JP2007175895A - Manufacturing method of inkjet recording paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inkjet recording paper which is improved in curling in an environment of high temperature and high humidity or low temperature and low humidity, causes little cockling (undulation of original paper) after printing and excels in gloss and image quality. <P>SOLUTION: In a manufacturing method of the inkjet recording paper which has an ink accepting layer finished by a casting method on one side of a paper base or has the ink accepting layer and a gloss revealing layer finished by the casting method on one side of the paper base, a peak in a pore diameter distribution curve of the ink accepting layer is only 0.06 μm or less substantially and besides a backing layer constituted mainly of a water-soluble resin is formed on the other side of the paper base before finishing by the casting method, so that the air permeability (JIS-P-8117) be 500-3,000 seconds. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording paper, and more particularly to an ink jet recording paper having a glossy surface having an ink jet recording surface formed by a casting method.

  The ink jet recording system that ejects water-based ink from fine nozzles toward ink jet recording paper and forms an image on the recording surface has low noise during recording operation, easy formation of full-color images, and high-speed recording This is widely used in terminal printers, facsimiles, plotters, form printing, and the like because of the fact that it is possible and the recording cost is lower than other printing apparatuses.

  In recent years, the rapid spread of printers and higher definition and higher speed have been accompanied. As a result, ink jet recording papers are required to have higher ink absorption speed than ever before. There is a strong demand for high uniformity of images comparable to silver salt photography. Further, in order to bring the quality of a recorded image closer to that of a photographic image, further improvement in the color density and glossiness of the recorded image is desired.

  In order to obtain high ink absorptivity, in the ink jet recording paper provided with one or more ink receiving layers, one peak of the hole distribution curve of the uppermost layer is 0.2 to 10 μm and the entire ink receiving layer There is a proposal of an ink jet recording paper designed at two places where the peak of the pore distribution curve is at least 0.2 to 10 μm and 0.05 μm or less (see, for example, Patent Document 1). Although this proposal has a remarkable effect of improving ink absorbency, in order to obtain such an ink jet recording paper, it is indispensable to design the ink receiving layer based on a pigment having an average particle diameter of 1 μm or more (micron order) as a main component. By using a micron order pigment, the image density is low as well as the gloss, and the circularity of the dots cannot be obtained, so the uniformity of the image is extremely low.

In addition, although an inkjet recording paper using a fine pigment having an average particle size of 0.1 μm or less and having cracks in the coating film controlled is described (for example, see Patent Document 2), the inkjet recording paper is excellent in gloss and image density. However, since the speed of the printer has been remarkably advanced, there remains a great difficulty in terms of ink absorption.
Similarly, in order to obtain an ink jet recording paper that places importance on transparency and high gloss, the pore distribution is reduced to approximately 50 nm (0.05 μm) or less by making all layers of the ink receiving layer into submicron order pigments. Although there is a proposal of a controlled ink jet recording paper (see, for example, Patent Document 3), high ink absorbability has not been achieved. In addition, since a large amount of submicron-order pigment is used, there is a disadvantage that the cost increases.

  In order to satisfy the improvement in ink absorbency and gloss at the same time, the first coating layer having a peak in the pore diameter distribution curve on the substrate of 0.1 to 10 μm and the pores on the first coating layer An ink jet recording paper having a second coating layer having a peak in a diameter distribution curve of substantially 0.06 μm or less has been proposed, and the second coating layer was applied simultaneously with application or during drying of the formed coating layer. Before the coating layer exhibits a reduced rate of drying, the coating layer is controlled to be cracked by thickening or cross-linking the coated coating, and an ink jet recording paper having an excellent image density can be obtained (for example, (See Patent Documents 4 and 5.) However, although such an ink jet recording sheet is extremely excellent in print quality, it has a large curl in an environment of high temperature and high humidity or low temperature and low humidity.

  On the other hand, in order to increase the smoothness and gloss of the ink jet recording paper, for example, in the ink jet recording paper in which the base material, the coating layer, and the outermost layer are sequentially provided, the outermost layer is made of general-purpose colloidal silica. There has been proposed a method (so-called casting method) or the like for pressure-bonding to a heated mirror drum surface (see, for example, Patent Document 6). The ink jet recording paper finished by this casting method is excellent in gloss and smoothness, but since the outermost layer is attached to the mirror drum and is dried, the curl of the recording body tends to be further increased.

In order to correct the curl of the ink jet recording paper, a recording medium (for example, a back surface comprising an ink receiving layer containing vapor phase method silica, a hydrophilic binder, and a latex having a glass transition temperature (Tg) of 60 ° C. or more (for example, , See Patent Document 7). This corrects the curl, but the air permeability is too high to be finished by the casting method, and the smoothness and gloss of the ink jet recording paper are insufficient.
In addition, there is a method in which a polyolefin resin-containing layer is provided on the back surface after finishing by the casting method (see, for example, Patent Document 8), but the glossy surface is easily damaged and curl correction is not always sufficient.

In order to satisfy all of the excellent image quality, high gloss, and curl correction, a method of providing a back layer identical to the ink receiving layer using fine pigments and then finishing by a casting method has been proposed (for example, patents) Reference 9). As a result, a recording material excellent in image density and gloss and having good curling can be obtained, but it is disadvantageous in terms of cost because a coating layer containing an expensive fine pigment must be provided on both sides.
JP 58-110287 A Japanese Patent Laid-Open No. 7-117334 JP 7-276789 A JP 2005-199550 A JP-A-2005-2225070 JP 2004-167959 A Japanese Patent No. 3619927 Japanese Patent No. 3551047 JP 2004-209654 A

  The present invention improves the curling of the glossy inkjet recording paper formed by the casting method on the surface on which the inkjet recording is performed in the environment of high temperature and high humidity or low temperature and low humidity, and the cockling after printing (the wave of the base paper) is improved. Provided is a method for manufacturing an inkjet recording paper that is small and excellent in image quality.

  As a result of intensive studies to solve such problems, the present inventors have adopted a specific ink-receiving layer, and before processing the surface by the casting method, the air permeability before casting is in a specific range. The present inventors have found that by forming a back surface layer containing a water-soluble resin as a main component so as to satisfy the requirements, curling is improved and cockling after printing is minimized, and the present invention has been achieved.

The present invention includes the following embodiments.
[1] Manufacture of ink jet recording paper having an ink receiving layer finished on one side of a paper substrate by a casting method or an ink receiving layer finished on one side of a paper substrate and a gloss developing layer finished by a casting method In the method, the peak in the pore diameter distribution curve of the ink receiving layer is substantially only 0.06 μm or less, and before the finishing by the casting method, the air permeability ( A method for producing an ink jet recording paper, wherein a back layer mainly composed of a water-soluble resin is formed so that JIS-P-8117) is 500 to 3000 seconds.
[2] The method for producing an ink jet recording paper according to [1], wherein the back layer is formed so that the air permeability is 1200 to 2500 seconds.
[3] Gas phase method silica, alumina having an average secondary particle size of 0.7 μm or less formed by agglomerating primary particles having an average primary particle size of 0.003 to 0.04 μm as the inorganic pigment of the ink receiving layer, The method for producing an inkjet recording paper according to [1] or [2], which is any one of alumina hydrates.
[4] The method for producing an inkjet recording paper according to any one of [1] to [3], wherein the water-soluble resin of the back layer is starch or polyvinyl alcohol having a saponification degree of 85 or more.
[5] An undercoat layer containing an inorganic pigment having a pore volume by BET of 0.5 ml / g or less and an average primary particle size of 1 μm or less and an emulsion latex is provided between the paper substrate and the ink receiving layer. [1] to [4] The method for producing an inkjet recording paper according to any one of [1] to [4].
[6] The gloss developing layer is a monodispersed colloidal pigment having an average primary particle diameter of 0.01 to 0.06 μm, alumina having an average secondary particle diameter of 1 μm or less, alumina hydrate, and an average secondary particle diameter of 0.7 μm. The method for producing an inkjet recording paper according to any one of [1] to [5], wherein at least one pigment selected from the group consisting of the following vapor phase method silica and wet gel method silica is used as a main component.
[7] An ink jet recording paper manufactured by the method for manufacturing an ink jet recording paper according to any one of [1] to [6].

