JP2007190762A - Inkjet recording paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording paper which has a high gloss and a high printing density, suppresses cohesive variation of an ink when it is printed, exhibits high ink absorbing capacity and absorbing speed, is excellent in inkjet recording suitability, and is excellent in surface strength. <P>SOLUTION: The inkjet recording paper has a substrate and at least two coating layers supported on this substrate, and the surface part of this coating layer forms an outermost surface layer being a glossy face made by a gloss-making treatment. Between the substrate and the outermost surface layer, an ink receiving layer which absorbs an ink and fixes the coloring matter in the ink and a solvent absorbing layer which absorbs the solvent in the ink, are provided. This solvent absorbing layer comprises pigments selected respectively at least one kind from a pigment with a small particle diameter composed of a single substance with a mean particle diameter of 1-500 nm and a pigment with a large particle diameter with a mean particle diameter of 1-15 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording paper, and more particularly, to an ink jet recording paper having excellent absorbency and gloss and excellent ink jet recording suitability.

An ink jet recording method in which an aqueous ink is ejected from a fine nozzle to form an image,
There are advantages such as easy full colorization, high-speed recording, and lower printing costs than other printing apparatuses in the case of printing a small number of copies. Therefore, this ink jet recording system is widely used in terminal printers, facsimiles, plotters, form printing, and the like.
In recent years, ink jet printers have been rapidly spread and have high definition and high speed, and accordingly, ink jet recording papers are required to have higher ink absorption speed and higher surface strength than ever before. Furthermore, with the widespread use of digital cameras, inkjet recording paper is strongly required to be able to print recorded images taken with digital cameras with high image quality comparable to silver halide photographs. Further improvement is required.

Therefore, in order to increase the gloss of the paper, a method has been proposed in which the outermost layer formed by coating is subjected to a casting process in which the outermost layer is pressed against a heated mirror drum, and the mirror surface is copied. . A certain level of gloss can be obtained by this method (Patent Document 1).
However, in the outermost layer, cracks occur due to the casting process, and the ink flows along the cracked portion, and a whisker-like stain called feathering occurs, and there are many dyes and colored pigments in the ink at this portion. Absorption causes unevenness in the image, and the print density is low. The paper produced by this method has poor image uniformity, and has a problem in print density and printability with respect to pigment ink.
Further, the paper is provided with an ink receiving layer between the paper base and the outermost layer so as to absorb and fix the printed ink. It was not possible to cope with the absorption of a large amount of ink supplied by the printer or the rapidly supplied ink in high-speed printing.

In order to solve such a problem of recording paper, two or more coating layers are provided on the base of the recording paper, the surface layer of which is an coating liquid containing an aggregate pigment having an average particle diameter of 1 μm or less While the recording layer formed by coating the material with a cast process that presses it against a heated mirror drum while it is in a wet state, the problems such as gloss and print density are solved. The undercoat layer formed on the substrate is formed by containing a pigment having a large particle diameter of 1 to 20 μm, and the ink is absorbed by absorbing a large amount or rapidly supplied ink by the above printing. Technologies that try to solve the problem have been proposed.
That is, this undercoat layer is provided for the purpose of increasing the ink absorption capacity and absorption speed, and this undercoat layer is applied to the undercoat layer of the coating liquid that forms the recording layer as a subcomponent of the pigment. In order to suppress the permeability of the pigment, a pigment having a small particle size is blended (Patent Document 2).

  However, with the recent increase in the definition and speed of printers, this recording paper has not always been sufficient to absorb a large amount of ink that is rapidly supplied by the above printing. In addition, the movement of the ink is not smooth at the interface between the recording layer and the undercoat layer, which inhibits ink absorption.

Also, a cast that has an undercoat layer containing a pigment and an adhesive for holding the pigment on a paper substrate, is provided on the undercoat layer, fixes a dye component in the ink, and develops gloss by a cast process. In an inkjet recording paper having a coating layer, a polymer resin and colloidal silica obtained by polymerizing amorphous silica having a large particle diameter of 2 to 8 μm in average particle diameter and a monomer having an ethylenically unsaturated bond in the undercoat layer The thing containing the composite_body | complex with is known. In this recording paper, the composite of the polymer resin and colloidal silica suppresses the penetration of the cast coating layer into the undercoat layer while maintaining the ink absorbability of the undercoat layer. (Patent Document 3).
However, even in this recording paper, there is a possibility that the mobility of the ink at the interface between the cast coating layer and the undercoat layer is not smooth in absorbing a large amount of ink in photographic printing and rapidly supplied ink. there were.

Japanese Unexamined Patent Publication No. 7-117335 JP 2001-10220 A JP-A-11-34486

The present invention has been made in view of the above circumstances, and as a result of diligent studies to solve the above problems, the present inventors have developed a recording layer into an undercoat layer containing a conventional pigment having a large particle diameter. Supports the coating layer, not a small particle size pigment added as an accessory component or a small particle size pigment constituting the composite to suppress penetration of the coating liquid into the undercoat layer The solvent absorption layer provided between the support and the outermost layer of the recording paper contains a pigment having a small particle size and a large particle size within a predetermined range, thereby finding that the above problem is solved. The present invention has been reached.
The technical problem to be solved by the present invention is an inkjet recording that has high gloss and printing density, suppresses ink aggregation unevenness when printed, and has high ink absorption capacity and absorption speed, and excellent ink jet recording suitability. Is to provide paper.

  The glossy inkjet recording paper of the present invention for solving the above problems has a support and two or more coating layers supported on the support, and the surface portion of the coating layer is glossy. In an inkjet recording paper having an outermost layer having a glossy surface formed by treatment, an ink receiving layer that absorbs ink and fixes a pigment in the ink between the support and the outermost layer, and an ink A solvent-absorbing layer that absorbs the solvent therein, the solvent-absorbing layer having a small particle size pigment composed of a single substance having an average particle size of 1 to 500 nm, and an average particle size of 1 to 15 μm It contains at least one pigment selected from each of the pigments having a large particle size.

