JPH0788389B2 - Fluoran compound and color forming recording material using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a novel compound that develops color by the action of a color developer, and the colored dye absorbs electromagnetic waves in the wavelength range from the visible region to the near infrared region. The present invention relates to a fluoran compound and a color forming recording material using the same.

[Conventional technology]

In recent years, in association with the development of both electronics and information management systems, there is a tendency that recording / reading devices sensitive to electromagnetic waves having wavelengths from a long wavelength portion of visible light to a near infrared portion are widely used.

Along with that, a coloring dye that is colorless or light in itself but develops color by the action of a color developer, and the coloring dye absorbs electromagnetic waves in the wavelength range as described above is proposed. Also belongs to the phthalide series, thiofluorane series and fluorene series compounds.

Therefore, the present inventors have specified a compound having an oligoaniline skeleton substituent at the 3-position as a fluoran-based color-forming dye that develops a color with a developer and absorbs electromagnetic waves in the wavelength range from the visible region to the near-infrared region. Japanese Patent Application No. 60-126149 (Japanese Patent Laid-Open No. 61-28485) and Japanese Patent Application No. 61-181224 (Japanese Patent Laid-Open No. 63-181224)
-37158) and a compound having a substituent on (7'-position) (4'-phenylamino) phenylamino, Japanese Patent Application No. 61-3750.
It was previously proposed as No. 6 (JP-A-62-196177).

[Problems to be solved by the invention]

However, there is a strong demand for a fluoran-based color-forming dye whose recording dye absorbs electromagnetic waves from the visible region to the near-infrared region and a recording material containing the same.

[Means for solving problems]

Therefore, the present inventors have completed the present invention as a result of further exploration of a fluorane-based color forming dye that satisfies the above-mentioned demand.

That is, the present invention is a general formula useful as a color forming component of a recording material. (In the formula, R ₁ , R ₄ and R ₅ each independently represent a hydrogen atom, a halogen atom or a lower alkyl group, and R ₂ , R ₃ and R ₆
And R ₇ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, a phenyl group or an aralkyl group, and R ₂ and R ₃ and R ₆ and R ₇ are bonded to each other to form an adjacent nitrogen atom. To form a pyrrolidino group or a piperidino group, provided that R ₂ and R ₃ and R ₆ and R ₇
Does not become a hydrogen atom at the same time)).

A second object of the present invention is to provide a recording material which contains the compound represented by the above general formula as a color-forming component and absorbs electromagnetic waves from the visible region to the near infrared region. .

Recently, the use of bar codes has become popular as a means of managing distribution of products.

Regarding the reading of the marking, there is a tendency that a reading device using a semiconductor laser is frequently used because the device is inexpensive. Since the semiconductor laser emits visible light and near infrared light having a wavelength of 650 nm or more, the marking read by this device must absorb visible light or near infrared light in this wavelength range.

Therefore, the present invention provides a chromic recording material containing the fluoran compound represented by the above general formula (I) and one or several kinds of the fluoran compound as a color-forming component for forming such a marking. To do.

In the substituent of the fluorane compound represented by the general formula (I), when they are lower alkyl groups, the number of carbon atoms is 1
In the case of an alkyl group, those having 1 to 8 carbon atoms are preferable, and in the case of a cycloalkyl group, those having 5 or 6 carbon atoms are preferable. Further, the benzene ring of the phenyl group and the alkyl group may be substituted with an alkyl group, an alkoxy group and a halogen atom.

