JP4521435B2 - Color-forming compound, dye compound, and image forming material - Google Patents

Description

The present invention relates to a color developable compound suitable for use as a dye, a dye compound obtained by reacting the same with a developer, and an image forming material using the dye compound.

Forest protection is an absolute requirement in order to protect the global environment and reduce the greenhouse effect of CO _2, and in order to maintain new logging to a minimum and maintain a balance with reforestation, including afforestation. The major issue is how to efficiently use the paper resources we already have. The current reuse of paper resources is “recycling” where paper fibers that have undergone the deinking process to peel off the image forming material are re-spread on poor quality paper and used separately for different purposes. The possibility of new environmental pollution due to the treatment of sewage is pointed out.

  On the other hand, until now, as in the case of pencils, poppies, and writing tools, correction liquids have been put to practical use for hard copy reuse by image correction. Recently, special paper rewritable paper has been proposed for the purpose of reusing hard copy paper. Here, “reuse”, which is used multiple times for the same purpose to prevent paper quality deterioration as much as possible, is a different concept from “recycle”, which is used for other purposes while reducing paper quality. From the viewpoint of protecting paper resources, This is a more important concept. If effective “reuse” is performed at each “recycle” stage, waste of new paper resources can be minimized.

  The present inventors have paid attention to the fact that when the interaction between the color developing compound and the developer is increased, the color developing state is obtained, and when the interaction is decreased, the color developing state is achieved. By adding a new color erasing agent that captures the developer to the composition system containing the color, the coloring state is stably present at a temperature near room temperature, and the treatment with heat or a solvent causes long-term erasing at the practical temperature. An image forming material that fixes a color state, an image erasing process, and an image erasing apparatus have been proposed as an effective paper reuse technology to replace the current recycling technology. Our proposed image materials have high stability in coloring and erasing states of images, and also have high material safety, and can be used for all electrophotographic toners, liquid inks, ink ribbons, and writing utensils. In addition, it has a merit not found in the prior art that a large-scale erasure process is possible.

  As described above, the invention of the prior application promotes the reuse and recycling of paper and can significantly reduce paper waste, so that it has a great effect on resource saving. In the process of further studying this erasable ink, the image recording medium is a polar polymer represented by paper, and the amount of dye captured by the binder of the image forming material increases due to temperature rise or contact with a solvent. In the case of a non-polar material having enhanced properties, the image recording medium can be erased only a few times without adding a developer-capturing type decolorizer to the image-forming material due to the ability of the image recording medium to capture the developer. It was discovered that a color can be formed, and an image forming material that does not contain a color erasing agent that captures the developer and an erasing method therefor have also been developed (see Patent Document 1).

  However, in the course of developing this composition system, several problems have emerged. The first problem is the limit of contrast between color development and color erasing in thermal color erasing. In this composition system, both coloring and decoloring are determined by the balance between the action of the dye and the developer in the softened binder. For this reason, the limit of the contrast is determined by the temperature dependence of the equilibrium constant in the binder, and the limit value is determined by the process temperature of forming the image forming material and the temperature of the color erasing process. That is, the color density is uniquely determined by the combination of the selected materials.

Conventionally used leuco dyes are relatively well soluble in non-polar solvents such as toluene, but the developer is difficult to dissolve because it is difficult to dissolve, but it turns out that it dissolves and colors when added with a polar solvent. Yes. However, none of the usable product resins has been found to correspond to such a polar solvent, and the product is produced under conditions that are disadvantageous to the dye / developer.
JP 2005-205625 A

The present invention has been made in order to improve the problems of these conventional erasable image recording materials. In an image forming material which can be erased by controlling thermal history or contacting an erasing solvent, a clear image can be obtained. An object of the present invention is to provide an image forming material which can be formed and can erase images with good quality.

The color-forming compound of the first invention is a color-forming compound containing an electron-accepting phenyl-indole-phthalide-based compound, and the skeleton of the color-forming compound has 3 carbon atoms that are terminally amino-substituted. To 6 linear alkyl groups.

