Thermal recording medium and image forming method

Abstract

To provide a thermosensitive recording medium that can inhibit coloring due to heating after ultraviolet irradiation even when the amount of ultraviolet light irradiated is small.SOLUTION: A thermosensitive recording medium comprises a thermosensitive coloring layer containing an electron-donating dye precursor, a radical photopolymerization initiator, and an electron-accepting compound with a radical polymerizable group, where the electron-accepting compound with a radical polymerizable group includes a compound A represented by the formula (1) in the figure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermosensitive recording medium and an image forming method using the same. [Background technology]

[0002] Conventionally, thermosensitive recording media have been widely used, which utilize a mechanism for color development by reacting a leuco dye with a color developer. Because thermosensitive recording media do not require consumables such as ink or toner and are relatively inexpensive, they are widely used as recording media for fax machines, receipts, and other applications. A typical thermosensitive recording medium is manufactured by printing or coating a water-containing thermosensitive color-developing composition in the form of a coating liquid onto a substrate, followed by drying to form a thermosensitive color-developing layer.

[0003] A method of forming a thermosensitive coloring layer by irradiating a UV-curable thermosensitive coloring composition with UV rays has also been investigated. For example, Patent Document 1 proposes a photosensitive and thermosensitive recording material having a photosensitive and thermosensitive layer containing (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. According to Patent Document 1, UV exposure slows the diffusion of the electron-accepting and polymerizable vinyl monomer, thereby preventing contact with the electron-donating dye precursor. Therefore, the cured portion does not develop color even when heated after UV exposure.

[0004] Furthermore, Patent Document 2 proposes a polymerizable phenol derivative and a photopolymerizable composition containing the derivative, which have high polymerization sensitivity and excellent storage stability, in a method of converting a polymer image obtained by photocuring into a visible image by thermal development, and a recording material.

[0005] Furthermore, Patent Document 3 proposes a thermosensitive recording medium that suppresses the occurrence of problems that occur during storage before image formation, such as background fogging, and that enables the formation of images with excellent color development. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 3-72358 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-012609 [Patent Document 3] Japanese Patent Publication No. 2020-142513 Summary of the Invention [Problem to be solved by the invention]

[0007] However, according to the investigations of the present inventors, the photosensitive and heat-sensitive recording materials proposed in Patent Documents 1 to 3 are irradiated with a certain amount of accumulated light (approximately 1,000 mJ / cm ) in order to suppress color development after ultraviolet irradiation. 2 On the other hand, in order to reduce the size and power consumption of the ultraviolet irradiation device, it was necessary to further reduce the amount of ultraviolet light to be irradiated.

[0008] Therefore, an object of the present invention is to provide a thermosensitive recording medium that can suppress color development due to heating after ultraviolet irradiation even when the amount of ultraviolet light irradiated is low. Another object of the present invention is to provide an image forming method using the above thermosensitive recording medium. [Means for solving the problem]

[0009] The above object can be achieved by the present invention as follows.

[0010] That is, according to the present invention, there is provided a thermosensitive recording medium having a thermosensitive color-forming layer containing an electron-donating dye precursor, a photoradical polymerization initiator, and an electron-accepting compound having a radical polymerizable group, the thermosensitive recording medium comprising: The electron-accepting compound having a radical polymerizable group is represented by the following formula: 2 The present invention provides a thermosensitive recording medium characterized by containing a compound A represented by the formula:

[0011] [ka]

[0012] (formula( 2 ) inside, R 21 and R 22 each independently represents a hydrocarbon group having 1 to 8 carbon atoms, R 23 represents a hydrogen atom or a methyl group, X 2 is , charcoal Prime numbers 1~ 49 represents a hydrocarbon group of the formula X The methylene group in the group represented by 2 is 、- NHCOO-, -NHCO-, -O-, -CO-, -COO-, or -N R 24 -, optionally substituted with R 24 represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, d and e each independently represents an integer of 0 to 4, f represents an integer between 1 and 10.

[0013] According to the present invention, there is also provided an image forming method comprising the step of heating the above-mentioned thermosensitive recording medium to form an image. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a thermosensitive recording medium that can suppress color development due to heating after ultraviolet irradiation even when the amount of ultraviolet light irradiated is low. Also, according to the present invention, it is possible to provide an image forming method using the above thermosensitive recording medium. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing one embodiment of a thermosensitive recording medium of the present invention. [Figure 2]FIG. 2 is a cross-sectional view showing another embodiment of the thermosensitive recording medium of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Thermal recording medium> The present invention will be described in detail below with reference to preferred embodiments, but is not limited to the following embodiments. The thermosensitive recording medium of the present invention is a thermosensitive recording medium having a thermosensitive color-forming layer containing an electron-donating dye precursor, a photoradical polymerization initiator, and an electron-accepting compound having a radical polymerizable group.

[0017] The electron-accepting compound having a radically polymerizable group includes a compound A ((meth)acrylate compound A) represented by the following formula (1).

[0018] [ka]

[0019] (In formula (1), R 11 and R 12 each independently represents a hydrocarbon group having 1 to 8 carbon atoms, R 13 represents a hydrogen atom or a methyl group, X1 represents a single bond or a hydrocarbon group having 1 to 50 carbon atoms; The methylene group in the group represented by X1 is a heterocycle, -NHCOO-, -NHCO-, -O-, -CO-, -COO-, or -NR 14 -, optionally substituted with R 14 represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, a and b each independently represent an integer of 0 to 4; and c represents an integer of 1 to 10.

[0020] The term "(meth)acrylate compound" refers to "acrylate" and "methacrylate."

[0021] In the present invention, the electron-accepting compound having a radical polymerizable group has, in the same molecule, both a structure that acts as an electron-accepting compound (developer) that develops color upon contact with an electron-donating dye precursor, and a structure that acts as a radical polymerizable compound that undergoes a polymerization reaction upon reaction with the radical polymerization initiator. This makes it easy to fix the electron-accepting compound having a radical polymerizable group in the UV-cured product. Therefore, even with low-intensity UV irradiation, the electron-accepting compound having a radical polymerizable group is less likely to move within the thermosensitive recording layer upon heating, thereby suppressing color development upon contact with the electron-donating dye precursor.

[0022] (Electron-donating dye precursor) The thermosensitive color-forming layer contains an electron-donating dye precursor (leuco dye). The electron-donating dye precursor is usually colorless or light-colored. The electron-donating dye precursor has the property of developing color by donating electrons or accepting protons from an acid or the like. Specific examples of electron-donating dye precursors are listed below.

[0023] Examples of electron-donating dye precursors that develop red or vermilion colors include 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3,6-bis(diethylamino)fluoran-γ-(p-nitro)anilinolactam, 3,6-bis(diethylamino)fluoran-γ-(o-chloro)anilinolactam, 3-dimethylamino-7-bromofluoran, 3-diethylaminofluoran, 3-diethylamino-6-methylfluoran, 3-diethylamino-7-methylfluoran, and 3- Examples include diethylamino-7-chlorofluoran, 3-diethylamino-7-bromofluoran, 3-diethylamino-7,8-benzofluoran, 3-diethylamino-6,8-dimethylfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-tert-butylfluoran, 3-(N-ethyl-N-tolylamino)-7-ethylfluoran, and 3-(N-ethyl-N-isobutylamino)-6-methyl-7-chlorofluoran.

[0024] Further examples of the electron donating dye precursors that develop red or vermilion colors include 3-cyclohexylamino-6-chlorofluoran, 3-di(n-butyl)amino-6-methyl-7-bromofluoran, 3-di(n-butyl)amino-7,8-benzofluoran, 3-tolylamino-7-methylfluoran, 3-tolylamino-7-ethylfluoran, 2-(N-acetylanilino)-3-methyl-6-di(n-butyl)aminofluoran, 2-(N-propionylanilino)-3-methyl-6-di(n-butyl)aminofluoran, and 2-(N-benzoylanilino)-3-methyl-6-di(n-butyl)aminofluoran. fluoran, 2-(N-carbobutoxyanilino)-3-methyl-6-di(n-butyl)aminofluoran, 2-(N-formylanilino)-3-methyl-6-di(n-butyl)aminofluoran, 2-(N-benzylanilino)-3-methyl-6-di(n-butyl)aminofluoran, 2-(N-allylanilino)-3-methyl-6-di(n-butyl)aminofluoran, 2-(N-methylanilino)-3-methyl-6-di(n-butyl)aminofluoran, 3-diethylamino-7-phenoxyfluoran, 2-methyl-6-(Np-tolyl-N-ethylamino)-fluoran, and the like.

[0025] Examples of electron-donating dye precursors that produce magenta colors include 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide, 3,3-bis(1-n-octyl-2-methylindol-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], and 7-(N-ethyl-Nn-hexylamino)-3-methyl-1-phenylspiro[(1,4-dihydrochromeno[2,3-c]pyrazole)-4,3'-phthalide].

[0026] Further examples of electron-donating dye precursors that develop magenta color tones include 3-(N-ethyl-N-isoamylamino)-7,8-benzofluoran, 3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalide, and 3-(N-ethyl-N-isoamylamino)-7-phenoxyfluoran.

