JPH0569664A - Thermally reversible image forming method and recording medium used therein - Google Patents

Abstract

PURPOSE:To provide a thermally reversible image forming method using a recording material constituted so as to repeatedly perform sharp printing. CONSTITUTION:A recording material is formed by coating a base material with a composition (thermoplastic discoloring recording material containing an electron donative color forming compound, an electron acceptive compound a discoloring temp. control agent and a low volatility solvent as essential components and further containing a nucleating agent if necessary. Pref., the thermoplastic discoloring recording material is included in a microcapsule and applied to the base material along with a binder. By the use of this recording material, an image is erased by natural standing and the formation of an image can be repeatedly performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoreversible color-changing sheet which reversibly changes color in response to temperature changes and a recording method using the same. The present invention relates to an image forming method capable of being repeatedly used which exhibits reversible thermochromic erasing, and a recording medium useful for carrying out the method.

[0002]

2. Description of the Related Art A printing system using a device such as a word processor is widely used in offices and general households. In the process of creating documents, drawings, etc. with these devices, when printing the screen displayed on the display after input, the text, layout, typographical errors, etc. on the display are not usually checked, calibrated, or corrected sufficiently. To
Work to check after printing once is done.

In general, even if confirmation work is performed on the display, work requiring further correction often occurs due to printout. No special means is currently used for the prints required for checking, proofreading, correcting, etc., and recently some work has been done by printing out on thermal paper to check, calibrate, correct, etc. There are also cases where the final print is printed by thermal transfer with an ink ribbon, but in most cases, normal printing is performed to check, calibrate,
The reality is that work such as modification is being done. Therefore, in a thermal printer using a thermal head, waste of consumables such as paper and ink ribbon is generated.

By the way, Japanese Laid-Open Patent Publication No. 60-52388 discloses a paper recycling printing method using a thermal printer. This is for the purpose of reusing printing paper. Use a thermo sheet coated with a reversible heat-sensitive material in a low temperature atmosphere such as Ag ₂ HgI ₄ , and when reusing it, a low temperature, for example, 5 ° C or less. It is cooled down to be used again as a recording medium. However, the heat-sensitive material used here is colored from the beginning,
There are problems that the contrast is poor (Ag ₂ HgI ₄ changes from yellow to yellow-orange), and that a reuse requires a cooling device to erase the print contents.

In addition to this, in connection with such recycling of printing paper, recycled paper of OA equipment paper by re-papermaking (Japanese Patent Laid-Open Nos. 1-95082 and 1-10157).
No. 6, JP-A-2-55195, etc.), printing is performed on a sheet which is not soaked with ink, and the sheet is wiped with an erasing liquid for reproduction (JP-A-1-90582), and the printed matter is passed through a solvent. The ink is dissolved and removed (Japanese Patent Laid-Open No. 101576/1989), the ink peeling body is overlaid on the one printed on the release layer on the surface of the support, and the ink is transferred to the peeling body side through a heat roll to remove it. 2-5
No. 5195), repeated printing is performed with paper using a photochromic material (Japanese Patent Laid-Open No. 64-3874).
No. 2), a thermosensitive recording material using a thermochromic material composed of an electron-donating color-developing organic compound and a hydroxybenzoic acid ester derivative as an electron-accepting compound is used for printing and erasing. 52-14
No. 0483) is proposed.

[0006] However, the production of recycled paper is currently expensive because it involves the steps of collecting used paper, deinking, pulping and remaking paper. In the above, since an ink removing device is required, or a solvent and a peeling body are required, there is a problem of a recycling treatment of these. In the above, many problems such as restriction of light source due to ultraviolet irradiation, sensitivity, and stability remain. Further, in the above, further improvement is required in heat responsiveness, color density, decoloring property and reversibility.

[0007]

SUMMARY OF THE INVENTION The present invention solves the problems described above, and after confirming the printed contents of a document, drawing, etc. by a thermal printer, it can be easily erased by leaving it naturally, resulting in good contrast. It is intended to provide a method capable of repeating clear printing and a thermoreversible recording medium useful for the method. A typical example of the thermoreversible recording medium here is printer paper used for checking, proofreading, and correcting sentences, layouts, typographical errors, etc. used in printers such as word processors.

[0008]

The first aspect of the present invention is a thermoreversible image forming method, which comprises an electron-donating color-forming organic compound, an electron-accepting compound, a color-changing temperature controlling compound and a low volatility compound on a substrate. A microcapsule containing a thermoreversible color-changing material containing a hydrophilic solvent as an essential component is applied together with a binder to prepare a recording medium, and an image is formed by printing characters and symbols on the recording medium using a thermal head. The feature is that the image is erased by leaving it for a while and the image is repeatedly formed.

