JP2007076251A - Thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording medium using a plastic support which has excellent performance (permeation density of a non-printing part, transparency and scuff resistance), without any problems such as the double feed of a film during its carry-out and damage to a thermal resistor of a thermal head caused by electric charge or a print defect by dust deposition on a film surface. <P>SOLUTION: This thermal recording medium has a thermal recording layer composed mainly of at least a colorless or pale-color leuco dye, a developer which makes the leuco dye develop a color by heat and a binder resin as a binding agent formed on a plastic support and a protecting layer containing a resin formed on the thermal recording layer. In addition, a back layer containing resin is formed on a support on the opposite side to the thermal recording layer. Further, an antistatic agent composed of polyalkylene glycol and lithium perchlorate are added to the thermal recording medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording medium using a color developing reaction between an electron-donating color-forming compound and an electron-accepting compound, and relates to a heat-sensitive recording medium with less charging during printing and less trouble with conveyance and dust adhesion to a printing screen. .

  Various recording media have been proposed that utilize a coloring reaction between a colorless or light-colored leuco dye and a developer that develops color when contacted by heat and pressure. One heat-sensitive recording medium does not require complicated processing such as development and fixing, and can be recorded in a short time with a relatively simple device, has less noise, and has a lower cost. It is useful as various recording media such as electronic computers, facsimiles, ticket vending machines, label printers, and recorders.

  These heat-sensitive recording media are generally produced by applying the above-mentioned color-forming dye and developer on paper. In recent years, mainly in the medical field, a waste film processing problem caused by a wet process of silver salt X-ray film and the digitization of images have required a dry film system that can be easily output. There is a thermal recording process using a thermal recording medium as a system that meets such requirements, and the thermal recording medium used for such applications is required to have rigidity and transparency comparable to conventional silver salt X-ray films. The above-described color-forming dye and developer are coated on a plastic support instead of paper.

  Thermal recording media using such a plastic support are more easily charged during printing than when paper is used as a support. There were problems such as damage to the heating resistor, and dust and dust adhering to the film surface, causing printing defects. Also, when a highly smooth support such as a plastic film is used, the coated surface becomes smooth, and such dust and dust are sandwiched between the thermal recording medium and the thermal head during printing, There is a problem that a phenomenon in which an image is striped in the vicinity (hereinafter referred to as white streaks) easily occurs. In order to solve these problems, a heat-sensitive recording medium has been proposed in which an antistatic agent is contained in the recording surface or the opposite surface (hereinafter referred to as a back layer).

A method of containing an electron conductive metal oxide or a composite oxide thereof in the coating layer (for example, see Patent Documents 1 and 2), or a method of containing an ion conductive cationic polymer in the coating layer (for example, , Patent Documents 3 and 4), a method of containing a normal paraffin sulfonate (see, for example, Patent Document 5) and the like have been proposed, but the antistatic agent is colored and the film is colored or the film is transparent. Thermal recording medium using plastic support, such as reducing the properties, promoting the color development reaction between the leuco dye and the developer to cause background fogging, and insufficient antistatic effect under low humidity environment There are still problems to adapt to.
JP-A-01-222989 JP 2005-035030 A JP 2000-263935 A JP 2002-21868 A JP 2002-326460 A

  Therefore, the present invention has been made in view of the above, and there are no problems such as damage to the heating resistor of the double feed or thermal head during film unloading due to charging, and dust or dust adhering to the film surface to cause a printing defect. Another object of the present invention is to provide a heat-sensitive recording medium using a plastic support, which is excellent in the performance of the heat-sensitive recording medium (transmission density of non-printed portion, transparency, scratch resistance).

  As a result of diligent studies to solve the above-mentioned problems, at least a colorless or light-colored leuco dye on a plastic support, and a heat-sensitive material mainly composed of a developer that heat-colors the leuco dye and a binder resin as a binder. A heat-sensitive recording medium comprising a recording layer, a protective layer containing a resin thereon, and a back layer containing the resin on a support opposite to the heat-sensitive recording layer, and a polyalkylene glycol and lithium perchlorate The present invention has been completed by finding that the above problems can be solved by containing an antistatic agent comprising: In particular, in the present invention, there are no problems such as damage to the heating resistor of the double feed or thermal head during film unloading due to charging, and dust or dust adhering to the film surface, causing print defects, and appearance performance and color development of the thermal recording medium. A thermal recording medium with excellent performance can be obtained.

  The configuration of the present invention is as follows.

  That is, the invention according to claim 1 is a heat-sensitive recording layer comprising, as a main component, at least a colorless or light leuco dye on a plastic support, a color developer that heat-colors the leuco dye, and a binder resin as a binder. Further, in the thermal recording medium further comprising a protective layer containing a resin on the thermal recording layer, and further having a back layer containing the resin on a support opposite to the thermal recording layer, a polyalkylene glycol and perchloric acid A heat-sensitive recording medium comprising an antistatic agent comprising a lithium salt.

