JP2006123208A - Thermosensitive recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive recording material, which settles problematic points such as the density and storage stability of a color-developed image and satisfies the demand level of an medical media use application such as the higher density and higher storage stability of the color-developed image, especially of black color-developed image. <P>SOLUTION: In the thermosensitive recording material, which is formed by providing a thermosensitive recording layer mainly made of a leuco dye, a developer and a binding agent on a support, the very excellent properties satisfying especially the demand level of an transparent type medical media use are found out to be obtained by including wax in the thermosensitive recording layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  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) using a color developing reaction between an electron-donating color-forming compound and an electron-accepting compound. The present invention relates to a heat-sensitive recording material suitable for use as a medical image-forming sheet having a high image quality, a high density and a high storage stability, similar to a silver salt film, for the purpose of diagnosis and reference of images such as CT.

  Conventionally, various recording materials using a thermosensitive coloring process have been proposed. This heat-sensitive recording material is generally produced by applying a coating solution in which a colorless or light leuco dye and a developer are dissolved or dispersed on paper, synthetic paper or a plastic film. In particular, mainly in the medical field, a dry film system that can be easily output has been demanded from the waste liquid treatment problem caused by the wet process of silver salt X-ray film and the trend of digitization of images. There are three current dry processes for medical use: a light exposure thermal fixing system, a thermal transfer system, and a direct thermal recording system. Thermal recording material, one of them, has been used as various recording materials for electronic computers, facsimiles, ticket vending machines, label printers, recorders, etc., and needs to be subjected to frequent processing such as development and fixing. In recent years, the market has been rapidly expanding due to advantages such as a relatively simple structure and the ability to record in a short time with a compact device and less noise generation.

  Various characteristics are required for medical image output films (hereinafter referred to as medical media). For example, a high density can be raised to ensure high gradation. In general, there are many opinions that the maximum density required for medical media is, for example, 2.5 or more for transmissive media. However, in transmissive media for mammography, which has attracted particular attention in recent years, only the conventional low-concentration portion can be used. First, since it is necessary to increase the luminance of the shaukasten (backlight) and refer to it so that the light and shade of the high density portion can be understood, color development with a higher density, for example, a transmission density of 4.0 or more is required.

  In reflective medical media, it is possible to increase the density to some extent by increasing the thickness of the thermal recording layer. However, the increase in density over a certain area becomes dull, and the density of the background increases. Therefore, a structure with good coloring efficiency is required. The same can be said for transmission-type medical media for general use. If it is possible to obtain the same concentration as a conventional thin film, it is advantageous in terms of performance such as background concentration and transparency as well as in manufacturing processes such as cost and residual solvent.

In addition, since wet silver salt type medical media require storage of a diagnostic film for more than 10 years, long-term image robustness is also required if an alternative is desired. In particular, in medical media, gradation is very important, and it is fatal that preservation is not ensured. Thus, in medical applications, the demand for high concentration and high storage is much higher than in the field where conventional thermal recording media are used. For example, when an alternative to a transmission silver salt film is considered, it is required to store at least 2.5 or more in terms of transmission density and 10 years or more in terms of storage stability. Under such a background, as a condition of the developer necessary for achieving the quality for medical use in the thermal recording of the leuco dye type, the leuco dye can be strongly developed and the image can be stored for a long period of time. It is required that the sex is possible. There are proposals to solve these problems from the viewpoint of materials such as a developer, but the present demand has not yet met the demands for the highest density and high storage stability of black-colored images (for example, Patent Document 1).
JP 2002-160451 A

  The present invention solves the density and storability of the developed color image, which has been a problem of the above-mentioned prior art, and satisfies the required level for medical media applications where the developed color image, particularly the black developed image has high density and high storability. It is an object to provide a heat-sensitive recording material.

  As a result of intensive studies, the present inventor has provided a heat-sensitive recording layer mainly composed of a colorless or light leuco dye, a color developer that heat-colors the leuco dye, and a binder resin as a binder. In the heat-sensitive recording material thus obtained, it has been found that by including a wax in the heat-sensitive recording layer, a very excellent performance satisfying the required level of a medical medium of a transparent type can be obtained.

