JP2000313171A - Reversible heat-sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely and uniformly execute erasing of an image in a wide width temperature range by adding a specific compound as an achromatization accelerator by using a compound represented by the specific formula as a reversible developer in a reversible heat-sensitive recording material. SOLUTION: In the reversible heat-sensitive recording material containing a dye precursor and a reversible developer for generating a reversible color tone change in the precursor according to a difference of cooling speeds after heating on a support, as the developer, at least one type of compounds represented by formulae I to III is used, and as an achromatization accelerator, at least one type of a compound represented by formula IV is contained, wherein m, q and r are ach 1 to 3, n is 0 or 1, R1, R3 and R5 are each 1-18C bivalent hydrocarbon group, R2, R4 and R6 are each 1-14C hydrocarbon group, X, Z, Q and T are each a bivalent group having at least one or above-CONH- bond in the formulae I to III, and R2 to R9 are each an alkyl group, an aralkyl group or the like, and R10 is 6-24C hydrocarbon group.

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 images by controlling thermal energy.

[0002]

2. Description of the Related Art In general, a heat-sensitive recording material comprises a support having thereon a heat-sensitive recording layer mainly composed of an electron-donating usually colorless or pale-color dye precursor and an electron-accepting developer. By heating with a thermal head, a hot pen, a laser beam, or the like, the dye precursor and the developer react instantaneously to obtain a recorded image. Japanese Patent Publication No. 43-4160, Japanese Patent Publication No. Sho 4
It is disclosed in JP-A-5-14039.

In general, it is impossible for such a heat-sensitive recording material to form an image once and erase that portion and return to the state before image formation. There was no choice but to add to the formation. For this reason, when the area of the heat-sensitive recording portion is limited, there has been a problem that the recordable information is limited and all necessary information cannot be recorded.

In recent years, reversible thermosensitive recording materials capable of repeatedly forming and erasing images have been devised to address such problems. For example, JP-A-54-119377 and JP-A-63-119377 disclose a reversible thermosensitive recording material. 39377, JP-A-63-4
Japanese Patent No. 1186 describes a heat-sensitive recording material composed of a resin base material and an organic low-molecular compound dispersed in the resin base material. However, in this method, the transparency of the heat-sensitive recording material is reversibly changed by heat energy, so that the contrast between the image forming portion and the non-image forming portion is insufficient.

In the methods described in Japanese Patent Application Laid-Open Nos. 50-81157 and 50-105555, since the image to be formed changes according to the environmental temperature, the image forming state and the erasing state are changed. Are different from each other, and these two states cannot be stably maintained for an arbitrary period at room temperature.

Further, Japanese Patent Application Laid-Open No. Sho 59-120492 discloses that an image forming state is controlled by keeping a recording material in a hysteresis temperature range by utilizing a hysteresis characteristic of a coloring component.
Although a method for 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 range. 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.
No. 11898 describes a reversible thermosensitive recording medium comprising a leuco dye and a color-reducing agent which causes the leuco dye to develop and decolor the color by heating. The color-developing agent is an amphoteric compound having an acidic group for coloring the leuco dye and a basic group for decolorizing the colored leuco dye. One is preferentially generated to perform color development and decoloration. However, in this method, it is impossible to completely switch between the coloring reaction and the decoloring reaction only by controlling the heat energy, and since both reactions occur at a certain ratio at the same time, a sufficient coloring density cannot be obtained. Can't do it perfectly. Therefore, sufficient image contrast cannot be obtained. Also,
Since the decolorizing action of the basic group also acts on the colored portion at room temperature,
The phenomenon that the density of the color-developed portion decreases over time is inevitable.
Further, JP-A-5-124360 describes a reversible thermosensitive recording medium that develops and decolorizes a leuco dye by heating, and as an electron accepting compound, an organic phosphonic acid compound, an α-hydroxy aliphatic carboxylic acid, Specific phenolic compounds such as fatty acid dicarboxylic acids and alkylthiophenols having an aliphatic group having 12 or more carbon atoms, alkyloxyphenols, alkylcarbamoylphenols, and alkyl gallates are exemplified. However, even with this recording medium, the two problems of low color density or incomplete erasing cannot be solved at the same time, and the stability of the image over time is satisfactory for practical use. Absent. Further, Japanese Patent Application Laid-Open
No. 2,294,063, as a decolorizing accelerator for improving the erasability of the reversible thermosensitive recording medium, fatty acids, waxes, higher alcohols, various esters of phosphoric acid / benzoic acid / phthalic acid or oxyacid, silicone oil There are disclosed liquid crystal compounds, surfactants, and saturated hydrocarbons of fatty acids having 10 or more carbon atoms, but the effects are small, and the image density at the time of erasing is still high and cannot be said to be practical.

