JPH08300834A - Reversible thermal recording medium - Google Patents

Abstract

PURPOSE: To provide a reversible thermal recording medium reduced in the deterioration of an image, the generation of a damage and the lowering of the transparency of a transparent part even if the formation and erasure of an image are repeated by a heating element such as a thermal head. CONSTITUTION: In a reversible thermal recording medium consisting of a support and a thermal recording layer composed of a resin matrix in which a monomeric org. compd. is dispersed and reversibly changed in transparency in dependence on a temp. change, an overcoat layer having pencil hardness of 2H-5H is provided on the thermal recording layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium for recording and erasing by utilizing the reversible change in transparency of the thermosensitive medium with temperature.

[0002]

2. Description of the Related Art As a recording medium capable of reversible recording and erasing, JP-A-54-119377 and 55-
It is known from Japanese Patent No. 154198 that a thermosensitive recording layer in which a low molecular weight organic compound such as higher alcohol or higher fatty acid is dispersed in a resin matrix such as polyester is provided on a support. The transparency of the thermosensitive recording layer changes depending on the temperature, and recording and erasing are possible.

However, in the conventional reversible thermosensitive recording medium, when an image is formed by heating with a heating body such as a thermal head, the surface is easily deformed by the heat and pressure of the heating body, so that the image formation is not performed. There is a drawback that the amount of deformation increases as the erasing is repeated, and the transparency of the portion that should be transparent decreases.

To solve this problem, Japanese Patent Laid-Open No. 62-
In Japanese Patent No. 55650, there has been proposed a method of providing an overcoat layer of silicon resin, silicon rubber or the like to reduce the friction coefficient of the surface. However, since this overcoat layer has insufficient adhesion to the heat-sensitive recording layer, it is repeatedly used. There is a problem that the image is deteriorated by being peeled off by the mechanical work.

Further, Japanese Patent Laid-Open No. 6-58035 discloses that
It is described that an adhesive containing polyvinyl acetate is used to improve the adhesion between the surface of a reversible thermosensitive recording material and an overcoat layer containing a curable resin, and JP-A-6-48029. Is formed on a release film having a smooth surface by forming a protective layer made of a curable resin coating film, and an adhesive layer is formed on the protective layer. A method for producing a visible recording medium is described, which comprises transferring the resin to the surface of a reversible thermosensitive recording medium and then curing the resin of the protective layer. The curable resin in these protective layers (overcoat layers) is a modified acrylate. It is a general monomer or oligomer such as, but is not intended to avoid the occurrence of cracks or scratches in the protective layer itself.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above problems in the prior art, and even if image formation and erasure are repeatedly performed by a heating body such as a thermal head, image deterioration, scratches, and transparent area It is an object of the present invention to provide a reversible thermosensitive recording medium with less decrease in transparency, and an image display method using the same.

[0007]

SUMMARY OF THE INVENTION The present inventors have developed 2H-5
It has been found that the above object can be achieved by providing an overcoat layer having a pencil hardness of H on the thermosensitive recording layer. However, the pencil hardness referred to here is JIS K 5
Using the pencil scratch tester for coating film described in 401,
It is evaluated according to the method described in SK 5400.

That is, according to the present invention, a thermosensitive recording comprising a support, a resin matrix, and a low-molecular organic compound dispersed in the resin matrix as a main component, whose transparency reversibly changes depending on temperature changes. A reversible thermosensitive recording medium provided with a layer, wherein an overcoat layer having a pencil hardness of 2H to 5H is provided on the thermosensitive recording layer. The reversible thermosensitive recording medium is characterized in that is composed of a thermoplastic resin as a main component, and the reversible sensation is characterized in that the overcoat layer is composed of a thermosetting resin composition as a main component. A thermal recording medium is provided, and the reversible thermal recording medium is characterized in that the overcoat layer is composed of an ultraviolet curable resin composition as a main component. A reversible thermosensitive recording medium is provided, wherein the overcoat layer is composed of an electron beam curable resin composition as a main component, and the overcoat layer is an additive as a subcomponent. There is provided the reversible thermosensitive recording medium characterized by comprising a resin composition containing, further characterized in that an image is formed by printing between the thermosensitive recording layer and the overcoat layer. There is provided a reversible thermosensitive recording medium, and further, there is provided an image display method characterized in that the reversible thermosensitive recording medium is used and image formation and erasing are performed by a thermal head.

