EP0459754A2

EP0459754A2 - Cook-in package method and apparatus

Info

Publication number: EP0459754A2
Application number: EP19910304806
Authority: EP
Inventors: David F. Kuethe
Original assignee: Oscar Mayer Foods Corp
Current assignee: Oscar Mayer Foods Corp
Priority date: 1990-05-30
Filing date: 1991-05-28
Publication date: 1991-12-04
Also published as: JPH04239436A; EP0459754A3; CA2042733A1

Abstract

A method and apparatus for manufacturing a cook-in package (10) which is capable of withstanding a cook/pasteurization cycle while having edges capable of unaided manual tear initiation. The package (10) is made from non-peelable laminated films and has a hermetically-sealed interior pouch for containing a food product. Unaided manual tear initiation is facilitated by a plurality of punctures (30) which are formed in edge portions (16) of the package during or after heat sealing of upper and lower walls (12 and 14) of the package to one another. The punctures (30) are preferably formed along an area which is subsequently trimmed to ensure that the perforated area extends entirely to the edges of the package. Hermeticity of the package is ensured by maintaining an unperforated sealed area (31) inwardly of the perforated areas.

Description

Background of the Invention

The invention relates generally to cook-in packaging for food products, and particularly to a method and apparatus for packaging and processing a food product in a cook-in package with means to facilitate opening.
In the past it has been found that, for certain food products, efficiency in packaging and preservation of freshness can be achieved by sealing the product in a package in a form, fill seal apparatus, and subsequently cooking and/or pasteurizing the product in its package. Certain laminated plastic films are known to be suitable for such packaging, which is known as "cook-in" packaging.
In one particular example of an application for which this technology has been employed, a food product is subjected to a cooking/pasteurization cycle of about 50 minutes duration at a temperature of about 200°F (93.4°C). Such a cycle places relatively high mechanical stresses on the package, because the internal pressure rises substantially. Such a cycle also places thermal stresses on the package, and some films are subject to delamination during this type of cycle. Thus, the materials for such packages must have relatively high strength and toughness, as well as tolerance to prolonged exposure to relatively high temperatures, and the ability to maintain barrier properties during and after exposure to a high pressure differential across the wall at high temperatures.
In the past, the preferred materials for the walls of such cook-in packages have included non-peelable laminated films having combined thicknesses of .01 in. (0.25 mm) or more. One particular type of film which has been found suitable for such packaging has a relatively tough nylon outer layer and a modified linear low-density polyethylene inner layer.
While packaging made from such materials has been successfully employed and used commercially, such packaging has a drawback in that it is generally difficult for the consumer to open without the use of scissors or the like.
Recent efforts to provide a package of the type described which is suitable for cooking or pasteurization, and which can subsequently be opened without the use of scissors or the like, have included the use of a film wherein weakened areas are provided along the side edges by forming scratches or punctures in at least one layer of the laminated film prior to its being fed into the packaging apparatus. In tests, the film has been fed into a form, fill and seal machine, and the finished package then run through the cook/pasteurization cycle described above. However, it has been found that after the edge portions of the above materials are sealed and the cooking/pasteurization cycle completed, the weakened areas are ineffective in facilitating unaided manual tear initiation in the context of the above-described packaging.
Other means for facilitating opening of plastic packaging generally include the provision of a V-notch in one of the edges of the package. However, it has been found that such notches, while theoretically enabling unaided manual tear initiation, in practice are difficult to use in cook-in packages of the type described herein, due to the toughness of the films. Unless sufficient tearing force is applied with relatively high precision at the center of the V-notch, the package will not tear.
Also, in attempting to provide a notch or slit, or attempting any other treatment of package seal areas, it must be noted that the seal areas tend to warp or curl during or after cooking/pasteurization, which makes handling and cutting, etc., of such portions difficult to accomplish with precision after the cooking/pasteurization step. However, any modification of package seal areas prior to cooking/pasteurization must be evaluated in terms of how it will be affected by the exposure to prolonged heating. Any edge treatment which causes delamination of the package walls during cooking/pasteurization is also unacceptable.
There remains a need for an improved cook-in package of the type described with means to facilitate opening by the consumer.
Accordingly, it is a general object of the invention to provide a cook-in package for commercial use in processing and packaging food for retail sale, having means to permit unaided manual tear initiation along the edge of the package.
It is a further object of the invention to provide a method and apparatus for manufacturing such a package is conjunction with a cooking/pasteurization cycle.

