JP4389802B2 - Inkjet recording paper - Google Patents

Description

  The present invention relates to an ink jet recording paper used for an ink jet recording type output device.

  2. Description of the Related Art Inkjet recording type output devices are used in various fields including printers because they are low in noise, capable of high-speed recording, and easily multi-colored. As inkjet recording paper applied to such an output device, high-quality paper devised so as to be rich in ink absorbability, coated paper coated with a porous pigment on the surface, and the like are applied. In addition, in a field where a recording paper having high gloss is required, a layer containing an extremely fine porous pigment or single particles or a layer containing a hydrophilic resin is provided on a layer containing a porous pigment, By using a coating method such as die head coating, curtain head coating, or cast coating, an ink jet recording sheet having a high surface glossiness and an excellent appearance is used.

Many of these recording papers use paper as a base material. A paper base material is excellent in absorbability of ink solvents (water and hydrophilic substances) and is recyclable, so it can be said that it is a very excellent base material. However, a paper base material has an inevitable characteristic inherent in cellulose, in which a volume change occurs when water is absorbed. In paper made by a paper machine, the cellulose fibers constituting the paper have the property of being oriented in the flow direction of the paper machine. And when a cellulose fiber absorbs water, it is said that it expands about 30% in the thickness direction of a fiber.
When ink jet recording is performed on an ink jet recording paper having a recording layer coated on such a substrate, the coloring component in the ink remains in the recording layer, but the solvent component cannot be completely absorbed in the recording layer, and the substrate It penetrates up to and remains absorbed by the cellulose fibers of the substrate. In this case, the cellulose fibers of the base material swell in the lateral direction, but the solvent component of the ink absorbed by the base material varies depending on the amount of ink applied, which is the difference in the lateral extension of the base material. As a result, the recording paper is blurred and so-called cockling occurs.

The occurrence of cockling not only detracts from the appearance of the recorded material, but if this is severe, the recording paper is lifted to reduce the recording accuracy, and the recording paper collides with a recording head that slides left and right, causing the recording paper to It may become dirty or torn, and in some cases, the head may be broken.
In order to reduce such cockling, the following measures have been taken. One is a means for reducing the amount of solvent penetrating into the paper substrate, and the other is a means for enhancing the dimensional stability of the substrate so that the substrate does not swell even when the solvent penetrates.

The following is a typical example of the former method.
(A) A method in which a film layer such as polyethylene is provided between the paper substrate and the recording layer so that the ink solvent does not reach the substrate (for example, see Patent Document 1).
(Ii) A method of increasing the amount of solvent that can be retained in the recording layer by increasing the coating amount of the recording layer and reducing the amount of ink solvent that reaches the substrate (for example, see Patent Document 2).
(Iii) A method of relatively reducing the amount of ink solvent permeation per paper substrate weight by increasing the weight (thickness) of the paper substrate (see, for example, Patent Document 3).
The following is mentioned as a typical method of the latter.
(E) A method of increasing the dimensional stability of the paper with respect to the solvent by adding a water-proofing agent to the paper base material, and suppressing blurring (for example, see Patent Document 4).

In the method (A), cockling can be completely suppressed, but the base material cannot absorb the ink solvent, so that the recording is easily blurred. To cope with this, it is necessary to increase the coating amount of the recording layer, which is not economical. Further, the moisture retention component contained in the solvent remains in the ink absorption layer, so that the moisture-preserving resistance of the printed matter is inferior. In addition, since the recording paper provided with the resin layer is difficult to recycle, the burden on the environment is increased, and it is difficult to say that it is a preferable mode.
In the method (ii), although recycling is possible, it is difficult to completely suppress cockling, and it is difficult to say that it is economical because it is necessary to apply an expensive recording layer as in the case (a). Since the recording density tends to decrease, it is difficult to say that this is a preferable mode.
In the method (ii), although it is possible to recycle, it cannot be applied to a recording sheet of a grade having a low basis weight, and it is difficult to say that it is a preferable mode.
In the method (e), it is difficult to completely suppress cockling and recycling is difficult, and it is difficult to say that it is a preferable mode.

  In this way, each has both advantages and disadvantages, so it is the current situation that some of the above methods are combined and balanced, so that cockling can be solved and recycled. It has not reached the recording paper.

JP 2000-71605 A [0005] JP-A-7-186519 JP 11-321067 A [0023] JP-A-9-66663

  The present invention provides an ink jet recording paper used for an output device of an ink jet recording system, and provides an ink jet recording paper that does not cause cockling when used for these output devices. Furthermore, the present invention intends to solve the following problems.

The elongation of the pulp fibers as described above also affects the recording layer provided on the surface. That is, the pulp fiber swollen with a solvent containing water gradually approaches the original state as it dries, but does not completely return to its original state, and deformation remains on the surface of the recording layer, resulting in a decrease in gloss. Due to this reduction in glossiness, a difference in glossiness between the blank paper portion and the print portion occurs, but even in the print portion, a difference in glossiness occurs depending on the amount of ink applied, resulting in an image that gives an unnatural impression.
As a means to reduce the difference in glossiness between the blank paper portion and the printed portion, the ink for gloss adjustment is installed in the printer, and a lot of this gloss adjustment ink is applied to the light-colored portion where the amount of ink is small. Efforts have been made to reduce the difference in glossiness by reducing the difference in the total amount of ink applied to each portion by applying a small amount to the dark portion. However, it is also uneconomical to drive such ink into a place where it is not necessary, and it is not a preferable direction because it tends to cause ink bleeding.
Thus, a method for easily and economically solving the difference in glossiness between the blank paper portion and the printed portion has not been found.

  Also, in general, in an ink jet printer, the recording paper is pressed with a gear immediately after passing through the recording head to prevent the recording paper from being lifted after ink has been applied, so that the flatness is maintained and the recording paper is sent stably. It has become. When the surface is pressed with a presser gear when the ink is driven into the ink jet recording paper and the pulp fiber of the paper base material is swollen by the solvent of the ink, the mold is formed. While the recording paper is fed as it is printed, the gear teeth follow the pattern, creating a continuous mark like a needle hole in the sewing machine. Even if the ink dries, the trace does not completely recover, and becomes a press gear trace, which degrades the quality of the printed matter.

