WO2006091466A1

WO2006091466A1 - Novel time/temperature indicators

Info

Publication number: WO2006091466A1
Application number: PCT/US2006/005446
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: GB0503631D0; GB2423359A

Abstract

A time/temperature indicator comprises a combination of a leuco dye and a thioxanthonium salt cationic photoinitiator printed on a substrate. The initiator is initialised by exposure to UV radiation and can be used to monitor the shelf life of perishable materials, such as food or drugs.

Description

NOVEL TIME/TEMPERATURE INDICATORS

The present invention relates to new time/temperature indicators based on cationic photoinitiator technology.

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 Inc.'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.

DOCSNY.182726.1 S9025.0096 2

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 converts the leuco base to a thermally active product. 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.

We have now discovered that thioxanthonium cationic photoinitiators may be used in a formulation similar to that of US Patent No. 4,917,503. These photoinitiators are commonly used in UV-cured inks on food packaging and do not pose a health hazard, especially as the by-products after UV irradiation of these compounds are harmless and cause no residual odour. They are, therefore, suitable for use in association with foodstuffs and similar perishable materials.

DOCSNY.182726.1 S9025.0096 3

Thus, the present invention consists in a time/temperature indicator comprising a combination of a leuco dye and a tnioxanthoniurn salt cationic photoinitiator printed on a substrate.

The term "cationic photoinitiator" means a compound which, upon exposure to incident radiation, such as ultraviolet, forms a cation capable of initiating the polymerisation of an epoxide monomer.

The invention is further illustrated with reference to the accompanying drawing, which illustrates the spectra of coatings produced as described in Examples 2-4 monitored through a period of time at temperatures of 10⁰C and 24⁰C.

The thioxanthoniurn salt cationic photoinitiators, which are described, for example, in WO 03/072567 Al, WO 03/072568 Al, and WO 2004/055000 Al, are known as photoinitiators for use in coating compositions, but have not previously been suggested for use in association with leuco dyes for use in time/temperature indicators.

A preferred class of thioxanthonium photoinitiators which may be used in the present invention is those compounds of formula (I):

DOCSNY.182726.1 S9025.0096

in which:

R , R , R^ and R^ are independently selected from hydrogen atoms and substituents α, defined below;

or R^ represents a group of formula (II):

DOCSNY.182726.1 S9025.0096

R5 represents a direct bond, an oxygen atom or a -CH^- group;

R", R', R°, R" and R^ are independently selected from hydrogen atoms, hydroxy groups, C1-C4 alkyl groups, and phenyl groups which are unsubstituted or substituted by at least one substituent selected from the group consisting of C_j - C4 alkyl groups and C_j - C4 alkoxy groups;

or R' and R^ are joined to form a fused ring system with the benzene rings to which they are attached;

or, except where R^ represents a group of formula (II), R^ represents a group of formula (III):

DOCSNY.182726.1 S9025.0096

n is a number from 1 to 12;

RI 1 represents a hydrogen atom, a methyl group or an ethyl group, and, when n is greater than 1, the groups or atoms represented by R* * may be the same as or different from each other;

A represents a group of formula — [O(CHR¹²CHR¹³)_a]_y— , — [O(CH₂)bCO]_y— , or -[O(CH₂)_bCO]₍-_y_₁)-[O(CϊϊR¹²CHR¹³)_a]-, where:

one of RI² and R*³ represents a hydrogen atom and the other represents a hydrogen atom, a methyl group or an ethyl group;

DOCSNY.182726.1 S9025.0096 7 a is a number from 1 to 2;

b is a number from 4 to 5;

Q is a residue of a polyhydroxy compound having from 2 to 6 hydroxy groups;

x is a number greater than 0 but no greater than one less than the number of available hydroxyl groups in Q;

y is a number from 1 to 10;

p is 0 or 1 ;

said substituents α are: a C_j-C2o alkyl group, a C_j-C20 alkoxy group, a C2-C20 alkenyl group, a halogen atom, a nitrile group, a hydroxyl group, a Cg-C^o aryl group, a C7-C13 aralkyl group, a Cg-C_jQ aryloxy group, a Cy-C^ aralkyloxy group, a Cg-C^ arylalkenyl group, a C3-C3 cycloalkyl group, a carboxy group, a C2-Cy carboxyalkoxy group, a C2-C7 alkoxycarbonyl group, a Cy-C_j 3 aryloxycarbonyl group, a C2-C7 alkylcarbonyloxy group, a C_j-Cg alkanesulphonyl group, a Cg-C_jQ arenesulphonyl group, a C_j-Cg alkanoyl group or a Cy-C _{j j} arylcarbonyl group; and

X^" represents an anion;

and esters thereof.

