JP2005280117A - Manufacturing method of thermal recording body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a thermal recording body excellent in recording sensitivity, an image quality and head matching properties. <P>SOLUTION: The thermal recording body is formed by laying an undercoat layer and a thermal recording layer sequentially on a substrate. After a coating solution of the undercoat layer made to contain a fluidity modifier is applied in this manufacturing method of the thermal recording body, the thermal recording layer is provided by curtain coating. As for the fluidity modifier, carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate or hydroxyalkyl etherified starch is preferable. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a thermal recording material utilizing a color development reaction between a basic colorless dye and a developer.

In general, a heat-sensitive recording medium is usually a colorless or light-colored basic colorless dye and an organic developer such as a phenolic compound, which are ground and dispersed into fine particles, and then mixed together to obtain a binder and sensitivity. A coating liquid obtained by adding an improving agent, a lubricant and other auxiliary agents is applied to a support such as paper, synthetic paper, film, plastic, thermal head, hot stamp, thermal pen, Color is developed by an instantaneous chemical reaction by heating with laser light or the like, and a recorded image is obtained. Such heat-sensitive recording methods are characterized by low noise during recording, no need for development and fixing, maintenance-free, relatively inexpensive and compact equipment, and very clear color development. It has been used in the facsimile and computer fields, cash register paper, various measuring instruments and labels. In recent years, the use of cash vouchers / tickets and handy terminals has been diversified, so various printers have been introduced for each application, and high-quality recorded images can be obtained in a wide range of applied energy. It has been demanded.
In addition to this, since printing speed and low energy are increasing in recent years due to the miniaturization and high performance of printers for energy saving purposes, high density and high quality images can be obtained even with minute heat energy. It is requested.

As a method for satisfying these requirements, conventionally, the smoothness of the surface of the heat-sensitive recording layer has been generally increased by a super calender or the like, but satisfactory image quality has not necessarily been obtained. In order to obtain high image quality, it is known that the coating uniformity of the undercoat layer is important. For example, it is known to improve the smoothness of the undercoat layer by using a super calendar. In Patent Document 1, in order to provide a thermosensitive recording material having excellent dot reproducibility, a first intermediate layer and a second intermediate layer are sequentially laminated between the support and the thermosensitive coloring layer, and the first intermediate layer is provided. It is described that the Oken smoothness of the layer is 700 seconds or more and the density of the second intermediate layer is 0.1 or less.
On the other hand, in order to obtain a high-sensitivity heat-sensitive recording sheet, for example, in Patent Document 2, two or more intermediate layers are provided between the support and the color-developing layer, and carboxymethyl cellulose and / or hydroxyethyl cellulose is used as the uppermost layer. It is described that it is contained in an amount of 0.3 to 3% by weight based on the pigment.
Patent Document 3 describes that a thermal recording layer is curtain-coated in order to obtain a thermal recording material excellent in sensitivity, image quality, and head matching.

JP 2000-108518 A JP-A-4-3488989 JP 2003-182229 A

However, in the case of the technique related to the undercoat layer, the supercalender method impairs the porosity of the undercoat layer due to the calendar pressure, loses the heat insulation, and lowers the sensitivity. The method of laminating a plurality of intermediate layers is disadvantageous in manufacturing because the process is complicated. Curtain coating is a coating method that is greatly affected by the object to be coated. Even if the thermal recording layer is curtain coated, it is good if a material suitable for curtain coating is not used. Can't get good quality.
Therefore, an object of the present invention is to provide a method for producing a thermosensitive recording material that has a high recording sensitivity and can obtain a high-quality recorded image without causing these problems.

