JP2010116646A - Method for producing coated printing paper - Google Patents

Abstract

An object of the present invention is to provide a method for producing a coated paper for printing excellent in whiteness, smoothness and printing smoothness at low cost.
In a method for producing a coated paper for printing in which at least one coating layer containing a pigment and an adhesive is provided on at least one side of a base paper, 50% or more of bleached pulp used for the base paper is eucalyptus material. Alternatively, the paper material containing the bleached pulp produced by the multi-stage bleaching process including the ozone bleaching stage is pulped by the kraft cooking method using acacia wood as a raw material and dividedly added to the cooking liquor. A process that forms wet paper, a process that squeezes wet paper with a press part, a paper making process that dries wet paper with a dryer part, a process that applies a coating liquid with a blade method, and a calendar that consists of a metal roll and an elastic roll. The coating layer formed in the coating step has a step of flattening and ₅₀ heavy calcium carbonate having an average particle diameter (D ₅₀ ) of 0.5 to 2.5 μm. It is characterized by containing at least% by volume.
[Selection figure] None

Description

  The present invention relates to a method for producing a coated paper for printing, and particularly relates to a method for producing a coated paper for printing excellent in white paper and printing quality.

  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 subjected to multicolor printing or single color printing, and are widely used as commercial printed materials such as leaflets, brochures, and posters, or as publications such as books and magazines. In recent years, with the progress of visualization and colorization of printed materials, the demand for higher quality of coated paper for printing has increased, and the appearance of gloss, smoothness, whiteness, etc. has become more important than ever before. . In particular, for commercial printing such as flyers, brochures, posters, etc., low cost and high quality are desired for the purpose of advertising media.

  As a means of increasing the whiteness of the coated paper for printing, it is possible to blend a fluorescent dye in the coating layer, or to blend heavy calcium carbonate with high whiteness in the pigment used in the coating layer. Known (see Patent Documents 1 and 2). However, the blending of fluorescent dyes improves the whiteness of coated paper for printing, but tends to cause a decrease in whiteness over time due to heat and light, and maintains the quality requirement level required for coated paper for printing. There was a problem that made it impossible. On the other hand, heavy calcium carbonate can maintain a high level of whiteness over a long period of time, but generally used heavy calcium carbonate has a larger particle size than kaolin and exhibits high smoothness. It was difficult to do.

  In addition, as a means for obtaining coated paper with excellent smoothness, pigments such as engineered kaolin, delaminated kaolin, and plastic pigment, which have a high level of smoothness when calendering, are blended. Is effective (see Patent Documents 3 and 4). However, these pigments are expensive and there is a problem that the production cost of the coated paper for printing becomes high. Furthermore, since whiteness is lower than that of heavy calcium carbonate, in order to maintain the required whiteness, blending of fluorescent dyes is unavoidable and may cause the above-mentioned problems due to blending of fluorescent dyes. there were.

  Furthermore, in recent years, paper machines, coating machines, and finishing machines have been widened and speeded up for the purpose of labor saving and manufacturing cost reduction, and even under such circumstances, There is a strong need to find a method of producing a coated paper for printing that can provide a higher quality level.

JP-A-3-294598 JP 2004-3057 A JP 2002-194698 A JP 2006-249607 A

  The present invention provides a method for inexpensively producing a coated paper for printing excellent in whiteness, smoothness and printing smoothness of white paper.

The present invention relates to a method for producing a coated paper in which at least one layer of a base paper is coated with one or more layers of a coating liquid mainly composed of a pigment and an adhesive, and 50% or more of the bleached pulp used for the base paper is eucalyptus Alternatively, the raw material is acacia wood, and the bleached pulp is pulped by a cooking method in which cooking liquor is added in portions, and further produced in a multi-stage bleaching process including an ozone bleaching stage, A process of forming wet paper with a gap former type wire part in which a paper stock containing pulp is jetted between two wires forming a loop from a head box and dehydrated with a forming roll to form a paper layer, wet paper in the press part The process of squeezing water, the papermaking process of drying wet paper in the dryer part, the process of coating the coating liquid by the blade method, and the combination of metal roll and elastic roll The coating layer formed in the coating step has an average particle diameter (D ₅₀ ) measured by a sedimentation method of 0.5 to 2.5 μm. It is a manufacturing method of the coated paper for printing characterized by containing 50 mass% or more of heavy calcium carbonate in the range.

The coating layer has at least two layers, an average particle diameter measured by sedimentation method for the outermost coating layer (D ₅₀₎ is a heavy calcium carbonate in the range of 0.5～1.2Myuemu 50 wt% It is preferable to contain above.

The heavy calcium carbonate contained in the outermost coating layer has a particle size (D ₇₅ ) corresponding to ₇₅ cumulative mass% and a particle size (D ₂₅ ) corresponding to 25 cumulative mass% of the particle size distribution curve by the precipitation method. The ratio (D ₇₅ / D ₂₅ ) is preferably in the range of 1.5 to 3.3.

  In the blade type coating process, it is preferable that the method of supplying the coating liquid is a jet fountain type.

  It is preferable that a calendar formed by a combination of the metal roll and the elastic roll is composed of three or more rolls and two or more nips.

  It is preferable that the calendar rolls are inclined.

