JP2007268928A - Inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording medium which has especially high gloss, enough ink absorbing properties and pigment ink suitability, and has a good surface strength of a coating layer, and is close to a texture of a photographic paper for a silver salt photograph. <P>SOLUTION: A cast-coat inkjet recording medium consisting of an ink absorbing layer, a gloss exhibiting layer and a protective layer on a substrate, is characterized in that the ink absorbing layer is a coating composition comprising a water-absorbing inorganic pigment, a latex, boric acid or its salt, the gloss exhibiting layer is a coating composition comprising a sub-micron pigment, and polyvinyl alcohol, and the protective layer at least comprises a colloidal silica with a primary particle diameter of ≥5 nm and ≤55 nm and a ratio of a secondary particle diameter to the primary particle diameter of 1.5-3.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet recording medium, and particularly to an ink jet recording medium having high gloss, sufficient ink absorption, suitable for pigment ink, and good surface strength of a coating layer, and close to the texture of photographic paper for silver salt photography. Is.

  In recent years, due to remarkable progress of inkjet printers and plotters, full-color and high-definition images can be easily obtained.

  The ink jet recording system records images, characters, and the like by causing micro droplets of ink to fly and adhere to a recording material such as paper according to various operating principles. Inkjet printers and plotters are rapidly spreading in various applications in recent years as hard copy creation apparatuses for image information such as letters and various graphics created by a computer. In particular, color images formed by the multi-color ink jet method can be recorded inferior to multi-color printing by the plate making method and printing by the color photographic method, and in applications where the number of copies is small. Is widely applied because it is cheaper than printing and photographic technologies. In particular, with the recent rapid digitization and the spread of digital cameras, the ink jet recording method has been used as an output method for digital data, that is, as an alternative method for silver salt photography.

  In particular, with the advancement of ink jet printer technology, price reduction, and the spread of digital cameras, it has become possible to easily output photos at home. In order to reproduce gradation smoothly or to make ink dots that form an image inconspicuous, current printers use inks that are lighter than conventional ones to reduce the size of ink droplets or reduce the size of ink droplets. Accordingly, by changing the size of the recording medium, a recorded material having an image quality equal to or higher than that obtained by a general silver salt photography method is being obtained. As a result, the amount of ink used for image formation has increased compared to the prior art, and along with this, ink jet recording media are required to have a property of absorbing and drying ink sufficiently and quickly. In addition, the same texture and storability as photographic paper used in silver salt photography, that is, gloss and scratch resistance, have been demanded.

  Further, in the case of a use for outputting a photographic image, the use is for indoor / outdoor exhibition or personal record storage, so that weather resistance and image storage stability of images are required more than ever. In response to such demands, inks and papers have been improved, and much better storage stability than before can be obtained. However, in particular, the light resistance has not yet reached the level of silver salt photography, and the current situation is that the requirements are not satisfied.

  In order to satisfy such demands, pigment type inks have recently been used. It is known that the pigment ink has little light deterioration and does not re-dissolve with water, so that the weather resistance and the image storage stability are improved as compared with the dye type ink. However, the color material pigment used in the pigment ink is insoluble in the solvent unlike the dye. Therefore, it is necessary to stably disperse the color material pigment, and the ratio of the color material pigment in the pigment ink cannot be easily increased. In addition, the coloring efficiency is not high like a dye type ink, and it is difficult to obtain a clear color. Therefore, the amount of ink used for image formation tends to be larger than that of dye ink. In particular, boundary bleeding (bleeding) is likely to occur between heavy color portions with a large amount of ink.

  As a method for improving the coloring efficiency of the pigment ink, that is, the color developability, a method of reducing the dispersed particle diameter of the colorant pigment is conceivable (for example, see Patent Document 1). The study of atomizing the average dispersed particle size of the pigment ink has been made for a long time (for example, see Non-Patent Documents 1, 2, and 3), and is a very effective means for improving the color developability. However, reducing the average dispersed particle size reduces the light resistance that is characteristic of pigment inks. Further, the surface energy of the particles increases due to the atomization of the colorant pigment particles, and the dispersion stability is impaired. If the colorant pigment particles themselves are atomized and an excessive dispersant is added to ensure dispersion stability, the pigment ink becomes more penetrating into the ink jet recording paper, and the colorant pigment ink jet recording paper. Since the abundance ratio in the vicinity of the surface decreases, the color developability may decrease.

  In particular, along with recent progress in inkjet technology, inkjet recording paper with gloss has been frequently used in response to the fact that inkjet recording has been used as an alternative to silver halide photography. Conventionally, cast coated paper as proposed in Patent Documents 2 and 3 has been used as an inkjet recording medium having gloss. However, although the recording medium manufactured by these technologies has a certain level of gloss, it cannot be said that it has the same texture as photographic paper used for silver salt photography, and an inkjet printer that can realize the current photographic image quality. When used in the ink, the ink absorbability and the sharpness of the image were not sufficient.

  Further, as in Patent Document 4, a three-layer structure in which an intermediate layer made of cationic fine particles is provided on an ink absorption layer and a gloss layer mainly composed of colloidal silica is provided thereon in order to achieve high gloss. Inkjet recording papers have been proposed. Although it is possible to obtain high gloss by this method, it is difficult to avoid cracks on the surface of the coating layer, and when printed with pigment ink, the color developability is lowered. Further, as in Patent Document 5, by using colloidal silica in which the elongation percentage of the binder of the ink receiving layer is within a specific range and spherical colloidal silica having a primary particle diameter of 10 to 100 nm is aggregated in a tuft shape as a pigment. Ink jet recording paper in which cracks on the outermost surface of the coating layer are controlled has been proposed. However, even by this method, cracks cannot be completely eliminated, and the surface strength of the coating layer is lowered.

