JPH1016391A - Reversible thermosensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold stable coloring properties and decoloring properties and to enable correspondence to use conditions in a wide range and environmental conditions by furthermore containing fullerene compound in a recording layer. SOLUTION: Coating liquid is produced by dissolving a developer, a coloring agent, fullerene and binder resin in a suitable solvent or uniformly dispersing them in the suitable solvent. A reversible thermal recording medium is made by applying the coating liquid on a substrate and providing a recording layer. The content of fullerene compound in the recording layer is changed by combination of the used coloring agent and a developer but regulated to a range within 0.01-0.5 favorab1y a range within 0.02-0.2 for 1 of a coloring component (the sum of the coloring agent and the developer). When the amount of fullerene compound is less than this range, desired effect is not obtained. Further, in the case of exceeding the range, undesirable coloring is caused in the recording layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium utilizing a color development reaction between an electron-donating color-forming compound and an electron-accepting compound. The present invention relates to a reversible thermosensitive recording medium capable of forming and erasing a color image.

[0002]

2. Description of the Related Art Conventionally, an electron-accepting color-forming compound (hereinafter, referred to as an electron-accepting color-forming compound)
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, according to the patent publication, a recording medium capable of reversibly developing and erasing colors has been proposed. For example, Japanese Patent Application Laid-Open No. 60-1985 discloses a method using a combination of gallic acid and phloroglucinol as a color developer. No. 193691, JP-A No. 61-237684 using a compound such as phenolphthalein or thymolphthalein as a developer, and a recording layer containing a homogeneous solution of a color former, a developer and a carboxylic acid ester in a recording layer. JP-A-62-138556, JP-A-62-138
568 and JP-A-62-140881, and JP-A-63-173 using an ascorbic acid derivative as a developer.
No. 684,684, JP-A-2-188293 and JP-A-2-1882 using a salt of bis (hydroxyphenyl) acetic acid or gallic acid and a higher aliphatic amine as a developer.
No. 94 is disclosed. However, the conventional reversible thermosensitive recording medium described above has a problem in terms of compatibility between color stability and decoloration, or stability in color density and repetition, and practical recording. It is not satisfactory as a medium.

[0004] The present applicant has previously disclosed in Japanese Patent Laid-Open No. 5-124360.
In the publication, an organic phosphoric acid compound having a long-chain aliphatic hydrocarbon group, an aliphatic carboxylic acid compound or a phenol compound is used as a color developer, and by combining this with a leuco dye as a color former, color development and decoloration are performed. Reversible color development that can be easily performed by heating and cooling conditions, and that its color development and decoloration states can be stably maintained at room temperature, and that color development and decoloration can be repeated stably A composition and a reversible thermosensitive recording medium using the same in a recording layer were 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, use of a specific structure for a phenol compound having a long-chain aliphatic hydrocarbon group has been proposed (Japanese Patent Application Laid-Open No.
210954), which also had a similar problem.

[0005]

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

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by the recording layer further containing a fullerene compound in the reversible thermosensitive recording medium, and have reached the present invention. . That is, the present invention contains an electron-donating color-forming compound and an electron-accepting compound as main components, and forms a state in which color is relatively developed and a state in which color is erased due to a difference in a heating temperature and / or a cooling rate after heating. A reversible thermosensitive recording medium comprising a recording layer provided on a support, wherein the recording layer further contains a fullerene compound.

The reversible thermosensitive recording medium of the present invention is capable of forming 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 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 discoloring occurs at a lower temperature T ₂ than the coloring temperature (E from D), returns the beginning when the temperature decreases from here to the same decolored state (A). The actual color development temperature and decolorization temperature vary depending on the combination of the color developer and color developer used, and can be selected according to the purpose. In addition, the density in the molten color development state and the color development density after quenching do not always match, and may differ.

The composition comprising the color developer and the color former contained in the recording layer of the present invention is in a color development state (C) obtained by quenching from a molten state. They are in a mixed state where possible, which often forms a solid 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 cohesive structure changes at this temperature, resulting in phase separation and development of a color developer.

