JPH09315009A - Reversible thermally coloring composition and reversible thermally recording medium using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible thermally coloring composition capable of being erased especially at a high speed and a reversible thermally recording medium by a method wherein they hold stabilized color development and color erazing, and can deal with wide ranged use conditions and environmental conditions. SOLUTION: In a reversible thermally coloring composition wherein an electron donative color developing compound and an electron acceptive compound are used, and a relatively colored state and a color erased state can be formed by a difference of heating temperature and/or cooling speed after heating, a phenolic compound expressed by the formula is used as the electron acceptive compound. In the formula, (n) is an integer of 1 to 3, and R is an 8 or higher C aliphatic hydrocarbon group which may contain a hetero-atom.

Description

Detailed Description of the Invention

[0001]

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, and a reversible thermosensitive coloring composition. The present invention relates to a reversible thermosensitive recording medium capable of forming and erasing a color image by controlling thermal energy.

[0002]

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

On the other hand, according to the patent publication, there is proposed a recording medium capable of reversibly performing coloring and erasing. For example, JP-A-60-193691 using a combination of gallic acid and phloroglucinol as a developer, JP-A-61-237684 using a compound such as phenolphthalein or thymolphthalein as a developer, JP-A-62-138556, JP-A-62-138568 and JP-A-62-1408, in which a homogeneous solution of a color former, a developer and a carboxylic acid ester is contained in a recording layer.
No. 81, JP-A-63-173684 using an ascorbic acid derivative as a developer, and JP-A-2-188293 using a salt of bis (hydroxyphenyl) acetic acid or gallic acid and a higher fatty acid amine as a developer. And JP-A-2-188294.

However, the above-described conventional reversible thermosensitive recording media have problems in that they are compatible with the stability of color development and the erasability, or in terms of the density of color development and the stability in repetition. Recording medium is not satisfactory.

On the other hand, the inventors of the present invention disclosed in JP-A-5-12436.
In JP-A-0, No. 0,037,037, 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 developer, and by combining this with a leuco dye which is a color developing agent, color development and decolorization are performed. Colors can be easily heated and cooled, and their colored and decolored states can be maintained stably at room temperature. Furthermore, reversible coloring and decoloring can be stably repeated. A color developing composition and a reversible thermosensitive recording medium using the same as a recording layer have been proposed. This has a practical level of performance in terms of the balance between color stability and erasability and color density, but it will be improved in terms of compatibility with a wider range of usage environments and the range of application of color erasing conditions. There was room to do it. After that, it was proposed to use a phenol compound having a long chain aliphatic hydrocarbon group with a specific structure (Japanese Patent Laid-Open No. 6-210954), but this also had the same problem.

[0006]

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

[0007]

The inventors of the present invention develop the color developability of a developer having a long-chain aliphatic group in such a reversible color development / decoloration phenomenon of the color developer and the developer. We considered that the balance between the ability and the cohesive force between molecules is important, and investigated compounds with various structures. As a result, they have found that the intended purpose can be achieved by using a specific phenolic compound as a developer, and have completed the present invention.

The present invention uses an electron-donating color-forming compound and an electron-accepting compound to form a relatively colored state and a relatively decolored state depending on the difference in heating temperature and / or cooling rate after heating. In the reversible thermosensitive coloring composition, a phenolic compound represented by the following general formula (I) is used as the electron accepting compound.

[0009]

(In the formula, n represents an integer of 1 to 3, and R represents an aliphatic hydrocarbon group having 8 or more carbon atoms which may contain a hetero atom.)

The present invention also provides a reversible thermosensitive recording medium comprising a support and a recording layer containing the reversible thermosensitive coloring composition, wherein the reversible thermosensitive coloring composition described above is used. It is characterized by using a color forming composition.

Among the compounds represented by the general formula (I), it is preferable that the aliphatic hydrocarbon group of R has a large number of carbon atoms.
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, more preferably 11 or more.

Further, R is preferably the following general formula (II)
Represents a group represented by. R ₁ —X—R ₂ — (II) In the above formula, R ₁ and R ₂ represent a hydrocarbon group which may have a substituent, and these may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. It may be a hydrocarbon group composed of both of them. 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. Further, when the sum of the carbon numbers of R ₁ and R ₂ is 7 or less, the stability of color development and the decoloring property are deteriorated. Therefore, the number of carbons is preferably 8 or more, more preferably 11 or more.

