JP6862893B2 - Rubber composition for studless tires - Google Patents

Description

The present invention relates to a rubber composition for a studless tire that improves on-ice performance, wet grip performance and wear resistance.

In order to improve the performance of studless tires on ice, it is known to increase the surface roughness (unevenness) of the tread rubber and improve the suppleness (flexibility and adhesiveness) at low temperatures. When the surface roughness is increased, the concave portion takes in the water film existing on the ice and the convex portion comes into contact with the ice upper surface, which has the effect of increasing the contact area with the ice upper surface as compared with the tread rubber having a smooth surface. Conceivable. For this reason, a method of increasing the roughness of the entire rubber by blending a foaming agent, heat-expandable microcapsules, or the like with the tread rubber is common. However, although rubber having a large surface roughness takes in a water film, on the other hand, the area that can come into contact with the ice surface is reduced, so that it can be said that the effect of improving the performance on ice due to the surface roughness is limited. Further, when a foaming agent or a heat-expandable microcapsule is blended, there is a problem that the wear resistance of the tread rubber is lowered.

By improving the suppleness of the tread rubber at low temperatures, the contact area with the top surface of the ice can be increased and the performance on ice can be improved. Therefore, Patent Documents 1 and 2 propose that a tire tread rubber composition is blended with liquid polyisoprene having a carboxyl group or a hydroxyl group and / or liquid polybutadiene. However, the rubber composition containing these liquid polyisoprene and liquid polybutadiene has a problem that the effect of improving the performance on ice is not always sufficient, and the wet grip performance and wear resistance of the tread rubber are lowered.

However, in recent years, the expectations of consumers for improving on-ice performance, wet grip performance, and wear resistance of studless tires have become higher, and further improvements have been required.

Japanese Unexamined Patent Publication No. 2007-31521 Japanese Unexamined Patent Publication No. 2007-31521

An object of the present invention is to provide a rubber composition for a studless tire that improves on-ice performance, wet grip performance and wear resistance.

Rubber composition for a studless tire of the present invention to achieve the above object, 100 parts by mass of the diene rubber, carbon black and / or white filler 30 to 100 parts by weight, and (meth) acrylic-based liquid polymer 30 A low molecular weight polymer or epoxy containing only a mass portion and the (meth) acrylic liquid polymer is only a (meth) acrylic monomer which is an alkyl (meth) acrylate and / or an alicyclic alkyl (meth) acrylate. It said modified by groups and / or alkoxysilyl group is a low molecular weight polymer, the glass transition temperature of its is -30 ° C. or less, the weight average molecular weight is characterized in that it is a 1,000 to 15,000.

Studless tire rubber composition of the present invention has a glass transition temperature of -30 ° C. or less, a weight average molecular weight of Ru der 1,000 to 15,000 (meth) acrylic-based liquid polymer, (meth) acrylic acid alkyl and / or Since a low molecular weight polymer consisting only of a (meth) acrylic monomer which is an alicyclic alkyl (meth) acrylic acid, or the low molecular weight polymer modified with an epoxy group and / or an alkoxysilyl group is blended, the polymer is blended on ice. Performance, wet grip performance and abrasion resistance can be improved beyond the conventional level.

Further, the (meth) acrylic liquid polymer is preferably modified with at least one selected from a hydroxy group, a carboxy group, an epoxy group and an alkoxysilyl group. In addition to these functional groups, it is preferable that the functional group is further modified with a long-chain alkyl group.

The studless tire having a tread portion made of the rubber composition for a studless tire of the present invention can improve on-ice performance, wet grip performance and wear resistance more than the conventional level.

The diene rubber that composes the rubber composition for studless tires of the present invention is not particularly limited, and is, for example, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, styrene-isoprene rubber, styrene-isoprene-butadiene. Examples include rubber, acrylonitrile-butadiene rubber and the like. Of these, natural rubber, butadiene rubber, and styrene-butadiene rubber are preferable, and natural rubber and butadiene rubber are more preferable. These diene rubbers may be modified diene rubbers whose molecular chain ends and / or side chains are modified with an epoxy group, a carboxy group, an amino group, a hydroxy group, an alkoxy group, a silyl group, an amide group, or the like.