The second aspect of the present invention is a thermoreversible recording medium, in which the following four components (a), (b), (c) and (d) are encapsulated in microcapsules and coated with a binder. A recording medium comprising a thermoreversible color change recording layer formed thereon. Component (a): Electron-donating color-developing organic compound that is a color former (b) Component: Electron-accepting compound that is the developer of the component (a) (c) Component: Specific time and / or specific temperature range Discoloration Temperature Controlling Compound for Reversibly Coloring and Decoloring in (d) Component: Low Volatility Solvent for Improving Thermal Response and Coloring Density

In order to achieve the above-mentioned object, the inventors of the present invention investigated the work such as confirmation, proofreading and correction of the sentence, layout, typographical error, etc. after printing from the word processor etc., and as a result, the confirmation work was A-4. 2 to 5 minutes for size paper
It is about 10 minutes at the longest, and the printing density is preferably 0.8 or more, but it was confirmed that the object can be sufficiently achieved if the printing density is 0.6 or more. Furthermore, repeated reuse after confirmation does not require immediate use of the same sheet if multiple sheets of paper are prepared, and may be reused on the next day. I confirmed that there was no problem.

This is shown in the attached drawing (graph shown in FIG. 1).
The explanation is as follows. The vertical axis of the graph represents the printing density, the horizontal axis represents the time, the solid line represents the color development process by printing, and the broken line represents the confirmation / erasure process after printing. The unit of the time on the horizontal axis is different between the solid line and the broken line, but in order to understand the repeating characteristics, they are displayed as arbitrary times on the same graph.
A is the density before printing, that is, the color is decolored, and B is the density obtained by printing with the thermal head at time t ₁ and developing the color. During time t ₂ ~t ₃ is a time required for the verification procedure, the print during concentration comes down from C to D. Times t _{3 to} t ₄ show the time required for erasing after the confirmation work, and the density shows that the density returns to A which is the decolored state before printing.

From the above viewpoints, the present inventors have conducted various studies on the heat-coloring type thermoreversible color-changing material having such characteristics, and as a result, the electron-donating color-developing organic compound,
By adding a specific solvent (low volatile solvent) to the three-component system consisting of an electron-accepting compound and a color-changing temperature controlling compound, it exhibits a reversible change from colorless state to color when heated, and has excellent thermal response. It was found that a thermoreversible discoloring material with high color density can be obtained, and by adding a nucleating agent to these four-component type materials, the thermal responsiveness is improved and a decolored state with no residual color is formed. I also found out to do.
These have been completed in the present invention.

The present invention will be described in more detail below.
As described above, the thermoreversible color-changing material that develops color by heating of the present invention includes (a) an electron-donating color-developing organic compound that is a color former as an essential component, (b) the color development of the (a) compound. An electron-accepting compound which is an agent, (c) a color-changing temperature controlling compound for causing reversible color development and decolorization at a specific time and in a specific temperature range, and (d) a low color temperature improving compound for improving thermal responsiveness and color density. It is composed of four components of volatile solvents. In the reversible color-changing material according to the present invention, as mentioned above, it is desirable to add a nucleating agent for improving the decoloring property as the component (e) to the four components. A thermoreversible recording sheet intended for repeated use of the present invention is prepared by encapsulating these thermoreversible color-changing materials in microcapsules and providing them together with a binder as a layer on a substrate.

