Thermal recording medium and image forming method

Abstract

To provide a thermosensitive recording body which suppresses the occurrence of color turbidity and can form an image excellent in color development while having two or more thermal color developing layers.SOLUTION: There is provided a thermosensitive recording body 100 which comprises a support 50 and a first thermal color developing layer 10, a first intermediate layer 15 and a second thermal color developing layer 20 which are arranged on the support 50 in the remote order from the support 50. The first thermal color developing layer 10 and the second thermal color developing layer 20 contain an electron-donating dye precursor, an electron-accepting compound, a radical polymerizable compound and a photo-radical polymerization initiator, respectively and the first intermediate layer 15 contains an ultraviolet absorber.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, thermal recording media that utilize a mechanism for color development by reacting a leuco dye with a color developer have been widely used. Thermal recording media do not require consumables such as ink or toner and are relatively inexpensive, so they are widely used as recording media for faxes, receipts, and other applications.

[0003] In recent years, there has been an increasing demand for a thermosensitive recording medium capable of recording colors other than black, and various color thermosensitive recording mediums have been proposed. For example, a color thermosensitive recording medium and an image forming method using the same have been proposed, in which multiple color-forming layers are provided, the outermost color-forming layer is heated to develop color and then fixed, and the other color-forming layers below are then heated and fixed (Patent Document 1). Also, an image forming method has been proposed in which the temperature and heating time during color development of each coloring material are controlled to develop color only in a specific layer, and no fixing process is performed (Patent Document 2). Furthermore, a method for producing a thermosensitive recording medium has been proposed, which includes a step of irradiating a film formed of a thermosensitive color-developing composition containing an electron-donating dye precursor, an electron-accepting compound, an electron beam or ultraviolet light curable compound, and an epoxy compound with an electron beam or the like to form a thermosensitive color-developing layer (Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 3-43293 [Patent Document 2] JP 2008-30486 A [Patent Document 3] JP 2016-78445 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the image forming method proposed in Patent Document 1 uses decomposition of diazonium salt by ultraviolet light for fixing, so there are few options for color materials, and it is difficult to adopt color materials with better color development. In addition, the image forming method proposed in Patent Document 2 does not perform a fixing process, so if the heat energy applied to improve color development is increased, unexpected colors may develop, a phenomenon also known as "color turbidity."

[0006] Furthermore, the thermosensitive recording medium produced by the method proposed in Patent Document 3 may develop color unintentionally during storage before image formation, a phenomenon also called "background fogging." In order to suppress this background fogging, Patent Document 3 proposes irradiating the thermosensitive color-forming composition applied to the support with electron beams or ultraviolet rays to cure the thermosensitive color-forming composition. However, when using a thermosensitive recording medium having a thermosensitive recording layer formed by curing the thermosensitive color-forming composition, a problem occurs that the color development of the formed image is likely to decrease, and an improvement has been desired.

[0007] Therefore, an object of the present invention is to provide a thermosensitive recording medium having two or more thermosensitive coloring layers, capable of suppressing color turbidity and forming an image with excellent color development. Another object of the present invention is to provide an image forming method using the thermosensitive recording medium. [Means for solving the problem]

[0008] The above object is achieved by the present invention. That is, according to the present invention, there is provided a thermosensitive recording medium comprising a support, and a first thermosensitive coloring layer, a first intermediate layer, and a second thermosensitive coloring layer, which are arranged on the support in the order of furthest from the support, the first thermosensitive coloring layer and the second thermosensitive coloring layer each containing an electron donating dye precursor, an electron accepting compound, a radical polymerizable compound, and a photoradical polymerization initiator, the first intermediate layer containing an ultraviolet absorbing agent, and the ultraviolet absorbing agent being represented by the following general formula: (2) A compound represented by, a compound represented by the following general formula (4): and titanium oxide. TIFF0007634941000001.tif52170 (In the general formula (2), R3 and R4 each independently represent a hydrogen atom, a methyl group, or a hydroxyl group. R5, R6, and R7 each independently represent an alkyl group having 1 to 8 carbon atoms which may have a substituent or an alkoxy group having 1 to 8 carbon atoms which may have a substituent, and o, p, and q each independently represent an integer of 0 to 4.) TIFF0007634941000002.tif28170 (In the above general formula (4), R 10 R represents an alkyl group having 1 to 18 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent. 11 represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent, and t represents an integer of 0 to 4. Effect of the Invention

[0009] According to the present invention, it is possible to provide a thermosensitive recording medium having two or more thermosensitive color-developing layers, capable of suppressing color turbidity and forming an image with excellent color development. Also, according to the present invention, it is possible to provide an image forming method using the above thermosensitive recording medium. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing one embodiment of a thermosensitive recording medium of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of a recording device used in the examples. [Diagram 3] FIG. 2 is a schematic diagram showing a thermosensitive recording medium on which an image is formed in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <Thermal recording medium> The present invention will be described in detail below with reference to preferred embodiments, but the present invention is not limited to the following embodiments. The thermosensitive recording medium of the present invention is a thermosensitive recording medium comprising a support, and a first thermosensitive coloring layer, a first intermediate layer, and a second thermosensitive coloring layer, which are arranged on the support in the order of furthest from the support. The first thermosensitive coloring layer and the second thermosensitive coloring layer each contain an electron-donating dye precursor, an electron-accepting compound, a radically polymerizable compound, and a photoradical polymerization initiator. The first intermediate layer contains an ultraviolet absorber.

[0012] When heat is applied to the first and second thermosensitive coloring layers, the electron donating dye precursor and the electron accepting compound in these layers react to develop color. When the thermosensitive recording medium after color development is irradiated with ultraviolet light, the photoradical polymerization initiator in the first and second thermosensitive coloring layers absorbs the ultraviolet light, the radical polymerizable compound polymerizes, and these thermosensitive coloring layers are cured, and color development is maintained. In addition, the first intermediate layer contains an ultraviolet absorbing agent. By adjusting the absorption wavelength range of the ultraviolet absorbing agent in the first intermediate layer and the absorption wavelength range of the photoradical polymerization initiator in the second thermosensitive coloring layer, the timing of curing the first and second thermosensitive coloring layers can be controlled. That is, the timing of curing the first and second thermosensitive coloring layers can be controlled in accordance with the color development of the first and second thermosensitive coloring layers, so that an image with excellent color development can be formed while suppressing the occurrence of color turbidity.

[0013] (Thermal coloring layer) The first and second thermosensitive coloring layers each contain an electron donating dye precursor, an electron accepting compound, a radical polymerizable compound, and a photoradical polymerization initiator. Hereinafter, when simply referring to the "thermosensitive coloring layer", it means all the thermosensitive coloring layers. In the thermosensitive coloring layer, it is preferable that the electron donating dye precursor and the electron accepting compound are dispersed in the binder without contacting each other. For example, the electron donating dye precursor and the electron accepting compound may be encapsulated, that is, encapsulated, by a radical polymerizable compound or a photoradical polymerization initiator. Furthermore, the radical polymerizable compound or the photoradical polymerization initiator may be used as a binder. The electron donating dye precursor and the electron accepting compound are each preferably dispersed in the binder with a particle size of 10 nm or more and 1,000 nm or less, and more preferably dispersed in the binder with a particle size of 50 nm or more and 300 nm or less. If the particle size is 10 nm or more, or even 50 nm or more, the occurrence of background fogging due to storage can be suppressed. Furthermore, when the particle size is 1,000 nm or less, and further 300 nm or less, unnecessary light scattering in the thermosensitive color developing layer is reduced, and image density can be increased.

[0014] The first and second thermosensitive coloring layers constituting the thermosensitive recording medium are arranged in the order of furthest from the support, namely, the first thermosensitive coloring layer and the second thermosensitive coloring layer. It is also preferable to further include a third thermosensitive coloring layer arranged between the second thermosensitive coloring layer and the support. That is, in this case, in the thermosensitive recording medium, the first thermosensitive coloring layer, the second thermosensitive coloring layer, and the third thermosensitive coloring layer are arranged in the order of furthest from the support, namely, the first thermosensitive coloring layer, the second thermosensitive coloring layer, and the third thermosensitive coloring layer. It is preferable that the third thermosensitive coloring layer contains an electron-donating dye precursor and an electron-accepting compound. It is also preferable that the third thermosensitive coloring layer further contains a radical polymerizable compound and a photoradical polymerization initiator.

[0015] (Electron-donating dye precursor) The thermosensitive color-developing 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 the electron-donating dye precursor are listed below.

[0016] 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 of the fluoran 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.

[0017] Further examples of the electron donating dye precursors which develop a red or vermilion color tone 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, 2-(N-benzoylanilino)-3-methyl-6-di(n-butyl)aminofluoran, and 2-(N-benzoylanilino)-3-methyl-6-di(n-butyl)aminofluoran. fluoran, 2-(N-carbotoxyanilino)-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 can be mentioned.

[0018] Examples of electron donating dye precursors that develop magenta-based hues 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].

[0019] 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.

[0020] 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.

[0021] Examples of electron donating dye precursors that produce blue-based 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-diethylaminophenyl)phthalide. fluoran, 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, and 3-diphenylamino-6-diphenylaminofluoran.

[0022] 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.

[0023] Examples of electron donating dye precursors that develop a blue or cyan color tone 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.

[0024] Examples of electron donating dye precursors that develop yellow tones 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, and 4-(2,6-diphenyl-4-pyridinyl)-N,N-dimethylbenzeneamine. Examples of the benzeneamine include 4-[2,6-bis(2-butoxyphenyl)-4-pyridinyl]-N,N-dimethylbenzeneamine, 4-[2,6-bis(2-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-dimethoxyfluoran, and 1-(4-n-dodecyloxy-3-methoxyphenyl)-2-(2-quinolyl)ethylene.

[0025] As the electron donor dye precursor that develops a yellow 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.

[0026] 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.

[0027] 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.

[0028] Examples of electron donating dye precursors that produce 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-a 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.

[0029] As the electron donor 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.

[0030] 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. oran, 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.

[0031] The electron-donating dye precursor is preferably contained in the thermosensitive coloring layer in a state where it is encapsulated in particles made of a radical polymerizable compound and a photoradical polymerization initiator. 2 More than 2.00g / m 2 If it is equal to or less, an image with a sufficient optical density can be formed, which is preferable.

[0032] (Electron Accepting Compound) The thermosensitive coloring layer contains an electron-accepting compound (developer) that has the property of causing the electron-donating dye precursor to develop color upon contact. As the electron-accepting compound, it is preferable to use a compound that has the property of liquefying or dissolving upon an increase in temperature. Examples of the electron-accepting compound include organic acidic substances such as phenolic compounds, aromatic carboxylic acids, and polyvalent metal salts of these compounds.

