JP2518287B2 - Thermal recording paper - Google Patents

Description

Detailed Description of the Invention

[Field of Industrial Application] The present invention relates to a novel heat-sensitive recording paper in which a colored state is reversibly changed by heat and an electric field, and more particularly to a heat-sensitive recording paper which is easily multicolored. [Outline of the Invention] The present invention uses a mixture of at least two kinds of dyes having different oxidation potentials or reduction potentials (or both) and different colors in a heat-sensitive recording paper whose color state is reversibly changed by heat and electric field. This makes it possible to control the color development state of each dye thermally and electrically by utilizing the difference in the oxidation / reduction potential of each dye, and to develop a new thermal recording paper that can easily achieve multiple colors. It is the one we are trying to provide. [Prior Art] In the field of thermal recording paper, as a display material, a leuco dye dispersed in a binder in a microcrystalline state together with a developer is used. Are contacted at the molecular level to develop color. Therefore, as a conventional thermal recording paper, a paper in which fine crystals of a leuco dye and a phenolic color-developing compound are dispersed and coated on a base paper (support) such as synthetic paper together with a hydrophilic binder is widely used. However, in the conventional thermal recording paper having such a configuration,
Considering the manufacturing process and the like, so-called background fog (slightly colored before printing) has inevitably occurred. That is, it is inevitable that the leuco dye and the fine crystals of the phenolic color-developing compound slightly react in the hydrophilic binder during the kneading step, the coating step, the drying step, etc. As a result, the entire thermal recording paper is printed before printing. However, under the present circumstances, it is difficult to obtain a heat-sensitive recording paper in a good white state because the color is slightly grayed. Further, the above-mentioned conventional thermosensitive recording paper cannot suppress the color development due to careless heating, and for example, even when it is stored or after printing, when heat is applied, the color is further developed and the print information becomes unreadable. Or, the image quality is remarkably deteriorated. Alternatively, in recent years, the amount of documents in office work has been increasing, and from the viewpoint of space saving and resource saving, thermal recording paper that can be repeatedly used has been demanded. Furthermore,
In order to improve the visibility of the document, multi-color thermal recording paper is being studied. However, it is difficult for conventional thermal recording papers to meet these demands, and repeated use by reproduction is almost impossible. Further, regarding the multi-coloring of the thermal recording paper, a mono-colored one has been mainly used in the past, and a multi-colored one is not general. That is, in the conventional thermal recording paper, in order to realize multiple colors, it is conceivable to mix and use materials having different sensitive temperatures, but the heating temperature can be accurately and uniformly applied during printing (or printing). Difficult to control,
The current situation is that it has not reached the level of practical use. [Problems to be Solved by the Invention] As described above, the conventional thermal recording paper has problems such as lack of stability, difficulty in multicoloring, and difficulty in repeated use. The realization of a new thermal recording paper that can be resolved is awaited. Therefore, the present invention has been proposed in view of such conventional circumstances, and an object of the present invention is to provide a thermosensitive recording paper that does not cause inadvertent color development, is easily multicolored, and has vivid color development. [Means for Solving Problems] The inventors of the present invention have developed a novel thermal recording paper capable of thermally and electrically controlling the coloring and decoloring state, and as a result of earnest research over a long period of time, In a material layer that exhibits solid-liquid change, an electrode reaction that induces redox of the dye can be caused by heating and melting the material layer, and if multiple dyes with different redox potentials are used, the color development of each dye can be controlled individually. We have come to the knowledge that we can do it. The thermosensitive recording paper of the present invention was completed based on such findings, and is a material layer which contains at least two kinds of dyes having different redox potentials and different colors and a supporting electrolyte and which undergoes solid-liquid change by heating and cooling. And an electrode that is laminated on at least one surface of the material layer and applies a current to the material layer, and the dye is oxidized by applying a current to the material layer in a liquefied state of the material layer. It is characterized in that it is reduced and / or develops and disappears. Here, as the dye used in the material