IE47516B1 - Record material - Google Patents

Abstract

Thermosensitive registration material consists of a support sheet carrying a heat sensitive compsn. comprising (a) a first system capable of producing a colour and (b) a second system developing a colour using a precursor (I) and a co-reactive substance (II). (I) is thermally decomposed into a chromogenic cpd. which can then react with the (II) to give a colour change. This decomposition takes placed at a temp. >the temp. at which the system (a) produces a colour. Pref. the chromogenic cpd. in system (a) contains a lactone ring and is esp. a phthalide or a fluorane, esp. 3,3-bis(1-ethyl-2-methylindol)-3-yl) phthalide, etc. The prods. are useful heat-sensitive copying materials which can be used to give two-colour copies, the colour depending on the temp. used. The system gives a more distinct colour change than prior art two colour systems.

Description

This invention relates to thermally responsive record material.

Thermally responsive record material is well known in the art and is described in many patents, for example U.S. patents 3 293 055, 3 445 261, 3 451 338, 3 539 375, and 3 674 535. Essentially it consists of a support sheet which is coated with a thermally responsive composition that embodies a colour-forming system utilizing a colour former and a co-reactant. When the composition coating is heated, with the aid of a suitable imaging tool, to normal thermographic temperatures, the co-reactant melts and/or vaporizes and reacts with the colour former to produce a coloured mark or image corresponding in configuration to the area of the coating which was heated.

In certain applications including data recording, it is often expedient to use record material that is capable of producing more than one colour; in this way, data, for -instance, can be presented in differing colours on a sheet ; according to some pre-determined colour code. With record : material of this kind, the thermally responsive composition : contains' more than one colour-forming system and* according • to the temperature to which it is heated, one or another colour can be produced.

'Japanese patent application 47/86269 discloses such record material in which the thermally responsive composition contains two colour forming systems. The colour 47S16 - 2 formers are both fluoran compounds having widely different melting points, and the same co-reactant, a phenolic compound, is used for each system. The colours are generated by melting of the co-reactant and subsequent mixing with the colour formers. The first colour is produced at a lower thermographic temperature from the fluoran compound having the lower melting point, and the second colour, being a combination of colours, is produced at a higher thermographic temperature from both fluoran compou10 nds. But, because of the dissolution of the fluoran with the higher melting point in the melt of the other, there is an interference of the generation of one colour with the development of the other, i.e. there is overlapping colour formation and no distinct but a gradual colour change between the two temperatures at which the fluoran compounds melt. This problem is moreover aggravated by the presence of any impurities in the fluoran melts.

Japanese patent application 48/53703 also discloses a two-colour record material in which two colour-forming systems are contained within the thermally responsive composition. The system operative at the lower thermographic temperature employs two colour formers and a phenolic co-reactant which, on melting or vaporisation of tne co-reactant, react together to give a colour that is in fact a combination of two colours - one produced from each of the colour formers. The system operative at the higher thermographic temperature on the other hand utilises - 3 a de-colourizing agent, such as a guanidine derivative, which acts upon one oi the two combined colours to a greater degree than the other thereby engendering a colour change. However, the effect oi such de-colourising agents is not exclusive to one oi the two combined colours and moreover may vary with temperature. As a result, there is no sharp colour change.

A iurther two-colour record material is disclosed in Japanese patent application 48/7003. This material includes two colour-forming systems contained within the thermallyresponsive composition. One system employs an acidic colour former and a basic co-reactant while the other employs a basic colour former and an acidic co-reactant having a widely different melting point from that of the basic co-reactant. At the lower thermographic temperature, the lower melting co-reactant melts and reacts with the appropriate colour former to produce a colour. At the higher thermographic temperature, the second co-reactant melts, neutralises the first co-reactant and thereby decolourises the colour obtained at the lower thermographic temperature. It then reacts with the second colour former to produce a different colour. Again however, the change from one colour to another is not as sharp as is desired.

