JP2021066015A - Thermosensitive recording medium and method for manufacturing the same - Google Patents

Abstract

To provide a thermosensitive recording medium which gives a high and clear printing quality with less omission of printing, and is excellent in recording density in a half tone with high sensitivity.SOLUTION: A thermosensitive recording medium has an undercoat layer containing hollow particles, an adhesive and a water retention agent on a support body, and a thermosensitive recording layer containing a leuco dye and a coloring agent in this order, and has a maximum average particle diameter (D100) of the hollow particles of 10-30 μm. The adhesive in the undercoat layer is preferably a water-dispersible adhesive composed of a water-insoluble resin. The water-insoluble resin is preferably a styrene-butadiene copolymer.SELECTED DRAWING: None

Description

The present invention relates to a thermal recorder.

A thermal recorder that records a color-developed image by utilizing a heating color-developing reaction between a colorless or light-colored leuco dye and a phenol or an organic acid has been widely put into practical use. Such a heat-sensitive recording body has advantages such as a compact recording device, easy maintenance of the recording device, and less noise generation because a color-developed image is formed simply by heating. Therefore, the thermal recorder is widely used as various information recording materials in issuing machines such as label printers, automatic ticket vending machines, CD / ATMs, order slip output machines such as restaurants, and data output machines of scientific research equipment. There is.

As thermal recorders are used in a variety of applications, there are increasing demands for improving the performance of thermal recorders. That is, there are quality demands such as that the image is deeply and clearly colored, and that the image quality is high without white spots (printing defects).

Therefore, many improved technologies have been developed in response to such demands. For example, there is a method of improving the sensitivity of the thermal recording body by containing hollow particles in the undercoat layer provided between the support of the thermal recording body and the thermal recording layer to improve the heat insulating property of the undercoat layer. Are known. Many more improved techniques have been developed for the method of incorporating hollow particles into the undercoat layer.

For example, in Patent Document 1, in the undercoat layer containing hollow particles and a binder resin, the hollow ratio is 60 to 98%, and the maximum particle size (D100) is 5.0 to 10.0 μm. A heat-sensitive recording material using hollow particles in which the ratio D100 / D50 of the maximum particle size to the particle size (D50) having a frequency of 50% by volume is 1.5 to 3.0 is disclosed.
Further, in Patent Document 2, the thermosetting resin particles used for the undercoat layer preferably have an average particle size of 1 to 25 μm when not expanded, and the volume expands 10 to 50 times by heating, resulting in a hollow coefficient. It is disclosed that those having a value of 80% or more are preferable.

Japanese Patent No. 4108380 Japanese Patent No. 5781885

The heat-sensitive recording material described in Patent Document 1 has a small maximum particle size (D100) of 5.0 to 10.0 μm and insufficient heat insulating properties, so that printing energy is easily diffused and the recording density is high. There was room for improvement.
Further, the heat-sensitive recording material described in Patent Document 2 does not have a viewpoint of making the particle size of the heat-expandable resin particles uniform, and the smoothness of the surface of the undercoat layer is improved due to the large variation in the particle size after foaming. Since it deteriorates, there is room for improvement in image quality.

The present invention has been made in view of such a situation. That is, the main object of the present invention is to provide a heat-sensitive recorder that provides high-quality and clear print image quality with few print defects, high sensitivity, and excellent recording density in halftones.

In order to solve the above problems, the present inventors have proceeded with studies on hollow particles used for the undercoat layer. As a result, it was found that the above problem can be solved by using coarse hollow particles and further using a water retention agent. The present invention has been completed based on such findings. That is, the present invention has the following configuration.

Item 1: An undercoat layer containing hollow particles, an adhesive and a water-retaining agent and a heat-sensitive recording layer containing a leuco dye and a color-developing agent are provided on the support in this order, and the maximum particle size of the hollow particles (D100). ) Is 10 to 30 μm.
Item 2: The heat-sensitive recording material according to Item 1, wherein the adhesive in the undercoat layer is a water-dispersible adhesive made of a water-insoluble resin.
Item 3: The heat-sensitive recorder according to Item 2, wherein the water-insoluble resin is a styrene-butadiene copolymer.
Item 4: The heat-sensitive recorder according to Item 3, wherein the glass transition temperature of the styrene-butadiene copolymer is 10 ° C. or lower.
Item 5: The heat-sensitive recorder according to Item 3 or 4, wherein the styrene-butadiene copolymer has a particle size of 150 to 300 nm.
Item 6: The heat-sensitive recorder according to any one of claims 1 to 5, wherein the water-retaining agent in the undercoat layer is a water-soluble water-retaining agent made of a water-soluble resin.
Item 7: The heat-sensitive recorder according to Item 6, wherein the water-soluble resin is at least one selected from the group consisting of starch, polyvinyl alcohol and carboxymethyl cellulose.
Item 8: The heat-sensitive recording body according to any one of Items 1 to 7, wherein the hollow ratio of the hollow particles is 65% or more.
Item 9. The heat-sensitive recording material according to any one of Items 1 to 8, wherein the content ratio of the hollow particles is 5 to 90% by mass based on the total solid content of the undercoat layer.
Item 10: The method for manufacturing a heat-sensitive recorder according to any one of Items 1 to 9, wherein the undercoat layer coating material containing hollow particles, an adhesive and a water-retaining agent is applied by a curtain coating method. Manufacturing method of recording material.

The heat-sensitive recorder of the present invention provides high-quality and clear print image quality with few print defects, and is excellent in high sensitivity and recording density in halftones.

An embodiment of the present invention will be described. However, the embodiments of the present invention are not limited to the following embodiments. In the present specification, the expression "including, containing" includes the concepts of "including", "consisting of substance only", and "consisting of only".

The present invention has an undercoat layer containing hollow particles, an adhesive and a water-retaining agent, and a heat-sensitive recording layer containing a leuco dye and a color-developing agent on the support in this order, and the maximum particle size of the hollow particles. (D100) is a thermal recorder having a size of 10 to 30 μm.

