Recording paper

Abstract

[Problem] To provide a recording paper having excellent thermosensitive recording suitability and ink jet recording suitability together, and also having excellent heat resistance and recording layer strength. [Means to solve the Problem] A recording paper having a substrate, and a recording layer comprising a leuco dye and an electron accepting color developing agent on the substrate, wherein the recording layer contains the electron accepting color developing agent and the solubility of the electron-accepting color developing agent in 99.5% ethanol is 0.3 g / ml or less, and the recording layer contains a silica as an ink-receiving pigment, and the solid content of the silica with respect to the recording layer is 20 weight % or more.

Description

[Field of the Invention]

[0001] The present invention relates to a recording paper having ink jet recording suitability.[Background of the Invention]

[0002] A recording paper such as a thermosensitive recording medium is obtained by grinding a colorless or pale colored basic leuco dye (henceforth referred to as " leuco dye") and an electron accepting color developing agent (henceforth referred to as "color developing agent") each into fine particles, preparing dispersions, blending the dispersions, preparing a coating solution by adding a binder, a pigment, a sensitivity enhancer(sensitizer ), a lubricant and other aids and applying the coating solution on a support material such as paper, synthetic paper, film, plastic and the like.

[0003] The thermosensitive recording medium is less noisy when recording, does not require a developing / fixing agent and is maintenance free, the device is relatively inexpensive and compact, and the color developed is very bright. Therefore, the thermosensitive recording mode is used in a broad range of applications such as facsimile devices, computer terminal printers, automatic ticket vending machines, meter recorders, handy terminals and the like.

[0004] Furthermore, the thermosensitive recording medium is sometimes required to have ink jet recording suitability in addition to thermosensitive recording. For example, in applications such as ATMs and labels, a common layout is printed in advance using UV ink or the like, and different information such as currency or barcodes is then thermally recorded. However, when printing is performed on a recording paper such as a thermosensitive recording medium using an ink jet recording method, background color development due to color development of the thermosensitive recording layer in the recording area overlaps, causing problems such as darkening or blurring of the ink jet recorded image.

[0005] Therefore, a technology is known that uses a color developing agent having a specific range of solubility in acetonitrile to make a thermosensitive recording medium suitable for inkjet recording (Patent Document 1).[Prior Art Document][Patent Document]

[0006] Patent Document 1: Japanese Patent Application Laid-Open (kokai) 2003-226076 Patent Document 2: Japanese Patent Application Laid-Open (kokai) 2022-151636 [Summary of the Invention][Problems to be solved by the Invention]

[0007] However, when the color developing agent described in Patent Document 1 was used, heat resistance was insufficient.

[0008] Furthermore, in the case of the technology described in Patent Document 2, since ethanol was used as a solvent in the coating solution for the recording layer, the strength of the recording layer was insufficient. If the coating layer strength is weak, there is a risk of problems when printing with an ink jet continuous feed printer, and the ink jet recording suitability will deteriorate.

[0009] Therefore, an object of the present invention is to provide a recording paper that has excellent thermosensitive recording suitability and ink jet recording suitability together, and that also has excellent heat resistance and recording layer strength.[Means For Solving the Problem]

[0010] As a result of intensive studies, the present inventors have found that the above problems can be solved by specifying a solubility of an electron accepting color developing agent in ethanol, and thus completed the present invention.

[0011] The present invention provides a recording paper having a substrate, and a recording layer comprising a leuco dye and an electron accepting color developing agent on the substrate, wherein the recording layer contains the electron accepting color developing agent and the solubility of the electron-accepting color developing agent in ethanol is 0.3 g / ml or less, and the recording layer contains a silica as an ink-receiving pigment, and the solid content of the silica with respect to the recording layer is 20 weight % or more.[Effect of the Invention]

[0012] A recording paper of the present invention has excellent thermosensitive recording suitability and ink jet recording suitability together, and also has excellent heat resistance and recording layer strength.[Modes For Carrying out the Invention]

[0013] Hereinafter, the present invention will be described in detail below.

[0014] A recording paper of the present invention has a substrate, and a recording layer comprising a leuco dye and an electron accepting color developing agent on the substrate. The recording layer contains the electron accepting color developing agent and the solubility of the electron-accepting color developing agent in ethanol is 0.3 g / ml or less. And the recording layer contains a silica as an ink-receiving pigment, and the solid content of the silica with respect to the recording layer is 20 weight % or more.

[0015] Hereinafter, various materials used in the recording layer of the recording paper of the present invention will be illustrated, however, binders, cross-linking agents, pigments and the like can also be used for other coating layers within the range that does not impair the desired advantages on the above-mentioned problems.

[0016] This recording layer serves as, for example, a thermosensitive recording layer or an ink-receiving layer.

[0017] The recording layer contains the electron accepting color developing agent and the solubility of the electron-accepting color developing agent in ethanol is 0.3 g / ml or less.

[0018] When the solubility of the developing agent in ethanol is 0.3 g / ml or less, both the thermosensitive recording suitability and the ink jet recording suitability are excellent. The reason for this is not clear, but it is thought that this is because an ink jet ink typically use an organic solvent as a solvent, and the lower the solubility of the developing agent in ethanol, the more the developing agent is prevented from melting coused by the ink jet ink.

[0019] Furthermore, when the solubility of the developing agent in ethanol is 0.3 g / ml or less, heat resistance is excellent. This is because the color development starting point of the developing agent becomes lower when the solubility of the developing agent in ethanol exceeds 0.3 g / ml.

