JPH05294066A - Reversible thermal recording material - Google Patents

Abstract

PURPOSE:To provide a reversible thermal recording material imparting a high contrast image, excellent in image preserbability, having a high transparentizing temp. range, wide not only in a transparentizing temp. range but also in a transparentizing voltage range and excellent in repeated durability. CONSTITUTION:A reversible thermal recording material is obtained by providing a thermal layer based on a resin matrix and three or more org. monomeric substances different in m.p. dispersed in the resin matrix and reversibly changed in its transparent state in dependence on temp. on a support.

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 capable of repeatedly forming and erasing an image by utilizing the reversible change in transparency depending on the temperature of a thermosensitive layer.

[0002]

2. Description of the Related Art In recent years, reversible thermosensitive recording materials have been attracting attention because they enable temporary image formation and can erase the image when it is no longer needed. As a typical example thereof, 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 (Japanese Patent Laid-Open Publication No. Sho. 54-11
9377, JP-A-55-154198, etc.).

Image formation and erasure using this type of recording material utilizes the reversible change in transparency of the heat-sensitive layer depending on temperature, but the width of the temperature range in which the opaque portion becomes transparent is 2 to.
It had the drawback of being as narrow as 4 ° C. Therefore, when at least a part of the opaque recording material is made transparent, or when a transparent image is formed on the opaque recording material,
Temperature control was difficult.

Therefore, in consideration of these points, the present inventors have previously described a certain organic low-molecular substance and its compound in Japanese Patent Laid-Open Nos. 63-39378 and 63-130380. It was shown that the temperature range for making transparent can be expanded by using a substance that is easily eutectic with an organic low molecular weight substance. However, in these, the transparentization temperature is expanded to a low temperature range, so that an inconvenient phenomenon that an image sometimes disappears in an environment of 50 to 60 ° C. was recognized.

In consideration of such circumstances, the present inventors have further found that it is possible to extend the clearing temperature to a high temperature range by using an aliphatic dicarboxylic acid having a high melting point, and first of all, found out. Proposed. As a result, the transparentization temperature range could be widened and the image storability could be improved. However, when a heating element such as a thermal head was used as a printing means for forming and erasing an image on the recording material, the heat An organic low-molecular substance used for the heat-sensitive layer when an image is formed or erased with a short time of energy application,
For example, for higher fatty acids, those with a low melting point are used,
Although the transparent voltage range can be further widened by the combination with the above aliphatic dicarboxylic acid, on the other hand, when such a reversible recording material is repeatedly printed with a heating element such as a thermal head, an image during image formation is formed. The concentration deteriorates,
It is recognized that there is a drawback that the contrast is lowered, and this is more remarkable when the higher fatty acid has a small number of carbon atoms and a low melting point.

On the contrary, in the case of a combination of a higher fatty acid having a large number of carbon atoms and a high melting point and an aliphatic dicarboxylic acid, the image deterioration of the repeating durability described above is good, but the transparent voltage range can be widened. There was a drawback that it was difficult to do.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned inconveniences and drawbacks, high contrast, easy heating control, excellent image storability, and a short time in a heating element such as a thermal head. Even when heat energy is applied, the transparent voltage range is wide and a uniform transparent state can be obtained. Further, even when printing is repeated with a heating element such as a thermal head, the image density is less deteriorated and the durability is excellent. Another object is to provide a reversible thermosensitive recording material.

[0008]

According to the present invention, a resin base material and an organic low molecular weight substance dispersed in the resin base material are contained as a main component on a support, and a transparent state and a cloudiness are obtained depending on temperature. A reversible thermosensitive recording material provided with a thermosensitive layer whose state changes reversibly, characterized in that, as the organic low molecular weight substance, three or more organic low molecular weight substances having different melting points are used in combination. Material is provided.

That is, the reversible thermosensitive recording material of the present invention forms an image and erases it by utilizing the change in transparency.
Since the transparent temperature of the heat-sensitive layer can be made higher than before and the temperature range can be expanded, and in addition to the above, the transparent voltage range is wide even when heating with a heating element such as a thermal head for a short time. To obtain a uniform transparent state,
Furthermore, the inventors have found that even if printing is repeated with a heating element such as a thermal head, the image density is less deteriorated and the durability is excellent in repetition, the present invention has been completed.

