Coated paper for printing

Abstract

The object of the present invention is to provide a coated paper for printing that, despite a low coating amount, is bulky, has high surface strength, excellent print surface feel, high opacity, good printability, and is environmentally friendly. [Solution] A coated paper for printing having one or more coating layers containing pigment and adhesive on a base paper containing 80% by weight or more of chemical pulp relative to the dry weight of the pulp, wherein the coating amount on one side of the coating layer is 0.5 g / m². 2 More than 9g / m 2 Below are the basis weights of coated paper for printing: 50 g / m² 2 More than 200g / m 2 The following describes a density of coated paper for printing: 0.50 g / cm³ 3 More than 0.75g / cm 3 The following is a coated paper for printing in which the base paper contains an organic compound that inhibits interfiber bonding of pulp fibers, and the coating layer contains, as an adhesive, 20 parts by weight or more of a starch-based adhesive and 10 parts by weight or less of latex per 100 parts by weight of pigment.

Description

[Technical Field]

[0001] This invention relates to coated paper for printing. In particular, this invention relates to coated paper for printing that is bulky, has excellent printability such as print surface feel and surface strength, and has good printability. [Background technology]

[0002] In recent years, there has been a growing demand for lighter printing paper to reduce transportation and postage costs. However, simply reducing the paper weight, i.e., lowering the basis weight, is undesirable because it reduces the paper's thickness and diminishes the volume of the booklet. What paper users are looking for in terms of lighter paper is to reduce the paper's weight while maintaining its thickness, or even increasing its thickness. Therefore, making paper lighter and bulkier is a crucial technological challenge in recent years.

[0003] On the other hand, with the increasing visualization and colorization of printed materials, the demand for coated printing paper, which has a smooth coating layer as an ink-receiving layer compared to uncoated printing paper, is increasing year by year. However, pigment coating layers, which mainly consist of inorganic pigments such as calcium carbonate and kaolin, have a higher specific gravity than coated base paper, which is mainly made from pulp. Therefore, reducing the amount of coating is effective in reducing the weight of coated paper. Also, from the perspective of increasing bulk, it is possible to increase the bulkiness of the coated base paper. One method for reducing the density (bulkiness) of paper is to consider the pulp used for papermaking.

[0004] While wood pulp is generally used for papermaking, to achieve low density, mechanical pulps such as wood pulp (made by grinding wood with a grinder), refiner mechanical pulp (made by crushing wood with a refiner), or thermomechanical pulp (made by crushing wood with a refiner) are more effective than chemical pulp (made by extracting lignin, a reinforcing material in wood fibers, using chemicals) because the fibers are more rigid. However, mechanical pulp has a lower whiteness compared to chemical pulp, leading to problems such as reduced whiteness in printing paper and yellowing (fading) of the paper over time. Furthermore, mechanical pulp production produces high greenhouse gas emissions, raising concerns about its environmental impact, and its reduction is desired.

[0005] Furthermore, from the perspective of papermaking, methods for increasing the bulkiness (reducing the density) of uncoated paper and coated base paper are known, including the use of bulking agents. Known bulking agents include, for example, paper bulking agents containing specific alcohols and / or their polyoxyalkylene adducts (Patent Document 1), nonionic surfactants (Patent Document 2), and paper bulking agents consisting of ester compounds of polyhydric alcohols and fatty acids (Patent Document 3). Technologies applying these paper bulking agents to cardboard (Patent Document 4) have also been proposed.

[0006] Furthermore, from the perspective of reducing transportation costs as mentioned above, there is a growing demand for lighter coated paper. Technology has been disclosed for low-basis-weight lightly coated paper that, despite a low coating amount, has particularly excellent white paper appearance and rigidity, and is suitable for printing and bookbinding (Patent Document 5).

