Boilable Bakeable Package And Method

Abstract

A laminated or multi-layer wall tray is provided which has a self-supporting outer layer or wall portion of paperboard which can be formed and handled as an independent self-supporting unit during manufacture of the laminated tray. A plastic liner is heat-vacuum formed into the paperboard tray or carton to provide a boilable, bakeable, liquid-tight, leakproof lining for the tray which in its entirety is of a boilable or bakeable character, and to provide a strengthened structure of the composite tray of the outer paperboard supporting structure and inner plastic film liner in supporting structure. Both the liner and the paperboard are preferably made of a thinness or caliper of a dimension less than cqn be normally employed in such structures when used alone. At the bottom of the paperboard outer structure has certain formed indents around its bottom corner edge which provide resting portions or stops for nesting of the tapered trays to be handled as a stack, and also provide exit openings or vents for air from within the carton or tray at required positions to the outside during the thermo-vacuum forming of the liner. The method of fabricating or combining the components of such a tray comprises the steps of forming the outer paperboard structure or layer with the corners locked or secured together in self-supporting fashion to receive the plastic liner by thermo-vacuum forming process drawn inside of the self-supported paperboard outer structure to correspond identically to the inner profile of the paperboard container thereby locking and if desired, adhering the molten plastic material to the inside paperboard structure. A laterally horizontally extending flange may be provided around the upper edge of either the paperboard or the plastic, or both.

Description

DESCRIPTION OF THE INVENTION

This invention relates to vacuum-thermoformed laminated packages such as tray or cartons, each package consisting of a fabricated paperboard outer layer which has its respective corners secured together in some conventional fashion, such as by a "Klik-Lok" construction, or similar construction, or by adhesive securing so that a self-supporting outer structure of paperboard is formed to be used in manufacture and for the application of any graphic art material desired in connection with the product container therein. The second lamina comprises an inner layer of film which is thermo-vacuum formed inside of the finished outer paperboard lamina. The finished tray or carton is filled with product and closed by a suitable lid or layer of film or coated paperboard. The product can be heated by boiling or baking to the desired temperature for use.

Packages somewhat similar to this have been known previously for packing margarine, for example, the "Tritello" package employed in Sweden under the "Flora" margarine label, wherein the manufacturing machine contains machine molds for trapping precut paperboard within the mold and forming it in the shape of a tray. Then the film or plastic layer is formed adhesively inside the paperboard to hold structures paperboard together in finished form. With these prior structure it was necessary for the plastic to be in place and secured to the paperboard to make a self-supporting structure, the paperboard by itself being non self-supporting.

In accordance with the instant invention a competitive type package of improved character is provided with a lower cost basis.

It is an object of the invention, therefore, to provide a combination paperboard and film carton or tray of suitable character to be subjected to either boiling or baking.

Another object of the invention is to provide a package of the above character in which the tray can be constructed for nesting in a stack and be provided with nesting indexing means or stops, which also provide vents for the exhausting of air during the thermo-vacuum forming of the liner.

Still a further object of the invention is to provide a structure for a package of the above character wherein the package can be used with a seal flange, a trap flange, with outer flange and with a cover seal, either a separate cover or hinge type cover.

A further object of the invention is to provide a tray of a laminated construction wherein a thinner thickness of outer layer of paperboard and a thinner thickness of inner layer film can be used while still obtaining a structure which equals or exceeds the rigidity of a higher caliper or thickness of paperboard material.

A further object of the invention is to provide a combination laminated structure wherein an outer structure or layer of paperboard of self-supporting character and an inner structure or layer of film are provided wherein by subjecting the package to a vacuum at the time of sealing the closure, the inner layer can be formed to permit the exhausting of the air during the filling operation so that no head space remains.

The above and other objects of the invention are attained as described in connection with certain preferred embodiments of the invention, as illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view of nested trays or containers embodying the invention;

FIG. 2 is a transverse sectional view through FIG. 1; It will be understood that the thickness of the paperboard 10 and the film 11 has been exaggerated in FIG. 2 to enable clarity of the sectional view;

FIG. 2a is an enlarged view similar to FIG. 2 of a top corner of a tray;

FIG. 3 is a side view of a finished package which is closed by a lid under vacuum conditions so that the inner liner is drawn in, in the process of eliminating head space;

FIG. 4 is a sectional schematic view of a tray in the process of manufacture, the self-supporting outer paperboard structure being supported in a vacuum cup beneath the film for the inner layer.

