Coated paper for printing

Abstract

To provide coated paper for printing which has glossy feeling in a printed part, good blister resistance, resistance against weak contrast, and golden red reproducibility.SOLUTION: Coated paper for printing has base paper containing wood pulp and a filler, a first coating layer containing a white pigment and a binder on at least one surface of the base paper, and a second coating layer containing a white pigment and a binder with respect to the outside of the first coating layer with the base paper as a reference, wherein the white pigment of the first coating layer contains heavy calcium carbonate and kaoline, the white pigment of the second coating layer contains light calcium carbonate, heavy calcium carbonate, kaoline and an organic pigment, L* shown by an L*a*b* color system defined by CIE is 92.0 or more, a* is 0.00 or more and 1.70 or less, and b* is -2.00 or more and 0.00 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a coated printing paper suitable for multicolor web offset printing. [Background technology]

[0002] While printing machine manufacturers are announcing digital printing machines, offset printing machines are still used in the printing industry to produce commercial printed materials such as magazines, books, art books, photo books, art books, MOOK books, booklets, catalogs, flyers, and pamphlets. For mass production of commercial printed materials, offset rotary printing machines are used. Paper used for commercial printed materials is not limited to glossy paper and matte paper. In recent years, paper has various qualities in terms of gloss and matte finish, smoothness, color, and texture. Traditionally, catalogs, art books, photo books, art books, art books, and MOOK books have used printing coated paper with good whiteness and gloss. However, printing coated paper with high gloss has poor visibility of characters. A recent trend, especially for catalogs and MOOK books, is to use printing coated paper with dull or semi-gloss tone and good gloss of the printed part. This is because such printing coated paper has good visibility of characters while providing clear printing quality of photos and pictures.

[0003] For example, a coating layer of an undercoat layer and a topcoat layer containing a pigment and an adhesive are provided on a base paper, the base paper contains an organic compound having an effect of inhibiting interfiber bonding of pulp, the undercoat layer contains, as a pigment, 50 parts by weight or more of delaminated clay having a volume distribution average particle diameter of 3.5 to 20 μm per 100 parts by weight of pigment, the topcoat layer contains, as a pigment, 70 parts by weight or more of kaolin having a volume distribution average particle diameter of 0.80 μm or less per 100 parts by weight of pigment, and the coated paper density is 1.00 g / cm 3 Dull coated paper characterized by the following properties is known (see, for example, Patent Document 1). Such dull coated paper has a high glossiness in the printed area and little minute gloss unevenness in the image area while being bulky and having a rough feel. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-133278 A Summary of the Invention [Problem to be solved by the invention]

[0005] Offset printing presses are classified into sheet-fed printing presses and web printing presses. Web printing presses are characterized by high-speed, large-volume printing using rolled printing paper. Offset web printing presses are equipped with dryers because the ink needs to be dried before the paper is wound up after printing or before it is cut and folded after printing. A problem specific to offset web printing is the phenomenon in which moisture inside the printing paper and / or the solvent components in the ink components that have permeated the inside of the printing paper are vaporized in the dryer and cannot escape completely, resulting in blisters in the printing paper, i.e., blistering. Blisters are likely to occur when the paper is coated paper for printing and / or when printing images with multiple colors and high color density is performed.

[0006] In offset rotary printing presses, once a roll of paper is loaded onto the press and transport begins, it cannot be changed again, so printing paper must have the printing capabilities for the offset rotary printing press. Coated printing paper with a coating layer has better smoothness and ink receptivity than uncoated printing paper, and therefore has improved printing capabilities. On the other hand, offset rotary printing presses use a soft rubber blanket to transfer ink to the printing paper and allow it to be sufficiently applied in the thickness direction of the printing paper, so the smoothness is less affected between coated printing paper and uncoated printing paper. Rather, when printing on coated printing paper with an offset rotary printing press, excessive color development may cause the light and dark or color differences in the printed area to become blurred, weakening the contrast.

[0007] "Golden red" is a color often used in commercial prints to highlight areas. Golden red is often produced using spot color ink, and in terms of hue, it is expressed mainly as a mixture of 90% to 100% magenta and 100% yellow. When printing golden red spot color, the printer may be instructed to use DIC color numbers DIC159 or DIC565. In printing, the hue and color development are important so that the golden red printed on the coated printing paper turns out to be the desired golden red.