  According to the present invention, the curling of ink jet recording paper in a high temperature, high humidity or low temperature, low humidity environment is improved, the cockling after printing is small, the glossiness and image quality are excellent, and ink jet recording by the casting method is performed. Paper can be provided.

(About layer structure)
The ink jet recording paper produced by the present invention has an ink receiving layer formed by a casting method on one side of a paper substrate and a back surface layer on the other side, an ink receiving layer and a casting method on one side of the paper substrate. Is a structure having a glossy layer formed on the other side and a back layer on the other side, but may have an undercoat layer between the paper substrate and the ink receiving layer, or a plurality of ink receiving layers may be laminated. .
In the present invention, in producing such an ink jet recording paper, the back layer is formed before the ink receiving layer or the gloss developing layer is formed by the casting method, and the ink receiving layer or the gloss developing method is formed by the casting method. By setting the air permeability at the time of forming a layer to 500 to 3000 seconds, curling and cockling are improved, and a high gloss inkjet recording paper can be obtained. First, a paper base material and each layer are demonstrated.

(About paper base)
The paper substrate is not particularly limited, and for example, a substrate such as high-quality paper, medium-quality paper, coated paper, art paper, cast-coated paper and the like can be used.
The paper base is generally composed mainly of wood pulp and a filler containing it if necessary.
As the wood pulp, various chemical pulps, mechanical pulps, regenerated pulps and the like can be used, and these pulps can be adjusted in a beating degree by a beating machine in order to adjust paper strength, papermaking suitability, and the like. The beating degree (freeness) of the pulp is not particularly limited, but is generally about 250 to 550 ml (CSF: JIS P8121). In order to improve smoothness, it is desirable to advance the beating degree. However, when recording on paper, the paper waving (cockling) caused by moisture in the ink and the blurring of the recorded image are better if the beating is not advanced. Often get. Accordingly, the freeness is preferably about 300 to 500 ml.

The filler is blended for the purpose of imparting opacity and the like, and calcium carbonate, calcined kaolin, clay, silica, titanium oxide and the like can be used. In particular, calcium carbonate is preferable because it becomes a substrate with high whiteness and glossiness of the ink jet recording paper is enhanced. The content (ash content) of the filler in the paper substrate is preferably about 1 to 20%, and if it is too much, the paper strength may be reduced. If the amount is too small, the air permeability of the paper base material is deteriorated. Therefore, the preferable filler content is 7 to 20%. Within this range, the smoothness, air permeability, and paper strength are balanced, and as a result, it is easy to obtain an ink jet recording paper with excellent gloss.
A sizing agent, a fixing agent, a paper strength enhancer, a cationizing agent, a yield improving agent, a dye, a fluorescent brightening agent, and the like can be added to the paper base as an auxiliary agent. Furthermore, in the size press process of the paper machine, starch, polyvinyl alcohol, cationic resin, and the like can be applied and impregnated to prepare surface strength, sizing degree, and the like.

Although there is no restriction | limiting in particular about the kind of paper base material, a shape, a dimension, etc., the thickness of a paper base material has preferable about 180-280 micrometers, and the tension | tensile_strength is about 0.75-0.95 g / cm < ² >. Furthermore, the thickness of the base material is preferably 200 to 250 μm because the effect of improving curling and cockling is great. Also in basis weight, about 160-230 g / m < ² > is preferable and 180-220 g / m < ² > is still more preferable.

The Steecht sizing degree (as 100 g / m ² paper) is preferably about 1 to 200 seconds. If the sizing degree is low, there may be operational problems such as wrinkling during coating, and if it is high, the paint may not be applied uniformly. A more preferred range of sizing is 4 to 120 seconds.

  The smoothness of the paper substrate is not particularly limited, but the Beck smoothness is preferably 70 seconds (Oken type, J. TAPPI No. 5) or more in order to obtain a highly glossy and highly smooth surface. Further, the opacity of the substrate is not particularly limited, but in order to obtain a silver salt photograph-like appearance (particularly visual whiteness), the opacity (JIS P8138) is preferably 85% or more. More preferably, it is 93% or more.

  In addition, the air permeability (JIS P8117) of the paper base material is preferably 20 to 500 seconds, and more preferably 30 to 300 seconds. Incidentally, the blur of the ink jet recording paper can be greatly reduced by setting the air permeability to 20 seconds or more. On the other hand, by setting it to 500 seconds or less, the solvent of the ink when ink jet recording is performed is absorbed by the paper base material from the ink receiving layer, so that it does not re-transfer into the ink receiving layer, and bleeding occurs over time. It becomes good.

(Undercoat layer)
In order to increase the smoothness of inkjet recording paper and to reduce cockling by reducing the excess ink solvent absorbability to the paper base material, one or more undercoat layers are provided between the paper base material and the ink receiving layer. Also good. The undercoat layer is a layer containing a pigment and a binder.

  Examples of the pigment used in the undercoat layer include calcium carbonate, kaolin, calcined kaolin, clay, calcined clay, zinc oxide, aluminum hydroxide, satin white, magnesium silicate, magnesium carbonate, titanium dioxide, and plastic pigment. Can be used together. Among these, monodispersed colloidal silica, wet silica, alumina, kaolin, titanium dioxide, and calcium carbonate are preferable, and monodispersed colloidal silica, wet silica, and calcium carbonate are particularly preferable because of excellent solvent absorbability. Further, it is more preferable to use the pigment dispersed in water as primary particles or secondary particles in which primary particles are aggregated. In order to suppress cockling, it is preferable to contain a pigment having a pore volume by the BET method of 0.5 ml / g or less and an average particle size of 1.5 μm or less.

  As the binder used in the undercoat layer, known binders can be used. For example, water-soluble resins (for example, polyvinyl alcohols such as polyvinyl alcohol, cationic polyvinyl alcohol, modified polyvinyl alcohol such as silyl-modified polyvinyl alcohol, casein, soybean protein) , Synthetic proteins, starch, cellulose derivatives such as carboxymethylcellulose and methylcellulose), or water-dispersible resins (for example, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, acrylonitrile-butadiene copolymer, etc.) Copolymer latex, acrylic copolymer, vinyl copolymer latex such as ethylene-vinyl acetate copolymer, styrene copolymer latex, (poly) urethane polymer polymer Various binders such as tex etc. are used alone or in admixture of two or more.

