WO2002046741A1

WO2002046741A1 - Elapsed time indicator

Info

Publication number: WO2002046741A1
Application number: PCT/AU2001/001468
Authority: WO
Inventors: Gareth Lewis
Original assignee: Chroma Cfhem Pty Ltd.
Priority date: 2000-12-04
Filing date: 2001-11-13
Publication date: 2002-06-13
Also published as: AU1481402A; AUPR186000A0

Abstract

Measuring elapsed time using a device consisting of a generally laminar structure (2) having an upper reactive layer (b) and a lower oxygen impermeable layer (c). The reactive layer includes one or more reactive materials capable of reacting with oxygen to create a colour change over time (3). The reactive layer is constructed so that the oxygen permeability of the layer is greater towards the periphery of the device and lesser towards the centre (1). The device has particular application for monitoring freshness of packaged foodstuffs, pharmaceutical products or frozen products.

Description

Elapsed Time Indicator

Field Of The Invention

The present invention relates to an elapsed time indicator. The elapsed time indicator of the present invention is adapted for use in connection with foodstuff packaging, pharmaceutical products and packaging of general articles where the measurement of time is of importance.

Background Of The Invention

The measurement of time is not new and there are many existing devices and technologies for the measurement of time in various circumstances. The present invention is concerned with the measurement of time elapsed from an initial condition and with the display of the elapsed time in a semi-quantitative manner.

In many circumstances it would be helpful to be able to indicate the time for which any product might have been in a particular condition. Examples of products requiring such indications include foodstuffs, frozen products, blood products, vaccines and other similar items.

Foodstuffs, whether fresh, frozen, processed or otherwise are often packaged in relatively flimsy packaging. In such packaging the products may be subject to a time-dependent decline in quality. Many food items contain, on their packaging date indicators, such as 'use by', 'best before' and other such like comments. However, identifying these dates is not always easy and the printing is not always clear. What is more, if the purchaser does locate the relevant date a form of mental calculation has to be undertaken to determine the likely remaining time available before a product is unusable.

Faced with such situations consumers are often wary of purchasing some fresh products and do not have a high degree of confidence in the quality of the products they purchase. It could also be noted that the incidence of food poisoning has risen sharply in recent years. In some part, at least, this may be the result of the purchase and consumption of foodstuffs that have been shelved for an unsuitably long time. An elapsed time indicator, providing a simple visual indication of elapsed time would assist consumer confidence in the freshness of their purchase. Similarly, articles on sale in retail environments may be stored together in a haphazard fashion with articles more recently acquired being co-located with older articles. Whilst the products may be exactly the same from a purchaser's point of view, the store owner has an interest in moving stock so that older items are sold first. A simple elapsed time indicator would assist the store owner to identify older stock items. Such information could then lead to an identification of the preferred locations from which articles are selected and other useful sales information.

Elapsed time indicators are known from their prior art. Typically an indicator might include two or more chemical reagents that react together to produce a changed colour reaction product.

Japanese patent number 8327468 describes an indicator based on an organic peroxide supported on a resin layer which reacts with an encapsulated phenethiazine dye to produce a colour change when the capsule dissipates. The development of the colour change provides an indication of time.

United States patent number 5756356 discloses an indicator including an oxidation polymerisable dyestuff and an oxidising agent. The products are held in a non contact state and allowed to mix over time to produce a coloured reaction product.

Alternative reactants are disclosed in international patent application WO 9205415 in which p-nitrophenyl phosphate undergoes an enzyme catalysed reaction using alkaline phosphatase to produce a coloured reaction product.

Indicators have also been produced in which the reactants are held in a gel form, or similar physically separated forms, the products gradually diffusing towards one another to react. Examples of such technology include Japanese patent number 1160883, and Japanese patent number 1141973.

A further example of an elapsed time indicator is given in European patent application number 47101. In this case a reduced vat dye is dispersed in a liquid gel or polymer and applied to a substrate. An anti-oxidant reducing layer, or an oxygen permeable barrier layer is placed over the dye. As oxygen diffuses through the barrier layer an observable colour change occurs. It is important to note, that the device is equipped with a permeability barrier of constant thickness and the colour development process provides a constant or fixed hue across the entire surface at any given time and does not give a visually discernible indication of elapsed time.

