JP3474366B2 - Reversible thermosensitive recording material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible heat-sensitive recording material capable of forming and erasing an image by controlling heat energy.

[0002]

2. Description of the Related Art A heat-sensitive recording material generally comprises a support provided with a heat-sensitive recording layer containing an electron-donating, usually colorless or pale-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, the dye precursor and the 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 forming portion and the image non-forming portion is 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 holding temperatures are different, and these two states cannot be held for an arbitrary period at room temperature.

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. One of them is preferentially generated, and coloring and erasing are performed. However, in this method, it is not possible to completely switch the coloring reaction and the erasing reaction only by controlling the thermal energy, and since both reactions occur at a certain ratio at the same time, sufficient coloring density cannot be obtained, and the erasing Can not be done completely. Therefore, sufficient image contrast cannot be obtained. Also,
Since the decoloring action of the basic group also acts on the color development part at room temperature,
The phenomenon that the density of the color-developed portion decreases with time cannot be avoided.
Further, JP-A-5-124360 describes a reversible thermosensitive recording medium that develops and decolorizes a leuco dye by heating, and an organic phosphonic acid compound, an α-hydroxyaliphatic carboxylic acid as an electron-accepting compound, Specific phenol compounds such as alkylthiophenol, alkyloxyphenol, alkylcarbamoylphenol, and gallic acid alkylester having a fatty acid dicarboxylic acid and an aliphatic group having 12 or more carbon atoms are exemplified. However, even this recording medium has a low color density, or
The two problems of incomplete decolorization cannot be solved at the same time, and the temporal stability of the image is not satisfactory in practice. Furthermore, Japanese Patent Laid-Open No. 5-2
No. 94063, fatty acids, waxes, higher alcohols, various esters of phosphoric acid / benzoic acid / phthalic acid or oxyacids, silicone oils, as decoloring accelerators for improving the erasability of the reversible thermosensitive recording medium. Liquid crystal compounds, surfactants, and fatty acid saturated hydrocarbons having 10 or more carbon atoms are disclosed, but the effect is small, so
The image density at the time of erasing is still high and it cannot be said to be practical.

As described above, according to the conventional technique, a practical reversible image having a clear image contrast, capable of forming a high-density image and completely erasing, and capable of holding a stable image with time in an environment of daily life. The production of the thermosensitive recording material has been difficult. On the other hand, the applicants have already disclosed in JP-A-6-210954 that the normally colorless or light-colored electron-donating dye precursor undergoes reversible color tone change by heating, that is, electron accepting property which causes coloration and decolorization. Compound (reversible developer)
However, in order to obtain even better image quality and easy-to-use recording medium in practical use, there is room for improvement in image density during erasing, erasing start temperature, erasing temperature range, etc. was there.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording material capable of forming / erasing an image with good contrast and capable of holding a stable image over time in an environment of daily life. That is. More specifically, the invention provides a reversible thermosensitive recording material which has a lower image density during erasing, less erasing residue, and can be erased uniformly at a lower temperature and in a wider temperature range. This is an issue.

[0010]

DISCLOSURE OF THE INVENTION The inventors of the present invention cause a reversible change in color tone of a dye precursor, which is usually colorless or light-colored, on a support and a difference in cooling rate after heating. In a reversible thermosensitive recording material containing a reversible color developing agent, as a result of diligent studies to improve its erasability, as a result of incorporating at least one kind of a specific compound represented by the following general formula (1) The inventors have found that a reversible thermosensitive recording material capable of completely and uniformly erasing an image in a wide temperature range can be obtained, and completed the present invention.

[0011]

[Chemical 3]

In the formula (1), A represents a heteroaromatic ring. R ¹
Represents a hydrocarbon group having 6 to 24 carbon atoms. m represents an integer of 1 or 2. X represents an anion, and n represents the number required to adjust the charge in the molecule to zero.

