WO2006091464A1

WO2006091464A1 - Improved time/ temperature indicators

Info

Publication number: WO2006091464A1
Application number: PCT/US2006/005442
Authority: WO
Inventors: Farid Azizian; Michael William Leonard; Shaun Lawrence Herlihy
Original assignee: Sun Chemical Corporation
Priority date: 2005-02-22
Filing date: 2006-02-16
Publication date: 2006-08-31
Also published as: GB2423361A; GB0503633D0

Abstract

A time/temperature indicator comprises a substrate supporting a first and a second layer, the first layer comprising a dye which will change colour in the presence of an acid or a base, and the second layer comprising a neutral compound which, upon ultraviolet irradiation, forms an acid or a base, one of the first and second layers overlying the other of the first and second layers.

Description

IMPROVED TIME/TEMPERATURE INDICATORS

The present invention relates to new and improved time/temperature indicators using a dye that changes colour in the presence of an acid or of a base.

Many packaged goods, notably foodstuffs and medicines, have a limited shelf life, and such goods commonly have a "use by" date printed on packaging associated with the goods. However, this is, at best, only a crude indication, as the rate at which such goods deteriorate is a function of the temperature at which they are kept as well as the length of time for which they are kept. Moreover, the temperature may vary considerably during the life of the goods. For example, a product may be bought from a shop, where it is kept in a refrigerator, carried through a sunny car park, where its temperature rises, stored in a car, where its temperature rises further, and finally stored in a domestic refrigerator, where its temperature is lowered, but may still go up and down as the refrigerator door is opened and closed.

It would, therefore, be desirable to provide an indicator on packaging associated with the goods which will react to changing temperatures over time in the same way as do the goods themselves. These are referred to as "time/temperature indicators". A number of proposals have been made for such time/temperature indicators. For example, 3M's MonitorMark (trade mark) uses the principle of diffusion along a wick to provide a time/temperature indicator. VITSAB 's Time/Temperature Indicator is based on the colour change caused by the controlled enzymatic hydrolysis of a lipid substrate. Lifelines Lie's FreshCheck (trade mark) is based on a polymerisation reaction leading to a coloured polymer, and is suggested for use, inter alia, with foodstuffs. Although all of these are successful in their fields, they are all relatively expensive and add significantly to the cost of the products to which they are applied. They cannot, therefore, be used in practice with lost cost, low margin items, particularly everyday foodstuffs.

To meet this requirement, it would be desirable to provide a time/temperature indicator that makes use of relatively cheap components and which can be applied easily, for example by printing at the time that the packaging is printed. Moreover, if the time/temperature indicator is applied to the packaging before the perishable product is packed in it, it is desirable that the indicator should be inactive until a time close to the time of packaging and then should be activated so that its response closely parallels that of the perishable product.

US Patent No. 4,917,503 discloses a time/temperature indicator which comprises a thermally inactive compound comprising a leuco base and a photosensitive compound that, on exposure to actinic radiation (e.g. ultraviolet), forms an acid that oxidises the colourless leuco base to a coloured leuco dye at a rate determined by the reaction temperature. The photosensitive compounds suggested for use in this patent include o-nitrobenzaldehyde and derivatives thereof and trihaloalcohols. However, the use of o-nitrobenzaldehyde is restricted in Europe and there are indications that it may be mutagenic. Moreover, certain of the trihaloalcohols are used as anaesthetics. The compounds proposed also tend to be malodorous. Furthermore, the products of irradiation of these compounds are generally recognised to be harmful to health. For these reasons, it is difficult to use the time/temperature indicator of US Patent No. 4,917,503 in practice in association with foodstuffs or other perishable materials that may be ingested by humans.

WO 92/09870 discloses a time/temperature indicator comprising an indicating tape, an activating tape and a barrier between the two tapes. However, as soon as the tapes are put together, they start to react. There is no facility for assembling the indicator but delaying the commencement of the reaction. We have now discovered that a more flexible time/temperature indicator may be produced by putting the dye and the photoactive compound which causes it to change colour into two separate but adjacent layers, so that, upon irradiation, the acid or base released by the irradiation has to migrate through a layer before it can contact the dye and begin to change its colour.

