JPH09295458A - Reversible thermosensitive coloring composition and reversible thermosensitive recording medium using that - Google Patents

Abstract

PROBLEM TO BE SOLVED: To erase color of a reversible thermosensitive recording medium at an especially high speed according to a wide range use condiction and environmental condition by keeping stable coloring properties and color erasing properties by a method wherein a phenol compound expressed by a specific formula as an electron acceptive compound is used. SOLUTION: A phenol compound expressed by the formula as an electron acceptive compound is used. In the formula, X indicates a bivalent group including a hetero atom, R expresses a 8 or higher C hydrocarbon which may have a substituent, and n indicates 1 to 3. R may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and may be composed of both of them. The aliphatic hydrocarbon group may be of linear chain or branched, and may have unsaturated bond. As the substituent fitted to the hydrocarbon group, there are a hydroxyl group, a halogen atom, an alkoxy group, etc. Further, in order to form colored recording, the compound is quenched after heating at a temperature wherein it is once mixed by being melted with a thermal head or the like. In order to erase the color, the compound is slowly cooled from the heated state, or heated to a temperature slightly lower than the coloring temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive coloring composition utilizing a coloring reaction between an electron-donating color-forming compound and an electron-accepting compound. The present invention also relates to a reversible thermosensitive recording medium capable of forming and erasing a color image by controlling the thermal energy using the reversible thermosensitive coloring composition.

[0002]

2. Description of the Related Art Conventionally, electron-donating color-forming compounds (hereinafter referred to as
Thermal recording media utilizing a color development reaction between a color former or a leuco dye and an electron-accepting compound (hereinafter also referred to as a developer) are widely known, such as facsimile machines, word processors, and scientific measuring instruments. Used in printers. However, these conventional recording media that have been put into practical use all have irreversible color development, and once recorded images cannot be erased and used repeatedly.

However, according to the patent publication, a recording medium capable of reversibly developing and erasing colors has been proposed. For example, Japanese Patent Laid-Open No. Sho 60-58 uses a combination of gallic acid and phloroglucinol as a developer. No. 193,691; JP-A-61-237684, wherein a compound such as phenolphthalein or thymolphthalein is used as a color developer. A recording layer contains a homogenous solution of a color developer, a color developer and a carboxylic acid ester. JP-A-62-138556 and JP-A-62-1
38568 and JP-A-62-140881, and JP-A-63-63163 using an ascorbic acid derivative as a developer.
-173684, JP-A-2-188293 and JP-A-2-18 using a salt of bis (hydroxyphenyl) acetic acid or gallic acid and a higher aliphatic amine as a color developer.
No. 8294, etc. are disclosed. However, the conventional reversible thermosensitive recording medium shown above has a problem in that it is compatible with the stability of color formation and the decolorization property, or in terms of the density of color formation and the stability in repetition,
It is not satisfactory as a practical recording medium.

[0004] The present inventors have previously described Japanese Patent Application Laid-Open No. Hei 5-12436.
In JP-A-0, No. 0,058,032, an organic phosphoric acid compound, an aliphatic carboxylic acid compound or a phenol compound having a long-chain aliphatic hydrocarbon group is used as a color developing agent, and by combining this with a leuco dye which is a color developing agent, color development is achieved. Decoloring can be easily performed under heating / cooling conditions, and the colored state and decolored state can be maintained stably at room temperature, and the colored state and decolored state can be stably repeated. A reversible thermosensitive color-developing composition and a reversible thermosensitive recording medium using the same for a recording layer have been proposed. This has practical performance in terms of the balance between color stability and color erasure and color density, but it is also improved in terms of compatibility with a wider range of usage environments and the range of application of color erasure conditions. There was room to be. After that, use of a specific structure for a phenol compound having a long-chain aliphatic hydrocarbon group was proposed (Japanese Patent Laid-Open No. 6-210954), but this also had the same problem.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to maintain stable color development and erasability and to be able to handle a wide range of use conditions and environmental conditions. It is intended to provide a thermochromic composition and a reversible thermosensitive recording medium.

