JP7123926B2 - Coated paper for printing - Google Patents

Description

TECHNICAL FIELD The present invention relates to a coated printing paper that achieves both ink drying property and printing glossiness.

Coated paper is broadly classified into glossy coated paper and matte coated paper. Glossy coated paper includes art paper and super art paper conventionally used for high-grade printing, and coated paper used for catalogs, pamphlets, etc., and these have high white paper glossiness and printing glossiness. Glossy tone.

The matte coated paper is a coated paper having lower white paper glossiness and printing glossiness than glossy coated paper, and includes dull coated paper and matte coated paper. In particular, the demand for matte coated paper has been increasing in recent years because the difference between white paper glossiness and printing glossiness is large compared to glossy coated paper, and characters after printing are easy to read. Methods for producing matte coated paper include using pigments with large particle diameters as coating pigments, and increasing unevenness on the paper surface by not performing calendering after pigment coating. is mentioned. Coated paper for matte printing has a larger surface unevenness than glossy coated paper, and ink on the surface of the paper sinks easily. Since it is necessary to transfer a large amount of ink in order to increase the printing density, the coated paper for matte printing tends to transfer a large amount of ink, resulting in a decrease in ink drying property. If the ink drying property is poor, problems such as set-off due to the transfer of ink to the other side of the printed matter, smearing of the printed surface, and reduced work efficiency due to the inability to proceed to the next process occur. do. Therefore, particularly in coated paper for matte printing, high ink drying property is required.

On the other hand, if the ink drying property is high, leveling of the printed ink surface does not proceed, and unevenness is formed on the printed surface, which often results in a low printing glossiness. As a technique for increasing the printing glossiness, there is a method of pursuing smoothness by calendering. However, it is not suitable for coated paper for matte printing because the glossiness of white paper increases as well as the glossiness of printing. In order to achieve both high ink drying property and high print gloss, Patent Document 1 discloses using a specific amount of a specific adhesive in a pigment coating layer.

JP-A-2007-51388

An object of the present invention is to provide a coated printing paper, particularly a coated matte printing paper, which achieves both printing glossiness and excellent ink drying property and has excellent printing quality.

In view of the above problems, the present inventors have made earnest studies and found that a coated printing paper provided with a pigment coating layer containing specific fine particles of calcium carbonate can solve the above problems. That is, the above problems are solved by the present invention described below.
(Aspect 1) At least one side of the base paper is provided with two or more pigment coating layers,
A coated printing paper, wherein the outermost pigment coating layer contains calcium carbonate having an average particle size (D50) of 0.80 μm or less.
(Aspect 2) The coated printing paper according to Aspect 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.
(Aspect 3) The coated printing paper according to Aspect 1 or 2, wherein the calcium carbonate has an average particle size (D50) of 0.50 to 0.75 μm.
(Aspect 4) The coated printing paper according to Aspect 1, which has a white paper glossiness of 40% or less and a printing glossiness of the magenta printed portion of 58 to 75%.
(Aspect 5) The coated printing paper according to Aspect 2, wherein 75 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.
(Aspect 6) The coated printing paper according to any one of Aspects 1 to 5, wherein the coating amount of the outermost pigment coating layer is larger than the coating amount of the innermost pigment coating layer.
(Aspect 7) The coated printing paper according to any one of Aspects 1 to 6, which has a white paper glossiness of 40% or less.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a coated printing paper, particularly a coated matte printing paper that achieves both excellent printing glossiness and excellent ink drying property and has excellent printing quality.

The present invention will be described in detail below. In the present invention, "-" includes its end points. That is, "X through Y" includes the values of X and Y. Also, "X or Y" means either one of X and Y, or both.

1. Coated Printing Paper Coated printing paper is paper for printing that has a pigment coating layer provided on top of the base paper. A pigment coating layer is a layer containing a white pigment as a main component. The coated printing paper of the present invention has two or more pigment-coated layers, and the outermost pigment-coated layer contains calcium carbonate having an average particle diameter (D50) of 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. Examples include, but are not limited to, magazines, posters, envelopes, calendars, and the like.