It is notable that the prior art elapsed time indicators, as exemplified by those discussed above, are subject to a number of constraints that limit their use in practical situations. In many cases a number of reactants have to be produced and brought together in a time dependent manner. In practice this is clearly not easy to achieve with any degree of reliability. A further limitation on the prior art devices is the relatively indistinct nature of the colour development process.

The present invention is addressed to the above issues and provides the public with a useful alternative to existing devices.

The device of the invention may be used to detect the presence of oxygen in a product where the product has previously been stored in an oxygen-starved environment. For example, some fresh foodstuffs are stored in carbon dioxide environments as a result of storage under dry ice. Other examples of products in which the visual indication of elapsed time is an advantage include medicines, vaccines, and other pharmaceutical products the quality of which may deteriorate over time.

Summary Of The Invention

The present invention provides an elapsed time indicator that would be able to be used in the situations outlined above. It should be noted that the indicator of the present invention is not restricted to use in the situations outlined above and that these are merely examples of the many circumstances in which the indicator is of use.

Therefore, according to a first aspect of the present invention, although this need not be the broadest nor indeed the only aspect of the invention, there is provided a device for measuring elapsed time, said device consisting of a generally laminar structure having an upper reactive layer and lower oxygen impermeable layer, said reactive layer including therein one or more reactive materials capable of reacting with oxygen to created a colour changed product, wherein said reactive layer is constructed such that the oxygen permeability of said reactive layer is greater towards the periphery of the device and lesser towards a centre thereof.

Thus, the invention provides a decreasing differential in the flow of oxygen from the periphery of the device towards a centre thereof.

The present invention is therefore predicated on the use of atmospheric oxygen to react with the reactants held in the reactive layer to produce the resulting colour changed product. The invention can thereby avoid the need to create a matrix in which reactants are separated by some barrier that is compromised over time or by a physical barrier, such as a gel, designed to hinder the free movement of reacting molecules.

Furthermore, by creating a laminar structure in which oxygen can most easily access the reactive layer at the annular regions and decreasing towards the centre of the device, the device of the invention ensures that oxygen is effectively prevented from a generalised diffusion across the entire surface of the structure and directed to a diffusion pattern starting at the lateral edges of the device and the periphery of the device, gradually moving to the centre of the structure. In such a way diffusion of oxygen into the structure, and hence development of a colour changed product occurs initially at edges of the device migrating gradually towards a centre of the device.

In a preferred form of the invention, the device is disc shaped, such that a colour changed product forms as an outer ring located circumferentially on edges of the disc and gradually occupying the whole of the disc. It will be readily appreciated that such a 'target' shaped colour changed product provides a highly visual indication of colour change. Furthermore, by selecting an appropriate range of reactants, disc size, reactant concentrations, and reactant layer thickness it is possible to create a device capable of determining elapsed time in a semi- quantitative fashion.

In one form the invention is embodied in a device consisting of oxygen impermeable upper and lower layers separating the reactive layer. In such a case the diffusion of oxygen into the device to create the colour changed product occurs almost exclusively laterally.

In a further form of the invention, the upper layer of the device consists of a material semi-permeable to the diffusion of oxygen therethrough said semi- permeable material being arranged as a convex layer of greater thickness of reactive layer towards a centre thereof to thereby create a differential flow of oxygen diffusion across the layer to the reactive layer below.

In a still further form of the invention, the device consists of two layers, the first layer of which consists of a material which is semi-permeable to the diffusion of oxygen therethrough said semi-permeable material having an oxygen sensitive material as a component therein, the semi-permeable layer comprising the reactive layer, said layer being arranged as a convex structure above and being bonded to a lower oxygen impermeable second layer.

Preferably, the device includes an outer oxygen impermeable cover, said cover containing an inert or non reactive gas such as carbon dioxide or nitrogen and mixtures thereof which may be removed at a selected time, nominally time zero, to allow atmospheric oxygen to begin the diffusion process into the device and hence to commence the development of the colour change.

The elapsed time indicator of the present invention therefore takes advantage of the diffusion across the reactive layer.

