JP2008238488A - Ink jet recording paper and method for producing the same - Google Patents

Abstract

An inkjet recording paper having high coating film strength, excellent gloss, and image quality is provided.
In an inkjet recording paper having a substrate and two or more coating layers on the substrate, the lower layer in contact with the substrate contains a pigment having an average particle diameter of 0.1 to 1 μm and is in contact with the lower layer. The upper layer is coated with a coating solution containing a fine secondary pigment having an average particle size of 0.01 to 1 μm, a boron compound, and polyvinyl alcohol, and is subjected to a mirror finish by pressing onto a heated mirror drum while in a wet state. It is characterized by.
[Selection figure] None

Description

  The present invention is a glossy inkjet recording paper and a method for producing the same.

  For printing paper with high surface gloss, coated paper with high gloss, coated with a plate-like pigment on the surface and calendered as necessary, or heated drum surface with a mirror coating on the wet coating layer A so-called cast-coated paper is known which is obtained by copying the mirror surface by pressure-bonding and drying. Cast coated paper has a high surface gloss and superior surface smoothness compared to normal coated paper with a supercalender finish, and provides an excellent printing effect. Although it is used exclusively for applications, it has various difficulties when used for inkjet recording paper.

  For example, the inkjet recording paper disclosed in Patent Document 1 has a layer structure having an ink receiving layer and a glossy layer on a base material, but does not contain a hardener that crosslinks the adhesive to the glossy layer. It was difficult to control cracks, and it was difficult to obtain high image quality and high gloss. Further, since the ink receiving layer is mainly composed of a micron-order porous pigment, there is a problem that the coating strength is remarkably insufficient.

  In order to obtain high gloss, Patent Document 2 discloses that a boric acid / borax mixed treatment solution is applied on the recording layer, and the casting treatment is performed while the recording layer is in a wet state. Then, although cracking of the upper layer was suppressed, there was a problem that sticking to the drum was bad and it was difficult to obtain gloss. Further, since the lower layer is mainly composed of a micron-order porous pigment, the problem of insufficient coating strength cannot be solved.

  In Patent Documents 3, 4, and 5, the lower layer uses fine alkaline earth metal such as calcium carbonate as a main component, and the coating strength is improved, but the upper layer is not treated with a hardener. For this reason, there is a problem that it is difficult to control cracks in the coating film and it is difficult to obtain high gloss.

  Patent Document 6 discloses that the lower layer uses an alkaline earth metal such as calcium carbonate, the upper layer is coated with a boric acid / borax mixture as a coagulating liquid, and the casting process is performed while the upper layer is in a wet state. Yes. With this method, sticking to the upper drum was poor, and it was difficult to obtain gloss. Further, since the obtained recording medium contains a large amount of boric acid / borax in a portion close to the surface layer, there is a possibility that the image quality is deteriorated and the ink absorbability is inferior.

In Patent Document 7, in order to obtain high gloss and high ink absorbency, a temperature-sensitive polymer compound is contained in the upper layer. The fine pigment in the temperature-sensitive polymer-containing coating tends to aggregate, and the sticking to the drum is poor, so that there is a problem that glossiness is hardly generated. Moreover, temperature control at the time of application was difficult.
In recent years, with the expansion of applications such as high-speed inkjet recording, high definition of recorded images, and full color, there has been a demand for higher gloss and higher image quality. It is difficult to achieve.
JP-A-11-34486 JP 2002-283597 A JP 2002-356059 A JP 2002-292996 A JP 2005-271444 A JP 2003-285543 A JP 2004-216766 A

  The technical problem of the present invention is to provide an inkjet recording paper having a high coating film strength, excellent gloss and image quality, and a method for producing the same. The present invention provides a method for efficiently producing cracks and easily controlling cracks because the layer for fixing dyes and pigments in the ink and the glossy layer are integrated with the upper layer in the present invention. To do.

The present invention has been made in view of the above circumstances, and as a result of intensive studies, the present inventors have, on the base material, a lower layer containing a pigment having an average particle diameter of 0.1 to 1 μm, an average An upper layer coated with a coating liquid containing a fine secondary pigment having a particle diameter of 0.01 to 1 μm, a boron compound, and a water-soluble resin binder, and press-bonded to a heated mirror drum while in a wet state to finish the mirror surface. By configuring, the present inventors have found that the above problems can be solved, and have completed the present invention. That is, the present invention
(1) In an inkjet recording paper having a base material and two or more coating layers on the base material, the lower layer in contact with the base material contains a pigment having an average particle size of 0.1 to 1 μm and is in contact with the lower layer Is coated with a coating solution containing a fine secondary pigment having an average particle size of 0.01 to 1 μm, a boron compound, and polyvinyl alcohol, and is pressed onto a heated mirror drum while in a wet state to be mirror finished. Inkjet recording paper characterized by the above.
(2) The inkjet recording paper according to (1), wherein the lower layer pigment contains at least one of calcium carbonate, kaolin, and clay.
(3) The upper layer polyvinyl alcohol is an inkjet recording paper according to (1) or (2), wherein the polyvinyl alcohol has a saponification degree of 85 to 97% and a polymerization degree of 2000 to 5000.

