JP2021138000A - Heat-sensitive recording body - Google Patents

Abstract

To provide a heat-sensitive recording body which has an excellent image quality with less omission of printing, and is excellent in half tone printing density.SOLUTION: A heat-sensitive recording body has an undercoat layer formed on one surface of a support and a heat-sensitive recording layer formed on the undercoat layer. The heat-sensitive recording layer contains a leuco dye and a coloring agent, the undercoat layer contains hollow particles and a binder resin, the hollow particles are composed of two kinds of hollow particles of at least large particle diameter hollow particles and small particle diameter hollow particles, the large particle diameter hollow particles have a maximum particle diameter (D100) of 10-80 μm and a particle diameter (D50) in the frequency of 50 vol.% of 7.5-25 μm, and the small particle diameter hollow particles have a particle diameter (D50) in the frequency of 50 vol.% of 0.7-6 μm.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. Specifically, there are quality demands such as an image that develops a deep and clear color, high image quality without white spots (printing defects), and excellent halftone print density.

Many improved technologies have been developed in response to such demands. For example, it is known that the undercoat layer provided between the support of the thermal recording body and the thermal recording layer contains hollow particles to improve the heat insulating property of the undercoat layer and improve the sensitivity of the thermal recording body. Has been done. More improved techniques have been developed for methods of including hollow particles in the undercoat layer.

For example, in Patent Document 1, hollow particles A having a particle size of 1 μm or less and a hollow ratio of 80% or less and hollow particles B having a particle size of 3 to 10 μm and a hollow ratio of 80% or more are mixed as hollow particles. The heat-sensitive recording material used is disclosed.
Further, in Patent Document 2, in the undercoat layer containing hollow particles and a binder resin, the hollow ratio is 60 to 98%, the maximum particle size (D100) is 5.0 to 10.0 μm, and the maximum. A heat-sensitive recording material using hollow particles in which the ratio D100 / D50 of the particle size (D100) to the particle size (D50) having a frequency of 50% by volume is 1.5 to 3.0 is disclosed.
Further, in Patent Document 3, the heat-expandable 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. 3176693 Japanese Patent No. 4108380 Japanese Patent No. 5781885

The heat-sensitive recording material described in Patent Document 1 has a small particle size of hollow particles and insufficient heat insulating properties, so that printing energy is easily diffused and there is room for improvement in recording density. Further, since the particle size of the hollow particles was small and the cushioning property of the coating layer was low, there was room for improvement in the printing image quality.
Further, in the heat-sensitive recording material described in Patent Document 2, the maximum particle size (D100) of the hollow particles is as small as 5.0 to 10.0 μm, and the heat insulating property is insufficient, so that the printing energy is easily diffused for recording. There was room for improvement in the concentration.
Further, the heat-sensitive recording material described in Patent Document 3 has room for improvement in image quality because the smoothness of the surface of the undercoat layer is lowered due to the large variation in the particle size after foaming.

The present invention has been made in view of such a situation. That is, an object of the present invention is to provide a heat-sensitive recorder having excellent image quality with few printing defects and excellent halftone printing density.

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 has been found that the above problem can be solved by forming an undercoat layer containing two types of hollow particles having different maximum particle diameters and containing the hollow particles in a specific amount with a specific particle size distribution. The present invention has been completed based on such findings. That is, the present invention has the following configuration.

(1) A heat-sensitive recording body including an undercoat layer formed on one surface of a support and a heat-sensitive recording layer formed on the undercoat layer, and the heat-sensitive recording layer is presented with a leuco dye. The undercoat layer contains hollow particles and a binder resin, and the hollow particles have at least two types of hollow particles, a large particle diameter hollow particle and a small particle diameter hollow particle. The large particle size hollow particles have a maximum particle size (D100) of 10 to 80 μm, a particle size (D50) having a frequency of 50% by volume is 7.5 to 25 μm, and the small particle size hollow particles have a frequency of 50% by volume. A heat-sensitive recording body having a diameter (D50) of 0.7 to 6 μm.

(2) The above-mentioned (1), wherein the maximum particle size (D100) of the large particle size hollow particles is 10 to 50 μm, and the particle size (D50) of 50% by volume frequency is 7.5 to 15 μm. Thermal recording body.

(3) The heat-sensitive recorder according to (1) or (2) above, wherein the large particle size hollow particles have a D100 / D50 of 1.8 to 10.0.

(4) Any of the above (1) to (3), wherein the hollow ratio of the large particle diameter hollow particles is 80 to 98%, and the hollow ratio of the small particle diameter hollow particles is less than 80%. The heat-sensitive recording body according to item 1.

(5) The heat-sensitive recorder according to any one of (1) to (4) above, wherein the undercoat layer contains 5 to 40% by mass of the large-diameter hollow particles.

(6) The heat-sensitive recorder according to any one of (1) to (5) above, wherein the coating amount of the undercoat layer after drying is 2.0 to 10 g / m ^2.

