JPH05185720A - Manufacture of reversible heat-sensitive recording material - Google Patents

Abstract

PURPOSE:To obtain the recording material, concerned, by which the lowering of image density hardly occurs even after the repetition of the formation and erasion of image with a thermal head, by a method wherein the thermal drying of base is performed simultaneously with and just after the application of heat-sensitive layer material under the condition that the temperature at one side, onto which the heat-sensitive layer material is applied, of the base is held below the temperature at the other side or rear side of the base. CONSTITUTION:Resinous base material and organic low molecular substance-containing heat- sensitive layer material is applied on base and then dried so as to form heat-sensitive layer, the transparency of which reversibly changes in dependence on temperature. A heating roll drying facility 2 is arranged so as to hold the temperature at one side, onto which the heat- sensitive layer material is applied, of the base below the temperature at the other side or rear side of the base at that time in order to thermally dry the base simultaneously with or just after the application of the heat-sensitive layer material with an application facility 3. As a result the reversible heat-sensitive recording material wherein gradient is developed in the particle diameter of the organic low molecular substance in the heat-sensitive recording layer, by which the lowering of image density hardly occurs even by repeating the formation and erasion of image with a thermal head and also no adhesion of the tailings on the thermal head develops, is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a reversible thermosensitive recording material capable of repeatedly forming and erasing an image by utilizing the reversible transparency change with temperature of a thermosensitive layer. ..

[0002]

2. Description of the Related Art In recent years, reversible thermosensitive recording materials have been attracting attention because they enable temporary image formation and can erase the image when it is no longer needed. As a typical example, the glass transition temperature (Tg) is from 50 to 60 ° C. to 8
A reversible thermosensitive recording material 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
54198 and the like).

When producing these reversible heat-sensitive materials,
Tetrahydrofuran is used as a basic solvent capable of dissolving or dispersing both a resin base material and an organic low molecular weight substance. Since this type of organic solvent has a very low boiling point and a high evaporation rate, the solvent on the surface evaporates at the stage before coating and drying, forming a film of the resin base material on the surface, and evaporating the solvent inside the layer. Not only does it hinder volatilization, but the particle size of the organic low molecular weight substance dispersed in the resin matrix becomes large, and it deposits on the surface of the layer with time. Further, there is a defect that the contact property is deteriorated at the interface between the support and the layer due to the residual solvent in the layer. Therefore, in addition to the coating problem that another layer cannot be smoothly laminated on this surface, while applying pressure using a thermal head etc. and simultaneously heating and repeating image formation-erasing many times, There is a drawback that the particles of the organic low-molecular substance gradually become particles having a larger diameter, the effect of scattering light is lost, the white turbidity decreases, and finally the contrast of the image decreases. Also, since particles of organic low molecular weight substance are deposited on the surface, even if a protective layer is stacked on top of it, particles of organic low molecular weight substance gradually migrate into the protective layer and adhere to the head residue due to contact with the thermal head. Occurs, and there is a drawback that it cannot be repeated many times.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks and makes uniform even if image forming-erasing is repeated many times by using a heating means such as a thermal head which applies heat and pressure at the same time. The present invention provides a method for producing a reversible heat-sensitive recording material which is capable of forming various images and which is free of head shavings.

[0005]

According to the present invention, a solution in which a resin base material and an organic low molecular weight substance are dissolved in a solvent or a dispersed dispersion liquid is applied onto a support and dried, In the method for producing a reversible thermosensitive recording material that forms a thermosensitive layer in which the transparent state and the cloudy state reversibly change depending on the temperature of the surface of the support on the side to which the solution or dispersion is applied. Is T ₁ and the temperature of the back surface of the support is T ₂ , heating and drying so that T ₁ ≦ T ₂ , specifically, at the same time as the application of the solution or the dispersion. Heating the backside of the support, or afterheat drying the backside of the support immediately after coating, especially as these heating equipment,
A method for producing a reversible thermosensitive recording material characterized by using hot roll drying equipment, hot air drying equipment, hot plate drying equipment, and using a thermal back roll drying equipment as heating equipment at the time of coating and simultaneous heating, respectively. Provided.

In a reversible thermosensitive recording material provided with a thermosensitive layer in which the transparent state and the cloudy state reversibly change depending on heat, the particle size of the organic low molecular weight substance is closer to the support than to the surface part. It is important to provide a gradient in the particle size of the organic low molecular weight substance in the depth direction of the heat sensitive layer so that the value becomes large.