In the method for producing a thermal recording body in which an undercoat layer and a thermosensitive recording layer are sequentially laminated on a support, the above-described problem is solved by applying a primer layer coating liquid containing a fluidity modifier and then performing thermal recording. This was achieved by providing the layer by curtain coating.
The reason why an excellent effect is obtained in the present invention is not clear, but is presumed as follows. As one of the causes of image quality degradation, it is considered that when a coating liquid is applied on a support, a water-soluble component in the coating liquid migrates (moves) to the coated body. As a result, the binder distribution and pigment orientation in the coating layer become non-uniform, and heat energy cannot be transmitted uniformly during recording. As a result, particularly in low-energy printing, since sufficient heat energy cannot be applied, it is considered that the dots become uneven and the image quality deteriorates. In addition, when a heat-sensitive recording layer is applied on a non-uniform undercoat layer, the coating liquid sinks and the heat-sensitive recording layer becomes non-uniform, resulting in a decrease in image quality. End up.
As another cause of image quality degradation, when a thermal recording layer is provided on the undercoat layer by blade coating generally used, the surface of the thermal recording layer becomes smooth by scraping the blade. Usually, the surface of the undercoat layer is directly affected by the unevenness of the base paper and is not smooth compared to the surface of the thermosensitive recording layer. As a result, the thickness of the heat-sensitive recording layer becomes non-uniform, and when heat energy is applied, the amount of the color forming material varies depending on the location, resulting in uneven color development. In particular, in high energy printing, the color is more intense in the thick part and the image quality is degraded.
On the other hand, in the present invention, by applying curtain coating to the heat-sensitive recording layer, the coating liquid is not scraped off and contour coating can be performed. Therefore, it is considered that the heat-sensitive recording layer is formed along the contour of the undercoat layer, the thickness of the recording layer becomes uniform, the print density is not uneven, and the image quality is improved.

Moreover, since the fluidity modifier is contained in the undercoat layer, the water retention and fluidity of the coating liquid are improved and the movement of the water-soluble component is suppressed, so that a uniform undercoat layer is formed. As a result, the heat energy is uniformly transmitted and the sink of the coating liquid is suppressed, and the image quality is improved. The present inventors have found that carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, and hydroxyalkyl etherified starch are particularly effective as the fluidity modifier. By providing a heat-sensitive recording layer by curtain coating on an undercoat layer using these, it becomes possible to provide a heat-sensitive recording material having high image quality and sensitivity, and a heat-sensitive recording material with good head matching. It is possible to obtain
In general, exposure of an undercoat layer that contains a large amount of pigment with high head wear resistance deteriorates head matching and promotes head wear and causes dot dropout.In the present invention, curtain coating is performed. This makes it possible to provide a heat-sensitive recording layer having a very high coatability of the undercoat layer, and it is considered that the effect of improving the head matching property can be obtained.

  According to the present invention, it is possible to obtain a heat-sensitive recording material having good recording sensitivity and image quality, good head matching, and high practicality.

Embodiments of the present invention will be described below.
The undercoat layer in the present invention contains a pigment and a binder as main components, and preferably contains carboxymethyl cellulose and hydroxyethyl cellulose, sodium alginate, or hydroxyalkyl etherified starch as a fluidity modifier. Hereinafter, each case will be described.

[Carboxymethylcellulose]
In the present invention, it is desirable to use carboxymethyl cellulose having an etherification degree of 0.55 to 0.75. Here, the degree of etherification represents an average value obtained by replacing the hydroxyl group of cellulose with a carboxymethyl group. The lower the degree of etherification, the more hydroxyl groups there are, and the easier it is to form hydrogen bonds with water molecules, so the water retention of the coating liquid tends to improve, but the hydrogen bonds between the molecules of carboxymethyl cellulose become stronger (the crystallinity increases). Therefore, it is difficult to dissolve in water, and it becomes difficult to prepare a coating solution, resulting in poor operability. On the other hand, when the degree of etherification is high, the reverse is true, but the water retention of the coating liquid is inferior. In the present invention, the degree of etherification is preferably 0.55 to 0.75, and more preferably 0.55 to 0.65 from the balance of both.
In addition, the higher the degree of polymerization of carboxymethylcellulose, the higher the water retention because water can be taken into the molecule. However, on the other hand, since the viscosity of the aqueous solution becomes high, if the degree of polymerization is too large, coating or preparation of the coating solution becomes difficult. Therefore, the polymerization degree of carboxymethyl cellulose is desirably 2000 or less, and more preferably 500 to 1500 in consideration of water retention.
The amount of carboxymethylcellulose used is not sufficient water retention when the amount of carboxymethylcellulose is too small, and the preferred amount is about 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the pigment. More preferably, it is 0.3 parts by weight or more and 2.0 parts by weight or less.