Preferably, said reactants included in the reactive layer are reduced vat dyes such as blue indigo, or dye like chemicals in the form of benzoylamino anthraquinone, dibenzanthrone dye (caledon jade green), methylene blue, indanthrene blue, alizarin cyanine green F, anthralin, isatin, kermesic acid, and hypericin.

The reactant layer may, in some forms of the invention, additionally contain retardants to slow the development of any colour-changed product. Such retardants may include anti-oxidants such as alpha tocopherol (vitamin E), butylated hydroxytoluene (BHT) or butylated hydroxyanisole (BHA).

In further forms of the invention the reactant layer may additionally include anti- evaporative materials to slow the evaporative loss of solvent from the reactive layer, for example glycerol and/or polyalcohols may be added to the reactive layer to retard evaporation of water from the reactive layer.

Typical concentrations of materials in a reactive layer of a water based reactive layer are as follows:

Vat dye 0.07 micro molar to 0.5 molar sodium hydroxide 0.5 micro molar to 6 molar sodium dithionite 0.5 micro molar to 5 molar pH 7-14

Typical concentrations of materials in a reactive layer of a polymer based reactive layer are as follows:

Vat dye 0.001 % -50 % by weight

Synthetic polymer (eg synthetic rubber) 50-99.999 % pH 4-10

Suitable polymers for a polymer based reactive layer include, polyvinyl alcohol, polyvinyl acetate, co-polymers of polyvinyl alcohol and polyvinyl acetate, co- polymers of soluble starch and polyvinyl alcohol, methyl-cellulose, cellulose acetate, cellulose nitrate, polystyrene, polyethylene. Where an elapsed time indicator is based on a polymeric material the indicator may be incorporated into packaging materials, or indeed, may be included in an entire packaging surface. It is also possible for an elapsed time indicator to be applied to a surface as a printed indicia which become visible as time progresses thereby providing an opportunity for a warning to be included on a product or for other information relevant to product viability to be included on packaging.

In further forms of the invention the reactant layer may additionally include accelerator materials used to increase the speed of colour development, for example products releasing oxygen over a period of time, such as peroxides together with ferrous or copper ions.

Brief Description Of The Drawings The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which,

FIG 1 illustrates in side view and in plan view an elapsed time indicator in accordance with a first aspect of the present invention;

FIG 2a illustrates in side view and in plan view an elapsed time indicator in accordance with a second aspect of the present invention;

FIG 2b illustrates in side view and in plan view an elapsed time indicator in accordance with a third aspect of the present invention;

FIG 3 illustrates in side view an elapsed time indicator generally as shown in FIG 2a and FIG 2b with markings of iso oxidation contours;

FIG 4 represents schematically colour development in differently constituted elapsed time indicators built generally in accordance with the device illustrated in FIG 1 ; and

Description Of The Preferred Embodiment

Shown in FIG 1 is an elapsed time indicator in accordance with a first aspect of the present invention. The elapsed time indicator is constructed in the form of a disc to be attached to the surface of any article for which an elapsed time measurement needs to be made. The indicator is shown in (1) plan view, (2) side view and (3) in plan view as a colour change reaction occurs.

As seen in the drawing the device is essentially constructed of three separate layers, designated layers 'a', 'b' and 'c'. Layer 'a' is an oxygen impermeable, clear plastic upper layer. The use of the clear transparent plastic upper layer allows rapid visual inspection of the device to be made. The lower layer 'c' is also an oxygen impermeable plastic layer. The layer may be transparent or opaque, depending the use to which the device is to be put and the possibility of interference from coloured product or packaging to which the device is to be attached. The lower layer 'c' has an adhesive lower surface to facilitate attachment to any product. Sandwiched between layers 'a' and 'c' is the reactive layer 'b'. The reactive layer 'b' includes one or more of the oxygen sensitive materials referred to hereinabove, or alternative oxygen sensitive colour generating materials such as would be within the knowledge of the person skilled in the art. The materials are contained in a reduced form. Additionally, the device may include materials added as reaction accelerators or reaction retardants as outlined above. Additionally, the device may also include anti-evaporative materials added to prevent or retard solvent loss from the reactant layer. In the example given the reactants are a reduced form of indigo in a solution form in a fibrous cellulose matrix. The initial product colour was a yellow colour.

