GB2163272A - Recording material containing fluoran derivative as color former - Google Patents

Abstract

A recording material comprises, by weight, 1-6 parts of a sheet, e.g. of paper, coated with a layer of (a) a phenol derivative e.g. an alkylenebisphenol, as developer, (b) 1-2 parts of a 2-arylamino, 3- aryl 6-amine residue fluoran derivative as a color former, preferably of the general formula: <IMAGE> where R1 = amine residue, R2, R3 = aryl and R4 = H, Cl or (substituted) alkyl, and 1-15 parts of a binder. For a heat-sensitive, material, 1-30 parts of a heat-fusible agent are included in the layer. Methods of synthesis of the derivative (l), e.g. from an aminophenol, are described. Other known color formers may also be present. The material produces colored images of good intensity and stability e.g. from exposure to a facsimile machine thermal head.

Description

SPECIFICATION Recording material containing fluoran derivative as color former This invention relates to a recording material and, more particularly, to a recording material having improved color developability and improved developed color image stability, wherein an electron-donating colorless dye (or dye precursor) and an electron-accepting compound are used.

Recording materials using electron-donating colorless dyes and electron-accepting compounds are known as disclosed, e.g., in Japanese Patent Publication Nos. 14039/70 (corresponding to U.S. Patent 3,539,375) and 4160/68. These 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 to 1 00,C. However, it is difficult to control the melting point of phenolic compounds that are widely employed as electron-accepting compounds at present and also phenolic compounds per se become expensive. Therefore, adjustment of a 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 "unexamined published application"); a method of using carboxylic esters, e.g., dimethyl isophthalate, diphenyl phthalate, dimethyl terephthalate, etc., as sensitizers; and a method of using hindered phenols as described in British Patent Publications 2,074,335A.

However, none of these conventional methods have been successful in providing heatsensitive 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., 2,2 '-methylene-bis(4-methyl-6-t- butylphenol); Japanese Patent Application (OPI) No. 17347/78 describes addition of waterinsoluble modified phenol resins, e.g., rosin-modified phenol resins; and Japanese Patent Application (OPI) No. 72996/81 proposes 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 heat-sensitive recording material which has satisfactory color developability, provides a sufficiently stable color image and also satisfies other required conditions.

According to this invention a recording material has a sensitive layer containing a fluoran derivative with an arylamino group, an aryl group and an amine residue at the 2-, 3- and 6positions thereof, respectively, and a phenol derivative.

Fluoran derivatives having an arylamino group at the 2-position thereof and a wide variety of substituents at the 3-position thereof have now been developed. As a result, it has now been unexpectedly found that fluoran derivatives having an aryl group at the 3-position thereof are colorless crystals which have much lower melting points and higher oil-solubility and are less fogged as compared with the corresponding fluoran derivatives having a methyl group at the 3position thereof. The present invention has been based on this finding.It was further found that the effect of the fluoran derivatives used in the present invention is markedly increased when they are used in combination with a heat-fusible agent having a melting point of from about 70 to about 130"C, whereby a pure black color having satisfactory storability can be rapidly formed.

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

wherein R, represents an amine residue; R2 and R3 each represents an aryl group and R4 represents a hydrogen atom, a chlorine atom, an alkyl group or a substituted alkyl group.

Examples of suitable amine residues for R, include an amino group, a primary amine residue and a secondary amine residue. Specific examples of these residues are primary or secondary amine residues with one or two of groups having up to 1 8 carbon atoms, e.g., a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, an amyl group, an isoamyl group, a hexyl group, a cyclohexyl group, a 2-ethylhexyl group, an octyl group, a benzyl group, a stearyl group, a phenethyl group, a phenyl group, a tolyl group, etc., such as dioctylamino, dihexylamino, N-ethyl-N-p-tolylamine, N-methyl-N-cyclohexylamino, piperidino, benzylamino, toluidino, p-ethyltoluidino, cyclohexylamino, dibutylamino, N-ethyl-N-isoamylamino, N-methyl-N-butylamino, N-n-hexyl-N-methyiamino, N-methyl-N-isoamylamino, N-ethyl-N fi-phenethylamino, diethylamino, N-ethyl-N-octylamino, N-methyl-N-fl-phenoxyethylamino, N ethyl-N-ss-phenoxypropylamino, N-isobutyl-N-ss-phenoxyethylamino, N-methyl-N-ss-ethoxyethylam- ino, and the like.