[0007] However, as described in Patent Document 5, reducing the amount of pigment coating makes it easier for uneven coating to occur on the coated surface. In particular, with high-bulk base paper, which has low surface smoothness, this can easily lead to a deterioration in the printed surface quality due to uneven ink adhesion during printing. Furthermore, the surface strength of the coated paper is also lower compared to when the coating amount is high. Moreover, if the basis weight is low, the strength decreases drastically, leading to problems such as paper breakage during printing. Thus, it has been difficult to manufacture a coated paper for printing that is high-bulk, has high surface strength, and has excellent printed surface quality, while having a low coating amount and low basis weight. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 98 / 03730 brochure [Patent Document 2] Japanese Patent Application Publication No. 11-200283 [Patent Document 3] Patent No. 2971447 [Patent Document 4] Patent No. 3041294 [Patent Document 5] Japanese Patent Publication No. 2004-124289 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0009] In view of these circumstances, the object of the present invention is to provide a coated paper for printing that, despite a low coating amount, is bulky, has high surface strength, excellent print surface feel, high opacity, and good printability. [Means for solving the problem]

[0010] In other words, the present invention provides the following [1] to [4]. [1] A coated paper for printing having one or more coating layers containing pigment and adhesive on a base paper containing 80% by weight or more of chemical pulp relative to the dry weight of the pulp, wherein all of the following (1) to (5) are satisfied. (1) The coating amount on one side of the coating layer is 0.5 g / m 2 More than 9g / m 2 below. (2) The basis weight of the coated paper for printing is 50 g / m². 2 More than 200g / m 2 below. (3) The density of the coated paper for printing is 0.50 g / cm³ 3 More than 0.75g / cm 3 below. (4) The base paper contains an organic compound having an action of inhibiting the fiber-to-fiber bonding of pulp. (5) The coating layer contains a starch-based adhesive of 20 parts by weight or more and a latex of 10 parts by weight or less with respect to 100 parts by weight of the pigment as an adhesive. The coated paper for printing according to [1], wherein the starch-based adhesive is white dextrin. The coated paper for printing according to [1] or [2], wherein the base paper contains 90% by weight or more of kraft pulp with respect to the dry weight of the pulp. The coated paper for printing according to [1] or [2], having an opacity of 90% or more.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a coated paper for printing which is bulky, has high surface strength, excellent printing surface feeling, high opacity, and good printing workability, despite having a low basis weight and a low coating amount.

Embodiments for Carrying Out the Invention

[0012] The present invention is a coated paper for printing (hereinafter, also simply referred to as "coated paper") using a low-density paper as the base paper.

[0013] The present inventors have found a new problem of developing a coated paper having a low density, a low coating amount, and excellent various qualities of the paper. In order to achieve this, various contrivances have been made, such as finding conditions where a synergistic effect of two elements can be seen.

[0014] First, regarding the relationship between the low density and the coating amount, generally, when the coated base paper is made bulky, there are many voids in the base paper. Then, when applying a pigment coating liquid containing an adhesive and a pigment (hereinafter, also simply referred to as "coating liquid"), the coating liquid easily penetrates into the base paper, and it is difficult to uniformly cover the surface of the base paper with a low coating amount. If it cannot be uniformly covered, the printing surface feeling deteriorates due to uneven ink laydown during printing, and the whiteness of the paper also becomes lower compared to the case where the coating amount is large.

[0015] If the base paper is calendered before coating to reduce the amount of voids in the base paper, the paper, which was made low-density, will become high-density again due to the calendering process. However, if calendering is not performed, problems such as a decrease in the smoothness of the paper surface and a deterioration in the surface texture of the coated paper may occur.

[0016] Furthermore, when using bulking agents to reduce the density of the base paper, these agents inhibit interfiber bonding and lower the paper's density, resulting in a significant decrease in paper strength in the low basis weight range. When coated paper is manufactured using low-basis-weight base paper with added bulking agents, the tensile strength is reduced, which can contribute to problems such as paper breakage in offset web printing.

[0017] Therefore, in order to maintain tensile strength while keeping the base paper low density, we decided to add a paper strengthening agent to the base paper.

[0018] Generally, when a small amount of coating is applied to a low-density base paper made with this type of pulp composition, the penetration of the coating solution into the base paper becomes significant. However, we found that by using a coating solution with optimized starch-based adhesive and latex content in the pigment coating layer, the fluidity of the coating solution and its penetration into the base paper can be controlled, significantly suppressing the decrease in the base paper's coverage.

