JP2008044227A - Thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording medium which exhibits a high sensitivity and a high definition image quality. <P>SOLUTION: In the thermal recording medium keeping a support overlaid with an undercoat layer composed mainly of a pigment and a binder and a thermal recording layer composed mainly of an electron-donative lueco dye and an electron-receptive developer, the undercoat layer contains at least kaolin as pigment and a coating material prepared by blending kaolin having an average particle diameter of not greater than 2 μm with calcium carbonate having an average particle diameter of not greater than 1 μm is provided on the undercoat layer by a film transfer method, exhibiting excellent effects. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording material using a color development reaction between an electron-donating leuco dye and an electron-accepting developer.

  In general, a heat-sensitive recording material that obtains a recorded image by utilizing a coloring reaction caused by heat between a colorless or light-colored electron-donating leuco dye (hereinafter referred to as a dye) and an electron-accepting developer (hereinafter referred to as a developer). Is widely used in POS cash registers, fax machines, various measuring instruments, etc., because the color is very clear, there is no noise during recording, the device is relatively inexpensive and compact, and maintenance is easy. Yes. In recent years, the thermal printer has been reduced in weight, high-speed printing, and power saving, and various improvements in quality are desired for the thermal recording medium. In particular, it is required that high sensitivity and high definition images can be reproduced at low applied energy.

  In order to obtain a heat-sensitive recording material with high sensitivity and high-definition image quality, the smoothness and heat insulation of a support with an undercoat layer can be achieved by providing an undercoat layer between the base paper and the heat-sensitive recording layer. It has been proposed to increase. For example, a heat-sensitive recording material has been proposed in which a second undercoat layer is provided on a first undercoat layer by blade coating (Patent Document 1). However, the heat-sensitive recording material of Patent Document 1 has a problem that streaks or scratches frequently occur during blade coating, and sufficient image quality cannot be obtained. In order to cope with this, a heat-sensitive recording material has been proposed in which an undercoat layer is provided in which a paint containing calcium carbonate having an average particle diameter of 3 μm or more is applied by a film transfer method (Patent Document 2).

JP-A 1-1118482 JP 2001-30631 A

  However, the thermal recording material of Patent Document 2 has a problem that sufficient color development sensitivity and high-definition image quality cannot be obtained. Accordingly, an object of the present invention is to provide a heat-sensitive recording material that exhibits high sensitivity and high definition image quality.

  As a result of intensive studies, the present inventors have found that an undercoat layer mainly composed of a pigment and a binder, and a thermosensitive recording layer mainly composed of an electron-donating leuco dye and an electron-accepting developer are formed on a support. The present inventors have found that a heat-sensitive recording body having a high sensitivity and a high-definition image can be obtained when the undercoat layer contains at least kaolin as a pigment. In particular, a high effect can be exhibited by providing the undercoat layer with a coating material containing kaolin having an average particle diameter of 2 μm or less and calcium carbonate having an average particle diameter of 1 μm or less by a film transfer method.

  According to the present invention, it is possible to obtain a thermosensitive recording material that exhibits high sensitivity and high definition image quality.

  Embodiments of the present invention will be described below.

The present invention provides an undercoat layer mainly composed of a pigment and a binder, a colorless or light-colored electron-donating leuco dye (hereinafter referred to as a dye) and an electron-accepting developer (hereinafter referred to as a developer) on a support. A heat-sensitive recording material provided with a heat-sensitive recording layer comprising as a main component, wherein the undercoat layer contains at least kaolin as a pigment. In particular, a high effect can be obtained by providing the undercoat layer with a film transfer system (gate roll, rod metering size press, etc.) containing a paint containing kaolin having an average particle size of 2 μm or less and calcium carbonate having an average particle size of 1 μm or less. Can be expressed.
If necessary, in addition to the heat-sensitive recording layer, a single layer or a plurality of protective layers can be provided on the heat-sensitive recording layer, an intermediate layer between the undercoat layer and the heat-sensitive recording layer, and heat-sensitive recording on the support. It is also possible to provide a protective layer or a layer for curling correction on the surface opposite to the layer. Furthermore, it is possible to carry out a calendar process even after any coating layer such as an undercoat layer, an intermediate layer or a heat-sensitive recording layer is provided.