According to the present invention, it is possible to provide a heat-sensitive recording material suitable for medical media for displaying images such as MRI and CT, which has a black colored image with high image quality and high density and excellent storage stability.

  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 heat-sensitive recording layer mainly composed of a color developer and a binder resin that heat-colors the leuco dye, and a wax in the heat-sensitive recording layer. It is included.

In the present invention, the wax preferably contained in the heat-sensitive recording layer in order to obtain a high color density is one or more of the following.
Microcrystalline wax, carnauba wax, ceresin, Fischer-Tropsch wax, polyethylene wax, wood wax, beeswax, whale wax, ibota wax, wool wax, shellac wax, candelilla wax, petrolatum, polyester wax.

  The content of the wax in the heat-sensitive recording layer is preferably a mass ratio of 0.2% or more and 2.0% or less with respect to the entire heat-sensitive recording layer in order to obtain a high density and high storage stability of the target color image. In addition, the volume average particle size of the wax in the background portion is preferably 1.0 μm or less, more preferably 0.4 μm or less in order to obtain better transparency. It is also preferred that the wax is contained in the heat-sensitive recording layer in a uniform state instead of dispersed particles.

  The method for incorporating the wax into the heat-sensitive recording layer is basically the same as in the case of the leuco dye described later. However, the difference is that in the case of a wax, it is heated to the melting point or higher and stirred to form an emulsion or solution, which is cooled while stirring to solidify the wax to obtain dispersed particles. The dispersion medium and the binder are preferably the same as those used for dispersing the dye precursor, particularly in the case of a transparent thermosensitive recording material, from the viewpoint of maintaining transparency.

  When the boiling point of the dispersion medium is lower than the melting point of the wax, it is necessary to use an autoclave. Further, in the cooling process, it is preferable to create an atmosphere that is cut off from the outside air or depressurized in order to prevent dissolved air from entering. For further advanced degassing, a known technique such as vacuum defoaming or ultrasonic defoaming may be used.

  Even when the wax is partially or completely dissolved in the dispersion medium when heated, it often separates during cooling, and this is not a problem in production. If it is in a solution state even after cooling, it may be used as a solution.

  Hereinafter, the structure of the heat-sensitive recording material of the present application will be described. First, the thermal recording layer will be described.

  The leuco dye used in the present invention is a compound exhibiting an electron donating property, and is applied alone or in combination of two or more. However, the leuco dye is a colorless or light-colored dye precursor, and is not particularly limited and is a conventionally known one. For example, triphenylmethanephthalide, triallylmethane, fluorane, phenothiocyan, thiofluorane, xanthene, indophthalyl, spiropyran, azaphthalide, chromenopyrazole, methine, rhodamine anilinolactam, Preferred are leuco compounds such as rhodamine lactam, quinazoline, diazaxanthene and bislactone. Particularly preferred are fluoran and phthalide leuco dyes. Examples of such compounds include, but are not limited to, those shown below.

  The heat-sensitive recording material of the present application is not limited by the color hue, but when black color is developed by using a leuco dye alone or in combination of two or more, the advantages of high density and high storage stability are apparent as compared with the prior art. Of course, blue coloring is also superior. Although the specific example of the leuco dye used for this invention below is enumerated, this invention is not limited to these.

  2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6- (di-n-butylamino) fluorane, 2-anilino-3-methyl-6- (di-n-pentyl) Amino) 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, -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-Np-toluidino) fluorane, 2-anilino-3-methyl- 6- (N-methyl-Np-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- -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-diethylamino) Phenyl) phthalide, 3- [1,1-bis (4-diethylaminophenyl) ethylene-2-yl] -6-dimethylaminophthalide, and the like.

  Next, the developer will be described. As the developer, a compound represented by the following general formula (1) or a zinc salt thereof is excellent in background fogging and storage stability. Specific examples are also listed below.

（式中、Ｒ²は炭素数８〜１１である直鎖アルキル基又は炭素数８〜１１である直鎖アルキルオキシ基を表す。）

(In the formula, R ² represents a linear alkyl group having 8 to 11 carbon atoms or a linear alkyloxy group having 8 to 11 carbon atoms.)

