KR20230062811A - thermal recorder - Google Patents

Abstract

Disclosed is an undercoat layer containing hollow particles having a hollow ratio of 80 to 98% on one side of a paper support, and a thermal recording layer containing a leuco dye and a developer in this order, and the other side of the paper support A heat-sensitive recording material having a back layer containing pigment on one side, wherein the back layer has a royal smoothness of 500 seconds or more, and the content of the hollow particles is 5 to 30 mass% of the total solid mass of the undercoat layer. it is a record

Description

thermal recorder

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

Conventionally, a heat-sensitive recording material using a color development reaction by heat between a leuco dye and a color developer is well known. Since these thermal recording materials are relatively inexpensive, the recording equipment is compact, and their maintenance is relatively easy, they can be used not only as facsimiles, various labels, and other recording media for output, but also as non-destructive inspection devices such as ultrasonic images and X-ray images. Alternatively, it is also widely used as a recording medium for so-called image diagnosis used in printers of medical diagnostic devices.

In image printers that require uniformity and high resolution of recorded images, synthetic paper having a multi-layer structure and a heat-sensitive recording material using a biaxially stretched thermoplastic resin film containing inorganic pigments as a support is used. In recent years, out of high environmental concern, there is a demand for a heat-sensitive recording material that uses reproducible paper as a support, has excellent gradation reproducibility from low to high concentrations, and can obtain high-quality recorded images comparable to silver halide photographs this is rising

And, in order to prevent head scum adhesion and sticking, it is proposed to apply a heat-sensitive coloring layer to base paper containing synthetic silica and/or synthetic aluminum silicate (see Patent Document 1). In addition, a heat-sensitive recording material in which the support is paper containing an inorganic pigment with an oil absorption of 100 ml/100 g or more (refer to Patent Document 2), and a heat-sensitive recording material in which the support is paper containing 15 to 30% by weight of calcium carbonate with an oil absorption of 70 ml/100 g or more. (See Patent Literature 3) has been proposed. These thermal recording materials are intended to improve dot reproducibility by suppressing and preventing head scum adhesion, so-called scum removal effect, but compared to synthetic paper or thermoplastic resin film as a support, color unevenness is remarkable, and it is used as a recording medium for image diagnosis. Regarding the required image quality, the present condition is that satisfactory results are not necessarily obtained. In addition, the cutter and slitter in the flat plate processing and small winding finish in the manufacturing process, or the cutter attached to the printer, easily cause pigment fall-off and paper fluff, causing defects in the image, and in the medical field cause hygiene problems.

In order to solve this problem, a heat-sensitive recording material using a paper support containing amorphous silica having a specific surface area of 180 m 2 /g or more as a filler and having a density of 0.60 to 0.85 g / cm 2 has been proposed (see Patent Document 4).

In addition, image paper substrate thermal recording paper requires high sensitivity and clear printing images in a low energy area, and a thermal recording material with no white spots and uniform and clear printing image quality is required even at low energy.

Japanese Unexamined Patent Publication No. 61-68291 Japanese Unexamined Patent Publication No. 61-98584 Japanese Unexamined Patent Publication No. 5-58027 Japanese Unexamined Patent Publication No. 2012-101396

The main object of the present invention is to provide a thermally sensitive recording material that provides a clear printed image with high sensitivity and excellent image quality in a low energy region.

As a result of repeated intensive studies in order to solve the above object, the present inventors have found that hollow particles having a hollow rate of 80 to 98% are contained in the undercoat layer at a rate of 5 to 30% by mass of the total solid amount of the undercoat layer, By setting the royal smoothness of the layer to 500 seconds or more, it was found that the above problems could be solved, and the present invention was solved. That is, the present invention relates to the following heat-sensitive recording material.

Item 1. A paper support having on one side an undercoat layer containing hollow particles having a hollow ratio of 80 to 98%, and a thermal recording layer containing a leuco dye and a developer, in this order, on the other side of the paper support. A heat-sensitive recording material having a back layer containing pigment on the surface,

Wang Yeon-style smoothness of the back layer is more than 500 seconds,

A heat-sensitive recording material in which the content of the hollow particles is 5 to 30% by mass based on the total solid amount of the undercoat layer.

Item 2. The heat-sensitive recording material according to Item 1, wherein the back layer has a royal smoothness of 1000 seconds or more.

Item 3. The heat-sensitive recording material according to item 1 or 2, wherein the back layer has a dry mass of 3.0 g/m 2 or more.

Item 4. The heat-sensitive recording material according to any one of Items 1 to 3, wherein kaolin is contained in the back layer.

Item 5. The heat-sensitive recording material according to any one of Items 1 to 4, wherein an adhesive having a glass transition temperature of -10°C or lower is contained in the undercoat layer.

Item 6. The heat-sensitive recording material according to any one of Items 1 to 4, wherein an adhesive having a glass transition temperature of -30°C or lower is contained in the undercoat layer.

Item 7. The heat-sensitive recording material according to any one of Items 1 to 6, wherein an adhesive is contained in the undercoat layer, and the adhesive contains latex.

Item 8. The heat-sensitive recording material according to any one of Items 1 to 7, wherein the surface having the thermal recording layer has a royal smoothness of 4000 seconds or more.

Item 9. The average particle diameter (D50) of the hollow particles is 3 to 15 μm, the maximum particle diameter (D100) of the hollow particles is 10 to 30 μm, and the maximum particle diameter (D100) and the average particle diameter of the hollow particles are The heat-sensitive recording material according to any one of items 1 to 8, wherein the ratio of diameters (D50) (D100/D50) is 1.8 to 3.0, and the volume percentage of the hollow particles having a particle diameter of 2.0 μm or less is 1% or less.