[Support]
The support in the present invention is not particularly limited in type, shape, size, etc., for example, high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassin paper, etc. In addition to resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, non-woven fabric, synthetic resin film, etc., various transparent supports and the like can be appropriately selected and used. The thickness of the support is not particularly limited, and is usually about 20 to 200 μm. The density of the support is not particularly limited, and is preferably about ^{0.60 to 0.85 g / cm 3.}

[Undercoat layer]
The thermal recording body of the present invention has an undercoat layer between the support and the thermal recording layer. The undercoat layer contains hollow particles having a maximum particle size (D100) of 10 to 30 μm, and further contains an adhesive and a water retention agent.

(Hollow particles)
The hollow particles are preferably made of an organic resin from the viewpoint of improving cushioning properties. The undercoat layer having high heat insulating properties by containing the hollow particles can prevent the diffusion of heat applied to the heat-sensitive recording layer and increase the sensitivity as a heat-sensitive recording body.

Hollow particles made of an organic resin can be divided into a foamed type and a non-foamed type depending on the difference in the manufacturing method. Of these two types, the foamed type hollow particles generally have a larger average particle size and a higher hollow ratio than the non-foamed type hollow particles. Therefore, the foamed type hollow particles can obtain better sensitivity and image quality than the non-foamed type hollow particles, but the smoothness of the undercoat layer tends to decrease. Therefore, the adhesive is supported by containing a water retaining agent. It is possible to suppress migration to the body side, maintain the film thickness of the coating layer, and improve smoothness.

On the other hand, the non-foaming type hollow particles generally have a small average particle diameter and a low hollow ratio. Therefore, in order to obtain good sensitivity and image quality, it is necessary to increase the content of hollow particles in the undercoat layer. When the content of the hollow particles is increased, the water retention of the undercoat layer coating material is lowered, and the coatability tends to be lowered.

A typical method for producing foam-type hollow particles is described below.
First, hollow particles can be produced by producing particles containing a volatile liquid inside the resin, softening the resin by heating, and vaporizing and expanding the liquid inside the particles.

The foam-type hollow particles have a large hollow ratio and high heat insulating properties by heating and expanding the liquid inside in the manufacturing process, so that the sensitivity of the thermal recording body can be increased and the recording concentration can be improved. .. Improving the sensitivity is particularly important when developing a halftone region in which the heat energy applied to the thermal recording layer is small. Further, if the heat-sensitive recording layer is formed through the undercoat layer having a high heat insulating property, the diffusion of the heat applied to the heat-sensitive recording layer is prevented, so that the image uniformity is excellent and the image quality can be improved. Therefore, in the present embodiment, it is preferable to use foam-type hollow particles having excellent heat insulating properties of the undercoat layer.

Resins that can be used for foam-type hollow particles include styrene-acrylic resin, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyacetal resin, chlorinated polyether resin, polyvinylidene chloride resin, polyvinylidene chloride resin, and the like. Examples thereof include acrylic resins (for example, acrylic resins containing acrylonitrile as a constituent), styrene resins, vinylidene chloride resins, and thermoplastic resins such as copolymer resins mainly composed of polyvinylidene chloride and acrylic nitrile. As the gas contained inside the foam-type hollow particles, propane, butane, isobutane, air and the like are generally used.
Among the above-mentioned various resins, the resin used for the hollow particles is preferably an acrylonitrile resin or a copolymer resin mainly composed of polyvinylidene chloride and acrylic nitrile from the viewpoint of strength for maintaining the shape of the foamed particles.

On the other hand, in the method for producing non-foaming type hollow particles, the seed is polymerized in a solution, another resin is polymerized so as to wrap the seed, and then the seed inside is swollen and dissolved to be removed. It forms a cavity in. When the seed inside is swollen and dissolved to be removed, an alkaline aqueous solution or the like is used. Non-foaming type hollow particles having a relatively large average particle size can also be obtained by subjecting core-shell particles in which core particles having alkaline swelling property are coated with a shell layer having no alkaline swelling property to an alkaline swelling treatment. ..

Examples of the monomer suitable for the method for producing non-foaming type hollow particles include vinyl-based monomers such as styrene-based, acrylic-based, and acrylonitrile-based. Examples of the styrene-based monomer include styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, diethylstyrene, triethylstyrene, propylstyrene, butylstyrene, chlorostyrene, t-butylstyrene and the like. Examples of the acrylic monomer include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, n-methacrylate. Examples thereof include butyl, isobutyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate and the like. Examples of the acrylonitrile-based monomer include acrylonitrile and methacrylonitrile. Examples of other vinyl-based monomers include dimethylmaleate, dimethylfumaric acid, maleic anhydride, N-methylmaleimide, and N-phenylmaleimide.

Among the above-mentioned various monomers, the combination of the styrene-based monomer and the acrylic-based monomer is preferable from the viewpoint of ease of production, and the combination of the styrene-based monomer and the (meth) acrylic acid ester is preferable. More preferable. That is, the hollow particles are preferably made of a styrene-acrylic resin, and more preferably made of a styrene- (meth) acrylic acid ester copolymer resin.

The maximum particle size of the hollow particles in the present invention is 10 to 30 μm, preferably 15 to 25 μm. The maximum particle size is also referred to as D100.
When the maximum particle size of the hollow particles is 10 μm or more, the cushioning property of the undercoat layer is improved, so that the adhesion of the heat-sensitive recording body to the thermal head at the time of printing is improved, and a high-quality heat-sensitive recording body can be obtained. .. This high image quality can bring about an improvement in the recording density in the halftones that develop color at a lower energy that gives the maximum recording density (Dmax).
On the other hand, when the maximum particle size of the hollow particles is 30 μm or less, the smoothness of the undercoat layer is improved, so that the heat-sensitive recording layer provided via the undercoat layer can be made uniform, and the heat-sensitive recording in which whiteout of the image is unlikely to occur. The body is obtained.
The maximum particle size (D100) of the hollow particles can be measured by a laser diffraction type particle size distribution measuring device. Further, the particle size may be measured from the particle image (SEM image) using an electron microscope and indicated by an average value of 10 particles.