[Hydroxyethyl cellulose]
Since the hydroxyethyl cellulose used in the present invention itself has a structural viscosity, the fluidity in a state where the shear is applied is high, and it tends to be immobilized in a place where the shear is low. Therefore, it is presumed that when the coating liquid is applied, the coating extends smoothly, and after coating, the coating immediately solidifies to form a uniform coating layer, thereby providing an undercoat layer that contributes to image homogeneity.
Moreover, it is thought that hydroxyethyl cellulose has an improvement effect also about the water retention of a coating liquid, The etherification degree has preferable 0.8-2.0, More preferably, it is 1.0-1.5. The reason for this is the same as for carboxymethylcellulose. The lower the degree of etherification, the better the water retention, but the water solubility tends to be poor. Conversely, the higher the degree of etherification, the lower the water retention, This is because the solubility is improved and the handling becomes easier. In addition, the etherification degree of hydroxyethyl cellulose represents an average value obtained by substituting the hydroxyl group of cellulose with ethylene oxide.
The preferred amount of use of hydroxyethyl cellulose is 0.3 to 3.5 parts by weight with respect to 100 parts by weight of the pigment. If the amount of hydroxyethyl cellulose used is too small, the water retention and fluidity will not be sufficiently improved. Conversely, if the amount is too large, the viscosity will increase and coating will be difficult. As for the usage-amount of a hydroxyethyl cellulose, it is desirable to contain 0.5-5.0 weight part with respect to 100 weight part of pigments in total with carboxymethylcellulose. More preferably, the amount is 0.5 to 3.5 parts by weight with respect to 100 parts by weight of the pigment.

[Sodium alginate]
The sodium alginate used in the present invention has the effect of improving the water retention of the coating solution, thereby improving the migration of the binder and obtaining a uniform coating layer. When the amount of sodium alginate blended is too small, sufficient water retention cannot be obtained. Conversely, when it is too large, the viscosity becomes high and coating becomes difficult and the operability deteriorates. In this invention, it is desirable to contain 0.01-0.05 weight part of sodium alginate with respect to 100 parts of pigments. More preferably, the content is 0.01 to 1 part by weight with respect to 100 parts by weight of the pigment.

[Hydroxyalkyl etherified starch]
The hydroxyalkyl etherified starch used in the present invention functions as a fluidity modifier and a part of a binder, and can improve water retention and fluidity. Thus, migration of the binder is prevented, and a uniform coating layer is obtained and considered to be effective. In addition, when the number of the hydroxyalkyl etherified starch is too small, sufficient water retention is not obtained, and conversely, when it is too large, the proportion of the pigment is relatively low, The ability of will decline.
As the hydroxyalkyl etherified starch used in the present invention, hydroxyethyl etherified starch and hydroxypropyl etherified starch are practical, and the former is particularly desirable. The hydroxyalkyl ether in the present invention preferably has a molecular weight of 200,000 to 1,000,000, more preferably 500,000 to 850,000, and a degree of substitution of 0.02 to 0.065. The hydroxyalkyl etherified starch is desirably contained in an amount of 0.1 to 25.0 parts by weight with respect to 100 parts by weight of the pigment. More preferably, it is 1.0 to 10.0 parts by weight with respect to 100 parts by weight of the pigment.

