JP2007160641A - Coating for thermal recording medium, thermal recording medium and manufacturing method of thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain coating for a thermal recording medium which prevents a coating defect of an image part resulting from a foam in the coating on the occasion when a layer constituting the thermal recording medium, particularly the outermost layer, is formed by curtain-method coating, and the thermal recording medium which is free from the defect of the image part resulting from the foam in the coating. <P>SOLUTION: The thermal recording medium, at least the outermost layer thereof, is formed by using the coating for the thermal recording medium wherein the amount of dissolved oxygen is 2.0 mg/l or less. By defoaming treatment under the condition of a vacuum value of -99 Kpa or less, in particular, the coating for the thermal recording medium having the amount of dissolved oxygen of 2.0 mg/l or less can be obtained. An excellent effect can be attained when the outermost layer of the thermal recording medium is formed by the curtain coating. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a heat-sensitive recording material, and more particularly to a paint for a heat-sensitive recording material that is applied by a curtain coating method, a heat-sensitive recording material using the same, and a method for producing the same.

In general, a heat-sensitive recording material that obtains a recorded image by utilizing a color development reaction of a colorless or light-colored basic leuco dye and a developer with heat is very clear in color, and there is no noise during recording. Due to the advantages of being relatively inexpensive, compact, and easy to maintain, it has been widely put into practical use in the fields of facsimiles, computers, various measuring instruments and the like. Furthermore, recently, in addition to labels and tickets, applications are rapidly expanding as output media for various printers and plotters such as small portable terminals (handy terminals) for outdoor measurement and delivery slips. With the expansion of this application, the quality of the thermal recording material is required to have higher color development sensitivity and superior image reproducibility than ever before.

In order to improve the color development sensitivity and image reproducibility, it is important to uniformly provide a heat-sensitive recording layer or a protective layer provided on the heat-sensitive recording layer. As a method for forming the heat-sensitive recording layer and the protective layer, air knife coating, blade coating, gate roll coating and the like are known. However, since air knife coating produces a unique pattern called a so-called wind pattern, the disadvantage is that the color development sensitivity is likely to be uneven, and the coating amount derived from the uneven thickness of the support in blade coating. There is a disadvantage that unevenness is likely to occur, and in roll coating, there is a disadvantage that unevenness in coating amount is likely to occur when the coating liquid is transferred from a roll called a so-called split pattern to a support.
One of the methods for eliminating the disadvantages derived from these coating methods is curtain coating. This curtain coating allows the paint to fall freely or under pressure from the clearance in the curtain coating head, and it will not be scraped off after the paint has been applied to the support. Unevenness of color development sensitivity and image reproducibility is not caused. The curtain coating method does not scrape the paint after the paint is applied on the support, so if foam is mixed in the paint, the part containing the foam tends to be cratered There are problems with color development sensitivity and image reproducibility due to the influence of the bubbles.

With respect to this problem, Patent Document 1 discloses a technique for suppressing the occurrence of an uncoated part during curtain coating by defining a steady viscosity with respect to the shear rate of the paint. Techniques for defining the ratio of shear viscosity are disclosed. Patent Document 3 discloses a technique for performing vacuum defoaming so that the specific gravity of the paint is 95% or more of the true specific gravity.

JP 2001-038284 A JP 09-29166 A Japanese Patent Laid-Open No. 05-92656

However, since the techniques disclosed in Patent Document 1 and Patent Document 2 do not remove the bubbles contained during the adjustment of the paint, the effect is insufficient. Patent Document 3 discloses a method of vacuum defoaming treatment so that the specific gravity of the paint is 95% or more of the true specific gravity. Under general conditions, however, very fine bubbles in the paint are removed. The effect is insufficient.

  Accordingly, the problem to be solved by the present invention is to prevent coating defects derived from bubbles in the paint when the thermal recording material, particularly the outermost layer, is coated by the curtain method.