  The invention according to claim 2 is the heat sensitive sensor according to claim 1, wherein an antistatic agent comprising the polyalkylene glycol and lithium perchlorate is contained in a protective layer and / or a back layer. It is a recording medium.

  The invention according to claim 3 is the heat-sensitive recording medium according to claim 1 or 2, wherein the polyalkylene glycol has a molecular weight of 1000 to 2000 and is a copolymer of ethylene glycol and propylene glycol. It is.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the protective layer and / or the back layer contains an antistatic agent comprising polyalkylene glycol and lithium perchlorate. In addition, the recording medium further comprises a crosslinking agent for crosslinking the polyalkylene glycol.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the content of the antistatic agent in the protective layer is 5% by weight with respect to the resin in the protective layer. The heat-sensitive recording medium is characterized in that the content of the antistatic agent in the back layer is 5% by weight or more of the total weight of the back layer.

  The invention according to claim 6 is the heat-sensitive recording medium according to claim 4, wherein the crosslinking agent is an isocyanate compound.

  The invention according to claim 7 is the invention according to any one of claims 4 to 6, wherein the content of the crosslinking agent in the protective layer is 10 with respect to the antistatic agent and the resin in the protective layer. A heat-sensitive recording medium, wherein the content of the crosslinking agent in the back layer is from 10% to 100% by weight with respect to the antistatic agent in the back layer. is there.

  The invention according to claim 8 is the heat-sensitive recording medium according to any one of claims 1 to 7, wherein the particle size of the recording layer dispersion is 1.0 μm or less. .

  The invention according to claim 9 is the heat-sensitive recording medium according to any one of claims 1 to 8, wherein the protective layer has a thickness of 0.1 to 20 μm.

  The invention according to claim 10 is the thermal recording medium according to any one of claims 1 to 9, wherein the resin of the back layer is an acrylic resin having a Tg of 90 to 150 ° C. It is.

  The invention according to an eleventh aspect is the invention according to any one of the first to tenth aspects, wherein the plastic support is a transparent polyester film having a thickness of 5 μm to 250 μm, and the haze degree according to JIS K7105 of the thermal recording medium is high. The heat-sensitive recording medium is characterized by being 30% or less.

  According to a twelfth aspect of the present invention, in the invention according to any one of the first to eleventh aspects, the thermal recording is performed by printing using a heating means including a thermal pen, a thermal head, and laser heating. It is a medium.

  According to the present invention, by containing an antistatic agent composed of polyalkylene glycol and lithium perchlorate, when the film is unloaded due to charging, the heating resistor of the double feed or thermal head is damaged, and dust and dust adhere to the film surface. There is no problem such as causing printing defects, and it is possible to obtain a thermal recording medium excellent in appearance performance and color development performance of the thermal recording medium.

  In addition, it contains an antistatic agent composed of polyalkylene glycol and lithium perchlorate and a cross-linking agent that crosslinks polyalkylene glycol, so that the antistatic effect over time, film scratch resistance, thermal head, etc. And a thermal recording medium excellent in matching performance can be obtained.

  Further, a transparent polyester film can be applied to the plastic support of the heat-sensitive recording medium of the present invention, and a heat-sensitive recording medium having a haze degree of 30% or less can be provided.

  Hereinafter, embodiments of the thermal recording medium of the present invention will be described.

  Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims of the present invention.

  The heat-sensitive recording medium of the present invention comprises at least a colorless or light-colored leuco dye on a plastic support, a color developing agent that heat-colors the leuco dye, and a binder resin as a binder as a main component, and A protective layer containing a resin is provided thereon, and a back layer containing a resin is provided on the support opposite to the thermosensitive recording layer.

  The plastic support is a polyester film such as polyethylene terephthalate or polybutylene terephthalate, a cellulose derivative film such as cellulose triacetate, a polyolefin film such as polypropylene or polyethylene, a polystyrene film, or a film obtained by bonding these. When used as a transparent heat-sensitive recording medium, the transparency of the support also affects the transparency of the entire sheet. Therefore, in the present invention, the support has a haze of 10% or less, preferably 5% or less. It is preferable to use the support. The thickness of the support is preferably 5 μm to 250 μm for thermal recording applications although it varies depending on the application.

  In addition to the leuco dye, developer, and binder resin as main components, the heat-sensitive recording layer may be added with an antistatic agent comprising polyalkylene glycol and lithium perchlorate as an antistatic agent, if necessary. Fillers, pigments, surfactants, heat fusible substances can be added.

