JP3357998B2 - Image deletion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for erasing an image on a display medium using a reversible thermosensitive recording medium capable of repeatedly forming and erasing an image by heating a recording layer.

[0002]

2. Description of the Related Art In recent years, reversible thermosensitive recording media capable of temporarily forming an image and erasing the image when it is no longer needed have attracted attention. A typical example is a glass transition temperature (Tg) of 50 to 60 ° C to 8 ° C.
A reversible thermosensitive recording medium is known 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-vinyl acetate copolymer having a low glass transition temperature of less than 0 ° C. JP-A-54-119377, JP-A-55-1
No. 54198).

In this reversible thermosensitive recording medium, a recording layer is distorted during repeated image formation and erasing by a heating element such as a thermal head for a plurality of times, and the image density at the time of image formation is reduced.
There is a disadvantage that the contrast is reduced, and it has not been solved yet.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages, and the image density at the time of image formation does not decrease even if image formation and erasure are repeated many times with a heating element such as a thermal head. An object of the present invention is to provide an image erasing method capable of maintaining high contrast.

[0005]

According to the present invention, a resin base material and an organic low-molecular substance dispersed in the resin base material are mainly used on a support, and an image can be formed and erased by heating. In an image erasing method for erasing an image by heating a display medium made of a reversible thermosensitive recording material provided with a possible thermosensitive recording layer, the erasing temperature is set to a central value of a transparent temperature range at which an image of the display medium can be erased. Above temperature and pressurizing pressure
An image erasing method is provided wherein the image is erased by heating at 0.1 kg / cm ² or more . Further, in particular, at least one of a thermal head, a hot stamp, a heat roller, and a heat block is used as a heating means for erasing an image on the display medium. In particular, a hot stamp is used. a child with .1 seconds, some have the the image erasing method and respectively, characterized in that arranged cushioning material made of a polymer organic compound to a metal surface of the hot stamping is provided. Further, the image erasing method is provided , wherein the reversible thermosensitive recording material is a card having the thermosensitive recording layer and the magnetic recording layer.

The present inventors have analyzed and studied the mechanism of the cause of the decrease in image density caused by repeated use of forming and erasing an image on the reversible recording medium. As a result, when an image was formed by pressing a heating element such as a thermal head against the surface of the recording medium, the following phenomenon was observed. In a reversible recording medium having a recording layer in which an organic low-molecular substance is dispersed in a resin base material, a recording layer is formed before or after applying energy or when the number of repetitions is small when performing image formation and erasing with a heating element. As shown in FIG. 1A, there is no distortion such that the existing state of the material changes, and the organic low-molecular substance particles are uniformly dispersed in the resin base material. By the way, at the time of image formation, if the image forming unit is relatively moved while pressing the recording medium, stress is applied to the inside of the recording layer. While the application of energy in the same direction is repeated, the stress is a main cause of distortion inside the recording layer in the direction of application of energy as shown in FIG. Is in a deformed state. Then, while the energy application is further repeated in the same direction, the strain progresses, and aggregation of the deformed organic low-molecular substance particles starts as shown in FIG.
Eventually, as shown in FIG. 1 (d), the aggregated particles re-aggregate, and the organic low-molecular substance particles are maximized. In such a state, it is almost impossible to form an image, which is a so-called deteriorated state. It is considered that these phenomena are related to the cause of a decrease in image density after repeated formation and erasure of an image on the reversible recording medium.

The inventors of the present invention have studied a method for recovering the above-mentioned distortion and preventing the deterioration, and found that an image is formed on the reversible recording medium by a heating element such as a thermal head. At this time, the image formation is repeated by applying energy such as heat and pressure of a thermal head or the like, and FIG.
From the state in which the organic low-molecular substance particles are uniformly dispersed in the resin base material as shown in (a), the resin is displaced as shown in FIG. 2 (b), and the organic low-molecular substance particles are slightly deformed. That is, even if a distortion occurs in the recording layer, as shown in FIG. 2 (c), the image is erased by the image erasing means and simultaneously heated at a temperature higher than or equal to the center value of the transparentizable temperature range as described above. Thereby, the deformed particles return to the initial shape because the strain is restored, so that aggregation and maximization of the particles are unlikely to occur, and the image density after repeated image formation and erasure does not decrease, It was confirmed that high contrast could be maintained. Further, when a hot stamp is used as the image erasing means and the heating is performed on the high temperature side which is equal to or higher than the central value of the above-mentioned transparent temperature range, the heating time is set to 0.1 second or more, and 0 . It was recognized that the above effect was further improved by pressing at a pressure of 1 kg / cm ² or more and heating at the same time, and further disposing a buffer made of a high molecular weight organic compound on the metal surface of the hot stamp.

