GB2278133A - Pressure or heat-sensitive materials - Google Patents

Abstract

Pressure or heat sensitive material comprises as a colour-former a diphenyl carbinol of general formula (1): <IMAGE> wherein R<1> and R<2> are each independently a morpholino, pyrrolidino, piperidino, or substituted amino group, and X is a hydroxyl or alkoxyl group. In pressure sensitive materials the colour-former is placed in microcapsules on a support placed in contact with a receptor containing acid such as clay and pressure applied to form an image. In heat sensitive materials the colour-former is mixed with a developer such as bisphenol and applied as layer to support. The colour-former produces a blue image which are fast to light.

Description

RECORDING MATERIAL This invention relates to a recording material for obtaining colored images by the interaction of an electron-donating pigment and an electron-accepting developer. In particular, this invention relates to the recording material comprising as the electron-donating pigment, i.e. a coupler, a diphenyl carbinol compound which forms a blue color.

The recording materials for obtaining the colored images by the interaction of the electron-donating pigment and the electronaccepting developer, such as pressure-sensitive recording materials, heat-sensitive recording materials, photosensitive recording materials, electro-thermo recording materials and heat-sensitive transfer recording materials, are well known.

Such materials are fully described in British Patent No.

2140449, U.S. Patent Nos. 4480052, 4436920, Japanese Patent Publication (KOKOKU) No. 60-23992, Japanese Patent Application Laying-Open (KOKAI) Nos. 57-179836, 60-123556, and 60-123557, etc.

In particular, the couplers having various structures have been proposed for pressure-sensitive and heat-sensitive recording materials. Typical couplers include flucans and phthalides.

These couplers should meet the following rezirements: (1) they themselves are colorless or of a pale color; (2) they have a high color developing speed, a high color density, and a high fastness to light; (3) they themselves do not develop by aging; and (4) the colored images are excellent in resistance to chemicals and plasticizers.

However, very few couplers which form the blue colors have such requirements. Conventional couplers, even if not limited to those forming the blue colors, generally have a problem in that the colors of the images fade away during storage for a long period after the color is totally formed. Such a problem has been pointed out since the beginning when pressure-sensitive and heat-sensitive recording systems were adopted.To solve this problem, a method has been used in which the coupler having the low color developing speed but the high fastness to light (known as a secondary coupler), e.g., benzoyl leucomethylene blue, is used in combination with the above coupler (known as a primary coupler) Especially in a pressure-sensitive recording system, a vegetable oil has been used as an oil for microcapsules, and the coupler showing a high-performance when combined with the vegetable oil has been obtained.

In systems usig the secondary coupler described above, several problems have been pointed out, such as that paper is gradually colored due to the combined use of a slow color-developing coupler such as benzoyl leucomethylene blue, that the control of the color tone is difficult, that the high color density is hardly obtained, and the slow color developing secondary couplers do not form the colors when an organic compound such as phenolic compounds and polyvalent metal salicylates is used as the developer.

To solve such problems, single couplers which develop the color immediately upon contact with the developer, have the high color density, do not develop or change color by aging, produce the images with fastness to light, and are inexpensive, have been required.

When the vegetable oil is used as the oil for the pressuresensitive recording system, a suitable coupler is not currently available because vegetable oil itself contains unsaturated double bonds and comprises an ester of carboxylic acid.

While, the use of a diphenyl carbinol or ether derivatives thereof, as defined in this invention, is shown as disclosed in British Patent Nos. 1465669 and 1456208. The compounds described therein have no amino group on both ends as an auxochromic group, and their color developing properties and their fastness to light are different fre those of the pigment of this invention The inventors of this invention have found that the diphenyl carbinol compounds represented by general formula (1) are suitable as the couplers in order to solve the above problems.

This invention relates to a recording material comprising, as a coupler, a diphenyl carbinol compound represented by the following general formula (1):

wherein R1 and R2 are each independently a orphorino, pyrrolidino, piperidino, or substituted amino group, and X is a hydroxyl or alkoxy group.

Although the number of carbon atoms when X n general formula (1) is an alkoxy group is not limited, the highly pure compounds of general formula (1) containing many carbon atoms are difficult to obtain. Preferably, the number of carbon atoms in this alkoxy group is 8 or less for synthesizing the compounds of general formula (1).