  These developers can be used alone or in admixture of two or more. In addition, various known developers can be mixed in order to further improve the effect. Next, specific examples of the developer preferably used in the present invention are listed, but the present invention is not limited to these lists. In addition, some of the listed compounds are included in the general formula (1).

  4- (n-octyloxycarbonylamino) salicylic acid, 4- (n-nonyloxycarbonylamino) salicylic acid, 4- (n-decyloxycarbonylamino) salicylic acid, 4- (n-undecyloxycarbonylamino) salicylic acid, 4 -(N-dodecyloxycarbonylamino) salicylic acid, 4- (n-nonanoylamino) salicylic acid, 4- (n-decanoylamino) salicylic acid, 4- (n-undecanoylamino) salicylic acid, 4- (n- Butanoylamino) salicylic acid, 4- (n-hexanoylamino) salicylic acid, 4- (n-octanoylamino) salicylic acid, 4- (n-dodecanoylamino) salicylic acid, 4- (hexadecanoylamino) salicylic acid, 4 -(N'-n-butylcarbamoylamino) salicylic acid, 4- (N'- -Hexylcarbamoylamino) salicylic acid, 4- (N'-n-octylcarbamoylamino) salicylic acid, 4- (N'-n-decylcarbamoylamino) salicylic acid, 4- (N'-n-dodecylcarbamoylamino) salicylic acid, 4 -(N'-hexadecylcarbamoylamino) salicylic acid, 3- (n-octyloxycarbonylamino) salicylic acid, 3- (n-nonyloxycarbonylamino) salicylic acid, 3- (n-decyloxycarbonylamino) salicylic acid, 3- (N-undecyloxycarbonylamino) salicylic acid, 3- (n-dodecyloxycarbonylamino) salicylic acid, 3- (n-nonanoylamino) salicylic acid, 3- (n-decanoylamino) salicylic acid, 3- (n- Undecanoylamino) salicylic acid, 3- (n Butanoylamino) salicylic acid, 3- (n-hexanoylamino) salicylic acid, 3- (n-octanoylamino) salicylic acid, 3- (n-dodecanoylamino) salicylic acid, 3- (hexadecanoylamino) salicylic acid, 3 -(N'-n-butylcarbamoylamino) salicylic acid, 3- (N'-n-hexylcarbamoylamino) salicylic acid, 3- (N'-n-octylcarbamoylamino) salicylic acid, 3- (N'-n-decyl) Rucarbamoylamino) salicylic acid, 3- (N′-n-dodecylcarbamoylamino) salicylic acid, 3- (N′-hexadecylcarbamoylamino) salicylic acid and the like.

  4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-n-propoxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-hydroxydiphenylsulfone, 4 -Hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-methoxydiphenylsulfone, 4-hydroxy-4'-ethoxydiphenylsulfone, 4-hydroxy-4'-n-butoxydiphenylsulfone, 4-hydroxy-4 '-Benzyloxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (3,5-dibromo-4-hydroxyphenyl) sulfone, bis (3,5-dichloro-4-hydroxyphenyl) sulfone, 3,4-dihydro Sidiphenylsulfone, 3,4-dihydroxy-4'-methyldiphenylsulfone, 3,4,4'-trihydroxydiphenylsulfone, 3,4,3 ', 4'-tetrahydroxydiphenylsulfone, 2,3,4 Trihydroxydiphenylsulfone, 3-phenylsulfonyl-4-hydroxydiphenylsulfone, 2,4-bis (phenylsulfonyl) phenol,

  4-phenylphenol, 4-hydroxyacetophenone, 1,1-bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) pentane, 1,1-bis (4-hydroxyphenyl) hexane, , 1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyphenyl) hexane, 1,1-bis (4-hydroxyphenyl)- 2-ethylhexane, 2,2-bis (3-chloro-4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,3-di- [2- (4 -Hydroxyphenyl) -2-propyl] benzene, 1,3-di- [2- (3,4-dihydroxyphenyl) -2-propyl] benzene Zen, 1,4-di- [2- (4-hydroxyphenyl) -2-propyl] benzene, 4,4′-hydroxydiphenyl ether, 3,3′-dichloro-4,4′-hydroxydiphenyl sulfide, bis ( 2-hydroxynaphthyl) methane,

