JPH05221127A - Reversible thermal color developing composition and recording medium using same - Google Patents

Abstract

PURPOSE:To provide a reversible thermal color developing compsn. characterized by that color development and color erasure can be easily performed only by heating and a color developed state and a color erased state can be held at room temp. and color erasing temp. is lower than color developing temp. and the formation and erasure of an image can be repeated by a temp. change without generating a problem. CONSTITUTION:In a thermal color developing compsn. utilizing the color developing reaction between an electron donating color forming compd. and an electron acceptive compd., as the electron acceptive compd., a compd. represented by general formula (1) (R1-S-CH2-COO)2M (wherein R1 is a 10-18 alkyl group or an alkenyl group and M is a metal atom such as Sn, Mg, Zn or Cu) is used and a combination of both compds. showing a heat generation peak in a temp. rising process in the differential scanning heat quantity analysis or differential heat analysis of a mixture of a color developed state obtained by heating, melting and cooling the electron acceptive compd. and the electron donating color developing compd. 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 thermochromic composition utilizing a color reaction between an electron-donating color-forming compound and an electron-accepting compound. The present invention also relates to a reversible thermosensitive recording medium using this composition.

[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 the conventional products have irreversible color development, and it is not possible to repeat the color development and the color erasing alternately.

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 substance obtained by thermally coloring this substance 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 recording storability, and furthermore, there is a problem that the color erasing device for erasing the color developing body becomes large. 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 forms a color-developing material by heating and gradually cooling it, while it can be decolored by heating the color-developing material once to a temperature higher than the color density 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-62-140881
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).
The use of a salt of acetic acid or butyric acid and a higher aliphatic amine is shown. This one develops heat in a specific temperature range,
Although it is possible to erase the color by heating at a higher temperature, it is difficult to control these effects thermally because the color developing effect and the color reducing effect occur competitively, and good image contrast can be obtained. It is hard to be caught. 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.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems found in the prior art in a reversible thermochromic composition utilizing the reaction between a color former and a developer, and develops its color. And the decoloring can be easily performed only by heating, the coloring state and the decoloring state can be maintained at room temperature, and the decoloring temperature is lower than the coloring temperature, and further, image formation And a reversible thermochromic composition that can be repeatedly erased and erased without any problem due to temperature change, and by utilizing this composition, stable color development and decolorization can be repeated, It is an object to provide a thermal recording medium.

[0005]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a compound of the following general formula (1) is used as an electron-accepting compound in a thermochromic composition utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound. The electron accepting compound showing an exothermic peak during the temperature rising process in a differential scanning calorimetric analysis or a differential thermal analysis of a mixture in a colored state obtained by heating, melting and rapidly cooling the electron accepting compound and the electron donating color-forming compound. There is provided a reversible thermochromic composition characterized by using a combination of a color-forming compound and an electron-donating color-forming compound. (R ₁ —S—CH ₂ —COO) ₂ M (1) (In the formula, R ₁ represents an alkyl group or an alkenyl group having 10 to 18 carbon atoms, and M represents a metal atom of Sn, Mg, Zn, or Cu. Represent)

