JP2024046389A - heat sensitive recording material - Google Patents

Abstract

[Problem] To provide a thermal recording medium that has high sensitivity, excellent heat resistance to background fogging, and excellent plasticizer resistance in the printed portion. [Solution] A thermal recording medium in which a thermal recording layer containing a leuco dye, a color developer, and an adhesive on a support contains a compound represented by the following general formula (1): TIFF2024046389000009.tif51170 (wherein R1 to R5 are the same or different and represent a hydrogen atom or the like) as a first color developer, and 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide or N-[2-(3-phenylureido)phenyl]benzenesulfonamide as a second color developer. [Selected Figure] None

Description

The present invention relates to a thermal recording medium.

2. Description of the Related Art Thermosensitive recording materials that record colored images by utilizing a heated coloring reaction between colorless or light-colored leuco dyes and phenols or organic acids have been widely put into practical use. Such a thermal recording medium forms a colored image simply by heating, so it has advantages such as a compact recording device, easy maintenance of the recording device, and low noise generation. Therefore, thermal recording materials are widely used as various information recording materials in issuing machines such as label printers, automatic ticket vending machines, CD/ATMs, order slip output machines in restaurants, data output machines in scientific research equipment, etc. There is.

Generally, color developers with phenolic hydroxyl groups have disadvantages such as poor thermal response and poor water resistance of printed areas, and phenolic compounds such as bisphenol A have endocrine problems. Therefore, there is a growing demand, especially in Europe, for thermal recording paper that uses non-phenolic color developers, and various new non-phenolic color developers are being developed.

For example, Patent Document 1 proposes a thermal recording medium that uses 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, a type of non-phenolic color developer, as the color developer, and reports that the printed area has excellent water resistance and the background exhibits high stability against heat.

In addition, Patent Document 2 reports that a thermal recording medium using a combination of the 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate and a urea urethane compound represented by the following general formula (3) as a developer has excellent print running properties.

However, in Patent Documents 1 and 2, heat-resistant background fogging of such color developers is evaluated only up to 90°C. Recent market needs require higher heat resistance, and 90°C heat resistance is insufficient, and improvements are required.

Patent No. 6529197 Patent No. 7072130

The main object of the present invention is to provide a heat-sensitive recording material that is highly sensitive, has excellent heat resistance to background fog, and has excellent plasticizer resistance in the printed area.

As a result of intensive studies to solve the above object, the present inventors have found that the above problem can be solved by combining a compound represented by the following general formula (1) and a specific color developer. They discovered this and completed the present invention. That is, the present invention relates to the following heat-sensitive recording material.

Item 1: In a heat-sensitive recording material having on a support at least an undercoat layer containing hollow particles and an adhesive, and a heat-sensitive recording layer containing a leuco dye, a color developer, and an adhesive in this order, the first layer of the heat-sensitive recording layer 1 The following general formula (1) as a color developer:

（式中、Ｒ^１～Ｒ^５は、同一又は異なって、水素原子、ハロゲン原子、ニトロ基、アミノ基、アルキル基、アルコキシ基、アリールオキシ基、アルキルカルボニルオキシ基、アリールカルボニルオキシ基、アルキルカルボニルアミノ基、アリールカルボニルアミノ基、アルキルスルホニルアミノ基、アリールスルホニルアミノ基、モノアルキルアミノ基、ジアルキルアミノ基又はアリールアミノ基を表す。）で表される化合物を含有し、第２顕色剤として５－（Ｎ－３－メチルフェニル－スルホンアミド）－Ｎ’，Ｎ’’－ビス－（３－メチルフェニル）－イソフタル酸ジアミド又はＮ－［２－（３－フェニルウレイド）フェニル］ベンゼンスルホンアミドを含有し、第２顕色剤が第１顕色剤１質量部に対して０．４～２．５質量部含まれることを特徴とする感熱記録体。
項２：前記一般式（１）で表される化合物が３－［（フェニルカルバモイル）アミノ］フェニル－４－メチルベンゼンスルホナート、２－［（フェニルカルバモイル）アミノ］フェニル－４－メチルベンゼンスルホナート、及び４－［（フェニルカルバモイル）アミノ］フェニル－４－メチルベンゼンスルホナートからなる群より選ばれる少なくとも１種である、項１に記載の感熱記録体。
項３：前記一般式（１）で表される化合物が３－［（フェニルカルバモイル）アミノ］フェニル－４－メチルベンゼンスルホナートである、項１に記載の感熱記録体。
項４：前記第２顕色剤が、前記第１顕色剤１質量部に対して０．９～２．５質量部含まれる、項１～３のいずれか１項に記載の感熱記録体。
項５：前記第２顕色剤が５－（Ｎ－３－メチルフェニル－スルホンアミド）－Ｎ’，Ｎ’’－ビス－（３－メチルフェニル）－イソフタル酸ジアミドである、項１～４のいずれか１項に記載の感熱記録体。
項６：前記感熱記録層が、テレフタル酸ジメチル、１，２－ジ（３－メチルフェノキシ）エタン、ステアリン酸アミド、及びジフェニルスルホンから選ばれる少なくとも１種の増感剤を含有する、項１～５のいずれか１項に記載の感熱記録体。
項７：前記感熱記録層が、テレフタル酸ジメチル及び１，２－ジ（３－メチルフェノキシ）エタンから選ばれる少なくとも１種の増感剤を含有する、項１～６のいずれか１項に記載の感熱記録体。
項８：前記中空粒子は、最大粒子径（Ｄ１００）が１０～３０μｍであり、平均粒子径（Ｄ５０）が４．０～１５μｍであり、最大粒子径（Ｄ１００）と平均粒子径（Ｄ５０）との比Ｄ１００／Ｄ５０が１．８～３．０であり、粒子径２.０μｍ以下の体積％が１％以下である、項１～７のいずれか１項に記載の感熱記録体。
項９：前記中空粒子の中空率が８０～９８％である、項１～８のいずれか１項に記載の感熱記録体。
項１０：前記下塗り層の接着剤が、ガラス転移温度が－１０℃以下である結着剤樹脂を含む、項１～９のいずれか１項に記載の感熱記録体。
項１１：前記下塗り層の接着剤が、ガラス転移温度が－３０℃以下である結着剤樹脂を含む、項１～１０のいずれか１項に記載の感熱記録体。
項１２：更に支持体の少なくとも一方面に粘着層を有する、項１～１１のいずれか１項に記載の感熱記録体。

