JPH0615955A - Method for erase of image - Google Patents

Abstract

PURPOSE:To form a uniform erasing condition of an image and to improve durability of repeating by heating a display medium wherein a heat-sensitive layer with a reversibly changable transparency with temp. is laminated with a heat of the substrate itself. CONSTITUTION:A heat-sensitive layer 2 is heated by scanning a thermal head from a protective layer 1 side of a display medium wherein a substrate 2 with a built-in heater 5 therein and the protective layer 1 are successively laminated. On the other hand, when the image formed by scanning this thermal head is eliminated, an electric current is energized in the heater 5 to heat at a temp. where the image of the heat-sensitive layer 2 can be eliminated. As the heat- sensitive layer 2 is directly heated in this method, elimination of the image can be uniformly performed and as no pressure is applied for heating, durability of repeating of image formation-erase is improved. In addition, when a protective layer 4 for the substrate is provided between the heat-sensitive layer 2 and the substrate 3, a solvent used for formation of the heat-sensitive layer 2 dissolves the substrate 3 and in the case when it gives a trouble to the heater 5, the effect of the protective layer is exhibited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image erasing method, and more particularly to an image erasing method for a display medium using a reversible thermosensitive recording material capable of repeating writing and erasing of information depending on temperature. Regarding

[0002]

2. Description of the Related Art In recent years, reversible recording materials (used in the form of, for example, electronic blackboards) capable of temporarily forming images and erasing the images when they are no longer needed are used everywhere. Is becoming more common. As a typical reversible recording material, a reversible thermosensitive recording material having a thermosensitive layer in which an organic low molecular weight substance such as a higher fatty acid is dispersed in a resin matrix such as a vinyl chloride resin is known. (JP-A-54-119377, JP-A-55)
-154198 and other publications). However, since these have a narrow temperature range of 2 to 4 ° C for making the opaque part transparent,
It was difficult to limit the temperature when forming a transparent image on an opaque reversible thermosensitive recording material.

The present inventors previously proposed a reversible thermosensitive recording material in which the temperature range for making the opaque part transparent can be widened by changing the material (Japanese Patent Laid-Open No. 63-63).
39378, JP-A-63-178079 and the like). According to these proposed reversible heat-sensitive recording materials, the intended purpose can be achieved, but when trying to make transparent by making the speed of a heat roller or the like short and making the heating temperature short, it is always necessary to have uniform transparency. There was a tendency that it was not always obtained.

Further, the present inventors have already proposed a method of stably erasing an image by heating the thermoreversible thermosensitive recording medium (display medium) from the support side (Japanese Patent Laid-Open No. 142279/1993). ). The image erasing method clarified therefor employs a method of simultaneously applying heat and pressure by a heat roller, a heat plate, a heat belt, a thermal head, or the like. However, if image formation-erasing is repeated many times by means of applying heat and pressure at the same time, the resin base material around the organic low molecular weight substance particles is deformed and finely dispersed organic low molecular weight substance particles. May gradually become particles with a large diameter, the effect of scattering light may be reduced (white turbidity may be rapidly deteriorated), and finally the image contrast may be lowered. When heating from the heat-sensitive layer side (thermoreversible heat-sensitive recording material layer side), if dust or dust adheres to the surface (heat-sensitive layer surface), heat will not be transferred to that part of the heat-sensitive layer and will be uniform. However, there is a drawback that it is difficult to erase the image because it is not heated, and when heating from the support side, it can be uniformly erased, but since it is heated through the support, it is heated at a higher temperature than when heating from the heat sensitive layer side. There is also a problem that the temperature inside the apparatus becomes high, and if the support is made of heat-sensitive polyvinyl chloride or the like, it will be deformed.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the disadvantages and problems such as the above-mentioned drawbacks, and makes uniform by the heat of the support itself without using an erasing means for simultaneously applying heat and pressure. It is intended to provide an image erasing method for a reversible thermosensitive recording medium, which can form an image erasing state and can improve durability against repetition.

[0006]

According to the present invention, a resin base material and an organic low molecular weight substance dispersed in the resin base material are main components on a support, and the transparency is reversible depending on temperature. In a method of erasing an image by heating a display medium on which a heat-sensitive layer that changes to the above is erased, the image display is erased by the heat of the support itself.

