JPH06297843A - Reversible heat-sensitive recording material - Google Patents

Abstract

PURPOSE:To provide a reversible recording material wherein a printing and heating device applying heat and pressure at the same time such as a thermal head is used, a form of a heat-sensitive recording body is not changed even if formation and elimination of an image are repeated, excellent conveying properties are kept on, deterioration of heat sensitivity is little even if a thickness of a substrate is increased and contrast is high. CONSTITUTION:A precoated layer 2 is provided between a paper substrate 1 and heat-sensitive layer, resin of the precoated layer 2 is taken as specified resin such as water-soluble resin and microscopic hollow particles are added internally along the inside of the layer. Then a reversible heat-sensitive recording material is obtained by either adding internally a colorant to the precoated layer 2 or providing a pigmented layer or a light reflecting layer on the foregoing precoated layer 2.

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 material for recording and erasing by utilizing the reversible change in transparency depending on the temperature of a thermosensitive layer, and the field of image recording which can be repeatedly used independently. Or, it relates to a reversible thermosensitive recording material used in the display field in combination with a magnetic recording sheet or the like.

[0002]

2. Description of the Related Art In recent years, reversible heat-sensitive recording materials have been attracting attention because they can form images temporarily and can erase the images when they are no longer needed. As a typical example thereof, a resin matrix such as a vinyl chloride-vinyl acetate copolymer having a low glass transition temperature having a glass transition temperature (Tg) of 50 ° C. to less than 80 ° C. is used in an organic material such as a higher fatty acid. Reversible thermosensitive recording materials in which a low-molecular substance is dispersed are known (Japanese Patent Laid-Open Nos. 54-119377 and 55-1541).
Bulletins such as No. 98). However, these reversible thermosensitive recording materials have a drawback that they are deformed and curled toward the thermosensitive layer when recording and erasing of an image are repeated many times by using a heating means such as a thermal head. Further, when the thickness of the substrate is increased, the recording material itself is less likely to be deformed, and the contact area between the heating element and the heat-sensitive recording material is relatively reduced when forming an image by heating and printing with the thermal head. There was also a drawback that the saturation concentration (maximum white turbidity) and the thermal sensitivity were lowered.

In order to solve the above-mentioned drawbacks, JP-A-4-189585 proposes a reversible thermosensitive recording material using a paper having a plastic film adhered on both sides thereof as a support. Although this has the effect of eliminating the drawbacks such as curling to the heat sensitive layer side, the saturation density and the decrease in thermal sensitivity as described above, while repeating image formation and erasing with a heating element such as a thermal head. In addition, if the adhesive strength of the part where the paper and the plastic film are adhered is weak, there is a drawback that this part is peeled off, which may change the shape of the reversible thermosensitive recording sheet. In addition to the above-mentioned drawbacks, the reversible thermosensitive recording material is formed by sticking plastic films on both sides of paper, so that the opposite surface of the thermosensitive layer coating is a plastic film. Has a smoother surface and less unevenness than paper, so it is easy to slip on the contact surface with the platen roll when forming and erasing images with a heating element such as a thermal head. Since it is not possible to follow the rotation of the roll and thermal printing from the heating element is repeated at the same location on the heat-sensitive layer, deterioration of durability against repeated use of this portion progresses, and the entire surface is uniform. The drawback is that the desired image uniformity is a problem.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks and is heat-sensitive even when image formation and erasure are repeated by using a print heating means such as a thermal head which applies heat and pressure at the same time. The shape of the recording medium does not change, and even if the thickness of the support increases, there is little decrease in saturation density and thermal sensitivity when printing with a thermal head to form an image, and heat generated by the thermal head. An object of the present invention is to provide a reversible thermosensitive recording material which does not cause defective conveyance even when image formation and erasing are repeated on the body and has good durability against repeated use.

