GB2552167A

GB2552167A - Time temerature indicator label

Info

Publication number: GB2552167A
Application number: GB1612003.2A
Authority: GB
Inventors: Robinson John; Wintersgill Stephen; Hancock Andy; Peacock Martin; Akbar Sarah
Original assignee: Intray Ltd
Current assignee: Intray Ltd
Priority date: 2016-07-11
Filing date: 2016-07-11
Publication date: 2018-01-17
Also published as: WO2018011565A9; CN109690267B; JP2019528465A; CA3030541A1; SG10202100193XA; US11398167B2; EP3482178A1; JP7129705B2; AU2017295964B2; AU2017295964A1; US20200043377A1; WO2018011565A1; CN109690267A; SG11201900050RA; GB201612003D0

Abstract

A time-temperature integrating (TTi) indicator label comprises an initiator reservoir and a target reservoir, said initiator reservoir containing a pH modification system and said target reservoir comprising a pH responsive indicator. The pH modification system is pereferably an acid generation system that produces an acid via a chemical reaction following exposure to a pre-defined stimulus. As the acid is generated the pH indicator changes colour. The acid generation system is preferably photo-initiated and comprises silver chloride entrained an a hydrogel polymer. The label is activated by removal of a light impermeable cover over the initiator reservoir. The reservoirs are preferably separated by hydrogel polymer plugs which de-swell upon exposure to the acid thereby allowing the acid into the target reservoir.

Description

(54) Title of the Invention: Time temerature indicator label

Abstract Title: Time temperature integrating indicator (TTI) label (57) A time-temperature integrating (TTi) indicator label comprises an initiator reservoir and a target reservoir, said initiator reservoir containing a pH modification system and said target reservoir comprising a pH responsive indicator. The pH modification system is pereferably an acid generation system that produces an acid via a chemical reaction following exposure to a pre-defined stimulus. As the acid is generated the pH indicator changes colour. The acid generation system is preferably photo-initiated and comprises silver chloride entrained an a hydrogel polymer. The label is activated by removal of a light impermeable cover over the initiator reservoir. The reservoirs are preferably separated by hydrogel polymer plugs which de-swell upon exposure to the acid thereby allowing the acid into the target reservoir.

Time Temperature Indicator Label

The present invention relates to a time and temperature integrating (TTi) indicator label, particularly but not exclusively, a time indicator device suitable for use on food and other perishable products, such as pharmaceuticals and cosmetics. Preferably said indication takes the form of a traffic light sequence, beginning in a 'green state' indicating that everything is alright, transitioning to an amber/caution state and finally a red, do not use condition. The use of a traffic light system is preferred due to the universally recognisable colour signals.

The present invention will be described with reference to its use on food products, however it is recognised and will be readily apparent that the invention could also find application in other fields such as pharmaceutical products, cosmetics and any other products which have a limited life.

There are currently a number of different target dates provided to the consumer as indicators of the likely level of freshness of food (and other perishable) products. The current practice is to provide one or more of the following: a 'Sell By' date; a 'Best Before' date; a 'Use by' date; and/or a Once opened, use within' date.

A 'Sell By' date, the date after which the retailer should no longer offer a product for sale, is an indicator to the retailer of the expected shelf life of a product, but provides the consumer with no useful information as to how long after this date a product is still safe or desirable to consume.

A 'Best Before' date, the date after which the product may not be at its premium quality of performance. This does provide the consumer with an indication of the 'best product life', but is not an indicator of the actual freshness or safety or efficacy of a product.

Furthermore, this date is generally only a reliable measure if the primary packaging is in an unopened state and the product has been stored properly.

A 'Use by' date, the date after which a product is nationally no longer safe to consume (the product may still be safe, but the retailer/manufacturer will no longer warrant such). Again, this date relies on the integrity of the primary product packaging and also appropriate storage conditions,

A 'Once opened, use within XX days' date, attempts to reflect the accelerated decay of the produce following breach of the primary packaging. Whilst the use of a Once opened, use within XX days' date is an advance on the previous state of the art, its effectiveness relies totally on the consumer remembering when a product was first opened. This is more evident when the open life is short (e.g. 3 days for orange juice); however, some products have an open life of several weeks or even months, at which point the consumer's memory becomes an unreliable measure, with people tending to rely on 'self preservation' i.e., the smell or visual appearance of the product.. This is unsatisfactory both for the consumer, who will get poor performance from the product, or who may suffer an upset stomach or other such complaint as a result of eating tainted food, and also for the manufacturer, who will probably lose a future customer, due to their dissatisfaction with the product. This date also relies on the produce being stored in appropriate conditions after opening.

