JP2009270203A - Coated paper for printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide coated paper having high brightness and excellent printing gloss and smoothness in high productivity by coating base paper with a coating liquid containing heavy calcium carbonate having a specific particle diameter as a main pigment and having excellent flowability. <P>SOLUTION: In coated paper for printing obtained by coating at least one side of base paper with two or more layers of coating layers comprising a pigment and an adhesive as components, ≥50% of bleached pulp used in the base paper comprises eucalyptus material and/or Acacia material as a raw material, the bleached pulp is pulped by a kraft cooking method of divided addition of a cooking liquor and produced by a multistage bleaching process including an ozone bleaching step. The topcoating layer arranged in the outermost layer of the coated paper comprises ≥50 mass% of ground calcium carbonate having an average particle diameter of 0.5-1.2 μm, the undercoating layer in contact with the base paper comprises ≥50 mass% of heavy calcium carbonate having an average particle diameter of 0.5-2.5 μm and the undercoating layer is coated by a film transfer roll coating method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a coated paper for printing, and relates to a coated paper for printing excellent in whiteness, printed gloss, and smoothness.

  In general, coated paper for printing is manufactured by coating and drying a coating liquid mainly composed of pigment and adhesive on a base paper, and depending on the coating amount of the coating liquid and the finishing method of the coated paper, It is classified into paper, art paper, coated paper, finely coated paper, and the like. These coated papers are widely used as commercial prints such as leaflets, brochures, posters, etc., or as publications such as books and magazines by performing multicolor printing or single color printing. In recent years, the visualization and colorization of printed matter has progressed, and the appearance of the coated paper for printing, such as whiteness and smoothness, has become more important than ever.

  Therefore, as a means to obtain a coated paper for printing with high smoothness, first, an undercoat coating layer is provided on the base paper to level the unevenness of the base paper, and then the topcoat coating is applied on the undercoat coating layer. Multilayer coatings that provide layers are known. According to this method, it is possible to obtain a coated paper for printing which is generally excellent in smoothness as compared with a case where a top coat layer is provided as a single layer on a base paper.

  There are two methods for producing coated paper: an off-machine method in which papermaking and coating are performed in separate steps, and an on-machine method in which papermaking and coating are performed simultaneously on a single machine. Compared to the off-machine method, it is known that the manufacturing cost of a product can be reduced, and a product with price competitiveness can be manufactured. In particular, in the case of multilayer coated paper, a cheaper product can be produced by continuously applying the undercoating and topcoating liquids on-machine.

  In particular, the film transfer roll coating performed by undercoating in the on-machine method has high productivity such as a compact apparatus and a small installation area, and continuous coating with a small amount of paper cut on-machine. However, since the smoothness and uniformity of the coated surface are inferior to blade coating, there have been proposals that specify paint properties. (See Patent Document 1)

  Furthermore, the pigment used for the coating layer includes mineral pigments such as kaolin, heavy calcium carbonate, light calcium carbonate, aluminum hydroxide, satin white, talc and titanium dioxide, and organic synthetic pigments such as plastic pigments. Among them, heavy calcium carbonate has high whiteness, is inexpensive, has low adhesive requirements, and can be used to prepare a coating solution with excellent fluidity. Although widely used as a white pigment, the coated paper is inferior in smoothness and glossiness compared to kaolin and the like.

  For this reason, it is known to improve the printing gloss, whiteness, opacity, etc. of coated paper by reducing the particle size of heavy calcium carbonate or adjusting the particle size distribution to a specific range. Yes. However, this not only deteriorates the fluidity of the coating solution, but also causes inconveniences such as a decrease in printing gloss and an increase in the required amount of adhesive.

  In addition, when heavy calcium carbonate is used for the undercoat coating layer in contact with the base paper, heavy calcium carbonate having a relatively large particle size and low cost is often used. It is the present condition that the property cannot be obtained. In recent years, coated paper has been required to have high productivity and high whiteness, and in addition to high productivity by transfer roll coating, a proposal to simultaneously satisfy high whiteness, white paper, and printing smoothness has been required. ing.

JP 07-189188 A JP 54-129040 A

  The present invention is to prepare a coating liquid excellent in fluidity containing inexpensive heavy calcium carbonate as a main pigment in the coating liquid, and to produce a coated paper excellent in high whiteness, printing gloss and smoothness. It is to provide with high productivity.

