JP2002160451A - Heat-sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive recording material suitable as a medical image forming sheet such as an MRI, a CT or the like and having a high concentration, a high image quality and excellent preservability. SOLUTION: The heat-sensitive recording material comprises a colorless or pale leuco dye on a transparent support and a heat-sensitive recording layer containing a developer for heating the leuco dye for color development and a binder resin as a binding agent as main components. The developer is a compound represented by formula (1), wherein R1 is a 4-16C linear alkyl group or an alkylamino group. The binder resin is a cellulose acetate resin having a specific constituent unit.

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 (for example, 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. And especially M
High image quality, high density with silver halide film-like for the purpose of diagnosis and reference of images such as RI and CT with Schaukasten
The present invention relates to a heat-sensitive recording material suitable as a high-preservation medical image forming sheet.

[0002]

2. Description of the Related Art Hitherto, various recording materials utilizing a thermosensitive coloring process have been proposed. This thermal recording material
Generally, it is produced by applying a coating solution in which a colorless or pale-colored leuco dye and a developer are dissolved or dispersed on paper, synthetic paper or a plastic film. Particularly in recent years, especially in the medical field, there is a demand for a dry film system that can be easily output 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. Currently, there are three dry processes for medical use: light exposure heat fixing system, thermal transfer system, and direct thermal recording system. Thermal recording materials, one of them, have been used as various recording materials for computers, facsimile machines, ticket vending machines, label printers, recorders, etc., and require frequent processing such as development and fixing. In recent years, the market has been rapidly expanding in recent years due to advantages such as being able to record in a short time with a relatively simple structure and a compact device, generating less noise, and being inexpensive.

A film for medical image output (hereinafter, referred to as a film)
Various characteristics are required for medical media. For example, a high density is required to secure high gradation. In general, the highest density required for medical media is, for example, 2.5 or higher for transmission media, but in transmission media for mammography, which has recently attracted special attention, if only the low density portion as in the past is used, Instead, it is necessary to increase the luminance of the Schaukasten (backlight) and refer to it so that the density of the high-density portion can be recognized. Therefore, a color having a higher density, for example, a transmission density of 4.0 or more is required.

[0004] In the case of reflective medical media,
It is possible to increase the density to a certain extent by increasing the thickness of the heat-sensitive recording layer.However, the increase in density over a certain area is slowed down, and adverse effects such as an increase in background density occur. A good configuration is required. The same can be said for transmission-type medical media for general use. If it is possible to obtain the same concentration with a thin film as before,
In terms of performance such as background density and transparency, it is also advantageous in manufacturing processes such as cost and residual solvent.

[0005] Further, in the case of medical media of the wet silver salt type, storage of the diagnostic film for 10 years or more is required. Therefore, long-term image fastness is required in order to replace the diagnostic film. Particularly in medical media, since the gradation is very important, it is fatal that the preservability is not ensured. As described above, in medical applications, there is an extremely high demand for high density and high preservability as compared with the field in which conventional thermosensitive recording media are used. For example, when considering a substitute for a transmission silver halide film, it is required that the storage be at least 2.5 or more in transmission density and 10 years or more in storage stability. Against this background, the condition of the developer required to achieve the quality for medical use in the leuco dye type thermal recording is that the leuco dye can be strongly colored and has high image storage for a long period of time. There is a need to be able to.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording material which achieves high density and high storage stability and is suitable for medical image display applications.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a colorless or light-colored leuco dye is formed on a support, and a color developer or a binder resin as a binder for coloring the leuco dye by heating. In a heat-sensitive recording material comprising a heat-sensitive recording layer having a main component of, a specific salicylic acid derivative as a color developer suitable for a medical medium that satisfies the above conditions is particularly useful when designing a transparent type medical medium. As a binder resin which has been found to have excellent performance, and moreover exhibits its coloring property most efficiently, a cellulose acetate-based resin is suitable, and by combining these, a heat-sensitive recording material achieving high density and high storage stability is achieved. Was obtained, and the present invention was completed.

That is, according to the present invention, a heat-sensitive recording layer mainly composed of a colorless or light-colored leuco dye, a developer for causing the leuco dye to heat and a binder resin as a binder is provided on the support. In the heat-sensitive recording material provided, the developer is a compound represented by the following general formula (1), and the binder resin is a cellulose acetate resin having a structural unit represented by the following general formula (2). A thermosensitive recording material is provided.

