JP5322558B2 - Rubber composition for tire - Google Patents

Description

  The present invention relates to a tire rubber composition, and more particularly to a tire rubber composition having an increased frictional force on ice, for example, a tire tread rubber composition that suppresses performance degradation such as increase in hardness over time.

  As a technique for increasing the frictional force between rubber and ice required for the tread rubber of a studless tire, a technique of blending a thermally expandable microcapsule or thermally expandable graphite with a diene rubber has been devised (Patent Documents 1 to 3). ), A further improvement in the frictional force between rubber and ice has been demanded, and the increase in the hardness of the tread rubber over time has caused the problem of, for example, a decrease in performance after the second year.

  By the way, Patent Document 4 discloses a rubber composition in which capsule particles containing a water-repellent substance (silicone oil or the like) are blended in a rubber matrix. However, since this capsule does not thermally expand, friction on ice is disclosed. The improvement in power was insufficient. Patent Document 5 describes that the surface of a thermally expandable microcapsule is preliminarily coated with an oily substance in producing a rubber composition containing the thermally expandable microcapsule. The problem of performance degradation caused by the increase in hardness of the tread rubber over time has not been solved.

Japanese Patent Laid-Open No. 10-316801 Japanese Patent Laid-Open No. 11-035736 Japanese Patent Laid-Open No. 13-279020 JP 2003-327745 A JP 2003-105138 A

  Accordingly, an object of the present invention is to suppress the increase in hardness over time of a tire rubber composition in which a thermally expandable microcapsule is blended with a diene rubber.

  According to the present invention, (i) 100 parts by weight of a diene rubber, and (ii) 0.5 to 25 parts by weight of thermally expandable microcapsules enclosing a substance that generates gas by being vaporized or expanded by heat and nonpolar oil. A rubber composition for a tire comprising a thermoplastic resin obtained by polymerizing a monomer mixture containing 40% by weight or more of a nitrile monomer, wherein the shell material of the thermally expandable microcapsule comprises Is done.

  According to the present invention, the non-polar oil is encapsulated in the heat-expandable microcapsule blended with the diene rubber, thereby removing the water film caused by the friction between the tire and the icy road surface, and the frictional force between the rubber and ice. The oil contained in the capsule migrates gradually into the rubber over time, and the increase in hardness over time can be suppressed.

  As a result of researches to solve the above problems, the present inventors have made it possible to encapsulate a non-polar oil in a thermally expandable microcapsule in a rubber composition containing a diene-based rubber, thereby making the capsule shell material over time. The oil migrated into the rubber and successfully suppressed the increase in hardness over time.

  According to the present invention, 0.5 to 25 parts by weight of a heat-expandable microcapsule containing a non-polar oil and a substance that generates a gas by vaporization or expansion by heat in 100 parts by weight of a diene rubber, preferably 1 to A rubber composition containing 15 parts by weight, wherein the shell material of the thermally expandable microcapsule is composed of a thermoplastic resin obtained by polymerizing a monomer mixture containing 40% by weight or more of a nitrile monomer. The rubber composition achieves the above object.

  In the rubber composition of the present invention, if the amount of thermally expandable microcapsules encapsulating nonpolar oil is small, it is not preferable because the frictional force on ice and the increase in hardness over time are not improved. Although the increase in hardness is improved, it is not preferable because the wear resistance may be lowered.

  In the thermally expandable microcapsules to be blended with the rubber composition of the present invention, as the nonpolar oil, any known naphthenic oil, paraffin oil and aroma oil which are commercially available for rubber blending can be used. These can be used alone or in any mixture. If the oil is not nonpolar, it will not be compatible with the rubber and the effect of suppressing the increase in hardness cannot be obtained, which is not preferable. The weight fraction of the nonpolar oil in the total weight of the nonpolar oil and the substance that is vaporized or expanded by heat in the thermally expandable microcapsule and the nonpolar oil is preferably 1 to 20% by weight, More preferably, it is 10 weight%. There is an appropriate value between the amount of oil and the expansion rate. If the amount of oil is too small, there is no effect. On the other hand, if the amount is too large, expansion is difficult and sufficient frictional force on ice may not be obtained.

  As the diene rubber compounded in the rubber composition of the present invention, any diene rubber that can be used as a rubber composition for tires can be used. Specifically, natural rubber (NR), polyisoprene rubber (IR), polybutadiene can be used. Examples thereof include rubber (BR), styrene butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber, and the like, and these can be used alone or as any blend.