(1) Pigment Coating Layer 1) Pigment The pigment coating layer contains calcium carbonate having an average particle size (D50) of 0.80 μm or less (hereinafter also referred to as “first calcium carbonate”). D50 is the volume 50% average particle size. The particle size distribution and D50 of the pigment by the sedimentation method can be measured by Mastersizer 3000 manufactured by Malvern. The upper limit of D50 of calcium carbonate is preferably 0.75 μm or less, more preferably 0.70 μm or less. The lower limit is preferably 0.50 μm or more.

When pigment coating layers are present on both sides of the base paper, the outermost pigment coating layer on at least one side may contain the first calcium carbonate.

The lower limit of the amount of the first calcium carbonate compounded in the outermost pigment coating layer is preferably 40 parts by weight or more, more preferably 45 parts by weight or more, based on 100 parts by weight of the pigment in the pigment coating layer. preferable. However, if the amount of the first calcium carbonate compounded in the outermost pigment coating layer is too large, the white paper glossiness will be excessively increased and the matte tone will be impaired. , preferably 70 parts by weight or less, more preferably 60 parts by weight or less, and even more preferably 55 parts by weight or less. Pigment coating layers other than the outermost coating layer may not contain the first calcium carbonate, but if they do, the amount is preferably within the above range. The first calcium carbonate is preferably heavy calcium carbonate or light calcium carbonate produced in the causticizing step of the pulp manufacturing process (causticized light calcium carbonate, see Japanese Patent No. 5274077).

As the white pigment other than the first calcium carbonate in the pigment coating layer, pigments commonly used in the art can be used. Examples include kaolin, clay, engineered kaolin, delaminated clay, ground calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silica, silicates, colloidal silica, satin. Inorganic pigments such as white and organic pigments such as solid, hollow, or core-shell types are included. These pigments may be used in combination of multiple types.

As the white pigment other than the first calcium carbonate, it is preferable to use heavy calcium carbonate or light calcium carbonate having a D50 exceeding 0.80 μm (hereinafter also referred to as “second calcium carbonate”). Since calcium carbonate has excellent binding properties with an adhesive (binder) and improves whiteness, it improves ink drying properties and achieves higher whiteness and printability. The total amount of the first and second calcium carbonates is preferably 90 parts by weight or more, more preferably 100 parts by weight, based on 100 parts by weight of the pigment in the outermost pigment coating layer. Although the total amount of the first and second calcium carbonates in the other pigment coating layer is not limited, it is preferably within the above range. The second calcium carbonate is preferably ground calcium carbonate or causticized light calcium carbonate.

2) Adhesive The pigment coating layer contains an adhesive (binder) as a matrix. The adhesive is not limited, and known adhesives can be used. Examples include styrene/butadiene copolymers, styrene/acrylic copolymers, ethylene/vinyl acetate copolymers, butadiene/methyl methacrylate copolymers, vinyl acetate/butyl acrylate copolymers, anhydrous Latexes such as maleic acid copolymers and acrylic acid/methyl methacrylate copolymers; polyvinyl alcohols such as completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol; casein, soybeans Proteins such as proteins and synthetic proteins; oxidized starch, positive starch, urea phosphate esterified starch, etherified starch such as hydroxyethyl etherified starch, starch such as dextrin; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose etc. These multiple types can be used in combination.

The amount of the adhesive is preferably 5 to 30 parts by weight, more preferably 8 to 25 parts by weight, based on 100 parts by weight of the pigment in the entire pigment coating layer, from the viewpoint of printability and coatability. more preferred. If the total amount of the adhesive exceeds 25 parts by weight, the viscosity of the pigment coating liquid becomes high, and operational troubles tend to occur during coating. Furthermore, there is a tendency that the drying property of the ink is lowered. On the other hand, when the total amount of adhesive is less than 5 parts by weight, it becomes difficult to obtain sufficient surface strength.