The dye compound of the second invention is a reaction product of a color developing compound containing an electron-accepting phenyl-indole-phthalide compound and a developer,
The skeleton of the color-forming compound has a linear alkyl group having 3 to 6 carbon atoms substituted with a terminal amino group.

The image forming material of the third aspect of the present invention is selected from a color-forming compound containing an electron-accepting phenyl-indole-phthalide compound , a gallate ester compound, a hydroxybenzophenone compound, and a hydroxyacetophenone compound. A reaction product with at least one developer and a decolorizer capable of capturing the developer, wherein the skeleton of the color developing compound has a terminal amino-substituted carbon number of 3 to It has 6 linear alkyl groups.

As described above, the erasable image forming material using the color developable compound of the present invention has excellent color developability and can greatly improve the image density, so that its industrial value is great. .

The present invention provides a leuco dye having a high color developability. In addition to thermal paper, pressure-sensitive paper, or rewritable material used in the past, images used for electrophotography, particularly printers, copiers, fax machines, thermal transfer recordings, writing instruments, or printing. It can also be used as a forming material.
The dye can be used for an image forming material capable of erasing an image by controlling a thermal history or contacting an erasing solvent.

The present invention has been made in order to obtain a decolorizable dye capable of forming a clear image and having improved afterimage performance, and is a novel color-forming electron-accepting compound. A novel colorant formed by synthesizing a color developable compound comprising the above and reacting with a developer, and a decolorable image forming material using the colorant are formed.
Hereinafter, embodiments of these inventions will be sequentially described.

[Leuco dye coloring compound]
The color developing compound of the present embodiment is a compound belonging to a so-called leuco dye, in which a linear alkyl group having an amino group at the end is bonded to a color-forming electron accepting compound skeleton having a leuco lactone ring. Is. This color developing compound can be colored by reacting with a developer described later.

  Examples of the color-forming electron-accepting color-forming compounds that can be used in the present embodiment include leucooramines, diaryl phthalides, polyaryl carbinols, acyl auramines, aryl auramines, rhodamines. Examples thereof include electron donating organic substances such as B-lactams, indolines, spiropyrans, and fluorans. Specifically, crystal violet lactone (CVL), malachite green lactone, 2-anilino-6- (N-cyclohexyl-N-methylamino) -3-methylfluorane, 2-anilino-3-methyl-6- ( N-methyl-N-propylamino) fluorane, 3- [4- (4-phenylaminophenyl) aminophenyl] amino-6-methyl-7-chlorofluorane, 2-anilino-6- (N-methyl-N -Isobutylamino) -3-methylfluorane, 2-anilino-6- (dibutylamino) -3-methylfluorane, 3-chloro-6- (cyclohexylamino) fluorane, 2-chloro-6- (diethylamino) fluorane 7- (N, N-dibenzylamino) -3- (N, N-diethylamino) fluorane, 3,6-Bis ( Ethylamino) fluorane-γ- (4′-nitro) anilinolactam, 3-diethylaminobenzo [a] -fluorane, 3-diethylamino-6-methyl-7-aminofluorane, 3-diethylamino-7-xylidinofluor Oran, 3- (4-diethylamino-2-esoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-diethylaminophenyl) -3- (1 -Ethyl-2-methylindol-3-yl) phthalide, 3-diethylamino-7-chloroanilinofluorane, 3-diethylamino-7,8-benzofluorane, 3,3-Bis (1-n-butyl- 2-Methylindol-3-yl) phthalide, 3,6-dimethylethoxyfluorane, 3-diethylamino-6-methoxy Ci-7-aminofluorane, DEPM, ATP, ETAC, 2- (2-chloroanilino) -6-dibutylaminofluorane, crystal violet carbinol, malachite green carbinol, N- (2,3-dichlorophenyl) leucoora Min, N-benzoyl auramine, rhodamine B lactam, N-acetyl auramine, N-phenyl auramine, 2- (phenyliminoethanedilidene) -3,3-dimethylindoline, N-3,3-trimethylindolino Benzospiropyran, 8'-methoxy-N-3,3-trimethylindolinobenzospiropyran, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-6- Benzyloxyfluorane, 1,2 Benz-6-diethylaminofluoran, 3,6-di -p- toluidino-4,5-dimethyl fluoran - phenyl hydrazide -γ- lactam, 3-amino-5-methyl fluoran, and the like. These can be used alone or in combination of two or more. Appropriate selection of a color developing compound makes it possible to obtain various colors, and thus it is easy to handle colors. Among these, particularly suitable materials are triphenylmethane-based, fluoran-based, and phenyl-indole-phthalide-based color formers.