[0033] Examples of electron-accepting compounds include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-dihydroxydiphenyl ether, 4,4'-cyclohexylidenediphenol, 1,1-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis(3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxydiphenyl sulfone, and 4-hydroxydiphenyl sulfone. Examples of the alkyl group include 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-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea, Np-tolylsulfonyl-p-butoxycarbonylphenylurea, N-(p-toluenesulfonyl)-N'-phenylurea, and 4,4'-bis(3-tosylureido)diphenylmethane.

[0034] Further examples of the electron-accepting compound include phenolic compounds such as 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, and 4,4'-dihydroxydiphenyl ether; aromatic carboxylic acids such as benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic acid, 3,5-(α-methylbenzyl)salicylic acid, and 3,5-di-tert-butylsalicylic acid; and organic acidic substances such as salts of these compounds with polyvalent metals such as zinc, magnesium, aluminum, and calcium.

[0035] The electron-accepting compound is preferably contained in the thermosensitive color-forming layer in a state where it is encapsulated in particles made of a radical polymerizable compound and a photoradical polymerization initiator. 2 More than 10.00g / m 2 It is preferable that the content of the electron-accepting compound in the thermosensitive coloring layer is 100% by mass or more and 1,000% by mass or less relative to the electron-donating dye precursor. By making the content of the electron-accepting compound relative to the electron-donating dye precursor 100% by mass or more, the color development of the image can be further improved. On the other hand, by making the content of the electron-accepting compound relative to the electron-donating dye precursor 1,000% by mass or less, the deterioration of texture due to an increase in film thickness can be suppressed and the film strength can be improved.

[0036] (Radical polymerizable compound) The thermosensitive color developing layer contains a radically polymerizable compound. The radically polymerizable compound is preferably a compound that is solid at 25° C. That is, the melting point of the radically polymerizable compound that is solid at 25° C. is higher than 25° C.

[0037] The melting point of the radical polymerizable compound is preferably 60° C. or higher. By using a radical polymerizable compound having a melting point of 60° C. or higher, it is possible to suppress background fogging caused by storage. In addition, the glass transition point of the radical polymerizable compound is preferably 40° C. or higher. By using a radical polymerizable compound having a glass transition point of 40° C. or higher, it is possible to suppress background fogging caused by storage. Both the melting point and the glass transition point of the radical polymerizable compound can be measured by differential scanning calorimetry (DSC). The scanning speed can be, for example, 10° C. / min.

[0038] Examples of the radically polymerizable compound that is solid at 25° C. include a radically polymerizable monomer, a radically polymerizable oligomer, and a radically polymerizable polymer.

[0039] Examples of radically polymerizable monomers that are solid at 25°C include stearyl acrylate, behenyl acrylate, cyclohexanedimethanol diacrylate, bisphenol A diacrylate, ethoxylated bisphenol A diacrylate, propoxylated bisphenol A diacrylate, hydrogenated bisphenol A diacrylate, ethoxylated hydrogenated bisphenol A diacrylate, propoxylated hydrogenated bisphenol A diacrylate, and tris(2-hydroxyethyl)isocyanurate triacrylate.

[0040] Examples of the radically polymerizable oligomer that is solid at 25° C. include urethane oligomers, epoxy oligomers, polyester oligomers, and other oligomers to which an acrylate group is bonded. An appropriate linking group may be interposed between the oligomer and the acrylate group.

[0041] Examples of the radically polymerizable polymer that is solid at 25° C. include polymers such as acrylic polymers, urethane polymers, epoxy polymers, and polyester polymers to which an acrylate group is bonded. An appropriate linking group may be interposed between the above-mentioned polymer and the acrylate group.

[0042] Two or more kinds of radical polymerizable compounds may be used in combination. When two or more kinds of radical polymerizable compounds are used, the melting point of the radical polymerizable compounds means the melting point of the mixture of the radical polymerizable compounds. When two or more kinds of radical polymerizable compounds are used, the glass transition point of the radical polymerizable compounds means the glass transition point of the mixture of the radical polymerizable compounds.

[0043] The molecular weight of the radical polymerizable compound is preferably 1,000 or more, more preferably 10,000 or more. When a radical polymerizable compound having a molecular weight of 1,000 or more is used, the color development of the image is maintained for a longer period of time, and the storage stability of the image can be further improved. In addition, when a radical polymerizable compound having a molecular weight of 1,000 or more is used, the storage stability of the image can be improved even when the amount of radical generation is reduced by reducing the amount of ultraviolet irradiation, etc. In addition, reducing the amount of ultraviolet irradiation is preferable because it can improve the image formation speed (print speed).

[0044] From the viewpoint of the handleability of the coating liquid for forming the thermosensitive color developing layer, the molecular weight of the radical polymerizable compound is preferably 1,000,000 or less. In this specification, the molecular weight of the radical polymerizable compound means the molecular weight for a radical polymerizable monomer, and means the weight average molecular weight (Mw) for a radical polymerizable oligomer and a radical polymerizable polymer.

[0045] The weight-average molecular weight of the radical polymerizable compound is a polystyrene-equivalent value measured by size exclusion chromatography (SEC). Measurement of the weight-average molecular weight by SEC can be performed according to the procedure shown below. First, add the sample to the eluent below so that the concentration becomes 1.0 mass%, and leave it at room temperature for 24 hours to prepare a sample. Next, filter the sample with a solvent-resistant membrane filter with a pore size of 0.2 μm, and then separate according to the conditions shown below to measure the weight-average molecular weight of the radical polymerizable compound. - Apparatus: High-speed GPC apparatus "HLC-8220GPC" (manufactured by Tosoh) Column: 2-row MIXED-C Eluent: THF (with sodium trifluoroacetate) ·Flow rate: 1.0mL / min Oven temperature: 40℃ Sample injection volume: 0.025mL

[0046] In calculating the weight average molecular weight, a molecular weight calibration curve can be used that is prepared using standard polystyrene resins (Tosoh Corporation, TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500).

[0047] The radical polymerizable compound is preferably contained in the thermosensitive coloring layer in a state in which at least one of the electron donor dye precursor and the electron acceptor compound is encapsulated. In the present invention, the term "encapsulation" does not necessarily mean that the electron donor dye precursor or the electron acceptor compound is completely encapsulated in the radical polymerizable compound, and also includes the case in which a part of them is exposed to the outside of the radical polymerizable compound. In order to further suppress the contact between the electron donor dye precursor and the electron acceptor compound, it is preferable that at least one of the electron donor dye precursor and the electron acceptor compound is encapsulated in a state in which it is not exposed to the outside of the radical polymerizable compound. The form of the radical polymerizable compound in the thermosensitive coloring layer is not particularly limited, and may be in the form of a particle or a layer. As long as the electron donor dye precursor and the electron acceptor compound are in a state in which they are difficult to contact each other, the radical polymerizable compound may encapsulate both the electron donor dye precursor and the electron acceptor compound. However, in order to prevent the electron-donating dye precursor and the electron-accepting compound from coming into contact with each other during storage of the thermal recording medium, it is preferable that the radical polymerizable compound is contained in the thermal color-forming layer in a state in which the electron-donating dye precursor and the electron-accepting compound are separately encapsulated therein.

[0048] For example, when the radical polymerizable compound is contained in the thermosensitive coloring layer in the form of a layer, the thermosensitive coloring layer preferably has a first layer containing a radical polymerizable compound encapsulating an electron-donating dye precursor and a second layer containing a radical polymerizable compound encapsulating an electron-accepting compound. Hereinafter, the first layer containing a radical polymerizable compound encapsulating an electron-donating dye precursor is also referred to as an "electron-donating dye precursor layer" or a "leuco layer". In addition, the second layer containing a radical polymerizable compound encapsulating an electron-accepting compound is also referred to as an "electron-accepting compound layer" or a "developer layer".

[0049] In addition, when the radical polymerizable compound is contained in the thermosensitive coloring layer in the form of particles, the radical polymerizable compound is preferably contained in the thermosensitive coloring layer in the form of first particles containing an electron donating dye precursor and in the form of second particles containing an electron accepting compound. The radical polymerizable compounds forming the first particles and the second particles may be the same or different. At least one of the first particles and the second particles preferably contains a photoradical polymerization initiator described below.

[0050] The particle size of the first particles is preferably 10 nm or more and 1,000 nm or less, more preferably 50 nm or more and 300 nm or less. The particle size of the second particles is preferably 10 nm or more and 1,000 nm or less, more preferably 50 nm or more and 300 nm or less. When the particle size of the first particles and the second particles is 10 nm or more, or even 50 nm or more, respectively, the radical polymerization reactivity is increased, and the image storage stability can be further improved. On the other hand, when the particle size of the first particles and the second particles is 1,000 nm or less, or even 300 nm or less, respectively, unnecessary light scattering in the thermosensitive coloring layer is reduced, and the image density can be increased. The particle size in this specification means the 50% particle size (D50) based on the volume distribution.

[0051] The content of the radical polymerizable compound in the thermosensitive coloring layer is preferably 10% by mass or more and 1,000% by mass or less, more preferably 50% by mass or more and 500% by mass or less, based on the electron donor dye precursor. By making it 10% by mass or more, background fogging is unlikely to occur, and by making it 50% by mass or more, background fogging is even less likely to occur. On the other hand, by making it 1,000% by mass or less, the color development of the image is unlikely to decrease, and by making it 500% by mass or less, the color development of the image is even more improved.

[0052] The content of the radical polymerizable compound in the particles consisting of the electron accepting compound, the radical polymerizable compound, and the photoradical polymerization initiator is preferably 10% by mass or more and 1,000% by mass or less, based on the electron accepting compound. Also, it is more preferably 50% by mass or more and 500% by mass or less. By making it 10% by mass or more, background fogging is less likely to occur, and by making it 50% by mass or more, background fogging is even more unlikely to occur. On the other hand, by making it 1,000% by mass or less, the color development of the image is less likely to decrease, and by making it 500% by mass or less, the color development of the image is even more improved.

[0053] (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. It is preferable that the photoradical polymerization initiator in the second thermosensitive coloring layer generates radicals by light with a longer wavelength than the wavelength at which the photoradical polymerization initiator in the first thermosensitive coloring layer generates radicals.

[0054] Examples of the photoradical polymerization initiator include 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 (such as thiophenyl group-containing compounds), α-aminoalkylphenone compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having carbon-halogen bonds, and alkylamine compounds. Radical generators described in JP 2018-35369 A and JP 2018-39265 A can also be used.

