JPH04239689A - Reversible heat-sensitive recording material - Google Patents

Abstract

PURPOSE:To obtain a reversible heat-sensitive recording material which permits formation of a uniform image and which is free from contamination with head residue by a method wherein a mixture of 1,4-dioxane and tetrahydrofuran are used as an organic solvent, when a supporting body is coated with a solution having a base resin material and an organic low-molecular substance dissolved in a solvent and this coat is dried to form a heat-sensitive layer. CONSTITUTION:1,4-dioxane and tetrahydrofuran are mixed together in such weight ratios as ranging from 2:8 to 8:2, preferably from 3:7 to 7:3. A reversible heat-sensitive recording material is produced by coating a supporting body such as plastic film, glass pane and metal plate with a solution having the two components of a base resin material and an organic low-molecular substance dissolved therein and drying this coat to form a heat-sensitive layer. The base resin material used is to be such as to form a layer in which the organic low- molecular substances are dispersed and retained uniformly and produce an effect on transparency at the time of its maximum transparency. The organic low-molecular substance may be any one, so long as it is changeable by heat from polycrystal to single crystal in a recording layer, preferably with a melting point of 50-150 deg.C.

Description

[Detailed description of the invention]

0001

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

0002

BACKGROUND OF THE INVENTION In recent years, reversible thermosensitive recording materials have attracted attention in which temporary images can be formed and the images can be erased when no longer needed. Typical examples include glass transition temperatures (Tg) ranging from 50 to 60°C to 80°C.
Reversible heat-sensitive recording materials are known that have a heat-sensitive layer in which a low-molecular-weight organic substance such as a higher fatty acid is dispersed in a resin base material such as a vinyl chloride-vinyl acetate copolymer having a low glass transition temperature of less than 0°C. (Japanese Patent Application Laid-open No. 54-119377,
Publications such as Japanese Unexamined Patent Publication No. 55-154198).

Furthermore, reversible heat-sensitive recording materials are also known in which a protective layer is provided on the heat-sensitive layer in order to protect the heat-sensitive layer (
JP-A-1-133781, JP-A-2-566, JP-A-63-221087, JP-A-63-317385, etc.), and for protecting the heat-sensitive layer from monomer components and solvents of the protective layer liquid. Also known is a reversible heat-sensitive recording material in which an intermediate layer using an alcohol solvent is provided between a protective layer and a heat-sensitive layer (Japanese Unexamined Patent Publication No. 1-133781).

[0004] When producing these reversible thermosensitive materials,
Tetrahydrofuran is used as a basic solvent that can dissolve or disperse both the resin matrix and the organic low-molecular substance. This type of organic solvent has an extremely low boiling point and a fast evaporation rate, so the solvent on the surface evaporates during the coating stage before drying, forming a film of the resin base material on the surface, and the solvent inside the layer evaporates. Not only does this hinder volatilization, but the particle size of the organic low-molecular substance dispersed in the resin base material increases, and over time, it precipitates on the surface of the layer. Furthermore, there was a defect in that adhesiveness at the interface between the support and the layer deteriorated due to residual solvent in the layer. Therefore, there is a problem in coating that another layer cannot be smoothly laminated on this surface. In addition, as the image formation and erasure are repeated many times by applying pressure and heating using a thermal head, etc., the particles of the organic low molecular weight substance in the resin base material are not formed uniformly. This has the disadvantage that the particles gradually become larger in diameter, lose the light scattering effect, reduce white turbidity, and eventually reduce the contrast of the image. Furthermore, since particles of organic low-molecular substances are precipitated on the surface, even if a protective layer is laminated on top of the particles, the particles of organic low-molecular substances gradually migrate into the protective layer and adhere to head residue due to contact with the thermal head. This had the disadvantage that it could not be repeated many times.

