GB2270857A

GB2270857A - Tamperproof container

Info

Publication number: GB2270857A
Application number: GB9318423A
Authority: GB
Inventors: Antony Brian Jennings
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-09-04
Filing date: 1993-09-06
Publication date: 1994-03-30
Anticipated expiration: 2013-09-06
Also published as: GB2270857B; GB9318423D0

Abstract

A treated substrate forming or adapted to form part of an adhesively-closable tamperproof container, whose adhesive is liable to lose tackiness on significant change in temperature, has applied thereto at least one temperature sensitive area, the said area being adapted to permanently change its appearance following subjection of it to a loss-of-tackiness temperature change and being positioned or positionable close to the container's closure adhesive.

Description

Tamperroof Container The present invention relates to a treated substrate forming or adapted to form part of an adhesively-closable tamperproof container, particularly though not exclusively a bag or envelope for containing bank notes.

Certain bank note envelopes are closed by means of adhesive of a type which can be released at relatively high or low temperature, that is close to the boiling point or below the freezing point of water.

The object of my invention is to adapt the envelope or other container - to indicate that it has been opened without authority.

According to my invention, I provide a treated substrate forming or adapted to form part of an adhesively-closable tamperproof container, whose adhesive is liable to lose tackiness on significant change in temperature, the substrate having been treated by the application of at least one temperature sensitive area to it, the said area being adapted to permanently change its appearance following subjection of it to a loss-of-tackiness temperature change and being positioned or positionable close to the container's closure adhesive.

The temperature sensitive area may be adapted to change appearance as a direct result of temperature subjection.

For instance, the area - or a part of it - may be treated with a dye, which permanently changes its colour on subjection to an increase in temperature such as to cause the adhesive to lose tackiness. The dye may be an organic dye which changes colour from a light shade to a deep shade on exposure to a temperature of the order of 800C, such as may be applied to the adhesive by steam, exposure to radiant heat from an electric flat iron or hot air from a hair dryer.

Alternatively, the temperature sensitive area may be adapted to change appearance as an indirect result of temperature subjection. For instance, the area - or a part of it - may be treated with a substance which changes appearance on exposure to moisture resulting from condensation on cooling of the envelope to cause the adhesive to lose tackiness.

The substance itself may change appearance simply from being moistened, or as a result of another effect resulting from moistening. In the first case, the substance may change appearance from one colour when dry to another when wet. For instance, potassium permanganate is brown when dry and purple when wet. In the second case, the substance may change colour due to a change in its surroundings. For instance the substance may be an acid/alkali indicator arranged to change appearance due to transport of acid or alkali to it in the condensation moisture, the acid or alkali being spacedly arranged with respect to the indicator. In either case the substance will usually be provided at discrete positions and allowed to disperse by the presence of the moisture.

The temperature sensitive dye or other colour change substance, when combined with a suitable carrier may be applied to the substrate as by screen or flexographic printing. Where the substrate is of plastics material, typically polythene sheeting, the surface of the substrate will usually require to be corona discharge treated.

Alternatively to printing other means of applying of the temperature sensitive substance, such as ink jet, may be used.

The moisture sensitive substance will usually be carried by a capillary action prone patch applied to the envelope, typically polypropylene fabric. Further, the surface may be provided of for instance conventional paper.

Alternatively at the temperature sensitive area or at least part of it, the substrate is treated to provide a surface with enhanced capillary action for diffusion of substances across it in condensed water and/or to provide a surface which can be written on.

In my European Patent application, No 89301180.9, (hereinafter "My European Application") I claim: "A method of providing a substrate with a writing surface, wherein a coating comprising an adhesive medium and a pigment is applied over a region of the substrate which is to constitute the writing surface, and the applied coating is allowed or caused to dry or set, characterised in that, after the coating has been applied and before it has dried or set, a dry, powdery, absorbent material is applied over the coating." This method provides one means of enhancing the capillary action/writability of the substrate. Alternatively, the surface can be formed by applying to the substrate a conventional flexographic ink loaded with a powder.

Further, the surface may be provided of for instance conventional paper.

In a preferred method of treating the substrate to render it temperature sensitive, the enhanced capillary/writable surface has applied to it a particulate dye in such quantity as to negligibly, incompletely or only lightly shade the surface, whereby when - to induce a loss-of-tackiness temperature change - the surface is either steamed or has condensation formed on it as a result of cooling - for illicit opening - moisture is drawn into the surface by capillary action and allows the dye to spread, causing the surface to appear shaded where the shading was previously negligible or more completely or more darkly shaded where the shading was incomplete or light.

In accordance with another feature of my invention, the temperature sensitive area includes a message display, the temperature sensitive substance being applied selectively, whereby on subjection of the temperature sensitive substance to a loss-of-tackiness increase in temperature, the message becomes readily visible by development of the temperature sensitive substance.

