Rubber composition for tires and tires

Abstract

Provided are: a rubber composition which is for a tire and provides excellent fuel efficiency and on-ice performance when used for a tire, and from which good fracture resistance characteristics can be obtained; and a tire which provides excellent fuel efficiency and on-ice performance and exhibits good fracture resistance characteristics by using the rubber composition. The rubber composition for a tire includes a rubber component and a copolymer obtained by polymerizing monomer components including glycidyl (meth)acrylate and stearyl (meth)acrylate.

Description

Technical Field

[0001] The present invention relates to a rubber composition for tires and a tire.

Background Art

[0002] When a tire runs on an icy or snowy road surface, the tire slips due to the water film formed between the road surface and the tire, and the braking performance deteriorates. For this reason, in the case of a studless tire, improvement in ice performance such as effective grip even on an icy or snowy road surface and easy braking of the vehicle is required.

[0003] As a method for enhancing ice performance, it is known to increase the surface roughness (surface irregularities) of the tread rubber or to improve the flexibility (flexibility and adhesiveness) at low temperatures.

[0004] When the surface roughness is increased, it is considered that the concave portions take in the water film on the ice, and the convex portions come into contact with the ice surface, thereby increasing the contact area with the ice surface compared to a tread rubber having a smooth surface. As a method for increasing the surface roughness of the tread rubber, it is common to blend a foaming agent or thermally expandable microcapsules into the rubber composition (for example, Patent Document 1).

[0005] By reducing the elastic modulus of the tread rubber at low temperatures, the contact area with the ice surface can be increased and the ice performance can be enhanced. Patent Document 2 discloses a rubber composition containing a silyl group-terminated (meth)acrylate polymer and a (meth)acrylamide polymer as a crosslinkable oligomer or polymer. In Patent Document 2, by forming an aggregate of the copolymer and the white filler, the aggregate is effectively dispersed in the diene rubber to improve the ice performance and abrasion resistance.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] In the method exemplified in Patent Document 1, although the water film can be taken in as the surface roughness increases, the area in contact with the ice surface decreases. For this reason, it can be said that there is a limit to the effect of improving the performance on ice due to the surface roughness. In addition, when a foaming agent, a thermally expandable microcapsule, or the like is blended, there is a problem that the fracture resistance characteristics of the tread rubber deteriorate. In the rubber composition of Patent Document 2, although an improvement in performance on ice was observed, the fracture resistance characteristics and the rolling resistance were not evaluated. Further, since the oligomer or polymer added in Patent Document 2 is in a liquid state, there is also a problem that weighing and charging into the mixer are complicated.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide a rubber composition for a tire that, when used in a tire, has excellent low fuel consumption and performance on ice, and obtains good fracture resistance characteristics. Another object is to provide a tire that is excellent in low fuel consumption and performance on ice and exhibits good fracture resistance characteristics by using the rubber composition. Means for Solving the Problems

[0009] In order to solve the above problems, the present invention provides the following [1] to

[15] . [1] A rubber composition for a tire, comprising a rubber component and a copolymer obtained by polymerizing a monomer component containing glycidyl (meth) acrylate and stearyl (meth) acrylate. [2] The rubber composition for a tire according to [1], wherein in the monomer component, the proportion of the glycidyl (meth) acrylate is 5 to 98 mol%, and the proportion of the stearyl (meth) acrylate is 2% by mass to 95% by mass. [3] The rubber composition for tires according to [1] or [2], wherein the copolymer is further obtained by polymerizing a monomer component containing 2-hydroxyethyl (meth)acrylate. [4] The rubber composition for tires according to [3], wherein in the monomer component, the proportion of glycidyl (meth)acrylate is 4 to 51 mol%, the proportion of stearyl (meth)acrylate is 2 to 35 mol%, and the proportion of 2-hydroxyethyl (meth)acrylate is 27 to 94 mol%. [5] The rubber composition for tires according to [3] or [4], wherein the copolymer is further obtained by polymerizing a monomer component containing methyl (meth)acrylate. [6] The rubber composition for tires according to [5], wherein in the monomer component, the proportion of glycidyl (meth)acrylate is 4 to 46 mol%, the proportion of stearyl (meth)acrylate is 1 to 20 mol%, the proportion of 2-hydroxyethyl (meth)acrylate is 20 to 87 mol%, and the proportion of methyl (meth)acrylate is 6 to 44 mol%. [7] The rubber composition for tires according to any one of [1] to [6], wherein the copolymer is solid at room temperature. [8] The rubber composition for tires according to any one of [1] to [7], wherein the polystyrene-reduced weight average molecular weight of the copolymer is 2,000 to 20,000. [9] The rubber composition for tires according to any one of [1] to [8], which contains 0.1 to 20 parts by mass of the copolymer with respect to 100 parts by mass of the rubber component.

[10] The rubber composition for tires according to any one of [1] to [9], which further contains silica as a filler.

[11] The rubber composition for tires according to any one of [1] to

[10] , which further contains at least one selected from the group consisting of a foaming agent, a thermally expandable microcapsule, a metal sulfate, porous cellulose particles, and a lignin derivative.

[12] The rubber composition for tires according to any one of [1] to

[11] , wherein the rubber component contains natural rubber, polybutadiene rubber, and styrene-butadiene rubber.

[13] The rubber composition for a tire according to

[12] , wherein the proportion of the natural rubber is 20 to 60% by mass, the proportion of the polybutadiene rubber is 20 to 60% by mass, and the proportion of the styrene-butadiene rubber is 10 to 40% by mass.

[0010]

[14] A tire using a vulcanizate of the rubber composition for a tire according to any one of [1] to

[13] .

[15] The tire according to

[14] , wherein the tread rubber is a vulcanizate of the rubber composition for a tire according to any one of [1] to

[13] .

