JP3352639B2 - Rubber composition for tire tread with increased frictional force on ice and pneumatic tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire tread, and more particularly, to a rubber composition comprising thermally expandable thermoplastic resin particles enclosing a liquid or a solid which generates gas by being vaporized, decomposed or chemically reacted by heat. A rubber composition for a tire tread in which a gas-encapsulated thermoplastic resin and short fibers, hard particles and / or a liquid polymer are blended with a diene rubber and made hollow by being expanded by heat at the time of vulcanization, and the rubber composition is used for a tread. The present invention relates to a pneumatic tire having increased on-ice friction.

[0002]

2. Description of the Related Art Conventionally, a method of blending hard foreign matter and hollow particles with rubber to form micro unevenness on the rubber surface to remove a water film generated on the surface of ice and improve friction on ice has been conventionally used. Many have been considered but have not yet reached a satisfactory level. For example, examples of blending the above hard foreign materials include JP-A-60-258235 (ceramic fine powder), JP-A-2-274740 (ground plant), and JP-A-2-281052 (metal However, these methods have a problem in that the hardness of the rubber increases, and the flexibility of the rubber is lost, so that the ability to follow the road surface is poor. Examples of blending the hollow particles are described in JP-A-2-170840, JP-A-2-208336 and JP-A-4-5.
No. 543, etc., these methods have a problem that the hardness of the rubber similarly increases, or the hollow particles are broken during the mixing.

Under such circumstances, we have previously prepared a tire tread in which diene rubber is blended with elastic gas-filled thermoplastic resin particles having an average particle size of 5 to 300 μm to increase the frictional force on ice. Rubber composition was developed. This gas-filled thermoplastic resin compounded rubber has the effect of forming irregularities on the tread surface and efficiently removing the water film.Also, since the elastic gas-filled thermoplastic resin is compounded, the rubber hardness is reduced. A pneumatic tire that maintains the flexibility of the rubber without rising and exhibits a high frictional force on ice can be obtained.

[0004]

However, although the gas-filled thermoplastic resin exhibits a high frictional force on ice, it reduces the rigidity of the block of the tire. It turned out that there was a new problem that it could not be obtained. Accordingly, an object of the present invention is to provide a rubber composition for a tire tread in which a frictional force on ice is further enhanced by reinforcing a tire block, and a pneumatic tire using the same.

[0005] Another object of the present invention is to eliminate all the problems of the prior art described above, so that the rubber is light, does not increase the hardness of the rubber, maintains the suppleness of the rubber, and protects against ice. To provide a rubber composition for a tire tread and a pneumatic tire using the same, exhibiting a scratching effect and also having a spike effect on an ice surface while removing a water film, thereby further increasing the frictional force on ice. It is in.

An object of the present invention is to provide a rubber composition for a tire tread and a pneumatic tire using the same, which can further increase the frictional force on ice and suppress the transfer of a softener to maintain a high frictional force on ice for a long period of time. To provide.

[0007]

According to the present invention, 100 parts by weight of a diene rubber and the weight of (meth) acrylonitrile are
The coalesced or copolymerized , heat-expandable thermoplastic resin particles encapsulating a liquid or solid that evaporates by heat, decomposes or chemically reacts to generate a gas, are expanded by heat during rubber vulcanization to form a hollow, Elastic gas-filled thermoplastic resin particles having an average particle size of 5 to 300 µm, 1 to 20 parts by weight, short fibers, Vickers hardness of 35 to 1000, and an average particle size of 20 to
A rubber composition for a tire tread, comprising 1 to 20 parts by weight of at least one kind of 500 μm hard particles.