It is apparent therefore that the above known multicolour record materials dll suffer from the same problem to a greater or lesser degree. They generate over a given thermographic temperature range a wide gradation of colours - 4 extending from the hue of the first, through all combinations of the first and the second, to the hue of the second; there is thus no sharp colour change.

It is therefore an object of the present invention to provide a thermally responsive record material capable of producing more than one colour and, in so doing, undergoing a sharp colour change.

The present invention provides a thermally responsive record material comprising a support sheet bearing a thermally responsive composition which contains a first colour forming system capable of producing a colour and a second colour forming system that employs a precursor and a co-reactant, the precursor being capable of thermal decomposition into a colour former which can then react with the co-reactant to produce a colour change, the decomposition occurring at a higher temperature than that at which the colour is produced from the first colour forming system, wherein the precursor is a benzoindolino spiropyran as described later herein.

Such record material unrestricted to the above particular precursor is the subject of our application number 46938/78 filed 1 December 1978, from which the present application is divided.

Conveniently the first colour forming system employs a colour former and a co-reactant which is the same as or different from that employed in the second colour forming system, one of the colour former and the co-reactant being capable of melting or vaporising so as to react with the other and thereby produce the colour.

The colour former of use with the first colour forming system may be one or more compounds which are generally basic and which usually have a lactone ring, for example a phthalide or fluoran compound, or mixture thereof. Particular types of •such compounds include alkyl-, phenyl-, ;indol-, pyrol-and carbazol substituted phthalides (especially those disclosed in U.S. patents 3 491 111, 3 491 112, 3 491 116 and 3 509 174) and nitro-, amino, amido-, sulphonamido-, aminobenzylidene halo-, and anilino-substi47 SI - 5 tuted fluorans (especially those disclosed in U.S. patents 3 624 107, 3 627 787, 3 641 Oil, 3 642 828 and 3 681 390).

The most preferred compounds are Crystal Violet Lactone (3,3-his(4-dimethylaminophenyl) -6-dimethylamino phthalide); e'-diethylamino-l*,2’-benzofluoran; 3,3-bis(l-ethyl-2-methyl indol-3~yl) phthalide; 6’-diethylamino-2’-anilinofluoran; ’ -diethylamino-2’-benzyl-aminofluoran; 6’—diethylamino2’-hutoxyfluoran; and 6’-diethylamino-2'-bromo-3’-methylfluoran.

· The co-reactants of use with the first colour-forming system and the second colour-forming system may be the same or different - the choice of co-reactant largely depending upon its effectiveness in reacting with the colour former of the first or second system to produce the required colour, or colour change. Generally though, the coreactant is an acidic material, such as a mono-or diphenol including those described in U.S. patent 3 451 338. Particularly preferred are 4-t-butyl phenol; 4-phenyl phenol; 4-hydroxydiphenyl oxide; a-naphthol; β-naphthol; methyl20 4-hydroxybenzoate; 4-hydroxyacetophenone; 4-t-octylcatechol; 2,2*-dihydroxydiphenyl; 2,2’-methylene bis-(4chlorophenol); 2,2’-methylene-bis-(4-methy1-6-t-butylphenol); 4,4'-i-propylidenediphenol; 4,4’—i-propylidenebis-(2-chlorophenol); 4,4'-i-propylidene4bis-(2,6-dibromo25 phenol); 4,4’-i-propylidene-bis-(2,6-dichlorophenol); 4, 4’-ί-propylidene-bis-(2-methylphenol); 4,4’-l-propylidenebis-(2,6-dimethylphenol); 4,4’-j.-propylidene-bis-(2-t-butylphenol); 4,4’-s^butylidene-bis-(2-methylphenol); 4,4’47516 - 6 cyclohexylidene phenol; 4,4’-cyclohexylidene-bis-(2~methyl phenol); 2,2’~thJo-bis~(4,6-dichlorophenol) and 4,4'-thiodiphenol.

Although not preferred, other acidic materials may 5 be used as the co-reactant in the present invention.