Thus, the present invention consists in a time/temperature indicator comprising a substrate supporting a first and a second layer, the first layer comprising a dye which will change colour in the presence of an acid or a base, and the second layer comprising a neutral compound which, upon ultraviolet irradiation, forms an acid or a base, one of the first and second layers overlying the other of the first and second layers.

The invention is further illustrated by the accompanying drawings, in which Figure 1 (two colours formulation) and Figure 2 (three colours formulation), illustrate the spectra of coatings monitored through a period of time at temperatures of 0°C, 27°C and 5O⁰C and prepared as described in the subsequent Examples.

Upon exposure to UV, the neutral compound generates an acid or a base, which migrates from its own layer to the layer containing the dye, where it acts upon the dye to change its colour. Thus, the change of colour is not only dependent upon the reaction speed but is also dependent upon the speed of migration of the acidic or basic entity generated by the UV radiation.

If desired, the first and second layers may be in direct contact with each other. Alternatively, there may be another layer or layers between them, provided that those layer(s) do not form a barrier to the migration of the acidic or basic entity.

The order of the layers may have an influence on the rate of colour change and may be chosen as desired, provided that the first and second layers are not separated by anything which would form a barrier to the migration of the acidic or basic entity. Thus, if desired, the first layer may be between the substrate and the second layer. Alternatively, the second layer may be between the substrate and the first layer. The natures of the dyes and neutral compounds employed are, of course, interrelated. For example, in one embodiment of the present invention, the dye in one layer is a dye which changes colour in the presence of an acid, for example a leuco dye or a vat dye in its non-activated (reduced) state, in which case the neutral compound is a cationic photoinitiator.

The term "cationic photoinitiator" as used herein means a compound which, upon exposure to incident radiation, such as ultraviolet, forms a cation capable of initiating the polymerisation of an epoxide monomer. It will, of course, be understood that no such polymerisation is necessarily envisaged in the present invention.

In another embodiment of the present invention, the dye in one layer is a dye which changes colour in the presence of a base, for example a leuco dye or a vat dye in its activated (oxidised) state, and the neutral compound in the other layer is a photolatent base. A photolatent base is a compound which, upon exposure to incident radiation, such as ultraviolet, generates a base.

In a further embodiment of the present invention, one layer comprises a dye which changes colour in the presence of a base, for example a leuco dye or a vat dye in its activated (oxidised) state, and a photolatent base. The other layer contains the neutral compound, which, in this case, is a cationic photoinitiator.

In a still further embodiment of the present invention, one layer comprises a dye which changes colour in the presence of an acid, for example a leuco dye or a vat dye in its non-activated (reduced) state, and a cationic photoinitiator. The other layer contains the neutral compound, which, in this case, is a photolatent base.

In the last two embodiments referred to above, upon exposure to, for example, UV radiation, the dye in the one layer changes colour as a result of the generation of a base (if that layer also contains a photolatent base) or an acid (if that layer also contains a cationic photoinitiator). However, simultaneously, the cationic photoinitiator or photolatent base in the other layer generates an acid or a base, respectively, and this subsequently converts the dye to its other state, thus again changing its colour, but not necessarily into the same colour as its original state.

Where the time/temperature indicator of the present invention uses a cationic photoinitiator, there is no particular restriction on the particular compound used, and any cationic photoinitiator known in the art may be employed. Examples of such cationic photoinitiators include sulphonium salts (such as the mixture of compounds available under the trade name UVI6992 from Dow Chemical), thianthrenium salts (such as Esacure 1187 available from Lamberti), iodonium salts (such as IGM 440 from IGM) and phenacyl sulphonium salts. However, particularly preferred cationic photoinitiators are the thioxanthonium salts, such as those described in WO 03/072567 Al, WO 03/072568 Al, and WO 2004/055000 Al, the disclosures of which are incorporated herein by reference.

Particularly preferred thioxanthonium salts are those of formulae (I) and (II):

(I)

in which each R represents a group of formula (III):

where n is a number and X^" is an anion, especially the hexafluorophosphates, which are available from Robinson Brothers Ltd. under the trade marks "Meerkat" and "Bobcat", respectively.

