JP2002144741A - Transparent thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent thermal recording material which upgrades the light resistance of an image without influencing other properties, even when the addition amount of the material is small. SOLUTION: In the transparent thermal recording material comprising a thermal recording layer containing a leuco dye and a developer which makes the leuco dye thermally develop a color, formed on at least a transparent support, and further, a protecting layer formed on the thermal recording layer, the developer is an organic sulfonic acid compound and an N-1 substituted aniline derivative represented by formula (1) is contained in the recording layer. (In formula (1), R1 is an alkyl group or an alkenyl group (No. of carbon atoms: 4-22) which may be branched; R2-R6 are independently a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkoxy carbonyl group, an aryloxy carbonyl group, an alkylthio group and an arylthio group, or may be connected to an adjacent site together to form a ring).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material (a transparent heat-sensitive sheet such as a film for a video printer) utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound. Especially MRI and CT
The present invention relates to a transparent heat-sensitive recording material suitable as a medical image forming sheet for forming a black color with high image quality like a silver halide film for the purpose of diagnosis and reference.

[0002]

2. Description of the Related Art Various recording materials utilizing a thermosensitive coloring process have been proposed. This heat-sensitive recording material is generally produced by coating the above-described color former (dye etc.) and color former (color developer etc.) on paper. In particular, in recent years, especially in the medical field, a transparent dry film system that can be easily output has been demanded in view of a waste liquid treatment problem caused by a wet process of a silver halide X-ray film and a flow of digitization of images. Current medical dry processes include (i) light exposure heat fixing systems, (ii) thermal transfer systems, and (iii)
There are three direct thermal recording systems.

One of them is a heat-sensitive recording material, which does not require frequent processing such as development and fixing, can be recorded in a short time by a relatively simple apparatus, has little noise, and has a low cost. Due to its advantages such as low cost, it has been conventionally used as various recording materials for electronic computers, facsimile machines, ticket vending machines, label printers, recorders and the like.

[0004] As color-forming dyes used in conventional heat-sensitive recording materials, for example, colorless or light-colored leuco dyes having a lactone, lactam or spiropyran ring, and as color developers, organic acids, phenolic substances and the like have hitherto been used. Used.

[0005] Organic phosphonic acids are known to exhibit high maximum concentrations and excellent storage stability due to their high acidity. Further, it is a very preferable material as a transparent thermosensitive recording material because of its low solubility in organic solvents and good dispersibility. However, on the other hand, light resistance is inferior, and its improvement has been demanded. For example, in the case of a heat-sensitive recording material in which nothing is added other than a leuco dye, a developer, and a binder resin, yellowing of the background color gradually occurs when exposed to strong light such as under ultraviolet irradiation for a long time. In addition, image recognizability deteriorates due to redness of the image color tone and the like.

[0006] As a measure for preventing this, a light-resistance auxiliary agent such as an ultraviolet absorber is added to any layer constituting the heat-sensitive recording material in order to improve the yellowing of the background. These additives have been studied conventionally,
For example, a benzotriazole-based ultraviolet absorber (JP-A-61
193883, etc.), a fluorescent whitening agent (Japanese Unexamined Patent Publication No.
JP-A-2-184880, etc.), hindered amine light stabilizers (JP-A-63-137887, etc.),
Inorganic oxide fine particles (described in JP-A-7-25147) or a combination thereof (JP-A-8-282)
No. 114, etc.).

On the other hand, with respect to red discoloration of the image area, the above compounds are added, and N, N-dialkylanilines described in JP-A-5-273745 and JP-A-6-11 are disclosed.
N-alkyldiphenylamines and triphenylamines described in JP-A-8640, JP-A-11-5895
The improvement has been achieved by adding an organic amine or the like mentioned in JP-A-9. The greater the amount of the light-resistant auxiliary in the heat-sensitive recording material, the more the discoloration due to such light can be suppressed.

[0008] However, the effect is similarly exhibited when a phosphonic acid developer is used, but when the addition amount is large, the maximum density and image storability, etc., which are the characteristics of a thermosensitive recording material using an organic phosphonic acid, are greatly affected. Has been found to exert. For this reason, at present, the amount of the light-fastening auxiliary is determined by balancing the effect on image stability and the side effect, and it is not possible to obtain further light fastness. There is a need for a compound that improves the light fastness of an image without affecting it.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a transparent heat-sensitive recording material which improves the light fastness of an image without affecting other characteristics. It is in.

[0010]

The object of the present invention is to provide a thermosensitive recording layer containing at least a leuco dye and a developer capable of heating and developing the leuco dye on at least a transparent support of the present invention. In a heat-sensitive recording material provided with a protective layer thereon, the developer is an organic phosphonic acid compound, and the recording layer contains an N-1-substituted aniline derivative represented by the following general formula (1). A transparent thermosensitive recording material characterized by the following.

