GB2166882A - Recording materials - Google Patents

Abstract

A recording material having improved properties with respect to color developability and developed color image stability comprises (i) a fluoran derivative having an arylamino group at the 2-position thereof, an aryl group, an aralkyl group, an alkyl group, an alkoxy group, a halogen atom or a hydrogen atom at the 3-position thereof and an alkylamino group having an alkyl moiety of not less than 10 carbon atoms at the 6-position thereof, and (ii) an organic or inorganic acidic compound capable of effecting color-development upon contact with the fluoran derivative.

Description

SPECIFICATION Recording materials This invention relates to recording materials having improved color developability and improved developed color image stability, and which utilises an electro-donating colorless dye and an electron-accepting compound.

Recording materials using electron-donating colorless dyes (color formers) and electron-accepting compounds (color developers) are known, as disclosed, e.g., in Japanese Patent Publication Nos. 14039/70 (corresponding to U.S. Patent 3,539,375) and 4160/68. Such recording materials should satisfy at least the following requirements: (1) the developed color density and color developing sensitivity should be sufficient; (2) fog (i.e., color development during storage before use) does not occur; and (3) the color image after color development should have sufficient fastness. However, a recording material completely satisfying these requirements has not yet been obtained.

With the recent increase in speed of recording systems, studies on requirement (1) above have, in particular, been conducted. Referring to heat-sensitive recording materials, the electronaccepting compound is sometimes selected so as to have a melting point of from about 60"C to 100 C. However, it is difficult to control the melting point of phenolic compounds that are widely employed as electron-accepting compounds, and also phenolic compounds per se are very expensive. Therefore, adjustment of melting point of the phenolic compounds is not practical.

Other methods that have been proposed to improve color density and color developing sensitivity include a method of using a combination of organic acids and phenolic compounds or a polyvalent metal salt of a compound having an alcoholic hydroxyl group as an electronaccepting substance as disclosed in Japanese Patent Publication Nos. 17748/74 and 39567/76; a method of using a copolymer of hydroxyethyl cellulose and maleic anhydride as disclosed in Japanese Patent Publication No. 29945/76 (corresponding to U.S. Patents 3,859,112 and 3,936,309); a method of using waxes as disclosed in Japanese Patent Publication No.

27599/76 and Japanese Patent Application (OPI) No. 19231/73 (the term "OPI" as herein used means an "unexamined published application"); a method of using carboxylic esters, e.g., dime thyl isophthalate, diphenyl phthalate, dimethyl terephthalate, as sensitizers; and a method of using hindered phenols as described in British Patent Publication 2,074,335A.

However, none of these conventional methods have been completely satisfactory in providing heat-sensitive recording materials with sufficient color density and color developing sensitivity.

Further, many attempts have been made to improve the stability of color images. For example, Japanese Patent Publication No. 43386/76 (corresponding to U.S. Patent 3,937,864) discloses addition of phenol derivatives, e.g., a 2,2'-methylene-bis(4-methyl-6-t-butylphenol); Japanese Patent Application (OPI) No. 17347/78 describes addition of water-insoluble modified phenol resins, e.g., rosin-modified phenol resins; and Japanese Patent Application (OPI) No. 72996/81 describes addition of terephthalic esters.

However, none of the heat-sensitive recording materials prepared by these methods has sufficient image stability.

Accordingly, an object of this invention is to provide a recording material which has satisfactory color developability, provides a sufficiently stable color image and also satisfies other required conditions.

The above-described object of this invention is accomplished by a recording material comprising (i) a fluoran derivative having an arylamino group at the 2-position thereof, an aryl group, an aralkyl group, an alkyl group, an alkoxy group, a halogen atom or a hydrogen atom at the 3position thereof and an alkylamino group having an alkyl moiety of not less than 10 carbon atoms at the 6-position thereof, and (ii) an organic or inorganic acidic compound capable of color-development upon contact with the fluoran derivative.