The average glass transition temperature of the above-mentioned diene rubber is preferably −50 ° C. or lower, more preferably −60 ° C. to −100 ° C. By keeping the average glass transition temperature of diene rubber to -50 ° C or less, the suppleness of the rubber compound at low temperatures is maintained and the adhesion to the ice surface is increased, so it is suitable for the tread part of studless tires. can do. The glass transition temperature is set to the midpoint temperature of the transition region by measuring the thermogram under the condition of a heating rate of 20 ° C./min by differential scanning calorimetry (DSC). When the diene-based rubber is an oil-extended product, the glass transition temperature of the diene-based rubber is set in a state where the oil-extended component (oil) is not contained. The average glass transition temperature is the total (weighted average value of the glass transition temperature) obtained by multiplying the glass transition temperature of each diene rubber by the mass fraction of each diene rubber. The total mass fraction of all diene rubbers is set to 1.

The rubber composition for a studless tire of the present invention contains a carbon black and / or white filler. The total amount of the carbon black and / or white filler is 30 to 100 parts by mass, preferably 40 to 90 parts by mass, and more preferably 45 to 45 parts by mass with respect to 100 parts by mass of the diene rubber. It is 80 parts by mass. By setting the blending amount of the carbon black and the white filler to 30 parts by mass or more, the mechanical properties of the rubber composition can be improved and the wear resistance can be improved. Further, by setting the blending amount of the carbon black and the white filler to 100 parts by mass or less, the suppleness of the rubber composition can be maintained and the performance on ice can be ensured. In addition, it is possible to suppress an increase in weight when the tire is used.

Examples of the carbon black include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPF, HMF, and SRF, and these may be used alone or in combination of two or more. The nitrogen adsorption specific surface area of carbon black is not particularly limited, but is preferably 70 to 240 m ² / g, and more preferably 90 to ²⁰⁰ m 2 / g. By setting the nitrogen adsorption specific surface area of carbon black to 70 m ² / g or more, the mechanical properties and wear resistance of the rubber composition can be ensured. Further, by setting the nitrogen adsorption specific surface area of carbon black to 240 m ² / g or less, the performance on ice can be improved. In the present specification, the nitrogen adsorption specific surface area of carbon black shall be measured in accordance with JIS K6217-2.

Examples of the white filler include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, and calcium sulfate. These may be used alone or in combination of two or more. Among them, silica is preferable, and the performance on ice can be improved.

Examples of silica include wet silica (hydrous silicic acid), dry silica (silicic anhydride), calcium silicate, aluminum silicate and the like, and these may be used alone or in combination of two or more. The CTAB adsorption specific surface area of silica is not particularly limited, but is preferably 80 to 260 m ² / g, and more preferably 140 to ²⁰⁰ m 2 / g. By setting the CTAB adsorption specific surface area of silica to 80 m ² / g or more, the wear resistance of the rubber composition can be ensured. Further, by setting the CTAB adsorption specific surface area of silica to 200 m ² / g or less, wet performance and low rolling resistance can be improved. In the present specification, the CTAB specific surface area of silica is a value measured by ISO 5794.

In the present invention, a silane coupling agent may be blended together with silica. By blending the silane coupling agent, the dispersibility of silica with respect to the diene rubber can be improved, and the balance between wear resistance and on-ice performance can be further improved.

The type of silane coupling agent is not particularly limited as long as it can be used in a rubber composition containing silica, and for example, bis- (3-triethoxysilylpropyl) tetrasulfide and bis (3-) Sulfur-containing silane coupling agents such as triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane can be exemplified. ..

The blending amount of the silane coupling agent is preferably 3 to 15% by mass, more preferably 5 to 10% by mass, based on the weight of silica. If the blending amount of the silane coupling agent is less than 3% by mass of the silica blending amount, the silica dispersion may not be sufficiently improved. If the blending amount of the silane coupling agent exceeds 15% by mass of the silica blending amount, the silane coupling agents are condensed with each other, and the desired hardness and strength in the rubber composition cannot be obtained.

