JP2005320374A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition composed of a diene rubber compounded with a thermally expandable microcapsule, eliminating the problem caused by the compounding of silica, and having improved expandability and aging resistance without lowering abrasion resistance. <P>SOLUTION: The rubber composition contains 100 pts.wt. of a diene rubber, 1-25 pts.wt. of thermally expandable microcapsules and 2-30 pts.wt. of a silica surface-treated with at least one kind of a silane coupling agent X expressed by formula (I): Y<SB>3</SB>SiC<SB>3</SB>H<SB>6</SB>SC(=O)R (Y groups are each independently a group selected from methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy and acetoxy groups; and R is a 1-18C hydrocarbon group selected from cyclic or branched alkyl, alkenyl, aryl and aralkyl groups). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rubber composition containing silica surface-treated with a silane coupling agent, and more specifically, in a rubber composition containing silica, a reaction involving the silane coupling agent during compounding without impairing the reinforcing property. The present invention relates to a rubber composition useful for a tread of a pneumatic tire containing silica that has been surface-treated with an organosilane compound that can suppress, improve dispersibility of silica, and improve wear resistance, skid performance on ice, and the like.

  In recent years, in tread compounds for passenger car tires, silica has become the mainstream in order to reduce tire fuel consumption and improve wet skid performance. In such a silica-containing rubber composition, a silane coupling agent having an alkoxysilyl group that chemically reacts with silica in the molecule is used for the purpose of improving the reinforcement and processability. However, such a silica-containing rubber composition involves a reaction between a silane coupling agent and silica or a reaction between silica and a polymer via a silane coupling agent during mixing. As a result, alcohol is generated to cause porosity, and the mixing temperature must be controlled (for example, 140 to 165 ° C.), resulting in a decrease in productivity. For this reason, it is proposed not to add a silane coupling agent to a rubber composition but to pre-treat silica with a silane coupling agent (see, for example, Patent Documents 1 to 6).

  By the way, in order to ensure the performance on ice such as driveability, braking performance, and handling stability of studless tires on snowy and snowy road surfaces, conventionally, from the viewpoint of improving rubber quality, a rubber composition containing natural rubber has a glass transition temperature. Rubbers that are hard to cure even at low temperatures have been improved by blending polymers such as low butadiene rubber, increasing the blending amount of softeners, and blending silica-based fillers, short fibers, porous materials, etc. However, since the wear resistance and handling stability are lowered, improvement of the low temperature characteristics of the rubber alone is not satisfactory.

  On the other hand, Patent Document 7 has already proposed that a rubber composition having excellent frictional force on ice can be provided by blending thermally expandable microcapsules with diene rubber. In this compounding system, ethanol generated by the reaction of silica with moisture and a silane coupling agent inhibits microcapsule expansion, and the silica reaction requires a mixing temperature of 145 to 160 ° C. At such a high temperature, there was a problem that the rubber molecular chain was broken during mixing to generate a polymer radical, and the generated radical increased the hardness change during aging.

US Pat. No. 4,141,751 EP0177664 JP 59-206469 A Japanese Patent Laid-Open No. 5-17705 Japanese Patent Laid-Open No. 9-328631 JP 2002-3652 A JP 11-35736 A

  Accordingly, an object of the present invention is to eliminate the problems caused by silica compounding in a system in which thermally expandable microcapsules are blended with a diene rubber, to improve the expansibility without impairing the wear resistance, and The object is to provide a rubber composition having improved aging properties.

According to the present invention, 100 parts by weight of diene rubber, 1 to 25 parts by weight of thermally expandable microcapsules, and formula (I):
Y ₃ SiC ₃ H ₆ SC (═O) R (I)
Wherein Y is independently a group selected from a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group and an acetoxy group, and R is a cyclic or branched alkyl group or an alkenyl group. a hydrocarbon radical is a C ₁ -C ₁₈ selected from aryl and aralkyl groups)
A rubber composition for a tire tread comprising 2 to 30 parts by weight of silica surface-treated with at least one silane coupling agent X represented by the formula:

  In the present invention, silica surface-treated with an organic silane compound (I) such as 3-octanoylthio-propyltriethoxysilane is blended with 100 parts by weight of diene rubber and 1 to 25 parts by weight of thermally expandable microcapsules. This makes it possible to improve the expandability by suppressing the generation of ethanol without reducing the wear resistance, and to reduce the change in hardness during aging by suppressing the breakage of the rubber molecular chain by mixing at a low temperature (below 145 ° C). It becomes.