As described above, according to the conventional technology, a practical reversible image having a clear image contrast, capable of forming and completely erasing a high-density image, and capable of maintaining a stable image over time in an environment of daily life. It was difficult to produce a thermosensitive recording material. On the other hand, in the specification of Japanese Patent Application No. Hei 10-93313, the present applicants have disclosed that an electron-donating dye precursor, which is usually colorless or light-colored, causes a reversible color change by heating, that is, an electron which causes color development and decoloration. Although it has been found that a receptive compound (reversible developer) exists, in order to obtain a practically better image quality and an easy-to-use recording medium,
There is room for improvement in the image density at the time of erasing, the erasing start temperature, the erasing temperature range, and the like.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material capable of forming and erasing an image with good contrast and capable of maintaining a stable image over time in an environment of daily life. That is. More specifically, the present invention provides a reversible thermosensitive recording material having lower image density at the time of erasing, less erasure remaining, and capable of performing uniform erasing at a lower temperature and a wide temperature range with respect to the erasing temperature. That is the task.

[0010]

Means for Solving the Problems The inventors of the present invention produce a colorless or pale-colored dye precursor on a support and cause the dye precursor to undergo a reversible color change due to a difference in cooling rate after heating. In a reversible thermosensitive recording material containing a reversible developer, the reversible developer is represented by the following general formula (1):
When the compound represented by (2) or (3) is used, as a result of intensive studies to further improve the erasability, at least one of the specific compounds represented by the following general formula (4) is used as a decolorizing accelerator. The present 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 by the addition of, and the present invention has been completed.

[0011]

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In the formula 1, m represents an integer of 1 or more and 3 or less, and n represents 0 or 1. R ¹ represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ² represents a hydrocarbon group having 1 to 24 carbon atoms which may contain an oxygen atom or a sulfur atom in the chain. X represents a divalent group having at least one —CONH— bond. However, when n = 0, Y is -NHCON
Excludes H-bonds.

[0013]

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In the formula 2, q represents an integer of 1 or more and 3 or less.
R ³ represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ⁴ represents a hydrocarbon group having 1 to 24 carbon atoms which may contain an oxygen atom or a sulfur atom in the chain. Y represents an oxygen atom or a sulfur atom, and Z represents a divalent group having at least one -CONH- bond.

[0015]

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In the formula 3, r represents an integer of 1 or more and 3 or less.
R ⁵ represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ⁶ represents a hydrocarbon group having 1 to 24 carbon atoms which may contain an oxygen atom or a sulfur atom in the chain. Q and T have the same meaning and may be the same or different from each other.
It represents a divalent group having at least one ONH-bond.

[0017]

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In the formula 4, R ⁷ , R ⁸ and R ⁹ have the same meaning and represent an alkyl group or an aralkyl group which may be the same as or different from each other. May also form a ring with each other. R ¹⁰ represents a hydrocarbon group having 6 to 24 carbon atoms. t represents 1 or 2. A represents an anion, and w represents a number necessary to adjust the intramolecular charge to zero.