That is, in such a reversible heat-sensitive recording material, the portion of the heat-sensitive layer in the vicinity of the support is not easily affected by the heat and pressure of the thermal head. Even if pressure is applied, the particle size does not change, and the same image formation as in the initial stage can be obtained. Further, in the vicinity of the surface of the heat sensitive layer, the influence of heat and pressure of the thermal head is great, but since the particle size of the organic low molecular weight substance is small, the periphery of the particle is thickly covered with the resin base material. Therefore, even if the heat and pressure of the thermal head are repeated many times, the organic low molecular weight substance dispersed in the resin base material is maintained as fine particles, so that the image contrast is not deteriorated at all. Furthermore, since the particles of the organic low molecular weight substance on the surface of the heat-sensitive layer are covered with the resin base material, there is no migration. Therefore, even if repeated with the thermal head, no residue adheres to the thermal head, and uniform image formation can be obtained.

Further, the average particle size of the organic low molecular weight substance in the heat-sensitive layer is 0.1 to 5.0 μm, preferably 0.3 to 3.0 μm in the vicinity of the support of the heat-sensitive layer. The area near the surface of the heat-sensitive layer is 0.05 to 1.0 μm, preferably 0.
A particle size of 1 to 0.8 μm is preferable. When the particle diameter in the vicinity of the support is 0.1 μm or less, the resin base material is sufficiently covered, and the change in the cloudy state and the transparent state is insufficient at low energy and the image contrast is lowered. On the other hand, when it is 5.0 μm or more, the effect of scattering is reduced and the white turbidity is lowered. When the particle diameter in the vicinity of the surface of the heat-sensitive layer is 0.05 μm or less, it becomes difficult to form a polycrystalline state in the dispersed matrix during crystal growth, and the opacity decreases.
When the thickness is 1.0 μm or more, the covering of the matrix material becomes insufficient, the growth of the particle size is promoted, and the particles are deposited on the surface, resulting in the problem of head residue adhesion.

The present inventors have earnestly studied a production method for obtaining a reversible thermosensitive recording material in which a particle diameter of an organic low molecular weight substance has a gradient in a depth direction of a thermosensitive layer, and as a result, the thermosensitive material on a support was found. Simultaneously with application of the solution or dispersion for forming a layer,
Alternatively, immediately after coating, by heating the support with at least one equipment such as hot roll drying equipment, hot air drying equipment, hot plate drying equipment, or thermal back roll drying equipment, the temperature of the coated surface of the support can be Is heated below the temperature of the back of the
Since the evaporation rate and diffusion rate of the solvent before coating and drying are adjusted appropriately, the growth of the particle size of the organic low molecular weight substance is suppressed without forming a film of the heat-sensitive layer, and particles from the vicinity of the support It was found that a heat-sensitive layer having a gradient of particle diameter was formed because of being formed.

According to the production method of the present invention, the particle size of the organic low molecular weight substance is 0.1 to 5.0 μm in the vicinity of the support, and 0.05 to 1.0 in the vicinity of the surface of the heat sensitive layer.
A particle size of μm is obtained. As the heating temperature of the support at this time, 50 ° C. to 140 ° C. is preferable, while maintaining the temperature of the coated surface of the support below the temperature of the back surface of the support, 70 ° C. to 120 ° C.
It is particularly preferable to set the temperature to ° C. When the heating temperature is 50 ° C. or lower, the particle size grows and becomes large, and further deposits on the surface of the heat-sensitive layer, which adversely affects head residue adhesion and durability. On the contrary, when the temperature is 140 ° C. or higher, there is a problem that the support expands and contracts due to heat.

Although the reason for simultaneous heat drying or after heat drying and particle formation of the present invention is not clear, the estimated melanism is as shown in FIG. In the case of the method, the temperature of the coating surface of the support becomes higher than the temperature of the back surface of the support because hot air is blown to the coating surface side, and evaporation of the solvent on the surface of the heat sensitive layer progresses from the coating liquid before drying, Since a film containing the resin base material and organic low molecular weight substance inside is formed on the surface, the solvent remains from the surface of the heat-sensitive layer to the inside of the layer, and particles grow due to the influence of this residual solvent between before drying and during the drying process. It becomes large, and a large particle layer is formed on the entire heat-sensitive layer. However, as shown in FIG. 2 (a), when the support is heated at the same time as or immediately after the coating of the present invention, or the like, while keeping the temperature of the coated surface of the support below the temperature of the support, Drying of the solvent and the resin base material begins near the support, and then evaporation of the solvent on the surface and evaporation of the solvent between the drying steps with the organic low molecular weight substance fixed to the resin base material by drying the resin base material. It is presumed that the particle growth is suppressed and a small particle layer is formed by completely drying and fixing the resin base material.

