JP3352627B2 - 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 containing thermoplastic resin particles encapsulating a gas, and more particularly, to a liquid or solid which generates a gas by being vaporized, decomposed or chemically reacted by heat. Is formed by expanding the heat-expandable thermoplastic resin particles enclosing the rubber by heat at the time of rubber vulcanization to form a hollow shape, comprising hollow particles made of an elastic gas-encapsulated thermoplastic resin having a particle size of 5 to 300 μm. The present invention relates to a rubber composition for a tire tread and a pneumatic tire using the same.

[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.

[0003]

Therefore, in the present invention,
In order to overcome the problems of the prior art described above, compounding hollow particles made of an elastic gas-filled thermoplastic resin, the rubber is light, without increasing the hardness of the rubber, the flexibility of the rubber is maintained, and It is an object of the present invention to provide a rubber composition for a tire tread that is not broken by shearing force at the time of mixing and has excellent performance on ice.

[0004]

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, A rubber composition for a tire tread, comprising 1 to 20 parts by weight of elastic gas-filled thermoplastic resin particles having a particle size of 5 to 300 μm.

According to the present invention, a diene rubber is
Expansion is started by blending (meth) acrylonitrile polymer or copolymer with heat-expandable thermoplastic resin particles in which a liquid or solid that generates a gas by vaporization, decomposition or chemical reaction by heat is enclosed in a thermoplastic resin. The heat-expandable thermoplastic resin particles are uniformly mixed at a temperature lower than the temperature and expanded by heating the obtained preliminary rubber composition at a temperature equal to or higher than the expansion start temperature of the heat-expandable particles. Diameter 5-3
Provided is a method for producing a rubber composition for a tire tread, in which a gas-filled thermoplastic resin having an elasticity of 00 μm is uniformly dispersed in rubber.

According to a preferred embodiment of the present invention, as the diene rubber, an average value of glass transition temperature (Tg) (where “average value” is a weighted average value of Tg values of a plurality of diene rubbers) the point) is a rubber composition for a tire tread using the rubber is -55 ° C. or less, or, with respect to 100 parts by weight of rubber, N ₂ SA (nitrogen adsorption specific surface area) of 70m ² /
20 to 80 parts by weight of carbon black having a DBP oil absorption of 105 ml / 100 g or more and a wet silica
A rubber composition for a tire tread further comprising 50 parts by weight is provided.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration, operation and effect of the present invention will be described below. According to the invention, the particle size is between 5 and 3
A rubber composition for a tire tread having a structure in which 00 μm elastic gas-filled thermoplastic resin particles are uniformly dispersed in a vulcanized rubber matrix can be obtained. According to the present invention, a predetermined amount of heat-expandable thermoplastic resin particles containing a liquid or solid containing a liquid or a solid that generates a gas by preliminarily vaporizing, decomposing, or chemically reacting with a rubber material is blended, and first, a temperature lower than the expansion start temperature. By kneading uniformly at a temperature to form a preliminary rubber composition, and then vulcanizing the preliminary rubber composition at a temperature at which the thermally expandable thermoplastic resin particles contained therein are at or above the expansion start temperature, the heat The expandable thermoplastic resin particles are expanded to form expanded hollow body particles, thereby obtaining a rubber composition for a tire tread in which the gas-encapsulated thermoplastic resin particles, which are the expanded hollow body particles, are uniformly dispersed in a vulcanized rubber matrix. It is characterized by:

[0008] The gas-filled thermoplastic resin particles used in the present invention include thermally expandable thermoplastic resin particles in which a liquid or solid that generates gas by vaporization, decomposition or chemical reaction by heat is contained in the thermoplastic resin. It is heated and expanded at a temperature equal to or higher than the expansion start temperature, usually at a temperature of 140 to 190 ° C., and a gas is enclosed in an outer grain made of the thermoplastic resin. Is 5-300
μm, more preferably 10 to 10 μm.
It is 200 μm.

The volume ratio of the hollow portion of the obtained gas-filled thermoplastic resin particles to the rubber is preferably 5 to 35.
%, More preferably 6 to 30%, particularly preferably 7 to 2%.
5%, most preferably 8-20%. 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.