In the compounds of general formula (1) of flis invention, other couplers such as fluoran derivatives and ptalide derivatives may be combined to improve the storage life of colored images or to obtain the images of various color tones.

Other near-infrared absorbing compounds may also be added to the extent that they do not degrade the properties of the compounds of general formula (1) of this invention.

For example, compounds which may be used iclude: 3,3-bis-[2-(4 dimethylaminophenyl)-2-(4-methoxyphenyl)vinxl]-4,5,6,7- tetrachlorophthalide, 3,3-bis[2-(4-pyrrolidino-phenyl)-2-(4methoxy phenyl)vinyl]-4,5,6,7-tetrachloro pthalide, 2-chloro-3methyl-6-(p-(p'-phenylamino-phenyl amino) phenyl amino)fluoran, 3,6, 6'-tris (dimethylamino) spiro[fluorene-9,3'-phthalide], 3-(4 diethylamino-2-methoxyphenyl) -3-fl- (4-chlorophenyl) -1,3- butadienyl)phthalide, 3,3-bis[4-dimethylamlnophenyl-3-yl]-4- azaphthalide, 3,3-bis[4-diethylaminophenyl-3-yl]-4-azaphthalide, 3,3-bis[4-dibutylaminophenyl-3-yl]-4-azaphthalide, 3,3-bis[4diamylaminophenyl-3-yl]-4-azaphthalide, 3,3-bis[4-dibenzylamino -phenyl-3-yl]-4-azaphthalide, and 3,3-bis[-ethylbenzylamino phenyl-3-yl]-4-azaphthalide.

In preparing a pressure-sensitive recording material using as the coupler the compound represented by general formula (1), known methods such as the methods described in U.S. Patent Nos.

2800458 and 2800457 may be used.

Developers used may include clays such as clay, bentonite, activated clay and acid clay; salicylic acid and metal salts of salicylic acid derivatives; p-phenyl phenol-formaldehyde resins, p-octyl phenol-formaldehyde resins, and metal salts thereof.

Among these, the metal salts of salicylic acid derivatives are preferable for color density and image stability. The salicylic acid derivatives include salicylic acid, 3-nethyl-5-tert-butyl salicylate, 3,5-tert-butyl salicylate, 3-cizlohexyl salicylate, 5-cyclohexyl salicylate, cresotinic acid, 5-nonyl salicylate, 5cumyl salicylate, 3-phenyl salicylate, 2,5-dihydroxy salicylate, naphthoic acid, hydroxy naphthoic acid, 3-tert-butyl-5-a-methyl benzyl salicylate, and 3,5-di(a-methylbenzç~) salicylate.

Polyvalent metals forming the salts with these salicylic acid derivatives include zinc, magnesium, calcium, aluminum, nickel, and copper, among which zinc, magnesium, and calcium are preferable, with zinc being the most preferable.

Binders used for preparing the pressure-sensitive recording materials may include polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, gum arabic, gelatin, casein, starch, polyvinyl pyrrolidone, and styrenemaleic anhydride copolymers. Organic solvents used for dissolving the couplers may include alkyl benzene, alkyl naphthalene, alkyl diphenyl, diaryl ethane, hydrogenated terphenyl, and chlorinated paraffin solvents, or mixtures thereof. For microencapsulation, coacervation, surface polymerization, and in-situ methods may be used.

Various antioxidants, ultraviolet absorbers, or surface active agents may be added as required.

For preparing the heat-sensitive recording materials, known methods such as the method described in Japanese Patent Publication vKOKOKU) No. 45-14039 may be used.

As the binders for preparing the heat-sensitive recording paper, common binders such as polyvinyl alcohol, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cel u:ose, gum arabic, gelatin, casein, starch, polyvinyl pyrrolid^ne, and styrenemaleic anhydride copolymers may be used for heat-sensitive recording paper.