R2 can represent a phenyl group or a phenyl group substituted with a halogen atom, an alkyl group or an alkoxy group. R3 can represent a phenyl group, a chlorophenyl group or a tolyl group.

The fluoran derivatives represented by the above-described formula (I) have a pure black color upon contact with phenol derivatives. The synthesis of the fluoran derivatives having a pure black color is very difficult. For example, the fluoran compounds wherein R3 represents dichloroanilino have a red color.

Of these fluoran derivatives, those having a melting point of from about 80 to about 180"C are preferred, and can appropriately be selected in conformity with phenol derivatives and heatfusible 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 markedly stable without substantially undergoing 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, are free from denaturation or coloration during storage for a long time.

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

(1) 2-Anilino-3-phenyl-6-diethylaminofluoran (2) 2-Anilino-3-phenyl-6-N-methyl-N-hexylaminofluoran (3) 2-p-Chloroanilino-3-phenyl-6-N-ethyl-N-isoamylaminofluoran (4) 2-Anilino-3-p-chlorophenyl-6-dibutylaminofluoran (5) 2-Anilino-3-tolyl-6-N-ethyl-N-hexylaminofluoran (6) 2-P-Chloroanilino-3-tolyl-6-dimethylaminofluoran (7) 2-Anilino-3-dimethylphenyl-6-N-methyl-N-hexylaminofluoran (8) 2-Anilino-3-phenyl-6-N-methyl-N-isoamylaminofluoran (9) 2-Anilino-3-tolyl-6-p-butylanilinofluoran (10) 2-Anilino-3-phenyl-6-N-methyl-N-ss-phenoxyethylaminofluoran (11) 2-Anilino-3-phenyl-6-N-ethyl-N-benzylaminofluoran (12) 2-Anilino-3-phenyl-6-N-methyl-N-phenoxypropylaminofluoran The phenol derivatives which are preferably used as electron-accepting compounds are compounds having at least one phenolic hydroxyl group, and are more preferably those compounds wherein either of the 2- and 6-positions is unsubstituted, such as bis-(4-hydroxyphe nyl)alkane derivatives, bis-(3-chloro-4-hydroxyphenyl)alkane derivatives, bis-(4-hydroxyphenyl)sul- fone, (4-hydroxyphenyl)-(4'-alkoxyphenyl)sulfone derivatives, p-hydroxybenzoic ester derivatives, resorcylic ester derivatives, orsellinic ester derivatives, gallic ester derivatives, saiicyclic 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) fi-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) 2,6-dimethylphenoxyethyl-ssresorcylate (18) 2,4,6-trichlorophenoxyethyl-ss-resorcylate Of these phenol derivatives, alkylenebisphenols, cycloalkylenebisphenols and phenol compounds having an electron-attractive group are particularly useful.

In general, terra abla, silica gel, calcined clay, and the like that are used in pressure-sensitive papers, etc. form colored products upon contact with the above described fluoran derivatives, but the products do not have a pure black color.

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 to about 130"C, and preferably from 90 to 120"C.

Specific examples of suitable heat-fusible agents include stearic acid amide, stearic acid anilide, ethylenebisstearamide, benzoin, a-naphthol benzoate, ssnaphthol p-methylbenzoate, p-tbutylphenol phenoxyacetate, p-phenylphenol p-chlorophenoxyacetate, 4,4'-cyclohexyldenediphenol diacetate, 4, 4'-isopropylidenediphenol dimethyl ether, ssphenylethyl-p-phenylphenol ether, phenyl hydroxynaphthoate, p-methoxycarbonylbenzoic acid ethylamide, stearylurea phenyl ester, ssbenzyloxynaphthalene, 1 ,2-diphenoxyethane, 1 -phenoxy-2-p-methoxyethane, and the like.

Typical processes for synthesizing the fluoran derivatives according to the present invention include (1) a process comprising reacting a 2-hydroxy-4-substituted amino-2'-carboxybenzophenone and a 2-aryl-4-hydroxy- or alkoxydiarylamine in the presence of an acid catalyst; and (2) a process comprising reacting a 2-amino-3-aryl-6-substituted aminofluoran and bromobenzene or iodobenzene in the presence of a copper catalyst.

Acid catalysts which can be used in the process (1) above include Lewis acids, e.g., zinc chloride, aluminum chloride, magnesium chloride, calcium chloride, etc.; 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 2aminofluoran derivatives and arylation agent, include copper compounds, e.g., copper powder, copper oxide, cuprous iodide, cupric iodide, etc., nickel compounds, cobalt compounds, and the like, 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 preferred starting materials used to synthesize the fluoran derivatives of the present invention are aminophenol derivatives represented by the formula (ill):

wherein R5 represents a hydrogen atom or a lower alkyl group; and R; represents a hydrogen atom or an acyl group.

