JPH106655A - Reversible thermosensitive color developing composition and reversible recording medium using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible thermosensitive color developing composition and a reversible thermosensitive recording medium which retain stable color developing and discharging properties and can deal with a wide range of use and environmental conditions. SOLUTION: This reversible thermosensitive color developing composition consists of an electron-donative and coloring compound and an electron-receptive compound and forms relatively a color developed state and a decolored state by a difference in the heating temperature and the cooling rate after heating. A phenolic compound expressed by formula is used as the electron-receptive compound. In the formula, X is a divalent group containing a hetero atom; R is a hydrocarbon group with at least, eight carbon atoms; and n is an integer of 1-3.

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, an electron-donating color-forming compound (hereinafter, referred to as an electron-donating color-forming compound) has been proposed.
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.

On the other hand, a recording medium capable of reversibly performing coloring and decoloring has also been proposed in patent publications and the like. For example, Japanese Patent Application Laid-Open No. 60-193691 discloses gallic acid and phlorog as developing agents. Japanese Unexamined Patent Publication No. Sho 62-138556 and Japanese Unexamined Patent Publication No. Sho 62-138556 disclose the use of a compound such as phenolphthalein or thymolphthalein as a color developing agent. -138568 and JP-A-62
JP-A-140881 discloses that a recording layer contains a homogeneous solution of a color former, a developer and a carboxylic acid ester, and JP-A-63-173684 discloses that an ascorbic acid derivative is used as a developer. JP-A-2-188293 and JP-A-2-188294 disclose the use of bis (hydroxyphenyl) acetic acid or a salt of gallic acid with a higher aliphatic amine as a developer, respectively. Various techniques have been disclosed. However,
The conventional reversible thermosensitive recording media disclosed in these publications have problems in terms of compatibility between color stability and decoloration, or stability in color density and repetition. Is not satisfactory.

[0004] The present inventors have previously described Japanese Patent Application Laid-Open No. Hei 5-12436.
No. 0, use an organic phosphoric acid compound having a long-chain aliphatic hydrocarbon group, an aliphatic carboxylic acid compound or a phenol compound as a color developer, and combine this with a leuco dye as a color former to form color and decolorize. Can be easily performed by heating and cooling conditions, and its color development and decoloration can be stably maintained at room temperature. A thermochromic composition and a reversible thermosensitive recording medium using the same in 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. Thereafter, the use of a specific structure for a phenol compound having a long-chain aliphatic hydrocarbon group was proposed (Japanese Patent Application Laid-Open No. 6-210954), but this also had a similar problem.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a reversible thermosensitive coloring composition and a reversible thermosensitive recording medium which maintain stable coloring and decoloring properties and can be used in a wide range of use conditions and environmental conditions. To provide.

[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 phenolic compound having a specific structure as a color developer.

Therefore, according to the present invention, in a reversible thermosensitive coloring composition utilizing a coloring reaction of an electron-donating color-forming compound with an electron-accepting compound, the following general formula (1) is used as the electron-accepting compound in the present invention. And a reversible thermosensitive recording medium having a recording layer containing the color forming composition as a main component provided on a support.

[0008]

Embedded image In the general formula (1), X represents a divalent group containing a hetero atom.
R represents a hydrocarbon group which may have a substituent, and may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group;
Further, a hydrocarbon group composed of both of them may be used. 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, and an alkoxy group. When the number of carbon atoms in R is 7 or less, the stability of color formation and the decoloring property are reduced, so the number of carbon atoms is preferably 8 or more, and more preferably 11 or more. N represents 1 to 3.
X represents a divalent group containing a hetero atom, preferably

[0009]

Embedded image Represents a divalent group having at least one group represented by Examples include the following.

[0010]

Embedded image Further, it may be a divalent group having at least one of the above groups via a hydrocarbon group such as alkylene. That is, compounds having the structures shown below are exemplified.

[0011]

Embedded image Here, R 'represents a divalent group and a bond similar to those of R described above, and m represents an integer of 1 to 4. X and R 'repeated at this time may be the same or different. More specific examples of the color developer in the present invention include the compounds shown in Table 1, but are not limited thereto.