  The amount of addition of the antistatic agent comprising polyalkylene glycol and lithium perchlorate is preferably 10 to 50% by weight with respect to the total weight of the thermosensitive recording layer.

  The leuco dye used in the heat-sensitive recording layer of the present invention is a compound exhibiting electron donating properties, and is applied alone or in combination of two or more, but is itself a colorless or light dye precursor, and is not particularly limited. Conventionally known ones such as triphenylmethane phthalide, triallyl methane, fluorane, phenothiocyan, thioferolane, xanthene, indophthalyl, spiropyran, azaphthalide, chromenopyrazole, methine, Preferred are leuco compounds such as rhodamine anilinolactam, 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.

2-anilino-3-methyl-6-diethylaminofluorane,
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-p-toluidino) fluorane,
2-anilino-3-methyl-6- (N-methyl-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,
3- [1,1-bis (4-diethylaminophenyl) ethylene-2-yl] -6-dimethylaminophthalide and the like.

  The developer used in the heat-sensitive recording layer of the present invention is an electron-accepting compound, and various conventionally known electron-accepting developers can be used. The stability of the color image can be obtained by using a developer as in 63-95979.

  Specific examples of the developer are shown below.

  A salicylic acid derivative having an amino group

式中、Ｒは置換アミノ基を、Ｘは水素原子、アルキル基、フェニル基、アルコキシ基またはハロゲン原子を、Ｍは水素原子又はｎ価の金属原子を表わし、ｎは整数を表わす。

In the formula, R represents a substituted amino group, X represents a hydrogen atom, alkyl group, phenyl group, alkoxy group or halogen atom, M represents a hydrogen atom or an n-valent metal atom, and n represents an integer.

  Among the substituted amino groups represented by R, an acylamino group having 2 to 18 carbon atoms, an arylsulfonylamino group, an alkylaminocarbonylamino group, an arylaminocarbonylamino group, a dialkylamino group, and an alkylarylamino group are preferable. Among the substituents represented by X, a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a phenyl group, a chlorine atom and a fluorine atom are preferable, and among the groups represented by M Hydrogen atom, zinc, aluminum, magnesium and calcium are preferred.

  Specific examples of the salicylic acid derivative include, for example, 4-myristoylaminosalicylic acid, 4-decanoylaminosalicylic acid, 4-phenylacetylaminosalicylic acid, 4-phenoxyacetylaminosalicylic acid, 4-benzoylaminosalicylic acid, 4-toluoylaminosalicylic acid, 4 -N-stearylcarbamoylaminosalicylic acid, 4-N-phenylcarbamoylaminosalicylic acid, 4-P-toluenesulfonylaminosalicylic acid, 4-dibenzylaminosalicylic acid, 5-myristoylaminosalicylic acid, 4-phenylacetylaminosalicylic acid, 4- There are benzoylaminosalicylic acid and metal salts thereof, and these are used alone or in combination.