  When the ink receiving layer described later is formed using a crosslinkable compound (method (B)), when an emulsion latex is used as the binder of the undercoat layer, the undercoat layer is cured by the crosslinkable compound. Does not occur, which is preferable because it prevents the coating film from cracking. Furthermore, a compound having a crosslinking property with respect to the binder of the ink receiving layer can be blended in the undercoat layer coating liquid, which is particularly preferable. The emulsion latex is not particularly limited, but an acrylic resin emulsion, a urethane resin emulsion, and a styrene resin emulsion are preferably used because the storage stability of white paper is good.

  The peak in the pore diameter distribution curve of the undercoat layer is not necessarily limited to 0.06 μm or less, and is not particularly limited, but a peak having a peak of 1 μm or more is preferable because curl tends to be improved.

Although there is no restriction | limiting in the dry solid content coating mass of an undercoat layer, Generally it is about 2-10 g / m < ² >. If the coating amount is too small, the smoothness of the recording medium may be insufficient, and if the coating amount is too large, it will be disadvantageous in terms of cost.
For coating the undercoat layer, various coating apparatuses such as a blade coater, an air knife coater, a roll coater, a bar coater, a gravure coater, a rod blade coater, a lip coater, a curtain coater, and a die coater can be used.

  The air permeability in the laminated state of the paper base material and the undercoat layer is not particularly limited, but is preferably about 30 to 500 seconds, and more preferably 35 to 300 seconds. The ink solvent at the time of performing ink jet recording from an air permeability of 500 seconds can be absorbed from the ink receiving layer into the undercoat layer and the paper substrate. In addition, when it is lower than 30 seconds, the effect of suppressing cockling tends to decrease.

(About ink receiving layer)
The ink receiving layer of the present invention is a layer having at least a pigment and a binder, and the peak in the pore diameter distribution curve needs to be substantially 0.06 μm or less.
In order to realize a photographic ink jet recording image quality, the transparency of the ink receiving layer to which the dye or pigment in the ink is fixed is indispensable. The more transparent the ink-receiving layer, the better the dye fixed in the ink-receiving layer can be seen from the outside. Therefore, the depth of the image, that is, the depth, is more similar to a silver salt photograph.

  A coating layer with high transparency is generally said to be difficult to absorb ink, but it is a coating layer having a pigment and a binder and eliminates pores larger than the wavelength of light on the coating layer. The ink-receiving layer can be formed with both film-forming properties and ink-absorbing properties, and the ink-absorbing layer has a peak in the pore diameter distribution curve of 0.06 μm or less, which is substantially smaller than the wavelength of light. And transparency of the coating layer were achieved at the same time. Such an ink receiving layer has no crack in the coating film and is a continuous film made of a pigment and a binder.

  In order to form an ink receptive layer having the above pore diameter distribution, the ink receptive layer is immediately after coating or in the course of drying the coated liquid layer, and the coating liquid layer is reduced. Before showing the rate of drying rate, it is preferable that the coating is made by thickening or crosslinking to form a film. Specifically, the methods listed in the following (A) to (C) can be exemplified and can be appropriately adopted, but are not limited to these methods.

For example,
(A) It contains a hydrophilic resin that forms a hydrogel by electron beam irradiation, and immediately after coating or during the drying of the coated coating layer, the coating layer has a reduced drying rate. Before showing, thickening the coating layer by electron beam irradiation (form hydrogel),
(B) A coating liquid containing a binder, immediately after coating, or in the middle of drying of the coated coating liquid layer, before the coating liquid layer exhibits a reduced rate of drying, A method of thickening and crosslinking a coating with a crosslinkable compound;
(C) For example, a thermosensitive polymer compound as a binder (showing hydrophilicity in a temperature range below a certain temperature (temperature sensitive point) described in JP 2003-40916 A), and in a temperature range higher than the temperature sensitive point A method of increasing the viscosity of the coating liquid layer by reducing the temperature of the coating liquid layer immediately after coating,
Etc. can be illustrated.

  When the ink receiving layer is formed by the method (A), a hydrophilic binder that does not have a radical polymerizable unsaturated bond and forms a hydrogel by irradiating an aqueous solution with an electron beam is used as the binder. Use, after applying a coating liquid containing 1 to 100 parts by weight of a hydrophilic binder with respect to 100 parts by weight of the pigment, and then irradiating an electron beam to hydrogel the applied coating liquid. The ink receiving layer may be formed by drying.

  Examples of the hydrophilic binder that does not have a radical polymerizable unsaturated bond and forms a hydrogel by irradiating an aqueous solution with an electron beam include, for example, polyvinyl alcohol, polyethylene oxide, polyalkylene oxide, polyvinyl pyrrolidone, water-soluble Polyvinyl acetal, poly-N-vinylacetamide, polyacrylamide, polyacryloylmorpholine, polyhydroxyalkyl acrylate, polyacrylic acid, hydroxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, gelatin, casein, and water-soluble derivatives thereof, Moreover, these copolymers etc. can be illustrated and it is good to use these individually or in combination.

As the electron beam irradiation method, for example, a scanning method, a curtain beam method, a broad beam method, or the like is adopted, and an acceleration voltage at the time of irradiation with an electron beam is appropriately about 50 to 300 kV. The amount of electron beam irradiation is preferably adjusted in the range of about 1 to 200 kGy. If it is less than 1 kGy, it is not sufficient to gel the coating layer, and irradiation exceeding 200 kGy is not preferable because it may cause deterioration or discoloration of the substrate or the coating layer.
As a method of performing electron beam irradiation, (1) coating, electron beam irradiation, and drying may be repeated, or (2) the next layer may be coated and dried after electron beam irradiation, (3) There are methods such as applying multiple layers simultaneously and irradiating with an electron beam.

When the ink receiving layer is formed by the method (B), a known binder used for inkjet recording paper can be used. Examples thereof include water-soluble resins such as polyvinyl alcohol, polyvinyl pyrrolidone, casein, soybean protein, synthetic proteins, starch, carboxymethyl cellulose, and cellulose derivatives such as methyl cellulose. In particular, polyvinyl alcohol having high adhesion to the pigment is preferably used. In particular, in order to improve the balance between film formability and ink absorbability, it is preferable to use polyvinyl alcohol having a polymerization degree of 2000 or more, and polyvinyl alcohol having a polymerization degree of 3600 to 5000 is more preferable. In order to improve ink absorptivity etc., two or more binder materials (for example, a mixture of two or more water-soluble resins, a mixture of one or more water-soluble resins and one or more latexes) are used. Also good.
In this case, the dry solid content mass ratio of the pigment and the water-soluble resin in the ink receiving layer is preferably in the range of 2 to 50 parts by mass with respect to 100 parts by mass of the pigment. In order to further improve the balance between the ink absorbability and the coating film strength, the content is preferably 5 to 30 parts by mass, and more preferably 10 to 25 parts by mass.

  Various known crosslinking agents and gelling agents can be used as the compound having crosslinkability with the binder. Examples of the compound having crosslinkability with respect to polyvinyl alcohol include boron compounds, epoxy compounds, glycidyl compounds, zirconium compounds, aluminum compounds, chromium compounds and the like. Among these, a boron compound is particularly preferable because thickening or gelation occurs quickly.

