Pigment-coated paper

Abstract

The present invention addresses the problem of providing a pigment-coated paper having little color unevenness. To solve the problem, provided is a pigment-coated paper having at least two pigment-coated layers on at least one surface of a base paper, wherein: the coating amount per one surface of a bottom coated layer closest to the base paper is at least 10 g / m2; and the color difference ∆EU-B between the base paper and the bottom coated layer and the color difference ∆ET-B between the base paper and a top coated layer farthest from the base paper satisfy ∆EU-B≤1 and ∆EU-B<∆ET-B.

Description

pigment coated paper

[0001] The present invention relates to pigment coated paper.

[0002] Pigment-coated paper is used for a variety of purposes, including books, posters, packaging materials, and packaging for paper cartons. Printing is often performed on the pigment-coated surface. There are various printing methods, including offset printing, gravure printing, letterpress printing, laser printing, and inkjet printing. Regardless of the printing method, the appearance of the printed product is an important quality. One type of appearance is color unevenness. Color unevenness refers to subtle differences in hue on the paper surface when a color is added to the pigment-coated surface. Even with high smoothness and whiteness, poor color unevenness can result in a poor paper surface feel. Furthermore, color unevenness is further accentuated in halftone dots during printing, reducing the value of the printed material. A similar phenomenon to color unevenness is white unevenness, which occurs due to subtle differences in whiteness on the paper surface.

[0003] It is known that whiteness unevenness occurs when there is a large difference between the whiteness of the base paper and the whiteness of the coating layer, and is particularly noticeable when the coating layer has poor coating unevenness. To reduce whiteness unevenness by bringing the whiteness of the coating layer and the base paper closer together, methods have been proposed, such as increasing the opacity of the pigment coating layer to 50% or more and increasing the whiteness difference between the outermost layer of the multilayer base paper and the layer immediately below it to more than 12% (Patent Document 1), and incorporating a black dye into the coating pigment to reduce the whiteness of the base paper and the whiteness of the coating layer to within 6% (Patent Document 2). Furthermore, even when using recycled paper pulp, which is prone to whiteness unevenness, a technique has been proposed in which a uniform coating layer is formed using a contour coating method to improve the hiding power of the base paper and reduce whiteness unevenness (Patent Document 3). In addition, methods have been proposed for efficiently reducing the visibility of dust and improving whiteness and printability while using paper containing a large amount of recycled paper pulp, such as increasing the amount of coating applied to the surface and incorporating large amounts of organic pigments with high hiding power, such as titanium dioxide, structured kaolin, and plastic pigments (Patent Documents 4 and 5).

[0004] JP 2009-41131 A JP 1-97295 A JP 2016-191164 A JP 6-166991 A JP 2003-306892 A

[0005] An object of the present invention is to provide pigment coated paper with little color unevenness.

[0006] The means for solving the problems of the present invention are as follows: 1. A base paper has two or more pigment coating layers on at least one side thereof, and the coating weight of the undercoating layer closest to the base paper is 10 g / m per side. ２ The color difference ΔE between the base paper and the under-coating layer is Ｕ－Ｂ and the color difference ΔE between the base paper and the top coating layer farthest from the base paper. Ｔ－Ｂ But, ΔE Ｕ－Ｂ ≦1 and ΔE Ｕ－Ｂ <ΔE Ｔ－Ｂ 2. Pigment coated paper according to 1., characterized in that the DAV2 value is 18 or less. 3. Pigment coated paper according to 1. or 2., characterized in that the top coating layer contains a colorant, and the colorant content of the under coating layer is 20% or less of the colorant content of the top coating layer. 4. ΔE Ｔ－Ｂ 5. Pigment coated paper according to any one of 1. to 3., characterized in that the PPS smoothness (soft, clamping pressure 1 MPa) of the base paper is 5 μm or more. 6. Pigment coated paper according to any one of 1. to 5., characterized in that the PPS smoothness (soft, clamping pressure 1 MPa) of the top coating layer is 2 μm or less.

[0007] The pigment coated paper of the present invention has little color unevenness and is capable of high-quality printing. The pigment coated paper of the present invention can reduce the amount of colorant in the undercoating layer, which reduces costs compared to when the entire pigment coating layer contains colorant.