The reversible thermosensitive recording medium of the present invention utilizes the change from the transparent state to the cloudy opaque state and the change from the cloudy opaque state to the transparent state due to the temperature dependence of the transparency of the thermosensitive recording layer, respectively. It can be recorded and erased. The difference between the transparent state and the cloudy opaque state is presumed as follows.

That is, (i) in the transparent state, the low-molecular weight organic compound particles dispersed in the resin base material are present as relatively large particles, and the light incident from one side is transmitted to the other side without being scattered. To look transparent,
(Ii) In the cloudy state, the low-molecular weight organic compound particles are composed of polycrystals of fine crystals, and the crystal axes of them are oriented in various directions. However, this is because it is refracted many times and appears white because it is scattered.

In FIG. 1 (change in transparency due to heat),
The heat-sensitive layer mainly composed of the particle base material and the low molecular weight organic compound dispersed therein is in a cloudy and opaque state at a temperature of T ₀ or lower, for example. When it is heated to a temperature T, it becomes transparent, and the transparent state is maintained even if the state is returned to normal temperature below T ₀ . It is considered that this is because the low-molecular weight organic compound is in a semi-molten state from the temperature T ₂ to T ₀ or lower and the crystal grows from a polycrystal to a single crystal. Further heating to a temperature of T ₃ or higher brings about an intermediate state between the maximum transparent state and the maximum opaque state. Next, it is considered that the low molecular weight organic compound is melted at a temperature of T ₃ or higher from this state and then cooled to cause polycrystals to precipitate. It should be noted that when this opaque state is heated to a temperature of T _{1 to} T ₂ and then cooled to room temperature, that is, a temperature of T ₀ or lower, it becomes an intermediate state between transparent and opaque. When the transparent material at room temperature is heated to a temperature of T ₃ or higher and then returned to room temperature, the cloudy and opaque state is restored. That is, it can be in an opaque or transparent state and an intermediate state at room temperature.

Therefore, by selectively applying heat to the surface of the heat-sensitive recording material having the heat-sensitive layer as described above, the heat-sensitive layer is selectively heated to form a cloudy image when transparent and a transparent image on a cloudy background. Can be done and the change can be repeated many times. Then, a white image can be formed on the background of such a heat-sensitive layer on the background of the color of the coloring sheet. Also, OHP (overhead projector)
When projected with, for example, the cloudy part becomes a dark part, and the transparent part transmits light to become a bright part on the screen.

Image formation and erasure using such a reversible thermosensitive recording medium are performed by two thermal heads for image formation and image erasure, or image formation is performed by changing applied energy conditions. It is effective to use a single thermal head for image erasing. In the former case, the cost of the apparatus is relatively high because two thermal heads are required, but by setting each thermal head to different application conditions in one apparatus, an image can be formed in one pass. And can be erased. In the latter case, in order to simultaneously form and erase an image in one pass, it is necessary to change the conditions of the energy applied to the thermal head in a short time according to the portion where the image is formed and the portion where the image is erased. In order to form and erase an image in two passes, it is necessary to erase the image and then run the thermal recording medium in the opposite manner to the erase to form the image under another energy condition. However, the operation becomes complicated, but the cost of the apparatus is relatively low because it is performed by a single thermal head.

The present invention will be described in more detail below. The reversible thermosensitive recording medium of the present invention has a recording density of 2H to 5H
An overcoat layer having a pencil hardness of 1 is provided on the upper surface of the reversible recording layer.

