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Thermoplastic elastomer composition

Thermoplastic elastomer composition description/claims

The present invention relates to a thermoplastic elastomer composition, more particularly relates to a thermoplastic elastomer composition which can be obtained from dynamically cross-linking of a thermoplastic resin and a modified butyl rubber composition with a cross-linking agent.

A thermoplastic elastomer (i.e., TPE) is a polymer material exhibiting a thermoplasticity similar to a thermoplastic resin at a high temperature and exhibiting a rubber elasticity similar to an elastomers at an ordinary temperature. Generally, by a blend of a thermoplastic resin and elastomer containing the domain phase of an elastomer closely and uniformly dispersed in a continuous phase of a thermoplastic resin, the characteristic properties of TPE are exhibited. On the other hand, a polymer blend prepared by a dynamically cross-linking process of mixing a cross-linkable elastomer in a continuous phase of a thermoplastic resin, cross-linking the elastomer in a kneaded state, and finely dispersing the cross-linkable elastomer in the continuous phase exhibits the characteristic properties of TPE and has superior characteristic properties compared with a simple blend of the two polymer components. Rubber. Chem. Technol. 55, 116 (1982) and U.S. Pat. No. 3,037,954 disclose technologies for preparation of TPE by dynamic cross-linking and describe, among these, using polypropylene as the thermoplastic resin and butyl rubber as the cross-linkable elastomer to prepare a PP/IIR-based TPE, wherein, the cross-linking of the butyl rubber uses resin cross-linking.

Butyl rubber has an extremely low degree of unsaturation, and therefore, is excellent in weatherability, heat resistance, ozone resistance, etc. and is also has a low air permeability, and, therefore, is suitable for use as a sealant, adhesive, etc. As methods for cross-linking the butyl rubber, sulfur cross-linking, quinoid cross-linking, resin cross-linking, etc. are known, but currently it is hard to say that any method is satisfactory in practice. That is, sulfur cross-linking requires cross-linking at a high temperature over a long time. Further, quinoid cross-linking usually uses toxic red lead oxide as an oxidizing agent to activate the quinoid and, therefore has environmental problems. Further, the resin cross-linking has a remarkably slow reaction rate and requires heating at a high temperature over a long time. Thus, the result is liable to be a product in a state not completely cross-linked, and therefore there is the problem that, during the use thereof, a cross-linking reaction is liable to occur and the physical properties are liable to greatly change. Further, among the methods of cross-linking a diene-based rubber, etc., the cross-linking with an organic peroxide, which is extremely excellent in heat resistance, is almost never used as a method for cross-linking butyl rubber. This is because, if this cross-linking is applied to butyl rubber, the decomposition reaction of the main chain is liable to occur in preference and the resultant product is liable to be softened rather than cross-linked. On the other hand, partially cross-linked butyl rubber is commercially available as a butyl rubber capable of being cross-linked with an organic peroxide, but this has the problem of insufficient processability. Further, Japanese Patent Publication (A) No. 6-172547 discloses a method of cross-linking an un-crosslinked butyl rubber in the presence of an organic peroxide and a polyfunctional monomer containing an electron-attractive group, but, according to this method, severe reversion is liable to occur.

The present inventors previously found a modified butyl rubber composition including a modified butyl rubber capable of being cross-linked with an organic peroxide by adding, to the butyl rubber, (a) a compound such as TEMPO (i.e., 2,2,6,6-tetramethylpiperidine 1-oxyl) derivative stable at an ordinary temperature even in the presence of oxygen and having, in the molecule thereof, a nitroxide-free radical, (b) a radical initiator and (c) a bifunctional or higher functional radical polymerizable monomer, followed by reacting the mixture (see Japanese Patent Application No. 2006-131780). Thus, as stated above, the TPE of butyl rubber/polyolefin is currently dynamically cross-linked by resin cross-linking. There are no examples in which dynamic cross-linking by peroxide cross-linking is applied to the butyl rubber/polyolefin.

Accordingly, the object of the present invention is to provide a butyl rubber/polyolefin-based TPE obtained by dynamic cross-linking by peroxide cross-linking of a butyl rubber having superior weatherability, heat resistance, ozone resistance and the like and having low air permeability.

In accordance with the present invention, there is provided a thermoplastic elastomer composition comprising a dynamically cross-linked composition of

(A) 10 to 70 parts by weight of a thermoplastic resin,

(B) 30 to 90 parts by weight of a modified butyl rubber composition containing a modified butyl rubber modified by reacting, to butyl rubber, (a) a compound containing, in the molecule thereof, a nitroxide free radical stable at an ordinary temperature, preferably a room temperature in the presence of oxygen, and (c) a bifunctional or higher functional radical polymerizable monomer, and,

(C) 0.01 to 15 parts by weight of a cross-linking agent.

According to the present invention, by using a modified butyl rubber composition capable of being cross-linked with a peroxide, preparation of a butyl rubber/polyolefin-based TPE using dynamic cross-linking by peroxide cross-linking becomes possible and a thermoplastic elastomer composition have improved heat aging resistance and settability can be obtained.

FIG. 1 shows cross-linking curves showing the cross-linking characteristics of the rubber compositions obtained in Examples 1 to 2 and Comparative Example 2.

The inventors engaged in intensive studies to enable ordinary butyl rubber to be cross-linked with an organic peroxide and, as a result, found that the desired thermoplastic elastomer composition can be obtained by dynamically cross-linking a composition containing (A) 10 to 70 parts by weight, preferably 10 to 50 parts by weight, of a thermoplastic resin, (B) 30 to 90 parts by weight, preferably 50 to 90 parts by weight, of a modified butyl rubber composition containing a modified butyl rubber modified by reacting, to butyl rubber, (a) a compound having, in the molecule thereof, a nitroxide-free radical stable at an ordinary temperature in the presence of oxygen, (b) a radical initiator and (c) a bifunctional or higher functional radical polymerizable monomer and (C) 0.01 to 15 parts by weight, preferably 0.1 to 10 parts by weight, of a cross-linking agent.

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