Clearly there is a need, both from the manufacturer's and the consumer's perspective, for a simple, inexpensive and reliable indicator on such perishable product containers in order to better safeguard the consumer's health, assist the consumer in better consumption habits or management, and also to improve customer's perception of the manufacturers product. A number of means to accomplish this objective have been attempted in the past and are known in the art; however, ai! have their drawbacks.

in some earlier devices the timing mechanism is activated upon manufacture or application of the device, whereas in other devices user initiation is employed. Both these systems have inherent problems, certain devices are acceptable as 'Use By' indicators, but due to their initiation at manufacture this can take no account of the accelerated rate of product decay upon breach of primary packaging exposing the product to oxygen, locally introduced bacteria and other suchlike present in the atmosphere. Equally the user- activated devices rely on a consumer remembering to activate the device upon opening their product, this is easily forgotten and could leave unaffected exactly the problems they are intended to address.

A few attempts have been made to address the aforementioned shortcomings of the above products. For example, a reservoir may be breached by the act of opening the closure/iid of a container holding the perishable product. A multi-component lid can be used with various moving parts designed to puncture a reservoir containing a reactive compound. These devices borrow heavily from known art in the field of tamper evidence and suffer from the same main drawback, which is that a multi- component lid/closure is difficult to manufacture and assemble and therefore too costly to gain mainstream commercial acceptance.

Various attempts to overcome these issues have been made in the past, the most relevant of which are discussed below.

US 8,104,949 82 (ROBINSON et ak) provides a time temperature indicator label comprising first and second interconnected reservoirs containing first and second liquids respectively, a first barrier being provided between said first and second liquids to prevent said liquids mixing, wherein said first barrier is connected via a conduit to a third reservoir containing a third liquid which is adapted to pass along said conduit over a first predetermined time period and to effect removal of said first barrier upon contact to facilitate mixing of said first and second liquids and generation of a first liquid mixture within the second reservoir of different colour to the second liquid prior to mixing and thereby provide an indication of when said first predetermined time period has elapsed.

In the preferred embodiment of ROBINSON et ak the barrier discussed above is a lipid plug, which is subsequently broken down by an enzyme present in said third liquid. The problem with this is linked to an intrinsic problem of using fine capillaries to transport reactive label components. Due to the restrictive size of the capillaries, bulk transport of fluids is impossible, hence it is only possible to deliver a steady drip drip of enzyme to the lipid plug, this means that the rate at which the plug can be broken down is severely restricted, placing concomitant restrictions on the timescales over which such a label can be effective. Furthermore, the lipid plug is likely to be broken down both slowly and preferentially along the side from which the enzyme is delivered thereto, this could easily lead to partial breakdown of the plug resulting in leakage past the barrier in a retarded manner, thereby delivering a slow and gradual colour change, rather than a more desirable, rapid transition.

Whilst this development overcomes some of the issues discussed above, the construction of a label to the specifications outlined is both technically and physically very challenging, thereby reducing the speed at which such a label could be manufactured, bringing with it inherent cost implications. The complexity of design and construction, and the proportion of label failures which could result from such an approach, would render any such solution partial and unreliable at best. The complexity of manufacture is described in graphic detail in the related patent US 8,936,693 B2 (MANES et aL). The die cutting and laminating down of the capillary elements (used for timing) presents particular challenges in terms of uniformity, integrity and the propensity for media losses through thin film evaporation,

A further difficulty in the manufacture of labels as per the ROBINSON et ak patent is the materials handling issues arising from the application of liquid components into a multilayered label wherein many of the layers are very thin films (of the order of 10 - 20 microns) and sealing thereafter. This issue has been partially addressed (albeit inadvertently) by KEEP-TF TECHNOLOGIES in both EP 1,228,366 BI and EP 2,697,617 BI, both of which use hydrogel polymer matrices to immobilise liquid components. However, that is the only lesson taken from these patents in this instance, as beyond this their teaching, diverges somewhat from the objects of the present invention.

An object of the present invention is to obviate or mitigate one or more of the problems and/or drawbacks associated with prior art time indicator devices mentioned above.

