JPH06293183A - Composition for reversible heat sensitive recording medium and reversible heat sensitive recording sheet - Google Patents

Abstract

PURPOSE:To obtain the composition of reversible heat sensitive recording medium, forming a fresh picture with a high density and leaving no remaining image at the time of elimination, by a method wherein color developing and tone reducing agent, having an average grain size lower than a specified value, is blended with leuco compound having an average grain size smaller than the same of the color developing and tone reducing agent. CONSTITUTION:A composition for reversible heat sensitive recording medium is obtained by mixing a color developing and tone reducing agent, having an average grain size of 10mum or less, leuco compound, having an average grain size smaller than the same of the color developing and tone reducing agent and a binder resin such as polyvinyl alcohol or the like. The composition is molten or dispersed into water, organic solvent or the like to prepare a coating while the coating is applied on a substrate such as synthetic paper, plastic film or the like, then, is dried to form a recording layer and obtain a reversible heat sensitive recording sheet. A preferable example of this color developing and tone reducing agent is 2-amino-benzoic acid, 3-aminosalicylic acid, nicotinic acid, picolinic acid or the like, which is provided with an average grain size smaller than 10mum. On the other hand, a preferable example of the leuco compound is crystal violet lactone or the like, having an average grain size smaller than the same of the color developing and tone reducing agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible composition for a thermosensitive recording medium and a reversible thermosensitive sheet capable of forming an image using the composition. For more details,
The present invention relates to a reversible heat-sensitive recording composition which can be repeatedly written or erased by changing the way of applying heat energy, and a reversible heat-sensitive recording sheet using this composition.

[0002]

2. Description of the Related Art In recent years, information processing equipment such as word processors, personal computers, facsimiles, etc. have rapidly spread. Along with this, there is an increasing need for making hard copies of outputs from these terminals using printers. As a recording method for such a hard copy printer, various recording methods such as a heat-sensitive recording method, a thermal transfer method, an electrophotographic method, and an ink jet method have been proposed and put into practical use.

However, in these currently used recording systems, the recorded contents once output are semipermanently retained as they are, and the paper used for recording cannot be reused. Therefore, a large amount of recording paper is consumed in terminals of various information devices. In recent years, awareness of global environment conservation and resource protection has increased, and it has been required to use recyclable materials for recording media used in printers and the like. However, at present, a recording sheet capable of repeatedly performing image formation and erasing has not been obtained.

Furthermore, in recent years, payment of payments using credit cards, prepaid cards, etc. has become widespread, and so-called cashless has been progressing. The information recorded on these credit cards and prepaid cards is generally recorded as magnetic recording information, optical recording information, IC memory and the like. Information that is recorded on such a card and cannot be detected by the naked eye must be visible information for the convenience of the user.

From such a viewpoint, a recording sheet provided with a reversible thermosensitive recording material in which a low molecular weight organic compound such as a higher fatty acid is dispersed in a binder as a thermosensitive recording layer has been proposed and put into practical use (European Patent EP868). . However, due to the difference in crystal size, this recording sheet records heat as a cloudy state in a transparent state. In principle, sufficient image density and contrast cannot be obtained, and colorization is difficult. is there.

On the other hand, in International Publication WO / 11898 (Japanese Patent Application No. 2-505365), an amphoteric compound having a hydroxyl group and a carboxyl group and essentially an amino group is used as a color-developing and reducing agent. A composition capable of color development and decolorization by controlling energy to cause a chemical reaction has been proposed. This composition is applied on a substrate and is colored by heating for a short time (several milliseconds to tens of milliseconds) with a thermal head or the like, and decolorized when heated for a long time (several hundreds of milliseconds to several seconds). To do. Then, a color reversible thermosensitive recording medium which can be repeatedly colored and erased and has good visibility is obtained.

[0007]

However, although such a color recording medium has good visibility, it has a low color density and cannot be said to have sufficient performance in practical use. If the recording energy of the thermal head is increased in order to avoid such a drawback, the number of times of rewriting can be reduced, and the storability is deteriorated, which is not preferable.

[0008]

[Means for Solving the Problems] The present inventors have conducted extensive studies on such a composition in order to solve the above problems. As a result, the average particle size of the color-developing / reducing agent used in the composition for the reversible thermosensitive recording medium was 10 μm or less, and the average particle size of the leuco compound was smaller than that of the color-developing / color-reducing agent. The present invention has been completed based on the finding that the above problem can be solved.