The present invention has been made based on these findings. Hereinafter, the method of the present invention will be described in more detail.
The reversible thermosensitive recording medium in the present invention is a material that causes a visible change reversibly due to a temperature change. Visible changes can be divided into color changes and shape changes,
In the present invention, a material that causes a change in color tone is mainly used. Changes in color tone include changes in transmittance, reflectance, absorption wavelength, scattering degree, and the like, and an actual reversible thermosensitive recording medium performs display by combining these changes. More specifically,
(A) A material that changes reversibly between a transparent state and a cloudy state.
(B) Materials such as dyes that change color reversibly. 2
At present, they can be classified into different types. (A) As described in the prior art, as described in the prior art, a recording layer in which organic low-molecular substances such as higher alcohols and higher fatty acids are dispersed in a resin base material such as polyester and an auxiliary agent is added if necessary. And (b) include those in which the reversibility of a conventional leuco-based thermosensitive recording material is enhanced (eg, Yoshihiro Hino, Nie Watanabe, Japan Hardcopy '90, P147) .

Hereinafter, the present invention will be described focusing on the recording medium (a) . The reversible thermosensitive recording medium of (b) is, for example, the temperature transparency change (transparent state, clouded opaque state) by such as utilizes the difference between the cloudy opaque state and the transparent state is as follows Guessed.
That is, (i) in the case of transparency, the particles of the organic low-molecular substance dispersed in the resin base material are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered and is opposite. It looks transparent because it penetrates to the side,
(Ii) In the case of cloudiness, the particles of the organic low-molecular-weight substance are composed of polycrystals in which fine crystals of the organic low-molecular-weight substance are aggregated. Since the crystal axes of the individual crystals are oriented in various directions, they are incident from one side. The light is refracted many times at the interface between the crystals of the organic low-molecular substance particles, and is scattered.

In FIG. 3 (representing a change in transparency due to heat), a heat-sensitive layer mainly composed of a resin base material and an organic low-molecular substance dispersed in the resin base material is, for example, T
_At a room temperature of ₀ or less, it is cloudy and opaque. This is called temperature T ₂
When the temperature is returned to room temperature below T ₀ , the film remains transparent. This is from temperature T ₂ to T ₀
It is considered that the crystal grows from a polycrystal to a single crystal through the semi-molten state of the organic low-molecular substance until the following.
Upon further heating to T ₃ or more temperature becomes translucent state intermediate between the maximum transparency and the maximum opacity. Next, when the temperature is lowered, the state returns to the original cloudy and opaque state without taking the transparent state again. This after low-molecular organic material is melted at a temperature T ₃ or more, presumably because the polycrystals precipitated by being cooled. When the opaque state is heated to a temperature between T _{1 and} T ₂ and then cooled to room temperature, that is, a temperature lower than T ₀ , an intermediate state between transparent and opaque can be obtained. Also, by returning to room temperature After heating to be again T ₃ or more temperature which became clear at the normal temperature, the flow returns to cloudy opaque state again. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be taken.

Therefore, the recording layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent ground and a transparent image on a cloudy ground, and the change can be repeated many times. It is possible. If a colored sheet is disposed on the back of such a recording layer, an image of the color of the colored sheet on a white background or an image of a white background on the ground of the colored sheet can be formed. Further, when projected by an OHP (overhead projector) or the like, the cloudy portion becomes a dark portion, the transparent portion transmits light, and becomes a bright portion on the screen.