  By the production method of the present invention, a coated paper for printing excellent in whiteness, smoothness and printing smoothness of white paper can be produced at low cost.

  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 pulp used for paper must be made from eucalyptus or acacia. Don't be. Eucalyptus materials include E.camaldulensis, E.citriodora, E.deglupta, E.globulus, E.grandis, E.maculata, E.punctata, E.saligna, E.terelicornis, E.urophylla, E.camaldulensis, etc. These hybrids are mentioned, and as acacia wood, A.aulacocarpa, A.auriculiformis, A.catechu, A.crassicarpa, A.decurrens, A.holosericea, A.leptocarpa, A.maidenii, A.mangium A. mearnsii, A. melanoxylon, A. neriifolia, A. silvestris, etc. and their hybrids. Pulp made from eucalyptus wood or acacia wood has a small fiber width, so when a paper sheet is formed, the number of fibers per unit US tsubo increases, and a sheet with high smoothness or when the pulp is beaten Since the load is small, when a paper sheet is formed from the pulp after beating, a sheet with low paper density can be obtained.

  As the cooking method for obtaining the pulp used in the present invention, known cooking methods such as kraft cooking, polysulfide cooking, soda cooking, alkali sulfite cooking, etc. can be used. It needs to be cooked. By adding the cooking liquor in a divided manner, the alkali concentration throughout the cooking can be kept low, and the elution of hemicellulose in the material can be suppressed. This is because a pulp having a high hemicellulose content is obtained as a result, and the use of a pulp having a high hemicellulose content is one of the matters indispensable 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 split-added cooking method, but the cooking methods such as the Lo-solids method, the Compact cooking method, the Kobudomari cooking method, etc., use a small amount of energy for cooking. It is preferably used from the standpoint of incidental effects such as good bleachability of the pulp to be produced.

  For example, when the kraft cooking method is used, the degree of sulfidation of the cooking liquor is 5 to 75%, preferably 15 to 45%, and the effective alkali addition rate is 5 to 30% by weight, preferably 10 to 25% by weight, based on the mass of absolutely dry wood. The 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 alkaline oxygen bleaching step, it is a preferred embodiment that the alkali oxygen bleaching is continuously performed 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 from eucalyptus wood and acacia wood 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 to 100 ° C., preferably 20 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. To this paper material, fillers, internal sizing agents, anionic, nonionic, cationic or amphoteric yield improvers, drainage improvers, paper strength enhancers, and other internal additive agents for papermaking, It can be added as necessary.

  Examples of the filler used in the present invention include heavy calcium carbonate, light calcium carbonate, calcium sulfite, gypsum, talc, clay, calcined kaolin, white carbon, amorphous silica, delaminated kaolin, diatomaceous earth, magnesium carbonate. Examples include inorganic pigments such as 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. Filled fillers can also 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, filter pigment 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 softening agent is generally about 0.05 to 2.0% by mass with respect to the pulp.

  The paper stock prepared as described above is supplied to the wire part of a paper machine to form a paper layer. In the wire part of the present invention, a gap former is used. In the gap former, the paper material is ejected from the head box between two looped wires to form a paper layer, and then after the dehydration process of the roll or blade dewatering mechanism, the suction box, blade, and suction couch While passing through a roll, a high vacuum box, etc., a wet paper dehydrated to about 15 to 25% as dryness is formed. At this time, since the paper is sandwiched between two wires from the beginning, the paper part is less disturbed compared to the long net paper machine and on-top hybrid former, and a uniform paper layer is produced at high speed. Can be formed. The operation speed of the gap former is not particularly limited, but is generally 1000 m / min or more in papermaking speed, and preferably 1300 m / min or more in consideration of productivity.

  The head box installed in the gap former may be installed in the horizontal direction with the downstream side. However, under the high-speed papermaking intended by the present invention, points such as formation, interlayer strength, front / back difference, fiber orientation angle, etc. Therefore, it is desirable that the head box is an upward head box in which the influence of gravity is small. Therefore, the head box is preferably installed upward in a state of being inclined vertically or downstream. In this case, the discharge angle between the paper discharge direction line and the horizontal line is preferably 30 degrees or more as a lower limit, more preferably 50 degrees or more and 90 degrees or less as an upper limit.

  The shape of the head box flow path (tube) is circular on the inlet side and rectangular on the outlet side, and a flow sheet is arranged on the paper outlet side in the head box, and a turbulence generator (turbulence generator) is located in front of it. Can be exemplified.

  It is preferable to dispose a flow rate profile adjusting mechanism in the head box because the width direction basis weight profile of the obtained paper can be improved. An example of the flow rate profile adjustment mechanism is a density adjustment type profile adjustment mechanism. The density adjustment type profile adjustment mechanism has a flow rate profile of the paper discharged from the head box tip even if the properties of the paper change by arranging a dilution water injection system that can adjust the flow rate profile in the width direction. Therefore, this is a preferable mode. In addition, although clear water can be used as dilution water, from the viewpoint of effective use of resources, white water generated from a wire by dehydration of paper is preferably used. In addition, the control pitch of the flow rate profile using dilution water is preferably in the range of 55 to 70 mm because both the effect of improving the flow rate profile and the head box manufacturing efficiency are compatible.

