JP2021172733A - Rubber composition for tires - Google Patents

Abstract

To provide a rubber composition for tires which improves thermal aging resistance and water-resistant adhesiveness.SOLUTION: The rubber composition for tires contains 100 pts.mass of a sulfur-vulcanizable rubber containing 50 mass% or more of a natural rubber, 0.05-1 pt.mass of an organic acid cobalt or a cobalt complex as cobalt, 1-8 pts.mass of a phenol derivative, 1-15 pts.mass of a specific cyclic polysulfide, sulfur, and optionally a polyhydric methylolmelamine. When the blending amount of the sulfur is a pts.mass, the blending amount of the cyclic polysulfide is b pts.mass, the blending amount of the phenol derivative is c pts.mass, and the blending amount of the polyhydric methylolmelamine is d pts.mass, relationships of 5≤a+(2b/3)≤11 and d≤c/4 are satisfied.SELECTED DRAWING: None

Description

The present invention relates to a rubber composition for a tire having improved heat aging resistance and water adhesion resistance.

In recent years, in order to improve the long-term durability of a tire, a rubber material having excellent heat resistance and aging resistance has been used as a tire component. For example, Patent Document 1 proposes that a rubber composition containing a cyclic polysulfide as a vulcanizing agent improves heat aging resistance and mechanical properties such as tensile elongation at break. Here, a rubber material that is required to have adhesiveness to a metal may contain a large amount of sulfur, and in that case, the change in physical properties due to aging tends to be large. Therefore, it is conceivable to improve the heat aging property by blending cyclic polysulfide as a vulcanizing agent with a rubber material that is required to have adhesiveness to a metal.

However, the rubber composition containing the cyclic polysulfide has a problem that the adhesiveness to the metal, particularly the water resistant adhesiveness, cannot be sufficiently obtained. For this reason, it has been difficult to add cyclic polysulfide to members that require adhesion to metal cords such as belt coats, carcass coats, belt edge cushions, belt cushions, under treads, and tie rubber, and members adjacent to them. .. Therefore, it is required to improve the heat-resistant aging property and the heat-resistant aging property of the rubber composition for a tire covering the metal cord or adjacent to the rubber covering the metal cord to a level higher than the conventional level.

Japanese Unexamined Patent Publication No. 2006-193679

An object of the present invention is to provide a rubber composition for a tire having improved heat aging resistance and water adhesion resistance to a level higher than the conventional level.

（式（Ｉ）中、Ｒは置換もしくは非置換の炭素数２〜２０のアルキレン基、置換もしくは非置換の炭素数２〜２０のオキシアルキレン基、または芳香族基を含むアルキレン基を示し、ｘは平均２〜６の数、ｎは１〜２０の整数を表す。） The rubber composition for tires of the present invention that achieves the above object has 0.05 to 1 part by mass of sulfur-vulverable rubber containing 50% by mass or more of natural rubber and 0.05 to 1 part by mass of cobalt organic acid or cobalt complex. , 1 to 8 parts by mass of a phenol derivative, 1 to 15 parts by mass of a cyclic polysulfide represented by the following formula (I), sulfur, and optionally polyvalent methylol melamine, and the amount of the sulfur compounded is a parts by mass. When the blending amount of the cyclic polysulfide is b parts by mass, the blending amount of the phenol derivative is c mass parts, and the blending amount of the polyvalent methylol melamine is d parts by mass, the following relational expressions (1) to (3) are satisfied. It is characterized by that.
5 ≤ a + (2b / 3) ≤ 11 (1)
d ≤ c / 4 (2)

In the formula (I), R represents a substituted or unsubstituted alkylene group having 2 to 20 carbon atoms, a substituted or unsubstituted oxyalkylene group having 2 to 20 carbon atoms, or an alkylene group containing an aromatic group, and x Represents a number of 2 to 6 on average, and n represents an integer of 1 to 20.)