The rubber composition for a studless tire of the present invention improves on-ice performance and wear resistance by blending a specific (meth) acrylic liquid polymer that is incompatible with diene-based rubber. Here, "incompatible with diene-based rubber" does not mean incompatible with all types of rubber components included in diene-based rubber, but specifically contained in the rubber composition for studless tires. It may be incompatible with the diene rubber. A specific (meth) acrylic liquid polymer that is incompatible with the diene rubber forms a phase-separated structure with the diene rubber, so that the performance on ice can be improved. As used herein, the term "liquid polymer" refers to a polymer that is liquid, that is, has fluidity at a temperature of room temperature or higher and at least 20 ° C.

The (meth) acrylic liquid polymer is blended in an amount of 1 to 30 parts by mass, preferably 4 to 30 parts by mass, and more preferably 7 to 25 parts by mass with respect to 100 parts by mass of the diene rubber. By setting the blending amount of the (meth) acrylic liquid polymer to 1 to 30 parts by mass, it is possible to improve the on-ice performance and the wet grip performance more than the conventional level while ensuring a high level of wear resistance.

The glass transition temperature of the (meth) acrylic liquid polymer that is incompatible with the diene rubber is −30 ° C. or lower, preferably −30 ° C. to −90 ° C., and more preferably −35 ° C. to −80 ° C. By keeping the glass transition temperature of the (meth) acrylic liquid polymer below -30 ° C, the suppleness of the rubber compound at low temperatures is maintained and the adhesion to the ice surface is increased, so it can be used on the tread of studless tires. It can be preferably used. The glass transition temperature is set to the midpoint temperature of the transition region by measuring the thermogram under the condition of a heating rate of 20 ° C./min by differential scanning calorimetry (DSC).

The weight average molecular weight of the (meth) acrylic liquid polymer is 1000 to 15000, preferably 1500 to 13000, and more preferably 2000 to 10000. By setting the weight average molecular weight of the (meth) acrylic liquid polymer to 1000 or more, bleed-out of the (meth) acrylic liquid polymer can be suppressed while improving the performance on ice. Further, by setting the weight average molecular weight of the (meth) acrylic liquid polymer to 15,000 or less, the performance on ice can be improved. In the present specification, the weight average molecular weight of the (meth) acrylic liquid polymer shall be measured by gel permeation chromatography (GPC) and determined by standard polystyrene conversion.

The (meth) acrylic liquid polymer constituting the rubber composition for a studless tire of the present invention is a low molecular weight polymer composed only of a (meth) acrylic monomer. The (meth) acrylic monomer is not particularly limited, but is limited to methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, and (meth) acrylic. Butyl acid, isobutyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, neopentyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate Alkyl (meth) acrylate, such as lauryl (meth) acrylate, tridecyl (meth) acrylate and stearyl (meth) acrylate; cyclohexyl (meth) acrylate, isobornyl (meth) acrylate and tri (meth) acrylate. (Meta) alicyclic alkyl acrylates such as cyclodecynyl; ε-caprolactone of hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxypropyl (meth) acrylate and hydroxyethyl (meth) acrylate Hydroxyalkyl (meth) acrylates such as addition reactants; 2-methoxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, chloroethyl (meth) acrylate, trifluoroethyl (meth) acrylate and (meth) ) Heteroatom-containing (meth) acrylic acid esters such as tetrahydrofurfuryl acrylate can be mentioned, but is not limited thereto. Further, as these acrylic monomers, one kind or two or more kinds can be used. Further, the (meth) acrylic monomer may be obtained by copolymerizing a (meth) acrylic acid ester with another copolymerizable monomer. Examples of copolymerizable monomers include vinyl monomers such as α-olefins, vinyl esters and vinyl ethers. The alkyl group constituting the (meth) acrylic monomer described above may have any functional group such as an alkoxy group, an alkyl group, a hydroxy group, a carboxy group and an epoxy group. These (meth) acrylic monomers can be polymerized alone or in combination of a plurality of types. The type and polymerization ratio of the (meth) acrylic monomer can be arbitrarily set in order to adjust the characteristics such as the glass transition temperature.