  Furthermore, by having a flow path (hereinafter referred to as a channel) divided into a plurality of parts in the vertical direction as the paper flow path in the head box, the formation can be improved. This is for the purpose of obtaining a good formation by uniform mixing of the stock, and it is preferable to generate a turbulent state instead of a laminar flow in the headbox, but the occurrence of the turbulent state also forms flocs in which pulp fibers are intertwined. In order to induce, it is necessary to control the state of turbulence. For this purpose, a plurality of channels in the flow path in the head box is preferably used. The plurality of flow paths need not have the same shape throughout the entire area of the head box, and an effect is produced when at least one portion is a plurality of channels. In addition, when the number of channels is too large, the efficiency of manufacturing the head box is lowered, so that the number of channels is preferably 3 to 8. Moreover, although there is no restriction | limiting about the partition wall thickness between channels, it is in the state which discharges the paper material from the head box tip at least as a single fluid from a viewpoint which makes operativity and formation favorable. It is necessary to adjust accordingly. The flow rate from the head box is generally in the range of 120 to 330L per second per 1m width. However, the operability is improved by improving the dryness of the wet paper after the dehydration mechanism, and the quality of the obtained paper is improved. In consideration, 150 to 250 L is a preferable range as the flow rate.

  The initial dewatering starts immediately after the paper discharged from the head box moves between the two wires, but either the roll dewatering mechanism or the blade dewatering mechanism should be used as the dewatering mechanism used for the initial dewatering. It is possible to use one or a plurality of dewatering mechanisms selected from a roll dewatering mechanism or a blade dewatering mechanism. In the case of installing a plurality, a roll dewatering mechanism and a blade dewatering mechanism can be used in combination. Under high-speed papermaking conditions, a configuration in which a blade dewatering mechanism is arranged subsequent to a roll dewatering mechanism is preferable from the viewpoints of formation of the obtained paper, interlayer strength, front / back difference, fiber orientation angle and the like.

  In the roll dewatering mechanism, the paper material discharged from the head box tip is discharged between two wires positioned between a roll with a pressure reducing mechanism (hereinafter referred to as a forming roll) and a roll facing the roll. Dehydrated. The diameter of the forming roll used in the roll dewatering mechanism is determined in consideration of the installation space of the paper machine and the quality of the obtained paper. The forming roll diameter is generally 800 to 2000 mm, but if the forming roll diameter is too small, the difference between the front and back of the resulting paper tends to expand, and if it is too large, the initial dehydration becomes too strong and the formation is lowered. Since it becomes easy, as a diameter of a forming roll, 1500-1800 mm is a more preferable range. The vacuum pressure of the forming roll can be changed and operated as appropriate in order to adjust the operating conditions and the properties of the paper to be obtained. However, if the vacuum pressure is too high, the formation will be lowered and the front and back will be different. On the other hand, if it is too low, the dehydration / drying load in the press part and the dryer part is increased and the operability is lowered, which is not preferable. The vacuum pressure applied by the forming roll is appropriately adjusted depending on the operating conditions, the properties of the paper stock, and the properties of the paper to be obtained, but is generally 2 to 30 kPa.

  The larger the angle between the forming roll side contacted with the forming roll and the point where it is depressurized and separated from the forming roll, and the angle between the forming roll centers (hereinafter referred to as the wire wrap angle), the stronger the initial dewatering strength. There is a merit that it is easy to operate because it can improve the dryness of wet paper when moving to the process, but at the same time it has a demerit that it tends to cause a decrease in formation, so the operating conditions, the nature of the paper fee, the required paper It is appropriately adjusted depending on the properties. The wire wrap wrap angle is generally 15 to 35 degrees, and 18 to 29 degrees is a preferable range from the viewpoint of compatibility between operability and paper quality.

  As the blade dewatering mechanism, a configuration in which the surface in contact with the wire is composed of a suction box (sometimes called a forming shoe) and an opposite dewatering blade (sometimes called a counter blade) in contact with the wire on the opposite surface is exemplified. be able to.

  The blade material used for the blade dewatering mechanism is not particularly limited, and metal, resin, ceramic, etc. blades can be used. However, considering long-term use in a humid environment, ceramic or resin The use of made blades is preferred.

  In the blade dewatering mechanism, in the forming shoe installed opposite to the counter blade, the dynamic pressure generated by the blade disposed in the forming shoe (sometimes referred to as the forming shoe blade) and the moving wire (Hydrodynamic Pressure). Although it is dewatered, as the form of the forming shoe blade, a wedge-shaped serrated, scraping-type cera slide, a type called a venter shoe, or the like can be used. Further, from the viewpoint of preventing quality deterioration at the end of the paper layer formed between the two wires, the width of the forming shoe is preferably wider than the wire width.

  In addition, after the dehydration by the roll dehydration mechanism or the blade dehydration mechanism is performed, further dehydration is performed in the press part, but before moving to the press part, a couch roll with a pressure reducing mechanism (hereinafter referred to as a suction couch roll), Installation of a suction box or a high vacuum box having a curved surface or a flat surface in contact with the wire can contribute to a reduction in dehydration load in the press part and a reduction in front and back differences, which is a preferable mode. The vacuum pressure applied by the suction box, the suction couch roll, and the high vacuum box is also determined in consideration of operability and paper quality, but is generally 1 to 30 kPa.