  According to a preferred configuration aspect of the present invention, the mixing ratio of the small particle size pigment and the large particle size pigment contained in the solvent absorption layer is 20/80 to 80/20 in mass ratio.

  According to another preferred configuration aspect of the present invention, the solvent absorption layer contains an adhesive for holding the respective pigment, and the adhesive contains polyvinyl alcohol having a saponification degree of 95% or more, and preferably Has a polymerization degree of 3500 to 5000.

  According to another preferred embodiment of the present invention, the outermost layer contains a pigment having an average particle diameter of 3 to 500 nm, and preferably, the outermost layer pigment is colloidal silica mainly composed of primary particles. The average particle diameter is 3 to 200 nm.

  The ink jet recording paper of the present invention has high gloss and print density, suppresses ink aggregation unevenness when printed, has a high ink absorption capacity and absorption speed, and is excellent in ink jet recording suitability.

The ink jet recording paper according to the present invention will be described in detail based on the following embodiments.
The ink jet recording paper of the present embodiment has a support and two or more coating layers supported on the support, and the surface portion of the coating layer has a glossy surface by glossing treatment. Ink-jet recording paper having an outermost layer formed thereon, absorbing an ink between the support and the outermost layer, and absorbing a dye in the ink, and absorbing a solvent in the ink And a solvent absorption layer.
And this solvent absorption layer has at least 1 from each of the small particle size pigment comprised with a single substance with an average particle diameter of 1-500 nm, and the large particle size pigment with an average particle diameter of 1-15 micrometers. Contains pigments selected for each type.
In addition, the coating layer is provided on the ink-receiving layer, the solvent-absorbing layer comprising a single undercoat layer provided on a paper base material as a support, an ink-receiving layer described later provided thereon, and the ink-receiving layer. It consists of three layers with the outermost layer.

<Support>
The support is not particularly limited, but a paper substrate that is a gas-permeable support, a resin film or sheet material having gas permeability can be used, and in particular from the gas-permeable surface, a paper substrate. Is preferably used.
For the paper substrate as the support, a commonly used known paper substrate can be used as long as the effects of the present invention are not impaired. For example, fine paper, art paper, coated paper, cast coated paper Kraft paper, baryta paper, paperboard, impregnated paper, vapor-deposited paper, acid paper used for general coated paper, neutral paper, and the like are appropriately used.
The paper base material contains wood pulp as a main component, and fillers, various auxiliaries and the like are added as necessary.

The outline | summary of these paper base materials is demonstrated.
As the wood pulp, various chemical pulps, mechanical pulps, recycled pulps and the like can be used. These pulps can be adjusted with a beating machine to adjust paper strength, papermaking suitability, etc., and the beating degree (freeness) is not particularly limited, but is 250 to 550 ml (CSF: JIS-P-8121). Is preferred.

  As the filler added to the paper substrate, for example, calcium carbonate, calcined kaolin, silica, titanium oxide and the like are preferably used. Of these, calcium carbonate is preferred because it provides a paper substrate with high whiteness and increases the glossiness of inkjet recording paper. The filler content (ash content) in the paper substrate is preferably about 1 to 20% by mass. Within this range, smoothness, air permeability, paper strength and rigidity are balanced, and an ink jet recording paper excellent in balance of glossiness, image clarity and rigidity can be easily obtained.

Examples of the auxiliary agent added to the paper substrate include a sizing agent, a fixing agent, a paper strength enhancer, a cationizing agent, a yield improving agent, a dye, and a fluorescent brightening agent.
The degree of sizing of the paper substrate is preferably about 1 to 300 seconds, and more preferably 4 to 120 seconds. If the degree of sizing is less than 1 second, there is a possibility of causing operational problems such as wrinkling during coating, and if it exceeds 300 seconds, ink absorbability decreases, and curling and cockling after printing (absorption) This is not preferable because there is a possibility that the wrinkles) may become remarkable.
Although the basic weight of a paper base material is not specifically limited, About 20-400 g / m < ² > is preferable.
The Oken type air permeability of the paper substrate is preferably 10 to 350 seconds, more preferably 10 to 200 seconds, and still more preferably 20 to 100 seconds. If the air permeability is less than 10 seconds, the solvent absorbing layer coating liquid may permeate the paper substrate excessively. If the air permeability exceeds 350 seconds, the operability is reduced when press-contacting the cast drum. This is not preferable.

<Solvent absorption layer>
The solvent absorption layer is for improving the ink absorption capacity and absorption speed, and is not limited to one layer, and a plurality of layers may be provided.
In the present embodiment, the solvent absorption layer is composed of a single undercoat layer formed on the paper substrate.
The solvent absorption layer includes a pigment having a small particle diameter composed of a single substance having an average particle diameter of 1 to 500 nm, a pigment having a large particle diameter of 1 to 15 μm and an adhesive for holding the pigment. This adhesive is preferably polyvinyl alcohol which is a water-soluble adhesive.
By providing this solvent absorbing layer on the support, the ink jet recording paper is provided with very good ink absorptivity and excellent in bleeding, printing unevenness, printing uniformity and printing density.