  As the rubber component to be blended in the rubber composition according to the present invention, any diene rubber that can be used for tires and other general uses, such as various natural rubbers (NR), various polyisoprene rubbers (IR), Examples include various styrene-butadiene copolymer rubbers (SBR), various polybutadiene rubbers (BR), various acrylonitrile-butadiene copolymer rubbers (NBR), and these can be used alone or as any blend. .

  As a preferred component, NR / BR of natural rubber (NR) and butadiene rubber (BR) = 30 to 80/70 to 20 (parts by weight), more preferably 40 to 70/60 to 30 (parts by weight). Can give a blend. If the blending ratio of NR in this blending is too large, the wear resistance and the frictional force on ice at low temperatures may be reduced. Conversely, if the blending ratio is too small, the strength of the rubber may be lowered. The natural rubber can be any natural rubber conventionally used in the rubber industry, and the same applies to polybutadiene rubber. As natural rubber and polybutadiene rubber, it is more preferable to use polybutadiene rubber having a glass transition temperature of −55 ° C. or lower.

  As the thermally expandable microcapsule used in the present invention, it is possible to use thermally expandable thermoplastic resin particles in which a liquid or solid that generates gas by vaporization, decomposition or chemical reaction by heat is encapsulated in a thermoplastic resin, These are heated and expanded at a temperature equal to or higher than the expansion start temperature, usually 140 to 190 ° C., and contain a gas in the outer shell made of the thermoplastic resin. The particle size is preferably 5 to 300 μm, more preferably 10 to 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 25%, and most preferably 8 to 20%. %. When this volume ratio is too small, the frictional force on ice is not sufficiently improved. On the other hand, if it is too large, the wear resistance is remarkably deteriorated and there is a possibility that it is lacking in practicality.

  As such heat-expandable thermoplastic resin particles (unexpanded particles), for example, the trade name “Expancel 091DU-80” or “Expancel 092DU-120” from EXPANCEL in Sweden, or It is available from Matsumoto Yushi Seiyaku Co., Ltd. under the trade name “Matsumoto Microsphere F-85” or “Matsumoto Microsphere F-100”.

  The thermoplastic resin constituting the outer shell 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 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 (meth) acrylonitrile content is preferably used. As the other monomer (comonomer) in the case of the copolymer, monomers such as vinyl halide, vinylidene halide, styrene monomer, (meth) acrylate monomer, vinyl acetate, butadiene, vinylpyridine, chloroprene are used. . In addition, said thermoplastic resin is divinylbenzene, ethylene glycol di (meth) acrylate, tothiethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, It may be crosslinkable with a crosslinking agent such as allyl (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 liquids or solids that generate gas by vaporization, decomposition, or chemical reaction by heat include hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, petroleum-ether, methyl chloride, Liquids such as chlorinated hydrocarbons such as methylene chloride, dichloroethylene, trichloroethane, trichloroethylene, or azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, toluenesulfonylhydrazide derivatives, aromatic succinylhydrazide derivatives Such solids.

  In the rubber composition according to the present invention, 1 to 25 parts by weight, preferably 3 to 10 parts by weight of thermally expandable microcapsules are blended with 100 parts by weight of the diene rubber. If the amount is too small, the frictional force on ice decreases, which is not preferable. On the other hand, if the amount is too large, the wear resistance decreases, which is not preferable.

The silica used in the present invention may be any silica that can be used for tires, such as natural silica, synthetic silica, more specifically precipitated silica, dry silica, and wet silica. According to the present invention, this silica is used after being uniformly mixed with the silane coupling agent X represented by the formula (I) and subjected to a surface treatment. This surface treatment is by chemical or physical bonding such as reaction between silica and the trialkoxysilyl group (—SiT ₃ ) of the silane coupling agent X of the formula (I). The silane coupling agent X may be subjected to surface treatment on silica after pretreatment such as hydrolysis and condensation. In order to complete the reaction between silica and the silane coupling agent X, a method of hydrolyzing and condensing the silane coupling agent X in advance and then reacting with silica, a method of heat aging, a catalyst (for example, acid, alkali, A method of adding a reaction accelerator such as an organometallic catalyst such as tin / aluminum can also be used.