[0005]

That is, the present invention relates to a reversible thermosensitive recording material having a thermosensitive layer whose transparency reversibly changes depending on temperature in a reversible thermosensitive recording material using paper as the support. A reversible thermosensitive recording material further comprising a precoat layer provided between the support and the thermosensitive layer, preferably the precoat layer is a water-soluble resin, a water-based emulsion resin, and an electron beam curable resin (EB). resin)
Alternatively, it is characterized by being a layer containing as a main component at least one resin of an ultraviolet curable resin (UV resin). Further, the present invention is preferably characterized in that fine hollow sphere particles are internally added to the precoat layer, a colorant is contained in the precoat layer, or a coloring layer or a light reflecting layer is provided on the precoat layer. ,
Still more preferably, a water-soluble resin on the back surface of the support,
At least one resin selected from the group consisting of an aqueous emulsion resin and an EB resin or a UV resin, and a back layer containing an inorganic or organic fine powder as a main component are provided.

The present inventors further studied a reversible thermosensitive recording material in which a thermosensitive layer whose transparency reversibly changes depending on temperature was provided on the support, and as a result, paper was used as the support, and further the support was used. By providing a precoat layer containing at least one of a water-soluble resin, an aqueous emulsion resin, an EB resin or a UV resin as a main component and containing minute hollow sphere particles internally, a reversible thermosensitive recording material The present invention has been found to reduce the decrease in saturation density and thermal sensitivity when an image is formed by printing and heating the surface with a thermal head or the like.

In the present invention, since paper is used as the support, the rigidity of the support is lower than that of the plastic film, and when an image is formed by a thermal head or the like, the support is easily deformed according to the head shape. There is little decrease in thermal sensitivity and saturation concentration even if body thickness increases,
Further, since the precoat layer is provided between the support and the heat-sensitive layer, the unevenness of the surface of the paper support is smoothed by the precoat layer, so that the smoothness of the surface of the heat-sensitive layer or protective layer laminated thereon is Since the adhesion with the thermal head is enhanced, the thermal sensitivity and the saturation density are improved. In addition, by internally adding the fine hollow sphere particles to the precoat layer, the precoat layer functions as a heat insulating layer, and the minute heat transferred from the thermal head or the like is released to the outside of the heat sensitive layer. To be able to hold without
The above effects can be further improved. It is also possible to further improve the contrast of a recorded image by including a coloring agent in the above precoat layer or providing a coloring layer or a light reflecting layer on the precoat layer.

In addition to the above effects, the present invention improves image durability without causing defective conveyance even when image formation and erasing are repeatedly performed with a heating element such as a thermal head. The reason is as follows. Is thought to be. In other words, since paper is used as the support, when performing image formation and erasing with a heating element such as a thermal head, the surface of the platen roll has more surface irregularities than the plastic film when it is conveyed by the platen roll, and slips on the contact surface with the platen roll. It is considered that the transport is performed normally because it is difficult, and the heat application to the same portion of the heat-sensitive layer is not repeated, so that the durability against the repetition is improved. In addition, this effect is obtained by providing at least one of the above-mentioned water-soluble resin, water-based emulsion resin, and EB resin or UV resin, and a layer containing inorganic or organic fine powder as a main component on the back surface of the support, thereby making the surface uneven. It is considered that the size is further increased and the transportability is further improved.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing a typical constitution of a reversible thermosensitive recording material according to the present invention.
A precoat layer 2 having a colorant internally added is provided on the top of which a reversible thermosensitive recording layer (TC layer) and a protective layer are sequentially laminated. FIG. 2 is an example of the precoat layer 2 of FIG. 1 containing fine hollow sphere particles. In addition, FIG.
This is an example in which a back layer 5 containing at least one of a water-soluble resin, an aqueous emulsion resin, an EB resin or a UV resin and an inorganic or organic fine powder as a main component is provided on the back surface of the support paper. Further, in FIG. 4, in order to further improve the contrast of the recorded image, the precoat layer of FIG. 1 does not contain a coloring agent, and the coloring layer or the light reflecting layer 6 is provided on the upper side of the precoat layer containing no coloring agent. It is an example.