  Methyl 2,2-bis (4-hydroxyphenyl) acetate, 2,2-bis (4-hydroxyphenyl) butyl acetate, 4,4'-thiobis (2-tert-butyl-5-methylphenol). Dimethyl 4-hydroxyphthalate, benzyl 4-hydroxybenzoate, methyl 4-hydroxybenzoate, benzyl gallate, stearyl gallate, pentaerythritol tetra (4-hydroxybenzoic acid) ester, pentaerythritol tri (4-hydroxybenzoic acid) ) Ester, dehydration condensate of 2,2-bis (hydroxymethyl) -1,3-propanediol polycondensate and 4-hydroxybenzoic acid,

  N, N′-diphenylthiourea, 4,4′-bis [3- (4-methylphenylsulfonyl) ureido] diphenylmethane, N- (4-methylphenylsulfonyl) -N′-phenylurea, N- (benzenesulfonyl) ) -N '-[3- (4-toluenesulfonyloxyphenyl)] urea, N- (4-toluenesulfonyl) -N'-[3- (4-toluenesulfonyloxyphenyl)] urea,

  Salicylanilide, 5-chlorosalicylanilide, salicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, 4- [2 ′-(4-methoxyphenoxy) ethyloxy] salicylic acid, 3- (octyloxycarbonylamino) salicylic acid or metal salts of these salicylic acid derivatives,

  N- (4-hydroxyphenyl) -4-toluenesulfonamide, N- (2-hydroxyphenyl) -4-toluenesulfonamide, N-phenyl-4-hydroxybenzenesulfonamide and the like.

  As the binder for the heat-sensitive recording layer, when the dispersion medium is an organic solvent, polyvinyl butyral, polyvinyl acetoacetal, cellulose acetate resin, polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, polybutyl acrylate Polystyrene, acrylic acid ester / styrene copolymer, polyester resin, poly α-methylstyrene, ABS resin, coumarone resin, nitrocellulose, ethylene / vinyl acetate copolymer and the like are preferably used. As will be described later, it is preferable to use an organic solvent as the dispersion medium because better transparency is obtained than when water is used.

  Examples of the binder when the dispersion medium is water include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, fully saponified or partially saponified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, and diacetone acrylamide-modified polyvinyl. Alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / acrylic acid copolymer, styrene / acrylic Water-soluble adhesives such as alkali salts of acid copolymers, styrene / butadiene latex, acrylic latex, urethane Latex such as latex and the like.

  The use ratio of the binder is preferably 10 to 45% by mass with respect to the heat-sensitive recording layer. Within this range, the color image has a high density and high sensitivity as required, and the strength and transparency of the layer are maintained.

  A method for forming a heat-sensitive recording layer in the present invention will be described. When an organic solvent or water is used and a coating solution is prepared by mixing a leuco dye dispersion (or solution), a developer dispersion, or a dispersion (or emulsion or solution) of other components, and then applied to a support. Especially good. Examples of the organic solvent 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-dioxolane, acetone, methyl ethyl ketone (hereinafter, MEK), ketones such as 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 these, toluene, MEK, methyl isobutyl ketone, ethyl acetate, and butyl acetate are preferable. In particular, a solvent selected from toluene, methyl isobutyl ketone, and ethyl acetate is contained in 50% by weight or more of the solvent components in the organic solvent-based coating solution. When the mixed solvent is used, a heat-sensitive sheet excellent in background fog is obtained.

  Specific examples of the support used in the present invention include tracing paper, fine paper, neutral paper, acid paper, recycled paper, coated paper, polyolefin resin laminated paper, synthetic paper, cellulose derivative films such as cellulose triacetate, Examples thereof include polyolefin films such as polypropylene and polyethylene, polystyrene films, and films obtained by laminating them. Polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are preferable, but not limited thereto. Among these, in order to obtain a highly transparent sheet, 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 the case of a paper-based support, a transparent support is obtained by impregnation with an oil and fat component. Further, in order to improve the adhesion of the coating layer of the thermal recording layer coating solution, at least one surface can be surface-modified by corona discharge treatment, oxidation reaction treatment (chromic acid, etc.), etching treatment, or the like.