In the compound represented by the general formula (1), A is preferably a 5- or 6-membered heteroaromatic ring, and specific examples thereof include a 5-membered ring such as a pyrazole ring and an imidazole ring, Examples of 6-membered rings such as a triazole ring, an oxazole ring, a thiazole ring, and a thiadiazole ring include a pyridine ring, a pyrimidine ring, a pyrazine ring, and a triazine ring. Furthermore, the aromatic ring may be substituted with a lower alkyl group, an aralkyl group, an aryl group, or the like, and may form a condensed ring such as an indole ring. R ¹ is specifically a monovalent or divalent hydrocarbon group having 6 to 24 carbon atoms, preferably an alkylene group having 8 to 24 carbon atoms, and an ether bond or a sulfide bond is contained in the group. May be included.
X represents a counter anion, and specific examples thereof include halogen, substituted sulfonate, substituted borate, substituted phosphate and the like.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Specific examples of the compound represented by the general formula (1) are shown below (1-1) to (1-33).
However, the present invention is not limited to this.

[0015]

[Chemical 4]

[0016]

[Chemical 5]

[0017]

[Chemical 6]

[0018]

[Chemical 7]

The amount of the compound represented by the general formula (1) is preferably 0.5% by weight or more and 1000% by weight or less, more preferably 1% by weight or more and 200% by weight or less, based on the dye precursor. Further, considering the heat-resistant storage stability of the printed image, 5% by weight or more and 100% by weight or less is most preferable.
These compounds can be used alone or in combination of two or more kinds.

The reversible color developer used in the present invention is preferably an electron-accepting compound, which causes a reversible change in color tone which can be retained by a difference in cooling rate after heating in the presence of an electron-donating dye precursor. It is not particularly limited as long as it is, but the one represented by the following general formula (2) is particularly preferable in terms of color density and decoloring property. However, the following general formula (2)
Compounds out of these ranges can be used in the present invention as long as they have the same characteristics as the compound (1). The method for synthesizing the compound represented by the general formula (2) is described in JP-A-6-210954 by the present applicant.
Japanese Patent Application No. 5-160547, Japanese Patent Application No. 5-256
825, Japanese Patent Application No. 5-317555, Japanese Patent Application No. 5-32
No. 8101 and Japanese Patent Application No. 6-10310.

[0021]

[Chemical 8]

In the equation (2), q is an integer of 1 to 3, i, j
And k each represent 0 or 1. However, when i is 1,
j indicates 1. R ² and R ³ represent a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ⁴ represents a hydrocarbon group having 1 to 24 carbon atoms. L ¹ represents a divalent group having at least one or more -CONH- bond, L ² represents at least one or more having a divalent group, an oxygen atom or a sulfur atom -CONH- bond.

In the compound represented by the above formula (2), R ² and R ³ are divalent hydrocarbon groups having 1 to 18 carbon atoms, but the group may contain an aromatic ring, and the aromatic ring may also be included. May be only. Specific examples of the divalent group having at least one —CONH— bond represented by L ¹ and L ² include amide (—CONH—, —NHCO—), urea (—NHCO).
NH-), urethane (-NHCOO-, -OCONH
-), Diacylamine (-CONHCO-), diacylhydrazide (-CONHNHCO-), oxalic acid diamide (-NHCOCONH-), acylurea (-CONH)
CONH-, -NHCONHCO-), 3-acylcarbazide acid ester (-CONHNHCOO-), semicarbazide (-NHCONHNH-, -NHNHCONH)
-), Acyl semicarbazide (-CONHNHCONH
-, - NHCONHNHCO-), diacyl aminomethane (-CONHCH ₂ NHCO-), 1- acylamino-1- Ureidometan (-CONHCH ₂ NHCONH
-, - NHCONHCH ₂ NHCO-), a group such as malonamide (-NHCOCH ₂ CONH-).

The compound represented by the general formula (2) is an electron-accepting compound and has a specific decoloring effect, that is, a reversible effect, although it has an ability to develop a color of a leuco dye. It should be noted that the electron-accepting compounds used in ordinary thermal recording materials, that is, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, benzyl 4-hydroxybenzoate, etc. No reversible effect is seen. Specific examples of the electron-accepting compound represented by the general formula (2) are shown below, but the invention is not limited thereto.