  The paper stock exiting the head box is dehydrated through two wires (referred to as a top wire and a bottom wire) before moving to the press part. The difference between the front and back of the paper obtained when the dewatering amounts on the top and bottom wires are almost the same is reduced, but each part such as forming roll, forming shoe + counter blade, suction box, suction couch roll, high vacuum box, etc. The difference between the front and the back can also be improved by adjusting the amount of dehydration. However, if the roll dewatering mechanism or blade dewatering mechanism is extremely one-side dewatering, the difference between the front and back becomes too large, so the ratio of the amount of dewatering on the top wire / bottom wire side (the amount of white water generated by dewatering) , Preferably in the range of 35/65 to 65/35, and more preferably in the range of 45/55 to 55/45.

  The tension of the wire is generally 3 to 20 kN / m, and 5 to 12 kN / m is a preferable range from the viewpoint of operability and the quality of the obtained paper.

  The J / W ratio is not particularly limited, but is generally adjusted between 0.93 and 1.07 in terms of the quality of the obtained paper.

  The wet paper formed with the wire part as described above is continuously squeezed with the press part until the dryness reaches about 50%. In the present invention, since the wire part is a gap former for high-speed papermaking, it is preferable that the wet press device of the press part is also an apparatus that meets the high-speed papermaking conditions. That is, in order to increase the solid content concentration of the wet paper, it is necessary to increase the linear pressure only with the wet press device that passes the wet paper along with the felt through the narrow nip formed between the rolls / rolls. Therefore, in the nip, the water pressure in the vicinity of the roll surface increases rapidly, and crushing occurs between the paper layers. For this reason, it is preferable to use a wet press apparatus having a shoe-type wide nip adapted to high-speed papermaking conditions.

  The wet paper squeezed by the press part as described above is subsequently dried by the dryer part. In general, in a paper machine, a multi-cylinder dryer is used in which wet paper is pressed with a canvas on the surface of a large number of dryer cylinders and dried. Also in the present invention, a multi-cylinder dryer can be used as the dryer part.

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. Two-roll type, gate roll type, transfer type, etc. can be used as the size press device. However, the size press device attached to and used in the gap former type high-speed paper machine is easy to operate during high-speed operation. The transfer type 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, one or more coating layers mainly composed of a pigment and an adhesive are provided on at least one side of the base paper. As the pigment used for the coating layer, heavy calcium carbonate is used for printing. It is suitable from the viewpoint of the quality and cost of the paper, and contains 50% by mass or more of those having an average particle size (D ₅₀ ) measured by a sedimentation method in the range of 0.5 to 2.5 μm as the average particle size. Preferably, the heavy calcium carbonate has a ratio (D D) of a particle size (D ₇₅ ) corresponding to ₇₅ cumulative mass% and a particle size (D ₂₅ ) corresponding to 25 cumulative mass% of the particle size distribution curve by the sedimentation method (D more _{preferably 75} / _{D 25)} is in the range of 1.5 to 3.3. Other pigments are not particularly limited. For example, kaolin, talc, clay, calcined kaolin, heavy calcium carbonate, light calcium carbonate, titanium dioxide, satin white, calcium sulfite, gypsum, barium sulfate, white carbon In addition to inorganic pigments such as amorphous silica, diatomaceous earth, magnesium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bentonite, sericite, urea formalin resin fine particles, Pigments known for general coating, such as organic pigments such as fine hollow particles, can be used, and one or more kinds can be appropriately selected and used as necessary.

If the average particle size of the heavy calcium carbonate used here is less than 0.5 μm, it is not preferable because the printing gloss is reduced and the required amount of adhesive increases, and if it exceeds 2.5 μm, the coated paper An effect satisfying the expression of smoothness cannot be obtained. The ratio (D ₇₅ / D ₂₅ ) of the particle size (D ₇₅ ) corresponding to 75% by mass of the particle size distribution measurement curve to the particle size (D ₂₅ ) corresponding to 25% by mass is in the range of 1.5 to 3.3. In this case, an effect satisfying the expression of the smoothness and the printing gloss of the coated paper can be obtained. The average particle diameter described above means a particle diameter corresponding to 50 cumulative mass% of the particle size distribution measurement curve drawn using Micromeritics Co. Sedigraph 5100 (D _50). For the particle size (D ₇₅ ) corresponding to ₇₅ cumulative mass% and the particle size (D ₂₅ ) corresponding to 25 cumulative mass% of the particle size distribution curve used for the definition of the particle size distribution, Cedigraph 5100 can be used similarly. It is a thing.

Further, when the coating coating layer provided two or more layers, as the heavy calcium carbonate blended in the outermost coating layer, the average particle diameter measured by sedimentation method (D ₅₀₎ is 0.5 to 1. It is preferable to contain 50% by mass or more of the material in the range of 2 μm. Further, the heavy calcium carbonate blended in the top coat layer has a particle size (D ₇₅ ) corresponding to ₇₅ cumulative mass% and a particle size (D ₂₅ ) corresponding to 25 cumulative mass% of the particle size distribution curve by the precipitation method. When the ratio of _(D 75 _/ D ₂₅₎ is in the range of 1.5 to 3.3, the effect of satisfying the smoothness of expression and print gloss of the expression of the coated paper is obtained.

