JPH08282125A - Reversible thermal recording material - Google Patents

Abstract

PURPOSE: To erase an image at lower temp. by adding a dye precursor and a specific electron acceptive compd. generating a reversible hue change in the dye precursor by heating to a reversible thermal recording material capable of forming and erasing an image by heating. CONSTITUTION: A reversible thermal recording material capable of forming and erasing an image by heating and capable of erasing an image at a low temp. of 100 deg.C or lower contains a usually colorless or light-colored electron donating dye precursor and an electron acceptive compd. represented by formula generating a reversible hue change in the dye precursor by heating. In the formula, n is an integer of 1-3, X is a CH2 group or an 0-atom and R1 is a 2-12C divalent group and R2 is a 10-22C hydrocarbon group. As a concrete example of the electron acceptive compd., there is N-(4-hydroxyphenyl)-N'-[3-(n- tetradecanoyloxy)-n-propyl]urea.

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 material capable of forming and erasing an image by heating.

[0002]

2. Description of the Related Art A heat-sensitive recording material generally comprises a support and a heat-sensitive recording layer containing an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting developer as main components. By heating with a thermal head, a heating pen, a laser beam or the like, a dye precursor and a developer react instantaneously to obtain a recorded image. JP-B-43-4160 and JP-B-45-
No. 14039 is disclosed.

In general, such a heat-sensitive recording material cannot erase the portion of the image once formed and return to the state before the image is formed. Therefore, when further information is recorded, the image is not recorded. There was no choice but to add to the formation part. Therefore, when the area of the heat-sensitive recording portion is limited, there is a problem that the recordable information is limited and it is impossible to record all the necessary information.

In recent years, reversible thermosensitive recording materials capable of repeating image formation and image erasing have been devised in order to deal with such a problem, for example, JP-A-54-119377 and JP-A-63-63. 39377, JP-A-63-4
Japanese Patent No. 1186 describes a heat-sensitive recording material composed of a resin base material and organic low-molecules dispersed in the resin base material. However, since this method reversibly changes the transparency of the heat-sensitive recording material by heat energy, the contrast between the image-formed area and the image-unformed area was insufficient.

Further, in the methods described in JP-A-50-81157 and JP-A-50-105555, since the image to be formed changes according to the ambient temperature, the image forming state and the erasing state. The temperatures at which the two are held are different, and under normal temperature, these two states could not be held for an arbitrary period.

Further, in Japanese Patent Laid-Open No. 59-120492, the hysteresis characteristic of the color-developing component is utilized to keep the recording material in the hysteresis temperature range, thereby forming an image.
Although a method of maintaining the erased state is described, this method requires a heating source and a cooling source for image formation and erasure, and the temperature range in which the image formation state and the erased state can be maintained is limited to the hysteresis temperature region. However, it is still insufficient for use in the temperature environment of daily life.

On the other hand, JP-A-2-188293, JP-A-2-188294, and International Publication No. WO90 /
No. 11898 describes a reversible thermosensitive recording medium composed of a leuco dye and a color-developing and decoloring agent for coloring and decoloring the leuco dye by heating. The color-developing agent is an amphoteric compound having an acidic group for coloring the leuco dye and a basic group for decoloring the colored leuco dye, and the coloring effect by the acidic group or the decoloring effect by the basic group is controlled by controlling thermal energy. One of them is preferentially generated, and coloring and erasing are performed. However, in this method, it is impossible to completely switch the color development reaction and the color removal reaction only by controlling the thermal energy, and since both reactions occur at a certain ratio at the same time, sufficient color development density cannot be obtained, and the color removal However, a sufficient image contrast could not be obtained. Further, since the decoloring action of the basic group also acts on the color-developed portion at room temperature, the phenomenon that the concentration of the color-developed portion decreases with time cannot be avoided. JP-A-5-124360 describes a reversible thermosensitive recording medium that develops and decolorizes a leuco dye by heating, and an organic phosphoric acid compound, an α-hydroxyaliphatic carboxylic acid, as an electron-accepting compound. Specific phenol compounds such as fatty acid dicarboxylic acids and alkylthiophenols having an alkyl group having 10 or more carbon atoms, alkyloxyphenols, alkylcarbamoylphenols, and gallic acid alkyl esters are exemplified. However, even with this recording medium, the two problems of low color density or incomplete decolorization could not be solved at the same time.

