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US006313066B1 (12) United States Patent (10) Patent N0.: US 6,313,066 B1 Takayama (45) Date of Patent: Nov. 6, 2001

(54) DECOLORABLE IMAGE FORMING 5,663,115 9/1997 Naito et al...... 503/201 MATERIAL AND DECOLORING METHOD 5,849,651 12/1998 Takayama ct a1~ OF THE SAME 5,922,115 7/1999 Sano et a1...... 106/3132 FOREIGN PATENT DOCUMENTS (75) Inventor: Satoshi Takayama, Kawasaki (JP) 0 980 02s 2/2000 (EP) . (73) Assignee: Kabushiki Kaisha Toshiba, Kawasaki 0 987 123 3/2000 (EP) - (JP) 58-111873 7/1983 (JP) . 01-138274 5/1989 (JP). ( * ) Notice: Subject to any disclaimer, the term of this 01438275 5/1989 (JP) - patent is extended or adjusted under 35 07-025167 1/1995 (JP) . U.S.C. 154(b) by 0 days. Primary Examiner—Bruce Hess (74) Attorney, Agent, or Firm—Oblon, Spivak, McClelland, (21) Appl. N0.: 09/539,320 Maier & Neustadt, PC. (22) Filed: Mar. 30, 2000 (57) ABSTRACT (30) Foreign Application Priority Data A decolorable image forming material containing a color former, a developer and a binder resin, in Which the binder Mar. 31, 1999 (JP) ...... 11-094207 resin has a property that it is compatible With the color (51) Int. Cl.7 ...... B41M 5/132 former When the material is in contact With a and that (52) US. Cl...... 503/201; 503/214 it keeps the compatible state When the solvent is removed, (58) Field of Search ...... 503/201, 205, or has a property that it shifts an equilibrium betWeen the 503/214 color former and the developer to a non-developed side When the of the material is raised and that it (56) References Cited keeps the state shifted to the non-developed side When the temperature of the material is loWered. U.S. PATENT DOCUMENTS

5,407,890 4/1995 Ishikawa ...... 503/201 4 Claims, 1 Drawing Sheet

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I l l RoUM FIXING DECOLORING; TEMPERATURE TEMPERATURE TEMPERATURE TEMPERATURE U.S. Patent Nov. 6,2001 US 6,313,066 B1

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_IIIII1'T_T_-_:::-_:l':_—__—__-._—_ ROOM FIXING DECOILORING; TEMPERATURE TEMPERATURE TEMPEH ATURE TEMPERATURE US 6,313,066 B1 1 2 DECOLORABLE IMAGE FORMING According to an aspect of the present invention, there is MATERIAL AND DECOLORING METHOD provided a decolorable material comprising a color former, OF THE SAME a developer and a binder resin, Wherein the binder resin has a property that it is compatible With the color former When CROSS-REFERENCE TO RELATED the material is in contact With a solvent and that it keeps the APPLICATIONS compatible state When the solvent is removed. This application is based upon and claims the bene?t of According to another aspect of the present invention, priority from the prior Japanese Patent Application No. there is provided a decolorable material comprising a color 11-094207, ?led Mar. 31, 1999, the entire contents of Which former, a developer and a binder resin, Wherein the binder are incorporated herein by reference. 10 resin has a property that it shifts an equilibrium betWeen the color former and the developer to a non-developed side BACKGROUND OF THE INVENTION When the temperature of the material is raised and that it The present invention relates to an image forming mate keeps the state shifted to the non-developed side When the rial that can be formed into an image by electro temperature of the material is loWered. photography, thermal transfer recording, Writing tools or 15 According to still another aspect of the present invention, printing, and that can be decolored by control of thermal there is provided a paper medium comprising a paper sheet hysteresis or by contact With a solvent. and a decolorable material applied to the paper sheet and With the recent progress of of?ce automation, the comprising a color-former, a developer and a binder resin, amounts of various pieces of information are signi?cantly Wherein the binder resin has a property that it shifts an increasing, and information output is increasing accordingly. equilibrium betWeen the color former and the developer to Information output is represented by display output and hard a non-developed side When the temperature of the material copy output from printers to paper sheets. HoWever, display is raised and that it keeps the state shifted to the non output requires a large-scale circuit board in a display unit developed side When the temperature of the material is and hence has problems in portability and cost. Hard copy loWered. 25 output uses a large amount of paper as a recording medium According to yet another aspect of the present invention, When the information amount increases, leading to problems there is provided a decoloring method of an image using a about the protection of resources. In addition, in order to material comprising a color former, a developer and a binder recycle paper sheets on Which images are printed With a resin, comprising steps of heating the image forming mate printer or a copier, it is necessary to use a large amount of rial so that the binder resin adsorbs the color former When bleaching agent and Water, Which brings about a rise in the temperature of the material is raised, thereby shifting an recycling cost. Thus, it is proposed to reduce the consump equilibrium betWeen the color former and the developer to tion of paper sheets substantially by printing an image on a a non-developed side, and keeping the state shifted to the paper sheet using a decolorable image forming material, non-developed side When the temperature of the material is decoloring the formed image to return the paper sheet to a loWered. 35 blank sheet, reusing the blank sheet, and recycling the sheet According to yet another aspect of the present invention, at the time When damage of the sheet becomes serious so there is provided a decoloring method of an image using a that the sheet cannot be reused. material comprising a color former, a developer and a binder Recently, reWritable paper has been proposed in order to resin, Which is applied to a paper sheet, comprising steps of reuse hard copy paper sheets. HoWever, this reWritable paper heating the paper sheet so that the binder resin adsorbs the is applicable only to thermal recording and is not recyclable color former and a cellulose component of the paper sheet because it is made of special paper, although it is reusable. adsorbs the developer When the temperature of the paper Heretofore, an image forming material that can be decol sheet is raised, thereby shifting an equilibrium betWeen the ored by heating has been proposed in, for eXample, Pub color former and the developer to a non-developed side, and keeping the state shifted to the non-developed side When the lished Unexamined Japanese Patent Application No. 45 7-81236. The image forming material includes a color temperature of the paper sheet is loWered. former such as a leuco dye, a developer, and an organo According to yet another aspect of the present invention, phosphoric compound having decoloring ability. When such there is provided a decoloring method of an image using a an image forming material is used, hoWever, decoloration is material comprising a color former, a developer and a binder insuf?cient and, as a result, a paper sheet is hard to return to resin, Which is applied to a paper sheet, comprising