  Further, 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 a commercially available heavy carbonate available as a granular material. Calcium can be crushed and classified as necessary and used. For the pulverization here, for example, pulverization by a dry pulverizer such as a roll mill, jet mill, dry ball mill, impact pulverizer, wet ball pulverizer, vibration mill, stirring tank mill, flow tube mill, coball mill, etc. 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.

  The adhesive used in the pigment coating layer of the present invention is not particularly limited, and as an adhesive used in the ordinary coated paper field, for example, a water-soluble adhesive, oxidized starch, esterified starch, cold water Various starches such as soluble starch, proteins such as casein, soy protein, synthetic protein, cellulose derivatives such as carboxymethylcellulose and methylcellulose, polyvinyl alcohol and modified products thereof, and styrene-butadiene as a dispersion adhesive Copolymer, conjugated diene polymer latex such as methyl methacrylate-butadiene copolymer, acrylic polymer latex, vinyl polymer latex such as ethylene-vinyl acetate copolymer, etc. can be used, One type or two or more types are appropriately selected and used as necessary. The blending amount of the adhesive is not particularly limited, but is 1 to 50 parts by mass per 100 parts by mass of the pigment.

  In addition, the pigment coating liquid for the pigment coating layer of the present invention includes, as necessary, blue or purple dyes or colored pigments, fluorescent dyes, thickening water retention agents, antioxidants, anti-aging agents, Various auxiliary agents such as a conductivity-inducing agent, an antifoaming agent, an ultraviolet absorber, a dispersant, a pH adjuster, a mold release agent, a water-resistant agent, and a water-repellent agent can be appropriately blended.

  The solid content concentration of the coating liquid containing the pigment, adhesive, and auxiliary agent used as necessary in the coating liquid for a pigment coating layer of the present invention can be selected in the range of 25 to 70% by mass.

  As a coating apparatus used for forming a pigment coating layer, generally, a roll coater such as a two-roll size press, a metering size press, and a gate roll, a non-contact coating apparatus such as a curtain coater and a spray coater, a blade Examples include post-weighing type coating devices such as coaters, rod coaters, bar coaters, and air doctor coaters. In the present invention, a blade coater capable of producing a coated paper that can be applied at high speed and wide width and has excellent quality such as smoothness is used. The blade coater used for forming the pigment coating layer may be on-machine or off-machine.

  There are fountain type, roll type, short dwell type, jet fountain type, etc. as applicator methods for supplying the coating liquid to the base paper in the blade coater. From the viewpoint of high speed supply and uniformity of the coated surface, jet fountain A type of applicator is preferred. Jet fountain type applicators include a validwell type that can change the distance between the applicator and the blade (hereinafter referred to as dwell length), a type in which a backing roll is provided in each of the applicator part and the blade part, and a dwell length that is long. There are types with blades attached, etc., which can be selected and used according to various purposes.

  The dwell length is not particularly limited, but when using an applicator of a type that can change this distance, it is preferably adjusted within a range of 50 to 1700 mm. A dwell length of 50 mm or less is not preferable because the fountain nozzle is soiled by the excess coating liquid scraped off by the measuring blade. On the other hand, if it is 1700 mm or more, the coating liquid supplied to the base paper is dehydrated more than necessary, so that the fluidity is deteriorated and it may be difficult to measure the desired coating amount. This is not preferable because coating defects such as streak and bleeding may occur.

  The slit width of the slit-like nozzle that sprays the coating liquid in the jet fountain type applicator is not particularly limited, but it is preferably adjusted within a range of 0.5 to 5.0 mm during steady operation. When the slit width is 0.5 mm or less, foreign particles such as coarse particles or aggregates in the coating liquid are liable to stay between the slits, deteriorating the coating amount profile. It is not preferable because it may be formed. On the other hand, when the thickness is 5.0 mm or more, the collision speed of the coating liquid jet to the base paper is lowered, and normal coating may not be performed. If foreign matter stays between the slits, it is possible to temporarily open the lip opening beyond the range during steady operation.

  In the jet fountain type applicator, the supply amount of the coating liquid sprayed from the slit nozzle can be appropriately changed with respect to the desired coating amount. However, considering the metering with the metering blade, the desired coating on the base paper is possible. It is preferably about 5 to 30 times the work amount, and more preferably 10 to 25 times from the balance between the stability of the coating liquid jet and the meterability with the metering blade.

  The jet angle formed between the backing roll tangent at the collision point of the base paper and the coating liquid jet and the coating liquid jet is not particularly limited, but if the jet angle is too small, a transfer surface defect occurs. When it is too large, backflow is likely to occur. Therefore, a preferable range is 15 to 90 °, and 20 to 70 ° is particularly preferable in order to more effectively prevent both transfer surface defects and backflow. The jet angle can be adjusted by changing the fountain angle.

  In order to prevent thick coating at both ends of the base paper, dry edge forming means can be provided. The means is not particularly limited, but it is general that seal members are installed at both ends of the fountain nozzle, and the spray of the coating liquid is partially stopped. Can be moved manually. In order to prevent overdrying in the dry edge drying process, it is possible to provide a device for supplying water or the like to the dry edge portion.

