JP2008162239A - Ink jet recording paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet recording paper which keeps an absorbing capacity and an absorbing rate of an ink solvent large, and coating layer strength enough, and makes environmental curling, after printing curling and fold splitting hard to generate. <P>SOLUTION: The ink jet recording paper includes two or more coating layers on a paper base material of a basis weight of 105-250 g/m<SP>2</SP>, wherein a first coating layer which contacts with a paper base material includes at least one kind selected from calcium carbonate and kaolin (including clay), a second coating layer which contacts with the first coating layer includes a fine secondary pigment of 0.01-1 μm of a mean particle diameter and a water soluble resin binder, and the coating amount of the second coating layer is smaller than the coating amount of the first coating layer, and is 0.01-0.06 times of the paper base material basis weight. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inkjet recording paper having a high coating film strength and hardly causing environmental curling, post-printing curling, and cracking. Depending on the manufacturing method, high gloss can be achieved.

  The ink jet recording method that forms an image by ejecting water-based ink from fine nozzles is low in recording noise, easy to make full color, capable of high-speed recording, and in the case of printing a small number of copies. It has advantages such as a lower printing cost than other printing apparatuses. For this reason, this ink jet recording method is widely used in terminal printers, facsimiles, plotters, form printing, and the like.

  Ink jet recording paper is required to have an ink absorption capacity and an ink absorption speed. Therefore, a first coating layer (mainly absorbing solvent in ink) and a second coating layer (fixing dye in ink) are required. In general, an ink absorption capacity and an ink absorption speed are improved by providing two or more coating layers including a main function) (Patent Document 1). Since these coating layers are formed by including pigment silica fine particles and a binder, it is inevitable that the strength of the coating layer decreases as the coating layer becomes thicker due to multilayering. Further, since silica fine particles are used for all layers, environmental curling and post-printing curl are likely to occur.

  In order to improve gloss, absorbency, coating layer strength, etc., alkaline earth metal salts (for example, calcium carbonate) are used in addition to silica fine particles as a lower layer pigment, and polyvinyl alcohol or latex adhesive is used as a binder. What forms the coating layer is also known (patent documents 2, 3, and 4). These recording sheets were able to obtain a certain coating layer strength. In order to achieve high gloss and high image quality, the upper layer is formed with a submicron order fine pigment. As the pigment becomes smaller, the pores of the coating layer become smaller, and there has been a problem that the recording material curls due to environmental changes (particularly humidity change) and moisture evaporation after printing. In addition, the coating film under low humidity tends to break.

JP 2004-167959 A JP 2002-292996 A JP 2002-356059 A JP 2005-271444 A

The technical problem of the present invention is to provide an ink jet recording paper having a large ink solvent absorption capacity and absorption speed, sufficient coating layer strength, and less likely to cause environmental curling, post-printing curling and cracking. . In addition, the structure of the present invention can achieve high gloss by the manufacturing method.
In general, in order to obtain high image quality, a highly transparent submicron level pigment is used. As the pigment becomes smaller, the number of pores in the coating film increases, the pore diameter becomes smaller, and the stretching force by the capillary tube becomes larger. Moisture absorption to moisture release of the coating film, particularly product curl after the solvent component in the ink was evaporated after printing was a big problem. Although it is better that the coating amount of the second coating layer containing a highly transparent pigment and having large expansion and contraction is small, there is a problem that high image quality cannot be obtained. As a result of intensive studies, the present invention has been achieved by reducing the coating amount of the second coating layer of the first coating layer and maintaining the high image quality while maintaining the balance with the basis weight of the base material. It was found that the problem was solved and the cracking under low humidity was also greatly improved.

The present invention has been made in view of the above circumstances, and as a result of intensive studies, the present inventors have found a first coating layer containing a specific pigment on a paper substrate having a constant basis weight. The second coating layer provided and in contact with the first coating layer contains a fine secondary pigment having an average particle diameter of 0.01 to 1 μm and a water-soluble resin binder, and the coating amount of the second coating layer is the first coating layer. It has been found that the above problems can be solved by making the paper layer basis weight 0.01 to 0.06 times less than the coating amount of the construction layer, and the present invention has been completed.
In the inkjet recording paper having two or more coating layers on a paper substrate having a basis weight of 105 to 250 g / m ² , the first coating layer in contact with the paper substrate is composed of calcium carbonate, kaolin (containing clay). The second coating layer in contact with the first coating layer contains a fine secondary pigment having an average particle diameter of 0.01 to 1 μm and a water-soluble resin binder, and contains the second coating layer. The inkjet recording paper is characterized in that the coating amount of the working layer is smaller than the coating amount of the first coating layer and is 0.01 to 0.06 times the basis weight of the paper substrate.