The thickness of the recording layer is preferably 1 to 30 μm,
2-20 μm is more preferred. If the recording layer is too thick, heat distribution within the layer will occur, making it difficult to achieve uniform transparency. On the other hand, if the recording layer is too thin, the turbidity decreases and the contrast decreases. The turbidity can be increased by increasing the amount of the fatty acid in the recording layer.

The reversible thermosensitive recording medium (a) used in the present invention can be formed as a film or a sheet on a support member by the following method, for example. 1) A method of dissolving a resin base material and an organic low-molecular substance in a solvent, applying this on a support member, and evaporating the solvent to form a film or sheet. 2) The resin base material is dissolved in a solvent in which only the resin base material is dissolved, and the organic low-molecular substance is pulverized or dispersed therein by various methods, applied to a support member, and the solvent is evaporated to form a film. Or a method of forming a sheet. 3) A method in which a resin base material and an organic low-molecular substance are heated and melted and mixed without using a solvent, and the resulting mixture is formed into a film or a sheet and cooled. As the recording layer or the solvent for preparing a thermosensitive recording medium, various types can be selected depending on the types of the resin base material and the organic low-molecular substance.
Examples include tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. It is to be noted that the organic low-molecular substance is precipitated as fine particles in the recording layer obtained when the solution is used, as well as when the dispersion is used, and exists in a dispersed state.

In the present invention, the resin used as the resin base material of the recording layer of the reversible thermosensitive recording medium is preferably a resin which can form a film or sheet, has good transparency, and is mechanically stable. Examples of such a resin include polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-acrylate copolymer. Vinylidene chloride-based copolymer such as polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer; polyester; polyamide; polyacrylate or polymethacrylate or acrylate -Methacrylate copolymers; silicone resins and the like. These may be used alone or as a mixture of two or more.

On the other hand, as the organic low-molecular substance, any substance that changes from polycrystal to single crystal by heat in the recording layer (a substance that changes within the temperature range of T _{1 to} T ₃ shown in FIG. 3) may be used.
Generally, those having a melting point of about 30 to 200 ° C, preferably about 50 to 150 ° C are used. Such organic low molecular weight substances include alkanol; alkane diol; halogen alkanol or halogen alkane diol; alkylamine; alkane; alkene; alkyne; halogen alkane; halogen alkene; halogen alkyne; cycloalkane; cycloalkene; cycloalkyne; 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; Esters, amides or ammonium salts thereof; thioalcohols; thiocarboxylic acids or their esters, amides
De or ammonium salts; carboxylic acid esters of thio alcohol and the like. These may be used alone or in combination of two or more. These compounds have 10 to 10 carbon atoms.
60, preferably 10 to 38, particularly preferably 10 to 30. The alcohol group in the ester may be saturated, may not be saturated, and may be halogen-substituted. In any case, the organic low molecular weight substance contains at least one kind of oxygen, nitrogen, sulfur and halogen in the molecule, for example, -OH, -COOH, -CONH, -COOR, -N
Compounds containing H, -NH2, -S-, -SS-, -O-, halogen, and the like are preferable.

More specifically, these compounds include higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, araginic acid and oleic acid; methyl stearate Esters of higher fatty acids such as tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate, dodecyl behenate; And ether or thioether. Among them, in the present invention, higher fatty acids, especially palmitic acid, pentadecanoic acid,
Nonadecanoic acid, arachiic acid, stearic acid, behenic acid,
Higher fatty acids having 16 or more carbon atoms such as lignoceric acid are preferable, and higher fatty acids having 16 to 24 carbon atoms are more preferable.

The weight ratio of the organic low-molecular substance to the resin base material in the recording layer is preferably about 2: 1 to 1:16, more preferably 1: 2 to 1: 8. When the ratio of the resin base material is less than this, it becomes difficult to form an organic low-molecular substance in a film held in the resin base material. Becomes difficult. The thickness of the recording layer is preferably 1 to 30 μm,
-20 μm is more preferable. If the recording layer is too thick, heat distribution within the layer will occur, making it difficult to achieve uniform transparency. On the other hand, if the recording layer is too thin, the turbidity decreases and the contrast decreases. Further, the turbidity can be increased by increasing the amount of the organic low-molecular substance in the heat-sensitive layer.