  The color developing compound of the present embodiment is obtained by introducing a terminal amino group-substituted linear alkyl group into the skeleton, and the linear alkyl group preferably has 3 to 6 carbon atoms. Those having 2 or less carbon atoms are extremely difficult to synthesize, while those having 7 or more carbon atoms are difficult to synthesize.

  As an electron-accepting color-forming compound having such a terminal amino-substituted linear alkyl group, 7- [2- (4-Amino-butoxy) -4-diethylamino-phenyl] -7- (1-ethyl-2- methyl-1H-indol-3yl) -7H-furo [3,4-b] pyridin-5-one.

[Dye compound]
The dye compound of the present embodiment is obtained by reacting the color developing compound with a developer. Hereinafter, the developer will be described.

(Developer)
The dye compound of the present embodiment can be obtained by allowing a developer to act on the above-described electron accepting compound having a terminal amino group-substituted linear alkyl group.
As the developer of the present embodiment, phenols, phenol metal salts, carboxylic acid metal salts, benzophenones, sulfonic acid, sulfonate, phosphoric acid, phosphoric acid metal salt, acidic phosphate ester, acidic phosphate ester Examples thereof include metal salts, phosphorous acids, and metal phosphites, which are used alone or in combination. Among these materials, particularly preferred materials are specifically described. Color-degrading acid, methyl-dichromate, ethyl-dichromate, n-propyl-dichromate, i-propyl-dichromate, color-develop Dichromic acid esters such as butyl acid, dihydroxybenzoic acid such as methyl 2,3-dihydroxybenzoate, methyl 3,5-dihydroxybenzoate and esters thereof, 2,4-dihydroxyacetophenone, 2,5-dihydroxyacetophenone, 2,6 -Hydroxyacetophenones such as dihydroxyacetophenone, 3,5-dihydroxyacetophenone, 2,3,4-trihydroxyacetophenone, 2,4-dihydroxybenzophenone, 4,4'-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 2,4,4′-trihydroxybenzophenone, 2,2 ′, 4,4 ′ -Hydroxybenzophenones such as tetrahydroxybenzophenone, 2,3,4,4'-tetrahydroxybenzophenone, biphenols such as 2,4'-biphenol and 4,4'-biphenol, 4-[(4-hydroxyphenyl) methyl] -1,2,3-benzenetriol, 4-[(3,5-dimethyl-4-hydroxyphenyl) methyl] -1,2,3-benzenetriol, 4,6-bis [(3,5-dimethyl- 4-hydroxyphenyl) methyl] -1,2,3-benzenetriol, 4,4 ′-[1,4-phenylenebis (1-methylethylidene) bis (benzene-1,2,3-triol)], 4 , 4 ′-[1,4-phenylenebis (1-methylethylidene) bis (1,2-benzenediol)], 4,4 ′, 4 ″ -ethylidenetris Phenol, 4,4 '- (1-methylethylidene) bisphenol, and polyhydric phenols such as methylene tris -p- cresol.
Among these, particularly suitable materials are gallic acid ester-based, hydroxybenzophenone-based, and hydroxyacetophenone-based materials, and ethyl gallate or propyl gallate is suitable.
The developer is preferably blended in an approximately equimolar amount with respect to the dye compound.

[Image forming materials]
The image forming material of the present embodiment is obtained by blending the above-mentioned dye compound with a decoloring agent and, if necessary, other additives, coloring at room temperature, and processing with heating or a solvent. The color is erased by. Hereinafter, these materials will be described.

