JP2006131714A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread excellent in the performance on ice, wherein effects achieved by compounding silica and a thermally expansible microcapsule are increased. <P>SOLUTION: The rubber composition for the tire tread comprises 100 pts.wt. diene rubber, 10-60 pts.wt. silica, 5-15 wt.% 3-octanoylthiopropyltriethoxysilane against the weight of the silica and 1-20 pts.wt. thermally expansible microcapsule. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rubber composition for tire treads, and more particularly to a rubber composition for tire treads that is excellent in performance on ice and is suitable for studless tires, in which silica and thermally expandable microcapsules are blended with a diene rubber.

  Various improvements have been made in the field of tire tread rubber compositions to meet market needs. As one of them, wet performance and low fuel consumption performance can be obtained by using silica instead of carbon black, which has been widely used as a filler for rubber reinforcement, or by using silica and further using a silane coupling agent together with silica. Has been improved. On the other hand, there is also a technology to increase friction on ice by blending a granulated material such as thermally expandable microcapsules into the rubber composition to form micro unevenness on the tire surface and removing water film generated on the ice surface. Are known.

  By the way, when a thermally expandable microcapsule is blended with silica as a tread rubber composition for a studless tire, for example, with a high silica blending amount, the thermally expandable capsule does not expand sufficiently as desired, and the expected performance on ice does not appear. Has been confirmed.

  According to our recent knowledge, the heat-expandable microcapsules do not expand sufficiently in the rubber composition with a high silica content as described above because the water derived from silica reacts with the silane coupling agent and silica. It was found that there was a cause in the ethanol generated at the time. That is, in order to sufficiently expand the thermally expandable microcapsules in a rubber composition having a high silica content, it is important to remove moisture and ethanol depending on the rubber composition.

  In order to solve the above-mentioned problem, for example, Patent Document 1 proposes blending a silane coupling agent and a polysiloxane compound with a compound in which silica and thermally expandable microcapsules are blended. However, in this method, it is difficult to suppress the generation of alcohol when silica and a silane coupling agent and silica and a polysiloxane compound react with each other, and sufficient expansion of the thermally expandable microcapsules cannot be obtained.

  On the other hand, in Patent Document 2, when silica and a thermally expandable microcapsule are used in combination, the reaction of silica and the silane coupling agent is completely terminated in the first mixing step, and the water and alcohol generated next are removed. It has been proposed to re-knead (remill) in order to completely volatilize. However, this method is concerned about burning of the silica compound, and the mixed productivity is deteriorated.

JP 2002-356484 A JP 2003-105138 A

  Accordingly, an object of the present invention is to achieve sufficient performance on ice by sufficiently expanding a thermally expandable capsule as desired in a rubber composition for a studless tire, for example, in which silica and a thermally expandable microcapsule are blended. An object of the present invention is to provide a rubber composition that can be used.

  According to the present invention, 100 parts by weight of a diene rubber, 10 to 60 parts by weight of silica and 5 to 15% by weight of silica weight of 3-octanoylthiopropyltriethoxysilane and 1 to 20 parts by weight of thermally expandable microcapsules are added. A tire tread rubber composition comprising the same is provided.

  According to the present invention, there is also provided a rubber composition obtained by further adding expanded graphite to the rubber composition.

  According to the present invention, by using a novel coupling agent, heating a rubber composition of a specific mixed formulation containing silica and thermally expandable microcapsules to thermally expand the thermally expandable microcapsules, A rubber composition for a tire tread having sufficient performance on ice can be obtained.

  Examples of the diene rubber blended in the rubber composition according to the present invention include natural rubber (NR), polyisoprene rubber (IR), various polybutadiene rubbers (BR), various styrene-butadiene copolymer rubbers (SBR), and acrylonitrile. Examples thereof include butadiene copolymer (NBR) rubber and butyl rubber (IIR), and these can be used alone or as an arbitrary mixture.

  As a silica-type filler mix | blended with the rubber composition which concerns on this invention, it is set as arbitrary silica conventionally used for the tires etc., for example, natural silica, synthetic silica, more specifically, dry silica, wet silica. be able to. These silicas are blended in an amount of 10 to 60 parts by weight, preferably 15 to 50 parts by weight, based on 100 parts by weight of the diene rubber. If the blending amount is too small, the effect of improving the performance on ice and the wet performance is not sufficient, which is not preferable. On the other hand, if the blending amount is too large, mixing may be difficult.