[0006]

SUMMARY OF THE INVENTION The inventors of the present invention have studied the reversible color-decoloring phenomenon of a composition of a color former and a color developer by using a color developer of a color developer having a long-chain aliphatic group. Considering that the balance between the ability to develop color and the cohesive force between molecules is important, compounds having various structures were examined. As a result, they have found that the above problem can be solved by using a phenol compound having a specific structure as a color developer.

That is, in a reversible thermosensitive coloring composition utilizing a coloring reaction of an electron-donating color-forming compound with an electron-accepting compound, in the present invention, a phenol represented by the following general formula (1) is used as the electron-accepting compound. A compound is used.

Embedded image In the formula, X represents a divalent group containing a hetero atom, and R represents a hydrocarbon group having 8 or more carbon atoms and optionally having a substituent. Moreover, n shows 1-3.

In the above general formula (I), R represents a hydrocarbon group which may have a substituent, which may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, or both of them. It may be a hydrocarbon group composed of Further, the aliphatic hydrocarbon group may be linear or branched, and may have an unsaturated bond. Examples of the substituent attached to the hydrocarbon group include a hydroxyl group, a halogen atom, and an alkoxy group. R
When the number of carbon atoms is 7 or less, the stability of color development and the decoloring property are deteriorated. Therefore, the number of carbon atoms is preferably 8 or more, and more preferably 11 or more.

X represents a divalent group containing a hetero atom, preferably

Embedded image Represents a divalent group having at least one group represented by Examples thereof include those shown in Table 1 below.

[0010]

[Table 1]

Further, it may be a divalent group further having one or more of the above groups via a hydrocarbon group such as alkylene. That is, a group represented by the general formula (2) having the structure shown below can be mentioned.

Embedded image Here, R ′ represents a divalent hydrocarbon group which may have a substituent, and this hydrocarbon group may be aliphatic or aromatic, and may be composed of both of them. Moreover, m represents the integer of 1-4. X repeated at this time
And R'may be the same or different.

More specific examples of the color developer in the invention include the compounds shown in Table 2, but the invention is not limited thereto.

[0013]

[Table 2- (1)]

[0014]

[Table 2- (2)]

[0015]

[Table 2- (3)]

[0016]

[Table 2- (4)]

[0017]

[Table 2- (5)]

[0018]

[Table 2- (6)]

[0019]

[Table 2- (7)]

[0020]

[Table 2- (8)]

[0021]

[Table 2- (9)]

The reversible thermosensitive color-forming composition of the present invention is basically composed of a combination of the color developer and the color-developing agent. The color former used in the present invention has an electron donating property and is itself a colorless or light-colored dye precursor (leuco dye), and is not particularly limited, and may be a conventionally known one such as a phthalide compound or an azaphthalide compound. , A fluoran compound, a phenothiazine compound, a leuco auramine compound, and the like. Specific examples of the color former are shown below.

Preferred color formers for use in the present invention include compounds represented by the following general formula (3) or (4).

Embedded image

Embedded image (However, R ₁ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ₂ represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group or an optionally substituted phenyl group. Substituent for the phenyl group Is a methyl group, an alkyl group such as an ethyl group, an alkoxy group such as a methoxy group or an ethoxy group, or a halogen atom, etc. R ₃ is a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, an alkoxy group or a halogen atom. R ₄ represents a hydrogen atom, a methyl group, a halogen atom or an optionally substituted amino group.
Examples of the substituent for the amino group include an alkyl group, an optionally substituted aryl group, and an optionally substituted aralkyl group. The substituents here are an alkyl group, a halogen atom, an alkoxy group, etc.). Specific examples of such a color former include, for example, the following compounds.