(Decolorizer)
In order to constitute a decolorable image forming material, it is formed by adding a decoloring agent (sometimes called an erasing agent) to the dye compound. The color erasing agent used in the present embodiment is a material preferentially compatible with one of the color developing compound and the color developer, and this color erasing is performed when the image forming material is heated to a high temperature. The agent is preferentially compatible with the color developing compound or the developer to make the image forming material unemployed.
Examples of the decolorizer include sterol compounds, cholic acid, lithocholic acid, testosterone, cortisone, and hydroxyl group-containing alicyclic compounds. As these decoloring agents (erasing agents), for example, those described in JP-A-10-088046 can be used.

(Other additives)
In the erasable toner using the coloring matter, a wax for controlling the fixing property may be blended if necessary. The waxes used in the present invention are preferably composed of components composed of higher alcohols, higher ketones and higher aliphatic esters, and are preferably 10 or less if defined by the acid value. Further, those having a weight average molecular weight of 102 to 104 are preferably used. Within such a range, low molecular weight polypropylene, low molecular weight polyethylene, low molecular weight polybutylene, low molecular weight polyalkane and the like can also be used. These added amounts are preferably 0.5 to 10 parts by weight.

(How to use image forming materials)
The image forming material of the present embodiment can be used in various forms. For example, ink for thermal printers; ink for inkjet printers; toner for copiers (PPC), laser beam printers, fax machines, etc .; printing ink for screen printing, type printing, etc .; ink for writing instruments such as ballpoint pens and fountain pens it can. Thermal printer ink is used by mixing a color developing compound, a developer, a color erasing agent, a wax and the like and applying the mixture to a plastic sheet. Ink jet printer ink is used by dispersing a color developing compound, a developer, a decoloring agent, and the like in a solvent. The toner is prepared by pulverizing a composition containing a color developing compound, a developer, a color erasing agent, a binder and the like. In this case, typical binders include polystyrene, styrene-acrylic copolymer, polyester, epoxy resin, and the like.
An image formed with this image forming material can be decolored by heating, and the paper on which the image is formed can be reused.

Example 1
A color-forming compound having an amino group at the tip of an alkyl straight chain was synthesized by the method represented by the following chemical formula 2.
As a result of elemental analysis, the obtained compound had a molecular formula of C ₃₂ H ₃₈ N ₄ O ₃ and was a pale yellow powder having a molecular weight of 526.68.
This compound was analyzed by LC-MS analysis (liquid chromatography mass spectrum analysis), IR (infrared absorption spectrum), and NMR spectrum. As a result, the parent peak was 527 in LC-MS analysis. In IR analysis, characteristic peaks such as 3420 cm ⁻¹ (broad NH ₂ ) and 1757 cm ⁻¹ (C═O: carbonyl of the leucolactone ring) were detected.
The results of NMR analysis were as follows.

¹ H-NMR TMS standard ppm
1.1 (m, 2H x 2, −OCH ₂ − CH ₂ − CH ₂ −CH ₂ −NH ₂ )
1.1 (t, 3H x 2, J = 7.0Hz)
1.2 (t, 3H x2, J = 7.0Hz): Derived from N-ethyl group of indole ring
2.4 (s, 3H): derived from the methyl group of the indole ring
3.1 (q, 2H x2, J = 7.0Hz): derived from diethylamino group
3.2 (m, 2H x2, indole ring _{N- CH 2, CH 2 -NH 2} )
2.2 (s, 3H, CH ₃ )
4.1 (q, 2H, O−CH ₂ )
6.1−8.8 (s, d, dd, m, etc.CH = x10)

¹³ C { ¹ H}
NMR TMS standard ppm
11.2, 12.3, 14.7 = one in CH ₃ x4 is equivalent
24.9, 25.5, 36.9, 43.5, 66.8, 67.0 = one of CH ₂ x7 is equivalent
91.4 Quaternary carbon of lactone ring
95.9 to 168.2 The aromatic ring has 19 carbon atoms. Inner tertiary carbon x10, quaternary carbon x9
95.9, 102.6, 108.9, 118.7, 120.1, 121.1,
123.3, 131.4, 133.4, 154.1: tertiary carbon
108.9, 111.7, 119.2, 125.9, 134.1, 134.9,
149.7, 158.4, 168.2: quaternary carbon
172.7
C = O carbon of lactone ring

As a result of these analyses, the compound is represented by Formula 1.
7- [2- (4-Amino-butoxy) -4-diethylamino-phenyl] -7- (1-ethyl-2-methyl-1H-indol-3yl) -7H-furo [3,4-b] pyridin- It was confirmed to be 5-one.