[0055] Among them, aromatic ketone compounds, acylphosphine oxide compounds, benzoin alkyl ether compounds, benzoin ether compounds, thioxanthone compounds, benzophenone compounds, and benzoate compounds are preferred. The photoradical polymerization initiators can be used alone or in combination of two or more. The content of the photoradical polymerization initiator in the thermosensitive coloring layer is preferably 0.1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 25% by mass or less, based on the radical polymerizable compound. When the first particles and the second particles each contain a photoradical polymerization initiator, these photoradical polymerization initiators may be the same or different.

[0056] 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, methylbenzoylformate, 4-[(4-methylphenyl)thio]benzophenone, 4,4'-bis(diethylamino)benzophenone, N,N'-tetramethyl-4,4'-diaminobenzophenone (Michler's ketone), Examples of the hydroxycyclohexyl phenyl ketone include 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.

[0057] Examples of the acylphosphine oxide compound include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)-diphenylphosphine oxide.

[0058] Examples of the benzoin alkyl ether compound include benzoin methyl ether, benzoin ethyl ether, benzoin butyl ether, and benzoin isopropyl ether.

[0059] Examples of the benzoin ether compounds include methyl benzoin and ethyl benzoin.

[0060] Examples of the thioxanthone compound include 2-chlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, and 2-methylthioxanthone.

[0061] Examples of the benzophenone compound include benzophenone, 4-methylbenzophenone, 4-phenylbenzophenone, 4-(4-methylphenylthio)benzophenone, and 4,4'-bis(diethylamino)benzophenone.

[0062] Benzoate compounds include ethyl-4-(dimethylamino)-benzoate, ethylhexyl-4-dimethylaminobenzoate, methyl-o-benzoylbenzoate, 3-methylbutyl p-(dimethylamino)benzoate, and the like.

[0063] Among the above, the photoradical polymerization initiator is preferably at least one selected from the group consisting of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-chlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, 4-phenylbenzophenone, 4-(4-methylphenylthio)benzophenone, 4,4'-bis(diethylamino)benzophenone, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one.

[0064] (Other Ingredients) The thermosensitive coloring layer may contain a storage stability improver. By containing a storage stability improver in 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 phenol; epoxy compounds such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenyl sulfone, 4-(2-methyl-1,2-epoxyethyl)diphenyl sulfone, and 4-(2-ethyl-1,2-epoxyethyl)diphenyl sulfone; and isocyanuric acid compounds such as 1,3,5-tris(2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl)isocyanuric acid.

[0065] The thermosensitive coloring layer may contain a thermal sensitizer, which can increase the recording sensitivity. Examples of the thermal sensitizer include stearic acid amide, methoxycarbonyl-N-stearic acid benzamild, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylene bisstearic acid amide, behenic acid amide, methylene bisstearic acid amide, N-methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, benzyl p-benzyloxybenzoate, 1-hydroxy-2-naphthoic acid phenyl, 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) ether, Examples of the benzene-2-phenylene ether 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, the content is preferably 2% by mass to 40% by mass, more preferably 5% by mass to 25% by mass, of the total solid content of the thermosensitive coloring layer.

[0066] Auxiliaries such as a storage stability improver and a thermal sensitizer may be mixed in the form of fine particles dispersed in water (solid dispersion fine particles) into the coating solution for forming the thermosensitive coloring layer. These auxiliaries may also be dissolved in a solvent and used in an emulsified state using a water-soluble polymeric compound as an emulsifier. Furthermore, the storage stability improver and the thermal sensitizer may be contained in particles containing an electron-donating dye precursor or an electron-accepting compound.

[0067] The heat-sensitive color developing layer may contain a polymerization accelerator, such as a benzoate compound or an amine compound.

[0068] Benzoate compounds 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, triethanolamine, and the like.

[0069] The thermosensitive coloring layer may contain a sensitizer. The sensitizer may be any sensitizer that sensitizes the photoradical polymerization initiator by an electron transfer mechanism or an energy transfer mechanism. Examples of the sensitizer 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 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 1 part by mass or more and 5 parts by mass or less, relative to 1 part by mass of the photoradical polymerization initiator.

[0070] 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 sensitization assistant in the thermosensitive coloring layer. Examples of the sensitization assistant 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 assistant in the thermosensitive coloring layer is preferably 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 0.5 parts by mass or more and 5 parts by mass or less, per part by mass of the sensitizer.

[0071] 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.

[0072] Examples of the radical polymerization inhibitor include phenolic hydroxyl group-containing compounds, methoquinone (hydroquinone monomethyl ether), hydroquinone, quinones such as 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 polyalkylenepolyamines, sulfur-containing compounds such as phenothiazine, complexing agents based on tetraazaannulene (TAA), and hindered amines.

[0073] Among them, the radical polymerization inhibitor is preferably phenols, N-oxyl free radical compounds, 1,1-diphenyl-2-picrylhydrazyl free radical, phenothiazine, quinones, or hindered amines. Also, N-oxyl free radical compounds are more preferable. The content of the radical polymerization inhibitor in the thermosensitive coloring layer is preferably 1 ppm or more and 5,000 ppm or less by mass based on the content of the radical polymerizable compound.

[0074] The thermosensitive coloring layer may contain a pigment with a high whiteness and an average particle size of 10 μm or less. By containing such a pigment, the whiteness of the thermosensitive coloring layer can be improved and the uniformity of the image can be improved. Examples of the pigment 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 and silica; and organic pigments such as urea-formaldehyde resin, styrene-methacrylic acid copolymer resin, and polystyrene resin. The content of the pigment 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 mass or less of the total solid content of the thermosensitive coloring layer.

[0075] A binder can be used as a component for constituting the thermosensitive coloring layer. In addition, crosslinking agents, waxes, metal soaps, colored dyes, colored pigments, fluorescent dyes, etc. can be added as necessary. 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 such as 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.

[0076] The water resistance of the thermosensitive coloring layer can be improved by adding a crosslinking agent to the thermosensitive coloring layer. Examples of the crosslinking agent 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; 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 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 thermosensitive coloring layer.

[0077] 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 stearic acid amide and ethylene bisstearic acid amide; higher fatty acid esters and derivatives thereof; and examples of the metal soap include higher fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate.

[0078] When the thermosensitive recording medium is a two-color thermosensitive recording medium, it is preferable to add a color dye or a color pigment having a color tone that is complementary to the low-temperature color tone in the thermosensitive coloring layer. By adding such a color dye or a color pigment to the thermosensitive coloring layer, the color tone of the thermosensitive recording medium before and after image formation can be adjusted. Furthermore, various auxiliary agents such as oil repellents, defoamers, and viscosity regulators can be added to the thermosensitive coloring layer as necessary.

[0079] The thermosensitive coloring layer can be formed, for example, by applying a coating solution for the thermosensitive coloring layer, which contains each component 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 More preferably, it is 2 g / m or less. 2 More than 10g / m 2 It is particularly preferred that:

[0080] It is preferable to use a surfactant to prepare the first and second particles. Examples of the surfactant include anionic surfactants such as sodium alkylsulfonate, sodium alkylbenzenesulfonate, sodium dialkylsulfosuccinate, and sodium alkylcarboxylate; 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.

[0081] 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 surface activity.

[0082] A dispersing agent can also be used to prepare the first and second particles.The dispersing agent can 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.

[0083] 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 each of the first particles and the second particles.

[0084] (Middle class) Between the first thermosensitive coloring layer and the second thermosensitive coloring layer, a first intermediate layer (also called the first ultraviolet absorbing layer) containing an ultraviolet absorbing agent is disposed. In addition, it is preferable to have a second intermediate layer (also called the second ultraviolet absorbing layer) and a third thermosensitive coloring layer disposed between the second thermosensitive coloring layer and the support in the order of furthest from the support. Furthermore, it is preferable to have a protective layer and a protective intermediate layer (also called the ultraviolet absorbing layer under the protective layer) disposed on the first thermosensitive coloring layer. In other words, it is preferable to dispose an intermediate layer between the multiple thermosensitive coloring layers disposed and between the thermosensitive coloring layer and the protective layer. Hereinafter, when simply saying "intermediate layer", it means all intermediate layers.

[0085] The transmittance of the first intermediate layer for light having a wavelength of 365 nm is preferably smaller than the transmittance of light having a wavelength of 405 nm. Furthermore, the transmittance of the first intermediate layer for light having a wavelength of 365 nm is preferably 5% or less. Moreover, the transmittance of the first intermediate layer for light having a wavelength of 405 nm is preferably 20% or more.

[0086] The material constituting the intermediate layer may be a water-soluble polymeric material or a water-insoluble polymer that is used in known thermosensitive recording media.Specific examples of the material constituting the intermediate layer may include the same as the binder that is a component constituting the thermosensitive coloring layer.Also, the intermediate layer may contain, as an auxiliary, particles with high porosity such as silica or calcined kaolin, plastic pigments, hollow particles, foams, and organic compounds such as polyethylene wax having a glass transition point or melting point.

[0087] The intermediate layer can be formed, for example, by applying a coating liquid for the intermediate layer containing each component 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 even more preferable that:

[0088] The first intermediate layer contains an ultraviolet absorbing agent. By containing an ultraviolet absorbing agent, the ultraviolet transmittance of the first intermediate layer can be controlled to a desired value. The ultraviolet absorbing agent contained in the first intermediate layer is preferably one that absorbs ultraviolet rays of a wavelength at which the photoradical polymerization initiator in the first thermosensitive coloring layer generates radicals. It is preferable to contain an ultraviolet absorbing agent in intermediate layers other than the first intermediate layer, since the ultraviolet absorbing rate can be controlled. The content of the ultraviolet absorbing agent in the intermediate layer is not particularly limited, as long as it is an amount that allows the ultraviolet absorbing rate of the intermediate layer to be a desired value.

[0089] Examples of the ultraviolet absorbent that can be used include benzotriazole-based ultraviolet absorbents, triazine-based ultraviolet absorbents, benzophenone-based ultraviolet absorbents, cyanoacrylate-based ultraviolet absorbents, salicylic acid-based ultraviolet absorbents, and titanium oxide. The ultraviolet absorbent is preferably at least one selected from the group consisting of compounds represented by the following general formulas (1) to (5) and titanium oxide. The first intermediate layer preferably contains at least one of the compound represented by general formula (1) and the compound represented by general formula (2).

[0090] TIFF0007634941000003.tif29170 (In the general formula (1), R1 represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, or a halogen atom; n represents an integer of 0 to 4. R2 represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aralkyl group having 7 to 12 carbon atoms which may have a substituent, or an alkylene group having 1 to 8 carbon atoms which may have a substituent; and m represents an integer of 0 to 4. When R2 is an alkylene group having 1 to 8 carbon atoms which may have a substituent, a plurality of (2-hydroxy-phenyl)-benzotriazole structures may be bonded via the alkylene group.)