  The silane coupling agent X used in the present invention can be synthesized by a known method. Specifically, using the method disclosed in JP-A No. 2001-505225 (filler-containing rubber), by the reaction of the corresponding mercaptosilane and acid anhydride or acid chloride or the transesterification of the corresponding mercaptosilane and thioester. Can be obtained. Note that 3-octanoylthiopropyltriethoxysilane is commercially available as NXT silane from Nippon Unicar Co., Ltd.

  Silica particles can be surface treated using known methods. Specific examples include a dry reaction method and a wet reaction method. The dry reaction method is a method in which silica particles are charged into an apparatus capable of high-speed stirring such as a Henschel mixer, and the silane coupling agent X or a partial hydrolysis solution of the silane coupling agent X is dropped while stirring. The dripping method is preferably a method capable of uniformly reacting the silane coupling agent X, and a known method can be used. For example, a method of gradually dropping, a method of spraying in a mist, and a method of introducing gaseous silane are known. The wet reaction method is a method in which silica particles are reacted in a state dispersed in a solution of a silane coupling agent, and then dried if necessary. As the solvent to be used, water, alcohol or a mixture thereof is preferable. In any of the dry reaction method and the wet reaction method, a known method for increasing the reactivity of the hydroxyl group on the surface of the silane coupling agent and the silica particles can be used. Examples thereof include a method of post-heat treatment, and a method of using a condensation catalyst such as an acid, an alkali, or an organic metal (for example, one based on tin or aluminum).

  In the present invention, the bulk density retention rate of silica formed by surface treatment with the silane coupling agent X is preferably 50 to 150%, more preferably 60 to 110%. Here, the bulk density retention rate (%) is a numerical value derived from the following formula (II). The silane coupling agent treatment rate (%) is the ratio of the silane coupling agent used to treat the silica surface, (weight of silane coupling agent / weight of silica before treatment) × It means a numerical value derived from the equation of 100.

  If the bulk density retention is too small, a sufficient amount of surface treatment cannot be obtained, so that a desired effect is difficult to obtain. On the other hand, if it is too large, the surface treatment is not uniformly performed, and dispersibility in rubber and processability are sufficient. This is not preferable because there is a risk that it will disappear. The bulk density was measured according to JIS K-5101 and evaluated with three test samples randomly sampled from surface-treated silica.

  The silica surface-treated with the silane coupling agent X used in the present invention is blended in an amount of 2 to 30 parts by weight, preferably 5 to 25 parts by weight, per 100 parts by weight of the rubber component. If this amount is too small, the temperature dependence of E ′ (storage modulus) increases, which is not preferable because the frictional force on ice decreases, and conversely if too large, the dispersibility of silica deteriorates and wear resistance decreases. This is not preferable. The silane coupling agent treatment rate of the silane coupling agent X according to the present invention is not particularly limited, but is preferably 1 to 25%, and more preferably 4 to 25%.

  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 that are generally blended for tires such as plasticizers and other general rubbers can be blended. These additives are kneaded and vulcanized by a general method to obtain a composition, and then vulcanized. Or it can be used to crosslink. 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 1-6 and Comparative Examples 1-4
Sample preparation In the formulation shown in Table I, ingredients other than the vulcanization accelerator and sulfur were kneaded for 5 minutes with a 3 liter closed mixer, and released when the temperature reached 145 ± 5 ° C to obtain a master batch. A vulcanization accelerator and sulfur were kneaded with this masterbatch with an open roll to obtain a rubber composition. Using this rubber composition, unvulcanized physical properties were evaluated by the following test methods. The results are shown in Table I.

  Next, the resulting rubber composition was vulcanized in a 15 × 15 × 0.2 cm mold at 160 ° C. for 30 minutes to prepare a vulcanized rubber sheet. The physical properties of the vulcanized rubber were measured by the following test methods. It was measured. The results are shown in Table I.

Rubber physical property evaluation test method

  Abrasion resistance: A wear loss volume was measured under the conditions of a temperature of 23 ° C. and a slip ratio of 50% using a Lambourn abrasion tester. The result was expressed as an index with the value of Standard Example 1 as 100. It shows that it is excellent in abrasion resistance, so that this figure is large.