A photolatent base (sometimes called a "photobase generator") is a compound which, in its normal state, is essentially neutral, but which, upon irradiation with ultraviolet light, generates a basic compound. In general, these include classes of compounds such as carbamates, O-acyloximes, O-carbamoyloximes, formamide, amineimide and onium salts. Specific examples of such photolatent bases include: Quaternary ammonium salts, such as l-phenacyl-(l-azonia-4-azabicyclo[2,2,2]- octane)bromide; l,4-dimethyl-l-phenacyl-(l-azonia-4-azabicyclohexane) bromide; and l-naphthoylmethyl-l-phenacyl-(l-azonia-4-azabicyclo[2,2,2]octane)bromide;

Carbamates, such as l-phenacyl-(l-azonia-4-azabicyclo[2,2,2]octane)-N,N- dimethylthiocarbamate; 1 -methyl- l-phenacyl-(l -azoniacyclohexane)-N,N- dimethyldithiocarbamate; 1 ,4-dimethyl- 1 -phenacyl-( 1 -azoniacyclohexane)-N,N- dimethyldithiocarbamate; and l-naphthoylmethyl-(l-azonia-4-azabicyclo[2,2,2]octane- N,N-dimethyldithiocarbamate;

Amineimides, such as l,l-dimethyl-l-(2-hydroxy-3-phenoxypropyl)amine-p- nitrobenzimide, l,l-dimethyl-l-(2-hydroxy-3-phenoxypropyl)amine-p-cyanobenzimide; and 1,1 -dimethyl- l-(2-hydroxy-3-phenoxypropyl)amine benzimide.

N-substituted 4-(o-nitrophenyl)dihydropyridines, optionally substituted with alkyl ether and/or alkyl ester groups, such as N-methyl nifedipine (Macromolecules 1998, 31, 4798), N-butyl nifedipine, N-butyl 2,6-dimethyl-4-(2-nitrophenyl) 1,4- dihydropyridine 3,5-dicarboxylic acid diethyl ester, and N-methyl 2,6-dimethyl 4-(4,5- dimethoxy-2-nitrophenyl)-l,4-dihydropyridine 3,5-dicarboxylic acid diethyl ester;

Quaternary organo-boron photoinitiators such as those disclosed in GB-A-2 307 473, the disclosure of which is incorporated herein by reference;

α-Aminoacetophenones, such as 4-(methylthiobenzoyl)-l -methyl- 1- morpholinoethane (IrgacureR 907 ex Ciba Specialty Chemicals) and (4- morpholinobenzoyl)-l -benzyl- 1-dimethylaminopropane (IrgacureR 369 ex Ciba Specialty Chemicals); and

The α-ammonium ketones, iminium ketones or amidinium ketones in the form of their tetraaryl- or triarylalkylborate salts as disclosed in US 6,551,761 Bl, the disclosure of which is incorporated herein by reference.

Preferred photolatent bases are the quaternary ammonium salts, carbamates, O- acyloximes, O-carbamoyloximes, formamides, amineimides and oniurn salts. The most preferred are 4-methoxybenzyloxycarbonyl azide, 1-benzylimidazole, benzyl-4-oxo-l- piperidinecarboxylate, fluorenylmethoxycarbonyl-4-piperidone, N- (benzyloxycarbonyl)glycinamide, N-(benzyloxycarbonyl)- 1 -H-pyrazole- 1 - carboxamidine, or N-(benzyloxycarbonyl)-2-aminoacetonitrile.

Preferably, the dye is one which can be bleached by an acid or a base. However, it is also possible to use a dye which simply changes from one colour to another in the presence of an acid or a base. One preferred class of dyes which may be used in the present invention is the class of leuco dyes, which are used in their activated state if they are to be contacted with a base, or in their inactivated state, if they are to be contacted with an acid. Leuco dyes are generally synthetic organic colourless powders which, upon oxidation/acidification (collectively referred to herein as "activation") become coloured. More details of such dyes may be found in "Chemistry and Applications of Leuco Dyes", edited by R Muthyala, published in 1997 by Plenum Publishing Corporation, the disclosure of which is incorporated herein by reference.