Synthesis examples of two fluoran derivatives used in the present invention are described below.

SYNTHESIS EXAMPLE A 3-aryl-4-aminophenol or anisole that is used as a starting material of the synthesis can be prepared by various processes, such as reduction transformation of 2-arylnitrobenzenes, reaction between 3-arylphenols and diazonium salts followed by reduction, reaction between 4-nitroanisole and arylmagnesium halides, and the like. Further, 3-aryl-4-arylaminoanisoles can directly be prepared by reacting 3-aryl-4-halogen-substituted anisoles with acetamide derivatives of aromatic amines.

(a) Synthesis of 2-Phenyl-4-Methoxydiphenylamine 3-Phenyl-4-aminophenol was stirred. with 1.2 molar equivalents of acetic anhydride to form 3phenyl-4-acetamidophenol having a melting point of from 146 to 148"C.

The product was treated with dimethyl sulfate in the presence of sodium hydroxide to obtain 2-phenyl-4-methoxyacetanilide as crystals having a melting point of 1 3 to 11 4 C.

In a 100 ml-volume flask equipped with a stirrer and a cooling tube were charged 5.6 g of 2phenyl-4-methoxyacetanilide prepared as above, 1.2 molar equivalents of iodobenzene, 2.5 g of potassium carbonate and 0.2 g of a copper powder, and the mixture was maintained at 1 60 C to 240"C for 6 hours while stirring to obtain 2-phenyl-4-methoxy-N-acetyldiphenylamine To the reaction mixture were added 1 5 ml of dipropylene glycol and 1.8 g of potassium hydroxide, and the mixture was maintained at 145 to 185"C for 4 hours, followed by filtration while hot. The filtrate was poured into ice-water to precipitate crystals to obtain semisolid 2phenyl-4-methoxydiphenylamine.

(b) Synthesis of 2-Anilino-3-Phenyl-6-Diethylaminofluoran [Compound (1)] 2-Phenyl-4-methoxydiphenylamine (0.015 mol) prepared as in (a) above and 0.017 mol of 2hydroxy-4-diethylaminobenzylbenzoic acid were subjected to condensation using 1 5 ml of concentrated sulfuric acid as a catalyst. The reaction mixture was poured into an ice-cooled aqueous solution of sodium hydroxide to separate the reaction product. The product was developed using silica gel as a carrier and toluene-ethyl acetate as an eluent. The solvent was removed by distillation and the residue was recrystallized from a mixed solvent of benzene etherhexane to isolate the desired fluoran derivative as pure white crystals having a melting point of 122 to 125"C.

(c) Synthesis of 2-Anilino-3-Phenyl-6-N-Methylisoamylaminofluoran [Compound (8)] Condensation with 2-phenyl-4-methoxydiphenylamine was carried out in the same manner as described in (b) above except for using 2-hydroxy-4-N-methylisoamylaminobenzoylbenzoic acid in place of 2-hydroxy-4-diethylaminobenzoylbenzoic acid. The reaction mixture was allowed to stand under ice-cooling for 2 hours and then at room temperature overnight and poured into an aqueous sodium hydroxide solution to form a solid precipitate. After filtration, the product was developed using silica gel as a carrier and a hexane-ethyl acetate mixed solvent as an eluent.

The solvent was removed by distillation to obtain crude crystals. The resulting crystals showed a deep black-purple color on thin layer chromatography (TLC) 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 2,1 09,946. For the production of heat-sensitive recording materials, 1 to 2 parts by weight of a dye precursor containing the fluoran derivative of the present invention, 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 1 to 1 5 parts by weight of a binder as described hereinafter dissolved or dispersed in 20 to 30 parts by weight of a solvent or dispersing medium.Up to 1 5 parts by weight of an inorganic pigment, such as kaolin, talc, calcium carbonate, etc., 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, etc., a defoaming agent, an ultraviolet absorbent, and the like. The coating composition comprising the above-described components may be prepared either by simultaneously mixing all the components followed by pulverization, or by separately pulverizing each component or appropriate combinations thereof followed by mixing.