The developers for this purpose include well-known phydroxybenzoic acid methyl ester, p-hydroxybenzoic acid benzyl ester, 2,2-bis(p-hydroxyphenyl)propane (bisphenol A), 3,4'isopropylidene diphenol, 2,2-bis(p-hydroxyphenyl)-4-methyl pentane, 2,2-bis(4-hydroxy-3-allylphenyl)propane, bis (4- hydroxyphenyl)acetic acid, 1, 1-bis (4-hydroxyphenyl) butyl acetate, 4,4'-cyclohexylidene diphenol, 4,4'-thio diphenol, bis(4-hydroxy-3-methyl phenyl)sulfide, bis(4-hydroxy-3-tertbutyl-6-methyl phenyl)sulfide, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 3, 4-dihydroxy-4' - methyldiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfone, 4,4'-dihydroxy3,3'-diallyldiphenyl sulfone, 4-hydroxyphthalate dimethyl, bis[2-(4-hydroxyphenylthio)ethyl]ether, 4,4'-methylene bis(oxyethylene thio)diphenol, l-benzyl-2-naphthol, 1,1'methylene di-2-naphthol, p-hydroxyphenyl salicylic amide, 1,3diphenyl thiourea, 1,3-ditolyl thiourea, 1,3-dichlorophenyl thiourea, and mixtures thereof.

Sensitivity-improving agents (sensitizers: which may be used in this invention include paraffin wax, carna-ba wax, higher fatty acid esters, higher fatty acid amides, diber.zyl oxalate, di-p methylbenzyl oxalate, di-p-chlorobenzyl oxafflate, phthalic esters, terephthalic esters, benzyl 4-benzyffloxybenzoate, naphthol benzyl ether, 1,4-dialkoxy naphthaene, 1,5-dialkoxy naphthalene, m-terphenyl, p-benzyl biphenl, dibenzyl benzene, l-hydroxy-2-naphthoic acid ester, 1-pheno..i-2-naphthoxy (1) ethane, 1,2-diphenoxyethane, 1, 2-di (3-methyl phenoxy)ethane, 1 (2-isopropyl phenoxy)-2-naphthoxy (2) ethane, bis(pmethoxyphenoxyethyl)ether, 2-hydroxy-3-naphthoic acid ester, 4,4'-dialkoxydiphenyl sulfone, benzamide, diphenyl amine, benzene sulfonamide, benzene sulfonanilide, l,4-dibenzyl oxybenzene, l,4-di(vinyl oxyethoxy)benzene, 1,3-di(vinyl oxyethoxy)benzene, diphenyl carbonate, and mixtures thereof.

In addition to the sensitizers, various antioxidants, preservatives (degradation-prevention agents), or ultraviolet absorbers may be added to improve the fastness to light of images and storage stability. Alternatively, a heat-sensitive paper may be coated with polymeric substance.

The compo,n-i,s represented by general formula (1) can be synthesizet according to methods as shown in the following.

Scheme 1

Scheme 1 comprises the first step for obtaining a diphenyl methane derivative (2) by condensing a benzene derivative with formalin in an organic solvent such as methanol, ethanol, ipropyl alcohol, ethyl cellosolve, chloroform, tetrachlorcethylene, benzene, toluene, chlorobenzene, and o dichlorobezene, at a temperature between room temperature and 1500C, preferably between 50 and 800C, in the presence of an acid catalyst such as formic acid, acetic acid, acetic anhydride, -toluene sulfonic acid, phosphorus oxychloride, sulfuric acid, hydrochloric acid, and nitric acid; the second step for obtaining a benzophenone derivative (3) by oxidizing tre resultant diphenyl methane derivative (2) using an organic ox- ant such as chloranil and tetracyano-p-benzoquinone or an inoranic oxidant such as potassium dichromate, potassium permanganate, and hydrogen peroxide, in an organic solvent such as methanol, ethanol, i-propyl alcohol, ethyl cellosolve, chloroform, zetrachloroethylene., benzene, toluene, chlorobenzene, and o-dichlorobenzene, at a temperature between room temperature and 1000C;; the third step for obtaining a diphenyl carbinol derivative (4) by reducing the resultant benzophenone derivatives (3) using a reductant such as lithium aluminum hydride, sodium borohydride and aluminum i-propoxide, in an organic solvent such as methanol, ethanol, i-propyl alcohol, ethyl cellosolve, chloroform, tetrachloroethylene, benzene, toluene, chlorobenzene, and o-dichlorobenzene, at a temperature between room temperature and 1000C; followed by the fourth step for etherifying the resultant diphenyl carbinol derivatives (4) as required.