(In the formula, R ¹ to R ⁵ are the same or different, hydrogen atom, halogen atom, nitro group, amino group, alkyl group, alkoxy group, aryloxy group, alkylcarbonyloxy group, arylcarbonyloxy group, alkylcarbonyl represents an amino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group. -(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide or N-[2-(3-phenylureido)phenyl]benzenesulfonamide A heat-sensitive recording material containing 0.4 to 2.5 parts by mass of the second color developer per 1 part by mass of the first color developer.
Item 2: The compound represented by the general formula (1) is 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, 2-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate , and 4-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, the thermosensitive recording material according to item 1.
Item 3: The heat-sensitive recording material according to item 1, wherein the compound represented by the general formula (1) is 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate.
Item 4: The heat-sensitive recording material according to any one of Items 1 to 3, wherein the second color developer is contained in an amount of 0.9 to 2.5 parts by mass per 1 part by weight of the first color developer. .
Item 5: Items 1 to 4, wherein the second color developer is 5-(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. The thermosensitive recording material according to any one of the above.
Item 6: Items 1 to 6, wherein the heat-sensitive recording layer contains at least one sensitizer selected from dimethyl terephthalate, 1,2-di(3-methylphenoxy)ethane, stearamide, and diphenylsulfone. 5. The thermosensitive recording material according to any one of Item 5.
Item 7: The heat-sensitive recording layer contains at least one sensitizer selected from dimethyl terephthalate and 1,2-di(3-methylphenoxy)ethane, according to any one of Items 1 to 6. heat-sensitive recording material.
Item 8: The hollow particles have a maximum particle diameter (D100) of 10 to 30 μm, an average particle diameter (D50) of 4.0 to 15 μm, and a maximum particle diameter (D100) and an average particle diameter (D50) of The heat-sensitive recording material according to any one of Items 1 to 7, wherein the ratio D100/D50 is 1.8 to 3.0, and the volume % of particles with a particle size of 2.0 μm or less is 1% or less.
Item 9: The heat-sensitive recording material according to any one of Items 1 to 8, wherein the hollow particles have a hollowness ratio of 80 to 98%.
Item 10: The thermosensitive recording material according to any one of Items 1 to 9, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of -10° C. or lower.
Item 11: The thermosensitive recording material according to any one of Items 1 to 10, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of -30° C. or lower.
Item 12: The heat-sensitive recording material according to any one of Items 1 to 11, further comprising an adhesive layer on at least one side of the support.

The thermal recording medium of the present invention has high sensitivity, excellent resistance to heat-induced background fogging, and excellent resistance to plasticizers in the printed area.

In this specification, the expression "comprise" includes the concepts of "comprise," "consist essentially of," and "consist only of."

In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits.

Latex in the present invention includes the state of a gel or a dried film formed by drying a dispersion medium.

The present invention relates to a thermosensitive recording medium having, on a support, at least an undercoat layer containing hollow particles and an adhesive, and a thermosensitive recording layer containing a leuco dye, a developer and an adhesive, in that order, and a compound represented by the following general formula (1) as a first developer in the thermosensitive recording layer:

（式中、Ｒ^１～Ｒ^５は、同一又は異なって、水素原子、ハロゲン原子、ニトロ基、アミノ基、アルキル基、アルコキシ基、アリールオキシ基、アルキルカルボニルオキシ基、アリールカルボニルオキシ基、アルキルカルボニルアミノ基、アリールカルボニルアミノ基、アルキルスルホニルアミノ基、アリールスルホニルアミノ基、モノアルキルアミノ基、ジアルキルアミノ基又はアリールアミノ基を表す。）で表される化合物を含有し、第２顕色剤として５－（Ｎ－３－メチルフェニル－スルホンアミド）－Ｎ’，Ｎ’’－ビス－（３－メチルフェニル）－イソフタル酸ジアミド又はＮ－［２－（３－フェニルウレイド）フェニル］ベンゼンスルホンアミドを含有し、第２顕色剤が第１顕色剤１質量部に対して０．４～２．５質量部含まれることを特徴とする。

(In the formula, R ¹ to R ⁵ are the same or different, hydrogen atom, halogen atom, nitro group, amino group, alkyl group, alkoxy group, aryloxy group, alkylcarbonyloxy group, arylcarbonyloxy group, alkylcarbonyl represents an amino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group. -(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide or N-[2-(3-phenylureido)phenyl]benzenesulfonamide 0.4 to 2.5 parts by mass of the second color developer per 1 part by mass of the first color developer.

[Support]
The support in the present invention is not particularly limited in type, shape, size, etc., and can be appropriately selected from, for example, high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassine paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, nonwoven fabric, synthetic resin film, and various transparent supports. The thickness of the support is not particularly limited, and is usually about 20 to 200 μm. The density of the support is also not particularly limited, and is preferably about 0.60 to 0.85 g/ ^cm3 .

[Undercoat layer]
The heat-sensitive recording material of the present invention has an undercoat layer between the support and the heat-sensitive recording layer. The undercoat layer contains hollow particles and an adhesive.

(Hollow particles)
The hollow particles are preferably made of an organic resin from the viewpoint of improving cushioning properties. The undercoat layer, which has high heat insulating properties due to the inclusion of hollow particles, can prevent the diffusion of heat applied to the thermal recording layer and can increase the sensitivity as a thermal recording medium.

Hollow particles made of organic resin can be divided into foamed types and non-foamed types depending on the manufacturing method. Of these two types, expanded type hollow particles generally have a larger average particle diameter and higher hollowness ratio than non-expanded type hollow particles. Therefore, foamed hollow particles can provide better sensitivity and image quality than non-foamed hollow particles.

Non-foaming type hollow particles are made by polymerizing seeds in a solution, then polymerizing another resin to enclose the seeds, and then removing the seeds by swelling and dissolving them to form a cavity inside. It can be manufactured by An alkaline aqueous solution or the like is used to swell and dissolve the internal seeds and remove them. Non-expandable hollow particles with a relatively large average particle diameter can also be obtained by subjecting core-shell particles, in which a core particle with alkali swelling property is coated with a shell layer without alkali swelling property, to an alkali swelling treatment. .

Foamed hollow particles can be produced by creating particles with a volatile liquid trapped inside the resin, softening the resin by heating, and vaporizing and expanding the liquid inside the particles.

The foamed hollow particles have a large hollow ratio and high thermal insulation due to the internal liquid being heated and expanded during the manufacturing process, which can increase the sensitivity of the thermal recording medium and improve the recording density. Improving sensitivity is particularly important when coloring a mid-tone region where the thermal energy applied to the thermal recording layer is small. In addition, if the thermal recording layer is formed via a highly insulating undercoat layer, the diffusion of heat applied to the thermal recording layer can be prevented, resulting in excellent image uniformity and improved image quality. Therefore, in this embodiment, it is preferable to use foamed hollow particles that are excellent at improving the thermal insulation of the undercoat layer.

Resins that can be used for the expanded type hollow particles include thermoplastic resins such as styrene-acrylic resin, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyacetal resin, chlorinated polyether resin, polyvinyl chloride resin, polyvinylidene chloride resin, acrylic resin (e.g., acrylic resin containing acrylonitrile as a component), styrene resin, vinylidene chloride resin, and copolymer resin mainly composed of polyvinylidene chloride and acrylonitrile. Typical gases contained inside the expanded type hollow particles include propane, butane, isobutane, and air. Among the various resins mentioned above, acrylonitrile resin and copolymer resin mainly composed of polyvinylidene chloride and acrylonitrile are preferred as the resins used for the hollow particles from the viewpoint of the strength to maintain the shape of the expanded particles.

The maximum particle diameter of the hollow particles in the present invention is preferably 10 to 30 μm, more preferably 10 to 25 μm. The maximum particle diameter is also referred to as D100. If the maximum particle diameter of the hollow particles is 10 μm or more, the cushioning properties of the undercoat layer will improve, so the adhesion of the heat-sensitive recording material to the thermal head during printing will improve, and a heat-sensitive recording material with high image quality can be obtained. . This high image quality can bring about an improvement in the recording density in halftones where colors are developed with lower energy than that which provides the maximum recording density (Dmax). On the other hand, if the maximum particle diameter of the hollow particles is 30 μm or less, the smoothness of the undercoat layer will improve, so the heat-sensitive recording layer provided through the undercoat layer can be made uniform, and white spots in the image are less likely to occur in the heat-sensitive recording. You get a body.

