JP6863060B2 - Rubber composition for tires - Google Patents

Description

The present invention relates to a rubber composition for a tire, and more particularly to a rubber composition for a tire having excellent on-ice performance and wet performance.

Pneumatic tires for ice and snow roads (studless tires) are required to have both on-ice performance and wet performance at a high level. By forming a large number of bubbles in the tread rubber as a configuration for improving the performance on ice, these bubbles absorb and remove the water film on the ice surface when the tread steps on the ice surface, and the tread separates from the ice surface. It is known that sometimes the absorbed water is repeatedly separated by centrifugal force. Patent Document 1 proposes that a heat-expandable microcapsule is blended in a rubber composition for a studless tire as a means for forming such bubbles. Since the heat-expandable microcapsules expand by heating in the vulcanization step, a large number of bubbles (resin-coated bubbles) coated on the shell of the expanded microcapsules are formed on the rubber compound of the tire after vulcanization. Further, in order to improve the performance on ice, it is necessary to secure the flexibility in a low temperature state, and for this reason, the glass transition temperature (Tg) of the base rubber is often designed to be low. However, if the Tg of the base rubber is lowered, it becomes difficult to secure the wet performance.

In order to improve the wet performance, for example, by blending a resin having a high softening point such as an aromatic-modified terpene resin, the wet performance (tan δ at 0 ° C.) is not deteriorated without deteriorating the rolling resistance (tan δ at 60 ° C.). ) Is known to improve. However, as described above, when a resin having a high softening point is added to the tread rubber composition of a studless tire, the rubber hardness at low temperatures becomes high, the suppleness and adhesive force of the rubber are impaired, and the performance on ice deteriorates. Resulting in. For this reason, on-ice performance and wet performance require contradictory characteristics, and it has been difficult to improve both at a high level.

Therefore, a technique for improving both on-ice performance and wet performance of statless tires has not yet been established.

Japanese Unexamined Patent Publication No. 10-316801

An object of the present invention is to provide a rubber composition for a tire having improved on-ice performance and wet performance beyond the conventional level.

The rubber composition for tires of the present invention that achieves the above object comprises 100 parts by mass of crosslinked polyurethane beads and 0.5 to 20 parts by mass of heat-expandable microcapsules in 100 parts by mass of diene rubber. The crosslinked polyurethane beads are characterized by having coated silica on the surface of crosslinked polyurethane fine particles having a glass transition temperature lower than −40 ° C., and having an average particle size of 1 to 200 μm.

The rubber composition for a tire of the present invention has a coated silica on the surface of fine particles of crosslinked polyurethane having a glass transition temperature of −40 ° C. or lower together with heat-expandable microcapsules, and has an average particle size of 1 to 200 μm. Since the beads are blended, the performance on ice and the wet performance can be improved more than the conventional level.

The rubber composition for a tire of the present invention can suitably form a tread portion of a pneumatic tire, particularly a tread portion of a studless tire. This studless tire can further improve on-ice performance and wet performance.

The rubber composition for a tire of the present invention is suitable for forming a tread portion of a pneumatic tire, particularly a tread portion of a studless tire.

In the rubber composition for tires of the present invention, the diene-based rubber used may be any diene-based rubber that usually constitutes the tread portion of the studless tire, for example, natural rubber, isoprene rubber, butadiene rubber, various styrene-butadiene rubber, and butyl rubber. , Ethylene-propylene-diene rubber and the like are exemplified. Of these, natural rubber, butadiene rubber, and styrene-butadiene rubber are preferable, and natural rubber and / or butadiene rubber is more preferable. By containing natural rubber and / or butadiene rubber, the frictional performance on ice can be improved when the tire is made into a pneumatic tire.

In the present invention, the average glass transition temperature (Tg) of the diene rubber is preferably −50 ° C. or lower, more preferably −100 ° C. to −50 ° C., and more preferably −90 ° C. to −60 ° C. By setting the glass transition temperature (Tg) of the diene rubber to −40 ° C. or lower, the flexibility of the tread portion of the studless tire in a low temperature state can be ensured, and the on-ice performance and the wet performance can be improved.

In the present specification, the glass transition temperature (Tg) of the diene rubber is the total (mass average value of the glass transition temperature) obtained by multiplying the glass transition temperature of the constituent diene rubbers by the mass fraction of each diene rubber. .. The total mass fraction of all diene rubbers is set to 1. The glass transition temperature (Tg) of each diene rubber is the glass transition temperature of the diene rubber in a state where the oil spreading component (oil) is not contained. The glass transition temperature (Tg) is set to the temperature at the midpoint of the transition region by measuring the thermogram by differential scanning calorimetry (DSC) under the heating rate condition of 20 ° C./min.