In the rubber composition for tires of the present invention, 0.05 to 1 part by mass of sulfur-vulverable rubber containing 50% by mass or more of natural rubber, 0.05 to 1 part by mass of an organic acid cobalt or cobalt complex as cobalt, and 1 part of a phenol derivative are added. ~ 8 parts by mass, 1 to 15 parts by mass of cyclic polysulfide represented by the above formula (I), sulfur, and optionally polyvalent methylol melamine, sulfur compounding amount a mass part, cyclic polysulfide compounding amount b mass part , The compounding amount c by mass of the phenol derivative and the compounding amount d mass part of the polyvalent methylol melamine are the following relational expressions;
5 ≤ a + (2b / 3) ≤ 11 (1)
d ≤ c / 4 (2)
Since the above conditions are satisfied, the heat aging resistance and the water resistance adhesion to the metal cord can be improved more than the conventional level.

The phenol derivative is preferably a resorcin resin, a cresol resin, or parahydroxybenzoic acid, and can have excellent water resistance and adhesiveness to a metal cord.

A tire in which at least one selected from a belt coat, a carcass coat, a belt edge cushion, a belt cushion, an under tread, and a tie rubber is formed by the above-mentioned rubber composition has excellent heat aging resistance and water resistance and adhesion to a metal cord. Therefore, the tire durability can be improved more than the conventional level.

In the present invention, the rubber composition for a tire contains a sulfur vulcanizable rubber as a rubber component. The sulfur vulcanizable rubber contains 50% by mass or more, preferably 80 to 100% by mass of natural rubber. By containing 50% by mass or more of natural rubber, it is possible to impart metal adhesiveness to the rubber composition and increase the elastic modulus. The rubber composition for tires can contain other sulfur smeltable rubbers other than natural rubbers, such as diene rubbers such as polyisoprene rubber, polybutadiene rubber, styrene-butadiene rubber, chloroprene rubber and their partial waters. Additives and the like can be mentioned, which can be contained with natural rubber alone or as an optional blend.

（式（Ｉ）中、Ｒは置換もしくは非置換の炭素数２〜２０のアルキレン基、置換もしくは非置換の炭素数２〜２０のオキシアルキレン基、または芳香族基を含むアルキレン基を示し、ｘは平均２〜６の数、ｎは１〜２０の整数を表す。） By blending the cyclic polysulfide represented by the following formula (I) and sulfur in the rubber composition for a tire, the heat aging property can be improved and the mechanical properties of the rubber composition can be enhanced. Therefore, the tire durability and wear resistance can be improved more than the conventional level.

In the formula (I), R represents a substituted or unsubstituted alkylene group having 2 to 20 carbon atoms, a substituted or unsubstituted oxyalkylene group having 2 to 20 carbon atoms, or an alkylene group containing an aromatic group, and x Represents a number of 2 to 6 on average, and n represents an integer of 1 to 20.)

In formula (I), R represents a substituted or unsubstituted alkylene group having 2 to 20 carbon atoms, a substituted or unsubstituted oxyalkylene group having 2 to 20 carbon atoms, or an alkylene group containing an aromatic group, preferably. , Substituent or unsubstituted alkylene group having 4 to 8 carbon atoms, substituted or unsubstituted oxyalkylene group having 4 to 8 carbon atoms, or an alkylene group containing an aromatic group.

Examples of the alkylene group include linear or branched alkylene groups such as ethylene, propylene, butylene, pentylene, hexylene, octylene, nonylene, decylene and 1,2-propylene, and these alkylene groups are phenyl group and benzyl group. It may be substituted with a substituent such as.

As the oxyalkylene group, for example, the group (CH ₂ CH ₂ O) _p and the group (CH ₂ ) _q (in the formula, p is an integer of 1 to 5 and q is an integer of 0 to 2) are arbitrarily bonded. Oxyalkylene group can be mentioned. As a preferred oxyalkylene
−CH ₂ CH ₂ OCH ₂ CH ₂ −, − (CH ₂ CH ₂ O) ₂ CH ₂ CH ₂ −,
(−CH ₂ CH ₂ O) ₃ CH −CH ₂ −, − (CH ₂ CH ₂ O) ₄ CH ₂ CH ₂ −,
− (CH ₂ CH ₂ O) ₅ CH ₂ CH ₂ −, − (CH ₂ CH ₂ O) ₂ CH ₂ −,
−CH ₂ CH ₂ OCH ₂ OCH ₂ CH ₂ − and the like can be exemplified.

