JP2000160041A - Black leuco dye for erasable image-forming material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a black leuco dye, which is applied to an erasable image- forming material in combination with a color developer and a bleaching agent, thereby realizing a high image intensity when a color is developed and a low image intensity when the color is bleached, thus ensuring a good contrast. SOLUTION: This black leuco dye is of the formula. In the formula, X represents a hydrogen atom or an alkyl group; Y represents an unsubstituted or substituted anilino group; R1 and R2 independently represent an alkyl group provided that at least one thereof is a 5C or higher alkyl group. It is preferred that at least one of R1 and R2 is a branched alkyl group, and more preferably, the branched group includes, for example, an isopentyl group, 2-methylbutyl group or 1-methylbutyl group. The color developer includes, for example, a gallate, 2,3-dihydroxybenzoic acid or the like. The bleaching agent is broadly classified into a low molecular weight bleaching agent and a high molecular weight bleaching agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a black leuco dye used for an erasable image forming material containing a leuco dye, a developer and a decolorant.

[0002]

2. Description of the Related Art In recent years, as office automation has progressed, the amount of various types of information has increased remarkably, and the output of information by hard copy has also increased accordingly. Hard copy output is the most basic information display means,
Excellent versatility and storage stability. However, in the case of hard copy output, as information increases, a large amount of paper is used as a recording medium, which leads to an increase in the cutting of wood used as a raw material for paper. Forest resources are very important in terms of maintaining the global environment and controlling the greenhouse effect of carbon dioxide. For this reason, logging of new timber is minimized,
A major challenge is to make efficient use of paper resources that we already have.

Conventionally, the reuse (recycling) of paper resources is
It is carried out by treating paper on which an image forming material is printed with a large amount of bleach and water, and remaking the paper fibers to produce recycled paper of poor paper quality. Such a method not only increases the cost of recycled paper, but also causes new environmental pollution associated with the treatment of waste liquid.

On the other hand, the present inventors have proposed leuco dyes,
Contains a developer and a decoloring agent compatible with these compounds, can form an image in the same manner as a normal image forming material, and can be erased by treating with heat or a solvent. We are developing image forming materials. When such an erasable image forming material is used, the paper whose image has been erased and returned to a blank state can be reused (reused) many times while minimizing deterioration of the paper quality. Since the paper may be recycled when the quality of the paper due to reuse becomes remarkable, the utilization efficiency of the paper resources is dramatically improved. In this manner, substantial paper usage can be reduced, and logging of timber can be minimized. In addition, the high cost of recycled paper and the environmental pollution caused by waste liquid treatment, which are problems in the current recycling system, can be avoided as much as possible.

[0005] Leuco dyes as color-forming compounds have been applied to heat-sensitive paper and pressure-sensitive paper. In such applications, an appropriate leuco dye is selected with emphasis on good color development, light stability and stability over time. But,
The erasable image forming material needs to satisfy both conditions of high image density at the time of coloring and low image density at the time of erasing. In this regard, the most appropriate leuco dye for an erasable image forming material has not always been selected, and it has not been clear what leuco dye is suitable.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a black leuco dye which is applied to an erasable image forming material and exhibits a high image density at the time of color development and a low image density at the time of color erasure, and provides good contrast. Is to provide.

[0007]

The first black leuco dye for an erasable image forming material according to the present invention is an erasable image forming material containing a leuco dye, a developer and a decolorant. A black leuco dye used in the following general formula (I)

[0008]

Embedded image

Wherein X is selected from the group consisting of a hydrogen atom and an alkyl group; Y is an unsubstituted or substituted anilino group; R ₁ and R ₂ are alkyl groups; 5 or more alkyl groups.)
It is characterized by being represented by

The second black leuco dye for an erasable image forming material according to the present invention comprises a leuco dye, a color developer and a binder resin, and the binder resin is contacted with a solvent or heated to form the leuco dye. Or a black leuco used in an erasable image forming material which is compatible with any one of the color developing agents, and maintains the compatible state even after the solvent is volatilized or cooled, and maintains the erased state of the image. A dye having the following general formula (I)

[0011]

Embedded image

(Wherein X is selected from the group consisting of a hydrogen atom and an alkyl group, Y is an unsubstituted or substituted anilino group, R ₁ and R ₂ are alkyl groups, at least one of which has carbon atoms 5 or more alkyl groups.)
It is characterized by being represented by

The third black leuco dye for an erasable image forming material of the present invention contains a leuco dye, a color developer, and a binder resin, and is contacted with a solvent or heated to develop the leuco dye. Equilibrium with the colorant shifts to the non-color-developing side, and even after volatilization or cooling of the solvent, the equilibrium shifted to the non-color-developing side is maintained so that the image remains erased. A leuco dye having the following general formula (I)