The rubber composition constituting the tread portion contains 0.5 to 20 parts by mass, preferably 1 to 18 parts by mass, and more preferably 2 to 15 parts by mass of the heat-expandable microcapsules with respect to 100 parts by mass of the diene-based rubber described above. Mix in parts. If the blending amount of the heat-expandable microcapsules is less than 0.5 parts by mass, the volume of the resin-coated bubbles in the tread rubber is insufficient, and sufficient performance on ice cannot be obtained. If the blending amount of the microcapsules exceeds 20 parts by mass, the wear resistance performance of the tread rubber deteriorates.

The heat-expandable microcapsules are composed of a shell material formed of a thermoplastic resin containing a heat-expandable substance. Therefore, when an unvulcanized tire having a tread portion made of a rubber composition mixed with heat-expandable microcapsules is molded and the heat-expandable microcapsules in the rubber composition are heated during vulcanization, a shell material is used. The heat-expandable substance contained in the tread expands to increase the particle size of the shell material and forms a large number of resin-coated bubbles in the tread rubber. By forming a large number of resin-coated air bubbles in the tread rubber in this way, when the tread steps on the ice road surface, it absorbs and removes the water film on the ice road surface, and when it leaves the ice road surface, the water is separated by centrifugal force and the ice again. By repeatedly stepping on the road surface, the water film can be removed and the frictional force of the tread on the icy road surface can be improved. In addition, since a micro edge effect can be obtained, the frictional force on ice is improved.

The shell material of the heat-expandable microcapsules can be formed of a nitrile polymer. Further, the heat-expandable substance contained in the shell material of the microcapsules has a property of being vaporized or expanded by heat, and for example, at least one selected from the group consisting of hydrocarbons such as isoalkane and normal alkane is exemplified. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, 2,2,4-trimethylpentane, and examples of normal alkanes include n-butane, n-propane, n-hexane, and the like. Examples thereof include n-heptane and n-octane. These hydrocarbons may be used alone or in combination of two or more. As a preferable form of the heat-expandable substance, a hydrocarbon obtained by dissolving a gaseous hydrocarbon at room temperature in a liquid hydrocarbon at room temperature is preferable. By using such a mixture of hydrocarbons, a sufficient expansion force can be obtained from a low temperature region to a high temperature region in the vulcanization molding temperature region (150 to 190 ° C.) of the unvulcanized tire.

Examples of such heat-expandable microcapsules include the trade name "EXPANCEL 091DU-80" or "EXPANCEL 092DU-120" manufactured by Expandel, Sweden, or the trade name "Microsphere" manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. "F-85D" or "Microsphere F-100D" or the like can be used.

The rubber composition for a tire of the present invention is wet by blending crosslinked polyurethane beads having an average particle size of 1 to 200 μm having coated silica on the surface of crosslinked polyurethane fine particles having a glass transition temperature lower than −40 ° C. Performance and on-ice performance can be improved. The blending amount of the fine particles of the crosslinked polyurethane is 1 to 30 parts by mass, preferably 2 to 20 parts by mass with respect to 100 parts by mass of the diene rubber. If the amount of the crosslinked polyurethane fine particles is less than 1 part by mass, the effect of improving the on-ice performance and the wet performance cannot be sufficiently obtained. Further, if the fine particles of the crosslinked polyurethane exceed 30 parts by mass, the workability deteriorates and it becomes difficult to prepare a rubber composition for a tire.

The size of the fine particles of the crosslinked polyurethane has an average particle size of 1 to 200 μm, preferably 2 to 100 μm, and more preferably 5 to 50 μm. If the average particle size of the crosslinked polyurethane fine particles is less than 1 μm, the effect of on-ice performance cannot be obtained. If the average particle size exceeds 200 μm, the wear resistance deteriorates.

Crosslinked polyurethane beads have coated silica on their particle surface. That is, the surface of the crosslinked polyurethane beads is coated with silica. Thereby, the wet performance of the rubber composition for a tire can be improved. The method of coating the surface of the crosslinked polyurethane beads with silica is not particularly limited, and silica can be coated by a usual method.

The raw material of the crosslinked polyurethane beads is not particularly limited as long as it is polyurethane, and it is assumed that the crosslinked polyurethane beads are crosslinked. Urethane beads can be elastic bodies. Further, the shape of the urethane beads is preferably substantially spherical. The shape of the urethane beads is spherical (bead-shaped) and more preferably true spherical from the viewpoint of greater friction on ice and excellent wear resistance. Further, the sphericity of the urethane beads is preferably 0.9 to 1.0 from the viewpoint of greater friction on ice and excellent wear resistance. The sphericity of urethane beads can be analyzed by particle shape analysis.