[Pigment]
Examples of the small particle size pigment having an average particle size of 1 to 500 nm include colloidal silica mainly composed of primary particles, fine silica mainly composed of secondary particles, and alumina sol.
If this average particle size is less than 1 nm, the particles may be too small to improve ink absorbability, and if it exceeds 500 nm, the outermost layer that is glossed by cast processing has sufficient smoothness and gloss. It is not preferable because there is a possibility that it may not exhibit the property.
Of these, colloidal silica is particularly preferably used.
Colloidal silica has an alkaline type and an acidic type, and is appropriately selected according to physical properties such as pH of the solvent absorbing layer coating solution.
As this colloidal silica, either spherical or non-spherical can be used. As for the ease of developing gloss, spherical colloidal silica is better, and non-spherical colloidal silica is better in terms of ink absorption. Alternatively, the two are mixed or used.
In addition, these small particle size pigments may be used alone or in combination of two or more.
“Small particle size pigment composed of a single substance” does not mean a substance having the same structure, but a category of substances having similar properties. This is a concept showing a pigment including a difference between a single or several simple aggregate structures.

Large pigments with an average particle size (agglomerated particle size in the case of an agglomerated pigment) of 1 to 15 μm include kaolin, clay, calcined clay, amorphous silica (amorphous silica), synthetic amorphous silica, oxidation Zinc, titanium oxide, aluminum hydroxide, calcium carbonate, satin white, aluminum silicate, alumina, zeolite, synthetic zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, diatomaceous earth, styrene plastic pigment, hydrotalcite , Urea resin-based plastic pigments, benzoguaminane-based plastic pigments, and the like.
If this average particle size is less than 1 μm, ink absorption speed may decrease and ink blur may occur when the amount of ink is large. If it exceeds 15 μm, the surface smoothness after the undercoat layer is provided Since it becomes insufficient, the gloss becomes insufficient, and the appearance may be inferior. Further, as will be described later, when a glossy expression layer is provided by a casting method, the adhesion to the cast drum becomes insufficient, and the surface may become rough or gloss unevenness may occur, resulting in poor appearance.
Among these, amorphous silica, alumina, and zeolite having high ink absorbability are preferably used, and amorphous silica is particularly preferably used.

Furthermore, this amorphous silica mainly consists of secondary particles in which primary particles of primary particles are aggregated, and has an average particle diameter of 1 to 15 μm.
The average particle diameter of the secondary particles is a particle diameter obtained by observing the silica particles being dispersed with an electron microscope (SEM, TEM), and is obtained by measuring the Martin diameter of the silica dispersed particles and averaging the particles. (See "Particle Handbook", Asakura Shoten, p. 52, 1991).
The average particle diameter of the primary particles that are aggregated to become secondary particles is not particularly limited, but is, for example, 3 nm to 50 nm.
In addition, the pigment having a large particle diameter is used alone or in combination of two or more.

The blending ratio of the small particle size pigment and the large particle size pigment is preferably 20/80 to 80/20 in mass ratio.
The blending ratio is less than 20 for small pigments and over 80 for large pigments, there is a risk that the gloss will decrease. If the pigment is less than 20, the ink absorptivity is lowered and the ink may flow on the surface and the printing may be blurred.

〔adhesive〕
In the solvent absorption layer, a commonly used known adhesive is used as a holding material for the pigment.
Examples of the adhesive include (i) proteins such as casein, soy protein, synthetic protein, (b) various starches such as starch and oxidized starch, (c) polyvinyl alcohol, cationic polyvinyl alcohol, silyl-modified polyvinyl alcohol, etc. (Ii) Cellulose derivatives such as carboxymethylcellulose and methylcellulose, (e) Conjugated diene polymers of styrene-butadiene copolymer and methylmethacrylate-butadiene copolymer, (f) Known adhesives generally used for coated paper, such as acrylic polymers, vinyl polymers such as ethylene-vinyl acetate copolymers and styrene-acrylic copolymers, can be mentioned.
These adhesives may be used alone or in combination of two or more.

Among these, it is preferable to use polyvinyl alcohol from the viewpoint of surface strength.
This polyvinyl alcohol preferably has a saponification degree of 95% or more, more preferably 98% or more.
When the degree of saponification is less than 95%, the strength of the coating layer is weakened, and foaming occurs at the time of adjusting the coating solution, so that the production efficiency of the coating solution is poor.
The polyvinyl alcohol preferably has a polymerization degree of 3500 or more, particularly preferably 3500 to 5000. If the degree of polymerization is less than 3500, the coating layer is weak and cracks are likely to occur, which may lead to the generation of paper dust during cutting. If it exceeds 5000, sufficient ink absorbability cannot be obtained. At the same time, the handling surface in adjusting the coating liquid may be difficult, which is not preferable.

The blending ratio of the pigment and the adhesive is generally adjusted in the range of 1 to 100 parts by weight, preferably 2 to 50 parts by weight with respect to 100 parts by weight of the pigment, although it depends on the type.
In the solvent-absorbing layer, various auxiliary agents such as dispersants, thickeners, antifoaming agents, antistatic agents, preservatives and the like used in the production of general coated paper are appropriately added as other compounding agents.
Moreover, you may add a fluorescent dye and a coloring agent in this solvent absorption layer.
Furthermore, a cationic compound ink fixing agent can be blended in the solvent absorbing layer as needed for the purpose of fixing the dye component in the ink for ink jet recording.
However, the ink dye is preferably fixed on the ink receiving layer provided on the solvent absorption layer or the outermost layer as much as possible in order to increase the printing (recording) density. A large amount of a cationic compound is blended in the layer or the outermost layer.

[Ink fixing agent]
Since this cationic compound fixes the pigment of the dye ink, it is particularly effective for the water resistance of the printed image.
Examples of the cationic compound include a cationic resin and a low molecular weight cationic compound (for example, a cationic surfactant). A cationic resin is preferable in terms of the effect of improving printing density, and it can be used as an aqueous solution of a water-soluble resin or an emulsion solution of a water-insoluble resin.