The temperature profile at this time is shown in FIG.
FIG. 3A shows the temperature profile of the support during drying by the manufacturing method of the present invention, and FIG. 3B shows the temperature profile of the support during drying by the conventional manufacturing method. This profile is obtained by measuring the temperature with thermocouples attached to both sides of the support and calculating by the finite element method using this data as a condition. The temperature profile in the coating film is estimated.

Examples of the heating and drying equipment of the present invention include hot roll drying equipment, hot air drying equipment, hot plate drying equipment and thermal back roll drying. It is effective for the contact drying method, that is, hot roll drying equipment and hot plate drying equipment. Further, in the hot air drying equipment, the effect of heat on the support is improved by making the gap between the support and the hot air outlet as narrow as possible. Examples of the hot roll drying equipment method of the present invention include steam heating, infrared heating, electromagnetic heating, dielectric heating and the like. Examples of hot air drying equipment methods include steam heating and infrared heating. Furthermore, steam heating, infrared heating, electromagnetic heating, dielectric heating and the like can be mentioned as hot plate drying equipment methods.

The heating and drying method of the present invention will be described with reference to FIGS. 4 and 5 show a hot roll drying method, in which a solution or a dispersion liquid is applied to the support fed from the unwinder by the coating facility 3. At this time, as shown in FIG. 4, the heating roll drying equipment 2 can be arranged on the back surface to perform simultaneous heating. FIG. 5 shows an afterheat drying method in which the hot roll drying equipment 2 is installed immediately after coating. FIG. 6 shows a hot plate drying equipment 7 installed in place of the hot roll drying equipment of FIG. 5, and FIG. 7 shows an after-heat drying method in which a hot air drying equipment 8 is also arranged. After these drying operations, it is passed through the annealing box 5 and wound up by the winder 6.

The reversible thermosensitive recording material of the present invention utilizes the transparency change (transparent state, cloudy opaque state) as described above, and the difference between the transparent state and the cloudy opaque state is presumed as follows. . That is, (i) in the case of transparency, 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 and is opposite. It appears to be transparent because it is transmitted to the side, and (ii) in the case of turbidity, the particles of the organic low-molecular substance are composed of polycrystals of fine crystals of the organic low-molecular substance, and the crystal axis of each crystal Since the light is directed in various directions, the light incident from one side is refracted many times at the interface of the crystal of the organic low molecular weight substance particles, and is scattered and thus appears white.

In FIG. 1 (representing the change in transparency due to heat), a 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
It is cloudy and opaque at room temperature below ₀ . 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 conceivable that the organic low-molecular-weight substance undergoes a semi-molten state until the following and the crystal grows from a polycrystal to a single crystal.
Further heating to a temperature of T ₃ or higher results in a semitransparent state between the maximum transparency and the maximum opacity. Next, when this temperature is lowered, the initial cloudy opaque state is restored without taking the transparent state again. It is considered that this is because the organic low molecular weight substance is melted at a temperature of T ₃ or higher and is then cooled to precipitate polycrystals. It should be noted that 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 when heated again to a temperature of T ₃ or higher and then returned to room temperature. That is, it can take both opaque and transparent forms at room temperature and intermediate forms thereof. Therefore,
The heat-sensitive layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent background or a transparent image on a cloudy background, and the change can be repeated many times. By arranging a coloring sheet on the back surface of such a heat-sensitive layer, an image of the color of the coloring sheet or a white image of the background of the coloring sheet can be formed on a white background. 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.

In order to form and erase an image using such a reversible thermosensitive recording material, it is necessary to have two thermal heads for image formation and image erasure, or to change the applied energy conditions. Therefore, it is effective to use a thermal head having a single thermal head for image formation and image deletion. In the former case, the cost of the apparatus increases because two thermal heads are required, but if the reversible heat-sensitive recording material is passed once with different energy application conditions for each thermal head, image formation and erasure can be performed. You can do it. In the latter case, an image is formed and erased by one thermal head. Therefore, the conditions for applying energy to the thermal head at one time when the thermal recording material passes are adjusted according to the image forming portion and the erasing portion. The operation is complicated, but the operation is complicated, such as changing finely, or once erasing the image on the thermosensitive recording material and then running the thermosensitive recording material in the reverse direction again to form an image under different energy conditions. Therefore, the equipment cost is reduced.