As a result of intensive studies, the present inventors have found that coating defects due to bubbles in the paint can be prevented by setting the dissolved oxygen content in the paint for thermal recording media to 2.0 mg / l or less. Reached.
That is, the present invention
1) A heat-sensitive recording material paint, wherein the paint has a dissolved oxygen content of 2.0 mg / l or less.
2) The present invention is the heat-sensitive recording paint described in 1) above, which is defoamed under a vacuum value of −99 Kpa or less.
3) A method for producing a heat-sensitive recording material, wherein at least the outermost layer of the heat-sensitive recording material is formed using the heat-sensitive recording material paint described in 1) or 2).
4) The method for producing a heat-sensitive recording material according to claim 3, wherein a curtain coating method is used.

According to this invention, the coating defect derived from the foam in a coating material can be prevented by making the coating material for thermal recording bodies for curtain coating into 2.0 mg / l or less. In particular, it is very useful when a thermal recording material coating material is applied to a support by a curtain coating method.

The present invention will be specifically described below.
The heat-sensitive recording material coating material of the present invention comprises an electron-donating leuco dye (hereinafter sometimes referred to as a dye) and an electron-accepting color developer (hereinafter also referred to as a color developer) that constitute the heat-sensitive recording material. Used in an undercoat layer provided between the support and the thermal recording layer, a protective layer provided on the thermal recording layer, and an intermediate layer provided between the thermal recording layer and the protective layer. be able to. That is, in the present invention, the heat-sensitive recording material paint is any one of a heat-sensitive recording layer paint, an undercoat paint, a protective layer paint, and an intermediate paint. The heat-sensitive recording material of the present invention is one in which any one of the layers constituting the heat-sensitive recording material is formed using a paint having a dissolved oxygen content of 2.0 mg / l or less.

In the present invention, when a layer is formed using a paint having a dissolved oxygen amount of 2.0 mg / l or less, the formed layer does not generate coating defects due to bubbles in the paint. When used for a layer, the occurrence of white spots in a solid image portion can be suppressed. In addition, when used in the protective layer, heat from the thermal head is uniformly transmitted to the thermal recording layer, and when used in the undercoat layer, the heat insulating effect becomes uniform, thereby suppressing uneven color development sensitivity in the solid image area. be able to.

In the present invention, the coating for the heat-sensitive recording layer includes an electron-donating leuco dye and a color developer, and, if necessary, a sensitizer, a binder, a pigment, an image stabilizer, an ultraviolet absorber, an ultraviolet blocking agent, a lubricant, and the like. These materials are included. Examples of these materials are shown below, but the present invention is not particularly limited thereto.

  As the electron-donating leuco dye, any of those known in the field of conventional pressure-sensitive or thermal recording paper can be used, and is not particularly limited. However, triphenylmethane compounds, fluorane compounds, fluorene compounds, A divinyl compound is preferred. Specific examples of typical ones are shown below. These dye precursors can 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-benzylanilinofluorane 3-diethylamino-6-methyl-7-dibenzylanilinofluorane 3-diethylamino-6-chloro -7-methylfluorane 3-diethylamino-6-chloro-7-anilinofluorane 3-diethylamino-6-chloro-7-p-methylanilinofluorane 3-diethylamino-6-ethoxyethyl-7-anilino Fluorane 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) fluor Down 3-diethylamino-7-(o-fluoroanilino) fluoran 3-diethylamino - benzo [a] fluoran 3-diethylamino - benzo [c] fluoran

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-7-chlorofluorane 3-dibutylamino-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-anilinofluorane 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-isobutane) Arylamino) -6-methyl-7-anilinofluoran 3- (N- ethyl--N- ethoxypropylamino) -6-methyl-7-anilinofluoran