Summary of the Invention

In accordance with the invention, a food product is hermetically sealed in a package formed of one or more laminated polymeric films which are provided with means to facilitate unaided manual tear initiation, and the product is then subjected to a cooking/pasteurization cycle. The cook-in package is made of laminated plastic films which include relatively thick, tough outer layers having relatively high strength, and has a peripheral seal area surrounding a hermetically sealed pouch. In accordance with the method of the invention, an edge portion of the seal area is treated with a plurality of punctures either simultaneously with or after sealing, but before the cooking/pasteurization cycle. The punctures are restricted to the outer portion of the seal area to avoid disturbing the integrity of the hermetic seal.
The apparatus for forming the subject package preferably comprises a horizontal form, fill and seal machine fed by upper and lower webs of plastic film which form the respective upper and lower walls of the finished package. The apparatus preferably includes a vertically reciprocable sealing head to seal the webs to one another along longitudinal side edge portions as well as transverse end portions, to provide the punctures in the seal areas, the apparatus may employ a plurality of studs mounted on the sealing head, or a roller with studs thereon.
The punctures preferably are distributed within about 1/8 in. (3.2 mm) of the edge of the package, at a density of about 30-35 punctures per linear inch (about 11-13 punctures per linear cm.). Each puncture preferably has a diameter of about .05 in. (about 1.3 mm).

Brief Description of the Drawings

Figure 1 is a diagrammatic plan view illustrating apparatus in accordance with the invention;
Figure 2 is a bottom view, shown on an enlarged scale relative to Figure 1, of a sealing head used in the apparatus of Figure 1 in accordance with a first embodiment of the invention;
Figure 3 is a sectional view taken substantially along line 3-3 in Figure 2, shown on an enlarged scale relative to Figure 2;
Figure 4 is a sectional view similar to Figure 3, but showing the sealing head in a lowered position relative to its position in Figure 3;
Figure 5 is a plan view of a package in accordance with the invention;
Figure 5a is a fragmentary sectional elevational view taken substantially along line 5a-5a in Figure 5, shown on an enlarged scale relative to Figure 5;
Figure 6 is a plan view illustrating apparatus for forming perforations in accordance with a second embodiment of the invention; and
Figure 7 is an elevational view, partially in section, taken substantially along line 7-7 in Figure 6.