Examples of such other materials include phenolic novolak resins which are the product of a reaction between, for example, formaldehyde and a phenol, such as an alkylphenol, e.g. p-octylphenol, or other phenol, such as p-phenyl10 phenol. Also included are acidic mineral materials, such as colloidal silica, kaolin, bentonite, attapulgite, halloysite, and the like. Some of these resins and minerals do not melt or vaporize within the range of normal thermographic temperatures but still undergo reaction with the colour former as a result of melting or vaporising of the latter within such ranges.

Alternatively, a metallic co-reactant may be used in which the cation is preferably at least divalent, such as a cation,of-nickel, iron,, lead, mercury, copper, cobalt, manganese, zinc, aluminium, magnesium, calcium, strontium and the like. The anion to be used with the cation is only important in so far as the resulting co-reaetant has a melting point falling within the normal thermographic temperattire range, and in so far as it allows availability of the cation to the colour former. Examples of suitable anions include resinate, naphthenate, stearate, oleate, acetylacetonate, acetate, undecylenate, ricinalate and the like. 7 516 - 7 The precursor is a reaction-blocked benzoindolinospiropyran which breaks down at its decomposition temperature into the required colour former, a henzoindolinospiropyran, and a by-product derived from the blocking group. Generally, the blocking group is attached to the 4' carbon atom and is an indolenyl group in which case the precursor is a so-called dicondensed henzoindolinospiropyran compound. Examples of spiropyran colour formers which can be blocked at the 4' position by an indolenyl group include those disclosed in U.S. patents 293 055 and 3 451 338. However, the present invention further uses a novel and preferred class of spiropyran precursors which are the subject of a divisional application herefrom and are represented by the following general formula:4 7 516 Β wherein R5 and R6 are the same or different and each is a Cj-C^ alkyl group, preferably / methyl group, or a phenyl group, R* is a hydrogen or halog gen, or a Cj-C4 alkoxy or alkyl group, R is a Cj-C^alkoxy group, R9 and R10 are the same or different and each is hydrogen or halogen, preferably chlorine, and R^ is a Cj-C^alkoxy group or hydrogen.

Examples of specific compounds falling within formula (II) include 4’-(l-phenyl-3,3’,-dimethylindol10 enyl)-8'-methoxy-l-pheny1-3,3-dimethylbenzoindolinospiropyran; · '4 ’-(1”,3,3-trimethylindolenyl)-5’-chloro-8'methoxy-l,3,3-trimethylbenzoindolinospiropyran; 4’-(l, 3,3-trimethylindoleuy) -5’,6’-dichloro-8’-metboxy=4,3, 3,-trimethylbenzoindolinospiropyran; and 4*-(l,',3,315 trimethylindolenyl)-4,7,8*-trimethoxybenzoindolinospiropyran.

The most preferred reaction-blocked spiropyran precursors are given below together with their respective decomposition temperature.

Spiropyran Precursor Decomposition temp.' (°C) 1. 4,-(l,3,3-trimethylindolenyl)-6’-chloro-8’-ethoxy-1, 205-207 3.3- trimethyl-benzoindolinospiropyran 2. 4*-(l,'3”,3-trimethylindol- 204-206 enyl)-6’-chloro-8 ’-methoxy-l, 3.3- trimethyl benzoindolinospiropyran 3. 4’-(l,3,3-trimethylindol- 208-210 enyl)-8'-methoxy-l,3,3,trimethyl-benzoindolino-spiropyran 4. 4'-(l,3”,3”-trimethylindol- 200-202. enyl)-8’-ethoxy-1,3,3 trimetfiylbenzoindolino-spiropyran A spiropyran precursor which, at its decomposition temperature generates the corresponding spiropyran as the colour former, is advantageously used with a phenolic co-reactant of the type previously mentioned herein.

The preparation of the dicondensed benzoindolinospiropyrans and, in particular, those of formula (II) is described generally in Techniques of Chemistry, Vol. Ill, Chapter III, pages 254-257, published by Wiley-Interscienee, 1971. In brief, they are prepared by a condensation reaction between two molecules of the corresponding indole compound and one molecule of the corresponding salicylaldehyde.