(4) In a method for producing an inkjet recording paper having a substrate and two or more coating layers on the substrate, a lower layer coating solution containing a pigment having an average particle diameter of 0.1 to 1 μm is formed on the substrate. Apply and dry to form a lower layer, while an upper layer coating solution containing a fine secondary pigment having an average particle size of 0.01 to 1 μm, a boron compound, and polyvinyl alcohol is applied on the lower layer and is in a wet state A method of manufacturing an ink jet recording sheet, wherein the mirror surface finish is formed by pressure-bonding to a heated mirror drum.
(5) The upper secondary fine pigment is cationic, and the upper coating liquid is adjusted by adding a water-soluble resin binder after adding a boron compound to the aqueous dispersion of the fine secondary pigment. (4) The method for producing an ink jet recording paper according to (4).
(6) After the upper layer coating solution is applied on the lower layer, the coating solution temperature is lowered by 2 to 15 ° C. from the coating solution temperature just before the coating, and is then pressed onto a mirror drum to be mirror finished (4) or (5) The method for producing an inkjet recording paper according to any one of the above.

  According to the present invention, it is possible to provide an ink jet recording paper having high coating film strength, suppressing cracks in the upper layer, and excellent in gloss and image quality. In the present invention, since the layer for fixing the dye or pigment in the ink and the gloss developing layer are integrated with the upper layer in the present invention, it can be efficiently produced.

<Base material>
Examples of the substrate include those having a paper substrate such as high-quality paper, medium-quality paper, coated paper, art paper, and cast-coated paper. The paper base is preferably manufactured using wood pulp as the main material. As the wood pulp, various chemical pulps, mechanical pulps, regenerated pulps and the like can be used as appropriate. The paper strength, smoothness, papermaking suitability, etc. can be adjusted by adjusting the pulp beating degree by a beating machine. The beating degree (CSF tester value: JIS-P-8121) is not particularly limited, but is generally preferably about 250 to 550 ml.
In addition, chlorine-free pulp in the bleaching process of these pulps, for example, ECF (Elemental Chlorine Free) pulp that uses chlorine compounds without using chlorine itself for pulp bleaching, bleaching agent that does not contain any elemental chlorine in pulp bleaching It is preferable to use TCF (Total Chlorine Free) pulp or the like using In addition to wood pulp, non-wood pulp, chemical fiber, metal fiber, and the like can be combined.

  In addition to pulp, a filler or sizing agent can be added to the paper base as necessary. As the filler, talc, calcium carbonate, clay, kaolin, calcined kaolin, silica, zeolite, titanium dioxide and the like are preferably used. The filler is added to increase the opacity and smoothness, but if added excessively, the paper strength may be reduced, and the addition amount is preferably about 1 to 20% by mass with respect to the wood pulp.

  As sizing agents, (A) natural polymers such as starch and cationized starch, (B) synthetic polymers such as polyvinyl alcohol, carboxy-modified polyvinyl alcohol, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, cellulose sulfate, (C) Proteins such as gelatin and casein, (d) alkyl ketene dimer, (e) anionized polyacrylamide resin, (f) polyamide polyamine epichlorohydrin resin, (g) sodium polyacrylate, styrene-maleic anhydride copolymer Known sizing agents used for general paper substrates such as salts of synthetic polymer such as sodium and sodium polystyrene sulfonate are used.

  Increasing the air permeability can be achieved, for example, by adjusting the tightness per unit volume of the paper substrate by adding a sizing agent or pressing. For the purpose of improving the adhesion between the paper base material and the coating layer on the coating layer forming surface of the paper base material, an undercoat layer may be formed in advance. The smoothness is not particularly limited, but in order to obtain a highly glossy and highly smooth surface, the Beck smoothness is preferably 300 seconds (Oken type, J. TAPPI No. 5) or more. A calendar process may be performed in advance.

  The opacity of the paper base material is not particularly limited, but the opacity (JIS-P-8138) is 85% or more in order to obtain an appearance (particularly visual whiteness) comparable to a silver salt photograph. Is more preferable, and 93% or more is more preferable.

  It is also possible to perform processing such as transportability improvement processing, antistatic processing, and antiblocking processing on the back surface of the paper substrate. These backside treatments may be, for example, chemical treatment with an antistatic agent, an antiblocking agent, or the like, or may be appropriately added with another configuration such as providing a coat layer.

The rice base and thickness of the paper substrate are not particularly limited, but in order to obtain a photographic tone, the tensity of 0.75 to 1.15 g / m ³ and the thickness of 120 to 250 μm are preferable ranges. More preferably, the tenacity is 0.85 to 1.0 g / m ³ and the thickness is 160 to 210 μm.