(7) Any of the above (1) to (6), wherein the small particle size hollow particles are contained in a ratio of 0.1 to 10 parts by mass with respect to 1 part by mass of the large particle size hollow particles. The heat-sensitive recording body according to item 1.

(8) The heat-sensitive recorder according to any one of (1) to (7) above, wherein the small particle size hollow particles have a maximum particle size (D100) of 1 to 7 μm.

(9) The heat-sensitive recorder according to any one of (1) to (8) above, wherein the binder resin contains at least styrene-butadiene latex.

(10) The heat-sensitive recorder according to (9), wherein the Tg of the styrene-butadiene latex is −10 ° C. or lower.

(11) The heat-sensitive recorder according to (9) above, wherein the Tg of the styrene-butadiene latex is −30 ° C. or lower.

The heat-sensitive recorder of the present invention has excellent image quality with few printing chips and is excellent in halftone print density.

An embodiment of the present invention will be described. However, the embodiments of the present invention are not limited to the following embodiments.

The heat-sensitive recording body of the present embodiment includes an undercoat layer formed on one surface of the support and a heat-sensitive recording layer formed on the undercoat layer. The heat-sensitive recording layer is a layer on which characters, designs, etc. are displayed by developing a color in the portion when heat is applied. The undercoat layer is a layer having a role of improving the fixation of the heat-sensitive recording layer, improving the heat insulating property for preventing the heat from diffusing, and the like.
Hereinafter, the materials constituting the thermal recording body will be described.

[Support]
There are no particular restrictions on the type, shape, dimensions, etc. of the support, for example, high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassin paper, resin laminated paper. , Polyolefin-based synthetic paper, synthetic fiber paper, non-woven fabric, synthetic resin film, etc., and various transparent supports and the like can be appropriately selected and used. The thickness of the support is not particularly limited, but is usually about 20 to 200 μm. The density of the support is also not particularly limited, but is preferably about ^{0.60 to 0.85 g / cm 3.}

[Undercoat layer]
The undercoat layer is provided between the support and the thermal recording layer. The undercoat layer contains hollow particles and a binder resin. The undercoat layer preferably further contains a thickener.

(Hollow particles)
Hollow particles made of an organic resin can be contained in the undercoat layer to enhance the heat insulating property of the undercoat layer. The undercoat layer having a high heat insulating property 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 foam type hollow particles have properties suitable for improving the heat insulating property of the undercoat layer.

A typical method for producing foam-type hollow particles is described below.
First, particles containing a volatile liquid inside the resin are prepared. Then, the resin is softened by heating and the liquid inside the particles is vaporized and expanded to obtain hollow particles.

Since the foam-type hollow particles have a large hollow ratio and high heat insulating properties, the sensitivity of the thermal paper can be increased and the recording density 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 high heat insulating properties, it is possible to prevent the heat applied to the heat-sensitive recording layer from diffusing, and as a result, prevent blurring of the image and improve the image quality. Can be done.
Therefore, in the present embodiment, foam-type hollow particles having excellent heat insulating properties of the undercoat layer are used.

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 various resins described above, 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.

The undercoat layer in the present embodiment has at least large particle size hollow particles (hereinafter, also referred to as first hollow particles) and small particle size hollow particles (hereinafter, also referred to as second hollow particles) having different maximum particle diameters as hollow particles. ) Is contained.
The maximum particle size of the first hollow particles is 10 to 80 μm, preferably 10 to 65 μm, and more preferably 10 to 50 μm. The maximum particle size is the maximum particle size of the distribution and is also referred to as D100.
If the maximum particle size of the first hollow particles is less than 10 μm, the cushioning property of the undercoat layer is lowered, so that the adhesion of the thermal paper to the thermal head at the time of printing is lowered, and it is difficult to obtain high image quality. On the other hand, if the maximum particle size of the first hollow particles is more than 80 μm, the smoothness of the undercoat layer is lowered, so that it is difficult to make the heat-sensitive recording layer provided on the undercoat layer uniform, and the color development density is lowered.

On the other hand, the maximum particle size of the second hollow particles is preferably 1 to 7 μm, more preferably 2 to 5 μm.
The maximum particle size (D100) of the hollow particles can be measured by a laser diffraction type particle size distribution measuring device. It is also possible to actually measure using an electron microscope.

Since the second hollow particles have a smaller maximum particle size than the first hollow particles, when both are used in combination, the second hollow particles can be filled in the gaps between the first hollow particles in the undercoat layer. By filling the gaps between the first hollow particles with the second hollow particles, the undercoat layer can be made to have even better heat insulating properties, and a heat-sensitive recorder having high image quality and excellent halftone printing density can be obtained. Can be done. The mixing ratio of the first hollow particles and the second hollow particles is preferably 0.1 to 10 parts by mass of the second hollow particles with respect to 1 part by mass of the first hollow particles, and the second hollow particles are 0. More preferably, it is contained in a ratio of 5 to 5 parts by mass.