The present invention has been made based on the above findings. Hereinafter, the present invention will be described in more detail. 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, in the case of (i) transparent, the particles of the organic low-molecular substance dispersed in the resin base material 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. 1 (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 conceivable that the organic low-molecular-weight substance undergoes a semi-molten state until the following and the crystal grows from a polycrystal to a single crystal.
Further heating to a temperature of T ₃ or higher results in a semitransparent state between the maximum transparency and the maximum opacity. Next, when this temperature is lowered, the initial cloudy opaque state is restored without taking the transparent state again. It is considered that this is because the organic low molecular weight substance is melted at a temperature of T ₃ or higher and is then cooled to precipitate polycrystals. It should be noted that when this opaque state is heated to a temperature between T _{1 and} T ₂ and then cooled to room temperature, that is, a temperature of T ₀ or lower, an intermediate state between transparent and opaque can be obtained. Also, the transparent material that has become transparent at room temperature returns to the cloudy and opaque state when heated again to a temperature of T ₃ or higher and then returned to room temperature. That is, it can take both opaque and transparent forms at room temperature and intermediate forms thereof. Therefore,
The heat-sensitive layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent background or a transparent image on a cloudy background, and the change can be repeated many times. By arranging a coloring sheet on the back surface of such a heat-sensitive body, it is possible to form an image of the color of the coloring sheet on the white background or an image of the white background on the background of the coloring sheet. Also, O
When projected with an HP (overhead projector) or the like, the cloudy portion becomes a dark portion, the transparent portion transmits light, and becomes a bright portion on the screen.

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

In the recording material of the present invention which causes such image formation and erasure, the transparent temperature of the heat-sensitive layer is higher than that of the conventional one, and the temperature range can be expanded because the organic low molecular weight substance is contained in the heat-sensitive layer. As an organic low molecular weight substance having three or more components having different melting points, for example, two kinds of higher fatty acids having different melting points and an aliphatic saturated dicarboxylic acid having a higher melting point than these higher fatty acids are mixed and used. It is considered that the eutectic temperature when heated is higher than that of the higher fatty acid alone.

In addition to the above-mentioned action, the transparent voltage range can be expanded even when the heating element such as a thermal head is heated for a short time, and a uniform transparent state can be obtained in the above-mentioned transparent temperature range. It is thought to be due to the same reason as the expansion.

Furthermore, even if printing is repeated with a heating element such as a thermal head, the deterioration of the image density is small and the repeated durability is excellent because it will be explained from the relationship with the melting point and carbon number of the higher fatty acid described below. ..

In the case where only the low melting point higher fatty acid among the higher fatty acids having different melting points and the aliphatic saturated dicarboxylic acid are mixed and used as the organic low molecular weight substance in the heat sensitive layer, the influence of the low melting point higher fatty acid is exerted. Since the eutectic temperature becomes low, the thermal strength of the organic low molecular weight substance particles against the thermal energy stress is weak when thermal energy is applied from a heating element such as a thermal head, so that the particles can maintain a stable state. However, the particles are aggregated and maximized, and the image density deteriorates. Furthermore, due to the physical properties of higher fatty acids, those with a low melting point have a small number of carbon atoms, and in this respect, those with a low melting point have a resin as a matrix material that surrounds the organic low molecular weight substance particles in the molten state. Since it has a good compatibility, it is difficult to exist as stable particles.
Maximization is likely to occur. From the above points, higher fatty acids having a low melting point and a small number of carbon atoms cause a large deterioration in image density due to repeated durability.