In order to form a color image using the reversible thermosensitive recording medium of the present invention, the color image is heated once to a color development temperature or higher and then rapidly cooled. Specifically, for example, when the recording layer is heated for a short time by a thermal head or a laser beam, the recording layer is locally heated. Therefore, the heat is immediately diffused, rapid cooling occurs, and 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 with the thermal head, and so-called overwriting can be performed. Of course, it can be erased by heating to a decoloring temperature range by a heat roller or a heat stamp.

The materials used in the reversible thermosensitive recording layer coating solution and the reversible thermosensitive recording medium of the present invention are described below. The color former used in the present invention is a compound having an electron donating property, and is used alone or in combination of two or more.
The dye precursor itself is a colorless or light-colored dye precursor, and is not particularly limited, and can be selected from conventionally known ones, for example, triphenylmethanephthalide, fluoran, phenothidiane, leuco auramine, indolinophthalide, and the like. The coloring agent is shown below. Preferred color formers used in the present invention include compounds represented by the following general formula (a) or (b).

[0011]

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(Provided that R ₁ represents hydrogen or an alkyl group having 1 to 4 carbon atoms, R ₂ represents an alkyl group having 1 to 6 carbon atoms, cyclohexyl group or a phenyl group which may be substituted. Examples of the group 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, 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, an aralkyl which may be substituted; Wherein the substituent is an alkyl group, a halogen,
And an alkoxy group. The following are specific examples of such color formers, but the present invention is not limited thereto.

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
-Iso-amyl-N-ethylamino) fluoran, 2
-Anilino-3-methyl-6- (Nn-propyl-N
-Isopropylamino) 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- (N-n
-Hexyl-N-ethylamino) fluoran, 2- (o
-Chloroanilino) -6-diethylaminofluoran,
2- (o-bromoanilino) -6-diethylaminofluoran, 2- (o-chloroanilino) -6-dibutylaminofluoran, 2- (o-fluoroanilino) -6-dibutylaminofluoran, 2- (m-toluene) Fluoromethylanilino) -6-diethylaminofluoran, 2-
(P-acetylanilino) -6- (Nn-amyl-N
-N-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-dimethylanilino) 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) fluoran, 2-ethylamino-6- (N-methyl-2,4-dimethyl Anilino) 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-methylanilino) fluoran, 2
-Dipropylamino-6- (N-ethylanilino) fluoran, 2-amino-6- (N-methylanilino) fluoran, 2-amino-6- (N-ethylanilino) fluoran, 2-amino-6- (N-propyl Anilino) 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-dimethylaniline) Rino) fluorane, 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-trifluoromethylanilino) -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-ethyl-N-cyclohexylamino) fluoran, 1,2-
Benzo-6- (N-ethyl-toluidino) fluoran,
Other.

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-partimylamino) fluoran, 2- (p-chloroanilino) -6
-(Di-n-octylamino) fluoran, 2-benzoylamino-6- (N-ethyl-p-toluidino) fluoran, 2- (o-methoxybenzoylamino) -6
(N-ethyl-p-toluidino) fluoran, 2-dibenzylamino-4-methyl-6-diethylaminofluoran, 2-dibenzylamino-4-methoxy-6- (N
-Methyl-p-toluidino) fluoran, 2-dibenzylamino-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-N-p-chlorophenyl-methylamino) -6-pyrrolidinofluoran, 2- (Nn-propyl-m-trifluorome Ruanirino) -6-morpholinophenyl fluoran, 1,2-benzo-6- (N-ethyl -
Nn-octylamino) fluoran, 1,2-benzo-6-diallylaminofluoran, 1,2-benzo-6
-(N-ethoxyethyl-N-ethylamino) fluoran, benzoleucomethylene blue, 2- [3,6-bis (diethylamino)]-6- (o-chloroanilino) xanthyl benzoate lactam, 2- [3,6- Bis (diethylamino)]-9- (o-chloroanilino) xanthylbenzoic acid lactam, 3,3-bis (p-dimethylaminophenyl) phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthaly (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, 3,6-bis (dimethylamino) fluorene Spiro (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-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-benzoindolino-spiropyran, 6'-bromo-2'-methoxy-benzoindolino-spiropyran and the like.