The present invention is a composition for a reversible thermosensitive recording medium containing a color-developing agent and a leuco compound, wherein the color-developing agent has an average particle size of 10 μm or less, and the leuco compound has an average particle-size reducing color. The present invention provides a composition for a reversible thermosensitive recording medium, which is smaller than the average particle size of the agent.

The composition of the present invention contains a color-developing agent and a leuco compound as essential components. The color-developing / reducing agent used in the composition of the present invention may be a compound having at least one of a carboxyl group and a phenolic hydroxyl group and having an amino group or a pyridine skeleton.

As the color-developing agent used in the composition of the present invention, a compound having at least one of a carboxy group and a phenolic hydroxyl group and having an amino group or a pyridine skeleton is used. The developer / color-reducing agent used has an average particle size of 10 μm or less.

Examples of the developer / color-reducing agent having an amino group include:
2-aminobenzoic acid, 3-aminobenzoic acid, 4-aminobenzoic acid, 3-aminosalicylic acid, 4-aminosalicylic acid, 2-aminophenol, 3-aminophenol, 4
Examples thereof include aminophenol and the like, or those in which these amino groups are alkyl-substituted, but the present invention is not limited thereto.

Further, examples of the color-developing agent having a pyridine skeleton include nicotinic acid, isonicotinic acid, picolinic acid,
Pyridine-2,3-dicarboxylic acid, pyridine-2,4-
Dicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, 2-pyridone, 3-pyridone, 4-pyridone 2,3-pyridinediol, 2,4-pyridinediol, 2,5-pyridinediol, 2,6-pyridinediol, 3,4-pyridinediol, 3,5-pyridinediol, citrazine Examples thereof include acids, but not limited to these.

On the other hand, as the leuco compound used in the composition of the present invention, any conventionally known leuco compound that develops and decolorizes by heating can be used. For example, crystal violet lactone (blue), 2-anilino-3
-Methyl-6-dibutylaminofluorane (black), 2-
(2-chloroanilino) -6-dibutylaminofluorane
(Black), 2- (2-chloroanilino) -6-diethylaminofluorane (black), 2-N, N-dibenzylanilino-6
-Diethylaminofluorane (green), 6-diethylamino-benzo [a] -fluorane (red) and the like are mentioned, but not limited thereto.

The average particle size of the color-developing / reducing agent blended in the composition of the present invention is adjusted to 10 μm or less. If the particle size of the color-developing / reducing agent is larger than 10 μm, a sufficient color density cannot be obtained. Further, the average particle size of the leuco compound is adjusted to be smaller than the average particle size of the color-developing / reducing agent. If the average particle size of the leuco compound is more than the average particle size of the color-developing / reducing agent, sufficient color density cannot be obtained.

The particle size of these color-reducing agent and leuco compound may be adjusted by dispersing them with a disper, a ball mill, a triple roll, a dyno mill, etc., but by further pulverizing or devising in the synthesis stage, The average particle size can be further reduced. Further, if it can be dissolved, it may be dissolved. The surface particle size is a value obtained by the centrifugal sedimentation method.

To prepare the composition of the present invention, suitable binders soluble in water or an organic solvent can be used. Examples of such resins include polyvinyl alcohol, methyl cellulose, ethyl cellulose, cellulose acetate, nitrocellulose, polystyrene, polyvinyl chloride, polyvinyl acetate, saturated polyester, polymethyl methacrylate, polyethyl methacrylate, polymethyl methacrylate, poly Examples thereof include homo- or copolymers of ethyl acrylate, phenoxy, polycarbonate, polyurethane, polyvinyl butyral, etc., but are not limited thereto. Further, an appropriate modifier such as a lubricant can be added to the composition of the present invention.

The leuco compound is used in an amount of 1 part by weight of the color-developing and reducing agent.
It is desirable to add 0.1 to 1.5 parts by weight. If the compounding amount of the leuco compound is less than this, a sufficient concentration cannot be obtained, while if it is more than this, the erasing becomes insufficient. Further, the compounding amount of the binder is preferably 5 parts by weight or less with respect to 1 part by weight of the color developing and reducing agent. If it is more than this range, a sufficient concentration cannot be obtained.

To produce the reversible thermosensitive recording sheet of the present invention, the above composition is dissolved or dispersed in water, an organic solvent or the like to prepare a coating material, and the coating material is applied on a suitable support, The recording layer. At the time of coating, a suitable additive such as a thickener can be added to the paint. Any support can be used as the support, and examples thereof include paper, synthetic paper, and plastic film. Further, for the purpose of improving the adhesion of the recording layer, or as an antistatic property,
Various treatments may be performed on the support.