The present inventors have studied from various angles to achieve the above-mentioned object, and as a result, when the image erasing of the display medium using the specific support according to the present invention was performed, Since no pressure is required for erasing, compared to the conventional image erasing method in which heat and pressure are applied at the same time, there is no deformation of the resin base material, and therefore the organic low molecular weight substance particles finely dispersed in the resin base material have a large diameter. It was confirmed that since the particles are not formed, the durability of repeating image formation-erasing is improved, and in addition, even if dust, dust or the like adheres to the surface of the heat-sensitive layer, the heat is applied from the side of the support so that erasing can be performed uniformly. The method of the present invention is made by this.

The method of the present invention will be described in more detail below with reference to the accompanying drawings. FIG. 2A shows a display medium having a structure in which a heat sensitive layer 2 and a protective layer 1 are sequentially stacked on a support (planar heater) in which a heater 5 is embedded in a support 3. Image formation on this type of display medium requires protection layer 1
The thermal layer 2 is heated by scanning, for example, a thermal head (not shown) from the side. On the other hand, when erasing the image formed by the scanning of this thermal head,
An electric current is passed through the heater 5 to heat it at a temperature at which the image on the thermosensitive layer 2 can be erased. In this method, since the heat-sensitive layer 2 is directly heated, the image can be erased uniformly, and since pressure is not applied during heating, durability of repeated image formation-erasure is improved.

2B is different from the display medium of FIG. 2A in that a support protective layer 4 is provided between the heat sensitive layer 2 and the support 3. ing. This is because the formation of the support protective layer 4 is effective when the solvent used for forming the heat sensitive layer 2 dissolves the support 3 and damages the heater 5.

If the card of the structure shown in FIGS. 2 (a) and 2 (b) is made into a card size as shown in FIG. 6, it can be carried and the image can be easily displayed by inserting the card-shaped display medium into the apparatus. Can be erased uniformly.

As the material of the support protective layer 4, the following thermosetting resins and thermoplastic resins can be used in addition to those mentioned later as the resin base material in the heat sensitive layer 2. That is, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane,
Examples thereof include saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate and polyamide. The thickness of the support protective layer 4 is about 0.1 to 2 μm, preferably about 0.1 to 1.0 μm.
Examples of the solvent that is difficult to dissolve in the solvent of the heat sensitive layer include D-hexane, methyl alcohol, ethyl alcohol and isopropyl alcohol.

As shown in FIGS. 2A and 2B, the support 3
A controlled heating type including a heater 5 embedded therein can be made compact and does not require a heating temperature control type, and thus has high utility value (the same applies to FIGS. 5 and 6).

However, the self-temperature control type heat-generating material here has the characteristic that the electric resistance of the heat-generating body itself increases as the temperature rises, and a heat-generating body made of this material is always used even without control. It is kept at a constant temperature. Examples of this type of material include certain types of conductive ceramics and conductive resin compositions. A heating device using such a material has a feature that it can perform highly accurate temperature control despite its simple structure, but has a disadvantage that it is difficult to change it to an arbitrary temperature.

FIGS. 5 (a) and 5 (b) show a light-reflecting layer or colored layers 13 and 13 'provided between the support 3 and the heat-sensitive layer 2. When the light-reflecting layer is used, the amount of light reflection is increased. The effect of increasing the visibility is enhanced and, on the other hand, in the case of the colored layer, when the background part or the image part is in a transparent state, the back of the image part or the background part can be colored, and the visibility is improved. can do. Furthermore, in the display medium (FIG. 5 (b)) in which the support (transparent support 14) having a visible light transmittance of 50% or more and the surface of the support embedded with the heater in the support are closely integrated, By providing the non-adhesive portion 16 having an air layer between the support 14 and the support embedded with the heater in the support, the organic polymer material used as the main component of the heat-sensitive layer has a refractive index of 1. It is about 4 to 1.6 and has a large difference from the refractive index of 1.0 of air, so that light is reflected at the interface between the heat-sensitive layer 2 and the non-adhesive portion 16, and when the heat-sensitive layer 2 is in a white turbid state, the white turbidity is Since this is amplified and the visibility is improved, this non-adhered portion can be used as a display portion.

Further, since the non-adhesion portion has air inside the non-adhesion portion 16, the non-adhesion portion 16 serves as a heat insulating layer to improve the thermal sensitivity. Further, the non-adhered portion also serves as a cushion, so that the pressure actually applied to the heat-sensitive layer 2 becomes low even if pressure is applied by the thermal head during image formation, and the deformation of the resin base material is small even if heat is applied, Repeatability is improved without the expansion of organic low-molecular substance particles.