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) aminoanilino Fluorane 2-methoxy-6-p- (p-dimethylaminophenyl) aminoanilinofluorane 2-chloro-3-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane 2-chloro- 6-p- (p-dimethylaminophenyl) aminoanilinofluorane 2-nitro-6-p- (p-diethylaminophenyl) amino Nilinofluorane 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-phenylaminophenyl) aminoanilinofluorane 2-hydroxy-6-p- (p-phenylaminophenyl) aminoani Linofluorane 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-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-diacetylethane bis- [2,2,2 ', 2'-tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

Developers include activated clay, attapulgite, bisphenol A, 4-hydroxybenzoic acid esters, 4-hydroxyphthalic acid diesters, phthalic acid monoesters, bis- (hydroxyphenyl) sulfides, 4-hydroxyphenyl Aryl sulfones, 4-hydroxyphenyl aryl sulfonates, 1,3-di [2- (hydroxyphenyl) -2-propyl] -benzenes, 4-hydroxybenzoyloxybenzoic acid esters, bisphenol sulfones, JP-A-8 Aminobenzenesulfonamide derivatives described in No. -59603, diphenylsulfone bridged compounds described in International Publication No. WO 97/16420, phenolic compounds described in International Publication No. WO 02/081229 or JP-A No. 2002-301873, A phenyl novolak type condensation composition described in WO 02/098774 or WO 03/029017, a urea urethane compound described in International Publication WO 00/14058 or JP 2000-143611, N, N′-di-m-chlorophenylthiourea The thiourea compound etc. are mentioned, These can also be used individually or in mixture of 2 or more types. Of these, 4,4'-dihydroxydiphenylsulfone (bisphenol S) and 4-hydroxy-4'-isopropoxydiphenylsulfone are most preferable in terms of color tone and storage stability.

Furthermore, a sensitizer can be used for the purpose of improving the color development sensitivity. Examples of the sensitizer include saturated fatty acid monoamide, ethylene bis fatty acid amide, montanic acid wax, polyethylene wax, 1,2-di- (3-methyl). Phenoxy) ethane, p-benzylbiphenyl, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, 4,4'-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyl Oxymethane, 1,2-di (3-methylphenoxy) ethylene, 1,2-diphenoxyethylene, bis [2- (4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate, p-benzyloxy Benzyl benzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4 Diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, 4- (m-methylphenoxymethyl) biphenyl, phthalic acid dimethyl, naphthyl benzyl ether, oxalic acid-di- (p-methylbenzyl), oxalic acid-di- ( p-Chlorobenzyl), 4-acetylbiphenyl and the like can be exemplified, but are not particularly limited thereto.

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, styrene-butadiene copolymer and cellulose derivatives such as ethyl cellulose and acetyl cellulose, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid Esters, polyvinyl butyllar, polystyrene and their copolymers, polyamide resins, silicone resins, petroleum resins Terpene resins, ketone resins, and the Khumalo resin. These polymer substances are used by dissolving them in solvents such as water, alcohol, ketones, esters, hydrocarbons, etc., and are used in the state of being emulsified or pasted in water or other media to achieve the required quality. It can also be used in combination.

As an image stabilizer, 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-butylphenyl) butane, etc. It 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, and these can be used alone or in combination of two or more. Other materials include waxes and other lubricants, benzophenone and triazole UV absorbers, water-resistant agents such as glyoxal, crosslinking agents, dispersants, antifoaming agents, antioxidants, and fluorescent dyes.

In addition to electron-donating leuco dyes and color developers, materials such as sensitizers, binders, pigments, image stabilizers, UV absorbers, UV blockers, and lubricants are used as necessary. It can be used after being atomized to a particle size of several microns or less by a pulverizer such as a glider or a suitable emulsifying device. The amount of developer and dye, and the types and amounts of other various components are determined according to the required performance and recording suitability, and are not particularly limited. It is preferable that 0.1 to 2 parts of colorless dye and 0.5 to 4 parts of filler are used, and the binder is suitably 5 to 25% in the total solid content, and the coating amount is 2 to 12 g / m2. Furthermore, the coating method of the thermal recording layer coating is not particularly limited, and well-known ones such as an air knife coater, blade coater, roll coater, curtain coater can be used, but a coating layer with a uniform thickness is formed. It is desirable to use a non-scraping type curtain coater that is capable of suppressing the occurrence of white spots in the image area.

