WO2022045191A1 - Heat-sensitive recording body and image forming method - Google Patents

Abstract

A heat-sensitive recording body which is provided with a heat-sensitive color developing layer that contains an electron-donating dye precursor, an electron-accepting compound, a radically polymerizable compound and a radical photopolymerization initiator, and which is characterized in that the radical photopolymerization initiator contains an oxime ester compound that has a group represented by formula (1).

Description

Thermal recording body and image forming method

The present invention relates to a heat-sensitive recorder and an image forming method using the same.

Conventionally, a heat-sensitive recorder using a mechanism for reacting a leuco dye with a color developer to develop a color has been widely used. Thermal recorders do not require consumables such as ink or toner and are relatively inexpensive, so they are widely used as recording media for fax machines, receipts, and other applications. A general heat-sensitive recorder is manufactured by printing or coating a water-containing liquid-coated heat-sensitive color-developing composition on an arbitrary support and then drying to form a heat-sensitive color-developing layer.

Further, a method of irradiating an ultraviolet curable heat-sensitive color-developing composition with ultraviolet rays to form a heat-sensitive color-developing layer is also being studied. For example, Patent Document 1 contains (1) a photocurable composition containing an electron-accepting and polymerizable vinyl monomer and a photopolymerizable compound, and (2) microcapsules containing an electron-donating colorless dye. A photosensitive / heat-sensitive recording material having a photosensitive / heat-sensitive layer has been proposed. According to Patent Document 1, UV exposure slows the diffusion of electron-accepting and polymerizable vinyl monomers, thereby suppressing contact with electron-donating dye precursors. Therefore, even when heated after exposure to ultraviolet rays, the cured portion does not develop color.

Japanese Unexamined Patent Publication No. 3-72358

However, according to the study by the present inventors, the photosensitive / heat-sensitive recording material proposed in Patent Document 1 has an integrated light intensity (about 1000 mJ / cm ² or more) of a certain level or more in order to suppress color development after ultraviolet irradiation. It turned out to be necessary. On the other hand, from the viewpoint of downsizing of the ultraviolet irradiation device and reduction of power consumption, it is necessary to further reduce the amount of ultraviolet light to be irradiated.

Therefore, an object of the present invention is to provide a heat-sensitive recorder capable of suppressing color development due to heating after irradiation with ultraviolet rays even when the amount of ultraviolet rays to be irradiated is low. Another object of the present invention is to provide an image forming method using the above-mentioned heat-sensitive recorder.

The above object is achieved by the following invention.

That is, according to the present invention, it is a heat-sensitive recorder provided with a heat-sensitive color-developing layer containing an electron-donating dye precursor, an electron-accepting compound, a radically polymerizable compound, and a photoradical polymerization initiator.
A heat-sensitive recorder is provided in which the photoradical polymerization initiator contains an oxime ester compound having a group represented by the following formula (1).

(In the formula (1), R ₁ and R ₂ each independently contain a hydrogen atom, a halogen atom, a nitro group, a cyano group, a hydrocarbon group having 1 to 20 carbon atoms, or a heterocycle. Represents 2 to 20 groups
The hydrogen atoms in the groups represented by R ₁ and R ₂ are halogen atom, nitro group, cyano group, hydroxyl group, amino group, carboxyl group, methacryloyl group, acryloyl group, epoxy group, vinyl group, vinyl ether group and mercapto group. , An isocyanate group, or a group having 2 to 20 carbon atoms containing a heterocycle may be substituted.
The methylene groups in the groups represented by R ₁ and R ₂ are -O-, -CO-, -COO-, -OCO-, -NR _3- , -NR ₃ CO-, -S-, -CS-. , -SO _2- , -SCO-, -COS-, -OCS-, -CH = CH-, -CC-, or -CSO- may be substituted, where R ₃ is a hydrogen atom or a carbon atom. Represents a hydrocarbon group of number 1 to 20
m represents 0 or 1 and represents
* Represents a binding site with another structure, and the binding site may form a ring together with a group represented by _R1 . )

Further, according to the present invention, a step of applying a heat pulse to the heat-sensitive recording body by applying a heat pulse to the heat-sensitive recording body and irradiating the heat-sensitive recording body on which the image is formed with ultraviolet rays are performed. Provided is an image forming method characterized by having a step of fixing the heat-sensitive color-developing layer.

According to the present invention, it is possible to provide a heat-sensitive recorder capable of suppressing color development due to heating after irradiation with ultraviolet rays even when the amount of ultraviolet rays to be irradiated is low. Further, according to the present invention, it is possible to provide an image forming method using the above-mentioned heat-sensitive recording body.

It is sectional drawing which shows one Embodiment of the heat-sensitive recording body of this invention. It is sectional drawing which shows the other embodiment of the heat-sensitive recording body of this invention.

<Thermal recording body>
Hereinafter, the details of the present invention will be described with reference to preferred embodiments, but the present invention is not limited to the following embodiments. The heat-sensitive recorder of the present invention is a heat-sensitive recorder provided with a heat-sensitive color-developing layer containing an electron-donating dye precursor, an electron-accepting compound, a radically polymerizable compound, and a photoradical polymerization initiator. The photoradical polymerization initiator contains an oxime ester compound having a group represented by the following formula (1).

(In the formula (1), R ₁ and R ₂ each independently contain a hydrogen atom, a halogen atom, a nitro group, a cyano group, a hydrocarbon group having 1 to 20 carbon atoms, or a heterocycle. Represents 2 to 20 groups
The hydrogen atoms in the groups represented by R ₁ and R ₂ are halogen atom, nitro group, cyano group, hydroxyl group, amino group, carboxyl group, methacryloyl group, acryloyl group, epoxy group, vinyl group, vinyl ether group and mercapto group. , An isocyanate group, or a group having 2 to 20 carbon atoms containing a heterocycle may be substituted.
The methylene groups in the groups represented by R ₁ and R ₂ are -O-, -CO-, -COO-, -OCO-, -NR _3- , -NR ₃ CO-, -S-, -CS-. , -SO _2- , -SCO-, -COS-, -OCS-, -CH = CH-, -CC-, or -CSO- may be substituted, where R ₃ is a hydrogen atom or a carbon atom. Represents a hydrocarbon group of number 1 to 20
m represents 0 or 1 and represents
* Represents a binding site with another structure, and the binding site may form a ring together with a group represented by _R1 . )

In the configuration of the present invention, the oxime ester compound having a group represented by the above formula (1) efficiently cleaves the NO-bonded portion by irradiation with ultraviolet rays to generate radicals. Therefore, the polymerization reaction of the radically polymerizable compound proceeds sufficiently even when irradiated with ultraviolet rays having a low light amount, and the electron donating dye precursor and the electron accepting compound can be fixed in the ultraviolet cured product.

As a result, even if the electron-donating dye precursor and the electron-accepting compound are heated after irradiation with ultraviolet rays, it becomes difficult for the electron-donating dye precursor and the electron-accepting compound to move in the heat-sensitive color-developing layer, and the color is developed by the contact between the electron-donating dye precursor and the electron-accepting compound. It can be suppressed.

Further, when the oxime ester compound having the group represented by the formula (1) was used, the electron-donating dye precursor tended to be easily included in the heat-sensitive color-developing layer. Although the detailed mechanism is unknown, the present inventors speculate that one of the following two points may be involved. One is that the oxime ester compound having a group represented by the formula (1) has good compatibility with the electron-donating dye precursor. As a result, it can be uniformly present in the heat-sensitive color-developing layer without being localized. The other is that a part of the oxime ester compound having a group represented by the above formula (1) is localized on the surface of the heat-sensitive color-developing layer. As a result, the electron-donating dye precursor can be encapsulated without being exposed on the surface of the heat-sensitive color-developing layer.

Therefore, the electron-donating dye precursor is easy to generate radicals of the oxime ester compound having a group represented by the formula (1), and the electron-donating dye precursor is easy to be included in the heat-sensitive color-developing layer. The present inventors speculate that it may have been possible to suppress color development due to contact with the electron-accepting compound.

(Electron-donating dye precursor)
The heat-sensitive color-developing layer contains an electron-donating dye precursor (also referred to as a leuco dye). Electron-donating dye precursors are usually colorless or pale in color. The electron-donating dye precursor has a property of donating an electron or receiving a proton such as an acid to develop a color. Specific examples of electron-donating dye precursors are listed below.

Examples of electron-donating dye precursors that develop a red or vermilion color tone include 3,6-bis (diethylamino) fluorane-γ-anilinolactam and 3,6-bis (diethylamino) fluorane-γ- (p-nitro). ) Anilinolactam, 3,6-bis (diethylamino) fluorane-γ- (o-chloro) anilinolactam, 3-dimethylamino-7-bromofluorane, 3-diethylaminofluorane, 3-diethylamino-6-methyl Fluolan, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-bromofluorine, 3-diethylamino-7,8-benzofluorine, 3-diethylamino-6 , 8-Dimethylfluorane, 3-diethylamino-6-methyl-7-chlorofluorine, 3-diethylamino-7-tert-butylfluorane, 3- (N-ethyl-N-tolylamino) -7-ethylfluorine , 3- (N-ethyl-N-isobutylamino) -6-methyl-7-chlorofluorane and the like.