The average particle diameter of the hollow particles in the present invention is preferably 4.0 to 15 μm, more preferably 4.5 to 15 μm. Here, the average particle diameter is the diameter at which the volume occupied by the larger particle and the smaller particle is equal when the particle diameter is divided into two, that is, the median diameter which is the particle diameter with a 50 volume % frequency, and is also called D50. If the average particle diameter of the hollow particles is 4.0 μm or more, the cushioning property of the undercoat layer is improved, so that the adhesion of the thermal recording medium to the thermal head during printing is improved, and a thermal recording medium with high image quality can be obtained. This high image quality can bring about an improvement in the recording density in intermediate tones that are developed with lower energy than that which gives the maximum recording density (Dmax). On the other hand, if the average particle diameter of the hollow particles is 15 μm or less, the smoothness of the undercoat layer is improved, so that the thermal recording layer provided through the undercoat layer can be made uniform, and a thermal recording medium with less white gaps in the image can be obtained.

The maximum particle size (D100) and average particle size (D50) of hollow particles can be measured using a laser diffraction particle size distribution analyzer. Alternatively, particle sizes can be measured from particle images (SEM images) using an electron microscope and expressed as the average value of 10 particles.

The ratio D100/D50 of the maximum particle diameter (D100) to the average particle diameter (D50) of hollow particles is an index showing the degree of particle size distribution. This ratio D100/D50 is preferably 1.8 to 3.0, more preferably 2.0 to 2.8. When the D100/D50 of the hollow particles is 1.8 or more, the hollow particles are sufficiently expanded, the maximum particle diameter is sufficiently large, the hollow ratio is high, and the heat insulation of the undercoat layer can be improved. On the other hand, when the D100/D50 of the hollow particles is 3.0 or less, the size of the hollow particles is uniform, so the smoothness of the undercoat layer is improved and white spots in the image can be suppressed.

In the particle size distribution determined by a laser diffraction particle size analyzer, the volume percentage of hollow particles with a particle diameter of 2.0 μm or less is preferably 1% or less. The volume percentage of hollow particles with a particle diameter of 2.0 μm or less is preferably 0.5% or less, and more preferably none are present. Hollow particles with a particle diameter of 2 μm or less are too small to provide sufficient hollow areas, and therefore are thought to contribute very little to heat insulation. By keeping the volume percentage of hollow particles with a particle diameter of 2 μm or less in the undercoat layer to 1% or less, it is possible to improve recording density, image quality, etc.

The hollow particles preferably have a hollowness ratio of 80 to 98%, more preferably 90 to 98%. When the hollowness ratio of the hollow particles is 80% or more, high heat insulation properties can be imparted to the undercoat layer containing the hollow particles. On the other hand, when the hollowness ratio of the hollow particles is 98% or less, the strength of the film surrounding the hollow portion is improved, so that the hollow particles do not collapse even when forming the undercoat layer.

The hollow ratio of the hollow particles is determined as follows from the true specific gravity value measured by the IPA method.
(1) Pretreatment of the sample: Dry the sample at 60°C overnight to prepare the sample.
(2) Reagents: Isopropyl alcohol (IPA: first-grade reagent)
(3) Measurement method: Accurately weigh the volumetric flask (W1).
-Put about 0.5 g of the dried sample into a measuring flask and weigh it accurately (W2).
Add about 50 mg of IPA and shake thoroughly to completely remove any air outside the capsule.
Add IPA up to the mark and evaluate (W3).
- As a blank, add only IPA to the measuring flask up to the mark and measure carefully (W4).
(4) Calculation of true specific gravity True specific gravity = {(W2 - W1) x ((W4 - W1) / 100)} / {(W4 - W1) - (W3 - W2)}
(5) Calculation of hollow ratio Hollow ratio (%) = {1-1/(1.1/true specific gravity)} x 100

The hollow ratio can also be determined by the following formula (d ³ /D ³ )×100, where d is the inner diameter of the hollow particle, and D is the outer diameter of the hollow particle.

Since the hollow particles in the present invention have a relatively large particle size, their content in the undercoat layer can be reduced. The content of hollow particles is preferably 5 to 40% by mass, more preferably 5 to 35% by mass, based on the total solid content of the undercoat layer. When the content of hollow particles is 5% by mass or more, the heat insulation properties of the undercoat layer can be improved. On the other hand, when the content of hollow particles is 40% by mass or less, problems are unlikely to occur in terms of coatability, etc., it is easy to form a uniform undercoat layer, and recording density can be improved. Further, the strength of the coating film of the undercoat layer can be increased.

(glue)
Examples of adhesives include polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester, etc. Water-soluble polymer materials such as polymers, acrylamide-acrylic acid ester-methacrylic acid ester copolymers, styrene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, casein, gelatin, and derivatives thereof; Also, emulsions such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, or styrene-butadiene copolymer, styrene. Examples include latex of water-insoluble polymers such as -butadiene-acrylic copolymers. Among these, it is preferable to use an adhesive containing latex. The content of the adhesive can be selected from a wide range, but generally it is preferably about 20 to 70% by mass, more preferably about 25 to 60% by mass of the total solid content of the undercoat layer.

Preferably, the adhesive contains a binder resin having a glass transition temperature (Tg) of -10°C or lower. Since the glass transition temperature is −10° C. or lower, image quality can be improved even in a low energy range. The glass transition temperature is more preferably −30° C. or lower because image quality can be further improved in a low energy range. On the other hand, temperatures below -50°C are unfavorable as stickiness occurs, so temperatures above -40°C are preferred.

The undercoat layer can contain an oil-absorbing pigment having an oil absorption amount of 70 ml/100 g or more, particularly about 80 to 150 ml/100 g. Here, the above-mentioned oil absorption amount is a value determined according to the method of JIS K 5101.

Various kinds of oil-absorbing pigments can be used, and specific examples include inorganic pigments such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle diameter of the primary particles of these oil-absorbing pigments is preferably about 0.01 to 5 μm, particularly about 0.02 to 3 μm. The amount of the oil-absorbing pigment to be used can be selected from a wide range, but is generally preferably about 20 to 60% by weight, more preferably about 25 to 55% by weight, based on the total solid amount of the undercoat layer.

The undercoat layer is formed by applying, for example, a coating solution for the undercoat layer prepared by mixing hollow particles, an adhesive, an oil-absorbing pigment, an auxiliary agent, etc. in water as a medium, and then drying the coating solution on the support. is formed. The coating amount of the coating liquid for the undercoat layer is not particularly limited, but is preferably about 2 to 20 g/m ² in terms of dry mass, more preferably about 2 to 12 g/m ² .

Examples of auxiliary agents contained in the coating solution for the undercoat layer include dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, fatty acid metal salts, zinc stearate, calcium stearate, and polyethylene. Examples include waxes such as wax, carnauba wax, paraffin wax, and ester wax, water-resistant agents such as hydrazide compounds, boric acid, dialdehyde starch, glyoxylates, and epoxy compounds, antifoaming agents, colored dyes, and fluorescent dyes.

[Thermal recording layer]
(Leuco dye)
The heat-sensitive recording layer of the heat-sensitive recording medium of the present invention may contain various known colorless or light-colored leuco dyes. Specific examples of such leuco dyes are given below.

