Coated paper for printing

Abstract

To provide coated paper for printing which has an excellent effect of suppressing printing ink bleed through and a paper breakage suppressing effect despite having a low basis weight.SOLUTION: There is provided coated paper for printing, comprising: base paper; an undercoating layer laminated on at least one side of the base paper; and a coating layer containing a white pigment. Raw material pulp contains bleached hardwood kraft pulp, bleached softwood kraft pulp, and disintegrated and deinked waste paper pulp, the undercoating layer contains starch and a sizing agent, the coating layer contains a white pigment, the white pigment contains calcium carbonate, first kaolin and second kaolin, a content of calcium carbonate in the white pigment is 45 mass% or more and 70 mass% or less, a content of the first kaolin in the white pigment is 10 mass% or more and 20 mass% or less, a content of the second kaolin in the white pigment is 10 mass% or more and 35 mass% or less, a basis weight is less than 50 g / m2, and a value obtained by dividing a printing opacity by the basis weight is 1.70 [% m2 / g] or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to coated printing paper. [Background technology]

[0002] Coated printing paper is becoming lighter in weight in order to conserve resources and reduce transportation costs. One way to reduce weight is to reduce the base paper weight, but this reduces the base paper thickness, which can lead to the problem of ink seepage in full-color printed matter. 2 More than 50g / m 2 Less than 20g / m 2 More than 40g / m 2 In order to prevent print ink from striking through in coated paper with a thickness of less than 100 mm, a technique has been proposed in which the pulp used in the base paper contains mechanical pulp with high opacity (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-154951 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when mechanical pulp with a high pitch content is blended as in the above-mentioned conventional technology, a decrease in strength occurs in the pitch portion, and the strength-reduced portion around the pitch may break, causing the paper to break during papermaking or printing. In this field of coated printing paper, even if the paper is made lighter, it is required to have a level of strength that makes it difficult for printing ink to strike through in the printed matter after printing and makes it difficult for the paper to break during papermaking or printing.

[0005] The present invention has been made based on the above circumstances, and has a basis weight of 50 g / m 2The object of the present invention is to provide a coated printing paper which, despite having a basis weight of less than 100 g / m2, is excellent in preventing print ink from striking through and in preventing paper breakage. [Means for solving the problem]

[0006] A coated printing paper according to one embodiment of the present invention comprises a base paper mainly composed of raw pulp, an under-coating layer laminated on at least one side of the base paper, and a coating layer laminated on the surface of the under-coating layer and containing a white pigment, the raw pulp containing hardwood bleached kraft pulp, softwood bleached kraft pulp and disintegrated and deinked waste paper pulp, the under-coating layer containing starch and a sizing agent, the coating layer containing a white pigment, the white pigment containing calcium carbonate, a first kaolin and a second kaolin, and the first kaolin containing a second kaolin. the aspect ratio of the first kaolin is 15 or more and 25 or less, and the average particle size is 2.0 μm or more and less than 3.0 μm, the aspect ratio of the second kaolin is 5 or more and 15 or less, and the average particle size is 2.5 μm or more and 4.0 μm or less, the content of the calcium carbonate in the white pigment is 45% by mass or more and 70% by mass or less, the content of the first kaolin in the white pigment is 10% by mass or more and 20% by mass or less, the content of the second kaolin in the white pigment is 10% by mass or more and 35% by mass or less, and the basis weight is 50 g / m 2 The print opacity divided by the basis weight is less than 1.70[% m 2 / g] or more. Effect of the Invention

[0007] According to the invention, the basis weight is 50 g / m 2 This makes it possible to provide a coated printing paper that is excellent in preventing print ink from striking through and in preventing paper breakage, despite having a basis weight of less than 100 g / m2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Description of the embodiment of the present invention] A coated printing paper according to one embodiment of the present invention comprises a base paper mainly composed of raw pulp, an under-coating layer laminated on at least one side of the base paper, and a coating layer laminated on the surface of the under-coating layer and containing a white pigment, the raw pulp containing hardwood bleached kraft pulp, softwood bleached kraft pulp and disintegrated and deinked waste paper pulp, the under-coating layer containing starch and a sizing agent, the coating layer containing a white pigment, the white pigment containing calcium carbonate, a first kaolin and a second kaolin, and the first kaolin containing a second kaolin. the aspect ratio of the first kaolin is 15 or more and 25 or less, and the average particle size is 2.0 μm or more and less than 3.0 μm, the aspect ratio of the second kaolin is 5 or more and 15 or less, and the average particle size is 2.5 μm or more and 4.0 μm or less, the content of the calcium carbonate in the white pigment is 45% by mass or more and 70% by mass or less, the content of the first kaolin in the white pigment is 10% by mass or more and 20% by mass or less, the content of the second kaolin in the white pigment is 10% by mass or more and 35% by mass or less, and the basis weight is 50 g / m 2 The print opacity divided by the basis weight is less than 1.70[% m 2 / g] or more.

