JP2014156676A - Coated paper for printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated paper for printing extremely high in whiteness with 100% or more of ISO whiteness defined by JIS P-8148 and excellent in quality of a printed surface.SOLUTION: There is provided coated paper for printing having at least one or more coated layers containing a pigment, an adhesive agent and a fluorescent whitener set on a base paper, ISO whiteness defined by JIS P-8148 of 100% or more, and the coated layer of an outermost surface layer containing calcium carbonate having less than 5 mass%of particles having a particle diameter of 2.0 μm or more and 15 mass% or less of particles having a particle diameter of less than 0.5 μm, and 1.0 pts.mass or more and less than 4.0 pts.mass of a polyvinyl alcohol having a polymerization degree of 800 or less and/or a derivative thereof based on 100 pts.mass of the calcium carbonate.

Description

  The present invention relates to a coated paper for printing having an extremely high whiteness with an ISO whiteness defined by JIS P-8148 of 100% or more and excellent print quality. Specifically, the present invention relates to a coated paper for offset printing.

  In recent years, in the printed coated paper market, excellent color reproducibility of coated surfaces, excellent printed surface quality, and the like have been demanded by visualizing and coloring printed materials. In order to obtain this excellent color reproducibility, it has been found that the higher the non-image area is, the higher the effect is. The whiteness of the coated paper for printing greatly depends on the whiteness of the pigment used on the coated surface, and the effect of improving the whiteness can be expected by using pigments with high whiteness, that is, calcium carbonate, titanium dioxide, etc. . However, calcium carbonate, particularly heavy calcium carbonate, which is finely pulverized by grinding, has a low glossiness. If a large amount is added, the gloss of the coated paper for printing is lowered. Lightly synthesized calcium carbonate, which is produced by chemical synthesis, has a relatively high gloss, but is prone to streak and scratches, poor coating suitability with a blade coater, and coating layer strength of coated paper Tend to be weak. Titanium dioxide is extremely excellent in whiteness, but has problems such as high unit price and reduced printing gloss.

  In addition, as a method for increasing the whiteness, a fluorescent whitening agent such as a diaminostilbene-disulfonic acid derivative is generally used as disclosed in Patent Document 1. The reason why whiteness can be increased by using a fluorescent whitening agent is considered to be because the fluorescent whitening agent absorbs ultraviolet rays, and as a result, has the property of increasing the reflectance in the blue region of visible light. Yes. In addition, fluorescent whitening agents are widely used particularly in the manufacture of paper because of their high adsorptivity to cellulose fibers.

  As a method for effectively expressing the performance of the optical brightener, a method using polyvinyl alcohol and / or a derivative thereof together with the optical brightener is known. Patent Document 2 proposes a method of obtaining a coated printing paper with extremely high whiteness by containing 4 to 15% by mass of polyvinyl alcohol having a polymerization degree of 800 or less and / or its derivative with respect to the white pigment.

  In general, polyvinyl alcohol and / or its derivatives are also used as an adhesive for printing paper for printing, but there is a problem that the viscosity of the coating liquid is increased when blended in high amounts. Although the viscosity of the coating liquid can be lowered by lowering the polymerization degree of polyvinyl alcohol and / or its derivative, in Patent Document 2, polyvinyl alcohol and / or its derivative having a low polymerization degree of 800 or less Is highly blended at 4 to 15% by mass with respect to the white pigment, the viscosity of the coating solution increases, the coating suitability decreases, and the white paper surface quality of the coated paper deteriorates. When the white paper surface quality of the coated paper deteriorates, it greatly affects the print surface quality. For this reason, the coated paper for printing which is extremely high in whiteness and satisfies the printing surface quality has not been obtained so far.

JP-A-3-294598 Japanese Patent No. 4873520

  There has not yet been established a coated paper for printing which has an extremely high whiteness with an ISO whiteness of 100% or more as defined in JIS P-8148 and satisfies an excellent printing surface quality. An object of the present invention is to provide a coated paper for printing having an extremely high whiteness with an ISO whiteness defined by JIS P-8148 of 100% or more and an excellent printing surface quality.

