JP2001113919A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire that uses sidewalls excellent in weather and bending fatigue resistance and free from discoloration and crystallization. SOLUTION: The pneumatic tire uses sidewall rubber that has a two-layered structure consisting of an inner layer of rubber adjoining the carcass and an outer layer of rubber outside the inner layer rubber. The outer layer rubber comprises, as its rubber components, at least one type of unsaturated diene rubber selected from the group of natural rubber, polyisoprene rubber, styrene- butadiene rubber and polybutadiene rubber in an amount of 40 to 90% by weight, and rubber of a halogenated copolymer of isomonoolefin with a carbon number of 4 to 1 and para-alkylstyrene in an amount of 10 to 60% by weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having a sidewall which has improved ozone resistance and flex fatigue resistance and does not discolor even after long-term use.

[0002]

2. Description of the Related Art Conventionally, the rubber component of the sidewall of a tire has been composed of a highly unsaturated rubber such as natural rubber having a double bond in the main chain of the molecule, isoprene rubber, butadiene rubber and the like. However, these highly unsaturated rubbers have a double bond in the main chain, so they are susceptible to oxidation reaction by ozone in the air, have poor ozone resistance, heat resistance, etc., and crack due to long-term storage and use. There was something to do. Therefore, in order to prevent this, an amine-based antioxidant, wax and the like have been blended.

However, these amine antioxidants and waxes have problems such as blooming on the sidewall surface due to long-term storage and use, and discoloration of the sidewall surface.

[0004] To solve these problems, it has been proposed to use a rubber having good weather resistance such as EPDM (Japanese Patent Publication No. 52-1761, Japanese Patent Application Laid-Open No. 56-11933, Japanese Patent Application Laid-Open No.
297307, JP-A-8-231773). However, since EPDM has an ethylene bonding unit in its molecular structure, there has been a problem that the ethylene bonding portion is crystallized at the time of cooling after the temperature rises to nearly 100 ° C. during use of the tire, and becomes a starting point of a crack.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic tire having a sidewall which is excellent in weather resistance and bending fatigue resistance, does not cause discoloration, and does not cause cracks due to crystallization. Aim.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a pair of left and right bead cores, a toroidal carcass which is locked at both ends of the bead core, and a belt layer disposed on a crown portion of the carcass in a circumferentially outer position. And a tread portion disposed outside the belt layer, and a pneumatic tire including a sidewall rubber disposed outside the side portion of the carcass, wherein the sidewall rubber has an inner layer rubber adjacent to the carcass and an outer layer rubber. The outer rubber layer has a two-layer structure, and the outer rubber layer has a rubber component of at least one unsaturated diene rubber selected from the group consisting of natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, and polybutadiene rubber. 90% by weight, a halogenated copolymer of an isomonoolefin having 4 to 7 carbon atoms and a paraalkylstyrene. Is the pneumatic tire which comprises a mixture of 10-60 wt%.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pneumatic tire according to the present invention will be described with reference to the drawings. FIG. 1 shows a right half of a cross-sectional view of a pneumatic tire of the present invention.
Is a toroidal carcass 3 whose end is folded back onto the bead core 2, a belt layer 4 disposed circumferentially outside a crown portion of the carcass, a tread portion 5 disposed outside the belt layer, and The carcass is composed of a side wall rubber 6 arranged outside the side portion. The sidewall rubber 6 is composed of two layers, an inner rubber 6a disposed adjacent to the carcass and an outer rubber 6b disposed outside the inner rubber 6a.

Here, the thickness t of the outer layer rubber is 60% or less of the thickness T of the side wall rubber, especially 20 to 50%.
Is preferably within the range.

As rubber components of the outer layer rubber, natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber,
One or more selected from the group consisting of polybutadiene rubber.
Tensile properties, particularly breaking strength and bending resistance, are important for the outer layer rubber of the sidewall portion. By using one or more of these rubber components and further mixing 40 to 90% by weight or more in the rubber component, Various characteristics can be maintained.

Here, a solution-polymerized styrene-butadiene copolymer rubber and an emulsion-polymerized styrene-butadiene copolymer rubber can be used as the styrene-butadiene copolymer rubber. Are preferably used.

Next, as the other rubber component of the outer layer rubber, a rubber obtained by halogenating a copolymer of isomonoolefin having 4 to 7 carbon atoms and paraalkylstyrene (hereinafter, referred to as halogenated PMS modified rubber) is used.

The isomonoolefin used herein includes, for example, isobretine, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, 2,3-
And dimethyl-2-butene. Halogen is chlorine, bromine or iodine.

The halogenated PMS modified rubber can be produced as follows.

[0014]

Embedded image

Wherein R is an alkyl group having 1 to 5 carbon atoms;
R 'has 1 to 5 carbon atoms in which a part of hydrogen is replaced by halogen.
X represents halogen.