(Undercoat layer)
In the present invention, the thermal recording material is characterized in that the undercoat layer contains at least kaolin as a pigment. In particular, a high effect can be exhibited by providing the undercoat layer with a paint containing kaolin having an average particle diameter of 2 μm or less and calcium carbonate having an average particle diameter of 1 μm or less by a film transfer method.

  In the present invention, by containing kaolin in the undercoat layer, sufficient surface smoothness of the undercoat layer can be obtained, and excellent image quality can be obtained. Further, the combined use of calcium carbonate improves the fluidity of the paint. When kaolin and calcium carbonate are used in combination, the blending ratio (parts by weight) is preferably 20/80 to 100/0, and more preferably 30/70 to 70/30. When the amount of kaolin is small, sufficient smoothness of the surface of the undercoat layer is difficult to obtain, and sufficient image quality may not be obtained. Moreover, since the smoothness of the surface of an undercoat layer will fall when calcium carbonate mix | blends excessively, there exists a possibility that sufficient image quality may not be obtained.

The average particle diameter of kaolin contained in the undercoat layer of the present invention is preferably 0.40 to 2.50 μm, more preferably 0.80 μm to 1.60 μm. The object of the present invention can be achieved even with a pigment having an average particle size of 0.8 μm or less, but generally, when the particle size of the pigment is small, it tends to be expensive, so it is not necessary that the pigment is 0.8 μm or less. On the other hand, an average particle size of 2.50 μm or more is not preferable because the effect of improving the image quality is small.
The calcium carbonate contained in the undercoat layer of the present invention in combination with kaolin is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. When the average particle diameter of calcium carbonate is larger than 1 μm, it is difficult to obtain the coverage of the support surface with the same coating amount.

In the present invention, it is desirable from the viewpoint of image quality to apply kaolin or an undercoat paint containing kaolin and calcium carbonate by a film transfer method. Examples of film transfer coating methods include gate roll coating and rod metering size press coating, and any coating method can be used. This is preferable because it is suitable for high-speed coating. Further, in the rod metering size press, there are a plain rod and a grooved (grooved) rod, but in the study of the present inventors, the same effect can be obtained in the obtained heat-sensitive recording medium by using either rod. It was. However, when a plain rod and a grooved rod are compared with the same coating amount, the plain type is more preferable because a high-concentration paint can be used and the coating surface feeling is excellent.

The coating amount of the undercoat layer of the present invention is preferably 0.5 to 5 g / m ² on one side, and more preferably 1 to 3 g / m ² . When the coating amount is less than 0.5 g / m ^2, it is difficult to obtain a sufficient effect. On the other hand, when the coating amount is 5 g / m ² or more, mist is generated at the time of coating. Problems may occur in the quality (particularly the print density) after long-term storage.