  As a result of intensive investigations to solve the above-mentioned problems, the present invention uses a pulp produced by a specific method on a base paper, and further contains a specific amount of specific heavy calcium carbonate, thereby improving fluidity. It was found that a coated paper having a high whiteness and excellent print gloss and smoothness can be obtained with high productivity. That is, according to the present invention, in a coated paper for printing in which at least one surface of a base paper is provided with two or more coating layers mainly composed of a pigment and an adhesive, 50% or more of the bleached pulp used in the base paper is eucalyptus. The pulp is made from wood and / or acacia, and the bleached pulp is pulped by a kraft cooking method in which a cooking liquor is added in portions, and further produced in a multistage bleaching process including an ozone bleaching stage. The topcoat coating layer disposed in the outermost layer of the coated paper contains 50% by mass or more of heavy calcium carbonate having an average particle size of 0.5 to 1.2 μm and is in contact with the base paper The layer contains heavy calcium carbonate having an average particle size of 0.5 to 2.5 μm in an amount of 50% by mass or more of the total pigment, and the undercoat coating layer is applied by a film transfer roll coating method. It is characterized by being.

The ratio of the particle diameter (D ₇₅ ) corresponding to 75 mass% of the particle size distribution measurement curve to the particle diameter (D ₂₅ ) corresponding to 25 mass% of the heavy calcium carbonate contained in the top coat layer, D ₇₅ / _{D 25} is preferably in the range of 1.5 to 3.3.

  According to the present invention, high smoothness is obtained on the base paper, and high whiteness is achieved by stably applying a coating liquid excellent in fluidity due to heavy calcium carbonate with high blending by a film transfer coating method. A coated paper for printing excellent in white paper smoothness, printing smoothness and printing gloss can be obtained.

  Details of the present invention will be described below.

  The raw material of the pulp used in the present invention may be hardwood, softwood or non-wood, but 50% or more of the bleached pulp used for paper is made from eucalyptus and / or acacia. There must be. This is because pulp made of eucalyptus and acacia materials has a small fiber width, an increased number of fibers per unit US tsubo, and high smoothness can be obtained on a paper sheet. For example, as eucalyptus materials, E.camaldulensis, E.citriodora, E.deglupta, E.globulus, E.grandis, E.maculata, E.punctata, E.saligna, E.terelicornis, E.urophylla, E.camaldulensis etc. and their hybrids are mentioned, and as acacia wood, A.aulacocarpa, A.auriculiformis, A.catechu, A.crassicarpa, A.decurrens, A.holosericea, A.leptocarpa, A.leptocarpa maidenii, A. mangium, A. mearnsii, A. melanoxylon, A. neriifolia, A. silvestris, etc. and their hybrids.

  As the cooking method for obtaining the pulp, known cooking methods such as kraft cooking, polysulfide cooking, soda cooking, alkali sulfite cooking, etc. can be used, but it is necessary to divide and add the cooking liquid. By adding the cooking liquor in a divided manner, the alkali concentration throughout the cooking can be kept low, and elution of hemicellulose in the material is suppressed, resulting in a pulp having a high hemicellulose content. The use of pulp having a high hemicellulose content is also an indispensable factor for the expression of the paper physical properties of the present invention. The cooking method is not particularly limited as long as it is a cooking method in which the cooking liquid is added in portions. However, cooking methods such as the Lo-solids method, the Compact cooking method, and the Kobudomari cooking method are manufactured with a small amount of energy used during cooking. It is preferably used from the viewpoint of incidental effects such as good bleachability of the pulp.

  Here, exemplifying the case of using the kraft cooking method, the sulfidity of the cooking solution is 5 to 75%, preferably 15 to 45%, and the effective alkali addition rate is 5 to 30% by mass, preferably 10 ˜25 mass%, cooking temperature is 130 to 170 ° C., and the cooking method may be either a continuous cooking method or a batch cooking method.

  In cooking, a known cyclic keto compound as a cooking aid in the cooking solution to be used, for example, benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthroquinone and quinone-based compounds such as alkyl, amino, or the like, or the quinone-based compound One kind selected from hydroquinone compounds such as anthrahydroquinone which is a reduced form of 9,10-diketohydroanthracene compound which is a stable compound obtained as an intermediate of anthraquinone synthesis method by Diels Alder method Or 2 or more types may be added and the addition rate is 0.001-1.0 mass% per the absolute dry mass of a material.

  In this invention, the unbleached pulp obtained by the well-known cooking method is delignified by the well-known alkaline oxygen bleaching method through a washing | cleaning, a rough selection, and a selection process. This is because delignification by the alkaline oxygen bleaching method can reduce the amount of bleaching chemicals used in the subsequent multistage bleaching step and minimize damage to the pulp quality. As the alkaline oxygen bleaching method used in the present invention, a known medium concentration method or a high concentration method can be applied as it is, but a medium concentration method which is currently used at a pulp concentration of 8 to 15% is widely used. preferable.

  In the alkali oxygen bleaching method by the medium concentration method, caustic soda or oxidized kraft white liquor can be used as the alkali, and oxygen gas is oxygen from a cryogenic separation method, from PSA (Pressure Swing Adsorption). Oxygen, oxygen from VSA (Vacuum Swing Adsorption), etc. can be used. The oxygen gas and alkali are added to a medium-concentration pulp slurry in a medium-concentration mixer, and after sufficiently mixed, sent to a reaction tower capable of holding a mixture of pulp, oxygen and alkali for a certain period of time under pressure, Delignified.