The hollow ratio of the hollow particles is preferably 65% or more, more preferably 70% or more, and further preferably 80% or more.

The hollow ratio of hollow particles is determined by measuring the true specific gravity by the IPA method and using the true specific gravity value as follows.
(1) Sample pretreatment ・ The sample is dried at 60 ° C. for a whole day and night to prepare a sample.
(2) Reagent / Isopropyl alcohol (IPA: First-class reagent)
(3) Measurement method-The volumetric flask is precisely weighed (W1).
-Put about 0.5 g of the dried sample in a volumetric flask and weigh it precisely (W2).
-Add about 50 mg of IPA and shake well to completely remove the air outside the capsule.
・ Add IPA up to the marked line and evaluate it carefully (W3).
-As a blank, add only IPA to the volumetric flask up to the marked line and evaluate it carefully (W4).
(4) Calculation of true specific gravity True specific gravity = {(W2-W1) x ((W4-W1) / 100)} / {(W4-W1)-(W3-W2)}
(5) Calculation of hollow ratio Hollow ratio (%) = {1-1 / (1.1 / true specific gravity)} × 100

The hollow ratio is also a value obtained by the following equation (d ³ / D ^{3) × 100.} In the formula, d indicates the inner diameter of the hollow particle, and D indicates the outer diameter of the hollow particle. The average particle size of the hollow particles is preferably about 0.5 to 12 μm, more preferably about 3 to 12 μm.

The content ratio of the hollow particles is preferably 5 to 90% by mass, more preferably 5 to 70% by mass, still more preferably 5 to 50% by mass, based on the total solid content of the undercoat layer. , 10 to 50% by mass is particularly preferable. When the content ratio of the hollow particles is 5% by mass or more, the heat insulating property of the undercoat layer can be improved. On the other hand, when the content ratio of the hollow particles is 90% by mass or less, problems are less likely to occur in terms of coatability and the like, a uniform undercoat layer can be easily formed, and the recording density can be improved.
It is also preferable to add an oil-absorbing pigment to the undercoat layer. By adding an oil-absorbing pigment to the undercoat layer, printing problems such as sticking and head residue can be effectively suppressed. Examples of the oil-absorbing pigment include calcined kaolin. The content ratio of the oil-absorbing pigment is preferably 2 to 80% by mass based on the total solid content of the undercoat layer.

(adhesive)
As the adhesive, a water-dispersible adhesive made of a water-insoluble resin is preferable. Examples of the water-dispersible adhesive include polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyacrylic acid, polyacrylic acid ester, and vinyl chloride. -Vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, silylated urethane, acrylic-silicon composite, acrylic-silicon-urethane composite, urea resin, melamine resin, amide resin, polyurethane resin, etc. Latex. Of these, a styrene-butadiene copolymer is preferable. The latex content can be selected in a wide range, but generally, 5% by mass or more is preferable, and 10% by mass or more is more preferable, based on the total solid content of the undercoat layer. On the other hand, 40% by mass or less is preferable, 30% by mass or less is more preferable, and 20% by mass or less is further preferable. By setting the latex content to 10% by mass or more, the cushioning property of the undercoat layer can be further enhanced.

The glass transition temperature (Tg) of the adhesive (particularly latex) is not particularly limited, and is preferably 10 ° C. or lower, more preferably 5 ° C. or lower, and even more preferably −10 ° C. or lower. By using an adhesive having a glass transition temperature of 10 ° C. or lower, the cushioning property of the undercoat layer can be further enhanced. On the other hand, if the temperature is −50 ° C. or lower, stickiness occurs, which is not preferable. Therefore, −40 ° C. or higher is preferable.

The average particle size of the adhesive (particularly latex) is not particularly limited, and is preferably 150 nm or more, more preferably 165 nm or more, and even more preferably 190 nm or more. On the other hand, 300 nm or less is preferable, and 250 nm or less is more preferable. By setting the average particle size to 150 nm or more, migration of the latex to the support side can be effectively suppressed, and a uniform undercoat layer can be formed. By setting the average particle size to 300 nm or less, it is possible to suppress the formation of voids due to the fusion of latex, suppress the penetration of the paint for the heat-sensitive recording layer, and form a uniform heat-sensitive recording layer.

(Water retention agent)
By containing the water retention agent in the undercoat layer, it is possible to suppress the migration of the paint for the undercoat layer to the support side, particularly the migration of the adhesive component, and to form an undercoat layer in which the hollow particles are evenly distributed. .. If the uneven distribution of the hollow particles is reduced, the smoothness of the undercoat layer is improved, so that the heat-sensitive recording layer provided via the undercoat layer can be made uniform. As a result, hollow particles having a relatively large maximum particle size of 10 to 30 μm can be uniformly distributed in the undercoat layer, white spots in the image can be suppressed, and the maximum color development density can be improved. The water retention agent is preferably a water-soluble water retention agent made of a water-soluble resin. In the present invention, when the undercoat layer contains hollow particles having a maximum particle size (D100) of 10 to 30 μm, the water-soluble resin contained in the undercoat layer corresponds to a water-retaining agent, and the adhesive Not applicable.

