Recording paper

Abstract

To provide a recording paper excellent in both thermal recording suitability and ink jet recording suitability, and also excellent in heat resistance and recording layer strength. [Solution] A recording paper having a support and a recording layer provided on the support and containing a leuco dye and an electron-accepting color developer, wherein the recording layer contains the electron-accepting color developer and the solubility of the electron-accepting color developer in ethanol is 0.3 g / ml or less, the recording layer contains silica as a pigment that accepts ink, and the solid content of silica in the recording layer is 20 mass% or more.

Description

[Technical Field]

[0001] The present invention relates to a recording paper suitable for inkjet recording. [Background technology]

[0002] Generally, recording paper such as a thermal recording medium is made by grinding and dispersing a colorless or pale-colored electron-donating leuco dye (hereinafter also referred to as "leuco dye") and an electron-accepting developer (hereinafter also referred to as "developer") such as a phenolic compound into fine particles, mixing the two, adding binders, pigments, sensitivity enhancers (sensitizers), lubricants and other auxiliary agents to obtain a coating liquid, which is then coated on a support such as paper, synthetic paper, film or plastic.The color develops due to an instantaneous chemical reaction when heated with a thermal head, hot stamp, heat pen, laser light, etc., and a recorded image is obtained.

[0003] Thermal recording media have the following characteristics: they are quiet during recording, do not require development and fixing, are maintenance-free, the equipment is relatively inexpensive, they are compact, and the resulting color is very vivid. They are therefore widely used in facsimiles, computer terminal printers, automatic ticket vending machines, measurement recorders, handheld terminals, etc.

[0004] In addition, thermal recording media are sometimes required to be suitable for inkjet recording in addition to thermal recording. For example, in applications such as ATMs and labels, UV inks or the like are printed in advance in a common layout, and different information such as currency or barcodes is thermally recorded. However, when printing is performed on recording paper such as a thermal recording media using an inkjet recording method, the background color generated by the color generated by the thermal recording layer in the recording area overlaps, causing problems such as darkening or blurring of the inkjet recorded image. Therefore, a technique is known in which a color developer having a solubility in acetonitrile within a specific range is used to impart inkjet recording suitability to a thermal recording medium (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-226076 [Patent Document 2] Japanese Patent Publication No. 2022-151636 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the color developer described in Patent Document 1 was used, the heat resistance was insufficient. Furthermore, in the case of the technology described in Patent Document 2, ethanol is used as a solvent in the coating liquid for the recording layer, and therefore the strength of the recording layer is insufficient. If the coating layer strength is weak, problems may occur when printing with an inkjet continuous feed printer, and the suitability for inkjet recording may be reduced. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a recording paper that is excellent in both thermal recording suitability and ink jet recording suitability, and that is also excellent in heat resistance and recording layer strength. [Means for solving the problem]

[0007] As a result of extensive investigations, the present inventors have found that the above problems can be solved by specifying the solubility of the electron-accepting developer in ethanol, and have thus completed the present invention. That is, the present invention provides a recording paper having a support and a recording layer provided on the support and containing a leuco dye and an electron-accepting color developer, The electron-accepting color developer is represented by a urea compound represented by the following general formula (1): [ka] (wherein X represents —O— or —NH—; R 1 is a hydrogen atom or -SO 2 -R 3 represents R 3 represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group, and R 2 represents a hydrogen atom or an alkyl group, and m represents 0 or 1.The recording layer contains the electron-accepting color developer, and the solubility of the electron-accepting color developer in ethanol is 0.3 g / ml or less, and the recording layer contains silica as a pigment that accepts ink, and the solid content of the silica in the recording layer is 20 mass% or more. [Effects of the Invention]

[0008] According to the present invention, it is possible to obtain a recording paper that is excellent in both thermal recording suitability and ink jet recording suitability, and that is also excellent in heat resistance and recording layer strength. DETAILED DESCRIPTION OF THE INVENTION

[0009] Specific details of the present invention will be described below. The recording paper of the present invention has a support and a recording layer provided on the support, the recording layer containing a leuco dye and an electron-accepting color developer. The recording layer contains an electron-accepting color developer, and the solubility of the electron-accepting color developer in ethanol is 0.3 g / ml or less. The recording layer also contains silica as an ink-receiving pigment, and the solid content of silica in the recording layer is 20 mass% or more.