The paper support used in the present invention is mainly made of new natural pulp, but it is also possible to mix partially recycled fibers, synthetic fibers or synthetic pulp, or inorganic fibers. As the natural pulp, any of softwood pulp, hardwood pulp, straw pulp, esparto pulp, bagasse pulp and the like can be used, but a hardwood pulp which is a single fiber and has a smoothness is preferable. The beating of the pulp is performed by a beater, a disc refiner, a conical refiner, a Jordan refiner, or the like. The freeness is preferably 500 to 200 cc (C.S.F.), and particularly preferably 400 to 300 cc (C.S.F.). )
Is.

The following auxiliary components can be added as raw materials other than pulp. That is, as a sizing agent, rosin, paraffin wax, higher fatty acid, alkenylsuccinic acid, fatty acid anhydride, styrene-maleic anhydride copolymer, alkyl ketene dimer, epoxidized fatty acid amide, etc. Reaction products of polymers and polyalkylene polyamines, quaternary ammonium salts of higher fatty acids, aluminum sulfate, aluminum chloride, polyamide polyamine epichlorohydrin, etc. as fixing agents, other dyes, fluorescent dyes, antistatic agents, defoaming agents, etc. Can be added as required. The addition amount of the sizing agent, the size of the paper support after papermaking 30 g / cm ² or less as Kobusaizu degree, preferably it is preferable to adjust the amount so that the 20~10g / cm ^2.

The paper support used in the present invention is a paper made by a Fourdrinier paper machine or a cylinder paper machine after mixing these raw materials, and has a basis weight of about 30 to 400 g / m ² . Is appropriate. It is to be noted that those finished with a density of 0.80 to 0.98 g / cm ³ by on-machine calendering or off-machine super calendering are used. Further, preferred characteristics of the present invention are that it does not curl to the heat-sensitive layer side and that it has good saturation concentration and thermal sensitivity. Specifically, it has high smoothness and is hard to curl. It is necessary. Considering these points, the paper support containing mainly hardwood pulp as described above is preferable. Further, a coated paper in which a coating layer is provided on the surface of the paper support to improve layer smoothness,
Art paper is also preferably used as a support for the same reason. These paper supports may be white or colored with dyes, pigments, metal powders and the like.

The water-soluble resin or water-based emulsion resin used in the precoat layer in the present invention includes the following. As the water-soluble resin, carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, methyl cellulose, viscose, soluble starch, carboxymethyl starch, dialdehyde starch, gelatin, casein, polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, isobutylene-
Examples thereof include, but are not limited to, maleic anhydride copolymer and water-soluble nylon.

Examples of the water-based emulsion resin include those in which the polymer is made into fine particles and protected with warm water colloid and dispersed in water, and those in which the polymer is dissolved in a solvent other than water and dispersed in water, and the like. Is an olefin resin, polyester resin, epoxy resin, urethane resin, acrylic resin, amide resin,
Examples thereof include vinyl chloride resin, vinyl acetate resin, petroleum resin, phenol resin, polystyrene resin, and fluorine resin. The thickness of the layer containing the water-soluble resin or the aqueous emulsion resin as a main component is 0.01 to 10 μm, preferably 0.1 to 5 μm.

Further, the UV resin or E in the present invention
Any resin can be used as the B resin as long as it is a solvent-free liquid state at the time of application and is cured by radiation such as ultraviolet rays or electron beams after application to form a film. As a specific example of the material, the material used in the "overcoat layer containing an ultraviolet curable resin or an electron beam curable resin as a main component" disclosed in JP-A-2-000566 is used. For example, any monomers, oligomers, and prepolymers that undergo a polymerization reaction by irradiation with ultraviolet rays or electron beams to be cured and become a resin can be used. Examples of such a monomer include (poly) ester acrylate and (polyester). ) Urethane acrylate, epoxy acrylate, polybutadiene acrylate, silicone acrylate,
Melamine acrylate etc. are mentioned. The thickness of the layer whose main component is UV resin or EB resin is 0.01 to
10 μm, preferably 0.1 to 5 μm is suitable.