layer, any dye can be used as long as it develops, decolorizes or changes color by an electrical oxidation / reduction reaction, and these coloring, decoloration or discoloration are reversible or irreversible. It does not matter whether it is present or not. If the coloring and decoloring is reversible, it can be used repeatedly, and if it is irreversible, it can be used as a write-once type (so-called write-once type) thermal recording paper. Examples of such dyes include leuco dyes having a lactone ring such as triphenylmethanephthalides, fluoranes, thiofluoranes, indolylphthalides, rhodamine lactams, and azaphthalides, and the following compounds are exemplified. First, examples of triphenylmethanephthalides include crystal violet lactone and malachite green lactone, and examples of fluoranes include 3-diethylamino-6-methyl-7-chlorofluorane and 3-diethylamino-7-methoxyfluorane. , 3-Diethylamino-6-benzyloxyfluorane, 1,2-benz-6-diethylaminofluorane, 3,6-di-p-toluidino-4,
5-Dimethylfluorane-phenylhydrazide-γ-lactam, 3-amino-5-methylfluorane, 2-methyl-
3-amino-6-methyl-7-methylfluorane, 2,3-
Butylene-6-di-n-butylaminofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7- (paratoluidino) -fluorane, 7-acetamino-3-diethylaminofluorane, 2-bromo- 6
-Cyclohexylaminofluorane, 2,7-dichloro-3
-Methyl-6-n-butylaminofluorane and the like can be mentioned. As thiofluoranes, 3-diethylamino-6-methyl-7-dimethylamino-thiofluorane, 3
-Diethylamino-7-dibenzylamino-thiofluorane and the like, and as indolylphthalides 8-
(4-Diethylaminophenyl) -8- (1-ethyl-
2-Methylindol-8-yl) phthalide, 3,3-bis (1-ethyl-2-methyl-8-yl) phthalide, 3,3-
Bis (2-phenylindol-3-yl) phthalide, 3
-(4-Di-n-butylaminophenyl) -3- (2-
Phenylindol-3-yl) phthalide, 8- [4-
(Dimethylamino) phenyl] -3- [N, N-bis-
(4-octylphenyl) amino] phthalide and the like can be mentioned. Further, rhodamine lactams include rhodamine lactone, and azaphthalides include 3,3-bis (1-
Ethyl-2-methylindol-3-yl) -7-azaphthalide and the like can be mentioned. Others, leuco basic cyanine, leuco marachite green, leuco crystal violet, p, p'-
Tetradimethyldiaminobenzophenone (Michler's ketone), Oxazine-based leuco thermal dye (Hodogaya Chemical Co., Ltd., trade name CSB-12, etc.), Spiropyran-based leuco thermal dye (Hodogaya Chemical Co., Ltd., trade name CSR-13, etc.), Quinoline-based leuco thermosensitive dye Dye (Hodogaya Chemical Co., Ltd., trade name CSY-13
Etc.) can be used. Among these, leuco dyes having a lactone ring, such as fluoran compounds and phthalide compounds, are preferable. When the leuco dye having this lactone ring is used, a favorable reversible oxidation / reduction reaction occurs, and therefore, color development and decoloration are reversibly repeated. Further, in the present invention, among these dyes, a plurality of dyes having different redox potentials that cause color development, decolorization or discoloration are mixed and used. That is, for example, when each dye is a dye that develops color by oxidation, at least a plurality of dyes having different oxidation potentials are selected from these dyes, and conversely, when each dye is a dye that develops color by reduction. Among these dyes, at least a plurality of dyes having different reduction potentials are selected and used. Further, in consideration of multicoloring, it is preferable that the coloring of each dye is different. For example, if three kinds of dyes that develop red, blue, and green (or yellow, magenta, and cyan) and have different redox potentials are used, the color development state of each of these dyes can be controlled electrically to increase It is possible to realize color display. The concentration of each of the above-mentioned dyes added to the material layer may be appropriately set according to the required color density. However, since the dye needs to be completely dissolved in the material layer, the upper limit of the concentration is necessarily the solubility limit in the insulating medium, supporting electrolyte, and the like described later. The lower limit is not particularly limited, but considering the contrast at the time of color development and erasing, it is preferable that the material layer contains 1/10 ⁷ or more by weight ratio. On the other hand, the supporting electrolyte is added in order to secure conductivity when the material layer is melted and to accelerate the oxidation / reduction reaction of the dye, and tetra-n-butylammonium tetrafluoroborate, tetra-perchlorate tetra-borate Aliphatic quaternary ammonium salts such as n-butylammonium, cetyltrimethylammonium bromide and dioctadecyldimethylammonium chloride, benzalkonium salts such as myristyldimethylbenzylammonium chloride, benzyldimethyl