  The heat-expandable microcapsules blended in the rubber composition of the present invention include thermoplastic resin particles encapsulating a substance that generates a gas by being vaporized or expanded by heat and a nonpolar oil.

  The shell material of the thermally expandable microcapsule used in the present invention is composed of a nitrile monomer (I) as a main component monomer and a monomer (II) having an unsaturated double bond and a carboxyl group in the molecule. And, if necessary, a monomer (III) having two or more polymerizable double bonds, and a thermoplastic polymerized from the monomer (IV) copolymerizable with the monomer in order to adjust the expansion characteristics Consists of resin. This thermoplastic resin contains 40% by weight or more of nitrile monomer (I), preferably 40 to 90% by weight, more preferably 50 to 85% by weight, particularly preferably 55 to 70% by weight. It becomes. If the amount is small, it is difficult to achieve the object of the present invention.

The shell material of the thermally expandable microcapsule used in the present invention further contains, if necessary, 7 to 50% by weight, preferably 10 to 45%, of monomer (II) having an unsaturated double bond and a carboxyl group in the molecule. % By weight, more preferably 15-40% by weight,
0 to 5% by weight of monomer (III) having two or more polymerizable double bonds, preferably 0.05 to 5% by weight, more preferably 0.2 to 3% by weight, for adjusting the expansion characteristics The monomer (IV) copolymerizable with 0 to 20% by weight, preferably 0 to 15% by weight, more preferably 1 to 10% by weight, can be obtained by polymerization according to a conventional method.

  The heat-expandable microcapsules preferably have a volume retention of 50% or more, more preferably 70 to 100% after applying a load of 15 MPa to the expanded body heated and expanded in a state where it is not blended with rubber. A range is preferable.

  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 monomer (II) having an unsaturated double bond and a carboxyl group in the molecule that can be used as necessary in the present invention is not limited to these, but examples thereof include acrylic acid (AA). Methacrylic acid (MAA), itaconic acid, styrene sulfonic acid or sodium salt, maleic acid, fumaric acid, citraconic acid and mixtures thereof. If the amount used is too large, it may be difficult to achieve the object of the present invention. Conversely, if the amount used is too small, foamability in a high temperature region may be lowered.

  The monomer (III) having two or more polymerizable double bonds that can be used as necessary in the present invention is not limited to these, and examples thereof include divinylbenzene, divinylnaphthalene, and the like. Aromatic divinyl compound, allyl methacrylate, triacryl formal, triallyl isocyanate, 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-decandiol di (meth) acrylate, PEG # 200 di (meth) acrylate, PEG # 400 di (meth) acrylate, PEG # 600 di (Meth) acrylate, neo Nthyl glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, glycerin di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate , Dipentaerythritol hexa (meth) acrylate, neopentyl glycol acrylic acid benzoate, trimethylolpropane acrylic acid benzoate, 2-hydroxy-3-acryloyloxypropyl (me ) Acrylate, hydroxypivalate neopentyl glycol di (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, 2-butyl-2-ethyl-1,3-propanediol di (meth) acrylate, polytetramethylene glycol di ( (Meth) acrylate, phenylglycidyl ether acrylate hexamethylene diisocyanate urethane prepolymer, phenylglycidyl ether acrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate Isophorone diisocyanate Retanine prepolymers and the like and any mixtures thereof are included.

  Examples of the copolymerizable monomer (IV) for adjusting the expansion property that can be used as necessary in the present invention are not limited to these, but examples thereof include vinylidene chloride and vinyl acetate. , Methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth ) (Meth) acrylic acid esters such as acrylate and β-carboxyethyl acrylate, styrene, styrenesulfonic acid or its sodium salt, styrene monomers such as α-methylstyrene and chlorostyrene, acrylamide, substituted acrylamide, methacrylamide, substituted Metacri An amide, which is a common monomer polymerization reaction proceeds by a radical initiator, and any mixtures thereof.

  Examples of the polymerization initiator that can be used to polymerize the monomer mixture are as follows, but are not limited thereto. Preferably, the peroxide compound is a dialkyl peroxide, a diacyl peroxide, a peroxy acid ester, a peroxydicarbonate and an azo compound, and preferably has a half-life of 1 to 25 hours, more preferably 5 to 20 hours at the reaction temperature. It is produced by subjecting the monomer mixture to suspension polymerization using what it has.

  As the thermally expandable microcapsule used in the present invention, a conventional method for producing a thermally expandable microcapsule is generally used. That is, inorganic fine particles such as silica and magnesium hydroxide are used as an aqueous dispersion stabilizer. In addition, a condensation product of diethanolamine and aliphatic dicarboxylic acid, polyvinyl pyrrolidone, methyl cellulose, polyethylene oxide, polyvinyl alcohol, various emulsifying agents, and the like can be used as a dispersion stabilizing aid.