  In order to achieve the same texture, high gloss, ink absorbency and color development as photographic paper for silver salt photography, a glossy layer containing alumina hydrate and polyvinyl alcohol is provided as in Patent Document 6, for example. Ink jet recording paper has been proposed in which this is treated with a treatment liquid containing boric acid or borate, and then pressed and dried on a mirror drum heated in a wet state. By this method, cracks on the outermost surface of the coating layer can be reduced and high gloss can be obtained, but the thickness of the coating layer is increased to absorb the ink in a single layer, and a crosslinking agent is used. Therefore, embrittlement of the coating layer becomes remarkable, and cracking of the coating layer may easily occur when stress such as bending is applied. In addition, the surface of the coating layer formed of alumina hydrate tends to diffusely reflect light due to rubbing, and some scratches are very conspicuous and the texture is impaired.

Further, as in Patent Document 7, a porous material containing boehmite and polyvinyl alcohol on the treated surface of a substrate surface-treated with one or more selected from the group consisting of boric acid or borate and a paper surface treating agent An ink jet recording material having an ink absorbing layer or a coating comprising a borax aqueous solution, fine silica particles and polyvinyl alcohol on a first coating layer comprising a pigment, polyvinyl alcohol, and a cationic compound, as in the example of Patent Document 8. Inkjet recording paper has been proposed in which a working solution is applied wet-on-wet, dried, and further provided with a third coating layer made of colloidal silica and polyvinyl alcohol. However, when the aqueous solution of the crosslinking agent of the hydrophilic binder is applied to the coating layer as described above, the coating unevenness caused by the coating layer state and the coating method to be applied causes uneven crosslinking, and a uniform surface without cracks. It was difficult to form, and it was very difficult to provide a paper satisfying the same texture as silver salt photographic printing paper, scratch resistance of the coating layer surface, and suitability for pigment ink.
JP 2003-55951 A (page 4) JP-A-63-264391 Japanese Patent Laid-Open No. 2-27487 JP 2004-195781 A JP 2005-1334 A JP 2002-293004 A JP 11-291621 A JP 2004-167959 A (page 12) Color materials lecture material "Current status of ink-jet color materials and recent research trends", Color Material Association, October 2000, pages 23-34 IS &T's NIP13 、 D. E. Burner, 1997, 667-669. Coloring material, 1998, Vol 7, [7], pp. 458-464.

  An object of the present invention is to provide an ink jet recording medium which has been difficult to realize in the past, has particularly high gloss, sufficient ink absorbability, suitability for pigment ink, and good surface strength of a coating layer.

  As a result of studying this problem, in the ink jet recording medium of the present invention, that is, in the cast coat ink jet recording medium comprising an ink absorbing layer, a glossy expression layer and a protective layer on a gas-permeable support, the ink absorbing layer is water-absorbing. Coating composition containing inorganic pigment, latex, boric acid or its salt, gloss developing layer is submicron pigment, coating composition containing polyvinyl alcohol, primary particle diameter is 5 nm or more and 55 nm or less in protective layer and primary It is characterized by containing at least colloidal silica having a ratio of the secondary particle diameter to the particle diameter of 1.5 to 3.0, and has particularly high gloss, sufficient ink absorption, and pigment ink suitability. In addition, it is possible to provide a cast-coated inkjet recording medium having a coating layer with good surface strength and close to the texture of photographic paper for silver salt photography. It was.

  In particular, when the submicron pigment of the gloss developing layer coating composition is an alumina hydrate, it is possible to obtain particularly high gloss.

  In addition, by using wet synthetic silica as the water-absorbing inorganic pigment in the coating composition of the ink absorbing layer, it is possible to obtain an ink jet recording medium having excellent ink absorbability.

  Furthermore, since the coating composition of the ink absorbing layer contains colloidal silica, it is possible to obtain an ink jet recording medium having particularly excellent ink absorbability.

  According to the present invention, there can be obtained an ink jet recording medium having a particularly high gloss, sufficient ink absorptivity and suitability for pigment ink, which has not been obtained conventionally, and having a good surface strength of the coating layer.

  Hereinafter, the inkjet recording material of the present invention will be described in detail.

  In the present invention, paper is usually used as the air-permeable support, but a support other than paper, such as a nonwoven fabric, can be used as necessary.

  In the present invention, the cast treatment refers to pressing a coated layer in a wet state onto a heated mirror surface, transferring the mirror surface shape to the surface of the coating layer, and removing moisture from the coated layer to dry the recording medium. Say the process to give. The apparatus used for the casting process (casting apparatus) is usually an apparatus having a structure in which the coated paper is continuously crimped to the surface of the cylinder whose surface is chrome-plated using an elastic roll. An apparatus having another structure having the same action may be used. As a method of casting used for producing the ink jet recording medium of the present invention, a so-called rewetting method in which a coating composition is coated, dried once, reapplied with moisture, and then pressure-bonded to a mirror surface of a casting apparatus, coating A method such as a so-called coagulation method (gelation method) can be used in which a coating composition is applied to a mirror surface of a casting apparatus after the coating composition is wet and then gelled by a coagulation treatment. .

  In the present invention, the ink absorbing layer refers to a coating layer formed on the side closer to the support of the recording medium, and in the present invention, the gloss developing layer refers to a coating formed on and formed on the ink absorbing layer. Say the construction layer. These coating compositions are usually used in the form of an aqueous liquid in which each material is dissolved or dispersed in water. In the present invention, the ink absorbing layer and the gloss developing layer are usually adjacent to each other, but one or two layers are provided between the ink absorbing layer and the gloss developing layer as long as the interaction between the ink absorbing layer and the gloss developing layer is not strongly inhibited. One or more intermediate layers may be provided, and one or two or more coating layers may be provided between the ink absorbing layer and the support. In the present invention, the protective layer refers to a coating layer formed on the outermost surface, which is a coating layer formed by drying a coating composition in a wetting liquid or a coagulating liquid by a casting process.

  In the present invention, the water-absorbing inorganic pigment means that water is used in place of linseed oil, and when a test according to the test method for oil absorption defined in JIS K 5101 is performed, 100 ml or more of water per 100 g is reached by the end point. Examples of inorganic pigments used include heavy calcium carbonate, light calcium carbonate, wet synthetic silica, diatomaceous earth, calcium silicate, talc, magnesium hydroxide, halloysite, activated clay, acid clay, hydrotalc. Site, alumina hydrate, aluminum hydroxide, bentonite clay, zeolite, kaolin, calcined kaolin, gypsum, titanium oxide, barium sulfate and the like. One of these pigments may be used alone, or two or more thereof may be used in combination.