Advantages of the Invention

[0011] According to the present invention, when used for a tire, it is possible to provide a rubber composition for a tire that has excellent low fuel consumption and ice performance, and good fracture resistance characteristics. Further, by using the rubber composition, it is possible to provide a tire that has excellent low fuel consumption and ice performance, and exhibits good fracture resistance characteristics.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be illustrated and described in detail based on its embodiments. In the following description, the description of "A to B" indicating a numerical range represents a numerical range including the endpoints A and B, and represents "A or more and B or less" (when A < B), or "A or less and B or more" (when A > B). Also, parts by mass and mass% are synonymous with parts by weight and weight%, respectively.

[0013] [Rubber Composition for a Tire] The rubber composition for a tire of the present invention includes a rubber component and a copolymer obtained by polymerizing a monomer component including glycidyl (meth) acrylate and stearyl (meth) acrylate. The rubber composition of the present invention contains a copolymer obtained by polymerizing a monomer component containing glycidyl (meth) acrylate and stearyl (meth) acrylate, thereby ensuring good grip performance on ice and snow roads, having excellent ice performance, reducing rolling resistance, and enabling a tire with excellent low fuel consumption. Furthermore, by using the rubber composition of the present invention, a tire showing good fracture resistance characteristics can be obtained. The rubber composition of the present invention is particularly effective when applied to a tread rubber composition.

[0014] Hereinafter, the rubber composition for a tire of the present invention and the details of the tire will be described. <Rubber component> In the rubber composition for a tire of the present invention, the type of rubber is not particularly limited. For example, natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), butyl rubber (IIR), ethylene-propylene-diene copolymer (EPDM), acrylonitrile-butadiene copolymer (NBR), and rubbers obtained by combining these can be mentioned.

[0015] In the present invention, it is preferable that the rubber component contains natural rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber. Among them, it is particularly preferable that the proportion of natural rubber in the rubber component is 20 to 60% by mass, the proportion of polybutadiene rubber is 20 to 60% by mass, and the proportion of styrene-butadiene rubber is 10 to 40% by mass. The polybutadiene rubber may be a modified butadiene rubber or an unmodified butadiene rubber, but a modified butadiene rubber is more preferable. The styrene-butadiene copolymer rubber may be a modified styrene-butadiene copolymer rubber or an unmodified styrene-butadiene copolymer rubber, but a modified styrene-butadiene copolymer rubber is more preferable. For example, the modified conjugated diene polymer described in International Publication No. 2019 / 146323 can be applied.

[0016] <Copolymer> The copolymer added to the rubber composition for tires of the present invention is obtained by polymerizing a monomer component containing glycidyl (meth)acrylate and stearyl (meth)acrylate as monomer components. In the present invention, glycidyl (meth)acrylate refers to glycidyl methacrylate or glycidyl acrylate. In the present invention, not only the case where glycidyl methacrylate or glycidyl acrylate is contained alone, but also the case where a mixture of glycidyl methacrylate and glycidyl acrylate is contained is included. In the present invention, stearyl (meth)acrylate refers to stearyl methacrylate or stearyl acrylate. In the present invention, not only the case where stearyl methacrylate or stearyl acrylate is contained alone, but also the case where a mixture of stearyl methacrylate and stearyl acrylate is contained is included. In the present invention, it is preferable that the copolymer contains glycidyl methacrylate (GMA) and stearyl methacrylate (SMA) as monomer components. Examples of such a copolymer include a binary copolymer obtained by polymerizing glycidyl methacrylate (GMA) and stearyl methacrylate (SMA) as monomer components.

[0017] In the monomer component, the proportion of glycidyl (meth)acrylate is preferably 5 to 98 mol%, and the proportion of stearyl (meth)acrylate is preferably 2 to 95 mol%. More preferably, the proportion of glycidyl (meth)acrylate is 5 to 50 mol%, and the proportion of stearyl (meth)acrylate is 50 to 95 mol%. Even more preferably, the proportion of glycidyl (meth)acrylate is 5 to 25 mol%, and the proportion of stearyl (meth)acrylate is 75 to 95 mol%. Among them, it is particularly preferable that the proportion of glycidyl methacrylate is 5 to 98 mol%, and the proportion of stearyl methacrylate is 2 to 95 mol%. More particularly preferably, the proportion of glycidyl methacrylate is 5 to 50 mol%, and the proportion of stearyl methacrylate is 50 to 95 mol%.

[0018] The copolymer is preferably formed by polymerizing a monomer component containing 2-hydroxyethyl (meth)acrylate. In the present invention, 2-hydroxyethyl (meth)acrylate refers to 2-hydroxyethyl methacrylate or 2-hydroxyethyl acrylate. In the present invention, not only the case where 2-hydroxyethyl methacrylate or 2-hydroxyethyl acrylate is contained alone, but also the case where a mixture of 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate is contained is included. By forming the copolymer by polymerizing a monomer component containing 2-hydroxyethyl (meth)acrylate, the fracture resistance characteristics can be particularly improved. Among them, it is more preferable that the copolymer is formed by polymerizing a monomer component containing 2-hydroxyethyl methacrylate (HEMA). In the present invention, it is more preferable that the copolymer is formed by polymerizing a monomer component containing glycidyl methacrylate (GMA), stearyl methacrylate (SMA), and 2-hydroxyethyl methacrylate (HEMA). Examples of such a copolymer include a terpolymer obtained by polymerizing glycidyl methacrylate (GMA), stearyl methacrylate (SMA), and 2-hydroxyethyl methacrylate (HEMA) as monomer components.