[0008] The pigment coated paper of the present invention has two or more pigment coating layers on at least one side of the base paper, and the coating weight of the undercoating layer closest to the base paper per side is 10 g / m ２ The color difference ΔE between the base paper and the undercoating layer is Ｕ－Ｂ and the color difference ΔE between the base paper and the top coating layer farthest from the base paper. Ｔ－Ｂ But ΔE Ｕ－Ｂ ≦1 and ΔE Ｕ－Ｂ <ΔEＴ－Ｂ In this specification, the expression "A to B (A and B are numbers)" means a numerical range including the values ​​of A and B, that is, A or more and B or less.

[0009] "Base Paper" Base paper is a sheet made of papermaking fibers, fillers, various auxiliaries, etc. Wood pulp is preferably used as the papermaking fibers. Examples of wood pulp include chemical pulps such as softwood kraft pulp, hardwood kraft pulp, and sulfite pulp; mechanical pulps such as thermomechanical pulp, stone-grind pulp, and refiner-grind pulp; and recycled paper pulp obtained from newspaper, coated paper, and fine paper. One or more of these wood pulps can be used in combination. If necessary, one or more fiber materials other than cellulose fibers, such as non-wood pulp from kenaf, hemp, or bamboo, glass fiber, or polyethylene fiber, can be blended. From the viewpoint of the strength of pigment-coated paper, it is preferable that the total papermaking fibers contain wood pulp at 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass or more. On the other hand, recycled paper pulp may be added to reduce costs and promote recycling, but from the viewpoint of strength, the recycled paper pulp content is preferably 40% by mass or less. Furthermore, the ISO brightness of the pulp used is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. If pulp with an ISO brightness of less than 70% is used for the base paper, the color of the base paper may show through the coating layer, making the coating layer look dull and making coating unevenness in the coating layer more noticeable.

[0010] The base paper may contain a filler. Examples of fillers that can be used include known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, and synthetic resin fillers. In the present invention, the filler is an optional component, and the base paper may not contain a filler. Examples of auxiliary agents that can be used as needed include aluminum sulfate and various anionic, cationic, nonionic, or amphoteric retention aids, drainage aids, paper strength agents, and internal sizing agents. Furthermore, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, pitch control agents, slime control agents, and the like may also be added as needed.

[0011] The basis weight of the base paper of the present invention is 150 g / m ２ More than 400g / m ２ The basis weight of the base paper is preferably 150 g / m or less. ２ If the base paper has a basis weight of less than 400 g / m, the strength may be insufficient for packaging applications such as paper boxes. ２ If the weight exceeds 160 g / m, the workability such as bending will be reduced, and the pigment coated paper will become heavy, resulting in high costs for transportation. ２ More than 170 g / m ２ More preferably, 180 g / m or more ２ More preferably, 350 g / m ２ Preferably, 300 g / m or less ２ More preferably, 250 g / m or less ２ The following is even more preferred:

[0012] The base paper of the present invention has a density of 0.90 g / cm ３ From the viewpoint of weight reduction, it is preferable that the density of the base paper is 0.85 g / cm or less. ３ The lower limit of the density of the base paper is not particularly limited, but from the viewpoint of strength, it is preferably 0.65 g / cm ３ More than 0.70 g / cm ３ The above is more preferable.

[0013] The method for producing the base paper (papermaking) is not particularly limited, and the base paper can be produced by acidic papermaking or neutral papermaking using a known Fourdrinier former, on-top hybrid former, gap former machine, etc. The base paper may be composed of one layer or two or more layers.

[0014] The surface of the base paper can be treated with various chemicals (external addition, clear coating). Examples of chemicals that can be used include known external additives such as polyacrylamide, polyvinyl alcohol, surface sizing agents, starch, latex, water-resistant agents, water retention agents, thickeners, and lubricants, and these can be used alone or in combination of two or more. The method for surface treatment of the base paper is not particularly limited, but known coating devices such as rod metering size presses, pond-type size presses, gate roll coaters, spray coaters, blade coaters, and curtain coaters can be used. The amount of external additive coating is not particularly limited, but should be 0.1 to 3.0 g / m2 in solids per side. ２ is preferably 0.2 to 2.0 g / m ２ is more preferred.

