JPH0477018B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a crosslinked foam made of butadiene polymer rubber that has excellent wet skid properties and mold flow properties, good abrasion resistance, and a high expansion ratio. Foams using 1,2-polybutadiene (1,2-PBD), ethylene/vinyl acetate copolymer (EVA), natural rubber, synthetic rubber, and the like are known as crosslinked foams having rubber elasticity. this house,
It is difficult to obtain a high expansion ratio with foams using natural rubber and synthetic rubber, and dimensional accuracy is poor due to large shrinkage after vulcanization. Furthermore, it has the disadvantage that it is difficult to mold using a complicated mold due to poor mold flowability. On the other hand, foams using 1,2-PBD and EVA are generally known to be able to obtain foams with a high expansion ratio without shrinkage problems by only one-stage crosslinking; It is widely used in applications that require weight reduction, such as outer soles, inner soles, and midsoles. The main performance of the outer sole is its wet skid property, which shows the resistance to slipping on wet roads when walking or running, and its abrasion resistance.
In recent years, lighter sponges have come into use due to the demand for weight reduction. Furthermore, there is a demand for complex and deep designs for the soles of shoes, which has created a need for materials with good mold flow properties. However, foams using EVA have a practical problem of poor wet skid properties, although they have reasonably good mold flow properties and can produce highly foamed products. In addition, foams using 1,2-PBD are also EVA
Although the wet skid property, which is a drawback of foam, has been improved, it is not sufficient, and furthermore, it is difficult to balance mold flowability and abrasion resistance. An object of the present invention is to provide a crosslinked foam made of butadiene polymer rubber which has excellent wet skid properties and mold flow properties, good abrasion resistance, and has a high expansion ratio. According to the present invention, (A) 1,2 bond content is 70% or more and crystallinity is 5
% or more and an intrinsic viscosity [η] (measured in toluene at 30°C) of 30 to 90% by weight of 1,2-polybutadiene of 0.5 dl/g or more, (B) 3 to 30% by weight of bound styrene, 1 of the butadiene portion , 5-60% by weight of random styrene-butadiene copolymer rubber with 50-95% of 2 bonds, and (C) natural rubber, diene-based synthetic rubber (however, the above (B)
(excluding copolymer rubbers) and block copolymers of aromatic vinyl compounds and conjugated diene compounds. A crosslinked foam of a butadiene polymer is provided. The 1,2-PBD of component (A) used in the present invention is:
In order to obtain a foam with a uniform cell structure, the 1,2-bond content is 70% or more, preferably 85% or more, and the crystallinity is 5% or more, preferably 10 to 40%.
It is PBD. Further, the molecular weight can be selected over a wide range, but in order to obtain a uniform and fine foam, the above [η] needs to be 0.5 dl/g or more, and more preferably 1 to 1. It is 3 dl/g. In addition, the random styrene-butadiene copolymer rubber of component (B) is, for example,
48-41038, by polymerizing styrene and butadiene monomers in a hydrocarbon solvent under an ether or a tertiary amine using an organolithium compound as an initiator. Furthermore, a styrene-butadiene copolymer rubber having a high degree of randomization which is preferable for the purpose of the present invention is prepared by combining styrene and butadiene monomers described in JP-A-52-101287 in a hydrocarbon solvent with ether or a tertiary amine and -SO ₃ H group or -OSO ₅ M group (M is Na,
It can be obtained by polymerization using an organolithium compound as an initiator in the presence of an anionic surfactant having K). The copolymer rubber has a bonded styrene content of 3 to 3 from the viewpoint of wet skid properties and abrasion resistance.
30% by weight, preferably 5-20% by weight, and 50-95% of 1,2 bonds in the butadiene moiety, preferably 70-95%
