GB2064465A - Heat-sealed skin packages - Google Patents

Abstract

A skin pack comprises a transparent, cold-distendible film 2 adhered round its edges to cover an aperture 4 in a display card 3. A backing sheet 5 is adhered to the display card 3 using a heat-sensitive adhesive, the heat being applied only around the edge of the aperture so that the transparent film over the aperture is not heated. The display card 3 and backing sheet 5 may be identical, the heat-sensitive adhesive being constituted by that portion of the film situated between the card 3 and the sheet 5. The heat is applied by a heated platen press comprising two apertured platens (7, 8, figure 4, not shown), each of which includes a face sheet (15, figure 6, not shown) and an array of aluminium blocks (19) for varying the depth of the platen aperture. <IMAGE>

Description

SPECIFICATION Sealing packages The invention relates to a method and apparatus for sealing packages. The packages with which the invention is concerned are called skin packs and have the distinguishing feature that an article or articles is displayed, visible through an aperture in a card, and is held in position in the pack between a transparent plastics film spanning the aperture and a transparent or opaque backing.

Early skin packs were formed using a heatstretchable film over the aperture in the card. The article to be packaged is placed on the film, and the backing adhered to the card using heat and pressure. If desired the backing can be a solid card onto one surface of which a heat sensitive adhesive has been applied. Alternatively the backing can be an apertured card with a similar heat-stretchable film over the aperture, so that with the apertures of the two cards in alignment the packaged article is displayed suspended in the window formed by the aligned apertures.One Patent Specification describing such a pack is British Patent Specification No. 1,197,052. The heat-stretching of the film and the heat-sealing together of the two halves of the pack is achieved in that Specification using two heated platens both of which are hollowed out to conform to the shape of the article to be packed.

Accurate temperature control of the platens is necessary lest they burn a hole in the film, which requires costly tooling. The platens must be hollowed to accommodate the article to be packed while providing uniform heating to the whole of the heat-stretchable film. Furthermore this method of packaging is not suitable for all articles, as the article itself may be damaged by the heat applied to stretch the film.

An alternative method of forming skin packs is described in our Patent Specification No.

1,548,870. In that Specification the film is described as being capable of distending without the application of heat, and without heating the film the article is pressed against the transparent film to distend the film. The backing sheet and card are secured together by an applied adhesive, and the Specification suggests the use of a pressure-sensitive adhesive.

The above method of packaging is an improvement on that of Specification No.

1,197,052 in that it avoids the relatively expensive tooling needed to provide shaped heated platens with accurate film temperature control. Furthermore it is suitable even for packaging heat-sensitive articles which could be damaged if the plastics film were heat-shrunk around them. However it is restrictive on the adhesive effect that is obtained between the apertured card and the backing sheet. Pressuresensitive adhesives are generally inferior to heatsensitive adhesives in their adhesion, and other cold-setting adhesives do not provide an instant bond.

This invention provides a method of packaging an article which comprises placing the article on a sheet of a transparent plastics material that is capable of being distended without the application of heat, the sheet being secured around its periphery to an apertured display card so as to span the aperture, bringing a backing sheet into face-to-face contact with the display card so as to press the article against the transparent sheet, and applying local heat to the mutually contacting areas of the display card to activate a heatsensitive adhesive substance therebetween to adhere the display card to the backing sheet without heating the sheet of transparent plastics material.

Using the method of this invention a better adhesion can be obtained between the display card and backing sheet than when using pressuresensitive adhesives such as latex adhesives, and this has enabled much thicker articles to be packaged. Previously the adhesive parted before the transparent plastics film reached the limit of its stretch, so that it was in fact the adhesive and not the film that dictated the maximum thickness of article that could be packaged.