<Lower layer>
Among the coating layers, the lower layer in contact with the base material contains a pigment and an adhesive for holding the pigment, and absorbs the ink solvent after the dye ink and the pigment ink pigment are fixed or captured in the upper layer described later. This is the main function. However, it is also possible to capture dyes that are not fixed on the upper layer. Furthermore, this lower layer is also a layer that covers the irregularities of the paper substrate and improves the surface smoothness of the ink jet recording paper. Moreover, you may serve as the layer which has a function which improves concealability and improves whiteness. Moreover, you may have a barrier function of reducing the gas which degrades ink dyes and pigments, such as ozone and NOx which approach into an upper layer from the base material side.

[Pigment]
This lower layer contains a pigment having an average particle size of 0.1 to 1 μm. If the average particle size is less than 0.1 μm, the ink absorbability may be lowered, and if it exceeds 1 μm, the smoothness of the lower layer may be significantly lowered, and cracks in the upper layer may not be controlled.

Examples of the pigment include kaolin, clay, calcium carbonate, titanium oxide, zinc oxide, amorphous silica (including colloidal silica), aluminum oxide, zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide. Diatomaceous earth, styrene plastic pigment, hydrotalcite, urea resin plastic pigment, benzoguanamine plastic pigment, and the like, which may be used alone or in combination. From the viewpoint of smoothness and coating strength, calcium carbonate, kaolin and clay are preferably selected. From the viewpoint of ink absorbability, it is preferably selected from calcined kaolin.
Calcium carbonate, kaolin, and clay may be used alone or in combination, but are preferably used in combination from the balance between absorbency and strength. In particular, it is preferable to use calcium carbonate and kaolin (or clay) in combination. In this case, if the blending ratio of calcium carbonate and kaolin (or clay) used in combination is in the range of 5:95 to 70:30 by mass ratio, a synergistic effect is expected to improve the coating layer strength and absorbency. it can.
In the undercoat layer, it is preferable to incorporate amorphous silica, particularly gel silica, in order to quickly stabilize the color after printing (dry down).

When used in combination, the pigment having a predetermined particle size may be dispersed and mixed in an aqueous solution to adjust the coating solution. However, if the pigment is larger than the predetermined particle size, After pulverizing and dispersing until the particle diameter is reached, a predetermined amount of each aqueous solution can be mixed to form a coating solution.
In order to efficiently perform the dispersion and pulverization, a commercially available dispersant such as an anionic dispersant and a cationic dispersant may be appropriately selected and used.

〔adhesive〕
As the adhesive, a latex adhesive and a water-soluble resin adhesive can be used alone or in combination. From the viewpoint of the strength of the coating film and the physical properties of the paint, it is particularly preferable to use a latex adhesive as the main component.
Examples of the latex adhesive include vinyl polymers such as styrene-butadiene copolymer, conjugated diene polymer latex of methyl methacrylate-butadiene copolymer, acrylic polymer latex, and ethylene-vinyl acetate copolymer. Examples include latex. Of these, styrene-butadiene copolymer latex and acrylic polymer latex are particularly preferred. These latex adhesives may be used alone or in combination of two or more.

Examples of water-soluble resin adhesives include proteins such as casein, soybean protein, and synthetic protein, various starches such as starch and oxidized starch, and modified polyvinyl alcohols such as polyvinyl alcohol, cationic polyvinyl alcohol, and silyl-modified polyvinyl alcohol. Examples include polyvinyl alcohols, cellulose derivatives such as carboxymethyl cellulose and methyl cellulose, aqueous polyurethane resins, aqueous polyester resins, and the like.
The adhesive selected and used in combination may be a single adhesive or two or more adhesives. Moreover, it is also possible to use a water-soluble adhesive as a coating solution viscosity modifier.

  The blending amount of the lower layer adhesive is preferably 7 to 70 parts by mass, more preferably 10 to 40 parts by mass with respect to 100 parts by mass of a so-called pigment containing calcium carbonate, kaolin, and clay. When the blending amount is 7 parts by mass or more, sufficient coating strength can be obtained, and when the blending amount is 70 parts by mass or less, the ink absorbability can be prevented from being impaired.

  In addition to the above-mentioned components, various auxiliary agents such as dispersants, thickeners, antifoaming agents, wetting agents, antistatic agents, preservatives and the like may be appropriately added to the lower layer. it can. In addition, fluorescent dyes / pigments, colorants, and the like can be added.

The dry coating amount of the lower layer, although there is no restriction, in general is preferably 3~35g / ^{m 2,} more preferably 5 to 25 g / ^{m 2,} more preferably from 7~20g / ^{m 2.} If the dry coating amount is less than 3 g / m ² , although it depends on the upper layer to be formed, the ink absorbency of the lower layer may be insufficient, and if it exceeds 35 g / m ² , the coating strength may be lowered.
The lower layer is prepared by applying a lower layer coating solution comprising the above-described components onto the substrate and drying. The solid concentration of the lower layer coating solution is preferably 20 to 60% by mass, and most preferably 30 to 50% by mass. In addition, the lower layer may be applied in multiple times or may be applied in multiple layers at the same time.