1. Preparation of a Water Based Elapsed Time Indicator

The reactive layer used in the device of FIG 1 is prepared as follows:

1 (a) Preparation of leuco indigo

Indigo (100mg) in the oxidised form was added to a solution containing aqueous sodium hydroxide (3mL of 10.5M solution). Aqueous sodium dithionite (17mL of 1.4M solution) was added together with distilled water to 50mL. The mixture was stored in a 50mL light proofed vessel to avoid oxidation by contact with air or photo-oxidation. The solution was initially a green colour and become yellow (the leuco indigo form) on standing for one hour. Concentrations of the reactants in the final solution prepared in step (a) are:

Indigo 7.6 mM Sodium hydroxide 0.6M Sodium dithionite 0.5M pH greater than 8.5

1 (b)(i) Preparation of reactive gel (1 )

A solution of agar-agar was prepared by the addition of 2g agar powder to 10OmL heated distilled water. The mixture was stirred until all powder was dissolved.

2mL of the solution prepared in step (a) was added to 2mL of the agar solution by pipette to avoid the inclusion of any entrained air. The solution was stirred and maintained a temperature of 100°C in the absence of air. Concentrations of the reactants in the reactive gel prepared in step (b) are: Indigo 3.8mM Sodium hydroxide 0.3M Sodium dithionite 0.24M pH greater than 8.5

1 (b)(ii) Preparation of reactive gel (2)

An adhesive solution was prepared by adding 4mL of 0.5M aqueous sodium hydroxide to a powdered mixture of 1.5g casein hydrochloride, 0.5g gum Arabic and 0.2g urea. The mixture was stirred and maintained at a temperature of 100°C for 45 minutes. 1mL of the solution prepared in step (a) was added to the adhesive solution by pipette to avoid inclusion of any entrained air. The solution was stirred and maintained at 100°C in the absence of air. Concentrations of reactants in the reactive gel prepared are as follows: Indigo 1.5mM

Sodium hydroxide 0.5M Sodium dithionite 0.1 M pH greater than 8.5

1 (c) Preparation of indicator device

A sheet of absorbent tissue paper was adhered to a sheet of transparent adhesive coated plastic. The composite was placed tissue side uppermost and the oxygen reactive gel (1 ) prepared in step (b)(i) or the reactive gel (2) prepared in step (b)(ii) was quickly poured onto the tissue surface and then quickly sealed beneath a second sheet of adhesive coated plastic placed adhesive side down. The development of colour change on oxidation of the leuco indigo was monitored as shown in FIG 1.

The structure of the resulting product is:

Transparent plastic Tissue Paper Reactive Gel (1 ) or (2) Tissue Paper Transparent plastic

In the drawings the blackish areas indicate the oxidised form of the reactants used, ie the development of the colour change, in this case to a blue colour. As the upper layer is an oxygen impermeable layer, oxygen is only able to enter the device by diffusing laterally into the reactive layer 'b'. Hence, as illustrated in plan view in (3), the development of the colour change occurs gradually from an initial time t=0 when the indicator is exposed to the oxygenated environment from the outer edges of the device and spreads inwardly as time progresses. This has been likened to a contour and can be spoken of in terms of an iso-oxidation contour. The development of a complete colour change is shown in the five discs in the lower portion of the drawing.

An alternative colour elapsed time indicator can be made from the solution prepared in step (a). To 35mL of the solution and 14mL diethyl ether, citric acid (solid) was added in sufficient quantity to reduce the pH of the solution to pH 2. The resulting solution was shaken and any evolved gases released. A white emulsion product emerged. The product was fashioned into the elapsed time indicator as previously described in steps (b) and (c) above. The effective colour change was now from white to blue. Such an emulsion is also capable of incorporation into a reactive layer based of synthetic polymers.

The effects of adding retardants or accelerators are indicated schematically in FIG 4 where the development of the colour change is held back or brought forward as the case may be for any selected reactant composition.

