US3709702A - Hermetically sealed food package - Google Patents

Abstract

PACKAGE COMPRISES A FLANGED CONTAINER OF SEMI-RIGID, GAS-IMPERMEABLE, TRANSPARENT PLASTIC CONTAINING A FOOD PRODUCT AND A SHEET OF STRETCHABLE GAS-IMPREABLE FILM SEALED TO THE FLANGES. THE PACKAGE IS EVACUATED PRIOR TO SEALING AND CAN INCLUDE AN INERT GAS ATMOSPHERE. A RIGID BOARD IS ATTACHED TO THE FILM AT THE FLANGE AREA WITH A BOND STRONGER THAN THAT BETWEEN THE FILM AND CONTAINER. APPARATUS FOR FORMING THE PACKAGE INCLUDES A FIRST PACKAGING STATION WHERE THE FILM IS SEALED AROUND A PORTION OF THE FLANGE AREA BY HEAT SEAL BARS AND VACUUM MEANS TO DRAW THE FILM INTERIOR OF THE FLANGE TOWARD A HEATING ELEMENT INTERIORR OF THE SEAL BARS. SECOND PACKAGING STATION INCLUDES MEANS TO EVACUATE THE PACKAGE, COMPLETE THE SEAL BETWEEN THE FILM AND THE CONTAINER, AND A CHECK VALVE WHICH VENTS THE AREA ABOVE THE FILM WHILE MAINTAINING THE VACUUM BELOW THE CONTAINER. THE ATMOSPHERIC PRESSURE CAUSES THE STRETCHED FILM TO BE PASSED INTO TIGHT FITTING CONTACT WITH THE UPPER SURFACE OF THE FOOD PRODUCT.

Description

Jan. 9, 1973 R. A. MAHAFFY ETAL 3,709,702

HERMETICALLY SEALED FOOD PACKAGE Original Filed Sept. 1, 1965 3 Sheets-Sheet 1 INVENTORS R/ed JLMahaffy Joel A. Hamilon Wesley WPzLnne BY j M 74 ATTORNEYS Jan. 9, 1973 MAHAFFY ETAL HERMETICALLY SEALED FOOD PACKAGE Original Filed Sept. 1. 1965 s Sheets-Sheet 2 "I'IIIIIIIIIIIIIII.

J 9, 1973 R. A. MAHAF'FY ETAL 3,709,702

, HERMETICALLY SEALED FOOD PACKAGE Original Filed Sept. 1, 1965 3 Sheets-Sheet 3 Patented Jan. 9, 1973 3,709,702 HERMETICALLY SEALED FOOD PACKAGE Reid A. Mahaffy, Montclair, Joel A. Hamilton, Clifton,

US. Cl. 99174 7 Claims ABSTRACT OF THE DISCLOSURE Package comprises a flanged container of semi-rigid, gas-impermeable, transparent plastic containing a food product and a sheet of stretchable gas-impermeable film sealed to the flanges. The package is evacuated prior to scaling and can include an inert gas atmosphere. A rigid board is attached to the film at the flange area with a bond stronger thanpthat between the film and container. Apparatus for forming the package includes a first packaging station where the film is sealed around a portion of the flange area by heat seal bars and vacuum means to draw the film interior of the flange toward a heating element interior of the seal bars. Second packaging station includes means to evacuate the package, complete the seal between the film and the container, and a check valve which vents the area above the film while maintaining the vacuum below the container. The atmospheric pressure causes the stretched film to be pressed into tight fitting contact with the upper surface of the food product.

This application is a continuation of Ser. No. 484,284, filed on September 1, 1965, and now abandoned.

This invention relates to packaging food products and the like in hermetically-sealed containers. More particularly, this invention relates to improved automatic packaging apparatus, packaging methods, and the packages made thereby.