steps of the blank state. bringing the image forming material on the paper sheet into We have been developing a decolorable image forming contact With a solvent, thereby making the binder resin and material in Which a color former, a developer and a decolo the color former into a compatible state and keeping the rant having high affinity With the developer are dispersed in compatible state When the solvent is removed. a binder resin. NoW, it becomes possible to attain an eXcel 55 In the present invention, the binder resin used is prefer lent decolored state in various material systems by selecting ably a non-polar resin. In the present invention, a binder an appropriate decolorant. HoWever, a complete decolored resin consisting of a copolymer of a polar monomer and a state is not alWays obtained in all material systems. Thus, it non-polar monomer may be used. In this case, the copoly has been recogniZed that components of the decolorable mer preferably comprises 90% or more by Weight of the image forming material can be desirably selected from a non-polar monomer. Wide variety of materials. BRIEF DESCRIPTION OF THE SEVERAL BRIEF SUMMARY OF THE INVENTION VIEWS OF THE DRAWING An object of the present invention is to provide an image The accompanying draWings, Which are incorporated in forming material, containing no decolorant, that can form a 65 and constitute a part of the speci?cation, illustrate presently clear image and that the image thereof can be decolored preferred embodiments of the invention, and together With Well. the general description given above and the detailed descrip US 6,313,066 B1 3 4 tion of the preferred embodiments given below, serve to high affinity With the developer are dispersed in a binder explain the principles of the invention. resin. As shoWn in FIG. 2A, When an image is formed on a FIG. 1A is a schematic vieW shoWing a color-developed paper sheet by using this image forming material, the color state of an image forming material comprising a color former and the developer dispersed in the binder interact former, a developer and a binder, according to the present With each other and are in a color-developed state. When the image forming material on the paper sheet is brought into invention, and contact With a solvent, the color former and the developer do FIG. 1B is a schematic vieW shoWing an decolored state not interact With each other, so that the color is lost, i.e., the of the image forming material by contact With a solvent; image is decolored. This is because the developer is com FIG. 2A is a schematic vieW shoWing a color-developed patible With the decolorant but the color former has loW 10 state of an image forming material comprising a color af?nity With the decolorant. Further, When the solvent is former, a developer, a decolorant and a binder resin, and removed due to evaporation, the color former and the FIG. 2B is a schematic vieW shoWing an decolored state developer, Which is captured by the decolorant, are separated of the image forming material by contact With a solvent; and in the binder resin, so that the dye components are ?xed in FIG. 3 is a graph shoWing temperature dependency of the 15 a colorless state (FIG. 2B). optical density of an image forming material comprising a As described above, the principles of decoloration of the color former, a developer and a binder, according to the image forming materials shoWn in FIGS. 1A and 1B and in present invention. FIGS. 2A and 2B are similar, but are different in that the color former and the binder resin have high af?nity With DETAILED DESCRIPTION OF THE each other in the case shoWn in FIGS. 1A and 1B and the INVENTION developer and the decolorant have high affinity With each other in the case shoWn in FIGS. 2A and 2B. As understood The present invention Will be more speci?cally described from this fact, in order to attain an excellent decolored state, hereinafter. it is suf?cient that either one of the color former and the A decolorable image forming material of the present developer is ?xed. Of course, both of the color former and invention comprises a color former, a developer and a binder the developer may be separately ?xed at the same time. but does not comprise any decolorant. The image forming The image of the image forming material of the present material is prepared by dispersing the color former and the invention can also be decolored by heating. The decoloring developer (these may be referred to as a dye components), method by heating is advantageous for treating, in a batch, in a color-developed state, in the binder resin. When the a bundle of paper sheets on Which the decolorable image image forming material is applied to a paper sheet by a forming material applied. The principle of decoloration in method such as electrophotography, a clear image can be this case Would be either one of the folloWing tWo. The ?rst formed. Images of the image forming material can be principle is substantially the same as the case shoWn in decolored by contact With a solvent or by heating. FIGS. 1A and 1B. That is, When the material is heated, the In a ?rst decolorable image forming material of the 35 binder resin becomes selectively compatible With the color present invention, used is a binder resin having a property former, so that the color is lost. According to the second that it is compatible With the color former When the material principle, equilibrium betWeen the color former and the is in contact With a solvent and that it keeps the compatible developer is shifted to a non-developed side When the state When the solvent is removed. That the binder resin is temperature of the material is raised, and the state shifted to compatible With the color former When the material is in the non-developed side is kept by means of the binder resin contact With a solvent means a phenomenon that the color When the temperature of the material is loWered. The second former diffuses in the binder resin that is in a sWelled state principle Will be described With reference to FIG. 3. by the solvent, and release of the color former from the In a state that an image is formed on a paper sheet using binder resin is made dif?cult by steric hindrance or interac the image forming material of the present invention, the rate tion. On the other hand, the binder resin has loW af?nity With 45 of the color former and the developer that interact With each the developer. other is large, and they are dispersed in a color-developed Referring to FIGS. 1A and 1B, the folloWing Will describe state in the binder resin. The optical density thereof shoWs a principle of decoloration of an image of the image forming the maximum value as the temperature of the material is material according to the present invention in Which a color raised. Even if the image forming material is cooled from former and a developer are dispersed in a binder resin. As this state, the color-developed state is kept. HoWever, When shoWn in FIG. 1A, When an image is formed on a paper sheet the temperature is further raised, the equilibrium of inter by using the image forming material of the present action betWeen the color former and the developer in the invention, the color former and the developer dispersed in binder is shifted to a non-developed side (a non-bonded