The boron compound is an oxygen acid having a boron atom as a central atom and a salt thereof. Examples include orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid, and their sodium, potassium, and ammonium salts. Among these, orthoboric acid and disodium tetraborate are preferably used because they have an effect of moderately thickening the paint.
Although content of a boron compound is based also on the polymerization degree of a boron compound and polyvinyl alcohol, it is preferable to contain 0.01-1.5 g / m < ² > on the single side | surface of a base material. When the amount is more than 1.5 g / m ² , the crosslinking density with the hydrophilic binder increases, the coating film becomes hard and is easily broken. On the other hand, when the amount is less than 0.01 g / m ² , the crosslinking with the hydrophilic binder is weak, the gelation of the paint is weakened, and the coating film is easily cracked.

  The ink receiving layer is applied by, for example, blending a cross-linking agent in the ink coating layer coating liquid, or coating the ink coating layer coating liquid and then applying the cross-linking agent, It may be produced by a method such as applying to and contained in an undercoat layer provided between the base material and the ink receiving layer, and applying a coating liquid for the ink coating layer thereon. It is preferable that the cross-linking agent moves to the ink receiving layer and the ink receiving layer thickens or gels uniformly.

  When the ink receiving layer is formed by the above method (C), a temperature-sensitive polymer compound that exhibits hydrophilicity in a temperature region below the temperature sensitive point and exhibits hydrophobicity in a temperature region higher than the temperature sensitive point is used as a binder. Use it.

  When this thermosensitive polymer compound is used, coating is performed at a temperature higher than the temperature sensitive point, and by cooling to a temperature lower than the temperature sensitive point, the applied layer is thickened or gelled and then dried. A recording layer may be formed. The temperature sensitive point is preferably in the range of 5 to 35 ° C. The range of 15-30 degreeC is still more preferable. Examples of such temperature-sensitive polymer compounds include those disclosed in JP-A-2003-40916, which are obtained by polymerization in the presence of polyvinyl alcohol and / or polyvinyl alcohol derivatives. it can.

As the pigment used in the ink receiving layer, a fine pigment which is a dispersion of secondary particles formed by agglomerating primary particles having an average primary particle diameter of 0.003 to 0.04 μm is preferable.
The average secondary particle diameter of the fine pigment is preferably 0.7 μm or less. When an inorganic pigment having an average secondary particle diameter of more than 0.7 μm is used, the printing density is lowered. In order to adjust the particle diameter to 0.7 μm or less, it can be produced by, for example, a method of applying a strong force by mechanical means, that is, a so-called breaking down method (a method of subdividing a bulk material). The mechanical means include: ultrasonic homogenizer, pressure homogenizer, liquid collision type homogenizer, high-speed rotary mill, roller mill, container drive medium mill, medium agitation mill, jet mill, mortar, and crusher (coating in a bowl-shaped container). A device for grinding and kneading the pulverized product with a bowl-shaped stirring bar), a sand grinder, a nanomizer and the like. In order to reduce the particle size, classification and pulverization can be repeated. On the other hand, if the average secondary particle diameter is smaller than 0.03 μm, cracks are likely to occur in the coating film.

  Further, the pore volume of the fine pigment by the BET method is preferably 0.8 ml / g or more. If it is less than 0.8 ml / g, ink absorbability is insufficient. More preferably, it is 1.0-1.2 ml / g.

Examples of the pigment used in the present invention include vapor-phase method silica, alumina, and alumina hydrate. Among them, vapor-phase method silica is preferable from the viewpoint of film formability of the coating layer and image density after printing. Most preferably used.
Vapor phase silica is a method by high-temperature vapor phase hydrolysis of silicon halide (flame hydrolysis method), a method in which silica sand and coke are heated and reduced and vaporized by an arc in an electric furnace and oxidized with air ( Anhydrous silica fine particles obtained by the arc method).

Vapor phase silica is different from wet silica such as gel silica and sedimentation silica in that it has different properties due to differences in surface silanol group density and pore volume. In the case of wet silica, the density of silanol groups on the fine particle surface is large at 5 to 8 / nm ² , and the fine pores with a pore diameter of 0.06 μm or less are liable to agglomerate silica fine particles. Although the volume is low, in the case of vapor phase method silica, the density of silanol groups on the surface of the fine particles is as small as ² to 3 / nm2, which results in loose soft agglomeration and high pore volume. As a result, a three-dimensional structure having a high porosity is formed.

  Alumina is generally called aluminum oxide having crystallinity. Generally, alumina having χ, κ, γ, δ, θ, η, ρ, pseudo γ, and α crystals can be mentioned. From the viewpoint of glossiness and ink absorbability, vapor-phase method alumina and alumina having γ, δ, and θ crystals are preferably selected. Vapor phase alumina (fumed alumina) having a sharp particle size distribution and particularly excellent film formability is particularly preferred. Vapor phase alumina is formed by high temperature hydrolysis of gaseous aluminum trichloride.

  The alumina hydrate is not particularly limited, but boehmite or pseudoboehmite is preferably selected from the viewpoints of ink absorbability and film formability. The production method of alumina hydrate includes, for example, a method of hydrolyzing aluminum isopropoxide with water (BE Yoldas, Amer. Ceram. Soc. Bull., 54, 289 (1975), etc.) and aluminum alkoxide. (Japanese Patent Laid-Open No. 06-064918) and the like.

The ink receiving layer preferably contains a cationic polymer in order to improve the water resistance and storage stability of the recorded image. Examples of the cationic polymer include polyalkyleneamine compounds (for example, polyethylenepolyamine, polypropylenepolyamine), acrylic resins having secondary, tertiary amino groups, or quaternary ammonium groups, polyvinylamine, polyvinylamidine, and five-membered rings. Amidine compound formed, dicyan cation resin (for example, dicyandiamide-kilmaldehyde polycondensate), epoxychlorohydrin-dimethylamine addition polymer, dimethylallyl ammonium chloride-SO ₂ copolymer, diallylamine-SO ₂ co-polymer Examples thereof include polymers, dimethyldiallylammonium chloride polymers, allylamine salt polymers, dialkylaminoethyl (meth) acrylate ammonium salt polymers, acrylamide-diallylamine salt copolymers, and the like. You can use. These cationic polymers may have a molecular weight of 5000 or more because they may inhibit ink absorbability when the molecular weight is lower than 5000.

In general, in the case of silica, since silanol groups are present on the surface, it is electrically negative and aggregates when mixed with a cationic polymer. Therefore, when silica is used in the form of composite particles treated with a cationic polymer, the dispersibility is excellent, the printing density and the image water resistance are excellent, and an excellent quality comparable to a silver salt photograph can be obtained.
In order to obtain such composite particles, for example, an aggregate particle of a cationic polymer-silica obtained by mixing and aggregating vapor phase method silica and a cationic polymer in water and having an average particle diameter is obtained. It is preferable to produce the cationic polymer-silica composite particles by pulverizing and dispersing to 0.1 to 1 μm, preferably 0.1 to 0.7 μm, more preferably 0.1 to 0.5 μm.
The cationic polymer is appropriately selected from the above exemplified cationic polymers and used alone or in combination. In order to improve the fixability of the dye and pigment in the ink and the dispersibility of the silica dispersion, it is more preferable to use a polymer of 5-membered amidines, dimethyldiallylammonium chloride, and alkoxycarbonyl-modified allylamine salt. . The addition amount of the cationic compound is preferably 1 to 30 parts by mass, and more preferably 2 to 15 parts by mass with respect to 100 parts by mass of the pigment.