Scheme 2

Scheme 2 comprises the first step for obtaining a diphenyl carbinol derivative (4) by condensing a benzene derivative with a benzaldehyde derivative in an organic solvent such as methanol, ethanol, i-propyl alcohol, ethyl cellosolve, chloroform, tetrachloroethylene, benzene, toluene, chlorobenzene, and o-dichlorobenzene, at a temperature between room temperature and 1500C, for several tens or minutes to several tens of hours, optionally in the presence of an acid catalyst such as formic acid, acetic acid, acetic anhydride, ptoluene sulfonic acid, phosphorus oxychloride, sulfuric acid, hydrochloric acid, and nitric acid; followed by the second step for etherifyir. the resultant diphenyl carbinol derivative (5) as required.

Scheme 3

Scheme 3 comprises the first step for obtaining a diphenyl methane derivative (2) by condensing a benzene derivative with formalin in an organic solvent such as methanol, ethanol, ipropyl alcohol, ethyl cellosolve, chloroform, tetrachloroethylene, benzene, toluene, chlorobenzene, and o- dichlorobenzene, at a temperature between room temperature and 1500C, preferably between 50 and 1000C, for several tens of minutes to several tens of hours, optionally in the presence of an acid catalyst such as formic acid, acetic acid, acetic anhydride, p-toluene sulfonic acid, phosphorous oxychloride, sulfuric acid, hydrochloric acid, and nitric acid; the second step for obtaining a diphenyl carbinol derivative (4) by oxidizing the resultant diphenyl methane derivative (2) using an oxidant such as lead dioxide and lead tetraacetate; followed by the third step for etherifying the resultant diphenyl carbinol derivative (4) as required.

In the above schemes, the diphenyl carbincffi derivative (4) may be sulfinated before etherification.

This invention is described further in the following examples which are for illustrative purposes only and which are not intended to limit the scope of the invention Svnthesis example 1 Synthesis of 4 4'-bis(N-methyl-N-p-methoxyphenyl amino)benzhvdrol of the formula (7)

In the mixture of 200 cc of toluene and 100 cc of methanol, 13.6 g of 4,4'-bis-(N-methyl-N-p-methoxyphenyl)benzophenone was dissolved at 500C. Into this solution, 6 g of sodium borohydride was added by portions over a period of about 2.5 hours. After the reduction reaction was completed, the solution was poured into ice water and a toluene layer collected.After the toluene layer was treated with activated charcoal, it was concentrated and 12,0 g of a yellowish viszous oil having the above structure was obtained.

The product dveloped a bluish green cob on TLC, and the color developed by acetic acid was Xrnax of 622 r.r..

Synthesis example 1' Synthesis of 4,4'-bis(N-methyl-N-p-methoxynyl amino)benzhvdrol-n-ethyl ether of the form (7')

The yellowish viscous oil obtained in Synthesis example 1 was purified through a column using toluene-ethyl acetate as a carrier to yield a white crystal. The melting point was 560C.

The product developed a bluish green color on TLC, and the color developed by acetic acid was wax of 622 nm.

Synthesis example 2 Synthesis of 4,4' -bis (N-ethvl-N-benzvl aminothenvi) benzhvdrol of the formula (8)

In the mixture of 150 cc of toluene and 100 cc of methanol, 13.6 g of 4,4'-di(N-ethyl-N-benzylamino)benzoph^^one was dissolved.

The solution was heated to 500C, and 15 g c- NaBH4 was added by portions at the same temperature over a period of 9 hours.

The reaction solution was poured into ice pater and organic matter extracted with 100 cc of toluene. e toluene layer separated was treated with activated charcoal, and toluene was distilled off to yield 13.6 g of bis-(N-ethyl-N-benzyl aminophenyl)benzhydrol as a yellowish viscous oil.

The product developed a bluish green color on TLC, and the color developed by acetic acid was # max of 622 nm.