Further, 3-cyclohexylamino-6-chlorofluorane and 3-di (n-butyl) amino-6-methyl-7-bromofluorane are examples of electron-donating dye precursors that develop a red or vermilion color. , 3-Di (n-butyl) amino-7,8-benzofluorine, 3-tolylamino-7-methylfluorane, 3-tolylamino-7-ethylfluorane, 2- (N-acetylanilino) -3 -Methyl-6-di (n-butyl) aminofluorane, 2- (N-propionylanilino) -3-methyl-6-di (n-butyl) aminofluorane, 2- (N-benzoylanilino) -3-Methyl-6-di (n-butyl) aminofluorane, 2- (N-carbobtoxyanilino) -3-methyl-6-di (n-butyl) aminofluorane, 2- (N-formylanilino) ) -3-Methyl-6-di (n-butyl) aminofluorane, 2- (N-benzylanilino) -3-methyl-6-di (n-butyl) aminofluorane, 2- (N-allylanilino) ) -3-Methyl-6-di (n-butyl) aminofluorane, 2- (N-methylanilino) -3-methyl-6-di (n-butyl) aminofluorane, 3-diethylamino-7-phenoxyflu Oran, 2-methyl-6- (N-p-tolyl-N-ethylamino) -fluorane and the like can be mentioned.

Examples of electron-donating dye precursors that develop magenta tones include 3,3-bis (1-ethyl-2-methylindole-3-yl) phthalide and 3,3-bis (1-n-octyl-). 2-Methylindole-3-yl) phthalide, 7- (N-ethyl-N-isoamylamino) -3-methyl-1-phenylspiro [(1,4-dihydrochromeno [2,3-c] pyrazole)) -4,3'-phthalide], 7- (N-ethyl-N-isoamylamino) -3-methyl-1-p-methylphenylspiro [(1,4-dihydrochromeno [2,3-c] pyrazole] ) -4,3'-phthalide], 7- (N-ethyl-Nn-hexylamino) -3-methyl-1-phenylspiro [(1,4-dihydrochromeno [2,3-c] pyrazole) ) -4,3'-phthalide] and the like.

Further, as electron-donating dye precursors that develop colors in magenta tones, 3- (N-ethyl-N-isoamylamino) -7,8-benzofluorine, 3,3-bis (1-n-) Butyl-2-methylindole-3-yl) phthalide, 3- (N-ethyl-N-isoamylamino) -7-phenoxyfluorane and the like can be mentioned.

Examples of electron-donating dye precursors that develop red, vermilion, or magenta tones include 3-diethylamino-7-chlorofluorane, 3-diethylamino-6,8-dimethylfluorane, and 3- (N-ethyl). -N-isoamylamino) -7,8-benzofluorine, 2-methyl-6- (Np-tolyl-N-ethylamino) -fluorane, 3-di (n-butyl) amino-6-methyl- It is preferable to use at least one selected from the group consisting of 7-bromofluorane and 3,3-bis (1-n-butyl-2-methylindole-3-yl) phthalide.

Examples of electron-donating dye precursors that develop a bluish tint include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylamino-2-methylphenyl) -3. -(4-Dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindole-3-yl) -4-azaphthalide, 3- (1-Ethyl-2-methylindole-3-yl) -3- (4-diethylaminophenyl) phthalide, 3- (1-ethyl-2-methylindole-3-yl) -3- (2-methyl) -4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindole-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-) Ethyl-2-methylindole-3-yl) -3- (2-n-hexyloxy-4-diethylaminophenyl) -4-azaphthalide, 3-diphenylamino-6-diphenylaminofluorane and the like can be mentioned.

As an electron donating dye precursor that develops a cyan color tone, 3- (1-ethyl-2-methylindole-3-yl) -3- (4-diethylamino-2-methylphenyl) -4-azaphthalide is used. , 3- [1,1-bis (p-diethylaminophenyl) ethylene-2-yl] -6-dimethylaminophthalide, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide, 3 , 3'-Bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide and the like.

Examples of electron-donating dye precursors that develop a blue or cyan color tone include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylamino-2-methylphenyl). ) -3- (4-Dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4 -Azaphthalide, 3- (1-ethyl-2-methylindole-3-yl) -3- (4-diethylamino-2-methylphenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3) -Il) -3- (2-n-hexyloxy-4-diethylaminophenyl) -4-azaphthalide, 3- [1,1-bis (p-diethylaminophenyl) ethylene-2-yl] -6-dimethylaminophthali It is preferable to use at least one selected from the group consisting of do and 3,3'-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide.

Examples of electron-donating dye precursors that develop a yellowish hue include 4- [2- [2- (butoxy) phenyl] -6-phenyl-4-pyridinyl] -N, N-dimethylbenzeneamine, 4-[. 2- [2- (octyloxy) phenyl] -6-phenyl-4-pyridinyl] -N, N-dimethylbenzeneamine, 4- [2- [2- (ethoxy) phenyl] -6-phenyl-4-pyridinyl ] -N, N-dimethylbenzeneamine, 4- [2,6-bis (2-ethoxyphenyl) -4-pyridinyl] -N, N-dimethylbenzeneamine, 4- (2,6-diphenyl-4-pyridinyl) ) -N, N-dimethylbenzeneamine, 4- [2,6-bis (2-butoshikiphenyl) -4-pyridinyl] -N, N-dimethylbenzeneamine, 4- [2,6-bis (2-6-bis) Octyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzeneamine, 4- [2- [2- (hexyloxy) phenyl] -6-phenyl-4-pyridinyl] -N, N-dimethylbenzeneamine, 4- [2,6-bis (2-hexyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzeneamine, 3,6-dimethoxyfluorane, 1- (4-n-dodecyloxy-3-methoxy) Examples thereof include phenyl) -2- (2-quinolyl) ethylene.

Examples of the electron-donating dye precursor that develops a yellowish hue include 4- [2- [2- (octyloxy) phenyl] -6-phenyl-4-pyridinyl] -N, N-dimethylbenzeneamine, 3, It is preferable to use at least one selected from the group consisting of 6-dimethoxyfluorane and 1- (4-n-dodecyloxy-3-methoxyphenyl) -2- (2-quinolyl) ethylene.

Examples of the electron-donating dye precursor that develops a greenish tone include 3- (N-ethyl-Nn-hexylamino) -7-anilinofluorane, 3-diethylamino-7-dibenzylaminofluorane, and the like. 3-Pyrrolidino-7-dibenzylaminofluorane, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide, 3- (N-ethyl-N-p-tolylamino) -7- (N) -Phenyl-N-methylamino) fluorane, 3- [p- (p-anilinoanilino) anilino] -6-methyl-7-chlorofluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3' -(6'-Dimethylamino) phthalide and the like can be mentioned.

As the electron-donating dye precursor that develops a greenish color tone, at least one selected from the group consisting of 3-diethylamino-7-dibenzylaminofluorane and 3-pyrrolidino-7-dibenzylaminofluorane. It is preferable to use.

Examples of electron-donating dye precursors that develop a blackish tone include 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, and 3-. Diethylamino-6-methyl-7- (m-methylanilino) fluorane, 3- (N-isoamyl-N-ethylamino) -7- (o-chloroanilino) fluorane, 3- (N-ethyl-p-toluizino) -6 -Methyl-7-anilinofluolane, 3- (N-ethyl-N-2-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-anilino Fluolane, 3-di (n-butyl) amino-6-methyl-7-anilinofluoran, 3-di (n-amyl) amino-6-methyl-7-anilinofluoran, 3- (N-) Isoamyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3- (Nn-hexyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3- [N- (3-ethoxypropyl) -N-ethylamino) -6-methyl-7-anilinofluoran, 3- [N- (3-ethoxypropyl) -N-methylamino) -6-methyl-7-anilino Fluolane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-di (n-butyl) amino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (2,6-dimethylanilino) fluorane, 3-diethylamino-6-methyl-7- (2,4-dimethylanilino) fluorane, 2,4-dimethyl-6- Examples thereof include (4-dimethylaminoanilino) fluorane and 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-anilinofluorane.

As electron-donating dye precursors that develop a blackish color tone, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane and 3-di (3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (n-butyl), which have relatively excellent light resistance, are used as electron-donating dye precursors. n-amyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (2,6-dimethylanilino) fluorane, 3-diethylamino-6-methyl-7- (2) , 4-Dimethylanilino) fluorane, and 2,4-dimethyl-6- (4-dimethylaminoanilino) fluorane, it is preferable to use at least one selected from the group.

