JP2003034083A - Transparent heat sensitive recording material and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent heat sensitive recording material, which has high image quality, is excellent in transparency and preservability and especially suitable for medical use, and its manufacturing method. SOLUTION: In the transparent heat sensitive recording material, which is formed by providing a heat sensitive recording layer having at least a colorless or light-colored leuco dye, a developer for color-developing the leuco dye, under heat and a binder resin as a bonding agent as a major agent is provided on a transparent support. As the manufacturing method of the transparent heat sensitive recording material, first of all, a solvent solution is prepared by solving the transparent heat sensitive recording material, in which a compound represented by general formula (1) as the developer and a thermally fusible compound are employed, and the binder resin as the bonding agent of the colorless or light-colored leuco dye and then, after mixing a dispersant obtained by dispersing the developer or color-developing the leuco dye under heat and the thermally fusible compound with the solution, the resultant mixture is applied onto the transparent support and dried, resulting in forming the heat sensitive recording layer. In formula (1), R<1> represents a 4-16C straight-chained alkyl group or straight- chained alkylamino group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent heat-sensitive recording material and a method for producing the same, more specifically, a heat-sensitive recording material utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound. (Transparent heat-sensitive sheets such as films for video printers), especially MRI and CT
The present invention relates to a transparent heat-sensitive recording material suitable as a medical image forming sheet having high image quality, high density and high storability like a silver salt film, and a method for producing the same, for the purpose of diagnosing and referencing images such as Schaukasten.

[0002]

2. Description of the Related Art Various recording materials utilizing a thermosensitive coloring process have been proposed, but generally, a colorless or light-colored leuco dye and a color developer are dissolved or dispersed on a paper. It is manufactured by applying liquid. 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 salt X-ray film and a trend of digitizing an image. The current medical dry processes include three systems: light exposure heat fixing system heat transfer system and direct thermal recording system.

A heat-sensitive recording material, which is one of them, has been conventionally used as various recording materials for electronic computers, facsimiles, ticket vending machines, label printers, recorders and the like, and frequently undergoes frequent processing such as development and fixing. The market has been rapidly expanding in recent years because of advantages such as the fact that it is not necessary to perform the above, recording can be performed in a short time by a compact device having a relatively simple structure, the generation of noise is small, and the cost is low.

By the way, media used for medical purposes are desired to have the following characteristics. First, it is necessary to develop a single color tone from the low density region to the high density region. In the case of a medium using a certain type of leuco dye, if it is a reflective medium, the incident light is attenuated by diffusion in the recording layer other than absorption by the leuco color former, resulting in a broad absorbance curve. In the case of a transparent heat-sensitive sheet having high transparency, the contribution of factors other than absorption by the color-forming material is small, and therefore the irregularity of the absorbance curve is severe and the color tone varies greatly depending on the density. Therefore, it is necessary to adjust the color tone by mixing a plurality of leuco dyes, but if the concentration storability of each leuco dye to be added is different, these phenomena will appear remarkably in high temperature and high humidity storage, and the sheet immediately after printing When the print sheets after storage are lined up, the color tones of the two look very different. Therefore, in order to prevent the color tone from changing, even leuco dyes which develop different color tones must show an equally high concentration storage stability.

Next, since the diagnosis is carried out by using Schaukasten, it is necessary to ensure transparency. When the transparency is low, the light rays are diffused and the image recognition property is deteriorated. In order to increase the transparency, there is a method in which the particulate material added to the recording layer, the protective layer, or the like is made into fine particles, or the proportion of the adhesive is increased, but that alone is not sufficient in transparency. Currently, the dependence on materials is high. Further, in particular, in order to make the contrast clear and improve the image recognition property, it is necessary to reproduce a wide density range. For that purpose, in addition to the transparency as described above, it is necessary to achieve a high density with no fog in the non-image area and a maximum color density of at least 2.5 or more, preferably 3.0 or more.