[0019] When the copolymer is obtained by polymerizing a monomer component further containing 2-hydroxyethyl (meth)acrylate, in the monomer component, the proportion of glycidyl (meth)acrylate is 4 to 51 mol%, the proportion of stearyl (meth)acrylate is 2 to 35 mol%, and the proportion of 2-hydroxyethyl (meth)acrylate is preferably 27 to 94 mol%, the proportion of glycidyl (meth)acrylate is preferably 10 to 40 mol%, the proportion of stearyl (meth)acrylate is preferably 10 to 32 mol%, and the proportion of 2-hydroxyethyl (meth)acrylate is preferably 35 to 80 mol%, and the proportion of glycidyl (meth)acrylate is preferably 20 to 30 mol%, the proportion of stearyl (meth)acrylate is preferably 20 to 30 mol%, and the proportion of 2-hydroxyethyl (meth)acrylate is more preferably 40 to 60 mol%. Among them, the proportion of glycidyl methacrylate is 4 to 51 mol%, the proportion of stearyl methacrylate is 2 to 35 mol%, and the proportion of 2-hydroxyethyl methacrylate is preferably 27 to 94 mol%, the proportion of glycidyl methacrylate is preferably 10 to 40 mol%, the proportion of stearyl methacrylate is preferably 10 to 32 mol%, and the proportion of 2-hydroxyethyl methacrylate is particularly preferably 35 to 80 mol%.

[0020] The copolymer may also be obtained by polymerizing a monomer component further containing methyl (meth)acrylate. In the present invention, methyl (meth)acrylate refers to methyl methacrylate or methyl acrylate. In the present invention, not only the case where methyl methacrylate or methyl acrylate is contained alone but also the case where a mixture of methyl methacrylate and methyl acrylate is contained is included. By the copolymer being obtained by polymerizing a monomer component containing methyl (meth)acrylate as a monomer component, the melting point of the copolymer can be increased. As a result of being able to increase the melting point of the copolymer, as will be described later, weighing etc. are performed as a solid in the production stage, so that handling becomes easy. Among these, it is preferable that the copolymer is formed by polymerizing a monomer component containing methyl methacrylate (MMA). In the present invention, it is more preferable that the copolymer is formed by polymerizing a monomer component containing glycidyl methacrylate (GMA), stearyl methacrylate (SMA), 2-hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA). Examples of such a copolymer include a quaternary copolymer obtained by polymerizing glycidyl methacrylate (GMA), stearyl methacrylate (SMA), 2-hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA) as monomer components.

[0021] When the copolymer is formed by polymerizing a monomer component further containing methyl (meth) acrylate, in the monomer component, the proportion of glycidyl (meth) acrylate is 4 to 46 mol%, the proportion of stearyl (meth) acrylate is 1 to 20 mol%, the proportion of 2-hydroxyethyl (meth) acrylate is 20 to 87 mol%, and the proportion of methyl (meth) acrylate is preferably 6 to 44 mol%. More preferably, the proportion of glycidyl (meth) acrylate is 10 to 40 mol%, the proportion of stearyl (meth) acrylate is 5 to 17 mol%, the proportion of 2-hydroxyethyl (meth) acrylate is 30 to 75 mol%, and the proportion of methyl (meth) acrylate is 8 to 35 mol%. Even more preferably, the proportion of glycidyl (meth) acrylate is 20 to 35 mol%, the proportion of stearyl (meth) acrylate is 7 to 15 mol%, the proportion of 2-hydroxyethyl (meth) acrylate is 40 to 63 mol%, and the proportion of methyl (meth) acrylate is 10 to 20 mol%. Among them, it is particularly preferable that the proportion of glycidyl methacrylate is 4 to 46 mol%, the proportion of stearyl methacrylate is 1 to 20 mol%, the proportion of 2-hydroxyethyl methacrylate is 20 to 87 mol%, and the proportion of methyl methacrylate is 6 to 44 mol%. More particularly preferably, the proportion of glycidyl methacrylate is 10 to 40 mol%, the proportion of stearyl methacrylate is 5 to 17 mol%, the proportion of 2-hydroxyethyl methacrylate is 30 to 75 mol%, and the proportion of methyl methacrylate is 8 to 35 mol%.

[0022] The copolymer may be in any form such as a random copolymer, a block copolymer, an alternating copolymer, etc. In particular, a random copolymer is preferred.

[0023] In the present invention, the copolymer is preferably solid at room temperature. By being such a copolymer, the weighing of the copolymer becomes easy at the production stage of the rubber composition. Also, at the kneading stage of the rubber composition, it becomes easier to charge the copolymer into the mixer. Furthermore, since fluctuations in the amount of the copolymer charged into the rubber composition between batches can be suppressed, there is also an advantage that compositional fluctuations between batches can be suppressed. There is no particular limitation on the form of the copolymer as long as it is in a solid state, and it can be used for kneading the rubber composition in the form of granules, powder, or the like. In the present invention, "room temperature" refers to 25 ± 5°C.

[0024] In the present invention, the polystyrene-reduced weight average molecular weight of the copolymer is preferably 2,000 to 20,000. By the polystyrene-reduced weight average molecular weight being 2,000 or more, the copolymer becomes solid at room temperature. Also, when it is made into a rubber composition mixed with a rubber component, it is possible to obtain a tire that is excellent in ice performance and fracture resistance without sacrificing low fuel consumption. The polystyrene-reduced weight average molecular weight of the copolymer is more preferably 2,300 or more, and even more preferably 2,500 or more. On the other hand, considering the miscibility with the rubber component, the polystyrene-reduced weight average molecular weight of the copolymer is more preferably 20,000 or less, even more preferably 18,000 or less, and particularly preferably 15,000 or less.