化学式１

Chemical formula 1

化学式２

Chemical formula 2

This color developing compound was reacted in toluene with an equimolar amount of ethyl gallate as a developer to obtain a dye compound. When the visible spectrum was measured in toluene, the maximum absorption wavelength was 590 nm and the absorption intensity was 1.4. The dye of blue 203 (Yamada Chemical), which has the same color development skeleton as this dye, does not develop much color with toluene alone, and the color development rate is about 1/13. In this blue 203, it is known that the color development rate increases when a little acetone is added, and the color disappears when a certain amount or more is added.
The dye system was decolorized in the same manner when 5% acetone was added. The relationship between acetone content and absorbance was measured. The result is shown in FIG.

  It was confirmed that the dye developed blue with a normal phenolic developer and was erased by heating or solvent.

  This dye compound is presumed to be stabilized by hydrogen bonding of ethyl gallate (abbreviated as EG), the developer, with the amino group at the end of the linear alkyl group. As in this example, it is considered that the amino group in the newly introduced dye contributes to the dissolution of the developer in this family of compounds.

(Comparative Example 1)
In the above Examples, instead of the amino group introduced at the end of the linear alkyl group, a color developing compound having a hydroxyl group was synthesized by the method shown in the following chemical formula 4.
As a result of elemental analysis, the obtained compound was a white powder having a molecular formula of C ₃₂ H ₃₇ N ₃ O ₄ and a molecular weight of 527.67.

化学式３

Chemical formula 3

化学式４

Chemical formula 4

This compound was analyzed by LC-MS analysis (liquid chromatography mass spectrum analysis), IR (infrared absorption spectrum), and NMR spectrum.
As a result, the parent peak was 528 in LC-MS analysis. As a result of IR analysis, characteristic peaks such as 3438 cm ⁻¹ (broad OH) and 1759 cm ⁻¹ (C═O: carbonyl of the leucolactone ring) were detected.
The results of NMR analysis were as follows.
¹ H-NMR TMS standard ppm
1.04 to 1.09 (m, 4H, −OCH ₂ − CH ₂ − CH ₂ −CH ₂ −OH)
1.06 (t, 6H, J = 7.0Hz, CH ₂ x2: diethylamino group)
1.2 (t, 3H, J = 7.0Hz, CH ₃ )
1.2 (t, 3H x2, J = 7.0Hz): Derived from N-ethyl group of indole ring
2.4 (s, 3H): derived from the methyl group of the indole ring
3.1 (q, 2H x2, J = 7.0Hz): derived from diethylamino group
3.2 ~3.3 (m, 2H, the indole ring _{N- CH 2, CH 2 -NH 2} )
3.6 (m, 2H, CH ₂ OH)
4.1 (m, 3H, O-CH _2, OH)
6.1−8.8 (s, d, dd, m, etc.CH = x10)

¹³ C { ¹ H}
NMR TMS standard ppm
12.3, 12.3, 14.7 = one in CH ₃ x3 is equivalent
24.8, 28.5, 36.9, 43.5, 60.1, 67.1 = one of CH ₂ x7 is equivalent
91.4 Quaternary carbon of lactone ring
95.8 to 168.2 The aromatic ring has 19 carbon atoms. Inner tertiary carbon x10, quaternary carbon x9
95.8, 102.6, 108.9, 118.7, 120.1, 121.1,
123.2, 131.4, 133.4, 154.0: tertiary carbon
108.9, 111] .7, 119.2, 125.9, 134.1, 134.9,
149.7, 158.4, 168.2: quaternary carbon
172.8
C = O carbon of lactone ring

From these information, the compound is represented by the chemical formula 3.
7- [4-Diethylamino-2- (4-hydroxy-butoxy) -phenyl] -7- (1-ethyl-2-methyl-1H-indol-3yl) -7H-furo [3,4-b] pyridin- It was confirmed to be 5-one.