[0027] As the electron-donating dye precursor that develops a red, vermilion, or magenta color tone, it is preferable to use at least one selected from the group consisting of 3-diethylamino-7-chlorofluoran, 3-diethylamino-6,8-dimethylfluoran, 3-(N-ethyl-N-isoamylamino)-7,8-benzofluoran, 2-methyl-6-(Np-tolyl-N-ethylamino)-fluoran, 3-di(n-butyl)amino-6-methyl-7-bromofluoran, and 3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalide.

[0028] Examples of electron-donating dye precursors that develop blue tones include 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, and 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylaminophenyl)phthalide. amide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-methyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-n-hexyloxy-4-diethylaminophenyl)-4-azaphthalide, 3-diphenylamino-6-diphenylaminofluoran, and the like can be mentioned.

[0029] Examples of electron-donating dye precursors that develop cyan color tones include 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylamino-2-methylphenyl)-4-azaphthalide, 3-[1,1-bis(p-diethylaminophenyl)ethylene-2-yl]-6-dimethylaminophthalide, 3,3-bis(4-diethylamino-2-ethoxyphenyl)-4-azaphthalide, and 3,3'-bis(4-diethylamino-2-ethoxyphenyl)-4-azaphthalide.

[0030] Examples of electron donating dye precursors that develop blue or cyan colors include 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, and 3-(1-ethyl-2-methylindol-3-yl)-3-(4 It is preferable to use at least one selected from the group consisting of 3-(1-ethyl-2-methylindol-3-yl)-3-(2-n-hexyloxy-4-diethylaminophenyl)-4-azaphthalide, 3-[1,1-bis(p-diethylaminophenyl)ethylene-2-yl]-6-dimethylaminophthalide, and 3,3'-bis(4-diethylamino-2-ethoxyphenyl)-4-azaphthalide.

[0031] Examples of electron-donating dye precursors that develop yellow tones include 4-[2-[2-(butoxy)phenyl]-6-phenyl-4-pyridinyl]-N,N-dimethylbenzenamine, 4-[2-[2-(octyloxy)phenyl]-6-phenyl-4-pyridinyl]-N,N-dimethylbenzenamine, 4-[2-[2-(ethoxy)phenyl]-6-phenyl-4-pyridinyl]-N,N-dimethylbenzenamine, 4-[2,6-bis(2-ethoxyphenyl)-4-pyridinyl]-N,N-dimethylbenzenamine, and 4-(2,6-diphenyl-4-pyridinyl)-N,N-dimethylbenzenamine. Examples thereof include 4-[2,6-bis(2-butoxyphenyl)-4-pyridinyl]-N,N-dimethylbenzenamine, 4-[2,6-bis(2-octyloxyphenyl)-4-pyridinyl]-N,N-dimethylbenzenamine, 4-[2-[2-(hexyloxy)phenyl]-6-phenyl-4-pyridinyl]-N,N-dimethylbenzenamine, 4-[2,6-bis(2-hexyloxyphenyl)-4-pyridinyl]-N,N-dimethylbenzenamine, 3,6-dimethoxyfluoran, and 1-(4-n-dodecyloxy-3-methoxyphenyl)-2-(2-quinolyl)ethylene.

[0032] As the electron-donating dye precursor that develops a yellowish color tone, it is preferable to use at least one selected from the group consisting of 4-[2-[2-(octyloxy)phenyl]-6-phenyl-4-pyridinyl]-N,N-dimethylbenzeneamine, 3,6-dimethoxyfluoran, and 1-(4-n-dodecyloxy-3-methoxyphenyl)-2-(2-quinolyl)ethylene.

[0033] Examples of electron-donating dye precursors that develop green tones include 3-(N-ethyl-Nn-hexylamino)-7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, 3-pyrrolidino-7-dibenzylaminofluoran, 3,3-bis(4-diethylamino-2-ethoxyphenyl)-4-azaphthalide, 3-(N-ethyl-Np-tolylamino)-7-(N-phenyl-N-methylamino)fluoran, 3-[p-(p-anilinoanilino)anilino]-6-methyl-7-chlorofluoran, and 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide.

[0034] As the electron-donating dye precursor that develops a greenish color tone, it is preferable to use at least one selected from the group consisting of 3-diethylamino-7-dibenzylaminofluoran and 3-pyrrolidino-7-dibenzylaminofluoran.

[0035] Examples of electron-donating dye precursors that develop black tones include 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-diethylamino-6-methyl-7-(m-methylanilino)fluoran, 3-(N-isoamyl-N-ethylamino)-7-(o-chloroanilino)fluoran, and 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran. Nilinofluoran, 3-(N-ethyl-N-2-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 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-anilinofluoran, 3-( Nn-hexyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-ethylamino)-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-methylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-di(n-butyl)amino-7-(2-chloroanilino)fluoran , 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(2,6-dimethylanilino)fluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino)fluoran, 2,4-dimethyl-6-(4-dimethylaminoanilino)fluoran, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluoran, and the like can be mentioned.

[0036] As the electron-donating dye precursor that develops a black color tone, it is preferable to use at least one selected from the group consisting of 3-di(n-butyl)amino-6-methyl-7-anilinofluoran, 3-di(n-amyl)amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(2,6-dimethylanilino)fluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino)fluoran, and 2,4-dimethyl-6-(4-dimethylaminoanilino)fluoran, which have relatively excellent light resistance.

[0037] Examples of electron-donating dye precursors having absorption in the near infrared region include 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-anilinoanilino)anilino]-6-methyl-7-chlorofluoran, and 3-[p-(p-dimethylaminoanilino)anilino]-6-methyl-7-chlorofluoran. fluoran, 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, bis(p-dimethylaminostyryl)-p-tolylsulfonylmethane, 3-[p-(p-dimethylaminoanilino)anilino]-6-methylfluoran, 3-di(n-pentyl)amino-6,8,8-trimethyl-8,9-dihydro-(3,2,e)pyridofluoran, 3-di(n-butyl)amino-6,8,8-trimethyl-8,9-dihydro-(3,2,e)pyridofluoran, 3-(pn-butylaminoanilino)-6-methyl-7-chlorofluoran, 2-mesidino-8-diethylamino-benz[C]fluoran, and the like can be mentioned.

[0038] The content of electron-donating dye precursor in the heat-sensitive coloring layer is 0.01 g / m 2 More than 2.00g / m 2If it is less than this, an image with a sufficient optical density can be formed, which is preferable.

[0039] (Photoradical polymerization initiator) The thermosensitive coloring layer contains a photoradical polymerization initiator. The photoradical polymerization initiator may be any compound capable of generating radicals by the action of light. As the photoradical polymerization initiator, various known compounds such as radical generators, radical polymerization initiators, and photoradical polymerization initiators can be used.

[0040] Examples of photoradical polymerization initiators that efficiently carry out a curing reaction under ultraviolet light include oxime ester compounds, aromatic ketone compounds, acylphosphine oxide compounds, benzoin alkyl ether compounds, benzoin ether compounds, thioxanthone compounds, benzophenone compounds, benzoate compounds, aromatic onium salt compounds, organic peroxides, thio compounds (e.g., thiophenyl group-containing compounds), α-aminoalkylphenone compounds, hexaarylbiimidazole compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds. Radical generators described in JP 2018-35369 A and JP 2018-39265 A can also be used. Among these, aromatic ketone compounds, oxime ester compounds, acylphosphine oxide compounds, benzoin alkyl ether compounds, benzoin ether compounds, thioxanthone compounds, benzophenone compounds, and benzoate compounds are preferred, with oxime ester compounds being more preferred.

[0041] The photoradical polymerization initiator may be used alone or in combination of two or more. The content of the photoradical polymerization initiator in the thermosensitive color developing layer is preferably 10% by mass or more and 200% by mass or less, and more preferably 25% by mass or more and 100% by mass or less, based on the content of the electron-accepting compound having a radical polymerizable group.

[0042] Examples of the oxime ester compound include 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime), (9-ethyl-6-nitro-9H-carbazol-3-yl)-(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone-o-acetyloxime, and 1-[4-[[4-(2-hydroxyethoxy)phenyl]thio]phenyl-1]-1,2-propanedione-2-(O-acetyloxime).

[0043] Aromatic ketone compounds include acetophenone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 4-methylbenzophenone, 2,2'-phenyl p-tert-butyltrichloroacetophenone, p-tert-butyldichloroacetophenone, benzophenone, 4-phenylbenzophenone, methylbenzoyl formate, 4-[(4-methylphenyl)thio]benzophenone, 4,4'-bis(diethylamino)benzophenone, N,N'-tetramethyl-4,4'-diaminobenzophenone (Michler's ketone), Examples include 1-hydroxycyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methylpropane, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propane, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, and 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one.

[0044] Examples of the acylphosphine oxide compound include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)-diphenylphosphine oxide.

[0045] Examples of the benzoin alkyl ether compound include benzoin methyl ether, benzoin ethyl ether, benzoin butyl ether, and benzoin isopropyl ether.