  Specific examples of the leuco dye, the developer, the binder (binder resin), the solvent to be used, and the like, which are the main components of the heat-sensitive recording material of the present invention, have been given above, but are not limited thereto. Also, if necessary, known dispersants, fillers, pigments, surfactants, lubricants, antistatic agents, antioxidants, ultraviolet absorbers, infrared absorbers, blue colored pigments, fluorescent whitening agents, heat A fusible substance or the like can be contained in the heat-sensitive recording layer.

  The heat-sensitive recording layer of the present invention is produced by uniformly dispersing or dissolving a leuco dye and a developer together with a binder resin, and applying and drying the mixture on a support. The coating method is a die fountain method, a curtain coating method. , Wire bar method, gravure method, air knife method, blade coater method and the like are not particularly limited. Among these, a die fountain method or a curtain coating method that can be applied without contacting the support is preferred as a coating layer that can achieve uniformity. In the recording layer liquid, the particle size of the dispersion is greatly related to the transparency of the entire recording material, the surface roughness of the protective layer, and thus the dot reproducibility during printing. When the thickness is 0.5 μm or less, the transparency is remarkably improved. The film thickness of the recording layer is about 1 to 50 μm, preferably about 3 to 20 μm, depending 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 as necessary for the purpose of improving the coating property 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 to the thermal head. The protective layer provided on the heat-sensitive recording layer is ideally a resin-only layer from the viewpoint of transparency, but the protective layer made of resin alone is too smooth, and printing by sticking or dust dragging. It is difficult to obtain sufficient performance in terms of defects. 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 tends to be reduced and dust tends to be dragged. 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 of the resin alone may cause alteration 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 for improving the performance against sticking, dust dragging, etc., a filler is generally contained. However, in the case of a transparent thermosensitive recording material, if the protective layer contains a filler as used in a conventional reflective recording material, the transparency often decreases. 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 roughening the surface by adding a small amount of a large particle size filler. In the present invention, the protective layer can be formed by combining the above two methods as necessary. The coefficient of friction on the surface of the protective layer is in the range of 0.07 to 0.14 in terms of both head matching (in the direction of increasing the slipperiness) and prevention of dragging of dust that tends to occur in the plastic film (in the direction of decreasing the slipperiness). preferable.

  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 addition to a water-soluble resin, and these can be used together as necessary. is there. From the viewpoint of transparency, it is preferable to use a material in which the refractive index of the recording layer and the protective layer is in the range of 0.8 to 1.2 in terms of the ratio 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, polyacrylamide resin, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetal, cellulose acetate resin, and copolymers thereof. Moreover, a crosslinking agent can be used with resin, and conventionally well-known compounds, such as an isocyanate compound and an epoxy compound, can be used as this crosslinking agent. Specific examples of the isocyanate compound include toluylene diisocyanate, its dimer, diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate, hexamethylene diisocyanate, polyisocyanate, and derivatives thereof having two or more isocyanate groups in the molecule. It is done. Specific examples of the epoxy compound include ethylene glycol diglycidyl ether, butyl glycidyl ether, polyethylene glycol diglycidyl ether, and epoxy acrylate.

  Examples of fillers include phosphate fiber, potassium titanate, acicular magnesium hydroxide, whiskers, talc, mica, glass flakes, calcium carbonate, plate calcium carbonate, aluminum hydroxide, plate aluminum hydroxide, silica, clay , Inorganic fillers such as calcined clay, kaolin and hydrotalcite, crosslinked polystyrene resin particles, urea-formalin copolymer particles, silicone resin particles, crosslinked polymethyl methacrylate resin particles, guanamine-formaldehyde copolymer particles, melamine -Organic fillers of formaldehyde copolymer particles. In the present invention, from the viewpoint of head wear, the organic filler is preferably melamine-formaldehyde copolymer particles, and the inorganic filler is preferably kaolin, talc, or aluminum hydroxide. However, the present invention is not limited to this, and a plurality of fillers may be used at the same time in order to impart various characteristics.