[Pigment]
The undercoat layer and the heat-sensitive recording layer of the present invention include silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, aluminum hydroxide, aluminum oxide, magnesium carbonate, aluminum silicate, magnesium silicate. Inorganic or organic fillers such as calcium silicate can be used as appropriate.
In particular, in the undercoat layer, it is desirable to use a calcined kaolin having an oil absorption (based on the JIS K5101 method) of 80 cc / 100 g to 120 cc / 100 g because the balance between color development sensitivity and image quality is good. This is because, by blending a calcined kaolin with a high hollowness, a sufficient heat insulating effect is given and the sensitivity is increased, and since the binder is not absorbed too much by the pigment, a uniform coating layer is formed. It is thought that. On the other hand, the use of calcined kaolin tends to be inferior in fluidity of the coating liquid because of its generally flat shape, and since it is calcined, the hydroxyl group of silanol does not exist on the surface, and it binds with water. It is considered that the water retention of the coating liquid tends to be lowered. On the other hand, in the present invention, it is considered that the fluidity and water retention of the coating solution are improved by the action of carboxymethylcellulose, hydroxyethylcellulose, sodium alginate, hydroxyalkyl etherified starch and the like.

[binder]
As a binder in the undercoat layer and the heat-sensitive recording layer of the heat-sensitive recording material of the present invention, fully saponified polyvinyl alcohol having a polymerization degree of 200 to 1900, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, and 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 and acetyl cellulose, polyvinyl chloride, poly Vinyl acetate, polyacrylamide, polyacrylate, polyvinyl butyllar polystyrene, and copolymers thereof, polyamide resin, Con resins, petroleum resins, terpene resins, ketone resins, Khumalo resin, colloidal silica, and the like can be exemplified acrylic emulsion. 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.

[dye]
As the colorless to light-colored basic colorless dye used in the heat-sensitive recording layer of the present invention, all conventionally known dyes in the field of conventional heat-sensitive or pressure-sensitive recording paper can be used, and are not particularly limited. Triphenylmethane compounds, fluorane compounds, fluorene compounds, divinyl compounds and the like are preferable. Specific examples of typical colorless or light-colored basic colorless dyes are shown below. These basic colorless dyes 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-dibutylamino-6- Methyl-fluorane 3-dibutylamino-6-methyl-7-anilinofluorane 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane 3-dibutylamino-7- (o-chloroanilino ) Fluorane 3-dibutylamino-7- (o-fluoroanilino) fluorane 3-n-dipentylamino-6-methyl-7-anilinofluorane 3- (N-ethyl-N-isoamylamino) -6-methyl -7-anilinofluorane 3- (N-ethyl-N-isoamylamino) -6-chloro-7-anilinofluor Lan 3-cyclohexylamino-6-chlorofluorane <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-dimethylaminopheny L) -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-diacetylethanebis- [2,2,2 ', 2'-tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

[Developer]
As the developer used in the heat-sensitive recording layer of the present invention, a conventionally known developer that develops a colorless or light basic dye can be used in combination. Examples of the color developer include bisphenol A, 4-hydroxybenzoic acid esters, 4-hydroxyphthalic acid diesters, and phthalic acid monoesters described in JP-A-3-207688 and JP-A-5-24366. Esters, bis- (hydroxyphenyl) sulfides, 4-hydroxyphenylaryl sulfones, 4-hydroxyphenylaryl sulfonates, 1,3-di [2- (hydroxyphenyl) -2-propyl] -benzenes, Examples thereof include 4-hydroxybenzoyloxybenzoic acid esters, bisphenol sulfones, diphenylsulfone bridged compounds described in International Publication No. WO 97/16420, and compounds described in International Publication No. WO 02/081229 or JP-A No. 2002-301873.

[Sensitizer]
A conventionally known sensitizer can be used in the heat-sensitive recording layer of the present invention. Such sensitizers include fatty acid amides such as stearic acid amide and palmitic acid amide, 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, dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate, Dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis -(Phenyl ether), 4- (m-methyl) Phenoxymethyl) biphenyl, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, bis [2- (4-methoxy-phenoxy) ) Ethyl] ether, methyl p-nitrobenzoate, and phenyl p-toluenesulfonate, but are not particularly limited thereto. These sensitizers may be used alone or in combination of two or more.