Formulas (1) to (1) used in the present invention.
The reversible developer represented by (3) is disclosed in JP-A-7-108761 and 7-1790, which have been previously found by the present applicant.
No. 43, No. 7-164746, and Japanese Patent Application No.
No. 69787, Japanese Patent Application No. 10-315252 and the like, and also describes a synthesis method.

In the compound represented by the general formula (1), R ¹ represents a divalent hydrocarbon group having 1 to 18 carbon atoms, preferably a divalent hydrocarbon group having 1 to 11 carbon atoms. . n represents 0 or 1, but is preferably 1. R ² represents a hydrocarbon group having 1 to 24 carbon atoms, preferably a hydrocarbon group having 6 to 11 carbon atoms. R ² may further contain an oxygen atom and a sulfur atom, but when such a hetero atom is contained, a sulfur atom which is convenient for synthesis is preferable. Further, when the compound contains a hetero atom, the hydrocarbon group via the hetero atom preferably has 6 to 11 carbon atoms. In this case, it is particularly preferable that the sum of the number of carbon atoms is 11 or more and 22 or less. This is because if the total number of carbon atoms is less than this, the color developability is good, but the erasability and image storability tend to be worse. Is better, but the color developability tends to be worse, so it is considered to be a well-balanced one that does not impair the coloring / erasing contrast or image storability. Specifically, R ¹ and R ² mainly represent an alkylene group and an alkyl group, respectively.
Each may contain an aromatic ring in the radical, in particular R ¹
In such a case, only the aromatic ring may be used. On the other hand, X in the formula 1 is -CO
It represents a divalent group having at least one NH-bond, and specific examples thereof include amides (-CONH-, -N
HCO-), urea (-NHCONH-), urethane (-
NHCOO-, -OCONH-), diacylamine (-
CONHCO-), diacyl hydrazide (-CONNHN)
HCO-), oxalic acid diamide (-NHCOCONH)
-), Acyl ureas (-CONHCONH-, -NHCO
NHCO-), 3-acylcarbazates (-C
ONHNHCOO-), semicarbazide (-NHCON)
HNH-, -NHNHCONH-), acyl semicarbazide (-CONHNHCONH-, -NHCONNHNH
CO-), diacyl aminomethane (-CONHCH ₂ N
HCO -), 1-acylamino-1-Ureidometan (-CONHCH ₂ NHCONH -, - NHCONHC
H ₂ NHCO-), malonamide (-NHCOCH ₂ CO
NH-) and the like. However, when n = 0, X excludes a urea bond.

Hereinafter, specific examples of the electron accepting compound represented by the general formula (1) are shown in Chemical formulas 9 to 11, but the present invention is not limited thereto.

[0022]

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[0023]

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[0024]

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In the compound represented by formula (2), R ³ has the same meaning as R ^{1 in} formula (1). Similarly, R ⁴ is R
² and Z have the same meanings as X. Y represents an oxygen atom or a sulfur atom, but when it is an oxygen atom, the hydrocarbon group of R ³ and R ⁴ is further represented by X because the erasability is generally good. As for the linking group having an amide bond as a minimum constitutional unit, the smaller the hydrogen bonding ability, the better the coloring property and the better the balance of coloring and erasing tend to be. On the other hand, Y
In the case where is a sulfur atom, on the contrary to the case of an oxygen atom, the coloring property is good, so that the hydrocarbon group is longer to compensate for the erasability, and furthermore, the connection with the amide bond as the minimum constituent unit The hydrogen bonding ability of the group should be designed to be relatively large.

Hereinafter, specific examples of the electron accepting compound represented by the general formula (2) are shown in Chemical formulas 12 and 13, but the present invention is not limited thereto.

[0027]

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[0028]

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In the compound represented by formula (3), R ⁵ has the same meaning as R ^{1 in} formula (1). Similarly, R ⁶ is R
² , Q and T have the same meanings as X.