Embedded image (In the formula, R ¹ represents a linear alkyl group or an alkylamino group having 4 to 16 carbon atoms.)

Embedded image (Wherein R ² is independently a hydrogen atom, an acetyl group,
Represents a propionyl group or a butanoyl group. According to the present invention, there is provided the heat-sensitive recording material as described above, wherein the developer is a compound represented by the following general formula (3).

Embedded image (In the formula, R ² represents a straight-chain alkyl group having 6 to 12 carbon atoms.) According to the present invention, four or more different leuco dyes are present in the thermosensitive recording layer. A heat-sensitive recording material according to any one of the above. Further, according to the present invention, in a heat-sensitive recording material comprising a heat-sensitive recording layer of any one of the above, wherein a protective layer is provided on the heat-sensitive recording layer, the protective layer is coated such that the main component of the solvent is ethyl acetate. A heat-sensitive recording material characterized by being formed by applying and drying a liquid is provided. According to the present invention,
The heat-sensitive recording material according to any one of the above, wherein the drying temperature at the time of forming the heat-sensitive recording layer and the protective layer is 80 ° C. or more. Further, according to the present invention, there is provided the heat-sensitive recording material according to any one of the above, wherein the support is a transparent polyethylene terephthalate film. Further, according to the present invention, there is provided the heat-sensitive recording material as described above, wherein the non-image portion of the heat-sensitive recording material has a haze defined by JIS K7105 of 50% or less. You. Further, according to the present invention, there is provided the heat-sensitive recording material according to any of the above, which is colored blue.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The present invention relates to a heat-sensitive recording material comprising a colorless or light-colored leuco dye, a developer capable of heating and developing the leuco dye, and a heat-sensitive recording layer containing a binder resin as a main component. And a compound represented by the following general formula.

Embedded image (In the formula, R ¹ represents a linear alkyl group or an alkylamino group having 4 to 16 carbon atoms.)

Specific examples of the compound represented by the general formula (1) include 4- (n-butanoylamino) salicylic acid, 4- (n-hexanoylamino) salicylic acid,
(N-octanoylamino) salicylic acid, 4- (hexadecanoylamino) salicylic acid, 4- (N'-n-butylcarbamoylamino) salicylic acid, 4- (N'-n-
Hexylcarbamoylamino) salicylic acid, 4- (N '
-N-octylcarbamoylamino) salicylic acid, 4-
(N′-hexadecylcarbamoylamino) salicylic acid and the like.

In particular, as the developer, the following general formula (3)
Are excellent in background fog and preservability.

Embedded image (In the formula, R ² represents a straight-chain alkyl group having 6 to 12 carbon atoms.) These compounds can be used alone or in combination of two or more. In addition, various known color developers can be mixed for the purpose of further improving the effect.

The salicylic acid derivative represented by the above general formula (1) is preferred as the color developer because (a) a salicylic acid skeleton having high performance in color development as a color developing group, and (b) color development and storage. Bonding base part that contributes to the
It is considered that the quality required for a medical image output medium is realized at a high level due to three factors, namely, (c) a background density and an alkyl group portion which is effective in suppressing a decrease in density. As for (a), when a compound having a phenol group found in a general color developer is used instead of a compound having a salicylic acid skeleton, the concentration is low and storage stability is difficult. Regarding (b), for example, when an electron-withdrawing group is used by reversing -NH and -C = O, the storage stability is remarkably reduced, and the associativeness of the developer molecules is poor with other bonding groups. Seems to be the cause. As for (c), the carbon number is 4
When the carbon number is less than 16, the solubility in water or an organic solvent is increased, so that the background fog is severe. Conversely, when the carbon number is more than 16, the storage stability is reduced. Therefore, the above (a) and (b)
The combination of (c) is important, and the compound represented by the general formula (1) is extremely excellent in achieving the quality required for a medical image output medium as a color developer.

The binder resin used in the present invention is a cellulose acetate resin represented by the following general formula (2), and can achieve high color developability and storage stability. As such a cellulose acetate-based resin, a cellulose derivative such as cellulose acetate, cellulose acetate propionate, or cellulose acetate butyrate is preferable. Among them, those having a high glass transition temperature are preferable because they improve the storage stability and have a large margin for the drying temperature, so that the amount of the residual solvent can be reduced.