The present inventors have developed fluoran derivatives having an arylamino group at the 2position thereof and a wide variety of substituents at the 3-position thereof, and have found that fluoran derivatives having a long-chain alkyl group at the 3-position thereof exhibit excellent properties for the recording material. As a result of further study on various substituents at the 6-position, it has unexpectedly been found that fluoran derivatives having an amino group substituted with an alkyl group of not less than 10 carbon atoms at the 6-position have markedly improved properties with respect to (1) developed color image stability and (2) resistance to polar solvents of developed color image, as compared to the corresponding fluoran derivatives having a dioctylamino group at the 6-position thereof.

Preferred fluoran derivatives according to the present invention are those represented by the following general formula (I):

wherein R1 represents an alkyl group having not less than 10 carbon atoms, preferably from 10 to 18 carbon atoms; R2 represents a lower alkyl group, preferably having not more than 10 carbon atoms; R3 represents an aryl group, preferably having from 6 to 9 carbon atoms, an aralkyl group, preferably having from 7 to 12 carbon atoms, an alkyl group, preferably having from 1 to 6 carbon atoms, an alkoxy group, preferably having from 1 to 4 carbon atoms, a halogen atom, or a hydrogen atom; Ar represents an aryl group; and R4 represents a hydrogen atom, a chlorine atom or an alkyl group preferably having from 1 to 4 carbon atoms, which may be substituted, e.g., with a halogen atom or an alkoxy group.

The alkyl group of R1 is more preferably a straight-chain alkyl group having an even number of carbon atoms. Particularly preferred examples include a tetradecyl group, a hexadecyl group, an octadecyl group, a decyl group and a dodecyl group.

R2 more preferably represents a lower alkyl group having a methylene group at the a-position thereof, and most preferably one having from 1 to 8 carbon atoms, e.g., an octyl group, a 2methylheptyl group, a hexyl group, an isoamyl group, an amyl group, a butyl group, an isobutyl group, a propyl group, an ethyl group or a methyl group.

R3 more preferably represents an aryl group having 6 or 7 carbon atoms (e.g., a phenyl group, a chlorophenyl group, or a tolyl group), an aralkyl group having from 7 to 10 carbon atoms (e.g., a benzyl group, an a-methylbenzyl group, a phenethyl group or a cinnamyl group), a methyl group, an ethyl group, a propyl group, a butyl group, a methoxy group, a phenoxy group, a thiomethoxy group, a thiophenoxy group or a halogen atom. Of these, a halogen atom or an alkyl group are particularly preferred for R3.

Ar may represent an unsubstituted or substituted aromatic ring, such as a phenyl group, a chlorophenyl group, a tolyl group, a butylphenyl group, a dibutylaminophenyl group, or an anaphthyl group. The fluoran derivatives having a phenyl, chlorophenyl or tolyl group as Ar have a pure black color upon contact with phenol derivatives, although synthesis of fluoran derivatives having a pure black color has generally been considered very difficult.

The fluoran derivatives of the present invention can be advantageously used in pressuresensitive recording materials, in that the amount of aromatic diarylalkane used for encapsulation can be significantly reduced and an inexpensive and odorless paraffin oil can be used therefor.

When the fluoran derivatives of the present invention are used in heat-sensitive recording materials, those having a melting point of from about 80"C to about 180"C are preferably used, and they can be appropriately selected in conformity with phenol derivatives and heat-fusible agents to be used.

The heat-sensitive recording materials containing the above-described fluoran derivatives exhibit sufficient color density and color developing sensitivity, and the dyes developed therefrom are very stable without undergoing substantially any decoloration or discoloration even when exposed to light, heat or humidity for a long time as compared with those obtained from conventional color formers. Therefore, the heat-sensitive recording materials of the present invention are particularly advantageous from the standpoint of retention of recorded information for an extended period of time. In addition, the fluoran derivatives themselves exhibit nearly ideal performances as color formers in that they have excellent stability and are free from denaturation or coloration during storage for a long time.