2-anilino-3-methyl-6-diethylaminofluorane 2-anilino-3-methyl-6- (di-n-butylamino) fluorane, 2-anilino-3-methyl-6- (N
-N-propyl-N-methylamino) fluorane, 2-
Anilino-3-methyl-6- (N-isopropyl-N-
Methylamino) fluorane, 2-anilino-3-methyl-6- (N-isobutyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane , 2-anilino-3-
Methyl-6- (N-sec-butyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N
-N-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (N-iso-amyl-N-
Ethylamino) fluorane, 2-anilino-3-methyl-6- (Nn-propyl-N-isopropylamino)
Fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluorane, 2-anilino-3 -Methyl-6- (N
-Methyl-p-toluidino) fluorane, 2- (m-trichloromethylanilino) -3-methyl-6-diethylaminofluorane, 2- (m-trifluoromethylanilino) -3-methyl-6-diethylaminofluor Oran,
2- (m-trichloromethylanilino) -3-methyl-
6- (N-cyclohexyl-N-methylamino) fluorane, 2- (2,4-dimethylanilino) -3-methyl-6-diethylaminofluorane, 2- (N-ethyl-)
p-toluidino) -3-methyl-6- (N-ethylanilino) fluorane, 2- (N-ethyl-p-toluidino) -3-methyl-6- (N-propyl-p-toluidino) fluorane,

2-anilino-6- (Nn-hexyl-
N-ethylamino) fluoran, 2- (o-chloroanilino) -6-diethylaminofluoran, 2- (o-chloroanilino) -6-dibutylaminofluoran, 2-
(M-Trifluoromethylanilino) -6-diethylaminofluorane, 2- (p-acetylanilino) -6-
(Nn-amyl-Nn-butylamino) fluorane, 2-benzylamino-6- (N-ethyl-p-toluidino) fluorane, 2-benzylamino-6- (N-
Methyl-2,4-dimethylanilino) fluorane, 2-
Benzylamino-6- (N-ethyl-2,4-dimethylanilino) fluorane, 2-dibenzylamino-6-
(N-methyl-p-toluidino) fluoran, 2-dibenzylamino-6- (N-ethyl-p-toluidino) fluoran, 2- (di-p-methylbenzylamino) -6
-(N-ethyl-p-toluidino) fluoran, 2-
(Α-phenylethylamino) -6- (N-ethyl-p
-Toluidino) fluorane, 2-methylamino-6-
(N-methylanilino) fluorane, 2-methylamino-6- (N-ethylanilino) fluorane, 2-methylamino-6- (N-propylanilino) fluorane, 2
-Ethylamino-6- (N-methyl-p-toluidino)
Fluoran, 2-methylamino-6- (N-methyl-
2,4, -Dimethylanilino) fluorane, 2-ethylamino-6- (N-ethyl-2,4, -dimethylanilino) fluorane, 2-dimethylamino-6- (N-methylanilino) fluorane, 2- Dimethylamino-6-
(N-ethylanilino) fluoran, 2-diethylamino-6- (N-methyl-p-toluidino) fluoran,
2-diethylamino-6- (N-ethyl-p-toluidino) fluorane, 2-dipropylamino-6- (N-methyl-anilino) fluorane, 2-dipropylamino-
6- (N-ethyl-anilino) fluoran, 2-amino-6- (N-methylanilino) fluoran, 2-amino-6- (N-ethylanilino) fluoran, 2-amino-6- (N-propylanilino) Fluoran, 2-amino-6- (N-methyl-p-toluidino) fluoran,
2-amino-6- (N-ethyl-p-toluidino) fluoran, 2-amino-6- (N-propyl-p-toluidino) fluoran, 2-amino-6- (N-methyl-p
-Ethylanilino) fluoran, 2-amino-6- (N
-Ethyl-p-ethylanilino) fluorane, 2-amino-6- (N-propyl-p-ethylanilino) fluorane, 2-amino-6- (N-methyl-2,4-dimethylanilino) fluorane, 2-amino -6- (N-Ethyl-2,4-dimethylanilino) fluorane, 2-amino-6- (N-propyl-2,4-dimethylanilino)
Fluorane, 2-amino-6- (N-methyl-p-chloroanilino) fluorane, 2-amino-6- (N-ethyl-p-chloroanilino) fluorane, 2-amino-6
-(N-propyl-p-chloroanilino) fluorane,