The (meth) acrylic liquid polymer preferably contains 50 to 95% by mass of methacrylic acid ester. If this ratio is less than 50% by mass, the performance on ice deteriorates, and if it is more than 95% by mass, the vinyl polymer (B) does not have a sufficient plasticizing effect and the performance on ice deteriorates.

In the present invention, the (meth) acrylic liquid polymer may be modified with at least one selected from a hydroxy group, a carboxy group, an epoxy group and an alkoxysilyl group. These functional groups can exist as side chains to the skeleton (main chain) of the (meth) acrylic liquid polymer. In addition, these functional groups can act on the white filler, particularly silica, to improve its dispersibility. Conventionally, modified liquid rubbers such as liquid isoprene rubbers and liquid butadiene rubbers modified with hydroxy groups and carboxy groups have been blended in rubber compositions for tires, but these modified liquid rubbers are compatible with diene rubbers. Since it is incorporated, the effect of improving the dispersibility of silica could not be sufficiently obtained. On the other hand, in the present invention, a (meth) acrylic liquid polymer that is incompatible with the diene rubber is blended and modified with a hydrophilic functional group particularly selected from a hydroxy group, a carboxy group, an epoxy group and an alkoxysilyl group. As a result, the dispersibility of the silica can be further improved, and the rubber composition can be imparted with suppleness at low temperatures. Further, by modifying the (meth) acrylic liquid polymer with a hydrophilic functional group, it is possible to impart hydrophilicity to the tread rubber and further improve the wet grip performance.

The (meth) acrylic liquid polymer may be modified with the above-mentioned hydrophilic functional group and may be modified with a long-chain alkyl group. By modifying the (meth) acrylic liquid polymer with hydrophilic functional groups and long-chain alkyl groups, the affinity for rubber is improved and the performance on ice is improved while bleeding out of the (meth) acrylic liquid polymer. Can be suppressed. Examples of the hydrophilic functional group used together with the long-chain alkyl group include a hydroxy group, a carboxy group, an epoxy group and an alkoxysilyl group, and an alkoxysilyl group is particularly preferable. Examples of the long-chain alkyl group include preferably an alkyl group having 1 to 24 carbon atoms, and more preferably an alkyl group having 3 to 18 carbon atoms.

In the present invention, as the epoxy group, at least one selected from the group consisting of an epoxy group, a glycidyl group, and an alkyl group having an epoxy group can be mentioned. The alkoxysilyl group may be any of an alkoxydialkylsilyl group, a dialkoxyalkylsilyl group, and a trialkoxysilyl group. Examples of the alkoxydialkylsilyl group include a methoxydimethylsilyl group, a methoxydiethylsilyl group, an ethoxydimethylsilyl group, an ethoxydiethylsilyl group, and the like. Examples of the dialkoxyalkylsilyl group include a dimethoxymethylsilyl group, a dimethoxyethylsilyl group, a diethoxymethylsilyl group, and a diethoxyethylsilyl group. Examples of the trialkoxysilyl group include a trimethoxysilyl group, a triethoxysilyl group, a tripropoxysilyl group, and a tributoxysilyl group.

The rubber composition for studless tires of the present invention is generally used for rubber compositions for tires such as vulcanization or cross-linking agents, vulcanization accelerators, anti-aging agents, plasticizers, processing aids, terpene resins, and thermosetting resins. Various additives to be used can be blended within a range that does not impair the object of the present invention. In addition, such additives can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or cross-linking. The blending amount of these additives can be a conventional general blending amount as long as it does not contradict the object of the present invention. The rubber composition for a studless tire of the present invention can be produced by mixing each of the above components using a normal rubber kneading machine, for example, a Banbury mixer, a kneader, a roll, or the like.