  This dye reacts with the developer EG in toluene and is slightly colored, but the strong color developing effect as in Example 1 was not observed. In other words, the amino group was found to be more effective.

It was confirmed that the dye developed blue with a normal phenolic developer and was erased by heating or solvent.

(Example 2)
In the same manner as in Example 1 above, as shown in Table 1 below, a coloring compound synthesized by changing the number of carbon atoms of a linear alkyl group and a compound containing a hydroxyalkyl group for comparison were synthesized and the characteristics thereof were obtained. evaluated. In addition, the characteristics of the leuco dye compound having no linear alkyl group were evaluated.
In Table 1, various leuco dyes may be abbreviated as “CnNH 2”. This indicates that a linear alkyl group having n carbon atoms is bonded to the electron-accepting color developing compound, and an amino group is bonded to the terminal. “BlueC5OH” represents that a linear alkyl group having a carbon number is bonded to the skeleton of the leuco dye compound of the following chemical formula 5, and a hydroxyl group is bonded to the terminal.

化学式５

Chemical formula 5

  In addition, it is impossible to synthesize an aminoalkyl group-containing color-forming compound when the alkyl group has 2 carbon atoms, whereas when the alkyl group has 7 or more carbon atoms, synthesis is extremely difficult. The synthesis was not practical.

  In Table 1 above, Blue 203 is a commercial product of Yamada Chemical and is a compound represented by the following chemical formula 5.

  As shown in the above comparative example, it is the color developing compound of the present invention in which an amino group is attached to the end of a straight chain that can react with EG in a toluene alone solvent, and is effective in the comparative compound having a hydroxyl group. It was reconfirmed that there was no. Also from this table, it can be seen that the alkyl group having 5 carbon atoms has a slightly large absorption strength. Moreover, it is imagined that the color development in acetic acid is governed by completely different conditions even from the size of ε.

  Further, FIG. 2 shows the color development depending on the temperature for straight chain alkyl groups having 3, 4, 5, 6 carbon atoms. As a result, it can be seen that the compound having 5 carbon atoms is exceptionally superior to the temperature change.

From this, the relationship between the temperature characteristics and the equilibrium constant was calculated. The result is shown in FIG.
From the above results, it can be estimated that the compound having an alkyl group having 5 carbon atoms has an advantageous length when dissolving the EG crystal.

In addition, an equilibrium standard generation enthalpy change was obtained for the color developing compound of the present invention. As a result, it was found that the standard enthalpy of formation of the compound having 5 carbon atoms had a smaller absolute value than the other compounds, and it was quantitatively shown that it was advantageous for the formation of the chromophore.

(Example 3)
C4 dye [MW. 526.68], developer EG (ethyl gallate) [MW: 198.17] 22 g, polystyrene butadiene copolymer resin 997 g, LR147 (Nippon Carlit) as a charge control agent, polypropylene wax 55 g Mix and knead with a kneader. The kneaded product was cooled, coarsely pulverized, then finely pulverized with a jet mill, and classified to obtain an image forming material which was a blue powder of about 10 microns. When the powder concentration was measured with a Minolta color difference meter, it was 0.85, indicating a sufficient concentration. When this powder was put on acetone, the color disappeared, and it was confirmed that it could be used as an erasable toner. The powder concentration was lower than expected.