Examples of leuco dyes which may be used in the present invention include the known leuco dyes such as triphenylmethane compounds, fluoran compounds, phenothiazine compounds, auramine compounds, spiropyran compounds, indolinophthalide and the like. These leuco dyes may be used alone or in combination. Specific examples of such leuco dyes include the following compounds:

3,3-bis(p-dimethylaminophenyl)phthalide, 3,3-bis(p-dimethylaminophenyl)-6- dimethylaminophthalide (i.e., crystal violet lactone), 3,3-bis(p-dimethylaminophenyl)- 6-diethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide, 3,3-bis(p- dibutylaminophenyl)phthalide, 3-cyclohexylamino-6-chlorofluoran, 3-dimethylamino- 5,7-dimethylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7,8-benzfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-(N-p- tolyl-N-ethylammo)-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7- anilinofluoran, 2-[N-(3-trifluoromethylphenyl)amino]-6-diethylaminofluoran, 2-[3,6- bis(diethylamino)-9-o-chloroanilino]xanthylbenzoic acid lactam, 3-diethylamino-6- methyl-7-(m-trichloromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-di-n-butylamino-7-(o-chloroaiήlino)fluoran₅ 3-N-methyl-N-n-amylamino-6-methyl-7- anilinofluoran, S-N-methyl-N-cyclohexylamino-ό-methyl-T-aiiilinofluoran, 3- diethylaniino-6-methyl-7-anilinofluoran, 3-(N,N-diethylamino)-5-methyl-7-(N,N- dibenzylamino) fluoran, 24-benzoyl leuco methylene blue, 6'-chloro-8'-methoxy- benzoindolinospiropyran, 6'-bromo-3 '-methoxybenzoindolinospiropyran, 3 (2'-hydroxy- 4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chloroplienyl)phtlialide, 3-(2'-hydroxy-4'- dimethylaminophenyl)-3-(2^l-methoxy-5'-nitrophenyl)phthalide, 3-(2'-hydroxy-4'- diethylaminoplienyl)-3-(2'- methoxy-5^l-methylphenyl)plithalide, 3-(2'-methoxy-4'- dimethylammophenyl) -3-(2'-hydroxy-C-chloro-5'-metliylplienyl)plithalide, 3-(N-ethyl- N-tetrahydrofurfuryl)amino-6-metliyl-7-anilmofluoran, 3-N-ethyl-N-(2- ethoxypropyl)amino-6-methyl-7-anilinofluoran, 3-N-methyl-N-isobutyl-6-methyl-7- anilinofluoran, 3 -morpholino-7-(N-propyl-trifluorometliylanilino)fluoran, 3 - pyrrolidino-7-m-trifluoromethylanilinofluoran, 3-diethylamino-5-chloro-7-(N-benzyl- trifluoromethylanilino)fluoran, 3-pyrrolidino-7-(di-p-chlorophenyl)methylammofluoran, 3-diethylamino-5-chloro-7-α-phenylethylammo)fluoran, 3-(N-ethyl-p-toluidino)-7-α- phenylethylamino)fluoran, 3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran, 3-diethylamino-5-methyl-7-(α-phenylethylamino)fluoran, 3-diethylamino-7- piperidinofluoran, 2-chloro-3-(N-methyltoluidino)-7-(p-n-butylanilino)fluoran, 3-(N- methyl-N-isopropylamino)-6-methyl-7-anilinofluoran, 3-di-n-butylamino-6-metliyl-7- anilinofluoran, 3 ,6-bis(dimethylamino)fluorenespiro(9,3 ')-6'-dimethylaminophthalide, 3-(N-benzyl-N-cyclohexylamino)-5,6-benzo-7-α-naphthylamino-4'-bromofluoran, 3- diethylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-methyl-7-mesidino-4',5'- benzofluoran, 3-N-methyl-N-isoproyl-6-methyl-7-anilinofluoran, 3-N-ethyl-N-isoamyl- 6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(2^l,4'-dimethylanilino)fluoran, and the like.

The more preferred leuco dyes for use in the present invention include carbazolyl blue, indolyl red, leuco crystal violet, leuco malachite green, bis (p- dimethylaminophenyl)(9-ethylcarbazol-3-yl) methane, bisarylcarbazolylmethane, 3,3- bis(l-N-octyl-2-methyl-indol-3-yl) phthalide, 3-(N,N-diethylamino)-7- (N,N- dibenzylamino)fluoran and crystal violet lactone. A single such dye, or a mixture of any two or more such dyes, may be used.

