JP7655876B2 - Coated paper for printing - Google Patents

Description

The present invention relates to coated printing paper suitable for multicolor offset web printing.

While printing machine manufacturers are announcing digital printing machines, the printing industry still uses offset printing machines 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. The recent trend, especially for catalogs and MOOK books, is to use printing coated paper with dull or semi-gloss finish and good gloss in the printed area. This type of coated printing paper provides clear print quality for photographs and pictures while also providing good visibility for text.

For example, a dull coated paper is known in which a base paper is provided with an undercoat layer and a topcoat layer containing a pigment and an adhesive, the base paper contains an organic compound that inhibits interfiber bonding of pulp, the undercoat layer contains 50 parts by weight or more of delaminated clay having a volume distribution average particle size of 3.5 to 20 μm per 100 parts by weight of pigment, the topcoat layer contains 70 parts by weight or more of kaolin having a volume distribution average particle size of 0.80 μm or less per 100 parts by weight of pigment, and the coated paper density is 1.00 g/ ^cm3 or less (see, for example, Patent Document 1). Such a dull coated paper is bulky and has a rough feel, yet has a high glossiness in the printed area and little minute gloss unevenness in the image area.

JP 2005-133278 A

There are two types of offset printing presses: sheet-fed and rotary. Rotary printing presses are characterized by high-speed, large-volume printing using rolled printing paper. Rotary offset 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 rotary printing is the phenomenon of blisters, in which moisture inside the printing paper and/or the solvent components in the ink that have permeated the inside of the printing paper are vaporized in the dryer and cannot escape completely, resulting in the printing paper swelling. Blisters are likely to occur when the paper is coated paper and/or when printing images with multiple colors or high color density.

In offset rotary printing presses, once the paper roll is loaded onto the press and transport begins, it cannot be redone, so printing paper must be capable of being printed on by the offset rotary printing press. Coated printing paper, which has a coating layer, has better printing performance than uncoated printing paper, as the coating layer improves smoothness and ink acceptance. On the other hand, offset rotary printing presses use a soft rubber blanket to transfer the ink to the printing paper and ensure sufficient ink adhesion 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 can cause the light and dark or color differences in the printed area to become blurred, weakening the contrast.

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

In view of the above, the object of the present invention is to provide a coated printing paper that has a glossy printed area, good blister resistance, low contrast resistance, and gold-red reproducibility.

As a result of intensive research by the inventors to solve the above problems, the object of the present invention is achieved as follows.
A coated printing 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, wherein the white pigment of the first coating layer contains heavy calcium carbonate and kaolin, and the white pigment of the second coating layer contains light calcium carbonate, heavy calcium carbonate, kaolin and an organic pigment, and wherein L ^* , as shown in the L ^* a ^* b ^* color system defined by the 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.

The present invention allows the coated printing paper to have good gloss in the printed area, resistance to blistering, resistance to low contrast, and golden red reproducibility.

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 a first coating layer on both sides of the base paper, and a 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.

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 purposes such as improving printability and interlayer strength. In at least one embodiment, there is no intermediate layer. The reason for this is that it is less expensive to manufacture.

The wood pulp is a pulp 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 papermaking factories.
In some embodiments, the base paper contains non-wood pulp that 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.

The freeness of the wood pulp is not particularly limited. The freeness is the CSF freeness determined in accordance with 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. This is because the strength and smoothness of the resulting base paper can be well balanced with dimensional stability.

The fillers are white pigments that are conventionally known in the papermaking field. Examples of fillers 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 resin, acrylic resin, vinyl acetate resin, olefin resin, vinyl chloride resin, urea resin, and melamine resin. Examples of organic pigments include microcapsules. The filler is one or more types selected from the group consisting of these.

In some embodiments, the base paper contains talc and light calcium carbonate as fillers. In at least one embodiment, the base paper contains talc and light calcium carbonate as fillers, and the total content of talc and light 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.

Talc is conventionally known in the papermaking art.
Talc is a layered clay mineral that exists as both naturally occurring and synthetic products, and has a basic structure in which a tetrahedral sheet of two-dimensionally continuous Si-O tetrahedra and an octahedral sheet of two-dimensionally continuous Mg-(OH) octahedra are sandwiched together in a ratio of 2:1, and is represented by the chemical formula Mg ₃ Si ₄ O ₁₀ (OH) _2. Talc also has the characteristics of cleavage, softness (Mohs hardness 1), and slipperiness due to the weak bonds between the layer units of the 2:1 sandwich. Clay minerals, including talc, generally carry an electric charge by partially replacing Mg2+ in the octahedral sheet with another metal ion having a different valence. In talc, Si ⁴⁺ in the tetrahedral sheet can be replaced with Al ³⁺ , or Mg ²⁺ in the octahedral sheet can be replaced with Fe ³⁺ , Fe ²⁺ , or Al ³⁺ . However, talc has a very small amount of substitution so that it is nearly electrically neutral and, as a result, has hydrophobic behavior.

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.

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 light calcium carbonate in the base paper of talc:light calcium carbonate = 6:4 to 4:6. The reason for this is that the blister resistance of the coated printing paper tends to improve.