  As the coating method for the lower layer coating solution, various known coating methods such as blade coater, air knife coater, roll coater, brush coater, Champlex coater, bar coater, lip coater, gravure coater, curtain coater, slot die coater, slide coater, etc. A coating method using any of the apparatuses can be used. Further, the coated lower layer is preferably subjected to a smoothing process such as a super calendar.

<Upper layer>
Among the coating layers, the upper layer in contact with the lower layer is a layer containing a fine secondary pigment having an average particle diameter of 0.01 to 1 μm, polyvinyl alcohol, and a boron compound. The upper layer is a layer whose main function is fixing or capturing of dyes of dye ink and pigment ink. In order to better fix the dye or pigment in the ink, it is preferable to contain a cationic ink fixing agent.

[Fine secondary pigment]
Examples of the fine secondary pigment include kaolin, clay, calcium carbonate, titanium oxide, zinc oxide, amorphous silica, alumina, alumina hydrate, zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, and oxidation. Among magnesium, diatomaceous earth, styrene plastic pigment, hydrotalcite, urea resin plastic pigment, benzoguanamine plastic pigment and the like, a fine secondary pigment having an average particle size of 0.01 to 1 μm is used alone or in combination. If the average particle diameter is less than 0.01 μm, the ink absorbability may be lowered. If it exceeds 1 μm, the transparency of the coating film is inferior and the print density may be significantly lowered. Among these, amorphous silica, alumina, and alumina hydrate are preferable, amorphous silica is more preferable, and dry method silica is particularly preferable.

  Further, silica-cationic compound aggregate particles obtained by mixing the amorphous silica and the cationic compound are preferable, and this is pulverized and dispersed to form the aggregate fine particles having an average particle diameter of 0.01 to 1 μm. Used. The aggregate fine particles most preferably have an average particle size in the range of 0.03 to 0.3 μm.

  For the upper layer, a known pigment used for a normal ink jet recording paper can be used in combination with the above pigment within a range not impairing the effects of the present invention. As these pigments, the same pigments as the lower layer pigments described above can be used, and the pigments selected and used in combination may be used alone or in combination of two or more.

[Polyvinyl alcohol]
The upper layer uses polyvinyl alcohol as an adhesive. Among them, polyvinyl alcohol having a saponification degree of 85 to 97% is preferable, and polyvinyl alcohol having a saponification degree of 87 to 93% is more preferable. Incidentally, in the case of polyvinyl alcohol exceeding 97%, the swellability is remarkably lowered, and the ink absorbability may be lowered.

  This polyvinyl alcohol preferably has a degree of polymerization of 2000 to 5000, and most preferably 2500 to 4500. If the degree of polymerization is less than 2000, the adhesive strength is weak and the coating film may be cracked. If it exceeds 5000, handling properties may be deteriorated in the preparation of the upper layer coating solution, which is not preferable.

  The blending amount of the polyvinyl alcohol is preferably 6 to 30 parts by mass with respect to 100 parts by mass of the pigment from the viewpoint of maintaining a balance between ink absorptivity, coating film strength, and cracking suppression of the coating layer. 8 to 25 parts by mass, more preferably 10 to 20 parts by mass. If the blending amount is less than 6 parts by mass, cracks may occur in the upper layer, and there is a problem that paper dust is generated during cutting due to a decrease in the layer strength. If it exceeds 30 parts by mass, the ink absorbability may be lowered, which is not preferable.

In the upper layer, a known adhesive used for ordinary inkjet recording paper can be used in combination with the polyvinyl alcohol as long as the effects of the present invention are not impaired.
Examples of binders that can be used in combination include water-soluble resin systems such as polyvinyl acetal, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, casein, soy protein, synthetic proteins, and starch, styrene-butadiene copolymers, polyester systems, acrylic systems, and urethane systems. And the like.
These adhesives used in combination may be used alone or in combination of two or more. Acrylic and urethane latexes are preferably blended because they have an effect of improving the adhesive strength and gloss as a binder. From the viewpoint of dye fixing properties, a cationic binder is preferably selected as the latex binder. The average particle diameter of the latex is not particularly limited as long as the transparency of the coating film is not impaired, but a range of 5 to 100 nm is preferable.

  The amount is 5 to 50 parts, preferably 10 to 30 parts, based on 100 parts of the pigment. When the blending amount is less than 5 parts, the effect of improving the adhesive strength and gloss is small. On the other hand, if it exceeds 50 parts, the ink absorbability may be impaired.

[Boron compounds]
Boron-based compounds need to be included in the upper layer coating solution in advance in order to achieve both castability of the upper layer (sticking to the cast drum, releasability, glossiness, etc.) and prevention of cracking of the coating layer. .
The boron-based compound is selected from boric acid and salts thereof, and borax, and may be used alone or in combination. Content of a boron compound is 1-20 mass parts with respect to 100 mass parts of pigment components including the fine secondary pigment of an upper layer, Preferably it is 2-10 mass parts. If the content is less than 1 part by mass, it is difficult to control cracks, and if it exceeds 20 parts by mass, the coating solution tends to thicken, which is not preferable.