X represents a direct bond or a divalent group containing a hetero atom, preferably

[0014]

It represents a divalent group having at least one group represented by: Examples thereof include those shown in Table 1 below.

[0015]

[Table 1]

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

[0017]

Wherein R ₂ represents a bond other than the above groups,
Further, m represents an integer of 1 to 4. When m is 2 or more, repeated X and R ₂ may be the same or different.

Hereinafter, the present invention will be described in detail. Specific examples of the color developer in the invention are shown in Tables 2 to 25. However, the present invention is not limited to these.

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Table 5]

[0023]

[Table 6]

[0024]

[Table 7]

[0025]

[Table 8]

[0026]

[Table 9]

[0027]

[Table 10]

[0028]

[Table 11]

[0029]

[Table 12]

[0030]

[Table 13]

[0031]

[Table 14]

[0032]

[Table 15]

[0033]

[Table 16]

[0034]

[Table 17]

[0035]

[Table 18]

[0036]

[Table 19]

[0037]

[Table 20]

[0038]

[Table 21]

[0039]

[Table 22]

[0040]

[Table 23]

[0041]

[Table 24]

[0042]

[Table 25]

The reversible thermosensitive color-forming composition of the present invention is basically constituted by combining the above-mentioned color developer and color-developing agent. 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. Specific examples of such a color former are shown below.

The preferred color former used in the present invention is a compound represented by the following general formula (IV) or (V).

[0045]

Embedded image

[0046]

Embedded image

(In the formula, R ₃ represents hydrogen or an alkyl group having 1 to ₄ carbon atoms, R ₄ represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group or an optionally substituted phenyl group. Examples of the substituent for R are 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 atom, etc. R ₅ is hydrogen, an alkyl group having 1 to 2 carbon atoms, an alkoxy group or a halogen atom. R ₆ represents hydrogen, a methyl group, halogen or an optionally substituted amino group, and examples of the substituent for the amino group include an alkyl group, an optionally substituted aryl group, and an optionally substituted aryl group. There are good aralkyl groups, etc. The substituent here is an alkyl group, a halogen or an alkoxy group, etc.) Specific examples of such color formers include, for example: Thing, and the like.

2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-
(Di-n-butylamino) fluorane, 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- (N-cyclohexyl-N-methylamino) fluoran, 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-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-
Methyl-p-toluidino) -3-methyl-6- (N-propyl-p-toluidino) fluorane, 2-anilino-
6- (Nn-hexyl-N-ethylamino) fluorane, 2- (o-chloroanilino) -6-diethylaminofluorane, 2- (o-bromoanilino) -6-diethylaminofluorane, 2- (o- Chloranilino) -6
-Dibutylaminofluoran, 2- (o-fluoroanilino) -6-dibutylaminofluoran, 2- (m-trifluoromethylanilino) -6-diethylaminofluoran, 2- (p-acetylanilino) -6 − (N−n−
Amyl-n-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) fluorane, 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)
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) fluoran, 2-ethylamino-6- (N-ethyl-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) fluorane, 2-cypropylamino-6- (N-methylanilino) fluorane, 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
-Diethylaminofluorane, 2- (o-chloroanilino) -3-chloro-6-cyclohexylaminofluorane, 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) fluorane, 1, 2-benzo-6-dibutylaminofluorane, 1,2-benzo-6- (N-methyl-N-cyclohexylamino) fluorane, 1,2-
Benzo-6- (N-ethyl-p-toluidino) fluorane and the like.

Specific examples of other color formers 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) fluorane, 2- (p-chloranilino) -6- (Nn-palmitylamino) fluorane, 2- (p-chloranilino) -6- (di-n
-Octylamino) fluoran, 2-benzoylamino-6- (N-ethyl-p-toluidino) fluoran, 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-methoxycarbonylanilino) -6-diethylaminofluorane, 2-acetylamino-6- (N-methyl-p-toluidino) fluorane, 3-diethylamino-6- (m-trifluoromethylanilino) fluorane, 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-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- (The-N
-P-chlorophenyl-methylamino) -6-pyrrolidinofluorane, 2- (N-n-propyl-m-trifluoromethylanilino) -6-morpholinofluorane,
1,2-benzo-6- (N-ethyl-N-n-octylamino) fluorane, 1,2-benzo-6-diallylaminofluorane, 1,2-benzo-6- (N-ethoxyethyl-N -Ethylamino) fluorane,

Benzoyl leuco methylene blue, 2-
[3,6-bis (diethylamino)]-6- (o-chloroanilino) xanthylbenzoate lactam, 2- [3
6-bis (diethylamino)]-9- (o-chloroanilino) xanthyl 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) fluorensviro (9,3 ′) -6′-Dimethylaminophthalide, 6′-chloro-8′-methoxy-benzoindolino-spiropyran, 6′-bromo-2′-methoxy-benzindolinosepyropyran and the like.