[0020] Here, the solubility refers to the value obtained by dissolving the developing agent powder in 10 ml of 99.5% ethanol at room temperature until it becomes supersaturated, filtering by suction, measuring the weight of the incompletely dissolved powder remaining on the filter paper, and calculating the weight that will dissolve in 1 ml of ethanol from the difference between the weight of the powder added and the weight of the remaining powder.

[0021] Furthermore, it is preferable that the recording layer contain only one type of the specific electron accepting color developing agents described above. This is because if two or more types of electron accepting color developing agents are contained, " background color development " will occur in which the recording layer develops color after ink jet recording, which is one of the issues with the ink jet recording suitability, and the ink jet recorded image may become dark or unclear.

[0022] The reason for this is not clear, but it is thought that the use of two or more types of color developing agents forms a type of eutectic mixture, which has higher reactivity than a single type of color developing agent.

[0023] Furthermore, when two or more types of color developing agents are used to form a eutectic mixture, the melting point decreases, which may also reduce heat resistance.

[0024] The term "containing only one type of electron accepting color developing agent" in the recording layer means that the recording layer contains only one type of electron accepting color developing agent whose solubility in ethanol falls within the above range. In other words, the recording layer does not contain two or more types of electron accepting color developing agents, even if the electron accepting color developing agents have a solubility in ethanol that falls within the above range.

[0025] It is preferable when the solubility of the above-mentioned electron accepting developing agent in 99.7% IPA (isopropyl alcohol) is 0.5 g / ml or less, as this further prevents the developing agent from being melted by the ink jet ink.

[0026] The solubility in IPA is determined by dissolving the developing agent powder in 10 ml of IPA at room temperature until it becomes supersaturated, filtering by suction, measuring the weight of the undissolved powder remaining on the filter paper, and calculating the weight that will dissolve in 1 ml of IPA from the difference between the weight of the powder added and the weight of the remaining powder.

[0027] As a specific example of the electron accepting color developing agent is a urea compound represented by the general formula (Chemical Formula 1). (wherein X represents -O- or -NH-, R 1< represents a hydrogen atom or -SO 2 -R 3< , R 3< represents a substituted or unsubstituted alkyl group, an aralkyl group or an aryl group, R 2< represents a hydrogen atom or an alkyl group, m represents 0 or 1).

[0028] In the above general formula (Formula 1), R 3< is preferably represented by a substituted or unsubstituted aryl group, more preferably represented by the following formula: (In the formula, R 4< to R 8< may be identical or different from each other, represent a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group.)

[0029] In the above general formula (Chemical Formula 1), R 3< represents an alkyl group, an aralkyl group or an aryl group, all of which may be substituted or unsubstituted. The alkyl group is, for example, a linear, branched or alicyclic alkyl group, preferably having 1 to 12 carbon atoms. The carbon number of the aralkyl group is preferably 7 to 12, and the carbon number of the aryl group is preferably 6 to 12. When these are substituted, the substituent is preferably an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or a halogen atom. Further, the plurality of R 3< may be the same or different.

[0030] The position of R 1< - O- in the benzene ring in the general formula (Chemical Formula 1) may be the same or different, and is preferably the 3-position, 4-position or 5-position.

[0031] The position of R 3< -SO 2 -O- in the benzene ring in the general formula (Chemical Formula 1) may be the same or different, and is preferably the 3-position, 4-position or 5-position.

[0032] The alkyl group includes methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, iso-butyl group, t-butyl group, cyclopentyl group, hexyl group, cyclohexyl group, 2-ethylhexyl group, a lauryl group and the like.

[0033] The aralkyl group may be an unsubstituted aralkyl group or an aralkyl group substituted by alkyl group, alkoxy group, aralkyl group, aryl group or halogen atom. Examples thereof include benzyl group, 1-phenylethyl group, 2-phenylethyl group, 3-phenylpropyl group, p-methylbenzyl group, m-methylbenzyl group, methylbenzyl group, p-ethylbenzyl group, p-iso-propylbenzyl group, p-t-butylbenzyl group, p-methoxybenzyl group, m-methoxybenzyl group, o-methoxybenzyl group, m, p-di-methoxybenzyl group, p-ethoxy-m-methoxybenzyl group, p-phenylmethylbenzyl group, p-cumylbenzyl group, p-phenylbenzyl group, o-phenylbenzyl group, m-phenylbenzyl group, p-tolylbenzyl group, m-tolylbenzyl group, o-tolylbenzyl group and a p-chlorobenzyl group, and the like.

[0034] The aryl group may be an unsubstituted aryl group or an aryl group substituted by alkyl group, alkoxy group, aralkyl group, aryl group or halogen atom. Examples thereof include phenyl group, p-tolyl group, m-tolyl group, o-tolyl group, 2,5-dimethylphenyl group, 2,4-dimethylphenyl group, 3,5-dimethylphenyl group, 2, 3-dimethylphenyl group, 3,4-dimethylphenyl group, mesitylene group, p-ethylphenyl group, p-iso-propylphenyl group, p-t-butylphenyl group, p-methoxyphenyl group, 3,4-dimethoxyphenyl group, p-ethoxyphenyl group, p-chlorophenyl group, 1-naphthyl group, 2-naphthyl group, t-butylated naphthyl group, and the like.

[0035] R 2< represents a hydrogen atom or an alkyl group, preferably a hydrogen atom. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, which is, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, t-butyl group and the like.

