JP4764216B2 - Thermal recording material - Google Patents

Description

  The present invention relates to a heat-sensitive recording medium using a color development reaction between an electron-donating compound having color developability and an electron-accepting compound having color developability, and more particularly to curling on a print screen before and after printing. The present invention relates to a sheet-like heat-sensitive recording material for a heat-sensitive printer.

  Various recording materials have been proposed that utilize a coloring reaction between a colorless or light-colored leuco dye and a developer that develops the leuco dye when contacted by heat and pressure. The heat-sensitive recording material of this type does not require complicated processing such as development and fixing, can be recorded in a short time with a relatively simple device, has less noise, and is low in cost. It is useful as a recording material for various thermal printers such as electronic computers, facsimiles, ticket vending machines, label printers, and recorders. These heat-sensitive recording materials are generally produced by applying a leuco dye (color-forming dye) and a color developer as a heat-sensitive recording layer on paper as a support.

On the other hand, in recent years, there has been a demand for a dry film system that can be easily output, mainly in the medical field, due to waste liquid processing problems caused by the wet process of silver salt X-ray films and the flow of digitization of images. As a system that meets this requirement, there is a thermal recording process using a thermal recording material.
The heat-sensitive recording material used for such applications is required to have the same rigidity and printing uniformity as a conventional silver salt X-ray film. For this reason, it is required that there is no paper dust that can lead to printing defects. Instead of conventional paper, the above-mentioned color developability on a support made of a plastic material, particularly on synthetic paper or plastic film (for example, polyester film). In most cases, dyes and developers are applied and manufactured.

However, a heat-sensitive recording material using a support made of a plastic material has a low heat resistance of the support itself as compared with a case where conventional paper is used as a support. For this reason, there is a so-called curling phenomenon that the support is contracted by the heating at the time of printing with the thermal head and the film is lifted to the printing screen side.
In addition, when a thermosensitive recording material is produced by applying and drying a thermosensitive recording layer or a protective layer on a so-called support before printing, the surface (the thermosensitive recording layer or the protective layer is formed by stretching of the support or the application layer). The problem of curling on the provided side) occurs. Curling due to expansion and contraction of the coating layer is particularly noticeable in the case of a heat-sensitive recording medium provided with a layer mainly composed of a resin having a high Tg on the surface. In order to give the surface a high glossiness with a glossiness of 60% or more, it is necessary to form a layer mainly composed of a resin having a high Tg.

As a method for improving such curling, for example, a thermosensitive coloring layer and a coating layer mainly composed of a leuco dye and a developer are provided on the surface of the support, and a neutral paper sizing agent is provided on the back of the support. There has been proposed a heat-sensitive recording material in which a back layer mainly composed of an anionic styrene acrylic resin is provided to prevent curling (see, for example, Patent Document 1).
In addition, an electron-donating dye, an electron-accepting acid for coloring the dye, and a thermosensitive recording layer mainly composed of an adhesive are provided on the surface of the support, and a core-shell type acrylic resin is contained as a binder on the back surface of the support. A heat-sensitive recording sheet provided with a backing layer and improved curling, and a production method having the same structure have been proposed (see, for example, Patent Documents 2 and 3).

  According to the above proposal, there is a certain anti-curl effect in the case of a support that does not shrink too much. However, when a support such as a plastic film as described above is used, curling strongly occurs due to shrinkage. Therefore, the above-mentioned proposed method is insufficient as a countermeasure for preventing such surface curling. .

  The present applicant provides a heat-sensitive recording material in which a heat-sensitive color-developing layer mainly composed of a leuco dye and a developer is provided on the surface of a support, and a protective layer, and a back layer made of a water-soluble acrylic resin is provided on the back surface of the support. (For example, refer to Patent Document 4). In addition, the surface of the support made of plastic film or synthetic paper is provided with a thermosensitive coloring layer mainly composed of a leuco dye and a developer, and a protective layer mainly composed of a water-soluble polymer compound and a crosslinking agent. Proposed a heat-sensitive recording material provided with a back layer containing a non-foamable plastic hollow filler, a styrene-acrylic copolymer having an acid value of 200 or more and an abnormal Tg of 80 ° C., and an acrylic emulsion resin on the back surface of , See Patent Document 5).