  The oxygen gas addition rate is 0.5 to 3% by mass per mass of dry pulp, the alkali addition rate is 0.5 to 4% by mass, the reaction temperature is 80 to 120 ° C., the reaction time is 15 to 100 minutes, and the pulp concentration Is 8 to 15%, and other known conditions can be applied. In the present invention, in the alkali oxygen bleaching step, it is a preferred embodiment that the alkali oxygen bleaching is continuously carried out a plurality of times and delignification proceeds as much as possible.

  The pulp that has been subjected to alkaline oxygen bleaching is then sent to a washing step. After washing, the pulp is sent to a multistage bleaching process.

  In the multistage bleaching step for obtaining the bleached pulp used in the present invention, the ozone bleaching stage (Z) is always used. This is because by using the ozone bleaching stage, hexeneuronic acid contained in a large amount in the pulp can be decomposed, and the color return of the pulp due to hexeneuronic acid can be suppressed. The treatment conditions of the ozone bleaching stage of the present invention are not particularly limited, but when ozone is reacted excessively, the pulp strength is impaired. It is 0.1% to 1.0%, and more preferably 0.3% to 0.7%. The treatment temperature is 10 ° C to 100 ° C, preferably 20 ° C to 70 ° C, the treatment time is 1 second to 60 minutes, preferably 10 seconds to 5 minutes, and the treatment pH is 1.5 to 7, preferably 2 to 4. . The pulp concentration in the ozone bleaching stage may be medium or high, and is not limited. If necessary, chlorine dioxide and other bleaching chemicals can be used in combination.

  The bleaching stage that can be used in the multistage bleaching process of the present invention is not particularly limited except that an ozone bleaching stage is used, and a known bleaching stage can be used. Known bleaching stages include chlorine dioxide bleaching stage (D), alkali extraction stage (E), oxygen bleaching stage (O), hydrogen peroxide bleaching stage (P), peracid bleaching stage (PA), acid washing stage (a ), Acid treatment stage (A) and the like. Examples of the multi-stage bleaching process include ZEPD, ZEDP, ZEPP, AZPEPD, and AZED. -P, A-Z-E-P-AP, a-Z-E-P-D, a-Z-E-D-P, a-Z-E-P-AP, Z / D-E-P -D, Z / D-E-D-P, Z / D-E-P-AP, AZ / D-E-P-D, AZ / D-E-D-PA-Z / D -E-P-AP, a-Z / D-E-P-D, a-Z / D-E-D-P, a-Z / D-E-P-AP, Z-EO-P-D , Z-EO-DP, Z-EO-P-AP, AZ-EO-PD, AZ-EO-DP, AZ-EO-P-AP, a-Z -EO-P-D, a-Z-EO-DP, a-Z-EO-P-AP, Z / D-EO-PD, Z / D-EO-DP, Z / D -EO-P- P, AZ / D-EO-PD, AZ / D-EO-DP, AZ / D-EO-P-AP, aZ / D-EO-PD, Examples include aZ / D-EO-DP, aZ / D-EO-P-AP, and a hygienic section can be provided. Further, a bleaching stage can be further added, or another bleaching stage can be incorporated in the bleaching stage and used together, and is not particularly limited. The pulp after multistage bleaching is sent to a beating process or a papermaking process.

  In addition, to the above-mentioned pulp, as long as the effects of the present invention are not impaired, mechanical pulp such as crushed wood pulp, pressurized ground wood pulp, refiner ground wood pulp, thermomechanical pulp, deinked waste paper pulp, waste paper, etc. are used as appropriate can do.

  The pulp constituting the base paper is subjected to a beating process, and then sent to a paper machine as a paper stock which is a slurry-like pulp aqueous dispersion. For this paper material, fillers, internally added sizing agents, anionic, nonionic, cationic or amphoteric retention improvers, drainage improvers, paper strength enhancers, etc. It can be added as necessary.

  Examples of the filler used for forming the base paper in the present invention include heavy calcium carbonate, light calcium carbonate, calcium sulfite, gypsum, talc, clay, calcined kaolin, white carbon, amorphous silica, delaminated kaolin, Examples include inorganic pigments such as diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide, and organic pigments such as urea / formalin resin fine particles and fine hollow particles. Fillers contained in paper can be reused. Two or more fillers can be used in combination. The blending amount of the filler is generally added so that the paper (base paper) ash content is in the range of 3 to 20% by mass.