In the present invention, it is desirable to provide a calendar process after providing the undercoat layer. Since the smoothness of the undercoat layer can be improved by the calendar process, the image quality of the heat-sensitive recording material is improved. In the calendar process, a machine calendar, a soft calendar, a super calendar, a shoe calendar, or the like can be used, but a soft calendar or a shoe calendar is preferably used in terms of improving smoothness without reducing the bulk of the coated paper. .
In the present invention, as the binder that can be used for the undercoat layer, a generally used water-soluble polymer or hydrophobic polymer emulsion or the like can be appropriately used. For example, cellulose derivatives such as polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch, modified starch, polyacrylic acid soda, acrylamide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid copolymer , Styrene / maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, casein and other water-soluble polymers, polyvinyl acetate, polyurethane, styrene / butadiene latex, polyacrylic acid, sodium polyacrylate, polyacrylic Such as acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer emulsion, styrene / butadiene / acrylic copolymer latex, etc. It can be used an emulsion of sexual polymer. Among these, it is preferable to use starch, modified starch and styrene / butadiene latex in combination from the viewpoint of fluidity and high concentration of the paint. Moreover, about 5-40 parts are preferable with respect to 100 weight part of pigment solid content, as for all the binders, it is more preferable that it is 10-30 parts, and it is still more preferable that it is 12-25 parts. If the blending ratio of the binder is larger than this range, the desensitization of the heat-sensitive recording material derived from the binder and the air resistance of the support after coating the undercoat layer become too high, so that an upper layer such as a heat-sensitive recording layer is formed. There may be a problem that the paper is likely to meander during coating. On the other hand, if the blending ratio of the binder is too small, the surface strength of the coated paper becomes insufficient, resulting in problems such as the surface strength of the resulting heat-sensitive recording material is lowered and printability is inferior, and paper dust increases during small roll processing. Occurs.

When starch (including modified starch) and styrene / butadiene latex are used in combination, the blending ratio (parts by weight) of latex and starch is desirably 1/1 to 10/1, and 1.2 / 1 to 5 More preferably, it is / 1. When the starch ratio increases, the coating concentration decreases, so the operation load increases, and desensitization due to starch occurs, which may cause a problem of decrease in print density when the thermal recording medium is stored for a long time. . On the other hand, when the ratio of latex increases, the water retention of the paint decreases, so that the operability (particularly, coating suitability) may decrease.
In the present invention, various auxiliary agents such as fluorescent dyes, dyes, lubricants, printability improvers, pH adjusters, sizing agents, and surfactants can be added as necessary.

(Support)
The support in the present invention is typically made of paper (base paper) that can be mixed with pulp fiber, neutral sizing agent, filler, and various auxiliaries and made with a paper machine. It may be an acidic paper. In addition, an arbitrary material such as a synthetic paper, a film, a plastic film, a foamed plastic film, and a nonwoven fabric can be appropriately selected and used depending on the application. Moreover, you may use the composite sheet which combined these as a support body.

  As the pulp fiber, softwood bleached sulfate pulp (NBKP), hardwood bleached sulfate pulp (LBKP), waste paper pulp and the like can be used, and any wood-based cellulose pulp is not particularly limited. Also, the freeness is not particularly limited.

  As filler, silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, aluminum hydroxide and other inorganic fillers or polystyrene resins, styrene-methacrylic copolymer resins, styrene-acrylic copolymer resins, Examples include nylon powder, polyethylene powder, benzoguanamine resin, urea / formalin resin, and organic fillers such as raw starch particles. When the filler is added in an amount of preferably 5 to 25 parts by weight and less than 5 parts by weight based on 100 parts by weight of the total pulp, it is not possible to obtain a product with sufficient image quality when thermal printing is performed. On the other hand, when the amount exceeds 25 parts by weight, the strength of the base paper becomes weak, which is not preferable.

  Examples of the internally added sizing agent include rosin sizing agents, alkyl ketene dimers, alkenyl succinic anhydrides, petroleum resins, styrene resins, and higher alcohols. The addition amount is 0.05 to 1.5% by weight with respect to the pulp. Moreover, as a fixing agent for these neutral sizing agents, sulfuric acid band, polyamide, acrylamide, cationized starch and the like can be used.

  As the size press liquid, starch, PVA, alkyl ketene dimer, alkenyl succinic anhydride, petroleum-based resin, styrene-based resin, etc. can be used alone or in combination, and if necessary, a water-resistant agent such as glyoxal can be used. It can also be added.

  A stock is prepared using the above materials, and is made by a production apparatus such as a long net paper machine or a circular net paper machine.

(Middle layer)
In the present invention, it is preferable to provide an intermediate layer mainly composed of a pigment and a binder between the undercoat layer and the heat-sensitive recording layer from the viewpoint of the sensitivity and image quality of the heat-sensitive recording material.