[0025] In the rubber composition for a tire of the present invention, the content of the copolymer is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component. By the content of the copolymer being 1 part by mass or more, it is possible to obtain a tire that is excellent in ice performance and fracture resistance. On the other hand, from the viewpoint of wear resistance performance, the content of the copolymer with respect to 100 parts by mass of the rubber component is preferably 20 parts by mass or less.

[0026] <Filler> The rubber composition of the present invention contains a filler that reinforces the rubber composition. By the rubber composition containing a filler, the strength of the vulcanized rubber portion where the rubber composition is vulcanized can be increased. In the present invention, from the viewpoint of improving the performance on ice and fracture resistance characteristics by the interaction with the above copolymer, it is preferable to contain silica as a filler.

[0027] <<Silica>> In the present invention, the type of silica is not particularly limited, and examples include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. Among these, wet silica is preferable. These silicas may be used alone or in combination of two or more. Also, the cetyltrimethylammonium bromide specific surface area (CTAB) of the silica used in the present invention is not particularly limited. For example, the cetyltrimethylammonium bromide specific surface area (CTAB) of silica is preferably 40 to 350 m 2 / g, more preferably 100 to 250 m 2 / g. The CTAB specific surface area of silica is a value measured by a method conforming to the method of ASTM-D3765-80.

[0028] The content of silica in the rubber composition is not particularly limited and can be appropriately selected according to the required performance. However, from the viewpoint of achieving both fracture resistance characteristics and performance on ice at a higher level while suppressing the deterioration of low heat build-up, the content of silica is preferably 5 to 120 parts by mass, more preferably 15 to 100 parts by mass, based on 100 parts by mass of the rubber component.

[0029] The rubber composition for tires of the present invention preferably further contains carbon black as a filler. Also, the rubber composition for tires of the present invention may contain inorganic fillers such as clay, talc, calcium carbonate, aluminum hydroxide, etc., in addition to silica and carbon black.

[0030] <<Carbon black>> The carbon black is not particularly limited, and examples thereof include carbon blacks of GPF, FEF, HAF, ISAF, and SAF grades. These carbon blacks may be used alone or in combination of two or more.

[0031] From the viewpoint of wear resistance performance, the content of carbon black in the rubber composition is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, based on 100 parts by mass of the rubber component. Further, from the viewpoint of reducing rolling resistance, the content of carbon black in the rubber composition is preferably 70 parts by mass or less, more preferably 50 parts by mass or less, based on 100 parts by mass of the rubber component.

[0032] The total of the content of silica and the content of carbon black is preferably 25 to 130 parts by mass, more preferably 50 to 90 parts by mass.

[0033] <Blowing agent, thermally expandable microcapsule, metal sulfate, porous cellulose particles> The rubber composition for a tire of the present invention contains at least one void-introducing agent selected from the group consisting of a blowing agent, a thermally expandable microcapsule, a metal sulfate, porous cellulose particles, and a lignin derivative.

[0034] When the rubber composition for a tire contains a blowing agent, bubbles are generated in the vulcanized rubber by the blowing agent during vulcanization of the rubber composition, and the vulcanized rubber can be made into a foamed rubber. Even when the rubber composition for a tire contains thermally expandable microcapsules, bubbles are generated in the vulcanized rubber by the thermally expandable microcapsules during vulcanization of the rubber composition, and the vulcanized rubber can be made into a foamed rubber. Since the foamed rubber has flexibility, the tire surface using the vulcanized rubber is likely to adhere to the icy road surface. Further, holes (foam holes) derived from the bubbles are formed on the surface of the vulcanized rubber and the tire surface due to the bubbles, and function as water channels for draining water.

[0035] Metal sulfates have the property of dissolving vulcanized rubber when they come into contact with water. Therefore, when a rubber composition for tires contains a metal sulfate, if the metal sulfate is exposed on the tire surface obtained by vulcanizing the rubber composition, voids will occur in the tire due to the water on the ice and snow road surface, and the water between the tire and the road surface can be removed.

[0036] When a rubber composition for tires contains porous cellulose particles, if the porous cellulose particles are exposed on the tire surface obtained by vulcanizing the rubber composition, the water on the ice and snow road surface will be absorbed by the porous cellulose particles, and the water between the tire and the road surface can be removed. In addition, due to the presence of cellulose, which is a polysaccharide, an interaction between the tire and the water on the ice and snow road surface occurs, so the interaction between the tire and water by the modified polyoxyalkylene glycol can be further enhanced.

[0037] When a rubber composition for tires contains a lignin derivative, the effect of improving the performance on ice can be enhanced.

[0038] As described above, by containing a blowing agent, thermally expandable microcapsules, a metal sulfate, porous cellulose particles, and a lignin derivative in the rubber composition for tires of the present invention, the resulting vulcanized rubber and tire have voids on the surface. Due to the presence of such voids, the water generated between the tire and the ice and snow road surface can be removed, and the grip force of the tire can be increased. In addition, a tire in which bubbles are generated by a blowing agent or thermally expandable microcapsules is likely to adhere to the ice and snow road surface, and the grip force can be increased. Here, the voids include bubbles, which are spaces in the form of closed systems generated in the vulcanized rubber, and pores, which are spaces in the form of open systems. The pores may penetrate or part of them may be closed.

[0039] As the foaming agent, specifically, for example, azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), dinitrosopentastyrenetetramine, benzenesulfonyl hydrazide derivatives, p,p'-oxybis(benzenesulfonyl hydrazide) (OBSH), ammonium bicarbonate that generates carbon dioxide, sodium bicarbonate, ammonium carbonate, nitrososulfonyl azo compounds that generate nitrogen, N,N'-dimethyl-N,N'-dinitrosophthalamide, toluenesulfonyl hydrazide, p-toluenesulfonyl semicarbazide, p,p'-oxybis(benzenesulfonyl semicarbazide), etc. can be mentioned. Among them, from the viewpoint of production processability, azodicarbonamide (ADCA) and dinitrosopentamethylenetetramine (DPT) are preferable. These foaming agents may be used alone or in combination of two or more. Also, the content of the foaming agent in the rubber composition for tires is not particularly limited, but is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, based on 100 parts by mass of the rubber component.