  According to Patent Document 4, even when a label (a pressure-sensitive adhesive and a release mount are laminated) is used, curling is small, and even if water penetrates, the adhesive does not peel. In addition, according to Patent Document 5, the anti-blocking property in roll storage, adhesion, etc. are improved, and even when used as a label (adhesive and release mount are laminated), there is little curling due to low molecular compound penetration, The adhesive does not peel off due to water penetration. However, in order to print a high-definition and high-gradation image using a plastic film or the like as a support, further improvement in curling suppression is desired.

Japanese Patent Laid-Open No. 10-181205 JP 2003-276330 A Japanese Patent Laid-Open No. 6-239019 (Japanese Patent No. 3131409) JP 2004-284089 A JP 2005-81626 A

  The present invention has been made in view of the above prior art, and suppresses the occurrence of curling due to shrinkage of a support (synthetic paper or plastic film) before and after printing, and achieves high definition with a thermal recording system. Another object of the present invention is to provide a heat-sensitive recording material suitable for printing a high gradation image.

  As a result of intensive studies, the present inventors have constituted a back layer of a heat-sensitive recording material mainly comprising a copolymer (polymethacrylate resin) of isobornyl methacrylate (ISBM) and methacrylate (MA) other than ISBM. As a result, the inventors have found that the above-mentioned problems can be solved, and have reached the present invention. The present invention will be specifically described below.

That is, the present invention contains a leuco dye, a developer that develops color of the leuco dye by heating, and a solvent-soluble resin on one surface of a support made of a synthetic paper or plastic film having a thickness of 5 to 250 μm. Including a heat-sensitive recording layer having a thickness of 1 to 50 μm, a solvent-soluble resin, and a filler, and sequentially providing a protective layer having a thickness of 0.1 to 20 μm, and further providing a back layer on the other surface of the support. in becomes the heat-sensitive recording material, wherein the back layer comprises a polyester methacrylate resin consisting of a copolymer of i Seo isobornyl methacrylate (ISBM) and methacrylates other than the ISBM (MA) as a main component, a film thickness of 1 A heat-sensitive recording material having a thickness of ˜50 μm .

  By providing a back layer containing the above polymethacrylate resin, the state of the recording material before printing as well as the occurrence of curling is suppressed even after printing with a thermal pen, thermal head, laser heating, etc. Can be printed.

  In the heat-sensitive recording material, the present invention is characterized in that the polymethacrylate resin has a glass transition temperature (Tg) of 110 ° C. or higher.

  If the Tg of the polymethacrylic ester resin is 110 ° C. or higher, the curl reduction effect can be made more remarkable.

  In the heat-sensitive recording material, the present invention is characterized in that the methacrylate (MA) other than the ISBM is methyl methacrylate.

  If a copolymer of methyl methacrylate and isobornyl methacrylate is used, the glass transition temperature (Tg) of the polymethacrylate resin can be increased, and the curl reduction effect before and after printing can be increased.

  In the heat-sensitive recording material, the content ratio of the polymethacrylic ester resin in the total weight of the back layer is 50% by weight or more.

  By making the content ratio of the polymethacrylic ester resin 50% by weight or more, curling can be suitably suppressed.

According to the present invention, in the heat-sensitive recording material, the 75 ° glossiness of the surface on the side provided with the protective layer is 60% or more.

  By setting the glossiness of the surface to 60% or more, the visibility of the printed image can be improved and it can be made suitable as a heat-sensitive recording material.

  According to the present invention, in the heat-sensitive recording material, the support is a plastic film made of biaxially stretched polypropylene.

  A plastic film mainly composed of biaxially stretched polypropylene has characteristics required for a heat-sensitive recording material, and is suitable for producing a heat-sensitive recording material having a surface glossiness of 60% or more.

  According to the heat-sensitive recording material of the present invention, the occurrence of curling is suppressed not only before printing but also after printing by the heat-sensitive recording system. The heat-sensitive recording material having such a structure can print a high-definition and high-gradation image, for example, as a dry film in the medical field, or a recording material such as an electronic computer, facsimile, ticket vending machine, label printer, recorder Can be suitably used.