The heat-sensitive recording medium of the present invention has high sensitivity and excellent image quality in the low-energy region, and provides a clear printed image without color unevenness.

In this specification, the expression "includes" or "contains" includes the concepts of "comprises", "consisting only of substance", and "consisting only of".

In this specification, the numerical range indicated using "-" means the range which includes the numerical value described before and after "-" as a lower limit and an upper limit.

The latex in the present invention includes a state of a gel or dry film formed by drying a dispersion medium.

In the present invention, the "average particle diameter" refers to the volume-based median diameter measured by laser diffraction. More simply, it is also possible to measure particle diameters from particle images (SEM images) using an electron microscope, respectively, and express them as an average of 10 values.

The present invention has, on one side of a paper support, an undercoat layer containing hollow particles having a hollow ratio of 80 to 98%, and a thermal recording layer containing a leuco dye and a developer, in this order, and the other side of the paper support A heat-sensitive recording material having a back layer containing pigment on the surface,

Wang Yeon-style smoothness of the back layer is more than 500 seconds,

It is characterized in that the content ratio of the hollow particles is 5 to 30 mass% of the total solid amount of the undercoat layer.

[Paper support]

The paper support in the present invention is not particularly limited to the type, shape, size, etc., and examples thereof include high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast coated paper, glassine paper, and resin laminated paper. , polyolefin-based synthetic paper, synthetic fiber paper, etc. may be appropriately selected and used. The thickness of the paper support is not particularly limited and is usually about 20 to 200 μm. The density of the paper support is not particularly limited, and is preferably about 0.60 to 1.00 g/cm 3 , more preferably about 0.60 to 0.85 g/cm 3 .

[Undercoat layer]

In the heat-sensitive recording material of the present invention, an undercoat layer containing hollow particles having a hollowness ratio of 80 to 98% is provided between the paper support and the heat-sensitive recording layer. Accordingly, the permeation of the coating liquid for the thermal recording layer into the paper support can be suppressed, and image quality can be improved. In addition, the presence of hollow particles having a hollowness ratio of 80 to 98% makes it possible to suppress white spots in the printing portion even at low energy, and the halftone printing concentration can be increased. Examples of the hollow particles include conventionally known ones, for example, particles whose membrane material is made of an acrylic resin, a styrene resin, a vinylidene chloride resin, and the like. Here, the hollowness ratio is a value determined by (d/D) × 100. In the formula, d represents the inner diameter of the hollow particle, and D represents the outer diameter of the hollow particle. The hollowness ratio is preferably 90 to 98% from the viewpoint of improving image quality. The average particle diameter of the hollow particles is preferably about 3 to 15 μm, and more preferably about 4 to 12 μm. Here, the average particle diameter is a particle diameter at a frequency of 50% by volume, and is also called a median diameter or D50. The particle diameter and particle size distribution can be measured with a laser diffraction type particle size distribution analyzer. In addition, actual measurement using an electron microscope is also possible. The content of the hollow particles is 5 to 30% by mass, preferably about 7 to 28% by mass, and more preferably about 9 to 26% by mass, based on the total solid amount of the undercoat layer. By setting it as 5 mass % or more, even if it is low energy, white spots of a printing part can be suppressed and image quality can be improved. By setting it as 30 mass % or less, color unevenness can be suppressed and a printed image becomes clearer. In addition, it should be noted that the use of specific hollow particles for the undercoat layer and the application of a back layer described below can remarkably increase the smoothness of the surface having the thermal recording layer, and at the same time, the hollow particles of the undercoat layer It is possible to increase the elasticity of the coating layer, suppress white spots and uneven color development in the low-energy region, and improve thermal quality. By adjusting the average particle diameter, the maximum particle diameter, and the ratio (D100/D50) of the maximum particle diameter (D100) to the average particle diameter (D50) of the hollow particles, white spots and color unevenness in the low energy portion can be effectively suppressed.

The maximum particle diameter of the hollow particles is preferably 10 to 30 μm, more preferably 10 to 25 μm, and still more preferably 10 to 20 μm. On the other hand, the maximum particle diameter is also called D100.

The ratio (D100/D50) of the maximum particle diameter (D100) and the average particle diameter (D50) is an index indicating the degree of particle size distribution. It is preferable that it is 1.8-3.0, and, as for D100/D50, it is more preferable that it is 1.8-2.8.

In the particle size distribution, the volume percentage of hollow particles having a particle diameter of 2.0 μm or less is preferably 1% or less. Further, the hollow particles having a particle diameter of 2.0 μm or less preferably have a volume percentage of 0.5% or less, and more preferably do not contain the hollow particles.

The undercoat layer may include an oil absorbing pigment and/or thermally expandable particles having an oil absorption of 70 ml/100 g or more, particularly 80 to 150 ml/100 g. Here, the oil absorption amount is a value obtained according to the method of JIS K 5101.

Although various types of pigments can be used as the oil absorption pigment, specific examples include inorganic pigments such as calcined kaolin, amorphous silica, precipitated calcium carbonate, and talc. The average particle diameter of the primary particles of these oil absorptive pigments is preferably about 0.01 to 5 μm, particularly about 0.02 to 3 μm. The amount of the oil absorptive pigment used can be selected from a wide range, but is generally preferably about 2 to 95% by mass, and more preferably about 5 to 90% by mass, based on the total solid amount of the undercoat layer.

The undercoat layer is generally prepared by mixing adhesives, hollow particles, oil absorbing pigments, various auxiliary agents, etc. using water as a dispersion medium. , More preferably, it is formed by coating and drying so as to be about 5 to 12 g/m 2 .