95% random styrene-butadiene copolymer rubber, including those with branched or linear structures.
The Mooney viscosity can be selected over a wide range, but a Mooney viscosity (ML ₁₊₄ 100°C) of 20 to 150 is preferred from the viewpoint of mechanical properties such as tear strength, abrasion resistance, workability, and mold flowability. Furthermore, in component (C), diene-based synthetic rubber (however,
Examples of the rubbers other than component (B) include cis-polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR) other than (B), high-styrene rubber, and acrylonitrile-butadiene rubber. There are copolymer rubber (NBR), chloroprene rubber (CR), etc. Among these, natural rubber, cis-polyisoprene rubber, polybutadiene rubber, etc. are preferred. The blending amounts of components (A), (B) and (C) are (A)/(B)/ in weight%.
(C)=30-90/5-60/0-5, preferably 30-90/5-60/5-50, more preferably 40-50
It is 80/20 to 50/5 to 30. If the amount of (A) is less than 30% by weight, it will be difficult to obtain a foam with a high lung power, and the shrinkage will be large. If the amount of component (B) is less than 5% by weight, wet skid properties will not be improved. If the amount of component (C) exceeds 50% by weight, it will be difficult to obtain a foam with a high expansion ratio. The crosslinking agent (referred to as component (D)) used in the present invention is not particularly limited, and includes sulfur, thiazoles such as dibenzotazole disulfide, thiurams such as tetramethylthiuram monosulfide, 2-mercapto These include imidazoles such as imizadrine, dithiocarbamates such as zinc dimethyl dithiocarbamate, guanidines such as diphenylguanidine, xanthates such as butyl xanthate disulfide, and organic peroxides such as dicumyl peroxide. . Among these, combinations of sulfur and thiazoles such as dibenzothiazole disulfide, thiurams such as tetramethylthiuram monosulfide, or organic peroxides such as dicumyl peroxide are preferred. In addition, there are no particular restrictions on the blowing agent (component (E)), but sodium bicarbonate, ammonium bicarbonate,
Examples include sodium carbonate, ammonium carbonate, azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), dinitrosoterephthalamide, azobisisobutyronitrile, pallium azodicarboxylate, and sulfonyhydrazide. These foaming agents may be used in combination with known foaming aids such as urea and urea derivatives. The amounts of the crosslinking agent and blowing agent used are not particularly limited, but can be appropriately determined within the range commonly used in the fields of rubber, EVA, and the like. In addition to the above (A) to (E), the foam composition of the present invention includes other compounding agents that are blended in general rubber compositions,
That is, reinforcing agents, fillers, anti-aging agents, processing aids, softeners, pigments, etc. may be added as appropriate. There are no particular restrictions on the method of mixing the above (A) to (E) and other compounding agents, and any mixing method used for general rubber compounds such as a Banbury mixer, pressure kneader, or open roll may be used. Preferably, mixing is carried out at a temperature in the range of 140°C. The mixture thus obtained is fed into a mold and heated under pressure in a temperature range of 130 to 180°C, preferably 140 to 170°C, and at a temperature higher than the decomposition temperature of the blowing agent to crosslink and foam the compound. Decompose the agent. The mold clamping pressure is required to substantially suppress the expansion of the gas generated by the decomposition of the blowing agent, and is usually carried out at a pressure of 80 kg/cm ² or more. Next, the present invention will be specifically explained by showing Examples and Comparative Examples. In the Examples and Comparative Examples, the hardness (Hs) was measured using a rubber tester type C (manufactured by Kobunshi Keiki,
The specific gravity was measured by the buoyancy method using a sponge hardness tester). Abrasion resistance was measured by Akron abrasion in accordance with BS903, and wet skid properties were evaluated on a five-point scale based on the slippery feeling when running on a wet tile road surface while wearing jogging shoes.