As the water retention agent, various known materials such as cellulose and its derivatives, high molecular weight polysaccharides, modified polyacrylic acid, sodium alginate, and maleic anhydride copolymer can be appropriately used. Among these, at least one water-soluble resin selected from the group consisting of starch, polyvinyl alcohol and carboxymethyl cellulose is preferable. Specific examples of polyvinyl alcohol include modified polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol. Specific examples of starch include derivatives such as starch, oxidized starch, hydroxyethyl starch, and acetate starch. The content ratio of the water retention agent is not particularly limited, but is preferably in the range of 0.3 to 5% by mass, more preferably in the range of 0.5 to 2% by mass, based on the total solid content of the undercoat layer. By setting the content to 0.3% by mass or more, migration can be suppressed even more effectively. By setting the content to 5% by mass or less, an increase in the viscosity of the paint is suppressed and the coating suitability is excellent. In addition, there is no possibility that the water resistance is lowered, expansion (blistering) occurs due to the permeation of water, and the undercoat layer is peeled off.

The undercoat layer is generally dried after applying a paint for the undercoat layer prepared by mixing hollow particles, an adhesive and a water retention agent, an oil-absorbing pigment such as calcined kaolin, an auxiliary agent, etc. using water as a medium. And formed on the support. The coating amount of the undercoat layer coating material is not particularly limited, is preferably about 2 to 20 g / ^{m 2} by dry weight, about 2~12g / ^{m 2} is more preferable.

[Thermal recording layer]
The heat-sensitive recording layer in the heat-sensitive recording body of the present invention may contain various known leuco dyes of colorless or light color. Specific examples of such leuco dyes are given below.

Specific examples of the leuco dye include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl). Blue color dyes such as phenyl) -6-dimethylaminophthalide and fluorane, 3- (N-ethyl-N-p-tolyl) amino-7-N-methylanilinofluorane, 3-diethylamino-7-ani Green color dyes such as linofluorane, 3-diethylamino-7-dibenzylaminofluorane, rhodamine B-anilinolactam, 3,6-bis (diethylamino) fluorane-γ-anilinolactam, 3-cyclohexylamino- Red-coloring dyes such as 6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6 -Methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3 -Di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-) Isoamylamino) -6-methyl-7-alininofluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3- (N-isoamyl-N-ethylamino) -7- (o-) Chloroanilino) fluorane, 3- (N-ethyl-N-2-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3- (Nn-hexyl-N-ethylamino) -6-methyl -7-anilinofluorane, 3- [N- (3-ethoxypropyl) -N-ethylamino] -6-methyl-7-anilinofluorane, 3- [N- (3-ethoxypropyl) -N -Methylamino] -6-methyl-7-anilinofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-di (n-butylamino) -7- (2-chloroanilino) fluorane, 4, 4'-Bis-dimethylaminobenzhydrinbenzyl ether, N-2,4,5-trichlorophenylleucoauramine, 3-diethylamino-7-butylaminofluorane, 3-ethyl-tolylamino-6-methyl-7- Anilinofluorane, 3-cyclohexyl-methyla Mino-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7- (β-ethoxyethyl) aminofluorane, 3-diethylamino-6-chloro-7- (γ-chloropropyl) amino Fluolan, 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N-isoamyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3-dibutylamino-7-chloro Anilinofluorane, 3-diethylamino-7- (o-chlorophenylamino) fluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-p) -Truizino) -6-Methyl-7- (p-Truizino) Fluoran, 3- (N-ethyl-N-Tetrahydrofurfurylamino) -6-Methyl-7-anilinofluorane, 3-diethylamino-6-chloro -7-anilinofluorane, 3-dimethylamino-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-ani Renofluorane, 2,2-bis {4- [6'-(N-cyclohexyl-N-methylamino) -3'-methylspiro [phthalide-3,9'-xanthen-2'-ylamino] phenyl} propane, Black color dyes such as 3-diethylamino-7- (3'-trifluoromethylphenyl) aminofluorane, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene -2-yl] -4,5,6,7-tetrachlorophthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-yl]- 4,5,6,7-Tetrachlorophthalide, 3-p- (p-dimethylaminoanilino) anilino-6-methyl-7-chlorofluorane, 3-p- (p-chloroanilino) anilino-6- Examples thereof include dyes having an absorption wavelength in the near infrared region such as methyl-7-chlorofluorane and 3,6-bis (dimethylamino) fluorene-9-spiro-3'-(6'-dimethylamino) phthalide. .. Of course, the present invention is not limited to these, and two or more kinds of compounds can be used in combination if necessary.

The content ratio of the leuco dye is not particularly limited, and is preferably about 3 to 30% by mass, more preferably about 5 to 25% by mass, still more preferably about 7 to 20% by mass, based on the total solid content of the heat-sensitive recording layer. .. By setting the content to 3% by mass or more, the color development ability can be enhanced and the print density can be improved. Heat resistance can be improved by setting the content to 30% by mass or less.

