JPH05169842A - Reversible thermal recording material - Google Patents

Abstract

PURPOSE:To provide a reversible thermal recording material in which the migration of an organic low molecular substance into a protective layer is reduced, no tailing adheres even when the formation-erasing of an image are repeated a number of times by a thermal head and the formation-erasing of the uniform image are enabled, and the manufacture of the material. CONSTITUTION:In a reversible thermal recording material, in which a heat- sensitive layer composed of an organic low molecular substance, transparency of which reversibly changes while depending upon a temperature, and a resin matrix, to which the organic low molecular substance is dispersed, is formed onto a supporter, and a protective layer is formed onto the heat-sensitive layer, the protective layer is constituted of a solventless material. Or the protective layer is cured and formed by radiation or shaped through lithography or letterpress printing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes a reversible change in transparency depending on the temperature of a heat-sensitive layer so that an image can be formed and erased over and over, and a method for producing the same. Regarding

[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).

Further, the precipitation of fatty acids on the heat-sensitive layer is suppressed,
In order to improve the contrast, a layer containing a resin as a main component may be provided on the heat-sensitive layer (JP-A-63-39376),
A reversible thermosensitive recording material is known in which a protective layer is provided on the heat-sensitive layer in order to protect the heat-sensitive layer from heat and pressure such as from a thermal head (JP-A-63-221087 and JP-A-6-20687).
No. 3-317385, JP-A-1-133781, JP-A-2-566, etc.).

However, these protective layers are formed as a layer by coating a coating solution prepared by dissolving or dispersing a resin or the like in a solvent and heating and drying it, but the organic low molecular weight substance in the heat-sensitive layer is dissolved in various solvents at room temperature. It is difficult to dissolve, but it becomes very easy to dissolve at high temperature (for example, solubility of stearic acid in toluene ⇒ 20 ℃, about 0.5%, 70 ℃, about 400%),
The organic low-molecular weight substance in the heat-sensitive layer is dissolved in the coating liquid in the process of applying the coating solution on the heat-sensitive layer and then heating and drying, and the organic low-molecular weight substance migrates into the protective layer during the formation of the protective layer. .

When an image is formed or erased by heating with a thermal head from above the protective layer, the organic low molecular weight substance migrated in the protective layer is melted and the organic low molecular weight substance existing in the protective layer is also deposited on the surface. It has a drawback that it adheres to the thermal head as dust and makes image formation difficult.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks, and in a reversible thermosensitive recording material in which a transparent state and a cloudy state reversibly change depending on temperature, image formation and It is an object of the present invention to provide a reversible heat-sensitive recording material capable of forming and erasing a uniform image without depositing dust even if the erasing is repeated many times, and a method for producing the same.

[0007]

According to the present invention, a resin base material and an organic low molecular weight substance dispersed in the resin base material are used as main components on a support, and transparency is reversible depending on temperature. In the reversible heat-sensitive recording material provided with a heat-sensitive layer that changes to a protective layer thereon, the reversible heat-sensitive recording material is characterized in that the protective layer is composed of a solventless material, Further, the protective layer is cured by radiation,
The reversible thermosensitive recording material is provided which is formed or the protective layer is formed by lithographic printing or letterpress printing.

That is, by forming a protective layer on the heat-sensitive layer without using a solvent, the organic low molecular weight substance is not dissolved in the solvent in the coating liquid for the protective layer and migrates into the protective layer. Since the protective layer is formed by radiation curing such as ultraviolet rays and electron beams, there is no need to heat it for drying like when using a solvent, so it can be dissolved in the monomer or oligomer before curing used for the protective layer. There is no migration.

The solvent-free material used for forming the protective layer is
Any material may be used as long as it is solventless and liquid at the time of coating and becomes a solid after coating to form a film. For example, monomer,
Those containing an oligomer, a prepolymer or the like as a main component, and those which are cured by radiation such as ultraviolet rays or electron beams after coating are particularly preferable. As an example of a specific material, Japanese Patent Laid-Open No.
The material used for the "overcoat layer containing an ultraviolet curable resin or an electron beam curable resin as a main component" shown in No. 566 is used. For example, a monomer that undergoes a polymerization reaction by irradiation of ultraviolet rays or electron beams and becomes a resin by curing,
Any oligomer or prepolymer can be used, and examples of such a monomer include (poly) ester acrylate, (poly) urethane acrylate, epoxy acrylate, polybutadiene acrylate, silicone acrylate, and melamine acrylate.