As described above, the heat-sensitive recording material of the present invention comprises, on one surface of a support, a leuco dye, a color developer that develops the leuco dye by heating, and a binder resin, and a resin. In the heat-sensitive recording material in which a protective layer is sequentially provided and a back layer is provided on the other surface of the support, isobornyl methacrylate (ISBM) and methacrylates other than ISBM (MA) are used as constituent materials of the back layer. And a polymethacrylic acid ester resin made of a copolymer with a main component. In the present invention, the expression “methacrylate” is synonymous with “methacrylate”.
Hereinafter, the heat-sensitive recording material of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing one structural example of a heat-sensitive recording material in the present invention.
In FIG. 1, on one surface (surface) of a support 2, a thermal recording layer 3 containing a leuco dye, a color developer for developing the leuco dye by heating, and a binder resin, and protection (including resin) A heat-sensitive recording material having a structure in which a layer 4 is sequentially provided and a back layer 1 is provided on the other surface (back surface) of the support 2 is shown.
That is, the back layer 1 contains a copolymer of isobornyl methacrylate (ISBM) and a methacrylate (MA) other than ISBM as a main component, so that the state of the heat-sensitive recording material before printing, the thermal head, etc. In the state of the heat-sensitive recording material after printing, the occurrence of curling is suppressed, and a sheet-like heat-sensitive recording material for a heat-sensitive printer with high image quality (high definition, high gradation, etc.) can be obtained.
As the heat-sensitive recording material according to the present invention, the heat-sensitive recording layer 3 and the protective layer 4 containing a resin are sequentially provided on one surface (front surface) of the support 2, and the back layer is formed on the other surface (back surface) of the support 2. If it has 1, other layers other than the above may be formed as necessary.
Hereinafter, the details of each constituent layer in the heat-sensitive recording material according to the present invention and the forming method thereof will be described together.

[Back layer]
As shown in FIG. 1, the back layer is provided on the other surface (back surface) of the support opposite to the thermosensitive recording layer, and has a curl prevention function as described above. Further, it also has functions such as antistatic and improved transportability. Note that improved transportability means that when a recording material is transported in a printer during printing, the adhesion between the stacked sheet-like thermal recording materials is reduced to facilitate transport of each sheet. is there.
For this reason, as a constituent material of the back layer, in addition to a polymethacrylic acid ester resin composed of a copolymer of isobornyl methacrylate (ISBM) and methacrylate (MA) other than ISBM as a main component, an antistatic agent, Fillers and the like are contained. Further, if necessary, various additives such as a resin other than the polymethacrylate resin, a crosslinking agent, or a surfactant for improving the coating property can be added.

The polymethacrylate resin comprising a copolymer of ISBM and MA is composed of isobornyl methacrylate as an essential component and selected from any methacrylate (MA) other than ISBM, such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate. A copolymer comprising at least one.
ISBM is obtained, for example, by a reaction (for example, an esterification reaction) between the corresponding acrylic acid or a derivative thereof and isoborneol or a derivative thereof.

  The copolymer can be obtained by polymerizing isobornyl methacrylate (ISBM) and the methacrylate (MA) in a suitable solvent using a polymerization catalyst (for example, a radical polymerization catalyst). The reaction conditions are selected so that desired properties (molecular weight, glass transition temperature (Tg), etc.) can be obtained. As MA to be copolymerized with ISBM, methyl methacrylate is preferable in that the Tg of the resulting resin can be increased.

  The ratio of isobornyl methacrylate (ISBM) and methacrylate (MA) constituting the copolymer is not particularly limited, but in the polymethacrylate resin, the ratio of ISBM is 5 to 60% by weight. It is desirable that When the ISBM ratio is less than 5% by weight, the effect of curling is reduced. On the other hand, when the ISBM ratio is more than 60% by weight, cracking or peeling occurs when a film is formed using a coating liquid prepared from this resin. May occur.

  Moreover, it is desirable that the molecular weight of the present polymethacrylic ester resin is 5,000 to 400,000. Within this range, the curl reduction effect and other performances required for the back layer are exhibited in a well-balanced manner, and the coatability is also good. The glass transition temperature (Tg) of the polymethacrylic ester resin is preferably 110 ° C. or higher. When the Tg of the polymethacrylic ester resin is 110 ° C. or higher, the curl reduction effect becomes significant.

  Moreover, it is preferable that the content ratio which occupies for the back layer whole weight of polymethacrylic ester resin is 50 weight% or more. When the content ratio of the polymethacrylic ester resin is less than 50% by weight, the curl reduction effect is not sufficiently exhibited, and it becomes difficult to suitably suppress the curling.

  Moreover, it is also possible to add resin components other than polymethacrylic ester resin as needed for the improvement of adhesiveness with a support body and characteristic improvement. Examples of such resins include acrylic resins, styrene resins, polyester resins, epoxy resins, polyvinyl resins, and polycarbonates.

