WO2009144714A2

WO2009144714A2 - Food container sealing

Info

Publication number: WO2009144714A2
Application number: PCT/IL2009/000519
Authority: WO
Inventors: Yehuda Yamay
Original assignee: Hefestus Ltd
Priority date: 2008-05-27
Filing date: 2009-05-26
Publication date: 2009-12-03
Also published as: IL191736A0; WO2009144714A3

Abstract

A method of sealing a stamped tray. The method including aligning the stamped tray with a heated welding plate comprising a knurled portion, interspersing a polymeric sheet between the tray and the welding plate, and causing the knurled portion of the welding plate to press the polymeric sheet to the tray with an applied pressure force, thereby welding the polymeric sheet to the tray.

Description

FOOD CONTAINER SEALING

FIELD OF THE INVENTION

This invention relates to sealing of food containers.

BACKGROUND OF THE INVENTION

Modernization has contributed to an increased reliance on prepared foods.

Initially, canned foods were regarded as a great convenience due to their long shelf life. Frozen foods were the next innovation in the food industry. These products also have a long shelf life.

From frozen foods, the idea of prepackaged individual servings developed. Initially dubbed "TV dinners" or "heat and eat" meals, these products represented an advance in packaging technology more than in food preservation. In many cases, the individual serving is packaged as a meal with several components, each component in a separate compartment on a tray. The components are often selected to provide a "balanced" meal (e.g. meat, starch and cooked vegetable). Initial development employed trays stamp pressed from relatively thin aluminum sheets. Such products require cold storage. The stamp pressed aluminum trays are typically covered with a cardboard cover, a cardboard cover with an aluminum coating, or aluminum foil.

With the advent of microwave cooking technology, plastic trays (e.g. OCT) were use to make "microwaveable" TV dinners. The plastic trays are typically covered with a plastic sheet, typically a transparent plastic sheet. The sheet often seals the tray.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the invention relates to concentrating applied pressure force during heat welding of a plastic sheet to wrinkled edges of a stamp pressed tray.

In some exemplary embodiments of the invention, a knurled surface of a heat welding plate concentrates the applied pressure force. Optionally, the applied pressure force is 500, 550, 600, 650, 700, 750 or 800 kgf/cm² or intermediate or greater values. In some exemplary embodiments of the invention, increasing the pressure force contributes to sealing quality.

In some exemplary embodiments of the invention, knurling of the surface of the heat welding plate creates indentations with a depth of 0.3; 0.4; 0.5; 0.6; 0.7 or 0.8 mm or intermediate or greater depths. Optionally, increased depth contributes to concentration of the applied pressure force. Knurling patterns suitable for use in various exemplary embodiments of the invention include, but are not limited to, straight knurling and diamond knurling. Optionally, the knurling is coarse, medium or fine.

Equipment suitable for knurling of a heat welding plate is commercially available from, for example, Hommel and Keller Prazionwerkzeuge GmbH (Aldingen; Germany). One of ordinary skill in the art will be able to purchase commercially available knurling equipment and use it to produce knurled heat welding plates according to exemplary embodiments of the invention without undue experimentation.

In some exemplary embodiments of the invention, only a portion of the welding plate is knurled. Optionally, the edge is knurled. Alternatively or additionally, portions of the plate which correspond to dividers in a specific tray configuration are knurled.

In some exemplary embodiments of the invention, heat welding is conducted by heating the welding plate to a temperature of at least 160⁰C. Optionally, temperatures of 170, 180, 190, 200, 210 or 220 °C or intermediate or greater temperatures are employed.

In some exemplary embodiments of the invention, there is provided a method of sealing a package, the method includes:

(a) aligning a stamped tray with a heated welding plate including a knurled portion;

(b) interspersing a polymeric sheet between the tray and the welding plate; and

(c) causing the knurled portion of the welding plate to press the polymeric sheet to the tray with an applied pressure force, thereby welding the sheet to the tray.

The method may further comprise before step (a), placing the tray in a receptacle having support edges corresponding to edges of the tray, the support edges being adapted to seat and support the edges of the tray when said knurled portion is caused to press the polymeric sheet to said tray. Optionally, the tray is characterized by a thickness not exceeding 3mm. Optionally, the polymeric sheet includes at least one polymer selected from the group consisting of OPET and CPET.

Optionally, the welding plate is heated to at least 160⁰C.