Of these, a more preferred class of compounds for use in the present invention comprises those compounds of formula (IV):

DOCSNY.182726.1 S9025.0096

in which:

R¹, R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are as defined above; and

R*⁴ represents a hydrogen atom or a group or atom selected from substituents α, defined above.

A further more preferred class of compounds for use in the present invention comprises those compounds of formula (V):

DOCSNY.182726.1 S9025.0096

in which:

R⁶, R⁷, R⁸, R⁹, X^", A and Q are as defined above; and

z is a number greater than 1 but no greater than the number of available hydroxyl groups in Q.

A still further more preferred class of compounds for use in the present invention comprises those compounds of formula (VI):

DOCSNY.182726.1 S9025.0096

10

in which:

R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹¹, n, p, X^", A and Q are as defined above; and

Where R , R², R^ or R⁴ represents an alkyl group having from 1 to 20, preferably from 1 to 10, more preferably from 1 to 6 and most preferably from 1 to 3, carbon atoms, this may be a straight or branched chain group, and examples of such groups include the methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl, 2-methylbutyl, 1-ethylpropyl, 4-methylpentyl, 3-methylpentyl, 2-

DOCSNY.182726.1 S9025.0096 11 methylpentyl, 1-methylpentyl, 3,3-dimethylbutyl, 2,2-dimethylbutyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,3-dimethylbutyl, 2-ethylbutyl, hexyl, isohexyl, heptyl, octyl, nonyl, decyl, dodecyl, tridecyl, pentadecyl, octadecyl, nonadecyl and icosyl groups, but preferably the methyl, ethyl, propyl, isopropyl and t-butyl groups, and most preferably the ethyl or isopropyl group.

Where R^, R^, R^ or R^ represents an alkoxy group having from 1 to 20, preferably from 1 to 10, more preferably from 1 to 6 and most preferably from 1 to 3, carbon atoms, this may be a straight or branched chain group, and examples of such groups include the methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, pentyloxy, isopentyloxy, neopentyloxy, 2-methylbutoxy, 1-ethylpropoxy, 4- methylpentyloxy, 3-methylpentyloxy, 2-methylpentyloxy, 1-methylpentyloxy, 3,3- dimethylbutoxy, 2,2-dimethylbutoxy, 1,1-dimethylbutoxy, 1,2-dimethylbutoxy, 1,3- dimethylbutoxy, 2,3-dimethylbutoxy, 2-ethylbutoxy, hexyloxy, isohexyloxy, heptyloxy, 2-ethylhexyloxy, octyloxy, nonyloxy, decyloxy, dodecyloxy, tridecyloxy, pentadecyloxy, octadecyloxy, nonadecyloxy and icosyloxy groups, but preferably the methoxy, ethoxy, t-butoxy and 2-ethylhexyloxy groups, and most preferably the 2- ethylhexyloxy group.

Where R , R , R^ or R represents an alkenyl group having from 2 to 20, preferably from 2 to 10, more preferably from 2 to 6 and most preferably from 2 to 4, carbon atoms, this may be a straight or branched chain group, and examples of such groups include the vinyl, 1-propenyl, allyl, isopropenyl, methallyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, dodecenyl, tridecenyl, pentadecenyl, octadecenyl, nonadecenyl and icosenyl groups, but preferably the allyl, methallyl and butenyl groups, and most preferably the allyl group.

Where R*, R , R^ or R^ represents a halogen atom, this may be, for example, a fluorine, chlorine, bromine or iodine atom, preferably a chlorine atom.

Where R*, R , R-* or R^ represents an aryl group, this has from 6 to 10 carbon atoms in one or more aromatic carbocyclic rings (which, if there are more than one, may

DOCSNY.182726.1 S9025.0096 12 be fused together). Such a group may be substituted or unsubstituted, and, if substituted, the substituent(s) is preferably an alkyl or alkoxy group (as defined above), or an alkoxycarbonyl group (as defined below). Preferred aryl groups are the phenyl and naphthyl (1- or 2-) groups, the phenyl group being most preferred.

Where R , R , R³ or R^ represents an aryloxy group, this may be any of the aryl groups above bonded to an oxygen atom, and examples include the phenoxy and naphthyloxy groups.