The coating method is not particularly limited, and various coating machines such as a bar coater, a bleed coater, an air knife coater, a gravure coater, a kiss coater, a fan ten coater and a fan ten reverse coater can be used.
The dry coating amount is preferably 3 to 10 g / m ² . Furthermore, a protective layer may be provided on the recording layer.

The recording layer of the composition of the present invention develops color by heating for a short time. The heating time required for color development is extremely short, and for example, heating with a thermal head for several milliseconds to several tens of milliseconds may be sufficient. The temperature may be the same as the heating temperature of a normal thermal head. Further, this recording layer is erased by heating for a long time. The long-time heating means heating for a long time as compared with the time required for color development, which is only several hundred milliseconds to several seconds. The temperature required for erasing is generally 80 to 150 ° C., and when erasing at this temperature, almost no unerased residue remains. Further, at a temperature lower than the color erasing temperature, color erasing is hardly performed and the color development information is sufficiently retained.

[0022]

[Function] Usually, a leuco compound is acidic and causes a color-developing reaction.
If it is basic, it causes a decoloring reaction. The acidic substance opens the lactone ring of the colorless leuco compound by the applied thermal energy to obtain a color. On the other hand, when the compound reaction in which the lactone ring is opened is brought into contact with a basic substance, the lactone ring is closed and the original colorless compound is obtained. The developer and decolorizer used in the composition of the present invention is an amphoteric substance, and has a carboxyl group or phenolic hydroxyl group showing acidity and an amino group showing basicity or an N atom of a pyridine ring in one molecule. When this color-developing / reducing agent comes into contact with the leuco compound and is heated, it is considered that the color-developing reaction and the color-erasing reaction proceed simultaneously.
However, the reaction rate is higher in the color development reaction, which is why
It is speculated that the colored state is maintained by heating with a thermal head or the like for a short time (several milliseconds to tens of milliseconds) and cooling. On the other hand, when heated for a long time (several hundreds of milliseconds or more), an equilibrium state is reached, but this state is considered to be a decolored state, and it is presumed that this state is maintained when cooled.

When the present inventors examined the presence states of the color-developing agent and the leuco compound in the composition in various systems,
It was found that the leuco compound adhered to the surface of the particles of the color-developing agent and the color was developed or erased on the surface of the particles of the color-developing agent. Therefore, the smaller the average particle size of the color-developing / reducing agent, the larger the surface area of the particles of the color-developing / reducing agent, and the higher the color density. Further, it is considered that the smaller the particle size of the leuco compound compared to the color-developing / reducing agent, the more effectively it contacts the surface of the color-developing / reducing agent.

[0024]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. In addition, the part in an Example sentence shows a weight part.

[Example 1] Liquid A

[Chemical 1] 10 parts Acrylic copolymer resin 7.5 parts (Dianal BR-60, manufactured by Mitsubishi Rayon Co., Ltd.) Toluene 40 parts Methyl ethyl ketone 10 parts B liquid

[Chemical 2] 10 parts Acrylic copolymer resin 7.5 parts (Dianal BR-60, manufactured by Mitsubishi Rayon Co., Ltd.) Toluene 40 parts Methyl ethyl ketone 10 parts The above solutions A and B were dispersed in a ball mill for 5 hours. The average particle size of the leuco compound is 1 μm,
The average particle size of the developer / color-reducing agent in the liquid B was 4 μm. Subsequently, 5 parts of solution A, 5 parts of solution B and 3.2 parts of toluene 0.8 parts of methyl ethyl ketone were thoroughly mixed to prepare a coating solution.
A reversible thermosensitive recording sheet was produced by applying a recording layer having a dry coating amount of 5 g / m ² using a wire bar on a white polyester film having a thickness of 188 μm with this coating solution.

[Example 2] Liquid A

[Chemical 3] 10 parts Polyvinyl butyral resin 10 parts (S-REC BM-1, Sekisui Chemical Co., Ltd.) Phosphate ester surfactant 1 part Ethanol 50 parts B liquid

[Chemical 4] 10 parts Polyvinyl butyral resin 10 parts (S-REC BM-1, manufactured by Sekisui Chemical Co., Ltd.) Ethanol 50 parts The above-mentioned solutions A and B were dispersed in a ball mill for 5 hours, and the average particle size of the leuco compound in solution A was measured. Is 3 μm,
The average particle size of the developer / color-reducing agent in the liquid B was 9 μm. Subsequently, 2 parts of solution A, 3 parts of solution B, and 3 parts of ethanol were sufficiently mixed to prepare a coating solution. This coating liquid was applied onto a high-quality paper having a basis weight of 60 g / m ² using a wire bar in the same manner as in Example 1 to apply a recording layer having a dry coating amount of 8 g / m ² ,
A reversible thermosensitive recording sheet was prepared.