For example, in the equation (2), i = 0 / j = 0 / k
Examples of the compound of = 0 include 4'-hydroxyhexadecaneanilide, N-octadecyl-4-hydroxybenzamide, N- (4-hydroxyphenyl) -N'-octadecylurea, N- (4-hydroxybenzo) -N '.
-Octadecanohydrazide, N- (3,4-dihydroxyphenyl-N'-octadecyloxamide, etc.,

In the formula (2), compounds having i = 0 / j = 1 / k = 0 include N- [2- (4-hydroxyphenyl) ethyl] -N'-octadecylurea and N- [3 −
(4-Hydroxyphenyl) propiono] -N'-octadecanohydrazide, N- [3- (4-hydroxyphenyl) propiono] -N'-docosanohydrazide, 1-
[3- (4-hydroxyphenyl) propionyl] amino-1-octadecanoylaminomethane, 1- (4-hydroxyphenylacetyl) -4-octadecyl semicarbazide and the like,

In the formula (2), compounds having i = 1 / j = 1 / k = 0 include N-hexadecyl- (4-hydroxyphenylthio) acetamide and N- [2- (4-hydroxyphenylthio). ) Ethyl] -N'-octadecyl urea, N- (4-hydroxyphenylthio) aceto-N '
-Docosanohydrazide, N- [11- (4-hydroxyphenylthio) undecano] -N'-decanohydrazide, N- [2- (4-hydroxyphenylthio) ethyl] -N'-octadecyloxamide, N -[4- (4
-Hydroxyphenylthio) phenyl] -N'-octadecyloxamide, N- [4- (4-hydroxyphenylthiomethyl) benzo] -N'-docosanohydrazide and the like,

In the formula (2), a compound in which i = 0 / j = 0 / k = 1 is N- (4-hydroxyphenyl)-
3-dodecylthiopropanamide, N- (4-hydroxyphenyl) -N'-3-octadecylthiopropylurea, 4-hydroxy-4'-octadecyloxybenzanilide, 4-hydroxy-4'-dodecylthiobenzanilide, 2- (4-octadecanoylaminophenyl) -4'-hydroxyacetanilide, 2- [4-
(N'-octadecylureido) phenyl] -4'-hydroxyacetanilide and the like,

In the formula (2), a compound in which i = 0 / j = 1 / k = 1 is N- [3- (4-hydroxyphenyl) propiono] -N '-(3-dodecylthiopropiono). ) Hydrazide, N- [3- (3,4-dihydroxyphenyl) propiono] -N '-(11-decylthioundecano) hydrazide and the like,

In the formula (2), a compound in which i = 1 / j = 1 / k = 1 is N- [3- (4-hydroxyphenylthio) propiono] -N '-(3-octadecylthiopropion Ono) hydrazide, N- [11- (3,4,5-
Trihydroxyphenylthio) undecano] -N'-
(11-octadecyl thioundecano) hydrazide and the like.

These reversible developers may be used alone or in admixture of two or more, and the amount of the reversible developer based on the dye precursor is 5 to 5000% by weight, preferably It is 10 to 3000% by weight.

The usually colorless or light-colored electron-donating dye precursor used in the present invention is typified by known compounds generally used for pressure-sensitive recording paper, heat-sensitive recording paper and the like, 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-N-tolyl) amino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl- 7-anilinofluoran, 3-
(N-ethyl-N-tolyl) amino-6-methyl-7-
Phenethylfluorane, 3-diethylamino-7- (4
-Nitroanilino) fluorane, 3-dibutylamino-
6-methyl-7-anilinofluorane, 3- (N-methyl-N-propyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamyl) amino-6- Methyl-7-anilinofluorane, 3- (N-
Methyl-N-cyclohexyl) amino-6-methyl-7
-Anilinofluorane, 3- (N-ethyl-N-tetrahydrofuryl) amino-6-methyl-7-anilinofluorane and the like.

(4) Thiazine type 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.

Specific examples of the method for producing the reversible thermosensitive recording material of the present invention include a dye precursor and a reversible developer as main components, and a compound according to the present invention as an additive component on a support. And a method of forming a reversible heat-sensitive recording layer by coating the above.

As a method for preparing a coating solution for incorporating the dye precursor, the reversible developer and the compound according to the present invention into the reversible thermosensitive recording layer, each compound is dissolved in a solvent or dispersed in a dispersion medium. After that, a method of mixing each compound and then dissolving in a solvent or dispersing in a dispersion medium, a method of dissolving each compound by heating and homogenizing and then cooling, and dissolving in a solvent or dispersing in a dispersion medium, etc. Is not specified. At the time of dispersion, a dispersant may be used if necessary. When water is the dispersion medium, examples of the dispersant include water-soluble polymers such as polyvinyl alcohol and various surfactants. A water-soluble organic solvent such as ethanol may be mixed when the aqueous dispersion is performed. In addition to this, when an organic solvent represented by hydrocarbons is a dispersion medium, lecithin, phosphoric acid esters or the like may be used as a dispersant.