[0005]

[Problems to be Solved by the Invention] An object of the present invention is to eliminate the drawbacks of the conventional method and to provide a uniform image even when images are formed and erased many times using a heating means such as a thermal head that applies heat and pressure at the same time. The present invention provides a method for producing a reversible heat-sensitive recording material which can form images and which is free from adhesion of head residue.

[0006]

[Means for Solving the Problems] The present invention provides, on a support,
A solution obtained by dissolving a resin base material and an organic low-molecular substance in an organic solvent is applied and dried to uniformly disperse the organic low-molecular substance in the resin base material, which becomes transparent depending on the temperature. In the method for producing a reversible thermosensitive recording material having a thermosensitive layer in which the state and the cloudy state reversibly change, as the organic solvent,
A method for producing a reversible thermosensitive recording material characterized by using a mixture of 1,4-dioxane and tetrahydrofuran, in particular, using a mixture of 1,4-dioxane and tetrahydrofuran as the organic solvent at a weight ratio of 8:2. The present invention provides a method for producing a reversible thermosensitive recording material, characterized in that it is used in a ratio of 2:8.

That is, in the present invention, when forming a heat-sensitive layer on a support using a heat-sensitive layer solution consisting of at least two types of organic solvents having different vapor pressures, the above-mentioned coating and drying of the heat-sensitive layer are carried out. The evaporation rate and diffusion rate of the solvent are appropriately adjusted, and the resin base material and organic low-molecular substance in the heat-sensitive layer are evaporated during drying without forming a film of the heat-sensitive layer from coating to drying. Since the layer is formed in a uniformly dispersed state, the growth of the particle size of the organic low molecular weight substance is suppressed, making it possible to form a layer with an extremely small particle size. Therefore, it is possible to prevent the precipitation of organic low molecular weight substances on the surface, and as a result, the conventional problem of head dregs adhesion due to surface precipitation of organic low molecular weight substances and decrease in transparency concentration due to large particle size of organic low molecular weight substances is achieved. , it is possible to prevent a decrease in contrast caused by a decrease in cloudy density.

In the present invention, the mixing ratio of 1,4-dioxane and tetrahydrofuran is 1,4-dioxane and tetrahydrofuran in weight ratio as described above.
The ratio of dioxane:tetrahydrofuran is in the range of 2:8 to 8:2, preferably 3:7 to 7:3. If the amount of 1,4-dioxane is large, the dissolution of the organic low molecular weight substance will be insufficient, resulting in the disadvantage that the organic low molecular weight substance will precipitate over time, making coating impossible. Furthermore, if the amount of 1,4-dioxane is small, the evaporation rate becomes high and the particle size of the organic low-molecular substance cannot be controlled, resulting in defects such as poor adhesion of head residue and a decrease in contrast.

The reversible thermosensitive recording material obtained by the production method of the present invention utilizes the above-mentioned change in transparency (transparent state, cloudy opaque state), and the difference between the transparent state and the cloudy opaque state is as follows. It is assumed that. That is,
(I) In the case of transparency, the particles of organic low-molecular substances dispersed in the resin matrix are composed of large particles of organic low-molecular substances, and light incident from one side is not scattered and travels to the other side. (II) In the case of white turbidity, the particles of the organic low-molecular substance are composed of polycrystals, which are aggregates of fine crystals of the organic low-molecular substance, and the crystal axes of the individual crystals vary. This is due to the fact that light incident from one side is refracted and scattered many times at the interface of the crystals of the organic low-molecular-weight particles, which causes it to appear white.