[0040] The rubber composition for tires may further use urea, zinc stearate, zinc benzenesulfinate, zinc white, etc. as a foaming aid. These may be used alone or in combination of two or more. By using the foaming aid in combination, the foaming reaction can be promoted, the completion degree of the reaction can be increased, and unnecessary deterioration over time can be suppressed.

[0041] The thermally expandable microcapsule has a structure in which a thermally expandable substance is encapsulated in a shell material formed of a thermoplastic resin. The shell material of the thermally expandable microcapsule can be formed of a nitrile-based polymer. In addition, the thermally expandable substance encapsulated in the shell material of the microcapsules has the property of vaporizing or expanding upon heating. For example, at least one selected from the group consisting of hydrocarbons such as isoalkanes and normal alkanes is exemplified. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, 2,2,4-trimethylpentane, etc., and examples of normal alkanes include n-butane, n-propane, n-hexane, n-heptane, n-octane, etc. These hydrocarbons may be used alone or in combination of two or more. A preferred form of the thermally expandable substance is a mixture in which a hydrocarbon gas at normal temperature is dissolved in a hydrocarbon liquid at normal temperature. By using such a mixture of hydrocarbons, sufficient expansion force can be obtained from the low temperature region to the high temperature region in the vulcanization molding temperature range (150°C to 190°C) of the unvulcanized tire. Examples of such thermally expandable microcapsules include those with the trade names "EXPANCEL 091DU-80" or "EXPANCEL 092DU-120" manufactured by Expancel AB of Sweden, or those with the trade names "Matsumoto Microsphere F-85D" or "Matsumoto Microsphere F-100D" manufactured by Matsumoto Yushi Seiyaku Co., Ltd., etc. In addition, the content of the thermally expandable microcapsules in the rubber composition for tires is not particularly limited, but is preferably 1 to 30 parts by mass, more preferably 5 to 20 parts by mass, per 100 parts by mass of the rubber component.

[0042] Specific examples of the metal sulfate include, for example, magnesium sulfate, potassium sulfate, calcium sulfate, etc. These metal sulfates may be used alone or in combination of two or more. In addition, the content of the metal sulfate in the rubber composition for tires is not particularly limited, but is preferably 1 to 40 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the rubber component.

[0043] The porous cellulose particles are cellulose particles having voids due to their porous structure. The particle size of the porous cellulose particles is not particularly limited, but from the viewpoint of abrasion resistance, those having an average particle size of 1000 μm or less are preferred. These porous cellulose particles may be used alone or in combination of two or more. As such porous cellulose particles, those with the trade name "BISCOPAL" manufactured by Rayonier Japan Co., Ltd. can be used. Also, the content of the porous cellulose particles in the rubber composition for tires is not particularly limited, but is preferably 1 to 40 parts by mass, more preferably 5 to 30 parts by mass, based on 100 parts by mass of the rubber component.

[0044] As the lignin derivative, lignin sulfonate is preferably used. Examples of lignin sulfonate include alkali metal salts, alkaline earth metal salts, ammonium salts, and alcohol amine salts of lignin sulfonic acid, and at least one of these can be used in combination. Preferably, they are alkali metal salts and / or alkaline earth metal salts of lignin sulfonic acid, and examples include potassium salts, sodium salts, calcium salts, magnesium salts, lithium salts, barium salts, etc., and mixed salts thereof may also be used. The content of the lignin derivative in the rubber composition for tires is not particularly limited, but is preferably 0.1 to 40 parts by mass, more preferably 0.3 to 20 parts by mass, based on 100 parts by mass of the rubber component.

[0045] In the vulcanized rubber obtained by vulcanizing a tire rubber composition containing a foaming agent and a tire rubber composition containing thermally expandable microcapsules, the foaming ratio is usually 1 to 50%, preferably 5 to 40%. When a foaming agent is blended, if the foaming ratio is 50% or less, the voids on the rubber surface do not become too large, a sufficient contact area can be ensured, the formation of bubbles that function effectively as drainage grooves can be ensured, and the amount of bubbles can be appropriately maintained, so there is no risk of impairing durability. Here, the foaming ratio of the vulcanized rubber means the average foaming ratio Vs, and specifically means the value calculated by the following formula (1). Vs = (ρ0 / ρ1-1) × 100(%) (1) In formula (1), ρ1 is the density of vulcanized rubber (foamed rubber) (g / cm 3 ), and ρ0 is the density of the solid phase in the vulcanized rubber (foamed rubber) (g / cm 3 The density of the vulcanized rubber and the density of the solid phase of the vulcanized rubber are calculated by measuring the mass in ethanol and the mass in air. The foaming ratio can be appropriately changed by changing the type and amount of the foaming agent and foaming assistant.

[0046] The rubber composition for tires of the present invention may contain an organic acid as necessary. The organic acid has the effect of improving the foaming rate of the vulcanized rubber by balancing the rate of decomposition and foaming reaction of the foaming agent and the rate of vulcanization reaction of the rubber composition during vulcanization of the rubber composition. Therefore, by blending an organic acid in the rubber composition, the foaming rate of the vulcanized rubber can be improved while maintaining good workability of the rubber composition, and by applying a rubber composition containing an organic acid to a tire, the tire's performance on ice can be further improved.