Examples of the adhesive include polyvinyl alcohol and derivatives thereof, starch and derivatives thereof, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylate, and polyvinyl Pyrrolidone, acrylamide-acrylic acid ester copolymer, acrylamide-acrylic acid ester-methacrylic acid ester copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, casein, gelatin, and derivatives thereof Emulsions such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, or styrene-butadiene copolymer and latexes of water-insoluble polymers such as polymers and styrene-butadiene-acrylic copolymers. Among these, it is preferable to use an adhesive containing latex. The content of the adhesive can be selected from a wide range, but is generally preferably about 5 to 30% by mass, and more preferably about 10 to 20% by mass, based on the total solid amount of the undercoat layer.

The glass transition temperature (Tg) of the adhesive is not particularly limited, but is preferably -10°C or lower. When the glass transition temperature is -10°C or lower, image quality can be improved even in a low energy region. Since the glass transition temperature can further improve image quality in a low energy range, it is more preferably -30°C or lower.

Auxiliaries contained in the coating liquid for the undercoat layer include, for example, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, metal salts of fatty acids, zinc stearate, calcium stearate, polyethylene wax , waxes such as carnauba wax, paraffin wax, and ester wax, hydrazide compounds, glyoxal, boric acid, dialdehyde starch, glyoxylates, methylol urea, water-resistant agents such as epoxy compounds, antifoaming agents, colored dyes, fluorescent dyes etc. can be mentioned.

[Thermal recording layer]

In the thermal recording layer of the thermal recording medium of the present invention, various known colorless or light-colored leuco dyes may be incorporated. Specific examples of such leuco dye are given below.

Specific examples of the leuco dye include, for example, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4 -Dimethylaminophenyl)-6-dimethylaminophthalide, blue color-developing dyes such as fluorane, 3-(N-ethyl-N-p-tolyl)amino-7-N-methylanilinofluorane, 3-diethylamino -7-anilinofluorane, 3-diethylamino-7-dibenzylaminofluorane, green color-developing dyes such as rhodamine B-anilinolactam, 3,6-bis(diethylamino)fluorane-γ- Red chromogenic dyes such as anilinolactam, 3-cyclohexylamino-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-anilinofluoran, 3-di(n-butyl)amino-6-methyl-7-anilinofluoran, 3-di(n-pentyl)amino-6-methyl -7-anilinofluorane, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-(m-trifluoromethylanilino ) Fluorane, 3-(N-isoamyl-N-ethylamino)-7-(o-chloroanilino)fluoran, 3-(N-ethyl-N-2-tetrahydrofurfurylamino)-6- Methyl-7-anilinofluorane, 3-(N-n-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)fluoran, 3-di(n-butylamino)-7-(2-chloroanilino)fluoran, 4,4'-bis-dimethylaminobenzhydrinbenzyl ether, N- 2,4,5-trichlorophenylleucoramine, 3-diethylamino-7-butylaminofluoran, 3-ethyl-tolylamino-6-methyl-7-anilinofluoran, 3-cyclohexyl-methyl Amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7- (β-ethoxyethyl) aminofluorane, 3-diethylamino-6-chloro-7- (γ -Chloropropyl)aminofluoran, 3-diethylamino-6-methyl-7-anilinofluorane, 3-(N-isoamyl-N-ethylamino)-6-methyl-7-anilinofluorane, 3-Dibutylamino-7-chloroanilinofluoran, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-(N-ethyl-p-toluidino)-6-methyl- 7-Anilinofluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluoran, 3-(N-ethyl-N-tetrahydrofurfuryl Amino) -6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-p Rolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 2,2-bis{4-[6'-(N-cyclohexyl-N -Methylamino)-3'-methylspiro[phthalide-3,9'-xanthene]-2'-ylamino]phenyl}propane, 3-diethylamino-7-(3'-trifluoromethylphenyl) Black chromogenic dyes such as aminofluorane, 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylene-2-yl]-4,5,6,7-tetra Chlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthale Lead, 3-p-(p-dimethylaminoanilino)anilino-6-methyl-7-chlorofluorane, 3-p-(p-chloroanilino)anilino-6-methyl-7-chlorofluorane , 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, and other dyes having an absorption wavelength in the near infrared region. Of course, it is not limited to these, and two or more types of compounds may be used in combination as needed.

The content 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, and still more preferably about 7 to 20% by mass, based on the total solid amount of the thermal recording layer. do. By setting it as 3 mass % or more, color development ability can be improved and printing density|concentration can be improved. Heat resistance can be improved by setting it as 30 mass % or less.