In addition to the above components, additives such as a surfactant and a high-boiling solvent can be added to the recording layer in order to facilitate formation of a transparent image. Specific examples of these additives are as follows. Examples of high boiling solvents: tributyl phosphate, tri-2-ethylhexyl phosphate,
Triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, phthalate Dioctyldecyl acid, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate, di-n-hexyl adipate, di-2-adipate
Ethylhexyl, di-2-ethylhexyl azelate, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetyl ricinoleate, methyl acetyl ricinoleate, butyl phthalyl Butyl glycolate, tributyl acetyl citrate.

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 alkyl phenol, higher fatty acid higher alkyl amine, higher fatty acid amide Lower olefin oxide adducts of fats and oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salts of higher alkylbenzene sulfonic acids; higher fatty acids, aromatic carboxylic acids, higher fatty acid sulfonic acids, aromatic sulfonic acids, monoesters of sulfuric acid Or Ca, Ba or Mg salts of phosphoric acid mono- or di-esters; low sulfated oils; poly long chain alkyl acrylates; acrylic oligomers;
Poly long chain alkyl methacrylate; long chain alkyl methacrylate-amine-containing monomer copolymer; styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer.

When the image formed on the recording medium (a) is used as a reflection image, it is desirable to provide a light reflecting layer on the back of the recording layer. Further, even if the thickness of the recording layer to have a reflective layer can increase the contrast. Specific examples include vapor deposition of Al, Ni, Sn and the like (described in JP-A-64-14079).

The recording layer may be provided with a protective layer for protecting the recording layer. Protective layer (thickness 0.1-1
0 μm) include silicone rubber, silicone resin (described in JP-A-63-221087), polysiloxane graft polymer (Japanese Patent Application No. 62-1525).
No. 50) or an ultraviolet curable resin or an electron beam curable resin (described in Japanese Patent Application No. 63-310600). In any case, a solvent is used at the time of coating, and it is preferable that the solvent does not easily dissolve the resin of the recording layer and the organic low-molecular substance. Examples of the solvent that hardly dissolves the resin of the recording layer and the organic low-molecular substance include n-hexane, methyl alcohol, ethyl alcohol, and isopropyl alcohol, and an alcohol-based solvent is particularly desirable in terms of cost.

An intermediate layer may be provided between the protective layer and the recording layer to protect the recording layer from a solvent, a monomer component, and the like of the protective layer forming liquid. (Japanese Unexamined Patent Publication No. 1-1337
No. 81). As the material of 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 recording 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.

Further, a magnetic recording layer may be provided and used as a card (see Japanese Utility Model Application Laid-Open No. 2-3876).

In the present invention, there are various types of thermal recording image display devices for displaying images, and a typical one is an image forming device for performing image formation / erasing on a reversible recording medium. The means and the image erasing means are the same heating element, for example, a thermal head, and a thermal recording image display device capable of performing image processing by changing energy applied to the thermal head, or the image forming means is a thermal head, image erasing means a thermal head, hot stamp, heat roller, a heat-sensitive recording an image display device selected from one out <br/> contact pressing type hand stage to adhere a heating element such as a heat block.
Specifically, for example, a thermal recording and erasing apparatus as shown in FIGS. 4A, 4B and 4C can be mentioned.

FIG. 4A is a schematic view of a contact-pressing type heating device which presses a hot stamp 2 against a stationary reversible thermosensitive recording medium 1 to make it transparent. In the figure, reference numeral 3 denotes a balance table. When using a hot stamp as the image erasing means, the heating time is at least 0.1 second or more, preferably 0.3 second or more, and more preferably 1.0 second or more. The pressurizing pressure is at least 0.1 kg / cm ² , preferably 0.3 kg / cm ² or more, and more preferably 1.0 kg / cm ² or more. By heating under such conditions, the heat transfer from the hot stamp to the display medium becomes uniform, the effect of eliminating the distortion of the recording layer becomes large, and the heat distribution of the display medium becomes uniform. A transparent state can be obtained.

