JPH06240050A - Rubber composition for side wall - Google Patents

Abstract

PURPOSE:To obtain the subject compsn. which has improved resistances to ozone and flex fatigue. CONSTITUTION:This rubber compsn. is prepd. by compounding 100 pts.wt. rubber component comprising 30-80 pts.wt. rubber obtd. by halogenating an isoolefin/p- methylstyrene copolymer, 20-60 pts.wt. natural and/or polyisoprene rubber, and 0-50 pts.wt. another diene rubber with 2.5-7 pts.wt. 10-20C satd. fatty acid, tall rosin or their mixture.

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 tire sidewalls having improved ozone resistance, appearance and flex fatigue resistance.

[0002]

2. Description of the Related Art Generally, the sidewall of a tire is exposed to sunlight, and therefore, when it is strongly exposed to ultraviolet rays, a crack called ozone crack may occur in the sidewall. Conventionally, in order to prevent the occurrence of ozone cracks, that is, in order to improve ozone resistance, a rubber composition for a sidewall is mixed with an antioxidant or a wax. This anti-aging agent or wax functions to prevent ozone cracks by exuding (blooming) on the surface of the side wall to form a thin layer and preventing ozone or oxygen from directly contacting the rubber of the side wall. do.

However, when such a bloom occurs, the appearance of the side wall is deteriorated due to the contamination with the antioxidant or wax, and the commercial value of the tire is reduced, which is not preferable. Therefore, an attempt was made to blend an isobutylene-based polymer such as IIR (isobutylene-isobutyl rubber). However, in this case, although ozone resistance and bending fatigue resistance are good, there is a problem that the tensile strength is low.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and provides a rubber composition for a sidewall, which has improved ozone resistance, appearance, and flex fatigue resistance. The purpose is to

[0005]

A rubber composition for a side wall of the present invention comprises 30 to 80 parts by weight of a rubber obtained by halogenating a copolymer obtained by reacting an isoolefin with paramethylstyrene, and a natural rubber. And / or 20 to 60 parts by weight of polyisoprene rubber and 0 to 50 parts by weight of other diene rubber to 100 parts by weight of a rubber component, saturated fatty acid having 10 to 20 carbon atoms, tall oil rosin or a mixture thereof is added.
It is characterized by containing 2.5 to 7 parts by weight.

As described above, according to the present invention, since a saturated fatty acid or tall oil rosin is used in addition to a specific rubber obtained by halogenating a copolymer obtained by reacting an isoolefin with paramethylstyrene, ozone resistance is improved. It is possible to improve the toughness, appearance, tensile strength, and bending fatigue resistance. Hereinafter, the configuration of the present invention will be described in detail.

Paramethylstyrene as an isoolefin
A rubber obtained by halogenating a copolymer obtained by reacting (PMS) (hereinafter referred to as a halogenated PMS-modified polymer). The isoolefin used here is, for example, isobutylene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl.
-2-butene, 2,3-dimethyl-2-butene and the like. Further, halogen is chlorine, bromine, iodine or the like. This halogenated PMS modified polymer can be manufactured as follows.

[0008] This halogenated PMS-modified polymer is a novel compound having a weight average molecular weight of 550,000 to 700,000 and a glass temperature of -60 ° C.
It is about -40 ° C. Since this halogenated PMS-modified polymer has no double bond in the main chain molecule, it is less susceptible to oxidative deterioration or ozone deterioration due to oxygen or ozone in the air. Further, this halogenated PMS-modified polymer is cross-linked in the metal oxide / sulfur combination system as described below to form a three-dimensional network structure.

[0009] Other diene rubber. It is a diene rubber other than natural rubber and polyisoprene rubber. The diene rubber may be a usual one used for tires. For example, natural rubber (NR)
, Isoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), butyl rubber (IIR), halogenated butyl rubber (halo-II
R), ethylene / propylene / diene terpolymer rubber
One or more of (EPDM, EPT) can be used. As the BR, vinyl cis BR (VCR), neodymium BR (SE-BR) or trans BR may be used.

A saturated fatty acid having 10 to 20 carbon atoms. For example, adipic acid, lauric acid, linoleic acid, stearic acid, etc., and a mixture thereof may be used.
As the tall oil rosin, a general commercial product may be used. The rubber composition of the present invention comprises 30 to 80 parts by weight of the halogenated PMS modified polymer, 20 to 60 parts by weight of natural rubber and / or polyisoprene rubber, and 0 to 50 parts by weight of the other diene rubber. 2.5 to 7 parts by weight of the above saturated fatty acid, tall oil rosin or a mixture thereof is mixed with 100 parts by weight of the rubber component consisting of.