2,3-Dimethyl-6-dimethylaminofluorane, 3-methyl-6- (N-ethyl-p-toluidino) fluorane, 2-chloro-6-diethylaminofluorane, 2-bromo-6-diethylamino Fluorane, 2-chloro-6-dipropylaminofluorane, 3
-Chloro-6-cyclohexylaminofluorane, 3-
Bromo-6-cyclohexylaminofluorane, 2-chloro-6- (N-ethyl-N-isoamylamino) fluorane, 2-chloro-3-methyl-6-diethylaminofluorane, 2-anilino-3-chloro-6. -Diethylaminofluorane, 2- (o-chloroanilino) -3-
Chloro-6-cyclohexylaminofluoran, 2-
(M-Trifluoromethylanilino) -3-chloro-6
-Diethylaminofluorane, 2- (2,3-dichloroanilino) -3-chloro-6-diethylaminofluorane, 1,2-benzo-6-diethylaminofluorane,
1,2-benzo-6- (N-ethyl-N-isoamylamino) fluoran, 1,2-benzo-6-dibutylaminofluoran, 1,2-benzo-6- (N-methyl-N
-Cyclohexylamino) fluorane, 1,2-benzo-6- (N-ethyl-toluidino) fluorane, and others.

Specific examples of other color formers preferably used in the present invention are as follows. 2-anilino-3-methyl-6- (N-2-ethoxypropyl-N-ethylamino) fluoran, 2- (p-chloroanilino) -6- (Nn-octylamino) fluoran, 2- (p- Chloroanilino) -6- (Nn-
Palmitylamino) fluorane, 2- (p-chloroanilino) -6- (di-n-octylamino) fluorane,
2-benzoylamino-6- (N-ethyl-p-toluidino) fluorane, 2- (o-methoxybenzoylamino) -6- (N-methyl-p-toluidino) fluorane, 2-dibenzylamino-4-methyl -6-diethylaminofluorane, 2-dibenzylamino-4-methoxy-6- (N-methyl-P-toluidino) fluorane,
2-benzylamino-4-methyl-6- (N-ethyl-
P-toluidino) fluorane, 2- (α-phenylethylamino) -4-methyl-6-diethylaminofluorane, 2- (p-toluidino) -3- (t-butyl) -6
-(N-methyl-p-toluidino) fluorane, 2-
(O-Methoxycarbonylamino) -6-diethylaminofluorane, 2-acetylamino-6- (N-methyl-p-toluidino) fluorane, 3-diethylamino-
6- (m-trifluoromethylanilino) fluorane,
4-Methoxy-6- (N-ethyl-p-toluidino) fluorane, 2-ethoxyethylamino-3-chloro-6
-Dibutylaminofluorane, 2-dibenzylamino-
4-chloro-6- (N-ethyl-p-toluidino) fluorane, 2- (α-phenylethylamino) -4-chloro-6-diethylaminofluorane, 2- (N-benzyl-p-trifluoromethylani) Rhino) -4-chloro-
6-diethylaminofluorane, 2-anilino-3-methyl-6-pyrrolidinofluorane, 2-anilino-3-
Chloro-6-pyrrolidinofluorane, 2-anilino-3
-Methyl-6- (N-ethyl-N-tetrahydrofurfurylamino) fluorane, 2-mesidino-4 ', 5'-
Benzo-6-diethylaminofluorane, 2- (m-trifluoromethylanilino) -3-methyl-6-pyrrolidinofluorane, 2- (α-naphthylamino) -3,4
-Benzo-4'-bromo-6- (N-benzyl-N-cyclohexylamino) fluorane, 2-piperidino-6
-Diethylaminofluorane, 2- (N-n-propyl-p-trifluoromethylanilino) -6-morpholinofluorane, 2- (di-Np-chlorophenyl-methylamino) -6-pyrrolidinoflu Oran, 2- (N-
n-propyl-m-trifluoromethylanilino) -6
Morpholinofluoran, 1,2-benzo-6- (N
-Ethyl-Nn-octylamino) fluoran, 1,
2-benzo-6-diallylaminofluoran, 1,2-
Benzo-6- (N-ethoxyethyl-N-ethylamino) fluorane,