[0019] pulp The base paper for coated printing paper in this invention consists of pulp, fillers, and various auxiliary agents. As the pulp, chemical pulp, semi-chemical pulp, mechanical pulp (wood pulp, refined wood pulp, thermomechanical pulp (TMP)), recycled paper pulp, deinking pulp (DIP), etc. can be used, but chemical pulp is preferred because it does not fade and has high whiteness. Chemical pulp is pulp made by chemically processing wood and other fibrous raw materials, and includes sulfite pulp, kraft pulp, soda pulp, etc., but kraft pulp is preferred among them. In addition, the raw materials for pulp include coniferous trees and hardwoods, but in this invention, hardwood pulp is preferred in terms of print quality, etc.

[0020] In the present invention, the base paper used contains 80% by weight or more of chemical pulp relative to the dry weight of the pulp. Preferably, it contains 90% by weight or more of chemical pulp, more preferably 95% by weight or more, and even more preferably 100% by weight. The base paper may also contain 90% by weight or more of kraft pulp relative to the total dry weight of the pulp, preferably 95% by weight or more, and more preferably 100% by weight. The filtration efficiency of the kraft pulp can be 280-600 mL (CSF), with 380-460 mL being more preferable.

[0021] If you want to improve the whiteness, it is preferable to use kraft pulp that has been bleached by one or more known bleaching processes. In this case, an oxidizing agent such as hydrogen peroxide, ozone, or peracetic acid, or a reducing agent such as hydrosulfite (sodium dithionite), sodium bisulfate, sodium borohydride, or formamidine sulfinic acid (FAS) can be used.

[0022] filler In this invention, a filler of 10% by weight or more can be added to the base paper to impart opacity. Furthermore, the coating properties of the base paper can be improved by filling the voids in the base paper and suppressing the penetration of the coating liquid. In this invention, if the ash content in the base paper is less than 10% by weight, the opacity may decrease, the penetration of the coating liquid into the base paper will be significant, resulting in uneven coating of the coating liquid after application and deterioration of the printed surface, which is undesirable. To make the ash content in the base paper (base paper ash content) 10% by weight or more, this can be achieved by adding 10% by weight or more of filler per unit weight of base paper. The base paper ash content is preferably 10% by weight or more, and more preferably 12% by weight or more. Furthermore, considering that if the base paper ash content is too high, the strength of the paper will decrease significantly, the effect of the sizing agent will be suppressed, and the penetration of the coating liquid will increase, the base paper ash content is preferably 40% by weight or less, more preferably 30% by weight or less, and even more preferably 20% by weight or less.

[0023] In this invention, the ash content in the base paper refers to the ash content of the paper before coating with a coating solution containing pigment and adhesive, and the ash content of the coated paper refers to the ash content of the printed coated paper as a finished product. Both values ​​were measured in accordance with JIS P 8251 "Paper, cardboard and pulp - Ash content test method - 525°C combustion method".

[0024] In the present invention, there are no restrictions on the type of filler, but known fillers such as light calcium carbonate, heavy calcium carbonate, white carbon, talc, kaolin, clay, titanium dioxide, zeolite, and synthetic resin fillers can be used. In the present invention, it is preferable to use light calcium carbonate as the filler used in the base paper. When light calcium carbonate is used, particularly excellent bulkiness, opacity improvement effect, and good base paper surface properties can be obtained under conditions in which mechanical pulp is blended as a raw material.

[0025] Light calcium carbonate can be either calcite or aragonite, and can be in any shape, including needle-shaped, columnar, fusiform, spherical, cubic, or rosette-shaped. However, the rosette shape is preferred in terms of opacity and improved back-printing. The rosette shape refers to a form in which spindle-shaped primary particles of light calcium carbonate are aggregated into a chestnut-burr shape, and it is characterized by a higher specific surface area and oil absorption than other types of light calcium carbonate.

[0026] Furthermore, the coated paper for printing of the present invention may be used with aluminum sulfate and various anionic, cationic, nonionic, or amphoteric yield improvers, water drainage improvers, paper strength enhancers, and internal sizing agents as needed. In addition, papermaking additives such as dyes, fluorescent whitening agents, pH adjusters, defoamers, pitch control agents, and slime control agents may be added as needed.