  Specific examples of the internally added sizing agent used in the present invention include, for example, sizing agents such as alkyl ketene dimer, alkenyl succinic anhydride, styrene-acrylic, higher fatty acid, petroleum resin, and rosin. Is mentioned. Specific examples of yield improvers, drainage improvers, and paper strength enhancers include, for example, polyvalent metal compounds such as aluminum (specifically, sulfate bands, aluminum chloride, sodium aluminate, basic aluminum compounds). Etc.), various starches, polyacrylamide, urea resin, polyamide / polyamine resin, polyethyleneimine, polyamiin, polyvinyl alcohol, polyethylene oxide and the like. Moreover, it is also possible to use a bulking agent and a softening agent having a function of inhibiting the binding between pulp fibers as long as the effects of the present invention are not hindered. Specific examples of bulking agents and softeners include, for example, ester compounds of polyhydric alcohols and fatty acids, polyoxyalkylene compounds of polyhydric alcohols and fatty acid ester compounds, fatty acid polyamidoamines, polyhydric alcohol surfactants, An ionic surfactant etc. can be illustrated. The amount of the bulking agent and the softening agent is generally about 0.05 to 2.0% by mass relative to the pulp in terms of dry weight.

  There are no particular limitations on the papermaking (former) format, and twin wire formers, on-top formers, gap formers, and the like can be used. When making a base paper at a high speed exceeding 1200 m / min, it is preferable to make a paper in a gap former format that is excellent in operability and quality of the obtained base paper.

Regarding the papermaking conditions of the base paper, any system such as acidic papermaking, neutral papermaking, and weak alkali papermaking may be used. The base paper can be subjected to a normal size press treatment using an adhesive such as a starch derivative, polyvinyl alcohol, or polyacrylamide, and can also be subjected to a smoothing finishing treatment using a machine calendar, a soft calendar, or the like. As the size press apparatus, a two-roll type, a gate roll type, a film transfer type, and the like can be used. In the case of operation at a high speed of 1000 m / min or more, a film transfer type having excellent operability is preferable. The basis weight of the base paper made under these paper making conditions is preferably in the range of 30 to 150 g / m ² .

In the present invention, it is preferable to contain 50% by mass or more of heavy calcium carbonate having an average particle size in the range of 0.5 to 1.2 μm in the top coat layer, and the heavy calcium carbonate has a particle size distribution. The ratio of the particle size (D ₇₅ ) corresponding to 75% by mass of the measurement curve to the particle size (D ₂₅ ) corresponding to 25% by mass, D ₇₅ / D ₂₅ being in the range of 1.5 to 3.3. Is more preferable. As a reminder, D ₇₅ / D ₂₅ means that the smaller the value, the narrower the particle size distribution.

By containing 50% by mass or more of heavy calcium carbonate having an average particle size in the range of 0.5 to 1.2 μm, a coated paper having high whiteness and excellent smoothness and printing gloss can be obtained. If the average particle size is less than 0.5 μm, it is not preferable because the printing gloss decreases and the required amount of adhesive increases, and if it exceeds 1.2 μm, the effect of satisfying the expression of smoothness of the coated paper is obtained. I can't get it. Furthermore, the ratio of the particle diameter (D ₇₅ ) corresponding to the cumulative mass 75% of the heavy calcium carbonate particle size distribution measurement curve to the particle diameter (D ₂₅ ) corresponding to the cumulative mass 25%, D ₇₅ / D ₂₅ is When it is in the range of 1.5 to 3.3, a remarkable effect is obtained in the expression of the smoothness of the coated paper and the expression of the printing gloss.

Here, the average particle size referred to with respect to the pigment particles in the present invention means a particle size (D ₅₀ ) corresponding to 50% by mass of a particle size distribution measurement curve drawn using a Sedi graph 5100 manufactured by Shimadzu Corporation. To do. The particle size (D ₇₅ ) corresponding to 75% by mass and the particle size (D ₂₅ ) corresponding to 25% by mass of the particle size distribution curve used for the definition of the particle size distribution were similarly determined using the Cedi graph 5100.

  The undercoat coating layer in the present invention is coated by a film transfer roll coating method. By using the film transfer roll coating method rather than the conventional blade coating method, it is possible to produce coated paper with less productivity and high productivity.

  Moreover, it is preferable that the heavy calcium carbonate contained in the said undercoat coating layer is the range whose average particle diameter is 0.5-2.5 micrometers. By containing 50% by mass or more of heavy calcium carbonate in the particle size range in the undercoat coating layer, even when applied by the film transfer roll coating method, the whiteness is high, and smoothness and printing gloss are excellent. Coated paper is obtained. When the average particle size is larger than 2.5 μm, even if the above-described topcoat coating solution is applied onto the undercoat coating layer, an effect satisfying the expression of the smoothness of the coated paper cannot be obtained. On the other hand, if the average particle size is smaller than 0.5 μm, the printing gloss is lowered or the required amount of adhesive is increased, which is not preferable.

  As the film transfer roll coating apparatus in the present invention, a gate roll coater, a blade or a rod metering size press coater can be used.