Furthermore, it is necessary to reproduce the density with good gradation from the low energy region of the thermal energy of the thermal head to the high energy region. In particular, in order to secure a wide range of thermal energy for controlling the color density and achieve high gradation, it is necessary to control the color development characteristics in the low energy region where color development starts.

From the above, there is a need for a heat-sensitive recording material which satisfies the requirements of high density storage stability, high transparency, low non-image area density, high maximum color density and high gradation. In conventional reflection type thermal recording materials, the color density,
Various methods have been reported for improving the storability, etc., but even if these methods were used for a transmission type heat-sensitive recording material, a sufficient effect could not be achieved.

[0008] Japanese Patent Application Laid-Open Nos. 4-91983 and 10
JP-A-278431 discloses a method for achieving black color development, high transparency and high density in a transparent heat-sensitive sheet using a general color developer, but these color developers have a long shelf life. Not well-balanced materials that satisfy the above conditions have not yet been developed.

[0009]

In view of the above circumstances, the present invention has a high image quality, excellent gradation, transparency and storability, and a transparent thermosensitive recording material particularly suitable for medical use, and a method for producing the same. The task is to provide the.

[0010]

In order to solve the above problems, the present inventors have conducted trial and error and focused their attention on the color developer, and as a result, have completed the present invention. It was

That is, according to the present invention, firstly, at least a colorless or light-colored leuco dye, a developer that allows the leuco dye to be colored by heating and a binder resin that is a binder are used as main components on a transparent support. A transparent heat-sensitive recording material provided with a heat-sensitive recording layer, wherein a heat-fusible compound is used as the developer together with a compound represented by the following general formula (1). Will be provided.

[0012]

[Chemical 4] [In the formula (1), R ¹ represents a linear alkyl group having 4 to 16 carbon atoms or a linear alkylamino group. ]

The first invention includes the following (1) to (6):
The transparent heat-sensitive recording material described in 1. is included. (1) A transparent thermosensitive recording material in which the heat-fusible compound is an oxalic acid dibenzyl ester compound or a fatty acid amide compound. (2) A transparent heat-sensitive recording material, wherein the compound represented by the general formula (1) is a compound represented by the following general formula (2).

[0014]

[Chemical 5] [In Formula (2), R < ² > shows a C6-C12 linear alkyl group. (3) A transparent thermosensitive recording material in which one or both of the developer and the heat-fusible compound have a volume average particle diameter of 0.5 μm or less. (4) A transparent thermosensitive recording material in which the binder resin is a resin represented by the following general formula (3).

[0015]

[Chemical 6] [In the formula (3), R ³ represents a linear alkyl group having 1 to ³ carbon atoms, l, m, and n represent mol%, and the sum of l, m, and n is 1
00. (5) A transparent thermosensitive recording material in which the transparent support is a polyethylene terephthalate film.

(6) A transparent heat-sensitive recording material having a haze of 50% or less in the non-image area. In addition, according to the present invention, secondly, a colorless or light-colored leuco dye and a binder resin which is a binder are dissolved in an organic solvent to prepare a solvent solution, and the solution is heated to develop the leuco dye. A thermosensitive recording layer is formed by mixing a dispersion obtained by dispersing a color developing agent and a heat-fusible compound in an organic solvent, coating the mixture on a transparent support and drying the mixture. A method for producing the transparent heat-sensitive recording material is provided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a heat-sensitive material containing, as a main component, at least a colorless or light-colored leuco dye and a binder resin which is a developer and a binder for heating and coloring the leuco dye on a transparent support. In the heat-sensitive recording material comprising a recording layer, and optionally a protective layer on the recording layer and a back layer on the back surface of the support, a compound represented by the following general formula (1) is used as a developer. By using a heat-fusible compound, high concentration, high storability, high transparency,
It has been found that a transparent heat-sensitive recording material that achieves high gradation can be obtained.