Specific examples of leuco dyes include 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylamino Phenyl)-6-dimethylaminophthalide, blue coloring dyes such as fluoran, 3-(N-ethyl-Np-tolyl)amino-7-N-methylanilinofluorane, 3-diethylamino-7-ani Green dyes such as linofluoran, 3-diethylamino-7-dibenzylaminofluoran, rhodamine B-anilinolactam, 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3-cyclohexylamino- Red coloring dyes such as 6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-chlorofluoran, 3-(N-ethyl-N-isoamyl)amino-6 -Methyl-7-anilinofluorane, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3 -di(n-butyl)amino-6-methyl-7-anilinofluorane, 3-di(n-pentyl)amino-6-methyl-7-anilinofluorane, 3-(N-ethyl-N- isoamylamino)-6-methyl-7-alininofluorane, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-(N-isoamyl-N-ethylamino)-7-(o- chloroanilino)fluorane, 3-(N-ethyl-N-2-tetrahydrofurfurylamino)-6-methyl-7-anilinofluorane, 3-(Nn-hexyl-N-ethylamino)-6-methyl -7-anilinofluorane, 3-[N-(3-ethoxypropyl)-N-ethylamino]-6-methyl-7-anilinofluorane, 3-[N-(3-ethoxypropyl)-N -Methylamino]-6-methyl-7-anilinofluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-di(n-butylamino)-7-(2-chloroanilino)fluoran, 4, 4'-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-trichlorophenylleucoauramine, 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-isoamyl-N-ethylamino)-6-methyl-7-anilinofluoran Oran, 3-dibutylamino-7-chloroanilinofluorane, 3-diethylamino-7-(o-chlorophenylamino)fluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane Oran, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluorane, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilino Fluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3 -piperidino-6-methyl-7-anilinofluorane, 2,2-bis{4-[6'-(N-cyclohexyl-N-methylamino)-3'-methylspiro[phthalide-3,9'-xanthene -2'-ylamino]phenyl}propane, black coloring dyes such as 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluorane, 3,3-bis[1-(4-methoxyphenyl)- 1-(4-dimethylaminophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrroli) dinophenyl)ethylene-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, 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, etc. in the near-infrared region Examples include dyes having absorption wavelengths. Of course, the compounds are not limited to these, and two or more kinds of compounds can be used in combination if necessary.

The content of the leuco dye is not particularly limited, and is preferably about 3 to 30% by mass, more preferably about 5 to 25% by mass, and even more preferably about 7 to 20% by mass, of the total solid content of the thermal recording layer. By making it 3% by mass or more, the color development ability can be improved and the recording density can be improved. By making it 30% by mass or less, the heat resistance can be improved.

(color developer)
In the present invention, the color developer includes a first color developer and a second color developer, and the first color developer contains a compound represented by the above general formula (1).

Examples of the halogen atom for R ¹ to R ⁵ include a fluorine atom, a chlorine atom, and a bromine atom, with a fluorine atom and a chlorine atom being preferred.

The alkyl group may be linear, branched, or cyclic, and is preferably a linear or branched alkyl group, and more preferably a linear alkyl group. Usually, the alkyl group has 1 to 12 carbon atoms, preferably has 1 to 8 carbon atoms, more preferably has 1 to 6 carbon atoms, and even more preferably has 1 to 4 carbon atoms.

The alkoxy group may be linear, branched, or cyclic, and is preferably a linear or branched alkoxy group, and more preferably a linear alkoxy group. Usually, the alkoxy group has 1 to 12 carbon atoms, preferably an alkoxy group having 2 to 8 carbon atoms, more preferably an alkoxy group having 2 to 6 carbon atoms, and even more preferably an alkoxy group having 2 to 4 carbon atoms.

The alkylcarbonyloxy group may be linear, branched, or cyclic, and is preferably a linear or branched alkylcarbonyloxy group, more preferably a linear alkylcarbonyloxy group. In addition, an alkylcarbonyloxy group having 1 to 10 carbon atoms is preferred.

The alkylcarbonylamino group may be linear, branched, or cyclic, and is preferably a linear or branched alkylcarbonylamino group, more preferably a linear alkylcarbonylamino group. In addition, an alkylcarbonylamino group having 1 to 10 carbon atoms is preferred.

The alkylsulfonylamino group may be linear, branched, or cyclic, and is preferably a linear or branched alkylsulfonylamino group, more preferably a linear alkylsulfonylamino group. In addition, an alkylsulfonylamino group having 1 to 10 carbon atoms is preferred.

The aryl group means a monocyclic or polycyclic group consisting of a 5- or 6-membered aromatic hydrocarbon ring. Examples of the aryl group include phenyl group, naphthyl group, and biphenyl group.

The aryloxy group is preferably an aryloxy group having 6 to 12 carbon atoms. The arylcarbonyloxy group is preferably an arylcarbonyloxy group having 6 to 12 carbon atoms. The arylcarbonylamino group is preferably an arylcarbonylamino group having 6 to 12 carbon atoms. The arylsulfonylamino group is preferably an arylsulfonylamino group having 6 to 12 carbon atoms.

The monoalkylamino group may be linear, branched or cyclic, preferably a linear or branched monoalkylamino group, more preferably a linear monoalkylamino group. Furthermore, a monoalkylamino group in which the alkyl group has 1 to 10 carbon atoms is preferred.

The dialkylamino group may be linear, branched or cyclic, preferably a linear or branched dialkylamino group, more preferably a linear dialkylamino group. Further, a dialkylamino group in which the alkyl group has 1 to 10 carbon atoms is preferred.

Examples of the arylamino group include a monoarylamino group and a diarylamino group, preferably a monoarylamino group having 6 to 12 carbon atoms.

As a specific example of the compound represented by the general formula (1), R ¹ to R ⁵ are an alkyl group or a hydrogen atom, preferably R ¹ to R ⁵ are a linear alkyl group having 1 to 8 carbon atoms or a hydrogen atom. atoms, more preferably R ¹ to R ⁵ are linear alkyl groups having 1 to 4 carbon atoms or hydrogen atoms, and even more preferably R ¹ to R ⁵ are methyl groups or hydrogen atoms.

Other specific examples of the compound represented by general formula (1) include R ¹ , R ² , R ⁴ and R ⁵ are hydrogen atoms, and R ³ is a hydrogen atom, a halogen atom, a nitro group, an amino group, Alkyl group, alkoxy group, aryloxy group, alkylcarbonyloxy group, alkylcarbonylamino group, arylcarbonylamino group, alkylsulfonylamino group, arylsulfonylamino group, monoalkylamino group, dialkylamino group, or arylamino group (preferably is a hydrogen atom or an alkyl group, more preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, even more preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and particularly preferably a methyl group.

The substitution position of the substituent bonded to one of the benzene rings of the diphenylurea structure in general formula (1) can be the ortho, meta, or para position relative to the aminocarbonyl group on the benzene ring, preferably the ortho or meta position, and more preferably the meta position.

The compound represented by general formula (1) is not particularly limited, but is preferably at least one selected from the group consisting of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, 2-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, and 4-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate. Among these, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate is preferred.

The content of the first developer is not particularly limited and may be adjusted according to the leuco dye used. In general, it is preferably 0.5 parts by mass or more relative to 1 part by mass of leuco dye, more preferably 0.8 parts by mass or more, even more 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. On the other hand, the content of the first developer is preferably 10 parts by mass or less relative to 1 part by mass of leuco dye, more preferably 5 parts by mass or less, even more preferably 4 parts by mass or less, and particularly preferably 3.5 parts by mass or less. By making it 0.5 parts by mass or more, it is possible to improve recording performance. On the other hand, by making it 10 parts by mass or less, it is possible to effectively suppress background fogging in a high-temperature environment.

The second developer contains 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide or N-[2-(3-phenylureido)phenyl]benzenesulfonamide. This allows the material to exhibit high sensitivity, excellent heat resistance to background fogging at high temperatures (especially 100°C and 110°C), and plasticizer resistance. As the second developer, 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide is preferred.