Usually this will give a black on white message display.

Alternatively, the temperature sensitive substance is applied uniformly and selectively desensitised, whereby on subjection of the temperature sensitive substance to a loss-of-tackiness increase in temperature, the message becomes readily visible by development of the temperature sensitive substance.

Usually this will give a white on black message display.

Preferably, the substrate and/or the enhanced capillary/writable surface and the temperature sensitive substance are substantially the same colour and shade, whereby the message display is not readily visible prior to development.

The temperature sensitive substance can be selectively applied by conventional printing means, such as screen printing.

The temperature sensitive substance can be desensitized in the selected areas by the application of an oxidising agent. Typically, the oxidising agent will be applied in liquid form, suitably at a viscosity in the region of 3 centipoise The oxidising agent can be selectively applied by conventional printing means, such as screen printing, ink jet or stencil spraying.

Where the capillary action of the capillary enhanced/writable surface on the plastics material is high, it can be modified by spraying with a fixitive, for instance starch or other non-elastomeric adhesive.

Whilst I expect this feature, in both its alternatives, to be most effective when using the "writing" surface of My European Application, I do envisage that it may be employed were the "writing" surface is replaced by the other enhanced capillary/writable surfaces mentioned above.

I envisage that this feature will be particularly useful in displaying a message to the effect that a container has been tampered with. It may be used not only for flexible plastics material items but for rigid items also.

I have discovered that I can effectively screen print thermochromic ink directly onto polyethylene sheeting, which has been corona discharged as for conventional flexographic printing. To achieve the selective application of the thermochromic ink, I have employed screen printing.

The thermochromic ink which I have used is white coloured. I applied this by screen printing to white pigmented polyethylene sheeting, which had been corona discharge treated. The result was a surface which to casual inspection appeared to be uniform and indeed not printed on at all. Once the sheeting was heated, the thermochromic ink developed and the message of the printing screen was readily readable.

In one embodiment of the invention, the substrate forms part of a bag or envelope of sheet material. The part can be a side of the bag or envelope. Alternatively, the part can be a closure flap of the bag or envelope. The closure adhesive can be applied to the closure flap or a side of the bag or envelope onto which the closure flap closes.

The closure flap may be an integral part of the other side of the bag or envelope. However I prefer an embodiment wherein the closure flap is welded to the other side of the bag or envelope.

Alternatively, the substrate is a tape, lamina or label adhesively securable to the container. The tape, lamina or label can be adapted to close a bag or envelope of sheet material.

The lamina or label is envisaged as an alternative to direct printing, at least of the high temperature sensitive material, onto the container.

The lamina or label will preferably be provided with both hot and cold sensitive areas. Conveniently the lamina or label will be in strip form; although it is envisaged that it may be provided as part of a writable label to be affixed to the tamperproof container.

I envisage that the lamina or label can replace the closure means and be used itself for closing the container.

For instance this could be by folding back the end of a flexible container and securing it in its closed position by a temperature sensitive label. The container could be opened only by interfering with the label, which would be irremovable except by heating or cooling to which it would react. If it were removed and replaced by another label, its replacement would have to reproduce unique markings preferably applied before or at the time of sealing.

As an alternative, a strip of thermal paper could be applied to the container via a suitable adhesive, such as double sided adhesive tape.

Both in the case of use of the lamina or not, the high temperature sensitive area may be covered by a transparent impermeable layer to prevent chemical treatment of the area to cause it to revert to its original appearance after subjection to elevated temperature. The impermeable area can be a specially provided layer or may be the closure flap of the container.

Another possibility is for the high temperature sensitive material to be provided in the capillary action prone patch.

To help understanding of the invention, two specific embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an envelope according to the invention; Figure 2 is a perspective view of another container of the invention prior to closure with a closure flap folded back to expose the opening of the container; Figure 3 is a diagrammatic, scrap side view of the container of Figure 2 prior to closure with the closure flap folded back; and Figure 4 is similar side view of the container of Figure 2 with the flap closing the opening.

Referring to Figure 1, the container 1 thereshown is an envelope for containing bank notes (not shown). It comprises a single sheet of polyethylene, folded at one end 2 to define upper and lower skins 3,4. These are welded together at their edges 5,6. A mouth is provided at the other end 7 by the free edge 8 of the upper skin 3. The lower skin 4 has a continuation 9 beyond the mouth, which forms a closure flap. This has hot melt adhesive 10 applied to it, with a release film 11 prior to closure. In these respects the envelope is conventional.

It is closed by removal of the release film 11 and folding of the flap onto upper skin 3, where it sticks.

Normally, the envelope cannot now be opened without tearing of its polyethylene skins. However, if the temperature of the adhesive is raised as by steaming, or if it is cooled to less than OOC, the adhesive loses its tackiness and the flap can be opened without plastic deformation of the polyethylene.