Further, a filler can be mixed in the protective layer 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.

Further, it is possible not only to provide a protective layer formed of an inorganic material directly on the heat-sensitive layer, but also to provide one or more layers between them. For example, a high-hardness coating liquid containing a solvent is applied on the heat-sensitive layer (in which organic low-molecular substances have migrated from the heat-sensitive layer), and a solvent-free material is applied on top of it to form a protective layer. To form. As the material of the layer provided between the heat-sensitive layer and the protective layer, an ultraviolet ray or electron beam curable resin using a solvent described in JP-A-2-566 or JP-A-1-133781 using a solvent is disclosed. The thermosetting or thermoplastic resins shown in 1.

As a method of forming this protective layer, lithographic printing or letterpress printing is preferably used. When a material that can be cured by radiation is used as the protective layer material, ultraviolet rays can be used as the radiation, but electron beams have higher energy and higher penetrating power than ultraviolet rays, so when a filler or the like is added to the protective layer. Is preferable because the electron beam reaches the inside.

The protective layer may be provided not only on the entire surface of the heat-sensitive layer but also on a necessary part. further,
Partially print characters, images, etc. between the heat-sensitive layer and the protective layer,
It is also possible to use it as the protective layer and the protective layer for character or image printing. Further, as described above, after laminating one or more layers on the heat-sensitive layer, a protective layer may be formed after printing characters or images.

Any material can be used for the heat-sensitive layer of the present invention as long as its transparency reversibly changes with temperature. For example, colorless to black, blue, red, etc. as shown in JP-A-2-188293. Examples thereof include those whose color tone changes, and those which reversibly change to a transparent state and a cloudy state as disclosed in JP-A-55-154198. In particular, a material consisting of a resin base material and an organic low-molecular substance dispersed in the resin base material, which is reversibly changed between a transparent state and an opaque state by heat, has a good durability against repeated use and has a high thermal sensitivity. To have.

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 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 heat sensitive member, 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 prepare the reversible thermosensitive recording material used in the present invention, generally, (1) a resin matrix and an organic low molecular weight substance are used.
A plastic containing a dispersion liquid of the components or (2) a solution of the resin base material (a solvent that does not dissolve at least one of the organic low molecular weight substances) is dispersed in the form of fine particles. It may be applied on a support such as a film, a glass plate or a metal plate and dried to form a laminated heat-sensitive layer. The solvent for forming the heat-sensitive layer or the heat-sensitive recording material can be variously selected depending on the type of the resin base material and the organic low molecular weight substance, for example, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. Can be mentioned. Of course, when using the dispersion,
Even when a solution is used, the organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the obtained heat-sensitive layer.

The resin base material used for the heat-sensitive layer is a material that forms a layer in which an organic low molecular weight substance is uniformly dispersed and held, and affects the transparency at the time of maximum transparency. Therefore, the resin base material is preferably a resin having good transparency, mechanical stability, and good film forming property. Such resins include polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinyl acetate-vinyl alcohol copolymer, vinyl chloride-
Vinyl chloride-based copolymers such as vinyl acetate-maleic acid copolymers and vinyl chloride-acrylate copolymers; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-based copolymers such as vinylidene chloride-acrylonitrile copolymers Copolymer; Polyester; Polyamide; Polyacrylate or polymethacrylate or acrylate-
Methacrylate copolymers; silicone resins and the like can be mentioned. Of course, these resins may be used alone or in combination 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, 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
Steal; Etc., such as ether or thioether. Above all, the present invention
Higher fatty acids, especially palmitic acid, stearic acid,
Higher fats with 16 or more carbon atoms such as henic acid and lignoceric acid
Acids are preferable, and higher fatty acids having 16 to 24 carbon atoms are more preferable.
Good.

In order to increase the range of temperatures that can be made transparent,
The organic low molecular weight substances described in this specification may be appropriately combined, or such an organic low molecular weight substance may be combined with another material having a different melting point. These are disclosed in, for example, JP-A-63-39378 and JP-A-63-130380, Japanese Patent Application No. 63-14754, Japanese Patent Application No. 1-14.
However, the present invention is not limited thereto.

The thickness of the heat sensitive layer is preferably 1 to 30 μm,
2 to 20 μm is more preferable. 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 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).

