JPH05286239A - Reversible thermal recording medium - Google Patents

Abstract

PURPOSE:To provide a reversible thermal recording medium utilizing the reaction between a specific color former and a specific developer, excellent in color forming properties, color erasing properties and the repetition properties of both properties and having a long life. CONSTITUTION:A recording layer wherein an electron donating color forming compd. such as a fluorane compd. and an electron acceptive compd. having a long chain aliphatic group are dispersed in a resin matrix is provided on a support. This recording layer is heated and melted to form a color recording state and heated at temp. lower than color forming recording temp. to form a color erased non-recording state. As the resin matrix of this reversible thermal recording medium, a styrene/acrylonitrile copolymer resin and/or a styrene/ butadiene/acrylonitrile copolymer resin is used.

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 reaction between an electron-donating color-forming compound and an electron-accepting compound.

[0002]

2. Description of the Related Art Conventionally, heat-sensitive recording utilizing a color-forming reaction between an electron-donating color-forming compound (hereinafter also referred to as a color-developing agent) and an electron-accepting compound (hereinafter also referred to as a color-developing agent). The medium is widely known, and the output of electronic computers, facsimiles, vending machines, printers of scientific measuring machines, C
Widely applied to RT medical measurement printers. However, all of the conventional products are irreversible in color development, and it is not possible to alternately repeat color development and color erasing.

On the other hand, according to the patent publication, there have been proposed some thermosensitive recording media which utilize a color-forming reaction between a color-developing agent and a color-developing agent to reversibly perform color development and decolorization. For example, according to Japanese Patent Laid-Open No. 60-193,691,
The use of a combination of gallic acid and phloroglucinol as a color developer is shown. The color-developing material obtained by thermally coloring this material is decolorized with water or steam.
However, in the case of this heat-sensitive recording medium, there is a problem in that it is difficult to make it water resistant, and there is a problem in the storage stability of the recording medium. JP-A-61-237684 discloses a rewritable optical recording medium using a compound such as phenolphthalene, thymolphthalene or bisphenol as a color developer. This product can be decolored by heating it and gradually cooling it to form a coloring material, while heating the coloring material once to a temperature higher than the coloring temperature and then rapidly cooling it. However, in the case of this recording medium, the process of coloring and erasing is complicated, and some color is still seen in the erasable body obtained by erasing the chromophore, and a colored image with good contrast is obtained. I can't. JP-A-62-14088
1, JP-A-62-138568 and JP-A-62-1.
No. 38,556 shows a homogeneous compatible solution of a color former, a developer and a carboxylic acid ester. This one shows a completely colored state at a low temperature and a completely decolored state at a high temperature, and can keep the colored or decolored state at an intermediate temperature between them, and by printing with a thermal head on this medium,
White characters (decolored body) can be recorded on the colored background (colored body). Therefore, in the case of this recording medium, since the image to be recorded is a negative image, its use is limited, and it is necessary to keep the image within a specific temperature range for storing the recorded image. JP-A-2-188294 and JP-A-2-188293 disclose, as a developer, a salt of gallic acid and a higher aliphatic amine that reversibly perform a color developing action and a color reducing action, and bis (hydroxyphenyl). ) A salt of acetic acid or butyric acid and a higher aliphatic amine is used. This product can be thermally colored in a specific temperature range and decolorized by heating at a higher temperature than that, but since its color developing action and color reducing action occur competitively,
It is difficult to control these effects thermally, and it is difficult to obtain good image contrast. As described above, the conventional reversible thermosensitive recording medium utilizing the reaction between the color former and the color developer has various problems and is still unsatisfactory.

The present applicant previously used organic phosphoric acid having a long-chain aliphatic group as a color developer, and compounds such as carboxyl compounds, phenol compounds and hydroxyphosphonic acid,
By combining this with a fluoran compound or the like as a color former, it is possible to easily perform the coloring and decoloring only by heating, and it is possible to maintain the colored state and the decolorized state at room temperature, In addition, a reversible thermochromic composition has been proposed, which has a decoloring temperature lower than the coloring temperature, and moreover, image formation and erasing can be repeated many times by changing the temperature. However, in a reversible thermosensitive recording medium comprising a recording layer having such a thermochromic composition, the properties such as color forming property and decoloring property, and reproducibility of color forming and decoloring properties are necessary for forming the recording layer. It was also found that it was affected by the required resin base material and that a practical problem could occur depending on the type of resin base material. That is, in such a reversible thermosensitive recording medium, a vinyl chloride-vinyl acetate copolymer resin is preferably used as a resin base material, but even in a reversible thermosensitive recording medium using the resin, coloring occurs when used many times. In many cases, the discoloration property and the decoloring property are deteriorated, which is not yet satisfactory.

[0005]

The present invention solves the above problems in a reversible thermosensitive recording medium utilizing the reaction between a color former such as a fluorane compound and a developer having a long-chain aliphatic group, It is an object of the present invention to provide a reversible thermosensitive recording medium having improved reproducibility with less deterioration in color development and decolorization even when color development and decolorization are repeated many times.

[0006]

The inventor of the present invention has completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a recording layer containing a color former and a color developer dispersed in a resin base material is provided on a support, a color recording state is formed by heating and melting, and the temperature is lower than the color development temperature. In a reversible thermosensitive recording medium which forms a decolored state in which recording disappears by heating, a styrene-acrylonitrile copolymer resin or a styrene-butadiene-acrylonitrile copolymer resin is used as the resin matrix. A reversible thermosensitive recording medium is provided.

The heat-sensitive recording medium of the present invention instantly develops color upon heating, and the color-developed state thereof is stable even at room temperature, but the recording layer in the color-developed state is instantly decolored by heating below the color-developing temperature. The erased state is stable even at room temperature. The principle of coloring and erasing, that is, image forming and image erasing of the thermosensitive recording medium according to the present invention will be described with reference to the graph shown in FIG. The vertical axis of the graph represents the color density and the horizontal axis represents the temperature. The solid line 1 shows the image forming process by heating and the broken line 3 shows the image erasing process by heating. A is the density in the completely erased state, B is the density in the completely colored state when heated to a temperature of T ₁ or higher, C is the density at the temperature of T ₀ or lower in the completely colored state, and D is T _0. It shows the concentration when heat erasing is performed at a temperature between T _{1 and} T ₁ . The thermal recording medium of the present invention is
It is in a colorless state (A) at a temperature of T ₀ or lower. In order to perform recording, heating to a temperature of T ₁ or higher with a thermal head or the like is performed, and color development (B) is performed to form a recorded image. Even if the recorded image is returned to the temperature of T ₀ or less according to the solid line 2, the state (C) is maintained as it is, and the recording memory property is not lost. Next, in order to erase the recorded image, the formed recorded image may be heated to a temperature between T _{0 and} T _{1 which} is lower than the coloring temperature, and the state becomes colorless (D). In this state, even if the temperature is returned to T ₀ or lower, the colorless state (A) is maintained as it is. That is, in the process of forming the recorded image, the recording is held up to C by the path of the solid line ABC. In the process of erasing the recorded image, the erased state is maintained up to A by the path of the broken line CDA. The behavioral characteristics of forming and erasing the recorded image are reversible and can be repeated many times.

