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
2000-12-06
2002-07-09
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...
C525S240000
Reexamination Certificate
active
06417275
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a propylene-based copolymer composition, and more particularly, to a propylene-based copolymer composition which is excellent not only in heat resistance, flexibility and transparency, but also in mechanical properties such as tensile strength and impact resistance.
Propylene homopolymer has been extensively used in various applications such as injection-molded products, sheets, films and containers because of excellent heat resistance and stiffness thereof. Further, it has been positively studied to use polyolefins as alternate materials for building materials such as decorative sheets, and packages for foodstuffs, which have been conventionally made of polyvinyl chloride. For this reason, it has been required to develop polyolefins capable of exhibiting excellent flexibility, heat resistance and transparency. The propylene homopolymer is excellent in heat resistance but is deteriorated in flexibility and transparency. Also, polyethylene and ethylene/&agr;-olefin copolymers are excellent in flexibility and transparency but are deteriorated in heat resistance. In consequence, these polyolefins are used only in limited applications.
In the above application fields, there have been conventionally used random copolymers produced by copolymerizing propylene with a small amount of ethylene and/or an &agr;-olefin having 4 to 6 carbon atoms. These random copolymers are excellent in transparency but exhibit only a low flexibility. Further, the copolymers suffer from such an essential problem that the heat resistance thereof is considerably deteriorated.
As the method of improving the flexibility and transparency of polypropylene, for example in Japanese Patent Application Laid-Open (KOKAI) No. 8-100037(1996), there has been proposed a process for the production of propylene/ethylene block copolymers exhibiting excellent heat resistance and flexibility comprising producing a propylene homopolymer having a specific intrinsic viscosity ratio and then producing a copolymer having an ethylene content of 25 to 65% by weight by a two-stage polymerization. Also, in Japanese Patent Application Laid-Open (KOKAI) Nos. 10-316810(1998) and 11-92619(1999), there have been described propylene-based block copolymers containing random polypropylene as matrix and exhibiting good flexibility and transparency.
However, propylene-based polymer compositions which are well-balanced and improved in heat resistance, transparency and flexibility, have not been obtained until now.
As a result of the present inventors' earnest studies for solving the above problems, it has been found that by first producing a specific polymer component (A) comprising propylene as a main component, and then producing a specific copolymer component (B) comprising propylene and other &agr;-olefin having not more than 8 carbon atoms and containing propylene and ethylene as essential components, the obtained propylene-based copolymer composition can exhibit not only good flexibility and transparency, but also excellent mechanical properties such as tensile strength and impact resistance. The present invention has been attained based on this finding.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a propylene-based copolymer composition exhibiting not only excellent flexibility and transparency as well as heat resistance substantially identical to that of propylene homopolymer, but also excellent mechanical properties such as tensile strength and impact resistance.
To accomplish the aim, in a first aspect of the present invention, there is provided a propylene-based copolymer composition comprising:
10 to 60% by weight of a polymer component (A); and
40 to 90% by weight of a copolymer component (B),
wherein said composition is obtained by producing the component (A) by first-stage polymerization and then producing the component (B) by second-stage polymerization,
wherein said polymer component (A) comprises propylene as a main component and has an isotactic index of not less than 90%, and
said copolymer component (B) comprises propylene and other &agr;-olefin having not more than 8 carbon atoms and contains propylene and ethylene as essential components,
said copolymer component containing a fraction insoluble in xylene at room temperature (hereinafter referred to as “cold xylene insolubles”) in an amount of from more than 20 to 70% by weight based on the weight of whole polymers, and a fraction soluble in xylene at room temperature (hereinafter referred to as “cold xylene solubles”) in an amount of 10 to 60% by weight based on the weight of whole polymers, and said cold xylene solubles containing an &agr;-olefin other than propylene in an amount of less than 20% by weight.
In a second aspect of the present invention, there is provided the propylene-based copolymer composition according to the above aspect of the present invention, wherein said component (A) is a propylene homopolymer, and other &agr;-olefin having not more than 8 carbon atoms of said component (B) is ethylene.
In a third aspect of the present invention, there is provided the propylene-based copolymer composition according to the above aspects of the present invention, which has a flexural modulus of 100 to 600 MPa, a haze of a 2 mm-thick sheet of not more than 70%; and a tensile strength at break of not less than 30 MPa.
In a fourth aspect of the present invention, there is provided the propylene-based copolymer composition according to the above aspects of the present invention, which satisfies the followings (1) to (4):
(1) a propylene content of 85 to 95% by weight;
(2) a content of the cold xylene solubles (hereinafter sometimes referred to merely as “CXS”) in the whole polymers of 10 to 60% by weight;
(3) a content (wt. %) of the &agr;-olefin other than propylene (hereinafter sometimes referred to merely as “&agr;t”) and the content of the cold xylene solubles (CXS), satisfying the following formula:
CXS>5&agr;t−25 (5≦&agr;t≦15);
and
(4) a melting peak temperature of not less than 160° C.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
The component (A) as one of constituents of the propylene-based copolymer composition according to the present invention, is a polymer comprising propylene as a main component and has an isotactic index of not less than 90%. The component (A) is usually composed of crystalline cold xylene insolubles and amorphous cold xylene solubles. The content of the cold xylene insolubles is substantially identical to the isotactic index.
Here, the polymer comprising propylene as a main component means such a polymer containing propylene-derived constituent units in an amount of usually not less than 70% by weight, preferably not less than 90% by weight, more preferably not less than 95% by weight based on the weight of the polymer. The most preferred polymer comprising propylene as a main component is a propylene homopolymer.
When the isotactic index of the component (A) is less than 90%, the obtained composition tends to be deteriorated in heat resistance.
The component (B) as the other constituent of the propylene-based copolymer composition according to the present invention, is a copolymer of propylene and other &agr;-olefin having 2 to 8 carbon atoms, which comprises propylene and ethylene as essential components.
Examples of other &agr;-olefins used in the present invention may include, in addition to ethylene as the essential component, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene or the like. The more preferred copolymers are those produced only from propylene and ethylene.
In accordance with the present invention, the copolymer component (B) contains cold xylene insolubles in an amount of from more than 20 to 70% by weight based on the weight of whole polymers, and cold xylene solubles in an amount of 10 to 60% by weight based on the weight of whole polymers, and further the cold xylene solubles contains the &agr;-olefin other than propylene in an
Mizukami Shigeo
Takayanagi Kenjiro
Tsuji Tatsumi
Alexander John R.
Conlin David G.
Edwards & Angell LLP
Mitsubishi Chemical Corporation
Nutter Nathan M.
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