According to the present invention, the diene rubber 10
0 parts by weight of a (meth) acrylonitrile polymer or
The polymer is expanded by heat at the time of rubber vulcanization to expand the heat-expandable thermoplastic resin particles enclosing a liquid or solid that evaporates, decomposes, or undergoes a chemical reaction to generate a gas by heat. 1 to 20 parts by weight of elastic gas-filled thermoplastic resin particles of 5 to 300 μm, short fibers, Vickers hardness of 35 to 1000, and average particle size of 20 to 500 μm
A rubber composition comprising 1 to 20 parts by weight of at least one of the hard particles of the above, and the short fibers are oriented along the block surface and side surfaces of the tread portion, and / or the hard particles Is provided three-dimensionally uniformly in the tread portion.

According to the present invention, 100 parts by weight of a diene rubber and a polymer or copolymer of (meth) acrylonitrile
In addition, heat-expandable thermoplastic resin particles encapsulating a liquid or solid that evaporates, decomposes or undergoes a chemical reaction to generate gas by heat are expanded by heat during rubber vulcanization to form a hollow, having an average particle diameter of 5 to 5. 1 to 50 parts by weight of 300 μm elastic gas-filled thermoplastic resin particles, and a weight average molecular weight of 6,
000-100,000 and glass transition temperature (Tg)
A rubber composition for a tire tread comprising 5-55 parts by weight of a liquid polymer having a temperature of -50 ° C or lower, and a pneumatic tire using the same in a tread.

According to the present invention, the diene rubber further comprises:
Expansion is started by blending (meth) acrylonitrile polymer or copolymer with heat-expandable thermoplastic resin particles in which a liquid or solid that generates gas by vaporization, decomposition or chemical reaction by heat is enclosed in a thermoplastic resin. Evenly compounded at a temperature lower than the temperature, the obtained preliminary rubber composition is expanded by heating at a temperature equal to or higher than the expansion start temperature of the thermally expandable particles, so that the thermally expandable thermoplastic resin particles are hollowed out and averaged. An elastic gas-filled thermoplastic resin having a particle size of 5 to 300 μm is uniformly dispersed in rubber, and a predetermined amount of short fibers, Vickers hardness of 35 to 1000, and an average particle size of 20 to 500 μm
And a pneumatic tire using the same in a tread.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a half-sectional view in the meridian direction of an example of the pneumatic tire of the present invention. In FIG. 1, a pneumatic tire A of the present invention includes a pair of left and right bead portions 11, 11, a pair of left and right side wall portions 12, 12 connected to the bead portions 11, 11, and a portion between the side wall portions 12, 12. And a tread portion 13 disposed on the tread portion 13. A carcass layer 1 is provided between the pair of left and right bead portions 11 and 11.
In the tread portion 13, a belt layer 15 is disposed so as to surround the outer periphery.
10 is a tread surface. In the present invention, the tread portion 13 is composed of rubber, a gas-filled thermoplastic resin, and short fibers.

According to the present invention, the average particle size is 5 to 300 μm.
m of the elastic gas-encapsulated plastic resin particles, together with the short fibers, hard particles and / or liquid polymer, is uniformly dispersed in a vulcanized rubber matrix to obtain a rubber composition for a tread of a pneumatic tire. it can. This rubber composition is prepared by preliminarily evaporating a rubber material by heat, decomposing or chemically reacting to form a gas or a liquid or solid containing a thermally expandable thermoplastic resin particles, a predetermined amount of the short fibers, hard particles and And / or compounded with a liquid polymer, and first kneaded uniformly at a temperature lower than the expansion start temperature to form a preliminary rubber composition. Then, the preliminary rubber composition contains heat-expandable thermoplastic resin particles contained therein. By vulcanizing at a temperature equal to or higher than the expansion start temperature, the thermally expandable thermoplastic resin particles are expanded into expanded hollow body particles, and the gas-filled thermoplastic resin particles as the expanded hollow body particles are used as the short fibers. To obtain a rubber composition for a pneumatic tire tread uniformly dispersed in a vulcanized rubber matrix together with hard particles and / or a liquid polymer.

