JP2002284927A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire having a sidewall rubber having excellent ozone crack resistance without lowering visual quality such as discoloration. SOLUTION: This pneumatic tire has a sidewall composed of a rubber composition prepared by mixing 20-50 pts.wt. of a natural rubber and/or polyisobutylene rubber with 10-20 pts.wt. of a halogenated butyl rubber, 20-50 pts.wt. of a polybutadiene rubber and 10-20 pts.wt. of a low-unsaturation degree rubber and making up the rubber component to 100 pts.wt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having a sidewall rubber which is excellent in ozone crack resistance and does not deteriorate appearance quality such as discoloration.

[0002]

2. Description of the Related Art Conventionally, a sidewall portion of a pneumatic tire contains a highly unsaturated rubber component such as natural rubber, polybutadiene rubber or polyisoprene rubber having a relatively large content of double bonds in the main chain of rubber molecules. It is used. The double bond in the main chain of the rubber molecule reacts with ozone to cause cleavage of the molecular bond. In particular, when the tire is left in a place where the ultraviolet ray is strong or a place where the ozone concentration is high, an ozone crack is generated in combination with mechanical fatigue due to severe repeated bending deformation of the sidewall portion due to running of the tire.

In particular, in a radial tire in which a highly rigid belt layer such as a steel cord is disposed on a tire tread portion, a rigidity step is generated from both ends of the belt layer to a region of a sidewall portion, and stress concentration is severe. Thus, the occurrence of cracks in the sidewall portion is promoted by repeated deformation during tire running.

Conventionally, an amine-based antioxidant or wax has been blended to reduce the ozone cracks in the side wall portion. When such an anti-ozone cracking agent is added to the rubber composition, the anti-ozone cracking agent blooms on the surface of the side wall rubber to impair its appearance. In particular, the amine-based antioxidant discolors brown under the influence of air and light, and impairs aesthetic appearance.

Therefore, there are few double bonds in the main chain of the molecule,
By mixing so-called low unsaturated rubber components,
Attempts have also been made to improve the ozone crack resistance of the rubber composition itself (JP-A-62-143955).
However, in such a technique, the adhesion between the sidewall rubber and the tread rubber and the carcass ply adjacent thereto is reduced, and the rubber may be separated from each other as the tire is used for a long period of time.

[0006]

SUMMARY OF THE INVENTION The present invention provides a pneumatic pneumatic tire having a sidewall rubber having improved adhesion to an adjacent tread rubber and carcass ply, excellent ozone crack resistance, and reduced appearance discoloration. The purpose is to provide tires.

[0007]

According to the present invention, natural rubber and / or polyisoprene rubber is 20 to 50 parts by weight, halogenated butyl rubber is 10 to 20 parts by weight, and polybutadiene rubber is 20 to 50 parts by weight. 10 unsaturated rubbers
A pneumatic tire comprising a side wall rubber made of a rubber composition having a rubber component of 100 parts by weight by mixing up to 20 parts by weight.

[0008] The rubber composition for the sidewall is prepared by adding carbon black to 20 to 7 parts by weight per 100 parts by weight of the rubber component.
It is preferable to add 0 parts by weight. Preferably, the low-unsaturation rubber is EPDM.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber composition for a tire sidewall according to the present invention contains 20 to 40% by weight of a natural rubber and / or a polyisoprene rubber in a rubber component. When the content of the natural rubber or the polyisoprene rubber is less than 20 parts by weight, basic properties such as tensile strength cannot be maintained, and the sidewall rubber is repeatedly deformed during running of the tire. Will be higher. The mixing ratio of the natural rubber and the polyisoprene rubber can be arbitrarily selected.

Next, the rubber composition of the side wall portion of the present invention comprises a halogenated butyl rubber as a second rubber component.
It is contained in an amount of 0 to 20 parts by weight. 10 halogenated butyl rubber
If the amount is less than parts by weight, the ozone crack resistance cannot be improved. On the other hand, if the halogenated butyl rubber exceeds 20 parts by weight, the vulcanization adhesion to other adjacent tire components, for example, carcass ply and tread rubber, decreases, and heat generation during tire running increases. Here, the halogenated butyl rubber is preferably a chlorinated butyl rubber or a brominated butyl rubber. Halogenated butyl rubber is commercially available from JSR Chlorobutyl and JSR
Bromobutyl, also Exxon's EXXON chlorobutyl and EXXON bromobutyl, and Policer's P
There are OLYSAR chlorobutyl and POLYSAR bromobutyl.

Next, the rubber composition for the side wall portion of the present invention comprises a polybutadiene rubber (B) as a third rubber component.
R) in an amount of 20 to 40 parts by weight. As the polybutadiene rubber, a so-called high cis polybutadiene rubber containing preferably at least 60% by weight, particularly at least 90% by weight of cis 1,4 bonds is used. By blending 20 to 40% by weight of the polybutadiene rubber, the bending fatigue resistance, which is an important property of the sidewall rubber, is improved.