Representative specific examples of the fluorane compound represented by the general formula (I) include, for example, 3-Nn-amyl-N-ethylamino-6-methyl-
7- [4 '-(4 "-phenylamino) phenylamino] phenylaminofluorane, 3-N-tolyl-N-ethylamino-6-methyl-7-
[4 '-(4 "-phenylamino) phenylamino] phenylaminofluorane, 3-pyrrolidino-7- [4'-(4" -phenylamino) phenylamino] phenylaminofluorane, 3-pyrrolidino-6-methyl- 7- [4 '-(4 "-N,
N-dimethylamino) phenylamino] phenylaminofluorane, 3-N, N-diethylamino-6-methyl-7- [4'-
(4 "-N, N-dimethylamino) phenylamino] phenylaminofluorane, 3-N, N-dimethyl-7- [4 '-(4"-(4 "-N, N-dibutylamino) phenylamino] phenylaminofur Oran, 3-pyrrolidino-7- [4 '-(4 "-N-butyl-N
-Methylamino) phenylamino] phenylaminofluorane, 3-N-tolyl-N-methyl-7- [4 '-(4 "-pyrrolidino) phenylamino] phenylaminofluorane, 3-N, N-diethylamino- 6-chloro-7- [4'-
(4 "-N-phenyl-N-methylamino) phenylamino] phenylaminofluorane, 3-N-cyclohexyl-N-methyl-7- [4'-
(4 ″ -N, N-dibutylamino) phenylamino] phenylaminofluorane, and the like, but are not limited thereto.

The fluorane compound represented by the general formula (I) is, for example, (Wherein R ₄ , R ₅ , R ₆ and R ₇ are the same as defined above, and R ₈ represents a hydrogen atom, a lower alkyl group or an acyl group) and a formula (Wherein R ₁ , R ₂ and R ₃ are the same as defined above and R ₉ represents a hydrogen atom or an alkyl group) and are obtained by reacting the benzoic acid derivative in an approximately equimolar amount. However, the manufacturing method is not limited to this.

The reaction between the compound (II) and the compound (III) may be carried out in accordance with the usual method for producing a fluorane compound, and for example, in sulfuric acid at a temperature of 0 to 50 ° C. for several hours to several tens hours. The method to do is mentioned.

Typical examples of the color developer used for developing the color of the fluorane compound of the present invention represented by the general formula (I) are shown below, but the invention is not limited to these examples.

As its representative developer, for example, acid clay, activated clay,
Inorganic acid substances such as Atabargite, Bentonai, Colloidal silica, Aluminum silicate, Magnesium silicate, Zinc silicate, Tin silicate, Calcined kaolin and Talc, Aliphatic acids such as silicic acid, maleic acid, tartaric acid, citric acid, succinic acid and stearic acid Carboxylic acid, benzoic acid, p-tert-
Butylbenzoic acid, 4-hydroxybenzoic acid, phthalic acid,
Phthalamic acid, 2,3,4,5-tetrachloro-N, N-dibutylphthalamic acid, salicylic acid, 3-isopropylsalicylic acid, 3-phenylsalicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-butyl Salicylic acid, 3-methyl-5-benzyl salicylic acid, 3-phenyl-5- (2,
Aromatic carboxylic acids such as 2-dimethylbenzyl) salicylic acid, 3,5-di- (2-methylbenzyl) salicylic acid, 2-hydroxy-1-benzyl-3-naphthoic acid, these aromatic carboxylic acids and zinc, tin, Salts with metals such as magnesium, calcium, aluminum, titanium,
A phenol resin-based developer such as p-phenylphenol-formalin resin or p-butylphenol-acetylene resin, a mixture of these phenol resin-based developer and a metal salt of the aromatic carboxylic acid, and bisphenol A,
4,4'-Secondary butylidene bisphenol, 4,4 '
-Bisphenol compounds such as cyclohexylidene bisphenol, 2,2'-dihydroxydiphenyl, pentamethylene-bis (4-hydroxybenzoate), 1,7
-Sulfur-containing bisphenol compounds such as di (4-hydroxyphenylthio) -3,5-dioxaheptane, benzyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4-hydroxy 4-hydroxybenzoic acid esters such as isopropyl benzoate, butyl 4-hydroxybenzoate, isobutyl 4-hydroxybenzoate, chlorobenzyl 4-hydroxybenzoate, methylbenzyl 4-hydroxybenzoate and diphenylmethyl 4-hydroxybenzoate, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-
Hydroxysulfones such as hydroxy-4'-butoxydiphenyl sulfone, dimethyl 4-hydroxyphthalate, dicyclohexyl 4-hydroxyphthalate, 4-hydroxyphthalic acid diesters such as diphenyl 4-hydroxyphthalate, such as 2-hydroxy- Esters of hydroxynaphthoic acid such as 6-carboxynaphthalene, or hydroxyacetophenone, p-phenylphenol, benzyl 4-hydroxyphenylacetate,
p-Benzylphenol, hydroquinone-monobenzyl ether and the like, nitrobenzoic acid derivatives such as 4-nitrobenzoic acid and 2-chloro-4-nitrobenzoic acid, and 3-nitrobenzenesulfonic acid, 2-methyl-5-
Nitrobenzenesulfonic acid derivatives such as nitrobenzenesulfonic acid, salts of aromatic acids having these nitro groups as substituents with metals such as zinc, tin, magnesium, calcium, aluminum and titanium, antipyrine, pyridine and zinc thiocyanate. And an organic halogen compound such as tribromomethylphenyl sulfone, trichloromethylphenyl sulfone, and tribromomethyl-p-chlorophenyl sulfone that generates a halogen radical by heat or light.