[0013] The gas-filled thermoplastic resin particles used in the present invention include thermally expandable thermoplastic resin particles in which a liquid or a solid that generates a gas by being vaporized, decomposed, or chemically reacted by heat is contained in the thermoplastic resin. Heating and expanding at a temperature equal to or higher than the expansion start temperature, usually at a temperature of 140 to 190 ° C., encapsulates a gas in an outer grain made of the thermoplastic resin, and the gas-encapsulated thermoplastic resin particles are preferably It has a true specific gravity of 0.1 or less and an average particle size of 10 to 200 µm, more preferably 30 to 150 µm.

The volume ratio of the hollow portion of the obtained gas-filled thermoplastic resin particles to the rubber is preferably 2 to 40.
%, More preferably 5 to 35%, particularly preferably 10 to
30%, most preferably 10-25%. If the volume ratio is too small, the frictional force on ice will not be sufficiently improved.
On the other hand, if it is too large, the abrasion resistance is significantly deteriorated, and the practicability may be lacking.

Such thermally expandable thermoplastic resin particles (expandable particles) are currently available from Swedish EXPAN.
Product name “EXPANCEL 091DU-8” from CEL
0 "or" EXPANCEL 092DU-120 "or the like, or from Matsumoto Yushi Co., Ltd. under the trade name" Matsumoto Microsphere F-85 "or" Matsumoto Microsphere F-100 ".

The thermoplastic resin constituting the outer grain component of the gas-filled thermoplastic resin particles has an expansion start temperature of 100.
C. or higher, preferably 120 ° C. or higher, and a maximum expansion temperature of 1
Those having a temperature of 50 ° C. or higher, preferably 160 ° C. or higher are preferable. As such a thermoplastic resin, for example, a polymer of (meth) acrylonitrile or a copolymer having a high content of (meth) acrylonitrile is suitably used. As the partner monomer (comonomer) in the case of the copolymer, monomers such as vinyl halide, vinylidene halide, styrene-based monomer, (meth) acrylate-based monomer, vinyl acetate, butadiene, vinylpyridine, and chloroprene are used. . In addition, the above thermoplastic resins are divinylbenzene, ethylene glycol di (meth)
Crosslinking agents such as acrylate, triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, allyl (meth) acrylate, triacrylformal, triallyl isocyanurate May be made crosslinkable. The crosslinked form is preferably not crosslinked, but may be partially crosslinked so as not to impair the properties as a thermoplastic resin.

The liquid or solid which vaporizes, decomposes or undergoes a chemical reaction by heat to generate a gas includes, for example, hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane and petroleum ether. , Methyl chloride, methylene chloride, dichloroethylene,
Liquids such as chlorinated hydrocarbons such as trichloroethane, trichloroethylene, or azodicarbonamide;
Dinitrosopentamethylenetetramine, azobisisobutyronitrile, toluenesulfonylhydrazide derivative,
Solids such as aromatic succinyl hydrazide derivatives are included.

The rubber component used in the tread portion of the pneumatic tire according to the present invention includes, for example, natural rubber (N
R), various butadiene rubbers (BR), various styrene-butadiene copolymer rubbers (SBR), polyisoprene rubbers (IR), acrylonitrile butadiene rubbers (NB
R), diene such as chloroprene rubber (CR), ethylene-propylene-diene copolymer rubber (EPDM), styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber System rubber. These rubbers are used alone or as a mixture. When the rubber is used as the tire tread of the present invention, the glass transition temperature (Tg) is required to improve the low rolling resistance, abrasion resistance and low-temperature performance at the same time. ) Is preferably -55 ° C or less on average, and more preferably Tg is -60 to -1 on average.
00 ° C.