Further, the precoat layer can be mixed with a filler to form a stronger film. The filler used may be either inorganic or organic, and examples thereof include silica, calcium carbonate, aluminum hydroxide, and styrene polymer fine particles. As a method for forming this precoat layer, lithographic printing or letterpress printing is preferably used. Further, when the precoat layer material that can be cured by radiation is used, ultraviolet rays can be used as the radiation, but since the electron beam has a larger energy and a higher penetrating power than ultraviolet rays, a filler or the like is added to the precoat layer. Is preferable because the electron beam reaches the inside.

The following are examples of the hollow microsphere particles used in the precoat layer in the present invention. 1) Expanded heat-expandable microspheres Hollow particles having a thermoplastic material as a capsule wall, and a substance containing a volatile expander inside the particles. Thermoplastics; vinylidene chloride-acrylonitrile copolymer, etc. Volatile expansion agents; n-butane, isobutane, neopentane, petroleum ether, etc. Thermal conductivity = 0.02-0.06 W / mK Example: Matsumoto Yushi Co., Ltd. : Microbar, manufactured by Chemanode: E
xpamcel. 2) Glass micro hollow sphere powder Mayurosphere of borosilicate glass Thermal conductivity = 0.11 W / mK Example: Microcel M manufactured by Graberbell. 3) Aluminosilicate micro hollow sphere powder Premix for low-foam injection molding and standard injection mold Thermal conductivity = 0.007 W / mK Example: Phillite manufactured by Nippon Philite. The amount of the fine hollow sphere particles to be added is 1 of water-soluble resin, water-based emulsion resin, EB resin or UV resin.
0.01 to 30 parts by weight is suitable for parts by weight,
It is preferably 0.1 to 10 parts by weight.

The colorant used in the precoat layer in the present invention is only required to be able to recognize the change in transparency and white of the upper reversible thermosensitive recording layer as a reflection image, and red,
Dyes, pigments, metal powders and the like having colors such as yellow, blue, navy blue, purple, black, brown, grey, orange and green, and colors such as silver and gold that reflect light are used. An appropriate amount of the colorant added is 0.01 to 25 parts by weight, more preferably 0.05 to 5 parts by weight, based on 1 part by weight of the resin. Further, a colored layer can be provided on the precoat layer of the present invention, and such a colored layer may be any one having absorption of visible light, such as various organic and inorganic materials such as black, blue, red and green. It can be formed by mixing a dye and a pigment with a resin and applying the mixture on a support or vapor deposition. The thickness of the colored layer is 0.01 to 10 μm, preferably 0.1 to 5
About μm is suitable.

When the image of the recording material is used as a reflection image in the present invention, 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, JP-A 64-14079
The method of vapor-depositing Al, Ni, Sn, etc. described in Japanese Patent Publication can be used.

The back layer preferably provided on the back surface of the support in the present invention comprises a water-soluble resin, a water-proofing agent, and E.
B resin or UV resin and inorganic or organic fine powder are used.

As the water-soluble resin, there are generally known polyvinyl alcohol, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, starch, gelatin, methoxy cellulose, etc.
Examples thereof include polyacrylamide. Examples of the water resistance agent for improving the water resistance of the water-soluble resin include formalin, glyoxal, chrome alum, melamine, formalin, amide resin, and polyamide-epichlorohydrin resin. The EB resin or UV resin used for the back layer may be the same as that used for the precoat layer. As the inorganic or organic fine powder used for the back layer, calcium carbonate, silica,
Other than inorganic fine powders such as zinc carbonate, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, kaolin, talc, surface-treated calcium and silica,
Examples include organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, styrene resin and vinylidene chloride resin. The thickness of this back layer is
0.01 to 20 μm, preferably 0.1 to 10 μm.