Next, the color developing agent used in combination with the color forming agent in the present invention is an electron-accepting compound, and has a structure exhibiting a color developing ability capable of coloring the color forming agent in the molecule and a cohesive force between the molecules. Is a compound having a long-chain structure portion that controls the following, for example, an organic phosphoric acid compound having an aliphatic group having 12 or more carbon atoms, an aliphatic carboxylic acid compound having 12 or more carbon atoms, and a phenol having an aliphatic group having 12 or more carbon atoms And the like. The aliphatic group includes a linear or branched alkyl group and alkenyl group, and may have a substituent such as a halogen, an alkoxy group, and an ester.

Specific examples of the color developer will be described below. (A) Organophosphate Compound A compound represented by the following general formula (1) is used.

[0017]

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(R ₅ represents a straight-chain alkyl group having 12 or more carbon atoms) Specific examples of the organic phosphoric acid compound represented by the general formula (1) include the following. Dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid, docosylphosphonic acid, tetracosylphosphonic acid, hexacosylphosphonic acid, octacosylphosphonic acid and the like.

(B) Aliphatic carboxylic acid compounds α-hydroxy fatty acids represented by the following general formula (2) are preferably used. R ₆ —CH (OH) —COOH (2) (where R ₆ represents an aliphatic group having 12 or more carbon atoms) Examples of the α-hydroxyaliphatic carboxylic acid compound represented by the general formula (2) include The following are mentioned.

Α-hydroxydecanoic acid, α-hydroxytetradecanoic acid, α-hydroxyhexadecanoic acid, α-hydroxydecanoic acid
Hydroxyoctadecanoic acid, α-hydroxypentadecanoic acid, α-hydroxyeicosanoic acid, α-hydroxydocosanoic acid, α-hydroxytetracosanoic acid, α-hydroxyhexacosanoic acid, α-hydroxyoctacosanoic acid, and the like.

The aliphatic carboxylic acid compound is an aliphatic carboxylic acid compound having an aliphatic group having 12 or more carbon atoms and substituted with a halogen element, at least in the α-position or β-position.
Those having a halogen element at the carbon at the position are also preferably used. Specific examples of such compounds include, for example, the following. 2-bromohexadecanoic acid, 2-bromoheptadecanoic acid, 2-bromooctadecanoic acid, 2-bromoeicosanoic acid, 2-bromodocosanoic acid, 2-bromotetracosanoic acid, 3-bromooctadecanoic acid, 3-bromoeicosanoic acid 2,2-dibromooctadecanoic acid, 2-fluorododecanoic acid, 2-fluorotetradecanoic acid, 2-fluorohexadecanoic acid, 2-fluorooctadecanoic acid, 2-fluoroeicosanoic acid, 2-
Fluorodocosanoic acid, 2-iodohexadecanoic acid, 2-
Iodooctadecanoic acid, 3-iodohexadecanoic acid, 3
-Iodooctadecanoic acid, perfluorooctadecanoic acid and the like.

The aliphatic carboxylic acid is an aliphatic carboxylic acid compound having an oxo group in the carbon and having an aliphatic group having 12 or more carbon atoms, at least in the α-position, the β-position or the γ-position.
Those having an oxo group at the carbon atom are preferably used. Specific examples of such compounds include, for example, the following.

2-oxododecanoic acid, 2-oxotetradecanoic acid, 2-oxohexadecanoic acid, 2-oxooctadecanoic acid, 2-oxoeicosanoic acid, 2-oxotetracosanoic acid, 3-oxododecanoic acid, 3-oxo Tetradecanoic acid, 3-oxohexadecanoic acid, 3-oxooctadecanoic acid, 3-oxoeicosanoic acid, 3-oxotetracosanoic acid, 4-oxohexadecanoic acid, 4-oxooctadecanoic acid, 4-oxodokosanoic acid and the like. As the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (3) is also preferably used.