As an electron donating dye precursor having absorption in the near infrared region, 3,3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7- Tetrabromophthalide, 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-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3-[p-(p -Anilino anilino) anilino] -6-methyl-7-chlorofluorine, 3- [p- (p-dimethylaminoanilino) anilino] -6-methyl-7-chlorofluorane, 3,6-bis (dimethylamino) ) Fluoren-9-spiro-3'-(6'-dimethylamino) phthalide, bis (p-dimethylaminostyryl) -p-tolylsulfonylmethane, 3- [p- (p-dimethylaminoanilino) anilino]- 6-Methylfluorane, 3-di (n-pentyl) amino-6,8,8-trimethyl-8,9-dihydro- (3,2e) pyridofluorane, 3-di (n-butyl) amino-6 , 8,8-trimethyl-8,9-dihydro- (3,2e) pyridofluorane, 3- (pn-butylaminoanilino) -6-methyl-7-chlorofluorine, 2-mesidino-8 -Diethylamino-benz [C] fluorane and the like can be mentioned.

The electron donating dye precursor is preferably contained in the heat-sensitive color-developing layer in a state of being encapsulated in particles composed of a radically polymerizable compound and a photoradical polymerization initiator. It is preferable that the content of the electron-donating dye precursor in the heat-sensitive color-developing layer is 0.01 g / m ² or more and 2.00 g / m ² or less because an image having a more sufficient optical density can be formed.

(Electron accepting compound)
The heat-sensitive color-developing layer contains an electron-accepting compound (also referred to as a color developer) having a property of developing an electron-donating dye precursor by contact with the color-sensitive color-developing layer. As the electron-accepting compound, it is preferable to use a compound having a property of liquefying or dissolving when the temperature rises. Examples of the electron-accepting compound include phenol compounds, aromatic carboxylic acids, and organic acidic substances such as polyvalent metal salts of these compounds.

Examples of the electron-accepting compound include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidene diphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4, 4'-isopropyridene diphenol, 4,4'-dihydroxydiphenyl ether, 4,4'-cyclohexylidene diphenol, 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxyphenyl) -1-Phenylethane, 4,4'-dihydroxydiphenylsulfide, 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone , 4-Hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone , 4,4'-Bis [(4-Methyl-3-phenoxycarbonylaminophenyl) ureido] diphenyl sulfone, 4- [4'-(1'-methylethyloxy) phenyl] sulfonylphenol, N- (p-toluene) Sulfonyl) -N'-(3-p-toluenesulfonyloxyphenyl) urea, Np-tolylsulfonyl-p-butoxycarbonylphenylurea, N- (p-toluenesulfonyl) -N'-phenylurea, 4,4 '-Bis (3-tosylureido) diphenylmethane and the like can be mentioned.

Examples of the electron-accepting compound include 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, -sec-butyl 4-hydroxybenzoate, and 4-hydroxybenzoic acid. Phenolic compounds such as phenyl, benzyl 4-hydroxybenzoate, trill 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, 4,4'-dihydroxydiphenyl ether; benzoic acid, p-tert-butyl benzoic acid, trichlor benzoic acid, Aromatic carboxylic acids such as terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic acid, 3,5- (α-methylbenzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid. Examples include organic acidic substances such as salts of these compounds with polyvalent metals such as zinc, magnesium, aluminum and calcium.

(Radical polymerizable compound)
The heat-sensitive color-developing layer contains a radically polymerizable compound. Examples of the radically polymerizable compound include a radically polymerizable monomer, a radically polymerizable oligomer, and a radically polymerizable polymer, but a radically polymerizable monomer is preferable from the viewpoint of being efficiently cured by ultraviolet rays.

The radically polymerizable compound is preferably at least one compound selected from the group consisting of a pentaerythritol derivative, an isocyanurate derivative, and a trimethylolpropane derivative. Further, the ratio of at least one compound selected from the group consisting of the pentaerythritol derivative, the isocyanurate derivative and the trimethylolpropane derivative among the radically polymerizable compounds is preferably 80% by mass or more and 100% by mass or less. ..

Examples of the pentaerythritol derivative include pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, ethylene oxide-modified pentaerythritol tri (meth) acrylate, propylene oxide-modified pentaerythritol tri (meth) acrylate, and ethylene oxide-modified pentaerythritol tetra. Examples thereof include (meth) acrylate, propylene oxide-modified pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and tripentaerythritol (meth) acrylate. Among them, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and tripentaerythritol (meth) acrylate are preferable. In addition, "(meth) acrylate" means methacrylate or acrylate. Commercially available products of the pentaerythritol derivative include, for example, light acrylate PE-3A; manufactured by Kyoeisha Chemical Co., Ltd., light acrylate PE-4A; manufactured by Kyoeisha Chemical Co., Ltd., light acrylate DPE-6A; manufactured by Kyoeisha Chemical Co., Ltd., SR295. ; Sartmer Co., Ltd., Viscort # 300; Osaka Organic Chemical Industry Co., Ltd., MT-3549; Toa Synthetic Co., Ltd., NK Oligo U-6LPA; Shin Nakamura Chemical Co., Ltd., U-15HA; New Nakamura Kagaku Co., Ltd., KAYARAD D-310; Nihonkayaku Co., Ltd., KAYARAD D-310; Nihonkayaku Co., Ltd., KAYARAD D-330; Nihonkayaku Co., Ltd., A-DPH; Nakamura Chemical Co., Ltd., A-TMMT; Shin-Nakamura Chemical Co., Ltd., etc. may be mentioned.

As the isocyanurate derivative, tris (2-hydroxyethyl) isocyanurate di (meth) acrylate, tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, and polyfunctional penta having a hydroxyl group in isocyanurate-type polyisocyanate. Examples thereof include a urethane acrylate-type isocyanurate derivative in which an erythritol derivative or a polyfunctional trimethylol derivative is reacted and polyfunctionalized via a urethane bond. Among them, tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate and urethane acrylate type isocyanurate derivative are preferable. Commercially available isocyanurate derivatives include, for example, Funkryl FA-731A; Hitachi Chemical Co., Ltd., SR368; Sartmer Co., Ltd., Aronix M-315; Toagosei Co., Ltd., U-15HA; Shin-Nakamura Chemical Co., Ltd. Made by Co., Ltd.

Examples of the trimethylolpropane derivative include trimethylolpropane tri (meth) acrylate, propoxylated trimethylolpropane tri (meth) acrylate, ethylene oxide-modified trimethylolpropane triacrylate, propylene oxide-modified trimethylolpropane, and ditrimethylolpropane tetra. Examples include acrylate. Among them, as the trimethylolpropane derivative, trimethylolpropane tri (meth) acrylate and trimethylolpropane tetraacrylate are preferable. Commercially available products of trimethylolpropane derivatives include, for example, Sunester TMP; manufactured by Sanshin Chemical Industry Co., Ltd., Viscort # 295; manufactured by Osaka Organic Chemical Industry Co., Ltd., Lightester TMP; manufactured by Kyoeisha Chemical Co., Ltd., Acryester. TMP; Mitsubishi Chemical Holdings Co., Ltd., Miramar M410; Toyo Chemicals Co., Ltd., Miramar M300; Toyo Chemicals Co., Ltd., Miramar M301; Toyo Chemicals Co., Ltd., EBECRYL140; Daicel Oknex Co., Ltd., EBECRYL1142; manufactured by Daicel Okunex Co., Ltd., SR355; manufactured by Sartmer Co., Ltd., AD-TMP; manufactured by Shin-Nakamura Chemical Co., Ltd., A-TMPT; manufactured by Shin-Nakamura Chemical Co., Ltd. and the like.

The radically polymerizable compound is preferably contained in the heat-sensitive color-developing layer in a state of being mixed in advance with the electron-donating dye precursor. The form of the radically polymerizable compound in the heat-sensitive color-developing layer is not particularly limited, and examples thereof include morphology of particles and layers. For example, when the radically polymerizable compound is contained in the heat-sensitive color-developing layer in the form of a layer, the heat-sensitive color-developing layer contains the first layer containing the radical-polymerizable compound mixed with the electron-donating dye precursor and the electron-accepting compound. It is preferable to have a second layer containing. Hereinafter, the first layer containing the radically polymerizable compound mixed with the electron-donating dye precursor is also referred to as an “electron-donating dye precursor layer” or a “leuco dye layer”. Further, the second layer containing the electron-accepting compound is also referred to as an "electron-accepting compound layer" or a "color developer layer".

Further, the radically polymerizable compound can be contained in the heat-sensitive color-developing layer in the form of particles. The method for preparing the radically polymerizable compound in the form of particles is not particularly limited, but it is preferably prepared by the O / W emulsion method, and the electron donating dye precursor and the photoradical polymerization initiator described later are radically polymerizable compounds. It is preferable that the mixture is prepared in a state of being premixed with. Further, it may be prepared by using an electron accepting compound instead of the electron donating dye precursor. That is, it is preferable that the heat-sensitive color-developing layer contains particles containing any one of the electron-donating dye precursor and the electron-accepting compound, the radical-polymerizable compound, and the photoradical polymerization initiator. The particle size of the particles of the radically polymerizable compound is preferably 10 nm or more and 1000 nm or less, and more preferably 50 nm or more and 300 nm or less. When the particle size of the particles is 10 nm or more, and further 50 nm or more, the radical polymerization reactivity becomes high, and the image storage stability can be further improved. On the other hand, when the particle size of the particles is 1000 nm or less and 300 nm or less, respectively, unnecessary light scattering in the heat-sensitive color-developing layer can be reduced and the image density can be increased. The particle size of the particles in the present specification means a 50% particle size (D50) based on the volume distribution.