[0046] Examples of the benzoin ether compounds include methyl benzoin and ethyl benzoin.

[0047] Examples of the thioxanthone compound include 2-chlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, and 2-methylthioxanthone.

[0048] Examples of the benzophenone compound include benzophenone, 4-methylbenzophenone, 4-phenylbenzophenone, 4-(4-methylphenylthio)benzophenone, and 4,4'-bis(diethylamino)benzophenone.

[0049] Examples of the benzoate compound include ethyl-4-(dimethylamino)-benzoate, ethylhexyl-4-dimethylaminobenzoate, methyl-o-benzoylbenzoate, and 3-methylbutyl p-(dimethylamino)benzoate.

[0050] Among the above, commercially available examples of oxime ester compounds that are preferred photoradical polymerization initiators include Irgacure OXE01 (manufactured by BASF Japan Ltd.), Irgacure OXE02 (manufactured by BASF Japan Ltd.), Irgacure OXE03 (manufactured by BASF Japan Ltd.), Irgacure OXE04 (manufactured by BASF Japan Ltd.), ADEKA ARCLES N-1919 (manufactured by ADEKA Corporation), ADEKA ARCLES NCI-831 (manufactured by ADEKA Corporation), and ADEKA ARCLES NCI-930 (manufactured by ADEKA Corporation).

[0051] (Electron-accepting compound having a radically polymerizable group) The thermosensitive color-forming layer contains an electron-accepting compound having a radically polymerizable group. The electron-accepting compound having a radically polymerizable group has, in the same molecule, both a structure that acts as an electron-accepting compound (developer) that develops color upon contact with an electron-donating dye precursor, and a structure that acts as a radically polymerizable compound that undergoes polymerization upon reaction with the radically polymerizable initiator.

[0052] The mechanism will be explained in detail below.

[0053] When a thermosensitive recording medium is heated, the electron-donating dye precursor contained in the thermosensitive coloring layer comes into contact with and reacts with an electron-accepting compound having a radical polymerizable group, causing the heated area to develop color and form an image. However, when a thermosensitive recording medium with an image formed thereon is heated again, color may develop in areas that have not been colored. Therefore, a preferred method for forming an image on a thermosensitive recording medium is an image-forming method that includes a step of applying heat pulses to the thermosensitive recording medium using a thermal head to form an image, and a step of irradiating the thermosensitive recording medium with ultraviolet light to fix the thermosensitive coloring layer. Furthermore, when this image-forming method is employed, the thermosensitive coloring layer of the thermosensitive recording medium preferably contains a photoradical polymerization initiator and an electron-accepting compound having a radical polymerizable group. In this image-forming method, the thermosensitive coloring layer in the area where color development is desired is first heated with a thermal head.

[0054] On the other hand, areas not heated by the thermal head do not develop color. An image is formed on the thermosensitive recording medium depending on whether or not the thermosensitive coloring layer develops color. Next, to maintain the state of whether or not the thermosensitive coloring layer develops color, the thermosensitive recording medium on which the image has been formed is irradiated with ultraviolet light. This cleaves the photoradical polymerization initiator in the thermosensitive coloring layer, generating radicals.

[0055] The generated radicals then propagate the electron-accepting compound having a radical polymerizable group in the thermosensitive coloring layer, forming a cured product with a three-dimensional network structure in which polymer chains are crosslinked. Because the electron-accepting compound having a radical polymerizable group is fixed within the cured product, the opportunity for contact between the electron-donating dye precursor and the electron-accepting compound having a radical polymerizable group is reduced. Since the electron-accepting compound having a radical polymerizable group is a single molecule, it can be assumed that it is virtually unable to move within the thermosensitive recording layer after curing, further reducing the opportunity for contact with the electron-accepting compound. This prevents the thermosensitive coloring layer from coloring even when heated after UV irradiation, maintaining the coloration or non-coloration state of the thermosensitive coloring layer prior to UV irradiation.

[0056] In the present invention, the electron-accepting compound having a radically polymerizable group includes a compound A represented by the following formula (1).

[0057] [ka]

[0058] (In formula (1), R 11 and R 12 each independently represents a hydrocarbon group having 1 to 8 carbon atoms, R 13 represents a hydrogen atom or a methyl group, X1 represents a single bond or a hydrocarbon group having 1 to 50 carbon atoms; The methylene group in the group represented by X1 is a heterocycle, -NHCOO-, -NHCO-, -O-, -CO-, -COO-, or -NR 14 -, optionally substituted with R 14 represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, a and b each independently represent an integer of 0 to 4; and c represents an integer of 1 to 10.

[0059] Specific examples of the compound A represented by the formula (1) include the following compounds (D-1) to (D-5).

[0060] [ka]

[0061] In addition, the methylene group in the group represented by X1 in formula (1) is a heterocycle, -NHCOO-, -NHCO-, -O-, -CO-, -COO-, or -NR 14 To explain the case where X1 is substituted with - using compound (D-5) as an example, X1 in compound (D-5) is a hydrocarbon group having two carbon atoms, in which one methylene group is substituted with -O- and the other methylene group is substituted with a pyrrole ring.

[0062] Furthermore, from the viewpoint of more efficiently carrying out the curing reaction by ultraviolet light, it is preferable that the compound A represented by the formula (1) is represented by the following formula (2): As represented by the following formula (2), the (meth)acrylate compound A has an -NHCOO- (urethane bond) in its molecule, which is thought to improve the flexibility of the molecule and accelerate the radical polymerization reaction, thereby making the curing reaction proceed more efficiently.

[0063] [ka]

[0064] (In formula (2), R 21 and R 22 each independently represents a hydrocarbon group having 1 to 8 carbon atoms, R 23 represents a hydrogen atom or a methyl group, X2 represents a hydrocarbon group having 1 to 49 carbon atoms; The methylene group in the group represented by X2 is -NHCOO-, -NHCO-, -O-, -CO-, -COO-, or -NR 24 -, optionally substituted with R 24 represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, d and e each independently represent an integer of 0 to 4, f represents an integer from 1 to 10.

[0065] Specific examples of the compound A represented by the formula (2) include the following compounds (D-6) to (D-38).

[0066] [ka]

[0067] [ka]

[0068] [ka]

[0069] [ka]

[0070] [ka]

[0071] [ka]

[0072] Furthermore, from the viewpoint of more efficiently carrying out the curing reaction by ultraviolet light, the compound A represented by the formula (1) is preferably represented by the following formula (3): As represented by the formula (3), when X3 in the molecule of the (meth)acrylate compound A is a methylene group or a methylene group substituted with an -O- (ether bond), it is presumed that the flexibility of the molecule is improved and the radical polymerization reaction is further accelerated, so that the curing reaction proceeds more efficiently.

[0073] [ka]

[0074] (In formula (3), R 31 and R 32 each independently represents a hydrocarbon group having 1 to 8 carbon atoms, R 33 represents a hydrogen atom or a methyl group, X3 represents a hydrocarbon group having 1 to 49 carbon atoms; The methylene group in the group represented by X3 may be substituted with —O—. g and h each independently represent an integer of 0 to 4; and i represents an integer from 1 to 10.

[0075] Specific examples of the compound A represented by the formula (3) include the following compounds (D-39) to (D-48).

[0076] [ka]

[0077] Next, the form of the electron-accepting compound having a radical polymerizable group in the thermosensitive coloring layer will be described. The form of the electron-accepting compound having a radical polymerizable group in the thermosensitive coloring layer is not particularly limited, and examples include particles and layers. For example, when the electron-accepting compound having a radical polymerizable group is contained in the thermosensitive coloring layer in the form of a layer, the thermosensitive coloring layer preferably has a first layer containing an electron-donating dye precursor and a second layer containing an electron-accepting compound having a radical polymerizable group. Hereinafter, the first layer containing the electron-donating dye precursor will also be referred to as an "electron-donating dye precursor layer" or a "leuco layer." Furthermore, the second layer containing the electron-accepting compound having a radical polymerizable group will also be referred to as an "electron-accepting compound layer having a radical polymerizable group" or a "developer layer."

[0078] The thermosensitive coloring layer preferably contains particles containing an electron-accepting compound having a radical polymerizable group and a photoradical polymerization initiator. The method for preparing particles containing an electron-accepting compound having a radical polymerizable group and a photoradical polymerization initiator is not particularly limited, but an O / W emulsion method is preferred. In this case, the photoradical polymerization initiator is preferably premixed with the electron-accepting compound having a radical polymerizable group before preparation. The particle diameter of the particles containing the electron-accepting compound having a radical polymerizable group and the photoradical polymerization initiator is preferably 10 nm to 1,000 nm, and more preferably 50 nm to 300 nm. Having particle diameters of 10 nm or more, or even 50 nm or more, enhances radical polymerization reactivity and improves image storage stability. Having particle diameters of 1,000 nm or less, or even 300 nm or less, reduces unnecessary light scattering in the thermosensitive coloring layer and increases image density. In this specification, the particle size of particles means the 50% particle size (D50) based on volume distribution.