The coated printing paper of the present invention preferably contains 10 to 80% by weight of a styrene-butadiene copolymer latex in the form of an emulsion in the total adhesive, and preferably contains 15 to 70% by weight of the latex. is preferred, and the latex preferably contains a styrene/butadiene latex. The coated printing paper of the present invention comprises two or more pigment-coated layers, the layer closest to the base paper preferably containing 10 to 80 wt. It preferably contains 60% by weight of latex. It is particularly preferable to use starches as other adhesives, and the amount thereof is preferably 30 to 90% by weight of the total adhesive for the layer closest to the base paper, and 40 to 70% by weight for the layer far from the base paper. Preferably. Compared with latex, starches increase the water retention of the pigment coating liquid, so that the coating liquid is less likely to sink into the base paper, and the base paper can be effectively coated with the pigment coating layer. In other words, when starches are used, the coverage of the base paper with the pigment coating layer is improved. As a result, an improvement in print quality, especially print glossiness, and an improvement in ink drying property can be expected. In the present invention, the ratio of latex to starch is preferably 3:5 to 5:7.

3) Other additives If necessary, the pigment coating layer may contain dispersants, thickeners, water retention agents, antifoaming agents, water resistance agents, dyes, coloring pigments, and other general coated paper pigments. Various adjuvants to be blended may be included. In the present invention, it is preferable to use organic particles having a particle size larger than that of the white pigment. By containing the organic particles in the outermost coating layer farthest from the base paper, it is possible to reduce paper surface contamination due to rubbing between papers after printing and improve printability. Starch granules that have not been steamed are preferable as the organic particles, and the above effect can be obtained by adding 0.5 to 10% by weight of the organic particles to the above-mentioned pigment. As for the particle size of the organic particles, the average particle size (D50) measured with a laser diffraction particle size distribution analyzer is preferably 8 to 25 μm.

4) Coating amount The coating amount of the pigment coating layer is preferably 2 g/m ² or more, more preferably 5 g/m ² or more, and still more preferably 10 g/m ² or more in solid content per side. If the coating amount is less than 5 g/m ² , the irregularities on the surface of the paper substrate cannot be sufficiently covered, and the receptivity of the printing ink may be remarkably lowered. On the other hand, the coating amount of the pigment coating layer is preferably 50 g/m ² or less, more preferably 40 g/m ² or less, and even more preferably 35 g/m ² or less. The coating amount is the total value of all pigment coating layers per side, and the coating amount of the innermost pigment coating layer (pigment coating layer adjacent to the base paper) is preferably 2 to 15 g/m ² . , more preferably 5 to 12 g/m ² . The coating amount of the outermost pigment coating layer is preferably 6-20 g/m ² , more preferably 8-15 g/m ² . Since the ink drying property is greatly affected by the outermost coating layer, the coating amount of the outermost coating layer is preferably larger than the coating amount of the innermost pigment coating layer.

(2) Base Paper 1) Pulp A known pulp can be used as the base paper. Known pulps include chemical pulp, groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), chemigrand pulp (CGP), semi-chemical pulp (SCP). , waste paper pulp, etc. In the present invention, it is preferred to use chemical pulp. Chemical pulp includes those manufactured by the kraft pulp method and those manufactured by the sulfite pulp method, and both of them can be used in the present invention, but the chemical pulp manufactured by the kraft method is lower in production cost. It is suitable from the aspect. The content of the chemical pulp in the raw material pulp is preferably 60% by weight or more, more preferably 80% by weight or more, still more preferably 90% by weight or more, and particularly 95% by weight or more, from the viewpoint of whiteness etc. preferable.

2) Fillers Known fillers may be used for the base paper. Known fillers include heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, delaminated kaolin, white carbon, talc, magnesium carbonate, barium carbonate, barium sulfate, water. Inorganic fillers such as aluminum oxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, amorphous silica produced by neutralizing sodium silicate with mineral acid, urea-formalin resin, melamine organic fillers such as polystyrene resins, polystyrene resins, and phenolic resins. 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 above-mentioned first calcium carbonate or the second calcium carbonate, but light calcium carbonate is preferred. The filler content in paper is not particularly limited, but is preferably 1 to 40% by weight, more preferably 10 to 35% by weight. Considering the strength of the base paper, etc., it is more preferably 10 to 20% by weight.

3) Others Known additives for papermaking can also be used. For example, aluminum sulfate, various anionic, cationic, nonionic, or amphoteric retention improvers, drainage improvers, various paper strength agents, internal sizing agents, and other internal additives for papermaking are added as needed. can be used Examples of dry strength improvers include polyacrylamide and cationized starch, and examples of wet strength improvers include polyamidoamine epichlorohydrin. These chemicals are added within a range that does not affect formation, workability, and the like. Examples of internal sizing agents include alkyl ketene dimer, alkenyl succinic anhydride, and rosin sizing agents. Furthermore, dyes, pigments, fluorescent whitening agents, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like can be added as necessary.