[0036] The position of R 2< in the benzene ring in the general formula (Formula 1) may be the same or different, and is preferably 3-position, 4-position, or 5-position.

[0037] Further, the examples of the urea compound used in the present invention includes, N, N'-di- [3- (benzenesulfonyloxy) phenyl] urea, N, N'-di- [3-(benzenesulfonyloxy) -4-methyl-phenyl] urea, N, N'-di- [3- (benzenesulfonyloxy) -4-ethyl-phenyl] urea, N, N'-di- [3- (benzenesulfonyloxy) -5-methyl-phenyl] urea, N, N'-di- [3- (benzenesulfonyloxy) -4-propyl-phenyl] urea, N, N'-di- [3- (o-toluenesulfonyloxy) phenyl] urea, N, N'-di- [3- (m-toluenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-toluenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-toluenesulfonyloxy) -4-methyl-phenyl] urea, N, N'-di- [3- (p-xylenesulfonyloxy) phenyl] urea, N, N'-di- [3- (m-xylenesulfonyloxy) phenyl] urea, N, N'-di- [3-(mesitylene sulfonyloxy) phenyl] urea, N, N'-di- [3- (1-naphthalenesulfonyloxy) phenyl] urea, N, N'-di- [3- (2-naphthalenesulfonyloxy) phenyl] urea, N, N'-di- [3-(p-ethylbenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-propylbenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-isopropylbenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (pt-butylbenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-methoxybenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (m-methoxybenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (o-methoxybenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (m, p-dimethoxybenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-ethoxybenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-propoxybenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-butoxybenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-cumylbenzylsulfonyloxy) phenyl] urea, N, N'-di- [3- (p-cumylbenzenesulfonyloxy) phenyl] urea, N, N'-di- [3-(o-phenylbenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-phenylbenzenesulfonyloxy) phenyl] urea, N, N'-di- [3- (p-chlorobenzenesulfonyloxy) phenyl] urea, N, N'-di- [4- (benzenesulfonyloxy) phenyl] urea, N, N'-di- [4- (p-toluenesulfonyloxy) phenyl] urea, N, N'-di- [3-(ethanesulfonyloxy) phenyl] urea, N, N'-di- [3- (benzylsulfonyloxy) phenyl] urea, and the like. However, the first urea compound of the present invention is not limited to these.

[0038] Furthermore, as the urea compound of the present invention, a urea urethane compound (trade name UU, manufactured by Fine Ace) represented by the chemical formula (Chemical Formula 3) can be used.

[0039] The content (in solid) of the urea compound in the thermosensitive recording layer of the present invention is from 1.0 to 70.0 weight %, preferably from 5.0 to 65.0 weight %, more preferably 10.0 to 60.0 weight parts.

[0040] The content of the urea compound in the recording layer of the present invention is from 1.0 to 50.0 weight %, preferably 5.0 to 40.0 weight %.

[0041] The recording layer contains a silica as a pigment that receives ink, and the solid content of the silica with respect to the recording layer is 20 weight % or more.

[0042] Examples of the silica include precipitated silica and gel silica.

[0043] The use of the silica improves color development (density) of an ink jet recorded image and provides excellent ink drying property. Other pigments (such as kaolin) are unable to absorb all the ink, resulting in problems such as bleeding in ink jet recorded image.

[0044] The solid content of the silica with respect to the recording layer is typically 10%-12 weight %. If the solid content of the silica is less than 10 weight %, ink receiving ability of the recording layer may decrease, resulting in reduced ink jet recording suitability.

[0045] The upper limit of the solid content of the silica is not limited as long as it is within a range that achieves both the thermosensitive recording suitability and the ink jet recording suitability, but it is, for example, 45.0 weight %. The solid content of the silica is preferably 25.0-45.0 weight %, and more preferably 25.0-40.0 weight %.

[0046] If oil absorption of the silica is 130 ml / 100 g or more, the ink receiving ability of the recording layer increases, further improving the ink jet recording suitability.

[0047] All of the leuco dyes well known in the conventional field of pressure sensitive and thermosensitive recording media may be used as the electron donating leuco dye in the present invention. Although the leuco dye is not particularly restricted, triphenylmethane type compounds, fluorane type compounds, fluorene type compounds, divinyl type compounds and the like are preferred as the leuco dye. Specific examples of the typical colorless to pale colored basic colorless leuco dye (leuco dye precursors) are shown below. In addition, these leuco dye precursors may be used individually and also in mixtures of at least two of them.<Triphenylmethane type leuco dyes>

[0048] 3,3-bis(p-Dimethyl aminophenyl)-6-dimethylaminophthalide [alternate name: crystal violet lactone] and 3,3-bis(p-Dimethyl aminophenyl) phthalide [alternate name: malachite green lactone]<Fluorane type leuco dyes>