[0010] Below, various materials that can be used in the recording layer of the recording paper of the present invention are exemplified, but binders, crosslinking agents, pigments, etc. can also be used in each coating layer provided as needed, as long as they do not impede the desired effects on the above-mentioned problems. This recording layer serves as, for example, a heat-sensitive recording layer or an ink-receiving layer.

[0011] The recording layer contains an electron-accepting color developer, and the solubility of the electron-accepting color developer in ethanol is 0.3 g / ml or less. When the solubility of the developer in ethanol is 0.3 g / ml or less, both the thermal recording suitability and the ink-jet recording suitability are excellent. The reason for this is not clear, but it is thought that the lower the solubility of the developer in ethanol, the less the developer is melted by the ink-jet ink, since an organic solvent is usually used as the solvent for ink-jet ink. Furthermore, when the solubility of the developer in ethanol is 0.3 g / ml or less, the developer has excellent heat resistance, because when the solubility of the developer in ethanol exceeds 0.3 g / ml, the color development starting point of the developer becomes low.

[0012] Here, solubility refers to the value obtained by dissolving the developer 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 dissolves in 1 ml of ethanol from the difference between the weight of the powder added and the weight of the remaining powder.

[0013] Furthermore, it is preferable that the recording layer contains only one of the above-mentioned specific electron-accepting color developers. This is because if two or more electron-accepting color developers are contained, the recording layer may develop a "background color" after inkjet recording, which is one of the inkjet recording suitabilities, and the inkjet recorded image may become dark or unclear. The reason for this is not clear, but it is thought that the use of two or more types of color developers results in a kind of eutectic mixture, which increases the reactivity compared to using a single type of color developer. Furthermore, when two or more types of color developers are used to form a eutectic mixture, the melting point decreases, which may result in a decrease in heat resistance.

[0014] The recording layer "containing only one type" of electron-accepting color developer means that the recording layer contains only one type of electron-accepting color developer 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 developers, even if the electron-accepting color developers have a solubility in ethanol that falls within the above range.

[0015] It is preferable that the solubility of the electron-accepting developer in 99.7% IPA (isopropyl alcohol) is 0.5 g / ml or less, since this further suppresses the dissolution of the developer by the ink-jet ink. The solubility in IPA is determined by dissolving the developer powder in 10 ml of IPA 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 dissolves in 1 ml of IPA from the difference between the weight of the powder added and the weight of the remaining powder.

[0016] A specific example of the electron-accepting color developer is a urea compound represented by the general formula (Chemical Formula 1). [ka] (wherein X represents —O— or —NH—; R 1 is a hydrogen atom or -SO2-R 3 represents R 3 represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group, and R 2 represents a hydrogen atom or an alkyl group, and m represents an integer of 0 to 1. In the above general formula (Chemical Formula 1), R 3 is preferably a substituted or unsubstituted aryl group, and more preferably a group represented by the following formula: [ka] (In the formula, R 4 ~R 8 may be the same or different and each 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.

[0017] In the general formula (chemical formula 1), R 3represents an alkyl group, an aralkyl group, or an aryl group, which may be substituted or unsubstituted. The alkyl group is, for example, a linear, branched, or alicyclic alkyl group, and preferably has 1 to 12 carbon atoms. The aralkyl group preferably has 7 to 12 carbon atoms, and the aryl group preferably has 6 to 12 carbon atoms. 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. In addition, when multiple R 3 may be the same or different. R in the benzene ring of general formula (Chemical formula 1) 1 The positions of -O- may be the same or different, and are preferably the 3-, 4- or 5-positions. R in the benzene ring of general formula (Chemical formula 1) 3 The positions of -SO2-O- may be the same or different, and are preferably the 3-, 4- or 5-positions.

[0018] Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a 2-ethylhexyl group, and a lauryl group.

[0019] Examples of the aralkyl group include unsubstituted or aralkyl groups substituted with an alkyl group, an alkoxy group, an aralkyl group, an aryl group, or a halogen atom, such as a benzyl group, 1-phenylethyl group, 2-phenylethyl group, 3-phenylpropyl group, p-methylbenzyl group, m-methylbenzyl group, m-ethylbenzyl group, p-ethylbenzyl group, pi-propylbenzyl group, pt-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 p-chlorobenzyl group.