Hereinafter, specific examples of the electron-accepting compound represented by the general formula (3) are shown in Chemical formula 14, but the present invention is not limited thereto.

[0031]

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In the compound represented by the general formula (4), R ⁷ ,
R ⁸ and R ⁹ may be the same or different and represent an alkyl group, an aralkyl group, an alkenyl group or an aryl group, preferably a lower alkyl group having 6 or less carbon atoms. Further, these may be connected to each other to form an alicyclic structure, but at this time, a hetero atom such as an oxygen atom or a nitrogen atom may be contained in the chain. R ¹⁰ represents a monovalent or divalent hydrocarbon group having 6 to 24 carbon atoms, preferably an aliphatic hydrocarbon group, specifically a monovalent hydrocarbon group having 8 to 18 carbon atoms. A represents a counter anion, and specific examples thereof include a halogen, a substituted sulfonate, a substituted borate, a substituted phosphate and the like, and preferably a halogen and a substituted sulfonate.

Specific examples of the compound represented by the general formula (4) include compounds represented by the following formulas (15) and (16), but the present invention is not limited thereto.

[0034]

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[0035]

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The preferred amount of the compound represented by the general formula (4) is 0.1% by weight or more and 1000% by weight or less based on the electron accepting compound represented by the general formulas (1) to (3). And more preferably 0.5% by weight or more and 200% by weight or less. Furthermore, considering the heat-resistant storage stability of the printed image,
Most preferably, it is not less than 100% by weight and not more than 100% by weight. The compounds represented by the general formula (4) can be used alone or in combination of two or more.

The electron accepting compound according to the present invention may be used alone or as a mixture of two or more kinds. Usually, the amount of the electron accepting compound according to the present invention to be used for a colorless or pale color dye precursor is 5 to 5%. It is 5,000 to 5000% by weight, preferably 10 to 3,000% by weight.

The generally colorless or light-colored electron-donating dye precursor used in the present invention is typified by known compounds generally used in pressure-sensitive recording paper and heat-sensitive recording paper, but is not particularly limited. . Specific examples include, for example, the following, but the present invention is not limited thereto.

(1) Triarylmethane compounds 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- (4-diethylamino-2-
Ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) phthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2)
-Methylindol-3-yl) -4-azaphthalide,
3- (4-diethylamino-2-ethoxyphenyl)-
3- (1-ethyl-2-methylindol-3-yl)
-4,7-diazaphthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -7-azaphthalide, 3-
(P-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,
2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-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, 3,3-bis (p-dimethylaminophenyl) -4
-Azaphthalide and the like.

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

(3) Xanthene compounds rhodamine B anilinolactam, rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3- Diethylamino-7-phenylfluoran, 3-diethylamino-7-phenoxyfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7- (3 , 4-Dichloroanilino) fluorane, 3-diethylamino-7-
(2-chloroanilino) fluoran,

3-Diethylamino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl- 7-anilinofluoran, 3-
(N-ethyl-N-tolyl) amino-6-methyl-7-
Phenethylfluoran, 3-diethylamino-7- (4
-Nitroanilino) fluoran, 3-dibutylamino-
6-methyl-7-anilinofluoran, 3- (N-methyl-N-propyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-isoamyl) amino-6 Methyl-7-anilinofluoran, 3- (N-
Methyl-N-cyclohexyl) amino-6-methyl-7
-Anilinofluoran, 3- (N-ethyl-N-tetrahydrofuryl) amino-6-methyl-7-anilinofluoran and the like.

(4) Thiazine compounds Benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue and the like.

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

The above colorless or pale color dye precursors may be used alone or in combination of two or more.

As a specific example of the method for producing the reversible thermosensitive recording material of the present invention, a dye precursor and a reversible developer are used as main components, to which the compound according to the present invention is added and coated on a support. To form a reversible thermosensitive recording layer.