The support 3 or 6 preferably has a thickness of 20 to 300 μm. If it is too thick, the repeated durability will be deteriorated. On the contrary, if it is too thin, the curl of the support after application of the heat-sensitive layer will be large and the adhesion will be poor.

3 (a) and 3 (b), a pipe is embedded in a support, and a heated fluid (liquid or gas) flows in the pipe to form an image formed on the heat-sensitive layer 2. An example suitable for erasing is shown. Similar to the heater embedded in the support, this method also has improved uniform erasability, image formation, and repeated erasing durability.

4 (a) and 4 (b) are similar to the display medium of FIG. 3, two pipes are embedded in the support body, one type of pipe 8 is for heating, and the other type is The pipe 1
2 has a pipe for cooling embedded therein. The heat-sensitive layer 2 is heated by the heating pipe 8 to erase the image, the liquid or gas in the heating pipe 8 is stopped, and then a cooled fluid (liquid or gas) is flown in the cooling pipe 12 to heat the room temperature. Layer 2
Is a method of cooling. By providing this cooling pipe 12, the thermosensitive layer 2 can be cooled faster than that shown in FIG. 3, and the resin base material can be stabilized. Also, FIG.
By using the heater 5 shown in FIG. 4 and the cooling pipe 12 shown in FIG. 3 embedded in the support, the resin base material can be quickly stabilized in the same manner as in FIG.

The heat-sensitive layer used in the present invention utilizes, for example, the change in transparency (transparent state, cloudy opaque state) depending on temperature as described above. The difference between the transparent state and the cloudy opaque state is as follows. Is speculated to be. That is,
(I) When transparent, the particles of the organic low-molecular substance dispersed in the resin matrix are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered to the other side. It looks transparent because it penetrates. (Ii) In the case of cloudiness, the particles of the organic low-molecular substance are composed of polycrystals of fine crystals of the organic low-molecular substance, and the crystal axes of the individual crystals are various. Since it is oriented in such a direction, the light incident from one side is refracted many times at the crystal interface of the organic low molecular weight substance particles,
It comes from the fact that it looks white because it is scattered.

In FIG. 1 (representing the change in transparency due to heat), the heat-sensitive layer mainly composed of a resin base material and an organic low molecular weight substance dispersed in the resin base material is, for example, T _0.
It is cloudy and opaque at room temperature below. This is the temperature T ₂
When it is heated to ₀ , it becomes transparent, and even if it is returned to room temperature below T _{0 in} this state, it remains transparent. This is the temperature T ₂ to T ₀
It is considered that the organic low molecular weight substance is in a semi-molten state until the following and the crystal grows from a polycrystal to a single crystal.
Upon further heating to T ₃ or more temperature becomes translucent state intermediate between the maximum transparency and the maximum opacity. Next, when this temperature is lowered, the first cloudy opaque state is restored without taking the transparent state again. It is considered that this is because when the organic low molecular weight substance is melted at a temperature of T ₃ or higher, the polycrystal is deposited by being cooled. When this opaque state is heated to a temperature between T _{1 and} T ₂ and then cooled to room temperature, that is, a temperature of T ₀ or lower, an intermediate state between transparent and opaque can be obtained. Also, the transparent material that has become transparent at room temperature returns to the cloudy and opaque state again when heated to a temperature of T ₃ or higher and then returned to room temperature. That is, both opaque and transparent forms at room temperature and intermediate forms thereof can be obtained.

Therefore, the heat-sensitive layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent background and a transparent image on a cloudy background, and the change can be repeated many times. It is possible. Then, as mentioned above, by arranging the coloring sheet on the back surface of such a heat-sensitive layer, it is possible to form an image of the color of the coloring sheet on the white background or an image of the white background on the background of the coloring sheet (Fig. 5). When the image is used as a reflection image, it is desirable to provide a light reflecting layer on the back surface of the recording layer. Further, if the reflective layer is provided, the contrast can be increased even if the thickness of the recording layer is reduced. Specifically, vapor deposition of Al, Ni, Sn and the like can be mentioned (FIG. 5).

To make the display medium used in the present invention,
In principle, for example, the heat sensitive layer is formed as a film on the support by the following method. 1) A method in which a resin base material and an organic low molecular weight substance are dissolved in a solvent, which is applied onto a support, and the solvent is evaporated to form a film. 2) Dissolve the resin base material in a solvent that dissolves only the resin base material, add an organic low molecular weight substance therein, pulverize and disperse by various methods, coat this on a support, and evaporate the solvent. Method of forming a film. The solvent for forming the heat-sensitive layer can be variously selected depending on the type of the resin base material and the organic low molecular weight substance, and specifically, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene, etc. Can be mentioned. The organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the heat-sensitive layer obtained not only when the dispersion liquid is used but also when the solution is used.