[0011]

Embedded image (Where R ₁ is an optionally branched alkyl group or alkenyl group (having 4 to 22 carbon atoms), and R _{2 to} R ₆ are each independently a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylthio group, an arylthio group. Alternatively coupled together with the adjacent sites may form a ring.) ", (2) the" the aniline derivative of R ₁ (3) The transparent thermal recording material according to (1), wherein the carbon adjacent to nitrogen is secondary. (3) The aniline derivative is N-iso-butylaniline. And (4) "the aniline derivative is in an inactive state before printing in the recording layer or in the intermediate layer adjacent to the recording layer." And Mashimashi, the second is characterized by activating the heating due to printing (1) term, second (3)
Item 5), wherein the aniline derivative is present in the heat-sensitive recording layer as a zinc dithiocarbamate derivative, and the aniline derivative is released into the heat-sensitive recording layer by printing. (6) "the leuco dye comprises at least two or more leuco dyes having different colors, and one of the leuco dyes has a black color. It is a fluoran derivative and has a weight ratio of 50 to the entire leuco dye.
% Or more, wherein the transparent thermosensitive recording material according to any one of the above items (1) to (5) ",
(7) The transparent heat-sensitive recording material according to the above (6), wherein the fluoran derivative is a compound represented by the following general formula (2).

[0012]

Embedded image (Where R ₇ and R ₈ are each independently a hydrogen atom, an optionally branched alkyl group (1-6 carbon atoms), an aryl group, or a 5- to 8-membered ring formed by bonding R ₇ and R ₈ may also form a .R ₉ represents a hydrogen atom or a methyl group.) ", (8) characterized in that said"該顕color agent is octadecyl phosphonic acid subsection (1), second ( (7) The transparent heat-sensitive recording material according to any one of the above (1) to (9), wherein the recording layer contains a hindered phenolic antioxidant. (10) The transparent thermosensitive recording material according to any one of the items (1) to (10), wherein the transparent thermosensitive recording material is sealed in a light-shielding and moisture-proof bag in a product form. The transparent thermosensitive recording material according to any one of the items (9) to (9) ".

That is, according to the present invention, there is provided a transparent heat-sensitive recording material comprising a transparent support, a leuco dye thereon, and a developer for developing the leuco dye, and a protective thermosensitive recording layer. The color developing agent is an organic phosphonic acid compound, and further comprises N as represented by the general formula (1).
A transparent heat-sensitive recording material containing a 1-substituted aniline derivative is provided.

[0014]

Embedded image (Where R ₁ is an optionally branched alkyl group or alkenyl group (having 4 to 22 carbon atoms), and R _{2 to} R ₆ are each independently a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, An aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylthio group, or an arylthio group, or may be connected to an adjacent site to form a ring.

Since a general aliphatic amine compound has a high basicity, the coating solution tends to increase in viscosity and agglomerate. Even without such a change, the pot life is never long. Diphenylamine compounds and triphenylamines do not cause such thickening, but have a small effect on light resistance. N, N-dialkylaniline is effective in a small amount, but at the same time, heat resistance is drastically reduced. However, the N-1-substituted aniline represented by the general formula (1) has such a bad effect, and a large effect can be obtained with a small amount.

The N-1-substituted aniline derivative in the present invention is a secondary amine in which an aryl group, an alkyl group and a hydrogen atom are substituted one by one on nitrogen. If the length of the alkyl chain is short, there is a reaction activity and it is not preferable from the viewpoint of safety. If the length is too long, the effect on light resistance is not exhibited. Therefore, the number of carbon atoms constituting the alkyl chain is preferably 4 to 22. Examples of the linear alkyl group include butyl, pentyl, hexyl, octyl, decyl, dodecyl, tetradecyl, octadecyl, eicosyl, and behenyl. In the branched one, iso-butyl, tert-butyl, 2-ethylhexyl, ter
t-tetradecyl and the like. The alkyl group may further have a substituent, for example, it may have a substituent such as a halogen atom, a hydroxyl group, a nitro group and the like.

The higher the amount of the compound, the more pronounced the light fastness becomes. However, as a characteristic of the compound, there is a property that a small amount of the compound is effective. The amount of the compound added in the present invention is 0.5 to 10 with respect to the total amount of the leuco dye.
It is preferably 0% by weight, particularly preferably 1 to 50% by weight.

Specific examples of the N-1-substituted aniline of the present invention include Nn-butylaniline, N-iso-butylaniline, N-tert-butylaniline, Nn-pentylaniline, N-hexylaniline, N-octylaniline, N-decylaniline, N-dodecylaniline,
N-octadecylaniline, N-behenylaniline and the like can be mentioned. Among these compounds, when the carbon adjacent to the nitrogen atom in R ₁ is tertiary or higher, the carbon is preferably tertiary because the effect is slightly reduced due to steric hindrance. Among them, N-iso-butylaniline is particularly preferable. Most preferred.