On the other hand, the applicant of the present invention previously disclosed in Japanese Patent Laid-Open No. 6-2109
Japanese Patent Laid-Open No. 54-54 proposes a novel reversible thermosensitive recording material which solves the problems of these conventional techniques. Here, by using a specific novel reversible developer, a reversible thermosensitive recording material with unprecedented performance that can perform image formation and deletion with good contrast only by heating is obtained. Has been.

Among the novel reversible color developers exemplified in the publication, a phenol derivative containing a urea bond in the molecule is excellent in both color developing property and decoloring property and is easy to synthesize. It is one of the preferred reversible developers. However, a reversible thermosensitive recording material prepared by using this requires a high temperature of 100 ° C. or higher to completely erase the image, and therefore the apparatus for image erasing becomes large and repeated use is required. There are still major problems in practical use, such as the progress of thermal deterioration of recording materials.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is that it is possible to form and erase images by heating with good contrast, and to erase images at a lower temperature than known materials. To provide a reversible thermosensitive recording material having a high temperature.

[0011]

As a result of research to solve this problem, the present inventors have found that a colorless or light-colored electron-donating dye precursor is reversibly changed in color tone by heating, that is, color development and By using an electron-accepting compound represented by the following general formula 2 as a reversible developer that causes decolorization, an image can be formed at a low temperature of 100 ° C. or lower without impairing the image forming ability and erasability. They have found that they can be erased, and completed the present invention.

[0012]

Embedded image

In Formula 2, n represents an integer of 1 to 3. X
Represents a CH ₂ group or an O atom, and R ₁ has 2 to 1 carbon atoms.
2 represents a divalent group, and R ₂ represents a hydrocarbon group having 10 to 22 carbon atoms.

Among the compounds represented by the above general formula, n =
It is preferable that R 1 and R ₂ have a hydrocarbon group having 14 or more carbon atoms.

[0015]
Specific examples of the electron-accepting compound represented by the general formula 2 which can cause a reversible color change in the normally colorless or light-colored electron-donating dye precursor used in the present invention include the followings. However, the present invention is not limited to this.

N- (4-hydroxyphenyl) -N'-
[3- (n-tetradecanoyloxy) -n-propyl] urea, N- (4-hydroxyphenyl) -N'-
[4- (n-hexadecanoyloxy) -n-butyl]
Urea, N- (4-hydroxyphenyl) -N '-[3-
(N-Octadecanoyloxy) -n-propyl] urea, N- (3,4-dihydroxyphenyl) -N'-
[3- (n-octadecanoyloxy) -n-propyl] urea, N- (4-hydroxyphenyl) -N'-
[5- (n-octadecanoyloxy) -n-pentyl] urea, N- (4-hydroxyphenyl) -N'-
[6- (n-docosanoyloxy) -n-hexyl] urea, N- (3,4,5-trihydroxyphenyl)-
N '-[6- (n-docosanoyloxy) -n-hexyl] urea, N- (4-hydroxyphenyl) -N'-
[12- (n-dodecanoyloxy) -n-dodecyl]
Urea, N- (4-hydroxyphenyl) -N '-[3-
(N-Hexadecyloxycarbonyloxy) -n-propyl] urea, N- (4-hydroxyphenyl) -N '
-[5- (n-hexadecyloxycarbonyloxy)
-N-pentyl] urea.

The electron-accepting compound of the present invention can be synthesized very easily from various readily available raw materials in accordance with well-known organic synthesizing methods, and the practicality of the present invention is also high in this respect.

The electron-accepting compound according to the present invention may be used alone or in admixture of two or more kinds. Usually, the amount of the electron-accepting compound according to the present invention to be used with respect to a colorless or pale dye precursor is 5 or less. ˜5000 wt%, preferably 10-3000 wt%.

The usually colorless or light-colored electron-donating dye precursor used in the present invention is represented by those generally used for pressure-sensitive recording paper, heat-sensitive recording paper, etc., but is not particularly limited. Specific examples include the followings, but the present invention is not limited thereto.