The content of the radically polymerizable compound in the heat-sensitive color-developing layer is preferably 500% by mass or more and 2000% by mass or less, preferably 600% by mass or more and 1500% by mass or less, based on the content of the electron-donating dye precursor. It is more preferable to have. When the content is 500% by mass or more, the background fog is less likely to occur, and when the content is 600% by mass or more, the background fog is less likely to occur. On the other hand, when the content is 2000% by mass or less, the color development of the image is less likely to decrease, and when the content is 1500% by mass or less, the color development of the image is further improved.

(Photoradical polymerization initiator)
The heat-sensitive color-developing layer contains a photoradical polymerization initiator. The photoradical polymerization initiator contains an oxime ester compound having a group represented by the following formula (1).

(In the formula, R ₁ and R ₂ each independently contain a hydrogen atom, a halogen atom, a nitro group, a cyano group, a hydrocarbon group having 1 to 20 carbon atoms, or a heterocycle having 2 to 20 carbon atoms. Represents the basis of
The hydrogen atoms in the groups represented by R ₁ and R ₂ are halogen atom, nitro group, cyano group, hydroxyl group, amino group, carboxyl group, methacryloyl group, acryloyl group, epoxy group, vinyl group, vinyl ether group and mercapto group. , An isocyanate group, or a group having 2 to 20 carbon atoms containing a heterocycle may be substituted.
The methylene groups in the groups represented by R ₁ and R ₂ are -O-, -CO-, -COO-, -OCO-, -NR _3- , -NR ₃ CO-, -S-, -CS-. , -SO _2- , -SCO-, -COS-, -OCS-, -CH = CH-, -CC-, or -CSO- may be substituted, where R ₃ is a hydrogen atom or a carbon atom. Represents a hydrocarbon group of number 1 to 20
m represents 0 or 1 and represents
* Represents a binding site with another structure, and the binding site may form a ring together with a group represented by _R1 . )

The oxime ester compound preferably has a structure represented by the following formula (2).

(In the formula (2), R ₁ , R ₂ , and m are the same as R ₁ , R ₂ , and m in the formula (1), respectively.
R ₄ and R ₅ independently have a hydrogen atom, a nitro group, a cyano group, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an arylalkyl group having 7 to 20 carbon atoms. Alternatively, it represents a group containing 2 to 20 carbon atoms and contains a heterocycle.
X ₁ represents -O-, -S-, -Se-, -CR ₆ R _7- , -CO-, -NR _8- , or -PR _9- .
X ₂ represents a single bond, a hydrocarbon group having 1 to 20 carbon atoms, -CO-, or a hydrogen atom bonded to a separate aromatic ring without bonding.
R ₆ to R ₉ independently represent a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, or a group having 2 to 20 carbon atoms containing a heterocycle.
The hydrogen atom in the group represented by R ₄ to R ₉ may be substituted with a halogen atom, a nitro group, a cyan group, a hydroxyl group, a carboxyl group or a heterocyclic group.
The methylene group among the groups represented by R ₄ to R ₉ may be substituted with -O- or -CO- in a state where oxygen atoms are not adjacent to each other.
R ₄ to R ₉ may independently form a ring together with an adjacent benzene ring.
g represents an integer from 0 to 4 and represents
h represents an integer of 0 to 3. )

Since the oxime ester compound has the structure represented by the above formula (2), the polymerization reaction of the radically polymerizable compound proceeds more efficiently.

Further, from the viewpoint of ease of production, it is more preferable that the oxime ester compound has a structure represented by the following formula (3) or (4).

(In formulas (3) and (4), R ₁ , R ₂ , R ₄ , R ₅ , R ₈ , g, h, and m are R ₁ , R ₂ , R ₄ , and R 4 in the above formula (2), respectively. Same as R ₅ , R ₈ , g, h, and m.)

Specific examples of the oxime ester compound having a group represented by the formula (1) include the following compounds (I-1) to (I-20).

Commercially available products of the oxime ester compound having a group represented by the formula (1) include, for example, IRGACURE OXE01, IRGACURE OXE02, IRGACURE OXE03, IRGACURE OXE04 (all manufactured by BASF), ADEKA ARCULS N-1919, NCI-831. Examples include NCI-930 (all manufactured by ADEKA).

The photoradical polymerization initiator can be used alone or in combination of two or more. The content of the photoradical polymerization initiator in the heat-sensitive color-developing layer is preferably 4% by mass or more, preferably 10% by mass or more, based on the content of the radically polymerizable compound from the viewpoint of improving the reactivity. More preferred. The upper limit of the content of the photoradical polymerization initiator is not particularly limited, but is preferably 40% by mass or less based on the content of the radically polymerizable compound, for example.

(Other ingredients)
The heat-sensitive color-developing layer may contain a storage stability improving agent. By including the preservability improving agent in the heat-sensitive color-developing layer, the preservability of the developed image can be further improved. Examples of the storage improving agent include 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane and 1,1,3-tris (2-methyl-4-hydroxy-5-tert-). Butylphenyl) butane, 1,1-bis (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4'-[1,4-phenylenebis (1-methylethylidene)] bisphenol, 4 , 4'-[1,3-phenylenebis (1-methylethylidene)] bisphenol and other phenol compounds; 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy) phenyl sulfone, 4 -Epoxy compounds such as (2-methyl-1,2-epoxyethyl) diphenyl sulfone, 4- (2-ethyl-1,2-epoxyethyl) diphenyl sulfone; 1,3,5-tris (2,6-dimethyl) Examples thereof include isocyanuric acid compounds such as benzyl-3-hydroxy-4-tert-butyl) isocyanuric acid.

The heat-sensitive color-developing layer can contain a heat sensitizer. By including the heat sensitizer in the heat-sensitive color-developing layer, the recording sensitivity can be improved. Examples of the heat sensitizer include stearate amide, methoxycarbonyl-N-benzyl stearate, N-benzoyl stearate amide, N-eicosanoic acid amide, ethylene bisstea acid amide, behenic acid amide, methylene bisstea acid amide, and N. -Methylol stearate amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, oxalic acid dibenzyl ester, p-tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1, 2 -Di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ethane, 1,2-di (4-methoxyphenoxy) ethane, 1,2-di (4-chlorophenoxy) ethane, 1 , 2-Diphenoxyetane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetotoluiside, p-acet Phenetidine, 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. The content of the heat sensitizer in the heat-sensitive color-developing layer may be an amount effective for heat sensitization. Specifically, the total solid content of the heat-sensitive color-developing layer is preferably 2% by mass or more and 40% by mass or less, and preferably 5% by mass or more and 25% by mass or less.

Auxiliary agents such as a storage improver and a heat sensitizer may be mixed with a coating liquid for forming a heat-sensitive color-developing layer in the state of fine particles (solid dispersed fine particles) dispersed in water. Further, these auxiliaries can be dissolved in a solvent and used as an emulsified state by using a water-soluble polymer compound as an emulsifier. Further, the storage stability improving agent and the heat sensitizer may be contained in the particles containing the electron-donating dye precursor and the electron-accepting compound.

The heat-sensitive color-developing layer can contain a polymerization accelerator. Examples of the polymerization accelerator include benzoate compounds and amine compounds.

Examples of the benzoate compound and the amine compound include ethyl-4- (dimethylamino) -benzoate, ethylhexyl-4-dimethylaminobenzoate, methyl-o-benzoylbenzoate, p- (dimethylamino) 3-methylbutyl benzoate, N, N-. Examples thereof include dimethylaminobenzoic acid ethyl ester, N, N-dimethylaminobenzoic acid isoamyl ester, pentyl4-dimethylaminobenzoate, triethylamine, triethanolamine and the like.

The heat-sensitive color-developing layer can contain a sensitizer. The sensitizer may be one that sensitizes the photoradical polymerization initiator by an electron transfer mechanism or an energy transfer mechanism. Examples of the sensitizer include aromatic polycondensate compounds such as anthracene, 9,10-dialkoxyanthracene, pyrene and perylene; aromatic ketone compounds such as acetophenone, benzophenone, thioxanthone and Michler ketone; and phenothiazine and N-aryloxazolidinone. Heterocyclic compounds can be mentioned. The content of the sensitizer in the heat-sensitive color-developing layer is preferably 0.1 part by mass or more and 10 parts by mass or less with respect to 1 part by mass of the photoradical polymerization initiator, and is preferably 1 part by mass or more and 5 parts by mass or less. It is more preferable to do so.