The rubber composition for the tread portion of the pneumatic tire of the present invention contains short fibers, hard particles and / or a liquid polymer in addition to the rubber and the gas-filled thermoplastic resin. When short fibers are used, the short fibers need to be substantially oriented along the block surface and side surfaces of the tread portion. That is, in the present invention, the short fibers are oriented along the block surface and the side surface of the tread portion 13. FIGS. 2 and 3 show the state of the short fiber orientation. FIG. 2 is an explanatory plan view of a tread portion of an example of the pneumatic tire of the present invention, and FIG. 3 is a sectional view taken along line KK 'of FIG. As shown in FIGS. 2 and 3, the short fibers 17 are oriented in the tire circumferential direction EE ′ along the surface a and the side surface b of the block 16 of the tread portion 13.

In order to obtain such short fiber orientation,
At the time of extrusion molding of the tread portion 13, the fact that fibers having a certain length / diameter ratio tend to be arranged in the flow direction of the matrix rubber is used. This tendency is such that when the tire is vulcanized, the unvulcanized tread rubber flows along the mold by the protrusions of the mold, and as a result, the short fibers 17 are oriented along the mold protrusions. Thereby, the short fibers 17 are oriented along the surface a and the side surface b of the block 16 of the tread portion 13. However,
If the length of the short fibers 17 is too short, the short fibers 17 will be randomly arranged in the tread rubber and will not be oriented.

As described above, the short fiber 1 is applied to the surface a and the side surface b.
The block 16 in which the 7 is oriented exhibits anisotropy of the elastic modulus such that the rigidity of the entire block is extremely high but the elastic modulus in the direction perpendicular to the orientation direction, that is, the direction from the surface to the inside is not so high. The expression of this anisotropy reinforces the block rigidity of the soft base rubber, which has a high adhesion effect, and maximizes both the block edge effect and the rubber adhesion effect.
Performance on icy and snowy roads can of course improve performance on general roads. Therefore, in the present invention, the dynamic Young's modulus E _{1 in} the block circumferential direction and the dynamic Young's modulus E
₂ and is, it is preferable to carry out the orientation of the short fibers 17 so as to satisfy the following equations (1) and (2) below.

1.03 ≦ E ₁ / E ₂ (1) 3 [MPa] ≦ E ₂ ≦ 20 [MPa] (2)

The short fibers preferably have an average diameter of 0.1 μm or more and an average length of 50 to 5000 μm. More preferably, 0.1 to 50 μm and 100 to 2 respectively.
Preferably, the length / diameter ratio is from 10 to 1,000, more preferably from 100 to 1,000.
Such short fibers include, for example, natural fibers such as cotton and silk, cellulosic fibers, polyamide fibers represented by nylon fibers, polyester fibers, chemical fibers such as polyvinyl alcohol fibers such as vinylon, and inorganic fibers such as carbon fibers. Can be used. Preferably, cellulosic short fibers such as rayon are used. Short metal fibers such as steel short fibers and copper-based metal short fibers may be used. Furthermore, a material that has been subjected to a surface treatment to enhance dispersibility in rubber, SB
It is preferable to use a masterbatch dispersed in R, NR, or the like in advance.

The gas-filled thermoplastic resin contained in the rubber composition for the tread portion of the pneumatic tire of the present invention is preferably 100 parts by weight of rubber and 1 to 20 parts of the gas-filled thermoplastic resin.
Parts by weight, more preferably 2 to 15 parts by weight. The short fibers are 1 to 20 short fibers per 100 parts by weight of the diene rubber.
Parts by weight, more preferably 1 to 10 parts by weight.

The hard particles used in the present invention are blended for the purpose of scratching against ice. In this sense, the hard particles are harder than ice (Vickers hardness Hv = 30) and asphalt (Hv = 1000). Softer Vickers hardness 35-1000, preferably 40-800
Having an average particle diameter of 20 to 500 μm, preferably 40 to 200 μm. If the particle size of the hard particles is less than 20 μm, the effect of scratching the ice is not sufficient, and if it is more than 500 μm, the actual ground contact area on the ice surface becomes too small, and the frictional force on ice is preferably reduced. Absent.