4) Basis Weight of Base Paper The basis weight of the base paper of the coated printing paper of the present invention is preferably 40 to 160 g/m ² , more preferably 45 to 150 g/m ² , still more preferably 50 to 140 g/m ² .

5) Clear Coating Layer The coated printing paper of the present invention may have a clear (transparent) coating layer on one or both sides of the base paper described above. By applying clear coating to the base paper, the surface strength and smoothness of the base paper can be improved, and the coating suitability for pigment coating can be improved. The amount of clear coating is preferably 0.1 to 3.0 g/m ² , more preferably 0.2 to 2.0 g/m ² , still more preferably 0.5 to 2.0 g/m 2 in terms of solid content per side. ^m2 .

In the present invention, the clear coating means, for example, using a coater (coating machine) such as a 2-roll pound size press, a gate roll coater, a pre-metering size press, a curtain coater, and a spray coater to coat starch, oxidized starch, A coating liquid (surface treatment liquid) mainly composed of water-soluble polymers such as polyacrylamide, polyvinyl alcohol, and other starches such as various modified starches (self-modified, cation-modified, etc.) is applied onto the base paper ( size press). A sizing agent may be contained in the clear coating liquid for coating. In the present invention, it is preferable to apply starch.

2. Production Method The coated printing paper of the present invention can be produced by a known method, but is preferably produced by coating a base paper with a pigment coating liquid containing a pigment and an adhesive.
(1) Preparation of Base Paper The raw materials used for the base paper used in the present invention are as described above. The base paper is manufactured by a known papermaking method. For example, using a fourdrinier machine including a top wire, an on-top former, a gap former, a cylinder paper machine, a paperboard machine using both a fourdrinier paper machine and a cylinder paper machine, a Yankee dryer machine, etc. can be done. The pH during papermaking may be acidic, neutral or alkaline, preferably neutral or alkaline. The papermaking speed is also not particularly limited. The base paper used in the present invention may be single-layered or multi-layered, but single-layered base paper is preferably used.

(2) Smoothing Treatment of Base Paper It is preferable to smoothen the base paper by various calendering devices before coating the obtained base paper with the pigment coating liquid. As such a calender, a generally used calender such as a super calender and a soft calender can be appropriately used. As calender finishing conditions, rigid roll temperature, calender pressure, number of nips, roll speed, paper moisture content before calendering, etc. are appropriately selected according to the required quality. In the present invention, the base paper is preferably calendered to impart smoothness while maintaining the matte texture. Calendering the base paper improves the smoothness of the base paper and improves the suitability for pigment coating.

(3) Preparation of Pigment Coating Liquid The pigment coating liquid can be prepared by dispersing or dissolving the pigment, adhesive, and, if necessary, additives in water. The blending of each component is adjusted so that the pigment coating layer can be formed. When blade coating is performed, the solid content concentration of the pigment coating solution is preferably 40 to 70% by weight, more preferably 60 to 70% by weight. The viscosity of the pigment coating liquid is preferably in the range of 500 to 5000 mPa·s in B-type viscosity measured at 60 rpm at room temperature. Further, when coating is performed by a roll coater, the solid content of the pigment coating liquid is preferably 50 to 70% by weight, more preferably 60 to 70% by weight. If the solid content weight is too low, backflow or the like will occur.

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

The coated printing paper of the present invention needs to be provided with two or more pigment coating layers in order to increase the printing glossiness. By using two or more pigment-coated layers, the fiber coverage is improved and the smoothness is also increased. If the number of layers is 3 or more, the amount of coating can be increased, and the quality of the coated paper is improved. As described above, a clear coating layer may be provided on the base paper, and two or more pigment coating layers may be provided thereon.

(5) Other steps 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 as necessary for the coated paper produced as described above. is desirable. In the case of calendering, a commonly used calender such as a super calender or soft calender can be used as appropriate. As calender finishing conditions, rigid roll temperature, calender pressure, number of nips, roll speed, paper moisture content before calendering, etc. are appropriately selected according to the required quality. is preferably calendered at a low pressure in order to produce a matte texture.