[0008] In view of the above, an object of the present invention is to provide a coated printing paper having a glossy printed area, good blister resistance, low contrast resistance and gold-red reproducibility. [Means for solving the problem]

[0009] As a result of intensive research by the inventors to solve the above problems, the object of the present invention is achieved as follows. The present invention relates to a paper substrate that contains wood pulp and a filler, a first coating layer that contains a white pigment and a binder on at least one side of the paper substrate, and a second coating layer that contains a white pigment and a binder on the outer side of the first coating layer based on the paper substrate, the white pigment of the first coating layer contains heavy calcium carbonate and kaolin, the white pigment of the second coating layer contains light calcium carbonate, heavy calcium carbonate, kaolin and an organic pigment, and the white pigment of the first coating layer contains calcium carbonate, heavy calcium carbonate, kaolin and an organic pigment, and the white pigment of the second coating layer contains ... * a * b * L shown in the color system * is 92.0 or more, a * is 0.00 or more and 1.70 or less, and b * A coated printing paper having a coefficient of refraction (R) of -2.00 or more and 0.00 or less. Effect of the Invention

[0010] According to the present invention, the coated printing paper has good gloss in the printed area, and has good resistance to blistering, low contrast and golden red reproducibility. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below. The coated printing paper comprises a base paper containing wood pulp and a filler, a first coating layer on at least one side of the base paper, and a second coating layer on the outer side of the first coating layer relative to the base paper. That is, the coated printing paper comprises the base paper, the first coating layer, and the second coating layer in that order. The printing surface of the coated printing paper which exhibits the effects of the present invention is the surface having the first coating layer and the second coating layer. The coated printing paper may have the first coating layer and / or the second coating layer on the surface opposite the base paper. Since commercial printed matter is usually double-sided in many cases, in at least one embodiment, the coated printing paper comprises the first coating layer on both sides of the base paper and the second coating layer on the outer side of the first coating layer relative to the base paper. When the first and second coating layers are present on only one side of the base paper, a conventionally known backcoat layer can be provided on the opposite side of the base paper that does not have the first and second coating layers, for example, to prevent curling of the coated paper for printing.

[0012] In some embodiments, the coated printing paper has an intermediate layer containing a white pigment and a binder or containing a resin between the base paper and the first coating layer and / or between the first coating layer and the second coating layer, as necessary, for the purpose of improving printability and interlayer strength, etc. In at least one embodiment, there is no intermediate layer. The reason for this is that it is advantageous in terms of production costs.

[0013] The wood pulp is a pulp that has been conventionally known in the papermaking field. Examples of wood pulp include chemical pulp such as Leaf Bleached Kraft Pulp (LBKP) and Needle Bleached Kraft Pulp (NBKP), mechanical pulp such as Groundwood Pulp (GP), Pressure GroundWood Pulp (PGW), Refiner Mechanical Pulp (RMP), ThermoMechanical Pulp (TMP), ChemiThermoMechanical Pulp (CTMP), and ChemiMechanical Pulp (CMP), semi-chemical pulp such as ChemiGroundwood Pulp (CGP), waste paper pulp such as DeInked Pulp (DIP), and pulp obtained by disintegrating spoilage generated in paper mills. In some embodiments, the base paper contains non-wood pulp, which is conventionally known in the papermaking field, in addition to the wood pulp. This is because it is an effective use of plant resources. Examples of raw materials for non-wood pulp include woody bast such as paper mulberry, Mitsumata, and Gampi, herbaceous bast such as flax, hemp, and kenaf, leaf fibers such as Manila hemp, abaca, and sisal, grass plants such as rice straw, wheat straw, sugarcane baca, bamboo, and esparto, and seed hairs such as cotton and linter. In some embodiments, the base paper contains 90% by mass or more of wood pulp relative to the pulp of the base paper. In at least one embodiment, the base paper does not contain non-wood pulp. The reason for this is that it is advantageous in terms of production costs.

[0014] The freeness of the wood pulp is not particularly limited. The freeness is the CSF freeness determined according to ISO5627-2:2001 "Pulps-Determination of drainability-Part 2 Canadian Standard freeness method". In some embodiments, the freeness of the wood pulp is 380 ml or more and 530 ml or less. The reason for this is that the strength and smoothness of the obtained base paper can be well combined with the dimensional stability.

[0015] The filler is a white pigment conventionally known in the papermaking field. Examples of the filler include inorganic pigments such as light calcium carbonate, heavy calcium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, activated clay, diatomaceous earth, silica, alumina, aluminum hydroxide, lithopone, zeolite, magnesium carbonate, and magnesium hydroxide, and organic pigments of various shapes such as medium-density, hollow, bowl-shaped, and confetti-shaped, made of various resins such as styrene-based resins, acrylic-based resins, vinyl acetate-based resins, olefin-based resins, vinyl chloride-based resins, urea-based resins, and melamine-based resins. In addition, examples of organic pigments include microcapsules. The filler is one or more selected from the group consisting of these.

[0016] In some embodiments, the base paper contains talc and precipitated calcium carbonate as fillers. In at least one embodiment, the base paper contains talc and precipitated calcium carbonate as fillers, and the total content of talc and precipitated calcium carbonate relative to the fillers in the base paper is 80 mass% or more. The reason for this is that the blister resistance of the coated printing paper tends to improve.