Typical examples of fluoran derivatives according to the present invention are listed below.

(1) 2-Anilino-3-methyl-6-N-hexadecyl-N-methylaminofluoran (2) 2-Anilino-3-methyl-6-N-octadecyl-N-methylaminofluoran (3) 2-p-Chloroanilino-3-chloro-6-N-dodecyl-N-isoamylaminofluoran (4) 2-Anilino-3-pentadecyl-6-N-decyl-N-ethylaminofluornn (5) 2-Anilino-3-chloro-6-N-octadecyl-N-ethylaminofluoran (6) 2-p-Chloroanilino-3-ethyl-6-N-hexadecyl-N-methylaminofluoran (7) 2-Anilino-3-n-amyl-6-N-butyl-N-octadecylaminofluoran (8) 2-Anilino-3-phenyl-6-N-decyl-N-isoamylaminofluoran (9) 2-Toluidino-3-methyl-6-N-hexadecyl-N-butylaminofluoran (10) 2-o-Toluidino-3-methyl-6-N-ethyl-N-octadecylaminofluoran (11) 2-o-Toluidino-3-methyl-6-N-ethyl-N-dodecylamino-4'-t-butylfluoran The fluoran derivatives of the present invention can provide a pure black color upon contact with an organic or inorganic acid such as acid clay, activated clay, phenol resins, and zinc salts of alkyl- or aralkyl-substituted salicyclic acid. Further, the phenol derivatives which are preferably used in the heat-sensitive recording materials are compounds having at least one phenolic hydroxyl group, and are more preferably those compounds wherein either of the 2- and 6positions is unsubstituted, such as bis(4-hydroxyphenyl)alkane derivatives, bis(3-chloro-4-hydroxyphenyl)alkane derivatives, bis(4-hydroxyphenyl)sulfone, (4-hydroxyphenyl)-(4'-alkoxyphenyl)sulfone derivatives, p-hydroxybenzoic ester derivatives, resorcylic ester derivatives, orsellinic ester derivatives, gallic ester derivatives, salicylic acid or its alkyl- or aralkyl-substituted derivatives or zinc salts thereof.

Typical examples of the above-described phenol derivatives are shown below: (1) 2,2-Bis(4-hydroxyphenyl)propane (2) 1,1 -Bis(4-hydroxyphenyl)hexane (3) 1,1 -Bis(3-chloro-4-hydroxyphenyl)cyclohexane (4) 1,1 -Bis(3-chloro-4-hydroxyphenyl)-2-ethylbutane (5) Benzyl p-hydroxybenzoate (6) Zinc 3,5-di-a-methylbenzylsalicylate (7) 4,4'-Dihydroxy-3'-isopropyldiphenylsulfone (8) 1,1 -Bis(4-hydroxyphenyl)cyclohexane (9) Cinnamyl resorcylate (10) ss-Phenethyl orsellinate (11) Cinnamyl orsellinate (12) ss-o-Chlorophenoxy orsellinate (13) ss-Phenoxyethyl resorcylate (14) o-Methylbenzyl resorcylate (15) 2,4-Dimethylphenoxyethyl resorcylate (16) ss,ss'-Bis-4-hydroxyphenyl thioethyl ether (17) ss-Phenoxyethyl resorcylate (18) ss,ss'-Bis-4-hydroxyphenolthioethyWoxymethane Of these phenol derivatives, alkylenebisphenols, cycloalkylenebisphenols and phenol compounds having an electron-attractive group are particularly useful.

In preparation of the heat-sensitive recording materials, the fluoran derivatives of the present invention are preferably used in combination with a heat-fusible agent having a melting point of from 70"C to 140"C, whereby color developing speed is markedly increased, making it suitable, e.g., for a high-speed facsimile system. The heat-fusible agents that can be used in the present invention are selected from derivatives of phenol compounds, aniline compounds, amine compounds, etc., preferably compounds selected from ethers, esters, amides, and having a melting point of from about 70"C to about 1300C, and preferably from 90"C to 1200C.