[0027] Furthermore, in the base paper of the present invention, bulking agents (densitizing agents) such as surfactants, which are organic compounds that inhibit the interfiber bonding of pulp fibers, can be used. Organic compounds that inhibit the interfiber bonding of pulp fibers (hereinafter abbreviated as bonding inhibitors) are compounds that have hydrophobic and hydrophilic groups, and examples include compounds shown in WO98 / 03730, JP-A-11-200284, JP-A-11-350380, JP-A-2003-96694, JP-A-2003-96695, etc. Specifically, ethylene and / or propylene oxide adducts of higher alcohols, polyhydric alcohol-type nonionic surfactants, ethylene oxide adducts of higher fatty acids, ester compounds of polyhydric alcohols and fatty acids, ethylene oxide adducts of ester compounds of polyhydric alcohols and fatty acids, or fatty acid polyamidoamines, fatty acid diamidoamines, fatty acid monoamides, or polyalkylene polyamine-fatty acid-epichlorohydrin condensates can be used, and these can be used alone or in combination of two or more. Commercially available bulking agents include BASF's Suruzol VL, Bayer's Bivolume P Liquid, Kao Corporation's KB-08T, 08W, KB110, 115, and Sansho Co., Ltd.'s ReactoPake, which can be used alone or in combination of two or more. In the coated paper of the present invention, the preferred amount of bulking agent added in the papermaking process is 0.1 to 2% by weight relative to the dry weight of pulp in the base paper.

[0028] In this invention, an internal paper strength agent is added to the base paper. In this invention, the internal paper strength agent used can be any substance that is generally used as a paper strength agent or paper strength enhancer, but examples include internal starch and internal paper strength agent.

[0029] Examples of internal starches added to the base paper include cationized starch and amphoteric starch, which may be crosslinked. In the present invention, cationized starch is preferred. Furthermore, polyacrylamide-based paper strength enhancers are preferred as paper strength enhancers added to the base paper. In the present invention, since the addition of bulking agents tends to reduce interfiber bonding, it is preferable to use a paper strength enhancer and internal starch in combination to compensate for this.

[0030] In the present invention, the amount of internally added paper strength agent is preferably 0.1% by weight or more and 5% by weight or less relative to the dry weight of pulp in the base paper, as the total amount of various paper strength agents. Adding more than 5% by weight will result in the effect of weakening the interfiber bonds of the pulp reaching its upper limit, thus reducing the paper strength enhancement effect and bulkiness effect. Furthermore, if the amount added is less than 0.1% by weight, the effect of weakening the interfiber bonds of the pulp will not be sufficiently exhibited, and therefore the bulkiness effect will not be achieved.

[0031] Paper making method In the papermaking method for coated paper for printing according to the present invention, it is preferable to use a twin-wire former. Compared to a halftone former, a twin-wire former performs dewatering on both sides, so by controlling the dewatering conditions on the front and back sides with the pulp composition and base paper ash content of the present invention, it is easier to control the fine fibers and ash content on the base paper surface, and even in the coating amount range of the present invention, it is possible to suppress the penetration of the coating liquid and obtain a good coated surface. In the present invention, in order to make it easier to retain the internal filler on the surface, it is preferable to use an on-top hybrid former or a gap former.

[0032] Papermaking can be carried out using any of the following methods: acidic papermaking, neutral papermaking, or alkaline papermaking. In this invention, the basis weight of the coated base paper is 40 to 200 g / m², which is commonly used for coated paper. 2 A suitable material of a certain degree can be used. As a drying method after formering, it is preferable to dry with a dryer that includes a cylinder dryer, as this can smooth the surface of the base paper. As long as a cylinder dryer is included, there are no restrictions on the drying method, and it can be used in combination with other drying equipment such as an air dryer.

[0033] In the present invention, if necessary, an adhesive such as starch may be used to apply a clear coating to the base paper before pigment coating by sizing press or the like. The adhesive used for the clear coating is not particularly limited, but for example, starches such as oxidized starch, hydroxyethyl etherified starch, and oxygen-modified starch, polyacrylamide (PAM), polyvinyl alcohol (PVA), etc., can be used individually or in combination. Furthermore, if necessary, auxiliary agents such as surface sizing agents, water-resistant agents, water-retaining agents, thickeners, and lubricants may be added to perform the clear coating.