[0017] Talc is conventionally known in the papermaking art. Talc exists as both a natural and synthetic substance, and its basic structure is a sandwich of a tetrahedral sheet of two-dimensionally connected Si-O tetrahedrons and an octahedral sheet of two-dimensionally connected Mg-(OH) octahedrons stacked in a 2:1 ratio, with the chemical formula Mg3SiO10 Talc is a layered clay mineral represented by the formula (OH)2. Talc has the characteristics of cleavage, softness (Mohs hardness 1) and slipperiness due to the weak bonds between the layer units in a 2:1 sandwich structure. Clay minerals, including talc, generally become electrically charged by replacing some of the Mg2+ in the octahedral sheets with other metal ions of different valences. In talc, the tetrahedral sheets have Si 4+ Al 3+ or in the octahedral sheet Mg 2+ Fe 3+ , Fe 2+ Or Al 3+ However, talc has such a small amount of substitution that it is nearly electrically neutral and, as a result, has hydrophobic behavior.

[0018] Precipitated calcium carbonate is conventionally known in the papermaking art. Light calcium carbonate is a synthetic calcium carbonate chemically produced from limestone, and has a relatively uniform shape and a relatively narrow particle size distribution. Light calcium carbonate has a crystal structure and a specific refractive index. Light calcium carbonate also has a larger apparent specific gravity and specific surface area than heavy calcium carbonate, which will be described later.

[0019] In some embodiments, the base paper has a filler content of 100 parts by mass or more and 200 parts by mass or less per 1000 parts by mass of pulp in the base paper. In some embodiments, the base paper has a mass ratio of talc to precipitated calcium carbonate in the base paper of talc:precipitated calcium carbonate=6:4 to 4:6. This is because the blister resistance of the coated printing paper tends to improve.

[0020] In addition to the pulp and filler, the base paper may contain various additives as necessary, such as sizing agents, fixing agents, retention agents, cationization agents, binders, paper strength agents, bulking agents, pigment dispersants, thickeners, flow improvers, defoamers, foam inhibitors, release agents, foaming agents, penetrating agents, colorants, fluorescent whitening agents, ultraviolet absorbers, antioxidants, preservatives, mold inhibitors, water-resistant agents, wet strength agents, and dry strength agents.

[0021] The base paper can be obtained by making a stock containing pulp, a filler, and, if necessary, various additives, using a conventionally known papermaking machine, such as a Fourdrinier papermaking machine, a twin-wire papermaking machine, a combination papermaking machine, a cylinder papermaking machine, or a Yankee papermaking machine.

[0022] The base paper can be subjected to a size press treatment with a sizing liquid containing a surface sizing agent. Surface sizing agents are well known in the papermaking field, and examples of surface sizing agents include various starches and polyvinyl alcohol. The size press treatment can be achieved by a size press conventionally known in the papermaking field. Examples of size presses include inclined size presses, horizontal size presses, and film transfer type rod metering size presses, roll metering size presses, and blade metering size presses. Examples of rod metering size presses include shim sizers, opti sizers, speed sizers, and film presses, and examples of roll metering size presses include gate roll coaters. Other examples include bill blade coaters, twin blade coaters, Belbapa coaters, tab size presses, and calendar size presses.

[0023] The base paper may be subjected to a calendering process. Calendering is a process for making the paper smooth and even by passing it between rolls. The apparatus used for calendering is a conventionally known apparatus in the papermaking field, such as a machine calender, a soft nip calender, a super calender, a multi-stage calender, and a multi-nip calender.

[0024] The method of providing coating layers such as the first coating layer, the second coating layer, and the backcoat layer on the base paper is not particularly limited. For example, the method may be a method of coating and drying the coating liquid for each coating layer using a coating device and a drying device conventionally known in the field of coated paper. Examples of the coating device include a comma coater (registered trademark), a film press coater, a rod coater, an air knife coater, a rod blade coater, a bar coater, a blade coater, a gravure coater, a curtain coater, an E-bar coater, and a size press. Examples of the drying device include a hot air dryer such as a linear tunnel dryer, an arch dryer, an air loop dryer, and a sine curve air float dryer, an infrared heating dryer, and a dryer using microwaves, etc.

[0025] At each stage of providing a first coating layer on a base paper and / or a second coating layer on the first coating layer, the coated printing paper can be subjected to a calendering treatment. The calendering apparatus used is the same as that described above.