[0024]

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(Where R ₇ represents an aliphatic group having 12 or more carbon atoms, X represents an oxygen atom or a sulfur atom,
Represents 1 or 2. As specific examples of the dibasic acid represented by the general formula (3),
For example, the following are mentioned.

Dodecyl malic acid, tetradecyl malic acid, hexadecyl malic acid, octadecyl malic acid, eicosyl malic acid, docosyl malic acid, tetracosyl malic acid, dodecyl thiomalic acid, tetradecyl thiomalic acid, hexadecyl thiomalic acid Acid, octadecylthiomalic acid, eicosylthiomalic acid, docosylthiomalic acid, tetracosylthiomalic acid, dodecyldithiomalic acid, tetradecyldithiomalic acid, eicosyldithiomalic acid, docosyldithiomalic acid, tetracosyl Rudithiomalic acid and the like. As the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (4) is also preferably used.

[0027]

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(However, R ₈ , R ₉ , and R ₁₀ represent hydrogen or an aliphatic group, at least one of which is an aliphatic group having 12 or more carbon atoms.) Specific examples of the basic acid include:
For example, the following are mentioned.

Dodecyl butane diacid, tridecyl butane diacid, tetradecyl butane diacid, pentadecyl butane diacid, octadecyl butane diacid, eicosyl butane diacid,
Docosyl butane diacid, 2,3-dihexadecyl butane diacid, 2,3-dioctadecyl butane diacid, 2-methyl-
3-dodecyl butane diacid, 2-methyl-3-tetradecyl butane diacid, 2-methyl-3-hexadecyl butane diacid, 2-ethyl-3-dodecyl butane diacid, 2-propyl-3-dodecyl butane Diacid, 2-octyl-3-hexadecylbutanedioic acid, 2-tetradecyl-3-octadecylbutanedioic acid and the like. As the aliphatic carboxylic acid compound,
A dibasic acid represented by the following general formula (5) is also preferably used.

[0030]

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(However, R ₁₁ and R ₁₂ represent hydrogen or an aliphatic group, at least one of which is an aliphatic group having 12 or more carbon atoms.) The dibasic acid represented by the general formula (5) As a specific example,
For example, the following are mentioned.

Dodecylmalonic acid, tetradecylmalonic acid, hexadecylmalonic acid, octadecylmalonic acid, eicosylmalonic acid, docosylmalonic acid, tetracosylmalonic acid, didetecylmalonic acid, ditetradecylmalonic acid, dihexadecylmalonic acid, Dioctadecylmalonic acid, dieicosylmalonic acid, didcosylmalonic acid, methyloctadecylmalonic acid, methyldocosylmalonic acid, methyltetracosylmalonic acid, ethyloctadecylmalonic acid, ethyleicosylmalonic acid, ethyldocosylmalonic acid, ethyl Tetracosylmalonic acid and the like. As the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (6) is also preferably used.

[0033]

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(However, R ₁₃ represents an aliphatic group having 12 or more carbon atoms, n represents 0 or 1, m represents 1, 2 or 3, and when n is 0, m represents 2 or 3) Yes,
When n is 1, m represents 1 or 2. As specific examples of the dibasic acid represented by the general formula (6),
For example, the following are mentioned.

2-dodecyl-pentanedioic acid, 2-hexadecyl-pentanedioic acid, 2-octadecylpentanedioic acid, 2-eicosyl-pentanedioic acid, 2-docosyl-pentanedioic acid, 2-dodecyl-hexanedioic acid, 2-pentadecyl-hexane diacid, 2-octadecyl-hexane diacid, 2-eicosyl-hexane diacid, 2-docosyl-hexane diacid, and the like. As the aliphatic carboxylic acid compound, a tribasic acid such as citric acid acylated with a long-chain fatty acid is also preferably used. Specific examples include the following.

[0036]

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As the phenol compound, a compound represented by the following general formula (7) is used.

