JP2005316454A - Decolorable image forming material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decolorable image forming material improved in heat decoloring performance. <P>SOLUTION: The decolorable image forming material has a color former, a developer, a binder resin and a surfactant. Alternatively, the decolorable image forming material has a powder including a color former, a developer and a binder resin, and a surfactant externally added to the powder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming material erasable by heating or contact with a solvent.

Forest protection is an absolute requirement in order to protect the global environment and to suppress the greenhouse effect caused by CO _2, and in order to keep 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” in which 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, in the past, practical use has been made regarding the reuse of hard copies by correcting images, such as an eraser for pencils and a correction fluid for writing instruments. However, it is clear that these methods have significant problems in terms of paper quality deterioration and reuse inefficiency. Recently, special paper rewritable paper has been proposed for the purpose of reusing hard copy paper. However, rewritable paper is a technique that can be “reused” because it uses special paper, but cannot be “recycled”, and has a drawback that recording techniques other than thermal recording cannot be applied. Here, “reuse”, which prevents paper quality deterioration as much as possible and uses it multiple times for the same purpose, is more important from the viewpoint of protecting paper resources, unlike “recycle”, which is used for other purposes while reducing paper quality. It can be said that it is a concept. If effective “reuse” is performed at each “recycle” stage, waste of new paper resources can be minimized.

  The present inventors pay attention to the fact that when the interaction between the color developing compound and the developer increases, the color developing state is obtained, and when the interaction decreases, the color developing compound enters the color erasing state. By adding a new color erasing agent that captures the developer to the contained composition system, the color development state is stable at temperatures near room temperature, and the color erasure state is fixed at a practical temperature for a long time by treatment with heat or solvent. Possible image forming materials, image erasing processes and image erasing apparatuses related to these image forming materials have been proposed as a paper reuse technique. These image forming materials have high stability in the coloring and erasing states of images, and are also highly safe in materials, and can be used for all of electrophotographic toners, liquid inks, ink ribbons, and writing instruments. In addition, it has a merit not found in the prior art that a large-scale erasure process is possible.

  As described above, the erasable image forming material proposed by us promotes reuse / recycling and can significantly reduce paper dust, so that the resource saving effect is great. In the process of further studying this erasable image forming material, the image recording medium is a polar polymer such as paper, and the binder contained in the image forming material is heated by a nonpolar material. If it has the property of facilitating capturing of the color developing compound by contact with a solvent, a decolorizing agent having the property of capturing the developer by utilizing the ability of capturing the developer by the image recording medium (paper). It has been found that the image can be erased even with an image forming material not added. An image forming material that does not contain a color erasing agent that captures the developer and a color erasing method thereof have also been proposed (see, for example, Patent Document 1).

In the image forming material that does not contain the color erasing agent, since the image recording medium (paper) has a function of capturing the color developer, the color erasing performance depends on the diffusion of the color developer. However, if the diffusion of the developer is thermally accelerated, the erasing performance is improved by being limited by the thermal properties of the image recording medium (paper) and the components of the image forming material (for example, binder resin in the case of toner). It was difficult to do.
JP 2000-284520 A

  An object of the present invention is to provide an erasable image forming material having improved thermal erasing performance.

  The erasable image forming material according to one embodiment of the present invention contains a color developing compound, a developer, a binder resin, and a surfactant.

  An erasable image forming material according to another aspect of the present invention comprises a powder containing a color former, a developer and a binder resin, and a surfactant externally added to the powder. To do.

  Since the erasable image forming material according to the embodiment of the present invention has improved thermal erasing performance, the paper resource can be easily reused, and its industrial value is great.

  The erasable image forming material containing a color developing compound, a developer, a binder resin and a surfactant according to an embodiment of the present invention is a surface active together with the color developing compound, the developer and the binder resin. The agent is added internally. An erasable image forming material according to another embodiment of the present invention comprises a powder containing a color former, a developer and a binder resin, and a surfactant externally added to the powder. It contains.

  In the erasable image forming material in which a trace amount of surfactant is added to the color developing compound, the developer and the binder resin (which may be internal or external), the heat of the developer It has been found that diffusion is promoted and thermal erasure performance is improved.