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, UV absorbers, antioxidants, preservatives, mold inhibitors, water resistance agents, wet strength agents, and dry strength agents.

The base paper can be obtained by making a stock containing pulp, a filler, and, if necessary, various additives, using a conventional papermaking machine. Examples of papermaking machines include a Fourdrinier papermaking machine, a twin-wire papermaking machine, a combination papermaking machine, a cylinder papermaking machine, and a Yankee papermaking machine.

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 art of papermaking, and examples of surface sizing agents include various types of starch 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, optisizers, 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.

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.

There is no particular limitation on the method for providing coating layers such as the first coating layer, the second coating layer, and the backcoat layer on the base paper. For example, the method may involve 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 that uses microwaves, etc.

At each stage where a first coating layer is applied to the base paper and/or a second coating layer is applied to the first coating layer, the printing coated paper can be subjected to a calendaring process. The equipment used for the calendaring process is the same as that described above.

In some embodiments, the coated printing paper has a coating weight of the first coating layer of 5 g/ ^m2 or more and 10 g/ ^m2 or less in terms of dry solids. Also, in some embodiments, the coated printing paper has a coating weight of the second coating layer of 4 g/m2 or ^more and 9 g/ ^m2 or less in terms of dry solids. In at least one embodiment, the coated printing paper has a coating weight of the first coating layer of 5 g/m2 or ^more and 10 g/ ^m2 or less in terms of dry solids and a coating weight of the second coating layer of 4 g/m2 or ^more and 9 g/ ^m2 or less in terms of dry solids, 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.

The first coating layer and the second coating layer contain a white pigment and a binder.
The white pigment is a well-known one 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.

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.

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. Its shape is non-uniform and the particle size distribution range is generally relatively wide. Heavy calcium carbonate also has a smaller apparent specific gravity and specific surface area than light calcium carbonate.

Kaolin is conventionally known in the papermaking art.
Kaolin is a clay mineral that generally consists mainly of Al ₂ O _{3.2SiO 2.2H 2} O and has 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, for example, through processes such as crushing, washing, iron removal, and classification. Kaolin also includes highly processable kaolins such as delaminated kaolin, which is made into a thin plate shape 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 improved cohesion. Kaolin is a plate-shaped particle, and the flat parts of the particles are usually negatively charged and the edges are positively charged.

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 the low-contrast resistance and/or gold-red reproducibility of the coated paper for printing is improved. The hollow organic pigment is an organic pigment having one or more voids (hollow) inside the particle.

In some embodiments, the first coating layer has a content mass ratio of heavy calcium carbonate to kaolin in the first coating layer of heavy calcium carbonate:kaolin=65:35 to 85:15. In some embodiments, the second coating layer has a content mass of light calcium carbonate, heavy calcium carbonate, kaolin and organic pigment in the second coating layer 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 gold red reproducibility of the coated printing paper are improved.
In at least one embodiment, the first coating layer has a content 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 content 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.

The binder is a water-dispersible binder or a water-soluble binder 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 of these, 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 versions of these, soy protein, natural polymer resins such as pullulan, gum arabic, karaya gum, and albumin, or derivatives of these, sodium alginate, and maleic acid-based resins.

In some embodiments, the binder of the first coating layer is a combination of starch and styrene-butadiene copolymer resin. Also, 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 to 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.

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 relative to 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 relative to 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 mass or more and 15 parts by mass or less per 100 parts by mass of the white pigment in the first coating layer, and the content of the binder in the second coating layer is 8 parts by mass or more and 28 parts by mass or less per 100 parts by mass of the white pigment in the second coating layer.

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

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.
Fluorescent brighteners are compounds that absorb invisible ultraviolet light and convert it into visible bluish-white light (fluorescence), and are additives for increasing the apparent whiteness of paper. In a coating layer that contains a fluorescent brightener, the fluorescence of the fluorescent brightener increases the apparent whiteness of the paper. The inventors have found, through trial and error, that by including a fluorescent brightener in the second coating layer, the low contrast resistance of coated printing paper can be achieved. In other words, coated printing paper that contains a fluorescent brightener in the second coating layer can not only increase the apparent whiteness, but also achieve low contrast resistance.

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 wood pulp and white pigments such as kaolin are not strictly white but slightly colored, the colorant is adjusted to match the wood pulp and white pigment. In addition, the base paper, the first coating layer, and/or the second coating layer contain a colorant, and in combination 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, the printing coated paper can have an L ^* of 92.0 or more, an a ^{* of 0.00 to 1.70, and a b* of} -2.00 to 0.00 in the L ^* a ^* b ^* color system defined by the CIE.
In the L ^* a ^* b ^* color system defined by the CIE, L ^* indicates brightness, positive a ^* indicates red chromaticity, negative a ^* indicates green chromaticity, and positive b ^* indicates yellow chromaticity and negative b ^* indicates blue chromaticity. Coated printing paper with L ^* a ^* b ^* in the above range has high brightness and a pale gray color. Coated printing paper with L ^* a ^* b ^* in the above range can obtain low contrast resistance and gold red reproducibility resistance.