The inventors of the present invention have intensively studied a method for improving the coating quality while keeping the effect of the N-alkylaniline derivative, and found that a coating layer in the recording layer or adjacent to the recording layer (the undercoat layer of the recording layer, the recording layer and the protective layer). It has been found that this can be achieved by being physically or chemically inert in an intermediate layer (e.g., between layers).

Specifically, (a) a method of dispersing or dissolving in a layer adjacent to the recording layer and diffusing it into the recording layer by heating accompanying printing, (b) heating or heating A method of dispersing and dissolving in the recording layer in the form of a compound that easily decomposes due to various environmental changes (acid / basicity, density, etc.) to generate the aniline derivative, There is a method of isolating the fine particles containing the aniline derivative from the external environment, or a method of combining them.

In (a), the aniline derivative is dissolved or dispersed in another layer in the form of an intermediate layer or an undercoat layer. At this time, a binder resin having a low glass transition temperature is preferably used so that the components of the layers can be easily diffused.

In (b), the aniline derivative can be generated by a method such as decarboxylation or transfer reaction. Among them, zinc dithiocarbamates (for example, Nn-
When used as zinc butyl-N-phenyldithiocarbamate, zinc N-decyl-N-phenyldithiocarbamate), this substance is a compound that is easy to synthesize and chemically stable before heating, but is Is particularly preferable because it is rapidly decomposed by an acidic field generated by dissolution to form an N-1-substituted aniline derivative, and other decomposed products have little effect on other properties of the heat-sensitive recording material.

As the method used in (c), a microcapsule of a type that releases the contents (N-1-substituted aniline derivative) when part or all of the outer wall is broken by heat or pressure, or a thermoplastic outer wall is used. There are microcapsules that release the contents when the resin matrix is relaxed by the retained heat.Of these, the use of thermoplastic resin as the outer wall of the microcapsules adds the heat and the release of the contents. It is preferable because of its good thermal response.

In the present invention, it has been found that a hindered phenol compound is effective for further exhibiting the effect. The hindered phenol compound is preferably present in the same layer as the aniline compound, and is used in a ratio of 5 to 1000% by weight based on the aniline compound.

As the hindered phenolic antioxidant which can be used in combination with the N-1-substituted aniline used in the present invention, various known compounds can be used. For example, 2-methylphenol, 2,6-dimethylphenol , 2,4,6-trimethylphenol, 2,6-dimethyl-4-octylphenol, 2-t-butylphenol, 2,6-di-t-butylphenol, 2,4,6
-Tri-t-butylphenol, 2,6-di-t-butyl-4-octylphenol, triethylene glycol bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6 -Hexanediol bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis (n
-Octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3,5-triazine, pentaerythrityltetrakis [3- (3,5-di-t-
Butyl-4-hydroxyphenyl) propionate],
2,2-thiodiethylenebis [3- (3,5-di-t-
Butyl-4-hydroxyphenyl) propionate],
Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxyhydrocinnamide), 3 , 5-Di-t-butyl-4
-Hydroxybenzylphosphonate diethyl ester, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)
Benzene, tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 2,4-bis [(octylthio) methyl] -o-cresol, N,
N'-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and the like.

The present invention relates to a medical output medium, and is assumed to be used in various environments. For example, continuous exposure to the air, continuous exposure to light, contact with moisture, and the like can be considered. If left in such an environment, yellowing of the background is inevitable. It is preferable that the product is sealed in a light-shielding and moisture-proof bag in the form of a product, because it is protected from external deterioration factors.

[0027] The material having a moisture-proof property is polyethylene,
There are polypropylene, vinyl chloride, polyethylene-polyvinyl alcohol copolymer, polyester and the like, and the provision of light-shielding ability can be achieved by a method such as vapor deposition of a metal such as aluminum, or kneading of metal oxide ultrafine particles or carbon black into a resin. Combine multiple of these materials,
It is obtained by laminating and laminating. The mouth of the bag can be sealed with a heat seal, adhesive tape, clip or the like.
An inert gas such as nitrogen may be filled.

The leuco dye used in the present invention is a compound having an electron donating property and may be used alone or as a mixture of two or more kinds. However, it is a colorless or light-colored dye precursor per se, and is not particularly limited. Known ones, for example, triphenylmethanephthalide type, triallylmethane type, fluoran type, phenothidiane type, thioferoran type, xanthene type, indophthalyl type, spiropyran type, azaphthalide type, chromenopyrazole type, methine type, rhodamine Leuco compounds such as anilinolactams, rhodamine lactams, quinazolines, diazaxanthenes and bislactones are preferably used. Examples of such a compound that develops black color include, for example, the following compounds, but are not limited thereto. 2-
Anilino-3-methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6- (di-n-butylamino) fluoran, 2-anilino-3-methyl-6
(Nn-propyl-N-methylamino) fluoran,
2-anilino-3-methyl-6- (N-isopropyl-
N-methylamino) fluoran, 2-anilino-3-methyl-6- (N-isobutyl-N-methylamino) fluoran, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino ) Fluoran, 2-anilino-
3-methyl-6- (N-sec-butyl-N-ethylamino) fluoran, 2-anilino-3-methyl-6
(Nn-amyl-N-ethylamino) fluoran, 2
-Anilino-3-methyl-6- (N-iso-amyl-
N-ethylamino) fluoran, 2-anilino-3-methyl-6- (Nn-propyl-N-isopropylamino) fluoran, 2-anilino-3-methyl-6- (N
-Cyclohexyl-N-methylamino) fluoran, 2
-Anilino-3-methyl-6- (N-ethyl-N-p-
Toluidino) fluoran, 2-anilino-3-methyl-
6- (N-methyl-Np-toluidino) fluoran and the like.