[0018]

[Chemical 7] [In the formula (1), R ¹ represents a linear alkyl group having 4 to 16 carbon atoms or a linear alkylamino group. ]

Specific examples of the compound represented by the general formula (1) include 4- (n-butanoylamino) salicylic acid and 4
-(N-hexanoylamino) salicylic acid, 4- (n-
Octanoylamino) salicylic acid, 4- (octadecanoylamino) salicylic acid, 4- (N'-n-butylcarbamoylamino) salicylic acid, 4- (N'-n-hexylcarbamoylamino) salicylic acid, 4- (N'- n-
Octylcarbamoylamino) salicylic acid, 4- (N '
-Octadecylcarbamoylamino) salicylic acid and the like.

Particularly, as the color developer, the following general formula (2) is used.
The compound represented by the formula (1) is preferable because it has excellent background fog and excellent storage stability.

[0021]

[Chemical 8] [In Formula (2), R < ² > shows a C6-C12 linear alkyl group. These compounds can be used alone or in combination of two or more. Further, for the purpose of further improving the effect, various known color developers can be mixed.

In the general formula (1), salicylic acid compounds are preferred because (a) salicylic acid having high performance as a color-developing group, (b) a bonding group that contributes to color developability and storage stability, and (c). It is considered that this is because the quality required for the medical image output medium is realized at a high level by the three factors of the background density and the alkyl group which is effective in suppressing the density decrease. Regarding (a), when a phenol group found in a general color developer is used instead of salicylic acid, the concentration is low and a problem occurs in storage stability. Regarding (b), for example, when -NH and -C = O are reversed and an electron-withdrawing group is used, the storage stability is significantly reduced.
This is probably due to the poor association of the developer molecules with other conjugating groups. Regarding (c), when the carbon number is less than 4, the background fog is severe, and conversely, when the carbon number is more than 16, the storage stability is deteriorated. Therefore, the combination of the above (a), (b) and (c) is preferable, and the compound represented by the general formula (1) is extremely excellent in achieving the quality required for the medical image output medium.

The heat-fusible compound used in the present invention includes:
Oxalic acid dibenzyl ester compounds or fatty acid amide compounds are preferred. Examples of the oxalic acid dibenzyl ester compound include oxalic acid dibenzyl ester and oxalic acid di-p.
-Chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, etc., has at least 1 hydrogen atom, alkyl group and halogen in benzyl of oxalic acid dibenzyl ester.
And a fatty acid amide compound is N-hydroxymethylstearic acid amide, stearic acid amide, palmitic acid amide, oleic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoylstearic acid amide. , N-eicoic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylolstearic acid amide, etc., and compounds obtained by acylating an amine with a higher fatty acid. The melting point of these heat fusible compounds is preferably in the range of 60 to 160 ° C. These heat fusible compounds are used alone or in combination of two or more.

The reason why these heat-fusible compounds are preferable is that they are easily compatible with the developer of the general formula (1) when heat energy is applied, and the color of the general formula (1) is also developed. A material that is suitable for controlling the gradient of the coloring characteristic with respect to the energy for starting the coloring when using an agent and the thermal energy in the low energy region can be mentioned. That is, it is possible to freely control the color developing characteristics of the low energy part by changing the kind, particle size and addition amount of these heat fusible compounds. Further, in general, adding a particulate component to the recording layer impairs transparency,
These heat-fusible compounds are less likely to impair the transparency of the recording material, and when the heat volume average particle diameter is 0.5 μm or less, there is almost no effect on the transparency and a transparent heat-sensitive recording material can be obtained. You can

The leuco dye used in the present invention is a compound exhibiting an electron-donating property, and is used alone or in combination of two or more kinds, but it is a colorless or light-colored dye precursor per se.
Without particular limitation, conventionally known compounds, for example, triphenylmethanephthalide system, triallylmethane system, fluorane system, phenothidian system, thioferorane system, xanthene system, indophthalyl system, spiropyran system, azaphthalide system, chromeno Preferable leuco compounds such as pyrazole-based, methine-based, rhodamine-anilinolactam-based, rhodamine-lactam-based, quinazoline-based, diazaxanthene-based, and bislactone-based compounds are preferably used.

