production of Terminally Modified Polybutadiene Rubber (P3)) A solid terminally modified polybutadiene rubber (P3) was obtained in the same manner as in Production Example 1, except that 0.038 parts of tetramethylethylenediamine was added before the start of polymerization in the production of the terminally modified polybutadiene rubber (P1) in Production Example 1. The obtained terminally modified polybutadiene rubber (P3) was measured in the same manner as in Production Example 1, and the results are shown in Table 1.

[0161] [Production Example 4] (Production of Terminally Modified Polybutadiene Rubber (P4)) A solid terminally modified polybutadiene rubber (P4) was obtained in the same manner as in Production Example 1, except that 0.058 parts of tetramethylethylenediamine was added before the start of polymerization in the production of the terminally modified polybutadiene rubber (P1) in Production Example 1. The obtained terminally modified polybutadiene rubber (P4) was measured in the same manner as in Production Example 1, and the results are shown in Table 1.

[0162] [Production Example 5] (Production of Tin-Coupled Polybutadiene Rubber (P5)) 525 parts of cyclohexane and 56.8 parts of 1,3-butadiene were charged into an autoclave equipped with a stirrer under a nitrogen atmosphere, and then 2.7 parts of n-butyllithium was added and polymerization was initiated at 50°C. 10 minutes after the start of polymerization, 39.6 parts of 1,3-butadiene were continuously added over 60 minutes. Thereafter, 3.5 parts of 1,3-butadiene were continuously added over 10 minutes, and the mixture was stirred for another 10 minutes. The maximum temperature during the polymerization reaction was 75°C. After confirming that the polymerization conversion rate was in the range of 95% to 100%, 0.008 parts of tin tetrachloride was added and the reaction was allowed to proceed for 20 minutes. Thereafter, methanol was added as a polymerization terminator in an amount equivalent to twice the molar amount of n-butyllithium used, to obtain a polymer solution containing tin-coupled polybutadiene rubber (P5). To this polymer solution, 0.25 parts of Irganox 1520L (manufactured by BASF) was added as an antioxidant relative to 100 parts of the polymer component contained in the polymer solution. Next, the solvent was removed by steam stripping, and a solid tin-coupled polybutadiene rubber (P5) was obtained by hot air drying.

[0163] [Production Example 6] (Production of Terminally Modified Polybutadiene Rubber (P6)) A solid terminally modified polybutadiene rubber (P6) was obtained in the same manner as in Production Example 1, except that 0.067 parts of tetramethylethylenediamine was charged before the start of polymerization in the production of the terminally modified polybutadiene rubber (P1) in Production Example 1. The obtained terminally modified polybutadiene rubber (P6) was measured in the same manner as in Production Example 1, and the results are shown in Table 1.

[0164]

[0165] [Example 1] In a 250 ml Banbury mixer, 50 parts of natural rubber, 20 parts of the terminal-modified polybutadiene rubber (P1) obtained in Production Example 1, and 30 parts of a terminal-modified styrene-butadiene copolymer (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol NS612", styrene unit content 15% by weight) were masticated for 30 seconds. Then, silica (1) (manufactured by Solvay, trade name "Zeosil 1165MP", nitrogen adsorption specific surface area measured by the BET method: 165 m ２ / g), 25 parts of carbon black (1) (manufactured by Tokai Carbon Co., Ltd., trade name "SEAT 9H", nitrogen adsorption specific surface area measured by BET method: 142 m ２ 25 parts of zinc oxide (1,3-dimethylbutyl)-p-phenylenediamine (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac 6C") and 2.0 parts of a silane coupling agent, bis(3-(triethoxysilyl)propyl)tetrasulfide (manufactured by Evonik Co., Ltd., trade name "Si69"), were added and mixed for 1.5 minutes at a starting temperature of 110°C, followed by addition of 3 parts of zinc oxide, 2 parts of stearic acid, and 2 parts of an antioxidant, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac 6C"), and mixed for an additional 2.5 minutes, after which the kneaded product was discharged from the mixer. The temperature of the kneaded product at the end of kneading was 150°C. The kneaded product was cooled to room temperature and then kneaded again in the Banbury mixer at a starting temperature of 110°C for 3 minutes, after which the kneaded product was discharged from the mixer. Next, the resulting kneaded mixture was kneaded using an open roll at 50°C with a mixture of 1.75 parts of sulfur, 1.0 part of a crosslinking accelerator: N-(tert-butyl)-2-benzothiazole sulfenamide (manufactured by Sanshin Chemical Industry Co., Ltd., trade name "Suncerer NS-G"), and 0.53 parts of a crosslinking accelerator: 1,3-diphenylguanidine (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccelaer D"), and then a sheet-shaped rubber composition was taken out. The resulting rubber composition was press-crosslinked at 160°C for 7 minutes to prepare test specimens of the crosslinked rubber. These test specimens were then evaluated for low heat buildup, abrasion resistance, and chipping resistance. The results are shown in Table 2.