Alternatively, if necessary, the cross-linking reaction is effected with a terminal functional group contained in the polymethacrylate resin or other resin to further improve the curl reduction effect of the back layer or improve the strength of the back layer. It is also effective to use a crosslinking agent that forms a structure in combination.
As such a crosslinking agent, conventionally known compounds such as isocyanate compounds, epoxy compounds and aldehydes can be used. Of these crosslinking agents, isocyanate compounds are particularly preferred.

  Specific examples of the isocyanate compound include, for example, tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, water-added diphenylmethane diisocyanate, water-added xylylene diisocyanate, tetramethyl-m-xylidene diisocyanate, norbornane. Examples thereof include compounds having two or more isocyanate groups in the molecule such as diisocyanate and derivatives thereof.

  Examples of the isocyanate derivative include adduct type, burette type, isocyanurate type, dimer type, allophanate type, uretdione type, and prepolymer type with trimethylolpropane. In the case where the polymethacrylate resin or other resin is a resin having a polyol structure, an adduct is particularly preferable in order to prevent an increase in viscosity due to reaction with the polyisocyanate in the prepared coating liquid.

  The filler contained as a constituent material of the back layer is added to form unevenness on the surface of the layer and prevent adhesion between the sheets when the heat-sensitive recording material is overlaid. 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 buried in the back layer.

  Specific examples of the filler include, for example, phosphate fiber, potassium titanate, acicular magnesium hydroxide, whisker, talc, mica, glass flake, calcium carbonate, plate calcium carbonate, aluminum hydroxide, plate aluminum hydroxide, silica Inorganic fillers such as clay, 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 And organic fillers such as melamine-formaldehyde copolymer particles. However, the present invention is not limited to this, and a plurality of fillers may be used simultaneously in order to impart various required properties.

As an antistatic agent contained as a constituent material of the back layer, there are those having a general ion conduction type or electron conduction type.
Specific examples of the antistatic agent of the ionic conduction type include inorganic salts such as sodium chloride, anionic polymers such as sodium polystyrene sulfonate, and resins containing an electrolyte cationic quaternary ammonium salt. Specific examples of the antistatic agent of the electron conductive type include conductive metal compounds such as conductive tin and antimony oxide, and conductive polymers such as polyaniline.

The back layer can be formed by applying and drying using a coating liquid. The coating liquid is prepared by dispersing a polymethacrylate resin, an antistatic agent, a filler and the like in a suitable solvent. If necessary, a crosslinking agent, a surfactant, and other additives are added as appropriate.
The back layer coating method is not particularly limited, and can be applied by a conventionally known method. The film thickness of the back layer is about 1 to 50 μm, preferably about 2 to 20 μm.

[Support]
Next, a support for the heat-sensitive recording material will be described.
Examples of the support include synthetic paper and film made of a plastic material. Examples of the film include polyolefin films such as polypropylene and polyethylene, polyester films such as polyethylene terephthalate and polybutylene terephthalate, cellulose derivative films such as cellulose triacetate, polystyrene films, and films obtained by bonding the films.
Among these, a plastic film made of biaxially stretched polypropylene is suitable as a support for coating and forming the heat-sensitive recording layer, protective layer and back layer in the present invention, and has a surface glossiness of 60% or more. Suitable for manufacturing.

  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 haze degree (Haze degree: haze) of the support is preferably 10% or less, preferably Is preferably 5% or less. Further, the thickness of the support is preferably 5 to 250 μm for thermal recording applications although it varies depending on the application.

(Thermosensitive recording layer)
Next, the heat sensitive recording layer of the heat sensitive recording material will be described.
The heat-sensitive recording layer contains a leuco dye, a color developer that develops the leuco dye by heating, and a binder resin. If necessary, a known filler, pigment, surfactant, heat-fusible substance is used. Further, an antistatic agent or the like may be contained.

The leuco dye used in the heat-sensitive recording layer in the present invention is a compound exhibiting electron donating properties, and is used alone or in combination of two or more.
The leuco dye to be used is a colorless or light-colored dye precursor itself, and is not particularly limited, and is a conventionally known one, for example, triphenylmethanephthalide, triallylmethane, fluoran, phenothiocyan, thioferolan. , Xanthene, indophthalyl, spiropyran, azaphthalide, chromenopyrazole, methine, rhodamine anilinolactam, rhodamine lactam, quinazoline, diazaxanthene, bislactone, and other leuco compounds are preferably used. . Particularly preferred are fluoran and phthalide leuco dyes. Examples of such compounds include, but are not limited to, those shown below.

