JP2007302850A - Rubber composition and pneumatic tire using same in tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition comprising thermally expandable microcapsules having a specific moisture content under undried condition. <P>SOLUTION: The rubber composition contains 100 pts.wt. of a diene rubber and 1-20 pts.wt. of thermally expandable thermoplastic resin microcapsules moistened with water and comprising a thermoplastic resin enclosing a substance generating a gas by vaporizing or expanding by heat. The shell material of the thermally expandable microcapsules comprises a thermoplastic resin prepared by the copolymerization of a nitrile monomer (I) as a main component, a monomer (II) having an unsaturated double bond and a carboxy group in the molecule, a monomer (III) having two or more polymerizable double bonds and optionally a co-polymerizable monomer (IV) for adjusting the characteristic feature of thermal expansion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition, and more particularly to a rubber composition containing wetted thermally expandable microcapsules having a specific moisture content in an undried state.

  Conventionally, heat expansion microcapsules and / or heat expansion graphite with silica and acrylonitrile polymer as a shell material are blended with diene rubber to improve performance on ice of tires. Patent Document 1 proposes a technique for stabilizing the quality at the time. However, the conventional thermally expandable microcapsules have a problem in that the strength of the shell is lowered in the presence of polar substances such as moisture, and the desired expansion performance cannot be exhibited.

JP 2002-356484 A

  In the present invention, since a specific modified acrylonitrile-based polymer is used as a shell material, the strength of the shell does not decrease even in the presence of moisture. The objective is to further improve the expansion rate of the microcapsules and to reduce the manufacturing cost of the thermally expandable microcapsules. Another object of the present invention is to provide a pneumatic tire using a rubber composition obtained by blending the thermally expandable microcapsule in a diene rubber for a tire tread and having a significantly improved frictional force on ice.

  According to the present invention, there is provided a rubber composition comprising 100 parts by weight of a diene rubber and 1 to 20 parts by weight of thermally expandable microcapsules comprising thermoplastic resin particles encapsulating a substance that is vaporized or expanded by heat to generate a gas. A nitrile monomer (I) whose main component is a shell material of the thermally expandable microcapsule, a monomer (II) having an unsaturated double bond and a carboxyl group in the molecule, two or more It is composed of a monomer (III) having a polymerizable double bond and, if necessary, a thermoplastic resin polymerized from a copolymerizable monomer (IV) for adjusting thermal expansion characteristics, and A rubber composition is provided in which the thermally expandable microcapsules are moistened with moisture.

  Moreover, according to this invention, the pneumatic tire which used the said rubber composition for the tire tread part is provided.

  When a wet thermally expandable microcapsule having a specific moisture content in an undried state in the production stage according to the present invention is used, the moisture present on the surface of the shell material of the microcapsule is first vaporized during heating expansion, Subsequently, a two-stage expansion occurs in which the expansion agent of the core agent is vaporized and expanded, so that the final expansion rate of the thermally expandable microcapsule is remarkably improved. Thereby, in the pneumatic tire using the rubber composition containing the thermally expandable microcapsule for the tire tread portion, a completely expanded uniform microcapsule is formed during the vulcanization and heating. The frictional force of the tire on ice is greatly improved.

The heat-expandable microcapsules made of acrylonitrile polymer as a shell material, which has been used in the past, are obtained by moistening a completely dried product at the final stage of production with paraffin. In the heat-expandable microcapsule using the coalescence as a shell material, drying at the final stage of production can be obtained by drying until a constant moisture content is obtained using a pressure-adjusted filter press. The moisture content is preferably 3 to 40% by weight, more preferably 5 to 30% by weight, based on the moisture content of the microcapsules. If the moisture content is less than 3% by weight or more than 40% by weight, the desired vulcanized rubber expansion coefficient and frictional force on ice cannot be obtained, which is not preferable. Here, the moisture content is obtained by measuring the initial weight, then measuring the dry weight after drying at 105 ° C. for 60 minutes, and calculating by the following formula.
(Initial weight−dry weight) × 100 / initial weight