Benzoleucomethylene blue, 2- [3,
6-bis (diethylamino)]-6- (o-chloroanilino) xanthyl benzoate lactam, 2- [3,6-bis (diethylamino)]-9- (o-chloroanilino)
Lactam xanthylbenzoate, 3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-bis (p-
Dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-
Bis (p-dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3- (2 -Methoxy-
4-dimethylaminophenyl) -3- (2-hydroxy-4,5-dichlorophenyl) phthalide, 3- (2-hydroxy-4-dimethylaminophenyl) -3- (2-
Methoxy-5-chlorophenyl) phthalide, 3- (2-
(Hydroxy-4-dimethoxyaminophenyl) -3-
(2-Methoxy-5-chlorophenyl) phthalide, 3-
(2-hydroxy-4-dimethylaminophenyl) -3
-(2-Methoxy-5-nitrophenyl) phthalide, 3
-(2-hydroxy-4-diethylaminophenyl)-
3- (2-methoxy-5-methylphenyl) phthalide,
3- (2-methoxy-4-dimethylaminophenyl)-
3- (2-hydroxy-4-chloro-5-methoxyphenyl) phthalide, 3,6-bis (dimethylamino) fluorene spiro (9,3 ')-6'-dimethylaminophthalide, 3- (1-ethyl) -2-Methylindole-3-
Yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-octyl-2-
Methylindol-3-yl) -3- (2-ethoxy-
4-diethylaminophenyl) -4-azaphthalide, 3
-(1-Ethyl-2-methylindol-3-yl)-
3- (2-ethoxy-4-diethylaminophenyl)-
7-azaphthalide, 3,3-bis (2-ethoxy-4-
Diethylaminophenyl) -4-azaphthalide, 3,3
-Bis (2-ethoxy-4-diethylaminophenyl)
-7-azaphthalide, 6'-chloro-8'-methoxy-
Benzindolino-spiropyran, 6'-bromo-2 '
-Methoxy-benzoindolino-spiropyran, and others.

The reversible thermosensitive coloring composition of the present invention can form a relatively colored state and a decolored state depending on the heating temperature and / or the cooling rate after heating. This basic coloring / decoloring phenomenon will be described. FIG. 1 shows the relationship between the coloring density of this composition and the temperature. When the temperature of the composition which is initially in the decolored state (A) is increased, color formation occurs at the temperature T ₁ at which melting starts, and the state changes to the molten color development state (B). When the color is rapidly cooled from the molten color-developed state (B), the temperature can be lowered to room temperature while maintaining the color-developed state, and the solid color-developed state (C) results. Whether or not this coloring state can be obtained depends on
Depends on the rate of temperature decrease from the molten state, bleaching occurs in the process of temperature decrease during slow cooling, and the state where the concentration is relatively lower than the same color erasing state (A) or rapid cooling color developing state (C) as in the beginning It is formed. On the other hand, when the temperature of the rapidly cooled coloring state (C) is increased again, decoloring occurs at a temperature T ₂ lower than the coloring temperature (D to E), and when the temperature is lowered from here, the same decoloring state (A) as that at the beginning is obtained. Return. The actual color-developing temperature and decoloring temperature vary depending on the combination of the color-developing agent and the color-developing agent used, and can be selected according to the purpose. Further, the density in the melted color state and the color density in the case of rapid cooling do not always coincide with each other, but often differ. For example, there is a composition in which almost no color develops in the heated molten state (B), but color develops in the process of rapid cooling, resulting in the formation of a stable color developed state (C) at room temperature. The present invention includes all compositions exhibiting these various coloring and decoloring properties.

