GB2423360A - Time/Temperature Indicator, Preparation and Use - Google Patents

Abstract

A time/temperature indicator comprises an activated leuco dye or similar dye, e.g. a vat dye, which undergoes a colour change, for example is bleached, in the presence of a base, in association with a photolatent base. The base is a quaternary ammonium salt, an O-acyloxime, an O-carbamoyloxime, a formamide, an amineimide or an onium salt. The dye and base may be used as a mixture, also comprising a resin and may be printed on substrate.

Description

TIME/TEMPERATURE INDICATORS, THEIR PREPARATION AND USE The present

invention relates to a novel time/temperature indicator comprising an activated leuco dye or similar dye which undergoes a colour change in the presence of a base, for example can be bleached by a base, in association with a photolatent 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 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.

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 onitrobenzaldehydc and derivatives thereof and trihaloalcohols. However, the use of o-nitrobcnzaldehyde 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 the problems with the prior art may be overcome by the use of a dye which undergoes a colour change in the presence of a base, in association with a photolatent base.

Thus, the present invention consists in a time/temperature indicator, comprising a dye which undergoes a colour change in the presence of a base, in association with a photolatent base.

Preferably, the dye is one which can be bleached by a base. However, it is also possible to use a dye which simply changes from one colour to another in the presence of a base. One preferred class of dyes which may be used in the present invention is the class of activated leuco dyes. 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 activated forms of known leuco dyes such as triphenylmethane compounds, fluoran compounds, phenothiazine compounds, aurarnine 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 activated forms of the following compounds: 3,3-bis(p-dimethylaminophenyl)phtl-ialide, 3,3 -bis(p-dimethylaminophenyl) -6- dimethylaminophthalide (i.e., crystal violet lactone), 3,3 -bis(p- dimethylaminophenyl)6-diethylaminophthalide, 3,3 -bis(p-dimethylaminophenyl)-6chlorophthaljde, 3,3.-bis(p- dibutylaminophenyl)phthalide, 3 -cyclohexylamino-6-chlorofluoran, 3- dimethylamino- 5,7-dimethyl fluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7- methylfluoran, 3-di ethylamino-7,8-benzfluoran, 3-di ethylamino-6-methyl-7-chlorofluoran, 3-(N-p- tolyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7- anilinofluoran, 2-[N-(3-trifluoromethylpheny1)amino]6diethylaminofluoran, 2-[3,6- bis(di ethylarnino)-9-o-chloroanilino]xanthylbenzojc acid lactam, 3diethylamino-6- rnethyl-7-(m-trichlororncthylani lino)fluoran, 3-diethylarnino-7-(o- chloroanj lino)fluoran, 3-di -n-hutylamrno-7-(o-chloroanilino)fluoran, 3-N-methyl-N-n-amylamino-6methyl7 anilinofluoran, 3-N-methyl-N-cyclohexyIamino-o-methyJ7aniIjnofluor 3- diethylamino-6-methyl-7-anjlinofluoran, 3-(N,N-diethylamino)-5 -methyl-7- (N,N- dibenzylamino) fluoran, 24-benzoyl leuco methylene blue, 6'-chloro-8'- methoxy- benzoindolinospiropyran, 6'-bromo-3 -methoxybenzoindolinospn-opyran, 3 (2'-hydrox y4'-dirnethylaminophenyl)-3 -(2'-methoxy-S -chlorophenyl)phthalide, 3-(2'hydroxy-4'- dimethylaminophenyl)-3 -(2'-methoxy-5 -nitrophcnyl)phthalide, 3 -(2'- hydroxy-4'- diethylarninophenyl)-3 -(2'- methoxy-5 -methylphenyl)phthalide, 3-(2'- methoxy-4'- dimethylaminophenyl) -3-(2'-hydroxy-C-chloro-5 -methylphenyl)phthalide, 3- (N-cthylN-tetrahydrofurfiiryl)amino-6-methyl7..ani linofluoran, 3-N-ethyl-N-(2ethoxypropyl)amino-6-methyl7aniljnofluoran, 3-N-methyl-N-i sobutyl-6methyl-7- am linofluoran, 3-morpholino-7-(N-propyltrifluoromethy1ani lino)fluoran, 3- pyrrolidino-7-m-trifluoromethylanilinofluoran 3 -diethylamino-5-chloro-7- (N-benzyl- trifluoromethylanilino)fluoran, 3 -pyrrolidino-7-(di-p-chlorophenyl) methylaminof]uoran, 3-dicthylamino-5 -chloro-7-a-phcnyl ethyl arnino)fluoran, 3-(N-ethyl-p- toluidino)-7-aphenylethyl amino)fluoran, 3 -di ethylamino-7-(omethoxycarbonylphenylamjno)fluoran 3-di ethylamino-5 -methyl-7-(a-phenylethylaniino)fl uorari, 3- diethylamino-7piperidinofluoran, 2-chloro-3-(N-methyltoluidino)7(pnbuty1anu1jno)fluor, 3-(N- methyl-N-isopropylamino)-6methy17anilinofluoran 3-di-n-butylamino-6methyl-7- anilinofluoran, 3,6-bis(dimethylamino)fluorenesp iro(9,3)-6'dimethylaminophthalide, 3 -(N-benzyl-N-cyclohexylarnino)-5 3- di ethylamino-6-chloro-7-anilinofluoran, 3-di ethylamino-6-methyl-7mesidino-4',5' benzofluoran, 3 -N-methyl-N-isoproyl-6-methyl7anuIjnofluoran 3 -N-ethyl-N- isoamyl6-methyl-7-anihnofluoran, 3-diethylamino-6-methyl-7-(T,4'-djmethylaniljno) fluoran arid the like.