It is also possible to use a substance capable of forming a charge transfer complex as another developer, and examples of such a substance include tetrachlorobenzoquinone, tetracyanobenzoquinone, tetracyanoethylene, 9-dicyanomethylene-
There are 2,4,7-trinitrofluorenone or quinodimethane derivatives such as tetracyanoquinodimethane, tetracyanonaphthoquinodimethane, tetracyanoanthraquinodimethane or anthrone derivatives. Due to these substances capable of forming a charge transfer complex, the fluoran compound of the present invention exhibits a color that extremely strongly absorbs electromagnetic waves in the near infrared region.

The fluorane compound of the present invention represented by the general formula (I) can be used for a color forming recording material in the same manner as a known fluoran compound. Examples of the color-forming recording material include a heat-sensitive recording sheet or a pressure-sensitive copying sheet, as well as, for example, heat-sensitive transfer recording, electric heat-sensitive recording, electrophotography using a toner containing an acidic substance as a developer, ultrasonic recording, photosensitive recording,
It can be used as a recording material for electron beam recording, marking material, stamp ink, typewriter ribbon and the like.

At this time, the fluoran compound represented by the general formula (I) may be used alone or in combination of several kinds thereof in the color forming recording material, and may be used together with another color forming dye in the color forming recording. It may be used as a material.

The other type of color-forming dye may be used in combination with a compound that forms a dye that absorbs electromagnetic waves from the visible region to the near-infrared region, such as the above-mentioned fluorene-based, phthalide-based, or thiofluorane-based compounds. Known color-forming dyes such as crystal violet lactone, benzoylriyucomethylene blue, 2,3-dimethyl-7- (1-
Octyl-2-methyl-indolyl-3-yl) -7-
A blue color-developing dye such as (4-N, N-diphenylaminophenyl) -5,7-dihydrofuro [3,4-b] pyrazin-5-one, 3-diethylamino-5-methyl-7-dibenzyl. Green chromogenic dyes such as aminofluorane, 3-N-isobutyl-ethylamino-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-cyclohexylamino-6-chlorofluor. Red color-forming dyes such as oran or 3,3-bis (1'-octyl-2'-methylindol-3'-yl) phthalide, or 3-diethylamino-6-methyl-7.
-Phenylaminofluorane, 3-N-methyl-cyclohexylamino-6-methyl-7-phenylaminofluorane, 3-N-methyl-n-propylamino-6-methyl-7-phenylaminofluorane , 3-N-isopentyl-ethylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7-m-trifluoromethylphenylaminofluorane, 3-di-n-butylamino-7- Chlorophenylaminofluorane, 3
It can also be used in combination with a black color-forming dye such as -N-ethyltoluidino-6-methyl-7-phenylaminofluorane.