In order to improve such a presser gear mark, the following method can be considered.
(A) A method of reducing the force applied per unit area by changing the gear to a roll.
(A) A method of reducing the force applied per unit area by rounding the tip of the gear.
(C) A method of reducing the force applied to the recording paper by reducing the pressure of the gear.
(D) A method of applying a resin coating on the surface of a paper substrate and providing a layer for absorbing ink thereon.

In the method (a), the force per unit area is greatly reduced, and troubles such as dents in the inkjet recording paper are greatly reduced. However, since the roll comes into contact with the surface where the ink that has been driven in is not sufficiently absorbed, there is a high possibility that the ink adheres to the roll and the printed matter becomes dirty. Ink adheres even with a gear, but because the area is small, stains are not noticeable. Therefore, it is not a good idea to use rolls instead of gears.
In the method (A), the force applied per unit area is reduced, and troubles such as dents in the ink jet recording paper tend to be reduced. However, the gear contacts the surface where the ink that has been driven in is not sufficiently absorbed, so that the ink adheres to the tooth tip, and the area becomes larger, so the dirt on the printed matter may be noticeable, It is also difficult to round the tooth tip. Therefore, it is hard to say that this is a fundamental improvement.

In the method (c), damage is reduced as the force applied to the recording paper is reduced, and troubles that the ink jet recording paper is recessed are greatly reduced. However, since recent printers have a mechanism that feeds paper not only on the platen roll but also on the gear part so that borderless printing can be performed, the pressing force with the presser gear is stronger than previous printers. It is the actual situation that must be done. Therefore, this method cannot be adopted.
The method (d) is the same as the method (a) described above for reducing cockling, and it is ensured that the solvent of the ink driven into the ink jet recording paper penetrates the base paper and the pulp fibers swell. Therefore, the problem that the ink jet recording paper is recessed does not occur.

However, since the base material cannot absorb the ink solvent, the recording tends to be blurred. To cope with this, it is necessary to increase the recording layer coating amount, which is not economical. Furthermore, since the moisture retention component contained in the solvent also remains in the ink absorption layer, the moisture resistance storage stability of the printed matter tends to be inferior, and the recording paper provided with the resin layer is difficult to recycle, so the burden on the environment is large. It is difficult to say that it is a preferable method.
As described above, as an effective method for improving the presser gear mark, neither a method for improving a printer nor a method for improving ink jet recording paper has been found.

  The present invention is an ink jet recording paper used for an output device of an ink jet recording system. When used for these output devices, there are few cocklings and presser gear traces, high gloss, a blank paper portion and a print portion. It is an object of the present invention to provide an ink jet recording paper that can obtain an excellent recorded image with a small difference in glossiness.

As a result of intensive studies aimed at solving the above-mentioned problems, the inventors of the present invention have a hollow structure that absorbs water so that the amount of hollow particles attached is at least 2 g / m ^{2 on} at least one side of the paper substrate. Undercoat layer containing particles and preventing ink solvent from reaching paper substrate (however, inorganic pigment 50 to 95 parts by weight, voided organic pigment 5 to 50 parts by weight, and pigment 100 parts by weight Except for the case where the binder is 15 to 65 parts by weight with respect to the intermediate layer ) , which contains a porous pigment, a cationic resin and an adhesive on the undercoat layer, and mainly fixes dyes and pigments in inkjet inks. By forming the cast coating layer through the layer, there is little cockling and presser gear marks, high gloss, small difference in glossiness between the blank paper portion and the printed portion, recyclable and economical for inkjet recording It found that can be obtained, and have completed the present invention.

The present invention includes the following aspects.
(1) In an ink jet recording paper having a paper base material and a cast coating layer formed by a casting method and performing ink jet recording on the surface of the cast coating layer, water absorption is performed between the paper base material and the cast coating layer. A subbing layer containing inorganic particles 50 and an adhesive, and having an adhesion amount of the hollow particles of 2 g / m ² or more and suppressing the ink solvent from reaching the paper substrate (however, the inorganic pigment 50 -95 parts by weight, and 5-50 parts by weight of organic pigment having voids, except for the case where the binder is 15-65 parts by weight with respect to 100 parts by weight of pigment) , cast coating layer and subbing layer An ink jet recording paper comprising an intermediate layer containing a porous pigment, a cationic resin, and an adhesive, and fixing a dye or pigment in the ink jet ink.
(2) The inkjet recording paper according to (1), wherein the hollow particles contained in the undercoat layer have a porosity of 30% or more.
(3) The inkjet recording paper according to (1) or (2), wherein the coating amount of the undercoat layer is in the range of 5 to ²⁰ g / m ² as the coating amount after drying.
(4) The inkjet recording paper according to any one of (1) to (3), wherein the cast coating layer contains colloidal silica.

  The ink jet recording paper according to the present invention is capable of obtaining an excellent recorded image with high gloss, little cockling and pressing gear marks, and a small difference in glossiness between a white paper portion and a printed portion.

The present invention comprises a paper substrate, an undercoat layer containing hollow particles having water absorption, an intermediate layer formed as necessary, and a cast coating layer formed by a casting method. An ink jet recording paper that performs ink jet recording on the surface of a coating layer.
In the present invention, the provision of an undercoat layer containing hollow particles having water absorption and an adhesive greatly improves cockling and press gear traces of inkjet recording paper, and further includes a blank paper portion and a printing portion. The difference in glossiness between the two becomes smaller. The reason for this is not clear, but is considered as follows.