[0020] Examples of the aryl group include unsubstituted or aryl groups substituted with an alkyl group, an alkoxy group, an aralkyl group, an aryl group, or a halogen atom, such as a phenyl group, a p-tolyl group, a m-tolyl group, an o-tolyl group, a 2,5-dimethylphenyl group, a 2,4-dimethylphenyl group, a 3,5-dimethylphenyl group, a 2,3-dimethylphenyl group, a 3,4-dimethylphenyl group, a mesitylene group, a p-ethylphenyl group, a p-propylphenyl group, a p-butylphenyl group, a p-methoxyphenyl group, a 3,4-dimethoxyphenyl group, a p-ethoxyphenyl group, a p-chlorophenyl group, a 1-naphthyl group, a 2-naphthyl group, and a t-butylated naphthyl group.

[0021] R 2 represents a hydrogen atom or an alkyl group, preferably a hydrogen atom, and the alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, or a t-butyl group. R in the benzene ring of general formula (Chemical formula 1) 2 may be the same or different, and is preferably the 3rd, 4th or 5th position.

[0022] Furthermore, examples of the urea compound of the present invention include 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-(mesitylenesulfonyloxy)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,Examples of such urea include, but are not limited to, 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, and N,N'-di-[3-(benzylsulfonyloxy)phenyl]urea.

[0023] Furthermore, as the urea compound of the present invention, a urea urethane compound (trade name UU, manufactured by Fine Ace Co., Ltd.) represented by the chemical formula (Chemical Formula 3) can be used. [ka]

[0024] The content (solid content) of the electron-accepting developer in the recording layer of the present invention is 1.0 to 70.0% by weight, preferably 5.0 to 65.0% by weight, and more preferably 10.0 to 60.0 parts by weight. The content of the urea compound in the recording layer of the present invention is 1.0 to 50.0% by weight, preferably 5.0 to 40.0% by weight.

[0025] The recording layer contains silica as a pigment that receives ink, and the solid content of the silica in the recording layer is 20% by mass or more. Examples of silica include precipitated silica and gel silica. The use of silica improves the color density of inkjet recorded images and also improves the drying time of the ink. Other pigments (such as kaolin) cannot absorb the ink completely, resulting in problems such as bleeding in inkjet recorded images.

[0026] The solid content of silica in the recording layer is usually 10% to 12% by weight. If the solid content of silica is less than 10% by weight, the ink receiving ability of the recording layer may decrease, and the suitability for inkjet recording may decrease. The upper limit of the solid content of silica is not limited as long as it is within a range that satisfies both suitability for thermal recording and suitability for inkjet recording, and is, for example, 45.0% by mass. The solid content of silica is preferably 25.0 to 45.0% by mass, and more preferably 25.0 to 40.0% by mass.

[0027] When the oil absorption of silica is 130 ml / 100 g or more, the ink receiving ability of the recording layer increases, and the suitability for ink jet recording is further improved.

[0028] The leuco dye used in the present invention can be any known leuco dye in the field of conventional pressure-sensitive or heat-sensitive recording paper, and is not particularly limited. However, preferred examples include triphenylmethane compounds, fluoran compounds, fluorene compounds, and divinyl compounds. Specific examples of typical colorless or pale-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination.

[0029] <Triphenylmethane leuco dye> 3,3-Bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis(p-dimethylaminophenyl)phthalide (also known as malachite green lactone)