Specific examples of the color former include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxy. Diphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidenediphenyl, 4,4'-cyclohexylidenediphenol, 1,1-bis (4-hydroxyphenyl) -ethane, 1,1- Bis (4-hydroxyphenyl) -1-phenylethane, 4,4'-bis (p-tolylsulfonylaminocarbonylamino) diphenylmethane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2'-bis [ 4- (4-Hydroxyphenyl) phenoxy] diethyl ether, 4,4'-dihydroxydiphenylsulfide, 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenylsulfone, 2 , 4'-Dihydroxydiphenylsulfone, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 2,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy- 4'-n-propoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, bis (P-Hydroxyphenyl) butyl acetate, bis (p-hydroxyphenyl) methyl acetate, hydroquinone monobenzyl ether, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4- Allyloxy-4'-hydroxydiphenylsulfone, 3,4-dihydroxyphenyl-4'-methylphenylsulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4 -Hydroxybenzoic acid-sec-butyl, 4-hydroxybenzoate phenyl, 4-hydroxybenzoate benzyl, 4-hydroxybenzoic acid benzyl ester, 4-hydroxybenzoate trill, 4-hydroxybenzoate chlorophenyl, 4,4'- Pphenolic compounds such as dihydroxydiphenyl ether, or benzoic acid, p-c Lolobenzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzyl salicylic acid, 3- (α-methylbenzyl) salicylic acid, 3, 5-Di-tert-butylsalicylic acid, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2-p-) Aromatic carboxylic acids such as methoxyphenoxyethoxy) cumyl] salicylic acid, 4-{3- (p-tolylsulfonyl) propyloxy] zinc salicylate, and these phenolic compounds, aromatic carboxylic acids and, for example, zinc, magnesium, aluminum, calcium. , Salts with polyhydric metals such as titanium, manganese, tin, nickel, and organic acidic substances such as antipyrine complex of zinc thiocyanate, complex zinc salt of terephthalaldehyde acid and other aromatic carboxylic acids, Np. -Toluenesulfonyl-N'-3- (p-toluenesulfonyloxy) phenylurea, N-p-toluenesulfonyl-N'-p-butoxycarbonylphenylurea, N-p-tolylsulfonyl-N'-phenylurea, 4 , 4'-bis (p-toluenesulfonylaminocarbonylamino) diphenylmethane, 4,4'-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] urea compounds such as diphenylsulfone, N, N'-di Thiourea compounds such as −m-chlorophenylthiourea, N- (p-toluenesulfonyl) carbamoyl acid p-cumylphenyl ester, N- (p-toluenesulfonyl) carbamoyl acid p-benzyloxyphenyl ester, N- [2- (3-phenyl ureido) phenyl] benzenesulfonamide, N-(o-toluoyl)-p-organic compound having a _-SO 2 NH- bond in the molecule such as toluene sulfonamide, activated clay, attapulgite, colloidal silica, silicate Examples thereof include inorganic acidic substances such as aluminum.

Further, as the coloring agent, 4,4'-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone represented by the following general formula (1), 4,4'-bis [((4-methyl-3-phenoxycarbonylaminophenyl) ureido] 2-Methyl-5-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, 4- (2-methyl-3-phenoxycarbonylaminophenyl) ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl) ureidodiphenylsulfone Ureaurethane derivatives such as, diphenylsulfone derivatives represented by the following general formula (2), and the like can be mentioned.

(In the formula, n represents an integer of 1 to 6.)
The color former is, of course, not limited to these, and two or more compounds can be used in combination if necessary.

The content of the color-developing agent is not particularly limited and may be adjusted according to the leuco dye used. Generally, 0.5 part by mass or more is preferable with respect to 1 part by mass of the leuco dye, and 0.8 part by mass is preferable. The above is more preferable, 1 part by mass or more is further preferable, 1.2 parts by mass or more is further preferable, and 1.5 parts by mass or more is particularly preferable. The content of the color-developing agent is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, further preferably 4 parts by mass or less, and particularly preferably 3.5 parts by mass or less with respect to 1 part by mass of the leuco dye. .. Recording performance can be improved by setting the content to 0.5 parts by mass or more. On the other hand, when the amount is 10 parts by mass or less, it is possible to effectively suppress the background fog in a high temperature environment.

In the present invention, a storage stability improving agent can be further contained in the heat-sensitive recording layer, mainly in order to further enhance the storage stability of the color development image. Examples of such a storage improving agent include 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane and 1,1,3-tris (2-methyl-4-hydroxy). -5-tert-butylphenyl) butane, 1,1-bis (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4'-[1,4-phenylenebis (1-methylethylidene) )] Phenol compounds such as bisphenol, 4,4'-[1,3-phenylenebis (1-methylethylidene)] bisphenol; 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy) ) Epoxy compounds such as phenylsulfone, 4- (2-methyl-1,2-epoxyethyl) diphenylsulfone, 4- (2-ethyl-1,2-epoxyethyl) diphenylsulfone; and 1,3,5-tris (2,6-Dimethylbenzyl-3-hydroxy-4-tert-butyl) At least one selected from isocyanuric acid compounds such as isocyanuric acid can be used. Of course, the present invention is not limited to these, and two or more kinds of compounds can be used in combination if necessary.

When a storage stability improving agent is used, the amount used may be an amount effective for improving the storage stability, and is usually preferably about 1 to 30% by mass based on the total solid amount of the heat-sensitive recording layer. About 20% by mass is more preferable.

A sensitizer can also be contained in the heat-sensitive recording layer in the present invention. Thereby, the recording sensitivity can be increased. Examples of the sensitizer include stearic acid amide, methoxycarbonyl-N-benzyl stearate, N-benzoyl stearate amide, N-eicosanoic acid amide, ethylene bisstearic acid amide, behenic acid amide, methylene bisstearic acid amide, N-Methylol stearate amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenylsulfone, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthylbenzyl ether, m-terphenyl , P-benzylbiphenyl, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, oxalic acid dibenzyl ester, p-tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1, 2-di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ethane, 1,2-di (4-methoxyphenoxy) ethane, 1,2-di (4-chlorophenoxy) ethane, 1,2-Diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetotoluide, p- Acetphenetidine, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenyl Examples thereof include ethane, di-o-chlorobenzyl adipate, 1,2-bis (3,4-dimethylphenyl) ethane, 1,3-bis (2-naphthoxy) propane, diphenyl, benzophenone and the like. These can be used together as long as there is no problem. The content ratio of the sensitizer may be an amount effective for sensitization, and is usually preferably about 2 to 40% by mass, more preferably about 5 to 25% by mass, based on the total solid content of the heat-sensitive recording layer. preferable.

In order to improve the whiteness of the heat-sensitive recording layer and improve the uniformity of the image, a fine particle pigment having a high whiteness and an average particle size of 10 μm or less can be contained in the heat-sensitive recording layer. For example, calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, surface-treated calcium carbonate, surface-treated silica. Inorganic pigments such as, and organic pigments such as urea-formalin resin, styrene-methacrylic acid copolymer resin, and polystyrene resin can be used. The content ratio of the pigment is preferably an amount that does not reduce the color development concentration, that is, 50% by mass or less of the total solid amount of the heat-sensitive color development layer.

Adhesives can be used as other component materials constituting the heat-sensitive recording layer, and if necessary, cross-linking agents, waxes, metal soaps, water-resistant agents, dispersants, colored dyes, fluorescent dyes and the like can be used.