  That is, 2-anilino-3-methyl-6-diethylaminofluorane; 2-anilino-3-methyl-6- (di-n-butylamino) fluorane; 2-anilino-3-methyl-6- (Nn 2-anilino-3-methyl-6- (N-isopropyl-N-methylamino) fluorane; 2-anilino-3-methyl-6- (N-isobutyl-N-methyl) -propyl-N-methylamino) fluorane; Amino) fluoran; 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane; 2-anilino-3-methyl-6- (N-sec-butyl-N-ethylamino) 2-anilino-3-methyl-6- (Nn-amyl-N-ethylamino) fluorane; 2-anilino-3-methyl-6- (N-iso-amyl-N-e) 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- 1,3-dimethyl-6-diethylaminofluorane; 1,3-dimethyl-6-di-n-butylaminofluorane; 3-diethylamino-7-methylfluorane; 3-diethylamino-7-chloro Fluorane; 3-diethylamino-6-methyl-7-chlorofluorane; 10-diethylamino-2-ethylbenzo [1, 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-diethylamino) Phenyl) ethylene-2-yl] -6-dimethylaminophthalide and the like.

The developer used for the heat-sensitive recording layer of the present invention is an electron-accepting compound, and various conventionally known electron-accepting developers can be used. More preferred in the present invention is a developer as described in JP-A-63-95979. By using such a developer, the stability of the color image can be obtained.
Specific examples of the developer include salicylic acid derivatives having an amino group represented by the following general formula (1).

Wherein 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 a positive integer. )

  The substituted amino group represented by R in the above formula includes 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. Is preferred. The substituent represented by X is preferably 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 or a fluorine atom, and a group represented by M As a hydrogen atom, zinc, aluminum, magnesium and calcium are preferable.

  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, which are used alone or in combination.

In addition to the above salicylic acid derivative, other well-known electron-accepting compounds such as salicylic acid derivatives, phenyl derivatives, phenyl resins, and acid clay may be used in combination.
Examples of such electron-accepting compounds include 4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide-α-naphthol, β-naphthol, hexyl-4-hydroxybenzoate, and 2,2′-dihydroxy. Biphenyl, 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-butyryl Dendiphenol, 4-p-methylphenylphenol, 4,4'-isopen Ridenphenol, 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′-dihydroxydiphenyl sulfone, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, polyvinylbenzyloxy Carbonylphenol, 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, 4-hydroxybenzoic acid tolyl, 4-hydroxybenzoic acid α-phenylbenzyl ester, 4-hydroxybenzoic acid phenylpropyl, 4-hydroxybenzoic acid Phenethyl acid, 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-hydroxy 2 ', 4'-dimethyldiphenyl sulfone β-phenethyl orsellinate, cinnamyl orse elinate, orthoric acid-o-chlorophenoxyethyl ester, o-ethylphenoxyethyl orcerine O-phenylphenoxyethylorselinate, m-phenylphenoxyethylorselinate, 2,4-dihydroxybenzoic acid-β-3′-tert-butyl-4′-hydroxyphenoxyethyl ester, 4-N— Benzylsulfamoylphenol, 2,4-dihydroxybenzoic acid-β-phenoxydiethyl ester, 2,4-dihydroxy-6-methylbenzoic acid benzyl ester, methyl bis-4-hydroxyphenylacetate, ditrideurea, 4, 4′- Diacetyldiphenylthiourea, 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-methylbenzyl) Lithic 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-octyl Myrsalicylic 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-cumylsalicylic acid 3- (α-methylbenzyl) -6-methylsalicylic acid, 3- (α-methylbenzyl) -6-phenylsali Phosphoric 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 various other 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 by weight, preferably 2 to 10 parts by weight, per 1 part by weight 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.

As the binder resin used in the heat-sensitive recording layer of the present invention, various known resins can be used as long as the properties of the recording layer are not impaired. Examples of such resins include polyethylene, polyvinyl acetate, polyacrylamide, maleic acid copolymer, polyacrylic acid and its ester, polymethacrylic acid and its ester, vinyl chloride / vinyl acetate copolymer, styrene copolymer. polymer, polyester, polyurethane, polyvinyl butyral, ethyl cellulose, polyvinyl acetal, polycarbonate, epoxy resins, poly amide, and the like, can be used alone or two or more kinds.