  As a result of intensive studies, the inventor contains calcium carbonate having a specific particle size distribution as a coating liquid containing a fluorescent brightening agent, and contains a specific amount of polyvinyl alcohol and / or a derivative thereof. As a result, the above-mentioned problems have been solved. That is, in a coated paper for printing in which at least one coating layer containing a pigment, an adhesive and a fluorescent brightening agent is provided on a base paper, the ISO whiteness specified in JIS P-8148 is 100% or more. And, in the outermost coating layer, calcium carbonate having a particle diameter of 2.0 μm or more of less than 5% by mass and particles having a particle diameter of less than 0.5 μm of 15% by mass or less, and 100 parts by mass of the calcium carbonate It was achieved by a coated paper for printing characterized by containing polyvinyl alcohol and / or a derivative thereof having a polymerization degree of 800 or less with respect to 1.0 to 4.0 parts by mass.

  The outermost coating layer is preferably provided by a blade coating method.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a coated paper for printing having an extremely high whiteness with an ISO whiteness defined by JIS P-8148 of 100% or more and an excellent printing surface quality.

  Hereinafter, embodiments of the coated paper for printing of the present invention will be described in detail. The blank surface quality of the coated paper here refers to the unevenness of the coated surface. In addition, the excellent print surface quality means that there is no uneven ink deposit or imperfection during printing, and there is no gritty feel on the printed surface due to the unevenness of the coated paper.

  The coated paper for printing of the present invention is provided with at least one coating layer containing a pigment, an adhesive and a fluorescent brightening agent on a base paper. The outermost coating layer in the present invention is a coating layer provided on the farthest side when viewed from the base paper. Any number of coating layers containing a pigment, an adhesive, and a fluorescent brightening agent may be provided between the base paper and the outermost coating layer, or a coating layer containing no pigment or fluorescent brightening agent. Any number of layers may be provided. Moreover, in this invention, the coating layer containing a pigment, an adhesive agent, and a fluorescent whitening agent may be one layer on a base paper. In this case, the coating layer is the outermost coating layer.

<The outermost coating layer>
The polyvinyl alcohol and / or derivative thereof used in the present invention has a degree of polymerization of 800 or less, and is contained in an amount of 1.0 part by mass or more and less than 4.0 parts by mass with respect to 100 parts by mass of calcium carbonate in the outermost coating layer. To do. When the degree of polymerization exceeds 800, the viscosity of the coating solution increases remarkably, so that the solid content concentration of the coating solution cannot be increased, and the binding property to calcium carbonate and adhesive increases, so the coating solution This is not preferable because it tends to solidify.

  Further, if the content of polyvinyl alcohol and / or its derivative is less than 1.0 part by mass, the effect of the fluorescent brightening agent cannot be sufficiently exhibited, and the whiteness cannot be increased. Absent. On the other hand, when the amount is 4.0 parts by mass or more, the viscosity of the coating solution becomes too high, so that the coating suitability is lowered and the white paper surface quality of the coated paper is lowered. When the white paper surface quality of the coated paper is lowered, there is a problem that the printing surface quality is also lowered.

  Furthermore, the saponification degree of polyvinyl alcohol and / or its derivative is not limited at all, but it is preferable to use one having 80 mol% or more. In addition, the types of polyvinyl alcohol and / or derivatives thereof are not limited to those obtained by saponifying a vinyl acetate polymer, but esterification, etherification, acetalization, copolymerization, silanol modification, carboxyl modification, carbonyl Modified products such as modified products can also be used.

  The calcium carbonate used in the present invention has a particle size distribution in which particles having a particle size of 2.0 μm or more are less than 5% by mass and particles having a particle size of less than 0.5 μm are 15% by mass or less. The particle size distribution described in the present invention is a volume distribution measured by a particle size analyzer: Microtrac MT3000II (manufactured by Nikkiso Co., Ltd.). By containing calcium carbonate having a particle size distribution as defined in the present invention, the coated surface is smooth and uniform when the coating layer is formed, the blank surface quality of the coated paper is improved, and ink deposition during printing is excellent. A coated paper for printing can be obtained. Calcium carbonate having a particle size distribution outside the range defined in the present invention, that is, calcium carbonate having a particle size distribution of 5% by mass or more of particles having a particle size of 2.0 μm or more is not coated with a smooth coating surface. This is not preferable because it causes poor inking of the ink and a feeling of roughness. In addition, calcium carbonate having a particle size distribution in which particles having a particle size of less than 0.5 μm are more than 15% by mass tends to reagglomerate particles in the coating solution, resulting in increased viscosity or foreign matter during coating. This is not preferable because it occurs and causes a streak.