Reference is made to copending application Ser. No. 64,034, filed by W. E. Young et al., on July 22, 1970, showing basic subject matter of the present application. To clarify the relationship between these two applications, it is noted that said copending application is directed to the broad packaging concepts wherein a semi-rigid evacuated package comprising a cup-like receptacle or container is provided with a stretch-formed top arranged to reduce the transmittal of distorting stresses from the top to the container cup. Such package may be formed with a sequenced pressure application wherein pressure first is applied to the top and thereafter to the semi-rigid bottom. The top may be stretched subsequent to package evacuation, as by application of atmospheric pressure upon venting the evacuation chamber, or the top may be prestretched prior to assembly and completion of the package, as by application of differential pressure prior to the evacuation phase of the package operation. This application, on the other hand, is directed to specific features including (a) a trapezoidal-like bacon package configuration, (b) the use of a stiff protective member as a third package element, and bonding techniques therefor, (c) the technique wherein the top is stretched by first moving it away from the semi-rigid container (and the product contained therein) to a region adjacent a heater, and thereafter forcing the top towards the container to stretch it, and (d) the use of a check valve to obtain the sequenced pressure-application technique more broadly claimed in said copending application.

For a number of years now, extensive use has been made of automatic apparatus for packaging products in evacuated containers formed of flexible plastic packaging material. In some cases, the products were inserted in preformed pouches which were then evacuated and sealed along the opening. Subsequently (see, for example, US. Pat. 3,061,984), completely automatic machines were developed to form packages from two sheets of flexible plastic film drawn from respective supply rolls. In either case, the resulting container was formed entirely of thin flexible film. Thus the ultimate evacuation of the container caused the film to be forced inwardly by atmospheric pressure into close and intimate pressure-contact with the enclosed product, and distorting the film into a shape conforming to the product profile.

For many products, such as luncheon meat and frankfurters, this approach provided reasonably acceptable results. However, it was not really satisfactory for certain other types of products. For example, when packaging a shingled group of bacon slices it has been found that the pressure applied by the atmosphere through the film to all parts of the bacon tends to cause undesirable cohesion of the individual strips of bacon after the container is opened by the purchaser. Also, the resulting container does not afford prospective customers the best presentation of the bacon through the stretched and distorted parts of the film.

Accordingly, it is one object of this invention to provide an evacuated package which is superior to those available heretofore. Another object of this invention is to provide improved vacuum packaging apparatus and methods. Still another object of this invention is to provide novel techniques for packaging certain specialty products such as bacon. Other objects, aspects and advantages of this invention will in part be pointed out in, and in part apparent from, the following description considered together with the accompanying drawings, in which:

FIG. 1 is a longitudinal vertical section through a part of the packaging machine;

FIG. 2 is a detail horizontal section (from below), showing the preliminary sealing means of the packaging head;

FIG. 3 is a perspective view of a completed package;

FIG. 4 is a cross-section taken along line 4-4 of FIG. 3;

FIG. 5 is a detail view, greatly magnified, of one corner of FIG. 4;

FIG. 6 is a detail view, like FIG. 5, but showing a modified package construction; and

FIG. 7 is a perspective view showing the package of FIG. 6 with its top folded back.

Referring now to FIG. 1, the packaging apparatus comprises a series of trays 10 each adapted to receive and snugly support a corresponding cup-like receptacle 12 carrying the product 14, in this case a one pound shingled group of bacon slices. These trays are power-driven from right to left with an intermittent cyclical indexing movement to permit certain sequential packaging operations to be performed at respective stations along the path of movement.

Receptacles 12 are made of transparent, calendere'd non-plasticized polyvinyl chloride, advantageously having a thickness in the range of five to fifteen mils. Such polyvinyl chloride is semi-rigid, meaning that it is self-supporting and substantially retains its shape under normal conditions of use, e.g. with a normal product load such as might be simulated by filling the receptacle with water. The receptacles are in the shape of a truncated triangular prism, best illustrated in FIG. 3, and having a cross-section in the form of an isosceles trapezoid as shown in FIG. 4. The receptacles are formed with flat peripheral flanges 16 extending entirely around the opening, and lying in a common plane.

Above two adjacent positions of the trays 10 is a packaging head generally indicated at 18 and mounted (by conventional means, not shown) for vertical reciprocating movement in synchronism with the indexing of the trays. That is, when the trays stop, head 18 moves down to carry out certain operations to be described, and then rises just before the next indexing movement, so as to permit the trays to be shifted horizontally without interference.