  The method for adding this boron compound to the coating solution for the upper layer is not particularly limited, but the boron compound is added as a solid content to the pigment slurry used in the upper layer, especially the silica-cationic compound aggregate particle slurry. After dispersion and dissolution, it is preferable to adjust by adding polyvinyl alcohol. Even if the concentration of the coating solution adjusted in this order is high, the viscosity of the coating solution is kept low, and castability and crack control are good.

[Ink fixing agent]
The ink fixing agent is generally a cationic compound, and the cationic compound has an effect of fixing a dye pigment in the ink for ink jet recording, and particularly has an effect of imparting water resistance to a printed image. As the cationic compound, known compounds can be used, for example, (a) polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, and (b) secondary or tertiary amino groups and quaternary ammonium. Acrylic polymers having a group, or copolymers of these acrylamides, (c) polyvinylamines and polyvinylamidines, (d) dicyandiamide-formalin typified dicyan-based cationic compounds, (e) dicyandiamide- polyamine cationic compound represented by polyethylene amine copolymer, (f) epichlorohydrin - dimethylamine copolymers, (g) a polycondensate of diallylamine salts and diallyldimethylammonium and SO _2, (h) diallyldimethylammonium chloride Polymer, (li) allylamine salt copolymer, (nu) dialkylaminoethyl (meth) acrylate quaternary salt copolymer, (le) acrylamide-diallylamine copolymer, (e) having a 5-membered ring amidine structure Cationic substances, (wa) [3- (2-aminoethyl) aminopropyl] trimethoxylane-containing amino group-containing organosilane compounds, (f) polyvalent metal compounds such as aluminum compounds and zirconium compounds Etc.
These fixing agents are used alone or in combination of two or more. From the viewpoint of coating concentration of the upper layer coating solution, stability over time, castability, and crack control, polydimethyldiallylammonium chloride having a molecular weight in the range of 1,000 to 20,000, a copolymer thereof, and an amino group-containing organosilane compound are preferable. . Cationic resins are preferable from the viewpoint of improving printing density, and these resins are used as an aqueous solution of a water-soluble resin or an emulsion of a water-insoluble resin.

  The compounding quantity of a cationic compound can be used in 1-30 mass parts with respect to 100 mass parts of pigments, More preferably, it is 2-15 mass parts. If the blending amount is less than 1 part by mass, the water resistance of the printed image may be insufficient, and if it exceeds 30 parts by mass, the ink absorbability may be lowered, which is not preferable.

  In the present embodiment, the pigment in the upper layer is preferably pigment-ink fixing agent composite particles obtained by treating the pigment surface with an ink fixing agent. Specifically, amorphous silica and a cationic compound are mixed to form silica-cationic compound aggregate particles, which are pulverized and dispersed to form ultrafine particles to form silica-cationic compound aggregate fine particles. It is preferable to use this. As the amorphous silica, dry silica is most preferable. By using such silica-cationic compound aggregate fine particles, there is a feature that it is easy to balance the transparency of the coating film, the ink absorbability, and the printing water resistance.

  In the upper layer, in addition to the above-described components, a dispersant, a crosslinking agent, a thickener, an antifoaming agent, an antistatic agent, an antiseptic, an ultraviolet absorber, a shelf life improving agent, which are used in general inkjet recording paper production, Various additives such as a fluorescent brightener and a colorant can be appropriately added.

  The solid content concentration of the upper layer coating solution is preferably 5 to 27% by mass, and more preferably 8 to 20% by mass. If the solid content concentration is less than 5% by mass, the drying efficiency of the upper layer may be lowered, and if it exceeds 27% by mass, the viscosity of the coating solution is high, and coating may be difficult.

  As the coating method for the upper layer coating solution, various known and publicly available methods such as blade coaters, air knife coaters, roll coaters, brush coaters, Champex coaters, bar coaters, lip coaters, gravure coaters, curtain coaters, slot die coaters, slide coaters, sprays, etc. A coating method in which coating is performed using any of the above coating apparatuses can be used.

  The upper layer is obtained by a so-called casting method, which is applied to a heated mirror drum while the upper layer coating solution is wet, peeled off after drying. In general, the cast method is easy to crack the coating layer having ink fixing ability, but the structure and the production method of the present invention can suppress cracking, and can obtain a high gloss, high image quality dye / pigment combined glossy ink jet recording paper. Is possible.