  In order to further improve head matching, friction coefficient is added by adding wax and oil to the protective layer, mixing and modifying the resin modified with silicone as the resin, adjusting the ratio of resin and filler, etc. Can be adjusted. The waxes that can be used here include stearic acid amide, palmitic acid amide, oleic acid amide, lauric acid amide, ethylene bisstearyl amide, methylene bisstearyl amide, methylol stearyl amide, paraffin wax, polyethylene, carnauba wax, Examples thereof include oxidized paraffin and zinc stearate. As the oil, general silicone oil or the like can be used. The wax used in the heat-sensitive recording layer of the present invention may be added to the protective layer.

  The solvent that can be used in the protective layer coating solution of the present invention is not particularly limited. For example, water and organic solvents suitable for the recording layer coating solution described above are used alone or as a mixed solvent. Among these, when a solvent having a particularly high dissolving ability is used, the leuco dye is eluted from the recording layer when the protective layer solution is applied, so that the dye content in the recording layer is lowered and an adverse effect on storage stability is observed. When a solvent having a low solubility is used, low molecules do not diffuse into the protective layer, so that the strength of the protective layer is not reduced, and the background fogging after the recording layer is applied can be reduced only with the solvent. Moreover, when a high boiling point solvent is used, the solvent tends to remain in the layer, which is also not preferable for storage stability. Therefore, it is particularly preferable to use a protective layer coating solution containing ethyl acetate as a main component (70% by weight or more) from the viewpoint that the solubility of the leuco dye is low and the boiling point is low.

  There is no restriction | limiting in particular in the coating method of a protective layer coating liquid, It can apply by a conventionally well-known method. The preferred protective layer thickness is 0.1 to 20 μm, more preferably 0.5 to 10 μm. If the protective layer thickness is too thin, the recording material's storability and the function as a protective layer such as head matching will be insufficient, and if it is too thick, the thermal sensitivity of the recording material will decrease, and it will be disadvantageous in terms of cost. is there.

  In the present invention, the heat-sensitive recording layer and the protective layer are formed by applying the coating liquid of each layer, and subsequently transporting to a drying box and drying. The temperature of the gas used for this drying is preferably 80 ° C. or higher. . Even if the drying temperature is less than 80 ° C., a coating film is formed, but immediately after the drying process is completed, the solvent used in the coating solution is not sufficiently removed, and the storage stability is affected. Further, in order to stabilize the performance of the product, curing is often performed for several days to several weeks in an environment of 30 to 60 ° C. However, there is a concern about blocking in this process, and the curing is performed. Since time is extended, it is not preferable in production management. The higher the drying temperature, the better. However, if the temperature is too high, it will cause unevenness of the coating film and affect the quality of the background fog and the like. Since the background fog is reduced to a certain level by applying the protective layer, the particularly preferable drying temperature range is 80 to 150 ° C. Below this upper limit temperature, the heat-sensitive recording layer does not cause melting or color development of various components due to the heat of evaporation of the organic solvent or water.

  The cloudiness defined by JIS K7105 of the non-image part of the heat-sensitive recording material of the present invention 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 shaw casten is attached is lacking.

In the present invention, an intermediate layer such as a pigment, a binder, or a heat-fusible layer may be used as necessary between the support and the heat-sensitive recording layer and between the protective layer and the heat-sensitive recording layer, for example, to improve adhesion and smoothness. A layer containing a substance or the like can be provided. When synthetic paper or 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 very high. In addition, transportability may be reduced due to static electricity. On the other hand, it is preferable to carry out antistatic by providing a back layer having antistatic ability by containing an antistatic material. Examples of the antistatic material include known materials such as an electron conduction type and an ion conduction type, and the surface resistance value is preferably 1 × 10 ¹⁰ ohm / m ² or less, which is effective against dust adhesion. Further, in the heat-sensitive recording material of the present invention, it is possible to provide a back layer for curl adjustment, transportability adjustment, and a back layer containing a matting agent in a silver salt film-like, and this is also 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 preferably about 0.3 to 10 μm, and the thickness of the back layer is preferably in the range of 0.1 to 10 μm.