  The shell material of the heat-expandable microcapsule used in the present invention is a monomer whose main component is a nitrile monomer (I) and has an unsaturated double bond and a carboxyl group in the molecule (II) from the monomer (III) having two or more polymerizable double bonds and, if necessary, the monomer (IV) copolymerizable with the monomer in order to adjust the expansion property It is composed of a polymerized thermoplastic resin. The thermoplastic resin preferably has 40 to 95% by weight of nitrile monomer (I) as a main component, more preferably 50 to 90% by weight, and has an unsaturated double bond and a carboxyl group in the molecule. 7 to 60% by weight of monomer (II), more preferably 10 to 50% by weight, and more preferably 0.05 to 5% by weight of monomer (III) having two or more polymerizable double bonds Is 0.2 to 3% by weight, and, if necessary, 0 to 20% by weight, more preferably 0 to 15%, of monomer (IV) copolymerizable with the monomer in order to adjust the expansion characteristics. From the weight percent, it can be obtained by polymerization by a conventional method.

  The thermally expandable microcapsule preferably has a volume retention of 50% or more, more preferably 70% or more after applying a load of 15 MPa to the expanded body heated and expanded in a state where it is not blended with rubber. . Further, in order to obtain thermally expandable microcapsules by these polymerizations, the polymerization initiator is an oil-soluble peroxide or azo compound and has a half-life of 1 to 25 hours at the reaction temperature. It is preferable to use it.

  Examples of the nitrile monomer (I) that can be used in the present invention include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, and any mixture thereof. And / or methacrylonitrile is particularly preferred. The amount of the acrylic monomer used is preferably 40 to 95% by weight of the thermoplastic resin, more preferably 50 to 90% by weight. If it is less than 40% by weight, it is difficult to achieve the object of the present invention.

  Examples of the monomer (II) having an unsaturated double bond and a carboxyl group in the molecule include acrylic acid, methacrylic acid, itaconic acid, styrenesulfonic acid or a sodium salt thereof, maleic acid, fumaric acid, and citraconic acid. And mixtures thereof. The amount of the monomer (II) having an unsaturated double bond and a carboxyl group in the molecule is preferably 7 to 60% by weight, more preferably 10 to 50% by weight of the thermoplastic resin. If it exceeds 60 parts by weight, it is difficult to achieve the object of the present invention. If it is less than 7 weight part, there exists a possibility that the expansibility in a high temperature area | region may fall.

  Examples of the monomer (III) having two or more polymerizable double bonds include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene, allyl methacrylate, triacryl formal, triallyl isocyanate, and ethylene glycol. Di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10- Decanediol di (meth) acrylate, PEG # 200 di (meth) acrylate, PEG # 400 di (meth) acrylate, PEG # 600 di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,4-butanediol Di (meth) acrylate, 1,6-hexane All di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, EO modified trimethylolpropane tri (meth) acrylate, glycerin di (meth) acrylate, dimethylol-tricyclode Candi (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, neopentyl glycol acrylate benzoate, trimethylolpropane acrylate benzoate, 2 -Hydroxy-3-acryloyloxypropyl (meth) acrylate, hydroxypivalate neopentyl glycol di (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, -Butyl-2-ethyl-1,3-propanediol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, phenyl glycidyl ether acrylate hexamethylene diisocyanate urethane prepolymer, phenyl glycidyl ether acrylate toluene diisocyanate urethane prepolymer, Examples include pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, and any mixtures thereof. The amount of the monomer (III) having two or more polymerizable double bonds is preferably 0.05 to 5% by weight of the thermoplastic resin, more preferably 0.2 to 3% by weight. . If this amount is less than 0.05% by weight or exceeds 5% by weight, the expansion performance in the high temperature region becomes poor, and it may be difficult to achieve the object of the present invention.

  In the present invention, as the optional monomer (IV) for adjusting the softening point, for example, vinylidene chloride, vinyl acetate, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (Meth) acrylates such as (meth) acrylate, t-butyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, β-carboxyethyl acrylate, styrene, styrene sulfonic acid Or a styrene monomer such as sodium salt thereof, α-methylstyrene, chlorostyrene, acrylamide, substituted acrylamide, methacrylamide, substituted methacrylamide, or the like, a monomer that undergoes a polymerization reaction with a general radical initiator, and any of these Is a mixture The The amount of the monomer (IV) used is preferably 0 to 20% by weight, more preferably 0 to 15% by weight of the thermoplastic resin, and if it exceeds 20% by weight, the object of the present invention is achieved. May become difficult.