[0012]

[Table 1-1]

[0013]

[Table 1-2]

[0014]

[Table 1-3]

[0015]

[Table 1-4]

[0016]

[Table 1-5]

[0017]

[Table 1-6]

[0018]

[Table 1-7]

[0019]

[Table 1-8]

[0020]

[Table 1-9]

[0021]

[Table 1-10]

[0022]

[Table 1-11] The reversible thermosensitive color-forming composition of the present invention is basically constituted by combining the above-mentioned developer and color former. The color former used in the present invention has an electron donating property, and is itself a colorless or pale color dye precursor (leuco dye), and is not particularly limited, and may be a conventionally known one such as a triphenylmethanephthalide compound. Fluoran compounds, phenothiazine compounds, leuco auramine compounds, indolinophthalide compounds and the like. The coloring agent is shown below. Preferred color formers used in the present invention include compounds of the following general formula (3) or (4).

[0023]

Embedded image

[0024]

Embedded image

(Where R ₁ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ₂ is an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group or an optionally substituted phenyl group. Examples of the substituent include an alkyl group such as a methyl group and an ethyl group, an alkoxy group such as a methoxy group and an ethoxy group, and a halogen, etc. R ₃ represents hydrogen, an alkyl group having 1 to 2 carbon atoms, an alkoxy group, or a halogen. R ₄ represents hydrogen, methyl, halogen, or an amino group which may be substituted, for example, an alkyl group, an aryl group which may be substituted, or a substituted group; It shows a good aralkyl group, wherein the substituent is an alkyl group, a halogen, an alkoxy group, etc.) Specific examples of such a coloring agent include the following compounds. And the like.

2-anilino-3-methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6-di (n-butylamino) fluoran, 2-anilino-3-
Methyl-6- (Nn-propyl-N-methylamino)
Fluoran, 2-anilino-3-methyl-6- (N-isopropyl-N-methylamino) fluoran, 2-anilino-3-methyl-6- (N-isobutyl-N-methylamino) fluoran, 2-anilino- 3-methyl-6
(Nn-amyl-N-methylamino) fluoran, 2
-Anilino-3-methyl-6- (N-sec-butyl-
N-ethylamino) fluoran, 2-anilino-3-methyl-6- (Nn-amyl-N-ethylamino) fluoran, 2-anilino-3-methyl-6- (N-isoamyl-N-ethylamino ) Fluoran, 2-anilino-
3-methyl-6- (Nn-propyl-N-isopropylamino) fluoran, 2-anilino-3-methyl-6
-(N-cyclohexyl-N-methylamino) fluoran,

2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluoran, 2-anilino-3
-Methyl-6- (N-methyl-p-toluidino) fluoran, 2- (m-trichloromethylanilino) -3-methyl-6-diethylaminofluoran, 2- (m-trifluoromethylanilino) -3 -Methyl-6-diethylaminofluoran, 2- (m-trifluoromethylanilino) -3-methyl-6- (N-cyclohexyl-N-methylamino) fluoran, 2- (2,4-dimethylanilino) -3-methyl-6-diethylaminofluoran,
2- (N-ethyl-p-toluidino) -3-methyl-6
-(N-ethylanilino) fluoran, 2- (N-ethyl-p-toluidino) -3-methyl-6- (N-propyl-p-toluidino) fluoran, 2-anilino-6
(Nn-hexyl-N-ethylamino) fluoran,
2- (o-chloroanilino) -6-diethylaminofluoran, 2- (o-bromoanilino) -6-diethylaminofluoran, 2- (o-chloroanilino) -6-dibutylaminofluoran,

2- (o-bromoanilino) -6-dibutylaminofluoran, 2- (m-trifluoromethylanilino) -6-diethylaminofluoran, 2- (p-
Acetylanilino) -6- (Nn-amyl-Nn-
Butylamino) fluoran, 2-benzylamino-6-
(N-ethyl-p-toluidino) fluoran, 2-benzylamino-6- (N-methyl-2,4-dimethylanilino) fluoran, 2-benzylamino-6- (N-ethyl-2,4-dimethyl Anilino) fluoran, 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) fluoran, 2-
Methylamino-6- (N-methylanilino) fluoran, 2-methylamino-6- (N-ethylanilino) fluoran, 2-methylamino-6- (N-propylanilino) fluoran, 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)
Fluoran, 2-dimethylamino-6- (N-methylanilino) fluoran, 2-dimethylamino-6- (N-
Ethylanilino) fluoran, 2-diethylamino-6
-(N-methyl-p-toluidino) fluoran, 2-diethylamino-6- (N-ethyl-p-toluidino) fluoran, 2-dipropylamino-6- (N-methyl-
Anilino) fluoran, 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) fluoran, 2-amino-6- (N-propyl-p-ethylanilino) fluoran, 2-amino-6- (N-methyl-2,4-dimethylanilino) fluoran,