As the material of the hard particles used in the present invention, any material may be used as long as it is within the above hardness range.
Carbonaceous powders such as activated carbon particles, hard synthetic resin particles such as nylon resin, polyethylene resin and phenol resin, metal powders such as aluminum, copper and iron, mineral powders such as calcite and fluorite, or mixtures thereof. Can be used effectively.

The amount of the hard particles to be compounded in the rubber composition for a tire tread according to the present invention is as follows.
The hard particles are preferably used in an amount of 1 to 20 parts by weight, more preferably 1 to 10 parts by weight, based on parts by weight. If the amount is outside these ranges, the desired effects cannot be obtained sufficiently.

The liquid polymer (softening agent) to be incorporated into the rubber composition for a tire tread according to the present invention has a weight average molecular weight of 6,000 to 100,000, preferably 8,000 to 8,
000 and Tg of -50 ° C or less, preferably -1
It is a liquid polymer (preferably liquid polybutadiene, liquid polyisoprene) at 20 to -55 ° C.

The gas-filled thermoplastic resin-containing rubber forms irregularities on the tread surface, and efficiently removes a water film. In addition, since an elastic gas-filled thermoplastic resin is compounded, the flexibility of the rubber is maintained without increasing the hardness of the rubber, and a high frictional force on ice is exhibited. However, according to the present invention, the hardness of rubber increases with time. The main reason is the migration of the softener into the tire, or
Diffusion into the atmosphere. Therefore, by adding a liquid polymer having low migration / diffusion property, a change with time can be suppressed.

The rubber composition for a tread of a pneumatic tire according to the present invention may contain carbon black or carbon black and silica as a reinforcing agent usually added to the rubber composition. The carbon black used in the rubber composition for a tire tread of the present invention has an N ₂ SA (nitrogen adsorption specific surface area) of 70 m ² / g,
Those having a BP oil absorption of 105 ml / 100 g or more are preferable, and those having an N ₂ SA of 80 to 200 m ² / g and a DBP oil absorption of 110 to 150 ml / 100 g are more preferable. If this value is too low, the tensile strength, modulus, etc. decrease, which is not preferable. Conversely, if this value is too high, N ₂ SA
In this case, the calorific value becomes large, which is not preferable, and the DBP oil absorption is not preferable because it is difficult to produce carbon as carbon.
As the silica, wet silica, dry silica, surface-treated silica, or the like is used. Among them, it is preferable to use wet silica. As the compounding amount of these reinforcing agents, 20 to 80 parts by weight of carbon black and 0 to 50 parts by weight of silica are used based on 100 parts by weight of rubber. Silica may not be used, and if used,
It is preferable to use a compounding amount in a range in which the balance of tan δ is improved, and if this amount is too large, the electric conductivity is reduced, and the cohesive force of the reinforcing agent is increased, and the dispersion during kneading becomes insufficient. .

The rubber composition constituting the tread of the pneumatic tire according to the present invention may further contain a usual vulcanizing or crosslinking agent, a vulcanizing or crosslinking accelerator, various oils, an antioxidant,
Fillers, plasticizers, softeners, and other various additives commonly used for the rubber can be added.
As long as the amount of these additives is not contrary to the object of the present invention,
A conventional general compounding amount can be used.

The kneading and preforming of the thermally expandable thermoplastic resin particles in the rubber composition for a tread portion of the pneumatic tire of the present invention are carried out at a temperature lower than the expansion start temperature, preferably at least 10 ° C. lower than the expansion start temperature. It is carried out at a temperature, more preferably at a temperature lower by 15 ° C. or more. Otherwise, the thermally expandable resin particles may partially expand at this stage, and the particles expanded in the next step may be crushed. After kneading and pre-molding, the pre-molded product is heat-molded at a temperature at which the thermally expandable resin particles contained therein are at or above the expansion start temperature to expand the thermally expandable resin particles, thereby forming a gas-filled thermoplastic resin. Make particles. The heat molding temperature at this time is set at the maximum expansion temperature T of the heat-expandable resin particles so as to achieve sufficient expansion and to obtain the optimum physical properties of the rubber agent.
± 20 ° C. of max (preferably Tmax−20 ° C. to Tm
(ax + 5 ° C.). At the time of the heating, the rubber composition constituting the matrix is vulcanized and cured. Even if the thermally expandable resin particles expand to become gas-filled thermoplastic resin particles, the weight of the resin itself changes only slightly before and after the expansion.