  Among such water-absorbing inorganic pigments, wet synthetic silica is particularly preferably used because an inkjet recording medium having good ink absorbability can be obtained even with a small coating amount. In the present invention, wet synthetic silica refers to porous silicon dioxide obtained by mixing a silicate such as sodium silicate and an acid such as sulfuric acid, followed by steps such as washing, aging and pulverization. As the production method, a precipitation method and a gel method are known, and any of them can be preferably used for the ink absorbing layer coating composition of the present invention.

  The oil absorption amount of the wet synthetic silica used in the ink absorbing layer coating composition of the present invention is preferably high from the viewpoint of ink absorbency, but if the oil absorption amount is too high, the strength of the coating layer may be reduced. . Specifically, the oil absorption amount of the wet synthetic silica used in the ink absorbing layer coating composition of the present invention is preferably 1 to 5 ml / g, and more preferably 2 to 4 ml / g. In addition, if the particle size of the wet synthetic silica used in the ink absorbing layer coating composition of the present invention is too small, the viscosity of the coating composition may increase and the coating operation may be difficult. The gloss of the recording medium after processing may be difficult to express. Specifically, the particle diameter of the wet synthetic silica used in the ink absorbing layer coating composition of the present invention measured by the Marvin method is preferably 2 to 20 μm, and more preferably 3 to 15 μm.

The amount of boric acid or its salt added to the ink-absorbing layer coating composition of the present invention depends on the pH of the coating composition, but if it is too small, the glossy layer after drying will crack and gloss. If the amount is too large, the strength of the coating layer may decrease. Therefore, the water-absorbing inorganic pigment is converted to H ₃ BO ₃ on the basis of the boron atom to 0.2 to 10%. It is preferable to set it as the mass%, and it is more preferable to set it as 0.4-5 mass%.

In the present invention, it is preferable that the ink absorbing layer contains colloidal silica because an ink jet recording medium having particularly excellent ink absorbability can be obtained. In the present invention, colloidal silica is a method in which an acid such as sulfuric acid is allowed to act on an aqueous silicate solution such as sodium silicate, or a metal ion is removed by a cation exchange resin and then a process such as aging is performed. It is an aqueous dispersion of a silicate polymer to be produced, and is usually composed of spherical silicate particles having a specific surface area of 15 to 700 m ² / g by BET method.

As the colloidal silica used for the ink absorbing layer of the present invention, when the specific surface area is too small, the gloss after casting may be difficult to express, and when the specific surface area is too large, Since the effect of improving ink absorbency may not be sufficient, those having a specific surface area of 50 to 500 m ² / g by BET method are preferably used, and those having a specific surface area of 100 to 350 m ² / g are more preferably used. In addition, if the amount of colloidal silica added in the present invention is too small, the effect of improving ink absorbency may not be sufficient, and if it is too large, gloss after casting may be difficult to express. It is preferable to set it as 10-100 mass% with respect to the addition amount of, and it is more preferable to set it as 15-60 mass%.

  In the present invention, latex refers to a liquid material in which a substantially water-insoluble thermoplastic polymer compound is dispersed in water, and once dried, the latex is substantially insoluble in hot water. Is distinguished from the aqueous solution. Examples include vinyl acetate polymer, ethylene-vinyl acetate copolymer, (meth) acrylic acid ester polymer, styrene- (meth) acrylic acid ester copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene. Copolymers, isoprene copolymers, chloroprene copolymers, urethane-based polymers, copolymers in which two or more of the monomers constituting these polymers are combined in a random, graft or block manner, etc. And an aqueous dispersion of the synthetic polymer compound, natural rubber latex, and the like. One of these latexes may be used alone, or two or more thereof may be used in combination.

  In the present invention, if the amount of latex added to the ink absorbing layer coating composition is too small, the mechanical strength of the resulting recording medium may not be sufficient, and if it is too large, the ink absorbability will be insufficient. Or the gloss after casting may not be sufficiently obtained, the latex / (water-absorbing inorganic pigment + colloidal silica) mass ratio is preferably 10/100 to 60/100, and 15/100 to More preferably, it is 40/100.

  The ink absorbing layer coating composition of the present invention contains a water-soluble polymer compound such as a vinylpyrrolidone polymer, a (meth) acrylic acid polymer, and a (meth) acrylamide polymer to the extent that the effects of the present invention are not impaired. It can also be added. However, it is preferable that the water-soluble polymer compound having high crystallinity such as polyvinyl alcohol is not substantially contained since the gloss of the ink jet recording medium obtained after the casting treatment is remarkably lowered.

  In the present invention, the submicron pigment means that when the dispersion is dispersed on a substrate and observed with a scanning electron microscope, 80% or more of the area occupied by the particles in the observation field is composed of particles having a long side of 1 μm or less. It refers to the occupied inorganic pigment. The type of submicron pigment used in the glossy layer coating composition of the present invention is not particularly limited, and examples thereof include gel method silica, precipitation method silica, colloidal silica, gas phase method silica, gas phase method alumina, and pseudoboehmite. be able to. In particular, it is preferable to use an inorganic pigment in which particles having a long side of 400 nm or less occupy 80% or more of the area occupied by the particles in the observation field because particularly high surface gloss can be obtained. Further, when an inorganic pigment occupying 80% or more of the area occupied by the particles in the observation field and particles having a long side of 100 nm or more is used, the coating layer can be applied even if the glossy layer coating composition is dried at high speed after coating. It is preferable because defects such as tearing are not likely to occur.

As the submicron pigment used in the glossy layer coating composition of the present invention, a pigment having a specific surface area of a certain level or more is preferable because a high print density can be obtained. On the other hand, if the specific surface area is too large, the ink absorbability may decrease. Specifically, it is preferable to use one having a specific surface area of 60 to 600 m ² / g by the BET method, and more preferably 150 to 400 m ² / g. In addition, the pigment having such a specific surface area is usually a pigment formed by forming a higher order structure in which primary particles having a diameter of several tens of nm or less are combined and voids are formed inside the primary particles.