(1) Triarylmethane compound 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3-
(1,2-dimethylindol-3-yl) phthalide,
3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindole-
3-yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindole-3-)
Yl) -6-Dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5 -Dimethylaminophthalide, 3-p
-Dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethylaminophthalide and the like.

(2) Diphenylmethane compound 4,4'-bis (dimethylaminophenyl) benzhydrylbenzyl ether, N-chlorophenylleuco auramine, N-2,4,5-trichlorophenyl leuco auramine and the like.

(3) Xanthene compound Rhodamine B anilinolactam, rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3- Diethylamino-7-phenylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-7- (3,4-dichloroanilino) fluorane, 3 -Diethylamino-7
-(2-chloroanilino) fluorane,

3-Diethylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl) tolylamino-
6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-ethyl) tolylamino-6-methyl-7-phenethylfluorane, 3-diethylamino-7 -(4-Nitroanilino) fluorane, 3-dibutylamino-6-methyl-7
-Anilinofluorane, 3- (N-methyl) propylamino-6-methyl-7-anilinofluorane, 3- (N
-Ethyl) isoamylamino-6-methyl-7-anilinofluorane, 3- (N-methyl) cyclohexylamino-6-methyl-7-anilinofluorane, 3- (N-
Ethyl) tetrahydrofurylamino-6-methyl-7-
Anilino Fluoran, etc.

(4) Thiazine Compounds Benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue and the like.

(5) Spiro compound 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3'-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3 -Methoxybenzo) spiropyran, 3-propylspirobenzopyran and the like.

The usually colorless to light-colored dye precursors may be used either individually or in combination of two or more.

Next, a specific method for producing the reversible thermosensitive recording material of the present invention will be described, but the present invention is not limited to this.

As a specific example of the method for producing the reversible thermosensitive recording material of the present invention, a colorless or pale color dye precursor and the electron-accepting compound according to the present invention are mainly contained, and these are coated or printed on a support. And a reversible thermosensitive recording layer is formed.

Usually, a colorless or light-colored dye precursor and the electron-accepting compound according to the present invention are contained in the reversible thermosensitive recording layer. Each compound is dissolved in a solvent or dispersed in a dispersion medium. A method of mixing, a method of dissolving each compound in a solvent or dispersing in a dispersion medium, a method of dissolving each compound by heating and homogenizing and then cooling, and a method of dissolving in a solvent or dispersing in a dispersion medium, etc. However, it is not specified.

A binder may be added to the reversible thermosensitive recording layer for the purpose of improving the strength of the reversible thermosensitive recording layer. Specific examples of the binder include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic. Water-soluble polymer such as acid ester / methacrylic acid terpolymer, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / maleic anhydride copolymer, polyvinyl acetate, polyurethane, polyacrylic acid Examples include, but are not limited to, latex such as ester, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, ethylene / vinyl acetate copolymer, and the like. No.

Further, a heat-fusible substance can be contained in the reversible thermosensitive recording layer as an additive for controlling the color developing sensitivity and the decoloring temperature of the reversible thermosensitive recording layer. 60 ° C
Those having a melting point of ~ 200 ° C are preferable, and especially 80 ° C.
Those having a melting point of ˜180 ° C. are preferred. It is also possible to use a sensitizer which is used in general thermal recording paper. For example, waxes such as N-hydroxymethylstearic acid amide, stearic acid amide and palmitic acid amide, naphthol derivatives such as 2-benzyloxynaphthalene, biphenyl derivatives such as p-benzylbiphenyl and 4-allyloxybiphenyl, 1,2. -Bis (3-
Polyether compounds such as methylphenoxy) ethane, 2,2'-bis (4-methoxyphenoxy) diethyl ether, bis (4-methoxyphenyl) ether, diphenyl carbonate, dibenzyl oxalate, bis (p-methylbenzyl oxalate) Carbonic acid such as ester or oxalic acid diester derivative may be used in combination.

As the support used in the reversible thermosensitive recording material of the present invention, paper, various non-woven fabrics, woven fabrics, synthetic resin films, synthetic resin laminated papers, synthetic papers, metal foils, glass, etc., or a combination thereof is used. The composite sheet can be arbitrarily used according to the purpose, and may be transparent, semitransparent or opaque. Moreover, it is not limited to these.