[0049] 3-Diethylamino-6-methylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluorane, 3-diethylamino-6-methyl- 7-chlorofluoran, 3-diethylamino-6-methyl-7-(m-trifluoromethylanilino) fluorane, 3- diethylamino-6-methyl-7-(o-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-(p- chloroanilino) fluorane, 3-diethylamino-6-methyl-7-(o-fluoroanilino) fluorane, 3- diethylamino-6-methyl-7-(m-methylanilino) fluorane, 3-diethylamino-6-methyl-7-n- octylanilino fluorane, 3-diethylamino-6-methyl-7-n-octylamino fluorane, 3-diethylamino-6- methyl-7-benzylamino fluorane, 3-diethylamino-6-methyl-7-dibenzylamino fluorane, 3-diethylamino-6-chloro-7-methyl fluorane, 3-diethylamino-6-chloro-7-anilino fluorane, 3-diethylamino-6-chloro-7-p-methylanilino fluorane, 3-diethylamino-6-ethoxyethyl-7- anilino fluorane, 3-diethylamino-7-methyl fluorane, 3-diethylamino-7-chloro fluorane, 3-diethylamino-7-(m-trifluoromethylanilino) fluorane, 3-diethylamino-7-(o-chloroanilino) fluorane, 3-diethylamino-7-(p-chloroanilino) fluorane, 3-diethylamino-7-(o-fluoroanilino) fluorane, 3-diethylamino-benz[a] fluorane, 3-diethylamino-benz[c] fluorane, 3-dibutylamino-6-methyl-fluorane, 3-dibutylamino-6-methyl-7-anilino fluorane, 3-dibutylamino-6-methyl-7-(o,p-dimethylanilino) fluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-butylamino-6-methyl-7-(p-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7-(o-fluoroanilino) fluorane, 3-dibutylamino-6-methyl-7-(m- fluoroanilino) fluorane, 3-dibutylamino-6-methyl-chloro fluorane, 3-dibutylamino- 6-ethoxyethyl-7-anilino fluorane, 3-dibutylamino-6-chloro-7-anilino fluorane, 3-dibutylamino-6-methyl-7-p-methylanilino fluorane, 3-dibutylamino-7-(o-chloroanilino) fluorane, 3-dibutylamino-7-(o-fluoroanilino) fluorane, 3-di-n-pentylamino-6-methyl-7- anilino fluorane, 3-di-n-pentylamino-6-methyl-7-(p-chloroanilino) fluorane, 3-di-n- pentylamino-7-(m-trifluoromethylanilino) fluorane, 3-di-n-pentylamino-6-chloro-7-anilino fluorane, 3-di-n-pentylamino-7-(p-chloroanilino) fluorane, 3-pyrolidino-6-methyl-7-anilino fluorane, 3-piperidino-6-methyl-7-anilino fluorane, 3-(N-methyl-N-propylamino)-6-methyl-7-anilino fluorane, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-xylylamino)-6- methyl-7-(p-chloroanilino) fluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-isoamylamino)-6- chloro-7-anilino fluorane, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N- ethoxypropylamino)-6-methyl-7-anilino fluorane, 3-cyclohexylamino-6-chloro fluorane, 2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilino fluorane, 2-(4-oxahexyl)-3- diethylamino-6-methyl-7-anilino fluorane, 2-(4-oxahexyl)-3-dipropylamino-6- methyl-7-anilino fluorane, 2-methyl-6-o-(p-dimethylaminophenyl) aminoanilino fluorane, 2-methoxy-6-p-(p-dimethylaminophenyl) aminoanilino fluorane, 2-chloro-3-methyl-6-p-(p-phenylaminophenyl) aminoanilino fluorane, 2-chloro-6-p-(p-dimethylaminophenyl) aminoanilino fluorane, 2-nitro-6-p-(p-diethylaminophenyl) aminoanilino fluorane, 2-amino-6-p-(p-diethylaminophenyl) aminoanilino fluorane, 2-diethylamino-6-p-(p- diethylaminophenyl) aminoanilino fluorane, 2-phenyl-6-methyl-6-p-(p- phenylaminophenyl) aminoanilino fluorane, 2-benzyl-6-p-(p-phenylaminophenyl) aminoanilino fluorane, 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilino fluorane, 3-methyl-6-p-(p-dimethylaminophenyl) aminoanilino fluorane, 3-diethylamino-6- p-(p-diethylaminophenyl) aminoanilino fluorane, 3-diethylamino-6-p-(p- dibutylaminophenyl) aminoanilino fluorane and 2,4-dimethyl-6-[(4-dimethylamino) anilino] fluorane.<Fluorene type leuco dye>

[0050] 3,6,6-Tris(dimethylamino) spiro[fluorane-9,3'-phthalide] and 3,6,6'-tris (diethylamino) spiro[fluorane-9,3'-phthalide].<Divinyl type leuco dyes>

[0051] 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide, 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide, 3,3-bis-[1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] 4,5,6,7-tetra-bromophthalide, 3,3-bis-[1- (4-methoxyphenyl)-1-(4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrachlorophthalide<Others>

[0052] 3-(4-Diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide, 3-(4-cyclohexyl ethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4- azaphthalide, 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide, 3,6-bis(diethylamino)fluorane- γ-(3'-nitroanilinolactam, 3,6-bis(diethylamino)fluorane-γ-(4'-nitro) anilinolactam, 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrilethane, 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2-β-naphthoylethane, 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-diacetylethane and bis-[2,2,2',2'-tetrakis-(p-dimethylaminophenyl)-ethenyl]-methylmalonic acid dimethyl ester.

[0053] The previously wellknown sensitizers may be used as the sensitizer in the recording layer.

[0054] As such sensitizers, aliphatic acid amides such as stearic acid amide, palmitic acid amide and the like, ethylene bis-amide, montan acid wax, polyethylene wax, 1,2-di-(3-methylphenoxy) ethane, p-benzyl biphenyl, β-benzyloxy naphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di(p-chlorobenzyl) oxalate, di(p-methylbenzyl) oxalate, dibenzyl terephthalate, benzyl p-benzyloxy benzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis-(phenyl ether), 4-(m-methyl phenoxymethyl) biphenyl, 4,4'-ethylene dioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxy methane, 1,2-di(3-methylphenoxy) ethylene, bis[2-(4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate, phenyl p-toluene sulfonate, o-toluenesulfonamide, p-toluenesulfonamide, and the like may be listed as examples. These sensitizers may be used individually and as mixtures of at least two of them.