In the present invention, by mixing a plurality of leuco dyes that develop different colors, effective light resistance can be imparted particularly to short-term light irradiation. This is because a decrease in absorbance at a specific wavelength due to an absorption peak shift that occurs when a leuco dye deteriorates can be compensated for by a shift of another leuco dye. In addition, according to this method, since the absorption curve becomes nearly flat over the entire visible range, disadvantages such as the dependence of the color tone on the light source are also improved.

However, in medical media, it is preferable that the maximum density is high, but the color-forming efficiency is somewhat inferior when a large amount of dye is mixed little by little. Therefore, a method in which the fluoran-based leuco dye that produces black color is made the majority and the color development is supplemented with another leuco dye is preferable from the viewpoint of cost.

As the leuco dye which develops a different color to be combined with the above-described black-colored fluoran compound, if a leuco dye having an absorption at a minimum portion of the absorption of the main dye is used, the mutual absorption can be compensated. Leuco dyes that develop a red to orange color with an absorption maximum are preferred. Further, a combination with a leuco dye exhibiting a blue to green color, wherein the absorption maximum is on the longer wavelength side than 600 nm, is also preferable. However, since it is important to adjust the overall absorption curve, it is not particularly limited to this,
Of course, three or more types may be used.

The red-orange leuco dyes include:
3-diethylamino-7,8-benzofluoran, 3,
3-bis (1-n-butyl-2-methylindole-3
-Yl) phthalide, 1,3-dimethyl-6-diethylaminofluoran and the like, as leuco dyes having absorption at long wavelengths, include 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide, 10-diethylamino-2-ethylbenzo [1,4] thiazino [3,2
-B] fluoran and the like.

As the black-colored fluoran leuco dye, 2- (3'-trifluoromethylanilino) fluorans represented by the general formula (2) are particularly preferred because of their good light fastness.

[0034]

Embedded image (Where R ₇ and R ₈ are each independently a hydrogen atom, an optionally branched alkyl group (1-6 carbon atoms), an aryl group, or a 5- to 8-membered ring formed by bonding R ₇ and R ₈ R ₉ represents a hydrogen atom or a methyl group.)

Examples of the fluorans of the general formula (2) include, for example, the following, but are not limited thereto. 2- (3'-trifluoromethylanilino) -3-methyl-6-dimethylaminofluoran, 2- (3'-trifluoromethylanilino)-
3-methyl-6-diethylaminofluoran, 2-
(3′-trifluoromethylanilino) -6-diethylaminofluoran, 2- (3′-trifluoromethylanilino) -6- (N-ethyl-Np-toluidino) fluoran and the like.

Specific examples of the transparent support used in the present invention include a cellulose derivative film such as cellulose triacetate, a polyolefin film such as polypropylene and polyethylene, a polystyrene film, and a film obtained by laminating these. Terephthalate, polybutylene terephthalate, is a polyester film such as polyethylene naphthalate,
It is not limited to this. In order to improve the adhesiveness of the coating layer, at least one surface can be surface-modified by corona discharge treatment, oxidation reaction treatment (chromic acid or the like), etching treatment, or the like. In order to obtain a sheet having high transparency, the haze of the support alone is preferably 10% or less.

The transparent thermosensitive recording material can be colored blue for the purpose of improving the antiglare effect or the image recognizability. As a method of bluing, it is conceivable to apply bluing to the base itself or to bluish one or more of the coating layers.
The range of 15 to 0.25 is a ^* =-4 to-
^{12, b * = -5~-15} ; range of colors surrounded by (measurement condition d / 0, 10 degree field of view, in the light source D ₆₅ calculated by measuring the absorbance per 10 nm) are preferable.

Various known resins can be used as the binder resin used in the present invention.
Polyvinyl acetate, polyacrylamide, maleic acid copolymer, polyacrylic acid and its ester, polymethacrylic acid and its ester, vinyl chloride / vinyl acetate copolymer, styrene copolymer, polyester, polyurethane, polyvinyl butyral, ethyl cellulose , Polyvinyl acetal, polyvinyl acetoacetal, polycarbonate, epoxy resin, polyamide, polyvinyl alcohol, starch, gelatin and the like. The resins can be used alone or in combination of two or more.