In the present invention, the coating material for the undercoat layer contains a pigment and a binder as main components, and contains materials such as an ultraviolet absorber, an ultraviolet blocking agent, and a crosslinking agent as necessary. These materials can be appropriately selected from the above, and are not limited thereto.
The coating amount of the undercoat layer is preferably 1 to 15 g / m 2, and the blending amount of the binder with respect to 100 parts by weight of the pigment is preferably 30 to 300 parts by weight, and the coating method of the paint for the undercoat layer is particularly limited Not known, air knife coater, blade coater, roll coater, curtain coater, etc. can be used, but non-scraping type curtain coater that can form a coating layer of uniform thickness, or surface smoothness It is desirable from the viewpoint of image reproducibility to use a blade coater that improves.

In the present invention, the above-described pigment, binder, ultraviolet absorber, lubricant, antifoaming agent, water-resistant agent, crosslinking agent, thickener, and the like can be used for the coating material for the protective layer.
The coating amount of the protective layer is preferably 0.5 to 10 g / m2. Further, the coating method of the protective layer coating is not particularly limited, and well-known ones such as an air knife coater, a blade coater, a roll coater, and a curtain coater can be used, but a coating layer having a uniform thickness can be formed. It is desirable to use a non-scraping type curtain coater from the viewpoint of suppressing uneven color development sensitivity in the solid image area.

Examples of the support of the heat-sensitive recording material of the present invention include paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, non-woven fabric, and composite sheets thereof, but are particularly limited. is not. It is also possible to correct the curl by providing a backcoat layer on the opposite side of the support from the thermosensitive recording layer. Furthermore, various well-known techniques in the heat-sensitive recording material field, such as applying a smoothing process such as supercalendering after coating each layer, can be added as appropriate.

In the present invention, a method for removing the air dissolved in the paint by defoaming the paint is effective as a means for reducing the dissolved oxygen content of the paint for the thermal recording material to 2.0 ml / g or less. . For the defoaming method of the paint, a conventionally known stationary method, decompression method, stationary decompression method, a disk that rotates at high speed in a decompression tank, and ejects liquid droplets that are defoamed from the disk. The method of destroying bubbles by colliding with the wall surface (dispersion plate type defoaming method), or by extending the liquid to a thin film in a decompressed chamber to promote the bubble, and the pressure of the gas contained in the bubbles There is a method of destroying bubbles (vacuum thin film method), a method of inflating and floating bubbles in a liquid in a vacuum tank, and then injecting pressure air toward the bubbles that have floated to destroy the bubbles. It is not limited. However, when the defoaming process is performed under reduced pressure, it is an effective means for shortening the processing time required to reduce the residual oxygen amount to 2.0 ml / g or less by setting the vacuum value to −99 Kpa or less. It is also possible to use a combination of a plurality of these defoaming methods. For example, a paint treated by a dispersion plate type defoaming method can be further treated by a vacuum thin film method, and a defoamer having both a dispersion plate type defoaming method and a vacuum thin film method can be used.