The present invention will be described in more detail below. The reversible thermosensitive recording medium in the present invention is a material that reversibly causes a visible change due to a temperature change. The visible change can be divided into a change in color tone and a change in shape, but 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, etc., and an actual reversible thermosensitive recording medium displays by combining these changes. More specifically, (a) a material in which the transparent state and the cloudy state reversibly change. (B) A material such as a dye whose color changes reversibly. Currently, it can be classified into two types of systems. As (a), as described in the prior art, a recording layer is prepared by dispersing an organic low molecular weight substance such as a higher alcohol or a higher fatty acid in a resin base material such as polyester and adding an auxiliary agent if necessary. The representative examples are as follows, and (b) include those that enhance the reversibility of conventional leuco thermal recording materials (eg: Yoshihiro Hino, Nibo Watanabe Japan Hardcopy '90 Proceedings, P147). .

The present invention will be described below, focusing on the recording medium (a). The reversible thermosensitive recording medium of the above (a) uses, for example, the change in transparency (transparent state, cloudy opaque state) depending on the temperature as described above. The difference between the transparent state and the cloudy opaque 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 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 looks transparent because it penetrates to the side,
(Ii) In the case of white 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 axes of the individual crystals are oriented in various directions so that they enter from one side. The generated light is refracted many times at the interface of the crystals of the organic low-molecular substance particles, and is scattered and thus appears white.

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

Therefore, the recording layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent background and a transparent image on a cloudy background, and the change can be repeated many times. It is possible. By arranging a coloring sheet on the back surface of such a recording layer, it is possible to form an image of the color of the coloring sheet on a white background or an image of the white background on the background of the color of the coloring sheet. 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 to 20 μm is more preferable. If the recording layer is too thick, heat distribution will occur in the layer and it will be difficult to make it transparent uniformly. On the other hand, if the recording layer is too thin, the white turbidity is lowered and the contrast is lowered. The white turbidity can be increased by increasing the amount of fatty acid in the recording layer.

In order to produce the reversible thermosensitive recording medium (a) used in the present invention, it can be formed on the supporting member as a film 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) The resin base material is dissolved in a solvent that dissolves only the resin base material, and the organic low molecular weight substance is pulverized or dispersed therein by various methods, and this is applied onto a support member, and the solvent is evaporated to form a film. Or the method of making 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 this is molded into a film or sheet and cooled. The solvent for forming the recording layer or the heat-sensitive recording medium can be variously selected depending on the types of the resin base material and the organic low molecular weight substance,
Examples thereof include tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. The organic low-molecular substance is precipitated as fine particles and exists in a dispersed state in the recording layer obtained not only when the dispersion is used but also when the solution is used.

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 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 polymers; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-based copolymers such as vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides; polyacrylates or polymethacrylates or acrylates -Methacrylate copolymer; silicone resin and the like can be mentioned. These may be used alone or in admixture of two or more.

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

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

The weight ratio of the organic low molecular weight substance to the resin base material in the recording layer is preferably about 2: 1 to 1:16, more preferably 1: 2 to 1: 8. If the ratio of the resin base material is below this range, it will be difficult to form a film in which the organic low molecular weight material is retained in the resin base material. Becomes difficult. The thickness of the recording layer is preferably 1 to 30 μm, and 2
˜20 μm is more preferred. If the recording layer is too thick, heat distribution will occur in the layer and it will be difficult to make it transparent uniformly. On the other hand, if the recording layer is too thin, the white turbidity is lowered and the contrast is lowered. Further, the white turbidity can be increased by increasing the amount of the organic low molecular weight substance in the heat sensitive layer.

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

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

When the image formed on the recording medium of (a) is used as a reflection image, it is desirable to provide a layer for reflecting light on the back surface of the recording layer. Further, if the reflective layer is provided, the thickness of the recording layer can be reduced and the contrast can be greatly improved. Specifically, vapor deposition of Al, Ni, Sn and the like can be mentioned (described in JP-A No. 64-14079).