The reversible thermochromic composition of the present invention instantly develops color upon heating, and the color development state thereof is stable even at room temperature. However, the composition in the color development state is instantaneously heated by heating below the color development temperature. The color is erased, and the erased state is stable even at room temperature. The principle of coloring and decoloring of the reversible thermochromic composition of the present invention, that is, image formation and image erasing 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.
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, and C is T _{0 in the} completely colored state.
It is the density at the following temperatures, and D represents the density when heat erasing is performed at a temperature between T _{0 and} T ₁ . The reversible thermochromic composition of the present invention 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. This recorded image is T ₀ according to the solid line 2.
Even if the temperature is returned to the following temperature, 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 is subjected to T ₀ lower than the coloring temperature.
It suffices to heat it to a temperature between T _{1 and} T _{1, and} it becomes a colorless state (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, in which 1 is a support and 2 is a recording layer containing the reversible thermochromic composition of the present invention. The image forming steps (A) → (B) are achieved by recording and printing at a temperature of T ₁ or higher in FIG. 1 by a heat source for image formation, for example, the thermal head 4. 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 thermochromic composition of the present invention contains a color former and a color developer as essential components. Then, the color development of the reversible thermochromic composition of the present invention, a color former formed by the eutectic reaction of the developer and the color former constituting the composition,
It is obtained by cooling to room temperature. Since this composition has a decoloring 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 melted coloring state to room temperature while maintaining the color development. When gradually cooled, decolorization occurs when passing through the decolorization temperature region, and the density is often lowered. It is considered that in the color former, 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 thermochromic composition of the present invention, the composition that is in the color-developed state at room temperature is in a solidified state due to the cohesive force between these molecules. The color-developed state of the conventional thermosensitive color-developing composition often does not become an aggregated solid. The composition of the present invention is an agglomerated solid in the colored 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 the formation of such a cohesive structure is presumed to be related to the decoloring phenomenon of the composition of the present invention. It

The reversible thermochromic composition of the present invention can be decolored by heating the color-developed state in a specific temperature range. In this decoloring process, the aggregate structure of the color-developed state changes, and finally the developer molecules are separated and crystallized from the color-developing substance to form crystals of the color-developing agent alone, resulting in a stable color-erasing state. Confirmed by. 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 the reversible thermochromic composition of the present invention. It is a feature of things. Therefore, it has been confirmed that the decoloring temperature can be controlled by the length of the long chain portion of the developer, and that the longer the chain length is, the more the coloring and decoloring temperature shifts to the high temperature side. This is because the aggregation and motility of the developer molecule change depending on the length of the long chain portion.

The reversible thermochromic composition of the present invention basically comprises the above-mentioned developer having a long chain structure and a leuco dye (color former).
And a preferred color former is present for each developer. The combination of the color developing agent and the color developing agent used in the reversible thermochromic composition of the present invention occurs when a composition in a color developing state obtained by heating both of them is heated to a temperature lower than the melting temperature. It is appropriately selected depending on easiness of erasing, that is, erasability and characteristics such as color tone of a color-developed state. Regarding the decoloring property, a differential thermal analysis (DT) of a composition in a colored state obtained by the combination was used.
A) or the presence or absence of an exothermic peak appearing in the temperature rising process in differential scanning calorimetry (DSC). 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 reversible thermochromic composition of the present invention, for example, the reversible decoloring behavior can be maintained even when a polymer compound is present.

In the present invention, the metal salt (R ₁ —S—CH ₂ —COO) ₂ M (1) of the alkyl or alkenyl mercaptoacetic acid represented by the general formula (1) is used as the color developer. In the general formula (1), the higher alkyl group or alkenyl group represented by R ₁ is preferably a linear or branched one having 10 to 18 carbon atoms. The metal salt is preferably tin, magnesium, zinc or copper salt. Specific examples of the color developing agent suitable for the present invention are as follows. Decylmercaptoacetic acid tin salt, dodecylmercaptoacetic 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, decylmercaptoacetic acid zinc salt, dodecylmercaptoacetic acid zinc salt, tetradecylmercaptoacetic acid zinc salt, hexadecylmercaptoacetic acid zinc salt, octadecylmercaptoacetic acid zinc salt, decylmercaptoacetic acid copper salt Salt, dodecyl mercapto acetic acid copper salt, tetradecyl mercapto acetic acid copper salt, hexadecyl mercapto acetic acid copper salt, octadecyl mercapto acetic acid copper salt .

The reversible thermochromic composition of the present invention is basically constituted by combining a color former with the color developer. 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. The preferred color former used in the present invention is a fluorane compound represented by the following general formula (2).