Where R , R , R^ or R^ represents an aralkyl group, this is an alkyl group having from 1 to 4 carbon atoms which is substituted by one or two aryl groups as defined and exemplified above. Examples of such aralkyl groups include the benzyl, α- phenylethyl, β-phenylethyl, 3-phenylpropyl, 4-phenylbutyl, diphenylmethyl, 1- naphthylmethyl and 2-naphthylmethyl groups, of which the benzyl group is preferred.

Where R , R , R³ or R^ represents an aralkyloxy group, this may be any of the aralkyl groups above bonded to an oxygen atom, and examples include the benzyloxy, α-phenylethoxy, β-phenylethoxy, 3-phenylpropoxy, 4-phenylbutoxy, diphenylmethoxy, 1-naphthylmethoxy and 2-naphthylmethoxy groups, of which the benzyloxy group is preferred.

Where R , R², R³ or R^ represents an arylalkenyl group having from 8 to 12 carbon atoms, the aryl and alkenyl parts of this group may be as defined and exemplified above for the respective component parts. Specific examples of such groups are the styryl and cinnamyl groups.

Where R*, R², R³ or R^ represents a cycloalkyl group having from 3 to 8 carbon atoms, this may be, for example, the cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl or cyclooctyl group.

Where R¹, R², R³ or R^ represents a carboxyalkoxy group, this may be any of the alkoxy groups having from 1 to 6 carbon atoms described above which is substituted

DOCSNY.182726.1 S9025.0096 13 by a carboxy group. Preferred examples include the carboxymethoxy, 2-carboxyethoxy and 4-carboxybutoxy groups, of which the carboxymethoxy group is preferred.

Where R*, R^, R^ or R^ represents an alkoxycarbonyl group, this has from 1 to

6 carbon atoms in the alkoxy part, and thus a total of from 2 to 7 carbon atoms. It may be a straight or branched chain group, and examples of such groups include the methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, t-butoxycarbonyl, pentyloxycarbonyl, isopentyloxycarbonyl, neopentyloxycarbonyl, 2-methylbutoxycarbonyl, 1- ethylpropoxycarbonyl, 4-methylpentyloxycarbonyl, 3-methylpentyloxycarbonyl, 2- methylpentyloxycarbonyl, 1-methylpentyloxycarbonyl, 3,3-dimethylbutoxycarbonyl, 2,2-dimethylbutoxycarbonyl, 1,1-dimethylbutoxycarbonyl, 1,2- dimethylbutoxycarbonyl, 1,3-dimethylbutoxycarbonyl, 2,3-dimethylbutoxycarbonyl, 2- ethylbutoxycarbonyl, hexyloxycarbonyl and isohexyloxycarbonyl groups, but preferably the methoxycarbonyl, ethoxycarbonyl and t-butoxycarbonyl groups, and most preferably the methoxycarbonyl or ethoxycarbonyl group.

Where R , R , R^ or R^ represents an aryloxycarbonyl group having from 7 to 13 carbon atoms, the aryl part of this may be any of the aryl groups defined and exemplified above. Specific examples of such groups include the phenoxycarbonyl and naphthyloxycarbonyl groups.

Where R*, R , R^ or R^ represents an alkylcarbonyloxy group having from 2 to

7 carbon atoms, this may be any of the alkoxycarbonyl groups defined and exemplified above bonded to an oxygen atom.

Where R*, R% R^ or R^ represents an alkanesulphonyl group, this has from 1 to 6 carbon atoms and is a straight or branched chain group. Examples of such groups include the methanesulphonyl, ethanesulphonyl, propanesulphonyl, isopropanesulphonyl, butanesulphonyl, isobutanesulphonyl, t-butanesulphonyl, pentanesulphonyl and hexanesulphonyl groups, of which the methanesulphonyl group is preferred.

DOCSNY.182726.1 S9025.0096 14

Where R\ R , R^ or R^ represents an arenesulphonyl group, the aryl part may be as defined and exemplified above, and examples include the benzenesulphonyl and p_-toluenesulphonyl groups.

Where R*, R², R^ or R represents an alkanoyl group having from 1 to 6 carbon atoms, and preferably from 1 to 4 carbon atoms, this may be a straight or branched chain group, and examples include the formyl, acetyl, propionyl, butyryl, isobutyryl, pivaloyl, valeryl, isovaleryl, and hexanoyl groups, of which the acetyl group is most preferred.