Specific examples of suitable heat-fusible agents include stearic acid amide, stearic acid anilide, ethylenebisstearamide, benzoin, a-naphthol benzoate, ss-naphthol p-methylbenzoate, p-t-butylphe nol phenoxyacetate, p-phenylphenol p-chlorophenoxyacetate, 4,4'-cyclohexylidenediphenol diacetate, 4,4'-isopropylidenediphenol dimethyl ether, ss-phenylethyl-p-phenylphenol ether, phenyl hydroxynaphthoate, p-methoxycarbonylbenzoic acid ethylamide, stearylurea phenyl ester, fl-benzy- loxynaphthalene, ditolyl carbonate.

Typical processes for synthesizing the fluoran derivatives (e.g., 3-methyl fluoran derivatives) according to the present invention include: (1) a process comprising reacting a 2-hydroxy-4-substituted amino-2'-carboxybenzophenone and a 2-methyl-4-alkoxy-diarylamine in the presence of an acid catalyst; and (2) a process comprising reacting a 2-amino-3-methyl-6-substituted amino-fluoran and bromobenzene or iodobenzene in the presence of a copper catalyst, etc.

Acid catalysts which can be used in the process (1) above include Lewis acids, e.g., zinc chloride, aluminium chloride, magnesium chloride, calcium chloride, and organic or inorganic acids, e.g., sulfuric acid, fuming sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, polyphosphoric acid.

Catalysts which can be used in the process (2) above, which comprises reacting 2-aminofluoran derivatives and an arylation agent, include copper compounds, e.g., copper powder, copper oxide, cuprous iodide, cupric iodide, nickel compounds, cobalt compounds, with copper powder being preferred. It is preferable that these catalysts be used in combination with iodine, a carbonic acid salt, magnesia or potassium iodide.

The 2-hydroxy-4-substituted amino-2'-carboxybenzophenone which is used in the process (1) set forth above can be synthesized by the reaction

wherein R4 is as defined above and R5 represents a hydrocarbon group having not less than 10 carbon atoms (preferably from 10 to 18 carbon atoms) and preferably an alkyl group, which may be substituted with one or more of a halogen atom, an alkoxy group, a hydroxy group, an acryloxy group, and an aryl group, and R6 represents a hydrocarbon group and preferably an alkyl group having not more than 10 carbon atoms. R5 is preferably a straight-chain alkyl group having an even number of carbon atoms, such as a dodecyl group, a decyl group, a hexadecyl group, a tetradecyl group or an octadecyl group.R6 is preferably an alkyl group having a methylene group at the a-position thereof and more preferably a methyl group, an ethyl group, a propyl group, a butyl group, an isoamyl group, a hexyl group, a 2-ethylhexyl group, an octyl group, an isobutyl group or a diisobutyl group.

In the reaction, the m-aminophenyl derivative is preferably added in an excess amount with respect to the phthalic anhydride, so as to prevent production of dye as a by-product, and the molar ratio of phthalic anhydride to m-aminophenol derivative is preferably from 1.06/1 to 1.5/1, and more preferably from 1.1/1 to 1.2/1. Further, inert solvents such as halogenated solvents or aromatic solvents (e.g., toluene, dichlorobenzene, trichloroethylene, tetrachloro-ethane, ligroin, nitrobenzene), inert gas (e.g., nitrogen gas, argon gas), and inorganic catalyst (zinc chloride, magnecium chloride) may be used for the reaction.The reaction temperature is preferably from 80"C to 145"C. When it is higher than 1600C, a rhodamine dye is produced as a byproduct which is difficult to separate from the desired product, even though the reaction time is minimized.

Preferred examples of the 2-hydroxy-4-substituted amino-2'-carboxybenzophenone are listed below.