FIG. 2 is an explanatory view showing an example of image formation and image erasure, wherein 1 is a support and 2 is a reversible thermosensitive recording layer of the present invention. In the image forming process (A) → (B), the image forming heat source, for example, the thermal head 4 is used to perform the T of FIG.
_This is achieved by recording and printing at a temperature of ₁ or higher. Next, the image erasing step (B) → (A) is achieved by heating the image erasing heat source, for example, the heating roller 5 to a temperature between T _{0 and} T ₁ . In FIG. 2, 3 indicates a color image.

The reversible thermosensitive recording medium of the present invention contains a color former and a color developer as essential components. The color development of the reversible thermosensitive recording medium according to the present invention is obtained by cooling the color-forming material composition formed by the eutectic reaction of the developer and the color-forming agent constituting the recording layer by heating to room temperature. Is. Since this color-forming material composition has an erasing temperature region on the lower temperature side than the melting temperature, it is generally preferable to perform rapid cooling in order to cool from the melt-colored state to room temperature while maintaining the color development. When gradually cooled, some color disappears when passing through the color-erasing temperature range, and the density often decreases. It is considered that in the color former composition, the molecules of the color former and the developer interact with each other to open the lactone ring of the color former to develop a color.
The composition from the molten state to the rapidly cooled state contains a color former molecule and a color former molecule that are not directly involved in the formation of the color former. In the reversible thermosensitive recording medium of the present invention, the color former composition at room temperature is in a solidified state due to the cohesive force acting between these molecules. The color-developed state of the conventional thermosensitive color-developing composition often does not become an aggregated solid. The color former composition formed in the recording layer of the present invention is an aggregated solid in the color developed state. The aggregate structure in this state often shows some regularity. The degree of regularity may be very regular or not very regular, which depends on the combination of the developer and the color former, the amount ratio, or the cooling conditions. The formation of such an aggregate structure is basically the long-chain structure part of the developer molecule forming the color former and the excess long-chain structure part of the developer molecule not forming the color former. It is presumed that the cohesive force acting between the two is mainly acting, and that the formation of such an aggregating structure is associated with the decoloring phenomenon of the color-forming composition formed in the recording layer of the present invention. It is presumed to be related.

The color-forming composition formed in the recording layer of the present invention can be decolored by heating its color-developing state to a specific temperature range. In this decoloring process, the aggregate structure of the color-developing state changes, and finally the developer molecules are separated and crystallized from the color-forming composition to form a crystal of the developer alone, which may result in a stable decoloring state. Confirmed by X-ray. As described above, in the present invention, it is clear that the long-chain portion of the color developer plays a large role in the formation of the aggregated colored state and the decoloring process thereof, which is formed in the recording layer of the present invention. This is a characteristic of the color forming composition. Therefore, it becomes possible to control the erasing temperature by the length of the long chain part of the color developer.
It was confirmed that the longer the chain length, the higher the color development and decolorization temperature shifted. This is because the aggregation and motility of the developer molecule change depending on the length of the long chain portion.

The color-forming composition formed in the recording layer of the present invention is basically a composition in which the above-mentioned color developer having a long-chain structure and the color-developing agent are combined with each other. Preferred color formers are present. The combination of the color-developing agent and the color-developing agent used in the color-forming composition formed in the recording layer of the present invention includes heating a composition in a color-developed state obtained by heating both of them to a temperature lower than the melting temperature. Ease of discoloration that occurs when
That is, it is appropriately selected depending on the characteristics such as the decoloring property and the color tone of the coloring state. Among them, the decoloring property can be judged by the presence or absence of an exothermic peak appearing in the temperature rising process in the differential thermal analysis (DTA) or the differential scanning calorimetry (DSC) of the composition in the colored state obtained by the combination. This exothermic peak corresponds to the decoloring phenomenon that characterizes the present invention, and serves as a criterion for selecting a combination having a good decoloring property. The third substance may be present in the heat-sensitive recording layer of the present invention, and for example, the reversible decoloring behavior can be maintained even when a polymer compound is present.

The long-chain developer used in combination with the color former in the thermosensitive recording medium of the present invention basically has a structure showing a color-developing ability capable of developing the color former in the molecule and an intermolecular structure. It is a compound that also has a long aliphatic chain structure part that controls the cohesive force, and is an organic phosphoric acid compound, an aliphatic carboxylic acid compound, or a phenol compound having an aliphatic group having 12 or more carbon atoms, or a fat having 10 to 18 carbon atoms. It is a metal salt of mercaptoacetic acid having a group. 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 group.

As the organic phosphoric acid compound, a compound represented by the following general formula (1) is used. R ₁ -PO (OH) ₂ (1) Specific examples of (wherein, R ₁ represents a number of 12 or more aliphatic groups carbons) organic phosphoric acid compound represented by the general formula (1), for example, the following Is mentioned. Dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid, docosylphosphonic acid, tetracosylphosphonic acid, hexacosylphosphonic acid, octacosylphosphonic acid, etc.

As the aliphatic carboxylic acid compound, α-hydroxy fatty acids represented by the following general formula (2) are used. R ₂ —CH (OH) —COOH (2) (wherein R ₂ represents an aliphatic group having 12 or more carbon atoms) Examples of the α-hydroxyaliphatic carboxylic acid compound represented by the general formula (2) are shown below. The ones are listed. α-hydroxydodecanoic acid, α-hydroxytetradecanoic acid, α-hydroxyhexadecanoic acid, α-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 substituted with a halogen element, and having a halogen element at at least the α-position or β-position carbon. Is also used. Specific examples of such compounds include the followings. 2-chlorooctadecanoic acid, heptadecaflornonadecanoic acid, 2-bromohexadecanoic acid, 2-bromoheptadecanoic acid, 2-bromooctadecanoic acid, 2-bromoeicosanoic acid, 2-bromodocosanoic acid, 2-bromotetracosanoic acid , 3-bromooctadecanoic acid, 3-bromoeicosanoic acid, 2,3-dibromooctadecanoic acid, 2-flordodecanoic acid, 2-fluorotetradecanoic acid, 2-fluorohexadecanoic acid, 2-fluorooctadecanoic acid, 2-fluoroeicosane Acid, 2-flordocosanoic acid, 2-iodohexadecanoic acid, 2-iodooctadecanoic acid, 3-iodohexadecanoic acid, 3-iodooctadecanoic acid, perfluorooctadecanoic acid and the like.

The aliphatic carboxylic acid compound is an aliphatic carboxylic acid compound having an oxo group having 12 or more carbon atoms in the carbon chain, and at least the carbon at the α-position, β-position or γ-position is oxo. The underlying one is also used. Specific examples of such compounds include the followings. 2-oxododecanoic acid,
2-oxotetradecanoic acid, 2-oxohexadecanoic acid, 2-oxooctadecanoic acid, 2-oxoeicosanoic acid, 2-oxotetracosanoic acid, 3-oxododecanoic acid, 3-oxotetradecanoic acid, 3-oxohexadecanoic acid, 3-oxooctadecanoic acid, 3-oxoeicosanoic acid, 3-oxotetracosanoic acid, 4-oxohexadecanoic acid, 4-oxoheptadecanoic acid, 4-oxooctadecanoic acid, 4-oxodocosanoic acid and the like.