Particularly preferred are fluorane-based and phthalide-based leuco dyes, and examples of such compounds include 2-anilino-3-methyl-6-diethylaminofluorane and 2-anilino-3-methyl. -6-
(Di-n-butylamino) fluorane, 2-anilino-
3-Methyl-6- (Nn-propyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N
-Isopropyl-N-methylamino) fluorane, 2-
Anilino-3-methyl-6- (N-isobutyl-N-methylamino) fluorane, 2-anilino-3-methyl-
6- (Nn-amyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-sec-butyl-N-ethylamino) fluorane, 2-anilino-
3-Methyl-6- (Nn-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (N
-Iso-amyl-N-ethylamino) fluorane, 2
-Anilino-3-methyl-6- (Nn-propyl-N
-Isopropylamino) fluorane, 2-anilino-3
-Methyl-6- (N-cyclohexyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N
-Ethyl-N-p-toluidino) fluorane, 2-anilino-3-methyl-6- (N-methyl-N-p-toluidino) fluorane, 3-diethylamino-7,8-benzofluorane, 1,3- Dimethyl-6-diethylaminofluorane, 1,3-dimethyl-6-di-n-butylaminofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-chlorofluorane,
3-diethylamino-6-methyl-7-chlorofluorane, 10-diethylamino-2-ethylbenzo [1,
4] thiazino [3,2-b] fluorane, 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,
Examples thereof include 3- [1,1-bis (4-diethylaminophenyl) ethylene-2-yl] -6-dimethylaminophthalide.

The binder resin used in the present invention is
Various known resins can be used, such as polyethylene,
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, polycarbonate, epoxy resin, polyamide, polyvinyl alcohol, starch, gelatin and the like. These resins may be used alone or in combination of two or more.

Among them, the resin represented by the following general formula (3) is preferable.

[Chemical 9] [In the formula (3), R ³ represents a linear alkyl group having 1 to ³ carbon atoms, l, m and n represent mol%, and the sum of l, m and n is 100. ]

Examples of the binder resin represented by the general formula (3) include polyvinyl acetal and polyvinyl butyral. This type of resin is obtained by saponifying vinyl acetate into polyvinyl alcohol and then further converting it into butyralization / acetalization, but a complete reaction is difficult and there is no choice but to leave a hydroxyl group derived from polyvinyl alcohol. This hydroxyl group is useful in terms of dispersion of fine particles, but at the same time, it acts on the leuco dye to induce fog in the non-image area, and therefore it is not preferable to use it in too much amount. When n (polyvinyl alcohol component) represented by the general formula (3) is 30% or less, a recording sheet with less fog can be obtained. Examples of commercially available resins include KS-1 (30% polyvinyl alcohol component) manufactured by Sekisui Chemical Co., Ltd. as a polyvinyl acetal, and BL-S (26% same) manufactured by Sekisui Chemical Co., Ltd. for polyvinyl butyral. Regarding the ratio of l, m, and n, JIS K67
It is measured according to the measuring method of the molar ratio of the polyvinyl alcohol component in the polyvinyl butyral resin defined by No. 28.

The amount of the binder resin used in the recording layer is not particularly limited, but in order to secure gradation and transparency, it is 15% with respect to the total solid amount of the coating liquid.
The above range is preferable, and a more preferable range in consideration of adhesiveness to a support, color developability and the like is adjusted in the range of 25 to 60%.

In order to form the heat-sensitive recording layer in the present invention, it is particularly preferable to use an organic solvent and prepare a coating solution in which a leuco dye is dissolved and apply it to a support. Examples of the organic solvent include hydrocarbons such as benzene, toluene, xylene, hexane, cyclohexane, methylcyclohexane and cyclopentane, chloroform,
Halogenated hydrocarbons such as methylene chloride, chlorobenzene and dichlorobenzene, alcohols such as methanol, ethanol, propanol, isopropanol and butanol, ethyl ether, isopropyl ether, 1,3
-Ethers such as dioxolane, acetone, methyl ethyl ketone (MEK), ketones such as diethyl ketone, methyl isobutyl ketone, cyclohexanone, esters such as methyl acetate, ethyl acetate, butyl acetate, etc. are used alone or as a mixed organic solvent .