  The heavy calcium carbonate used in the coated paper for printing of the present invention can of course be prepared by a method of pulverizing and classifying natural limestone, but it can be obtained as a commercially available heavy calcium carbonate. Can be used by pulverizing and classifying as necessary. The pulverization referred to here includes, for example, pulverization by a dry pulverizer such as a roll mill, jet mill, dry ball mill, impact pulverizer, wet pulverizer such as a wet ball mill, a vibration mill, a stirred tank mill, a flow tube mill, and a coball mill. The pulverization by a machine is mentioned, and these pulverizers are used in appropriate combination. The classification method includes, for example, sieving such as resonant vibration sieve, low head screen, electromagnetic screen, dry classification such as micron separator, cyclone, etc., wet classification such as decanter centrifuge, liquid cyclone, drug classifier, etc. These classifiers are used in appropriate combination.

  In the present invention, in addition to the heavy calcium carbonate, pigments that can be used when a coating layer is provided on the base paper include, for example, various natural mineral pigments such as various kaolins, talc, and heavy calcium carbonate, light calcium carbonate , Composite synthetic pigments of calcium carbonate and other hydrophilic organic compounds, satin white, lithopone, titanium dioxide, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate, calcined kaolin, hollow organic pigment, dense organic pigment, There are plastic pigments, binder pigments, plastic beads, and microcapsules. In particular, when using a pigment other than the overcoating layer and the undercoating layer co-heavy calcium carbonate, kaolin is preferable, and an average particle size of 1.0 μm or less is more preferable because blank paper smoothness and printing smoothness are improved.

  The binder used in the coating layer includes starch purified from natural plants, hydroxyethylated starch, oxidized starch, etherified starch, phosphate esterified starch, enzyme-modified starch, and cold water soluble starch obtained by flash drying them. Natural polysaccharides such as dextrin, mannan, chitosan, arabinogalactan, glycogen, inulin, pectin, hyaluronic acid, carboxymethylcellulose, hydroxyethylcellulose, and oligomers thereof, and modified forms thereof. Furthermore, natural polymers such as casein, gelatin, soybean protein, and collagen, and modified products thereof, and synthetic polymers and oligomers such as polylactic acid and peptides can be mentioned. In addition, copolymer latex such as styrene butadiene, acrylic, polyvinyl acetate, ethylene vinyl acetate, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyacrylamide, urea, melamine / formalin resin, polyethylene Examples thereof include water-soluble synthetic compounds such as imine and polyamide polyamine / epichlorohydrin. One or more of these can be used. In addition, the use of a known natural or synthetic organic compound is not particularly limited.

  In addition, as a thickener used in the coating liquid, water-soluble polymers such as carboxymethylcellulose, sodium alginate, methylcellulose, hydroxymethylcellulose, casein, sodium polyacrylate, polyacrylate, styrene maleic anhydride copolymer And synthetic polymers such as silicates and inorganic polymers such as silicates.

  In addition, various auxiliary agents that are usually used such as a dispersant, an antifoaming agent, a water-proofing agent, and a coloring agent, and those obtained by cationizing these auxiliary agents are suitably used as necessary.

  In the present invention, the method for coating a coating layer other than the undercoat coating layer is not particularly limited, and includes various blade coaters such as trailing, flexible, roll application, fountain application, short dwell, size press, Various transfer coaters such as gate rolls and shim sizers, air knife coaters, bar coaters, rod coaters, rod blade coaters, champ flex coaters, gravure coaters, curtain coaters, die coaters, direct fountain coaters, spray coaters, cast coaters, etc. Is used as appropriate. These devices may be on-machine or off-machine.

Although there is no particular limitation on the coating amount of the coating composition of the coating liquid, generally, the undercoat coating layer and the topcoat coating layer have a dry weight of about 3 to 15 g / m ² per side and are obtained for printing. Considering the white paper quality, print quality and printability of the coated paper, as well as the drying capacity during the production of the coated paper, the total of about 10 to 30 g / m ² per side of the undercoat and topcoat layers It is desirable to be in the range. As a method for drying the wet coating layer, for example, various methods such as steam drying, gas heater drying, electric heater drying, infrared heater drying and the like can be adopted.

Regarding the coated paper for printing of the present invention, the description has so far been centered on the two-layer configuration of the topcoat layer disposed on the outermost layer of the coating layer and the undercoat layer in contact with the base paper. Further, an intermediate coating layer in contact with the undercoat coating layer may be formed between the undercoat coating layer and the like to form a structure of three or more layers. The composition and coating amount of the intermediate coating layer are not particularly limited, and a coating liquid mainly composed of an arbitrary pigment and an adhesive is about 0.5 to 10 g / m ² per side by dry weight. Then, coating and drying may be performed with a gate roll coater, a blade coater or the like.