Generally the colour former to be used in the first colour forming system should be one that produces a colour having an appearance of a relatively pure hue, such as red, blue or green, and the precursor should be one that is decomposable into a colour former capable of producing a colour change by generating a colour which, in. combin47S16 ation with the first, gives rise to a more or less neutral hue, noticeably different from the first colour.

The practical minimum amounts of the components of the colour forming systems are controlled by image darkness requirements and the practical maximum amounts are controlled by economic considerations and desired handling characteristics of the coated sheets. Such amounts including the optimum amounts to be used with this invention can readily be determined by those skilled in the present art.

The temperatures at which the colour and colour changes are produced are important only in that they should be within a reasonable range of intended operation, i.e. a thermographic temperature range, and that, in use with a thermally responsive record material, there should be an appreciable difference therebetween. A reasonable range of intended operation is from about 60 to about 2OO°C. An appreciable difference between the temperatures is from about 20 to about 30°C although smaller differences may be employed if desired.

The present invention includes within its scope the possibility of using more than one precursor so as to give rise to thermally responsive record material in which there are more than two colour forming systems. Any additional precursor should decompose at an appreciably higher melting point than the precursor already present and should give rise to a colour former capable of producing a further colour change by generating a colour which, in combination 47S16 - 11 with the first and second, is noticeably different from that produced from the combination of the first and second alone, and also from that produced from the first alone.

Of course the colour forming system employing the addition5 al precursor, and the first and second colour forming systems should not interfere with each other.

The thermally responsive composition may be coated onto the support sheet as a single layer with all the colour forming systems contained therein or as a plurality of layers with each layer containing only one colour forming system. However, a support sheet coated with a single-layer composition has advantages over a sheet coated with a multi-layer composition in that a sharper and more .distinct» thermal image can be obtained. Moreover, the use of a single-layer composition requires less materials and reduces manufacturing costs. It also results in a sheet with more desirable handling characteristics. Accordingly, a sheet bearing a single-layer thermally responsive composition is preferred. in addition to the components of the colour forming systems, the thermally responsive composition contains a thermographically acceptable binder throughout which the components are uniformly dispersed. The binder serves to retain the components upon the support sheet and also protects them against brushing and handling occasioned by storage and use· of the record material. Preferred water . t soluble binders, include polyvinyl alcohol, hydroxy ethylcellulose, methylcellulose, starch, modified starches, gelatin, and the like. In some instances, latexes may be used as binders and examples thereof Include polyacrylates, polyvinylacetates, polystyrene, and the like. The binder should be used in an amount sufficient to carry out its function but which will not interfere with reactive contact being achieved between the appropriate colour forming components. Generally, from 1,preferably 5, to about 30%, by weight of the dry composition, of binder is used, ln the one or, where appropriate, each layer.

The thermally responsive composition may also contain if desired, an additive, such as a wax, clay, filler colourant or obscurant in an amount suitable for achieving its purpose but which does not adversely affect the thermal response of the resulting record material.

The nature of the support sheet is not critical to the present invention. It may be a web, ribbon, tape, belt, film, card or the like which can be opaque, transparent or translucent and can even be coloured. It may be made from a film of, for example, cellophane or synthetic polymeric sheet but is preferably made from fibrous material, including in particular cellulose fibres. Sheet paper is very much the preferred support sheet.

In the manufacture of the record material of the present invention in which the thermally responsive coropo25 sition consists of only one layer, a dispersion in an aqueous medium is prepared of the colour forming components of each system /and a thermographically acceptable binder, and the resulting dispersion is then coated on to a support sheet and dried. 516 - 13 In the much less preferred construction wherein the thermally responsive composition consists of a plurality of layers with each layer containing a colour forming system, a dispersion of the colour forming components and binder in aqueous media are prepared for each layer, and then the dispersion for the first layer is coated on to a support sheet and dried, and the dispersion for the second layer is coated on to the previous layer and dried.