In order to form the heat-sensitive recording layer, a coating solution prepared by uniformly dispersing or dissolving a leuco dye, a developer, and a binder resin in an organic solvent is used on one surface (surface) of the support. It is particularly good to produce by coating and drying.
Examples of the organic solvent to be used include hydrocarbons such as benzene, toluene, xylene, hexane, cyclohexane, methylcyclohexane and cyclopentane, halogenated hydrocarbons such as chloroform, methylene chloride, chlorobenzene and dichlorobenzene, methanol, ethanol, Alcohols such as propanol, isopropanol and butanol, ethers such as ethyl ether, isopropyl ether and 1,3-dioxolane, acetone, methyl ethyl ketone (hereinafter sometimes abbreviated as MEK), diethyl ketone, methyl isobutyl ketone, cyclohexanone And the like, and esters such as methyl acetate, 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.

  There are no particular restrictions on the coating method used to form the heat-sensitive recording layer by applying the coating liquid onto the surface of the support and drying it, such as the die fountain method, wire bar method, gravure method, and air knife method. Used. 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.

The particle size of the dispersion in the coating liquid for forming the heat-sensitive recording layer, that is, the recording layer coating liquid, is greatly related to the transparency of the entire recording material, the surface roughness of the protective layer, and also the dot reproducibility during printing. . For this reason, when the particle diameter of the dispersion is 1.0 μm or less, particularly in the present heat-sensitive recording material, the transparency is remarkably improved when it is 0.5 μm or less due to the influence of the refractive index.
The film thickness of the recording layer varies depending on the composition of the heat-sensitive recording layer or the application of the heat-sensitive recording material, but is about 1 to 50 μm, preferably about 3 to 20 μm. As described above, various additives such as a surfactant can be added to the recording layer coating solution as necessary for the purpose of improving the coating property and recording characteristics.

[Protective layer]
Next, the protective layer of the heat sensitive recording material will be described.
The protective layer is provided on the heat-sensitive recording layer and is configured to maintain a surface glossiness of 60% or more, as well as chemical resistance, water resistance, friction resistance, light resistance, and head matching to a thermal head, etc. Has a role to improve.
In addition, when the glossiness of the surface on which the protective layer is provided is lower than 60%, the visibility of the printed image is deteriorated, which is not preferable.

From this demand, the protective layer is an organic solvent, a binder resin (substantially, resin), a filler as the main components, a lubricant if required (waxes, oils), tree fat crosslinking agents, surface active agents It can be formed by coating and drying on a heat-sensitive recording layer using a coating solution prepared by uniformly dispersing or dissolving the above.

  Specific examples of the filler used for forming the protective layer include phosphate fiber, potassium titanate, acicular magnesium hydroxide, whisker, talc, mica, glass flake, calcium carbonate, plate-like calcium carbonate, aluminum hydroxide, plate-like Inorganic fillers such as aluminum hydroxide, silica, clay, calcined clay, kaolin, hydrotalcite, crosslinked polystyrene resin particles, urea-formalin copolymer particles, silicone resin particles, crosslinked poly (methyl methacrylate) resin particles, guanamine-formaldehyde Examples thereof include organic particles of copolymer particles and melamine-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 simultaneously in order to impart various required properties.

As a resin used for forming the protective layer, an aqueous emulsion, a hydrophobic resin, an ultraviolet ray, an electron beam curable resin, or the like can be used in combination as required, in addition to the resin similar to the heat-sensitive recording layer.
Specific examples of the resin include polyacrylic acid ester, polymethacrylic acid ester, polyurethane resin, polyester resin, polyvinyl acetate resin, styrene acrylate resin, polyolefin resin, polystyrene resin, polyvinyl chloride resin, poly There are ether resins, polyamide resins, polycarbonate resins, polyethylene, polypropylene, polyacrylamide and the like.

In addition, when the above-described resin has a functional group (for example, a hydroxyl group, a carboxyl group, an amino group, etc.), it is also effective to use a crosslinking agent that reacts with the functional group.
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 the isocyanate compound include tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, water-added diphenylmethane diisocyanate, water-added xylylene diisocyanate, tetramethyl-m-xylylene. Examples thereof include dendiisocyanate, norbornane diisocyanate, and derivatives thereof, and compounds having two or more isocyanate groups in the molecule. Examples of the isocyanate derivative include the adduct type, burette type, isocyanurate type, dimer type, allophanate type, uretdione type, prepolymer type and the like described above with trimethylolpropane.
The addition amount of the crosslinking agent varies depending on the type of resin used and the crosslinking agent, but is preferably about 10% by weight to 100% by weight based on the resin.

