Heat treatment of thin polymer films

Abstract

Stretch film is treated by passing a web of tackifier-containing, unbloomed thin polymer film through a heater so that the web is heated to a temperature sufficient to cause tackifier bloom prior to the web reaching a next stage in an in-line process. Also, a pattern can be applied to a thin polymer film. An oriented web of thin polymer film is passed across at least one heated roller having the pattern engraved thereon to define face regions and relief regions collectively conforming to the pattern. As the web contacts each roller surface, portions of the web positioned over the relief regions receive less heat than portions of the web positioned over the face regions, thereby causing the respective portions of the web to undergo differential, heat-induced shrinkage which imparts the pattern to the thin polymer film.

1 . A method for treating stretch film and applying a pattern thereto, the method comprising:
 passing a web of oriented thin polymer film across at least one heated roller;   the at least one heated roller having the pattern engraved on a surface thereof so as to define face regions and relief regions on the surface, with the face regions and relief regions collectively conforming to the pattern;   so that as the web contacts the surface of the at least one roller, portions of the web positioned over the relief regions receive relatively less heat from the at least one roller than portions of the web positioned over the face regions of the at least one roller;   thereby causing the respective portions of the web to undergo differential, heat induced shrinkage whereby the differential heat-induced shrinkage imparts the pattern to the thin polymer film.   
     
     
         2 . The method of  claim 1 , wherein:
 the web contains tackifier;   the web is unbloomed when passed across a first one of the at least one heated roller; and   the portions of the web positioned over the face regions of the at least one roller are heated to a temperature sufficient to cause tackifier bloom prior to the web reaching a winder.   
     
     
         3 . The method of  claim 1 , wherein the pattern is formed by changeable type on the roller. 
     
     
         4 . The method of  claim 3 , wherein the changeable type is arranged into an expiry date for a product which is to be wrapped by the web of thin polymer film. 
     
     
         5 . The method of  claim 1 , wherein the web is passed across the at least one heated roller before stretching of the web. 
     
     
         6 . The method of  claim 1 , wherein the web is passed across the at least one heated roller after stretching of the web. 
     
     
         7 . The method of  claim 1 , wherein the web is passed across the at least one heated roller in an unstretched state and is passed to the winder in an unstretched state. 
     
     
         8 . A thin polymer film carrying a pattern defined by at least one first region that has undergone greater heat induced shrinkage than at least one second region. 
     
     
         9 . The thin polymer film of  claim 8 , wherein:
 the thin polymer film contains tackifier;   the tackifier in the at least one first region is bloomed; and   the tackifier in the at least one second region is unbloomed.   
     
     
         10 . A method for treating thin polymer film, the method comprising:
 heating a web of tackifier-containing, unbloomed thin polymer film to a temperature sufficient to cause tackifier bloom prior to the web reaching a next step in an in-line process;   so that the web of tackifier-containing, unbloomed thin polymer film becomes a web of tackifier-containing, bloomed thin polymer film prior to the web reaching the next step in the in-line process.   
     
     
         11 . The method of  claim 10 , wherein the step of heating the web of tackifier-containing, unbloomed thin polymer film is carried out before stretching of the web. 
     
     
         12 . The method of  claim 10 , wherein the step of heating the web of tackifier-containing, unbloomed thin polymer film is carried out after stretching of the web. 
     
     
         13 . The method of  claim 10 , wherein the step of heating the web of tackifier-containing, unbloomed thin polymer film is carried out with the web in an unstretched state and the resulting web of tackifier-containing, bloomed thin polymer film is passed to a winder in an unstretched state. 
     
     
         14 . The method of  claim 10 , wherein the step of heating the web of tackifier-containing, unbloomed thin polymer film comprises passing the web of tackifier-containing, unbloomed thin polymer film through a heater. 
     
     
         15 . The method of  claim 14 , wherein the heater comprises at least one heated roller. 
     
     
         16 . The method of  claim 14 , wherein the heater comprises an infrared heater assembly. 
     
     
         17 . The method of  claim 14 , wherein the heater comprises an electrical resistance element oven assembly. 
     
     
         18 . The method of  claim 10 , wherein the method comprises a step of, before heating the web of tackifier-containing, unbloomed thin polymer film, producing the web of tackifier-containing, unbloomed thin polymer film as part of the in-line process.