In order to improve the electron transfer efficiency or energy transfer efficiency between the sensitizer and the photoradical polymerization initiator, it is preferable to include a sensitizing aid in the heat-sensitive color-developing layer. Examples of the sensitizing aid include naphthalene compounds such as 1,4-dihydroxynaphthalene, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 4-methoxy-1-naphthol, and 4-ethoxy-1-naphthol; 1 , 4-Dihydroxybenzene, 1,4-dimethoxybenzene, 1,4-diethoxybenzene, 1-methoxy-4-phenol, 1-ethoxy-4-phenol and other benzene compounds can be mentioned. The content of the sensitizing aid in the heat-sensitive color-developing layer is preferably 0.1 part by mass or more and 10 parts by mass or less, and 0.5 parts by mass or more and 5 parts by mass or less with respect to 1 part by mass of the sensitizer. Is preferable.

The heat-sensitive color-developing layer can contain a radical polymerization inhibitor. The photoradical polymerization initiator is slightly decomposed into a radical compound during storage of the heat-sensitive recorder. Since polymerization caused by this radical compound may be caused, it is preferable to include a radical polymerization inhibitor in the heat-sensitive color-developing layer in order to prevent this polymerization.

Examples of the radical polymerization inhibitor include phenolic hydroxyl group-containing compounds, methquinone (hydroquinone monomethyl ether), hydroquinone, quinones such as 4-methoxy-1-naphthol, hindered amine antioxidants, and 1,1-diphenyl-2-picryl. Hydrazyl-free radicals, N-oxyl-free radical compounds, nitrogen-containing heterocyclic mercapto compounds, thioether-based antioxidants, hindered phenol-based antioxidants, ascorbic acids, zinc sulfate, thiocitanoates, thiourea derivatives, various Of saccharides, phosphoric acid antioxidants, nitrites, sulfites, thiosulfates, hydroxylamine derivatives, aromatic amines, phenylenediamines, imines, sulfonamides, urea derivatives, oximes, dicyandiamides and polyalkylene polyamines. Examples thereof include polycondensates, sulfur-containing compounds such as phenothiazine, tetraazaannulene (TAA) -based complexing agents, and hindered amines.

Among them, as the radical polymerization inhibitor, phenols, N-oxyl-free radical compounds, 1,1-diphenyl-2-picrylhydrazyl-free radicals, phenothiazines, quinones, and hindered amines are preferable. Further, N-oxyl-free radical compounds are more preferable. The content of the radical polymerization inhibitor in the heat-sensitive color-developing layer is preferably 1 ppm or more and 5,000 ppm or less on a mass basis with respect to the content of the radically polymerizable compound.

The heat-sensitive color-developing layer can contain a pigment having a high whiteness with an average particle diameter of 10 μm or less. By containing such a pigment, the whiteness of the heat-sensitive color-developing layer can be improved and the uniformity of the image can be improved. Pigments include calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, surface-treated calcium carbonate and silica. Inorganic pigments; organic pigments such as urea-formalin resin, styrene-methacrylic acid copolymer resin, and polystyrene resin can be mentioned. The content of the pigment in the heat-sensitive color-developing layer is preferably an amount that does not reduce the color-developing density of the image. Specifically, it is preferably 50% by mass or less in the total solid content of the heat-sensitive color-developing layer.

A binder can be used as a component for forming the heat-sensitive color-developing layer. Further, if necessary, a cross-linking agent, waxes, metal soap, colored dye, colored pigment, fluorescent dye and the like can be contained. Examples of the binder include polyvinyl alcohol and its derivatives; starch and its derivatives; cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose and ethyl cellulose; sodium polyacrylic acid, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymers, and the like. Water-soluble polymer materials such as acrylamide-acrylic acid ester-methacrylic acid ester copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, casein, gelatin and derivatives thereof; vinyl acetate , Polyacrylic acid, Polyacrylic acid, Polyacrylic acid ester, Vinyl chloride-vinyl acetate copolymer, Polybutyl methacrylate, Ethylene-vinyl acetate copolymer and other emulsions; Examples thereof include latex of a water-insoluble polymer such as a polymer.

By including a cross-linking agent in the heat-sensitive color-developing layer, the water resistance of the heat-sensitive color-developing layer can be improved. Examples of the cross-linking agent include aldehyde compounds such as glioxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxyphosphates, dimethylolurea compounds, aziridine compounds, and organic compounds such as blocked isocyanate compounds; In addition to inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, potassium tetraborate, etc .; examples thereof include boric acid, borate triester, borane polymer, hydrazide compound, glyoxylate and the like. The content of the cross-linking agent in the heat-sensitive color-developing layer is preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the total solid content of the heat-sensitive color-developing layer.

Examples of the wax include waxes such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax and polyethylene wax; higher fatty acid amides such as stearate amide and ethylene bisstearic acid amide; higher fatty acid esters and derivatives thereof. can. Examples of the metal soap include higher fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate.

When the heat-sensitive recording body is a two-color heat-sensitive recording body, it is preferable that the heat-sensitive color-developing layer contains a colored dye or a colored pigment having a color tone that is complementary to the low-temperature color-developing color tone. By incorporating such a colored dye or a colored pigment in the heat-sensitive color-developing layer, the color tone of the heat-sensitive recorder before and after forming an image can be adjusted. Further, if necessary, various auxiliary agents such as an oil repellent, an antifoaming agent, and a viscosity adjusting agent can be contained in the heat-sensitive color-developing layer.

For the heat-sensitive color-developing layer, for example, water is used as a dispersion medium, and a coating liquid for a heat-sensitive color-developing layer containing each component constituting the heat-sensitive color-developing layer is applied onto a support to form a coating layer, and then this coating is applied. It can be formed by drying the layer. The amount of the coating liquid to be applied is preferably 2 g / m ² or more and 20 g / m ² or less, more preferably 2 g / m ² or more and 15 g / m ² or less, and 2 g / m ² or more and 10 g in terms of dry mass. It is particularly preferable that it is / m ² or less.

It is preferable to use a surfactant to prepare the above-mentioned first particles and second particles. Surfactants include anionic surfactants such as sodium alkylsulfonate, sodium alkylbenzenesulfonate, sodium dialkylsulfosuccinate, sodium alkylcarboxylate; polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene polyoxy. Nonionic surfactants such as propylene glycol, sorbitan alkyl ester, polyoxyethylene sorbitan alkyl ester, glycerin alkyl SL, polyoxyethylene hydrogenated castor oil; cations such as alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, alkylbenzyldimethylammonium chloride. Sexual surfactants; amphoteric surfactants such as alkylbetaine and alkyldimethylamine oxide can be mentioned. Further, a polymer-type surfactant such as a sodium salt of a naphthalene sulfonic acid formarin condensate or sodium polyacrylate can be used.

Ionic groups such as sulfonic acid groups, carboxylic acid groups and amino groups; radical polymerizable compounds imparted with surface active ability by binding hydrophilic nonionic groups such as polyoxyethylene groups and polyglyceryl groups to radically polymerizable compounds. Can also be used.

A dispersion aid can also be used to prepare the first and second particles described above. Dispersion aids include polyvinyl alcohol and its variants, polyacrylic acid amides and derivatives thereof, ethylene / vinyl acetate copolymers, styrene / maleic anhydride copolymers, ethylene / maleic anhydride copolymers, isobutylene / anhydrous. Water-soluble polymers such as maleic acid copolymer, polyvinylpyrrolidone, ethylene / acrylic acid copolymer, vinyl acetate / acrylic acid copolymer, carboxymethyl cellulose, methyl cellulose, casein, gelatin, starch derivative, arabiya rubber, sodium alginate, etc. be able to.

The amount of the surfactant and the dispersion aid added is preferably 0.1% by mass or more and 10% by mass or less based on the respective masses of the first particle and the second particle, and 0. It is more preferably 5% by mass or more and 5% by mass or less.

(Middle layer)
When the heat-sensitive color-developing layer has an electron-donating dye precursor layer (leuco dye layer) and an electron-accepting compound layer (color developer layer), an intermediate layer can be provided between these layers. As the material constituting the intermediate layer, a water-soluble polymer material or a water-insoluble polymer used in a known heat-sensitive recording material can be used. Specific examples of the material constituting the intermediate layer include the same materials as the binder which is a component for constituting the heat-sensitive color-developing layer. Further, particles having a high void ratio such as silica and calcined kaolin and organic compounds such as plastic pigments, hollow particles, foams, and polyethylene wax having a glass transition point or a melting point may be contained in the intermediate layer as an auxiliary agent.

The intermediate layer is formed by, for example, using water as a dispersion medium, applying a coating liquid for an intermediate layer containing each component constituting the intermediate layer to form a coating layer, and then drying the coating layer. can do. The amount of the coating liquid to be applied is preferably 1 g / m ² or more and 40 g / m ² or less, and more preferably 2 g / m ² or more and 10 g / m ² or less in terms of dry mass.

Further, an intermediate layer may be provided between the two types of heat-sensitive color-developing layers. The intermediate layer arranged between the heat-sensitive color-developing layer and the heat-sensitive color-developing layer preferably contains an ultraviolet absorber. By containing an ultraviolet absorber in this intermediate layer, the ultraviolet transmittance of the intermediate layer can be controlled to a desired value.