The heat-sensitive adhesive substance may be applied to a part or the whole of the relevant face of the display card or the backing sheet, before assembly of pack by bringing the display card and backing sheet into face-to-face contact with one another. The adhesive substance may be applied as a wet film and allowed to dry before assembly of the pack. It may be applied to the display card and to the periphery of the sheet of transparent plastics material so that the mutually contacting areas of the display card and backing sheet adhere together right up to the edge of the aperture, thus giving a particularly neat and attractive appearance to the finished pack.Alternatively the transparent plastics sheet itself may be heatsensitive so that it acts as the adhesive substance between the display card and the backing sheet on the application of local heat to the mutually contacting areas thereof.

The application of local heat to the display card and backing sheet around the aperture may be achieved using a shaped heated platen press of which one or both platens are recessed to conform to the shape of the aperture. The recess should be sufficiently deep to ensure that the transparent sheet covering the article to be packaged does not contact the heated platen or platens in use. Thus one set of platens can be used to package a variety of articles using the same combination of apertured display card and backing sheet, as long as the size and shape of the aperture does not vary. This is a substantial advance on the prior art method of British Patent No. 1,197,052 which requires costly apparatus to heat-stretch the film.

Because according to this invention the recesses in the platens do not have to be contoured to the shape of the articles to be packaged, the press can easily be designed with interchangeable platen faces and provided with a set of such faces to correspond to the range of shapes and sizes of aperture in the display cards.

Either these platen faces can be fretted out of solid blocks of thermally conductive material such as aluminium or they can be fretted out of relatively thin plates of thermally conductive material and assembled onto the press using spacer blocks of thermally conductive material to provide the necessary depth of recess.

The invention lends itself equally to packaging articles between the transparent plastics sheet and an opaque backing sheet, for example of card, and packaging the articles between two transparent plastics sheets extending across corresponding apertures in the display card and the backing sheet respectively. The display card and backing sheet may be initially separate or may be formed from a single piece of card folded at the centre.

The invention is illustrated with reference to the drawings of which: Figure 1 is a schematic plan view of packaging for a torch battery before assembly into a pack according to this invention; Figure 2 is a side elevation of the pack after assembly; Figure 3 is a side elevation of an alternative pack assembled according to the method of the invention; Figure 4 is a schematic perspective view of a heated platen press used to assemble the pack of Figure 2; Figure 5 is a perspective view of one platen of the press, showing one possible form of construction; and Figure 6 is an exploded perspective view corresponding to that of Figure 5, showing another possible form of construction of the platen.

Referring first to Figures 1 and 2, a torch battery 1 is to be packaged in a display pack by the method of this invention. The battery 1 is first placed over a transparent plastics film 2 that is adhered around its periphery to a display card 3, spanning an aperature 4 in the card. A backing sheet 5 is constructed in an entirely similar fashion, with a transparent plastics film 2' adhered around its periphery to a backing card 3', spanning an aperture 4' in the card. The cards 3 and 3' are exactly the same size and shape, and when the cards are placed face to face the apertures 4 and 4' are in exact alignment as are peg holes 6 and 6' for hanging the assembled pack at a retail point of sale.

The plastics film 2 and 2' is a non-oriented polypropylene film which is capable of being distended without the application of heat. Printed onto the backing sheet 5 over the whole of the surface area up to but not including the aperture 4' is a heat-sensitive adhesive.

Initially the display card 3 and backing sheet 5 are flat, which is ideal for storage purposes. On assembly into the pack of Figure 2, the backing sheet 5 is placed over the display card 3 as shown by the arrows in Figure 1, and localized heat and pressure applied to the contacting surfaces around the aperture until the heat-sensitive adhesive forms a bond between the backing sheet 5 and display card 3. It has been found that this bond is sufficient to hold the two together right up to the edge of the apertures 4 and 4'. Moreover the pack has been assembled without the application of heat to the films 2 and 2', so that the method could have been used to package a heat-sensitive article in place of the battery 1.

Figure 3 illustrates a similar pack of which the backing sheet 5 is not apertured as in Figures 1 and 2 but forms an opaque backing for the aperture 4.

Figure 4 shows a heated platen press for providing the localized heat and pressure around the aperture 4 for the pack of Figure 2. One or both platens may be heated.