As the adhesive used for the paint for the heat-sensitive recording layer, for example, a water-soluble or water-dispersible water-based adhesive can be used. Examples of the water-soluble adhesive include polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, modified polyvinyl alcohol such as silicon-modified polyvinyl alcohol, starch and its derivatives, methoxycellulose, carboxymethylcellulose, and hydroxy. Cellulous derivatives such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylic acid, polyvinylpyrrolidone, polyamide, diisobutylene-maleic anhydride copolymer salt, styrene-acrylic acid copolymer salt, styrene- Maleic anhydride copolymer salt, ethylene-maleic anhydride copolymer salt, acrylic acid amide-acrylic acid ester copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid copolymer, polyacrylamide, sodium alginate, gelatin , Casein, Arabic gum and the like. Water-dispersible adhesives include polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride-acetic acid. Latex such as vinyl copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, silylated urethane, acrylic-silicon composite, acrylic-silicon-urethane composite, urea resin, melamine resin, amide resin, polyurethane resin, etc. Can be mentioned. These can be used alone or in combination of two or more. At least one of these is blended in a range of preferably about 5 to 50% by mass, more preferably about 10 to 40% by mass, based on the total solid content of the thermal recording layer.

A cross-linking agent that cures the adhesive of the thermal recording layer or other layers can be contained in the thermal recording layer. Thereby, the water resistance of the thermal recording layer can be improved. Examples of the cross-linking agent include aldehyde compounds such as glioxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxyphosphates, dimethylolurea compounds, aziridine compounds, blocked isocyanate compounds; ammonium persulfate. , Inorganic compounds such as ferric chloride, magnesium chloride, sodium tetraborate, potassium tetraborate; boric acid, borate triester, borane polymer, hydrazide compound, glyoxyphosphate and the like. These may be used individually by 1 type, or may be used in combination of 2 or more type. The amount of the cross-linking agent used is preferably in the range of about 1 to 10 parts by mass with respect to 100 parts by mass of the total solid content of the heat-sensitive recording layer. Thereby, the water resistance of the thermal recording layer can be improved.

Examples of the wax include waxes such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, and polyethylene wax; for example, higher fatty acid amides such as stearic acid amide and ethylene bisstearic acid amide, higher fatty acid esters, and derivatives thereof. Can be mentioned.

Examples of the metal soap include higher fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. Further, if necessary, various auxiliary agents such as an oil repellent, an antifoaming agent, and a viscosity modifier can be further added to the heat-sensitive recording layer as long as the effects of the present invention are not impaired.

The heat-sensitive recording layer generally uses water as a dispersion medium, and contains a leuco dye and a color-developing agent, and if necessary, a sensitizer and a storage improving agent together or separately, such as a ball mill, a coball mill, an attritor, a vertical type and a horizontal type sand mill, etc. Disperse with water-soluble synthetic polymer compounds such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, styrene-maleic anhydride copolymer salt, and other surfactants with various stirrers and wet grinders. Then, using the dispersion obtained by dispersing so that the average particle size was 2 μm or less, a paint for a heat-sensitive recording layer prepared by mixing a pigment, an adhesive, an auxiliary agent, etc., if necessary, was applied. After that, it is dried and formed on the undercoat layer. The coating amount of the heat-sensitive recording layer is not particularly limited, it is preferably about 1~12g / ^{m 2} of the coating amount after drying, more preferably 2 to 10 g / ^{m 2,} more preferably 2.5~8g / ^{m 2} 3 to 5.5 g / m ² is particularly preferable. The heat-sensitive recording layer can be formed into two or more layers as needed, and the composition and coating amount of each layer may be the same or different.

[Protective layer]
In the thermal recording body, a protective layer may be provided on the thermal recording layer, if necessary. The protective layer preferably contains a pigment and an adhesive. Further, the protective layer preferably contains a lubricant such as polyolefin wax or zinc stearate for the purpose of preventing sticking to the thermal head, and may also contain an ultraviolet absorber. Further, by providing a protective layer having a gloss, it is possible to increase the added value of the product.

The adhesive contained in the protective layer is not particularly limited, and a water-soluble or water-dispersible water-based adhesive can be used. The adhesive can be appropriately selected from those that can be used for the thermal recording layer.

The protective layer is generally formed on a heat-sensitive recording layer by applying a protective layer paint prepared by using water as a dispersion medium and mixing a pigment, an adhesive, and if necessary, an auxiliary agent, and the like, and then drying the protective layer. The coating amount of the coating for the protective layer is not particularly limited, it is preferably about 0.3~15g / ^{m 2} by dry weight, more preferably about ^{0.3~10g / m 2, 0.5~8g / m} 2 more preferably the extent, particularly preferably about 1-8 g / ^{m 2,} about 1 to 5 g / ^{m 2} is more preferable. The protective layer can be formed into two or more layers as needed, and the composition and coating amount of each layer may be the same or different.

[Other layers]
In the present invention, in order to increase the added value of the heat-sensitive recording body, it can be further processed to obtain a heat-sensitive recording body having higher functions. For example, an adhesive paper, a re-wet adhesive paper, a delayed tack paper, or the like can be obtained by applying a coating process on the back surface with an adhesive, a re-wet adhesive, a delayed tack type adhesive, or the like. Further, the back surface can be used to impart functions as thermal transfer paper, inkjet recording paper, carbonless copy paper, electrostatic recording paper, zeography paper, and the like to obtain a recording paper capable of double-sided recording. Of course, it can also be a double-sided thermal recorder. Further, it is also possible to suppress the permeation of oil and plasticizer from the back surface of the thermal recording body, and to provide a back layer for curl control and antistatic.

It is also possible to obtain a linerless label that does not require a release paper by applying a release layer containing silicone on the protective layer and applying an adhesive on the back surface.