Examples of the cationic resin include (a) polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, (b) acrylic polymers having secondary or tertiary amino groups and quaternary ammonium groups, or These acrylamide copolymers, (c) polyvinylamine and polyvinylamidines, (d) dicyan-based cationic compounds represented by dicyandiamide-formalin copolymer, and (e) dicyandiamide-polyethyleneamine copolymer. Polyamine-based cationic compounds, (he) epichlorohydrin-dimethylamine copolymer, (to) diallyldimethylammonium-SO ₂ polycondensate, (thi) diallylamine salt-SO ₂ polycondensate, (li) diallyldimethylammonium chloride polymerization , (Nu) allylamine salt copolymer, (le) dialkylaminoethyl (meth) acrylate quaternary salt copolymer, (e) acrylamide-diallylamine copolymer, (wa) cationic having a 5-membered ring amidine structure Substances and the like.
These fixing agents are used alone or in combination of two or more.

  The cationic compound can be used in the range of 0.5 to 10 parts by mass, more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the pigment. If the blending amount is less than 0.5 parts by mass, the effect of improving the water resistance of the printed image may be difficult to obtain, and if it exceeds 10 parts by mass, the print density may be lowered, which is not preferable.

[Method for producing solvent absorbing layer]
The solvent absorption layer coating liquid composed of the above materials is generally adjusted to a solid content concentration of about 5 to 50% by mass, and ² to 100 g / m ² , preferably 5 to 50 g in dry mass on the paper substrate. / M ² , more preferably 10 to 20 g / m ² .
When the coating amount is less than 2 g / m ^2, or poor ink absorption, gloss when provided with a cast layer there is a possibility that may or may not appear sufficiently exceeds 100 g / m ^2, printing density This is not preferred because it may decrease or the strength of the coating layer may decrease and powder may easily fall off.

The solvent absorbing layer coating liquid is any one of various publicly known coating apparatuses such as blade coaters, air knife coaters, roll coaters, brush coaters, Champlex coaters, bar coaters, lip coaters, die coaters, gravure coaters and curtain coaters. Used to be coated on a paper substrate.
Further, the coated solvent absorbing layer may be subjected to a smoothing process such as super calendering or brushing as necessary.

<Ink receiving layer>
In the ink jet recording paper of the present embodiment, an ink receiving layer is provided on the solvent absorption layer. The ink receiving layer is applied as an aqueous coating solution on the solvent absorbing layer.
The ink receiving layer contains at least one selected from silica, alumina, and alumina hydrate as a pigment, and contains an adhesive that holds the pigment. As the pigment, in particular, amorphous silica is used. Preferably, polyvinyl alcohol is particularly preferably used as the adhesive.
The amorphous silica is a secondary particle having an average particle diameter of 90 to 500 nm, and the polyvinyl alcohol having a polymerization degree of 3500 or more is used.
The ink receiving layer composed of these is added with an ink fixing agent as necessary, and is coated so that the dry coating amount is 5 to 20 g / m ² .
By providing this ink receiving layer, this ink jet recording paper has high absorbency and print density, excellent water resistance of the ink, and high glossiness.

[Pigment]
If the average particle diameter of the amorphous silica as a pigment is less than 90 nm, the ink absorbability may not be sufficient, and the solvent may not sufficiently penetrate into the solvent absorption layer. The glossiness of the surface may be lowered, which is not preferable.
As the amorphous silica, wet method silica, gas phase method silica and the like are preferably used.
The ink receiving layer needs to contain at least one kind of pigment. However, within the range not impairing the effects of the present invention, one or more other known pigments usually used in the ink receiving layer are used. Two or more types can be used in combination.
These pigments to be used in combination are the same as those of the solvent absorption layer described above.

〔adhesive〕
The polyvinyl alcohol used in the ink receiving layer preferably has a degree of polymerization of 3500 or more, particularly preferably 3500 to 5000. If the degree of polymerization is less than 3500, the strength of the ink receiving layer is weak, which may lead to paper dust generation at the time of cutting. If it exceeds 5000, sufficient ink absorptivity cannot be obtained, and in coating liquid adjustment The handling surface may be difficult, which is not preferable.

The ink-receiving layer is not limited to the polyvinyl alcohol, and a known adhesive that is usually used can be used as long as the effects of the present invention are not impaired.
As this adhesive, the same adhesive as the above-mentioned adhesive used in the solvent absorbing layer can be used, and the adhesive selected and used from these can be used alone or in combination of two or more kinds It may be used in combination.

  In the ink receiving layer, an ink fixing agent, a dispersing agent, a crosslinking agent, a thickener, an antifoaming agent, an antistatic agent, an antiseptic, an ultraviolet absorber, a storage stability improving agent, a fluorescent whitening agent, and Various additives such as a colorant can be appropriately added.

  The above-mentioned ink fixing agent is for fixing the dye of the dye ink in the ink receiving layer, and in order to obtain good color developability and storage stability of the dye ink and ink absorption, the above-mentioned ink fixing agent is used for the above-mentioned solvent absorption layer. The same ink fixing agent is used.

[Method for producing ink receiving layer]
The ink receiving layer is produced by applying an ink receiving layer coating liquid comprising the above-described components onto the solvent absorbing layer.
The dry coating amount of the ink receiving layer is preferably 10 to ²⁰ g / m ² .
If the dry coating amount is less than 10 g / m ² , sufficient glossiness and ink absorbability may not be obtained, and if it exceeds 20 g / m ² , cracking of the coating layer tends to occur, It is not preferable because it is difficult to obtain good dot roundness and the printing density of pigment ink and dye ink may be insufficient.
The solid content concentration of the ink receiving layer coating liquid is preferably 5 to 50% by mass, and more preferably 5 to 20% by mass.
If the solid content concentration is less than 5% by mass, the drying efficiency of the ink receiving layer may be lowered, and if it exceeds 50% by mass, the coating layer may be easily cracked.
As a coating method of the ink receiving layer coating liquid, in addition to the coating apparatus used for the solvent absorbing layer described above, coating is performed using any of various known and publicly known coating apparatuses such as sprays. A construction method is mentioned.