  Various known pigments can be used for the pigment used in the intermediate layer. For example, inorganic pigments such as kaolin, clay, zinc oxide, calcined clay, calcined kaolin, aluminum hydroxide, magnesium hydroxide, titanium oxide, diatomaceous earth, calcium carbonate, micro-shaped silica, polystyrene resin, styrene-methacrylic copolymer resin And organic pigments such as styrene-acrylic copolymer resin, nylon powder, polyethylene powder, benzoguanamine resin, urea / formalin resin, and raw starch particles.

  As the binder, a generally used water-soluble polymer or hydrophobic polymer emulsion or the like can be appropriately used. For example, cellulose derivatives such as polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch, modified starch, polyacrylic acid soda, acrylamide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid copolymer , Styrene / maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, casein and other water-soluble polymers, polyvinyl acetate, polyurethane, styrene / butadiene latex, polyacrylic acid, sodium polyacrylate, polyacrylic Such as acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer emulsion, styrene / butadiene / acrylic copolymer latex, etc. It can be used an emulsion of sexual polymer.

  Furthermore, various auxiliary agents can be added as necessary. For example, in order to further improve the water resistance, curing agents such as glyoxal, boric acid, dialdehyde starch, epoxy-based compound melamine formaldehyde resin, and ammonium zirconium carbonate are added. Add as appropriate.

  The coating method is not particularly limited and can be applied according to well-known conventional techniques. For example, an off-machine coating machine or an on-machine equipped with various coaters such as an air knife coater, a rod blade coater, a blade coater, a roll coater, and a curtain coater. A coating machine is appropriately selected and used.

(Thermosensitive recording layer)
-Developer In the present invention, as the developer contained in the heat-sensitive recording layer, all known ones in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, although not particularly limited For example, inorganic acidic substances such as activated clay, attapulgite, colloidal silica, aluminum silicate, 4,4′-isopropylidenediphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4- Hydroxyphenyl) -4-methylpentane, 4,4′-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4,4′-dihydroxydiphenyl sulfone, 2,4′-dihydroxydiphenyl sulfone, 4- Hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4 ' -N-propoxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 3,4-dihydroxyphenyl -4'-methylphenylsulfone, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxa Pentane, bis (p-hydroxyphenyl) butyl acetate, methyl bis (p-hydroxyphenyl) acetate, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α -(4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α -Methyl-α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis ( 4-tert-octylphenol), diphenylsulfone cross-linking compounds described in International Publication WO 97/016420, phenolic compounds described in International Publication WO 02/081229 or JP-A 2002-301873, International Publication WO 02/098774 or WO 03 A phenyl novolak type condensation composition described in / 029017, a urea urethane compound described in WO 00/14058 or JP 2000-143611, a thiourea compound such as N, N′-di-m-chlorophenylthiourea, p-chlorobenzoic acid, gallic Stearyl, bis [4- (n-octyloxycarbonylamino) salicylate zinc] dihydrate, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-tolylsulfonyl) propyl Oxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid aromatic carboxylic acid, and zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel of these aromatic carboxylic acids Examples thereof include salts with polyvalent metal salts such as zinc, antipyrine complexes of zinc thiocyanate, and complex zinc salts of terephthalaldehyde acid with other aromatic carboxylic acids. These developers can be used alone or in combination of two or more. In addition, a metal chelate color-developing component such as a higher fatty acid metal double salt and a polyvalent hydroxyaromatic compound described in JP-A-10-258577 can also be contained.

Basic leuco dyes Any known basic leuco dyes in the field of conventional pressure-sensitive or thermal recording paper can be used, and are not particularly limited, but include triphenylmethane compounds and fluorane compounds. Fluorene series, divinyl series compounds and the like are preferable. Specific examples of typical colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination of two or more.