To the right of packaging head 18, a web of flexible plastic packaging film 20 descends vertically to a lay down roll 21. This roll aids in applying the film to the top of the trays as they are shifted into the first position under the packaging head 18. The film is drawn from a supply roll (not shown) and has a Width suflicient to cover the receptacles 12 including the side flanges thereof. In the disclosed embodiment, film 20.is a laminate of sarancoated polyester and polyvinyl chloride, and the polyvinyl chloride side faces down to engage the polyvinyl chloride receptacles 12. Thus the heat-sealing properties of the film are compatible with those of the receptacles and both provide a good oxygen barrier.

The packaging head 18 includes both a preliminary seal means, generally indicated at 22, and an evacuation and final seal means, generally indicated at 24. The preliminary seal means further comprises peripheral heat-sealing bars 26 (see FIG. 2) arranged to extend around three flanges of the receptacle 12 and partially along the fourth flange. The gap in the heat-sealing bar along the fourth flange is filled with a low thermal conductivity, heat-re sistant elastomer 28, e.g. silicone rubber, the lower edge of which is in the same plane as the heat sealing bars, or projects slightly below. Thus, when the head 18 descends, it presses the film 20 tightly against all of the flanges 16, sealing the film against air leakage around the entire periphery of the preliminary sealing means.

Also carried by the packaging head 18, within the preliminary seal means 22, is a flat platen the lower surface of which is about /s" above the plane of the heatsealing bars 26. The Side edges of this platen are spaced a small distance from the interior side walls of the heatsealing bars. This platen is formed to receive a set of heater elements 32, additional to the sealing heaters 33, to maintain the platen at a moderately elevated temperature.

When the packaging head 18 is in its lower position, the chamber defined by the preliminary sealing means 22 is evacuated by a vacuum line 36. As shown in FIG. 1, this causes the film 20 to be forced uniformly up against the platen 30 so that the film becomes somewhat softened by the heat. Such softening makes it readily possible, by application of reasonable pressure, to stretch the film, e.g. beyond its elastic limit, for purposes as will be described subsequently.

While the receptacle 12 is in the preliminary seal position, the heated bars 26 operate in known manner to heat-seal the film 20 to the corresponding receptacle 12 along three of the flanges 16. Since the elastomer 28 is not heated, that end of the receptacle is not sealed to the film.

The head 18 thereafter rises and the partially sealed receptacle 12 is indexed to the next position Where the evacuation and final sealing of the package take place. To this end, each tray 10 is provided with a captive weblifter 38 which, in accordance with prior. art techniques, is shifted up (through a previously formed cut-out 12a in the receptacle 12) to raise the end of the film 20 opposite the unsealed flange of the receptacle. The package then is evacuated through the channel thus created between the film and the receptacle. The vacuum is drawn through the web-lifter passage in the tray, through a vertically reciprocable gasketed coupler 40, a line 42 including a check valve 44 and the main vacuum valve 46 to which is connected a vacuum conduit 48. This main valve 46 also connects vacuum through a line 50 to the chamber above the film 20.

After evacuation, main valve 46 is shut oh and an inert gas is admitted into the package from a gas line 52. The gas passes through an internal conduit in the Web-lifter support, and exits into the package through an aperture in the top of the web-lifter. When the proper amount of gas has been admitted, the web-lifter is allowed to drop back down to its normal rest position and the usual heated final seal bar descends from above the the film 20 to complete the heat-sealing of the film to the receptacle 12. This final seal extends along the side of the receptacle interiorly of the aperture 12a, and overlaps the preliminary seal lines so as to make the package completely gas-proof.

Thereafter, main valve 46 is shifted to its vent position, admitting atmospheric air through line 50 into the final seal chamber above the film 20. The check valve 44 momentarily restrains the flow of air into the trays 10, but the air pressure above and below the package equalizes fairly quickly because some air will flow downward into the web-lifter passage which is imperfectly closed off by the final seal bar in its lowered position. In some cases, it may be desirable to speed up this pressure equalization by providing an adjustable-restriction by-pass valve around the check valve 44.