As the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (3) is also used. (However, R ₃ represents an aliphatic group having 12 or more carbon atoms,
X represents an oxygen atom or a sulfur atom, and n represents 1 or 2. Specific examples of the dibasic acid represented by the general formula (3) include:
For example: Dodecylmalic acid, tetradecylmalic acid, hexadecylmalic acid, octadecylmalic acid, eicosylmalic acid, docosylmalic acid, tetracosylmalic acid, dodecylthiomalic acid, tetradecylthiomalic acid, hexadecylthiomalic acid, octadecyl Thiomalic acid, eicosylthiomalic acid, docosylthiomalic acid, tetracosylthiomalic acid, dodecyldithiomalic acid, tetradecyldithiomalic acid, hexadecyldithiomalic acid, octadecyldithiomalic acid, eicosyldithiomalic acid, Docosyldithiomalic acid, tetracosyldithiomalic acid, etc.

As the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (4) is also used. (However, R ₄ , R ₅ , and R ₆ 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 dibasic acid represented by the general formula (4) For example,
For example: Dodecyl butanedioic acid, tridecyl butanedioic acid, tetradecyl butanedioic acid,
Pentadecyl butanedioic acid, octadecyl butanedioic acid, eicosyl butanedioic acid, docosyl butanedioic acid, 2,3-dihexadecyl butanedioic acid, 2,3-dioctadecyl butanedioic acid, 2-methyl-3-dodecyl butane Diacid, 2-methyl-3-tetradecylbutanedioic acid, 2-methyl-3-
Hexadecyl butanedioic acid, 2-ethyl-3-dodecyl butanedioic acid, 2-propyl-3-dodecyl butanedioic acid, 2
-Octyl-3-hexadecyl butanedioic acid, 2-tetradecyl-3-octadecyl butanedioic acid and the like.

As the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (5) is also used. (However, R ₇ and R ₈ represent hydrogen or an aliphatic group, and at least one of them is an aliphatic group having 12 or more carbon atoms.) Specific examples of the dibasic acid represented by the general formula (5) ,
For example: Dodecyl malonic acid,
Tetradecylmalonic acid, hexadecylmalonic acid, octadecylmalonic acid, eicosylmalonic acid, docosylmalonic acid, tetracosylmalonic acid, didodecylmalonic acid, ditetradecylmalonic acid, dihexadecylmalonic acid, dioctadecylmalonic acid, Dieicosylmalonic acid, didocosylmalonic acid, methyloctadecylmalonic acid, methyleicosylmalonic acid, methyldocosylmalonic acid, methyltetracosylmalonic acid, ethyloctadecylmalonic acid, ethyleicosylmalonic acid, ethyldocosylmalonic acid, Ethyl tetracosyl malonic acid etc.

As the aliphatic carboxylic acid compound, a dibasic acid represented by the following general formula (6) can also be used. (However, R ₉ represents an aliphatic group having 12 or more carbon atoms,
n represents 0 or 1, m represents 1, 2 or 3, m is 2 or 3 when n is 0, and m is 1 or 2 when n is 1) ) As a specific example of the dibasic acid,
For example: 2-dodecyl-pentanedioic acid, 2-hexadecyl-pentanedioic acid, 2-octadecyl-pentanedioic acid, 2-eicosyl-pentanedioic acid, 2-docosyl-pentanedioic acid, 2-dodecyl-hexanedioic acid, 2- Pentadecyl-hexanedioic acid, 2-octadecyl-hexanedioic acid, 2-eicosyl-hexanedioic acid, 2-docosyl-hexanedioic acid and the like.

As the aliphatic carboxylic acid compound, a tribasic acid such as citric acid acylated with a long chain fatty acid can also be used. Specific examples thereof include the following.

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

[Chemical 1] (However, Y is -S-, -O-, -CONH-, or-
Represents COO-, R ₁₀ 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, 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-hexadecylcarbamoyl Phenol, p-octadecylcarbamoylphenol, p
-Eicosylcarbamoylphenol, p-docosylcarbamoylphenol, p-tetracosylcarbamoylphenol, hexadecyl gallate, octadecyl gallate, eicosyl gallate,
Dodecyl gallate, tetracosyl gallate, etc.

As the organic phosphoric acid compound, the following general formula (8)
It is also possible to use an α-hydroxyalkylphosphonic acid represented by (However, R ₁₁ is an aliphatic group having ₁₁ to 29 carbon atoms.) Specific examples of the α-hydroxyalkylphosphonic acid represented by the general formula (8) include α-hydroxydodecylphosphonic acid and α-hydroxytetracarboxylic acid. Decylphosphonic acid, α-
Examples thereof include hydroxyhexadecylphosphonic acid, α-hydroxyoctadecylphosphonic acid, α-hydroxyeicosylphosphonic acid, α-hydroxydocosylphosphonic acid, and α-hydroxytetracosylphosphonic acid.

As the metal salt of mercaptoacetic acid, a metal salt of alkyl or alkenyl mercaptoacetic acid represented by the general formula (9) is used. (R ₁₂ —S—CH ₂ —COO) ₂ M (9) (wherein R ₁₂ represents an aliphatic group having 10 to 18 carbon atoms, and M represents tin, magnesium, zinc or copper) General formula (9 Specific examples of the mercaptoacetic acid metal salt represented by the formula (1) include the following. Decyl mercapto acetic acid tin salt, dodecyl mercapto acetic acid tin salt,
Tetradecylmercaptoacetic acid tin salt, hexadecylmercaptoacetic acid tin salt, octadecylmercaptoacetic acid tin salt, decylmercaptoacetic acid magnesium salt, dodecylmercaptoacetic acid magnesium salt, tetradecylmercaptoacetic acid magnesium salt, hexadecylmercaptoacetic acid magnesium salt, octadecylmercaptoacetic acid magnesium salt Salt, decylmercaptoacetic acid zinc salt, dodecylmercaptoacetic acid zinc salt, tetradecylmercaptoacetic acid zinc salt, hexadecylmercaptoacetic acid zinc salt, octadecylmercaptoacetic acid zinc salt, decylmercaptoacetic acid copper salt, dodecylmercaptoacetic acid copper salt, tetradecylmercaptoacetic acid Copper salt,
Hexadecyl mercapto acetic acid copper salt, octadecyl mercapto acetic acid copper salt, etc.

The color-forming composition formed in the reversible thermosensitive recording layer of the present invention is basically formed by combining a color-developing agent with the color-developing agent. The color-forming agent used in the present invention is one that exhibits an electron-donating property and is a colorless or light-colored dye precursor itself, and is not particularly limited, and conventionally known ones such as triphenylmethanephthalide-based compounds and fluoran-based compounds. , Phenothiazine compounds, leuco auramine compounds, indolinophtalide compounds and the like are used. Specific examples of the color former are shown below. As a preferred color former used in the present invention, there is a fluoran compound represented by the following general formula (10).