  In the jet fountain type applicator, entrained air removal means for removing the entrained air due to the running of the base paper and preventing the coating liquid jet from being disturbed and skip coating can be provided. The means is not particularly limited. For example, a counter air method, a blade method, a rod blade method, or the like is provided on the upstream side of the collision point between the base paper and the coating liquid jet, and the accompanying air can be removed. . Further, in the jet fountain type applicator, a partition plate may be provided between the measuring blade and the fountain nozzle in order to prevent the fountain nozzle from being soiled by the excessive coating liquid scraped off by the measuring blade.

  As a blade coating method, there are a bevel coating method in which the blade edge is angled and the portion is used, and a vent coating method in which the blade is brought into contact with the surface. The former is for a low coating amount, and the latter is for a high coating amount. Depending on the physical properties of the coating liquid such as the concentration and viscosity, the physical properties of the base paper such as smoothness and absorbency, the target coating amount, and the like, they can be appropriately selected from both methods. Here, in the case of coating at a relatively high coating speed of 1000 m / min or more, the coating liquid adhesion amount tends to increase due to the pressure of the coating liquid (hydrodynamic counter pressure). In the coating in the region, it is preferable to select a bevel coating method.

  The form of the measuring blade used for controlling the coating liquid supplied by the applicator to a desired coating amount is not particularly limited, but the thickness of the blade is about 0.2 to 2.0 mm. In general, an angle of about 0 to 50 ° is used. Further, not only a single cutting edge but also a plurality of chamfered portions or a rounded corner portion can be used.

  The material of the measuring blade to be used is not particularly limited. For example, carbon tool steel, high speed tool steel, alloy tool steel, spring steel, stainless steel, cast steel, aluminum, copper, ceramic, heat resistant plastic, etc. can be used, and the blade of the material is used as a base material. A blade in which various coating materials are coated on the entire surface or a part of the base material can also be used. The coating material is not particularly limited. For example, hard chrome plating, alloy plating, or other plating can be used, and oxide ceramics such as alumina, zirconia, and titania, and carbides such as silicon carbide and tungsten carbide. Various ceramics such as ceramics, borides, and nitrides, and cermets can also be used by thermal spraying or pasting. On the other hand, not only the hard materials such as plating and ceramic described above, but also an elastic material made of an organic polymer such as polyurethanes and styrene butadiene polymers can be used as the coating material.

  The thickness of the coating material is about 3 to 500 μm in the case of a hard material such as plating or ceramic, and on the other hand, about 0.5 to 5.0 mm in the case of using an elastic material as the coating material. It is general that it is. In addition, the characteristics of the blade coating portion when a hard material such as plating or ceramic is used as the coating material are Vickers hardness of 500 to 2000 Hv, surface roughness of about 0.01 to 1 μm, and elastic material In general, the shore A hardness of the blade coating portion is about 50 to 100 when using as a coating material.

  As a function of the coater head for mounting the blade and executing the coating amount control, it is preferable to have a blade pressing amount adjusting function and a blade angle adjusting function, and moreover, each function can be controlled so as not to be influenced by each other. preferable. Here, when the coating amount is controlled with a coater head that has only one of the two functions, the contact angle between the blade and the base paper cannot be kept constant, and coating defects such as streak and bleeding occur. In addition, problems such as variations in coating amount due to blade wear and tear tend to occur, which is not preferable. Other functions provided include manual or automatic coating amount profile control devices installed at regular intervals in the coater head width direction, an automatic coating amount control system in the flow direction, and during coating operations. There is a system for moving the coater head by the amount of wear of the measuring blade in the above.

  The measuring blade mounted on the coater head is supported by the blade backstop from the anti-backing roll side, but the length from the blade backstop fulcrum to the blade tip (hereinafter referred to as blade extension) is not particularly limited. However, if the blade extension is made shorter than necessary, the elasticity of the tip of the blade is lacking, which causes an increase in the number of pieces of paper, blade wear and tear, and a horizontal coating pattern due to vibration, which is not preferable. On the other hand, if it is too long, it is possible to suppress an increase in the amount of coating liquid adhering due to the pressure of the coating liquid (hydrodynamic counter pressure), particularly when coating at a relatively high speed of 1000 m / min or more. Since it disappears, it is not preferable. After all, the range of the blade extension is preferably 2 to 30 mm. There are a rigid back system and an air tube system for the blade back stop, which can be properly used depending on the coating system (bevel and vent) and the coating operation status.

  In the blade coater, a backing roll for supporting and running the base paper from the side opposite to the coated surface is formed by coating a rubber layer having a relatively low hardness on an iron roll, and the Shore A hardness of the rubber layer is 50. Generally it is ~ 100. In addition, instead of the rubber layer, a material coated with a high hardness rubber or a polymer material such as fluororesin, or a chrome plating or ceramic coating applied to the surface of a metal roll to have a Shore D hardness of 60 or more is backed. It can also be used as a roll. The diameter of the backing roll is selected within the range of about 500 to 2000 mm.