3. Paper Quality (1) White Paper Glossiness White paper glossiness is an index showing the degree of glossiness of white paper, and is measured according to JIS-P8142 in the present invention. In one aspect, the coated printing paper of the present invention is a matte coated printing paper having a large difference between white paper gloss and printing gloss. In this case, the white paper glossiness is preferably 40% or less, more preferably 36% or less, and more preferably less than 32%. Although the lower limit of the white paper glossiness is not limited, it is preferably 15% or more.

(2) Print glossiness (difference in glossiness)
The printing glossiness is an index indicating the glossiness of printed matter after printing, and is measured by the method described later in the present invention. The matte coated printing paper preferably has a printing glossiness (CM) of 57 or more, preferably 58% or more. Although the upper limit of the printing glossiness in this case is not limited, it is preferably 75% or less. In the present invention, if the difference in glossiness obtained by subtracting the white paper glossiness from the print glossiness is 15 or more, the difference in glossiness between the printed part and the white paper part is sufficiently obtained, and it can be said that the printed matter is clearer. .

(3) Ink Drying Property The coated printing paper of the present invention has excellent ink drying property in spite of its high printing glossiness. The superiority or inferiority of the ink drying property of coated printing paper is generally identified by confirming set-off, which is the transfer of ink to the other side of the printed matter after printing, and rubbing stains on the printed surface.

(3-1) Evaluation by nitrogen adsorption method (total pore volume of paper) In the present invention, the pore structure of the pigment coating layer is evaluated by a nitrogen adsorption method that can be measured under low pressure conditions. , the ink drying property of the coated printing paper of the present invention can be evaluated. As for the relationship between the pigment coating layer and the solvent absorbency, the Lucas-Washburn equation shown in Equation (1), which captures a large number of fine pores present in the pigment coating layer as an aggregate of capillaries, is widely used. ing. where L is the penetration depth of the solvent, r is the average radius of the capillary, t is the time, γ is the surface tension of the solvent, θ is the contact angle between the capillary wall and the solvent, and η is the viscosity of the solvent. Assuming that the pore structure of the pigment coating layer is an array of n cylindrical pipes with an average radius of r, the ink solvent permeation amount ν into the pigment coating layer is expressed by the formula (2). (1) can be transformed into equation (3). d is the thickness of the pigment coating layer, V is the pore volume of the pigment coating layer, and k is the ink viscosity. That is, it is thought that the larger the pore diameter and pore volume in the pigment coating layer and the smaller the thickness of the pigment coating layer, the greater the amount of solvent permeation per certain period of time, and the better the ink drying property. In the present invention, the pore volume obtained by TriStar 3000 is considered as the pore volume of the pigment coating layer, and the average pore diameter is considered as the average pore diameter of the pigment coating layer.

The pore volume V of the coated printing paper of the present invention is preferably more than 0.04 cm ³ /g, more preferably 0.045 cm ³ /g or more. The upper limit is preferably 0.09 cm ³ /g or less, more preferably 0.085 cm ³ /g or less, and even more preferably 0.08 cm ³ /g or less. A coated printing paper having a pore volume V of more than 0.04 cm ³ /g is excellent in ink drying property.

The total pore volume (cm ³ /m ² ) of the coated printing paper of the present invention is defined by pore volume V (cm ³ /g) × coating amount c (g/m ² ), and the value is It is preferably 0.55 cm ³ /m ² or more, more preferably 0.60 cm ³ /m ² or more, and even more preferably 0.80 cm ³ /m ² or more. The upper limit of the total pore volume is preferably 1.00 cm ³ /m ² or less, more preferably 0.95 cm ³ /m ² or less.

The average pore diameter m of the coated printing paper of the present invention is preferably 30 nm or more. The upper limit of the average pore diameter m is preferably 60 nm or less. Specifically, in the present invention, the average pore diameter is obtained from the desorption isotherm obtained by the nitrogen adsorption method. For the purposes of this application, the average pore diameter obtained with Tristar 3000 is considered the average pore diameter of the pigmented coating.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited by these. Parts by weight and % by weight are values in terms of solid content.