(1) 2-(2'-hydroxy-4'-M-methyl-N-octadecylamino benzoyl)-benxoic acid (m.p. 94-95"C) (2) 2-(2'-hydroxy-4'-N-ethyl-N-octadecylaminobenzoyl)-benzoic acid (m.p. 94-96"C) (3) 2-(2'-hydroxy-4'-N-ethyl-N-dodecylaminobenzoyl)-benzoic acid (m.p. 186-193 C) (4) 2-(2'-hydroxy-4'-N-ethyl-N-hexadecylaminobenzoyl)-benzoic acid (m.p. 97-98"C) (5) 2-(2'-hydroxy-4'-N-butyl-N-dodecylaminobenzoyl)-benzoic acid (semisolid) (6) 2-(2'-hydroxy-4'-N-octyl-N-dodecylaminobenzoyl)-benzoic acid (viscous liquid) (7) 2-(2'-hydroxy-4'-N-methyl-N-hexadecylaminobenzoyl)-benzoic acid (viscous liquid) (8) 2-(2'-hydroxy-4'-N-methyl-N-tetradecylaminobenzoyl)-benzoic acid (m.p. 46-51"C) A Synthesis Example for a fluoran derivative according to the present invention is set out below. Unless otherwise indicated herein, all parts, percents, ratios, and the like are by weight.

SYNTHESIS EXAMPLE 7 Synthesis of 2-Anilino-3-methyl-6-N-octadecyl-N-methylaminofluoran (1) Preparation of 3-N-octadecyl-N-methylaminophenol A 200 ml three-necked flask equipped with a stirrer and a reflux condenser was charged with 44 g of N-octadecyl-N-methylamine, 19 g of resorcinol, 1.2 g of anthranilic acid and 50 ml of xylene, followed by vigorous stirring and heating. After the reaction was completed, xylene was evaporated from the resulting solution and the remaining material was poured into water in a conventional manner to thereby separate a reaction product having a melting point of from 40"C to 43"C.

(2) Preparation of 2-oxy-4-N-octadecyl-N-methylamino-benzoylbenzoic acid 0.15 mole of the aminophenol derivative obtained in (1) and 0.18 mole of phthalic anhydride were weighed and charged into a three-necked flask equipped with a stirrer and a reflux condenser. Then, 10 ml of toluene was added thereto, and the reaction was performed under reflux condition by heating while stirring. After the reaction was completed, 150 ml of toluene was further added and the resulting mixture was washed three times with 300 ml of warm water, and then solvent was removed. The reaction product was purified by column chromatography using silica gel as a carrier and chloroform as an eluent.

(3) Synthesis of the fluoran. derivative 0.1 mole of the benzoic acid derivative obtained in (2) was weighed and charged into a threenecked flask equipped with a stirrer and a reflux condenser, and 100 ml of a sulfuric acid-fuming sulfuric acid mixture was slowly added to dissolve the benzoic acid derivative. After the addition of 0.1 mole of 4-methoxy-2-methyl-diphenylamine, the reaction system was allowed to stand at from 20"C to 60"C for 24 hours. The reaction mixture was then poured into an aqueous sodium hydroxide solution to adjust the pH to 9, whereby a reaction product containing small amounts of colored compounds and phthalides are separated. The product was subjected to the purification as in (2) above.The resulting crystals showed a deep black-purple color in thin layer chromatography, but turned black upon contact with benzyl p-hydroxybenzoate.

SYNTHESIS EXAMPLE 2 Synthesis of 2-Anilino-3-methyl-6-N-octadecyl-N-ethylaminofluoran (1) Preparation of 2-hydroxy-4-N-octadecyl-N-ethylaminobenzoylbenzoic acid The same procedure as in Synthesis Example 1-(2) was repeated, except that 3-N-octadecyl-Nethylaminophenol was used in place of 3-N-octadecyl-N-methylaminophenol. The reaction product had a melting point of from 94"C to 96"C.