The hollow particles having water absorption contain water in the hollow portion in the state of the coating liquid, and the internal water evaporates in the drying step after coating to form cavities. Therefore, the shell part has a fine hole through which water can enter and exit. When printing on the surface of an ink jet recording sheet with an ink jet printer, the dye or pigment in the ink is fixed by the cast coating layer or intermediate layer located on the surface, and the solvent reaches the undercoat layer. In the undercoat layer, the solvent is first absorbed into the hollow particles by capillary action of fine holes existing on the surface of the hollow particles. Since the solvent is prevented from reaching the paper substrate, cockling can be prevented. Thereafter, the absorbed solvent gradually diffuses into the air through the fine pores on the surface of the hollow particles, and finally is dried.
Therefore, compared with the case where the undercoat layer does not contain hollow particles, the amount of solvent that reaches the paper substrate directly decreases significantly. The degree of occurrence of cockling is greatly reduced, and at the same time, even if the presser gear hits, the degree of deformation due to it is reduced, and the presser gear trace is also greatly reduced. Further, since the swelling of the base material of the ink jet recording paper is reduced and the volume change is also small, the deformation of the base material of the printed portion is reduced, and as a result, the difference in glossiness between the blank paper portion and the printed portion is reduced. As described above, in the present invention, since the layer where the dye stays and the layer where the moisturizing component in the ink solvent permeates are different, it is also possible to avoid a decrease in the moisture-preserving stability of the printed matter.

  Below, the structural aspect of this invention is demonstrated in detail.

"About paper substrates"
The paper base in the present invention is not particularly limited, such as acidic paper, neutral paper, etc., and can be appropriately selected from paper bases that can be generally coated. The paper base is composed mainly of wood pulp and a filler containing it as necessary.

  As the wood pulp, various chemical pulps, mechanical pulps, regenerated pulps and the like can be used, and these pulps can be beaten by a beating machine in order to adjust paper strength, papermaking suitability, and the like. The beating degree (freeness) of the pulp is not particularly limited, but is generally about 250 to 550 ml (CSF: JIS-P-8121). In order to improve smoothness, it is desirable to advance the beating degree. However, when recorded on paper, paper blur and recording image bleeding caused by moisture in the ink often gives better results if the beating is not advanced. . Accordingly, the freeness is preferably about 300 to 500 ml.

  The filler is blended for the purpose of imparting opacity or the like, and calcium carbonate, calcined kaolin, synthetic zeolite, silica, titanium oxide, alumina, talc, clay and the like can be used. In particular, calcium carbonate is preferable because it becomes a substrate with high whiteness and glossiness of the ink jet recording paper is enhanced. The content (ash content) of the filler in the paper substrate is preferably about 1 to 20%, and if it is too much, the paper strength may be reduced. If the amount is too small, the air permeability of the paper base material is deteriorated. Within this range, the smoothness, air permeability, and paper strength are balanced, and as a result, a highly glossy ink jet recording sheet can be easily obtained.

  Use of porous pigments such as calcined kaolin, synthetic zeolite, silica, and light calcium carbonate as the filler absorbs ink solvent that could not be absorbed by the primer layer containing hollow particles, thus preventing cockling. Can be preferred. When there is no undercoat layer, it is necessary to contain a lot of porous pigment, and it is about 3 to 25% as ash. Among them, silica with a large oil absorption amount has a content of about 5 to 10% and medium. Although it is necessary to use about 7 to 12% for synthetic zeolite and calcined kaolin and about 10 to 15% for light calcium carbonate having a relatively small specific surface area, in the present invention, an intermediate layer containing hollow particles on a paper substrate is used. Since it has a function of absorbing the solvent of the ink, it is not necessary to expect a large amount of absorption of the solvent in the porous pigment contained in the paper base material, and its content may be small. In the present invention, the content in the case of silica is preferably 5% or less, 9% or less in the case of synthetic zeolite or calcined kaolin, and 12% or less in the case of light calcium carbonate. When the amount of filler is small, the ability to absorb the solvent that has penetrated the paper substrate tends to be inferior. On the other hand, if it is too high, the paper strength will be weak and the paper will be damaged by the feed roll when printing with a printer. It tends to be easy, or paper dust tends to come out when cutting, and this tends to get into the printer and clog the head nozzles or make the roll dirty and not feed.

In general, the Stechtian sizing degree of the paper base material of the ink jet recording paper is preferably 50 seconds or less in the paper base material of 150 g / m ² in order to quickly absorb the solvent in the ink. In this case, by adjusting to 100 seconds or less, preferably 70 seconds or less, it is possible to obtain a base paper that obtains good recording properties.

A sizing agent, a fixing agent, a paper strength enhancer, a yield improver, a dye, and the like can be appropriately added to the paper base. Starch, polyvinyl alcohol, a cationic resin, a dye, and the like are applied by a size press device. In particular, it is preferable to apply starch by size press in terms of controlling the water absorption of the paper substrate and the degree of sizing of the paper base, imparting paper strength, economy, and operability. The starch coating amount in the size press is about 0.5 to 7 g / m ² , preferably 1 to 4 g / m ² as a dry mass. If it is less than 0.5 g / m ² , the effect is small, and if it exceeds 7 g / m ² , the effect is sufficient and there is no problem in quality, but it tends to cause operational problems such as contamination of the after dryer.

In addition, it does not specifically limit as a paper machine which manufactures a paper base material, It is a Yankee as a dryer, such as a well-known long net paper machine, a cylindrical paper machine, a Yankee paper machine, a twin wire former, and an inclined wire former. Various known paper machines such as dryers and multi- cylinder dryers can be used. Known processing such as calendar processing is also possible.

“Undercoat”
The undercoat layer in the present invention contains hollow particles having water absorption and an adhesive as essential components. The hollow particles having water absorption are not particularly limited, but those having a particle diameter of 0.2 to 5 μm such as styrene and styrene-acrylic copolymer are preferable. When the particle diameter is less than 0.2 μm, the smoothness of the coated surface is good, but the effect of preventing cockling tends to decrease because the absorption rate of the ink solvent becomes slow. When it exceeds 5 μm, the absorbability of the solvent is good, but the smoothness of the coated surface is inferior.