The method for producing a heat-sensitive recording paper using the fluorane compound of the present invention represented by the general formula (I) is the same as in the case of known color forming dyes, for example, Japanese Patent Publication Nos. 39-27579 and 43-43. 4160, Japanese Patent Publication No. 45-14039 or Japanese Patent Laid-Open No. 59
It can be manufactured according to the method described in, for example, JP-A-7087.

That is, for example, a suspension obtained by dispersing fine particles of the fluorane compound of the present invention represented by the general formula (I) or a mixture of the fluorane compound of the present invention and another coloring dye and fine particles of the developer acidic substance in an aqueous solution of a water-soluble binder. By coating the paper with the liquid and drying it, a thermosensitive recording paper having excellent color developability can be obtained. When a sensitizer is added to the suspension, it is possible to obtain a heat-sensitive recording paper with extremely high sensitivity. The suspension may further contain a filler, a dispersant, a color image stabilizing agent, an antioxidant, a desensitizing agent, an anti-tacking agent, a defoaming agent, a light stabilizer, an optical brightening agent and the like.

To use the fluoran compound of the present invention represented by the general formula (I) in pressure-sensitive copying paper, U.S. Pat. The pressure-sensitive copying paper can be produced according to the method described in JP-A-112041 or JP-A-58-139738.

As pressure-sensitive copying paper, an upper leaf paper having microcapsules containing an organic solvent solution of a color-forming dye applied and carried on the lower surface, and a lower paper paper having a developer (acidic substance) applied and carried on the upper surface are used. Unit (a sheet of paper with a developer on the top and microcapsules on the bottom can also be added to the unit), or the microcapsules and the developer are applied to the same paper surface. It may be so-called self-content paper.

As the organic solvent, for example, a diphenylmethane type, an alkylnaphthalene type, an alkyltriphenyl type, or the like, which is inactive and non-volatile in which a color forming dye is well dissolved, is used.

The use of the fluorane compound of the present invention represented by the general formula (I) for thermal transfer is described, for example, in JP-A-58-212985 and JP-A-58-212985.
59-33185, JP-A-59-42995 or JP-A-59-22
It can be used according to the method described in JP-A-5986.
JP-A-48-101935 or JP-A-49-11344, and for use in electrophotography, for example, the method described in JP-A-52-24530 or JP-A-52-56932. It can be used according to. Further, the use of the fluorane compound of the present invention for photosensitive recording is described in, for example, Japanese Patent Publication
38-24188, JP45-10550, JP49-45978
No. 50, No. 80120, No. 50-126228, No. 5
It can be used according to the method described in JP-A 2-141633 or JP-A-54-147829. In this case, as an acid precursor which generates a protonic acid or a Lewis acid by an energy ray, for example, an organic halogen compound described in JP-A-55-13780 (which can also be sensitized by an amine compound) ), Diazonium salts, iodonium salts, etc., as well as sulfonium salts such as dimethylphenacylsulfonium hexafluorophosphate or triphenylsulfonium hexafluoroantimonate (V) salts.

Also used for ultrasonic recording French Patent No. 2,120,922,
For use in electron beam recording Belgium Patent No. 7,959,986,
It can be used according to the method described in JP-B-49-3923 for use in electrostatic recording and the method described in JP-A-48-12104 for use in photosensitive printing materials.

The recording paper produced according to these methods can be provided with a protective layer on the front surface if necessary, and an adhesive layer can be provided on the back surface for convenient use as a label.

Further, the recording body manufactured according to these methods is not only used for the above-mentioned bar code, but also for copying books, documents, etc., multiple copying of forms, electronic computer, facsimile,
It is used for ticket machines, various cards, labels, etc., and can also be applied to forgery prevention, duplication prevention, unlocking device or laser disk etc. where the information entered with higher density or the recorded information cannot be seen with the naked eye. Its field of use is extremely wide.

Next, specific examples will be described.