Embedded image (Wherein R ² is independently a hydrogen atom, an acetyl group,
Represents a propionyl group or a butanoyl group. R ² is independent, for example, a hydrogen atom or acetyl group for cellulose acetate, a hydrogen atom or acetyl group or propionyl group for cellulose acetate propionate, a hydrogen atom or acetyl group for cellulose acetate butyrate. Group or butanoyl group.

The reason why the above-mentioned cellulose acetate resin exhibits such properties is not clear, but seems to be closely related to the scattered hydroxyl groups in the resin.
There are other resins with hydroxyl groups in the resin, but many have a high degree of freedom because they are composed of straight-chain saturated carbon chains, whereas cellulose acetate has mostly a cyclic portion, and the leuco dye and the above It is considered that the compound acts to maintain the state of association of the color developer represented by the general formula (1). The amount of the binder resin used in the recording layer is not particularly limited. However, in order to ensure gradation, transparency, and adhesion to the support, the amount is preferably 15% by weight based on the total solids of the coating solution. % Or more, and more preferably in the range of 30 to 60% by weight in consideration of coloring properties and the like.

The leuco dye used in the present invention is a compound having an electron-donating property and is used alone or as a mixture of two or more kinds. However, it is a colorless or light-colored dye precursor, and is not particularly limited. Known ones, for example, triphenylmethanephthalide type, triallylmethane type, fluoran type, phenothidiane type, thiofluoran type, xanthene type, indophthalyl type, spiropyran type, azaphthalide type, chromenopyrazole type, methine type, rhodamine anilino Leuco compounds such as lactams, rhodamine lactams, quinazolines, diazaxanthenes and bislactones are preferably used. Particularly preferred are fluoran-based and phthalide-based leuco dyes. Examples of such compounds include, for example, the following, 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,
3-diethylamino-7,8-benzofluorane, 1,
3-dimethyl-6-diethylaminofluoran, 1,3
-Dimethyl-6-di-n-butylaminofluoran, 3
-Diethylamino-7-methylfluoran, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluoran, 10-diethylamino-2-ethylbenzo [1,4] thiazino [3,2
-B] fluoran, 3,3-bis (1-n-butyl-2
-Methylindol-3-yl) phthalide, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4
-Azaphthalide, 3- [2,2-bis (1-ethyl-2
-Methyl-3-indolyl) vinyl] -3- (4-diethylaminophenyl) phthalide, 3- [1,1-bis (4-diethylaminophenyl) ethylene-2-yl]
-6-dimethylaminophthalide and the like.

In the heat-sensitive recording material of the present invention, it is preferable to mix a plurality of leuco dyes in order to achieve pure blackening of the color tone in the entire color density range. Among them, it is particularly preferable to mix four or more leuco dyes. Particularly preferred are those that exhibit green to black color when used alone,
One dye is a dye having two absorption maxima in the visible region (for example, 2-anilino-3-methyl-6-diethylaminofluoran) in a composition ratio of all leuco dyes of 50% or more, and at least three other dyes are used. Is selected from those which develop colors different from each other including the above-mentioned dyes when used alone (the color tone is a * -b * in the CIE-LAB color system).
When plotted on a plane, one or more quadrants that fit in a single quadrant in almost the entire concentration range are selected), 5% each
With the above composition ratio, a color medium suitable for medical image display can be obtained.

In the present invention, in order to form the heat-sensitive recording layer, it is particularly preferable to use an organic solvent, prepare a coating solution in which a leuco dye is dissolved, and apply the coating solution to a support. Examples of such organic solvents include hydrocarbons such as benzene, toluene, xylene, hexane, cyclohexane, methylcyclohexane, and cyclopentane; halogenated hydrocarbons such as chloroform, methylene chloride, chlorobenzene, and dichlorobenzene; methanol, ethanol, and propanol. ,
Alcohols such as isopropanol and butanol, ethers such as ethyl ether, isopropyl ether and 1,3-dioxolan, ketones such as acetone, methyl ethyl ketone (hereinafter, MEK), diethyl ketone, methyl isobutyl ketone and cyclohexanone, methyl acetate,
Esters such as ethyl acetate and butyl acetate are used alone or as a mixed organic solvent. Of which, toluene,
MEK, methyl isobutyl ketone, ethyl acetate, and butyl acetate are preferred, and a mixed solvent containing a solvent selected from toluene, methyl isobutyl ketone, and ethyl acetate in at least 50% by weight of the solvent component in the organic solvent-based coating solution. Then, a heat-sensitive sheet excellent in background fog can be obtained.

