Thermosensitive recording body

Abstract

Disclosed is a heat-sensitive recording body which has, on one side of a paper support, a primer layer containing hollow particles having a hollow ratio of 80 to 98% and a heat-sensitive recording layer containing a leuco dye and a color developer in this order, and on the other side of the paper support, a back layer containing a pigment, wherein the back layer has a Gurley smoothness of 500 seconds or more, and the hollow particles are contained in a proportion of 5 to 30% by mass in the total solid content of the primer layer.

Description

Technical Field

[0001] This invention relates to a thermosensitive recorder that utilizes the colorimetric reaction between a leuco dye and a colorimetric agent. Background Technology

[0002] Thermal recorders, which utilize the thermally induced colorimetric reaction of leuco dyes and developers, have long been known. These thermal recorders are relatively inexpensive, and the recording devices are small and easy to maintain. Therefore, they are widely used not only as recording media for fax machines, various labels, and other outputs, but also as recording media for printers used in non-destructive testing devices such as ultrasound and X-ray imaging, or in medical diagnostic devices—so-called image diagnostic recording media.

[0003] In image printers where uniformity and high resolution of image recording are essential, multi-layered synthetic paper and thermal recorders using biaxially stretched thermoplastic resin films containing inorganic pigments as a support are employed, as needed. In recent years, due to increased emphasis on environmental protection, there has been a strong demand for thermal recorders that use renewable paper as a support, offer excellent grayscale reproducibility from low to high concentrations, and produce high-quality images comparable to silver halide photographs.

[0004] Furthermore, to prevent the adhesion and sticking of thermal printhead residue, a scheme has been proposed to coat a thermal colorimetric layer onto a base paper containing synthetic silica and / or synthetic aluminum silicate (see Patent Document 1). Additionally, a thermal recorder has been proposed, which is paper with an oil absorption of 100 ml / 100 g or more made of inorganic pigment in the support (see Patent Document 2); another thermal recorder has been proposed, which is paper with an oil absorption of 15-30% by weight of calcium carbonate with an oil absorption of 70 ml / 100 g or more made of calcium carbonate in the support (see Patent Document 3). These thermal recorders aim to improve ink dot reproducibility by suppressing and preventing the adhesion of thermal printhead residue, i.e., the so-called residue removal effect. However, currently, compared with synthetic paper and recording media using thermoplastic resin films as supports, the color development is significantly uneven, and the image quality required for recording media used in image diagnostics cannot be obtained satisfactorily. In addition, due to the lithography process in the manufacturing process and the cutting and slitting machines in the small roll finishing process, or the cutting machine attached to the printer, pigment powder is easily dropped and paper fuzzing occurs, which can cause image defects and cause hygiene problems in medical settings.

[0005] To solve this problem, a method with a specific surface area of ​​180m² was proposed. 2 Amorphous silica with a density of 0.60–0.85 g / cm³ is used as a filler. 2 A thermal recorder with a paper support (see Patent Document 4).

[0006] In addition, for thermal recording paper with image paper substrate, it is necessary to achieve high sensitivity and clear printed images in low energy regions, and to obtain thermal recorders with white spot-free, uniform and clear printed image quality even at low energy.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 61-68291

[0010] Patent Document 2: Japanese Patent Application Publication No. 61-98584

[0011] Patent Document 3: Japanese Patent Application Publication No. 5-58027

[0012] Patent Document 4: Japanese Patent Application Publication No. 2012-101396 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] The main objective of this invention is to provide a thermal recorder that provides high-quality, clear printed images with high sensitivity in a low-energy region.

[0015] Methods for solving problems

[0016] To achieve the above objectives, the inventors conducted repeated and in-depth research and discovered that by including hollow particles with a hollow rate of 80-98% in the base coating at a proportion of 5-30% by mass of the total solids in the base coating, and by achieving a smoothness of 500 seconds or more in the back layer, the aforementioned problems can be solved, thus completing the present invention. Specifically, the present invention relates to the following thermal recording medium.

[0017] Item 1. A thermal recorder comprising, on one side of a paper support, a base coating containing hollow particles with a hollowness ratio of 80-98% and a thermal recording layer containing a leuco dye and a developer, and on the other side of the paper support, a back layer containing pigment, wherein,

[0018] The smoothness of the back layer, as determined by Wang Yanshi, exceeds 500 seconds.

[0019] The aforementioned hollow particles constitute 5-30% of the total solids in the base coating.

[0020] Item 2. The thermal recorder according to Item 1, wherein the smoothness of the aforementioned back layer is greater than 1000 seconds.

[0021] Item 3. The thermal recorder according to item 1 or 2, wherein the dried mass of the aforementioned back layer is 3.0 g / m³. 2 above.

[0022] Item 4. The thermal recorder according to any one of items 1 to 3, wherein the aforementioned back layer contains kaolin.

[0023] Item 5. The thermal recorder according to any one of items 1 to 4, wherein the aforementioned undercoat contains an adhesive with a glass transition temperature of -10°C or less.

[0024] Item 6. The thermal recorder according to any one of items 1 to 4, wherein the aforementioned undercoat contains an adhesive with a glass transition temperature of -30°C or less.

[0025] Item 7. The thermal recorder according to any one of items 1 to 6, wherein the aforementioned base coating contains an adhesive, and the aforementioned adhesive contains latex.

[0026] Item 8. The thermal recorder according to any one of items 1 to 7, wherein the surface having the thermal recording layer has a smoothness of 4000 seconds or more.

[0027] Item 9. The thermal recorder according to any one of items 1 to 8, wherein the average particle size (D50) of the aforementioned hollow particles is 3 to 15 μm, the maximum particle size (D100) of the aforementioned hollow particles is 10 to 30 μm, the ratio of the maximum particle size (D100) to the average particle size (D50) of the aforementioned hollow particles (D100 / D50) is 1.8 to 3.0, and the volume percentage of the aforementioned hollow particles with a particle size of 2.0 μm or less is 1% or less.