[Chemical 1] (In the formula, R ₂ represents a hydrogen atom, an alkyl group, an allyl group, a cyclic alkyl group, or an alkoxyalkyl group, and R ₃
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. )

The compound of the general formula (2) is specifically shown as follows.
The following compounds are exemplified. 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- (N-n-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- (N
-N-amyl-N-n-propylamino) fluorane,
2-anilino-3-methyl-6- (Nn-amyl-N
-N-butylamino) fluorane, 2-anilino-3-
Methyl-6- (Nn-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- (Nn-butyl-Nn-propylamino) fluorane, 2-anilino-3-methyl-6- (N-ethyl-N-sec-butylamino) fluorane, 2-anilino-3-methyl-
6- (N-n-butyl-N-iso-propylamino)
Fluoran, 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) fluone, 2-anilino-3-methyl-6- (N-cyclohexyl-) N-iso
-Amylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-N-n-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-diethylaminofluorane, 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-Nn-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) ) Fluoran, 2
-Anilino-3-ethoxymethyl-6- (N-cyclohexyl-Nn-hexylamino) fluorane, 2-anilino-3-ethoxymethyl-6- (di-n-amylamino) fluorane, 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-is
o-amylamino) fluorane, 2- (2,4-dimethylanilino) -3-methyl-6- (di-n-hexylamino) fluorane, 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- (o-chloroanilino) -6-diethylaminofluorane, 2- (o-
Bromoanilino) -6-diethylaminofluorane, 2
-(O-chloroanilino) -6-dibutylaminofluorane, 2- (o-fluoroanilino) -6-dibutylaminofluorane, 2- (p-chloroanilino) -6- (N
-N-octylamino) fluorane, 2- (p-chloroanilino) -6- (N-n-palmitylamino) fluorane, 2- (p-chloroanilino) -6- (di-n-octylamino) fluorane, 2 -(P-acetylanilino) -6-diethylaminofluorane, 2- (m-trifluoromethylanilino) -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-Nn-amylamino) fluorane, 2- (p-acetylanilino) -6- (di-
n-amylamino) fluorane, 2- (p-acetylanilino) -6- (Nn-amyl-Nn-butylamino) fluorane, 2- (p-acetylanilino) -6-
(N-cyclohexyl-Nn-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-
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-dimethylamino-6- (N-methyl-p-toluidino) fluorane, 2-dimethylamino- 6- (N-ethyl-p-toluidino) fluorane, 2
-Dipropylamino-6- (N-methyl-p-toluidino) fluorane, 2-dipropylamino-6- (N-ethyl-p-toluidino) fluorane, 2-acetylamino-3-methyl-6-diethylaminofluor Oran, 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) fluorane, 2-acetylamino-6- (N-methyl-p-toluidino) fluorane,

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-methyl-3-methyl-6-diethylaminofluorane, 1-methyl-3-methyl-6- (di-
n-butylamino) fluorane, 1-methyl-3-methyl-6- (di-n-amylamino) fluorane, 1-methyl-3-methyl-6- (di-n-hexylamino) fluorane, 1-methyl- 3-methyl-6- (N-cyclohexyl-N-n-butylamino) fluorane, 2-methyl-3-methyl-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) fluorane, 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, 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, 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-diethylaminofluorane, 2- (2,3-dichloroanilino)-
3-chloro-6-diethylaminofluorane, 2-ethoxyethylamino-3-chloro-6-dibutylaminofluorane, 2-dibenzylamino-4-chloro-6-
(N-ethyl-p-toluidino) fluorane, 2- (α
-Phenylethylamino) -4-chloro-6-diethylaminofluorane, 2- (N-benzyl-p-trifluoromethylanilino) -4-chloro-6-diethylaminofluorane and the like.