  Hardness change due to aging: Hardness before and after aging (80 ° C x 96 hours) (measured at 80 ° C according to JIS K-6200) is measured, and the value of the ratio (after aging / before aging) is a standard example The value of 1 was taken as 100 and expressed as an index. The smaller this value, the smaller the hardness change due to aging.

  Friction force on ice: The coefficient of friction on ice was measured with an inside drum type on-ice friction tester. The measurement temperatures were −1.5 ° C. and −5 ° C., and the result was expressed as an index with the value of standard example 1 being 100. The larger this number, the higher the frictional force on ice.

Table I Footnote NR: Natural rubber (TSR20)
BR: Nippon Pol 1220 manufactured by Nippon Zeon Co., Ltd.
Silica: Nippon Silica Industry Co., Ltd. nip seal AQ
A-1289: Nippon Unicar Co., Ltd. bis (3-triethoxysilylpropyl) tetrasulfane A-1589: Nihon Unicar Co., Ltd. bis (3-triethoxysilylpropyl) disulfane NXT: Nihon Unicar Co., Ltd. NXT silane (3-octanoylthio-propyltrialkoxysilane)

A-1289 surface-treated silica and A-1589 surface-treated silica: NUCA-1289 silane or NUCA-1589 manufactured by Nihon Unicar Co., Ltd. was slowly added to Nippon Sil AQ (Nippon Silica Industry) under stirring with a Henschel mixer, and dry-type reaction silica particles Adjusted. The silane coupling agent-reacted silica particles were obtained by drying in an explosion-proof furnace set at 150 ° C. for 1 hour.
NXT-treated silica: The above NXT silane was slowly added to Nipsil AQ (Nippon Silica Kogyo Co., Ltd.) being stirred with a Henschel mixer to prepare dry-reacted silica particles. The silane coupling agent-reacted silica particles were obtained by drying in an explosion-proof furnace set at 150 ° C. for 1 hour. The bulk density retention was determined as described above, and the results are shown in Table I.

Microsphere: Matsumoto Yushi Seiyaku Co., Ltd. Thermally expandable microcapsule Microsphere F100D
GrarGuard: UCAR GRAPHITE expanded graphite GRAF Guard160-80N

CB: Show Black N339 manufactured by Showa Cabot Co., Ltd.
6C: SANTOFLEX 6PPD made by FLEXSYS
Zinc Hana: Toho Zinc Co., Ltd.
Stearic acid: Beads stearic acid YR manufactured by NOF Corporation
Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
NS: SANTOCURE NS made by FLEXSIS
Sulfur: Sulfur refined at Karuizawa Refinery (5% oil content)

  As is clear from the results in Table I, in Examples 1 to 6, the wear resistance and the frictional force on ice are improved, and the change in hardness is small. On the other hand, when A-1589 and 3-octanoylthiopropyltriethoxysilane were added as in Comparative Examples 1 and 2, the abrasion resistance and friction on ice were higher than those of A-1289 in Standard Example 1. Power is inferior. Further, as in Comparative Examples 3 to 4, when silica pretreated with A-1289 and A-1589 is blended, the wear resistance and frictional force on ice are improved as compared with the addition of liquid, but NXT treated silica blending is performed. Not as effective.

  As described above, since the rubber composition according to the present invention can achieve both wear resistance and frictional force on ice, it is useful as a rubber composition for a tread of a pneumatic tire.

Claims (4)

100 parts by weight of diene rubber, 1 to 25 parts by weight of thermally expandable microcapsules and formula (I):
Y ₃ SiC ₃ H ₆ SC (═O) R (I)
Wherein Y is independently a group selected from a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group and an acetoxy group, and R is a cyclic or branched alkyl group or an alkenyl group. , A C _{1 to} C ₁₈ hydrocarbon group selected from an aryl group and an aralkyl group)
A rubber composition for a tire tread, comprising 2 to 30 parts by weight of silica surface-treated with at least one silane coupling agent X represented by the formula:   The rubber composition for a tire tread according to claim 1, wherein the bulk density retention of the silica surface-treated with the silane coupling agent X is 50 to 150%.   The rubber for tire treads according to claim 1 or 2, wherein a surface treatment amount of the silica with the silane coupling agent X satisfies a relationship of 1 ≦ (weight of silane coupling agent / weight of silica before treatment) × 100 ≦ 25. Composition.   The rubber composition for a tire tread according to any one of claims 1 to 3, wherein an average glass transition temperature of the diene rubber is -55 ° C or lower.