[0079] The electron-accepting compound having a radical polymerizable group can be used alone or in combination of two or more. The content of the electron-accepting compound having a radical polymerizable group in the thermosensitive color-forming layer is preferably 500% by mass or more, more preferably 1500% by mass or more, based on the content of the electron-donating dye precursor, from the viewpoint of efficient curing with ultraviolet light. There is no particular upper limit to the content of the electron-accepting compound having a radical polymerizable group, but it is preferably 5000% by mass or less, based on the content of the electron-donating dye precursor.

[0080] [Method for synthesizing compound A represented by formula (1)] Compound A represented by formula (1) is available as a commercially available product. Compound A that is not commercially available can also be obtained by a known synthesis method.

[0081] For example, the above compounds (D-6) to (D-38) can be obtained by selecting and reacting at least one of the following compounds (a) to (c).

[0082] Compound (a): a polyfunctional acrylate compound containing at least one OH group or one —COOH group in the molecule. Commercially available products include SR295 (manufactured by Sartomer Co., Ltd.), SR399 (manufactured by Sartomer Co., Ltd.), and Aronix M510 (manufactured by Toagosei Co., Ltd.).

[0083] Compound (b): Diisocyanate compounds such as HDI (hexamethylene diisocyanate), MDI (diphenylmethane diisocyanate), PDI (1,5-pentamethylene diisocyanate), IPDI (isophorone diisocyanate), and TDI (toluene diisocyanate).

[0084] Compound (c): an electron-accepting compound having a diphenyl sulfone skeleton and containing two or more OH groups in the molecule. Examples of commercially available products include TGSH(H) manufactured by Nippon Kayaku Co., Ltd. and BPS-24C manufactured by Nicca Chemical Co., Ltd.

[0085] The above compounds (D-39) to (D-48) can be obtained, for example, by the scheme of the following method (i).

[0086] [ka]

[0087] (In formulas (3) to (5), R 31 and R 32 each independently represents a hydrocarbon group having 1 to 8 carbon atoms, R 33 represents a hydrogen atom or a methyl group, X3 represents a hydrocarbon group having 1 to 49 carbon atoms; The methylene group in the group represented by X3 may be substituted with —O—. g and h each independently represent an integer of 0 to 4; and i represents an integer from 1 to 10.

[0088] The compound represented by formula (3) is obtained by adding the compound represented by formula (5) to the compound represented by formula (4) and stirring for a predetermined period of time. At this time, a condensation reaction occurs between the -OH group in the compound represented by formula (4) and the -NCO group in the compound represented by formula (5).

[0089] The amount of the compound represented by formula (5) added is preferably 100 mol % or more and 150 mol % or less based on the compound represented by formula (4), from the viewpoint of reacting about 50% of the -OH groups in the compound represented by formula (4).

[0090] Method (i) can be performed without a solvent, but is preferably performed in the presence of a solvent to prevent the reaction from proceeding too rapidly. The solvent is not particularly limited as long as it does not inhibit the reaction, but examples include esters such as methyl acetate, ethyl acetate, and propyl acetate; ethers such as diethyl ether, tetrahydrofuran, and dioxane; hydrocarbons such as benzene, toluene, xylene, hexane, and heptane; and halogenated hydrocarbons such as dichloromethane, dichloroethane, and chloroform. Two or more of the above solvents can be mixed and used, and the mixing ratio when mixed can be determined arbitrarily depending on the solubility of the solute. The amount of the solvent used can be determined arbitrarily, but from the perspective of reaction rate, it is preferably in the range of 100% by mass to 1000% by mass of the compound represented by formula (4) above.

[0091] Method (i) is usually carried out at a temperature range of 20°C to 100°C and is usually completed within 48 hours.

[0092] Next, compounds represented by formulas (4) and (5) will be described. Commercially available products of the compound represented by formula (4) include TGSH(H) manufactured by Nippon Kayaku Co., Ltd., and BPS-24C manufactured by Nicca Chemical Co., Ltd. Commercially available products of the compound represented by formula (5) include Karenz BEI manufactured by Showa Denko K.K., Karenz AOI manufactured by Showa Denko K.K., Karenz MOI manufactured by Showa Denko K.K., and Karenz MOI-EG manufactured by Showa Denko K.K.

[0093] The molecular structure of the synthesized compound represented by formula (1) can be identified using NMR (nuclear magnetic resonance), IR (infrared spectrophotometer), MS (mass spectrometer), or the like.

[0094] (Other ingredients) The thermosensitive coloring layer may contain a storage stability improver. By incorporating a storage stability improver into the thermosensitive coloring layer, the storage stability of the colored image can be further improved. Examples of 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. phenol compounds such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenyl sulfone, 4-(2-methyl-1,2-epoxyethyl)diphenyl sulfone, and 4-(2-ethyl-1,2-epoxyethyl)diphenyl sulfone; and isocyanuric acid compounds such as 1,3,5-tris(2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl)isocyanuric acid.

[0095] The thermosensitive coloring layer may contain a thermal sensitizer, which can enhance the recording sensitivity. Examples of thermal sensitizers include stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylene bisstearic acid amide, behenic acid amide, methylene bisstearic acid amide, N-methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p-benzyl biphenyl, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, oxalic acid dibenzyl ester, p-tolyl biphenyl ether, di(p-methoxyphenoxyethyl) ether, 1,2-di(3-methylphenoxy) ethene, Examples of suitable benzene derivatives include benzene, 1,2-di(4-methylphenoxy)ethane, 1,2-di(4-methoxyphenoxy)ethane, 1,2-di(4-chlorophenoxy)ethane, 1,2-diphenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, p-methylthiophenylbenzyl ether, 1,4-di(phenylthio)butane, p-acetotoluidide, p-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, and benzophenone. The content of the thermal sensitizer in the thermosensitive coloring layer should be an amount effective for thermal sensitization, specifically, preferably from 2 to 40% by mass, and more preferably from 5 to 25% by mass, of the total solid content of the thermosensitive coloring layer.

[0096] Auxiliaries such as shelf-life improvers and heat sensitizers may be mixed in the form of fine particles dispersed in water (solid-dispersed fine particles) into the coating solution for forming the thermosensitive color-developing layer. These auxiliaries may also be dissolved in a solvent and emulsified using a water-soluble polymer compound as an emulsifier. Furthermore, shelf-life improvers and heat sensitizers may be incorporated into particles containing an electron-donating dye precursor or an electron-accepting compound.

[0097] The thermosensitive color-forming layer may contain a polymerization accelerator, such as a benzoate compound or an amine compound.

[0098] Examples of the benzoate compound and amine compound include ethyl 4-(dimethylamino)benzoate, ethylhexyl 4-dimethylaminobenzoate, methyl o-benzoylbenzoate, 3-methylbutyl p-(dimethylamino)benzoate, N,N-dimethylaminobenzoic acid ethyl ester, N,N-dimethylaminobenzoic acid isoamyl ester, pentyl 4-dimethylaminobenzoate, triethylamine, and triethanolamine.

[0099] The thermosensitive coloring layer may contain a sensitizer. The sensitizer may be any sensitizer that sensitizes the photoradical polymerization initiator via an electron transfer mechanism or an energy transfer mechanism. Examples of sensitizers include aromatic polycondensed ring compounds such as anthracene, 9,10-dialkoxyanthracene, pyrene, and perylene; aromatic ketone compounds such as acetophenone, benzophenone, thioxanthone, and Michler's ketone; and heterocyclic compounds such as phenothiazine and N-aryloxazolidinone. The content of the sensitizer in the thermosensitive coloring layer is preferably 10% by mass or more and 1000% by mass or less, and more preferably 100% by mass or more and 500% by mass or less, based on the content of the photoradical polymerization initiator.

[0100] To improve the electron transfer efficiency or energy transfer efficiency between the sensitizer and the photoradical polymerization initiator, it is preferable to incorporate a sensitization aid into the thermosensitive color-forming layer. Examples of sensitization aids include naphthalene compounds such as 1,4-dihydroxynaphthalene, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 4-methoxy-1-naphthol, and 4-ethoxy-1-naphthol; and benzene compounds such as 1,4-dihydroxybenzene, 1,4-dimethoxybenzene, 1,4-diethoxybenzene, 1-methoxy-4-phenol, and 1-ethoxy-4-phenol. The content of the sensitization aid in the thermosensitive color-forming layer is preferably 10% by mass or more and 1,000% by mass or less, and more preferably 50% by mass or more and 500% by mass or less, based on the content of the sensitizer.

[0101] The thermosensitive coloring layer may contain a radical polymerization inhibitor. The photoradical polymerization initiator decomposes slightly during storage of the thermosensitive recording medium to form a radical compound. This radical compound may cause polymerization, so it is preferable to contain a radical polymerization inhibitor in the thermosensitive coloring layer to prevent this polymerization.