  Examples of the polymerization initiator that can be used to polymerize the monomer mixture include dialkyl peroxide, diacyl peroxide, peroxy acid ester, peroxydicarbonate, and azo compound, which are preferably peroxides, Further, those having a half-life of preferably 1 to 25 hours, more preferably 5 to 20 hours at the reaction temperature. Such a polymerization initiator is effectively used for suspension polymerization of the monomer mixture.

  In the present invention, a wetted thermally expandable microcapsule having a specific moisture content in an undried state is obtained by subjecting the above monomer mixture to suspension polymerization by the same method as the conventional method for producing a thermally expandable microcapsule. After obtaining the heat-expandable microcapsule, it can be obtained by drying the heat-expandable microcapsule until the water content becomes 3 to 40% by weight using a pressure-adjusted filter press. As the dispersion stabilizer in the aqueous system used in the polymerization step, inorganic fine particles such as silica and magnesium hydroxide are used. In addition, as a dispersion stabilizing aid, a condensation product of diethanolamine and aliphatic dicarboxylic acid, polyvinylpyrrolidone, methylcellulose, Polyethylene oxide, polyvinyl alcohol, various emulsifiers and the like are used.

  Examples of the diene rubber used in the rubber composition of the present invention include any diene rubber conventionally used for tires and others, such as natural rubber (NR), polyisoprene rubber (IR), and various styrene-butadiene copolymers. Examples thereof include polymer rubber (SBR), various polybutadiene rubbers (BR), acrylonitrile-butadiene copolymer rubber, and the like. These rubbers can be used alone or as any blend.

  In the rubber composition of the present invention, 1 to 20 parts by weight, preferably 3 parts by weight of wet thermally expandable microcapsules having a moisture content of 3 to 40% by weight in the undried state with respect to 100 parts by weight of diene rubber It is mix | blended in the quantity of -10 weight part. If the blending amount is less than 1 part by weight, the desired frictional force on ice cannot be obtained. Conversely, if it exceeds 20 parts by weight, the wear resistance is remarkably lowered, which is not preferable.

  In addition to the heat-expandable microcapsules, the rubber composition according to the present invention can further contain heat-expandable graphite in an amount of 1 to 20 parts by weight, preferably 3 to 15 parts by weight. When the heat-expandable graphite is used in combination with the heat-expandable microcapsule according to the present invention, the expansion coefficient of the vulcanized rubber and the friction force on ice can be further improved.

  The heat-expandable graphite is a known material and is manufactured by a known manufacturing method. In general, graphite particles are immersed in a mixed solution of a strong acid substance and an oxidizing agent, and an acid is inserted between layers of the graphite particles by an intercalation process. For example, concentrated sulfuric acid is used as the strong acid substance and nitric acid is used as the oxidizing agent, thereby obtaining thermally expandable graphite in which sulfuric acid is inserted between the particles. This thermally expandable graphite expands when the interlayer is opened by the evaporation of the interlayer material by heat treatment.

  The rubber composition used in the pneumatic tire of the present invention further includes reinforcing agents such as carbon black and silica, vulcanization or crosslinking accelerators, various oils, anti-aging agents, fillers, plasticizers, and other general rubbers. Various compounding agents generally blended in the above can be blended, and the blending amounts of these blending agents can be set to conventional conventional blending amounts as long as the object of the present invention is not violated.

  EXAMPLES Hereinafter, although this invention is further demonstrated by an Example and a comparative example, it cannot be overemphasized that the technical scope of this invention is not limited to these Examples.

Preparation of wetted product of thermally expandable microcapsule used in the present invention After adding 45 g of colloidal silica having a solid content of 40% by weight, 1 g of diethanolamine-adipic acid condensate, 150 g of sodium chloride and 500 g of ion-exchanged water, and mixing. The pH was adjusted to 3.5 to produce an aqueous dispersion medium. As an oil system, 70 g of acrylonitrile, 70 g of methacrylonitrile, 70 g of methacrylic acid, 3 g of ethylene glycol dimethacrylate, and 1 g of azobis (2,4-dimethylvaleronitrile) are mixed to form a monomer mixture of a uniform solution. 20 g and 2-methylpentane 30 g were charged into an autoclave and mixed. Thereafter, the aqueous dispersion medium was charged into the autoclave, stirred for 5 minutes at 700 rpm, purged with nitrogen, and reacted at a reaction temperature of 60 ° C. for 8 hours. The reaction pressure was 0.5 MPa, and stirring was performed at 350 rpm. After the reaction, it was dried with a filter press so that the moisture content was 30% by weight, and a moisture-humidified product of the thermally expandable capsule according to the present invention was obtained.