Normally, each colour forming component is first 10 individually dispersed with a binder in an aqueous medium and then ground to an average particle size of about 5 microns. Thereafter, for a single layer composition, the dispersions are all combined into one, whereas, for a multi-layer^composition, the dispersions of colour former and co-reactant are separately combined so as to give a dispersion for each layer as described above.

The dispersions preferably contain a surface active agent and, as examples of such, there are mentioned the following defoamers - sodium lauryl sulphonate, octanol, an acetylenic glycol, a silicone, and a fatty acid ester.

The coating weight for a composition consisting of a single layer is not of critical importance, and is generally from ahopt 2 to 8 grams per square metre. Also, in single layer compositions, the weight ratio of the first colour forming sysrem to the second is preferably from 1:1 to 1: , and the weight ratio of colour former or precursor to co-reactant is preferably from 1:1 to 1:12, more preferably from 1:1 to 1:6. 7 516 - 14 For compositions consisting oi a plurality of layers however, care must be exercised to utilise weights sufficient to yield distinctive colours and, at the same time, to allow adequate heat transfer from one layer to the next.

Coating weights for such layers may conveniently be from 1.5 to 8, preferably from 3 to 6 grams per square metre.

As a general rule, colour forming components in layers beneath the surface layer should be present in increased amounts so as to overcome the masking effect of the layer(s) above.

In order to understand the invention more clearly and appreciate its advantages, the following Is a detailed description of a prior art comparative example and three examples of the invention, in which all parts are parts by weight.

Prior Art Comparative Example In this comparative example and in all following examples, a dispersion of each colour forming component was first prepared by milling the component in a solution of polyvinyl alcohol (of a film forming, water soluble grade) in water containing a surface active agent until a particle size of 3 microns was achieved. The milling was accomplished in a ball mill or by using an attritor.

The proportions of the constituents of the resulting dispersions were as follows:Constituent Paxts -30 Colour forming component Polyvinyl alcohol 1-5 0-0.1 Surface active agent 0-0.1 Water 65—89 Dispersions were thus prepared wherein the colour forming component was (i) Z’-methoxy-e’—diethylamino5 fluoran; (ii) Z’-anilino-e’-diethylaminofluoran; and (iii) 4,4 *-i-propylidenediphenol.

Four parts of (iii) were mixed'with one part of (i) and the resulting combined dispersion (1) coated onto a paper sheet at a weight of about 5 grams per square metre (dry).

This coating, when dried and heated to about 100°C produced a red colour.

Four parts of (iii) were mixed with one part of (ii) and the resulting combined dispersion (2) coated onto a paper at about 5 grams per square metre (dry). This coating, when dried, produced no colour below about 110 degrees but turned green at about 120°C and above.

The two combined dispersions (1 and 2) made above were coated onto a sheet of paper in two layers, one upon the other. The two combined dispersions (1 and 2) were then themselves combined and coated onto another sheet as a single layer. The’ sheet bearing a two-layer composition turned blackish-red at about 100°C and the blackish-red colour gradually darkened to black as the temperature was raised to about 120°C. The sheet bearing the single-layer composition on the other hand turned black immediately at about 100°c. This was because the low temperature melt of one colour former served as a cosolvent for the other, and thus both colour formers produced a colour together In addition, the two combined dispersions (1 and 2) made above were coated onto a sheet of paper in two layers interfacially separated by a clear layer of insulating polymeric material. A red colour was produced at about 100°C and remained fairly pure in hue until the temperature was raised above about HO^C. Above 120°C, the combination of red and green produced a black colour change. The insulating polymeric layer in such a coated sheet of paper provide the desirable, sharp colour change characteristic of the present invention but is cumbersome and expensive to manufacture.