[0030] <Fluoran-based leuco dyes> 3-Diethylamino-6-methylfluoran, 3-Diethylamino-6-methyl-7-anilinofluoran, 3-Diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran, 3-Diethylamino-6-methyl-7-chlorofluoran, 3-Diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran, 3-Diethylamino-6-methyl-7-(o-chloroanilino)fluoran, 3-Diethylamino-6-methyl-7-(p-chloroanilino)fluoran, 3-Diethylamino-6-methyl-7-(o-fu (fluoroanilino)fluoran, 3-diethylamino-6-methyl-7-(m-methylanilino)fluoran, 3-diethylamino-6-methyl-7-n-octylanilinofluoran, 3-diethylamino-6-methyl-7-n-octylaminofluoran, 3-diethylamino-6-methyl-7-benzylaminofluoran, 3-diethylamino-6-methyl-7-dibenzylaminofluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-chloro o-7-p-methylanilinofluoran, 3-diethylamino-6-ethoxyethyl-7-anilinofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-(p-chloroanilino)fluoran, 3-diethylamino-7-(o-fluoroanilino)fluoran, 3-diethylamino-benzo[a]fluoran, 3-diethylamino -benzo[c]fluoran, 3-dibutylamino-6-methyl-fluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-(o,p-dimethylanilino)fluoran, 3-dibutylamino-6-methyl-7-(o-chloroanilino)fluoran, 3-dibutylamino-6-methyl-7-(p-chloroanilino)fluoran, 3-dibutylamino-6-methyl-7-(o-fluoroanilino)fluoran, 3-dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran,3-dibutylamino-6-methyl-7-chlorofluoran, 3-dibutylamino-6-ethoxyethyl-7-anilinofluoran, 3-dibutylamino-6-chloro-7-anilinofluoran, 3-dibutylamino-6-methyl-7-p-methylanilinofluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-dibutylamino-7-(o-fluoroanilino)fluoran, 3-di-n-pentylamino-6-methyl-7-anilinofluoran, 3-di-n-pentylamino-6-methyl-7-(p-chloroanilino)fluoran, 3-Di-n-pentylamino-7-(m-trifluoromethylanilino)fluoran, 3-Di-n-pentylamino-6-chloro-7-anilinofluoran, 3-Di-n-pentylamino-7-(p-chloroanilino)fluoran, 3-Pyrrolidino-6-methyl-7-anilinofluoran, 3-Piperidino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran (N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-xylamino)-6-methyl-7-(p-chloroanilino)fluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isobutylamino) -6-methyl-7-anilinofluoran, 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran, 3-cyclohexylamino-6-chlorofluoran, 2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilinofluoran, 2-(4-oxahexyl)-3-diethylamino-6-methyl-7-anilinofluoran, 2-(4-oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran, 2-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran,2-Methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 2-chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 2-nitro-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 2-amino-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 2-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 2-phenyl-6-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran, 2,4-dimethyl-6-[(4-dimethylamino)anilino]-fluoran,

[0031] <Fluorene-based leuco dye> 3,6,6'-Tris(dimethylamino)spiro[fluorene-9,3'-phthalide], 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide]

[0032] <Divinyl leuco dye> 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-tetrabromophthalide, 3,3-bis-[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide

[0033] <Other> 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-cyclohexylethylamino-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)fluoran-γ-(3'-nitro)anilinolactam, 3,6-bis(diethylamino)fluoran-γ-(3'-nitro)anilinolactam (amino)fluoran-γ-(4'-nitro)anilinolactam, 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrileethane, 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, bis-[2,2,2',2'-tetrakis-(p-dimethylaminophenyl)-ethenyl]-methylmalonic acid dimethyl ester

[0034] The recording layer may contain a conventionally known sensitizer. Examples of such sensitizers include fatty acid amides such as stearic acid amide and palmitic acid amide, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-bis-(3-methylphenoxy)ethane, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di(p-chlorobenzyl) oxalate, di(p-methylbenzyl) oxalate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α- Examples of sensitizers include naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis-(phenyl ether), 4-(m-methylphenoxymethyl)biphenyl, 4,4'-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di(3-methylphenoxy)ethylene, bis[2-(4-methoxy-phenoxy)ethyl]ether, methyl p-nitrobenzoate, phenyl p-toluenesulfonate, o-toluenesulfonamide, p-toluenesulfonamide, etc. These sensitizers may be used alone or in combination of two or more.

[0035] If the total content of the sensitizers in the recording layer is 30% by weight or less, the heat resistance is improved and background color development is suppressed, which is preferable.

[0036] Examples of binders used in the present invention include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohols, 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 butyral, polystyrose and copolymers thereof, polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, coumarone resin, and the like. These polymeric substances can be used by dissolving them in a solvent such as water, alcohol, ketones, esters, or hydrocarbons, or by dispersing them in water or other media in an emulsified or paste-like form, and these can also be used in combination depending on the required quality.

[0037] The lubricants used in the present invention include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, silicone resins, and the like.

[0038] In the present invention, stabilizers such as 4,4'-butylidene(6-t-butyl-3-methylphenol), 2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulfonyldiphenol, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane can be added to improve the oil resistance of image areas, provided that the desired effects for the above-mentioned problems are not impaired. In addition, benzophenone-based or triazole-based ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, etc. can also be used.

[0039] The types and amounts of leuco dye, developer, sensitizer, and other components used in the recording layer of the present invention are determined according to the required performance and recording suitability and are not particularly limited, but typically, 0.5 to 10 parts by weight of developer, 0.1 to 10 parts by weight of sensitizer, 0.01 to 10 parts by weight of stabilizer, and 0.01 to 10 parts by weight of other components are used per part by weight of leuco dye. The binder content is preferably about 5 to 25% by weight of the solid content of the recording layer.