When the powder is divided into two with a certain particle size, the diameter at which the volumes occupied by the large particles and the small particles are equal, that is, the particle size with a frequency of 50% by volume is called the median size. The median diameter is also referred to as D50.
The median diameter (D50) of the first hollow particles is 7.5 to 25 μm, preferably 7.5 to 15 μm. If the median diameter (D50) of the first hollow particles is less than 7.5 μm, the cushioning property of the undercoat layer is lowered, so that the adhesion of the thermal paper to the thermal head during printing is lowered, and high image quality can be obtained. hard. On the other hand, if the median diameter (D50) of the first hollow particles exceeds 25 μm, the smoothness of the undercoat layer is lowered, so that it is difficult to make the heat-sensitive recording layer provided on the undercoat layer uniform, and the color development density is lowered.
The second hollow particles have a median diameter (D50) of 0.7 to 6 μm, preferably 0.7 to 4 μm, and more preferably 0.7 to 3 μm.
The median diameter (D50) of the hollow particles can be measured by a laser diffraction type particle size distribution measuring device. It is also possible to actually measure using an electron microscope.

The ratio D100 / D50 of the maximum particle size (D100) and the median size (D50) is an index indicating the degree of particle size distribution. The D100 / D50 of the first hollow particles is preferably 1.8 to 10.0, more preferably 1.8 to 5.0, and even more preferably 1.8 to 3.0. ..
If the D100 / D50 of the first hollow particles is less than 1.8, the particle size distribution becomes very sharp, which may make production difficult. On the other hand, if the D100 / D50 of the first hollow particles is more than 10.0, the maximum particle size becomes too large, so that the smoothness of the undercoat layer may decrease and the color development density may decrease.

The hollow ratio of the first hollow particles is preferably 80 to 98%, more preferably 90 to 98%. When the hollow ratio of the hollow particles is 80% or more, high heat insulating properties can be imparted to the undercoat layer containing the hollow particles. On the other hand, when the hollow ratio of the hollow particles is 98% or less, the strength of the film surrounding the hollow portion is improved, so that the hollow particles can be obtained so as not to be crushed even when the undercoat layer is formed.
On the other hand, the hollow ratio of the second hollow particles is preferably less than 80%, more preferably less than 60%. When the hollow ratio of the second hollow particles is less than 80%, there is an advantage that the particles can be easily produced and inexpensive regardless of the foamed type or the non-foamed type of the hollow particles.

The content of the mixture of the first hollow particles and the hollow particles containing the second hollow particles is 5 to 75% by mass, preferably 7 to 50% by mass, based on the total solid content of the undercoat layer.
If the content of the mixture of hollow particles is less than 5% by mass, it is difficult to improve the heat insulating property. On the other hand, if the content of the mixture of hollow particles is more than 75% by mass, problems are likely to occur in terms of coatability and the like.
The content of the first hollow particles is 5 to 40% by mass, preferably 5 to 30% by mass, based on the total solid content of the undercoat layer.

(Thickener)
The thickener is preferably contained in the coating liquid for the undercoat layer. When the thickener is contained in the coating liquid for the undercoat layer, it is possible to suppress the bias of the hollow particles in the coating liquid for the undercoat layer. As the thickener, 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 the above, cellulose derivatives such as carboxymethyl cellulose (CMC) and high molecular weight polysaccharides are suitable as thickeners.

Since the first hollow particles have a large maximum particle size, they have a large buoyancy and tend to gather upward in a liquid having low viscosity. When a cellulose derivative or a high molecular weight polysaccharide is used as a thickener in the coating liquid for the undercoat layer, the first hollow particles are less likely to float in the coating liquid for the undercoat layer, and the dispersibility of the first hollow particles is improved. If the dispersibility of the first hollow particles is improved, 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 white spots in the image can be suppressed. ..

(Bundling resin)
The binder resin can be appropriately selected from the binders used for the heat-sensitive recording layer described later. For example, oxidized starch, starch-vinyl acetate graft copolymer, carboxymethylated cellulose, polyvinyl alcohol, latex and the like can be mentioned, and latex is preferable.

The latex is not particularly limited, but for example, polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyacrylic acid, polyacrylic acid ester, etc. Vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, silylated urethane, acrylic-silicon composite, and acrylic-silicon-urethane composite, urea resin, melamine resin, amide resin, polyurethane Examples thereof include water-insoluble polymers such as resins. Among the latexes, it is preferable to contain at least a styrene-butadiene copolymer (styrene-butadiene latex).

The Tg of the styrene-butadiene latex is preferably −10 ° C. or lower, more preferably −30 ° C. or lower. When the Tg of the styrene-butadiene latex is lower, the image quality is further improved.

The undercoat layer is generally a coating solution for an undercoat layer prepared by mixing and stirring hollow particles, a binder resin, and if necessary, an oil-absorbing pigment, an auxiliary agent, etc. using water as a medium, and is applied and dried on the support. It is formed by doing. The coating amount of the undercoat layer coating solution is not particularly limited, the coating amount after drying is preferably ^{2.0~10g / m 2, 2.5~7g / m} 2 Gayori preferable.