[Other additives]
For the heat-sensitive recording material of the present invention, conventionally known image stabilizers can be used for the purpose of imparting an oil resistance effect to the recorded image. Such image stabilizers include 4,4'-butylidene (6-tert-butyl-3-methylphenol), 2,2'-di-tert-butyl-5,5'-dimethyl-4,4'-sulfonyldi Phenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, etc. Can be illustrated.
In addition, conventionally known surfactants can be used for adjusting the coating solution for the undercoat layer or the heat-sensitive recording layer. Among them, a surfactant having ethylene oxide and propylene oxide added to tetra-methyl-decyne-diol is used. Agents are desirable because they exhibit very good performance. In particular, it is desirable to use a surfactant having an ethylene oxide / propylene oxide ratio of 1/9 to 9/1.
In addition, release agents such as fatty acid metal salts, lubricants such as waxes, UV absorbers such as benzophenones and triazoles, water resistance agents such as glyoxal, dispersants, antifoaming agents, antioxidants, fluorescent dyes, A thickener or the like can be added.

[Support]
For the support in the present invention, known paper, recycled paper, synthetic paper, film, plastic film, and foamed plastic film can be used, and are not particularly limited. Moreover, you may use the composite sheet which combined these as a support body.
The base paper used for the paper support is manufactured by making paper from wood pulp. As wood pulp, either softwood pulp or hardwood pulp can be used, but hardwood pulp that is short fiber and easy to produce smoothness is more desirable. If necessary, a part of the wood pulp may be replaced with synthetic pulp made of polyethylene, polypropylene or the like, or synthetic fiber made of polyester, polyvinyl alcohol, nylon or the like. An internal sizing agent such as rosin, paraffin wax, higher fatty acid salt, alkenyl succinate, fatty acid anhydride, and alkyl ketene dimer may be added to the base paper. As internal chemicals other than the internal size, polyacrylamide, starch, polyvinyl alcohol, melamine formaldehyde condensate, etc., paper strength enhancer, reaction product of maleic anhydride copolymer and polyalkylene polyamine, higher fatty acid quaternary ammonium salt Softeners such as calcium carbonate, talc, clay, kaolin, titanium dioxide, urea resin fine particles, fixing agents such as sulfate bands, polyamide polyamine epichlorohydrin, fluorescent dyes, etc. are added to the base paper as necessary. Also good.
In addition, a conventionally known surface sizing agent may be applied to the surface of the base paper, and an undercoat layer according to the present invention may be provided thereon. Examples of the surface sizing agent include polyvinyl alcohol, starch, polyacrylamide, gelatin, casein, styrene maleic anhydride copolymer, alkyl ketene dimer, polyurethane, epoxidized fatty acid amide and the like.

[Production method of undercoat]
The undercoat layer in the present invention can be applied according to well-known conventional techniques. For example, an off-machine coating machine or an on-machine coating machine equipped with various coaters such as an air knife coater, a rod blade coater, a bill blade coater, a roll coater, and a curtain coater. A machine can be used as appropriate, but high-concentration coating is possible, giving uniform orientation to the components in the coating liquid, and blade coating is desirable. Vent blade coating that can be most desirable. The coating amount of the undercoat layer is about 1 to 15 g / m ² and is not particularly limited.
In applying the undercoat layer, the concentration of the coating solution is desirably 32% or more, and more desirably 35% or more. Further, it is desirable that the coating liquid viscosity has a Brook fillet type viscosity (B type viscosity) at 25 ° C. of 200 cps or more. Furthermore, the viscosity at a shear rate of 4.0 × 10 ⁻⁵ sec ^{−1 to} 8.0 × 10 ⁻⁵ sec ⁻¹ at 25 ° C. is desirably 20 cps or more, and more desirably 30 cps.
The former type B viscosity corresponds to the viscosity with respect to the shear when the coating liquid is supplied to the support by the applicator, while the latter corresponds to the coating liquid being scraped off from the support by a blade or the like. It is the viscosity with respect to the market share. If the coating liquid does not have an appropriate viscosity when supplied by the applicator, it will be difficult to uniformly supply the coating liquid, and it may be due to capillarity, etc., after being supplied to the support and then scraped off. Penetration of the coating liquid to the support tends to occur. Moreover, if it does not have an appropriate viscosity with respect to the share at the time of scraping, the coating liquid will be excessively pushed into the support by the pressure of scraping. On the other hand, it is considered that by using the coating liquid exhibiting the above viscosity, the movement of the coating liquid to the support is suppressed, and a uniform coating layer with good covering is formed.