It is also possible to add a binder 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 Ester, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, ethylene / vinyl acetate copolymer, ethylene / vinyl chloride copolymer, polyvinyl chloride, ethylene Vinylidene chloride copolymers, such as latex of polyvinylidene chloride and the like but not limited thereto.

Further, a heat-fusible substance may be contained in the reversible thermosensitive recording layer as an additive for controlling the color developing sensitivity of the reversible thermosensitive recording layer. Those having a melting point of 60 ° C. to 200 ° C. are preferable, and those having a melting point of 80 ° C. to 180 ° C. are particularly preferable. It is also possible to use a sensitizer which is used for general thermal recording paper. Examples of these compounds include waxes such as N-hydroxymethylstearic acid amide, behenic acid amide, stearic acid amide and palmitic acid amide, naphthol derivatives such as 2-benzyloxynaphthalene, p-benzylbiphenyl,
Biphenyl derivatives such as 4-allyloxybiphenyl,
1,2-bis (3-methylphenoxy) ethane, 2,2
′ -Bis (4-methoxyphenoxy) diethyl ether, polyether compounds such as bis (4-methoxyphenyl) ether, diphenyl carbonate, dibenzyl oxalate,
Carbonic acid such as oxalic acid bis (p-methylbenzyl) ester or an oxalic acid diester derivative may be mentioned, and two or more kinds thereof may be added 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 such as polyethylene terephthalate and polypropylene, paper laminated with synthetic resins such as polyethylene and polypropylene, synthetic Paper, metal foil, glass, etc., or a composite sheet in which these are combined can be arbitrarily used according to the purpose, but the invention is not limited to these, and these may be opaque, translucent or transparent. Good. In order to make the background look white or other specific color, a white pigment, a colored dye or pigment, or bubbles may be contained in the support or on the surface. Especially in the case of aqueous coating such as films, when the hydrophilicity of the support is small and it is difficult to coat the reversible thermosensitive recording layer, the same water-soluble polymer as used for the hydrophilic treatment of the surface by corona discharge or the binder The substance may be subjected to an easy-adhesion treatment such as coating on the surface of the support.

The layer constitution of the reversible thermosensitive recording material of the present invention is as follows:
Only the reversible thermosensitive recording layer may be used. If necessary,
Providing a protective layer on the reversible thermosensitive recording layer also provides an intermediate layer containing one or more of water-soluble polymer, white or colored dye / pigment and hollow particles between the reversible thermosensitive recording layer and the support. It can also be provided. 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. The reversible thermosensitive recording layer may also be a multi-layered structure having two or more layers by containing each component one by one or changing the compounding ratio for each layer. Further, a material capable of electrically, optically, and magnetically recording information in the reversible thermosensitive recording layer and / or on the surface opposite to the surface on which another layer and / or the reversible thermosensitive recording layer is provided. 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 blocking, curling and charging.

The method for forming the reversible thermosensitive recording material of the present invention by laminating each layer in the present invention on a support is not particularly limited, and it can be formed by a conventional method. For example, it is possible to use a smearing device such as an air knife coater, a blade coater, a bar coater, or a curtain coater, and various printing machines such as planographic printing, letterpress, intaglio printing, flexo, gravure, screen, and hot melt. In addition to the usual drying process, UV irradiation /
Each layer can be held by EB irradiation.

The reversible thermosensitive recording layer is prepared by mixing each dispersion obtained by finely pulverizing each component, coating on a support and drying, and each solution obtained by dissolving each component in a solvent. It can be obtained by a method of mixing, coating on a support and drying. Drying conditions also differ depending on the dispersion medium or solvent such as water. In addition to this, there is also a method in which the respective components are mixed and heated to melt a fusible component, and coating is performed while hot.

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. In addition to pigments such as aluminum and urea-formalin resin, zinc stearate, higher fatty acid metal salts such as calcium stearate, paraffin, oxidized paraffin, polyethylene, polyethylene oxide, stearic acid amide, and the like for the purpose of preventing head wear and sticking. Waxes such as castor wax may also be contained in addition to a dispersant such as sodium dioctylsulfosuccinate, a surfactant, and a fluorescent dye.