The coating composition thus prepared is coating on a support, such as paper, a synthetic resin sheets, resin-laminated paper, a metal film, etc., 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 dye precursor which can be used in the preparation of the coating composition may be one of or a mixture 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 heatsensitive papers, such as Crystal Violet lactones and fluoran derivatives other than those of the present invention. Water is the most preferred dispersing medium or solvent.

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-Nethyl-N-isoamylaminofluoran, 2-anilino-3-chloro-6-diethylaminofluoran, 2-propionylamino-6-diethylaminofluoran, and the like).

The fluoran derivatives of the present invention are preferably used in the proportion of 10% by weight or more, more preferably 30% by weight or more per total weights of the color formers used.

The binder which can be used in the present invention can be a styrene-butadiene copolymer, an alkyd resin, an acrylamide copolymer, a vinyl chloride-vinyl acetate copolymer, a styrenemaleic anhydride copolymer, a synthetic rubber, gum arabic, polyvinyl alcohol, hydroxyethyl cellulose, etc.

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

The present invention is now illustrated in greater detail with reference to the following examples.

EXAMPLE 1 Five grams of 2-anilino-3-phenyl-6-diethylaminofluoran 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 ym.

A mixture of 10 g of bisphenol A, 10 g of ss-naphtholbenzyl 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 ym.

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 a facsimile machine 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 1.18.

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 2 A recording paper was produced in the same manner as described in Example 1 except for replacing half of the fluoran derivative as used in Example 1 with 2-anilino-3-chloro-6dibutylaminofluoran.

Heat at 35 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 3 A heat-sensitive recording material was prepared in the same manner as described in Example 1 except that half of the fluoran derivative as used in Example 1 was replaced with 2-anilino-3phenyl-6-N-methylisoamylaminofluoran, phenylphenolbenzyl ether was used in place of ss- naphtholbenzylether, and stearic acid amide was used in place of stearic acid anisidide. The developed color density was determined in the same manner as Example 1 and was found to be 1.02.

EXAMPLE 4 A heat-sensitive recording material was prepared in the same manner as described in Example 1 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 1 except that the ssnaphtholbenzyl ether and stearic acid anisidide as used in Example 1 were not used. When the resulting recording material was processed in the same manner as in Example 1, the developed color image had a density of 0.98.

Claims (14)

1. A recording material containing a fluoran derivative with an arylamino group, an aryl group and an amine residue at the 2-, 3- and 6-positions of the fluoran ring, respectively, as a color forming compound, and a phenol derivative as a color developing compound.

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

wherein R, represents an amine residue; R2 and R3 which may be the same or different each represents an aryl group; and R4 represents a hydrogen atom, a chlorine atom, an alkyl group or a substituted alkyl group.

3. A recording material as claimed in Claim 2, wherein R1 represents an amino group or a primary or secondary amine residue with each of the groups having up to 1 8 carbon atoms.

4. A recording material as claimed in Claim 2, wherein R2 represents a phenyl group or a phenyl group substituted with a halogen atom, an alkyl group or an alkoxy group.

5. A recording material as claimed in Claim 2, 3 or 4, wherein R3 represents a phenyl group, a chlorophenyl group or a tolyl group.

6. A recording material as claimed in any preceding claim, wherein said fluoran derivative has a melting point of about 80 to about 180"C.

7. A recording material as claimed in any preceding claim, wherein the fluoran derivative was prepared from an aminophenol derivative represented by the formula (ill):

wherein R5 represents a hydrogen atom or a lower alkyl group; and R6 represents a hydrogen atom or an acyl group.

8. A recording material as claimed in any preceding claim, wherein said fluoran derivative is any of those numbered (1) to (12) listed hereinbefore.

9. A recording material as claimed in any preceding claim, wherein said phenol derivative is a compound wherein either one of 2- and 6-positions relative to the phenolic hydroxyl group is unsubstituted.

10. A recording material as claimed in any preceding claim, wherein said phenol derivative is an alkylenebisphenol, a cycloalkylenebisphenol or a phenol compound having an electronattractive group.

11. A recording material as claimed in any preceding claim, which is heat-sensitive and also contains a heat-fusible agent having a melting point of 70 to 130"C.

1 2. A recording material as claimed in Claim 11, wherein said heat-fusible agent has a melting point of 90 to 120"C.

1 3. A recording material as claimed in Claim 11 or 12, wherein said heat-fusible agent is an ether, ester or amide.

14. A recording material as claimed in Claim 1, substantially as hereinbefore described with reference to any of Examples 1 to 5.

1 5. A recording material as claimed in any preceding claim bearing a visible image formed by local heating or pressure.