Stock material or miscellaneous articles – Composite – Of fluorinated addition polymer from unsaturated monomers
Reexamination Certificate
2001-01-21
2002-10-15
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of fluorinated addition polymer from unsaturated monomers
C428S421000, C428S515000, C428S516000, C428S520000, C428S522000, C428S523000, C428S910000
Reexamination Certificate
active
06465103
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to oriented multilayer films. More particularly, the invention pertains to coextruded or laminated films having at least one layer of a fluoropolymer such as poly(chlorotrifluoro ethylene) (PCTFE) homopolymer or copolymer, a layer of a polyolefin homopolymer or polyolefin containing copolymer and an intermediate adhesive layer of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid and/or anhydride thereof.
2. Description of the Prior Art
It is well known in the art to produce oriented polymeric films. See, e.g. U.S. Pat. No. 4,011,874. However, such films tend to expand in the direction perpendicular to the direction of stretching.
It is also known in the art to produce single layer and multilayer fluoropolymer films. See, e.g. U.S. Pat. Nos. 4,677,017; 4,659,625 and 5,139,878, all of which are incorporated herein by reference. However, fluoropolymers are difficult to orient due to their unique crystallization properties. More particularly, PCTFE is exceptionally difficult to orient due to its extremely fast crystallization rate and thermally induced self-orientation. Its fast crystallization rate produces a highly crystalline structure that hinders orientation and actually prevents further orientation beyond a certain point. Its thermally induced self-orientation results in a film which, upon unconstrained heating, self extends in the machine or longitudinally stretched direction and shrinks in the transverse direction.
Most earlier attempts to stretch PCTFE films have failed either due to its high degree of film crystallinity, nonuniform crystallinity, self-orientation or a combination of these factors. Prior art studies of the orientation of PCTFE homopolymer report a limit of a three to four times orientation or stretch ratio in either the machine direction (MD) or transverse direction (TD). For example, U.S. Pat. No. 4,544,721 describes a substantially amorphous chlorotrifluoroethylene polymer monolayer film which is oriented at least 2.5 times its original length, but no more than five times in the MD. It also disclosed therein that attempts to stretch crystalline PCTFE result in films that contain holes or tears, or which are uneven in thickness. Other known attempts to stretch PCTFE homopolymer more than five times its unstretched length result in film fibrilation and ultimate breakage. See, e.g. U.S. Pat. No. 4,510,301 (orients film containing a copolymer of ethylene and chlorotrifluoroethylene).
It would be desirable to produce a much more highly oriented, dimensionally stable fluoropolymer film since as the higher the degree of attainable orientation is increased, the properties of mechanical strength, toughness, and water vapor barrier capability are significantly improved without increasing the film gauge. It would also be desirable to produce a multilayered film structure which is dimensionally stable and uniform across its entire width.
SUMMARY OF THE INVENTION
The invention provides a multilayer film which comprises at least one fluoropolymer layer and at least one polyolefin layer comprising at least one polyolefin homopolymer, polyolefin containing copolymer or blends thereof, attached to a surface of the fluoropolymer layer by an intermediate adhesive layer comprised of at least one polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof, which film has been uniaxially stretched at least five times in one linear direction, and wherein each of the fluoropolymer layer, adhesive layer and polyolefin layer have a viscosity of less than or equal to about 10,000 Pascal seconds at a temperature in the range of from about 280° C. to about 400° C.
The invention also provides a method of producing an oriented, multilayer film which comprises coextruding at least one layer of a fluoropolymer, and at least one layer of a polyolefin homopolymer or a polyolefin containing copolymer attached to a surface of the fluoropolymer layer by a coextruded intermediate adhesive layer, which intermediate adhesive layer is comprised of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride, wherein said coextruding is conducted at a temperature of from about 280° C. to about 400° C.; casting the film and then stretching the film at least five times in either its longitudinal or transverse direction.
The invention further provides a method of producing an oriented, multilayer film which comprises laminating at least one layer of a fluoropolymer to the surface of a layer of a polyolefin homopolymer or a polyolefin containing copolymer by an intermediate adhesive layer, which intermediate adhesive layer is comprised of a polyolefin having at least one functional moiety of an unsaturated carboxylic acid anhydride and then stretching the film article at least five times in either its longitudinal or transverse direction.
The invention still further provides an article which comprises a thermoformed film of the above multilayered film.
The present invention achieves a highly oriented fluoropolymer containing film by producing a multilayer structure by either a coextrusion or a lamination process. Without the additional layers in the film structure, many fluoropolymers such as PCTFE can only be stretched to a maximum of five times its original length and usually only three times stretching. With this structure, the polyolefin layer allows the fluoropolymer containing layer to be stretched more than five-times its original length, and usually up to ten times its original length.
It has been further found that when fluoropolymer films are coextruded with polyolefins and adhered with the above intermediate adhesive layer at a temperature range of from about 280° C. to about 400° C., a stable, uniform film is produced.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
For purposes of this invention, the terms “orienting” and “stretching” shall be used interchangeably. As used herein, “copolymers” shall include polymers having two or more monomer components.
The fluoropolymer layer may be comprised of PCTFE homopolymers or copolymers or blends thereof as are well known in the art and are described in, for example, U.S. Pat. Nos. 4,510,301; 4,544,721; and 5,139,878 which are incorporated herein by reference. Of these, particularly preferred fluoropolymers suitable to form multilayer barrier films of the present invention include homopolymers and copolymers of chlorotrifluoroethylene and copolymers of ethylene-chlorotrifluoroethylene. Such copolymers may contain up to 10%, and preferably up to 8% by weight of other comonomers such as vinylidine fluoride and tetrafluoroethylene. Most preferred are chlorotrifluoroethylene homopolymers and copolymers of chlorotrifluoroethylene and vinylidine fluoride and/or tetrafluoroethylene. Such may also be purchased commercially as ACLON® resin from AlliedSignal Inc. of Morristown, N.J.
Adjacent to the fluoropolymer layer is an adhesive layer, also referred to in the art as a “tie” layer, between each film layer. In accordance with the present invention, suitable adhesive polymers includes modified polyolefin compositions having at least one functional moiety selected from the group consisting of unsaturated polycarboxylic acids and anhydrides thereof. Such unsaturated carboxylic acid and anhydrides include maleic acid and anhydride, fumaric acid and anhydride, crotonic acid and anhydride, citraconic acid and anhydride, itaconic acid an anhydride and the like. Of these, the most preferred is maleic anhydride. 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 which are incorporated herein by reference. The preferred modified polyolefin composition comprises from about 0.001 and about 10 weight percent of the functional moiety, based on the total weight of the modified polyolefin. More preferably the functional moiety comprises from about 0.005 and about 5 weigh
Khanna Yash Pal
Mackey Joseph Edgar
Tsai Mingliang Lawrence
Allied-Signal Inc.
Chen Vivian
Criss Roger H.
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