Here, the test method limited to JIS K 5400 means that a high-grade product inspected by a public institution, for example, the Japan Paint Inspection Association, as a pencil, has a weight of 1000 g at an angle of 45 ° ± 1 °. Apply a load to the center of the pencil.Fix the test piece on the flat test piece mounting base by fixing it to the weight base, and fix the pencil fixed on the weight mounting base on the test base. The test piece mounting base is moved in the horizontal direction and the vertical direction while keeping it in contact with the one surface of the test piece, and this is carried out for pencils with different hardness until a predetermined flaw is generated on the one surface of the test piece. Is to evaluate. In the present invention, the pencil hardness of the overcoat layer provided on the upper surface of the reversible recording layer is 1
When it is H or less, a large number of irregularities are formed on the surface of the overcoat layer by forming and erasing the image several times to several tens of times, the trace of the previous image formation remains at the time of erasing, and when it is 6H or more, When the image is formed and erased 50 to 300 times, the overcoat layer is cracked and the image formed on the recording layer becomes unclear. The softer the tendency, the more easily the image is formed and erased repeatedly, and the harder the image is, the harder the image is formed and the smaller the number of times the image is erased. Therefore, the pencil hardness of the overcoat layer provided on the reversible recording layer is 2H to 5H. It is preferably 3H to 4H.

As a method for obtaining an overcoat layer having a pencil hardness of 2H to 5H, a thermoplastic resin, a thermosetting resin composition, an ultraviolet curable resin composition or an electron beam curable agent is used as a main component of the overcoat layer. A method of using a resin composition and using a lubricity additive as an auxiliary component can be mentioned, but they may not be used alone, but a plurality of them may be combined.

As the thermoplastic resin, aromatic polyether-ketone, aromatic polyether-sulfone, polybenzoxazole, polybenzimidazole, polybenzothiazole, polyparabanic acid, polyparabanic acid copolymer, polyiminohydantoin copolymer. , Aramid, aramid copolymer, polyimide, polyimide copolymer, polyamide imide, polyamide imide copolymer, polyarylate, polyarylate copolymer or silicon modified products thereof.

The thermosetting resin composition comprises a polymer and / or a polymeric compound having a functional group capable of reacting with a cross-linking agent to form a covalent bond, a cross-linking agent and an optional cross-linking accelerator and a catalyst. Become. Examples of the polymer and the polymeric compound having a functional group capable of reacting with a cross-linking agent to form a covalent bond include polyvinyl alkyl carbamate, polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, ethyl cellulose, cellulose acetate, nitrocellulose, and polyurea. , Polyurethane, urethane prepolymer, carboxy modified polyurethane, amino modified polyurethane, polyurethane acrylate, polyester acrylate, epoxy acrylate, unsaturated polyester, polyether acrylate, N-methylol acrylamide, melamine, methylolated melamine, alkyd resin, phenol resin, silicone Examples thereof include resins, furan resins, resorcinol resins, epoxy resins and the like. Examples of the cross-linking agent include polyisocyanates, aziridine compounds, and organic or inorganic compounds containing two or more amino groups, hydroxyl groups and / or carboxylic acids. The cross-linking accelerator and the catalyst can be appropriately selected and used according to the combination of the polymer and / or the polymeric compound having a functional group capable of reacting with the cross-linking agent to form a covalent bond and the cross-linking agent.

The ultraviolet curable resin composition comprises a photopolymerizable monomer (reactive diluent), a photopolymerizable oligomer and a photoinitiator. As the photopolymerizable monomer, a monofunctional monomer such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-ethylhexyl acrylate or 2-hydroxyethyl acryloyl phosphate, 1,3-butanediol diacrylate, 1,
Bifunctional such as 4-butanediol diacrylate, 1,6-hexanediol acrylate, diethylene glycol diacrylate, tripropylene glycol diacrylate, neopentyl glycol diacrylate, polyethylene glycol diacrylate or hydroxypivalate neopentyl glycol diacrylate Examples of the monomer include trifunctional or higher functional monomers such as dipentaerythritol, pentaerythritol triacrylate, and trimethylolpropane triacrylate.

Examples of the photopolymerizable oligomer include polyester acrylate, epoxy acrylate, polyurethane acrylate, polyether acrylate, silicon acrylate, alkyd acrylate, and melamine acrylate.

As the photoinitiator, benzophenone, methyl benzoylbenzoate, diethoxyacetophenone, 2
-Hydroxy-2-methyl-1-phenylpropane-1
-One, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- (4- (methylthio) phenyl-
2-) morpholino propane-1, benzoin isobutyl ether, benzoin isopropyl ether, benzoin ethyl ether, benzyl methyl ketal, benzyl dimethyl ketal, 2-chlorothioxanthone or 2,
4-diethylthioxanthone and the like can be mentioned.