[0009] The coated printing paper contains bleached hardwood kraft pulp, bleached softwood kraft pulp, and disintegrated and deinked waste paper pulp, and has a basis weight of 50 g / m2. 2 Despite the fact that the thickness of the coated printing paper is less than 100 μm, the strength of the base paper is improved, and the coated printing paper is more effectively prevented from breaking during papermaking or printing. In addition, high opacity is ensured, and the coated printing paper contributes to the effective use of resources and reduces costs. By providing the coated printing paper with an undercoating layer, the flatness, printability, etc. of the coated printing paper can be improved. The coating layer contains a white pigment, which allows the printing coated paper to have good whiteness and improves the effect of suppressing print ink from striking through while allowing ink to penetrate the coating layer. The white pigment contains calcium carbonate, a first kaolin, and a second kaolin, and the first kaolin has an aspect ratio of 15 to 25 and an average particle size of 2.0 μm to less than 3.0 μm, the second kaolin has an aspect ratio of 5 to 15 and an average particle size of 2.5 μm to 4.0 μm, the white pigment contains calcium carbonate at 45% by mass to 70% by mass, and the white pigment contains first kaolin at 10% by mass to 20% by mass, thereby improving the whiteness and the effect of suppressing print ink from striking through. The content of the second kaolin in the white pigment is preferably from 10% by mass to 35% by mass, which can enhance prevention of print ink from striking through. Print opacity divided by basis weight is 1.70[% m 2 / g] or more, the effect of suppressing print ink from striking through to the back can be improved. Therefore, the printing coated paper has a basis weight of 50 g / m 2 Despite its low basis weight of less than 100 g / m2, it has excellent effects of suppressing print ink strike-through and paper breakage.

[0010] The "aspect ratio" refers to the shape of an inorganic particle, and is the ratio of its major axis (longest axis) to its thickness (shortest axis). The above aspect ratio is obtained by measuring the major axis (longest axis) and thickness (shortest axis) for each particle, dividing the major axis by the thickness for each particle, and calculating the average. The aspect ratio can be obtained, for example, by particle image analysis using a laser diffraction / scattering particle distribution measuring device, "LA 950" manufactured by Horiba, Ltd., or by photographing powder particles with an electron microscope and dividing the major axis by the thickness for 500 randomly selected particles to obtain the average value. The "average particle size" can be measured by a laser diffraction / scattering method using, for example, "LA 950" manufactured by Horiba or "MT3300" manufactured by Microtrack Bell. The median diameter (D 50 ) is defined as the "average particle size."

[0011] In the coated printing paper, the content of disintegrated and deinked waste paper pulp relative to the total pulp in the base paper is preferably 10% by mass or more and 50% by mass or less. By having the content of disintegrated and deinked waste paper pulp relative to the total pulp in the base paper be 10% by mass or more and 50% by mass or less, opacity can be further improved.

[0012] [Details of the embodiment of the present invention] The present invention will be described in detail below. The following description of the components may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments.

[0013] <Coated paper for printing> The coated printing paper comprises a base paper, an undercoating layer laminated on at least one side of the base paper, and a coating layer laminated on the surface of the undercoating layer and containing a white pigment.

[0014] [Base paper] The base paper is mainly composed of raw pulp. The base paper may be a single layer or multiple layers. The base paper preferably contains a sizing agent. By containing a sizing agent, the base paper can effectively prevent the coated printing paper from breaking during papermaking or printing.

[0015] (Raw pulp) The raw pulp contains bleached softwood kraft pulp (NBKP), bleached hardwood kraft pulp (LBKP) and disintegrated and deinked waste paper pulp.

[0016] Hardwood bleached kraft pulp (LBKP) is produced from eucalyptus or acacia wood. By blending hardwood bleached kraft pulp, the texture becomes good, the paper strength becomes stable, and the printability becomes better. The lower limit of the content of hardwood kraft pulp (LKP) relative to the total pulp components is 30% by mass, and preferably 35% by mass. On the other hand, the upper limit of the content of hardwood kraft pulp (LKP) relative to the total pulp components is 75% by mass, and preferably 70% by mass. By having the content of hardwood bleached kraft pulp be 30% by mass or more and 75% by mass or less, the texture becomes good, the paper strength becomes stable, and the printability becomes better.

[0017] In the case of bleached coniferous kraft pulp (NBKP), pines, such as radiata pine, are preferably used as the tree species. By blending bleached coniferous kraft pulp with long fiber length, the strength of the obtained paper can be ensured, and further, cushioning and drainage can be improved. The lower limit of the content of the coniferous kraft pulp (NKP) relative to the total pulp components is 10% by mass, and preferably 12% by mass. On the other hand, the upper limit of the content of the coniferous kraft pulp (NKP) relative to the total pulp components is 25% by mass, and preferably 23% by mass. By making the content of the bleached coniferous kraft pulp pulp 10% by mass or more and 25% by mass or less, the strength of the base paper can be improved.

[0018] Hardwood kraft pulp (LKP) has short fiber length, which allows the gaps between the fibers of the resulting base paper to be relatively small. In contrast, softwood kraft pulp (NKP) has long fiber length, which allows the bonds between the fibers of the resulting base paper to be strengthened. Therefore, by making the base paper contain hardwood kraft pulp (LKP) and softwood kraft pulp (NKP) in the above ratio, the strength of the base paper is improved and the coated printing paper is excellent in preventing breakage.

[0019] In the coated printing paper, the content of bleached hardwood kraft pulp relative to the total pulp in the base paper is preferably 30% by mass or more and 75% by mass or less, and the content of bleached softwood kraft pulp relative to the total pulp in the base paper is preferably 10% by mass or more and 25% by mass or less. By having the contents of bleached hardwood kraft pulp and bleached softwood kraft pulp relative to the total pulp in the base paper within the above ranges, the strength of the base paper can be increased, and the effect of preventing paper breaks during papermaking or printing of the coated printing paper can be improved.

