JP7839617B2 - Coated paper for printing - Google Patents

Description

This invention relates to a coated paper for printing that has high white gloss and high strength.

Coated paper is broadly classified into glossy coated paper and matte coated paper. Among glossy coated papers, high-gloss coated paper includes art paper and super art paper, traditionally used for high-quality printing, as well as coated paper used for catalogs and brochures. These papers have a high gloss finish, both in terms of white paper gloss and print gloss. Matte coated paper, on the other hand, has lower white paper gloss and print gloss than high-gloss coated paper, and includes dull-finish coated paper and matte-finish coated paper.

Generally, high-gloss coated paper achieves its glossiness by using large quantities of flat pigments such as kaolin or clay, or by using plastic pigments with good gloss-producing properties. The main surface of flat pigments such as kaolin or clay is acidic, while the sides are basic (Non-Patent Literature 1), and adhesives such as latex commonly used in coated paper contain acidic groups. Therefore, the main surface of kaolin or clay is acidic, resulting in low affinity with adhesives such as latex. On the other hand, the sides of kaolin or clay are basic, resulting in high affinity with adhesives, but the small surface area prevents sufficient bonding area from being achieved, leading to the problem of low strength development efficiency.

Kaolin or clay are pigments with yellow to brown hues, and coated papers that use a lot of these pigments tend to have a strong yellow tint, resulting in a tendency for high-gloss coated papers to have a yellowish hue. The degree of yellowness is indicated by b ^* in the L ^* a ^* b ^* colorimetric system, and papers with a strong yellow tint tend to have a high b ^* value. When printing on papers with a strong yellow tint, the overall yellowness of the printed material becomes strong, resulting in a tendency for the printed material to have poor color reproduction.

Plastic pigments are extremely expensive materials, making them difficult to use in general-purpose glossy coated paper such as flyers. Furthermore, there is a growing trend to avoid the use of plastic pigments, which are organic pigments, due to environmental concerns.

In addition, regarding high-gloss coated paper, a technique has been proposed to improve glossiness using very fine calcium carbonate with an average particle size of 0.50 μm or less (Patent Document 2). However, calcium carbonate with excessively fine particle size also increases the specific surface area, which increases the binder requirement and potentially leads to a decrease in paper strength.

Japanese Patent Publication No. 2007-231457 Japanese Patent Application Publication No. 7-229091

Journal of the Japan Pulp and Paper Technology Association, Vol. 62 (2008), No. 6, pp. 694-699

The present invention aims to provide a coated paper for printing that possesses high white gloss and high strength.

In view of the above problems, the inventors conducted extensive research and found that a printed coated paper having a pigment coating layer containing specific fine calcium carbonate particles solves the above problems. That is, the above problems are solved by the present invention as described below.
[1] The base paper has a pigment coating layer on at least one side,
The outermost pigment coating layer contains calcium carbonate having an average particle size (D50) greater than 0.50 μm and less than or equal to 0.80 μm.
Coated paper for printing with a white gloss level (75°) of 60% or higher.
[2] The printing coated paper according to [1], wherein 40 parts by weight or more of the calcium carbonate is contained in 100 parts by weight of the pigment in the outermost pigment coating layer.
[3] The coated paper for printing according to [1] or [2], wherein the average particle size (D50) of the calcium carbonate is 0.55 to 0.75 μm.
[4] A coated paper for printing according to any of [1] to [3], wherein the print gloss of the blue-red printed area is 70% or higher.
[5] The printing coated paper according to [2], wherein the outermost pigment coating layer contains 75 parts by weight or more of calcium carbonate in 100 parts by weight of pigment.
[6] A printing coated paper according to any one of [1] to [5], comprising multiple pigment coating layers, wherein the coating amount of the outermost pigment coating layer is greater than the coating amount of the innermost pigment coating layer.
[7] A printed coated paper according to any of [1] to [6], wherein the amount of the outermost coating layer is 7 g/ ^m² or more.