  The thermally expandable microcapsule blended in the rubber composition according to the present invention is blended in an amount of 1 to 20 parts by weight, preferably 3 to 10 parts by weight, based on 100 parts by weight of the diene rubber. If the blending amount is too small, the desired effect on ice performance is not sufficient, which is not preferable. Conversely, if the blending amount is too large, the wear resistance of the rubber composition is lowered, which is not preferable. The thermally expandable microcapsule used in the present invention is a thermally expandable thermoplastic resin particle in which, for example, a liquid that is vaporized by heat to generate a gas is included in a thermoplastic resin, and the temperature of the particle is equal to or higher than its expansion start temperature. For example, by heating and expanding at a temperature of 140 to 190 ° C., preferably 150 to 180 ° C., gas-encapsulated thermoplastic resin particles in which a gas is enclosed in an outer shell made of the thermoplastic resin are obtained. The particle value of the thermally expandable microcapsule is not particularly limited, but is preferably 5 to 300 μm before expansion, more preferably 10 to 200 μm. Such a heat-expandable microcapsule is, for example, trade name “Expancel 091DU-80” or “Expancel 092DU-120” from EXPANCEL, Sweden, or trade name “Matsumoto Yushi Seiyaku Co., Ltd.” It can be obtained as “Matsumoto Microsphere F-85” or “Matsumoto Microsphere F-100”.

  As the thermoplastic resin constituting the outer shell component of the gas-filled thermoplastic resin particles, for example, a polymer of (meth) acrylonitrile and a copolymer having a high (meth) acrylonitrile content are preferably used. As the other monomer (comonomer) of the copolymer, a monomer such as vinyl halide, vinylidene halide, styrene monomer, (meth) acrylate monomer, vinyl acetate, butadiene, vinylpyridine, chloroprene, or the like is used. The 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, allyl. It may be made crosslinkable with a crosslinking agent such as (meth) acrylate, triacryl formal, triallyl isocyanurate or the like. The crosslinked form is preferably uncrosslinked, but may be partially crosslinked so as not to impair the properties as a thermoplastic resin.

  Examples of the liquid that is vaporized by the heat contained in the thermally expandable microcapsule to generate a gas include hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, petroleum ether, methyl chloride, Examples thereof include chlorinated hydrocarbons such as methylene chloride, dichloroethylene, trichloroethane, and trichloroethylene.

  In the rubber composition according to the present invention, expanded graphite can be used as an optional component in addition to the essential components, preferably 1 to 10 parts by weight, more preferably 100 parts by weight of diene rubber. 2 to 8 parts by weight is blended and can be used in combination with the above-described thermally expandable microcapsules. If the amount is too small, the desired effect cannot be obtained, which is not preferable. On the other hand, if the amount is too large, the contact area at the micro level between the rubber surface and the icing road surface is decreased. . Moreover, when there are too many compounding quantities, since the abrasion resistance and mechanical strength of a rubber composition also fall, it is unpreferable. This expandable graphite is a powder substance having a particle size of 30 to 600 μm, preferably 100 to 350 μm, which encloses a substance that is vaporized by heat between graphite particles, and expands due to heat during vulcanization to expand the graphite. (Expanded Graphite) is preferred.

  The expanded graphite is a known material, and its manufacturing method is also known. For example, “Graph Guard 160-50” or “Graph Guard 160-80” manufactured by UCAR Graphtech of the United States is available from Sakai Industries. Goods are available.

  In the present invention, the thermally expandable microcapsule and the expanded graphite are desirably not expanded in the kneading step and the extrusion forming step of the rubber composition, but are expanded in the vulcanization step, and the expansion start temperature is preferably 120 to 200. One having a temperature of 140 ° C., more preferably 140 to 190 ° C. is used. If the expansion start temperature is less than 120 ° C., it is not preferable because it expands at the time of kneading or extrusion, and the processability may be impaired due to the change in the specific gravity of rubber during the process. Further, when the expansion start temperature exceeds 200 ° C., the processing temperature in the vulcanization process must be set to 200 ° C. or more, and the thermal deterioration of the diene rubber molecules as the main component of the rubber composition tends to become remarkable. This is not preferable.

  In the present invention, 3-octanoylthiopropyltriethoxysilane is used as an essential component as a coupling agent, and is first mixed with a diene rubber and silica at a high temperature of preferably 100 to 180 ° C, more preferably 140 to 180 ° C. Thus, it is possible to remove moisture contained in silica and ethanol generated when silica and a coupling agent react, and then add thermally expandable microcapsules to expand at a temperature of 120 to 200 ° C. As a result, the thermally expandable microcapsules are sufficiently expanded, and the expected performance on ice can be obtained. In the present invention, 3-octanoylthiopropyltriethoxysilane represented by the following formula (1) is blended in an amount of 5 to 15% by weight, preferably 6 to 12% by weight based on the silane weight. If the blending amount is too small, the dispersion becomes poor, which is not preferable. Conversely, if the blending amount is too large, a condensation reaction is likely to occur, and the desired performance is deteriorated.