[0055] When the total content of the above sensitizers with respect to the recording layer is 30 weight % or less, it is preferable since the heat resistance is improved and the background color development is suppressed.

[0056] As a binder used in the present invention, completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, modified polyvinyl alcohols such as acetoacetylated polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose,-styrene-maleic anhydride copolymer, styrene-butadiene copolymer, cellulose derivatives such as ethyl cellulose and acetyl cellulose, casein, gum Arabic, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butylal, polystyrol and their copolymers, silicone resins, petroleum resins, terpene resins, ketone resins, cumaron resins and the like may be listed as examples. The polymeric substances may be used upon dissolving them in a solvent such as water, alcohol, ketones, esters, hydrocarbons and the like or upon emulsifying or dispersing into a paste in water or other media. These polymeric materials may also be used in combinations according to the qualities demanded.

[0057] As a lubricant used in the present invention, fatty acid metal salts such as zinc stearate, calcium stearate, and the like, waxes, silicone resins, and the like may be cited.

[0058] Stabilizing agents that improve oil resistance of recorded images and the like, such as 4,4'-butylidene (6-t-butyl-3-methylphenol), 2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulfonyl diphenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane and the like may also be added in the range that does not adversely affect the desired effects for the problems described above.

[0059] In addition, a benzophenone type and triazole type UV absorbers, dispersion agent, de-foaming agent, antioxidant, fluorescent dye and the like may also be used.

[0060] The types and amounts of the leuco dye, color developing agent, sensitizer and other various ingredients used in the thermosensitive recording medium of the present invention may be determined according to the required performance and printability. Although the amounts of the color developing agent, the sensitizer, the pigment, the stabilizing agent and the other ingredients are not particularly restricted, from 0.5 parts to 10 parts of the color developing agent, from 0.1 parts to 10 parts of the sensitizer, from 0.5 parts to 20 parts of the pigment, from 0.01 parts to 10 parts of the stabilizing agent and from 0.01 parts to 10 parts of the other ingredients are ordinarily used per 1 part of the leuco dye. The content (in solid) of the binders in the thermosensitive recording layer is suitably around from 5 to 25 weight %.

[0061] The leuco dye, the color developing agent and the other materials added as needed are finely ground into particles with several microns or smaller in size, by using a grinder or a suitable emulsification device such as a ball mill, attritor, sand grinder and the like. The coating solutions are prepared by adding a binder and various additives to these depending on the objective. Water, alcohol and the like can be used as the solvent for the coating solution and the content (in solid) of the coating solution is about from 20 to 40 weight %.

[0062] In particular, when the alcohol is used as the solvent, the coating solution may penetrate into the paper, resulting in a decrease in the strength of the coating layer. So, it is preferable to use the water as the solvent.

[0063] The recording paper of the present invention may further have an undercoat layer between the substrate and the recording layer.

[0064] The undercoat layer comprises mainly a binder and a pigment.

[0065] As the binder used for the undercoat layer, the binders usable in the recording layer described above can be used appropriately. These binder(s) may be used individually and as mixtures of at least two of them.

[0066] Examples of the pigments that can be used in the undercoat layer include an inorganic pigment such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, kaolin, calcined kaolin, clay, and talc, and an organic pigment such as hollow plastic particle. These pigment(s) may be used alone or in combination of two or more. As the pigment other than the plastic hollow particle, it is preferable to use calcined kaolin.

[0067] The content of the pigment in the undercoat layer is usually 50 to 95 weight %, preferably 70 to 90 weight %, based on the solid content of the undercoat layer. The content of the hollow plastic particles in the undercoat layer is 50 weight % or more, preferably 70 to 100 weight %, more preferably 80 to 100 weight %, based on the solid content of the pigment in the undercoat layer.

[0068] Various aids such as a dispersion agent, plasticizer, pH controlling agent, de-foaming agent, water retention agent, preservative, coloring dye, UV absorber and the like may be added to the cating solution for the undercoat layer, as required.

[0069] In the present invention, it is preferable that no other layers such as a protective layer are provided on the surface of the recording layer, and that the recording layer is the outermost layer of the recording paper (the surface of the recording layer is exposed).

[0070] In this way, when a protective layer or the like is not provided on the recording layer, water resistant blocking property is improved.

[0071] The water resistant blocking property is evaluated whether the recording layer (or the protective layer) is peeling off by dropping tap water onto the surface of the recording layer (or the protective layer) of the recording paper, folding it in half so that the surface is on the inside, leaving it to stand, and then peeling it off.

[0072] The reason why the water resistant blocking property is improved when a protective layer or the like is not provided is that the protective layer or the like usually contain a relatively large amount of binder such as PVA (polyvinyl alcohol). So, if a protective layer or the like is provided, the binder will bond the coated surfaces together via water.

[0073] In the present invention, the method for coating the recording layer and other coating layers, such as protective layer and undercoat layer, is not limited in particular, but any known conventional techniques may be used. The method for coating may be appropriately selected from off-machine coating machines and on-machine coating machines, which are equipped with coaters such as air knife coater, rod blade coater, bent blade coater, bevel blade coater, roll coater, curtain coater and the like.