The electron-donating color-developing organic compound (component a) used in the present invention may be used alone or as a mixture of two or more kinds, and is itself a colorless or pale color dye precursor, for example, triphenylmethane. There are phthalide compounds, fluoran compounds, spiropyran compounds, indinophthalide compounds and the like. For the purpose of the present invention, such as text, layout, check of typographical errors, proofreading, correction, etc., black, blue,
It is preferable to select a material that develops green or the like, but the material is not particularly limited. Specific examples of the electron-donating color developing organic compound include the following. 3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-bis (p-dimethylaminophenyl) -6
-Dimethylaminophthalide (also known as crystal violet lactone), 3-diethylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7-
(O-Chloranilino) fluorane, 3-pyrrolidino-
6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane,
3-N-methyl-N-isopropylamino-6-methyl-7-anilinofluorane, 3-N-methyl-N-isobutylamino-6-methyl-7-anilinofluorane,
3-N-methyl-N-amylamino-6-methyl-7-
Anilinofluorane, 3-N-ethyl-N-isoamylamino-6-methyl-7-anilinofluorane, 3-N
-Methyl-N-cyclohexylamino-6-methyl-7
-Anilinofluorane, 3-Np-tolyl-N-ethylamino-6-methyl-7-anilinofluorane, 3-
Diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-5-methyl-7-dibenzylaminofluorane, 3-N-ethyl-N- (2-ethoxypropyl) amino-6-methyl-7. -Anilinofluorane, 2-anilino-3-methyl-N-ethyl-N-p-tolyl-aminofluorane, 6'-chloro-8'-methoxybenzoindolinose pyropyran, 3,3-bis (1- Ethyl-2-methyl-8-yl) phthalide, 3-bis (2
-Phenylindol-3-yl) phthalide, benzoyl leuco methylene blue. Among these, especially 2-anilino-3-methyl-
The use of N-ethyl-Np-tolyl-aminofluorane is preferred. The reason is that this compound is
This is because a small amount of the electron-accepting compound and the temperature controlling compound is used to exhibit an excellent effect on thermoreversibility, in particular, image decoloring property. These characteristics are considered to be related to the bond strength due to temperature change, dissolution, etc. in the system with the electron accepting compound and the temperature controlling compound.

The electron-accepting compound used in the present invention for coloring the electron-donating color-forming organic compound by heating.
The component (b) can be selected from the color developers generally used for thermal paper, but its selection range is narrower than that of a system that reversibly decolorizes by heating, and a particularly preferred electron-accepting compound Specific examples include dodecyl gallate, cetyl gallate, gallic acid esters such as stearyl gallate,
Parahydroxybenzoic acid esters such as methyl parahydroxybenzoate, ethyl parahydroxybenzoate, propyl parahydroxybenzoate, stearyl protocatechuate, protocatechuate esters such as benzyl protocatechuate, or phenolic hydroxyl group-containing compounds such as urea can give. Among these, particularly preferable electron-accepting compounds are gallic acid esters.

Examples of the discoloration temperature controlling compound (component (c)) used in the present invention include high boiling point alcohols, esters, acid amides, carboxylic acids, ethers and ketones. For example, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, behenyl alcohol, stearyl myristate, propyl palmitate, ethyl stearate, butyl stearate, glycerin tristearate, glycerin trimyristate, propylene glycol distearate, glycerin monocetyl. There are ether, myristic acid, palmitic acid, lauric acid, didecyl ether, didodecyl ether, stearic acid amide and the like.

Examples of the low volatile solvent (d component) used in the present invention include alkylnaphthalene compounds, diarylalkane compounds, alkylbiphenyl compounds, terphenyl compounds and triarylmethane compounds. Specifically, ethylnaphthalene, butylnaphthalene, hexylnaphthalene, dimethylnaphthalene,
Diethylnaphthalene, dipropylnaphthalene, diisopropylnaphthalene, methylpropylnaphthalene, ethylpropylnaphthalene, methylbutylnaphthalene, dimethylpropylnaphthalene, 1-methyl-1-dimethylphenyl-1-phenylmethane, 1-methyl-1-ethylphenyl-1 -Phenylmethane, dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, hydrogenated terphenyl, tritoluylmethane and the like.

The nucleating agent (component e) used in the present invention promotes crystallization of the discoloration temperature controlling compound and the electron-accepting compound during cooling to improve the decoloring speed and decoloring concentration, as described above. It has the role of decreasing the supercooling degree of crystallization, increasing the number of crystal nuclei, refining the crystal and accelerating the crystallization speed, and as a result, the thermal response is improved and there is no residual color. A decolored state can be obtained. As a result of studying various inorganic and organic nucleating agents, preferred nucleating agents include, for example, dibenzylidene sorbitols such as P-methyldibenzyl den sorbitol, dimethyl dibenzylidene sorbitol, P-ethyl dibenzyl den sorbinol, D
-Condensation products of sorbitol and benzaldehyde, etc. may be mentioned.

It is necessary to select an appropriate ratio for the mixing ratio of each component depending on the physical properties of the materials used, but in practice, it can be selected in a considerably wide range, and the electron-donating color-forming organic compound (component a) can be selected. ): Electron-accepting compound (component b): Discoloration temperature adjusting compound (component c): Low volatility solvent (component d) in a mixing ratio (weight) of 1.0: 0.5 to 4.0: 5 to 5 .0:
A range of 0.2 to 4.0 is suitable. The low-volatile solvent (component d) preferably accounts for 20 to 80% by weight of the total amount of the components a, b, c and d.
If it is less than the above range, the thermal response speed and the color density are not improved so much. On the contrary, if it is too much, the reversibility of the color development and the color erasing is deteriorated, and the color erasing is not sufficiently performed.