This invention provides a coated paper for printing that possesses high white gloss and high strength.

The present invention will now be described in detail. In this invention, "~" includes its endpoint. That is, "X~Y" includes the values of X and Y. Also, "X or Y" means either X or Y, or both.

1. Coated Printing Paper Coated printing paper is a type of paper for printing that has a pigment coating layer provided on a base paper. The pigment coating layer is a layer mainly composed of white pigment. The coated printing paper of the present invention contains calcium carbonate in the outermost pigment coating layer, which has an average particle size (D50) greater than 0.50 μm and 0.80 μm or less. The coated printing paper of the present invention can be subjected to commercial printing such as offset printing, gravure printing, and on-demand printing (laser method, inkjet method, electrophotographic method) on the paper surface, and its uses include, but are not limited to, books, magazines, posters, envelopes, and calendars.

(1) Pigment Coating Layer 1) Pigment The pigment coating layer contains calcium carbonate (hereinafter also referred to as "first calcium carbonate") with an average particle size (D50) greater than 0.50 μm and 0.80 μm or less. D50 is the 50% volume average particle size. The particle size distribution and D50 of the pigment can be measured by laser diffraction using a Malvern Mastersizer 3000 or the like. The upper limit of the D50 of calcium carbonate is preferably 0.75 μm or less, and preferably 0.70 μm or less. The lower limit is preferably 0.55 μm or more from the viewpoint of the specific surface area of the pigment and the amount of binder required. If D50 is within the above range, the coating layer becomes denser and therefore has high gloss, and furthermore, the amount of binder required is less compared to when a pigment of less than 0.50 μm is used, so a printed coated paper with excellent strength can be obtained.

If the pigment coating layer is present on both sides of the base paper, it is sufficient that the outermost pigment coating layer on at least one side contains the first calcium carbonate.

The lower limit of the amount of first calcium carbonate blended in the outermost pigment coating layer is preferably 40 parts by weight or more, more preferably 75 parts by weight or more, and even more preferably 80 parts by weight or more, per 100 parts by weight of pigment in the pigment coating layer. The entire amount may be first calcium carbonate. The first calcium carbonate is preferably heavy calcium carbonate or light calcium carbonate produced in the causticization process of the pulp manufacturing process (caustic light calcium carbonate, see Japanese Patent No. 5274077).

As the first white pigment in the pigment coating layer, other than calcium carbonate, pigments commonly used in the field can be used. Examples include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, or core-shell types. Multiple types of these pigments may be used in combination.

As a white pigment other than the first calcium carbonate, it is preferable to use heavy calcium carbonate or light calcium carbonate (hereinafter also referred to as "second calcium carbonate") with a D50 of more than 0.80 μm. Calcium carbonate has excellent bonding properties with adhesives (binders) and improves whiteness, thus achieving high strength, whiteness, and printability. The total amount of the first and second calcium carbonates in 100 parts by weight of pigment in the outermost pigment coating layer is preferably 90 parts by weight or more, and more preferably 100 parts by weight. When there are two or more pigment coating layers, the total amount of the first and second calcium carbonates in the pigment coating layers other than the outermost coating layer is not limited, but is preferably within the above range. The second calcium carbonate is preferably heavy calcium carbonate or caustic light calcium carbonate.

2) Adhesives The pigment coating layer contains an adhesive (binder) as a matrix. The adhesive is not limited, and known adhesives can be used. Examples include latex such as styrene-butadiene copolymers, styrene-acrylic copolymers, ethylene-vinyl acetate copolymers, butadiene-methyl methacrylate copolymers, vinyl acetate-butyl acrylate copolymers, maleic anhydride copolymers, and acrylic acid-methyl methacrylate copolymers; polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol; proteins such as casein, soy protein, and synthetic protein; starches such as oxidized starch, positive starch, urea phosphate esterified starch, hydroxyethyl etherified starch, and dextrin; and cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, and hydroxymethylcellulose. Multiple types of these can be used in combination.