[0028] Invention Effects

[0029] The thermal recorder of the present invention provides clear printed images with excellent image quality and no color unevenness in a low-energy region with high sensitivity. Detailed Implementation

[0030] In this specification, the terms "comprising" and "containing" include the concepts of "comprising", "consisting of only", and "containing only".

[0031] The numerical range indicated by “~” in this specification refers to the range including the values ​​recorded before and after “~” as the lower and upper limits.

[0032] The latex in this invention includes a state of gel or dried film formed by drying the dispersion medium.

[0033] Furthermore, in this invention, "average particle size" refers to the median particle size of a volume reference measured by laser diffraction. More simply, the particle size can be determined individually from particle images (SEM images) using an electron microscope and expressed as the average of 10 images.

[0034] The thermal recorder of the present invention comprises a base coating containing hollow particles with a hollow ratio of 80-98% and a thermal recording layer containing a leuco dye and a developer on one side of a paper support, and a back layer containing pigment on the other side of the paper support. The thermal recorder is characterized in that the smoothness of the back layer is 500 seconds or more, and the proportion of the aforementioned hollow particles is 5-30% by mass of the total solids in the base coating.

[0035] [Paper Support]

[0036] The type, shape, and size of the paper support in this invention are not particularly limited. For example, it can be appropriately selected and used from high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassine paper, resin-laminated paper, polyolefin synthetic paper, synthetic fiber paper, etc. The thickness of the paper support is not particularly limited, and is typically around 20–200 μm. Furthermore, the density of the paper support is not particularly limited, but is preferably 0.60–1.00 g / cm³. 3 Approximately, more preferably 0.60–0.85 g / cm³. 3 about.

[0037] [Base Coating]

[0038] In the thermal recorder of the present invention, an undercoat containing hollow particles with a hollowness ratio of 80-98% is provided between the paper support and the thermal recording layer. This suppresses the penetration of the coating liquid of the thermal recording layer into the paper support, improving image quality. Furthermore, the presence of hollow particles with a hollowness ratio of 80-98% suppresses white spots in the printed area even at low energy levels, improving the printing density of midtones. Examples of hollow particles include those known in the art, such as particles of acrylic resins, styrene resins, and vinylidene chloride resins in the film material. Here, the hollowness ratio is a value calculated by (d / D) × 100. In this formula, d represents the inner diameter of the hollow particle, and D represents the outer diameter of the hollow particle. From the viewpoint of improving image quality, a hollowness ratio of 90-98% is preferred. The average particle size of the hollow particles is preferably about 3-15 μm, more preferably about 4-12 μm. Here, the average particle size refers to the particle size at a 50% volume frequency, also known as the median particle size or D50. Particle size and particle size distribution can be measured using a laser diffraction particle size distribution measuring device. Alternatively, they can be measured using an electron microscope. The content of the hollow particles is 5-30% by mass in the total solids of the base coating, preferably about 7-28% by mass, and more preferably about 9-26% by mass. By setting it to 5% by mass or more, white spots in the printing area can be suppressed and image quality improved even at low energy. By setting it to 30% by mass or less, color unevenness can be suppressed and the printed image becomes clearer. More importantly, by using specific hollow particles in the base coating and applying them to the back layer described later, the smoothness of the surface with the thermal recording layer can be significantly improved, and the elasticity of the coating layer can be improved by the hollow particles in the base coating, white spots and color unevenness in the low energy area can be suppressed, and thermal quality can be improved. By adjusting the average particle size, maximum particle size, and the ratio of the maximum particle size (D100) to the average particle size (D50) of the hollow particles (D100 / D50), white spots and color unevenness in the low energy area can be effectively suppressed.

[0039] The maximum particle size of the hollow particles is preferably 10–30 μm, more preferably 10–25 μm, and even more preferably 10–20 μm. It should be noted that the maximum particle size is also referred to as D100.

[0040] The ratio of the maximum particle size (D100) to the average particle size (D50) (D100 / D50) is an indicator of the degree of particle size distribution. D100 / D50 is preferably 1.8 to 3.0, and more preferably 1.8 to 2.8.

[0041] In the particle size distribution, the volume percentage of hollow particles with a particle size of 2.0 μm or less is preferably 1% or less. Furthermore, the volume percentage of hollow particles with a particle size of 2.0 μm or less is more preferably 0.5% or less, and even more preferably, it is absent.

[0042] The base coat may contain oil-absorbing pigments and / or thermally expandable particles with an oil absorption of 70 ml / 100g or more, particularly around 80 to 150 ml / 100g. Here, the aforementioned oil absorption is a value determined based on the method in JIS K 5101.

[0043] Various oil-absorbing pigments can be used as the aforementioned oil-absorbing pigments. Specific examples include calcined kaolin, amorphous silica, light calcium carbonate, talc, and other inorganic pigments. The average particle size of the primary particles of these oil-absorbing pigments is approximately 0.01 to 5 μm, and particularly preferably approximately 0.02 to 3 μm. The amount of oil-absorbing pigment used can be selected from a wide range, but it is generally preferred to be approximately 2 to 95% by mass in the total solids content of the base layer, and more preferably approximately 5 to 90% by mass.

[0044] The base coat is typically formed as follows: a base coat solution prepared by mixing water as a dispersion medium with binders, hollow particles, oil-absorbing pigments, various additives, etc., is applied at a density preferably 3–20 g / m³ based on dry weight. 2 Approximately 5-12 g / m² 2 It is formed by coating the support in a left-right manner and then drying.