Furthermore, in order to improve head matching properties, wax or oils are added to the protective layer, a resin modified with silicone is used as a binder resin, the ratio of the resin to the filler is adjusted, etc. The friction coefficient can be adjusted by this method.
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. Moreover, general silicone oil etc. can be used as oil.

  The protective layer is formed by coating and drying on the heat-sensitive recording layer using the coating liquid containing the above-mentioned necessary components, but there is no particular limitation on the coating method used, and coating is performed by a conventionally known method. can do. A preferable protective layer thickness is 0.1 to 20 μm, more preferably 0.5 to 10 μm. If the protective layer thickness is less than 0.1 μm, the storage medium storage function and the head matching function are insufficient, and if it is more than 20 μm, the thermal sensitivity of the recording medium is lowered and the cost is increased. It is a factor and disadvantageous.

  The method for recording the heat-sensitive recording material having the above-described configuration of the present invention can be selected without particular limitation, such as a thermal pen, a thermal head, or laser heating, depending on the purpose of use. The heat-sensitive recording material of the present invention is suitable for printing a high-definition and high-gradation image such as a medical image, and printing is performed using a thermal head from the viewpoint of cost, output speed, and compactness of the apparatus. Most preferred.

  Hereinafter, although an example and a comparative example are given and the present invention is explained still in detail, the present invention is not restricted by these examples. In the following, parts and% are based on weight.

Example 1
In order to produce a thermosensitive recording material, a recording layer coating solution [A solution] required for forming a recording layer was first prepared by mixing the components of the following formulation with a ball mill, and pulverizing and dispersing to an average particle size of 0.3 μm. .

<Prescription of 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

  The recording layer coating solution [A solution] prepared as described above was applied on one surface (surface) of a polypropylene film (FGS-200 manufactured by YUPO CORPORATION) prepared by biaxial stretching with a thickness of 200 μm, and 70 ° C. 1 Partial drying was performed to form a heat-sensitive recording layer having a thickness of 11 μm.

  Next, a protective layer coating solution [Liquid B] necessary for forming a protective layer of a thermosensitive recording material was prepared by uniformly dissolving and dispersing the components of the following formulation.

<Prescription of B 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 Methyl ethyl ketone: 119 parts

  The protective layer coating solution [Liquid B] prepared as described above was subjected to ultrasonic treatment for 15 minutes, then coated on the previously formed heat-sensitive recording layer, dried at 70 ° C. for 1 minute, A protective layer having a thickness of 2.5 μm was provided.

Next, a back layer coating solution [D solution] necessary for forming the back layer of the thermosensitive recording material was prepared by sufficiently stirring the components of the following formulation. The resin solution for back layer [C solution] used in the formulation of D solution was synthesized as follows.
<Synthesis of resin solution for back layer [C solution]>
In a reaction vessel, 20 parts by weight of isobornyl methacrylate and 80 parts by weight of methyl methacrylate are dissolved in 300 parts by weight of ethyl cellosolve, and 0.75 parts by weight of azobisisobutyronitrile is added under a nitrogen atmosphere. By reacting for a time, a polymethacrylate resin (molecular weight: about 100,000, glass transition temperature (Tg): 120 ° C.) was obtained. Further, the obtained resin was diluted with ethyl cello solubilized so as to have a resin concentration of 15% to obtain a resin solution for back layer [solution C]. The glass transition temperature (Tg) is measured with a differential scanning calorimeter (DSC) using a resin solid obtained by sufficiently evaporating the solvent of the obtained resin solution and drying it.

<Prescription of D liquid>
[Liquid C]: 100 parts antimony oxide composite (30 wt% MEK solution, manufactured by Ishihara Sangyo,
SMS-10M): 20 parts Polymethylmethacrylate fine particles (manufactured by Soken Chemical Co., MX-500): 0.15 parts

  The back layer coating solution [D solution] prepared as described above was applied to the other side (back side) of the protective layer-formed polypropylene film to a thickness of 3 μm, and then dried at 70 ° C. for 1 minute. Thus, a back layer was formed, and the heat-sensitive recording material of Example 1 was obtained.

(Example 2)
A thermosensitive recording material of Example 2 was obtained in the same manner as in Example 1 except that the formulation of the back layer coating liquid [D liquid] used in Example 1 was changed to the following [E liquid].