The electron beam curable resin composition comprises an unsaturated prepolymer, an oligomer and a reactive diluent (monomer). Examples of unsaturated prepolymers and oligomers include unsaturated polyester, polyester acrylate, epoxy acrylate, polyurethane acrylate, polyether acrylate, unsaturated acrylic resin, unsaturated silicone or unsaturated fluorine resin.

Examples of the reactive diluent include n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxypropyl acrylate, trimethylolpropane triacrylate and pentaerythritol triacrylate.

The overcoat layer having a pencil hardness of 2H to 5H of the present invention has a thickness of 0.5 to 10 μm, preferably 2 to 6 μm.

Further, in order to adjust the pencil hardness of the overcoat layer, an additive such as a filler, a surfactant, an organic salt or silicone oil may be contained. As the filler, calcium carbonate, kaolin, silica,
Aluminum hydroxide, alumina, aluminum silicate,
Magnesium hydroxide, magnesium carbonate, titanium oxide,
Inorganic and organic fine powders such as zinc oxide, barium sulfate or urea-formalin resin may be mentioned. The shape of the filler is spherical, and the particle size is 0.010 to 10.0μ.
m, preferably 0.1 to 5.0. The amount of the filler contained in the overcoat layer having a pencil hardness of 2H to 5H is 0.1 to 8 with respect to the total weight of the overcoat layer.
0 wt% is suitable.

Examples of the surfactant include sulfuric acid ester salts of higher alcohols such as sodium lauryl alcohol sulfate ester, sodium myristyl alcohol sulfate ester, sodium cetyl alcohol sulfate ester, sodium stearyl alcohol sulfate ester or sodium oleyl alcohol sulfate ester, octyl sulfonic acid. Sodium, sodium octylbenzene sulfonate,
Sulfonates such as sodium decyl sulfonate, sodium dodecyl sulfonate, sodium nonylnaphthalene sulfonate, sodium dodecyl naphthalene sulfonate or potassium dodecyl naphthalene sulfonate, or higher such as sodium monostearyl ester phosphate or distearyl ester phosphate. Examples thereof include phosphate ester salts of alcohols, but are not limited thereto. The amount of the surfactant contained in the overcoat layer having a pencil hardness of 2H to 5H is appropriately 0.001 to 5 wt% with respect to the total weight of the overcoat layer.

Examples of the organic salts include zinc stearate, calcium stearate, magnesium stearate, hexyl ammonium chloride, sodium sulfosalicylate, potassium succinate, potassium benzoate and potassium adipate. The amount of organic salts contained in the overcoat layer having a pencil hardness of 2H to 5H is 0.01 to 15 with respect to the total weight of the overcoat layer.
wt% is suitable.

To obtain the reversible thermosensitive recording medium of the present invention,
1) A matrix resin and a low molecular weight organic compound are dissolved in a solvent, and the resulting solution is applied onto a support to evaporate the solvent to form a film or sheet. 2) A solvent that dissolves only the matrix resin, Dissolve the matrix resin, disperse the pulverized low molecular weight organic compound in the solution, coat the resulting dispersion on the support, evaporate the solvent to form a film or sheet, or 3) do not use solvent There is a method in which the matrix resin and the low molecular weight organic compound are heated and melted and mixed, and the resulting molten mixture is molded into a film or sheet and cooled.

The solvent used for forming the heat-sensitive recording layer can be variously selected depending on the types of the matrix resin and the low molecular weight organic compound, and examples thereof include ethyl acetate, butyl acetate, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, methylene chloride, chloroform and tetraethyl ether. Examples thereof include carbon chloride, methanol, ethanol, toluene, xylene and benzene. The low-molecular weight organic compound is precipitated as fine particles in the heat-sensitive layer obtained not only when the dispersion liquid is used but also when the solution is used, and is present in a state dispersed in the matrix resin.