[0074] The coating amounts of the recording layer and other coating layers are not limited in particular, but may be determined according to the required performance and the recording suitability. The typical coating amount (in solid) of the thermosensitive recording layer is ordinarily in the range of from 2 to 12g / m 2< and the coating amount of the protective layer is preferably in the range of from 0.5 to 5.0 g / m 2< .

[0075] Furthermore, various technologies known in the recording paper field, such as a flattening treatment such as super calendaring and the like can be applied as needed after coating individual coating layers.

[0076] If the strength of the coating layer that serves as the recording layer is weak, there is a risk that the printed area will peel off along with the coating layer after printing with an inkjet continuous feed printer. To maintain a normal condition after inkjet printing, the coating layer must be strong enough to prevent peeling when, for example, adhesive tape is applied to a substrate and then peeled off.

[0077] Specifically, a force required to peel a tape (peel strength) is measured using a digital force gauge in the cellopic test described below. A peel strength of 150 N / m or more is sufficient, and to ensure sufficient strength, a peel strength of 250 N / m or more is desirable.

[0078] It is preferable when a tensile strength (JIS P8113) of the recording paper in a longitudinal direction is 3 kN / m or more, as this improves the operability of an inkjet continuous feed printers. Even in the field of inkjet paper, a continuous feed printer that print continuously, like offset printing machines, is used for industrial purpose. In such a case, if the tensile strength is low, it is not possible to apply tension during printing, resulting in poor running performance, and applying excessive tension can lead to paper breakage.

[0079] In order to achieve the tensile strength of 3 kN / m or more, measures include increasing basis weight and thickness of a base paper, and increasing the amount of paper strength agent in the base paper.

[0080] It is preferable when a color density obtained by contacting the recording layer side of the recording paper with a 90°C hot plate at 0.1 MPa for 5 seconds to be 0.40 or less, as this suppresses background color development due to drying when printing with an inkjet continuous feed printer.

[0081] Methods for achieving the color density of 0.40 or less include reducing the coating weight of the recording layer, changing the color development agent, reducing the proportion of sensitizer used, or not using it at all.[Examples]

[0082] The following Examples illustrate the present invention, but the Examples are not intended to limit the scope of the present invention. In the following description, the terms parts and % indicate parts by weight and weight %, respectively.

[0083] Each dispersion and coating solution was prepared as follows for the production of a recording paper.[Preparationof each coating solution]

[0084] Undercoat layer coating solution was prepared by dispersing and stirring the following formulation.[Undercoat layer coating solution]

[0085] Calcined kaolin (Ansilex 90)100.0 partsStyrene-butadiene copolymer latex (ST5526)10.0 partsWater50.0 parts

[0086] Color developing agent dispersions (Solutions A1 to A5), a leuco dye dispersion (Solution B) and a sensitizer dispersion (Solution C) with the following formulations were separately wet ground using sand grinders until the average particle sizes were about 0.5 µm.Color developing agent dispersion (Solution A1)

[0087] N, N'-di- [3- (p-toluenesulfonyloxy) phenyl] urea as "urea compound 1 (indicated as U1 in Table 1) ")(hereinafter referred to6.0 partsAqueous solution of completely saponified polyvinyl alcohol (Kuraray Co., Ltd., PVA117, solid content: 10%)5.0 partsWater1.5 parts Color developing agent dispersion (Solution A2)

[0088] N-[2-(3-phenylureido) phenyl] benzenesulfonamide (hereinafter referred to as "urea compound 2 (indicated as U2 in Table 1)")6.0 partsAqueous solution of completely saponified polyvinyl alcohol (PVA117)5.0 partsWater1.5 parts Color developing agent dispersion (Solution A3)

[0089] Urea urethane compound represented by the chemical formula Formula 3) (UU manufactured by Fine Ace)(Chemical6.0 parts Aqueous solution of completely saponified polyvinyl alcohol (PVA117)5.0 partsWater1.5 parts Color developing agent dispersion (Solution A4)

[0090] 4,4'-dihydroxydiphenyl sulfide (Trade name 44BPS, manufactured by KONISHI CHEMICAL IND CO.,LTD)6.0 partsAqueous solution of completely saponified polyvinyl alcohol (PVA117)5.0 partsWater1.5 parts Leuco dye dispersion (Solution B)

[0091] 3-Dibutylamino-6-methyl-7-anilinofluorane (Yamamoto Chemicals Inc., ODB-2)6.0 partsAqueous solution of completely saponified polyvinyl alcohol (PVA117)5.0 partsWater1.5 parts Sensitizer dispersion (Solution C)

[0092] 1,2-bis(2-Methylphenoxy) ethane (Sanko Co. Ltd, KS232)6.0 partsAqueous solution of completely saponified polyvinyl alcohol (PVA117)5.0 partsWater1.5 parts

[0093] Next, each dispersion was mixed in the following percentage to prepare a recording layer coating solution.<Recording layer coating solution>

[0094] Color developing agent dispersion (solution A1)36.0 partsLeuco dye dispersion (solution B)18.0 partsSensitizer dispersion (solution C)18.0 partsSilica dispersion(Mizusawa Industrial Chemicals, Ltd. MIZUKASIL P-537, solid content 25%)140 partsFully saponified polyvinyl alcohol aqueous solution (PVA117)25.0 parts

[0095] Next, a protective layer coating solution was prepared by mixing the following formulations:<Protective layer coating solution>

[0096] Aluminum hydroxide dispersion (Martinsberg: Martifin OL, solid content: 50%)9.0 partsCarboxy-modified polyvinyl alcohol solution (Kuraray Co., Ltd., trade name: KL318, degree of polymerization: about 1800, degree of saponification: 85 to 90 mol%)30.0 partsPoly(amide epichlorohydrin) resin (Seiko PMC Corporation, trade name: WS4030, solid content 25%)4.0 partsModified polyamine resin (Taoka Chemical Co., Ltd. trade name: Sumirez Resin SPI-102A, solid content 45%)2.2 partsZinc stearate (Chukyo Yushi Co., Ltd., trade name: HydrinZ-7-30, solid content 30%)2.0 parts [Example 1]

[0097] The undercoat layer coating solution was applied on one side of a substrate (groundwood free paper with a basis weight of 47 g / m 2< ) by using a bent blade coater with a coating amount (in solid) of 10.0 g / m 2< , and was dried to prepare an undercoated paper.