[0020] Disintegrated and deinked waste paper pulp (DIP) is broadly divided into fine and medium types. Fine waste paper pulp includes pulp prepared from waste paper such as white, ruled, card, imitation, colored, Kent, white art, and milk carton. Medium waste paper pulp includes pulp prepared from newspapers, magazines, cut-outs, medium waste rolls, brown imitation, corrugated cardboard, mounts, ground notes, and cardboard. In particular, fine waste paper pulp made from fine waste paper contains a large amount of inorganic filler derived from waste paper (filler that is still present in the raw pulp even after the deinking process), and since the inorganic filler derived from waste paper is fixed to the raw pulp, it can ensure high opacity. In addition, by making the content of disintegrated and deinked waste paper pulp in the total pulp of the above-mentioned base paper 10% to 50% by mass, the printing coated paper contributes to the effective use of resources and can reduce costs.

[0021] In the coated printing paper, the content of disintegrated and deinked waste paper pulp relative to the total pulp in the base paper is preferably 10% by mass or more and 50% by mass or less. By having the content of disintegrated and deinked waste paper pulp relative to the total pulp in the base paper be 10% by mass or more and 50% by mass or less, opacity can be improved.

[0022] (Internal sizing agent) By containing the internal sizing agent in the base paper, sinking of the paint during coating can be suppressed, and the paper breakage during papermaking and the paper breakage due to the influence of dampening water during printing can be effectively suppressed. As the internal sizing agent, a styrene-based sizing agent, an alkyl ketene dimer, an alkenyl succinic anhydride, a rosin sizing agent, a wax sizing agent, or a combination thereof is preferable. In particular, a rosin sizing agent is preferable from the viewpoint of obtaining sizing properties in a short aging period.

[0023] The amount of the internal sizing agent added is 0.20% by mass or more and 0.80% by mass or less in terms of solid content. By making the content of the sizing agent in the base paper within the above range, the amount of ink impregnated into the base paper during printing can be appropriately adjusted, so that the effect of suppressing print ink strike-through in the coated printing paper can be improved. Furthermore, the coated printing paper can effectively suppress paper breaks during papermaking or printing.

[0024] (Other additives) In addition to the pulp and sizing agent, other additives may be used as components of the base paper, if necessary. Examples of other additives that may be used include paper strength agents, fillers, coagulants, flocculants, defoamers, fluorescent dyes, aluminum sulfate, retention aids, drainage aids, wet strength agents, coloring dyes, dye fixing agents, coloring pigments, water resistance agents, etc. These additives may be used alone or in combination.

[0025] [Undercoating layer] The coated printing paper has an undercoating layer on the surface of the base paper on which the coating layer is laminated, thereby improving the flatness, printability, etc. of the coated printing paper. The undercoating layer contains starch and a sizing agent.

[0026] Examples of starch include enzyme-decomposed starch, oxidized starch, hydroxyethylated starch, cationic starch, urea phosphate starch, and modified oxidized starch, which are obtained by modifying raw starch such as corn, wheat, tapioca, and potato starch by various methods.

[0027] By containing a sizing agent, the undercoating layer can suppress sinking of the paint during coating, and effectively suppress paper breaks during papermaking and paper breaks due to the influence of dampening water during printing. As the surface sizing agent, a styrene-based sizing agent, an alkyl ketene dimer, an alkenyl succinic anhydride, a rosin sizing agent, a wax sizing agent, or a combination thereof is preferred. In particular, a styrene-based sizing agent is preferred from the viewpoint of obtaining sizing properties in a short aging period.

[0028] The amount of starch applied is 0.30 g / m2 in terms of solid content. 2 More than 1.0g / m 2 The following is preferred. By setting the coating amount of starch in the under-coating layer within the above range, the risk of paper breakage due to the paper becoming hard due to starch can be reduced.

[0029] The amount of surface sizing agent applied is 0.02 g / m2 in terms of solid content. 2 More than 0.10g / m 2 The following is preferred. By setting the coating weight of the surface sizing agent in the under-coating layer within the above range, the amount of ink impregnated into the base paper during printing can be appropriately adjusted, and therefore the effect of suppressing print ink strike-through in the coated printing paper can be improved. Furthermore, the coated printing paper can be effectively prevented from breaking during papermaking or printing.

[0030] [Coating layer] The coating layer is laminated on at least one side of the base paper. The coating layer contains a white pigment. When the coating layer contains a white pigment, the printing coated paper has good whiteness and has ink permeability into the coating layer, while improving the effect of suppressing print ink from striking through to the back. The coating layer may also contain a purple pigment, a blue pigment, and a fluorescent dye. When the coating layer contains a purple pigment, a blue pigment, and a fluorescent dye, the printing coated paper has better whiteness and can further improve the effect of suppressing print ink from striking through to the back.

[0031] (White pigment) The coating layer contains, as white pigments, a first kaolin having an aspect ratio of 15 or more and 25 or less, a second kaolin having an aspect ratio of 13, and calcium carbonate. Since the coating layer contains the first kaolin, the second kaolin, and calcium carbonate as white pigments, the penetration of printing ink into the coating layer is effectively suppressed, and strike-through of the printing ink can be effectively suppressed. The first kaolin and the second kaolin are clay minerals used for surface coating.