[0102] Examples of the radical polymerization inhibitor include phenolic hydroxyl group-containing compounds, quinones such as methoquinone (hydroquinone monomethyl ether), hydroquinone, and 4-methoxy-1-naphthol, hindered amine antioxidants, 1,1-diphenyl-2-picrylhydrazyl free radicals, N-oxyl free radical compounds, nitrogen-containing heterocyclic mercapto compounds, thioether antioxidants, hindered phenol antioxidants, ascorbic acids, zinc sulfate, thiocyanates, thiourea derivatives, various sugars, phosphoric acid antioxidants, nitrites, sulfites, thiosulfates, hydroxylamine derivatives, aromatic amines, phenylenediamines, imines, sulfonamides, urea derivatives, oximes, polycondensates of dicyandiamide and polyalkylenepolyamine, sulfur-containing compounds such as phenothiazine, complexing agents based on tetraazaannulene (TAA), and hindered amines.

[0103] Among these, preferred radical polymerization inhibitors are phenols, N-oxyl free radical compounds, 1,1-diphenyl-2-picrylhydrazyl free radicals, phenothiazine, quinones, and hindered amines. N-oxyl free radical compounds are even more preferred. The content of the radical polymerization inhibitor in the thermosensitive color-forming layer is preferably 1 ppm or more and 5,000 ppm or less by mass relative to the content of the radical polymerizable compound.

[0104] The thermosensitive coloring layer can contain a highly white pigment with an average particle diameter of 10 μm or less. The inclusion of such a pigment improves the whiteness of the thermosensitive coloring layer and the uniformity of the image. Examples of pigments include inorganic pigments such as calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, and surface-treated calcium carbonate or silica; and organic pigments such as urea-formaldehyde resin, styrene-methacrylic acid copolymer resin, and polystyrene resin. The pigment content in the thermosensitive coloring layer is preferably an amount that does not reduce the color density of the image. Specifically, it is preferably 50% by weight or less of the total solids content of the thermosensitive coloring layer.

[0105] A binder can be used as a component of the thermosensitive coloring layer. Optionally, crosslinkers, waxes, metal soaps, colored dyes, colored pigments, fluorescent dyes, etc. can also be added. Examples of binders 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; emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers; and latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers.

[0106] The inclusion of a crosslinking agent in the thermosensitive coloring layer can improve the water resistance of the thermosensitive coloring layer. Examples of crosslinking agents include organic compounds such as aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, dimethylol urea compounds, aziridine compounds, and blocked isocyanate compounds; inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, and potassium tetraborate; and boric acid, boric acid triesters, boron-based polymers, hydrazide compounds, and glyoxylates. The content of the crosslinking agent in the thermosensitive coloring layer is preferably 1% by mass or more and 10% by mass or less, based on the total solids content of the thermosensitive coloring layer.

[0107] Examples of waxes include waxes such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, and polyethylene wax; higher fatty acid amides such as stearic acid amide and ethylene bisstearic acid amide; higher fatty acid esters and their derivatives; and examples of metal soaps include polyvalent metal salts of higher fatty acids such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate.

[0108] When the thermosensitive recording medium is a two-color thermosensitive recording medium, it is preferable to incorporate a color dye or color pigment in the thermosensitive coloring layer, which has a color tone complementary to the low-temperature color tone. By incorporating such a color dye or color pigment in the thermosensitive coloring layer, the color tone of the thermosensitive recording medium can be adjusted before and after image formation. Furthermore, various auxiliary agents such as oil repellents, antifoaming agents, and viscosity adjusters can be incorporated into the thermosensitive coloring layer as needed.

[0109] The thermosensitive coloring layer can be formed, for example, by applying a coating solution for the thermosensitive coloring layer containing the components constituting the thermosensitive coloring layer to a support using water as a dispersion medium to form a coating layer, and then drying the coating layer. The coating amount of the coating solution is 2 g / m2 in terms of dry mass. 2 More than 20g / m 2 It is preferable that the density is 2 g / m or less. 2 More than 15g / m 2 It is more preferable that the concentration is 2 g / m or less. 2 More than 10g / m 2 It is particularly preferred that:

[0110] To prepare particles containing an electron-accepting compound having a radical polymerizable group and a photoradical polymerization initiator, it is preferable to use a surfactant. Examples of surfactants include anionic surfactants such as sodium alkyl sulfonate, sodium alkylbenzene sulfonate, sodium dialkyl sulfosuccinate, and sodium alkyl carboxylate; nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, polyoxyethylene polyoxypropylene glycol, sorbitan alkyl ester, polyoxyethylene sorbitan alkyl ester, glycerin alkyl ester, and polyoxyethylene hydrogenated castor oil; cationic surfactants such as alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and alkylbenzyldimethylammonium chloride; and amphoteric surfactants such as alkylbetaine and alkyldimethylamine oxide. Furthermore, polymeric surfactants such as sodium salt of naphthalenesulfonic acid formalin condensate and sodium polyacrylate can be used.

[0111] It is also possible to use radical polymerizable compounds to which an ionic group such as a sulfonic acid group, a carboxylic acid group, or an amino group, or a hydrophilic nonionic group such as a polyoxyethylene group or a polyglyceryl group is bonded to impart surfactant properties.

[0112] A dispersing aid can also be used to prepare the particles. Examples of the dispersing aid include water-soluble polymers such as polyvinyl alcohol and its modified products, polyacrylic acid amide and its derivatives, ethylene / vinyl acetate copolymer, styrene / maleic anhydride copolymer, ethylene / maleic anhydride copolymer, isobutylene / maleic anhydride copolymer, polyvinylpyrrolidone, ethylene / acrylic acid copolymer, vinyl acetate / acrylic acid copolymer, carboxymethylcellulose, methylcellulose, casein, gelatin, starch derivatives, gum arabic, and sodium alginate.

[0113] The amount of surfactant or dispersing aid added is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less, based on the mass of the particles.

[0114] (middle class) When the thermosensitive coloring layer has an electron-donating dye precursor layer (leuco layer) and an electron-accepting compound layer (developer layer) having a radically polymerizable group, an intermediate layer can be provided between these layers. Materials constituting the intermediate layer can be water-soluble polymeric materials or water-insoluble polymers used in known thermosensitive recording media. Specific examples of materials constituting the intermediate layer include those similar to the binders that constitute the thermosensitive coloring layer. Furthermore, the intermediate layer may contain, as an auxiliary agent, particles with high porosity such as silica or calcined kaolin, plastic pigments, hollow particles, foams, or organic compounds such as polyethylene wax having a glass transition point or melting point.

[0115] The intermediate layer can be formed, for example, by applying a coating liquid for the intermediate layer containing the components constituting the intermediate layer using water as a dispersion medium to form a coating layer, and then drying the coating layer. The coating amount of the coating liquid is 1 g / m2 in terms of dry mass. 2 More than 40g / m 2 It is preferable that the density is 2 g / m or less. 2 More than 10g / m 2 It is more preferable that:

[0116] An intermediate layer may also be provided between the two thermosensitive coloring layers. The intermediate layer disposed between the thermosensitive coloring layers preferably contains an ultraviolet absorber. By incorporating an ultraviolet absorber into this intermediate layer, the ultraviolet transmittance of the intermediate layer can be controlled to a desired value.

[0117] As the ultraviolet absorber, a benzotriazole-based ultraviolet absorber, a triazine-based ultraviolet absorber, a benzophenone-based ultraviolet absorber, a cyanoacrylate-based ultraviolet absorber, a salicylic acid-based ultraviolet absorber, or titanium oxide can be used.

[0118] (protective layer) It is preferable to have a protective layer on the thermosensitive coloring layer. The protective layer may be a protective layer used in known thermosensitive recording media. For example, it is preferable to provide a protective layer containing a water-soluble polymer material and particles. The water-soluble polymer material and particles may be the same as those that can be contained in the thermosensitive coloring layer. It is also preferable to add a crosslinking agent to impart water resistance to the protective layer.

[0119] The inclusion of microcapsules encapsulating UV absorbers or solid dispersion particles of UV absorbers in the protective layer can significantly improve light resistance. Microcapsules with walls made of polyurethane-polyurea resins or aminoaldehyde resins are particularly preferred because they have excellent heat resistance and exhibit additional benefits, such as suppressing sticking to thermal heads. Furthermore, microcapsules with walls made of polyurethane-polyurea resins or aminoaldehyde resins have a lower refractive index than microcapsules with walls made of other resins. Furthermore, because of their spherical shape, even if a large amount of these microcapsules is added to the protective layer, they are less likely to experience a decrease in density due to diffuse reflection of light.

[0120] Furthermore, it is preferable to include particles in the protective layer, since this can prevent adhesion of dirt and sticking to the thermal head. The oil absorption of the particles is preferably 50 mL / 100 g or more. The content of particles in the protective layer is preferably an amount that does not reduce the color density, and specifically, it is preferably 60 mass % or less of the total solid content of the protective layer.