In order to disperse or pulverize the mixture or aggregate of the silica and the cationic polymer, a homomixer, a pressure homogenizer, an ultrasonic homogenizer, a microfluidizer, an optimizer, a nanomizer, a high-speed rotary mill, a roller mill, and a container drive A medium mill, a medium stirring mill, a jet mill, a sand grinder, a Clare mix, etc. are used.
When the average particle diameter exceeds 1 μm, it is sufficiently dispersed if treated with a weak mechanical force such as a homomixer, but it is effective to apply a stronger mechanical force to pulverize the average particle diameter to 1 μm or less, It is preferable to use a pressure type dispersion method.
Examples of the high-pressure pulverizer that is a pressure dispersion method include a pressure homogenizer, an ultrasonic homogenizer, a microfluidizer, and a nanomizer. Particularly, a microfluidizer and a nanomizer are preferable as a high-speed flow collision type homogenizer.

  Further, for example, an aqueous dispersion of silica fine particles is optionally pulverized to reduce its average secondary particle size to a desired value, and a silane coupling agent having an ammonium salt or polybasic chloride is added to the dispersion. An aluminum compound such as aluminum is added to form a silica-cation compound aggregate, which is then pulverized to have an average secondary particle diameter of 500 nm or less.

The dry solids coating weight of the ink receiving layer, but is not limited, it is preferable that generally is 5 to 20 g / ^{m 2,} more preferably about a 7~18g / ^{m 2.} If the coating amount is too small, the high-definition and high-speed printer may have insufficient ink absorbability. If the coating amount is too large, it may be difficult to control cracks in the coating film. The ink receiving layer may be applied in a plurality of times, or may be formed by overlapping a plurality of layers simultaneously.
For coating the ink receiving layer, use various coating devices such as blade coater, air knife coater, roll coater, bar coater, gravure coater, rod blade coater, lip coater, die coater, slide bead coater and curtain coater. Can do.

  In the present invention, when a glossy expression layer is provided on the ink receiving layer, it is preferable to form the ink receiving layer by drying with hot air at 80 to 150 ° C. because it is advantageous in terms of cost. The air permeability of (paper base material + ink receiving layer) or (paper base material + undercoat layer + ink receiving layer) is preferably 100 to 2000 seconds, and more preferably 300 to 1500 seconds. If the air permeability is higher than 2000 seconds, it is not preferable because the mold release becomes worse at the time of casting after the back layer is provided.

In the present invention, when the ink receiving layer is formed by a casting method, it is necessary to form a back surface layer described later before forming the ink receiving layer.
When formed by the casting method, while the ink receiving layer is in a wet state, it is pressed against a heated mirror drum, dried, and the mirror surface is copied to the coating layer, so that a highly glossy surface can be formed. it can. As the casting method, a wet casting method, a rewet casting method, a gelled casting method, and the like that are conventionally known in the field of coated paper for printing can be applied. In particular, the rewetting method in which the ink receiving layer is applied, dried or semi-dried, wetted by applying a wetting liquid, and then immediately pressed onto a mirror drum and dried. This is preferable because gloss and image quality comparable to those of photographs can be obtained.

  The surface temperature of the heated mirror surface is preferably controlled within the range of 80 to 120 ° C. in view of drying efficiency. In order to make it easy to peel off the ink receiving layer from the pressure-bonded mirror surface, a release agent such as stearamide, polyethylene wax, ammonium oleate or the like may be contained in the aqueous solution, or applied to the mirror surface. Also good. Among these, it is particularly preferable to use a cationic release agent, and the addition amount of the release agent is not particularly limited, but is generally 0.1 to 5 parts by mass with respect to 100 parts by mass of the aqueous solution. .

(About glossy layer)
In the present invention, an ink jet recording paper can also be formed by providing a gloss developing layer which is further pressed against a mirror drum and dried on the ink receiving layer. In the present invention, it is necessary to form a back layer described later before forming the glossy layer by the casting method.

  Examples of the pigment contained in the glossy layer include monodispersed colloidal pigments having an average primary particle size of 0.01 to 0.06 μm, alumina and alumina hydrate having an average secondary particle size of 1 μm or less, and an average secondary particle size. Vapor phase silica or wet gel silica having a particle size of 0.7 μm or less is preferably used.

In addition to the fine pigment, the glossy layer may contain a binder. The binder may be a water-soluble resin such as polyvinyl alcohol or a water-insoluble emulsion resin. In the case of water-soluble resin, there is no restriction | limiting in molecular weight etc., The dry solid content mass ratio of a pigment and a binder has preferable 100 / 10-100 / 0. When the addition rate is more than 10%, the ink absorption rate is slow. In the case of an emulsion resin, in order to increase the color density of the recorded image, the average particle diameter of the resin-containing particles is preferably 100 nm or less, more preferably 10 to 80 nm, and the dry solid mass of the pigment and binder. The ratio is preferably 100/30 to 100/5.
The coating material for the glossy layer preferably has a pH of 8 or less and a viscosity of 100 mPa · s or less. Since the gloss decreases when the viscosity is higher than 100 mPa · s, the type and amount of the binder may be appropriately adjusted so as to obtain a low-viscosity paint.

There is no particular limitation on the binder used in the glossy layer, but a water-insoluble emulsion resin having a cationic substituent is preferable in order to improve the fixing property and water resistance of the ink.
In particular, an acrylic ester emulsion resin having a cationic substituent in the ester group, or an acrylic ester emulsion resin having at least one component of a methacrylic ester as a copolymerization component, a copolymer of an isocyanate and a polyol having a cationic substituent. A urethane emulsion resin in which polymer ionomer resin particles are dispersed is preferably used.
The glass transition temperature is not particularly limited, but the particle diameter of the emulsion resin is preferably 20 to 50 nm. If the particle diameter is smaller than 20 nm, the ink absorption rate is slow, and if it is larger than 50 nm, the image density is lowered, which is not preferable.

Dry the solid coating amount of the glossy layer is preferably in the range of ^{0.3~5g / m 2, 0.5~3g / m} 2 is more preferable. If the coating amount is too small, the coating film becomes excessively thin and an interference color due to light tends to be generated. On the other hand, if the coating amount is excessive, the ink absorption rate may be remarkably reduced. In order to improve the balance between the ink absorption speed and the ink absorption capacity, the coating amount of the ink receiving layer is preferably 5 to 30 times, more preferably 7 to 20 times the coating amount of the glossy layer. Further preferred.

While the gloss developing layer is in a wet state, it is applied by a casting method in which the gloss developing layer is pressed against a heated mirror drum and dried to copy the mirror surface onto the coating layer. As the casting method, a wet casting method, a rewet casting method, a gelled casting method, and the like that are conventionally known in the field of coated paper for printing can be applied.
Also, immediately before the ink receiving layer is pressed against the mirror drum, a glossy layer coating liquid is applied between the ink receiving layer surface on the press roll and the mirror drum, and the surface is mirror-finished by immediately pressing and drying ( Hereinafter, it is also possible to perform a nip cast finishing, and a recording material obtained by this method is preferable because gloss and image quality comparable to a silver salt photograph can be obtained.

  At this time, in order to prevent cracking and increase the drying efficiency, the surface temperature of the heated mirror surface is preferably controlled within the range of 80 to 120 ° C. In order to make it easy to peel off the glossy layer from the pressed mirror surface, a release agent such as stearamide, polyethylene wax, ammonium oleate or the like may be included in the glossy layer or coated on the mirror surface. May be. Among these, it is particularly preferable to use a cationic release agent. The amount of the release agent added is not particularly limited, but generally it is preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the pigment contained in the glossy layer.