Example 1 (Synthesis Example) 4-methoxy-2-methyl-4 '-(4 "-phenylamino) phenylaminodiphenylamine (the following compound ( a)) 7.
0 g and 2- (2'-hydroxy-4'-N-amyl-N-
After adding 6.3 g of ethylaminobenzoyl) benzoic acid (the following compound (b)) and continuing stirring at room temperature (about 25 ° C.) for 24 hours, the reaction product was precipitated by pouring into 300 ml of ice water and collected. . The collected precipitate was washed with water and heated and refluxed for 1 hour while stirring with 200 ml of water, 20 g of caustic soda and 200 ml of toluene. The mixture was subjected to liquid separation at the time of heating to remove the aqueous layer, and the toluene layer was sufficiently washed with warm water, and then toluene was distilled off and concentrated, followed by cooling to precipitate crystals. The crystals were separated and recrystallized using toluene to give 3-N
-N-amyl-N-ethylamino-6-methyl-7-
5.6 g of [4 ′-(4 ″ -phenylamino) phenylamino] phenylaminofluorane (the following compound (c)) was obtained as off-white crystals having a melting point of 129 to 131 ° C.

Example 2 (Synthesis example) 4-methoxy-2-methyl-4 '-(4 "-dimethylamino) phenylaminodiphenylamine (the following compound (d)) 4.9 g and 2- (2'-hydroxy-4) '-Pyrrolidinobenzoyl) benzoic acid (4.4 g of the following compound (e) was subjected to reaction post-treatment and recrystallization according to the synthetic method of Example 1 to give 3-pyrrolidino-6-methyl-7- [4'- (4 ″
4.1 g of -dimethylamino) phenylamino] phenylaminofluorane (the following compound (f)) was obtained as gray-green crystals having a melting point of 269 to 272 ° C.

Example 3 Compound (a) of Example 1 and 2- (2′-hydroxy-)
4′-N-tolyl-N-ethylaminobenzoyl) benzoic acid, and the compound (d) of Example 2 and 2- (2 ′).
-Hydroxy-4'-diethylaminobenzoyl) benzoic acid, respectively according to the synthesis method of Example 1,
The following fluoran compounds (g) and (h) were obtained by separating by column chromatography instead of post-treatment and recrystallization.

(G) 3-N-tolyl-N-ethylamino-6-methyl-7- [4 '-(4 "-phenylamino) phenylamino] phenylaminofluorane (melting point 174-175 ° C, gray blue crystal) (h ) 3-N, N-diethylamino-6-methyl-7-
[4 ′-(4 ″ -Dimethylamino) phenylamino] phenylaminofluorane (melting point 237-238 ° C., grey-blue crystal) Example 4 4-methoxy-4 ′-(4 ″ -phenylamino) phenylaminodiphenyl The amine and the compound (e) of Example 2 were reacted according to the synthetic method of Example 1 and post-treated to give 3-pyrrolidino-7- [4 ′-(4 ″ -phenylamino) phenylamino] phenylamino. Although fluoran was synthesized, even if toluene was recovered and concentrated, the fluoran compound was not precipitated and could not be obtained as a crystal.

Toluene was added to this concentrated solution and dissolved again. Clay lower paper and resin lower paper (phenol-formalin resin)
When a few drops were added to and the toluene was volatilized, all developed a color from blue to blue-green, and these dyes had absorption in the electromagnetic wave in the near infrared region.

Example 5 (Thermal recording paper) Dye dispersion (A-1) Compound synthesized in Example 14 14 parts Clay 23 parts 15% PVA aqueous solution 83 parts Water 80 parts Developer dispersion (B-1) Bisphenol A 21 parts Clay 16 parts 15% PVA aqueous solution 83 parts Water 80 parts Developer dispersion (B-2) 4-hydroxy-4'-isopropoxydiphenyl sulfone 21 parts Clay 16 parts 15% PVA aqueous solution 83 parts Water 80 parts Developer dispersion (B-3) 4-Nitrobenzoic acid zinc salt 21 parts Clay 16 parts 15% PVA aqueous solution 83 parts Water 80 parts Developer dispersion (B-4) Salicylic acid zinc salt 21 parts Clay 16 parts 15 % PVA aqueous solution 83 parts Water 80 parts Developer dispersion (B-5) Tribromomethylphenyl sulfone 7 parts Clay 30 parts 15% PVA aqueous solution 83 parts Water 80 parts (These mixing ratios are all parts by weight) .