Another class of dyes which may be used are the vat dyes. Vat dyes are a class of water insoluble dyes, such as indigo and anthraquinone derivatives. These dyes in their reduced and water soluble form, reduced by a base, are colourless or different from their original colour, whilst when oxidised, which may be by an acid, they return to their original colour and their insoluble form. Examples are Vat Blue 3, Blue 5, Vat Green 1, Methylene Violet 3RAX, Light green SF Yellowish, Leuco xylene cyanole FF and Nile Blue A. Vat dyes are especially fast to light and produce brilliant colours with high lightfastness.

A further class of dyes which may be used comprises pH indicators which change colour on going from a neutral or acidic environment to a basic one, or vice versa. Examples of such compounds include: methyl violet, crystal violet, ethyl violet, ethyl orange, malachite green, methyl green, cresol red, thymol blue, bromophenol blue, bromophenol red, Congo red, methyl orange, resorcin blue, alizarin red, methyl red, litmus, bromocresol purple, chlorophenol red, bromothymol blue, phenol red, neutral red, tumaric curcumin, phenolphthalein, thymophthalein, alizarin yellow R, alizarin yellow GG, Clayton yellow, methyl yellow, tropaeolin O sodium salt, bromoxylenol blue, bromochlorophenol blue, brilliant green, metanil yellow, benzyl orange, Tashiro's indicator solution, quinaldine red, tetrabromophenol blue, α-naphthyl red hydrochloride, brilliant yellow, phenol violet, thymol violet, tropaeolin, ethyl orange sodium salt, turmeric, /?-xylenol blue, bromocresol green sulphone, bromophenol blue sodium salt, rø-cresol purple sodium salt, m-cresolsulphonephthalein sodium salt, quercetin dihydrate, o-cresolphthalein, α-naphtholphthalein, 2-nitrophenol, 4- nitrophenol, 3-nitrophenol,j!?-rosolic acid, and thymolphthalein.

A single such dye, or a mixture of any two or more such dyes, may be used.

The amounts of dye and photolatent base in the time/temperature indicator composition of the present invention may vary depending on the required properties. However, in general, we prefer to employ from 0.01 to 10.0% by weight, more preferably from 1.0 to 3.0% by weight, of the leuco dye and from 0.01 to 10.0% by weight, more preferably from 0.05 to 2.0% by weight, of the photolatent base, based on the weight of the whole composition. However, these amounts are not critical to the invention and amounts outside these ranges may be used, if desired. In particular, for a greater intensity of coloration, higher amounts may be used.

In addition to the dye and the photolatent base, the composition may contain other components to render the composition printable. Such other components may include, for example, resins, solvents and binders [such as polyvinyl butyral (PVB), nitrocellulose, polyurethanes (PU), polyesters, cellulose acetate propionate (CAP), polyacrylates, polyamides and polyvinyl alcohol].

In particular, the compositions of the present invention may contain a polymer having a sharp and predictable melting point so that it melts at a pre-determined temperature but remains solid until that temperature is reached. Such polymers are available under the trade name "Intelimer" from Landec. Intelimer polymers can abruptly change their permeability, adhesion or viscosity when heated or cooled by just a few degrees.

An advantage of the time/temperature indicator compositions of the present invention is that they may be printed using many conventional printing techniques, of which the flexographic and gravure printing techniques are preferred. The compositions of the present invention will, of course, be formulated in accordance with the specific requirements of the printing technique used, as is well known in the art.