[2- [2- (p-1,1,3,3-tetramethylbutylphenoxy) ethoxy] ethyl] Benzedonium chlorides such as ammonium chloride, alkylpyridinium salts, imidazolinium salts and the like can be used. In addition, an ionic surfactant such as an anionic surfactant can be used as the supporting electrolyte. Examples of the anionic surfactant include carboxylic acid salts represented by fatty acid soap, sodium palmitate, potassium stearate, alkyl ether carboxylic acid, etc., alkylbenzene sulfonates such as sodium laurylbenzenesulfonate, sodium naphthalenesulfonate, etc. Naphtalene sulfonates, sodium naphthalene sulfonate / formalin condensates, sulfonates represented by dialkoxysulfosuccinate ester salts, alkyl sulfates, alkyl ether sulfates, polyoxyethylene alkyl ether sulfates, alkylphenyl Illustrative are sulfuric acid ester salts such as ether sulfates, alkyl phosphoric acid ester salts, phosphoric acid ester salts such as alkyl ether phosphoric acid ester salts, and the like. However, when these ionic surfactants are used as the supporting electrolyte, the above-mentioned ammonium salt is preferably used as the supporting electrolyte because the exothermic color or the like due to the acidic substance may occur. As the concentration of the supporting electrolyte, when it is compatible with and melts in an insulating medium that undergoes solid-liquid change as described later, it is necessary to completely dissolve it in the insulating medium to be used, so the upper limit is naturally set. The solubility limit is reached. The lower limit is the lowest concentration that provides the electrical conductivity for redox of the dye at the electrode. Therefore, depending on the type of insulating medium, the concentration range of the supporting electrolyte in the material layer is 10 ^-10 mol / mol.
~ It is preferably the solubility limit. More preferably 10 ^-3
Mol / ~ 10 ^-1 mol /. However, when the supporting electrolyte itself shows a solid-liquid change and does not dissolve the insulating medium, the above concentration range is not applied, and only the concentration of the dye compatible with the supporting electrolyte is set to a predetermined range. Good. Each of the above-mentioned dyes and supporting electrolyte is made compatible with each other in an insulating medium to form a material layer, but the insulating medium to be used dissolves the plurality of dyes and supporting electrolytes, and solid-liquid change by heating and cooling. It is required to do so. Any material may be used as long as it is an insulating medium that satisfies the above requirements, but examples thereof include polyethylene, polyacrylate, polymethacrylate, and polyacrylamide, and homopolymers or copolymers thereof can be used. Among them, a high molecular weight compound having a long-chain alkyl in the side chain is preferable. These polymers should be polymerized by linear polymerization in the presence of other monomers, such as higher fatty acid esters of acrylic acid or methacrylic acid, by a method such as radical polymerization or radical copolymerization to achieve high molecular weight. Can be synthesized. Alternatively, a cyanobiphenyl polymer,
Copolymerized polymer of cyanophenyl benzoate and methoxybiphenyl benzoate, phenyl benzoate
Liquid crystalline polymer materials such as azomethyl-based polymers and azomethine-based polymers can also be used. Further, when the heat-sensitive recording paper of the present invention is used as a rewritable heat-sensitive recording paper, a polymer having at least one carbonyl group (C═O) represented by ester, ketone or the like in the molecular skeleton is used, It is preferable to use a mechanism that assists the reversible reduction of the leuco dye thermally. Further, this insulating medium does not exhibit electrochromic properties unless the above-mentioned supporting electrolyte is compatible with it in a solid state or at least a liquid state, but as a measure of compatibility of this insulating medium, there is a relative dielectric constant, for example, Considering the solubility of the quaternary ammonium salt (supporting electrolyte), it is preferable to use a material having a relative dielectric constant of 10 or more. When the supporting electrolyte itself exhibits a solid-liquid change, this insulating medium is not necessarily used, and a dye may be compatible with the supporting electrolyte to form the material layer. The material layer containing the above-mentioned dye, supporting electrolyte, insulating medium, etc. is formed as a film on a support such as paper, synthetic paper, plastic film, etc., and further a thin film electrode is formed to obtain a thermal recording paper. It A protective layer or the like may be formed if necessary. The electrodes may be laminated on both surfaces of the material layer or on at least one of the drawings. In this case, it is desirable that at least the electrode provided on the side where the material layer is viewed is transparent. Further, for the electrode on the support side, a conductive material or a plastic film in which a conductive material is mixed may be used for the support so that the support plays the role. In the heat-sensitive recording paper of the present invention, when the above-mentioned material layer is in a liquid state, a redox reaction of the dye occurs by applying an electric current through the electrode, and the color develops and disappears. Therefore, it becomes possible to form an image or a print on the material layer by combining the heating means and the current applying means. Various combinations are adopted as the combination of the heating means and the current applying means. First, there is a method in which electrodes are formed on both surfaces of the material layer, an electric current is applied between these electrodes, and an image and a print are formed by a selective heating means. In this case, the redox reaction of the dye