Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-09-29
2003-12-16
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S458000, C428S483000, C428S516000, C428S518000, C428S520000
Reexamination Certificate
active
06663974
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to structures containing a non-oriented multilayer film comprising a polyolefin core. The multilayer film is particularly useful as a protective coating for metal surfaces.
2. Description of Related Art
Multilayer polymeric films having polyolefin cores have utility, for example, as moisture barriers, adhesive structures, packaging materials, and as protective coatings for metal surfaces. The polyolefin core enhances the moisture barrier properties and flexibility of the film. Examples of multilayer polymeric films having polyolefin cores include those disclosed in the following U.S. patents.
U.S. Pat. No. 4,188,443 discloses an optically clear multilayer polyester/polyolefin shrink film. The shrink film is oriented after formation so as to establish shrink tension in at least one direction. Shrink tension is disadvantageous in a film coated on a substrate, such as a metal surface, since the film tends to delaminate from the substrate as the shrink tension is relieved.
U.S. Pat. No. 4,705,707 discloses a non-oriented, heat-sealable, co-extruded, three- or five-layer moisture barrier film. The film has an “ABC” or “ABCBA” structure where layer “A” is a polyester, copolyester or blend thereof. Unfortunately, polyesters and copolyesters do not offer optimal adhesion to modified polyolefin layers, tend to be costly, and tend to absorb moisture.
U.S. Pat. No. 4,716,061 discloses a non-oriented, heat-sealable, co-extruded, three- or five-layer moisture barrier film similar to U.S. Pat. No. 4,705,707 except where layer “C” comprises polypropylene instead of polyethylene.
U.S. Pat. No. 6,027,776 discloses a five-layer film useful for packaging and administering medical solutions. The five-layer film comprises an interior layer, first and second exterior layers, and first and second adhesive layers between the interior layer and the first and second exterior layers, respectively. The interior layer consists of homogeneous ethylene/alpha-olefin copolymer or blends of homogeneous ethylene/alpha-olefin copolymers. Homogeneous ethylene/alpha-olefin copolymers are more expensive than alternative polyolefins. Homogeneous ethylene/alpha-olefin copolymers also tend to be less thermally stable than heterogeneous polymers.
A multilayer film that has the moisture barrier properties and flexibility provided by a polyolefin core yet is non-oriented so as to minimize shrink tension is desirable. A non-oriented multilayer film further comprising an adhesive layer that overcomes the disadvantages listed for polyesters and copolyesters is even more desirable. Still more desirable is a non-oriented film further comprising a core layer that comprises a polymer other than a homogeneous ethylene/alpha-olefin copolymer.
BRIEF SUMMARY OF THE INVENTION
The present invention is a structure comprising a non-oriented multilayer film, wherein said multilayer film comprises: (a) a first tie layer having opposing first and second surfaces; (b) a polyolefin core layer comprising 40 weight-percent or less homogeneous ethylene/alpha-olefin copolymer and having opposing first and second surfaces with the first surface of the core layer adhered to the first surface of the first tie layer; (c) a second tie layer having opposing first and second surfaces with the first surface of the second tie layer adhered to the second surface of the core layer; and (d) a first adhesive layer having opposing first and second surfaces with the first surface of the first adhesive layer adhered to the second surface of the second tie layer; the adhesive layer comprising a blend of polar-modified polyolefin and a polyester, copolyester, or polyester/copolyester blend. Additional layers, such as a second adhesive layer and a thermoplastic layer may be included in the multilayer film. The multilayered film may be adhered to a metal surface.
In a first preferred embodiment, the film of the present invention further comprises: (e) a second adhesive layer having opposing first and second surfaces with the first surface of the second adhesive layer adhered to the second surface of the first tie layer; (f) a thermoplastic layer comprising an oriented polyester and having opposing first and second surfaces with the first surface of the thermoplastic layer adhered to the second surface of the second adhesive layer; and (g) a primed metal surface to which the second surface of the first adhesive layer is adhered.
A second preferred embodiment is similar to the first preferred embodiment accept that thermoplastic layer (f) comprises a non-oriented amorphous or semicrystalline polyester, copolyester, or polyester/copolyester blend.
Designation of first and second surfaces herein is for ease of illustration. In general, the first and second surfaces are interchangeable so long as the surface of one layer is adhered to a proximate surface of an adjacent layer.
The film of the present invention advances the art by providing a non-oriented multilayer film with an adhesive layer comprising a blend of a polar-modified polyolefin and a polyester, copolyester, or polyester/copolyester blend and a polyolefin core layer that comprises 40 wt % or less homogeneous ethylene/alpha-olefin. The multilayer film of the present invention is particularly useful as a protective coating for metal surfaces.
Definitions
“Non-oriented multilayer film” refers to a multilayered film structure that is substantially free of post-formation orientation. However, individual layers of the non-oriented multilayer film may be oriented prior to creating the multilayered film structure. A non-oriented multilayer film structure does not include, for example, oriented multilayered shrink films.
“Homogeneous ethylene/alpha-olefin” and “homogeneous ethylene/alpha-olefin copolymer” refer to ethylene/alpha-olefin polymerization reaction products of relatively narrow molecular weight distribution (M
w
/M
n
) and relatively narrow composition distribution, as defined in U.S. Pat. No. 6,027,776 column 5, line 66 through column 7, line 22 (incorporated herein by reference). Homogeneous ethylene/alpha-olefin copolymers are structurally different from heterogeneous ethylene/alpha-olefin copolymers in that homogeneous ethylene/alpha-olefins exhibit a relatively even sequencing of comonomers within a chain, a mirroring of sequence distribution in all chains, and a similarity of length of all chains, i.e., a narrower M
w
/M
n
. Furthermore, homogeneous ethylene/alpha-olefin copolymers are typically prepared using metallocene, or other single-site type catalysts rather than Ziegler Natta catalysts. Homogeneous ethylene/alpha-olefin copolymers generally have a M
w
/M
n
of less than 2.7 (as determined by gel permeation chromatography, for example), a composition distribution breadth index greater than about 70 percent, and an essentially singular melting point characteristic with a peak melting point as determined by Differential Scanning Calorimetry of from about 60° C. to about 110° C.
“Heterogeneous polyolefin” refers to a polyolefin having a relatively wide M
w
/M
n
, prepared using conventional Ziegler-Natta or other heterogeneous catalysts. Heterogeneous catalysts contain several kinds of active sites which differ in Lewis acidity and steric environment. Examples of Ziegler-Natta heterogeneous catalysts include a metal halide activated by an organometallic co-catalyst, such as titanium chloride, optionally containing magnesium chloride, complexed to trialkyl aluminum. Homogeneous ethylene/alpha-olefins are not included in the definition of heterogeneous polyolefin.
Heterogeneous polyolefins can include, for example, polypropylene polymers and copolymers, linear low-density polyethylene, linear medium density polyethylene, very low-density polyethylene, ultra low-density polyethylene, and ethylene/alpha olefin resins wherein the ethylene is copolymerized with alpha-olefin monomers such as butene, hexene and octene.
DETAILED DESCRIPTION OF THE INVENTION
Non-oriented multilayer film of the present invention comprise a
Kelch Robert H.
McGee Robert L.
Dow Global Technology Inc.
Mork Steven W.
Tarazano D. Lawrence
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