  Moreover, as calcium carbonate used for this invention, either one or both of light calcium carbonate and heavy calcium carbonate can be contained. Light calcium carbonate has a crystal structure of aragonite, calcite, and vaterite, but is not limited to any structure. When calcium carbonates having different particle diameters or crystal structures are mixed and used, the particle diameter distribution when mixed is a particle having a particle diameter of 2.0 μm or more, less than 5% by mass and particles having a particle diameter of less than 0.5 μm. Is 15% by mass or less. In addition, when the particle size distribution is uniform, the white paper surface quality of the coated surface is improved, and a coated paper for printing having a good printing surface quality can be obtained. Here, the term “uniform particle size distribution” means that the peak is sharp when a line graph of the particle size distribution is drawn.

  In addition, the method for providing the outermost coating layer in the present invention is not limited at all, but it is preferably provided by blade coating. Further, from the viewpoint of the white paper surface quality at the time of blade coating, heavy calcium carbonate is better for calcium carbonate than light calcium carbonate.

  Adhesives used in the present invention include, in addition to polyvinyl alcohol and / or derivatives thereof, esterified starches such as cationized starch, oxidized starch, and phosphate esterified starch, etherified starch, acetylated starch, and enzyme-modified starch. Starch, carboxymethylcellulose, cellulose derivatives such as hydroxyethylcellulose, casein, soy protein, styrene-butadiene latex, acrylic latex, styrene-acrylic latex, vinyl acetate latex, and other emulsion latex. Resins, polyurethane resins, melamine resins, urea resins and the like can be appropriately selected and used within the range of ISO whiteness in the present invention.

  The fluorescent whitening agent contained in the present invention is appropriately selected from conventionally known ones such as stilbene, coumarin, pyrazoline, naphthalimide, benzoxazole, imidazole, thiazole, and distyrylbiphenyl. can do.

  The content of the optical brightener in the present invention is preferably in the range of 1 to 7 parts by mass with respect to 100 parts by mass of the total pigment solid content in the outermost coating layer. When the amount is less than 1 part by mass, the whitening effect of the fluorescent whitening agent is often insufficient. When the amount exceeds 7 parts by mass, the dispersibility of the fluorescent whitening agent cannot be ensured in many cases. It is not preferable because it aggregates and exhibits the original color of the fluorescent brightening agent.

  The coating liquid for forming the outermost coating layer in the present invention includes polyvinyl alcohol and / or a derivative thereof, calcium carbonate, a fluorescent brightener, an adhesive other than polyvinyl alcohol and / or a derivative thereof, and a cellulose derivative. Conventional materials such as water retaining agents, crosslinking agents, curing agents, antifoaming agents, thickeners, water resistance agents, mold release agents, lubricants, preservatives, antifungal agents, dyes, colored pigments, etc. It can be appropriately selected and contained within the range of ISO whiteness in the invention.

<Coating device>
In the present invention, a blade coater is preferably used as an apparatus for applying a coating liquid for forming the outermost coating layer. Since the blade coater can apply a high-concentration coating solution, a high blank paper quality can be imparted to the resulting coated paper. That is, it is possible to obtain a coated paper for printing excellent in printing surface quality.

<Solid content concentration / coating amount of coating liquid>
The solid content concentration of the coating solution for forming the outermost coating layer is preferably in the range of 58 to 67% by mass. When it is less than 58% by mass, the viscosity of the coating solution is excellent, but migration occurs in which the adhesive moves with moisture during drying, resulting in uneven distribution of the adhesive inside the coating layer. The uneven distribution of the adhesive is not preferable because it causes uneven ink deposition during printing and lowers the printing surface quality. When it exceeds 67% by mass, the viscosity of the coating liquid is increased and the coating suitability is lowered. The coating amount is not particularly limited, but the weight after drying is preferably 8 to 25 g / m ² per side.

<Intermediate coating layer>
In the present invention, a coating layer (hereinafter referred to as “intermediate coating layer”) can be provided between the outermost coating layer and the base paper. In the intermediate coating layer, conventionally known pigments, adhesives and various auxiliaries used for coated paper for printing can be appropriately selected and contained.