The layer structure of the reversible thermosensitive recording material of the present invention is as follows:
Only the reversible thermosensitive recording layer may be used. If necessary,
A protective layer may be provided on the reversible thermosensitive recording layer, or an intermediate layer may be provided between the reversible thermosensitive recording layer and the support. In this case, the protective layer and / or the intermediate layer may be composed of a plurality of layers of 2 layers or 3 layers or more. Further, information can be recorded electrically, magnetically, or optically in the reversible thermosensitive recording layer and / or on the surface provided with another layer and / or the reversible thermosensitive recording layer and / or on the opposite surface. The material may be included. Further, a back coat layer may be provided on the surface opposite to the surface on which the reversible thermosensitive recording layer is provided for the purpose of preventing curling and preventing electrification.

The reversible thermosensitive recording layer is prepared by mixing each dispersion obtained by finely pulverizing each color forming component and coating the mixture on a support.
It can be obtained by a method of printing and drying, a method of dissolving each color forming component in a solvent, mixing each solution, coating on a support, printing and drying. in this case,
For example, each color-forming component may be contained in one layer to form a multilayer structure.

The reversible thermosensitive recording layer and / or the protective layer and / or the intermediate layer include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, and hydroxide. Aluminum, pigments such as urea-formalin resin, and other higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearamide, and castor wax, A dispersant such as sodium dioctylsulfosuccinate, a surfactant, a fluorescent dye and the like can be added.

[0036]

The electron-accepting compound according to the present invention has a specific decoloring effect, that is, a reversible effect, although it has the ability to develop the color of the leuco dye. This is totally unexpected, and it is an electron-accepting compound used in a conventional heat-sensitive recording material, that is, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, 4- No such reversible effect is observed with benzyl hydroxybenzoate and the like.

The principle of image formation and erasure of the heat-sensitive recording material of the present invention is not clear yet, but it is considered as follows. When a colorless or light-colored dye precursor is heated together with an electron-accepting compound such as a phenolic compound, electron transfer from the dye precursor to the electron-accepting compound occurs to develop a color.
At this time, it is considered that the electron-accepting compound molecule exists in the extremely close vicinity of the dye molecule that has developed color. Further, when the electron-accepting compound molecule is separated from the color-developed dye molecule, the color-developed dye molecule receives the electron again and becomes in the state of the dye precursor before color development. It is considered that the present invention changes the distance between the molecule of the electron-accepting compound and the molecule of the dye by heating to perform coloring and decoloring.

More specifically, since the electron-accepting compound according to the present invention has a large hydrocarbon chain in its structure, the electron-accepting compound has a low compatibility with the dye precursor molecule and the colored dye molecule, and is in a solidified state. Then it seems that they are almost incompatible with each other. Further, in a state where the dye precursor molecule and the electron-accepting compound molecule according to the present invention can freely move like a heating and melting state, the dye precursor molecule and the electron-accepting compound molecule according to the present invention are mixed with each other at a certain ratio to form a color. It becomes a state. Therefore, when the colored mixture in the molten state is slowly cooled, the electron-accepting compound according to the present invention and the dye molecule become insoluble in each other and phase-separate and disappear when the temperature is lowered. At this time, since the electron-accepting compound according to the present invention contains a urea bond having a hydrogen bonding ability in the molecule, it is rapidly crystallized by the intermolecular hydrogen bond. On the other hand, when the material is rapidly cooled, it solidifies before phase separation, that is, in the colored state, so that the colored state is fixed and the colored state is stably maintained even after the solidification.

When the solidified product in the colored state is heated again, the same phase separation as above starts at a certain temperature or higher,
Decolorization progresses. That is, if the color-developed product is kept at the decolorization temperature or higher for a certain period of time or more, the color can be completely decolored. At that time, the reason why the electron-accepting compound of the present invention exhibits a lower decolorization temperature than that of a conventionally known analog is not clear, but by introducing a specific functional group into a hydrocarbon chain, It is considered that mobility is improved and the phase separation start temperature is lowered.