The matrix resin in the thermosensitive recording layer of the reversible thermosensitive recording medium is preferably capable of forming a film, and the film is excellent in transparency and 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 and vinyl chloride-acrylate copolymer. Vinyl chloride-based copolymers such as polymer, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer and vinylidene chloride-copolymers such as vinylidene chloride-acrylonylolyl copolymer, polyester, polyamide, polyacrylate, polymethacrylate, poly Examples thereof include acrylate-polymethacrylate copolymers and silicone resins. These may be used alone or in combination of two or more.

On the other hand, the low molecular weight organic compound may be any one that can change from polycrystal to single crystal by heat in the recording layer, and generally has a melting point of 30 to 200 ° C., preferably 50 to 200 ° C.
A low molecular weight organic compound having a melting point of 150 ° C. is used. Such low molecular weight organic compounds include alkanols; alkanediols; halogenated alkanols; halogenated alkanediols; alkylamines; alkanes;
Alkenes; Alkynes; Halogenated alkanes; Halogenated alkenes; Halogenated alkynes; Cycloalkenes; Cycloalkenes; Cycloalkynes; Saturated or unsaturated mono- or dicarboxylic acids or their esters, amides or salts, saturated or unsaturated halogenated fatty acids or These esters,
Amides or salts; allylcarboxylic acids or their esters, amides or salts; halogenated allylcarboxylic acids or their esters, amides or salts; thioalcohols; thiocarboxylic acids or their esters, amides or salts; carboxylic esters of thioalcohols And so on. These may be used alone or in combination of two or more. The carbon number of these compounds is 10 to 60, preferably 10 to 3
8 and especially 10-30 are preferable. The alcohol group moiety in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, a low molecular weight organic compound has at least one oxygen atom in the molecule,
Groups containing nitrogen, sulfur and halogen, such as -OH,
_{-COOH, -CONH 2, -COOR, -NH} -, -
NH _2, -S -, - is preferably a S-S- and -O- compound having like.

More specifically, these compounds include lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, arachidic acid, eicosanoic acid, tricosanoic acid, lignoceric acid, Higher fatty acids such as pentacosanoic acid, cerotic acid, heptacosanoic acid, montanic acid, melissic acid and oleic acid, higher stearic acid such as methyl stearate, tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate and dodecyl behenate. Examples include esters, and the following ethers, thioethers, secondary amines, and the like.

[0033]

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[0034]

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[0035]

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[0036]

[Chemical 4]

[0037]

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[0038]

[Chemical 6]

[0039]

[Chemical 7]

[0040]

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[0041]

[Chemical 9]

[0042]

[Chemical 10]

[0043]

[Chemical 11]

[0044]

[Chemical 12]

[0045]

[Chemical 13]

[0046]

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In the present invention, among them, higher fatty acids, particularly palmitic acid, pentadecanoic acid, nonadecanoic acid, arachidic acid,
Higher fatty acids having 16 or more carbon atoms such as eicosanoic acid, tricosanoic acid, stearic acid, behenic acid, and lignoceric acid are preferable, and higher fatty acids having 16 to 24 carbon atoms are more preferable.

Further, in order to widen the range of temperature which can be made transparent, the above-mentioned low molecular weight organic compound may be appropriately combined, or such a low molecular weight organic compound may be combined with another material having a different melting point. These are, for example, JP-A-6
3-39378, JP-A-63-130380, Japanese Patent Application No. 63-14754, JP-A-3-2089, etc., but the present invention is not limited thereto.

The ratio of the low molecular weight organic compound to the matrix resin in the heat-sensitive recording layer is about 2: 1 to 1: 1 by weight.
16 is preferable, and 1: 2 to 1: 6 is more preferable. When the ratio of the matrix resin is less than this, it becomes difficult to form a film in which the low molecular weight organic compound is held in the matrix resin, and when the ratio is higher than this, opacity becomes difficult because the amount of the low molecular weight organic compound is small.

The thickness of the thermosensitive recording layer is preferably 1 to 30 μm, more preferably 2 to 20 μm. When the heat-sensitive recording layer is too thick, the heat sensitivity is lowered and it becomes difficult to make it transparent uniformly. On the other hand, if the heat-sensitive recording layer is too thin, the white turbidity is lowered and the contrast is lowered. Further, it is possible to increase the turbidity, which increases the amount of low molecular weight organic compounds in the heat-sensitive recording layer.