[0166] Example 2 In Example 1, 25 parts of silica (1) were replaced with silica (2) (trade name "Ultrasil 9100GR" manufactured by Evonik, nitrogen adsorption specific surface area measured by the BET method: 235 m ２ 25 parts of carbon black (1) were replaced with 25 parts of carbon black (2) (manufactured by Tokai Carbon Co., Ltd., trade name "SEAST 7HM", nitrogen adsorption specific surface area measured by the BET method: 126 m ２ A rubber composition was obtained, and a test piece of the cross-linked rubber was prepared and evaluated in the same manner as in Example 1, except that 25 parts of the hydroxybenzoate (100%) was used. The results are shown in Table 2.

[0167] Examples 3 to 5 Rubber compositions were obtained, and test pieces of cross-linked rubber were prepared and evaluated in the same manner as in Example 1, except that 20 parts of each of the terminal-modified polybutadiene rubbers (P2) to (P4) obtained in Production Examples 2 to 4 were used instead of 20 parts of the terminal-modified polybutadiene rubber (P1) obtained in Production Example 1. The results are shown in Table 2.

[0168] A rubber composition was obtained, and a test piece of the cross-linked rubber was prepared and evaluated in the same manner as in Example 1, except that 20 parts of the tin-coupled polybutadiene rubber (P5) obtained in Production Example 5 was used instead of 20 parts of the terminal-modified polybutadiene rubber (P1) obtained in Production Example 1. The results are shown in Table 2.

[0169] A rubber composition was obtained, and a test piece of the cross-linked rubber was prepared and evaluated in the same manner as in Example 1, except that 20 parts of the terminal-modified polybutadiene rubber (P6) obtained in Production Example 6 was used instead of 20 parts of the terminal-modified polybutadiene rubber (P1) obtained in Production Example 1. The results are shown in Table 2.

[0170]

[0171] As shown in Tables 1 and 2, the cross-linked rubber products obtained using the rubber compositions containing silica and a conjugated diene polymer having a glass transition temperature (Tg) of −60° C. or lower and having a functional group capable of interacting with silica were excellent in low heat buildup, abrasion resistance, and chipping resistance, and could be suitably used for heavy load tires (Examples 1 to 5).

[0172] On the other hand, a cross-linked rubber product obtained using a polybutadiene rubber having a glass transition temperature (Tg) of −60° C. or lower but not having a functional group capable of interacting with silica was insufficient in low heat buildup, abrasion resistance, and chipping resistance (Comparative Example 1).

[0173] Furthermore, a cross-linked rubber product obtained using a terminal-modified polybutadiene rubber having a glass transition temperature (Tg) higher than −60° C., although having a functional group capable of interacting with silica, had insufficient abrasion resistance (Comparative Example 2).

Claims

1. A rubber composition for heavy-duty tires contains silica and a conjugated diene polymer having a glass transition temperature (Tg) of -60°C or lower and having a functional group capable of interacting with silica.

2. 2. The rubber composition for a heavy load tire according to claim 1, wherein the conjugated diene monomer units constituting the conjugated diene polymer have a vinyl bond content of 5 to 40% by weight.

3. The nitrogen adsorption specific surface area of ​​the silica measured by the BET method is 30 to 500 m ２ 3. The rubber composition for a heavy load tire according to claim 1, wherein the tensile strength is 1 / g.

4. 3. The rubber composition for a heavy-duty tire according to claim 1, wherein the content of said silica is 10 to 200 parts by weight based on 100 parts by weight of the rubber component containing said conjugated diene polymer.

5. 3. The rubber composition for a heavy load tire according to claim 1, further comprising carbon black.

6. The carbon black has a nitrogen adsorption specific surface area of ​​30 m as measured by the BET method. ２ 6. The rubber composition for a heavy load tire according to claim 5, wherein the modulus of elasticity is 1 / g or more.

7. 6. The rubber composition for a heavy-duty tire according to claim 5, wherein the content of said carbon black is 10 to 200 parts by weight based on 100 parts by weight of the rubber component containing said conjugated diene polymer.

8. 3. The rubber composition for a heavy-duty tire according to claim 1, wherein the content of the conjugated diene polymer is 10 to 80% by weight based on 100% by weight of the total rubber component.

9. Further containing natural rubber, 3. The rubber composition for a heavy-duty tire according to claim 1, wherein the content of the natural rubber is 10 to 80% by weight based on 100% by weight of the total rubber component.

10. The functional group capable of interacting with silica in the conjugated diene polymer is Si-OR ａ (In the formula, R ａ 3. The rubber composition for a tire for heavy loads according to claim 1, wherein R is a group having a structure represented by the formula:

11. 3. The rubber composition for a heavy-duty tire according to claim 1, further comprising a silane coupling agent.

12. 3. The rubber composition for a heavy load tire according to claim 1, further comprising a crosslinking agent.

13. A cross-linked rubber product obtained by cross-linking the rubber composition for heavy load tires according to claim 1 or 2.

14. A heavy-duty tire comprising the cross-linked rubber according to claim 13.