occurs only in the portion of the material layer melted by the selective heating means, and this portion develops or erases color to form an image or print. Examples of the selective heating means include a thermal head and a laser beam, and a method of utilizing Joule heat or the like may be used. However, in particular, when selective heating is performed by a photothermal conversion action of laser light or the like, a sensitizing dye that efficiently absorbs the laser light in the material layer, for example, an infrared sensitizing dye in the case of a semiconductor laser, is used. It is preferable that the light-to-heat conversion efficiency be improved by mixing them. Contrary to the above-described method, the following is a method of selectively applying a current to the material layer while heating the entire surface of the material layer. Examples of a method for selectively applying a current to the material layer include a method in which XY matrices of transparent electrodes are formed on both surfaces of the material layer. In this case, if the material layer is heat-melted by the entire surface heating means and a predetermined electric signal is supplied to the selective current applying means, an image, a print or the like is written according to the electric signal. Further, when the writing by the entire surface heating means is stopped and the material layer is cooled, the material layer is assimilated and the image and print are fixed. Furthermore, it is possible to combine the selective heating means and the selective current application means. As the selective heating means and the selective current application means, the same methods as those described above can be adopted. That is, for example, an electrode may be formed on the entire surface of only one side surface of the material layer on the support side, and heat and an electric current may be supplied by the thermal head and the needle-shaped counter electrode. In this case, if at least one of the thermal head and the needle-shaped counter electrode is driven according to an image signal or a print signal, an image or a print is formed in accordance with this. [Operation] Ordinary organic substances are considered to be insulative in the solid state, and even if the electrolyte is used as a medium to make them compatible, a dramatic improvement in conductivity cannot be expected. Therefore, even if a redox dye is made compatible with these, color development by electrical redox cannot be expected. This is because the molecules are frozen in the solid state and the diffusion constant is low, and the electrolyte (carrier) is almost immobile. However, when the organic substance that is the medium is liquefied, the diffusion constant is increased by 10 ³ to 10 ⁵ , and the diffusion of the electrolyte and the ionic conduction due to thermal motion are developed. As a result, the conductivity of these compatible systems (that is, the material layer) is significantly improved, and the reversible color development / decoloration of the dye (in other words, the redox reaction) can be controlled by the application of an external current. That is, in the thermosensitive recording paper of the present invention, when the material layer is in the solid state, the coloring and decoloring state is fixed irrespective of the presence or absence of the application of current. On the other hand, when the material layer is melted into a liquid state by some heating means and a voltage is applied from the electrode, a current flows as a result in the system, and electrons are deprived on the positive electrode side to cause an oxidation reaction of the dye. The dye in the vicinity of the plus color develops (in some cases, disappears or discolors). Further, in this liquid state, when a voltage having a polarity opposite to that applied previously is applied, an electron is given to the oxidized dye to cause a reduction reaction, and the dye is decolored (in some cases, colored or discolored). To do. The coloring and decoloring mechanism in the material layer described above can be summarized as follows. Here, if a plurality of dyes having different redox potentials and different colors are selected and used and the applied voltage from the electrode is changed, the dyes that develop color are limited according to the applied voltage, and a plurality of colored states are adopted. You will get it. [Examples] Hereinafter, specific examples of the present invention will be described in detail. Prior to the description of the examples, the experimental results regarding the display material used for the material layer in the thermal recording paper of the present invention will be described. Experimental Example 1 It was confirmed that the leuco dye undergoes an oxidation / reduction reaction due to the solid-liquid change of the insulating medium and the application of a current, and the coloring and decoloring are repeated. First, a composition having the following composition was stirred at 100 ° C. for 1 hour to obtain a compatibilized product in which each component was compatible with each other, and then preheated to 100 ° C. while maintaining the compatibilized product at 100 ° C. It was sandwiched between glass plates coated with ITO vapor deposition film, cooled, and kept at room temperature.