The reversible thermosensitive coloring composition of the present invention is capable of forming a relatively colored state and a relatively decolored state depending on the heating temperature and / or the cooling rate after heating. This basic coloring and decoloring phenomenon will be described below.

FIG. 1 shows the relationship between the color density of this composition and temperature. Introduction gradually heated a composition in the decolorized state (A), a molten colored state occurs coloration at temperatures T ₁ begins to melt (B). Melt coloring state (B)
When the mixture is rapidly cooled, the temperature can be lowered to room temperature in the color-developed state, and the color-developed 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, when the temperature of the rapidly cooled color development state (C) is raised again, the temperature T ₂ lower than the color development temperature is reached.
Then, the color is erased (from D to E), and when the temperature is lowered from this point, the color returns to the same erased state (A) as the first time.

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, in the heated molten state (B),
Although there is almost no color development, there is also a composition in which color formation occurs in the process of rapid cooling, resulting in formation of a stable color development 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 quenching from the molten state is a state in which the color-developing agent and the color-developing agent are mixed in such a state that the molecules can be contact-reacted with each other. 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 in which 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 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, they are the same in that they both temporarily separate at a temperature at which they phase separate or at least one crystallizes. The quenching in the formation of a colored state is to prevent the phase separation 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 coloring agent and the head coloring agent.

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 color developing agent is less or more than this range, the density of the color-developed state is lowered and it is not suitable for practical use.

The reversible thermosensitive recording medium of the present invention comprises a support having thereon 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. Generally, it may be a state in which a color former and a developer are finely and uniformly dispersed in a binder resin. . 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 once melting or dissolving the color former and the developer. 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. These additives include, for example, dispersants, surfactant conductive agents,
Examples include fillers, lubricants, antioxidants, light stabilizers, ultraviolet absorbers, color development stabilizers, and decolorization accelerators.

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, polyacrylate, polymethacrylate, acrylic acid copolymer, maleic acid copolymer, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, starch, etc. There is. 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, 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.

For the purpose of improving the adhesion 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, an intermediate layer is provided between the two. 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 the oxidation of the color former and the developer in the recording layer.

A heat insulating undercoat layer may be provided between the support and the recording layer in order to effectively utilize 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 can contain a filler such as calcium carbonate, magnesium carbonate, titanium oxide, silicon oxide, aluminum hydroxide, kaolin, and talc. Other lubricants
A surfactant dispersant or the like can be contained.

In order to form a color image using the reversible thermosensitive recording material of the present invention, it is sufficient to heat once above the color development temperature and then rapidly cool it. More 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, so that 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, 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 entire temperature of the recording medium rises over a wide range, 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, for example, the applied voltage to the thermal head or the pulse width may be adjusted so that the applied energy is slightly lower than that at the time of recording. With this method, recording and erasing can be performed only with the thermal head, and so-called overwriting can be performed. Of course, heat roller,
It can also be erased by heating to a erasing temperature range with a heating stand.

[0069]

EXAMPLES The present invention will now be described in more detail with reference to Examples. The parts and% shown below are based on weight.

Example 1 2- (o-chloroanilino) -6-dibutylaminofluorane was used as a color former, and N- (4-hydroxyphenylcarbonyl) -N'-n-octadecylurea was used as a color developer. The composition of the present invention was prepared as follows. First, the color developing agent and the color developing agent are mixed at a mixing ratio of 1: 3 (molar ratio).
And crushed and mixed in a mortar. Thickness 1.2
A mm mm glass plate was heated on a hot plate to a temperature of 170 ° C. A small amount of the above mixture was melted on the glass plate. The mixture developed a color upon melting and turned black. Subsequently, a cover glass was placed over the molten mixture, the melt was spread to a uniform thickness, and immediately the entire glass plate was immersed in ice water prepared for rapid cooling. Immediately after the temperature was lowered, the composition was removed from the ice water to remove adhering water, thereby obtaining a thin film-shaped composition of the present invention.