In order to prevent cracking of the ink receiving layer, it is preferable to crosslink the adhesive using a crosslinking agent for crosslinking the adhesive in the ink receiving layer or a gelling agent that crosslinks and gels. .
These crosslinking agents (including gelling agents) are added to the ink receiving layer coating solution, or are applied in advance as an aqueous coating solution on the surface of the solvent absorbing layer before coating the ink receiving layer. Alternatively, the ink receiving layer may be applied to the surface after coating, or may be applied to the surface of the paper substrate before coating with the solvent absorbing layer.
As a crosslinking agent, the well-known crosslinking agent which has the crosslinking | crosslinked property with respect to an adhesive agent, or various well-known gelling agents which gelatinize an adhesive agent can be used.
When the adhesive is polyvinyl alcohol, examples of the cross-linking agent include aldehyde-based cross-linking agents such as glyoxal which is a compound having cross-linkability to polyvinyl alcohol, epoxy-based cross-linking agents such as ethylene glycol diglycidyl ether, bisvinylsulfonyl Examples of the vinyl-based cross-linking agent such as methyl ether and the gelling agent that cross-links and gels polyvinyl alcohol include boron-containing compounds such as boric acid and borax, zirconium compounds, aluminum compounds, and chromium compounds. Can be mentioned.
In the present embodiment, among these, a boron-containing compound that is a gelling agent is particularly preferably used because thickening or gelation occurs quickly.

Here, the boron-containing compound is an oxygen acid having a boron atom as a central atom and a salt thereof. Specific examples include orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid, and sodium, potassium and ammonium salts thereof.
Of these, orthoboric acid and disodium tetraborate are preferably used because they have an effect of increasing the viscosity of the coating solution to an appropriate degree.
The compounding amount of the boron-containing compound depends on the kind of the boron-containing compound and the degree of polymerization of polyvinyl alcohol, and is 0.01 to 2.0 g / m as a dry coating amount on either side of the solvent absorption layer or the ink receiving layer. ² to be contained.
When the coating amount of this boron-containing compound is less than 0.01 g / m ² , the crosslinking property with the hydrophilic adhesive and the gelation of the coating solution are not sufficient, and the coating layer may be cracked. There is. If the coating amount exceeds 2.0 g / m ² , the high crosslinking density with the adhesive is saturated, and the effect of preventing cracking of the coating layer is not further improved, so that it is not effective.

<Outermost layer>
In the present embodiment, an outermost layer composed of a glossy expression layer is provided on the ink fixing layer.
This outermost layer has a glossy surface by being cast as a glossing treatment.
The outermost layer is mainly composed of a pigment having a small particle diameter and an adhesive for holding the pigment.
This outermost layer is formed by applying a coating liquid prepared containing the above components to the surface of the ink receiving layer.

[Pigment]
As the pigment having a small particle diameter, those having an average particle diameter of 3 to 500 nm are used, and are dispersed as colloidal particles in the outermost coating liquid.
The form of the colloidal particles may be a single particle dispersion or an aggregate particle dispersion. However, in order to obtain a high printing density and high gloss, the colloidal particles are mainly composed of a single particle dispersion or an aggregate particle dispersion. Among them, those having a small particle diameter are preferably used.
Examples of the pigment include, for example, colloidal silica mainly composed of primary particles, gas phase method silica, mesoporous silica, fine silica composed of secondary particles such as wet method silica produced by condensing activated silicic acid, alumina, and alumina. Hydrates are mentioned.
Of the above pigments, vapor-phase process silica, colloidal silica, and alumina are preferably used because excellent gloss is obtained, and colloidal silica is generally used.
The average particle diameter has a more preferable predetermined range depending on the type of pigment used.

When colloidal silica is used as the pigment, the average particle size is preferably 3 to 200 nm, and is mainly a single particle dispersion in the coating solution.
In order to obtain a high printing density and a high glossiness, the outermost layer has a predetermined particle size and is preferably 5 to 90 nm.
When this average particle diameter exceeds 200 nm, it becomes difficult to obtain high print density and high gloss.
Colloidal silica can also be used sufficiently if the average particle size is 3 to 500 nm.

When fine silica of aggregated particles (secondary particles) is used as the pigment, the preparation method is not particularly limited. For example, secondary particles that are generally commercially available and have an average particle diameter of about several microns. The synthetic amorphous silica is preferably pulverized by mechanical means to give fine silica having an average particle size of 10 to 400 nm. The average particle diameter is more preferably 10 to 300 nm, further preferably 15 to 150 nm, and most preferably 20 to 100 nm.
Examples of the mechanical means include an ultrasonic homogenizer, a pressure homogenizer, a high-speed rotary mill, a roller mill, a container drive medium mill, a medium stirring mill, a jet mill, a sand grinder, and a nanomizer.

The small particle size pigment thus obtained is generally used as an aqueous dispersion (slurry or colloidal particles) having a solid content concentration of about 5 to 20%.
If the average particle size of the pigment having the small particle diameter is less than 3 nm, the ink absorbability may be lowered, and if it exceeds 500 nm, the glossiness and the print density may be lowered.
The small particle size pigments may be used alone or in combination of two or more.

〔adhesive〕
As the adhesive used for the outermost layer, a known adhesive used for ink jet recording paper, that is, the same adhesive as the above-described adhesive used for the solvent absorbing layer is used.
In addition, when an ink fixing agent is blended in the outermost layer coating solution, the adhesive is particularly preferably a cationically modified one.