Optionally, the knurled portion has a pattern characterized by a depth of at least 0.3 mm.

Optionally, the knurled portion has a pattern characterized by a depth not exceeding 0.8 mm.

Optionally, the applied pressure force is at least 500 kgf/cm².

Optionally, the applied pressure force does not exceed 800 kgf/cm².

Optionally, the method includes flushing the tray with an inert gas.

In some exemplary embodiments of the invention, there is provided a package sealing system, the system includes:

(a) an alignment mechanism adapted to align a stamped tray with a welding plate;

(b) a welding plate comprising a knurled portion;

(c) a sheet feeder adapted to feed a polymeric sheet between said tray and said welding plate;

(d) a welding plate operation mechanism adapted to press said knurled portion of said welding plate to said polymeric sheet and said tray with an applied pressure force, thereby welding said sheet to said tray; and

(e) a controller adapted to coordinate operation of said alignment mechanism, said sheet feeder and said welding plate operation mechanism.

Optionally, the system includes a heater configured to heat the welding plate to at least 160°C.

Optionally, the applied pressure force is at least 500 kgf/cm².

Optionally, the applied pressure force does not exceed 800 kgf/cm².

Optionally, the alignment mechanism includes at least one receptacle adapted to support a portion of said tray to be engaged by the knurled portion of the welding plate via the polymeric sheet, during application of said applied pressure force

Optionally, the system includes a tray feeder adapted to place the tray in the alignment mechanism.

Optionally, the system includes a cutter adapted to cut the polymeric sheet. Optionally, the system includes a gas exchange mechanism adapted to flush the tray with an inert gas.

In some exemplary embodiments of the invention, there is provided a package sealing apparatus, the apparatus includes:

(a) a receptacle adapted to support at least a portion of a stamped tray in alignment with a heated welding plate includes a knurled portion;

(b) a sheet feeder adapted to feed a polymeric sheet between the tray and the welding plate; and

(c) a welding plate operation mechanism adapted to press the knurled portion of the welding plate to the polymeric sheet and the tray with an applied pressure force, thereby welding the sheet to the tray.

Optionally, the apparatus includes a heater configured to heat the welding plate to at least l60°C.

Optionally, the apparatus applies a pressure force of at least 500 kgf/cm².

Optionally, the apparatus appliers a pressure force which does not exceed 800 kgf/cm².

Optionally, the apparatus includes a gas exchange mechanism adapted to flush the tray with an inert gas.

Optionally, the apparatus includes a cutter adapted to cut the polymeric sheet.

In some exemplary embodiments of the invention, there is provided a welding plate comprising a knurled portion.

Optionally, the knurled portion is disposed at a peripheral edge of the plate and/or at a non- peripheral edge of the plate.

Optionally, the welding plate further comprises a heating element. The heating element may be disposed at the knurled portion. The heating element may be adapted to heat said knurled portion to at least 16O⁰C.

Optionally, the knurled portion is characterized by a width of at least 3 mm.

It will be appreciated that the use of the term 'stamped tray¹ hereinabove and below refers to a container with one or more compartments. The tray may be made of aluminum or any malleable metal or metal alloy by stamp pressing or a similar industrial process. Typically, the metal is characterized by a thickness of 0.2; 0.5; 1; 1.5 or 2 mm or intermediate or greater thickness.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although suitable methods and materials are described below, methods and materials similar or equivalent to those described herein can be used in the practice of the present invention. In case of conflict, the patent specification, including definitions, will control. All materials, methods, and examples are illustrative only and are not intended to be limiting.

As used herein, the terms "comprising" and "including" or grammatical variants thereof are to be taken as specifying inclusion of the stated features, integers, actions or components without precluding the addition of one or more additional features, integers, actions, components or groups thereof. This term is broader than, and includes the terms "consisting of and "consisting essentially of as defined by the Manual of Patent Examination Procedure of the United States Patent and Trademark Office.

The phrase "consisting essentially of or grammatical variants thereof when used herein are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof but only if the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method.

The term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of architecture and/or computer science.

Implementation of the method and system of the present invention involves performing or completing selected tasks or steps manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of preferred embodiments of methods, apparatus and systems of the present invention, several selected steps could be implemented by hardware or by software on any operating system of any firmware or a combination thereof. For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit. As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, selected steps of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions.

