JPH0726066A - Tire tread rubber composition - Google Patents

Abstract

PURPOSE:To provide a tire tread rubber composition markedly reduced in heat buildup without detriment to the workability. CONSTITUTION:The rubber composition comprises 100 pts.wt. at least one rubber component selected from natural and synthetic diene rubbers, 20-100 pts.wt. reinforcing filler, 0.1-10 pts.wt. heat buildup preventive and 0.1-20 pts.wt. organic unsaturated fatty acid having at least two C-C double bonds in the molecule and containing at least 10wt.% conjugated dienoic acid having at least one pair of conjugated C-C double bonds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire tread, which has low heat buildup.

[0002]

2. Description of the Related Art Conventionally, it is already known to reduce the heat generation of a rubber composition for a tire tread by using a hydrazide type chemical or the like. However, the use of the conventional low heat-generating agent has a problem that the viscosity of the rubber composition for a tire tread is significantly increased and the workability is impaired due to burning or the like. Further, when a softening agent such as aroma oil is used in a rubber composition for a tire tread to improve workability, there is a problem that breaking properties, particularly breaking properties at high temperature and exothermic properties are impaired.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to significantly improve the workability such as viscosity increase and burn, which are problems of the low exothermic agent, while maintaining the low exothermic property of the low exothermic agent. It is to provide a rubber composition for a tire tread.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that at least one rubber component selected from the group consisting of natural rubber and diene synthetic rubber. On the other hand, when a low heat buildup improver and a specific unsaturated fatty acid were combined in combination, it was found that while exhibiting the low heat buildup effect, excellent workability was exhibited, and the present invention was completed. is there. That is, the rubber composition for a tire tread of the present invention contains the following components (a) to (c) with respect to 100 parts by weight of at least one rubber component selected from the group consisting of natural rubber and diene-based synthetic rubber. It is characterized by doing. (A) Reinforcing filler 20 to 100 parts by weight (b) Low exothermicity improver 0.1 to 10 parts by weight (c) The molecule contains at least one set of two carbon-carbon double bonds in a conjugated relationship. Organic unsaturated fatty acid containing 2 or more carbon-carbon double bonds in the molecule containing 10% by weight or more of conjugated dienoic acid 0.1 to 20 parts by weight

The contents of the present invention will be described below. The rubber used in the rubber composition for tire tread of the present invention is at least one selected from the group consisting of natural rubber and diene synthetic rubber, for example, natural rubber, butadiene rubber, synthetic isoprene rubber, styrene-butadiene rubber. One kind of rubber selected from the following, or a copolymer thereof,
A mixture may be mentioned.

The reinforcing filler used in the present invention means a filler which increases at least one of tensile strength, tear strength and abrasion resistance of rubber. Examples of such a reinforcing filler include carbon black such as SAF, ISAF, and HAF, or silica. The amount of the reinforcing filler compounded is 20 to 10 with respect to 100 parts by weight of the rubber component.
The amount is 0 parts by weight, preferably 30 to 90 parts by weight, more preferably 35 to 80 parts by weight. Reinforcing filler content is 20
When it is less than 100 parts by weight, both 300% tensile stress and hardness are unfavorable, and when it exceeds 100 parts by weight, both tensile strength and elongation are unfavorably decreased.

The low heat buildup improving agent used in the present invention includes:
For example, the following compounds can be mentioned. The following formula (I)

[Chemical 1] Lactams represented by, specifically, γ-thiobutyrolactam, ω-thiolaurinlactam, N-methyl-γ
-Thiobutyrolactam and the like.

The following formula (II)

[Chemical 2] 4-trifluoromethyl-2-thiouracil represented by:

The following formula (III) or (IV)

[Chemical 3]

[Chemical 4] [In the formula (III) or (IV), R ₁ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a 2-alkyliminocyclopentanedithiocarbonyl group, and R ₂ is an alkyl group having 1 to 6 carbon atoms, or 5 to 6 cycloalkyl groups, M represents an alkaline earth metal, copper or nickel. ] Specifically, a cyclic compound represented by the formula: 2-methyliminopentanedithiocarboxylic acid, bis (2-methyliminocyclopentylthiocarbonyl) disulfide, methyl 2-methyliminocyclopentanedithiocarboxylate, 2-methylimino Zinc cyclopentanedithiocarboxylic acid, 2-cyclohexyliminocyclopentanedithiocarboxylic acid, 2-
Methyliminocyclopentanedithiocarboxylic acid-n-hexyl, nickel 2-methyliminocyclopentanedithiocarboxylic acid and the like can be mentioned.

