JP7328508B2 - Steel cord coating rubber composition and pneumatic tire containing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a steel cord coating rubber composition having excellent adhesion to steel cords and a pneumatic tire containing the same.

In some pneumatic tires, the tread portion is composed of a carcass layer and a belt layer in which steel cords are coated with a coating rubber (rubber composition for metal adhesion). If the adhesiveness between these metal members and the rubber members is lowered, failures are likely to occur, and there is a risk that tire durability will be lowered. In addition to high initial adhesiveness to metal members, it is also required to maintain adhesiveness even in severe heating or moist heat environments.

Patent Literature 1 proposes improving the adhesiveness of steel cords by using a rubber composition obtained by blending a diene rubber with a cobalt salt of an organic acid. However, there is a demand for the development of a rubber composition that uses a more general-purpose reagent and has metal adhesiveness equal to or greater than that of the rubber composition described in Patent Document 1.

JP-A-2007-99868

SUMMARY OF THE INVENTION An object of the present invention is to provide a rubber composition for coating steel cords, which is improved in adhesion to steel cords beyond the conventional level.

The steel cord coating rubber composition of the present invention, which achieves the above objects, comprises 100 parts by mass of a diene rubber containing 80% by mass or more of natural rubber and/or synthetic isoprene rubber, and 1 to 10 parts by mass of an organic tin compound. It is characterized by

The rubber composition for metal bonding of the present invention contains 100 parts by mass of a diene rubber containing 80% by mass or more of natural rubber and/or synthetic isoprene rubber, and 0.1 to 10 parts by mass of an organic tin compound. Adhesion to the can be maintained and improved. In particular, the adhesiveness (hereinafter sometimes referred to as "durable adhesiveness") in a hot or moist heat environment can be improved beyond the conventional level.

The organotin compound is preferably at least one selected from fatty acid tin and an organotin complex, and further preferably at least one selected from tin stearate, tin acetylacetonate, and tin dibutylacetylacetonato. Moreover, it is preferable to mix 3 parts by mass or more and less than 10 parts by mass of sulfur with respect to 100 parts by mass of the diene rubber.

A pneumatic tire containing the rubber composition for metal adhesion of the present invention in at least one selected from a belt layer, a carcass layer, and a bead portion has excellent adhesion to metal members, and has tire durability higher than the conventional level. can be improved to

In the rubber composition for metal bonding of the present invention, the diene rubber must contain natural rubber and/or synthetic isoprene rubber, either natural rubber or synthetic isoprene rubber, or both natural rubber and synthetic isoprene rubber. can be done. The content of natural rubber and synthetic isoprene rubber is 80% by mass or more, preferably 90 to 100% by mass, based on 100% by mass of diene rubber. By setting the content of the natural rubber and the synthetic isoprene rubber to 80% by mass or more, it is possible to ensure the adhesiveness (for example, cross-ply peel strength) to metal members.

The rubber composition for metal bonding of the present invention can be blended with diene rubber other than natural rubber and synthetic isoprene rubber as the diene rubber. Examples of other diene rubbers include butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, butyl rubber, and halogenated butyl rubber. Among them, butadiene rubber, styrene-butadiene rubber, and halogenated butyl rubber are preferable. These diene-based rubbers can be used alone or as any blend. The content of the other diene rubber is 20% by mass or less, preferably 0 to 10% by mass, based on 100% by mass of the diene rubber.

The rubber composition for metal adhesion of the present invention is enhanced in adhesiveness to metal members by blending an organic tin compound. The amount of the organic tin compound compounded is 0.1 to 10 parts by mass, preferably 0.2 to 8 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the diene rubber. If the amount of the organotin compound is less than 0.1 parts by mass, the initial adhesion and durable adhesion to metal members cannot be sufficiently enhanced. On the other hand, if the amount of the organic tin compound exceeds 10 parts by mass, the durable adhesion to metal members during heating is rather lowered.

Organotin compounds are organic compounds containing tin, such as dialkyltin dihalides, trialkyltin halides, dialkyltin dicarboxylic acids, dialkyltin sulfides, trialkyltin sulfides, dialkyltin oxides, trialkyltin oxides, Examples include trialkyltin alkoxides, fatty acid tins, and organic tin complexes such as trialkyltin acetylacetonates and dialkyltin bisacetylacetonates.

The organotin compound is preferably at least one selected from fatty acid tin and organotin complexes. The fatty acid of fatty acid tin may be either saturated fatty acid or unsaturated fatty acid, and may be linear fatty acid or branched fatty acid. Also, the main chain and/or the branched chain may have a ring structure. Although the number of carbon atoms in the fatty acid is not particularly limited, it is preferably 10-20, more preferably 10-18. Fatty acids such as capric acid, lauric acid, myristic acid, pentadecyl acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, oleic acid, vaccenic acid, linoleic acid, (9,12,15)-linolenic acid, (6 ,9,12)-linolenic acid, eleostearic acid, arachidic acid, mead acid, arachidonic acid, behenic acid, lignoceric acid, naphthenic acid, neodecanoic acid, 2-ethylhexanoic acid and the like. Among them, preferred fatty acid tins include tin laurate, tin palmitate, tin stearate, tin oleate, tin naphthenate, tin neodecanoate, and the like.

