JP2009155430A - Rubber composition for tire bead filler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire bead fillers, which can improve processability and low exothermic property, while enhancing hardness. <P>SOLUTION: Provided is the rubber composition for the tire bead fillers, characterized by compounding a rubber component containing natural rubber as a main component with a polymer gel comprising dienic polymer particles having a glass transition point of 10 to 80°C. The polymer gel preferably has a toluene swelling index Qi of <16. The polymer gel is preferably blended in an amount of 1 to 20 pts.wt. based on 100 pts.wt. of the rubber component. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a bead filler rubber composition used for a bead filler of a pneumatic tire.

  In recent years, as the improvement in driving stability of automobiles has been demanded, bead portions that affect driving stability, especially bead fillers arranged in the bead portions, are required to have higher hardness, that is, higher elasticity. Has been.

  Conventionally, as measures for increasing the hardness of a bead filler, blending a phenol resin, increasing the amount of carbon black which is a reinforcing filler, and the like are known (see Patent Documents 1 to 3 below). However, when trying to meet the above requirements with these conventional techniques, there is a problem that workability deteriorates because a large amount of carbon black or a large amount of resin needs to be blended. Further, in order to reduce the fuel consumption of tires, bead fillers are also required to have low heat generation, but the above-described conventional technology cannot meet such demands.

Recently, a technology has been proposed in which a rubber gel (polymer gel) is added to a rubber composition such as a tire tread to improve wet slip resistance and the like (see Patent Document 4 below). However, there is no disclosure of using a polymer gel having a high glass transition point as in the present invention in a rubber composition for a tire bead filler containing a rubber component mainly composed of natural rubber.
JP 2002-105249 A JP 2002-105248 A Japanese Patent Laid-Open No. 11-240981 Special table 2004-530760 gazette

  This invention is made | formed in view of the above point, and provides the rubber composition for tire bead fillers which can improve workability (process property) and low exothermic property, aiming at high hardness. For the purpose.

  The present inventor has solved the above problem by replacing a part of carbon black compounded as a reinforcing filler in a rubber composition for tire bead filler mainly composed of natural rubber with a specific polymer gel. As a result, the present invention has been completed.

  That is, the rubber composition for tire bead filler according to the present invention is obtained by blending a polymer component, which is a diene polymer particle having a glass transition point of 10 to 80 ° C., with a rubber component mainly composed of natural rubber. is there. Moreover, the pneumatic tire according to the present invention is provided with a bead filler made of the rubber composition.

  According to the present invention, by blending the specific polymer gel with the bead filler rubber composition, it is possible to improve the workability by reducing the viscosity while increasing the hardness, and to reduce the heat generation. be able to.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the rubber composition according to the present invention, the rubber component contains natural rubber as a main component. That is, the rubber component is composed of natural rubber alone or a blend of natural rubber and other rubber. In the case of blend, the rubber component contains 50% by weight or more of natural rubber. Preferably, the rubber component contains 80% by weight or more of natural rubber.

  The other rubber is not particularly limited. For example, isoprene rubber, styrene butadiene rubber, butadiene rubber, styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, Examples include diene rubbers such as chloroprene rubber and nitrile rubber, butyl rubber, and halogenated butyl rubber. These may be used alone or in combination of two or more.

  The rubber composition according to the present invention is blended with a polymer gel that is specific diene polymer particles (rubber particles). Such a polymer gel can be produced by crosslinking a rubber dispersion. Examples of the rubber dispersion include rubber latex produced by emulsion polymerization, rubber dispersion obtained by emulsifying solution-polymerized rubber in water, and examples of the crosslinking agent include organic peroxides and organic azo compounds. And sulfur-based crosslinking agents. The rubber particles can also be crosslinked by copolymerization with a polyfunctional compound having a crosslinking action during the emulsion polymerization of the rubber. Specifically, the methods disclosed in Japanese Patent No. 3739198, Japanese translations of PCT publication No. 2004-504465, Japanese translations of PCT publication No. 2004-506058, Japanese translations of PCT publication No. 2004-530760 can be used.

  Examples of the diene polymer constituting the polymer gel include the various diene rubbers described above, and these can be used alone or in combination of two or more. In particular, those containing styrene butadiene rubber (SBR) as a main component are preferable.

  In the present invention, the polymer gel having a glass transition point (Tg) of 10 to 80 ° C. is used. The higher the glass transition point, the better the physical properties, so that the glass transition point is more preferably 20 ° C. or higher, and further preferably 50 ° C. or higher. By using a material having such a high glass transition point, the hardness of the rubber composition can be effectively increased. Here, the glass transition point is a value (temperature increase rate 20 ° C./min) measured using differential scanning calorimetry (DSC) in accordance with JIS K7121.