[0045] Examples of adhesives include: polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylate copolymer, acrylamide-acrylate-methacrylate copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, casein, gelatin and their derivatives, and other water-soluble polymers such as latex, polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, and latex of water-insoluble polymers such as styrene-butadiene copolymer and styrene-butadiene-acrylic copolymer. Among these, adhesives containing latex are preferred. The proportion of the adhesive can be selected from a wide range, but it is generally preferred to be about 5 to 30% by mass in the total solids of the primer, and more preferably about 10 to 20% by mass.

[0046] The glass transition temperature (Tg) of the adhesive is not particularly limited, but is preferably below -10°C. By setting the glass transition temperature to below -10°C, image quality can be improved even in the low-energy region. To further improve image quality in the low-energy region, the glass transition temperature is more preferably below -30°C.

[0047] Examples of additives contained in the coating liquid for the primer layer include: sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, dispersants such as fatty acid metal salts, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester waxes and other waxes, acyl hydrazide compounds, glyoxal, boric acid, dialdehyde starch, glyoxylate, hydroxymethyl urea, epoxy compounds and other water-resistant agents, defoamers, coloring dyes, fluorescent dyes, etc.

[0048] [Thermal Recording Layer]

[0049] The thermal recording layer of the thermal recorder of the present invention may contain various known leuco dyes that are colorless or light-colored. Specific examples of such leuco dyes are given below.

[0050] Specific examples of leuco dyes include: 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, blue dyes such as fluorane, 3-(N-ethyl-N-p-tolyl)amino-7-N-methylaniline fluorane, 3-diethylamino-7-aniline fluorane, 3-diethylamino-7-dibenzylaminofluorane, and rhodamine B-aniline. Dyes that show green color, such as lactams; 3,6-bis(diethylamino)fluorane-γ-aniline lactams; 3-cyclohexylamino-6-chlorofluorane; 3-diethylamino-6-methyl-7-chlorofluorane; 3-diethylamino-7-chlorofluorane and other dyes that show red color; 3-(N-ethyl-N-isopentyl)amino-6-methyl-7-aniline fluorane; 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-aniline fluorane; 3-diethylamino-6-methyl-7-aniline fluorane. Alkane, 3-di(n-butyl)amino-6-methyl-7-anilinofluorane, 3-di(n-pentyl)amino-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-(N-isopentyl-N-ethylamino)-7-(o-chloroanilino)fluorane, 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)fluorane, 3-di(n-butylamino)-7-(2-chloroanilino)fluorane, 4,4'-bis-dimethylaminobenzoindanol benzyl ether, N-2,4,5-Trichlorophenylcatecholamine, 3-Diethylamino-7-butylaminofluorane, 3-Ethyl-Tolylamino-6-methyl-7-anilinofluorane, 3-Cyclohexyl-methylamino-6-methyl-7-anilinofluorane, 3-Diethylamino-6-chloro-7-(β-ethoxyethyl)aminofluorane, 3-Diethylamino-6-chloro-7-(γ-chloropropyl)aminofluorane, 3-Diethylamino-6-methyl-7-anilinofluorane, 3-(N-Isopentyl-N-ethylamino)-6-methyl 3-Dibutylamino-7-chloroanilinofluorane, 3-Diethylamino-7-(o-chlorophenylamino)fluorane, 3-(N-ethyl-p-toluidine)-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-toluidine)-6-methyl-7-(p-toluidine)fluorane, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluorane, 3-Diethylamino-6-chloro-7-anilinofluorane, 3-Dimethylamino-6-methyl-7- Aniline fluorane, 3-pyrrolidinyl-6-methyl-7-aniline fluorane, 3-piperidinyl-6-methyl-7-aniline fluorane, 2,2-bis{4-[6'-(N-cyclohexyl-N-methylamino)-3'-methylspiro[phthalimide-3,9'-xanthine]-2'-ylamino]phenyl}propane, 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluorane, etc., are dyes that show black color, as are 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylene- Dyes with absorption wavelengths in the near-infrared region include 2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinylphenyl)vinyl-2-yl]-4,5,6,7-tetrachlorophthalide, 3-p-(p-dimethylaminoanilino)anilino-6-methyl-7-chlorofluorane, 3-p-(p-chloroanilino)anilino-6-methyl-7-chlorofluorane, and 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. Of course, these are not the only examples, and two or more compounds can be used in combination as needed.

[0051] The proportion of the leuco dye is not particularly limited, but it is preferably about 3 to 30% by mass in the total solids of the thermal recording layer, more preferably about 5 to 25% by mass, and even more preferably about 7 to 20% by mass. Setting it to 3% by mass or more can improve color development ability and printing density. Setting it to 30% by mass or less can improve heat resistance.

[0052] Specific examples of color-developing agents include: 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylene diphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylene diphenol, 4,4'-cyclohexylene diphenol, 4,4'-cyclohexylene diphenol, 1,1-bis(4-hydroxyphenyl)-ethane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 4,4'-bis(p-toluylsulfonylaminocarbonylamino)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)-diethyl ether, etc. (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)acetic acid butyl ester, bis(p-hydroxyphenyl)acetic acid methyl ester, hydroquinone monobenzyl ether, bis(3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, 3,4-dihydroxyphenyl-4'-methyl Phenolic compounds such as methyl sulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, toluene 4-hydroxybenzoate, 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)ethoxy]salicylic acid, 4-[3-( Aromatic carboxylic acids such as p-toluyl(sulpho)propoxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and 4-[3-(p-toluyl)propoxy]salicylic acid zinc, as well as these phenolic compounds, salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, and antipyrine complexes of zinc thiocyanate, complex zinc salts of p-formylbenzoic acid and other aromatic carboxylic acids, N-p-toluyl-N'-3-(p-toluyloxy)phenylurea, N-p-toluyl-N'-p-butoxycarbonylphenylurea, N-p-toluyl-N'-phenylurea, 4,4'-bis(p-toluylaminocarbonylamino)diphenylmethane, 4,Urea compounds such as 4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureo]diphenyl sulfone; thiourea compounds such as N,N'-di-m-chlorophenylthiourea; organic compounds with intramolecular -SO₂NH₄ bonds such as N-(p-toluenesulfonyl)carbamate, N-(p-toluenesulfonyl)carbamate, N-[2-(3-phenylureo)phenyl]benzenesulfonamide, and N-(o-tolyl)-p-toluenesulfonamide; and inorganic acidic substances such as activated clay, attapulgite, colloidal silica, and aluminum silicate.