[0032] <No. 1 Kaolin> The lower limit of the aspect ratio of the first kaolin is 15. If the aspect ratio of the first kaolin is less than 15, there is a risk that sufficient ink strike-through suppression effect cannot be obtained. On the other hand, the upper limit of the aspect ratio of the first kaolin is 25. If the aspect ratio of the first kaolin exceeds 25, the permeability is impaired, so that the ink drying property during printing is deteriorated, and blocking may occur. In the coating layer of the printing coated paper, by including the first kaolin having a large aspect ratio of 15 to 25 and a high flatness, the ink during printing remains on the surface of the coating layer, improving the print density and print gloss, and also improving the effect of suppressing the print ink strike-through. As the first kaolin, from the viewpoint of high whiteness and high aspect ratio, delaminated kaolin (flat kaolin) is preferable.

[0033] The lower limit of the average particle size of the first kaolin is 2.0 μm, preferably 0.5 μm. Meanwhile, the upper limit of the average particle size of the first kaolin is 3.0 μm, preferably 5.0 μm. By having the average particle size of the first kaolin in the above range, the ink drying property and printing gloss of the printing coated paper can be improved.

[0034] The lower limit of the content of the first kaolin relative to the white pigment in the coating layer is 10% by mass, preferably 12% by mass. Meanwhile, the upper limit of the content of the first kaolin relative to the white pigment is 20% by mass, preferably 18% by mass. When the content of the first kaolin relative to the white pigment is less than 10% by mass, the ink drying property is improved, but the print gloss and the effect of suppressing print ink from striking through may be reduced. Meanwhile, when the content of the first kaolin relative to the white pigment exceeds the upper limit, the ink drying property is deteriorated during printing, and blocking may occur, resulting in a deterioration in print quality.

[0035] <No. 2 Kaolin> The lower limit of the aspect ratio of the second kaolin is 5, and preferably 6. On the other hand, the upper limit of the aspect ratio of the second kaolin is 15, and preferably 14. By including the second kaolin having an aspect ratio of 5 or more and 15 or less, it is possible to prevent ink sinking during printing and to increase print opacity.

[0036] The lower limit of the average particle size of the second kaolin is 2.5 μm, preferably 2.7 μm. Meanwhile, the upper limit of the average particle size of the second kaolin is 4.0 μm, preferably 3.8 μm. By having the average particle size of the second kaolin in the above range, it is possible to prevent ink sinking during printing and to increase print opacity.

[0037] The lower limit of the content of the second kaolin relative to the white pigment in the coating layer is 10% by mass, and more preferably 22% by mass. Meanwhile, the upper limit of the content of the second kaolin relative to the white pigment is 35% by mass, and preferably 33% by mass. If the content of the second kaolin relative to the white pigment is less than 10% by mass, the printing ink may sink quickly during printing, and sufficient ink strike-through prevention effect may not be obtained. On the other hand, if the content of the second kaolin relative to the white pigment is more than 35% by mass, the ink permeability of the printing ink may be impaired, and the ink drying property during printing may be deteriorated, and blocking may occur.

[0038] <Calcium carbonate> By including calcium carbonate in the coating layer, the ink drying properties are excellent, and bleeding and unevenness in printing are suppressed, resulting in good print quality.

[0039] The lower limit of the content of the calcium carbonate relative to the white pigment in the coating layer is 45% by mass, preferably 50% by mass. Meanwhile, the upper limit of the content of the calcium carbonate relative to the white pigment is 70% by mass, preferably 68% by mass. If the content of the calcium carbonate relative to the white pigment is less than the lower limit, the effect of suppressing print ink strike-through may be reduced. On the other hand, if the content of the calcium carbonate relative to the white pigment is more than the upper limit, the absorbency of the print ink may be reduced, resulting in a low print density.

[0040] The coating layer may contain other white pigments other than calcium carbonate and kaolin. The other pigments are not particularly limited, and examples thereof include white pigments such as titanium dioxide. These may be used alone or in combination of two or more. The content of the other pigments is preferably 5% by mass or less relative to 100% by mass of the white pigment.

[0041] (Fluorescent dye) The coating layer preferably contains a fluorescent dye. The fluorescent dye can color the coating layer and improve the whiteness. As the fluorescent dye, for example, a stilbene-based, benzimidazole-based, imidazole-based, imidazolone-based, pyrazoline-based, coumarin-based, or naphthalimide-based dye can be used.

[0042] The content of the fluorescent dye in the coating layer is preferably 0.10 to 0.25 parts by mass, more preferably 0.12 to 0.20 parts by mass, per 100 parts by mass of the white pigment. By keeping the content of the fluorescent dye within the above range, the whiteness of the coated printing paper and the effect of suppressing printing unevenness can be improved.

[0043] (Purple and blue pigments) The coating layer preferably contains a blue pigment and a purple pigment. By containing the blue pigment and the purple pigment, the coating layer can improve the effect of suppressing strike-through during printing and the effect of suppressing uneven printing. The blue pigment and the purple pigment may be either inorganic or organic. The purple pigment and the blue pigment have better light resistance than dyes, and are highly effective in suppressing discoloration and coloring of the paper over time.