[0034] The coating method and coating apparatus used in the size press treatment of the present invention are not particularly limited, and known coating apparatus can be used, and it is preferable to use a rod metering type size press, a pound type size press, a gate rod coater, a spray coater, a blade coater, a curtain coater, etc.

[0035] glue In the present invention, the adhesive in the coating layer containing the pigment and adhesive (also called the "pigment coating layer") contains a starch-based adhesive and latex. Examples of starch-based adhesives include starch, such as various modified starches, and starch compounds such as dextrin obtained by hydrolyzing starch. Starch refers to a mixture consisting of amylose and amylopectin, and generally, the mixing ratio differs depending on the plant from which the starch is derived. Examples of modified, altered, or processed starches include oxidized starch, hydroxyesterified starch (HES), phosphate ester starch, esterified starch, and dextrin. Preferred raw materials for the starch-based adhesive used in the present invention include corn, potato, and tapioca, with waxy corn and tapioca being particularly preferred.

[0036] In the present invention, it is preferable to use low-viscosity hydroxyethyl starch (HES), oxidized acetylated tapioca starch, dextrin, etc., because they have low viscosity, viscosity stability, and excellent strength. It is more preferable to use dextrin, and among these, roasted dextrin is particularly preferable. Dextrin is a general term for high-molecular-weight compounds derived from starch obtained by hydrolyzing starch, in which α-glucose is polymerized by glycosidic bonds, and is also called starch paste. Ordinary starch has a large molecular weight, but dextrin is an intermediate product produced in the hydrolysis process of starch and is said to have a molecular weight of only about the same as an oligomer (a bond of several to about 20 glucose units). Roasted dextrin is dextrin produced by adding acid and roasting with dry heat, and there are types such as white dextrin, yellow dextrin, and British gum. In the present invention, it is particularly preferable to use white dextrin. Further hydrolysis of white dextrin yields so-called yellow dextrin. However, yellow dextrin has low stability and may cause discoloration of the pigment coating layer. Therefore, in this invention, the use of white dextrin is preferred.

[0037] In the present invention, the molecular weight of the white dextrin can be 50,000 MW to 800,000 MW by weight average molecular weight. The higher the molecular weight, the higher the viscosity of the paste solution and the viscosity when compounded with the coating solution. Therefore, the molecular weight is preferably 100,000 MW to 350,000 MW, and more preferably 150,000 MW to 300,000 MW. In the present invention, it is preferable for the white dextrin to have a high degree of branching. A high degree of branching makes it easier to develop strength. The degree of branching is related to the radius of inertia. For the same molecular weight, a small radius of inertia indicates a high degree of branching, while a large radius of inertia indicates a low degree of branching, resulting in a linear structure. Therefore, in the present invention, it is preferable for the white dextrin to have a small radius of inertia.

[0038] When a starch compound is contained in a coating liquid as a starch-based adhesive, heating is required to dissolve the starch compound. Therefore, the viscosity of the slurry after cooking under certain conditions is important. In the present invention, when white dextrin is used as the starch-based adhesive, the viscosity of the slurry after cooking is low, so the slurry can be made into a high concentration. In the present invention, for example, as the white dextrin, one having an RVA viscosity of 3000 mPa·s or less can be used. Preferably it is 1000 mPa·s or less. The RVA viscosity can be measured using a measuring instrument called a Rapid Visco Analyzer (RVA, model RVA-4, manufactured by New Port Scientific). In the present invention, the RVA viscosity is the viscosity at 50°C 16 minutes after the start of cooking when a starch compound slurry with a concentration of 35% by weight is cooked under the following cooking conditions.

[0039] <RVA Viscosity Measurement Conditions> Rotate the paddle under the following conditions, measure the torque applied to the stirring paddle, and calculate the viscosity. (Stirring Conditions) · 10 seconds after the start of measurement: 960 rpm · Thereafter: 160 rpm (Cooking Conditions) · 0 - 5 minutes: Heat up to 98°C in 5 minutes · 5 - 9 minutes: Hold at 98°C · 9 - 12 minutes: Cool down to 50°C in 3 minutes · 12 - 16 minutes: Hold at 50°C

[0040] For example, cold-water-soluble starches typified by pregelatinized starches also have a low slurry viscosity, but these cold-water-soluble starches are processed to be soluble in cold water, and dextrin and the like are more advantageous in terms of the expression of surface strength. Therefore, as the white dextrin, it is preferable that the solubility in water at 20°C is less than 20%.