The rubber composition for a studless tire of the present invention is suitable for forming a tread portion of a studless tire. The studless tire in which the tread rubber is composed of the rubber composition for a studless tire of the present invention can improve the performance on ice and the wear resistance more than the conventional level.

Hereinafter, the present invention will be further described with reference to Examples, but the scope of the present invention is not limited to these Examples.

Twelve types of rubber compositions for studless tires having the common composition shown in Table 2 and containing the (meth) acrylic liquid polymer, liquid rubber, and aroma oil shown in Table 1 (Examples 1 to 5, Standard Examples). In preparing Comparative Examples 1 to 6), the components excluding sulfur, the vulcanization accelerator, and the heat-expandable microcapsules were kneaded in a 1.7 L polymer mixer for 5 minutes, and when the temperature reached 145 ° C, they were released and cooled. It was made into a master batch. Sulfur, a vulcanization accelerator, and heat-expandable microcapsules were added to the obtained masterbatch and kneaded with an open roll at 70 ° C. to obtain 12 kinds of rubber compositions for studless tires. The blending amounts of the (meth) acrylic liquid polymer, liquid rubber, and aroma oil shown in Table 1 are expressed as parts by mass with respect to 100 parts by mass of the diene rubber shown in Table 2.

The obtained rubber composition for a studless tire is vulcanized at 170 ° C. for 10 minutes using a mold having a predetermined shape (inner dimensions; length 150 mm, width 150 mm, thickness 2 mm) to prepare a vulcanized rubber test piece. did. Using the obtained vulcanized rubber test piece, the frictional performance on ice and the wear resistance were measured by the test method shown below. In addition, the obtained rubber composition for studless tires was used to evaluate tan δ at 0 ° C., which is an index of wet grip performance.

Friction performance on ice The obtained vulcanized rubber test piece is attached to a flat cylindrical base rubber, and using an inside drum type friction tester on ice, the measurement temperature is -1.5 ° C, the load is 5.5 kg / cm ² , and the drum. The coefficient of friction on ice was measured under the condition of a rotation speed of 25 km / h. The obtained coefficient of friction on ice is shown in the column of "performance on ice" as an index with the value of the standard example as 100. The larger the index value, the larger the coefficient of friction on ice and the better the performance on ice.

Wet grip performance Using the obtained rubber composition for studless tires, using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho) in accordance with JIS K6394: 2007, stretch deformation strain rate 10 ± 2%, frequency 20 Hz , Tan δ (0 ° C.) was measured under the condition of a temperature of 0 ° C. The results are shown in the "Wet performance" column, with the value of the standard example as an index of 100. The larger this index is, the better the wet grip performance is.

Abrasion resistance The obtained vulcanized rubber test piece is used in accordance with JIS K6264 with a lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.) at a temperature of 20 ° C., a load of 39 N, a slip ratio of 30%, and a time of 4 minutes. The amount of wear was measured under the conditions. The obtained result was used as an index to set the reciprocal of the standard example to 100, and is shown in the "wear resistance" column. The larger this index is, the better the wear resistance is, and if the index is 95 or more, it can be put into practical use.

The types of raw materials used in Table 1 are shown below.
-Liquid polymer A: Unmodified (meth) acrylic liquid polymer, ARUFON UP-1110 manufactured by Toagosei Co., Ltd., weight average molecular weight of 3500, glass transition temperature of -64 ° C.
-Liquid polymer B: (meth) acrylic liquid polymer having an epoxy group, ARUFON UG-4010 manufactured by Toagosei Co., Ltd., weight average molecular weight of 3700, glass transition temperature of -57 ° C.
-Liquid polymer C: (meth) acrylic liquid polymer having an alkoxysilyl group, ARUFON US-6150 manufactured by Toagosei Co., Ltd., weight average molecular weight of 7000, glass transition temperature of -48 ° C.
-Liquid BR-1: Unmodified liquid polybutadiene, RICON 130 manufactured by Clay Valley, weight average molecular weight 2500, glass transition temperature -100 ° C.
-Liquid IR: Unmodified liquid polyisoprene, Kuraray LIR-30, weight average molecular weight 3000, glass transition temperature -63 ° C
-Liquid BR-2: Epoxy-modified liquid polybutadiene, Clay Valley RICON 657, weight average molecular weight 2500, glass transition temperature -105 ° C.
-Liquid BR-3: Epoxy-modified liquid polybutadiene, JP-200MA manufactured by Nippon Soda Corporation, weight average molecular weight of 2000, glass transition temperature of -10 ° C.
・ Aroma oil: Aroma oil manufactured by Fuji Kosan Co., Ltd.