[0098] The recording layer coating solution was applied on the undercoat layer of the undercoated paper by using a rod blade coater with a coating amount (in solid) of 6.0 g / m 2< and was dried and super calendared so that the smoothness was 100-500 seconds to prepare a thermosensitive recording layer coated paper.[Example 2]

[0099] A recording paper was prepared in the same manner as described in Example 1 with the exception of changing the solution A1 to the solution A2 in the recording layer coating solution.[Example 3]

[0100] A recording paper was prepared in the same manner as described in Example 1 with the exception of changing the amount of the silica dispersion in the recording layer coating solution was changed to 100 parts.[Example 4]

[0101] A recording paper was prepared in the same manner as described in Example 1 with the exception of changing the amount of the silica dispersion in the recording layer coating solution was changed to 200 parts.[Example 5]

[0102] A recording paper was prepared in the same manner as described in Example 1 with the exception of changing the amount of the solution C in the recording layer coating solution was changed to 48 parts.[Comparative Example 1]

[0103] A recording paper was prepared in the same manner as described in Example 1 with the exception of the amount of the solution A1 in the recording layer coating solution was changed to 18 parts, and 18 parts of solution A3 was added to the recording layer coating solution.[Comparative Example 2]

[0104] A recording paper was prepared in the same manner as described in Example 1 with the exception of changing the solution A1 to the solution A4 in the recording layer coating solution.[Comparative Example 3]

[0105] A recording paper was prepared in the same manner as described in Example 3 with the exception of changing the solution A1 to the solution A4 in the recording layer coating solution.[Comparative Example 4]

[0106] A recording paper was prepared in the same manner as described in Example 1 with the exception of changing the amount of the silica dispersion in the recording layer coating solution was changed to 40 parts.[Comparative Example 5]

[0107] A recording paper was prepared in the same manner as described in Example 1 with the exception of changing the amount of the silica dispersion in the recording layer coating solution was changed to 70 parts, and 35 parts of aluminum hydroxide dispersion was added to the recording layer coating solution.[Comparative Example 6]

[0108] A recording paper was prepared in the same manner as described in Example 1 with the exception that the same amount of 20% ethanol was used instead of water as the solvent in the Color developing agent dispersion (solution A1), the leuco dye dispersion (solution B), and the sensitizer dispersion((solution C) in the recording layer coating solution.

[0109] The prepared recording paper were evaluated as below.<Thermosensitive recording suitability (Barcode reading suitability) >

[0110] A barcode (CODE39) was printed on the prepared recording paper by using a label printer 140XiIII manufactured by Zebra at the printing level of +10 and the printing speed of 30.4 cm / sec (12 inches / sec) in a vertical direction (i.e., so that the moving direction of the printer head and the barcode are orthogonal to each other.) and a horizontal direction (i.e., so that the moving direction of the printer head and the barcode are parallel.) respectively.

[0111] Then, the printed barcode was read by a barcode verification machine (Honeywell, QCPC600, light source 640 nm) to evaluate the barcode reading suitability. The evaluation results were shown in the ANSI standard symbol grade.

[0112] Symbol grade: The barcode is divided into 10 parts in the direction perpendicular to the bar, and a reading test is performed once at each location, and the average value is represented by a 5-point scale of (excellent) A, B, C, D and F (poor).<Inkjet Recording Suitability (Bleeding)>

[0113] The prepared recording paper was solid printed in four solid colors of black, cyan, magenta, and yellow (with the character "NO (Japanese)" printed as a whiteout) using a Canon PIXUS MG7130 inkjet printer (mode: plain paper / standard). Bleeding was evaluated using the following criteria: Excellent: The ink was dry immediately after printing, and there was no blurring or feathering. Fair: The ink was dry immediately after printing, but there was a little blurring or feathering. Poor: The ink was not dry immediately after printing, or there was blurring or feathering. <Inkjet Recording Suitability (Background color development)>

[0114] The prepared recording paper was solid printed in one color of yellow using a Canon PIXUS MG7130 inkjet printer (mode: plain paper / standard), and was allowed to stand for 1 day. Thereafter, the background color development of the solid printing area was evaluated using the following criteria: Excellent: No background color development occurs Good: Difficult to distinguish with the naked eye, but the Bk value is slightly elevated when measured with a densitometer Fair: Slight background color development is noticeable with the naked eye. Poor: Background color development occurs <Heat Resistance>

[0115] The prepared recording paper was colored using a thermal gradient tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.) under conditions of a pressure of 0.1 MPa, a contact time of 5 seconds, and a temperature of 90°C. The black(Bk) density of the printed area was measured using a Macbeth densitometer (RD-914, amber filter used). Excellent: Bk density of 0.20 or less Good: Bk density of 0.21 or more, but not more than 0.40 Fair: Bk density of 0.41 or more, but not more than 0.60 Poor: Bk density of 0.61 or more <Water resistant blocking property >

[0116] 10 ml of tap water was dropped on the surface of the protective layer of the prepared recording paper, which was then folded in half so that the surface of the protective layer is inside. After a load of 20 gf / cm2 was applied on this for 24 hours, the folded recording paper is opened.

