Successively peelable coextruded polymer film with extended uv stability

Abstract

Multilayered polymer films are configured so that successive constituent layer packets can be delaminated in continuous sheet form from the remaining film. The films are compatible with known coextrusion manufacturing techniques, and can be made without adhesive layers between layer packets that are tailored to be individually peelable from the film. Instead, combinations of polymer compositions are used to allow non-adhesive polymer layers to be combined such that irreversible delamination of the film is likely to occur at interfaces between layer packet pairs. Some polymer layers, including at least one embedded layer, may include an ultraviolet (UV) light stabilizer such as a UV absorber, antioxidant, or hindered amine light stabilizer (HALS), and these layers may be positioned at the front of each layer packet. After the UV-stabilized layer of one packet has been used, the packet can be peeled away to expose a new UV-stabilized layer of the next layer packet.

1 . A film comprising a stack of polymer layers, the polymer layers being organized into layer packets, each of the layer packets having at least two of the polymer layers;
 wherein attachment between adjacent layer packets is weak enough to permit the layer packets to be separately irreversibly delaminated from a remainder of the stack, and the stack is configured to promote such irreversible delamination between such layer packets;   wherein all of the polymer layers in the stack of polymer layers have respective polymer compositions that are coextrudable with each other; and   wherein at least one of the polymer layers in a plurality of the layer packets comprises one or more ultraviolet (UV) light stabilizer.   
     
     
         2 . The film of  claim 1 , wherein at least one of the polymer layers in each of the layer packets comprises the one or more UV light stabilizer. 
     
     
         3 . The film of  claim 2 , wherein the one or more UV light stabilizer includes a first UV light stabilizer, and wherein the at least one polymer layer in each layer packet that comprises the one or more UV light stabilizer comprises the first UV light stabilizer. 
     
     
         4 . The film of  claim 2 , wherein for each layer packet in the stack, the at least one polymer layer comprising the one or more UV light stabilizer is disposed at a front of such layer packet. 
     
     
         5 . The film of  claim 2 , wherein each layer packet in the stack further includes at least one polymer layer that comprises substantially no UV light stabilizer. 
     
     
         6 . The film of  claim 2 , wherein each layer packet has only one polymer layer that comprises the one or more UV light stabilizer. 
     
     
         7 . The film of  claim 1 , wherein the one or more UV light stabilizer comprises a UV absorber. 
     
     
         8 . The film of  claim 1 , wherein the one or more UV light stabilizer comprises an antioxidant. 
     
     
         9 . The film of  claim 1 , wherein the one or more UV light stabilizer comprises a hindered amine light stabilizer (HALS). 
     
     
         10 . The film of  claim 1 , wherein an attachment between any two adjacent layer packets is characterized by a peel force in a range from 2 to 100 grams per inch (0.8 to 38.6 N/m). 
     
     
         11 . The film of  claim 1 , wherein the stack is configured with access tabs that provide access to interfaces between adjacent layer packets. 
     
     
         12 . The film of  claim 1 , wherein the polymer layers are arranged in a repeating AB sequence. 
     
     
         13 . The film of  claim 1 , wherein the polymer layers are arranged in a repeating ABC sequence. 
     
     
         14 . The film of  claim 1 , wherein the stack is configured such that for every pair of adjacent layer packets in the stack, attachment between the layer packets is weaker than attachment between the polymer layers within the layer packets, such that irreversible delamination tends to occur between the layer packets rather than within the layer packets. 
     
     
         15 . The film of  claim 14 , wherein an attachment between adjacent layer packets is characterized by a first peel force, and wherein a weakest attachment of polymer layers within each layer packet is characterized by a second peel force, and wherein the second peel force is at least two times the first peel force. 
     
     
         16 . The film of  claim 14 , wherein the polymer layers are arranged in a repeating ABC sequence. 
     
     
         17 . The film of  claim 16 , wherein attachment between polymer layers A and C is weaker than attachment between polymer layers A and B, and is also weaker than attachment between polymer layers B and C. 
     
     
         18 . 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 melt temperature of 204 degrees C. (400 degrees F.) or greater. 
     
     
         19 . 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. 
     
     
         20 . The film of  claim 1 , wherein none of the polymer layers that are disposed at interfaces of adjacent layer packets are tacky at room temperature. 
     
     
         21 . 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). 
     
     
         22 . The film of  claim 1 , wherein the polymer layers are organized into at least N layer packets, where N is at least 5. 
     
     
         23 . The film of  claim 22 , wherein N is at least 10, and wherein the film has an overall thickness of no more than 15 mils (380 microns). 
     
     
         24 . The film of  claim 1 , wherein the stack of polymer layers has an average transmission over visible wavelengths of at least 80% and an optical haze of less than 15%. 
     
     
         25 . The film of  claim 24 , wherein the stack of polymer layers has an optical haze of less than 8%. 
     
     
         26 . A method, comprising:
 providing a film comprising a stack of polymer layers, the polymer layers being organized into layer packets with each layer packet having at least two of the polymer layers, the stack being configured to promote irreversible delamination between such layer packets, all of the polymer layers in the stack having respective polymer compositions that are coextrudable with each other;   exposing the film to a sufficient amount of ultraviolet (UV) light such that the film exhibits optical degradation due to the UV light exposure, the optical degradation being primarily associated with a first one of the layer packets; and   delaminating the first layer packet from a remainder of the stack.   
     
     
         27 . The method of  claim 26 , wherein at least one of the polymer layers in a plurality of the layer packets comprises one or more UV light stabilizer. 
     
     
         28 . The method of  claim 26 , wherein the optical degradation comprises an increase in optical haze of 3% or more, and/or an increase in CIE b* color coordinate of 2 or more.