[0040] In the present invention, the leuco dye, developer, and other optional additives are pulverized to particle sizes of several microns or less using a grinder such as a ball mill, attritor, or sand grinder, or an appropriate emulsifier, and then a binder and various additives depending on the purpose are added to prepare a coating liquid. The solvent used in this coating liquid can be water or alcohol, and the solid content is about 20 to 40% by weight. In particular, when alcohol is used as the solvent, the coating liquid may penetrate into the paper, resulting in a decrease in the strength of the coating layer, so it is preferable to use water as the solvent.

[0041] The recording paper of the present invention may have an undercoat layer between the support and the recording layer. The primer layer is primarily composed of a binder and a pigment. The binder used in the undercoat layer may be any of the binders usable in the recording layer described above, and these binders may be used alone or in combination of two or more.

[0042] Examples of pigments that can be used in the undercoat layer include inorganic pigments such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, kaolin, calcined kaolin, clay, and talc, and organic pigments such as hollow plastic particles. These pigments may be used alone or in combination. As a pigment other than hollow plastic particles, calcined kaolin is preferably used. The content of the pigment in the primer layer is usually 50 to 95% by weight, preferably 70 to 90% by weight, based on the solid content of the primer layer. The content of the hollow plastic particles in the primer layer is 50% by weight or more, preferably 70 to 100% by weight, more preferably 80 to 100% by weight, based on the solid content of the pigment in the primer layer. The coating liquid for the undercoat layer may contain various auxiliary agents such as dispersants, plasticizers, pH adjusters, antifoaming agents, water-retaining agents, preservatives, coloring dyes, and ultraviolet protection agents, as needed.

[0043] In the present invention, it is preferred that no other layer such as a protective layer is 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). In this way, when no protective layer or the like is provided on the recording layer, water blocking resistance is improved. Water-resistant blocking resistance is evaluated by dropping tap water onto the surface of the recording layer (or 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 to evaluate whether or not the recording layer (or protective layer) has peeled off. The reason why water blocking resistance improves when a protective layer is not provided is that protective layers usually contain a relatively large amount of binder such as PVA (polyvinyl alcohol), and when a protective layer is provided, the binder bonds the coated surfaces together via water.

[0044] In the present invention, the means for applying the recording layer and other coating layers, i.e., the protective layer, undercoat layer, etc., is not particularly limited, and they can be applied according to well-known conventional techniques. For example, an off-machine or on-machine coater equipped with various coaters such as an air knife coater, rod blade coater, bent blade coater, bevel blade coater, roll coater, or curtain coater can be appropriately selected and used. The coating weight of the recording layer and the coating layers other than the recording layer is determined according to the required performance and recording suitability, and is not particularly limited. However, the typical coating weight of the recording layer is 2 to 12 g / m2 in terms of solid content. 2 The coating amount of the protective layer is about 0.5 to 5.0 g / m2 in solid content. 2 is preferred. Furthermore, various well-known techniques in the field of recording paper can be added as necessary, such as smoothing treatment such as supercalendering after coating each coating layer.

[0045] If 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 state after inkjet printing, the coating layer must be strong enough to not peel off, for example, when adhesive tape is attached to the substrate and then peeled off. Specifically, the force required to peel the tape (peel strength) is measured using a digital force gauge in the Ceropic 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.

[0046] A longitudinal tensile strength (JIS P8113) of the recording paper of 3 kN / m or more is preferable, as it improves the operability of inkjet continuous feed printers. Even in the field of inkjet paper, continuous feed printers that print continuously, like offset printing machines, are used for industrial purposes. In this case, if the tensile strength is low, tension cannot be applied during printing, resulting in poor running performance, and applying excessive tension can lead to paper breakage. In order to achieve a tensile strength of 3 kN / m or more, it is possible to increase the basis weight and thickness of the base paper, increase the amount of paper strength agent in the base paper, and so on.