In addition to the above components, the heat-sensitive recording layer may contain additives such as a high melting point solvent and a surfactant in order to facilitate the formation of a transparent image.

As the high melting point solvent, 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-phthalate.
2-ethylhexyl, diisononyl phthalate, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate, di-n adipate
-Hexyl, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-
2-ethylbutyrate, methyl acetylricinoleate,
Examples include butyl acetylricinoleate, butylphthalylbutyl glycolate, tributyl acetylcitrate, and the like.

As the surfactant 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 adduct of fats and oils or polypropylene glycol; acetylene glycol; Na, Ba, Ca or Mg salt of higher alkylbenzene sulfonic acid; higher fatty acid, aromatic carboxylic acid, higher aliphatic sulfonic acid, aromatic sulfonic acid, sulfuric acid monoester Or Ca, Ba or Mg salt of phosphoric acid mono- or diester; low degree of sulfated oil; poly long chain alkyl acrylate; acrylic oligomer; poly long chain alkyl methacrylate; long chain alkyl methacrylate-amine-containing mono Over copolymer; a styrene - maleic acid copolymer and olefin anhydride - like maleic anhydride copolymer.

As the support for the reversible thermosensitive recording medium, a plastic film, a glass plate, a metal plate or the like is used.

In the present invention, a light reflection layer may be provided on the back surface of the recording layer in order to improve the image contrast of this recording material. In this case, high contrast can be obtained even if the thickness of the recording layer is reduced. Specifically, A1, Ni described in JP-A No. 64-14079,
Examples thereof include a method of vapor depositing Sn, Au, Ag, and the like.

For a material whose support has a poor adhesion to a resin such as an A1 vapor-deposited layer, a method of providing an adhesive layer between the support and a heat-sensitive layer may be used. Good. Further, in order to protect the reversible recording material from the solvent and the monomer component of the protective layer forming liquid, JP-A 1-1
The method of providing an intermediate layer between the protective layer and the reversible recording material described in Japanese Patent No. 33781 may be used.

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 heat sensitive 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 about 0.
1-2 μm is preferable. If it is less than this, the protective effect is reduced, and if it is more than this, the thermal sensitivity is lowered. Further, the magnetic recording layer described in Japanese Utility Model Publication No. 2-2876 is provided,
It can also be used as a magnetic reversible thermosensitive recording medium capable of recording by magnetism and heat.

[0059]

EXAMPLES Next, examples and comparative examples of the present invention will be shown. All "parts" and "%" shown below are based on weight.

Example 1 100 μm thick polyethylene terephthalate (PET)
A solution consisting of diallyl phthalate 2 parts eicosane diacid 4 parts behenic acid 6 parts vinyl chloride-vinyl acetate copolymer 35 parts tetrahydrofuran 150 parts toluene 50 parts was coated on a film with a wire bar and dried by heating to about 15 μm. A thick reversible thermosensitive recording layer was provided. Silicon having a repeating unit represented by the following formula on the recording layer

[0061]

[Chemical 15] An 8% cyclohexanone solution of the contained parabanic acid multi-block copolymer was applied with a wire bar and dried by heating to provide an overcoat layer having a thickness of about 5 μm to prepare a reversible thermosensitive recording medium of the present invention. The pencil hardness of the overcoat layer was 2H.

Example 2 After providing a heat-sensitive recording layer in the same manner as in Example 1, silicone modified polyurethane resin SP901 (manufactured by Dainichiseika) 70 parts Polyisocyanate D70 (manufactured by Dainichiseika) 30 Part methyl ethyl ketone 220 parts toluene 30 parts was applied with a wire bar and dried at 80 ° C. for 10 minutes to provide an overcoat layer having a thickness of about 5 μm to prepare a reversible thermosensitive recording medium of the present invention. The pencil hardness of the overcoat layer was 2H.