Next, a method of coloring and decoloring the reversible thermosensitive recording material of the present invention will be described. 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. or,
It can be decolored by slow cooling after heating, and it can be performed by using, for example, a thermal head, a heat roll, a heat stamp, high frequency heating, hot air, radiant heat from a light source such as an electric heater and a tungsten lamp or a halogen lamp.

[0050]

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 many electron-accepting compounds, which have been called reversible color developers, have a fatty chain in their structure, the phase of the dye precursor molecule and the dye molecule that has formed a color is changed. It is considered that the solubility is low and that they hardly dissolve in the solidified state. Further, in the state where the dye precursor molecule and the reversible developer molecule can freely move like the heating and melting state, the dye precursor molecule and the reversible developer molecule are melted to each other at a certain ratio to be in a colored state. Therefore, when the colored mixture in a molten state is slowly cooled, the reversible developer molecule and the dye molecule do not dissolve in each other and phase-separate and the color disappears as the temperature decreases. In particular, the electron-accepting compound represented by the general formula (2), which is preferably used in the present invention, contains a bond having a hydrogen bonding ability such as an amide bond in the molecule, so that the intermolecular hydrogen bond causes a rapid reaction. It is thought to crystallize into. 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.

Since the decolorization-accelerating compound represented by the general formula (1) used in the present invention has a fatty chain in the molecule like the above-mentioned reversible developer, the coloring state is destroyed by heating and the reversibility is reversible. It is believed that the developer acts as a nucleus for crystallization when it separates from the dye. On the other hand, the compound represented by the general formula (1) according to the present invention has a highly polar group called ammonium, and in general, these compounds are re-dissolved immediately after being melted by heating and then cooled. Many do not crystallize and solidify into glass. That is, a compound that is slowly recrystallized, such as the decolorization accelerator used in the present invention, has sufficient time for phase separation between the electron-donating dye precursor and the electron-accepting reversible developer after cooling. It is believed that the color can be accelerated, and as a result, the color can be erased at a lower temperature and in a wider temperature range.

Part of the specific method for producing the decoloring accelerator of the present invention will be illustrated below, but the present invention is not limited thereto.

Synthesis Example 1 Synthesis of Exemplified Compound (1-6). A flask equipped with a stirrer, a condenser and a calcium chloride drying tube was charged with 3.7 g of 1-methylimidazole and 10.0 g of octadecyl p-toluenesulfonate, and 1
The mixture was stirred at 20 ° C for 5 hours. The reaction mixture was cooled to room temperature, and the precipitated crystals were collected by filtration under reduced pressure. Recrystallization from acetone gave 10.9 g of the desired product. Melting point 71 [deg.] C.

Synthesis Example 2 Synthesis of Exemplified Compound (1-16). 3.8 g of thiazole and 10.0 g of 1-bromooctadecane were placed in a flask equipped with a stirrer, a condenser and a calcium chloride drying tube, and the mixture was stirred at 120 ° C for 5 hours.
The reaction mixture was cooled to room temperature, and the precipitated crystals were collected by filtration under reduced pressure. Recrystallization from a mixed solvent of acetone and methanol gave 9.1 g of the desired product. Melting point 83 [deg.] C.

Synthesis Example 3 Synthesis of Exemplified Compound (1-17). A flask equipped with a stirrer, a condenser and a calcium chloride drying tube was charged with 4.2 g of 3-octadecyl thiazolium bromide and 10.0 g of methanol, and then 2.1 g of sodium perchlorate was added. After the addition is complete, 20
Heated to reflux for minutes. After cooling the reaction mixture to room temperature,
The precipitated crystals were collected by filtration under reduced pressure. The obtained crystals were washed with acetone to obtain 3.8 g of the desired product. Melting point 91 [deg.] C.

Synthesis Example 4 Synthesis of Exemplified Compound (1-20). In a flask equipped with a stirrer, a condenser and a calcium chloride drying tube, 5.0 g of p-toluenesulfonic acid octadecyl ester and 9.3 g of pyridine were charged and heated under reflux for 6 hours. The reaction mixture was cooled to room temperature, and the precipitated crystals were collected by filtration under reduced pressure. The obtained crystals are washed with acetone,
5.9 g of the target product was obtained. Melting point 133 [deg.] C.

