GB2271546A

GB2271546A - Vacuum packaging chamber and method

Info

Publication number: GB2271546A
Application number: GB9221924A
Authority: GB
Inventors: Enzo Pasetti
Original assignee: WR Grace and Co Conn; WR Grace and Co
Current assignee: WR Grace and Co Conn; WR Grace and Co
Priority date: 1992-10-19
Filing date: 1992-10-19
Publication date: 1994-04-20
Also published as: GB9221924D0; NZ248962A

Abstract

A vacuum chamber has a lower chamber portion 11 with at least one groove 16a, 16b formed in the internal surface of the side wall 14 adjacent the rim of the chamber. The grooving results in a reduction of the incidence of wrinkles in the cover film of a finished pack because surplus film at its edges can be accommodated in the grooves as the film is drawn downwardly to cover a filled tray located in a recess 21 in a support plate 17. The film is heated by an upper heating plate 19 prior to being drawn downward. The grooves are of arcuate, eg. parabolic, cross-section and may be provided along two opposed side walls which are parallel to the direction of introduction of the film (or along all four side walls). <IMAGE>

Description

VACUUM PACKAGING CHAMBER AND METHOD The present invention relates to a vacuum packaging chamber of the type in which a product on a lower support is subjected to vacuum while it is underneath a heated film which is (i) being softened by the heating process and is then (ii) released on to the product and the support, to form a vacuum pack therewith. The invention also relates to a method of vacuum packaging.

Particularly in the case where the support is a tray having upwardly inclined side walls towards the tray rim, there arises the incidence of wrinkles in the upper film due to the need to provide sufficient spare film during the heating process to allow for the film to descend fully into the troughlike space left around the exterior of the product and inboard of the raised rim of the tray. Such wrinkles are unsightly and may even give rise to micro-channels through the seal on the tray rim, resulting in reject packages in which the vacuum is progressively lost during the life of the pack during storage, transport and display at the point of sale. Such wrinkles frequently occur along lines which are generally parallel to the line of a web of film supplied to the packaging apparatus to provide the cover film.

It is an object of the present invention to provide a vacuum packaging chamber in which the incidence of wrinkling in the cover film of the pack is considerably reduced or totally eliminated, in comparison with the prior art machines.

Accordingly, one aspect of the present invention provides a vacuum chamber comprising an upper chamber portion and a lower chamber portion, with at least one groove defined on the internal surface of said lower chamber portion along at least one upstanding wall thereof.

A second aspect of the invention provides a vacuum packaging method comprising:- heating a cover film while positioned above a support film having at least one product article thereon, by conduction resulting from holding said cover film in contact with a heated surface in a vacuum chamber upper portion; drawing a vacuum between said cover film and said base film and at least one product; displacing said cover film downwardly into contact with said product article and base film in a lower chamber portion in the closed configuration of the chamber, while accommodating displacement of said cover film laterally near the walls of said chamber, into at least one recess in the internal wall of the chamber, to reduce the incidence of wrinkling of the cover film in the finished pack; and sealing the cover film to the base film as a result of mutual contact during the downward displacement of the cover film.

In order that the present invention may more readily be understood the following description is given, merely by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a vertical section through a vacuum packaging chamber in accordance with the present invention, showing the upper and lower chamber parts; FIGURE 2 is a detailed section of the lower chamber part taken on the line 2-2 of Figure 1; FIGURE 3 is a section taken on the line 3-3 of Figure 2 but showing an alternative form of the chamber and illustrating a product support plate within the lower chamber portion and a heating plate in the upper chamber portion; FIGURE 4 is a perspective view of a prior art pack showing the incidence of wrinkling in the upper film; and FIGURE 5 is a view corresponding to that of Figure 4 but showing a pack formed by use of the packaging chamber in accordance with the present invention; and FIGURE 6 corresponds to Figure 3 but shows the configuration of the chamber when the cover film has been draped onto the product at the completion of the pack-closing step in accordance with the present invention.

Figure 1 shows the lower chamber part 1 as comprising a front wall 2, a rear wall 3, and side walls 4 of which one is visible in the drawing.

The chamber furthermore comprises an upper chamber part 5 in which the heating means for the upper (cover) film is provided. Both the upper and lower chamber parts are communicated with vacuum to control the movement of the cover film during the sealing process and the atmospheric pressure below the cover film which will become the atmospheric pressure within the sealed pack. The vacuum conduits are not visible in Figure 1.

Figure 1 also shows the existence of a groove 6 near the upper edge of the side wall 4, and extending substantially along the full length of the side wall 4 on the inner face thereof. This groove is shown in more detail in the transverse sectional view shown in Figure 2. The direction of introduction of the cover film to seal the trays (not shown) in the chamber 1, 5 is from left to right in Figure 1.

An alternative embodiment of the vacuum chamber in accordance with the present invention is shown in more detail in Figure 3 in which the lower chamber portion 11 has its side wall 14 provided with two separate parallel grooves 16a and 16b each of the form illustrated in Figure 2.

As shown in Figures 2 and 3, the grooves are preferably arcuate in cross-section and in this particular case they are substantially parabolic in that they are tapered from the outer portion to the floor of the groove.

If desired the grooves 16 in Figure 1, and 16a and 16b in Figure 2, may also be formed in the other two upstanding walls of the chamber lower part 1 or 11.

Figure 3 also shows a heating plate 19 which fits closely within the upper chamber portion 15 and is spaced from the vertical walls 18 of the upper chamber portion so as to allow vacuum introduced through a port 23 to be communicated both around the edges of the heating plate 19, and through apertures 24 therethrough, to a space above a cover film (not shown) stretched across the rim of the lower chamber portion 11.

Sealing between the upper and lower chamber portions 15 and 11, respectively, is achieved by way of a seal 20 received in the rim of the upper chamber portion 15.