A polyethylene film was used as a spacer between the glass plates, and the thickness of the compatible material was set to about 50 μm. Composition p-dodecyloxycyanobiphenyl (solid solution insulating medium) ・ ・ ・ 50 parts by weight Dioctadecyldimethylammonium chloride (supporting electrolyte) ・ ・ ・ 50 parts by weight 2- (2′-chlorophenylamino) -6-di- n-Butylaminofluorane (leuco dye) [Hodogaya Chemical Co., Ltd., trade name TH107] 15 parts by weight The structural formula of the leuco dye used is as shown in the following formula (I). A compatible material having the above composition is a solid at room temperature,
It was liquefied at 50 ° C and reversibly repeated solid-liquid change. Next, when a direct current of 9 V was applied between the electrodes (ITO vapor-deposited film) formed on both glass plates at room temperature (the compatible material was in a solid state), no color change was observed. The resistance value between the electrodes at this time was about 400 kΩ. Then, the entire glass cell composed of the glass plate was heated to 60 ° C., and a direct current of 9 V was applied in the same manner while maintaining this heating state (the compatibilized material was in a liquid state), and immediately colored dark green (the positive side interface was It was colored), and the color disappeared when the voltage (current) application direction was reversed. When the voltage was further applied in this state (in which the polarity of the applied voltage was reversed), the opposite interface developed color. This electrical coloration / erasing was repeatable at least ten times. Moreover, when the electric resistance between the electrodes at the time of this heat melting was measured, it was lowered to about 10 kΩ. Example 2 Next, the following experiment was conducted in order to study the multicoloring of display materials. A display material solution having the following composition was prepared, and the oxidation potential of the leuco dye used was measured by cyclic voltammography. At the time of measurement, a platinum wire was used as a working electrode and a counter electrode Pt was used. Composition Leuco dye: 0.54 parts by weight Tetra-n-butylammonium perchlorate (supporting electrolyte): 3.4 parts by weight Acetonitrile (solution): 100 parts by weight The types of leuco dye used are as follows. Is. Leuco dye A: a phthalide compound that introduces a substituent into the phthalide skeleton to develop a cyan color (Hodogaya Chemical Co., trade name HC-1) Leuco dye B: Obtained by changing the substituent of the fluoran skeleton Fluoran compound that develops magenta (manufactured by Hodogaya Chemical Co., Ltd., trade name HM-1) Leuco dye C: Fluoran compound obtained by changing the substituent of the fluoran skeleton and develops yellow (manufactured by Hodogaya Chemical Co., Ltd., trade name HY -1) Cyclic voltammograms based on Ag / AgCl electrodes in acetonitrile are shown in FIGS. 1 to 3. 1 is a cyclic voltammogram of a display material solution using leuco dye A, FIG. 2 is a cyclic voltammogram of a display material solution using leuco dye B, and FIG. 3 is a display material solution using leuco dye C. It is a cyclic voltammogram. When the rising potential of the oxidation current of each leuco dye in acetonitrile was obtained from FIGS. 1 to 3, it was found that the leuco dye A ... + 800 mV leuco dye B ... + 900 mV leuco against the Ag / AgCl electrode. The dye C was +1700 mV. In the above-mentioned cyclic voltammography, it was found that the pattern similar to that shown in FIGS. 1 to 3 was obtained even if the scanning was repeated a plurality of times, and that the redox reaction of each leuco dye was reversible. . Next, instead of the platinum wire as the working electrode in this solution
Immerse the plate electrode with ITO (Indium Tin Oxide) vapor-deposited on it and apply 1.0V to the reference (reference) electrode.
Was applied (resulting in that an electric current was applied), and the change in absorption spectrum on the surface of the plate electrode was measured. The results are shown in FIGS. 4 to 6. In FIGS. 4 to 6, the solid line shows the absorption spectrum when voltage is applied (oxidation), and the broken line is when voltage is not applied (reduction).
The absorption spectrum of is shown. Each display material solution exhibits the same spectral characteristics as the state in which each leuco dye is developed by a phenolic developer in an acrylic acid-based polymer, and depending on the type of leuco dye contained by applying a voltage, cyan (leuco dye Dye A),
Magenta (leuco dye B), yellow (leuco dye C)
Respectively, and was erased by applying a voltage of opposite polarity. Therefore, it was found from FIGS. 1 to 3 and FIGS. 4 to 6 that the almost ideal yellow, magenta, and cyan coloring / erasing colors can be electrically controlled. A thermal recording paper was prepared on the basis of the above experimental results relating to the display material. Example A polyethylene terephthalate film having an ITO vapor-deposited film (2) deposited on the surface thereof was used as a support (1), and a compatible material having the following composition on the support (1) as shown in FIG. Wet coating and drying to form a solid coating (3),
Further, a heat-resistant polyethylene terephthalate film (5) having an ITO vapor-deposited film (4) on one side was thermocompression bonded at a temperature not lower than the melting point of the solid coating (3) to obtain a thermosensitive recording film. Composition Polystearyl acrylate (melting point 48 ° C.): 200 parts by weight Leuco dye A: 2 parts by weight Leuco dye B: 2 parts by weight Leuco dye C: 2 parts by weight Dioctadecyldimethylammonium chloride ...