Where R , R , R^ or Rr represents an arylcarbonyl group, the aryl part has from 6 to 10, more preferably 6 or 10, and most preferably 6, ring carbon atoms and is a carbocyclic group, which is unsubstituted or has from 1 to 5, preferably from 1 to 3 substituents, as defined and exemplified above. The preferred groups are the benzoyl and naphthoyl groups.

We particularly prefer those compounds of formula (I) in which R , R², R^ and R^ are individually the same or different and each represents a hydrogen atom, an alkyl group having from 1 to 10 carbon atoms, an alkoxy group having from 1 to 10 carbon atoms, a halogen atom, or a cycloalkyl group having from 3 to 8 carbon atoms More preferred compounds are those in which either two or three of R*, R , R^ and R^ represent hydrogen atoms, and still more preferably those in which one or two of R*, R², R^ and R^ represents an ethyl or isopropyl group, or those in which three or four of R , R , R^ and R^ represent hydrogen atoms. The most preferred compounds are those in which one or two of R¹, R², R-³ and R⁴ represent ethyl groups or in which one of R¹, R², R^ and R^ represents an isopropyl group and the others represent hydrogen atoms.

Where R , R , R° or R^ represents an alkyl group, this may be a straight or branched chain alkyl group having from 1 to 4 carbon atoms, and examples include the methyl, ethyl, propyl, isopropyl, butyl, isobutyl and t-butyl groups, of which the methyl group is preferred.

DOCSNY.182726.1 S9025.0096 15

Where R^, R7, R⁸ or R^ represents a phenyl group, this may be unsubstituted or it may be substituted with one or more substituents selected from the group consisting of C^ - C4 alkyl and C^ - C4 alkoxy groups. The alkyl and alkoxy substituents may be

any of the alkyl groups exemplified above in relation to R", R^, R⁸ or R^ above or any of the alkoxy groups having from 1 to 4 carbon atoms selected from the alkoxy groups exemplified in relation to R* , R , R^ or R^ above. Examples of such substituted and unsubstituted groups include the phenyl group, the o-, m- or p- tolyl group, the o-, m- or p- methoxyphenyl group, the o-, m- or p- ethoxyphenyl group, the o-, m- or p- propoxyphenyl group, the o-, m- or p- butoxyphenyl group, the o-, m- or p- 1- butoxyphenyl group, the 2,4,6-trimethylphenyl group and the 2,4,6-trimethoxyphenyl group. Of these, the unsubstituted phenyl group is preferred.

In one preferred embodiment of the present invention, β is 0, R° is a phenyl group, and R^ is a hydrogen atom. In this embodiment, we particularly prefer that R^ represents a group of formula (III) and that the group of formula -0-(CHR* ^)_n- should

be attached to the benzene ring on which R⁸ is a substituent in the para position to R , and the sulphur atom of the thioxanthonium ring system should be in the para position to R⁸.

We prefer those compounds of formula (I) in which two, three or four of R^, R^, R⁸ and R^ represent hydrogen atoms, and especially those in which all of R , R', R⁸ and R^ represent hydrogen atoms.

When R ' and R^, together with the benzene rings to which they are attached, form a fused ring system, this may be, for example, a biphenylene, fluorene or phenanthrene system, preferably fluorene.

R-> may be a direct bond (so that the two groups joined by R^ together form a biphenylyl group), an oxygen atom (so that the two groups joined by R^ together form a

DOCSNY.182726.1 S9025.0096 16 phenoxyphenyl group), or a methylene group (so that the two groups joined by R? together form a benzylphenyl group).

Where R² represents a group of formula (II) or R¹⁰ represents a group of formula (III), n is a number from 1 to 12, more preferably from 1 to 6, and most preferably 1.

We particularly prefer compounds in which R* * represents a hydrogen atom, and especially compounds in which R^ * represents a hydrogen atom and n is 1. Alternatively, we prefer compounds in which n is a number from 2 to 6 and one group

RI * represents a hydrogen atom, or a methyl or ethyl group and the other or others of RI * represent hydrogen atoms.

hi the compounds of the present invention, we prefer that A should represent a group of formula -[O(CHR^CHR^)_a]_y- where a is an integer from 1 to 2, and y is as defined above, preferably a number from 3 to 10, more preferably a group of formula -[OCH₂CH₂]_y-, -[OCH₂CH₂CH₂CH₂Jy- or -[OCH(CH₃)CH₂]_y-, where y is as defined above, or a group of formula

-[O(CH₂)_bCO]_y- or -[O(CH₂)_bCO]_(y4y[O(CHR¹³CHR¹⁴)_a]-, ^{where b is a} number from 4 to 5 and y is as defined above. Still more preferably, y is a number from 1 to 6.