[0026] In some embodiments, the coated printing paper has a coating weight of the first coating layer of 5 g / m2 in terms of dry solids. 2 More than 10g / m 2 In some embodiments, the coated paper for printing has a coating weight of the second coating layer of 4 g / m2 in terms of dry solids. 2 More than 9g / m 2 In at least one embodiment, the coated printing paper has a coating weight of the first coating layer of 5 g / m2 in terms of dry solids. 2 More than 10g / m 2 The coating weight of the following and second coating layers is 4g / m2 in terms of dry solids. 2 More than 9g / m 2 or less, and the coating weight of the second coating layer is less than the coating weight of the first coating layer. The reason for this is that the blister resistance, low contrast resistance and / or gold-red reproducibility of the coated printing paper are improved.

[0027] The first coating layer and the second coating layer contain a white pigment and a binder. The white pigment is a conventionally known pigment in the field of coated paper. Examples of the white pigment include inorganic pigments such as light calcium carbonate, heavy calcium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, activated clay, diatomaceous earth, silica, alumina, aluminum hydroxide, lithopone, zeolite, magnesium carbonate, and magnesium hydroxide, and organic pigments of various shapes such as medium-density, hollow, bowl-shaped, and confetti-shaped, made of various resins such as styrene-based resins, acrylic-based resins, vinyl acetate-based resins, olefin-based resins, vinyl chloride-based resins, urea-based resins, and melamine-based resins. Examples of the organic pigments include microcapsules.

[0028] The white pigment in the first coating layer includes heavy calcium carbonate and kaolin. The white pigment in the second coating layer includes light calcium carbonate, heavy calcium carbonate, kaolin, and an organic pigment. The coated printing paper can obtain blister resistance, low contrast resistance, and gold red reproducibility by having the first coating layer include heavy calcium carbonate and kaolin as white pigments, and the second coating layer include light calcium carbonate, heavy calcium carbonate, kaolin, and an organic pigment as white pigments. The coated printing paper can have a glossy printed portion by having the white pigments in the first coating layer and the second coating layer have the above-mentioned composition. Although the reason for this is unclear, the inventors speculate that it is a synergistic effect due to the attributes of the light calcium carbonate, heavy calcium carbonate, kaolin, and the organic pigment. In some embodiments, the first coating layer has a total content of heavy calcium carbonate and kaolin of 90% by mass or more relative to the white pigment in the first coating layer, and the second coating layer has a total content of light calcium carbonate, heavy calcium carbonate, kaolin and organic pigment of 90% by mass or more relative to the white pigment in the second coating layer, because the blister resistance, low contrast resistance and / or golden red reproducibility of the coated printing paper are improved.

[0029] The precipitated calcium carbonate is the same as that explained above in relation to the filler, and therefore a detailed explanation thereof will be omitted here. Heavy calcium carbonate is a well-known substance in the papermaking field. Heavy calcium carbonate is a naturally occurring calcium carbonate obtained by directly grinding limestone, which is the main component of the heavy calcium carbonate. It has an irregular shape and generally has a relatively wide particle size distribution range. Heavy calcium carbonate also has a smaller apparent specific gravity and specific surface area than light calcium carbonate.

[0030] Kaolin is conventionally known in the papermaking art. Kaolin is a clay mineral, generally composed of Al2O3·2SiO2·2H2O, with a structure in which silicon-oxygen layers and aluminum-hydroxyl layers are alternately stacked. Kaolin is an industrially refined and processed product of naturally occurring kaolin ores, such as kaolinite, nacrite, dickite, halloysite, and hydrated halloysite, and is produced through processes such as crushing, washing, iron removal, and classification. Kaolin also includes highly processable kaolins, such as delaminated kaolin, which is made into thin plates by applying shear force to improve the aspect ratio, engineered kaolin, which is adjusted to have a sharp particle size distribution, and calcined kaolin, which has high cohesion. Kaolin is a flat particle, and the flat parts of the particles are usually negatively charged and the edges are positively charged.

[0031] Organic pigments are conventionally known in the coated paper art. The organic pigment is a white pigment composed of an organic resin and has various shapes. In some embodiments, the organic pigment is a hollow organic pigment. This is because it improves the low-contrast resistance and / or gold-red reproducibility of coated printing paper. The hollow organic pigment is an organic pigment having one or more voids (hollow) inside the particle.