[0010] Such thermally expandable thermoplastic resin particles (unexpanded particles) include, for example, currently available from Swedish EX.
PANCEL brand name "EXPANCEL 091DU-8"
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 150 ° C. or higher, preferably Those having a temperature of 160 ° C. or higher are preferably used. 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 other 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 said thermoplastic resin is divinylbenzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, It may be made crosslinkable with a crosslinker such as allyl (meth) acrylate, triacrylformal, triallyl isocyanurate and the like. The crosslinked form is preferably not crosslinked, but may be partially crosslinked so as not to impair the properties as a thermoplastic resin.

Examples of the liquid or solid that generates gas by being vaporized, decomposed, or chemically reacted by the heat include, for example, n-
Liquids such as hydrocarbons such as pentane, isopentane, neopentane, butane, isobutane, hexane, petroleum ether, chlorinated hydrocarbons such as methyl chloride, methylene chloride, dichloroethylene, trichloroethane, and trichloroethylene, or azodicarbonamide; Solids such as dinitrosopentamethylenetetramine, azobisisobutyronitrile, a toluenesulfonylhydrazide derivative, and an aromatic succinylhydrazide derivative are exemplified.

The rubber components used in the diene rubber according to the present invention include, for example, natural rubber (NR), various butadiene rubbers (BR), various styrene-butadiene copolymer rubbers (SBR), polyisoprene rubber (IR) ), Acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), ethylene-propylene-diene copolymer rubber (EPDM), styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber,
And isoprene-butadiene copolymer rubber.
When used as the tire tread of the present invention, the diene rubber has a glass transition temperature (Tg) of -55 on average in order to improve the low rolling resistance, abrasion resistance and low-temperature performance at the same time. It is preferable to use one having a temperature of not more than ℃, more preferably Tg is -60 to -100 ℃ on average.

The rubber composition for a tread of a pneumatic tire of the present invention is preferably 1 to 20 parts by weight of a gas-filled thermoplastic resin, more preferably 2 to 15 parts by weight, per 100 parts by weight of rubber.
Mix parts by weight.

The rubber composition for a tire tread according to the present invention is generally blended with carbon black or carbon black and silica as a reinforcing agent blended in 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 or more and a DBP oil absorption of 105.
preferably has at ml / 100 g or more, more N ₂ SA
Is 80 to 200 m ² / g, and the DBP oil absorption is 110 to 15
More preferably, it is 0 ml / 100 g. If this value is too low, the tensile strength, modulus, etc., decrease, which is not preferable. Conversely, if this value is too high, it is not preferable because N ₂ SA generates a large amount of heat, and the DBP oil absorption is not preferable because it is difficult to produce carbon as carbon. Further, 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 when used, it is better to use a compounding amount in a range in which the balance of tan δ is improved.If it is too large, the electric conductivity is reduced, and the cohesive force of the reinforcing agent is strong. And the dispersion during kneading becomes insufficient, which is not preferable.

The rubber composition for a tire tread according to the present invention further comprises a usual vulcanization or crosslinking agent, a vulcanization or crosslinking accelerator, various oils, an antioxidant, a filler, a plasticizer,
A softening agent and other various compounding agents generally compounded for the rubber can be compounded. The compounding amounts of these additives can also be conventional general compounding amounts as long as they do not contradict the purpose of the present invention.

The kneading and preforming of the thermally expandable thermoplastic resin particles in the rubber composition for a tire tread of the present invention are performed at a temperature lower than the expansion start temperature, preferably at a temperature lower by at least 10 ° C. than the expansion start temperature, more preferably. Is 15 ° C
This is performed at a lower temperature. 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 to ± maximum expansion temperature Tmax of the heat-expandable resin particles so as to achieve sufficient expansion and to obtain optimum physical properties of the rubber material.
20 ° C. (preferably Tmax−20 ° C. to Tmax + 5
C.). At the time of the heating, the rubber component 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, microscopic spheroidal gas-filled thermoplastic resin particles having a particle size of 5 to 300 μm are three-dimensionally and uniformly dispersed 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 a structure obtained in this manner has a structure in which, when used as a tire, a gas-encapsulated thermoplastic resin compounded as the tread wears out due to its structure and physical properties. In addition to 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 friction on ice is also improved. Performance is improved. Further, since the elastic gas-filled thermoplastic resin is compounded, the hardness of the tire rubber does not increase and its flexibility is maintained.

[0019]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but it goes without saying that the technical scope of the present invention is not limited to these Examples.