<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide [also known as crystal violet lactone] 3,3-bis (p-dimethylaminophenyl) phthalide [also known as malachite green lactone]
<Fluoran leuco dye>
3-diethylamino-6-methylfluorane 3-diethylamino-6-methyl-7-anilinofluorane 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane 3-diethylamino-6-methyl -7-chlorofluorane 3-diethylamino-6-methyl-7- (m-trifluoromethylanilino) fluorane 3-diethylamino-6-methyl-7- (o-chloroanilino) fluorane 3-diethylamino-6-methyl- 7- (p-chloroanilino) fluorane 3-diethylamino-6-methyl-7- (o-fluoroanilino) fluorane 3-diethylamino-6-methyl-7- (m-methylanilino) fluorane 3-diethylamino-6-methyl- 7-n-octylanilinofluorane 3-diethylamino- 6-methyl-7-n-octylaminofluorane 3-diethylamino-6-methyl-7-benzylaminofluorane 3-diethylamino-6-methyl-7-dibenzylaminofluorane 3-diethylamino-6-chloro-7 -Methylfluorane 3-diethylamino-6-chloro-7-anilinofluorane 3-diethylamino-6-chloro-7-p-methylanilinofluorane 3-diethylamino-6-ethoxyethyl-7-anilinofluorane 3-diethylamino-7-methylfluorane 3-diethylamino-7-chlorofluorane 3-diethylamino-7- (m-trifluoromethylanilino) fluorane 3-diethylamino-7- (o-chloroanilino) fluorane 3-diethylamino- 7- (p-chloroanilino) fluorane -Diethylamino-7- (o-fluoroanilino) fluorane 3-diethylamino-benzo [a] fluorane 3-diethylamino-benzo [c] fluorane 3-dibutylamino-6-methyl-fluorane 3-dibutylamino-6-methyl- 7-anilinofluorane 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane 3-dibutylamino-6-methyl-7- (o-chloroanilino) fluorane 3-dibutylamino-6 -Methyl-7- (p-chloroanilino) fluorane 3-dibutylamino-6-methyl-7- (o-fluoroanilino) fluorane 3-dibutylamino-6-methyl-7- (m-trifluoromethylanilino) Fluorane 3-dibutylamino-6-methyl-chlorofluorane 3-dibutyla Mino-6-ethoxyethyl-7-anilinofluorane 3-dibutylamino-6-chloro-7-anilinofluorane 3-dibutylamino-6-methyl-7-p-methylanilinofluorane 3-dibutylamino -7- (o-chloroanilino) fluorane 3-dibutylamino-7- (o-fluoroanilino) fluorane

3-di-n-pentylamino-6-methyl-7-anilinofluorane 3-di-n-pentylamino-6-methyl-7- (p-chloroanilino) fluorane 3-di-n-pentylamino-7 -(M-trifluoromethylanilino) fluorane 3-di-n-pentylamino-6-chloro-7-anilinofluorane 3-di-n-pentylamino-7- (p-chloroanilino) fluorane 3-pyrrolidino -6-methyl-7-anilinofluorane 3-piperidino-6-methyl-7-anilinofluorane 3- (N-methyl-N-propylamino) -6-methyl-7-anilinofluorane 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane 3- (N-ethyl-N-cyclohexylamino) -6-methyl-7-ani Nofluorane 3- (N-ethyl-N-xylamino) -6-methyl-7- (p-chloroanilino) fluorane 3- (N-ethyl-p-toluidino) -6-methyl-7-anilinofluorane 3- ( N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane 3- (N-ethyl-N-isoamylamino) -6-chloro-7-anilinofluorane 3- (N-ethyl- N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane 3- (N-ethyl-N-isobutylamino) -6-methyl-7-anilinofluorane 3- (N-ethyl-N- Ethoxypropylamino) -6-methyl-7-anilinofluorane 3-cyclohexylamino-6-chlorofluorane 2- (4-oxahexyl) -3-dimethylamino -6-methyl-7-anilinofluorane 2- (4-oxahexyl) -3-diethylamino-6-methyl-7-anilinofluorane 2- (4-oxahexyl) -3-dipropylamino-6 -Methyl-7-anilinofluorane