For the production of the halogenated PMS modified rubber, for example, isobutylene and paraalkylstyrene are mixed at a predetermined ratio, and a copolymer is obtained by a usual polymerization method. Further, the hydrogen of the alkyl group of the paraalkylstyrene is partially substituted with a halogen such as chlorine.

Here, the content of paraalkylstyrene in the halogenated PMS modified rubber is 3 to 20% by weight. When the content of the paraalkylstyrene is less than 3% by weight, the adhesion to the diene rubber is inferior, and when it exceeds 20% by weight, the hardness is increased, the tensile properties are deteriorated, and the bending resistance is reduced.
And the halogenated PMS modified rubber is 10 to 10% of all rubber components.
60% by weight is blended. If it is less than 10% by weight, the ozone resistance is not improved, and if it exceeds 60% by weight, the breaking strength is reduced, and the adhesion to the diene rubber is further reduced, so that it cannot be put to practical use.

The halogenated PMS modified rubber has a weight average molecular weight of 300,000 to 700,000 and a glass transition point of -60.degree.
40 ° C. And since it has no double bond in the main chain molecule, it is less susceptible to oxidative degradation by ozone. It is considered that the crosslinking is usually performed by mixing metal oxide and sulfur, whereby the halogen substituted by the alkyl group of paraalkylstyrene is eliminated, and this reacts with the phenyl group of the adjacent paraalkylstyrene to form a crosslink. I have.

The outer layer rubber of the present invention is preferably a rubber softener, for example, a petroleum softener, a paraffin softener, an aromatic softener, a naphthene softener, a fatty oil softener, a synthetic resin softener. Etc. is 100 parts by weight of the rubber component.
5 to 5 parts by weight are blended. The halogenated PMS modified rubber is difficult to knead with a diene rubber such as natural rubber and polybutadiene rubber, and is liable to cause poor dispersion. Then, by blending 0.5 to 5 parts by weight of a rubber softener, the compatibility between the two can be increased and the dispersibility can be improved, and the bending resistance and the ozone resistance of the vulcanized rubber are improved. Particularly preferably, the amount is in the range of 0.7 to 3 parts by weight. The rubber softener is a mixture of aliphatic, aromatic and phenolic resins, for example, Stractol 40MS or Stractol 60MS, a product of S & S Japan.

The outer layer rubber is prepared by appropriately adding a compounding agent generally used as a side wall rubber, for example, carbon black, process oil, wax, an antioxidant, metal oxide, stearic acid, sulfur, and a vulcanization accelerator. Can be changed and blended. The outer layer rubber has a JISA hardness after vulcanization of 52 to 59, preferably 54 to 54.
Adjusted to ~ 58.

Next, the rubber component used for the inner layer rubber of the present invention is a rubber component generally used as a side wall rubber, for example, natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber,
One or more of butyl rubber, halogenated butyl rubber, and ethylene / propylene / diene terpolymer rubber (EPDM / EPT) can be used.

Further, a compounding agent such as carbon black, a rubber softener, an antioxidant, a metal oxide, stearic acid, sulfur, a vulcanization accelerator, etc. is selected and compounded in a predetermined amount according to the required characteristics.

In the present invention, the side wall rubber is made into two layers, and the function is shared by the inner layer rubber and the outer layer rubber. In other words, while the halogenated PMS modified rubber is compounded in the outer rubber and the JISA hardness (H _SO ) is adjusted to 52 to 59, the relationship between the inner rubber and the JISA code (H _SI ) is expressed by the following equation (1). Adjust to be satisfied.

H _SI −10 ≦ H _SO ≦ H _SI −3 (1) As described above, the rigidity of the sidewall portion is maintained by making the hardness of the inner layer rubber larger than the hardness of the outer layer rubber within a certain range. The bending resistance of the portion can be improved.

[0025]

EXAMPLES Sidewall rubbers were produced with the inner rubber composition shown in Table 1 and the outer rubber composition shown in Table 2.

As a compounding agent, a chemical other than sulfur and a vulcanization accelerator is kneaded in a 1.7 liter Banbury, and then a sulfur and vulcanization accelerator are mixed with a roll to form an unvulcanized rubber sheet. Using. Table 2 shows the evaluation results.

The components used in the examples and comparative examples are as follows. NR: RSS3 BR: Nipol 1220 (manufactured by Zeon Corporation) EPDM: Esplen 582F (Sumitomo Chemical Co., Ltd.)
EXXPRO: halogenated PMS modified rubber, EXXPR
O 90-10 Exxon Chemical Co., Ltd.) (halogen content: 2 wt%, P-methylstyrene content: 7.5 wt%) Carbon black: Seast SO (Tokai Carbon Co., Ltd.)
Process oil: Diana process oil PW32 (manufactured by Idemitsu Kosan Co., Ltd.) Wax: Sunnock (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Antioxidant: Nocrack 60 (N-phenyl-N'-)
(1,3-dimethylbutyl) -P-phenylenediamine Rubber softener: Stractol 40MS (manufactured by S & S Japan) Vulcanization accelerator: Noxeller DM (dibenzothiazyl disulfide) Ouchi Shinko Chemical Co., Ltd. (1) Ozone resistance The above rubber was vulcanized at 170 ° C. for 15 minutes to prepare a vulcanized rubber sheet. Using these, JIS K630
According to No. 1, the test was carried out under the test conditions of a temperature of 40 ° C., an ozone concentration of 50 pphm, an elongation of 50%, and 96 hours. Judgment of the crack state of the test piece also followed JIS K6301.