The following commercially available products were used for the components used in the following examples and comparative examples. Natural rubber: RSS # 3 NIPOL 1220: BR glass transition temperature of Nippon Zeon = −101 ° C. NIPOL 1502: SBR glass transition temperature of Nippon Zeon = −51 ° C. SHOBLACK N220: Carbon black manufactured by Showa Cabot N ₂ SA: 111 m ² / g , DBP oil absorption: 111 ml /
100 g NIPSIL AQ: Wet silica made by Nippon Silica Kogyo SANTOFLEX 6PPD: Anti-aging agent made by FLEXSIS Zinc oxide No. 3: Made by Shodo Chemical Co., Ltd. Stearic acid: Aroma oil made by Nippon Yushi: Santocure NS made by Fujikosan Sulfur vulcanization accelerator made by FLEXSIS Sulfur : (Karuizawa Refinery) EXPANCEL 091DU-80: EXPANCEL expandable particles (expansion start temperature 122 ° C, maximum expansion temperature 176 ° C) Matsumoto Microsphere F-100: Matsumoto oil and fat expandable particles (expansion start temperature 138) ° C, maximum expansion temperature 183
C) EXPANCEL 091DE-80: EXPANCEL expanded particles Nylon fine particles: Alamin (Toray) Shirasu balloon: (Shirasu)

Preparation of Sample Using a 16-liter closed Banbury mixer, a compounding agent such as a vulcanization accelerator, sulfur, rubber excluding 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. Next, this rubber composition was
By vulcanizing at 160 ° C. for 20 minutes under a pressure of MPa, a sheet having a thickness of 2 mm was prepared and subjected to a hardness (Hs) test. Also 10
The sheet was vulcanized at 160 ° C. for 20 minutes under a pressure of MPa to prepare a sheet having a thickness of 5 mm, which was subjected to a Lambourn abrasion test. 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 was placed in a mold and vulcanized at a temperature of 165 ° C. for 15 minutes to produce a test tire of size 185 / 65R14, which was subjected to a braking test on ice.

The measurement and evaluation methods in each example are as follows. (1) Hardness (Hs): Measured according to JIS K 6301 5.2 (spring hardness, A type). (2) Hollow polymer volume ratio (%): 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 compounded with the hollow polymer. In addition,
The specific gravity ρ and ρ ′ were measured by the balance method of 5.1 of JIS K0061. (3) Lambourn abrasion resistance index: JIS K 6264
The wear loss was measured according to No. 7 Lambourn abrasion.
The results are shown by an index with Comparative Example 1 being 100. Larger numbers indicate better abrasion resistance. (4) On-ice braking test: four test tires with displacement of 180
Attached to a 0cc passenger car, on an ice plate surface with an outside temperature of -5 ° C,
The braking distance from an initial speed of 40 km / h was measured. The distance is shown as an index (the value of Comparative Example 1 is set to 100), and the smaller the value, the better.

Examples 1 to 7 and Comparative Examples 1 to 6 These examples are based on natural rubber, SBR-2 rubber, or natural rubber and SBR-1 rubber. It shows the evaluation results of a rubber compound blended with Pancel 091DU-80 or Matsumoto Microsphere F-100) and heat-treated. Table 1 shows the results.

[0024]

[Table 1]

[0025]

As can be seen from the results shown in Table 1, the rubber composition according to the present invention is rich in elasticity and flexibility. It can be seen that the frictional force on ice is superior to that using a Shirasu balloon.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-198241 (JP, A) JP-A-9-255813 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08L 9/00 C08K 7/22

Claims (6)

(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. Particle size 5 to 300μ
m of elastic gas-filled thermoplastic resin particles of 1 to 20 parts by weight. 2. The rubber composition for a tire tread according to claim 1, wherein a volume ratio of the hollow portion of the gas-filled thermoplastic resin to the rubber is 5 to 35%. 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. A pneumatic tire using the rubber composition for a tire tread according to claim 1 in a tread of the tire. 6. Thermoexpandable thermoplastic resin particles comprising a diene rubber and a (meth) acrylonitrile polymer or copolymer encapsulating a liquid or solid which generates gas by vaporization, decomposition or chemical reaction by heat. Are mixed uniformly at a temperature lower than the expansion start temperature, and the obtained preliminary rubber composition is heated at a temperature equal to or higher than the expansion start temperature of the heat expandable particles to expand the heat expandable thermoplastic resin. A method for producing a rubber composition for a tire tread, wherein particles are hollow and an elastic gas-filled thermoplastic resin having a particle size of 5 to 300 μm is uniformly dispersed in rubber.