[Method for producing thermosensitive recording layer]
The types and amounts of basic colorless dyes, developers, and other various components used in the heat-sensitive recording layer of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. About 0.5 to 10.0 parts of developer and 0.5 to 10.0 parts of filler are used with respect to 1 part of the neutral colorless dye.
Basic colorless dyes, color developers, and materials to be added as necessary are finely pulverized to a particle size of several microns or less with a pulverizer such as a ball mill, attritor, or sand glider, or an appropriate emulsifying device. Add ingredients to make a coating solution. By applying this coating liquid, the desired heat-sensitive recording material is obtained.
The heat-sensitive recording layer in the present invention is applied by a conventionally known curtain coating. Examples of the curtain coating apparatus to be used include an extrusion hopper type curtain coating apparatus and a slide hopper type curtain coating apparatus, but are not particularly limited. Further, the coating amount of the thermosensitive recording layer is not particularly limited, and is usually in the range of ² to 12 g / m ^{2 by} dry weight. It is also possible to apply a plurality of layers simultaneously with a curtain coating device. Examples of the combination of layers for simultaneous multilayer coating include an undercoat layer and a thermal recording layer, a thermal recording layer and an over layer, an undercoat layer, a thermal recording layer and an over layer, a combination of a plurality of thermal recording layers, and the like. There is no particular limitation.

[Other laminated structures]
The heat-sensitive recording material of the present invention is further provided with an overcoat layer such as a polymer substance on the heat-sensitive recording layer for the purpose of improving storage stability, or a backcoat layer is provided on the opposite surface of the support to the heat-sensitive recording layer, It is also possible to correct the curl. Also, various known techniques in the heat-sensitive recording material field, such as a smoothing process such as a super calendar process after application of each layer, can be added as necessary.
〔Example〕

The thermosensitive recording material of the present invention will be described below with reference to examples. In the description, parts and% indicate parts by weight and% by weight, respectively. Various solutions, dispersions, or coating solutions were prepared as follows.
[Example 1]
A composition comprising the following composition was stirred and dispersed to prepare an undercoat layer coating solution.
Undercoat layer coating solution Firing kaolin (trade name: Ansilex 90 manufactured by Engelhard)
100.0 parts Styrene-butadiene copolymer latex (solid content 48%) 40.0 parts Polyvinyl alcohol 10% aqueous solution 30.0 parts Carboxymethyl cellulose 2% aqueous solution (Polymerization degree: 500-600, ether value: 0.55 ~ 0.65)
25.0 parts Hydroxyethyl cellulose 2% aqueous solution (Ether number: 1.21)
25.0 parts Water 122.0 parts Then, after applying the undercoat layer coating solution to one side of the support (100 g / m ² base paper) by the vent plate coating method, drying is performed, and the coating amount is 10.0 g / An undercoat layer of m ² was obtained.
The developer dispersion liquid (liquid A) and the basic colorless dye dispersion liquid (liquid B) having the following composition were separately wet-ground with a sand grinder until the average particle diameter 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 Liquid B (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 Subsequently, the dispersion was mixed in the following ratio to obtain a coating solution for the heat-sensitive recording layer.
Thermosensitive recording layer coating liquid A liquid (developer dispersion) 36.0 parts B liquid (basic colorless dye dispersion) 9.2 parts fine silica (30% dispersion) 33.3 parts polyvinyl alcohol 10% aqueous solution 25 0.0 part Next, the heat-sensitive recording layer coating solution is applied onto the undercoat layer of the undercoat layer-formed paper by using a slide hopper type curtain coating apparatus so that the coating speed is 400 m / min and the coating amount is 6.0 g / m ^2. After coating, the sheet was dried, and this sheet was processed with a super calender so that the smoothness was 500 to 600 seconds to obtain a heat-sensitive recording material.