[Thermal recording layer]
(Dye precursor)
The thermal recording layer generally contains a dye precursor and a color-developing agent (color developer). A typical dye precursor is a colorless or light-colored leuco dye. Leuco dyes include triphenylmethane-based compounds, fluorane-based compounds, diphenylmethane-based compounds, and the like, and can be appropriately selected and used. Further, the leuco dye includes a dye having a color tone such as red, vermilion, magenta, blue, cyan, yellow, green, and black, and can be appropriately selected and used.

Examples of the dye precursor include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl)-. Blue coloring dyes such as 6-dimethylaminophthalide and fluorane, 3- (N-ethyl-N-p-tolyl) amino-7-N-methylanilinofluorane, 3-diethylamino-7-anilinofluorane , 3-Diethylamino-7-dibenzylaminofluorane and other green color dyes, 3,6-bis (diethylamino) fluorane-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino- Red-coloring dyes such as 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-diethylamino-7- (o-chlorophenylamino) fluorane, 3- (N-) Ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 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-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 2,2-bis {4- [6'-(N-cyclohexyl-N-methyl) Amino) -3'-methylspiro [phthalide-3,9'-xanthen-2'-ylamino] phenyl} propane, 3-diethylamino-7- (3'-trifluoromethylphenyl) Aminofluorane and other black coloring dyes , 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3,3-bis [1- (4-Methylphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-i Le] -4,5,6,7-tetrachlorophthalide, 3-p- (p-dimethylaminoanilino) anilino-6-methyl-7-chlorofluorene, 3-p- (p-chloroanilino) anilino Dyes having an absorption wavelength in the near infrared region such as -6-methyl-7-chlorofluorene, 3,6-bis (dimethylamino) fluorene-9-spiro-3'-(6'-dimethylamino) phthalide, etc. Can be mentioned. Of course, the present invention is not limited to these, and two or more kinds can be used in combination as needed. Among them, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, and 3- (N). -Ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane is preferably used because it has excellent recording sensitivity and print storage stability.

The content of the dye precursor is preferably 5 to 30% by mass, more preferably 7 to 30% by mass, still more preferably 7 to 25% by mass, based on the total solid content of the thermal recording layer. When the content of the dye precursor is 5% by mass or more, the color development density is improved, and when the content of the dye precursor is 30% by mass or less, the heat resistance is improved. The content of the dye precursor in the heat-sensitive recording layer per unit area is preferably 0.2 to 2.0 g / m ² , and more preferably 0.4 to 1.5 g / m ² . The content of the dye precursor per unit area can be measured by a high performance liquid chromatography method or the like.

(Coloring agent)
Specific examples of the color former (color developer) include, for example, 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4 , 4'-Dihydroxydiphenylmethane, 4,4'-isopropyridendiphenol, 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'-dihydroxydiphenyl sulfide, 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'- Dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone , 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'-methyl Phenolic compounds such as phenolic compounds such as diphenyl sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, Methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, -sec-butyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, 4-hydroxybenzoate Trill acid acid, chlorophenyl 4-hydroxybenzoate, 4,4'-dihydroxydiphenyl Pharmonic compounds such as ether, or benzoic acid, p-chlorobenzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic 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-methoxyphenoxyethoxy) cumyl] salicylic acid, 4-{3- (p-tolylsulfonyl) propyloxy] aromatic carboxylic acids such as zinc salicylate, and phenolic compounds thereof. Salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel, as well as antipyrine complexes of zinc thiocyanate, terephthalaldehyde acids and other aromatic carboxylic acids. Organic acidic substances such as complex zinc salts of N-p-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, thiourea compounds such as N, N'-di-m-chlorophenylthiourea, N- (p-toluenesulfonyl) carbamoyl acid p-cumylphenyl ester, N- (p-toluenesulfonyl) carbamoyl _{-SO 2} NH-bonds in molecules such as acid p-benzyloxyphenyl ester, N- [2- (3-phenylureido) phenyl] benzenesulfonamide, N- (o-tol oil) -p-toluenesulfoamide, etc. Examples thereof include organic compounds, active white clay, attapulsite, colloidal silica, inorganic acidic substances such as aluminum silicate, and the like.

（式中、ｎは１〜６の整数を表す。） Further, specific examples of the color former include 4,4'-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenyl sulfone represented by the following general formula (1), 4,4'-. Bis [(2-methyl-5-phenoxycarbonylaminophenyl) ureido] diphenyl sulfone, 4- (2-methyl-3-phenoxycarbonylaminophenyl) ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl) Examples thereof include urea urethane derivatives such as ureidodiphenyl sulfone, and diphenyl sulfone derivatives represented by the following general formula (2). Of course, the color former is not limited to these, and two or more compounds can be used in combination if necessary.

(In the formula, n represents an integer of 1 to 6.)

