Note: Descriptions are shown in the official language in which they were submitted.
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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,
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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.
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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.
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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
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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.