Although the foregoing description applies particularly to packaging machines of the type where evacuation is effected at one end of the package, this invention also is applicable to machines of the center evacuation type as illustrated in US. Pat. 3,061,984. For such center evacuation machines, two assemblies as illustrated in FIG. 2 are used in a side-by-side relationship with the elastomers 28 adjacent each other. The operation is identical, except that during venting to atmosphere no air will pass from the final seal chamber to the web-lifter passage since there is no exposed edge of the film around which it can pass. Hence the air that is admitted to the final seal chamber is somewhat more effective in forming the film downward into the trays 12. It also may particularly be desirable to bleed air slowly through a by-pass valve around check valve 44 so that the coupler 40 will not adhere to the tray.

The inrush of atmospheric pressure above the film 20 serves to force this film down into the receptacle 12, causing the film to be stretched. The extent of stretching depends upon how much gas had previously been admitted into the package. Preferably, the admission of gas is adjusted to that amount which results in the edges of the bacon being pressed lightly against the interior surface of the receptacle 12 when the package is in its normal upright position as shown in FIG. 3.

The stretching of the film 20 interiorly of the flanges 16 is aided by the heat applied in the preceding preliminary seal operation. Thus the film is somewhat softened so that it can be stretched, advantageously to an amount resulting in a permanent set of the plastic material. In any event, the film is force-fitted and stretched by the atmospheric pressure around all of the contours of the exposed pieces of bacon. The receptacle 12, being made of semi-rigid material, is not so formed about the bacon but instead contacts the edges of the bacon with the desired pressure engagement sufficient to assure that the bacon is immobilized within the package. This arrangement particularly is advantageous because shifting of the bacon can smear grease on the interior of the receptacle and interfere with a prospective customers inspection of the product.

The pressure of the product against the interior of the receptacle 12 should be suflicient to press any large flat product surfaces, such as that of the end slice 14a, into full contact with the interior of the receptacle. However, the pressure desirably is low enough to avoid squashing the bacon edges 14b flat against that interior. This degree of pressure provides a superior package appearance while preventing shifting of the product, disarray and grease smearing.

The film 20 can be vacuum-formed, i.e. stretched beyond its elastic limit, while in the preliminary sealing stage, for example to such an extent that no further stretching is needed in the final seal stage. Such stretching may be useful in some ap lications, and is facilita d by the effective air-tight seal around all four sides at the preliminary seal means, as well as by the heat transferred to the film by the platen 30. When forming the film in the preliminary sealing position, the platen 30 advantageously is placed more than /s" above the plane of the heat sealing bars 26, e.g. at a distance approximately equal to the extent of forming desired. For some applications, the need for pre-heating and/or pre-stretching the film may be reduced or even avoided, as by the use of film material having suitable characteristics of stretchability at normal ambient operating temperatures.

In the final seal stage, physical stretching of the interior marginal portions of the film 20 inwardly to the product 14, especially to a permanent set dimension, is desirable because it tends to eliminate any substantial buildup of tension in the film. As shown in FIG. 5, the film is formed inwardly at 20a to follow the side wall contour of the receptacle 12. Thus the force of the atmospheric pressure is carried essentially by the packaged product, aided by the internal gas pressure. This avoids placing portions of the package under heavy stress, and minimizes distortion of the semi-rigid receptacle from its original shape.

FIGS. 6 and 7 show a modified package construction suitable for certain particular applications. The basic arrangement is generally the same, in that the package comprises a semi-rigid plastic member 12 (serving as the top in the normal upright position of the package) sealed around its flanges 16 to the plastic film 20 to form an evacuated container. After the package-making operations are completed as in the first embodiment, a paper board member 60 is secured to the film 20. This board is thicker than film 20, preferably between 5 and 12 mils, thus providing additional rigidity. Advantageously, the board is secured to the film around all of the marginal edges, as by means of a sealant 62, and can be so secured while the evacuated container is still in its tray 10. The sealant 62 can for example be of the type which is activated by conventional heating means.

Preferably, this sealant 62 forms a bond substantially stronger than that between film 2.0 and semi-rigid member 12. By this means, it becomes more readily possible to open the package simply by peeling the film and paper board, as a unit, away from the semi-rigid member 12, as shown in FIG. 7.

'One side of the semi-rigid member 12 is formed with a finger tab 64 to aid in opening the package. When the package is opened, the board 60 will bend about a longitudinal line running along the back of the package, the board being somewhat pliable relative to the semi-rigid member 12. The first embodiment of the invention (FIG. 3) also may include a finger tab 64 to aid in peeling the film 20 away from the semi-rigid member.