[0091] TIFF0007634941000004.tif53170 (In the general formula (2), R3 and R4 each independently represent a hydrogen atom, a methyl group, or a hydroxyl group. R5, R6, and R7 each independently represent an alkyl group having 1 to 8 carbon atoms which may have a substituent or an alkoxy group having 1 to 8 carbon atoms which may have a substituent, and o, p, and q each independently represent an integer of 0 to 4.)

[0092] TIFF0007634941000005.tif32170 (In the above general formula (3), R 15 represents a hydrogen atom, a methyl group, or a hydroxyl group. R8 represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, an aralkyl group having 7 to 12 carbon atoms which may have a substituent, or an alkylene group having 1 to 8 carbon atoms which may have a substituent, and r represents an integer from 0 to 4. When R8 is an alkylene group having 1 to 8 carbon atoms which may have a substituent, a plurality of 2-hydroxy-benzophenone structures may be bonded via the alkylene group. R9 represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent, and s represents an integer from 0 to 4.

[0093] TIFF0007634941000006.tif33170 (In the above general formula (4), R 10 R represents an alkyl group having 1 to 18 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent. 11 represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent, and t represents an integer of 0 to 4.

[0094] In the general formula (5), u represents an integer of 1 to 4. When u is 1, R 14 represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent. When u is 2 to 4, R 14 represents a linking group having a valence of u.

[0095] Commercially available benzotriazole-based ultraviolet absorbers include, under the following trade names, Tinuvin PS, Tinuvin 99-2, Tinuvin 326, Tinuvin 328, Tinuvin 384-2, Tinuvin 900, Tinuvin 928, Tinuvin 1130, Tinuvin CarboProtect, UVA-805 (all manufactured by BASF); Adeka STAB LA-36 (manufactured by ADEKA), and the like.

[0096] Commercially available triazine-based ultraviolet absorbers include the following trade names: Tinuvin 400, Tinuvin 405, Tinuvin 460, Tinuvin 477, Tinuvin 479, Tinuvin 400-DW(N), Tinuvin 477-DW(N), Tinuvin 479-DW(N) (all manufactured by BASF); LA-F70, LA-46 (all manufactured by ADEKA), and the like.

[0097] Commercially available benzophenone-based UV absorbers include UVA-935LH (manufactured by BASF); Adeka STAB 1413 (manufactured by ADEKA) under the following trade names. Commercially available salicylic acid-based UV absorbers include methyl salicylate, butyl salicylate, octyl salicylate, phenyl salicylate, etc. Commercially available cyanoacrylate-based UV absorbers include Uvinul 3035, Uvinul 3039, Uvinul 3030 (all manufactured by BASF) under the following trade names. Titanium oxide includes rutile-type titanium oxide and anatase-type titanium oxide.

[0098] (protective layer) It is preferable to have a protective layer on the thermosensitive coloring layer. As the protective layer, a protective layer used in a known thermosensitive recording medium can be used. For example, it is preferable to provide a protective layer containing a water-soluble polymer material and particles. In addition, an intermediate layer (hereinafter also referred to as a "protective intermediate layer") below the protective layer may be provided between the first thermosensitive coloring layer and the protective layer. In other words, it is preferable that the thermosensitive recording medium further includes a protective layer and a protective intermediate layer disposed on the first thermosensitive coloring layer. As the water-soluble polymer material and particles, the same materials that can be contained in the thermosensitive coloring layer can be used. Furthermore, it is also preferable to add a crosslinking agent to impart water resistance to the protective layer.

[0099] By incorporating microcapsules containing an ultraviolet absorber or solid dispersion fine particles of an ultraviolet absorber into 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 exhibit an excellent additional effect of suppressing sticking to a thermal head. In addition, microcapsules having a wall film made of polyurethane-polyurea resin or aminoaldehyde resin have a lower refractive index than microcapsules having a wall film made of other resins. Furthermore, since they are spherical in shape, they are preferable because even if a large amount is added to the protective layer, a decrease in concentration due to diffuse reflection of light is unlikely to occur.

[0100] In addition, it is preferable to include particles in the protective layer, since this can prevent adhesion of dirt 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 density, and specifically, it is preferably 60 mass % or less of the total solid content of the protective layer.

[0101] The protective layer can be formed, for example, by applying a coating solution for the protective layer containing each component 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. 2 More than 8g / m 2 It is even more preferable that:

[0102] (Resin layer) A resin layer made of a resin cured by electron beams or ultraviolet rays can be provided on each of the thermosensitive coloring layer, the intermediate layer, and the protective layer. The resin cured by electron beams can be, for example, the resin described in JP-A-58-177392. The resin constituting the resin layer may be appropriately added with auxiliary agents such as non-electron beam cured resins, particles, defoamers, leveling agents, lubricants, surfactants, and plasticizers. Among them, it is preferable to add particles such as calcium carbonate and aluminum hydroxide, and lubricants such as waxes and silicone, since this can suppress sticking to the thermal head.

[0103] (Other layers) By processing the thermal recording medium to give it higher functions, the added value of the thermal recording medium can be increased. For example, by applying an adhesive, a remoistening adhesive, a delayed tack type adhesive, or the like to the back surface, it can be made into adhesive paper, remoistening adhesive paper, or delayed tack paper. In addition, by giving the functions of thermal transfer paper, inkjet recording paper, carbonless paper, electrostatic recording paper, xeography paper, or the like to the back surface, it can be made into a recording paper capable of double-sided recording. Furthermore, by disposing a thermal coloring layer on the back surface, it can be made into a double-sided thermal recording medium. In addition, a back layer can be provided on the back surface of the thermal recording medium to suppress the penetration of oil or plasticizer from the back surface, or to control curling or prevent static electricity.

[0104] (Layer structure of thermal recording medium) FIG. 1 is a cross-sectional view showing one embodiment of the thermosensitive recording medium of the present invention. The thermosensitive recording medium 100 shown in FIG. 1 is provided with a sheet-like support 50. On one side of the support 50, a third thermosensitive coloring layer 30, a second intermediate layer 25, a second thermosensitive coloring layer 20, a first intermediate layer 15, a first thermosensitive coloring layer 10, a protective intermediate layer 5, and a protective layer 1 are laminated in this order. Hereinafter, the side closer to the support 50 is referred to as the lower layer, and the opposite side is referred to as the upper layer. The thermosensitive recording medium 100 according to the embodiment of the present invention may not be provided with the third thermosensitive coloring layer 30, the second intermediate layer 25, the protective intermediate layer 5, and the protective layer 1 as shown in FIG. 1.

[0105] That is, the thermosensitive coloring layers other than the bottom layer (the second thermosensitive coloring layer 20 and the first thermosensitive coloring layer 10) contain a radical polymerizable compound and a photoradical polymerization initiator. In consideration of outdoor installation, it is preferable that the protective intermediate layer 5 contains an ultraviolet absorbing agent to improve light resistance. However, it is preferable that the transmittance of the protective intermediate layer 5 at a wavelength of 365 nm is 10% or more. The second intermediate layer 25 is a layer for suppressing the occurrence of color turbidity caused by contact between the second thermosensitive coloring layer 20 and the third thermosensitive coloring layer 30. It is preferable that the second intermediate layer 25 is made of a resin that is solid at 25°C.

[0106] The support 50 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 support 50 include paper, synthetic paper, and various plastics. Examples of plastics include PET (polyethylene terephthalate) and OPP (oriented polypropylene). It is preferable to subject the surface of the support 50 to a corona discharge treatment, sandblasting treatment, primer treatment (lamination of an undercoat layer), etc., as necessary. By subjecting the surface of the support 50 to these treatments, the wettability of the surface of the support 50 can be improved, the surface can be roughened, or the surface can be made more adhesive, and the formability of a coating film made of the thermosensitive coloring composition can be improved.

[0107] A coating film can be formed by applying or printing the thermosensitive coloring composition on the support 50. Examples of means for applying or printing the thermosensitive coloring 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. The intermediate layer (including the protective intermediate layer) and the protective layer can be formed using an intermediate layer composition or an overcoat composition prepared by the same method as the method for preparing the thermosensitive coloring composition. The coating film can be formed by applying these intermediate layer compositions and overcoat compositions to a predetermined location. After each coating film is formed, each layer can be formed by drying, and the desired thermosensitive recording medium can be obtained. The coating film may be applied and dried one layer at a time, or the same coating liquid may be applied and dried in two or more separate applications. Furthermore, simultaneous multi-layer coating in which two or more coating liquids are applied simultaneously may be performed. After each layer is formed, or after all layers are formed, it is preferable to perform a smoothing treatment by a known method such as a super calendar or a soft calendar at any stage. 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.

[0108] <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 (a) of heating the above-mentioned thermosensitive recording medium 100 to color the first thermosensitive coloring layer 10, and a step (b) of irradiating the colored thermosensitive coloring layer 10 with a first ultraviolet ray 1 to polymerize the radical polymerizable compound in the first thermosensitive coloring layer 10. Furthermore, the image forming method of the present invention includes a step (c) of heating the thermosensitive recording medium 10 after the ultraviolet ray irradiation to color the second thermosensitive coloring layer 20, and a step (d) of irradiating the colored second thermosensitive coloring layer 20 with a second ultraviolet ray 2 to polymerize the radical polymerizable compound in the second thermosensitive coloring layer 20. In step (c), the thermosensitive recording medium 100 after irradiation with the first ultraviolet ray 1 is heated at a temperature higher than the heating temperature of the thermosensitive recording medium 100 in step (a) to color the second thermosensitive coloring layer 20. In step (d), the colored second thermosensitive coloring layer 20 is irradiated with second ultraviolet ray 2 having a wavelength longer than that of the first ultraviolet ray 1 to polymerize the radical polymerizable compound in the second thermosensitive coloring layer 20. When using a thermosensitive recording medium 100 having a second intermediate layer 25 and a third thermosensitive coloring layer 30 arranged in order from the farthest from the support between the second thermosensitive coloring layer 20 and the support 50, the method further includes step (e) of heating the thermosensitive recording medium 100 after irradiation with the second ultraviolet ray 2 in step (d) to color the third thermosensitive coloring layer 30.

[0109] To heat the thermal recording medium 100, for example, a thermal head is used, and the applied voltage is kept constant while controlling the width of one pulse and the number of repetitions. Alternatively, the applied voltage is changed while controlling the width of one pulse. By controlling in this way, an image can be formed while appropriately setting the applied heat energy.