An alternative form of an elapsed time indicator in accordance with the invention is shown in FIG 2a. In this case the device again consists of a three-layer device, the lower layer being an oxygen impermeable layer having adhesive means for attachment to a chosen article. The reactants are again contained in an inner layer in matrix form with any necessary accelerators or retardants. However, in this case the upper layer is an oxygen semipermeable material formed as a gently curving convex disc. A still further example of a device in accordance with the present invention is shown in Fig 2b. The structure of the device is similar to that of FIG 2a. However, in this case the device is composed of two layers, an upper layer 'b' forming the reactive layer and a lower layer 'c' forming an impermeable base layer. Again because of the increasing thickness of the device towards the centre the colour development process is enhanced such that deeper hues develop towards the centre, thereby enhancing the visual appeal of the product.

The use of the oxygen semi-permeable upper layer creates a generalised diffusion across the surface of the disc, as represented by the colour development profile shown at the bottom of the drawing. Where rapid colour development occurs the product illustrated would demonstrate a quick-change colour reaction which could be beneficial in certain circumstances.

Figure 3 illustrates in side view the presence of iso oxidation contours in accordance with the devices illustrated in figures 2a and 2b.

As shown in figure 3 an estimation of elapsed time is made by visual inspection. However, it is to be understood that electronic scanning devices can also be used to determine the extent of elapsed time.

The invention is also embodied in the form of a colour change plastic wherein a colour change material is incorporated in a matrix of plastics material. In such a form a tag as illustrated in figures 1-4 can be formed with an enhanced degree of flexibility.

2. Preparation of a Polymer Based Elapsed Time Indicator.

2(a) Preparation of leuco indigo

Indigo in the oxidised form (1g) was added to a solution of sodium hydroxide (0.63M) and sodium dithionite (0.49M) in a 500ml vessel. The solution was thoroughly mixed and stored in a light proofed vessel to avoid oxidation by contact with air or photo-oxidation.

2 (b) Preparation of Polymer Material 200mL of polyvinyl acetate solution (available as wood glue) was diluted with methanol to a volume of 600mL with stirring and slow careful addition of methanol. A homogeneous translucent emulsion of polyvinyl acetate in methanol was produced.

2(c) Preparation of Colour Change Plastics Material

A reaction vessel was purged with a continuous supply of carbon dioxide to establish anaerobic reaction conditions. 50mL of the solution prepared in step 2(a) above was introduced into the reaction vessel. 150mL of the solution prepared in step 2(b) above was then added slowly to the reaction vessel with stirring.

During the addition of the emulsion (b) a matrix of polymer material and colour change solution is formed and separated from the surrounding reaction solution. The reaction liquid was then removed from the reaction vessel by aspiration. The reaction product is a pliable pale yellow material. Any residual salts, and water were removed from the reaction product by sequential washing steps using solvents of decreasing polarity for each step. Thus, the reaction product was washed in sequence with carbon dioxide treated water, methanol, and acetone.

The reaction product was finally emulsified in a mixture of methyl ethyl ketone and heptane and concentrated through heating to evaporate remaining solvents.

The polymer based material prepared in steps 2(a)-2(c) can be used in a variety of ways and can be used to prepare indicators with the structures shown in figures 1- 4 as described hereinabove. The reaction product is a pliable plastic material that is, in addition, adapted to be drawn into a fine thread and which may be used through a jet or nozzle for application to a surface as a printed indicia or incorporated into packaging material.

Modifications and variations of the present invention, such as would be apparent to a skilled addressee are deemed to be within the scope of the invention. The examples are used for purposes of illustration only and are not to be taken as limiting the form of the invention.

Claims

1. A device for measuring elapsed time, said device consisting of a generally laminar structure having an upper reactive layer and lower oxygen impermeable layer, said reactive layer including therein one or more reactive materials capable of reacting with oxygen to create a colour changed product, wherein said reactive layer is constructed such that the oxygen permeability of said reactive layer is greater towards the periphery of the device and lesser towards a centre thereof.

2. A device for measuring elapsed time according to claim 1 , characterised in that the device is disc shaped, such that a colour changed product forms as an outer ring located circumferentially on edges of the disc and gradually occupying the whole of the disc.