[0015] From the viewpoint of preventing penetration of the paint for the pigment coating layer into the base paper, the base paper preferably has a Stoeckigt sizing degree (JIS P 8122 Paper and paperboard - Sizing degree test method - Stoeckigt method) of 30 seconds or more, more preferably 40 seconds or more, and even more preferably 50 seconds or more. By making the base paper have a Stoeckigt sizing degree of 30 seconds or more, penetration of the binder components and colorants in the coating solution into the base paper is suppressed, making it possible to obtain pigment coated paper with excellent coating layer strength and excellent color development of the colorants.

[0016] According to the present invention, paper with no color unevenness can be obtained even if the base paper has an uneven surface. However, when a smooth base paper is used, paper with even less color unevenness can be obtained. Therefore, the base paper of the present invention may be subjected to a calendering treatment. The calendering method is not particularly limited, and a normal smoothing treatment device such as a super calender, gloss calender, soft nip calender, heat calender, or shoe calender can be used, and two or more types may be combined.

[0017] "Pigment Coating Layer" A pigment coating layer is a layer formed from a coating solution containing at least a pigment and an adhesive. The pigment coated paper of the present invention needs to have at least two pigment coating layers: an undercoating layer closest to the base paper and a top coating layer farthest from the base paper, and can also have three or more pigment coating layers. In addition to the pigment and adhesive, the pigment coating layer can optionally contain various known auxiliary agents that are blended into pigment coating layers, such as dispersants, thickeners, water retention agents, antifoaming agents, and waterproofing agents.

[0018] Pigments Pigments known in the papermaking field can be used without particular limitation. For example, inorganic pigments such as calcium carbonate (heavy / light), kaolin, engineered kaolin, clay, delaminated clay, talc, titanium dioxide, aluminum hydroxide, mica, illite, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as solid, hollow, or core-shell organic pigments, can be used alone or in combination. Among these, calcium carbonate and kaolin are preferred, and it is more preferable to use these in combination. As calcium carbonate, heavy calcium carbonate is preferred. Kaolin is a flat pigment, which makes it easy to form a smooth surface with excellent printability. Calcium carbonate is inexpensive, has excellent fluidity, and makes it easy to form a surface with high whiteness.

[0019] When kaolin is used, the 50% volume average particle size (D50, hereinafter also referred to as average particle size) of kaolin measured by a laser diffraction / scattering method is preferably 0.2 μm or more and 10 μm or less from the viewpoint of hiding power, more preferably 0.5 to 6 μm, and even more preferably 1 to 3 μm. Examples of measuring devices for the laser diffraction / scattering method include a particle size distribution measuring device "Partica" from Horiba, Ltd. and a particle size distribution measuring device "MASTER SIZER S" from Malvern Instruments. Furthermore, from the viewpoint of thick film coating properties, the aspect ratio of kaolin is preferably 1.2 to 100, more preferably 2 to 80, and even more preferably 5 to 50. The aspect ratio was calculated using the measured value of the "MASTER SIZER S" according to the calculation method described in "Basic Research on the Relationship between Coating Pigment Properties and Coated Paper Quality" in the Journal of the Japan Paper and Pulp Technical Association, Vol. 65, No. 12.

[0020] When calcium carbonate is used, the average particle size (D50) of the calcium carbonate is preferably 0.2 μm or more and 3.0 μm or less, more preferably 0.2 μm or more and 2.0 μm or less. Furthermore, it is preferable that the proportion of particles of 2 μm or less calculated from a particle size distribution curve by a sedimentation method is 60 to 98% from the viewpoints of white paper smoothness, surface feel, and paint fluidity.

[0021] The undercoating layer preferably contains kaolin in an amount of 10% by mass or more, more preferably 14% by mass or more, and even more preferably 18% by mass or more, and preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less, based on the total amount of pigment. The undercoating layer preferably contains calcium carbonate in an amount of 20% by mass or more, more preferably 40% by mass or more, and even more preferably 60% by mass or more, and preferably 90% by mass or less, more preferably 86% by mass or less, and even more preferably 82% by mass or less, based on the total amount of pigment.