In the composition of the present invention, the color-developed state (C) obtained by rapid cooling from the molten state is a state in which the color-developing agent and the color-developing agent are mixed in a state in which they can react with each other by molecules. This state is a state in which the color developer and the color forming agent aggregate to maintain the color development, and it is considered that the color formation is stabilized by the formation of the aggregate structure. On the other hand, the decolored state is a state where both are phase-separated. This state is a state in which molecules of at least one compound are aggregated to form a domain or crystallize, and it is a state in which the color former and the developer are separated and stabilized by aggregation or crystallization. Conceivable. In many cases, the present invention causes more complete decoloration due to phase separation of the two and crystallization of the color developer. In both the decolored state from the molten state by slow cooling and the decolored state by heating from the colored state shown in FIG. 1, the aggregation structure changes at this temperature, and phase separation and crystallization of the developer occur.

When the composition of the present invention is used as a reversible thermosensitive recording medium, color recording may be formed by heating with a thermal head or the like to a temperature at which it is melt-mixed and then rapidly cooled. The decoloring is performed by two methods: a method of gradually cooling from a heating state and a method of heating to a temperature slightly lower than a coloring temperature. However, these are the same in the sense that both are phase-separated, or at least one is temporarily kept at a temperature at which crystallization occurs. The rapid cooling in the formation of a color-developed state is for preventing the phase separation temperature or the crystallization temperature from being maintained. Here, the rapid cooling and the slow cooling are relative to one composition, and the boundary changes depending on the combination of the color former and the developer.

The ratio of the color-developing agent to the color-developing agent in the composition varies depending on the combination of the compounds used, but the molar ratio of the color-developing agent to the color-developing agent is generally 0.1 to 20.
The range is from 0.2 to 10, preferably from 0.2 to 10. If the amount of the developing agent is less or more than this range, the density of the color-developed state is lowered, which is not suitable for practical use.

The reversible thermosensitive recording medium of the present invention comprises a support and a recording layer containing the above composition as a main component. Paper, resin film, synthetic paper,
Any material such as metal foil, glass, or a composite thereof, which can hold the recording layer, may be used. Other recording layers such as a magnetic recording layer and a non-reversible thermosensitive recording layer may be formed on the support.

The recording layer may be of any type as long as the composition of the present invention is present, but generally a state in which a color former and a developer are finely and uniformly dispersed in a binder resin is used. The color former and the developer may form particles individually, but more preferably form a dispersed state as composite particles. This can be achieved by melting or dissolving the color former and the developer once. To form such a recording layer, a liquid obtained by dispersing and dissolving each material in a solvent, or a liquid obtained by mixing and dispersing or dissolving each material in a solvent is applied to a support and dried. Done by The color former and the developer can be used by being encapsulated in microcapsules.

In the reversible thermosensitive recording medium of the present invention, if necessary, an additive for improving or controlling the coating characteristics of the recording layer and the coloring and decoloring characteristics can be used. Examples of these additives include a dispersant, a surfactant, a conductive agent, a filler, a lubricant, an antioxidant, a light stabilizer, an ultraviolet absorber, a color development stabilizer, and a decolorization accelerator.

As the binder resin used for forming the recording layer, for example, polyvinyl chloride, polyvinyl acetate,
Vinyl chloride vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polyacrylic acid ester, polymethacrylic acid ester, acrylic acid copolymer, maleic acid Examples thereof include copolymers, polypinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, and starches. The role of these binder resins is to maintain a state in which the materials of the composition are uniformly dispersed without bias due to the application of heat for recording and erasing. Therefore, it is preferable to use a resin having high heat resistance as the binder resin. For example, the binder resin may be cross-linked by heat, ultraviolet rays, electron beams, or the like.

The reversible thermosensitive recording medium of the present invention basically has the above-mentioned recording layer provided on a support, but in order to improve the characteristics as a recording medium, a protective layer, an adhesive layer,
An intermediate layer, an undercoat layer, a back coat layer and the like can be provided.

In printing using a thermal head, the surface of the recording layer may be deformed due to heat and pressure, and so-called dents may be formed. In order to prevent this, it is preferable to provide a protective layer on the surface. For the protective layer, in addition to polyvinyl alcohol, styrene maleic anhydride copolymer, carboxy-modified polyethylene, melamine-formaldehyde resin, urea-formaldehyde resin, UV curable resin and electron beam curable resin can be used. Further, an additive such as an ultraviolet absorber can be contained in the protective layer.