As a method for preparing a coating liquid for incorporating the dye precursor, the reversible developer and the compound of the present invention in the reversible thermosensitive recording layer, each compound is dissolved alone in a solvent or dispersed in a dispersion medium. Mixing each compound, dissolving in a solvent or dispersing in a dispersion medium, mixing each compound by heating and dissolving and homogenizing, cooling, dissolving in a solvent or dispersing in a dispersion medium, etc. However, there is no particular limitation. At the time of dispersion, a dispersant may be used if necessary. When water is used as the dispersion medium, a water-soluble polymer such as polyvinyl alcohol and various surfactants can be used as the dispersant. In the case of aqueous dispersion, a water-soluble organic solvent such as ethanol may be mixed.
In addition, when an organic solvent typified by hydrocarbons is a dispersion medium, lecithin, phosphates, and the like may be used as a dispersant.

Further, 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, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylamide / acrylate copolymer, acrylamide / acryl. Water-soluble polymers 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, latexes such as polyvinylidene chloride. The role of these binders is to maintain a state in which each material of the composition is uniformly dispersed without unevenness due to application of heat for printing and erasing. Therefore, it is preferable to use a resin having high heat resistance as the binder resin. Recently, high value-added reversible thermosensitive recording materials such as prepaid cards and stored cards are increasingly used, and with this, high durability products such as heat resistance, water resistance and adhesiveness are required. It is becoming. Curable resins are particularly preferred for such requirements.

Examples of the curable resin include a thermosetting resin, an electron beam curable resin, and an ultraviolet curable resin.
Examples of the thermosetting resin include resins that are cured by reacting a hydroxyl group and a carboxyl group with a crosslinking agent such as a phenoxy resin, a polyvinyl butyral resin, and a cellulose acetate propionate resin. Examples of the crosslinking agent at this time include isocyanates, amines, phenols, epoxies and the like.

Monomers, bifunctional monomers, polyfunctional monomers and the like typified by acrylics can be used as the monomers used for the electron beam and the curing beam resin. And a photopolymerization accelerator.

Further, as an additive for adjusting the color development sensitivity of the reversible thermosensitive recording layer, a thermofusible substance may be contained in the reversible thermosensitive recording layer. Those having a melting point of 60 ° C to 200 ° C are preferred, and those having a melting point of 80 ° C to 180 ° C are particularly preferred. A sensitizer used in general thermosensitive recording paper can also be used. Examples of these compounds include waxes such as N-hydroxymethyl stearamide, behenamide, stearamide, palmitamide, naphthol derivatives such as 2-benzyloxynaphthalene, p-benzylbiphenyl,
Biphenyl derivatives such as 4-allyloxybiphenyl,
1,2-bis (3-methylphenoxy) ethane, 2,
Polyether compounds such as 2'-bis (4-methoxyphenoxy) diethyl ether and bis (4-methoxyphenyl) ether, diphenyl carbonate, dibenzyl oxalate,
Examples thereof include carbonic acid or oxalic acid diester derivatives such as bis (p-methylbenzyl) oxalate and the like, and two or more kinds thereof can be added in combination.

As the support used in the reversible thermosensitive recording material of the present invention, paper, various nonwoven fabrics, woven fabrics, synthetic resin films such as polyethylene terephthalate and polypropylene, paper laminated with synthetic resins such as polyethylene and polypropylene, synthetic resins Paper, metal foil, glass or the like, or a composite sheet combining these can be used arbitrarily according to the purpose, but is not limited thereto, and they are either opaque, translucent or transparent. Is also good. In order to make the background appear white or another specific color, a white pigment, a colored dye or a bubble may be contained in or on the support. In particular, in the case of aqueous coating of films, etc., when the hydrophilicity of the support is small and it is difficult to apply the reversible thermosensitive recording layer, the same water-soluble polymer as used for the hydrophilic treatment of the surface by corona discharge etc. or the binder May be subjected to an easy adhesion treatment such as coating on the surface of a support.