Synthesis example 3 Svnthesis of 4,4'-tetrabenzvl diaminobenzhvdrol of the formula .(9)

In the mixture of 200 cc of toluene and 150 cc of methanol, 38.9 g of 4,4'-tetrabenzyl diaminobenzophenone was dissolved, and 23.1 g of sodium borohydride was slowly added by portions at 600C. The mixture was then reacted at 600C for 18 hours. After the reaction was completed, the solution was poured into water, and the organic matter was extracted with toluene and concentrated. The extract was crystallized from toluene to yield 30.7 g o a crystal. The melting point was 122.8-127.4 C.

The product developed a bluish green cob on TLC, and the color developed by acetic acid was #max of 622 nm.

Synthesis example 4 Synthesis of 4 4'-tetrabenzyl diaminobenzhvdrol-n-butvl ether of the formula (10)

11.2 g of bis-(4-dibenzyl aminophenyl)-p-toluene sulfinyl methane, 150 ml of n-butanol, and 2.47 g of KOH were mixed and reacted at 850C for 7.5 hours. After the reaction was completed, the solution was poured into water, and the organic matter was extracted with toluene. The extract was treated with activated clay and concentrated to yield 10.1 g of a light brown viscous liquid.

The product developed a bluish green color on TLC, and the color developed by acetic acid was Smax of 622 nm.

In the same procedures as in Synthetic example 1, the compounds of the following formulas (11) and (12) were obtained. Xmax values of these products were shown below the formulas.

Xmax: 600m

Xmax: 627 nm In the following examples, all parts are by weight unless otherwise indicated.

Example 1 Into 90 parts of KMC-113 (alkyl naphthalene, solvent for pressure-sensitive copying paper from Kureha Chemical Industry Co., Ltd.), 10.0 parts of the compound o synthesis example 1 was dissolved. In this solution, a solution containing 24 parts of gelatin and 24 parts of gum arabic dissolved in 400 parts of water, the pH of which was adjusted to 7, was added. The mixture was emulsified using a homogenizer, and 1000 parts of hot water added. The solution was stirred for 30 minutes at 500C, and after about 1 part of a 10% sodium hydroxide solution was added, the mixed solution was stirred or a further 30 minutes at 500C.A diluted acetic acid was then added slowly to adjust the pd at 4.5, and the solution vas stirred for about one hour at 500C, cooled to 0-50C, and stirred for a further 30 minutes. Capsules were cured by slowly adding 35 parts of a 4% glutaraldehyde aqueous solution, the pH was adjusted to 6 with an aqueous sodium hydroxide solution, and an encapsulation was completed by stirring for several hours at room temperature.

This capsule suspension was uniformly applied onto paper using a wire bar and dried to obtain coated paper (upper sheet).

This upper sheet was laid over a lower sheet on which clay as a color developer had been coated. Writing with a ball point or with keys of a typewriter, a dark bluish green image appeared immediately on the lower sheet.

This image was exposed to sunlight for a unit time, and the change in discoloration was measured using a Macbeth RD514 (Macbeth Company). The results are shown in Table 1.

Example 2 Example 1 was repeated, with the exception of using the compound in synthesis example 2 in place of the con pound of synthesis example 1, and a bluish green image was obtained.

This image was exposed to sunlight for a it time, and the change in discoloration was measured using a Macbeth RD514 (Macbeth Company). The results are shown in Table 1.

Example 3 Example 1 was repeated, with the exception of using the compound in synthesis example 3 in place c the compound of synthesis example 1, and a bluish green image was eained.

This image was exposed to sunlIght for a unit time, and the change in discoloration was measured using a Macbeth RD514 (Macbeth Company). The results are shown in Table 1.

Examole 4 Example 1 was repeated, with the exception of using the compound in synthesis example 4 in place of the compound of synthesis example 1, and a bluish green image was obtained.

This image was exposed to sunlight for a unit time, and the change in discoloration was measured using a Macbeth RD514 (Macbeth Company). The results are shown in Table 1.

Comparative example 1 Example 1 was repeated, with the exception of using crystal violet lactone in place of the compound in synthesis example 1 to produce pressure-sensitive copying paper. The fastness to light of the blue image obtained was tested in the same manner.

The results are shown in Table 1.

Tabffie 1

Initial concentration Residual rate after 5-hour exposure Compound for Example 1 0.96 94% Compound for Example 2 1.04 88% Compound for Example 3 0.86 82% Compound for Example 4 1.02 80% Compound for Comp. 0.74 70% example A similar test was performed using rapeseed oil in place of KMC113. The results are shown in Table 2.