An intermediate layer is provided between the recording layer and the protective layer for the purpose of improving the adhesiveness, preventing deterioration of the recording layer by coating the protective layer, and preventing migration of additives in the protective layer to the recording layer. Is also preferable. Further, it is preferable to use a resin having low oxygen permeability for the protective layer and the intermediate layer provided on the recording layer. This makes it possible to prevent or reduce the oxidation of the color former and the color developer in the recording layer.

In order to effectively utilize the applied heat,
A heat-insulating undercoat layer can be provided between the support and the recording layer. The heat insulating layer can be formed by applying organic or inorganic fine hollow particles using a binder resin. An undercoat layer may be provided for the purpose of improving the adhesion between the support and the recording layer and preventing the penetration of the recording layer material into the support.

For the intermediate layer and the undercoat layer, the same resin as the resin for the recording layer can be used. Further, the protective layer, the intermediate layer, the recording layer and the undercoat layer include calcium carbonate, magnesium carbonate, titanium oxide,
A filler such as silicon oxide, aluminum hydroxide, kaolin, and talc can be contained. In addition, a lubricant, a surfactant, a dispersant and the like can be contained.

In order to form a color image using the reversible thermosensitive recording medium of the present invention, it is sufficient that the color image is heated once above the color development temperature and then rapidly cooled. In particular,
For example, when the recording layer is heated for a short time with a thermal head or laser light, the recording layer is locally heated, so that the heat is immediately diffused and rapid cooling occurs, so that the coloring state can be fixed. On the other hand, in order to erase the color, it may be heated and cooled for a relatively long time using an appropriate heat source, or may be temporarily heated to a temperature slightly lower than the coloring temperature. If the recording medium is heated for a long time, the temperature of a wide area of the recording medium rises, and the subsequent cooling is slowed down. As a heating method in this case, a heat roller, a heat stamp, hot air, or the like may be used, or heating may be performed for a long time using a thermal head. In order to heat the recording layer to the decoloring temperature range, the applied energy may be slightly reduced from that at the time of recording, for example, by adjusting the applied voltage and the pulse width to the thermal head. With this method,
Recording and erasing can be done only with the thermal head, and so-called overwriting becomes possible. Of course, it can be erased by heating to a decoloring temperature range by a heat roller or a heat stamp.

[0043]

The present invention will be described in more detail with reference to the following examples. In the examples, “parts” and “%” are based on weight.

Example 1 2-anilino-3-methyl-6-dibutylaminofluorane was used as the color-developing agent, and the specific compound No. 4 was used to make a composition of the present invention as follows. First, the color former and the developer were weighed so as to have a mixing ratio (molar ratio) of 1: 1 and pulverized and mixed in a mortar. A glass plate having a thickness of 1.2 mm is placed on a hot plate at a temperature of 210
Heated to ° C. Subsequently, a cover glass was put over the molten mixture, the melt was spread to a uniform thickness, and immediately the whole glass plate was immersed in ice water prepared for rapid cooling. Immediately after cooling, remove from ice water, remove attached water,
A composition of the present invention that formed a thin film was obtained. Next, when the composition sample in the above-mentioned colored state was placed on a hot plate heated to 110 ° C., the color was instantaneously erased. When this decolorized composition sample was heated again to 210 ° C., it turned black. From this, it was confirmed that the composition of the present invention had a repeating property of coloring and decoloring. In a similar manner, compound N
o. 7, and No. The repeating characteristics of color development and decoloration were also confirmed for the composition using No. 8.

