JP2010037390A - Rubber composition for bonding steel cord and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for bonding a steel cord having an excellent balance of adhesiveness, such as initial adhesiveness, heat-resistant adhesiveness and wet heat resistant adhesiveness, and improved resistance to oxidative degradation. <P>SOLUTION: The rubber composition for bonding a steel cord contains a diene-based rubber, a metal alkane dithiol represented by general formula (1) below, a phenol compound or a phenol resin obtained by condensation of the phenol compound with formaldehyde, hexamethylenetetramine or a melamine derivative as a methylene donor thereof. The formula is Zn<SP>2+</SP>[S-(CH<SB>2</SB>)<SB>m</SB>-S]<SP>2-</SP>(1), wherein m is 4-8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rubber composition for bonding a steel cord, and in particular, a rubber composition suitably used for a rubber covering a steel cord such as a belt of a pneumatic tire, a carcass or a chacher or a rubber member adjacent to the covering rubber, The present invention also relates to a pneumatic tire using the rubber composition.

  The deterioration of rubber during tire use has become harsher due to deterioration under high heat generation due to higher speed and higher output of vehicles in recent years, deterioration due to thermal history accompanying tire life extension, oxidation deterioration, etc. Yes. Therefore, a higher level of rubber aging resistance (oxidation degradation resistance) is required.

  Conventionally, for example, brass plated steel cords are used as reinforcing materials for belt layers of passenger car tires, belt layers of large tires such as trucks and buses, carcass layers, and chacher layers. In the steel cord, when the surrounding rubber deteriorates and the rubber breaking resistance is lowered, cracks are likely to occur in the rubber layer. Also, the interface between the rubber and the steel cord is easily peeled off due to a decrease in heat-resistant adhesiveness against thermal history, moisture penetration during tire use, and moisture resistance and heat-resistant adhesion due to moisture absorption and temperature rise during tire manufacture and storage. . As a result, there is a problem that separation occurs.

  In order to improve the adhesion between the rubber composition and the steel cord, an organic acid metal salt is added to the rubber composition, or a methylene acceptor such as a resorcin derivative and a methylene donor such as a melamine derivative are added. It has been known. However, in any of the conventional techniques, although the individual adhesiveness is good, it is difficult to satisfy all of the initial adhesiveness, heat resistant adhesiveness and wet heat resistant adhesiveness at the same time. .

  By the way, in order to improve adhesiveness and durability in a rubber composition conventionally used for coating a steel cord, 1,6-hexamethylenedithiosulfate sodium dihydrate or 1,6-bis It is known to blend a compound having a methylene group linearly linked between sulfur atoms, such as (N, N-dibenzylthiocarbamoyldithio) hexane (see Patent Documents 1 to 4 below).

On the other hand, Patent Document 5 below proposes using a metal alkanedithiol as a crosslinking agent containing a diene rubber. Patent Document 6 below proposes using metal alkanedithiol as a surface treatment agent for improving the adhesion of a metal reinforcing material.
JP 2006-124474 A Japanese Patent Application Laid-Open No. 2004-323661 Japanese Patent Laid-Open No. 2003-082586 Japanese Patent Laid-Open No. 10-195237 JP 2005-320545 A Japanese Patent Laid-Open No. 02-248243

  1,6-hexamethylenedithiosulfate sodium dihydrate and 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane used in Patent Documents 1 to 4 described above are hybrid crosslinking agents. And can be used to replace part of it with sulfur. These hybrid cross-linking agents can improve adhesion compared to the case of using sulfur alone, but the improvement effect is not necessarily sufficient to satisfy the recent higher required performance. In particular, it has been found that the effect of improving adhesiveness after wet heat aging is insufficient.

  Patent Document 5 listed below discloses that a rubber composition in which a metal alkanedithiol is blended with a diene rubber as a crosslinking agent is used as a tire belt coating agent or the like. There is no disclosure of excellent effects when used.

  Further, the metal alkanedithiol described in the following Patent Document 6 is not only different from the present invention in that the metal is cobalt or nickel, but also uses the metal alkanedithiol as a surface treatment agent for steel cords, There is no disclosure about blending the steel cord rubber composition.