  In the present invention, examples of the pigment contained in the intermediate coating layer include heavy calcium carbonate, light calcium carbonate, clay, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, amorphous silica, and colloidal. Silica, alumina, hydrated alumina, magnesium carbonate, magnesium oxide, magnesium aluminosilicate, calcium silicate, white carbon, satin white, bentonite, zeolite, sericite, smectite, polystyrene resin, styrene-acrylic copolymer Examples thereof include organic pigments such as resins, urea resins, melamine resins, acrylic resins, vinylidene chloride resins and benzoguanamine resins, and other conventionally known pigments used for coated paper for printing. Moreover, at least 1 sort can be suitably selected and contained from these.

  In the present invention, as the adhesive contained in the intermediate coating layer, polyvinyl alcohol and / or derivatives thereof, cationized starch, oxidized starch, esterified starch such as phosphate esterified starch, etherified starch, acetylated starch, Starches such as enzyme-modified starch, cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose, various copolymers such as casein, soybean protein, styrene-butadiene latex, acrylic latex, styrene-acrylic latex, vinyl acetate latex And emulsion latex resin, polyurethane resin, melamine resin, urea resin and the like. Moreover, at least 1 sort can be suitably selected and contained from these.

  In the present invention, the intermediate coating layer is used for producing coated paper such as a fluorescent whitening agent, a dispersant, a water retention agent, an antifoaming agent, a water resistant agent, a colorant, and a pH adjuster as necessary. Various conventionally known auxiliaries can be selected and contained as appropriate.

  In the present invention, the method of coating the intermediate coating layer is not limited at all, but conventionally known, for example, blade coater, air knife coater, roll coater, bar coater, curtain coater, short dwell coater, shim sizer, gate roll coater, etc. Various coating methods can be used.

  In the present invention, the coating amount of the intermediate coating layer is not limited at all.

<Base paper>
The base paper used in the present invention is not particularly limited, such as the type of raw materials, the papermaking method such as acidic papermaking or neutral papermaking, the type of papermaking machine, surface properties, basis weight, etc. At least the outermost layer coating When the layer is provided, those within the ISO whiteness range in the present invention can be appropriately selected and used. For example, kraft pulp, sulfite pulp, soda pulp, dissolving pulp, semi-chemical pulp, mechanical pulp, thermomechanical pulp, wood pulp such as groundwood pulp, non-wood such as cotton, hemp, bamboo, sugarcane, corn, kenaf, straw One or more kinds of fibers such as animal fibers such as pulp, wool, silk, cellulose regenerated fibers such as rayon, semi-synthetic fibers such as cellulose acetate, synthetic fibers such as polyester fibers and polyurethane fibers, waste paper, etc. Light calcium carbonate, heavy calcium carbonate, kaolin, clay, talc, synthetic amorphous silica, titanium oxide and other fillers as needed, rosin sizing agents, emulsions used in normal acid or neutral papermaking Sizing agent, sizing agent such as alkyl ketene dimer, alkenyl succinic anhydride, cationic starch Pregelatinized starch, amphoteric starch, polyacrylamide, polyvinyl alcohol, polyamine polyamide-epichlorohydrin and other paper strength enhancers, sulfuric acid bands, drainage improvers, yield improvers, pitch control agents, slime control agents, polymers It can contain raw materials and chemicals conventionally used for papermaking, such as fixing agents, antifoaming agents, dyes, colored pigments and fluorescent brightening agents.

As the paper machine, a long net paper machine, a circular net paper machine, a combination of a long net and a circular net, a twin wire paper machine, an on-top twin wire paper machine, or the like can be used as necessary. The base paper can be subjected to an embossing treatment with a pattern such as a blanket, a roll, or a canvas, or a calendar treatment with a smoothness such as chilled, cotton, or resin. The basis weight, single-layer, multi-layer, by ^lamination, those 20g / ^{m 2} ~400g / m 2 are generally used.

  In addition, sheets such as synthetic paper, films, and wet or dry nonwoven fabrics mainly composed of a synthetic material such as polyolefin can be used as the base paper. Also, a coated paper provided with a clear coat such as starch, polyvinyl alcohols, polyacrylamides, etc. on a base paper, a coated paper provided with one or more coating layers comprising a pigment, an adhesive and a fluorescent brightening agent, or A coated paper provided with one or more coating layers composed of a pigment, an adhesive or a fluorescent brightening agent can also be used as the base paper.