[0022] The top coating layer preferably contains 20% by mass or more of kaolin relative to the total pigment, more preferably 25% by mass or more, even more preferably 30% by mass or more, and preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less. Furthermore, in order to obtain a smooth surface, it is preferable that the kaolin content of the top coating layer relative to the total pigment is higher than that of the under coating layer. Specifically, this difference is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. The top coating layer preferably contains 30% by mass or more of calcium carbonate relative to the total pigment, more preferably 35% by mass or more, even more preferably 40% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0023] Adhesives: The adhesive (binder) used in the pigment coating layer can be any adhesive known in the papermaking field, without any particular limitation. For example, synthetic adhesives such as various copolymers such as styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, butadiene-methyl methacrylate, and vinyl acetate-butyl acrylate, polyvinyl alcohol, maleic anhydride copolymers, and acrylic acid-methyl methacrylate copolymers can be used alone or in combination. Proteins such as casein, soy protein, and synthetic protein can be used. Starches such as oxidized starch, cationic starch, urea phosphate esterified starch, and etherified starch such as hydroxyethyl etherified starch, and dextrin can be used. Cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose can be used alone or in combination. In the present invention, the undercoating layer preferably uses a combination of a synthetic adhesive and a starch from the viewpoint of workability. The top coating layer can also use a combination of a synthetic adhesive and a starch, but when used in combination, it is preferable to use more synthetic adhesive than starch from the viewpoint of smoothness and gloss.

[0024] Colorant The top coating layer contains a colorant. Both dye-based colorants and pigment-based colorants can be used as colorants. Dye-based colorants include various types of dyes, such as fluorescent dyes, cationic dyes, direct dyes, acid dyes, basic dyes, and reactive dyes. Pigment-based colorants include various types, such as insoluble azo pigments, azo lake pigments, phthalocyanine pigments, vat dye pigments, quinacridone pigments, and dioxazine pigments. These colorants can be used alone or in combination of two or more types. However, dye-based colorants (including basic and direct dyes) are prone to fading over time, which can lead to uneven coloring. Therefore, pigment-based colorants are preferred. The undercoating layer may also contain a colorant, but from the viewpoint of suppressing color unevenness, the content of the colorant in the undercoating layer is preferably 20% by mass or less of the content of the colorant in the top coating layer, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 3% by mass or less, even more preferably 1% by mass or less, even more preferably 0.5% by mass or less, even more preferably 1% by mass or less, and most preferably zero.

[0025] The undercoating layer preferably contains 8 to 35 parts by mass of adhesive per 100 parts by mass of pigment. When coating is performed by blade coating, the adhesive preferably contains 8 to 20 parts by mass of adhesive per 100 parts by mass of pigment. Furthermore, among synthetic adhesives, styrene-butadiene copolymers or styrene-acrylic copolymers are preferred, with styrene-acrylic copolymers being more preferred. In the undercoating layer, it is preferable to use a synthetic adhesive and a starch-based adhesive in combination, with the ratio of synthetic adhesive:starch-based adhesive being preferably 3:7 to 7:3, and more preferably 4:6 to 6:4.

[0026] The top coating layer preferably contains 8 to 20 parts by mass of adhesive per 100 parts by mass of pigment. Furthermore, among synthetic adhesives, styrene-butadiene copolymers or styrene-acrylic copolymers are preferred, with styrene-acrylic copolymers being more preferred. In the top coating layer, synthetic adhesives and starches can be used in combination, but from the viewpoint of smoothness and gloss, it is preferable for the synthetic adhesive to be contained in greater amounts than the starches. Since this makes it easier to obtain a smoother surface, the top coating layer preferably contains a higher kaolin content relative to the total pigment than the under-coating layer.

