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
2001-07-13
2002-10-01
Nutter, Nathan M. (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...
C525S232000, C525S240000
Reexamination Certificate
active
06458893
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermoplastic resin composition. More specifically, the present invention relates to a thermoplastic resin composition comprising a specific saponified ethylene-vinyl acetate copolymer resin, a vinyl aromatic-conjugated diene copolymer and/or a hydrogenated derivative thereof. The composition has a good moldability and is suitably used for toys and automobile interior parts.
DESCRIPTION OF THE PRIOR ART
A rotational powder molding method is suitable for molding articles of complicated shapes. The method gives a high production yield and a uniform thickness of a molded article with ease. Thus, the method is widely used to produce toys and automobile interior parts. In the rotational powder molding, raw material powder which has not stuck to a mold is recovered and reused in a subsequent molding operation. The recovered powder tends to agglomerate after it is heated in the precedent molding to partly melt on the surface. The granules of agglomerated powder tend to cause pinholes in molded articles. Pinholes also take place in an unmelted part of a material where a molding temperature is lower than the melting. Moreover, when a gas evolves from the material, conformity of a shape of a molded article to a mold is deteriorated. Therefore, it is desired to use a raw material that meets product requirements and, moreover, does not show the aforesaid problems in molding.
As raw material resins for rotational powder molding, use is made of polyvinyl chloride resins, polyolefinic elastomers, and thermoplastic polyurethane elastomers. The polyvinyl chloride resin contains a large quantity of a low molecular weight plasticizer and, therefore, a molded article therefrom tends to lose a soft-to-touch property at a temperature lower than the solidifying point of the plasticizer. In a long term use, there arises a problem that a matting effect and a soft-to-touch property are lost due to migration of the plasticizer to the molded articles'surface. The polyolefinic elastomer is cheaper and has good weatherability, but is poor in moldability and scratch resistance. Some compositions were examined which had improved scratch resistance through compositional designs and modification of surfaces, e.g., by coating. However, they are costly and, therefore, not practical. The thermoplastic polyurethane elastomer has a longer molding cycle time and tends to be stringy or to agglomerate in molding. In addition, a molded article therefrom does not have a smooth backside. When a foaming resin is shaped on the backside, an evolved gas leaks from the uneven backside surface. Further, it is expensive and inferior in weatherability and resistance to flame.
An ethylene-vinyl acetate copolymer(EVA) or a saponified derivative thereof, an ethylene-ethyl acrylate copolymer(EEA) can be molded at a lower temperature than the aforesaid resins. A composition is described in Japanese Patent Publication No.H2-60687/1990, which comprises a saponified derivative of an ethylene-vinyl acetate copolymer and a copolymer of a vinyl aromatic compound with a conjugated diene compound or a hydrogenated derivative thereof. However, the present inventors have found that the composition is not suitable for the rotational powder molding.
A composition containing a thermoplastic polyurethane elastomer can be molded at a temperature similar to that for the saponified derivative of an ethylene-vinyl acetate copolymer. However, as described above, molded articles therefrom are inferior in weatherability and backside smoothness.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thermoplastic elastomeric composition which solves the aforesaid problems in rotational powder molding, i.e., to provide a composition which does not generate gas, pinholes, or agglomeration and which provides molded articles having superior weatherability, resistance to flame and smooth backside.
The present inventors have found that the above problems can be solved by using a saponified ethylene-vinyl acetate copolymer having a specific ethylene content and a degree of saponification and a copolymer of a vinyl aromatic compound and a conjugated diene compound. Thus the present invention is (1) a thermoplastic resin composition comprising
40 to 95 parts by weight of (a) a saponified ethylene-vinyl acetate copolymer resin and
60 to 5 parts by weight of (b) at least one selected from the group consisting of copolymers of a vinyl aromatic compound with a conjugated diene compound, and hydrogenated derivatives thereof, characterized in that
the saponified ethylene-vinyl acetate copolymer resin (a) has an ethylene content of 40 to 95 wt % based on a weight of the saponified ethylene-vinyl acetate copolymer resin and a degree of saponification of the vinyl acetate of at least 80 wt % and
(b) at least one selected from the group consisting of copolymers of a vinyl aromatic compound with a conjugated diene compound ,and hydrogenated derivatives there of is selected from the group consisting of
(b-1) block copolymers of a vinyl aromatic compound with a conjugated diene compound, and hydrogenated derivatives thereof and
(b-2) hydrogenated random copolymers of a vinyl aromatic compound with a conjugated diene compound, the copolymers having a vinyl aromatic compound content of at most 50 wt %, a number average molecular weight (Mn) of from 5,000 to 1,000,000, a polydispersity(Mw/Mn) of at most 10, and a content of vinyl bonds derived from the conjugated diene compound of at least 10% based on bonds derived from the conjugated diene compound. Preferred embodiments of the above invention are as follows.
(2) The thermoplastic resin composition described (1) above, wherein component (b) is a hydrogenated styrene-isoprene-styrene block copolymer having a weight average molecular weight of from 5,000 to 1,500,000, wherein 70 to 100 wt % of the isoprene is in 1,4-micro structure and at least 90% of aliphatic double bonds derived from the isoprene are hydrogenated.
(3) The thermoplastic resin composition described (1) above, wherein component (b) is a hydrogenated styrene-butadiene random copolymer wherein at least 70% of olefinic unsaturated bonds are hydrogenated.
(4) The thermoplastic resin composition described in any one of (1) to (3) above, wherein the composition further comprises 0.01 to 3 parts by weight of (c) an organic peroxide and 0.01 to 5.5 parts by weight of (d) a cross-linking aid, based on 100 parts by weight of component (a) and component (b) in total.
(5) The thermoplastic resin composition described in any one of (1) to (4) above, wherein the composition further comprises 1 to 20 parts by weight of (e) (poly)hydroxyalkyl (meth)acrylate, based on 100 parts by weight of component (a) and component (b) in total.
(6) The thermoplastic resin composition described in any one of (1) to (5) above, wherein the composition further comprises at least one component selected from the group consisting of 5 to 150 parts by weight of (f)a thermoplastic polyurethane resin,
0.1 to 20 parts by weight of (g) a liquid polybutadiene,
0.05 to 5 parts by weight of (h) an unsaturated carboxylic acid or a derivative thereof,
0.05 to 30 parts by weight of (i) a peroxide-decomposing polyolefin resin, and
0.05 to 30 parts by weight of (j) a peroxide-crosslinking polyolefin resin,
wherein a total amount of component (a) and component (b) is 100 parts by weight.
PREFERRED EMBODIMENTS OF THE INVENTION
The components constituting the present composition will be explained below.
Component (a) Saponified Ethylene-Vinyl Acetate Copolymer
The present composition is characterized in that it contains a saponified ethylene-vinyl acetate copolymer resin, hereinafter referred to as “EVOH.” The EVOH in the composition improves weatherability of the composition and makes the backside of a molded article have smoother.
The EVOH has an ethylene content of from 40 to 95 wt %, preferably from 60 to 90 wt %, and a degree of saponification of the vinyl acetate component of at least 80 wt %, preferably at least 90 wt %. If
Tasaka Michihisa
Yamanaka Toshimi
Nutter Nathan M.
Pitney Hardin Kipp & Szuch LLP
Riken Vinyl Industry Co., Ltd.
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