[0044] As the blue pigment and the purple pigment, both inorganic and organic pigments can be used. Specific examples of blue pigments include ultramarine, azurite, Prussian blue, ultramarine, smalt, cobalt blue (cobalt aluminate), cerulean blue (cobalt stannate), cobalt chrome blue, cobalt aluminum silicon oxide, cobalt zinc silicon oxide, manganese blue, and phthalocyanine. Specific examples of purple pigments include inorganic pigments such as cobalt violet (cobalt arsenate, cobalt phosphate, cobalt lithium phosphorus oxide, ammonium cobalt phosphate hydrate, cobalt borate, etc.), purple ultramarine, iron oxide purple, manganese violet, and mineral violet, and organic pigments such as indigoid, quinacridone, oxazine, anthraquinone, carbonium, and xanthene.

[0045] The coating amount of the blue pigment in the coating layer is 0.5 mg / m 2 More than 4.0mg / m 2 Less than 1.5 mg / m is preferred. 2 More than 3.8mg / m 2 The coating amount of the purple pigment is preferably 3.0 mg / m or less. 2 More than 7.5mg / m 2 Less than 4.0 mg / m is preferred. 2 More than 6.5mg / m 2 The coating amount of the blue pigment in the coating layer is preferably 0.5 mg / m or less. 2 More than 4.0mg / m 2 The coating weight of the purple pigment is 3.0 mg / m or less. 2 More than 7.5mg / m 2 By satisfying the above condition, the opacity can be improved, the effect of suppressing print-through during printing can be enhanced, and printing unevenness can be further suppressed. The above content was quantified using the following calculation formula. Total content of blue or purple pigment (mg / m 2 )=(total coating amount (g / m 2 ) × total mass parts of blue pigment or purple pigment (mass parts) / total mass parts of solids in coating liquid (mass parts) × 1000 The above parts by mass are values ​​calculated on a solid content basis.

[0046] (binder) The coating layer preferably contains a binder. The binder for the coating layer is not particularly limited, and examples thereof include starch derivatives such as cationic starch, etherified starch, phosphate-esterified starch, hydroxyethyl-etherified starch, and carbamic acid-esterified starch; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; casein, gelatin, soy protein, polyvinyl alcohol or a derivative thereof; polyvinylpyrrolidone, maleic anhydride resin, conjugated diene copolymer latexes such as styrene-butadiene copolymers and methyl methacrylate-butadiene copolymers; acrylic polymer latexes such as polymers or copolymers of acrylic acid esters and methacrylic acid esters; vinyl polymer latexes such as ethylene-vinyl acetate copolymers; and cationic groups are used in these various polymers to form cationic polymers. Examples of the latex include ionized latex, latex with the polymer surface cationized by a cationic surfactant, latex polymerized under cationic polyvinyl alcohol and the cationic vinyl alcohol distributed on the polymer surface, and latex polymerized in a suspension dispersion of cationic colloidal particles and the cationic colloidal particles distributed on the polymer surface; water-based adhesives such as thermosetting synthetic resins such as melamine resins and urea resins; polymers or copolymers of acrylic acid esters and methacrylic acid esters such as polymethyl methacrylate; synthetic resin adhesives such as polyurethane resins, unsaturated polyester resins, vinyl chloride-vinyl acetate copolymers, polyvinyl butyral, and alkyd resins, and these can be used alone or in combination of two or more. Among these, from the viewpoint of cost-effectiveness, a combination of a highly versatile styrene-butadiene copolymer latex and a starch derivative (SBR) is preferably used. In addition, the glass transition temperature of the styrene-butadiene copolymer is preferably low so that it can have excellent flexibility, and can be, for example, less than 0°C.

[0047] The lower limit of the content of the binder in the coating layer (based on solid content) is preferably 5 parts by mass, more preferably 6 parts by mass, per 100 parts by mass of the white pigment. On the other hand, the upper limit of the content of the binder in the coating layer is preferably 20 parts by mass, more preferably 15 parts by mass, per 100 parts by mass of the white pigment. If the content of the binder in the coating layer is less than the lower limit, the strength of the coating layer may not be sufficient. On the other hand, if the content of the binder in the coating layer exceeds the upper limit, the adhesion in the coating layer may increase, and blocking, sticking, etc. may occur in the manufacturing process. On the other hand, if the content of the binder is within the above range, the physical properties such as the strength and adhesion of the coating layer can be suitably adjusted.

[0048] In addition to the white pigment, purple pigment, blue pigment, fluorescent dye, and binder, additives such as pigment dispersants, thickeners, flow improvers, defoamers, foam inhibitors, lubricants, release agents, foaming agents, penetrating agents, ultraviolet absorbers, antioxidants, preservatives, antifungal agents, water-resistant agents, dyes, and fixing agents may be appropriately blended into the above-mentioned coating layer (coating liquid) as required.

[0049] The lower limit of the coating amount (solid content equivalent) on both sides of the coating layer is 10.0 g / m 2 On the other hand, the upper limit of the coating amount (in terms of solid content) of the coating layer is 20.0 g / m 2 is preferred, and 18.0 g / m 2 If the coating weight of the coating layer is less than the lower limit, sufficient printability may not be obtained. On the other hand, if the coating weight of the coating layer is more than the upper limit, the flexibility may decrease due to hardening of the coating layer, and the processability of the coated printing paper may decrease.

[0050] [Physical properties of coated printing paper] (Basic weight) "Basis weight" is a value measured in accordance with JIS-P-8124 (2011). The upper limit of the basis weight of the printing coated paper is 50.0 g / m 2 Less than 49.0 g / m 2More preferably, 48.0 g / m 2 It is more preferable that the lower limit of the basis weight of the coated printing paper is 50.0 g / m 2 This allows the coated printing paper to be lighter. The lower limit of the basis weight of the coated printing paper is 40.0 g / m 2 It is preferable that the lower limit of the basis weight of the coated printing paper is 40.0 g / m 2 This makes it possible to achieve both the effect of suppressing print ink strike-through and the effect of suppressing paper breakage.