Referring to FIGS. 1 and 2, each of the trays comprises an outer paperboard structure 10 or lamina of upwardly diverging side wills 10a and a bottom 10b, and an inner layer of film 11 which is thermo-vacuum formed inside of the outer paperboard structure 10 and the divergent sidewalls provide for nesting of the structures. The film employed is preferably a high temperature film such as nylon, high density polyethylene, or the like. In practice, the thickness of the film will be from 0.006 to 0.010 mills, and the thickness of the paperboard will be from 0.009 to 0.020 mills. In thermo-vacuumforming a film into a recess the wall thickness is reduced as film is stretched and thinned, and an 0.008 inch thick film, for example, may be reduced to as little as 0.003 inch or 0.004 inch mills.

As shown in FIGS. 1 and 2, the paperboard structure or lamina has its corner portions secured together by means of a conventional "Klik-Lok" or similar structure 12. Other conventional securing means such as by gluing, sealing, etc., can be employed at the corners. In any event, the outer paperboard structure is self-supporting and can be nested and stacked for subsequent use in completing the package.

In the matter of nesting, a series of angle-shaped, indent, struck-out portions or slots 16 (FIGS. 1 & 2) are provided at spaced locations around the bottom edge of a carton to provide supporting steps or resting means for another carton as shown, for example, in FIG. 2 and these angle-shaped portions 16 are formed inwardly, provide side apertures 16a for emission of air during the vacuuming cycle and the processing operations as will be described. As shown there are six of the indents provided in each tray as a resting means and as an air emission means.

At the top the inner layer 11 extends outwardly in a flange 17 (FIG. 2a) to permit heat sealing of a coated paperboard lid to the flange or heat sealing of a similar plastic layer to the flange to form a weld. The flange 17 of the film is normally thinner than the paperboard lid to which it is heat sealed but for purposes of illustration in the drawings its thickness has been exaggerated.

Referring to FIG. 3, a carton is shown filled with a product 20 and has been closed by a paperboard lid 21 which is coated or film lined so as to be heat sealed to the flange 17. At the time of placing of this cover in place, the interior of the package is subjected to a vacuum operation so that the inner layer 11 is moved to a new position at 11a in certain portions, and 11b in others to force the produce 20 from a level 22 upwardly toward the lid 21 at a level 23.

Referring to FIG. 4 the process of manufacture of the tray is illustrated schematically. The apparatus includes, for example, a rectangular conveyor frame 32 suitably mounted in elevated position so as to engage about a carton adjacent its top and locate it with its bottom resting in a vacuum cup 31. The conveyor frame 32 is shown above a pair of support rods 33, below a rectangular station clamp frame 34. At the station, there is a supply of film 36 fed across the top of the outer paperboard structure 10 and a suitable cut off knife 37 is provided to cut the desired length of film to be clamped by the rectangular clamp frame 34 against the rectangular support frame 32.

Suitable guides 38 may be provided at either side to ensure proper indexing of the carton with the vacuum cup 31 having a lower position indicated in dotted lines at 31a and an upper position shown in full lines where its raised side flanges 42 engage the four walls of the paperboard structure 10. The bottom wall 43 of the cup 31 has suitable vacuum passages 44 leading to a vacuum fitting 46 by means of which vacuum can be applied to the space within the cup and through the vent openings 16a to the inside of the outer structure 10 of the carton or tray. At the same time an overhead electric heater 47 is energized and brought to active position to soften the film 36 so that it can be drawn inside of the carton to form the inner layer 11. When the struck-out portion 16 is formed with tapered side walls as seen in FIG. 4 the film drawn into this shape of opening will be effectively locked in place and can only be withdrawn with great difficulty. When the slot 16 is formed with straight side walls as shown at 16b in FIG. 3, a releasable interconnection or latch is provided by an indented film portion 16c.

If desired, the inner layer of film 11 may be secured adhesively to the outer paperboard structure 10 or the film may be heat sealed to this outer structure where a compatible coating exists on the paperboard.

While the above structure is schematic in nature, there are conventional vacuumizing arrangements manufactured which are capable of performing this operation in the manner described above or in another manner, for example, the U.S. Pat. No. to Bergstrom, 3,492,773.

While I have shown and described a preferred form of the invention, it is apparent that the invention is capable of variation and modification from the form shown so that the scope thereof should be limited only by the proper scope of the claims appended hereto.