Synthesis Example 5 Synthesis of Exemplified Compound (1-31). A flask equipped with a stirrer, a condenser and a calcium chloride drying tube was charged with 9.8 g of 1,12-dibromododecane and 24.0 g of pyridine, and the mixture was heated under reflux for 7 hours. The reaction mixture was cooled to room temperature, and the precipitated crystals were collected by filtration under reduced pressure. The crystals obtained were washed with acetone to obtain the desired product 14.
9 g was obtained. Melting point 111 [deg.] C.

Synthesis Example 6 Synthesis of Exemplified Compound (1-32). A flask equipped with a stirrer, a condenser and a calcium chloride drying tube was charged with 4.9 g of 1,12-pyridinium dodecane dibromide and 60.0 g of distilled water, and then a hexafluorophosphoric acid, 60% solution was added dropwise. After the dropping is completed,
Stir at room temperature for 10 minutes. After the reaction was completed, the precipitated crystals were collected by filtration under reduced pressure. The crystals obtained were thoroughly washed with water and then recrystallized from methanol to obtain 5.5 g of the desired product. Melting point 1
20 ° C.

[0060]

The present invention will be described in more detail with reference to the following examples. The parts and percentages in the examples are on a weight basis.

Example 1 (A) Preparation of reversible heat-sensitive coating liquid 40 parts of 3-diethylamino-6-methyl-7-anilinofluorane in 2.5% polyvinyl alcohol aqueous solution 90 parts
The mixture was pulverized together with the parts using a paint conditioner to obtain a dye precursor dispersion liquid (liquid A). Then, 100 parts of N- (4-hydroxyphenyl) -N'-octadecyl urea was added to 1.
A reversible developer dispersion liquid (B) was pulverized with a paint conditioner together with 400 parts of a 25% polyvinyl alcohol aqueous solution.
Liquid) was obtained. Furthermore, 20 parts of magnesium carbonate and 0.2%
47 parts of an aqueous polyvinyl alcohol solution was similarly pulverized (C liquid). Also, 10 parts of the exemplified compound (1-6) was added to 1.25
% Aqueous solution of polyvinyl alcohol and pulverized with a paint conditioner to obtain a discoloration accelerator dispersion (D liquid). After mixing these four kinds of dispersion liquids of liquids A, B, C and D, 170 parts of 10% polyvinyl alcohol aqueous solution and 350 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 2.6 g /
After coating and drying so as to have a m ² of 5%, an aqueous 5% polyvinyl alcohol solution was coated and dried so as to have a solid content of 2 g / m ^2, and processed by a super calender to obtain a reversible thermosensitive recording material.

Example 2 A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that the exemplified compound (1-5) was used in place of the exemplified compound (1-6) used in Example 1. It was

Example 3 A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that the exemplified compound (1-16) used in Example 1 was replaced with the exemplified compound (1-16). It was

Example 4 A reversible thermosensitive recording material was obtained in the same manner as in Example 1, except that the exemplified compound (1-17) was used in place of the exemplified compound (1-6) used in Example 1. It was

Example 5 A reversible thermosensitive recording material was obtained in the same manner as in Example 1, except that the exemplified compound (1-20) was used in place of the exemplified compound (1-6) used in Example 1. It was

Example 6 A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that the exemplified compound (1-21) was used in place of the exemplified compound (1-6) used in Example 1. It was

Example 7 A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that the exemplified compound (1-31) was used in place of the exemplified compound (1-6) used in Example 1. It was

Example 8 A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that the exemplified compound (1-32) was used in place of the exemplified compound (1-6) used in Example 1. It was

Comparative Example 1 Except that the exemplified compound (1-6) used in Example 1 was excluded,
A reversible thermosensitive recording material was obtained in the same manner as in Example 1.

Comparative Example 2 A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that stearic acid amide was used in place of the exemplified compound (1-6) used in Example 1.

Comparative Example 3 Instead of the exemplified compound (1-6) used in Example 1, 2
Example 1 except that -benzyloxynaphthalene was used
A reversible thermosensitive recording material was obtained in the same manner as.