The organotin complex is preferably a complex with a diketone, more preferably a complex with a conjugated diketone. Diketones include, for example, acetylacetone and organic compounds having an acetylacetone group. Among them, suitable organic tin complexes include, for example, tin acetylacetonate, tin dibutylacetylacetonato, and the like.

The metal bonding rubber composition preferably contains 3 parts by mass or more and less than 10 parts by mass of sulfur in 100 parts by mass of the diene rubber. The content of sulfur is more preferably 4 to 9 parts by mass, still more preferably 5 to 8 parts by mass, and even more preferably 6 to 8 parts by mass. When the amount of sulfur compounded is 3 parts by mass or less, it is possible to suppress deterioration in durable adhesion and rubber hardness during wet heat. Further, if the sulfur content is less than 10 parts by mass, deterioration of the aging resistance properties of the rubber and durability adhesion during wet heat can be suppressed.

The rubber composition for metal bonding preferably contains 20 to 80 parts by mass of carbon black and 5 to 12 parts by mass of zinc oxide in 100 parts by mass of diene rubber.
Carbon black preferably has a nitrogen adsorption specific surface area N ₂ SA of 20 to 150 m ² /g, more preferably 40 to 140 m ² /g. If the N ₂ SA is less than 20 m ² /g, there is a risk that the reinforcing properties will deteriorate. On the other hand, if the N ₂ SA exceeds 150 m ² /g, there is a possibility that the heat build-up will increase. In this specification, the N ₂ SA of carbon black shall be measured according to JIS K6217-7.

Carbon black is blended in an amount of preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass with respect to 100 parts by mass of diene rubber. If the amount of carbon black to be blended is less than 20 parts by mass, the rubber hardness may be insufficient, and the durable adhesion during heating and wet heat may deteriorate. On the other hand, if the amount of carbon black compounded exceeds 80 parts by mass, the rubber viscosity and heat build-up may increase. The rubber composition for metal adhesion should preferably not contain silica, and if silica is blended, there is a risk that the durable adhesion during heating and wet heat will deteriorate.

In addition, the amount of zinc oxide compounded in the metal bonding rubber composition is preferably 5 to 12 parts by mass, more preferably 8 to 10 parts by mass, per 100 parts by mass of the diene rubber. If the amount of zinc oxide is less than 5 parts by mass, the durable adhesion during heating and wet heat will deteriorate. Furthermore, heat build-up increases and rubber hardness decreases. On the other hand, if the content of zinc oxide exceeds 12 parts by mass, the durable adhesion during heating will rather deteriorate.

A cobalt-containing compound can be blended in the rubber composition for metal adhesion. By containing a cobalt-containing compound, the adhesiveness and durable adhesiveness of the rubber composition for metal adhesion can be made more excellent. The amount of the cobalt-containing compound compounded is preferably 0 to 1.5 parts by mass, more preferably 0 to 1.0 parts by mass, per 100 parts by mass of the diene rubber.

Examples of cobalt-containing compounds include organic acid cobalt salts and organic cobalt complexes, such as cobalt naphthenate, cobalt neodecanoate, cobalt stearate, cobalt rosinate, cobalt versatate, cobalt tall oil, cobalt neodecanoate borate, acetyl Acetonate cobalt and the like can be mentioned. Among these organic acid cobalt salts, organic acid cobalt salts containing boron are preferable, and for example, a composite salt in which a part of the organic acid is replaced with boric acid or the like is preferable.

Various additives commonly used in rubber compositions for tires, such as vulcanization accelerators, various oils, anti-aging agents, and plasticizers, can be added to the rubber composition for metal adhesion. can be kneaded in a conventional manner to form a rubber composition and used for vulcanization or cross-linking. The blending amount of these additives can be a conventional general blending amount as long as it does not contradict the object of the present invention. The metal bonding rubber composition of the present invention can be produced by mixing the above components using a conventional rubber kneading machine such as a Banbury mixer, a kneader, and a roll.

The rubber composition for metal adhesion is suitable as a rubber material for contacting with or covering a metal member, and is particularly suitable for constituting a covering rubber for steel cords of pneumatic tires, and is suitable for belt layers and/or carcasses. Steel cords in layers and/or beads can be used to coat and contact rubber materials.

EXAMPLES The present invention will be further described with reference to examples below, but the scope of the present invention is not limited to these examples.

In preparing 13 types of rubber compositions (Examples 1 to 9, Reference Example 1, Comparative Examples 1 to 3) having the formulations shown in Table 1, each component except sulfur and a vulcanization accelerator was weighed, and 1 After kneading for 5 minutes in a 7 liter internal Banbury mixer, the masterbatch was discharged out of the mixer and allowed to cool to room temperature. This masterbatch was supplied to the same Banbury mixer, sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition for metal adhesion.