The support plate 17 for both the product and the lower film web is provided with tray-defining recesses 21 in which individual trays can be sat, either severed from one another or still joined by selvage to allow a large sheet of trays to be passed through the machine on a continuous basis. The support plate 17 is removably carried by a lifting plate 25 mounted on a vertically reciprocable column 26. The floor 14' of the lower chamber portion 11 furthermore has at least one vacuum port 22 which, by way of the space around the periphery of the lifting plate 25 and the support plate 17, defined between the plates and the vertical walls 14 of the lower chamber portion 11, allows vacuum to be communicated to the space below a cover film stretched across the rim of the lower chamber portion 11.

Although only Figure 3 shows the lifting tray 25 and the support tray 17 for products and articles, it will of course be understood that Figure 1 includes such plates.

Furthermore, although the support tray 17 is shown in Figure 3 as having provision for several trays, it is conceivable for only one tray-receiving recess 21 to be provided in the chamber, and it is indeed possible alternatively for the support to be flat without a tray-receiving recess, in the case where the support sheet of the package will be flat.

In operation of the device shown in Figures 1 and 2 and that shown in the alternative embodiment of Figure 3, a plurality of trays is first of all placed on the support plate (such as 17 in Figure 3) and products are placed on the individual trays. This may be effected automatically during operation of an automatic machine in which a continuous web of thermoformed tray stock material is advanced stepwise together with product articles into the open vacuum chamber where the products and the supports are covered with a flexible cover film 30 (Figure 6) by the process about to be described.

With the product and support tray(s) in position on the support plate 17 of Figure 3, and a web of cover film stretched across the rim of the lower chamber portion 11, the upper chamber portion 15 is lowered into the closed position as shown in Figure 3 and heat is applied to the cover film by virtue of contact of the film with the upper heating plate 19 against which the cover film may be drawn by the application of suction through the port 23.

When the temperature of the cover film has risen sufficiently to permit draping on to the product and the support tray with a thermoforming action, the cover film is caused to descend. However, before this descent begins there will already have been the application of suction to the space beneath the cover film (by way of the vacuum port 22 and the space around the periphery of the plate 17) but with the proviso that the vacuum below the cover film is initially "softer" than the "hard" vacuum above the cover film in order that the film may remain in contact with the heating plate 19.

When draping of the cover film is required, the vacuum above the cover film is released and the film is thus sucked, by the vacuum in the lower chamber portion, down on to the product and tray.

The process so far described is a standard vacuum skin packaging (VSP) process.

In the standard process the need to provide sufficient film to drape adequately on to the rear of the tray and down into the "trough" (see 29 in Figure 5) around the product has in the past given rise to the incidence of wrinkles extending along a direction generally into the paper in Figure 3 (or from left to right in Figure 1).

In accordance with the present invention the lower chamber portion has at least one groove formed in its inner surface along at least one of the side walls. The groove 6 in Figure 1 shows an example of a single groove configuration, whereas the twin grooves 16a and 16b in Figure 3 show a multiple groove configuration. More than two grooves may be provided. The completion of the pack-closing step is shown in Figure 6.

It is thought that the present invention eliminates wrinkling by presenting the inner surface of the upstanding side wall of the lower chamber portion (1 in Figure 1 and 2 or 11 in Figure 3) with an increased surface area as compared with a flat side wall, and hence provides a space into which the surplus film material 30 may be drawn by the vacuum in such a way that the film is more firmly stretched across the top of the tray, but nevertheless sufficiently yieldably to allow the film material to fill the trough around the products.

By way of illustration of the advantages of the vacuum chamber in accordance with the present invention, Figure 4 shows the tray 27 with visible evidence of wrinkles 28 on it, whereas Figure 5 shows a similar tray 27' without wrinkling, by virtue of use of the vacuum chamber in accordance with the present invention.

Claims

1. A vacuum chamber comprising an upper chamber portion and a lower chamber portion, with at least one groove defined on the internal surface of said lower chamber portion along at least one upstanding wall thereof.

2. A chamber according to claim 1 wherein there is at least one said groove along both of two opposite upstanding walls of said lower chamber portion.

3. A chamber according to claim 2, wherein there are two grooves along each of said upstanding walls.

4. A chamber according to any one of the preceding claims, wherein the or each said groove is of arcuate crosssection.

5. A chamber according to claim 4, wherein the or each said groove tapers from the outside towards the floor of the groove.

6. A chamber according to any one of the preceding claims, wherein there is at least one said groove in each of four upstanding walls of the lower chamber portion.

7. Packaging apparatus including the chamber of any one of the preceding claims, and means for introducing a packaging film into said chamber between the rims of the upper and lower chamber parts, said grooves being formed along at least those walls which are parallel to the direction of introduction of said web.

8. A vacuum chamber substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 and 2, or Figure 3, of the accompanying drawings.

9. A vacuum packaging method comprising:- heating a cover film while positioned above a support film having at least one product article thereon, by conduction resulting from holding said cover film in contact with a heated surface in a vacuum chamber upper portion; drawing a vacuum between said cover film and said base film and at least one product; displacing said cover film downwardly into contact with said product article and base film in a lower chamber portion in the closed configuration of the chamber, while accommodating displacement of said cover film laterally near the walls of said chamber, into at least one recess in the internal wall of the chamber, to reduce the incidence of wrinkling of the cover film in the finished pack; and sealing the cover film to the base film as a result of mutual contact during the downward displacement of the cover film.

10. A method according to claim 9 wherein said base film is in the form of elongate trays and the lateral displacement of the cover film is effected in a direction outwardly relative to the longitudinal sides of the tray.

11. A vacuum packaging method substantially as hereinbefore described with reference to the accompanying drawings.