[0121] The protective layer can be formed, for example, by applying a coating solution for the protective layer containing the components constituting the protective layer using water as a dispersion medium onto the thermosensitive color-developing layer to form a coating layer, and then drying the coating layer. The coating amount of the coating solution is 0.1 g / m2 in terms of dry mass. 2 More than 15g / m 2 It is preferable that the density is 0.5 g / m or less. 2More than 8g / m 2 It is more preferable that:

[0122] (resin layer) A resin layer composed of a resin cured by electron beams or ultraviolet light can be provided on each of the thermosensitive coloring layer, intermediate layer, and protective layer. Examples of resins cured by electron beams include those described in JP-A-58-177392. The resin constituting the resin layer may contain additives such as non-electron beam curable resins, particles, antifoaming agents, leveling agents, lubricants, surfactants, and plasticizers. Adding particles such as calcium carbonate and aluminum hydroxide, or lubricants such as waxes and silicones is particularly preferred because it can prevent sticking to the thermal head.

[0123] (Other layers) By processing a thermal recording medium to impart enhanced functionality, the added value of the thermal recording medium can be increased. For example, by applying a pressure-sensitive adhesive, rewettable adhesive, delayed-tack pressure-sensitive adhesive, or the like to the back surface, it can be made into adhesive paper, rewettable adhesive paper, or delayed-tack paper. Furthermore, by imparting functionality such as thermal transfer paper, inkjet recording paper, carbonless paper, electrostatic recording paper, or xeography paper to the back surface, it can be made into a recording paper capable of double-sided recording. Furthermore, by providing a thermal color-developing layer on the back surface, it can be made into a double-sided thermal recording medium. A back layer can also be provided on the back surface of the thermal recording medium to suppress penetration of oil or plasticizer from the back surface, or to control curl or prevent static electricity.

[0124] (Layer structure of the thermal recording medium) Fig. 1 is a cross-sectional view showing one embodiment of a thermosensitive recording medium of the present invention. The thermosensitive recording medium 100 shown in Fig. 1 includes a sheet-like support 101. An electron-donating dye precursor layer 102, an intermediate layer 103, an electron-accepting compound layer 104 having a radical polymerizable group, and a protective layer 105 are laminated in this order on one side of the support 101. In a thermosensitive recording medium according to an embodiment of the present invention, the order of the electron-donating dye precursor layer 102 and the electron-accepting compound layer 104 having a radical polymerizable group may be reversed, and the protective layer 105 shown in Fig. 1 may not be provided.

[0125] Fig. 2 is a cross-sectional view showing another embodiment of the thermosensitive recording medium of the present invention. The thermosensitive recording medium 200 shown in Fig. 2 comprises a sheet-like support 201, and on one side of the support 201, an electron-donating dye precursor layer 202, an electron-accepting compound layer 203 having a radical polymerizable group, and a protective layer 204, which are laminated in this order. In the thermosensitive recording medium of the present invention, the order of the electron-donating dye precursor layer 202 and the electron-accepting compound layer 203 having a radical polymerizable group may be reversed, and the protective layer 204 shown in Fig. 2 may not be provided.

[0126] The supports 101 and 201 may be made of any material capable of forming a coating film using a coating liquid for a thermosensitive coloring layer (thermosensitive coloring composition). Examples of materials for the supports 101 and 201 include paper, synthetic paper, and various plastics. Examples of plastics include PET (polyethylene terephthalate) and OPP (oriented polypropylene). The surfaces of the supports 101 and 201 are preferably subjected to corona discharge treatment, sandblasting, primer treatment (lamination of a primer layer), or the like, as needed. These treatments can improve the wettability of the surfaces of the supports 101 and 201, roughen them, or make them more adhesive, thereby enhancing the formability of a coating film from the thermosensitive coloring composition.

[0127] A coating film can be formed by applying or printing a thermosensitive color-forming composition onto the support 101 or 201. Examples of methods for applying or printing the thermosensitive color-forming composition include blade coaters, rod coaters, reverse roll coaters, die coaters, offset printing machines, gravure printing machines, flexographic printing machines, letterpress printing machines, and silk screen printing machines. Intermediate layers (including protective intermediate layers) and protective layers can be formed using intermediate layer compositions and overcoat compositions prepared by methods similar to those used to prepare the thermosensitive color-forming composition. Coating films can be formed by applying these intermediate layer compositions and overcoat compositions to predetermined locations. Each coating film can be formed and then dried to form the desired layer, thereby obtaining the desired thermosensitive recording medium. The coating films can be applied and dried one layer at a time, or the same coating solution can be applied and dried two or more times. Simultaneous multilayer coating, in which two or more coating solutions are applied simultaneously, can also be performed. After forming each layer or after forming all layers, it is preferable to smooth the surface using known methods such as supercalendering or soft calendering. By carrying out the surface smoothing treatment, it is possible to improve the recording sensitivity and also to increase the uniformity of the formed image.

[0128] <Image forming 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 heating the above-mentioned thermosensitive recording medium to form an image (image forming step). The method for heating the thermosensitive recording medium is not particularly limited, and any known heating method can be used. Among these, from the viewpoint of miniaturizing the image forming apparatus, it is preferable to heat the thermosensitive recording medium using a thermal head. Specifically, it is preferable to heat the thermosensitive recording medium by applying a heat pulse to the thermosensitive recording medium using a thermal head.

[0129] The temperature of the heat pulse applied to the thermosensitive recording medium in the image formation process 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 thermosensitive coloring layer of the thermosensitive recording medium while a thermal head is in contact with the thermosensitive recording medium. Specifically, the application of a heat pulse causes heating to dissolve the radical polymerizable compound contained in the thermosensitive coloring layer. When the radical polymerizable compound dissolves, the electron-donating dye precursor and the electron-accepting compound come into contact with each other, causing the thermosensitive coloring layer to color, forming an image.

[0130] The image forming method preferably further comprises a step of irradiating the thermosensitive recording medium on which the image has been formed with ultraviolet light to fix the thermosensitive coloring layer (fixing step).

[0131] In the fixing process, ultraviolet light is irradiated onto the thermosensitive recording medium on which the image has been formed. The wavelength of the irradiated ultraviolet light may be any wavelength capable of inducing a reaction with the radical polymerization initiator contained in the thermosensitive coloring layer, for example, 365 nm to 425 nm. The irradiation of ultraviolet light causes the radically polymerizable compound to polymerize, thereby fixing the thermosensitive coloring layer. Once the thermosensitive coloring layer has been fixed, the thermosensitive coloring layer will not develop color even if thermal energy reaching the coloring initiation temperature is subsequently applied, thereby maintaining the color development of the formed image for a long period of time. Note that the wavelength of ultraviolet light in this specification refers to the peak wavelength of the irradiated ultraviolet light. Fixing the thermosensitive coloring layer refers to fixing the color development state of the thermosensitive coloring layer. [Example]

[0132] The present invention will be described in more detail below 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 invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0133] <Production of thermal recording media (1)> Example 1 [Production of Electron-Accepting Compound Having a Radical Polymerizable Group] Compound (D-39), which is an exemplary compound of the electron-accepting compound having the above-mentioned radical polymerizable group, was produced by the following method.

[0134] First, 55 parts of TGSH(H) (manufactured by Nippon Kayaku Co., Ltd.) were dissolved in 202 parts of ethyl acetate, and 43 parts of Karenz BEI (manufactured by Showa Denko K.K.) were added thereto, followed by stirring at 55°C for 24 hours to obtain compound (D-39).

[0135] [Analysis of electron-accepting compounds with radically polymerizable groups] In order to confirm that the obtained compound had the structure of compound (D-39), the compound was subjected to appropriate pretreatment and then to the following analyses (1) to (4).

[0136] (1) 1 H-NMR measurement: 600MHz, CDCl3, room temperature δ [ppm] = 7.2 (a), 5.1 (b)

[0137] [ka]

[0138] (2) 13 C-NMR measurement: 600MHz, CDCl3, room temperature δ[ppm]=152(c)

[0139] [ka]

[0140] The results of analyses (1) and (2) confirmed the formation of -NHCO- (urethane bond).

[0141] (3) LC-MS measurement: LC (liquid chromatography) measurement conditions: Unison UK-Phenyl (particle size 3 μm × 150 mm) column, 40°C, water / methanol = 40 / 60 MS (mass spectrometry) measurement conditions: ESI, positive, 380°C The results of the analysis (3) confirmed that the molecular weight was consistent with that of compound (D-39).

[0142] (4) FT-IR measurement: ATR method, germanium, room temperature From the results of the analysis of (4), it was confirmed that the -NCO (isocyanate group) peak in Karenz BEI (Showa Denko KK) decreased due to the reaction.

[0143] From the above analysis, it was confirmed that the obtained compound had the structure of compound (D-39).