It is preferable to provide a buffer on the metal surface of the hot stamp, and the thickness of the buffer is preferably 0.2 to 2 mm, more preferably 0.2 to 1.0.
mm. Specific examples of the buffer composed of a high-molecular organic compound used for the hot stamp of the present invention are as follows. As the material and structure of the cushioning material, in addition to using a so-called rubber-like substance whose material itself exhibits elasticity in a mainly plate-like form, sponge, steel wool, or even a highly heat-conductive and hard material such as metal or ceramic. It can be used in a form easily elastically deformed such as a spring. It can be used in the form of a sponge. In the case of a sponge-like form, the air in the sponge impedes the conduction of heat. Therefore, it is also effective to fill the sponge with a fluid having high heat conductivity instead of air. In addition, since the surface of the cushioning material becomes uneven in the sponge-like form, it is also effective to provide a thin film of a soft material such as a vinyl sheet on the surface.

The material exhibiting rubber-like elasticity is roughly divided into natural rubber and synthetic rubber. Synthetic rubber further includes polyisoprene and polybutadiene as diene rubbers and copolymers thereof with other vinyl compounds. Examples include olefin rubber such as butyl rubber and ethylene-propylene rubber, polyurethane rubber, silicon rubber, and fluorine rubber known under the trade name Viton. Above all, silicon rubber and fluorine rubber are excellent materials for the cushioning material because of their high heat resistance and thermal conductivity. It is also effective to fill a rubber-like substance with a material having high thermal conductivity such as silica to enhance thermal conductivity. The hardness of such a cushioning material is 75 or less in terms of spring hardness Hs, but is preferably in the range of 25 to 75, and more preferably in the range of 25 to 50. Here, the hardness of the cushioning material is JIS K6.
ASKERA manufactured by Kobunshi Keiki Co., Ltd. as a tester according to the spring hardness test (A type) of 301-1971.
This is a value measured by using a mold rubber hardness meter to bring the pressurized surface of the tester into contact with a test piece serving as a cushioning material. That is, the hardness is not a value measured in a state where the buffer material is arranged in the erasing heating means, but a value measured using the buffer material itself as a test piece.

FIG. 4B is a schematic view of a contact-type heating device for making the heat roller 4 transparent. In the figure, 5
Indicates an idle roller. In this apparatus, a heat roller 4 and the idle roller 5 is rotating at equal circumferential speed, reversible thermosensitive recording medium 1 between which Ru is moved while being sandwiched. FIG. 4C is a schematic diagram of a contact-pressing type heating device that performs transparency by the heat block 6 . In the figure, reference numeral 7 denotes a feed roller.
Although not mentioned in 4 this figure, it goes without saying that it is possible to use a thermal head as an image erasing apparatus as cited in FIG.

Next , the mechanism for eliminating the distortion by the contact pressing type erasing method is as follows. As described above, on the high temperature side of the center value or more of the transparent possible temperature range,
By simultaneously performing the heating and the pressurization, the resin caused by the heat is softened and the stress is applied by the pressurization in order to eliminate the distortion caused by the shift stress, so that the effect of eliminating the shift stress is further improved. That is, when heated under such conditions, the organic low-molecular substance dispersed in the resin base material of the reversible thermosensitive recording medium becomes a molten state, and the surrounding resin base material is also at a temperature higher than the softening point. In this state, the particles of the organic low-molecular substance return to the original spherical shape due to the interfacial tension acting between the organic low-molecular substance and the resin base material, and the distortion caused by the shift stress is eliminated. Further, it is considered that the effect of eliminating the displacement stress is improved by applying a stress by pressurizing at the same time.