[Chemical 2] (Wherein, R ₁₃ represents a hydrogen atom, an alkyl group, an allyl group, a cyclic alkyl group, or an alkoxyalkyl group, R ₁₄
Represents an alkyl group, a cyclic alkyl group, an allyl group, an alkoxyalkyl group, or an optionally substituted phenyl group. X represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, an alkoxyalkyl group, or a halogen atom. Y represents a lower alkyl group, an amino group, a substituted amino group, a cyano group, or a halogen atom. )

Specific examples of the compound represented by the general formula (10) include the following compounds. 2-anilino-3-methyl-6- (Nn-hexyl-N-iso-amylamino) fluorane, 2-anilino-3-methyl-6-
(Di-n-hexylamino) fluorane, 2-anilino-3-methyl-6- (di-n-amylamino) fluorane, 2-anilino-3-methyl-6- (di-n-octylamino) fluorane, 2 -Anilino-3-methyl-6
-(Di-n-butylamino) fluorane, 2-anilino-3-methyl-6- (di-n-propylamino) fluorane, 2-anilino-3-methyl-6- (Nn-propyl-N-) Methylamino) fluorane, 2-anilino-
3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-dimethylaminofluorane, 2
-Anilino-3-methyl-6- (N-isopropyl-N
-Methylamino) fluorane, 2-anilino-3-methyl-6- (Nn-octyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (Nn-octyl-N-iso) -Propylamino) fluorane, 2
-Anilino-3-methyl-6- (Nn-amyl-N-
n-propylamino) fluorane, 2-anilino-3-
Methyl-6- (Nn-amyl-Nn-butylamino) fluorane, 2-anilino-3-methyl-6- (N
-N-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane, 2-anilino-3-methyl-6
-(N-iso-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (Nn-propyl-N-isopropylamino) fluorane, 2-anilino-3-methyl-6- ( N-n-butyl-N-n-propylamino) fluorane, 2-anilino-3-methyl-
6- (N-ethyl-N-sec-butylamino) fluorane, 2-anilino-3-methyl-6- (Nn-butyl-N-iso-propylamino) fluorane, 2-anilino-3-methyl- 6- (N-n-butyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6
-(N-isobutyl-N-methylamino) fluorane.

2-anilino-3-methyl-6- (N-cyclohexyl-Nn-tetradecylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-Nn-dodecylamino) Fluoran, 2-anilino-3-methyl-6- (N-cyclohexyl-Nn
-Decylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-Nn-octylamino) fluorane, 2-anilino-3-methyl-6- (N
-Cyclohexyl-Nn-hexylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-Nn-amylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-) N-is
o-amylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-Nn-butylamino) fluorane, 2-anilino-3-methyl-6- (N
-Cyclohexyl-N-n-propylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-N-ethylamino) fluorane, 2-anilino-
3-Methyl-6- (N-cyclohexyl-N-methylamino) fluorane, 2-anilino-3-methyl-6-
(Dicyclohexylethylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexylethyl-Nn-hexylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexylethyl-N-
n-amylamino) fluorane, 2-anilino-3-methyl-6- (dicyclohexylmethylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexylmethyl-Nn-hexylamino) fluorane, 2
-Anilino-3-methyl-6- (N-cyclohexylmethyl-Nn-amylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexylmethyl-N
-N-butylamino) fluorane, 2-anilino-3-
Methyl-6- (N-cyclohexylmethyl-N-cyclohexylamino) fluorane.

2-anilino-3-methyl-6- (diallylamino) fluorane, 2-anilino-3-methyl-6
-(Nn-octyl-N-allylamino) fluorane, 2-anilino-3-methyl-6- (Nn-hexyl-N-allylamino) fluorane, 2-anilino-3
-Methyl-6- (Nn-amyl-N-allylamino)
Fluorane, 2-anilino-3-methyl-6- (N-ethyl-N-allylamino) fluorane, 2-anilino-
3-Methyl-6- (N-2-ethoxypropyl-N-ethylamino) fluorane, 2-anilino-3-methyl-
6- (diethoxyethylamino) fluorane, 2-anilino-3-methyl-6- (N-ethoxyethyl-Nn)
-Hexylamino) fluorane, 2-anilino-3-methyl-6- (N-ethoxyethyl-Nn-amylamino) fluorane, 2-anilino-3-methyl-6- (N
-Ethoxyethyl-N-iso-amylamino) fluorane, 2-anilino-3-methyl-6- (N-ethoxyethyl-Nn-butylamino) fluorane, 2-anilino-3-methyl-6- (N- Ethoxyethyl-N-ethylamino) fluorane, 2-anilino-3-methyl-
6- (N-ethoxymethyl-Nn-hexylamino)
Fluorane, 2-anilino-3-methyl-6- (N-ethoxymethyl-Nn-amylamino) fluorane, 2
-Anilino-3-methyl-6- (N-ethoxymethyl-
N-iso-amylamino) fluorane, 2-anilino-3-methyl-6- (Nn-hexadecylamino) fluorane, 2-anilino-3-methyl-6- (Nn-)
Octylamino) fluorane, 2-anilino-3-methyl-6- (Nn-hexylamino) fluorane, 2-
Anilino-3-methyl-6- (N-ethyl-p-toluidino) fluorane, 2-anilino-3-methyl-6-
(N-methyl-p-toluidino) fluorane,

2-anilino-3-methoxy-6- (di-
n-hexylamino) fluorane, 2-anilino-3-
Methoxy-6- (di-n-amylamino) fluorane,
2-anilino-3-methoxy-6- (Nn-hexyl-N-iso-amylamino) fluorane, 2-anilino-3-methoxy-6- (N-cyclohexyl-Nn
-Hexylamino) fluorane, 2-anilino-3-ethoxy-6- (di-n-amylamino) fluorane, 2
-Anilino-3-ethoxy-6- (di-n-butylamino) fluorane, 2-anilino-3-ethoxy-6-diethylaminofluorane, 2-anilino-3-ethoxy-6- (N-cyclohexyl-N- n-hexylamino) fluorane, 2-anilino-3-ethoxy-6-
(N-cyclohexyl-Nn-amylamino) fluorane, 2-anilino-3-ethoxyethyl-6- (di-
n-amylamino) fluorane, 2-anilino-3-ethoxyethyl-6- (di-n-butylamino) fluorane, 2-anilino-3-ethoxyethyl-6-diethylaminofluorane, 2-anilino-3-ethoxymethyl -6- (Di-n-butylamino) fluorane, 2-anilino-3-ethoxymethyl-6- (N-cyclohexyl-Nn-hexylamino) fluorane, 2-anilino-3-ethoxymethyl-6- ( Di-n-amylamino)
Fluoran, 2-anilino-3-methoxymethyl-6-
(N-cyclohexyl-Nn-hexylamino) fluorane, 2-benzylamino-3-methyl-6- (di-
n-butylamino) fluorane, 2-benzylamino-
3-methyl-6- (di-n-amylamino) fluorane, 2-benzylamino-3-methyl-6- (N-cyclohexyl-Nn-hexylamino) fluorane, 2
-(M-Trichloromethylanilino) -3-methyl-6
-Diethylaminofluorane, 2- (m-trifluoromethylanilino) -3-methyl-6-diethylaminofluorane, 2- (m-trifluoromethylanilino) -3-
Methyl-6- (N-cyclohexyl-N-methylamino) fluorane, 2- (2,4-dimethylanilino)-
3-Methyl-6- (Nn-hexyl-N-iso-amylamino) fluorane, 2- (2,4-dimethylanilino) -3-methyl-6- (di-n-hexylamino)
Fluoran, 2- (2,4-dimethylanilino) -3-
Methyl-6- (di-n-amylamino) fluorane, 2
-(2,4-Dimethylanilino) -3-methyl-6-
(Di-n-butylamino) fluorane, 2- (2,4-
Dimethylanilino) -3-methyl-6-diethylaminofluorane, 2- (N-ethyl-p-toluidino) -3
-Methyl-6- (N-ethylanilino) fluorane, 2
-(N-methyl-p-toluidino) -3-methyl-6-
(N-propyl-p-toluidino) fluorane,