Some of the advantages of the present invention may include: sealing a compartment of a tray with a polymeric sheet;

- sealing a compartment of a tray which has wrinkled surfaces;

- sealing a compartment of a collapsible tray by providing pressure to the edge portions of the tray, while simultaneously preventing such tray from collapsing during the sealing process;

- providing a method, system and product which allows sealed packaging of foods while maintaining a high quality of taste; and

- providing a method, system and product which allows food to be stored with a long shelf-life.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying figures. In the figures, identical and similar structures, elements or parts thereof that appear in more than one figure are generally labeled with the same or similar references in the figures in which they appear. Dimensions of components and features shown in the figures are chosen primarily for convenience and clarity of presentation and are not necessarily to scale. The attached figures are:

Fig. 1 is a photograph of a conventional stamp pressed aluminum tray;

Fig. 2 is a simplified flow diagram depicting a method according to some exemplary embodiments of the invention;

Fig. 3 is a schematic representation of a package sealing system according to exemplary embodiments of the invention;

Figs. 4A and 4B are photographs in plan view and top perspective view, respectively, of a heat welding plate according to an exemplary embodiment of the invention; Fig. 5 is a photograph in a top perspective view of a food package comprising food, according to an exemplary embodiment of the invention;

Fig. 6A is a schematic representation of a welding plate comprising knurled portions; and

Fig. 6B is a schematic representation of a stamped aluminum tray having wrinkled portions.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the invention relate to packaging methods, packaging systems, a packaging apparatus and a heat welding plate adapted for use in the packaging method and/or packaging apparatus and/or system.

Specifically, some embodiments of the invention can be used to heat weld a plastic sheet to a wrinkled border of a stamped aluminum tray.

The principles and operation of a packaging methods and/or packaging systems and/or packaging apparatus and/or a heat welding plate according to exemplary embodiments of the invention may be better understood with reference to the drawings and accompanying descriptions.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

Fig. 1 depicts a stamped aluminum tray, generally designated as 100. Peripheral wrinkled edges 102 resulting from a stamping process are indicated by arrows. Wrinkling occurs also at dividers or partitions 104 as indicated.

Fig. 2 is a simplified flow diagram depicting an exemplary method 200 of sealing a package. Method 200 includes the steps of aligning 210 a stamped aluminum tray with a heated welding plate having knurled portions. Alignment 210 brings knurled portions of the welding plate into a correct relative position with respect to wrinkled edges and/or wrinkled dividers in the tray. In some exemplary embodiments of the invention, the aluminum tray is characterized by a thickness not exceeding 2 to 3 mm. Depicted method 200 includes interspersing 220 a polymeric sheet between the aluminum tray and the welding plate. The polymeric sheet can be constructed of, for example OPET (Oriented Polyethylene Terephthalate e.g. IXAN® or DIOFAN®; Solvay Polymers inc. Houston TX, USA) or CPET (Crystalline polyethylene terephthalate). The sheet optionally has a thickness of 1, 5, 10, 50, 100, 500, 1000, 1500 or 2000 microns or intermediate or greater thickness. In some exemplary embodiments of the invention, a thicker sheet contributes to increased impermeability.

According to method 200, knurled portions of the welding plate are caused to press the polymeric sheet to at least some of the edges the aluminum tray with an applied pressure force 230, thereby welding 240 the sheet to the tray, and sealing at least one compartment of the tray with the sheet. Notably, all of the tray's compartments may be sealed or only selected compartments thereof. Causation can be via any mechanical, electromechanical or electronic means known in the art. In some exemplary embodiments of the invention, applied pressure force is provided manually. Optionally, the welding plate is heated to at least 160°C. In some exemplary embodiments of the invention, knurled portions, optionally edges, of the welding plate have a pattern characterized by a depth of at least 0.3 mm and/or a depth not exceeding 0.8 mm. In some exemplary embodiments of the invention, the applied pressure force is 500, 600, 700 or 800 kgf/cm2 or intermediate or greater forces.

Optionally, method 200 includes flushing 250 the tray with an inert gas. Flushing of this type has been described in US 6,912,828 by the same inventor as the instant application. In some exemplary embodiments of the invention, apparatus as described in US 6,912,828 are employed and welding plate 160 (according to the enumeration of figures in US 6,912,828) is provided as a knurled welding plate.