The terms acid generator and/or acid generation are used herein to refer to either a system which produces an acid via chemical reaction or releases an acid, subsequent to exposure to a pre-defined stimulus.

The term hydrogel polymer refers to a group of chemicals which are hydrophilic, with extraordinarily high rates of absorption of aqueous media, said aqueous media being entrapped within said hydrogels. Common uses for hydrogels include nappy linings, women's sanitary products, desiccant pouches, medical applications such as burns dressings, optical contact lenses, and some materials used in hydroponic growing systems. Typically with hydrogels, once an aqueous medium has been absorbed, it remains entrapped within the hydrogel polymer matrix and is thereby prevented from interacting with outside media.

The term stimuii-responsive hydrogel polymer refers to a subset of hydrogel polymers as defined above, Stimuii-responsive hydrogel polymers which are responsive to light, pH, magnetism, electricity, ionic strength, temperature, and enzymatic action are known, the response generally being to de-swell, that it to say that, upon exposure to the relevant stimulus, the hydrogel becomes hydrophobic, contracts, and releases some or all of the aqueous media previously entrained therein.

According to the present invention there is provided a time-temperature indicator label comprising an initiator reservoir and a target reservoir, said initiator reservoir containing a pH modification system and said target reservoir comprising a pH responsive indicator.

Said pH modification system is preferably an acid generation system.

Said initiator reservoir and said target reservoir may be physically separate reservoirs, alternatively, they may be different portions of the same reservoir.

Preferably, said acid generation system comprises a photo-initiated acid generation system.

Preferably, said acid generation system comprises a silver halide salt, most preferably silver chloride.

Preferably said initiator reservoir is (at least partially) filled with a hydrogel polymer or other high viscosity medium.

Preferably said acid generation system is entrained either within a matrix formed by said hydrogel polymer or within said high viscosity medium.

Said acid generation system may comprise an acid generator entrained within a pH sensitive hydrogel polymer, said combination of acid generator and pH sensitive hydrogel polymer becoming a fast acting photo-sensitive hydrogel polymer, such that, upon exposure to light said hydrogel polymer de-swells effecting release of said acid, or the passage of other acidic material.

Preferably, at least a portion of said initiator reservoir is arranged such that it can be exposed to light, more preferably said light exposure is achieved by the removal of a peelable light impermeable upper layer of said label.

Said target reservoir comprises at least a portion which is visible from outwith said label, thereby providing visual indicia for a user as to the current usability of the produce upon which said label is being used.

Preferably, said time temperature indicator label comprises an initiator reservoir, an accumulator reservoir and a target reservoir, said reservoirs being physically separated by stimuli-responsive hydrogel polymer plugs.

Preferably said stimuli-responsive hydrogel plugs are pH responsive hydrogel plugs.

Preferably said first hydrogel plug (separating said initiator and accumulator reservoirs) comprises a first hydrogel, and said second hydrogel plug (separating said accumulator and target reservoirs) comprises the same hydrogel.

Optionally said first hydrogel plug (separating said initiator and accumulator reservoirs) comprises a first hydrogel, and said second hydrogel plug (separating said accumulator and target reservoirs) comprises a second, different hydrogel.

Preferably said first and second hydrogels respond to different levels of the same stimulus.

Preferably said first and second hydrogels respond to different pH levels.

Optionally, said first and second hydrogels may be responsive to two entirely different 20 stimuli.

Preferably said accumulator reservoir is filled with a further hydrogel polymer, or a high viscosity medium, to retard diffusion of hydrogen ions through said reservoir.

The use of accumulator reservoirs in the foregoing examples allows for the gradual build-up of hydrogen ions proximal the target reservoir, without the two being allowed to come into contact with each other until such time as the pH within the accumulator reservoir causes rapid de-swelling and collapse of the reactive plug, thus allowing for rapid pH change in the target reservoir, and therefore colour change, within said target reservoir.

In one embodiment of the present invention, upon activation of said label, the acid generation system generates an acid which causes the pH in the initiator reservoir to drop, the reduced pH in the initiator reservoir causes said first hydrogel plug to de-swell, thereby providing a fluid connection between said initiator reservoir and said accumulator reservoir. Upon de-swelling of said first hydrogel plug, hydrogen ions begin to diffuse from said initiator reservoir into said accumulator reservoir, the rate of said diffusion being dependent upon both the relative pH of the two reservoirs, physical size of the reservoirs, the size (cross sectional area) of the entrance gate, and the viscosity of the gel or hydrogel (which is itself temperature dependent), over time the pH of the accumulator reservoir drops to such a level that the reduced pH in the accumulator reservoir causes said second hydrogel plug to de-swell, thereby providing a fluid connection between said accumulator reservoir and said target reservoir, providing a massive and proximal supply of low pH to initiate a rapid colour change reaction. Upon de-swelling of said second hydrogel plug, hydrogen ions begin to rapidly diffuse from said accumulator reservoir into said target reservoir wherein they interact with said acid responsive indicator to effect a rapid colour change.