2-anilino-6- (di-n-hexylamino) fluorane, 2-anilino-6- (Nn-hexyl-N-iso-amylamino) fluorane, 2-anilino-6- (di-n -Amylamino) fluoran, 2
-Anilino-6-diethylaminofluorane, 2-anilino-6- (Nn-hexyl-N-ethylamino) fluorane, 2-anilino-6- (N-cyclohexyl-
N-n-hexylamino) fluorane, 2-anilino-
6- (N-cyclohexyl-Nn-amylamino) fluorane, 2-anilino-6- (N-cyclohexyl-
N-methylamino) fluorane, 2-anilino-6-
(Diethoxyethylamino) fluorane, 2-anilino-6- (N-ethoxyethyl-N-iso-amylamino) fluorane, 2-anilino-6- (N-ethoxyethyl-Nn-amylamino) fluorane, 2- Anilino-6- (N-ethoxyethyl-Nn-butylamino) fluorane, 2-anilino-6- (Nn-octylamino) fluorane, 2-anilino-6- (Nn-)
Hexylamino) fluorane, 2-anilino-6- (N
-N-amylamino) fluorane, 2- (N-methylanilino) -6- (N-ethyl-p-toluidino) fluorane, 2- (o-chloroanilino) -6-diethylaminofluorane, 2- (o-bromoanilino)- 6-diethylaminofluorane, 2- (o-chloroanilino)-
6-dibutylaminofluorane, 2- (o-floranilino) -6-dibutylaminofluorane, 2- (p-chloranilino) -6- (Nn-octylamino) fluorane, 2- (p-chloranilino)- 6- (N-n-
Palmitylamino) fluorane, 2- (p-chloroanilino) -6- (di-n-octylamino) fluorane,
2- (m-trifluoromethylanilino) -6-diethylaminofluorane, 2- (p-acetylanilino) -6
-Diethylaminofluorane, 2- (p-acetylanilino) -6- (Nn-hexyl-N-iso-hexylamino) fluorane, 2- (p-acetylanilino)
-6- (di-n-hexylamino) fluorane, 2-
(P-Acetylanilino) -6- (Nn-hexyl-
N-n-amylamino) fluorane, 2- (p-acetylanilino) -6- (di-n-amylamino) fluorane, 2- (p-acetylanilino) -6- (Nn-amyl-N-) n-butylamino) fluorane, 2- (p-
Acetylanilino) -6- (N-cyclohexyl-N-
n-hexylamino) fluorane, 2- (p-acetylanilino) -6- (N-ethoxyethyl-N-iso-
Amylamino) fluorane, 2- (p-acetylanilino) -6- (N-ethoxyethyl-Nn-amylamino) 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-benzoylamino-6- (N-ethyl-p-toluidino) fluorane, 2
-(O-Methoxybenzoylamino) -6- (N-methyl-p-toluidino) fluorane, 2-dibenzylamino-6- (di-n-butylamino) fluorane, 2-dibenzylamino-6- (di -N-amylamino) fluorane, 2-dibenzylamino-6- (di-n-hexylamino) fluorane, 2-dibenzylamino-6- (N
-N-hexyl-N-iso-amylamino) fluorane, 2-dibenzylamino-6- (di-n-propylamino) fluorane, 2-dibenzylamino-6- (N-
Cyclohexyl-N-n-amylamino) fluorane,
2-dibenzylamino-6- (N-cyclohexyl-N
-N-hexylamino) fluorane, 2-dibenzylamino-6- (N-methyl-p-toluidino) fluorane, 2-dibenzylamino-6- (N-ethyl-p-toluidino) fluorane, 2- (di -P-methylbenzylamino) -6- (N-ethyl-p-toluidino) fluorane, 2-dibenzylamino-4-methyl-6-diethylaminofluorane, 2-dibenzylamino-4-methyl-6- ( Di-n-propylamino) fluorane, 2-
Dibenzylamino-4-methyl-6- (di-n-butylamino) fluorane, 2-dibenzylamino-4-methyl-6- (di-n-amylamino) fluorane, 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- (α-phenylethylamino) -6- (N- Ethyl-p-toluidino) fluorane, 2- (o-methoxycarbonylanilino) -6-diethylaminofluorane,

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) fluorane, 2-
Ethylamino-6- (N-ethyl-p-toluidino) fluorane, 2-methylamino-6- (N-methyl-2,
4, -Dimethylanilino) fluorane, 2-ethylamino-6- (N-ethyl-2,4, -dimethylanilino)
Fluorane, 2-dimethylamino-6- (N-methylanilino) fluorane, 2-dimethylamino-6- (N-
Ethylanilino) fluorane, 2-diethylamino-6
-(N-methyl-p-toluidino) fluorane, 2-diethylamino-6- (N-ethyl-p-toluidino) fluorane, 2-dipropylamino-6- (N-methylanilino) fluorane, 2-dipropylamino- 6- (N
-Ethylanilino) fluorane, 2-acetylamino-
3-Methyl-6-diethylaminofluorane, 2-acetylamino-3-methyl-6- (di-n-butylamino) fluorane, 2-acetylamino-3-methyl-6
-(Di-n-amylamino) fluorane, 2-acetylamino-3-methyl-6- (di-n-hexylamino)
Fluoran, 2-acetylamino-6- (N-methyl-
p-toluizino) fluoran,