[0027] The coating method for the pigment coating layer is not particularly limited, and coating can be performed using known coating equipment and coating systems. Examples of coating equipment include blade coaters, bar coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, gravure coaters, spray coaters, size press coaters, and gate roll coaters. Of these, a roll coater or blade coater is preferred for the undercoating layer, and a blade coater is preferred for the top coating layer. A water-based coating system using water as the main medium is preferred. In the present invention, either an on-machine coater, in which the papermaking machine and the coating equipment are integrated, or an off-machine coater may be used, but coating using an on-machine coater is more preferred. When coating is performed using an off-machine coater, which is a separate machine from the coating device, the base paper is made on the paper machine, then wound up onto a reel, and then the reel is put into the off-machine coater for coating.However, when coating is performed using an on-machine coater, the steps of winding up the base paper and putting it into the coater can be omitted, resulting in better production efficiency.

[0028] The coating amount of the undercoating layer is 10 g / m2 in solid content per side. ２ The coating amount of the undercoating layer is 10 g / m ２ If the coating amount of the undercoating layer is less than 10.5 g / m, the suppression of color unevenness will be insufficient. ２ More than 11 g / m ２ More preferably, 11.5 g / m or more ２More preferably, 12 g / m ２ The upper limit of the coating amount is not particularly limited, but is preferably 20 g / m ２ Preferably, the thickness is 20 g / m or less. ２ If the coating amount of the undercoating layer exceeds 18 g / m, the effect of suppressing color unevenness saturates and there is almost no improvement, and the costs required for raw materials and drying increase. ２ More preferably, 16 g / m or less ２ The following is even more preferred:

[0029] The coating amount of the top coating layer is not particularly limited, but in order to form a uniform surface, it is set to 3 g / m2 in solid content per side. ２ More than 4 g / m is preferable. ２ More preferably, 5 g / m or more ２ More preferably, 6 g / m ２ The upper limit of the coating amount is not particularly limited, but it is preferably 15 g / m ２ Preferably, the thickness is 15 g / m or less. ２ Even if the coating amount exceeds 14 g / m, the effect of suppressing color unevenness and the surface smoothness saturate and there is almost no improvement, and the costs required for raw materials, drying, etc. increase. ２ More preferably, 13 g / m or less ２ The following is even more preferred:

[0030] Furthermore, in the present invention, it is preferable that the coating weight of the top coating layer is equal to or less than the coating weight of the under-coating layer. The pigment coating layer of the present invention forms a surface that is flatter and has less color unevenness compared to the base paper due to the under-coating layer, so that it is easy to obtain a smooth pigment coated paper with less color unevenness even with a small coating weight of the top coating layer. The difference in coating weight between the under-coating layer and the top coating layer (under-top) is 1 g / m or less. ２ More than 1.5 g / m is preferable. ２ More preferably, 2 g / m or more ２ If the coating weight of the under-coating layer is too large compared to the coating weight of the top-coating layer, the drying load of the under-coating layer increases, which may reduce runnability, and if the coating weight of the top-coating layer is too small, the surface feel of the coated paper may deteriorate. ２Preferably, 9 g / m or less ２ More preferably, 8 g / m or less ２ The following is even more preferred:

[0031] The present invention makes it possible to obtain pigment coated paper with little color unevenness. This is because the color unevenness and unevenness of the base paper are reduced by the under-coating layer, and the top coating layer is applied on the under-coating layer with little color unevenness and unevenness. In the present invention, since the unevenness of the base paper is filled by the under-coating layer, it is not necessary to perform a smoothing treatment such as a calendaring treatment on the base paper before forming the pigment coating layer, and the PPS smoothness (PPS Ｂ ) can be, for example, 5.0 μm or more, 5.5 μm or more, 6.0 μm or more, 6.5 μm or more, 7.0 μm or more, etc. Smoothing treatment of the base paper is optional, and if a higher degree of smoothness is required, smoothing treatment can be performed.

[0032] Smoothness of undercoating layer (PPS Ｕ ) is preferably 5.5 μm or less. Ｕ When the thickness of the PPS film is 5.5 μm or less, it is easy to form a smooth top coating layer thereon. Ｕ The thickness is more preferably 5.2 μm or less, even more preferably 4.9 μm or less, and even more preferably 4.6 μm or less. The pigment coated paper of the present invention has a smooth surface due to the top coating layer provided on the under coating layer, so the under coating layer does not need to have a high degree of smoothness. Ｕ It is sufficient if the thickness is about 4.0 μm or more.