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,
Providing a protective layer on the reversible thermosensitive recording layer may also include an intermediate layer containing at least one of a water-soluble polymer, a white or colored dye or 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 two or three or more layers. The reversible thermosensitive recording layer may also be formed as a multilayer of two or more layers by containing each component in one layer or changing the mixing ratio for each layer. Further, a material capable of recording information electrically, optically, and magnetically in the reversible thermosensitive recording layer and / or on the surface opposite to the surface on which the reversible thermosensitive recording layer is provided. May be included. Further, a back coat layer can 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, a smearing apparatus such as an air knife coater, a blade coater, a bar coater, and a curtain coater, and various printing machines using a method such as lithographic, letterpress, intaglio, flexo, gravure, screen, and hot melt can be used. In addition to the usual drying process, UV irradiation and
Each layer can be held by EB irradiation.

The reversible thermosensitive recording layer is prepared by mixing each dispersion obtained by pulverizing each component, coating the mixture on a support and drying, and dissolving each component in a solvent. It can be obtained by, for example, a method of mixing and coating and drying on a support. Drying conditions vary depending on a dispersion medium or solvent such as water. In addition, there is a method in which the components are mixed and heated to melt a fusible component, and the mixture is heated and applied.

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, etc., in addition to head abrasion prevention, anti-sticking, zinc stearate, higher fatty acid metal salts such as calcium stearate, paraffin, paraffin oxide, polyethylene, polyethylene oxide, stearamide, Waxes such as caster wax, and a dispersant such as dioctyl sodium sulfosuccinate, a surfactant, a fluorescent dye, and an ultraviolet absorber can also be contained.

Next, the method of coloring and decoloring the reversible thermosensitive recording material of the present invention will be described. In order to perform color development, rapid cooling may be performed subsequent to heating, for example, by heating with a thermal head, laser light, or the like. or,
The color can be erased by slow cooling after heating, for example, by using radiant heat from a light source such as a thermal head, a hot roll, a hot stamp, high-frequency heating, hot air, an electric heater, a tungsten lamp, a halogen lamp, or the like.

[0058]

The principle of image formation and erasing of the heat-sensitive recording material of the present invention is not clear yet, but can be considered as follows. Generally, when a colorless or pale color 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 takes place and color is formed. At this time, it is considered that the electron accepting compound molecule exists very close to the colored dye molecule. When the electron-accepting compound molecule is separated from the dye molecule that has developed color, the dye molecule that has developed color receives electrons again, and is in a state of a dye precursor before color development. It is considered that the present invention changes the distance between the electron-accepting compound molecule and the dye molecule by heating to perform coloring and decoloring.

More specifically, most electron-accepting compounds, which have been referred to as reversible developers, have a fatty chain in their structure. It is considered that they have low solubility and hardly dissolve in the solidified state. Further, in a state where the dye precursor molecule and the reversible color developer molecule can move freely, such as in a heated and melted state, the dye precursor molecule and the reversible color developer molecule are dissolved at a certain ratio to each other to form a color. Therefore, when the colored mixture in the molten state is cooled slowly, the reversible developer molecules and the dye molecules become insoluble with each other and phase-separate as the temperature decreases, and the color is erased. In particular, since the electron-accepting compound represented by the general formulas 9 to 14, which is preferably used in the present invention, contains a bond having a hydrogen bonding ability such as an amide bond in the molecule, the compound has an intermolecular hydrogen bond. It is thought that it will crystallize quickly. On the other hand, when cooling is performed rapidly, the solidified state is obtained before the phase separation, that is, in the state of the color development, so that the color development state is fixed and the color development state is stably maintained after the solidification.