In the present invention, it is preferable to use alumina hydrate as the submicron pigment of the glossy layer coating composition because an inkjet recording medium having particularly high gloss can be obtained. The alumina hydrate used in the present invention can be represented by the general formula Al ₂ O ₃ .nH ₂ O. Alumina hydrates are classified into dipsite, vialite, norstrandite, boehmite, boehmite gel (pseudoboehmite), diaspore, amorphous amorphous, etc., depending on the composition and crystal form. In particular, in the above formula, when the value of n is 1, it represents an alumina hydrate having a boehmite structure, and when n is more than 1 and less than 3, it represents an alumina hydrate having a pseudo boehmite structure, where n is 3 or more represents an amorphous alumina hydrate. In particular, the preferred alumina hydrate for the present invention is an alumina hydrate having a pseudo boehmite structure in which at least n is more than 1 and less than 3.

  In order to stabilize the dispersion of alumina hydrate, various acids are usually added to the dispersion. Examples of such acids include nitric acid, hydrochloric acid, hydrobromic acid, acetic acid, formic acid, ferric chloride, aluminum chloride and the like, but the present invention is not limited thereto.

  The alumina hydrate used in the present invention can be produced by a known method such as hydrolysis of aluminum alkoxide such as aluminum isopropoxide, neutralization of aluminum salt with alkali, hydrolysis of aluminate. The physical properties of alumina hydrate, such as particle size, pore size, pore volume, and specific surface area, should be controlled by conditions such as precipitation temperature, aging temperature, aging time, solution pH, solution concentration, and coexisting compounds. Can do.

  As methods for obtaining alumina hydrates from alkoxides, JP-A-57-88074, JP-A-62-256321, JP-A-4-275717, JP-A-6-64918, JP-A-7-10535, JP-A-7-267633, US Pat. No. 2,656,321 and the like disclose a method for hydrolyzing aluminum alkoxide. These aluminum alkoxides include isopropoxide, 2-butoxide and the like.

  The alumina hydrate used in the present invention is preferably an alumina hydrate having an average primary particle size of 3 nm to 40 nm. A particularly preferable average primary particle diameter is 5 nm to 30 nm.

  As the polyvinyl alcohol used in the glossy layer coating composition of the present invention, polyvinyl alcohol having various saponification degrees from 70 mol% to 100 mol% can be used. It is preferable because it becomes easy. Also, modified polyvinyl alcohol in which various functional groups such as silyl group, carboxyl group, amino group, and acetoacetyl group are introduced, and other monomers such as ethylene are introduced randomly, grafted, or in blocks are also used. Can do. If the amount of polyvinyl alcohol added in the present invention is too small, cracks may occur during drying, or the surface strength of the formed inkjet recording medium may be insufficient. Absorbability may be reduced. Specifically, the addition amount of polyvinyl alcohol is preferably 2 to 40% by mass, more preferably 5 to 25% by mass of the submicron pigment.

  Since the polyvinyl alcohol of the glossy layer coating composition of the present invention has a higher viscosity of its aqueous solution, cracks are less likely to occur when the coated coating composition is dried even if the amount added is relatively small. The addition amount can be reduced, and as a result, the ink absorbability can be improved, which is preferable. On the other hand, if the viscosity of the aqueous solution is too high, the viscosity of the coating composition obtained according to the present invention may become too high, making the coating operation difficult. Specifically, the viscosity of an aqueous solution having a solid content concentration of 4% by mass measured at 25 ° C. using an Ubbelohde viscometer based on JIS Z8803 is preferably 15 to 400 mPa · sec, and 30 to 200 mPa · sec. More preferably. One of these polyvinyl alcohols may be used alone, or two or more thereof having different saponification degree, viscosity, modification and the like may be used in combination.

  In the present invention, the wetting liquid refers to re-wetting the coating layer coated on the support during the rewetting casting process, and press-drying the coating layer on a heated mirror drum in a wet state. It has the function of a so-called rewet liquid that efficiently transfers the surface of the mirror drum to the coating layer and a further surface modification effect by the component of the wetting liquid. Further, in the present invention, the coagulating liquid means that the surface of the mirror drum is efficiently applied to the coating layer by coagulating (gelling) the polyvinyl alcohol of the gloss developing layer during the coagulation method casting treatment and drying it by pressure on the heated mirror drum. It has both the function of transferring to the surface and the further surface modification effect by the coagulating liquid constituents. As the coagulation liquid, any aqueous solution containing a compound capable of coagulating polyvinyl alcohol can be used, but an aqueous solution containing boric acid or a salt thereof alone or mixed is particularly preferable. .

  In the present invention, the average primary particle diameter is 5 nm to 55 nm in the wetting liquid or the coagulation liquid, and the ratio of the secondary particle diameter to the primary particle diameter (secondary particle diameter / primary particle diameter) is from 1.5. At least colloidal silica of 3.0 is contained. By including this in the wetting liquid or coagulating liquid, the colloidal silica can be efficiently distributed in the vicinity of the surface of the glossy layer, and as a result, a protective layer having high gloss and ink absorbability and surface strength is obtained. It became possible.

  The colloidal silica contained in the wetting liquid or coagulating liquid of the present invention is a spherical single colloidal that accounts for 80% or more of the area occupied by particles in the observation field when the dispersion is dispersed on a substrate and observed with a scanning electron microscope. The particles are composed of 2 to 3 continuous (aggregated) silica (primary particles). Such an agglomerated state is expressed as an eyebrow for convenience. The ratio of the secondary particle diameter to the primary particle diameter of the colloidal silica (secondary particle diameter / primary particle diameter) is preferably 1.5 to 3.0 because good ink absorbability can be obtained. More preferably, it is 1.5-2.5. Furthermore, it is preferable that the primary particle diameter of the colloidal silica is 5 nm or more and 55 nm or less because a high printing density can be obtained. More preferably, it is 10 nm or more and 40 nm or less. As colloidal silica which can be used by this invention, the brand name Quarton made from Fuso Chemical Industry can be mentioned, for example. A state where at least 5 or more, usually 10 or more spherical single colloidal silicas are aggregated is represented as a chain for convenience.