In general, in the compounds of the present invention, y is preferably a number from 1 to 6. We also prefer compounds of formula (I) in which x is 2 and y is a number from 1 to 10.

It preferred in the present invention that the compounds should be of a generally polymeric nature. The polymeric nature may be provided by either the group represented by Q or the group represented by A or by both.

The polymeric polyhydroxy residue of formula Q-(A-)_χ, which forms the core of the compounds of the present invention has a major influence on the behaviour of the

DOCSNY.182726.1 S9025.0096 17 compounds. It is an advantage that it should have a polymeric nature, since the resulting compounds tend to be liquid or of low melting point, thus aiding dispersion. Compounds having a similar structure but not polymeric tend to be solid and/or insoluble. However, we prefer that the core residue, of formula Q-(A-)_χ, should not have too high a molecular weight, and prefer that the residue of formula Q-(A-)_χ should have a molecular weight no greater than 2000, preferably no greater than 1200, still more preferably no greater than 1000, and most preferably no greater than 800.

We particularly prefer that Q should be a residue of ethylene glycol, propylene glycol, butylene glycol, glycerol, trimethylolpropane, di-trimethylolpropane, pentaerythritol or di-pentaerythritol.

It will be appreciated that, when the compounds used in the present invention are analysed, the numbers a, b and y in the above formulae need not be integral, and, indeed, it is unlikely that they will be integral, since the compounds of the present invention may be mixtures of several compounds in which the numbers a, b and y differ. In accordance with the present invention, provided that the average value of each of these numbers is as defined above, this will be satisfactory. Of course, for each individual molecule of the compounds of the present invention, a, b and y will be integral, and it might be possible to separate out such individual compounds, but, in practice, mixtures of these compounds are used.

X^" represents an anion. In general, there is no particular limitation on the nature of the anion to be used. Preferably, the anion should be non-nucleophilic, or essentially non-nucleophilic.

Examples of non-nucleophilic anions are well known to those skilled in the art, and include anions of formula MZ_S ^" where M represents a phosphorus, boron, antimony, arsenic, chlorine or carbon atom, Z represents a halogen atom except where M represents a halogen atom, an oxygen atom or a sulphite group, and s is an integer dependent upon the valence of M and Z. Preferred examples of such groups include the

DOCSNY.182726.1 S9025.0096 18

PF₆ ^', SbF₆ ^", AsF₆ ^", BF₄ ^", B(C₆F₅)₄ ^", R^bB(Ph)₃ ^"(where R^b represents an alkyl group

having from 1 to 6 carbon atoms and Ph represents a phenyl group), R⁰SO₃ ^" (where R^c represents an alkyl or haloalkyl group having from 1 to 6 carbon atoms or an aryl group), ClO₄ ^" and ArSO₃ ^" (where Ar represents an aryl group) groups, of which the

PF₆ ^", SbF₆ ^", AsF₆ ^", CF₃SO₃ ^" and BF₄ ^" groups are preferred and the PF₆ ^" group is most preferred.

Where the compounds of the present invention contain a carboxy group, i.e. where R¹, R², R³ or R7 represents a carboxy or carboxyalkoxy group, the resulting compounds may form esters, and these esters also form a part of the present invention. There is no particular limitation on the nature of the ester, other than those constraints well known to those skilled in the art, and preferred examples of esters include the alkyl esters, particularly those having from 1 to 12 carbon atoms, such as those containing the C ^ -C 12 alkyl groups, and those derived from a polyalkylene glycol ether ester

(especially the C^-C₄ alkyl ethers), such as esters containing groups of formula:

-[OR¹⁵JtOR¹⁶

where R*^ represents an alkylene group having from 1 to 8 carbon atoms, R¹" represents an alkyl group having from 1 to 4 carbon atoms, and t is a number from 2 to 20, preferably from 5 to 10. More preferred are groups of formula:

-[OCH₂CHR¹⁷JtOR¹⁶

where R¹" and t are as defined above and R¹⁷ represents an alkyl group having from 1 to 4 carbon atoms.

Any combination of the preferred substituent groups and atoms listed above in respect of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R^{1 1}, R¹², etc. is also envisaged by the present invention.