  The 3-octanoylthiopropyltriethoxysilane of the formula (1) is a silane coupling agent having a triethoxysilyl group on one side and an octylic acid group on the other side. Since this coupling agent does not release any free sulfur, there is no possibility of rubber burning unlike the conventional case. For this reason, compared with the conventionally used bis (3 ′ triethoxysilylpropyl) tetrasulfide (for example, Si69), it can be mixed at a significantly high temperature, and moisture and alcohol can be easily volatilized during mixing. . Furthermore, it is expected that the amount of alcohol generated when reacting with a silanol group is small, so that it can be blended without inhibiting the expansion of the thermally expandable microcapsules and without worrying about the burning of the compound. .

  In addition to the above-described essential components, the rubber composition according to the present invention includes other reinforcing agents (fillers) such as carbon black, vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, various oils, anti-aging agents, Various additives generally blended for tires such as plasticizers and other general rubbers can be blended, and these additives are kneaded by a general method into a composition, which is vulcanized or crosslinked. Can be used for The blending amounts of these additives may be conventional conventional blending amounts as long as the object of the present invention is not adversely affected.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, it cannot be overemphasized that the scope of the present invention is not limited to these Examples.

Standard Example 1, Examples 1-5 and Comparative Examples 1-2
Sample preparation In the formulation shown in Table I, ingredients other than the vulcanization accelerator, sulfur and thermally expandable microcapsules were kneaded for 3 to 5 minutes in a 1.8 liter closed mixer, and the temperature reached 165 ± 5 ° C. When it was released, a master batch was obtained. A vulcanization accelerator, sulfur and thermally expandable microcapsules were kneaded with this master batch with an 8-inch open roll to obtain a rubber composition. Next, the obtained unvulcanized rubber composition was press vulcanized at 160 ° C. for 20 minutes in a 15 × 15 × 0.2 cm mold to prepare a vulcanized rubber sheet (test sample). The physical properties of vulcanized rubber were measured by the method. The results are shown in Table I.

Rubber physical property evaluation test method
Expansion coefficient The specific gravity of vulcanized rubber measured according to JIS K2249 was divided by the calculated specific gravity (theoretical value) obtained from the specific gravity of each compounding agent and the blending amount, and the difference from 1.0 was defined as the expansion coefficient. The results are shown as an index with the standard example 1 being 100.
A sheet obtained by vulcanizing each braking compound on ice was attached to a flat cylindrical base rubber, and measured using an inside drum type on-ice friction tester at a measurement temperature of -1.5 ° C, a load of 0.54 MPa, and a drum rotation speed of 25 km / h. It was measured. The value of standard example 1 was set to 100 and displayed as an index. Larger values indicate better performance on ice.
The asphalt road surface wetted and flooded was run at an initial speed of 40 km / h, the braking distance when braking was measured, and the value of standard example 1 was set to 100 and displayed as an index. The larger the value, the better the braking performance.

Table I footnote BR: BR1220 manufactured by ZEON (MW: 570,000)
NR: Natural rubber (TSR20)
Carbon Black: Show Black Cabot Show Black N234 (N ₂ SA = 125 m ² / g, CTAB = 119 m ² / g)
Silica: Rhodia Z1165MP
Aroma oil: Showa Shell Aromatic Oil Anti-aging agent: Flexis Santoflex 6PPD
Zinc flower: Zinc oxide 3 types manufactured by Shodo Chemical Industry Stearic acid: Nippon Oil & Fats Si69: Degussa silane coupling agent NXT: Crompton coupling agent (see formula (1) above)
Thermally expandable microcapsule: Matsumoto Microsphere F100 manufactured by Matsumoto Yushi Seiyaku
Sulfur: Tsurumi Chemical Vulcanization accelerator: Flexis accelerator CBS

  As described above, according to the present invention, by adding 3-octanoylthiopropyltriethoxysilane represented by the above formula (1) to a rubber composition containing silica and thermally expandable microcapsules, For example, the microcapsule is suitable for use as a tire tread of a studless tire because the degree of expansion of the microcapsule can be increased and thereby high performance on ice can be obtained.

Claims (2)

  For tire treads comprising 100 parts by weight of diene rubber, 10 to 60 parts by weight of silica and 5 to 15% by weight of silica, 3-octanoylthiopropyltriethoxysilane and 1 to 20 parts by weight of thermally expandable microcapsules Rubber composition.   The rubber composition according to claim 1, further comprising 1 to 20 parts by weight of expanded graphite with respect to 100 parts by weight of the diene rubber.