JP5356047B2 - Rubber composition for covering steel cord and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition, which is, on the adhesiveness to a steel cord even when the amount of zinc in a rubber composition is decreased, excellent in the adhesion balance between the initial adhesion, the heat resistant adhesion and the wet-heat resistant adhesion, and has the excellent resistance to oxidative deterioration. <P>SOLUTION: This rubber composition for use in the coating of a steel cord contains a diene-based rubber, a phenol compound or the phenol-based resin in which a phenol compound is condensed with formaldehyde, hexamethylenetetramine or a melamine derivative as a methylene donor, and composite zinc oxide particles of which surfaces comprise zinc oxide and in which a proportion of zinc oxide component accounting for the whole particles is 5-95 wt.%, wherein the composite zinc oxide particles as a zinc element component of from more than 1.8 to not more than 15 pts.wt. is blended with 100 pts.wt. of the diene-based rubber. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a rubber composition, and more specifically, a rubber composition suitably used mainly for coating steel cords such as belts, carcass, and chachers of pneumatic tires, and the rubber composition The present invention relates to a pneumatic tire using a steel cord coated rubber.

  In general, zinc and its compounds, which are heavy metals, are concerned about environmental impacts, particularly the effects on water and aquatic organisms, and it is desired to reduce or remove them from the rubber composition. In addition, zinc has a large price fluctuation worldwide, and due to the recent rise in zinc price, zinc reduction is desired from the viewpoint of cost reduction.

  Conventionally, it has been proposed to use activated zinc white having a large specific surface area as zinc oxide to be blended in a rubber composition (see Patent Document 1 below). Since the physical properties of rubber can be improved by using activated zinc white, it is conceivable to reduce the blending amount of zinc oxide while maintaining the physical properties of rubber.

  In recent years, due to the trend of resource saving, improvement in tire durability performance is required as the tire extends its life, and the adhesion between the steel cord and the rubber composition covering it is increasingly important for the tire durability performance. It has become. That is, in a tire, a steel cord is used as a reinforcing material for a belt layer of a passenger car tire, a belt layer of a large tire such as a truck / bus, a carcass layer, and a chacher layer. If the rubber around the steel cord deteriorates and the fracture resistance and curing resistance are impaired, 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, separation occurs.

  Under such circumstances, in the rubber composition covering the steel cord, when ordinary zinc oxide such as zinc white 3 is replaced while reducing the amount of activated zinc white, the oxidation deterioration resistance of the steel cord and rubber Adhesiveness will be insufficient.

  By the way, it is known that a composite zinc oxide particle having a zinc oxide layer on the particle surface and containing an inorganic metal salt is blended in a rubber composition (see Patent Documents 2 and 3 below). However, Patent Document 2 is mainly intended for tire treads, and does not disclose that the composite zinc oxide particles are used in combination with a methylene acceptor such as a resorcin derivative and a methylene donor such as a melamine derivative. Moreover, the compounding amount of zinc element is too small. Patent Document 3 only discloses a tire as an application, and does not disclose that the composite zinc oxide particles are used in combination with the methylene acceptor and the methylene donor.

JP 2003-0555505 A JP 2001-316527 A Japanese Patent Laid-Open No. 60-262841

  The present invention has been made in view of the above points, and even when the amount of zinc in the rubber composition is reduced, the initial adhesion, heat-resistant adhesion, and moisture-heat-resistant adhesion with respect to the steel cord can be improved. An object of the present invention is to provide a rubber composition for coating a steel cord, which has an excellent adhesion balance and can exhibit excellent oxidation deterioration resistance.

As a result of intensive studies in view of the above problems, the present inventor has used the composite zinc oxide particles whose particle surfaces are composed of zinc oxide in substitution for ordinary zinc oxide, thereby preventing oxidation deterioration and steel. It has been found that the amount of zinc in the rubber composition can be reduced while maintaining good adhesion to the cord. Furthermore, by reducing the amount of the zinc component having a high specific gravity, the weight of the tire can be reduced, and the CO ₂ reduction and fuel efficiency improvement of the vehicle can be achieved. As a result, it has been conceived that the burden on the environment can be reduced.

The present invention is based on the above findings, the gist of which is a diene rubber, 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. A composite zinc oxide particle whose surface is composed of zinc oxide and the ratio of the zinc oxide component in the entire particle is 5 to 95% by weight, and the diene system using the composite zinc oxide particle as a zinc element component It is a rubber composition for coating a steel cord formed by blending 1.9 parts by weight to 6.0 parts by weight with respect to 100 parts by weight of rubber.

  The present invention also relates to a pneumatic tire in which the rubber composition for covering a steel cord is used as a rubber for covering a steel cord that reinforces at least one of a belt layer, a carcass layer, and a chacher layer of the tire.

  According to the present invention, by mixing a predetermined amount of the composite zinc oxide particles together with a phenolic compound or a phenolic resin and hexamethylenetetramine or a melamine derivative, initial adhesiveness, heat resistant adhesiveness and It is excellent in the adhesion balance of moisture and heat resistance and can exhibit excellent oxidation deterioration resistance. Therefore, for example, the amount of zinc in the rubber composition can be reduced without deteriorating the adhesiveness and oxidation deterioration resistance, so that the weight of the tire can be reduced.