  When a jet fountain type applicator is used, it is preferable to introduce a defoamer in the coating liquid circulation line in order to prevent defects such as skip coating due to foam in the coating liquid. The type of defoamer that can be introduced is not particularly limited, and examples thereof include a vacuum defoamer, a centrifugal defoamer, a natural defoaming type, and a multi-column tube type utilizing centrifugal force. Among them, it is particularly preferable to introduce a multi-column tube type defoamer using centrifugal force which is excellent in defoaming efficiency and excellent in maintainability. The installation location of the defoaming machine in the coating liquid circulation line is not particularly limited. However, since it is intended to defoam the coating liquid to be transferred, it is preferably installed in front of the applicator. Alternatively, two or more units can be installed in parallel or in series.

  In order to prevent coating defects such as streaks due to foreign matters in the coating liquid, it is preferable to introduce a screening device into the coating liquid circulation line. There are no particular limitations on the type of screening device that can be introduced. For example, there are open-type vibrating screens, multi-tube vibrating pressurization filters, mechanical pressurization filters, shear type mesh filters, etc., one or two of these devices. The above can be used in parallel or in series.

  There are no particular limitations on the type of pump that delivers the coating liquid to the applicator. For example, a non-volumetric pump such as a vortex pump or a diaphragm pump, a volumetric pump such as a gear pump or a screw pump, or other special type pumps can be appropriately selected and used. However, there is no pulsation and stable liquid feeding is possible. In particular, it is preferable to use a screw pump because the flow rate control is easy.

  In order to prevent the coating amount profile from being disturbed by the uneven shape of the roll surface formed by using the backing roll for a long time, a backing roll polishing means can be provided. In order to suppress the occurrence of bleeding, it is possible to provide a device for supplying water or steam to the tip portion of the measuring blade.

  In order to prevent paper breakage in the blade coater, it is possible to incorporate a sequence in which the supply of the coating liquid is temporarily interrupted when the splice portion where the base papers are joined passes through the coater head. Moreover, in order to prevent blade burning when the blade is in a dry touch state, such as when the coating liquid supply is interrupted as described above, or when the coater head is newly touched, water jet cooling, etc. It is also possible to provide blade cooling means.

  In order to prevent coating wear such as streaking and bleeding, etc. on the backing roll and measuring blade, it is also possible to provide means that each of the backing roll, measuring blade and base paper can slide relative to the width direction. It is.

  It does not specifically limit as a coating speed, It can change suitably with various operation conditions, such as desired coating amount, the capability of drying equipment, coating-liquid physical property, and coater head conditions, Generally 100-3000m / Adjust in minutes.

  The method for drying the pigment coating layer is not particularly limited, and various methods such as steam drying, gas heater drying, electric heater drying, and infrared heater drying can be employed.

The dry coating amount of the pigment coating layer of the present invention is adjusted in the range of 1 to 40 g / m ² per side as the total dry mass on the base paper layer by one coating, and further improves the coverage. In this sense, it is preferably ² g / m ² or more.

  In the present invention, after the pigment coating layer is formed, the paper is passed through a calender device comprising a combination of a heated metal roll and an elastic roll to perform a smoothing finishing process. The calender device may be any calender device as long as it has at least two rolls and can form one nip or more, and is preferably a calender device composed of three or more rolls and two or more nips. It is also possible to use a combination of two or more rolls as one stack and two or more stacks arranged in series. Furthermore, it is preferable that the calender is a thermal calender such as a soft nip calender or a multi-nip calender in which the roll arrangement in each stack is a combination of an elastic roll and a metal roll. In addition, the combination of rolls in a single or a plurality of stacks can be arranged vertically, and can be arranged in an inclined arrangement or a horizontal arrangement in order to reduce the influence of the roll weight. These calendar devices include an on-type integrated with the coater and an off-type separated from the coater, but both can be used.

  The calender roll pressurization method to be used is not particularly limited, but generally there are a bottom pressurization type and a top pressurization type, both of which are adjusted to a necessary nip line pressure by a hydraulic method or the like. It is also possible to use a mechanism that has a pressure mechanism that can cancel the influence of the roll's own weight and achieve a uniform linear pressure from the upper nip to the lower nip, or that can control the nip pressure independently of all stages. it can.

  The nip linear pressure in the thermal calendar is 10 to 600 kN / m, and the surface temperature of the metal roll can be adjusted at 60 to 500 ° C. The calendar operation speed can be set to 400 to 2000 m / min. However, any of them is not particularly limited, and can be appropriately adjusted depending on the water content of the paper, the target paper thickness, gloss, smoothness, and the like. is there.

  The paper passing method is not particularly limited, and it is possible to reduce the number of nips by opening all the nips or changing the paper path as well as passing all nips. It can be appropriately changed depending on the quality such as smoothness.

  As the elastic roll used for the thermal calendar, a roll whose surface is covered with an elastic material is used. The material of the elastic material is not particularly limited, and can be composed of, for example, a polyurethane, epoxy, or polyether synthetic resin, an aramid fiber such as an aromatic polyamide fiber, or a rubber. The hardness of the elastic roll is not particularly limited, but is preferably set to a Shore D hardness of 60 or more. Here, when the roll hardness is Shore D60 or less, there is a possibility that operational problems such as deformation and breakage due to use under high temperature and high pressure may occur.