Brief Description of Preferred Embodiments

The invention is generally embodied in a cook-in package 10, arid a novel method and apparatus for manufacturing the package.
As illustrated in Figures 5 and 5a, the package 10 in the illustrated embodiment comprises an upper wall 12 and a lower wall 14 which are joined to one another about a peripheral seal area 16 to provide a hermetically sealed interior pouch 17 for containing a food product. It may be noted that, while the package in Figures 5 and 5a is shown with a relatively flat, planar peripheral seal area 16, the seal area in practice may become wrinkled or curled during processing, particularly during the cooking/pasteurization cycle described below.
To provide the package 10 with sufficient strength and toughness to withstand the mechanical stresses of a cooking/pasteurization cycle while maintaining hermeticity, relatively thick, tough, non-peelable laminated films are used for the walls. In one particular package with which the invention has been successfully tested, the bottom wall 14 is made of a film that is commercially available from Curwood, Inc., known as Curlon 686, which has a thickness of approximately .007 in. (approximately 0.18 mm), comprising a nylon outer layer 18 of .002 in. (0.05 mm) thickness, and a modified linear lower density polyethylene inner layer 20 of .005 in. (0.13 mm) thickness, with a tie layer 22 therebetween. The upper wall is made of a similar film, also available from Curwood, Inc., known as Curlon 687. This film has an outer nylon layer 24 of .001 in. (0.02 mm) thickness, and an inner layer 26 of modified linear low-density polyethylene of .003 in. (0.08 mm) thickness, with a tie layer 28 therebetween. Both films have a heat seal range of 302°F - 320°F (150°C - 160°C). The tie layers 22 and 28 have negligible thickness, and the illustration of the tie layers 22 and 28 in Figure 5a is not intended to represent their thicknesses. Thus, the combined thickness of the walls in the illustrated embodiment is about .01 in. (about 0.25 mm). In other embodiments, even thicker walls may be employed.
In the past, such films have been used successfully in the manufacture of commercial "cook-in" packages for consumer sale of food products. However, opening of packages made from such films has generally been very difficult or impossible without the use of scissors or other implements to cut or initiate tearing of the package.
In accordance with the invention, tear initiation is facilitated by a plurality of punctures 30 formed through the peripheral seal area 16. The punctures 30 are preferably formed in a band or strip having a width of about 1/8 in. (about 3.2 mm), extending along at least two opposite edges of the package, with about 30-35 punctures per linear inch (about 11-13 punctures per linear cm). The punctures are distributed substantially uniformly or randomly in the perforated area. Disposed inwardly of the perforated area defined by the punctures 30 is an imperforate portion 31 of the seal area 16 which completely and uninterruptedly surrounds the pouch 17 to preserve its hermeticity. Each puncture preferably has a diameter of about .05 in. (about 1.3 mm). Each puncture extends entirely through all of the layers of the package material.
It will be appreciated that the package of the invention may be used for a wide variety of food products. In Figures 5 and 5a, the package is shown containing a generally rectangular tray 34 with a food product 36 supported thereon.
While packages in accordance with the invention may be manufactured with various different types of apparatus, a specific apparatus 32 suitable for this purpose is described below for purposes of example, and illustrated in Figures 1 through 4.
The apparatus 32 generally comprises conventional means for placing food products on a travelling lower web 38, laying an upper web 40 over the food product 36 and lower web, and sealing the webs to one another to form sealed packages, and separating and trimming the packages. The upper and lower webs are supplied by rolls 44 and 42, respectively, supported on the apparatus.
The lower web 38 is first fed into a thermoforming station 46 located beneath the roll 42 supplying the lower web. The thermoforming station forms recesses in the lower web 38 for receiving product. The lower web with the recesses formed therein travels in the direction of the arrows 48 in Figure 1 to a product loading station 47 where the food product is placed on the lower web. In the illustrated embodiment, the recesses are formed in pairs, side by wide.
The food product is carried by the lower web 38 into a vacuate/gas flush/heat seal station 49, in which the upper web 40 is laid over the lower web, and sealed thereto after oxygen has been substantially removed from the interior of the packages being formed.