In FIG. 1 (which shows the change in transparency due to heat), the heat-sensitive layer whose main components are a resin base material and an organic low-molecular substance dispersed in the resin base material is, for example, T
At room temperature below 0, it is cloudy and opaque. This temperature is T
When heated to 2, it becomes transparent, and even if it is returned to room temperature below T0 in this state, it remains transparent. This is considered to be because the organic low-molecular substance passes through a semi-molten state and crystals grow from polycrystal to single crystal from temperature T2 to below T0. Further heating to a temperature of T3 or higher results in a translucent state intermediate between maximum transparency and maximum opacity. Next, when this temperature is lowered, the liquid returns to its initial cloudy and opaque state without becoming transparent again. This is considered to be because polycrystals precipitate when the organic low-molecular substance is melted at a temperature of T3 or higher and then cooled. Note that when this opaque state is heated to a temperature between T1 and T2 and then cooled to room temperature, that is, a temperature below T0, it can take an intermediate state between transparent and opaque. In addition, if the material that becomes transparent at room temperature is heated again to a temperature of T3 or higher and then returned to room temperature,
It returns to a cloudy, opaque state. That is, it can take both opaque and transparent forms, as well as an intermediate state between them, at room temperature.

[0011] Therefore, by selectively applying heat, it is possible to selectively heat the heat-sensitive layer to form a cloudy image on a transparent background, and a transparent image in addition to the cloudiness, and this change can be repeated many times. It is possible. By disposing a colored sheet on the back side of such a heat-sensitive layer, it is possible to form an image in the color of the colored sheet on a white background or a white image on the background of the color of the colored sheet. Furthermore, if the image is projected using an OHP (overhead projector) or the like, the cloudy areas become dark areas, and the transparent areas allow light to pass through and become bright areas on the screen.

In the method for producing a reversible thermosensitive recording material of the present invention, the above-mentioned solution in which two components, a resin base material and an organic low-molecular substance are dissolved, is applied onto a support such as a plastic film, a glass plate, or a metal plate. It can be made by drying to form a heat sensitive layer.

The resin base material used in the heat-sensitive layer is a material that forms a layer in which a low-molecular-weight organic substance is uniformly dispersed, and also influences the transparency at maximum transparency. Therefore, the resin base material is preferably a resin that has good transparency, is mechanically stable, and has good film-forming properties.

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-vinyl acetate copolymer. Vinyl chloride copolymers such as acrylate copolymers; vinylidene chloride copolymers such as polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides; polyacrylates or Examples include methacrylate or acrylate-methacrylate copolymer; silicone resin, and the like. These may be used alone or in combination of two or more.

On the other hand, the organic low-molecular substance may be one that changes 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 150°C.
A certain degree is used. Such organic low-molecular substances include alkanols; alkanediols; halogenalkanols or halogenalkanediols; alkylamines; alkanes; alkenes; alkynes; halogenalkanes; halogenalkenes; halogenalkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or Unsaturated mono- or dicarboxylic acids or their esters, amides or ammonium salts; Saturated or unsaturated halogenated fatty acids or their esters, amides or ammonium salts; Allylcarboxylic acids or their esters, amides or ammonium salts; Halogenated allylcarboxylic acids or their esters, amides or ammonium salts; Examples include esters, amides or ammonium salts thereof; thioalcohols; thiocarboxylic acids or esters, amines or ammonium salts thereof; carboxylic acid esters of thioalcohols. These may be used alone or in combination of two or more. The carbon number of these compounds is 10~
60, preferably 10-38, especially 10-30. Even if the alcohol group in the ester is saturated,
Further, it may not be saturated or may be substituted with halogen. In any case, the organic low-molecular substance contains at least one of oxygen, nitrogen, sulfur, and halogen in the molecule, such as -OH, -COOH, -CONH-, -COOR, -N
Preferably, it is a compound containing H-, -NH2, -S-, -S-S-, -O-, halogen, or the like.

More specifically, these compounds include higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, arginic acid, and oleic acid; methyl stearate; , esters of higher fatty acids such as tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate, dodecyl behenate; and ethers or thioethers. Among these, in the present invention, higher fatty acids, particularly higher fatty acids having 16 or more carbon atoms such as palmitic acid, stearic acid, behenic acid, and lignoceric acid are preferred, and higher fatty acids having 16 to 24 carbon atoms are more preferred.