The glass transition temperature (Tg) of the crosslinked polyurethane is lower than −40 ° C., preferably lower than −45 ° C. When the Tg of the crosslinked polyurethane is −40 ° C. or higher, the performance on ice deteriorates. The Tg of the crosslinked polyurethane can be adjusted by changing the molecular structure between the urethane bonds. In the present specification, the Tg of the crosslinked polyurethane is measured by a differential scanning calorimetry (DSC) under a heating rate condition of 20 ° C./min, and the temperature is set to the midpoint temperature of the transition region.

Silica can be blended in the rubber composition for tires. The blending amount of silica is preferably 10 to 100 parts by mass, and more preferably 20 to 90 parts by mass with respect to 100 parts by mass of the diene rubber. By blending silica within such a range, desired hardness, strength, wear resistance and the like can be obtained.

The silica, from the viewpoint of the reinforcing property and the like of the processability and studless tires during mixing of the rubber composition, CTAB specific surface area is preferably is preferably a ^{80~190m 2 / g, 100~180m 2 /} g Is more preferable. In the present specification, the CTAB specific surface area of silica shall be measured based on JIS K6217-3.

Carbon black can be blended in the rubber composition for tires of the present invention. The blending amount of carbon black is preferably 10 to 100 parts by mass, and more preferably 20 to 90 parts by mass with respect to 100 parts by mass of the diene rubber. By blending carbon black within such a range, desired hardness, strength, wear resistance and the like can be obtained.

_{Carbon black preferably has a nitrogen adsorption specific surface area (N 2} SA) of 10 to 300 m ² / g from the viewpoint of workability when the rubber composition is mixed and the reinforcing property of the studless tire, and ^{is 20 to 200 m 2.} more preferably from / g, to improve the wet performance of the studless tire, for the reasons ice performance becomes better, is preferably from 50 to 150 m ² / g, in the range of 70~130m ² / g More preferred. In the present specification, the nitrogen adsorption specific surface area of carbon black shall be measured based on JIS K6217-2.

A silane coupling agent can be added to the rubber composition for tires. By blending a silane coupling agent, the dispersibility of silica with respect to diene-based rubber can be improved and the reinforcing property with rubber can be enhanced.

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 blending amount of silica. If the blending amount of the silane coupling agent is less than 3% by mass of the silica blending amount, the dispersion of silica cannot be sufficiently improved. If the blending amount of the silane coupling agent exceeds 15% by mass of the silica blending amount, the desired hardness, strength and wear resistance cannot be obtained.

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 rubber composition for a tire may contain a filler other than carbon black and silica as long as it does not impair the achievement of the subject of the present invention. Examples of other fillers include clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, titanium oxide and the like.

Rubber compositions for tires include vulcanization or cross-linking agents, vulcanization accelerators, anti-aging agents, plasticizers, processing aids, liquid polymers, tackifying resins, thermosetting resins and the like. Various commonly used compounding agents can be blended. Such a compounding agent 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 blending agents 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 tire can be produced by kneading and 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 prepared rubber composition can be vulcanized by using it in the tread portion of a studless tire by a usual method.

The rubber composition for a tire of the present invention can preferably form a tread portion of a studless tire. The studless tire made of this rubber composition for a tire can have better on-ice performance and wet performance 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.

Eleven kinds of rubber compositions (Examples 1 to 5, Standard Examples, Comparative Examples 1 to 5) having the compounding agents shown in Table 2 as a common composition and having the composition shown in Table 1 were prepared by using heat-expandable microcapsules, sulfur, and the like. The ingredients excluding the vulcanization accelerator are kneaded in a 1.8 L closed mixer for 5 minutes, released and cooled, and then heat-expandable microcapsules, sulfur, and the vulcanization accelerator are added and mixed with an open roll to make rubber. The composition was prepared. The blending amount of the compounding agent shown in Table 2 is shown in parts by mass with respect to 100 parts by mass of the diene rubber shown in Table 1.

The obtained nine kinds of rubber compositions were press-vulcanized at 170 ° C. for 10 minutes in a predetermined mold to prepare a test piece having a predetermined shape composed of a rubber composition for a tire. The wet performance (tan δ at 0 ° C.) and the on-ice performance (friction coefficient on ice) of the obtained test piece were measured by the methods shown below.

Wet performance (tan δ at 0 ° C)
The dynamic viscoelasticity of the obtained test piece was measured at an initial strain of 10%, an amplitude of ± 0.5%, and a frequency of 20 Hz using a fully automatic viscoelasticity analyzer manufactured by Ueshima Seisakusho, and tan δ at an ambient temperature of 0 ° C. was measured. Calculated. The obtained results are represented by an exponent with the value of the standard example as 100, and are shown in the “Wet performance” column of Table 1. The larger this index is, the larger the tan δ at 0 ° C. is, which means that the wet performance when made into a tire is excellent.