[0144] [Preparation of raw material composition] Solutions [A] to [D] were prepared as follows: Solution [A]: a composition containing an electron-accepting compound having a radical polymerizable group ·Compound (D-39) 30 parts Photoradical polymerization initiator (Irgacure OXE01; manufactured by BASF Japan Ltd.) 8 parts 62 parts ethyl acetate The above materials were mixed and dissolved to obtain solution [A]. [B] Liquid: Dispersion of particles containing electron-donating dye precursor Electron-donating dye precursor (BLUE220, manufactured by Fukui Yamada Chemical Co., Ltd.) 3 parts Dispersant (Pelex NBL, manufactured by Kao Corporation) 0.3 parts ·Wednesday 96.7 parts The above materials were mixed and then pulverized and dispersed using a bead mill to obtain solution B. When measured using a particle size distribution analyzer (Nanotrac, manufactured by Microtrac), the particle diameter (D50) of the electron-donating dye precursor-containing particle dispersion was found to be approximately 700 nm. [C] Liquid: Coating liquid for intermediate layer 10 parts polyvinyl alcohol (Kuraray Poval 5-88; manufactured by Kuraray) ·Wednesday 90 parts The above materials were mixed and dissolved to obtain solution [C]. [D] Liquid: Kaolin dispersion liquid 59.5 parts kaolin (HYDRAGLOSS90, manufactured by KaMin, LLC) ·Dispersant (Aron T-50; manufactured by Toagosei Co., Ltd., solid content concentration 40%) 0.5 part ·Water 40 parts The above materials were dispersed for 1 hour using a Coles disperser to obtain solution [D].

[0145] [Formation of thermosensitive coloring layer] Liquid [B] was applied to a 130 μm thick synthetic paper (Yupo, manufactured by Yupo) using a printability tester, and then dried with a dryer. The applied amount of liquid [B] after drying was 40.0 g / m 2 The coating amount of BLUE220 was 1.2 g / m 2 Next, the liquid [C] was applied using a printability tester and then dried with a dryer. The amount of liquid [C] applied after drying was 0.2 g / m 2 After that, the liquid [A] was applied using a printability tester and then dried with a dryer to form a thermosensitive coloring layer. The coating amount of the liquid [A] after drying was 60.0 g / m 2 The coating amount of compound (D-39) was 18.0 g / m 2 It was.

[0146] [Protective layer formation] 210 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol A, 80 parts of a 20% aqueous solution of acetoacetyl-modified polyvinyl alcohol B, 100 parts of [D] solution, 5.6 parts of an aqueous dispersion of zinc stearate, and 2.5 parts of polyethylene wax emulsion were prepared. These components were mixed and stirred to obtain a coating solution for a protective layer. As the acetoacetyl-modified polyvinyl alcohol A, "GOHSEFIRMER 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, "GOHSEFIRMER 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, "HYDRIN Z-8-36" (manufactured by Chukyo Yushi, solids concentration 36%) was used. The polyethylene wax emulsion used was "Chemipearl W-400" (solid content concentration 40%, manufactured by Mitsui Chemicals).

[0147] The obtained coating liquid for the protective layer was applied to the heat-sensitive color developing layer in a coating amount of 1.5 g / m after drying. 2 After forming a protective layer by coating and drying the coating, the surface was smoothed by a supercalender to obtain a thermal recording medium.

[0148] (Example 2 14 and Reference Examples 1-2 ) The electron-donating dye precursor, the photoradical polymerization initiator, and the electron-accepting compound having a radical polymerizable group used in Example 1 were changed as shown in Table 1, and Examples 2 to 3 were prepared. 14 and Reference Examples 1-2 A thermosensitive recording medium of the above formula was obtained.

[0149] <Production of thermal recording media (2)> Example 17 [Preparation of raw material composition] Solutions [E] to [I] were prepared as follows. [E] Solution: A composition containing an electron-accepting compound having a radical polymerizable group ·Compound (D-39) 30 parts Photoradical polymerization initiator (Irgacure OXE01; manufactured by BASF Japan Ltd.) 8 parts 62 parts ethyl acetate The above materials were mixed and dissolved to obtain solution [E]. [F] Liquid: Dispersion liquid of particles containing electron-donating dye precursor Electron-donating dye precursor (BLUE220, manufactured by Fukui Yamada Chemical Co., Ltd.) 3 parts Dispersant (Pelex NBL, manufactured by Kao Corporation) 0.3 parts ·Wednesday 96.7 parts The above materials were mixed and then pulverized and dispersed using a bead mill to obtain solution [F]. When measured using a particle size distribution analyzer (Nanotrac, manufactured by Microtrac), the particle diameter (D50) of the electron-accepting compound-containing particle dispersion was found to be approximately 700 nm. [G] Liquid: Liquid containing dispersant Dispersant (Pelex NBL, manufactured by Kao Corporation) 10 parts ·Water 100 parts The above materials were mixed and dissolved to obtain solution [G]. [H] Liquid: Dispersion liquid of particles containing an electron-accepting compound having a radical polymerizable group 50 parts of solution [E] and 50 parts of solution [G] were mixed and emulsified using an ultrasonic homogenizer (UH-600S, manufactured by SMT). Next, ethyl acetate was removed under reduced pressure using a rotary evaporator to obtain a particle dispersion [H] containing an electron-accepting compound having a radical polymerizable group. The particle diameter (D50) of the particles in the particle dispersion containing an electron-accepting compound having a radical polymerizable group, as measured using a particle size distribution analyzer (Nanotrac, manufactured by Microtrac), was 160 nm. [I] Liquid: Kaolin dispersion 59.5 parts kaolin (HYDRAGLOSS90, manufactured by KaMin, LLC) ·Dispersant (Aron T-50, manufactured by Toagosei, solid content concentration 40%) 0.5 part ·Water 40 parts The above materials were dispersed for 1 hour using a Coles disperser to obtain liquid [I].

[0150] [Formation of thermosensitive coloring layer] The [F] solution was applied to a 130 μm thick synthetic paper (Yupo, manufactured by Yupo) using a printability tester, and then dried with a dryer. The applied amount of [F] solution after drying was 40.0 g / m 2 The coating amount of BLUE220 was 1.2 g / m 2 After that, the [H] liquid was applied using a printability tester and then dried with a dryer to form a thermosensitive coloring layer. The coating amount of [H] liquid after drying was 60.0 g / m 2 The coating amount of compound (D-39) was 18.0 g / m 2 It was.

[0151] [Protective layer formation] 210 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol A, 80 parts of a 20% aqueous solution of acetoacetyl-modified polyvinyl alcohol B, 100 parts of solution [I], 5.6 parts of an aqueous dispersion of zinc stearate, and 2.5 parts of polyethylene wax emulsion were prepared. These components were mixed and stirred to obtain a coating solution for a protective layer. As the acetoacetyl-modified polyvinyl alcohol A, "GOHSEFIRMER 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, "GOHSEFIRMER 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, "HYDRIN Z-8-36" (manufactured by Chukyo Yushi, solids concentration 36%) was used. The polyethylene wax emulsion used was "Chemipearl W-400" (solid content: 40%, manufactured by Mitsui Chemicals). The obtained coating liquid for the protective layer was applied to the thermosensitive color developing layer in a coating amount of 1.5 g / m2 after drying. 2 After forming a protective layer by coating and drying the coating, the surface was smoothed by a supercalender to obtain a thermal recording medium.

[0152] The obtained coating liquid for the protective layer was applied to the heat-sensitive color developing layer in a coating amount of 1.5 g / m after drying. 2 After forming a protective layer by coating and drying the coating, the surface was smoothed by a supercalender to obtain a thermal recording medium.

[0153] (Comparative Examples 1 to 4) The electron-donating dye precursor, photoradical polymerization initiator, and electron-accepting compound having a radical polymerizable group used in Example 1 were changed as shown in Table 1, and thermosensitive recording materials of Comparative Examples 1 to 4 were obtained.

[0154] <Production of thermal recording media (3)> (Comparative Example 5) [Preparation of raw material composition] Solutions [J] to [M] were prepared as follows: [J] Solution: Composition containing an electron-donating dye precursor Electron-donating dye precursor (BLUE220, manufactured by Fukui Yamada Chemical Co., Ltd.) 3 parts Radical polymerizable compound (8KX-078, manufactured by Taisei Fine Chemical Co., Ltd.) 30 parts Photo-radical polymerization initiator (Omnirad TPO, manufactured by IGM Resins) 9 parts 58 parts ethyl acetate The above materials were mixed and dissolved to obtain liquid [J]. [K] liquid: Dispersion liquid of particles containing electron-accepting compounds Electron-accepting compound (TGSH(H), manufactured by Nippon Kayaku Co., Ltd.) 40 parts Dispersant (Pelex NBL, manufactured by Kao Corporation) 4 parts ·Wednesday 56 parts The above materials were mixed and then pulverized and dispersed using a bead mill to obtain solution [K]. When measured using a particle size distribution analyzer (Nanotrac, manufactured by Microtrac), the particle diameter (D50) of the electron-accepting compound-containing particle dispersion was found to be approximately 700 nm. [L] Liquid: Intermediate layer coating liquid 10 parts polyvinyl alcohol (Kuraray Poval 5-88, manufactured by Kuraray) ·Wednesday 90 parts The above materials were mixed and dissolved to obtain liquid [L]. [M] Liquid: Kaolin dispersion 59.5 parts kaolin (HYDRAGLOSS90, manufactured by KaMin, LLC) ·Dispersant (Aron T-50, manufactured by Toagosei, solid content concentration 40%) 0.5 part ·Water 40 parts The above materials were dispersed for 1 hour using a Coles disperser to obtain liquid [M].