The amount of the nucleating agent (e component) added is a component,
0.5 to 20 of b component, c component, d component and e component total amount
It preferably appears to be weight percent. If it is less than 0.5% by weight, the effect of the addition of the nucleating agent is poor, and if it is more than 20% by weight, the whiteness of the nucleating agent interferes with the color density.

The thermoreversible recording medium of the present invention having each of these components has a coloring temperature of 50 ° C. to avoid coloration during handling or storage and in consideration of thermal response.
It is preferably in the range of 120 ° C., and this is achieved by selecting an appropriate combination of components and mixing ratio.

In the present invention, the thermoreversible color-changing material having the above constitution is used by being encapsulated in microcapsules. Microencapsulation can be performed, for example, by coacervation method, interfacial polymerization method,
1 to several tens of μ by known techniques such as in situ polymerization method
It can be used in the form of microcapsules having a particle size of about m. The thermoreversible recording sheet intended for repeated use according to the present invention can be prepared by dispersing the obtained microcapsules together with a binder such as polyvinyl alcohol and coating the dispersion on a substrate.

The substrate may be paper, a plastic sheet, or a composite thereof, which has been conventionally used for various recording and printing purposes, and is not particularly limited. These substrates may be white or lightly colored for the purpose of identification or the like so as not to interfere with the confirmation work.

Further, the thermoreversible recording sheet of the present invention is preferably used in which a protective layer containing a water-soluble polymer or an aqueous emulsion of a polymer as a main component is formed on the surface of the thermoreversible color-change recording layer. Is. A water-soluble polymer or an aqueous emulsion of a polymer has excellent film-forming properties, and therefore has excellent chemical resistance, water resistance, sweat resistance, heat resistance and abrasion resistance, and the film-forming temperature is room temperature. Or because it is below room temperature,
No need to add extra heat. Since the types of the water-soluble polymer and the polymer aqueous emulsion used in the present invention are not limited, various conventionally known compounds can be used.

Specific examples of the water-soluble polymer include, for example,
Polyvinyl alcohol, modified polyvinyl alcohol, starch and its derivatives, cellulose derivatives (methyl cellulose, methoxy cellulose, hydroxyethyl cellulose, etc.), casein, gelatin, polyvinyl pyrrolidone, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, Diisobutylene-maleic anhydride copolymer, polyacrylamide, modified polyacrylamide, methyl vinyl ether-maleic anhydride copolymer, carboxy-modified polyethylene, polyvinyl alcohol-acrylamide block copolymer, melamine-formaldehyde resin, urea-formaldehyde resin, etc. Examples of the aqueous emulsion include, for example,
Polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-butadiene-acrylic copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer Examples thereof include polymers. These may be used alone or as a mixture, and if necessary, a curing agent may be added to cure the resin.

There is no particular limitation on the coating method and coating amount of the protective layer, but the coating amount is 1 g / m 2 in terms of solid content.
² or more, preferably 3 to 15 g / m ² is applied.

In the thermoreversible recording sheet of the present invention, various additives may be added to the protective layer in order to prevent sticking during recording. The additives used in the present invention include inorganic and organic fillers, for example, aluminum hydroxide, heavy and light calcium carbonate, zinc oxide, titanium oxide, barium sulfate, silica gel, activated clay, talc, cresatin white, Kaolinite, calcined kaolinite, diatomaceous earth, synthetic kaolinite, polyolefin particles, polystyrene particles, urea-formaldehyde resin particles and the like, and, as the lubricant, there are waxes, for example, stearic acid amide, zinc stearate, Palmitic acid amide, oleic acid amide, lauric acid amide, ethylenebisstearylamide, methylenebisstearylamide, methylosestearylamide,
Examples include paraffin wax. Further, higher alcohol, higher fatty acid, higher fatty acid ester and the like may be added to the film forming resin to form the protective layer.

[0028]

EXAMPLES Specific examples of the present invention will be shown below. Part here,
Both% are based on weight.

