JPH08150783A - Reversible heat-sensitive recording medium - Google Patents

Abstract

PURPOSE: To provide a reversible heat-sensitive recording medium in which color developing sensitivity is improved and also repeated printing resistance is improved. CONSTITUTION: A reversible heat-sensitive recording medium is provided with a color developing and reducing agent having at least one of a leuco compound, a phenolic hydroxyl or carboxyl group and also an amino group as a functional group or as a part of a salt compound and also applied to the leuco compound and color developing or color reducing the same, and its recording layer is color developed or color erased by the control of heat energy, and the recording medium is composed of a powder of an integrated mixture of the leuco compound, a color developing and reducing agent and a sensitizer. The action of sensitivity increase can be performed as a binder is not interposed among the three components, and when the medium is compared with the conventional examples in which the color developing and reducing agent and the sensitizer are dispersed individually, the blend ratio of the sensitizer can be reduced proportionately.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention comprises a recording layer containing a leuco compound, a color-developing / reducing agent, a sensitizer, and a binder as main components, and controls thermal energy applied to the recording layer to develop the color of the recording layer. The present invention relates to a reversible thermosensitive recording medium for (recording) and erasing (erasing), and in particular, a reversible thermosensitive recording medium capable of improving color forming sensitivity, decoloring sensitivity and erasing rate, and also improving durability against repeated printing. Related to the improvement of.

[0002]

2. Description of the Related Art In recent years, a reversible thermosensitive recording medium has been actively developed in which recording and erasing can be repeatedly performed by appropriately controlling applied thermal energy.

For example, JP-A-54-119377, JP-A-63-39377, and JP-A-63-41.
No. 186, JP-A-2-188294, etc., a reversible thermosensitive recording medium having a recording layer mainly composed of a resin base material and an organic low molecular weight substance dispersed in the resin base material. Is listed. In this reversible thermosensitive recording medium, the transparency of the recording layer is physically changed by controlling the thermal energy, and recording and erasing are performed reversibly.

However, in this reversible thermosensitive recording medium, the transparency of the recording layer is physically changed to indirectly perform recording and erasing, and the recording layer itself is directly colored or erased for recording. It was not a recording medium for erasing.

On the other hand, a reversible thermosensitive recording medium for directly recording and erasing by chemically coloring or erasing the recording layer itself is disclosed in JP-A-2-188294 and JP-A-2.
No. 505365. That is,
This reversible thermosensitive recording medium comprises a leuco compound and a color-developing agent (amphoteric compound) having at least one of a phenolic hydroxyl group and a carboxyl group and having an amino group as a functional group or as a part of a salt compound as main components. The recording layer was prepared.

Since the above-mentioned developer / color-reducing agent which is an amphoteric compound exhibits the properties of an acid or the properties of a base by the action of heat, hydrogen ions released by acting as an acid under high temperature heating act as an lactone ring of a leuco compound. Ring-opens to develop the leuco compound, while under low temperature heating it acts as a base to close the lactone ring and reduce the color of the leuco compound.
Therefore, since the recording layer itself chemically develops or erases color, it functions as a medium capable of directly recording and erasing.

By the way, since the above-mentioned developing / reducing agent and leuco compound which are amphoteric compounds are composed of compounds having a relatively high melting point, as will be apparent from the specific examples described later,
There is a problem in heating responsiveness when heat energy is applied to the recording layer, and there is a problem that the coloring and decoloring sensitivities are not so good.

Therefore, in this type of reversible thermosensitive recording medium, a sensitizer having a relatively low melting point and having compatibility with the above leuco compound or the color-developing agent (for example, a melting point depressant comprising stearic acid amide) is recorded. By mixing it in the layer, the color developing sensitivity and the color erasing sensitivity of the recording layer were improved.