Specific examples of the support used in the present invention include high quality paper, neutral paper, acidic paper, recycled paper, coated paper, polyolefin resin laminated paper, synthetic paper, cellulose derivative films such as cellulose triacetate, and polypropylene. And a polyolefin film such as polyethylene, a polystyrene film or a film obtained by laminating these, and the like. A polyester film such as polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate is preferred, but is not limited thereto. Among these, a polyethylene terephthalate film in which the haze of the support alone (haze defined by JIS K7105, haze) is 10% or less is particularly preferable in order to obtain a sheet having high transparency. Further, in order to improve the adhesiveness of the coating layer of the heat-sensitive recording layer coating solution, 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.

The specific examples of the leuco dye, the developer, the binder resin, and the solvent used, which are the main components of the heat-sensitive recording material of the present invention, have been described above, but are not limited thereto.
Also, if necessary, known fillers, pigments, surfactants,
A heat fusible substance 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, coating this on a support and drying it. The coating method is a die fountain method. There is no particular limitation on the wire bar method, gravure method, air knife method, and the like.
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. In the recording layer liquid, since the particle size of the dispersion greatly affects the transparency of the entire recording material or the surface roughness of the protective layer and, consequently, the dot reproducibility during printing, the particle size is 1.0 μm or less, particularly the refractive index. When the thickness is 0.5 μm or less, the transparency is significantly improved. The thickness of the recording layer depends on the composition of the recording layer and the use of the heat-sensitive recording material, but is about 1 to 50 μm, preferably 3 to 20 μm.
m. 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, it is preferable to provide a protective layer on the heat-sensitive recording layer in order to improve chemical resistance, water resistance, friction resistance, light resistance and head matching with a thermal head. From the viewpoint of transparency, it is ideal to provide a protective layer provided on the heat-sensitive recording layer with a resin layer alone. However, a protective layer made of only a resin has too high smoothness, and is printed by sticking and dust dragging. It is difficult to obtain sufficient performance in terms of defects. In particular, when a plastic film is used as the support, the head matching is reduced since the film tends to be smoother than when the paper is used as the support,
Trash tends to be dragged. In addition, in the case of a general thermoplastic resin, since the glass transition point is lower than that of heating by a thermal head, the protective layer made of the resin alone may cause deterioration of the surface or exposure of the recording layer. Such printing defects and defects are fatal as materials for outputting medical images. As a means of improving performance against sticking, dust dragging, and the like, a filler is generally contained. However, in the case of a transparent thermosensitive recording material, the transparency often decreases when the protective layer contains a filler as used in 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 partially adding a large particle size filler to partially roughen the surface. In the present invention, it is possible to form a protective layer by combining the above two methods as needed. 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.

As the resin used for the protective layer in the present invention, in addition to a water-soluble resin, an aqueous emulsion, a hydrophobic resin, an ultraviolet ray, an electron beam curable resin, and the like can be used.
These can be used together 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 polyacrylate resin, polymethacrylate resin, polyurethane resin, polyester resin, polyvinyl acetate resin, styrene acrylate resin, polyolefin resin, polystyrene resin, and polyvinyl chloride resin. ,
Polyether resin, polyamide resin, polycarbonate resin, polyethylene resin, polypropylene resin,
Examples thereof include polyacrylamide resin, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetal, cellulose acetate resin, and copolymers thereof. Further, a crosslinking agent can be used together with the resin, and a conventionally known compound such as an isocyanate compound and an epoxy compound can be used as the crosslinking agent.
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.