In order to widen the range of temperatures at which transparency can be achieved, it is possible to appropriately combine the organic low molecular weight substances described in this specification, or to combine such organic low molecular weight substances with other materials having different melting points. . These are, for example, JP-A-63
-39378, Japanese Patent Application Laid-Open No. 63-130380, Japanese Patent Application No. 14754-1983, Japanese Patent Application No. 1-1401
Although it is disclosed in specifications such as No. 09, it is not limited thereto. The weight ratio of the organic low-molecular substance to the resin base material in the heat-sensitive layer is preferably about 2:1 to 1:16, more preferably 1:1 to 1:3. If the ratio of the resin base material is less than this, it will be difficult to form a film that retains the organic low molecular weight substance in the resin base material, and if it is higher than this, the amount of organic low molecular weight substance will be small and the film will become opaque. becomes difficult.

In addition to the above-mentioned components, additives such as surfactants and high boiling point solvents may be added to the heat-sensitive layer in order to facilitate the formation of transparent images. 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 azelaic acid
-Ethylhexyl, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetyl ricinoleate, butyl acetyl ricinoleate, butyl phthalyl butyl glycolate, acetyl citric 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 alkyl amine, higher fatty acid amide , lower olefin oxide adducts of fats and oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salts of higher alkylbenzene sulfonic acids; higher fatty acids, aromatic carboxylic acids, higher fatty acid sulfonic acids, aromatic sulfonic acids, sulfuric acid monoesters or Ca, Ba or Mg salts of phosphoric acid mono- or di-esters; low sulfated oils; poly long-chain alkyl acrylates; acrylic oligomers; poly long-chain alkyl methacrylates; long-chain alkyl methacrylate-amine-containing monomer copolymers ; Styrene-maleic anhydride copolymer; Olefin-maleic anhydride copolymer.

When the image of this recording material is used as a reflective image, by providing a layer that reflects light on the back side of the recording layer, the contrast can be increased even if the thickness of the recording layer is reduced. Specifically, it is possible to evaporate Al, Ni, Sn, etc. (described in JP-A-64-14079).
.

[0021] Furthermore, a protective layer can be provided on the heat-sensitive layer to protect the heat-sensitive layer. Materials for the protective layer (thickness: 0.1 to 5 μm) laminated on the heat-sensitive layer include silicone rubber, silicone resin (described in Japanese Patent Application Laid-Open No. 63-221087), polysiloxane graft polymer (Japanese Patent Application No. 1983-221087), -152550), ultraviolet curing resin or electron beam curing resin (described in Japanese Patent Application No. 63-310600)
etc. In either case, a solvent is used during coating, but it is desirable that the solvent is difficult to dissolve the resin and organic low-molecular substance of the heat-sensitive layer. Examples of solvents that are difficult to dissolve the resin and organic low-molecular substance of the heat-sensitive layer include n-hexane, methyl alcohol, ethyl alcohol, and isopropyl alcohol, and alcohol-based solvents are particularly desirable from the viewpoint of cost.

Furthermore, an intermediate layer can be provided between the protective layer and the heat-sensitive layer in order to protect the heat-sensitive layer from the solvent, monomer components, etc. of the protective layer-forming solution (see Japanese Patent Laid-Open No. 1-133).
(described in Publication No. 781). As the material for 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. Namely, 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.