In the present invention, the resin used as the resin base material of the thermosensitive layer composed of the reversible thermosensitive recording material is preferably a resin which can form a film and has good transparency and which is mechanically stable. Examples of such resins include polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer. Vinyl chloride copolymers such as coalesce; polyvinylidene chloride,
Vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-acrylonitrile copolymers and other vinylidene chloride copolymers; polyesters; polyamides; polyacrylates or polymethacrylates or acrylate-methacrylate copolymers; silicone resins and the like. These may be used alone or in admixture of two or more.

On the other hand, as the organic low molecular weight substance, any substance that changes from polycrystal to single crystal due to heat in the recording layer (changes within the temperature range of T _{1 to} T ₃ shown in FIG. 1) may be used.
Generally, those having a melting point of 30 to 200 ° C., preferably about 50 to 150 ° C. are used. Such organic low-molecular substances include alkanols; alkane diols; halogen alkanols or halogen alkane diols; alkylamines; alkanes; alkenes; alkynes; halogen alkanes; halogen alkenes; halogen alkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or Unsaturated mono- or dicarboxylic acids or their esters, amides or ammonium salts; saturated or unsaturated halogen fatty acids or their esters, amides or ammonium salts; allylcarboxylic acids or their esters, amides or ammonium salts; halogenallylcarboxylic acids or Of their esters, amides or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amines or ammonium salts; of thioalcohols Carboxylic acid esters, and the like. These may be used alone or in admixture of two or more. The carbon number of these compounds is 10
60, preferably 10-38, particularly 10-30 are preferred. The alcohol group moiety in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, the organic low molecular weight substance is at least one of oxygen, nitrogen, sulfur and halogen in the molecule, for example, -OH, -COOH, -CONH, -COOR, -N.
_{H, -NH 2, -S -,} - S-S -, - O-, is preferably a compound containing a halogen and the like.

More specifically, as these compounds,
Uric acid, dodecanoic acid, myristic acid, pentadecane
Acid, palmitic acid, stearic acid, behenic acid, nonadeca
Higher fatty acids such as acid, araginic acid and oleic acid; steer
Methyl phosphate, tetradecyl stearate, stearin
Acid octadecyl, octadecyl laurate, palmitin
Of higher fatty acids such as tetradecyl acid acid and dodecyl behenate
Stell; C₁₆H₃₃-OC₁₆H₃₃ , C₁₆H₃₃-S-
C₁₆H₃₃ , C₁₈H₃₇-SC₁₈H₃₇ , C₁₂H_{twenty five}−
S-C₁₂H_{twenty five} , C₁₉H₃₉-SC₁₉H₃₉ , C₁₂H
_{twenty five}-S-S-C₁₂H_{twenty five} ， Etc., such as ether or thioether. Above all, the present invention
Higher fatty acids, especially palmitic acid, pentadecanoic acid,
Nonadecanoic acid, arachidic acid, stearic acid, behenic acid,
Higher fatty acids having 16 or more carbon atoms such as lignoceric acid are preferred.
However, higher fatty acids having 16 to 24 carbon atoms are more preferable.

The weight ratio of the organic low molecular weight substance to the resin base material in the heat sensitive layer is preferably about 2: 1 to 1:16, more preferably 1: 1 to 1: 5. If the ratio of the resin base material is below this range, it will be difficult to form a film in which the organic low molecular weight material is retained in the resin base material. Becomes difficult. The thickness of the heat sensitive layer is preferably 1 to 30 μm, and 2
˜20 μm is more preferred. If the heat-sensitive layer is too thick, heat distribution will occur in the layer and it will be difficult to achieve uniform transparency. On the other hand, if the heat-sensitive layer is too thin, the white turbidity is lowered and the contrast is lowered. Further, the white turbidity can be increased by increasing the amount of the organic low molecular weight substance in the heat sensitive layer.

In addition to the above components, additives such as a surfactant and a high boiling point solvent may be added to the heat-sensitive layer in order to facilitate the formation of a transparent image. Specific examples of these additives are as follows. Examples of high boiling point solvents: tributyl phosphate, tri-2-phosphate
Ethylhexyl, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate , Dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate,
Dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, di-2 azelaate
-Ethylhexyl, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetylricinoleate, butyl acetylricinoleate, butylphthalylbutyl glycolate, acetylcitric acid Tributyl.