Further, the recording layer may be provided with a protective layer for protecting the recording layer. Protective layer (thickness 0.1 to 1
(0 μm), silicone rubber, silicone resin (described in JP-A-63-221087), polysiloxane graft polymer (Japanese Patent Application No. 62-1525).
No. 50), an ultraviolet curable resin, an electron beam curable resin (described in Japanese Patent Application No. 63-310600), and the like. In any case, a solvent is used at the time of application, but it is desirable that the solvent is difficult to dissolve the resin of the recording 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 recording layer include n-hexane, methyl alcohol, ethyl alcohol, isopropyl alcohol and the like, and an alcohol solvent is particularly preferable from the viewpoint of cost.

An intermediate layer may be provided between the protective layer and the recording layer in order to protect the recording layer from the solvent of the protective layer forming liquid, the monomer components and the like. (Japanese Patent Laid-Open No. 1-1337
81 gazette). 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, the reversible thermosensitive recording material of the present invention may be provided with a magnetic recording layer to be used as a card (described in Japanese Utility Model Laid-Open No. 2-3876).

[0037]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In addition, both parts and% are based on weight. Example 1 Commercially available high-quality paper (basis weight: 157 g / cm ² ) was used as a support, and carbon black 5 parts PVA 10% aqueous solution 50 parts water 45 parts The above composition was dispersed with a homomixer and applied with a wire bar. Then, it was dried by heating to provide a precoat layer having a thickness of about 2 μm. Furthermore, stearic acid 6 parts Eicosane diacid 4 parts Diisododecyl phthalate 2 parts Vinyl chloride-vinyl acetate / phosphoric acid ester copolymer 20 parts (Denka vinyl; 1000P) THF 150 parts Toluene 15 parts Was applied and heated and dried to form a precoat layer having a thickness of about 5 μm. Polyamide resin (Toray Xie; CM8000) 5 parts Methyl alcohol 90 parts solution was applied on it with a wire bar, and dried by heating to provide an intermediate layer of about 0.3 μm thickness, and urethane acrylate on top of it. A butyl acetate solution of a UV-curable resin (Dainippon Ink and Co .; Unidic C7-157) is applied with a wire bar, and after heating and drying, it is irradiated with an 80 W / cm UV lamp for 3 seconds and overcoated to a thickness of about 3 μm. Layers were provided to make a reversible thermosensitive recording material.

Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that the precoat layer had the following composition. Thermally expandable microspheres (Matsumoto Yushi Co., Ltd .; Micropearl F-30) 5 parts Carbon black 5 parts PVA 10% aqueous solution 50 parts Water 40 parts

Example 3 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that a solution having the following composition was applied to the back surface of the paper support and dried by heating to provide a back layer having a thickness of about 2 μm. . PVA 10% aqueous solution 50 parts Polyamide-epichlorohydrin resin 3 parts Calcium carbonate (manufactured by Shiraishi Calcium Co .; Callite SA) 5 parts Water 87 parts

Example 4 The precoat layer was changed to the following composition, and Al was formed thereon.
Was vacuum-deposited to about 400 Å, and a reversible thermosensitive material was prepared in the same manner as in Example 1 except that a light reflecting layer was provided. Thermally expandable microspheres (Matsumoto Yushi Co., Ltd .; Micropearl F-30) 10 parts PVA 10% aqueous solution 50 parts water 40 parts

Example 5 A reversible thermosensitive material was prepared in the same manner as in Example 4 except that the precoat layer was changed as follows. 80 W after forming a film of about 2 μm on a paper support by lithographic printing (offset printing) using a solvent-free UV offset printing ink (Dainippon Ink and Chemicals; DICURE TMOP varnish NY-A)
A pre-coat layer was provided by irradiating with a UV lamp of / cm for 5 seconds.

Example 6 A reversible thermosensitive material was prepared in the same manner as in Example 3 except that the back layer was changed as follows. Solvent-free UV offset printing ink on paper support surface (Dainippon Ink and Chemicals;
Dicure OLOP Varnish HP No. 80W after forming a film about 2μm thick by lithographic printing (offset printing) using 2)
The back layer was provided by irradiating ultraviolet rays for 5 seconds with an ultraviolet lamp of / cm.