[0041] In one aspect of the present invention, white dextrin is used as a starch-based adhesive for the pigment coating layer, and its adhesive strength as an adhesive (binder) is achieved by steaming (cooking) the slurry.

[0042] In this invention, using white dextrin as a starch-based adhesive results in good fluidity when incorporated into the coating solution. Improved fluidity allows for higher concentrations of the coating solution, suppresses penetration of the coating solution into the base paper, and increases the effective coating layer, thereby improving various coated paper qualities such as whiteness, opacity, print surface feel, and surface strength.

[0043] As for the latex, one or more types can be appropriately selected and used from various copolymer latexes such as styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, butadiene-methyl methacrylate, and vinyl acetate-butyl acrylate.

[0044] Furthermore, as adhesives to be used in combination with starch-based adhesives and latex, one or more can be appropriately selected and used from among synthetic adhesives such as polyvinyl alcohol, maleic anhydride copolymer, and acrylic acid / methyl methacrylate copolymer, proteins such as casein, soy protein, and synthetic protein, and cellulose derivatives such as carboxymethylcellulose, hydroxymethylcellulose, and hydroxyethylcellulose.

[0045] In the present invention, the preferred amount of adhesive to be blended is preferably 25 parts by weight or more and 100 parts by weight or less of starch-based adhesive and latex per 100 parts by weight of pigment, and more preferably 27 parts by weight or more, from the viewpoint of penetration into the base paper, printability, surface strength, and coating suitability. Furthermore, the breakdown is preferably 20 parts by weight or more of starch-based adhesive and 10 parts by weight or less of latex. Preferably, it contains 25 parts by weight or more of starch-based adhesive and 0 parts by weight or more and 10 parts by weight or less of latex. More preferably, it contains 2 parts by weight or more and 10 parts by weight or less of latex, and particularly preferably, it contains 5 parts by weight or more and 10 parts by weight or less of latex. By blending the starch-based adhesive within the above range, high water retention can be imparted to the pigment coating liquid, so that the base paper can be sufficiently coated even with lightly coated paper with a low coating amount. Furthermore, by blending the latex to 10 parts by weight or less, the amount of petroleum-based materials used can be reduced, resulting in an environmentally friendly product. However, from the viewpoint of water resistance of the coated paper for printing, it is preferable to contain 2 parts by weight or more of latex, and more preferable to contain 5 parts by weight or more.

[0046] pigment The pigments used in the pigment coating layer can be those conventionally used for coated paper. For example, inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as dense, hollow, or core-shell types, can be used individually or in mixtures of two or more types as needed. Furthermore, among the pigment types, heavy calcium carbonate is preferable to kaolin, engineered clay, kaolin, and delaminated clay because it can suppress the increase in viscosity of the coating solution, resulting in a higher concentration of the coating solution. This suppresses the penetration of the coating solution and makes it easier to exhibit a bulking effect. The preferred heavy calcium carbonate content in the pigment is 90 parts by weight or more per 100 parts by weight of pigment, more preferably 95 parts by weight or more, and even more preferably 100 parts by weight.

[0047] In the present invention, when providing a coating layer containing a pigment and an adhesive, various commonly used auxiliary agents such as a dispersant, a thickener, a water retention agent, an antifoaming agent, a water resistance agent, a dye, a fluorescent dye, etc. can be used as auxiliary agents in the coating liquid.

[0048] Coating method The coating layer of the coated paper for printing of the present invention may be one or more layers.

[0049] Regarding the coating method when providing a pigment coating layer in the present invention, it is not particularly limited, and a known coating apparatus can be used. For example, a blade coater, a bar coater, a gate roll coater, an air knife coater, a reverse roll coater, a curtain coater, a spray coater, a size press coater, etc. can be mentioned. However, as a method of coating within the preferable coating amount range in the present invention, it is preferable to use a roll coater typified by a gate roll coater that can suppress the penetration of the coating liquid into the base paper under low coating amount conditions. Further, in the case of an on-machine coater in which a paper machine and a coater are integrated, since the temperature of the base paper before coating is higher than that of an off-machine coater, the coating liquid is likely to penetrate into the base paper. As one point of the present invention, it can be mentioned that by using a specific pulp blend and a specific base paper ash content, the base paper covering property can be improved even with a low coating amount. Therefore, the effect of the present invention becomes more remarkable when coating under conditions where the coating liquid is likely to penetrate into the base paper with an on-machine coater. The papermaking speed of the on-machine coater is preferably 500 to 2000 m / min.