the binder interact With each other and are in a color side). In other Words, the rate of the color former and the developed state. When the image forming material on the 55 developer that interact With each other becomes extremely paper sheet is brought into contact With a solvent, the color small. As a result, the optical density is decreased as the former and the developer do not interact With each other, so temperature of the material is raised, so that the color is lost. that the color is lost, i.e., the image is decolored. This is At that time, the binder resin adsorbs the color former and because the color former is compatible With the binder resin a cellulose component of the paper sheet adsorbs the devel but the developer has loW affinity With the binder resin. oper. Therefore, even if the temperature of the material is Further, When the solvent is removed due to evaporation, the loWered to room temperature, this state can be substantially color former and the developer are separated in the binder kept, so that the decolored state is kept. At resin, so that the dye components are ?xed in a colorless beloW the glass transition temperature of the binder resin, state (FIG. 1B). the decolored state does not return easily to the color For reference, FIGS. 2A and 2B shoW a principle of 65 developed state in spite of the shift of the equilibrium. decoloration of an image of the image forming material in The components used in the image forming material of Which a color former, a developer and a decolorant having the present invention Will noW be described in detail. US 6,313,066 B1 5 6 Examples of the color former are electron-donating methylethylidene)bis(1,2-benZenediol)], 4,4‘,4“ organic substances such as leucoauramines, ethylidenetrisphenol, 4,4‘-(1-methylethylidene)bisphenol, diarylphthalides, polyarylcarbinoles, acylauramines, and methylenetris-p-cresol. These developers can be used arylauramines, Rhodamine B lactams, indolines, singly or in the form of a mixture of tWo or more species. spiropyrans, and ?uorans. In the image forming material of the present invention, it Speci?c examples of the color former are Crystal Violet is desired to take the content of polar groups in the binder lactone (CVL), Malakite Green lactone, 2-anilino-6-(N resin and the compatibility of the binder resin With the color cyclohexyl-N-methylamino)-3-methyl?uoran, 2-anilino-3 former into consideration. As the content of the polar groups methyl-6-(N-methyl-N-propylamino)-?uoran, 3-[4-(4 in the binder resin becomes loWer, the optical density of the phenylaminophenyl)aminophenyl]amino-6-methyl-7 1O image formed using the image forming material prepared by chloro?uoran, 2-anilino-6-(N-methyl-N-isobutylamino)-3 kneading generally becomes higher and simultaneously the methyl?uoran, 2-anilino-6-(dibutylamino)-3-methyl?uoran, compatibility of the binder resin With the color former also 3-chloro-6-(cyclohexylamino)-?uoran, 2-chloro-6 becomes higher. Therefore, it is preferable to use a resin (diethylamino)?uoran, 7-(N,N-diethylamino)-3-(N,N close to non-polar as the binder resin capable of improving the contrast betWeen the developed state and the decolored diethylamino)?uoran, 3,6-bis(diethylamino)?uoran-y-(4‘ 15 nitroanilino)lactam, 3-diethylaminobenZo[a]?uoran, state. Speci?cally, a binder resin composed only of a non 3-dietylamino-6-methyl-7-amino?uoran, 3-diethylamino-7 polar monomer or a binder resin that is a copolymer of a xylidino?uoran, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1 polar monomer and a non-polar monomer and comprises ethyl-2-methylindole-3-yl)-4-aZaphthalide, 3-(4 90% or more by Weight of non-polar monomer. diethylaminophenyl)-3-(1-ethyl-2-methylindole-3-yl) Examples of suitable binder resin used in the present phthalide, 3-diethylamino-7-chloroanilino?uoran, invention are polystyrene, polystyrene derivatives and sty 3-diethylamino-7,8-benZo?uoran, 3,3-bis(1-n-butyl-2 rene copolymers. Speci?c examples of a styrene-based methylindole-3-yl)phthalide, 3,6-dimethylethoxy?uoran, monomer used for producing these polymers are styrene, 3,6-diethylamino-6-methoxy-7-amino?uoran, DEPM, ATP, o-methylstyrene, m-methylstyrene, p-methylstyrene, ETAC, 2-(2-chloroanilino)-6-dibutylamino?uoran, Crystal 25 p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, Violet carbinol, Malachite Green carbinol, N-(2,3 p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n dichlorophenyl)leucoauramine, N-benZoylauramine, nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, Rhodamine B lactam, N-acetylauramine, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, and N-phenylauramine, 2-(phenyliminoethanedilydene)-3,3 3,4-dichlorostyrene. These monomers can be used singly or dimethylindoline, N,3,3-trimethylindolinobenZospiropyran, in a combination of tWo or more species. 8‘-methoxy-N,3,3-trimethylindolinobenZospiropyran, A styrene-based monomer may be copolymeriZed With a 3-diethylamino-6-methyl-7-chloro?uoran, 3-diethylamino monomer having a polar group. Examples of monomer 7-methoxy?uoran, 3-diethyamino-6-benZyloxy?uoran, 1,2 having a polar group are methyl methacrylate, ethyl benZo-6-diethyamino?uoran, 3,6-di-p-toluidino-4,5 methacrylate, isobutyl methacrylate, cyclohexyl dimetyl?uoran, phenylhydraZide-y-lactam, and 3-amino-5 35 methacrylate, ethylhexyl methacrylate, lauryl methacrylate, methyl?uoran. These color formers can be used singly or in stearyl methacrylate, vinyl , vinyl propionate, the form of a mixture of tWo or more species. If color methacrylonitrile, dimethyl maleate, diethyl maleate, dim formers are selected properly, a variety of color developed ethyl fumarate, dibutyl fumarate, dimethyl itaconate, dibutyl states can be obtained, and thus a multicolor image can be itaconate, methylvinylether, ethylvinylether, formed. n-butylvinylether, and isobutylether. These monomers hav Examples of the developer are , metal phenolates, ing a polar group can be used singly or as a combination of carboxylic acids, metal carboxylates, benZophenones, sul tWo or more species. Speci?c examples of suitable binder fonic acids, sulfonates, phosphoric acids, metal phosphates, resin consisting of a copolymer are styrene-n-butyl acidic phosphoric , acidic phosphoric metal salts, methacrylate, styrene-isobutyl methacrylate, styrene-ethyl phosphorous acids, and metal phosphites. These developers 45 acrylate, styrene-n-butyl acrylate, styrene-methyl can be used singly or in the form of a mixture of tWo or more methacrylate, styrene-glycidyl methacrylate, styrene species. dimethylaminoethyl methacrylate, styrene Speci?c examples of the developer are gallic acid; gal diethylaminoethyl methacrylate, styrene lates such as methyl gallate, ethyl gallate, n-propyl gallate, diethylaminopropyl acrylate, styrene-2-ethylhexyl acrylate, i-propyl gallate, and butyl gallate; dihydroxybenZoic acids styrene-butyl acrylate-N-(ethoxymethyl)acrylamide, and their esters such as 2,3-dihydroxybenZoic acid and styrene-ethyleneglycol methacrylate, styrene-4 3,5-dihydroxybenZoic acid methyl; deriva hexa?uorobutyl methacrylate, a styrene-butadiene tives such as 2,4-dihydroxyacetophenone, 2,5 copolymer, an acrylonitrile-acrylic rubber-styrene dihydroxyacetophenone, 2,6-dihydroxyacetophenone, 3,5 terpolymer, an acrylonitrile-styrene-acrylate terpolymer, a