2-amino-6-diethylaminofluorane, 2-amino-6- (di-n-butylamino) fluorane, 2-amino-6- (di-n-amylamino) fluorane, 2-amino-6- (Di-n-hexylamino)
Fluoran, 2-amino-6- (N-cyclohexyl-
N-n-amylamino) fluorane, 2-amino-6-
(N-methylanilino) fluorane, 2-amino-6-
(N-ethylanilino) fluorane, 2-amino-6-
(N-propylanilino) fluorane, 2-amino-6
-(N-methyl-p-toluidino) fluorane, 2-amino-6- (N-ethyl-p-toluidino) fluorane, 2-amino-6- (N-propyl-p-toluidino) fluorane, 2-amino- 6- (N-methyl-p-
Ethylanilino) fluorane, 2-amino-6- (N-
Ethyl-p-ethylanilino) fluorane, 2-amino-6- (N-propyl-p-ethylanilino) fluorane, 2-amino-6- (N-methyl-2,4-dimethylanilino) fluorane, 2-amino- 6- (N-ethyl-2,4-dimethylanilino) fluorane, 2-amino-6- (N-propyl-2,4-dimethylanilino) fluorane, 2-amino-6- (N-methyl-p -Chloranilino) fluorane, 2-amino-6- (N-ethyl-p-chloroanilino) fluorane, 2-amino-6-
(N-propyl-p-chloroanilino) fluorane,
2-Amino-3-methyl-6-diethylaminofluorane, 2-amino-3-methyl-6- (di-n-butylamino) fluorane, 2-amino-3-methyl-6- (di-n-amylamino) ) Fluoran, 2-amino-3-methyl-6- (di-n-hexylamino) fluoran, 2
-Amino-3-methoxy-6- (di-n-butylamino) fluorane, 2-amino-3-methoxy-6- (di-n-amylamino) fluorane, 2-amino-3-methoxy-6- (di -N-hexylamino) fluorane,

1,3-Dimethyl-6-diethylaminofluorane, 1,3-dimethyl-6- (di-n-butylamino) fluorane, 1,3-dimethyl-6- (di-n-)
Amylamino) fluorane, 1,3-dimethyl-6-
(Di-n-hexylamino) fluorane, 1,3-dimethyl-6- (N-cyclohexyl-Nn-butylamino) fluorane, 2,3-dimethyl-6-dimethylaminofluorane, 2-methyl-6 -Dimethylaminofluorane, 2-methyl-6-diethylaminofluorane, 2
-Methyl-6- (di-n-propylamino) fluorane, 2-methyl-6- (di-n-butylamino) fluorane, 2-methyl-6- (di-n-amylamino) fluorane, 2-methyl- 6- (di-n-hexylamino)
Fluoran, 2-methyl-6- (N-cyclohexyl-
N-n-amylamino) fluorane, 2-methyl-6-
(N-cyclohexyl-N-methylamino) fluorane, 3-diethylamino-6- (m-trifluoromethylanilino) fluorane, 3-methyl-6- (N-ethyl-p-toluidino) fluorane, 2-methyl- 6- (N
-Ethyl-p-toluidino) fluorane, 4-methoxy-6- (N-ethyl-p-toluidino) fluorane, 2
-Cyano-6-diethylaminofluorane, 2-cyano-6- (di-n-butylamino) fluorane, 2-cyano-6- (di-n-amylamino) fluorane, 2-cyano-6- (di-n -Hexylamino) fluorane, 2
-Cyano-6- (N-cyclohexyl-Nn-hexylamino) fluorane, 2-cyano-6- (N-cyclohexyl-Nn-decylamino) fluorane.

2-chloro-6-diethylaminofluorane, 2-bromo-6-diethylaminofluorane, 2-
Chlor-6-dipropylaminofluorane, 2-chloro-6-dibutylaminofluorane, 3-chloro-6-cyclohexylaminofluorane, 3-bromo-6-cyclohexylaminofluorane, 2-chloro-6- ( N-
Ethyl-N-isoamylamino) fluorane, 2-chloro-3-methyl-6-diethylaminofluorane, 2-
Anilino-3-chloro-6-diethylaminofluorane, 2- (o-chloroanilino) -3-chloro-6-cyclohexylaminofluorane, 2- (m-trifluoromethylanilino) -3-chloro-6-diethylamino Fluoran, 2- (2,3-dichloroanilino) -3-chloro-6-diethylaminofluorane, 2-ethoxyethylamino-3-chloro-6-dibutylaminofluorane, 2-benzylamino-4-chloro-6 -(N-ethyl-p-toluidino) fluorane, 2-dibenzylamino-4-chloro-6- (N-ethyl-p-toluidino)
Fluorane, 2- (α-phenylethylamino) -4-
Chlor-6-diethylaminofluorane, 2- (N-benzyl-p-trifluoromethylanilino) -4-chloro-6-diethylaminofluorane and the like.

Besides the general formula (10), there are many fluoran compounds preferable as the color former used in the present invention, and specifically, the following compounds are exemplified. 2-anilino-3-
Methyl-6-pyrrolidinofluorane, 2-anilino-3
-Chlor-6-pyrrolidinofluorane, 2-anilino-
3-Methyl-6- (N-ethyl-tetrahydrofurfurylamino) fluorane, 2-mesidino-3-methyl-
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- (Np-chlorophenyl-p-chloranilino) -6-pyrrolidinofluorane, 2- (N-n-propyl-m-trifluoromethylanilino) -6-morpholinoflu Olane, 1,2-benzo-6-diethylaminofluorane, 1,2-benzo-
6- (N-ethyl-N-isoamylamino) fluorane, 1,2-benzo-6-dibutylaminofluorane,
1,2-benzo-6- (di-n-amylamino) fluorane, 1,2-benzo-6- (di-n-hexylamino) fluorane, 1,2-benzo-6- (N-methyl-)
N-cyclohexylamino) fluorane, 1,2-benzo-6- (N-ethyl-Nn-octylamino) fluorane, 1,2-benzo-6- (N-ethyl-p-toluidino) fluorane, 1, 2-benzo-6-diallylaminofluorane, 1,2-benzo-6- (N-ethoxyethyl-N-ethylamino) fluorane and the like.

There are many compounds other than the fluoran compound which are preferable as the color former used in the present invention, and the following compounds are specifically mentioned. Benzoleucomethylene blue, 2- [3,6-bis (diethylamino)]-6-
(0-chloranilino) xanthyl lactam benzoate,
2- [3,6-bis (diethylamino)]-9- (0-
Chloranilino) xanthyl lactam benzoate, 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-)
Chlor-5-methoxyphenyl) phthalide, 3,6-bis (dimethylamino) fluorenspiro (9,3 ′)-
6'-dimethylaminophthalide, 6'-chloro-8'-
Methoxy-benzoindolino-spiropyran, 6'-bromo-2'-methoxy-benzoindolino-spiropyran and the like.

The ratio of the color former to the developer in the reversible thermosensitive recording layer constituting the reversible thermosensitive recording medium of the present invention needs to be appropriately selected depending on the physical properties of the compound used. The range is about 1 to 20 and preferably 2 to 10 in terms of molar ratio of the color developer to the color developer. If the amount of the color developing agent is at least or more than this range, the density of the color-developed state becomes low, which is a practical problem.
Further, even in the above preferable range, the decoloring property changes depending on the ratio of the color developing agent and the color developing agent. When the amount of the color developing agent is relatively large, the decoloring start temperature becomes low, and when it is relatively small, The decolorization becomes sharp with respect to temperature. Therefore, this ratio must be appropriately selected according to the application and purpose. The reversible thermochromic composition constituting the reversible thermosensitive recording layer of the present invention basically comprises the above-mentioned color developer and color former, but has various characteristics such as decoloring property and storability. For the purpose of improving the above, an additive having an effect of controlling the crystallization of the color developer can be contained. The reversible thermosensitive recording medium of the present invention is one in which a recording layer containing the above-mentioned reversible thermochromic composition is provided on a support, and the basic configuration of the recording medium comprises a support at the bottom layer, An undercoat layer, a recording layer, and a protective layer are sequentially laminated on top. The support used here is paper, synthetic paper, plastic film or a composite of these,
It may be a glass plate or the like as long as it can hold the recording layer.