Examples of surfactants and other additives; polyhydric alcohol higher fatty acid ester; polyhydric alcohol higher alkyl ether; polyhydric alcohol higher fatty acid ester, higher alcohol, higher alkylphenol, higher fatty acid higher alkylamine, higher fatty acid amide , Lower olefin oxide adducts of fats and oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salt of higher alkylbenzene sulfonic acid; higher fatty acid, aromatic carboxylic acid, higher fatty acid sulfonic acid, aromatic sulfonic acid, sulfuric acid monoester Or Ca, Ba or Mg salt of phosphoric acid mono- or di-ester; low degree of sulfated oil; poly long chain alkyl acrylate; acrylic orgomer; poly long chain alkyl methacrylate; long chain alkyl methacrylate-amine containing mono Over copolymer; a styrene - maleic anhydride copolymer; olefin - maleic anhydride copolymer.

A protective layer 1 may be provided on the heat sensitive layer 2. As the material of the protective layer (thickness 0.1 to 10 μm), silicone rubber and silicone resin (Japanese Patent Laid-Open No. Sho 6-62)
3-221087), a polysiloxane graft polymer (described in Japanese Patent Application No. 62-152550), an ultraviolet curable resin or an electron beam curable resin (Japanese Patent Application 63/63).
-310600 specification) etc. are mentioned. In any case, a solvent is used at the time of coating, but it is desirable that the solvent does not dissolve the resin of the heat sensitive layer and the organic low molecular weight substance. Examples of the solvent that hardly dissolves the resin of the heat-sensitive layer and the organic low-molecular substance include n-hexane, methyl alcohol, ethyl alcohol, isopropyl alcohol, and the like, and the alcohol solvent is particularly preferable from the viewpoint of cost.

If necessary, an intermediate layer (not shown) is provided between the protective layer 1 and the thermosensitive layer 2 in order to protect the thermosensitive layer from the solvent, monomer components, etc. of the protective layer forming liquid. (Described in JP-A-1-133781). As the material for the intermediate layer, the following thermosetting resins and thermoplastic resins can be used in addition to those listed as the resin base material in the heat sensitive layer. That is, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate, polyamide and the like can be mentioned. The thickness of the intermediate layer is preferably about 0.1 to 2 μm.

[0031]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. In addition, both parts and% are based on weight.

Example 1 A sheet heater manufactured by Idemitsu Co., Ltd. was used as a support, an Al layer was provided on the support, and further 10 parts of a vinyl chloride-vinyl acetate-phosphate ester copolymer (Electrochemical Industry Co., Ltd.) was used. The product: Denka Vinyl # 1000P) A solution of 90 parts of tetrahydrofuran was applied with a wire bar and dried by heating to provide an adhesive layer having a thickness of about 0.5 μm. Further thereon, palmitic acid 2 parts, stearic acid 3 parts, eicosane diacid 5 parts, diisodecyl phthalate 3 parts, vinyl chloride-vinyl acetate copolymer 39 parts (Denka vinyl # 1000MT manufactured by Denki Kagaku Kogyo Co., Ltd.) tetrahydrofuran 100 parts toluene 65 Part of the solution is applied with a wire bar and dried by heating to about 5
A heat-sensitive layer having a thickness of μm was provided. Further, a solution consisting of 10 parts of polyamide resin (manufactured by Toray Industries, Inc .: CM8000) and 90 parts of methanol was coated on the surface with a wire bar, and dried by heating to about 1
A μm thick intermediate layer was provided. Furthermore, a urethane acrylate-based UV curable resin 75% butyl acetate solution (Dainippon Ink and Chemicals, Inc .: Unidick C7-157) 10 parts Toluene 10 parts is applied with a wire bar on it, and after heating and drying 80 W
It was cured with a UV lamp of 1 cm / cm and a protective layer having a thickness of about 2 μm was provided to prepare a display medium. The heat sensitive layer of this product was transparent. The heat-sensitive layer is printed with a thermal head to form a cloudy image, and an electric current is passed through the heater to heat the heat-sensitive layer to 80 ° C.
The white turbid image could be uniformly erased. When formation and erasing of this cloudy image were repeated 50 times, the durability (white cloudy deterioration was smaller) was better than that of the following comparative example.