A second embodiment of the present invention differs from the first in that said label is provided with two initiator reservoirs, each connected to a separate accumulator reservoir, said connections each being blocked by separate, stimuli-responsive hydrogel plugs, said separate accumulator reservoirs each being connected, via a further two separate stimuliresponsive hydrogel plugs, to said target reservoir, in operation, said label is very similar to that discussed in said first embodiment; upon activation of said label, the acid generation systems in each accumulator reservoir generates an acid which causes the pH in said initiator reservoirs to drop, the reduced pH in the initiator reservoirs causes said first hydrogel plugs to de-swell, thereby providing a fluid connection between said initiator reservoirs and said accumulator reservoirs. Upon de-swelling of said first hydrogel plugs, hydrogen ions begin to diffuse from said initiator reservoirs into said accumulator reservoirs, over time the pH of the accumulator reservoirs drops to such a level that the reduced pH in the accumulator reservoirs causes said second hydrogel plugs to de-swell, thereby providing a fluid connection between said accumulator reservoirs and said target reservoir. Upon de-swelling of said second hydrogel plugs, hydrogen ions begin to diffuse from said accumulator reservoirs into said target reservoir wherein they interact with said acid responsive indicator to effect a colour change.

Preferably said label is arranged such that said first and second accumulator reservoirs 5 cause the de-swelling of said plugs separating them from said target reservoir at disparate points in time, such that the contents of said first accumulator reservoir diffuse into said target reservoir earlier than the contents of said second accumulator reservoir, such that two distinct colour changes are effected.

Said time differentials discussed above may be achieved through the provision of different 10 hydrogel polymer materials for the various plugs, and the variable parameters of the respective accumulator reservoirs.

Said time differentials discussed above may be achieved through the generation of different levels of acidity in said respective initiator reservoirs.

Said time differentials discussed above may be achieved through the provision of different 15 hydrogel polymers within said different accumulator reservoirs.

Said time differentials may be achieved through the physical parameters of the label's component parts, including, but not restricted to the relative sizes of the various reservoirs, the size of the connecting 'passages' between the various reservoirs or the geometry of said connecting passages.

Preferably said time differentials discussed above are achieved through a combination of the above stated factors.

Preferably said label is of a laminar construction, more preferably comprising a base layer, an intermediate layer and a top layer, preferably with a further, peelable strip preventing the inadvertent ingress of light to said initiator reservoir(s).

Preferably said base layer and top layer are unitary, unbroken polymer films.

Preferably said reservoirs are formed by die-cutting and removal of portions of said intermediate layer.

Optionally, said reservoirs are formed via the deposition of materials onto a base layer in a 3D printing set up.

Optionally said reservoirs are formed via screen printing of UV curable materials onto a base layer.

Preferably said target reservoir contains one or more pH reactive inks arranged to enhance the colour change of said acid responsive indicator. Alternatively, said acid responsive indicator may comprise said one or more pH reactive inks.

Preferably, said pH reactive materials are entrapped within a polymer matrix contained within said target reservoir.

Preferably said polymer matrix comprises an aqueous (non re-solublising ink) or a UV cured polymer ink.

Preferably said stimuli responsive hydrogel polymers are selected from the group comprising poly (vinyl aicohoi)/poly (acrylic acid) [PVA/PAA]; poly (methacrylic acid) [PMAA] and 2-(dimethyiamino) ethyimethacrylate/N-vinyi pyrrolidone [DNAEMA/NVP], it should be evident to the educated reader that were one to substitute the acid generator for a light activated source of hydroxide ions then a similar effect could be achieved using bases as is delivered in the above examples through use of an acid. This possibility/eventuality has been envisaged by the present inventors and is thus incorporated herein.

Claims

1. A time-temperature integrating (TTi) indicator label comprises an initiator reservoir and a target reservoir, said initiator reservoir containing a pH modification system and said target reservoir comprising a pH responsive indicator.