  The ionicity of the colloidal silica used in the wetting liquid or coagulation liquid of the present invention is not particularly limited, and is usually a general anionic colloidal silica, a cationic resin such as a quaternary ammonium salt on the particle surface, an aluminum compound, etc. Cationic colloidal silica treated with can be used. In particular, anionic colloidal silica reacts strongly with a glossy layer coating composition that is cationic in ionicity even without a water-soluble binder such as polyvinyl alcohol, and the surface coating layer does not hinder ink absorbability. It is preferable because the strength is greatly increased.

  In the present invention, it is preferable to incorporate a surfactant in the wetting liquid together with the colloidal silica. By adding a surfactant to the wetting liquid of the present invention, adhesion of the wetting liquid to the coating layer becomes uniform, and the uniformity of the finally formed surface is significantly improved. The surfactant used here is not particularly limited as long as there is no problem with miscibility with colloidal silica, and is usually a general surfactant, for example, a dialkylsulfosuccinate such as sodium bis (2-ethylhexyl) sulfosuccinate. Anionic surfactants such as ammonium salts of polyoxyethylene alkyl ether sulfates, sodium dodecyl benzene sulfonate and sodium laurate; cationic surfactants such as fatty acid amine salts, quaternary ammonium salts, sulfonium salts and phosphonium; Non-ionic such as polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkylamine, acetylene glycol Such as sexual surfactants can be used. In particular, acetylene glycol-based surfactants are preferable because the wetting liquid can be uniformly attached to the surface of the coating layer without foaming and can impart an appropriate swelling effect.

  The surfactant adjusts the wettability of the gloss developing layer surface and the wetting liquid, has an effect of uniformly wetting with the wetting liquid, and an effect of promoting re-swelling of the coating layer to be rewet. The concentration of the surfactant in the wetting liquid is not particularly limited. However, if the amount is too small, the surface of the coating layer may not be uniformly wetted. If the amount is too large, the wetting liquid may penetrate into the coating layer. The amount is preferably in the range of 0.005% by mass to 0.05% by mass, since it may cause a decrease in coating layer strength and poor gloss.

In the present invention, it is desirable that the wetting liquid is provided in an amount necessary and sufficient for re-swelling the coating layer. The amount of the wetting liquid depends on the cast treatment equipment, the time from wetting to the cast treatment, the coating layer for re-swelling, etc. However, it is preferably about 40 to 120 g / m ² in terms of the amount of adhesion immediately after wetting. Here, when the adhesion amount of the wetting liquid is less than 40 g / m ² , the coating layer is not sufficiently re-swelled, and the gloss may be deteriorated or the gloss may be partially lost. . Moreover, when the adhesion amount exceeds 120 g / m ² and is excessive, irregularities appear on the surface of the coating layer after the casting treatment, and the surface quality may be deteriorated.

In the present invention, it is desirable that the coagulation liquid is applied in an amount necessary and sufficient for gelling the coating layer, and the amount of the coagulating liquid is cast processing equipment, the time from gelation to cast processing, and the coating layer to be gelled. Although it varies depending on the concentration of boric acid or a salt thereof in the coagulation liquid, it is preferably about ²⁰ to 80 g / m ² in terms of the adhesion amount at the time of gelation. Here, when the adhesion amount of the coagulating liquid is less than 20 g / m ² , the coating layer is not sufficiently gelled, which may cause a gloss failure such that the gloss is lowered or the gloss is not partially obtained. . Moreover, when the adhesion amount exceeds 80 g / m < ² > and is excessive, unevenness may appear on the surface of the coating layer after the casting treatment, and the surface quality may deteriorate.

The coating amount of the protective layer formed on the outermost surface of the coating layer by the wetting liquid or the coagulating liquid in the present invention is not particularly limited as long as it does not deteriorate various properties as an inkjet recording medium. From the characteristics such as surface strength and gloss, 0.3 to 5 g / m ² is preferable, and 1 to 3 g / m ² is more preferable. Further, the concentration of colloidal silica in the wetting liquid and coagulation liquid in the present invention is not particularly limited, but from the above coating amount of the protective layer necessary to maintain good characteristics as an inkjet recording medium, 0.5 mass%-5 mass% are preferable, and 1-3 mass% is still more preferable. Here, when the concentration of colloidal silica is too low, that is, when the amount of dry adhesion is small, the effect of improving the surface strength may be particularly low, and when the concentration of colloidal silica is high, that is, when the amount of dry adhesion is large, The color developability may decrease, and the glossiness of the surface may become glaring.

  A water-soluble binder, a thermoplastic resin and an emulsion, an ink fixing agent, and the like can be added to the wetting liquid or the coagulating liquid in the present invention as long as the characteristics of the final inkjet recording medium are not deteriorated.

  For each coating layer of the present invention, various additives such as a surfactant, an antifoaming agent, a thickening agent, a color adjusting agent, a fluorescent brightening agent, an antioxidant, and an ultraviolet absorber are added as necessary. It can also be added.

  In the present invention, there is no particular limitation on the method of applying the coating composition of each coating layer, or the method of adhering the wetting liquid or the coagulating liquid to the coating layer. Air knife coater, blade coater, rod blade coater, bar Various coating methods such as a coater, a reverse roll coater, a comma coater, a gate roll coater, a film transfer coater, a lip coater, a die coater, and a curtain coater can be used. Among these, the curtain coater has a high uniformity of the obtained coating layer, and also gives a very good surface quality that prevents the coating composition from penetrating into the ink absorption layer when coating the glossy layer. Therefore, it is particularly preferably used for coating of the glossy layer coating composition.

There are no particular restrictions on the amount of the ink-absorbing layer and gloss-applying layer coating composition of the present invention applied on the support, but in order to achieve both ink absorbency and economy, each layer is usually a solid component. each it is preferable to coat the 10 to 30 g / ^{m 2} in total of 5 to 20 g / ^{m 2} the two layers. However, particularly when it is required to absorb a large amount of ink, it may be preferable to apply a maximum of about 50 g / m ^{2 in} total for both layers.