  Examples of the substance that generates gas upon vaporization by heat include, for example, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, isohexane, n-heptane, n-octane, isooctane, and n-decane. , Hydrocarbons such as isodecane, petroleum ether, liquids such as chlorinated hydrocarbons such as methyl chloride, methylene chloride, dichloroethylene, trichloroethane, trichloroethylene, or azodicarbonamide, dinitrosopentamethylenetetramine, azobisiso Examples thereof include solids such as butyronitrile, toluenesulfonyl hydrazide derivatives, and aromatic succinyl hydrazide derivatives.

  The heat-expandable microcapsule used in the present invention includes, for example, a substance that generates a gas by being vaporized or expanded by heat, a nonpolar oil, a monomer (I) (and, if necessary, a monomer (II) to a simple substance). The monomer (IV)) and a polymerization initiator are dispersed in an aqueous dispersion medium and suspension polymerization is performed.

  The thermally expandable microcapsule used in the present invention preferably contains substantially no ferromagnetic material. When a ferromagnetic material is contained, the material becomes ferromagnetic and contamination of equipment due to the ferromagnetic material may occur when the thermally expandable microcapsules are destroyed in the mixing, extrusion, and molding process. The phrase “substantially free of ferromagnetic material” means that the weight ratio of the ferromagnetic material is 5% by weight or less of the total of the substances that generate gas by vaporizing or expanding by heat and the nonpolar oil. It is preferably 3% by weight or less, more preferably 1% by weight or less, still more preferably 0.1% by weight or less, and most preferably 0% by weight.

  The heat-expandable microcapsules of the present invention do not expand in the mixing / extrusion / molding process, and are preferably expanded by the heat of vulcanization at a temperature of 140 to 180 ° C., more preferably 150 to 170 ° C.

  In addition to the components described above, the rubber composition according to the present invention includes a reinforcing agent (filler) such as carbon black and silica, a vulcanization or crosslinking agent, a vulcanization or crosslinking accelerator, various oils, an anti-aging agent, a plasticizer. Various additives that are generally blended for tires such as additives and other rubber compositions can be blended, and these additives are kneaded into a composition by a general method to be vulcanized or crosslinked. Can be used to do. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used.

  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.

Examples 1-8 and Comparative Example 1
Sample preparation In the formulation shown in Table I or Table II, ingredients other than the vulcanization accelerator, sulfur, thermally expandable microcapsules, and expanded graphite were kneaded in a 1.7 liter Banbury mixer for 5 minutes and reached 145 ° C. When released, a master batch was obtained. A vulcanization accelerator, sulfur, and thermally expandable microcapsules were kneaded with this master batch at 70 ° C. with an open roll to obtain a rubber composition.

  Next, the obtained rubber composition was vulcanized in a 15 × 15 × 0.2 cm mold at 170 ° C. for 10 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 as an index with the value of Comparative Example 1 being 100.

Rubber physical property evaluation test method
Friction force measurement on ice A sheet-like rubber piece vulcanized with each compound was attached to a flat cylindrical base rubber, and the friction coefficient on ice was measured with an inside drum type on-ice friction tester (measurement temperature was -1.5 ° C, load 5.5 kg / cm ³ , drum rotation speed 25 km / h). The result is expressed as an index with the value of Comparative Example 1 being 100, and the larger this number, the better the frictional force between rubber and ice.

Aging process is performed by air-heating aging treatment under conditions of 80 ° C. and 168 hours, and the hardness before and after aging treatment is measured according to JIS K 6253, [(hardness after aging−hardness before aging) / aging. Pre-hardness] × 100 was calculated. The result is expressed as an index with the value of Comparative Example 1 being 100, and the smaller this number, the smaller the rate of increase in hardness over time, and the better.

  -Abrasion resistance: Abrasion measured in accordance with JIS K6264 using a Lambourn Abrasion Tester (Iwamoto Seisakusho Co., Ltd.) under the conditions of load 6Kg (= 49N), slip rate 25%, time 4 minutes, room temperature. The weight loss is shown as an index, and the result is shown as an index with Comparative Example 1 being 100. The larger this figure, the better the uneven wear resistance.