[0051] (Knob size) The Cobb sizing degree in the present invention is a value measured by contacting the surface of the base paper with water for 60 seconds in accordance with JIS-P8140 (1998). The Cobb sizing degree can be adjusted by the content of the sizing agent in the base paper. The lower limit of the Cobb sizing degree of the coated printing paper is 30 g / m 2 is preferred, and 35 g / m 2 On the other hand, the upper limit of the Cobb sizing degree of the printing coated paper is 60 g / m 2 is preferred, and 55 g / m 2 20 seconds is more preferable. Cob size is 30g / m 2 By setting the Cobb sizing degree of the printing coated paper at 60 g / m or more, excessive penetration of the printing ink can be suppressed, and the effect of suppressing the print-through of the printing ink can be improved. 2 By satisfying the above condition, it is possible to improve the effect of suppressing paper breaks and printing unevenness during paper making.

[0052] The printing coated paper has a basis weight of 50 g / m 2 Despite its low basis weight of less than 100 g / m2, it has excellent effects of suppressing print ink strike-through and paper breakage.

[0053] [Manufacturing method of coated printing paper] The method for producing the coated printing paper includes, for example, a step of laminating an under-coating layer on at least one side of a base paper mainly composed of raw pulp, and a step of laminating a coating layer on the surface of the under-coating layer. Other steps preferably include, for example, a step of making a raw pulp slurry and subjecting it to a press part and a pre-drier part to produce a base paper, and a step of carrying out a calendaring process. Furthermore, the method may include a step of carrying out a surface treatment on the surface of the base paper, followed by drying and flattening.

[0054] In the step of laminating the undercoating layer and the coating layer, from the viewpoint of being able to apply a large coating weight, for example, a blade coater is used as a coating device for applying the coating liquid.

[0055] As the calendering device in the calendering step, various calenders such as a super calender, a gross calender, a soft compact calender, etc., which are a combination of a metal or drum and an elastic roll, can be used appropriately in on-machine or off-machine specifications.

[0056] In the manufacturing method of the coated printing paper, the raw pulp contains bleached hardwood kraft pulp, bleached softwood kraft pulp and disintegrated and deinked waste paper pulp, the coating liquid of the undercoating layer contains starch and a sizing agent, and the coating liquid of the coating layer contains a white pigment. The white pigment further comprises calcium carbonate, a first kaolin, and a second kaolin, the first kaolin having an aspect ratio of 15 to 25 and an average particle size of 2.0 μm to less than 3.0 μm, the second kaolin having an aspect ratio of 5 to 15 and an average particle size of 2.5 μm to 4.0 μm, the content of the calcium carbonate in the white pigment is 45% by mass to 70% by mass, the content of the first kaolin in the white pigment is 10% by mass to 20% by mass, the content of the second kaolin in the white pigment is 10% by mass to 35% by mass, and a value obtained by dividing the print opacity by basis weight is 1.70 [% m 2Thus, the method for producing the coated printing paper includes a step of laminating an undercoating layer and a coating layer by a blade coater, and the base paper contains bleached hardwood kraft pulp, bleached softwood kraft pulp, and disintegrated and deinked waste paper pulp, and the compositions of the coating fluid of the undercoating layer and the coating fluid of the coating layer are as described above, so that the basis weight is 50 g / m or more. 2 This makes it possible to reliably produce coated printing paper that is excellent in preventing print ink from striking through and in preventing paper breakage, despite having a basis weight of less than 100 g / m2.

[0057] <Other embodiments> The present invention is not limited to the above-described embodiment, and can be embodied in various other forms in addition to the above-described forms with various modifications and improvements. EXAMPLES

[0058] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0059] [Example 1] (Base paper) A pulp slurry containing hardwood bleached kraft pulp, softwood bleached kraft pulp, and disintegrated and deinked waste paper pulp in the amounts shown in Table 1 was added with an internal sizing agent (rosin sizing agent ``NS75P'' manufactured by Harima Chemical Co., Ltd.) in the amount shown in Table 1 to prepare a base paper.

[0060] (Undercoating layer) Next, a coating liquid for the undercoating layer, containing starch and a styrene-based surface sizing agent ("SE2066" manufactured by Seiko PMC Corporation), was applied to both sides of the base paper in the amount shown in Table 1, and the resulting layer was dried with a dryer to form an undercoating layer.

[0061] (Coating layer) Next, on both sides of the base paper after the undercoating layer was formed, a coating liquid containing the first kaolin ("HC Clay" manufactured by Imerys) with an aspect ratio of 15 to 25 as a white pigment in the amounts shown in Table 2, the second kaolin ("Hydresperse" manufactured by KaMin) with an aspect ratio of 13, calcium carbonate (manufactured by Onsite), a blue pigment ("SA Blue 12422" manufactured by Mikuni Sekiso Co., Ltd.), a purple pigment ("SA Violet BOX" manufactured by Mikuni Sekiso Co., Ltd.), a fluorescent dye ("Kayahole SIM(L)" manufactured by Nippon Kayaku Co., Ltd.), and latex ("PB-8900" manufactured by Nippon A&L Co., Ltd.) and starch ("RC#20" manufactured by Nippon Shokuhin Kako Co., Ltd.) as binders was applied at a rate of 15.0 g / m on both sides. 2 (solid content equivalent) was applied by blade coating method. The basis weight was 46.2 g / m 2 The average particle size [μm] of the white pigment shown in Table 2 was obtained by calculating the average value of 100 particles using a laser diffraction / scattering type particle size distribution measuring device (Microtrack Bell's "MT3300").