Glass beads (diameter 1-1.5 mm) for each of the above liquids 1
Put it in a polyethylene bottle together with 50 g, stopper tightly, and grind for several hours with a paint controller manufactured by Red Devil Co., and dye dispersion A-1 and developer dispersions B-1, B-2, B-3. ,
B-4 and B-5 were obtained. Next, each of the color developer dispersions was mixed with the dye dispersion at a weight ratio of 1: 2 to prepare a coating liquid.

Each of these coating solutions was coated on a white base paper and dried to produce each thermal recording paper I, II, III, IV and V.

Both sides of the thermal recording papers I, II, III, IV and V were heated at a temperature of 200 ° C. using a dry heat tester (manufactured by Xino Scientific Co., Ltd.) to develop color. The color developed on these recording papers was black.

Regarding the color part of these thermal recording papers, the reflection absorption curve (wavelength 400 to 1300 nm) and reflectance (wavelength 700, 800, 900 and 10
00 nm) and the reflectance (the same as above) for the uncolored portion were measured using a spectral sensitometer (U-3400 manufactured by Hitachi Ltd. and an integrating sphere attached thereto).

These reflection absorption curves are shown in the drawings, and the reflectance is shown in Table 1 below.

It is clear from FIG. 1 that the fluoran compound having the oligoaniline skeleton of the present invention as a substituent has absorption of electromagnetic waves from the visible region to the near infrared region (that is, the reflectance from the visible region to the near infrared region is low). Furthermore, it has been shown that the absorption wavelength range of electromagnetic waves in the near infrared region changes depending on the type of the color developer.

Further, it is clear from Table 1 that the fluoran compound of the present invention has a clear color development and a clear contrast between the uncolored part and the colored part.

Example 6 (Thermal recording paper) Dye dispersion (A-2) Compound synthesized in Example 2 14 parts Clay 23 parts 15% PVA aqueous solution 83 parts Water 80 parts Developer dispersion (B-6) Tetracyanoquino Dimethane 21 parts Clay 16 parts 15% PVA aqueous solution 83 parts Water 80 parts (The mixing ratios of these represent parts by weight).

The liquid having the above composition was treated in the same manner as in Example 5 to obtain respective dispersions. Dye dispersion A-2 and developer dispersion B-6
A coating solution was prepared by mixing in a weight ratio of 1: 2.

Thereafter, the same operation as in Example 5 was carried out to produce a thermosensitive recording paper VI using this coating solution to develop a color. The colored pigment was black. Furthermore, when the reflectance of the color-developed portion of this thermal recording paper VI was measured, it had absorption of electromagnetic waves in the near-infrared portion. The measured values of the reflectance are shown in Table 2.

Example 7 With respect to the fluorane compounds (g) and (h) synthesized in Example 3, 0.14 g of each fluorane compound was finely pulverized in an agate mortar, transferred to a glass vial, and further clay 0.23 g, 15% PVA. 0.83 g of an aqueous solution and 0.8 g of water were added, and the mixture was sufficiently dispersed using an automatic mixer (S-100 type, manufactured by Taiyo Kagaku Kogyo Co., Ltd.) to obtain a dye dispersion. Further, the color developer dispersion B-used in Example 5 was used.
A coating solution was prepared by adding 24 g.

Thereafter, the same operations as in Example 5 were carried out to produce thermosensitive recording papers VII and VIII to develop color. These colored pigments were red-black and black.