[0014]

Embedded image

(Wherein X is selected from the group consisting of a hydrogen atom and an alkyl group, Y is an unsubstituted or substituted anilino group, R ₁ and R ₂ are alkyl groups, at least one of which has at least one carbon atom 5 or more alkyl groups.)
It is characterized by being represented by

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The image forming material according to the first aspect of the invention is a material from which very good color development / decoloration performance can be obtained. here,
The image density in the color-developed state is D _C , the image density in the decolored state is D _D ,
When the reflection density of paper (background) is D _P ,
The contrast between the colored portion and the erased portion is (D _C -D _P ) / (D
_D− D _P ). The first image forming material of the present invention aims to obtain good color development / erasing performance with an image density of 1.05 or more at the time of color development and a contrast of 20 or more.

The image forming material according to the first aspect of the present invention is capable of developing and decoloring by using a leuco dye, a color developer and a decolorant. That is, the leuco dye develops color by interaction with the color developer (mainly transfer of electrons). on the other hand,
When the composition is heated or brought into contact with a solvent, the color developer mixes with the decolorant and the leuco dye does not interact with the color developer, so that the color is erased. Therefore, in order to obtain a high image density at the time of color development, the leuco dye is well bonded to the color developer, and to obtain a low image density at the time of color erasing, when the color developer and the decolorant are compatible, It is necessary that the dye no longer binds to the developer. These phenomena are thought to be governed by the electron-withdrawing properties and the three-dimensional structure of the leuco dye,
The molecular structure of the leuco dye is an important factor.

In the present invention, a high image density at the time of coloring and a low image density at the time of erasing are realized by using the black leuco dye represented by the general formula (I).

X in the general formula (I) is selected from the group consisting of a hydrogen atom and an alkyl group. The alkyl group preferably has 1 to 4 carbon atoms, and most preferably a methyl group or an ethyl group. Y in the general formula (I) is an unsubstituted or substituted anilino group, for example, anilino group, N-methylanilino group, 2,4-dimethylanilino group, 2,4,6-trimethylanilino group, 3-trifluoro And a methylanilino group.

In the general formula (I), R ₁ and R ₂ are alkyl groups, at least one of which is an alkyl group having 5 or more carbon atoms.

[0022] When R ₁ and R ₂ are both alkyl groups having 5 or more carbon atoms, higher image density D _C of the colored state, it is possible to lower the image density D _D decoloring state. 5 carbon atoms
Is preferably 10 to 10, and more preferably 5 to 8.

R ₁ is a linear alkyl group having 5 or more carbon atoms,
When R ₂ is an alkyl group having 4 or less carbon atoms, it is possible to lower the image density D _D of colorless state to a practical level. In this case, in order to improve the image density D _C of the color state,
R ₁ is preferably a straight-chain alkyl group having 6 to 10 carbon atoms.

R ₁ is a branched alkyl group having 5 or more carbon atoms,
Even when R ₂ is an alkyl group having 4 or less carbon atoms, an image density D _C of colored state high, it is possible to lower the image density D _D decoloring state. As particularly preferred branched alkyl groups,
Examples include an isopentyl group, a 2-methylbutyl group, and a 1-methylbutyl group.

On the other hand, when R ₁ and R ₂ are both alkyl groups having 4 or less carbon atoms, often the image density D _D of decolored state is not lowered, also the image density D _C of the colored state may not be sufficient is there.

[0026] At least one of R ₁ and R _2, for example, when a structure having an aromatic ring such as tolyl, often the image density D _C of the colored state is not sufficient,
The aging stability may be deteriorated. This is considered to be because the positive charge generated at the nitrogen atom adjacent to the aromatic ring in the color-developing state is further delocalized, and the interaction with the color developer is weakened.

When R ₁ is an alicyclic structure having 5 or more carbon atoms, an alkyl group containing an oxo group, or a structure containing an anilino group, and R ₂ is an alkyl group having 3 or less carbon atoms or a hydrogen atom, the color development state image density D _C is often not sufficient.

Examples of the color developing agent used in the present invention include phenol, phenol metal salt, carboxylic acid metal salt, benzophenone, sulfonic acid, sulfonate, phosphoric acid, metal phosphate, acid phosphate, acid phosphate. Acid compounds such as ester metal salts, phosphorous acid, and metal phosphites are exemplified. Among these, preferred color developers include gallic acid ester, 2,3-dihydroxybenzoic acid, dihydroxybenzoic acid ester, hydroxyacetophenone, hydroxybenzophenone and biphenol.
These can be used alone or in combination of two or more.

The color erasing agent used in the first invention is roughly classified into a low molecular weight erasing agent and a high molecular weight erasing agent.