  Further, after the ink absorbing layer coating composition or the gloss developing layer coating composition is applied and dried, or after both, the smoothness is increased by a calendar device such as a soft calendar or a super calendar, and then the cast treatment is performed. It is also possible.

  In addition, a release agent such as an oily substance or an aqueous dispersion of an oily substance may be added to the coating composition, the wetting liquid or the coagulating liquid for the purpose of improving the peelability from the mirror surface in the casting apparatus. It is preferable that coating is performed prior to the casting process, which enables stable production over a long period of time. Examples of substances that can be used as a release agent in the present invention include higher alkylamines such as dimethyloctylamine and dimethyloctadecylamine or salts thereof, higher alkyl quaternary ammoniums such as trimethyloctylammonium chloride and trimethyloctadecylammonium chloride. Examples thereof include salts, higher carboxylic acids such as oleic acid, stearic acid and caprylic acid or salts thereof, higher alcohols such as octyl alcohol and octadecyl alcohol, liquid paraffin, polyethylene wax and silicone oil.

  Examples of the present invention will be described below. In the examples, unless otherwise specified, parts are parts by mass, and% is mass%.

[Example 1]
[Preparation of Ink Absorbing Layer Coating Composition 1]
6 parts of sodium tetraborate decahydrate (0.97 parts in terms of H ₃ BO ₃ ) was dissolved in 350 parts of water, and 100 parts of wet synthetic silica (Fine Seal X-37B manufactured by Tokuyama Corporation) was added thereto. It was fully dispersed using a disperser having a post-saw blade. Next, 83.3 parts (solid content 40 parts) of styrene-butadiene (SBR) latex having a solid content of 48% (JSR Corporation 0623N) was added and mixed to obtain an ink absorbing layer coating composition 1. In addition, about the wet synthetic silica used here, water was used instead of linseed oil, and when a test according to the oil absorption test defined in JIS K 5101 was performed, 300 ml of water per 100 g was obtained by the end point. Used.

[Preparation of Alumina Hydrate Sol]
1 part of acetic acid is mixed with 299 parts of water, 100 parts of alumina hydrate having a pseudo boehmite structure (Dispersal HP14 manufactured by Sasol, average primary particle diameter: 14 nm) is added, and the mixture is stirred as it is for 2 hours to peptize, An alumina hydrate sol having a solid concentration of 25% was obtained. When this dispersion was diluted 100 times with water, dispersed on a glass substrate and observed with a scanning electron microscope, 80% or more of the area occupied by particles in the observation field was occupied by particles having a long side of 100 to 400 nm. It was.

[Preparation of glossy layer coating composition 1]
To 100 parts (solid content 25 parts) of the alumina hydrate sol obtained above, a 10% aqueous solution of polyvinyl alcohol (PVA235 manufactured by Kuraray Co., Ltd.) having a saponification degree of 88 mol% and a 4% aqueous solution having a viscosity of 95 mPa · s at 25 ° C. 70 parts (7 parts of solid content) were added, and glossy layer coating composition 1 was prepared.

[Preparation of Wetting Solution 1]
Eyebrow colloidal silica having a solid content of 20% in 89.975 parts of water (Quortron PL-2 manufactured by Fuso Chemical Co., Ltd., primary particle diameter 23 nm, secondary particle diameter 51 nm, secondary particle diameter / primary particle diameter 2.2) 10 Part (2 parts solids) was added, and then 0.025 part of a 100% solids surfactant (Olfin E1010; manufactured by Nissin Chemical Industry Co., Ltd.) was added and mixed to obtain Wetting Liquid 1.

[Preparation of inkjet recording medium]
^On a base paper having a basis weight of 157 g / m ² (Diafoam manufactured by Mitsubishi Paper Industries Co., Ltd.), the ink absorbing layer coating composition 1 is applied using an air knife coater so that the coating amount after drying is 10 g / m ^2. And dried using a hot air dryer. Subsequently, after processing the obtained coated paper using a soft calender, the gloss expression layer coating composition 1 was coated using an air knife coater so that the mass after drying was 10 g / m ^2, and hot air was applied. It was dried using a mold dryer. Furthermore, the obtained coated paper was processed using a soft calendar. The coated surface of this coated paper was wetted by contacting with the wetting liquid 1 for 5 seconds, and then pressure-bonded to a mirror surface chrome plating cylinder of a casting apparatus heated to a temperature of 95 ° C. at a linear pressure of 20 kN / m and a speed of 25 m / min. The ink jet recording medium of Example 1 was produced by peeling from the cylinder after drying. At this time, the amount of the wetting liquid deposited before drying was 64 g / m ² , and the coating amount of the protective layer was 1.3 g / m ² .

[Example 2]
An inkjet recording medium of Example 2 was obtained in the same manner as in Example 1 except that the wetting liquid 1 of Example 1 was changed to the following wetting liquid 2. The coating amount of the protective layer at this time was 0.6 g / m ² .
[Preparation of Wetting Solution 2]
Eyebrow colloidal silica with a solid content of 20% in 94.975 parts of water (Quortron PL-2 manufactured by Fuso Chemical Co., Ltd., primary particle diameter 23 nm, secondary particle diameter 51 nm, secondary particle diameter / primary particle diameter 2.2) 5 Part (solid part 1 part) was added, and then 0.025 part of a 100% solid surfactant (Olfin E1010; manufactured by Nissin Chemical Industry Co., Ltd.) was added and mixed to obtain a wetting liquid 2.

[Example 3]
An ink jet recording medium of Example 3 was obtained in the same manner as Example 1 except that the wetting liquid 1 of Example 1 was changed to the following wetting liquid 3. The coating amount of the protective layer at this time was 3.2 g / m ² .
[Preparation of Wetting Solution 3]
Mayuform colloidal silica with a solid content of 20% in 74.975 parts of water (Quortron PL-2 manufactured by Fuso Chemical Co., Ltd., primary particle size 23 nm, secondary particle size 51 nm, secondary particle size / primary particle size 2.2) 25 Part (5 parts solids) was added, and then 0.025 part of a 100% solids surfactant (Olfin E1010; manufactured by Nissin Chemical Industry Co., Ltd.) was added and mixed to obtain Wetting Liquid 3.