If the amount of the halogenated PMS-modified polymer is less than 30 parts by weight, the ozone resistance is not improved, and if it exceeds 80 parts by weight, the tensile properties, particularly the breaking strength, are greatly deteriorated and it becomes unusable for practical use. When the amount of the fatty acid or tall oil rosin or the mixture thereof is less than 2.5 parts by weight, the tensile strength is not improved, and when it exceeds 7 parts by weight, other physical properties are deteriorated and the cost is not preferable. Further, more preferably, 0.5 to 5 parts by weight of a fatty acid other than stearic acid (adipic acid, lauric acid, linolenic acid, etc.), tall oil rosin, or a mixture thereof is contained in 2.5 to 7 parts by weight.

In addition to these, a compounding agent such as carbon black or sulfur can be appropriately compounded, if necessary. The blending amount of carbon black is preferably 30 to 80 parts by weight with respect to 100 parts by weight of the rubber component.

[0013]

[Examples] Rubber compositions having the formulation contents (parts by weight) shown in Table 1
(Rubber compositions 1 to 7 of the present invention and comparative rubber compositions 1 to 2) were tested for constant strain fatigue to evaluate flexural fatigue resistance, ozone resistance, and tensile strength. . The results are shown in Table 1.

Test method for constant strain fatigue : Fa from Monsanto
Using a tigue Tester, the measurement was performed according to the method specified in ASTM-D 4482, except that the condition of 100% strain rate was applied, until fracture. The number of times until breakage is shown in index form in Table 1. The higher the value, the better the bending fatigue resistance. This index is the ratio of the number of breaks when the halogenated PMS-modified polymer was blended to the case where the number of breaks when BR was set to 100.

Ozone resistance evaluation method : In accordance with the ozone deterioration test method specified in JIS K 6301, ozone concentration 100pphm
It was judged based on the result after 48 hours under the condition that the elongation rate was 50%. The results are shown in Table 1. The number and size of cracks generated in the test piece after the ozone test were judged according to the following criteria.

Number: A = 1 to less than 10 B = 10 to less than 50 C = 50 or more K = break of sample Size: 1 = visible to the naked eye 2 = 1 mm or less 3 = 1 mm or more to less than 3 mm 4 = 3 mm or more and less than 5 mm 5 = 5 mm or more N = No occurrence of cracks Evaluation method of tensile strength : Tensile strength (TB) was measured according to the tensile test method defined in JIS K 6301. The value is converted into an index and shown in Table 1. The larger the value is, the larger the tensile strength is. This index is also the ratio of the number of breaks when the halogenated PMS-modified polymer was blended to the case where the number of breaks when BR was set to 100.

[0017]

In Table 1, the comparative rubber composition 2 is a composition in which a halogenated PMS-modified polymer is used in place of the BR in the comparative rubber composition 1, and the rubber compositions 1 to 1 of the present invention are used.
No. 3 is a rubber composition in which tall oil rosin, lauric acid, and linoleic acid are further added to the comparative rubber composition 2, and the rubber compositions 4 to 6 of the present invention are those in which the compounding amounts thereof are further increased. From Table 1, the comparative rubber composition 2 is halogenated P
Compared with the rubber composition 1 in which the MS-modified polymer is not used, the flexural fatigue resistance and ozone resistance are excellent, but the tensile strength is significantly inferior. However, the rubber compositions 1 to 6 of the present invention
Shows that by using tall oil rosin, lauric acid, and linolenic acid in the comparative rubber composition 2, the flexural fatigue resistance and ozone resistance of the comparative rubber composition 2 are further improved, and the tensile strength is also improved. I understand.

[0019]

As described above, according to the present invention, a specific rubber obtained by halogenating a copolymer obtained by reacting an isoolefin with paramethylstyrene is used, and a saturated fatty acid or tall oil rosin is used. As a result, ozone resistance can be increased without adding an antioxidant or wax, and flex resistance and tensile strength can be improved. Further, since it is not necessary to add an antioxidant or a wax, when the rubber sidewall of the present invention is used to form a tire sidewall, the sidewall has a good appearance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C08L 25/16 LEK 9166-4J

Claims (1)

[Claims] 1. A rubber obtained by halogenating a copolymer obtained by reacting an isoolefin with paramethylstyrene.
30 to 80 parts by weight, 20 to 60 parts by weight of natural rubber and / or polyisoprene rubber, and 0 to 50 parts by weight of other diene rubber to 100 parts by weight of a rubber component, and saturated fatty acid having 10 to 20 carbon atoms Or tall oil rosin or mixtures thereof 2.
A rubber composition for a side wall, containing 5 to 7 parts by weight.