  In the present invention, the void ratio of the hollow particles is preferably 30% or more, and more preferably 40 to 90%. If the porosity is less than 30%, the ink solvent absorption rate tends to be slow, and the effect of preventing cockling tends to decrease. If the porosity exceeds 90%, the hollow particle shell tends to become unstable. is there. The void ratio of the hollow particles is the percentage of the volume of the hollow portion in the entire hollow particles expressed in%. For example, when the hollow particle has a diameter of 0.3 μm and the hollow part has a diameter of 0.2 μm, the void ratio of the hollow particle is 30%.

In order to produce hollow particles, several methods as exemplified below have been proposed.
(1) A method in which a foaming agent is contained in polymer particles, and this is subsequently foamed to obtain hollow particles.
(2) A method in which a volatile substance such as butane is encapsulated in a polymer, which is then gasified and expanded to obtain hollow particles.
(3) A method in which a polymer is melted, a jet of air or the like is sprayed thereon, and bubbles are enclosed.
(4) A method in which a polymerizable monomer component is dispersed in water to form an oil-in-water emulsion and polymerized to obtain hollow particles.
(5) A method in which an alkali-swellable substance is contained in the polymer particles, and an alkaline liquid is infiltrated into the polymer particles to expand the alkali-swellable substance to obtain hollow particles.

  The hollow particles having water absorption in the present invention need to have fine holes in the shell portion, and therefore not all of the above exemplified materials can be used. For example, the methods (1) and (2) do not have fine holes in the shell and are inappropriate as a method for producing hollow particles used in the present invention. The method (3) is not preferable as the hollow particles used in the present invention because it is difficult to control the particle diameter and the porosity.

  A preferable method for producing the hollow particles used in the present invention is the method (4) or (5) in the above examples, and among them, the method (5) has many types of monomers that can be used. preferable. Further, among the methods (5), for example, an unsaturated carboxylic acid is copolymerized by ordinary emulsion polymerization to prepare seed particles, and then the particle surface layer is covered with an ethylenically unsaturated monomer. Next, the ethylenic monomer was polymerized, and the obtained particles were neutralized with a volatile basic substance such as ammonia, and the particles were swollen to obtain hollow particles, or an unsaturated carboxylic acid was copolymerized. A particularly preferable production method is a method in which particles are prepared, then neutralized and swollen with a basic substance such as potassium hydroxide, and then acid-treated to obtain hollow particles.

In the undercoat layer, in addition to the hollow particles, the following pigments may be used in combination.
Examples include kaolin, clay, calcined clay, silica, colloidal silica, zinc oxide, aluminum oxide, titanium oxide, aluminum hydroxide, calcium carbonate, magnesium carbonate, satin white, aluminum silicate, aluminosilicate, synthetic zeolite, smectite, hydro Examples include talcite and urea resin-based plastic pigments.
In particular, it is preferable to use a fine particle pigment selected from silica, aluminosilicate, and alumina.

  The average particle diameter of these pigments other than hollow particles is preferably about 1 to 20 μm, more preferably 2 to 15 μm, and further preferably 3 to 12 μm. If it is less than 1 μm, the ink absorption rate tends to be slow, and if it exceeds 20 μm, the smoothness after coating of the undercoat layer tends to be inferior, and therefore the glossiness and smoothness after casting tend to be inferior.

  As an adhesive, polyvinyl alcohols (polyvinyl alcohol, cation-modified polyvinyl alcohol, silyl-modified polyvinyl alcohol, etc.), proteins (casein, soybean protein, synthetic protein, etc.), starches (starch, oxidized starch, modified starch, etc.), Celluloses (carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, etc.), conjugated diene polymer latex (styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, etc.), vinyl copolymer latex (styrene-vinyl acetate) Copolymers, etc.), water-based acrylic resins, water-based polyurethane resins, water-based polyester resins, and other various publicly known and commonly used adhesives in the coated paper field are used alone or in combination. When a cationic compound is blended in the undercoat layer, a cationic or nonionic adhesive is preferable because the stability of the coating composition is good. In particular, silyl-modified polyvinyl alcohol is particularly preferable because a strong adhesive effect can be obtained with a small amount.

  The blending ratio of the adhesive is adjusted in the range of 1 to 200 parts by mass, preferably 5 to 100 parts by mass, and more preferably 7 to 30 parts by mass with respect to 100 parts by mass of the pigment. If the amount of the adhesive is too small, the coating layer strength becomes weak, and the coating layer peeling or coating layer powder is generated at the time of cutting. On the other hand, if the amount of the adhesive is too large, the ink absorption capacity becomes small, the printed ink bleeds, the ink absorption speed becomes slow, and a desired image cannot be obtained.

Because colorants Lee inkjet inks are usually anionic, it is possible to insolubilize the coloring agent in the coating layer by a cationic compound, or to improve the recording density or impart water resistance. When the water resistance of the colorant is insufficient in the intermediate layer or cast coating layer, a cationic compound may be added to the undercoat layer. Incidentally, the intermediate layer and cast-coated layer, lever have blended sufficient cationic compound to the ink fixing, cationic compound need not be contained in the subbing layer. Be contained in the cast coating layer and the intermediate layer, if Kere such is contained in the undercoat layer, it means that the ink dye remains near the surface, it is advantageous in terms of recording density, preferred.

The undercoat layer may be divided into two or more coating layers in order to match the desired quality characteristics. Subbing layer composition generally adjust the solid concentration to about 5 to 50 mass%, 2~100g / ^{m 2} as dry weight on paper substrate, preferably 5 to 50 g / ^{m 2,} more preferably It is good to apply so that it may become 5-20 g / m < ² >. If the coating amount is small, the ink absorption may be insufficient, or there may be insufficient gloss when the cast coating layer is provided. Conversely, if the coating amount is too large, the print density may decrease, The coating layer strength may be reduced, and powder may be easily removed or scratched.

The amount of hollow particles contained in the undercoat layer is preferably ² g / m ² or more as the coating amount. When the amount is less than 2 g / m ² , the amount of voids is insufficient, so that the effect that the hollow particles absorb the solvent component of the ink and make it difficult to swell the base paper tends to be small.