Sealing of the upper web 40 to the lower web 38 is accomplished by a sealing head 50, shown in bottom view in Figure 2. The sealing head has four generally rectangular cavities 52 for simultaneous formation of four separate packages. To heat seal the upper wall of each package to its lower wall, a heating element 54 extends about the periphery of each cavity 52 in the sealing head. The lower surface of the sealing head comprises four rectangular sealing surfaces 53, one extending about the periphery of each of the acvities 52.
The sealing head 50 is vertically reciprocable between an upper position illustrated in Figure 3 and a lower position illustrated in Figure 4. As each set of four food items 36 is brought into position beneath the sealing head, with a respective item aligned beneath each of the four cavities 52 in the sealing head, the advancement of the respective upper and lower webs 40 and 38 is temporarily interrupted and the sealing head travels downward from the upper position to the lower position and heat seals the upper web to the lower web in the peripheral heat seal areas 16 at a temperature of between 302°F and 320°F (150°C and 160°C).
In accordance with the invention, means are provided to form punctures through outer edge portions 58 of the seal areas 16 of the respective packages. In the embodiment of Figures 2-4, the means for providing the perforations comprise a plurality of studs 60, each having an effective diameter of approximately .050 in. (1.3 mm). As illustrated in Figure 2, the studs 60 are arranged in outer portions 56 of the four generally rectangular sealing surfaces 53. Vertically reciprocable bars 62 are provided beneath the sealing surfaces 53 to support the lower web 38 during sealing and perforation.
The width of each of the perforated areas formed by the sealing head is preferably at least about 1/4 in. to 1/2 in. (about 6.35 mm to 12.7 mm). These areas are subsequently reduced in width as described below.
After the heat sealing and perforation are completed, the webs 38 and 40 resume travel in the direction of the arrows 48 in Figure 1 to a cutting and trimming station 64 where conventional means are employed to separate the packages from one another and trim the edges. Each of the cuts in the package material at the cut and trim station 64 is made through a perforated area so that each package has, on all four edges, a perforated area having a width of about 1/8 in. (about 3.2 mm). The cutting and trimming through the perforated areas ensures that the perforations 30 are effective to facilitate tear initiation along the edges of the finished packages.
The travel of the webs is controlled by conventional drive means which may be located, e.g. in the vacuate/gas flush/heat seal station 49. After cutting and trimming, the packages 12 are carried by conveyor 78 to an off-loading station, from where they are transferred to a heating/pasteurization station 80 in which the food product and package are heated to a temperature of about 200°F (about 93.4°C) for about 50 minutes. It has been found that this heating cycle, in addition to cooking and pasteurizing the food product, tends to warp and curl the package seal area 16, but does not impair the effectiveness of the punctures 30 in facilitating unaided manual tear initiation. Moreover, the punctures 30 do not cause unacceptable delamination of the films, or loss of hermeticity.
A second embodiment of the invention employs studded rollers 66 and 68 to provide the perforations in the packages, as illustrated in Figures 6 and 7. Each of the studded rollers 66 and 68 illustrated in Figure 6 comprises a generally cylindrical wheel having a plurality of pointed studs 70 extending radially outward from its peripheral surface. Each wheel is supported on a horizontal axis, and positioned such that the studs engage the longitudinal outer edge portions 58 of the packages after sealing. As shown in Figure 7, the film is supported in contact with the studded wheels 66 and 68 by lower wheels 74 and 76. The lower wheels 74 and 76 may be made of, for example, hard rubber, or a high molecular weight plastic.
A knife 72 is located immediately downstream from the studded wheels 66 and 68 to trim the perforated edge areas, ensuring that the perforations extend to the edges of the finished packages, as described above.
In the second embodiment, the sealing head is similar to that shown in Figure 2, except that the rectangular surfaces framing each of the cavities are substantially planar, rather than having studded perforation areas thereon. Otherwise, the second embodiment is substantially the same as the first embodiment described above.
From the foregoing, it will be appreciated that the invention provides an improved method and apparatus for packaging and processing a food product in a cook-in package. The invention is not limited to the particular embodiments described above, but rather is defined in the claims set forth below.