3. A device for measuring elapsed time according to claim 1 , characterised in that the device consists of oxygen impermeable upper and lower layers separating the reactive layer and wherein the colour changed product is as a result of the lateral diffusion of oxygen into the device.

4. A device for measuring elapsed time according to claim 1 , characterised in that, the upper layer of the device consists of a material semi-permeable to the diffusion of oxygen therethrough said semi-permeable material being arranged as a convex layer of greater thickness of reactive layer towards a centre thereof to thereby create a differential flow of oxygen diffusion across the layer to the reactive layer below.

5. A device for measuring elapsed time according to claim 1 , characterised in that, the device consists of two layers, the first layer of which consists of a material which is semi-permeable to the diffusion of oxygen therethrough said semi-permeable material having an oxygen sensitive material as a component therein, the semi-permeable layer comprising the reactive layer, said layer being arranged as a convex structure above and being bonded to a lower oxygen impermeable second layer.

6. A device for measuring elapsed time according to claim 1 , characterised in that the device includes an outer oxygen impermeable cover, said cover containing an inert or non reactive gas such as carbon dioxide or nitrogen and mixtures thereof which may be removed at a selected time, nominally time zero, to allow atmospheric oxygen to begin the diffusion process into the device and hence to commence the development of the colour change.

7. A device for measuring elapsed time according to claim 1 , characterised in that said reactants included in the reactive layer are reduced vat dyes such as blue indigo, or dye like chemicals in the form of benzoylamino anthraquinone, dibenzanthrone dye (caledon jade green), methylene blue, indanthrene blue, alizarin cyanine green F, anthralin, isatin, kermesic acid, hypericin and adducts thereof.

8. A device for measuring elapsed time according to claim 1 , characterised in that the reactant layer additionally contain retardants to slow the development of any colour changed product.

9. A device for measuring elapsed time according to claim 1 , characterised in that the retardants may include anti-oxidants such as alpha tocopherol (vitamin E), butylated hydroxytoluene (BHT) or butylated hydroxyanisole (BHA).

10. A device for measuring elapsed time according to claim 1 , characterised in that the reactant layer additionally include anti-evaporative materials to slow the evaporative loss of solvent from the reactive layer, for example glycerol and/or polyalcohols may be added to the reactive layer to retard evaporation of water from the reactive layer.

11. A device for measuring elapsed time according to claim 1 , characterised in that the reactant layer may additionally include accelerator materials used to increase the speed of colour development, for example products releasing oxygen over a period of time, such as peroxides together with ferrous or copper ions.

12. A device for measuring elapsed time according to claim 1 , characterised in that the upper reactive layer is a water based reactive layer containing a vat dye in the concentration range 0.07 micro molar to 0.5 molar, sodium hydroxide 0.5 micro molar to 6 molar, and sodium dithionite 0.5 micro molar to 5 molar the reactive layer having a pH in the range pH 7-14.

13. A device for measuring elapsed time according to claim 1 , characterised in that the upper reactive layer is a polymer based reactive layer

14. A device for measuring elapsed time according to claim 13, characterised in that the polymer of the reactive layer includes one or more of polyvinyl alcohol, polyvinyl acetate, co-polymers of polyvinyl acetate and polyvinyl alcohol, co- polymers of soluble starch and polyvinyl alcohol, methyl cellulose, cellulose acetate, cellulose nitrate, polystyrene, polyethylene and adducts thereof.

15. A device for measuring elapsed time according to claim 13, characterised in that the device is incorporated into packaging materials,

16. A device for measuring elapsed time according to claim 13, characterised in that, the device forms an entire packaging surface.

7. A device for measuring elapsed time according to claim 13, characterised in that is the device is applied to a surface as a printed indicia which become visible over and optionally reveals or obscures messages as a colour change product develops

18. A device for measuring elapsed time according to claim 13, characterised in that the upper reactive layer is a polymer based reactive layer containing a vat dye in the concentration range 0.001 % -50 % by weight, polymer 50-99.999 %, pH 4-10.

Dated this 29 November 2001

GARETH LEWIS

By his Patent Attorneys Lesicar Perrin