[0053] Furthermore, examples include 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureo] diphenyl sulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureo] diphenyl sulfone, 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureo-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureo diphenyl sulfone, and diphenyl sulfone derivatives of general formula (2) below.

[0054]

[0055]

[0056] (In the formula, n represents an integer from 1 to 6.)

[0057] Color developers are not limited to these, and more than two compounds can be used in combination as needed.

[0058] The content of the developer is not particularly limited and can be adjusted according to the leuco dye used. Generally, it is 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, even more preferably 1.2 parts by mass or more, and particularly preferably 1.5 parts by mass or more, relative to 1 part by mass of the leuco dye. Furthermore, the content of the developer 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, relative to 1 part by mass of the leuco dye. Setting it to 0.5 parts by mass or more improves recording performance. On the other hand, setting it to 10 parts by mass or less effectively suppresses background fogging under high-temperature environments.

[0059] In this invention, primarily to further improve the preservation of the colorimetric image, the thermal recording layer may also contain a preservation enhancer. Such a preservation enhancer can be selected from, 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-methylethoxy)]bisphenol, 4,4'-[1,3-phenylenebis(1-methylethoxy)]bisphenol, etc. At least one of the following: phenolic compounds such as bisphenol (-methylethoxy) bisphenol; epoxy compounds such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenyl sulfone, 4-(2-methyl-1,2-epoxyethyl)diphenyl sulfone, and 4-(2-ethyl-1,2-epoxyethyl)diphenyl sulfone; and isocyanuric compounds such as 1,3,5-tris(2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl)isocyanuric acid. Of course, this is not limited to these, and two or more compounds may be used in combination as needed.

[0060] When using a preservation improver, the amount used should be an amount that is effective in improving preservation. It is usually about 1 to 30% by mass in the total solids content of the thermal recording layer, and more preferably about 5 to 20% by mass.

[0061] The thermal recording layer in this invention may also contain a sensitizer. This improves recording sensitivity. Examples of sensitizers include stearamide, methoxycarbonyl-N-stearamide, N-benzamide stearamide, N-arachidamide, ethylene bis-stearamide, behenamide, methylene bis-stearamide, N-hydroxymethylstearamide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, benzyl terephthalate, 1-hydroxy-2-naphthoic acid phenyl ester, 2-naphthyl benzyl ether, m-terphenyl, p-benzyl biphenyl, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, dibenzyl oxalate, p-tolyl diphenyl ether, di(p-methoxyphenoxyethyl) ether, 1,2-di(3-methylphenoxy)ethane, 1,2-di(4-methylphenoxy)ethane, and so on. 1,2-(4-methoxyphenoxy)ethane, 1,2-di(4-chlorophenoxy)ethane, 1,2-diphenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, p-methylthiophenyl benzyl ether, 1,4-di(phenylthio)butane, p-acetyltoluidine, p-acetylethylaniline, N-acetylacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, bis(β-biphenylethoxy)benzene, p-bis(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, biphenyl, benzophenone, etc. These can be used in combination without causing interference. The proportion of sensitizer is only required to be an amount effective for sensitization, and it is usually about 2 to 40% by mass in the total solids content of the thermal recording layer, more preferably about 5 to 25% by mass.

[0062] To improve the whiteness of the thermal recording layer and enhance image uniformity, the thermal recording layer may contain microparticle pigments with high whiteness and an average particle size of less than 10 μm. Inorganic pigments such as calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium dioxide, aluminum hydroxide, barium sulfate, and surface-treated calcium carbonate and silica, as well as organic pigments such as urea-formaldehyde resin, styrene-methacrylic acid copolymer resin, and polystyrene resin, can be used. The preferred pigment content is an amount that does not reduce the color development concentration, i.e., less than 50% by mass in the total solids of the thermal color development layer.

[0063] Other components of the thermal recording layer can include adhesives, and crosslinking agents, waxes, metal soaps, water-resistant additives, dispersants, colored dyes, fluorescent dyes, etc., as needed.

[0064] Examples of adhesives used in coating solutions for thermal recording layers include water-based adhesives and water-dispersible adhesives. Examples of water-based adhesives include: polyvinyl alcohol (PVA), modified PVA such as carboxyl-modified PVA, acetoacetyl-modified PVA, diacetone-modified PVA, and silicone-modified PVA; starch and its derivatives; cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropyl methylcellulose, methylcellulose, and ethylcellulose; sodium polyacrylate; polyvinylpyrrolidone; polyamide; diisobutylene-maleic anhydride copolymer salts; styrene-acrylic acid copolymer salts; styrene-maleic anhydride copolymer salts; ethylene-maleic anhydride copolymer salts; acrylamide-acrylate copolymers; acrylamide-acrylate-methacrylic acid copolymers; polyacrylamide; sodium alginate; gelatin; casein; and gum arabic. Examples of water-dispersible adhesives include emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, etc., or latexes of water-insoluble polymers such as styrene-butadiene copolymer, styrene-butadiene-acrylic acid copolymer, etc. These can be used alone or in combination of two or more. Preferably, at least one of these is incorporated into the total solids content of the thermal recording layer in the range of about 5 to 50% by mass, more preferably about 10 to 40% by mass.

[0065] The thermal recording layer may contain a crosslinking agent for curing the adhesive of the thermal recording layer or other layers. This improves the water resistance of the thermal recording layer. Examples of crosslinking agents include: aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, dimethylolurea compounds, aziridine compounds, and end-capped isocyanate compounds; inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, and potassium tetraborate; and boric acid, triborate, boron polymers, hydrazide compounds, and glyoxylates. These can be used individually or in combination. The amount of crosslinking agent used is preferably in the range of about 1 to 10 parts by weight relative to 100 parts by weight of the total solids of the thermal recording layer. This improves the water resistance of the thermal recording layer.

[0066] Examples of waxes include: paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, polyethylene wax, etc.; and higher fatty acid amides such as stearamide and ethylene distearate, higher fatty acid esters, and their derivatives.

[0067] Examples of metal soaps include polyvalent metal salts of higher fatty acids, such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. Furthermore, as needed, various additives such as oil-repellent agents, defoamers, and viscosity modifiers can be added to the thermal recording layer without impairing the effects of the present invention.

[0068] The thermal recording layer is typically formed on the base layer as follows: Using water as the dispersion medium, a leuco dye, a color developer, a sensitizer and a preservation modifier as needed, are dispersed together or separately using various stirred / wet mills such as ball mills, CoBall mills, grinders, vertical or horizontal sand mills, along with water-soluble synthetic polymers such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, and styrene-maleic anhydride copolymer salts, and other surfactants to prepare a dispersion. This dispersion is then dispersed to an average particle size of 2 μm or less. The resulting dispersion is mixed with pigments, binders, and additives as needed. The thermal recording layer prepared in this way is then coated with a coating solution and dried, thereby forming the base layer. The coating amount of the thermal recording layer is not particularly limited, but is preferably 1–12 g / m³ based on the dried mass. 2 Approximately, more preferably 2–10 g / m 2 More preferably 2.5–8 g / m 2 The preferred concentration is 3–5.5 g / m³. 2 It should be noted that the thermal recording layer can be formed in two or more layers as needed, and the composition and coating amount of each layer can be the same or different.

[0069] [Protective Layer]

[0070] In the thermal recorder of the present invention, a protective layer is preferably provided on the thermal recording layer to improve preservation or improve mobility during recording. The protective layer can be obtained by mixing water as a medium, a binder and pigment as main components, and various additives added as needed, applying the resulting protective layer onto the thermal recording layer with a coating liquid and drying it.

[0071] Pigments used as protective layers include, for example, amorphous silica, kaolin, light calcium carbonate, heavy calcium carbonate, calcined kaolin, titanium dioxide, magnesium carbonate, aluminum hydroxide, colloidal silica, synthetic layered mica, urea-formalin resin fillers, and other plastic pigments.

[0072] Furthermore, there are no particular limitations on the adhesive used in the coating liquid for the protective layer; examples include water-soluble adhesives and water-dispersible adhesives. The adhesive can be appropriately selected from adhesives suitable for thermal recording layers. Among these, polyvinyl alcohol or modified polyvinyl alcohol is preferred from the perspective of its excellent adhesion effect to pigments and its particularly good preservation of the recording part against solvents such as plasticizers and oils; acetylacetyl modified polyvinyl alcohol, carboxyl modified polyvinyl alcohol, diacetone modified polyvinyl alcohol, and other modified polyvinyl alcohols are especially preferred.

[0073] The adhesive content in the total solids of the protective layer is preferably about 20 to 85% by mass, and more preferably about 35 to 80% by mass.

[0074] In addition, known additives such as lubricants, defoamers, wetting agents, preservatives, fluorescent whitening agents, dispersants, thickeners, colorants, antistatic agents, crosslinking agents and other additives can be appropriately added to the protective layer.

[0075] The coating amount of the protective layer using the coating liquid is 0.5–10 g / m² based on dry weight. 2 Approximately, preferably 1-5 g / m³ 2 Left and right. It should be noted that the protective layer can be formed in two or more layers as needed, and the composition and coating amount of each layer can be the same or different.

[0076] [Back layer]

[0077] In the thermal recorder of the present invention, a back layer containing pigment is provided on the back side of the paper support (opposite to the side having the thermal recording layer). The smoothness of the back layer is 500 seconds or more, preferably 1000 seconds or more, and more preferably 2000 seconds or more. This suppresses uneven color development, resulting in a clearer printed image. In image printers where recording devices are relatively small, the pressure applied to the opposing thermal head decreases when driven by a pressure roller, making it easy for uneven color development and white spots to occur in mid-tone areas where grayscale reproduction is required. The thermal recorder of the present invention provides a clear printed image without uneven color development even in low-energy areas (mid-tone energy areas). This is because increasing the smoothness of the back layer makes the pressure on the pressure roller more uniform. On the other hand, from the viewpoint of suppressing adhesion to the pressure roller, the smoothness of the back layer is preferably 100,000 seconds or less. On the other hand, from the viewpoint of effectively suppressing uneven color development, the O-Ken smoothness of the surface with the thermal recording layer, when measured on the thermal recording layer side, is preferably 5000 seconds or more, more preferably 6000 seconds or more. There is no particular upper limit to the O-Ken smoothness of the surface with the thermal recording layer, but from the viewpoint of improving winding properties such as curling slip and adhesion, it is preferably 100,000 seconds or less. The surface with the thermal recording layer refers to the outermost surface of the thermal recording body on the side with the thermal recording layer. The O-Ken smoothness is measured using the back layer side or the surface with the thermal recording layer as the measurement surface, according to the method specified in JIS P8155:2010.

[0078] Examples of pigments 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. Kaolin is particularly preferred for improving smoothness. The proportion of pigment is not particularly limited, but it is generally preferred to be about 20–90% by mass in the total solids of the backing layer, and more preferably about 30–85% by mass.

[0079] The backing layer is typically formed as follows: a backing layer prepared by mixing water as a dispersion medium with adhesives, pigments, etc., is coated with a coating liquid at a density preferably 3.0 g / m³ based on dry weight. 2 More preferably 3.0 to 10 g / m 2 It is formed by coating the substrate in a left-right manner and then drying. The coating is set to 3.0 g / m³. 2 The above can improve smoothness, which in turn can suppress uneven color development and make the printed image clearer.