However, in contrast to the above, in the present invention,
In the combination of the two-component higher fatty acid having different melting points and the aliphatic saturated dicarboxylic acid, even if the low melting point higher fatty acid is used, the higher fatty acid having a higher melting point is used in combination. Compared to the case of using only the eutectic, the decrease in the eutectic temperature is less, and the thermal strength of the organic low molecular weight substance particles is improved, so that the particles are in a stable state and the deterioration of the image density is considered to be less. Be done. Regarding the carbon number of the higher fatty acid mentioned above, even if a higher fatty acid having a low melting point and a small number of carbon atoms is used,
Since higher fatty acids having a higher melting point and a higher number of carbon atoms are used in combination, the compatibility with the matrix resin is poorer than that in the case where only the higher fatty acid having a lower melting point and a lower number of carbon atoms is used. Since cohesion and maximization of each other are prevented, it is considered that deterioration of image density due to repeated durability is excellent.

In the present invention, a reversible thermosensitive recording material is prepared by dissolving a resin base material and an organic low molecular weight substance or a resin base material solution (at least one organic low molecular weight substance is dissolved as a solvent). If not necessary, disperse spacer particles in a dispersion liquid in which organic low-molecular substances are dispersed in the form of fine particles, and then coat and dry on a support such as a plastic film, glass plate, metal plate, etc. The heat sensitive layer may be formed. 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. The organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the heat-sensitive layer obtained not only when the dispersion liquid is used but also when the solution is used.

In the present invention, the resin used as the resin base material of the thermosensitive layer of the reversible thermosensitive recording material is preferably a resin which can form a film or a sheet, has good transparency and is mechanically stable. Examples of such resins include polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer. Vinyl chloride-based copolymers such as 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. Of course, these may be used alone or in combination with two or more kinds.

On the other hand, the organic low molecular weight substance has a temperature T ₀ to
It may be appropriately selected according to the selection of T ₁ . As such an organic low molecular weight substance, it is preferable to use, for example, a mixture of at least two components of a higher fatty acid having 16 or more carbon atoms and at least one kind of an aliphatic saturated dicarboxylic acid.

Specific examples of the higher fatty acids having 16 or more carbon atoms include palmitic acid, margaric acid, stearic acid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, behenic acid, lignoceric acid, pentacosanoic acid, serotic acid, heptacosanoic acid, montan. Acid, nonacosanoic acid, melissic acid, 2-hexadecenoic acid, trans-3-hexadecenoic acid, 2-heptadecenoic acid, trans-2-octadecenoic acid, cis-2-octadecanoic acid, trans-4-octadecenoic acid, cis-6- Octadecenoic acid, elaidic acid,
Vacenic acid, trans-gondoinic acid, erucic acid, plasic acid, ceracoleic acid, trans-ceracoleic acid,
Trans-8, trans-10-octadecadienoic acid,
Linoelaidic acid, α-eleostearic acid, β-eleostearic acid, pseudoeleostearic acid, 12,
20-heneicosadienoic acid and the like can be mentioned.

The aliphatic saturated dicarboxylic acid is shown in Table 1 below.
The compounds shown in can be exemplified.

[Table 1]

Among the above aliphatic saturated dicarboxylic acids, those having a melting point of 80 to 200 ° C. are preferable. When the aliphatic saturated dicarboxylic acid and the higher fatty acid are mixed and used, it is preferable to selectively use the aliphatic saturated dicarboxylic acid having a melting point higher than that of the higher fatty acid.

With the intention of protecting the heat-sensitive layer,
In the case of laminating a protective layer or the like on the heat-sensitive layer as described below, in order to prevent the aliphatic saturated dicarboxylic acid from being released to the surface by dissolving in a solvent of the protective layer coating liquid, Among saturated dicarboxylic acids, those having 20 or more carbon atoms are preferable. Further, the ratio of the higher fatty acid to these aliphatic saturated dicarboxylic acids is 95: 5 to 50: 5 by weight.
A range of 0 is preferred.

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, more preferably 1: 1 to 1: 6. 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.

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.

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 , 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.

In the present invention, as the support of the reversible thermosensitive recording material, a plastic film as described above,
A glass plate, a metal plate or the like is used. In order to improve the image contrast of this recording material, it is possible to provide a light reflecting layer on the back surface of the recording layer. In this case, high contrast can be obtained even if the thickness of the recording layer is reduced. Specifically, vapor deposition of Al, Ni, Sn, Au, Ag and the like can be mentioned (described in JP-A No. 64-14079). In the case where the support is made of a material such as an Al vapor-deposited layer that has poor adhesiveness to the resin, an adhesive layer may be provided between the support and the heat sensitive layer.
(JP-A-3-7377).