In accordance with the invention, a strip 15 of ink containing a dye, which irreversibly changes colour on heating to temperatures above 800C, is printed along the upper skin 3 adjacent the free edge 8, that is onto the polyethylene of the skin, which forms a substrate for the ink. Next to the ink strip 15 a woven polypropylene band 16 is welded along its length to the upper skin 3. The strip 15 and the band 16 are applied to the polyethylene sheet prior to the welding of the edges 5,6. The ends 17,18 of the strip change colour as they are raised in temperature during the welding to above the dye colour change temperature. The ends of the band become incorporated with the edge welds, the materials being compatible.

Incorporated along the band are small spots 19 of bright dye such as fluorescein sodium, which is in powder form such as to not to appreciably colour the band. The band 16 is in such a position as to be not covered by the closure flap when closed normally.

If after closure, the flap 9 is heated to cause the adhesive to lose tackiness, the dye in the strip 15 will change colour, indicating tampering. Alternatively, if the envelope is cooled for the same purpose, frost and/or dew will form on the band 16. This will cause the dye spots 19 to dissolve and its colour to spread throughout the band, again indicating tampering.

In a non-illustrated alternative, the band 16 is replaced by a strip of "writing surface" in accordance with my European Application No.89301180.9.

Referring now to Figures 2 to 4, the container 101 is a bag of corona-discharge-treated, white-pigmented polyethylene sheeting. It has one side 102 shorter than the other side 103, whereby the other side has an extension 104 beyond the opening 105 of the bag. Along the edge of the one side 102 of the bag at the opening, a message 106 is screen printed in thermochromic ink of a white tint to be not normally be immediately noticeable.

The extension 104 has a flap 107 of clear polyethylene heat welded to it, such that it can be folded back to expose the opening 102, as shown in Figures 2 and 3. The flap has a pattern 108 of black ink flexographically printed onto it.

The pattern has a clear stripe 109 through it, which is not printed onto. When the flap is closed, this stripe registers with the message 106, whereby the message is visible if the container is at least locally heated to a temperature such as cause the thermochromic ink to change colour, that is to black.

The flap 107 is of non-corona-discharged polyethylene.

It is treated with sprayed on lines of adhesive 110. This is covered with a release strip 111 until the container is sealed. This construction of the flap is conventional and is not my invention. When the flap is closed onto the side 102, if the container is cooled to a temperature whereby the adhesive loses its tackiness, because the flap has not been corona discharge treated and the side 102 has, the adhesive tends to stay adhered to the side 102 and not the flap. The pattern 108 tends to remain on the adhesive lines and separates from the flap at the lines. The pattern is difficult to realign if the flap is re-closed after tampering with.

In a further development, I propose to flexographically print a thermal ink message onto the flap, for instance along the stripe 109 as opposed to onto the bag. The adhesive could be printed onto the flap in lines over both the black and the thermochromic inks. Alternatively, the thermochromic ink could be printed onto the opposite side from the adhesive. This would be particularly appropriate where the this other side included a "writing surface" of My European Application and the thermochromic printing was onto this surface, typically of a word such as "Bandit". The "writing surface" could also be treated with dusting of particulate dye, adapted to spread and be exposed on moistening of the surface as by condensation. Such a flap could be sold as a tape long enough for many flaps for welding onto plain plastics material envelopes or even envelopes of other material. A release strip 111 could be provided or the tape could be sold in a reel as with ordinary self-adhesive tape. The flaps need not be welded onto the the envelopes and may be used in the manner of ordinary self-adhesive sealing tape.

As an alternative, the flap need not be provided with adhesive, which latter could be provided on the container usually with a release strip.

Claims

CLAIMS:

1. A treated substrate forming or adapted to form part of an adhesively-closable tamperproof container, whose adhesive is liable to lose tackiness on significant change in temperature, the substrate having been treated by the application of at least one temperature sensitive area to it, the said area being adapted to permanently change its appearance following subjection of it to a loss-of-tackiness temperature change and being positioned or positionable close to the container's closure adhesive.

2. A treated substrate as claimed in claim 1, wherein the temperature sensitive area - or a part of it - is adapted to change appearance as a direct result of a loss-of-tackiness temperature change.

3. A treated substrate as claimed in claim 1 or claim 2, wherein the temperature sensitive area is treated with a thermochromic dye, which permanently changes its colour on subjection to a loss-of-tackiness increase in temperature.

4. A treated substrate as claimed in claim 3, wherein the dye is an organic dye which changes colour from a light shade to a deep shade on exposure to a temperature of the order of 800C.

5. A treated substrate as claimed in claim 1, wherein the temperature sensitive area - or a part of it - is adapted to change appearance as an indirect result of a loss-of-tackiness temperature change.