Besides the general formula (2), there are many preferable fluoran compounds as the color former used in the present invention, and the following compounds are specifically exemplified. 2-anilino-3-methyl-6-pyrrolidinofluorane, 2-anilino-3-chloro-6-pyrrolidinofluorane, 2-anilino-3-methyl-6- (N-ethyl-
Tetrahydrofurfurylamino) fluorane, 2-mesidino-4 ', 5'-benzo-6-diethylaminofluorane, 2- (m-trifluoromethylanilino) -3-methyl-6-pyrrolidinofluorane, 2- (Α-naphthylamino) -3,4-benzo-4′-bromo-6- (N-
Benzyl-N-cyclohexylamino) fluorane, 2
-Piperidino-6-diethylaminofluorane, 2-
(Nn-propyl-p-trifluoromethylanilino)
-6-morpholinofluorane, 2- (Np-chlorophenyl-p-chloranilino) -6-pyrrolidinofluorane, 3- (Nn-propyl-m-trifluoromethylanilino) -6- Morpholino Fluoran, 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-N-n-octylamino) fluorane, 1,
2-benzo-6- (N-ethyl-p-toluidino) fluorane, 1,2-benzo-6-diallylaminofluorane, 1,2-benzo-6- (N-ethoxyethyl-N-
Ethylamino) fluoran 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-chloroanilino) xanthyl lactam benzoate, 2- [3,6-bis (diethylamino)]-9- (0-chloroanilino) xanthyl Lactam benzoate, 3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-bis (p-dimethylaminofezyl) -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-dimethyl) Aminophenyl) -3- (2-hydroxy-4-chloro-5-methoxyphenyl) phthalide, 3,6-bis (dimethylamino) fluorene spiro (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 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 of the present invention is basically composed of the above-mentioned color developer and color developer, but for the purpose of improving various properties such as decoloring property and storability, Additives that have the effect of controlling the crystallization of the agent can be included.

Next, a reversible thermosensitive recording medium using the reversible thermochromic composition of the present invention will be described. 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 if necessary, a protective layer may be provided on the upper surface of the recording layer or a recording layer. An undercoat layer having various purposes may be provided on the lower surface. The support used here is, for example, paper, synthetic paper, a plastic film or a composite thereof, a glass plate, and the like, as long as it can hold the recording layer. The recording layer may have any form as long as the above-mentioned thermochromic composition is present, and a color developer and a color former may be mixed and melted to form a film, which may be cooled to form a recording layer. However, it is usually preferable to sufficiently disperse the color developer and the color developing agent in the binder resin to form a recording layer, and a reversible thermosensitive recording medium having a long life can be obtained by this method. As the binder resin, for example, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polyacrylic acid esters, Polymethacrylic acid esters,
Acrylic acid copolymers, maleic acid copolymers, polyvinyl alcohol, chlorinated vinyl chloride resins, mixtures of the above binder resins and the like are used.

The color developing agent and the color developing agent can be used as they are or in a microcapsule.
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. The recording layer can be formed by a method known in the art by uniformly dispersing or dissolving a color former and a developer together with a binder resin in water or an organic solvent, and then directly depositing this on a support laminated with an undercoat layer or directly. It can be carried out by coating and drying on a support. The role of the binder resin in the recording layer is to prevent the reversible thermochromic composition from aggregating due to repeated coloring and decoloring, and to maintain a state in which the colorable composition is uniformly dispersed. In particular, since the composition often agglomerates and becomes non-uniform when heat is applied during color development, it is preferable that the binder resin has high heat resistance. In the reversible thermosensitive recording medium utilizing the present invention, various additives, such as a dispersant and a surfactant, which are usually used in thermosensitive recording paper, are used for the purpose of improving coating properties or recording properties, if necessary. A polymeric cationic conductive agent, a filler, a color image stabilizer, an antioxidant, a light stabilizer, a lubricant and the like can be added to the recording layer.

Since the protective layer prevents the surface from being deformed or discolored by heat and pressure when heat is applied, it is extremely effective to install the protective layer for many uses. 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, heat resistance is improved as described above, and resistance to contact with organic solvents, plasticizers, oils, sweat, water, etc. is also increased, which causes a problem of image formation and deletion even in a bad environment. It is possible to obtain a recording medium that can be repeated without any trouble. 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 0.5-10 μ
About m is good.

The undercoat layer improves heat insulation, improves adhesion between the support and the recording layer, improves resistance of the support to the solvent when the recording layer is formed, and prevents absorption of heat-melting ink by the support 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 and erasing recording without waste. It can be done sharply. 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 small hollow body of about 50 μm
It may be well dispersed in a solvent together with the binder resin, and uniformly applied 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 heating 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.