  As described above, although metal alkanedithiol itself has been known per se, in combination with resorcin and its methylene donor in combination with diene rubber, oxidation degradation resistance, initial adhesion, heat resistance adhesion It has not been known that an excellent effect can be obtained in the adhesion balance between the heat resistance and the wet heat resistance.

  The present invention has been made in view of the above points, and is excellent in the adhesion balance between the initial adhesion, the heat-resistant adhesion, and the moist-and-heat-resistant adhesion with respect to the steel cord, and improves the oxidation deterioration resistance. It is an object to provide a rubber composition for bonding steel cords.

  As a result of diligent study in view of the above problems, the present inventor used a predetermined metal alkanedithiol as a crosslinking agent in a diene rubber composition, and used this as a phenol compound or a phenol resin and hexamethylene tetramine or a melamine derivative. By using in combination, it has been found that the oxidation degradation resistance can be improved, and the adhesion performance that cannot be obtained individually, in particular, the initial adhesion, heat-resistant adhesion, and moist heat-resistant adhesion can be improved in a balanced manner. It came to be completed.

That is, the steel cord bonding rubber composition according to the present invention is a phenolic resin obtained by condensing a diene rubber, a metal alkanedithiol represented by the following general formula (1), and a phenolic compound or a phenolic compound with formaldehyde. And hexamethylenetetramine or a melamine derivative as the methylene donor.
Zn ²⁺ [S— (CH ₂ ) _m —S] ²⁻ (1)
In the formula, m = 4 to 8.

  In the pneumatic tire according to the present invention, the rubber composition for bonding a steel cord is used for a rubber covering a steel cord of a tire or a rubber member adjacent to the covering rubber.

  According to the present invention, oxidation degradation resistance can be improved by using the predetermined metal alkanedithiol as a crosslinking agent. In addition, by using a phenolic compound or phenolic resin and hexamethylenetetramine or melamine derivative in combination with the metal alkanedithiol, not only initial adhesiveness but also heat and moisture resistant adhesive properties can be improved in a balanced manner. it can. Therefore, it is possible to obtain a rubber composition for adhering steel cords having excellent adhesive properties as well as rubber breaking properties, and it is possible to provide a pneumatic tire having excellent durability performance using the rubber composition.

  Embodiments of the present invention will be described below.

  In the rubber composition according to the present invention, a diene rubber is used as a rubber component. As the diene rubber, natural rubber (NR) and / or diene synthetic rubber can be used. Examples of the diene-based synthetic rubber include isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), chloroprene rubber (CR), and nitrile rubber (NBR). These diene rubbers can be used alone or in a blend of two or more. Among these, it is preferable to use NR, which is easy to stretch and crystallize, and has excellent fracture characteristics, that is, it is preferable to use NR alone or a blend of NR 60% by weight and diene synthetic rubber 40% by weight.

  The metal alkanedithiol represented by the above formula (1) is blended with the rubber composition according to the present invention. By using such a metal alkanedithiol as a crosslinking agent, the oxidation deterioration resistance of the rubber composition can be improved. Specific examples of the metal alkanedithiol include zinc salts such as 1,4-butanedithiol, 1,6-hexanedithiol, and 1,8-octanedithiol, and zinc of 1,6-hexanedithiol. A salt (m = 6 above) is particularly preferably used. The metal alkanedithiol can be obtained by reacting an alkanedithiol such as 1,6-hexanedithiol and a zinc salt in an appropriate solvent as described in JP-A-2005-320545.

  The compounding amount of the metal alkanedithiol is preferably 0.1 to 4 parts by weight with respect to 100 parts by weight of the diene rubber, and with a relatively small amount, the oxidation deterioration resistance, the methylene acceptor described later and In the adhesiveness as a combined effect with a methylene donor, an excellent effect can be exhibited.

  A methylene acceptor and a methylene donor are blended in the rubber composition of the present invention. Adhesion between the rubber and the steel cord can be enhanced by a curing reaction between the hydroxyl group of the methylene acceptor and the methylene group of the methylene donor.

  As the methylene acceptor, a phenolic compound or a phenolic resin obtained by condensing a phenolic compound with formaldehyde is used. Examples of the phenol compounds include phenol, resorcin, and alkyl derivatives thereof. Alkyl derivatives include derivatives of relatively long-chain alkyl groups such as nonylphenol and octylphenol, as well as methyl group derivatives such as cresol and xylenol. The phenol compound may contain an acyl group such as an acetyl group as a substituent.