[0033] Smoothness of top coating layer (PPS Ｔ ) is preferably 2.5 μm or less in order to further improve printability. Ｔ is more preferably 2.3 μm or less, even more preferably 2.1 μm or less, and even more preferably 1.9 μm or less.

[0034] The method for drying the pigment coating layer is not particularly limited, and conventional methods such as steam heaters, gas heaters, infrared heaters, electric heaters, hot air heaters, microwaves, and cylinder dryers can be used. Paper provided with a pigment coating layer can be subjected to smoothing treatments such as supercalendering and high-temperature soft nip calendering, as needed. Smoothing treatments can further improve the smoothness and gloss of pigment-coated paper. However, smoothing treatments can result in unevenness in the area of ​​contact with the calender, leading to density variations in the pigment coating layer and resulting in whiteness variations. However, because the pigment-coated paper of the present invention has an excellent top coating layer with excellent smoothness, whiteness variations can be suppressed to the same level as untreated paper, even after smoothing treatments. When smoothing treatments are performed, soft nip calendering is preferred. Soft nip calendering improves both whiteness and opacity.

[0035] "Pigment coated paper" The pigment coated paper of the present invention has a color difference ΔE between the base paper and the undercoating layer. Ｕ－Ｂ and the color difference ΔE between the base paper and the top coating layer Ｔ－Ｂ But ΔE Ｕ－Ｂ ≦1 and ΔE Ｕ－Ｂ <ΔE Ｔ－Ｂ By satisfying this relationship, pigment coated paper with little color unevenness can be obtained. ＊ a ＊ b ＊ Color system value L ＊ Value, a ＊ value, b ＊ It is a value calculated from the value. Ｕ－Ｂ is 1 or less. From the viewpoint of suppressing color unevenness, ΔE Ｕ－Ｂ is preferably 0.9 or less, more preferably 0.8 or less, even more preferably 0.7 or less, even more preferably 0.6 or less, and even more preferably 0.5 or less.

[0036] ΔE Ｔ－Ｂ is ΔE Ｕ－Ｂ greater than (ΔE Ｕ－Ｂ <ΔE Ｔ－Ｂ ). ΔE Ｔ－Ｂ and ΔE Ｕ－Ｂ The difference (ΔE Ｔ－Ｂ -ΔEＵ－Ｂ ) is preferably 0.5 or more, more preferably 1 or more, even more preferably 1.5 or more, even more preferably 2 or more, even more preferably 2.5 or more, and even more preferably 3 or more. Ｔ－Ｂ is preferably 2 or more and 5 or less, more preferably 2.5 or more, even more preferably 3 or more, more preferably 4.5 or less, and even more preferably 4 or less.

[0037] The pigment coated paper of the present invention preferably has a DAV2 value of 18 or less. DAV2 is a value measured using an appearance analyzer manufactured by DuPont, and the higher this value, the greater the color unevenness. The DAV2 value is more preferably 17 or less, even more preferably 16 or less, even more preferably 15 or less, and even more preferably 14 or less.

[0038] The present invention will be specifically illustrated by the following examples, but the present invention is not limited to the descriptions in the examples. Furthermore, parts by mass in the examples refer to parts by mass on an bone-dry basis unless otherwise specified.

[0039] Preparation of Under Coating Liquid 30 parts by mass of heavy calcium carbonate A (proportion of particles with a particle size of 2 μm or less by precipitation method: 90%, D50 = 1.23 μm) and 40 parts by mass of heavy calcium carbonate B (proportion of particles with a particle size of 2 μm or less by precipitation method: 75%, D50 = 1.61 μm) were mixed as pigments, and 30 parts by mass of first-grade kaolin (particle size 2 μm, aspect ratio 10) were added, and 9 parts by mass of acrylic ester-styrene copolymer latex and 9 parts by mass of starch were added as adhesives, and water was further added to obtain an under coating liquid with a solids concentration of 64.4% by mass. The under coating liquid did not contain any colorant. Preparation of top coating liquid 50 parts by mass of heavy calcium carbonate A and 50 parts by mass of first-grade kaolin were mixed as pigments, and to this were added 15 parts by mass of acrylic ester-styrene copolymer latex as an adhesive, 0.15 parts by mass of a synthetic water retention agent, and 0.11 parts by mass of a colorant, and water was further added to obtain a top coating liquid with a solids concentration of 65.6% by mass.