Fig. 3 is a schematic diagram of an exemplary package sealing system 300 according to an exemplary embodiment of the invention. System 300 includes an alignment mechanism 362 adapted to align a stamped aluminum tray 100 with a knurled heated welding plate 320. Alignment mechanism 362 depicted symbolically as a four headed arrow can be provided, for example, as a rotating platform or conveyor belt fitted with one or more receptacles 360 to engage tray 100. In some exemplary embodiments of the invention, receptacle 360 is adapted to support edges 101 of tray 100 when edges 330 of plate 320 press down on it. Thus the receptacle may have a compartment 103 which is adapted to receive the tray 100 therein. The compartment 103 having upper edges 105 adapted to form a seating for the edges 101 of the tray which are intended to be welded to the sheet 374. To form such seating, the upper edges 105 are adapted to have an upper surface area corresponding roughly in size and position to a lower surface of the edges 101 of the tray seated thereon. Optionally, this contributes to an ability of tray 100 to tolerate a greater applied force. In the figure, plate 320 is seen in cross section and knurled edges 330 are depicted by diagonal stripes.

Depicted exemplary system 300 includes a sheet feeder 370 adapted to feed a polymeric sheet 374 between aluminum tray 100 and welding plate 330. Optionally, feeder 370 includes a cutting tool 372 which cuts sheet 374.

Depicted exemplary system 300 includes a welding plate operation mechanism adapted to press knurled edges 330 of welding plate 320 to polymeric sheet 374 and aluminum tray 100 with an applied pressure force, thereby welding the sheet to the tray.

In the exemplary embodiment of Fig. 3, the welding plate operation mechanism includes a ridged post 312 and a drive mechanism 310. Drive mechanism 310 can include one or more gears which engage ridges on post 312. Rotation of the gears in one direction drives post 312 and plate 320 downwards and rotation in an opposite direction raises post 312 and plate 320.

Depicted exemplary system 300 is an automated system including a controller 340adapted to coordinate operation of alignment mechanism 362, sheet feeder 370 and welding plate operation mechanism 310; 312. In some exemplary embodiments of the invention, operation of system 300 by controller 340 constitutes practice of method 200 as described above.

Optionally, welding plate 320 includes a heater configured to heat at least edges 330 of welding plate 320 to at least 160⁰C. Optionally, the heater is thermostatically controlled. In some exemplary embodiments of the invention, the thermostat is provided in controller 340 and/or within plate 320.

Optionally, drive mechanism 310 is adapted to provide an applied pressure force least 500; 600; 700 or 800 kgf/cm² or intermediate or greater forces through edges 330 of plate 320 to sheet 374 and to edges 110 of tray 100. The upper edges 105 prevent the tray 110 from being flattened during the welding action.

Depicted exemplary system 300 includes an optional tray feeder adapted to place trays 100 in receptacles 360 of alignment mechanism 362. The depicted tray feeder includes a supply 120 of trays 100 which are available to a robotic device. Supply 120 is depicted as a vertical stack of trays 100 for clarity. In some exemplary embodiments of the invention, supply 120 includes a linear array of trays 100, optionally filled with one or more food products. Filling can be accomplished by any means known in the art. Optionally, supply 120 takes the form of trays exiting a conveyor belt. The robotic device includes a robotic drive 380 adapted to provide axial and rotational translation relative to a vertical post 382 and extension/retraction of a horizontal arm 386 equipped with robotic fingers 384. Drive 380 is further adapted to cause fingers 384 to engage and/or release a tray 100 at appropriate times and/or positions. In the depicted exemplary embodiment of the invention, controller 340 controls robotic drive 380 so that it retrieves trays 100 from supply 120 and places them in receptacle 360 as needed.

In the depicted exemplary embodiment of the invention, a gas exchange mechanism (depicted as gas conduit 350) adapted to flush each tray 100 with an inert gas as it is being sealed is provide. Optionally, controller 340 coordinates provision of gas through conduit 350 during operation of system 300.

In other exemplary embodiments of the invention, a package sealing apparatus 300 is provided. Apparatus 300 includes, a receptacle 360 adapted to support at least a portion of a stamped aluminum tray 200 in alignment with a knurled 330 heated welding plate 320 and a sheet feeder 370 adapted to feed a polymeric sheet 374 between aluminum tray 100 and welding plate 320. The apparatus further includes a welding plate operation mechanism adapted to press knurled edges 330 of welding plate 320 to polymeric sheet 374 and aluminum tray 100 with an applied pressure force, thereby welding sheet 374 to tray 100. Optionally, the welding plate operation mechanism includes a ridged post 312 and drive mechanism 310 including one or more gears adapted to engage ridges on post 312 as described above. In some exemplary embodiments of the invention, drive mechanism 310 is adapted for manual operation, for example by a lever 311 which is operably connected to the gears.