Table I and II Footnote NR: Natural rubber RSS # 3
BR: Nippon Zeon Co., Ltd. polybutadiene rubber Nipol BR1220
Carbon black: Carbon black seast 6 manufactured by Tokai Carbon Co., Ltd.
Silica: Nippon Sil AQ manufactured by Nippon Silica Industry Co., Ltd.
Si69: Dexa SI69
Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Beads stearic acid manufactured by Nippon Oil & Fats Co., Ltd. Anti-aging agent: 6PPD manufactured by Flexis
Aroma oil: Aroma oil manufactured by Fuji Kosan Co., Ltd. Sulfur: Fine powder sulfur containing Jinhua seal oil manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Thermally expandable microcapsule A: Microsphere F100D manufactured by Matsumoto Yushi Seiyaku Co., Ltd.
Thermally expandable microcapsules (oil inclusion) BF: manufactured and used in the following manner.

Thermally expandable microcapsule B
As an aqueous component, 45 g of colloidal silica having a solid content of 40%, 1 g of diethanolamine-adipic acid condensate, 150 g of sodium chloride and 500 g of ion-exchanged water were mixed and adjusted to pH 3.5 to produce an aqueous dispersion medium. Next, as an oil component, 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-dimethylylvaleronitrile) are mixed to obtain a monomer mixture in a uniform solution. Prepared. To this monomer mixture, 20 g of isopentane, 30 g of 2-methylpentane and 0.5 g of aroma oil were added, and the mixture was charged into an autoclave, and an aqueous dispersion medium was further charged. After stirring the charged product at 700 rpm for 5 minutes, the inside of the autoclave was 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. Thermal expansion analysis of the thermal expansion microcapsules obtained by this reaction was performed. That is, when the expansion characteristics were analyzed by the method described in JP-A-11-002616 using a TMA-7 model manufactured by PerkinElmer, the foaming start temperature was 160 ° C., and the maximum expansion temperature was 210 ° C. there were.

Thermally expandable microcapsule C
The reaction was performed in the same procedure as the thermally expandable capsule B except that the amount of the aroma oil was changed to 2.6 g. The resulting thermally expandable microcapsule had a foaming start temperature of 159 ° C. and a maximum expansion temperature of 210 ° C.

Thermally expandable microcapsule D
The reaction was performed in the same procedure as that of the thermally expandable capsule B except that the amount of the aroma oil was changed to 8.8 g. The resulting thermally expandable microcapsule had a foaming start temperature of 162 ° C. and a maximum expansion temperature of 209 ° C.

Thermally expandable microcapsule E
The reaction was performed in the same procedure as that of the thermally expandable capsule B except that the amount of the aroma oil was changed to 12.5 g. The resulting thermally expandable microcapsule had a foaming start temperature of 160 ° C. and a maximum expansion temperature of 210 ° C.

Thermally expandable microcapsule F
The reaction was performed in the same procedure as the above-described thermally expandable microcapsule C, except that the aroma oil of the thermally expandable microcapsule C was changed to naphthen oil (Koumo Rex No. 2 manufactured by Nippon Oil Corporation). The resulting thermally expandable microcapsule had a foaming start temperature of 155 ° C. and a maximum expansion temperature of 215 ° C.

  According to the present invention, the non-polar oil is encapsulated in the heat-expandable microcapsules to be blended, so that the oil migrates from the capsule shell material into the rubber over time and suppresses the increase in hardness over time in addition to water absorption. Therefore, it is suitable for use as a tread rubber for a pneumatic tire tread, particularly a studless tire.

Claims (3)

(I) 100 parts by weight of a diene rubber and (ii) 0.5 to 25 parts by weight of thermally expandable microcapsules encapsulating a substance that generates gas by being vaporized or expanded by heat and a nonpolar oil, The shell of the thermally expandable microcapsule is composed of a thermoplastic resin obtained by polymerizing a monomer mixture containing 40% by weight or more of a nitrile monomer , and the nonpolar oil is composed of naphthenic oil and aroma oil. At least one kind of oil selected from the group, wherein the weight fraction of the non-polar oil in the total weight of the non-polar oil and the substance that is vaporized or expanded by heat to generate a gas of the thermally expandable microcapsule is The rubber composition for tires which is 1 to 20% . The tire rubber composition according to claim 1, wherein a weight fraction of the nonpolar oil is 5 to 20%, and a blending amount of the thermally expandable microcapsule is 5 to 25% by weight.   The shell material of the thermally expandable microcapsule is a nitrile monomer (I), a monomer (II) having an unsaturated double bond and a carboxyl group in the molecule, and, if necessary, two or more 3. A thermoplastic resin obtained by polymerizing a monomer (III) having a polymerizable double bond and a copolymerizable monomer (IV) for adjusting expansion characteristics. Rubber composition for tires.