  Among the adhesives, casein is preferable because it is excellent in releasability from a cast drum when developing gloss. Acrylic polymer emulsions and styrene-acrylic copolymer emulsions are preferred because the recorded images have excellent sharpness and gloss. These can also be used in combination.

When using an emulsion as said adhesive agent, a preferable mass mean molecular weight is 1000-10 million, More preferably, it is 5000-5 million.
If the molecular weight is less than 1000, the glossy layer may have insufficient strength, and if it exceeds 10 million, the stability of the emulsion may be insufficient.

[Production method of outermost layer]
The amount of the adhesive is adjusted in the range of 1 to 200 parts by mass, more preferably 10 to 100 parts by mass with respect to 100 parts by mass of the pigment. If this blending amount is less than 1 part by mass, the strength of the coating layer may be weakened and the surface may be easily damaged, or powder may fall off. If it exceeds 200 parts by mass, the ink absorbency will decrease, There is a possibility that desired ink jet recording suitability may not be obtained, which is not preferable.

  In addition, on this outermost layer, an ink fixing agent, a dispersant, a cross-linking agent, a thickener, a fluid denaturant, an antifoaming agent, an antistatic agent, an antiseptic, an ultraviolet absorber, a storage stability improving agent, Various additives such as a fluorescent brightening agent, a coloring agent, a water-proofing agent, and a printability improving agent can be appropriately added.

  As the ink fixing agent, the same ink fixing agent as that used in the solvent absorbing layer can be used.

  Examples of the thickener and flow modifier include synthetic resins such as styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer, proteins such as casein, soybean protein, and synthetic protein, and various starches such as starch and oxidized starch. , Cellulose derivatives such as polyvinyl alcohol, carboxymethylcellulose and methylcellulose, polycarboxylic acid, polyacrylic acid, acrylic emulsion, polyamide, polyester, alkali thickening type and nonionic surfactant are suitably used.

  Examples of the above water-proofing agent and printability improver include sodium chloride, ammonium chloride, zinc chloride, magnesium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, zinc sulfate, magnesium sulfate, ferrous sulfate, sodium nitrate, ammonium nitrate, first Sodium phosphate, ammonium phosphate, calcium phosphate, sodium polyphosphate, sodium hexametaphosphate, sodium formate, ammonium formate, sodium acetate, potassium acetate, sodium monochloroacetate, sodium malonate, sodium tartrate, potassium tartrate, potassium citrate, Ammonium and metal salts of inorganic and organic acids such as sodium lactate, sodium gluconate, sodium adipate, sodium dioctylsulfosuccinate and sodium aluminate, Amines such as ruamine, diethanolamine, diethylenetriamine, diisopropylamine, triethanolamine, ethanolamine, ethanolamine, phosphate ester, polyoxyethylene alkylphenol ether phosphate ester salt, polyoxyethylene ether phosphate ester salt, alkylphenol ether phosphate Phosphate esters such as ester salts, polyoxyethylene, alkyl ether, polyoxyethylene and ammonia water, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether and diglycidyl adipate Polyfunctional epoxy compounds such as esters, urea-formaldehyde, polyamide-epi Rorohidorin system, glyoxal and the like are used as appropriate.

The various additives are added to the outermost layer coating solution in the range of 0.05 to 10% by mass, preferably 0.1 to 5% by mass as the solid content concentration.
Furthermore, various auxiliary agents such as a dispersant, an antifoaming agent, a colorant, a fluorescent dye, an antistatic agent, and a preservative can be appropriately added to the outermost layer coating solution.
In addition, pigments such as alumina, colloidal silica, fine silica, clay and calcium carbonate can be added as other auxiliary agents.
In addition, when performing the rewetting process mentioned later, you may add these adjuvants to the wetting liquid used for a rewetting liquid except a pigment.

[Glossing treatment]
The outermost layer is formed on the glossy surface by various glossing treatments after coating a coating liquid containing the above components on the ink receiving layer and drying it.
Glossing can be done with a super calender, but in order to provide high gloss and excellent ink jet recording suitability, a cast method using a mirror drum or a film transfer method (hereinafter, combined with this) It is preferably performed by “casting”.

In general, cast processing means that a coating layer is dried on a smooth cast drum (mirror finish metal, plastic, glass, etc.), mirror finish metal plate, plastic sheet or film, glass plate, By copying these smooth surfaces onto the coating layer, a smooth and glossy coating layer surface is obtained. The method of obtaining a glossy surface by casting using a mirror drum heated in this,
(B) After forming the outermost layer by applying the above outermost layer coating solution on the substrate or the coating layer of the substrate, heating while the outermost layer coating solution is in a wet state Pressure-dried to the mirror-finished drum, dried to finish the outermost layer with a glossy surface (wet cast method),
(B) A method in which the outermost layer coating liquid is once dried to form the outermost layer, and then the outermost layer is rewet and pressed onto a heated mirror drum and dried to give a glossy surface (rewet casting method).
The outermost layer on the substrate or the coating layer of the substrate is gelled to form a gel-like outermost layer, and this outermost layer is pressed against a heated mirror drum and dried to give a glossy surface (gelation cast method) ),
(C) Without coating the outermost layer coating solution on the base material, apply the outermost layer coating solution directly to the heated mirror drum, and then press contact with the base material or the coating layer of the base material , Drying, moving the outermost layer onto the base material or the coating layer of the base material to finish the glossy surface (precast method),
Is mentioned.
In these casting processes, the temperature of the heated mirror drum is, for example, 50 to 150 ° C, preferably 70 to 120 ° C.