The content of the color-developing agent is not particularly limited and may be adjusted according to the leuco dye used. The content of the color-developing agent is generally preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, further preferably 1 part by mass or more, and 1.2 parts by mass or more with respect to 1 part by mass of the leuco dye. Is even more 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, based on 1 part by mass of the leuco dye. preferable. By setting the content of the color-developing agent to 0.5 parts by mass or more, the recording performance can be improved. On the other hand, by setting the content of the color-developing agent to 10 parts by mass or less, it is possible to effectively suppress the background fog in a high temperature environment.

In the present embodiment, the heat-sensitive recording layer may further contain a storage stability improving agent, 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) )] Sulfone compounds such as bisphenol, 4,4'-[1,3-phenylenebis (1-methylethylidene)] bisphenol; 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy) ) Epoxy compounds such as phenyl sulfone, 4- (2-methyl-1,2-epoxyethyl) diphenyl sulfone, 4- (2-ethyl-1,2-epoxyethyl) diphenyl sulfone; 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 may be contained in the heat-sensitive recording layer of the present embodiment. 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, and the like. 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.

The heat-sensitive recording layer can contain a binder. As the binder used in the coating liquid for the heat-sensitive recording layer, for example, either a water-soluble adhesive or a water-dispersible adhesive can be used. Examples of the water-soluble adhesive include modified polyvinyl alcohols such as polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol, starch and derivatives thereof, methoxycellulose, carboxymethylcellulose, and hydroxy. Cellulous derivatives such as ethyl 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, Examples include arabic gum. 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. Water 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. Examples thereof include latex of an insoluble polymer. 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.

The thermal recording layer may contain a cross-linking agent that cures the binder of the thermal recording layer or other layers. By including a cross-linking agent in the heat-sensitive recording layer, the water resistance of the heat-sensitive 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.

If necessary, the heat-sensitive recording layer may be provided with known waxes, metal soaps, colored dyes, colored pigments, fluorescent dyes, oil repellents, antifoaming agents, viscosity modifiers, etc., as long as the effects of the invention are not impaired. Can be contained.

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 coating liquid for the heat-sensitive recording layer is, for example, a dispersion liquid in which water is used as a dispersion medium and fine particles of a dye precursor and a color-developing agent, a binder, a storage improving agent, a sensitizer, etc. are dispersed together or separately. Prepared using. Heat-sensitive recording layer coating solution, preferably a dry weight 2~12g / ^{m 2,} more preferably 2 to 8 g / ^{m 2,} more preferably coated on a support so as to 2~7g / ^{m 2} NS.

[Protective layer]
A protective layer can be further provided on the thermal recording layer. The protective layer is prepared by mixing, for example, a binder, optionally a pigment, a wax, a cross-linking agent, and other auxiliaries. As the binder and the pigment, materials as exemplified in the above-mentioned thermal recording layer can be used. By containing a pigment or wax, it is possible to prevent debris from adhering to the thermal head and sticking. Further, by adding a cross-linking agent to the protective layer, it is possible to impart water resistance to the protective layer. As the protective layer, water is used as a dispersion medium, and the coating liquid for the protective layer is heat-sensitively recorded so as to ^{have a dry weight of preferably 0.1 to 15 g / m 2} , more preferably 0.5 to 8 g / m ^2. It is formed by applying it on the layer.

[Other layers]
In the present embodiment, 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, adhesive paper, re-wet adhesive paper, delayed tack paper 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, and zeography paper 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 or plasticizer from the back surface of the heat-sensitive 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 such as, etc. may be used. Further, each coating liquid may be applied and dried one layer at a time to form each layer, or the same coating liquid 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.

From the viewpoint of increasing the recording sensitivity and suppressing white spots and the like, it is preferable to perform smoothing treatment using a known method such as a super calendar or a soft calendar after the formation of each layer or after the formation of all layers.

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.

