Coextruded polymer film configured for successive irreversible delamination

Abstract

Multilayered polymer films are configured so that successive constituent layer packets can be delaminated in continuous sheet form from the remaining film. The new films are compatible with known coextrusion manufacturing techniques, and can also be made without the use of adhesive layers between layer packets that are tailored to be individually peelable from the remainder of the film. Instead, combinations of polymer compositions are used to allow non-adhesive polymer layers to be combined in such a way that delamination of the film is likely to occur along a plurality of delamination surfaces corresponding to interfaces between particular pairs of layers for which the peel strength is reduced relative to the peel strength at other layer interfaces within the film. The absence of an adhesive between peelable layer packets results in the delamination being irreversible.

1 . A film comprising a stack of polymer layers, the polymer layers being organized into layer packets, each of the layer packets having a front major surface, a back major surface, and at least three of the polymer layers between the front and back major surfaces;
 wherein for every pair of adjacent first and second layer packets in the stack, the first layer packet includes a backmost polymer layer that on one side thereof contacts an interior polymer layer of the first layer packet and that on an opposite side thereof contacts a frontmost polymer layer of the second layer packet, the backmost polymer layer having a weaker attachment to the frontmost polymer layer than to the interior polymer layer such that the first layer packet tends to irreversibly delaminate from the second layer packet along a delamination surface corresponding to an interface between the backmost polymer layer and the frontmost polymer layer; and   wherein all of the polymer layers in the stack of polymer layers have respective polymer compositions that are coextrudable with each other.   
     
     
         2 . The film of  claim 1 , wherein the stack of polymer layers includes polymer layers A, polymer layers B, and polymer layers C composed of different polymer compositions A, B, and C, respectively, and wherein the backmost polymer layers has the polymer composition C. 
     
     
         3 . The film of  claim 2 , wherein the polymer composition C is a blend of propylene copolymer and styrenic block copolymer. 
     
     
         4 . The film of  claim 2 , wherein the polymer composition C is a blend of propylene copolymer and an ethylene alpha olefin copolymer. 
     
     
         5 . The film of  claim 2 , wherein the polymer composition C is a blend of propylene copolymer and an olefin block copolymer. 
     
     
         6 . The film of  claim 2 , wherein the interior polymer layer has the polymer composition B, and wherein the frontmost polymer layer has the polymer composition A. 
     
     
         7 . The film of  claim 6 , wherein the polymer composition C is a blend of propylene copolymer and styrenic block copolymer, and wherein the polymer composition B is an immiscible blend of copolyester and an olefin. 
     
     
         8 . The film of  claim 6 , wherein the polymer composition C is a blend of propylene copolymer and styrenic block copolymer, the polymer composition B is an amorphous copolyester, and the polymer composition A is a semi-crystalline polyester. 
     
     
         9 . The film of  claim 6 , wherein the polymer composition C is a blend of propylene copolymer and ethylene/octene copolymer, the polymer composition B is an amorphous copolyester, and the polymer composition A is a semi-crystalline polyester. 
     
     
         10 . The film of  claim 6 , wherein the polymer composition C is a blend of propylene copolymer and olefin block copolymer, the polymer composition B is an amorphous copolyester, and the polymer composition A is a semi-crystalline polyester. 
     
     
         11 . The film of  claim 6 , wherein the polymer composition C is at least partially miscible with the polymer composition B, and the polymer composition B is at least partially miscible with the polymer composition A, but the polymer composition C is not miscible with the polymer composition A. 
     
     
         12 . The film of  claim 1 , wherein all of the polymer layers in the stack of polymer layers have respective polymer compositions that are melt processable at a temperature of 204 degrees C. (400 degrees F.) or greater. 
     
     
         13 . The film of  claim 1 , wherein at least some of the polymer layers in the stack are oriented and have a birefringence of at least 0.05. 
     
     
         14 . The film of  claim 1 , wherein none of the polymer layers in the stack are pressure sensitive adhesives. 
     
     
         15 . The film of  claim 14 , wherein none of the polymer layers in the stack are adhesives. 
     
     
         16 . The film of  claim 1 , wherein each of the layer packets in the stack has a thickness of no more than 2 mils (50 microns). 
     
     
         17 . The film of  claim 1 , wherein the polymer layers are organized into at least N layer packets, where N is at least 5. 
     
     
         18 . The film of  claim 17 , wherein N is at least 10, and wherein the film has an overall thickness of no more than 15 mils (380 microns). 
     
     
         19 . The film of  claim 17 , wherein at least N−1 of the layer packets have a same number M of the polymer layers, wherein M is at least 3. 
     
     
         20 . The film of  claim 19 , wherein the M polymer layers are arranged in a sequence that is the same for the N−1 layer packets. 
     
     
         21 . The film of  claim 1 , wherein the attachment of the backmost polymer layer to the frontmost polymer layer is characterized by a peel force in a range from 2 to 100 grams per inch (0.8 to 38.6 N/m). 
     
     
         22 . The film of  claim 1 , wherein the attachment of the backmost polymer layer to the frontmost polymer layer is characterized by a first peel force, and wherein the attachment of the backmost polymer layer to the interior polymer layer is characterized by a second peel force, and wherein the second peel force is at least two times the first peel force. 
     
     
         23 . The film of  claim 22 , wherein the second peel force is at least three times the first peel force. 
     
     
         24 . The film of  claim 1 , wherein the attachment of the backmost polymer layer to the frontmost polymer layer is characterized by a first peel force, and wherein the attachment of the frontmost polymer layer to the interior polymer layer is characterized by a third peel force, and wherein the third peel force is at least two times the first peel force. 
     
     
         25 . The film of  claim 24 , wherein the third peel force is at least three times the first peel force.