Regarding the heating temperature, it is expected that the resin base material is very soft because it is at a temperature higher than the softening point, as described above, in the above-mentioned transparent temperature range. In such a state, by setting the heating temperature to a high temperature side that is equal to or higher than the center value of the transparentizable temperature range, the softening of the resin base material proceeds further, and the effect of eliminating the distortion of the recording layer is further enhanced. It is expected that the repetition durability of an image is improved by the method of the present invention.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments. All parts and percentages here are on a weight basis. Example 1 (Preparation of a reversible thermosensitive recording medium)
A1 vapor-deposited layer on a 400-m thick polyester film
光 A light reflecting layer was provided by vacuum evaporation to a thickness. Furthermore, stearic acid 5 parts Eicosane diacid (Okamura Oil Co., Ltd .: SL-20) 5 parts Diisodecyl phthalate 2 parts Vinyl chloride-vinyl acetate copolymer 25 parts (Denki Kagaku Kogyo Co., Ltd., # 1000MT) THF 150 A solution consisting of 15 parts of toluene was applied and dried by heating to form a recording layer (reversible thermosensitive recording layer) having a thickness of about 5 μm. Further, a solution consisting of 10 parts of polyamide resin (manufactured by Toray Industries, Ltd .: CM8000) and 90 parts of methanol was applied thereon and dried by heating to form an intermediate layer having a thickness of about 1 μm. Furthermore, a solution consisting of 10 parts of a 75% butyl acetate solution of a urethane acrylate-based ultraviolet-curable resin (manufactured by Dainippon Ink and Chemicals, Unidick C7-157) and 10 parts of toluene was applied by a wire bar, and dried by heating. , 8
The composition was cured with an ultraviolet lamp of 0 w / cm, and a protective layer having a thickness of about 2 μm was provided to prepare a reversible thermosensitive recording medium.

(Measurement of Transparency Temperature Range) The transparency temperature range and width of the reversible thermosensitive recording material of Example 1 thus obtained were measured as follows. First, the recording material obtained in Example 1 was in a transparent state. The recording material was heated in a thermostat at 120 ° C. for 1 minute, and then cooled to room temperature to make it opaque and opaque. Next, the recording material was heated to 60 ° C. using the hot stamp of FIG.
After heating at a pressure of 1 kg / cm ² for 1.0 sec from 2 ° C. to 120 ° C., the mixture was cooled to room temperature, and the reflection density was measured with a Macbeth reflection densitometer (RD-914). At this time, the temperature at which the reflection density exceeded 1.2 was defined as the transparency temperature, and the range and width were measured. Table 1 shows the results.

[Table 1] Here, an Al block is used for the hot stamp 2 shown in FIG. 4 (a), and a spring hardness Hs
In this case, a material using a cushioning material to which a silicone rubber of 45 was adhered with a thickness of 0.2 mm was used.

(Durability Test) Further, the reversible thermosensitive recording medium of Example 1 was subjected to a repeated durability test of image formation and erasing as follows. As an image forming apparatus, a thermal head print test apparatus manufactured by Yashiro Electric Co., Ltd. was used, and a thermal head of 8 dots / mm manufactured by Ricoh Co., Ltd. was used.
An opaque image was formed under the conditions of an applied voltage of 25.0 V, and the image was erased using a hot stamp having a clearing temperature range. The image erasing conditions were set at an erasing temperature of 87.5 (center value), an applied pressure of 1 kg / cm ² , The image was erased by setting the application time to 1.0 sec. It was considered that one cycle of forming and erasing the white turbid image was regarded as one cycle, and the durability test was repeated under the same conditions until a total of 100 cycles. Regarding the cloudy image density in the repeated durability test,
The cloudiness density of each of the first cycle and the 100th cycle was measured with a Macbeth reflection densitometer (RD914). Table 2 shows the results.

Example 2 A repetitive durability test was performed in the same manner as in Example 1 except that the erasing temperature of the hot stamp was changed to 93 ° C. using the same reversible thermosensitive recording medium as in Example 1. Done. Table 2 shows the results.

Example 3 The same reversible thermosensitive recording material as in Example 1 was used, except that the image erasing condition of the hot stamp was changed to an erasing temperature of 101 ° C. (upper limit), and was repeated in the same manner as in Example 1. A durability test was performed. Table 2 shows the results.

Example 4 Using the same reversible thermosensitive recording material as in Example 1, except that the image erasing conditions of the hot stamp were changed to an erasing temperature of 101 ° C. and an application time of 0.5 second. And a durability test was performed. Table 2 shows the results.

Example 5 Using the same reversible thermosensitive recording material as in Example 1, the same as in Example 1 except that the image erasing conditions of the hot stamp were changed to an erasing temperature of 101 ° C. and an application time of 0.2 seconds. And a durability test was performed. Table 2 shows the results.