Next, the developer corresponding to the leuco dye used in the present invention is a phosphonic acid developer containing a long-chain alkyl group in the molecule as disclosed in JP-A-5-124360. For example, an organic phosphonic acid compound having an aliphatic group having 12 or more carbon atoms, an acidic phosphonic acid ester having an aliphatic group having 16 or more carbon atoms, or the like is used. Aliphatic groups include:
It includes a linear or branched alkyl group or alkenyl group, and may have a substituent such as a halogen atom, an alkoxy group, or an ester. Hereinafter, specific examples of the developer will be described. Those represented by the following general formula (3) are preferably used.

[0040]

Embedded image (In the formula, R ₁₀ represents a linear alkyl group having 12 to 24 carbon atoms.)

Specific examples of the organic phosphonic acid compound represented by the general formula (3) include the following. Dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid, docosylphosphonic acid, tetracosylphosphonic acid, hexacosylphosphonic acid, octacosylphosphonic acid and the like.

As the organic phosphonic acid compound, α-hydroxyalkylphosphonic acid represented by the following general formula (4) is also preferably used.

[0043]

Embedded image (In the formula, R ₁₁ is an aliphatic group having ₁₁ to 29 carbon atoms.)

Specific examples of the α-hydroxyalkylphosphonic acid represented by the general formula (4) include α-hydroxydodecylphosphonic acid, α-hydroxytetradecylphosphonic acid, α-hydroxyhexadecylphosphonic acid, and α-hydroxyhexadecylphosphonic acid.
Examples include hydroxyoctadecylphosphonic acid, α-hydroxyeicosylphosphonic acid, α-hydroxydocosylphosphonic acid, and α-hydroxytetracosylphosphonic acid.

As the organic phosphonic acid compound, an acidic organic phosphonic acid ester represented by the following general formula (5) is also used.

[0046]

Embedded image (In the formula, R ₁₂ represents an aliphatic group having 16 or more carbon atoms, and R ₁₃ represents a hydrogen atom or an aliphatic group having 1 or more carbon atoms.)

Specific examples of the acidic organic phosphonic acid ester represented by the general formula (5) include dihexadecyl phosphate, dioctadecyl phosphate, dieicosyl phosphate, didocosyl phosphate, monohexadecyl phosphate, and monooctadecyl phosphate. , Monoeicosyl phosphate, monodocosyl phosphate,
Examples include methyl hexadecyl phosphate, methyl octadecyl phosphate, methyl eicosyl phosphate, methyl docosyl phosphate, amyl hexadecyl phosphate, octyl hexadecyl phosphate, lauryl hexadecyl phosphate, and the like.

In the heat-sensitive recording material of the present invention, the amount of the developer is 0.5 to 20 parts by weight, preferably 2 to 10 parts by weight, per 1 part by weight of the leuco dye. The developers can be used alone or in combination of two or more.

In addition, in the present invention, various light-fastening aids described below can be used in combination, if necessary. These auxiliaries can be used for the recording layer, and can also be applied to the protective layer, the back layer, and other intermediate layers.

Various known compounds can be used as the benzotriazole-based ultraviolet absorber, and 2- (5-methyl-
2-hydroxyphenyl) benzotriazole, 2-
(3,5-di-t-butyl-2-hydroxyphenyl)
-5-chlorobenzotriazole, 2- (3-t-butyl-5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3,5-di-t-amyl-2-hydroxyphenyl) Benzotriazole, 2-
(3,5-di-t-butyl-2-hydroxyphenyl)
Benzotriazole, 2- (5-t-butyl-2-hydroxyphenyl) benzotriazole, 2- (5-t-
Octyl-2-hydroxyphenyl) benzotriazole and the like.

As the benzophenone-based ultraviolet absorber, various known compounds can be used. For example, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, , 2'-dihydroxy-4-methoxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'
-Dimethoxybenzophenone and the like.

Various known brightening agents can be used. Examples thereof include pyrazoline derivatives, coumarin derivatives, stilbene derivatives and the like.
A mixture of more than one species can be used. Alternatively, a polymer in which the skeleton of each of the above-mentioned light resistance assistants is pendant can be used alone as a binder or in combination with another resin.

As the metal oxide-based ultraviolet shielding agent, various known compounds can be used, and examples thereof include cerium oxide fine particles, titanium oxide fine particles, zinc oxide fine particles, and those coated with these, but are not limited thereto. Not something. The finer the particle size, the better, and the average particle size is 3 μm or less, preferably 0.7 μm or less.

As mentioned above, specific examples of the leuco dye, the developer, the N-1-substituted aniline derivative, the binder resin, and the light-fast auxiliary which are the main components of the heat-sensitive recording material of the present invention have been given, but the present invention is not limited thereto. Also, if necessary, known fillers, pigments,
Surfactants and heat-fusible substances can be added.