[0032] In some embodiments, the first coating layer has a content ratio by mass of heavy calcium carbonate to kaolin of heavy calcium carbonate:kaolin=65:35 to 85:15. In some embodiments, the second coating layer has a content by mass of light calcium carbonate, heavy calcium carbonate, kaolin, and organic pigment of 35 to 55 parts by mass of light calcium carbonate, 18 to 38 parts by mass of heavy calcium carbonate, 10 to 30 parts by mass of kaolin, and 4 to 16 parts by mass of organic pigment relative to 100 parts by mass of white pigment in the second coating layer. The reason for this is that the blister resistance, low contrast resistance, and / or golden red reproducibility of the printing coated paper are improved. In at least one embodiment, the first coating layer has a mass ratio of heavy calcium carbonate to kaolin of heavy calcium carbonate:kaolin=65:35 to 85:15, and the second coating layer has a mass ratio of light calcium carbonate, heavy calcium carbonate, kaolin and organic pigment of 35 parts by mass or more and 55 parts by mass or less of light calcium carbonate, 18 parts by mass or more and 38 parts by mass or less of heavy calcium carbonate, 10 parts by mass or more and 30 parts by mass or less of kaolin, and 4 parts by mass or more and 16 parts by mass or less of organic pigment.

[0033] The binder is a water-dispersible binder or a water-soluble binder that is conventionally known in the field of coated paper. Examples of water-dispersible binders include styrene-based resins such as styrene-butadiene-based copolymer resins, conjugated diene-based copolymer resins such as (meth)acrylonitrile-butadiene-based copolymer resins, acrylic resins such as (meth)acrylic acid ester butadiene-based copolymer resins, (meth)acrylic acid ester styrene-based copolymer resins and (meth)acrylic acid ester-based copolymer resins, vinyl-based copolymer resins such as ethylene vinyl acetate-based copolymer resins and vinyl chloride vinyl acetate-based copolymer resins, polyurethane-based resins, alkyd-based resins, unsaturated polyester-based resins, and modified resins using various monomers thereof, as well as thermosetting synthetic resins such as urea-based resins and melamine-based resins. Examples of water-soluble binders include starches, cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose, polyvinyl alcohol (a general term including unmodified polyvinyl alcohol and modified polyvinyl alcohol such as silanol-modified polyvinyl alcohol), casein, gelatin, or modified products thereof, soy protein, natural polymer resins such as pullulan, gum arabic, karaya gum, and albumin, or derivatives thereof, sodium alginate, and maleic acid-based resins.

[0034] In some embodiments, the binder of the first coating layer is a combination of starch and styrene-butadiene copolymer resin. In some embodiments, the binder of the second coating layer is a combination of polyvinyl alcohol and styrene-butadiene copolymer resin. The reason for this is that the blister resistance of the coated printing paper tends to improve due to the synergistic effect of the binder attributes. The attributes are, for example, that styrene-butadiene copolymer resin has excellent binding properties for white pigments, starch has excellent gelling properties and stiffness imparting properties, and polyvinyl alcohol has excellent crystallization properties and film-forming properties. In at least one embodiment, the binder of the first coating layer is one or more selected from the group consisting of starches and a styrene-butadiene-based copolymer resin, and the binder of the second coating layer is one or more selected from the group consisting of polyvinyl alcohols and a styrene-butadiene-based copolymer resin.

[0035] In some embodiments, the content of the binder in the first coating layer is 5 parts by mass or more and 15 parts by mass or less, based on 100 parts by mass of the white pigment in the first coating layer. In some embodiments, the content of the binder in the second coating layer is 8 parts by mass or more and 28 parts by mass or less, based on 100 parts by mass of the white pigment in the second coating layer. The reason for this is that blister resistance tends to improve. In at least one embodiment, the content of the binder in the first coating layer is 5 parts by weight or more and 15 parts by weight or less per 100 parts by weight of the white pigment in the first coating layer, and the content of the binder in the second coating layer is 8 parts by weight or more and 28 parts by weight or less per 100 parts by weight of the white pigment in the second coating layer.

[0036] The first coating layer and the second coating layer may contain, in addition to the white pigment and binder, various additives conventionally known in the field of coated paper, as necessary, such as thickeners, flow improvers, defoamers, foaming agents, lubricants, penetrants, colorants, fluorescent brighteners, ultraviolet absorbers, antioxidants, preservatives, mold inhibitors, and printability improvers.

[0037] In some embodiments, the second coating layer contains a fluorescent whitening agent. This is because the resistance to low contrast is improved. The fluorescent whitening agent is a conventionally known agent in the field of coated paper. Examples of the fluorescent whitening agent include fluorescein-based compounds, thioflavin-based compounds, eosin-based compounds, rhodamine-based compounds, coumarin-based compounds, imidazole-based compounds, oxazole-based compounds, triazole-based compounds, carbazole-based compounds, pyridine-based compounds, imidazolone-based compounds, and naphthalic acid-based compounds, as well as stilbene-based compounds such as stilbene disulfonic acid derivatives, stilbene tetrasulfonic acid derivatives, and stilbene hexasulfonic acid derivatives. In some embodiments, the fluorescent whitening agent is a stilbene-based compound conventionally known in the field of papermaking. A fluorescent brightening agent is a compound that absorbs invisible ultraviolet light and converts it into visible bluish-white light (fluorescence), and is an additive for increasing the apparent whiteness of paper. In a coating layer that contains a fluorescent brightening agent, the fluorescence of the fluorescent brightening agent increases the apparent whiteness of the paper. The inventors have found, through trial and error, that by including a fluorescent brightening agent in the second coating layer, the low contrast resistance of the coated printing paper can be obtained. In other words, a coated printing paper that contains a fluorescent brightening agent in the second coating layer can not only increase the apparent whiteness, but also obtain low contrast resistance.