  In the production of the coated paper for printing of the present invention, after the formation of the top coat layer, smoothing treatment is performed in various calendar devices, such as a calendar device, a super calendar, a soft calendar, Commonly used calendar devices such as a gloss calendar, a compact calendar, a mat super calendar, and a mat calendar can be used as appropriate. As the calender finishing conditions, the temperature of the rigid roll, the calender pressure, the number of nips, the roll speed, the paper moisture before the calender, and the like are appropriately selected according to the required quality. Furthermore, the calendar device includes an off type that is different from the coater and an on type that is integrated with the coater, but can be used in either case. The material of the calendar apparatus to be used is a roll which is mirror-finished with a metal or a hard chrome plating on the surface of the rigid roll. As the elastic roll, a roll obtained by molding a resin roll such as urethane resin, epoxy resin, polyamide resin, phenol resin, or polyacrylate resin, cotton, nylon, asbestos, aramid fiber, or the like is appropriately used. In addition, it is also possible to use suitably combining the water coating apparatus, electrostatic humidification apparatus, steam humidification apparatus, etc. for humidity control and humidification of the coated paper after finishing with a calendar.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples. In addition, unless otherwise indicated, the part and% in an example show a mass part and the mass%, respectively. Moreover, the addition amount of the used chemical | medical agent shows the mass part of solid content conversion.

Example 1
(Manufacture of pulp)
Using a Lo-solids digester (manufactured by Andritz Co., Ltd.), hardwood chips composed of acacia mangum: eucalyptus grandis = 30: 70 (mass ratio) were kraft-cooked by the Lo-solids cooking method. Here, using white liquor with a sulfidity of 28%, the white liquor addition rate is 10% per chip dry weight as an active alkali, divided into 8% in the cooking zone and 2% in the washing zone And the cooking temperature was 146 ° C. After digesting the chips after cooking, unbleached pulp was obtained through a washing process, a screen process, and a washing process again.

  To the unbleached pulp, 1.7% of caustic soda and 1.8% of oxygen per weight of dry pulp were added, and two-stage alkaline oxygen bleaching was performed under the conditions of a pulp concentration of 10% and 98 ° C. for 50 minutes. Here, caustic soda was added all at once in the first stage, and oxygen gas was added in 1.0% in the first stage and 0.8% in the second stage. The pulp after alkaline oxygen bleaching was washed in the washing step.

  After 1.2% sulfuric acid was added to the pulp after the alkali oxygen bleaching and the pulp concentration was 10%, 60 ° C. and 60 minutes, the pulp was washed in the washing step. Next, after adding 0.5% ozone and 0.5% chlorine dioxide per weight of dry pulp, medium concentration ozone / chlorine dioxide bleaching was performed under the conditions of pulp concentration 10%, 58 ° C., 60 minutes, then washed. It was washed in the process. Next, 1.0% caustic soda and 0.1% hydrogen peroxide per weight of dry pulp are added, and after alkali extraction under conditions of pulp concentration 10%, 60 ° C, 90 minutes, washing treatment is performed in the washing step. did. Finally, 0.2% chlorine dioxide is added to the dry pulp weight, chlorine dioxide is bleached at a pulp concentration of 10%, 70 ° C, 120 minutes, and then washed in the washing step. Obtained. The obtained bleached pulp had an ISO whiteness of 90.1%, a length-weighted average fiber length of 0.68 mm, and a fiber width of 16.0 μm. The xylan content was 13.5%.

Here, the xylan content in the bleached pulp was measured by the following method.
350 mg of absolutely dried bleached pulp was collected, 3 ml of 72% sulfuric acid was added thereto, and the mixture was stirred well, and then allowed to stand for 2.5 hours. Thereafter, 84 ml of distilled water was added and stirred well, followed by reaction at 121 ° C. for 1 hour to hydrolyze the polysaccharide of the bleached pulp to a monosaccharide. Monosaccharides were quantified using ion chromatography (DX-500, manufactured by Dionex) equipped with a column (CarboPac PA1), and the ratio of the xylose content in the total monosaccharide content was defined as the xylan content of bleached pulp.

(Preparation of base paper)
After adding light calcium carbonate (trade name: Tama Pearl TP-121, manufactured by Okutama Kogyo Co., Ltd.) as a filler to 100% of the pulp slurry obtained by beating the bleached pulp up to 450 ml of CSF, so that the base paper ash content becomes 10% , 0.5% aluminum sulfate, cationic starch (trade name: Ace K100, manufactured by Oji Cornstarch Co., Ltd.) 0.5%, alkyl ketene dimer sizing agent (trade name: Size Pine K-287) Arakawa Chemical Industries, Ltd.) 0.1% and polyacrylamide (trade name: Polystron 851, Arakawa Chemical Industries, Ltd.) 0.2% were sequentially added to prepare a paper stock. A paper layer was formed from the paper stock by a gap former at an operation paper making speed of 1500 m / min, squeezed with two shoe presses, and then dried with a multi-cylinder dryer to obtain 53 g / m ² of base paper.