dihydroxyacetophenone, and 2,3,4 55 styrene-acrylonitrile copolymer, an acrylonitrile-chlorinated trihydroxyacetophenone; benZophenone derivatives such as polystyrene-styrene terpolymer, an acrylonitrile 2,4-dihydroxybenZophenone, 4,4‘-dihydroxybenZophenone, ethylenevinyl acetate-styrene terpolymer, a styrene-p 2,3,4-trihydroxybenZophenone, 2,4,4‘ chlorostyrene copolymer, a styrene-propylene copolymer, trihydroxybenZophenone, 2,2‘,4,4‘ styrene-butadiene rubber, a styrene-maleic ester copolymer, tetrahydroxybenZophenone, and 2,3,4,4‘ and a styrene-maleic anhydride copolymer. tetrahydroxybenZophenone; biphenols such as 2,4‘-biphenol In the case Where a styrene-based monomer is copoly and 4,4‘-biphenol; and polyhydric phenols such as 4-[(4 meriZed With another monomer such as butadiene and hydroxyphenyl)methyl]- 1 ,2,3-benZenetriol, 4-[(3,5 chloroprene, the Weight ratio of these monomer components dimethyl-4-hydroxyphenyl)methyl]-1,2,3-benZenetriol, 4,6 is desirably set to 10% or less. bis[(3,5-dimethyl-4-hydroxyphenyl)methyl]-1 ,2,3 65 Ablend of polystyrene and polyacrylate can also be used. benZenetriol, 4,4‘-[1,4-phenylenebis(1-methylethylidene)bis In this case, polyacrylate can be a homopolymer or a (-1,2,3-triol)], 4,4‘-[1,4-phenylenebis(1 copolymer. US 6,313,066 B1 7 8 Ablend of polystyrene-based polymer and polyester can The Weight-average molecular Weight of this Wax compo also be used. Polyester is synthesized by reaction betWeen a nent is preferably 102 to 105, and more preferably, 102 to carboxylic acid and a polyhydric . Examples of the 104. LoW-molecular Weight polypropylene, loW-molecular carboxylic acid monomer are terephthalic acid, fumaric acid, Weight polyethylene, loW-molecular Weight polybutylene, or maleic acid, succinic acid, glutaric acid, adipic acid, pimelic loW-molecular Weight polyalkane may be used as a Wax acid, suberic acid, aZelaic acid, sebacic acid, brassilic acid, component, if the Weight-average molecular Weight is in the pyromellitic acid, citraconic acid, glutaconic acid, mesa above range. The addition amount of the Wax component is conic acid, itaconic acid, teraconic acid, phthalic acid, preferably 0.1 to 30 parts by Weight, and more preferably, isophthalic acid, hemimellitic acid, mellophanic acid, tri 0.5 to 15 parts by Weight. For toner to be thermally ?xed mesic acid, prehnitic acid, trimellitic acid, and their deriva 10 With heat rolls, the Wax component is added to impart tives. Examples of the polyhydric alcohol are release property from the heat rolls. In this case, the content glycol, propylene glycol, butanediol, neopentyldiol, of the Wax component is set to 5 parts by Weight or less. In hexamethylenediol, heptanediol, octanediol, pentaglycerol, an electrophotographic toner to be ?xed by , the pentaerythritol, cyclohexanediol, cyclopentanediol, pinacol, main component of the toner is the Wax component, Which glycerin, etheri?ed diphenol, catechol, resorcinol, 15 constitutes a core of a microcapsule structure. pyrogallol, benZenetriol, phloroglucinol, benZenetetraol, When the image forming material is used for toner, an and their derivatives. These monomers can be used singly or external additive may be added to control the ?oWability, in the form of a copolymer of tWo or more species. It is also storage stability, blocking resistance, or photosensitive body possible to blend tWo or more polyesters. polishing characteristics. As the external additive, silica ?ne The decolorable image forming material of the present 20 particles, metal oxide ?ne particles, a cleaning assistant, and invention can be applicable to electrophotographic toner, the like can be used. Examples of the silica ?ne particles are liquid ink, and a thermal transfer ink ribbon, etc. Asoftening silicon dioxide, sodium silicate, silicate, and magne point and a glass transition point represent thermal charac sium silicate. Examples of the metal oxide ?ne particles are teristics of, for example, the binder resin for toner. Binder Zinc oxide, magnesium oxide, Zirconium oxide, strontium resin suitable for toner preferably has a softening point of 60 25 titanate, and barium titanate. Examples of the cleaning to 190° C. and a glass transition point of 20 to 110°. The assistant are resin ?ne poWders of polymethyl methacrylate, softening point is measured as a temperature (T1 /2) When the polyvinylidene ?uoride, and polytetra?uoroethylene. These sample ?oW amount reaches the half value under conditions external additives may be subjected to surface processing to of noZZle: 1.0 mm¢><10.0 mm, load: 30 kgf, heating rate: 3° make hydrophilic. For negative charge toner, treatment C./min, and sample amount: 1.0 g by using a How tester 30 agents such as a silane coupling agent, a titanium coupling (CFT-500 manufactured by ShimadZu Corp.) The glass agent, and silicone oil are used. For positive charge toner, transition point is measured by DSC as the temperature of a treatment agents such as an amino silane-based compound shoulder value after melt quench. Binder resin suitable for a and silicone oil having in a side chain are used. The thermal transfer ink ribbon preferably has a glass transition addition amount of these external additives is preferably point of 70° C. or less from a vieWpoint of thermal transfer 35 0.05 to 5 parts by Weight, and more preferably, 0.1 to 3.0 sensitivity. parts by Weight With respect to 100 parts by Weight of the Next, in the case Where the image forming material of the toner. Silica ?ne particles Whose number-average particle present invention is used in various applications, usable siZe of primary particles is 10 to 20 nm are often used, and materials other than a color former, a developer and a binder particles up to 100 nm are also used. In the case of a material resin Will be described. 40 other than silica, particles having a large number-average A charge control agent may be used Where the image particle siZe of, for example, 0.05 to 3 pm are used. forming material is used as toner. In the present invention, The particle siZe range of the decolorable toner according it is required that any color does not remain When the image to the present invention is preferably such that the volume is decolored, and therefore a charge control agent is prefer average particle siZe is 6 to 20 pm, the content of particles ably colorless or transparent. In vieW of this requirement, 45 of 5 pm or less is 2 to 20 number % in the number folloWing negative charge control agents and positive charge distribution, the content of particles of 5 pm or less is 0 to control agents are suitable. Examples of the negative charge 5 volume % in the volume distribution, and the content of control agent are E-84 (Zinc salicylate compound) manufac particles of 20 pm or more is 0 to 5 volume % in the volume tured by Orient Kagaku K.K., N-1, N-2, and N-3 ( distribution. These values are measured With Coulter Mul based compounds) manufactured by NIPPON KAYAKU 50 tisiZer (Coulter Corp.) The conductivity of the decolorable CO. LTD., FCA-1001N (styrene-sulfonic acid-based resin) toner is preferably 1011 to 1016 Q-cm, and more preferably, manufactured by FUJIKURA KASEI CO. LTD., and 1013 to 1015 Q-cm. In dual-component development, an iron LR-147 manufactured by Nippon Carret Inc. Examples of poWder, ferrite