The more preferred leuco dyes for use in the present invention include the activated forms of carbazolyl blue, indolyl red, leuco crystal violet, leuco malachite green, bis (p-dimethylaminophenyl)(9-ethylcarbazol3yl) methane, bisarylcarbazolylmethane, 3,3-bis( I -N-octyl-2-methyl-indol-3-yl) phthalide, 3-(N,N- diethylamino)-7(N,N-dibenzylarnino) fluoran and crystal violet lactone. A single such dye, or a mixture of any two or more such dyes, maybe 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 I, 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 Iightfastness.

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. 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, aizarin red, methyl red, litmus, bromocresol purple, chlorophenol red, bromothymol blue, phenol red, neutral red, tumaric curcumin, phenolphthalein, thymophthalein, alzarin yellow R, aizarin yellow GG, clayton yellow, methyl yellow, tropaeolin 0 sodium salt, bromoxylenol blue, broniochiorophenol blue, brilliant green, metanil yellow, benzyl orange, Tashiro's indicator solution, quinaldine red, tetrabromophenol blue, a-naphthyl red hydrochloride, brilliant yellow, phenol violet, thymol violet, tropaeolin, ethyl orange sodium salt, turmeric, p-xylenol blue, bromocresol green sulfone, bromophenol blue sodium salt, m-cresol purple sodium salt, m-cresolsulfonphthalein sodium salt, quercetin dihydrate, o-crcsolphthalein, a-naphtholphthalein, 2nitrophenol, 4- 1 5 nitrophenol, 3-nitrophenol, p-rosolic acid, and thymolphthalein.

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

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, 0acyloximes, 0-carbamoyloximes, formamide, arnineimide and onium salts. Specific examples of such photolatent bases include: Quaternary ammoniurn salts, such as 1 -phenacyl-( I -azonia-4- azabicyclo[2,2,2]octanc)bromide; I,4-dimethyl- 1 -phenacyl-( 1 -azoni a-4-azahicyclohexane) bromide; and I -naphthoylmethyl- 1 -phenacyl-( 1 -azonia-4-azabicyclo [2, 2,2}octane)brornide; Carbamates, such as 1 -phenacyl-( 1 -azonia-4-azabicyclo [2,2,2}octane)-N, N- dimethyithiocarbamate; 1-methyl -1 -phenacyl-( I -azoniacyclohexane)-N,N- dirnethyldithiocarbamate; 1,4-dirnethyl- 1 -phenacyl-( I - azoniacyclohexane)-N,Ndimcthyldithiocarbamate; and I -naphthoylrnethyl-( 1 -azoni a-4azabicyclo[2,2,2]octane N,N-dinielhyldithiocarbamate; Amineimides, such as 1,1 -dimethyl- I -(2-hydroxy-3-phenoxypropyl)amine-p- nitrobenzimide, 1,1 -dimethyl- 1 -(2-hydroxy-3 -phenoxypropyl)amine-p- cyanobenzimide; and 1,1 -dirnethyl- I -(2-hydroxy-3 -phenoxypropyl)amine benzimide.

N-substituted 4-(o-ni trophenyl)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-(4,5dimethoxy-2-nitrophenyl)- I,4-dihydropyridrne 3,5-dicarboxylic acid diethyl ester; Quatemary organo-boron photoinitiators such as those disclosed in GB-A-2 307 473, the disclosure of which is incorporated herein by reference; (x-Anhinoacetophenones, such as 4-(rnethylthiobenzoyl)- 1-methyl-i - morpholinoethane (IrgacureR 907 ex Ciba Specialty Chemicals) and (4- morpholinobenzoyl)- I -benzyl- 1 -dimethylaminopropane (IrgacureR 369 ex Ciba Specialty Chemicals); and The a-ammonium ketones, iminium ketones or amidinium ketones in the form of their tetraaryl- or triarylalkylborate salts as disclosed in US 6,551,76 I B 1, the disclosure of which is incorporated herein by reference.

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.

The dye and the photolatent base may be employed in a single composition and printed to form a single layer on a substrate, or they may each be used as a separate composition and printed to forni two layers, one on top of the other, on the substrate.

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].

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 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 (AB S), acrylonitri le-styrene-acrylate (AS A), p01 ycarbonate, polystyrene, polyether suiphone, polyether ketones, polyimides, and copolyniers 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 maybe 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 Edition, by J. H. Briston, published by Longrnan 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 Huls as Synthetic Resin SK.