2-Methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane 2-methoxy-6-p- (p-dimethylaminophenyl) aminoanilinofluorane 2-chloro-3-methyl-6- p- (p-phenylaminophenyl) aminoanilinofluoran 2-chloro-6-p- (p-dimethylaminophenyl) aminoanilinofluoran 2-nitro-6-p- (p-diethylaminophenyl) aminoani Linofluorane 2-amino-6-p- (p-diethylaminophenyl) aminoanilinofluorane 2-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane 2-phenyl-6-methyl-6 -P- (p-phenylaminophenyl) aminoanilinofluorane 2-benzyl-6-p- (p-fe Ruaminophenyl) aminoanilinofluorane 2-hydroxy-6-p- (p-phenylaminophenyl) aminoanilinofluorane 3-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane 3 -Diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane 3-diethylamino-6-p- (p-dibutylaminophenyl) aminoanilinofluorane 2,4-dimethyl-6-[(4- Dimethylamino) anilino] -fluorane

<Fluorene leuco dye>
3,6,6′-tris (dimethylamino) spiro [fluorene-9,3′-phthalide]
3,6,6′-tris (diethylamino) spiro [fluorene-9,3′-phthalide]
<Divinyl leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide 3,3-bis- [2- ( p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ethylene -2-yl] -4,5,6,7-tetrabromophthalide 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-yl]- 4,5,6,7-tetrachlorophthalide <Others>
3- (4-Diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide 3- (4-diethylamino-2-ethoxyphenyl) -3- (1 -Octyl-2-methylindol-3-yl) -4-azaphthalide 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4- Azaphthalide 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide 3,6-bis (diethylamino) fluorane-γ- (3′-nitro) anilinolactam 3,6-bis (diethylamino) Fluorane-γ- (4′-nitro) anilinolactam 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -Ethenyl] -2,2-dinitrileethane 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2-β-naphthoylethane 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2, 2-diacetylethane bis- [2, 2, 2 ′, 2'-Tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

-Other components The heat-sensitive recording layer may contain various additives such as a sensitizer, a stabilizer, and a pigment as long as the desired effects on the above-described problems are not impaired. As sensitizers, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-di- (3-methylphenoxy) ethane, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, 1, 2-diphenoxyethylene, bis [2- (4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate, dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate ), Dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolylca Nate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, 4- (m-methylphenoxymethyl) biphenyl, orthotoluenesulfonamide, paratoluenesulfonamide However, the present invention is not particularly limited thereto. These sensitizers may be used alone or in combination of two or more.

  As stabilizers, 4,4′-butylidene (6-tert-butyl-3-methylphenol), 2,2′-di-tert-butyl-5,5′-dimethyl-4,4′-sulfonyldiphenol 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenylbutane, 4- Benzyloxy-4 ′-(2,3-epoxy-2-methylpropoxy) diphenyl sulfone, epoxy resin, and the like can also be added.

  Examples of the pigment include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide. In addition, lubricants such as waxes, benzophenone and triazole ultraviolet absorbers, water resistance agents such as glyoxal, dispersants, antifoaming agents, antioxidants, fluorescent dyes, and the like can be used.

  As the binder, fully saponified polyvinyl alcohol having a polymerization degree of 200 to 1900, partially saponified polyvinyl alcohol, carboxy modified polyvinyl alcohol, amide modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, butyral modified polyvinyl alcohol, other modified polyvinyl alcohol, Hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, styrene-maleic anhydride copolymer, and cellulose derivatives such as ethyl cellulose, acetyl cellulose, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyllar polystyrene And their copolymers, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, B resin can be exemplified. These polymer substances are used by dissolving in water, alcohol, ketones, esters, hydrocarbons and other solvents, and are also used in the form of emulsification or paste dispersion in water or other media, depending on the required quality. Can also be used together.