According to a preferred aspect of the present invention, the second coating layer is subjected to a mirror finish by pressing onto a heated mirror drum while in a wet state.
According to a preferred configuration aspect of the present invention, the second coating layer contains at least one cationic latex having an average particle diameter of 6 to 100 nm.
According to a preferred configuration aspect of the present invention, the second coating layer contains at least one boron compound.
According to the preferable structure aspect of this invention, it has a 3rd coating layer further on a 2nd coating layer, and the application quantity of a 3rd coating layer is 0.01 to 0.5 time of a 2nd coating layer. And contains colloidal particles.
According to a preferred aspect of the present invention, the third coating layer is subjected to a mirror finish by being pressed against a heated mirror drum while in a wet state.

  According to the present invention, an ink jet recording paper having a large ink solvent absorption capacity and absorption speed, sufficient coating layer strength, environmental curling, post-printing curling and cracking hardly occurring, and good print image quality can be obtained. It is done.

  Hereinafter, the paper base material, the first coating layer, the second coating layer, and the third coating layer formed as necessary will be described in detail.

<Paper base material>
Examples of the paper substrate include high-quality paper, medium-quality paper, coated paper, art paper, and cast-coated paper. These paper base materials are preferably manufactured using wood pulp as a 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. of these pulps can be adjusted by adjusting the beating degree by a beating machine, and the beating degree (CSF tester value: JIS-P-8121) is not particularly limited. However, generally about 250-550 ml is preferable.

  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

  A filler can be added to these wood pulps as necessary. As the filler, talc, calcium carbonate, clay, kaolin, calcined kaolin, silica, zeolite 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.

  The sizing agent includes (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, Protein) such as gelatin and casein, (d) alkyl ketene dimer, (e) anionized polyacrylamide resin, (f) polyamide polyamine epichlorohydrin resin, (g) sodium polyacrylate, sodium styrene-maleic anhydride copolymer, Known sizing agents used for general paper base materials such as a salt of a synthetic polymer such as sodium polystyrene sulfonate are used.

  Increasing the air permeability can be achieved, for example, by adding a sizing agent or adjusting the tightness per unit volume of the paper substrate by pressing. For the purpose of improving the adhesiveness, adhesion treatment or adhesion treatment may be performed in advance. The smoothness is not particularly limited, but in order to obtain a highly glossy and highly smooth surface, the Oken-style smoothness is preferably 300 seconds (J. TAPPI No. 5) or more. The opacity of the paper substrate 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. Preferably, it is 93% or more.

  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.

In the present invention, a paper substrate having a basis weight of 105 to 250 g / m ² is used. If it is less than 105 g / m ² , the paper tends to be environmentally curled, and the solvent absorption capacity also decreases, which is not preferable. When it exceeds 250 g / m ² , the surface quality of the coating layer may be inferior.

<First coating layer>
In the inkjet recording paper of the present embodiment, the first coating layer is provided on the paper base material. The first coating layer contains a pigment and a binder for holding the pigment, and mainly absorbs the ink solvent after the dye and the pigment ink are fixed or captured in the second coating layer described later. It is to act. However, it is also possible to capture a dye that is not fixed by the second coating layer. And this 1st coating layer is possible also as a barrier layer which covers the unevenness | corrugation of a paper base material, raises the surface smoothness of an inkjet recording paper, improves concealment property, and improves whiteness. Moreover, it has the effect | action of reducing the gas which degrades ink dyes and pigments, such as ozone and NOx which approach into a 2nd coating layer from a base material side.

The present invention contains at least one of calcium carbonate and kaolin (containing clay) as a pigment of the first coating layer, and appropriately uses a latex adhesive and a water-soluble resin as a binder for holding these pigments. Selected. The latex adhesive is preferably selected as a main component from the viewpoint of coating strength and coating suitability.
By providing such a first coating layer on a paper substrate, the ink jet recording paper produced according to the present embodiment has good ink absorbability, print density, print bleeding, solid uniformity, etc. It will be excellent.

[Pigment]
The calcium carbonate and kaolin (containing clay) are not particularly limited, but from the standpoint of solvent absorption, it is preferable to use heavy calcium carbonate as the calcium carbonate and calcined kaolin as the kaolin. Kaolin and clay generally have the structural formula Al ₂ O ₃ .nSiO ₂ .mH ₂ O. In view of the balance between strength and ink absorbability, the average particle size of calcium carbonate and kaolin (containing clay) of the present invention is preferably 0.1 to 2 μm. If the average particle size is less than 0.1 μm, the ink absorbability may be lowered, and if it exceeds 2 μm, the strength of the first coating layer may be lowered, which is not preferable.

  From the strength of the coating film, calcium carbonate and kaolin (containing clay) are preferably used as main components. Although it may be used alone or in combination, it is preferable to use it in combination from the balance between absorbency and strength. In particular, a combined system of calcium carbonate and kaolin is preferred. If the blending ratio of calcium carbonate and kaolin is in the range of 5:95 to 70:30 in terms of mass ratio, an improvement in coating layer strength and absorbency can be expected due to a synergistic effect.

