Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
1998-06-03
2001-10-23
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C428S421000, C428S476300, C428S483000, C428S515000, C428S516000, C428S518000, C428S519000, C428S520000, C428S522000, C428S523000
Reexamination Certificate
active
06306503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to multilayer fluoropolymer films; and more particularly to films containing polychlorotrifluoroethylene (PCTFE) homopolymer or copolymer resin.
2. Description of the Prior Art
It is well known in the art to produce fluoropolymer films. These polymers are inert to most chemicals, resist high temperatures and have low coefficients of friction. Most fluoropolymers, especially PCTFE and ethylene-chlorotrifluoroethylene (ECTFE), exhibit excellent barrier properties, making them exceptionally good polymers as barrier packaging material. However, use of such fluoropolymers is restricted to specialty packaging applications due to their relatively high cost.
A suitable means of reducing the cost of a packaging material fabricated from a costly polymer is to form multilayer structures in which the polymer film is laminated with other, less costly, polymer films. This approach is particularly desirable for fluoropolymer packaging applications since a thin layer of the fluoropolymer is often all that is needed to take advantage of the desirable properties of fluoropolymers while minimizing the cost. However, fluoropolymers do not adhere strongly to most other polymers; in fact, most fluoropolymers are known for their non-stick characteristics.
Various attempts have been made to produce multilayer fluoropolymer films. For example, multilayer structures wherein at least one layer is a fluoropolymer and the other layer is a polyolefin or a thermoplastic homopolymer or copolymer, and particularly polyethylene terephthalate (PET), have been used for the production of highly oriented, dimensionally stable fluoropolymer films. In both structures, a tie layer or intermediate adhesive layer is utilized to provide good bonding between the film layers. Such multilayer structures are preferably coextruded and thereafter stretched in one or two directions. Multilayer films containing PCTFE and thermoplastic polymer layers have been proposed; see, for example, U.S. patent application Ser. No. 08/690,712, filed Jul. 31, 1996 and U.S. patent application Ser. No. 08/763,138, filed Dec. 10, 1996, the disclosure of which is expressly incorporated herein by reference.
Although the multilayer structures described above have excellent properties, including mechanical strength, toughness and water vapor barrier capabilities, in some instances multilayer films having greater adhesion between the layers is required. It would therefore be desirable to provide a multilayer structure having improved adhesion between the PCTFE or other fluoropolymer layer and the thermoplastic layer.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided a multilayer film which comprises at least one fluoropolymer layer and at least one thermoplastic layer comprising a thermoplastic homopolymer or copolymer, attached to a surface of the fluoropolymer layer by an intermediate adhesive layer. The intermediate adhesive layer comprises a blend of (1) an olefin-containing polymer selected from the group consisting of at least one functionalized polyolefin; at least one copolymer of ethylene and at least one comonomer selected from the group consisting of acrylic acid, alkyl acrylic acid, acrylates and alkyl acrylates; and blends thereof and (2) a styrene-containing rubber. Preferably, the rubber is a hydrogenated styrene-butadiene-styrene block copolymer, also referred to as a styrene-ethylene-butylene-styrene block copolymer.
It has been unexpectedly found that the presence of a relatively small amount of the styrene-containing rubber in the intermediate adhesive layer greatly increases the adhesion of the fluoropolymer and thermoplastic layers over a similar structure in which only the functionalized polyolefin is used as the intermediate adhesive layer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The multilayer film structure of the present invention comprises at least one fluoropolymer layer and at least one thermoplastic layer comprising at least one thermoplastic homopolymer or copolymer attached to the surface of the fluoropolymer layer by an intermediate adhesive layer. The multilayer film structure provides superior adhesive properties.
Fluoropolymers suitable to form the fluoropolymer layer of the multilayer film of the present invention include, but are not limited to, ECTFE copolymer, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene-propylene copolymer, perfluoroalkoxyethylene, PCTFE, polytetrafluoroethylene, polyvinylfluoride, polyvinylidene fluoride, and copolymers and blends thereof. Particularly preferred fluoropolymers include homopolymers and copolymers of chlorotrifluoroethylene and copolymers of ECTFE. Such copolymers may contain up to 10%, and preferably up to 8% by weight of other comonomers, such as vinylidene fluoride and tetrafluoroethylene. Most preferred fluoropolymers are chlorotrifluoroethylene homopolymers and copolymers of chlorotrifluoroethylene and vinylidene fluoride and/or tetrafluoroethylene, which are available from AlliedSignal Inc. as Aclon® fluoropolymer resins. Fluoropolymer film layers are described, for example, in U.S. Pat. Nos. 4,510,301; 4,544,721 and 5, 139,878.
Also present in the multilayer structure is a layer of a thermoplastic homopolymer or copolymer. The thermoplastic layer non-exclusively includes a material selected from the group consisting of polyolefins, polyamides, polyesters, polystyrene, polycarbonates, vinyl polymers, and copolymers and blends thereof Preferably, the thermoplastic layer is a polyolefin, preferably a poly(&agr;-olefin) or copolymers or blends thereof, wherein the &agr;-olefin monomers have from about 2 to about 10 and preferably from about 2 to about 6 carbon atoms. Non-limiting examples of polyolefins include polyethylenes, including ultralow, low, linear low, medium, high and ultrahigh density polyethylene; polypropylene; polybutylene; polybutene-1; polypentene-1;poly-3-methylbutene-1; poly-4-methylpentene-1; polyhexene; copolymers of polyolefins; copolymers of olefins and other polymers such as polyvinyl chloride, polystyrene and polyurethane, etc., and mixtures of these.
Between the fluoropolymer layer and the thermoplastic layer is an adhesive layer, also referred to in the art as a “tie” layer. In accordance with the present invention, the tie layer comprises a blend of polymeric materials, namely (1) an olefin-containing polymer selected from the group consisting of at least one functionalized polyolefin; at least one copolymer of ethylene and at least one comonomer selected from the group consisting of acrylic acid, alkyl acrylic acid, acrylates and alkyl acrylates; and blends thereof and (2) a styrene-containing rubber. One type of olefin-containing polymer is a functionalized olefin polymer which contains at least one functional moiety. Among the functional moieties that may be employed are unsaturated carboxylic acids, unsaturated carboxylic acid anhydrides, amines and epoxies. Examples of olefins employable for the preparation of the modified polyolefins include homopolymers or copolymers of an &agr;-olefin such as ethylene, propylene, butene-1, pentene-1, hexene-1, 4-methyl-pentene-1 and octene-1. Unsaturated carboxylic acids and anhydrides useful to modify the polyolefins include maleic acid and anhydride, fumaric acid and anhydride, crotonic acid and anhydride, citraconic acid and anhydride, itaconic acid and anhydride and the like. Of these, the most preferred is maleic anhydride. Suitable amines include aliphatic or aromatic, primary, secondary and tertiary amines, such as 2,4,6-tribromoaniline, methylamine, ethylamine, propylamine, dimethylamine, N-methylaniline, ethylmethylamine, 2-(N-methylamine)heptane, sec-butyldimethylamine, N-ethyl-N-methylaniline, trimethylamine, N,N-dimethylanaline, and the like. Suitable epoxies include those having from about 2 to about 20 carbon atoms. The modified polyolefins suitable for use in this invention include compositions described in U.S. Pat. Nos. 3,481,910; 3,480,580; 4,612,155 and 4,751,270 wh
Allied-Signal Inc.
Criss Roger H.
Thibodeau Paul
Zacharia Ramsey
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