As the UV absorber, a benzotriazole-based UV absorber, a triazine-based UV absorber, a benzophenone-based UV absorber, a cyanoacrylate-based UV absorber, a salicylic acid-based UV absorber, or titanium oxide may be used. can.

(Protective layer)
It is preferable to have a protective layer on the heat-sensitive color-developing layer. As the protective layer, a protective layer used in a known heat-sensitive recording body can be used. For example, it is preferable to provide a protective layer containing a water-soluble polymer material and particles. As the water-soluble polymer material and particles, the same materials as those that can be contained in the heat-sensitive color-developing layer can be used. Further, it is also preferable to add a cross-linking agent to impart water resistance to the protective layer.

By including microcapsules containing an ultraviolet absorber and solid dispersed fine particles of an ultraviolet absorber in the protective layer, the light resistance can be significantly improved. Among them, microcapsules having a wall film made of polyurethane-polyurea resin or aminoaldehyde resin are preferable because they have excellent heat resistance and also exhibit excellent accompanying effects such as suppressing sticking to the thermal head. Further, the microcapsules having a wall film made of a polyurethane-polyurea resin or an aminoaldehyde resin have a lower refractive index than the microcapsules having a wall film made of another resin. Further, since the shape is spherical, even if a large amount is added to the protective layer, the concentration decrease due to diffused reflection of light is unlikely to occur, which is preferable.

Further, it is preferable to contain particles in the protective layer because it is possible to prevent dirt from adhering to the thermal head and sticking. The oil absorption of the particles is preferably 50 mL / 100 g or more. The content of the particles in the protective layer is preferably an amount that does not reduce the color development density, and specifically, is preferably 60% by mass or less in the total solid content of the protective layer.

For the protective layer, for example, water is used as a dispersion medium, and a coating liquid for the protective layer containing each component constituting the protective layer is applied onto the heat-sensitive color-developing layer to form a coating layer, and then this coating layer is applied. It can be formed by drying. The amount of the coating liquid to be applied is preferably 0.1 g / m ² or more and 15 g / m ² or less, and more preferably 0.5 g / m ² or more and 8 g / m ² or less in terms of dry mass.

(Resin layer)
A resin layer made of a resin cured by an electron beam or ultraviolet rays can be provided on each of the heat-sensitive color-developing layer, the intermediate layer, and the protective layer. As the resin cured by an electron beam, for example, the resin described in JP-A-58-177392 can be used. Auxiliary agents such as non-electron beam curable resin, particles, defoaming agent, leveling agent, lubricant, surfactant, and plasticizer may be appropriately added to the resin constituting the resin layer. Among them, it is preferable to add particles such as calcium carbonate and aluminum hydroxide; waxes and lubricants such as silicon because sticking to the thermal head can be suppressed.

(Other layers)
By processing the heat-sensitive recording body to give it a higher function, the added value of the heat-sensitive recording body can be increased. For example, by applying an adhesive, a re-wet adhesive, a delayed tack type adhesive, or the like to the back surface, it is possible to obtain an adhesive paper, a re-wet adhesive paper, or a delayed tack paper. Further, by imparting functions such as thermal transfer paper, inkjet recording paper, carbonless copy paper, electrostatic recording paper, and zeography paper to the back surface, it is possible to obtain a recording paper capable of double-sided recording. Furthermore, by arranging a heat-sensitive color-developing layer on the back surface, a double-sided heat-sensitive recording body can be obtained. Further, a back layer may be provided on the back surface of the heat-sensitive recording body in order to suppress the penetration of oil or plasticizer from the back surface, or to control curl or prevent static electricity.

(Layer structure of thermal recording body)
FIG. 1 is a cross-sectional view showing an embodiment of the heat-sensitive recording body of the present invention. The heat-sensitive recording body 100 shown in FIG. 1 includes a sheet-shaped support 101. An electron-donating dye precursor layer 102, an intermediate layer 103, an electron-accepting compound layer 104, and a protective layer 105 are laminated and arranged in this order on one surface side of the support 101. In the heat-sensitive recorder according to the embodiment of the present invention, the order of the electron-donating dye precursor layer 102 and the electron-accepting compound layer 104 may be reversed, and the protective layer 105 as shown in FIG. 1 may not be provided. good.

FIG. 2 is a cross-sectional view showing another embodiment of the heat-sensitive recording body of the present invention. The heat-sensitive recording body 200 shown in FIG. 2 has a sheet-shaped support 201 and an electron-donating dye precursor layer 202, an electron-accepting compound layer 203, and a protective layer 204 on one surface side of the support 201. They are stacked and arranged in order. In the heat-sensitive recorder according to the embodiment of the present invention, the order of the electron-accepting compound layer 202 and the electron-donating dye precursor layer 203 may be reversed, and the protective layer 204 as shown in FIG. 2 may not be provided. good.

The supports 101 and 201 may be made of a material capable of forming a coating film using a coating liquid (heat-sensitive color-developing composition) for the heat-sensitive color-developing layer. Examples of the constituent materials of the supports 101 and 201 include paper, synthetic paper, and various plastics. Examples of the plastic include PET (polyethylene terephthalate) and OPP (oriented polypropylene). If necessary, the surfaces of the supports 101 and 201 are preferably subjected to a corona discharge treatment, a sandplast treatment, a primer treatment (lamination of the undercoat layer) and the like. By applying these treatments, the wettability of the surfaces of the supports 101 and 201 can be improved, the surface can be roughened or easily adhered, and the formability of the coating film by the heat-sensitive color-developing composition is enhanced. It is possible.

A coating film can be formed by applying or printing a heat-sensitive color-developing composition on the supports 101 and 201. Examples of means for applying or printing the heat-sensitive color-developing composition include a blade coater, a rod coater, a reverse roll coater, a die coater, an offset printing machine, a gravure printing machine, a flexographic printing machine, a letterpress printing machine, and a silk screen printing machine. be able to. The intermediate layer (including the protective intermediate layer) and the protective layer can be formed by using an intermediate layer composition or an overcoat composition prepared by the same method as the method for preparing a heat-sensitive color-developing composition. A coating film can be formed by applying these intermediate layer compositions and overcoat compositions to predetermined locations. By forming each coating film and then drying it, each layer can be formed, and a target heat-sensitive recording body can be obtained. The coating film may be applied and dried one layer at a time, or the same coating film may be applied and dried in two or more times. Further, simultaneous multi-layer coating may be performed in which two or more coating liquids are simultaneously coated. It is preferable to perform smoothing treatment by a known method such as a super calendar or a soft calendar in an arbitrary process such as after each layer is formed or after all layers are formed. By the surface smoothing treatment, the recording sensitivity can be improved and the uniformity of the formed image can be improved.

<Image formation method>
Next, the image forming method of the present invention will be described. The image forming method of the present invention includes a step of applying a heat pulse to the above-mentioned heat-sensitive recording body by applying a heat pulse (image forming step) and irradiating the heat-sensitive recording body on which the image is formed with ultraviolet rays. Then, it has a step of fixing the heat-sensitive color-developing layer (fixing step).

The temperature of the heat pulse applied to the heat-sensitive recorder in the image forming step can be, for example, 80 ° C. or higher and 120 ° C. or lower. A desired image can be formed by applying a heat pulse to the heat-sensitive color-developing layer of the heat-sensitive recording body in a state where the thermal head is in contact with the heat-sensitive recording body. Specifically, the radically polymerizable compound contained in the heat-sensitive color-developing layer is dissolved by applying a heat pulse and heating. When the radically polymerizable compound is dissolved, the electron-donating dye precursor and the electron-accepting compound come into contact with each other to develop a color-sensitive color-developing layer, and an image can be formed.

In the fixing process, the heat-sensitive recorder on which the image is formed is irradiated with ultraviolet rays. The wavelength of the ultraviolet rays to be irradiated may be a wavelength at which the photoradical polymerization initiator contained in the heat-sensitive color-developing layer can react, and may be, for example, 365 nm or more and 425 nm or less. By irradiating with ultraviolet rays, the radically polymerizable compound can be polymerized and the heat-sensitive color-developing layer can be fixed. If the heat-sensitive color-developing layer is fixed, the heat-sensitive color-developing layer does not develop color even if the heat energy reaching the color-developing start temperature is subsequently applied, so that the color-developing property of the formed image can be maintained for a long period of time. The wavelength of ultraviolet rays in the present specification means the peak wavelength of ultraviolet rays to be irradiated. Further, fixing the heat-sensitive color-developing layer means fixing the color-developing state of the heat-sensitive color-developing layer.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. Unless otherwise specified, those described as "parts" and "%" regarding the amount of components are based on mass.