[0047] The SP value (solubility parameter) of organic acids is 9.15 to 16.0 (cal / cm 3 ) 1 / 2 It is preferable that the SP value of the organic acid is 9.15 (cal / cm 3 ) 1 / 2 When the SP value of the organic acid is 16.0 (cal / cm 3 ) 1 / 2 By setting the SP value of the organic acid to 10.5 to 14.3 (cal / cm), it is possible to prevent the rubber composition from adhering to manufacturing equipment such as rolls during the production of the rubber composition, thereby preventing the workability of the rubber composition from deteriorating. 3 ) 1 / 2 In this specification, the SP value of an organic acid is calculated according to the Fedors method.

[0048] The organic acid may be any of monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, etc., and may be aliphatic or aromatic. The organic acid may further have a functional group other than a carboxyl group, such as a hydroxyl group, a ketone group, an ethylenically unsaturated group, etc. As the organic acid, those having an aromatic ring (aromatic) are preferred, and monocarboxylic acids are preferred. When the organic acid has an aromatic ring, the adhesion of the rubber composition to the production equipment can be further reduced, and the workability of the rubber composition can be further improved. Regarding stearic acid, which is widely used as a vulcanization aid for rubber compositions, the SP value is 9.12 (cal / cm 3 ) 1 / 2 and it has a low effect of promoting the decomposition of the foaming agent. Examples of aliphatic monocarboxylic acids include palmitic acid and the like. Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and the like. Examples of aromatic monocarboxylic acids include benzoic acid, salicylic acid and the like. Examples of aromatic dicarboxylic acids include phthalic acid and the like. Examples of organic acids having a functional group other than a carboxyl group include tartaric acid, malic acid, maleic acid, glycolic acid, α-ketoglutaric acid and the like. The organic acid may be used alone or in combination of two or more. It is particularly preferable to use benzoic acid as the organic acid. When benzoic acid is blended into the rubber composition, the adhesion of the rubber composition to the production equipment can be further reduced, and the workability of the rubber composition can be further improved.

[0049] From the viewpoints of the workability of the rubber composition, the foaming ratio of the vulcanized rubber, and the ice performance of the tire, the content of the organic acid is preferably 0.1 to 7 parts by mass, more preferably 1.5 to 7 parts by mass, and still more preferably 3 to 7 parts by mass with respect to 100 parts by mass of the rubber component. From the viewpoints of the foaming ratio of the vulcanized rubber and the ice performance of the tire, the total content of the foaming agent and the organic acid is preferably 3 parts by mass or more and less than 15 parts by mass, more preferably in the range of 5 parts by mass or more and less than 15 parts by mass, and still more preferably in the range of 7 parts by mass or more and less than 15 parts by mass with respect to 100 parts by mass of the rubber component. The mass ratio of the blowing agent to the organic acid (blowing agent: organic acid) is preferably in the range of 1:0.5 to 1:1.5, more preferably in the range of 1:0.7 to 1:1.3, from the viewpoints of the foaming ratio of the vulcanized rubber and the ice performance of the tire.

[0050] <Hydrophilic short fiber> The rubber composition for a tire of the present invention may contain hydrophilic short fibers. When the rubber composition for a tire contains hydrophilic short fibers, after vulcanization of the rubber composition, long bubbles are present in the tire (especially the tread), and the long bubbles are exposed on the tire surface due to wear of the tire, forming cavities, which can easily function as drainage channels for efficient drainage. Here, the cavities may be in any shape of a hole shape, a depression shape, or a groove shape. Furthermore, since the short fibers are hydrophilic, the cavities derived from the short fibers formed on the tire surface are likely to absorb water.

[0051] Here, the hydrophilic short fiber refers to a short fiber having a contact angle with water of 5 to 80 degrees. Regarding the contact angle of the hydrophilic short fiber with water, a test piece obtained by forming the hydrophilic short fiber into a smooth plate shape is prepared, and using an automatic contact angle meter DM-301 manufactured by Kyowa Interface Science Co., Ltd., under the conditions of 25 °C and a relative humidity of 55%, water is dropped onto the surface of the test piece, and when observed from the side immediately after that, the angle formed by the straight line formed by the test piece surface and the tangent line of the water droplet surface can be obtained by measuring the angle.

[0052] As the hydrophilic short fiber, a resin having a hydrophilic group in the molecule (sometimes referred to as a hydrophilic resin) can be used, and specifically, it is preferably a resin containing at least one selected from an oxygen atom, a nitrogen atom, and a sulfur atom. For example, resins containing at least one kind of substituent selected from the group consisting of -OH, -COOH, -OCOR (R is an alkyl group), -NH2, -NCO, and -SH can be mentioned. Among these substituents, -OH, -COOH, -OCOR, -NH2, and -NCO are preferable.

[0053] The hydrophilic resin preferably has a small contact angle with water and is hydrophilic to water, but the hydrophilic resin is preferably insoluble in water. Since the hydrophilic resin is insoluble in water, when water adheres to the vulcanized rubber surface and the tire surface, it is possible to prevent the hydrophilic resin from dissolving in the water, and it is possible to retain the water absorption capacity of the voids derived from the short fibers.

[0054] More specifically, examples of the hydrophilic resin having a large contact angle with water and being insoluble in water as described above include ethylene-vinyl alcohol copolymer, vinyl alcohol homopolymer, poly(meth)acrylic acid resin or its ester resin, polyamide resin, polyethylene glycol resin, carboxyvinyl copolymer, styrene-maleic acid copolymer, polyvinylpyrrolidone resin, vinylpyrrolidone-vinyl acetate copolymer, mercaptoethanol and the like. Among them, at least one selected from the group consisting of ethylene-vinyl alcohol copolymer, vinyl alcohol homopolymer, poly(meth)acrylic acid resin, polyamide resin, aliphatic polyamide resin, aromatic polyamide resin, polyester resin, polyolefin resin, polyvinyl alcohol resin, and acrylic resin is preferable, and ethylene-vinyl alcohol copolymer is more preferable.