[0038]

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(Where Y is -S-, -O-, -CON
_{H -, - NHSO 2 -,} - CH = CHCONH -, - N
HCO -, - NHCONH-, or -COO- a represents, R ₁₄ represents a number of 12 or more aliphatic group having a carbon, n is an integer of 1, 2 or 3. Specific examples of the phenol compound represented by the general formula (7) include the following. p-
(Dodecylthio) phenol, p- (tetradecylthio) phenol, p- (hexadecylthio) phenol, p- (octadecylthio) phenol, p- (eicosylthio) phenol, p- (docosylthio) phenol, p- (tetracosylthio) phenol Phenol, p- (dodecyloxy) phenol, p- (tetradecyloxy) phenol, p- (hexadecyloxy) phenol, p- (octadecyloxy) phenol, p- (eicosyloxy) phenol, p- (docosyloxy)
Phenol, p- (tetracosyloxy) phenol,
p-dodecylcarbamoylphenol, p-tetradecylcarbamoylphenol, p-hexadecylcarbamoylphenol, p-octadecylcarbamoylphenol, p-eicosylcarbamoylphenol, p-docosylcarbamoylphenol, p-tetracosylcarbamoylphenol, hexagallate Decyl ester,
Octadecyl gallate, eicosyl gallate, docosyl gallate, tetracosyl gallate, N-dodecyl-p-hydroxycinnamamide, N-tetradecyl-p-hydroxycinnamamide, N-octadecyl-p -Hydroxycinnamamide, N-docosyl-p-hydroxycinnamamide, N
-Dodecyl-p-hydroxycinnamamide, N-octacosyl-p-hydroxycinnamamide, 4'-hydroxytridecaneanilide, 4'-hydroxyheptadecaneanilide, 4'-hydroxynonadecaneanilide,
3'-hydroxynonadecaneanilide, 4- (N-docosylsulfonylamino) phenol, 4- (N-octadecylsulfonylamino) phenol, N- (4-hydroxyphenyl) -N'-dodecylurea, N- (4 -Hydroxyphenyl) -N'-octadecylurea, N-
(4-hydroxyphenyl) -N'-docosyl urea and the like.

In the present invention, the color developer is not limited to the compounds described above, and various other electron-accepting compounds can be used. In the present invention, a fullerene compound added for improving light resistance is a fullerene represented by the general formula Cn (where n is 30 to 1).
00), or a derivative thereof, in which an ionic species is introduced into a locally deformed structure or a hollow portion thereof, a carbon atom in which a part of carbon atoms is substituted by another atom, or a functional group is bonded. Can be used.

Specific examples of the fullerene compound used in the present invention are shown below.

C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C ₈₂ , C ₈₄ , C
₉₀ , C ₉₆ and mixtures thereof, K ₃ C ₆₀ , Rb ₃ C ₆₀ ,
LaC ₈₂ , C ₆₀ Pt (Rh ₃ ) ₂ , JP-A-247273
No. ₆₀ and N- (α-chlorobenzylidene)-
Reaction product with N'-phenylhydrazine
(Reaction product of C ₆₀ and triphenylphosphorane) methanofullerene described in JP 87627, JP-A -
187628, an aminoureidofullerene derivative, an aminothioureidofullerene derivative, and others. The binder resin used for forming the recording layer is a polymer compound having film forming properties, and these are all known.
Specific examples of usable binder resins are shown below.