The heat-sensitive recording layer of the present invention is prepared by uniformly dispersing or dissolving a leuco dye and a developer together with a binder resin in an organic solvent, coating the solution on a support, and drying it. The die fountain method, wire bar method, gravure method, air knife method and the like are not particularly limited. Among them, a die fountain method capable of applying without contacting the support is preferable as a material capable of obtaining uniformity of the coating layer. When a dispersion liquid is used as the coating liquid for the recording layer, the particle diameter of the dispersion is 1.0 μm or less, and the particle diameter is 1.0 μm or less, because the particle diameter of the dispersion greatly affects the surface roughness of the protective layer and, consequently, the dot reproducibility during printing. 5μ
m or less is preferable. The thickness of the recording layer is about 1 to 50 μm, preferably about 3 to 20 μm, although it depends on the composition of the recording layer and the use of the heat-sensitive recording material. In addition, various additives such as a surfactant can be added to the recording layer coating liquid, if necessary, for the purpose of improving coatability or recording characteristics.

In the present invention, a protective layer is provided on the heat-sensitive coloring layer in order to improve chemical resistance, water resistance, friction resistance, light resistance and head matching with a thermal head. Ideally, the protective layer of the thermosensitive recording material should be provided with a resin alone layer from the viewpoint of transparency.However, a protective layer made of only a resin has too high a smoothness to prevent printing defects due to sticking and dust dragging. It is difficult to obtain sufficient performance in terms of surface. In particular, when a plastic film is used as the support, it tends to be smoother than when paper is used as the support, so that the head matching is reduced and the tendency to drag dust is remarkable. Such printing defects and defects are fatal as materials for outputting medical images. As a means for improving performance against sticking and dust dragging, a filler is generally contained. However, in the case of a transparent heat-sensitive recording material, the transparency often decreases when a filler is contained in the protective layer as in the case of a conventional reflection recording material. In order to maintain transparency by adding a filler, there are a method of finely roughening the surface with a small particle size filler and a method of adding a small amount of a large particle size filler to partially roughen the surface.

In the present invention, if necessary, the above two methods can be combined to form a protective layer. The coefficient of friction of the surface of the protective layer is in the range of 0.07 to 0.14 when viewed from both sides of head matching (in the direction of increasing the lubricity) and preventing dragging of dust easily generated in the plastic film (in the direction of decreasing the lubricity). preferable.

Examples of the filler include phosphate fiber, potassium titanate, acicular magnesium hydroxide, whisker, talc, mica, glass flake, calcium carbonate, plate charcoal, aluminum hydroxide, plate aluminum hydroxide, and silica. , Clay, kaolin, calcined clay,
Inorganic fillers such as hydrotalcite, crosslinked polystyrene resin particles, urea-formalin copolymer particles, silicone resin particles, crosslinked polymethylmethacrylate resin particles, guanamine-formaldehyde copolymer particles, melamine-formaldehyde copolymer particles Organic fillers are exemplified. In the present invention, an organic filler is preferable from the viewpoint of head wear, and a melamine-formaldehyde copolymer particle (Nippon Shokubai Eposter S) is an example of a preferable filler having a small particle size, and a guanamine-particle is an example of a large particle size filler. Examples include formaldehyde copolymer particles and silicone resin particles. However, the present invention is not limited to this.

As the resin used for the protective layer in the present invention, an aqueous emulsion, a hydrophobic resin, an ultraviolet ray, an electron beam curable resin and the like can be used in combination with a water-soluble resin as in the case of the recording layer, if necessary. . From the viewpoint of transparency, it is preferable to use a material in which the refractive index of the resin of the recording layer and the resin of the protective layer falls within the range of 0.8 to 1.2 in terms of the refractive index of the support. Specific examples of the resin include poly (meth) acrylate resin, polyurethane resin, polyester resin,
Polyvinyl acetate resin, styrene acrylate resin,
Polyolefin resins, polystyrene resins, polyvinyl chloride resins, polyether resins, polyamide resins, polycarbonate resins, polyethylene resins, polypropylene resins, polyacrylamide resins, and the like. As the crosslinking agent used with the resin, a conventionally known compound such as an isocyanate compound and an epoxy compound can be used.

Specific examples of the isocyanate compound include:
Compounds having two or more isocyanate groups in a molecule such as toluylene diisocyanate, a dimer thereof, diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate, hexamethylene diisocyanate, polyisocyanate and derivatives thereof. Can be Specific examples of the epoxy compound include ethylene glycol diglycidyl ether, butyl glycidyl ether, polyethylene glycol diglycidyl ether, and epoxy acrylate.

In order to further improve the head matching property, wax and oils are added to the protective layer, a resin modified with silicone is used as a binder resin, and the ratio of the resin to the filler is adjusted. Can raise and lower the coefficient of friction to adjust. Examples of the waxes that can be used here include stearic acid amide, palmitic acid amide, oleic acid amide, lauric acid amide, ethylenebisstearamide, methylenebisstearamide, methylol stearoamide, paraffin wax, polyethylene, and carnauba Wax, paraffin oxide, zinc stearate and the like. As the oil, a general silicone oil or the like can be used.