[0038] In some embodiments, the base paper, the first coating layer, and / or the second coating layer contain a colorant selected from the group consisting of color pigments and color dyes. The colorant is not particularly limited and is selected to have a hue as described below. Since white pigments such as wood pulp and kaolin are not strictly white but slightly colored, the colorant is adjusted to match the wood pulp and white pigment. And, the printing coated paper is a colorant that is combined with the wood pulp of the base paper, the white pigment of the first coating layer, and / or the white pigment of the second coating layer to produce a color according to the CIE definition L * a * b * L shown in the color system * is 92.0 or more, a * is 0.00 or more and 1.70 or less, and b *can be between -2.00 and 0.00. CIE definition of L * a * b * In the color system, L * indicates brightness, and positive a * indicates the chromaticity of the red side, negative a * indicates the chromaticity of the green side and positive b * indicates the yellow chromaticity, and negative b * indicates the chromaticity of the blue side. * a * b * Coated printing paper having the above range has high brightness and a pale gray color. * a * b * A coated printing paper having a value within the above range can obtain resistance to low contrast and resistance to gold and red reproduction.

[0039] In some embodiments, the coated printing paper has a 75 degree specular gloss of 35% or more and 75% or less based on ISO8254-1:1999 "Paper and board-Measurement of specular gloss-Part 1:75 degree gloss with a converging beam, TAPPI method." When the 75 degree specular gloss is in the above range, the coated printing paper has a semi-gloss look. The gloss of the coated printing paper can be adjusted by a method conventionally known in the field of coated paper. The gloss of the coated printing paper can be adjusted, for example, by the calendering conditions of the base paper, the type and content of the white pigment in the first and second coating layers, and the calendering conditions of each coating layer. In general, a treatment that increases the smoothness of the coated printing paper tends to increase the gloss. In addition, with respect to the white pigment, an increase in the content of kaolin usually increases the gloss, and an increase in the content of ground calcium carbonate usually decreases the gloss.

[0040] In some embodiments, the coated printing paper has a base paper containing wood pulp and a filler, a first coating layer containing a white pigment and a binder on at least one side of the base paper, and a second coating layer containing a white pigment and a binder on the outer side of the first coating layer based on the base paper, the white pigment of the first coating layer containing ground calcium carbonate and kaolin, the white pigment of the second coating layer containing light calcium carbonate, ground calcium carbonate, kaolin and an organic pigment, and has a white pigment content according to the CIE definition L * a * b * L shown in the color system * is 92.0 or more, a * is 0.00 or more and 1.70 or less, and b * is -2.00 or more and 0.00 or less, and the second coating layer further contains a fluorescent whitening agent.

[0041] In some embodiments, the coated printing paper has a base paper containing wood pulp and a filler, a first coating layer containing a white pigment and a binder on at least one side of the base paper, and a second coating layer containing a white pigment and a binder on the outer side of the first coating layer based on the base paper, the white pigment of the first coating layer containing heavy calcium carbonate and kaolin, and the weight ratio of the heavy calcium carbonate to the kaolin in the first coating layer is heavy calcium carbonate:kaolin=65:35 to 85:15. the white pigment of the second coating layer contains light calcium carbonate, heavy calcium carbonate, kaolin and an organic pigment, the contents of the light calcium carbonate, heavy calcium carbonate, kaolin and organic pigment in the second coating layer are 35 parts by mass or more and 55 parts by mass or less of light calcium carbonate, 18 parts by mass or more and 38 parts by mass or less of heavy calcium carbonate, 10 parts by mass or more and 30 parts by mass or less of kaolin, and 4 parts by mass or more and 16 parts by mass or less of organic pigment, relative to 100 parts by mass of the white pigment in the second coating layer, and the L * a * b * L shown in the color system * is 92.0 or more, a * is 0.00 or more and 1.70 or less, and b * is between -2.00 and 0.00 inclusive.