Of these, toluene, MEK, methyl isobutyl ketone, ethyl acetate and butyl acetate are preferable,
In particular, when a solvent selected from toluene, methyl isobutyl ketone, and ethyl acetate is used as a mixed solvent containing 50% or more of the solvent components in the organic solvent-based coating liquid, a heat-sensitive sheet having excellent background fog can be obtained.

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 or a film obtained by laminating these, and the like. Polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, but not limited to these.

In order to improve the adhesiveness of the coating layer, at least one surface is subjected to corona discharge treatment, oxidation reaction treatment (chromic acid, etc.),
The surface can be modified by etching or the like.
In order to obtain a highly transparent sheet, a polyethylene terephthalate film having a haze of the support alone (haze, haze defined by JIS K7105) of 10% or less is particularly preferable.

The transparent heat-sensitive recording material may be colored in blue for the purpose of antiglare effect or improvement of image recognizability. As a method for bluing, it is possible to knead a blue pigment to a support, add a blue dye or a blue pigment to any one or more layers of the coating layer, and the concentration level for bluing is determined by the transmission density. The range of 0.15 to 0.25 has a color tone of a * = − 4 to −15, b * = − 5 to −15 (measurement condition: d / 0, 10 degree field of view, 10 nm at light source D ₆₅₎ . A color in a range surrounded by (measured by measuring absorbance for each) is preferable. The blue pigment and blue dye that can be used are not particularly limited, and various known materials can be used.

Specific examples of the main components of the heat-sensitive recording material of the present invention, such as leuco dyes, developers, binder resins, etc., have been described above. If necessary, known fillers, pigments, surfactants,
A heat fusible substance can be added.

The heat-sensitive recording material of the present invention is prepared by uniformly dispersing or dissolving a leuco dye, a color developing agent and the like together with a binder resin, coating this on a support and drying it. The coating method is as follows. Die fountain method, wire bar method,
The gravure method and the air knife method are not particularly limited. Among these, the die method is preferable because it can provide the coating layer with uniformity and can be applied without contacting the support. In the recording layer liquid, since the particle size of the dispersion has a great influence on the transparency of the entire recording material or the surface roughness of the protective layer, and thus the dot reproducibility during printing, the particle size is 1.0 μm or less, especially in this material. Due to the influence of the refractive index, the transparency is remarkably improved when the thickness is 0.5 μm or less. The film thickness of the recording layer is about 1 to 50 μm, preferably about 3 to 20 μm, though it depends on the composition of the recording layer and the use of the heat-sensitive recording material. Further, the recording layer coating liquid,
If necessary, various additives such as a surfactant may be added for the purpose of improving coatability or recording characteristics.

In the present invention, a protective layer is provided on the heat-sensitive recording layer in order to improve chemical resistance, water resistance, abrasion resistance, light resistance and head matching with a thermal head. From the viewpoint of transparency, it is ideal to provide a resin-only layer as the protective layer of the heat-sensitive recording material.However, a protective layer made of only resin has too high smoothness, and sticking and dust may cause printing defects. It is difficult to obtain sufficient performance. 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 head matching is lowered and dust tends to be easily dragged. Further, in the case of a general thermoplastic resin, the glass transition point is lower than that by heating by a thermal head, so that the protective layer of the resin alone may cause surface alteration or exposure of the recording layer. Such printing defects and defects are fatal as a material for outputting a medical image. A filler is generally contained as a means for improving the performance against such sticking and dust dragging.

However, in the case of a transparent heat-sensitive recording material, if the protective layer contains a filler as used in conventional reflective recording materials, the transparency is often lowered. In order to maintain transparency by adding a filler, there are methods such as finely roughening the surface with a small particle size filler and partially roughening the surface with a large particle size filler. In the present invention, it is possible to form the protective layer by combining the above two methods, if necessary. The coefficient of friction of the surface of the protective layer is head matching (direction to improve lubricity)
From the perspective of preventing the drag of dust, which tends to occur with plastic films (to reduce slippage), from 0.07 to
The range of 0.14 is preferable.