(2) Synthesis of the fluoran derivative The same procedure as in Synthesis Example 1-(3) was repeated, except for using the benzoic acid derivative obtained in (1) above. The resulting crystal showed a deep black-purple color on this layer chromatography, but turned black upon contact with benzyl p-hydroxybenzoate.

A process which can be generally used for producing the recording material in accordance with the present invention is described, for example, in British Patent 2,109,946. For the production of heat-sensitive recording materials, from 1 to 2 parts by weight of color former containing the fluoran derivative of the present invention, from 1 to 6 parts by weight of a phenol derivative as described above, and, if desired, up to 30 parts by weight of a heat-fusible agent as described above are thoroughly pulverized to fine particles and mixed with from 1 to 15 parts by weight of a binder as described hereinafter dissolved or dispersed in from 20 to 30 parts by weight of a solvent or dispersing medium. Up to 15 parts by weight of an inorganic pigment, such as kaolin, talc, calcium carbonate, are then added thereto to prepare a coating composition.If desired, the coating composition may further contain a paraffin wax emulsion, a latex type binder, a sensitivity-improving agent, a metal soap, an antioxidant, a hindered phenol, an electric charge-controlling agent, e.g., sodium sulfate, sodium chloride, sorbitol, a defoaming agent, an ultraviolet absorbent, and the like. The coating composition comprising the abovedescribed components may be prepared either by simultaneously mixing all of the components followed by pulverization, or by separately pulverizing each component, or appropriate combinations thereof, followed by mixing. Water is the most preferred dispersion medium or solvent.

The coating composition thus prepared is coated on a support, such as paper, synthetic resin sheet, resin-laminated paper or metal film and then dried.

The preferred amount (solid coverage) of the coating composition coated on a support is about 2.5 to 8 g/m2.

The color former which can be used in the preparation of the coating composition may be one or more of the fluoran derivatives of the present invention or a mixture of one or more of the fluoran derivatives of the present invention or a mixture of one or more of the fluoran derivatives of the present invention with known color formers for heat-sensitive papers, such as Crystal Violet lactones and fluoran derivatives other than those of the present invention.

As the known color formers, typical examples thereof include compounds as described, for example, in British Patent 2,109,946, such as triarylmethane dyes, diphenylmethane dyes, spiropyran dyes, and fluoran dyes (e.g., 3,6-bis-diphenylaminofluoran, 2-anilino-3-methyl-6-N-ethyl-Nisoamylaminofluoran, 2-anilino-3-chloro-6-di-ethylaminofluoran, 2-propionylamino-6-diethylaminofluoran.

The fluoran derivatives of the present invention are preferably used in a proportion of 10% by weight or more, and more preferably 30% by weight or more, based on the total weight of color formers used in the heat-sensitive recording material.

The binders which can be used in the present invention include a styrene-butadiene copolymer, an alkyl resin, an acrylamide copolymer, a vinyl chloride-vinyl acetate copolymer, a styrene-maleic anhydride copolymer, a synthetic rubber, gum arabic, polyvinyl alcohol, and hydroxyethyl cellulose.

From the standpoint of compatibility with the solvent or dispersing medium, water-soluble binders, such as gum arabic, polyvinyl hydroxymethyl cellulose, and carboxymethyl cellulose are preferred.

Pressure-sensitive recording materials using the fluoran derivatives of the present invention can be produced in various manners as described in U.S. Patents 2,505,470, 2,505,471, 2,505,489, 2,548,366, 2,712,507, 2,730,456, 2,730,457, 3,103,404, 3,418,250 and 4,010,038, and the pressure-sensitive recording material generally consists of a couple of sheet wherein the fluoran derivative of the present invention and an electron-accepting compound (color developer) are provided on separate sheets, respectively.