Further, a protective layer may be provided on the heat-sensitive layer of the present invention in order to prevent the transparency of the transparent portion from being lowered due to the deformation of the surface due to the heat and pressure of the heating means such as a thermal head. good. A protective layer (thickness: 0.
(1 to 10 μm), silicone rubber, silicone resin (described in JP-A-63-221087), polysiloxane graft polymer (JP-A-63-210).
No. 317385), an ultraviolet curable resin, an electron beam curable resin (described in JP-A-2-566), and the like.
In any case, a solvent is used at the time of coating, but it is desirable that the solvent is difficult to dissolve the resin of the heat sensitive layer and the organic low molecular weight substance. Examples of the solvent that hardly dissolves the resin of the heat-sensitive layer and the organic low-molecular substance include n-hexane, methyl alcohol, ethyl alcohol, isopropyl alcohol, and the like, and the alcohol solvent is particularly preferable from the viewpoint of cost.

Further, an intermediate layer can be provided between the protective layer and the reversible recording material in order to protect the reversible recording material from the solvent, monomer component and the like of the protective layer forming liquid (JP-A-1-133781). No. publication). As the material for the intermediate layer, the following thermosetting resins and thermoreversible resins can be used in addition to those listed as the resin matrix in the heat sensitive layer.
That is, specifically, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate, polyamide and the like can be mentioned. Although the thickness of the intermediate layer varies depending on the use, it is preferably about 0.1 to 2 μm. If it is less than this, the protective effect is lowered, and if it is more than this, the thermal sensitivity is lowered. Further, a magnetic recording layer may be provided and used as a card (described in Japanese Utility Model Laid-Open No. 2-3876).

[0032]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. The parts here are based on weight.

Example 1 On a polyester film having a thickness of about 188 μm, an Al vapor-deposited layer was vacuum-deposited to a thickness of about 400 Å to form a light-reflecting layer. Furthermore, palmitic acid (manufactured by Tokyo Chemical Industry Co., Ltd .: palmitic acid reagent mp 63-64 ° C.) 2.5 parts Stearic acid (manufactured by NOF Corporation: NAA180 mp 71.5-72 ° C.) 2 .5 parts Eicosane diacid (Okamura Oil Co., Ltd .: SL-20) 5 parts Diisodecyl phthalate 2 parts Vinyl chloride-vinyl acetate copolymer (manufactured by Denki Kagaku Kogyo: # 1000MT) 25 parts THF 150 parts Toluene 15 parts The resulting solution was applied and dried by heating to provide a thermosensitive layer (reversible thermosensitive recording layer) having a thickness of about 5 μm. Further, a solution consisting of 10 parts of polyamide resin (CM8000, manufactured by Toray Industries, Inc .: CM8000) and 90 parts of methanol was applied on it, and dried by heating to form an intermediate layer of about 1 μm thickness. A 75% butyl acetate solution of urethane acrylate-based UV-curable resin (Unidick C7-157, manufactured by Dainippon Ink and Chemicals, Inc.) 10 parts A solution consisting of 10 parts toluene was applied with a wire bar, and after heating and drying, 8
A reversible thermosensitive recording material was prepared by curing with a 0 w / cm ultraviolet lamp and providing an overcoat layer having a thickness of about 2 μm.

Example 2 The stearic acid obtained in Example 1 was replaced with behenic acid (NIPPON OIL & CO., LTD .: N).
AA222S m. p. A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that the temperature was changed to 81 to 82 ° C.

Comparative Example 1 Palmitic acid 5 parts Eicosane diacid 5 parts Diisodecyl phthalate 2 parts Vinyl chloride-vinyl acetate copolymer 25 parts THF 150 parts Toluene 15 parts A solution consisting of 15 parts is applied on an Al vapor deposition layer and heated. A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that a thermosensitive layer having a thickness of about 5 μm was provided by drying.