Examples of the filler include phosphate fiber, potassium titanate, acicular magnesium hydroxide, whisker, talc, mica, glass flake, calcium carbonate, plate-like calcium carbonate, aluminum hydroxide, plate-like aluminum hydroxide, Inorganic fillers such as silica, clay, calcined clay, kaolin, and hydrotalcite, crosslinked polystyrene resin particles, urea-formalin copolymer particles, silicone resin particles, crosslinked polymethacrylate methyl acrylate resin particles, guanamine-formaldehyde copolymer And melamine-formaldehyde copolymer particles. In the present invention, melamine-formaldehyde copolymer particles are preferable as the organic filler and kaolin, talc, and aluminum hydroxide are preferable as the inorganic filler from the viewpoint of head wear. However, the present invention is not limited to this, and a plurality of fillers may be used simultaneously in order to impart various properties.

In order to further improve the head matching property, wax and oils are added to the protective layer, or a resin modified with silicone is used as a resin.
The coefficient of friction can be adjusted by adjusting the ratio of the resin to the filler. Examples of waxes that can be used here include stearic acid amide, palmitic acid amide, oleic acid amide, lauric acid amide, ethylenebisstearylamide, methylenebisstearylamide,
Methylol stearyl amide, paraffin wax, polyethylene, carnauba wax, paraffin oxide, zinc stearate and the like. As the oil, a general silicone oil or the like can be used.

The solvent that can be used in the coating solution for the protective layer of the present invention is not particularly limited. For example, water and the above-mentioned organic solvents suitable for the coating solution for the recording layer are used alone or as a mixed solvent. Among them, particularly when a solvent having a high solubility is used, the leuco dye is eluted from the recording layer at the time of applying the protective layer liquid, so that the dye content in the recording layer is reduced, and the storage stability is adversely affected. When a solvent having a low solubility is used, the low molecules do not diffuse into the protective layer, so that the strength of the protective layer does not decrease, and the background fog after coating the recording layer can be reduced with the solvent alone. When a high-boiling solvent is used, the solvent tends to remain in the layer, which is also not preferable for storage stability. Accordingly, it is particularly preferable to use a protective layer coating solution containing ethyl acetate as a main component (70% by weight or more), since the solubility of the leuco dye is low and the boiling point is low.

The method for applying the coating liquid for the protective layer is not particularly limited, and can be applied by a conventionally known method. The preferred protective layer thickness is 0.1 to 20 μm, more preferably 0.5 to
10 μm. If the thickness of the protective layer is too thin, the recording material is insufficient in function as a protective layer such as storage stability and head matching, and if too thick, the thermal sensitivity of the recording material is reduced and the cost is disadvantageous. is there.

In the present invention, the heat-sensitive recording layer and the protective layer are formed by applying a coating solution for each layer, and then transporting the coating solution to a drying box and drying the coating solution.
It is preferable that the temperature is not lower than ° C. Even if the drying temperature is lower than 80 ° C., a coating film is formed, but immediately after the drying step, the solvent used for the coating liquid is not sufficiently removed, which affects the storage stability. 30 ~ 60 ℃ for stabilization of product performance
Curing is often performed for several days to several weeks under the above environment, but there is a concern about blocking in this step, and the time required for curing is extended, which is not preferable in production control. The higher the drying temperature, the better. However, if the drying temperature is too high, it leads to unevenness of the coating film and also affects the quality of background fog. Since the background fog is reduced to a certain level by applying the protective layer, a particularly preferable drying temperature range is 80 to 150 ° C.

JIS of non-image area of heat-sensitive recording material of the present invention
The cloudiness defined by K7105 is preferably 50% or less, more preferably 30% or less, from the viewpoint of transmission image diagnosis in medical applications. If it exceeds 50%, the sharpness of the image when the Schaukasten is attached is poor.

This thermosensitive recording material can be colored blue for the purpose of improving the antiglare effect or the image recognizability. A method of kneading a blue pigment on a support, a method of adding a blue dye or a blue pigment to at least one of the coating layers, and the like are employed as a method of blue tinting. range of 0.15 to 0.25 is, the color a * = - 4~-15, b * = - 5~-15 ( measurement conditions; d / 0, 10 degree field of view, 10 nm each in the light source D ₆₅ The color is preferably in the range enclosed by the above formula (calculated by measuring the absorbance). The blue pigment and blue dye that can be used are not particularly limited, and various known materials can be used.