<Manufacturing of thermal recording body (1)>
(Example 1)
[Preparation of raw material composition]
The liquids [A] to [D] were adjusted as follows.
[A] Liquid: Composition containing electron-donating dye precursor-Electron-donating dye precursor (BLUE220, manufactured by Fukui Yamada Chemical Industry Co., Ltd.)
3 parts ・ Radical polymerizable compound (SR368, manufactured by Arkema Co., Ltd.) 30 parts ・ Photo-radical polymerization initiator (the compound (I-15)) 9 parts ・ Ethyl acetate 58 parts

The above materials were mixed and dissolved to obtain a liquid [A].
[B] Liquid: Dispersion of electron-accepting compound-containing particles ・ Electron-accepting compound (TGSH (H), manufactured by Nippon Kayaku Co., Ltd.) 40 parts ・ Dispersant (Perex NBL, manufactured by Kao Corporation) 4 parts・ 56 parts of water

After mixing the above materials, they were pulverized and dispersed using a bead mill to obtain a liquid [B]. When measured using a particle size distribution measuring device (Nanotrack, manufactured by Microtrac), the particle size (D50) of the electron-accepting compound-containing particles in the liquid [B] was about 700 nm.
[C] Liquid: Coating liquid for intermediate layer, polyvinyl alcohol (Kuraray 5-88, manufactured by Kuraray) 10 parts, water 90 parts

The above materials were mixed and dissolved to obtain a solution [C].
[D] Liquid: Kaolin dispersion liquid, kaolin (HYDRAGLOSS90, KaMin, 59.5 parts manufactured by LLC, dispersant (Aron T-50, manufactured by Toagosei, solid content concentration 40%) 0.5 parts, 40 parts water

The above material was dispersed using a choles for 1 hour to obtain a liquid [D].

[Formation of thermal color layer]
The solution [A] was applied to a synthetic paper (manufactured by YUPO, YUPO) having a thickness of 130 μm using a printability tester, and then dried with a dryer to evaporate ethyl acetate. The coating amount of the liquid [A] after drying was 40.0 g / m ² , and the coating amount of BLUE 220 was 1.20 g / m ² . Then, the liquid [C] was applied using a printability tester, and then dried with a dryer. The amount of the [C] solution applied after drying was 0.2 g / m ² . Then, the liquid [B] was applied using a printability tester, and then dried with a dryer. The coating amount of the [B] solution after drying was 30.0 g / m ² , and the coating amount of TGSH (H) was 12.0 g / m ² .

[Formation of protective layer]
210 parts of 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol A, 80 parts of 20% aqueous solution of acetoacetyl-modified polyvinyl alcohol B, 100 parts of [D] solution, 5.6 parts of aqueous dispersion of zinc stearate, and polyethylene wax emulsion 2. .5 copies were prepared. These components were mixed and stirred to obtain a coating liquid for a protective layer. As the acetoacetyl-modified polyvinyl alcohol A, the trade name "Gosefimer Z-200" (saponification degree 99.4 mol%, average polymerization degree 1,000, modification degree 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used. .. As the acetoacetyl-modified polyvinyl alcohol B, the trade name "Gosefimer Z-100" (saponification degree 99.4 mol%, average polymerization degree 500, modification degree 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used. As the aqueous dispersion of zinc stearate, the trade name “Hydrin Z-8-36” (manufactured by Chukyo Oil & Fat Co., Ltd., solid content concentration 36%) was used. As the polyethylene wax emulsion, the trade name "Chemipal W-400" (solid content concentration 40%, manufactured by Mitsui Chemicals) was used.

The obtained protective layer coating liquid is applied onto the heat-sensitive color-developing layer so that the coating amount after drying is 1.5 g / m ² , and dried to form a protective layer, and then the surface is smoothed with a super calendar. I got a heat-sensitive recorder.

(Examples 2 to 31 and 33)
The photoradical polymerization initiator, radically polymerizable compound, electron donating dye precursor and electron accepting compound used in Example 1 were changed as shown in Table 1, and the heat-sensitive recorders of Examples 2 to 31 and 33 were obtained. Obtained.

<Manufacturing of thermal recording body (2)>
(Example 32)
[Preparation of raw material composition]
The [oil phase E] liquid, [F] liquid, [aqueous phase G] liquid, [H] liquid and [D] liquid were adjusted as follows.
[Oil phase E] Liquid: Composition containing electron donating dye precursor ・ Electron donating dye precursor (BLUE220, manufactured by Fukui Yamada Chemical Industry Co., Ltd.) Part 3 ・ Radical polymerizable compound (SR368, Alchema Co., Ltd.) (Manufactured) 30 parts, photoradical polymerization initiator (compound (I-15)) 9 parts, ethyl acetate 58 parts

The above materials were mixed and dissolved to obtain a [oil phase E] liquid.
[F] Liquid: Dispersion of electron-accepting compound-containing particles ・ Electron-accepting compound (TGSH (H), manufactured by Nippon Kayaku Co., Ltd.) 40 parts ・ Dispersant (Perex NBL, manufactured by Kao Corporation) 4 parts・ 56 parts of water

After mixing the above materials, liquid [F] was obtained. When measured using a particle size distribution measuring device (Nanotrack, manufactured by Microtrac), the particle size (D50) of the electron-accepting compound-containing particles in the [F] solution was about 700 nm.
[Aquatic phase G] Liquid:
・ Dispersant (Perrex NBL, manufactured by Kao Corporation) 15 copies ・ Water 110 copies

The above materials were mixed and dissolved to obtain a [Aquatic Phase G] solution.
[H] liquid: Dispersion liquid of electron-donating dye precursor-containing particles After mixing 40 parts of [oil phase E] liquid and 50 parts of [aqueous phase G] liquid, an ultrasonic homogenizer (UH-600S, manufactured by SMT) is used. Used and emulsified. Then, ethyl acetate was removed under reduced pressure using a rotary evaporator to obtain a liquid [H], which is a dispersion liquid of electron-donating dye precursor-containing particles. The particle size (D50) of the electron-donating dye precursor-containing particles in the [H] liquid measured using a particle size distribution measuring device (Nanotrack, manufactured by Microtrac) was 160 nm.
[D] Liquid: Kaolin dispersion liquid / kaolin (HYDRAGLOSS90, KaMin, manufactured by LLC)
59.5 parts, dispersant (Aron T-50, manufactured by Toagosei, solid content concentration 40%) 0.5 parts, water 40 parts

The above material was dispersed using a choles for 1 hour to obtain a liquid [D].

[Formation of thermal color layer]
The [H] solution was applied to a synthetic paper (manufactured by YUPO, YUPO) having a thickness of 130 μm using a printability tester, and then dried with a dryer. The coating amount of the [H] liquid after drying was 40.0 g / m ² , and the coating amount of BLUE 220 was 1.20 g / m ² . Then, the liquid [F] was applied using a printability tester and then dried with a dryer to form a heat-sensitive color-developing layer. The amount of the liquid [F] applied after drying was 30.0 g / m ² , and the amount of TGSH (H) applied was 12.0 g / m ² .

[Formation of protective layer]
210 parts of 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol A, 80 parts of 20% aqueous solution of acetoacetyl-modified polyvinyl alcohol B, 100 parts of [C] solution, 5.6 parts of aqueous dispersion of zinc stearate, and polyethylene wax emulsion 2. .5 copies were prepared. These components were mixed and stirred to obtain a coating liquid for a protective layer. As the acetoacetyl-modified polyvinyl alcohol A, the trade name "Gosefimer Z-200" (saponification degree 99.4 mol%, average polymerization degree 1,000, modification degree 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used. .. As the acetoacetyl-modified polyvinyl alcohol B, the trade name "Gosefimer Z-100" (saponification degree 99.4 mol%, average polymerization degree 500, modification degree 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used. As the aqueous dispersion of zinc stearate, the trade name “Hydrin Z-8-36” (manufactured by Chukyo Oil & Fat Co., Ltd., solid content concentration 36%) was used. As the polyethylene wax emulsion, the trade name "Chemipal W-400" (solid content concentration 40%, manufactured by Mitsui Chemicals) was used. The obtained protective layer coating liquid is applied onto the heat-sensitive color-developing layer so that the coating amount after drying is 1.5 g / m ² , and dried to form a protective layer, and then the surface is smoothed with a super calendar. I got a heat-sensitive recorder.

The obtained protective layer coating liquid is applied onto the heat-sensitive color-developing layer so that the coating amount after drying is 1.5 g / m ² , and dried to form a protective layer, and then the surface is smoothed with a super calendar. I got a heat-sensitive recorder.

(Comparative Examples 1 to 12)
The photoradical polymerization initiator, radically polymerizable compound, electron donating dye precursor and electron accepting compound used in Example 1 were changed as shown in Table 1 to obtain heat-sensitive recorders of Comparative Examples 1 to 12. ..

<Image formation and evaluation>
(UV fixability)
An ultraviolet irradiation device (GC77 (irradiation wavelength: 365 nm), manufactured by HAMAMATSU) equipped with a linear irradiation type UV-LED was used for the heat-sensitive recorders obtained in Examples 1 to 33 and Comparative Examples 1 to 12, and the conveyor speed was 100 m. Ultraviolet rays were irradiated once at / min and 10 m / min. Separately, when the integrated light amount under the same conditions was measured with an ultraviolet integrated photometer (C9536-01, manufactured by HAMAMATSU), it was 100 mJ / cm ² and 1000 mJ / cm ² , respectively.