  General casting methods are as follows: (a) Coating the gloss layer coating liquid on the substrate or the coating layer of the substrate, and then pressing and drying the heated mirror drum as it is to finish the gloss layer to a glossy surface. Method (wet cast method), (b) After the coated coating solution for glossy layer is dried once to form a glossy layer, this glossy layer is rewet with a wetting liquid, and then applied to a heated mirror drum. Method of pressing and drying to finish glossy surface (rewet casting method), (c) Applying a gloss layer coating solution on the substrate or coating layer of the substrate, and then applying a coagulant that solidifies the coating solution , Solidify the gloss layer coating solution, press the solidified coating layer against a heated mirror drum and dry it to give a glossy surface (gel cast method), (2) for the gloss layer on the substrate Without applying the coating liquid, the coating liquid for the surface gloss layer is directly applied to the heated mirror drum. After coating, a method (precast method) is applied that presses and dries on the substrate or the coating layer of the substrate, and moves the surface glossy layer onto the substrate or the coating layer of the substrate to finish the glossy surface (precast method). Can be mentioned.

In the present invention, since the upper layer coating solution contains a fine secondary pigment, a boron compound, and polyvinyl alcohol, it is not necessary to apply a coagulant later, and can be pressed against a mirror drum as it is. Along with the crosslinking reaction of polyvinyl alcohol, the coating solution coagulates without applying a coagulant, so that the upper layer is hardly cracked.
The coating solution temperature immediately before coating is preferably adjusted in the range of 25 to 45 ° C. from the fluidity and coating uniformity of the coating solution. More preferably, it is 28-40 degreeC. In particular, after the upper layer coating solution is applied on the lower layer, it is lowered by 2 to 15 ° C., preferably 3 to 12 ° C., and most preferably 5 to 10 ° C. from the coating solution temperature immediately before coating, and then it is pressure-bonded to the mirror drum. preferable. By reducing the temperature, the gloss during casting tends to be high, which is also effective for crack control. If it is less than 2 ° C, the effect of crack control tends to be insufficient, and if it is 15 ° C or more, productivity may be lowered. The method for lowering the coating solution temperature is not particularly limited, and examples thereof include a method of applying cold air. In these casting processes, the temperature of the heated mirror drum is, for example, 50 to 150 ° C, preferably 70 to 120 ° C.

When the upper layer is cast-finished, it is preferable to use a release agent in order to smoothly peel off from the cast drum. The release agent is used by any one of a method of adding to the upper layer coating solution and a method of coating on the cast drum surface.
Examples of the mold release agent include higher fatty acid amides such as stearic acid amide and oleic acid amide, polyolefin waxes such as polyethylene wax, polyethylene oxide wax, and polypropylene wax, calcium stearate, zinc stearate, potassium oleate, and ammonium oleate. Higher fatty acid alkali salts, silicone compounds such as lecithin, silicone oil and silicone wax, and fluorine compounds such as polytetrafluoroethylene. Among these, a cationic release agent is particularly preferably used.

  In the above casting processes, when the upper layer coating solution is applied, various known coating methods can be used, for example, coating of blades, brush coaters, Champex cook coaters, bar coaters, gravure coaters, etc. A coating method of coating using any of the apparatuses can be used. Calendar processing and recasting are possible to further increase gloss.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Moreover, unless otherwise indicated, the part and% in an example are solid content except water, and show a mass part and mass%, respectively.

Example 1
[Adjustment of lower layer coating solution]
70 parts of light calcium carbonate (product name: Brilliant S-15, manufactured by Shiroishi Chemical Co., Ltd.) having an average particle size of 0.8 μm, colloidal silica (product name: ST-20L, manufactured by Nissan Chemical Co., Ltd.) 30 having an average particle size of 0.045 μm Part and 15 parts of styrene butadiene latex (trade name: OJ-1000, manufactured by JSR Corporation) were mixed and dispersed to prepare a 35% lower layer coating solution.

[Adjustment of upper layer coating solution]
4 parts of boric acid is added to 100 parts of the following silica fine particles A, and after dispersion and dispersion, 13 parts of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name: PVA-235, polymerization degree: 3500, saponification degree: 88.5%) are added. Then, 3 parts of a cationic release agent (modern science, trade name: Pertol N-856) was added to prepare a 15% upper layer coating solution.
"Silica fine particles A"
To 780 g of water, 20 g of a cationic compound having a diallyldimethylammonium chloride (so-called DADMAC) structure (Daiichi Kogyo Co., Ltd., trade name: Charol DC902P) was added, and 200 g of vapor phase silica was stirred while stirring the aqueous cation solution. (Nippon Aerosil Co., Ltd., trade name: Aerosil A200, average primary particle size: about 14 nm) was gradually added to prepare a 22% dispersion. The dispersion was further pulverized and dispersed with a pressure homogenizer until the average particle size reached 70 nm to prepare a 20% aqueous dispersion.

[Preparation of inkjet recording paper]
The lower layer coating solution was applied and dried on a commercial paper (manufactured by Oji Paper Co., Ltd., trade name: Marshmallow, 104.7 g / m ² ) so as to have a dry coating amount of 12 g / m ² , linear pressure 100 kg / cm, temperature 40 A calendar treatment at 0 ° C. was performed. On the lower layer, an upper layer coating solution having a coating solution temperature of 30 ° C. is applied so that the dry coating amount becomes 7 g / m ^2, and the temperature of the coating surface is lowered by 4 ° C. with a fan and then 80 ° C. in a wet state. The ink-jet recording paper was obtained by pressure-bonding to a mirror drum (cast drum), drying, and peeling.