[0042] In at least one embodiment, the coated printing paper has a base paper containing wood pulp and a filler, a first coating layer containing a white pigment and a binder on at least one side of the base paper, and a second coating layer containing a white pigment and a binder on the outer side of the first coating layer based on the base paper, the white pigment of the first coating layer containing heavy calcium carbonate and kaolin, and the weight ratio of the heavy calcium carbonate to the kaolin in the first coating layer is heavy calcium carbonate:kaolin=65:35 to 85:15. the white pigment of the second coating layer contains light calcium carbonate, heavy calcium carbonate, kaolin and an organic pigment, the contents of the light calcium carbonate, heavy calcium carbonate, kaolin and organic pigment in the second coating layer are 35 parts by mass or more and 55 parts by mass or less of light calcium carbonate, 18 parts by mass or more and 38 parts by mass or less of heavy calcium carbonate, 10 parts by mass or more and 30 parts by mass or less of kaolin, and 4 parts by mass or more and 16 parts by mass or less of organic pigment, relative to 100 parts by mass of the white pigment in the second coating layer, and the L * a * b * L shown in the color system * is 92.0 or more, a * is 0.00 or more and 1.70 or less, and b * is -2.00 or more and 0.00 or less, and the second coating layer further contains a fluorescent whitening agent. EXAMPLES

[0043] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. Here, "parts by mass" and "% by mass" refer to the amount of dry solids or the amount of substantial components, respectively. The amount of coating refers to the amount of dry solids.

[0044] Coated printing papers of the Examples and Comparative Examples were prepared according to the following procedure.

[0045] <Base paper> The paper stock was prepared as follows: LBKP (freeness 430mlcsf) 750 parts by mass NBKP (freeness 480mlcsf) 250 parts by mass Talc 70 parts by weight Light calcium carbonate 70 parts by mass Aluminum sulfate 10 parts by mass Alkyl ketene dimer sizing agent 0.7 parts by mass Cationic starch 9 parts by weight Polyacrylamide retention agent 0.1 parts by weight Colorant as needed

[0046] The above paper stock was made into paper using a Fourdrinier paper machine, and starch was used as a surface sizing agent and coated on both sides using a size press. The coating amount was 1 g / m 2 After size pressing, the paper was calendered to a basis weight of 55 g / m 2 A base paper of the above formula was obtained.

[0047] <Coating fluid for the first coating layer> The coating layer coating solution was prepared according to the following ingredients. White pigment: Type and quantity are listed in Tables 1 to 3. Starch 3 parts by mass SBR 7 parts by mass Lubricant (calcium stearate) 0.4 parts by weight Polyamide printability improver 0.5 parts by weight Colorant as needed The above ingredients were mixed and dispersed in water to adjust the concentration to 60% by mass.

[0048] <Coating liquid for second coating layer> The coating layer coating solution was prepared according to the following ingredients. White pigment: Type and quantity are listed in Tables 1 to 3. PVA 2 parts by mass SBR 18 parts by mass Fluorescent whitening agent 0 parts by weight / 0.3 parts by weight Lubricant (calcium stearate) 0.4 parts by weight Polyamide printability improver 0.5 parts by weight Colorant as needed The above ingredients were mixed and dispersed in water to adjust the concentration to 46% by mass.

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3]

[0052] The materials used are as follows: For the talc, Hyogo Clay Talc was used. For the light calcium carbonate, Okutama Kogyo Tama Pearl (registered trademark) TP-123 was used. For the heavy calcium carbonate, Hyogo Clay WH90 was used. For the kaolin, Nissei Kyoeki Hydrafine 90 was used. For the silica, Mizusawa Chemical Industry Mizukasil (registered trademark) P-73 was used. For the organic pigment 1, JSR AE850, a hollow white organic pigment, was used. For the organic pigment 2, Asahi Kasei L8801, a medium-density organic pigment, was used. For the PVA (polyvinyl alcohol), Japan Vinyl Acetate-Poval JF-04 was used. For the starch, Oji Cornstarch P140 was used. For the SBR (styrene butadiene copolymer resin), Asahi Kasei E1585 was used. For the fluorescent whitening agent, Clariant Leucophor (registered trademark) U liq, a stilbene compound.

[0053] <Coated paper for printing> The coating solution for the first coating layer was applied to both sides of the base paper using a blade coater and dried using a hot air dryer. Then, the coating solution for the second coating layer was applied to both sides of the first coating layer using an air knife coater and dried using a hot air dryer, to obtain a coated paper for printing. The coating amount of the first coating layer was 8 g / m. 2 The coating weight of the second coating layer is 7 g / m 2 The coating conditions were adjusted so that the above-mentioned result was obtained.

[0054] The resulting coated printing papers were evaluated for the following items.