By the above-mentioned heat vulcanization molding, sphere-like gas-filled thermoplastic resin particles having a particle size of 5 to 300 μm and having a particle size of 5 to 300 μm are uniformly dispersed three-dimensionally in a matrix made of vulcanized rubber. A rubber molded product having the above structure can be obtained. The rubber composition for a tire tread having the structure obtained in this manner has a structure in which, when used as a tire, the gas-filled thermoplastic resin compounded as the tread wears on the surface due to its structure and physical properties. Appearing and forming a convex part, a concave part is formed because a part of the gas-filled thermoplastic resin falls off, whereby the water film is efficiently removed, and the actual ground contact property is improved, and the friction performance on ice is improved. Is improved. In addition, the elasticity of the gas-filled heat-soluble resin is compounded, so that the hardness of the tire rubber does not increase and its flexibility is maintained.

[0034]

EXAMPLES The present invention will be further described with reference to the following examples, but it goes without saying that the scope of the present invention is not limited to these examples.

Preparation of Samples 1 to 7 and Comparative Examples 1 to 7 Using a 16-liter closed Banbury mixer, a compounding agent such as a vulcanization accelerator, sulfur, rubber excluding hollow polymer, carbon black, etc. was added for 5 minutes. After mixing, a master batch was prepared. After cooling the masterbatch to room temperature, the masterbatch and the remaining ingredients were mixed in a 16 liter hermetic Banbury mixer and the rubber temperature was set to 110 ° C.
At the time it was reached. On the other hand, after the rubber composition was cooled to room temperature, it was extruded with a 3.5-inch extruder at a head temperature of 92 ° C. to produce a tread. A green tire (unvulcanized molded tire) produced from this tread is put in a mold and vulcanized at a temperature of 165 ° C. for 15 minutes.
A test tire having a size of 185 / 65R14 was prepared and subjected to a braking test on ice. The on-ice braking test method is as follows, and the results are shown in Table I.

1) Volume ratio of hollow polymer (%): Calculated from (1−ρ ′ / ρ) × 100 from the specific gravity ρ of the rubber excluding the hollow polymer and the specific gravity ρ ′ of the rubber mixed with the hollow polymer. The specific gravity ρ and ρ ′ were measured by the balance method of 5.1 of JIS K0061. 2) Brake test on ice: 4 tires for each test were used for displacement of 1800
The vehicle was mounted on a cc passenger car, and the braking distance from an initial speed of 40 km / h was measured on an ice sheet road at an outside temperature of -5 ° C. The distance is shown as an index (the value of Comparative Example 1 is set to 100).
The smaller the value, the better.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

Standard Example 1, Examples 8 to 14 and Comparative Example 8
Preparation of １３13 Samples Using a 16-liter closed Banbury mixer, a compounding agent such as a vulcanization accelerator, sulfur, rubber excluding a hollow polymer, and carbon black was mixed for 5 minutes to prepare a master batch. After cooling the masterbatch to room temperature, the masterbatch and the remaining ingredients were mixed in a 16 liter hermetic Banbury mixer and the rubber temperature was set to 110 ° C.
At the time it was reached. On the other hand, after the rubber composition was cooled to room temperature, it was extruded with a 3.5-inch extruder at a head temperature of 92 ° C. to produce a tread. A green tire (unvulcanized molded tire) produced from this tread is put in a mold and vulcanized at a temperature of 165 ° C. for 15 minutes.
A test tire having a size of 185 / 65R14 was prepared and subjected to a braking test on ice. The on-ice braking test method was as described above, and the results are shown in Table II.