Methods for encapsulation include a method utilizing coacervation of hydrophilic colloidal sol as described in U.S. Patents 2,800,457 and 2,800,458, and an interfacial polymerization method as described in British Patents 867,797, 950,443, 989,264 and 1,091,076.

In general, one or more of the fluoran derivatives of the present invention with or without other leuco dyes (such as triarylmethane dyes, diphenylmethane dyes, xanthene dyes, thiazine dyes or spiropyran dyes, e.g., Crystal Violet lactone, benzoyl leuco methylene blue, 2-anilino-3methyl-6-N-ethyl-N-isoamylaminofluoran, are dissolved in a solvent (such as synthetic oils, e.g., alkylated naphthalene, alkylated diphenyl, alkylated diphenylmethane, alkylated terphenyl; vegetable oils, e.g., cotton oil, castor oil; animal oils; mineral oils; and mixtures thereof) and encapsulated. Thereafter the encapsulated color formers are coated on a support such as paper, plastic sheet and resin-coated paper to prepare a color former sheet.As described before, the fluoran derivatives of the present invention have an advantage in that they can be used in the form of a solution substantially of paraffin as a solvent for encapsulation. On the other hand, a color developer sheet is prepared by coating one or more color developers dispersed in a binder such as styrene-butadiene latex and polyvinyl alcohol on a support such as paper, plastic sheet, or resin-coated paper.

The fluoran derivatives of the present invention are preferably used in a proportion of 10% by weight or more, and more preferably 305G by weight or more, based on the total weight of color formers used in the pressure-sensitive recording materials.

The amounts of the color former and color developer vary depending on the desired coated thickness, type of pressure-sensitive paper, method of encapsulation, etc., and they can easily be determined by one skilled in the art. In general, the coated amounts of the color former and the color developer are from 0.02 to 2.0 g/m2 (preferably from 0.05 to 1.0 g/m2) and from 0.05 to 3.5 g/m2 (preferably from 0.1 to 2.0 g/m2), respectively.

The present invention is now illustrated in greater detail in the following Examples, but it should be understood that these Examples are not to be construed as limiting the present invention.

EXAMPLE 1 a) Preparation of Color Former Sheet 1 g of 2-anilino-3-methyl-6-N-octadecyl-N-ethyl-aminofluoran (color former) was dissolved in a mixture of 5 g of alkylated naphthalene and 20 g of paraffin having from 10 to 16 carbon atoms. The solution was added to 50cg of water containing 6 g of gelatin and 4 g of gum arabic with vigorous stirring to emulsify until the oil droplets become 1 to 10 Am in size (diameter). Then, acetic acid was gradually added thereto to adjust the pH to 4, whereby coacervation occured to encapsule the oil droplets with gelatin and gum arabic as the wall components. Thereafter the wall was hardened by adjusting the pH to 9 with the addition of formalin (37 wt% formaldehyde solution).

The thus-obtained microcapsule dispersion was coated on paper in an amount (solid coverage) of 6 g/m2 and dried to prepare a color former sheet.

b) Preparation of Color Developer Sheet 20 g of a mixture of zinc salt of 3,5-di-a-methylbenzylsalicylic acid (color developer) and a polystyrene resin (mixing weight ratio: 9/1) was dispersed in 200 g of a 5% aqueous solution of polyvinyl alcohol, and 20 g of kaolin (Georgia Kaolin) was further added and dispersed. The thusobtained coating composition was coated on paper in an amount (solid coverage) of 5.5 g/m2 and dried to prepare a color developer sheet.

c) Preparation and Test of Pressure-Sensitive Recording Material The color former sheet was placed on the color developer sheet so that the microcapsulecarrying face came into contact with the color developer-carrying face. When pressure or impact was applied to the thus prepared pressure-sensitive recording material, a black image was immediately formed. The black image had excellent properties with respect to image density, light-fastness and heat resistance.

