Heat sealable and peelable film
View Patent ↗A multilayer, heat-sealable film includes at least a first outer layer and a second, heat-sealable inner layer having a first surface adhered to the outer layer and a second, opposed surface adapted to be heat sealed to and peeled from another surface. The first outer layer comprises a mixture of a polypropylene and a second polymer immiscible in the polypropylene, with the polypropylene constituting over 50% by weight of the mixture. The second layer is free of polybutylene and is formed predominantly of polymers from the group consisting of propylene-ethylene copolymers, ethylene-propylene-butene-1 terpolymers and propylene-butene-1 copolymers, wherein the propylene in the copolymers and terpolymers constitutes over 50%, by weight, of such copolymers and terpolymers. The films have a peel strength of less than 250 g/in. with peel separation taking place at the interface between the second layer and the first outer layer and/or through the first outer layer. The films of this invention are stand-alone films that can be employed by themselves and/or can be laminated to one or more additional outer films to form a composite film structure.
1. A multilayer, heat-sealable film including at least a first layer and a second heat-sealable layer, said second layer having a first surface adhered to said first layer and a second, opposed surface intended to be heat sealed to another surface, said first layer comprising a mixture of a polypropylene and a second polymer immiscible in said polypropylene, to provide a weakened interface between the first layer and the second heat-sealable layer, said polypropylene constituting over 50% by weight of the mixture, said second layer being free of polybutylene and being formed predominantly of polymers selected from the group consisting of propylene-ethylene copolymers, ethylene-propylene-butene-1 terpolymers and propylene-butene-1 copolymers wherein the propylene in the copolymers and terpolymers constitute over 50%, by weight, of such copolymers and terpolymers, said film with said second opposed surface of said heat-sealable layer heat sealed to said another surface having a peel strength of less than 250 g/in. with peel separation taking place at the interface between the second layer and the first layer and/or through said first layer, said peel strength being less than the peel strength of the second, opposed surface of said heat-sealable layer to said another surface to thereby maintain the seal integrity between said second heat-sealable layer and said another surface.
2. The multilayer, heat-sealable film according to claim 1 , wherein said second polymer that is immiscible in said polypropylene is selected from the group consisting of low density polyethylene, linear low density polyethylene, medium density polyethylene and a polar modified polyethylene.
3. The multilayer, heat-sealable film according to claim 1 , wherein said second polymer that is immiscible in said polypropylene is a low density polyethylene.
4. The multilayer, heat-sealable film of claim 1 , wherein said second polymer that is immiscible in said polypropylene is a medium density polyethylene polymer.
5. The multilayer, heat-sealable film of claim 1 , wherein said first layer is an internal core layer, further including a functional skin layer on the side of the core layer remote from the side adhered to the second heat-sealable layer.
6. The multilayer, heat-sealable film of claim 5 , wherein said second heat-sealable layer and said functional skin layer are thinner than said core layer.
7. The multilayer, heat-sealable film of claim 1 , wherein said second heat-sealable layer is formed predominantly of a propylene-ethylene copolymer including no more than 10%, by weight, of ethylene therein.
8. The multilayer, heat sealable film of claim 1 , wherein said second heat-sealable layer is formed predominantly of a propylene-ethylene copolymer including no more than 6%, by weight, of ethylene therein.
9. The multilayer, heat-sealable film of claim 1 , wherein said second heat-sealable layer is formed predominantly of the propylene-ethylene-butene-1 terpolymer.
10. The multilayer, heat-sealable film of claim 1 , wherein said second polymer that is immiscible in said polypropylene is present in the range of approximately 4% to approximately 20%, by weight, based upon the weight of the polymers in said first layer.
11. The multilayer, heat-sealable film of claim 1 , wherein said second polymer that is immiscible in said polypropylene is present in the range of approximately 4% to approximately 16%, by weight, based upon the weight of the polymers in said first layer.
12. The multilayer, heat-sealable film of claim 1 , wherein said second polymer that is immiscible in said polypropylene is present in an amount no greater than 12% by weight of the polymers in said first layer.
13. The multilayer, heat-sealable film of claim 1 , said film having the peel strength of less than 225 g/in.
14. The multilayer, heat-sealable film of claim 1 , said film having the peel strength of less than 215 g/in.
15. The multilayer, heat-sealable film of claim 1 , said film being a stand-alone film.
16. The multilayer, heat-sealable film of claim 1 , said film being laminated to another plastic film to form a composite packaging film.
17. The composite packaging film of claim 16 , said another plastic film being a multilayer, biaxially oriented polyolefin film.
18. The composite packaging film of claim 16 , said another plastic film being a multilayer, biaxially oriented metallized film.