<Evaluation method>
(1) Basis Weight Measured according to JIS P 8124.
(2) ISO whiteness: Measured in accordance with JIS P8148 with a color difference meter CMS-35SPX manufactured by Murakami Shiki Co., Ltd. under conditions including ultraviolet light.
(3) White paper glossiness Measured based on JIS-P8142.

(4) Ink drying property Using offset sheet-fed ink (NEX-M manufactured by Toyo Ink) on a Roland sheet-fed offset printing machine (4 colors) at a printing speed of 8000 sheets/hr. After printing so that black 2.00, the solid black printed portion was touched with a fingertip every 10 minutes immediately after printing, and the speed of ink drying was sensory evaluated.
A: good B: bad

(5) Print glossiness (difference in glossiness)
Offset sheet-fed ink (NEX-M manufactured by Toyo Ink Co., Ltd.) was used on a Roland sheet-fed offset printing machine (4 colors) at a printing speed of 8000 sheets/hr, and the ink density of the solid area was indigo 1. 0.60 and red 1.50 were printed in the order of magenta (CM). The glossiness of the magenta (CM) solid printed portion of the obtained print was measured according to JIS P-8142. The value obtained by subtracting the white paper glossiness from the printing glossiness is the glossiness difference, and if the glossiness difference is 15 points or more, the glossiness difference between the printed part and the white paper part is sufficiently obtained, and it can be said that the printed matter has a good appearance. .
Glossiness difference = printing glossiness (%) - white paper glossiness (%)

(6) Pore volume, etc. (i) Sample preparation and measurement The pore volume, total pore volume and average pore diameter of the coated paper were determined by the nitrogen adsorption method.
(Sample preparation)
A paper sample of 40 cm long×15 cm wide was divided into two layers so as to be even in the thickness direction to obtain a laminate containing a pigment coating layer and a base paper layer. In the case of double-sided coated paper, two such laminates are obtained, and in the case of single-sided coated paper, one such laminate and one layer consisting mainly of the base paper layer are obtained. A laminate containing a pigment coating layer and a base paper layer was used as a sample sheet for the measurement. In the case of double-sided coated paper, one of them was used as a sample sheet for measurement. The basis weight t (g/m ² ) of the sample sheet was measured. Four points were selected from one sample sheet, cut into strips, and placed in a measurement cell so that the absolute dry weight of the measurement sample was about 1 to 2 g. The absolute dry weight at this time was defined as w (g). Pretreatment was carried out overnight under vacuum at a treatment temperature of 120°C.

(measurement)
The pore volume and the average pore diameter were measured from the pigment coating layer side of the measurement sample using the above apparatus. Specifically, the pore volume and average pore diameter of the measurement sample are obtained from the desorption isotherm using the BJH method, the average value of the 4 samples is taken, and the pore volume V' and average pore diameter of the measurement sample are obtained. m'. The pore volume V' was converted to a value per unit coating weight and defined as the pore volume V of the pigment coating layer of the present invention. The obtained average pore diameter m' was taken as the average pore diameter m of the pigment coating layer of the present invention. The pigment coating layer weight of the measurement sample is pigment coating layer weight (g) = absolute dry weight w (g) of measurement sample × coating amount c (g/m ² ) ÷ basis weight of sample sheet t (g/ m ² ). The coating amount c (g/m ² ) was obtained by the measurement method described later. Tristar 3000 manufactured by Shimadzu Corporation was used for measurement and analysis.

(Coating amount)
The coating amount was measured according to the method described in Japanese Patent No. 5827187. Specifically, it was measured by the following procedure.
1) A measurement sample (paper) was cut into a size of 5 cm×5 cm, and the weight x was measured after conditioning at a temperature of 23° C. and a relative humidity of 50%.
2) The sample was placed on a styrene polymer plate so that the pigment-coated layer was in contact with the sample, sandwiched between a watch glass and fixed with a clip.
3) Placed in a drier at 120 to 150°C to melt the styrene polymer and adhere it to the pigment coating layer, allow to cool, and then adjust the humidity for about half a day at a temperature of 23°C and a relative humidity of 50% to measure the weight y. .
4) After immersing the measurement sample obtained in the previous step in the copper ethylenediamine solution for about 3 to 4 hours, the base paper layer and the pigment coating layer were carefully peeled off using a brush. This process was repeated until no pulp fibers adhered to the pigment coating layer.
5) The pigment coating layer was washed with water and dried, and after about half a day of humidity conditioning at a temperature of 23° C. and a relative humidity of 50%, the weight z was measured.
6) The coating amount was calculated by the following formula.
Coating amount c (g/m ² ) = (xA) x 400
A = y-z