To prepare the reversible thermosensitive recording material used in the present invention, it can be formed as a film on a supporting member or formed into a sheet 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 member, and the solvent is evaporated to form a film or sheet. 2) Dissolve the resin base material in a solvent that dissolves only the resin base material, pulverize or disperse the organic low molecular weight substance in the solvent by various methods, apply this to a support member, evaporate the solvent, and form a film. Or the method of making a sheet. As the solvent for forming the heat-sensitive layer or the heat-sensitive recording material, various selections can be made according to the types of the resin base material and the organic low-molecular substance,
Examples thereof include tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. 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 of the reversible thermosensitive recording material is preferably a resin which can form a film or a sheet, has good transparency and 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-based copolymers such as polymer; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, vinylidene chloride copolymer such as vinyl chloride-acrylate copolymer; polyester; polyamide A polyacrylate or polymethacrylate or an acrylate-methacrylate copolymer; a silicone resin or 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 in the recording layer due to heat (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 weight substances include alkanols; alkane diols; halogen alkanols or halogen alkane diols; alkylamines; alkanes; alkenes; alkynes; halogen alkanes; halogen alkenes; halogen alkynes; cycloalkanes; cycloalkenes; cycloalkynes; 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 portion 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, these compounds include higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, alginic acid and oleic acid; methyl stearate. , Esters of higher fatty acids such as tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate and dodecyl behenate; C ₁₆ H ₃₃ -O-C ₁₆ H ₃₃ , C ₁₆ H ₃₃ -S-C ₁₆ H _{33
, C 18 H 37 -S-C} 18 H 37, C 12 H 25 -S-C 12 H 25
, C ₁₉ H ₃₉ -S-C ₁₉ H ₃₉ , C ₁₂ H ₂₅ -S-S-C ₁₂
H ₂₅ , Etc., such as ether or thioether. Among them, in the present invention, higher fatty acids, particularly higher fatty acids having 16 or more carbon atoms such as palmitic acid, stearic acid, behenic acid, and lignoceric acid are preferable, and higher fatty acids having 16 to 24 carbon atoms are more preferable.

In order to widen the temperature range in which the material can be made transparent, the organic low molecular weight substances described in this specification may be appropriately combined, or such organic low molecular weight substances may be combined with other materials having different melting points. .. These are disclosed, for example, in JP-A-63
No. 39378, Japanese Patent Application Laid-Open No. 63-130380, etc., Japanese Patent Application No. 63-14754, Japanese Patent Application No. 1-1401.
However, the present invention is not limited thereto.

The thickness of the heat sensitive layer is preferably 1 to 3 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. 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, and more preferably 1: 1 to 1: 3. When the ratio of the resin base material is less than this, it becomes difficult to form a film in which the organic low molecular weight substance is retained in the resin base material, and when it exceeds the ratio, the amount of the organic low molecular weight substance is small, so that it becomes opaque. Becomes difficult.

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 , Fats or lower olefin oxide adduct of 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 to amine-containing mono Chromatography copolymers; styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer.

When an image of this recording material is used as a reflection surface image, if a layer that reflects light is provided on the back surface of the recording layer, 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 (described in JP-A No. 64-14079).

In addition, a protective layer may be provided on the heat-sensitive layer of the present invention in order to prevent the transparency of the transparent portion from being lowered due to the deformation of the surface due to the heat and pressure of a heating means such as a thermal head. good. A protective layer (thickness: 0.
(1 to 5 μm), silicone rubber, silicone resin (described in JP-A-63-221087),
Polysiloxane graft polymer (JP-A-63-317)
No. 385), an ultraviolet curable resin, an electron beam curable resin (described in JP-A-2-566), and the like. In any case, a solvent is used at the time of coating, but it is desirable that the solvent is difficult to dissolve the resin of the heat sensitive layer and the organic low molecular weight substance. Examples of the solvent that hardly dissolves the resin and the organic low molecular weight substance in the heat-sensitive layer include n-hexane, methyl alcohol, ethyl alcohol, isopropyl alcohol and the like, and the alcohol solvent is particularly preferable from the viewpoint of cost.

Further, an intermediate layer may be provided between the protective layer and the reversible recording material in order to protect the reversible recording material from the solvent, monomer component and the like of the protective layer forming liquid (JP-A-1-133781). Issue). As the material for the intermediate layer, the following thermosetting resins and thermoreversible resins can be used in addition to those listed as the resin base material in the thermosensitive layer.
That is, specifically, 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 varies depending on the use, but is preferably about 0.1 to 2 μm. If it is less than this, the protective effect is lowered, and if it is more than this, the thermal sensitivity is lowered.