Next, the composition sample in the above-mentioned color-developed state is treated with 120
When placed on a hot plate heated to ℃, the color disappeared instantly. 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.

Comparative Example 1 The same operation as in Example 1 was carried out except that N- (4-hydroxyphenylcarbonyl) -N′-n-ethylurea was used as a developer in place of the developer of Example 1. Thus, a thin film colored composition was obtained. When the composition in the color-developed state was observed while increasing the temperature from room temperature at a temperature increase rate of 4 ° C./min, no color disappeared. In addition, the composition sample in this colored state
No discoloration was observed even when placed on a hot plate heated to 0 ° C.

Example 2 A recording layer coating solution was prepared by pulverizing and dispersing the following composition into a particle size of 1 to 4 μm using a ball mill. 2- (o-chloroanilino) -6-dibutylaminofluorane 3 parts N- (4-hydroxyphenylcarbonyl) -N'-n-octadecyl urea 7 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 is applied on a polyester film having a thickness of 100 μm using a wire bar and dried to obtain a recording layer having a thickness of about 6.0 μm. A reversible thermosensitive recording medium was prepared.

Example 3 A recording layer coating liquid was prepared by pulverizing and dispersing the following composition into a particle size of 1 to 4 μm using a ball mill. 2-anilino-3-methyl-6-dibutylaminofluorane 4 parts N- (4-hydroxyphenylcarbonyl) -N'-n-octadecyl urea 8 parts vinyl chloride-vinyl acetate copolymer (VYHH manufactured by Union Carbide). ) 12 parts Methyl ethyl ketone 110 parts A recording layer coating solution having the above composition is applied on a polyester film having a thickness of 100 μm using a wire bar and dried to have the recording layer having a thickness of about 6.0 μm. A recording medium was produced.

Comparative Example 2 In Example 2, eicosylphosphonic acid was used in place of N- (4-hydroxyphenylcarbonyl) -N'-n-octadecylurea, and 2- (o-chloroanilino).
Reversible sensation for comparison as in Example 2 except that 2-anilino-3-methyl-6- (N-ethyl-Np-tolylamino) fluorane was used instead of -6-dibutylaminofluorane. A thermal recording medium was produced.

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 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 placed in a thermostatic chamber at 120 ° C. for about 20 seconds, and then the density was measured. further,
When the reversibility of color development was examined by repeating the above-mentioned color development operation and decolorization operation 10 times, it was confirmed that the color development and decolorization of the combination of Examples 2 and 3 could be repeated. Further, the color-developed recording medium was heated at a decoloring temperature of 130 ° C. for 1 second using a thermal gradient tester, and then the density was measured. Table 26 shows the measurement results.

[0077]

[Table 26] From Table 26, it can be seen that the recording medium of the present invention is erased to the same level as the background density by heating for 1 second.
Further, the recording medium for comparison did not erase the color to the initial background density by heating for 1 second, and an unerased residue was generated, and heating for 1 minute was required to reduce to 0.16 which is almost equal to the background density. .

[0078]

Since the reversible thermosensitive composition of the present invention can be repeatedly formed in a stable colored state and a good decolored state, a reversible thermosensitive recording medium using this composition forms and erases an image with high contrast. Is possible with easy operation.
Further, the color image is stable under normal use conditions, has high durability against repeated recording and erasing, and a rewritable recording medium with high practicability capable of erasing at high speed can be obtained.

[Brief description of drawings]

FIG. 1 is a view showing the coloring and decoloring characteristics of the reversible thermosensitive coloring composition of the present invention.

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[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

[Table 10]

[Table 11]

[Table 12]

[Table 13]

[Table 14]

[Table 15]

[Table 16]

[Table 17]

[Table 18]

[Table 19]

[Table 20]

[Table 21]

[Table 22]

[Table 23]

[Table 24]

[Table 25]

[Table 26]

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kyoji Tsutsui 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

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. In the thermochromic composition, a reversible thermochromic composition comprising a phenolic compound represented by the following general formula (I) as the electron-accepting compound. (In the formula, n represents an integer of 1 to 3, and R represents an aliphatic hydrocarbon group having 8 or more carbon atoms which may contain a hetero atom.) 2. A reversible thermosensitive coloring medium according to claim 1, wherein the reversible thermosensitive coloring composition is a reversible thermosensitive recording medium in which a recording layer containing a reversible thermosensitive coloring composition is provided on a support. A reversible thermosensitive recording medium characterized by using a photosensitive composition.