  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.

  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 is compounded with composite zinc oxide particles whose particle surfaces are composed of zinc oxide (ZnO). As the composite zinc oxide particles, particles having a zinc oxide component ratio (that is, zinc oxide purity) to the entire particles of 5 to 95% by weight are used. When the ratio of the zinc oxide component is less than 5% by weight, it becomes difficult to exhibit the original effect of zinc oxide as a vulcanization acceleration aid. On the other hand, if it exceeds 95% by weight, the low specific gravity effect and the zinc content reduction effect as composite zinc oxide cannot be obtained. The ratio of the zinc oxide component is preferably 20 to 80% by weight, more preferably 30 to 70% by weight.

  As the composite zinc oxide particles, those having a zinc oxide layer on the particle surface and an internal component as a core (core) being an inorganic metal salt are preferably used. Since it is zinc oxide on the particle surface that reacts with the vulcanization accelerator blended in the rubber composition, a layer of zinc oxide is provided on the particle surface, and an inorganic metal salt other than zinc is used for the core Thus, the amount of zinc can be reduced without impairing the effect as a vulcanization acceleration aid. It does not specifically limit as an inorganic metal salt as an internal component, It can select suitably from what is generally used as inorganic fillers, such as a silica, Especially a calcium carbonate is mentioned as a preferable thing.

The zinc oxide layer on the particle surface is preferably made of active zinc white having a high specific surface area. By using the composite zinc oxide particles whose surface is activated, the oxidation deterioration resistance and the adhesiveness can be further improved. From such a point of view, the composite zinc oxide particles preferably have a nitrogen adsorption specific surface area of 6.0 m ² / g or more, more preferably 10 m ² / g or more, according to the BET method. The upper limit of the nitrogen adsorption specific surface area is not particularly limited, but is usually 100 m ² / g or less. The nitrogen adsorption specific surface area by the BET method is measured according to the BET method defined in ASTM D3037-89.

  The composite zinc oxide particles preferably have a true specific gravity of 5.0 or less, more preferably 4.0 or less. By reducing the true specific gravity, it is possible to reduce the weight of the rubber composition, which leads to a reduction in the weight of the tire. The lower limit of the true specific gravity is not particularly limited, but is usually 2.5 or more. The true specific gravity is measured by a gas phase substitution method (pycnometer method).

  The compounding quantity of the said composite zinc oxide particle exceeds 1.8 weight part with respect to 100 weight part of said diene rubbers as a zinc element component contained in this particle | grain. When the blending amount is 1.8 parts by weight or less, not only the effect of improving the oxidation deterioration resistance is insufficient, but also the adhesiveness as a combined effect with the methylene acceptor and the methylene donor, particularly the heat resistant adhesiveness and the moisture resistant property. The effect of improving thermal adhesiveness cannot be obtained. The lower limit of the amount of the composite zinc oxide particles is preferably 1.9 parts by weight or more, more preferably 2.0 parts by weight or more. On the other hand, the upper limit of the compounding amount of the composite zinc oxide particles is preferably 15 parts by weight or less, more preferably 6.0 parts by weight or less, still more preferably 4 from the viewpoint of weight reduction of the tire due to the reduction of the zinc amount. 0.0 parts by weight or less.

  The rubber composition according to the present invention may contain carbon black as a reinforcing filler. Although the compounding quantity of carbon black is not specifically limited, It is preferable that it is 30-80 weight part with respect to 100 weight part of diene rubbers at the point which makes the fracture | rupture characteristic and fatigue resistance performance of a rubber composition compatible. The type of carbon black is not particularly limited, and examples thereof include various grades such as ISAF, HAF, and FEF. In addition, you may mix | blend inorganic fillers, such as a silica, as a filler.

  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 organic acid nickel salts in addition to organic acid cobalt salts such as cobalt naphthenate, cobalt stearate, cobalt oleate, cobalt neodecanoate, cobalt rosinate, cobalt borate, and cobalt maleate. And organic acid molybdenum salts.

  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 coating rubber composition can be arbitrarily blended. Examples of such a compounding agent include stearic acid, wax, oil, anti-aging agent, processing aid, and the like, and can be appropriately compounded within a range not violating the object of the present invention.

  The rubber composition of the present invention can be prepared by kneading using a commonly used mixer such as a Banbury mixer or a kneader, and can be used as a rubber composition for coating various steel cords. In particular, it is preferably used as a steel cord covering (topping) rubber used as a reinforcing material for a belt layer, a carcass layer, a chacher layer, etc. of a pneumatic tire. This is used as a tire reinforcing member, and a pneumatic radial tire can be manufactured by molding and vulcanizing according to a conventional method.

