Thermoplastic multi-layer packaging film and bags made therefrom

Abstract

A thermoplastic, multi-layer packaging film is disclosed which comprises at least 5 layers in which one surface layer is a heat sealing layer and one of the internal layers is a barrier layer. The heat sealing surface layer comprises a copolymer of ethylene and an alpha-olefin having 4 to 8 carbon atoms per molecule and said copolymer comprises 90% to 75% ethylene and 10% to 25% alpha-olefin having 4 to 8 carbon molecules and a density of less than 915 kg/m 2 . The heat sealing layer may also comprise a blend of the aformentioned copolymer with an ethylene/vinyl-acetate copolymer or an ethylene/butyl-acrylate copolymer. The film can be oriented to be heat shrinkable and can be formed into bags by heat sealing portions of the sealing surfaces together. The heat seals have superior cold strength and minimize seal failure when the bags are loaded with relatively heavy products.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A multi-layer thermoplastic packaging film having improved heat shrink and cold seal properties, said film comprising: (a) a first surface layer which is a heat sealing surface, said layer comprising: (1) a copolymer of ethylene and an alpha-olefin having 4 to 8 carbon atoms per molecule; and,   (2) said copolymer comprising 90% to 75% ethylene and 10% to 25% alpha-olefin having 4 to 8 carbon molecules and a density of less than 915 kg/m 3  ;     (b) a second surface layer, said layer comprising a polymer selected from the group consisting of amide polymers, ethylene/vinyl-acetate copolymers, the copolymer of the first layer, and ionomers;   (c) a first core layer comprising an ethylene/vinyl-acetate copolymer;   (d) a second core or barrier layer comprising a polymer selected from the group consisting of copolymers of vinylidene chloride and hydrolyzed copolymers of ethylene/vinyl-acetate;   (e) said core layers being internal film layers positioned between said first and second surface layers;   (f) at least one adhesive layer to promote adhesion of the barrier layer to another layer; and   (g) said film comprising at least five layers.   
     
     
       2. The film of claim 1 wherein the first surface layer is cross-linked. 
     
     
       3. The film of claim 1 wherein the first surface layer comprises a blend of the copolymer defined in (a) (1) and (2) with a copolymer selected from the group consisting of copolymers of ethylene/vinyl-acetate and copolymers of ethylene/butyl-acrylate. 
     
     
       4. The film of claim 1 wherein the second core or barrier layer comprises a vinylidene chloride copolymer and the second surface layer comprises a polyamide. 
     
     
       5. A bag formed from the film of claim 1. .Iadd. 
     
     
       6.  A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties, said film comprising: (a) a first surface layer which is heat-sealing, said first surface layer comprising a blend of (i) a linear copolymer of 90% to 75% ethylene and 10% to 25% of an alpha-olefin having 4 to 8 carbon atoms per molecule, said linear copolymer having a density of less than 915 kg/m 3  and at least 906 kg/m 3 , and (ii) up to 50% by weight, based on the total weight of the first surface layer, of a polymer compatible with said linear copolymer selected from the group consisting of linear polyethylene copolymers having a density above 915 kg/m 3 , low density polyethylene, ethylene vinylacetate, acid-modified ethylene vinylacetate, polypropylene, copolymers of ethylene and propylene, ionomeric polymers and ethylene/alkylacrylate copolymers wherein the alkyl moiety has 1 to 8 carbon atoms; and   (b) a second surface layer comprising a polymer material selected from the group consisting of said linear copolymer of the first surface layer, ethylene-vinylacetate copolymers, polyamides and ionomeric resins. .Iaddend. .Iadd.7. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 6, said film further comprising:   (c) a first internal layer between said first surface layer and said second surface layer, said first internal layer comprising a core or barrier material. .Iaddend. .Iadd.8. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 7, said film further comprising:   (d) a second internal layer between said first internal layer and said second surface polymer layer, said second internal layer comprising a core or barrier material. .Iaddend. .Iadd.9. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 8, wherein said core or barrier materials of said first and second internal layers are selected from the group consisting of copolymers of ethylene vinylacetate and polyvinylidene chloride copolymers. .Iaddend. .Iadd.10. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 8, further comprising:   (e) an adhesive layer between said first surface layer and said second surface layer. .Iaddend. .Iadd.11. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 10, wherein said at least one adhesive layer contains acid-modified ethylene vinylacetate. .Iaddend. .Iadd.12. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 8, wherein the core or barrier material of said first internal layer contains a copolymer of ethylene vinylacetate and the core or barrier material of said second internal layer contains polyvinylidene chloride. .Iaddend. .Iadd.13. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 12, further comprising:   (e) an adhesive layer between said first internal layer and said second internal layer; and   (f) an adhesive layer between said second internal layer and said second surface layer. .Iaddend. .Iadd.14. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 13, wherein said adhesive layers contain acid-modified ethylene vinylacetate. .Iaddend. .Iadd.15. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 7, wherein said first surface layer is cross-linked. .Iaddend. .Iadd.16. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 6, wherein in the heat-sealing blend, said polymer compatible with the linear copolymer is selected from the group consisting of copolymers of ethylene vinylacetate, acid-modified ethylene vinylacetate, copolymers of ethylene and propylene, and ethylene-butylacrylate. .Iaddend. .Iadd.17. A bag formed from the film according to claim 16. .Iaddend. .Iadd.18. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties, said film comprising:   (a) an inner layer comprising a heat-sealing blend of (i) a linear copolymer of ethylene and x to y % by weight, based on the linear copolymer, of an alpha-olefin having 4 to 8 carbon atoms per molecule, wherein x=0.5n C  +8 and y=1.25n C  +15 with n C  being the number of carbon atoms in the alpha-olefin, said linear copolymer having a density of less than 915 kg/m 3  and at least 906 kg/m 3 , and (ii) up to 50% by weight, based on the total weight of the heat-sealing inner layer, of a polymer compatible with said linear copolymer selected from the group consisting of linear polyethylene copolymers having a density above 915 kg/m 3 , low density polyethylene, ethylene vinylacetate, acid modified ethylene vinylacetate, polypropylene, copolymers of ethylene and propylene, ionomeric polymers and ethylene/alkylacrylate copolymers wherein the alkyl moiety has 1 to 8 carbon atoms; and   (b) an outer layer comprising a polymer material selected from the group consisting of said linear copolymer of the inner layer, ethylene-vinylacetate copolymers, polyamides and ionomeric resins. .Iaddend. .Iadd.19. A multi-layer, heat-shrinkable thermoplastic packaging film having excellent heat shrink and cold seal properties as recited in claim 18, wherein in the heat-sealing blend, said polymer compatible with the linear copolymer is selected from the group consisting of copolymers of ethylene vinylacetate, acid-modified ethylene vinylacetate, copolymers of ethylene and propylene, and ethylene-butylacrylate. .Iaddend. .Iadd.20.   
     
     
        A bag formed from the film according to claim 18. .Iaddend. .Iadd.21.  A thermoplastic multilayer packaging film having superior heat shrink and cold seal properties comprising at least an outer polymer layer and an inner heat sealing layer, said heat sealing layer comprising a linear copolymer of ethylene and x to y % by weight, based on the copolymer, of an alpha-olefin with 4 to 8 carbon atoms per molecule, wherein x=0.5nc+8 and y=1.25nc+15 with nc being the number of carbon atoms in the alpha-olefin, said copolymer having a density of less than 0.915 g/cc and at least 0.906 g/cm 3 . .Iaddend.