Examples of the low-molecular color decoloring agent which functions alone include sterol compounds such as cholic acid, methyl cholate, pregnenolone, methylandrostenediol, β-sitosterol, and hecogenin, and derivatives thereof.

A polar organic low molecular compound that does not function alone as a decolorizing agent and an organic low molecular compound (phase separation inhibitor) having a high function of suppressing phase separation of each component are used in combination as a decolorizing agent. You may. Examples of the polar organic low molecular compound include alicyclic monohydric alcohols such as cyclododecanol, menthol, isomenthol, and terpineol; alicyclic polyhydric alcohols such as cyclohexanediol and cyclododecanediol; polycyclic alcohol derivatives; For example, borneol, isoborneol,
Adamantanol, camphor and the like; cyclic sugar alcohol derivatives such as 1,2,5,6-diisopropylidene-D-mannitol and the like. One or more of these can be used. Examples of the phase separation inhibitor include cyclic sugar alcohols and derivatives thereof, for example, D-glucose, D-mannose, D-galactose, D-fructose, vitamin C, saccharose, maltose, lactose and the like. One or more of these can be used.

Examples of the polymeric decolorizing agent (polymer or oligomer) include starch, cereal powder containing starch as a main component, starch derivatives (eg, methylated starch, acetylated starch, nitrated starch), cellulose, and cellulose derivatives. (Including cellulose acetate, ethylated cellulose, and nitrated cellulose), polysaccharides and derivatives thereof (such as dextrin, mannan, amylose, glycogen, chitin, and pectin), and polyamino acids (including skeletons such as threonine, serine, lysine, and histidine). thing),
Glycoproteins (collagen, Taka-amylase A, casein,
Germ glycoprotein, ovalbumin, etc.), polyvinyl alcohol, polyvinyl acetal, polyacrylonitrile, polyvinyl pyridine, polyvinyl imidazole, polyvinyl pyrrole, polyvinyl carbazole and other high molecular compounds and derivatives thereof, quaternary ammonium salt substituted polystyrene and ethylene diamine skeleton Substituted by an amino group having the formula:

The image forming material according to the first invention may contain, as other components, for example, a binder resin or a wax having a function of fixing on paper.

The binder resin that can be used in the first invention is not particularly limited as long as it is a resin used in a usual electrophotographic toner or ink ribbon. As the binder resin for a toner, those having a glass transition point of 40 ° C. or higher are preferable from the viewpoint of temperature stability. Specifically, polystyrene, styrene-acrylate copolymer,
Styrene-acrylic acid copolymer, styrene-methacrylate copolymer, styrene-methacrylic acid copolymer, polyester, epoxy resin, styrene-butadiene copolymer, styrene-propylene copolymer, styrene-maleic acid ester copolymer And a styrene-maleic anhydride copolymer. These may be used alone or in a blend. The binder resin for thermal transfer ink has a glass transition point of 70 from the viewpoint of thermal transfer sensitivity.
C. or lower is preferred. Specific examples include an ethylene-vinyl acetate copolymer and polyester. These may be used alone or in a blend.

Examples of the wax that can be used in the first invention include higher alcohols, higher ketones, higher fatty acid esters, low molecular weight polypropylene, low molecular weight polybutylene, low molecular weight polyalkane, and natural wax (for example, rice wax). . These preferably have a weight average molecular weight of 10 ² to 10 ⁵ , more preferably 10 ² to 10 ⁴ . The wax preferably has an acid value of 10 or less.

The image forming material according to the second or third invention comprises a composition containing leuco dye, a color developer and a binder resin as essential components and not containing a decoloring agent. Although good erasing performance is not obtained, it can be used sufficiently practically.

With respect to the image forming material according to the second or third aspect of the present invention, erasing means (a) the reflection density of the image area after erasure is reduced to 1/3 or less of the reflection density of the formed image. Or (b) the difference between the reflection density of the image area after erasing and the reflection density of the background is 0.1 or less. More preferably, both conditions (a) and (b) are satisfied. This condition requires a lower level of erasing performance than the condition applied to the first image forming material, in which the image density at the time of color development is 1.05 or more and the contrast is 20 or more.

In the above-described image forming material, the leuco dye (L), which is a color-forming compound, and the developer (D) are combined to form a complex (LD) in which color is developed. This reaction is reversible, and the following equilibrium holds.

[L] + [D] ← → [LD] In the image forming material according to the second or third invention, an image is erased by one of the following two mechanisms.

(1) When an image forming material containing a leuco dye, a developer and a binder resin is brought into contact with a solvent or heated, the binder resin is compatible with either the leuco dye or the developer, The compatible state is maintained even after the solvent is volatilized or cooled, and the state where the image is erased is maintained.

(2) When an image forming material containing a leuco dye, a developer and a binder resin is brought into contact with a solvent or heated, the equilibrium between the leuco dye and the developer is shifted to a non-color-developing side, Even after the solvent is volatilized or cooled, the equilibrium shifted to the non-color-developing side is maintained, and the state where the image is erased is maintained.

As described for the image forming material of the first invention, these mechanisms are also affected by the electron-withdrawing property and the three-dimensional structure of the leuco dye, and the black leuco represented by the general formula (I) is affected. By using a dye, a high image density at the time of color development and a low image density at the time of color erasure can be realized.

In the image forming material according to the second or third invention, the same compounds as described for the image forming material of the first invention can be used as the color developer.

The erasing performance of the image forming material according to the second or third aspect of the present invention is significantly affected by the binder resin. The binder resin used in the image forming material of the second or third invention is preferably one having high compatibility with the leuco dye and low compatibility with the color developer. Examples of such a binder resin include polystyrene, styrene-acrylate copolymer, styrene-acrylic acid copolymer, styrene-methacrylate copolymer, and styrene-methacrylic acid copolymer described for the image forming material of the first invention. , Polyester, epoxy resin, styrene-butadiene copolymer, styrene-propylene copolymer, styrene-maleic acid ester copolymer, styrene-maleic anhydride copolymer, among others, especially polystyrene, and the molar content of styrene units A copolymer having a ratio of 30% or more, more preferably 70% or more, is suitable.

In the image forming material according to the second or third aspect, the same wax component as that described for the image forming material according to the first aspect can be used.

The image formed by using the image forming material according to the present invention can be erased by heating or by bringing it into contact with an erasing solvent.

In the erasing of an image by heating, the heating temperature of the first image forming material is higher than the melting point when a low molecular weight decolorizing agent is used and higher than the melting point when a high molecular weight decolorizing agent is used. Is set above its softening point. For the second or third image forming material, the heating temperature is set to be equal to or higher than the softening point of the binder resin. Specifically, the heating temperature is preferably 80 ° C. or higher, and is preferably 250 ° C. or lower in order to prevent paper deterioration. The heating time is arbitrarily set within a range where the image is not erased and the paper quality is not deteriorated. Specifically, it is 1 to 24 hours at 150 ° C or less, 10 minutes to 1 hour at 150 to 200 ° C, and 10 minutes or less at 200 ° C or more.

The erasing solvent is required to have the following characteristics. (1) The erasing solvent facilitates the decoloring agent or the binder resin to physically or chemically adsorb and take in and retain the color developer. (2) The erasing solvent can penetrate into the inside of the image forming material on the paper surface, and does not dissolve the binder resin until volatilized.

Suitable erasing solvents include ethers such as ethyl ether, ethyl propyl ether, tetrahydrofuran, tetrahydropyran and the like; cellosolves such as 2-methoxyethanol, 2-ethoxyethanol, 1,2-dimethoxyethane, 1,1 2-diethoxyethane and the like; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, diethyl ketone,
Cyclopentanone, cyclohexanone, etc .; esters,
For example, ethyl acetate, ethyl lactate, methyl propionate, ethyl butyrate and the like can be mentioned. As other solvents, methylene chloride, N-methylpyrrolidinone, dimethylformamide, dimethylacetamide, dimethylsulfoxide and the like are also used. These solvents may be used alone or in combination of two or more. In this case, the mixing ratio is not particularly limited.

In addition to the erasing solvents described above, there are solvents that can exhibit erasing characteristics depending on the wax or binder resin used. Such solvents include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, and the like,
Water, a basic aqueous solution and the like can be mentioned. In particular, it is effective for an image forming material having a large proportion of wax, such as crayon.
When these solvents are added to the erasing solvents described above, erasing performance may be enhanced.

In order to improve the affinity with the binder resin, another solvent may be mixed. Such solvents include, for example, toluene, xylene, cresol,
Examples include dimethoxybenzene, cyclohexane, cyclopentane and petroleum fractions (petroleum ether, benzine, etc.).

In the present invention, a decoloring agent may be added to the erasing solvent. In this case, the addition amount of the decoloring agent to the erasing solvent is not particularly limited as long as the image can be effectively erased, but the addition amount is preferably in the range of 5 to 20 wt%. Further, a decoloring agent may be added to an image recording medium such as paper. Also in this case, the amount of the decoloring agent added to the image recording medium is not particularly limited as long as the image can be effectively erased. However, considering other characteristics, the addition amount is 5 to 5.
Preferably, it is in the range of 20 wt%.

[0053]

Embodiments of the present invention will be described below.

In the following examples, the following leuco dyes were used. (E1) to (E8) are included in the general formula (I), and (C1) to (C9) are not included in the general formula (I).

[0055]

Embedded image

[0056]

Embedded image

(E1) 2-anilino-6- (N, N-
Diisopentylamino) -3-methylfluoran mp 174-176 ° C.

(E2) 2-anilino-6- (N-ethyl-N- (2-methylbutyl) amino) -3-methylfluoran Melting point 121-140 ° C.

(E3) 2-anilino-6- (N-isopropyl-N-octylamino) -3-methylfluoran Melting point 117-120 ° C.

(E4) 2-anilino-6- (N, N-
Dioctylamino) -3-methylfluoran Melting point 94-96 ° C.

(E5) 2- (2 ', 4', 6'-triethylanilino) -6- (N-ethyl-N-hexylamino) -3-methylfluoran Melting point: 139-141 ° C.

(E6) 2- (2 ', 4', 6'-triethylanilino) -6- (N-ethyl-N-isopentylamino) -3-methylfluoran Melting point 154-157 ° C.

(E7) 2- (3'-trifluoromethylanilino) -6- (N-ethyl-N-isopentylamino) fluoran Melting point: 146-148 ° C.

(E8) 2-anilino-6- (N-ethyl-N-pentylamino) -3-fluoran Melting point: 186-187 ° C.

(C1) 2- (3′-trifluoromethylanilino) -6- (N-ethyl-N-tolylamino)
Fluoran Melting point 217-218 ° C.

(C2) 2- (2 ', 4', 6'-triethylanilino) -6- (N-ethyl-N-tolylamino) -3-methylfluoran Melting point: 208-209 ° C.

(C3) 2-anilino-6- (N-methyl-N-isobutylamino) -3-methylfluoran Nippon Soda.

(C4) 2-anilino-6- (N-methyl-N-propylamino) -3-methylfluoran Nippon Soda.

(C5) 2-anilino-6- (N-cyclohexyl-N-methylamino) -3-methylfluoran Nippon Soda.

(C6) 2-anilino-6- (N, N-
(Diethylamino) -3-methylfluoran manufactured by Yamamoto Kasei.

(C7) 2- (2'-chloroanilino)
-6- (N, N-diethylamino) fluoran Melting point 94-96 ° C. Made by Hodogaya Chemical.

(C8) 2-anilino-6- (N-ethyl-N-isopropylamino) -3-methylfluoran Melting point: 214-215 ° C.

(C9) 2- (2 ', 4', 6'-triethylanilino) -6- (N, N-dibutylamino)-
3-Methylfluoran mp 179-181 ° C.

Example 1 After an image was formed on paper as described below, an experiment was performed in which the image was erased by immersing the paper in a solvent. Image density D _{C in a} color-developed state using a colorimeter (CR-300 manufactured by Minolta)
And an image density D _D of decolored state was measured, using a reflection density D _P of the paper as a background value, (D _C -D _P) /
The contrast was calculated according to the formula (D _D -D _P ).

Propyl gallate as a color developing agent, 1-docosanol as a wax, stearyl alcohol as a wax, and cholic acid as a decolorizing agent were mixed at a weight ratio of 1: 5: 5: 10. The mixture was stirred while being heated to a uniform temperature, uniformly dispersed, and then rapidly cooled to be solidified. This mixture was ground sufficiently. With respect to this mixture, the chemical formulas (E1) to (E7) and (C1) to (C) are used such that the molar ratio of the developer to the leuco dye is 2.5 times.
Add any leuco dye of (C8),
While stirring well. In this state, the mixture was poured into a mold and solidified to produce a black crayon. In this case, the content of the leuco dye in the crayon as the image forming material is about 4.
It is 3 to 4.5% by weight.

Recycled paper (manufactured by Oji Paper) is placed on a hot plate heated to 110 ° C., the crayon obtained above is pressed against the recycled paper and melted, and excess crayon is squeezed using a glass plate. After the stripping, the crayon was removed from the hot plate and fixed to form a solid image for evaluation. The image density of the color-developed state of this sample was measured. This recycled paper was immersed in diethoxyethane for 3 minutes and then dried to remove the solid image. The image density of the decolored state of this sample was measured. From these measured values, the contrast of the image density at the time of coloring and at the time of erasing was calculated. In addition, the reflection density of the recycled paper, which is the background value, was 0.134. Table 1 shows these results.
Shown in Here, the image density at the time of color development is 1.05 or more,
Those having a contrast of 20 or more were judged to be good image forming materials.

As can be seen from Table 1, when the leuco dyes (E1) to (E7) included in the general formula (I) were used, the image density at the time of color development was 1.05 or more and the contrast was 2
The criterion of 0 or more is satisfied. On the other hand, the general formula (I)
When the leuco dyes (C1) to (C8), which are not included in (1) to (4), are used, the image density or contrast at the time of coloring is not satisfied.

[0078]

[Table 1]

Example 2 2 parts by weight of 2- (3'-trifluoromethylanilino) -6- (N-ethyl-N-isopentylamino) fluoran of the formula (E7) as a leuco dye and gallic as a developer 1.5 parts by weight of propyl acid, 1 part by weight of polypropylene wax as wax, 18 parts by weight of potato starch as polymer decolorizer, 450 molecular weight as binder resin
Of polystyrene, and 1 part by weight of a charge control agent (LR-147, Nippon Carlit Co., Ltd.), and kneaded sufficiently with a kneader. The kneaded product was pulverized with a pulverizer to obtain a powder having an average particle size of 10 μm. An electrophotographic toner was prepared by externally adding 1 wt% of hydrophobic silica to 100 wt% of this powder. In this case, the content of the leuco dye in the toner as the image forming material is 2% by weight. This toner is put into a toner cartridge of a copier (Primage 38 manufactured by Toshiba), and copy paper (Neusiedler
(500 BLATT, Inc.) to transfer a solid image for evaluation.

[0080] Measurement of the image density D _C of the colored state by similarly color colorimeter as in Example 1 (Minolta CR-300), was 1.15. Incidentally, the reflection density D _P of the copy paper to be background value was 0.06.
Further, it was found that when starch was used as the decoloring agent as described above, the offset characteristics were excellent. This is because the toner has a high affinity for the paper fibers and the toner is successfully transferred from the heat roller of the copier to the copy paper.

Next, the copy paper on which the solid image was formed was immersed in the solvent shown in Table 2 for 20 seconds and then dried or passed through a heating roller to erase the image. The result of measuring the image density D _D decoloring state shown in Table 2.

As shown in Table 2, the images could be almost completely erased using any of the solvents. Also, no trace of toner flow or afterimage due to image bleeding was observed. Even when the heating roller was used, the image was successfully erased. However, slight shine was observed in the portion where the toner remained. After leaving these copy papers at 60 ° C. for 300 hours, no change was observed in the decolored state.

[0083]

[Table 2]

Example 3 As in Example 1, after forming an image on paper, an experiment was conducted in which the image was erased by immersing the paper in a solvent, and the image density D _{C in} the color-developed state and the image density in the decolored state D _D, and determine the contrast.

Chemical formulas (E1) to (E7) and (C1)
To (C8), 2 parts by weight of a leuco dye, 1.5 parts by weight of propyl gallate as a color developer, 1 part by weight of a polypropylene wax as a wax, 18 parts by weight of cholic acid as a decolorant, and a molecular weight of 45,000 as a binder resin Of polystyrene, and a charge control agent (LR)
-147, Nippon Carlit Co., Ltd.) and kneaded sufficiently with a kneader. The kneaded product was pulverized with a pulverizer to obtain a powder having an average particle size of 10 μm. This powder 100w
1 wt% of hydrophobic silica was externally added to t% to prepare an electrophotographic toner. In this case, the content of the leuco dye in the toner as the image forming material is 2% by weight.

This toner is put into a toner cartridge of a copying machine (Primage 38 manufactured by Toshiba), and copy paper (Ne
solid image for evaluation was transferred to USEDLER (500 BLATT). The image density D _C of the colored state was measured. Next, the copy paper on which the solid image was formed was immersed in diethoxyethane for 20 seconds and then dried to erase the image.
Were measured image density D _D decoloring state. The contrast was calculated by using 0.06 as the background value. Table 3 shows the results. In Table 3, it does not fill a number in the column of contrast for a sample image density D _D of colorless state matches the background value. As in the first embodiment, the image density at the time of color development is 1.0
A toner having a contrast of 5 or more and a contrast of 20 or more was determined to be a good toner.

As can be seen from Table 3, when the leuco dyes (E1) to (E7) included in the general formula (I) were used, the image density at the time of color development was 1.05 or more and the contrast was 2
The criterion of 0 or more is satisfied. Table 3 compared to Table 1
Is lower in image density at the time of color development simply because Table 3 has a lower content of leuco dye in the image forming material.
On the other hand, when the leuco dyes (C1) to (C8), which are not included in the general formula (I), are used, the image density or contrast at the time of coloring is not satisfied.

