Packaging and Labelling Films

Abstract

The present invention provides a transparent, dimensionally stable, biaxially oriented PLA film having a haze value of less than 3% and exhibiting strain induced crystallinity having been oriented by stretching the film from a substantially non-crystalline state by more than three times its original areal dimensions. The processes for making such films are also disclosed.

1 . A transparent, dimensionally stable, oriented PLA film having a haze value of less than 3% and exhibiting strain induced crystallinity having been oriented from a substantially non-crystalline state by stretching the film by more than three times its original areal dimensions. 
     
     
         2 . The film according to  claim 1  which is biaxially oriented by simultaneous stretching in each of the transverse and longitudinal directions. 
     
     
         3 . The film according to  claim 1  which is biaxially oriented by sequential stretching in each of the transverse and longitudinal directions. 
     
     
         4 . The film according to  claim 1  which is monoaxially oriented. 
     
     
         5 . The film according to  claim 1 , having a haze value of less than 2.5%. 
     
     
         6 . The film according to  claim 1 , exhibiting a clarity of at least about 95%. 
     
     
         7 . The film according to  claim 1  which is oriented by stretching the film by at least four times its original dimensions simultaneously in each of the transverse and longitudinal directions. 
     
     
         8 . The film according to  claim 1 , exhibiting a longitudinal (machine direction) shrinkage and/or transverse direction shrinkage of less than 2% at 80° C. 
     
     
         9 . The film according to  claim 1 , exhibiting a longitudinal (machine direction) shrinkage and/or transverse direction shrinkage of less than 5% at 120° C. 
     
     
         10 . The film according to  claim 1 , exhibiting a longitudinal (machine direction) shrinkage and/or transverse direction shrinkage of less than 10% at 150° C. 
     
     
         11 . The film according to  claim 1 , exhibiting a longitudinal (machine direction) shrinkage and/or transverse direction shrinkage of less than 20% at 180° C. 
     
     
         12 . (canceled) 
     
     
         13 . The film according to  claim 1 , comprising crystallinity in the form of a stereocomplex of crystalline PLLA and PDLA formed during annealing of the film. 
     
     
         14 . The film according to  claim 13 , wherein α-form crystals of PLLA and/or PDLA are present in the film. 
     
     
         15 . The film according to  claim 14 , wherein any such α-form crystals are present in the film in amounts of less than 30% of the amount of stereocomplex present. 
     
     
         16 . A process for the manufacture of the film of  claim 1 , comprising the steps of:
 a. extruding a blend of a first PLA rich in L-lactate repeat units (optionally PLLA itself) and a second PLA rich in D-lactate repeat units (optionally PDLA itself) at a temperature of at least about 220° C. to provide an extrudate;   b. quenching the extrude directly after extrusion to a temperature below about 65° C. to hinder or prevent crystal formation in the extrudate;   c. reheating the quenched extrudate to a temperature of at least about 65° C. and subsequently immediately stretching the film to more than three times its original area to introduce orientation and crystallinity into the film, crystallinity being in the α-crystalline form and/or in the form of a stereocomplex of PLLA and/or PDLA; and   d. heat setting the stretched and oriented crystalline film at a temperature of at least about 170° C. to melt out at least a proportion of any α-crystallinity in the film and optionally introduce stereocomplex crystallinity or further stereocomplex crystallinity into the film.   
     
     
         17 . The process according to  claim 16 , wherein the film is stretched in step c) at a draw rate of greater than 150 μm/s in at least one of its machine and transverse directions. 
     
     
         18 . The process according to  claim 16 , wherein the L-lactate-rich PLA used in the blend is pure PLLA. 
     
     
         19 . The process according to  claim 16 , wherein the L-lactate-rich PLA used in the blend includes a minor amount of D-lactide. 
     
     
         20 . The process according to  claim 16 , wherein the D-lactate-rich PLA used in the blend is pure PDLA. 
     
     
         21 . The process according to  claim 16 , wherein the D-lactate-rich PLA used in the blend includes a minor amount of L-lactide. 
     
     
         22 . The process according to  claim 16 , wherein the blend of the first PLA and the second PLA (optionally including minor amounts of L isomer) comprises up to about 90% L-lactate repeat units. 
     
     
         23 . The process according to  claim 16 , wherein the blend of the first PLA and the second PLA comprises up to about 90% D-lactate repeat units. 
     
     
         24 . The process according to  claim 16 , wherein the first PLA and the second PLA are present in the blend in a ratio (first PLA:second PLA) of from 99:1 to 1:99. 
     
     
         25 . The process according to  claim 16 , wherein the first PLA is present in an amount of at least 50% by weight of the blend. 
     
     
         26 . The process according to  claim 16 , wherein the second PLA is present in an amount of 50% or less by weight of the blend. 
     
     
         27 . The process according to  claim 16 , wherein the extrusion temperature is at least about 230° C. 
     
     
         28 . The process according to  claim 16 , wherein the extrusion temperature is 250° C. to 260° C. 
     
     
         29 . The process according to  claim 16 , wherein the quenching temperature is below about 55° C. 
     
     
         30 . The process according to  claim 16 , wherein the quenching temperature is in the range of from 30° C. to 40° C. 
     
     
         31 . The process according to  claim 16 , wherein the reheat temperature to which the film heated immediately prior to stretching is at least about 70° C. 
     
     
         32 . The process according to  claim 16 , wherein heat setting of the film is conducted at a temperature of at least about 175° C. 
     
     
         33 . The process according to  claim 16 , wherein the extrudate after quenching but before stretching is substantially amorphous. 
     
     
         34 . A film produced by the process of  claim 16 . 
     
     
         35 . An article packaged or labelled with film of  claim 1 .