  Further, a salicylic acid derivative according to the present invention may be used in combination with a well-known electron-accepting compound such as a salicylic acid derivative, a phenyl derivative, a phenyl resin, or acid clay. These include, for example, 4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide-α-naphthol, β-naphthol, hexyl-4-hydroxybenzoate, 2,2′-dihydroxybiphenyl, 2,2-bis ( 4-hydroxyphenyl) propane (bisphenol A), 4,4′-isopropylidenebis (2-methylphenol), 1,1′-bis- (3-chloro-4-hydroxyphenyl) cyclohexane, 1,1′-bis (3-Chloro-4-hydroxyphenyl) -2-ethylbutane, 4,4′-sec-isooctylidenediphenol, 4-tert-octylphenol, 4,4′-sec-butylidenediphenol, 4-p-methyl Phenylphenol, 4,4'-isopentylidenephenol 4,4′-methylcyclohexylidenediphenol, 4,4′-dihydroxydiphenyl sulfide, 1,4-bis (4′-hydroxycumyl) benzene, 1,3-bis (4′-hydroxycumyl) benzene, 4,4′-thiobis (6-tert-butyl-3-methylphenol, 4,4′-dihydroxydiphenylsulfone, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, polyvinylbenzyloxycarbonylphenol, 2,4,4'-trihydroxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, 4-hydroxyphthalic acid, methyl dimethyl-4-hydroxybenzoate, 2,4,4'-trihydroxydiphenyl Sulfone, 1,5-bis -P-hydroxyphenylpentane, 1,6-bis-p-hydroxyphenoxyhexane, tolyl 4-hydroxybenzoate, α-phenylbenzyl ester of 4-hydroxybenzoic acid, phenylpropyl 4-hydroxybenzoate, 4-hydroxybenzoic acid Phenethyl, 4-hydroxybenzoic acid-p-chlorobenzyl, 4-hydroxybenzoic acid-p-methoxybenzyl, 4-hydroxybenzoic acid benzyl ester, 4-hydroxybenzoic acid-m-chlorobenzyl ester, 4-hydroxybenzoic acid- β-phenethyl ester, 4-hydroxy2 ′, 4′-dimethyldiphenylsulfone β-phenethylorcerineate, cinnamyl orthoserinete, orthelic acid-o-chlorophenoxyethyl ester, o-ethylphenoxyethylorceline O-phenylphenoxyethylorcerinate, m-phenylphenoxyethylorselinate, 2,4-dihydroxybenzoic acid-β-3′-tert-butyl-4′-hydroxyphenoxyethyl ester, 4-N-benzylsulfate Famoylphenol, 2,4-dihydroxybenzoic acid-β-phenoxydiethyl ester, 2,4-dihydroxy-6-methylbenzoic acid benzyl ester, methyl bis-4-hydroxyphenylacetate, ditrideurea, 4,4′-diacetyldiphenyl Thiourea, 3-phenylsalicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3-methyl-5-benzylsalicylic acid, 2-phenyl-5- (α, α-dimethylbenzyl) salicylic acid, 3,5 -Di- (α-methylben I) Salicylic acid, 5-tert-octylsalicylic acid, 3-chloro-5-cumylsalicylic acid, 3-methyl-5-tert-octylsalicylic acid, 3-methyl-5-α-methylbenzylsalicylic acid, 3-methyl-5- Cumylsalicylic acid, 3,5-di-tert-aminosalicylic acid, 3-phenyl-5-benzylsalicylic acid, 3-phenyl-5-tert-octylsalicylic acid, 3-phenyl-5-α-methylbenzylsalicylic acid, 3, 5 -Di-tert-octylsalicylic acid, 3,5-bis (α-methylbenzyl) salicylic acid, 3,5-dicumylsalicylic acid, α-methyl-5- (α-methylbenzyl) salicylic acid, 4-methyl-5-cumyl Salicylic acid, 3- (α-methylbenzyl) -6-methylsalicylic acid, 3- (α-methylbenzyl) -6-pheny Rusalicylic acid, 3-triphenylmethylsalicylic acid, 3-diphenylmethylsalicylic acid, 4-n-dodecylsalicylic acid, 4-tert-dodecylsalicylic acid, 4-n-pentadecylsalicylic acid, 4-n-heptadecylsalicylic acid, 5- (1 , 3-diphenylbutyl) salicylic acid, 5-n-octadecylsalicylic acid, 5-dodecylsulfonylsalicylic acid, 5-dodecylsulfosalicylic acid, 3-methyl-5-dodecylsulfosalicylic acid, and the like.

  In the present invention, the developer is not limited to the above-mentioned compounds, and other various electron-accepting compounds can be used. In the heat-sensitive recording medium of the present invention, the developer is used in an amount of 1 to 20 parts, preferably 2 to 10 parts, relative to 1 part of the color former. The developer can be applied alone or in combination of two or more, and the color former can be applied alone or in combination of two or more.

  Various known resins can be used as the binder resin used in the heat-sensitive recording layer of the present invention. For example, polyethylene, polyvinyl acetate, polyacrylamide, maleic acid copolymer, polyacrylic acid and its ester, polymethacrylic acid and Such esters, 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. The resins can be used alone or in admixture of two or more.

  In order to form the recording layer in the 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, 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 referred to as 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 preferred.

  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, and applying and drying the mixture on a support. The coating method is a die fountain method, a wire bar method. The gravure method, the air knife method, etc. are not particularly limited. Among these, a die system that can be applied without contacting the support is preferred as the one that can obtain the uniformity of the coating layer. In the recording layer liquid, the particle size of the dispersion is greatly related to the transparency of the entire recording medium, the surface roughness of the protective layer, and thus the dot reproducibility during printing. When the thickness is less than 0.5 μm, the transparency is remarkably improved. The film thickness of the recording layer is about 1 to 50 μm, preferably about 3 to 20 μm, although it depends on the composition of the recording layer and the application of the thermal recording medium. 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 addition to the antistatic function as described above, the protective layer is provided on the thermosensitive coloring layer to improve chemical resistance, water resistance, friction resistance, light resistance, and head matching to the thermal head. In addition to containing an antistatic agent consisting of polyalkylene glycol and lithium perchlorate, which is a feature of the present invention, a resin, filler, lubricant (wax, oil), if necessary, adding a crosslinking agent, a surfactant, etc. Can do.

  The addition amount of the antistatic agent comprising polyalkylene glycol and lithium perchlorate to the protective layer is preferably 5 to 100% by weight based on the resin in the protective layer. If it is less than 5%, the antistatic effect is low, and if it exceeds 100% by weight, the head and the film tend to adhere to each other when printing with a thermal head, and the print sound increases or normal printing is hindered. Sometimes.