2-amino-6- (N-ethyl-2,4-
Dimethylanilino) fluoran, 2-amino-6- (N
-Propyl-2,4-dimethylanilino) fluoran,
2-amino-6- (N-methyl-p-chloroanilino)
Fluoran, 2-amino-6- (N-ethyl-p-chloroanilino) fluoran, 2-amino-6- (N-propyl-p-chloroanilino) fluoran, 2,3-dimethyl-6-dimethylaminofluoran, 3 -Methyl-6
-(N-ethyl-p-toluidino) fluoran, 2-chloro-6-diethylaminofluoran, 2-bromo-6
-Diethylaminofluoran, 2-chloro-6-dipropylaminofluoran, 3-chloro-6-cyclohexylaminofluoran, 3-bromo-6-cyclohexylaminofluoran, 2-chloro-6- (N-ethyl- N
-Isoamylamino) fluoran, 2-chloro-3-methyl-6-diethylaminofluoran, 2-anilino-
3-chloro-6-diethylaminofluoran, 2- (o
-Chloroanilino) -3-chloro-6-cyclohexylaminofluoran, 2- (m-tolufluoromethylanilino) -3-chloro-6-diethylaminofluoran,

2- (2,3-dichloroanilino) -3-
Chloro-6-diethylaminofluoran, 1,2-benzo-6-diethylaminofluoran, 1,2-benzo-
6- (N-ethyl-N-isoamylamino) fluoran, 1,2-benzo-6-dibutylaminofluoran,
1,2-benzo-6- (N-methyl-N-cyclohexylamino) fluoran, 1,2-benzo-6- (N-ethyl-N-toluidino) fluoran, 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) fluoran, 2- (p-chloroanilino) -6- (di-n-octylamino) fluoran,
2-benzoylamino-6- (N-ethyl-p-toluidino) fluoran, 2- (o-methoxybenzoylamino) -6- (N-methyl-p-toluidino) fluoran, 2-dibenzylamino-4-methyl -6-diethylaminofluoran, 2-dibenzylamino-4-methoxy-6- (N-methyl-p-toluidino) fluoran,
2-benzylamino-4-methyl-6- (N-ethyl-
p-Toluidino) fluoran, 2- (α-phenylethylamino) -4-methyl-6-diethylaminofluoran, 2- (p-toluidino) -3- (t-butyl) -6
-(N-methyl-p-toluidino) fluoran,

2- (o-methoxycarbonylanilino)
-6-diethylaminofluoran, 2-acetylamino-6- (N-methyl-p-toluidino) fluoran, 3
-Diethylamino-6- (m-trifluoromethylanilino) fluoran, 4-methoxy-6- (N-ethyl-
p-Toluidino) fluoran, 2-ethoxyethylamino-3-chloro-6-dibutylaminofluoran, 2-
Dibenzylamino-4-chloro-6- (N-ethyl-p
-Toluidino) fluoran, 2- (α-phenylethylamino) -4-chloro-6-diethylaminofluoran, 2- (N-benzyl-p-trifluoromethylanilino) -4-chloro-6-diethylaminofluoran , 2
-Anilino-3-methyl-6-pyrrolidinofluoran,
2-anilino-3-chloro-6-pyrrolidinofluoran, 2-anilino-3-methyl-6- (N-ethyl-N
-Tetrahydrofurfurylamino) fluoran, 2-mesidino-4 ', 5'-benzo-6-diethylaminofluoran, 2- (m-trifluoromethylanilino) -3-
Methyl-6-pyrrolidinofluoran, 2- (α-naphthylamino) -3,4-benzo-4′-bromo-6- (N
-Benzyl-N-cyclohexylamino) fluoran,