Test 1 (coloring density = thermoresponsiveness) The thermal recording materials obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were applied to the Kuraray printing head KJT-256-8MGF1 with Okura Electric's thermal printing printer. TH-PMD
Was applied with an applied pulse of 1.1 milliseconds for an applied voltage of 26 V, and the density of the obtained color image was measured using a densitometer Macbeth RD918.

Test 2 (Image erasability) The thermosensitive recording materials obtained in Examples 1 to 8 and Comparative Examples 1 to 3 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 under the condition of an applied voltage of 26 V for an applied pulse of 1.1 msec, heated at 100 ° C. for 1 second using a heat stamp, and then the density was measured in the same manner as in Test 1.

Test 3 (Decoloring start temperature) The thermal recording materials obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were used as a thermal facsimile printing tester TH-manufactured by Okura Electric Co. with a print head KJT-256-8MGF1 manufactured by Kyocera. PMD
Printing with an applied pulse of 1.1 msec for an applied voltage of 26 V, and using a heat stamp to heat the sample from 60 ° C. to 150 ° C. at 10 ° C. intervals at a total of 10 points for 1 second each, and then test. Each concentration was measured in the same manner as in 1. The heating temperature at which the optical density of the printed image fell below 0.15 was taken as the decolorization start temperature.

Test 4 (Change in Color Density with Time = Image Stability) The thermal recording materials obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were heat-sensitive facsimiles manufactured by Okura Electric Co. with a print head KJT-256-8MGF1 manufactured by Kyocera. Printing tester TH-PMD
Was applied under the conditions of an applied voltage of 26 V with an applied pulse of 1.1 msec and stored in an atmosphere of a temperature of 35 ° C. and a relative humidity of 20% for 24 hours. The density was measured, and the image residual ratio was calculated by the following formula 1.

[0077]

## EQU1 ## A = (C / B) × 100 A: Image residual rate (%) B: Image density before test C: Image density after test

Tests 1 of Examples 1-8 and Comparative Examples 1-3
The results of No. 4 are shown in Table 1.

[0079]

[Table 1]

Example 9 (C) Preparation of reversible heat-sensitive coating liquid 40 parts of 3-diethylamino-6-methyl-7-anilinofluorane in a 2.5% aqueous polyvinyl alcohol solution 90
The mixture was pulverized together with the parts using a paint conditioner to obtain a dye precursor dispersion liquid (liquid A). Next, 200 parts of N- [3- (4-hydroxyphenyl) propiono] -N'-docosanohydrazide was crushed together with 800 parts of a 1.25% polyvinyl alcohol aqueous solution with a paint conditioner to prepare a reversible color developer dispersion (liquid B). ) Got. In addition, the exemplified compound (1
-20) 10 parts were pulverized together with 62 parts of a 1.25% polyvinyl alcohol aqueous solution by a paint conditioner to obtain a discoloration accelerator dispersion (C liquid). After mixing these three kinds of dispersion liquids of liquids A, B and C, 260 parts of 10% aqueous polyvinyl alcohol solution and 160 parts of water were added and mixed well to prepare a reversible heat-sensitive coating liquid.

(D) Preparation of reversible heat-sensitive recording material The reversible heat-sensitive coating liquid prepared in (C) was applied to a polyethylene terephthalate (PET) sheet to give a solid content of 2.6 g /
After coating and drying so as to have a m ² of 5%, an aqueous 5% polyvinyl alcohol solution was coated and dried so as to have a solid content of 2 g / m ^2, and processed by a super calender to obtain a reversible thermosensitive recording material.

Example 10 Instead of the exemplified compound (1-20) used in Example 9,
A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that the exemplified compound (1-5) was used.

Example 11 Instead of the exemplified compound (1-20) used in Example 9,
A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that the exemplified compound (1-16) was used.

Example 12 Instead of the exemplified compound (1-20) used in Example 9,
A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that the exemplified compound (1-17) was used.

Example 13 Instead of the exemplified compound (1-20) used in Example 9,
A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that the exemplified compound (1-19) was used.

Example 14 Instead of the exemplified compound (1-20) used in Example 9,
A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that the exemplified compound (1-21) was used.

Example 15 Instead of the exemplified compound (1-20) used in Example 9,
A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that the exemplified compound (1-31) was used.

Example 16 Instead of the exemplified compound (1-20) used in Example 9,
A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that the exemplified compound (1-32) was used.

Comparative Example 4 A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that the exemplified compound (1-20) used in Example 9 was omitted.