The content of the second developer is not particularly limited, but is about 0.4 to 2.5 parts by mass relative to 1 part by mass of the first developer, preferably 0.7 to 2.5% by mass, more preferably about 0.9 to 2.5 parts by mass, and even more preferably about 1.7 to 2.3 parts by mass. By making the content of the second developer 0.4 parts by mass or more, it is possible to improve the plasticizer resistance. On the other hand, by making it 2.5 parts by mass or less, it is possible to improve the recording performance.

Other color developers may be contained as long as they do not impair the effects of the present invention. Specific examples of other color developers include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidene diphenyl, 4,4'-cyclohexylidene diphenol, 1,1-bis(4-hydroxyphenyl)-ethane, 1,1-bis(4 -hydroxyphenyl)-1-phenylethane, 4,4'-bis(p-tolylsulfonylaminocarbonylamino)diphenylmethane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2'-bis[4-(4-hydroxyphenyl)phenoxy]diethyl ether, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis(3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydro 4-hydroxydiphenyl 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, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)acetate, hydroquinone monobenzyl ether, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, 4-hydroxy phenolic compounds such as propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate ester, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, and 4,4'-dihydroxydiphenyl ether; benzoic acid, p-chlorobenzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert- Aromatic carboxylic acids such as butyl salicylic acid, 3-isopropyl salicylic acid, 3-benzyl salicylic acid, 3-(α-methylbenzyl)salicylic acid, 3,5-di-tert-butyl salicylic acid, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and zinc 4-{3-(p-tolylsulfonyl)propyloxy]salicylate. acids and their phenolic compounds; salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; organic acidic substances such as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehydic acid and other aromatic carboxylic acids; diarylureas such as N,N'-di[3-(p-toluenesulfonyl)oxy]phenylurea; thiourea compounds such as N-p-toluenesulfonyl-N'-3-(p-toluenesulfonyloxy)phenylurea, N-p-toluenesulfonyl-N'-p-butoxycarbonylphenylurea, N-p-tolylsulfonyl-N'-phenylurea, and N,N'-di-m-chlorophenylthiourea; compounds having -SO in the molecule such as N-(p-toluenesulfonyl)carbamoyl acid p-cumylphenyl ester, N-(p-toluenesulfonyl)carbamoyl acid p-benzyloxyphenyl ester, and N-(o-toluoyl)-p-toluenesulfamide; Examples of the acidic substance include organic compounds having _2NH bonds, activated clay, attapulgite, colloidal silica, aluminum silicate, and other inorganic acidic substances.

In the present invention, a storage stability improver can be further incorporated into the thermal recording layer, mainly to further improve the storage stability of the color image. Examples of such storage stability improvers include 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-methylethylidene)]bisphenol, and 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisphenol. At least one selected from phenol compounds such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenylsulfone, epoxy compounds such as 4-(2-methyl-1,2-epoxyethyl)diphenylsulfone, and 4-(2-ethyl-1,2-epoxyethyl)diphenylsulfone, and isocyanuric acid compounds such as 1,3,5-tris(2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl)isocyanuric acid can be used. Of course, the present invention is not limited to these compounds, and two or more compounds can be used in combination as necessary.

When a storage stability improver is used, the amount used should be an amount effective for improving storage stability, and is usually preferably about 1 to 25% by weight, and more preferably about 5 to 20% by weight, of the total solid content of the thermal recording layer.

A sensitizer can also be added to the thermal recording layer in the present invention. This can increase the recording sensitivity. Examples of sensitizers include stearic acid amide, methoxycarbonyl-N-stearic acid benzamild, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylene bisstearic acid amide, behenic acid amide, methylene bisstearic acid amide, N-methylolstearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, benzyl p-benzyloxybenzoate, 1-hydroxy-2-phenyl naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p-benzyl biphenyl, di-p-chlorobenzyl ester of oxalic acid, di-p-methylbenzyl ester of oxalic acid, dibenzyl ester of oxalic acid, p-tolyl biphenyl ether, di(p-methoxyphenoxyethyl)ether, 1,2-di(3-methylphenoxy)ethyl ... p-methylthiophenylbenzyl ether, 1,4-di(phenylthio)butane, p-acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, diphenyl, benzophenone, and the like. Among these, dimethyl terephthalate, 1,2-di(3-methylphenoxy)ethane, stearic acid amide, and diphenyl sulfone are preferred, and from the viewpoint of obtaining a sensitization effect without decreasing heat resistance to background fogging at high temperatures, dimethyl terephthalate and 1,2-di(3-methylphenoxy)ethane are more preferred. These can be used in combination within a range that does not cause any problems. The content of the sensitizer may be an amount effective for sensitization, and is usually preferably 2 to 25% by mass, more preferably 5 to 20% by mass, and even more preferably 5 to 15% by mass of the total solid content of the thermal recording layer.

Other components that make up the thermal recording layer include adhesives, and if necessary, auxiliary agents such as pigments, crosslinking agents, waxes, metal soaps, water-resistant agents, dispersants, colored dyes, and fluorescent dyes can be used.

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, water-soluble polymer materials such as sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid ester copolymers, styrene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, casein, gelatin, and their derivatives, as well as emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene-vinyl acetate copolymers, and water-insoluble polymer latexes such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. Among these, polyvinyl alcohol and latex are preferred. The content of the adhesive can be selected from a wide range, but generally, it is preferably about 5 to 30% by mass, and more preferably about 10 to 20% by mass, of the total solid content of the thermal recording layer.

By incorporating a crosslinking agent into the heat-sensitive recording layer, the water resistance of the heat-sensitive recording layer can be improved. Examples of crosslinking agents include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, dimethylol urea compounds, aziridine compounds, blocked isocyanate compounds; ammonium persulfate. , ferric chloride, magnesium chloride, sodium tetraborate, potassium tetraborate, and other inorganic compounds; boric acid, boric acid triesters, boron-based polymers, hydrazide compounds, glyoxylates, and the like. These may be used alone or in combination of two or more. The amount of crosslinking agent used is preferably about 1 to 5% by mass based on the total solid amount of the heat-sensitive recording layer.

The heat-sensitive recording layer can be prepared, for example, by using water as a dispersion medium, and using a leuco dye and a color developer, optionally together with a sensitizer or a preservability improver, or separately using a ball mill, a coball mill, an attritor, a vertical type, and a horizontal type. Water-soluble synthetic polymer compounds such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, styrene-maleic anhydride copolymer salt, etc., and other surfactants are dispersed using various types of stirring/wet grinding machines such as sand mills. , a thermosensitive recording prepared by mixing pigments, adhesives, auxiliary agents, etc. as necessary, using the dispersion obtained by making each dispersion liquid and micronizing it so that the average particle size is 2 μm or less. After the layer coating liquid is applied, it is dried and formed on the undercoat layer. The coating amount of the heat-sensitive recording layer is not particularly limited, and the coating amount after drying is preferably about 1 to 12 g/m ² , more preferably 2 to 10 g/m ² , and even more preferably 2.5 to 8 g/m ² . , 3 to 5.5 g/m ² is particularly preferred. The heat-sensitive recording layer can be formed into two or more layers if necessary, and the composition and coating amount of each layer may be the same or different.

[Protective layer]
In the heat-sensitive recording material, a protective layer can be provided on the heat-sensitive recording layer, if necessary. Preferably, the protective layer contains a pigment and an adhesive. Furthermore, the protective layer preferably contains a lubricant such as polyolefin wax or zinc stearate for the purpose of preventing sticking to the thermal head, and may also contain a UV absorber. Further, by providing a protective layer with gloss, the added value of the product can be increased.