Example 1 3-N-Methyl-N-isopropylamino-6-methyl-7-anilinofluorane 1 part Stearyl gallate 5 parts Stearyl alcohol 15 parts Diisopropylnaphthalene (KMC-113, Kureha Chemical Co., Ltd.) 10 parts of thermoreversible color-changing material are uniformly dissolved at about 100 ° C. While heating 60 parts of a 3% aqueous solution of a styrene-maleic anhydride copolymer whose pH was adjusted to 4.5 to 80 ° C., 30 parts of the above-mentioned dissolved product was added dropwise and 2 to 10 using a mixer.
Emulsify and disperse into fine droplets of μm. Next, while stirring the obtained emulsion, a melamine-formalin prepolymer (manufactured by Sanwa Chemical Co., Ltd., Nikalac MX-54) 7.
0 part was added and the mixture was reacted at 70 ° C. for 3 hours to give an average particle size of about 3.
A 2 μm microcapsule dispersion was obtained. Was added to the resultant 30 parts 10% polyvinyl alcohol dispersion 30 parts a coating solution was coated so that the amount deposited during drying on a high-quality paper having a basis weight of 81.4 g / m ² is about 15 g / m ² To form a thermoreversible color change recording layer. When the thermoreversible recording sheet thus prepared for repeated use was printed by a word processor (My Report NL-1 manufactured by Ricoh Co., Ltd.), it was black and had a print density of 0.80.
The density after 10 minutes dropped to 0.71, but there was no problem in reading. After 12 hours of leaving, the printing disappeared and the original state was restored. The print density was measured with a Macbeth densitometer (RD-914 type manufactured by Macbeth Co., Ltd.) (hereinafter the same).
This test was repeated 10 times, but almost no deterioration in function was observed.

Example 2 3-Diethylamino-5-methyl-7-dibenzylaminofluorane 1 part Stearyl protocatechuate 5 parts Stearyl alcohol 10 parts Stearic acid amide 10 parts Diphenyl methane solvent (Nippon Petrochemical, SAS -296) 10 parts of the thermoreversible discoloring material are uniformly dissolved at about 100 ° C. 5% gelatin aqueous solution with pH adjusted to 7.0 10
While heating 0 part to 80 ° C., 30 parts of the above-mentioned dissolved substance is added dropwise, and emulsified and dispersed into a microdroplet of 2 to 10 μm using a mixer. Next, 120 parts of a 5% aqueous solution of gum arabic heated to 80 ° C. was added, diluted with 220 parts of 70 ° C. warm water, and 10% acetic acid was gradually added with stirring to adjust the pH to 4.3.
To cause coacervation, then 10
After cooling to ° C to cause gelation, 2 parts of 25% glutaraldehyde was added to adjust pH to 9 and stirring was continued for 1 hour to obtain a microcapsule dispersion having an average particle diameter of about 3.0 µm. To 30 parts of the obtained dispersion liquid, 30 parts of 10% polyvinyl alcohol was added to prepare a coating liquid having a basis weight of 81.4 g / m.
^The thermoreversible discoloration recording layer was formed by applying to a finely colored paper of No. ² lightly colored orange so that the amount of adhesion when dried was about 15 g / m ² . The thermoreversible recording sheet thus prepared was printed with a word processor (My Report N-11, manufactured by Ricoh Co., Ltd.) in the same manner as in Example 1, and the print density was 0.76 in green. The density after 10 minutes dropped to 0.71, but there was no problem in reading. After leaving for 10 hours, the print disappears and returns to the original state.
Almost no deterioration in function was observed due to repeated use.

Example 3 Crystal Violet Lactone 1 part Stearyl Gallate 5 parts Stearyl Alcohol 7.5 parts Myristyl Alcohol 7.5 parts Diisopropylnaphthalene 22.5 parts The same composition as in Example 1 was microencapsulated and averaged. A microcapsule dispersion having a particle diameter of about 3.5 μm was obtained. A thermoreversible recording sheet was prepared in the same manner as in Example 1 using a synthetic paper as a substrate, and a printing test was carried out. The printing density was blue and the printing density was 0.75. Although the density after 10 minutes had decreased to 0.70, there was no problem in reading and the repeated function was almost the same as in Example 1.