[Example 3] Liquid A

[Chemical 5] 10 parts Vinyl chloride vinyl acetate copolymer resin 7.5 parts (VYHH, Union Carbide) tetrahydrofuran 10 parts B liquid

[Chemical 6] 10 parts Vinyl chloride vinyl acetate copolymer resin 7.5 parts (VYHH, manufactured by Union Carbide Co.) Tetrahydrofuran 10 parts The above-mentioned solutions A and B were dispersed in a ball mill for 5 hours respectively, and the average particle of the leuco compound in solution A was obtained. The diameter is 5 μm,
The average particle size of the developer / color-reducing agent in the liquid B was 10 μm. Subsequently, 1 part of solution A, 2 parts of solution B, and 2 parts of tetrahydrofuran were thoroughly mixed to prepare a coating solution. A reversible thermosensitive recording sheet was prepared by applying a recording layer having a dry coating amount of 5 g / m ² on a polypropylene synthetic paper having a thickness of 150 μm with a wire bar using this coating solution as in Example 1. .

[Comparative Example 1] The average particle size of the leuco compound in the liquid A is 1 μm, and the average particle size of the color-developing and reducing agent in the liquid B is 12 μm.
A reversible thermosensitive recording sheet was prepared in the same manner as in Example 1 except that [Comparative Example 2] The average particle size of the leuco compound in the liquid A is 10 μm.
m, a reversible thermosensitive recording sheet was prepared in the same manner as in Example 2 except that the average particle size of the developer / color-reducing agent in the liquid B was 9 μm. [Comparative Example 3] The average particle size of the leuco compound in the liquid A is 10 μm.
A reversible thermosensitive recording sheet was prepared in the same manner as in Example 3 except that the average particle size of the color-developing / reducing agent in the liquid B and solution B was 15 μm.

The reversible thermosensitive recording sheets of Examples 1 to 3 and Comparative Examples 1 to 3 were applied to a thermal head (applied power: 0.5 w / dot,
The results of printing with a pulse width of 2 milliseconds) are shown in Table 1. All the images obtained were clear. However,
As is clear from Table 1, Examples 1 to 3 are Comparative Examples 1 to 3.
The concentration was higher than that of, and the level was practically sufficient. Further, when these printed samples were put into a hot air dryer set at 120 ° C. for several seconds, the images of all printed samples were completely erased and the original recording sheet was returned. Further, when the same printing and erasing were repeated, it was confirmed that it has reproducibility and can be used as a reversible thermosensitive recording sheet.

[0030]

The composition for reversible thermosensitive recording media of the present invention can obtain a clear image at a high concentration, has almost no remaining unerased upon erasing, and can be almost completely erased, resulting in coloring and erasing. Can be repeated. This composition can be applied to the surface of a credit card, a prepaid card or the like and used for visualizing invisible conventional methods. Further, it can be applied to paper or a plastic sheet and used as an output sheet for electronic information.

Claims (5)

[Claims] 1. A composition for a reversible thermosensitive recording medium containing a color-developing agent and a leuco compound, wherein the color-developing agent has an average particle size of 10 μm or less, and the average particle size of the leuco compound is a color-developing agent. The composition for reversible thermosensitive recording media is characterized in that it is smaller than the average particle size. 2. The reversible thermosensitive recording medium composition according to claim 1, wherein the color-developing agent is a pyridine derivative having at least one substituent selected from a carboxyl group and a phenolic hydroxyl group. 3. The reversible thermosensitive recording medium composition according to claim 1, wherein the color-developing agent has at least one substituent selected from a carboxyl group and a phenolic hydroxyl group, and has an amino group or an alkylamino group. . 4. The reversible thermosensitive recording medium composition according to claim 1, wherein the leuco compound is a fluoran dye. 5. A reversible recording layer comprising a developer / decolorizer having an average particle size of 10 μm or less and a leuco compound having an average particle size smaller than the average particle size of the developer / reducer, provided on a substrate. Sensitive heat recording sheet.