The coating method of the protective layer is not particularly limited, and it can be applied by a conventionally known method. The preferred protective layer thickness is 0.1-20 μm, more preferably 0.5-10 μm
m. If the protective layer thickness is too thin, the function as a protective layer such as storage stability and head matching of the recording medium is insufficient, and if too thick, the thermal sensitivity of the recording medium decreases,
It is disadvantageous in terms of cost.

The recording method of the heat-sensitive recording material of the present invention can be performed by using a hot pen, a thermal head, laser heating, etc.
Although not particularly limited, this thermosensitive recording material is suitable for printing high-definition and high-gradation images such as medical images,
It is most preferable to print using a thermal head from the viewpoints of cost, output speed, and compactness of the apparatus.

[0064]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. In the following, all parts and percentages are based on weight.
The following compositions were each ball milled to obtain a volume average particle size of 0.3.
The mixture was pulverized and dispersed to a thickness of μm to prepare a developer dispersion liquid [Solution A]. [Solution A] 30 parts of methyl ethyl ketone (hereinafter, MEK) 30 parts of toluene 25 parts of octadecylphosphonic acid 15 parts 10% solution of polyvinyl butyral (solvent: MEK) 30 parts

Next, the [solution B] prepared with the following composition was sufficiently stirred to prepare a recording layer coating solution. [Solution B] Solution A 50 parts 2- (3-t-butyl-5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole 0.1 part Compound X 0.3 part Leuco dye Y 3 parts 10% polyvinyl Acetoacetal solution (solvent: MEK) 80 parts MEK 17 parts

Similarly, the following composition was pulverized and dispersed in a ball mill to a volume average particle size of 0.3 μm, and a filler dispersion [C
Liquid]. [Liquid C] Silica powder 15 parts 10% polyvinyl acetoacetal solution (solvent: MEK) 15 parts MEK 70 parts

Further, the following composition was sufficiently stirred to prepare a protective layer coating solution [D solution]. [Liquid D] Liquid C 10 parts Silicon modified polyvinyl butyral (solid content 12.5%) 6 parts MEK 12 parts

The coating solution for recording layer [Solution B] and the coating solution for protective layer [Solution D] prepared as described above are sequentially coated on a 100 μm-thick transparent polyester film using a wire bar, and dried sufficiently. Heat-sensitive recording layer having a thickness of 10 μm,
A protective layer having a thickness of μm was formed.

Example 1 A transparent heat-sensitive recording sheet prepared by preparing a liquid using the compound shown in Table 1 as the compound X and the leuco dye Y, coating and drying the liquid.

Example 2 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as the compound X and the leuco dye Y, coating and drying the liquid.

Example 3 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as compound X and leuco dye Y, and coating and drying the liquid.

Example 4 The undercoat layer solution [solution E] prepared with the following composition was sufficiently stirred to prepare an undercoat layer coating solution. [Solution E] MEK 33 parts 20% polyester polyurethane solution (solvent: toluene) 65 parts N-iso-butylaniline 2 parts

The undercoat layer coating solution [solution E] prepared as described above, the recording layer coating solution [solution B] using the compound X and the compound shown in Table 1 as the leuco dye Y, and the protective layer coating solution [Liquid D] was sequentially coated on a 100 μm-thick transparent polyester film using a wire bar and dried sufficiently to form a 2 μm-thick undercoat layer, a 10 μm-thick thermosensitive recording layer, and a 3 μm-thick protective layer. did.

Example 5 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as compound X and leuco dye Y, and coating and drying the liquid. When the thermosensitive recording sheet after printing was analyzed by gas chromatography, N-iso-butylaniline was detected.

Example 6 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as the compound X and the leuco dye Y, coating and drying the liquid.

Example 7 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as compound X and leuco dye Y, and coating and drying the liquid.

Example 8 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as the compound X and the leuco dye Y, coating and drying the same.

Example 9 [Solution F] prepared with the following composition
Was sufficiently stirred to prepare a recording layer coating solution. [Solution F] Solution A 50 parts 2- (3-t-butyl-5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole 0.1 part Compound X 0.3 part 2,2-thiodiethylenebis [ 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] 0.2 part Leuco dye Y 3 parts 10% polyvinyl acetoacetal solution (solvent: MEK) 80 parts MEK 17 parts As described above. Layer coating solution [Solution F] and protective layer coating solution [Solution D] using the compounds X and leuco dye Y prepared in Table 1 on a transparent polyester film having a thickness of 100 μm. Coat sequentially using a bar, dry sufficiently, and heat-sensitive recording layer having a thickness of 10 μm.
A protective layer having a thickness of μm was formed.

Comparative Example 1 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as the compound X and the leuco dye Y, coating and drying the liquid.

Comparative Example 2 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as compound X and leuco dye Y, coating and drying the liquid.