  A coating solution may be prepared by dispersing and mixing calcium carbonate and kaolin (containing clay) having a predetermined particle size in an aqueous solution. However, if the pigment is larger than the predetermined particle size, Then, after pulverizing and dispersing until a predetermined particle diameter is obtained, a predetermined amount of each aqueous solution can be mixed to obtain a coating solution. In order to efficiently perform dispersion and pulverization, it is effective to add a general commercially available dispersant (both anion and cation are acceptable).

In the first coating layer, known pigments that are usually used for recording paper can be used in combination as long as the effects of the present invention are not impaired.
Examples of these pigments include amorphous silica, zinc oxide, aluminum oxide, titanium oxide, colloidal silica, zeolite, synthetic zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, and styrene. Examples thereof include plastic pigments, hydrotalcite, urea resin plastic pigments, and benzoguanamine plastic pigments. Amorphous silica is preferred in order to quickly stabilize the color after printing (dry down). Among amorphous silicas, gel method silica and colloidal silica are more preferable. The pigment selected and used in combination is preferably contained in a proportion of 15% or less with respect to the total pigment in terms of coating strength. Moreover, even if it is individual, 2 or more types may be sufficient.

[Binder]
As the binder, 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 and acrylic polymer latex are preferably used. These latex adhesives may be used alone or in combination of two or more.

Examples of water-soluble adhesives include protein such as casein, soybean protein and synthetic protein, various starches such as starch and oxidized starch, polyvinyl alcohol including modified polyvinyl alcohol such as polyvinyl alcohol, cationic polyvinyl alcohol and silyl modified polyvinyl alcohol. , 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 liquid viscosity modifier.

  It is preferable that the compounding quantity of the adhesive agent of a 1st coating layer is 7-70 mass parts with respect to 100 mass parts of what is called a pigment containing a calcium carbonate and a kaolin (containing clay), and is 10-40 mass parts. Is more preferable. If the blending amount is less than 7 parts by mass, the coating film strength may not be sufficient, and if it exceeds 70 parts by mass, the ink absorbability may be impaired.

  In addition to the components described above, various auxiliary agents such as dispersants, thickeners, antifoaming agents, antistatic agents, preservatives, and the like, which are used in general recording paper production, are appropriately added to the first coating layer. Can do. In addition, fluorescent dyes / pigments, colorants, and the like can be added.

The dry coating amount of the first coating layer is 3 to 35 g / m ² . Preferably it is 5-25 g / m < ² >, More preferably, it is 7-20 g / m < ² >. If the dry coating amount is less than 3 g / m ² , the ink absorbability of the first coating layer may be insufficient, and if it exceeds 35 g / m ² , the coating strength decreases, which is not preferable.
A 1st coating layer is produced by applying the coating liquid for 1st coating layers which consists of the above-mentioned component on the said paper base material, and drying. The solid content concentration of the first coating layer coating solution is preferably 10 to 60% by mass.

  Coating methods for the first coating layer coating solution include blade coaters, air knife coaters, roll coaters, brush coaters, Champlex coaters, bar coaters, lip coaters, gravure coaters, curtain coaters, slot die coaters, slide coaters, etc. A coating method using any of various known coating apparatuses can be used. Furthermore, you may perform smoothing processes, such as a super calender and a brushing, to this coated 1st coating layer as needed. Alternatively, it can be formed by on-machine coating applied on a paper machine.

<Second coating layer>
In the inkjet recording paper of the present embodiment, a second coating layer for fixing an ink image is provided on the first coating layer.
The second coating layer contains a pigment and a water-soluble resin adhesive as a binder for holding the pigment. In order to better fix the dye or pigment in the ink, it is preferable to contain an ink fixing agent.

[Pigment]
As the pigment of the second coating layer, a fine secondary pigment having an average particle diameter of 0.01 to 1 μm is used. It is preferably selected from silica, alumina, and alumina hydrate. Among these pigments, silica is particularly preferable, and dry silica is more preferable.
Further, the silica is preferably silica-cationic compound aggregate particles obtained by mixing silica and a cationic compound, and this is pulverized and dispersed to form 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.
If the particle diameter is less than 0.01 μm, the ink absorbability may be lowered, and if it exceeds 1 μm, the transparency of the coating film is inferior and the print density may be remarkably lowered.

  In the second coating layer, a known pigment used for ordinary 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 those for the first coating layer described above can be used. The pigments selected and used in combination can be used alone or in combination of two or more. Good.

〔adhesive〕
The water-soluble resin binder used for the second coating layer is preferably polyvinyl alcohol. The polyvinyl alcohol preferably has a degree of polymerization of 2000 to 6000, and most preferably 3000 to 5000. If the degree of polymerization is less than 2000, the adhesive strength is weak and the coating film may be cracked. If it exceeds 6000, the handleability may be inferior in the production of the second coating layer coating solution, such being undesirable.