<Finishing process>
Furthermore, the coated paper that has been coated and dried in a series of operations can be subjected to various finishing processes such as a calendar process, if necessary.

  Examples of the present invention will be described below. The ISO whiteness (%) and the print surface quality in Examples and Comparative Examples were evaluated by the following methods. Moreover, the mass part in an Example and a comparative example shows a solid content conversion value.

“ISO Whiteness (%)”
ISO whiteness (%) was measured based on JIS P-8148 using SPECTRO COLOR METER MODEL PF-10 (manufactured by Nippon Denshoku Industries Co., Ltd.).

"Print surface quality"
The printing surface quality was evaluated by performing sheet-fed offset printing with a diamond 3H printing machine, and visually evaluating the printing part in the following four stages. In the present invention, the number is 3 or more.
4: There is no ink unevenness or unevenness of ink, and the print quality is high. 3: There is some unevenness of ink, but there is no imperfection of the ink. There is a defect in the thickness of the ink, and it is an unpreferable level for practical use.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

[Example 1] to [Example 8] and [Comparative Example 1] to [Comparative Example 13]
According to the following content, the coated paper for printing of Examples 1-8 and Comparative Examples 1-13 was produced.

[Example 1]
<Base paper>
LBKP (freeness 400 mlcsf) 80 parts by weight NBKP (freeness 480 mlcsf) 20 parts by weight Light calcium carbonate 5 parts by weight Commercial cationized starch 1.0 part by weight Commercially available cationic polyacrylamide retention improver 0.05 parts by weight Pulp The internal additive was prepared with the above composition, and a base paper was made with a basis weight of 89.5 g / m ² .

A 0.80 g / m ² double-sided oxidized starch was adhered to the base paper by a size press to obtain a base paper for coating.

<Coating fluid>
The calcium carbonate of the coating solution was prepared by wet pulverization with a bead mill so that the particle size distribution was 3% by mass of particles having a particle size of 2.0 μm or more and 8% by mass of particles having a particle size of less than 0.5 μm. Heavy calcium carbonate was used. A polyacrylic acid dispersant (trade name “Aron T-61”) was used as the dispersant. 2. Polyvinyl alcohol (trade name “JF-04”, degree of polymerization 400, degree of saponification 98 mol%, manufactured by Nihon Acetate / Poval Inc., indicated as PVA in the table) with respect to 100 parts by mass of this calcium carbonate slurry 0 parts by mass, 3.0 parts by mass of optical brightener (trade name “Sun White CST”, manufactured by Sunrise Chemical Co., Ltd.), styrene-butadiene latex (average particle size 90 nm, gel content 90% by mass, Tg 5 ° C.) 9.0 parts by mass, 0.5 parts by mass of calcium stearate, 0.3 parts by mass of ammonium zirconium carbonate, adjusted to pH 9.8 with aqueous ammonia, and further coated with a solid content concentration of 65% by mass with adjusted water. A working solution was obtained.

With respect to the base paper for coating, the above-mentioned coating liquid was applied on both sides at a coating rate of 1200 g / m ² using a blade coater at a coating rate of 12 g / m ² per side and dried. The obtained coated paper was subjected to a finishing treatment using a soft calender device, and the coated paper for printing of Example 1 was obtained.

[Example 2]
In Example 1, it carried out similarly to Example 1 except having changed the compounding quantity of the polyvinyl alcohol in a coating liquid into 1.0 mass part, and was set as Example 2.

[Example 3]
In Example 1, it carried out similarly to Example 1 except having changed the compounding quantity of the polyvinyl alcohol in a coating liquid into 3.8 mass parts, and was set as Example 3.

[Example 4]
In Example 1, it carried out similarly to Example 1 except having changed the calcium carbonate in a coating liquid into the following light calcium carbonate 100 mass parts, and was set as Example 4. The light calcium carbonate used was prepared such that in the particle size distribution, particles having a particle diameter of 2.0 μm or more were 4.5 mass% and particles having a particle diameter of less than 0.5 μm were 1 mass%.