50 parts by weight Tetrahydrofuran ・ ・ ・ 500 parts by weight Polystearyl acrylate used here has excellent film-forming properties and flexibility, and has a relative permittivity that is compatible with leuco dyes and supporting electrolytes. It is meltable or phase-transparent. The heat-resistant polyethylene terephthalate film (5) was applied between the ITO vapor-deposited films (2) and (4) of the heat-sensitive recording film thus prepared, as shown in the following table. ) Printing (or printing) was performed with a thermal head from above. As a result, when the temperature reaches the melting point of the solid coating (3) or higher, that portion develops color, and the print (or image) is fixed by cooling (leaving) at room temperature. The applied voltage and color development are shown in the following table. From this table, it was found that the thermosensitive recording paper of this example can display three colors in multiple colors. In addition, when the voltage application is stopped, no color develops even when the non-printed area (non-image area) is heated, and no color development is observed during storage because there is no color developer. The storage stability of was excellent. Next, while heating the entire surface of the thermosensitive recording film to a temperature not lower than the melting point of the solid coating (3), a voltage having a weak opposite polarity (a polarity opposite to the voltage applied at the time of printing or printing) that does not lead to color development is applied. The applied voltage erased the already formed prints and images. By cooling (leaving) this and solidifying it, it was possible to return to the state where no image was formed. Note that it is not always necessary to apply the opposite polarity voltage during the erasing operation, and it is possible to erase only with heat, for example, but in the present example, the opposite polarity voltage is applied in consideration of practical speed. I decided to erase it. [Effects of the Invention] As is clear from the above description, the present invention is a thermosensitive recording paper in which the colored state is reversibly changed by heat and an electric field, in which a plurality of dyes having different redox potentials and different colors are mixed and used. Therefore, it is possible to achieve multicoloring very easily, and it is possible to reliably control the coloring and decoloring of each dye. Further, the thermal recording paper of the present invention can control the coloring state of the dye thermally and electrically by utilizing the solid-liquid change of the material layer and the oxidation / reduction reaction due to the application of the current from the electrode. Coloring, erasing or discoloring can be carried out at a desired speed, and the above-mentioned coloring, erasing or discoloring state can be fixed if necessary. Further, in the heat-sensitive recording paper of the present invention, unnecessary writing by only heat does not occur in principle, and therefore, color is not generated by careless heating, etc., and the storage stability and stability are excellent, and the color is vivid. There are advantages and the like. Furthermore, in the heat-sensitive recording paper of the present invention, by applying an electric field having a polarity opposite to that at the time of writing, the color-developed state can be easily returned to the decolorized state, and therefore, it can be repeatedly used.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a cyclic voltammogram of a phthalide-based leuco dye that develops a cyan color, FIG. 2 is a characteristic diagram showing a cyclic voltammogram of a fluoran-based leuco dye that develops a magenta color, and FIG. 3 is a yellow color. Fig. 4 is a characteristic diagram showing a cyclic voltammogram of a fluoran-based leuco dye that develops in Fig. 4, Fig. 4 is a characteristic diagram showing an absorption spectrum of a phthalide-based leuco dye that develops in cyan, and Fig. 5 is a fluoran-based leuco dye that develops in magenta. FIG. 6 is a characteristic diagram showing the absorption spectrum of FIG. 6, and FIG. 6 is a characteristic diagram showing the absorption spectrum of a fluoran-based leuco dye that develops yellow color. FIG. 7 is a schematic cross-sectional view of an essential part showing one structural example of the thermal recording paper to which the present invention is applied. 1 ... Support 2,4 ... ITO deposition film (electrode) 3 ... Solid film (material layer)

Claims (1)

(57) [Claims] 1. A material layer which contains at least two kinds of dyes having different redox potentials and different colors and a supporting electrolyte and which undergoes a solid-liquid change by heating and cooling, and a material formed by laminating on at least one surface of the material layer. A thermosensitive recording paper comprising an electrode for applying an electric current to the layer, wherein the dye is oxidized and / or reduced by applying an electric current to the material layer in a liquefied state of the material layer to develop and decolorize the material layer. .