Moreover, it is preferable that the peak in the pore diameter distribution curve of the glossy layer is substantially only at 0.06 μm or less as in the case of the ink receiving layer.
In the pore diameter distribution curve of the glossy layer, if the peak of the pore diameter is in a region exceeding 0.06 μm, the glossiness of the image becomes insufficient, and cracks occur in the glossy layer, resulting in dot formation in the recorded image. The roundness is lowered and the uniformity of the recorded image becomes poor.
That is, the peak in the pore diameter distribution curve of the glossy layer and the ink receiving layer adjacent thereto is present in the region of 0.06 μm or less so that the coating film is substantially free of cracks, thereby making the recorded image uniform. It became possible to improve the sex.

(About the back layer)
On the back surface of the paper substrate (the surface on which the ink receiving layer is not formed), a coating layer containing a water-soluble resin as a main component is provided in order to correct curling toward the front surface side. By providing the back layer, the penetration of the ink solvent into the base paper can be suppressed, which is effective in preventing cockling.
The back layer may be provided at any stage before the ink receiving layer or gloss developing layer is processed with the mirror drum, but it is high by finishing the inkjet recording paper by the casting method at the end of the manufacturing process. Gloss can be imparted. On the other hand, when a water-soluble resin is applied to the back surface of the inkjet recording paper after finishing by the casting method, curling can be corrected, but the gloss of the inkjet recording paper is reduced. In addition, the glossy surface of the ink jet recording paper is easily damaged.

When the back layer is applied after the ink receiving layer is applied, the air permeability of (back layer + paper substrate + ink receiving layer) or (back layer + paper substrate + undercoat layer + ink receiving layer) is 500. -3000 seconds are preferable, and 1200-2500 seconds are more preferable. When the air permeability is lower than 500 seconds, sticking to the mirror drum is weak and glossiness is insufficient. In addition, the curl correction effect is reduced. When the air permeability is higher than 3000 seconds, the release from the mirror drum is deteriorated, which is not preferable.
Further, when the back layer is applied before the ink-receiving layer is applied, the air permeability of (back layer + paper substrate) or (back layer + paper substrate + undercoat layer) is preferably 200 to 2000 seconds. .

  Examples of water-soluble resins used for the back layer include polyvinyl alcohol, polyvinyl pyrrolidone, casein, soy protein, synthetic proteins, starch, carboxymethylcellulose, cellulose derivatives such as methylcellulose, etc. Starch having a large effect or polyvinyl alcohol having a saponification degree of 85 or more is preferably used. When the saponification degree of polyvinyl alcohol is lower than 85, the water resistance of the recording material is lowered, which is not preferable. Although there is no limitation in particular in the polymerization degree of polyvinyl alcohol, 1000-3500 are easy to apply and are preferable.

  The back surface layer of the base material may be further treated with an antistatic agent, an antiblocking agent, or the like for a transportability improving process, an antistatic process, or an antiblocking process. Further, the back surface of the ink jet recording paper finished by the casting method may be further laminated with polyethylene or the like to make it closer to a photographic texture.

(Measurement method of average particle size)
The average particle diameter of the pigment in the present invention indicates the secondary particle diameter when primary particles are aggregated to form secondary particles, and indicates the primary particle diameter when monodispersed with only primary particles. Regardless of whether the pigment is in the form of a powder or a slurry.
The measurement method was to prepare 200 g of an aqueous dispersion having a pigment concentration of 3% by mass, apply this to a homomixer, stir and disperse at 1000 rpm for 30 minutes, and then immediately remove this dispersion with an electron microscope (SEM and TEM). ) For observation, take an electron microscope photograph of 10,000 to 400,000 times, and measure and average the martin diameter of particles present in an area of 5 cm × 5 cm square in the photograph. (See "Handbook of fine particles", Asakura Shoten, p52, 1991).

(Measurement of pore diameter distribution)
The peak in the prescribed pore diameter distribution curve of the present invention will be described. As a measurement method, in order to avoid the influence of the support, the coating layer of the obtained recording material was peeled off with a cutter or the like and used for measurement. The pore distribution was determined by a mercury intrusion method using a Micrometrics Posizer 9320 (manufactured by Shimadzu Corporation). The measurement of the pore diameter by the mercury intrusion method was calculated using the following formula derived assuming that the cross section of the pore was circular.
R = -2γCOSθ / P
In the formula, R: pore radius (2R = pore diameter), γ: surface tension of mercury, θ: contact angle, and P: pressure, respectively.
The surface tension of mercury is 482.536 dyn / cm, the working contact angle is 130 °, the low pressure part of mercury pressure (0 to 30 psia, measurement pore radius: 180 to 3 μm) and the high pressure part (0 to 30001 psia, measurement pores) Radius: 3 to 0.003 μm).
The pore diameter distribution is obtained by gradually changing the pressure applied to mercury using the above principle, measuring the volume of mercury entering the pores at that time, that is, the pore volume V, and converting it according to the above formula. The relationship between the pore diameter (2R) and the pore volume is drawn, and the differential coefficient dV / d (2R) of this relationship curve is determined as the vertical axis, and the pore diameter 2R is determined as the horizontal axis. The pore diameter distribution curve of the coating layer usually has 1 to several peaks.

(Measurement method of pore volume by BET method)
The pore volume measuring method by the BET method referred to in the present invention will be described. The inorganic pigment or the dispersion of the inorganic pigment was dried at 105 ° C. to obtain a powder sample for measurement. The pore volume of this powder sample was measured after vacuum degassing at 200 ° C. for 2 hours as a pretreatment using a nitrogen gas adsorption specific surface area / pore distribution measuring apparatus (SA3100 plus type manufactured by Coulter). As the pore volume, the value of the total pore volume (nitrogen relative pressure 0.991) having a pore diameter of 3 to 200 nm was used.

  The present invention will be described more specifically with reference to the following examples, but the technical scope of the present invention is not limited thereto. First, materials used in Examples and Comparative Examples will be described.

(1) Preparation of paper base In pulp slurry (NBKP; freeness 250 mlCSF and LBKP; freeness 280 mlCSF mixed at a mass ratio of 2: 8) with a concentration of 0.5% by weight Add 2.0% by weight of cationized starch, 0.4% by weight of alkyl ketene dimer, 0.1% by weight of anionized polyacrylamide resin, 0.7% by weight of polyamide polyamine epichlorohydrin resin, and stir well. And dispersed. The pulp slurry having the above composition was made with a long net machine, and passed through a drier, a size press, and a machine calendar to produce a paper base having a basis weight of 210 g / m ² and a tension of 0.9 g / cm ³ . The paper substrate had a thickness of 234 μm and an air permeability of 80 seconds.

(2) Preparation of cationic polymer-silica composite particle dispersion A (use of vapor phase silica: for ink receiving layer)
Gas phase method silica having an average particle diameter of 1.0 μm (manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil A300, average primary particle diameter: about 8 nm) was dispersed by a homomixer, and then the average secondary particle diameter was 800 nm. A 10% by mass silica fine particle dispersion was prepared by pulverizing and dispersing with a high-speed collision type homogenizer.
10 parts by mass of a cationic compound having a 5-membered ring amidine structure (product name: SC-700M, molecular weight: 30,000) having a 5-membered ring amidine structure is added to 100 parts by mass of this silica fine particle dispersion, and a high-speed flow collision type homogenizer is added. And 10% by weight of a cationic polymer-silica composite particle dispersion A having an average secondary particle diameter of 0.15 μm was prepared. The pore volume of this composite particle by BET was 1.1 ml / g.

