Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1987-02-18
1988-03-01
Seccuro, Carman J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525192, 525196, 525232, 525233, 525 78, 525193, 525197, 525211, 524504, 524572, C08L 2326, C08L 902, C08L 1502, C08L 5106
Patent
active
047286920
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a thermoplastic elastomer composition.
There are known thermoplastic elastomer compositions which are formed by partially crosslinking a composition composed of a polyolefin and a rubber component in the presence of a crosslinking agent. The crosslinking agent used in the production of these compositions is mainly an organic peroxide, sulfur, or a vulcanization accelerator for sulfur-cured rubber.
The crosslinking agent of organic peroxide has some disadvantages. It is so reactive that it is difficult to properly control the degree of crosslinking. It brings about the scission of molecules simultaneously with crosslinking, deteriorating the properties of a composition or increasing the melt index of a polyolefin. This in turn adversely affects the drawdown of the melt at the time of molding and causes the surface roughening of the moldings due to partial gelling. In addition, free radicals induced by an organic peroxide remain in the moldings to aggravate the thermal stability of the moldings. On the other hand, a crosslinking of sulfur forms the S-S linkage which adversely affects the thermal stability.
There is proposed in, for example, Japanese Patent Publication No. 23702/1979 a partially crosslinked thermoplastic elastomer composition which comprises (A) 5 to 40 wt% of polyisobutylene and/or butyl rubber, (B) 30 to 90 wt% of ethylene-propylene copolymer rubber and/or ethylene-propylene-non-conjugated diene terpolymer rubber, and (C) 5 to 40 wt% of polyolefin resin. The crosslinking agent used in this composition is substantially an organic peroxide, and the crosslinking of the composition takes place mainly in component (B). Therefore, the miscibility of the components and the oil resistance were less than perfect.
It is an object of the present invention to provide a partially crosslinked composition containing a polyolefin such as polypropylene and an olefin copolymer rubber such as ethylene-propylene copolymer rubber as well as other polymeric components. The composition is a thermoplastic elastomer composition superior in moldability, heat resistance, miscibility, and where nitrile rubber is included in the composition, oil resistance, in which there is no molecular scission and the olefin copolymer rubber is not substantially crosslinked. The present inventors conducted a series of experiments which led to the finding that when a composition of polyolefin such as polypropylene, olefin copolymer rubber, modified polyolefin, halogenated butyl rubber and optionally, nitrile rubber, is subjected to crosslinking with a crosslinking agent of a metal oxide and/or a metal chloride, the halogenated butyl rubber alone is selectively cross-linked.
SUMMARY OF THE INVENTION
A thermoplastic elastomer composition and process comprising (A) 10 to 90 parts by weight of crystalline polyolefin such as polypropylene, (B) 10 to 90 parts by weight of halogenated butyl rubber (with the total amount of (A) and (B) being 100 parts by weight), (C) 10 to 120 parts by weight of olefin copolymer rubber, (D) 1 to 90 parts by weight of modified polyolefin, and optionally (E) 2 to 50 parts by weight of nitrile rubber, said composition being partially crosslinked in the presence of a crosslinking agent of a metal oxide and/or a metal chloride.
DETAILED DESCRIPTION OF THE INVENTION
Components of the Composition
(A) Crystalline Polyolefin
This component comprises a homopolymer of propylene or a copolymer of propylene with an alpha-olefin such as ethylene, 1-butene, 1-hexene, and 4-methyl-1-pentene. It has a melt flow rate (abbreviated as MFR hereinafter) of 0.3 to 60 g/10 min, preferably 1 to 40 g/10 min, and more preferably 3 to 30 g/10 min. (This component is designated as component A hereinafter.)
Component A has the highest melting point among polyolefins; and it contributes to an improvement in heat resistance and mechanical strength.
(B) Halogenated Butyl Rubber
This component denotes a halogenated isobutylene-isoprene copolymer rubber. (It is designated as component B hereinafter.)
REFERENCES:
patent: 3904470 (1975-09-01), Fukuki et al.
patent: 4048261 (1977-09-01), Stramer
patent: 4130534 (1978-12-01), Coran et al.
patent: 4299931 (1981-11-01), Coran et al.
patent: 4409365 (1983-10-01), Coran et al.
Kanai Tsuyoshi
Mikami Takashi
Saito Masaaki
Sezaki Eiji
Tanaka Kikuo
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