and magnetite coated With silicone resin or the positive charge control agent are TP-302 (CAS#116810 acrylic resin are used as a carrier. The conductivity of the 46-9) and TP-415 (CAS#117342-25-2) manufactured by 55 carrier is preferably 109 Q-cm or less for an iron poWder, Hodogaya Chemical Co. Ltd., P-51 (quaternary amine about 106 to 1015 Qcm for ferrite, and 1013 Q-cm or more compound) and AFP-B (polyamine oligomer) manufactured for magnetite. When a magnetic poWder pulveriZed to about by Orient Kagaku K.K., and FCA-201PB (styrene-acrylic 50 pm is dispersed in a resin, the conductivity is preferably quaternary ammonium -based resin) manufactured by 1013 Q-cm or more. The conductivity is measured by form FUJIKURA KASEI CO. LTD. 60 ing the toner into disk-like tablets 20 mm in diameter and 1 When the image forming material of present invention is mm in thickness and applying a potential of 1 V><1 kHZ to used for toner, a Wax component can also be added to control the tablets. the ?xation. Examples of the Wax component are long-chain Next, a case Where the image forming material of the aliphatic alcohol, long-chain aliphatic , and long present invention is applied to liquid ink Will be described chain aliphatic acid ester. The Wax component preferably 65 beloW. Solid components of the liquid ink containing a color does not make the color former develop color. Therefore, the former, a developer and a binder resin as main components acid value of the Wax component is preferably 10 or less. like toner. As a liquid component, used is a solvent different US 6,313,066 B1 10 from a decoloring solvent described later. Examples of The decoloring solvent used in the present invention suitable organic solvent used for ink are aliphatic preferably has high af?nity With a binder resin and is capable hydrocarbons, alicyclic hydrocarbons and aromatic hydro of penetrating into the image forming material. Examples of . Examples of aliphatic hydrocarbon are hexane, the decoloring solvent are , and esters. More octane, decan, dodecan, tetradecan, octene, decene, speci?c examples are saturated ethers such as ethyl , dodecene, and tetradecan, their isomers, and a mixture ethyl propyl ether, ethyl isopropyl ether, isopentyl methyl thereof represented by liquid paraf?n. Examples of alicyclic ether, butyl ethyl ether, dipropyl ether, diisopropyl ether, hydrocarbon are cyclohexane, cyclooctane, cyclodecan, ethyl isopentyl ether, dibutyl ether, dipentyl ether, diisopen cyclododecane, cyclotetradecane, methylcyclohexane, tyl ether, and dihexyl ether; unsaturated ethers such as ethyl dimethylcyclohexane, ethylcyclohexane, 10 vinyl ether, aryl ethyl ether, diaryl ether, and ethyl propargyl propylcyclohexane, , menthane, , ether; ethers of dihydric such as 2-methoxyethanol, dipentene, terpinolene, carane, carene, thujane, and thujene. 2-ethoxyethanol, 2-butoxyethanol, 1,2-dimethoxyethane; Examples of aromatic hydrocarbon are benZene, , cyclic ethers such as oxetane, tetrahydrofuran, xylene, ethylbenZene, propylbenZene, and diethylbenZene. tetrahydropyran, dioxolane, dioxane, and trioxane; saturated In this case, polyole?n, polystyrene and the like are used for 15 ketones such as , methyl ethyl ketone, methyl propyl a vehicle resin. Water may be used as a solvent. In this case, ketone, diethyl ketone, isopropyl methyl ketone, butyl a Water-soluble resin such as gum arabic, shellac, dextrin, methyl ketone, ethyl propyl ketone, isobutyl methyl ketone, casein, and hydroxyethyl cellulose are used. pinacolone, methyl pentyl ketone, butyl ethyl ketone, dipro As a method of mixing or dispersing the color former and pyl ketone, diisopropyl ketone, hexyl methyl ketone, iso the developer into the binder resin, used is Wet dispersion hexyl methyl ketone, heptyl methyl ketone, and dibutyl method that uses a solvent in a device such as a high-speed ketone; unsaturated ketones such as ethylidene acetone, allyl dissolver, roll mill, or ball mill, or melt kneading that uses acetone, and mesityl oxide; cyclic kotones such as a roll, pressure kneader, internal mixer, or screW extruder. As cyclopentanone, cyclohexanone, and cyclooctanone; and a mixing means, a ball mill, V-mixer, Forberg, or Henschel esters such as ethyl formate, propyl formate, butyl formate, mixer can be used. 25 isobutyl formate, pentyl formate, isopentyl formate, ethyl Next, a case Where the image forming material of the acetate, isopropyl acetate, propyl acetate, butyl acetate, present invention is applied to a thermal transfer ink ribbon isobutyl acetate, pentyl acetate, isopentyl acetate, sec-amyl Will be described beloW. In a thermal transfer ink ribbon, a acetate, hexyl acetate, allyl acetate, 2-methoxyethyl acetate, soft resin having a relatively loW molecular Weight and a loW 2-ethoxyethyl acetate, 1,2-diacetoxy ethane, methyl glass transition point is suitably used as a binder resin from propionate, ethyl propionate, propyl propionate, isopropyl a vieWpoint of thermal transfer characteristics. Speci?c propionate, butyl propionate, pentyl propionate, isopentyl examples of binder resin are polyethylene, polypropylene, propionate, sec-amyl propionate, 2-methoxypropyl acetate, an ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate 2-ethoxypropyl acetate, methyl butyrate, ethyl butyrate, copolymer, ethylene-maleic anhydride copolymer, ethylene propyl butyrate, isopropyl butyrate, butyl butyrate, pentyl acrylate-maleic anhydride copolymer, propylene-vinyl 35 butyrate, isopentyl butyrate, sec-amyl butyrate, methyl acetate copolymer, propylene-ethyl acrylate copolymer, isobutyrate, ethyl isobutyrate, propyl isobutyrate, isopropyl propylene-maleic anhydride copolymer, propylene-acrylate isobutyrate, butyl isobutyrate, pentyl isobutyrate, isopentyl maleic anhydride copolymer, butylene-vinyl acetate isobutyrate, sec-amyl isobutyrate, methyl valerate, ethyl copolymer, butylene-butyl acrylate copolymer, butylene valerate, propyl valerate, isopropyl valerate, butyl valerate, maleic anhydride copolymer, and butylene-acrylate-maleic methyl hexanoate, ethyl hexanoate, propyl hexanoate, and anhydride copolymer. It is also possible to use a styrene isopropyl hexanoate. Examples of another other acrylate copolymer having a relatively loW molecular Weight than the above solvents are methylene chloride, besides the above ole?nic resin and a copolymer thereof. In y-butyrolactone, [3-propyolactone, N-methylpyrrolidinone, this case, acrylate monomers such as n-butyl methacrylate, dimethyl formamide, dimethyl acetoamide and dimethyl isobutyl methacrylate, ethyl acrylate, n-butyl acrylate, 45 sulfoxide. These solvents can be used singly or in the form methyl methacrylate, glycidyl methacrylate, dimethylami of a mixture of at least tWo compounds. noethyl methacrylate, diethylaminoethyl methacrylate, A solvent having loW af?nity With the binder may be diethylaminopropyl acrylate, 2-ethylhexyl acrylate, butyl mixed With the above solvent. Examples of such a solvent acrylate-N-(methoxymethyl) acrylamide, ethylene glycol are, for example, Water, methyl alcohol, ethyl alcohol, methacrylate, and 4-hexa?uolobutyl methacrylate can be propyl alcohol, , butyl alcohol, isobutyl used. It is also possible to use a polyester-based resin having alcohol, pentyl alcohol, 2-pentyl alcohol, 3-pentyl alcohol, a