In some embodiments, the coated printing paper has a 75 degree specular gloss of 35% or more and 75% or less based on ISO 8254-1:1999 "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 finish.
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.

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 relative to the base paper, wherein the white pigment of the first coating layer contains ground calcium carbonate and kaolin, the white pigment of the second coating layer contains light calcium carbonate, ground calcium carbonate, kaolin and an organic pigment, and L ^* , as shown in the L ^* a ^* b ^* color system defined by the 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, and the second coating layer further contains a fluorescent whitening agent.

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, relative to 100 parts by mass of the white pigment in the second coating layer, from 35 to 55 parts by mass of light calcium carbonate, from 18 to 38 parts by mass of heavy calcium carbonate, from 10 to 30 parts by mass of kaolin, and from 4 to 16 parts by mass of the organic pigment, and L ^* , as shown in the L ^* a ^* b ^* color system defined by CIE, is 92.0 or more, a ^* is 0.00 to 1.70, and b ^* is −2.00 to 0.00.

In at least one embodiment, a 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 comprises 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, relative to 100 parts by mass of the white pigment in the second coating layer, from 35 to 55 parts by mass of light calcium carbonate, from 18 to 38 parts by mass of heavy calcium carbonate, from 10 to 30 parts by mass of kaolin, and from 4 to 16 parts by mass of the organic pigment, and L ^* , as shown in the L ^* a ^* b ^* color system defined by CIE, is 92.0 or more, a ^* is 0.00 to 1.70, and b ^* is −2.00 to 0.00, and the second coating layer further contains a fluorescent whitening agent.

The present invention will be described in more detail below with reference to examples. Note that 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.

The coated printing papers of the examples and comparative examples were prepared according to the following procedure.

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

The above-mentioned paper material was made into paper by a fourdrinier paper machine, and starch was used as a surface sizing agent and coated on both sides by a size press. The coating amount was adjusted to 1 g/ ^m2 . After the size press, a calendering process was performed to obtain a base paper with a basis weight of 55 g/ ^m2 .

<Coating solution for first coating layer>
The coating layer coating solution was prepared according to the following ingredients.
White pigment: type and parts are shown in Tables 1 to 3 Starch: 3 parts by weight SBR: 7 parts by weight Lubricant (calcium stearate): 0.4 parts by weight Polyamide-based printability improver: 0.5 parts by weight Colorant: as needed The above contents were blended, mixed and dispersed in water to adjust the concentration to 60% by weight.

<Coating liquid for second coating layer>
The coating layer coating solution was prepared according to the following ingredients.
White pigment: type and number of parts are shown in Tables 1 to 3. PVA 2 parts by weight SBR 18 parts by weight Fluorescent brightening agent 0 parts by weight/0.3 parts by weight Lubricant (calcium stearate) 0.4 parts by weight Polyamide-based printability improver 0.5 parts by weight Colorant as appropriate The above contents were blended, mixed and dispersed in water to adjust the concentration to 46% by weight.

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

<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. The coating solution for the second coating layer was then 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 conditions were adjusted so that the coating weight of the first coating layer was 8 g/ ^m2 and the coating weight of the second coating layer was 7 g/ ^m2 .

The resulting coated printing paper was evaluated for the following items:

<Blister resistance>
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), four-color (CMYK) printing was performed on one side of the printing coated paper. 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 printing coated paper where the printing was stable. For printing, evaluation images were used in which CMYK, red, blue, and green solid images, as well as gold and red solid images, portrait images, landscape images, and character 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, if the printing coated paper is rated A or B, it is considered to have good blister resistance.
A: Blisters are hardly observed.
B: Although not blisters, slight swelling is observed.
C: worse than B above, slight presence of blisters observed.
D: Worse than C above, with the presence of blisters observed.

<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 was performed at a printing speed of 300 m/min and a paper surface temperature of 120° C. at the dryer outlet, and the observation was performed on 1000 m of the 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 weak contrast resistance was evaluated sensorily by visually observing the difference in brightness and vividness of the image in the obtained print, according to 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 light and dark 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.

<Gold and red reproduction>
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 was performed at a printing speed of 300 m/min and a paper surface temperature of 120° C. at the dryer outlet, and observation was 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-red solid image, a portrait image, a landscape photo 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 problem 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.

The evaluation results are shown in Tables 1 to 3.

Each example and comparative example had a semi-glossy finish. In addition, visual observation of the gloss of the printed area showed 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 gloss of the printed area, while Comparative Examples 6 to 9 and 11 to 14 were not coated printing papers with a sufficient gloss of the printed area.

From Tables 1 to 3, it can be seen that Examples 1 to 30, which correspond to the present invention, are coated printing papers that have a glossy printed area, good blister resistance, resistance to weak contrast, and gold-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 following: glossy printed area, blister resistance, resistance to weak contrast, and gold-red reproducibility.

Claims (1)

A coated printing 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, wherein the white pigment of the first coating layer contains heavy calcium carbonate and kaolin, and the white pigment of the second coating layer contains light calcium carbonate, heavy calcium carbonate, kaolin and an organic pigment, and wherein L ^* , as shown in the L ^* a ^* b ^* color system defined by the 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.