  In the embodiment of the present invention, a fatty acid metal salt can be suitably used as the surfactant. Specific examples of fatty acid metal salts include fatty acid alkali metal salts such as sodium stearate, sodium laurate, sodium oleate, potassium stearate, potassium laurate, potassium oleate; fatty acid alkaline earth metal salts such as calcium stearate, Calcium laurate, calcium oleate, barium stearate, barium laurate, barium oleate; other fatty acid metal salts such as zinc stearate, zinc laurate, zinc oleate, aluminum stearate, aluminum laurate, aluminum oleate, etc. Can be mentioned. Of these, calcium stearate, aluminum stearate, zinc stearate and the like are particularly preferable.

  In one embodiment of the present invention, when a surfactant is internally added together with the color former, the developer, and the binder resin, the content of the surfactant is 0.01 wt% or more, 0.03 wt% of the entire image forming material. % Or less is preferable. When the content of the surfactant is less than 0.01 wt% or exceeds 0.03 wt%, the thermal erasing performance of the image forming material cannot be improved.

  In another embodiment of the present invention, when the surfactant is externally added to the powder containing the color developable compound, the developer and the binder resin, the addition amount of the surfactant is 100 parts by weight of the powder. Is preferably 0.1 parts by weight or more and 1 part by weight or less, and more preferably 0.3 parts by weight or more and 0.5 parts by weight or less. When a surfactant is externally added, the effective amount of the surfactant that affects the thermal erasing performance of the image forming material is considered to be about 1/20 to 1/10 of the addition amount. In this embodiment, when the content of the surfactant is less than 0.1 part by weight or more than 1 part by weight, the thermal erasing performance of the image forming material cannot be improved.

  In the embodiment of the present invention, the following materials can be used as the color former, developer, and binder resin.

  Examples of color-forming compounds include electron donations such as leucooramines, diarylphthalides, polyarylcarbinols, acyloramines, arylolamines, rhodamine B lactams, indolines, spiropyrans, fluorans, etc. Organic materials. 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 (di Tilamino) fluorane-γ- (4′-nitro) anilinolactam, 3-diethylaminobenzo [a] -fluorane, 3-diethylamino-6-methyl-7-aminofluorane, 3-diethylamino-7-xylidinofluorane 3- (4-diethylamino-2-ethoxyphenyl) -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-7-a Minofluorane, DEPM, ATP, ETAC, 2- (2-chloroanilino) -6-dibutylaminofluorane, crystal violet carbinol, malachite green carbinol, N- (2,3-dichlorophenyl) leucooramine, N-benzoyl aura Min, Rhodamine B lactam, N-acetyl auramine, N-phenyl auramine, 2- (phenyliminoethanedilidene) -3,3-dimethylindoline, N-3,3-trimethylindolinobenzospiropyran, 8'- Methoxy-N, 3,3-trimethylindolinobenzospiropyran, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-6-benzyloxyfluorane, 1, 2-benzo- - 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.

  Developers include phenols, phenol metal salts, carboxylic acids, carboxylic acid metal salts, benzophenones, sulfonic acids, sulfonates, phosphates, phosphate metal salts, acidic phosphate esters, and acidic phosphate metal salts , Phosphorous acids, metal phosphites and the like. Specific examples of particularly suitable developers include gallic acid; gallic acid esters such as methyl gallate, ethyl gallate, n-propyl gallate, i-propyl gallate, butyl gallate, and the like; dihydroxybenzoic acid esters and Its esters such as 2,3-dihydroxybenzoic acid, methyl 3,5-dihydroxybenzoate and the like; hydroxyacetophenones such as 2,4-dihydroxyacetophenone, 2,5-dihydroxyacetophenone, 2,6-dihydroxyacetophenone, 3,5- Dihydroxyacetophenone, 2,3,4-trihydroxyacetophenone and the like; hydroxybenzophenones such as 2,4-dihydroxybenzophenone, 4,4′-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, , 4,4′-trihydroxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, 2,3,4,4′-tetrahydroxybenzophenone, etc .; biphenols such as 2,4′-biphenol, 4, 4'-biphenol and the like; polyhydric phenols such as 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-phenylene Bis (1-methylethylidene) bis (benzene-1,2,3-triol)], 4,4 ′-[1,4-phenylenebis (1-methylethyl) Den) bis (1,2-benzenediol)], 4,4 ', 4' '- ethylidene trisphenol, 4,4' - (1-methylethylidene) bisphenol, and the like methylene tris -p- cresol. These can be used alone or in admixture of two or more.

  In an image forming material containing a color former, a developer, and a binder resin, generally, the lower the amount of polar groups contained in the binder resin, the higher the color density of the image forming material prepared by kneading. The compatibility with the color developing compound is also increased. Therefore, it is advantageous to use a nonpolar resin as the binder resin in order to increase the contrast ratio between color development and decoloration of the image forming material.