As described above, the reversible thermosensitive recording material according to the present invention creates a compatible state and a phase separated state between the dye molecule and the electron-accepting compound according to the present invention, and develops a coloring and decoloring state. Conceivable. In order to develop a color, rapid cooling may occur after heating, and for example, heating with a thermal head, laser light or the like is possible. As the decoloring means, for example, a heat roll, a heat stamp, a thermal head, high frequency heating, hot air, radiant heat from a light source such as an electric heater or a halogen lamp can be used.

Next, a specific synthesis example of the electron-accepting compound represented by Chemical formula 2 is shown below, but the method for producing the compound of the present invention is not limited to this.

Synthesis Example 1 N- (4-hydroxyphenyl) -N '-[3- (n-
Octadecanoyloxy) -n-propyl] urea synthesis In a 300 ml flask equipped with stirrer, condenser, N
Phenyl- (4-hydroxyphenyl) carbamate, 5.5 g, 3-amino-n-propanol, 2.0 g,
70 ml of N, N-dimethylacetamide was charged, the mixture was stirred at room temperature for 16 hours, and then heated to 70 to 73 ° C. for 1 hour. 2.0 g of pyridine was added thereto, and a solution of 7.3 g of n-octadecanoic acid chloride in 50 ml of N, N-dimethylacetamide was added dropwise over 60 minutes while cooling with water.
After completion of dropping, the mixture was heated and stirred at 60 to 65 ° C. for 1 hour, the reaction solution was poured into ice water, and the precipitate was collected by filtration and washed. This was repeatedly recrystallized from methanol to obtain 7.1 g of the desired product. Melting point 112 [deg.] C.

Synthesis Example 2 N- (4-hydroxyphenyl) -N '-[5- (n-
Octadecanoyloxy) -n-pentyl] urea synthesis In a 300 ml flask equipped with a stirrer and condenser, N
5.0 g of phenyl 4- (4-hydroxyphenyl) carbamate, 2.3 g of 5-amino-n-pentanol,
After 60 ml of N, N-dimethylacetamide was charged, the mixture was stirred at room temperature for 16 hours and then heated to 70 to 73 ° C. for 1 hour. 1.8 g of pyridine was added thereto, and a solution of 6.7 g of n-octadecanoic acid chloride in 50 ml of N, N-dimethylacetamide was added dropwise over 60 minutes while cooling with water.
After completion of dropping, the mixture was heated and stirred at 60 to 65 ° C. for 1 hour, the reaction solution was poured into ice water, and the precipitate was collected by filtration and washed. This was repeatedly recrystallized from methanol to obtain 6.6 g of the desired product. Melting point 111 [deg.] C.

Synthesis Example 3 N- (4-hydroxyphenyl) -N '-[5- (n-
Hexadecyloxycarbonyloxy) -n-plier
]] In a 300 ml flask equipped with a urea stirrer and a condenser, N
5.0 g of phenyl 4- (4-hydroxyphenyl) carbamate, 2.3 g of 5-amino-n-pentanol,
50 ml of N, N-dimethylacetamide was charged, and the mixture was stirred at room temperature for 16 hours and then heated to 70 to 73 ° C. for 1 hour. 1.8 g of pyridine was added thereto, and a solution of 6.7 g of n-hexadecyl chloroformate in 25 ml of acetone was added dropwise over 60 minutes under ice cooling. Then, after stirring at 45 to 50 ° C. for 1 hour, the reaction solution was poured into ice water, and the precipitate was collected by filtration and washed. This was repeatedly recrystallized from ethanol to obtain 6.8 g of the desired product. Melting point 109 [deg.] C.

[0045]

The present invention will be described in more detail with reference to the following examples.

Example 1 (A) Preparation of reversible heat-sensitive coating liquid 40 parts of a dye precursor, 3-di-n-butylamino-6-methyl-7-anilinofluorane, was added to a 2.5% polyvinyl alcohol aqueous solution. It was pulverized together with 90 parts by a ball mill for 24 hours to obtain a dye precursor dispersion liquid. Then, 2.5 parts of 100 parts of N- (4-hydroxyphenyl) -N '-[3- (n-octadecanoyloxy) -n-propyl] urea was added.
It was pulverized with a ball mill for 24 hours together with 400 parts of an aqueous solution of polyvinyl alcohol to obtain a dispersion liquid. After mixing the above two kinds of dispersions, a 10% aqueous polyvinyl alcohol solution 200
Parts and 400 parts of water were added and mixed well to prepare a reversible heat-sensitive coating liquid.