Polyolefins such as polyethylene and polypropylene; polymethyl acrylate, polyethyl acrylate, poly (n-butyl acrylate), polymethyl methacrylate, polyethyl methacrylate, poly (isobutyl methacrylate), poly (n-butyl methacrylate), (Sec-butyl methacrylate), poly (tert-butyl methacrylate), poly (isobornyl methacrylate), poly (benzyl methacrylate), poly (2-ethylhexyl methacrylate), polyacrylic acid, polymethacrylic acid and copolymers thereof Acrylic polymers such as polystyrene,
Styrene metering polymers such as styrene-acrylonitrile copolymer; polyvinyl chloride, polyvinyl alcohol,
Polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal, vinyl alcohol
Such as vinyl butyral copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer Vinyl polymers; Fluorine polymers such as polytetrafluoroethylene, polytrifluoroethylene, and polyvinylidene fluoride; Nitrocellulose, cellulose acetate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, ethyl cellulose, methylcellulose Cellulose polymers; isobutylene-maleic anhydride copolymer; polyisobutyl ether; polyethylene oxide; polypropylene oxide; polycarbonate, polyarylate, polysulfone, Li (2,6-dimethyl -p- phenylene oxide), polyimide, polyamide-imide,
Engineering plastics such as polyetherimide; polyurethane; polyamide resins such as nylon 6, nylon 66; silicone resin; melamine-formaldehyde resin; urea-formaldehyde resin; phenol-formaldehyde resin;
Thermosetting resins such as xylene resins, furan resins, epoxy resins, unsaturated polyester resins, and maleic anhydride resins; rubber polymers such as natural rubber, styrene-butadiene rubber, and acrylonitrile-butadiene rubber;

The reversible thermosensitive recording medium of the present invention is prepared by coating a coating solution obtained by dissolving the above-described developer, color former, fullerenes and binder resin in an appropriate solvent or a coating solution obtained by uniformly dispersing the same on a support. It is created by processing and providing a recording layer. Specific examples of the solvent used in the coating liquid of the present invention are shown below.

Water; alcohols such as methanol, ethanol, isopropanol, n-butanol and methyl isocarbinol; ketones such as acetone, 2-butanone, ethyl amyl ketone, diacetone alcohol, isophorone and cyclohexanone; Amides such as dimethylformamide and N, N-dimethylacetamide;
Diethyl ether, isopropyl ether, tetrahydrofuran, 1,4-dioxane, 3,4-dihydro-2
Ethers such as H-pyran; 2-merethoxyethanol, 2-ethoxyethanol, 2-butoxyethanol,
Glycol ethers such as ethylene glycol dimethyl ether; glycol ether acetates such as 2-methoxyethyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate; methyl acetate;
Esters such as ethyl acetate, isobutyl acetate, amyl acetate, ethyl lactate and ethylene carbonate; aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as hexane, heptane, iso-octane and cyclohexane; Examples include halogenated hydrocarbons such as methylene, 1,2-dichloroethane, dichloropropane, and chlorobenzene; sulfoxides such as dimethyl sulfoxide; and pyrrolidones such as N-methyl-2-pyrrolidone and N-octyl-2-pyrrolidone. can do.

The coating liquid for the reversible thermosensitive recording layer can be prepared by using a known coating liquid dispersing apparatus such as a paint shaker, a ball mill, an attritor, a three-roll mill, a Keddy mill, a sand mill, a dyno mill, and a colloid mill.
The content of the fullerene compound in the recording layer varies depending on the combination of the color former and the developer used, but is in the range of 0.01 to 0.5 with respect to 1 of the color forming component (sum of the color former and the developer). , Preferably in the range of 0.02 to 0.2. If the amount of the fullerene compound is less than this range, the desired effect cannot be obtained. If the ratio exceeds this range, undesired coloring of the recording layer occurs.

The ratio of the color former to the color developer varies 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 generally in the range of 0.1 to 20. It is preferably in the range of 0.3 to 10. Even if the amount of the developer is at least larger than this range, there is a problem that the density of the color-developed state is lowered. The appropriate range of the ratio of the color-forming component to the binder resin varies depending on the combination of the compounds used. However, the ratio by weight of the color-forming component to the binder resin is generally in the range of 0.05 to 10 with respect to 1 and preferably 0.1 to 0.1.
It is in the range of 1 to 5. The reversible thermosensitive recording medium of the present invention is produced by applying the coating liquid for forming a reversible thermosensitive recording layer prepared above on a suitable support and providing a recording layer. Any type of support can be used, and examples thereof include paper, synthetic paper, plastic films such as polyester, metal films, and composite films obtained by laminating these.