Example 4 Color Developer and Coloring Temperature Region Using the color developing compound obtained in Example 1, the temperature dependence of color development was examined. Fig. 4 shows color development using leuco dyes with different linear lengths of amino groups by using two colorants, ethyl gallate (EG) and 2,4-Dhydroxybenzophenon (DHBP). The temperature dependence of was measured.
From this result, it became clear that even when any developer was used, the color disappeared more rapidly with the temperature rise, but when EG was used, the color was developed even in a high temperature region of about 20K (Kelvin). .
From this result, in the case of EG, a linear length of 5 carbon atoms is more colored than that of 4 carbon atoms or 6 carbon atoms, so an appropriate length is required. In the case of DHBPs having different structures, those having 4 carbon atoms and those having 5 carbon atoms are almost the same, so it is presumed that the linear amino group plays an important role in color development. In the color development of the leuco dye, it is considered that the phenolic hydroxyl group approaches the CO of the leucolactone ring and hydrogen bonds, and it has been found that there are at least two interactions between the dye and the developer.

(Example 5) Evaluation in benzoate system Using C5NH2 that was most colored by the above-mentioned several kinds of novel leuco dyes, this time, the developer was changed and the evaluation was performed in a toluene-only solvent. The developer used is a benzoate system shown below, and EG has an OH group at the 3,4,5-position. It can be quantitatively understood that the difference in performance is very large because only EG is carried out at a concentration one digit lower and this value is obtained. The color development rate of the leuco dye is complicated because it has a non-linear density dependency, but the 2,6-position and 4-position developers, which were difficult to develop, did not develop much color even when the density was increased. On this graph, in case of 4-, it is measured by adding 4 times amount. 2,6- did not develop color even when 10 times the amount (0.1 mol / l) was added.
2,6-dihydroxyethyl benzoate 2,4-dihydroxyethyl benzoate 3,5-dihydroxyethyl benzoate 4-hydroxyethyl benzoate 3,4-dihydroxyethyl benzoate 3,4,6-trihydroxyethyl benzoate 3 The relationship between the concentration of the dye using 1,4-dihydroxyethyl benzoate and the color development was examined. The result is shown in FIG.

This time, a compound having a structure similar to EG was evaluated by changing the number and position of OH groups. FIG. 6 below shows the results of changes in coloration rate (%) observed by changing the temperature. A very remarkable result was found that EG with three OHs had the greatest color developability and only one in the 2,6-position or 4-position contributed little to color development. From the results of 2,6-, it can be seen that even if the number of OH groups is the same, if the substitution position is bad, it cannot contribute to color development.

(Example 6)
In the pigment compound of Example 1, a pigment compound was formed using propyl gallate instead of ethyl gallate as the developer.
As a result, it was confirmed that the absorbance was 1.32 at 25 ° C. at a concentration of 1 × 10 ⁻³ mol / l. This was a good result compared to EG.

The graph which shows the relationship between acetone content and light absorbency in a mixed solvent. The graph which shows the relationship between temperature and a light absorbency. The graph which shows the relationship between temperature and an equilibrium constant. The graph which shows the relationship between the temperature and the light absorbency for every pigment | dye. The graph which shows the relationship between the pigment | dye density | concentration using 3, 4- dihydroxyethyl benzoate, and a light absorbency. The graph which shows the temperature dependence of the color development rate by BlueC5NH2 benzoate type developer.

Claims (5)

It is a color- forming compound containing an electron-accepting phenyl-indole-phthalide compound, and has a straight-chain alkyl group having 3 to 6 carbon atoms having a terminal amino substitution in the skeleton of the color-forming compound. Characteristic color developing compound. It is a reaction product of a color developing compound containing an electron-accepting phenyl-indole-phthalide compound and a developer, and the number of carbons having a terminal amino substitution on the skeleton of the color developing compound is 3 to 6 A dye compound having a straight-chain alkyl group of 3. The coloring compound according to claim 2, wherein the developer is at least one selected from gallic acid ester compounds, hydroxybenzophenone compounds and hydroxyacetophenone compounds. 4. The coloring compound according to claim 3, wherein the developer is a gallic acid ester compound. Reaction of a color-forming compound containing an electron-accepting phenyl-indole-phthalide compound with at least one developer selected from a gallate ester compound, a hydroxybenzophenone compound and a hydroxyacetophenone compound And a color erasing agent capable of capturing the developer, wherein the skeleton of the color developing compound has a linear alkyl group having 3 to 6 carbon atoms substituted with a terminal amino group. Image forming material

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