Examples of the filler include phosphate fiber, potassium titanate, acicular magnesium hydroxide,
Whiskers, talc, mica, glass flakes, calcium carbonate, plate-shaped calcium carbonate, aluminum hydroxide,
Inorganic fillers such as plate-shaped aluminum hydroxide, silica, clay, calcined clay, kaolin and hydrotalcite, crosslinked polystyrene resin particles, urea-formalin copolymer particles, silicone resin particles, crosslinked polymethylmethacrylate acrylate resin particles, guanamine Examples include organic fillers of formaldehyde copolymer particles 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.

As with the recording layer, the resin used in the protective layer in the present invention may be a water-soluble resin, an aqueous emulsion, a hydrophobic resin, ultraviolet rays, an electron beam curable resin, or the like, if desired. is there. From the perspective of transparency
It is preferable to use a material in which the refractive index of the resin of the recording layer and the protective layer is in the range of 0.8 to 1.2 in terms of the ratio with the refractive index of the support. Specific examples of the resin include polyacrylic acid ester resin, polymethacrylic acid ester resin, polyurethane resin, polyester resin, polyvinyl acetate resin,
Styrene acrylate resin, polyolefin resin,
Examples thereof include polystyrene resin, polyvinyl chloride resin, polyether resin, polyamide resin, polycarbonate resin, polyethylene resin, polypropylene resin, polyacrylamide resin and the like.

Further, as the cross-linking agent used with the resin,
Conventionally known compounds such as isocyanate compounds and epoxy compounds can be used. Specific examples of the isocyanate compound, toluylene diisocyanate,
Examples thereof include dimers, diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate, hexamethylene diisocyanate, polyisocyanates and their derivatives, and compounds having two or more isocyanate groups in the molecule. In addition, specific examples of the epoxy compound include ethylene glycol diglycidyl ether, butyl glycidyl ether, polyethylene glycol diglycidyl ether, and epoxy acrylate.

Further, in order to improve the head matching property, wax or oil is added to the protective layer, or a resin modified with silicone is mixed and used as a binder resin, and the ratio of the resin and the filler is adjusted. By doing
The coefficient of friction can be adjusted. As waxes that can be used here, stearic acid amide, palmitic acid amide, oleic acid amide, lauric acid amide, ethylenebisstearylamide, methylenebisstearylamide, methylolstearylamide, paraffin wax, polyethylene, carnauba wax, Examples include oxidized paraffin and zinc stearate. As the oil, general silicone oil or the like can be used.

The coating method of the protective layer is not particularly limited and can be applied by a conventionally known method. The thickness of the protective layer is preferably 0.1 to 20 μm, more preferably 0.5 to 10 μm.
m. If the protective layer is too thin, the function of the recording medium as a protective layer such as storability and head matching will be insufficient, and if it is too thick, the thermal sensitivity of the recording medium will be reduced and the cost will be disadvantageous. Is.

From the viewpoint of transmission image diagnosis for medical use, the haze of the transparent heat-sensitive recording material of the present invention is preferably 50% or less, and more preferably 30% or less. If it exceeds 50%, the sharpness of the image when the Schaukasten is attached may be lacking.

The recording method of the heat-sensitive recording material of the present invention is not particularly limited to a hot pen, a thermal head, laser heating, etc. depending on the purpose, but this heat-sensitive recording material prints a high-definition and high-gradation image such as a medical image. It is most preferable to print using a thermal head from the viewpoints of cost, output speed and compactness of the apparatus.

[0048]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following, all parts and% are based on weight.