The amount of adhesive is preferably 5 to 30 parts by weight, and more preferably 8 to 25 parts by weight, per 100 parts by weight of pigment in the total pigment coating layer, from the viewpoint of printability and coating suitability. The upper limit is more preferably 20 parts by weight or less, and most preferably 17 parts by weight or less. If the total amount of adhesive exceeds 30 parts by weight, the viscosity of the pigment coating solution increases, making operational problems more likely during coating. Furthermore, in this case, the drying properties of the ink tend to decrease. On the other hand, if the total amount of adhesive is less than 5 parts by weight, it becomes difficult to obtain sufficient surface strength.

The coated paper for printing of the present invention preferably contains 10 to 80% by weight of latex in the total adhesive, and more preferably 15 to 70% by weight of latex. Latex is an adhesive in the form of an emulsion. Styrene-butadiene latex is preferred as the latex. As mentioned above, calcium carbonate has better affinity with adhesives having acidic groups such as latex compared to kaolin or clay. Therefore, by using latex in the coated paper for printing of the present invention, a coated paper for printing with excellent strength development can be obtained. The coated paper for printing of the present invention has a pigment coating layer, and when there are two or more pigment coating layers, the layer closest to the base paper preferably contains 10 to 80% by weight of latex in the total adhesive, and the layer furthest from the base paper preferably contains 30 to 60% by weight of latex. As other adhesives, starches are particularly preferred, and the amount is preferably 30 to 90% by weight of the total adhesive in the layer closest to the base paper, and preferably 40 to 70% by weight in the layer furthest from the base paper.

3) Other additives The pigment coating layer may, as needed, contain various auxiliary agents commonly used in pigments for coated paper, such as dispersants, thickeners, water-retaining agents, defoaming agents, water-resistant agents, dyes, and coloring pigments.

4) Coating Amount The coating amount of the pigment coating layer is preferably 7 g/ ^m² or more in solid content per side, more preferably 10 g/ ^m² or more, and even more preferably 15 g/ ^m² or more. If the coating amount is less than 7 g/ ^m² , the unevenness of the paper substrate surface cannot be sufficiently covered, which may significantly reduce the receptivity of the printing ink and may not result in sufficient white paper gloss. On the other hand, the coating amount of the pigment coating layer is preferably 50 g/ ^m² or less, more preferably 40 g/ ^m² or less, and even more preferably 35 g/ ^m² or less. The said coating amount is the total value of all pigment coating layers per side, but if there are two or more pigment coating layers, the coating amount of the innermost pigment coating layer (the pigment coating layer adjacent to the base paper) is preferably 2 to 15 g/ ^m² , and more preferably 5 to 12 g/ ^m² . Furthermore, the coating amount of the outermost pigment coating layer is preferably 7 g/ ^m² or more, and more preferably 8 g/ ^m² or more. The upper limit is preferably 20 g/ ^m² or less, and more preferably 15 g/ ^m² or less. Since the outermost coating layer has a significant influence on gloss development, it is preferable that the coating amount of the outermost coating layer is greater than that of the innermost pigment coating layer.

(2) Base paper 1) Pulp Known pulps can be used for the base paper. Known pulps include chemical pulp, wood pulp (GP), refined wood pulp (RGP), thermomechanical pulp (TMP), chemothermetic pulp (CTMP), chemigland pulp (CGP), semi-chemical pulp (SCP), and recycled paper pulp. In the present invention, it is preferable to use chemical pulp. Chemical pulps include those produced by the kraft pulp method and those produced by the sulfite pulp method, and both can be used in the present invention, but chemical pulp produced by the kraft method is preferable in terms of production cost. From the viewpoint of whiteness and other factors, the chemical pulp content in the raw material pulp is preferably 60% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