(B) Preparation of reversible heat-sensitive recording material The reversible heat-sensitive coating liquid prepared in (A) was applied to a polyethylene terephthalate (PET) sheet to give a solid content of 4 g / m ^2.
To obtain a reversible heat-sensitive recording material.

Example 2 N- (4-hydroxyphenyl) -used in Example 1
Instead of N '-[3- (n-octadecanoyloxy) -n-propyl] urea, N- (4-hydroxyphenyl) -N'-[5- (n-octadecanoyloxy)-
A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that n-pentyl] urea was used.

Example 3 N- (4-hydroxyphenyl) -used in Example 1
Instead of N ′-[3- (n-octadecanoyloxy) -n-propyl] urea, N- (4-hydroxyphenyl) -N ′-[5- (n-hexadecyloxycarbonyloxy) -n A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that -pentyl] urea was used.

Comparative Example 1 N- (4-hydroxyphenyl) -used in Example 1
Example 1 was repeated except that a salt of gallic acid and stearylamine was used in place of N '-[3- (n-octadecanoyloxy) -n-propyl] urea.

Comparative Example 2 N- (4-hydroxyphenyl) -used in Example 1
Example 1 was repeated except that 2,2-bis (4-hydroxyphenyl) propane was used instead of N '-[3- (n-octadecanoyloxy) -n-propyl] urea.

Comparative Example 3 N- (4-hydroxyphenyl) -used in Example 1
Example 1 was repeated except that p- (n-octadecylthio) phenol was used instead of N '-[3- (n-octadecanoyloxy) -n-propyl] urea.

Comparative Example 4 N- (4-hydroxyphenyl) -used in Example 1
Example 1 was repeated except that N- (4-hydroxyphenyl) -N'-n-octadecylurea was used instead of N '-[3- (n-octadecanoyloxy) -n-propyl] urea. I did the same.

Test 1 (Color density = Thermal response) The thermal recording materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were applied to a thermal printing machine manufactured by Okura Electric Co. with a print head KJT-256-8MGF1 manufactured by Kyocera. TH-PMD
Was applied under the condition of an applied voltage of 26 V for an applied pulse of 1.1 milliseconds, and the density of the obtained color image was measured using a densitometer Macbeth RD918. The results are shown in Table 1.

Test 2 (Image erasability) The heat-sensitive recording materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were used as a thermosensitive facsimile printing tester TH-manufactured by Okura Electric Co. with a print head KJT-256-8MGF1 manufactured by Kyocera. PMD
Was applied at a voltage of 26 V for an applied pulse of 1.1 milliseconds, and the resulting color image area was heated at 70 ° C. for 1 second using a heat stamp, and then the density was changed in the same manner as in Test 1. It was measured. The results are shown in Table 1.

[0056]

[Table 1]

In Table 1, ∘ indicates that the density of the erased portion is less than 20% of the density of the colored portion, and the contrast between the colored portion and the erased portion is good,
Δ indicates that contrast is insufficient when the density of the erased portion is 20% or more and less than 80% of the density of the colored portion, and x indicates that reversibility is not observed when the density of the erased portion is 80% or more of the density of the colored portion.

[0058]

As shown in Table 1, it is usually represented by a colorless or light-colored electron-donating dye precursor and the general formula 2 which causes the dye precursor to reversibly change its color tone by heating. By using the reversible thermosensitive recording material containing the electron-accepting compound, it was possible to obtain a reversible thermosensitive recording material having extremely high practicality, which enables formation and deletion of an image with good contrast.

Claims (1)

[Claims] 1. A colorless or light-colored electron-donating dye precursor, and an electron-accepting compound represented by the following general formula 1 which causes a reversible color change in the dye precursor by heating. Reversible thermosensitive recording material. Embedded image (In formula 1, n represents an integer of 1 to 3. X represents a CH ₂ group or an O atom, R ₁ represents a divalent group having 2 to 12 carbon atoms, and R ₂ represents a divalent group. It represents a hydrocarbon group of 10 to 22.)