  The polymer gel preferably has a toluene swelling index Qi of less than 16. The toluene swelling index Qi is more preferably 1 to 15, and further preferably 3 to 8. When the toluene swelling index Qi is 16 or more, the particles become soft, the reinforcing effect is lost, and the strength is lowered. The gel content of the polymer gel is not particularly limited, but is preferably 94% by weight or more.

  Here, the toluene swelling index and the gel content are measured by swelling a polymer gel in toluene and then drying it. That is, 250 mg of polymer gel was swollen in 25 mL of toluene under shaking for 24 hours, centrifuged at 20000 rpm, weighed, then dried to a constant mass at 70 ° C., and then dried mass Weigh. The gel content is the weight ratio (%) of the polymer gel after drying to the polymer gel used. The toluene swelling index is determined by Qi = (wet mass of gel) / (dry mass of gel).

  As the polymer gel, those modified with a compound having a functional group such as OH (hydroxyl) group are preferably used. The polymer gel is composed of a diene polymer and has a C═C double bond on the particle surface. Therefore, by using a compound having an OH group and a reactivity with respect to the C═C double bond, Can incorporate OH groups.

  Examples of such compounds (modifiers) include hydroxyalkyl (such as hydroxybutyl acrylate or methacrylate, hydroxyethyl acrylate or methacrylate, hydroxypropyl acrylate or methacrylate, as described in JP-T-2004-506058. And (meth) acrylate.

  The particle size of the polymer gel is not particularly limited, but an average particle size (DVN value according to DIN 53 206) of about 20 to 600 nm is preferably used.

  The polymer gel is preferably blended at 1 to 20 parts by weight with respect to 100 parts by weight of the rubber component, and more preferably 3 to 20 parts by weight. If the amount of the polymer gel is too small, the above effect will be insufficient. On the contrary, if the amount of the polymer gel is too large, the reinforcing property is insufficient, which is not preferable.

  In the rubber composition according to the present invention, carbon black and / or an inorganic filler is usually blended as a filler. Although the compounding quantity of this filler is not specifically limited, It is preferable that it is 50-100 weight part with respect to 100 weight part of rubber components. Examples of the inorganic filler include silica, talc, and clay.

  You may mix | blend a phenol resin with the rubber composition which concerns on this invention. As a phenol resin, what is generally mix | blended for the hardness improvement in the rubber composition for bead fillers can be used. For example, novolak-type phenol resin, resorcin or a derivative thereof can be used. Although the compounding quantity of these phenol resins is not specifically limited, It is preferable that it is 1-40 weight part with respect to 100 weight part of rubber components.

  Examples of the novolac type phenol resin include unmodified phenol resin (straight phenol resin) obtained by condensing phenol and formaldehyde, alkyl-substituted phenol resin, and oil-modified phenol resin. Examples of the alkyl-substituted phenol resin include a cresol-formaldehyde resin using cresol instead of phenol, and an alkyl phenol resin using another alkyl phenol such as xylenol or octylphenol instead of phenol. Examples of the oil-modified phenol resin include novolak-type modified phenol resins modified with various oils such as cashew nut oil, tall oil, and rosin oil.

  Examples of the resorcin derivative include condensates of resorcin and formaldehyde such as resorcin / formaldehyde resin initial condensate and resorcin / alkylphenol co-condensed formaldehyde resin.

  Hexamethylenetetramine or a melamine derivative as a methylene donor can be used in combination with the phenol resin. Examples of the melamine derivative include hexamethoxymethyl melamine obtained by reacting melamine and formaldehyde, hexamethylol melamine pentamethyl ether, and polyvalent methylol melamine. The blending amount of these methylene donors is preferably 30 to 200 parts by weight with respect to 100 parts by weight of the phenol resin.

  In addition to the above-described components, the rubber composition according to the present invention is generally used in tire rubber compositions such as softeners, anti-aging agents, zinc white, stearic acid, vulcanizing agents, and vulcanization accelerators. Various additives can be blended.

  The rubber composition for a bead filler according to the present invention having the above is used as a rubber composition for constituting a bead filler of a pneumatic radial tire, and the bead filler can be formed by vulcanization molding according to a conventional method. it can. Here, the bead filler fills the space surrounded by the scooping portion formed when the end portion of the carcass ply is folded and locked along the bead core, the carcass ply body, and the bead core. Therefore, the bead filler is an annular rubber member disposed along the outer periphery of the bead core, and is generally formed in a triangular shape with a taper in a radially outward direction.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, a rubber composition for bead filler was prepared according to the composition shown in Table 1 below. Each component in Table 1 is as follows.