  The antistatic agent comprising polyalkylene glycol and lithium perchlorate used in the present invention is an ion dissociation of lithium perchlorate in polyalkylene glycol, and these dissociated ions move by molecular vibration of polyalkylene glycol. It is in a state that is easy to do, and expresses ionic conductivity. Therefore, the dependence of the antistatic ability on humidity is small compared to a substance that dissociates in the presence of water and exhibits ionic conductivity, such as an ordinary ion conductive antistatic agent.

  In addition, the antistatic agent is composed of lithium perchlorate dissolved in the polymer, so it is colorless and transparent, and when it is contained in the protective layer of the thermal recording medium, it hides the color image and lowers the image density. And the surface property of the film is not uneven, and the color developability is not deteriorated. Further, when applied to a transparent heat-sensitive recording medium, the transparency is hardly lowered. Therefore, the thermosensitive recording medium of the present invention using such an antistatic agent can be effectively used as a thermosensitive recording medium using a plastic support without impairing the performance of the thermosensitive recording medium.

  As the polyalkylene glycol which is a constituent of the antistatic agent used in the present invention, polyethylene glycol and polypropylene glycol are suitable, and these copolymers are particularly preferred, but are not particularly limited thereto. The molecular weight is not particularly limited, but about 1000 to 2000 is suitable.

  Specific 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-formaldehyde Examples thereof include organic fillers of 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.

  As the resin used for the protective layer, in addition to the water-soluble resin, an aqueous emulsion, a hydrophobic resin, an ultraviolet ray, an electron beam curable resin, and the like can be used in combination as necessary, as with the recording layer. 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. And polyether resins, polyamide resins, polycarbonate resins, polyethylene resins, polypropylene resins, polyacrylamide resins, and the like.

  For the purpose of improving the scratch resistance of the added layer, it is effective to use a crosslinking agent for crosslinking the hydroxyl group at the terminal of the polyalkylene glycol together with the antistatic agent and the resin. As the crosslinking agent, conventionally known compounds such as isocyanate compounds, epoxy compounds, and aldehydes can be used. Of these, isocyanate compounds are particularly preferred. Specific examples of isocyanate compounds include, for example, tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, water-added diphenylmethane diisocyanate, water-added xylylene diisocyanate, Examples include tetramethyl-m-xylidene diisocyanate, norbornane diisocyanate, and derivatives thereof, and compounds having two or more isocyanate groups in the molecule. Examples of the isocyanate derivative include adduct type, burette type, isocyanurate type, dimer type, allophanate type, uretdione type, prepolymer type, and the like with trimethylolpropane. In order to prevent the viscosity of the coating liquid from increasing due to the reaction between the polyol resin and the polyisocyanate, an adduct is particularly preferable.

  The addition amount of the crosslinking agent is preferably about 10 to 100% by weight based on the antistatic agent and the resin, although the addition amount suitable for the crosslinking agent to be used is different.

  In order to further improve the head matching, friction coefficient is added by adding wax and oil to the protective layer, using a resin modified with silicone as a binder 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.

  There is no restriction | limiting in particular in the coating system of a protective layer, 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 functions of the protective layer such as storage stability and head matching of the recording medium will be insufficient, and if it is too thick, the thermal sensitivity of the recording medium will decrease, and it will be disadvantageous in terms of cost. is there.

In addition to the antistatic function, as described above, the back layer is on the support opposite to the thermosensitive coloring layer, in order to prevent curling, reduce adhesion between films, and improve transportability in the printer during printing. In addition to containing an antistatic agent comprising polyalkylene glycol and lithium perchlorate, which is a feature of the present invention, a resin and a filler are the main components, and if necessary, a crosslinking agent, an antistatic agent, and a coating property Various additives such as a surfactant can be added for the purpose of improving the above.
As the content of the antistatic agent comprising polyalkylene glycol and lithium perchlorate, the back layer itself can be composed of the present antistatic agent or mixed with other materials. The content of 5% by weight or more in the weight is preferable from the antistatic effect.

  In order to stabilize the antistatic agent in the layer, it is effective to use a cross-linking agent that cross-links the terminal hydroxyl group of the polyalkylene glycol. As the crosslinking agent, conventionally known compounds such as isocyanate compounds, epoxy compounds, and aldehydes can be used. Of these, isocyanate compounds are particularly preferred. Specific examples of isocyanate compounds include, for example, tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, water-added diphenylmethane diisocyanate, water-added xylylene diisocyanate, Examples include tetramethyl-m-xylidene diisocyanate, norbornane diisocyanate, and derivatives thereof, and compounds having two or more isocyanate groups in the molecule. Examples of the isocyanate derivative include adduct type, burette type, isocyanurate type, dimer type, allophanate type, uretdione type, prepolymer type, and the like with trimethylolpropane. In order to prevent the viscosity of the coating liquid from increasing due to the reaction between the polyol resin and the polyisocyanate, an adduct is particularly preferable.