In the present invention, a resin matrix (also referred to as a binder resin) is provided in the reversible thermosensitive recording layer together with a color former and a developer.
Styrene-acrylonitrile copolymer resin and /
Alternatively, a styrene-butadiene-acrylonitrile copolymer resin is contained. These resins are known as binder resins used in the heat-sensitive recording layer, and as is clear from Examples and Comparative Examples, vinyl chloride-acetic acid is used when the recording medium is used for the first time or twice. There is almost no difference when the vinyl copolymer resin and the styrene copolymer are used. However, when the recording medium is repeatedly used, a large difference is recognized between the two (see Examples and Comparative Examples). The reason for this is that styrene-acrylonitrile copolymer resin and styrene-butadiene-acrylonitrile copolymer resin have higher heat resistance and impact resistance than vinyl chloride-vinyl acetate copolymer resin, which has the highest evaluation as a binder resin. It is presumed that the mechanical properties of are also good. In the recording layer, the binder resin not only retains a layered structure in which a color former and a color developer are uniformly dispersed, but
It is known to have functions such as preventing the color former and developer in the recording layer from aggregating due to repeated erasing, and preventing the recording layer from being deformed by the temperature and pressure when heat is applied. ing.
Therefore, it can be easily estimated that the life of the recording medium is improved by using a binder resin having excellent heat resistance and mechanical properties. However, in the binder resin for a recording medium, the dispersibility of the color former and the color developer is improved. In addition, since suitability is required in various fields such as adhesiveness to a support, it cannot be said that it is suitable as a binder resin that can be continuously used unless all of these are satisfied. The present inventor has examined in detail the suitability as a binder resin for a recording medium for a large number of resins having excellent heat resistance and mechanical properties, and as a result, a styrene-acrylonitrile copolymer resin and a styrene-butadiene-acrylonitrile copolymer resin It has reached the resin.

The styrene-acrylonitrile copolymer resin preferably used as the binder resin in the present invention has an acrylonitrile / styrene molar ratio of 0.1 to 0.1.
5 and particularly preferably 0.5 to 3. Further, in the styrene-butadiene-acrylonitrile copolymer resin, the composition ratio is 0.5 to 3: 0.1 to 2: in molar ratio.
1-5 are used, especially 1-2: 0.5-1: 2
Copolymers of ~ 4 are preferred. These copolymer resins may be used alone or as a mixture of both, and may be used as a mixture with a resin other than a styrene resin, for example, a chlorinated vinyl chloride resin. Further, it may be used as a mixture with a highly evaluated vinyl chloride-vinyl acetate copolymer resin as a binder resin, but when the styrene copolymer resin content of the present invention decreases, heat resistance and mechanical properties also decrease accordingly. Therefore, in order to obtain a thermosensitive recording medium in which the coloring property and the decoloring property are not deteriorated even when used many times, the content of the styrene-based copolymer resin in the binder resin is preferably 30% by weight or more. .. As described in detail above, styrene-acrylonitrile copolymer resin and / or styrene-
The butadiene-acrylonitrile copolymer resin prevents deformation and alteration of the recording layer due to a large number of heat applications due to its heat resistance and mechanical properties, so that the content in the recording layer is relatively large. It is desirable to do. But,
Increasing the content of the binder resin in the recording layer lowers the concentrations of the color former and the developer, leading to lower color density, which is not preferable as a recording medium. In consideration of these, in a reversible thermosensitive recording medium intended to be used a large number of times, the mixing ratio of the heat-resistant binder resin in the recording layer is 20 to 80% by weight, preferably 30 to 60% by weight. If it is limited to styrene-acrylonitrile copolymer resin or styrene-butadiene-acrylonitrile copolymer resin, the mixing ratio in the recording layer is 10 to 70% by weight, preferably 30 to 50% by weight. ─
It is good to

The recording layer according to the present invention is formed by uniformly dispersing or dissolving a color former and a developer together with a resin base material in water or an organic solvent according to a conventionally known method, and coating and drying the same on a support. You can do it. In this case, the color developing agent and the color developing agent can be used as they are or by being encapsulated in microcapsules. The color developer and the color former can be microencapsulated by a known method such as a coacervation method, an interfacial polymerization method, or an in situ polymerization method. Needless to say, the color-developing agent and the color-developing agent may be used alone or in combination of two or more.
In the reversible thermosensitive recording medium of the present invention, if necessary, various additives such as a dispersant, a surfactant and a polymer which are used in ordinary thermosensitive recording paper are used for the purpose of improving coating properties or recording properties. Cationic conductive agent, filler, color image stabilizer,
Antioxidants, light stabilizers, lubricants and the like can be added to the recording layer.

As described above, in the present invention, the protective layer is usually provided on the upper surface of the recording layer and the undercoat layer is provided on the lower surface, but these are not essential and may be omitted in a simple reversible thermosensitive recording medium. However, since the protective layer prevents the surface from being deformed or discolored by heat and pressure when heat is applied, it is extremely useful to install the protective layer for multiple uses, so install it except in special cases. Good to do. In addition to this, the protective layer may have a role of improving chemical resistance, water resistance, abrasion resistance, head matching property, and the like. Therefore, a material for forming the protective layer is preferably one having high heat resistance and high strength, and silicone rubber, silicone resin, polysiloxane graft polymer, ultraviolet curable resin, electron beam curable resin and the like are used. By forming such a protective layer,
As described above, the heat resistance is improved, and the resistance to contact with organic solvents, plasticizers, oils, sweat, water, etc. is also increased, and a recording medium capable of repeating image formation and erasing without problems even in a bad environment is obtained. be able to. Further, by containing a light stabilizer in the protective layer, it is possible to obtain a recording medium in which the light resistance of the image and the background are remarkably improved, and it is possible to prevent electrification by the addition of a polymer cationic conductive agent. By containing an organic or inorganic filler and a lubricant in the protective layer, a thermal recording medium having excellent reliability and head matching properties can be obtained without causing problems such as sticking caused by contact with a thermal head or the like. The effect of adding the antistatic agent is an effect of preventing the recording medium from being frictionally charged and sticking, an effect of preventing electric shock during handling, and the like. As with the recording layer formation method, the protective layer may be formed by uniformly dispersing or dissolving the components of the protective layer in water or an organic solvent, and uniformly coating and drying this on the recording layer. Is about 0.5 to 10 μm.