The types of raw materials used in Table 2 are shown below.
・ Natural rubber: RSS # 3
-Butadiene rubber: Polybutadiene rubber made by Nippon Zeon Corporation Nippon BR1220
-Carbon black: Carbon black seed 6 manufactured by Tokai Carbon Co., Ltd., nitrogen adsorption specific surface area is 119 m ² / g
-Silica: Nippon Silica Industry Co., Ltd. Nipponsil AQ, CTAB adsorption specific surface area is 145 m ² / g
-Coupling agent: Sulfur-containing silane coupling agent, Si69 manufactured by Dexa
・ Zinc oxide: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. ・ Stearic acid: Bead stearic acid manufactured by NOF Co., Ltd. ・ Anti-aging agent: 6PPD manufactured by Flexis Co., Ltd.
・ Microcapsules: Thermally expandable microcapsules, Matsumoto Microsphere F manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.
・ Sulfur: Fine powder sulfur containing Jinhua Ink Oil manufactured by Tsurumi Chemical Industry Co., Ltd. ・ Vulcanization accelerator 1: Noxeller CZ-G (CBS) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
-Vulcanization accelerator 2: Soxinol DG (DPG) manufactured by Sumitomo Chemical Co., Ltd.

As is clear from Table 1, it was confirmed that the rubber compositions for studless tires of Examples 1 to 5 improved the on-ice performance, the wet grip performance and the wear resistance more than the conventional level.

Since the rubber composition for a studless tire of Comparative Example 1 contains liquid polybutadiene instead of the (meth) acrylic liquid polymer, the wet grip performance is inferior.

Since the rubber composition for a studless tire of Comparative Example 2 contains liquid polyisoprene instead of the (meth) acrylic liquid polymer, it is inferior in wear resistance and wet grip performance.

Since the amount of the (meth) acrylic liquid polymer compounded in the rubber composition for a studless tire of Comparative Example 3 is less than 1 part by mass, the on-ice performance, wet grip performance and wear resistance cannot be improved.

The rubber composition for a studless tire of Comparative Example 4 is inferior in wet grip performance and wear resistance because the amount of the (meth) acrylic liquid polymer compounded exceeds 30 parts by mass.

Since the rubber composition for a studless tire of Comparative Example 5 contains an epoxy-modified liquid polybutadiene instead of the (meth) acrylic liquid polymer, the wet grip performance is inferior.

Since the rubber composition for a studless tire of Comparative Example 6 contains a maleic acid-modified liquid polybutadiene instead of the (meth) acrylic liquid polymer, it is inferior in on-ice performance and wear resistance.

Claims (3)

100 parts by mass of diene rubber, carbon black and / or white filler 30 to 100 parts by weight, and (meth) comprises 1 to 30 parts by mass of the acrylic liquid polymer, the (meth) acrylic-based liquid polymer, ( A low molecular weight polymer consisting only of a (meth) acrylic monomer which is an alkyl (meth) acrylic acid and / or an alicyclic alkyl (meth) acrylic acid, or the low molecular weight polymer modified by an epoxy group and / or an alkoxysilyl group. There, the glass transition temperature of its is -30 ° C. or less, a rubber composition for a studless tire, wherein the weight-average molecular weight of 1,000 to 15,000. The rubber composition for a studless tire according to claim 1 , wherein the (meth) acrylic liquid polymer is further modified with a long-chain alkyl group. A studless tire having a tread portion made of the rubber composition for a studless tire according to claim 1 or 2.