  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 of ink absorbability, coating film strength, and crack suppression, and 8 to 25 parts by mass. It is more preferable that it is a mass part, and it is still more preferable that it is 10-20 mass parts. If the blending amount is less than 6 parts by mass, cracks may occur in the second coating 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.

The 2nd coating layer can use the well-known binder used for a normal recording paper in combination with the said polyvinyl alcohol in the range which does not impair the effect of this invention.
Examples of these binders include water-soluble resin systems such as polyvinyl acetal, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, casein, soy protein, synthetic proteins, and starch. Examples of the latex type include styrene-butadiene copolymer, polyester type, acrylic type, urethane type and the like.
These binders used in combination may be used alone or in combination of two or more. Acrylic and urethane latexes have the effect of improving the adhesive strength and gloss as a binder, and are preferably blended. From the viewpoint of dye fixing properties, a cationic binder is preferably selected as the latex binder.

  The average particle size range of the acrylic and urethane latex is 6 to 100 nm, preferably 8 to 80 nm, and more preferably 10 to 60 nm. If it is less than 6 nm, a problem of inhibiting ink absorbability occurs. If it exceeds 100 nm, the transparency of the coating film may be significantly reduced. The glass transition temperature is in the range of −40 to 110 ° C., preferably −30 to 80 ° C., and more preferably −20 to 50 ° C. from the balance of adhesive strength and gloss. If it is less than −40 ° C., the gloss may be difficult to develop. On the other hand, if it exceeds 110 ° C., the adhesive strength may be significantly reduced. The blending amount is 6 to 50 parts, preferably 8 to 40 parts, more preferably 10 to 30 parts with respect to 100 parts of the pigment. When the blending amount is less than 6 parts, the effect of improving gloss is small. On the other hand, if it exceeds 50 parts, the ink absorbability may be impaired.

[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.
Examples of the cationic compound include a cationic resin and a low molecular weight cationic compound (for example, a cationic surfactant). 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.

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. From the viewpoint of dispersion stability of the paint, the molecular weight of the cationic resin is preferably in the range of 1,000 to 20,000.

  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, as the pigment and the ink fixing agent in the second coating layer, the pigment used in the first coating layer and the pigment that can be used together, and the cationic compound, particularly silica and the cation. It is preferable to use silica-cationic compound aggregate particles by mixing with an active compound to form silica-cationic compound aggregate particles, which are pulverized and dispersed to form ultrafine particles to form silica-cationic compound aggregate particles. As the 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.

[Crosslinking agent]
For the purpose of improving the film formability of the second coating layer and preventing cracking, it is preferable to add a cross-linking agent having cross-linkability with polyvinyl alcohol and gel the coating to cross-link. Content of this crosslinking agent is 0.001-10 mass parts with respect to 100 mass parts of polyvinyl alcohol, Preferably it is 0.01-5 mass parts, More preferably, it is 0.05-1 mass part. If the content is less than 0.001 part by mass, crosslinking may not be sufficiently achieved. If the content exceeds 10 parts by mass, the coating film becomes too hard and the coating layer is broken and paper dust is produced. There is a possibility that it becomes easy, and it is not preferable.

The method for adding the crosslinking agent is not particularly limited. For example, the crosslinking agent may be added to the second coating layer coating solution, contained in the first coating layer, or the first coating before the ink receiving layer is coated. Various methods such as coating on the surface of the working layer, whether the coating layer is coated or impregnated after the second coating layer is coated and before the coating layer exhibits a reduced drying rate It is done.
This cross-linking agent includes, for example, aldehyde-based cross-linking agents such as glyoxal, epoxy-based cross-linking agents such as ethylene glycol diglycidyl ether, vinyl-based cross-linking agents such as bisvinylsulfonylmethyl ether, boron-containing materials such as aluminum alum, boric acid and borax. Compounds.
In the present embodiment, it is particularly preferable to use a boron-containing compound having an excellent hardening effect, and among these, boric acid and borax are particularly preferable.

〔Additive〕
In the second coating layer, in addition to the above-described components, a dispersant, a thickener, an antifoaming agent, an antistatic agent, an antiseptic, an ultraviolet absorber, a preservability improving agent used in general recording paper production, Various additives such as a fluorescent brightener and a colorant can be appropriately added.