  In the image forming material according to the embodiment of the present invention, a styrene copolymer is particularly suitable as the binder resin. Specific examples of the styrene monomer used as a raw material for these binder resins include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pn. -Butyl styrene, p-tert-butyl styrene, pn-hexyl styrene, pn-octyl styrene, pn-nonyl styrene, pn-decyl styrene, pn-dodecyl styrene, p-methoxy styrene , P-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, and the like. These monomers can be used alone or in combination of two or more. Optimal vinyl monomers copolymerized with styrene monomers include rubber components such as butadiene, propylene and chloroprene. The content of the rubber component in the styrene-based copolymer is preferably 2 to 15 wt%, and more preferably 7 to 13 wt%.

  Other vinyl monomers that can be copolymerized with styrenic monomers include methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, ethyl hexyl methacrylate, lauryl methacrylate, stearyl methacrylate, vinyl acetate, Examples include vinyl propionate, methacrylonitrile, dimethyl maleate, diethyl maleate, dimethyl fumarate, dibutyl fumarate, dimethyl itaconate, dibutyl itaconate, methyl vinyl ether, ethyl vinyl ether, n-butyl vinyl ether, and isobutyl ether. These vinyl monomers can be used alone or in combination of two or more. The content of such a vinyl monomer in the styrene copolymer is preferably 10 wt% or less.

  Examples of styrene copolymers that can be used as binder resins include styrene / n-butyl methacrylate, styrene / isobutyl methacrylate, styrene / ethyl acrylate, styrene / n-butyl acrylate, styrene / methyl methacrylate, styrene / glycidyl methacrylate, Styrene-dimethylaminoethyl methacrylate, styrene-diethylaminoethyl methacrylate, styrene-diethylaminopropyl acrylate, styrene-2-ethylhexyl acrylate, styrene-butyl acrylate-N- (ethoxymethyl) acrylamide, styrene-ethylene glycol methacrylate, styrene-4 -Hexafluorobutyl methacrylate, styrene-butadiene copolymer, acrylonitrile copolymer Lyl rubber / styrene terpolymer, acrylonitrile / styrene / acrylic acid ester terpolymer, styrene / acrylonitrile copolymer, acrylonitrile / chlorinated polystyrene / styrene terpolymer, acrylonitrile / ethylene vinyl acetate / styrene terpolymer Examples thereof include an original copolymer, a styrene / p-chlorostyrene copolymer, a styrene / propylene copolymer, a styrene / butadiene rubber, a styrene / maleic acid ester copolymer, and a styrene / maleic anhydride copolymer. An acrylate monomer polymer may be blended with polystyrene. In this case, the polyacrylate component may be a homopolymer or a copolymer.

The thermal properties of the binder resin for toner are represented by values of softening point and glass transition point. The softening point is preferably 60 to 190 ° C, and the glass transition point is preferably 20 to 110 ° C. Here, the softening point is a flow tester (CFT-500 manufactured by Shimadzu Corporation), nozzle: 1.0 mmφ × 10.0 mm, load: 30 kg · f, temperature increase rate: 3 ° C./min, sample amount: 1. It is obtained as the temperature (T _1/2 ) when the sample flow rate reaches half under the condition of 0 g. The glass transition point is a temperature obtained as a shoulder value after melt quenching by DSC.

  As a method of mixing and dispersing the color developing compound and the developer with the binder resin, a wet dispersion method using a solvent in an apparatus such as a high-speed dissolver, a roll mill, a ball mill, a roll, a pressure kneader, an internal mixer, a screw Examples thereof include a melt-kneading method using a mold extruder. Also, as a mixing means, a ball mill, a V-type mixer, a Forberg, a Henschel mixer, or the like can be used.

  As the charge control agent for the erasable toner, it is necessary that the color of the charge control agent does not remain when erasing, and therefore, a colorless or transparent one is used. Suitable charge control agents include negatively charged materials such as Orient Chemical's E-84 (zinc salicylate compound), Nippon Kayaku's N-1, N-2, N-3 (both phenolic compounds), Fujikura Kasei FCA-1001N (styrene-sulfonic acid resin) and the like are Hodogaya Chemical's TP-302 (CAS # 116810-46-9), TP-415 (117342-25-2), Orient Chemical P-51 (quaternary amine compound), AFP-B (polyamine oligomer), and FCA-201PB (styrene-acrylic quaternary ammonium salt resin) by Fujikura Kasei.

In the erasable toner, if necessary, waxes for controlling the fixing property may be blended. As the wax, those composed of a higher alcohol, a higher ketone, and a higher aliphatic ester, which do not develop a color developing compound are preferable. When the acid value of the wax is defined, it is preferably 10 or less. As the wax, those having a weight average molecular weight of 10 ² to 10 ⁵ , more preferably 10 ² to 10 ⁴ 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 be used as the wax. The amount of the wax added is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 15 parts by weight. In the heat roll fixing toner, waxes are added to impart release performance from the heat roll, and the addition amount is set within 5 parts by weight. In the pressure fixing toner, the main component is a wax, which becomes a core part of a microcapsule structure.

  In the erasable toner according to the embodiment of the present invention, an external additive for controlling fluidity, storage stability, blocking resistance, photoconductor polishing property and the like may be blended as necessary. As the external additive, silica fine particles, metal oxide fine particles, cleaning aids and the like are used. Examples of the silica fine particles include silicon dioxide, sodium silicate, zinc silicate, magnesium silicate and the like. Examples of the metal oxide fine particles include zinc oxide, magnesium oxide, zirconium oxide, strontium titanate, and barium titanate. Examples of the cleaning aid include fine resin powders such as polymethyl methacrylate, polyvinylidene fluoride, and polytetrafluoroethylene. These external additives may be subjected to surface treatment such as hydrophobization. In most cases, the external additive used in the toner is hydrophobized. In the case of a negatively charged toner, a treatment agent such as a silane coupling agent, a titanium coupling agent, or silicone oil is used for the hydrophobic treatment of the external additive. In the case of a positively charged toner, a processing agent such as an aminosilane-based silicone oil having an amine in the side chain is used for the hydrophobic treatment of the external additive. The addition amount of the external additive is preferably 0.05 to 5 parts by weight, more preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the toner. Regarding the number average particle diameter of the primary particles of the external additive, 10 to 20 nm particles are often used as the silica fine particles, and particles of about 100 nm are also used. As fine particles other than silica, particles having a number average particle diameter of 0.05 to 3 μm, which is larger than that of silica fine particles, are often used.

Example 1
4.15 wt% of leuco dye Blue 203 manufactured by Yamada Chemical as a color developing compound, 2 wt% of ethyl gallate as a developer, 5 wt% of polypropylene wax as a wax component, 87.83 wt% of styrene-butadiene rubber as a binder resin, 1 wt% of LR-147 manufactured by Nippon Carlit Co., Ltd. as a charge control material and 0.02 wt% of zinc stearate as a surfactant were weighed and mixed thoroughly using a Henschel mixer. This mixture was kneaded and dispersed with three rolls. Further, the kneaded material was pulverized into fine powder having an average particle diameter of 11 μm by a pulverizer. Thereafter, 1 part by weight of hydrophobic silica was externally added to 100 parts by weight of the fine powder to produce a blue electrophotographic toner (Example 1).

  For comparison, a blue electrophotographic toner (Conventional Example 1) was prepared in the same manner as described above except that the surfactant zinc stearate was not added.

  Using each manufactured toner, an image (solid pattern) having several levels of reflection density is printed on a copy paper (Toshiba Tec P50S) by using a TOSHIBA TEC MFP (multifunction printer, Premage 351). This was used as an evaluation image for erasing performance. Using a thermostatic bath, thermal erasing was performed at 130 ° C. for 2 hours, and the reflection density of the afterimage was examined.

  FIG. 1 shows the result of the erase experiment. In FIG. 1, the horizontal axis represents (reflection density of initial image) − (reflection density of paper) before thermal erasure, and the vertical axis represents (reflection density of residual image) − (reflection density of paper) after thermal erasure. The slope of the regression line according to the least square method in FIG. 1 represents the thermal erasing performance of the toner, and the smaller the value, the higher the erasing performance.

  As shown in FIG. 1, the slope of the regression line is about 0.057 for the toner of Example 1 and about 0.074 for the toner of Conventional Example 1. In the toner of Example 1, it can be said that the reflection density of the afterimage is reduced by about 23% as compared with the toner of Conventional Example 1. In the erasable toner of this example, it was confirmed that the thermal erasability can be remarkably improved by adding 0.02 wt% of the surfactant.

Example 2
4.15 wt% of Yamada Chemical's leuco dye Blue 203 as the color developing compound, 2 wt% of ethyl gallate as the developer, 5 wt% of polypropylene wax as the wax component, 87.85 wt% of styrene-butadiene rubber as the binder resin, As a charge control material, 1 wt% of LR-147 manufactured by Nippon Carlit Co., Ltd. was weighed and sufficiently kneaded and dispersed using a kneader. Further, the kneaded material was pulverized into fine powder having an average particle diameter of 9.5 μm by a pulverizer. Thereafter, 1.4 parts by weight of hydrophobic silica and 0.3 part by weight of zinc stearate were externally added to 100 parts by weight of the fine powder to produce a blue electrophotographic toner (Example 2).

  For comparison, a blue electron was added in the same manner as above except that only 1.4 parts by weight of hydrophobic silica was externally added to 100 parts by weight of fine powder without adding zinc stearate as a surfactant. A photographic toner (Conventional Example 2) was prepared.

  Using each of the produced toners, an image (solid pattern) having several levels of reflection density is printed on a copy paper (Green 100 manufactured by Fuji Xerox) with a Ricoh printer (NX810), and this is used as an evaluation image for erasing performance. Using. Using a dedicated erasing device, thermal erasing was carried out at 140 ° C. for 2 hours, and the reflection density of the afterimage was examined.

  FIG. 2 shows the result of the erase experiment. As shown in FIG. 2, the slope of the regression line is about 0.0725 for the toner of Example 2 and about 0.087 for the toner of Conventional Example 2. In the toner of Example 2, it can be said that the reflection density of the afterimage is reduced by about 17% as compared with the toner of Conventional Example 2. In the erasable toner of this example, it was confirmed that the thermal erasability can be remarkably improved by the external addition of only 0.3 part by weight of a surfactant.

Example 3
4.15 wt% of Yamada Chemical's leuco dye Blue 203 as a color developing compound, 2 wt% of ethyl gallate as a developer, 5 wt% of polypropylene wax as a wax component, and 1 wt. Of LR-147 of Nippon Carlit as a charge control material %, Zinc stearate 0 to 0.2 wt% as a surfactant, and styrene / butadiene copolymer having a butadiene content of 10 wt% as a binder resin were weighed so that the total amount was 100 wt%. Each composition was thoroughly mixed using a Henschel mixer. The mixture was kneaded and dispersed with three rolls. Furthermore, the kneaded product was pulverized into fine powder having an average particle size of 11.3 μm by a pulverizer. Thereafter, 1 part by weight of hydrophobic silica was externally added to 100 parts by weight of the fine powder to prepare a blue electrophotographic toner.

  Using each prepared toner, an image (solid pattern) with several levels of reflection density is printed on a copy sheet by a TOSHIBA TEC MFP (multifunction printer, pre-mage 351), and this is used as an evaluation image for erasing performance. Using. Using a thermostatic bath, thermal erasure was performed at 130 ° C. for 2 hours.

  FIG. 3 shows the result of the erase experiment. In FIG. 3, the horizontal axis represents the amount of zinc stearate added, and the vertical axis represents the thermal erasing performance, that is, the slope value of the regression line obtained in the same manner as in FIG. As described with reference to FIG. 1, the smaller the value on the vertical axis, the higher the erasing performance.

  As shown in FIG. 3, the effect of improving the heat erasing performance is recognized when the amount of zinc stearate added is in the range of 0.01 to 0.03 wt%. However, even if zinc stearate is added in an amount of more than 0.03 wt%, the effect of improving the heat erasing performance is not recognized.

  FIG. 4 shows the reflection density of the powder. In FIG. 4, the horizontal axis represents the amount of zinc stearate added, and the vertical axis represents the powder reflection density. The reflection density of the powder was measured using a color difference meter (manufactured by Konica Minolta, trade name CR300) and placing the powder in a dedicated cell. A higher reflection density means a toner with better color development.

  As shown in FIG. 4, it can be seen that the color development of the powder is slightly improved when the amount of zinc stearate added is in the range of 0.01 to 0.03 wt%. However, when zinc stearate is added in an amount of more than 0.03 wt%, the color development of the powder rapidly decreases.

  From the results of this example, it can be seen that the erasable toner to which zinc stearate as a surfactant is added in the range of 0.01 to 0.03 wt% can simultaneously improve the erasing performance and the coloring performance.

Example 4
A blue electrophotographic toner is prepared in the same manner as in Example 3 except that aluminum stearate or calcium stearate is used instead of zinc stearate as the surfactant and the addition amount of the surfactant is 0.02 wt%. did. Table 1 shows the results of measuring the color density and thermal erasing performance of the powder in the same manner as in Example 3. Further, based on these results, the improvement rate I of contrast between the colored state and the decolored state was obtained. The improvement rate I is defined by the following equation.

