CA1210712A - Paperboard package - Google Patents

Abstract

PAPERBOARD PACKAGE

Abstract A plastic coated paperboard covering is fusibly sealed to a flanged, plastic coated paperboard tray with an intermediate release coating between the cooperative, plastic coat seal surfaces for subsequent separation by peeling the covering away from the flanged tray.

Description

7~;2 PAPERBOARD PACKAGE
Background Of The Invention . . ~
Field Of The Invention .
The present invention relates to paperb~ard pac~a~ing of food products for retail distribution and marketing. More particularly, the present invention relates to peelable lid closures for flanged, ovenable board tray containers suitable for final food preparation in either microwave or conventional heating ovens.
Description Of The Prior Art Food products in various stages of preparation prior to consumption have been marketed at the retail level in small, single serving or setting quantities with aluminum or plastic coated paperboard trays. The tray dimensions are usually suitable for consumption of the food contents directly from the tray.
To cover an aluminum tray opening after placement of the food contents, a plastic coated paperboard lid is placed over an integral tray flange and flange material extending beyond the lid perimeter is crimped over onto the lid topside. Although this system functions well for aluminum tray applications, the incompatibility of aluminum trays with microwave ovens has diminished the utility of such trays, generally.
Food marketing/serving trays fabricated from ovenable paperboard, which is compatible with either micro-wave or conventional heating ovens, are also covered with plastic coated paperboard lids. However, in this case, the inner plastic coating of the lid is heat fused to the plastic liner coating of the tray along and around a continuous, ,07~

integral flange portion of the tray.
To open a heat sealed paperboard tray it is necessary to cut the paperboard lid around a perimeter within the tray side perimeter. Due to the stiffness and strength of the paperboard lid, such lid cutting oEten proves to be a deft operation.
Peel removable coverings formed from aluminum foil or paper coated with a weak bond, heat sealable film have also been used in combination with polystyrene or polypropylene tubs or cups for the individual service of liquid food products such as milk or cream.
Prior efforts to apply the peel removal tech-nique to paperboard lids on paperboard trays have been frustrated due to the tenacious bond between the polyester or polyethylene terephthalate ~PET) coatings applied to the paperboard substrate. When the film respective to the lid and tray flange are heat sealed together, the two films fuse to form a tough, integral layer which cannot subsequently be separated by peeling or stripping.
Forced peel failure occurs between one or the other of the two films and the paperboard fiber. A ragged and uncon-trolled tear results.
An object of the present invention, thereEore, is to provide a peelably removable paperboard closure for flanged, paperboard containers.
Another object of the present invention is to provide a peelably releasable coating for heat sealing respectively opposite faces of a paperboard covering to a paper~oard tray flange.

- 2 -~Z:a07~2 Summary These and other objects of the present invention are achieved by applying a release coating to either, the inner, plastic coated surface of a paperboard closure piece or to the plastic coated seal facc of a paperboard tray flange.
The release coating may be a polyester base resin in a toluene isopr~ylalcohol solvent having talc as a filler proportioned to fuse with an extruded PET coating of the paperboard substrate at 275 to 450F with a dwell time of 1 to 4 seconds under 20 to 80 p.s.i. pressure. The peel strength of the film seal should range between 800 to 1500 grams per inch of seal width.

Brief_Description Of The Drawin~
Relative to the two figures of the drawing wherein like reference charac~ers designate like or similar elements of the invention throughout:
Figure 1 is an isometric pictorial of lid and tray elements of a food container; and, Fi~ure 2 is a partially sectioned orthographic view of the tray flange and lid elements.

Description Of The Preferred Embodiment A paperboard food tray 10, and covering 20 are formed of 0.012 to 0.030 inch caliper paperboard substrate.
Prior to ~ray forming, the subs~rate sheet s~ock is eXtrilsion coated with an approximately 0.00125 inch caliper coat-ing of PET for an approximately 26 lb./3000 ft 2 coverage.

17~2 Alternatively, polyethylene or polypropelene rnay be used as the extrusion applied plastic coating.
Physical characteristics o~ the lra~ 10 includes a bottom 11, sloped side walls 12 and a 1/4 to

3/8 inch wide flange 13 integrally formed from the same PET coated paperboard sheet blank. The PET coated side of the blank is oriented to form the inside surface of the tray and the upper face of the flange 13.
Similarly, the PET coated face of the covering 20 is oriented to the inside surface so that the two plastic coated paperboard surfaces are oppositely facing each other around the upper face of the flange 13.
Applied to either, the inside coated surface of the closure or to the upper surface of the flange 13 is an additional, peel film 30. Whether applied to the lid 20 or the tray flange 13, the coating may be applied uni-formly over the full inside surface area or selectively applied to the flange mating area.
One example of a suitable peel coatlmaterial is the polyester base resin such as ADCOTE 33R2B marketed by the Morton Chemical Co. of 2 North Riverside Plaza, Chicago, Illinois, as a ~oluene isopropyl alcohol solvent system mixed with talc as a filler. This alcohol solvent system is applied to the plastic coated paperboard substrate at the rate of 2 to 3 pounds per 3000 ft.3 of surface area.
Alternatively, an aqueous base peel coat system may be formulated with the polyester base resin ADCOTE*
37R345 marketed by Morton Chemical Co. and applied to the substrate surface at the rate of approximately 3 pounds 3~
* Trade Mark ~2~ 71Z

per 3000 Et. of surface area.
In practice, a peel coated lid 20 is fused to the tray flange 13 with a 275 to 450 F pressing iron applied at 20 to 80 psi pressure for a dwell time of 1 to

4 seconds. This fused seal should release at the interface between the closure 20 and flange 13 respective PET coatings under an applied peel stress of 800 to 1500 grams per inch of peel line.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A flanged paperboard container having a paperboard closure, both container and closure having first plastic coatings extrusively applied at least to the interior surface areas thereof, such container coated surface area extending continuously onto a flange surface portion surrounding the periphery of said container, the area of said closure overlapping said flange surface portion,and a peelable release second coating applied over said first coating on either said flange or said closure to provide a heat-fused seal area therebetween at which said flange and said closure will part under a peel stress of approximately 800 to 1500 grams per inch of seal width.

2. An article as described by Claim 1 wherein said seal area is fused by a heat range of 275° to 450°F applied within a dwell time of 1 to 4 seconds under a pressure of 20 to 80 pounds per square inch.

3. An article as described by Claim 1 wherein said first plastic coatings are selected from the group comprising polyethylene, polypropylene and polyethylene terephthalate.

4. An article as described by Claim 3 wherein said first coatings are applied to said paperboard surfaces at the approximate rate of 26 pounds per 3000 square fee of surface.

5. An article as described by Claim 1 wherein said flange and said closure can be parted at said heat-fused seal area without disturbing a bond between either of said flange or closure first coatings and the respective paperboard.

6. A paperboard container having a flanged periphery around an opening portion thereof and a paperboard closure element configured to overlie said opening and flange with a seal area between said closure and said flange, a first plastic coating selected from the group comprising polyethylene, polypropylene and polyethylene terephthalate applied at the approximate rate of 26 pounds per 3000 square fee of surface to the flange and interior surfaces of said container and closure paperboard and a second plastic coating applied over said first coating of said flange or seal area of said closure, said second plastic coating being blended and mixed with fine particulates to fuse and seal said closure to said flange by a heat range of 275°F to 450°F under a pressure of 20 to 80 pounds per square inch within a dwell time of 1 to 4 seconds and to release under a cold peel stress of approximately 800 to 1500 grams per inch of seal width.