  In the undercoat layer, various auxiliary agents such as dispersants, thickeners, antifoaming agents, antistatic agents, preservatives, fluorescent dyes, and coloring agents used in the production of general coated papers are appropriately added. The

  For the undercoat layer, the coating liquid composition as described above is applied to a blade coater, an air knife coater, a roll coater, a brush coater, a Chanplex coater, a bar coater, a lip coater, a gravure coater, a die coater, a curtain coater, and a slide coater. It coats and dries with various well-known publicly used coating apparatuses. The coating may be performed twice or more. Further, if necessary, after the undercoat layer is dried, a smoothing treatment such as super calender or gloss calender can be applied.

About the middle class
The intermediate layer in the present invention is mainly the coating layer of the purpose of fixing the dye or pigment in the inkjet ink, the cast-coated layer, it is a coating layer of the purpose of imparting gloss, print density Ya It is preferable because it is excellent in gloss. The intermediate layer is a layer containing a pigment, an adhesive, and a cationic compound.

  Examples of the pigment include kaolin, clay, calcined clay, silica, colloidal silica, zinc oxide, aluminum oxide, titanium oxide, aluminum hydroxide, calcium carbonate, magnesium carbonate, satin white, aluminum silicate, aluminosilicate, synthetic zeolite, and smectite. And pigments such as hydrotalcite and urea resin-based plastic pigment. In particular, it is preferable to use a fine particle pigment selected from silica, aluminosilicate, and alumina.

  As an adhesive, polyvinyl alcohols (polyvinyl alcohol, cation-modified polyvinyl alcohol, silyl-modified polyvinyl alcohol, etc.), proteins (casein, soybean protein, synthetic protein, etc.), starches (starch, oxidized starch, modified starch, etc.), Celluloses (carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, etc.), conjugated diene polymer latex (styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, etc.), vinyl copolymer latex (styrene-vinyl acetate) Copolymers, etc.), water-based acrylic resins, water-based polyurethane resins, water-based polyester resins, and other various publicly known and commonly used adhesives in the coated paper field are used alone or in combination.

  Examples of the cationic compound include a cationic resin and a low molecular weight cationic compound (for example, a cationic surfactant). In terms of the effect of improving the printing density, a cationic resin is preferable, and it can be used as a water-soluble resin or an emulsion. Furthermore, it can also be used as a cationic organic pigment in which a cationic resin is insolubilized by means of crosslinking or the like to form a particulate form. Such cationic organic pigments are obtained by copolymerizing a polyfunctional monomer into a crosslinked resin when polymerizing a cationic resin, or reactive functional groups (hydroxyl group, carboxyl group, amino group, acetoacetyl group, etc.) If necessary, a crosslinking agent is added to a cationic resin having a crosslinking resin by means of heat, radiation or the like. A cationic compound, particularly a cationic resin, may serve as an adhesive or a pigment dispersion aid. When a cationic compound is contained in the intermediate layer, the colorant of the ink jet ink is usually anionic. Therefore, the cationic compound insolubilizes the colorant in the intermediate layer to provide water resistance and improve recording density. can do.

Examples of the cationic resin include the following. In particular,
1) Polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof,
2) an acrylic polymer having a secondary amino group, a tertiary amino group or a quaternary ammonium group,
3) polyvinylamine and polyvinylamidines,
4) Dicyan-based cationic compounds represented by dicyandiamide / formalin copolymer,
5) Polyamine-based cationic compounds represented by dicyandiamide / polyethyleneamine copolymer,
6) Epichlorohydrin / dimethylamine copolymer,
7) diallyldimethylammonium-SO ₂ polycondensate,
8) diallylamine salt-SO ₂ polycondensate,
9) diallyldimethylammonium chloride polymer,
10) diallyldimethylammonium chloride-acrylamide copolymer,
11) Copolymer of allylamine salt,
12) Dialkylaminoethyl (meth) acrylate quaternary salt copolymer,
13) Acrylamide-diallylamine copolymer,
14) Cationic resin having a 5-membered ring amidine structure.

  The cationic compound also has an effect of improving the printed image water resistance. The amount of the cationic compound that can be blended in the intermediate layer can be used in the range of 1 to 100 parts by mass, preferably 5 to 50 parts by mass with respect to 100 parts by mass of the pigment. If the blending amount is small, it is difficult to obtain the effect of improving the print density. If the blending amount is large, the print density may be lowered, and the image may be blurred or uneven.

  For the intermediate layer, aldehyde crosslinking agents such as glioxal, epoxy crosslinking agents such as ethylene glycol diglycidyl ether, vinyl crosslinking agents such as bisvinylsulfonylmethyl ether, boron-containing compounds such as boric acid and borax, glycidyl compounds, zirconium A crosslinking agent such as a compound, an aluminum compound, a chromium compound, or the like can be blended. Furthermore, various auxiliary agents such as preservability improvers, antifoaming agents, colorants, fluorescent dyes, antistatic agents, preservatives, dispersants, thickeners and the like can be added as appropriate.

For the intermediate layer, the coating liquid containing the above materials is applied onto the undercoat layer, blade coater, air knife coater, roll coater, brush coater, chamber coater, bar coater, lip coater, gravure coater, curtain. The coating is formed by various known coating apparatuses such as a coater, a slot die coater, and a slide coater. The coating amount of the intermediate layer, 2~100g / ^{m 2} approximately as dry mass, but it is preferable 5 to 50 g / ^{m 2,} more preferably coated so that 5 to 20 g / ^{m 2.} A plurality of intermediate layers may be formed, and in that case, layers having different compositions may be used.

"About cast coating layer"
The cast coating layer is a layer provided mainly for the purpose of imparting gloss to the inkjet recording paper. Formed by a casting method that is provided on an undercoat layer or an intermediate layer, applied, and pressed against a heated mirror drum and dried while the coating solution is wet or rewet. Is a layer.

  The cast coating layer can also be formed using the same coating solution as the intermediate layer, but if a fine particle pigment is used, the fine irregularities on the surface of the undercoat layer or intermediate layer can be formed with the fine particle pigment. By covering the surface, irregular reflection of the surface is prevented and high gloss is imparted.