[Example 5]
In Example 1, the coating method of the coating liquid was changed to film transfer coating using a rod metering size press, the solid content concentration of the coating liquid was set to 60% by mass, and the coating amount was 8 g per side. Example 5 was carried out in the same manner as in Example 1 except that / m ² was changed.

[Example 6]
In Example 1, the coating method of the coating liquid was changed to curtain coating, the solid content concentration of the coating liquid was 53 mass%, the coating speed was 700 m / min, and the coating amount was 8 g / side. Example 6 was performed in the same manner as in Example 1 except that m ² was changed.

[Example 7]
In Example 1, except that the calcium carbonate in the coating solution was changed to a composition in which 50 parts by weight of heavy calcium carbonate used in Example 1 and 50 parts by weight of light calcium carbonate used in Example 4 were mixed. Example 7 was carried out in the same manner as in Example 1. At this time, the particle size distribution was 3% by mass of particles having a particle size of 2.0 μm or more and 7% by mass of particles having a particle size of less than 0.5 μm.

[Example 8]
In Example 1, the polyvinyl alcohol in the coating solution was changed to commercially available phosphated starch, and the intermediate coating layer was coated on the same base paper for coating as in Example 1 using a blade coater. The coating liquid was applied on both sides at a coating speed of 800 g / min and applied at a coating amount of 4 g / m ² per side and dried. Further, as the outermost coating layer, the same coating liquid as in Example 1 was used in the same manner as in Example 1 except that the coating speed was changed to 1100 m / min and the coating amount was changed to 8 g / m ² per side. Then, a coating layer was provided, and the resulting coated paper for printing was designated as Example 8.

[Comparative Example 1]
In Example 1, it carried out similarly to Example 1 except having changed the compounding quantity of the polyvinyl alcohol in a coating liquid into 4.5 mass parts, and was set as the comparative example 1.

[Comparative Example 2]
In Example 1, it carried out similarly to Example 1 except having changed the compounding quantity of the polyvinyl alcohol in a coating liquid into 10 mass parts, and was set as the comparative example 2.

[Comparative Example 3]
In Example 1, it carried out similarly to Example 1 except having changed the compounding quantity of the polyvinyl alcohol in a coating liquid into 0.5 mass part, and was set as Comparative Example 3.

[Comparative Example 4]
In Example 1, the polyvinyl alcohol in the coating solution was changed to the trade name “JF-10” (polymerization degree 1000, saponification degree 98 mol%, manufactured by Nippon Vinegar Poval Co., Ltd.), as in Example 1. And Comparative Example 4 was made.

[Comparative Example 5]
In Example 1, the polyvinyl alcohol in the coating liquid was changed to the trade name “JF-17” (polymerization degree 1700, saponification degree 98 mol%, manufactured by Nihon Acetate / Poval), as in Example 1. And Comparative Example 5 was obtained.

[Comparative Example 6]
In Example 1, the calcium carbonate of the coating solution was wet in a bead mill so that particles having a particle size of 2.0 μm or more were 10% by mass and particles having a particle size of less than 0.5 μm were 8% by mass in the particle size distribution. Comparative Example 6 was carried out in the same manner as in Example 1 except that heavy calcium carbonate was prepared by pulverization.

[Comparative Example 7]
In Example 1, the calcium carbonate of the coating solution was wet in a bead mill so that particles having a particle size of 2.0 μm or more were 50% by mass and particles having a particle size of less than 0.5 μm were 8% by mass in the particle size distribution. Comparative Example 7 was carried out in the same manner as in Example 1 except that heavy calcium carbonate prepared by pulverization was changed.

[Comparative Example 8]
In Example 1, the calcium carbonate of the coating solution was wet in a bead mill so that particles having a particle size of 2.0 μm or more were 3% by mass and particles having a particle size of less than 0.5 μm were 20% by mass in the particle size distribution. Comparative Example 8 was carried out in the same manner as in Example 1 except that heavy calcium carbonate was prepared by pulverization.

[Comparative Example 9]
In Example 1, the calcium carbonate of the coating solution was wet in a bead mill so that particles having a particle size of 2.0 μm or more were 3% by mass and particles having a particle size of less than 0.5 μm were 50% by mass in the particle size distribution. Comparative Example 9 was carried out in the same manner as in Example 1 except that heavy calcium carbonate was prepared by pulverization.