In the present invention, if necessary, an intermediate layer may be used as a pigment, a binder, or a heat-sensitive recording medium, if necessary, for improving the adhesiveness and smoothness between the support and the heat-sensitive recording layer and between the protective layer and the heat-sensitive recording layer. A layer containing a fusible substance or the like can be provided. When synthetic paper or a plastic film is used in the heat-sensitive recording material of the present invention, the possibility of dust adhesion due to charging or the like becomes extremely high. In addition, transportability may be reduced due to static electricity. On the other hand, it is preferable to provide a back layer having an antistatic property by including an antistatic material, and to perform antistatic. Examples of the antistatic material include known materials such as an electron conduction type and an ion conduction type.
It is preferable to be ¹⁰ ohm / m ² or less. Further, in the heat-sensitive recording material of the present invention, curl adjustment, a back layer for adjusting transportability, it is also possible to provide a back layer containing a matting agent in a silver halide film-like, also for the recording layer described above, Various known materials such as a material for the protective layer can be used. The particle size of the matting agent is 0.3
The thickness of the back layer is preferably in the range of 0.1 to 10 μm.

The thermosensitive recording material of the present invention is supplied to a printer for medical use in the form of a flat plate or a roll. In the case of a flat plate, the total thickness of the thermosensitive recording material is adjusted to be equivalent to a silver halide film. It is preferably 170 to 250 μm. In the case of a roll, the total thickness of the heat-sensitive recording material is preferably about 50 to 140 μm from the viewpoint of the winding length, curl curl and the like. In particular, when a plastic film is used as the support, the Gurley stiffness in the roll flow direction is 1
It is preferable to set it to 90 to 250 mgf.

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

[0033]

The present invention will be described below in detail with reference to examples. In the following, all parts and percentages are based on weight.

<Preparation of Recording Layer Coating Solution [Solution B]> First, the composition was pulverized and dispersed in a ball mill according to Table 1 below to prepare a developer dispersion [Solution A]. [Solution A] Developer 15 parts 15% binder resin solution (solvent: MEK / toluene = 5/5) 20 parts MEK 25 parts Toluene 40 parts Further, each component was mixed according to Table 1, and the recording layer coating solution [B Liquid]. [Solution B] [Solution A] 40 parts Leuco dye 6 parts 15% binder resin solution (solvent: MEK / toluene = 5/5) 48 parts Toluene 6 parts

[0035]

[Table 1]

In Table 1, the components in the recording layer coating solution are as follows. (1) Developer A: 4- (N'-decylcarbamoylamino) salicylic acid B: 4- (decanoylamino) salicylic acid C: 4- (N-decylcarbamoyl) salicylic acid D: 4- (N'-octadecylcarbamoyl) Amino) salicylic acid (2) Leuco dye (the following mixture) 2-anilino-3-methyl-6- (N-ethyl-N-p-toluidino) fluorane 65 parts 3,3-bis (1-n-butyl-2-) Methylindol-3-yl) phthalide 5 parts 1,3-dimethyl-6-diethylaminofluoran 15 parts 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide 15 parts (3) Binder resin a : CAP-482-0.5 manufactured by Eastman Chemical Company
(Glass transition temperature 142 ° C) b: CAP-551-0.2 manufactured by Eastman Chemical Company
(Glass transition temperature: 101 ° C) c: SREC KS-1 manufactured by Sekisui Chemical Co. (polyvinyl acetal having a glass transition temperature of 110 ° C)

<Preparation of Coating Solution for Protective Layer [Solution D]> First, the following composition was pulverized and dispersed in a ball mill to a volume average particle size of 0.3 μm to prepare a filler dispersion [Solution C]. [Solution C] Silica 15 parts 10% polyvinyl acetal solution (Slek KS-1 manufactured by Sekisui Chemical Co., Ltd., solvent: MEK) 15 parts MEK 70 parts Further, the following composition is sufficiently stirred, and a protective layer coating solution [Solution D] Was prepared. [Solution D] [Solution C] 10 parts 10% solution of polyvinyl acetal (Sekisui Chemical Co., Ltd. SLESK KS-1, solvent: MEK) 10 parts MEK 12 parts