[Application amount of second coating layer]
In the present invention, in order to prevent environmental curling and post-printing curling and improve coating cracking under low humidity, it is preferable that the coating amount be small. If the application amount of the second coating layer is simply reduced, there arises a problem that image quality and ink absorbability deteriorate. As a result of the extensive studies by the inventors, the coating amount of the second coating layer is less than that of the first coating layer and is 0.01 to 0.06 times the basis weight of 105 to 250 g / m ² paper substrate. It was found that the image quality, ink absorptivity, and curl (environmental curl, post-printing curl) can be balanced when the range is set. Moreover, the coating film cracking under low humidity is also significantly improved. The coating amount is preferably in the range of 0.02 to 0.05 times that of the paper substrate, and most preferably in the range of 0.03 to 0.04 times.
If the coating amount of the second coating layer is less than 0.01 times the paper substrate, there arises a problem that the image quality and ink absorbability are remarkably lowered. On the other hand, if it exceeds 0.06 times, environmental curl and post-printing curl are likely to occur, and cracking under low humidity is inferior, which causes a practical problem.
The solid content concentration of the second coating layer coating solution is preferably 5 to 27 mass%, more preferably 8 to 20 mass%. If the solid content concentration is less than 5% by mass, the drying efficiency of the second coating layer may be reduced, and if it exceeds 27% by mass, the coating solution viscosity is high and coating may be difficult. It is not preferable.

Coating methods for the coating liquid for the second coating layer include blade coaters, air knife coaters, roll coaters, brush coaters, champlex coaters, bar coaters, lip coaters, gravure coaters, curtain coaters, slot die coaters, slide coaters, and sprayers. A coating method in which coating is performed using any one of various publicly known coating apparatuses such as the above can be used.
In addition, in order to improve glossiness, the 2nd coating layer can be cast processed later. In this case, the second coating layer is a surface gloss layer.

<Third coating layer>
In the present embodiment, in order to further increase the glossiness, it is preferable to form a surface glossy layer that expresses gloss as the third coating layer on the second coating layer. This third coating layer is mainly composed of a pigment having a small particle diameter and an adhesive which is a binder thereof, and a coating liquid prepared containing these is applied to the surface of the second coating layer. Formed.
This surface glossy layer can be further glossed by various glossing treatments. For example, high gloss can be achieved by using a super calendar, but cast processing described later is most preferable.

[Casting]
In order to give high gloss and excellent ink jet recording suitability by the above glossing treatment, it is preferable to carry out by a cast method using a mirror drum or a film transfer method (hereinafter, collectively referred to as “cast processing”). .

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,
(A) After the surface glossy layer coating liquid is applied on the coating layer to form a surface glossy layer, the mirror drum heated while the surface glossy layer coating liquid is in a wet state Pressure-dried and dried to finish the glossy surface (wet cast method)
(B) The coated liquid for the glossy surface layer is once dried to form a glossy surface layer, and then the glossy surface layer is rewet with a wetting liquid, pressed against a heated mirror drum, dried and glossed Surface finishing method (Rewet cast method)
(C) A method in which the surface glossy layer on the coating layer is gelled to form a gel-like surface glossy layer, and this surface glossy layer is pressed against a heated mirror drum and dried to give a glossy surface (gelation cast method) ,
(2) After coating the surface gloss layer coating liquid directly on the heated mirror drum, press and dry the coating layer on the coating layer and move the surface gloss layer onto the substrate or the coating layer of the substrate. To finish 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,
(B) After the surface glossy layer coating liquid is applied onto the coating layer to form a surface glossy layer, a smooth film or sheet is stacked while the coating liquid is in a wet state, and then dried. After finishing the glossy surface by peeling off a smooth film or sheet,
(B) Apply the surface gloss layer required coating solution on a smooth material consisting of a smooth film or sheet, and apply this smoothing on the coating layer to be bonded or on a coating layer that is somewhat wet. After the material is pressed and dried, a smooth film or sheet is peeled off and the glossy surface is finished by moving the glossy surface layer onto the substrate or the coating layer of the substrate,
There is.
Compared to the film transfer method, the cast method using a heated mirror drum tends to be superior in surface smoothness and is more advantageous in terms of productivity and cost.

When the surface gloss layer is cast-finished, it is preferable to use a release agent in order to smoothly peel the surface gloss layer from the cast drum.
The release agent is preferably used by any one of a method of adding to the surface gloss layer coating solution, a method of applying to the cast drum surface, and a method of adding to the wetting solution.
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.

[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 surface gloss layer 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. Cationicity is preferably used rather than anionic.
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 5 to 150 nm, and is mainly a single particle dispersion in the coating solution.
In order to obtain a high printing density and high gloss, the surface glossy layer has a predetermined range with a small particle diameter, and is preferably 10 to 100 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 driving 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 (colloid particle liquid) having a solid content concentration of about 5 to 20%. If the average particle size of the pigment having a small particle size is less than 3 nm, the ink absorbability may be lowered, and if it exceeds 500 nm, the glossiness and print density may be lowered, which is not preferable. The small particle size pigments may be used alone or in combination of two or more.