EXAMPLE I Dispersions were prepared as followsr15 Constituent · Parts A 2 ’-Butoxy—6’—diethylamino fluoran 17 Polyvinyl alcohol 3 Water 80 B 4’-(1”,3,3-Trimethyl-indolenyl)6 * -chloro-8 ’ -ethoxy-1,3,3-trimethyl 17 henzoindolinospiropyran Polyvinyl alcohol 3 Water 80 C 4’ 4’-i-Propylidene diphenol 17 Polyvinyl alcohol 3 Water 80 The dispersions were then mixed as follows;47516 Parts and the resulting combined dispersion used to coat sheet paper of a coating weight of about 4.5 to 6.0 grams per square metre (dry) and dried.

Both the colour former of A, and the spiropyran resulting from decomposition of the precursor of B, react with the phenolic co-reactant of C. The sheet, heated to about 110°C, produced a red colour, which remained fairly pure to about 14O°C but turned brownish-black at about 150°C.

EXAMPLE II Dispersions were Constituents prepared as follows :Parts A 4 ’ - (I’1,3, 3-Trimethyl-indolenyl)6 ’ -chloro- 8 ’ -methoxy-1,3,3, -trimethyl henzoindolinospiropyran ’ -Bromo-3 * -roethyl-6 ’ -diethy laminofluoran 3,3-Bis (l-ethyl-2-methylindol) -3-yl) phthalide Polyvinyl alcohol Water B 4,4’-i-propylidene diphenol ACRAWAX-C*Binder Water ♦Reaction product of hydrogenated castor 8L oil and ethanolamine, insoluble In boiling water, melting point of 140 to - IB 143°C, flash point oi ,285°C (open cup), specific gravity starts of 0.07 at 25°C, and available as a fine powder from Glycol Chemicals, Inc., New York, U.S.A.

The dispersions were then mixed as follows:5 parts A 45 B, 102 and the resulting combined dispersion used to coat sheet paper as in the previous example. Both the fluoran and the phthalide colour formers of dispersion A and the spiropyran resulting .from the decomposition 'of the indolenylblocked spiropyran of dispersion A react with the diphenol co-reactant of dispersion B.

The sheet, heated tc 110°C Jjf&dilced a red colour, which remained fairly pure to about 140°C but turned black above about 150°C.

Thus it can be seen from the above examples that the record material of the present invention substantially reduces overlap and interference between the colours produced at different thermographic temperatures compared with the ptjlot art record material. The colour change of the present record material is moreover much sharper since no additional colour is produced until the decomposition temperature for the precursor is reached. At that temp25 erature, a second colour is produced which combines with the first to give a distinct change in colour.

Claims (26)

1. A thermally responsive record material comprising a support sheet bearing a thermally responsive composition which contains a first colour forming system capable of 5 producing a colour and a second colour forming system that employs a precursor and a co-reactant, the precursor being capable of thermal decomposition into a colour former which can then react with the co-reactant to produce a colour change, the decomposition occurring at a higher temperature 10 than that at which the colour is produced from the first colour forming system, wherein the precursor is a reactionblocked benzoindolinospiropyran.

2. A thermally responsive record material as in claim 1 wherein the benzoindolinospiropyran is reaction blocked at 15 the 4'-position.

3. A thermally responsive record material as in claim 2 wherein the benzoindolinospiropyran is reaction blocked at the 4'-position by an indolenyl group.

4. A record material according to any preceding claim, 20 wherein the first colour forming system employs a colour former and a co-reactant which is the same as or different from that employed in the second colour forming system, one of the colour former and the co-reactant being capable of melting or vaporising .so as to react with the other and thereby produce the colour. 25

5. A record material according to claim 4, wherein the colour former of the first colour-forming system contains a lactone ring.

6. A record material according to claim 5, wherein the lactone-ring colour former is a phthalide or fluoran conpound. 20 10

7. A record material according to claim 6, wherein the lactone-ring colour former is 3,3-bis(l-ethyl-2methylindol)-3-yl)phthalide; 3,3-bis(4-dimethylaminophenyl) -6-dimethylamino phthalide; 2’-bromo-3'-methyl-6’-diethylaminofluoran; or 2*-butoxy-6'-diethylaminofluoran.