[Example 2]
In the undercoat layer coating solution of Example 1, the carboxymethyl cellulose was changed to one having an ether value of 0.65 to 0.75, and the hydroxyethyl cellulose was changed to an ether value of 1.32. A heat-sensitive recording material was obtained.
[Example 3]
Heat sensitive in the same manner as in Example 1 except that the carboxymethyl cellulose aqueous solution and the hydroxyethyl cellulose aqueous solution were replaced with 5 parts of a 2% aqueous solution of sodium alginate and the number of parts of water was changed to 164.7 parts. A record was obtained.
[Example 4]
A heat-sensitive recording material was obtained in the same manner as in Example 3 except that in the undercoat layer coating liquid of Example 3, the number of parts of the 2% aqueous solution of sodium alginate was changed to 50 parts and the number of water parts was changed to 115 parts.
[Example 5]
Example 1 In the undercoat layer coating solution of Example 1, the carboxymethyl cellulose aqueous solution and the hydroxyethyl cellulose aqueous solution were replaced with 10 parts of a hydroxyethylated starch 10% aqueous solution, and the number of parts of water was changed to 162.2 parts. A heat-sensitive recording material was obtained.
[Example 6]
In the undercoat layer coating solution of Example 5, the number of parts of the 10% aqueous solution of hydroxyethylated starch was changed to 50 parts, the number of parts of the 10% aqueous solution of polyvinyl alcohol was changed to 20 parts, and the number of parts of water was changed to 60 parts. A heat-sensitive recording material was obtained in the same manner as in Example 5.

[Comparative Example 1]
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that the carboxymethyl cellulose aqueous solution and the hydroxyethyl cellulose aqueous solution were not blended in the undercoat layer coating solution of Example 1.
[Comparative Example 2]
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that the heat-sensitive layer was provided by blade coating.
[Comparative Example 3]
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that the heat-sensitive layer was provided by air knife coating.

<Image quality evaluation>
Printing was performed using TH-PMD (equipped with thermal recording paper printing tester, Kyocera thermal head) manufactured by Okura Electric Co., Ltd., and the solid print portion was visually evaluated.
Low energy part: Applied energy 0.18 mJ / dot
○: No white spots are observed.
Δ: Some white spots are observed.
X: A white portion is observed.
High energy part: Applied energy 0.33 mJ / dot
○: Printing unevenness is not observed.
Δ: Printing unevenness is slightly observed.
X: Printing unevenness is observed.

<Recording sensitivity evaluation>
Printed with an applied energy of 0.27 mJ / dot using TH-PMD (equipped with thermal recording paper printing tester, Kyocera thermal head) manufactured by Okura Electric Co., Ltd., and Macbeth densitometer (RD-914, using amber filter) Was measured and evaluated.

<Head wear evaluation>
The produced thermal recording medium was subjected to a long run test using a SII serial printer to evaluate whether a printing failure occurred.
○: No missing dot △: Blurred printing ×: Missing dot

Claims (5)

  In a method for producing a heat-sensitive recording material comprising a base layer and a heat-sensitive recording layer sequentially laminated on a support, after applying an undercoat layer coating solution containing a fluidity modifier, the heat-sensitive recording layer is curtain-coated. A method for producing a heat-sensitive recording material, characterized by being provided by a process.   2. The method for producing a heat-sensitive recording material according to claim 1, wherein the fluidity modifier is carboxymethyl cellulose having an ether value of 0.55 to 0.75 and / or hydroxyethyl cellulose having an ether value of 0.80 to 1.50.   The method for producing a heat-sensitive recording material according to claim 1, wherein the fluidity modifier is sodium alginate.   2. The method for producing a heat-sensitive recording material according to claim 1, wherein the fluidity modifier is a hydroxyalkyl etherified starch. The B-type viscosity at 25 ° C. of the undercoat layer coating solution is 200 cps or more, and the viscosity at a shear rate of 4.0 × 10 ⁻⁵ sec ^{−1 to} 8.0 × 10 ⁻⁵ sec ⁻¹ is 20 cps or more. 3. A method for producing a heat-sensitive recording material according to 3 or 4.