  In addition, phenolic resins obtained by condensing phenolic compounds with formaldehyde include resorcin-formaldehyde resins, phenolic resins (that is, phenol-formaldehyde resins), cresol resins (that is, cresol-formaldehyde resins), and a plurality of phenols. Formaldehyde resins made of compounds are included. These are uncured resins that have liquid or heat fluidity.

  Among these, from the viewpoint of compatibility with the rubber component and other components, and the density and reliability of the resin after curing, the methylene acceptor is preferably resorcin or a resorcin derivative, and in particular, resorcin or resorcin-alkylphenol. A co-condensed formalin resin is preferably used.

  The blending amount of these phenolic compounds or phenolic resins is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 4 parts by weight with respect to 100 parts by weight of the diene rubber.

  As the methylene donor, hexamethylenetetramine or a melamine derivative is used. Examples of the melamine derivative include methylol melamine, a partially etherified product of methylol melamine, a condensate of melamine, formaldehyde and methanol, and among them, hexamethoxymethyl melamine is particularly preferable.

  As a compounding quantity of a hexamethylenetetramine or a melamine derivative, it is preferable that it is 0.2-20 weight part with respect to 100 weight part of diene rubbers, More preferably, it is 1-8 weight part.

  The rubber composition according to the present invention may contain an organic acid metal salt in order to improve the rubber physical properties and adhesiveness after aging. The compounding amount of the organic acid metal salt is preferably 0.03 to 0.40 parts by weight, more preferably 0.1 to 0.3 parts by weight, in terms of metal, with respect to 100 parts by weight of the diene rubber. is there.

  Examples of organic acid metal salts include cobalt naphthenate, cobalt stearate, cobalt oleate, cobalt neodecanoate, cobalt rosinate, cobalt borate, cobalt maleate, and other organic acid nickel salts. And organic acid molybdenum salts.

  The rubber composition according to the present invention usually contains carbon black and / or silica as a reinforcing filler. The blending amount of both can be blended with 0 to 200 parts by weight of carbon black and 100 to 100 parts by weight of silica with respect to 100 parts by weight of diene rubber. It can mix | blend in 20-200 weight part.

  Preferably, carbon black is used as the reinforcing filler, and the fracture characteristics of the rubber composition are ensured by blending the carbon black at 30 to 80 parts by weight with respect to 100 parts by weight of the diene rubber. Becomes easy. Silica may or may not be blended, and when blended, it is preferably used at 15 parts by weight or less. This is because if the amount of silica exceeds 15 parts by weight, it is difficult to ensure dispersibility unless a silane coupling agent is added.

  In addition, it does not specifically limit as a kind of carbon black, For example, various grades, such as ISAF, HAF, and FEF, are mentioned. Examples of the type of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), and surface-treated silica.

  The rubber composition according to the present invention usually contains sulfur as a vulcanizing agent. The compounding amount of sulfur is preferably 1 to 10 parts by weight, more preferably 2 to 8 parts by weight with respect to 100 parts by weight of the diene rubber. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and oil-treated sulfur, and are not particularly limited.

  A vulcanization accelerator can be blended in the rubber composition according to the present invention. The vulcanization accelerator is not particularly limited, but N-cyclohexyl-2-benzothiazole sulfenamide (CBS), Nt-butyl-2-benzothiazole sulfenamide (BBS), N-oxydiethylene-2 -Sulfenamide-based additives such as benzothiazole sulfenamide (OBS), N, N-diisopropyl-2-benzothiazole sulfenamide (DPBS), N, N-dicyclohexyl-2-benzothiazole sulfenamide (DCBS) Sulfur accelerators are preferably used. The blending amount of the vulcanization accelerator is not particularly limited, but is preferably 0.3 to 2.0 parts by weight with respect to 100 parts by weight of the diene rubber.

  In the rubber composition according to the present invention, in addition to the above-described components, various compounding agents generally blended into a steel cord bonding rubber composition can be arbitrarily blended. Examples of such a compounding agent include zinc white, stearic acid, wax, oil, anti-aging agent, processing aid and the like, and they can be appropriately compounded within a range not departing from the object of the present invention.

