Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1999-07-08
2002-10-01
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S523000, C428S910000, C428S515000, C264S173150
Reexamination Certificate
active
06458469
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a film incorporating a metallocene catalyzed polyethylene layer having improved processability. More particularly, the present invention relates to an oriented multilayer film which may contain at least one intermediate or tie layer and at least one metallocene catalyzed polyethylene outer or skin layer having improved processability.
DESCRIPTION OF THE RELATED ART
Oriented polypropylene films are known for use in packaging operations. For example, U.S. Pat. No. 4,604,324 to Nahmias, et al. discloses multilayer polypropylene film structures comprising coextruded layers of a base layer of high stereoregularity polypropylene and a skin layer of comparatively low stereoregularity which contains surface-modifying additives. The skin layer may be, for example, random copolymers of ethylene and propylene and ethylene-propylene-butylene terpolymers. Further, the skin layer may contain up to 10% by weight of a natural or synthetic terpene resin, a wax or a low molecular weight polyethylene to improve the heat sealing characteristics or the optical properties of the film.
PCT Publication No. WO 93/03093 discloses heat sealed articles and heat sealable films incorporating ethylene interpolymer skins having a narrow composition distribution and a narrow molecular weight distribution or blends thereof. The publication states that metallocene catalysts may be used to form the ethylene interpolymers. This PCT publication, however, does not describe a multilayer film containing at least one tie layer and at least one skin layer of a metallocene catalyzed polyethylene, which skin layer is chosen for its performance as a layer to which further materials can be readily adhered and which may be unsuitable for a heat sealing film.
While multilayer films containing skin layers made from conventional Ziegler-Natta catalyzed polyethylene and propylene terpolymers have been used, an improvement in the characteristics of the surface layer that provide a base to which further materials can be readily adhered, and an improvement in operability over such skin layers would be desirable. For purposes of simplification, the characteristics of the surface layer that provide a base to which further materials can be readily adhered will be referred to as the adherability of that layer or surface. That layer or surface will be referred to as an adhesion layer. Conventional Ziegler-Natta catalyzed olefin polymers (e.g., low density polyethylene (LDPE)) often exhibit a tendency to stick to the contact rolls during orientation, thereby resulting in the destruction of product and/or time-consuming cleaning operations.
Accordingly, it is an object of the present invention to provide a multilayer film which has superior “adherability” and yet improved processability (i.e., less sticky to the contact rolls during orientation).
SUMMARY OF THE INVENTION
We have now discovered that the use of a metallocene catalyzed polyethylene outer or skin layer provides a multilayer film which meets the objectives of the present invention.
Specifically, the present invention relates to an oriented multilayer film comprising:
(a) a base layer containing a thermoplastic polymer;
(b) at least one tie layer; and
(c) at least one outer layer containing a metallocene catalyzed polyethylene.
In one embodiment, the present invention is directed to an oriented multilayer film comprising:
(a) a base layer containing a thermoplastic polymer;
(b) at least one tie layer; and
(c) at least one outer adhesion layer containing a metallocene catalyzed low density polyethylene.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The thermoplastic polymer contained in the base layer may be any suitable polymer useful in the manufacture of thermoplastic films. Particularly preferred polymers include propylene homopolymers and copolymers. Other useful polymers include, but are not limited to, polyesters, polycarbonates, polyamides, polyethylenes, etc. In a preferred aspect of the present invention, the thermoplastic polymer contained in the base layer should have a melting point that is higher than that of the metallocene catalyzed polyethylene (e.g., metallocene catalyzed low density polyethylene).
Propylene homopolymers which are particularly useful include polypropylene having an isotacticity of about 80 to about 99%, most preferably polypropylene having an isotacticity of about 87 to about 97 % (isotacticity measured according to meso pentads using C
13
NMR). Preferably, the propylene homopolymers have a melt flow ranging from about 0.5 to about 15 g/10 minutes, most preferably from about 1.5 to about 5 g/10 minutes (measured in accordance with the standard test for polypropylene under ASTM D1238) and a melting point of above about 150° C.
Syndiotactic polypropylene homopolymers are also suitable for the base layer of this invention. These would preferably comprise 60-95% racemic pentads, based on C
13
NMR. They would preferably have a melt flow ranging from about 0.5 to about 15 g/10 minutes.
Preferred propylene copolymers include propylene/ethylene copolymers, propylene/butene-1 copolymers, propylene/ -pentene copolymers, propylene/1-hexene copolymers, and propylene/4-methyl-1 -pentene copolymers, and the like. Most preferably, these propylene copolymers may be selected from 95-99.5/0.5-5 weight ratio propylene/ethylene copolymers, 65-99.5/0.5-35 weight ratio propylene/butene-1 copolymers, 50-99.5/0.5-50 weight ratio propylene/1-pentene copolymers, 50-99.5/0.5-50 weight ratio propylene/1-hexene copolymers, and 50-99.5/0.5-50 weight ratio propylene/4-methyl-1-pentene copolymers, and the like.
Commercially available olefin polymers, such as Fina 3371 isotactic polypropylene, and Fina EOD
95-01
and EOD
95-02
syndiotactic polypropylene, sold by Fina Oil and Chemical Co., may be used as the base layer material.
In addition to the base layer, the multilayer film structure of the present invention comprises at least one intermediate or tie layer between the base layer and at least one outer layer. The intermediate or tie layer preferably includes one or more polymers selected from metallocene and Ziegler-Natta catalyzed polyethylene, isotactic polypropylene, syndiotactic polypropylene, grafted polypropylenes, grafted polyethylenes, copolymers and terpolymers of ethylene and/or propylene with polar comonomers, etc., which preferably have a melt index of about 0.1 to about 10 g/10 minutes or a melt flow of about 0.5 to 15g/10 minutes (measured according to ASTM D1238) and a melting point of about 110° C. to about 165° C.
Among the polymers commercially available, Fina 3371 isotactic polypropylene and Fina EOD
95-01
and EOD
95-02
syndiotactic polypropylenes have demonstrated utility as the intermediate or tie layer material.
Metallocene catalyzed polyethylenes suitable for use as the outer layer in this invention are chosen on the basis of their adhesion performance. In most cases, use as a sealant layer is unsatisfactory due to unacceptably high minimum seal temperature (MST) or unacceptably low hot tack, or both.
Any suitable metallocene catalyzed polyethylene so chosen may be used as the outer layer in the present invention. Such metallocene catalyzed polyethylene includes homopolymers as well as copolymers, and may be produced according to known polymerization techniques. Typically, ethylene and optional comonomers are contacted with a catalyst composition comprising at least one metallocene compound and at least one activator under polymerization conditions.
The activators that may be used in combination with the metallocene compounds include, but are not limited to, aluminoxanes and substituted aluminoxanes as well as various ionic compounds.
Typically, the metallocene catalyzed polyethylene in the outer layer of the present invention has a melt index of about 0.1 to about 10 g/10 minutes (measured in accordance with ASTM D1238), a density of about 0.88 to about 0.965 g/cm
3
, a polydispersity M
w
/M
n
of about 2 to about 10, and a melting point of about 90 to about 140° C.
Commercially a
DeLisio John P.
Harley Lyle J.
Keung Jay K.
Peet Robert G.
ExxonMobil Chemical Company
James Rick F.
Santini Dennis P.
Tarazano D. Lawrence
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