Example 6 Using the same reversible thermosensitive recording material as in Example 1, the image erasing conditions of the hot stamp were changed to an applied pressure of 0.3 kg / cm.
^A durability test was performed in the same manner as in Example 1 except that the test was changed to ² . Table 2 shows the results.

Example 7 A durability test was performed using the same reversible thermosensitive recording medium as in Example 1, except that the image erasing conditions of the hot stamp were changed to an erasing temperature of 101 ° C. and an applied pressure of 0.3 kg / cm ^2. Was done. Table 2 shows the results.

Comparative Example 1 Using the same reversible thermosensitive recording medium as in Example 1, the image erasing conditions of the hot stamp were changed to an erasing temperature of 74 ° C. (lower limit).
The durability test was performed in the same manner as in Example 1 except that the test was changed to. Table 2 shows the results.

Comparative Example 2 Using the same reversible thermosensitive recording medium as in Example 1, the conditions for erasing the image of the hot stamp were changed to an erasing temperature of 74 ° C. and an application time of 10 seconds, in the same manner as in Example 1. A repeated durability test was performed. Table 2 shows the results.

Comparative Example 3 Using the same reversible thermosensitive recording medium as in Example 1, the conditions for erasing the image of the hot stamp were changed to an erasing temperature of 74 ° C. and an applied pressure of 0.3 kg / cm ^2. A repetitive durability test was performed in the same manner as described above. Table 2 shows the results.

[0043]

[Table 2]

[0044]

As is clear from the description of the examples and comparative examples, according to the method of the present invention, even when image formation and erasure are repeated, the white turbid image deterioration is small, the contrast change is small, and the repetition durability is low. An improved recorded image is obtained.

[Brief description of the drawings]

FIGS. 1A to 1D are diagrams showing the influence of a heat generating element on a heat-sensitive layer of a reversible thermosensitive recording medium in a conventional image display.

FIGS. 2A to 2C are diagrams showing the influence of a heating element on a heat-sensitive layer of a reversible thermosensitive recording medium according to the method of the present invention. FIG. 4D is a diagram illustrating a direction of a stress applied to eliminate a distortion caused by a shift stress generated on a contact surface between the heating element and the recording medium.

FIG. 3 is a diagram showing a change in transparency of a reversible thermosensitive recording medium according to the present invention due to heat.

FIG. 4 shows various specific examples of image erasing means in a thermosensitive recording image display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reversible thermosensitive recording medium 2 ... Hot stamping 3 ... Stamp stand 4 ... Heat roller 5 ... Idle roller 6 ...Heat block  7 ... Feed roller

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Makoto Kawaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Fumito Masuchi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (56) References JP-A-5-77549 (JP, A) JP-A-4-358879 (JP, A) JP-A-5-104857 (JP, A) JP-A-5-16536 ( JP, A) JP-A-60-961 (JP, A) JP-A-2-50897 (JP, A) JP-A-2-3876 (JP, U) JP-A-1-112969 (JP, U)

Claims (5)

(57) [Claims] 1. A reversible sensor comprising, on a support, a heat-sensitive recording layer having a resin base material and an organic low-molecular substance dispersed in the resin base material as main components and capable of forming and erasing an image by heating. In an image erasing method for erasing an image by heating a display medium made of a thermal recording material, the erasing temperature is set to a high temperature side equal to or higher than the center value of a transparent temperature range at the time of erasing an image on the display medium , and a pressing pressure is applied. Wherein the temperature is set to 0.1 kg / cm ² or more and heating is performed to erase the image. 2. The image erasing method according to claim 1, wherein at least one of a thermal head, a hot stamp, a heat roller, and a heat block is used as a heating unit for erasing an image on the display medium. . 3. The image erasing method according to claim 1, wherein a hot stamp is used as a heating means for erasing an image on the display medium, and a heating time is set to 0.1 second or more. 4. The hot stamp according to claim 1, wherein a hot stamp is used as a heating means for erasing an image on the display medium, and a buffer made of a high molecular organic compound is disposed on a metal surface of the hot stamp. Image erasing method. 5. The image erasing method according to claim 1, wherein the reversible thermosensitive recording material is a card having the thermosensitive recording layer and a magnetic recording layer.