PACKAGING FILMS FOR ULTRASONIC SEALING APPLICATIONS
The present invention is directed to delamination-resistant ultrasonic sealant films for packaging food, medical and/or pharmaceutical products having seals formed by ultrasonic sealing methods. The films according to the present invention have at least a sealant layer comprising a first propylene-ethylene copolymer and a second propylene-ethylene copolymer, a tie layer comprising at least one of the first or second propylene-ethylene copolymers of the sealant layer, and a barrier layer adjacent to the tie layer. The films according to the present invention may be used in aseptic, hot-fill and/or retort packaging applications.
1 . A delamination-resistant ultrasonic sealant film comprising:
a sealant layer comprising a first propylene-ethylene copolymer and a second propylene-ethylene copolymer;
a tie layer comprising at least one of the first or second propylene-ethylene copolymers of the sealant layer; and
a barrier layer contacting the tie layer and comprising a material selected from the groups consisting of polyamide, ethylene vinyl alcohol copolymer, polyvinyl chloride, polyvinylidene chloride, glass, thermoplastic polyurethane, polyethylene terephthalate copolymer and blends thereof.
2 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the first propylene-ethylene copolymer has a flexural modulus at 0.05 in/min (0.127 cm/min), 1% secant of between 2,000 and 100,000 psi as measured in accordance with ASTM D-790 test method.
3 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the first propylene-ethylene copolymer is present in an amount of between 10 and 90% by weight relative to the total weight of the sealant layer.
4 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the first propylene-ethylene copolymer is present in an amount of between 10 and 45% by weight relative to the total weight of the sealant layer.
5 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the second propylene-ethylene copolymer has a flexural modulus at 0.05 in/min (0.127 cm/min), 1% secant of between 101,000 and 300,000 psi as measured in accordance with ASTM D-790 test method.
6 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the second propylene-ethylene copolymer is present in an amount of between 10 and 90% by weight relative to the total weight of the sealant layer.
7 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the second propylene-ethylene copolymer is present in an amount of between 25 and 65% by weight relative to the total weight of the sealant layer.
8 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the sealant layer further comprises a first polyethylene copolymer and/or a second polyethylene copolymer.
9 . The delamination-resistant ultrasonic sealant film according to claim 8 , wherein the first polyethylene copolymer is a polyethylene block copolymer.
10 . The delamination-resistant ultrasonic sealant film according to claim 9 , wherein the polyethylene block copolymer has a tensile modulus at 100% secant of between 100 and 500 psi as measured in accordance with ASTM D-638 test method.
11 . The delamination-resistant ultrasonic sealant film according to claim 8 , wherein the second polyethylene copolymer is a metallocene ethylene-hexene copolymer.
12 . The delamination-resistant ultrasonic sealant film according to claim 8 , wherein each of the first and/or second polyethylene copolymers is present in an amount of between 1 and 35% by weight relative to the total weight of the sealant layer.
13 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the tie layer further comprises an anhydride modified polyethylene and an unmodified polyethylene.
14 . The delamination-resistant ultrasonic sealant film according to claim 13 , wherein the unmodified polyethylene is a high density polyethylene or an ethylene norbornene copolymer.
15 . The delamination-resistant ultrasonic sealant film according to claim 13 , wherein the anhydride modified polyolefin is a maleic anhydride grafted linear low density polyethylene with a level of maleic anhydride grafted onto the linear low density polyethylene of greater than 0.5% by weight relative to the total weight of the copolymer.
16 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the tie layer has a thickness of between 15 and 40% relative to the total thickness of the film.
17 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the barrier layer is an oxygen barrier and consists essentially of polyamide.
18 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the tie layer is adjacent to the sealant layer.
19 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the film exhibits no delamination between the tie and barrier layers after the sealant layer is sealed to itself or a polyolefin substrate by ultrasonic energy to form a package.
20 . The delamination-resistant ultrasonic sealant film according to claim 1 , wherein the film is suitable for hot-fill and/or retort packaging applications.