[Example 1]
A base paper having a basis weight of 75 g/m ² was prepared using 100% by weight of chemical pulp and containing 13.5% by weight of light calcium carbonate as a filler.
100 parts by weight of heavy calcium carbonate (manufactured by Fimatech Co., Ltd., trade name: FMT97, D50 = 0.88 μm) was used as a pigment, and 7 parts by weight of styrene-butadiene copolymer latex was used as an adhesive, and oxidized starch was added. 3 parts by weight were blended, and water was further added to obtain an undercoat pigment coating solution having a solid content concentration of 65% by weight.
55 parts by weight of ground calcium carbonate (manufactured by Fimatech Co., Ltd., trade name: FMT97, D50 = 0.88 μm), which is the second calcium carbonate, and fine grain ground calcium carbonate (manufactured by Fimatech Co., Ltd.) as the pigment Fimatec Co., Ltd., trade name: FMT100, D50 = 0.66 μm) was used, and 4 parts by weight of styrene-butadiene copolymer latex as an adhesive and 6 parts by weight of oxidized starch were blended. was added to obtain a topcoat pigment coating solution having a solid content concentration of 66% by weight.
The undercoat pigment coating solution was coated on both sides of the base paper with a blade coater so that the dry coating amount per side was 6.5 g/m ² and dried. Further, the topcoat pigment coating liquid was applied on both sides with a blade coater so that the dry coating amount per side was 10.5 g/m ² to obtain a coated printing paper. The coated printing paper was evaluated by the method described above.

[Example 2]
97 parts by weight of self-produced causticized light calcium carbonate (D50 = 1.38 µm) and 3 parts by weight of self-produced causticized lightly calcium carbonate (D50 = 1.02 µm) were used as pigments, and styrene-butadiene copolymer latex was used as an adhesive. and 21 parts by weight of oxidized starch, and further water was added to obtain an undercoat pigment coating solution having a solid content concentration of 50% by weight.
As pigments, 44.5 parts by weight of self-produced fine-grained causticized light calcium carbonate (D50 = 0.64 µm), which is the first calcium carbonate, and 55 parts by weight of self-produced causticized light calcium carbonate (D50 = 1.02 µm), which is the second calcium carbonate. 4 parts by weight of styrene-butadiene copolymer latex, 6 parts by weight of oxidized starch, and uncoiled starch granules (manufactured by Japan Corn Starch Co., Ltd., trade name: Y-3P) are added to this as an adhesive. 0.5 part by weight was added, and water was added to obtain a topcoat pigment coating solution having a solid content concentration of 66% by weight.
Both sides of the base paper were coated with the undercoat pigment coating solution using a gate roll coater so that the dry coating amount per side was 4.5 g/m ² and dried. Furthermore, the topcoat pigment coating liquid was applied on both sides with a blade coater so that the dry coating amount per side was 10.5 g/m ² to obtain a coated printing paper. The coated printing paper was evaluated by the method described above.

[Example 3]
The amount of the first calcium carbonate, the styrene-butadiene copolymer latex, and the oxidized starch in the topcoat pigment coating liquid prepared in Example 1 was changed to the amount shown in Table 1, and the starch was not steamed. A topcoat pigment coating solution was prepared by blending 0.5 parts by weight of grains (manufactured by Japan Corn Starch Co., Ltd., trade name: Y-3P). A coated printing paper was produced and evaluated in the same manner as in Example 1 except that the coating solution was used.