[0027]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. All parts and percentages herein are by weight. Example 1 γ-Fe ₂ O ₃ 10 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 10 parts (UCH VAGH) isocyanate (Nippon Polyurethane Coronate L 2 parts 50%) on white PET having a thickness of about 188 μm. Toluene solution) Methyl ethyl oketone 40 parts Toluene 40 parts is applied with a wire bar and dried by heating to about 1
A magnetic recording layer having a thickness of 0 μm was provided. A special acrylic UV-curable resin (Dainippon Ink and Chemicals, Inc., Unidick C7-164, 49% butyl acetate solution) 10 parts Toluene 4 parts A solution consisting of 4 parts was applied with a wire bar, and after heating and drying 80
Ultraviolet rays were irradiated for 5 seconds with a W / cm ultraviolet lamp to provide a smooth layer having a thickness of about 1.5 μm. About 40 A1 on it
It was vacuum-deposited so as to have a thickness of 0Å, and a light reflection layer was provided. Further thereon, a solution comprising 5 parts of stearic acid, 5 parts of eicosane diacid, 5 parts of diisodecyl phthalate, 3 parts of vinyl chloride-vinyl acetate-phosphate ester copolymer, 40 parts (# 1000P manufactured by Denki Kagaku Kogyo Co., Ltd.), THF of 120 parts and 80 parts of toluene. Was applied and heated and dried to form a heat-sensitive layer having a thickness of about 5 μm. In addition, a solventless UV offset printing ink (Daikyu TMOP varnish NY-A manufactured by Dainippon Ink & Chemicals, Inc.) was used to perform about 2 lithographic printing (offset printing).
After forming a film having a thickness of μm, the protective layer was formed by irradiating ultraviolet rays for 5 seconds with an 80 W / cm ultraviolet lamp to prepare a reversible thermosensitive recording material.

Example 2 From the magnetic recording layer to the formation of the heat-sensitive layer, the same procedure as in Example 1 was carried out, and a urethane acrylate UV-curable resin (Unidick C7-157, manufactured by Dainippon Ink and Chemicals, Inc.) was further formed thereon.
Was diluted with toluene and a solution having a solid content of 50% was applied by a wire bar, dried by heating at 120 ° C., and then cured by an 80 W / cm ultraviolet lamp to form a layer having a thickness of about 2 μm. Further, a reversible thermosensitive recording material was prepared by further providing a protective layer thereon using a solventless UV offset printing ink in the same manner as in Example 1.

Example 3 A reversible recovery heat recording material was prepared in the same manner as in Example 1 except that the solventless UV offset printing ink was (New Dicure GP OP varnish FT manufactured by Dainippon Chemical Co., Ltd.).

Comparative Example 1 A protective layer (UV offset printing ink) of Example 1 was diluted with toluene to a solution having a solid content of 50%, which was applied with a wire bar and dried by heating at 120 ° C., followed by UV irradiation with a UV lamp of 80 W / cm. Was irradiated for 5 seconds to form a reversible thermosensitive recording material in the same manner as in Example 1 except that the protective layer was formed.

Comparative Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 2 except that the solvent-free protective layer was omitted.

On the reversible thermosensitive recording material prepared as described above, 100 A4 A4 images were continuously formed with a thermal head. After that, the dust adhesion state of the thermal head was judged with a microscope, and the uniformity of the 100th image was visually evaluated. The results are shown in Table 1.

[0033]

[Table 1]

As described above, in the present invention, since the protective layer is formed of the solvent-free material, the migration of the organic low molecular weight substance into the protective layer is reduced, the adhesion of dust to the thermal head is reduced, and the image uniformity is improved. In addition, since it is hardened and formed by radiation without being dried by heating, migration of the organic low molecular weight substance is further reduced, and there is an effect that dust adhesion to the thermal head and image uniformity are improved.

[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.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Kawaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Company (72) Inventor Tetsuya Amano 1-3-6 Nakamagome, Ota-ku, Tokyo Shares Company Ricoh

Claims (3)

[Claims] 1. A heat-sensitive layer comprising a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component, the transparency of which reversibly changes depending on temperature is provided on a support, and A reversible thermosensitive recording material having a protective layer provided thereon, wherein the protective layer is composed of a solventless material. 2. The method for producing a reversible thermosensitive recording material according to claim 1, wherein the protective layer is formed by being cured by radiation. 3. The method for producing a reversible thermosensitive recording material according to claim 1, wherein the protective layer is formed by lithographic printing or letterpress printing.