[0062] The amounts of the additives described above were calculated as solid amounts relative to the bone dry pulp amount. The amount of coating on each side of the coating layer was approximately half the amount of coating on both sides.

[0063] [Examples 2 to 7 and Comparative Examples 1 to 6] The content of the sizing agent in the base paper, the starch and surface sizing agent in the undercoating layer, and the types, content ratios, and coating amounts of the white pigment, blue pigment, purple pigment, fluorescent dye, and binder in the coating layer are shown in Tables 1 and 2. Furthermore, the basis weight of the coated printing papers was set as shown in Table 3, and coated printing papers of Examples 2 to 7 and Comparative Examples 1 to 6 were obtained. The fine kaolin used was "Kaofine" manufactured by Seal Co., Ltd.

[0064] The configurations of the coated printing papers of Examples 1 to 7 and Comparative Examples 1 to 6 are shown in Tables 1 and 2 below.

[0065] [Table 1]

[0066] [Table 2]

[0067] [evaluation] The resulting coated printing papers were evaluated by the following methods.

[0068] (Basic weight) Basis weight (g / m 2 ) was measured in accordance with JIS-P-8124 (2011) "Paper and paperboard -- Determination of basis weight."

[0069] (Opacity) The opacity [%] was measured according to the method described in JIS-P8148 (2001) "Paper, paperboard and pulp - Measurement method for ISO whiteness (diffuse blue light reflectance)". An opacity of 85.0% or more is considered good.

[0070] (print opacity) Printing was carried out on coated printing paper under the following conditions to prepare print test specimens, and the print opacity was measured. (1)Printing machine ``RI-3 type'' manufactured by Mei Seisakusho Co., Ltd. (2) Ink "WebRex IMPACT BLACK" manufactured by Dainichi Seika Chemicals (3) Amount of ink 0.5ml on the top roll (4) Test method The ink was mixed for 3 minutes on the upper roll and the lower roll (after mixing for 2 minutes, the rolls were reversed and mixed for an additional minute), and the first print was made at an impression cylinder rotation speed of 30 rpm. The ink was mixed for 30 seconds and the second print was made at an impression cylinder rotation speed of 30 rpm. The ink was mixed for 30 seconds and the third print was made at an impression cylinder rotation speed of 30 rpm. 15 seconds after printing, the sheet was placed in a dryer for 5 seconds and removed, and then, after more than half a day had passed, the Y value of the XYZ color system was measured with a color difference meter, a graph was created based on the Y value, and the value for a reflectance of the printed surface of 6.5% was read and used as the print opacity value (reference standard: J.TAPPINo.45:2000 "Newspaper - Test method for opacity after printing"). Print opacity [%] = (reverse reflectance after printing / reverse reflectance before printing) x 100 (%) The back reflectance after printing and the back reflectance before printing were measured using a spectroscopic brightness colorimeter (manufactured by Suga Test Instruments Co., Ltd.) A print opacity of 78.0% or more is considered to be favorable because it has a high effect of suppressing the print ink from striking through to the back.

[0071] (dynamic contact angle) The dynamic contact angle [degrees] refers to the contact angle measured by a dynamic contact angle measuring device 60 seconds after dropping one drop of 2.0 μl of distilled water on the surface of the sample, and is used to judge the wettability of the coating layer surface. When distilled water is in contact with the surface of the sample, the contact angle indicates the angle that the free surface of the distilled water makes with the surface of the sample, and the more obtuse this angle is, the worse the wettability is, and conversely, the more acute the angle is, the better the wettability is. The dynamic contact angle of the coating layer after 60 seconds is preferably 35 degrees or more and 60 degrees or less, and more preferably 40 degrees or more and 55 degrees or less. When the dynamic contact angle of the coating layer after 60 seconds is within the above range, the ink can penetrate into the paper appropriately, resulting in a surface suitable for printing.

[0072] (Knob size) For the coated printing papers of Examples 1 to 7 and Comparative Examples 1 to 6, the surface of the base paper was contacted with water for 60 seconds in accordance with JIS-P8140 (1998) to measure the Cobb sizing degree [g / m 2 ] was measured.

[0073] (whiteness) The whiteness [%] was measured according to the method described in JIS-P8148 (2001) "Paper, paperboard and pulp - Measurement method for ISO whiteness (diffuse blue light reflectance)". A whiteness of 70.0% or more is considered good.

[0074] (color tone) The color tone was measured using a color difference meter CMS-35SPX manufactured by Murakami Shikisai Co., Ltd., in accordance with the method for measuring color (C / 2°) of paper and paperboard described in JIS-P8150 (2004) - diffuse lighting method, using a light source including ultraviolet light. * The values ​​were measured. * The value is preferably -8 or more and less than -3, and more preferably -7 or more and less than -4. * By lowering the value, the apparent whiteness of the printing paper can be increased, the opacity can be improved, and print-through can be prevented during printing.