Regarding mold flowability, details of the evaluation method are appended to the table, but evaluation was made by using a specific mold and applying a certain pressure to the rubber, and the distance of the rubber flowing into the mold. Example 1 1,2-PBD (manufactured by Japan Synthetic Rubber Co., Ltd., JSR
RB820, 1, 2 bond content 92%, crystallinity 25%,
[η] Toluene 30°C = 1.25), random styrene-butadiene copolymer rubber SBR-1 (bonded styrene 5% by weight, 1 and 2 bond content 86%, Mooney viscosity
ML ₁₊₄ 100℃=60), polyisoprene rubber (manufactured by Japan Synthetic Rubber Co., Ltd., JSR IR2200) and other compounding agents,
Mix using a pressure kneader at the mixing ratio shown in the table.
A foam was obtained by vulcanization at 160°C for 12 minutes. The physical property results are shown in the table. The 1,2 bond content was calculated using infrared absorption spectroscopy by Morello et al. (Chim.e.Ind., 41 , 758
(1959)). Further, the degree of crystallinity was determined by density measurement using a density gradient tube. Example 2 Random styrene-butadiene copolymer rubber
A foam was obtained in the same manner as in Example 1, except that SBR-2 (bonded styrene 20% by weight, 1,2 bond content 62%, Mooney viscosity ML ₁₊₄ 100°C=74) was used.
The physical property results are shown in the table. Example 3 1,2-PBD (Japan Synthetic Rubber Co., Ltd., JSR RB830,
A foam was obtained in the same manner as in Example 1 using 1,2 bond content of 93%, crystallinity of 29%, [η] toluene (30°C = 12.5) and other compounding agents in the proportions shown in the table. Ta. The physical property results are shown in the table. Comparative Example 1 Polybutadiene rubber with a 1,2 bond content of 5% or less and a crystallinity of almost 0 (manufactured by Japan Synthetic Rubber Co., Ltd.,
A foam was obtained in the same manner as in Example 1, except that 1,2PBD of Example 1 was used instead of JSRBR01).
Compared to Example 1, this foam had a larger specific gravity and poor foamability, and was inferior in mold flowability. Comparative example 2 1,2 bond content is 20%, bonded styrene 23.5%
A foam was obtained in the same manner as in Example 1, except that a styrene-butadiene copolymer rubber which was beyond the scope of the present invention was used. This foam has inferior wet skid properties and abrasion resistance compared to Example 1. Comparative example 3 EVA (manufactured by Toyo Soda Kogyo Co., Ltd., Ultrasen)
UE631, vinyl acetate content 20%, M.I 190℃ 2160gr=1.5gr/10min and other formulation examples,
Mix using a pressure kneader at the mixing ratio shown in the table.
A foam was obtained by vulcanization at 160°C for 20 minutes. This foam has extremely poor wet skid properties compared to Example 1.

【table】

[Table] Comparative example 4 1,2-PBD as 1,2-polybutadiene
(1,2 bond content 92%, crystallinity 0% [η]30
Example 1 except that ℃ (toluene) = 1.25) was used.
A foam was obtained in the same manner. The results are shown below.

【table】

【table】 [Brief explanation of drawings]

The drawing is a plan view of a mold for evaluating mold flowability, the thickness of the mold is 2 mm, the side flow is 190 mm, the width of the channel (B-B') is 8 mm, and A is the rubber injection part.

Claims (1)

[Scope of Claims] 1 (A) 1,2 bond content is 70% or more, crystallinity is 5% or more, and intrinsic viscosity [η] (30% in toluene)
(B) Random styrene-butadiene with 3-30% by weight of bound styrene and 50-95% of 1,2 bonds in the butadiene moiety. 5 to 60% by weight of copolymer rubber and (C) natural rubber, diene-based synthetic rubber (excluding copolymer rubber of (B) above), and block copolymerization of aromatic vinyl compound and conjugated diene compound A crosslinked foam of a butadiene polymer obtained by crosslinking and foaming a mixture containing 0 to 50% by weight of at least one selected from the group consisting of 0 to 50% by weight in the presence of a blowing agent.