Example 4 2-anilino-3-methyl-6-N-ethyl 5 parts -N-p-tolylaminofluorane lauryl gallate 10 parts myristyl alcohol 5 parts diisopropylnaphthalene (KMC-113, manufactured by Kureha Chemical Co., Ltd.) ) 10 parts of thermoreversible discoloration material are uniformly dissolved at about 100 ° C. 25 parts of the above-mentioned dissolved substance was added dropwise to 50 parts of a 3% aqueous solution of a styrene-maleic anhydride copolymer having a pH adjusted to 4.5, which was heated to 80 ° C., and 1 to 8 μ using a mixer.
It is softened and dispersed so as to become m microdroplets. Then, while stirring the obtained emulsion, a melamine-formalin prepolymer (manufactured by Sanwa Chemical Co., Ltd., Nikalac MX-54) 11.
0 part was added and the mixture was reacted at 70 ° C. for 3 hours to give an average particle size of about 3.
A 5 μm microcapsule dispersion was obtained. Resulting dispersion 30 parts was added with 30 parts of 10% polyvinyl alcohol as a coating liquid, a coating so that the amount of deposition after drying on a high-quality paper having a basis weight of 81.4 g / m ² is about 5 g / m ² I did. The thermoreversible recording sheet thus prepared for repeated use was printed with a word processor (Myliport NL-1 manufactured by Ricoh Co., Ltd.) in the same manner as in Example 1 to find that the printing density was 0.83 in black. Met. The density after 10 minutes dropped to 0.75, but there was no problem in reading. After 12 hours of standing, the print disappeared and the image returned to the original state with no afterimage. This test was repeated 10 times, but no functional deterioration was observed.

Example 5 2-anilino-3-methyl-6-N-ethyl 5 parts -N-p-tolylaminofluorane stearyl gallate 15 parts myristyl alcohol 5 parts storeyl alcohol 5 parts diphenylmethane solvent ( A thermoreversible discoloration material consisting of 5 parts of SAS-296 manufactured by Nippon Petrochemical Co., Ltd. is uniformly dissolved at about 100 ° C. While heating 50 parts of a 3% aqueous solution of styrene-maleic anhydride copolymer whose pH was adjusted to 4.5 to 80 ° C., 25 parts of the above-mentioned dissolved substance was dropped, and 1 to 8 μ was mixed using a mixer.
It is softened and dispersed so that it becomes a microdroplet of m. Then, the obtained emulsion was stirred while urea-formalin prepolymer (Mitsui Toatsu Chemicals, Inc., Yukarami P-1500) 11.
0 part was added and the mixture was reacted at 70 ° C. for 3 hours to give an average particle size of about 3.
A 5 μm microcapsule dispersion was obtained. Resulting dispersion 30 parts was added with 30 parts of 10% polyvinyl alcohol as a coating liquid, a coating so that the amount of deposition after drying on a high-quality paper having a basis weight of 81.4 g / m ² is about 5 g / m ² I did. When printed with a word processor (My Report NL-1 manufactured by Ricoh Co., Ltd.) in the same manner as in Example 1, it was 0.8 in black.
The print density was 2. The density after 10 minutes dropped to 0.71, but there was no problem in reading. After 10 hours of standing, the print disappeared and returned to the original state with no afterimage, and no deterioration of the function due to repeated use was observed.

Example 6 3-N-methyl-N-isopropylamino-6-l part methyl-7-anilinofluorane stearyl gallate 5 parts myristyl alcohol 7.5 parts stearyl alcohol 7.5 parts diisopropylnaphthalene (Kureha) KMC-113) 10 parts p-methyldibenzylidene sorbitol 2 parts (Shin Nippon Rika Co., Ltd. Gel All MD) a thermoreversible discoloring material is uniformly dissolved at about 100 ° C. While heating 50 parts of a 3% aqueous solution of styrene-maleic anhydride copolymer whose pH was adjusted to 4.5 to 80 ° C., 25 parts of the above-mentioned dissolved substance was dropped, and 1 to 8 μ was mixed using a mixer.
It is softened and dispersed so that it becomes a microdroplet of m. Then, while stirring the obtained emulsion, a melamine-formalin prepolymer (manufactured by Sanwa Chemical Co., Nikalac MX-54) 11.
0 part was added and the mixture was reacted at 70 ° C. for 3 hours to give an average particle size of about 3.
A 5 μm microcapsule dispersion was obtained. Resulting dispersion 30 parts was added with 30 parts of 10% polyvinyl alcohol as a coating liquid, a coating so that the amount of deposition after drying on a high-quality paper having a basis weight of 81.4 g / m ² is about 15 g / m ² I did.
The thermoreversible recording sheet thus prepared for repeated use was printed by a word processor (Myliport NL-1 manufactured by Ricoh Co., Ltd.) in the same manner as in Example 1 to find that the printing density was 0.83 in black. Met. The density after 10 minutes dropped to 0.75, but there was no problem in reading. After 12 hours of standing, the print disappeared and the image returned to the original state with no afterimage. This test was repeated 10 times, but no deterioration in function was observed.