EXAMPLE 2 5 g of 2-anilino-3-phenyl-6-N-dodecyl-N-ethylaminofluoran and 50 ml of a 5% aqueous solution of polyvinyl alcohol were mixed and ground in a lateral type sand mill to obtain a dispersion having a particle size of 1.6 pm.

A mixture of 10 g of bisphenol A, 10g of fi-naphthol benzyl ether, 20 g of kaolin and 100 ml of a 5% aqueous solution of polyvinyl alcohol was ground in the same manner as described above to obtain a dispersion having a particle size of 1.5 ,um.

These dispersions were thoroughly mixed, and to the mixture were added 5 g of a 50% dispersion of a paraffin wax emulsion and 8 g of a dispersion of stearic acid anisidide. The resulting coating composition was coated on a base paper of 50 g/m2 in a solid coverage of 5 g/m2, followed by drying.

The coated paper was heated at 35 mJ/cm2 by means of facsimile to develop a color. The color density of the color-developed area was determined by a Macbeth densitometer (RD type) and was found to be 1.03.

The resulting color image had excellent stability, particularly against light, and the hue or density did not substantially change even after exposure to light from an ultraviolet lamp for 1 hour.

EXAMPLE 3 A heat-sensitive recording material was produced in the same manner as described in Example 2 except for replacing half of the fluoran derivative as used in Example 2 with 2-anilino-3-chloro6-N-ethyl-N-octadecylaminofluoran.

Heat at 3E mJ/cm2 was applied to the resulting recording material and it rapidly developed a color of high density, and the thus developed color image had excellent stability.

EXAMPLE 4 A heat-sensitive recording material was prepared in the same manner as described in Example 2 but using 1,1-bis(4-hydroxyphenyl)cyclohexane in place of bisphenol A. The resulting recording material developed a distinct color.

EXAMPLE 5 A heat-sensitive recording material was prepared in the same manner as described in Example 2 except that the ss-naphthol benzyl ether and stearic acid anisidide as used in Example 2 were not used. When the resulting recording material was processed in the same manner as in Example 2, the developed color image had a density of 0.96.

EXAMPLE 6 A heat-sensitive recording material was prepared in the same manner as described in Example 2, except that 20 g of phenoxyethyl lS-resorcylate was used in place of bisphenol A and fi- naphthol benzyl ether. The resulting recording material developed a distinct color.

Claims (8)

1. A recording material comprising (i) a fluoran derivative having an arylamino group at the 2position thereof, an aryl group, an aralkyl group, an alkyl group, an alkoxy group, a halogen atom or a hydrogen atom at the 3-position thereof, and an alkylamino group having an alkyl moiety of not less than 10 carbon atoms at the 6-position thereof, and (ii) an organic or inorganic acidic compound capable of effecting color-development upon contact with the fluoran derivative.

2. A material as claimed in Claim 1, wherein said fluoran derivative is represented by the following formula (I):

wherein Rl represents an alkyl group having from 10 to 18 carbon atoms; R2 represents an alkyl group having not more than 10 carbon atoms; R3 represents an aryl group having from 6 to 9 carbon atoms, an aralkyl group having from 7 to 12 carbon atoms, an alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, a halogen atom or a hydrogen atom; Ar represents an aryl group; and R4 represents a hydrogen atom, a chlorine atom or an alkyl group having from 1 to 4 carbon atoms.

3. A material as claimed in Claim 2, wherein R1 represents a straight-chain alkyl group having an even number of carbon atoms and R2 represents an alkyl group having a methylene group at the a-position thereof.

4. A material as claimed in Claim 1 and substantially as herein described.

5. A material as claimed in Claim 1, wherein the fluoran derivative is one of the components herein before exemplified as (1) to (11).

6. A recording material substantially as herein before described with reference to any of the foregoing Examples 1 to 6.

7. A recording material bearing a color image obtained by imagewise exposure and development of a material as claimed in any preceding Claim.

8. The features as herein disclosed, or their equivalents, in any novel selection.