Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-03-02
2003-11-25
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S075000, C525S086000, C525S087000, C525S088000, C525S095000, C525S098000, C525S099000
Reexamination Certificate
active
06653401
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thermoplastic elastomer composition excellent in abrasion resistance, and, more particularly, to a thermoplastic elastomer composition comprising a thermoplastic resin containing a polystyrene resin, a rubber-like polymer obtained by partially or completely crosslinking an ethylene-&agr;-olefin copolymer and a compatibilizing agent.
As thermoplastic elastomers, there are known those of diene type, hydrogenated diene type, polyolefin type, polyvinyl chloride type, polyurethane type and polyamide type. Among them, thermoplastic elastomers of polyvinyl chloride type are not mild for environment, those of diene type are insufficient in weathering resistance, and those of hydrogenated diene type, polyurethane type and polyamide type are expensive. Therefore, the polyolefin thermoplastic elastomers which are mild for environment, excellent in weathering resistance and can be supplied at low cost are now being mainly used. Especially, olefinic thermoplastic elastomers are mainly used which are produced by so-called dynamic crosslinking, namely, by crosslinking a rubber-like polymer comprising EPDM (ethylene-propylene-diene copolymer) and PP (polypropylene) with melt kneading them in the presence of a crosslinking agent in an extruder or the like. These olefin thermoplastic elastomers are being widely used for automobile parts, business and office machines, building materials and others as substitutes for flexible polyvinyl chloride, and they are expected much in the future.
These materials comprise a matrix component comprising PP (polypropylene) having fluidity and a rubber-like polymer component dispersed in the matrix so as to give thermoplasticity. Moreover, for providing rubber-like properties, the rubber-like polymer is partially or completely crosslinked.
The olefinic thermoplastic elastomers comprising such components have rubber-like properties. However, these olefinic thermoplastic elastomers have serious problems when they are widely used for automobile parts, business and office machines, building materials, and the like. That is, the flexible polyvinyl chloride has superior characteristics that it is hardly flawed, and it can be easily coated, printed and solvent bonded, while the olefinic thermoplastic elastomers are not satisfactory in these performances, and restricted in uses. Therefore, development of thermoplastic elastomers which are hardly flawed and relatively cheap has been expected.
SUMMARY OF THE INVENTION
Under the circumstances, the object of the present invention is to provide a thermoplastic elastomer which is excellent in abrasion resistance, namely, hardly flawed.
As a result of intensive research conducted by the inventors to attain the above object, it has been found that a thermoplastic elastomer excellent in abrasion resistance can be obtained when a thermoplastic resin containing a polystyrene resin is used as a matrix component and a rubber-like polymer obtained by partially or completely crosslinking an ethylene-&agr;-olefin copolymer is used as a rubber component in the thermoplastic elastomer.
That is, the present invention relates to a thermoplastic elastomer composition which comprises (A) a thermoplastic resin containing a polystyrene resin, (B) a rubber-like polymer obtained by partially or completely crosslinking an ethylene-&agr;-olefin copolymer, and (C) a compatibilizing agent, the content of the component (B) being 40-90 parts by weight and the content of the component (C) being 0.1-40 parts by weight based on 100 parts by weight of the components (A), (B) and (C) in total.
Furthermore, when content of the polystyrene resin in the thermoplastic resin is not less than 1% by weight and less than 40% by weight and, especially, when the thermoplastic resin comprises a polystyrene resin and a polyolefin resin, the resulting thermoplastic elastomer composition maintains excellent permanent compression set and impact resilience which are characteristics of olefinic thermoplastic elastomers and, besides, is excellent in abrasion resistance, and, on the other hand, when content of the polystyrene resin in the thermoplastic resin is not less than 40% by weight (including 100% by weight), the resulting thermoplastic elastomer composition is excellent not only in abrasion resistance, but also in coatability, solvent bonding properties, printability, and the like. Moreover, when content of the polystyrene resin in the thermoplastic resin is not less than 40% by weight (including 100% by weight), the resulting thermoplastic elastomer composition is superior in heat adhesion to hard polystyrene resins such as polystyrene, high-impact polystyrene and the like, and can be made into layered products having softened surface by insert molding, co-extrusion or the like.
Furthermore, a thermoplastic elastomer composition which is also excellent in heat resistance can be obtained by allowing a resin compatible with polystyrene to coexist in the polystyrene resin as a thermoplastic resin.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be explained in detail below. First, the components of the present invention will be explained in detail.
The polystyrene resin which is one of the component (A) in the thermoplastic elastomer composition of the present invention is fundamentally a homopolymer of a styrene monomer, namely, polystyrene, or a copolymer of a styrene monomer with other monomers. Examples of the other monomers used for the copolymer are styrene monomers such as &agr;-methylstyrene, p-chlorostyrene, p-bromostyrene and 2,4,5-tribromostyrene, acrylate ester monomers such as methyl acrylate and butyl acrylate, methacrylate ester monomers such as methyl methacrylate and ethyl methacrylate, acid anhydride monomers such as maleic anhydride and itaconic anhydride, maleimide monomers such as maleimide, N-methylmaleimide and N-phenylmaleimide, and organic acid monomers such as acrylic acid and methacrylic acid. Among them, polystyrene is inexpensive and most preferred as the polystyrene resins. Moreover, molded products obtained from a thermoplastic elastomer composition which uses as the component (A) a polystyrene resin comprising a copolymer of styrene monomer with an acrylate ester monomer or a methacrylate ester monomer are excellent in weathering resistance.
Melt flow rate (MFR) of the polystyrene resin used is preferably in the range of 0.1-50 g/10 min (measured at 200° C. under a load of 5 kg), and, more preferably, in the range of 0.5-30 g/10 min. If the melt flow rate is less than 0.1 g/10 min, the resulting thermoplastic elastomer composition is low in fluidity. If it exceeds 50 g/10 min, molded products obtained from the resulting thermoplastic elastomer composition are low in mechanical strength.
The component (A) is a thermoplastic resin containing a polystyrene resin as an essential component. Content of the polystyrene resin in the thermoplastic resin is 1-100% by weight, and preferably 5-100% by weight. If the content of the styrene resin in the thermoplastic resin is less than 1% by weight, the desired improvement in abrasion resistance is low.
Here, when content of the polystyrene resin in the thermoplastic resin is not less than 1% by weight and less than 40% by weight and, especially, when the thermoplastic resin comprises a polystyrene resin and a polyolefin resin, the resulting thermoplastic elastomer composition maintains excellent characteristics of olefinic thermoplastic elastomers and, besides, is excellent in abrasion resistance.
When the thermoplastic resin consists of a polystyrene resin (when content of the polystyrene resin is 100% by weight), or when content of the polystyrene resin in the thermoplastic resin is not less than 40% by weight and less than 100% by weight, namely, when content of the polystyrene resin is not less than 40% by weight, the resulting thermoplastic elastomer composition is excellent in abrasion resistance, coatability, solvent bonding properties, printability and the like and, besides, can be laminated with a hard polystyr
Kinoshita Hideo
Ohtani Ikuji
Yasui Takeshi
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Mullis Jeffrey
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