Examples of the substituent with respect to the alkylene group and the oxyalkylene group include a phenyl group, a benzyl group, a methyl group, an epoxy group, an isocyanate group, a vinyl group, a silyl group and the like.

In formula (I), x is an average number of 2-6, preferably 3-5, more preferably 3.5-4.5. Further, n is an integer of 1 to 20, preferably an integer of 1 to 15, more preferably an integer of 1 to 10, and even more preferably an integer of 1 to 5. Such a cyclic polysulfide can be produced by a usual method, and for example, the production method described in JP-A-2007-92086 can be exemplified.

The cyclic polysulfide represented by the formula (I) is blended in an amount of 1 to 15 parts by mass, preferably 3 to 10 parts by mass, and more preferably 4 to 7 parts by mass with respect to 100 parts by mass of sulfur vulcanizable rubber. Heat resistance can be improved by setting the blending amount b of the cyclic polysulfide to 1 part by mass or more. Further, by setting the blending amount b of the cyclic polysulfide to 15 parts by mass or less, water resistance can be imparted to the rubber composition.

The rubber composition for a tire contains a cyclic polysulfide represented by the formula (I) and sulfur. When the amount of sulfur compounded with respect to 100 parts by mass of sulfur vulcanizable rubber is a part by mass and the amount of cyclic polysulfide compounded is b parts by mass, the following relational expression (1) is satisfied.
5 ≤ a + (2b / 3) ≤ 11 (1)
The amount a by mass of the sulfur compound is determined so as to satisfy the relational expression (1) with the amount b by mass of the cyclic polysulfide. By setting the blending amount value [a + (2b / 3)] to 5 or more, the rubber composition can be imparted with initial adhesiveness and water resistance. Further, by setting the value to 11 or less, curing due to heat aging can be suppressed. The value [a + (2b / 3)] is preferably 6 or more and 10 or less, and more preferably 7 or more and 9 or less.

In the present invention, the rubber composition for a tire can secure adhesiveness to a metal cord and water resistance by blending an organic acid cobalt or a cobalt complex. The organic acid cobalt or cobalt complex is 0.05 to 1 part by mass, preferably 0.1 to 0.5 parts by mass, and more preferably 0.1 to 0 parts as cobalt with respect to 100 parts by mass of sulfur vulcanizable rubber. . Mix 2 parts by mass. By adjusting the amount of cobalt organic acid or cobalt complex to 0.05 parts by mass or more as cobalt, the adhesiveness and water resistance of the tire rubber composition and the metal cord can be ensured. Further, by using 1 part by mass or less of cobalt, adhesiveness and water resistance can be ensured.

Examples of the organic acid of cobalt organic acid include saturated fatty acids and unsaturated fatty acids having 6 to 24 carbon atoms, which may be linear or branched. Examples of the organic acid include stearic acid, oleic acid, lauric acid, linoleic acid, neodecanoic acid, logonic acid, palmitic acid and the like. Examples of the cobalt organic acid or the cobalt complex include cobalt stearate, cobalt palmitate, cobalt octeneate, cobalt naphthenate, cobalt neodecanoate, cobalt trineodecanoate borate, and cobalt loginate.

In the present invention, the rubber composition for a tire can be further improved in adhesiveness to a metal cord and water resistance by blending a phenol derivative. The phenol derivative is blended in an amount of 1 to 8 parts by mass, preferably 2 to 6 parts by mass, and more preferably 2 to 4 parts by mass with respect to 100 parts by mass of sulfur vulcanizable rubber. By increasing the amount of the phenol derivative to 1 part by mass or more, the initial adhesiveness to the metal cord and the water resistance can be further improved. Further, by setting the content to 8 parts by mass or less, both water resistance and heat aging resistance can be achieved at the same time.

Examples of the phenol derivative include a phenol resin, a resorcin resin, a cresol resin, a cashew-modified phenol resin, and a parahydroxybenzoic acid. Preferably, resorcin resin, cresol resin, or parahydroxybenzoic acid is preferable.