Performance on ice (coefficient of friction on ice)
The obtained sheet-shaped rubber test piece was attached to a flat cylindrical base rubber, and the coefficient of friction on ice was measured with an inside drum type friction tester on ice. The measurement conditions were a temperature of -3 ° C, a load of 5.5 kg / cm ² , and a drum rotation speed of 25 km / h. The obtained results are represented by an index with the value of the standard example as 100, and are shown in the “Performance on ice” column of Table 1. The larger this index is, the larger the coefficient of friction on ice is, which means that the performance on ice when made into a tire is excellent.

The types of raw materials used in Table 1 are shown below.
-NR: Natural rubber, RSS # 3, glass transition temperature is -65 ° C
-BR: butadiene rubber, Nipol BR1220 manufactured by Nippon Synthetic Rubber Co., Ltd., glass transition temperature of -110 ° C.
・ Silica: Nippon Silica AQ manufactured by Japan Silica Industry Co., Ltd.
-Coupling agent: Silane coupling agent, Si69 manufactured by Dexa
-Urethane fine particles-1: Crosslinked polyurethane beads having coated silica on the particle surface, crosslinked urethane beads Artpearl JB800T manufactured by Negami Kogyo Co., Ltd., average particle size 6 μm, glass transition temperature -52 ° C.
-Urethane fine particles-2: Crosslinked polyurethane beads having coated silica on the particle surface, crosslinked urethane beads Artpearl JB600T manufactured by Negami Kogyo Co., Ltd., average particle size 10 μm, glass transition temperature -52 ° C.
-Urethane fine particles-3: Crosslinked polyurethane beads having coated silica on the particle surface, crosslinked urethane beads Artpearl JB400T manufactured by Negami Kogyo Co., Ltd., average particle size 15 μm, glass transition temperature -52 ° C.
-Urethane fine particles-4: Crosslinked polyurethane beads having coated silica on the particle surface, crosslinked urethane beads Artpearl BP892T manufactured by Negami Kogyo Co., Ltd., average particle size 6 μm, glass transition temperature -38 ° C.
-Urethane fine particles-5: Cross-linked polyurethane beads without coated silica, cross-linked urethane beads manufactured by Dainichiseika Kogyo Co., Ltd. Dimic beads UCN-8150CM, average particle size 15 μm, glass transition temperature -20 ° C
-Microcapsules: Thermally expandable microcapsules, Microsphere F100 manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.

The types of raw materials used in Table 2 are shown below.
・ Carbon black: Tokai Carbon Co., Ltd. Seest 6
・ Zinc oxide: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. ・ Stearic acid: Bead stearic acid manufactured by NOF Corporation ・ Anti-aging agent: 6PPD manufactured by Flexis Co., Ltd.
・ Wax: Paraffin wax manufactured by Ouchi Shinko Kagaku Co., Ltd. ・ Procell oil: Extract No. 4 S manufactured by Showa Shell Sekiyu Co., Ltd.
・ Sulfur: Fine powder sulfur containing Jinhua stamp oil manufactured by Tsurumi Chemical Industry Co., Ltd. ・ Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinko Kagaku Co., Ltd.

As is clear from Table 1, it was confirmed that the rubber compositions for tires of Examples 1 to 5 were superior in wet performance and on-ice performance to the conventional level or higher.

As is clear from Table 1, the rubber composition of Comparative Example 1 cannot improve the wet performance and the on-ice performance because the crosslinked polyurethane beads are less than 1 part by mass.
In the rubber composition of Comparative Example 2, since the crosslinked polyurethane beads exceeded 30 parts by mass, the rubber composition for a tire could not be prepared. Therefore, wet performance and on-ice performance cannot be evaluated.
The rubber composition of Comparative Example 3 is inferior in performance on ice because the glass transition temperature of the crosslinked polyurethane beads is −40 ° C. or higher.
The rubber composition of Comparative Example 4 is inferior in wet performance because it does not have a silica coating on the surface of the crosslinked polyurethane beads.
Since the rubber composition of Comparative Example 5 did not contain the heat-expandable microcapsules, the performance on ice was inferior.

Claims (2)

1 to 30 parts by mass of crosslinked polyurethane beads and 0.5 to 20 parts by mass of heat-expandable microcapsules are blended with 100 parts by mass of diene rubber, and the crosslinked polyurethane beads have a glass transition temperature lower than -40 ° C. A rubber composition for a tire, which has coated silica on the surface of fine particles of crosslinked polyurethane and has an average particle size of 1 to 200 μm. A studless tire having a tread portion made of the rubber composition for a tire according to claim 1.