[0088]

[Table 3]

Example 4 A leuco dye represented by any one of the chemical formulas (E1) to (E8) and (C1) to (C9) was weighed to 3.4% of the total weight, and the color was developed. Propyl gallate 1.2 times molar amount as an agent, 1 part by weight of a polypropylene wax as a wax component, a charge controlling agent (manufactured by Nippon Carlit Co.,
LR-147) and 93 parts by weight of polystyrene (SB-130, manufactured by Sanyo Chemical Industries) as a binder resin were added and mixed well. The mixture was kneaded with a kneader while keeping the temperature at 80 ° C. or lower, and when the shear was stopped, the kneader was stopped and taken out, and allowed to cool at room temperature.
After coarsely pulverizing the kneaded product, it was kneaded again with a kneader, and the leuco dye and the developer were uniformly dispersed in the binder resin. The kneaded product was pulverized with a pulverizer to obtain a powder having an average particle size of 10 μm. 1 wt% of hydrophobic silica was externally added to this powder, and further mixed with magnetic powder to prepare a black electrophotographic toner.

This toner is put into a toner cartridge of a copying machine (Toshiba Primage 38), and copy paper (Ne
solid image for evaluation was transferred to USEDLER (500 BLATT). The image density D _C of the colored state was measured. Next, the copy paper on which the solid image was formed was immersed in diethoxyethane for 20 seconds and then dried to erase the image.
Were measured image density D _D decoloring state. The contrast was determined using 0.06 as the background value. Table 4 shows the results.

As can be seen from Table 4, when the leuco dyes (E1) to (E8) included in the general formula (I) are used, the (C1) to (C9) not included in the general formula (I) are used. As compared with the case where the leuco dye is used, the image density at the time of color development is high and the image density at the time of color erasure is low, so that good contrast can be obtained.

[0092]

[Table 4]

Example 5 As a leuco dye prepared in Example 4, a compound of the formula (E8)
Using a toner containing 2-anilino-6- (N-ethyl-N-pentylamino) -3-fluoran, a solid image for evaluation was transferred to copy paper (Neusiedler, 500BLATT). Image density D _C during color development 1.
45.

The paper is heated and decolored on a hot plate under the following four conditions, and the image density D _D at the time of decoloration is obtained.
Was measured. The heating condition is 100 ° C. for 24 hours, 120
3 hours at 150C, 1 hour at 150C, or 5 minutes at 200C. Background value (reflection density D of copy paper
Using 0.06 as _P ), the contrast was determined. Table 5 shows the results. As shown in Table 5, the image was successfully erased under any of the heating conditions.

[0095]

[Table 5]

Example 6 As a leuco dye prepared in Example 4, a compound of the formula (E1)
Using a toner containing 2-anilino-6- (N, N-diisopentylamino) -3-methylfluoran in a copy paper (Neushiedler, 500BLATT)
A solid image for evaluation was transferred to the sample. Image density D _C at the time of color development
Was 1.41.

[0097] After immersion for 20 seconds in the erase solvents shown the paper table 6, and dried to measure the image density D _D during discoloring. Background values (reflection density D _P of the copy paper)
Was used as 0.06, and the contrast was determined. Table 6 shows the results. As shown in Table 6, the images were successfully erased using any of the erasing solvents.

Further, the erasing state by the erasing solvent was good, and no residual image due to traces of toner flow or bleeding was observed. The erased state was very stable, and no change was observed even after holding at 60 ° C. for 300 hours.

[0099]

[Table 6]

Example 7 A leuco dye represented by the chemical formula (E1) was weighed to 3.4% of the total weight thereof.
2 ′, 4,4′-Tetrahydroxybenzophenone
Double molar amount, 1 part by weight of polypropylene wax as a wax component, charge control agent (LR-
147) 1 part by weight and 93 parts by weight of a polystyrene-butyl acrylate copolymer (molecular weight 65,000) having a different polymerization ratio shown in Table 7 as a binder resin were added and mixed well. The mixture was kneaded with a kneader while keeping the temperature at 80 ° C. or lower, and when the shear was stopped, the kneader was stopped and taken out, and allowed to cool at room temperature. After coarsely pulverizing the kneaded product, it was kneaded again with a kneader, and the leuco dye and the developer were uniformly dispersed in the binder resin. The kneaded product was pulverized with a pulverizer to obtain a powder having an average particle size of 10 μm. 1 wt% of hydrophobic silica is externally added to this powder,
Further, it was mixed with magnetic powder to prepare a black electrophotographic toner.

This toner is put into a toner cartridge of a copying machine (Primage 38 manufactured by Toshiba), and copy paper (Ne
solid image for evaluation was transferred to USEDLER (500 BLATT). The image density D _C of the colored state was measured. Next, the copy paper on which the solid image was formed was immersed in diethoxyethane for 20 seconds and then dried to erase the image.
Were measured image density D _D decoloring state. The contrast was determined using 0.06 as the background value. Table 7 shows the results.