Example 3 After providing a thermosensitive recording layer in the same manner as in Example 1, silicon-modified polyurethane resin SP701 (manufactured by Dainichiseika) 82 parts Polyisocyanate D70 (manufactured by Dainichiseika) 18 Part Amino-modified silicone oil at both ends 2 parts Methyl ethyl ketone 190 parts Toluene 10 parts was applied with a wire bar and dried at 80 ° C. for 10 minutes to form an overcoat layer having a thickness of about 5 μm. Created the medium. The pencil hardness of the overcoat layer was 3H.

Example 4 After providing a thermosensitive recording layer in the same manner as in Example 1, an ultraviolet curable urethane acrylate resin Bs575CS-B (manufactured by Arakawa Chemical Co., Ltd.) 98 parts Silicon modifier KU450 (Arakawa Chemical Co., Ltd.) was formed on the layer. 2 parts) A solution consisting of 100 parts of isopropanol was applied with a wire bar, dried by heating, and then irradiated with ultraviolet rays of about 270 mJ / cm ² to about 5 μm.
A reversible thermosensitive recording medium of the present invention was prepared by providing a thick overcoat layer. The pencil hardness of the overcoat layer is 4H
Met.

Example 5 After providing a thermosensitive recording layer in the same manner as in Example 1, an ultraviolet curable urethane acrylate-epoxy acrylate resin C3-600 (manufactured by Dainippon Ink and Chemicals, Inc.) 80 parts isopropanol 48 was formed on the layer. Part of the solution is applied with a wire bar, heated and dried, and then irradiated with UV light of approximately 450 mJ / cm ² to approximately 5 μm.
A reversible thermosensitive recording medium of the present invention was prepared by providing a thick overcoat layer. The pencil hardness of the overcoat layer is 3H
Met.

Example 6 After providing a heat-sensitive recording layer in the same manner as in Example 1, UV-curable modified acrylate resin Bs270TS (manufactured by Arakawa Chemical Co., Ltd.) 92 parts Calcium carbonate homocal D (manufactured by Shiraishi Kogyo Co., Ltd. 8) Part A dispersion containing 100 parts of isopropanol is applied with a wire bar, dried by heating, and then irradiated with ultraviolet rays of about 450 mJ / cm ² to about 5 μm.
A reversible thermosensitive recording medium of the present invention was prepared by providing a thick overcoat layer. The pencil hardness of the overcoat layer is 4H
Met.

Example 7 After providing a thermosensitive recording layer in the same manner as in Example 1, electron beam curable ether acrylate prepolymer KAYARAD DPCA-30 (manufactured by Nippon Kayaku Co., Ltd.) 65 parts Hydroxypivalate ester Neopentyl glycol diacrylate KAYARAD MANDA (manufactured by Nippon Kayaku Co., Ltd.) 35 parts Methyl ethyl ketone 45 parts Toluene 45 parts Isopropanol 10 parts A solution consisting of 10 parts is applied with a wire bar, heated and dried, and then irradiated with an electron beam of about 1 Mrad. An overcoat layer having a thickness of 5 μm was provided to prepare a reversible thermosensitive recording medium of the present invention. The pencil hardness of the overcoat layer was 5H.

Example 8 After providing a thermosensitive recording layer in the same manner as in Example 1, electron beam curable ether acrylate prepolymer KAYARAD DPCA-30 (manufactured by Nippon Kayaku Co., Ltd.) 62 parts Hydroxipivalate ester Neopentyl glycol diacrylate KAYARAD MANDA (manufactured by Nippon Kayaku Co., Ltd.) 26 parts Calcium carbonate Homocal D (manufactured by Shiraishi Kogyo Co., Ltd.) 12 parts Methyl ethyl ketone 45 parts Toluene 45 parts Isopropanol 10 parts Dispersed liquid is applied with a wire bar and dried by heating. After that, the reversible thermosensitive recording medium of the present invention was prepared by irradiating with an electron beam of about 1 Mrad to provide an overcoat layer having a thickness of about 5 μm. The pencil hardness of the overcoat layer was 5H.