Preparation of test sample According to the blending system (parts by weight) shown in Table 1, sulfur, a vulcanization accelerator, a thermally expandable microcapsule, and the moisture content of the thermally expandable microcapsule obtained by the above method having a moisture content of 30% by weight Each component except the wet product and the heat-expandable graphite was loaded into a 1.7 L closed Banbury mixer, mixed for 5 minutes, the rubber was discharged to the outside of the mixer and cooled to room temperature. Moisture moistening of the heat-expandable microcapsules obtained by the above-mentioned production method in which the sulfur, the vulcanization accelerator, and the heat-expandable microcapsules, which were introduced above, were added to the Banbury mixer, and the water content thereof was 30% by weight Products, thermally expandable graphite and the like were blended and mixed to obtain a rubber composition. Next, a part of the rubber composition was vulcanized at 170 ° C. for 15 minutes in a cylindrical mold having a diameter of 3 cm and a height of 1.5 cm, and the rubber was sufficiently cooled in water after vulcanization. Was cut out and subjected to a vulcanized rubber expansion coefficient test. The remaining rubber composition was vulcanized at 160 ° C. for 20 minutes in a 15 cm × 15 cm × 0.2 cm mold to prepare a test sample (rubber sheet), which was subjected to a friction test on ice.

Test method 1) Expansion rate test of vulcanized rubber: Divide the specific gravity of vulcanized rubber of each compounding system measured according to JIS K2249 by the calculated specific gravity (theoretical value) obtained from the components and compounding amount of each compounding system. The difference from 1.0 (the rate of decrease in the specific gravity of the vulcanized rubber) was taken as the expansion rate of the vulcanized rubber. The comparative example 1 was set to 100 and displayed as an index. The larger the index, the greater the expansion rate of the vulcanized rubber.
2) Friction force on ice: The rubber sheet was attached to a flat cylindrical base rubber, and using an inside drum type on-ice friction tester, the measurement temperature was -1.5 ° C, the load was 0.54 MPa, and the drum rotation speed was 25 km / hour. It was measured. The comparative example 1 was set to 100 and displayed as an index. The larger the index, the better the performance on ice.

Examples 1-2 and Comparative Examples 1-3
The results are shown in Table 1 below.

  According to the results in Table 1, the moisture content of the thermally expandable microcapsules according to the present invention is 30% by weight as compared with the rubber composition (Comparative Example 2) containing the conventional dry product thermally expandable microcapsules. It can be seen that the rubber composition (Example 1) in which the moisture-humidified product is blended can provide the vulcanized rubber having an excellent expansion coefficient and frictional force on ice. In addition, in the rubber composition (Example 2) in which thermally expandable graphite is further blended in addition to the wet product, the vulcanized rubber has a higher expansion coefficient and frictional force on ice than the rubber composition of Example 1. It turns out that it is obtained.

  As shown in Table 1 above, the rubber composition according to the present invention is excellent in the expansion coefficient and frictional force on ice of vulcanized rubber, so that it is used as a rubber composition for a tread of a pneumatic tire. If used, it is extremely useful.

Claims (4)

  A rubber composition comprising 100 parts by weight of a diene rubber and 1 to 20 parts by weight of thermally expandable microcapsules comprising thermoplastic resin particles encapsulating a substance that generates gas by being vaporized or expanded by heat, the thermal expansion A nitrile monomer (I) whose main component is a shell material of a conductive microcapsule, a monomer (II) having an unsaturated double bond and a carboxyl group in the molecule, and two or more polymerizable double bonds A thermoplastic resin polymerized from a monomer (III) having a copolymerizable monomer (IV) for adjusting thermal expansion characteristics, if necessary, and the thermally expandable microcapsule A rubber composition characterized by being moistened with moisture.   The rubber composition according to claim 1, wherein the thermally expandable microcapsule is wetted with water so as to have a moisture content of 3 to 40% by weight.   The rubber composition in which the rubber composition according to claim 1 or 2 further contains 1 to 20 parts by weight of thermally expandable graphite.   A pneumatic tire using the rubber composition according to claim 1 for a tire tread portion.