[0050] As the dryer for drying the wet coating layer after coating, general ones can be used. For example, normal devices such as a steam heating heater, a gas heater, an infrared heater, an electric heater, a hot air heating heater, a microwave, a cylinder dryer, etc. can be used.

[0051] The coating amount per side of the paper in the present invention is 0.5 g / m 2 or more and 9.0 g / m 2 or less. When the coating amount is 0.5 g / m 2If the amount is less than 9.0 g / m², the coating amount cannot be reduced unless the coating solution concentration is lowered during pigment coating. As a result, significant penetration of the coating solution into the base paper occurs, leading to uneven coating, deterioration of the base paper's coverage, and ultimately, a deterioration in the print surface quality, which is undesirable. Furthermore, because the pigment coating layer has an extremely high density compared to the base paper layer, the coating amount must be 9.0 g / m². 2 If the coating amount is too high, the overall density of the coated paper increases, and it ceases to be bulky coated paper, which is undesirable. A more preferable single-sided coating amount in this invention is 0.5 g / m². 2 More than 8.5g / m 2 The following applies:

[0052] As described above, coated and dried printing paper can be calendered. However, in this invention, calendering may be omitted or only light calendering may be performed to improve the surface texture of the coated paper, as this may impair the bulkiness of the base paper. By omitting calendering, printing coated paper with high bulkiness can be obtained.

[0053] Basis weight The basis weight of the coated paper of the present invention (or the basis weight after calendering if calendering is performed) is 50 g / m². 2 More than 200g / m 2 The following is preferred: 60 g / m² 2 More than 200g / m 2 The following can be achieved. In the present invention, with the above basis weight, it is possible to achieve a low coating amount, good base paper coverage, and good printability such as ink adhesion and print gloss.

[0054] density The density of the coated paper of the present invention is 0.50 g / cm³. 3 More than 0.75g / cm 3 The following, preferably 0.55 g / cm³ 3 More than 0.70g / cm 3 The following applies. By setting the range as described above, it is possible to obtain bulky coated paper for printing while maintaining the surface strength required for coated paper for printing.

[0055] Opacity The opacity of the coated paper of the present invention is preferably 90% or higher, and more preferably 92% or higher. The opacity of the coated paper can be adjusted by increasing or decreasing the paper thickness, the amount of ash in the paper, and the amount of pigment coating layer applied. [Examples]

[0056] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. Unless otherwise specified, parts and percentages in this specification are based on weight, and numerical ranges are given including their endpoints.

[0057] (Evaluation method) The obtained coated paper for printing was tested based on the evaluation method described below. (1) Basis weight: Measured according to JIS P 8124. (2) Density: Measured according to JIS P 8118. (3) Whiteness: Measured according to JIS P 8148. (4) Opacity: Measured according to JIS P 8149. (5) Consideration for the environment The degree of environmental consideration was evaluated on a three-point scale based on whether or not mechanical pulp, which has high greenhouse gas emissions during manufacturing, and petroleum-based materials were used. ○: Contains only small amounts of mechanical pulp and petroleum-based materials, making it environmentally friendly. △: Contains mechanical pulp and petroleum-based materials, and is not very environmentally friendly. ×: Contains a large amount of mechanical pulp and petroleum-based materials, and is not environmentally friendly. (6) Printing workability Using an offset printing press (Toshiba Machine Co., Ltd.; OA-B2T-600), 20,000 copies were printed in four colors in the order of black → cyan → magenta → yellow, and the occurrence of paper breakage was observed. The evaluation criteria were as follows. ○: Paper breakage occurs very infrequently. △: Paper breakage may occasionally occur. ×: Paper breakage occurs frequently. (7) Print surface feel Using a Roland flatbed printing press (4 colors), printing was performed at a printing speed of 8000 sheets / hour using printing inks (Toyo Ink NEX-NV M) in the order of black → cyan → magenta → yellow. The print surface quality (unevenness in ink density, uneven gloss, etc.) of the two-color (cyan, magenta) printed areas, the solid cyan printed areas, and the halftone (50%) printed areas of the resulting printed materials was visually evaluated. The evaluation criteria were as follows. ◎: Excellent. 〇: Good. △: Slightly inferior. ×: Inferior. (8)Fade resistance The coated paper for printing according to the present invention was left undisturbed for one month in a windowsill exposed to direct sunlight, and the change in color was observed visually and evaluated according to the following criteria. ○: Does not fade. △: Slightly faded, but still usable. ×: Severe fading makes it unusable. (9) Surface strength Using an RI-I type printing press (manufactured by Akira Seisakusho), printing was performed using printing ink (NEX-Y manufactured by Toyo Ink). After printing, the print marks on the rubber roll were transferred to paper, and the degree of picking (white spots) was visually evaluated. The evaluation criteria were as follows: ○: Does not occur. △: Occurs slightly, but does not affect usability. ×: Too many to use.