Table 2

Initial concentration Residual rate after 5-hour exposure Compound for Example 1 0.83 84% Compound for Example 2 0.58 74% Compound for Example 3 0.66 79% Compound for Example 4 0.62 81% Compound for Comp. 0.71 42% example Example 5 oreparation of heat-sensitive recording taper 1) Preparation of coupler dispersion (S): 4,4'-tetrabenzyl diaminobenz:-ydrol 5 parts (compound of synthesis example 3) Kaolin: 15 parts 10% polyvinyl alcohol aqueous solution 100 parts Water: 85 parts The above mixture was ground using a paint shaker (Toyo Seiki kk) until the average particle size of the coupler became 2 microns.

2) Preparation of developer dispersion (B): Bisphenol A: 15 parts Zinc stearate: 10 parts 10% polyvinyl alcohol aqueous solution: 150 parts The above mixture was ground using a paint shaker until the average particle size became 3 microns.

3) Preparation and application o. heat-sensitive coating liquid: 10 parts of the dispersion (A) and 6.5 parts of the dispersion (B) were mixed and stirred to obtain a heat-sensitive coating liquid. This coating liquid was uniforl applied to paper using a wire bar so that the arcunt of time coating after drying became 8 g/m2 and dried to obtaIn heat-sensitive recording paper.

This heat-sensitive recording paper was ree from fog and virtually colorless, and develed dark bluish green colored promptly in printing using a thermal head. This color image excelled in fastness to light and moisture resistance. The coated surface also excelled In fastness to light, and no discoloration or degradation c color developing performance due to the radiation of sunlight was found.

The coupler of this invention excels in color developing performance and fastness to light when used in recording materials, and is produced easily. It may be used in combination with vegetable oil in a pressure-sensitive system.

Claims (16)

Claims:

1. A recording material comprising, as a coupler, a diphenyl carbinol compound represented by the following general formula (1):

wherein R1 and R2 are each independently a morpholino, pyrrolidino, piperidino, or substituted amino group, and X is a hydroxyl or alkoxy group.

2. A recording material as claimed in claim 1, wherein the number of carbon atoms in the alkoxy group is not more than 8.

3. A recording material as claimed in claim 1 or 2, the recording material further including fluoran derivatives and/or phthalide derivatives as couplers.

4. A recording material as claimed in claim 1, 2 or 3, the recording material further including one or more near-infrared absorbing compounds.

5. A recording material as claimed in claim 4, wherein the near-infrared absorbing compound is 3,3 bis-[2-(4-dimethylaminophenyl)-2-(4- methOxyphenyl)vinyl]-4,5,6,7-tetrachlorophthalide, 3,3bis[2-(4-pyrrolidino-phenyl-2-(4-methoxyphenyl)vinyl] 4,5,6,7-tetrachlorophthalide, 2-chloro-3-methyl-6-Cp- (p' -phenylamino-phenyl amino)phenyl amino) fluoran, 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'- phthalide], 3-(4-diethylamino-2-methoxyphenyl)-3-{1-(4- chlorophenyl)-1,3-butadienyl)phthalide, 3,3-bis[4 dimethylaminophenyl-3-yl] -4-azaphthalide, 3,3-bis[4 diethylaminophenyl-3-yl] -4-azaphthalide, 3, 3-bis[4- dibutylaminophenyl-3-yl] -4-azaphthalide, 3,3-bis[4- diamylaminophenyl-3-yl]-4-azaphthalide, 3, 3-bis[4- dibenzylaminophenyl-3-yl] -4-azaphthalide, or 3,3-bis[4- ethylbenzylamino phenyl-3-yl] -4-azaphthalide.

6. A recording material as claimed in any preceding claim, the recording material including, as a binder, one or more of: polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, gum arabic, gelatin, casein, starch, polyvinyl pyrrolidone, and styrene-maleic anhydride copolymers.

7. A recording material as claimed in any of claims 1 to 6, the recording material being sensitive to pressure and including, as a developer, one or more of: clay, bentonite, activated clay and acid clay; salicylic acid and metal salts of salicylic acid derivatives; p-phenyl phenol-formaldehyde resins, poctyl phenol-formaldehyde resins, and metal salts thereof.