[0047] It is preferable that the color density obtained by contacting the recording layer side of the recording paper with a hot plate at 90°C and 0.1 MPa for 5 seconds is 0.40 or less, since this suppresses background color development due to drying during printing with an inkjet continuous feed printer. The color density can be reduced to 0.40 or less by reducing the coating weight of the recording layer, changing the color developer, reducing the blending ratio of the sensitizer, or not blending it at all, and the like. [Example]

[0048] The present invention will be illustrated by the following examples, but is not intended to limit the scope of the present invention. In each example and comparative example, "parts" means "parts by weight" and "%" means "% by weight" unless otherwise specified.

[0049] For the production of recording paper, the dispersions and coating solutions were prepared as follows. [Preparation of each coating liquid] The following mixture was stirred and dispersed to prepare a coating liquid for the undercoat layer.

[0050] <Coating liquid for undercoat layer> Calcined kaolin (Ansilex 90) 100.0 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts Water 50.0 parts

[0051] The developer dispersions (Liquids A1 to A5), leuco dye dispersion (Liquid B), and sensitizer dispersion (Liquid C) having the following formulations were each wet-ground in a sand grinder until the average particle size reached 0.5 μm.

[0052] Developer dispersion liquid (A1 liquid) N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea (Hereinafter referred to as "Urea compound 1 (denoted as U1 in Table 1)"). 6.0 copies Aqueous solution of fully saponified polyvinyl alcohol (manufactured by Kuraray Co., Ltd., product name: PVA117, 10% solids 5.0 parts 1.5 parts water

[0053] Developer dispersion liquid (A2 liquid) N-[2-(3-phenylureido)phenyl]benzenesulfonamide (Hereinafter referred to as "Urea compound 2 (denoted as U2 in Table 1)"). 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0054] Developer dispersion liquid (A3 liquid) Urea urethane compound represented by the chemical formula (3) (Fine Ace Co., Ltd.) (Made by UU) 6.0 parts [ka] Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0055] Developer dispersion liquid (A4 liquid) 4,4'-dihydroxydiphenyl sulfone (Konishi Chemical Industry Co., Ltd., product name: 44BPS) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0056] Leuco dye dispersion (liquid B) 3-Dibutylamino-6-methyl-7-anilinofluoran (Yamamoto Chemical Co., Ltd.) (product name: ODB-2) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0057] Sensitizer dispersion (liquid C) 1,2-bis-(3-methylphenoxy)ethane (Sankosha, Product name: KS232) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0058] Next, the dispersions were mixed in the following proportions to prepare a coating liquid for the recording layer. <Coating liquid for recording layer> Developer dispersion liquid (A1 liquid) 36.0 parts Leuco dye dispersion (liquid B) 18.0 parts Sensitizer dispersion (liquid C) 18.0 parts Silica dispersion (Mizukasil P-537, manufactured by Mizusawa Chemical Industries, Ltd., solid content 25%) 140.0 copies 25.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0059] Next, a coating liquid for a protective layer was prepared by mixing the following ingredients in the following proportions. <Protective layer coating liquid> Aluminum hydroxide dispersion (Martinsberg, Product name: Martyfin OL, solids 50%) 9.0 parts Carboxy-modified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: KL318, degree of polymerization: about 1800, degree of saponification: 85~90mol%, Solid content 10%) 30.0 parts Polyamide epichlorohydrin resin (Seiko PMC Corporation, product name: WS4030 (25% solids) 4.0 parts Modified polyamine resin (manufactured by Taoka Chemical Co., Ltd., product name: Sumirez Resin SPI) -102A, solids 45%) 2.2 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin Z-7-30, Solid content 30%) 2.0 parts

[0060] [Example 1] Support (basis weight 47g / m 2The coating solution for the primer layer was applied to one side of the paper (high-quality paper) at a coating weight of 10.0 g / m2 (solid content). 2 After coating by the bent blade method so that the thickness was as follows, the coated paper was dried to obtain a primer layer coated paper. On the undercoat layer of this undercoat-coated paper, a coating solution for the recording layer was applied in a coating amount of 6.0 g / m2 in terms of solid content. 2 After coating by the rod blade method so that the coating was as follows, the coating was dried and then processed with a super calendar so that the smoothness was 100 to 500 seconds to prepare a recording paper.

[0061] [Example 2] A recording paper was prepared in the same manner as in Example 1, except that the A2 liquid was used instead of the A1 liquid in the recording layer coating liquid.

[0062] [Example 3] A recording paper was prepared in the same manner as in Example 1, except that the amount of silica dispersion in the recording layer coating liquid was changed to 100 parts.