Each of the rubber compositions obtained above was vulcanized at 170° C. for 10 minutes in a mold of a predetermined shape to prepare a test piece, and the tensile elongation at break was evaluated by the method described below.

Tensile Elongation at Break A JIS No. 3 dumbbell-shaped test piece was cut out from the obtained test piece according to JIS K6251. The tensile elongation at break was measured according to JIS K6251, and the obtained results are shown in the column of "Tensile elongation at break" in Table 1 as an index with the value of Comparative Example 1 as 100. The larger the index, the higher the tensile elongation at break and the better the tire durability.

Using the obtained rubber composition for metal adhesion, the adhesion to steel cord (with rubber after wet heat aging and after high pressure wet heat aging) was measured by the following method.

Rubber attachment after wet heat deterioration Using the obtained rubber composition, brass-plated steel cords arranged in parallel at intervals of 12.7 mm were coated, embedded with an embedded length of 12.7 mm, and heated at 160 ° C. for 20 minutes. A rubber-attached evaluation sample was prepared by vulcanization bonding under vulcanization conditions. Using the obtained rubber-attached evaluation sample, an accelerated wet heat deterioration test was carried out at a temperature of 80° C. and a relative humidity of 96% for 336 hours. In accordance with ASTM D-2229, a steel cord was pulled out from the rubber-attached evaluation sample that had been subjected to wet heat deterioration, and the amount (%) of rubber coating the surface was evaluated. The obtained results are described in the column of "Rubber attachment after wet heat deterioration" as an index to set the value of Comparative Example 1 to 100. It means that the larger the index, the better the durable adhesion to steel cord after wet heat deterioration.

Attaching rubber after high-pressure wet-heat deterioration Using the obtained rubber composition, it was coated with brass-plated steel cords arranged in parallel at intervals of 12.7 mm, embedded with an embedded length of 12.7 mm, and heated at 160 ° C. for 20 minutes. A rubber-attached evaluation sample was prepared by vulcanization bonding under vulcanization conditions. Using the obtained rubber-attached evaluation sample, an accelerated high-pressure wet heat deterioration test was performed at a pressure of 2 MPa, a temperature of 80° C., a relative humidity of 96%, and 336 hours. In accordance with ASTM D-2229, a steel cord was pulled out from the rubber-attached evaluation sample that had been subjected to high-pressure wet-heat deterioration, and the amount (%) of rubber coating the surface was evaluated. The obtained results are described in the column of "with rubber after high-pressure wet-heat deterioration" as an index with the value of Comparative Example 1 set to 100. It means that the larger the index, the better the durable adhesion to steel cord after high-pressure wet heat deterioration.

The types of raw materials used in Table 1 are shown below.
・NR: natural rubber, RSS#3
・ Carbon black: Seast 300 manufactured by Tokai Carbon Co., Ltd.
・ Cobalt stearate: manufactured by Tokyo Chemical Industry Co., Ltd. ・ Acetylacetonate tin: manufactured by Tokyo Chemical Industry Co., Ltd. ・ Dibutyl acetylacetonato tin: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・ Tin stearate: manufactured by Kishida Chemical Co., Ltd. ・ Zinc oxide: Same 3 types of zinc oxide manufactured by Kagaku Kogyo Co., Ltd. Anti-aging agent: Santoflex 6PPD manufactured by Flexis Co., Ltd.
・ Sulfur: Cristex HSOT20 manufactured by Akzo Nobel
・Vulcanization accelerator: Noccellar DZ manufactured by Ouchi Shinko Kagaku Co., Ltd.

As is clear from Table 1, it was confirmed that the rubber compositions for metal bonding of Examples 1 to 9 maintained and improved the tensile elongation at break and the rubber adhesion after wet heat deterioration and high pressure wet heat deterioration at or above conventional levels. .

Since the rubber composition of Comparative Example 2 contained more than 10 parts by mass of the organic tin compound, the rubber composition was inferior in rubber adhesion after wet heat deterioration.

Since the rubber composition of Comparative Example 3 contained more than 10 parts by mass of the organic tin compound, the rubber composition was inferior in rubber adhesion after wet heat deterioration.

Claims (5)

A rubber composition for coating steel cords , comprising 100 parts by mass of a diene rubber containing 80% by mass or more of natural rubber and/or synthetic isoprene rubber and 1 to 10 parts by mass of an organic tin compound. 2. The rubber composition for coating steel cords according to claim 1, wherein said organotin compound is at least one selected from fatty acid tin and organotin complexes. 3. The rubber composition for coating steel cords according to claim 1, wherein said organic tin compound is at least one selected from tin stearate, tin acetylacetonate and tin dibutylacetylacetonato. 4. The rubber composition for coating steel cords according to claim 1, wherein 3 parts by mass or more and less than 10 parts by mass of sulfur are blended with 100 parts by mass of the diene rubber. A pneumatic tire, wherein the steel cord coating rubber composition according to any one of claims 1 to 4 is contained in at least one selected from a belt layer, a carcass layer and a bead portion.