The decoloring accelerating compound represented by the general formula (4) used in the present invention is an ammonium salt. Such a compound is heated to a temperature above its melting point and then solidified when left to cool to room temperature. Many require a certain amount of time to do so. That is, it is considered that this property further promotes the decoloring time at the time of phase separation between the electron-donating dye precursor and the electron-accepting reversible developer after the temperature is lowered. Color is available.

[0061]

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

Example (A) Preparation of reversible thermosensitive coating liquid 3- (4-diethylamino-2-ethoxypheny) -3
-(1-ethyl-2-methylindol-3-yl)-
40 parts of 4-azaphthalide and 100 parts of N- [3- (p-hydroxyphenoxy) propiono] -N'-n-octadecanohydrazide were converted to 8% polyvinyl acetal (BL-1, manufactured by Sekisui Chemical Co., acetalization degree 63). (Mol%) of a tetrahydrofuran (THF) solution (9100 parts) and pulverized with a paint conditioner.
Liquid). Further, N-octadecyl succinimide 5
A part thereof was pulverized with a paint conditioner together with 20 parts of THF to obtain a discoloration accelerator dispersion (liquid B). These two dispersions of the liquids A and B were mixed to prepare a reversible thermosensitive coating liquid.

(B) Coating of Reversible Thermosensitive Recording Layer After adding 29 parts of Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) to the reversible thermosensitive coating liquid prepared in (A), a polyethylene terephthalate (PET) sheet was added. The smear was applied so that the solid content was 4.0 g / m ² . It was dried at 60 ° C. for 24 hours and treated with a super calender to obtain a reversible thermosensitive recording material.

(C) Coating of protective layer Aronix M80 was coated on the coated sheet prepared in (B).
90 (manufactured by Toagosei Chemical Industry Co., Ltd.) 90 parts, N-vinyl-2-
After adding 5 parts of pyrrolidone, 5 parts of Irgacure 500 (manufactured by Nippon Ciba Geigy), and 10 parts of nip seal E220A (manufactured by Nippon Silica), the mixture was stirred, and used as a coating liquid for a protective layer.
/ M ^2, and cured with an ultraviolet irradiation device to obtain a reversible thermosensitive recording material having a protective layer.

The electron donating dye precursor used in the examples is shown in Chemical formula 17.

[0066]

Embedded image

The electron-accepting reversible developer represented by the general formulas (1) to (3) and the decoloring accelerating compound represented by the general formula (4), which are preferably used in the present invention. Table 1 shows combinations of and electron donor dye precursors.

[0068]

[Table 1]

Comparative Example 1 A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that the decoloring accelerating compound used in Example 1 was omitted.

Comparative Example 2 A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that the decolorizing accelerating compound used in Example 5 was omitted.

Comparative Example 3 A reversible thermosensitive recording material was obtained in the same manner as in Example 1, except that 1,3-dioctadecyl urea was used in place of the decolorizing accelerating compound used in Example 9.

Test 1 (Coloring density = thermal response) The reversible thermosensitive recording materials obtained in Examples 1 to 10 and Comparative Examples 1 to 3 were applied to a Kyocera print head KJT-256-8MG.
Okura Electric Thermal Facsimile Printing Tester with F1 TH-
Using a PMD, an applied pulse of 1.1 milliseconds and an applied voltage of 26
Printing was performed under bolt conditions, and the density of the obtained color image was measured using a densitometer Macbeth RD918.

Test 2 (Erasability of Image) The reversible thermosensitive recording materials obtained in Examples 1 to 10 and Comparative Examples 1 to 3 were applied to a Kyocera print head KJT-256-8MG.
Okura Electric Thermal Facsimile Printing Tester with F1 TH-
Using a PMD, an applied pulse of 1.1 milliseconds and an applied voltage of 26
Printing was performed under bolt conditions, and this was printed using a heat stamp.
After heating at 0 ° C. for 1 second, the concentration was measured in the same manner as in Test 1.