[0041]

[Table 4]

[0042]

[Table 5]

Examples 15 to 22 and Comparative Examples 14 to 19 Preparation of Samples Tables were prepared using a 16-liter closed Banbury mixer.
Vulcanization accelerator, sulfur, rubber excluding hollow polymer, compounding agents such as carbon black, etc. were mixed for 5 minutes in the composition shown in III,
A master batch was prepared. After cooling the masterbatch to room temperature, the masterbatch and the remaining ingredients were mixed in a 16 liter hermetic Banbury mixer and released when the rubber temperature reached 110 ° C. ICE-μ (rubbing test on ice) of the obtained rubber composition and aged ICE-μ after aging in an oven at 80 ° C. for 96 hours were measured, and the results are shown in Table III.

[0044]

[Table 6]

[0045]

[Table 7]

Table III Footnote * 1: See Table I Footnote * 2: NIPOL1502: Styrene-butadiene copolymer rubber (SBR) manufactured by Zeon Corporation, Tg = -51
* 3: RICON-154: Liquid polybutadiene rubber manufactured by RICON RESIN Tg: -17 ° C, Mw: 13
000 * 4: POLYOIL 130: HULS liquid polybutadiene rubber Tg: -82 ° C, Mw: 16000 * 5: Ube Industries, Ltd. 6 nylon fiber / natural rubber / polyethylene masterbatch (diameter 0.3 μm, length 12)
* 6: Wood ceramic particles: After impregnating 100 parts by weight of a wood material with 100 parts by weight of a phenol resin, baking at 800 ° C. for 4 hours in an oxygen-free atmosphere, pulverizing to 100 μm and 4 μm.
Sizing with 5μm sieve. (Hv = 100)

The on-ice friction test (ICE-μ) was performed as follows. The friction test on ice is performed by pressing a rubber test piece with a constant load on an ice surface installed in a temperature-controlled constant temperature chamber and detecting a resistance (friction force) when the rubber test piece slides at a constant speed. The conditions of the friction test on ice shown in the comparative example were as follows: ice temperature −3 ° C., speed 20 km / h, contact pressure 3 kg / cm ^2.
It is. In addition, the result is shown by the index which made the value before the aging of the comparative example 14 used as a contrast 100, and shows that a coefficient is so large that a numerical value is large.

[0048]

As can be seen from the results of Table I, the pneumatic tire obtained from the rubber composition in which the predetermined gas-encapsulated thermoplastic resin particles and the short fibers or hard particles are blended with the diene rubber according to the present invention, It is clear that the frictional force on ice is superior to the conventional one.

[Brief description of the drawings]

FIG. 1 is a half sectional view in the meridian direction of an example of a pneumatic tire of the present invention.

FIG. 2 is an explanatory plan view of a tread portion of an example of the pneumatic tire of the present invention.

FIG. 3 is a sectional view taken along the line KK 'in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Tread surface 11 ... Bead part 12 ... Side wall 13 ... Tread part 14 ... Carcass layer 15 ... Belt layer 16 ... Block 17 ... Short fiber

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI C08K 3/36 C08K 3/36 7/02 7/02 7/22 7/22 (56) References JP-A-4-198241 ( JP, A) JP-A-6-328907 (JP, A) JP-A-8-217918 (JP, A) JP-A-9-255813 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) C08L 9/00 C08K 7/22 C08K 7/02

Claims (13)

