Freezable/microwavable packaging films and venting packages
View Patent ↗Multilayer freezable/microwaveable films and packages having both low temperature resistance to withstand subzero freezer storage temperatures and high temperature resistance to withstand microwave cooking temperatures. The freezable/microwaveable films and packages include, for example, a film having at least three coextruded layers comprising an inner heat sealable layer, at least one core layer adjacent to the heat sealable layer, and an outer skin layer adjacent the core layer opposite the heat sealable layer. Preferably, the films and packages further include an outer protective layer laminated to the outer skin layer. The freezable/microwaveable packages can include a venting system, such as vent slits or a vent valve in the package, or vents in at least one seal of the package, to facilitate microwave heating or cooking of the package contents.
1. A multilayer freezable, microwaveable film comprising:
(a) a polyolefin film comprising an inner heat sealable layer, at least one core layer adjacent to the heat sealable layer, and an outer skin layer adjacent to the at least one core layer, opposite the heat sealable layer;
wherein the inner heat sealable layer comprises at least one polypropylene/alpha-olefin copolymer having a melting point of at least about 105° C. and a melt flow rate of about 0.5 g/10 min. to about 45 g/10 min. at about 230° C.;
wherein the at least one core layer comprises a polymeric material having a melting point of at least 105° C.; and
wherein the outer skin layer comprises at least one polypropylene/alpha-olefin copolymer having a melting point of at least about 120° C.; and
(b) at least one outer protective layer bonded to the outer skin layer, the outer protective layer being formed from a heat resistant polymeric material;
wherein the multilayer freezable, microwaveable film can be exposed to a temperature in the range of about −20° C. to about 0° C. without fracturing, and wherein the multilayer freezable, microwaveable film is temperature resistant at temperatures of about 150° C.
2. The multilayer freezable, microwaveable film of claim 1 , wherein the outer skin layer comprises a propylene/ethylene copolymer, a propylene/butene copolymer, a propylene/hexene copolymer, a propylene/octene copolymer, a mixture thereof, or a blend thereof.
3. The multilayer freezable, microwaveable film of claim 1 , wherein the outer skin layer comprises at least one propylene/ethylene copolymer comprising from about 1% to about 8% by weight of an ethylene comonomer, and wherein the outer skin layer has a melt flow rate from about 0.5 g/10 min. to about 45 g/10 min. at about 230° C.
4. The multilayer freezable, microwaveable film of claim 1 , wherein the heat sealable layer comprises an ethylene comonomer in an amount of about 1% to about 8% by weight of the copolymer.
5. The multilayer freezable, microwaveable film of claim 1 , wherein the heat sealable layer comprises a blend of polypropylene/alpha-olefin copolymers.
6. The multilayer freezable, microwaveable film of claim 1 , wherein the core layer comprises a homopolymer polypropylene, a high density polyethylene, a blend thereof, or a mixture thereof.
7. The multilayer freezable, microwaveable film of claim 6 , wherein the homopolymer polypropylene has a melt flow rate of about 0.5 g/10 min. to about 25 g/10 min. at about 230° C.
8. The multilayer freezable, microwaveable film of claim 1 , wherein the outer protective layer is a polyethylene terephthalate film, a nylon film, a biaxially oriented polypropylene film, or a biaxially oriented propylene/ethylene copolymer film.
9. The multilayer freezable, microwaveable film of claim 1 , wherein the outer protective layer is bonded to the outer skin layer by an adhesive, by heat bonding, or by ultrasonic welding.
10. The multilayer freezable, microwaveable film of claim 1 , wherein the polyolefin film is a coextruded blown film, a coextruded cast film, or a laminated film.
11. A multilayer freezable, microwaveable package for packaging a frozen, microwaveable food product comprising:
(a) a polyolefin film comprising an inner heat sealable layer, at least one core layer adjacent to the heat sealable layer, and an outer skin layer adjacent to the core layer opposite the heat sealable layer;
wherein the heat sealable layer comprises at least one polypropylene/alpha-olefin copolymer having a melting point of at least about 105° C. and a melt flow rate of about 0.5 g/10 min. to about 45 g/10 min. at 230° C.;
wherein the at least one core layer comprises a polymeric material having a melting point of at least 105° C.; and
wherein the outer skin layer comprises at least one polypropylene/alpha-olefin copolymer having a melting point of at least about 120° C.; and
(b) an outer protective layer bonded to the outer skin layer, the outer protective layer being formed from a heat resistant polymeric material;
wherein parts (a) and (b) form a multilayer freezable, microwaveable package;
wherein the freezable, microwaveable film can be exposed to a temperature of from about 0° C. to about −20° C. without fracturing;
wherein the freezable, microwaveable film is temperature resistant at temperatures of about 150° C.; and
wherein the freezable, microwaveable package is a pouch-shaped package that is not closely fitted about the food product and allows the frozen product to be heated in a microwave oven without the package melting or bursting.