<Preparation of Protective Layer Coating Solution (D 'Solution)> Similarly, the following composition was ball-milled to obtain a volume average particle size of 0.3 μm.
This was ground and dispersed until a filler dispersion liquid [C 'liquid] was prepared. [Liquid C '] 15 parts of silica 15% solution of polyvinyl acetal (S-LEC KS-1 manufactured by Sekisui Chemical Co., Ltd., solvent: ethyl acetate) 15 parts 70 parts of ethyl acetate Further, the following composition was sufficiently stirred to obtain a main component of the solvent. A protective layer coating solution [D 'solution] was prepared using ethyl acetate. [D 'solution] [C' solution] 10 parts 10% polyvinyl acetal solution (Slek KS-1, Sekisui Chemical Co., Ltd., solvent: ethyl acetate) 10 parts Ethyl acetate 12 parts

<Preparation of Thermosensitive Recording Sheet> The recording layer coating liquid [solution B] and the protective layer coating liquid [D] prepared as described above were prepared.
Solution] or [D 'Solution] using a wire bar as shown in Table 2 on a 175 µm thick transparent polyester film (having a haze of 3%). And dried sufficiently to form a heat-sensitive recording layer and a protective layer. The thickness of the recording layer was 17 μm, and the thickness of the protective layer was 4 μm.

[0040]

[Table 2]

The evaluation method and the measurement method are as follows. Gray scale was printed on the thermal recording sheet produced as described above using a thermal printer UP-70XR manufactured by Sony Corporation. Of these, the transmission density is 0.
Images around 7 were used for the shelf life test. The transmission density was measured using a transmission densitometer TD-904 (black) manufactured by Gretag Macbeth. The storage test was performed at 50 ° C and 90% r. h. The test was left for 48 hours in a high-temperature, high-humidity storage set in the environment described above.
Concentration preservability was calculated by the following equation. If the variation is within 30%, the image is practically usable. If the variation is within 15%, it is difficult to identify a change in image density. Storage property (%) = [(density after storage−density before storage) ÷ density before storage] × 100 The haze of the non-image area was measured by a direct read haze computer HGM-2DP type manufactured by Suga Test Instruments Co., Ltd. The particle size was measured with a laser diffraction particle size analyzer LA-700 manufactured by Horiba, Ltd. Table 3 shows the evaluation results.

[0042]

[Table 3]

[0043]

According to the present invention, it is possible to provide a thermosensitive recording material having high image quality, high density and excellent storability, and particularly suitable as a medical image forming sheet for MRI and CT.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B41M 5/18 108 110

Claims (8)

[Claims] 1. A heat-sensitive recording material comprising a support having thereon a colorless or light-colored leuco dye, and a heat-sensitive recording layer containing, as a main component, a color developing agent for causing the leuco dye to heat and a binder resin as a binder. Wherein the developer is a compound represented by the following general formula (1), and the binder resin is a cellulose acetate resin having a structural unit represented by the following general formula (2): Recording material. Embedded image (In the formula, R ¹ represents a straight-chain alkyl group or alkylamino group having 4 to 16 carbon atoms.) (Wherein R ² is independently a hydrogen atom, an acetyl group,
Represents a propionyl group or a butanoyl group. ) 2. The heat-sensitive recording material according to claim 1, wherein the developer is a compound represented by the following general formula (3). Embedded image (In the formula, R ² represents a straight-chain alkyl group having 6 to 12 carbon atoms.) 3. The thermosensitive recording layer according to claim 1, wherein four or more different leuco dyes are present.
2. The heat-sensitive recording material according to item 1. 4. The heat-sensitive recording material according to claim 1, wherein a protective layer is provided on the heat-sensitive recording layer of the heat-sensitive recording material, wherein the main component of the solvent in the protective layer is ethyl acetate. A heat-sensitive recording material formed by applying and drying a coating solution. 5. The drying temperature at the time of forming the heat-sensitive recording layer and the protective layer is 80 ° C. or higher.
A heat-sensitive recording material according to any one of the above. 6. The support according to claim 1, wherein the support is a transparent polyethylene terephthalate film.
5. The heat-sensitive recording material according to any one of 5. 7. The JIS of a non-image portion of the heat-sensitive recording material
The heat-sensitive recording material according to any one of claims 1 to 6, wherein the haze specified by K7105 is 50% or less. 8. The heat-sensitive recording material according to claim 1, which is colored blue.