relatively loW molecular Weight and a loW glass transition isopentyl alcohol, l-hexanol, 2-hexanol, 3-hexanol, point. In the case of a decolorable thermal transfer ribbon, a cyclopentanol, cyclohexanol, ethylene glycol, propylene resin having 10% by Weight of polar groups such as a glycol, butylene glycol, and glycerin. polyole?n-based resin and loW-molecular Weight polysty 55 Further, a solvent having high af?nity With the binder may rene resin highly compatible With a color former can also be be used. Examples of such a solvent are, for example, used. toluene, ethylbenZene, propylbenZene, cumene, When the image forming material is used for a thermal butylbenZene, isobutylbenZene, sec-butylbenZene, transfer ink ribbon, a plasticiZer may be added to a binder pentylbenZene, diethylbenZene, mesitylene, xylene, cresol, resin. As a plasticiZer, Wax having a loW content of polar etylphenol, dimethoxybenZene, dimethoxytoluene, benZyl groups such as polyethylene Wax or polypropylene Wax is alcohol, tolyl carbinol, cumyl alcohol, acetophenone, suitable. Appropriate ink ?lm thickness for decolorable propiophenone, hexane, pentane, heptane, octane, thermal transfer ink ribbon is determined from image den cyclohexane, cyclopentane, cycloheptane, cyclooctane, and sity for minimum thickness and from thermal transfer char petroleum fractions such as petroleum ether and benZene. acteristics for maximum thickness. More speci?cally, the 65 When a natural material such as ethylbutylate (pineapple thickness is preferably 0.5 to 20 pm, more preferably, 2 to oil) is used as a solvent, in?uence to environment is made 8 pm. extremely loW, even if the solvent remains in Waste pro US 6,313,066 B1 11 12 duced When paper sheets including the image forming potato starch, and dogtooth violet starch; grain poWders material are recycled. containing starch as its main component such as Wheat ?our, If a decolorant is added in a decoloring solvent, an image barley ?our, rye ?our, and rice ?our; starch derivatives such formed from the image forming material of the present as methylstarch, ethylstarch, acetylstarch, and nitrostarch; invention Will be decolored more efficiently. cellulose; cellulose derivatives such as cellulose acetate, Examples of the decolorant (decoloring agent) are sterol methylcellulose, ethylcellulose, and nitrocellulose; polysac compounds such as animal sterins, plant sterins, and fungi charides and their derivatives such as dextrin, dextran, sterins. Examples of the animal sterins are , mannan, amylopectin, amylose, xylan, glycogen, inulin, lanosterol, lanostadial, agnosterol, cholestanol, coprostanol, lichenin, chitin, hemicellulose, pectin, vegetable gum, ostreasterol, actiniasterol, spongosterol, and clionasterol. agarose, carrageenin, and . Examples of the bile acid are cholanoic acid, cholic acid, Examples of polyamino acid are a homopolymer of amino hyodeoxycholic acid, and lithocholic acid. Examples of the acid having a hydroxyl group, amino group, or oxycarbonyl plant sterins are stegmasterol, ot-sitosterol, [3-sitosterol, group and a derivative of the amino acid, or a copolymer y-sitosterol, brassicasterol, and vitamin D. An example of containing 5% or more of the amino acid and its derivative the fungi sterin is ergosterol. These compounds can be used 15 such as threonine, serine, cystine, hydroxyproline, singly or in combination of tWo or more species. A material tryptophan, aspartic acid, glutamic acid, arginine, lycine, such as lanolin alcohol that is originally a mixture can also ornithine, and histidine. be used. Derivatives of above decolorant may be used. Glycoprotein in Which sugar and protein are bonded also Speci?c examples of such a decolorant are methyl cholate, functions as the polymer decolorant. Examples of the gly sodium cholate, methyl lithocholate, sodium lithocholate, coprotein are collagen, Taka-amylase A, casein, germ methyl hyodeoxycholate, choresterol methylcarbonate, glycoprotein, and egg albumin. pregnenolone, methylandrostenediol, estradiol benZoate, A polymer having a hydroxyl group may be any polymer epiandrostene, stenolone, [3-sitosterol, pregnenolone acetate, if only it can adsorb physically or chemically the developer [3-chorestanol, 5 ,16-pregnadiene-3[3-ol-20-one, 5ot-pregnen by donating electrons from lone-pair of atoms. From 3[3-ol-20-one, 5-pregnen-3[3,17-diol-20-one 21-acetate, this vieWpoint, a phenolic resin that has a phenolic hydroxyl 5-pregnen-3[3,17-diol-20-one 17-acetate, 5-pregnen-3[3,21 group and exhibits a developing function is not included in diol-20-one 21-acetate, 5-pregnen-3[3,17-diol diacetate, the polymer decolorant. Polyvinyl alcohol is a typical rockogenin, thigogenin, esmiragenin, heckogenin, and dios example of the polymer compound having a hydroxyl group. genin. These decolorants can be used singly or in a combi Humidity resistance of the image forming material can be nation of tWo or more species. A mixture such as lanolin improved by protecting a portion of side-chain hydroxyl alcohol can also be used. groups of polyvinyl alcohol With an acetyl group, an alkyl The decolorant includes cyclic sugar alcohols and their group, or the like. The ratio of substitution of a hydroxyl derivatives. Speci?c examples are D-glucose, D-mannose, group With another group is determined in accordance With the content of the polymer decolorant in the image forming D-galactose, D-fructose, L-sorbose, L-rhamnose, L-fucose, 35 D-ribodesose, ot-D-glucose pentaacetate, acetoglucose, material. diacetone-D-glucose, D-glucuronic acid, D-galacturonic A polymer having an amino group may be a polymer acid, D-glucosamine, D-fructosamine, D-isosaccharic acid, having an aromatic amine or may be a polymer having a vitamin C, erutorubic acid, trehalose, saccharose, maltose, non-aromatic amine if only it can adsorb physically or cellobiose, gentiobiose, lactose, melibiose, raf?nose, chemically the developer by donating electrons from lone gentianose, meliZitose, stachyose, methyl pair of atoms. Preferable examples of the polymer ot-glucopyranoside, salicin, amygdalin, euxanthic acid and compound having an amino group are homopolymers such 1,2:5,6-diisopropylidene-D-mannitol. One or more types of as polyvinylpyridine, polyvinylpyraZine, these compounds can be used. polyvinylpyrimidine, polyvinylimidaZole, polyvinylpyrrole, The decolorant includes non-aromatic cyclic compounds 45 polyvinylcarbaZole, polyvinylpyrrolidine, of a ?ve-membered or larger ring having a hydroxyl group polyvinylpiperidine, polyvinylpiperaZine, and other than cyclic sugar alcohols, and derivatives of cyclic polyvinylmorpholine, and a copolymer containing 5% or sugar alcohols. Speci?c examples are alicyclic monohydric more of any of monomers containing an amino group. A alcohols such as cyclododecanol, hexahydrosalicylic acid, polymer in Which an amino group is introduced to the , isomenthol, neomenthol, neoisomenthol, benZene ring of polystyrene is also usable as the polymer carbomenthol, ot-carbomenthol, piperithol, ot-terpineol, decolorant. Speci?c examples are polyvinylaniline, polysty [3-terpineol, y-terpineol, 1-p-menthene-4-ol, isopulegol, rene substituted by a quaternary ammonium salt used as an dihydrocarveol, and carveol; alicyclic polyhydric alcohols anion exchange resin, polystyrene substituted