DOCSNY.182726.1 S9025.0096

19

Particularly preferred compounds of the present invention are the compounds of formula (VII):

and (VIII):

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

DOCSNY.182726.1 S9025.0096

20

(Villa)

where n is a number and X^" is an anion; the number n is preferably such as to give a compound having a molecular weight of from 4500 to 5000. Particularly preferred are these compounds of formula (VII) and (VIII) in which X^" represents a PFg^" group.

Leuco dyes are generally colourless in their base form, but are coloured in the "activated" form, after contact with an acid. 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 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(jp-dimethylaminophenyl)-

DOCSNY.182726.1 S9025.0096 21

6-diethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide, 3,3-bis(p- dibutylaminophenyl)phthalide, S-cyclohexylamino-β-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-ethylamino)-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7- anilinofluoran, 2- [N-(3-trifluoromethylphenyl)amino]-6 diethylaminofluoran, 2-[3,6- bis(diethylammo)-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-chloroarrilino)fluoran, 3-N-methyl-N-n-amylamino-6-methyl-7- anilinofluoran, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluoran, 3- diethylamino-6-methyl-7-anilinofluoran, 3-(Η,N-diethylamino)-5-methyl-7-(N,N- dibenzylamino) fluoran, 24 benzoyl leuco methylene blue, 6'-chloro-8'-methoxy- benzoindolinospiropyran, 6'-bromo-3'-methoxybenzoindolmospiropyran, 3(2'-hydroxy- 4¹-dimeth.ylammoρhenyl)-3-(2'-methoxy-5'-chlorophenyl)phtlialide, 3-(2'-hydroxy-4'- dimethylaminophenyl)-3-(2'-methoxy-5'-nitrophenyl)phthalide, 3-(2'-hydroxy-4'- diethylaminophenyl)-3-(2'- methoxy-5'-methylphenyl)phthalide, 3-(2'-methoxy-4'- dimethylaminophenyl) -3-(2'-hydroxy-C-chloro-5'-methylphenyl)ρhthaπde, 3-(N-ethyl- N-tetrahydrofurfuryl)amino-6-methyl-7-anilinofluoran, 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-trifluoromethylanilino)fluoran, 3- pyrrolidino-7-m-trifluoromethylanilinofluoran, 3-diethylamino-5-chloro-7-(N-benzyl- trifluoromethylanilino)fluoran, 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluoran₅ 3-diethylamino-5-chloro-7-α-phenylethylamino)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-methyl-7- anilinofluoran, 3,6-bis(dimethylamino)fluorenespiro(9,3')-6'-dimethylaminophthalide, 3-(N-benzyl-N-cyclohexylamino)-5,6-benzo-7-α-naphthylamino-4'-broniofluoran, 3- diethylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-methyl-7-mesidmo-4',5'- benzofluoran, 3-N-methyl-N-isoproyl-6-methyl-7-anilinofluoran, 3-N-ethyl-N-isoamyl-

DOCSNY.182726.1 S9025.0096 22

6-methyl-7-ardlinofluoran_J 3-diethylaniino-6-methyl-7-(2^4'-dimethylamlino)fluoran₅ 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, bisarylcarbazolyknethane, 3,3- bis(l-N-octyl-2-methyl-indol-3-yl) phthalide, 3-(N,N-diethylamino)-7- (N₅N- dibenzylamino) fluoran and crystal violet lactone. A single such dye, or a mixture of any two or more such dyes, may be used.

The amounts of leuco dye and photoinitiator 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 photoinitiator, 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.

hi addition to the leuco dye and the photoinitiator, 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 acetyl propionate (CAP), polyacrylates, polyamides and polyvinyl alcohol].

The compositions 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 firms. Any plastic materials commonly used in the industry, especially

DOCSNY.182726.1 S9025.0096 23 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, ρoly(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.

EXAMPLE 1

(a) Bisarylcarbazolylmethane (0.1 g) and 3,3-bis(l-N-octyl-2-methyl-indol-3- yl) phthalide (0.3 g), both leuco dyes supplied by CIBA Speciality Chemicals, were dissolved in a solution of a neutral, unsaponifϊable, hydrogenated ketonic resin (supplied by HuIs as Synthetic Resin SK) 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 then a solution of photo initiator "A" in acetone at 2% by weight of the total resin solution was added.