2. A label according to claim 1, wherein said pH modification system comprises an acid generation system,

3. A label according to claim 1 or 2, further characterised in that said initiator and target reservoirs are separate portions of the same physical reservoir.

4. A label according to claim 1 or 2, wherein said initiator and target reservoirs are physically separate, distinct reservoirs.

5. A label according to any of claims 2 to 4, further characterised in that said acid generation system comprises a photo-initiated acid generation system.

6. A label according to claim 5, further characterised in that said photo-initiated acid generation system comprises a silver halide salt.

7. A label according to claim 6, wherein said silver halide salt is silver chloride.

8. A label according to any preceding claim, further characterised in that said initiator reservoir is (at least partially) filled with a hydrogel polymer.

9. A label according to claim 8, further characterised in that said acid generation system is entrained within a matrix formed by said hydrogel polymer.

10. A label according to either of claims 8 or 9, further characterised in that said acid generation system comprises an acid entrained within said hydrogel polymer, said hydrogel polymer being a photosensitive hydrogel polymer, such that on exposure to light said hydrogel polymer de-swells effecting release of said acid into said initiator reservoir.

11. A label according to any preceding claim, further characterised in that at least a portion of said initiator reservoir is arranged such that it can be exposed to light.

12. A label according to claim 11, wherein said arrangement to allow exposure to light is achieved via the provision of a peelable/removable, substantially light impermeable upper layer of said label.

13. A label according to any preceding claim, further characterised in that at least a portion of said target reservoir is visible from outwith said label to allow visual inspection thereof.

14. A label according to any preceding claim, further characterised in that it also comprises an accumulator reservoir, said reservoirs being arranged in series, initiator to accumulator to target reservoir.

15. A label according to claim 14, wherein said initiator and accumulator reservoirs are separated by a stimuli-responsive hydrogel polymer plug.

16. A label according to claim 14, wherein said accumulator and target reservoirs are separated by a stimuli-responsive hydrogel polymer plug.

17. A label according to claim 14, wherein said initiator and accumulator reservoirs are separated by a first stimuli-responsive hydrogel polymer plug, and said accumulator and target reservoirs are separated by a second stimuli-responsive hydrogel polymer plug.

18. A label according to claim 17, wherein said first stimuli-responsive hydrogel polymer plug and said second stimuli-responsive hydrogel polymer plug comprise different hydrogel polymers.

19. A label according to claim 17, further characterised in that said first stimuliresponsive hydrogel polymer plug and said second stimuli-responsive hydrogel polymer plug are both responsive to the same stimulus.

20. A label according to claim 19, wherein said first stimuli-responsive hydrogel polymer plug and said second stimuli-responsive hydrogel polymer plug are both responsive to different levels of the same stimulus.

21. A label according to claim 20, wherein said stimuli-responsive hydrogel polymer plugs comprise pH responsive hydrogel polymers.

22. A label according to claim 17, further characterised in that said first stimuliresponsive hydrogel polymer plug and said second stimuli-responsive hydrogel polymer plug are responsive to different stimuli.

23. A label according to any of claims 14 to 22, further characterised in that said accumulator reservoir is (at least partially) filled with a further hydrogel polymer.

24. A time-temperature indicator label comprising an initiator reservoir, an accumulator reservoir and a target reservoir arranged in series, said reservoirs each being separated by a pH responsive hydrogel polymer plug, said initiator reservoir containing silver chloride entrained within a hydrogel polymer, said initiator reservoir further being provided with a substantially light impermeable, peelable cover such that it can be selectively exposed to light, said accumulator reservoir further containing a hydrogel polymer matrix; said target reservoir further containing a pH indicator compound; such that upon removal of said peeiable layer said silver chloride is exposed to light, said silver chloride subsequently photodissociating in an aqueous environment to generate silver and hydrochloric acid, said hydrochloric acid then causing the de-swelling of the first pH responsive hydrogel polymer plug, allowing ingress of said hydrochloric acid into said accumulator reservoir, the contents of said accumulator reservoir hence becoming gradually more acidic as the hydrochloric acid diffuses in from said initiator reservoir; subsequently, as the level of hydrogen ions in said accumulator reservoir accumulates to a sufficient level said hydrochloric acid causes the de-swelling of said second pH responsive hydrogel polymer plug, thereby allowing ingress of said hydrochloric acid into said target reservoir wherein said hydrochloric acid interacts with said pH indicator compound to effect a colour change, said colour change being observable by the user through a viewing pane incorporated into said target reservoir.