In the present invention, the amount of dissolved oxygen in the paint can be easily measured with a commercially available dissolved oxygen meter. The amount of dissolved oxygen in the paint is preferably 2.0 mg / l or less, and more preferably 1.5 mg / l or less. When the amount of dissolved oxygen in the paint is greater than 2 mg / l, the defoaming of the paint is insufficient and defects such as craters derived from the foam in the paint tend to occur. This phenomenon is particularly prominent when applied with a curtain coater. The B-type viscosity of the heat-sensitive recording layer paint is preferably in the range of 100 to 1200 mPa · s, and the B-type viscosity of the protective layer paint is preferably in the range of 300 to 3000 mPa · s. When the paint viscosity is high, the defoaming treatment of the paint tends to be insufficient. In addition, when the viscosity of the paint is low, a problem is likely to occur in the suitability of the curtain film of the paint. The paint concentration is preferably in the range of 10 to 50%, more preferably in the range of 15 to 40%. When the coating concentration is less than 10%, the drying load increases, and when the coating concentration is higher than 50%, problems are likely to occur in terms of fluidity of the coating and suitability of the curtain film.

[Action]
The gas dissolved in the paint is air, and the air is a mixture of nitrogen and oxygen in a ratio of approximately 4: 1. Comparing the solubility of nitrogen and oxygen in water, the solubility of nitrogen at 25 ° C. is 1.41 × 102, whereas that of oxygen is 2.83 × 102, almost double the value (Chemical Handbook) II-158). For this reason, it is considered that oxygen is less likely to be removed even after deaeration treatment. Therefore, when the amount of dissolved oxygen is reduced to 2 mg / l or less, it is considered that the dissolved amount of air including nitrogen is sufficiently reduced to the extent that the curtain film does not break during curtain coating.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, “parts” and “%” indicate parts by weight and% by weight unless otherwise specified.

[Example 1]
A composition comprising the following composition was stirred and dispersed to prepare an undercoat layer paint.

(Undercoat paint)
Baked kaolin (trade name: Ensilex 90, manufactured by Engelhard)
<Oil absorption 90cc / 100g>)
100 parts Styrene-butadiene copolymer latex (solid content 48%) 40 parts Polyvinyl alcohol 10% aqueous solution 30 parts Water 146 parts Next, undercoat layer paint is applied to one side of the support (50 g / m2 base paper). After coating, drying was performed to obtain an undercoat layer coated paper having a dry coating amount of 10.0 g / m2.

  Developer liquid dispersion (A liquid), leuco dye dispersion liquid (B liquid), and sensitizer dispersion liquid (C liquid) of the following composition are each separately separately with a sand grinder until the average particle diameter becomes 0.5 microns. Wet grinding was performed.

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 (leuco 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 C liquid (sensitizer dispersion)
Dibenzyl oxalate 6.0 parts Polyvinyl alcohol 10% aqueous solution 18.8 parts Water 11.2 parts

Next, the defoaming treatment was performed by stirring the heat-sensitive recording layer paint having a coating concentration of 35% and a B-type viscosity of 300 mPas for 60 minutes under a reduced pressure of -99 kpa obtained by mixing the dispersion at the following ratio. A heat-sensitive recording layer coating of 0.8 mg / l was obtained.

(Thermosensitive recording layer paint)
Liquid A (developer dispersion) 36.0 parts Liquid B (leuco dye dispersion) 13.8 parts Liquid C (sensitizer dispersion) 36.0 parts Polyvinyl alcohol 10% aqueous solution 25 parts

Subsequently, the protective layer paint having a paint concentration of 20% and a B-type viscosity of 1000 mPas obtained by mixing at the following ratio was stirred for 60 minutes under a reduced pressure of -99 kpa to perform defoaming treatment. 1 overcoat layer paint was obtained.

(Protective layer paint)
Aluminum hydroxide (50% dispersion) 6.0 parts Polyvinyl alcohol 10% aqueous solution 30 parts Zinc stearate (trade name: Hydrin Z-7-30, solid content 30%,
(Particle size 5.5 microns, Chukyo Yushi) 1.7 parts

(Creation of thermal recording material)
After coating and drying the thermosensitive recording layer coating to 5.0 g / m2 (dry solid content) on the undercoat layer coated paper, a protective layer coating is applied to the thermosensitive recording layer by 3.0 g / m2 ( Coating and drying were performed so as to obtain a dry solid content), and a heat-sensitive recording material was obtained by processing with a super calendar so that the smoothness was 1000 to 2000 seconds.