[0040] The base paper contains 100% chemical pulp and has a basis weight of 190 g / m ２An undercoating liquid was applied to the base paper with a blade coater in a dry coating amount of 12.2 g / m2 on one side. ２ Then, top coating solution 1 was applied thereon using a blade coater to a dry coating amount of 7.3 g / m per side, and dried. ２ Thus, a pigment coated paper having two pigment coating layers was obtained.

[0041] Example 2: The dry coating amount of the undercoating liquid and the topcoating liquid per side was 12.3 g / m ２ , 8.8 g / m ２ Pigment coated paper was obtained in the same manner as in Example 1, except that the dry coating amount of the top coating liquid per side was 9.5 g / m. ２ Pigment coated paper was obtained in the same manner as in Example 1, except that the amount of synthetic water retention agent in the top coating liquid was 0.25 parts by mass, and the dry coating amount per side of the top coating liquid with a solid content concentration of 65.3% by mass was 12.2 g / m. ２ Pigment coated paper was obtained in the same manner as in Example 1, except that the blending amounts of colorant in the under coating liquid and the top coating liquid were both 0.05 parts by mass, and the dry coating amounts per side of the under coating liquid with a solid content concentration of 64.0 mass% and the top coating liquid with a solid content concentration of 65.6 mass% were each 11.1 g / m ２ , 9.7 g / m ２ A pigment coated paper was obtained in the same manner as in Example 1, except that:

[0042] Preparation of Under Coating Liquid 2: 20 parts by weight of heavy calcium carbonate A, 60 parts by weight of heavy calcium carbonate B, and 20 parts by weight of first-grade kaolin were used as pigments, and 9 parts by weight of acrylate ester-styrene copolymer latex and 9 parts by weight of starch were blended as adhesives. Water was then added to obtain Under Coating Liquid 2 with a solids concentration of 64.9% by weight. Under Coating Liquid 2 did not contain a colorant. Preparation of Top Coating Liquid 2: 40 parts by weight of heavy calcium carbonate A, 20 parts by weight of heavy calcium carbonate B, and 40 parts by weight of first-grade kaolin were mixed as pigments, and 15 parts by weight of acrylate ester-styrene copolymer latex as adhesives, 0.3 parts by weight of a synthetic water retention agent, and 0.11 parts by weight of a colorant were blended. Water was then added to obtain Top Coating Liquid 2 with a solids concentration of 65.8% by weight.

[0043] Example 5: Undercoating liquid 2 was applied to the base paper using a blade coater in a dry coating amount of 14.2 g / m per side. ２ Then, top coating solution 2 was applied on top of the above with a blade coater to a dry coating amount of 11.9 g / m per side. ２ Thus, a pigment coated paper having two pigment coating layers was obtained.

[0044] Example 6: Using a base paper (Stoeckigt sizing degree 380 seconds) smoothed using a machine calender, the dry coating amount per side of the undercoating liquid 2 and the top coating liquid 2 was 13.6 g / m ２ , 10.3 g / m ２ Pigment coated paper was obtained in the same manner as in Example 5, except that the dry coating amount per side of the undercoating liquid 2 and the top coating liquid 2 was 7.5 g / m. ２ , 14.7 g / m ２ A pigment coated paper was obtained in the same manner as in Example 5, except that:

[0045] The following measurements were carried out. The results are shown in Table 1. Basis weight: Measured in accordance with JIS P8124. Paper thickness: Measured in accordance with JIS P8118. Density: Calculated from basis weight and paper thickness. ISO brightness: Measured in accordance with JIS P 8148 "Paper, paperboard and pulp -- Determination of ISO brightness (diffuse blue light reflectance)," and the UV-in value was used.