There is no particular limitation on the coating method, and known methods such as blade coating, Meyer bar coating, spray coating, air knife coating, bead coating, curtain coating, gravure coating, and kiss coating are used. Can be used. The thickness of the recording layer is preferably in the range of 1 μm to 20 μm, and more preferably in the range of 2 μm to 15 μm. In the reversible thermosensitive recording medium of the present invention, an additive for improving or controlling the coating characteristics and the coloring and decoloring characteristics of the recording layer can be used as necessary. These additives include, for example, dispersants, surfactant conductive agents, fillers, lubricants, antioxidants, light stabilizers, ultraviolet absorbers, color stabilizers, and decolorization accelerators.

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 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, polyvinyl alcohol,
In addition to 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, additives 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 the application of the protective layer, and preventing migration of additives in the protective layer to the recording layer. It is also preferred. A protective layer to be placed on the recording layer,
It is preferable to use a resin having low oxygen permeability for the intermediate layer. It is possible to prevent or reduce oxidation of the color former and the developer in the recording layer. In addition, 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. The same resin as the above-mentioned resin for the recording layer can be used for the intermediate layer and the undercoat layer. The protective layer, the intermediate layer, the recording layer, and the undercoat layer can contain fillers such as calcium carbonate, magnesium carbonate, titanium oxide, silicon oxide, aluminum hydroxide, kaolin, and talc. Others
A lubricant, a surfactant dispersant and the like can be contained.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to Examples and Comparative Examples. In the examples, “parts” and “%” are based on weight. Example 1 A) 3.2 parts of docosylphosphonic acid B) 1.8 parts of 2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluoran C) vinyl chloride-vinyl acetate copolymer (VYHH, manufactured by Union Carbide Co., USA) 10 parts D) Fullerene C ₆₀ (purity 95%) 0.01 part E) 2-butanone 45 parts First, C and B are added to the above E and completely dissolved. Next, A and D were added to this solution, and this mixture was pulverized and dispersed for 96 hours using a paint shaker to obtain a recording layer coating liquid.

Next, the above coating solution was applied on a white polyester film having a thickness of 100 μm using a wire bar.
By heating and drying, a recording layer having a thickness of about 7 μm was provided. On this recording layer, a protective layer coating liquid having the following composition was applied using a wire bar, and then cured under a UV lamp having an irradiation energy of 80 W / cm at a transport speed of 9 m / min to cure the film.
A protective layer having a thickness of μm was provided, and a reversible thermosensitive recording medium of this example was prepared.

(Protective Layer Coating Solution) Urethane acrylate UV curable resin (C7-157, manufactured by Dai Nippon Ink Co., Ltd.) 50 parts Ethyl acetate 50 parts Example 2 A) docosyldithiomalic acid 3.2 parts B) 2 -Anilino-3-methyl-6- (N, N-diethylamino) fluoran 1.8 parts C) Cellulose acetate butyrate (CAB-551-0.2, manufactured by Eastman Kodak Company, USA) 5 parts D) Fullerene C ₇₀ (purity 97%) 0.2 part E) 30 parts of toluene F) 15 parts of 2-butanone C and B are added and completely dissolved in the mixed solvent composed of E and F. A and D were added to this solution, and this mixture was pulverized and dispersed for 96 hours using a paint shaker to obtain a recording layer coating liquid. Next, using this coating liquid, a recording layer was provided in the same procedure as in Example 1, and then a protective layer was provided in the same procedure as in Example 1, thereby producing a reversible thermosensitive recording medium of this example.

Example 3 A) 1.6 parts of N-4-hydroxyphenyl-N'-octadecylurea B) 0.9 parts of 2-anilino-3-methyl-6- (N, N-diethylamino) fluoran C ) Vinyl chloride-vinyl acetate copolymer (VYNS-3, manufactured by Union Carbide Co., USA) 5 parts D) Methanoflurane (reaction product of C60 and methylenetriphenylphosphorane) 0.08 parts E) Toluene 25 Part F) 15 parts of 2-butanone C and B are added and completely dissolved in the mixed solvent composed of E and F. A and D were added to this solution, and this mixture was pulverized and dispersed for 96 hours using a paint shaker to obtain a recording layer coating liquid. Next, using this coating liquid, a recording layer was provided in the same procedure as in Example 1, and then a protective layer was provided in the same procedure as in Example 1, thereby producing a reversible thermosensitive recording medium of this example.