Here, R _s is the reflection density of the powder containing the surfactant, R ₀ is the reflection density of the powder not containing the surfactant, E _s is the thermal erasing performance of the toner containing the surfactant, E ₀ Is the thermal erasing performance of a toner containing no surfactant. The unit of the improvement rate I is%.

  From Table 1, it was confirmed that even when aluminum stearate or calcium stearate was used as the surfactant, the contrast between the color developing state and the color erasing state of the erasable toner could be improved as in the case of zinc stearate. . Of the three surfactants, aluminum stearate is the most effective, and calcium stearate is slightly less effective.

Comparative Example 1
4.15 wt% of Yamada Chemical's leuco dye Blue 203 as a color developing compound, 2 wt% of ethyl gallate as a developer, 5 wt% of polypropylene wax as a wax component, and 1 wt. Of LR-147 of Nippon Carlit as a charge control material %, Aluminum stearate 0 to 0.2 wt% as a surfactant, polystyrene (Mitsui Chemicals, XPA6638) as a binder resin was weighed so that the total amount was 100 wt%. A blue electrophotographic toner was prepared in the same manner as in Example 3 using each composition. Each toner was evaluated in the same manner as in Example 3.

  FIG. 5 shows the result of the erase experiment. In FIG. 5, the horizontal axis represents the amount of aluminum stearate added, and the vertical axis represents the thermal erasing performance value. As shown in FIG. 5, in the comparative example, the effect of improving the thermal erasing performance is not recognized.

  FIG. 6 shows the reflection density of the powder. In FIG. 6, the horizontal axis represents the amount of aluminum stearate added, and the vertical axis represents the powder reflection density. As shown in FIG. 6, no improvement in the reflection density of the powder is observed in the comparative example.

  From the result of the comparative example, it can be seen that when the binder resin is polystyrene, the erasing performance and the coloring performance cannot be improved even if a surfactant is added.

FIG. 6 is a diagram showing the thermal erasing performance of the erasable toner of Example 1 and Conventional Example 1. FIG. 6 is a diagram showing the thermal erasing performance of erasable toners of Example 2 and Conventional Example 2. FIG. 10 is a graph showing the relationship between the amount of zinc stearate added in the erasable toner of Example 3 and the thermal erasing performance. FIG. 10 is a graph showing the relationship between the amount of zinc stearate added to the erasable toner of Example 3 and the reflection density of the powder. FIG. 6 is a graph showing the relationship between the amount of aluminum stearate added to the erasable toner of Comparative Example 1 and the thermal erasing performance. FIG. 6 is a graph showing the relationship between the amount of aluminum stearate added to the erasable toner of Comparative Example 1 and the reflection density of the powder.

Claims (14)

  An erasable image forming material comprising a color developing compound, a developer, a binder resin, and a surfactant.   The erasable image forming material according to claim 1, wherein the surfactant is a fatty acid metal salt.   The erasable image-forming material according to claim 2, wherein the fatty acid metal salt is selected from the group consisting of sodium stearate, potassium stearate, calcium stearate, zinc stearate, and aluminum stearate.   2. The erasable image forming material according to claim 1, wherein the content of the surfactant is 0.01 wt% or more and 0.03 wt% or less.   The erasable image forming material according to claim 1, wherein the developer is selected from gallic acid ester developers.   The erasable image forming material according to claim 1, wherein the binder resin is selected from styrene copolymers.   2. The erasable image forming material according to claim 1, wherein the erasable image forming material is printed on a paper medium in the form of a toner.   An erasable image forming material comprising: a powder containing a color former, a developer and a binder resin; and a surfactant externally added to the powder.   The erasable image forming material according to claim 11, wherein the surfactant is a fatty acid metal salt.   13. The erasable image forming material according to claim 12, wherein the fatty acid metal salt is selected from the group consisting of sodium stearate, potassium stearate, calcium stearate, zinc stearate, and aluminum stearate.   The erasable image forming material according to claim 11, wherein the addition amount of the surfactant is 0.1 part by weight or more and 1 part by weight or less with respect to 100 parts by weight of the powder.   12. The erasable image forming material according to claim 11, wherein the developer is selected from gallic acid ester developers.   The erasable image forming material according to claim 11, wherein the binder resin is selected from styrene copolymers.   12. The erasable image forming material according to claim 11, wherein the erasable image forming material is printed in the form of toner on a paper medium.

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