[Comparative Example 10]
In Example 1, the calcium carbonate of the coating solution was wet in a bead mill so that particles having a particle size of 2.0 μm or more were 10% by mass and particles having a particle size of less than 0.5 μm were 20% by mass in the particle size distribution. Comparative Example 10 was carried out in the same manner as in Example 1 except that heavy calcium carbonate was prepared by pulverization.

[Comparative Example 11]
In Example 1, the calcium carbonate of the coating solution was prepared so that the particle size distribution was 2.5% by mass of particles having a particle size of 2.0 μm or more and 10% by mass of particles having a particle size of less than 0.5 μm. Comparative Example 11 was carried out in the same manner as Example 1 except that the calcined kaolin was changed.

[Comparative Example 12]
In Example 1, the pigment contained in the coating solution was changed to a mixture of 95 parts by mass of calcium carbonate used in Example 1 and 5 parts by mass of a commercially available organic pigment (hollow particles). And Comparative Example 12 was obtained. The particle size distribution of the pigment slurry mixed at this time was 3.5% by mass of particles having a particle size of 2.0 μm or more and 8% by mass of particles having a particle size of less than 0.5 μm.

[Comparative Example 13]
In Example 1, it carried out similarly to Example 1 except having changed the polyvinyl alcohol of a coating liquid into commercially available phosphate esterified starch, and was set as Comparative Example 13.

  For Examples 1 to 8 and Comparative Examples 1 to 13, the type and particle size distribution of the pigment used, the content and degree of polymerization of polyvinyl alcohol, the number of coating layers provided on the base paper, the coating method, and the evaluated ISO Table 1 shows the results of whiteness (%) and print surface quality.

<Evaluation results>
As can be seen from Table 1, when Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 are compared, the ISO whiteness decreases when the polyvinyl alcohol content decreases, and the ISO content increases when the polyvinyl alcohol content increases. Whiteness increases. In addition, as the content of polyvinyl alcohol increased, the coating suitability decreased, so that the blank paper surface quality deteriorated and the printing surface quality also deteriorated.
From Example 1 and Comparative Examples 4 and 5, it can be seen that the higher the degree of polymerization of polyvinyl alcohol, the lower the coating suitability and the worse the print quality for the same reason.
From Examples 1, 4 and 7, in the calcium carbonate to be contained, the higher the ratio of heavy calcium carbonate, the better the coating suitability, and 50% by weight or more of the pigment contained in the outermost coating layer is heavy. It can be seen that the printing surface quality is excellent when it is calcium carbonate.
From Examples 5, 6, and 7, it can be seen that in the coating method of the outermost layer, the blade coater is excellent in the printing paper quality due to the excellent white paper surface quality.
From Example 8, it can be seen that even when an intermediate coating layer is provided, a coated paper for printing having an ISO whiteness of 100% or more and a high printing surface quality can be obtained.
From Comparative Examples 6, 7, 8, 9 and 10, as the number of particles having a particle size distribution of 2.0 μm or more increases, the printing surface quality deteriorates due to the increase in the unevenness of the white paper surface, and the particles having a particle size of less than 0.5 μm. It can be seen that as the amount increases, the viscosity increases due to agglomeration of fine particles, that is, the coating quality deteriorates, and the printing surface quality deteriorates due to the deterioration of the blank paper surface due to the increase in streak.
In addition, it can be seen from Comparative Examples 11 and 12 that the ISO whiteness does not become 100% or more when a pigment other than calcium carbonate is contained.
Furthermore, it can be seen from Comparative Example 13 that phosphoric acid esterified starch does not provide a whitening effect in ISO whiteness.

Claims (2)

  In a coated paper for printing in which at least one coating layer containing a pigment, an adhesive and an optical brightener is provided on a base paper, the ISO whiteness specified in JIS P-8148 is 100% or more. And, in the outermost coating layer, the calcium carbonate having a particle diameter of 2.0 μm or more is less than 5 mass% and the particle diameter of less than 0.5 μm is 15 mass% or less, and 100 parts by mass of the calcium carbonate A coated paper for printing comprising 1.0 part by mass or more and less than 4.0 parts by mass of polyvinyl alcohol and / or a derivative thereof having a polymerization degree of 800 or less.   The coated paper for printing according to claim 1, wherein the outermost coating layer is provided by a blade coating method.