The following composition was pulverized and dispersed by a ball mill until the volume average particle size became 0.5 μm or less, to prepare a color developer dispersion [solution A]. The particle size was measured with a laser diffraction particle size analyzer LA-700 manufactured by Horiba Ltd. [Liquid A] MEK 25 parts Toluene 40 parts Developer X 15 parts 15% Binder resin Y solution (solvent: MEK) 20 parts

The following composition was pulverized and dispersed by a ball mill until the volume average particle diameter became 0.5 μm or less, to prepare a color developer dispersion liquid [B liquid]. The particle size was measured with a laser diffraction particle size analyzer LA-700 manufactured by Horiba Ltd. [Liquid B] MEK 25 parts Toluene 40 parts Thermofusible substance Z 15 parts 15% Binder resin Y solution (solvent: MEK) 20 parts

[C liquid] prepared by the following composition was thoroughly stirred to prepare a recording layer coating liquid. [C liquid] [A liquid] 55 parts [B liquid] 10 parts 2-anilino-3-methyl-6-diethylaminofluorane 3 parts 15% binder resin Y solution (solvent: MEK) 30 parts MEK 2 parts

Similarly, the following composition was crushed by a ball mill to a volume average particle size of 0.3 μm and dispersed to obtain a filler dispersion [C
Liquid] was prepared. [C liquid] Silica 15 parts 10% Polyvinyl acetal solution (Sekisui Chemical Co., Ltd. S-REC KS-1, solvent: MEK) 15 parts MEK 70 parts

Further, the following composition was sufficiently stirred to prepare a protective layer coating liquid [D liquid]. [D liquid] [C liquid] 10 parts 12.5% silicon-modified polyvinyl butyral solution (SP712 manufactured by Dainichiseika Co., Ltd., solvent: MEK) 8 parts MEK 10 parts Table 1 shows each component at this time.

The recording layer coating liquid [B
Solution] and a protective layer coating solution [D solution] are sequentially applied on a transparent polyester film (thickness of 3%) having a thickness of 175 μm using a wire bar, and sufficiently dried to form a thermosensitive recording layer having a thickness of 15 μm. A 3 μm protective layer was formed.

[0055]

[Table 1]

Example 1 A transparent thermosensitive recording material was prepared according to the above using the corresponding developer, binder resin and heat-fusible substance shown in Table 1.

Example 7 A transparent thermosensitive recording material was prepared in the same manner as in Example 1 except that the above liquid [A] was used, the dispersion of which was stopped when the volume average particle size reached 0.7 μm. .

Example 8 A transparent thermosensitive recording material was prepared in the same manner as in Example 1 except that the above [solution C] was changed to the following [solution E]. [Solution E] [Solution A] 55 parts [Solution B] 20 parts 2-anilino-3-methyl-6-dibutylaminofluorane 3 parts 15% Binder resin Y solution (solvent: MEK) 30 parts MEK 2 parts

Comparative Examples 1 and 2 Using the corresponding developers and binder resins shown in Table 1, transparent thermosensitive recording materials were prepared according to the above.

The thus-prepared thermal recording material was printed with a gray scale by a printer with a variable applied energy equipped with a gradation head having a resolution of 300 dpi, and the following items were evaluated. The haze of the non-image area is the direct reading haze computer HGM- manufactured by Suga Test Instruments Co., Ltd.
It was measured by 2DP type. Transmission density is GretagMa
It was measured using a transmission densitometer TD-904 manufactured by cbeth. Gradation was evaluated by measuring the width of the energy to start color development and the energy to reach the maximum color density. The storage stability test was left for 100 hours in a high-temperature and high-humidity storage set in an environment of a temperature of 40 ° C. and a humidity of 90%. The evaluation results are shown in Table 2.

[0061]

[Table 2]

The evaluation levels are as follows. [Transparency] It was measured according to JIS K7105. When Schoukasten is attached, if it is 50% or less, you will feel transparency,
When it is less than 30%, it is difficult to feel cloudy. A: Haze 20% or less. ◯: Haze 30% or less. Δ: Haze 50% or less. X: Haze 50% or more.

[Non-Image Area Density] The density was measured with a transmission densitometer. 0.30 or less is preferable, and 0.10 or less is particularly preferable. A: Transmission density is 0.10 or less. ◯: Transmission density is 0.20 or less. Δ: Transmission density 0.30 or less. X: Transmission density of 0.30 or more.