[0155] [Formation of thermosensitive coloring layer] Using a printability tester, liquid [J] was applied to a 130 μm thick synthetic paper (Yupo, manufactured by Yupo Co., Ltd.), and then dried with a dryer to evaporate the ethyl acetate. After drying, the amount of liquid [J] applied was 40.0 g / m 2 The coating amount of BLUE220 was 1.20 g / m 2 Next, the [L] liquid was applied using a printability tester and then dried with a dryer. After drying, the amount of [L] liquid applied was 0.2 g / m 2 After that, the [K] liquid was applied using a printability tester and then dried with a dryer. After drying, the amount of [K] liquid applied was 30.0 g / m 2 The coating amount of TGSH(H) was 12.0 g / m 2 It was.

[0156] [Protective layer formation] 210 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol A, 80 parts of a 20% aqueous solution of acetoacetyl-modified polyvinyl alcohol B, 100 parts of [M] solution, 5.6 parts of an aqueous dispersion of zinc stearate, and 2.5 parts of polyethylene wax emulsion were prepared. These components were mixed and stirred to obtain a coating solution for a protective layer. The acetoacetyl-modified polyvinyl alcohol A used was "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.). The acetoacetyl-modified polyvinyl alcohol B used was "Gosefimer Z-100" (saponification degree 99.4 mol%, average polymerization degree 500, modification degree 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.). The aqueous dispersion of zinc stearate used was "Hydrin Z-8-36" (manufactured by Chukyo Yushi, solids concentration 36%). The polyethylene wax emulsion used was "Chemipearl W-400" (solid content concentration 40%, manufactured by Mitsui Chemicals).

[0157] The obtained coating liquid for the protective layer was applied to the heat-sensitive color developing layer in a coating amount of 1.5 g / m after drying. 2 After forming a protective layer by coating and drying the coating, the surface was smoothed by a supercalender to obtain a thermal recording medium.

[0158] <Image formation and evaluation> (Color development) A thermal head (KPE type, manufactured by Kyocera) was used in Examples 1 to 15, Reference examples 1-2, An image was formed by heating an area of ​​2 cm x 2 cm on the surface of the thermal recording medium obtained in Comparative Examples 1 to 5. At this time, the recording energy per unit area was 150 mJ / mm 2 The applied power and pulse width of the thermal head were set so that the optical reflection density of the formed image was measured using a reflection densitometer (product name "Xrite530", manufactured by Sakata Inx Engineering). The measurement results are shown in Table 2.

[0159] As shown in Table 2, Examples 1 to 12 and Example 15 and Examples 13 to 14 and Reference Examples 1-2 Comparing the results, it can be seen that the optical reflection density is higher when the content of the electron-accepting compound having a radical polymerizable group is 1500% by mass or more, based on the content of the electron-donating dye precursor, than when it is less than 1500% by mass.

[0160] (UV fixability) Example 1 15, Reference examples 1-2, The thermal recording media obtained in Comparative Examples 1 to 5 were irradiated once with ultraviolet light using three ultraviolet irradiation devices (ME12-L61, manufactured by Eye Graphics) equipped with metal halide lamps (120 W / cm) at conveyor speeds of 100 m / min and 10 m / min. Separately, the integrated light dose under the same conditions was measured using an ultraviolet integrating actinometer (C9536-01, manufactured by Hamamatsu). The integrated light dose was 100 mJ / cm for each. 2 and 1,000 mJ / cm 2 It was.

[0161] Then, a thermal head (KPE type, manufactured by Kyocera) was used to record the data with a recording energy of 150 mJ / mm2 The applied power and pulse width were set so that the ultraviolet light was irradiated. 15, Reference examples 1-2, A 2 cm x 2 cm image was formed on the thermal recording medium obtained in each of Comparative Examples 1 to 5. The optical reflection density of the formed image was measured using a reflection densitometer (product name "Xrite530", manufactured by Sakata Inx Engineering). The difference from the optical reflection density of the synthetic paper (Yupo, manufactured by Yupo) was taken as "Δ optical reflection density," and the results are shown in Table 2.

[0162] As shown in Table 2, Examples 1 to 15 and Reference Examples 1-2 At an integrated light intensity of 100mJ / cm 2 and 1,000 mJ / cm 2 From the absolute value of the optical reflection density of the image after irradiation, it was confirmed that all of the images were sufficiently fixed. 2 It was confirmed that even when the amount of ultraviolet light irradiation was low, color development due to heating after ultraviolet light irradiation was suppressed.

[0163] On the other hand, in Comparative Examples 1 to 4, the phenolic compounds (D-49) and (D-50) were used as the electron-accepting compounds having a radical polymerizable group, but the cumulative light dose was 1,000 mJ / cm 2 The optical reflection density Δ in Example 1 is 0.17 or more. 15 and Reference Examples 1-2 Furthermore, the cumulative light intensity is 100mJ / cm 2 The optical reflection density Δ in Examples 1 to 3 is 0.45 or more. 15 and Reference Examples 1-2 In other words, the cumulative light intensity is 100mJ / cm 2 When the temperature was as low as 100°C, the color development due to heating after ultraviolet irradiation could not be suppressed.

[0164] In Comparative Example 5, an electron-accepting compound having no radical polymerizable group and a radical polymerizable compound were used instead of an electron-accepting compound having a radical polymerizable group, but the cumulative light intensity was 1,000 mJ / cm 2 The optical reflection density is 0.18, and the integrated light amount is 100 mJ / cm 2The Δ optical reflection density in Example 1 is 0.20. 15 and Reference Examples 1-2 It is slightly more colored than the previous one.

[0165] [Table 1]

[0166] [Table 2]

[0167] The types of electron-accepting compounds having a radical polymerizable group (D-39) to (D-44) in Table 1 are the same as the exemplary compounds (D-39) to (D-44) of the electron-accepting compounds having a radical polymerizable group described above.

[0168] The structures of electron-accepting compounds having a radical polymerizable group other than (D-39) to (D-44) in Table 1 are shown in Table 3 below.

[0169] [Table 3]

[0170] The details of the types of electron donating dye precursors in Table 1 are shown in Table 4 below.

[0171] [Table 4]

[0172] The details of the types of photoradical polymerization initiators in Table 1 are shown in Table 5 below.

[0173] [Table 5]

[0174] The details of the types of electron-accepting compounds not having a radical polymerizable group in Table 1 are shown in Table 6 below.

[0175] [Table 6]

[0176] The types of radical polymerizable compounds in Table 1 are shown in detail in Table 7 below.

[0177] [Table 7] [Explanation of symbols]

[0178] 100,200 Thermal recording medium 101,201 Support 102,202 Electron-donating dye precursor layer 103 Middle Class 104,203 Electron-accepting compound layer having radically polymerizable groups 105,204 Protective layer

Claims

1. A thermosensitive recording medium having a thermosensitive color-forming layer containing an electron-donating dye precursor, a photoradical polymerization initiator, and an electron-accepting compound having a radical polymerizable group, A thermosensitive recording medium, wherein the electron-accepting compound having a radical polymerizable group contains a compound A represented by the following formula (2): 【Chemistry 1】 (In formula (2), R 21 and R 22 each independently represent a hydrocarbon group having 1 to 8 carbon atoms, R 23 represents a hydrogen atom or a methyl group; X2 represents a hydrocarbon group having 1 to 49 carbon atoms; a methylene group in the group represented by X2 may be substituted by —NHCOO—, —NHCO—, —O—, —CO—, —COO—, or —NR 24 —; R 24 represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms; d and e each independently represent an integer of 0 to 4; and f represents an integer of 1 to 10.

2. The thermosensitive recording material according to claim 1, wherein the compound A is represented by the following formula (3): 【Chemistry 2】 (In formula (3), R ３１ and R ３２ each independently represents a hydrocarbon group having 1 to 8 carbon atoms, R ３３ represents a hydrogen atom or a methyl group, X ３ represents a hydrocarbon group having 1 to 49 carbon atoms, X ３ The methylene group in the group represented by the formula (I) may be substituted with —O—, g and h each independently represent an integer of 0 to 4; and i represents an integer from 1 to 10.

3. 3. The thermosensitive recording medium according to claim 1, wherein the content of the electron-accepting compound having a radical polymerizable group is 1500% by mass or more based on the content of the electron-donating dye precursor.

4. 4. The thermosensitive recording medium according to claim 1, wherein the photoradical polymerization initiator comprises an oxime ester compound.

5. 5. The thermosensitive recording medium according to claim 1, wherein the thermosensitive coloring layer comprises particles containing the electron-accepting compound having the radical polymerizable group and the photoradical polymerization initiator.

6. 6. An image forming method comprising a step of heating the thermosensitive recording medium according to claim 1 to form an image.

7. 7. The image forming method according to claim 6, wherein the heating is performed by applying a heat pulse to the thermosensitive recording medium using a thermal head.

8. 8. The image forming method according to claim 6, further comprising the step of irradiating the thermosensitive recording medium on which the image has been formed with ultraviolet light to fix the thermosensitive coloring layer.

Images