[Thermal recording body]
Examples of the method for forming each of the above layers on the support include an air knife method, a blade method, a gravure method, a roll coater method, a spray method, a dip method, a bar method, a curtain method, a slot die method, a slide die method, and an extrusion method. Any of the known coating methods of is used. Further, each paint may be applied and dried one layer at a time to form each layer, or the same paint may be applied in two or more layers. Further, simultaneous multi-layer coating may be performed in which two or more layers are coated at the same time. In addition, smoothing can be performed using a known method such as a super calendar or a soft calendar in an arbitrary process after each layer has been formed or all layers have been formed.

The undercoat layer is preferably a layer formed by the curtain coating method. As a result, a layer having a uniform thickness can be formed, the effect of the hollow particles can be fully exerted, the recording sensitivity can be enhanced, and the barrier property against oil, plasticizer, alcohol, etc. can be enhanced. The curtain coating method is a method in which the paint is allowed to flow down and freely fall to be applied to the intermediate layer in a non-contact manner, and known methods such as a slide curtain method, a couple curtain method, and a twin curtain method can be adopted, and are particularly limited. It is not something that is done.

The present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" and "%" indicate "parts by mass" and "% by mass", respectively.

Example 1
(1) Preparation of paint for undercoat layer 59 parts of calcined kaolin (trade name: Ansilex 93, manufactured by BASF), styrene-butadiene copolymer (trade name: SR-104, manufactured by Japan A & L, solid content concentration 48%, Particle size 160 nm, glass transition temperature 3 ° C.) 41.7 parts, 4 parts of 25% aqueous solution of oxidized starch (trade name: Oji Ace A, manufactured by Oji Corn Starch), hollow particles A (foaming type, average particle size 9 μm, maximum) A composition consisting of 100 parts (particle size 20 μm, solid content concentration 20%) and 75.5 parts of water was mixed and stirred to obtain a coating material for an undercoat layer.

(2) Preparation of leuco dye dispersion (solution A) 40 parts of 3-di- (n-butyl) amino-6-methyl-7-anilinofluorane, polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%) 40 parts of 10% aqueous solution and 20 parts of water are mixed, and the median diameter is 0.5 μm by the laser diffraction type particle size measuring device SALD2200 (manufactured by Shimadzu Corporation) using a sand mill (manufactured by Imex, sand grinder). The mixture was pulverized to obtain a leuco dye dispersion liquid (solution A).

(3) Preparation of color-developing agent dispersion (solution B) 40 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone (manufactured by Nippon Soda Co., Ltd., D8), 10 parts of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%) 40 parts of% aqueous solution and 20 parts of water are mixed, and the median diameter is 0.7 μm by the laser diffraction type particle size measuring device SALD2200 (manufactured by Shimadzu Seisakusho) using a sand mill (manufactured by Imex, sand grinder). The mixture was pulverized to obtain a color developer dispersion liquid (solution B).

(4) Preparation of sensitizer dispersion (solution C) 40 parts of di-p-methylbenzyl ester oxalate (trade name: HS-3520, manufactured by DIC), polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%) 40 parts of 10% aqueous solution and 20 parts of water are mixed, and the median diameter is 1.0 μm by the laser diffraction type particle size measuring device SALD2200 (manufactured by Shimadzu Seisakusho) using a sand mill (manufactured by IMEX, sand grinder). It was pulverized until it became a sensitizer dispersion liquid (C liquid).

(5) Preparation of paint for heat-sensitive recording layer 29.5 parts of solution A, 59.1 parts of solution B, 45.4 parts of solution C, 20 parts of 5% aqueous solution of hydroxymethyl cellulose, completely saponified polyvinyl alcohol (degree of polymerization: 1000, 45 parts of 10% aqueous solution of saponification degree: 99 mol%, 9.4 parts of butadiene-based copolymer latex (trade name: L-1571, manufactured by Asahi Kasei Co., Ltd., solid content concentration 48%), light calcium carbonate (trade name:) Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd.) 17.1 parts, paraffin wax (trade name: Hydrin L-700, manufactured by Chukyo Oil & Fat Co., Ltd., solid content concentration 30%) 11.7 parts, dihydrazide adipate (manufactured by Otsuka Chemical Co., Ltd.) A composition consisting of 2 parts and 120 parts of water was mixed and stirred to obtain a paint for a heat-sensitive recording layer.

(6) Preparation of paint for protective layer Acetacetyl-modified polyvinyl alcohol (trade name: Gosenex Z-200, saponification degree: 99.4 mol%, average polymerization degree: 1000, modification degree: 5 mol%, Nippon Synthetic Chemical Industry Co., Ltd. 300 parts of 12% aqueous solution (trade name: HYDRAGLOSS90, manufactured by KaMin LLC), 35 parts of aluminum hydroxide (trade name: Heidilite H-42M, manufactured by Showa Denko), silica (trade name:) Composition consisting of 4 parts of Mizukasil P-527, manufactured by Mizusawa Chemical Co., Ltd., 2.5 parts of polyethylene wax (trade name: Chemipearl W-400, manufactured by Mitsui Chemical Co., Ltd., solid content concentration 40%), and 114.5 parts of water. Was mixed and stirred to obtain a coating material for a protective layer.

(7) on one side of fine paper produced a basis weight of 60 g / m ² of the heat-sensitive recording material, the undercoat layer coating material, heat-sensitive recording layer coating, and a coating material for protective layer coating amount after drying respectively 6.0 g / After applying to m ² , 4.0 g / m ² , 2.0 g / m ² , it is dried to form an undercoat layer, a thermal recording layer, and a protective layer in that order, and then the surface is smoothed with a super calendar. A heat-sensitive recording material was obtained. The undercoat layer was formed by applying the undercoat layer paint by a curtain coating method and then drying it.