(Preparation of pigment coating solution for undercoat coating layer)
In a pigment slurry composed of heavy calcium carbonate (trade name: Hydrocurve 60, manufactured by Bihoku Flour & Chemical Co., Ltd., average particle size 1.29 μm), starch (trade name: Ace A, 30 parts of Oji Corn Starch Co., Ltd.), 5 parts of styrene-butadiene copolymer latex (trade name: OJ-2000, JSR Co.) are added, and an antifoaming agent and a dye are sequentially added as auxiliary agents. A pigment coating solution for an undercoat coating layer having a solid content concentration of 23% was prepared.

(Preparation of pigment coating solution for top coat layer)
As a dispersant, sodium polyacrylate (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) is added to an aqueous solution in which 0.1 part of kaolin (trade name: Hydra Gloss 90, manufactured by Huber) is added to the dispersed kaolin. 50 parts, 50 parts of heavy calcium carbonate (trade name: Hydrocurve 90, manufactured by Bihoku Flour Chemical Co., Ltd., average particle size 0.81 μm, D ₇₅ / D ₂₅ = 3.76) are added and dispersed with a Coreless disperser. Thus, a pigment slurry was prepared. To 100 parts of this pigment slurry, 3 parts of oxidized starch (trade name: Oji Ace A, supra), 9 parts of styrene-butadiene copolymer latex (trade name: OJ-2000, manufactured by JSR), Further, an antifoaming agent and a dye were sequentially added as auxiliary agents to finally prepare a pigment coating solution for an overcoat coating layer having a solid content concentration of 63%.

(Create coated paper for printing)
The base paper (basis weight 53 g / m ² ) obtained above is coated with the coating liquid for the undercoat coating layer obtained above by the metalling size press method, and the dry coating amount per side becomes 8 g / m ^2. Thus, coating and drying were performed to form an undercoat layer on both sides. Next, using a blade coater that supplies the coating liquid for the top coating layer obtained above to each of the undercoat layers by a jet fountain method, the dry coating amount per side is 8 g / m. Coating and drying were performed so as to be ^2, and a top coating layer was provided on both sides. The coated paper obtained in this way is placed on a multi-nip calender in which a metal roll and a resin roll heated to 100 ° C. are inclined, and on one side, a metal roll and a resin roll under a linear pressure of 200 kN / m. A total of 8 nips were passed so that the papers were in contact with each other 4 times, and a coated paper for printing having a basis weight of 85 g / m ² was obtained.

Example 2
A coated paper for printing was obtained in the same manner as in Example 1 except that in the preparation of the pigment coating solution for the top coat layer of Example 1, 0 part of kaolin and 100 parts of heavy calcium carbonate were used.

Example 3
In the preparation of the pigment coating solution for the undercoat coating layer of Example 2, the same procedure as in Example 2 except that 50 parts of kaolin (trade name: Hydra Gloss 90, manufactured by Huber) and 50 parts of heavy calcium carbonate were used. Thus, a coated paper for printing was obtained.

Example 4
In the preparation of the pigment coating solution for the top coat layer of Example 1, heavy calcium carbonate (trade name: Cover Curve, manufactured by Omiya) having an average particle size of 0.63 μm and D ₇₅ / D ₂₅ = 2.70 was used. The coated paper for printing was obtained like Example 1 except having changed.

Comparative Example 1
In the production of the pulp of Example 1, bleached pulp D was prepared by changing the hardwood chip acacia mangum: eucalyptus grandis = 30: 70 (mass ratio) to birch = 100 and changing the cooking temperature to 157 ° C. Except for the above, a coated paper for printing was obtained in the same manner as in Example 1. The bleached pulp obtained had an ISO whiteness of 89.2%, a length-weighted average fiber length of 0.76 mm, and a fiber width of 20.2 μm.

Comparative Example 2
In Example 1, white liquor was used as an active alkali, added to the chip supply system by 20% per unit dry weight of the chip, no white liquor was added to the cooking zone and washing zone, and the cooking temperature was changed to 150 ° C. Was digested in the same manner as in Example 1 and subjected to two-stage oxygen bleaching to obtain pulp after alkaline oxygen bleaching. Next, the sulfuric acid treatment temperature of Example 1 was changed from 60 ° C. to 95 ° C., and the chlorine dioxide addition rate was changed to 1.0% without adding ozone in the medium concentration ozone / chlorine dioxide bleaching stage. Except for the above, the same bleaching treatment as in Example 1 was performed. The bleached pulp obtained had an ISO whiteness of 90.0% and a xylan content of 11.5%. A coated paper for printing was obtained in the same manner as in Example 1 except that the obtained bleached pulp was used.

Comparative Example 3
In the preparation of the pigment coating solution for the top coat layer of Example 1, heavy calcium carbonate had an average particle size of 0.3 μm and D ₇₅ / D ₂₅ = 2.4 (homemade), and Example 1 Similarly, a coated paper for printing was obtained.