(Preparation of paint and coating method)
The types and amounts of basic leuco dyes, developers, and other various components used in the heat-sensitive recording layer are determined according to the required performance and recording suitability, and are not particularly limited, but are usually basic leuco dyes. The developer is used in an amount of about 0.5 to 10 parts and about 0.5 to 10 parts of pigment. The binder is suitably about 5 to 25% by weight based on the solid content of the heat-sensitive recording layer.

  Basic leuco dye, color developer, and materials to be added as necessary are finely pulverized to a particle size of several microns or less by a pulverizer such as a ball mill, attritor or sand glider, or an appropriate emulsifying device. Depending on the conditions, various additive materials are added to obtain a coating solution. The thermal recording material of the present invention can be obtained by applying this coating liquid on the undercoat layer.

The means for applying is not particularly limited, and an off-machine coating machine or an on-machine coating machine equipped with various coaters such as an air knife coater, a bar coater, a blade coater, a roll coater, and a curtain coater is appropriately selected. The coating amount of the heat-sensitive recording layer is not particularly limited and is usually in the range of ² to 12 g / m ^{2 by} dry weight.

(Other)
The heat-sensitive recording material of the present invention is further provided with a protective layer (overcoat layer) such as a polymer material on the heat-sensitive recording layer for the purpose of improving the storage stability, or on the opposite surface of the support to the heat-sensitive recording layer. It is possible to correct the curl by providing a layer. Also, various known techniques in the heat-sensitive recording material field, such as supercalendering after the application of each layer other than the undercoat layer, can be appropriately added.

In the following, examples and comparative examples are given to further clarify the effects of the present invention, but the present invention is not limited to these examples. In addition, the part and% of an Example represent a weight part and weight%. The particle size of the pigment was measured with Mastersizer S manufactured by Malvern.

[Example 1]
1) Paper base paper and coating composition of the lowermost layer coating pulp is 95% LBKP (freeness 280 ml), NBKP (freeness 500 ml) 5%, and sizing agent is 0.13% for pulp as internal chemicals. After adding cationized starch to pulp 0.3%, wet paper strength enhancer 0.05% pulp, calcium carbonate 15% pulp as filler, and adding sulfuric acid band to pH 7.9. A base paper with a basis weight of 30 g / m ^{2 was made at} a paper making speed of 850 m / min using a twin wire sound top type paper machine. Next, a coating having the following composition was applied at a speed of 850 m / min using a rod metering size press (plain rod) method at 3 g / m ^{2 on} one side (6 g / m ^{2 on} both sides), and then watered with an after dryer. The paper was dried to 5%, treated with a soft calender and calendered with a linear pressure of 40 kN / m to produce a base paper coated with the lowermost layer.
(Undercoat paint)
Calcium carbonate (TP-123CS, manufactured by Okutama Kogyo, 60% slurry, particle size 0.41 μm)
62.5 parts kaolin (KCS, made by Imeris, particle size 1.40 μm, secondary kaolin)
37.5 parts latex (manufactured by Nippon Zeon, FT1344, concentration 50%) 22.5 parts starch (MS4600, phosphated starch, 30% solution) 12.5 parts water 45 parts
The smoothness of the obtained base paper was measured with a Beck smoothness meter and a Parker Print Surf Tester (PPS). The larger the value of Beck smoothness and the smaller the value of PPS, the higher the smoothness and the better.

2) Intermediate layer paint A composition comprising the following composition was stirred and dispersed to prepare an underlayer coating solution.
Baked kaolin (trade name: Ensilex 90, manufactured by Engelhard) 100 parts styrene / butadiene copolymer latex (solid content 48%) 40 parts polyvinyl alcohol (10% aqueous solution) 15 parts water 150 parts After coating on one side of the base paper obtained in 1) above with a blade coater, drying was performed to obtain an underpaper with a coating amount of 8 g / m ² .