As can be seen from Table 7, when a polystyrene-butyl acrylate copolymer having a butyl acrylate content of 20 wt% or less was used as the binder resin, the image density at the time of color development was high and the image density at the time of color erasure was high. And a good contrast is obtained.

[0103]

[Table 7]

Example 8 1 part by weight of a leuco dye represented by any of the chemical formulas (E1) to (E8) and (C1) to (C9), and 2,4,4
1 part by weight of 4'-trihydroxybenzophenone, polypropylene wax as a wax component (Mitsui Chemicals CPR)
600B) 5 parts by weight, paraffin wax (Nippon Seisaku H
After adding 5 parts by weight of NP-11) and 2 parts by weight of 1-docosanol, the mixture was heated to 80 ° C., stirred vigorously for 3 hours, and then molded to produce a crayon.

Using this crayon, paper (Neused)
(Ler, 500 BLATT) on a 3 cm × 3 cm area. The image density D _C of the colored state was measured. Next, the image was erased by rubbing the image area with a felt pen filled with diethoxyethane as an erasing solvent. Were measured image density D _D decoloring state. The contrast was determined using 0.06 as the background value. Table 8 shows the results.

As can be seen from Table 8, when the leuco dyes of (E1) to (E8) included in the general formula (I) were used, the (C1) to (C9) not included in the general formula (I) were used. As compared with the case where the leuco dye is used, the image density at the time of color development is high and the image density at the time of color erasure is low, so that good contrast can be obtained.

When methyl ethyl ketone or isopropyl alcohol was used as the erasing solvent, the same results as in Table 8 were obtained.

[0108]

[Table 8]

[0109]

As described above in detail, according to the present invention, when applied to an erasable image forming material, a high image density is exhibited at the time of color development and a low image density is exhibited at the time of color erasure, and good contrast is obtained. A black leuco dye can be provided. Accordingly, the range of application of the erasable image forming material is expanded, and the paper resources can be efficiently used.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Akira Takayama, 1st Toshiba R & D Center, Komukai Toshiba-cho, Saitama-ku, Kawasaki-shi, Kanagawa Prefecture No. 1 in the Toshiba R & D Center (72) Inventor Kenji Sano 1 in Komukai Toshiba-cho in Koyuki-ku, Kawasaki-shi, Kanagawa Prefecture In-Toshiba R & D Center (72) Inventor Eiichi Ishida Kyoto, Kyoto Yamada Chemical Industry Co., Ltd. (72) Inventor Manabu Yamada 1-1, Kamibawa Kamichochocho, Minami-ku, Kyoto-shi, Kyoto

Claims (5)

[Claims] 1. A black leuco dye for use in an erasable image forming material containing a leuco dye, a developer and a decolorant, which is represented by the following general formula (I): Wherein X is selected from the group consisting of a hydrogen atom and an alkyl group; Y is an unsubstituted or substituted anilino group;
₁ and R ₂ are alkyl groups, at least one of which is an alkyl group having 5 or more carbon atoms. A black leuco dye for an erasable image forming material, which is represented by the following formula: 2. A composition comprising a leuco dye, a color developer and a binder resin, wherein the binder resin is compatible with either the leuco dye or the color developer by contact with a solvent or by heating. Or a black leuco dye used in an erasable image forming material in which the compatible state is maintained even after cooling and the state in which the image is erased is maintained, and which is represented by the following general formula (I): Wherein X is selected from the group consisting of a hydrogen atom and an alkyl group; Y is an unsubstituted or substituted anilino group;
₁ and R ₂ are alkyl groups, at least one of which is an alkyl group having 5 or more carbon atoms. A black leuco dye for an erasable image forming material, which is represented by the following formula: 3. A composition comprising a leuco dye, a color developer, and a binder resin, wherein the equilibrium between the leuco dye and the color developer is shifted to a non-color-developing side by contact with a solvent or heating, and after the solvent is volatilized or A black leuco dye used for an erasable image forming material which maintains an equilibrium shifted to a non-color-developing side even after cooling and maintains an erased state of the image, and is represented by the following general formula (I): Wherein X is selected from the group consisting of a hydrogen atom and an alkyl group; Y is an unsubstituted or substituted anilino group;
₁ and R ₂ are alkyl groups, at least one of which is an alkyl group having 5 or more carbon atoms. A black leuco dye for an erasable image forming material, which is represented by the following formula: 4. The black leuco dye according to claim 1, wherein at least one of R ₁ and R ₂ is a branched alkyl group. 5. At least one of R ₁ and R ₂ is a pentyl group, isopentyl group, 2-methylbutyl group or 1
The black leuco dye for an erasable image forming material according to claim 1, comprising a methylbutyl group.