Specific examples of the developer include, for example, 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4 '-dihydroxydiphenylmethane, 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-hydroxy hydroxyphenyl) -4-methylpentane, 2,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-n-propoxydiphenyl Sulfone, 4-hydroxy-4'-allyloxydiphenylsulfone, 4-hydroxy-4'-benzyloxydiphenylsulfone, 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, Bis (p-hydroxyphenyl) butyl acetate, bis (p-hydroxyphenyl) methyl acetate, hydroquinone monobenzyl ether, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'- Methyl diphenyl sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 4-hydroxybenzophenone, 4-hydroxy dimethyl phthalate, 4- Methyl hydroxybenzoate, 4-hydroxybenzoate propyl, 4-hydroxybenzoate -sec-butyl, 4-hydroxybenzoate phenyl, 4-hydroxybenzoate benzyl, 4-hydroxybenzoate benzyl ester, 4-hydroxybenzoate tril phenolic compounds such as chlorophenyl 4-hydroxybenzoate, 4,4'-dihydroxydiphenyl 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-( Aromatic carboxylic acids such as p-tolylsulfonyl)propyloxy]zinc salicylate, and these phenolic compounds, aromatic carboxylic acids, for example, zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, etc. Organic acidic substances such as salts of polyvalent metals, antipyrine complexes of zinc thiocyanate, complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids, Np-toluenesulfonyl-N'-3-(p-toluenesulfonyl) Oxy) phenylurea, Np-toluenesulfonyl-N'-p-butoxycarbonylphenylurea, Np-tolylsulfonyl-N'-phenylurea, 4,4'-bis(p-toluenesulfonylaminocarbonyl Urea compounds such as amino)diphenylmethane, 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, N,N'-di-m-chlorophenylthio Thiourea compounds such as urea, N-(p-toluenesulfonyl)carbamoyl acid p-cumylphenyl ester, N-(p-toluenesulfonyl)carbamoyl acid p-benzyloxyphenyl ester, N-[2-( 3-phenylureido)phenyl]benzenesulfonamide, N-(o-toluoyl)-p-toluenesulfoamide, organic compounds having -SO ₂ NH- bonds in the molecule, activated clay, attapulgite, colloids and inorganic acidic substances such as silica and aluminum silicate.

Furthermore, 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone represented by the following formula (1), 4,4'-bis[(2-methyl-5 -Phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl ) Urea urethane derivatives, such as ureido diphenyl sulfone, and diphenyl sulfone derivatives represented by following formula (2), etc. are mentioned.

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

The developer is, of course, not limited thereto, and two or more compounds may be used in combination as needed.

The content of such a color developer is not particularly limited, and may be adjusted depending on the leuco dye used. Generally, 0.5 parts by mass or more is preferable, 0.8 parts by mass or more is more preferable, and 1 part by mass is 1 part by mass of the leuco dye. The above is more preferable, 1.2 parts by mass or more is still more preferable, and 1.5 parts by mass or more is particularly preferable. The content of the developer is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more 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. By setting it to 0.5 parts by mass or more, the recording performance can be improved. On the other hand, by setting it as 10 parts by mass or less, background haze in a high temperature environment can be effectively suppressed.

In the present invention, a preservability improver may be further contained in the heat-sensitive recording layer, mainly in order to further increase the preservability of color development. Such preservation improvers include, for example, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 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- phenol compounds such as methylethylidene)]bisphenol and 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisphenol; 4-Benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenylsulfone, 4-(2-methyl-1,2-epoxyethyl)diphenylsulfone, 4-(2-ethyl- Epoxy compounds, such as 1, 2- epoxyethyl) diphenyl sulfone; And at least one or more selected from isocyanuric acid compounds such as 1,3,5-tris(2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl)isocyanuric acid can be used. Of course, it is not limited to these, and two or more types of compounds may be used in combination as needed.

When using a preservative improver, the amount used may be an effective amount for improving the preservability. Usually, it is preferably about 1 to 30% by mass, and more preferably about 5 to 20% by mass, based on the total solid amount of the thermal recording layer. .

A sensitizer may be contained in the thermal recording layer in the present invention. Thus, the recording sensitivity can be increased. Examples of the sensitizer include stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoyl stearic acid amide, N-eicosacic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid Amide, N-methylolstearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenylsulfone, p-benzyloxybenzoate benzyl, 1-hydroxy-2-naphthoyl phenyl, 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-acetotoluidide, p-acetphenethidide, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di(β-biphenyl oxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, diphenyl, benzophenone, etc. are mentioned. These can be used together within the range which does not interfere. The content of the sensitizer may be in 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 amount of the thermal recording layer.

To improve the whiteness of the thermal recording layer and the uniformity of images, a fine particle pigment having a high whiteness and an average particle diameter of 10 μm or less may be incorporated into the thermal recording layer. inorganic pigments such as, 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, and silica; and organic pigments such as urea-formalin resin, styrene-methacrylic acid copolymer resin, and polystyrene resin. The content of the pigment is preferably an amount that does not lower the color density, that is, 50% by mass or less of the total solid amount of the heat-sensitive color development layer.

As other component materials constituting the thermal recording layer, adhesives are used, and crosslinking agents, waxes, metal soaps, water-resistance agents, dispersants, colored dyes, fluorescent dyes, and the like can be used if necessary.

Adhesives used in the coating liquid for the heat-sensitive recording layer include, for example, water-soluble adhesives and water-dispersible adhesives. Examples of water-soluble adhesives include modified polyvinyl alcohol 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; Cellulose derivatives such as toxycellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, polyamide, and diisobutylene -maleic anhydride copolymer salt, styrene-acrylic acid copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-maleic anhydride copolymer salt, acrylamide-acrylic acid ester copolymer, acrylamide-acrylic acid ester-methacrylic acid Copolymer, polyacrylamide, sodium alginate, gelatin, casein, gum arabic, etc. are mentioned. As the water-dispersible adhesive, an emulsion such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, or styrene-butadiene copolymer and latexes of water-insoluble polymers such as styrene-butadiene-acrylic copolymers. These can be used individually by 1 type or in combination of 2 or more types. 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, of the total solid amount of the thermal recording layer.

A crosslinking agent for curing the adhesive of the thermal recording layer or other layers may be contained in the thermal recording layer. Accordingly, the water resistance of the thermal recording layer can be improved. Examples of the crosslinking agent include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, dimethylol urea compounds, aziridine compounds, and block isocylate. Annette compounds; Inorganic compounds, such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, and potassium tetraborate; Boric acid, boric acid triester, a boron polymer, a hydrazide compound, a glyoxylate, etc. are mentioned. These may be used individually by 1 type, and may be used in combination of 2 or more type. The amount of the crosslinking agent is preferably in the range of about 1 to 10 parts by mass based on 100 parts by mass of the total solid mass of the thermal recording layer. Accordingly, 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; Examples thereof include higher fatty acid amides such as stearic acid amide and ethylenebisstearic acid amide, higher fatty acid esters, and derivatives thereof.