[0023]

EXAMPLES The present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. Note that both parts and percentages herein are based on weight. Example 1 Approximately 400 Å on a polyester film approximately 50 μm thick
A thick Al layer was provided. Furthermore, stearic acid

6 parts eicosane 2 acid
4th part
Diisodecyl phthalate

3 parts Vinyl chloride-vinyl acetate-phosphate ester copolymer 27 parts
(Denka Vinyl #1000P manufactured by Denki Kagaku Kogyo Co., Ltd.
=Tg78℃) 1,4-dioxane

112 parts Tetrahydrofuran
A solution consisting of 48 parts was applied with a wire bar and dried (drying temperature 100°C,
The drying time was 60 sec) to form a heat-sensitive layer with a thickness of about 4 μm. On top of that, polyamide resin (manufactured by Toray Industries, CM8000)
) 10 copies
Ethyl alcohol

A solution consisting of 90 parts was applied with a wire bar and dried by heating (drying temperature 80°C, drying time 60 seconds) for about 0.0%.
A 5 μm thick intermediate layer was provided. Furthermore, on top of that, 10 parts of 75% acetic acid of urethane acrylate-based ultraviolet curable resin butyl solution (manufactured by Dainippon Ink Chemical Co., Ltd., Unidic C7-1
57) Toluene

A solution consisting of 10 parts was applied with a wire bar, dried by heating (drying temperature 100°C, drying time 60 seconds), and then cured with an 80 W/cm ultraviolet lamp to form an overcoat layer with a thickness of about 2 μm to form a reversible thermosensitive recording. Created the material.

Example 2 The solvent mixing ratio of the heat-sensitive layer of Example 1 was changed to 1,4-dioxane:
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that tetrahydrofuran 7:3 was changed to 3:7.

00
25] Example 3 The solvent mixing ratio of the heat-sensitive layer of Example 1 was changed to 1,4-dioxane:
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that tetrahydrofuran 7:3 was changed to 9:1.

Comparative Example 1 A reversible heat-sensitive recording material was prepared in the same manner as in Example 1 except that tetrahydrofuran was used as the solvent for the heat-sensitive layer.

Comparative Example 2 A reversible heat-sensitive recording material was prepared in the same manner as in Example 1 except that 1,4-dioxane was used as the solvent for the heat-sensitive layer.

The reversible thermosensitive recording material prepared as described above was tested for strength using a thermal head of 8 dots/mm under normal printing conditions with increased applied energy (applied power 1 W, applied pulse width 0.7 msec). Print it cloudy with a heat roller (80-85℃, 10mm/
min) to make it transparent. Print-erase 1 under the same conditions
Repeated 00 times. Table 1 shows the results and the coatability of the reversible thermosensitive recording material.

[0029]

[Table 1] Clear density and cloudy density are measured using Macbeth reflection densitometer RD-5.
Measure at 14.

[0030]

Effects of the Invention As is clear from the description of the examples, the reversible heat-sensitive recording material of the present invention is composed of two types of organic solvents, 1,4-dioxane and tetrahydrofuran, which have different vapor pressures as solvents for the heat-sensitive layer. During the coating and drying of the heat-sensitive layer, the evaporation rate and diffusion rate of the solvent are adjusted appropriately, so that the resin base material and organic low-molecular substance in the heat-sensitive layer are formed in a uniformly dispersed state, and the organic Since the low-molecular substance is formed with a small particle size, the problem of coating properties can be solved, and even if image formation and erasing are repeated 100 times with a thermal head, there is no significant change in cloudy density or transparent density. No slight decrease in contrast was observed. Furthermore, there is an effect that there is no adhesion of head residue.

[Brief explanation of the drawing]

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

Claims (2)

[Claims] Claim 1: A solution obtained by dissolving a resin base material and an organic low-molecular substance in an organic solvent is coated on a support and dried to uniformly distribute the organic low-molecular substance in the resin base material. A method for producing a reversible heat-sensitive recording material comprising a dispersed heat-sensitive layer that reversibly changes between a transparent state and a cloudy state depending on the temperature, wherein 1,4-dioxane and tetrahydrofuran are mixed as the organic solvent. A method for producing a reversible thermosensitive recording material, characterized in that it is used as a reversible thermosensitive recording material. 2. The method for producing a reversible thermosensitive recording material according to claim 1, wherein 1,4-dioxane and tetrahydrofuran are used as the organic solvent in a weight ratio of 8:2 to 2:8. .