[0029]

EXAMPLES All parts and percentages herein are by weight. Example 1 Behenic acid 7 parts Eicosane diacid 3 parts Vinyl chloride-vinyl acetate copolymer 28 parts (VYHH manufactured by Union Carbide) Di-2 ethylhexyl phthalate 3 parts Tetrahydrofuran 128 parts on a transparent polyester film having a thickness of about 100 μm. A reversible thermosensitive recording layer was coated on a support under the following coating conditions by a simultaneous heating method using a hot roll drying method using a solution containing 14 parts of toluene. Line speed 6m / min Drying box temperature 120 ℃ Surface temperature of hot roll drying equipment 90 ℃ Contact time between support and hot roll drying equipment 5 seconds Coating method 1 nozzle coating method Drying time 1 minute Thickness of thermal recording layer About 5 μm

Example 2 A reversible thermosensitive recording layer was coated on a support under the following coating conditions by using the same solution as in Example 1 by an after-heat system using a hot roll drying system. Run speed 6 m / min Drying box temperature 120 ℃ Surface temperature of hot roll drying equipment 90 ℃ Contact time between support and thermal back roll drying equipment 5 seconds Coating method Nozzle coating method Drying time 1 minute Thickness of thermosensitive recording layer 5 μm

Example 3 A solution similar to that of Example 1 was prepared, and a reversible thermosensitive recording layer was coated on a support under the following coating conditions by an afterheat system by a hot plate drying system. Run speed 6 m / min Drying box temperature 120 ℃ Surface temperature of hot plate drying equipment 90 ℃ Contact time between support and hot plate drying equipment 5 seconds Coating method Nozzle coating method Drying time 1 minute Thermal recording layer thickness 5 μm

Example 4 A solution similar to that in Example 1 was prepared, and a reversible thermosensitive recording layer was coated on a support under the following coating conditions by an afterheat system by hot air drying. Run speed 6 m / min Drying box temperature 120 ℃ Hot air drying equipment temperature 90 ℃ Contact time between support and hot air drying equipment 5 seconds Coating method Nozzle coating method Drying time 1 minute Thermal recording layer thickness 5 μm

Comparative Example A solution similar to that of Example 1 was prepared, and neither hot roll drying equipment, hot plate drying equipment nor hot air drying equipment was used.
Coating was carried out in the same manner as in Example 1 to prepare a reversible thermosensitive recording layer.

Each of the five types of reversible thermosensitive recording layers prepared as described above was cut to A4 size, and a solution consisting of polyamide (Toray CM8000) 5 parts methanol 95 parts was applied with a wire bar, and the temperature was raised to 80 ° C. It is dried in a constant temperature bath to form an intermediate layer having a thickness of about 1 μm. Furthermore, as a protective layer on the intermediate layer, a UV curable resin (Unidick C7-157 manufactured by Dainippon Ink & Co., Ltd.) 10 parts A solution consisting of 10 parts IPA was applied with a wire bar, and after heating and drying, the protective layer was cured by irradiation with ultraviolet rays. A 4 μm protective layer was provided. The five types of reversible thermosensitive recording materials were evaluated for a printing durability test, a dust adhesion test on a thermal head, a particle size of fatty acids in the thermosensitive recording layer, and a deformation of the support. The results are shown in Table 1.

For the printing durability test, a thermal head printing tester manufactured by Yashiro Denki Co., Ltd. was used. The thermal head was a thin film full surface type manufactured by Ricoh. The pressure of the platen roll on the thermal head was 3 kg / head, the pulse width was 1 ms, and the voltage was 25 V. Printing was performed under the conditions to form an image. Next, the image was erased by passing through a heat roller set at 80 ° C. The printing and erasing were repeated 30 times, and the initial image density and the image density after 30 times printing were measured with a Macbeth reflection densitometer (RD514) to examine the difference in the image density between the initial and 30 times. Regarding the adhesion of dust to the thermal head, the adhesion of dust to the thermal head after printing 30 times was observed. Regarding the deformation of the support, the deformation of the support due to heat was visually determined. The particle size of fatty acids in the thermosensitive recording layer was measured from a cross-sectional photograph of the reversible thermosensitive recording material.