Fig. 5 is a photograph depicting an exemplary food package 500 in which a transparent polymeric sheet has been directly heat welded to wrinkled edges of an aluminum tray as described above.

Reverting to Figs. 4A and 4B, an example of a welded plate 800 is shown. The welding plate 800 comprises a knurled edge 802. For convenience during a manufacturing process, a support portion 804 extends between the knurled edges 802 of the plate 810. The support portion 804 is adapted to be held by a welding machine component (not shown) and to hold the knurled edges 802. In this example the support portion is a generally planar plate portion 804, which is recessed or spaced from a knurled surface 806 of the knurled edge 802. The spacing corresponds to the height of an inner side edge 807 of the knurled edge 802. This spacing may be beneficial as it allows only desired portions of the plate 800, i.e. the knurled edge 802 to engage a tray (not shown) to be welded, while keeping the plate portion 804 spaced from the tray. In this example the planar plate portion is shown with layered sections, two examples of which are identified as 808, 810, of differing height.

Fig. 6A is a diagram depicting a welding plate 320 according to an exemplary embodiment of the invention. Depicted exemplary plate 320 includes knurled edges 330 and/or 331 adapted to conform to edges 102 and/or dividers 104 of a stamped aluminum tray 100 (Fig. 6B). The welding plate 320 further comprises a heating element 610 adapted to heat said knurled edges 330 and/or 331. In this example the heating element is adapted to heat the knurled edges to 160⁰C. In some exemplary embodiments of the invention, knurled edges 330 and/or 331 have a pattern characterized by a depth of at least 0.3 mm. In some exemplary embodiments of the invention, knurled edges 330 and/or 331 have a pattern characterized by a depth not exceeding 0.8 mm. In some exemplary embodiments of the invention, knurled edges 330 and/or 331 are characterized by a width of at least 3 mm. Optionally, conformation to wrinkled edges is achieved by knurling a large portion, optionally substantially all of a surface of plate 320. The lower portion of Fig. 6B shows corresponding wrinkled edges 102 and dividers 104 of a stamped aluminum tray 100. This configuration is exemplary only. Many different tray configurations including, but not limited to, rectangular, square round and oval are prevalent in the food industry. Additionally, any tray configuration can be modified by addition of one or more dividers 104.

Fig. 6B illustrates that for any configuration of tray 100, edges 102 and dividers 104, and Fig. 6A illustrates a corresponding welding plate 320 with knurled edges 330 and/or 331 and a heating element 610.

It will be understood that welding plates with knurled edges and a heating element 610 may be arranged to correspond to any design of tray are within the scope of the invention. It is expected that during the life of this patent many types of plastic sheeting material will be developed and the scope of the invention is intended to include all such plastic sheeting a priori.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Specifically, a variety of numerical indicators have been utilized. It should be understood that these numerical indicators could vary even further based upon a variety of engineering principles, materials, intended use and designs incorporated into the invention. Additionally, components and/or actions ascribed to exemplary embodiments of the invention and depicted as a single unit may be divided into subunits. Conversely, components and/or actions ascribed to exemplary embodiments of the invention and depicted as sub-units/individual actions may be combined into a single unit/action with the described/depicted function.

Alternatively, or additionally, features used to describe a method can be used to characterize an apparatus and features used to describe an apparatus can be used to characterize a method.

It should be further understood that the individual features described hereinabove can be combined in all possible combinations and sub-combinations to produce additional embodiments of the invention. The examples given above are exemplary in nature and are not intended to limit the scope of the invention which is defined solely by the following claims.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

The terms "include", and "have" and their conjugates as used herein mean "including but not necessarily limited to".

Claims

CLAIMS:

1. A method of sealing a package, the method comprising:

(a) aligning a stamped tray with a heated welding plate comprising a knurled portion;

(b) interspersing a polymeric sheet between said tray and said welding plate; and

(c) causing said knurled portion of said welding plate to press said polymeric sheet to said tray with an applied pressure force, thereby welding said sheet to said tray.