The pigments contained in the protective layer are not particularly limited, and examples include inorganic pigments such as amorphous silica, kaolin, clay, light calcium carbonate, heavy calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, colloidal silica, and synthetic layered mica, and plastic pigments such as urea-formaldehyde resin filler.

The adhesive contained in the protective layer is not particularly limited, and a water-soluble or water-dispersible aqueous adhesive can be used. The adhesive can be appropriately selected from those that can be used in the thermal recording layer. Among these adhesives, various modified polyvinyl alcohols such as acetoacetyl-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and diacetone-modified polyvinyl alcohol are more preferably used.

The protective layer is formed on the thermosensitive recording layer by, for example, applying a coating solution for the protective layer, which is prepared by mixing a pigment, an adhesive, and, if necessary, an auxiliary, in water as a dispersion medium, and then drying the coating solution. The amount of the coating solution for the protective layer is not particularly limited, and is preferably about 0.3 to 15 g/ ^m2 in terms of dry mass, more preferably about ^0.3 to 10 g/ ^m2 , even more preferably about 0.5 to 8 g/ ^m2 , particularly preferably about 1 to 8 g/m2, and even more preferably about 1 to 5 g/ ^m2 . The protective layer can be formed in two or more layers as necessary, and the composition and coating amount of each layer may be the same or different.

[Other layers]
In the present invention, it is preferable that the support has an adhesive layer on at least one side. Thereby, the added value of the thermosensitive recording material can be increased. The adhesive layer can be made into adhesive paper, rewetting adhesive paper, delayed tack paper, etc. by coating one side with an adhesive, rewetting adhesive, delayed tack type adhesive, or the like. In addition, by using the side of the support opposite to the heat-sensitive recording layer, we can provide it with functions such as thermal transfer paper, inkjet recording paper, carbonless paper, electrostatic recording paper, zeography paper, etc., and double-sided recording. It is also possible to use recording paper that is capable of Of course, a double-sided thermosensitive recording medium can also be used. Further, a back layer may be provided to suppress penetration of oil and plasticizer from the back surface of the thermosensitive recording material, to control curling, and to prevent static electricity. By coating a release layer containing silicone on the protective layer and coating an adhesive on one side, it is also possible to obtain a linerless label that does not require release paper.

[Thermosensitive recording material]
The thermosensitive recording material can be manufactured by forming each of the above layers on a support. Methods for forming each of the above layers on the support include an air knife method, a blade method, a gravure method, a roll coater method, a spray method, a dip method, a bar method, a curtain method, a slot die method, a slide die method, an extrusion method, etc. Any of the known application methods may be utilized. Further, each coating liquid may be applied and dried one layer at a time to form each layer, or the same coating liquid may be applied in two or more layers. Furthermore, simultaneous multilayer coating, in which two or more layers are coated simultaneously, may be performed. Further, after forming each layer or after forming all layers, smoothing treatment can be performed using a known method such as a super calender or a soft calender.

The present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. Note that unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively. Particle diameters such as average particle diameter and maximum particle diameter were measured using a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation). Here, the average particle diameter is the median diameter (D50).

The hollow particles used in Examples and Comparative Examples are as follows.
Hollow particle A: Low Peik SN-1055 (manufactured by Dow) average particle diameter (D50) 1.0 μm, maximum particle diameter (D100) 1.8 μm, hollow ratio 55%, solid content concentration 26.5%
Hollow particles B: average particle diameter (D50) 11 μm, maximum particle diameter (D100) 23 μm, hollow ratio 93%, proportion of particles 2 μm or less 0 volume %, solid content concentration 15.0%
Hollow particles C: average particle diameter (D50) 5.0 μm, maximum particle diameter (D100) 13.5 μm, hollow ratio 90%, proportion of particles 2 μm or less 0.2% by volume, solid content concentration 15.0%
The average particle diameter (D50) and maximum particle diameter (D100) of each hollow particle were measured using a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) at a refractive index of 1.70-0.01i. .

The latexes used in the examples and comparative examples are as follows.
Latex A: styrene-butadiene copolymer latex (product name L-1571, manufactured by Asahi Kasei Corporation, Tg = -3°C, particle size 190 nm, solid content concentration 48%)
Latex B: Styrene-butadiene copolymer latex development product (Tg: -10°C, particle size 190 nm, solid content 48%)
Latex C: Styrene-butadiene copolymer latex development product (Tg: -35°C, particle size 300 nm, solid content 48%)

(Example 1)
(1) Preparation of coating liquid for undercoat layer Hollow particles A 56.6 parts, calcined kaolin (trade name Ansilex 93, manufactured by BASF, oil absorption 105 ml/100 g) 70 parts, latex A 22.9 parts, oxidized starch 25% 12 parts of the solution, 6.7 parts of a 15% aqueous solution of fully saponified polyvinyl alcohol (trade name: PVA105, degree of saponification: 99 mol%, average degree of polymerization: 500, manufactured by Kuraray Co., Ltd.) and 80 parts of water were mixed and stirred. A coating solution for an undercoat layer was obtained.

(2) Preparation of Leuco Dye Dispersion (Liquid A) 40 parts of 3-di-(n-butyl)amino-6-methyl-7-anilinofluoran, 40 parts of a 10% aqueous solution of polyvinyl alcohol (product name: PVA205, polymerization degree 500, saponification degree 88%, manufactured by Kuraray Co., Ltd.), and 20 parts of water were mixed and pulverized using a sand mill (sand grinder manufactured by Imex Co., Ltd.) until the average particle size became 0.5 μm, thereby obtaining a leuco dye dispersion (Liquid A).

(3) Preparation of color developer dispersion (liquid B) 40 parts of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, polyvinyl alcohol (trade name: PVA205, degree of polymerization 500, degree of saponification 88%, 40 parts of a 10% aqueous solution (manufactured by Kuraray Co., Ltd.) and 20 parts of water were mixed and ground using a sand mill (manufactured by Imex, sand grinder) until the average particle size was 1.0 μm to disperse the color developer. A liquid (liquid B) was obtained.

(4) Preparation of color developer dispersion liquid (liquid C) 40 parts of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide, 40 parts of a 10% aqueous solution of polyvinyl alcohol (product name: PVA205, polymerization degree 500, saponification degree 88%, manufactured by Kuraray Co., Ltd.), and 20 parts of water were mixed and pulverized using a sand mill (sand grinder manufactured by Imex Co., Ltd.) until the average particle size became 1.0 μm, to obtain a color developer dispersion liquid (liquid C).

(5) Preparation of sensitizer dispersion (solution D) 40 parts of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co., Ltd.), 10 parts of polyvinyl alcohol (trade name: PVA205, degree of polymerization 500, degree of saponification 88%, manufactured by Kuraray Co., Ltd.) % aqueous solution and 20 parts of water were mixed and ground using a sand mill (manufactured by Imex, sand grinder) until the average particle diameter was 1.0 μm to obtain a sensitizer dispersion (liquid D). Ta.

(6) Preparation of coating liquid for heat-sensitive recording layer 34.1 parts of liquid A, 46.7 parts of liquid B, 22.7 parts of liquid C, 35 parts of liquid D, fully saponified polyvinyl alcohol (trade name: PVA110, degree of saponification: 99 mol%, average degree of polymerization: 1000, manufactured by Kuraray Co., Ltd.) 63.7 parts of a 15% aqueous solution, 12.8 parts of Latex A (trade name: L-1571, manufactured by Asahi Kasei Co., Ltd., solid content concentration 48%), calcium carbonate (Product name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd., oil absorption 56 ml/100 g), 1 part of adipic acid dihydrazide (manufactured by Otsuka Chemical Co., Ltd.), and 150 parts of water were mixed and stirred to prepare a coating liquid for a heat-sensitive recording layer. Obtained.