2) Fillers Known fillers may be used in the base paper. Known fillers include inorganic fillers such as heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, delamikaolin, white carbon, talc, magnesium carbonate, barium carbonate, barium sulfate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium dioxide, and amorphous silica produced by neutralization of sodium silicate with mineral acids, as well as organic fillers such as urea-formaldehyde resin, melamine resin, polystyrene resin, and phenolic resin. Among these, heavy calcium carbonate and light calcium carbonate, which are typical fillers in neutral papermaking and alkaline papermaking, are preferably used to improve opacity. The calcium carbonate used as a filler may be the first calcium carbonate or the second calcium carbonate mentioned above, but light calcium carbonate is preferred. The filler ratio in the paper is not particularly limited, but 1 to 40% by weight is preferred, and 10 to 35% by weight is more preferred. Considering the strength of the base paper, it is more preferable to have 10 to 20% by weight.

3) Other known papermaking additives may also be used. For example, aluminum sulfate, various anionic, cationic, nonionic, or amphoteric yield improvers, water drainage improvers, various paper strength enhancers, and internal sizing agents may be used as needed. Examples of dry paper strength improvers include polyacrylamide and cationized starch, while examples of wet paper strength improvers include polyamidoamine epichlorohydrin. These chemicals are added within a range that does not affect the form or operability. Examples of internal sizing agents include alkyl ketene dimers, alkenyl succinic anhydride, and rosin sizing agents. Furthermore, dyes, pigments, fluorescent whitening agents, pH adjusters, defoamers, pitch control agents, slime control agents, etc., may also be added as needed.

4) Basis weight of the base paper The basis weight of the base paper for the coated printing paper of the present invention is preferably 40 to 160 g/ ^m² , more preferably 45 to 150 g/ ^m² , and even more preferably 50 to 140 g/ ^m² .

5) Clear Coating Layer The printed coated paper of the present invention may have a clear (transparent) coating layer on one or both sides of the base paper described above. Applying a clear coating to the base paper can improve the surface strength and smoothness of the base paper, and can also improve the coating suitability when applying pigment coating. The amount of clear coating is preferably 0.1 to 3.0 g/ ^m² in solid content per side, more preferably 0.2 to 2.0 g/ ^m² , and even more preferably 0.5 to 2.0 g/ ^m² .

In this invention, clear coating refers to the process of applying a coating liquid (surface treatment liquid) mainly composed of starches such as starch, oxidized starch, and various modified starches (automodified, cationically modified, etc.), and water-soluble polymers such as polyacrylamide and polyvinyl alcohol, to a base paper using a coater (coating machine) such as a two-roll pound size press, gate roll coater, pre-metalling size press, curtain coater, or spray coater, by sizing press. A sizing agent can also be included in the clear coating liquid during coating. In this invention, it is preferable to coat with starch.

2. Manufacturing Method The printed coated paper of the present invention can be manufactured by known methods, but it is preferable to manufacture it by coating a base paper with a pigment coating solution containing a pigment and an adhesive.

(1) Preparation of base paper The raw materials used for the base paper used in the present invention have already been described. The base paper is manufactured by known papermaking methods. For example, it can be manufactured using a wire screen paper machine including a top wire, an on-top former, a gap former, a round wire screen paper machine, a paperboard paper machine that uses a wire screen paper machine and a round wire screen paper machine in combination, a Yankee dryer machine, etc. The pH during papermaking may be acidic, neutral, or alkaline, but neutral or alkaline is preferred. The papermaking speed is not particularly limited. The base paper used in the present invention may be single-layer or multi-layer, but single-layer base paper is preferably used.

(2) Smoothing treatment of the base paper Before applying the pigment coating solution to the obtained base paper, it is preferable to smooth the base paper using various calendering devices. Commonly used calendering devices such as supercalenders and soft calenders can be used as appropriate. Calendering finishing conditions such as the temperature of the rigid rolls, calendering pressure, nip number, roll speed, and moisture content of the paper before calendering are appropriately selected according to the required quality. Calendering the base paper improves its smoothness and thus its suitability for pigment coating.