Next, the rubber composition of the side wall portion of the present invention comprises a low-unsaturated rubber as a fourth rubber component in an amount of 10 to 10.
20 parts by weight are mixed. Here, the low-unsaturation rubber refers to a rubber having a small or no double bond in the main chain of the rubber molecule, for example, ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (E
P) and the like. Here, the ethylene-propylene-diene rubber (EPDM) is an ethylene-propylene rubber (EDM).
PM) containing a third diene component, wherein the third diene component is a non-conjugated diene having 5 to 20 carbon atoms;
For example, 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 2,5-dimethyl-1,5
-Besides hexadiene and 1,4-octadiene,
Cyclic dienes such as 1,4-cyclohexadiene, cyclooctadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene, 2-methallyl-5-norbornene and
Alkenyl norbornenes such as isopropenyl-5-norbornene and the like can be used.

In addition, the rubber composition of the side wall rubber, in addition to the above four rubber components, is used in an amount of 10 parts by weight based on 100 parts by weight of the total rubber component within a range not to impair the effects of the present invention.
Other rubber components can be mixed in the range of not more than weight%. Here, as other rubber components, styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), butyl rubber (I
IR) and the like, and one or more of these rubber components can be mixed.

It is desirable that the rubber composition of the side wall rubber of the present invention contains 20 to 70 parts by weight of carbon black based on 100 parts by weight of the above rubber component.
If the compounding amount of carbon black is less than 20 parts by weight, the flexural fatigue resistance and fracture strength of the sidewall rubber decrease, and if the compounding amount of carbon black exceeds 70 parts by weight, the heat generation phenomenon during tire running becomes severe. It is.
Here, carbon black has a nitrogen adsorption specific surface area of 40 to
A range of 120 m ² / g is preferred. When the nitrogen adsorption specific surface area is less than 40 m ² / g, the bending resistance and the breaking strength of the side wall rubber decrease, and the nitrogen adsorption specific surface area becomes 1
When it is larger than 20 m ² / g, the heat generation of the sidewall rubber increases.

The sidewall rubber according to the present invention has a Shore D hardness after vulcanization of 40 to 60, preferably 4 to 60.
It is in the range of 2-45. If the Shore D hardness is less than 40, the bending deformation of the sidewall portion becomes severe, and the bending fatigue property is reduced. On the other hand, if the Shore D hardness exceeds 60, peeling off from the adjacent carcass ply and tread rubber tends to occur.

As the vulcanizing agent for the rubber composition of the present invention, an organic peroxide or a sulfur-based vulcanizing agent can be used alone or in a mixture thereof. Organic peroxides include benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butylperoxybenzene and di-t-butylperoxy-diisopropylbenzene. Examples of the sulfur vulcanizing agent include sulfur and morpholine disulfide.

The rubber composition according to the present invention may contain silica in a range of 60 parts by weight or less based on 100 parts by weight of the rubber component. Here, as the silica, a precipitated silica having a nitrogen adsorption specific surface area of preferably 100 to 200 m ² / g can be used. When silica is compounded, it is preferable to use a silane coupling agent in combination.

Further, the rubber composition of the present invention suitably contains zinc oxide, stearic acid, a softener, an antioxidant, a wax, an adhesive, an inorganic filler, a plasticizer, and a compounding agent for vulcanization accelerator. Can be done. Here, as the softener,
Petroleum softeners such as process oils, lubricating oils, paraffin, liquid paraffin, petroleum asphalt, petrolatum;
Fatty oil-based softeners such as castor oil, linseed oil, rapeseed oil and coconut oil; linoleic acid, palmitic acid, lauric acid and the like can be used.

As the antioxidant, amines, phenols, imidazoles, metal salts of carbamic acid, waxes and the like can be used. As the pressure-sensitive adhesive, a pressure-sensitive adhesive such as rosin-based, terpene-based, terpene-phenol-based, phenol-based, coumarone-indene-based resin, and petroleum resin can be used.

As plasticizers, DMP (dimethyl phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate), DOP
(Dioctyl phthalate) and the like can be used. Examples of the vulcanization accelerator include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Can be used.

The rubber composition according to the present invention is suitably used for a sidewall rubber of a pneumatic tire, for example, a tire for trucks and buses. FIG. 1 is a right half of a sectional view of a pneumatic radial tire for trucks and buses according to the present invention. In FIG. 1, a pneumatic radial tire T has a pair of beads 1, a pair of sidewalls 2, and a tread 3 continuous with both sidewalls 2, and is embedded in the pair of beads 1. There is provided a carcass 5 extending between the bead cores 4 and a belt 6 for reinforcing the tread portion 3 around the outer periphery of the carcass 5. The carcass 5 includes a carcass body extending between a pair of bead cores 4 and a periphery of the bead core 4 in a tire radial direction (hereinafter referred to as a radial direction).
And a folded portion 5a wound from the inside to the outside.
The carcass 5 consists of a ply rubber coated with a radially arranged cord of ultra-high strength organic fiber cord such as steel cord or aramid. The rubber composition of the present invention can be used as a sidewall rubber for tires of all categories, such as tires for passenger cars and light trucks, in addition to truck and bus tires having such a basic structure.

