Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Reexamination Certificate
2002-11-14
2004-11-09
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
C264S173150, C264S173160, C264S288400
Reexamination Certificate
active
06814913
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to polyester tray packages having lidding films which are directly sealable to the polyester tray and which contain glycol-modified copolyester sealant layers. More specifically, the present invention is directed to polyethylene terephthalate (PET) tray packages having lidding films which include glycol-modified polyethyelene terephthalate sealant layers.
BACKGROUND OF THE INVENTION
Polyethylene terephthalate (PET) trays are employed in packaging a wide variety of products. PET trays are especially preferred for use in packaging various food products because of the polymers superior mechanical properties, transparency, low extractability by contents and good flavor retention of contents. PET trays may be foamed or non-foamed, depending on the required end-use application, and are preferred over foamed and non-foamed polystyrene trays because of their recyclability.
However, PET has a very high melting point of 260° C. which makes heat sealing difficult. That is, readily available olefin-based lidding films cannot be heat sealed to PET trays because such films typically have a sealing window with an upper limit well below 260° C. and will burn at sealing temperatures above the upper end of that range. Some PET films can be sealed to PET trays at about 260° C. but such an elevated heat sealing operation is not commercially practicable in a typical packaging facility.
Monolayer films which consist of glycol-modified polyethylene terephthalate have been found to provide adequate seals to foamed and nonfoamed PET trays. Such glycol-modified PET films can be sealed to PET trays in a sealing window range of from about 115° C. to about 210° C. However, such monolayer films do not provide gas barrier properties which are desirable for certain end-use applications
SUMMARY OF THE INVENTION
In a first aspect, the present invention is directed to a package which includes a polyester support member, a product contained on the support member, and a multilayer lidding film containing the product and sealed to the periphery of the support member, the lidding film including a sealant layer of a polyester copolymer having greater than about 50% by mole of glycol polymerization units.
In a second aspect, the present invention is directed to a package which includes a polyester support member, a product contained on the support member, and a lidding film containing the product and sealed to the periphery of the support member, the lidding film including a sealant layer of a polyester copolymer having greater than about 50% by mole of glycol polymerization units and at least one further polymeric component.
In a third aspect, the present invention is directed to a method for making a package which includes the steps of coextruding a multilayer lidding film which includes a sealant layer of a polyester copolymer having greater than about 50% by mole of glycol polymerization units, providing a polyester support member, placing a product on the support member, extending the lidding film above the support member and product with the sealant layer being immediately above and adjacent to the support member and the product, and sealing the lidding film to the support member such that the product is enclosed by the film and such that the sealant layer is directly sealed to periphery of the support member.
In a fourth aspect, the present invention is directed to a method for making a package which includes the steps of extruding a multilayer lidding film which includes a sealant layer of a blend of a polyester copolymer having greater than about 50% by mole of glycol polymerization units and at least one further polymeric component, providing a polyester support member, placing a product on the support member, extending the lidding film above the support member and product with the sealant layer being immediately above and adjacent to the support member and the product, and sealing the lidding film to the support member such that the product is enclosed by the film and such that the sealant layer is directly sealed to periphery of the support member.
Definitions
As used herein, the phrase “abuse layer” refers to an outer film layer and/or an inner film layer, so long as the film layer serves to resist abrasion, puncture, and other potential causes of reduction of package integrity, as well as potential causes of reduction of package appearance quality. Abuse layers can comprise any polymer, so long as the polymer contributes to achieving an integrity goal and/or an appearance goal.
As used herein, “oxygen transmission rate”, also referred to as “OTR” and “oxygen permeability”, is measured according to ASTM D 3985, a test known to those of skill in the film art.
As used herein, the term “lamination”, and the phrase “laminated film”, refer to the process, and resulting product, made by bonding together two or more layers of film or other materials Lamination can be accomplished by joining layers with adhesives, joining with heat and pressure, and even spread coating and extrusion coating. The term laminate is also inclusive of coextruded multilayer films comprising one or more tie layers.
As used herein, the term “oriented” refers to a polymer-containing material which has been stretched at the softening temperature but below the melting temperature, followed by being “set” in the stretched configuration by cooling the material while substantially retaining the stretched dimensions. Upon subsequently heating unrestrained, unannealed, oriented polymer-containing material to its orientation temperature, heat shrinkage is produced almost to the original unstretched, i.e., pre-oriented dimensions
As used herein, the phrases hot blown or hot blowing refer an extrusion process as well as a characteristic of the resultant film. In a hot blown process, molten plastic material is forced through an annular die and is immediately inflated to a diameter typically two to four times that of the melt exiting the die. Hot blown films do possess orientation; but since the films are oriented at or very near to the melt temperature they will only shrink when heated to that high temperature which is much higher than the temperature required to shrink conventional oriented films. For this reason, hot blown films do not exhibit shrink within the temperature range useful for food packaging since the film must be heated to nearly melting in order to observe any appreciable degree of shrinkage. Hot blown films may be referred to as melt state oriented films.
As used herein, the term “comonomer” refers to a monomer which is copolymerized with at least one different monomer in a copolymerization reaction, the result of which is a copolymer.
As used herein, the term “polymer” refers to the product of a polymerization reaction, and is inclusive of homopolymers, copolymers, terpolymers, etc. In general, the layers of a film can consist essentially of a single polymer, or can have still additional polymers blended therewith.
As used herein, the term “homopolymer” is used with reference to a polymer resulting from the polymerization of a single monomer, i.e, a polymer consisting essentially of a single type of repeating unit.
As used herein, the term “copolymer” refers to polymers formed by the polymerization reaction of at least two different monomers. For example, the term “copolymer” includes the copolymerization reaction product of ethylene and an &agr;-olefin, such as 1-hexene. However, the term “copolymer” is also inclusive of, for example, the copolymerization of a mixture of ethylene, propylene, 1-hexene, and 1-octene
As used herein, the term “polymerization” is inclusive of homopolymerizations, copolymerizations, terpolymerizations, etc, and includes all types of copolymerizations such as random, graft, block, etc. In general, the polymers, in the films used in accordance with the present invention, can be prepared in accordance with any suitable catalytic polymerization process, including solution polymerization, slurry polymerization, gas phase polymerization, and high pre
Cryovac Inc.
Eashoo Mark
Quatt Mark B.
LandOfFree
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