EXAMPLE 1

(a) Pergascript Black I2R* (3-dibuty]arnino-6-methyl-7-anjljnofluoran 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 Supp] ied 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 I 5m/minute. The dark green colour instantly faded to a greyish colour.

(f Print (e) was placed under different temperature conditions of 0 C, 27 and 50 C. After 2 days, only the print at 50 C started to fade further.

EXAMPLE 2

(g) Pergascript Black I-2R solution was prepared according to Example 1(a) .

(h) Benzyl carbarnate was prepared according to Example 1(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 (j) was irradiated using a UV rig running at 15m/minute. The dark green colour instantly faded to a greyish colour.

(I) Print (k) was placed under different temperature conditions of 0 C, 27 and 50 C. After 2 days, only the print at 50 C started to fade further.

EXAMPLES 3 TO 9

Using the procedure described in Example 1, coating mixes were prepared by blending together a 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 I. All prints were irradiated using a UV rig running at lSm/minute. The examples and results are illustrated in Table 1.

Table I

Examples Leuco Dye Photolatent Colour prior to UV Colour after irradiation irradiation 3A 1 A Green Light grey 3B 2 A Green Light grey 3C 3 A Dark Green Light green 3D 4 A Green Green!beige 3E 5 A Pink Pink/beige 4A 1 B Green Light beige 4B 2 B:reen Light beige 4C 3 B Dark Green Light green 4D 4 B Green Green/beige 4E 5 B Light pink Beige 5A 1 C Green Light beige SB 2 C Green Light beige 5C 3 C Dark Green Light green SD 4 C Green Green/beige SE 5 C Pink Pinklbeige 6A I D Green Light beige 6B 2 D Green Light beige 6C 3 D Dark Green Light green 7A 1 E Green Light beige 7B 2 E Green Light beige 7C 3 E Dark Green Light green 8A I F Green Light beige 8B 2 F Green Light beige 8C 3 F Dark Green Light green 9A I G Green Light beige 9B 2 G Green Light beige

II

9C 3 G Dark Green Light green The leuco dyes used were: Black NI 02 (2Anilino-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 Y am am oto 4 Black- 21R (3-dibutylamino-6-methyl-7-anilinofluoran, supplied by CIBA Speciality Chemicals) 5 Red l-6B (3,3-Bis(l-N-octyl-2-methyl-indol-3-yl) phthalide, supplied by CIBA Speciality Chemicals) The photolatents used were: A 4Methoxybenzyloxycarbonyl azide (supplied by Aldrich) B I -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(Benzylox ycarbonyl)- I -H-pyrazole- 1 -carboxamidine (supplied by Aldrich) G N-(Benzyloxycarbonyl)-2-aminoacetonitrile (supplied by Aldrich)

Claims (10)

1. CLAIMS: I. A time/temperature indicator, compnsing a dye which undergoes a

   colour change in the presence of a base, in association with a photolatent base.
2. 2. A time/temperature indicator according to Claim 1, in which said dye is an activated leuco dye.
3. 3. A time/temperature indicator according to Claim 2, in which the activated leuco dye is the activated form of carbazolyl blue, indolyl red, leuco crystal violet, leuco malachite green, his (p-dimethylaminophenyl) (9-ethylcarbazol3 -yl)methane, bisarylcarbazolylmethane, 3,3 -bis( I -N-octyl-2-methyl-indol-3-yJ) phthaljde, 3-(N,Ndiethylarnino)-7-(N,N-dibenzylamino)fluoran or crystal violet lactone.
4. 4. A time/temperature indicator according to Claim I, in which said dye is a vat dye.
5. 5. A time/temperature indicator according to Claim 4, in which said vat dye is Vat Blue 3, BlueS, Vat Green 1, Methylene Violet 3RAX, Light green SF Yellowish, Leuco xylene cyanole FF or Nile Blue A.
6. 6. A time/temperature indicator according to any one of the preceding Claims, in which the photolatent base is a quaternary ammonium salt, a carbamate, an 0-acyloxime, an 0-carhamoyloxime, a formamide, an amineimide or an onium salt.
7. 7. A time/temperature indicator according to any one of the preceding Claims, in which the photolatent base is 4-methoxybenzyloxycarbonyl azide, I - benzylimidazole, benzyl- 4-oxo- I -piperidinecarboxyl ate, fluorenylmethoxycarhonyl-4-piperjdone, N- (benzyloxycarbonyl)glycinamide, N-(benzyloxycarbonyl)- 1 -H-pyrazole- 1- carboxamidine, or N-(benzyloxycarbonyl)-2-aminoacetonitnle.
8. 8. A lime/temperature indicator according to any one of the preceding Claims, in which the leuco dye and the photolatent base are employed as a mixture.
9. 9. A time/temperature indicator according to Claim 4, in which the mixture also comprises a resin.
10. 10. A time/temperature indicator according to any one of the preceding Claims, in which the leuco dye and the photolatent base are printed on a substrate.