The manifold arrangement of FIGS. 6 and 7 provides a package which not only is more rigid, but the addition of the paper board minimizes the chances that the package might be punctured, e.g. in shipment or handling. The presence of the board also makes the package easier to open; after the desired number of bacon slices have been removed, the package may readily be closed and returned to the refrigerator for storage.

When the package is first opened, the relief of the vacuum permits the film 20 to fall down to the level of the paper board 60. When the package is reclosed for storage of remaining bacon, it is possible to place the package in a stack of similar packages, or to place other articles on top without injuring the remaining product. Before the package is opened, it also is well adapted to stacking, the flexible film 20 acting as a diaphragm-like spring.

Although in the preferred embodiment described herein, the film 20 is drawn up to heated platen 30 by vacuum, this upward film movement can be obtained by a positive pressure within the interior of the package. Also, for some applications, it may be desirable to extend the platen out essentially to the region where the sealing bars contact the film, in order to provide additional heat in the interior marginal portions of the film where the most severe stretching should take place in the final sealing stage.

The completed package comprises a semi-rigid container shell (receptacle 12) the interior of which is evacuated and sealed from atmosphere by a closure panel in the form of stretched film 20 force-fitted against the product by atmospheric pressure. As shown in FIG. 7, the closure member has a portion extending out beyond a corresponding peripheral edge of the shell 12 to permit grasping of the extended portion to aid in opening the package.

Although preferred embodiments of the invention have been set forth in detail, it is desired to emphasize that this is not intended to be exhaustive or necessarily limitative; on the contrary, the showing herein is for the purpose of illustrating the invention and thus to enable others skilled in the art to adapt the invention in such ways as meet the requirements of particular applications, it being understood that various modifications may be made without departing from the scope of the invention as limited by the prior art.

We claim:

1. A hermetically sealed and evacuated package assembly adapted to contain a perishable food product and comprising a cup-shaped container member having peripheral flanges around its opening, said container member being made of relatively thick, semi-rigid, gas-impermeable, light-transmitting plastic material adapted to provide substantial mechanical protection for a contained product, the upper surface of said product being below the flanges of the container member at least in the region adjacent the container side walls;

a cover sheet of flexible and stretchable gas-impermeable material disposed over said opening of said container member and sealed to said flanges around the periphery of said opening to hermetically seal said package from outside atmosphere, said flexible material being substantially thinner than said semi-rigid container material and incapable of providing substantial mechanical protection for the contained product, said flexible material being stretched downwardly along said container side walls and being held by atmospheric pressure in tight and intimate form-fitting engagement with said product entirely across the upper surfaces thereof; and

a relatively stiff protective member secured in position substantially parallel to said container opening alongside of said thin flexible cover and spaced a short distance therefrom, said protective member defining a bottom element for the package when the semirigid container serves as the protective top element in the normal upright position of the completed package assembly, whereby with the hermetic seal broken and the package in the normal position with said semi-rigid container at the top, the product within the container will move with said flexible film down towards said stiff bottom element providing a visible indication that the hermetic seal has been broken.

2. A package as claimed in claim 1, wherein an inert gas atmosphere is included within the package.

3. A hermetically sealed and evacuated package assembly adapted to contain perishable food products or the like and comprising a cup-shaped container member having peripheral flanges around its opening, said container member being made of relatively thick, semirigid, gas-impermeable plastic material adapted to provide substantial mechanical protection for a contained product, the upper surfaces of said product being below the flanges of the container member at least in the region adjacent the container side walls;

a cover sheet of flexible and stretchable gas-impermeable material disposed over said opening of said container member and sealed to the flanges of said contained member around the periphery of said opening to hermetically seal said package from outside atmosphere, said flexible material being substantially thinner than said semi-rigid material so as to be incapable of providing substantial mechanical protection for the contained product, said flexible material being stretched downwardly along said container side walls and being held by atmospheric pressure in tight and intimate form fitting engagement with said product entirely across the upper surfaces thereof; and

a relatively stiff protective member secured in position substantially parallel to said opening alongside of said thin flexible cover and spaced a short distance therefrom, said protective member being bonded to said flexible cover in the regions thereof which are sealed to said container flanges, the bond between said protective member and said flexible cover being stronger than the seal between said flexible cover and said flanges, the stiffness of said protective member serving to aid in separating said flexible cover from said flanges to provide improved opening of said package.