There is no restriction on the nature of the substrate on which the composition of the present invention is printed. Examples include paper, cardboard, cellophane and various plastics films. Any plastic materials commonly used in the industry, especially for food wrapping, may be used as the plastics film. Examples of such materials include synthetic and semi-synthetic organic polymers, such as cellulose acetate, cellulose acetate butyrate (CAB), cellophane, polyvinyl chloride (PVC), polyvinyl fluoride, polyvinylidene chloride (PVDC), polyethylene, polypropylene (PP), polyamides, polyesters, polyphenylene oxide, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polymethyl methacrylate, poly(methyl pentene (TPX), polyvinyl acetal, polystyrene, acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylate (ASA), polycarbonate, polystyrene, polyether sulphone, polyether ketones, polyimides, and copolymers and/or mixtures thereof. If desired, films made from any of these polymers may be coated with coating materials well known in the art, and/or may be laminated to a film or films made of the same or different polymers. Further examples of such plastic materials may be found in standard reference texts, such as "Plastic Films", 3^rd Edition, by J. H. Briston, published by Longman Group in 1989.

The time/temperature indicator composition may be activated by exposure to UV radiation or similar energising radiation, including electron beam. The nature and amount of radiation used is similar to that used for the photoinitiation of UV-curable printing inks and is well known to those skilled in the art.

The invention is further illustrated by the following non-limiting Examples. The ketonic resin used in the Examples was a neutral, unsaponifiable, hydrogenated ketonic resin supplied by HuIs as Synthetic Resin SK.

Photoinitiator "A" used in certain of the Examples was obtained from Robinson Brothers Ltd. under the trade mark "Meerkat", and has the formula:

EXAMPLE 1

(a) Pergascript Black I-2R* (3-dibutylamino-6-methyl-7-anilinofluoran, a leuco dye, supplied by CIBA Speciality Chemicals) (0.5 g) was dissolved in a solution of ketonic resin in ethyl acetate at ratio of 40:60 (5 g), by gentle heating and stirring over a magnetic stirrer. The resulting clear and colourless solution was left to cool down and to this, a solution of 5% citric acid in isopropyl alcohol was added slowly until the colour of the solution turned dark green-black.

(b) Benzyl carbamate (0.1 g), a photolatent base generating material Supplied by Aldrich, was dissolved in a solution of ketonic resin in ethyl acetate at ratio of 40:60 (10 g), by gentle heating and stirring over a magnetic stirrer to give a clear colourless solution.

(c) Solution (a) was coated on a LENETA (N2A) chart using a No. 1 K Bar and left to dry. This produced a dark green image.

(d) Solution (b) was coated over the print (c) using a No. 1 K Bar and left to dry. The colour of the print still remained dark green. (e) Print (d) was irradiated using a UV rig running at 15m/minute. The dark green colour instantly faded to a greyish colour.

(f) Print (e) was placed under different temperature conditions of O⁰C, 27° and 50⁰C. After 2 days, only the print at 5O⁰C started to fade further.

EXAMPLE 2

(g) Pergascript Black I-2R solution was prepared according to Example l(a).

(h) Benzyl carbamate was prepared according to Example l(b).

(i) Solution (h) was coated on a LENETA (N2A) chart using a No. 1 K Bar and left to dry. This produced a clear and colourless print.

(j) Solution (g) was coated over the print (i) using a No. 1 K Bar and left to dry. The colour of the print still remained dark green.

(k) The print Q) was irradiated using a UV rig running at 15m/minute. The dark green colour instantly faded to a greyish colour.

(1) Print (k) was placed under different temperature conditions of O⁰C, 27° and 5O⁰C. After 2 days, only the print at 5O⁰C started to fade further.

EXAMPLES 3 TO 9

Using the procedure described in Example 1, coating mixes were prepared by blending together an oxidised leuco dye and a photolatent base generating material. The coating mixes were coated on LENETA (N2A) charts using a No. 1 K Bar, according to Example 1. AU prints were irradiated using a UV rig running at 15m/minute. The examples and results are illustrated in Table 1. Table 1

The leuco dyes used were:

1 Black Nl 02 (2-Anilino-6-diethylamino-3-methylfluoran, supplied by Yamamoto)

2 ODB-2 (2-Anilino-6-dibutylamino-3-methylfluoran, supplied by Yamamoto)

3 ODB-7 [6-Diethylamino-3-methyl-2-(3-toluidino) fluoride, supplied by Yamamoto]

4 Black- 2IR (3-dibutylamino-6-methyl-7-anilinofluoran, supplied by CIBA Speciality Chemicals) 5 Red I-6B (3,3-Bis(l-N-octyl-2-methyl-indol-3-yl) phthalide, supplied by CEBA Speciality Chemicals)