Furthermore, a film transfer method can also be adopted as the casting process.
As a film transfer system,
(A) After forming the outermost layer by applying the above outermost layer coating solution on the substrate or the coating layer of the substrate, a smooth film or the like can be used while the coating solution is in a wet state. A method of layering and drying, then peeling off a smooth film or sheet to finish the outermost layer with a glossy surface,
(B) Apply the coating liquid on a smooth material consisting of a smooth film or sheet, and apply the smoothing material on the base material to be bonded or on the base material coating layer that is in a somewhat wet state. After press-contacting and drying, a smooth film or sheet is peeled off, and the outermost layer is moved onto the substrate or the coating layer of the substrate to finish it as a glossy surface,
There is.
Compared with the film transfer method, the cast method using a heated mirror drum tends to be superior in surface smoothness, and is often advantageous in terms of productivity and cost.

In the present embodiment, the casting process described above is a casting process using a heated mirror drum, and the solvent absorption layer and the ink receiving layer provided with the coating liquid on the substrate are dried, and then Applying the outermost layer coating liquid to the heated mirror drum immediately, and then applying the wet cast method, which is dried and finished, it is easy to form a uniform coating layer, high print density, and gloss Is particularly preferable because an excellent outermost layer can be easily obtained.
Moreover, in the said cast process, it is preferable that the coating amount of outermost layer shall be 0.1-30 g / m < ² > by dry solid content.
If it is less than 0.1 g / m ² , the print density and gloss may not be sufficiently obtained. If it exceeds 30 g / m ² , the effect is almost saturated. Is not preferable.

  In each of the above casting processes, when applying the outermost layer coating liquid, various known coating methods can be used, for example, blades, brush coaters, champex coaters, bar coaters, gravure coaters, etc. A coating method in which coating is performed using any of the coating apparatuses can be used.

When performing the casting process, it is preferable to use a release agent in order to smoothly peel off the outermost layer from the cast drum or the like.
The mold release agent can be used by any one of a method of adding to the outermost layer coating solution, a method of applying to the surface of a cast drum, and a method of adding to the wetting solution.
Examples of the 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 oleic acid. Examples include higher fatty acid alkali salts such as ammonium, 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.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Further, “parts” and “%” in the following examples and comparative examples represent parts by mass and mass%, respectively, unless otherwise specified.

Example 1
<Production of support>
Wood pulp (LBKP; freeness 500 ml CSF) 100 parts, filler (calcium carbonate 3: talc 1 ratio) 15 parts, commercially available sizing agent (trade name Fibran 81K, Nippon NS Co., Ltd.) 0.05 parts, sulfate band 0.45 parts, 0.45 parts of starch, 0.4 parts of polyamide / epichlorohydrin resin (paper strength enhancer), a papermaking material consisting of a little yield improver and basis weight of 188 g / m ² on a long net paper machine A paper substrate as a support was obtained. The paper substrate had a steecht degree of 60 seconds, a thickness of 210 μm, and an air permeability of 30 seconds.

<Preparation of solvent absorption layer>
[Adjustment of solvent absorption layer coating solution]
Synthetic amorphous silica (trade name: Fine Seal X-45, manufactured by Tokuyama Co., Ltd., secondary particles) 50 parts as colloidal silica (trade name: Snowtex OL, 50 parts by Nissan Chemical Co., Ltd. and 20 parts by weight of polyvinyl alcohol (trade name: PVA145, manufactured by Kuraray Co., Ltd., degree of saponification 99%, degree of polymerization 4500) as a binder, and coating for a solvent absorption layer having a solid content concentration of 15% A liquid was prepared.

<Preparation of coating solution for ink receiving layer>
Gas phase method silica (trade name: Aerosil 300, manufactured by Nippon Aerosil Co., Ltd., secondary particles) as a pigment, polyamidine-based cationic polymer (trade name: Himax SC-700M, mass average molecular weight of about 20,000, manufactured by Hymo Co.) 25 parts of a 35% aqueous solution and 775 parts of ion-exchanged water were mixed. The mixture thus obtained was dispersed with a stirrer and then treated with a wet ultrafine atomizer Nanomizer to obtain fine silica having an average particle size of 300 nm.
Next, 360 parts of a 5% aqueous solution of polyvinyl alcohol (trade name: PVA145, manufactured by Kuraray Co., Ltd., saponification degree 99%, average polymerization degree 4500) as a binder, and a small amount of an antifoaming agent and a dispersing agent are added to the obtained treatment liquid. And water were added to prepare an ink-receiving layer coating solution having a solid concentration of 8%.

<Adjustment of outermost layer coating solution>
Single particle dispersion colloidal silica (trade name: Snowtex OL, manufactured by Nissan Chemical Co., Ltd.) having an average particle diameter of 45 nm as a pigment, 15 parts of an acrylic emulsion (trade name: Aquabrid 914, manufactured by Daicel) and casein as a binder 5 parts are mixed, and 1 part of potassium stearyl phosphate (trade name: Wopol 1800, manufactured by Matsumoto Yushi Co., Ltd.) is mixed as a release agent to prepare a coating solution for the outermost layer as the outermost layer having a solid content concentration of 10%. did.

<Preparation of inkjet recording paper>
The prepared solvent-absorbing layer coating solution was applied onto the produced paper substrate to form a solvent-absorbing layer.
After that, borax aqueous solution and separately prepared ink receiving layer coating liquid are applied in order on the solvent absorbing layer, dried to form an ink receiving layer, and the outermost layer coating liquid is applied thereon. Then, wet casting was performed to obtain an ink jet recording paper.

(Example 2)
50 parts of synthetic amorphous silica (trade name: Fine Seal X-45, manufactured by Tokuyama Corporation, secondary particles) having an average particle diameter of 4.5 μm as a pigment in the solvent absorbing layer coating liquid of Example 1, average particle Inkjet recording paper was obtained in the same manner as in Example 1 except that 50 parts of gel silica (trade name: Silojet 703A, manufactured by Grace Devison) consisting of secondary particles having a diameter of about 300 nm was used.