(3) Preparation of Pigment Coating Solution The pigment coating solution can be prepared by dispersing or dissolving the pigment, adhesive, and additives as needed in water. The composition of each component is adjusted so that the aforementioned pigment coating layer can be formed. When performing blade coating, the solid content concentration of the pigment coating solution is preferably 40 to 70% by weight, and more preferably 60 to 70% by weight. The viscosity of the pigment coating solution is preferably in the range of 500 to 5000 mPa·s when measured at 60 rpm at room temperature. When performing coating with a roll coater, the solid content of the pigment coating solution is preferably 30 to 60% by weight, and more preferably 40 to 60% by weight. If the solid content is too low, backflow may occur in blade coating, and if it is too high, the blade load will increase and blade wear will progress, and boiling may occur in roll coaters, affecting operability.

(4) Coating Method The coating method is not limited, and known coating methods such as roll coaters and blade coaters can be used. The coating speed is also not particularly limited, but 400 to 1800 m/min is preferred for blade coaters, and 400 to 2000 m/min is preferred for roll coaters. In the present invention, the pigment coating layer may be coated with a single-layer blade coater, or coated with a roll coater and then with a blade coater, or coated with a blade coater and then with another blade coater, but it is preferable to use a blade coater for coating the outermost coating layer in order to improve the smoothness of the surface.

The printed coated paper of the present invention has a pigment coating layer on at least one side, and may have two or more pigment coating layers. When there are two or more pigment coating layers, the fiber coverage is improved and the smoothness is also increased. If there are three or more layers, the amount of coating can be increased and the quality of the coated paper is improved, but from the viewpoint of cost and operability, it is preferable to have one or two layers. As described above, a clear coating layer may be provided on the base paper, and a pigment coating layer may be provided on top of that.

(5) Other processes The method for drying the wet coating layer is not limited, and for example, a steam heating cylinder, a heated hot air dryer, a gas heater dryer, an electric heater dryer, an infrared heater dryer, etc., can be used.

The coated paper for printing of the present invention may be surface-treated after being manufactured as described above, and calendering is preferred to obtain high gloss. When calendering is performed, commonly used calendering devices such as supercalenders and soft calenders can be used as appropriate. Calendering conditions such as the temperature of the rigid roll, calendering pressure, number of nips, roll speed, and moisture content of the paper before calendering are appropriately selected according to the required quality, but hot soft nip calendering is more preferable for the coated paper for printing of the present invention. The preferred conditions for this treatment are a linear pressure of 140 to 300 kN/m, a temperature of 70 to 300°C, and 5 nips or more. The processing speed is approximately 200 to 800 m/min.

3. Paper Quality (1) White Paper Gloss White paper gloss is an index indicating the degree of gloss on white paper, and in the present invention, it is measured in accordance with JIS-P8142 and is the specular gloss at an angle of 75° with respect to the normal of the paper surface. The coated printing paper of the present invention is a high-gloss coated printing paper with high white paper gloss. The white paper gloss of the coated printing paper of the present invention is 60% or more, preferably 65% or more, and more preferably 70% or more. There is no upper limit to the white paper gloss, but it is 100% or less.

(2) Print glossiness Print glossiness is an index that indicates the degree of glossiness of the printed material after printing, and in the present invention, it is measured by the method described below. The print glossiness (CM) of the blue and red printed area is preferably 70 or higher, and preferably 75% or higher.

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Parts by weight and weight percent are values on a solid content basis.

