JP3349847B2 - 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 thermosensitive recording material capable of forming and erasing an image by heating.

[0002]

2. Description of the Related Art A thermosensitive recording material generally comprises a support provided with a thermosensitive recording layer mainly comprising 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 color developer react instantaneously to obtain a recorded image. Japanese Patent Publication Nos. 43-4160 and 45-160
It is disclosed in, for example, Japanese Patent Publication No. 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, this method, since the thermal energy is intended to reversibly change the transparency of the heat-sensitive recording material, the contrast of the image forming portion and the unimaged 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 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, and has a coloring effect by an acidic group or a decolorizing effect by a basic group by controlling thermal energy. 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.
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 phosphoric acid compound, an α-hydroxy aliphatic carboxylic acid, Specific phenol compounds such as fatty acid dicarboxylic acids and alkylthiophenols having an aliphatic group having 10 or more carbon atoms, alkyloxyphenols, alkylcarbamoylphenols, and alkyl gallates are exemplified. However, this recording medium still has a low color density, or
The two problems of incomplete decolorization cannot be solved at the same time.

As described above, a highly practical reversible thermosensitive recording material capable of forming and erasing an image with good contrast has not been known in the prior art.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly practical reversible thermosensitive recording material capable of forming and erasing images with good contrast.

[0010]

The present inventors have conducted research to solve this problem, and as a result, they have found that a colorless or pale-colored electron-donating dye precursor can be reversibly changed in color tone by heating, that is, color development. The present inventors have found that an electron-accepting compound represented by the following general formula 2 that causes decoloration is present, and the present invention has been completed.

[0011]

Embedded image

In Formula 2, n is an integer of 1 to 3, and m is 0
Represents an integer from to 3. X represents an O or S atom, and k represents 0 or 1. R represents an aliphatic hydrocarbon group having 10 to 24 carbon atoms.

In the compounds represented by the above general formula, n =
1, m = 0, and R preferably has an aliphatic hydrocarbon group having 14 or more carbon atoms.

Specific examples of the electron-accepting compound used in the present invention, which causes a colorless or pale-colored electron-donating dye precursor to cause a reversible color change, include the following compounds. It is not limited to this.

N-tetradecylsuccinic acid [N- (4-hydroxyphenyl)] imide, n-hexadecylsuccinic acid [N- (4-hydroxyphenyl)] imide, n-octadecylsuccinic acid [N- (4- Hydroxyphenyl)] imide, n-docosenylsuccinic [N- (4-hydroxyphenyl)] imide, (n-octadecyloxy) succinic [N- (4-hydroxyphenyl)] imide, (n-tetradecylthio) succinate Acid [N- (4-hydroxyphenyl)] imide, (n-octadecylthio) succinic acid [N- (4-hydroxyphenyl)] imide, [(n-octadecylthio)] methylsuccinic acid [N
-(4-hydroxyphenyl)] imide, [2- (n-
[Hexadecylthio) ethyl] succinic [N- (4-hydroxyphenyl)] imide and [3- (n-dodecyloxy) propyl] succinic [N- (4-hydroxyphenyl)] imide.

The electron-accepting compound of the present invention can be very easily synthesized from various readily available raw materials by various synthetic routes in accordance with well-known organic synthesis techniques. The nature is high.

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 those generally used for pressure-sensitive recording paper, heat-sensitive recording paper and the like, 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, 3,3-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 compounds 4,4'-bis (dimethylaminophenyl) benzhydrylbenzyl ether, N-chlorophenylleucouramine, N-2,4,5-trichlorophenylleucouramine and the like.

(3) Xanthene compounds rhodamine B anilinolactam, rhodamine Bp-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3- Diethylamino-7-phenylfluoran, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7- (3,4-dichloroanilino) fluoran, 3 -Diethylamino-7
-(2-chloroanilino) fluoran,

3-diethylamino-6-methyl-7-anilinofluoran, 3- (N-ethyl) tolylamino-
6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3- (N-ethyl) tolylamino-6-methyl-7-phenethylfluoran, 3-diethylamino-7 -(4-nitroanilino) fluoran, 3-dibutylamino-6-methyl-7
-Anilinofluoran, 3- (N-methyl) propylamino-6-methyl-7-anilinofluoran, 3- (N
-Ethyl) isoamylamino-6-methyl-7-anilinofluoran, 3- (N-methyl) cyclohexylamino-6-methyl-7-anilinofluoran, 3- (N-
Ethyl) tetrahydrofurylamino-6-methyl-7-
Anilino fluoran 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.

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 thereto.

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 used, and these are coated or printed on a support. To form a reversible thermosensitive recording layer.

The method of incorporating the colorless or pale color dye precursor and the electron-accepting compound according to the present invention into the reversible thermosensitive recording layer usually includes dissolving each compound alone in a solvent or dispersing it in a dispersion medium. Examples include a method of mixing, a method of mixing and dissolving each compound in a solvent or dispersing in a dispersion medium, and a method of dissolving or dispersing in a solvent after dissolving or dispersing each compound in a solvent after heating and homogenizing each compound. But not specified.