The photolatents used were:

A 4-Methoxybenzyloxycarbonyl azide (supplied by Aldrich)

B 1 -Benzylimidazole (supplied by Aldrich)

C Benzyl-4-oxo- 1 -piperidinecarboxylate (supplied by Aldrich)

D 1 - Fluorenylmethoxycarbonyl-4-piperidone (supplied by Aldrich)

E Benzyloxycarbonyl-Glycinamide (supplied by Aldrich)

F N-(Benzyloxycarbonyl)- 1 -H-pyrazole- 1 -carboxamidine (supplied by Aldrich)

G N-(Benzyloxycarbonyl)-2-aminoacetonitrile (supplied by Aldrich)

EXAMPLE 10

(a) A bisarylcarbazolylmethane leuco dye supplied by CIBA Speciality Chemicals (0.3 g) and 3,3-bis(l-N-octyl-2-methyl-indol-3-yl)phthalide, supplied by CIBA Speciality Chemicals, (0.5 g) were dissolved in a solution of ketonic resin in ethyl acetate at ratio of 40:60 (10 g), by gentle heating and stirring over a magnetic stirrer. The resulting clear and colourless solution was left to cool down.

(b) A solution of 2% the Meerkat photoinitiator "A" in propylene carbonate and ketonic resin in ethyl acetate at ratio of 40:60 was prepared. The photoinitiator was first dissolved in propylene carbonate, which was then added to the ethyl acetate resin solution.

(c) Solution (a) was coated on a LENETA (N2A) chart using a No. 1 K Bar and left to dry.

(d) Solution (b) was coated over the print (c) using a No. 1 K Bar and left to dry. (e) Print (d) was irradiated using a UV rig running at 50m/minute. On irradiation a red-blue colour was produced.

(f) Prints were placed under different temperature conditions of 0°C and 27°C. After 24 hours, the intensity of the colours at 27°C started to increase and after few days reached their highest points, giving a dark blue-purple colour, whereas the increase in intensity of the colour at 0° was much slower.

EXAMPLE 11

Using the procedure described in Example 10, solutions (a) and (b) were prepared, however, the coatings were carried over in the reverse order so that solution (a) was coated over the coated solution (b).

Prints were placed under different temperature conditions of 0°C and 27°C. After 24 hours, the intensity of the colours at 27⁰C started to increase and after few days reached their highest points, giving a dark blue-purple colour, whereas the increase in intensity of the colour at 0° was much slower.

EXAMPLES 12 TO 22

Using the procedures described in Examples 10 and 11, blending together leuco dyes, and using a solution of the Meerkat photoinitiator "A", coating mixes were prepared. The coating mixes were coated on LENETA (N2A) charts using a No. 1 K Bar. All prints were irradiated using a UV rig running at 50m/minute. Prints were placed under different temperature conditions of 0°C, 27 and 50°C. In general, all coatings gave darker colours when solution (b) was coated over solution (a).

The examples and results are illustrated in Table 2 and in the accompanying drawings, in which Figure 1 (two colours formulation) and Figure 2 (three colours formulation), illustrate the spectra of coatings monitored through a period of time at temperatures of 0°C, 27°C and 50°C. Table 2

The leuco dyes used were:

1 Pergascript Blue SRB (Bisarylcarbazolylmethane, supplied by CIBA Speciality Chemicals)

2 Pergascript Orange I-G (Amino-fluoran compound, supplied by CIBA Speciality Chemicals) 3 Pergascript Red I-6B (Bisindolyl phthalide compound, supplied by Ciba Speciality Chemicals)

4 Pergascript Green I-2GN (Diaminofluoran compound, supplied by CIBA Speciality Chemicals)

5 Crystal Violet Lacton (supplied by Aldrich)

6 Leuco Crystal Violet (supplied by Aldrich)

7 Leucomalacbite green (supplied by Aldrich)

8 Pergascript Black I2-R (Diaminofluoran compound, supplied by Ciba Speciality

Chemicals)

EXAMPLE 23

Preparation of l-phenyl-(l-azonia-4-azabicyclo[2,2.,21octane) N,N- dimethyldithiocarbonate

A sample of the title compound, a photolatent base-generating material, was synthesised according to the reference in J. Polymer Science; part A; Polymer Chemistry; Vol. 39, 1329-1441 (2001).