Example 4 A) 1.6 parts of p- (docosylthio) phenol B) 0.9 parts of 2-anilino-3-methyl-6- (N, N-dibutylamino) fluoran C) Vinyl chloride-vinyl acetate copolymer (VYNS-3, manufactured by US Yu anion carbide Corporation) 5 parts D) a mixture of fullerene C ₆₀ and _{C 70 (C 60 / C 70} = 92/8) 0.15 parts E) toluene 25 parts F) 2-butanone 15 parts C and B are added and completely dissolved in the mixed solvent composed of E and F. A and D were added to this solution, and this mixture was pulverized and dispersed for 96 hours using a paint shaker to obtain a recording layer coating liquid. Next, using this coating liquid, a recording layer was provided in the same procedure as in Example 1, and then a protective layer was provided in the same procedure as in Example 1, thereby producing a reversible thermosensitive recording medium of this example.

Comparative Example 1 A recording layer and a protective layer were applied in the same manner as in Example 1 except that fullerene was not added, to prepare a reversible thermosensitive recording medium of this comparative example. Comparative Example 2 A recording layer and a protective layer were coated in the same manner as in Example 3 except that a compound represented by the following formula was used instead of methanofullerene in Example 3, and the reversibility of this comparative example was evaluated. A thermal recording medium was created.

[0057]

Embedded image

With respect to the reversible thermosensitive recording media prepared in Examples 1 to 4 and Comparative Examples 1 and 2, the repetition characteristics of image writing and erasing (Evaluation 1) and the light fastness of the background portion and the decolored portion were performed in the following procedure. (Evaluation 2) was evaluated, and the results shown in Table 1 were obtained.

Evaluation method: Evaluation 1) Using a commercially available thermal facsimile printing tester (TH-PMD, manufactured by Okura Electric Co., Ltd.), dot density: 8 dots / mm, applied voltage: 13.3 V,
Image writing was performed under the setting conditions of pulse width: 0.8 millisecond, and the reflection density was measured using a reflection densitometer (RD918, manufactured by Macbeth). Next, the color image obtained above was heated at 85 ° C. for 30 seconds (Examples 1, 2 and Comparative Example 1), 140 ° C. for 1 second (Example 3 and Comparative Example 2) or 8 using a heat stamp.
The decoloring operation was performed under the conditions of 5 ° C. for 1 second (Example 4), and the density of the decolored portion was measured. The above-described image writing and decoloring operations were repeated 100 times, and the first and 100th densities were measured.

Evaluation 2) With respect to the reversible thermosensitive recording media of Examples 1 to 4 and Comparative Examples 1 and 2 obtained in Evaluation 1), the densities of the background portion and the decolored portion were measured. Next, the color image written on the new medium sample was irradiated with light of 5000 lux under a fluorescent light source for 100 hours. The decoloring operation was performed in the same procedure as in the evaluation 1), and the reflection densities of the decolored portion and the background portion after irradiation were measured again.

[0061]

[Table 1]

[0062]

The reversible thermosensitive composition of the present invention can be repeatedly formed into a stable color-developed state and a good decolored 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 provides a highly practical rewritable recording medium.

[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.

Claims (1)

[Claims] Claims: 1. A color former, which is an electron-donating color-forming compound, and a developer, which is an electron-accepting compound, as main components,
In a reversible thermosensitive recording medium provided on a support with a recording layer capable of forming a state in which color is relatively developed and a state in which color is erased due to a difference in a heating temperature and / or a cooling rate after heating, the recording layer further comprises a fullerene compound A reversible thermosensitive recording medium comprising: