Thermosensitive recording body

Abstract

Disclosed is a heat-sensitive recording body, which is a heat-sensitive recording body provided with a primer layer formed on one side of a support and a heat-sensitive recording layer formed on the primer layer, the heat-sensitive recording layer containing a leuco dye and a color developer, the primer layer containing hollow particles and a binding resin, the maximum particle diameter (D100) of the hollow particles being 10 to 30 µm, the particle diameter (D50) of 50 vol% of the hollow particles being 4.0 to 15 µm, the ratio D100 / D50 of the maximum particle diameter (D100) to the particle diameter (D50) of the hollow particles being 1.8 to 3.0, and the vol% of the hollow particles having a particle diameter of 2.0 µm or less being 1% or less.

Description

Technical Field

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

[0002] Thermal recorders, which record color-developing images by reacting colorless or light-colored dyes with phenols or organic acids upon heating, are widely used in practical applications. Because such thermal recorders form color-developing images solely through heating, they offer advantages such as compact recording devices, ease of maintenance, and low noise generation. Therefore, thermal recorders are widely used as information recording materials in various applications, including label printers, ticket vending machines, CD and ATM machines, order slip output machines in restaurants, and data output devices in scientific research equipment.

[0003] As thermal recorders are used in a variety of applications, higher performance is expected of them. Specifically, there are requirements for image quality such as deep and vivid color reproduction and the absence of white gaps (print defects) to achieve high image quality.

[0004] In response to such requirements, numerous improved techniques related to thermal recorders have been developed. For example, it is known to improve the sensitivity of the thermal recorder by containing hollow particles in an undercoat layer disposed between the support and the thermal recording layer, thereby enhancing the thermal insulation of the undercoat layer.

[0005] As a further improvement to the method of making the base coating contain hollow particles, for example, Patent Document 1 discloses a thermal recording material in which filler A with a particle size of less than 1 μm and a hollowness of less than 80% is mixed with filler B with a particle size of 3 to 10 μm and a hollowness of more than 80%.

[0006] However, the thermal recording material described in Patent Document 1 has room for improvement in recording density because the hollow particles are small in size and have insufficient thermal insulation, making it easy for printing energy to diffuse. In addition, the small particle size of the hollow particles and the low buffering capacity of the coating layer also allow for improvement in image quality.

[0007] Patent Document 2 discloses a thermal recording material using hollow particles with a hollowness of 60-98%, a maximum particle size (D100) of 5.0-10.0 μm, and a ratio of maximum particle size to particle size at 50% volume percent frequency (D50) of D100 / D50 of 1.5-3.0. The hollow particles in Patent Document 2 contain 2.2-3.6% by volume hollow particles with a particle size of 2 μm or less.

[0008] However, the thermal recording material described in Patent Document 2 has insufficient thermal insulation because the maximum particle size (D100) of the hollow particles is as small as 5.0 to 10.0 μm. Therefore, the printing energy is easily diffused and there is room for improvement in terms of recording density.

[0009] Furthermore, Patent Document 3 discloses thermally expandable resin particles used as a base coating, preferably having an average particle size of 1 to 25 μm when unexpanded, and a volume expansion of 10 to 50 times when heated, resulting in a hollowness of 80% or more.

[0010] However, the thermal recording material described in Patent Document 3 does not have the viewpoint of uniformizing the particle size of thermally expandable resin particles. Due to the deviation in particle size after foaming, the smoothness of the surface of the base layer is reduced, thus leaving room for improvement in image quality.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent No. 3176693

[0014] Patent Document 2: Japanese Patent No. 4108380

[0015] Patent Document 3: Japanese Patent No. 5781885 Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] The main objective of this invention is to provide a thermal recorder with high sensitivity, excellent mid-tone printing density, the ability to display printed images with minimal printing defects, and high image quality and vividness. Furthermore, the main objective of this invention is to provide a thermal recorder with excellent mid-tone printing density, the ability to display printed images with minimal printing defects, high image quality and vividness, and excellent coating strength.

[0018] Methods for solving problems

[0019] The inventors conducted repeated and in-depth research to solve the above-mentioned problems, and found that by using foamed hollow particles with a particle size and distribution within a specified range and suppressing the ratio of extremely small particles, or by mixing the hollow particles with inorganic pigments, the above-mentioned problems can be solved, thereby solving the present invention. That is, the present invention relates to the following thermal recording medium.

[0020] Item 1. A thermal recorder comprising a base coating formed on one side of a support and a thermal recording layer formed on the base coating.

[0021] The aforementioned thermal recording layer contains colorless dyes and color developers.

[0022] The aforementioned base coating contains hollow particles and a binding resin.

[0023] The maximum particle size (D100) of the aforementioned hollow particles is 10–30 μm.

[0024] The particle size (D50) at 50% volume frequency of the above-mentioned hollow particles is 4.0–15 μm.

[0025] The ratio of the maximum particle size (D100) to the particle size at 50% volume frequency (D50) of the aforementioned hollow particles, D100 / D50, is 1.8 to 3.0.

[0026] The volume percentage of the aforementioned hollow particles with a particle size of 2.0 μm or less is less than 1%.

[0027] Item 2. The thermal recorder according to Item 1, wherein the content of the hollow particles is 5 to 40% by mass relative to the total solid content of the base coating.

[0028] Item 3. The thermal recorder according to Item 1 or 2, wherein the hollowness of the hollow particles is 80-98%.

[0029] Item 4. The thermal recorder according to any one of items 1 to 3, wherein the coating weight of the aforementioned base coating after drying is 2.0 to 10 g / m². 2 .

[0030] Item 5. The thermal recorder according to any one of items 1 to 4, wherein the colorimetric agent contains 4-hydroxy-4'-n-propoxydiphenyl sulfone or N-[2-(3-phenylurea)phenyl]benzenesulfonamide.

[0031] Item 6. The thermal recorder according to any one of items 1 to 5, wherein the aforementioned undercoat layer further contains inorganic pigments.

[0032] Item 7. According to the thermal recorder described in Item 6, the oil absorption (determination method: JIS K-5101) of the above-mentioned inorganic pigment is 90 ml / 100 g or more.

[0033] Item 8. The thermal recorder according to Item 6 or 7, wherein the content of the inorganic pigment is 20 to 70% by mass relative to the total solid content of the base coating.

[0034] Item 9. The thermal recorder according to Item 8, wherein the content of the inorganic pigment is 40 to 60% by mass relative to the total solid content of the base coating.

[0035] Item 10. The thermal recorder according to any one of items 6 to 9, comprising calcined kaolin and / or silica as the aforementioned inorganic pigment.

[0036] Item 11. The thermal recorder according to any one of items 1 to 10, comprising latex as the aforementioned adhesive resin.

[0037] Item 12. The thermal recorder according to any one of items 1 to 11, comprising an adhesive resin having a glass transition temperature of -10°C or less as the adhesive resin.

[0038] Item 13. The thermal recorder according to any one of items 1 to 12, comprising an adhesive resin having a glass transition temperature of -30°C or less as the adhesive resin.

[0039] Item 14. The thermal recorder according to any one of items 1 to 13, wherein it contains at least a styrene-butadiene latex as the aforementioned adhesive resin.

[0040] Item 15. According to the thermal recorder described in Item 14, the glass transition temperature of the above-mentioned styrene-butadiene latex is below -10°C.

[0041] Item 16. According to the thermal recorder described in Item 15, the glass transition temperature of the above-mentioned styrene-butadiene latex is below -30°C.

[0042] Item 17. The thermal recorder according to any one of items 1 to 16, wherein the hollowness of the hollow particles is 91% to 98%.

[0043] Item 18. The thermal recorder according to any one of items 1 to 17, wherein the content of the hollow particles is 5 to 30% by mass relative to the total solid content of the base coating.

[0044] Item 19. The thermal recorder according to any one of items 1 to 18, wherein the coating weight of the aforementioned base coating after drying is 3.0 to 10 g / m². 2 .

[0045] Item 20. A thermal recorder comprising a base coating formed on one side of a support and a thermal recording layer formed on the base coating.

[0046] The aforementioned thermal recording layer contains colorless dyes and color developers.

[0047] The aforementioned base coating contains hollow particles, inorganic pigments, and binding resin.

[0048] The maximum particle size (D100) of the aforementioned hollow particles is 10–30 μm.

[0049] The particle size (D50) at 50% volume frequency of the above-mentioned hollow particles is 4.0–15 μm.

[0050] The ratio of the maximum particle size (D100) to the particle size at 50% volume frequency (D50) of the aforementioned hollow particles, D100 / D50, is 1.8 to 3.0.

[0051] The hollowness of the aforementioned hollow particles is 80-98%.

[0052] The volume percentage of the aforementioned hollow particles with a particle size of 2.0 μm or less is less than 1%.

[0053] Item 21. According to the thermal recorder described in Item 20, the oil absorption (method: JIS K-5101) of the above-mentioned inorganic pigment is 90 ml / 100 g or more.

[0054] Item 22. The thermal recorder according to Item 20 or 21, wherein the hollowness of the hollow particles is 91% to 98%.

[0055] Item 23. The thermal recorder according to any one of items 20 to 22, wherein the content of the hollow particles is 5 to 30% by mass relative to the total solid content of the base coating.

[0056] Item 24. The thermal recorder according to any one of items 20 to 23, wherein the coating weight of the aforementioned base coating after drying is 3.0 to 10 g / m². 2 .

[0057] Item 25. The thermal recorder according to any one of items 20 to 24, wherein the content of the inorganic pigment is 20 to 70% by mass relative to the total solid content of the base coating.

[0058] Item 26. The thermal recorder according to Item 25, wherein the content of the inorganic pigment is 40 to 60% by mass relative to the total solid content of the base coating.

[0059] Item 27. The thermal recorder according to any one of items 20 to 26, comprising calcined kaolin and / or silica as the aforementioned inorganic pigment.

[0060] Item 28. The thermal recorder according to any one of items 20 to 27, wherein it contains at least a styrene-butadiene latex as the aforementioned adhesive resin.

[0061] Item 29. According to the thermal recorder described in Item 28, the glass transition temperature of the above-mentioned styrene-butadiene latex is below -10°C.

[0062] Item 30. According to the thermal recorder of Item 29, the glass transition temperature of the above-mentioned styrene-butadiene latex is below -30°C.

[0063] The effects of the invention

[0064] The thermal recorder of the present invention exhibits high sensitivity, excellent mid-tone printing density, and the ability to display printed images with minimal printing defects, high image quality, and vividness. Furthermore, the thermal recorder of the present invention also possesses excellent coating strength, excellent mid-tone printing density, and the ability to display printed images with minimal printing defects, high image quality, and vividness. Detailed Implementation

[0065] In this specification, the expression “containing” includes the concepts of “containing”, “substantially consisting of only”, and “consisting of only”.

[0066] In this specification, the numerical range indicated by “~” refers to the range of values ​​included before and after “~” as the lower and upper limits.

[0067] The styrene-butadiene latex and other latexes in this invention comprise a state of gel or dried film formed by drying the dispersion medium.

[0068] Furthermore, in this invention, "average particle size" refers to the median particle size of a volume reference determined 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.

[0069] The present invention is a thermal recording device comprising a base coating formed on one side of a support and a thermal recording layer formed on the base coating, characterized in that,

[0070] The aforementioned thermal recording layer contains colorless dyes and color developers.

[0071] The aforementioned base coating contains hollow particles and a binding resin.

[0072] The maximum particle size (D100) of the aforementioned hollow particles is 10–30 μm.

[0073] The particle size (D50) at 50% volume frequency of the above-mentioned hollow particles is 4.0–15 μm.

[0074] The ratio of the maximum particle size (D100) to the particle size at 50% volume frequency (D50) of the aforementioned hollow particles, D100 / D50, is 1.8 to 3.0.

[0075] The volume percentage of the aforementioned hollow particles with a particle size of 2.0 μm or less is less than 1%.

[0076] [Supporting Body]

[0077] There are no particular limitations on the type, shape, or size of the support. For example, it can be appropriately selected from high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, cellophane, resin-laminated paper, polyolefin synthetic paper, synthetic fiber paper, non-woven fabric, synthetic resin film, and various transparent supports. The thickness of the support is not particularly limited, typically around 20–200 μm. Furthermore, the density of the support is not particularly limited, but preferably 0.60–0.85 g / cm³. 3 about.

[0078] [Base Coating]

[0079] The primer layer is disposed between the support and the thermal recording layer, serving to fix and elevate the thermal recording layer, and to enhance the image clarity of the thermal recording layer by suppressing the diffusion of heat applied to it. The primer layer contains hollow particles and a binding resin, or contains hollow particles, inorganic particles, and a binding resin. Preferably, the primer layer further contains a thickener, and may contain additives as needed.

[0080] (Hollow particles)

[0081] Hollow particles made of organic resin are incorporated into the base coating, thereby improving its thermal insulation. The highly insulating base coating prevents heat diffusion applied to the thermal recording layer, thus improving the sensitivity of the thermal recorder.

[0082] Hollow particles made from organic resins can be classified into foamed and non-foamed types depending on their manufacturing method. Of these two types, foamed hollow particles have properties suitable for improving the thermal insulation of the base coating.

[0083] <Methods for Manufacturing Hollow Particles>

[0084] The following describes a representative manufacturing method for foamed hollow particles.

[0085] First, particles containing a volatile liquid are made. The resin is softened by heating, and the liquid inside the particles is vaporized and expanded, thereby creating hollow particles.

[0086] During the manufacturing process, the internal liquid is heated and expanded, thus increasing the hollowness of the foamed hollow particles. This high hollowness results in high thermal insulation, allowing the foamed hollow particles to improve the sensitivity of the thermal paper and increase recording density. This increased sensitivity is particularly important when producing color in mid-tone regions where the heat energy applied to the thermal recording layer is low. Furthermore, if the thermal recording layer is formed via a highly insulating undercoat, image bleeding can be prevented by preventing the diffusion of heat applied to the thermal recording layer, thereby improving image quality.

[0087] Examples of resins suitable for use in foamed hollow particles include styrene-acrylic resins, polystyrene resins, acrylic resins, polyethylene resins, polypropylene resins, polyacetal resins, chlorinated polyether resins, polyvinyl chloride resins, poly(1,1-dichloroethylene) resins, acrylic resins (e.g., acrylic resins with acrylonitrile as a constituent), styrene resins, 1,1-dichloroethylene resins, and thermoplastic resins such as copolymers of poly(1,1-dichloroethylene) and acrylonitrile. The gas contained within the foamed hollow particles is generally propane, butane, isobutane, or air. Among the various resins mentioned above, from the viewpoint of maintaining the strength and shape of the foamed particles, acrylonitrile resins and copolymers of poly(1,1-dichloroethylene) and acrylonitrile are preferred for use in hollow particles.

[0088] Maximum particle size

[0089] The maximum particle size of the hollow particles is 10–30 μm, preferably 10–25 μm, and more preferably 10–20 μm. This maximum particle size is also referred to as D100. If the maximum particle size of the hollow particles is 10 μm or more, the buffering capacity of the undercoat is improved, thus improving the adhesion between the thermal paper and the thermal print head during printing, resulting in a high-quality thermal recorder. Such a thermal recorder with high adhesion to the thermal print head can achieve increased recording density in the mid-tone regions where color is emitted with energy below the maximum recording density (Dmax). On the other hand, if the maximum particle size of the hollow particles is 30 μm or less, the smoothness of the undercoat is improved, thus homogenizing the thermal recording layer formed by the undercoat, resulting in a thermal recorder with high color density. Furthermore, the adhesion between the support and the undercoat is improved, resulting in a thermal recorder with excellent coating strength. The maximum particle size of the hollow particles can be measured using a laser diffraction particle size distribution measuring device. Alternatively, it can be measured using an electron microscope.

[0090] <Median Particle Size>

[0091] When powder is divided into two parts by a certain particle size, the particle size at which the volume occupied by the larger and smaller particles is equal, i.e., the particle size at a 50% volume frequency, is called the median particle size. The median particle size is also known as D50. The median particle size of hollow particles can be determined using a laser diffraction particle size distribution measuring device. Alternatively, it can be measured using an electron microscope. The median particle size of hollow particles is 4.0–15 μm, preferably 7.5–15 μm. By making the median particle size 4.0 μm or larger, buffering capacity can be improved. On the other hand, by making it 15 μm or smaller, smoothness can be improved.

[0092] <Ratio of maximum particle size to median particle size>

[0093] The ratio of the maximum particle size (D100) to the median particle size (D50) (D100 / D50) is an indicator of the degree of particle size distribution. D100 / D50 is 1.8 to 3.0, preferably 1.8 to 2.8, and more preferably 1.8 to 2.6. By making D100 / D50 1.8 or higher, the hollow particles are fully foamed, the maximum particle size is sufficiently increased, and the hollowness ratio is higher, which improves the thermal insulation of the undercoating layer. On the other hand, by making D100 / D50 3.0 or lower, the size of the hollow particles is uniform, thus improving the smoothness of the undercoating layer, suppressing image whitening, and further increasing recording density.

[0094] <Hollow particles with a diameter of less than 2 μm>

[0095] In the particle size distribution determined by a laser diffraction particle size distribution measuring device, the volume percentage of hollow particles with a diameter of 2.0 μm or less is 1% or less. Furthermore, the volume percentage of hollow particles with a diameter of 2.0 μm or less is preferably 0.5% or less, and more preferably absent. Since hollow particles with a diameter of 2 μm or less have such a small diameter to achieve sufficient hollow areas, their contribution to thermal insulation is considered extremely small. By ensuring that the volume percentage of hollow particles with a diameter of 2 μm or less in the undercoat layer is 1% or less, recording density, image quality, and other properties can be improved.

[0096] <Content>

[0097] Hollow particles preferably comprise 5 to 40% by mass of the total solids in the primer coating, more preferably 5 to 30% by mass. If the content of hollow particles is 5% by mass or more, the thermal insulation of the primer coating can be improved. On the other hand, if the content of hollow particles is 30% by mass or less, problems are less likely to occur regarding the strength of the coated surface.

[0098] <Hollow Rate>

[0099] The hollowness of the hollow particles is preferably 80-98%, more preferably 90-98%, and even more preferably 91-98%. If the hollowness of the hollow particles is 80% or more, high thermal insulation can be imparted to the undercoat containing the hollow particles, and image quality can also be improved. On the other hand, if the hollowness of the hollow particles is 98% or less, by increasing the strength of the film encapsulating the hollow portion, hollow particles can be formed without being crushed during the formation of the undercoat.

[0100] (Inorganic pigments)

[0101] Inorganic pigments, when incorporated into the base coat, improve smoothness, thereby enhancing image quality and increasing the printing density of midtones. Various substances can be used as inorganic pigments; specific examples include calcined kaolin, silica, light calcium carbonate, and talc, with calcined kaolin and silica being preferred. The average particle size of the primary particles in these inorganic pigments is preferably around 0.01–5 μm, particularly around 0.02–3 μm.

[0102] The oil absorption of the inorganic pigment is preferably 90 ml / 100g or more, more preferably about 90 to 170 ml / 100g. Here, the oil absorption is a value calculated according to the method of Japanese Industrial Standard (JIS) K-5101. If the oil absorption of the inorganic pigment is 90 ml / 100g or more, the image quality and midtone printing density can be improved. The content ratio of the inorganic pigment can be selected from a wide range, but it is generally preferably about 20 to 70% by mass in the total solids of the base coat, more preferably about 40 to 60% by mass. If the content of the inorganic pigment is 20% by mass or more, the image quality and midtone printing density can be improved. On the other hand, if the content of the inorganic pigment is 70% by mass or less, problems are less likely to occur in terms of the strength of the coating surface. Furthermore, the content of calcined kaolin in the total solids of the base coat is preferably 5 to 80% by mass.

[0103] (Thickener)

[0104] The thickener, by being incorporated into the base coat, can suppress the bias of hollow particles in the coating liquid used for the base coat. Various known materials can be appropriately used in the thickener, such as cellulose and its derivatives, high-molecular-weight polysaccharides, modified polyacrylic acid, sodium alginate, and maleic anhydride copolymers. Among the materials used in the thickener, cellulose derivatives such as carboxymethyl cellulose (CMC) and high-molecular-weight polysaccharides are preferred.

[0105] Hollow particles, due to their large maximum particle size, have high buoyancy and tend to concentrate at the top in low-viscosity liquids. If cellulose derivatives and high-molecular-weight polysaccharides are used as thickeners in the base coat coating liquid, the hollow particles are less likely to float in the base coat coating liquid, reducing their bias in the base coat, which is preferred. Reduced bias of the hollow particles improves the smoothness of the base coat, thus homogenizing the thermal recording layer formed by the base coat, suppressing image whitening, and increasing the maximum color concentration. The content of the thickener is not particularly limited, but it is preferably in the range of about 1 to 5% by mass in the total solids of the base coat. A content of 1% by mass or more effectively suppresses the floating of hollow particles and significantly improves the maximum color concentration. A content of 5% by mass or less effectively suppresses the increase in coating viscosity and provides excellent coating adaptability.

[0106] (Adhesive resin)

[0107] The primer layer may contain an adhesive resin (binder). As the adhesive used in the primer coating liquid, water-based adhesives, such as water-soluble and water-dispersible adhesives, can be used. Examples of water-soluble adhesives include, for example, modified polyvinyl alcohol (PVA), such as carboxyl-modified PVA, acetoacetyl-modified PVA, diacetone-modified PVA, silicone-modified PVA, starch and its derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, polyamide, diisobutylene-maleic anhydride copolymer salt, styrene-acrylic acid copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-maleic anhydride copolymer salt, acrylamide-acrylate copolymer, acrylamide-acrylate-methacrylic acid copolymer, polyacrylamide, sodium alginate, gelatin, casein, gum arabic, etc. 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 copolymer, etc. They can be used alone or in combination of two or more.

[0108] The base coating preferably contains a binder resin with a glass transition temperature (Tg) of -10°C or lower, and more preferably a binder resin with a glass transition temperature of -30°C or lower. By containing a binder resin with a glass transition temperature of -10°C or lower, the flexibility of the coating layer is improved and the cushioning is optimized, thereby further improving the image quality of the thermal recorder.

[0109] The bonding resin of the base coating preferably contains a latex with excellent surface strength. There are no particular limitations on the latex, and examples include latexes of water-insoluble polymers such as styrene-butadiene copolymers, styrene-butadiene-acrylonitrile copolymers, and acrylonitrile-butadiene copolymers. Among these latexes, styrene-butadiene-based latex (SBR) is preferred due to its high water resistance and surface strength. Specifically, styrene-butadiene-based latexes with a glass transition temperature of -10°C or lower are preferred. A glass transition temperature of -10°C or lower improves image quality and increases the printing density of midtones. To further increase the printing density of midtones, a glass transition temperature of -30°C or lower is more preferable for styrene-butadiene-based latexes. Furthermore, a glass transition temperature of -50°C or higher is preferred.

[0110] The content of the adhesive resin in the primer layer is preferably about 1 to 60% by mass, more preferably about 5 to 40% by mass. If the content of the adhesive resin is within the above range, the coatability becomes good when the primer layer is applied. In addition, the content of water-soluble polymers in the adhesive resin is preferably about 1 to 50% by mass, more preferably about 5 to 30% by mass.

[0111] (Applying of the primer coating liquid)

[0112] The base coating is formed by applying a base coating solution to a support and then allowing it to dry. The base coating solution is prepared by mixing and stirring the aforementioned base coating materials, such as hollow particles, inorganic pigments, and binder resin, with a solvent such as water. The preferred coating weight after drying is 2.0–10 g / m². 2 Approximately, more preferably 2.5–7.0 g / m³. 2 Approximately. Furthermore, the coating weight of the base coat solution after drying is preferably 2.5–11 g / m². 2 Approximately, more preferably 3.0–10 g / m³. 2 Approximately. Passing through 2.5g / m³ 2 The above can improve the thermal insulation of the base coating. On the other hand, by setting the value to 11 g / m... 2 Therefore, problems are less likely to occur in terms of the strength of the coated surface.

[0113] [Thermal Recording Layer]

[0114] The thermal recording layer is placed on the base layer and serves to display and record text, patterns, etc., by means of the color-emitting properties of the parts heated. The thermal recording layer contains colorless dyes and color developers, and may contain preservation modifiers, sensitizers, binding resins, crosslinking agents, etc., as needed.

[0115] (Colorless dye)

[0116] Thermal recording layers typically contain dye precursors and developers. Representative dye precursors include colorless or light-colored colorless dyes. Among colorless dyes are triphenylmethane, fluorane, and diphenylmethane compounds, which can be selected appropriately. Furthermore, colorless dyes also include those with hues such as red, vermilion, magenta, blue, cyan, yellow, green, and black, which can also be selected appropriately.

[0117] Examples of colorless dyes include cyan dyes such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, and fluorane; green dyes such as 3-(N-ethyl-N-p-tolyl)amino-7-N-methylaniline fluorane, 3-diethylamino-7-aniline fluorane, and 3-diethylamino-7-dibenzylamino fluorane; and dyes such as 3,6-bis(diethylamino)fluorane-γ-aniline lactam, 3-cyclohexylamino-6-chlorofluorane, and 3-diethylamino-6-methyl-7-... Red chromogenic dyes such as chlorofluorane and 3-diethylamino-7-chlorofluorane, 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, 3-di(n-butyl)amino-6-methyl-7-aniline fluorane, 3-di(n-pentyl)amino-6-methyl-7-aniline fluorane, 3-diethylamino-7-(o-chlorophenylamino)fluorane, 3-(N-ethyl-p-toluidine)-6-methyl-7-aniline fluorane, 3-(N-ethyl-p-toluidine)-chlorofluorane 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-aniline fluorane, 3-diethylamino-6-chloro-7-aniline fluorane, 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[phthaloyl-3,9'-xanthon]-2'-ylamino]phenyl}propane, 3-diethylamino-7-(3'-trifluoromethylphenyl)amino fluorane, etc. Color-emitting dyes, such as 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylidene-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinylphenyl)ethylidene-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, are dyes that have absorption wavelengths in the near-infrared region. Of course, these are not limited to these; more than two types can be used in combination as needed. Among them, 3-di(n-butyl)amino-6-methyl-7-aniline fluorane, 3-di(n-pentyl)amino-6-methyl-7-aniline fluorane, and 3-(N-ethyl-N-isopentylamino)-6-methyl-7-aniline fluorane are preferred due to their excellent recording sensitivity and printability.

[0118] The content of the colorless dye relative to the total solid content of the thermal recording layer is preferably about 5 to 30% by mass, more preferably about 7 to 30% by mass, and even more preferably about 7 to 25% by mass. If the content of the colorless dye is 5% by mass or more, the color concentration can be increased. On the other hand, if the content of the colorless dye is 30% by mass or less, the heat resistance can be improved. Furthermore, the content of the colorless dye per unit area in the thermal recording layer is preferably 0.2 to 2.0 g / m². 2 Approximately, more preferably 0.4–1.5 g / m 2 The content of colorless dye per unit area can be determined by methods such as high-performance liquid chromatography.

[0119] (Color developer)

[0120] Specific examples of colorimetric agents include, for instance, 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylene biphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylene biphenol, 4,4'-cyclohexylene diphenyl, 4,4'-cyclohexylene biphenol, 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-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 Phenolic compounds such as 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, 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-methoxyphenyl)] Aromatic carboxylic acids such as zinc zinc thiocyanate, 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, and these phenolic compounds, salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, further antipyrine coordination compounds of zinc thiocyanate, complex zinc salts of p-aldehyde benzoic acid and other aromatic carboxylic acids, N-p-tolylsulfonyl-N'-3-(p-tolylsulfonyl)phenylurea, N-p-tolylsulfonyl-N'-p-butoxycarbonylphenylurea, N-p-tolylsulfonyl-N'-phenylurea, 4,Urea compounds such as 4'-bis(p-toluenesulfonylaminocarbonylamino)diphenylmethane, thiourea compounds such as N,N'-di-m-chlorophenylthiourea, organic compounds with intramolecular -SO₂NH₄ bonds such as N-(p-toluenesulfonyl)carbamoyl acid p-cumylphenyl ester, N-(p-toluenesulfonyl)carbamoyl acid p-benzyloxyphenyl ester, and N-(o-toluenebenzoyl)-p-toluenesulfonamide, as well as inorganic acidic substances such as activated clay, magnesia, colloidal silica, and aluminum silicate.

[0121] In addition, examples of sulfonamide compounds such as N-[2-(3-phenylureo)phenyl]benzenesulfonamide, N-[2-(3-phenylureo)phenyl]-p-toluenesulfonamide, N-[2-(3-phenylureo)phenyl]-o-toluenesulfonamide, and N-[2-(3-(4-methylphenyl)ureo)phenyl]benzenesulfonamide, as shown in general formula (1), are given. Among these, N-[2-(3-phenylureo)phenyl]benzenesulfonamide is preferred from the viewpoints of suppressing heat-resistant background fog and improving printability, as well as from the viewpoints of ease of synthesis.

[0122]

[0123] In equation (1), R 1 and R 2 They can be the same or different, representing hydrogen atoms, alkyl groups with 1 to 4 carbon atoms, alkoxy groups with 1 to 4 carbon atoms, or halogen atoms, respectively.

[0124] Furthermore, examples include 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureo]diphenyl sulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureo]diphenyl sulfone, and 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureo-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureo diphenyl sulfone, all represented by the general formula (2) below. Among these, 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureo]diphenyl sulfone is preferred.

[0125] In addition, diphenyl sulfone derivatives represented by the following general formula (3) can also be cited.

[0126]

[0127] In equation (3), n represents an integer from 1 to 6. Of course, the colorimetric reagents are not limited to these, and more than two compounds can be used in combination as needed.

[0128] There are no particular limitations on the content of such a color developer; it can be adjusted according to the colorless dye used. The content of the color developer relative to 1 part by weight of the colorless dye is generally preferably 0.5 parts by weight or more, more preferably 0.8 parts by weight or more, further preferably 1 part by weight or more, even more preferably 1.2 parts by weight or more, and particularly preferably 1.5 parts by weight or more. Furthermore, the content of the color developer relative to 1 part by weight of the colorless dye is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, further preferably 4 parts by weight or less, and particularly preferably 3.5 parts by weight or less. By using 0.5 parts by weight or more, recording performance can be improved. On the other hand, by using 10 parts by weight or less, background fog (heat-resistant background fog) under high-temperature environments can be effectively suppressed.

[0129] (Preservative improver)

[0130] In this invention, the thermal recording layer may further contain a preservation enhancer, primarily to further improve the preservation of the color image. Such a preservation enhancer may be, for example, selected from 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-methylethylene)]bisphenol, 4,4'-[1,3-phenylenebis(1-methylethylene)]bisphenol, etc. Phenolic compounds such as bisphenol (-methylethylidene); 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 acid 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 compounds; additionally, two or more compounds may be used in combination as needed.

[0131] When using a preservation improver, the amount used is only the amount that is effective for preservation improvement. Generally, it is about 1 to 30% by mass in the total solid content of the thermal recording layer, and more preferably about 5 to 20% by mass.

[0132] (Sensitizer)

[0133] 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-benzoylstearamide, N-eicosanoamide, ethylene bis-stearamide, and others. Acetamide, methylene bis-stearamide, N-hydroxymethylstearamide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthylcarboxylate, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, 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, 1,2-di(4-methoxyphenoxy)ethane, 1,2-di(4-methoxyphenoxy)ethane, 1,2-di(4-methylphenoxy)ethane 1,2-Diphenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, p-methylthiophenyl benzyl ether, 1,4-di(phenylthio)butane, p-acetyltoluidine, acetyl-p-ethoxyaniline, 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 hindrance. The sensitizer content should be as small as possible to achieve effective sensitization; typically, it is about 2 to 40% by mass, more preferably about 5 to 25% by mass, in the total solids content of the thermal recording layer.

[0134] (Adhesive resin)

[0135] The thermal recording layer may contain an adhesive resin (binder). As the adhesive used in the coating liquid for the thermal recording layer, water-based adhesives, such as water-soluble adhesives and water-dispersible adhesives, can be used. Examples of water-soluble adhesives include, for example, modified polyvinyl alcohol (PVA), such as carboxyl-modified PVA, acetoacetyl-modified PVA, diacetone-modified PVA, silicone-modified PVA, starch and its derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, polyamide, diisobutylene-maleic anhydride copolymer salt, styrene-acrylic acid copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-maleic anhydride copolymer salt, acrylamide-acrylate copolymer, acrylamide-acrylate-methacrylic acid copolymer, polyacrylamide, sodium alginate, gelatin, casein, gum arabic, etc. 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 copolymer, etc. One or more of these can be used alone or in combination. Preferably, at least one of these adhesives is contained in 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.

[0136] (Cross-linking agent)

[0137] The thermal recording layer can contain a crosslinking agent that cures the adhesive of the thermal recording layer. By containing a crosslinking agent, the water resistance of the thermal recording layer can be improved. Examples of crosslinking agents include, for instance, aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, dimethylolurea compounds, aziridine compounds, blocked 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. One type of crosslinking agent can be used alone, or two or more can be used 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.

[0138] (other)

[0139] The thermal recording layer may contain, as needed and without impairing the effect of the invention, known waxes, metallic soaps, colored dyes, colored pigments, fluorescent dyes, etc.

[0140] Examples of waxes include paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, and polyethylene wax; for example, stearamide, ethylene distearate and other higher fatty acid amides, higher fatty acid esters and their derivatives.

[0141] 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 and without impairing the effects of the invention, various additives such as oil-repellent agents, defoamers, and viscosity modifiers can be added to the thermal recording layer. Alternatively, after dissolving these additives in a solvent to form a solution, the solution can be emulsified in water using an emulsifier for use. Water-soluble polymers can be used as emulsifiers.

[0142] (Coating of the thermal recording layer with coating solution)

[0143] The thermal recording layer is formed by coating a thermal recording layer with a coating solution onto a base layer and then drying it. The coating amount of the thermal recording layer with the coating solution is preferably 2–12 g / m² based on the dried mass. 2 Approximately, more preferably 2–8 g / m 2 Approximately, more preferably 2-7 g / m 2 Left and right. The coating liquid for the thermal recording layer uses water as the dispersion medium and is prepared by using a dispersion in which colorless dyes and color developers are dispersed together or separately, binder resin (adhesive), preservation improver, sensitizer, etc.

[0144] [Protective Layer]

[0145] A protective layer can be provided on the thermal recording layer to protect it from heat and various external factors. The protective layer can be formulated, for example, by mixing an adhesive, a pigment, wax, a crosslinking agent, and other additives as needed. As the adhesive, materials exemplified in the aforementioned thermal recording layer can be used. The presence of pigments and waxes prevents residue adhesion to the thermal head. Furthermore, the addition of a crosslinking agent imparts water resistance to the protective layer. Water is used as the dispersion medium for the protective layer, and the coating solution preferably contains 0.1 to 15 g / m³ of the protective layer by dry weight. 2 Approximately 0.5–8 g / m³, more preferably 0.5–8 g / m³ 2 It is formed by coating the thermal recording layer in a left-right manner.

[0146] [Other layers]

[0147] In addition to the layers described above, further layers can be added to enhance the added value of the thermal recorder, resulting in a thermal recorder with higher functionality. For example, by providing an adhesive layer containing adhesives, rewetting adhesives, delayed adhesives, etc., on the back side, the thermal recorder can be made into adhesive paper, rewetting adhesive paper, delayed adhesive paper, etc.

[0148] Furthermore, the back side can be used to function as thermal transfer paper, inkjet recording paper, carbonless paper, electrostatic recording paper, or electrostatic copying paper, making the thermal recorder a double-sided recording paper. Of course, it can also be a double-sided thermal recorder. In addition, a back layer can be provided to suppress the penetration of oil and plasticizers from the back side of the thermal recorder, or for curl control and antistatic purposes. By coating a release layer containing silicone onto the protective layer and coating the back side with an adhesive, linerless labels that do not require a release liner can also be produced.

[0149] [Thermal recording medium]

[0150] (Methods of forming each layer)

[0151] As a method for forming the aforementioned layers on the support, any of the known coating methods can be used, such as air knife coating, doctor blade coating, gravure coating, roller coating, spray coating, dip coating, rod coating, curtain coating, groove coating, sliding die coating, and extrusion coating. Furthermore, each coating liquid can be applied and dried one layer at a time to form the layers, or the same coating liquid can be applied in two or more layers. Moreover, simultaneous multi-layer coating of two or more layers is also possible.

[0152] (Smoothing process)

[0153] From the perspective of improving recording sensitivity and suppressing white spots, it is preferable to perform smoothing processing using known methods such as supercalenders or soft calenders after the formation of each layer or after the formation of all layers.

[0154] Example

[0155] The invention is further illustrated in detail by way of examples, but is not limited thereto. Additionally, unless otherwise specified, “parts” and “%” refer to “parts by mass” and “% by mass”, respectively.

[0156] The hollow particles used in the examples and comparative examples are as described below.

[0157] Hollow Particle A: Median particle size (D50) 11 μm, maximum particle size (D100) 23 μm, hollowness 93%, proportion of particles smaller than 2 μm 0% by volume, solid content 15.0%.

[0158] Hollow Particle B: Median particle size (D50) 8.1 μm, maximum particle size (D100) 20 μm, hollowness 90%, proportion of particles smaller than 2 μm 0% by volume, solid content 15.0%.

[0159] Hollow particle C: Median particle size (D50) 7.5 μm, maximum particle size (D100) 15 μm, hollowness 85%, proportion of particles smaller than 2 μm 0% by volume, solid content 15.0%.

[0160] Hollow particle D: Median particle size (D50) 6.2 μm, maximum particle size (D100) 15 μm, hollowness 77%, proportion of particles smaller than 2 μm 0% by volume, solid component concentration 15.0%.

[0161] Hollow particles E: Median particle size (D50) 5.0 μm, maximum particle size (D100) 13.5 μm, hollowness 90%, proportion of particles smaller than 2 μm 0.2% by volume, solid content 15.0%.

[0162] Hollow Particles F: Trade name A-380, hollow particles manufactured by Sansui Co., Ltd., median particle size (D50) 3.8 μm, maximum particle size (D100) 6.5 μm, hollowness 78%, proportion of hollow particles with a diameter of 2.0 μm or less 1.5% by volume, solid content 13.0%.

[0163] Hollow Particles G: Trade name Matsumoto Maicros Fair F series, hollow particles manufactured by Matsumoto Yushi Co., Ltd., with a median particle size (D50) of 3.7 μm, a maximum particle size (D100) of 12.6 μm, a hollowness ratio of 84%, a volume percentage of hollow particles with a particle size of 2.0 μm or less of 6.4%, and a solid content concentration of 15.0%.

[0164] Hollow particles H: Median particle size (D50) 12 μm, maximum particle size (D100) 124 μm, hollowness 94%, proportion of particles smaller than 2 μm 0% by volume, solid content 15.0%.

[0165] Hollow Particles I: Trade name Expansion 461WE20d36, hollow particles manufactured by Nurio, with a median particle size (D50) of 20μm, a maximum particle size (D100) of 80μm, a hollowness of 95%, a volume percentage of particles smaller than 2μm of 0%, and a solid content concentration of 15.0%.

[0166] Hollow particles J: Median particle size (D50) 12 μm, maximum particle size (D100) 45 μm, hollowness 94%, proportion of particles smaller than 2 μm 0% by volume, solid content 15.0%.

[0167] The median particle size (D50) and maximum particle size (D100) of each hollow particle were measured using a SALD2200 laser diffraction particle size analyzer (manufactured by Shimadzu Corporation) with a refractive index of 1.70-0.01i.

[0168] The inorganic pigments used in the examples and comparative examples are as follows.

[0169] Inorganic Pigment A: Calcined kaolin, trade name Ansilex 93, manufactured by BASF, oil absorption 104ml / 100g

[0170] Inorganic Pigment B: Silica, trade name Nipseil E743, manufactured by Higashi Sou, oil absorption 155ml / 100g

[0171] Inorganic Pigment C: Calcium Carbonate, trade name Callight SA, manufactured by Shiraishi Calshom, oil absorption 75ml / 100g

[0172] Inorganic pigment D: Kaolin, trade name HG90, manufactured by KaMin LLC, oil absorption 49ml / 100g. The latex used in the examples and comparative examples is as follows.

[0173] Latex A: Styrene / butadiene latex development product (Tg: -10℃, particle size 190nm, solids concentration 48%)

[0174] Latex B: Styrene / butadiene latex development product (Tg: -35℃, particle size 300nm, solids concentration 48%)

[0175] Latex C: Styrene / butadiene latex (trade name L-1571, manufactured by Asahi Kasei Corporation, Tg = -3℃, particle size 190nm, solids concentration 48%)

[0176] (Example 1-1)

[0177] (1) Preparation of coating liquid for base coating

[0178] A coating solution for a base coat was obtained by mixing and stirring 133.3 parts of hollow particles A, 50 parts of calcined kaolin (trade name: Ansilex 93, manufactured by BASF), 25 parts of latex A, 7.5 parts of a 20% solution of oxidized starch, 3.5 parts of carboxymethyl cellulose (trade name: Serogen AG Gam, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), and 75.0 parts of water.

[0179] (2) Preparation of colorless dye dispersion (solution A)

[0180] A colorless dye dispersion (solution A) was obtained by mixing 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%), 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and pulverizing the mixture using a sand mill (manufactured by Imex Co., Ltd.) until the median particle size obtained by laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) was 0.5 μm.

[0181] (3) Preparation of colorimetric reagent dispersion (solution B)

[0182] 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.) until the median particle size obtained by laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) was 1.0 μm, thus obtaining a colorimetric reagent dispersion (solution B).

[0183] (4) Preparation of sensitizer dispersion (C solution)

[0184] 40 parts of di-p-methylbenzyl oxalate (trade name: HS-3520, manufactured by DIC), 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.) until the median particle size obtained by laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) was 1.0 μm, thus obtaining a sensitizer dispersion (C solution).

[0185] (5) Preparation of coating solution for thermal recording layer

[0186] A coating solution for thermal recording layers was obtained by mixing and stirring 29.5 parts of solution A, 59.1 parts of solution B, 22.7 parts of solution C, 20 parts of a 5% aqueous solution of hydroxypropyl methylcellulose, 146 parts of a 10% aqueous solution of fully saponified polyvinyl alcohol (trade name: PVA110, degree of saponification: 99 mol%, average degree of polymerization: 1000, manufactured by Kurare Co., Ltd.), 9.4 parts of butadiene copolymer latex (trade name: L-1571, manufactured by Asahi Kasei Co., Ltd., solid content concentration 48%), 25.4 parts of light calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd.), 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.

[0187] (6) Preparation of coating liquid for protective layer

[0188] A protective coating liquid was obtained by mixing and stirring 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%), 19 parts of kaolin (trade name: HYDRAGLOSS90, KaMinLLC), 35 parts of aluminum hydroxide (trade name: Hydralight H-42M, Showa Denko), 4 parts of silica (trade name: Mizusawa Kagaku), 2.5 parts of polyethylene wax (trade name: Kemipar W-400, Mitsui Chemicals, solid content concentration 40%), and 114.5 parts of water.

[0189] (7) Fabrication of thermal recording devices

[0190] Weight per unit area: 60g / m² 2 On one side of high-quality paper, the base coating liquid, the thermal recording layer coating liquid, and the protective recording layer coating liquid are applied at a drying amount of 4.0 g / m². 2 4.0g / m 2 2.0g / m 2 The thermal recording body was obtained by coating and drying the substrate in sequence, forming a base layer, a thermal recording layer, and a protective layer, and then smoothing the surface with a supercalender.

[0191] (Examples 1-2)

[0192] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles A were made into hollow particles B. Otherwise, a thermal recorder was obtained in the same manner as in Example 1-1.

[0193] (Examples 1-3)

[0194] In the preparation of the coating liquid for the base coating in Example 1-1, the 133.3 parts of hollow particles A were changed to 46.7 parts, and the 50.0 parts of calcined kaolin were changed to 63.0 parts. Otherwise, the thermal recorder was obtained in the same manner as in Example 1-1.

[0195] (Examples 1-4)

[0196] In the preparation of the coating liquid for the base coating in Example 1-1, the hollow particle A was changed from 133.3 parts to 186.7 parts, and the calcined kaolin was changed from 50.0 parts to 42.0 parts. Otherwise, the thermal recorder was obtained in the same manner as in Example 1-1.

[0197] (Examples 1-5)

[0198] In the preparation of the coating liquid for the base coating in Example 1-1, the 133.3 parts of hollow particles A were changed to 26.7 parts, and the 50.0 parts of calcined kaolin were changed to 66.0 parts. Otherwise, the thermal recorder was obtained in the same manner as in Example 1-1.

[0199] (Examples 1-6)

[0200] In the preparation of the coating liquid for the base coating in Example 1-1, the 133.3 parts of hollow particles A were changed to 206.7 parts, and the 50.0 parts of calcined kaolin were changed to 39.0 parts. Otherwise, the thermal recorder was obtained in the same manner as in Example 1-1.

[0201] (Examples 1-7)

[0202] In the preparation of the coating liquid for the base coating in Example 1-1, the 133.3 parts of hollow particles A were changed to 240.0 parts, and the 50.0 parts of calcined kaolin were changed to 34.0 parts. Otherwise, the thermal recorder was obtained in the same manner as in Example 1-1.

[0203] (Examples 1-8)

[0204] In the fabrication of the thermal recorder in Example 1-1, the coating weight of the dried base layer was increased from 4.0 g / m². 2 Change to 8.0g / m 2 Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 1-1.

[0205] (Examples 1-9)

[0206] In the fabrication of the thermal recorder in Example 1-1, the coating weight of the dried base layer was increased from 4.0 g / m². 2 Change to 12.0g / m 2 Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 1-1.

[0207] (Examples 1-10)

[0208] In the fabrication of the thermal recorder in Example 1-1, the coating weight of the dried base layer was increased from 4.0 g / m². 2 Change to 2.0g / m 2 Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 1-1.

[0209] (Examples 1-11)

[0210] In the preparation of the coating liquid for the base layer in Example 1-1, latex A was changed to latex B, and the thermal recorder was obtained by operating in the same manner as in Example 1-1.

[0211] (Examples 1-12)

[0212] In the preparation of the coating liquid for the base layer in Example 1-1, latex A was changed to latex C. Otherwise, the same procedure as in Example 1-1 was followed to obtain a thermal recorder.

[0213] (Examples 1-13)

[0214] In the preparation of the colorimetric reagent dispersion in Example 1-1, 4-hydroxy-4'-n-propoxydiphenyl sulfone (Tomirac KN) was used instead of 4-hydroxy-4'-isopropoxydiphenyl sulfone (D8) manufactured by Nippon Soda Co., Ltd. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 1-1.

[0215] (Examples 1-14)

[0216] In the preparation of the colorimetric reagent dispersion in Example 1-1, N-[2-(3-phenylurea)phenyl]benzenesulfonamide (NKK-1304) was used instead of 4-hydroxy-4'-isopropoxydiphenyl sulfone (Nippon Soda Co., Ltd., D8). Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 1-1.

[0217] (Examples 1-15)

[0218] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles A were made into hollow particles C. Otherwise, the same operation as in Example 1-1 was performed to obtain a thermal recorder.

[0219] (Examples 1-16)

[0220] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles A were made into hollow particles D. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 1-1.

[0221] (Examples 1-17)

[0222] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles A were made into hollow particles E. Otherwise, the same operation as in Example 1-1 was performed to obtain a thermal recorder.

[0223] (Examples 1-18)

[0224] In the preparation of the colorimetric reagent dispersion in Examples 1-1, N-[2-(3-phenylureo)phenyl]benzenesulfonamide (NKK-1304) was used instead of 4-hydroxy-4'-isopropoxydiphenyl sulfone (D8, manufactured by Nippon Soda). Otherwise, the thermal recorder was obtained by operating in the same manner as in Examples 1-17.

[0225] (Comparative Example 1-1)

[0226] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles F153.8 parts were used instead of hollow particles A133.3 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 1-1.

[0227] (Comparative Examples 1-2)

[0228] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles A were made into hollow particles G. Otherwise, the same operation as in Example 1-1 was performed to obtain a thermal recorder.

[0229] (Comparative Examples 1-3)

[0230] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles A were made into hollow particles H. Otherwise, the same operation as in Example 1-1 was performed to obtain a thermal recorder.

[0231] (Comparative Examples 1-4)

[0232] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles A were made into hollow particles I. Otherwise, the same operation as in Example 1-1 was performed to obtain a thermal recorder.

[0233] (Comparative Examples 1-5)

[0234] In the preparation of the coating liquid for the base coating in Example 1-1, hollow particles A were made into hollow particles J. Otherwise, the same operation as in Example 1-1 was performed to obtain a thermal recorder.

[0235] The thermal recorders prepared in Examples 1-1 to 1-18 and Comparative Examples 1-1 to 1-5 above were evaluated as follows, and the results are shown in Table 1.

[0236] [Record Concentration]

[0237] A thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.) was used to record each thermal recorder with an applied energy of 0.17 mJ / point. The resulting print depth was measured using a Macbeth density meter (RD-914, manufactured by Macbeth Co., Ltd.) in visual mode. A higher value indicates a denser print. For practical purposes, a print density of 1.00 or higher is required; therefore, a density of 1.00 or higher is considered acceptable.

[0238] [Print quality]

[0239] Barcodes were recorded using a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.). The quality of the recorded images was visually observed and evaluated according to the following criteria. ◎, ○, and △ were marked as acceptable, and × was marked as unacceptable.

[0240] ◎: Absolutely no white spots, missing barcodes, or thickened areas in the image; exceptionally good.

[0241] ○: There are no white spots in the image, missing or thickened barcodes, and no problems.

[0242] △: There are almost no white spots in the image quality, missing or thickened barcodes, and there are no practical problems.

[0243] ×: The images have white gaps, and the barcodes are missing or thickened, which poses a problem in practical use.

[0244] [Heat-resistant background gray fog]

[0245] Each thermal recorder was placed at 80°C for 24 hours, and the reflectance concentration of the white paper portion was measured using the aforementioned macrobes concentration meter. If the measured value is 0.20 or less, there is no problem with its use; if it is 0.10 or less, it is even more preferable.

[0246] Table 1

[0247]

[0248] (Example 2-1)

[0249] (1) Preparation of coating liquid for base coating

[0250] A coating solution for a base coat was obtained by mixing and stirring 106.7 parts of hollow particles A, 50 parts of inorganic pigment A, 36.5 parts of dense plastic particles (Grossdale 130S, 52% solid content, manufactured by Mitsui Chemicals), 10 parts of latex A, 7.5 parts of a 20% solution of oxidized starch, 3.5 parts of carboxymethyl cellulose (trade name: Serogen AG Gam, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), and 75.0 parts of water.

[0251] (2) Preparation of colorless dye dispersion (A' solution)

[0252] A colorless dye dispersion (A' solution) was obtained by mixing 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%), 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and pulverizing the mixture using a sand mill (manufactured by Imex Co., Ltd.) until the median particle size obtained by laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) was 0.5 μm.

[0253] (3) Preparation of colorimetric reagent dispersion (B' solution)

[0254] 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.) until the median particle size obtained by laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) was 1.0 μm, thus obtaining a colorimetric reagent dispersion (B' solution).

[0255] (4) Preparation of sensitizer dispersion (C' solution)

[0256] 40 parts of di-p-methylbenzyl oxalate (trade name: HS-3520, manufactured by DIC), 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.) until the median particle size obtained by laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) was 1.0 μm, thus obtaining a sensitizer dispersion (C' liquid).

[0257] (5) Preparation of coating solution for thermal recording layer

[0258] A coating solution for thermal recording layers was obtained by mixing and stirring 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 hydroxypropyl methylcellulose, 46 parts of a 10% aqueous solution of fully saponified polyvinyl alcohol (trade name: PVA110, degree of saponification: 99 mol%, average degree of polymerization: 1000, manufactured by Kurare Co., Ltd.), 9.4 parts of butadiene copolymer latex (trade name: L-1571, manufactured by Asahi Kasei Co., Ltd., solid content concentration 48%), 25.4 parts of light calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd.), 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.

[0259] (6) Preparation of coating liquid for protective layer

[0260] A protective coating liquid was obtained by mixing and stirring 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%), 19 parts of kaolin (trade name: HYDRAGLOSS90, KaMinLLC), 35 parts of aluminum hydroxide (trade name: Hydralight H-42M, Showa Denko), 4 parts of silica (trade name: Mizusawa Kagaku), 2.5 parts of polyethylene wax (trade name: Kemipar W-400, Mitsui Chemicals, solid content concentration 40%), and 114.5 parts of water.

[0261] (7) Fabrication of thermal recording devices

[0262] Weight per unit area: 60g / m² 2 On one side of high-quality paper, the base coating liquid, the thermal recording layer coating liquid, and the protective recording layer coating liquid are applied at a drying amount of 4.0 g / m². 2 4.0g / m 2 2.0g / m 2 The thermal recording body was obtained by coating and drying the substrate in sequence, forming a base layer, a thermal recording layer, and a protective layer, and then smoothing the surface with a supercalender.

[0263] (Example 2-2)

[0264] In the preparation of the coating liquid for the base coating in Example 2-1, 106.7 parts of hollow particles A were changed to 106.7 parts of hollow particles B. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0265] (Examples 2-3)

[0266] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particle A106.7 parts were changed to 40.0 parts, and the plastic dense particle (Grossdale 130S, solid content concentration 52%, manufactured by Mitsui Chemicals) 36.5 parts were changed to 55.8 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0267] (Examples 2-4)

[0268] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particle A106.7 parts were changed to 186.7 parts, and the plastic dense particle (Grossdale 130S, solid content concentration 52%, manufactured by Mitsui Chemicals) 36.5 parts were changed to 13.5 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0269] (Examples 2-5)

[0270] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particles A106.7 parts were changed to 26.7 parts, and the plastic dense particles (Grossdale 130S, solid content concentration 52%, manufactured by Mitsui Chemicals) 36.5 parts were changed to 59.6 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0271] (Examples 2-6)

[0272] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particles A106.7 parts were changed to 213.3 parts, and the plastic dense particles (Grossdale 130S, solid content concentration 52%, manufactured by Mitsui Chemicals) 36.5 parts were changed to 5.8 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0273] (Examples 2-7)

[0274] In the fabrication of the thermal recorder in Example 2-1, the coating weight of the dried base layer was increased from 4.0 g / m². 2 Change to 12.0g / m 2 Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0275] (Examples 2-8)

[0276] In the fabrication of the thermal recorder in Example 2-1, the coating weight of the dried base layer was increased from 4.0 g / m². 2 Change to 8.0g / m 2 Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0277] (Examples 2-9)

[0278] In the fabrication of the thermal recorder in Example 2-1, the coating weight of the dried base layer was increased from 4.0 g / m². 2 Change to 2.0g / m 2 Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0279] (Example 2-10)

[0280] In the preparation of the coating liquid for the base layer in Example 2-1, 50 parts of inorganic pigment A were changed to 30 parts, and 36.5 parts of plastic dense particles (Grossdale 130S, solid content concentration 52%, manufactured by Mitsui Chemicals) were changed to 75.0 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0281] (Example 2-11)

[0282] In the preparation of the coating liquid for the base layer in Example 2-1, 50 parts of inorganic pigment A were changed to 65 parts, and 36.5 parts of plastic dense particles (Grossdale 130S, solid content concentration 52%, manufactured by Mitsui Chemicals) were changed to 7.7 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0283] (Example 2-12)

[0284] In the preparation of the coating liquid for the base layer in Example 2-1, 50 parts of inorganic pigment A were changed to 10 parts, and 36.5 parts of plastic dense particles (Grossdale 130S, solid content concentration 52%, manufactured by Mitsui Chemicals) were changed to 113.5 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0285] (Example 2-13)

[0286] In the preparation of the coating liquid for the base layer in Example 2-1, 50 parts of inorganic pigment A were replaced with 50 parts of inorganic pigment B. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0287] (Example 2-14)

[0288] In the preparation of the coating liquid for the base layer in Example 2-1, 50 parts of inorganic pigment A were changed to 50 parts of inorganic pigment C. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0289] (Example 2-15)

[0290] In the preparation of the coating liquid for the base layer in Example 2-1, 50 parts of inorganic pigment A were changed to 50 parts of inorganic pigment D. Otherwise, the same procedure as in Example 2-1 was followed to obtain a thermal recorder.

[0291] (Example 2-16)

[0292] In the preparation of the coating liquid for the base coating in Example 2-1, 10 parts of latex A were changed to 10 parts of latex B. Otherwise, the same procedure as in Example 2-1 was followed to obtain a thermal recorder.

[0293] (Example 2-17)

[0294] In the preparation of the coating liquid for the base coating in Example 2-1, 10 parts of latex A were changed to 10 parts of latex C. Otherwise, the same procedure as in Example 2-1 was followed to obtain a thermal recorder.

[0295] (Example 2-18)

[0296] In the preparation of the colorimetric reagent dispersion in Example 2-1, 4-hydroxyphenyl (4'-n-propoxyphenyl) sulfone (Tomirac KN, manufactured by Mitsubishi Kemikal Co., Ltd.) was used instead of 4-hydroxy-4'-isopropoxydiphenyl sulfone (D8, manufactured by Nippon Soda Co., Ltd.). Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0297] (Example 2-19)

[0298] In the preparation of the colorimetric reagent dispersion in Example 2-1, 2-phenylsulfonamide-N,N'-diphenylurea (NKK-1304) was used instead of 4-hydroxy-4'-isopropoxydiphenyl sulfone (Nippon Soda Co., Ltd., D8). Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0299] (Example 2-20)

[0300] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particle A106.7 parts was changed to hollow particle C106.7 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0301] (Comparative Example 2-1)

[0302] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particle A106.7 parts were changed to hollow particle H106.7 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0303] (Comparative Example 2-2)

[0304] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particle A106.7 parts were changed to hollow particle I106.7 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0305] (Comparative Examples 2-3)

[0306] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particles A106.7 parts were changed to hollow particles J106.7 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0307] (Comparative Examples 2-4)

[0308] In the preparation of the coating liquid for the base coating in Example 2-1, the hollow particles A106.7 parts were changed to hollow particles F123.1 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0309] (Comparative Examples 2-5)

[0310] In the preparation of the coating liquid for the base layer in Example 2-1, the hollow particle A106.7 parts were changed to hollow particle G106.7 parts. Otherwise, the thermal recorder was obtained by operating in the same manner as in Example 2-1.

[0311] The thermal recorders prepared in Examples 2-1 to 2-20 and Comparative Examples 2-1 to 2-5 above were evaluated as follows, and the results are shown in Table 2.

[0312] [Midtone recording density]

[0313] Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Denki), each thermal recorder was recorded in the mid-tone energy region at a printing speed of 4 inches / second and an applied energy of 0.16 mJ / dot. The resulting printed area was measured in visual mode using a Maxbes density meter (RD-914, manufactured by Maxbes). The higher the value, the denser the printing. In practical terms, a recording density of 1.00 or higher is required, and 1.20 or higher is preferred.

[0314] [Image Quality]

[0315] Using a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.), barcodes were recorded at a printing speed of 75 mm / second and a printing density of 6. The quality of the recorded images was visually observed and evaluated according to the following criteria.

[0316] ◎: Absolutely no white cast or barcode thickening in the image, exceptionally excellent.

[0317] ○: There is no white showing in the image quality or thickening of the barcode, so there is no problem.

[0318] △: There is almost no white showing in the image quality and the barcode is thickened, so there are no practical problems.

[0319] ×: The white space in the image and the thickening of the barcode pose practical problems.

[0320] [Coating surface strength]

[0321] For each thermal recorder, the coating strength was evaluated using a printability tester (manufactured by Kokubo Seiju) by conducting a dry pick test using 0.5g of SD50 Red BT-13 paper test ink (manufactured by T&K TOKA).

[0322] ◎: No coating peeling was observed.

[0323] ○: Sometimes slight peeling of the coating is observed.

[0324] △: Although slight peeling of the coating was observed, there were no problems in actual use.

[0325] ×: Numerous instances of coating peeling have been observed, posing a problem in practical use.

[0326]

Claims

1. A heat-sensitive recording body, characterized by comprising: comprises: a primer layer formed on one side of a support, and a heat-sensitive recording layer formed on the primer layer, wherein the heat-sensitive recording layer contains a leuco dye and a color developer, the primer layer contains hollow particles and a binding resin, the maximum particle diameter of the hollow particles is 13.5 to 25 μm, the particle diameter of 50 vol% of the hollow particles is 7.5 to 15 μm, the ratio D100 / D50 is 1.8 to 3.0, D100 representing the maximum particle diameter of the hollow particles and D50 representing the particle diameter of 50 vol% of the hollow particles, the vol% of the hollow particles having a particle diameter of 2.0 μm or less is 1% or less.

2. The heat-sensitive recording body according to claim 1, wherein the content of the hollow particles is 5 to 40 mass% with respect to the total solid content of the primer layer.

3. The heat-sensitive recording body according to claim 1, wherein the hollow rate of the hollow particles is 80 to 98%.

4. The heat-sensitive recording body according to any one of claims 1 to 3, characterized by The dried coating amount of the base coat layer is 2.0 to 10 g / m 2 .

5. The heat-sensitive recording material according to any one of claims 1 to 3, characterized by the color developer contains 4-hydroxy-4'-n-propoxydiphenylsulfone or N-[2-(3-phenylureido)phenyl]benzenesulfonamide.

6. The heat-sensitive recording body according to claim 1, wherein the primer layer further contains an inorganic pigment.

7. The heat-sensitive recording body according to claim 6, wherein the oil absorption amount of the inorganic pigment is 90 ml / 100 g or more as measured according to the measurement method of Japanese Industrial Standard K-5101.

8. The heat-sensitive recording body according to claim 6, wherein the content of the inorganic pigment is 20 to 70 mass% with respect to the total solid content of the primer layer.

9. The heat-sensitive recording body according to claim 8, wherein the content of the inorganic pigment is 40 to 60 mass% with respect to the total solid content of the primer layer.

10. The heat-sensitive recording body according to any one of claims 6 to 9, characterized in that, it contains at least one of calcined kaolin and silica as the inorganic pigment.

11. The heat-sensitive recording body according to any one of claims 1 to 3, characterized in that it contains latex as the binding resin.

12. The heat-sensitive recording material according to any one of claims 1 to 3, characterized by it contains a binding resin having a glass transition temperature of -10°C or lower as the binding resin.

13. The heat-sensitive recording material according to any one of claims 1 to 3, characterized in that it contains a binding resin having a glass transition temperature of -30°C or lower as the binding resin.

14. The heat-sensitive recording material according to any one of claims 1 to 3, characterized by it contains at least a styrene-butadiene latex as the binding resin.

Images