Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Extrusion molding
Reexamination Certificate
2001-05-15
2004-02-03
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Extrusion molding
C264S235800, C264S290200, C264S211000, C428S331000, C525S183000
Reexamination Certificate
active
06685871
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to biaxially oriented polyamide films. More particularly, it describes a method for producing toughened biaxially oriented polyamide films having superior strength and resistance to pinholes, cracks, and other structural defects.
2. Description of the Related Art
It is known in the art to produce biaxially oriented polyamide films. The production of such films typically involve the steps of subjecting a polyamide resin to melt extrusion, cooling and solidifying the extruded film, reheating the unoriented film and subjecting it to drawing in the machine direction (MD) and transverse direction (TD), and heat-setting the drawn film. Drawing is usually accomplished by sequential biaxial drawing in flat form, simultaneous biaxial drawing in flat form, or simultaneous biaxial drawing in tubular form.
Unfortunately, biaxially oriented polyamide films have been known to sometimes suffer from several disadvantages such as pinholes, cracks, and other structural defects. It would therefore be desirable to formulate a biaxially oriented polyamide film having superior strength and resistance to pinholes and the like. It would also be desirable to form a process for forming such films, which process does not require expensive capital improvements beyond the capabilities of existing technology.
SUMMARY OF THE INVENTION
The invention provides a method for forming a biaxially oriented film which comprises:
a) dry blending i) a polyamide homopolymer, copolymer, or blends thereof; and ii) a functionalized polyolefin terpolymer comprising maleic anhydride, ethyl acrylate, and an olefin, to thereby form a dry mixture;
b) melting the dry mixture to thereby form a polymer blend;
c) forming the polymer blend into a polymer film;
d) pinning edges of the film to a casting roll;
e) treating the film in at least one water bath to thereby plasticize the polymer film; and
f) biaxially orienting the film.
The invention further provides a biaxially oriented film formed by the above process.
The invention still further provides a method for forming a biaxially oriented film which comprises:
a) dry blending i) a polyamide homopolymer, copolymer, or blends thereof; and ii) a functionalized polyolefin terpolymer comprising maleic anhydride, ethyl acrylate, and an olefin, to thereby form a dry mixture; wherein the ethyl acrylate is present in the functionalized polyolefin terpolymer in an amount of from about 20% to about 40% by weight of the terpolymers; and wherein the maleic anhydride is present in the functionalized polyolefin terpolymer in an amount of from about 0.1% to about 1% by weight of the terpolymer; and wherein the olefin is present in the functionalized polyolefin terpolymer in an amount of from about 59% to about 79.9% by weight of the terpolymer;
b) melting the dry mixture to thereby form a polymer blend;
c) forming the polymer blend into a polymer film; and
d) biaxially orienting the film.
The invention also provides a method for forming an oriented film which comprises:
a) dry blending i) a polyamide homopolymer, copolymer, or blends thereof; and ii) a functionalized polyolefin terpolymer comprising maleic anhydride, ethyl acrylate, and an olefin, to thereby form a dry mixture;
b) melting the dry mixture to thereby form a polymer blend;
c) extruding the polymer blend through a circular die, blowing it into a polymer film and quenching to produce an intermediate oriented film;
d) reheating the intermediate oriented film and biaxially reorienting in both the machine and transverse directions;
e) heating the thusly produced film under conditions sufficient to set the orientation.
It has been unexpectedly found that the present invention provides a solution to the problems of the prior art. The present invention provides toughened biaxially oriented polyamide films. The films of the invention are prepared by dry blending i) a polyamide homopolymer, copolymer, or blends thereof; and ii) a functionalized polyolefin terpolymer comprising maleic anhydride, ethyl acrylate, and an olefin, to thereby form a dry mixture. The dry mixture is melted to form a polymer blend, which is then formed into a polymer film. The edges of the film are pinned to a casting roll, and the may optionally be plasticized, for example by using low molecular weight additives or a water bath. The polymer film is subsequently biaxially oriented. The result is a toughened biaxially oriented film which is resistant to pinholes, cracks, and other structural defects. Such films are particularly suited for making packaging materials for various food products.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A method is provided for forming a toughened biaxially oriented film. This method first comprises dry blending i) a polyamide homopolymer, copolymer, or blends thereof; and ii) a functionalized polyolefin terpolymer comprising maleic anhydride, ethyl acrylate, and an olefin, to thereby form a dry mixture. The mixture is then melted, formed into a film, optionally but preferably pinned to a casting roll, optionally but preferably treated in a water containing bath, and then biaxially oriented.
The polyamide homopolymer, copolymer, or blend thereof is preferably present in the form of small dry pellets or particles, such that the polyamide component may be dry blended with other components of the invention to form a dry mixture. Suitable polyamides nonexclusively include homopolymers, copolymers, or blends thereof of nylons such as nylon 6; nylon 6,12; nylon 6,6; nylon MDX-6, and the like, and blends thereof. Of these, nylon 6 is preferred. Nylon 6 is commercially available under the trade name Capron® from Honeywell International Inc. of Morristown, N.J., USA. The polyamide component is preferably present in the dry mixture from about 85 to about 99.5% by weight of the overall dry mixture, more preferably from about 89 to about 97.5% by weight of the overall dry mixture, and most preferably from about 93 to about 96% by weight of the overall dry mixture.
The functionalized polyolefin terpolymer serves as a toughening agent such that the resulting film of the invention is highly resistant to pinholes, cracking, and other structural defects. The terpolymer component is preferably present in the dry mixture from about 0.5 to about 15% by weight of the overall dry mixture, more preferably from about 1 to about 10% by weight of the overall dry mixture, and most preferably from about 2 to about 7.5 by weight % of the overall dry mixture. The terpolymer comprises maleic anhydride, ethyl acrylate, and an olefin. For example, an ethylene/ethyl acrylate/maleic anhydride terpolymer may be obtained commercially under the trade name Lotader, available from AutoFina of Philadelphia, Pa.
The maleic anhydride component is present in the functionalized polyolefin terpolymer in an amount from about 0.1 to about 1% by weight of the overall terpolymer, more preferably from about 0.1 to about 0.5% by weight of the overall terpolymer, and most preferably from about 0.2 to about 0.3% by weight of the overall terpolymer. Amounts of maleic anhydride above about 1% may have deleterious effects on orientation.
The olefin component is preferably present in the functionalized polyolefin terpolymer in an amount from about 59 to about 79.9% by weight of the overall terpolymer, more preferably from about 60 to about 78% by weight of the overall terpolymer, and most preferably from about 65 to about 75% by weight of the overall terpolymer. Suitable olefins nonexclusively include ethylene, methylene, propylene, butylene, and the like, and combinations thereof. Of these, ethylene is most preferred.
The ethyl acrylate component is preferably present in the functionalized polyolefin terpolymer in an amount from about 20 to about 40% by weight of the overall terpolymer, more preferably from about 25 to about 35% by weight of the overall terpolymer, and most preferably from about 28 to about 32% by weight of the overall terpolymer.
The components of the functionalized polyolefin terpolymer are pr
Bardzak Gary M.
Blissett Delroy G.
Crochunis Anthony B.
Majestic Ann M.
Moulton Jeffrey D.
Criss Roger H.
Eashoo Mark
Honeywell International , Inc.
Szigeti Virginia
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