  The addition amount of the crosslinking agent is preferably about 10% by weight to 100% by weight based on the antistatic agent, although the addition amount suitable for the crosslinking agent to be used is different.

  The resin preferably has good adhesion to the support, and examples thereof include acrylic resins, styrene resins, polyester resins, epoxy resins, polyvinyl resins, and polycarbonates. Particularly, acrylic resins having a Tg of 90 to 150 ° C. Particularly preferred. When Tg is less than 90 ° C., the effect of preventing curling is low, and when it exceeds 150 ° C., in the case of acrylic resin, a problem such as the coating layer being liable to break may occur.

  In particular, the filler is added to provide unevenness on the surface of the layer and prevent adhesion between the films. Therefore, it is preferable to use a filler having a particle size larger than the film thickness of the back layer so as not to be embedded in the back layer. Specific 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-formaldehyde Examples thereof include organic fillers of copolymer particles. 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.

  As the antistatic agent, there are general ion conduction type and electron conduction type. Specific examples of the ion conduction type include inorganic salts such as sodium chloride, anionic polymers such as sodium polystyrene sulfonate, and resins containing a quaternary ammonium salt that is electrolyte cationic. Specific examples of the electron conduction type include conductive metal compounds such as conductive tin and antimony oxide, and conductive polymers such as polyaniline. These are used together with an antistatic agent composed of polyalkylene glycol and lithium perchlorate used in the present invention, or an antistatic agent containing polyalkylene glycol and lithium perchlorate on the surface and listed on the back surface. It can be used by the method of making it contain.

  There is no restriction | limiting in particular in the coating system of a back layer, It can apply by a conventionally well-known method. The film thickness of the back layer is about 1 to 50 μm, preferably about 2 to 20 μm.

  The recording method of the thermal recording medium of the present invention is not particularly limited depending on the specification purpose, such as a thermal pen, thermal head, laser heating, etc., but this thermal recording medium is suitable for printing a high-definition and high-gradation image such as a medical image. In view of the cost, output speed, and compactness of the apparatus, it is most preferable to print using a thermal head.

  Next, the present invention will be described in more detail with reference to examples. In the following, parts and% are based on weight.

Example 1
The following composition was pulverized and dispersed with a ball mill to an average particle size of 0.3 μm to prepare a recording layer coating solution.
[Liquid A]
2-anilino-3-methyl-6-diethylaminofluorane 2 parts octadecylphosphonic acid 6 parts polyvinyl butyral (Denka Butyral # 3000-2, manufactured by Denki Kagaku Kogyo Co., Ltd.) 3 parts Toluene 22 parts Methyl ethyl ketone 22 parts Prepared as described above The [A liquid] was coated on a 175 μm thick polyester film (East Lermir) and the dried coating liquid was dried at 70 ° C. for 1 minute to form a 11 μm thick thermosensitive recording layer.

Next, the following composition was mixed to prepare (Liquid B).
[Liquid B]
Guanamin-formaldehyde copolymer particles (manufactured by Nippon Shokubai, Eposter S, average particle size 0.3 μm) 1 part Silicon modified polyvinyl butyral resin (manufactured by Dainichi Seika, SP-712, solid content 12.5%) 80 parts Polyvinyl acetoacetal resin solution (manufactured by Sekisui Chemical, KS-1,
10% MEK solution) 10 parts Methyl ethyl ketone 119 parts The protective layer coating solution [B solution] prepared as described above was subjected to ultrasonic treatment for 15 minutes, and then applied onto the previously obtained heat-sensitive recording layer. It dried at 70 degreeC for 1 minute, and provided the protective layer with a thickness of 2.5 micrometers.
(C liquid)
Polypropylene lithium perchlorate composite 1 part (Nihon Carlit PEL-100)
Acrylic resin (Mitsubishi Rayon Dianal BR-73) 2 parts Methyl ethyl ketone 12 parts The coating liquid (liquid C) prepared as described above and sufficiently stirred and dissolved so as to have a thickness of 6 μm on the back surface of the obtained support A back layer was applied to the film and dried at 70 ° C. for 1 minute to form a back layer, thereby obtaining the transparent thermosensitive recording medium of the present invention.