[0080] The adhesive used in the backing layer is not particularly limited, and examples include water-soluble adhesives and water-dispersible adhesives. The adhesive can be appropriately selected from adhesives that can be used in the primer layer. The proportion of the adhesive can be selected from a wide range, but it is generally preferred to be about 2 to 50% by mass in the total solids content of the backing layer, more preferably about 4 to 35% by mass.

[0081] [Thermal recording medium]

[0082] There are no particular limitations on the formation methods of the thermal recording layer, the base layer, the back layer, and the protective layer provided as needed. For example, they can be formed by the following methods: using a suitable coating method such as bar coating, air knife coating, Barry bar coating, pure blade coating, bar knife coating, short-stay coating, curtain coating, or mold coating, the back layer is coated with a coating liquid onto the support and dried. Then, the base layer is coated with a coating liquid onto the other side of the support and dried. The thermal recording layer coating liquid is then coated onto the base layer and dried. Finally, the protective layer coating liquid is then coated and dried.

[0083] The base coating layer is preferably formed by a doctor blade coating method. This eliminates the unevenness of the support structure, resulting in a thermal recording layer of uniform thickness, which improves recording sensitivity and enhances the barrier properties of the protective layer, which may be applied as needed. Doctor blade coating methods are not limited to those using angled or curved blades; they also include rod-blade methods, pure doctor blade methods, etc.

[0084] In this invention, it is preferable that at least one layer formed on the support is a layer formed by a curtain coating method. This allows for the formation of a layer with uniform thickness, improving recording sensitivity or barrier properties against oils, plasticizers, alcohols, etc. Curtain coating is a method of coating a support in a non-contact manner by allowing the coating liquid to flow down and fall freely. Known curtain coating methods such as sliding curtain coating, paired curtain coating, and double curtain coating can be used, without particular limitation. Curtain coating allows for the formation of layers with more uniform thickness by simultaneously applying multiple layers. In the case of simultaneous multi-layer coating, each coating liquid can be layered before coating, followed by drying to form each layer; alternatively, after applying the coating liquid for forming the lower layer, the coating liquid for forming the upper layer can be applied to the lower coating surface while it is still wet without drying, followed by drying to form each layer. In this invention, from the viewpoint of improving barrier properties, it is preferable to simultaneously apply multiple layers to both the thermal recording layer and the protective layer.

[0085] In this invention, from the viewpoint of improving recording sensitivity and image uniformity, it is preferable to use known methods such as supercalenders or flexible calenders for smoothing processing after the formation of each layer is completed, or at any time after the formation of all layers is completed.

[0086] In this invention, to further enhance the added value of the product, multicolor thermal recorders can also be manufactured. Typically, multicolor thermal recorders utilize heating temperature differences or thermal energy differences, usually constructed by sequentially stacking high-temperature and low-temperature color-developing layers of different hues on a support. These generally include achromatic and additive types, and can be manufactured using microencapsulation methods or by using composite particles composed of organic polymers and leuco dyes.

[0087] Example

[0088] The invention is illustrated in more detail by way of examples, but the invention is not limited to these examples. It should be noted that, unless otherwise stated, "parts" and "%" mean "parts by mass" and "% by mass," respectively.

[0089] Example 1

[0090] (1) Preparation of coating liquid for the back layer

[0091] 79 parts of calcined kaolin, 41.7 parts of styrene-butadiene copolymer (trade name: L-1571, manufactured by Asahi Kasei Chemicals Co., Ltd., glass transition temperature -3°C, solid content concentration 48%), 4 parts of 25% aqueous solution of oxidized starch (trade name: Oji Ace A, manufactured by Oji Cornstar Co., Ltd.), and 150 parts of water were mixed and stirred until homogeneous to obtain a coating liquid for the back layer.

[0092] (2) Preparation of coating liquid for primer layer

[0093] 79 parts of calcined kaolin, 41.7 parts of styrene-butadiene copolymer A (glass transition temperature -10℃, particle size: 190nm, solid content concentration 48%), 4 parts of a 25% aqueous solution of oxidized starch (trade name: Oji A, manufactured by Oji Cornstar Co., Ltd.), 68.2 parts of hollow particles A (average particle size 9μm, maximum particle size 23μm, D100 / D50 = 2.6, volume percentage of particles with a diameter of 2.0μm or less 0%, hollowness 92%, solid content concentration 22%), and 75 parts of water were mixed and stirred until homogeneous to obtain a coating liquid for the base coating.

[0094] (3) Preparation of leuco dye dispersion (solution A)

[0095] 40 parts of 3-di(n-butyl)amino-6-methyl-7-aniline fluorane, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and pulverized using a sand mill (Imex Corporation, Sandgrainer) until the median particle size measured by a SALD2200 laser diffraction particle size analyzer (Shimadzu Corporation) was 0.5 μm, thus obtaining a leuco dye dispersion (solution A).

[0096] (4) Preparation of colorimetric reagent dispersion (B-1 solution)

[0097] 40 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone (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 were mixed and pulverized using a sand mill (manufactured by Imex Co., Ltd., Sandgrainer) until the median particle size measured by a SALD2200 laser diffraction particle size analyzer (manufactured by Shimadzu Corporation) was 0.7 μm, thus obtaining a colorimetric reagent dispersion (solution B).

[0098] (5) Preparation of sensitizer dispersion (C solution)

[0099] 40 parts of 1,2-bis(3-methylphenoxy)ethane, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and pulverized using a sand mill (Imex Corporation, Sandgrainer) until the median particle size measured by a SALD2200 laser diffraction particle size analyzer (Shimadzu Corporation) was 1.0 μm, thus obtaining a sensitizer dispersion (C solution).