The materials used in Examples and Comparative Examples are as follows.
(1) Hollow particles (i) Hollow particles A: Trade name Expandel 461WE20d36, hollow particles manufactured by AkzoNobel, median diameter (D50) 20 μm, maximum particle diameter (D100) 80 μm, hollow ratio 95%, 2 μm or less Particle ratio 0% by volume, solid content concentration 15.0%
(Ii) Hollow particles B: median diameter (D50) 12 μm, maximum particle diameter (D100) 45 μm, hollow ratio 94%, proportion of particles of 2 μm or less 0 volume%, solid content concentration 15.0%
(Iii) Hollow particles C: median diameter (D50) 11 μm, maximum particle diameter (D100) 23 μm, hollow ratio 93%, proportion of particles of 2 μm or less 0 volume%, solid content concentration 15.0%
(Iv) Hollow particles D: Median diameter (D50) 8.1 μm, maximum particle diameter (D100) 20 μm, hollow ratio 90%, proportion of particles of 2 μm or less 0 volume%, solid content concentration 15.0%
(V) Hollow particles E: median diameter (D50) 7.5 μm, maximum particle diameter (D100) 15 μm, hollow ratio 85%, proportion of particles of 2 μm or less 0 volume%, solid content concentration 15.0%
(Vi) Hollow particles F: median diameter (D50) 12 μm, maximum particle diameter (D100) 124 μm, hollow ratio 94%, proportion of particles of 2 μm or less 0 volume%, solid content concentration 15.0%
(Vii) Hollow particles G: median diameter (D50) 6.2 μm, maximum particle diameter (D100) 15 μm, hollow ratio 77%, proportion of particles of 2 μm or less 0 volume%, solid content concentration 15.0%
(Viii) Hollow particle H: Trade name A-380, hollow particle manufactured by Sansuisha, median diameter (D50) 3.8 μm, maximum particle diameter (D100) 6.5 μm, hollow ratio 78%, particle diameter 2.0 μm or less Hollow particle ratio 1.5% by volume, solid content concentration 13.0%
(Ix) Hollow particles I: Median diameter (D50) 5.0 μm, maximum particle diameter (D100) 13.5 μm, hollow ratio 90%, proportion of particles of 2 μm or less 0.2% by volume, solid content concentration 15.0%
(X) Hollow particles J: Trade name Low Pake SN-1055, manufactured by Dow Chemical Co., Ltd., median diameter (D50) 1.0 μm, maximum particle diameter (D100) 2.0 μm, hollow ratio 55%, particle diameter 2.0 μm or less Percentage of hollow particles in 100% by volume, solid content concentration 26.5%
(2) Latex (i) Latex A: Styrene-butadiene latex developed product (Tg: -10 ° C, particle size 190 nm, solid content concentration 48%)
(Ii) Latex B: Styrene-butadiene latex developed product (Tg: -35 ° C, particle size 300 nm, solid content concentration 48%)
(Iii) Latex C: Styrene-butadiene latex (trade name L-1571, manufactured by Asahi Kasei Corporation, Tg = -3 ° C, particle size 190 nm, solid content concentration 48%)

(Example 1)
(1) Preparation of coating liquid for undercoat layer 120.0 parts of hollow particles A, 135.8 parts of hollow particles J, 18.0 parts of calcined kaolin (trade name: Ansilex 93, manufactured by BASF), 25 parts of latex A. , Carboxymethyl cellulose (trade name: Cellogen AG gum, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 75.0 parts of water were mixed and stirred to obtain a coating liquid for an undercoat layer.

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

(3) Preparation of color-developing agent dispersion (liquid B) 40 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone (manufactured by Nippon Soda Co., Ltd., D-8), 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 Corporation) using a sand mill (manufactured by Imex, sand grinder). The color-developing agent dispersion liquid (Liquid B) was obtained.

(4) Preparation of sensitizer dispersion liquid (C liquid) 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 instrument SALD2200 (manufactured by Shimadzu Seisakusho) using a sand mill (manufactured by Imex, sand grinder). The mixture was pulverized to obtain a sensitizer dispersion liquid (C liquid).

(5) Preparation of coating solution 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 hydroxypropylmethylcellulose, completely saponified polyvinyl alcohol (trade name) : PVA110, Saponification degree: 99 mol%, Average degree of polymerization: 1000, 46 parts of 10% aqueous solution manufactured by Kuraray Co., Ltd., butadiene-based copolymer latex (trade name: L-1571, manufactured by Asahi Kasei Co., Ltd., solid content concentration 48%) ) 9.4 parts, light calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd.) 25.4 parts, paraffin wax (trade name: Hydrin L-700, manufactured by Chukyo Oil & Fat Co., Ltd., solid content concentration 30%) 11 .7 parts, 2 parts of adipate dihydrazide (manufactured by Otsuka Chemical Co., Ltd.), and 120 parts of water were mixed and stirred to obtain a coating liquid for a heat-sensitive recording layer.

(6) Preparation of coating liquid for protective layer Acetacetyl-modified polyvinyl alcohol (trade name: Gosenex Z-200, saponification degree: 99.4 mol%, average degree of polymerization: 1000, modification degree: 5 mol%, Nippon Synthetic Chemistry 300 parts of 12% aqueous solution (manufactured by Kogyo Co., Ltd.), 19 parts of kaolin (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. The material was mixed and stirred to obtain a coating liquid for a protective layer.

(7) Preparation of thermal recording body On ^{one side of high-quality paper with a basis weight of 60 g / m 2} , the coating liquid for the undercoat layer, the coating liquid for the thermal recording layer, and the coating liquid for the protective layer recording are applied after drying. the amount each ^{4.0g / m 2, 4.0g / m} 2, was applied and dried so that 2.0 g / ^{m 2,} the undercoating layer, thermosensitive recording layer, and after sequentially forming a protective layer, Super The surface was smoothed with a calendar to obtain a thermal recorder.

(Example 2)
In the preparation of the coating liquid for the undercoat layer of Example 1, a heat-sensitive recorder was obtained in the same manner as in Example 1 except that the hollow particles A were changed to the hollow particles B.