Comparative Example 1 A reversible thermosensitive material was prepared in the same manner as in Example 1 except that a PET film (188 μm thick) was used as the support.

Comparative Example 2 Reversible in the same manner as in Example 1 except that a PET film (25 μm thick) / coated paper (100 μm thick) / PET film (75 μm thick) three-layer adhesive sheet was used as the support. A thermosensitive material was created.

The reversible thermosensitive recording material prepared as described above was subjected to 16-step gradation printing with an energy of 0.3 mJ to 0.8 mJ by a thermal head. The cloudy image at that time was measured by a Macbeth reflection densitometer. Further, the same thermal head as described above was used to repeat image formation / erasure 100 times, and the cloudy image after 100 times was measured with a Macbeth reflection densitometer. In addition, rank evaluation was performed on the transportability after 100 cycles. The results are shown in Table 1.

[0046]

[Table 1] (Note) Thermal sensitivity; energy required to reach saturation concentration (mJ) Saturation concentration; maximum white turbidity Transportability rank; 5 → 0 in 100 transport failures 4 → 〃 1-10 times 3 → 〃 11-20 2 times 〃 21 to 30 times 1 → 〃 31 times or more

[0047]

According to the present invention, paper is used as the support,
A precoat layer is provided between the support paper and the heat sensitive layer, and the resin of the precoat layer is a water-soluble resin, an aqueous emulsion resin,
And a reversible thermosensitive recording material which is at least one of an electron beam curable resin or an ultraviolet curable resin, in which fine hollow sphere particles are internally added, has improved thermal sensitivity and saturation concentration, and Further, even if image formation and erasing are repeatedly performed with a heating element such as a thermal head, the transportability is good and the image durability against repeated use is also excellent. Furthermore, a reversible thermosensitive recording material having an extremely high contrast can be obtained by internally adding a coloring agent to the precoat layer or providing a coloring layer or a light reflecting layer on the precoat layer.

[Brief description of drawings]

FIG. 1 is a sectional view showing a constitution of a reversible thermosensitive recording material of the present invention in which a precoat layer in which a colorant is internally added is formed on a support paper.

FIG. 2 is a cross-sectional view showing the structure of the reversible thermosensitive recording material of the present invention in which the precoat layer 2 of FIG. 1 contains fine hollow sphere particles.

3 is a cross-sectional view showing the constitution of the reversible thermosensitive recording material of the present invention in which a back layer 5 is provided on the back surface of the support paper of FIG.

FIG. 4 is a cross-sectional view showing the constitution of the reversible thermosensitive recording material of the present invention in which a colored layer or a light reflection layer is provided on the upper side of a precoat layer containing no colorant.

FIG. 5 is a diagram showing a change in transparency of a reversible thermosensitive recording material according to the present invention due to heat.

[Explanation of symbols]

1 ... paper support, 2 ... precoat layer, 3 ... TC layer,
4 ... Protective layer, 5 ... Back layer, 6 ... Coloring layer or light reflecting layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Kawaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (6)

[Claims] 1. A reversible thermosensitive recording material having a thermosensitive layer whose transparency reversibly changes depending on temperature, wherein a precoat layer is provided between the paper support and the thermosensitive layer. And a reversible thermosensitive recording material. 2. The precoat layer is a layer containing, as a main component, at least one resin selected from water-soluble resins, water-based emulsion resins, and electron beam curable resins or ultraviolet curable resins. Reversible thermosensitive recording material. 3. The reversible thermosensitive recording material according to claim 1, wherein fine hollow sphere particles are internally added to the precoat layer. 4. The reversible thermosensitive recording material according to claim 1, wherein the precoat layer contains a colorant. 5. The reversible thermosensitive recording material according to claim 1, wherein a colored layer or a light reflecting layer is provided on the precoat layer. 6. A back containing, as a main component, at least one resin selected from a water-soluble resin, a water-based emulsion resin, and an electron beam curable resin or an ultraviolet curable resin on the back surface of the support, and an inorganic or organic fine powder. A reversible thermosensitive recording material comprising a layer.