2. A method according to claim 1, further comprising before step (a), placing the tray in a receptacle having support edges corresponding to edges of the tray, the support edges being adapted to seat and support the edges of the tray when said knurled portion is caused to press the polymeric sheet to said tray.

3. A method according to claims 1 or 2, wherein said tray is characterized by a thickness not exceeding 3mm.

4. A method according to any one of claims 1 to 3, wherein said polymeric sheet comprises at least one polymer selected from the group consisting of OPET and CPET.

5. A method according to any one of claims 1 to 4, wherein said welding plate is heated to at least 160°C.

6. A method according to any one of claims 1 to 5, wherein said knurled portion has a pattern characterized by a depth of at least 0.3 mm.

7. A method according to any one of claims 1 to 6, wherein said knurled portion has a pattern characterized by a depth not exceeding 0.8 mm.

8. A method according to any one of claims 1 to 7, wherein said applied pressure force is at least 500 kgf/cm².

9. A method according to any one of claims 1 to 8, wherein said applied pressure force does not exceed 800 kgf/cm².

10. A method according to any one of claims 1 to 9, further comprising: flushing said tray with an inert gas.

11. A method according to any one of claims 1 to 10, wherein said stamped tray is made of aluminum.

12. A package sealing system, the system comprising:

(b) a welding plate comprising a knurled portion;

13. A system according to claim 12, comprising a heater configured to heat said welding plate to at least 160°C.

14. A system according to claim 12 or 13, wherein said applied pressure force is at least 500 kgf/cm².

15. A system according to any one of claims 12 to 14, wherein said applied pressure force does not exceed 800 kgf/cm².

16. A system according to any one of claims 12 to 15, wherein said alignment mechanism includes at least one receptacle adapted to support a portion of said tray to be engaged by the knurled portion of the welding plate via the polymeric sheet, during application of said applied pressure force.

17. A system according to any one of claims 12 to 16, comprising: a tray feeder adapted to place said tray in said alignment mechanism.

18. A system according to any one of claims 12 to 17, comprising: a cutter adapted to cut said polymeric sheet.

19. A system according to any one of claims 12 to 18, further comprising: a gas exchange mechanism adapted to flush said tray with an inert gas.

20. A system according to any one of claims 12 to 19, wherein said stamped tray is made of aluminum.

21. A package sealing apparatus, the apparatus comprising:

(a) a receptacle adapted to support at least a portion of a stamped tray in alignment with a heated welding plate comprising a knurled portion;

(b) a sheet feeder adapted to feed a polymeric sheet between said tray and said welding plate; and

(c) a welding plate operation mechanism adapted to press said knurled portion of said welding plate to said polymeric sheet and said tray with an applied pressure force, thereby welding said sheet to said tray.

22. An apparatus according to claim 21, comprising a heater configured to heat said welding plate to at least 16O⁰C.

23. An apparatus according to claim 21 or 22, wherein said applied pressure force is at least 500 kgf/cm².

24. An apparatus according to any one of claims 21 to 23, wherein said applied pressure force does not exceed 800 kgf/cm².

25. An apparatus according to any one of claims 21 to 24, comprising: a gas exchange mechanism adapted to flush said tray with an inert gas.

26. An apparatus according to any one of claims 21 to 25, comprising: a cutter adapted to cut said polymeric sheet.

27. An apparatus according to any one of claims 21 to 26, wherein said stamped tray is made of aluminum.

28. A welding plate comprising a knurled portion.

29. A welding plate according to claim 28, wherein said knurled portion is disposed at a peripheral edge of the plate.

30. A welding plate according to claim 28 or 29, wherein said knurled portion is disposed at a non- peripheral edge of the plate.

31. A welding plate according to any one of claims 28 to 30, further comprising a heating element.

32. A welding plate according to claim 31, wherein the heating element is disposed at the knurled portion.

33. A welding plate according to claims 30 or 31, wherein said heating element is adapted to heat said knurled portion to at least 160⁰C.

34. A welding plate according to any one of claims 28 to 32, wherein said knurled portion has a pattern characterized by a depth of at least 0.3 mm.

35. A welding plate according to any one of claims 28 to 34, wherein said knurled portion has a pattern characterized by a depth not exceeding 0.8 mm.

36. A welding plate according to any one of claims 28 to 35, wherein said knurled portion is characterized by a width of at least 3 mm.