WO1995013229A1

WO1995013229A1 - Closures for containers

Info

Publication number: WO1995013229A1
Application number: PCT/GB1994/002110
Authority: WO
Inventors: Malcolm George Collins; Richard Mark Beaumont
Original assignee: Carnaudmetalbox Plc
Priority date: 1993-11-10
Filing date: 1994-09-28
Publication date: 1995-05-18
Also published as: GB9323185D0; AU7703994A

Abstract

A vacuum closure (10) for a container of a food product is of metal and has a tamper-indicating button (20) formed in the centre of its generally plane closure panel. In order to enhance its visual distinctiveness for tamper-evidence the button is formed with a coating (30) of an embrittled material having a colour developer incorporated in it. The brittle coating acts as matrix in which microcapsules (32) of a dye precursor material are dispersed. Operation of the button when the closure is opened ruptures the microcapsules, so allowing the dye precursor and colour developer to mix intimately and form a colour which is indicative that opening has occurred.

Description

"CLOSURES FOR CONTAINERS"

This invention relates to closures for containers, of the kind which have a panel movable in response to changes in pressure within the container.

A particular, although not exclusive, application of tne invention is to vacuum closures for food products, of the kind which have a tamper-evident button which is normally held in a depressed condition by vacuum in the headspace of the container to which the closure is fitted, but which everts to a raised condition if for any reason the vacuum substantially reduces or disappears.

As is well known, such tamper-evident buttons of vacuum closures suffer from the drawback that their action is not irreversible, and various proposals have been made to provide them with an irreversible optical indication that they have everted. Proposals of this kind involving a colour-change are made, for example, in Patent Publications EP 0466391, EP 0467619, EP 0469933, EP 0480740 and WO 92/05083 each standing in the name of Continental White Cap Inc. A similar disclosure is made in EP 0421590 (Cambridge Consultants Ltd).

A primary difficulty encountered in providing colour-change indication for the tamper-evident button of a vacuum closure is to achieve an irreversible colour change which is sufficiently definite to be easily perceived even at a casual glance and in adverse conditions.

In the patent publication EP 0421590 mentioned above there is disclosed the use of a brittle coating to provide tamper-evidence for a portion of a closure subject to conformational change, by providing an optical change when movement occurs. It is further proposed that the optical change may be enhanced by the provision of a colourant, such as a micro-encapsulated dye which is dispersed by the conformational change. in the further patent publication EP 0467619 mentioned above, tamper-evidence for the button of a vacuum closure is provided by a two-part dye system both parts of which are microencapsulated and carried by a relatively flexible coating material. When the button everts, tension created in the coating material ruptures capsules of the two-part dye system, so that those parts are able to combine to provide a required colour change. Applicants have discovered, however, that a single part dye system such as is proposed in EP 0421590 suffers from the shortcoming that the coloured dye within the unruptured capsules is visible through the capsule wall, so that when the capsules are ruptured the colour change may not be sufficiently apparent for satisfactory tamperevicence.

On the other hand, a two-part dye system in wholly encapsulated form such as is described in EP 0421590 is also found to give unsatisfactory tamper-indication. Applicants believe that this is because, before a colour change occurs, capsules of both parts of the dye system have not only to rupture but also to be in sufficiently close physical contact for their contents to interact; also, it is believed, the use of a relatively flexible substrate for carrying the capsules may limit the number of capsules which are caused to rupture as desired.

Indeed, if the limited strain of button eversion is fully accommodated by flexibility of the substrate, no capsule rupture will occur.

The present application seeks to overcome, at least partially, shortcomings of prior art proposals, in particular those described above of EP 0421590 and EP 0467619, and accordingly provides a closure for a container, which has a movable portion formed with an indicator for providing an irreversible colour-change on movement of the movable portion, wherein the indicator has first and second physically separated parts which are capable of effecting said colour change when combined together, one only of the said parts being in encapsulated form, the other part being provided by a brittle coating formed on the movable portion and having the capsules of said encapsulated part dispersed therein.

Applicants have found that the use of a two-part dye system in a brittle substrate, with one part encapsulated and the other part unencapsulated but associated intimately with the brittle substrate material, enables intense and readily perceived colour changes to be achieved.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: -

Fig.l is a perspective view from above of a vacuum closure for a food product having a tamper-indicating button formed with a colour-change indicator in accordance with the invention; and

Fig.2 shows the button as seen in enlarged section taken along the line II-II of Fig.l, and revealing detail of the button and its indicator when the button is in a raised position. Referring now to the drawings a vacuum closure 10 for a jar of baby food (not shown) has a shell 11 pressed from lacquered steel plate. The shell has a generally plane closure panel 12 arranged to overlie the mouth of the jar, and a generally cylindrical skirt 14 which depends peripherally from the closure panel for surrounding the jar neck. The closure is of the kind usually known as a "PT cap", and accordingly it is to be understood that its interior surface has a lining of a plastisol material (not shown) which is located and capable of providing a seal with the top finish of the jar and, in addition, a screw thread formation on the skirt 14 to attach the closure to the jar for screw-off removal.

As described above the closure is conventional. It is also conventional in its provision of a tamper-evident button 20 which is coined in the centre of the closure panel 12 so as to have alternative raised and depressed positions.

In Fig.2 the raised position of the button is shown and indicated by the full lines, the depressed position being also shown and represented by broken lines. The button has a small central disc portion 22, and inner and outer surrounding annular portions 24, 26. The portions 22, 24 and 26 are integrally attached along integral lines of inflection 80, 82; a further line of inflection 84 attaches the button integrally to the remainder of the closure panel 12. As is evident from the drawing, most of the flexure of the button when changing between its alternative positions occurs at the inner annular portion 24, although some flexure also occurs at the portions 22, 26.

The depressed position of the button is an unstable position which the button is carried to adopt in response to a partial vacuum which under normal conditions will exist in the headspace of the jar to which the closure is fitted. If for any reason the partial vacuum is broken or seriously depleted, the button resiles to the stable raised position shown so as to provide an indication of that fact. However, the button movement described in the previous paragraph is reversible, and there exists the danger that a knowledgeable person may remove the closure and thereafter replace it with the button again located in its depressed position. In order to overcome this - 0 -

shortcoming, the button 20 is formed with a colour-changing indicator 21 covering the whole of its area. The indicator 21 (Fig.2) primarily consists of a coating 28 formed essentially of a brittle coating material 30 such as the 100% solids UV curable epoxy resin which is marketed in UK by Loctite Holdings Ltd under the type designation UV Retaining Compound 661.

For the purposes of this invention any plasticisers or rubber-like modifiers are omitted from the coating material. The coating material is therefore capable of being brittle but nevertheless adherent to the substrate provided by the closure shell 11. It is originally laid down on the shell as a liquid in which Zinc Salicylate has been dissolved in sufficient quantity to form a substantially saturated solution. It additionally includes well dispersed microcapsules 32 of Ciba Geigy "Pergascript 1-63 Red" dye precursor dissolved in a suitable solvent such as diethyl phthalate or diisopropyl naphthalate and encapsulated in an aminoplast wall material, either urea formaldehyde or melamine formaldehyde. It should be understood at this juncture that the Zinc Salicylate of the brittle coating material 30 and the dye precursor of the microcapsules 32 potentially form the component parts of a two-part dye system, the Zinc Salicylate forming the colour developer of the system. Because the Zinc Salicylate is a solute and therefore only exists at molecular level in the brittle coating material, it is not shown or specifically referenced. The coating material 30 including the dissolved Zinc Salicylate and the dispersed microcapsules 32 is initially coated onto the shell 11 when in liquid form by the closure manufacturer, and is then partially cross-linked by suitable radiation (e.g. UV light) to convert it to a flexible, solid form. In this form the closure is despatched by the food manufacturer to the food packer.

The packer steam-flow closes the closure onto a product-filled jar, so causing the button to be drawn to its depressed condition by vacuum created in the jar headspace. Subsequently the jar is thermally sterilised in a steam retort at a temperature typically of 121°C, an external overpressure within the retort ensuring not only that the closure remains in proper sealing relation with the jar but also that the button remains in its depressed condition.

The initial flexible condition of the coating material enables it to flex with the button without damage when the button is drawn to its depressed condition by the steam-flow closing operation as described. It also reduces the risk of mechanical damage to the coating material during transit etc.

After sterilisation, the jar is cooled to ambient temperature and is removed from the retort. It is then subjected to further radiation, for example UV radiation at a different frequency than before, to render the coating material 30 brittle as required for its tamperevident function. The jar is subsequently despatched for retail distribution and sale. After the embrittlement of the coating material 30 as described above, any subsequent removal of the closure from the jar will release the vacuum in the jar and allow the button to resile to its raised position. This will cause the coating material to craze or crack, so rupturing a substantial number of the capsules 32 along the lines of crazing or cracking. The dye precursor of the ruptured capsules is thereby released, and by reason of the intimate incorporation of the colour developer into the coating material comes into contact with colour developer and so forms an intense and clearly visible red colour which is indicative that the closure has been opened. The colour development is irreversible, and the tamper-indication will therefore remain even though it may be possible to reduce or remove the crazing/cracking of the coating material 30 by suitable treatment.

In Fig.2 four cracks are shown to have been formed in the brittle coating 28, and they are denoted by the reference numeral 36. However, it will be appreciated that in reality a large number of random cracks is formed. In order to prevent debris from the coating 28 from breaking free of the closure when the coating ruptures, a flexible overcoat 34 of a suitable plastics material covers the coating 28 and makes a firm attachment with the shell 11 around the periphery of the coating. The overcoat is chemically inert to the components of the coating; in addition, it has a low permeability to liquids and gases (e.g water, water vapour) which may effect the operation of the indicator system. In a second embodiment of the invention the colour developer is incorporated into the brittle coating material as functional groups which are grafted onto its chemical structure. The colour developer is thus chemically rather than, as in the previous embodiment, physically incorporated into the brittle coating material. In a modification of each of the embodiments described above the dye precursor and the colour developer are transposed, the dye precursor being incorporated physically^' or chemically (as appropriate) in the brittle coating material and the colour developer being in microencapsulated form.

Whilst of particular application to closures, especially but (not exclusively) metal closures, the invention may be applied to any component of a packaging container which is subject to movement in response to pressure changes within the container.

Claims

CLAIMS :

A closure for a container, which has a movable portion formed with an indicator for providing ah irreversible colour-change on movement of the movable portion, wherein the indicator has first and second physically separated parts which are capable of effecting said colour change when combined together, one only of the said parts being in encapsulated form, the other part being provided by a brittle coating formed on the movable portion and having the capsules of said encapsulated part dispersed therein.

A closure as claimed in claim 1, wherein the brittle coating comprises a brittle carrier material, and, incorporated into the carrier material, a substance capable of forming the said other part of the colour-change combination.

A closure as claimed in claim 2, wherein the said substance is physically incorporated in the brittle coating material.

A closure as claimed in claim 3, wherein the said substance is dissolved in the brittle coating material.

A closure as claimed in claim 2, wherein the said substance is chemically incorporated in the brittle coating material.

A closure as claimed in claim 5, wherein the said substance is provided by functional groups which are grafted onto the chemical structure of the brittle coating material.

A closure as claimed in any preceding claim, wherein the brittle coating has been originally laid down in liquid form. A closure as claimed in claim 7, wherein the brittle coating has been subjected to discrete stages of radiation to convert it from its liquid form to, in sequence, flexible solid form and brittle solid form.