[0055] The shape of the short fibers is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoint of efficiently forming long air bubbles that can function as micro drainage grooves in the vulcanized rubber obtained by vulcanizing the tire rubber composition containing the short fibers, as the average value of 100 short fibers, the length in the major axis direction is preferably 0.1 mm to 10 mm, and more preferably 0.5 mm to 5 mm. Also, from the same viewpoint, the average diameter (D) of the short fibers is preferably 10 μm to 200 μm, and more preferably 20 μm to 100 μm, as the average value of 100 short fibers. The content of the short fibers in the tire rubber composition is preferably 0.2 to 20 parts by mass, and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the rubber component.

[0056] <Various components> In addition to the components described above, the rubber composition for tires in the present invention may, if necessary, appropriately contain various components commonly used in the rubber industry, such as stearic acid, anti-aging agent, silane coupling agent, zinc white (zinc oxide), vulcanization accelerator, vulcanizing agent, processing improver, resin, wax, oil, etc., within the range that does not harm the object of the present invention.

[0057] [Preparation of rubber composition for tires] The rubber composition for tires of the present invention can be produced by blending the above-described components and kneading them using a kneading machine such as a Banbury mixer, roll, internal mixer, etc. The blending amount of each component is the same as the amount described above as the content in the rubber composition for tires. The kneading of each component may be carried out in one step, but it is preferably carried out in two or more steps. When kneading is carried out in two or more steps, at least the rubber component, the above copolymer, and silica are kneaded in the first step of kneading.

[0058] [Tire] The tire of the present invention is a vulcanized rubber obtained by vulcanizing the rubber composition for tires of the present invention, and is excellent in ice performance and fracture resistance characteristics and has low fuel consumption. The rubber composition for tires of the present invention is particularly preferably used for tread rubber.

Examples

[0059] [Preparation of rubber composition] Each component was kneaded in two steps with the blending composition shown in Table 1 below (the numerical values in the table are parts by mass) to prepare a rubber composition. The details of the components in the table are as follows.

[0060] 1. Rubber component NR: Natural rubber (RSS#3) BR: Modified polybutadiene rubber obtained by the following production method SBR: Modified styrene-butadiene copolymer rubber obtained by the following production method 2. Copolymer Copolymer 1: A methacrylic acid-based random copolymer obtained by polymerizing a monomer component consisting of 10 mol% GMA and 90 mol% SMA, polystyrene-equivalent weight average molecular weight 11,000, granular (room temperature) Copolymer 2: A methacrylic acid-based random copolymer obtained by polymerizing a monomer component consisting of 25 mol% GMA, 25 mol% SMA, and 50 mol% HEMA, polystyrene-equivalent weight average molecular weight 5,000, granular (room temperature) Copolymer 3: A methacrylic acid-based random copolymer obtained by polymerizing a monomer component consisting of 25 mol% GMA, 12.5 mol% SMA, 50 mol% HEMA, and 12.5 mol% MMA, polystyrene-equivalent weight average molecular weight 5,200, granular (room temperature) Copolymer 4: A methacrylic acid-based random copolymer obtained by polymerizing a monomer component consisting of 25 mol% GMA, 12.5 mol% SMA, 50 mol% HEMA, and 12.5 mol% MMA, polystyrene-equivalent weight average molecular weight 13,400, granular (room temperature) The above weight average molecular weight was measured at a measurement temperature of 40 °C using gel permeation chromatography [GPC: HLC-8121GPC / HT manufactured by Tosoh Corporation, column: GMH HR -H(S)HT × 2 pieces, detector: differential refractive index meter (RI)], and was determined based on monodisperse polystyrene. 3. Filler Silica: Silica with a cetyltrimethylammonium bromide specific surface area (CTAB) of 191 m 2 / g Carbon black: SAF grade carbon 4. Silane coupling agent Bis-(triethoxysilylpropyl)-polysulfide 5. Resin C5-based aliphatic hydrocarbon resin 6. Vulcanization accelerator A mixture of a sulfenamide-based vulcanization accelerator and a thiazole-based vulcanization accelerator

[0061] <Method for producing modified polybutadiene rubber> A glass bottle with a rubber stopper and a volume of about 1 liter was dried and purged with nitrogen. Into the glass bottle were charged a cyclohexane solution of dry and purified butadiene and dry cyclohexane, such that a cyclohexane solution containing 15.0% by mass of butadiene was charged in an amount of 330 g. To this was added 0.513 mmol of hexamethyleneimine (HMI). Next, 0.36 mL of tert-butyllithium (1.57 M) and 0.057 mL of 2,2-di(2-tetrahydrofuryl)propane (0.2 N) were added, and polymerization was carried out in a water bath at 50 °C for 4.5 hours. Thereafter, 0.10 mmol of tin(IV) chloride (SnCl4) was added and the reaction was carried out at 50 °C for 1 hour. Thereafter, reprecipitation was carried out in isopropanol containing a trace amount of 2,2'-methylene-bis(4-ethyl-6-t-butylphenol) (NS-5), and then drying was carried out in a drum to obtain a modified butadiene rubber. The yield was almost 100%.