Test 3 (Decoloring Start Temperature) The reversible thermosensitive recording materials obtained in Examples 1 to 10 and Comparative Examples 1 to 3 were applied to a Kyocera print head KJT-256-8MG.
Okura Electric Thermal Facsimile Printing Tester with F1 TH-
Using a PMD, an applied pulse of 1.1 milliseconds and an applied voltage of 26
Printing is performed under the condition of bolts, and this is
After heating for 10 seconds from 10 ° C. to 170 ° C. at 10 ° intervals, each concentration was measured in the same manner as in Test 1. The heating temperature at which the optical density of the printed image was lower than 0.15 was defined as the decolorization start temperature.

Test 4 (Temporal change in color density = image stability) The reversible thermosensitive recording materials obtained in Examples 1 to 10 and Comparative Examples 1 to 3 were applied to a Kyocera print head KJT-256-8MG.
Okura Electric Thermal Facsimile Printing Tester with F1 TH-
Using a PMD, an applied pulse of 1.1 milliseconds and an applied voltage of 2
Printing at 6 volts, temperature 50 ° C, relative humidity 20%
After storing in the atmosphere for 24 hours, the density of the color-developed portion was measured in the same manner as in Test 1, and the image remaining ratio was calculated by the following equation (1).

[0076]

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

Table 2 shows the results of Tests 1 to 4 of Examples 1 to 10 and Comparative Examples 1 to 3.

[0078]

[Table 2]

[0079]

As shown in Table 2, the dye precursors are usually colorless or light-colored, and are represented by the general formulas (1) to (3) which cause the dye precursor to undergo reversible color change upon heating. In a reversible thermosensitive recording material containing a reversible developer, an image can be formed / erased with a clear contrast by including a decoloration promoting compound represented by the general formula (4). A reversible thermosensitive recording material capable of maintaining a stable image over time under the above environment was obtained.

Claims (2)

[Claims] Claims: 1. A reversible colorant comprising a colorless or pale color dye precursor on a support and a reversible developer which causes a reversible color change in the dye precursor due to a difference in cooling rate after heating. In a thermosensitive recording material, at least one compound represented by the following general formula (1), (2) or (3) is used as the reversible developer, and the following general formula (4) is used as a decolorizing accelerator. A reversible thermosensitive recording material comprising at least one compound represented by the formula: Embedded image (In the formula 1, m is an integer of 1 or more and 3 or less, and n is 0 or 1.
Represents R ¹ represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ² represents a hydrocarbon group having 1 to 24 carbon atoms which may contain an oxygen atom or a sulfur atom in the chain. X is-
It represents a divalent group having at least one CONH-bond. However, when n = 0, X excludes a -NHCONH- bond. ) (In the formula 2, q represents an integer of 1 to ^3. R ³ represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ⁴ may contain an oxygen atom or a sulfur atom in the chain. Represents a hydrocarbon group having 1 to 24 carbon atoms, Y represents an oxygen atom or a sulfur atom, and Z represents a divalent group having at least one —CONH— bond. (In formula 3, r represents an integer of 1 to 3. R ⁵ represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ⁶ may contain an oxygen atom or a sulfur atom in the chain. Represents a hydrocarbon group having 1 to 24 carbon atoms, and Q and T have the same meaning and may be the same or different from each other.
Represents a divalent group having at least one bond. ) (In the formula 4, R ⁷ , R ⁸ , and R ⁹ have the same meaning, and represent an alkyl group, an aralkyl group, an alkenyl group, and an aryl group which may be the same or different from each other, and further, these may be a substituent. R ¹⁰ represents a hydrocarbon group having 6 to 24 carbon atoms, t represents 1 or 2, A represents an anion, and w represents an intramolecular bond. Represents the number required to adjust the charge to zero.) 2. The reversible developer according to claim 1, wherein the reversible developer is a compound represented by the general formula (2), wherein R ³ and R ⁴ are both a hydrocarbon group having 11 or less carbon atoms. Thermosensitive recording material.