[0031]

EXAMPLES The present invention will now be described more specifically by way of examples, but the present invention is not limited to these examples. All parts shown below are based on weight.

Example 1 2-anilino-3-methyl-6-diethylaminofluorane 10 parts Dodecyl mercaptoacetic acid tin salt 30 parts Ethylcellulose 15 parts Toluene 135 parts Methylethylketone 135 parts The above composition was put in a sample bottle together with a stainless ball and placed on a tabletop. Disperse with a ball mill for 48 hours, and disperse the dodecylmercaptoacetic acid tin salt to an average particle size of about 1 to 3 μm. The dispersion liquid prepared as described above was applied to a thickness of 100 μm.
A transparent polyester film of m was coated with a wire bar so that the coating thickness was about 8.0 μm, and dried to obtain a reversible thermosensitive recording medium. Further, this reversible thermosensitive recording medium was once colored at 120 ° C. and then put in a dryer at 70 ° C. for 5 minutes to erase the color, thus completing the recording medium.

Example 2 2-anilino-3-methyl-6- (Nn-propyl 10 parts -N-methylamino) fluorane tetradecyl mercaptoacetic acid tin salt 30 parts polyvinyl butyral 15 parts toluene 135 parts methyl ethyl ketone 135 parts The composition is put in a sample bottle together with a stainless ball and dispersed for 48 hours with a tabletop ball mill to disperse the tetradecylmercaptoacetic acid tin salt to an average particle size of about 1 to 3 μm. The dispersion liquid prepared as described above was applied to a thickness of 10
A reversible thermosensitive recording medium was obtained by coating a transparent polyester film of 0 μm with a wire bar so that the coating thickness was about 8.0 μm, and drying. Further, this reversible thermosensitive recording medium was once colored at 120 ° C. and then put in a dryer at 70 ° C. for 5 minutes to erase the color, thus completing the recording medium.

Example 3 2-anilino-3-methyl-6-10 parts (N-cyclohexyl-N-methylamino) fluorand dodecyl mercaptoacetic acid zinc salt 30 parts polyvinyl butyral 15 parts toluene 135 parts methyl ethyl ketone 135 parts The above composition It is put in a sample bottle together with a stainless ball and dispersed for 48 hours with a tabletop ball mill to disperse the zinc dodecylmercaptoacetate salt to an average particle size of about 1 to 3 μm. The dispersion liquid prepared as described above was applied to a thickness of 100 μm.
A transparent polyester film of m was coated with a wire bar so that the coating thickness was about 8.0 μm, and dried to obtain a reversible thermosensitive recording medium. Further, this reversible thermosensitive recording medium was once colored at 120 ° C. and then put in a dryer at 70 ° C. for 5 minutes to erase the color, thus completing the recording medium.

Example 4 2-Methyl-6-diethylaminofluorane 10 parts Tetradecyl mercaptoacetic acid zinc salt 30 parts Ethyl cellulose 15 parts Toluene 135 parts Methyl ethyl ketone 135 parts The above composition was put in a sample bottle together with a stainless ball and placed on a tabletop ball mill at 48. Disperse over time and disperse the tetradecyl mercaptoacetic acid zinc salt to an average particle size of about 1 to 3 μm. The dispersion liquid prepared as described above was applied to a thickness of 10
A reversible thermosensitive recording medium was obtained by coating a transparent polyester film of 0 μm with a wire bar so that the coating thickness was about 8.0 μm, and drying. Further, this reversible thermosensitive recording medium was once colored at 120 ° C. and then put in a dryer at 70 ° C. for 5 minutes to erase the color, thus completing the recording medium.