2,5-dimercapto-1,3,4-
Examples thereof include thiadiazole alone and a mixture of compounds represented by the following formulas (1) to (9).

[Chemical 5]

[Chemical 6]

[Chemical 7]

[Chemical 8]

[Chemical 9]

[Chemical 10]

[Chemical 11]

[Chemical 12]

[Chemical 13] [In the formulas (1) to (9), R ₃ , R ₆ , R ₉ and R ₁₁ have 8 to 8 carbon atoms.
18 alkyl and allyl groups, R ₄ , R ₅ , R ₇ , R ₈ ,
R ₁₀ is an alkyl group having 1 to 2 carbon atoms, R ₁₅ is an allyl group, a cyclohexyl group, R ₁₆ is an alkyl group having 1 to 6 carbon atoms, R
₁₇ and R ₁₈ are an alkyl group having 8 to ₁₈ carbon atoms, a benzyl group,
It is a hydrogen atom, and m and n each represent an integer of 1 to 3. ]

The following formula (VI)

[Chemical 14] (Wherein R ₁ and / or R ₂ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, R ₃ is a hydrogen atom, a methyl group, an ethyl group, R ₄
Represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. ) Dithiouracil compound, specifically, dithiouracil, 3-n-butyldithiouracil, 1-n-butyldithiouracil, 5-ethyldithiouracil, 4-n-
Hexyldithiouracil and the like can be mentioned.

The following formula (VII)

[Chemical 15] (R ₁ , R ₂ , R ₃ and R ₄ in the formula are individually a hydrogen atom, a chlorine atom, an alkyl group, an alkoxy group, a cyano group and a phenyl group.), Specifically, a benzoquinone derivative , P-benzoquinone, 2,5-dimethyl-P-benzoquinone, 2,5-di-t-butyl-P-benzoquinone,
2,5-dichloro-P-benzoquinone, 2,3-dichloro-5,6-dicyano-P-benzoquinone, 2,6-di-t-butyl-P-benzoquinone, 2,6-dichloro-
Examples thereof include P-benzoquinone, 2,6-dimethoxy-P-benzoquinone, 2-methyl-P-benzoquinone, 2-t-butyl-P-benzoquinone, tetracyano-P-benzoquinone and phenyl-P-benzoquinone.

The following formulas (VIII) to (X)

[Chemical 16]

[Chemical 17]

[Chemical 18] And at least one compound selected from benzoquinone, naphthoquinone, and anthraquinone compounds represented by the following formulas (10) to (11)

[Chemical 19]

[Chemical 20] A combination of at least one compound selected from the compounds represented by

Specifically, benzoquinones (VIII) include P-benzoquinone, 2,5-dimethyl-P-benzoquinone, 2,5-di-t-butyl-P-benzoquinone,
2,5-dichloro-P-benzoquinone, 2,3-dichloro-5,6-dicyano-P-benzoquinone, 2,6-di-t-butyl-P-benzoquinone, 2,6-dichloro-
Examples thereof include P-benzoquinone, 2,6-dimethoxy-P-benzoquinone, 2-methyl-P-benzoquinone, 2-t-butyl-P-benzoquinone, tetracyano-P-benzoquinone and phenyl-P-benzoquinone. The naphthoquinones (IX) include 1,4-naphthoquinone, 1,2-naphthoquinone and 2,3-dichloro-1,4.
-Naphthoquinone, 2-methyl-1,4-naphthoquinone,
Hydroxy-1,4-naphthoquinone, dihydroxy-
1,4-naphthoquinone and the like can be mentioned. Examples of the anthraquinones (X) include anthraquinone, hydroxyanthraquinone, dihydroxyanthraquinone, aminoanthraquinone and diaminoanthraquinone. formula
Specific examples of the compound represented by (10) include dibenzothiazyl sulfide, 5,5′-dithiobis (1,3,4-thiadiazole-2-thiol), tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetramethylthiuram. Examples thereof include disulfide and tetraisooctyl thiuram disulfide. Specific examples of the compound represented by the formula (11) include 2,5-dimercapto-1,3,4-thiadiazole, mercaptobenzimidazole, mercaptobenzothiazole, mercaptooxazole and 2-
Mercaptoethanol, 3-mercapto-2-propanol, 3-mercaptopropionic acid, 2-mercaptoethyl ether, 2-mercaptoethyl sulfide, 2-
Examples thereof include mercapto-5-nitroimidazole, 3-mercapto-1,2-propanediol, 2-mercaptopyridine, mercaptosuccinic acid and mercaptothiazoline.