Claims

A method of packaging and processing a food product in a cook-in package, comprising:
advancing the food product in a predetermined direction while advancing at least one web of laminated polymeric film in the same direction adjacent thereto;
substantially enclosing said food product in said at least one web of laminated film, said at least one web defining an upper package wall and a lower package wall;
heat sealing said upper wall to said lower wall to form a hermetically sealed package with a sealed edge portion;
forming a plurality of punctures in an outer portion of said sealed edge portion to define a perforated area thereof curing or after said heat sealing; and
heating the food product and package to a predetermined cooking temperature for a predetermined period of time after forming said punctures while said food product remains hermetically sealed in said package.
A method in accordance with claim 1, wherein the step of forming a plurality of punctures in an outer portion of said sealed edge portion occurs during said heat sealing and comprises driving a plurality of studs therethrough, and maintaining said studs in said punctures during said heat sealing; and wherein said method further comprises trimming the heat sealed edge portion to remove a peripheral portion of the perforated area prior to said heating of the food product and package.
A method in accordance with claim 2, wherein the advancement of said at least one web is intermittent, and wherein the step of sealing the upper wall to the lower wall comprises lowering a sealing head into contact with the upper wall while the advancement of the food product and the web have been temporarily interrupted, the sealing head having said studs mounted thereon to form said punctures as said sealing head is lowered.
A method in accordance with claim 3, wherein the sealing head has said studs mounted thereon to form said punctures in a substantially uniform distribution.
A method in accordance with claim 1, wherein the step of forming a plurality of punctures in an outer portion of said sealed edge portion occurs after said heat sealing and comprises driving a plurality of studs therethrough, and wherein the method further comprises the step of trimming the sealed edge portion to remove a peripheral portion of the perforated area after formation of said punctures and prior to the step of heating of the food product and package.
A method in accordance with claim 5, wherein the step of forming a plurality of punctures comprises rotating a studded whell in contact with said sealed edge portion.
A method in accordance with claim 5 or claim 6, wherein said studded wheel forms said punctures in a substantially uniform distribution.
A method in accordance with any one of claims 1 to 7 comprising:
advancing a lower web of laminated plastic film including a tough polymeric outer layer of at least .001 in. (at least 0.025 mm) thickness and one or more inner layers in a predetermined direction with said food product supported thereon;
advancing an upper web of laminated plastic film material incliding a tough polymeric outer layer of at least .001 in. (at least 0.025 mm) thickness and one or more inner layers above said food product in said predetermined direction;
said upper and lower webs having a combined thickness totalling at least about .01 in. (at least about 0.25 mm);
heat sealing said upper web to said lower web at temperatures between 302°F and 320°F (150°C and 160°C) to form a hermetically-sealed pouch containing said food product and a peripheral seal area extending about said pouch;
forming a plurality of punctures in an outer portion of said peripheral seal area to form a perforated area thereof, while leaving intact an inner portion of said peripheral seal area, by driving a plurality of studs through said outer portion, each of said punctures having a transverse dimension of about .05 in (about 1.3 mm);
trimming an edge portion of said perforated area so that the remaining perforated area on the package has a width of about 1/8 in. (about 3.2 mm) and about 30-35 punctures per linear inch (about 11 to about 13 punctures per linear cm); and
heating said food product and package to a temperature of about 200°F (about 93.4°C) for a period of about 50 minutes with said food product remaining hermetically sealed in said package, after forming said perforated area and trimming said edge portion.
Apparatus for packaging and processing a food product in a cook-in package, comprising:
at least one web of plastic film;
means for conveying the food product in a predetermined direction while advancing said at least one web of plastic film in the same direction adjacent thereto;
means to substantially enclose said food product in said at least one web of plastic film so that said at least one web of plastic film defines an upper package wall and a lower package wall;
means for heat sealing said upper wall to said lower wall to form a hermetically-sealed package with a sealed edge portion;
perforation means for forming a plurality of punctures in an outer portion of said sealed edge portion to define a perforated area thereof during or after said heat sealing; and;
means for cooking the food product at a predetermined temperature for a predetermined period of time with said food product hermetically sealed in said package, after formation of said punctures.
Apparatus in accordance with claim 9, wherein said perforation means comprises a plurality of studs adapted to penetrate said upper wall and said lower wall during said heat sealing.
Apparatus in accordance with claim 9, wherein said perforation means comprises a plurality of studs mounted on a wheel positioned for contact with said outer portion of said sealed edge portion after sealing, and prior to cooking of the food product.
Apparatus in accordance with any one of claims 9 to 11 further comprising means for trimming said sealed edge portion to remove a peripheral portion of said perforated area after formation of said punctures and prior to cooking of the food product.
A cock-in package having a hermetically sealed interior for containing a food product during and after a cooking/pasteurization cycle, comprising upper and lower walls having a combined thickness of at least about .0.1 in. (at least about 0.25 mm), said walls comprising non-peelable polymeric laminated films including relatively thick, tough outer layers;
said upper and lower walls being heat sealed to one another to define a hermetically-sealed interior pouch and a peripheral seal area extending around said pouch;
said peripheral seal area having a plurality of punctures formed through an outer portion thereof and substantially evenly distributed thereon to define a perforated area extending to the outer edges of the package to facilitate tear initiation, said peripheral seal area also having an imperforate portion disposed inwardly of said perforated area to maintain hermeticity.
A cock-in package in accordance with claim 13, wherein said perforated area has a width of about 1/8 in. (about 3.2 mm) and comprises about 30-35 punctures per linear inch (about 11-13 punctures per linear cm), and wherein each of said punctures has a maximum transverse dimension of about .05 in. (about 1.3 mm).
A cock-in package in accordance with claim 13 or claim 14, wherein said lower wall comprises an outer layer of nylon having a thickness of about .002 in. (about 0.05 mm), an inner layer of linear low-density polyethylene having a thickness of about .005 in. (about 0.13 mm), and a tie layer therebetween; and
said upper wall comprises an outer layer of nylon having a thickness of about .001 in. (about 0.02 mm), an inner layer of linear low-density polyethylene having a thickness of about .003 in. (about 0.08 mm), and a tie layer therebetween.