by an amino such as 1,4-cyclohexanediol, t-1,2-cyclohexanediol, group having an ethylenediamine skeleton, and their deriva phloroglucitol, quercitol, inositol, 1,2-cyclododecanediol, 55 tives. The substitution ratio of an amino group is arbitrary, quinic acid, 1,4-terpene, 1,8-terpene, pinol hydrate, and but preferably 5% or more. betulin; polycyclic alcohol derivatives such as , In order to bringing the solvent contact With the image isoborneol, adamantanol, norborneol, fenchol, and ; forming material on a paper sheet, the paper sheet may be and derivatives of cyclic sugar alcohols such as 1,215,6 immersed in a solution or the solvent may be sprayed onto diisopropylidene-D-mannitol. the paper sheet. Alternatively, stationary such as a decolor Examples of polymer decolorant are a polymer compound ing pen containing a decoloring solvent may be used. having a sugar skeleton, polyamino acid, a polymer com As for the image forming material of the present pound having a hydroxyl group, a polymer compound invention, it is found that a good decolored state can be having an amino group, polyvinylacetal, polyacrylonitrile, stably obtained under a condition Where pH of the image and their derivatives, and a mixture thereof. 65 forming material is 7 or more. Therefore, if the pH of the Examples of the polymer compound having a sugar image forming material is adjusted to about 8 by adding a skeleton are starch such as ot-starch, [3-starch, corn starch, pH control agent, a good decolored state can be obtained. An US 6,313,066 B1 13 14 example of the pH control agent is a basic substance. The order to obtain a good decolored state. When such a method basic substance is not particularly limited as long as it does is employed, it can be obtained an effect of controlling the not damage or discolor a paper sheet. state of paper sheet by removing completely the solvent Examples of suitable inorganic basic compounds are remaining in the paper sheet. calcium chloride, potassium hydroxide, calcium hydroxide, sodium hydroxide, barium hydroxide, magnesium EXAMPLES hydroxide, ammonium carbonate, potassium carbonate, cal Examples of the present invention Will be described cium carbonate, sodium carbonate, magnesium carbonate, hereinafter. In the folloWing examples, an image Was formed ammonium hydrocarbonate, potassium hydrocarbonate, on a paper sheet of 500BLATT manufactured by sodium hydrocarbonate, alkaline metal borates, tripotassium 10 phosphate, dipotassium hydrophosphate, calcium NEUSIEDLER, as long as otherWise speci?ed. phosphate, trisodium phosphate, and disodium hydrophos Example 1 phate. Examples of suitable organic basic compounds are pri TWo parts by Weight of Crystal Violet Lactone (CVL) as mary to tertiary and quaternary ammonium salts. 15 a color former, tWo parts by Weight of propyl gallate as a Examples of the counter ions of the quaternary ammonium developer, one part by Weight of polypropylene Wax as a salts are a hydroxyl ion, halogen ion, and alkoxide ion. Wax component, 94 parts by Weight of polystyrene (SB-130 Examples of the non-aromatic organic basic compounds manufactured by Sanyo Chemicals Co., Ltd.) as a binder are those having an aliphatic hydrocarbon group having 1 to resin and one part by Weight of charge control agent (LR 50 atoms or an alicyclic hydrocarbon group having 20 147 manufactured by Nippon Carret Inc.) Were mixed, and the mixture Was kneaded using a kneader. The kneaded 1 to 50 carbon atoms. These hydrocarbon groups may be substituted by at least one selected from the product Was pulveriZed by a pulveriZer to obtain a poWder group consisting of vinyl group, ethynylene group, ethynyl having an average particle siZe of 10 pm. One percent by Weight of hydrophilic silica Was externally added to the group, oxy group, oxycarbonyl group, thiocarbonyl group, dithiocarbonyl group, thio group, sul?nyl group, sulfonyl 25 poWder to prepare blue electrophotographic toner. The resultant toner Was put into a toner cartridge of a copier group, carbonyl group, hydraZo group, aZo group, aZido group, nitrilo group, diaZoamino group, imino group, urea (Premage 38 manufactured by TOSHIBA CORP), and a bar bond, thiourea bond, amide bond, urethane bond, and car code image Was transferred on a paper sheet. As a result, a bonyldioxy group. bar code image having re?ection density of about 0.6 could 30 be obtained. By reading the bar code image With a bar code Examples of aromatic organic basic compounds are those reader (BHT-5075-T manufactured by TEC Company), it having an aromatic ring such as benZene ring, biphenyl ring, naphthalene ring, tetralone ring, anthracene ring, phenan Was con?rmed that bar code data Were able to be input. threne ring, indene ring, indan ring, pentalene ring, aZulene The paper sheet on Which the bar code image Was formed Was immersed into diethoxyethane, and then Was air-dried. ring, heptalene ring, and ?uorene ring. The aromatic ring 35 may be substituted by an aliphatic hydrocarbon group hav After the immersion into the solvent, the re?ection density ing 1 to 50 carbon atoms or an alicyclic hydrocarbon group became about 0.1, and the image could not be read With the having 1 to 50 carbon atoms. Further, the hydrocarbon group bar code reader. may be substituted by a substituent given above. Abar code image Was transferred again to the paper sheet Examples of the cyclic amines are aZiridine, aZetidine, after decoloration by using the copier. As a result, a bar code pyrroline, pyrrolidine, indoline, pyridine, , 40 image having re?ection density of about 0.6 could be hydropyridine, quinoline, isoquinoline, tetrahydroquinoline, obtained. By reading this bar code image With the bar code tetrahydroisoquinoline, acridine, phenanthriZine, reader, it Was con?rmed that bar code data Were able to be phenanthroline, pyraZole, benZimidaZole, pyridaZine, input. Thereafter, as decoloration and image-formation Were repeated, the re?ection density of the background Was pyrimidine, pyraZine, , histamine, 45 decahydroquinoline, pyraZoline, imidaZoline, imidaZolidine, gradually raised. Therefore, When the bar code image piperaZine, cinnoline, phtharaZine, quinaZoline, quinoxaline, formed in the fourth transfer Was read With the bar code dihydrophenaZine, triaZole, benZotriaZole, triaZine, reader, any bar code data Were not able to be input. tetraZole, pentamethylenetetraZole, tetraZine, purine, The polystyrene resin has a high glass transition point and pteridine, carboline, naphthyridine, indoliZine, quinoliZine, is relatively hard. Thus, the resin is thermally metastable. quinuclidine, oxaZole, oxaZolidine, benZoxaZole, isoxaZole, The re?ection density of the image decolored by the immer anthranil, oxaZine, oxaZoline, thiaZole, thiaZolidine, sion into the solvent did not return to the original re?ection benZothiaZole, benZothiaZoline, isothiaZole, thiaZine, density, so that the image did not appear again. aZoxime, furaZane, oxadiaZine, thiadiaZole, benZothidiaZole, Example 2 thiadiaZine, dithiaZine, , 55 hexamethylenetetramine, and diaZabicycloundecene. TWo parts by Weight of 3-(4-dimethylamino-2 Examples of usable organic basic compounds other than ethoxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-4 those enumerated above are amidine, guanidine, aZaphthalide as a color former, tWo parts by Weight of propyl aminoguanidine, urea, thiourea, , gallate as a developer, one part by Weight of polypropylene thiosemicarbaZide, and carbonohydraZide. 