A top platen 7 is movable downwardly onto a bottom platen 8 to bring respective recesses 9 and 10 into alignment. An array of lays 11 in the bottom platen 8 enables the display card 3 and backing sheet 5 to be placed on the bottom platen with their apertures 4 and 4' in exact alignment with the recesses 9 and 10. The depth of the recesses 9 and 10 is sufficient to ensure that the heated platen does not contact the transparent plastics film 2 or 2', so that the heat transfer is confined to the zone around the apertures 4 and 4', which zone is coated with the temperaturesensitive adhesive.

For the pack of Figure 3 the same heated platen press could be used or one with only one recessed platen.

Figure 5 illustrates the simplest construction of a recessed heated platen for use in the press of Figure 4. The heated platen face is a face 12 of a solid block 13 of a heat-conductive material such as aluminium, out of which has been fretted or milled an aperture 14 passing completely through the block. The thickness of the block 13 defines the depth of the aperture 14, and the aperture is shaped closely to correspond to the aperture 4 in the display card.

One such platen or a pair of such platens would in practice be provided for each size and shape of aperture 4 in the display card 3. This can become relatively expensive in materials when a large number of different apertured blocks 13 is needed, and Figure 6 shows the construction of a platen designed to reduce this expense.

The platen of Figure 6 comprises a face sheet 15 from which has been cut the precise shape of the aperture 4 of the display card with which the platen is to be used. A side wall is formed from a band 16 passing around four corner angles 17 and fastenable by means of a toggle joint 18. In use the depth of the aperture in the face sheet 1 5 is increased by assembling an array of aluminium blocks 1 9 over the face sheet around the aperture, and clamping them in position with the band 1 6 and toggle joint 1 8. The assembly is held together and secured to the heated surface of a heated platen press by means not shown.

As assembled, the platen face piece of Figure 6 is in all material respects anaiogous to that of Figure 5. However to modify it to a different shaped aperture only the face sheet 1 5 need be replaced (and the blocks 1 9 rearranged and perhaps supplemented) so that the use of material is reduced substantiaily.

Claims (8)

1. A method of packaging an article which comprises placing the article on a sheet of a transparent plastics material that is capable of being distended without the application of heat, the sheet being secured around its periphery to an apertured display card so as to span the aperture, bringing a backing sheet into face-to-face contact with the display card so as to press the article against the transparent sheet, and applying local heat to the mutually contacting areas of the display card and backing sheet around the aperture of the display card to activate a heatsensitive adhesive substance therebetween to adhere the display card to the backing sheet without heating the sheet of transparent plastics material.

2. A method according to claim 1, wherein the backing sheet comprises a card having an aperture formed therein corresponding to the aperture in the display card, and a sheet of the transparent plastics material secured around its periphery to the card so as to span the aperture.

3. A method according to either preceding claim, wherein the heat-sensitive adhesive substance is applied to the display card right up to the edge of the aperture in the display card.

4. A method according to claim 1 or claim 2, wherein the transparent plastics film is heatsensitive and forms the heat-sensitive adhesive substance between the display card and backing sheet.

5. A method according to any preceding claim, wherein the application of local heat to the display card and backing sheet around the aperture is achieved using a heated platen press one or both platens of which are recessed to conform to the shape of the aperture in the display card.

6. A heated platen press for use in the method of claim 5, wherein the or each recessed platen is provided with a removable and interchangeable face block of thermally conductive material having an aperture formed therethrough corresponding to the size and shape of the aperture in the display card to be used.

7. A heated platen press for use in the method of claim 5, wherein the or each recessed platen is provided with a removable and interchangeable platen face comprising a sheet of thermally conductive material having an aperture formed therethrough corresponding to the size and shape of the aperture in the display card to be used, and spacer blocks of thermally conductive material for increasing the effective depth of the recess in the platen.

8. A method of packaging an article, substantially as described herein with reference to the drawings.