  The rubber composition for adhering steel cords of the present invention can be prepared by kneading using a commonly used mixer such as a Banbury mixer or a kneader, and used as a coating rubber composition for coating various steel cords. be able to. Moreover, it is used not only as a rubber composition for coating but also as a rubber composition provided adjacent to the rubber for coating and used to improve the adhesion between the steel cord and the rubber through the rubber for coating. Can do.

  Specifically, as a reinforcing material such as a rubber coated rubber of a steel cord in a pneumatic tire, for example, a belt layer (1), a carcass layer (2), and a chacher layer (3) of the large radial tire (T) shown in FIG. Steel cord topping rubber is preferably used as a steel cord covering (topping) rubber to be used, and a steel cord topping material is manufactured by a topping device such as a steel calender according to a conventional method, and this is used as a tire reinforcing member and molded and vulcanized according to a conventional method Thus, a pneumatic radial tire can be manufactured.

  Moreover, it can use suitably also as rubber members, such as a belt lower pad (4) adjacent to these steel cord members, and a belt edge tape (5). The belt lower pad (4) is provided in the shoulder portion so as to fill a space formed between the width direction end of the belt layer (1) and the radially inward carcass layer (2). It is a rubber member having a triangular cross section. The belt edge tape (5) is a thin rubber member disposed in the gap at the end in the width direction between the two belt layers (1).

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

  According to the composition shown in Table 1 below, each rubber composition of Examples and Comparative Examples was prepared by kneading according to a conventional method using a closed Banbury mixer. The detail of each component of Table 1 is as follows.

・ Natural rubber: RSS # 3,
Carbon black: HAF, “Seast 300” manufactured by Tokai Carbon Co., Ltd.
・ Zinc flower: “Zinc flower 3” manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: “Sant Flex 6PPD” manufactured by Flexis,
・ Resorcin: “Resorcin” manufactured by Sumitomo Chemical Co., Ltd.
Melamine derivative: Hexamethoxymethyl melamine, “Cyreet 963L” manufactured by Mitsui Cytec Co., Ltd.
Cobalt stearate: “Cobalt stearate” (Co content: 9.5% by weight) manufactured by Japan Energy Co., Ltd.
KA9188: 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane, “Vulcuren VP KA9188” manufactured by LANXESS,
HTS: 1,6-hexamethylenedithiosulfate sodium dihydrate, “Duralink-HTS” manufactured by Flexis,
Metal alkanedithiol: a zinc salt of 1,6-hexanedithiol represented by the formula (1) (provided that m = 6) manufactured by LANXESS
Insoluble sulfur: “Miklon HS OT-20” (80% by weight is sulfur content) manufactured by Flexis
・ Vulcanization accelerator DCBS: N, N-dicyclohexyl-2-benzothiazolesulfenamide, “Noxeller DZ-G” manufactured by Ouchi Shinsei Chemical Co., Ltd.
-Vulcanization accelerator BBS: Nt-butyl-2-benzothiazole sulfenamide, "Noxeller NS-P" manufactured by Ouchi Shinsei Chemical Co., Ltd.

  About each obtained rubber composition, while evaluating destruction resistance and hardening resistance as oxidation-deterioration resistance, adhesiveness (initial adhesiveness, heat-resistant adhesiveness, wet heat-resistant adhesiveness) was evaluated. The test evaluation method is as follows.

-Fracture resistance property: About the test piece vulcanized on condition of 150 degreeC x 30 minutes, the elongation at break before aging was measured according to the tensile test method (No. 3 dumbbell use) based on JIS K6251. Next, after aging the test piece in a gear oven at 90 ° C. for 192 hours, the elongation at break after aging was measured in the same manner, and the retention ratio against the elongation at break before aging was determined. The larger the value, the better the fracture resistance.

Curing resistance: 100% modulus was measured in the same manner as the measurement of elongation at break, and the retention of 100% modulus after aging with respect to 100% modulus before aging was determined. The smaller the value, the better the curing resistance.

