Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – With prevention of equipment fouling accumulations or deposits
Reexamination Certificate
2001-11-29
2004-08-03
Yoon, Tae H. (Department: 1714)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
With prevention of equipment fouling accumulations or deposits
C428S483000, C524S504000, C524S513000, C523S319000, C528S503000
Reexamination Certificate
active
06770234
ABSTRACT:
TECHNICAL FIELD
The invention herein is directed to a method whereby a co-polyester/ethyl methyl acrylate (EMA) film is maintained and extruded at temperatures well above the melt temperature of the film's base co-polyester polymer, the thermal stable nature of the co-polyester polymer during the extrusion process being imparted by a combination of one or more plastic compatibilizers, the resulting co-polyester film having enhanced physical barrier properties.
BACKGROUND OF THE INVENTION
The formation of finite thickness films from thermoplastic polymers is a well known practice. Thermoplastic polymer films can be formed by either dispersion of a quantity of molten polymer into a mold having the dimensions of the desired end product, known as a thermo-formed or injection-molded film, or by continuously forcing the molten polymer through a die, known as an extruded film. Extruded thermoplastic polymer films can either be formed such that the film is cooled then wound as a completed product, or dispensed directly onto a substrate material to form a composite material having performance of both the substrate and the film layers. Examples of suitable substrate materials include other films, polymeric or metallic sheet stock and woven or nonwoven fabrics.
The application of the extruded film directly onto a substrate material imparts the substrate material with enhanced physical properties. It is known in the art that the application of a thermoplastic polymer film having suitable flexibility and porosity onto a nonwoven fabric results in a composite material having significant barrier properties and is suitable for disposable protective garment manufacture.
To further improve the performance of the thermoplastic polymer film when used in composite material manufacture, various additives are admixed with the thermoplastic polymer prior to or during extrusion. Typical additives employed are those selected from various colorants or opacifiers, such as titanium dioxide. Water insoluble salts such as calcium carbonate may be added to the polymer mix resulting in a film that can be rendered micro-porous by the application of draft tension, as taught by U.S. Pat. No. 5,910,225, to McAmish. If there is a desire to form a composite wherein the thermoplastic polymer film will be exposed to a transitory temperature above the melting temperature of the polymer, antioxidants can be incorporated into the mix to aid in reducing thermal degradation. In the event where the family of thermoplastic polymers to be used in the extruded film exhibits a dissimilar characteristic such as surface energy from the thermoplastic polymer of the substrate material, compatibilizers are incorporated into the polymer mix.
Compatibilizers are crucial when attempting to form a composite material from film and substrate layers comprised of dissimilar polymers. Thermoplastic polymers used to form the film layer are heated to the respective melting point then applied uniformly to the substrate material. At the melting point of the thermoplastic polymer, the polymer has just reached the temperature at which the polymer phase transitions between solid and liquid states, and as such, exhibits a relatively high viscosity. When the highly viscous thermoplastic polymer is extruded onto the substrate material, the polymer extends only marginally into the interstices or pores of the substrate. The compatibilizer aids in attaining as much bond strength as possible with the marginal substrate surface contact.
One solution to obtaining a more durable adhesion of the film having a compatibilizer to the substrate material is to increase the pressure by which the film is extruded onto the substrate. Increasing the pressure of extrusion has a deleterious effect on both manufacture of the composite product and the quality of the film layer. The throughput of the line is necessarily reduced to allow for a higher residence time for the molten thermoplastic polymer to flow into the interstices of the substrate materials. An increase in pressure can also induce stress shearing in the polymer during extrusion, thus reducing the resulting durable performance of the thermoplastic polymer film.
While attempts have been made to attain durable adhesion between an extruded film and an associated substrate by temporarily increasing the extrusion temperature, thus reducing the polymer viscosity, an increase in the extrusion temperature ordinarily results in a discontinuous or broken polymer curtain, thus forming a product with regions of faulty or compromised composite structure. If the temperature is raised significantly, thermal degradation will further compromise the durable performance of the thermoplastic polymer. Heretofore, the use of antioxidants has been necessary to abate polymer degradation, with a corresponding disadvantageous effect on cost and compatibility with certain other desirable melt-additives.
There remains an unmet need for forming a composite material having an extruded thermoplastic polymer film whereby the film exhibits durable integration with the substrate material. Further, there remains an unmet need whereby the film can be extruded at a significantly elevated temperature which provides durable integration of the film with the substrate materials and can be performed without adversely affecting line speeds or polymer performance, without resort to the addition of expensive and typically unstable antioxidant compounds.
SUMMARY OF THE INVENTION
The present invention is directed to the method of extruding a thermoplastic co-polyester EMA (ethyl methyl acrylate) blended film at temperatures well above the melt temperature of the base thermoplastic co-polyester, the co-polyester/EMA film having enhanced barrier properties. Notably, the present invention contemplates extrusion of co-polyester compounds onto suitable substrates without the need to employ antioxidant compounds in the molten polymer material.
A further aspect of the present invention entails a film comprising an EMA and co-polyester thermoplastic admixed with a compatibilizer and extruded at a temperature at least 10% higher than the melt temperature, which in turn provides the co-polyester film with durable adhesive properties in addition to good breathability as measured by moisture vapor transmission rate (MVTR).
The thermal stability during processing of the thermoplastic co-polyester is imparted by the admixture of compatibilizers, the compatibilizers being incorporated to attain durable adhesion of the thermoplastic polymer film to a substrate material.
A particular embodiment of the present invention incorporates a co-polyester polymer base and a compatibilizer mix. Compatibilizers found suitable for use in high temperature extrusion of polyester include those selected from the group consisting of ethylene acrylate copolymers and maleic anhydride modified polyethylenes. The polyester admixture is extruded through a conventional film extruder at a temperature of between 500° F. and 560° F., a temperature significantly above the conventional extrusion maximum temperature of 450° F. employed by those skilled in the art.
The ethylene acrylate and maleic anhydride polyethylene compatibilizers are blended within the co-polyester and EMA melt at a 2:1 ratio. Preferably, the melt comprises 3% by weight maleic anhydride polyethylene and 1.5% by weight ethylene acrylate and more preferably, the melt comprises 1% by weight maleic anhydride polyethylene and 0.5% ethylene acrylate
It is further contemplated by the present invention that a barrier fabric is formed from a base polyester polymer/compatibilizer admix which is extruded at a temperature of between 500° F. and 560° F. onto a polypropylene spunbond.
REFERENCES:
patent: 5910225 (1999-06-01), McAmish et al.
patent: 6191221 (2001-02-01), McAmish et al.
patent: 2003/0091765 (2003-05-01), Ferrera et al.
McAmish Larry H.
Osborn Kevin Paul
Polymer Group Inc.
Wood Phillips Katz Clark & Mortimer
Yoon Tae H.
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