・ Natural rubber: RSS No. 3,
Polymer gel 1: “Micromov 1” manufactured by Rhein Chemie (polymer gel based on SBR, Tg = 65 ° C., toluene swelling index Qi = 7, gel content = 96 wt%, OH group-modified product)
Polymer gel 2: “Micromofu 30” manufactured by Rhein Chemie (polymer gel based on BR, Tg = −80 ° C., toluene swelling index Qi = 5.9, gel content = 97 wt%, OH group-modified product)
・ Carbon black: “Seast SO” manufactured by Tokai Carbon Co., Ltd.
・ Phenolic resin: “Sumilite Resin PR13349” manufactured by Sumitomo Bakelite Co., Ltd.
・ Hexamethylenetetramine: “Noxeller H” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Melamine derivative: Hexamethoxymethyl melamine, “CRA100” manufactured by Mitsui Cytec Co., Ltd.

  In each rubber composition, 6 parts by weight of oil (“Process NC140” manufactured by Japan Energy Co., Ltd.) and zinc white (“Zinc Hana 3” manufactured by Mitsui Mining & Smelting Co., Ltd.) are used as a common compound. 3 parts by weight, 2 parts by weight of stearic acid (“Lunac S-25” manufactured by Kao Corporation), 1 part by weight of an anti-aging agent (“Santflex 6C” manufactured by Flexis), and vulcanization accelerator NS (Emerging Ouchi) 1 part by weight of “Noxeller NS-P” manufactured by Chemical Industry Co., Ltd. and 3 parts by weight of sulfur (“Sanfel EX” manufactured by Sanshin Chemical Industry Co., Ltd.) were blended.

  Each rubber composition obtained was evaluated for processability (Mooney viscosity) in an unvulcanized state, and vulcanized at 160 ° C. for 30 minutes to produce a test piece of a predetermined shape. Was used to measure the hardness and the dynamic viscoelasticity test to measure and evaluate the elastic modulus and exothermicity. Each measurement / evaluation method is as follows.

-Workability (Mooney viscosity): Using a rotorless Mooney measuring machine manufactured by Toyo Seiki Co., Ltd., after preheating the unvulcanized rubber at 100 ° C for 1 minute, the torque value after 4 minutes was measured in Mooney units (ML (1 + 4) 100 ° C.). A result is displayed with the index | exponent which set the value of the comparative example 1 to 100, and it shows that a viscosity is so low that an index is small and it is excellent in workability (processability).

Hardness: Based on JIS K6253, the hardness was measured at 23 ° C. using a type A durometer (A type).

-Dynamic viscoelasticity test: Using a viscoelasticity spectrometer manufactured by Toyo Seiki Co., Ltd., with a test piece extended by 10%, under conditions of dynamic strain of 2% and frequency of 50 Hz at room temperature (23 ° C.) The dynamic elastic modulus (E ′) and the dynamic loss coefficient (tan δ) were measured.
Dynamic elastic modulus (E ′): Storage elastic modulus in the above dynamic viscoelasticity test, expressed as an index with the value of Comparative Example 1 as 100. A larger index indicates a higher elastic modulus and higher hardness.
Dynamic loss coefficient (tan δ): The ratio of loss elastic modulus to storage elastic modulus in the dynamic viscoelasticity test, expressed as an index with Comparative Example 1 taken as 100. The smaller the index, the less heat is generated and the lower the exothermic property.

  The results are as shown in Table 1, and in the example according to the present invention, higher hardness (higher elasticity) is achieved with respect to Comparative Example 1 which is a control, and moreover, workability due to a decrease in viscosity is achieved. In addition to being excellent, it was also excellent in low heat generation. On the other hand, in Comparative Example 2 in which the amount of carbon black was increased and Comparative Example 3 in which the amount of phenol resin was increased, although the hardness was increased, the workability was deteriorated and the low heat generation was also deteriorated. If it is an Example which concerns on this invention, it was able to improve workability and low exothermicity with respect to these comparative examples 2 and 3, maintaining high hardness. In Comparative Example 4 in which a polymer gel having a low glass transition point was blended, no increase in hardness was achieved.

  The rubber composition according to the present invention can be suitably used as a bead filler rubber for a pneumatic tire.

Claims (4)

  A rubber composition for tire bead fillers, comprising a rubber component mainly composed of natural rubber and a polymer gel that is a diene polymer particle having a glass transition point of 10 to 80 ° C.   The rubber composition for a tire bead filler according to claim 1, wherein the polymer gel has a toluene swelling index Qi of less than 16.   The rubber composition for a tire bead filler according to claim 1 or 2, comprising 1 to 20 parts by weight of the polymer gel with respect to 100 parts by weight of the rubber component.   The pneumatic tire provided with the bead filler which consists of a rubber composition of any one of Claims 1-3.