(Example 3)
In the preparation of the coating liquid for the undercoat layer of Example 1, a heat-sensitive recorder was obtained in the same manner as in Example 1 except that the hollow particles A were changed to the hollow particles C.

(Example 4)
In the preparation of the coating liquid for the undercoat layer of Example 1, a heat-sensitive recorder was obtained in the same manner as in Example 1 except that the hollow particles A were changed to the hollow particles D.

(Example 5)
A heat-sensitive recorder was obtained in the same manner as in Example 3 except that the hollow particles C were changed to 40.0 parts and the calcined kaolin was changed to 30.0 parts in the preparation of the coating liquid for the undercoat layer of Example 3.

(Example 6)
A heat-sensitive recorder was obtained in the same manner as in Example 3 except that the hollow particles C were changed to 186.7 parts and the calcined kaolin was changed to 8.0 parts in the preparation of the coating liquid for the undercoat layer of Example 3.

(Example 7)
A heat-sensitive recorder was obtained in the same manner as in Example 3 except that the hollow particles C were changed to 26.7 parts and the calcined kaolin was changed to 32.0 parts in the preparation of the coating liquid for the undercoat layer of Example 3.

(Example 8)
A heat-sensitive recorder was obtained in the same manner as in Example 3 except that the hollow particles C were changed to 213.3 parts and the calcined kaolin was changed to 4.0 parts in the preparation of the coating liquid for the undercoat layer of Example 3.

(Example 9)
In the preparation of the thermal recording body of Example 3, the thermal recording body was prepared in the same manner as in Example 3 except ^{that the coating amount of the undercoat layer after drying was changed from 4.0 g / m 2} to 12.0 g / m ^2. Obtained.

(Example 10)
In the preparation of the thermal recording body of Example 3, the thermal recording body was prepared in the same manner as in Example 3 except ^{that the coating amount of the undercoat layer after drying was changed from 4.0 g / m 2} to 8.0 g / m ^2. Obtained.

(Example 11)
In the preparation of the thermal recording body of Example 3, the thermal recording body was prepared in the same manner as in Example 3 except ^{that the coating amount of the undercoat layer after drying was changed from 4.0 g / m 2} to 2.0 g / m ^2. Obtained.

(Example 12)
In the preparation of the coating liquid for the undercoat layer of Example 3, heat sensitivity was the same as in Example 3 except that the hollow particles C were changed to 40.0 parts, the hollow particles J were changed to 249.1 parts, and the calcined kaolin was changed to 0 parts. I got a recording body.

(Example 13)
Similar to Example 3 in the preparation of the coating liquid for the undercoat layer of Example 3, except that the hollow particles C were changed to 186.7 parts, the hollow particles J were changed to 22.6 parts, and the calcined kaolin was changed to 38.0 parts. I got a thermal recorder.

(Example 14)
Similar to Example 3 in the preparation of the coating liquid for the undercoat layer of Example 3, except that the hollow particles C were changed to 186.7 parts, the hollow particles J were changed to 7.5 parts, and the calcined kaolin was changed to 42.0 parts. I got a thermal recorder.

(Example 15)
In the preparation of the coating liquid for the undercoat layer of Example 3, a heat-sensitive recorder was obtained in the same manner as in Example 3 except that latex A was changed to latex B.

(Example 16)
In the preparation of the coating liquid for the undercoat layer of Example 3, a heat-sensitive recorder was obtained in the same manner as in Example 3 except that latex A was changed to latex C.

(Example 17)
In the preparation of the coating liquid for the undercoat layer of Example 3, a heat-sensitive recorder was obtained in the same manner as in Example 3 except that 276.9 parts of hollow particles H were used instead of 135.8 parts of hollow particles J. ..

(Example 18)
In the preparation of the coating liquid for the undercoat layer of Example 3, a heat-sensitive recorder was obtained in the same manner as in Example 3 except that 240.0 parts of hollow particles I were used instead of 135.8 parts of hollow particles J. ..

(Example 19)
In the preparation of the color-developing agent dispersion of Example 3, 4-hydroxyphenyl (4'-n-propoxyphenyl) was used instead of 4-hydroxy-4'-isopropoxydiphenyl sulfone (D-8, manufactured by Nippon Soda Co., Ltd.). A heat-sensitive recorder was obtained in the same manner as in Example 3 except that sulfone (Tomirac KN manufactured by Mitsubishi Chemical Co., Ltd.) was used.

(Example 20)
In the preparation of the color-developing solution of Example 3, 2-phenylsulfonylamino-N, N'-diphenylurea was used instead of 4-hydroxy-4'-isopropoxydiphenyl sulfone (D-8, manufactured by Nippon Soda Corporation). A heat-sensitive recorder was obtained in the same manner as in Example 3 except that (NKK-1304 manufactured by Nippon Soda Co., Ltd.) was used.

(Example 21)
In the preparation of the coating liquid for the undercoat layer of Example 1, a heat-sensitive recorder was obtained in the same manner as in Example 1 except that the hollow particles A were made into hollow particles E.