[0022]

EXAMPLES The rubber compositions of the sidewall portions of Examples and Comparative Examples were prepared with the basic formulations shown in Table 1. Each of the examples and comparative examples contains the following compounding agents.

Carbon black: 30 parts by weight Zinc oxide: 3 parts by weight Stearic acid: 1 part by weight Wax: 1 part by weight Naphthenic oil: 10 parts by weight Sulfur: 2 parts by weight Vulcanization accelerator: 0.5 parts by weight Here carbon Black is HAF (nitrogen adsorption specific surface area:
Seat 3 manufactured by Tokai Carbon Co., Ltd. was used at 79 m ² / g).

The details of the ingredients shown in Table 1 are as follows.

[0025]

[Table 1]

Note 1) Halogenated butyl rubber: Chlorobutyl 1068 manufactured by Exxon was used.

Note 2) Low-unsaturation rubber: EP93 manufactured by Nippon Synthetic Rubber Co. was used. Note 3) Polybutadiene rubber: BR1 manufactured by Nippon Synthetic Rubber Co., Ltd.
5 was used.

Note 4) Antioxidant: Antigen 6C manufactured by Sumitomo Chemical Co. was used. The following methods were used to evaluate the performance of Comparative Examples and Examples of the present invention. <Appearance Discoloration Test> A sheet was prepared from the rubber composition having the composition shown in Table 1, and was exposed outdoors for one week, and the degree of discoloration was visually evaluated. <Adhesion and Peeling Test> The rubber sheet and the test sheet of the standard example shown in Table 1 were bonded and vulcanized, and a tensile test was performed so as to peel off the bonded interface. The interface peeling state or rubber cutting state between the rubber sheets was evaluated. <Evaluation of cracks> After an ozone test according to JIS K6259, the number of cracks generated was evaluated. Table 1 shows 96
The evaluation results after hours are shown. <Shore D hardness> Measured according to JIS K6253. <Elongation (Eb)> A tensile test was performed in accordance with JIS K6301, and the elongation was measured.

Table 1 shows the results of the evaluation by the above method.
In Comparative Example 1, the compounding amount of the halogenated butyl rubber was as small as 5 parts by weight, and the compounding amount of the low-unsaturation rubber was as large as 30 parts by weight. In Comparative Example 2, ozone cracks occurred because the blending amount of the halogenated butyl rubber was as large as 30 parts by weight and the amount of the low-unsaturation rubber was small. In Comparative Example 3, the compounding amount of the halogenated butyl rubber was 25.
Since the amount is as large as 25 parts by weight and the compounding amount of the low-unsaturation rubber is as large as 25 parts by weight, interfacial peeling occurs between the rubber sheets, resulting in poor adhesion. In Example 1 of the present invention, it was recognized that the rubber was peeled off, so that the adhesiveness was excellent and the ozone crack resistance was also improved.

It should be understood that the embodiments and examples disclosed this time are illustrative in all aspects 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.

[0031]

As described above, the present invention provides natural rubber and / or
Or a pneumatic tire having a sidewall rubber made of a rubber composition obtained by mixing a polyisoprene rubber, a halogenated butyl rubber, a polybutadiene rubber, and a low-unsaturation rubber in a predetermined amount range. The pneumatic tire can exhibit its characteristics effectively, and the sidewall rubber has improved adhesion to the adjacent tread rubber and carcass ply, and has excellent ozone crack resistance and reduced appearance discoloration.

[Brief description of the drawings]

FIG. 1 is a diagram showing a right half of a cross-sectional view of a pneumatic radial tire.

[Explanation of symbols]

T tires, 1 bead section, 2 sidewall sections, 3
Tread, 4 bead cores, 5 carcass, 6 belts.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C08L 23/28 C08L 23/28

Claims (3)

[Claims] 1. A natural rubber and / or polyisoprene rubber of 20 to 50 parts by weight and a halogenated butyl rubber of 1
0 to 20 parts by weight, 20 to 50 parts by weight of a polybutadiene rubber, and 10 to 20 parts by weight of a low-unsaturation rubber to provide a side wall rubber made of a rubber composition having a rubber component of 100 parts by weight. A pneumatic tire characterized by the following. 2. The pneumatic tire according to claim 1, wherein 20 to 70 parts by weight of carbon black is blended with respect to 100 parts by weight of the rubber component. 3. The pneumatic tire according to claim 1, wherein the low unsaturated rubber is EPDM.