Examples of the metal soap include polyvalent metal salts of higher fatty acids, such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. In addition, if necessary, various auxiliary agents such as an oil repellent agent, an antifoaming agent, and a viscosity modifier may be further added to the thermal recording layer within a range that does not impair the effects of the present invention.

In general, the heat-sensitive recording layer uses water as a dispersion medium, and mixes leuco dye, color developer, and, if necessary, a sensitizer and a preservation improver together or separately, using various agitation methods such as ball mill, coball mill, art liter, vertical and horizontal sand mill, etc. After dispersing with a water-soluble synthetic high molecular compound such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, styrene-maleic anhydride copolymer salt, and other surfactants by a wet mill to form a dispersion, A coating liquid for a thermal recording layer prepared by using a dispersion obtained by dispersing so as to have an average particle diameter of 2 μm or less and mixing pigments, adhesives, adjuvants, etc. as necessary is applied, and then dried to form on the undercoat layer. The coating amount of the thermal recording layer is not particularly limited, and is preferably about 1 to 12 g/m2, more preferably 2 to 10 g/m2, more preferably 2.5 to 8 g/m2, and even more preferably 3 to 5.5 g/m2 in terms of dry mass. is particularly preferred. Meanwhile, the thermal recording layer may be formed by dividing into two or more layers as needed, and the composition and coating amount of each layer may be the same or different.

[protective layer]

It is preferable to form a protective layer on the heat-sensitive recording layer of the present invention in order to improve preservability or performance during recording. The protective layer can be obtained by applying a coating solution for the protective layer obtained by mixing water as a medium, an adhesive and a pigment as main components, and various auxiliary agents added as necessary, onto the thermal recording layer and drying it.

Pigments used in the protective layer include, for example, amorphous silica, kaolin, light calcium carbonate, heavy calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, colloidal silica, synthetic layered mica, urea-formalin resin filler, etc. of plastic pigments, and the like.

Moreover, the adhesive used for the coating liquid for the protective layer is not particularly limited, and water-based adhesives such as water-soluble adhesives and water-dispersible adhesives are exemplified. The adhesive can be appropriately selected from those usable for the thermal recording layer. Among them, polyvinyl alcohol or modified polyvinyl alcohol is preferable, especially acetoacetyl-modified polyvinyl alcohol, carboxyl-modified polyvinyl Various denatured polyvinyl alcohols, such as alcohol and diacetone denatured polyvinyl alcohol, are more preferably used.

The content of the adhesive is preferably about 20 to 85% by mass, more preferably about 35 to 80% by mass, based on the total solid amount of the protective layer.

In addition, various auxiliary agents such as known auxiliary agents such as lubricants, antifoaming agents, wetting agents, antiseptic agents, optical whitening agents, dispersing agents, thickening agents, colorants, antistatic agents and crosslinking agents may be appropriately added to the protective layer.

The application amount of the coating liquid for the protective layer is about 0.5 to 10 g/m 2 in dry mass, preferably about 1 to 5 g/m 2 . On the other hand, the protective layer can be divided into two or more layers as needed, and the composition and coating amount of each layer may be the same or different.

[back layer]

In the thermal recording medium of the present invention, a backing layer containing a pigment is provided on the backside of the paper support (opposite to the side having the thermal recording layer). The royal smoothness of the back layer is 500 seconds or more, preferably 1000 seconds or more, more preferably 2000 seconds or more. This makes it possible to suppress uneven color development, and the printed image becomes clearer. In an image printer with a compact recording device, when a platen roll drive is adopted, the adhesion pressure to the opposing thermal head is reduced, and color unevenness and white spots are likely to occur in halftones that require gradation reproducibility. The heat-sensitive recording medium of the present invention can exhibit the effect of imparting a clear printed image without color unevenness even in a low energy region (half tone energy region). This is because the pressure applied to the platen roll can be made uniform by increasing the smoothness of the back layer. On the other hand, the royal smoothness of the back layer is preferably 100000 seconds or less from the viewpoint of suppressing sticking to the platen roll. On the other hand, the royal smoothness of the surface having the thermal recording layer is preferably 5000 seconds or more, and more preferably 6000 seconds or more, from the viewpoint of effectively suppressing uneven color development, with the thermal recording layer side as the measurement surface. The upper limit of the royal smoothness of the surface having the thermal recording layer is not particularly limited, and is preferably 100000 seconds or less from the viewpoint of improving winding characteristics such as winding slip and blocking. The surface having the thermal recording layer means the outermost surface of the thermal recording material on the side having the thermal recording layer. Royal smoothness is measured by the method specified in JIS P8155:2010 using the back side or the side having the thermal recording layer as the measurement side.

Examples of the pigment include calcium carbonate, magnesium carbonate, kaolin, calcined kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, and barium sulfate. Among them, kaolin is particularly preferably used because smoothness is improved. The content of the pigment is not particularly limited, and is usually preferably about 20 to 90% by mass, and more preferably about 30 to 85% by mass, based on the total solid amount of the back layer.

The back layer is generally prepared by using water as a dispersion medium and mixing adhesives, pigments, etc., onto a support, and preferably having a dry mass of preferably 3.0 g/m 2 or more, more preferably 3.0 to 10 g/m 2 . It is formed by applying and drying to a degree. By setting it as 3.0 g/m 2 or more, the smoothness can be increased, and as a result, uneven color development can be suppressed, and the printed image becomes clearer.