(Comparative Example 1)
In the preparation of the coating liquid for the undercoat layer of Example 1, a heat-sensitive recorder was obtained in the same manner as in Example 1 except that the hollow particles F were used instead of the hollow particles A.

(Comparative Example 2)
In the preparation of the coating liquid for the undercoat layer of Example 1, a heat-sensitive recorder was obtained in the same manner as in Example 1 except that the hollow particles G were used instead of the hollow particles A.

(Comparative Example 3)
In the preparation of the coating liquid for the undercoat layer of Example 1, a heat-sensitive recorder was obtained in the same manner as in Example 1 except that 138.5 parts of the hollow particles H were used instead of 120.0 parts of the hollow particles A.

(Comparative Example 4)
In the preparation of the coating liquid for the undercoat layer of Example 1, a heat-sensitive recorder was obtained in the same manner as in Example 1 except that the hollow particles I were used instead of the hollow particles A.

(Comparative Example 5)
In the preparation of the coating liquid for the undercoat layer of Example 3, a heat-sensitive recorder was obtained in the same manner as in Example 3 except that the hollow particles J were changed to 0 parts and the Ansilex 93 was changed to 54.0 parts.

The following performance evaluations were performed on the obtained heat-sensitive recorders of Examples 1 to 21 and Comparative Examples 1 to 5, and the results are shown in Table 1.

[Half tone recording density]
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.

[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 or thickening of the barcode, which is particularly excellent.
◯: There is no white spot in the image or thickening of the barcode, and there is no problem.
Δ: There is almost no white spots in the image 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.

As can be seen from Table 1, the heat-sensitive recorders of Examples 1 to 21 were excellent in both halftone recording density and print quality.
In the thermal recording body of Comparative Example 1, since the maximum particle size (D100) of the first hollow particles exceeds 80 μm, the smoothness of the undercoat layer is lowered, and the coating liquid for the thermal recording layer is not uniformly applied, and is intermediate. The recorded density was inferior.
In the thermal recording bodies of Comparative Examples 2 to 4, since the median diameter (D50) of the first hollow particles was less than 7.5 μm, the heat insulating property of the undercoat layer was insufficient, and the print quality was inferior. ..
In particular, in the thermal recording body of Comparative Example 3, the maximum particle size (D100) of the first hollow particles was less than 10 μm, the cushioning property was lowered, and the halftone recording concentration was also inferior.
The heat-sensitive recording material of Comparative Example 5 does not use the second hollow particles, the smoothness of the undercoat layer is lowered, the coating liquid for the heat-sensitive recording layer is not uniformly applied, and the halftone recording concentration is inferior. It was a thing.

Claims (11)

A heat-sensitive recording body including an undercoat layer formed on one surface of a support and a heat-sensitive recording layer formed on the undercoat layer.
The heat-sensitive recording layer contains a leuco dye and a color-developing agent.
The undercoat layer contains hollow particles and a binder resin, and contains
The hollow particles consist of at least two types of hollow particles, a large particle diameter hollow particle and a small particle diameter hollow particle.
The large particle size hollow particles have a maximum particle size (D100) of 10 to 80 μm and a particle size (D50) of 50% by volume frequency of 7.5 to 25 μm.
The small particle size hollow particles are heat-sensitive recorders having a particle size (D50) of 50% by volume and a particle size (D50) of 0.7 to 6 μm. The heat-sensitive recorder according to claim 1, wherein the maximum particle size (D100) of the large particle size hollow particles is 10 to 50 μm, and the particle size (D50) of 50% by volume frequency is 7.5 to 15 μm. .. The heat-sensitive recorder according to claim 1 or 2, wherein the large particle size hollow particles have a D100 / D50 of 1.8 to 10.0. The one according to any one of claims 1 to 3, wherein the hollow ratio of the large particle diameter hollow particles is 80 to 98%, and the hollow ratio of the small particle diameter hollow particles is less than 80%. The heat-sensitive recording body described. The heat-sensitive recorder according to any one of claims 1 to 4, wherein the undercoat layer contains 5 to 40% by mass of the large-diameter hollow particles. The heat-sensitive recorder according to any one of claims 1 to 5, wherein the coating amount of the undercoat layer after drying is 2.0 to 10 g / m ^2. The invention according to any one of claims 1 to 6, wherein the small particle size hollow particles are contained in a ratio of 0.1 to 10 parts by mass with respect to 1 part by mass of the large particle size hollow particles. Heat-sensitive recording body. The heat-sensitive recorder according to any one of claims 1 to 7, wherein the small particle size hollow particles have a maximum particle size (D100) of 1 to 7 μm. The heat-sensitive recording material according to any one of claims 1 to 8, wherein the binder resin contains at least styrene-butadiene latex. The heat-sensitive recorder according to claim 9, wherein the Tg of the styrene-butadiene latex is −10 ° C. or lower. The heat-sensitive recorder according to claim 9, wherein the Tg of the styrene-butadiene latex is −30 ° C. or lower.