[0117] Then the portion of the recording paper on which tap water was dropped is visually evaluated if there's peeling observed on the protective layer and the recording layer according to the following criteria. Excellent: No blocking occurs and no peeling observed on the protective layer and the recording layer Fair: Blocking occurs and the protective layer peels off slightly, while the recording layer causes no peel off. Poor: Strong blocking occurs and the protective layer and the recording layer are peeled off, or the recording paper is destroyed when opened. < Layer strength (Peel Strength) of the Recording Layer>

[0118] Layer strength of the recording layer (coating layer) was measured using a cellopic test (peel test) in a measurement environment of 23°C and 50% humidity. To measure, transparent adhesive tape (Nichiban Cellophane Tape(trademark), CT24, 24mm width ) was applied to the surface of the recording layer, and a rubber roller with a dead weight of 2.0 kg was pressed back and forth across on the tape 20 times. Then, the force required to peel the tape was then measured using a digital force gauge (SHIMPO FGX-2) (peel speed: 20m / min, peel angle: 180°).

[0119] The evaluation results are shown in following Table 1.

[0120] Table 1 lists the type of electron accepting color developing agent and its solubility in 99.5% ethanol (Et) and 99.7% IPA.

[0121] The solid content and total content in Table 1 are values with respect to the recording layer.

[0122] As shown in Table 1, each Example exhibited excellent thermosensitive recording suitability and ink jet recording suitability together.

[0123] In the case of Example 5, in which the total content of the sensitizer with respect to the recording layer exceeded 30 weight %, the heat resistance and the background color development were slightly low as compared to other Examples, but there is no practical problem.

[0124] On the other hand, in the case of Comparative Example 1, in which the recording layer contained two types of electron accepting color developing agents, the inkjet recording suitability (the background color development) was inferior, and the heat resistance was also poor.

[0125] In the case of Comparative Example 2, where the solubility of the electron accepting color developing agent in the recording layer in ethanol exceeded 0.3 g / ml, the inkjet recording suitability (bleeding) and the heat resistance were poor.

[0126] The reason for the reduced inkjet recording suitability (bleeding) is that inkjet inks are both water-based and solvent-based types, and the solvent-based ink uses organic solvent such as ethanol and IPA. Therefore, when using a developing agent with high solubility in ethanol, the developing agent melts in the inkjet ink and reacts with the dye, resulting in color development, resulting in and the background color development occurs. The reason for the reduced heat resistance is because the color development starting point of the developing agent becomes lower.

[0127] In the case of Comparative Example 3, in which the surface of the recording layer was not exposed and was covered with another layer (protective layer), the water resistant blocking property was poor.

[0128] In the cases of Comparative Examples 4 and 5, in which the solid content of silica with respect to the recording layer was less than 20 weight %s,the inkjet recording suitability (bleeding) was poor.

[0129] In the case of Comparative Example 6, in which ethanol was used as a solvent in the recording layer coating solution, the strength of the recording layer was reduced.

Claims

1. A recording paper having a substrate, and a recording layer comprising a leuco dye and an electron accepting color developing agent on the substrate, wherein the recording layer contains the electron accepting color developing agent and the solubility of the electron-accepting color developing agent in 99.5% ethanol is 0.3 g / ml or less, and the recording layer contains a silica as an ink-receiving pigment, and the solid content of the silica with respect to the recording layer is 20 weight % or more.

2. The recording paper of claim 1, wherein the recording paper is an ink jet recording medium having thermosensitive recording suitability.

3. The recording paper of claim 1, wherein the recording paper is a thermosensitive recording medium having ink jet recording suitability.

4. The recording paper of claim 1 or 2, wherein the recording layer contains only one type of the electron-accepting color developing agent.

5. The recording paper of claim 1 or 2, wherein the thermosensitive recording layer has a peel strength of 150 N / m or more in a cellopic test.

6. The recording paper of claim 1, wherein the solubility of the electron-accepting color developing agent in 99.7% IPA is 0.5 g / ml or less.

7. The recording paper of claim 1, wherein the electron-accepting color developing agent is a urea compound represented by the following general formula (1): (wherein X represents -O- or -NH-, R1 represents a hydrogen atom or -SO2-R3, R3 represents a substituted or unsubstituted alkyl group, an aralkyl group or an aryl group, R2 represents a hydrogen atom or an alkyl group, m represents 0 or 1).

8. The recording paper of claim 1 or 2, wherein an oil absorbance of the silica is 130 ml / 100 g or more.

9. The recording paper of claim 1 or 2, wherein the recording layer contains a sensitizer, and the total content of the sensitizer with respect to the recording layer is 30 weight % or less.

10. The recording paper of claim 1 or 2, wherein the tensile strength (JIS P8113) of the recording paper in a longitudinal direction is 3 kN / m or more.

11. The recording paper of claim 1 or 2, wherein a color density obtained by contacting the recording paper with a 90°C hot plate at 0.1 MPa for 5 seconds is 0.40 or less.

12. The recording paper of claim 1 or 2, wherein the recording layer is the outermost layer.

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