Example 7 3-Diethylamino-5-methyl-7-dibenzylaminofluorane 1 part Stearyl gallate 5 parts Cetyl alcohol 7.5 parts Storaryl alcohol 7.5 parts Diphenyl methane solvent (Japan Petrochemical Co., Ltd., SAS-296) 10 parts A thermoreversible discoloring material consisting of 1.5 parts of a condensate of D-sorbitol and benzaldehyde (Gelol D, manufactured by Shin Nippon Rika Co., Ltd.) is uniformly dissolved at about 100 ° C. While heating 50 parts of a 3% aqueous solution of styrene-maleic anhydride copolymer whose pH was adjusted to 4.5 to 80 ° C., 25 parts of the above-mentioned dissolved substance was dropped, and 1 to 8 μ was mixed using a mixer.
It is softened and dispersed so that it becomes a microdroplet of m. Then, the obtained emulsion was stirred while urea-formalin prepolymer (Mitsui Toatsu Chemicals, Inc., Yukarami P-1500) 11.
0 part was added and the mixture was reacted at 70 ° C. for 3 hours to give an average particle size of about 3.
A 5 μm microcapsule dispersion was obtained. Resulting dispersion 30 parts was added with 30 parts of 10% polyvinyl alcohol as a coating liquid, a coating so that the amount of deposition after drying on a high-quality paper having a basis weight of 81.4 g / m ² is about 15 g / m ² I did.
When printing was performed using a word processor (My Report NL-1 manufactured by Ricoh Co., Ltd.) in the same manner as in Example 1, it was found to be black with a value of 0.
The print density was 82. The density after 10 minutes dropped to 0.70, but there was no problem in reading. After 10 hours of standing, the print disappeared and returned to the original state with no afterimage, and no deterioration of the function due to repeated use was observed.

Example 8 A microcapsule dispersion was prepared in the same manner as in Example 7, except that crystal violet lactone was used instead of 3-diethylamino-5-methyl-7-dibenzylaminofluorane. A thermoreversible color-changing sheet was prepared using synthetic paper as a substrate, and a printing test was carried out. As a result, the color was blue and the density was 0.75. The density after 10 minutes had dropped to 0.68, but there was no problem in reading, and the decoloring property and repeatability were the same as in Example 1.

Example 9 A protective layer was formed by coating an acrylic emulsion (John Cryl 390, manufactured by Johnson Co.) on the thermoreversible color-changing recording layer of Example 1 so that the amount of adhesion when dried was about 5 g / m ^2. A thermoreversible recording sheet with This product showed almost no difference in print density as compared with Example 1, but
Superiority was recognized in chemical resistance, water resistance, sweat resistance, abrasion resistance and heat resistance. The "chemical resistance" was measured by attaching ethyl alcohol to a thermoreversible recording sheet,
(° C) and left for 15 minutes to evaluate stability visually. “Water resistance” means that the thermoreversible recording sheet is immersed in water and left at room temperature (24 ° C.) for 12 hours,
Stability was visually evaluated. “Sweat resistance” is a property in which sweat is adhered to a thermoreversible recording sheet, left at room temperature (24 ° C.) for one day, and stability is visually evaluated. "Abrasion resistance" is a value obtained by visually observing and observing a rubbing of a thermal head when printing a thermoreversible recording sheet using a word processor (My Report NL-1 manufactured by Ricoh Co., Ltd.) with a scanning electron microscope.