Comparative Example 1 After providing a heat-sensitive recording layer in the same manner as in Example 1, 80 parts of UV curable urethane acrylate resin C3-599 (manufactured by Dainippon Ink and Chemicals, Inc.) and 48 parts of isopropanol were formed on the layer. The solution is applied with a wire bar, heated and dried, and then irradiated with ultraviolet rays of about 450 mJ / cm ² to about 5 μm.
A reversible thermosensitive recording medium was prepared by providing a thick overcoat layer. The pencil hardness of the overcoat layer was 1H.

Comparative Example 2 UV curable ester acrylate-urethane acrylate resin C3-603 (manufactured by Dainippon Ink and Chemicals, Inc.) 72 parts Calcium carbonate homocal D (manufactured by Shiraishi Kogyo Co., Ltd.) 8 parts Isopropanol 48 parts Wire After coating with a bar and heat-drying, it is irradiated with UV light of about 450 mJ / cm ² to about 5 μm.
A reversible thermosensitive recording medium was prepared by providing a thick overcoat layer. The pencil hardness of the overcoat layer was 1H.

Comparative Example 3 UV-curable ester acrylate-urethane acrylate resin C3-596 (manufactured by Dainippon Ink and Chemicals, Inc.) 80 parts Isopropanol 48 parts A solution consisting of 48 parts was applied with a wire bar and dried by heating, then about 450 mJ / Approximately 5 μm when irradiated with cm ² of ultraviolet rays
A reversible thermosensitive recording medium was prepared by providing a thick overcoat layer. The pencil hardness of the overcoat layer was 7H.

Evaluation Method All the reversible thermosensitive recording media prepared as described above were printed with a printing and erasing device manufactured by Glory under a platen pressure of 1.0 kg and an applied energy of 30.1 mJ / mm ^2. Then, erasing was performed at an erasing temperature of 107 ° C., and the printing and erasing were continuously repeated 500 times. Every 100 times (corresponding to the dot size of the thermal head)
Occurrence of unevenness, cracking and peeling due to sticking was visually evaluated according to the following criteria. The results are summarized in the table below. Surface irregularities A: Not generated B: Slightly generated C: Clearly visible Peeling due to cracking and sticking G: Not generated NG: Generated

[0073]

[Table 1]

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As is clear from the above detailed and specific description, in the present invention, a thermosensitive recording layer whose transparency reversibly changes depending on temperature is provided, and an overcoat layer is further provided on the layer. In a reversible thermosensitive recording medium provided with
By using the overcoat layer having a pencil hardness of 2H to 5H, it is possible to prevent the occurrence of surface unevenness, cracking, and peeling due to sticking, and to provide a clear image even when used many times.

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[Procedure amendment]

[Submission date] August 25, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Added

[Correction content]

[Brief description of drawings]

FIG. 1 is a graph for explaining temperature-transparency characteristics of a heat-sensitive layer in a recording medium of the present invention.

[Explanation of symbols] T ₀ : normal temperature T ₁ : transparency non-increasing temperature T ₂ : maximum transparency temperature T ₃ : transparency decreasing temperature

Claims (8)

[Claims] 1. A reversible recording medium comprising a support and a thermosensitive recording layer in which a low molecular weight organic compound as a main component is dispersed in a resin matrix and whose transparency reversibly changes depending on temperature changes. A reversible thermosensitive recording medium comprising an overcoat layer having a pencil hardness of 2H to 5H on the layer. 2. The reversible thermosensitive recording medium according to claim 1, wherein the overcoat layer is made of a thermoplastic resin as a main component. 3. The reversible thermosensitive recording medium according to claim 1, wherein the overcoat layer is composed of a thermosetting resin composition as a main component. 4. The reversible thermosensitive recording medium according to claim 1, wherein the overcoat layer is mainly composed of an ultraviolet curable resin composition. 5. The electron beam-curable resin composition as a main component of the overcoat layer.
The reversible thermosensitive recording medium described. 6. The reversible thermosensitive recording medium according to claim 2, 3, 4 or 5, wherein the overcoat layer is made of a resin containing an additive as a subcomponent. 7. The reversible thermosensitive recording medium according to claim 1, wherein an image is formed by printing between the thermosensitive recording layer and the overcoat layer. 8. An image display method, wherein the reversible thermosensitive recording medium according to claim 1 is used, and image formation and erasing are performed by a thermal head.