6. A treated substrate as claimed in claim 5, wherein the area is treated with a substance which changes appearance on exposure to moisture resulting from condensation on it on subjection to a loss-of-tackiness decrease in temperature.

7. A treated substrate as claimed in claim 6, wherein the condensation sensitive substance changes appearance as a direct result of it being moistened.

8. A treated substrate as claimed in claim 6, wherein the condensation sensitive substance changes appearance as an indirect result of it being moistened.

9. A treated substrate as claimed in claim 8, wherein the condensation sensitive substance comprises an indicator and a reagent, the indicator and the reagent being spacedly arranged with respect to the indicator and able mix by diffusion in condensed moisture, whereby the indicator changes appearance.

10. A treated substrate as claimed in any one of claims 6 to 9, wherein the condensation sensitive substance is provided at discrete positions and allowed to disperse by the presence of the moisture.

11. A treated substrate as claimed in any preceding claim, wherein the temperature sensitive area includes a temperature sensitive substance applied by printing or the like coating method.

12. A treated substrate as claimed in claim 11, wherein the substrate is of plastics material and has been subjected to corona discharge treatment.

13. A treated substrate as claimed in any preceding claim, wherein, at the temperature sensitive area or at least part of it, the substrate is treated to provide a surface with enhanced capillary action for diffusion of substances across it in condensed water and/or to provide a surface which can be written on.

14. A treated substrate as claimed in claim 13, wherein the enhanced capillary/writable surface has applied to it a particulate dye in such quantity as to negligibly, incompletely or only lightly shade the surface, whereby when - to induce a loss-of-tackiness temperature change - the surface is either steamed or has condensation formed on it as a result of cooling, moisture is drawn into the surface by capillary action and allows the dye to spread, causing the surface to appear shaded where the shading was previously negligible or more completely or more darkly shaded where the shading was incomplete or light.

15. A treated substrate as claimed in claim 13 or claim 14, wherein the enhanced capillary/writable surface is formed by applying to the substrate with a coating comprising an adhesive medium and a pigment over a region which is to constitute the enhanced capillary/writable surface, before the applied coating has dried or set applying a dry, powdery, absorbent material over the coating, and allowing or causing the applied coating to dry or set.

16. A treated substrate as claimed in claim 13 or claim 14, wherein the enhanced capillary/writable surface is formed by applying to the substrate a conventional flexographic ink loaded with a powder.

17. A treated substrate as claimed in anyone of claims 11 to 16, wherein the temperature sensitive area includes a message display, the temperature sensitive substance having been applied selectively, whereby on subjection of the temperature sensitive substance to a loss-of-tackiness increase in temperature, the message becomes readily visible by development of the temperature sensitive substance.

18. A treated substrate as claimed in anyone of claims 11 to 16, wherein the temperature sensitive area includes a message display, the temperature sensitive substance having been applied uniformly and selectively desensitised, whereby on subjection of the temperature sensitive substance to a loss-of-tackiness increase in temperature, the message becomes readily visible by development of the temperature sensitive substance.

19. A treated substrate as claimed in claim 18, wherein the temperature sensitive substance has been selectively desensitized by the application of an oxidising agent.

20. A treated substrate as claimed in claim 19, wherein when the message display is on a enhanced capillary/writable surface which has a high capillary action, the surface is modified by spraying on of a fixitive prior to application of the oxidising agent.

21. A treated substrate as claimed in any one of claims 17 to 20, wherein the substrate and/or the enhanced capillary/writable surface and the temperature sensitive substance are substantially the same colour and shade, whereby the message display is not readily visible prior to development.

22. A treated substrate as claimed in any preceding claim, wherein the high temperature sensitive area may be covered by a transparent impermeable layer.

23. A treated substrate as claimed in any preceding claim, wherein the substrate forms part of a bag or envelope of sheet material.

24. A treated substrate as claimed in claim 23, wherein the part is a side of the bag or envelope.

25. A treated substrate as claimed in claim 24, wherein the part is a closure flap of the bag or envelope and the closure adhesive is applied to the closure flap or a side of the bag or envelope onto which the closure flap closes.

26. A treated substrate as claimed in claim 25, wherein the closure flap is an integral part of the other side of the bag or envelope.

27. A treated substrate as claimed in claim 26, wherein the closure flap is welded to the other side of the bag or envelope.

28. A treated substrate as claimed in any one of claims 1 to 22, wherein the substrate is a tape, lamina or label adhesively securable to the container.

29. A treated substrate as claimed in claim 28, wherein the tape, lamina or label is adapted to close a bag or envelope of sheet material.

30. A treated substrate substantially as hereinbefore described with reference to Figure 1 or Figures 2, 3 and 4 of the accompanying drawings.