Example 2 The following composition was pulverized and dispersed using a ball mill to a particle size of 1 to 4 μm to prepare a recording layer coating solution. 2-anilino-3-methyl-6-dibutylaminofluorane 2 parts Developer shown in Table 3 8 parts Vinyl chloride-vinyl acetate copolymer (VYHH manufactured by Union Carbide) 10 parts Methyl ethyl ketone 45 parts Toluene 45 parts The recording layer coating solution having the above composition was applied onto a polyester film having a thickness of 100 μm using a wire bar and dried to prepare a reversible thermosensitive recording medium of the present invention having a recording layer having a thickness of about 6.0 μm.

The obtained recording medium was printed with a thermal head of 8 dots / mm under the conditions of an applied voltage of 13.3 V and an applied pulse width of 1.2 ms to obtain a colored image. The optical density of this color image was measured using a Macbeth densitometer RD-914. Next, the color-developed recording medium was heated at the erasing temperature shown in Table 3 for 1 second using a thermal gradient tester, and then the density was measured. Table 3 shows the results. Table 3 shows that the recording medium of the present invention decolored to the same level as the background density by heating for 1 second. Further, it can be seen that printing and erasing are stably repeated. Therefore, it has been clarified that the recording medium of the present invention is a reversible thermosensitive recording medium that can be erased at high speed.

Comparative Example Eicosylphosphonic acid was used in place of the developer of the present invention, and 2-anilino-3-methyl-6- was used as a leuco dye.
A reversible thermosensitive recording medium was prepared in the same manner as in Example 2 except that (N-ethyl-Np-tolylamino) fluorane was used.

This recording medium was printed and erased in the same manner as in Example 2. In this recording medium, as shown in Table 3, the color was not erased to the initial background density by heating for 1 second, and an unerased portion was left. In addition, this colored recording medium required heating for one minute to reduce it to 0.16, which is almost equal to the background density.

[0049]

[Table 3]

[0050]

Since the reversible thermosensitive coloring composition of the present invention can be repeatedly formed into a stable coloring state and a good decoloring state, the reversible thermosensitive recording medium using the same can form a high-contrast image. Erasing is enabled by an easy operation.
Further, the color image is stable under normal use conditions, has high durability against repeated recording and erasing, and can provide a rewritable recording medium with high practicability which enables erasing at a high speed.

[Brief description of drawings]

FIG. 1 is a diagram showing color developing / decoloring characteristics of a reversible thermosensitive color developing composition of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromi Furuya 1-3-3 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd. (72) Katsuji Maruyama 1-3-6 Nakamagome, Ota-ku, Tokyo In stock company Ricoh (72) Inventor Kyoji Tsutsui 1-3-6 Nakamagome, Ota-ku, Tokyo In-house company Ricoh (72) Katsuyuki Sugiyama 4-66-1 Horikiri, Katsushika-ku, Tokyo Miyoshi Oil & Fat Co., Ltd. In-house (72) Inventor Katsuaki Kokubo 4-66-1 Horikiri Katsushika-ku, Tokyo Miyoshi Yushi Co., Ltd. (72) Inventor Katsuhisa Kamio 4-6-16-1 Horikiri Katsushika, Tokyo Miyoshi Yushi Co., Ltd. In-house (72) Inventor Kazuo Hosoda 4-66-1 Horikiri, Katsushika-ku, Tokyo Inside Miyoshi Oil & Fat Co., Ltd. (72) Inventor Masafumi, Masafumi 4-chome Horikiri, Katsushika-ku, Tokyo Sixty-six number, item Millau shea oils and fats in the Corporation

Claims (2)

[Claims] 1. A reversible sensation capable of forming a relatively colored state and a relatively decolorized state by using an electron-donating color-forming compound and an electron-accepting compound, depending on a difference in heating temperature and / or a cooling rate after heating. A reversible thermosensitive coloring composition, characterized in that a phenol compound represented by the following general formula (1) is used as an electron-accepting compound in the thermochromic composition. Embedded image In the formula, X represents a divalent group containing a hetero atom, and R represents a hydrocarbon group having 8 or more carbon atoms and optionally having a substituent. Moreover, n shows 1-3. 2. A reversible thermosensitive recording medium characterized in that a recording layer containing the reversible thermosensitive coloring composition of claim 1 as a main component is provided on a support.