Claims

I claim:

1. The method of manufacturing a laminated tray or carton structure which comprises first forming an outer part or lamina of paperboard in the shape of a tray or carton having a bottom and four side walls, securing the respective walls together to form a self-supporting paperboard part capable of being handled as an individual unit, forming openings adjacent the bottom of the paperboard part, supporting the paperboard part with openings in communication with a vacuum source, placing a sheet of film over the open top of the paperboard part, holding the sheet at its edge portions as positioned peripherally about the paperboard part, applying vacuum pressure to the inside of the paperboard part, simultaneously heating the sheet of film so that the film is drawn down into the tray or carton and against the bottom and side walls thereof and into conforming structural relation to form an inner part or lamina in mutual reinforcing relation with said outer paperboard part, the step of forming openings adjacent the bottom of the paperboard part is effected by forming struck-out portions at the bottom corners between the side walls and the bottom wall and in the vacuum forming of the heated film drawing the film partially into said openings so as to provide a holding engagement between the outer paperboard part and the inner film part.

2. The method of manufacturing a laminated tray or carton structure as recited in claim 1 wherein the holding engagement between said film and openings is readily releasable.

3. The method of manufacturing a laminated tray or carton structure as recited in claim 1 wherein the holding engagement between said film and openings is essentially unreleasable.

4. The method of manufacturing a laminated tray or carton structure as recited in claim 3 wherein the essentially unreleasable holding engagement is achieved by forming a portion of each opening in its associated side wall with a pair of upwardly diverging edges thus forming an interlock between the openings and the material drawn therein.

5. A method of manufacturing a laminated carton comprising the steps of folding a paperboard container blank to form an outer container having a bottom wall and a body wall terminating at a flangeless terminal uppermost edge, vacuum forming a sheet of plastic material in situ within said outer container to form a liner therefor, trimming the sheet in spaced outboard relationship to said flangeless edge to form a liner flange projecting radially beyond said terminal uppermost edge adapted to have a lid heat-sealed thereto, packaging a product in said liner prior to the heat sealing of the lid to said flange, and drawing a vacuum prior to the sealing of the lid to said flange sufficient to draw at least portions of the liner away from the outer container thereby reducing final liner volume and accordingly reducing final product head space.

6. A method of manufacturing a laminated carton comprising the steps of folding a paperboard container blank to form an outer container having a bottom wall and a body wall with openings at a juncture therebetween, conveying said outer container to an upwardly opening vacuum cup, forming a vacuum chamber between said cup and outer container by imparting relative telescopic movement therebetween, the height of the vacuum chamber being limited to the area of the juncture and immediately above the openings therein, heating a sheet of plastic material, drawing a vacuum through the openings to form a liner in situ within the outer container while a major surface area portion of the outer container body wall above the juncture area is free and unsupported, and trimming the sheet in spaced outboard relationship to the outer container body wall to form a liner flange adapted to have a lid heat sealed thereto.

7. A method of manufacturing a laminated carton comprising the steps of forming an outer container having a bottom wall and a body wall, forming a liner within the outer container, releasably interlocking a portion of the liner to a portion of the outer container, packaging a product in the liner, drawing a vacuum internally of the liner sufficient to draw the liner portion away from the container portion to release said interlock whereby the liner moves away from the outer container thereby reducing final liner volume and accordingly reducing final product head space, and thereafter hermetically securing a lid to said liner to maintain the evacuated condition thereof.

8. The method of manufacturing a laminated carton as defined in claim 7 comprising the further steps of forming openings in said outer container, and forming said liner by drawing a vacuum through said openings to form the liner in situ within the outer container.

9. The method of manufacturing a laminated carton as defined in claim 7 comprising the further step of forming a peripheral flange on the liner, and heat sealing said lid to said flange.

10. The method of manufacturing a laminated carton as defined in claim 7 comprising the further step of forming the body wall with an uppermost flangeless terminal edge, forming a peripheral flange on the liner projecting radially outboard of the flangeless terminal edge, and heat sealing the lid to the liner flange outboard of the flangeless terminal edge.

11. The method of manufacturing a laminated carton as defined in claim 8 wherein the releasably interlocked portions of the liner and outer container are those portions of the liner vacuum drawn into releasably interlocked engagement with said openings.

12. The method of manufacturing a laminated carton as defined in claim 8 comprising the further step of forming a peripheral flange on the liner, and heat sealing said lid to said flange.

13. The method of manufacturing a laminated carton as defined in claim 8 comprising the further step of forming the body wall with an uppermost flangeless terminal edge, forming a peripheral flange on the liner projecting radially outboard of the flangeless terminal edge, and heat sealing the lid to the liner flange outboard of the flangeless terminal edge.

14. The method of manufacturing a laminated carton as defined in claim 13 wherein the releasably interlocked portions of the liner and outer container are those portions of the liner vacuum drawn into releasably interlocked engagement with said openings.