(2) Flex resistance The rubber was vulcanized at 170 ° C for 15 minutes. JIS
A bending test was performed according to K6301. Test condition is 1
Evaluation was made based on the growth length (mm) of the crack after being repeatedly bent for 10,000 times.

(3) Flex resistance (high temperature) A test was conducted in an atmosphere at 80 ° C. in the same manner as in the flex test to evaluate the crack growth length (mm).

(4) Adhesiveness The above unvulcanized rubber sheet was mixed with Compound No. The rubber sheets of No. 1 were superposed and vulcanized and bonded at 170 ° C. for 15 minutes, and the width of the test piece was cut to 2.5 cm to prepare an adhesive peel test piece. This was peeled at a tensile speed of 500 mm / min, and the peel strength was evaluated. The unit is kgf / 2.5cm, 100kg
If f / 2.5 cm or more, the adhesiveness is good.

(5) Discoloration of Appearance Using a 4 mm-thick rubber plate vulcanized under the condition of 170 ° C. × 15 minutes, these test pieces were exposed outdoors without rainwater. After exposure for 30 days, the appearance was visually observed, and the degree of discoloration was evaluated on a five-point scale. The smaller the value, the greater the degree of discoloration.

From the results shown in Table 2, it was found that using EXXPRO (halogenated PMS modified rubber) resulted in a compound No. Compared with No. 1, not only the appearance discoloration is suppressed but also the ozone resistance is improved. In addition, the formulation No. No. 2 has good flexibility at room temperature, but has high flexibility at high temperatures, that is, in actual use in a tire, crack growth is likely to progress, which is not good. On the other hand, in the case of using EXXPRO, the degree of crack growth even at a high temperature can be controlled by the mixing No. Equivalent to 1, slightly better. However, if the compounding amount of EXXPRO exceeds 60 parts by weight, the compound No. which is a representative of other tire members is used. The adhesiveness of No. 1 becomes extremely poor. In addition, by blending Stractol 40MS as a softener for rubber, flex resistance is improved and adhesive strength is also improved.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

Next, a sidewall is constituted by a combination of the inner rubber and the outer rubber shown in Table 3, and a steel radial tire (size 195 / 65R1) for a passenger car having a structure shown in FIG.
5) was prototyped.

The side wall has a depth of 0.3 mm and a width of 5 mm.
An endurance test was performed using a machine with a cut wound of mm, and the results are shown in Table 3.

A pass is achieved if the vehicle completes without bursting for 1000 km. It can be seen that examples using EXXPRO as the outer layer rubber and having a certain relationship between the inner layer rubber hardness (H _SI ) and the outer layer rubber hardness (H _SO ) are particularly excellent in durability.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0040]

As described above, according to the present invention, the side wall rubber has a two-layer structure, and the outer layer rubber has a halogenated PM.
The use of S-modified rubber and the hardness of the inner layer rubber that is higher than the hardness of the outer layer rubber within a certain range improves ozone resistance and bending fatigue resistance, and does not discolor even when used for a long time and has excellent appearance. A pneumatic tire is obtained.

[Brief description of the drawings]

FIG. 1 is a right half of a cross-sectional view of a tire of the present invention.

[Explanation of symbols]

1 tires, 2 bead cores, 3 carcass, 4 belt layers, 5 treads, 6 sidewall rubber.

Claims (3)

[Claims] 1. A pair of left and right bead cores, a toroidal carcass which is locked to the bead core by folding back both ends, a belt layer disposed circumferentially outward on a crown portion of the carcass, and an outer side of the belt layer In a pneumatic tire comprising a tread portion disposed on the side of the carcass and a sidewall rubber disposed on the outside of the side portion of the carcass, the sidewall rubber is composed of an inner layer rubber adjacent to the carcass and an outer layer rubber disposed outside the carcass. The outer layer rubber has a rubber component of 40 to 90% by weight of at least one unsaturated diene rubber selected from the group consisting of natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, and polybutadiene rubber; Is a rubber which is halogenated with a copolymer of an isomonoolefin having 4 to 7 and a paraalkylstyrene.
The pneumatic tire according to claim 1, further comprising a mixture of 0 to 60% by weight. 2. The pneumatic tire according to claim 1, wherein a rubber softener is blended into an outer layer rubber of the side wall rubber. 3. JIS for outer layer rubber of sidewall rubber
A code (H _SO ) and JISA code of inner rubber (H _SI )
3. The pneumatic tire according to claim 1, wherein the relationship (1) satisfies the following expression (1). H _SI -10 ≦ H _SO ≦ H _SI -3 (1)