[0062] <Process for producing modified styrene-butadiene copolymer rubber> Into a dried and nitrogen-purged 800 mL pressure-resistant glass container were added a cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene so that the amounts were 67.5 g of 1,3-butadiene and 7.5 g of styrene. 0.6 mmol of 2,2-ditetrahydrofurylpropane was added, and after adding 0.8 mmol of n-butyllithium, polymerization was carried out at 50 °C for 1.5 hours. The polymerization conversion rate at this time was almost 100%. To this polymerization reaction system, 0.72 mmol of [N,N-bis(trimethylsilyl)-(3-amino-1-propyl)](methyl)(diethoxy)silane was added, and a modification reaction was carried out at 50 °C for 30 minutes. Thereafter, 2 mL of a 5% by mass isopropanol solution of 2,6-di-t-butyl-p-cresol (BHT) was added to stop the reaction, and drying was carried out according to a conventional method to obtain a modified styrene-butadiene copolymer rubber. As a result of measuring the microstructure of the obtained modified styrene-butadiene copolymer rubber, the bound styrene content was 10% by mass, the vinyl content of the butadiene moiety was 40%, and the polystyrene-equivalent peak molecular weight obtained by gel permeation chromatography was 200,000.

[0063] [Evaluation] 1. Rolling resistance (low fuel consumption evaluation) The rubber compositions of the examples and comparative examples were vulcanized at 145 °C for 33 minutes to obtain vulcanized rubbers. Test pieces were obtained from the obtained vulcanized rubbers, and using a viscoelasticity measuring machine, the loss tangent (tan δ) of the vulcanized rubber was measured under the conditions of dynamic strain: 10%, frequency: 15 Hz, and measurement temperature: 30 °C. Taking the tan δ of the vulcanized rubber of Comparative Example 1 as 100, the measured values of each example and each comparative example were expressed as an index (RR index). The results are shown in Table 1. The larger the index, the smaller the rolling resistance and the better the low fuel consumption performance.

[0064] 2. Ice performance evaluation The vulcanized rubber was cut into pieces of 25 mm × 25 mm and 2 mm in thickness. The frictional force generated when the cut sample was pressed against the fixed ice and reciprocated was detected with a load cell, and the dynamic friction coefficient (μ) was calculated. Taking the dynamic friction coefficient of Comparative Example 1 as 100, it was expressed as an index by the following formula. Ice performance index = (Dynamic friction coefficient of vulcanized rubber other than Comparative Example 1 / Dynamic friction coefficient of vulcanized rubber of Comparative Example 1) × 100 The larger the ice performance index, the better the ice performance.

[0065] 3. Fracture resistance performance For each vulcanized rubber, a tensile test was conducted at room temperature in accordance with JIS K6301-1995, and the tensile strength (TB) was measured. Taking the tensile strength of the test piece of Comparative Example 1 as 100, it was expressed as an index by the following formula. Fracture resistance index = (Tensile strength of test piece other than Comparative Example 1 / Tensile strength of test piece of Comparative Example 1) × 100 The larger the fracture resistance performance index, the more difficult it is for the tire to break and the better the fracture resistance performance. The allowable range of the fracture resistance performance index is 98 or more.

[0066]

Table 1

[0067] The tire using the rubber composition of Example 1 had the same level of fracture resistance characteristics as Comparative Example 1, but the results showed that it was excellent in ice performance and low fuel consumption. The tires using the rubber compositions of Examples 2 to 4 were excellent in all of ice performance, low fuel consumption, and fracture resistance characteristics compared to the comparative examples.

Claims

1. A rubber component, A copolymer obtained by polymerizing a monomer component containing glycidyl (meth) acrylate and stearyl (meth) acrylate, A rubber composition for tires containing, In the monomer component, the proportion of the glycidyl (meth) acrylate is 5 to 98 mol%, and the proportion of the stearyl (meth) acrylate is 2 to 95 mol%. A rubber composition for tires.

2. The rubber composition for tires according to claim 1, wherein the copolymer is obtained by further polymerizing a monomer component containing 2-hydroxyethyl (meth) acrylate.

3. In the monomer component, the proportion of the glycidyl (meth) acrylate is 4 to 51 mol%, the proportion of the stearyl (meth) acrylate is 2 to 35 mol%, and the proportion of the 2-hydroxyethyl (meth) acrylate is 27 to 94 mol%. The rubber composition for tires according to claim 2.

4. The rubber composition for tires according to claim 2 or claim 3, wherein the copolymer is obtained by further polymerizing a monomer component containing methyl (meth) acrylate.

5. In the monomer component, the proportion of the glycidyl (meth) acrylate is 4 to 46 mol%, the proportion of the stearyl (meth) acrylate is 1 to 20 mol%, the proportion of the 2-hydroxyethyl (meth) acrylate is 20 to 87 mol%, and the proportion of the methyl (meth) acrylate is 6 to 44 mol%. The rubber composition for tires according to claim 4.

6. The rubber composition for tires according to any one of claims 1 to 5, wherein the copolymer is solid at room temperature.

7. The rubber composition for tires according to any one of claims 1 to 6, wherein the polystyrene-reduced weight average molecular weight of the copolymer is 2,000 to 20,000.

8. The rubber composition for tires according to any one of claims 1 to 7, containing 0.1 to 20 parts by mass of the copolymer with respect to 100 parts by mass of the rubber component.

9. The rubber composition for tires according to any one of claims 1 to 8, further containing silica as a filler.

10. The rubber composition for tires according to any one of claims 1 to 9, further containing at least one selected from the group consisting of a foaming agent, a thermally expandable microcapsule, a metal sulfate, porous cellulose particles, and a lignin derivative.

11. The rubber composition for a tire according to any one of claims 1 to 10, wherein the rubber component contains natural rubber, polybutadiene rubber, and styrene-butadiene rubber.

12. The rubber composition for a tire according to claim 11, wherein the proportion of the natural rubber is 20 to 60% by mass, the proportion of the polybutadiene rubber is 20 to 60% by mass, and the proportion of the styrene-butadiene rubber is 10 to 40% by mass.

13. A tire using a vulcanizate of the rubber composition for a tire according to any one of claims 1 to 12.

14. The tire according to claim 13, wherein the tread rubber is a vulcanizate of the rubber composition for a tire according to any one of claims 1 to 12.

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