[Maximum Color Density] Measurement was carried out with a transmission densitometer. At least 2.5 or more is necessary, and 3.0 or more is particularly preferable. A: Transmission density of 3.0 or more. ◯: Transmission density of 2.5 or more. X: Transmission density is 2.5 or less.

[Preservability] “Change rate = (transmission density after storage−initial density) × 100 ÷
It was evaluated by the value calculated as "initial concentration". Since the density preservability in the examples of the present invention was stronger in the decoloring tendency, the comparison of the degree of preservability was judged in the negative direction. The storability was judged from the largest change in each gradation. ⊚: Change rate = −5% or less. I do not notice any change. ◯: Change rate = -10% or less. I hardly notice the change. Δ: rate of change = −30% or less. I don't notice much change. X: Change rate = -30% or less. I am worried about the change. XX: Almost decolored. Not practical.

[Gradation] Evaluation was made by "coloring energy width mj / mm = (energy to reach maximum color density)-(energy to start color development)". ◯: 50 mj / mm or more. Δ: 40 mj / mm to 50 mj / mm. X: 40 mj / mm or less.

[0067]

According to the present invention, a transparent heat-sensitive recording material having a high image quality, excellent gradation, transparency and storability and particularly suitable for medical use and a method for producing the same are provided, and particularly MRI and C
It is used as a recording material suitable as a medical image sheet for the purpose of diagnosis and reference in an image such as T in Schaukasten, and it greatly contributes to this field.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B41M 5/18 101C 111 H Z F term (reference) 2H026 AA07 BB26 CC10 DD02 DD43 DD45 DD53 EE05 GG10 HH03 4J002 AA001 AB041 BB021 BC041 BD031 BE021 BE061 BF021 BG001 BG131 BH021 CD001 CF001 CK021 CL001 EH097 EJ066 EP016 EP017 FD206 FD207

Claims (8)

[Claims] 1. A transparent heat-sensitive recording comprising, on a transparent support, at least a colorless or light-colored leuco dye, a developer for heating and coloring the leuco dye, and a heat-sensitive recording layer containing a binder resin as a binder as a main component. A transparent heat-sensitive recording material, which is a material comprising a compound represented by the following general formula (1) and a heat-fusible compound as the developer. [Chemical 1] [In the formula (1), R ¹ represents a linear alkyl group having 4 to 16 carbon atoms or a linear alkylamino group. ] 2. The transparent heat-sensitive recording material according to claim 1, wherein the heat-fusible compound is an oxalic acid dibenzyl ester compound or a fatty acid amide compound. 3. The compound represented by the general formula (1) is a compound represented by the following general formula (2).
The transparent thermosensitive recording material described in. [Chemical 2] [In Formula (2), R < ² > shows a C6-C12 linear alkyl group. ] 4. The volume average particle size of one or both of the developer and the heat-fusible compound is 0.5 μm or less.
4. The transparent thermosensitive recording material according to any one of 3 to 3. 5. The binder resin has the following general formula (3):
The transparent heat-sensitive recording material according to any one of claims 1 to 4, which is a resin represented by: [Chemical 3] [In the formula (3), R ³ represents a linear alkyl group having 1 to ³ carbon atoms, l, m, and n represent mol%, and the sum of l, m, and n is 1
00. ] 6. The transparent thermosensitive recording material according to claim 1, wherein the transparent support is a polyethylene terephthalate film. 7. The transparent heat-sensitive recording material according to claim 1, wherein the non-image area has a haze of 50% or less. 8. A colorless or light-colored leuco dye and a binder resin which is a binder are dissolved in an organic solvent to prepare a solvent solution, and the solution is heated with a developer and a heat-developing agent for coloring the leuco dye. A heat-sensitive recording layer is formed by mixing a dispersion obtained by dispersing a fusible compound in an organic solvent, coating the mixture on a transparent support and drying the mixture. 5. The method for producing a transparent thermosensitive recording material according to any one of 1.