・ Initial adhesion: A cord member in which brass-plated steel cords are arranged at 17/25 mm intervals and sandwiched between seated evaluation rubbers (thickness = 1 mm) is created, and the two cord members are stacked, 150 ° C. × 30 minutes The test piece for evaluation of 25 mm width was produced by vulcanization under the conditions of The obtained test piece was subjected to a peeling test between two layers of steel cords using an autograph “DCS500” manufactured by Shimadzu Corporation, and the rubber coverage of the steel cords after peeling was visually observed. Evaluation was made at 100%. The larger the numerical value, the better the initial adhesiveness.

Heat resistant adhesiveness: After aging the test piece in an oven at 100 ° C. for 96 hours, a peel test similar to the initial adhesiveness is performed, and the rubber coverage of the steel cord after peeling is visually observed. 0 to 100%. The larger the value, the better the heat resistant adhesiveness.

・ Heat and heat resistant adhesion: After leaving the test piece in a saturated steam at 105 ° C. for 96 hours, a peel test similar to the initial adhesion is performed, and the rubber coverage of the peeled steel cord is visually observed. 0 to 100%. The larger the value, the better the wet heat resistance.

  The results are as shown in Table 1, and by adding resorcin and its methylene donor as in Comparative Examples 2 and 3, an improvement in adhesion was observed with respect to Comparative Example 1, but the level was still It was inadequate and inferior in oxidation resistance. Further, in Comparative Example 4 in which the vulcanization accelerator was changed from DCBS to BBS, the adhesiveness was greatly deteriorated.

  Further, although Comparative Example 5 in which metal alkanedithiol was blended as a crosslinking agent but resorcin and its methylene donor were not used in combination, the effect of improving the oxidative degradation resistance was insufficient, and adhesion, particularly heat-resistant adhesion It was also inferior. On the other hand, in Comparative Example 6 in which the amount of the metal alkanedithiol was too large, the adhesiveness was worsened because the vulcanized rubber was too hard. Further, Comparative Example 7 using KA9188 instead of metal alkanedithiol and Comparative Example 8 using HTS instead of metal alkanedithiol were particularly inferior in wet heat resistance.

  On the other hand, in Examples 1-5 which combined the said metal alkanedithiol with resorcinol and its methylene donor, it was excellent in oxidation-deterioration resistance, and all adhesion | attachment of initial stage adhesiveness, heat-resistant adhesiveness, and heat-and-moisture resistant adhesiveness. The properties were balanced and an excellent adhesive effect was obtained. In particular, by combining the metal alkanedithiol, it was possible to suppress deterioration of the adhesive even when BBS was used as the vulcanization accelerator, and to achieve both excellent oxidation resistance and adhesion.

  The rubber composition for bonding a steel cord of the present invention is useful as a rubber for coating a steel cord, which is a reinforcing material for a pneumatic tire, or a rubber adjacent thereto, and is used for a belt layer of a passenger car tire, a large tire such as a truck / bus. It can be used for belt layers, carcass layers, chacher layers, under belt pads, belt edge tapes and the like.

1 is a half sectional view of a pneumatic tire according to an embodiment.

Explanation of symbols

T ... Pneumatic tire, 1 ... belt layer, 2 ... carcass layer, 3 ... chacher layer, 4 ... belt pad under belt, 5 ... belt edge tape

Claims (4)

A diene rubber, a metal alkanedithiol represented by the following general formula (1), a phenolic compound or a phenolic resin obtained by condensing a phenolic compound with formaldehyde, and a hexamethylenetetramine or melamine derivative as a methylene donor thereof. A rubber composition for bonding steel cords.
Zn ²⁺ [S— (CH ₂ ) _m —S] ²⁻ (1)
(Where m = 4-8)   The rubber composition for bonding steel cords according to claim 1, comprising 0.1 to 4 parts by weight of the metal alkanedithiol with respect to 100 parts by weight of the diene rubber.   The said phenolic compound or phenol-type resin is 0.1-10 weight part with respect to 100 weight part of said diene rubbers, The said hexamethylenetetramine or melamine derivative is contained 0.2-20 weight part. The rubber composition for bonding steel cords as described.   The pneumatic composition characterized in that the rubber composition for bonding a steel cord according to any one of claims 1 to 3 is used for a rubber covering a steel cord of a tire or a rubber member adjacent to the covering rubber. tire.

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