60 Wax as a Wax component, 94 parts by Weight of a styrene In the present invention, the basic compounds can be butyl acrylate copolymer, having an acrylate content of 6% mixed as they are With the other components of the image by Weight, as a binder resin and one part by Weight of charge forming material. Also, it is desirable to mix the basic control agent (LR-147 manufactured by Nippon Carret Inc.) compound encapsulated in microcapsules With the other Were mixed, and the mixture Was kneaded using a kneader. components of the image forming material. 65 The kneaded product Was pulveriZed by a pulveriZer to In the present invention, a step of heating the image obtain a poWder having an average particle siZe of 10 pm. forming material may be added after solvent decoloration in One percent by Weight of hydrophilic silica Was externally US 6,313,066 B1 15 16 added to this powder to prepare blue electrophotographic mixture Was kneaded using three rolls. The kneaded product toner. The resultant toner Was put into the toner cartridge of Was applied in an amount of about 7 g/m2 to a ?lm for the copier, and a bar code image Was transferred on a paper an ink ribbon, using a hot melt coater, so as to make a blue sheet. As a result, a bar code image having re?ection density thermal transfer ink ribbon. The ink ribbon Was set to a bar of about 0.8 could be obtained. By reading this bar code code printer (B-30 manufactured by TEC Company), and an image With the bar code reader, it Was con?rmed that bar image Was transferred to a thermal transfer paper sheet code data Were able to be input. (JW-Z103). As a result, a bar code image having re?ection The paper sheet on Which the bar code image Was formed density of about 0.7 could be obtained. By reading the bar Was immersed into diethoxyethane, and then Was air-dried. code image With the bar code reader, it Was con?rmed that After the immersion into the solvent, the re?ection density 10 bar code data Were able to be input. became about 0.12. It Was dif?cult to recogniZe the bar code On the other hand, 2-butanone Was put into Writing parts image With the naked eye, and the image could not be read (FV-0200 manufactured by I & J FISNER company) to With the bar code reader. make a decoloring pen. The decoloring pen Was caused to go Abar code image Was transferred again to the paper sheet and return several times on the bar code image formed on the after decoloration using the copier. As a result, a bar code 15 paper sheet so that the image Was brought into contact With image having re?ection density of about 0.8 could be the solvent, and then the paper sheet Was air-dried. After the obtained. By reading the bar code image With the bar code decoloring operation, blurs of the dye components Were reader, it Was con?rmed that bar code data Were able to be slightly generated on the paper sheet. The re?ection density input. Thereafter, When decoloration and image-formation became about 0.17, and the image could not be read With the Were repeated, the re?ection density of the background Was 20 bar code reader. only slightly increased. The bar code image formed in the Abar code image Was again transferred to the paper sheet tenth transfer could be read With the bar code reader. after decoloration using the bar code printer. As a result, a Any residual image due to ?oW or blur of the image bar code image having re?ection density of about 0.7 could forming material Was not observed on the paper sheet after 25 be obtained. By reading the bar code image With the bar code solvent decoloration. Thus, it Was unnecessary to perform an reader, it Was con?rmed that bar code data Were able to be operation to pass the paper sheet through heat rolls in order input. HoWever, since the ethylene-vinyl acetate copolymer to erase the image completely. has a loW glass transition point and is relatively soft, the image Was not thermally stable. Therefore, When the paper Example 3 30 sheet after solvent decoloration Was heated for a short time, Three parts by Weight of 2-chloro-6-(dimethylamino) it turned into a color-developed state easily. ?uorane as a color former, tWo parts by Weight of methyl Additional advantages and modi?cations Will readily gallate as a developer, and 95 parts by Weight of polystyrene occur to those skilled in the art. Therefore, the invention in as a binder resin Were mixed, and the mixture Was kneaded its broader aspects is not limited to the speci?c details and using a kneader. The kneaded product Was pulveriZed by a 35 representative embodiments shoWn and described herein. pulveriZer to obtain a red poWder having an average particle Accordingly, various modi?cations may be made Without siZe of about 0.5 pm. Forty parts by Weight of this poWder, departing from the spirit or scope of the general inventive 59 parts by Weight of limonene as a solvent, and one part by concept as de?ned by the appended claims and their equiva Weight of polyethylene Wax as a Wax component Were lents. mixed, and then suf?ciently dispersed With a paint shaker to 40 What is claimed is: prepare a red liquid ink. The liquid ink Was put on a pen 1. A decoloring method of an image using a material having a round head, and then an image Was hand-Written on comprising a color former, a developer and a binder resin, a paper sheet. As a result, an image having re?ection density Which is applied to a paper sheet, comprising steps of: of about 1.0 could be obtained. heating the paper sheet so that the binder resin adsorbs the 45 The paper sheet on Which the image Was formed Was color former and a cellulose component of the paper imersed into diethoxyehtane, and then Was air-dried. After sheet adsorbs the developer When the temperature of the immersion into the solvent, the re?ection density became the paper sheet is raised, thereby shifting an equilib about 0.12. Slight residual images Were observed on the rium betWeen the color former and the developer to a paper sheet, but any trace or blur due to ?oW of dye non-developed side; and components Was not observed. The residual images could be 50 sufficiently decolored by passing the paper sheet through keeping the state shifted to the non-developed side When the temperature of the paper sheet is loWered. heat rolls. The paper sheet after decoloration Was kept 2. The method according to claim 1, Wherein the binder standing at 60° C. for 300 hours, but any image did not appear again. The re?ection density after decoloration resin is a non-polar resin. remained unchanged. 55 3. The method according to claim 1, Wherein the binder resin comprises 90% or more by Weight of a non-polar Example 4 monomer. 4. The method according to claim 1, Wherein the binder One part by Weight of Crystal Violet Lactone (CVL) as a resin is selected from the group consisting of polystyrene, color former, one part by Weight of propyl gallate as a 60 and polystyrene derivatives and styrene copolymers com developer, and 18 parts by Weight of an ethylene-vinyl prising 90% or more by Weight of a styrene monomer. acetate copolymer (ELVAX500W manufactured by Mitsui Dupon Polychemical) as a binder resin Were mixed, and the * * * * *