[In the above formulas (VIII) to (X) and (10) to (11), R
_{1 to} R ₁₀ are a hydrogen atom, a chlorine atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a cyano group or a phenyl group, and R
_{11 to} R ₁₃ are a hydrogen atom, a hydroxyl group, an ester bond,
It represents an alkyl group having 1 to 4 carbon atoms containing an ether bond or a thioether bond, or a functional group having a heterocycle represented by the following formulas (12) to (20). ]

[Chemical 21]

[Chemical formula 22]

[Chemical formula 23]

[Chemical formula 24]

[Chemical 25]

[Chemical formula 26]

[Chemical 27]

[Chemical 28]

[Chemical 29]

A mercapto compound represented by the following formula (XI) may be mentioned.

[Chemical 30] (In the formula, R ₁ and R ₂ are each independently a hydrogen atom and a carbon number of 1 to 3.
Or an alkyl group of R ₁ to R ₂

[Chemical 31] Alternatively, an alkylene ring having 3 to 4 carbon atoms may be formed. )

Further, examples of the low exothermicity improver used in the present invention include not only those shown above but also hydrazide type, thiadiazole type and the like. The compounding amount of the low heat buildup improving agent is 0.1 to 100 parts by weight of the rubber component.
It is necessary to use 10 parts by weight, preferably 0.5 to 8 parts by weight. If the compounding amount of the low heat buildup improving agent is less than 0.1 parts by weight, the low heat buildup property of the rubber composition does not appear, and if it exceeds 10 parts by weight, the workability of unvulcanized rubber is significantly reduced. Unfavorable.

The organic unsaturated fatty acid used in the present invention contains 10% by weight or more of conjugated dienoic acid containing at least one pair of two carbon-carbon double bonds having a conjugated relationship in the molecule, and the carbon-carbon double bond is contained in the molecule. It is composed of an organic unsaturated fatty acid containing two or more bonds. In the organic unsaturated fatty acid used in the present invention, the “conjugated dienoic acid” refers to an organic unsaturated monocarboxylic acid containing at least one pair of carbon-carbon double bonds having a conjugated relationship in its molecule, and the conjugated relationship It is preferable that the carbon-carbon double bond in 1 is one pair, but there may be two or more pairs.
The organic unsaturated fatty acid containing two or more carbon-carbon double bonds in the molecule containing 10% by weight or more of the conjugated dienoic acid (hereinafter, simply referred to as organic unsaturated fatty acid) naturally contains the conjugated dienoic acid, but otherwise. The organic unsaturated fatty acid of 2 contains two or more carbon-carbon double bonds, but they are different from each other in that they are not in a conjugation relationship with each other.

The content of the conjugated dienoic acid in the organic unsaturated fatty acid is required to be 10% by weight or more, preferably 25% by weight or more, and 100% by weight, that is, the organic unsaturated fatty acid is all conjugated dienoic acid. May be. If the content of the conjugated dienoic acid is less than 10% by weight, the effect on wear resistance is not sufficient. Further, when the content of the conjugated dienoic acid is 25% by weight or more, the effect on wear resistance is further improved.

Examples of the conjugated dienoic acid include 2,4-
Pentadienoic acid, 2,4-hexadienoic acid, 2,4-decadienoic acid, 2,4-dodecadienoic acid, 9,11-octadecadienoic acid, α-eriostearic acid, 9,11,
13,15-octadecatetraenoic acid, 9,11,13
-Octadecatrienoic acid and the like.

A preferred example of the organic unsaturated fatty acid used in the present invention is dehydrated castor oil fatty acid. This dehydrated castor oil fatty acid is obtained by dehydrating castor oil. The content of the conjugated dienoic acid can be changed depending on the dehydration method, and for example, 35% by weight and 60% by weight can be obtained. In the case of this dehydrated castor oil fatty acid, the conjugated dienoic acid is mainly 9,11-octadecadienoic acid,
Other organic unsaturated fatty acids mainly contain non-conjugated octadecadienoic acid, and other examples include linoleic acid and linoleic acid. Further, in the present invention, conventionally used fatty acids represented by stearic acid may be used in combination with the dehydrated castor oil fatty acid.