  Examples of such fine particle pigments include fine particle pigments selected from silica, aluminosilicate, alumina, zeolite and the like having an average particle diameter of 1 μm or less. Silica and aluminosilicate are preferable, and silica is more preferable. The smaller the particle size, the better the transparency, and therefore, it is preferable because it shows gloss and does not decrease the concentration of the ink formed in the intermediate layer. Colloidal silica is more preferable as the fine particle pigment, and a true spherical one is particularly preferable.

  The average particle diameter of colloidal silica is 0.01 to 0.15 μm, preferably 0.015 to 0.12 μm, and more preferably 0.02 to 0.10 μm. When the average particle diameter is less than 0.01 μm, the ink absorbability is lowered. Conversely, when it exceeds 0.15 μm, the glossiness and the density of the recorded image are lowered.

  An adhesive can be blended in the cast coating layer. As an adhesive, polyvinyl alcohols (polyvinyl alcohol, cation-modified polyvinyl alcohol, silyl-modified polyvinyl alcohol, etc.), proteins (casein, soybean protein, synthetic protein, etc.), starches (starch, oxidized starch, modified starch, etc.), Celluloses (carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, etc.), conjugated diene polymer latex (styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, etc.), vinyl copolymer latex (styrene-vinyl acetate) Copolymers, etc.), water-based acrylic resins, water-based polyurethane resins, water-based polyester resins, and other various publicly known and commonly used adhesives in the coated paper field are used alone or in combination.

  Among them, casein is preferable because it is excellent in releasability when the cast coating layer is formed and dried by a casting method and peeled off from the mirror drum. Acrylic copolymer emulsions and styrene-acrylic copolymer emulsions are preferred because they are excellent in gloss and clearness of recorded images. It is more preferable to use casein in combination with an acrylic copolymer emulsion or a styrene-acrylic copolymer emulsion.

  The blending ratio of casein is adjusted in the range of 0.5 to 15 parts, preferably 1 to 10 parts with respect to 100 parts by mass of the pigment. If the casein content is too small, the coating layer strength may be weakened or the effect of improving mold release may be too small. On the other hand, if the amount is too large, the ink absorption speed becomes slow, and the image blurs or the desired image quality cannot be obtained.

  When an acrylic copolymer emulsion or a styrene-acrylic copolymer emulsion is used, the preferred average molecular weight is 1,000 to 10,000,000, more preferably 5,000 to 5,000,000. If the molecular weight is small, the strength of the cast coating layer tends to be weak, whereas if it is too large, the stability of the emulsion tends to be insufficient. The average particle size of the emulsion is preferably 0.02 to 0.15 μm. If it is less than 0.02 μm, the ink absorbency tends to be inferior. Conversely, if it exceeds 0.15 μm, the glossiness and recording density tend to decrease. Furthermore, the glass transition temperature of the emulsion is preferably 50 to 150 ° C. If the glass transition temperature is less than 50 ° C, the film formation of the adhesive proceeds with the heat of the cast drum, and the ink absorbability tends to be reduced. Conversely, if the glass transition temperature exceeds 150 ° C, no film formation is performed. The strength of the cast coating layer may be insufficient.

  The blending ratio of the acrylic copolymer emulsion or the styrene-acrylic copolymer emulsion is preferably 3 to 150 parts by weight, more preferably 7 to 100 parts by weight, and more preferably 10 to 70 parts by weight with respect to 100 parts by weight of the pigment. Further preferred. When the ratio of the adhesive is less than 3 parts by mass, the glossiness tends to be insufficient, whereas when it exceeds 150 parts, the recording density tends to decrease.

  The above-mentioned cast coating layers are various known coatings such as blade coaters, air knife coaters, roll coaters, brush coaters, Champlex coaters, bar coaters, lip coaters, gravure coaters, curtain coaters, slot die coaters, and slide coaters. The device can be used.

The coating amount of the cast coating layer is adjusted to 1 to 15 g / m ² , but the coating amount necessary to impart gloss is determined by the properties of the undercoat layer and the intermediate layer. When the intermediate layer is not provided, 5 to 15 g / m ^{2 is} required, but when the intermediate layer is provided with 5 to 10 g / m ² and the particle diameter of the pigment used in the intermediate layer is 0.5 to 3 μm Glossiness can be imparted at 1 to 5 g / m ² . Generally, if the coating amount is too small, gloss cannot be imparted. Conversely, if the coating amount is too large, the ink absorption speed becomes slow even if the glossiness is sufficient, and the image blurs. The desired image quality may not be obtained.

"About the casting method"
In the present invention, the outermost layer is given a gloss by finishing with a cast method.
As the casting method, a method of coating the above-mentioned coating liquid for the cast coating layer and pressing and drying the heated mirror drum while the coating layer is wet (wet casting method) The coating layer is once dried and then re-wet, and then pressed onto a heated mirror drum and dried to finish (rewet casting method). The coating layer is solidified into a deformable gel state without fluidity. And a method of pressing and drying on a heated mirror drum (gelation cast method) and the like. In addition, after applying the coating solution for the cast coating layer directly on the heated mirror drum, press the paper substrate side undercoat layer and intermediate layer surface, dry and laminate finish (precast method). Can do.

  In the cast coating layer coating solution, it is preferable to incorporate a release agent in order to smoothly peel the cast coating layer and the mirror drum during the production. Examples of mold release agents include higher fatty acids such as stearic acid, oleic acid and palmitic acid, higher fatty acid amides such as stearic acid amide and oleic acid amide, polyolefin waxes such as polyethylene wax, oxidized polyethylene wax and polypropylene wax, calcium stearate, Examples thereof include higher fatty acid salts such as zinc stearate, ammonium stearate, potassium oleate and ammonium oleate, silicone compounds such as lecithin and silicone wax, and fluorine compounds such as polytetrafluoroethylene.

  The compounding ratio of the release agent is adjusted in the range of 0.15 to 50 parts by mass, preferably 0.3 to 30 parts by mass, more preferably 0.5 to 15 parts by mass with respect to 100 parts by mass of the pigment. If the compounding ratio of the release agent is less than 0.15 parts by mass, the effect of improving the releasability tends to be too small. On the other hand, if it exceeds 50 parts by mass, the glossiness is insufficient or the ink absorbability is inferior. Or the recording density tends to be insufficient.