Comparative Example 4
Example 1 In the preparation of the pigment coating solution for the top coat layer of Example 1, except that 100 parts of heavy calcium carbonate (homemade) having an average particle size of 2.34 μm and D ₇₅ / D ₂₅ = 3.52 was used. In the same manner as in No. 1, a coated paper for printing was obtained.

Comparative Example 5
A coated paper for printing was obtained in the same manner as in Example 1 except that 90 parts of kaolin and 10 parts of heavy calcium carbonate were used in the preparation of the pigment coating solution for the top coat layer of Example 1.

Comparative Example 6
In the preparation of the pigment coating liquid for the undercoat coating layer of Example 1, the coated paper for printing was carried out in the same manner as in Example 1 except that 100 parts of heavy calcium carbonate (homemade) having an average particle size of 3.71 μm was used. Got.

Comparative Example 7
In the preparation of the pigment coating solution for the undercoat coating layer of Example 1, the coated paper for printing was carried out in the same manner as in Example 1 except that 100 parts of heavy calcium carbonate (homemade) having an average particle size of 0.14 μm was used. Got.

Comparative Example 8
In the preparation of the pigment coating solution for the undercoat coating layer of Example 1, the same procedure as in Example 1 was conducted except that 90 parts of kaolin (trade name Hydra Gloss 90, supra) and 10 parts of heavy calcium carbonate were used. A coated paper for printing was obtained.

Comparative Example 9
A coated paper for printing was obtained in the same manner as in Example 1 except that in the coating of the undercoat coating liquid of Example 1, coating was performed with a blade coater that supplied the coating liquid by the jet fountain method.

  The coated paper for printing obtained in Examples and Comparative Examples was evaluated by the following method, and the results are shown in Table 1. All the evaluation tests were performed in an environment of 23 ° C. and a relative humidity of 50%.

(Whiteness)
It measured using the whiteness meter according to ISO2470 (1999), and calculated | required the average value.

(Print smoothness and print gloss)
Using an RI printer (Made Seisakusho), printing was performed using 0.2 cc of printing ink (Values-G type, Dainippon Ink & Chemicals, Inc.), and ink transfer uniformity (printing smoothness), and The glossiness (printing gloss) of the printed surface was visually observed and evaluated.
A: Excellent in printing smoothness and printing gloss.
○: Excellent printing smoothness and printing gloss.
X: Inferior to printing smoothness and printing gloss.

(Surface printing strength)
With a RI printer (Meiji Seisakusho), 0.4 cc of printing ink (paper test SD50 red BT = 13 manufactured by T & K TOKA) is spread on a roll, and the transfer speed is adjusted slowly on the coated paper to be evaluated. After printing and printing, knead the ink again without wiping the ink on the roll, overprint it on the coated paper once printed, and then knead the ink again without wiping the ink on the roll twice. Overprinted on the printed coated paper and overprinted 3 times for convenience. Thereafter, the peeled state of the paper surface formed by the ink remaining on the roll was transferred to another paper, and the color loss of the transferred ink was visually evaluated.
A: No color loss.
○: Slightly missing color is observed.
X: The color is remarkably lost.

(Operability)
The occurrence of paper breakage during coating of coated paper was evaluated.
A: There is no occurrence of a piece of paper.
○: Paper breakage occurs rarely.
X: Paper breakage occurs remarkably.

  As apparent from Table 1, in the examples according to the present invention, coated paper having high printing smoothness and high printing gloss can be efficiently produced. On the other hand, in the comparative example, smoothness, printing gloss, and surface strength are inferior, and operability is a significant difficulty in blade coating.

Claims (2)

  In a coated paper for printing in which two or more coating layers mainly composed of pigment and adhesive are provided on at least one side of the base paper, 50% or more of the bleached pulp used in the base paper is eucalyptus and / or acacia A pulp produced by a kraft cooking method in which the bleached pulp is added by split addition of cooking liquor, and further produced in a multi-stage bleaching process including an ozone bleaching stage, the coated paper In the topcoat coating layer disposed in the outermost layer, an undercoat coating containing 50% by mass or more of heavy calcium carbonate having an average particle diameter in the range of 0.5 to 1.2 μm in contact with the base paper The layer contains heavy calcium carbonate having an average particle diameter of 0.5 to 2.5 μm in an amount of 50% by mass or more of the total pigment, and the undercoat coating layer is coated by a film transfer roll coating method. Printing characterized by Coated paper. The ratio of the particle size (D ₇₅ ) corresponding to 75% by mass and the particle size (D ₂₅ ) corresponding to 25% by mass of the heavy calcium carbonate contained in the top coat layer, D coated printing paper according to claim _{1, 75} / _{D 25} is equal to or is in the range of 1.5 to 3.3.