2-piperidino-6-diethylaminofluoran, 2- (Nn-propyl-p-trifluoromethylanilino) -6-morpholinofluoran, 2- (di-Np-chlorophenyl-methyl) Amino) -6-pyrrolidinofluoran, 2- (Nn-propyl-m-trifluoromethylanilino) -6-morpholinofluoran, 1,2-benzo-6- (N-ethyl-N- n-octylamino) fluorane, 1,2-benzo-6-diallylaminofluoran, 1,2-benzo-6- (N-ethoxyethyl-N-ethylamino) fluoran, benzoleucomethylene blue, 2- [3, 6-bis (diethylamino)]-6- (o-chloroanilino) xanthylbenzoate lactam, 2- [3,6-bis (diethylamino)]-9- (o-chloro Anilino) xanthylic benzoate lactam, 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) fluorenespiro (9,3 ′)-
6'-dimethylaminophthalide, 3- (1-ethyl-2
-Methylindol-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-methylindole-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-benzoindolino-spiropyran, 6'-bromo-2'-methoxy-benzoindolino-spiropyran, and others.

The reversible thermosensitive coloring composition of the present invention is capable of forming a relatively colored state and a decolored state due to a difference in heating temperature and / or cooling rate after heating. This basic coloring / decoloring phenomenon will be described. FIG. 1 shows the relationship between the color density and the temperature of this composition. Introduction gradually heated a composition in the decolorized state (A), a molten colored state occurs coloration at temperatures T ₁ begins to melt (B). When the color is rapidly cooled from the melted color development state (B), the temperature can be lowered to room temperature while maintaining the color development state, and a solid color development state (C) is obtained. Whether or not this color-developed state is obtained depends on the rate of temperature decrease from the molten state. In the case of slow cooling, decoloration occurs in the process of temperature decrease, and the same decolored state (A) or quenched color state (C) as at the beginning. A) is formed with a relatively lower concentration. On the other hand, rapidly cooled colored state (C) is again raised gradually and decoloration occurs with a color temperature lower than temperature T ₂ and (E from D), the same colorless state, including when the temperature decreases from which (A)
Return to The actual color forming temperature and color erasing temperature can be selected according to the purpose because they vary depending on the combination of the color developer and the color developing agent used. In addition, the temperature in the molten color development state and the color density after quenching do not always match, and may differ.

In the composition of the present invention, the color-developed state (C) obtained by quenching from the molten state is a state in which the developer and the color-developing agent are mixed in a state where they can react with each other in a molecule. It often forms a state. 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 crystallized, and it is considered that the color former and the developer are separated and stabilized by aggregation or crystallization. Can be In many cases, the present invention causes more complete decoloration due to phase separation of the two and crystallization of the color developer. In the decoloring by slow cooling from the molten state and the decoloring by raising the temperature 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 the mixture to a temperature at which it is melted and mixed once by a thermal head or the like, followed by rapid cooling. 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, they are the same in the sense that they both phase-separate or temporarily hold at a temperature at which at least one crystallizes. 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 varies depending on the combination of the color former and the developer.

The ratio of the color former to the color developer in the composition can be varied in an appropriate range depending on the combination of the compounds used, but the molar ratio of the color developer to the color developer is 0.1 to 20. It is in the range, preferably in the range of 0.2 to 10. If the amount of the developer is smaller or larger than this range, the density of the color-developed state is reduced, which is problematic.

The reversible thermosensitive recording medium of the present invention comprises a support and a recording layer containing the above composition as a main component. The support is paper, resin film, synthetic paper, metal foil, glass, or a composite thereof, and may be any as long as it can hold the recording layer.

The recording layer may be of any type as long as the composition of the present invention is present. In general, a state in which a color former and a color 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, an additive for improving or controlling the coating properties of the recording layer and the coloring and decoloring properties can be used as necessary. These additives include, for example, dispersants, surfactants, conductive agents, fillers, lubricants, antioxidants, light stabilizers, ultraviolet absorbers, color stabilizers, and decolorization accelerators.