Example 2
An ink jet recording paper was obtained in the same manner as in Example 1 except that the following lower layer coating solution was used in Example 1.
[Adjustment of lower layer coating solution]
80 parts of calcined kaolin having an average particle diameter of 0.7 μm (manufactured by Rysan Corporation, Ansilex 93), 20 parts of light calcium carbonate having an average particle diameter of 0.8 μm (trade name: Brilliant S-15, manufactured by Okutama Kogyo Co., Ltd.) 15 parts of styrene butadiene latex (trade name: OJ-1000, manufactured by JSR Corporation) was mixed and dispersed to prepare a 35% lower layer coating solution.

Example 3
An ink jet recording paper was obtained in the same manner as in Example 1 except that the following lower layer coating solution was used in Example 1.
[Adjustment of lower layer coating solution]
Heavy calcium carbonate with an average particle size of 0.7 μm (Bihoku Powder Chemical Co., Ltd., trade name: Softon 3200, 50% aqueous dispersion prepared beforehand), 100 parts of styrene butadiene latex (JSR, trade name: OJ) -1000) 15 parts of the mixture was mixed and dispersed to prepare a 35% lower layer coating solution.

Example 4
An ink jet recording paper was obtained in the same manner as in Example 1 except that the following lower layer coating solution was used in Example 1.
[Adjustment of lower layer coating solution]
100 parts of calcined kaolin having an average particle size of 0.7 μm or less (manufactured by Ryosan Shoji Co., Ltd., Ansilex 93) and 15 parts of styrene butadiene latex (manufactured by JSR, trade name: OJ-1000) are mixed and dispersed, and 35% lower layer The coating solution was adjusted.

Example 5
In Example 2, an inkjet recording paper was obtained in the same manner as in Example 2 except that the following upper layer coating solution was used.
[Adjustment of upper layer coating solution]
4 parts of boric acid is added to 100 parts of silica fine particles A, and after dispersion and dissolution, 10 parts of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name: PVA-235, polymerization degree: 3500, saponification degree: 88.5%), cationic urethane 20 parts of latex (average particle size 20 nm) was added, 3 parts of a cationic release agent (Modern Science, trade name: Pertol N-856) was added, and a 15% upper layer coating solution was prepared.

Example 6
In Example 2, after the upper layer was applied, the coating surface temperature was lowered by 7 ° C. from 30 ° C. with a cool air machine, and then the ink jet recording paper was obtained in the same manner as in Example 2 except that it was pressed onto a mirror drum, dried and peeled off. It was.

Example 7
In Example 2, an inkjet recording paper was obtained in the same manner as in Example 2 except that the following upper layer coating solution was used.
[Adjustment of upper layer coating solution]
13 parts of polyvinyl alcohol (made by Kuraray Co., Ltd., trade name: PVA-235, polymerization degree: 3500, saponification degree: 88.5%) is added to 100 parts of silica fine particles A, and then 4 parts of boric acid is added and dispersed and dissolved. Thereafter, 3 parts of a cationic release agent (modern science, trade name: Pertol N-856) was added to prepare a 15% upper layer coating solution.

Example 8
Example 2 except that the silica fine particles A of the upper layer coating solution were changed to dry alumina (manufactured by CABOT, trade name: PG003, average secondary particle size: about 0.2 μm), and the number of parts of polyvinyl alcohol was changed to 8 parts. Inkjet recording paper was obtained.

Comparative Example 1
An ink jet recording paper was obtained in the same manner as in Example 1 except that the total amount of the upper coating layer pigment was changed to a gel method silica slurry having an average particle diameter of 1.2 μm (product name: 712A, manufactured by Grace).

Comparative Example 2
Inkjet recording paper was obtained in the same manner as in Example 1 except that the total amount of the upper layer pigment was changed to heavy calcium carbonate having an average particle size of 1.1 μm (manufactured by PMMA Tech, trade name: AFF-95).

Comparative Example 3
An ink jet recording paper was obtained in the same manner as in Example 1 except that the following upper layer coating solution was used in Example 1.
[Adjustment of upper layer coating solution]
13 parts of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name: PVA-235, polymerization degree: 3500, saponification degree: 88.5%) is added to 100 parts of silica fine particles A, and a cationic release agent (modern science, trade name: 3 parts of Pertol N-856) was added to prepare a 15% upper layer coating solution.

Comparative Example 4
An ink jet recording paper was obtained in the same manner as in Example 1 except that the upper layer of Example 1 was dried in an oven at 100 ° C. without being pressed and dried on a mirror drum.

Comparative Example 5
The compounding ratio of borax / boric acid was 0.25 / 1, Na ₂ B ₄ O ₇ and 4% in terms of H ₃ BO ₃ , release agent (trade name: FL-48C, manufactured by Toho Chemical Industry Co., Ltd.) 0 A coagulation liquid was prepared by blending 2% (to the liquid). An ink jet recording paper was obtained in the same manner as in Example 1, except that the upper layer of Comparative Example 3 was solidified with a coagulating liquid while it was wet and cast.