<Evaluation Method>
(1) Basis weight was measured in accordance with JIS P 8124.
(2) ISO whiteness: Measured in accordance with JIS P8148 using a color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd., under conditions including ultraviolet light.
(3) White paper gloss was measured according to JIS-P8142.
(4) Print Glossiness Using a Roland offset sheet-fed printing press (4 colors), offset sheet-fed inks (NEX-M manufactured by Toyo Ink Co., Ltd.) were used to print in the order of blue-red (CM) and red (C) at a printing speed of 8000 sheets/hr, with the ink density of the solid areas being blue 1.60 and red 1.50. The glossiness of the solid blue-red (CM) printed areas of the obtained printed materials was measured according to JIS P-8142.
(5) Printed surface strength Using an RI-I type printing press (manufactured by Akira Seisakusho), printing was done using printing ink (NEX-Y manufactured by Toyo Ink). After printing, the print marks on the rubber roll were manually transferred to transfer paper, and the degree of picking was visually evaluated. The evaluation criteria were as follows.
A = rarely occurs, B = occurs

<Materials>
The following was used.
(1) Heavy calcium carbonate, manufactured by Fimatec Co., Ltd., product name: FMT97, D50 = 0.88 μm
Manufactured by Fimatec Co., Ltd., Product name: FMT75, D50 = 1.65 μm
Manufactured by Fimatec Co., Ltd., Product name: Curvital 90, D50 = 1.22 μm
Manufactured by Fimatec Co., Ltd., Product name: FMT100YF, D50 = 0.59 μm
Manufactured by Fimatec Co., Ltd., Product name: FMT100, D50 = 0.65 μm
Manufactured by Imerys Minerals Japan Co., Ltd., Product name: Curvital 97, D50 = 0.88 μm
(2) Clay, manufactured by Kamin, HydraGloss D50 = 0.22 μm
Made by Imerys Minerals Japan, Premier, D50 = 2.055 μm
(3) Adhesive: Styrene-butadiene copolymer latex, starch:
Dynacoat 68NB (manufactured by GSL Japan Co., Ltd.)
Biolatex (manufactured by Ecosynthetic)
(4) Dye: Purple dye (manufactured by Mikuni Pigment Co., Ltd.)
Blue dye (manufactured by Mikuni Pigment Co., Ltd.)
Black dye (manufactured by Mikuni Pigment Co., Ltd.)
Fluorescent dye: canwhite (manufactured by Kanasia Japan Co., Ltd.)

<Series 3>
[Example 1]
A base paper with a basis weight of 75 g/ ^m² was prepared using 100% chemical pulp by weight and containing 13.5% by weight of light calcium carbonate as filler.

100 parts by weight of heavy calcium carbonate (manufactured by Fimatec Co., Ltd., product name: FMT97, D50 = 0.88 μm) was used as the pigment. To this, 3 parts by weight of styrene-butadiene copolymer latex and 6 parts by weight of oxidized starch were added as adhesives, and water was added to obtain a primer pigment coating solution with a solid content of 65% by weight.

Using 100 parts by weight of fine-grained heavy calcium carbonate (manufactured by Fimatec Co., Ltd., product name: 100YF, D50 = 0.59 μm), 7.7 parts by weight of styrene-butadiene copolymer latex as an adhesive, 1.3 parts of starch-based binder "Biolatex" (indicated as BLx in the table), and the dyes as shown in Table 1, water was added to obtain a topcoat pigment coating solution with a solid content of 66% by weight.

On the aforementioned base paper, a primer pigment coating solution was applied to both sides using a blade coater so that the dry coating amount per side was 9.5 g/ ^m² , and then dried. Furthermore, a topcoat pigment coating solution was applied to both sides using a blade coater so that the dry coating amount per side was 8.5 g/ ^m² , and the paper was nipped using a resin roll and a metal roll. Calendering was performed under the conditions shown in Table 1 for temperature and nip line pressure to obtain coated paper for printing. This coated paper for printing was evaluated using the method described above.

[Example 2]
Printable coated paper was manufactured and evaluated in the same manner as in Example 1, except that the amount of latex in the undercoat coating solution was changed.

[Comparative Examples 1 and 2]
Printable coated paper was manufactured and evaluated in the same manner as in Example 1, except that the coating solution shown in Table 1 was used.