EXAMPLES 24 & 25

Using the procedure described in Example 1, coating mixes were prepared by blending together an oxidised leuco dye and the photolatent base generating material prepared as described in Example 23 or a sample of photolatent base CGI277 supplied by CIBA. The coating mixes were coated on LENETA (N2A) charts using a No. 1 K Bar, as described in Example 1. AU prints were irradiated using a UV rig running at 15m/minute. The examples and results are illustrated in Table 3. Table 3

Claims

CLAIMS:

1. A time/temperature indicator comprising a substrate supporting a first and a second layer, the first layer comprising a dye which will change colour in the presence of an acid or a base, and the second layer comprising a neutral compound which, upon ultraviolet irradiation, forms an acid or a base, one of the first and second layers overlying the other of the first and second layers.

2. A time/temperature indicator according to Claim 1, in which said first and second layers are in direct contact with each other.

3. A time/temperature indicator according to Claim 1 or Claim 2, in which the first layer is between the substrate and the second layer.

4. A time/temperature indicator according to Claim 1 or Claim 2, in which the second layer is between the substrate and the first layer.

5. A time/temperature indicator according to any one of the preceding Claims, in which the dye is a leuco dye.

6. A time/temperature indicator according to Claim 5, in which said leuco dye is in its activated form and the neutral compound is a photolatent base.

7. A time/temperature indicator according to Claim 6, in which said leuco dye is the activated form of carbazolyl blue, indolyl red, leuco crystal violet, leuco malachite green, bis (p-dimethylaminophenyl)(9-ethylcarbazol-3-yl)methane, bisarylcarbazolylmethane, 3 ,3 -bis( 1 -N-octyl-2-methyl-indol-3 -yl)phthalide, 3 -(N₅N- diethylammo)-7-(N,N-dibenzylamino)fluoran or crystal violet lactone.

8. A time/temperature indicator according to Claim 6 or Claim 7, in which the photolatent base is a quaternary ammonium salt, a carbamate, an O-acyloxime, an O- carbamoyloxime, a formamide, an amineimide or an onium salt.

9. A time/temperature indicator according to Claim 6 or Claim 7, in which the photolatent base is 4-methoxybenzyloxycarbonyl azide, 1-benzylimidazole, benzyl-4- oxo- 1 -piperidinecarboxylate, fluorenylmethoxycarbonyl-4-piperidone, N- (benzyloxycarbonyl)glycinamide, N-(benzyloxycarbonyl)- 1 -H-pyrazole- 1 - carboxamidine, or N-(benzyloxycarbonyl)-2-aminoacetonitrile.

10. A time/temperature indicator according to Claim 5, in which said leuco dye is in its reduced form and the neutral compound is a cationic photoinitiator.

11. A time/temperature indicator according to Claim 10, in which said leuco dye is carbazolyl blue, indolyl red, leuco crystal violet, leuco malachite green, bis (p- dimethylaminophenyl)(9-ethylcarbazol-3-yl)methane, bisarylcarbazolylmethane, 3,3- bis(l-N-octyl-2-methyl-indol-3-yl)phthalide, 3-(N,N-diethylamino)-7-(N,N- dibenzylamino)fluoran or crystal violet lactone.

12. A time/temperature indicator according to Claim 10 or Claim 11, in which said cationic photoinitiator is a thioxanthonium salt cationic photoinitiator.

13. A time/temperature indicator according to Claim 12, in which the cationic photoinitiator is a compound of formula:

14. A time/temperature indicator according to Claim 12, in which the cationic photoinitiator is a compound of formula:

in which n is a number and R is a terminal group.

15. A time/temperature indicator according to Claim 10 or Claim 11, in which said photoinitiator is a sulphonium salt, a thianthrenium salt, an iodonium salt or a phenacyl sulphonium salt.

16. A process for preparing a time/temperature indicator according to any one of the preceding Claims, which comprises printing onto the substrate an ink comprising the components of one of said first and second layers and then printing onto that layer an ink comprising the components of the other of said first and second layers.