DOCSNY.182726.1 S9025.0096

24

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

(b) The solution produced in step (a) above was coated on a glass slide and left to dry, which gave a clear colourless film. The clear film was irradiated by passing it at

50 m/minute under a 300 W/inch medium pressure mercury arc lamp, as a result of which a red-blue colour was obtained. After a period of time and at temperature of about 24°C the colour turned to dark purple.

(c) Prints were placed under different temperature conditions at either 10°C or 24°C. After 24 hours, the intensity of the colours started to increase and after few days reached their highest points.

EXAMPLES 2 TO 4

Using the procedure described in Example 1, coating mixes were prepared by blending bisarylcarbazolylmethane with one of a number of other dyes and with a photoinitiator at levels of 2% and 4%. The coating mixes were coated on low-density polyethylene film (LDPE) using a No. 4 K Bar. AU prints were irradiated using a UV rig running at different speeds of 25 and 50m/minute for varying dosage of the UV.

DOCSNY.182726.1 S9025.0096

25

The effect of increase on UV dosage for the colour change was much the same as the effect of a change in the level of photoinitiators. The results are illustrated in Table 1.

Figure 1, illustrates the spectra of coatings monitored through a period of time at temperatures of 10⁰C and 24°C.

Table 1

The leuco dyes used were :

1. Pergascript Blue SRB* (Bisarylcarbazolylmethane)

2. Pergascript Orange I-G* (Amino-fluoran compound)

3. Pergascript Red I-6B* (3,3-Bis(l-N-octyl-2-methyl-indol-3-yl) ρhthalide)

4. Pergascript Green I-2GN* (3-(N,N-diethylamino)-7- (N,N-dibenzylamino) fluoran)

all supplied by CIBA Speciality Chemicals.

DOCSNY.18272δ.l

Claims

S9025.009626CLAIMS:

1. A time/temperature indicator comprising a combination of a leuco dye and a thioxanthonium salt cationic photoinitiator printed on a substrate.

2. A time/temperature indicator according to Claim 1, in which said photoinitiator is a compound of formula (I):

in which:

R , R², R^ and R^ are independently selected from hydrogen atoms and substituents α, defined below;

or R^ represents a group of formula (II):

DOCSNY.182726.1 S9025.0096

27

R-> represents a direct bond, an oxygen atom or a -CH/j- group;

R , R', R°, R^ and R^ are independently selected from hydrogen atoms, hydroxy groups, C2-C4 alkyl groups, and phenyl groups which are unsubstituted or substituted by at least one substituent selected from the group consisting of C_j - C4 alkyl groups and C_j - C4 alkoxy groups;

or R ' and R" are joined to form a fused ring system with the benzene rings to which they are attached;

DOCSNY.182726.1 S9025.0096

28

n is a number from 1 to 12;

R* * represents a hydrogen atom, a methyl group or an ethyl group, and, when n is greater than 1, the groups or atoms represented by R* * may be the same as or different from each other;

A represents a group of formula— [O(CHR¹²CHR¹³)_a]_y— , — [O(CH₂)bCO]_y— , or

-[O(CH₂)_bCO]_(y.₁)-[O(CHR¹²CHR¹³)_a]-, where:

one of R*² and R*³ represents a hydrogen atom and the other represents a hydrogen atom, a methyl group or an ethyl group;

DOCSNY.182726.1 S9025.0096 29 a is a number from 1 to 2;

b is a number from 4 to 5;

Q is a residue of a polyhydroxy compound having from 2 to 6 hydroxy groups;

y is a number from 1 to 10;

p is 0 or 1 ;

said substituents α are: a CJ^Q alkyl group, a CJ^Q alkoxy group, a C2-C20 alkenyl group, a halogen atom, a nitrile group, a hydroxyl group, a Cg-C_jQ aryl group, a C7-C13 aralkyl group, a Cg-C_jQ aryloxy group, a CyC^ 3 aralkyloxy group, a Cg-C^ arylalkenyl group, a C3-Cg cycloalkyl group, a carboxy group, a C2-C7 carboxyalkoxy group, a C2-C7 alkoxycarbonyl group, a C7-CJ3 aryloxycarbonyl group, a C2-C7 alkylcarbonyloxy group, a C_j-Cg alkanesulphonyl group, a Cg-C_jQ arenesulphonyl group, a C_j-Cg alkanoyl group or a C7-CJ _j arylcarbonyl group; and

X^" represents an anion;

and esters thereof.