The adhesive contained in the back layer is not particularly limited, and includes water-soluble adhesives and water-dispersible adhesives. The adhesive can be appropriately selected from those that can be used for the undercoat layer. The content of the adhesive can be selected from a wide range, but is generally preferably about 2 to 50% by mass, and more preferably about 4 to 35% by mass, based on the total solid amount of the back layer.

[Thermal record material]

The method of forming the thermal recording layer, the undercoat layer, the back layer, and the protective layer formed as necessary is not particularly limited, and examples include bar coating, air knife coating, barber blade coating, pure blade coating, rod After applying and drying the coating liquid for the back layer on the support body by an appropriate coating method such as blade coating, short dwell coating, curtain coating, die coating, etc., the coating liquid for the undercoat layer is applied to the other side of the support body and drying, and the undercoat It is formed by a method such as applying and drying a coating liquid for a thermal recording layer or a coating liquid for a protective layer on the layer.

The undercoat layer is preferably a layer formed by a blade coating method. Accordingly, it is possible to form a heat-sensitive recording layer having a uniform thickness by eliminating irregularities of the support, increase recording sensitivity, and improve the barrier properties of the protective layer formed as needed. The blade coating method is not limited to a coating method using a blade represented by a bevel type and a bent type, but includes a rod blade method, a bill blade method, and the like.

In the present invention, it is preferable that at least one layer formed on the support is a layer formed by a curtain coating method. Accordingly, a layer having a uniform thickness can be formed, recording sensitivity can be increased, and barrier properties to oil, plasticizer, alcohol, and the like can be improved. The curtain coating method is a method in which the coating solution is allowed to fall freely and applied to the support without contact. A known method such as a slide curtain method, a couple curtain method, or a twin curtain method can be employed, and is not particularly limited. In the curtain coating method, a layer having a more uniform thickness can be formed by simultaneous multi-layer coating. In simultaneous multi-layer coating, each coating liquid may be applied after being laminated, and then each layer may be formed by drying. Each layer may be formed by applying a coating liquid for forming an upper layer thereto and then drying it. In the present invention, the simultaneous multi-layer coating of the thermal recording layer and the protective layer is preferable from the viewpoint of improving the barrier properties.

In the present invention, from the viewpoint of increasing recording sensitivity and improving image uniformity, after forming each layer or any process after forming all layers, well-known methods such as super calendering and soft calendering are used. Smoothing is preferred.

In the present invention, in order to further increase the added value of the product, a multi-color thermal recording material may be used. In general, a multi-color heat-sensitive recording medium is an attempt to use a difference in heating temperature or a difference in thermal energy, and is generally constructed by sequentially stacking a high-temperature color layer and a low-temperature color layer that develop color in different tones on a support. There are two types, a decolorization type and an additive color type, and a method using microcapsules and a method of manufacturing a multi-color thermal recording material using composite particles composed of organic polymer and leuco dye.

Example

Although the present invention will be described in more detail by examples, the present invention is not limited thereto. On the other hand, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

Example 1

(1) Preparation of the coating solution for the back layer

Calcined kaolin 79 parts, styrene-butadiene copolymer (trade name: L-1571, manufactured by Asahi Kasei Chemicals, glass transition point -3 ° C, solid content concentration 48%) 41.7 parts, oxidized starch (trade name: Oji Ace A, Oji Corn Starch Co., Ltd.) 4 parts of a 25% aqueous solution and 150 parts of water were uniformly mixed and stirred to obtain a coating liquid for the back layer.

(2) Preparation of coating solution for undercoat layer

Calcined kaolin 79 parts, styrene-butadiene copolymer A (glass transition temperature -10 ° C, particle diameter: 190 nm, solid content concentration 48%) 41.7 parts, 25% of oxidized starch (trade name: Oji Ace A, manufactured by Oji Corn Starch) 4 parts of aqueous solution, hollow particles A (average particle diameter 9 µm, maximum particle diameter 23 µm, D100/D50 = 2.6, volume % of particle diameter 2.0 µm or less is 0%, hollow ratio 92%, solid content concentration 22%) 68.2 parts , and 75 parts of water were uniformly mixed and stirred to obtain a coating liquid for an undercoat layer.

(3) Preparation of leuco dye dispersion (liquid A)

Mix 40 parts of 3-di-(n-butyl)amino-6-methyl-7-anilinofluorane, 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water, Using a sand mill (Sand Grinder, manufactured by Imex Co., Ltd.), pulverized until the median diameter by a laser diffraction type particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) becomes 0.5 μm to obtain a leuco dye dispersion (liquid A). got it

(4) Preparation of color developer dispersion (liquid B-1)

40 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone (manufactured by Nippon Soda Co., Ltd., D8), 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water are mixed , Using a sand mill (Sand Grinder, manufactured by Imex Co., Ltd.), pulverized until the median diameter by a laser diffraction type particle size meter SALD2200 (manufactured by Shimadzu Corporation) becomes 0.7 μm, and a color developer dispersion (liquid B) got

(5) Preparation of sensitizer dispersion (Liquid C)

40 parts of 1,2-di(3-methylphenoxy)ethane, 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water were mixed, and a sand mill (manufactured by Imex Co., Ltd.) Sand Grinder) was pulverized until the median diameter by a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) became 1.0 µm to obtain a sensitizer dispersion (Liquid C).