  The heat-sensitive recording material of the present invention is supplied in the form of a flat plate or roll to a printer for medical use. In the case of a flat plate, the total thickness of the heat-sensitive recording material is 170 to 250 μm so as to be equivalent to a silver salt film. It is preferable that 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 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 preferably 190 to 250 mgf.

  The recording method of the thermal recording material of the present invention is not particularly limited depending on the purpose of the specification, such as a thermal pen, thermal head, laser heating, etc., but this thermal recording material is used for printing a high-definition and high-gradation image such as a medical diagnostic image. Recording is most preferably performed using a thermal head from the viewpoint of the cost of the apparatus, the output speed, and compactness. However, laser heating is suitable for obtaining a fine image, and may be preferable if there is a request for a particularly fine image.

  Hereinafter, the present invention will be described specifically by way of examples. In the following, parts and% are based on mass.

<Adjustment of recording layer coating solution [B solution]>
First, according to the coating solution table below, the composition was heated in an autoclave to a melting point or higher of the wax used to form an emulsion or solution, and then cooled while continuing stirring to prepare a wax solution.
[Wax liquid]
Wax 10 parts 15% binder resin solution (solvent: MEK / toluene = 5/5) 20 parts MEK 25 parts Toluene 40 parts Next, the composition is pulverized and dispersed by a ball mill according to the following coating solution table, and the developer is dispersed. Liquid [A liquid] was prepared.
[Liquid A]
Developer 15 parts 15% binder resin solution (solvent: MEK / toluene = 5/5) 20 parts MEK 25 parts Toluene 40 parts Furthermore, each component is mixed according to the coating liquid table, and the recording layer coating liquid [B liquid] is obtained. Produced.
[Liquid B]
Wax liquid 10 parts [A liquid] 40 parts Leuco dye 6 parts 15% binder resin solution (solvent: MEK / toluene = 5/5) 48 parts Toluene 6 parts

(Coating solution table)
Coating liquid Developer Volume average particle diameter μm Binder resin Recording layer coating liquid 1 A 0.30 a
Recording layer coating solution 2 B 0.30 b
Recording layer coating solution 3 A 0.30 a
Recording layer coating solution 4 B 0.30 b
Recording layer coating solution 5 A 0.30 a
Recording layer coating solution 6 B 0.30 b
Recording layer coating solution 7 A 0.30 a
Recording layer coating solution 8 B 0.30 b
Recording layer coating solution 9 A 0.30 a
Recording layer coating solution 10 B 0.30 b
Recording layer coating solution 11 A 0.30 a
Recording layer coating solution 12 B 0.30 b
Recording layer coating solution 13 A 0.30 a
Recording layer coating solution 14 B 0.30 b
Recording layer coating solution 15 A 0.30 a
Recording layer coating solution 16 B 0.30 b

The components in the recording layer coating solution in the coating solution table are as follows. The recording layer coating solution 15-16 is for comparison.
(wax)
Coating liquid Wax used Recording layer coating liquid 1 Microcrystalline wax Recording layer coating liquid 2 Carnauba wax Recording layer coating liquid 3 Ceresin Recording layer coating liquid 4 Fischer-Tropsch wax Recording layer coating liquid 5 Polyethylene wax Recording layer coating liquid 6 Wood wax Recording layer Coating solution 7 Beeswax Recording layer coating solution 8 Whale wax Recording layer coating solution 9 Ibotaro Recording layer coating solution 10 Wool wax Recording layer coating solution 11 Shellac wax Recording layer coating solution 12 Candelilla wax Recording layer coating solution 13 Petrolatum Recording layer coating solution 14 Polyester wax Recording layer coating solution 15 Stearamide (not equivalent to the wax of the present invention)
Recording layer coating solution 16 Stearyl urea (not equivalent to the wax of the present invention)
(Developer)
A: Zinc 4- (n-octyloxycarbonylamino) salicylate B: Zinc 3- (n-octyloxycarbonylamino) salicylate (leuco dye) (the following mixture)
2-anilino-3-methyl-6- (N-ethyl-Np-toluidino) fluorane
65 parts 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide 5 parts 1,3-dimethyl-6-diethylaminofluorane 15 parts 3,3-bis (4-diethylamino-2) -Ethoxyphenyl) -4-azaphthalide
15 parts (binder resin)
a: Polyvinyl butyral resin b: Polyvinyl acetal resin