  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,
・ Resorcin: “Resorcin” manufactured by Sumitomo Chemical Co., Ltd.
Melamine derivative: Hexamethoxymethyl melamine, “Cyreet 963L” manufactured by Mitsui Cytec Co., Ltd.
Zinc oxide 1: “Zinc Hana 3” manufactured by Mitsui Mining & Smelting Co., Ltd. (Zinc oxide purity = 99.0% by weight or more, nitrogen adsorption specific surface area by BET method = 5 m ² / g, true specific gravity = 5.5) ,
Zinc oxide 2: “Activated zinc white” manufactured by LANXESS (Zinc oxide purity = 99.0% by weight or more, nitrogen adsorption specific surface area by BET method = 45 m ² / g, true specific gravity = 5.0),
Zinc oxide 3: “META-Z-L40” manufactured by Inoue Lime Industry Co., Ltd. (composite zinc oxide particles having an active zinc white layer on the particle surface and a core composed of light calcium carbonate as an internal component. Zinc oxide Purity = 40.3% by weight, nitrogen adsorption specific surface area by BET method = 15.5 m ² / g, true specific gravity = 3.3),
Zinc oxide 4: “META-Z-L50” manufactured by Inoue Lime Industry Co., Ltd. (composite zinc oxide particles having an active zinc white layer on the particle surface and a core made of light calcium carbonate as an internal component. Zinc oxide Purity = 50.8 wt%, nitrogen adsorption specific surface area by BET method = 16.3 m ² / g, true specific gravity = 3.6),
Zinc oxide 5: “META-Z-L60” manufactured by Inoue Lime Industry Co., Ltd. (composite zinc oxide particles having an active zinc white layer on the particle surface and having a core composed of light calcium carbonate as an internal component. Zinc oxide Purity = 60.8 wt%, nitrogen adsorption specific surface area by BET method = 16.5 m ² / g, true specific gravity = 3.8),
Carbon black: HAF, “Seast 300” manufactured by Tokai Carbon Co., Ltd.
・ Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.
Anti-aging agent: “Sant Flex 6PPD” manufactured by Flexis,
Cobalt stearate: “Cobalt stearate” (Co content: 9.5% by weight) manufactured by Japan Energy Co., Ltd.
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 Industry 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 when the composite zinc oxide particles (Comparative Example 2), resorcin and melamine derivative (Comparative Example 3) are blended individually, the effect of improving both oxidation resistance and adhesion is insufficient. Met. Further, as is clear from the comparison between Comparative Example 3 and Comparative Example 5, the amount of active zinc white (zinc oxide 2) is reduced by 2.4 parts by weight from the mixture containing 6 parts by weight of general-purpose zinc white No. 3. When replaced, the adhesion deteriorated significantly.

  On the other hand, when it is Examples 1-4 which used the composite zinc oxide particle, resorcinol, and the melamine derivative together, while being excellent in oxidation-resistant deterioration property, all adhesiveness of initial adhesiveness, heat-resistant adhesiveness, and heat-and-moisture resistant adhesiveness And an excellent adhesive effect was obtained. In particular, in Examples 1 to 3, compared to Comparative Examples 1 and 3, the oxidation deterioration resistance and adhesiveness could be improved while reducing the amount of zinc. Therefore, it is possible to reduce the weight while maintaining or improving the durability of the tire.

  In Comparative Example 6, despite the combined use of composite zinc oxide particles, resorcin and melamine derivatives, the combined effect of the above-described effects on oxidation resistance and adhesiveness was recognized because the amount of composite zinc oxide particles was small. There wasn't.

  The rubber composition for covering a steel cord of the present invention is useful as a rubber for covering a steel cord which is a reinforcing material for a pneumatic tire. A rubber-steel cord composite using the rubber composition is used as a belt for a tire for a passenger car. It can be used for belts, carcass, and chacher layers for large tires for trucks, trucks and buses.

Claims (6)

Diene rubber, phenolic compounds or phenolic resins obtained by condensing phenolic compounds with formaldehyde, hexamethylenetetramine or melamine derivatives as methylene donors, and zinc oxide whose particle surface is composed of zinc oxide and occupies the entire particle 5. Composite zinc oxide particles having a component ratio of 5 to 95% by weight, and 1.9 parts by weight or more with respect to 100 parts by weight of the diene rubber using the composite zinc oxide particles as a zinc element component . A rubber composition for coating a steel cord, blended in an amount of 0 part by weight or less . The rubber composition for coating a steel cord according to claim 1, wherein the composite zinc oxide particles have a nitrogen adsorption specific surface area of 6.0 m ² / g or more by BET method.   The rubber composition for coating a steel cord according to claim 1 or 2, wherein the true specific gravity of the composite zinc oxide particles is 5.0 or less.   The rubber composition for coating a steel cord according to any one of claims 1 to 3, wherein an internal component of the composite zinc oxide particles is an inorganic metal salt.   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 coating a steel cord according to any one of -4.   The pneumatic composition used for the steel cord covering rubber which reinforces at least one of a belt layer, a carcass layer, and a chacher layer of a tire using the rubber composition for covering a steel cord according to any one of claims 1 to 5. tire.