(6) Preparation of coating solution for thermal recording layer

29.5 parts of liquid A, 59.1 parts of liquid B, 45.4 parts of liquid C, 20 parts of 5% aqueous solution of hydroxymethylcellulose, 45 parts of 10% aqueous solution of completely saponified polyvinyl alcohol (degree of polymerization: 1000, degree of saponification: 99 mol%), Styrene-butadiene copolymer (trade name: L-1571, manufactured by Asahi Kasei Co., Ltd., glass transition point -3° C., solid content concentration: 48%) 9.4 parts, light calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd.) 17.1 parts, 11.7 parts of paraffin wax (trade name: Hydrin L-700, manufactured by Chukyo Yushi Co., Ltd., solid content concentration: 30%), 2 parts of adipic acid dihydrazide (manufactured by Otsuka Chemical Co., Ltd.), and 120 parts of water were mixed and stirred to obtain a coating solution for a thermal recording layer got

(7) Preparation of coating solution for protective layer

300 parts of a 12% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Gosenex Z-200, saponification degree: 99.4 mol%, average polymerization degree: 1000, denaturation degree: 5 mol%, manufactured by Nippon Kosei Chemical Co., Ltd.), kaolin (trade name: HYDRAGLOSS90, manufactured by KaMin LLC) 19 parts, aluminum hydroxide (trade name: Hydilight H-42M, manufactured by Showa Denko) 35 parts, silica (trade name: Mizukasil P-527, manufactured by Mizusawa Kagaku Co., Ltd.) 4 Part, a composition consisting of 2.5 parts of polyethylene wax (trade name: Chemipal W-400, manufactured by Mitsui Chemicals, 40% solid content concentration), and 114.5 parts of water was mixed and stirred to obtain a coating liquid for a protective layer.

(8) Production of thermal recording material

On one side of high-quality paper having a basis weight of 60 g/m2, a back layer coating liquid is applied and dried to a coating amount of 5.0 g/m2 to form a back layer, and then, on the opposite side, an undercoat layer coating liquid and a thermal recording layer coating liquid , and protective layer recording coating liquid were applied and dried so that the application amount after drying was 6.0 g/m2, 4.0 g/m2, and 2.0 g/m2, respectively, to sequentially form an undercoat layer, a thermal recording layer, and a protective layer. After that, the surface was smoothed with a super calender to obtain a heat-sensitive recording material.

Example 2

In the preparation of the coating liquid for undercoat of Example 1, hollow particles A (average particle diameter 9 μm, maximum particle diameter 23 μm, D100 / D50 = 2.6, volume percentage of particle diameter 2.0 μm or less is 0%, hollowness 92 %, solid content concentration 22%) 68.2 parts of hollow particles B (average particle diameter 8 μm, maximum particle diameter 18 μm, D100 / D50 = 2.3, particle diameter 2.0 μm or less volume % is 0.8%, hollow ratio 80%, solid content concentration 22%) A heat-sensitive recording material was obtained in the same manner as in Example 1 except for changing to 68.2 parts.

Example 3

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that the coating amount of the coating liquid for the back layer after drying was changed from 5.0 g/m 2 to 3.0 g/m 2 in manufacturing the heat-sensitive recording material of Example 1.

Example 4

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 79 parts of calcined kaolin was changed to 79 parts of kaolin (trade name: HYDRAGLOSS90, manufactured by KaMin LLC) in preparing the coating liquid for the back layer of Example 1.

Example 5

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 79 parts of calcined kaolin was changed to 79 parts of precipitated calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd.) in preparing the coating liquid for the back layer of Example 1.

Example 6

A heat-sensitive recording material was obtained in the same manner as in Example 5, except that the application amount of the coating liquid for the back layer after drying was changed from 5.0 g/m 2 to 3.0 g/m 2 in the preparation of the heat-sensitive recording material of Example 5.

Example 7

In the preparation of the heat-sensitive recording material of Example 1, OK top coat + (basic weight of 84.9 g/m 2 ) was used instead of the base material of high-quality paper with a basis weight of 60 g/m 2 , except that the coating liquid for the back layer was not applied. In the same manner, a heat-sensitive recording material was obtained.

Example 8

In the preparation of the coating liquid for the undercoat layer of Example 1, 41.7 parts of styrene-butadiene copolymer A (glass transition temperature -10°C, particle size: 190 nm, solid content concentration: 48%) B (trade name: L -1571, manufactured by Asahi Kasei Co., Ltd., glass transition point -3°C, solid content concentration 48%) A heat-sensitive recording material was obtained in the same manner as in Example 1 except for changing to 41.7 parts.

Example 9

In the preparation of the coating liquid for the undercoat layer of Example 1, 41.7 parts of styrene-butadiene copolymer A (glass transition temperature -10 ° C, particle diameter: 190 nm, solid content concentration 48%) C (glass transition temperature -30°C, particle size: 190 nm, solid content concentration: 48%) A heat-sensitive recording material was obtained in the same manner as in Example 1 except for changing to 41.7 parts.

Example 10

In the preparation of the coating liquid for undercoat of Example 1, hollow particles A (average particle diameter 9 μm, maximum particle diameter 23 μm, D100 / D50 = 2.6, volume percentage of particle diameter 2.0 μm or less is 0%, hollowness 92 %, solid content concentration 22%) 68.2 parts of hollow particles C (average particle diameter 5 μm, maximum particle diameter 14 μm, D100 / D50 = 2.8, particle diameter 2.0 μm or less volume % is 0.2%, hollowness 91%, solid content concentration 33%) with 45.5 parts, styrene-butadiene copolymer A (glass transition temperature -10 ° C, particle diameter: 190 nm, solid content concentration 48%) 41.7 parts styrene-butadiene copolymer D (glass transition temperature -35 ° C, particle diameter: A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 41.7 parts of 190 nm and 48% of solid content were changed and 75 parts of water were changed to 97.7 parts.