Example 2
The following composition was sufficiently stirred to obtain a thermal recording layer coating solution.
(Liquid D)
Liquid A 55 parts Polypropylene lithium perchlorate composite 5 parts (Nippon Carlit PEL-100)
The coating solution prepared as described above was applied to [D solution] on a 175 μm-thick polyester film (Toler mirror) and dried at 70 ° C. for 1 minute to form a thermosensitive recording layer having a thickness of 16 μm.
Protective layer coating solution [Liquid B] was subjected to ultrasonic treatment for 15 minutes, then coated on the previously obtained thermal recording layer and dried at 70 ° C. for 1 minute to provide a protective layer having a thickness of 2.5 μm. It was.
(E liquid)
Acrylic resin (Mitsubishi Rayon Dianal BR-73) 2 parts Methyl ethyl ketone 12 parts The coating liquid (liquid E) prepared as described above and sufficiently stirred and dissolved so that the thickness is 6 μm on the back surface of the obtained support. A back layer was applied to the film and dried at 70 ° C. for 1 minute to form a back layer, thereby obtaining the transparent thermosensitive recording medium of the present invention.

Example 3
In the same manner as in Example 1, [Liquid A] was applied on a 175 μm thick polyester film (Easterl Mirror) to form a 11 μm thick thermosensitive recording layer. Next, the following composition was mixed to prepare [F liquid].
(F liquid)
Guanamin-formaldehyde copolymer particles (manufactured by Nippon Shokubai, Eposter S, average particle size 0.3 μm) 1 part Silicon modified polyvinyl butyral resin (manufactured by Dainichi Seika, SP-712, solid content 12.5%) 80 parts Polyvinyl acetoacetal resin solution (manufactured by Sekisui Chemical, KS-1,
10% MEK solution) 10 parts Polypropylene lithium perchlorate composite 40 parts (Nippon Carlit PEL-100)
179 parts of methyl ethyl ketone The protective layer coating solution [F solution] prepared as described above was subjected to ultrasonic treatment for 15 minutes, then applied onto the previously obtained thermal recording layer and dried at 70 ° C. for 1 minute. A protective layer having a thickness of 2.5 μm was provided.

  Further, on the back surface of the heat-sensitive recording medium coated with the protective layer obtained above, [C solution] was applied in the same manner as in Example 1, and the back layer was applied to a thickness of 6 μm, and dried at 70 ° C. for 1 minute. A back layer was formed to obtain a transparent thermosensitive recording medium of the present invention.

Example 4
A non-transparent thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that a 150 μm-thick polypropylene film (YUPO Corporation YUPO FPG) was used as the support.

Example 5
A polypropylene lithium perchlorate composite (PEL-100 manufactured by Nippon Carlit) in [Liquid C] of Example 1 was changed to a polyethylene lithium polypropylene copolymer lithium perchlorate composite (PEL-20A manufactured by Nippon Carlit). Obtained a transparent thermosensitive recording medium of the present invention in the same manner as in Example 1.

Example 6
(G liquid)
Polyethylene polypropylene lithium perchlorate composite 1 part (Nihon Carlit PEL-20A)
Amino resin (Cytech Cymel 325) 0.4 parts acrylic resin (Mitsubishi Rayon Dianal BR-73) 2 parts Methyl ethyl ketone 12 parts A coating solution (G solution) prepared as described above and sufficiently stirred and dissolved was obtained.

  A transparent thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that [G liquid] was used instead of [C liquid] in Example 1.

Example 7
The present invention is the same as in Example 6 except that 0.4 part of the amino resin (Cytech Cymel 325) in Example 6 [Solution 325] is changed to 0.5 part of an isocyanate compound (Takenate D110N, Mitsui Takeda Chemical). A transparent thermosensitive recording medium was obtained.

Example 8
Polypropylene lithium perchlorate composite (PEL-100, manufactured by Nippon Carlit Co., Ltd.) in [Liquid C] of Example 1 was blended with a polyethylene polypropylene glycol copolymer and lithium perchlorate, trifluoromethane, lithium sulfonate composite (Nippon Carlit). A transparent thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that PEL-25 was manufactured.

Comparative Example 1
1 part of a polypropylene lithium perchlorate composite (PEL-100, manufactured by Nippon Carlit) in [Liquid C] of Example 1 is an acrylic resin having a quaternary ammonium salt substituent (40% by weight modified methanol solution, manufactured by Mitsubishi Chemical Corporation). A transparent heat-sensitive recording medium for comparison was obtained in the same manner as in Example 1 except that 2.5 parts by Saftomer ST2100).

Comparative Example 2
1 part of polypropylene lithium perchlorate composite (Nihon Carlit PEL-100) in [C liquid] of Example 1 was tin oxide, antimony oxide composite (30 wt% MEK solution, Ishihara Sangyo, SMS-10M) A comparative thermosensitive recording medium was obtained in the same manner as in Example 1 except that the amount was 3.3 parts.