(7) Preparation of coating solution for protective layer 292 parts of a 12% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Gosenex Z-200, manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.), 62 parts of kaolin (trade name: HYDRAGLOSS90, manufactured by KaMin LLC) A coating solution for a protective layer was prepared by mixing and stirring a composition consisting of 50 parts, 8.3 parts of zinc stearate (trade name: Hydrin Z-9-36, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 36%), and 150 parts of water. I got it.

(8) Preparation of heat-sensitive recording material On one side of high-quality paper with a basis weight of 60 g/ ^m2 , apply the coating liquid for the undercoat layer, the coating liquid for the heat-sensitive recording layer, and the coating liquid for the protective layer recording in the respective amounts after drying. After coating and drying to a thickness of 6.5 g/m ² , 3.5 g/m ² , and 2.3 g/m ² to form an undercoat layer, a heat-sensitive recording layer, and a protective layer in this order, the surface was coated with a super calendar. was smoothed to obtain a thermosensitive recording material.

(Example 2)
In the preparation of the coating solution for the heat-sensitive layer in Example 1, the steps were carried out except that the amount of dispersion C was changed to 34.1 parts instead of 22.7 parts, and the amount of calcium carbonate was changed to 16 parts instead of 21 parts. A thermosensitive recording material was obtained in the same manner as in Example 1.

(Example 3)
In the preparation of the coating solution for the heat-sensitive layer in Example 1, the same procedure was carried out except that the amount of dispersion C was changed to 45.5 parts instead of 22.7 parts, and the amount of calcium carbonate was changed to 11 parts instead of 21 parts. A thermosensitive recording material was obtained in the same manner as in Example 1.

(Example 4)
In the preparation of the heat-sensitive layer coating solution of Example 1, the amount of dispersion B was changed to 22.7 parts instead of 47.7 parts, and the amount of dispersion C was changed to 47.7 parts instead of 22.7 parts. A thermosensitive recording material was obtained in the same manner as in Example 1 except for the following.

(Example 5)
(9) Preparation of sensitizer dispersion (liquid E) 40 parts of 1,2-di(3-methylphenoxy)ethane (trade name: KS-232, manufactured by Sankosha), polyvinyl alcohol (trade name: PVA205, degree of polymerization) 500, saponification degree 88%, manufactured by Kuraray Co., Ltd.) and 20 parts of water were mixed and mixed using a sand mill (manufactured by Imex, sand grinder) until the average particle size became 1.0 μm. It was pulverized to obtain a sensitizer dispersion (liquid E).

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that Dispersion E was used in place of Dispersion D in the preparation of the coating liquid for heat-sensitive layer in Example 1.

(Example 6)
A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating solution for the thermosensitive layer in Example 1, 36.4 parts of Dispersion D were replaced with 64 parts of Himicron L-271 (main component stearic acid amide, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 25%).

(Example 7)
(10) Preparation of sensitizer dispersion (F solution) 40 parts of diphenyl sulfone (manufactured by NICCA Chemical Co., Ltd.), 10% of polyvinyl alcohol (trade name: PVA205, degree of polymerization 500, degree of saponification 88%, manufactured by Kuraray Co., Ltd.) 40 parts of an aqueous solution and 20 parts of water were mixed and ground using a sand mill (manufactured by Imex Corporation, sand grinder) until the average particle diameter was 1.0 μm to obtain a sensitizer dispersion (liquid F). .

A thermosensitive recording material was obtained in the same manner as in Example 1, except that Dispersion F was used in place of Dispersion D in the preparation of the coating solution for the undercoat layer in Example 1.

(Example 8)
(11) Preparation of color developer dispersion (Liquid G) 40 parts of N-[2-(3-phenylureido)phenyl]benzenesulfonamide (trade name: NKK-1304, manufactured by Nippon Soda Co., Ltd.), polyvinyl alcohol (trade name) : Mix 40 parts of a 10% aqueous solution of PVA205, polymerization degree 500, saponification degree 88%, manufactured by Kuraray Co., Ltd.) and 20 parts of water, and use a sand mill (manufactured by Imex Corporation, sand grinder) to reduce the average particle size to 1. The color developer dispersion (liquid G) was obtained by pulverizing the powder to a particle size of .0 μm.

A thermal recording medium was obtained in the same manner as in Example 1, except that dispersion G was used instead of dispersion C in the preparation of the coating liquid for the thermal layer in Example 1.

Example 9
A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the thermosensitive layer in Example 1, the amount of Dispersion B was changed from 47.7 parts to 22.7 parts, and Dispersion G was changed from 22.7 parts to 47.7 parts.

Example 10
A thermosensitive recording medium was obtained in the same manner as in Example 4, except that in the preparation of the coating solution for the undercoat layer of Example 4, 66.7 parts of hollow particles B were used instead of 56.6 parts of hollow particles A, 30 parts of calcined kaolin (trade name Ansilex 93, manufactured by BASF, oil absorption 105 ml/100 g) were used instead of 70 parts, 95.8 parts of latex A were used instead of 22.9 parts, 40 parts of a 25% solution of oxidized starch were used instead of 12 parts, and 0 part of water was used instead of 80 parts.

(Example 11)
A thermosensitive recording medium was obtained in the same manner as in Example 10, except that in the preparation of the coating solution for the undercoat layer of Example 10, 66.7 parts of hollow particles C were used instead of 66.7 parts of hollow particles B.

(Example 12)
A thermosensitive recording material was obtained in the same manner as in Example 10, except that 95.8 parts of Latex B was used in place of 95.8 parts of Latex A in the preparation of the coating solution for the undercoat layer in Example 10.

(Example 13)
A thermosensitive recording material was obtained in the same manner as in Example 10, except that 95.8 parts of Latex A was replaced with 95.8 parts of Latex C in the preparation of the coating solution for the undercoat layer in Example 10.

(Comparative Example 1)
(12) Preparation of color developer dispersion liquid (Liquid H) 40 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone (trade name: D-8, manufactured by Nippon Soda Co., Ltd.), 40 parts of a 10% aqueous solution of polyvinyl alcohol (trade name: PVA205, polymerization degree 500, saponification degree 88%, manufactured by Kuraray Co., Ltd.), and 20 parts of water were mixed and pulverized using a sand mill (sand grinder, manufactured by Imex Co., Ltd.) to an average particle size of 1.0 μm to obtain a color developer dispersion liquid (Liquid H).

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that Dispersion H was used in place of Dispersion B in the preparation of the coating liquid for heat-sensitive layer in Example 1.

(Comparative example 2)
(13) Preparation of color developer dispersion (J solution) 40 parts of N-p-toluenesulfonyl-N'-3-(p-toluenesulfonyloxy)phenylurea (trade name: PF201, manufactured by Solenis), polyvinyl alcohol ( Mix 40 parts of a 10% aqueous solution of (trade name: PVA205, polymerization degree 500, saponification degree 88%, manufactured by Kuraray Co., Ltd.) and 20 parts of water, and use a sand mill (manufactured by Imex Corporation, sand grinder) to determine the average particle diameter. The color developer dispersion (liquid J) was obtained by pulverizing the powder until the particle diameter was 1.0 μm.