[Example 4]
An inkjet recording medium of Example 4 was obtained in the same manner as in Example 1 except that the wetting liquid 1 of Example 1 was changed to the following wetting liquid 4. The coating amount of the protective layer at this time was 0.3 g / m ² .
[Preparation of Wetting Solution 4]
Eyebrows colloidal silica having a solid content of 20% in 97.475 parts of water (Quortron PL-2 manufactured by Fuso Chemical Co., Ltd., primary particle diameter 23 nm, secondary particle diameter 51 nm, secondary particle diameter / primary particle diameter 2.2) 2 0.5 parts (0.5 parts solids) is added, and then 0.025 part of a 100% solids surfactant (Olfin E1010; manufactured by Nissin Chemical Industry Co., Ltd.) is added and mixed to prepare the wetting liquid 4. Obtained.

[Example 5]
An ink jet recording medium of Example 5 was obtained in the same manner as Example 1 except that the ink absorbing layer coating composition 1 of Example 1 was changed to the following ink absorbing layer coating composition 2. The coating amount of the protective layer at this time was 1.3 g / m ² .
[Preparation of Ink Absorbing Layer Coating Composition 2]
6 parts of sodium tetraborate decahydrate (0.97 parts in terms of H ₃ BO ₃ ) are dissolved in 350 parts of water, and colloidal silica having a BET specific surface area of 230 m ² / g and a solid content of 40% (Nissan Chemical Industries) 25 parts (Snow part 10 parts) of Snowtex 40) were added. Further, after adding 100 parts of wet synthetic silica (Fine Seal X-37B manufactured by Tokuyama Corporation), the mixture was sufficiently dispersed using a disperser having a saw blade. Subsequently, 83.3 parts (solid content 40 parts) of SBR latex (JSR company 0623N) with a solid content of 48% was added and mixed to obtain an ink absorbing layer coating composition 2.

[Example 6]
An inkjet recording medium of Example 6 was obtained in the same manner as in Example 1 except that the wetting liquid 1 of Example 1 was changed to the following wetting liquid 5. The coating amount of the protective layer at this time was 1.3 g / m ² .
[Preparation of Wetting Solution 5]
Mayuform colloidal silica with solid content of 12% in 83.308 parts of water (Quortron PL-1, Fuso Chemical Co., Ltd., primary particle size 15 nm, secondary particle size 40 nm, secondary particle size / primary particle size 2.7) 16 .667 parts (2 parts solids) was added, and then 0.025 part of a 100% solids surfactant (Olfin E1010; manufactured by Nissin Chemical Industry Co., Ltd.) was added and mixed to obtain Wetting Liquid 5. .

[Example 7]
An ink jet recording medium of Example 7 was obtained in the same manner as in Example 1 except that the wetting liquid 1 of Example 1 was changed to the following wetting liquid 6. The coating amount of the protective layer at this time was 1.3 g / m ² .
[Preparation of Wetting Solution 6]
Eyebrow colloidal silica having a solid content of 20% in 89.975 parts of water (Quortron PL-3, Fuso Chemical Co., Ltd., primary particle size 35 nm, secondary particle size 70 nm, secondary particle size / primary particle size 2.0) 10 Part (2 parts solids) was added, and then 0.025 part of a 100% solids surfactant (Olfin E1010; manufactured by Nissin Chemical Industry Co., Ltd.) was added and mixed to obtain a wetting liquid 6.

[Example 8]
[Adjustment of coagulation liquid 1]
82 parts of water, 2 parts of borax (anhydride equivalent), 20% solids colloidal silica (Quortron PL-2 manufactured by Fuso Chemical Co., Ltd., primary particle diameter 23 nm, secondary particle diameter 51 nm, secondary particle diameter / The coagulating liquid 1 was obtained by adding and mixing 15 parts (solid content 3 parts) of the primary particle size 2.2).

[Preparation of inkjet recording medium]
^On a base paper having a basis weight of 157 g / m ² (Diafoam manufactured by Mitsubishi Paper Industries Co., Ltd.), the ink absorbing layer coating composition 1 is applied using an air knife coater so that the coating amount after drying is 10 g / m ^2. And dried using a hot air dryer. Next, the coated paper obtained was treated using a soft calender, and then the glossy layer coating composition 1 was coated using an air knife coater so that the mass after drying was 10 g / m ^2. After treatment with coagulating liquid 1 while the work surface is fluid, it is pressure-bonded to a mirror-finished chrome-plated cylinder of a casting apparatus heated to a temperature of 95 ° C. at a linear pressure of 20 kN / m and a speed of 25 m / min. Thus, an ink jet recording medium of Example 8 was produced. At this time, the adhesion amount of the coagulation liquid before drying was 45 g / m ² , and the coating amount of the protective layer was 2.3 g / m ² .

[Comparative Example 1]
An ink jet recording medium of Comparative Example 1 was obtained in the same manner as in Example 1 except that the wet treatment was performed with a wetting liquid not containing eyebrow colloidal silica.

[Comparative Example 2]
An ink jet recording medium of Comparative Example 2 was obtained in the same manner as in Example 1 except that the wetting liquid 1 of Example 1 was changed to the following wetting liquid 7.
[Preparation of Wetting Solution 7]
Mayuform colloidal silica with a solid content of 23% in 91.279 parts of water (Quortron PL-7, Fuso Chemical Co., Ltd., primary particle size 70 nm, secondary particle size 120 nm, secondary particle size / primary particle size 1.7) 8 .696 parts (2 parts solids) was added, and then 0.025 part of a 100% solids surfactant (Olfin E1010; manufactured by Nissin Chemical Industry Co., Ltd.) was added and mixed to obtain Wetting Liquid 7. . The coating amount of the protective layer at this time was 1.3 g / m ² .