[Binder]
As the binder used for the surface gloss layer, the same binder as the above-described binder used for the second coating layer is used.
In addition, when an ink fixing agent is blended in the surface gloss layer coating solution, the adhesive is particularly preferably a cationically modified one.

  Among the binders, casein is preferable because it is excellent in releasability from the cast drum when developing gloss. In addition, polyethylene latex, acrylic latex, and urethane latex are preferable because the recorded image has excellent sharpness and gloss. These can also be used in combination.

  When using an emulsion as the binder, the preferred average molecular weight is 1000 to 10 million, more preferably 5000 to 5 million. If the molecular weight is less than 1,000, the gloss layer may have insufficient strength, and if it exceeds 10 million, the stability of the emulsion may be insufficient.

  The amount of the binder is adjusted in the range of 1 to 200 parts, more preferably 10 to 100 parts, with respect to 100 parts of the pigment. If the blending amount is less than 1 part, the strength of the coating layer is weakened and the surface is easily damaged, and there is a risk of powder falling off. If it exceeds 200 parts, the ink absorbency is lowered, and the desired inkjet This is not preferable because recording suitability may not be obtained.

  In addition, the surface gloss layer is provided with an ink fixing agent, a dispersant, a crosslinking agent, a thickener, a flow modifier, an antifoaming agent, an antistatic agent, an antiseptic, an ultraviolet absorber, and a storage stability improving agent as necessary. Various additives such as a fluorescent brightener, a colorant, a water-proofing agent, and a printability improver can be appropriately added.

  As the ink fixing agent, the same ink fixing agent as that used in the second coating layer can be used.

  The various additives are added to the surface glossy layer coating liquid in a solid content concentration of 0.05 to 10% by mass, preferably in the range of 0.1 to 5% by mass. 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 a rewet cast method, you may add these additives to the wetting liquid except a pigment.

In the casting process described above, the first coating layer and the second coating layer provided with the above-described coating liquid on the substrate are dried, and then the surface glossy layer coating liquid is applied thereon, immediately. It is particularly preferable to use a wet casting method in which a heated mirror surface drum is pressed and dried to finish, since a uniform coating layer is easily formed, and a surface gloss layer having high printing density and excellent gloss can be easily obtained. .
In the casting process, the coating amount of the third coating layer is 0.01 to 0.5 times that of the second coating layer, preferably 0.05 to 0.2, from the balance between gloss and absorbency. Double the range. If it is less than 0.01 times, the effect of improving glossiness may not be obtained, and if it exceeds 0.5 times, the absorbability may be lowered.

In each of the above casting processes, when applying the surface gloss 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 above coating apparatuses can be used.
In the present embodiment, the surface gloss layer coating solution is formed on the second coating layer of the ink jet recording paper to form a surface gloss layer, and a press roll is applied while the surface gloss layer is in a wet state. By performing a nip cast that pressurizes and dries between the surface and the mirror drum, the surface gloss layer is dried, and the recording paper is peeled from the mirror drum to form a surface gloss layer as a third coating layer, The surface of the inkjet recording paper is glossed and exhibits an excellent gloss feeling.

  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
[First coating layer paint]
70 parts of light calcium carbonate (trade name: Brilliant, manufactured by Shiroishi Chemical Co., Ltd.) having an average particle diameter of 0.5 μm, 30 parts of gel method silica (trade name: HD3, manufactured by Grace Co., Ltd.) having an average particle diameter of 3 μm, styrene butadiene latex (JSR) 15 parts by trade name, product name: OJ-1000) and 5 parts by starch aqueous solution (trade name: Ace A, manufactured by Oji Constarch) were mixed and dispersed to prepare 35% of the first coating layer paint.

[Second coating layer paint]
100 parts of silica fine particles A as a pigment, 13 parts of PVA (manufactured by Kuraray Co., Ltd., trade name: PVA-235, degree of polymerization: 3500, degree of saponification: 88.5%) as a binder are added, and a second coating layer of 15%. The paint was adjusted.

[Silica fine particle A]
20 g of a cationic compound having a so-called DADMAC structure (Daiichi Kogyo Co., Ltd., trade name: Charol 902P) was added to 780 g of water, and 200 g of gas phase method silica (Japan) was added while stirring the aqueous cation solution. 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]
A commercial paper (made by Oji Paper Co., Ltd., trade name: marshmallow, 186 g / m ² ) was coated and dried with a coating of the first coating layer so as to be 12 g / m ² , linear pressure 100 kg / cm, temperature 40 ° C. The calendar processing was performed. On the first coating layer, 10% boric acid / borax = 1/1 mixed aqueous solution is applied with WET ON WET so that the second coating layer is 2.0 g / m ² and the second coating layer is 7 g / m ^2. It was dried and subjected to a calendar process at 50 kg / cm and a temperature of 40 ° C. to obtain an ink jet recording paper.