[0110] The image forming method will be described in detail with reference to the drawings. When forming an image on the thermosensitive recording medium 100 shown in FIG. 1, first, heat energy is applied that does not reach the color development start temperature of the second thermosensitive coloring layer 20 and the third thermosensitive coloring layer 30, but reaches the color development start temperature of the first thermosensitive coloring layer 10, thereby causing the first thermosensitive coloring layer 10 to develop color (step (a)). Next, the first thermosensitive coloring layer 10 is irradiated with a first ultraviolet ray having a wavelength that the photoradical polymerization initiator in the first thermosensitive coloring layer 10 can react with, thereby polymerizing the radical polymerizable compound in the first thermosensitive coloring layer 10, and the first thermosensitive coloring layer 10 is fixed (step (b)). The fixed first thermosensitive coloring layer 10 will not develop color further even if heat energy that reaches the color development start temperature is applied thereafter. Thereafter, the second thermosensitive coloring layer 20 is colored by applying thermal energy that does not reach the coloring start temperature of the third thermosensitive coloring layer 30 but reaches the coloring start temperature of the second thermosensitive coloring layer 20 (step (c)). Then, the second thermosensitive coloring layer 20 is irradiated with second ultraviolet light of a wavelength that the photoradical polymerization initiator in the second thermosensitive coloring layer 20 can react with, polymerizing the radical polymerizable compound in the second thermosensitive coloring layer 20 and fixing the second thermosensitive coloring layer 20 (step (d)). Next, the third thermosensitive coloring layer 30 is colored by applying thermal energy that reaches the coloring start temperature of the third thermosensitive coloring layer 30 (step (e)).

[0111] From the viewpoint of further suppressing the occurrence of color turbidity, it is preferable that the wavelength of the second ultraviolet ray irradiated to the second thermosensitive coloring layer 20 is longer by 20 nm or more than the wavelength of the first ultraviolet ray irradiated to the first thermosensitive coloring layer 10. It is also preferable that the transmittance of the first ultraviolet ray irradiated to the first thermosensitive coloring layer 10 through the first intermediate layer 15 is 5% or less, and the transmittance of the second ultraviolet ray irradiated to the second thermosensitive coloring layer 20 through the first intermediate layer 15 is 20% or more, from the viewpoint of further suppressing the occurrence of color turbidity. It is also preferable that the wavelength of the first ultraviolet ray irradiated to the first thermosensitive coloring layer 10 is 345 nm or more and 385 nm or less, more preferably 355 nm or more and 375 nm or less, and even more preferably 365 nm. The wavelength of the second ultraviolet ray irradiated to the second thermosensitive coloring layer 20 is preferably more than 385 nm and not more than 425 nm, more preferably 395 nm or more and not more than 415 nm, and even more preferably 405 nm. By setting the wavelengths of the first and second ultraviolet rays irradiated to the first thermosensitive coloring layer 10 and the second thermosensitive coloring layer 20 to be within the above ranges, respectively, the occurrence of color turbidity can be further suppressed. In this specification, the wavelength of ultraviolet ray means the peak wavelength of the irradiated ultraviolet ray.

[0112] The heating temperature of the thermal recording medium 100 in step (c) is higher than the heating temperature of the thermal recording medium 100 in step (a). It is also preferred that the heating temperature of the thermal recording medium 100 in step (a) is 120°C or higher and 140°C or lower, and that the heating temperature of the thermal recording medium 100 in step (c) is 150°C or higher and lower than 170°C.

[0113] When using a thermosensitive recording medium 100 having a second intermediate layer 25 and a third thermosensitive coloring layer 30 between the second thermosensitive coloring layer 20 and the support, it is preferable that the heating temperature of the thermosensitive recording medium 100 in step (e) is higher than the heating temperature of the thermosensitive recording medium 100 in step (c). Furthermore, the heating temperature of the thermosensitive recording medium 100 in step (e) is preferably 165° C. or higher. EXAMPLES

[0114] 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 without departing from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0115] Example 1 [Preparation of Coating Solution for First Thermosensitive Coloring Layer] The following materials were mixed and dissolved to prepare an [oil phase A1] liquid, an [oil phase B1] liquid, and an [aqueous phase C] liquid.

[0116] [Oil phase A1] liquid: composition containing electron-donating dye precursor Electron donor dye precursor (YELLOW435, Fukui Yamada Chemical Industry Co., Ltd.) 40 parts Radical polymerizable compound (SR355, Arkema) 47 parts 13 parts of photoradical polymerization initiator (Omnirad 184, iGM Resin) 120 parts ethyl acetate

[0117] [Oil phase B1] Liquid: Composition containing an electron-accepting compound Electron-accepting compound (D-8, Nippon Soda) 40 parts Radical polymerizable compound (SR355, Arkema) 47 parts 13 parts of photoradical polymerization initiator (Omnirad 184, manufactured by iGM Resin) 120 parts ethyl acetate

[0118] [Aqueous phase C] liquid Polyvinyl alcohol (Kuraray Poval 5-88, manufactured by Kuraray) 2.5 parts Sodium di-2-ethylhexyl sulfosuccinate 1.0 parts Sodium polyacrylate (Aron T-50, manufactured by Toagosei) 1.0 part Boric acid 0.02 parts Sodium tetraborate decahydrate 0.02 parts ·Wednesday 95.5 parts

[0119] After mixing 80 parts of the [oil phase A1] liquid and 100 parts of the [aqueous phase C] liquid, the mixture was 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 containing an electron-donating dye precursor. The particle diameter (D50) of the particles in the particle dispersion containing an electron-donating dye precursor, measured using a particle size distribution measuring device (Nanotrac, manufactured by Microtrac), was 150 nm.

[0120] After mixing 80 parts of the [oil phase B1] liquid and 100 parts of the [aqueous phase C] liquid, the mixture was 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 liquid containing an electron-accepting compound. The particle diameter (D50) of the particles in the particle dispersion liquid containing an electron-accepting compound, measured using a particle size distribution measuring device (Nanotrac, manufactured by Microtrac), was 140 nm.

[0121] 10 parts of the prepared electron-donating dye precursor-containing particle dispersion and 40 parts of the electron-accepting compound-containing particle dispersion were mixed to obtain a coating liquid for the first thermosensitive color developing layer.

[0122] [Preparation of Coating Solution for Second Thermosensitive Coloring Layer] The following materials were mixed and dissolved to prepare an [oil phase A2] liquid and an [oil phase B2] liquid, respectively.

[0123] [Oil phase A2] Liquid: Composition containing electron-donating dye precursor Electron-donating dye precursor (RED-40, Yamamoto Chemicals) 40 parts Radical polymerizable compound (SR355, Arkema) 47 parts 13 parts of photoradical polymerization initiator (Omnirad 184, manufactured by iGM Resin) 120 parts ethyl acetate

[0124] [Oil phase B2] Liquid: Composition containing an electron-accepting compound Electron-accepting compound (D-90, Nippon Soda) 40 parts Radical polymerizable compound (SR355, Arkema) 47 parts 13 parts of photoradical polymerization initiator (Omnirad 184, manufactured by iGM Resin) 120 parts ethyl acetate

[0125] After mixing 80 parts of the [oil phase A2] liquid and 100 parts of the [aqueous phase C] liquid, the mixture was 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 containing an electron-donating dye precursor. The particle diameter (D50) of the particles in the particle dispersion containing an electron-donating dye precursor, measured using a particle size distribution measuring device (Nanotrac, manufactured by Microtrac), was 150 nm.

[0126] After mixing 80 parts of the [oil phase B2] liquid and 100 parts of the [aqueous phase C] liquid, the mixture was 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 liquid containing an electron-accepting compound. The particle diameter (D50) of the particles in the particle dispersion liquid containing an electron-accepting compound, measured using a particle size distribution measuring device (Nanotrac, manufactured by Microtrac), was 140 nm.

[0127] 10 parts of the prepared electron-donating dye precursor-containing particle dispersion and 40 parts of the electron-accepting compound-containing particle dispersion were mixed to obtain a coating liquid for the second thermosensitive color developing layer.

[0128] [Preparation of Coating Solution for First Intermediate Layer] The following materials were mixed and dissolved to prepare an [oil phase D] liquid. [Oil phase D] liquid: composition containing an ultraviolet absorber 2-Oxyphenylbenzotriazole diphenyl phosphinate 50 parts 100 parts ethyl acetate

[0129] 80 parts of the [oil phase D] liquid and 100 parts of the [aqueous phase C] liquid were mixed and emulsified using an ultrasonic homogenizer (UH-600S, manufactured by SMT Co., Ltd.). Next, ethyl acetate was removed under reduced pressure using a rotary evaporator to obtain a coating liquid for the first intermediate layer.

[0130] [Manufacture of thermal recording media] On a synthetic paper (Yupo, made by Yupo) with a thickness of 130 μm, the coating amount after drying was 11.25 g / m 2 After coating the coating solution for the second thermosensitive coloring layer so that the coating amount after drying was 11.25 g / m, the coating solution was dried to form the second thermosensitive coloring layer. 2 The coating solution for the first intermediate layer was applied so that the coating amount after drying was 11.25 g / m2 on the formed first intermediate layer. 2 After the coating liquid for the first thermosensitive coloring layer was coated so as to form the first thermosensitive coloring layer, it was dried to obtain a thermosensitive recording medium.

[0131] [Image formation] An image was formed using a recording device having a configuration shown in Fig. 2. The recording device shown in Fig. 2 includes a recording head 101 provided on a one-axis stage 108. An image can be formed by scanning the recording head 101 with respect to a thermal recording medium 107 by the one-axis stage 108. The recording head 101 is provided with a thermal head 102 for the first thermosensitive coloring layer 10, a thermal head 104 for the second thermosensitive coloring layer 20, and a thermal head 106 for the third thermosensitive coloring layer 30, in that order from the front in the scanning direction. An ultraviolet light source 103 for the first thermosensitive coloring layer 10 is provided between the thermal head 102 for the first thermosensitive coloring layer 10 and the thermal head 104 for the second thermosensitive coloring layer 20. In addition, an ultraviolet light source 105 for the second thermosensitive coloring layer 20 is disposed between the thermal head 104 for the second thermosensitive coloring layer 20 and the thermal head 106 for the third thermosensitive coloring layer 30. The thermal heads 102, 104, and 106 used were Kyocera thermal heads (product name "KPZ-48", effective recording width 48 mm, total dot number 384). The temperatures of the thermal heads 102, 104, and 106 were controlled by the pulse width of the applied voltage. When forming an image on the thermosensitive recording medium 107, a heat pulse is applied to the thermosensitive coloring layer of the thermosensitive recording medium 107 while the thermal heads 102, 104, and 106 are in contact with the thermosensitive recording medium 107. This allows a desired image to be formed on the thermosensitive recording medium 107. A light source manufactured by Nichia Corporation (product name "NCSU275", wavelengths selected from four types of 365 nm, 375 nm, 385 nm, 395 nm, and 405 nm) was used as the ultraviolet light sources 103 and 105. The scanning speed of the recording head 101 with respect to the thermal recording medium 107 was 100 mm / min.