[0036]

[Table 1]

The reversible thermosensitive recording material of the present invention can be applied to the coated surface of the support by using the simultaneous heating method of the support or the after-heat drying method in the coating for forming the thermosensitive recording layer on the support. Since the temperature can be maintained below the temperature of the back surface of the support, the particle diameter of the organic low molecular weight substance in the thermosensitive recording layer has a gradient, and the particles of the organic low molecular weight substance on the surface of the thermosensitive recording layer are covered with the resin base material. be able to. As a result, there is almost no decrease in image density even when image formation-erasure is repeated by the thermal head, and there is an effect that no dust adheres to the thermal head.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in transparency of a reversible thermosensitive recording material according to the present invention due to heat.

FIG. 2 (a) shows a case where the temperature of the coated surface of the support is kept below the temperature of the back surface of the support in the formation of the heat sensitive layer by coating and drying the heat sensitive layer forming solution or dispersion on the support. The figure which showed the change of the particle diameter of the organic low molecular weight substance in this layer.
(B) shows a case where the temperature of the coated surface of the support is higher than the temperature of the back surface of the support in the formation of the heat sensitive layer by coating and drying the heat sensitive layer forming solution or dispersion on the support. The figure which showed the change of the particle diameter of an organic low molecular weight substance.

FIG. 3 (a) is a temperature profile of a support during drying according to the operation of the present invention. (B) is the temperature profile of the support during drying by conventional operation.

FIG. 4 is a schematic view showing a hot roll drying method which is an example of a simultaneous heating and drying method in forming a heat sensitive layer by coating and drying a heat sensitive layer forming solution or dispersion on a support.

FIG. 5 is a schematic diagram showing a hot roll drying method which is an example of an after-heat drying method in forming a heat-sensitive layer by coating and drying a heat-sensitive layer-forming solution or dispersion on a support.

FIG. 6 is a schematic view showing a hot plate drying method which is an example of an after-heat drying method in forming a heat-sensitive layer by coating and drying a heat-sensitive layer-forming solution or dispersion on a support.

FIG. 7 is a schematic diagram showing a hot-air drying method which is an example of an after-heat drying method in forming a heat-sensitive layer by coating and drying a heat-sensitive layer-forming solution or dispersion on a support.

[Explanation of symbols]

 1 Unwonder 2 Hot roll drying equipment 3 Coating equipment 4 Back roll 5 Drying box 6 Winder 7 Hot plate drying equipment 8 Hot air drying equipment

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiko Hotta 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Kunichika Moroboshi 1-3-6 Nakamagome, Ota-ku, Tokyo In stock company Ricoh (72) Inventor Makoto Kawaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh stock company (72) Inventor Akira Suzuki 1-3-6 Nakamagome, Tokyo Ota-ku In stock company Ricoh (72) Inventor Fumito Masuchibuchi 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (5)

[Claims] 1. A solution in which a resin base material and an organic low molecular weight substance are dissolved in a solvent or a dispersion liquid in which a resin is dispersed is applied on a support and dried to obtain a transparent state and a cloudy state depending on temperature. In the method for producing a reversible thermosensitive recording material which forms a thermosensitive layer in which the reversible temperature changes, the temperature of the surface of the support on the side coated with the solution or dispersion is T _1, and the back surface of the support is when the temperature was T ₂ of the method for producing a reversible thermosensitive recording material, characterized by drying by heating such that T ₁ ≦ T _2. 2. A solution in which a resin base material and an organic low molecular weight substance are dissolved in a solvent or a dispersion liquid in which a resin is dispersed is applied onto a support and dried to obtain a transparent state and a cloudy state depending on temperature. In the method for producing a reversible heat-sensitive recording material which forms a heat-sensitive layer in which the reversible temperature changes, a reversible heat-sensitive recording material characterized by heating the back surface of the support at the same time as coating the solution or the dispersion. Production method. 3. A solution in which a resin base material and an organic low molecular weight substance are dissolved in a solvent or a dispersion liquid in which a resin is dispersed is applied onto a support and dried to obtain a transparent state and a cloudy state depending on temperature. In the method for producing a reversible heat-sensitive recording material which forms a heat-sensitive layer in which the reversible temperature changes, the back surface of the support is afterheat-dried immediately after the application of the solution or the dispersion. Material manufacturing method. 4. The reversible thermosensitive recording material according to claim 1, wherein at least one of a hot roll drying equipment, a hot air drying equipment, and a hot plate drying equipment is used as the heat drying equipment. Method. 5. The method for producing a reversible thermosensitive recording material according to claim 2, wherein as the heating facility, a thermal back roll drying facility in which a back roll is heated is used.