Example 11

In the preparation of the coating liquid for undercoat of Example 10, the hollow particles C (average particle diameter 5 μm, maximum particle diameter 14 μm, D100/D50 = 2.8, volume percentage of particle diameter 2.0 μm or less is 0.2%, hollow ratio 91 %, solid content concentration 33%) A heat-sensitive recording material was obtained in the same manner as in Example 10 except for changing 45.5 parts to 22.7 parts.

Comparative Example 1

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that the coating liquid for the back layer was not applied in the fabrication of the heat-sensitive recording material of Example 1.

Comparative Example 2

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that the coating amount of the coating liquid for the back layer after drying was changed from 5.0 g/m2 to 1.0 g/m2.

Comparative Example 3

Thermal recording was carried out in the same manner as in Example 1 except that 68.2 parts of hollow particles A (average particle diameter of 9 µm, hollowness rate of 92%, solid content concentration of 22%) was changed to 13.6 parts in the preparation of the coating liquid for undercoat of Example 1. got a sieve

Comparative Example 4

In the preparation of the coating liquid for undercoat of Example 1, the hollow particles A (average particle diameter: 9 µm, hollowness rate: 92%, solid content concentration: 22%) were changed from 68.2 parts to 181.8 parts, and heat-sensitive in the same manner as in Example 1. record was obtained.

The heat-sensitive recording materials prepared in Examples 1 to 11 and Comparative Examples 1 to 4 were subjected to the following evaluation, and the results are shown in Table 1.

[Wang Yeon-sik smoothness]

It was measured based on JIS P8155:2010.

[thermal factor]

Using a thermal recording evaluator (trade name: TH-PMD, manufactured by Okura Denki Co., Ltd.), each thermal recording material was recorded in the half-tone energy region of applied energy: 0.32 mJ/dot, and the resulting printing portion was measured with a Macbeth densitometer (RD-914 , manufactured by Macbeth Co., Ltd.). Regarding the recording density, it is required to be 1.00 or more for practical purposes.

[Quality]

Recording quality by thermal printing was visually observed and evaluated according to the following criteria.

◎: There is no white point in image quality at all.

○: There are almost no white points in image quality.

Δ: A white spot in image quality is slightly conspicuous (within an acceptable range).

x: The white spots of the image are very conspicuous, and there are many of them.

[Printing part color stain]

Using a thermal recording evaluator (trade name: TH-PMD, manufactured by Okura Denki Co., Ltd.), each thermal recording material was recorded in the halftone energy region of applied energy: 0.16 mJ/dot, and the resulting beta factor of the printed portion was visually observed. , evaluated according to the following criteria.

◎: There is no color unevenness at all.

○: There is almost no color unevenness.

Δ: Color unevenness is slightly conspicuous (within tolerance).

x: Color unevenness is very conspicuous, and the printed part is non-uniform.

As can be seen from Table 1, the thermally sensitive recording materials of Examples 1 to 11 were highly sensitive and excellent in image quality in the low energy region, and produced clear printed images without uneven printing.

However, since Comparative Example 1 had no backing layer and had low smoothness, white spots and color unevenness were conspicuous, and it was an uneven factor. In Comparative Example 2, since the application amount of the back layer was insufficient and the smoothness was low, white spots and color unevenness were conspicuous, and it was a non-uniform factor. In Comparative Example 3, since the amount of hollow particles incorporated in the undercoat layer was small, there were many white spots in the printed portion, and the image quality was remarkably poor. In Comparative Example 4, since the blending amount of the hollow particles in the undercoat layer was too large, the coating layer of the heat sensitive layer became uneven, and color unevenness was conspicuous.

Claims (9)

On one side of the paper support, an undercoat layer containing hollow particles having a hollow ratio of 80 to 98%, and a thermal recording layer containing a leuco dye and a developer are provided in this order, and on the other side of the paper support, a pigment A heat-sensitive recording material having a backing layer containing
Wang Yeon-style smoothness of the back layer is more than 500 seconds,
The content of the hollow particles is 5 to 30% by mass of the total solid amount of the undercoat layer.
thermal recorder. According to claim 1,
The heat-sensitive recording material, wherein the royal-style smoothness of the back layer is 1000 seconds or more. According to claim 1 or 2,
A heat-sensitive recording material, wherein the back layer has a dry mass of 3.0 g/m 2 or more. According to any one of claims 1 to 3,
A heat-sensitive recording material containing kaolin in the backside layer. According to any one of claims 1 to 4,
A heat-sensitive recording material comprising an adhesive having a glass transition temperature of -10°C or lower in the undercoat layer. According to any one of claims 1 to 4,
A heat-sensitive recording material comprising an adhesive having a glass transition temperature of -30°C or lower in the undercoat layer. According to any one of claims 1 to 6,
A heat-sensitive recording material comprising an adhesive in the undercoat layer, and wherein the adhesive contains latex. According to any one of claims 1 to 7,
A heat-sensitive recording material having a surface having a heat-sensitive recording layer having a royal-type smoothness of 4000 seconds or more. According to any one of claims 1 to 8,
The average particle diameter (D50) of the hollow particles is 3 to 15 μm, the maximum particle diameter (D100) of the hollow particles is 10 to 30 μm, and the maximum particle diameter (D100) and average particle diameter (D50) of the hollow particles are ) ratio (D100/D50) is 1.8 to 3.0, and the volume percentage of the hollow particles having a particle diameter of 2.0 μm or less is 1% or less.