In the preparation of the coating liquid for the heat-sensitive layer in Example 1, dispersion J was used instead of dispersion B, the amount of dispersion C was changed to 0 parts instead of 22.7 parts, and the amount of calcium carbonate was 21 parts. A thermosensitive recording material was obtained in the same manner as in Example 1 except that 31 parts were used instead of 31 parts.

(Comparative Example 3)
A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the thermosensitive layer in Example 1, the amount of Dispersion C was changed from 22.7 parts to 0 parts, and the amount of calcium carbonate was changed from 21 parts to 31 parts.

(Comparative Example 4)
A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the thermosensitive layer in Example 1, the amount of Dispersion C was changed to 11.4 parts instead of 22.7 parts, and the amount of calcium carbonate was changed to 26 parts instead of 21 parts.

(Comparative example 5)
In preparing the coating solution for the heat-sensitive layer in Example 1, the amount of dispersion B was changed to 0 parts instead of 47.7 parts, the amount of dispersion C was changed to 44.7 parts instead of 22.7 parts, and carbonic acid A thermosensitive recording material was obtained in the same manner as in Example 1, except that the amount of calcium was changed to 31 parts instead of 21 parts.

(Comparative example 6)
(14) Preparation of color developer dispersion (K solution) 40 parts of diphenylsulfone crosslinked compound represented by the following general formula (2) (trade name: D-90, manufactured by Nippon Soda Co., Ltd.), polyvinyl alcohol (trade name: 40 parts of a 10% aqueous solution of PVA205 (polymerization degree 500, saponification degree 88%, manufactured by Kuraray Co., Ltd.) and 20 parts of water were mixed, and using a sand mill (manufactured by Imex Corporation, sand grinder), the average particle size was 1. The powder was ground to 0 μm to obtain a color developer dispersion (K solution).

（式中、ｎは１～６の整数を表す。）

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

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that Dispersion K was used in place of Dispersion C in the preparation of the coating liquid for heat-sensitive layer in Example 1.

(Comparative Example 7)
(15) Preparation of color developer dispersion (L solution) 40 parts of a urea urethane compound represented by the following general formula (3) (trade name: UU, manufactured by ChemiPro Kasei Co., Ltd.), polyvinyl alcohol (trade name: PVA205, polymerization degree 500, saponification degree 88%, manufactured by Kuraray Co., Ltd.) and 20 parts of water were mixed and mixed using a sand mill (manufactured by Imex, sand grinder) until the average particle size became 1.0 μm. It was pulverized to obtain a color developer dispersion (Liquid L).

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that Dispersion L was used in place of Dispersion C in the preparation of the coating liquid for heat-sensitive layer in Example 1.

The above Examples and Comparative Examples were evaluated by the following method. The results were as shown in Table 3.

[Recording density]
Using a thermal recording evaluation device (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was recorded at an applied energy of 0.18 mJ/dot (halftone color density), and the resulting printed area was It was measured with a spectrodensitometer (X-Rite504, manufactured by X-Rite). The larger the value, the darker the print density.
- The evaluation criteria for halftone color density were as follows.
Color density 1.25 or higher: Can also be used for high-speed printing, which is very good.
Color density 1.10 or more and less than 1.25: practically required.
Color density less than 1.10: Low sensitivity and many defects such as white spots, which is a practical problem.

Using a thermal recording evaluation device (product name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was recorded at an applied energy of 0.25 mJ/dot (maximum color density), and the resulting printed area was analyzed by spectroscopy. It was measured with a densitometer (X-Rite504, manufactured by X-Rite). The larger the value, the darker the print density.
- The maximum color density was evaluated according to the following criteria.
Color density 1.40 or higher: Can also be used for high-speed printing, which is very good.
Color density 1.30 or more and less than 1.40: practically required.
Color density less than 1.30: Low sensitivity and many defects such as white spots, which is a practical problem.

[Plasticizer resistance]
A polycarbonate pipe (diameter 40 mm) was wrapped three times with a wrap film (product name: HiSsoft, manufactured by Nippon Carbide Industries Co., Ltd.), and a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.) was used on top of it. Each color-developed heat-sensitive recording material was placed on it, a wrap film was wrapped three times on top of it, and the optical density of the recorded area was measured by a spectrodensitometer (X- Rite 504 (manufactured by X-Rite), and the residual rate was calculated as: (Print density after treatment) ÷ (Print density before treatment).
・The evaluation criteria for the survival rate were as follows.
Survival rate after processing: 65% or more: Barcodes can be read, which is excellent.
Remaining rate after treatment: 40% or more and less than 65%: Visually legible and poses no practical problem.
Remaining rate after processing is less than 40%: Printing disappears, causing a practical problem.

[Heat resistance at 100°C]
A sample of each thermal recording medium, which had been colored using a label printer (product name: L-2000, manufactured by Ishida Corporation), was left to stand for 1 hour in a chamber at 100°C, and the optical density of the blank area after processing was measured using a spectrodensitometer (X-Rite 504, manufactured by X-Rite Corporation).
The evaluation criteria were as follows:

[Heat resistance at 110°C]
A sample of each thermal recording medium, which had been colored using a label printer (product name: L-2000, manufactured by Ishida Corporation), was left to stand for 1 hour in a chamber at 110°C, and the optical density of the blank area after processing was measured using a spectrodensitometer (X-Rite 504, manufactured by X-Rite Corporation).
The evaluation criteria were as follows:

Claims (12)

A thermosensitive recording medium having, on a support, at least an undercoat layer containing hollow particles and an adhesive, and a thermosensitive recording layer containing a leuco dye, a developer and an adhesive in this order, comprising a compound represented by the following general formula (1) as a first developer in the thermosensitive recording layer:

(wherein R ¹ to R ⁵ are the same or different and each represents a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group), and the second developer is 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide or N-[2-(3-phenylureido)phenyl]benzenesulfonamide, and the second developer is contained in an amount of 0.4 to 2.5 parts by mass per part by mass of the first developer. The thermal recording medium according to claim 1, wherein the compound represented by the general formula (1) is at least one selected from the group consisting of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, 2-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, and 4-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate. The thermal recording medium according to claim 1, wherein the compound represented by the general formula (1) is 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate. The heat-sensitive recording material according to any one of claims 1 to 3, wherein the second color developer is contained in an amount of 0.9 to 2.5 parts by mass per 1 part by mass of the first color developer. Any one of claims 1 to 3, wherein the second color developer is 5-(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. The heat-sensitive recording medium according to item 1. The thermal recording medium according to any one of claims 1 to 3, wherein the thermal recording layer contains at least one sensitizer selected from dimethyl terephthalate, 1,2-di(3-methylphenoxy)ethane, stearic acid amide, and diphenyl sulfone. The thermal recording medium according to any one of claims 1 to 3, wherein the thermal recording layer contains at least one sensitizer selected from dimethyl terephthalate and 1,2-di(3-methylphenoxy)ethane. The hollow particles have a maximum particle diameter (D100) of 10 to 30 μm, an average particle diameter (D50) of 4.0 to 15 μm, and a ratio D100 of the maximum particle diameter (D100) to the average particle diameter (D50). /D50 is 1.8 to 3.0, and the volume % of particles with a particle diameter of 2.0 μm or less is 1% or less. The heat-sensitive recording material according to any one of claims 1 to 3, wherein the hollow particles have a hollowness ratio of 80 to 98%. The heat-sensitive recording material according to any one of claims 1 to 3, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of -10°C or lower. The thermal recording medium according to any one of claims 1 to 3, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of -30°C or lower. The thermal recording medium according to any one of claims 1 to 3, further comprising an adhesive layer on at least one side of the support.