Comparative Example 6
An inkjet recording paper was obtained in the same manner as in Comparative Example 3 except that a 3% borax aqueous solution was applied onto the lower layer of Example 1 so that the coating amount was 1 g / m ² .

Comparative Example 7
Inkjet recording paper was obtained in the same manner as in Example 1 except that sodium hydroxide was added instead of boric acid in Example 1 and the pH of the upper coating solution was adjusted to 5.5.

[Evaluation methods]
For Examples 1 to 7 and Comparative Examples 1 to 7, cast drum contamination during production, ink absorbability of the obtained inkjet recording paper, image quality of the recorded image, smoothness and glossiness of the recorded image, coating layer strength, coating The folding of the film was measured by the following method, and the result was evaluated according to a predetermined standard.

<Printer used>
Printing in glossy paper mode using a dye inkjet printer (trade name: PM-G820, manufactured by Epson Corporation).

<Drum dirt>
At the time of producing the recording material of the present invention, dirt remaining on the drum was observed and evaluated according to the following criteria.
○: The drum is not dirty at all.
X: Paint haze is seen on the drum.

<Ink absorbability>
This recording medium was printed with a solid color of green and blue with a printer, and the ink absorptivity was visually observed and evaluated according to the following criteria.
○: The ink absorption speed is fast, and there is no ink overflow or beading.
Δ: Some beading is recognized, but there is no practical problem.
×: Ink overflow and beading.

<Recorded image quality>
The black solid print portion was measured with a Macbeth reflection densitometer (trade name: Macbeth RD-920), and the value was compared as the print density.

<Smoothness and glossiness>
An ISO-400 image ("high-definition color digital standard image data ISO / JIS-SCID", p13, image name: fruit basket) is printed on this recording medium, and the image is inclined at a certain angle with respect to the recording medium surface. It observed visually from the angle and evaluated on the following reference | standard.
○: Glossiness close to a silver halide photograph.
(Triangle | delta): The glossiness more than a printing paper.
X: The glossiness is low.

<Coating layer strength>
In order to determine the coating layer strength, Cellotape (registered trademark) was applied to the recording surface and lightly pressed by hand, then the tape was peeled off at right angles to the recording surface, and the state was evaluated according to the following criteria.
○: There is almost no transition of the recording layer on the tape.
(Triangle | delta): There is little transition of a recording layer to a tape, and it is a level which is satisfactory practically.
X: There are many transitions of the recording layer on the tape, and there are practical problems.

<Break>
The recording medium was allowed to stand in a constant temperature and humidity chamber at 15 ° C. and 25% for 24 hours, and then the recording medium was wound around a cylinder having a diameter of 2 cm, and cracks at that time were observed and evaluated according to the following criteria.
○: Cracks are hardly seen in the coating film.
X: There are many cracks in a coating film, and there is a problem in practical use.

<Others>
The surface of the recording material of the present invention had almost no cracks, and the printed dots were perfect circles.

  As is apparent from Table 1, it can be seen that the ink jet recording paper of the present invention has very good ink absorptivity and print glossiness, has high coating layer strength, and is excellent in folding. Further, the production method of the present invention is excellent in continuous operability without contaminating the cast drum.

Claims (5)

In an inkjet recording paper having a substrate and two or more coating layers on the substrate, the lower layer in contact with the substrate contains a pigment having an average particle size of 0.1 to 1 μm, and the upper layer in contact with the lower layer is an average It is coated with a coating solution containing a fine secondary pigment having a particle diameter of 0.01 to 1 μm, a boron compound, and polyvinyl alcohol, and is subjected to a mirror finish by pressing onto a heated mirror drum while in a wet state. Characteristic inkjet recording paper. 2. The ink jet recording paper according to claim 1, wherein the lower layer pigment contains at least one of calcium carbonate, kaolin and clay. The inkjet recording paper according to claim 1 or 2, wherein the upper layer polyvinyl alcohol is polyvinyl alcohol having a saponification degree of 85 to 97% and a polymerization degree of 2000 to 5000. In a method for producing an inkjet recording paper having a substrate and two or more coating layers on the substrate, a coating solution for a lower layer containing a pigment having an average particle size of 0.1 to 1 μm is applied on the substrate and dried. Then, a lower layer was formed, and an upper layer coating solution containing a fine secondary pigment having an average particle size of 0.01 to 1 μm, a boron compound, and polyvinyl alcohol was applied on the lower layer and heated while in a wet state. A method for producing an ink jet recording paper, wherein the ink jet recording paper is mirror-finished by pressing on a mirror drum. The upper fine secondary pigment is cationic, and the upper coating liquid is prepared by adding a boron compound to the aqueous dispersion of the fine secondary pigment and then adding a water-soluble resin binder. The method for producing an inkjet recording paper according to claim 4.