Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-11-10
2002-06-04
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S128000, C524S232000, C524S323000, C525S053000, C525S240000, C525S320000, C525S324000
Reexamination Certificate
active
06399683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin composition for extruded forms that has improved workability, and excellent properties with respect to transparency, heat resistance, low-temperature resistance, impact strength, heat sealability, food sanitation, etc., and that may particularly be advantageously used for the formation of extruded forms such as films or sheets.
2. Description of the Related Art
Hitherto, a polypropylene resin has been known as a material for forming extruded forms, such as films and sheets, which are transparent. Since a film formed of a polypropylene (hereinafter abbreviated as “PP”) resin also has good rigidity, etc., a PP film is widely used as a wrapping/packaging material for various applications. However, the range of fields to which a PP film can be applied is limited by the fact that the film is unsuitable for forming by a general working technique, such as air-cooled inflation forming, and that the film has poor properties with respect to impact strength, low-temperature resistance and low-temperature heat sealability.
In view of these problems, a high-pressure low-density polyethylene (hereinafter abbreviated as “LDPE”), which is a resin capable of compensating for the problems of PP resin, has become widely used for the production of a general-use film. However, though LDPE is effective for the compensation of the problems of PP, LDPE has poorer transparency than PP.
A copolymer of ethylene and &agr;-olefin obtained by using a Ziegler catalyst in a method described, e.g., in Japanese Patent Publication No. 56-18132, is known as a linear low-density polyethylene (hereinafter abbreviated as “LLDPE”). LLDPE is a resin having better properties than an LDPE resin, described above, with respect to impact strength, heat sealability, hot tack, heat resistance, low-temperature resistance, etc. It is known that the transparency of LLDPE can be improved by subjecting it to special working by a certain technique, such as known T-die forming, water-cooled inflation forming, or air-cooled inflation forming using a special air ring.
However, when the surface of an LLDPE film is smoothed to produce a film having good transparency, the LLDPE has its low-crystallinity components bled out to the surface of the film (this phenomenon is referred to as bleedout). As a result, the anti-blocking property of the film is greatly impaired, making actual use of the film difficult.
In order to overcome these problems, a method of adding an anti-blocking agent or slip agent, such as silica or talc, to LLDPE has been adopted. However, the addition of such an anti-blocking agent involves scattering of light, resulting in impaired transparency. Thus, it has been difficult to improve the transparency of the LLDPE resin itself.
Recently, it has become possible to obtain LLDPE having a chemical composition variation range more limited than more conventional LLDPE by using a novel catalyst described in Japanese Patent Laid-Open No. 58-19309, etc. Hence, it has become possible for LLDPE to have better transparency and anti-blocking property than a more conventional LLDPE. However, the range of molecular-weight distribution is also narrowed, thereby greatly deteriorating workability.
Further, although such a conventional LLDPE has better heat resistance and low-temperature resistance than a pp or a low-density polyethylene, the conventional LLDPE has not been quite applicable to uses such as containers for pharmaceutical products or containers for cryogenic preservation, which containers must be transparent enough to be able to preserve contents in their readily visible state or must be free from breakage when at sterilized high-temperature and used for freeze-preservation at a temperature of −50® or lower, and more recently, at a temperature of −80® or lower.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a resin composition for forming extruded forms, in particular, films or sheets, that has good workability, and also has greatly improved properties with respect to transparency, heat resistance, low-temperature resistance, etc.
The present inventors have made various studies to obtain means for achieving a well-balanced material that has improved workability and that also assures excellent properties, finding that the object of the present invention can be achieved by blending together an LDPE having specific properties and an LLDPE having specific properties. The present invention has been formulated on the basis of the above knowledge.
A resin composition for extruded forms according to the present invention is characterized in that the resin composition contains component A and component B specified as follows:
Component A:
Component A is a copolymer of ethylene and olefin having a carbon number of 4 to 40, the component A being contained in the resin composition in an amount of 50 to 99% by weight, and having the following properties (a) to (d):
(a) a melt flow rate (MFR) of 0.1 to 5 g/10 min.;
(b) a density D of 0.88 to 0.925 g/cm
3
;
(c) an elution curve having a single peak of elution volume, as indicated by an elution curve obtained by temperature rising elution fractionation (TREF), said the peak corresponding to a temperature within a range from 30 to 100®, and the elution curve satisfying a relationship in which the ratio H/W is not less than 1 when H represents the height of the peak and W represents the width of the elution curve at half of the height H; and
(d) an elution volume Y (in % of the weight thereof with respect to the total weight of the component A) at an elution temperature of 50® in temperature rising elution fractionation, said elution volume Y satisfying the following condition {circle around (1)} or {circle around (2)}:
{circle around (1)} Y≦−4500D+4105 when the density D of the component A is less than 0.91 g/cm
3
, but Y≦100; or
{circle around (2)} Y≦10 when the density D of the component A is not less than 0.91 g/cm
3
.
Component B:
Component B is an ethylene-containing polymer, the component B being contained in the resin composition in an amount of 1 to 50% by weight, and having the following properties (a′) to (d′):
(a′) a melt flow rate of 0.1 to 20 g/10 min.;
(b′) a density of 0.88 to 0.93 g/cm
3
;
(c′) a memory effect (ME) of not less than 1.3; and
(d′) a melt tension (MT) of not less than 1.0 g.
DETAILED DESCRIPTION OF THE INVENTION
[I] Components
(1) Componenet A (Copolymer of Ethylene and &agr;-Olefin Having 4 to 40 Carbons)
(a) Properties of Component A
It is important that a copolymer of ethylene and &agr;-olefin having 4 to 40 carbons (such olefin will be referred to as “C
4
to C
40
&agr;-olefin” unless otherwise specified) contained as component A in a resin composition for extruded forms according to the present invention have the following properties {circle around (1)} to {circle around (4)}, preferably {circle around (1)} to {circle around (5)}:
{circle around (1)} Melt Flow Rate
The copolymer of ethylene and C
4
to C
40
&agr;-olefin used in the present invention should have a melt flow rate (MFR) within a range of from 0.1 to 5 g/10 min. as measured in accordance with Japanese Industrial Standards (JIS) K7210, preferably from 0.3 to 4 g/10 min., and more preferably from 0.7 to 3.5 g/10 min.
If the melt flow rate of the copolymer exceeds the upper limit of the range of from 0.1 to 5 g/10 min., heat resistance and low-temperature resistance may be impaired, and film formation may become unstable. A melt flow rate less than the lower limit of this range is not practical because resin pressure may become so great as to impair formability or reduce producibility.
{circle around (2)} Density
The copolymer of ethylene and C
4
to C
40
&agr;-olefin used in the present invention should have a density D within a range of from 0.88 to 0.925 g/cm
3
as measured in accordance with JIS K7112, preferably from 0.89 to 0.92 g/cm
3
, and more preferably from 0.90 to 0.915 g/cm
3
.
If
Ikeno Hajime
Shichijo Keiko
Yamamoto Koji
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