Further, the reflectance of the color-developed areas of these thermal recording papers VII and VIII was measured, and it was found that they had absorption of electromagnetic waves in the near-infrared area. The measured values of the reflectance are shown in Table 2.

Example 8 (Pressure Sensitive Copy Paper) 2.0 g of the compound f synthesized in Example 2 was substituted with alkyldiphenylmethane (“Hisol SAS296” by Nisseki Chemical Co., Ltd.) 2
5.0 g and 18.0 g of diisopropyl naphthalene (Kureha Chemical Co., Ltd. “KMC-113”) were mixed and heated to dissolve (A
liquid).

On the other hand, polyvinyl alcohol modified with sulfonic acid (10% aqueous solution of "Gosenol (KS-50)" by Nippon Synthetic Chemical Industry Co., Ltd.
15.0 g, ethylene-maleic anhydride copolymer (Monsanto "EMA-31") 10% aqueous solution 7.5% and water 34.0 ml were mixed, and further urea 2.5 g and resorcin 0.25 g were added and dissolved, then 20% The pH was adjusted to 3.4 using an aqueous solution of caustic soda (solution B).

Add solution A to solution B and make an emulsion using a homomixer, then add 17.0 g of 35% formalin aqueous solution,
Stirring was continued for 1 hour at a temperature of ~ 65 ° C. 28% after cooling to 40 ℃
Aqueous ammonia was added to adjust the pH to 7.5 to obtain a microcapsule dispersion.

27.0g of this dispersion, 3.5g of wheat starch, 8% wheat starch aqueous solution
A coating solution was prepared by mixing 8.5 g and 34.0 ml of water.

This coating solution was applied to a white base paper using a wire bar No. 12 and dried to prepare a top sheet of pressure-sensitive copying paper.

Two rolls, each of which is coated with a phenol formalin resin and dried, and is coated with a lower leaf paper for pressure-sensitive copying paper and a clay lower leaf paper (manufactured by Fuji Photo Film Co., Ltd.) on which the upper leaf paper is coated. Pressure was applied between the two to develop color. as a result,
The colored surfaces of both lower leaf papers were reddish black and bluish black, and had electromagnetic wave absorption in the near infrared region.

〔The invention's effect〕

As is clear from the above description and the description of each example, the fluoran compound represented by the general formula (I) of the present invention having an oligoaniline skeleton at the 7-position as a substituent has a function of a color developing agent. The dye that develops color has an excellent property of absorbing electromagnetic waves from the visible region to the near infrared region.

[Brief description of drawings]

The attached drawings show the reflection and absorption curves of the heat-developed color-developing part of the thermosensitive recording paper that was colored using different color developing agents. In the figure, (I) is the thermosensitive recording paper I and (II) is the thermosensitive recording paper. Recording paper
II, (III) is thermal recording paper III, (IV) is thermal recording paper
IV and (V) show the reflection absorption curves of the thermal recording paper V, respectively.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C09B 11/28 H

Claims (2)

[Claims] 1. A general formula (In the formula, R ₁ , R ₄ and R ₅ each independently represent a hydrogen atom, a halogen atom or a lower alkyl group, and R ₂ , R ₃ and R ₆
And R ₇ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, a phenyl group or an aralkyl group, and R ₂ and R ₃ and R ₆ and R ₇ are bonded to each other to form an adjacent nitrogen atom. To form a pyrrolidino group or a piperidino group, provided that R ₂ and R ₃ and R ₆ and R ₇
Does not become a hydrogen atom at the same time). 2. General formula (In the formula, R ₁ , R ₄ and R ₅ each independently represent a hydrogen atom, a halogen atom or a lower alkyl group, and R ₂ , R ₃ and R ₆
And R ₇ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, a phenyl group or an aralkyl group, and R ₂ and R ₃ and R ₆ and R ₇ are bonded to each other to form an adjacent nitrogen atom. To form a pyrrolidino group or a piperidino group, provided that R ₂ and R ₃ and R ₆ and R ₇
Does not become a hydrogen atom at the same time) as a color-forming component.