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 Latexes such as esters, styrene / butadiene copolymers, acrylonitrile / butadiene copolymers, methyl acrylate / butadiene copolymers, ethylene / vinyl acetate copolymers, and the like, but are not limited thereto. No.

Further, a heat-fusible substance can be contained in the reversible thermosensitive recording layer as an additive for adjusting the color development sensitivity and the decoloring temperature of the reversible thermosensitive recording layer. 60 ° C
Those having a melting point of 200 ° C to 200 ° C
Those having a melting point of -180 ° C are preferred. A sensitizer used in general thermosensitive recording paper can also be used. For example, waxes such as N-hydroxymethyl stearamide, stearamide, palmitamide, naphthol derivatives such as 2-benzyloxynaphthalene, biphenyl derivatives such as p-benzylbiphenyl and 4-allyloxybiphenyl, 1,2 -Screw (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 or oxalic acid diester derivatives such as esters 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, synthetic resin laminated paper, synthetic paper, metal foil, glass, etc., or a combination thereof are used. The composite sheet can be used arbitrarily according to the purpose, and may be transparent, translucent or opaque. Further, the present invention 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 can be provided on the reversible thermosensitive recording layer, or an intermediate layer can 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 two or three or more layers. Further, information can be recorded electrically, magnetically and optically in the reversible thermosensitive recording layer and / or on another layer and / or on the surface on which the reversible thermosensitive recording layer is provided and / or on the opposite surface. Materials 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 charging.

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

In the reversible thermosensitive recording layer and / or the protective layer and / or the intermediate layer, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, hydroxide Aluminum, pigments such as urea-formalin resin, in addition, zinc stearate, higher fatty acid metal salts such as calcium stearate, waxes such as paraffin, paraffin oxide, polyethylene, polyethylene oxide, stearic acid amide, caster wax, A dispersant such as sodium dioctyl sulfosuccinate, a surfactant, a fluorescent dye, and the like can also be contained.

[0035]

The electron-accepting compound according to the present invention has a specific decoloring effect, that is, a reversible effect, in spite of having the ability to form a leuco dye. This is completely unexpected, and the electron-accepting compounds used in ordinary thermosensitive recording materials, namely, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, Such a reversible effect is not seen at all with benzyl hydroxybenzoate and the like.

Although the principle of image formation and erasure of the heat-sensitive recording material of the present invention is not clear yet, it 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 dye molecule that has developed color. When the electron-accepting compound molecule is separated from the dye molecule which has developed color, the dye molecule which has developed color receives electrons again and becomes 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, since the electron-accepting compound according to the present invention has a large fatty chain in its structure, the electron-accepting compound has low compatibility with the dye precursor molecule and the colored dye molecule, and is in a solidified state. It is considered that they hardly mix 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, such as in a heated and melted state, the dye precursor molecule and the electron accepting compound molecule according to the present invention dissolve at a certain ratio with each other, and form color. State. Therefore, when the color-forming molten mixture is cooled slowly, the electron-accepting compound according to the present invention and the dye molecules become insoluble with each other and phase-separate and lose color as the temperature decreases . Hand, when the rapid cooling, prior to phase separation, i.e. to solidify remain colored state, the color development state after the colored state is fixed solidified are maintained stably.

As described above, the reversible thermosensitive recording material according to the present invention produces 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 color-developed state and a decolored state. Conceivable. In order to perform color development, rapid cooling may be performed following heating, and for example, heating by a thermal head, laser light, or the like is possible. Also, if you slowly cool after heating, the color will be erased, for example, hot roll, heat stamp, thermal head, high frequency heating,
It can be performed by using radiant heat from a light source such as a hot air, an electric heater or a halogen lamp.

Next, specific examples of the synthesis of the electron-accepting compound represented by Chemical Formula 2 are shown below, but the production method of the compound of the present invention is not limited thereto.

Synthesis Example 1 n-octadecylsuccinic acid [N- (4-hydroxyphene)
Nyl)] imide synthesis In a 300 ml flask equipped with a stirrer and condenser, 4
3.7 g aminophenol, 80 ethyl methyl ketone
Then, the mixture was stirred in a room temperature atmosphere. 12.0 g of powdery n-octadecylsuccinic anhydride was added little by little in several portions, and the mixture was heated and stirred at 70 to 75 ° C for 1 hour. Next, 120 ml of diglyme was added, and the mixture was heated while gently passing N ₂ gas, to evaporate ethyl methyl ketone first, and then slowly distill diglyme.
After most of the diglyme was distilled off (required time: about 3 hours), 120 ml of toluene was added to the residue, the mixture was allowed to cool, and the precipitated crystals were separated by filtration and washed. This was recrystallized from n-propanol to obtain 10.6 g of the desired product. 133-134
° C.