Example 2
Inkjet recording paper as in Example 1 except that the second coating layer pigment was changed to dry alumina (manufactured by CABOT, trade name: PG003, average secondary particle size: about 0.2 μm), and PVA was changed to 8 parts. Manufactured.

Example 3
3 parts of a cationic release agent (modern science, trade name: Pertol N-856) was added to the second coating layer of Example 1, pressed onto a cast drum at 80 ° C. while wet, peeled off after drying. Inkjet recording paper was obtained.

Example 4
An ink jet recording paper was obtained in the same manner as in Example 3 except that the binder of the second coating layer in Example 3 was changed to 10 parts of PVA and 20 parts of cationic urethane latex having an average particle diameter of 20 nm.

Example 5
[Third coating layer paint]
100 parts of cation-modified colloidal silica (manufactured by Nissan Chemical Co., Ltd., trade name: ST-AKL, average particle diameter: 45 nm), 25 parts of cationic urethane latex having an average particle diameter of 20 nm, cationic release agent (modern science, trade name: Pertor N) -856) 5 parts of a 5% mixture was used as the coating material for the third coating layer.

[Preparation of inkjet recording paper]
On the recording medium of Example 1, the third coating layer coating was applied so that the coating amount was 0.7 g / m ^{2, and} was wet-bonded to a cast drum at 80 ° C., dried, and peeled off. Inkjet recording paper was obtained.

Example 6
The pigment of the first coating layer is 80 parts of calcined kaolin (manufactured by Rishsan Corporation, Ansilex) with an average particle size of 2 μm or less, and 20 parts of acicular light calcium carbonate with an average particle size of 0.5 μm (manufactured by Okutama Kogyo Co., Ltd., product) Inkjet recording paper was obtained in the same manner as in Example 3 except that the name was changed to 123-CS).
Example 7
Except for changing the total amount of pigment in the first coating layer to heavy calcium carbonate having an average particle size of 0.7 μm (Bihoku Powder Chemical Co., Ltd., trade name: Softon 3200, 50% aqueous dispersion prepared in advance) Ink jet recording paper was obtained in the same manner as in Example 3.

Example 8
Inkjet recording paper was prepared in the same manner as in Example 3 except that the total amount of pigment in the first coating layer was changed to calcined kaolin of 2 μm or less (manufactured by Rysan Corporation, Ansilex, 50% aqueous dispersion prepared in advance). Manufactured.
Example 9
The same method as in Example 3 except that the total amount of pigment in the first coating layer was changed to calcined clay of 2 μm or less (product name: calcined clay, 50% aqueous dispersion prepared in advance). 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 first coating layer pigment was changed to gel silica having an average particle diameter of 3 μm (trade name: HD3, manufactured by Grace).
Comparative Example 2
An ink jet recording paper was obtained in the same manner as in Example 1 except that the second coating layer pigment was changed to a gel method silica slurry having an average particle diameter of 1.2 μm (product name: 712C, manufactured by Grace).

Example 10
An ink jet recording paper was obtained in the same manner as in Example 3 except that the coating amount of the first coating layer was changed to 8 g / m ² .

Comparative Example 3
An ink jet recording paper was obtained in the same manner as in Example 3 except that the basis weight of the paper substrate was changed to 100 g / m ² and the coating amount of the second coating layer was changed to 3.5 g / m ² .

Example 11
An ink jet recording paper was obtained in the same manner as in Example 3 except that the basis weight of the paper substrate was changed to 120 g / m ² .
Example 12
An ink jet recording paper was obtained in the same manner as in Example 3 except that the basis weight of the paper substrate was changed to 240 g / m ² .
Comparative Example 4
257 g / m 2 basis weight of the paper ^substrate, except changing the coating amount of the second coating layer to 10 g / m ^2, to obtain an ink jet recording paper in the same manner as in Example 3.

Example 13
An ink jet recording sheet was obtained in the same manner as in Example 3 except that the coating amount of the second coating layer was changed to 11 g / m ² .
Example 14
An ink jet recording paper was obtained in the same manner as in Example 3 except that the coating amount of the second coating layer was changed to 2.5 g / m ² .

Comparative Example 5
An ink jet recording paper was obtained in the same manner as in Example 3 except that the coating amount of the second coating layer was changed to 1.5 g / m ² .
Comparative Example 6
An ink jet recording paper was obtained in the same manner as in Example 3 except that the coating amount of the second coating layer was changed to 12 g / m ² .

Example 15
An ink jet recording paper was obtained in the same manner as in Example 3 except that the basis weight of the paper substrate was changed to 110 g / m ² and the coating amount of the second coating layer was changed to 1.5 g / m ² .
Example 16
Inkjet recording paper was obtained in the same manner as in Example 3 except that the basis weight of the paper substrate was changed to 110 g / m ² and the coating amount of the second coating layer was changed to 4 g / m ² .
Example 17
Inkjet recording paper was obtained in the same manner as in Example 3, except that the basis weight of the paper substrate was changed to 110 g / m ² and the coating amount of the second coating layer was changed to 6 g / m ² .