The coating amount of the cast coating layer coating solution is adjusted to 1 to 15 g / m ² , but the coating amount necessary to impart gloss is determined by the properties of the undercoat layer and the intermediate layer. When the intermediate layer is not provided, 5 to 15 g / m ^{2 is} required, but when the intermediate layer is provided with 5 to 10 g / m ² and the particle diameter of the pigment used in the intermediate layer is 0.5 to 3 μm Glossiness can be imparted at 1 to 5 g / m ² . Generally, if the coating amount is too small, gloss cannot be imparted. Conversely, if the coating amount is too large, the ink absorption speed becomes slow even if the glossiness is sufficient, and the image blurs. The desired image quality may not be obtained.

  When coating the coating solution for the cast coating layer on the undercoat layer or the intermediate layer provided thereon, blade coater, air knife coater, roll coater, champlex coater, bar coater, lip coater, gravure coater Various publicly known coating apparatuses such as die coaters and curtain coaters can be used. The coating layer of the coating liquid for cast coating layer is directly wetted or once dried and then rewet, and then pressed against a heated mirror drum, dried and then peeled off. It is also possible to rewet in a semi-dry state. Moreover, when performing re-wetting, a cationic compound, a preservability improving agent, a release agent may be blended in the wetting liquid, and a pigment such as colloidal silica may be blended.

  The surface temperature of the mirror drum is preferably 40 to 200 ° C, more preferably 60 to 150 ° C. When the surface temperature is less than 40 ° C., drying takes time, the production is inefficient, and the film formation of the resin is insufficient, and the strength of the cast coating layer tends to be insufficient. On the other hand, when the temperature exceeds 200 ° C., the film formation proceeds excessively, the surface porosity is lost, the ink absorption is deteriorated, and boiling occurs until the cast coating layer coating liquid dries, resulting in a mirror drum. In many cases, the sticking to the surface becomes insufficient, the surface becomes rough and the glossiness decreases.

Examples 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 examples represent “parts by mass” and “% by mass”, respectively, unless otherwise specified.

Example 1
[Creation of paper substrate]
Papermaking material with 100 parts of wood pulp (LBKP, freeness = 440 mL · CSF) plus filler (baked kaolin), sizing agent (modified rosin) 0.2 part, sulfuric acid band 1.0 part, and yield improver Paper is dried using a long paper machine, and then the oxidized starch is size-pressed and dried to an adhesion amount of 2.0 g / m ^2, and a paper base material having a starch basis weight of 150 g / m ² and an ash content of 8% is obtained. Obtained.

[Preparation of coating solution for undercoat layer]
100 parts of water-absorbing hollow particles (product name: Ropeke HP91, porosity 50%, manufactured by Rohm and Haas Co., Ltd.), SBR adhesive (product name: Smartex SN-113K, Japan A & L) 10 parts) and 10 parts of a water-soluble adhesive (product name: casein, manufactured by ITOCHU Fine Chemical Co., Ltd.) were added with stirring to obtain a coating solution having a concentration of 25%.

[Preparation of intermediate layer coating solution]
100 parts of amorphous silica (product name: Silojet P409, manufactured by Grace Japan Co., Ltd.), 15 parts of modified PVA adhesive (product name: Kuraray Poval R-1130, manufactured by Kuraray Co., Ltd.) 10 parts of a cationic compound (product name: Unisense CP104, manufactured by Senca Co., Ltd.) was added with stirring to obtain a coating solution having a concentration of 18%.

[Creation of coating solution for cast coating layer]
100 parts of colloidal silica / acrylic adhesive composite (product name: Aquabrid 906, manufactured by Daicel Chemical Industries, Ltd.) and 3 water-soluble adhesive (product name: casein, manufactured by ITOCHU Fine Chemical Co., Ltd.) Part, fatty acid-based mold release agent (product name: Nopco Sera LU-6418, manufactured by San Nopco Co., Ltd.), 0.5 part, was added with stirring to obtain a coating solution having a concentration of 30%.

[Creation of inkjet recording paper]
The surface of the obtained paper substrate was coated and dried with an air knife coater so that the coating amount after drying was 12 g / m ² using an air knife coater. Furthermore, the coating liquid for intermediate | middle layer was apply | coated to the surface, and it dried so that the coating amount after drying might be 10 g / m < ² > with an air knife coater. Further, a coating solution for a cast coating layer was applied to the surface with a cast coater, pressed against a heated drum while in a wet state, dried and peeled, and the coating amount after drying was 10 g / m ^2. Inkjet recording paper was obtained.

Example 2
Inkjet recording paper was obtained in the same manner as in Example 1 except that the following undercoat layer coating solution was used.
[Preparation of coating solution for undercoat layer]
100 parts of water-absorbing hollow particles (product name: SX866, porosity: 30%, manufactured by Nippon Synthetic Rubber Co., Ltd.), SBR adhesive (product name: Smartex SN-113K, Japan A & L Co., Ltd.) 10 parts) and 10 parts of a water-soluble adhesive (product name: casein, manufactured by ITOCHU Fine Chemical Co., Ltd.) were added with stirring to obtain a coating solution having a concentration of 20%.

Example 3
Inkjet recording paper was obtained in the same manner as in Example 1 except that the following undercoat layer coating solution was used.
[Preparation of coating solution for undercoat layer]
100 parts of water-absorbing hollow particles (product name: Nipol MH8101, porosity 50%, manufactured by Nippon Zeon Co., Ltd.), SBR adhesive (product name: Smartex SN-113K, Japan A & L Co., Ltd.) 10 parts) and 10 parts of a water-soluble adhesive (product name: casein, manufactured by ITOCHU Fine Chemical Co., Ltd.) were added with stirring to obtain a coating solution having a concentration of 20%.

Example 4
Inkjet recording paper was obtained in the same manner as in Example 1 except that the coating amount after drying the undercoat layer coating solution was 6 g / m ² .