Synthesis Example 2 (n-octadecylthio) succinic acid [N- (4-hydro
Synthesis of (Xiphenyl)] imide In a 300 ml flask equipped with a stirrer and a condenser, 11.5 g of n-octadecyl mercaptan, 0.2 g of triethylamine and 60 ml of 1,4-dioxane were charged.
Stir in a ~ 45 [deg.] C water bath. To this, a solution of 9.2 g of N- (4-acetoxyphenyl) maleimide in 75 ml of 1,4-dioxane was added dropwise over about 25 minutes. After the addition, the mixture was further stirred for 30 minutes. Then add 40 ml of methanol to 30 ml.
A solution to which 4.2 g of an aqueous solution of NaOH was added was dropped in an atmosphere at room temperature over about 25 minutes, and then stirring was continued for 30 minutes.
The reaction solution was neutralized with acetic acid and then poured into water. The precipitate is collected by filtration,
Washing was performed sequentially with warm water and aqueous methanol. This is iso-
Recrystallization from propanol gave 11.5 g of the desired product.
140.5-142 ° C.

[0042]

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

Example 1 (A) Preparation of reversible heat-sensitive coating solution 40 parts of 3-di-n-butylamino-6-methyl-7-anilinofluoran, a dye precursor, was added to a 2.5% aqueous solution of polyvinyl alcohol. 90 parts together with a ball mill for 24 hours to obtain a dye precursor dispersion. Next, 100 parts of n-octadecylsuccinic acid [N- (4-hydroxyphenyl)] imide was added to a 2.5% aqueous solution of polyvinyl alcohol 4
00 parts together with a ball mill for 24 hours to obtain a dispersion. After mixing the above two dispersions, 200 parts of a 10% aqueous solution of polyvinyl alcohol and 400 parts of water were added and mixed well to prepare a reversible thermosensitive coating liquid.

(B) Preparation of reversible thermosensitive recording material The reversible thermosensitive coating liquid prepared in (A) was applied to a polyethylene terephthalate (PET) sheet at a solids coating amount of 4 g / m ^2.
And dried and then treated with a super calender to obtain a reversible thermosensitive recording material.

Example 2 The n-octadecylsuccinic acid [N- (4
A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that (n-octadecylthio) succinic acid [N- (4-hydroxyphenyl)] imide was used instead of -hydroxyphenyl) imide. .

Comparative Example 1 The n-octadecylsuccinic acid [N- (4
-Hydroxyphenyl)] imide was the same as Example 1 except that a salt of gallic acid and stearylamine was used instead of imide.

Comparative Example 2 The n-octadecyl succinic acid [N- (4
-Hydroxyphenyl)] imide instead of 2,2-
Example 1 was repeated except that bis (4-hydroxyphenyl) propane was used.

Comparative Example 3 n-octadecyl succinic acid [N- (4
-Hydroxyphenyl)] imide, instead of p- (n
Same as Example 1 except that -octadecylthio) phenol was used.

Test 1 (Coloring density = thermal response) The thermal recording materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were applied to a thermal facsimile printing tester manufactured by Okura Electric with a print head KJT-256-8MGF1 manufactured by Kyocera. TH-PMD
Was printed under the conditions of an applied pulse of 1.1 millisecond and an applied voltage of 26 volts, and the density of the obtained color image was measured using a densitometer Macbeth RD918. The results are shown in Table 1.

Test 2 (Erasability of Image) The thermal recording materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were applied to a thermal facsimile printing tester TH- manufactured by Okura Electric Co. with a print head KJT-256-8MGF1 manufactured by Kyocera. PMD
Was applied under the conditions of an applied pulse of 1.1 millisecond and an applied voltage of 26 volts, and the obtained color image portion was heated at 120 ° C. for 1 second using a heat stamp. It was measured. The results are shown in Table 1.

[0051]

[Table 1]

In Table 1, .largecircle. Indicates that the density of the erased portion is less than 20% of the density of the color-developed portion and the contrast between the color-developed portion and the erased portion is good
Δ indicates that the contrast is insufficient when the density of the erased portion is 20% or more and less than 80% of the density of the color-developed portion, and X indicates that no reversibility is observed when the density of the erased portion is 80% or more of the density of the color-developed portion.

[0053]

As shown in Table 1, it is usually represented by a colorless or light-colored electron-donating dye precursor and the above-mentioned general formula 1 which causes a reversible color change in the dye precursor upon heating. By using a reversible thermosensitive recording material containing an electron-accepting compound, an extremely practical reversible thermosensitive recording material capable of forming and erasing images with good contrast was obtained.

Claims (1)

(57) [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 upon heating. Reversible thermosensitive recording material. Embedded image (In Formula 1, n represents an integer of 1 to 3, m represents an integer of 0 to 3. X represents an O or S atom, and k represents 0 or 1.
Is shown. R represents an aliphatic hydrocarbon group having 10 to 24 carbon atoms. )