Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-03-11
2001-04-10
Thibodeau, Paul (Department: 1773)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S348000, C526S348200, C526S348600, C526S943000
Reexamination Certificate
active
06214952
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a propylene random copolymer and a film laminate thereof. More specifically, the present invention relates to a propylene random copolymer and a film laminate thereof that has favorable blocking resistance, transparency, and low-temperature heat-sealing properties and that is typically applied as a heat sealant.
2. Description of the Related Art
Polypropylene has many excellent physical properties and is accordingly used in many different applications. Propylene random copolymers, typically used in wrapping films, can be prepared by random copolymerization of propylene with ethylene and/or other &agr;-olefins and have enhanced heat-sealing properties at low temperatures. These propylene random copolymers are generally produced with conventional Ziegler-Natta catalysts. The propylene random copolymers might have sufficient transparency and heat-sealing properties, which can be attributed to their low crystallinity and low melting point. However, the content of 20° C. xylene soluble fraction (CSX) in the propylene random copolymer, an undesirable property for food wrapping film application, greatly increases with increasing content of ethylene and/or &agr;-olefin.
In addition, the heat sealant layer that is applied to the surface of the wrapping film is typically treated by corona discharge for improving printing properties. The corona discharge treatment, however, leads to decomposition of the propylene random copolymer in the heat sealant layer, thereby deteriorating the low-temperature heat-sealing properties of the wrapping film.
A method disclosed in JP-A-1-266,116 describes a propylene random copolymer having less content of undesirable 20° C. xylene soluble fraction (CXS) prepared by random copolymerization of propylene with ethylene and/or an &agr;-olefin in the presence of a catalytic system comprising (1) a group IVB transition-metal compound having one or more cyclopentadienyl groups and (2) an alumoxane. Although the propylene random copolymer prepared by this method has a sufficiently low melting point, the copolymer still has a large CXS content and insufficient blocking resistance. Blocking resistance refers to the extent to which sheets or films stick to each other. Moreover, the catalytic residue of alumoxane is difficult to remove from the resulting propylene random copolymer which undesirably affects the optical properties of the propylene random copolymer.
In addition, a syndiotactic propylene-1-butene random copolymer containing 0.01 to 20% by weight of propylene is described in JP-A-4-175,317. This copolymer has a high content of 1-butene, which results in favorable low-temperature heat-sealing properties but insufficient blocking resistance.
In other work, a syndiotactic propylene-ethylene random copolymer containing 4.6% by weight of ethylene and having favorable low-temperature heat-sealing properties and favorable optical properties is described in JP-A-5-245,992. However, propylene-ethylene random copolymers generally have a large content of 20° C. xylene soluble fraction (CXS) and insufficient blocking resistance, and are thus not suitable for use as a sealant.
To date, propylene random copolymers that possess the contradictory properties of favorable blocking resistance and favorable low-temperature heat-sealing properties have not been prepared.
SUMMARY OF THE PRESENT INVENTION
One object of the present invention is to prepare a propylene random copolymer having excellent blocking resistance and transparency and yet substantially maintaining favorable low-temperature heat-sealing properties despite corona discharge treatment.
Another object of the present invention is to provide a film laminate comprising such a propylene random copolymer having favorable properties.
As a result of intensive studies, the inventors have found that these and other objects can be achieved by a propylene random copolymer having (1) a composition and intrinsic viscosity [&eegr;] in specific ranges, and (2) a specific relationship between melting point (Tm) and content of 20° C. xylene soluble fraction (CXS).
More specifically, the present invention is directed to a propylene random copolymer comprising a propylene component and an &agr;-olefin component having 4 to 10 carbon atoms, wherein
(A) the content of the &agr;-olefin component is in a range of about 6% to about 40% by weight,
(B) the intrinsic viscosity [&eegr;] of the propylene random copolymer, measured in tetralin at 135° C., is not lower than about 0.45 dl/g and not higher than about 5.0 dl/g, and
(C) the melting point (Tm), measured with use of a differential scanning calorimeter, and the content of 20° C. xylene soluble fraction (CXS) for the propylene random copolymer fulfills the relationship
Tm≦
140−35.693 log
10
(
CXS
).
The present invention is also directed to a film laminate comprising the propylene random copolymer of the present invention laminated upon a base layer.
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Naga Naofumi
Sadatoshi Hajime
Satoh Makoto
Pillsbury Madison & Sutro LLP
Sumitomo Chemical Co,. Ltd.
Tarazano D Lawrence
Thibodeau Paul
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