Gas-barrier shrink films and their use in deep-drawing applications
A multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film includes a first outer heat-sealable layer, an inner gas-barrier layer, and a second outer abuse resistant layer, the film containing at least 28%, by weight of the film, of polystyrene polymer, such as a high styrene styrene-butadiene block copolymer. The polystyrene copolymer can be present in the second outer abuse-resistant layer, and/or in one or more inner layers positioned between the first outer heat-sealable layer and the inner gas-barrier layer, and/or in one or more inner layers positioned between the gas-barrier layer and the second outer abuse layer. The film of the invention is particularly suitable to be deep-drawn to form a flexible container in a packaging process where the final vacuum lidded package is heat-shrunk.
1. A multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film comprising:
a) a first outer heat-sealable layer;
b) an inner gas-barrier layer; and
c) a second outer abuse resistant layer;
said film being characterized in that it contains at least 28%, by weight of the film, of polystyrene polymer,
wherein the film comprises one or more inner layers positioned between the inner gas-barrier layer and the second outer abuse resistant layer;
wherein the polystyrene polymer is present in
i) the second outer abuse resistant layer, or
ii) at least one inner layer positioned between the inner gas-barrier layer and the second outer abuse resistant layer, or
iii) both the second outer abuse resistant layer and at least one inner layer positioned between the inner gas-barrier layer and the second outer abuse resistant layer;
wherein at least 50 wt. % of the total amount of polystyrene polymer in the film is in the form of a styrene-butadiene copolymer.
2. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 1 wherein the styrene-butadiene copolymer comprises between 55 and 95 wt. % of a styrene component, based on the weight of the copolymer.
3. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 1 wherein at least 60 wt. % of the total amount of polystyrene polymer in the film is in the form of a styrene-butadiene copolymer.
4. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 1 wherein the inner gas-barrier layer is a PVDC layer.
5. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 1 wherein the first outer heat-sealable layer comprises one or more materials selected from the group consisting of one or more of polyethylenes having a den- sity of from about 0.900 g/cm 3 to about 0.950 g/cm 3 , and heterogeneous or homogeneous ethylene-α-olefin copolymer having a density of from about 0.880 g/cm 3 to about 0.945 g/cm 3 .
6. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 1 wherein the second outer abuse resistant layer comprises one or more materials selected from the group consisting of one or more polyolefins, modified polyolefins, polyesters/copolyesters, polyamides/ copolyamides, and polystyrene polymers.
7. A multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film comprising:
a) a first outer heat-sealable layer;
b) an inner gas-barrier layer; and
c) a second outer abuse resistant layer;
said film being characterized in that it contains at least 28%, by weight of the film, of polystyrene polymer,
wherein the film comprises one or more inner layers positioned between the first outer heat-sealable layer and the inner gas-barrier layer;
wherein the polystyrene polymer is present in
i) the second outer abuse resistant layer, or
ii) at least one inner layer positioned between the first outer heat-sealable layer and the inner gas-barrier layer, or
iii) both the second outer abuse resistant layer and at least one inner layer positioned between the first outer heat-sealable layer and the inner gas-barrier layer;
wherein at least 50 wt.% of the total amount of polystyrene polymer in the film is in the form of a styrene-butadiene copolymer.
8. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 7 wherein the styrene-butadiene copolymer comprises between 55 and 95 wt. % of a styrene component, based on the weight of the copolymer.
9. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 7 wherein at least 60 wt. % of the total amount of polystyrene polymer of the film is in the form of a styrene-butadiene copolymer.
10. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 7 wherein the inner gas-barrier layer is a PVDC layer.
11. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 7 wherein the first outer heat-sealable layer comprises one or more materials selected from the group consisting of one or more of polyethylenes having a density of from about 0.900 g/cm 3 to about 0.950 g/cm 3 , and heterogeneous or homogeneous ethylene-α-olefin copolymer having a density of from about 0.880 g/cm 3 to about 0.945 g/cm 3 .
12. The multi-layer, gas-barrier, biaxially oriented and heat-shrinkable film of claim 7 wherein the second outer abuse resistant layer comprises one or more materials selected from the group consisting of one or more polyolefins, modified polyolefins, polyesters/copolyesters, polyamides/ copolyamides, and polystyrene polymers.