[0009]

By the way, in the conventional reversible thermosensitive recording medium, as shown in FIG. 2, the leuco compound a, the color-developing agent b, and the powder of the sensitizer c are used in the recording layer 2. Since the sensitizer c is once melted by the applied thermal energy, the sensitizer c is dispersed in the binder d individually, and then the sensitizer c is dispersed in the vicinity thereof via the binder d. It acts on the compound a or the color-developing agent b to cause the leuco compound a and the color-developing agent b to develop or decolorize. In FIG. 2, 1 is a support and 3 is a protective layer.

Therefore, when the binder is interposed between the melted sensitizer and the leuco compound or the color-developing / reducing agent, the above-mentioned action of the sensitizer becomes difficult to function. There is a problem in that the sensitizing action is insufficient and the color developing sensitivity and the color erasing sensitivity cannot be improved.

If the sensitizer content is too high,
During color development (recording) and color erasing (erasing), the sensitizer melts and fluidizes, which softens the recording layer and reduces friction resistance. It also had problems that caused it.

The present invention has been made by paying attention to such a problem, and its object is to improve the coloring sensitivity, the decoloring sensitivity and the erasing rate, and also to improve the repetitive printing durability. An object of the present invention is to provide a reversible thermosensitive recording medium.

[0013]

That is, the invention according to claim 1 has a leuco compound and at least one of a phenolic hydroxyl group and a carboxyl group and an amino group as a functional group or as a part of a salt compound. On the support, a developing and decoloring agent that acts on the leuco compound to develop or reduce the color thereof, a sensitizer having compatibility with the leuco compound or the decolorizing agent, and a recording layer containing a binder as a main component. In preparation for the reversible thermosensitive recording medium in which the recording layer is colored or decolored by controlling heat energy,
The leuco compound, the developer / desensitizer, and the sensitizer are mixed together, and the leuco compound / developer / sensitizer integrated powder is dispersed in the recording layer to obtain the above leuco compound, the developer / desensitizer, and the sensitizer. It is characterized in that it is mixed in the recording layer.

Here, the principle of recording and erasing of the reversible thermosensitive recording medium according to the present invention is the same as that of the reversible thermosensitive recording medium according to the conventional example described above. That is, for a reversible thermosensitive recording medium having a recording layer containing a leuco compound / developer / decolorizer / sensitizer integrated powder as a main component, a decolorizer / developer and a sensitizer and a binder, for a thermal printer or the like. Thermal energy (h1), eg high temperature (300 ° C or higher),
When heat treatment is performed for a short time (several milliseconds to several hundreds of milliseconds),
Hydrogen ions are released from the phenolic hydroxyl group or carboxyl group of the color-developing / reducing agent and react with the leuco compound to open the leuco compound to form a colored image. For this image, another heat energy (h2) such as low temperature (a temperature near the melting point of the sensitizer or higher, for example, 10
When heat-treated for a long time (0 to 200 ° C.) (for 1 second or longer), hydrogen ions are deprived of the leuco compound by the action of the amino group of the developer and decolorizer, and the leuco compound is ring-closed to be colorless. It Furthermore, when the erased recording layer is again subjected to heat treatment with heat energy (h1), an image is formed again. This image formation and image deletion can be repeated, and the image formation state or the image deletion state is maintained unless heat energy is applied.

In the reversible thermosensitive recording medium according to the first aspect of the present invention, as shown in FIG. 1, the leuco compound, the decolorizing agent and the sensitizer contained in the recording layer 2 are leuco compound / developer. Since the colorant / sensitizer integrated powder f is used, the binder d is not present between these three components. Therefore, when heat energy is applied to the recording layer 2, the leuco compound / development / decoloring agent / sensitizer integrated powder f
The sensitizer inside is melted and instantly acts on the color-developing color-reducing agent or leuco compound to promote the reaction between the color-developing color-reducing agent and the leuco compound. It is possible to improve the coloring sensitivity and the erasing sensitivity as compared with the conventional reversible thermosensitive recording medium.