[0058] [Example 1] (Manufacturing of base paper) A pulp slurry consisting of 80% bleached hardwood kraft pulp (LBKP) (CSF 360mL) and 20% bleached softwood kraft pulp (NBKP) (CSF 550mL) was mixed with 1.0% aluminum sulfate, 0.9% cationized starch, 170ppm yielding agent (Realizer R280, manufactured by Somar), 0.5% bulking agent, 20% rosette-type light calcium carbonate as an internal filler, and 70g of black colorant per ton of dry pulp weight to prepare the pulp stock. This pulp stock was then paper-made at a speed of 770m / min using a Duoformer FD type paper machine (on-top twin-wire former) to produce paper with a density of 0.6g / cm³. 3 The basis weight is 49.8 g / m². 2A coated base paper was obtained.

[0059] (Preparation of coating solution) A coating solution was prepared by using 100 parts (solids) of finely granulated heavy calcium carbonate slurry (Carbital 90, manufactured by Imerys) as the pigment slurry, adding 4.5 parts (solids) of styrene-butadiene copolymer latex (SBR) and 35 parts of white dextrin (RVA viscosity: approximately 250 mPa·s, weight-average molecular weight: 152,000), and then adding water to bring the solids concentration to 40%.

[0060] (Manufacturing of coated paper for printing) The above coating liquid is applied to the above base paper, with a coating amount of 4.75 g / m² per side. 2 After coating both sides using a gate roll coater at a coating speed of 770 m / min, the coated paper was dried to a moisture content of 5.5% to obtain coated paper for printing.

[0061] As shown in Table 1, the formulations of the base paper and coating layer were changed to obtain the printing coated papers of Examples 2-4 and Comparative Examples 1-5.

[0062] Table 1 shows the properties of coated paper for printing.

[0063] [Table 1]

[0064] The results in Table 1 show that the coated printing paper of the present invention is environmentally friendly and has excellent fade resistance. Furthermore, it exhibited good printability, including printability, print surface feel, and surface strength.

Claims

1. A coated paper for printing having one or more coating layers containing pigment and adhesive on a base paper containing 80% by weight or more of chemical pulp relative to the dry weight of the pulp, wherein all of the following (1) to (5) are satisfied. (1) The coating amount on one side of the coating layer is 0.5 g / m². ２ 9g / m or more ２ below. (2) The basis weight of the coated paper for printing is 50 g / m². ２ More than 200g / m ２ below. (3) The density of the coated paper for printing is 0.50 g / cm³ ３ 0.75g / cm or more ３ below. (4) The base paper contains an organic compound that inhibits the interfiber bonding of the pulp fibers. (5) The coating layer contains, as an adhesive, 20 parts by weight or more of a starch-based adhesive and 10 parts by weight or less of latex per 100 parts by weight of pigment.

2. The coated paper for printing according to claim 1, wherein the starch-based adhesive is white dextrin.

3. The coated paper for printing according to claim 1 or 2, wherein the base paper contains 90% by weight or more of kraft pulp relative to the dry weight of the pulp.

4. A coated paper for printing according to claim 1 or 2, wherein the opacity is 90% or more.

Images