<Series 1>
[Examples 3 and 4]
A base paper with a basis weight of 69 g/ ^m² was prepared using 100% chemical pulp by weight and containing 13.5% by weight of light calcium carbonate as filler.
A primer pigment coating solution with a solid content of 65% by weight was obtained using the pigments and adhesives shown in Table 1. A topcoat pigment coating solution with a solid content of 65% by weight was obtained using the pigments and adhesives shown in Table 1.
Using these materials, coated paper for printing was manufactured and evaluated in the same manner as in Example 1.

[Comparative Examples 3 and 4]
Printable coated paper was manufactured and evaluated in the same manner as in Example 3, except that the topcoat liquid was changed as shown in Table 1.

<Series 2>
[Examples 5-8]
A base paper with a basis weight of 75 g/ ^m² was prepared using 100% chemical pulp by weight, containing 13.5% by weight of light calcium carbonate as a filler, and pressed with starch size. A pigment coating solution with a solid content of 65% by weight was obtained using the pigments and adhesives shown in Table 1.
Using these materials, a printed coated paper having a single pigment coating layer was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 5]
Printable coated paper was manufactured and evaluated in the same manner as in Example 5, except that the coating solution was changed as shown in Table 1.

In Examples 3 and 4 of Series 1, using calcium carbonate with a D50 of 0.80 μm or less improved the printed surface strength compared to Comparative Example 4, which incorporated clay, suggesting the possibility of reducing the amount of binder used. Furthermore, in Examples 3 and 4, high gloss was obtained even under the same calendering conditions as Comparative Example 3, which used calcium carbonate with a larger average particle size.

Series 2 relates to single-coated coated paper for printing. In Examples 5 to 8, which incorporated calcium carbonate with a D50 of 0.80 μm or less, a higher gloss was obtained compared to Comparative Example 5, which used calcium carbonate with a larger average particle size, similar to Series 1 (double coating). In Example 8, although the amount of starch, which is the binder, was reduced by 1 part by weight compared to Example 5, the print surface strength remained at a level that did not cause problems for printing, and no significant difference was observed between the two.

From Series 3 onwards, it has become clear that by using calcium carbonate with a D50 of 0.80 μm or less, it is possible to improve strength while maintaining equivalent white paper gloss compared to cases using clay or kaolin, and to obtain a printed coated paper with equivalent strength even with a reduced amount of adhesive. Therefore, it is clear that the printed coated paper of the present invention has high white paper gloss and excellent strength.

Claims (6)

A method for manufacturing coated paper for printing, wherein the base paper has a pigment coating layer on at least one side, the white paper gloss (75°) is 60% or more, and the print gloss of the blue and red printed area is 70% or more,
The process includes providing an outermost coating layer containing, as a first calcium carbonate, heavy calcium carbonate or caustic light calcium carbonate having an average particle size (D50) greater than 0.50 μm and less than or equal to 0.80 μm, and as a second calcium carbonate, heavy calcium carbonate or caustic light calcium carbonate with a D50 greater than 0.80 μm.
Manufacturing method. The manufacturing method according to claim 1, comprising the step of providing the outermost pigment coating layer containing 40 parts by weight or more of the first calcium carbonate in 100 parts by weight of the pigment. The manufacturing method according to claim 1 or 2, wherein the average particle size (D50) of the first calcium carbonate is 0.55 to 0.75 μm. The manufacturing method according to claim 2, comprising the step of providing an outermost coating layer containing 75 parts by weight or more of the first calcium carbonate in 100 parts by weight of pigment. A manufacturing method according to any one of claims 1 to 4 , comprising the step of providing multiple pigment coating layers, wherein the amount of the outermost pigment coating layer is greater than the amount of the innermost pigment coating layer. The manufacturing method according to any one of claims 1 to 5 , wherein the amount of the outermost pigment coating layer applied is 7 g/ ^m² or more.