Further, since there is no binder between the three components of the leuco compound, the decolorizing agent and the sensitizer, the sensitizing action of the sensitizer with respect to the decolorizing agent or the leuco compound can be increased, and along with this. Since the blending ratio of the sensitizer can be reduced, it is possible to improve the repeated printing durability.

Further, since the coloring or decoloring reaction in the thermosensitive recording medium occurs in the leuco compound / developing / reducing agent / sensitizer integrated powder, these reactions are less affected by the binder. It is possible to select a strong binder resin. Therefore, it becomes possible to further improve the repeated printing durability by selecting a strong binder resin.

Further, since the leuco compound / developer / desensitizer / sensitizer-integrated powder in which the three components of the leuco compound, the color-reducing agent and the sensitizer are integrally mixed, is applied, it is possible from the time of preparing the recording medium. The background density of the recording layer is the same as the background density when the coloring / erasing operation is performed once. Therefore, even if the rewriting operation is repeated, the fluctuation of the background density is small, and the erasing rate can be improved as compared with the conventional one.

The leuco compound / developer / decolorizer / sensitizer integrated powder is obtained by pulverizing a solid composition in which these leuco compound, developer / desensitizer and sensitizer are uniformly or substantially uniformly mixed. Obtainable. The solid composition is prepared by melting a compatible leuco compound, a color-reducing agent and a sensitizer at a temperature equal to or higher than the melting point and mixing them, or kneading with a three-roll machine or the like. Or at least one component of a leuco compound, a color-developing agent and a sensitizer is melted and kneaded with a melting machine and the rest of the components are dissolved by the melt, or a leuco compound, a color-developing agent and a sensitizer. And the like are dissolved in a cosolvent and the solvent is evaporated to prepare a solid composition.
Further, the solid composition may be composed of a solid solution of a leuco compound, a color-developing agent and a sensitizer, or a eutectic mixture (eutectic) of a leuco compound, a color-developing agent and a sensitizer. May be.

The inventions according to claims 2 to 6 relate to the invention in which the above-mentioned leuco compound / development / decoloring agent / sensitizer integrated powder and solid composition are specified, respectively.

That is, the invention according to claim 2 is premised on the reversible thermosensitive recording medium according to the invention according to claim 1, and a leuco compound, a decolorizing agent and a sensitizer are melted to prepare a solid composition. The leuco compound / development / desensitizer / sensitizer integrated powder is constituted by powder of this solid composition, and the invention according to claim 3 provides a leuco compound, a decolorization / desensitizer and a sensitizer. At least one component of the agent is melted and the remaining components are dissolved by the melt to prepare a solid composition, and the powder of the solid composition constitutes the above leuco compound / developer / sensitizer integrated powder. The invention according to claim 4 is characterized in that the leuco compound, the color-developing agent and the sensitizer are dissolved in a cosolvent and the solvent is evaporated to prepare a solid composition, and the solid composition is prepared. Depending on the composition powder, Compound-Arawagen colorant Sensitizer integrated powder is characterized by being composed.

The invention according to claim 5 is the invention according to claim 2
Based on the reversible thermosensitive recording medium according to the invention described in 4,
The solid composition is composed of a solid solution of a leuco compound, a color-developing agent and a sensitizer, and the invention according to claim 6 provides a eutectic mixture of a leuco compound, a color-developing agent and a sensitizer. Is characterized in that the above solid composition is constituted.

Next, each material constituting the thermosensitive recording medium according to the present invention will be described. First, as in the conventional case, as the support, a plastic material such as paper or plastic card, a metal material, a synthetic polymer, etc. Examples of the material include materials, but the material is not limited thereto.

As the leuco compound which constitutes a part of the recording layer, xanthene, spiropyran, lactone having a partial skeleton such as lactone, sultone and spiropyran,
Fluoran, sultone type and the like are used, and particularly triarylmethane type and fluoran type leuco compounds are used, but not limited to these. Specific examples of these include 3,3-bis (p-dimethylaminophenyl)
-6-Dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) phthalide, 3,3-bis (1,
2-Dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3-diethylamino-7-dibenzylaminofur Olane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-6-methyl-7-anilinoflu Oran, 3-
Piperidino-6-methyl-7-anilinofluorane, 3
-(N-Ethyl-n-tolyl) amino-6-methyl-7
-Anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3- (n-ethyl-n-
Examples thereof include isoamyl) amino-6-methyl-7-anilinofluorane and 3- (n-ethyl-n-tetrahydrofuryl) amino-6-methyl-7-anilinofluorane, but are not limited thereto. Not a thing. Moreover, you may use these 2 or more types simultaneously.

On the other hand, the above-mentioned color developing / reducing agent is a compound which reversibly releases protons by the action of heat energy and has both a color developing action and a color reducing action on the leuco compound. That is, it has both an acidic group consisting of a phenolic hydroxyl group or a carboxyl group and a basic group consisting of an amino group, becomes acidic or basic due to the difference in thermal energy, and develops (colors) or reduces the color of the above leuco compound ( It is what is erased. The basic group may be present as a functional group or may be present as a part of the salt compound. Examples of the color-developing / reducing agent having an acidic group and a basic group as functional groups include, for example,
Aminobenzoic acids, hydroxyaminobenzoic acids, aminophenols, aminonaphthoic acids, nicotinic acids and the like can be mentioned, and specific examples thereof include p-aminobenzoic acid, m-aminobenzoic acid, o-aminobenzoic acid and 4-amino-3. −
Methylbenzoic acid, 3-amino-4-methylbenzoic acid, 2
-Amino-5-ethylbenzoic acid, 3-amino-4-butylbenzoic acid, 4-amino-3-methoxybenzoic acid, 3-
Amino-4-ethoxybenzoic acid, 2-amino-5-chlorobenzoic acid, 4-amino-3-bromobenzoic acid, 2-amino-4-nitrobenzoic acid, 4-amino-3-nitrobenzoic acid, 3- Amino-4-nitrilebenzoic acid, aminosalicylic acid, diaminobenzoic acid, 2-methyl-5-aminonaphthoic acid, 3-ethyl-4-aminonaphthoic acid, nicotinic acid, isonicotinic acid, 2-methylnicotinic acid, 6-
There are chloronicotinic acid and the like. Further, as having a basic group as a part of the salt compound, a salt or complex salt of a compound having a phenolic hydroxyl group or a carboxyl group and a compound having an amino group, for example, hydroxybenzoic acids, hydroxysalicylic acids, gallic acid. Examples thereof include salts or complex salts of acids and acids such as bisphenolacetic acid with bases such as aliphatic amines, phenylalkylamines and triallylalkylamines. Specific examples thereof include p-hydroxybenzoic acid-alkylamine salt, p-hydroxybenzoic acid-phenylalkylamine salt, m-hydroxybenzoic acid-alkylamine salt, 2,4-dihydroxybenzoic acid-alkylamine salt, 4 , 5-Dihydroxybenzoic acid-tolylalkylamine salt, p-hydroxybenzoic acid methyl-alkylamine salt, p-hydroxybenzoic acid stearyl-alkylamine salt, gallic acid-alkylamine salt, gallic acid dodecyl-alkylamine salt, gallic acid Acid stearyl-alkylamine salt, bisphenolacetic acid-alkylamine salt, bisphenolacetic acid stearyl-
Examples thereof include alkylamine salts and octyl bisphenol acetate-alkylamine salts, and two or more of these may be used simultaneously.

Any sensitizer may be used as long as it has compatibility with the leuco compound and the color-developing / decoloring agent and functions as a melting point depressant. Since the effects on the color development-decolorization reaction are different, it is desirable to appropriately select it after confirming the compatibility such as melting point and compatibility. Specific examples thereof include esters such as terephthalic acid diester, stearyl phthalate, dibenzyl terephthalate, dibenzyl oxalate, oxalic acid- (p-chlorobenzyl), β-naphthol benzyl ether, ethylene glycol-m-toluyl ether, Ethers such as bis [2- (4methoxy) phenoxyethyl] ether, amide compounds such as behenic acid amide, stearic acid amide, palmitic acid amide, ethylenebisstearic acid amide, paraffin wax, carnauba wax, microcrystalline wax, etc. Examples thereof include waxes and sensitizers for various known heat-sensitive materials such as p-benzylbiphenyl and m-terphenyl. Incidentally, claim 7
The invention according to (1) relates to an invention in which a compound excellent in the sensitizing action among these sensitizers is specified.

That is, the invention according to claim 7 is based on the reversible thermosensitive recording medium according to any one of claims 1 to 6, wherein the sensitizer is behenic acid amide, stearic acid amide, and palmitin. It is characterized by being constituted by an amide compound selected from acid amides.

The recording layer of the reversible thermosensitive recording medium according to the present invention may have any form as long as it contains the leuco compound / developer / decolorizer / sensitizer integrated powder and a binder resin. Although it is good, it is usually formed by coating or drying a solution or dispersion in water or an organic solvent on the support. The binder resin at this time is not particularly limited, for example, acrylic resin, polyester, polyurethane, polyurea, melamine resin, polycarbonate,
Polymers such as polyamide, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl chloride, polyvinyl butyral, and waxes such as paraffin wax, polyethylene wax, carnauba wax, microcrystalline wax, stearamide, hydroxyethyl cellulose, carboxymethyl cellulose, Cellulose acetate, cellulose such as methoxycellulose,
Examples thereof include gelatin, casein, starch, and gums. Among these resins, in order to improve the repetitive characteristics and heat resistance of the reversible thermosensitive recording material, it is particularly preferable to apply a thermosetting resin or a heat resistant resin. Moreover, it is natural that two or more kinds of these resins may be used in combination.

In order to improve heat resistance, pressure resistance, abrasion resistance, light resistance, environment resistance, etc., the above leuco compound / development / desensitizer / sensitizer integrated powder is encapsulated in microcapsules. May be present in the recording layer. Various known methods are used as the microencapsulation method at this time, and examples thereof include an interfacial polymerization method, an in situ polymerization method, a coacervation method, a spray drying method, and a submerged drying method.

Further, in the recording layer of the reversible thermosensitive recording medium according to the present invention, in addition to the above leuco compound / development / decoloring agent / sensitizer integrated powder and binder resin, a general thermosensitive recording paper is used. Applicable additives may be added. Examples of such additives include a dispersant such as a surfactant, a color image stabilizer, an antioxidant, a light stabilizer, and a lubricant.

Further, a protective layer may be provided on the recording layer for the purpose of deformation of the surface of the recording layer due to heat, improvement of storage stability, prevention of sticking and the like. As the resin used for this protective layer, a resin having high heat resistance and mechanical strength is preferable, and for example, a thermosetting resin, an ultraviolet curable resin, an electron beam curable resin, a silicone resin or the like is used. If necessary, an undercoat layer may be provided between the recording layer and the support, and a backcoat layer may be provided on the surface of the support opposite to the surface on which the recording layer is formed.

[0032]

According to the reversible thermosensitive recording medium of the present invention, the leuco compound, the color-developing agent and the sensitizer contained in the recording layer are the leuco compound, the color-developing agent and the sensitizer. Since it is composed of the powder integrated with the sensitizer, no binder is present between these three components.

Therefore, when heat energy is applied to the recording layer, the sensitizer in the leuco compound / developer / decolorizer / sensitizer-integrated powder is melted and instantly acts on the decolorizer / leuco compound. In order to accelerate the reaction between the color-developing color-reducing agent and the leuco compound, the leuco compound, the color-reducing colorant and the sensitizer are individually dispersed to improve the color-developing sensitivity and the decoloring sensitivity as compared with the conventional reversible thermosensitive recording medium. Can be achieved.

Further, since no binder is present between the three components of the leuco compound, the decolorizing agent and the sensitizer, the sensitizing action of the sensitizer with respect to the decolorizing agent or the leuco compound can be increased, and along with this. Since the blending ratio of the sensitizer can be reduced, it is possible to improve the repeated printing durability.

Further, since the coloring or erasing reaction in this thermosensitive recording medium occurs in the powder containing the above leuco compound / developing / reducing agent / sensitizer, these reactions are less affected by the binder. It is possible to select a strong binder resin. Therefore, it becomes possible to further improve the repeated printing durability by selecting a strong binder resin.

Further, since the leuco compound / developer / desensitizer / sensitizer-integrated powder in which the three components of the leuco compound, the color-reducing agent and the sensitizer are integrally mixed, is applied, from the time of recording medium preparation The background density of the recording layer is the same as the background density when the coloring / erasing operation is performed once. Therefore, even if the rewriting operation is repeated, the fluctuation of the background density is small, and the erasing rate can be improved as compared with the conventional one.

[0037]

EXAMPLES Examples of the present invention will be described in detail below. In addition, "part" in an Example has shown the weight part.

[Example 1] (Preparation of leuco compound / developing / reducing agent / sensitizer integrated powder) Crystal violet lactone (leuco compound) 10 parts

[0039]

Embedded image Salt of bisphenolacetic acid and stearylamine (developing / reducing agent) 50 parts

[0040]

Embedded image Stearic acid amide (sensitizer) 30 parts The above composition is heated to 130 ° C. in a beaker, mixed well and cooled to obtain a solid composition composed of a leuco compound, a desensitizing agent and a sensitizer. After that, this was pulverized to prepare a leuco compound / development / decoloring agent / sensitizer integrated powder A. (Preparation of coating liquid for recording layer) Leuco compound / developing / reducing agent / sensitizer integrated powder A 100 parts Methacrylic resin (binder resin) 30 parts Toluene 500 parts After thoroughly mixing the above composition, dispersion by a ball mill for recording. A layer coating solution was obtained.

This was coated on a white polyester sheet of 188 μm with a Meyer bar to have a coating thickness of 15 μm after drying.
The recording layer was applied so that An ultraviolet curable resin monomer was applied onto this recording layer using a Mayer bar and cured by irradiation with ultraviolet rays to form a protective layer having a film thickness of 2 μm to prepare a reversible thermosensitive recording medium.

[Example 2] (Preparation of leuco compound / developing / reducing agent / sensitizer integrated powder) 2- (2-chlorophenylamino) -6-diethylaminofluorane (leuco compound) 10 parts

[0043]

Embedded image Salt of gallic acid and stearylamine (developer) 50 parts

[0044]

[Chemical 4] Dimethyl terephthalate (sensitizer) 30 parts The above composition is heated to 100 ° C. in a beaker, mixed well and cooled to obtain a solid composition composed of a leuco compound, a color-developing agent and a sensitizer. After that, this was powdered to prepare a leuco compound / development / decoloring agent / sensitizer integrated powder B. (Preparation of coating liquid for recording layer) Leuco compound / developing / reducing agent / sensitizer integrated powder B 150 parts Polyvinyl alcohol (binder resin) 50 parts Anionic surfactant [Kamo's trade name Demol EP] 10 parts Water 1000 parts A coating solution having the above composition was applied onto a high-quality paper of 60 g / m ² using a Meyer bar to apply a recording layer so that the weight after drying was 6 g / m ² . This was dried and then calendered to prepare a reversible thermosensitive recording medium.

[Example 3] (Preparation of leuco compound / development / decoloring agent / sensitizer integrated powder) 2- (2-chlorophenylamino) -6-diethylaminofluorane (leuco compound) 15 parts 4-amino-3 -Methoxybenzoic acid (developing / reducing agent) 50 parts Stearic acid amide (sensitizer) 20 parts The above composition was heated to 120 ° C in a beaker, mixed well and cooled to obtain a leuco compound, a decolorizing agent and After obtaining a solid composition comprising a sensitizer, this was pulverized to prepare a leuco compound / developer / decolorizer / sensitizer integrated powder C. (Preparation of coating liquid for recording layer) Leuco compound / developing / reducing agent / sensitizer integrated powder C 80 parts Methacrylic resin (binder resin) 30 parts Toluene 750 parts After thoroughly mixing the above composition, dispersing by a sand mill for recording A layer coating solution was obtained.

This was coated on a white polyester sheet of 188 μm with a Meyer bar so that the coating thickness after drying was 10 μm.
The recording layer was applied so that An electron beam curable resin monomer was applied onto this recording layer using a Mayer bar and cured by electron beam irradiation to form a protective layer having a film thickness of 2 μm to prepare a reversible thermosensitive recording medium.

[Comparative Example 1] A leuco compound (crystal violet lactone), a color-developing agent (a salt of bisphenolacetic acid and stearylamine) and a sensitizer (stearic acid amide) were individually dispersed and compounded in the recording layer. The reversible thermosensitive recording medium according to Example 1 is substantially the same as the reversible thermosensitive recording medium except for the above.

Comparative Example 2 Leuco compound [2- (2-chlorophenylamino) -6-diethylaminofluorane], a color-developing agent (salt of gallic acid and stearylamine).
Further, the reversible thermosensitive recording medium according to Example 2 is substantially the same as the reversible thermosensitive recording medium except that a sensitizer (dimethyl terephthalate) is individually dispersed and mixed in the recording layer.

[Comparative Example 3] Leuco compound [2- (2-chlorophenylamino) -6-diethylaminofluorane], color-developing agent (4-amino-3-methoxybenzoic acid)
The reversible thermosensitive recording medium according to Example 3 is substantially the same as the reversible thermosensitive recording medium except that the sensitizer (stearic acid amide) is dispersed and compounded in the recording layer.

[Confirmation Test] Next, the reversible thermosensitive recording media according to Examples 1 to 3 and the reversible thermosensitive recording media according to Comparative Examples 1 to 3 were measured using a thermal printer (Fujitsu product name Joy Writer). Printing is performed under the printing energy conditions of 0.3 mJ / dot, pulse width 2.5 ms and ON / OFF, and each printed recording medium is pressed by the hot stamp plate heated to 100 ° C. for 1 second to erase it, and The printing and erasing operations were repeated.

Then, the "background density", "erasure rate", obtained in the printing / erasing operation for each recording medium,
The respective data of "coloring density" and "number of repetitions" are shown in Table 1 below.

Each density in the table is a value obtained by measuring the optical reflection density with a Macbeth densitometer. The "erasure rate" is a value obtained by dividing the value obtained by subtracting the background density from the erase density by the value obtained by subtracting the background density from the color development density. Also, "repetition count"
Is the number of times until the print part is scratched when the printing / erasing operation is repeated.

Then, as is clear from the comparison of Example 1 with Comparative Example 1, Example 2 with Comparative Example 2, and Example 3 with Comparative Example 3 in Table 1, each Example is compared with each other. It can be confirmed that the erasing rate, the color density (color sensitivity), and the repeated print resistance are higher than those of the examples.

[0054]

[Table 1]

[0055]

According to the inventions according to claims 1 to 7,
Since the leuco compound, the developer / decolorizer and the sensitizer compounded in the recording layer are composed of a leuco compound / developer / decolorizer / sensitizer integrated powder, there is no binder between these three components. Therefore, when heat energy is applied to the recording layer, the sensitizer in the leuco compound / developer / decolorizer / sensitizer integrated powder is melted and instantly acts on the decolorizer / leuco compound to develop the decolorizer. And promote the reaction of the leuco compound.

Therefore, it has an effect of improving the color developing sensitivity and the color erasing sensitivity as compared with the conventional reversible thermosensitive recording medium in which the leuco compound, the color-reducing agent and the sensitizer are individually dispersed.

Further, since the binder is not present between the three components of the leuco compound, the decolorizing agent and the sensitizer, the sensitizing action of the sensitizer with respect to the decolorizing agent or the leuco compound can be increased, and along with this. Since the blending ratio of the sensitizer can be reduced, it has the effect of improving the repeated printing durability.

Further, since the coloring or decoloring reaction in this thermosensitive recording medium occurs in the above-mentioned leuco compound / developing / reducing agent / sensitizer integrated powder, these reactions are less susceptible to the influence of the binder, so that the reaction is stronger. It is possible to select a suitable binder resin. Therefore, by selecting a strong binder resin, it is possible to further improve the repeated printing durability.

Further, since the leuco compound / developer / desensitizer / sensitizer integrated powder in which the three components of the leuco compound, the developer / decolorizer and the sensitizer are integrally mixed is applied, it is possible from the time of preparing the recording medium. The background density of the recording layer is the same as the background density when the coloring / erasing operation is performed once. Therefore, even if the rewriting operation is performed repeatedly, the fluctuation of the background density is small, so that the erasing rate can be improved as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating the operation of a reversible thermosensitive recording medium according to the present invention.

FIG. 2 is a schematic cross-sectional view illustrating the operation of a reversible thermosensitive recording medium according to a conventional example.

[Explanation of symbols]

 1 support 2 recording layer 3 protective layer f leuco compound / developer / desensitizer / sensitizer integrated powder

Claims (7)

[Claims] 1. A leuco compound having at least one of a phenolic hydroxyl group and a carboxyl group and having an amino group as a functional group or as a part of a salt compound and acting on the above leuco compound to develop or reduce the color thereof. And a sensitizer having compatibility with the leuco compound or the color-developing and reducing agent, and a recording layer containing a binder as a main component are provided on a support, and the recording layer is colored by controlling thermal energy or In a reversible thermosensitive recording medium that erases color, the above leuco compound is prepared by dispersing a leuco compound, a decolorizing agent and a sensitizer-integrated powder in which a leuco compound, a decolorizing agent and a sensitizer are integrally mixed, in the recording layer. A reversible thermosensitive recording medium, characterized in that a compound, a color-developing agent and a sensitizer are mixed in the recording layer. 2. A leuco compound, a color-developing agent and a sensitizer are melted to prepare a solid composition, and the powder of the solid composition constitutes the above-mentioned leuco compound / development-degrading agent / sensitizer integrated powder. The reversible thermosensitive recording medium according to claim 1, wherein 3. A solid composition is prepared by melting at least one component of a leuco compound, a color-reducing agent and a sensitizer, and the remaining components are dissolved by the melt, and a powder of this solid composition is used to prepare the above leuco. 2. The reversible thermosensitive recording medium according to claim 1, wherein a compound / developer / color-reducing agent / sensitizer integrated powder is constituted. 4. A leuco compound, a color-developing agent and a sensitizer are dissolved in a cosolvent and the solvent is evaporated to prepare a solid composition, and the leuco compound and the color-developing agent are powdered with the solid composition. The reversible thermosensitive recording medium according to claim 1, characterized in that an agent / sensitizer integrated powder is constituted. 5. The reversible thermosensitive recording medium according to claim 2, wherein the solid composition is composed of a solid solution of a leuco compound, a color-reducing agent and a sensitizer. 6. The reversible thermosensitive recording medium according to claim 2, wherein the solid composition is composed of a eutectic mixture of a leuco compound, a color-reducing agent and a sensitizer. 7. The reversible sensitizer according to claim 1, wherein the sensitizer is composed of an amide compound selected from behenic acid amide, stearic acid amide, and palmitic acid amide. Thermal recording medium.