[0075] (Prevents ink from bleeding through) The coated printing papers of Examples 1 to 7 and Comparative Examples 1 to 6 were observed through the back of the printed surface under indoor fluorescent lighting and rated according to the following three-level evaluation criteria. Of the following evaluation criteria, cases A and B are deemed to be usable. A: There is absolutely no bleed-through. B: A small amount of bleed-through is observed, but it is barely noticeable and does not affect practical use. C: Strike-through was observed and the film could not be used in practice.

[0076] (Back-off index) The strike-through index was calculated by dividing the print opacity of each coated printing paper by the basis weight to calculate the print opacity per basis weight. A higher strike-through index indicates a higher effect of suppressing the strike-through of printing ink, despite the lower basis weight.

[0077] (Prevents paper breakage) The runnability during the production of coated printing paper and during printing on a rotary press was evaluated according to the following two-level evaluation criteria. Of the following evaluation criteria, the case of A is judged to be practically usable. A: It has good operability during the production of coated printing paper and during printing on a rotary press, and there are few problems with paper breaks, making it an excellent coated printing paper. B: When producing coated printing paper and when printing on a rotary press, operability is poor and problems such as paper breakage occur, making it difficult to use as coated printing paper.

[0078] The above measurement results and evaluation results are shown in Table 3.

[0079] [Table 3]

[0080] As shown in Table 3, the raw pulp contains hardwood bleached kraft pulp, softwood bleached kraft pulp, and disintegrated and deinked waste paper pulp, the undercoating layer contains starch and a sizing agent, the coating layer contains a white pigment, the white pigment contains calcium carbonate, a first kaolin, and a second kaolin, the calcium carbonate content in the white pigment is 45% by mass or more and 70% by mass or less, the first kaolin content in the white pigment is 10% by mass or more and 20% by mass or less, and the second kaolin content in the white pigment is 10% by mass or more and 35% by mass or less, and the basis weight is 50 g / m 2 The print opacity divided by the basis weight is less than 1.70[% m 2 / g] or more in Examples 1 to 7. 2 Despite the low basis weight of less than 1.80 [% m 2 / g] or more, Examples 1 to 4, 6 and 7 were excellent in the effect of suppressing print ink strike-through.

[0081] On the other hand, Comparative Example 1, which did not contain an internal sizing agent or a surface sizing agent, was inferior in the effect of suppressing paper breakage. Comparative Example 2, which does not contain disintegrated and deinked waste paper pulp, internal sizing agent, or surface sizing agent, had a poor effect of preventing paper breakage, and also had high brightness and low opacity.2 / g], and the effect of suppressing print ink strike-through was poor. In Comparative Example 3, which did not contain an internal sizing agent or a surface sizing agent and contained more than 70 mass% calcium carbonate, the paper breakage suppression effect was poor, and the whiteness was high and the opacity was low. 2 / g], and the effect of suppressing print ink strike-through was poor. In Comparative Example 4, which does not contain an internal sizing agent or a surface sizing agent and contains more than 35% by mass of second kaolin, the paper breakage prevention effect is poor and the strike-through index is 1.70 [% m 2 / g], and the effect of suppressing print ink strike-through was reduced. In Comparative Example 5, which did not contain an internal sizing agent or a surface sizing agent and contained less than 5% by mass of flat first kaolin, the paper break suppression effect was poor, a flat printed surface was not formed, and the strike-through index was 1.70 [% m 2 / g], and the effect of suppressing print ink strike-through was poor. In Comparative Example 6, which does not contain an internal sizing agent or a surface sizing agent and has a flat first kaolin content of more than 20 mass%, the paper break suppression effect is poor, and the alignment of the first kaolin and the second kaolin is not good, so a flat printed surface is not formed and the strike-through index is 1.70 [% m 2 / g], and the effect of suppressing print ink strike-through was poor.

[0082] As a result of the above, the coated printing paper has a basis weight of 50 g / m 2 It has been shown that the coated printing paper has excellent effects of suppressing print-through of printing ink and suppressing paper breakage, despite having a basis weight of less than 100 g / m2. Therefore, the coated printing paper is suitably used as a coated printing paper for use in, for example, offset printing.

Claims

1. A base paper mainly composed of raw pulp; An undercoating layer laminated on at least one surface of the base paper; a coating layer containing a white pigment, the coating layer being laminated on the surface of the undercoating layer; Equipped with The raw pulp contains hardwood bleached kraft pulp, softwood bleached kraft pulp, and disintegrated and deinked waste paper pulp, The undercoating layer contains starch and a sizing agent, The coating layer contains a white pigment, The white pigment comprises calcium carbonate, a first kaolin and a second kaolin, The first kaolin has an aspect ratio of 15 or more and 25 or less, and an average particle size of 2.0 μm or more and less than 3.0 μm, The second kaolin has an aspect ratio of 5 to 15 and an average particle size of 2.5 μm to 4.0 μm, The content of the calcium carbonate in the white pigment is 45% by mass or more and 70% by mass or less, The content of the first kaolin in the white pigment is 10% by mass or more and 20% by mass or less, The content of the second kaolin in the white pigment is 10% by mass or more and 35% by mass or less, Basis weight 50g / m ２ is less than The print opacity divided by the basis weight is 1.70 [% m ２ / g or more.

2. 2. The coated printing paper according to claim 1, wherein the content of disintegrated and deinked waste paper pulp relative to the total pulp in the base paper is 10% by mass or more and 50% by mass or less.

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