[Example 1]
"Formation of undercoat layer"
On one surface of the paper substrate, the coating liquid A having the following composition was coated with a bar so that the dry coating amount was 7 g / m ² and dried to obtain an undercoat layer. At this time, the air permeability of (paper base material + undercoat layer) was 70 seconds.
<Coating fluid A>
Acrylic polymer as a binder in 100 parts by mass (solid content) of acidic colloidal silica (manufactured by Nissan Chemical Co., Ltd., trade name: ST-OL, average particle size 0.045 μm, pore volume 0.3 ml / g, anionic) An aqueous dispersion (concentration: 20% by mass) was prepared by mixing 20 parts by mass (trade name: Primal P-376, emulsion type adhesive, manufactured by Rohm and Haas Co., Ltd.) in water.

"Formation of back layer"
On the opposite side of the surface provided with the undercoat layer, an 8% aqueous starch solution was applied with a bar so as to be 1.5 g / m ² and dried to obtain a back layer. At this time, the air permeability of (back layer + paper substrate + undercoat layer) was 1300 seconds.

"Formation of ink-receiving layer"
Next, an 8% borax aqueous solution was applied onto the undercoat layer, and then a coating liquid B having the following composition was applied to hydrogel the ink receiving layer. Subsequently, the hydrogelled coating liquid layer was pressed against a mirror drum heated to 90 ° C. and dried to prepare an ink jet recording paper. The dry coating amount of the ink receiving layer was 18 g / m ² .

<Coating fluid B>
As an inorganic pigment, 100 parts by weight (solid content) of the above cationic polymer-silica composite particle dispersion A, 18 parts by weight of polyvinyl alcohol having a polymerization degree of 3500 and a saponification degree of 88.5% as a binder, and a dispersant (Toa Gosei) An aqueous dispersion (concentration: 15% by mass) was prepared by mixing 0.05 part by mass, trade name: Aron SD-10) manufactured by the company.

[Example 2]
In the same manner as in Example 1, the ink receiving layer was hydrogelated and then dried with a hot air dryer at 120 ° C. At this time, the air permeability of (back layer + paper base material + undercoat layer + ink receiving layer) was 2800 seconds.
Next, at the nip between the mirror drum and the press roll, the ink receiving layer is on the mirror drum side, and a release agent (ammonium oleate) is added to 100 parts by weight of water between the ink receiving layer surface and the mirror drum. An aqueous solution added with 1% by mass was supplied to wet the ink receiving layer, and then immediately dried with a mirror drum (surface temperature of 95 ° C.) while pressing with a press roll to prepare an ink jet recording paper.

Example 3
After applying an 8% borax aqueous solution on the base material without applying the undercoat layer, the hydrogelated ink receiving layer was dried with a hot air dryer at 120 ° C. in the same manner as in Example 2. At this time, the air permeability of (back layer + paper substrate + ink receiving layer) was 1800 seconds.
Next, the ink receiving layer was wetted in the same manner as in Example 2, and then immediately dried with a mirror drum (surface temperature of 95 ° C.) while being pressure-bonded with a press roll to prepare an ink jet recording paper.

Example 4
"Formation of undercoat layer"
On one surface of the paper substrate, the coating liquid C having the following composition was coated with a bar so that the dry coating amount was 7 g / m ² and dried to obtain an undercoat layer. At this time, the air permeability of (paper base material + undercoat layer) was 100 seconds.
<Coating fluid C>
Acrylic emulsion latex as a binder in 100 parts by mass (solid content) of alkaline colloidal silica (manufactured by Nissan Chemical Co., Ltd., trade name: ST-20L, average particle size 0.045 μm, pore volume 0.2 ml / g, anionic) An aqueous dispersion (concentration: 20% by mass) was prepared by mixing 20 parts by mass (trade name: JK7000, manufactured by Meisei Chemical Co., Ltd.) and 13 parts by mass of borax in water.

"Formation of ink-receiving layer"
Next, the same coating liquid B as in Example 1 was applied onto the undercoat layer, the ink receiving layer was hydrogelated, and then dried with a hot air dryer at 120 ° C. The dry coating amount of the ink receiving layer was 18 g / m ² . At this time, the air permeability of (paper substrate + undercoat layer + ink receiving layer) was 900 seconds.

"Formation of back layer"
Next, an 8% aqueous starch solution was applied to the side opposite to the surface on which the ink receiving layer was provided in the same manner as in Example 1 so that the concentration was 1.5 g / m ² . At this time, the air permeability of (back layer + paper substrate + undercoat layer + ink receiving layer) was 2400 seconds.

"Glossy layer formation"
Next, at the nip between the mirror drum and the press roll, the ink receiving layer is on the mirror drum side, and the following coating solution D is supplied between the ink receiving layer and the mirror drum, and the coating is performed while pressing with the press roll. After that, it was dried as it is with a mirror drum (surface temperature is 95 ° C.) to form a glossy layer, and an ink jet recording paper was obtained. The dry coating amount was 1.5 g / m ² .
<Coating fluid D>
Cationic colloidal silica (produced by Grace, trade name: SJ4001, average particle size 0.04 μm) 100 parts by mass (solid content), emulsion type acrylic resin latex (average particle size: 0.06 μm, Tg = 100 ° C.) as a binder ) 10 parts by mass and 5 parts by mass of a release agent (ammonium oleate) were mixed in water to prepare an aqueous dispersion (concentration: 10% by mass).

Example 5
Inkjet recording paper was prepared in the same manner as in Example 1 except that the coating solution applied to the back layer was changed from an 8% starch aqueous solution to an 8% aqueous solution of polyvinyl alcohol having a saponification degree of 85. . At this time, the air permeability of (back layer + paper substrate + undercoat layer) was 1500 seconds.

Example 6
Inkjet recording paper was prepared in the same manner as in Example 5 except that the basis weight of the paper substrate used was changed to 180 g / m ² (thickness 205 μm). At this time, the air permeability of (back layer + paper substrate + undercoat layer) was 600 seconds.

Example 7
In Example 4, an inkjet recording paper was produced in the same manner as in Example 1 except that the back layer was applied before the undercoat layer was applied. At this time, the air permeability of (back layer + paper substrate + undercoat layer + ink receiving layer) was 2400 seconds.

Example 8
In the same manner as in Example 3, the undercoat layer was not applied, and the 8% borax aqueous solution was not applied on the base material. Immediately after coating to m ² , the ink receiving layer is hydrogelated by irradiating an electron beam with an accelerating voltage of 175 kV and an irradiation dose of 50 kGy by an electron beam irradiation device (electro curtain made by ESI) in a nitrogen gas environment. And dried with a hot air dryer at 120 ° C. to form an ink receiving layer.
Next, the back layer was applied in the same manner as in Example 4. At this time, the air permeability of (back layer + paper base material + ink receiving layer) was 2500 seconds.
Next, the ink receiving layer is placed on the mirror drum side at the nip portion between the mirror drum and the press roll, the coating liquid D of Example 4 is supplied between the ink receiving layer surface and the mirror drum, and the pressure is pressed by the press roll. Then, after coating, it was dried as it was with a mirror drum (surface temperature was 95 ° C.) to form a glossy layer, and an ink jet recording paper was obtained. The dry coating amount was 1.5 g / m ² .