The transparent heat-sensitive recording media of Examples and Comparative Examples obtained as described above were evaluated according to the following test methods.
(Charge amount during printing)
A uniform solid image is continuously printed so that the reflection density is 0.2 (measurement of reflection density is in accordance with Macbeth RD-914) using a printer with a variable applied energy equipped with a gradation head with a resolution of 300 dpi. The charge amount was measured by using an Electric Field Meter Model Number 19445 manufactured by Desco and separated from the film surface by 2.5 cm.
The measurement environment was implemented in two environments of 22 ° C., 50% RH (relative humidity) and 10 ° C. and 10% RH.
If the charge amount was within 3 kV, it was judged that printing could be performed with almost no problem, and the following standard evaluation was performed.
◎: Less than 1.0 kV ○: 1.0 kV or more and less than 3 kV ×: 3 kV or more (base transmission density)
The transmission density of the uncolored portion of the prepared sample was measured using X-rite 301 (manufactured by Xrite). The lower the base transmission density, the lower the background coloring. It is preferably 0.10 or less and particularly preferably 0.08 or less.
A: Transmission density 0.08 or less B: Transmission density 0.10 or less X: Transmission density 0.11 or more (haze)
A transparent thermosensitive recording medium of 50 mm × 50 mm is used as a test piece, and haze (haze) is measured with a direct reading haze meter manufactured by Suga Test Instruments in accordance with JIS K-7105. The lower the haze value, the better the transparency.
◎: Haze value 25% or less ○: Transmission density 30% or less ×: Transmission density 31% or more (ease of scratches)
The surface state (protective layer surface or back layer surface) on which the antistatic agent was added was rubbed 10 times with a nail with a length of about 10 cm, and the surface state was observed and evaluated according to the following criteria.
A: No trace is left. O: A trace remains, but the layer is not scraped.
X: Scraping of the layer is recognized.

  The evaluation results are shown in Table 1 below.

この表１から分かるように、本発明によって、印画中の帯電量が常湿及び低湿時低く、感熱記録媒体の性能（非印画部の透過濃度、透明性、傷付き性）にも優れている感熱記録媒体が提供される。

As can be seen from Table 1, according to the present invention, the charge amount during printing is low at normal humidity and low humidity, and the performance of the thermal recording medium (transmission density of non-printed portion, transparency, scratch resistance) is excellent. A thermal recording medium is provided.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Claims (12)

  A heat-sensitive recording layer comprising as a main component at least a colorless or light-colored leuco dye on a plastic support, a color developer that heat-colors the leuco dye and a binder resin as a binder, and a resin on the heat-sensitive recording layer. A heat-sensitive recording medium provided with a protective layer, and further provided with a back layer containing a resin on a support opposite to the heat-sensitive recording layer, containing an antistatic agent composed of polyalkylene glycol and lithium perchlorate A heat-sensitive recording medium.   2. The thermosensitive recording medium according to claim 1, wherein an antistatic agent comprising the polyalkylene glycol and lithium perchlorate is contained in a protective layer and / or a back layer.   3. The heat-sensitive recording medium according to claim 1, wherein the polyalkylene glycol has a molecular weight of 1000 to 2000 and is a copolymer of ethylene glycol and propylene glycol.   2. The protective layer and / or the back layer contains an antistatic agent comprising a polyalkylene glycol and a lithium perchlorate, and further contains a cross-linking agent that cross-links the polyalkylene glycol. 4. The thermal recording medium according to any one of 3 above.   The content of the antistatic agent in the protective layer is 5% by weight to 100% by weight with respect to the resin in the protective layer, and the content of the antistatic agent in the back layer is the back layer. The thermal recording medium according to claim 1, wherein the thermal recording medium is 5% by weight or more of the total weight of the recording medium.   5. The thermal recording medium according to claim 4, wherein the crosslinking agent is an isocyanate compound.   The content of the crosslinking agent in the protective layer is 10% to 100% by weight with respect to the antistatic agent and the resin in the protective layer, and the content of the crosslinking agent in the back layer is the back layer. The heat-sensitive recording medium according to any one of claims 4 to 6, wherein the content is 10% by weight to 100% by weight with respect to the antistatic agent in the layer.   The thermal recording medium according to claim 1, wherein a particle size of the recording layer dispersion is 1.0 μm or less.   The thermal recording medium according to claim 1, wherein the protective layer has a thickness of 0.1 to 20 μm.   The thermal recording medium according to claim 1, wherein the resin of the back layer is an acrylic resin having a Tg of 90 to 150 ° C.   11. The heat-sensitive material according to claim 1, wherein the plastic support is a transparent polyester film having a thickness of 5 μm to 250 μm, and the haze degree of the heat-sensitive recording medium is 30% or less according to JIS K7105. recoding media.   The thermal recording medium according to any one of claims 1 to 11, wherein the thermal recording medium is printed and recorded using a heating means including a thermal pen, a thermal head, and laser heating.