Polyester Film Having Latent Shrink Properties and Process for Producing Same

Abstract

A film layer is disclosed that is capable of shrinking when subjected to energy, such as heat. The film layer, for instance, can be formed and then stretched in one or two directions at a relatively low temperature. In particular, the film is stretched while the film layer is at a temperature near the glass transition temperature of the polymer used to form the film. Drawing the film at a relatively low temperature has been found to improve the shrink properties of the film. In one embodiment, the film layer is comprised of a non-modified polyester, such as polyethylene terephthalate. For example, the polyethylene terephthalate can be made by reacting terephthalic acid with ethylene glycol or polyethylene glycol.

1 . A film product comprising:
 a film layer comprising a polyester polymer, the film layer having been stretched in at least one direction, the polyester polymer being at least partially in crystalline form, and wherein the film layer shrinks at least 10% in the one direction when subjected to a temperature of 80° C. for three minutes.   
     
     
         2 . A film product as defined in  claim 1 , wherein the film layer comprises a mono layer of the polyester polymer. 
     
     
         3 . A film product as defined in  claim 1 , wherein the film product comprises a plurality of coextruded film layers. 
     
     
         4 . A film product as defined in  claim 1 , wherein the polyester polymer comprises polyethylene terephthalate. 
     
     
         5 . A film product as defined in  claim 1 , wherein the film layer has been biaxially stretched in both a longitudinal direction and in a lateral direction, and wherein the film layer shrinks at least 10% in both the lateral direction and the longitudinal direction when subjected to a temperature of 80° C. for three minutes. 
     
     
         6 . A film product as defined in  claim 1 , wherein the film layer has been biaxially stretched in both a longitudinal direction and in a lateral direction, and wherein the film layer shrinks at least 20% in both the lateral direction and the longitudinal direction when subjected to a temperature of 80° C. for three minutes. 
     
     
         7 . A film product as defined in  claim 1 , wherein the film layer contains a filler. 
     
     
         8 . A film product as defined in  claim 7 , wherein the filler comprises calcium carbonate particles. 
     
     
         9 . A film product as defined in  claim 1 , wherein the polyester polymer comprises a non-modified polyester polymer. 
     
     
         10 . A film product as defined in  claim 9 , wherein the polyester polymer comprises the polycondensation reaction product of ethylene glycol and terephthalic acid. 
     
     
         11 . A label incorporating the film product defined in  claim 1 . 
     
     
         12 . A label as defined in  claim 11 , further comprising an adhesive layer disposed on an exterior surface of the film product for adhering the label to adjacent objects. 
     
     
         13 . A label as defined in  claim 12 , further comprising a print layer containing printed matter, the print layer being visible from an exterior surface of the label opposite where the adhesive layer is disposed. 
     
     
         14 . A label as defined in  claim 13 , wherein the print layer is positioned in between the adhesive layer and the film layer. 
     
     
         15 . A label as defined in  claim 13 , wherein the film layer is positioned in between the adhesive layer and the print layer. 
     
     
         16 . A film product as defined in  claim 1 , wherein the product is in the shape of a continuous tube that is configured to be shrink wrapped over a container. 
     
     
         17 . A process for producing a shrinkable film comprising:
 forming a film layer, the film layer comprising a polyester polymer;   cooling the film layer to a temperature that is within about 30% of the glass transition temperature of the polyester polymer; and   thereafter stretching the film layer in at least one direction.   
     
     
         18 . A process as defined in  claim 17 , wherein the film layer is stretched both in a longitudinal direction and in a lateral direction. 
     
     
         19 . A process as defined in  claim 18 , wherein the film layer has an original length in the longitudinal direction and an original length in the lateral direction and wherein the film is stretched from about 1 to about 4 times its original length in both directions. 
     
     
         20 . A process as defined in  claim 17 , wherein the polyester polymer comprises a non-modified polyethylene terephthalate. 
     
     
         21 . A process as defined in  claim 17 , wherein the film layer is formed by heating the polyester polymer into a molten state and then extruding the molten polymer through an extruder. 
     
     
         22 . A process as defined in  claim 21 , wherein the film layer is extruded with at least one other film layer. 
     
     
         23 . A process as defined in  claim 17 , wherein the film layer is cooled by passing the film layer over a surface of a chilled roller, the surface of the chilled roller being at a temperature of less than about 30° C. 
     
     
         24 . A process as defined in  claim 17 , wherein the film layer is stretched while the film layer is at a temperature of less than about 120° C. 
     
     
         25 . A process as defined in  claim 17 , wherein the film layer is stretched while the film layer is at a temperature of less than about 90° C. 
     
     
         26 . A process as defined in  claim 17 , wherein the film layer is not heat treated after being stretched.