(57) [Claims] 1. 100 parts by weight of a diene rubber and (meth)
A polymer or copolymer of acrylonitrile is filled with a heat-expandable thermoplastic resin particle that encapsulates a liquid or solid that generates gas by vaporization, decomposition or chemical reaction by heat, and is expanded by the heat of rubber vulcanization to form a hollow body. Average particle size of 5 to 30
0 μm elastic gas-filled thermoplastic resin particles 1-2
0 parts by weight, short fibers and Vickers hardness 35-100
0 and at least one kind of hard particles having an average particle diameter of 20 to 500 μm, and 1 to 20 parts by weight of the rubber composition for a tire tread. 2. The rubber composition for a tire tread according to claim 1, wherein the volume ratio of the hollow portion of the gas-filled thermoplastic resin to the rubber is 2 to 40%. 3. The glass transition temperature (T) of the diene rubber.
The rubber composition for a tire tread according to claim 1 or 2, wherein the average value of g) is -55 ° C or less. 4. With respect to 100 parts by weight of the diene rubber,
Nitrogen adsorption specific surface area (N ₂ SA) 70 m ² / g or more and D
The rubber composition for a tire tread according to claim 1, 2, or 3, further comprising 20 to 80 parts by weight of carbon black having a BP oil absorption of 105 ml / 100 g or more and 0 to 50 parts by weight of wet silica. 5. The staple fiber has an average diameter of 0.1 μm or more and an average length of 50 to 5000 μm.
The rubber composition for a tire tread according to any one of the above. 6. The method according to claim 1, wherein the rubber composition for a tire tread is used for a tread portion of a tire, and the short fibers are oriented along a block surface and a side surface of the tread portion. And / or a pneumatic tire in which the hard particles are three-dimensionally and uniformly dispersed in a tread portion. 7. A thermally expandable thermoplastic resin particle in which a diene rubber and a (meth) acrylonitrile polymer or copolymer are encapsulated with a liquid or a solid which generates a gas by being vaporized, decomposed or chemically reacted by heat. Are mixed uniformly at a temperature lower than the expansion start temperature, and the obtained preliminary rubber composition is expanded by heating at a temperature equal to or higher than the expansion start temperature of the thermally expandable particles to thereby form a thermally expandable thermoplastic resin. The particles are hollow, and an elastic gas-filled thermoplastic resin having an average particle size of 5 to 300 μm is uniformly dispersed in rubber, and short fibers and Vickers hardness of 35 to 1000 and an average particle size of 20 to 5 are used.
A method for producing a rubber composition for a tire tread, comprising at least one kind of hard particles having a size of 00 μm. 8. 100 parts by weight of a diene rubber and (meth)
A heat-expandable thermoplastic resin particle enclosing a liquid or solid that generates a gas by vaporizing, decomposing, or chemically reacting with heat in a polymer or copolymer of acrylonitrile is expanded by the heat of rubber vulcanization to form a hollow Average particle size 5
300 μm elastic gas-filled thermoplastic resin particles 1
５０50 parts by weight and a weight average molecular weight of 6,000-100,
A rubber composition for a tire tread, comprising 5 to 55 parts by weight of a liquid polymer having a glass transition temperature (Tg) of 000 or less and -50 ° C or less. 9. Short fibers and Vickers hardness of 35 to 10
9. The rubber composition for a tire tread according to claim 8, further comprising 1 to 20 parts by weight of hard particles having an average particle diameter of 20 to 500 μm. 10. The volume ratio of the hollow portion of the gas-filled thermoplastic resin to rubber is 5 to 35%.
Or a rubber composition for a tire tread according to item 9. 11. The rubber composition for a tire tread according to claim 8, wherein the diene rubber has an average glass transition temperature (Tg) of -55 ° C. or less. 12. 20 to 80 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 70 m ² / g or more and a DBP oil absorption of 105 ml / 100 g or more and wet silica 0 to 100 parts by weight of the diene rubber. The rubber composition for a tire tread according to any one of claims 8 to 11, further comprising 50 parts by weight. 13. A pneumatic tire using the rubber composition for a tire tread according to any one of claims 8 to 12 in a tread portion of the tire.