Example 10 3-Diethylamino-5-methyl-7-dibenzylaminofluorane 1 part Stearyl gallate 5 parts Stearyl alcohol 7.5 parts Myristyl alcohol 7.5 parts Diisopropylnaphthalene (KMC-133 manufactured by Kureha Chemical Co., Ltd.) A thermoreversible color-changing material consisting of 10 parts is uniformly dissolved at about 100 ° C. 5% gelatin aqueous solution with pH adjusted to 7.0 10
0 part is heated to 80 ° C., 50 parts of the lysate is added dropwise, and the mixture is emulsified and dispersed using a homomixer to form microdroplets of 1-8 μm. Next, 5% arabic gum aqueous solution 1 heated to 80 ° C
Add 20 parts, dilute with 220 parts of warm water (70 ° C), gradually add 10% acetic acid with stirring to adjust pH to 4.3 to cause coacervation, and then cool to 10 ° C. And gel it, then 25% glutar artehide 2
The pH of the mixture was adjusted to 9 and stirring was continued for 1 hour to obtain a microcapsule dispersion having a number average particle diameter of about 4.0 μm. 30 parts of 10% polyvinyl alcohol was added to 300 parts of the obtained dispersion liquid to obtain a coating liquid, and the basis weight was 81.4 g / m ^2.
Was coated onto a fine-quality paper lightly colored in blue so that the adhesion amount when dried was about 15 g / m ² . Further, the coating amount of the following protective layer coating liquid on this recording layer when dried was about 4.0.
The coating was carried out so as to be g / m ² to prepare a thermoreversible recording sheet. [Protective Layer Coating Liquid] Carboxy group-modified polyvinyl alcohol 10% aqueous solution 50 parts Epichlorohydrin-polyamide copolymer 10% aqueous solution 20 parts Calcium carbonate 1 part Water 29 parts As in Example 1, a word processor (Ricoh's My Report Nl-1) was used. ), It was printed in black.
The print density was 84. The density after 10 minutes dropped to 0.63, but there was no problem in the continuation. After 10 hours of standing, the print disappeared and returned to the original state with no afterimage, and no deterioration in function due to repeated use was observed. This product was particularly excellent in chemical resistance, water resistance, sweat resistance, abrasion resistance and heat resistance.

Example 11 3-diethylamino-6-methyl-7-xylidinofluorane 1 part Stearyl gallate 5 parts Stearyl alcohol 10 parts Myristyl alcohol 5 parts Diisopropylnaphthalene (KMC-113 manufactured by Kureha Chemical Co., Ltd.) 10 parts The thermoreversible discoloration material was microencapsulated in the same manner as in Example 10. Next, the microcapsule dispersion was applied in the same manner as in Example 10. Further, the following coating solution for protective layer was applied onto the recording layer so that the amount of adhesion when dried was about 5.3 g / m ² , to prepare a thermoreversible recording sheet. [Protective layer coating liquid] Silica coated with calcium carbonate (P-832 manufactured by Mizusawa Chemical Industry Co., Ltd.) 4 parts Carboxy group-modified polyvinyl alcohol 10% aqueous solution 50 parts Zinc stearate 1 part Water 45 parts As in Example 1, the word processor ( When printed with Ricoh's My Report Nl-1), it was found to be black in color.
The print density was 84. The density after 10 minutes dropped to 0.63, but there was no problem in the continuation. After 10 hours of standing, the print disappeared and returned to the original state with no afterimage, and no deterioration of the function due to repeated use was observed. This product was particularly excellent in chemical resistance, water resistance, sweat resistance, abrasion resistance and heat resistance.

[0040]

According to the present invention, the printed contents of a document, drawing, etc. by a thermal printer can be easily erased by leaving it naturally after the work of checking, proofreading, correcting, etc. sentences, layouts, typographical errors, etc. Can be used repeatedly.

[Brief description of drawings]

FIG. 1 Concentration of thermoreversible color-changing material used in the present invention-
It is a graph which shows the characteristic of the relation with time, and is a figure for explaining the principle of recording and erasing.

Claims (5)

[Claims] 1. An electron-donating color-forming organic compound on a substrate,
A microcapsule containing a thermoreversible color-changing material containing an electron-accepting compound, a color-changing temperature controlling compound, and a low-volatile solvent as essential components is coated with a binder to prepare a recording medium, on which a character is printed using a thermal head. A thermoreversible image forming method characterized by forming an image by printing a symbol or the like, erasing the image by allowing it to stand, and repeating the image formation. 2. A thermoreversible discoloration recording layer is formed by encapsulating the following four components (a), (b), (c) and (d) in a microcapsule on a substrate and coating them with a binder. A recording medium characterized by. Component (a): Electron-donating color-developing organic compound that is a color former (b) Component: Electron-accepting compound that is the developer of the component (a) (c) Component: Specific time and / or specific temperature range Discoloration Temperature Controlling Compound for Reversibly Coloring and Decoloring in (d) Component: Low Volatility Solvent for Improving Thermal Response and Coloring Density 3. The recording according to claim 2, wherein a nucleating agent for improving decoloring property is further added as a component (e) to the four components (a), (b), (c) and (d). Medium. 4. The recording medium according to claim 2, wherein the component (a) is 2-anilino-3-methyl-6-N-ethyl-Np-tolylaminofluorane. 5. The recording medium according to claim 2, 3 or 4, wherein a protective layer containing a water-soluble polymer or an aqueous emulsion of a polymer as a main component is coated on the thermoreversible color-change recording layer.