Example 2 A display medium was prepared in the same manner as in Example 1 except that a Freon tube (manufactured by Daikin Industries, Ltd.) was provided as a support in a plastic container and an Al layer was provided on this support. The heat sensitive layer of this product was transparent. Then, the Freon tube was connected to a circulating constant temperature bath, and this heat-sensitive layer was printed with a thermal head to form a cloudy image. Next, when warm water at 80 ° C. was circulated in this flon tube, the cloudy image could be uniformly erased. The formation and deletion of this cloudy image is 5
When it was repeated 0 times, the durability (white turbidity deterioration was smaller) was better than that of the following comparative example.

Comparative Example 1 A PET film having a thickness of about 250 μm was used as a support,
A display medium was prepared in the same manner as in Example 1 except that an Al layer was provided on this support. The heat-sensitive layer of this product was printed with a thermal head to form a cloudy image, which was erased with the thermal head, but if there is dust, dust, or irregularities on the protective layer surface, the cloudy image cannot be erased and should be erased uniformly. I couldn't. When the formation and deletion of this cloudy image were repeated 50 times, the durability (white cloudy deterioration) was worse than that of the example.

Comparative Example 2 A test was conducted in the same manner as in Comparative Example 1 except that a hot stamp was used as a means for erasing the image. The thermosensitive layer of this display medium was transparent. The heat-sensitive layer of this product was printed with a thermal head to form a cloudy image, which was then erased with a hot stamp.However, where there is dust, dust, or irregularities on the protective layer surface, the cloudy image cannot be erased, so it can be erased uniformly. I couldn't. 50 formation and deletion of this cloudy image
When repeated, the durability (deterioration of cloudiness) was worse than that of the example. Further, when the pressure of the hot stamp was increased, the erasing could be performed uniformly, but the repeated durability (large cloudiness deterioration) was further deteriorated.

Comparative Example 3 A display medium was prepared in the same manner as in Comparative Example 1 except that the Al layer was not provided. The heat sensitive layer of this product was transparent. This heat-sensitive layer was printed with a thermal head to form a cloudy image, but the image density was lower than in Comparative Example 1 and the visibility was poor. Further, this heat-sensitive layer was printed with a thermal head to form a cloudy image and erased with the thermal head, but the cloudy image could not be erased where there was dust, dust, or irregularities on the surface of the protective layer, so it was uniformly erased. I couldn't.
After repeating the formation and deletion of this cloudy image 50 times,
The durability (greater deterioration of cloudiness) was worse than that of the example.

[0037]

According to the first aspect of the present invention, there is an effect that an image can be erased uniformly and that white turbidity is less likely to occur even when image formation-erasing is repeated. According to the inventions of claims 2 and 3, the image display can be erased by a simple operation. According to the invention of claim 4, an image of the color of the coloring sheet is white or an image of the white background is obtained on the background of the color of the coloring sheet, and the contrast can be increased.

[Brief description of drawings]

FIG. 1 is an explanatory view of forming and erasing an image depending on temperature in the method of the present invention.

FIG. 2 (a) is a side view of a display medium useful for carrying out the method of the present invention, and FIG. 2 (b) is a view of the display medium as seen from below (support side).

FIG. 3 (a) is a side view of another display medium useful for carrying out the method of the present invention, and FIG. 3 (b) is a view of the display medium seen from below.

FIG. 4A is a side view of another display medium useful for carrying out the method of the present invention, and FIG. 4B is a view of the display medium seen from below.

5A is a side view of another display medium useful for carrying out the method of the present invention, and FIG. 5B is a view of the display medium as seen from below.

6A is a side view of yet another display medium useful for carrying out the method of the present invention, and FIG. 6B is a perspective view thereof.

[Explanation of symbols]

 1 Protective Layer 2 Thermosensitive Layer 3 Support (Built-in Sheet Heater) 4 Support Protective Layer 5 Heater 6 Support (Built-in Pipe) 7 Circulation Heating Device 8 Heating Pipe 9 Circulation Cooling Device 10 Contact 11 Display 12 Cooling Pipe 13, 13 'Colored layer or light-reflecting layer 14 Transparent support

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Amano 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (4)

[Claims] 1. A heat-sensitive layer comprising a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component and having a transparency reversibly changed depending on temperature is laminated on a support. A method for erasing an image by heating a display medium, wherein the image display is erased by heat of the support itself. 2. The image erasing method according to claim 1, wherein the support is a planar heater, and the image display is erased by heating the heater. 3. The image erasing method according to claim 1, wherein a pipe is embedded in the support, and a heated fluid is flown in the pipe to erase the image display by heating the fluid. 4. The image erasing method according to claim 1, 2 or 3, wherein the support is colored, or at least a part of the support is provided with a light reflecting layer or a coloring layer.