[0100] (6) Preparation of coating solution for thermal recording layer

[0101] 29.5 parts of solution A, 59.1 parts of solution B, 45.4 parts of solution C, 20 parts of a 5% aqueous solution of hydroxymethyl cellulose, 45 parts of a 10% aqueous solution of fully saponified polyvinyl alcohol (degree of polymerization: 1000, degree of saponification: 99 mol%), 9.4 parts of styrene-butadiene copolymer (trade name: L-1571, manufactured by Asahi Kasei Corporation, glass transition temperature -3°C, solid content concentration 48%), 17.1 parts of light calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Corporation), 11.7 parts of paraffin wax (trade name: Hydrin L-700, manufactured by Chukyo Oils & Fats Co., Ltd., solid content concentration 30%), 2 parts of adipic 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.

[0102] (7) Preparation of coating liquid for protective layer

[0103] A composition consisting of 300 parts of a 12% aqueous solution of acetyl-acetyl modified polyvinyl alcohol (trade name: Gosenex Z-200, degree of saponification: 99.4 mol%, average degree of polymerization: 1000, degree of modification: 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 19 parts of kaolin (trade name: HYDRAGLOSS90, manufactured by KaMin LLC), 35 parts of aluminum hydroxide (trade name: Hydralight H-42M, manufactured by Showa Denko Co., Ltd.), 4 parts of silica (trade name: Mizusawa Chemical Co., Ltd.), 2.5 parts of polyethylene wax (trade name: Kemipar W-400, manufactured by Mitsui Chemicals Co., Ltd., solid content concentration 40%), and 114.5 parts of water was mixed and stirred to obtain a coating liquid for protective layer.

[0104] (8) Fabrication of thermal recording devices

[0105] At a base weight of 60g / m 2 On one side of high-quality paper, the coating amount after drying is 5.0 g / m². 2 After applying the back layer coating liquid and drying it to form the back layer, on the opposite side, the coating amount after drying is 6.0 g / m². 2 4.0g / m 2 2.0g / m 2 The base coating, thermal recording layer, and protective recording layer are sequentially formed by applying a base coating liquid, a thermal recording layer coating liquid, and a protective recording layer coating liquid and drying them. Then, the surface is smoothed using a supercalender to obtain a thermal recording body.

[0106] Example 2

[0107] In the preparation of the primer coating liquid in Example 1, 68.2 parts of hollow particles A (average particle size 9 μm, maximum particle size 23 μm, D100 / D50 = 2.6, volume % of particles with a diameter of 2.0 μm or less 0%, hollowness 92%, solid content concentration 22%) were replaced with 68.2 parts of hollow particles B (average particle size 8 μm, maximum particle size 18 μm, D100 / D50 = 2.3, volume % of particles with a diameter of 2.0 μm or less 0.8%, hollowness 80%, solid content concentration 22%). Otherwise, the thermal recorder was obtained in the same manner as in Example 1.

[0108] Example 3

[0109] In the fabrication of the thermal recorder in Example 1, the coating amount of the back layer after drying with the coating solution was 5.0 g / m². 2 Change to 3.0g / m 2 Otherwise, a thermal recorder was obtained in the same manner as in Example 1.

[0110] Example 4

[0111] In the preparation of the coating liquid for the back layer in Example 1, 79 parts of calcined kaolin were replaced with 79 parts of kaolin (trade name: HYDRAGLOSS90, manufactured by KaMin LLC), otherwise the thermal recorder was obtained in the same manner as in Example 1.

[0112] Example 5

[0113] In the preparation of the coating liquid for the back layer in Example 1, 79 parts of calcined kaolin were replaced with 79 parts of light calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd.), otherwise the thermal recorder was obtained in the same manner as in Example 1.

[0114] Example 6

[0115] In the fabrication of the thermal recorder in Example 5, the coating amount of the back layer after drying with the coating solution was increased from 5.0 g / m². 2 Change to 3.0g / m 2 Otherwise, a thermal recorder was obtained in the same manner as in Example 5.

[0116] Example 7

[0117] In the fabrication of the thermal recorder in Example 1, OK Top Coat+ (basic weight 84.9 g / m³) was used. 2 (Replaces 60g / m) 2 A thermal recorder was obtained using a high-quality paper substrate without a back coating liquid, otherwise in the same manner as in Example 1.

[0118] Example 8

[0119] In the preparation of the base coating liquid in Example 1, 41.7 parts of styrene-butadiene copolymer A (glass transition temperature -10°C, particle size: 190 nm, solid content concentration 48%) were replaced with 41.7 parts of styrene-butadiene copolymer B (trade name: L-1571, manufactured by Asahi Kasei Corporation, glass transition temperature -3°C, solid content concentration 48%). Otherwise, the thermal recorder was obtained in the same manner as in Example 1.

[0120] Example 9

[0121] In the preparation of the base coating liquid in Example 1, 41.7 parts of styrene-butadiene copolymer A (glass transition temperature -10°C, particle size: 190 nm, solid content concentration 48%) were changed to 41.7 parts of styrene-butadiene copolymer C (glass transition temperature -30°C, particle size: 190 nm, solid content concentration 48%), and the thermal recorder was obtained in the same manner as in Example 1.

[0122] Example 10

[0123] In the preparation of the primer coating liquid in Example 1, 68.2 parts of hollow particles A (average particle size 9 μm, maximum particle size 23 μm, D100 / D50 = 2.6, volume % of particles with a diameter of 2.0 μm or less 0%, hollowness 92%, solid content concentration 22%) were replaced with hollow particles C (average particle size 5 μm, maximum particle size 14 μm, D100 / D50 = 2.8, volume % of particles with a diameter of 2.0 μm or less 0.2%, hollowness 92%, solid content concentration 22%). The thermal recorder was obtained in the same manner as in Example 1, except that 45.5 parts of styrene-butadiene copolymer A (glass transition temperature -10°C, particle size: 190nm, solid content concentration 48%) were replaced with 41.7 parts of styrene-butadiene copolymer D (glass transition temperature -35°C, particle size: 190nm, solid content concentration 48%), and 75 parts of water were replaced with 97.7 parts.