[0132] The temperature of the thermal head 102 was set so that the temperature of the image recording section was 130°C. The temperature of the thermal head 104 was set so that the temperature of the image recording section was 160°C. The thermal head 106 was not used. The duty of the pulse width of the voltage applied to the thermal head was set to about 50% (the ratio of the time during which the voltage was applied during the heating time). The wavelength of the ultraviolet light source 103 was 365 nm, and the wavelength of the ultraviolet light source 105 was 405 nm, and they were set to be turned on during recording.

[0133] Under the above conditions, a 3 cm x 3 cm solid image was formed on the thermosensitive recording medium 107. Figure 3 is a schematic diagram showing the thermosensitive recording medium 107 on which an image was formed. As shown in Figure 3, an image 202 formed by the first thermosensitive coloring layer and an image 203 formed by the second thermosensitive coloring layer were formed on the thermosensitive recording medium 107. Note that an image 204 formed by the third thermosensitive coloring layer was not formed.

[0134] [Evaluation of color development and color turbidity] A reflection densitometer (product name "Xrite530", manufactured by Sakata Inx Engineering) was used to measure the optical reflection color density of the formed images (areas of image 202 and image 203 in FIG. 3). The optical reflection density of yellow (Y) in the area of ​​image 202 (hereinafter referred to as "area 202") was high, and the color developed well. The optical reflection density of magenta (M) in the area of ​​image 203 (hereinafter referred to as "area 203") was also high, and the color developed relatively well. Furthermore, the optical reflection density of yellow in area 203 was low, and there was almost no color turbidity due to yellow when magenta was colored in area 203.

[0135] Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1 described above, except that the amount of 2-oxyphenylbenzotriazole diphenyl phosphinate was changed to 200 parts. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1 described above. As a result, the optical reflection density of magenta in region 203 was improved. This is believed to be because the transmittance of the first intermediate layer to ultraviolet light (wavelength 365 nm) became 5% or less, and the transmittance of ultraviolet light (wavelength 405 nm) became 20% or more.

[0136] Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 100 parts of UVA-935LH (manufactured by BASF), which corresponds to the compound represented by general formula (3), was used as an ultraviolet absorber. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the optical reflection density of magenta in region 203 was further improved. This is believed to be because the transmittance of ultraviolet light (wavelength 365 nm) through the first intermediate layer was further reduced.

[0137] Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 100 parts of methyl salicylate, which corresponds to the compound represented by formula (4), was used as an ultraviolet absorber. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the same effect as in Example 3 was obtained.

[0138] Example 5 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 100 parts of Uvinul 3035 (manufactured by BASF), which corresponds to the compound represented by general formula (5), was used as the ultraviolet absorbent. In addition, using the obtained thermosensitive recording medium, an image was formed and evaluated in the same manner as in Example 1. As a result, the same effect as in Example 3 was obtained.

[0139] Example 6 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 100 parts of rutile-type titanium dioxide was used as the ultraviolet absorbent. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the same effect as in Example 3 was obtained.

[0140] Example 7 A thermosensitive recording medium was obtained in the same manner as in Example 1 described above, except that diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide was used as the photoradical polymerization initiator. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1 described above. As a result, the optical reflection density of yellow in region 203 decreased, and the color turbidity due to yellow during magenta color development was further suppressed. This is thought to be because the fixability of the thermosensitive color development layer was improved by changing the photoradical polymerization initiator.

[0141] Example 8 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide was used as the photoradical polymerization initiator. Using the obtained thermosensitive recording medium, an image was formed and evaluated in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0142] Example 9 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 2-chlorothioxanthone was used as the photoradical polymerization initiator. Using the obtained thermosensitive recording medium, an image was formed and evaluated in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0143] Example 10 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 2,4-diethylthioxanthone was used as the photoradical polymerization initiator. Using the obtained thermosensitive recording medium, an image was formed and evaluated in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0144] Example 11 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that isopropylthioxanthone was used as the photoradical polymerization initiator. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0145] Example 12 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 4-phenylbenzophenone was used as the photoradical polymerization initiator. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0146] Example 13 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 4-(4-methylphenylthio)benzophenone was used as the photoradical polymerization initiator. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0147] Example 14 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 4,4'-bis(diethylamino)benzophenone was used as the photoradical polymerization initiator. Using the obtained thermosensitive recording medium, an image was formed and evaluated in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0148] Example 15 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone was used as the photoradical polymerization initiator. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0149] (Example 16) A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 was used as the photoradical polymerization initiator. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0150] (Example 17) A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one was used as the photoradical polymerization initiator. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the same effect as in Example 7 was obtained.

[0151] (Example 18) A thermosensitive recording medium was obtained in the same manner as in Example 7, except that 100 parts of Tinuvin PS (manufactured by BASF), which corresponds to the compound represented by general formula (1), was used as an ultraviolet absorber. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, the optical reflection density of magenta in region 203 was further improved. This is believed to be because the transmittance of ultraviolet light (wavelength 365 nm) through the first intermediate layer was further reduced.

[0152] (Example 19) A thermosensitive recording medium was obtained in the same manner as in Example 7, except that 100 parts of Tinuvin 460 (manufactured by BASF), which corresponds to the compound represented by general formula (1), was used as the ultraviolet absorber. In addition, using the obtained thermosensitive recording medium, an image was formed and evaluated in the same manner as in Example 1. As a result, the same effect as in Example 18 was obtained.

[0153] (Example 20) [Preparation of Coating Solution for the Third Thermosensitive Coloring Layer] The following materials were mixed and dissolved to prepare an [oil phase A1] liquid, an [oil phase B1] liquid, and an [aqueous phase C] liquid.

[0154] [Oil phase A1] liquid: composition containing electron-donating dye precursor Electron-donating dye precursor (GN-2, Yamamoto Chemicals) 40 parts Amorphous polyester (Vylon 220, Toyobo) 60 parts 120 parts ethyl acetate

[0155] [Oil phase B1] Liquid: Composition containing an electron-accepting compound Electron-accepting compound (TGSH(H), Nippon Kayaku Co., Ltd.) 40 parts Amorphous polyester (Vylon 220, Toyobo) 60 parts 120 parts ethyl acetate

[0156] [Aqueous phase C] liquid Polyvinyl alcohol (Kuraray Poval 5-88, manufactured by Kuraray) 2.5 parts Sodium di-2-ethylhexyl sulfosuccinate 1.0 parts Sodium polyacrylate (Aron T-50, manufactured by Toagosei) 1.0 part Boric acid 0.02 parts Sodium tetraborate decahydrate 0.02 parts ·Wednesday 95.5 parts

[0157] After mixing 80 parts of the [oil phase A1] liquid and 100 parts of the [aqueous phase C] liquid, the mixture was 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 containing an electron-donating dye precursor. The particle diameter (D50) of the particles in the particle dispersion containing an electron-donating dye precursor, measured using a particle size distribution measuring device (Nanotrac, manufactured by Microtrac), was 150 nm.

[0158] After mixing 80 parts of the [oil phase B1] liquid and 100 parts of the [aqueous phase C] liquid, the mixture was 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 liquid containing an electron-accepting compound. The particle diameter (D50) of the particles in the particle dispersion liquid containing an electron-accepting compound, measured using a particle size distribution measuring device (Nanotrac, manufactured by Microtrac), was 140 nm.

[0159] 10 parts of the prepared electron-donating dye precursor-containing particle dispersion and 40 parts of the electron-accepting compound-containing particle dispersion were mixed to obtain a coating liquid for the third heat-sensitive color developing layer.

[0160] [Preparation of Coating Solution for Second Intermediate Layer] Polyvinyl alcohol was dissolved in pure water to prepare a 10% aqueous polyvinyl alcohol solution, which was used as a coating liquid for the second intermediate layer.

[0161] [Coating liquid for the first thermosensitive coloring layer, coating liquid for the second thermosensitive coloring layer, coating liquid for the first intermediate layer] The same coating liquids for the first thermosensitive color developing layer, the second thermosensitive color developing layer, and the first intermediate layer as those used in Example 19 were prepared.

[0162] [Manufacture of thermal recording media] On a synthetic paper (Yupo, made by Yupo) with a thickness of 130 μm, the coating amount after drying was 11.25 g / m 2 After coating the coating solution for the third thermosensitive coloring layer so that the coating amount after drying was 11.25 g / m, the coating solution was dried to form the third thermosensitive coloring layer. 2 The coating solution for the second intermediate layer was applied so that the coating amount after drying was 11.25 g / m2 on the formed second intermediate layer. 2 After coating the coating solution for the second thermosensitive coloring layer so that the coating amount after drying was 11.25 g / m, the coating solution was dried to form the second thermosensitive coloring layer. 2The coating solution for the first intermediate layer was applied so that the coating amount after drying was 11.25 g / m2 on the formed first intermediate layer. 2 After the coating liquid for the first thermosensitive coloring layer was coated so as to form the first thermosensitive coloring layer, it was dried to obtain a thermosensitive recording medium.

[0163] [Image formation] An image was formed using the same recording device (FIG. 2) as that used in Example 1. The temperature of the thermal head 106 was set so that the temperature of the image recording section was 170° C. A 3 cm×3 cm solid image was formed on the thermosensitive recording medium under the same conditions as in Example 1. As shown in FIG. 3, an image 202 formed by the first thermosensitive coloring layer, an image 203 formed by the second thermosensitive coloring layer, and an image 204 formed by the third thermosensitive coloring layer were formed on the thermosensitive recording medium 107.

[0164] [Evaluation of color development and color turbidity] The optical reflection color density of the formed image (area 202, area 203, and area of ​​image 204 in FIG. 3) was measured using a reflection densitometer (product name "Xrite530", manufactured by Sakata Inx Engineering). The color development and suppression of color turbidity in areas 202 and 203 were equivalent to those in Example 19. The optical reflection density of cyan (C) in the area of ​​image 204 (hereinafter also referred to as "area 204") was high, and the color was developed extremely well. Furthermore, there was almost no color turbidity during cyan color development in area 204.

[0165] Example 21 [Preparation of coating solution for protective layer] The following materials were mixed and dissolved to prepare a coating solution for the protective layer.

[0166] 350 parts of 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (product name: Gohsefimer Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) Amorphous silica (Mizukasil P-603, manufactured by Mizusawa Chemical Industry Co., Ltd.) 66 parts 6 parts of 36% aqueous dispersion of zinc stearate

[0167] [Preparation of Coating Solution for Protective Intermediate Layer] Tinuvin 479-DW(N) (manufactured by BASF) was dispersed in pure water to prepare a 10% aqueous dispersion, which was used as a coating solution for the protective intermediate layer.