Example 2
In the preparation of the undercoat paint of Example 1, styrene-butadiene copolymer (trade name: SR-104, manufactured by Japan A & L Co., Ltd., solid content concentration 48%, particle size 160 nm, glass transition temperature 3 ° C.) 41.7 parts Instead of using 41.7 parts of a styrene-butadiene copolymer (trade name: SR-107, manufactured by Japan A & L, solid content concentration 48%, particle size 170 nm, glass transition temperature -15 ° C), A heat-sensitive recording body was obtained in the same manner as in Example 1.

Example 3
In the preparation of the undercoat paint of Example 1, styrene-butadiene copolymer (trade name: SR-104, manufactured by Japan A & L Co., Ltd., solid content concentration 48%, particle size 160 nm, glass transition temperature 3 ° C.) 41.7 parts Except for using 41.7 parts of a styrene-butadiene copolymer (trade name: SR-103, manufactured by Japan A & L Co., Ltd., solid content concentration 48%, particle size 220 nm, glass transition temperature 7 ° C.) A heat-sensitive polymer was obtained in the same manner as in Example 1.

Example 4
In the preparation of the undercoat paint of Example 1, polyvinyl alcohol (trade name: PVA11-98, manufactured by Kuraray) was used instead of 4 parts of a 25% aqueous solution of oxidized starch (trade name: Oji Ace A, manufactured by Oji Corn Starch). A heat-sensitive recorder was obtained in the same manner as in Example 1 except that 6.7 parts of a 15% aqueous solution was used.

Example 5
In the preparation of the undercoat paint of Example 1, carboxymethyl cellulose (trade name: Cellogen 7A, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was used instead of 4 parts of a 25% aqueous solution of oxidized starch (trade name: Oji Ace A, manufactured by Oji Cornstarch). A heat-sensitive recorder was obtained in the same manner as in Example 1 except that one part was used.

Example 6
In the preparation of the undercoat paint of Example 1, the amount of calcined kaolin (trade name: Ansilex 93, manufactured by BASF) was changed to 19 parts instead of 59 parts, and hollow particles A (foam type, average particle size 9 μm, maximum particles) were used. A heat-sensitive recorder was obtained in the same manner as in Example 1 except that the amount (diameter 20 μm, solid content concentration 20%) was 300 parts instead of 100 parts.

Comparative Example 1
In the preparation of the undercoat paint of Example 1, hollow particles B (non-foaming type, trade name) were replaced with 100 parts of hollow particles A (foaming type, average particle size 9 μm, maximum particle size 20 μm, solid content concentration 20%). : Low Pake SN-1055, manufactured by Dow Chemical Co., Ltd., average particle size 1 μm, maximum particle size 2 μm, solid content concentration 26.5%) 75.5 parts were used, but a heat-sensitive recorder was obtained in the same manner as in Example 1. It was.

Comparative Example 2
In the preparation of the undercoat paint of Example 1, hollow particles C (foaming type, average particle size) were replaced with 100 parts of hollow particles A (foaming type, average particle size 9 μm, maximum particle size 20 μm, solid content concentration 20%). A heat-sensitive recorder was obtained in the same manner as in Example 1 except that 133 parts (20 μm, maximum particle size 40 μm, solid content concentration 15%) were used.

Comparative Example 3
A heat-sensitive recorder was used in the same manner as in Example 1 except that four parts of a 25% aqueous solution of oxidized starch (trade name: Oji Ace A, manufactured by Oji Cornstarch) was not used in the preparation of the undercoat paint of Example 1. Obtained.

The heat-sensitive recorder thus obtained was evaluated as follows. The results are as shown in Table 1.

[Recording concentration]
Using a heat-sensitive recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each heat-sensitive recorder was recorded in the halftone energy region of applied energy: 0.16 mJ / dot, and the obtained printed part was Macbeth. The measurement was performed in the visual mode of a densitometer (RD-914, manufactured by Macbeth). The larger the value, the darker the print density and the higher the sensitivity.

[Print quality]
Barcodes were recorded using a label printer (trade name: L-2000, manufactured by Ishida Co., Ltd.), and the recorded image quality was visually observed and evaluated according to the following criteria.
◯: There is no white spot in the image quality or thickening of the barcode, and there is no problem at all.
Δ: There is almost no white spots in the image quality or thickening of the barcode, and there is no problem in practical use.
X: There are white spots in the image and thick barcodes, which poses a practical problem.

Claims (10)

An undercoat layer containing hollow particles, an adhesive and a water-retaining agent and a heat-sensitive recording layer containing a leuco dye and a color-developing agent are provided on the support in this order, and the maximum particle size (D100) of the hollow particles is 10. Thermal recording body with a size of ~ 30 μm. The heat-sensitive recording body according to claim 1, wherein the adhesive in the undercoat layer is a water-dispersible adhesive made of a water-insoluble resin. The heat-sensitive recorder according to claim 2, wherein the water-insoluble resin is a styrene-butadiene copolymer. The heat-sensitive recorder according to claim 3, wherein the glass transition temperature of the styrene-butadiene copolymer is 10 ° C. or lower. The heat-sensitive recorder according to claim 3 or 4, wherein the styrene-butadiene copolymer has a particle size of 150 to 300 nm. The heat-sensitive recorder according to any one of claims 1 to 5, wherein the water-retaining agent in the undercoat layer is a water-soluble water-retaining agent made of a water-soluble resin. The heat-sensitive recorder according to claim 6, wherein the water-soluble resin is at least one selected from the group consisting of starch, polyvinyl alcohol and carboxymethyl cellulose. The heat-sensitive recorder according to any one of claims 1 to 7, wherein the hollow ratio of the hollow particles is 65% or more. The heat-sensitive recording material according to any one of claims 1 to 8, wherein the content ratio of the hollow particles is 5 to 90% by mass based on the total solid content of the undercoat layer. The heat-sensitive recording body according to any one of claims 1 to 9, wherein the undercoat layer coating material containing hollow particles, an adhesive, and a water-retaining agent is applied by a curtain coating method. Manufacturing method.