<Adjustment of protective layer coating solution [D solution]>
First, the following composition was pulverized and dispersed with a ball mill to a volume average particle size of 0.30 μm to prepare a filler dispersion [liquid C].
[C liquid]
Colloidal silica 15 parts 10% polyvinyl acetal solution (Sekisui Chemical Co., Ltd. ESREC KS-1, solvent: MEK) 15 parts MEK 70 parts Furthermore, the following composition is sufficiently stirred to prepare a protective layer coating liquid [D liquid] did.
[Liquid D]
[Liquid C] 10 parts 10% polyvinyl acetal solution (Sekisui Chemical Co., Ltd. ESREC KS-1, solvent: MEK) 10 parts MEK 12 parts

<Preparation of thermal recording sheet>
The recording layer coating solution [B solution] and the protective layer coating solution [D solution] prepared as described above were sequentially applied onto a transparent polyester film (having a haze of 3%) having a thickness of 175 μm using a wire bar. The film was sufficiently dried at a drying temperature of 85 ° C. to form a heat-sensitive recording layer and a protective layer. The recording layer thickness was 17 μm, and the protective layer was 4 μm thick. The one using the recording layer coating solution 1-14 is the thermosensitive recording material of Example 1-14, and the one using the recording layer coating solutions 15 and 16 is the thermosensitive recording material of Comparative Examples 1 and 2, respectively.

Evaluation methods and measurement methods are as follows. A gray scale was printed on the thermal recording sheet prepared as described above using a thermal printer UP-70XR manufactured by Sony Corporation. Among these, an image with a transmission density of about 0.7 was used for the storage stability test.
The transmission density was measured using a transmission densitometer TD-904 (black) manufactured by Gretag Macbeth.
The storage stability test was 60 ° C. and 90% r. h. The sample was left in a high-temperature and high-humidity storage set for 48 hours for 48 hours. Concentration preservability was calculated using the formula shown below. If the amount of change is within 30%, the image can withstand practical use, and if it is within 15%, it is difficult to identify a change in image density.
Preservability (%) = (Concentration after storage ÷ Concentration before storage) × 100
The haze of the non-image area was measured with a direct reading haze computer HGM-2DP manufactured by Suga Test Instruments.
The particle size was measured with a laser diffraction particle size analyzer LA-700 manufactured by Horiba.
The evaluation results are shown below.

(Evaluation results)
Color density Conservation% Background density Cloudiness%
Example 1 4.40 91 0.08 48
Example 2 4.38 92 0.09 42
Example 3 4.36 90 0.11 55
Example 4 4.37 89 0.10 49
Example 5 4.39 93 0.09 51
Example 6 4.38 89 0.10 45
Example 7 4.39 92 0.11 49
Example 8 4.40 91 0.12 50
Example 9 4.39 91 0.10 53
Example 10 4.37 92 0.09 47
Example 11 4.36 89 0.10 46
Example 12 4.39 91 0.08 52
Example 13 4.40 90 0.10 51
Example 14 4.39 90 0.11 48
Comparative Example 1 4.12 79 0.19 31
Comparative Example 2 4.18 78 0.18 30

  The heat-sensitive recording material of the present invention has a high concentration and high storage stability for medical image formation, video printer, OHP, second original drawing, etc. on the premise that the recording material is transparent or translucent. Benefits are utilized.

Claims (3)

  A heat-sensitive recording material comprising a heat-sensitive recording layer comprising, as a main component, a colorless or light-colored leuco dye, a developer that heat-colors the leuco dye, and a binder resin as a binder on a transparent support. A heat-sensitive recording material comprising a recording layer containing wax. The heat-sensitive recording material according to claim 1, wherein the wax is one or more of the following.
Microcrystalline wax, carnauba wax, ceresin, Fischer-Tropsch wax, polyethylene wax, wood wax, beeswax, whale wax, ibota wax, wool wax, shellac wax, candelilla wax, petrolatum, polyester wax.   The heat-sensitive recording material according to claim 1, wherein the support is a transparent polyethylene terephthalate film.