The rubber composition for tires may optionally contain polyvalent methylolmelamine. By blending polyvalent methylolmelamine, the rubber hardness of the rubber composition can be increased. The blending amount of polyvalent methylolmelamine is determined in relation to the blending amount of the phenol derivative. When the blending amount of the phenol derivative is c mass parts and the blending amount of polyvalent methylol melamine is d parts by mass with respect to 100 parts by mass of sulfur vulcanizable rubber, the following relational expression (2) is satisfied.
d ≤ c / 4 (2)
By reducing the amount d by mass of the polyvalent methylol melamine to 1/4 or less of the amount c by mass of the phenol derivative, the heat aging resistance and the water resistance to the metal cord can be improved. Further, the blending amount d of the multivalent methylolmelamine is preferably c / 8 or less, more preferably c / 10 or less. The blending amount d of the polyvalent methylolmelamine may be 0. That is, it is not necessary to have a curing agent for a phenol derivative such as polyvalent methylolmelamine.

The rubber composition for a tire may contain a reinforcing filler such as carbon black, silica, clay, aluminum hydroxide, and calcium carbonate. In addition, rubber compositions for tires are generally used for rubber compositions such as vulcanization or cross-linking agents, vulcanization accelerators, anti-aging agents, plastic agents, processing aids, liquid polymers, thermosetting resins, and thermoplastic resins. Various compounding agents used for the purpose can be blended. Such a compounding agent can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or cross-linking. The blending amount of these blending agents can be a conventional general blending amount as long as it does not contradict the object of the present invention. The rubber composition can be produced by mixing each of the above components using a known rubber kneading machine, for example, a Banbury mixer, a kneader, a roll, or the like.

The rubber composition for tires of the present invention can be suitably used for belt coats, carcass coats, belt edge cushions, belt cushions, under treads, tie rubbers and the like for pneumatic tires. The tire using the rubber composition of the present invention has excellent heat aging resistance and excellent water resistance and adhesiveness to the metal cord, so that the tire durability can be improved to a level higher than the conventional level.

Hereinafter, the present invention will be further described with reference to Examples, but the scope of the present invention is not limited to these Examples.

Using the formulations shown in Table 4 as common formulations, 25 types of rubber compositions (Examples 1 to 11, Standard Examples, Comparative Examples 1 to 13) composed of the formulations shown in Tables 1 to 3 were used as sulfur, a vulcanization accelerator, and the like. Sulfur, vulcanization accelerator, polyvalent methylol melamine and cyclic polysulfide were added to the master batch, which was released by kneading the components excluding polyvalent methylol melamine and cyclic polysulfide with a 1.8 L closed mixer at 160 ° C for 5 minutes, and opened. Prepared by kneading with a roll. The blending amount of the common compounding agent in Table 4 is represented by the mass part with respect to 100 parts by mass of the natural rubber shown in Tables 1 to 3. The heat aging resistance and water adhesion resistance of the obtained rubber composition were evaluated by the following methods, respectively.

The heat-resistant aging rubber composition was vulcanized at 160 ° C. for 20 minutes using a mold having a thickness of 2 mm, and the obtained vulcanized rubber sheet was punched with a JIS No. 3 dumbbell as a sample. The sample was heat-aged in a gear oven set at a temperature of 80 ° C. for 5 days, and then the elongation at break was measured with a tensile tester according to JIS K6251 together with the unaged sample. The ratio of the unaged elongation at break (Eb) to the elongation at break after aging (Ea) was taken, and Ea / Eb was used as an index of heat aging resistance. The value is expressed as an index with the index of the standard example as 100. When the index is 105 or less, the heat-resistant aging property is considered to be inferior.

Water resistance Adhesiveness Performed according to ASTM D2229. A brass-plated wire having a 3 + 9 + 15 structure was embedded in the rubber composition and vulcanized at 160 ° C. for 20 minutes using a predetermined mold to prepare a sample. The sample was placed in a constant temperature and humidity chamber set at a temperature of 70 ° C. and a humidity of 96% for 2 weeks, and then a drawing test was carried out, and the rubber coverage on the wire surface was visually judged and used as an index. The value is expressed as an index with the index of the standard example as 100. When the index is 95 or less, the water resistance is inferior.