[Comparative Example 1]
Inkjet recording paper was prepared in the same manner as in Example 1. However, finishing by the casting method was not performed.

[Comparative Example 2]
Inkjet recording paper was prepared in the same manner as in Example 1. However, a 4% borax aqueous solution was applied to the undercoat layer instead of the 8% borax aqueous solution. Small cracks were observed in the ink receiving layer of the obtained recording medium.

[Comparative Example 3]
Inkjet recording paper was prepared in the same manner as in Example 1. However, in place of the cationic polymer-silica composite particle dispersion A of Example 1, wet silica (manufactured by Tokuyama Corporation, trade name: Fine Seal X-30, average particle size: 3 μm, pore volume 2.0 ml / 10) parts by weight of a cationic compound having a 5-membered ring amidine structure (product name: SC-700M, molecular weight: 30,000) was added to 100 parts by weight of silica.

[Comparative Example 4]
Inkjet recording paper was prepared in the same manner as in Example 1. However, the back layer was not applied.

[Comparative Example 5]
Inkjet recording paper was prepared in the same manner as in Example 1. However, the coating amount of the back layer was changed from 1.5 g / m ² to 5 g / m ² .

[Comparative Example 6]
Inkjet recording paper was prepared in the same manner as in Example 1. However, the back layer was coated after being cast.

[Comparative Example 7]
Inkjet recording paper was prepared in the same manner as in Example 1. However, instead of coating the starch aqueous solution on the back layer, 5 g / m ^{2 of the following} coating solution E was applied.
<Coating fluid E>
To 100 parts by mass (solid content) of titanium dioxide (manufactured by Sakai Chemical Co., Ltd., trade name: R-21, average particle size 0.5 μm, pore volume 0.2 ml / g), an acrylic polymer (Rohm and Haas) as a binder An aqueous dispersion (concentration: 30% by mass) was prepared by mixing 20 parts by mass (trade name: Primal P-376, emulsion type adhesive) manufactured by the company in water.

Evaluation Method The obtained inkjet recording paper was evaluated for the color density, glossiness, environmental curl, and cockling of the recorded image by the following methods. For the evaluation, a dye ink jet printer (manufactured by EPSON, trademark: PM-G820, printing mode: EPSON photographic paper clean mode) was used. The evaluation results are shown in Table 1.

(1) Color density of recorded image Each color ink and heavy color portion were solid-printed, and the color density was measured with a Macbeth reflection densitometer (model: Macbeth RD-920, manufactured by Macbeth). The color density of black is shown in Table 1.

(2) Glossiness ISO-400 image ("High-definition color digital standard image data ISO / JIS-SCID", p13, image name: fruit basket) is printed on the tested ink jet recording paper, and the image is recorded. Visual observation was performed from the angle inclined with respect to the body surface, and the following four levels were evaluated.
A: There is a glossiness similar to that of a silver salt photograph.
○: Slightly inferior to silver salt photograph, but with sufficient gloss.
Δ: Glossy paper lacks glossiness.
X: There is almost no gloss and it is a level close to a mat.

(3) Environmental curl Recorded paper on which white paper of the tested inkjet recording paper and ISO-400 image (“high-definition color digital standard image data ISO / JIS-SCID”, p13, image name: fruit basket) are printed. Were placed in a room under the following conditions one by one in A4 size, and the curl situation was examined one day later.
(B) Normal temperature and humidity: Temperature 25 ° C, humidity 60%
(B) High temperature and high humidity: Temperature 35 ° C, humidity 85%
A: Blank paper and printed matter are both flat and flat under both conditions (a) and (b).
○: Under the condition (b), the printed material curls slightly on the printed surface, but does not cause a problem in use.
Δ: Under the condition (b), both blank paper and printed matter curl to the printing surface side.
×: Curling on the printing surface side for both blank paper and printed matter under the conditions of (A) and (B).

(4) Cock ring (Wave out of base paper)
The ink-jet recording paper (A4 size) that was tested was printed in solid green on the entire recording medium, and cockling immediately after printing was visually observed and evaluated in the following three stages.
A: Cockling is not seen at all.
○: Slight cockling is observed, but it is hardly noticeable.
X: Cock ring is conspicuous.

From Table 1, in an ink jet recording paper having an ink receiving layer finished on one side of a paper substrate by a casting method, or an ink receiving layer and a gloss developing layer finished on one side of a paper substrate by a casting method In addition, the peak in the pore diameter distribution curve of the ink receiving layer is substantially only 0.06 μm or less, and before finishing by the casting method, the air permeability (JIS-P-8117) is applied to the other surface of the substrate. ) Of the ink jet recording paper of the example in which the back layer mainly composed of a water-soluble resin is formed so as to be 500 to 3000 has improved curling and cockling in a high temperature and high humidity or low temperature and low humidity environment. The evaluation items were also good results.
On the other hand, the ink jet recording paper of the comparative example in which the ink receiving layer different from the peak in the pore diameter distribution curve was formed was inferior to any of the evaluation items. In addition, the inkjet recording paper of the comparative example in which the back layer is not formed so as to have the above air permeability, the back layer is formed after casting, or finishing by casting is not performed, all obtain good gloss. I could not.
Therefore, according to the present invention, the curling of the ink jet recording paper in the environment of high temperature and high humidity or low temperature and low humidity is improved, the cockling after printing is small, and the ink jet recording paper is excellent in gloss and image quality.

Claims (6)

In a method for producing an ink jet recording paper having an ink receiving layer finished on one side of a paper substrate by a casting method, or an gloss receiving layer finished on one side of a paper substrate by an ink receiving layer and a casting method, The peak in the pore diameter distribution curve of the ink receiving layer is substantially only 0.06 μm or less, and before finishing by the casting method, the air permeability (JIS-P) is applied to the other surface of the paper substrate. -8117) is a method for producing an ink jet recording paper, in which a back surface layer mainly composed of a water-soluble resin is formed so as to be 500 to 3000 seconds. The method for producing an inkjet recording paper according to claim 1, wherein the back layer is formed so that the air permeability is 1200 to 2500 seconds. Gas phase method silica, alumina, hydrated alumina having an average secondary particle diameter of 0.7 μm or less, wherein the inorganic pigment of the ink receiving layer is an aggregate of primary particles having an average primary particle diameter of 0.003 to 0.04 μm The method for producing an ink jet recording paper according to claim 1, wherein the ink jet recording paper is a product. The method for producing an ink jet recording paper according to any one of claims 1 to 3, wherein the water-soluble resin of the back layer is starch or polyvinyl alcohol having a saponification degree of 85 or more. An undercoat layer comprising an inorganic pigment having a pore volume by BET of 0.5 ml / g or less and an average primary particle diameter of 1 µm or less and an emulsion latex is provided between the paper substrate and the ink receiving layer. The manufacturing method of the inkjet recording paper as described in any one of 1-4. The gloss developing layer is a monodispersed colloidal pigment having an average primary particle diameter of 0.01 to 0.06 μm, alumina having an average secondary particle diameter of 1 μm or less, alumina hydrate, and an air having an average secondary particle diameter of 0.7 μm or less. The method for producing an inkjet recording paper according to any one of claims 1 to 5, comprising at least one pigment selected from the group consisting of phase method silica and wet gel method silica as a main component.