3) Heat sensitive layer paint The developer dispersion (liquid A) and the basic colorless dye dispersion (liquid B) having the following composition were separately wet-ground with a sand grinder until the average particle size became 1 micron. .
Liquid A (developer dispersion)
4-hydroxy-4'-isopropoxydiphenylsulfone 6.0 parts polyvinyl alcohol (10% aqueous solution) 18.8 parts water 11.2 parts B liquid (basic colorless dye dispersion)
3-dibutylamino-6-methyl-7-anilinofluorane (ODB-2) 2.0 parts polyvinyl alcohol (10% aqueous solution) 4.6 parts water 2.6 parts Thus, a recording layer coating solution was obtained.
A liquid (developer dispersion) 36.0 parts B liquid (basic colorless dye dispersion) 9.2 parts kaolin clay (50% dispersion) 12.0 parts This recording layer coating liquid is obtained in 2) After applying onto the under layer of the under paper using a blade coater so that the application amount is 3.0 g / m ² , drying is performed, and the smoothness of the sheet is 600 to 700 seconds with a super calendar. A heat-sensitive recording material was obtained.

[Example 2]
A heat-sensitive recording material of Example 2 was obtained in the same manner as in Example 1 except that the amount of the undercoat paint applied in Example 1 was 1.5 g / m ² on one side (3 g / m ^{2 on} both sides).
[Example 3]
Except that the undercoat paint of Example 1 was applied 3 g / m ² on one side (6 g / m ^{2 on} both sides) using a rod metering size press using a grooved rod (rod groove width: 0.2 mm), A heat-sensitive recording material of Example 3 was obtained in the same manner as Example 1.
[Example 4]
A heat-sensitive recording material of Example 4 was obtained in the same manner as in Example 1 except that the undercoat paint of Example 1 was changed to the following composition.
Calcium carbonate (TP-123CS) 54 parts Kaolin (KCS) 20 parts Latex (manufactured by Nippon Zeon, FT1344) 18.5 parts starch (MS4600, phosphate esterified starch) 18.5 parts Water 28 parts

[Comparative Example 1]
After making a base paper under the same conditions as in Example 1, a solution of oxidized starch (Ace B manufactured by Oji Cornstarch Co., Ltd.) = 3% on a single side 0.3 g / m ² (both sides 0. A heat-sensitive recording material of Comparative Example 1 was obtained in the same manner as in Example 1 except that 6 g / m ² ) was applied.

[Evaluation of thermal recording medium]
The thermal recording materials obtained in Examples and Comparative Examples were evaluated according to the following evaluation items.
(Print density evaluation)
Printing was performed using TH-PMD manufactured by Okura Electric Co., Ltd. with an applied energy of 0.34 mj / dot. The image density after printing was measured with a Gretag Macbeth densitometer RD-19I.
(Image quality evaluation)
Printing was performed using TH-PMD manufactured by Okura Electric Co., Ltd. with an applied energy of 0.21 mj / dot. The unevenness of the color image was visually evaluated.
○: Coloring unevenness is hardly seen. Δ: Coloring unevenness is slightly seen.
X: Coloring unevenness is observed.
(Storability)
After leaving for 24 hours under conditions of 50 ° C. and 90% RH, printing was performed at a applied energy of 0.34 mj / dot using TH-PMD manufactured by Okura Electric Co., Ltd. The image density after printing was measured with a Gretag Macbeth densitometer RD-19I.

Claims (4)

A heat-sensitive recording medium comprising a support and an undercoat layer mainly composed of a pigment and a binder, and a heat-sensitive recording layer mainly composed of an electron-donating leuco dye and an electron-accepting developer, wherein the undercoat layer Contains at least kaolin as a pigment. The heat-sensitive recording material according to claim 1, wherein the undercoat layer contains kaolin and calcium carbonate as pigments. The thermal recording material according to claim 2, wherein the average particle diameter of kaolin contained in the undercoat layer is 2 µm or less and the average particle diameter of calcium carbonate is 1 µm or less. The heat-sensitive recording material according to claim 1, wherein the undercoat layer is provided under a film transfer system.