3. A time/temperature indicator according to Claim 2, in which said cationic photoinitiator is a compound of formula (IV):

DOCSNY.182726.1 S9025.0096

30

in which:

R¹, R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are as defined in Claim 2; and

R!4 represents a hydrogen atom or a group or atom selected from substituents α, defined in Claim 2.

4. A time/temperature indicator according to Claim 2, in which said cationic photoinitiator is a compound of formula (V):

DOCSNYΛ 82726.1 S9025.0096

31

in which:

R⁶, R⁷, R⁸, R⁹, X^", A and Q are as defined in Claim 2; and

5. A time/temperature indicator according to Claim 2, in which said cationic photoinitiator is a compound of formula (VI):

DOCSNY.182726.1 S9025.0096

32

in which:

R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹¹, n, p, X^", A and Q are as defined in Claim 2; and

6. A time/temperature indicator according to any one of Claims 2 to 5, A represents a group of formula -[OCH₂CH₂Iy, -[OCH₂CH₂CH₂CH₂]_y- or -[OCH(CH₃)CH₂]_y-, where y is a number from 1 to 10.

DOCSNY.182726.1 S9025.0096 33

7. A time/temperature indicator according to any one of Claims 2 to 5, in which A represents a group of formula -[O(CH2)bCO]y-, where b is a number from 4 to 5 and y is a number from 1 to 10.

8. A time/temperature indicator according to any one of Claims 2 to 5, in which A represents a group of formula -[O(CH₂)bCO](_y.₁)-[O(CHR²CHR¹)_a]-, where a is a number from 1 to 2, b is a number from 4 to 5 and y is a number from 1 to 10.

9. A time/temperature indicator according to any one of Claims 2 to 8, in which the residue Q-(A-)_X has a molecular weight no greater than 2000.

10. A time/temperature indicator according to Claim 9, in which the residue Q-(A-)_X has a molecular weight no greater than 1200.

11. A time/temperature indicator according to Claim 10, in which the residue Q-(A-)_X has a molecular weight no greater than 1000.

12. A time/temperature indicator according to Claim 11, in which the residue Q-(A-)_X has a molecular weight no greater than 800.

13. A time/temperature indicator according to any one of Claims 2 to 12, in which Q is a residue of ethylene glycol, propylene glycol, butylene glycol, glycerol, trimethylolpropane, di-trimethylolpropane, pentaerythritol or di-pentaerythritol.

14. A time/temperature indicator according to any one of Claims 2 to 13, in which X^" represents a PF₆ ^", SbFg^", AsF₆ ^", BF₄ ^", B(C₆F₅)₄ ^", R^aB(Ph)₃ ^"(where R^a represents a

C_j-C₆ alkyl group and Ph represents a phenyl group), RbSO₃ ^" (where R"³ represents a

C_j-C₆ alkyl or haloalkyl group or an aryl group), ClO₄ ^" or ArSO₃ ^" (where Ar represents an aryl group) group.

15. A time/temperature indicator according to Claim 14, in which X^" represents a PF₆ ^",

DOCSNY.182726.1 S9025.0096

34

SbF₆ ^", AsF₆ ^", CF₃SO₃ ^" or BF₄ ^" group.

16. A time/temperature indicator according to Claim 14, in which X^" represents a PF₆ ^" group.

17. A time/temperature indicator according to any one of the preceding Claims, in which the cationic photoinitiator is a compound of formula:

18. A time/temperature indicator according to any one of the preceding Claims, in which the cationic photoinitiator is a compound of formula:

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

DOCSNY.182726.1 S9025.0096

35

(Villa)

where n is a number and X^" is an anion.

19. A time/temperature indicator according to any one of the preceding Claims, 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.

20. A time/temperature indicator according to any one of the preceding Claims, in which a mixture of leuco dyes is employed.

21. A time/temperature indicator according to any one of the preceding Claims, in which the leuco dye is employed in admixture with the cationic photoinitiator.

22. A time/temperature indicator according to any one of the preceding Claims, in which the leuco dye and the cationic photoinitiator are suspended in a resin.

23. A packaged perishable product where the packaging bears a time/temperature indicator according to any one of the preceding Claims.

DOCSNY.182726.1 S9025.0096 36

24. A product according to Claim 23, in which the perishable product is a food.

25. A product according to Claim 23, in which the perishable product is a drug.

26. A method of activating a time/temperature indicator in which a product according to any one of Claims 23 to 25 is exposed to ultraviolet radiation sufficient to convert said photoinitiator to an acid form.

DOCSNY.182726.1