Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2002-09-06
2004-08-10
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S515000, C428S516000
Reexamination Certificate
active
06773818
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a film that contains a skin layer of metallocene-catalyzed, substantially isotactic propylene homopolymer or metallocene-catalyzed propylene copolymer. The film may be oriented. The skin layer may be metallized on its outer surface.
BACKGROUND
Metallocene-catalyzed propylene polymers, which have low melting temperatures relative to conventional propylene polymers, are known. Due to their relatively low melting temperatures, metallocene-catalyzed propylene polymers have been described as a useful heat seal material, e.g., as the heat-sealable outer layer of a multilayer film in U.S. Pat. No. 5,468,440. The '440 patent suggests temperatures at which metallocene-catalyzed, isotactic polypropylene plaques or cast samples can be stretched in laboratory equipment. The suggested temperatures, however, are not suitable for continuous orientation processing. The '440 patent further fails to disclose metallizing the metallocene-catalyzed polypropylene layer or layers.
U.S. Pat. Nos. 5,529,843 and 5,462,807 also describe the advantages of a multilayer film that has an outer layer that contains a metallocene-catalyzed polymer. The '843 and '807 patents, however, fail to disclose or suggest the use of a metallocene-catalyzed propylene polymer in a metallized skin layer of a multilayer film.
Metallocene-catalyzed, isotactic polypropylenes have a very narrow molecular weight distribution, i.e., a very narrow range of chain lengths. Ziegler-Natta-catalyzed, isotactic polypropylenes, by contrast, have a broad range of chain lengths, which average out at the desired level. For good operability in the oriented polypropylene (OPP) process, those of skill in the art typically desire a broad molecular weight distribution. The high molecular weight tails of Ziegler-Natta-catalyzed polypropylenes tend to distribute the stretching forces more uniformly in oriented films, preventing stress concentrations, and ultimately providing more uniform orientation and improved operability. Therefore, although the narrow composition distribution of metallocene-catalyzed, isotactic propylene polymers causes them to be looked upon favorably for film properties, e.g., heat-sealability, their narrow molecular weight distribution causes them to be looked upon negatively for operability in the OPP process.
For this reason, multilayer films, and especially oriented multilayer films, disclosed in the prior art have generally used traditional Ziegler-Natta-catalyzed polymers, which have a broad molecular weight distribution, in the skin or metallization layer and/or the core layer to distribute orientation stresses more uniformly and avoid film breakage during orientation.
SUMMARY
There is provided an oriented multilayer film, comprising:
a) a core layer comprising a polyolefin; and
b) a first skin layer comprising a polyolefin selected from the group consisting of (i) a metallocene-catalyzed, substantially isotactic propylene homopolymer, (ii) a metallocene-catalyzed propylene copolymer, and (iii) blends thereof,
wherein the core layer has a first surface and a second surface, the first skin layer has a first and a second surface, the second surface of the first skin layer is contiguous to and in contact with the first surface of the core layer, and the first surface of the first skin layer is metallized.
The oriented multilayer film may optionally comprise a second skin layer on the side of the core layer opposite the first skin layer, and one or more tie layers between the core layer and the first skin layer and between the core layer and the second skin layer (if any). A coating may optionally be applied to one or both outer surfaces of the film, including the outer surface of the core layer if a second skin layer is not present, the outer surface of the second skin layer, and the metallized surface of the first skin layer. The film may optionally be laminated to a substrate at one or both of its outer surfaces, again including the outer surface of the core layer if a second skin layer is not present, the outer surface of the second skin layer, and the metallized surface of the first skin layer.
The oriented multilayer film may have an oxygen transmission rate (OTR) of ≦20 cc/m
2
/24 hr, as determined in accordance with ASTM D 3985 at 73° F. (23° C.) and 0% relative humidity (RH), and a water vapor transmission rate (WVTR) of ≦0.50 g/m
2
/24 hr, as determined in accordance with ASTM F 1249 at 100° F. (37.8° C.) and 90% RH.
There is also provided a process for producing an oriented multilayer film, comprising:
a) coextruding melts corresponding to the core layer and the first skin layer to form a coextruded sheet;
b) cooling the coextruded sheet;
c) orienting the coextruded sheet to form an oriented multilayer film; and
d) metallizing the oriented multilayer film on the first surface of the first skin layer.
A multilayer film according to the present invention provides several advantages, mainly as a result of the advantageous interface between the first skin layer and the metal layer deposited thereon. It possesses unexpectedly superior oxygen transmission rates (OTR) and water vapor transmission rates (WVTR), both initially after manufacture and throughout the various stages of the converting process. The film, moreover, is surprisingly operable in orientation processes, and, when subsequently metallized, demonstrates good metal adhesion between the metal layer and the metallizable skin layer, e.g., the first skin layer.
DETAILED DESCRIPTION
Skin Layers
First Skin Layer
A multilayer film according to the present invention comprises a first skin layer. The first skin layer may comprise a metallocene-catalyzed propylene homopolymer or a metallocene-catalyzed propylene copolymer. The metallocene-catalyzed propylene homopolymer may be a metallocene-catalyzed, substantially isotactic propylene homopolymer. The phrases “substantially isotactic propylene homopolymer” or “substantially isotactic polypropylene”, as used herein, generally refer to propylene polymers which have an isotacticity of 85% or greater (as measured by solubility in xylene). Exemplary isotactic propylene polymers and/or methods for making such polymers are described in the following patent documents: U.S. Pat. Nos. 5,529,843; 5,162,278; 5,158,920; 5,155,080; 5,036,034; 4,975,403; 4,892,851; and 4,794,096, all of which are incorporated herein by reference.
As described above, the metallocene-catalyzed propylene polymers of the first skin layer may include homopolymers and/or copolymers that contain other monomeric units, as in the case of a copolymer of propylene and ethylene or an &agr;-olefin having from 4 to 20 carbon atoms, e.g., butene-1, pentene-1, hexene-1, heptene-1, 4-methyl-1-pentene, octene-1 or combinations thereof. Also contemplated are metallocene-catalyzed propylene terpolymers, including, but not limited to, propylene-ethylene-butene-1, propylene ethylene-pentene-1, propylene-ethylene-hexene-1, propylene-ethylene-octene-1, and the like.
The metallocene-catalyzed propylene polymer, whether a homopolymer or copolymer, may have a melting point of ≦160° C., or ≦154° C., or ≦145° C., preferably from 120° C. to 155° C., e.g., from 130° C. to 150° C. The foregoing melting point ranges were determined by an ExxonMobil method outlined herein below. In general, the melt flow rate of the metallocene-catalyzed propylene polymers will be in the range of from 0.5 g/10 min to 20 g/10 min at 230° C., for example, from 2.5 g/10 min to 15 g/10 min, e.g., from 4 g/10 min to 9 g/10 min, as measured by ASTM D-1238 at 230° C.
The first skin layer may also comprise blends of two or more propylene homopolymers, or blends of two or more propylene copolymers, or at least one propylene homopolymer and at least one propylene copolymer, each differing in their molecular or macro properties or both. The only requirement of such blends, aside from the physical properties described above, is that they have a majority component or components, i.e., more than 50 weight percent, that are m
Amon Moris
Cretekos George F.
ExxonMobil Oil Corporation
James Rick F.
Tarazano D. Lawrence
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