4. A package as claimed in claim 3, wherein an inert gas atmosphere is included within the package.

5. The method of making a hermetically sealed package comprising the steps of:

inserting a product into a semi-rigid cup-like container with the product height being less than the height of the container side walls at least in the regions adjacent said side walls; positioning over the opening of said container a cover sheet of plastic to form a package assembly;

forcing said cover sheet in a direction away from the product in said container and towards a source of heat;

transferring heat from said source to said cover sheet sufficiently to soften said sheet for stretching; evacuating the package assembly;

hermetically sealing the package with the cover sheet sealed to the container; and

applying atmospheric pressure to the outside of said heated cover sheet to stretch the heated material in the regions thereof immediately inboard of the walls of the container defining said opening and thereby to effect a tight-fitting engagement of the cover sheet and the packaged product.

6. Apparatus for making packages comprising, in combination, a series of receiving elements adapted to be mounted in an endless loop arranged for movement past a series of packaging stations where sequential packaging operations are performed, said elements including means to support respective cup-like members of semi-rigid material adapted to receive products to be packaged; means to apply to said elements a film of flexible packaging material over the opening of each cup-like member in sequence; a packaging head at one of said stations and including means operable to seal said film to the respective cup-like member in a region extending around the periphery thereof; first vacuum means to withdraw air from the package and to reduce the pressure on the outside surface of said semi-rigid member during evacuation of the package; second vacuum means to reduce the pressure on the outside surface of said film during said evacuation; a source of vacuum; first and second vacuum lines connecting said source to said first and second vacuum means respectively; control means for venting said source of vacuum after the package has been evacuated; and a check valve in said first vacuum line to retain reduced pressure on the outside surface of said semi-rigid member while atmospheric pressure forces said flexible film inwardly against the product by stretching said film interiorly of said sealed region.

7. In apparatus for making hermetically sealed and evacuated packages comprising a series of receiving elements adapted to be mounted in an endless loop arranged for movement past a series of packaging stations where sequential packaging operations are performed, said elements including means to support semi-rigid packaging material formed into cup-like containers carrying products to be packaged; means to apply a cover sheet of flexi ble packaging material as a top over the opening of each cup-like container in sequence to make a complete package structure containing the product; packaging head means adjacent the path of movement of said elements and located at a position subsequent to the station where said cover sheet is applied to the containers; said packaging head means including means to seal said sheet to each cup-like container along a line extending around the periphery of the container opening; the improvement wherein said packaging head means includes a heating element positioned to lie adjacent the outside surface of said cover sheet and in a region thereof which is inboard of said peripheral sealing line; said packaging head means comprising differential pressure means operable to develop a first differential pressure across said cover sheet to force it away from the product in the corresponding container towards said heating element to effect a transfer of heat to said cover sheet so as to soften it for stretching, and operable thereafter to develop a second differential pressure in a reverse direction across said heated cover sheet to stretch the heated meateri'al thereof which is immediately inboard of said seal line so as to form marginal stretched portions which in the completed package are forced by atmospheric pressure into the cup-like container, along the side walls thereof, with the central area of the cover sheet within said marginal portions in tight engagement with the product.

References Cited UNITED STATES PATENTS 2,621,129 12/1952 Ramsbottom et al. 99171 2,834,686 5/1958 Reuman 99'17l 3,034,271 5/1962 Carpenter et al. 53184 3,079,057 2/ 1963 Calarusso 2293.5 3,196,590 7/1965 Ollier et al 53-112 3,226,236 12/ 1965 Weller 99171 3,298,158 1/1967 Schmidt 5,3112 3,347,011 10/1967 Lovas et al. 5322 3,467,244 9/1969 Mahaffy et al. 20645.34 3,498,018 3/1970 Seiferth et al. 99-171 X 3,522,687 8/1970 Mahaify 53-22 MORRIS O. WOLK, Primary Examiner S. B. DAVIS, Assistant Examiner US. Cl. X.R.

5322 A, 30, 39, 42, 112 A, 184; 99-171 LP, 171 TC, 171 LM, 189; 20646 F

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