[0063] [Example 4] A recording paper was prepared in the same manner as in Example 1, except that the amount of silica dispersion in the recording layer coating liquid was changed to 200 parts.

[0064] [Example 5] A recording paper was prepared in the same manner as in Example 1, except that the blending amount of Liquid C in the recording layer coating liquid was changed to 48 parts.

[0065] [Comparative Example 1] A recording paper was prepared in the same manner as in Example 1, except that the blending amount of A1 liquid in the recording layer coating liquid was changed to 18 parts, and 18 parts of A3 liquid was further added to the recording layer coating liquid. Comparative Example 2 A recording paper was prepared in the same manner as in Example 1, except that the A4 liquid was used instead of the A1 liquid in the recording layer coating liquid. Comparative Example 3 A recording paper was prepared in the same manner as in Example 3, except that the A4 liquid was used instead of the A1 liquid in the recording layer coating liquid.

[0066] Comparative Example 4 A recording paper was prepared in the same manner as in Example 1, except that the amount of silica dispersion in the recording layer coating liquid was changed to 40 parts.

[0067] Comparative Example 5 Recording paper was prepared in the same manner as in Example 1, except that the amount of silica dispersion in the recording layer coating liquid was changed to 70 parts and 35 parts of aluminum hydroxide dispersion was added to the recording layer coating liquid.

[0068] Comparative Example 6 Recording paper was prepared in the same manner as in Example 1, except that the same amount of 20% ethanol was used instead of water as the solvent in the developer dispersion (A1 liquid), leuco dye dispersion (B liquid), and sensitizer dispersion (C liquid) in the coating liquid for the recording layer.

[0069] The prepared recording paper was evaluated as follows.

[0070] <Thermal recording suitability (barcode reading suitability)> A barcode (CODE39) was printed on the prepared recording paper in the vertical direction (the direction of movement of the printer head was perpendicular to the barcode) and the horizontal direction (the direction of movement of the printer head was parallel to the barcode) using a Zebra 140XiIII label printer at a print level of +10 and a print speed of 30.4 cm / sec (12 in / sec). The printed barcode was then read using a barcode verifier (Honeywell, QCPC600, 640 nm light source) to evaluate its readability. The evaluation results were recorded using the ANSI standard symbol grade. Symbol grade: The barcode is divided into 10 parts vertically to the bars, and a reading test is conducted once for each part. The average value is expressed as a 5-level rating: A (excellent), B, C, D, F (poor).

[0071] <Inkjet recording suitability (bleeding)> The prepared recording paper was printed in four solid colors (black, cyan, magenta, and yellow) using a Canon PIXUS MG7130 inkjet printer (mode: plain paper / standard) (the character "no" was printed as a whiteout), and bleeding was evaluated according to the following criteria. Excellent: The ink is dry immediately after printing, and there is no blurring or feathering of the characters. Acceptable: The ink is dry immediately after printing, but there is some blurring or feathering of the characters. Unacceptable: The ink is not dry immediately after printing, or the characters are blurred or feathered.

[0072] <Suitability for inkjet printing (background color development)> A solid yellow print was made on the prepared recording paper using a Canon PIXUS MG7130 inkjet printer (mode: plain paper / standard), and the background color of the solid print after one day was evaluated according to the following criteria. Excellent: No background coloring at all Good: Difficult to distinguish with the naked eye, but when measured with a densitometer, the Bk value is slightly elevated Fair: There is some background coloring that can be seen with the naked eye. Unacceptable: Background color is present

[0073] <Heat resistance> The prepared recording paper was colored using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.) under conditions of a pressure of 0.1 MPa, a contact time of 5 seconds, and a temperature of 90°C, and the black density of the recorded area was measured using a Macbeth densitometer (RD-914, using an amber filter). Excellent: Black density is 0.20 or less Good: Black density is 0.21 or more and 0.40 or less Acceptable: Black density is 0.41 or more and 0.60 or less Unacceptable: Black density is 0.61 or more

[0074] <Water-blocking resistance> For the recording paper thus prepared, 10 ml of tap water was dropped onto the surface of the protective layer, the paper was folded in half so that the protective layer surface was on the inside, a load of 20 gf / cm2 was applied, and the paper was left to stand for 24 hours before being peeled off. The peeling of the protective layer and recording layer in the area where the water was dropped was visually evaluated according to the following criteria. Excellent: No blocking occurs, and the protective layer and recording layer do not peel off at all. Pass: Blocking occurs and the protective layer peels off slightly, but the recording layer does not peel off. Unacceptable: Strong blocking occurs, and the protective layer and recording layer peel off. Or the recording paper is destroyed when peeled off.