[0046] ・Hue (L ＊ a ＊ b ＊ Color system) Measurement was carried out in accordance with JIS P 8150 using a spectrophotometer (CMS-35SPX, Murakami Color Research Laboratory Co., Ltd.), and the UV-in value was used. ＊ a ＊ b ＊ The color is expressed as L ＊ , chromaticity indicating hue and saturation is a ＊ , b ＊ It is expressed as: ＊ Positive values ​​are redder, negative values ​​are greener, b ＊ Positive values ​​indicate yellow, negative values ​​indicate blue. ＊ value and b ＊ From the value, the saturation C is calculated according to the following formula: ＊ was calculated. ＊ = (a ＊２ +b ＊２ ) ０．５

[0047] PPS smoothness (PPS-R) In accordance with JIS P 8151 "Paper and paperboard -- Testing method for surface roughness and smoothness (air leak method) -- Printsurf tester method," smoothness was measured using a soft backing at a clamp pressure of 1 MPa.

[0048] - DAV2 Measured using a DuPont appearance analyzer. The DAV2 value indicates the degree of color unevenness; the higher the value, the more uneven the surface of the coated paper and the worse the whiteness of the paper. - Color unevenness Color unevenness seen on the surface of pigment coated paper was rated on a three-point scale according to the following criteria: ◎: DAV2 value 15 or less (no noticeable color unevenness). ○: DAV2 value 16-18 (mild color unevenness). ×: DAV2 value 19 or more (significant color unevenness observed, not suitable for practical use). - Vividness Three trained expert panelists jointly rated the vividness (absence of dullness) of pigment coated paper according to the following criteria: ◎: The color is well-developed and appears vivid. ○: The color appears slightly dull. ×: The color is poorly developed and appears dull. - Color strength Three trained expert panelists jointly evaluated the color strength of the pigment-coated paper according to the following criteria: ◎: The color of the added coloring material is deep and has a sufficient color tone. ○: The color of the added coloring material is slightly light, but appears to have a color tone. ×: The color of the added coloring material is light and has an insufficient color tone.

[0049]

[0050] From the results of Examples 1 to 4 and Comparative Example 1, ΔE Ｕ－Ｂ ≦1 and ΔE Ｕ－Ｂ <ΔE Ｔ－Ｂ From the results of Examples 5 and 6 and Comparative Example 2, it can be seen that the coating amount of the under layer is 10 g / m ２ It was confirmed that color unevenness was suppressed by the above. In particular, although the total amount of colorant contained in the pigment coating layer was the same in Example 3 and Comparative Example 1, the pigment coated paper of Example 3, which is the present invention, showed significantly less color unevenness than the pigment coated paper obtained in Comparative Example 1. The results of Examples 5 and 6 confirmed that smoothing treatment of the base paper made the surface of the top coating layer smoother. Although the evaluations as pigment coated papers were similar, the smoother pigment coated paper of Example 6 had superior print quality.

Claims

1. At least one side of the base paper has two or more pigment coating layers, and the coating weight of the undercoating layer closest to the base paper is 10 g / m ２ or more, and the color difference ΔE between the base paper and the under-coating layer Ｕ－Ｂ and a color difference ΔE between the base paper and the top coating layer farthest from the base paper. Ｔ－Ｂ But, ΔE Ｕ－Ｂ ≦1 and ΔE Ｕ－Ｂ <ΔE Ｔ－Ｂ A pigment coated paper characterized by satisfying the above.

2. Pigment coated paper according to claim 1, characterized in that the DAV2 value is 18 or less.

3. A pigment coated paper as described in claim 1 or 2, characterized in that the top coating layer contains a colorant, and the colorant content of the under coating layer is 20% or less of the colorant content of the top coating layer.

4. ΔE Ｔ－Ｂ 3. The pigment coated paper according to claim 1, wherein the densities are ≦4.

5. A pigment coated paper according to claim 1 or 2, characterized in that the PPS smoothness (soft, clamp pressure 1 MPa) of the base paper is 5 μm or more.

6. Pigment coated paper according to claim 1 or 2, characterized in that the PPS smoothness (soft, clamp pressure 1 MPa) of the top coating layer is 2 μm or less.

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