Comparative Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that the palmitic acid of Comparative Example 1 was changed to stearic acid.

Comparative Example 3 Palmitic acid of Comparative Example 1 was converted to myristic acid (mp 58).
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that the temperature was changed to ° C.

Comparative Example 4 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that the palmitic acid of Comparative Example 1 was changed to behenic acid.

The reversible thermosensitive recording materials of Examples and Comparative Examples thus obtained were subjected to a repeated durability test of image formation and erasure as follows. A thermal head printing tester manufactured by Yashiro Denki Co., Ltd. was used as a thermal recording printing apparatus, a Ricoh 8 dot / mm thermal head was used as a thermal head, and a pulse width was 1 msec and an applied voltage was 2
The white turbid image is formed under the condition of 5.0V, and the applied voltage is 2
The white turbid image was erased by changing to 0.0V. Further, regarding the printing direction of the reversible thermosensitive recording material, one cycle of forming and erasing a cloudy image was considered as one cycle, and a durability test was repeated under the same direction conditions until a total of 100 cycles. Regarding the cloudy image density in the repeated durability test, the cloudy density at the first cycle and the 100th cycle was measured with a Macbeth reflection densitometer (RD914). The measurement results are shown in FIG.

In addition to the durability test, the transparency temperature range, width and maximum transparent density and maximum cloudiness density of the reversible thermosensitive recording material were measured as follows. First, all the recording materials (Examples 1 and 2 and Comparative Examples 1 to 4) obtained as described above were in a transparent state. 120 these recording materials
After heating for 1 minute in a constant temperature bath at ℃, it was cooled to room temperature to make it white and opaque. Next, these recording materials are
After heating to 120 ° C. in steps of 1 ° C. for 1 minute, it was cooled to room temperature, and the reflection density was measured with a Macbeth reflection densitometer (RD-914). At this time, the temperature when the reflection density exceeded 1.0 was defined as the clearing temperature, and the range and width thereof were shown.
The results of the maximum transparent density and the maximum cloudy density are shown in Table 2 below.

[0041]

[Table 2]

Furthermore, the transparent voltage range and width when a thermal head was used as the printing means were measured as follows. As the thermal recording recording apparatus, the same printing test apparatus and thermal head as those used in the repeated durability test were used, and the cloudy image formation was performed under the same application conditions. Next, as the application condition for erasing the cloudy image, the applied voltage is changed in 16.0 V to 0.2 V steps to 24.0 V with a pulse width of 1.0 msec, and the cloudy image is erased at each voltage, and this is applied to the Macbeth reflection. The reflection density was measured with a densitometer (RD-914). At this time, the voltage when the reflection density exceeded 1.0 was defined as the clearing voltage, and its range and width were shown.
The results are shown in Table 3 below.

[0043]

[Table 3]

[0044]

As is clear from the description of the embodiments, the reversible thermosensitive recording material of the present invention has three or more organic low molecular weight substances having different melting points as organic low molecular weight substances, for example, higher fatty acids having different melting points. And a saturated aliphatic dicarboxylic acid are used in combination, the transparentization temperature range becomes high and the transparentization temperature range is widened, and the transparentization voltage is applied even when heat energy such as a thermal head is applied in a short time. It is a reversible recording material which has a wide range and has less deterioration of a white turbid image even when image formation and erasing are repeated with a heating element such as a thermal head, and which is capable of maintaining high contrast and having improved durability.

[Brief description of drawings]

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

FIG. 2 is a graph showing repetitive durability (change in cloudy image density with respect to the number of times of repeating image formation and erasing) for the reversible thermosensitive recording materials of Examples 1 and 2 and Comparative Examples 1 to 4.

Front Page Continuation (72) Inventor Makoto Kawaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (1)

[Claims] 1. A thermosensitive layer comprising a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component on a support, and a transparent state and a cloudy state reversibly change depending on temperature. In the reversible thermosensitive recording material, the reversible thermosensitive recording material is characterized in that, as the organic low molecular weight substance, three or more organic low molecular weight substances having different melting points are used in combination.