[0055] <Blister resistance> Four-color (CMYK) printing was performed on one side of the coated printing paper using an offset rotary printing press (Mitsubishi Heavy Industries, Lithopia (registered trademark) BT-2-600 type) and offset rotary printing ink (Dainippon Ink and Chemicals, Web World Terrace N). The printing speed was 300 m / min and the paper surface temperature at the dryer outlet was 120° C., and the observation was performed on 1000 m of coated printing paper where the printing was stable. For printing, evaluation images were used in which solid images of CMYK, red, blue, and green, as well as solid gold and red images, portrait images, landscape images, and text images were randomly arranged. The blister resistance was evaluated by visually observing the occurrence of blisters in the obtained printed matter and sensorily evaluating it according to the following criteria. In the present invention, a coated printing paper is considered to have good blister resistance if it is rated A or B. A: Blisters are generally not observed. B: Although not blisters, slight swelling is observed. C: Inferior to B above, slight presence of blisters observed. D: Inferior to C above, with the presence of blisters observed.

[0056] <Weak contrast resistance> Four-color (CMYK) printing was performed on one side of the coated printing paper using an offset rotary printing press (Mitsubishi Heavy Industries, Lithopia BT-2-600 type) and offset rotary printing ink (Dainippon Ink and Chemicals, Web World Terrace N). The printing speed was 300 m / min and the paper surface temperature at the dryer outlet was 120° C., and the observation was performed on 1000 m of coated printing paper where the printing was stable. For printing, evaluation images were used in which solid images of CMYK, red, blue, and green, solid gold and red images, portrait images, landscape images, and text images were randomly arranged. The weak contrast resistance was evaluated sensorily by visually observing the difference in brightness and vividness of the image in the obtained print and using the following criteria. In the present invention, a coated printing paper is considered to have good weak contrast resistance if it is rated A or B. A: The difference in brightness and vividness of the image is very clear and good. B: Although inferior to A above, The image has clear contrast between light and dark and vividness, and is generally good. C: Although inferior to B above, The image has a clear contrast between brightness and darkness and vividness, and is of usable quality. D: Worse than C above. The difference in brightness and vividness of the image is insufficient or slightly insufficient.

[0057] <Gold red reproducibility> Using an offset rotary printing press (Mitsubishi Heavy Industries, Lithopia BT-2-600) and offset rotary printing ink (Dainippon Ink and Chemicals, Web World Terrace N), four-color (CMYK) printing was performed on one side of coated printing paper. The printing speed was 300 m / min and the paper surface temperature at the dryer outlet was 120°C, and observations were performed on 1000 m of coated printing paper where the printing had stabilized. For printing, evaluation images were used in which CMYK, red, blue, and green solid images, as well as a gold and red solid image, a portrait image, a landscape image, and a text image were randomly arranged. The prints were given to 10 test subjects, who evaluated the color of the gold-red solid image in terms of hue and color development in comparison with DIC color numbers DIC159 and DIC565, according to the following criteria. The final score was calculated by averaging the evaluation results of the 10 test subjects and rounding off any decimal places. In the present invention, a coated printing paper with a rating of 3 or 4 is considered to have good gold-red reproducibility. 4: No problems with hue or color development. 3: Although it is inferior to 4 above, there are generally no problems with the hue and color development. 2: Although inferior to 3 above, the hue and color development are of practical quality. 1: Inferior to 2 above, and does not achieve practical quality in terms of hue and color development.

[0058] The evaluation results are shown in Tables 1 to 3.

[0059] Each of the Examples and Comparative Examples had a semi-glossy finish. Furthermore, visual observation of the glossiness of the printed portion revealed that Examples 1 to 30 and Comparative Examples 1 to 5 and 10, which correspond to the present invention, were coated printing papers with a sufficient glossiness of the printed portion, whereas Comparative Examples 6 to 9 and 11 to 14 were not coated printing papers with a sufficient glossiness of the printed portion.

[0060] From Tables 1 to 3, it can be seen that Examples 1 to 30 corresponding to the present invention are coated printing papers having a glossy printed area, and good blister resistance, resistance to weak contrast, and golden red reproducibility. On the other hand, Comparative Examples 1 to 14, which do not satisfy the configuration of the present invention, are coated printing papers that do not satisfies any of the glossy printed area, blister resistance, resistance to weak contrast, and golden red reproducibility.

Claims

【Request 1】 The present invention relates to a paper having a base paper containing wood pulp and a filler, a first coating layer containing a white pigment and a binder on at least one side of the base paper, and a second coating layer containing a white pigment and a binder on the outer side of the first coating layer based on the base paper, the white pigment of the first coating layer containing heavy calcium carbonate and kaolin, the white pigment of the second coating layer containing light calcium carbonate, heavy calcium carbonate, kaolin and an organic pigment, and a white pigment having a white pigment content of 100% or more as defined by the CIE. ＊ a ＊ b ＊ L shown in the color system ＊ is 92.0 or more, a ＊ is 0.00 or more and 1.70 or less, and b ＊ A coated printing paper having a coefficient of variation (Rc) of -2.00 or more and 0.00 or less.

Images