After that, using a thermal head (KPE type, manufactured by Kyocera), the applied power and pulse width were set so that the recording energy per unit area was 150 mJ / mm ² , and the heat-sensitive recorder after the above ultraviolet irradiation was 2 cm. An image of × 2 cm was formed. The optical reflection density of the image formed by using a reflection densitometer (trade name "Xrite530", manufactured by Sakata Inx Corporation) was measured. The difference from the optical reflection density of the above-mentioned synthetic paper (Yupo, manufactured by YUPO) is defined as "Δ optical reflection density", and the UV fixability (difficulty of color development due to heating after ultraviolet irradiation) is based on this Δ optical reflection density. Evaluation was performed. The evaluation results are shown in Table 2.

As shown in Table 2, in Examples 1 to 33, the absolute values of the Δ optical reflection densities of the images after the integrated light amounts of 100 mJ / cm ² and 1000 mJ / cm ² were sufficiently fixed. confirmed. That is, it was confirmed that even when the integrated light amount is 100 mJ / cm ² and the irradiation light amount of ultraviolet rays is low, the color development due to heating after the ultraviolet irradiation is suppressed.

On the other hand, in Comparative Examples 1 to 4, the acylphosphine oxide compounds (I-21) and (I-22) are used as the photoradical polymerization initiator. In Comparative Examples 1 to 4, the Δ optical reflection density at an integrated light amount of 1000 mJ / cm ² is 0.15 or more, and it can be seen that the color is slightly developed as compared with Examples 1 to 33. Further, the Δ optical reflection density at the integrated light amount of 100 mJ / cm ² is 0.58 or more, and it can be seen that the color is developed as compared with Examples 1 to 33. That is, when the integrated light amount is as low as 100 mJ / cm ² and the ultraviolet irradiation light amount is low, it is not possible to suppress the color development due to heating after the ultraviolet irradiation.

Further, in Comparative Examples 5 and 6, it is an α-aminoalkylphenone compound (I-23), in Comparative Examples 7 and 8, it is a benzophenone compound (I-24), and in Comparative Examples 9 and 10, it is a benzophenone compound. In Comparative Examples 11 and 12, which are thioxanthone compounds (I-25), ketocoumarin compounds (I-26) are used. It can be seen that in Comparative Examples 5 to 12, color development due to heating after irradiation with ultraviolet rays could not be suppressed in the case of irradiation with ultraviolet rays having an integrated light amount of 100 mJ / cm ² , as in Comparative Examples 1 to 4. ..

Further, comparing Examples 1 to 16 and 33 with Examples 17 to 20, when a pentaerythritol derivative, an isocyanurate derivative or a trimethylolpropane derivative was used as the radically polymerizable compound, compared with the case where a glycerin derivative was used. The Δ optical reflection density is small. In particular, in Examples 1 to 16 and 33, it can be seen that color development can be suppressed even when heated after irradiation with a low light amount (100 mJ / cm ² ) of ultraviolet rays.

Further, when Examples 17 to 20 and Examples 21 to 27 are compared, when the content of the photoradical polymerization initiator is 4% by mass or more, the Δoptical is compared with the case where the content is 3% by mass. The reflection density is low.

Further, when Examples 21 to 27 and Examples 28 to 29 are compared, the case where the oxime ester compound represented by the above formula (3) or (4) is used as the photoradical polymerization initiator is the case where the above formula is used. The Δ optical reflection density is smaller than that in the case of using an oxime ester compound other than (3) or (4).

Further, when Examples 28 to 29 and Examples 30 to 31 are compared, the case where the oxime ester compound represented by the above formula (2) is used as the photoradical polymerization initiator is different from the above formula (2). The Δ optical reflection density is smaller than that in the case of using the oxime ester compound represented by the above formula (1).

In addition, in Table 1, (I-1), (I-2), (I-4), (I-5), (I-8), (I-9), (I-11), (I) -13), (I-15), (I-16) and (I-17) are exemplary compounds (I-1), (I-2), (I-) of the photoradical polymerization initiator described above. 4), (I-5), (I-8), (I-9), (I-11), (I-13), (I-15), (I-16) and (I-17) Is the same as.

Tables 3 to 6 show the details of each component used in Examples and Comparative Examples.

The present invention is not limited to the above embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are attached in order to publicize the scope of the present invention.

This application claims priority based on Japanese Patent Application No. 2020-143834 submitted on August 27, 2020 and Japanese Patent Application No. 2021-135031 submitted on August 20, 2021. All of the contents are incorporated here.

Claims (7)

1. A heat-sensitive recorder provided with a heat-sensitive color-developing layer containing an electron-donating dye precursor, an electron-accepting compound, a radically polymerizable compound, and a photoradical polymerization initiator.
   A heat-sensitive recorder, wherein the photoradical polymerization initiator contains an oxime ester compound having a group represented by the following formula (1).
   

   

   
   (In the formula (1), R ₁ and R ₂ each independently contain a hydrogen atom, a halogen atom, a nitro group, a cyano group, a hydrocarbon group having 1 to 20 carbon atoms, or a heterocycle. Represents 2 to 20 groups
   The hydrogen atoms in the groups represented by R ₁ and R ₂ are halogen atom, nitro group, cyano group, hydroxyl group, amino group, carboxyl group, methacryloyl group, acryloyl group, epoxy group, vinyl group, vinyl ether group and mercapto group. , An isocyanate group, or a group having 2 to 20 carbon atoms containing a heterocycle may be substituted.
   The methylene groups in the groups represented by R ₁ and R ₂ are -O-, -CO-, -COO-, -OCO-, -NR _3- , -NR ₃ CO-, -S-, -CS-. , -SO _2- , -SCO-, -COS-, -OCS-, -CH = CH-, -CC-, or -CSO- may be substituted, where R ₃ is a hydrogen atom or a carbon atom. Represents a hydrocarbon group of number 1 to 20
   m represents 0 or 1 and represents
   * Represents a binding site with another structure, and the binding site may form a ring together with a group represented by _R1 . )
2. The heat-sensitive recorder according to claim 1, wherein the oxime ester compound has a structure represented by the following formula (2).
   

   

   
   (In the formula (2), R ₁ , R ₂ , and m are the same as R ₁ , R ₂ , and m in the formula (1), respectively.
   R ₄ and R ₅ independently have a hydrogen atom, a nitro group, a cyano group, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an arylalkyl group having 7 to 20 carbon atoms. , Or a group containing 2 to 20 carbon atoms containing a heterocycle.
   X ₁ represents -O-, -S-, -Se-, -CR ₆ R _7- , -CO-, -NR _8- , or -PR _9- .
   X ₂ represents a single bond, a hydrocarbon group having 1 to 20 carbon atoms, -CO-, or a hydrogen atom bonded to a separate aromatic ring without bonding.
   R ₆ to R ₉ independently represent a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, or a group having 2 to 20 carbon atoms containing a heterocycle.
   The hydrogen atom in the group represented by R ₄ to R ₉ may be substituted with a halogen atom, a nitro group, a cyan group, a hydroxyl group, a carboxyl group, or a heterocyclic group.
   The methylene group among the groups represented by R ₄ to R ₉ may be substituted with -O- or -CO- in a state where oxygen atoms are not adjacent to each other.
   R ₄ to R ₉ may independently form a ring together with an adjacent benzene ring.
   g represents an integer from 0 to 4 and represents
   h represents an integer of 0 to 3. )
3. The heat-sensitive recorder according to claim 2, wherein the oxime ester compound has a structure represented by the following formula (3) or (4).
   

   

   
   (In formulas (3) and (4), R ₁ , R ₂ , R ₄ , R ₅ , R ₈ , g, h, and m are R ₁ , R ₂ , R ₄ , and R 4 in the above formula (2), respectively. Same as R ₅ , R ₈ , g, h, and m.)
4. The heat-sensitive recorder according to any one of claims 1 to 3, wherein the content of the photoradical polymerization initiator is 4% by mass or more based on the content of the radically polymerizable compound.
5. The heat-sensitive recorder according to any one of claims 1 to 4, wherein the radically polymerizable compound contains at least one compound selected from the group consisting of a pentaerythritol derivative, an isocyanurate derivative, and a trimethylolpropane derivative.
6. Claims 1 to claim 1, wherein particles containing the radically polymerizable compound and the photoradical polymerization initiator are contained in the heat-sensitive color-developing layer, whichever is one of the electron-donating dye precursor and the electron-accepting compound. The heat-sensitive recorder according to any one of 5.
7. A step of forming an image by applying a heat pulse to the heat-sensitive recorder according to any one of claims 1 to 6 using a thermal head.
   A step of irradiating the heat-sensitive recording body on which the image is formed with ultraviolet rays to fix the heat-sensitive color-developing layer, and a step of fixing the heat-sensitive color-developing layer.
   An image forming method characterized by having.

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