[0124] Example 11

[0125] In the preparation of the primer coating liquid in Example 10, the amount of hollow particles C (average particle size 5 μm, maximum particle size 14 μm, D100 / D50 = 2.8, volume % of particles with a diameter of 2.0 μm or less of 0.2%, hollowness 91%, solid content concentration 33%) was changed from 45.5 parts to 22.7 parts, and the thermal recorder was obtained in the same manner as in Example 10.

[0126] Comparative Example 1

[0127] In the fabrication of the thermal recorder in Example 1, the back layer coating liquid was not applied, but otherwise the thermal recorder was obtained in the same manner as in Example 1.

[0128] Comparative Example 2

[0129] In the fabrication of the thermal recorder in Example 1, the coating amount of the back layer after drying with the coating solution was increased from 5.0 g / m². 2 Change to 1.0g / m 2 Otherwise, a thermal recorder was obtained in the same manner as in Example 1.

[0130] Comparative Example 3

[0131] In the preparation of the primer coating liquid in Example 1, the amount of hollow particles A (average particle size 9 μm, hollowness 92%, solid content concentration 22%) was changed from 68.2 parts to 13.6 parts, and the thermal recorder was obtained in the same manner as in Example 1.

[0132] Comparative Example 4

[0133] In the preparation of the primer coating liquid in Example 1, the amount of hollow particles A (average particle size 9 μm, hollowness 92%, solid content concentration 22%) was changed from 68.2 parts to 181.8 parts, and the thermal recorder was obtained in the same manner as in Example 1.

[0134] The thermal recorders prepared in Examples 1 to 11 and Comparative Examples 1 to 4 above were evaluated as follows, and the results are shown in Table 1.

[0135] [Wang Yan-style smoothness]

[0136] The determination was based on JIS P8155:2010.

[0137] [Thermal Printing]

[0138] A thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.) was used to record each thermal recorder at an applied energy of 0.32 mJ / dot in the mid-tone energy range. The resulting print area was measured in visualization mode using a Macbeth density meter (RD-914, manufactured by Macbeth Co., Ltd.). For practical purposes, a recording density of 1.00 or higher is required.

[0139] [Image quality]

[0140] The quality of the recorded image obtained by visual inspection of thermal printing is evaluated according to the following criteria.

[0141] ◎: White spots with absolutely no image quality.

[0142] ○: White spots with almost no image quality.

[0143] △: The white spots in the image are slightly noticeable (within acceptable limits).

[0144] ×: The white spots in the image are very obvious and exist in multiple places.

[0145] Uneven color development in the printing section

[0146] Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recorder was recorded in the mid-tone energy range with an applied energy of 0.16 mJ / dot. The resulting solid print of the printed portion was visually observed and evaluated according to the following criteria.

[0147] ◎: There is absolutely no uneven color development.

[0148] ○: There is almost no uneven color development.

[0149] △: Uneven color development is slightly noticeable (within acceptable limits).

[0150] ×: The color development is very uneven, and the printing area is not uniform.

[0151] [Table 1]

[0152]

[0153] As shown in Table 1, the thermal recorders of Examples 1 to 11 exhibit high sensitivity and excellent image quality in the low-energy region, producing clear printed images without printing unevenness.

[0154] However, Comparative Example 1, lacking a back layer and exhibiting low smoothness, resulted in noticeable white spots and uneven color development, leading to uneven printing. Comparative Example 2, with insufficient coating on the back layer and low smoothness, also resulted in noticeable white spots and uneven color development, resulting in uneven printing. In Comparative Example 3, the amount of hollow particles in the base layer was low, resulting in numerous white spots in the printed area and significantly poor image quality. In Comparative Example 4, the amount of hollow particles in the base layer was excessive, causing the thermal layer coating to become uneven and resulting in noticeable uneven color development.

Claims

1. A thermal recorder comprising, on one side of a paper support, a base coating containing hollow particles with a hollowness ratio of 80-98% and a thermal recording layer containing a leuco dye and a developer, and on the other side of the paper support, a back layer containing pigment, wherein, The smoothness of the back layer, as described by Wang Yanshi, is over 500 seconds. The dried mass of the back layer is 3.0 g / m³. 2 above, The hollow particles constitute 5-30% by mass of the total solids in the base coating. The average particle size (D50) of the hollow particles is 3 to 15 μm, the maximum particle size (D100) of the hollow particles is 10 to 30 μm, and the ratio of the maximum particle size (D100) to the average particle size (D50) of the hollow particles (D100 / D50) is 1.8 to 3.

0.

2. The thermal recorder according to claim 1, wherein, The smoothness of the back layer is greater than 1000 seconds.

3. The thermal recorder according to claim 1 or 2, wherein, The back layer contains kaolin.

4. The thermal recorder according to claim 1 or 2, wherein, The base coating contains an adhesive with a glass transition temperature below -10°C.

5. The thermal recorder according to claim 1 or 2, wherein, The base coating contains an adhesive with a glass transition temperature below -30°C.

6. The thermal recorder according to claim 1 or 2, wherein, The base coating contains an adhesive, and the adhesive contains latex.

7. The thermal recorder according to claim 1 or 2, wherein, The smoothness of the surface with the thermal recording layer is over 4000 seconds.

8. The thermal recorder according to claim 1 or 2, wherein, The volume percentage of the hollow particles with a particle size of 2.0 μm or less is less than 1%.

9. The thermal recorder according to claim 1 or 2, wherein, The volume percentage of the hollow particles with a particle size of 2.0 μm or less is 0.5% or less.

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