Comparative Example 7
An inkjet recording paper was obtained in the same manner as in Example 15 except that the coating amount of the second coating layer was changed to 1 g / m ² .
Comparative Example 8
An ink jet recording paper was obtained in the same manner as in Example 15 except that the coating amount of the second coating layer was changed to 7 g / m ² .

Example 18
Inkjet recording paper was obtained in the same manner as in Example 3, except that the basis weight of the paper substrate was changed to 240 g / m ² and the coating amount of the second coating layer was changed to 3 g / m ² .
Example 19
Inkjet recording paper was obtained in the same manner as in Example 3 except that the basis weight of the paper substrate was changed to 240 g / m ² and the coating amount of the second coating layer was changed to 9 g / m ² .
Example 20
Inkjet recording paper was obtained in the same manner as in Example 3 except that the basis weight of the paper substrate was changed to 240 g / m ² and the coating amount of the second coating layer was changed to 11.5 g / m ² .

Comparative Example 9
An ink jet recording paper was obtained in the same manner as in Example 18 except that the coating amount of the second coating layer was changed to 2 g / m ² .
Comparative Example 10
An inkjet recording paper was obtained in the same manner as in Example 18 except that the coating amount of the second coating layer was changed to 13 g / m ² .

[Evaluation methods]
For Examples 1 to 20 and Comparative Examples 1 to 10, the ink absorbability of the obtained ink jet recording paper, the image quality of the recorded image, the gloss of the recorded image, the coating layer strength, the coating film cracking, the environmental curl, and the printing The post curl 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 ink jet printer (trade name: PM-G820, manufactured by Seiko Epson Corporation).

<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 evaluated as the print density.

<Glossy>
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.
A: Glossiness similar to that of a silver salt photograph B: Not as high as that of a silver salt photograph, but high glossiness.
Δ: Glossiness equivalent to printing paper.
X: There is no glossiness.

<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.
○: There is no crack in the coating film.
Δ: Level where there are few cracks in the coating film and no problem in practical use.
X: There are many cracks in a coating film, and there is a problem in practical use.

<Environmental curl>
The A4 recording body was placed in a constant temperature and humidity chamber at 23 ° C. and 63% for 24 hours, then transferred to a constant temperature and humidity chamber at 15 ° C. and 25%, and placed on a flat surface for 4 hours with the recording surface facing upward. The height of four corners was measured. An average value (h) was determined and evaluated according to the following criteria.
○: 0 <h ≦ 10 mm.
Δ: 10 <h ≦ 20 mm.
×: h> 20 mm

<Curl after printing>
The A4 recording medium was placed in a constant temperature and humidity chamber at 23 ° C. and 63% for 24 hours, and then a green solid image was printed on the entire surface with a printer, and the recording surface was flat on the constant temperature and humidity chamber at 23 ° C. and 63%. After being placed for 24 hours, the height of the four corners was measured. An average value (h) was determined and evaluated according to the following criteria.
○: 0 <h ≦ 10 mm.
Δ: 10 <h ≦ 20 mm.
×: h> 20 mm

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

  As is apparent from Table 1, the ink jet recording paper of this example has excellent ink absorbability and strong coating layer strength, and is excellent in that it does not easily cause cracking, environmental curl, or print curl. I understand. Further, when silica fine particles are used in the second coating layer, an excellent recorded image having a high printing density can be obtained. Furthermore, it is possible to obtain a highly glossy recorded image by performing gloss processing.

Claims (5)

In an inkjet recording paper having two or more coating layers on a paper base having a basis weight of 105 to 250 g / m ² , the first coating layer in contact with the paper base is selected from calcium carbonate and kaolin (including clay) And the second coating layer in contact with the first coating layer contains a fine secondary pigment having an average particle diameter of 0.01 to 1 μm and a water-soluble resin binder, and the second coating layer. The inkjet recording paper is characterized in that the coating amount is less than the coating amount of the first coating layer and is 0.01 to 0.06 times the paper substrate basis weight. 2. The ink jet recording paper according to claim 1, wherein the second coating layer is mirror-finished by pressure bonding to a heated mirror drum while in a wet state. The inkjet recording paper according to claim 1, wherein the second coating layer contains at least one cationic latex having an average particle diameter of 6 to 100 nm. A second coating layer is further provided on the second coating layer, the coating amount of the third coating layer is 0.01 to 0.5 times that of the second coating layer, and contains colloidal particles. The inkjet recording paper according to any one of claims 1 to 3. 5. The ink jet recording paper according to claim 4, wherein the third coating layer is subjected to a mirror finish by pressure bonding to a heated mirror drum while in a wet state.