[0075] <Layer strength of recording layer (peel strength)> The layer strength of the recording layer (coating layer) was measured by a cellophane test (peel test) in a measurement environment of 23°C and 50% humidity. To measure, a transparent adhesive tape (Nichiban Cellophane Tape (registered trademark), CT24, width 24mm) was applied to the surface of the recording layer, and a rubber roller with a weight of 2.0 kg was pressed back and forth over the tape 20 times, and the force required to peel it off was measured using a digital force gauge (Shimpo FGX-2) (peel speed 20 m / min, peel angle 180°).

[0076] The results obtained are shown in Table 1. Table 1 shows the type of each electron-accepting developer and its solubility in 99.5% ethanol (Et) and 99.7% IPA. The solid content and total content in Table 1 are values ​​for the recording layer.

[0077] [Table 1]

[0078] As shown in Table 1, it can be seen that each example is excellent in both thermal recording suitability and ink jet recording suitability. In Example 5, in which the total content of the sensitizers in the recording layer exceeded 30% by weight, the heat resistance and background color development were slightly lower than those in the other Examples, but this was not a problem in practice.

[0079] On the other hand, in the case of Comparative Example 1 in which the recording layer contained two types of electron-accepting color developers, the inkjet recording suitability (background color development) was poor, and the heat resistance was also poor.

[0080] In the case of Comparative Example 2, in which the solubility in ethanol of the electron-accepting color developer in the recording layer exceeded 0.3 g / ml, the ink-jet recording suitability (bleeding) and heat resistance were poor. The reason for the decline in inkjet recording suitability (bleeding) is that inkjet inks come in water-based and solvent-based types, and solvent-based inks use organic solvents such as ethanol and IPA. Therefore, when using a color developer that is highly soluble in ethanol, the inkjet ink melts the color developer, which reacts with the dye and causes color development, resulting in background color development. The reason for the decline in heat resistance is that the color development start point of the color developer is low.

[0081] In the case of Comparative Example 3, in which the surface of the recording layer was not exposed but was covered with another layer (protective layer), the water blocking resistance was poor.

[0082] In the cases of Comparative Examples 4 and 5, in which the solid content of silica in the recording layer was less than 20% by mass, the inkjet recording suitability (bleeding) was poor.

[0083] In the case of Comparative Example 6, in which ethanol was contained as a solvent in the coating liquid for the recording layer, the strength of the recording layer decreased.

Claims

1. A recording paper having a support and a recording layer provided on the support and containing a leuco dye and an electron-accepting color developer, The electron-accepting color developer is represented by a urea compound represented by the following general formula (1): 【Chemistry 1】 (In the formula, 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, aralkyl group, or aryl group; R 2 represents a hydrogen atom or an alkyl group; and m represents 0 or 1.) the recording layer contains the electron-accepting color developer, and the solubility of the electron-accepting color developer in 99.5% ethanol is 0.3 g / ml or less; The recording paper, wherein the recording layer contains silica as a pigment that receives ink, and the solid content of the silica in the recording layer is 20% by mass or more.

2. 2. The recording paper according to claim 1, wherein the recording paper is an ink-jet recording medium suitable for thermal recording.

3. 2. The recording paper according to claim 1, wherein the recording paper is a thermal recording paper suitable for ink-jet recording.

4. 3. The recording paper according to claim 1, wherein the recording layer contains only one type of electron-accepting developer.

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

6. 3. The recording paper according to claim 1, wherein the solubility of said electron-accepting developer in 99.7% IPA is 0.5 g / ml or less.

7. A recording paper as described in claim 1 or 2, wherein the oil absorption of the silica is 130 ml / 100 g or more.

8. A recording paper as described in claim 1 or 2, wherein the recording layer contains a sensitizer, and the total content of the sensitizer in the recording layer is 30% by weight or less.

9. A recording paper as described in claim 1 or 2, wherein the longitudinal tensile strength (JIS P8113) of the recording paper is 3 kN / m or more.

10. A recording paper as described in claim 1 or 2, wherein the color density obtained by contacting the recording paper with a hot plate at 90°C and 0.1 MPa for 5 seconds is 0.40 or less.

11. A recording paper as described in claim 1 or 2, wherein the recording layer is the outermost layer.

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