The types of raw materials used in Tables 1 to 3 are shown below.
-NR: Natural rubber, RSS # 3
-Cobalt Organic Acid: Cobalt Neodecanoate, Cobalt Content 22% by Mass, dic DICNAME NBC-II
-Sulfur: Crytex HS OT20 manufactured by FLEXSYS
-Cyclic polysulfide: THIOPLAST CPS 200 manufactured by Akzo Nobel, in formula (I), R is -CH ₂ CH ₂ OCH ₂ OCH ₂ CH _2- , x (average) is 4, n is 10.
-Resorcin resin: TECHNIC B18S manufactured by TECHNO WAXCHEM
-Cresol resin: Sumikanol 610 manufactured by Taoka Chemical Industry Co., Ltd.
-Parahydroxybenzoic acid: Parahydroxybenzoic acid manufactured by Ueno Fine Chemicals Industry-HMMM: Hexamethoxymethylmelamine, Cyrez 964RPC manufactured by Allnex

The types of raw materials used in Table 4 are shown below.
-Carbon Black: Tokai Carbon Co., Ltd. Seest 300
-Anti-aging agent: VULKANOX4020 manufactured by LANXESS
-Zinc flower: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd.-Vulcanization accelerator: Noxeller DZ-G manufactured by Ouchi Shinko Chemical Co., Ltd.

As is clear from Tables 1 to 3, it was confirmed that the rubber compositions for tires of Examples 1 to 11 had improved heat aging resistance and water resistance adhesiveness more than the conventional level.

As is clear from Table 1, the rubber compositions of Comparative Examples 1 and 2 are inferior in water resistance and adhesiveness because the amount of the phenol derivative compounded is less than 1 part by mass.
The rubber composition of Comparative Example 3 is inferior in heat aging resistance because the compounding amount of the phenol derivative exceeds 8 parts by mass.

As is clear from Table 2, in the rubber compositions of Comparative Examples 4 and 5, since the blending amount of the cyclic polysulfide is less than 1 part by mass, no improvement in heat aging property is observed.
Since the rubber compositions of Comparative Examples 6 and 7 do not contain sulfur, they are inferior in water resistance and adhesiveness.
In the rubber compositions of Comparative Examples 8 and 9, since d exceeds 1/4 of the compounding amount c of the phenol derivative in the compounding amount of the polyvalent methylolmelamine, the heat aging property is inferior as compared with the case where it does not exceed.

As is clear from Table 3, the rubber compositions of Comparative Examples 10 to 13 are inferior in heat resistance because they do not contain the cyclic polysulfide.

Claims (5)

In 100 parts by mass of sulfur sulpable rubber containing 50% by mass or more of natural rubber, 0.05 to 1 part by mass of an organic acid cobalt or a cobalt complex as cobalt, and 1 to 8 parts by mass of a phenol derivative, the following formula (I) The cyclic polysulfide represented by is contained in an amount of 1 to 15 parts by mass, sulfur, and optionally polyvalent methylol melamine. A rubber composition for a tire, characterized in that the following relational expressions (1) and (2) are satisfied when the amount is c parts by mass and the blending amount of the polyvalent methylol melamine is d parts by mass.
5 ≤ a + (2b / 3) ≤ 11 (1)
d ≤ c / 4 (2)

In the formula (I), R represents a substituted or unsubstituted alkylene group having 2 to 20 carbon atoms, a substituted or unsubstituted oxyalkylene group having 2 to 20 carbon atoms, or an alkylene group containing an aromatic group, and x Represents a number of 2 to 6 on average, and n represents an integer of 1 to 20.) The rubber composition for a tire according to claim 1, wherein the phenol derivative is a resorcin resin. The rubber composition for a tire according to claim 1, wherein the phenol derivative is a cresol resin. The rubber composition for a tire according to claim 1, wherein the phenol derivative is parahydroxybenzoic acid. A tire in which at least one selected from a belt coat, a carcass coat, a belt edge cushion, a belt cushion, an under tread, and a tie rubber is formed by the rubber composition according to any one of claims 1 to 4.