25. A time-temperature indicator label comprising two or more initiator reservoirs, each connected to a separate accumulator reservoir, said connections each being blocked by separate, pH responsive hydrogel plugs, said separate accumulator reservoirs each being connected, via a further two separate pH responsive hydrogel plugs, to said target reservoir, said initiator reservoirs each containing silver chloride entrained within a hydrogel polymer, said initiator reservoirs further being provided with a substantially light impermeable, peeiable cover such that they can be selectively exposed to light, said accumulator reservoirs each further containing a hydrogel polymer matrix; said target reservoir further containing a pH indicator compound; such that upon removal of said peeiable layer said silver chloride is exposed to light, said silver chloride subsequently photo-dissociating to generate hydrochloric acid, said hydrochloric acid then causing the de-swelling of the first pH responsive hydrogel polymer plugs, allowing ingress of said hydrochloric acid into said accumulator reservoirs, the contents of said accumulator reservoir hence becoming gradually more acidic as the hydrochloric acid diffuses in from said initiator reservoirs; over time, diffusion of hydrogen ions causes the pH of the accumulator reservoirs to drop to such a level that the said second hydrogel plugs de-swell, thereby providing a fluid connection between said accumulator reservoirs and said target reservoir, wherein said hydrochloric acid interacts with said pH indicator compound to effect a colour change, said colour change being observable by the user through a viewing pane incorporated into said target reservoir.

26. A label according to claim 25, further characterised in that said first and second accumulator reservoirs cause the de-swelling of said plugs separating them from said target reservoir at disparate points in time, such that the contents of said first accumulator reservoir diffuse into said target reservoir earlier than the contents of said second accumulator reservoir, such that two distinct colour changes are effected.

27. A label according to claim 26, wherein said time differential is achieved through the provision of different hydrogel polymer materials for the pH responsive hydrogel plugs.

28. A label according to claim 26, wherein said time differential is achieved through the generation of different levels of acidity in said respective initiator reservoirs.

29. A label according to claim 26, wherein said time differential is achieved through the provision of different hydrogel polymer materials within said two or more accumulator reservoirs.

30. A label according to claim 26, wherein said time differential is achieved through variation in the relative sizes of said two or more accumulator reservoirs.

31. A label according to claim 26, wherein said time differential is achieved through a combination of one or more of the provision of different hydrogel polymer materials for the pH responsive hydrogel plugs, the generation of different levels of acidity in said respective initiator reservoirs, the provision of different hydrogel polymer materials within said two or more accumulator reservoirs and variation in the relative sizes of said two or more accumulator reservoirs.

32. A label according to any preceding claim, further comprises a three layer, laminar construction comprising a base layer, an intermediate layer and a top layer.

33. A label according to claim 32 further characterised in that said base layer and top layer are substantially unitary, unbroken polymer films.

34. A label according to either of claims 32 and 33, characterised in that said reservoirs are formed by die-cutting and removal of portions of said intermediate layer prior to

5 lamination.

35. A label according to any of claims 32 to 34, further comprising a peelable strip preventing the inadvertent ingress of light to said initiator reservoir(s).

36. A label according to any preceding claim, further characterised in that said target reservoir further contains one or more pH reactive inks arranged to enhance the

10 colour change of said acid responsive indicator,

37. A label according to any of claims 1 to 36, further characterised in that said target reservoir further contains one or more pH reactive inks, said one or more pH reactive inks fulfilling the role of said acid responsive indicator.

38. A label according to either of claims 36 and 37, wherein said pH reactive inks are

15 entrapped within a polymer matrix contained within said target reservoir.

39. A label according to claim 38, wherein said polymer matrix comprises a UV cured polymer matrix.

40. A label according to any preceding claim, further characterised in that said stimuliresponsive hydrogel polymers are selected from the group comprising poly (vinyl

20 alcohol)/poly (acrylic acid) [PVA/PAA]; poly (methacrylic acid) [PMAA] and 2(dimethylamino) ethylmethacrylate/N-vinyl pyrrolidone [DNAEMA/NVP],

41. A time-temperature indicator label substantially as hereinbefore described with reference to the claims and description.

Intellectual

Property

Office

Application No: GB1612003.2 Examiner: Dr Matthew Jefferson