Example 5
Ink jet recording paper was obtained in the same manner as in Example 1, except that the coating amount after drying the undercoat layer coating solution was 3 g / m ² .

Comparative Example 1
Ink jet recording paper was obtained in the same manner as in Example 1 except that the coating amount after drying the undercoat layer coating solution was 1.5 g / m ² .

Comparative Example 2
In Example 1, an inkjet recording paper was obtained in the same manner as in Example 1 except that the intermediate layer coating solution was directly applied onto the paper substrate without coating the undercoat layer coating solution. It was.

Comparative Example 3
Inkjet recording paper was obtained in the same manner as in Example 1 except that the following undercoat layer coating solution was used.
[Preparation of coating solution for undercoat layer]
100 parts of solid pigment (product name: Nipol V1004, porosity 0%, manufactured by Nippon Zeon Co., Ltd.), SBR adhesive (product name: Smartex SN-113K, manufactured by Nippon A & L Co., Ltd.) 10 parts of a water-soluble adhesive (product name: casein, manufactured by ITOCHU Fine Chemical Co., Ltd.) was added while stirring, and a coating solution having a concentration of 20% was obtained.

Comparative Example 4
[Preparation of undercoat layer coating solution]
50 parts of water-absorbing hollow particles (product name: Nipol MH8101, porosity 50%, manufactured by Nippon Zeon Co., Ltd.), amorphous silica (product name: Silojet P409, manufactured by Grace Japan Co., Ltd.) 50 parts, 15 parts of a modified PVA adhesive (product name: Kuraray Poval R-1130, manufactured by Kuraray Co., Ltd.) and 10 parts of a cationic compound (product name: Unisense CP104, manufactured by Senka Co., Ltd.) This was added to obtain a coating solution having a concentration of 18%.

[Creation of coating solution for cast coating layer]
100 parts of colloidal silica / acrylic adhesive composite (product name: Aquabrid 906, manufactured by Daicel Chemical Industries, Ltd.) and 3 water-soluble adhesive (product name: casein, manufactured by ITOCHU Fine Chemical Co., Ltd.) Part, fatty acid-based mold release agent (product name: Nopco Sera LU-6418, manufactured by San Nopco Co., Ltd.), 0.5 part, was added with stirring to obtain a coating solution having a concentration of 30%.

[Creation of inkjet recording paper]
On the surface of the paper substrate, the undercoat layer coating solution was coated and dried with an air knife coater so that the coating amount after drying was 15 g / m ² . Further, a coating solution for a cast coating layer was applied to the surface with a cast coater, pressed against a heated drum while in a wet state, dried and peeled, and the coating amount after drying was 10 g / m ^2. Inkjet recording paper was obtained.

"Evaluation of inkjet recording paper"
The ink jet recording paper obtained as described above was measured for the following quality items and summarized in Table 1.

"Glossiness of blank paper"
The cast coating layer surface of the inkjet recording paper was measured at an incident / reflection angle of 20 ° according to JIS-Z-8741.

"Glossiness of the printed part"
Black printing was performed with an inkjet printer (Deskjet 5650, manufactured by Hewlett-Packard Japan, print mode: other photo paper), and the printed portion was measured at an incident / reflection angle of 20 ° according to JIS-Z-8741.

"Recording density"
Black printing is performed with an inkjet printer (Nihon Hewlett-Packard, Deskjet 5650, printing mode: other photo paper), and the printed portion is recorded with an optical densitometer (Gretag Macbeth, RD-19I). Was measured.

"Bludge"
Red and green blocks were printed next to each other with an inkjet printer (Deskjet 5650, manufactured by Hewlett-Packard Japan, print mode: other photo paper), and the degree of blurring at the boundary portion was visually determined. Judgment with almost no bleed is ◎, Slightly admitted is ◯, Bleeding is observed but there is no practical problem △, Bleeding is large and practical problem is judged with × did.

"Cockling"
Black printing was performed with an inkjet printer (Deskjet 5650, manufactured by Hewlett-Packard Japan, print mode: other photo paper), and the degree of unevenness in the printed portion was visually determined. ◎: Slightly recognized ◎, Slightly recognized: ◯, Slightly recognized but no problem, △, Slightly large, practically problematic did.

"Presser gear mark"
Black printing was performed with an ink jet printer (Deskjet 5650, manufactured by Hewlett-Packard Japan, print mode: other photo paper), and the degree of presser gear marks on the printed portion was visually determined. ◎ indicates that the presser gear mark is hardly recognized, ◎ indicates that the presser gear mark is slightly recognized, △ indicates that the presser gear mark is recognized but has no problem in practice, △ indicates that the presser gear mark is strong, and causes a problem in practical use Was judged as x.

As shown in Table 1, the ink jet recording paper according to the present invention is highly glossy, has little cockling and press gear traces, and has a small difference in glossiness between the blank paper portion and the printed portion, and can obtain an excellent recorded image. It is.

Claims (4)

In an ink jet recording paper having a paper base material and a cast coating layer formed by a casting method and performing ink jet recording on the surface of the cast coating layer, the paper base material and the cast coating layer have water absorption. An undercoat layer containing hollow particles and an adhesive, wherein the adhesion amount of the hollow particles is 2 g / m ² or more, and prevents the ink solvent from reaching the paper substrate (however, inorganic pigment 50 to 95 weight) And 5 to 50 parts by weight of an organic pigment having voids and a binder of 15 to 65 parts by weight with respect to 100 parts by weight of the pigment) , and between the cast coating layer and the undercoat layer An ink jet recording paper comprising an intermediate layer containing a porous pigment, a cationic resin and an adhesive, and fixing a dye or pigment in ink jet ink. The inkjet recording paper according to claim 1, wherein the hollow particles contained in the undercoat layer have a porosity of 30% or more. The inkjet recording paper according to claim 1, wherein the coating amount of the undercoat layer is in the range of 5 to ²⁰ g / m ² as the coating amount after drying. The inkjet recording paper according to any one of claims 1 to 3, wherein the cast coating layer contains colloidal silica.