[0168] [Manufacture of thermal recording media] The first thermosensitive coloring layer of the same thermosensitive recording medium as that produced in Example 20 was coated with a coating weight of 11.25 g / m2 after drying. 2 The coating solution for the protective intermediate layer was applied so that the coating amount after drying was 1 g / m2 on the formed protective intermediate layer. 2 After the coating solution for the protective layer was applied so as to form a protective layer, the coating solution was dried to obtain a thermal recording medium.

[0169] [Image formation] In the same manner as in Example 20, an image 202 based on the first thermosensitive coloring layer, an image 203 based on the second thermosensitive coloring layer, and an image 204 based on the third thermosensitive coloring layer, as shown in FIG. 3, were formed on a thermosensitive recording medium.

[0170] [Evaluation of abrasion resistance] Within 3 minutes of forming the image, apply OK Topcoat+ (Oji Paper, basis weight 105g / m 2 ) and then place a 500g weight on top of it, with a contact area of ​​12.6cm 2 Then, an abrasion resistance test was performed by rubbing the OK topcoat+ once at a relative speed of 10 cm / s between the thermal recording medium on which the image was recorded and the OK topcoat+. After that, the weight on the OK topcoat+ was placed at the 12.6 cm 2 The dye attached to the inside of the recording medium was scanned with a scanner (multifunction printer iR3245F, manufactured by Canon, 600 dpi, gray scale, photo mode). The ratio of the area of ​​the portion with a brightness lower than 128 in 256 gradations (dye attached area ratio) was then calculated. As a result, the dye attached area ratio of the thermosensitive recording medium of Example 20, which did not have a protective layer, was 2% or more, whereas the dye attached area ratio of the thermosensitive recording medium of Example 21, which had a protective layer, was less than 2%.

[0171] [Lightfastness evaluation] Sunshine Long Life Carbon Arc Lamp (255W / m 2 After a lightfastness test was conducted in which an image formed using the above-mentioned acrylic resin was irradiated with light for 5 hours, the optical reflection density of the image was measured. The difference in the optical reflection density of the image before and after the lightfastness test was calculated. As a result, the optical reflection density of the thermal recording medium of Example 20, which does not have a protective intermediate layer, decreased by about 0.5, whereas the optical reflection density of the thermal recording medium of Example 21, which has a protective intermediate layer, did not decrease.

[0172] [Evaluation of color development and color turbidity] The optical reflection color density of the formed image (areas 202, 203, and 204 in FIG. 3) was measured in the same manner as in Example 20. As a result, slight yellow color turbidity occurred in areas 203 and 204. This is thought to be because the protective intermediate layer had a low transmittance of ultraviolet light at a wavelength of 365 nm, and the fixing of the first thermosensitive coloring layer was somewhat insufficient.

[0173] Example 22 A thermosensitive recording medium was obtained in the same manner as in Example 21 described above, except that a 10% aqueous dispersion of Tinuvin 400 (manufactured by BASF) (with a 365 nm UV transmittance of approximately 50%) was used as the coating liquid for the protective intermediate layer 5. In addition, using the obtained thermosensitive recording medium, image formation and various evaluations were performed in the same manner as in Example 21 described above. As a result, the optical reflection density of the image did not decrease even after the light fastness test. In addition, the yellow color turbidity was improved in areas 203 and 204. This is thought to be because the UV transmittance of the protective intermediate layer at a wavelength of 365 nm was increased, thereby allowing the first thermosensitive coloring layer to be sufficiently fixed.

[0174] Example 23 A thermosensitive recording medium was obtained in the same manner as in Example 22, except that UVECOAT9146 (manufactured by Daicel Allnex) was used as the radical polymerizable compound. In addition, using the obtained thermosensitive recording medium, image formation and various evaluations were performed in the same manner as in Example 21. As a result, the fixability of each thermosensitive color developing layer was improved, and color turbidity was improved.

[0175] (Example 24) A thermosensitive recording medium was obtained in the same manner as in Example 23, except that P1731 (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the electron donor dye precursor. Using the obtained thermosensitive recording medium, image formation and various evaluations were performed in the same manner as in Example 21. As a result, the same effects as in Example 23 were obtained.

[0176] (Example 25) A thermosensitive recording medium was obtained in the same manner as in Example 23, except that P2057 (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the electron donor dye precursor. In addition, using the obtained thermosensitive recording medium, image formation and various evaluations were performed in the same manner as in Example 21. As a result, the same effects as in Example 23 were obtained.

[0177] Comparative Example 1 Except for not using the electron-donating dye precursor, a thermosensitive recording medium was obtained in the same manner as in Example 1. An attempt was made to form an image using the obtained thermosensitive recording medium in the same manner as in Example 1, but no color was formed.

[0178] Comparative Example 2 Except for not using the electron-accepting compound, a thermosensitive recording medium was obtained in the same manner as in Example 1. An attempt was made to form an image using the obtained thermosensitive recording medium in the same manner as in Example 1, but no color was formed.

[0179] Comparative Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that no radically polymerizable compound was used. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, yellow became cloudy during magenta color development because the first thermosensitive coloring layer was not fixed.

[0180] Comparative Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that no photoradical polymerization initiator was used. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, yellow became cloudy during magenta color development because the first thermosensitive coloring layer was not fixed.

[0181] Comparative Example 5 Except for not forming the first intermediate layer, a thermosensitive recording medium was obtained in the same manner as in Example 1. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, when the first thermosensitive coloring layer 10 was fixed, the second thermosensitive coloring layer was also fixed, and magenta was not colored.

[0182] Comparative Example 6 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that a 10% solution of polyvinyl alcohol that does not have ultraviolet absorbing ability was used to form a first intermediate layer. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1. As a result, when the first thermosensitive coloring layer was fixed, the second thermosensitive coloring layer was also fixed, and magenta did not develop.

[0183] Comparative Example 7 Instead of the radical polymerizable compound and the photoradical polymerization initiator, 8 parts of a mixture of 1-methylpropylphenylphenylmethane and 1-(1-methylpropylphenyl)-2-phenylethane, which are high boiling point solvents, were used. Apart from this, a thermosensitive recording medium was obtained in the same manner as in Example 1 described above. As the mixture, a product named "Nippon Sekiseki Hisol SAS-310 (manufactured by Nippon Petrochemicals)" was used. In addition, an image was formed and evaluated using the obtained thermosensitive recording medium in the same manner as in Example 1 described above. As a result, the first thermosensitive coloring layer was not fixed, and yellow became cloudy during magenta color development.

[0184] (Example 26) Except for setting the temperature of the thermal head 102 so that the temperature of the image recording section was 115°C, images were formed and evaluated in the same manner as in Example 23 described above. As a result, there was no difference in the yellow coloring in area 202, but the color turbidity of magenta was suppressed. There was no difference in the magenta coloring in area 203, but the color turbidity of yellow was suppressed. Compared to Example 23, it is believed that the lower heating temperature of the first thermosensitive coloring layer contributed to the suppression of color turbidity.

[0185] Example 27 Except for setting the temperature of the thermal head 102 so that the temperature of the image recording section was 145°C, images were formed and evaluated in the same manner as in Example 26. As a result, the yellow color development in area 202 was improved. However, slight magenta color turbidity occurred in area 202. This is thought to be due to the heating temperature of the first thermosensitive coloring layer becoming higher.

[0186] (Example 28) The temperature of the thermal head 102 was set so that the temperature of the image recording section was 130°C. The temperature of the thermal head 104 was set so that the temperature of the image recording section was 146°C. Other than these, image formation and evaluation were performed in the same manner as in Example 26 described above. As a result, the yellow color development in area 202 was equivalent to that in Example 27. Meanwhile, the color turbidity of magenta in area 202 was suppressed. This is thought to be due to the lower heating temperature of the first thermosensitive coloring layer. Although the heating temperature of the first thermosensitive coloring layer was slightly lowered, it was not enough to affect the color development.

[0187] (Example 29) Except for setting the temperature of the thermal head 104 so that the temperature of the image recording section was 165°C, images were formed and evaluated in the same manner as in Example 28. As a result, the color development and suppression of color turbidity of yellow in area 202 were equivalent to those in Example 28. Also, the color development of magenta in area 203 was slightly improved, but slight color turbidity of cyan occurred. It is believed that the third thermosensitive coloring layer also developed slightly because the heating temperature of the second thermosensitive coloring layer was higher.

[0188] (Example 30) The temperature of the thermal head 104 was set so that the temperature of the image recording section was 160°C. The temperature of the thermal head 106 was set so that the temperature of the image recording section was 167°C. Except for these, the image was formed and evaluated in the same manner as in Example 29 described above. As a result, the color development of yellow in area 202 and the suppression of color turbidity were equivalent to those in Example 29. Also, the color development of magenta in area 203 was slightly decreased, but the color turbidity of cyan was suppressed. And the color development of cyan in area 204 was slightly decreased. This is thought to be due to a slight decrease in the heating temperature of the third thermosensitive coloring layer.

[0189] Comparative Example 8 The temperature of the thermal head 102 was set so that the temperature of the image recording section was 115°C. The temperature of the thermal head 104 was set so that the temperature of the image recording section was 160°C. The thermal head 106 was not used. The duty of the pulse width of the voltage applied to the thermal head was set to about 50%. The wavelength of the ultraviolet light source 103 was set to 405 nm, and the wavelength of the ultraviolet light source 105 was set to 395 nm, and they were set to be turned on during recording. Except for these, the image was formed and evaluated in the same manner as in the above-mentioned Example 26. As a result, the magenta in the area 203 did not develop. It is considered that the second thermosensitive coloring layer was also fixed when the first thermosensitive coloring layer was fixed because the wavelength of the ultraviolet light source 103 was set to 405 nm.

[0190] Comparative Example 9 The temperature of the thermal head 102 was set so that the temperature of the image recording section was 160°C. The temperature of the thermal head 104 was set so that the temperature of the image recording section was 115°C. The thermal head 106 was not used. The duty of the pulse width of the voltage applied to the thermal head was set to about 50%. The wavelength of the ultraviolet light source 103 was set to 395 nm, and the wavelength of the ultraviolet light source 105 was set to 405 nm, and they were set to be turned on during recording. Except for these, the image was formed and evaluated in the same manner as in Example 26 described above. As a result, the magenta color became muddy in the area 202. In addition, the magenta in the area 203 did not develop. It is considered that this is because the heating temperature of the first thermosensitive coloring layer was high, so that the second thermosensitive coloring layer developed at the same time, and because the heating temperature of the second thermosensitive coloring layer was low, so that the color did not develop.

[0191] Comparative Example 10 An image was formed and evaluated in the same manner as in Example 26, except that the ultraviolet light source 103 and the ultraviolet light source 105 were not used. As a result, yellow color turbidity occurred in the area 203. This is considered to be because the thermosensitive coloring layer was not fixed by ultraviolet irradiation.