Comparative Example 5 Instead of the exemplified compound (1-20) used in Example 9,
A reversible thermosensitive recording material was obtained in the same manner as in Example 9 except that 2-benzyloxynaphthalene was used.

Test 5 (coloring density = thermoresponsiveness) The thermal recording materials obtained in Examples 9 to 16 and Comparative Examples 4 and 5 were used in a thermal facsimile printing tester TH-PMD manufactured by Okura Electric Co., Ltd. equipped with a TDK printing head LH4409. An applied pulse of 1.2 ms was used to print under an applied voltage of 18.7 V, and the density of the obtained color image was measured with a densitometer Macbeth RD91.
8 was used for measurement.

Test 6 (Image erasability) The heat-sensitive recording materials obtained in Examples 9 to 16 and Comparative Examples 4 and 5 were subjected to a thermosensitive facsimile printing tester TH-PMD manufactured by Okura Electric Co., Ltd. with a print head LH4409 manufactured by TDK. Printing was performed with an applied pulse of 1.2 milliseconds for an applied voltage of 18.7 volts, and this was heated at 100 ° C. for 1 second using a heat stamp, and then the density was measured in the same manner as in Test 5.

Test 7 (Decoloring start temperature) The thermosensitive recording materials obtained in Examples 9 to 16 and Comparative Examples 4 and 5 were subjected to a thermosensitive facsimile printing tester TH-PMD manufactured by Okura Electric Co., Ltd. with a TDK print head LH4409. Printing was performed under the condition of an applied voltage of 18.7 volts with an applied pulse of 1.2 milliseconds, and this was heated from 60 ° C. to 150 ° C. at 10 ° C. intervals at a total of 10 positions for 1 second each using a heat stamp, and then the test 5 Each concentration was measured in the same manner as in. The heating temperature at which the optical density of the printed image fell below 0.15 was taken as the decolorization start temperature.

Test 8 (Change in Color Density with Time = Image Stability) The thermal recording materials obtained in Examples 9 to 16 and Comparative Examples 4 and 5 were heat-sensitive facsimile printing tester TH manufactured by Okura Electric Co. with a print head LH4409 manufactured by TDK. -Printed using PMD with an applied voltage of 1.2 milliseconds for an applied voltage of 18.7 volts, stored in an atmosphere of a temperature of 50 ° C and a relative humidity of 20% for 24 hours, and then tested as in Test 5. The density of the color-developed portion was measured, and the image residual rate was calculated by the above-mentioned equation 1.

Test 5 of Examples 9 to 16 and Comparative Examples 4 and 5
The results of ~ 8 are shown in Table 2.

[0096]

[Table 2]

[0097]

As shown in Tables 1 and 2, a colorless or light-colored dye precursor and a reversible developer which causes a reversible color change in the dye precursor by heating are contained. In the reversible thermosensitive recording material, by containing the compound represented by the general formula (1), an image can be formed / erased with a clear contrast, and a stable image can be retained over time in the environment of daily life. A possible reversible thermosensitive recording material could be obtained.

Claims (2)

(57) [Claims] 1. A reversible method comprising a dye precursor which is usually colorless or light-colored on a support, and a reversible developer which causes the dye precursor to undergo reversible color tone change due to a difference in cooling rate after heating. A reversible thermosensitive recording material, characterized in that the thermosensitive recording material contains at least one compound represented by the following general formula (1) as a decolorization accelerator. [Chemical 1] (In the formula (1), A represents a heteroaromatic ring. R ¹ has 6 carbon atoms.
To 24 hydrocarbon groups. m represents an integer of 1 or 2. X represents an anion, and n represents the number required to adjust the charge in the molecule to zero. ) 2. The reversible thermosensitive recording material according to claim 1, wherein the reversible developer is a compound represented by the following general formula (2). [Chemical 2] (In the formula (2), q represents an integer of 1 to 3, i, j and k each represent 0 or 1. However, when i is 1, j represents 1. R ² and R ³ are carbon atoms. 1 to 18 divalent hydrocarbon group, R ⁴ represents a hydrocarbon group having 1 to 24 carbon atoms, L ¹ represents a divalent group having at least one —CONH— bond, and L ² represents —. Represents a divalent group having at least one CONH-bond, an oxygen atom or a sulfur atom.)