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
2001-02-12
2002-07-30
Nutter, Nathan (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
06426385
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a resin composition and an injection-molded article. Particularly, the present invention relates to a resin composition that can provide a molded article superior in mold release properties, flexibility and heat resistance, especially when used in injection molding, and to the injection-molded article. The improved release properties of the resin composition according to the present invention are very desirable for the finish and productivity of the molded article. The resin composition according to the present invention is most suitably used for making, in particular, injection-molded articles to which are required flexibility and heat resistance, such as containers, caps, packings and gaskets.
BACKGROUND OF THE INVENTION
As resin compositions for obtaining articles that are required to have flexibility and heat resistance, such as containers, caps, packings and gaskets, by an injection molding method, there are known resin compositions disclosed in JP-A-6-313072 and JP-A-7-316352.
The former reference discloses a resin composition comprising a copolymer of ethylene and an &agr;-olefin of 4 or more carbon atoms which has specific properties and an olefin polymer such as a high-pressure-produced low-density polyethylene or a linear low-density polyethylene. The latter reference discloses a resin composition comprising an ethylene-&agr;-olefin copolymer having a relatively low density and a relatively low highest melting peak temperature measured with a differential scanning calorimeter (hereinafter referred to also as DSC) and an ethylene-&agr;-olefin copolymer having a relatively high density and a relatively high highest melting peak temperature measured with DSC.
The resin compositions disclosed in the above references, however, involve problems such as unsatisfactory mold release properties as an injection-molded article and insufficient flexibility and heat resistance as the resulting molded article.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a resin composition that can provide a molded article superior in mold release properties, flexibility and heat resistance, particularly when used in injection molding, and the injection-molded article.
The present inventor has earnestly done investigation in order to achieve the above object. As a result, the present inventor found that a resin composition comprising an ethylene-&agr;-olefin copolymer having specific properties, an ethylene homopolymer or ethylene-&agr;-olefin copolymer having specific properties, and a low-density polyethylene obtained by a high-pressure radical polymerization method and having specific properties can achieve the above object, whereby the present invention has been accomplished.
That is, the present invention relates to a resin composition comprising:
(A) an ethylene-&agr;-olefin copolymer meeting the following conditions (A-1), (A-2) and (A-3):
(A-1) the melt flow rate (MFR) is in the range of from 0.5 to 100 g/10 min,
(A-2) the density is in the range of from 860 to 920 kg/m
3
, and
(A-3) the highest melting peak temperature determined with a differential scanning calorimeter is in the range of from 50° C. to 110° C.;
(B) an ethylene homopolymer or ethylene-&agr;-olefin copolymer meeting the following conditions (B-1), (B-2) and (B-3):
(B-1) the melt flow rate (MFR) is in the range of from 0.5 to 100 g/10 min,
(B-2) the density is in the range of from 910 to 980 kg/m
3
, and
(B-3) the highest melting peak temperature determined with a differential scanning calorimeter is in the range of from 110° C. to 135° C.; and
(C) a low-density polyethylene as high-pressure radical polymerization product which meets the following conditions (C-1) and (C-2):
(C-1) the melt flow rate (MFR) is in the range of from 0.5 to 100 g/10 min, and
(C-2) the swell ratio (SR) is in the range of from 1.3 to 2.0, said resin composition comprising 40 to 90% by weight of component (A), 5 to 30% by weight of component (B) and 5 to 30% by weight of component (C) when the total proportion of component (A), component (B) and component (C) is taken as 100% by weight.
In addition, the present invention relates to an injection-molded article comprising the above-mentioned composition.
DETAILED DESCRIPTION OF THE INVENTION
The ethylene-&agr;-olefin copolymer (A) used in the present invention refers to a copolymer of ethylene and one or more &agr;-olefins of 3 to 12 carbon atoms. The &agr;-olefins include, for example, propylene, butene-1, pentene-1, 4-methyl-1-pentene, hexene-1, octene-1 and decene-1. Of these, propylene, butene-1, hexene-1 and octene-1 are preferable, and butene-1 and hexene-1 are more preferable.
The content of the structural units derived from ethylene (hereinafter referred to as “ethylene units”) in component (A) is preferably in the range of from 65 to 95% by weight, more preferably from 68 to 90% by weight. The content of the structural units derived from the &agr;-olefin(s) (hereinafter referred to as “&agr;-olefin units”) in component (A) is preferably in the range of from 5 to 35% by weight, more preferably from 10 to 32% by weight.
Component (A) includes, for example, ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-4-methyl-1-pentene copolymers, ethylene-hexene-1 copolymers, ethylene-octene-1 copolymers and ethylene-propylene-butene-1 terpolymers. Of these, ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers and ethylene-octene-1 copolymers are preferable, and ethylene-butene-1 copolymers and ethylene-hexene-1 copolymers are more preferable.
The melt flow rate (hereinafter referred to also as MFR) of component (A) is in the range of from 0.5 to 100 g/10 min, preferably from 1 to 50 g/10 min, more preferably from 2 to 25 g/10 min. When MFR is less than 0.5 g/10 min, the resulting resin composition has an insufficient flowability and hence it has a low injection moldability in some cases. On the other hand, when MFR is more than 100 g/10 min, an injection-molded article having an insufficient strength is obtained in some cases.
The density of component (A) is in the range of from 860 to 920 kg/m
3
, preferably from 863 to 910 kg/m
3
, more preferably from 865 to 905 kg/m
3
. When the density is less than 860 kg/m
3
, the resulting injection-molded article has an insufficient heat resistance in some cases. On the other hand, when the density is more than 920 kg/m
3
, the resulting injection-molded article has too high a stiffness and hence an insufficient flexibility in some cases.
The highest melting peak temperature of component (A) determined with a differential scanning calorimeter is in the range of from 50° C. to 110° C., preferably from 55° C. to 100° C., more preferably from 60° C. to 90° C. When said peak temperature is lower than 50° C., the resulting injection-molded article has an insufficient heat resistance in some cases. On the other hand, when said peak temperature is higher than 110° C., the resulting injection-molded article has too high a stiffness and hence an insufficient flexibility in some cases.
A process for producing component (A) is not limited, and a well-known copolymer may be used as component (A). A preferable production process of component (A) is a process comprising copolymerizing ethylene with one or more &agr;-olefins in the presence of a metallocene-based catalyst. The metallocene-based catalyst includes, for example, catalysts comprising a metallocene complex and an aluminoxane, and catalysts comprising a metallocene complex and an organoaluminum compound and/or a boron compound. Specific examples of the metallocene-based catalysts are a catalyst comprising dimethylsilylene(tetramethylcyclopentadienyl)(3-tert-butyl-2-phenoxy)titanium dichloride, triisobutyl-aluminum and N,N-dimethylanilinium (pentafluorophenyl)-borate (see JP-A-9-87313) and a catalyst comprising dimethylsilylene(tetramethylcyclopentadienyl)(3-tert-butyl-2-phenoxy)titanium dimethoxide, triisobutyl-aluminum and N,N-dimethylanilinium (pentafluorophenyl)-borate (se
Nutter Nathan
Sughrue & Mion, PLLC
Sumitomo Chemical Company Limited
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