The undercoat layer improves the heat insulating property, improves the adhesion between the support and the recording layer, improves the resistance of the support to the solvent at the time of forming the recording layer, and prevents the support from absorbing the heat-meltable ink when heat is applied. The purpose of the installation is to determine the presence or absence of the installation in consideration of the type of support. One of the important roles of the undercoat layer is to improve the heat insulating property, but this is to make the applied heat energy useful for forming thermal recording without waste, and by installing the heat insulating layer, coloring and decoloring can be sharpened. It can be performed, and it is possible to cope with a decrease in applied heat energy as the recording speed increases.
The undercoat layer for the purpose of heat insulation may be formed by coating fine hollow particles made of an organic or inorganic material on a support, and specifically, a particle diameter of 10 to 10 formed of glass or ceramics, plastic, or the like. A minute hollow body of about 50 μm may be well dispersed in a solvent together with a binder resin, and uniformly coated and dried on the support. When the support is a substance that easily absorbs liquid such as paper, it is sufficient to form an undercoat layer that is impermeable to liquid, and when a support soluble in a recording layer forming solvent is used. For the above, an undercoat layer insoluble in the solvent may be provided on the support.

The formation of a recorded image is not particularly limited by a hot pen, a thermal head, laser heating, etc. depending on the purpose of use. Similarly, the erasing of the recorded image is not particularly limited as long as the erasing temperature conditions such as the heating roller, the sheet heating element, the constant temperature bath, the warm air, and the thermal head are given. Further, so-called overwriting is possible in which the recorded image is erased by the thermal head set to the erasing temperature and at the same time the recorded image is formed by another thermal head set to the recording temperature.

[0045]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. All parts below are based on weight.

Example 1 The following composition was crushed and dispersed by a ball mill to a particle size of 1 to 4 μm to prepare a recording layer coating liquid. 2- (o-chloranilino) -6-dibutylaminofluorane 10 parts Hexadecylphosphonic acid 30 parts Styrene-acrylonitrile copolymer 30 parts Sunrex SAN-H (manufactured by Mitsubishi Monsanto Kasei Co., Ltd.) Methyl ethyl ketone 135 parts Toluene 135 parts The coating liquid prepared as described above was applied to a 100 μm-thick polyester film with a wire bar to give a coating thickness of 5.0 μm and dried to obtain a reversible thermosensitive recording sheet.

Example 2 A reversible thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the following composition was used. 2- (o-chloroanilino) -6-dibutylaminofluorane 10 parts α-hydroxyhexadecanoic acid 30 parts Styrene-acrylonitrile copolymer 30 parts LITAC A 330-DC (manufactured by Mitsui Toatsu Chemicals, Inc.) Methyl ethyl ketone 135 parts Toluene 135 parts

Example 3 A reversible thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the following composition was used as a raw material. 2- (o-chloroanilino) -6-dibutylaminofluorane 10 parts Octylmalic acid 30 parts Styrene-butadiene-acrylonitrile copolymer 30 parts Kaneace MUH (Kanebuchi Chemical Industry Co., Ltd.) Methyl ethyl ketone 135 parts Toluene 135 parts

Example 4 A reversible thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the following composition was used as a raw material. 2- (o-chloroanilino) -6-dibutylaminofluorane 10 parts Hexadecylphosphonic acid 30 parts Styrene-acrylonitrile copolymer 60 parts Sunlex SAN-H (manufactured by Mitsubishi Monsanto Kasei Co., Ltd.) Methyl ethyl ketone 120 parts Toluene 120 parts

Example 5 A reversible thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the following composition was used as a raw material. 2- (o-chloroanilino) -6-dibutylaminofluorane 10 parts Octylmalic acid 30 parts Styrene-butadiene-acrylonitrile copolymer 60 parts Kaneace MUH (Kanebuchi Chemical Co., Ltd.) Methyl ethyl ketone 120 parts Toluene 120 parts

Comparative Example 1 A reversible thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the following composition was used as a raw material. 2- (o-chloroanilino) -6-dibutylaminofluorane 10 parts Hexadecylphosphonic acid 30 parts Vinyl chloride-vinyl acetate copolymer VYHH 30 parts (made by Union Carbide) methyl ethyl ketone 135 parts Toluene 135 parts

Using the reversible heat-sensitive recording sheet prepared as described above, a thermal head of 8 dots / mm was used under a higher energy (applied power 1.
Printing was performed at 0 W and an applied pulse width of 1.2 msec) to develop a black color, which was then applied to a hot plate at 75 ° C. for 20 seconds to erase the color. Such a forced test is repeated 10 times, and the image area (black area) density and erased area (background area) of each time are repeated.
The density was measured with a Macbeth reflection densitometer RD-514, and Table 1
The measurement result (reflection density) shown in was obtained. As is clear from Table 1, in the examples, there was almost no change in the reflection densities of the color-developing part and the erasing part from the 1st time to the 10th time, and the high contrast was maintained up to the 10th printing of the experiment. In the comparative example, from around the 5th time, the decoloring property was deteriorated, the coloring density was lowered, and the contrast was gradually lowered. Also, when visually observing the image state of the recording layer,
In the examples, even if the number of prints was increased, it did not change, but in the comparative examples, uneven cohesion of the colored image due to the deformation of the resin was recognized. It is also confirmed from Table 1 that the coloring density is low in Examples 4 and 5 in which the amount of resin is large.

[0053]

[Table 1]

[0054]

The reversible thermosensitive recording medium of the present invention comprises a developer having a long-chain aliphatic group and a color former such as a fluorane compound, a styrene-acrylonitrile copolymer resin and / or styrene-butadiene-acrylonitrile. It has a reversible thermosensitive recording layer dispersed in a resin matrix containing a copolymer resin, and can develop color by heating, melting, and mixing the developer and color former in the recording layer. It is possible to change the state of the recording layer to the decolored state by heating it to a temperature lower than the coloring temperature. Although such coloring and decoloring can be performed repeatedly, in the present invention, this repeating property is obtained by using a styrene-acrylonitrile copolymer resin and / or a styrene-butadiene-acrylonitrile copolymer resin as a resin base material. It greatly improves. In the recording medium of the present invention, the colored state and the decolored state can be easily maintained at room temperature, and the obtained image has high contrast and high image erasability. In addition, the hue of the image can be freely selected by changing the color former, and by using a transparent film as the support, it is possible to obtain a transparent recording medium which is clear and can be repeatedly used.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the color density and temperature of a thermoreversible recording medium of the present invention, and is an explanatory diagram of the principle of color development and decolorization. The solid line (A → B → C) indicates the image formation process, and the broken line (C → B → C).
D → A) shows an image erasing process.

FIG. 2 is a diagram illustrating an image forming process and an image erasing process.

[Explanation of symbols]

 1 Support 2 Thermoreversible Recording Layer 3 Colored Image 4 Thermal Head 5 Heating Roller

Claims (2)

[Claims] 1. A recording layer containing, on a support, an electron-donating color-forming compound and an electron-accepting compound dispersed in a resin matrix, a color-recorded state is formed by heating and melting, and color-recording is performed. A reversible thermosensitive recording medium, wherein a styrene-acrylonitrile copolymer resin is used as the resin matrix in a reversible thermosensitive recording medium which forms a decolored state in which recording disappears by heating at a temperature lower than the temperature. 2. A recording layer containing, on a support, an electron-donating color-forming compound and an electron-accepting compound dispersed in a resin matrix, a color-recorded state is formed by heating and melting, and color-recording is performed. A reversible thermosensitive recording medium that forms a decolored state in which recording disappears by heating at a temperature lower than the temperature, characterized in that a styrene-butadiene-acrylonitrile copolymer resin is used as the resin base material. recoding media.