WO2002090204A1

WO2002090204A1 - Tamper evident closure

Info

Publication number: WO2002090204A1
Application number: PCT/GB2002/001775
Authority: WO
Inventors: Harold Eastman; Eric Fredolin Ahlquist; Dudley Keith Webb
Original assignee: Allied Domecq Spririts & Wine Limited
Priority date: 2001-05-03
Filing date: 2002-04-18
Publication date: 2002-11-14
Also published as: US20020195413A1; ATE316916T1; EP1385753B1; PL366472A1; CZ20033287A3; MXPA02004361A; YU98602A; HUP0301639A2; CN1397471A; RU2003134958A; BR0205114A; DE60208999D1; DE60208999T2; CO5550479A2; ZA200300071B; EP1385753A1; BG108406A; IL158725A0; HRP20030999A2; US6938757B2

Abstract

A tamper evident closure (1) includes a housing (5) containing a blister pack (2) and a substrate (3), wherein the blister pack (2) contains a first reagent which is visible prior to first opening and the substrate (3) contains a second reagent. First opening of the closure ruptures the blister pack thereby exposing the first reagent to the second reagent and effecting a reaction that causes a visual change that signals the closure has been opened. The tamper evident closure of the present invention is primarily intended to be used as an anti-counterfeit measure on a spirit or pharmaceutical bottle. In the preferred embodiment, the closure incorporates a liquid that when brought into contact with a reagent chemical contained in an absorbent pad, effects an irreversible colour change. This colour change will indicate to a consumer the bottle has been previously opened or tampered with. The design makes it very difficult for a counterfeiter to cover up or eradicate the visible effects. In particular, the only way a counterfeiter could do this would be to put in a replacement blister and an absorbent pad. Filling a blister pack with a liquid is a highly specialist task which makes replication very difficult. The ability to control the colour change to complement the branded goods provides a way of building up consumer recognition of the product and thereby establishing confidence in those products that carry the tamper evident closure of the present invention.

Description

TAMPER EVIDENT CLOSURE

Field of the Invention

The present invention relates to a tamper evident closure for a container, and in particular, a closure that acts as an effective anti-counterfeit measure.

Background to the Invention

It is not uncommon for containers for high value branded goods such as spirits to be reused by criminals whereby empty bottles are collected and recycled. Bottles are refilled with a local product that is inferior to the original product and then the package is resealed for resale.

An obstacle that must be overcome by the counterfeiter is the resealing of the bottle closure in a manner such that is virtually impossible for the consumer to determine that the bottle has already been opened. Various tamper evident anti- counterfeit measures have been used in the past in an effort to thwart these criminals. However, in recent times the level of sophistication of the counterfeiters has risen to a point where these measures are no longer effective for one reason or another.

The risk to the consumer is that the counterfeit goods may be in some way harmful. In the case of pharmaceuticals, the counterfeit goods may be wholly ineffective or worse, life threatening. The damage done to the brand owner's business through loss of goodwill or exposure to legal proceedings is also of serious commercial concern.

An important issue to be considered when designing a tamper evident closure is that it must not have a negative impact on the brand and it must have no adverse affect on the product or the consumer.

Summary of the Invention

According to a first aspect of the present invention, a tamper evident closure comprises a housing containing a blister pack and a substrate, wherein the blister pack contains a first reagent which is visible prior to first opening and the substrate contains a second reagent, and wherein first opening of the closure ruptures the blister pack thereby exposing the first reagent to the second reagent and effecting a reaction that causes a visual change that signals the closure has been opened. According to a second aspect of the present invention, there is provided a blister pack containing an oil entrained with a first reagent, capable of causing a visual change upon reaction with a second reagent.

The approach taken in the present invention is to provide a tamper evident closure that provides a visual signal to indicate that the closure has been opened. Preferably, the visual change is irreversible.

The blister pack is of a conventional structure such as a piece of thermoformed material bonded to a substantially flat material to form a closure. Preferably, the blister pack comprises one or more enclosures, adapted to retain fluid when sealed. More preferably, the blister pack contains a single enclosure.

Preferably, the blister pack has a membrane which is ruptured on opening of the closure. Blister technology is difficult to replicate by most counterfeiters. Not only is the technology not widely available, a blister pack is also very difficult to refill and reseal once it has been ruptured. The use of a blister pack is therefore an effective way of adding complexity to the closure design to make replication even more difficult for the counterfeiter.

Preferably, the blister pack is at least partially visible prior to first opening. This allows a user to see the visual change caused upon reaction of the first and second reagents. The blister pack is preferably formed from a suitable material capable of long term retention of fluid contents and, in particular, oil based fluid contents. The blister pack is preferably substantially transparent to visible light. Preferably, the blister pack is formed from a plastics material selected from the group consisting of nylon, polytetrafluoroethylene, acrylate polymers, polyvinylchloride, polyurethane, polycarbonate, polyolefins, silicone plastics, and derivatives, copolymers and mixtures thereof.

The blister pack may be formed from or may comprise additional components such as ultra-violet filters, materials which block the transport of fluids across the surface of the material, plasticizers and the like. In particular, oxygen barrier materials are preferably incorporated in the sealed enclosure, such as polyethylene terephthalate (PET) and ethylene vinyl alcohol (EVOH). These prevent oxygen from penetrating the package. Water barrier materials are also particularly preferred. Preferably, the blister pack substantially prevents the loss or ingress of water from or to the enclosure. Preferably, the first reagent is a fluid or is dissolved, dispersed or suspended in a fluid carrier. Most preferably the first reagent is dissolved to form a stable solution in a carrier liquid.

A particular problem associated with the prior art is the longevity (shelf life) of 5 the closure. Aqueous solutions and reagents are notoriously difficult to retain within blister packs and like enclosures. Water is known to bleed out of such enclosures and thereby decreases the shelf life of the reagents in the enclosure. Thus, in a preferred embodiment, the carrier liquid is an oil, preferably a mineral or synthetic oil or mixtures thereof. The liquid should have a viscosity such that the liquid is capable of flowing 0 out of a rupture in the blister pack under its own weight at ambient temperature and pressure.

Preferred oils are selected from the group consisting of silicone (including fluorinated silicone), petroleum, glycol, ester and fluorocarbon (including perfluorocarbon). In particular, silicone and paraffin oils are preferred. 5 Preferably, the carrier fluid has a kinematic viscosity in the range of

0.000001 m²/s to 0.0001 m²/s, more preferably 0.00001 m²/s to 0.00003m²/s, most preferably about 0.00002m²/s.

The carrier liquid may additionally comprise materials such as anti-oxidants, ultra-violet filters, stabilisers, solvents and the like. o Preferably, the closure comprises a substrate that carries the second reagent.

Preferably, the substrate comprises a support, preferably an absorbent pad. Preferably, the absorbent pad offers a degree of rigidity but remains compressible, and should preferably be able to absorb and disperse a fluid substantially throughout its structure. 5 The support is preferably formed from fibrous materials selected from cellulose fibres, polyacrylonitrile fibres, polyamide fibres, carbon fibre and mineral fibres. In a preferred embodiment, the absorbent pad is manufactured from cellulose fibres.

Preferably, the substrate is pre-treated with the second reagent. The substrate may be impregnated or coated with the second reagent. In a particularly preferred 0 embodiment, the support is spray coated with a solution second reagent. This provides a uniform coating, and thus optimises the reaction between the first and second reagent, which leads to a more uniform colour change. In a particularly preferred embodiment, a surface of the support is provided with a latent printed image that is developed upon exposure to the fluid. For example, the latent printed image may be a photographic image provided on an emulsion plate.

Preferably, the substrate undergoes a visible change, more preferably a colour change in response to exposure to the first reagent. Of course, any visible change may be selected to complement the brand associated with the product that the tamper evident closure is to be used with. Preferably, the substrate is visible through the blister pack such that as the first reagent, which is in itself visible prior to first opening, comes into contact with the substrate, the visible change takes place on the support, which is also visible on or after first opening of the closure.

The first and second reagents form a visual change due to reaction of their components. The reaction may be an acid/base reaction, a redox reaction, a precipitation reaction, a complex-formation reaction or a hydration reaction or other types of chemical or other organic compound reactions. For example, where the reaction is an acid/base reaction, the fluid may be acidic or basic and the indicating means may comprise a pH indicator which visibly changes on acidification or alkalisation respectively.

Where a redox reaction is utilised, the fluid may contain a compound which is oxidised or reduced upon exposure to the indicating means, or causes oxidation or reduction of the indicating means, either of which lead to a visible change.

Where a precipitation reaction is utilised, the reaction of the fluid with the indicating means causes the precipitation of a visibly contrasting material at the surface of the indicating means.

Where a complex-formation reaction is utilised, a visible change may be effected in the indicating means by the formation of a metal-indicator complex from a metal ion solution and a complexing agent.

Where a hydration reaction is utilised, the indicating means may comprise an anhydrous salt which undergoes a visible change upon exposure to an aqueous solution. Most preferably, an acid/base reaction is used. Preferably, the first reagent is a pH indicator and is selected from those commonly used. Some preferred indicators are tabulated below in table 1. This shows some physical characteristics of the indicators, in aqueous solution, at 25°C. Particularly preferred indicators are bromocresol green, methol red and phenolphthalein. Table 1

The indicator is generally entrained in the carrier liquid in a concentration of between 0.1 % to 10%, preferably 0.5% to 5%, most preferably 1 % to 3% based on the total volume of carrier liquid.

It is advantages to provide a stable solution of the indicator in the oil. This is important as a homogenous solution having a consistent initial colouring (or no colouring) is preferred, so as to accentuate the colour change which occurs upon reaction. Thus, depending on the nature of the indicator, it may be necessary to add solvents to the carrier liquid composition, or to predissolve the indicator in a suitable solvent which promotes miscibility of the solvent-indicator solution with the carrier liquid. Preferred solvents are selected from the group consisting of alcohols, aldehydes, ketones, alkoxyalcohols and glycols. Particularly preferred solvents include propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, butanone, 2-butoxyethanol, octan-1- ol, octan-2-ol and propane-1-2-diol. A particularly preferred solvent is propan-2-ol. In order for an acid/base indicator to work, water must be present. In the present invention the water may be specifically entrained in the liquid carrier, in the solvent, or on the substrate. In practice, it is difficult to exclude water from the blister pack, thus trace amounts are usually present, which precludes the need to specifically add water to the liquid carrier composition. Additionally, upon release of the carrier fluid onto the support, atmospheric water is usually sufficient to enable a significant reaction, thus, a visual change.

Where a solvent is used, the concentration is preferably in the range of 0.5% to 10%, more preferably 1% to 5%, most preferably about 2% by weight of carrier fluid composition.

Mixtures of indicators may also be used in order to provide a range of possible colour changes dependent upon the amount and types of indicators mixed.

Where the reagents are those for an acid/base reaction, the substrate is preferably coated or impregnated with an acid or base, capable of reacting with the indicator, present in the blister pack, to produce a colour change in the indicator.

Preferred second reagents are selected from organic acids, inorganic acids, organic alkalis and inorganic alkalis.

Preferred acids are selected from sulphuric, hydrochloric, nitric, tartaric, citric, malic, benzoic, sorbic, succinic, formic, acetic and propionic acid. Preferred alkalis are inorganic carbonates, hydroxides and bicarbonates, in particular, sodium carbonate, sodium hydroxide, sodium bicarbonate, calcium carbonate, calcium hydroxide, calcium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium hydroxide, and potassium carbonate, potassium hydroxide, potassium bicarbonate. It should be understood that the indicator may be present either in the blister pack or on the support, with the second reagent present on or in the alternative feature (the blister pack or substrate) not containing the indicator. However, preferably the blister pack contains the indicator and the support contains the second reagent.

Preferably, the closure comprises a cap and a cover, the sealed enclosure and the indicating means being housed within the cover, the cover being transparent over at least a portion of its surface to offer a view of at least a portion of the indicating means within the cover.

Preferably, the cap is a screw cap fitting or push-fitting for a container. More preferably, the cap and the cover together form a child safety closure. Preferably, the sealed enclosure is ruptured upon relative movement between the cap and the cover. More preferably, the relative movement is in an axial direction. Preferably, the closure comprises a number of projections that cause rupturing of the sealed enclosure upon opening of the closure. More preferably, the one or more projections are formed as an integral part of a closure cap. In this example, it is preferred that the indicating means comprises a number of apertures that receive the projections so that upon opening of the closure the projections pierce the bister pack thereby releasing the fluid.

According to a third aspect of the present invention, the combination of a container and a tamper evident closure according to the first aspect of the present invention.

The tamper evident closure of the present invention is primarily intended to be used as an anti-counterfeit measure on a spirit or pharmaceutical bottle. In the preferred embodiment, the closure incorporates a liquid that when brought into contact with a reagent chemical contained in an absorbent pad, effects an irreversible colour change. This colour change will indicate to a consumer the bottle has been previously opened or tampered with. The design makes it very difficult for a counterfeiter to cover up or eradicate the visible effects. In particular, the only way a counterfeiter could do this would be to put in a replacement blister and an absorbent pad. Filling a blister pack with a liquid is a highly specialist task which makes replication very difficult. The ability to control the colour change to complement the branded goods provides a way of building up consumer recognition of the product and thereby establishing confidence in those products that carry the tamper evident closure of the present invention.

Brief Description of the Drawings

Examples of the present invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of the components of one example of a tamper evident closure in accordance with the present invention; Figures 2 and 3 show partial cross-sectional views of an assembled tamper evident closure in an unopened and opened configuration, respectively; and,

Figures 4 and 5 show partial cross-sectional views of another example of a tamper evident closure in accordance with the present invention in an unopened or opened configuration respectively. Detailed Description

Figures 1 to 3 illustrate the components of an example of a tamper evident closure 1 in accordance with the present invention.

The device 1 consists of a thermo-formed blister 2, an absorbent pad 3, a screw cap 4, and a cover 5.

The thermo-formed blister 2 contains a very small volume of liquid paraffin (0.6ml). The blister consists of a hard outer shell made of a material such as PET and a much thinner membranous seal made of the same material. As will be described below, the membrane is punctured during the opening of the closure 1 to release the liquid content of the blister 2.

The absorbent pad 3 is provided to absorb the contents of the blister 2 on opening of the closure. In this example, the absorbent pad 3 incorporates a reagent that is sensitive to exposure to the liquid within the blister 2 to change colour and thereby signal that the closure has been opened. The pad 3 may be made of paper, pulp, cotton, plastics, or other absorbent material. A preferred absorbent pad is one made of cellulose fibres. It is preferred that the absorbent pad has a degree of rigidity to aid the assembly of the closure. It should also be compressible with a degree of resilience to facilitate the initial rupture of the blister 2 and dispersal of the contents thereof. The screw cap 4 is designed to act as the primary seal of a bottle having a correspondingly threaded neck portion. The screw cap 4 carries one or more projections 6 which cooperate with an aperture 7 formed in the absorbent pad 3 to provide a means of puncturing the blister 2 upon relative axial movement between the screw cap 4 and the cover 5. The screw cap 4 also includes a "male" serrated crown wheel 7, that forms one part of a child-safety type interlock required initially to open the closure.

The cover 5 is transparent over at least a portion of its extent to enable any colour change in the absorbent pad 3 to be seen by a consumer. The cover 5 carries a tear strip 8 to stop accidental activation of the tamper evident closure 1. The cover 5 includes a "female" serrated crown wheel 9 that cooperates with the corresponding male crown wheel 7 on the screw cap 4 when the closure 1 is first opened. As will be described in detail below, the cover 5 is also provided with a profiled internal cavity to receive the blister 2, absorbent pad 3 and screw cap 4. To assemble the tamper evident closure 1 , the cover 5 is first placed open side up. The thermo-formed blister 2 is then placed inside with the hard shell down and the membrane facing up. It sits in a cavity 10 within the cover 5 that is profiled to accept the blister. The absorbent pad 3 is then placed inside the cover 5 on top of the blister 2 within the cavity. The screw cap 4 is then located within the cover 5 by pressing a male retaining ring 11 carried by the screw cap 4 into a first female groove 12 provided within the cover 5. Once this retaining ring 11 has been snap fitted into its female counterpart 12 the tamper evident closure 1 is ready for application to a bottle.

The tamper evident closure 1 is fitted to a bottle 13 by screwing the cover 5 in a clockwise direction onto a correspondingly threaded neck. It is important that during this process the downward force used is not enough to active the mechanism. Once the tamper evident closure 1 has been screwed home the device is ready to be used.

In operation, the consumer simply removes the tear strip 8 from the circumference of the cover 5. This allows a relative downward axial movement of the cover 5 to engage the male serrations 7 carried by the screw cap 4 with the female serrations 9 carried by the cover. Simultaneously, the blister 2 is ruptured by the projection 6 carried on the screw cap and the contents of the blister are released onto the absorbent pad 3, thereby effecting a change in colour. At this time, the retaining ring 11 carried by the screw cap 4 engages irreversibly with a second female groove 14 carried by the cover 5. This operation is signalled by an audible "click" to provide another signal to the consumer that the closure has operated correctly.

As shown in Figure 3, once activated, the tamper evident closure is now in a locked state and can be used as a normal screw cap, albeit displaying the irreversible colour change through the transparent cover 5. The closure is applicable to most containers. Although the example above includes a conventional screw cap fitting, other fittings are also contemplated. Figures 4 and 5 show an example of a closure that uses a push-fitting.

The tamper evident closure 20 shown in Figures 4 and 5 comprises a cover 21 having a tear strip 22. The cover 21 houses a blister 23, an absorbent pad 24, and a screw cap 25 having a number of projections 26. In this example, the screw cap 25 is fitted to a complementary threaded push-fitting 27. The push-fitting 27 includes an integral skirt 28, plug 29 and threaded spout section 30.

During assembly, the push-fitting 27 is screwed onto the screw cap 27 and subsequently the entire assembly is snap-fitted onto the neck portion of a bottle 31. The present invention provides a tamper evident closure in which it is immediately obvious to a consumer as to whether or not the product has been tampered with. In the preferred example, the change in colour offers a highly visible indication of this. The visual change is irreversible once the closure has been opened. Furthermore, the design makes it very difficult for a counterfeiter to cover up or eradicate the visible effects. The only way a counterfeiter could do this would be to put in a replacement blister and an absorbent pad. Filling a blister pack with a liquid is a highly specialist task which makes replication very difficult. Furthermore, it is possible to construct the closure so that it will be broken by any attempt to disassemble it. The provision of a tear strip makes it difficult to inadvertently trigger the mechanism in a retail environment since the tear strip has first to be removed from the cover. This feature offers another indication that the closure has been tampered with.

It is possible to select the blister liquid and absorbent pad reagent to match or otherwise complement the branded product and so provide another way of building up consumer recognition and confidence in the product.

Examples

Example 1 Preparation of Substrate Acid Solutions.

5.0% solutions of tartaric, malic and citric acids was produced using distilled water. 200 grams of the solid acid was dissolved in 4.0 litres of distilled water and stirred for three minutes. A clear solution was obtained. This solution may then be spray coated onto the support.

Example 2

Preparation of sodium hydroxide solutions.

A 5.0% solution of sodium hydroxide was are produced using distilled water. 200 grams of sodium hydroxide was dissolved in 4.0 litres of distilled water and stirred for three minutes. A clear solution was obtained. This solution may then be spray coated onto the support.

Example 3

Preparation of 1.3% methyl red solution is obtained as follows: (1) 26 ml of the indicator methyl red were added to 1750 ml of light liquid paraffin and stirred well.

(2) The mixture was heated indirectly by using a water bath. The temperature of the water bath did not exceed 100°C. The mixture was left in the water bath for 10 to 12 minutes with continuous stirring.

(3) The mixture was removed from the water bath and left to cool down to room temperature. A clear yellow solution was obtained by the end of this step. This indicator works on paper pads which have been treated with citric, tartaric or malic acids and changes colour from yellow to red.

Example 4

Preparation of 2.0% bromocresol Green in a stable solvent combination is obtained as follows:

(1) 35 ml (2%) of propan-2-ol was added to 1750 ml of silicone oil (20 mn /s and stirred well. The solution is left for 3 minutes and a clear colourless solution was obtained.

(2) 35 ml of bromocresol green was added to the mixture and stirred.

(3) The mixture is indirectly heated in a water bath. The temperature of the water bath did not exceed 100°C. The mixture was left in the water bath for 10 to 12 minutes with continuous stirring. This enhances the indicator solubility.

(4) The mixture was removed from the water bath and left to cool down to room temperature. A clear yellow solution was obtained by the end of this step.

This indicator works on paper pads which have been treated with sodium hydroxide and changes colour from yellow to blue.

Example 5

Preparation of a mixture of two pH indicators.

A mixture of bromocresol green in silicone oil 20 mm²/s and methyl red in silicone oil 20 mm²/s at the ratio 1:1 was produced as follows:

5a. Preparation of bromocresol green combination:

(1) 17.5 ml of propan-2-ol were added to 900 ml of silicone oil 20 mm²/s and stirred well. The mixture was stirred for 3 minutes. A clear colourless solution was obtained. (2) 17.5 ml of bromocresol green were added to the mixture obtained from step 1 and stirred well.

(3) The temperature of the water bath did not exceed 100°C. The mixture was left in the water bath for 10 to 12 minutes with continuous stirring. This enhances the indicator solubility.

5b. Preparation of methyl red combination: (1) 13.5 ml of methyl red was added to 900 ml of silicone oil 20 mm²/s and stirred well.

(2) The mixture was heated indirectly using a water bath and keep stirring. The temperature of the water bath did not exceed 100°C.

(3) The mixture was taken out of the water bath and left to cool down to room temperature. A clear bright yellow solution should be obtained by the end of this step.

The two combinations of indicators are then mixed together in equal volume ratios and stirred for at least three minutes. This produces a final combination of a golden yellow colour. This combination works on paper pads that have been pretreated with sodium hydroxide and changes colour to green.

Example 6

Preparation of mixture of phenolphthalein and bromocresol green in a 3:1 ratio was obtained as follows:

(1) 27 ml of octan-1-ol were added to 1300 ml of silicone oil 20 mm²/s and stirred well. The mixture was stirred for 3 minutes. A clear colourless solution was obtained.

(2) 27 ml of phenolphthalein was added to the mixture of silicone oil and alcohol and stirred well.

(4) The mixture was removed from the water bath and left to cool down to room temperature. A colourless solution with white clouds should be obtained by the end of this step. The bromocresol solution was prepared as per Example 4, except that 9 ml of bromocresol green was dissolved in 450 ml of silicone oil 20mm²/s. The solutions were then mixed and stirred. The final solution colour was faint yellow. This combination works on paper pads that have been pre-treated with sodium hydroxide and changes colour to light mauve.

Claims

1. A tamper evident closure comprising a housing containing a blister pack and a substrate, wherein the blister pack contains a first reagent which is visible prior to first opening and the substrate contains a second reagent, and wherein first opening of the closure ruptures the blister pack thereby exposing the first reagent to the second reagent and effecting a reaction that causes a visual change that signals the closure has been opened.

2. A closure according to claim 1, wherein the substrate changes colour in response to exposure to the first reagent.

3. A closure according to any preceding claim, wherein the substrate carries a latent image that is developed upon exposure to the first reagent.

4. A closure according to any preceding claim, wherein the closure comprises a cap and a cover, a blister pack and a substrate housed within the cover, the cover being transparent over at least a portion of its surface to offer a view of at least a portion of the substrate and/or the blister pack within the cover.

5. A closure according to claim 4, wherein the cap is a fitting for a container.

6. A closure according to claim 5, wherein the cap and the cover together form a child-safety closure.

7. A closure according to any of claims 4 to 6, wherein the blister pack is ruptured upon relative movement between the cap and the cover.

8. A closure according to claim 7, wherein the relative movement is in an axial direction.

9. A closure according to any preceding claim, comprising a number of projections that cause rupturing of the blister pack upon first opening of the closure.

10. A closure according to claim 9 when dependent on claim 4, comprising a number of projections formed as an integral part of the cap.

11. A closure according to any preceding claim, wherein the first reagent is dissolved, dispersed or suspended in a carrier fluid.

12. A closure according to claim 11 , wherein the carrier fluid is an oil, preferably a mineral or synthetic oil or mixtures thereof.

13. A closure according to claim 11 or 12, wherein the carrier fluid is selected from the group consisting of silicone (including fluorinated silicone), petroleum, glycol, ester and fluorocarbon (including perfluorocarbon) oils.

14. A closure according to any of claims 11 and 13, wherein the carrier fluid has a kinematic viscosity in the range of 0.000001 m²/s to 0.0001 m²/s, preferably

0.00001 m²/s to 0.00003m²/s, most preferably about 0.00002m²/s.

15. A closure according to claim 4, wherein the substrate is pre-treated with the second reagent by impregnation or coating with the second reagent, preferably spray coated with a solution of the second reagent.

16. A closure according to any preceding claim, wherein the second reagent is selected from organic acids, inorganic acids, organic alkalis and inorganic alkalis.

17. A closure according to claim 16, wherein the second reagent is an acid selected from the group consisting of sulphuric, hydrochloric, nitric, tartaric, citric, malic, benzoic, sorbic, succinic, formic, acetic and propionic acid.

18. A closure according to claim 16, wherein the second reagent is an alkali selected from the group consisting of sodium carbonate, sodium hydroxide, sodium bicarbonate, calcium carbonate, calcium hydroxide, calcium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium hydroxide, potassium carbonate, potassium hydroxide and potassium bicarbonate.

19. A closure according to any preceding claims, wherein the first reagent is a pH indicator selected from the group consisting of methyl violet, thymol blue, methyl yellow, methyl orange, bromocresol green, methyl red, chlorophenol red, bromothymol blue, phenol red, cresol purple, phenolphthalein, thymolphthalein, alizarin yellow Rand indigo carmine.

20. A closure according to any of claims 11 to 19, wherein the first reagent is entrained in the carrier fluid in a concentration of between 0.1% to 10%, preferably 0.5% to 5%, most preferably 1% to 3% based on the total volume of carrier liquid.

21. A closure according to any preceding claim, wherein the blister pack contains a solvent selected from the group consisting of alcohols, aldehydes, ketones, alkoxyalcohols and glycols, preferably, propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, butanone, 2-butoxyethanol, octan-1-ol, octan-2-ol and propane 1-2-diol.

22. The combination of a container and a tamper evident closure according to any preceding claim.

23. A blister pack containing an oil entrained with a first reagent, capable of causing a visual change upon reaction with a second reagent.

24. A blister pack according to claim 23, wherein the oil is as defined in any of claims 12, 13 or 14.

25. A blister pack according to claim 23, wherein the first reagent is as defined in claim 20.

26. A blister pack according to claim 23, containing a solvent as defined in claim 21.

27. Use of a blister pack in accordance with any of claims 23 to 26, in a tamper evident closure.