[Comparative Example 3]
An ink jet recording medium of Comparative Example 3 was obtained in the same manner as in Example 1 except that the wetting liquid 1 of Example 1 was changed to the following wetting liquid 8. The coating amount of the protective layer at this time was 1.3 g / m ² .
[Preparation of Wetting Solution 8]
11. Linear colloidal silica having solid content of 16% in 87.475 parts of water (Snowtex OUP manufactured by Nissan Chemical Co., Ltd., primary particle size 15 nm, secondary particle size 100 nm, secondary particle size / primary particle size 6.7) 5 parts (2 parts solids) was added, and then 0.025 part of a 100% solids surfactant (Olfin E1010; manufactured by Nissin Chemical Industry Co., Ltd.) was added and mixed to obtain a wetting liquid 8.

[Comparative Example 4]
In Example 8, an ink jet recording medium of Comparative Example 4 was obtained in the same manner as in Example 8 except that the coagulation treatment was performed with a coagulating liquid containing no eyebrow colloidal silica.

[Comparative Example 5]
[Preparation of coagulation liquid 2]
78 parts of water, 2 parts of borax (anhydrous equivalent), chain colloidal silica with a solid content of 15% (Snowtex OUP, primary particle size 15 nm, secondary particle size 100 nm, secondary particle size / primary particle size 6 .7) 20 parts (solid content 3 parts) were added and mixed to obtain a coagulation liquid 2.
[Preparation of inkjet recording medium]
In Example 8, an ink jet recording medium of Comparative Example 5 was obtained in the same manner as Example 8 except that the coagulation treatment was performed with the coagulating liquid 2. The coating amount of the protective layer at this time was 2.4 g / m ² .

[Gloss evaluation]
For the evaluation of gloss, the 60-degree specular gloss was measured according to JIS-Z8741. Here, a recording medium having a glossiness of 60% or more has high gloss.

[Evaluation of image clarity]
The evaluation of image clarity was performed using a image clarity measuring device manufactured by Suga Test Instruments Co., Ltd. at a measurement angle of 45 ° and an optical comb width of 2.0 mm. In the measurement by this method, in general, a recording medium giving 60 or more image clarity has a high gloss feeling, and a recording medium giving 65 or more image clarity has a very high gloss feeling.

[Evaluation of ink absorbency]
A predetermined evaluation image was printed by an inkjet printer (PIXUS 850i) manufactured by Canon Inc., and the ink absorbability of each recording medium was classified into the following four stages based on the legibility of image details. Here, D is a practically problematic level.
A: No unevenness or blurring in the print portion, very good B: Some blurring is observed in the boundary portion of different colors in the print portion, but good C: Bleeding in the boundary portion of different colors becomes remarkable, and the solid portion Absorption unevenness is slightly confirmed in D: In general, bleeding can be confirmed at the boundary of the color, and uneven absorption in the solid portion is also remarkable.

[Evaluation of print density]
A solid pattern was printed with black ink using a Canon inkjet printer (PIXUS 850i), and the optical reflection density of the printed portion was measured with a Macbeth RD-918 model.

[Evaluation of suitability of pigment ink]
A black gradation pattern (100% -0% gradation) is printed by an ink-jet printer (PX-G900; using pigment ink) manufactured by Seiko Epson Co., Ltd. The standard was classified into the following four stages. Here, D is a level having a problem in practical use.
A: There is no color unevenness or poor color developability in the print portion, and it is very good. B: Although some color unevenness is seen in the print portion, there is no color developability failure, and C: Color unevenness is scattered in the print portion. D: Defect in color development is observed D: Remarkable color unevenness is visible in the print area, and color development is also poor due to ink drop.

[Evaluation of strength]
Place a commercially available high-quality paper on the glossy surface of the recording medium, and place a weight on which three rubber plates with a diameter of 5 mm are attached to the bottom of a cubic weight with a side of 5 cm and a mass of 1 kg. The paper was pulled and the degree of scratches on the glossy surface was visually judged. Here, D is a level causing a practical problem.
A; No scratches can be confirmed on the surface B; Some scratches can be visually recognized on the surface C; Thin scratches can be visually recognized on the surface D;

  Table 1 shows the gloss, image clarity, ink absorptivity, pigment ink suitability and strength of the recording media obtained in each Example and each Comparative Example.

  Table 1 shows that the ink absorbing layer is a water-absorbing inorganic pigment, a coating composition containing latex, boric acid or a salt thereof, the gloss developing layer is a submicron pigment, a coating composition containing polyvinyl alcohol, and a protective layer. Examples 1 to 8 containing at least colloidal silica having a particle diameter of 5 nm to 55 nm and a ratio of the secondary particle diameter to the primary particle diameter of 1.5 to 3.0 have high gloss and good ink absorbability. It can be seen that it has printing density and suitability for pigment ink and has good scratch resistance on the outermost surface of the coating layer. Furthermore, Example 5 which contains colloidal silica in an ink absorption layer coating composition has very high ink absorptivity.

  In Comparative Examples 1 and 4 without the protective layer, the strength of the coating layer surface is low and scratches are easily noticeable. In Comparative Examples 3 and 5 in which the protective layer is made of chain colloidal silica, there are many cracks on the surface of the coating layer, and the suitability of the pigment ink, the print density, and the surface strength are not sufficient. In Comparative Example 2 where the primary particle size of the eyebrow colloidal silica of the protective layer is as large as 70 nm, the ink absorption and the print density are not sufficient, and a vivid image cannot be obtained.

Claims (4)

  In a cast coat ink jet recording medium comprising an ink absorbing layer, a gloss developing layer and a protective layer on a gas-permeable support, the ink absorbing layer contains a water-absorbing inorganic pigment, latex, boric acid or a salt thereof, The gloss development layer is a coating composition containing a submicron pigment and polyvinyl alcohol, and the protective layer has a primary particle diameter of 5 nm to 55 nm and a ratio of the secondary particle diameter to the primary particle diameter of 1.5 to 3.0. A cast coated ink jet recording medium comprising at least a certain colloidal silica.   2. The ink jet recording medium according to claim 1, wherein the submicron pigment of the glossy layer coating composition is an alumina hydrate.   The cast coat ink jet recording medium according to claim 1 or 2, wherein the water-absorbing inorganic pigment of the ink absorbing layer coating composition is wet synthetic silica.   The cast coating ink jet recording medium according to any one of claims 1 to 3, wherein the ink absorbing layer coating composition contains colloidal silica.