8. A record material according to claim 6, wherein the lactone-ring colour former is 6'-diethylamino-l', 2'-benzofluoran or 6ldiethylamino-2'-benzylamino fluoran.

9. A record material according to any one of claims 4 to 7, wherein the co-reactant of the first colour forming system is a phenolic compound.

10. A record material according to claim 9, wherein the phenolic compound is a mono- or di-phenol.

11. A record material according to claim 10, wherein the di-phenol is 4.4'-ί-propylidenediphenol or 4,4’-thiodiphenol.

12. A record material according to claim 3 and any of claims 4 - 11 as appendant to claim 3, wnerein the spiropyran is a spiropyran of formula (II), wherein R° and R are the same or different and each is a Cj-c^alkyl group or a phenyl group, R is hydrogen or g halogen or a Cj-C^alkoxy or Cj-C^alkyl group, H is a C^-C^ 9 10 alkoxy group, R and R are the same or different and each - 21 is hydrogen or halogen, and R^ 1b a C^-C^alkoxy group or hydrogen.

13. A record material according to claim 12., wherein the alkyl groups are methyl groups, the alkoxy groups are 5. Methoxy or ethoxy groups, and the halogens are chlorines. 14i A record material according to claim 3, wherein the spiropyran is 4’-(l ,, ,3,3-trimethylindolenyl)-6 , -chloro8’-methoxy-1,3,3-trimethylbenzoindolino spiropyran; 4’(l· 1 ,3, 3-trimethylindolenyl)-6 ’ -chloro-8’ -ethoxy-1,3,310 trimethylbenzoindolino spiropyran; 4’—(1,3”,3-trlmethy1indolenyl)-8 ’ -methoxy-1,3,3-trimethylbenzoindolinospiropyran; or 4 , -(l ,, ,3”,3-trimethylindolenyl)-8’-ethoxy-l,3,3trimethylbenzoindolinospiropyran

15.- A record material according to any preceding claim,

15 wherein the co—reactant of the second colour—forming system is a phenolic compound.

16/ A record material according to claim 15 , wherein the phenolic compound is a mono- or di-phenol.

17 A record material according to claim 16 , wherein the 20 diphenol is 4 T 4 t -i-prop.vlidenediphenol or 4,4’-thiodiphenol.

18 . -A record material according to any one- of the preceding claims, wherein the thermally responsive composition contains a third colour-forming system that employs a precursor and a co-reactant, the precursor being capable 25 of thermal decomposition into a colour former which can then react with the co-reactant to produce a second colour change, the decomposition occurring at a higher temperature than that at which decomposition of the precursor oi the second colour-forming Bystem occurs. 5

19. A record material according to any one of the preceding claims, wherein the thermally responsive composition Is coated on to the support sheet as a single layer with all the colour-forming systems contained therein.

20. A record material according to any one of claims 1 10 to 17, wherein the thermally reSDnnsive composition is coated on to the support sheet as a plurality of layers with each layer containing only one colour-forming system.

21. A record material according to any one of the preceding claims, wherein the thermally responsive composition 15 Includes a polyvinyl alcohol binder.

22. A record material according to any one of the preceding claims, wherein the support sheet is sheet paper.

23 A process of preparing a thermally responsive record material as defined in claim 19, which comprises preparing 20 a dispersion, in an aqueous medium of the colour-forming components of each colour-forming system and a therroographIcally acceptable binder, and coating the resulting dispersion on to the support sheet and drying it.

24. A process of preparing a thermally responsive record 15 material, as defined In claim 20, which comprises preparing a dispersion for each layer of the colour-forming components of the respective colour-forming system and a thermographically acceptable binder, coating the dispersion for the 4751 - 23 first layer on to the support sheet and drying it, and then coating the dispersion for the second layer on to the dried first layer and drying it.

25. A thermally responsive record material 5 substantially as described hereinbefore with reference to Example I or II,

26. A process of preparing a thermally responsive record material substantially as described hereinbefore and with reference to Example I or II.