[Example 4]
100 parts by weight of heavy calcium carbonate (manufactured by Fimatech Co., Ltd., trade name: FMT90, D50 = 1.15 μm) was used as a pigment, and 7 parts by weight of styrene-butadiene copolymer latex was used as an adhesive, and oxidized starch was added. 3 parts by weight were blended, and further water was added to obtain an undercoat pigment coating solution having a solid content concentration of 70% by weight.
As a pigment, 55 parts by weight of heavy calcium carbonate (manufactured by Imerys, trade name: C90, D50 = 1.18 μm), which is the second calcium carbonate, and fine ground calcium carbonate (manufactured by Imerys, Carvirax) which is the first calcium carbonate. , D50 = 0.64 µm), 4 parts by weight of styrene-butadiene copolymer latex and 6 parts by weight of oxidized starch as adhesives, and uncoiled starch granules (Japan Corn Starch Co., Ltd. 0.5 parts by weight of Y-3P (trade name: Y-3P) was added, and water was further added to obtain a topcoat pigment coating solution having a solid content concentration of 66% by weight. Using these coating liquids, coated printing papers were produced in the same manner as in Example 1 and evaluated.

[Comparative Example 1]
85 parts by weight of heavy calcium carbonate (manufactured by Fimatech Co., Ltd., trade name: FMT75, D50 = 1.65 µm) as pigments, 15 parts by weight of kaolin (manufactured by Imerys, trade name: KCS, D50 = 4.05 µm), As an adhesive, 4.3 parts by weight of styrene-butadiene copolymer latex and 6.5 parts by weight of oxidized starch were blended, and water was added to obtain a pigment coating solution having a solid concentration of 66% by weight. A coated printing paper having one pigment coating layer was produced in the same manner as in Example 1 using the coating solution and evaluated.

[Comparative Example 2]
100 parts by weight of heavy calcium carbonate (manufactured by Imerys, trade name: C97, D50 = 0.91 μm) as a pigment, 7.6 parts by weight of styrene-butadiene copolymer latex as an adhesive, and 6 parts by weight of oxidized starch. After blending, water was further added to obtain a pigment coating solution having a solid content concentration of 66% by weight. A coated printing paper having one pigment coating layer was produced in the same manner as in Example 1 using the coating solution and evaluated.

[Comparative Example 3]
As pigments, 55 parts by weight of heavy calcium carbonate (manufactured by Fimatech Co., Ltd., trade name: FMT97, D50 = 0.88 µm), 45 parts by weight of kaolin (manufactured by Imerys, trade name: KCS, D50 = 4.05 µm), As an adhesive, 4 parts by weight of styrene-butadiene copolymer latex and 6 parts by weight of oxidized starch were blended, and water was added to obtain a pigment coating solution having a solid concentration of 66% by weight. A coated printing paper having one pigment coating layer was produced in the same manner as in Example 1 using the coating solution and evaluated.

[Comparative Example 4]
As pigments, 55 parts by weight of heavy calcium carbonate (manufactured by Fimatech Co., Ltd., trade name: FMT97, D50=0.88 μm) and fine ground calcium carbonate (manufactured by Fimatech Co., Ltd., trade name: FMT100YF, D50=0.88 μm) were used. 60 μm) 45 parts by weight, 4 parts by weight of styrene-butadiene copolymer latex as an adhesive, and 6 parts by weight of oxidized starch were blended, and further water was added to obtain a pigment coating solution having a solid content concentration of 66% by weight. . A coated printing paper having one pigment coating layer was produced in the same manner as in Example 1 using the coating solution and evaluated.

It is clear that the coated printing paper of the present invention has an excellent balance between ink drying property and printing glossiness.

Claims (6)

Equipped with two or more pigment coating layers on at least one side of the base paper,
A pigment coating layer containing a first calcium carbonate in which the outermost pigment coating layer has an average particle size (D50) of 0.80 μm or less and a second calcium carbonate having an average particle size (D50) of more than 0.80 μm A coated paper for printing. 2. The coated printing paper according to claim 1, wherein 40 parts by weight or more of the first calcium carbonate is contained in 100 parts by weight of the pigment in the outermost pigment coating layer. 3. The coated printing paper according to claim 1, wherein the average particle size (D50) of said first calcium carbonate is 0.50 to 0.75 μm. The coated printing paper according to any one of claims 1 to 3, which has a white paper glossiness of 40% or less, and a blue-red printed area having a printing glossiness of 58 to 75%. 3. The coated printing paper according to claim 2, wherein 75 parts by weight or more of the first calcium carbonate is contained in 100 parts by weight of the pigment in the outermost pigment coating layer. The coated printing paper according to any one of claims 1 to 5, wherein the coating amount of the outermost pigment coating layer is larger than the coating amount of the innermost pigment coating layer.