(Example 3)
50 parts of synthetic amorphous silica (trade name: Fine Seal X-45, manufactured by Tokuyama Corporation, secondary particles) having an average particle diameter of 4.5 μm as a pigment in the solvent absorbing layer coating liquid of Example 1, average particle Single particle dispersion colloidal silica having a diameter of 45 nm (trade name: Snowtex OL, manufactured by Nissan Chemical Co., Ltd.), gel silica composed of secondary particles having an average particle diameter of about 300 nm (trade name: Silojet 703A, Grace Devison) An ink jet recording paper was obtained in the same manner as in Example 1 except that 25 parts were used.

(Comparative Example 1)
100 parts of synthetic amorphous silica (trade name: Fine Seal X-45, manufactured by Tokuyama Co., Ltd., secondary particles) as the pigment of the solvent absorption layer, and polyvinyl alcohol (trade name: PVA117, Kuraray) as the binder Inkjet recording paper was obtained in the same manner as in Example 1 except that 20 parts of a saponification degree 99%, polymerization degree 1700) were mixed to prepare a solvent absorption layer coating solution having a solid content concentration of 15%.

(Comparative Example 2)
Gel part silica (trade name: Silojet 703A, manufactured by Grace Devison) 100 parts as secondary pigment having an average particle diameter of about 300 nm as a pigment of the solvent absorption layer, polyvinyl alcohol (trade name: PVA117, manufactured by Kuraray Co., Ltd.) as a binder, An ink jet recording paper was obtained in the same manner as in Example 1 except that 20 parts of a saponification degree of 99% and a polymerization degree of 1700) were mixed to prepare a solvent absorption layer coating solution having a solid content concentration of 15%.

(Evaluation method and evaluation criteria)
About the inkjet recording paper obtained by the said Example and the comparative example, the printability in inkjet recording and the glossiness of the paper surface were evaluated by the following method.

[Printability in inkjet recording]
Evaluation of printability using both dye ink and pigment ink type printers, evaluated according to the following items: print density, ink absorption, uniformity of solid print area, glossiness of print area, and glossiness of paper surface Went.

<Evaluation printer>
Commercially available dye ink type ink jet printer (trade name: PM-G800, manufactured by Seiko Epson Corporation).

<Print density>
Black solid printing was performed, and the printing density was measured with an X-light reflection densitometer (938 Spectrodensitometer).

<Ink absorbability>
Black, cyan, magenta, yellow, red, green, and blue solid colors are placed on the grid so that they are in contact with each other, and ink bleeding at the boundary between the colors is visually observed. Observed and evaluated according to the following criteria.
○: Printing blur is not recognized at all, and excellent level ○-: Printing blur is slightly, but there is no practical problem △: Printing blur is slightly, practically problematic level ×: Printing Level of serious blurring and a serious problem in practical use

<Uniformity of solid print part>
The printing unevenness (dark shading unevenness) of the solid printing portion of two colors of cyan ink and magenta ink was visually observed and evaluated according to the following criteria.
○: Excellent level with no printing unevenness.
Δ: Level of printing unevenness and slightly problematic in practical use.
X: Level at which printing unevenness is significant and becomes a serious problem in practical use.

<Glossiness of printed part>
Print photographic images (JIS-X-9204 compliant “High-Definition Color Digital Standard Image (XYZ / SCID) Data”, Image Identification Symbol: N1, Image Name: Glass and Women) It observed visually and evaluated by the following reference | standard.
◎: Excellent level with no unevenness in the print glossiness of the entire image ○: The print glossiness is slightly lower in areas with dark print coloration, but does not cause any problems x: Partially The level where printing gloss disappears and becomes a serious problem in practical use

<Glossiness of paper surface>
The glossiness was evaluated according to the following criteria by visually observing glossiness and smoothness from the lateral direction with respect to the surface of the blank recording paper.
◎: Very high glossiness ○: High glossiness ×: Inferior glossiness

  The evaluation results are shown in Table 1.

As is clear from the results shown in Table 1, in Examples 1 to 3 according to the present invention, all the above evaluation items are good, and in particular, Examples 1 and 3 are glossiness of the printed portion, and the surface of the paper. It is extremely excellent in glossiness.
On the other hand, Comparative Example 1 is a level that is practically a problem in the uniformity of the solid print portion, and Comparative Example 2 is a level that is a practical problem in the ink absorption and the uniformity of the solid print portion. there were.

Claims (6)

Inkjet recording comprising a support and two or more coating layers supported on the support, and a surface portion of the coating layer forming a glossy surface by glossing treatment In paper
Between the support and the outermost layer, an ink receiving layer that absorbs ink and fixes a pigment in the ink, and a solvent absorption layer that absorbs a solvent in the ink,
The solvent absorption layer is composed of at least one kind each of a pigment having a small particle size composed of a single substance having an average particle size of 1 to 500 nm and a pigment having a large particle size having an average particle size of 1 to 15 μm. Containing selected pigments,
Inkjet recording paper characterized by the above. The mixing ratio of the small particle size pigment contained in the solvent absorption layer and the large particle size pigment is 20/80 to 80/20 by mass ratio.
The inkjet recording paper according to claim 1. The solvent absorption layer contains an adhesive that holds the respective pigment, and the adhesive contains polyvinyl alcohol having a saponification degree of 95% or more.
The ink jet recording paper according to claim 1, wherein the ink jet recording paper is used. The polyvinyl alcohol has a polymerization degree of 3500 to 5000,
The inkjet recording paper according to claim 3. The outermost layer contains a pigment having an average particle diameter of 3 to 500 nm.
The inkjet recording paper according to any one of claims 1 to 4, wherein The pigment of the outermost layer is colloidal silica mainly composed of primary particles, and the average particle diameter is 3 to 200 nm.
The inkjet recording paper according to claim 5.