<Prescription of liquid E>
[Liquid C]: 100 parts antimony oxide composite (30 wt% MEK solution, manufactured by Ishihara Sangyo,
SMS-10M): 50 parts Polymethylmethacrylate fine particles (manufactured by Soken Chemical Co., MX-500): 0.15 parts

(Example 3)
In Example 1, the monomer composition (20 parts by weight of isobornyl methacrylate and 80 parts by weight of methyl methacrylate) used for the synthesis of the resin solution [C solution] for the back layer was changed to 30 parts by weight of isobornyl methacrylate and ethyl methacrylate. A heat-sensitive recording material of Example 3 was obtained in the same manner as in Example 1 except that the synthesized [C solution] was changed to 70 parts by weight.
The glass transition temperature (Tg) of the polymethacrylate resin was 110 ° C.

(Comparative Example 1)
A heat-sensitive recording material of Comparative Example 1 was obtained in the same manner as in Example 1 except that no back layer was provided in the heat-sensitive recording material of Example 1.

(Comparative Example 2)
In Example 1, the monomer composition (20 parts by weight of isobornyl methacrylate and 80 parts by weight of methyl methacrylate) used for the synthesis of the resin solution for the back layer [C solution] was changed to 100 parts by weight of methyl methacrylate and synthesized [ A heat-sensitive recording material of Comparative Example 2 was obtained in the same manner as in Example 1 except that C solution] was used.
The glass transition temperature (Tg) of the polymethacrylate resin was 100 ° C.

  The heat-sensitive recording materials (substantially films) of Examples 1 to 3 and Comparative Examples 1 and 2 obtained as described above were stored in an oven set at 40 ° C. for 24 hours and sufficiently dried. The glossiness and the curl before printing and printing were evaluated under the following evaluation conditions. The evaluation results are shown in Table 1 below.

[Glossiness]
The glossiness of the surface on the thermosensitive recording surface side was measured at an angle of 75 ° with VG-1001GP (S) manufactured by Nippon Denshoku Industries Co., Ltd.
[Curl of film before printing]
Cut the thermal recording material into A-4 size, place the thermal recording surface on a flat table, measure the height of the four raised corners, and use the maximum value as the curl measurement value according to the following criteria. evaluated.
◎: Curl value 2 mm or less ○: Curl value 3 to 5 mm
Δ: Curl value 6 to 10 mm
×: Curling value of 10 mm or more [Film curl after printing]
After printing a gray solid with a reflection density of about 1.5 using a printer with a variable applied energy equipped with a thermal head with a resolution of 300 dpi, the curl was measured in the same manner as the curl measurement of the film before printing. The reflection density was measured using a reflection densitometer RD-914 manufactured by Macbeth.

From the evaluation results of Table 1 above, it can be seen that the configuration of the present invention provides a heat-sensitive recording medium with small curl before printing and after printing.
Therefore, the heat-sensitive recording medium of the present invention is capable of high-quality printing, and is useful as a heat-sensitive recording material for the above-mentioned various heat-sensitive printers or a dry film heat-sensitive recording material in the medical field (such as X-ray film).

It is a schematic sectional drawing which shows one structural example of the thermosensitive recording material in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Back layer 2 Support body 3 Thermosensitive recording layer 4 Protective layer

Claims (6)

On one surface of a support made of synthetic paper or plastic film having a thickness of 5 to 250 μm, a leuco dye, a developer that develops the leuco dye by heating and a solvent-soluble resin are contained, and the film thickness is 1 to 50 μm heat-sensitive recording layer, a solvent-soluble resin, and a filler, the film thickness is provided in the protective layer sequentially is 0.1 to 20 [mu] m, the other surface on the said supporting lifting body further, heat-sensitive recording comprising providing a back layer In the material,
Said back layer comprises a polyester methacrylate resin consisting of a copolymer of i Seo isobornyl methacrylate (ISBM) and methacrylates other than the ISBM (MA) as a main component, the film thickness is 1~50μm Characteristic thermal recording material.   The thermosensitive recording material according to claim 1, wherein the polymethacrylate resin has a glass transition temperature (Tg) of 110 ° C. or higher.   The heat-sensitive recording material according to claim 1, wherein the methacrylate (MA) other than the ISBM is methyl methacrylate.   2. The heat-sensitive recording material according to claim 1, wherein the content ratio of the polymethacrylic acid ester resin in the total weight of the back layer is 50% by weight or more. The heat-sensitive recording material according to claim 1, wherein the surface on which the protective layer is provided has a 75 ° glossiness of 60% or more.   2. The heat-sensitive recording material according to claim 1, wherein the support is a plastic film made of biaxially stretched polypropylene.

Images