Example 5 [Recording Layer] The following compositions were each ball-milled to a particle size of 1 to 1.
Grind and disperse up to 4 μm [liquid A] [solution B] and [C
Liquid] was prepared. [Liquid A] 2-anilino-3-methyl-6-diethylaminofluorane 10 parts Methylcellulose 5% aqueous solution 20 parts Water 20 parts [Liquid B] Tetradecylmercaptoacetic acid zinc salt 10 parts Methylcellulose 5% aqueous solution 20 parts Water 20 parts [ Liquid C] Calcium carbonate 10 parts Methylcellulose 5% aqueous solution 20 parts Water 20 parts [A solution] 10 parts and [B solution] 3 obtained as described above.
A reversible thermosensitive recording medium was prepared by mixing 0 parts and 30 parts of [C liquid] to prepare a coating liquid, which was coated on a high-quality paper of a weight of 48 g / m ² so that the adhesion amount was 5 g / m ^2. Got [Recording layer] A mixture having the following composition is sufficiently crushed with a ball mill.
By dispersing, a protective layer coating solution was prepared. 2-Hydroxy-4-methoxybenzophenone 16 parts Calcium carbonate coated silica 4 parts (P-832 manufactured by Mizusawa Chemical Industry Co., Ltd.) Carboxyl group-modified polyvinyl alcohol 10% aqueous solution 50 parts Zinc stearate 1 part Water 45 parts The above reversible thermosensitive recording. The protective layer coating liquid was applied onto the recording layer of the medium using a wire bar and dried to obtain a reversible thermosensitive recording medium provided with a protective layer having a thickness of about 3.5 μm. Further, this reversible thermosensitive recording medium was once color-developed at 120 ° C. and then put in a dryer at 70 ° C. for 5 minutes to erase the color, thereby completing the recording medium.

Using the reversible thermosensitive recording medium produced as described above, a printing apparatus equipped with a thermal head (head 8 dots / mm, printing voltage 13.3 V, pulse width 0.8)
The image was recorded with the following evaluation test. The results are shown in Table 1. [Color tone] The color tone immediately after recording was visually observed. [Recording Density] The image density immediately after recording was measured with a Macbeth densitometer (RD-914 type manufactured by Macbeth Co.). [Repeatability] An image was recorded on the recording medium by the printing device and then erased under the decoloring conditions described in Examples. This operation was repeated 10 times, and the functional deterioration was visually observed. No functional deterioration… ○ Functional deterioration… ×

[0038]

[Table 1]

[0039]

INDUSTRIAL APPLICABILITY The reversible thermochromic composition of the present invention can be colored by heating and melting and mixing the color former and the color developer contained therein, while the composition in the color developing state is By heating at a temperature lower than the melting temperature, it is possible to change to the decolored state. Further, such coloring and erasing can be repeated, and the coloring and erasing states can be maintained at room temperature. Further, in the reversible thermochromic composition of the present invention,
The obtained image has high contrast, excellent image erasability, and the hue of the color image is not limited at all, and the hue can be freely selected by changing the color former.
If a transparent film is used as the support, a transparent recording medium that is clear and can be repeatedly used is obtained, and is useful as a recording medium for overhead projectors and second original drawings.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the color density and temperature of the reversible thermochromic composition of the present invention, and is an explanatory view of the principle of color development and decolorization. A solid line (A → B → C) shows an image forming process, and a broken line (C → D → A) shows an image erasing process.

FIG. 2 is an explanatory diagram of an image forming process and an image erasing process.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. In a thermochromic composition utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound, a compound of the following general formula (1) is used as the electron-accepting compound, This electron-accepting compound and an electron-donating color-developing compound are melted by heating and rapidly cooled to obtain an electron-accepting compound exhibiting an exothermic peak in the course of temperature rise in differential scanning calorimetry or differential thermal analysis of a mixture in a colored state. A reversible thermochromic composition comprising a combination of electron-donating color-forming compounds. _{(R 1 -S-CH 2 -COO} ) 2 M (1) ( In the formula, R ₁ represents an alkyl or alkenyl group having 10 to 18 carbon atoms, M is Sn, Mg, a metal atom of Zn or Cu Represent) 2. A reversible thermosensitive recording medium comprising a support and a recording layer comprising the reversible thermochromic composition according to claim 1 provided on the support.