Examples of the binder resin used for forming the recording layer include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, polyester, and aromatic polyester. , Polyurethane, polycarbonate, polyacrylate, polymethacrylate, acrylic acid copolymer, maleic acid copolymer, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, starches and the like. 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. However, in order to improve the characteristics of the 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, resulting in so-called dents. In order to prevent this, it is preferable to provide a protective layer on the surface. For the protective layer, besides polyvinyl alcohol, styrene-maleic anhydride copolymer, carboxy-modified polyethylene, melamine-formaldehyde resin, urea-formaldehyde resin, ultraviolet curable resin, electron beam curable resin and the like 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 between the recording layer and the protective layer, preventing deterioration of the recording layer due to coating of the protective layer, and preventing migration of additives in the protective layer to the recording layer. It is also preferred. 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. It is possible to prevent or reduce oxidation of the color former and the developer in the recording layer.

Further, a heat insulating undercoat layer can be provided between the support and the recording layer in order to effectively use the applied heat. 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 resins as those for the recording layer described above can be used. The protective layer, the intermediate layer, the recording layer, and the undercoat layer may contain fillers such as calcium carbonate, magnesium carbonate, titanium oxide, silicon oxide, aluminum hydroxide, kaolin, and talc. In addition, a lubricant, a surfactant dispersant and the like can be contained.

In order to form a color image using the reversible thermosensitive recording medium of the present invention, the color image may be heated once to a color development temperature and then rapidly cooled. In particular,
For example, if 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, heating may be performed by using an appropriate heat source for a relatively long time to cool, or heating may be temporarily performed 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 performed only by the thermal head, and so-called overwriting can be performed. Of course, it is also possible to erase the image by heating it to the decoloring temperature range using a heat roller or a heat stamp.

[0051]

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-dibutylaminofluoran was used as a color former, and 1- (4'-
A composition of the present invention was made using (hydroxyphenylmethylidene) -4-octadecylsemicarbazide as follows. First, a color former and a 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 170
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, the composition sample in the above color-developed state was
When placed on a hot plate heated to 00 ° C., the color was instantly erased. When the decolored composition sample was heated to 170 ° C. again, it turned black. From this, it was confirmed that the composition of the present invention had a repeating property of coloring and decoloring.

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 coating solution for a recording layer. 2-anilino-3-methyl-6-dibutylaminofluorane 2 parts 1- (4'-hydroxyphenylmethylidene) -4-octadecylsemicarbazide 8 parts Vinyl chloride-vinyl acetate copolymer (VYHH manufactured by Union Carbide Co., Ltd.) 10 parts Methyl ethyl ketone 45 parts Toluene 45 parts The recording layer coating solution of the above composition is applied on a 100 μm-thick polyester film using a wire bar, and dried to have a recording layer having a thickness of about 6.0 μm. A reversible thermosensitive recording medium was produced.

Example 3 In place of 1- (4'-hydroxyphenylmethylidene) -4-octadecylsemicarbazide in Example 2, N-
A reversible thermosensitive recording medium was produced in the same manner as in Example 2 except that (4'-hydroxyphenylmethylidene) -N'-octadecyloylhydrazide was used.

These recording media were 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 milliseconds to obtain a colored image. The optical density of this color image was measured using a Macbeth densitometer RD-914. Table 2 shows the measurement results. Next, the color-developed recording medium was erased at 180 ° C. for 1 second using a thermal gradient tester, and the erase density was measured. Further, the above-mentioned coloring and erasing operations were repeated 10 times, and the reversibility of coloring was examined. As a result, it was confirmed that the coloring and erasing could be repeated.

[0057]

[Table 2]

[0058]

As is clear from the above detailed and specific description, the reversible thermosensitive coloring composition of the present invention can be repeatedly formed into a stable coloring state and a good decoloring state.
A reversible thermosensitive recording medium using this can be formed by an easy operation of forming and erasing a high-contrast image. In addition, the color image is stable under normal use conditions, has high durability against repeated recording and erasure, and has an excellent effect of obtaining practicable rewritable recording.

[Brief description of the drawings]

FIG. 1 is a view showing the color development / decoloration characteristics of the reversible thermosensitive coloring composition of the present invention.

[Explanation of symbols]

 A Decoloring state B Melting color developing state C Solid color developing state D Decoloring process E Decoloring state

Continued on the front page (72) Inventor Hiroaki Matsui 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Masaru Shimada 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Kyoji Tsutsui 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (2)

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