Comparative Example 3 A transparent heat-sensitive recording sheet prepared in the same manner as in Example 1 by preparing a liquid using the compounds shown in Table 1 as compound X and leuco dye Y, coating and drying the liquid.

[0082]

[Table 1]

A 17-gradation image was printed on the heat-sensitive recording sheet produced as described above using a video printer UP-930 manufactured by Sony Corporation. Transmission density and color value
Gretag Macbeth Co. spectrophotometer Spectrolino: was measured using a (measurement conditions transparent mode, the aperture diameter 3 mm, the absorbance measurements d / 0, 10 degree field of view, in the light source D ₆₅ per 10 nm). a ^* max-a ^* min indicates the fluctuation range of the color tone, and the color value in the present embodiment has little fluctuation of b ^* , and the a ^* value fluctuates around the origin. It is considered to be almost equivalent to typical black.
As an environment for the deterioration test, the light resistance test was performed using a fluorescent light of 10.0 or less.
The heat resistance test was performed in a 50 ° C. constant temperature bath for 24 hours under irradiation of 00 lux. The coating of the recording layer liquid was performed without any problem. However, the evaluation of the ease of coating at the time of coating was given as ◎ if a streak pattern formed by a wire bar on the sheet surface after the coating of the recording layer was difficult to see. In addition, since a wire bar is used manually, a streak is easily generated. However, such a streak does not occur if the wire bar is adjusted and applied by the above-described die fountain method or the like. Table 2 shows the evaluation results.

[0084]

[Table 2]

Example 10 The sheet prepared according to Example 1 was cut into a size of 5 cm × 5 cm,
It was left for 2 weeks under 00 lux irradiation, and the color difference before and after irradiation was observed. Table 3 shows the evaluation results.

Example 11 A sheet prepared according to Example 1 was cut into a size of 5 cm × 5 cm, placed in an aluminum vapor-proof moisture-proof bag (Fine Lamizip: polyester-aluminum-polyethylene laminate), and sealed.
After leaving for 2 weeks under irradiation of 000 lux, the color difference before and after irradiation was observed. Table 3 shows the evaluation results.

[0087]

[Table 3]

From the above evaluation results, it can be seen that the transparent heat-sensitive recording material of the present invention can provide a heat-sensitive recording material having excellent light resistance.

[0089]

As is apparent from the detailed and concrete description, according to the present invention, a transparent heat-sensitive recording material which can improve the light fastness of an image with a small amount of addition without affecting other properties can be obtained. Can be provided.

Claims (10)

[Claims] 1. A leuco dye on at least a transparent support,
A heat-sensitive recording material comprising a heat-sensitive recording layer containing a developer capable of heating the leuco dye to form a color, and further comprising a protective layer thereon, wherein the developer is an organic phosphonic acid compound; N- represented by the following general formula (1)
A transparent thermosensitive recording material comprising a monosubstituted aniline derivative. Embedded image (Where R ₁ is an optionally branched alkyl group or alkenyl group (having 4 to 22 carbon atoms), and R _{2 to} R ₆ are each independently a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, An aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylthio group, or an arylthio group, or may be connected to an adjacent site to form a ring. 2. The transparent thermosensitive recording material according to claim ₁ , wherein the carbon adjacent to the nitrogen of R ₁ of the aniline derivative is secondary. 3. The transparent thermosensitive recording material according to claim 2, wherein the aniline derivative is N-iso-butylaniline. 4. The method according to claim 1, wherein the aniline derivative is present in an inactive state in the recording layer or in an intermediate layer adjacent to the recording layer before printing, and is activated by heating accompanying printing. The transparent heat-sensitive recording material according to claim 1. 5. The transparent heat-sensitive recording material according to claim 4, wherein the aniline derivative is present in the heat-sensitive recording layer as a zinc dithiocarbamate derivative, and the aniline derivative is released into the heat-sensitive recording layer by printing. . 6. The leuco dye comprises at least two or more leuco dyes that develop different colors.
The transparent heat-sensitive recording material according to any one of claims 1 to 5, wherein the seed is a fluoran derivative that develops a black color, and the weight ratio to the entire leuco dye is 50% or more. 7. The fluoran derivative represented by the following general formula (2)
The transparent thermosensitive recording material according to claim 6, which is a compound represented by the formula: Embedded image (Where R ₇ and R ₈ are each independently a hydrogen atom, an optionally branched alkyl group (1-6 carbon atoms), an aryl group, or a 5- to 8-membered ring formed by bonding R ₇ and R ₈ R ₉ represents a hydrogen atom or a methyl group.) 8. The transparent heat-sensitive recording material according to claim 1, wherein said color developer is octadecylphosphonic acid. 9. The transparent heat-sensitive recording material according to claim 1, wherein a hindered phenolic antioxidant is contained in the recording layer. 10. The transparent thermosensitive recording material according to claim 1, wherein the transparent thermosensitive recording material is sealed in a light-shielding and moisture-proof bag in a product form.