[Example 2]
A thermal recording material of Example 2 was prepared in the same manner as in Example 1 except that the defoaming conditions of the thermal recording layer coating material and the protective layer coating material were changed as follows. The dissolved oxygen content of the heat-sensitive recording layer coating material and the protective layer coating material was 1.3 mg / l.
Defoaming treatment: vacuum value -99 Kpa, stirring time 30 minutes

[Example 3]
A thermal recording material of Example 3 was prepared in the same manner as in Example 1 except that the defoaming conditions of the thermal recording layer coating material and the protective layer coating material were changed as follows. The dissolved oxygen content of the heat-sensitive recording layer coating material and the protective layer coating material was 1.7 mg / l.
Defoaming treatment: vacuum value -90 Kpa, stirring time 60 minutes

[Comparative Example 1]
A thermal recording material of Comparative Example 1 was prepared in the same manner as in Example 1 except that the defoaming conditions of the thermal recording layer coating material and the protective layer coating material were changed as follows. The dissolved oxygen content of the heat-sensitive recording layer paint and the protective layer paint was 2.5 mg / l.
Defoaming treatment: vacuum value -99 Kpa, stirring time 15 minutes

[Comparative Example 2]
A thermal recording material of Comparative Example 1 was prepared in the same manner as in Example 1 except that the defoaming conditions of the thermal recording layer coating material and the protective layer coating material were changed as follows. The dissolved oxygen content of the heat-sensitive recording layer coating material and the protective layer coating material was 5.0 mg / l.
Defoaming treatment: vacuum value -80 Kpa, stirring time 60 minutes

[Comparative Example 3]
A heat-sensitive recording material of Comparative Example 3 was prepared in the same manner as in Example 1 except that the degassing treatment of the heat-sensitive recording layer paint and the protective layer paint was not performed. The dissolved oxygen content of the heat-sensitive recording layer coating material and the protective layer coating material was 12.0 mg / l.
Defoaming treatment: vacuum value -99 Kpa, stirring time 15 minutes

<Amount of dissolved oxygen in paint>
Measurement was performed using a dissolved oxygen meter (manufactured by Yellow springs instrument, model 52, probe: 5905 type).

<Evaluation of coating defects>
200 sheets of A4 size coated paper were subjected to a solid baking process (105 ° C., 10 minutes), and the number of coating defects (number of white spots) was determined according to the following criteria.
A: The number of coating defects in 200 sheets is 0. There is no problem with barcode reading.
A: The number of coating defects in 200 sheets is 1 or more and 5 or less. Bar code reading is almost no problem.
Δ: The number of coating defects in 200 sheets is 5 or more and 10 or less. A level that can cause problems with barcode reading.
X: The number of coating defects in 200 sheets is 11 or more. A level that is likely to cause problems with barcode reading.

As is clear from Table 1, in Examples 1, 2 and 3, which are the present invention, a paint having a small amount of dissolved oxygen is curtain-coated, so that coating defects derived from bubbles hardly occur. . On the other hand, when the paint of Comparative Examples 1 and 2 where the defoaming treatment is insufficient or the Comparative Example 3 where the defoaming treatment is not performed is used for curtain coating, the coating derived from bubbles in the paint. A defect has occurred.

Claims (4)

A heat-sensitive recording material paint, wherein the paint has a dissolved oxygen content of 2.0 mg / l or less. 2. The thermal recording coating material according to claim 1, wherein the defoaming treatment is performed under a vacuum value of -99 Kpa or less.   A method for producing a heat-sensitive recording material, wherein at least the outermost layer of the heat-sensitive recording material is formed using the heat-sensitive recording material coating material according to claim 1. 4. The method for producing a thermal recording material according to claim 3, wherein a curtain coating method is used.