8. A recording material as claimed in claim 7, wherein the salicylic acid derivative is: 3-methyl-5tert-butyl salicylate, 3,5-tert-butyl salicylate, 3cyclohexyl salicylate, 5-cyclohexyl salicylate, cresotinic acid, 5-nonyl salicylate, 5-cumyl salicylate, 3-phenyl salicylate, 2,5-dihydroxy salicylate, naphthoic acid, hydroxynaphthoic acid, 3tert-butyl-5-a-methyl benzyl salicylate, and 3,5-di(amethylbenzyl) salicylate.

9. A recording material as claimed in claim 7 or 8 wherein the metal which forms salts with the salicylic acid derivatives is zinc, magnesium, calcium, aluminium, nickel, and copper.

10. A recording material as claimed in any preceding claim, the material further including at least one of: antioxidants, ultraviolet absorbers, or surface active agents.

11. A recording material as claimed in any of claims 1 to 6, the recording material being sensitive to heat and including, as a developer, one or more of: p-hydroxybenzoic acid methyl ester, p-hydroxybenzoic acid benzyl ester, 2,2-bis(p-hydroxyphenyl)propane (bisphenol A), 3,4'-isopropylidene diphenol, 2,2-bis(p hydroxyphenyl )-4-methyl pentane, 2,2-bis(4-hydroxy-3- allylphenyl)propane, bis(4-hydroxyphenyl)acetic acid, 1,1-bis(4-hydroxyphenyl)butyl acetate, 4,4'cyclohexylidene diphenol, 4,4'-thio diphenol, bis(4hydroxy-3-methyl phenyl)sulphide, bis( 4-hydroxy-3-tert- butyl-6-methyl phenyl)sulphide, 4,4'-dihydroxydiphenyl suiphone, 4-hydroxy-4'-methyldiphenyl sulphone, 3,4dihydroxy-4'- methyldiphenyl sulphone, 4-hydroxy-4'isopropoxydiphenyl sulphone, 4,4'-dihydroxy-3,3'dimethyldiphenyl sulphone, 4,4'-dihydroxy-3,3'diallyldiphenyl sulphone, 4-hydroxyphthalate dimethyl, bis[2-(4-hydroxyphenylthio)ethyl]ether, 4,4'-methylene bis(oxyethylene thio)diphenol, l-benzyl-2-naphthol, 1,1' -methylene di-2-naphthol, p-hydroxyphenyl salicylic amide, 1,3-diphenyl thiourea, 1,3-ditolyl thiourea and 1,3-dichlorophenyl thiourea.

12. A recording material as claimed in any preceding claim, the recording material further including as a sensitizer, one or more of: paraffin wax, carnauba wax, higher fatty acid esters, higher fatty acid amides, dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-chlorobenzyl oxalate, phthalic esters, terephthalic esters, benzyl 4-benzyloxybenzoate, naphthol benzyl ether, 1,4-dialkoxy naphthalene, 1,5dialkoxy naphthalene, m-terphenyl, p-benzyl biphenyl, dibenzyl benzene, l-hydroxy-2-naphthoic acid ester, 1phenoxy-2-naphthoxy (1) ethane, 1,2-diphenoxyethane, 1 2-di ( 3-methylphenoxy )ethane, 1- ( 2-isopropylphenoxy ) -2- naphthoxy (2) ethane, bis(p-methoxyphenoxyethyl) ether, 2-hydroxy-3-naphthoic acid ester, 4,4' -dialkoxydiphenyl sulphone, benzamide, diphenyl amine, benzene sulphonamide, benzene sulphonanilide, 1,4-dibenzyl oxybenzene, 1,4-di(vinyloxyethoxy)benzene, 1,3di(vinyloxyethoxy)benzene and diphenyl carbonate.

13. A recording material as claimed in claim 12, the recording material including antioxidants, degradation-prevention agents and/or ultraviolet absorbers.

14. A recording material comprising a first sheet of paper coated with a composition including the coupler of any preceding claim and a second sheet coated with a developer.

15. A recording material, the recording material comprising a sheet of paper coated with a composition including the coupler of any preceding claim and a developer.

16. A recording material substantially as hereinbefore described.