[0192] The results of the above examples and comparative examples are summarized in Tables 1-1 to 1-4, 2-1 and 2-2. Details of each component (abbreviations in Tables 1-1 to 1-4) used in the examples and comparative examples are shown in Tables 3 to 7.

[0193] TIFF0007634941000008.tif203170

[0194] TIFF0007634941000009.tif201170

[0195] TIFF0007634941000010.tif228170

[0196] TIFF0007634941000011.tif225170

[0197] TIFF0007634941000012.tif220170

[0198] TIFF0007634941000013.tif166170

[0199] TIFF0007634941000014.tif44170

[0200] TIFF0007634941000015.tif32170

[0201] TIFF0007634941000016.tif39170

[0202] TIFF0007634941000017.tif87170

[0203] TIFF0007634941000018.tif88170 [Explanation of symbols]

[0204] 1:Protective layer 5:Protective middle layer 10: First thermosensitive coloring layer 15: First middle layer 20: Second thermosensitive coloring layer 25: Second middle layer 30: Third thermosensitive coloring layer 50:Support 100, 107: Thermal recording medium 101: Recording head 102, 104, 106: Thermal head 103,105: Ultraviolet light source 108:1 axis stage 202, 203, 204: Images

Claims

1. A thermosensitive recording medium comprising a support, and a first thermosensitive coloring layer, a first intermediate layer, and a second thermosensitive coloring layer, which are arranged on the support in this order from the farthest side of the support, the first thermosensitive coloring layer and the second thermosensitive coloring layer each contain an electron donating dye precursor, an electron accepting compound, a radical polymerizable compound, and a photoradical polymerization initiator; The first intermediate layer contains an ultraviolet absorbing agent, The thermal recording medium is characterized in that the ultraviolet absorber is at least one selected from the group consisting of a compound represented by the following general formula (2), a compound represented by the following general formula (4), and titanium oxide: (In the general formula (2), R ３ and R ４ R each independently represents a hydrogen atom, a methyl group, or a hydroxyl group. ５ , R ６ , and R ７ each independently represents an alkyl group having 1 to 8 carbon atoms which may have a substituent or an alkoxy group having 1 to 8 carbon atoms which may have a substituent, and o, p, and q each independently represent an integer of 0 to 4. (In the general formula (4), R １０ R represents an alkyl group having 1 to 18 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent. １１ represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent, and t represents an integer of 0 to 4.

2. 2. The thermal recording medium according to claim 1, wherein the ultraviolet absorbing agent is a compound represented by the general formula (2).

3. 3. The thermal recording medium according to claim 1, wherein the transmittance of said first intermediate layer at a wavelength of 365 nm is smaller than the transmittance of said first intermediate layer at a wavelength of 405 nm.

4. 4. The thermal recording medium according to claim 1, wherein the first intermediate layer has a transmittance of 5% or less for light having a wavelength of 365 nm and a transmittance of 20% or more for light having a wavelength of 405 nm.

5. The thermal recording medium according to any one of claims 1 to 4, wherein the photoradical polymerization initiator is at least one selected from the group consisting of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-chlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, 4-phenylbenzophenone, 4-(4-methylphenylthio)benzophenone, 4,4'-bis(diethylamino)benzophenone, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one.

6. 6. The thermosensitive recording medium according to claim 1, further comprising a second intermediate layer and a third thermosensitive coloring layer disposed between the second thermosensitive coloring layer and the support in that order from farthest from the support.

7. 7. The thermosensitive recording medium according to claim 1, further comprising a protective layer and a protective intermediate layer disposed on said first thermosensitive color developing layer.

8. 8. The thermal recording medium according to claim 7, wherein the protective intermediate layer has a transmittance of 10% or more for light having a wavelength of 365 nm.

9. 9. The heat-sensitive recording material according to claim 1, wherein the radical polymerizable compound is a compound that is solid at 25[deg.]C.

10. a step (a) of heating the thermosensitive recording medium, the thermosensitive recording medium comprising a support, and a first thermosensitive coloring layer, a first intermediate layer, and a second thermosensitive coloring layer, which are arranged on the support in that order from the farthest from the support, the first thermosensitive coloring layer and the second thermosensitive coloring layer each containing an electron-donating dye precursor, an electron-accepting compound, a radically polymerizable compound, and a photoradical polymerization initiator, and the first intermediate layer containing an ultraviolet absorbing agent, to cause the first thermosensitive coloring layer to develop a color; (b) irradiating the first thermosensitive coloring layer with a first ultraviolet ray to polymerize the radical polymerizable compound in the first thermosensitive coloring layer; a step (c) of heating the thermosensitive recording medium after irradiating with the first ultraviolet ray at a temperature higher than the heating temperature of the thermosensitive recording medium in the step (a) to cause the second thermosensitive coloring layer to develop a color; (d) irradiating the second thermosensitive coloring layer with a second ultraviolet ray having a longer wavelength than the first ultraviolet ray to polymerize the radical polymerizable compound in the second thermosensitive coloring layer; An image forming method comprising the steps of:

11. 11. The image forming method according to claim 10, wherein the transmittance of the first intermediate layer at a wavelength of 365 nm is smaller than the transmittance of the first intermediate layer at a wavelength of 405 nm.

12. 12. The image forming method according to claim 10, wherein the first intermediate layer has a transmittance of 5% or less for light having a wavelength of 365 nm and a transmittance of 20% or more for light having a wavelength of 405 nm.

13. The image forming method according to any one of claims 10 to 12, wherein the ultraviolet absorber is at least one selected from the group consisting of compounds represented by the following general formulas (1) to (5) and titanium oxide: (In the general formula (1), R １ represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, or a halogen atom, and n represents an integer of 0 to 4. ２ represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aralkyl group having 7 to 12 carbon atoms which may have a substituent, or an alkylene group having 1 to 8 carbon atoms which may have a substituent, and m represents an integer of 0 to 4. ２ is an alkylene group having 1 to 8 carbon atoms which may have a substituent, a plurality of (2-hydroxy-phenyl)-benzotriazole structures may be bonded via the alkylene group. (In the general formula (2), R ３ and R ４ R each independently represents a hydrogen atom, a methyl group, or a hydroxyl group. ５ , R ６ , and R ７ each independently represents an alkyl group having 1 to 8 carbon atoms which may have a substituent or an alkoxy group having 1 to 8 carbon atoms which may have a substituent, and o, p, and q each independently represent an integer of 0 to 4. (In the general formula (3), R １５ represents a hydrogen atom, a methyl group, or a hydroxyl group. ８ represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, an aralkyl group having 7 to 12 carbon atoms which may have a substituent, or an alkylene group having 1 to 8 carbon atoms which may have a substituent, and r represents an integer of 0 to 4. ８ When R is an alkylene group having 1 to 8 carbon atoms which may have a substituent, a plurality of 2-hydroxy-benzophenone structures may be bonded via the alkylene group. ９ represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent, and s represents an integer of 0 to 4. (In the general formula (4), R １０ R represents an alkyl group having 1 to 18 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent. １１ represents an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, an alkoxy group having 1 to 8 carbon atoms which may have a substituent, or an aralkyl group having 7 to 12 carbon atoms which may have a substituent, and t represents an integer of 0 to 4. (In the general formula (5), u represents an integer of 1 to 4. When u is 1, R １４ represents an optionally substituted alkyl group having 1 to 8 carbon atoms, or an optionally substituted aralkyl group having 7 to 12 carbon atoms. When u is 2 to 4, R １４ represents a linking group having a valence of u.

14. 14. The image forming method according to claim 13, wherein the ultraviolet absorber is at least one selected from the group consisting of the compound represented by the general formula (2), the compound represented by the general formula (4), and titanium oxide.

15. The image forming method according to claim 13, wherein the ultraviolet absorbing agent is a compound represented by the general formula (2).

16. The image forming method according to any one of claims 10 to 15, wherein the photoradical polymerization initiator is at least one selected from the group consisting of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-chlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, 4-phenylbenzophenone, 4-(4-methylphenylthio)benzophenone, 4,4'-bis(diethylamino)benzophenone, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one.

17. 14. The image forming method according to claim 13, wherein the first intermediate layer contains at least one of the compound represented by formula (1) and the compound represented by formula (2).

18. 18. The image forming method according to claim 10, wherein the thermosensitive recording medium further comprises a second intermediate layer and a third thermosensitive coloring layer arranged between the second thermosensitive coloring layer and the support in order of furthest from the support.

19. 19. The image forming method according to claim 10, wherein the thermosensitive recording medium further comprises a protective layer and a protective intermediate layer disposed on the first thermosensitive color developing layer.

20. 20. The image forming method according to claim 19, wherein the protective intermediate layer has a transmittance of 10% or more for light having a wavelength of 365 nm.

21. 21. The image forming method according to claim 10, wherein the radical polymerizable compound is a compound that is solid at 25[deg.] C.

22. 22. The image forming method according to claim 10, wherein the wavelength of the second ultraviolet ray applied to the second thermosensitive coloring layer is longer than the wavelength of the first ultraviolet ray applied to the first thermosensitive coloring layer by 20 nm or more.

23. 23. An image forming method according to any one of claims 10 to 22, wherein the transmittance of the first ultraviolet ray irradiated to the first thermosensitive coloring layer through the first intermediate layer is 5% or less, and the transmittance of the second ultraviolet ray irradiated to the second thermosensitive coloring layer through the first intermediate layer is 20% or more.

24. the wavelength of the ultraviolet light irradiated onto the first thermosensitive coloring layer is 345 nm or more and 385 nm or less; 24. The image forming method according to claim 10, wherein the wavelength of the ultraviolet light irradiated onto the second thermosensitive color developing layer is longer than 385 nm and equal to or shorter than 425 nm.

25. The heating temperature of the thermal recording medium in the step (a) is 120° C. or more and 140° C. or less, 25. The image forming method according to claim 10, wherein the heating temperature of the thermal recording medium in the step (c) is 150[deg.] C. or higher and lower than 170[deg.] C.

26. the thermosensitive recording medium includes a second intermediate layer and a third thermosensitive coloring layer disposed between the second thermosensitive coloring layer and the support in that order from the farthest side of the support, 26. The image forming method according to claim 10, further comprising a step (e) of heating the thermosensitive recording medium after the ultraviolet ray irradiation in the step (d) to cause the third thermosensitive coloring layer to develop a color.

27. 27. The image forming method according to claim 26, wherein the heating temperature of the thermal recording medium in the step (e) is higher than the heating temperature of the thermal recording medium in the step (c).

28. 28. The image forming method according to claim 26, wherein the heating temperature of the thermal recording medium in the step (e) is 165[deg.] C. or higher.

Images