The organic unsaturated fatty acid used in the present invention is
The total unsaturated fatty acid has 10 to 22 carbon atoms, preferably 1 carbon atom.
75 unsaturated fatty acids having 2 to 22 long-chain alkyl groups
It is desirable that the content be at least%. 10 to 2 carbon atoms
When it is 2, the effect on the fracture resistance is further improved. Further, the degree of unsaturation of all unsaturated fatty acids is preferably 130 or more in terms of iodine value. When the iodine value is 130 or more, the effect on the elastic modulus of rubber is further improved.

The amount of the organic unsaturated fatty acid used in the present invention must be 0.1 to 20 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the rubber component. When the amount of the organic unsaturated fatty acid is less than 0.1 parts by weight, the workability cannot be improved, and when it exceeds 20 parts by weight, the rubber elastic modulus is lowered, which is not preferable.

In the present invention, in addition to the rubber component, the low heat build-up improving agent and the organic unsaturated fatty acid agent, for example, a process oil, a softening agent, an anti-aging agent, an additive which is usually used as a rubber compounding agent. Sulfurization accelerator, vulcanization acceleration aid, zinc white,
Sulfur, a foaming agent, etc. can be appropriately mixed. In addition to the above-mentioned organic unsaturated fatty acid, 10 parts by weight, preferably 6 parts by weight or less may be blended with 100 parts by weight of the rubber component.

[0025]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Examples 1 to 4, Comparative Examples 1 to 7) Table 1 below
A rubber composition for tire tread was prepared according to the compounding recipe. The Mooney viscosity (ML _{1 + 4} ) of this rubber composition, the fracture elongation (Eb) of the rubber after vulcanization of the rubber composition,
Table 1 below shows the results of measuring the elastic modulus at 25% elongation and 25% tan δ at 300%. Mooney viscosity (ML
_{1 + 4} ), fracture elongation (Eb), elastic modulus at 300% elongation (Mod), and 25 ° C. 2% tan δ were measured by the following methods.

(1) Mooney viscosity (ML _{1 + 4} ) It was measured at 130 ° C. using a Mooney viscometer manufactured by Shimadzu Corporation. The test method is based on JIS K6300 and ML.
Calculate _{1 + 4} (Moonie value after 1 minute preheating and 4 minutes operation),
Displayed as an index. (2) The fracture elongation (Eb) of the vulcanized rubber, the elastic modulus (Mod) at 300% elongation, and the Mooney viscosity were evaluated according to JIS K 6301. (3) 25 ° C, 2% tan δ Using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho, length 2
25 ° C for a sample of 0 mm x width 5 mm x thickness 2 mm, 2
Lost tangent tan δ was measured with% strain. The Mooney viscosity (M
L _{1 + 4} ), fracture elongation (Eb), elastic modulus at 300% elongation (Mod), and index at 25 ° C. 2% tan δ as 100.

[0028]

[Table 1]

From the results shown in Table 1, the following was found. Examples 1 to 4 are rubber compositions for tire treads included in the scope of the present invention, and have Mooney viscosity (ML _{1 + 4} ) and elongation at break as compared with Comparative Examples 1 to 7 not included in the scope of the present invention. (E
b), elastic modulus (Mod) at 300% elongation and 25 ° C
It was found that the 2% tan δ was significantly improved.

[0030]

According to the present invention, there is provided a rubber composition for a tire tread that exhibits excellent workability while maintaining the effect of improving low heat buildup.

Claims (1)

[Claims] 1. A tire comprising the following components (a) to (c) per 100 parts by weight of at least one rubber component selected from the group consisting of natural rubber and diene-based synthetic rubber. Rubber composition. (A) Reinforcing filler 20 to 100 parts by weight (b) Low exothermicity improver 0.1 to 10 parts by weight (c) The molecule contains at least one set of two carbon-carbon double bonds in a conjugated relationship. Organic unsaturated fatty acid containing 2 or more carbon-carbon double bonds in the molecule containing 10% by weight or more of conjugated dienoic acid 0.1 to 20 parts by weight