  In order to correct non-uniform nip due to pressurization, the elastic roll is preferably a roll with a crown shape that has been polished to a medium or high tendency, or a roll that can be crowned and changed by hydraulic pressure, and a uniform nip pressure profile in the width direction. Therefore, it is particularly preferable to use a type that can control the zone pressure in the width direction. In addition, although it is the control pitch in zone pressure control, in order to equalize a profile more efficiently, it is preferable that the pitch of the pressure control means built in the roll shall be 200 mm or less. Further, in order to prevent uneven temperature in the roll width direction and damage of the elastic material due to heat generation of the roll, a cooling means can be provided inside the roll.

  As the metal roll used for the thermal calendar, a roll whose surface is mirror-finished or polished is used. The material of the metal roll is not particularly limited. For example, the metal roll can be made of cast steel, forged steel, or a metal roll surface sprayed with a ceramic such as tungsten carbide or plated. The surface roughness of the metal roll is generally about 0.5 to 6.0 μm.

  Internal heating means such as oil heating system, steam heating system, hot water heating system, electromagnetic induction heating heating system, hot air heating system, etc. are used as the heating means for the metal roll. Furthermore, roll cooling means such as an air spraying device can be provided. In order to prevent uneven temperature in the roll width direction, it is preferable that both the heating means and the cooling means can be controlled in the width direction zone, and the control pitch is used to make the temperature more uniform. Is preferably 200 mm or less.

  As with the elastic roll, the metal roll used for the thermal calender should be a crown-shaped roll that has been polished to a medium-to-high tendency, or a roll that can be crowned and changed by hydraulic pressure, in order to correct non-uniform nip due to pressure. Furthermore, in order to make the width direction profile of the nip pressure uniform, it is possible to adopt a type in which the width direction zone pressure can be controlled. In addition, although it is the control pitch in zone pressure control, in order to equalize a profile more efficiently, it is preferable that the pitch of the pressure control means built in the roll shall be 200 mm or less.

  Although the diameter of each roll which comprises a thermal calendar is not specifically limited, It is preferable that all rolls are 300-2000 mm. When the roll diameter is 300 mm or less, the roll rotation speed increases during high-speed operation, which may lead to damage to the bearing part or the roll. Because there is a problem, it is not preferable.

  As a means for removing foreign matter adhering to the roll, a doctor made of metal, carbon, glass fiber, or the like can be installed on some or all of the rolls. The doctor can also be provided with a manual or automatic sliding device.

  In order to prevent damage to the elastic material due to overheating of the elastic roll, a temperature monitoring system such as an infrared thermometer can be provided. As such a system, an elastic roll surface temperature that can be measured over the entire width of the roll, a system that measures only a part of the roll end, and the like can be appropriately selected and used. Further, when overheating is detected constantly or by temperature measurement, it is possible to provide means for cooling the entire width or part of the elastic roll with water or cold air.

  With respect to the roll end portion where the passed paper does not travel, both ends of the elastic roll can be tapered in order to prevent generation of dirt and damage to the elastic roll due to the combined rolls coming into direct contact with each other.

  In order to prevent roll damage at the time of running out of paper, it is preferable to have a paper running detection means and a system capable of opening all nips in a very short time when paper running is detected.

  In the thermal calendar, in order to prevent roll contamination caused by water vapor generated from paper passing through the nip, an air spraying device or a drying device for removing the water vapor can be provided.

  In order to adjust the moisture content of the paper and efficiently obtain a smoothing action on the paper surface, it is possible to provide a humidifier such as a steam shower before the passed paper passes through the nip. Further, by providing an on-line moisture content measuring device, it is possible to provide a system that automatically adjusts the humidification amount in combination with the humidification device described above.

  In the thermal calendar, a cooling roll can be provided in order to prevent thermal discoloration of paper processed at high temperature.

  Various rolls such as a fly roll, an expander roll, and a tension paper roll can be installed in order to obtain a stable paper runnability.

  The moisture content of the paper to be passed is not particularly limited, but is preferably 3.0 to 8.5%. When the water content is 3.0% or less, it is not preferable because plasticization of the paper layer is difficult to proceed and the smoothing action of the paper surface cannot be obtained efficiently. On the other hand, when the water content is 8.5% or more, roll contamination is likely to occur due to an increase in the amount of water vapor generated from the paper passing through the nip.

  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. The white liquor is prepared with a sulfidity of 28%, and the white liquor addition rate is 10% per chip dry system, 8% in the cooking zone, 2% in the washing zone as the active alkali. Added in portions 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 mass of dry pulp were added, and two-stage alkaline oxygen bleaching was performed under the conditions of a pulp concentration of 10%, 98 ° C. for 50 minutes. 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 was retained under the conditions of 10% pulp concentration, 60 ° C. and 60 minutes, it was washed in the washing step. Next, after adding 0.5% ozone and 0.5% chlorine dioxide per mass of dry pulp, medium concentration ozone / chlorine dioxide bleaching was performed at a pulp concentration of 10%, 58 ° C. for 60 minutes, followed by washing. It was washed in the process. Subsequently, 1.0% caustic soda and 0.1% hydrogen peroxide per mass of dry pulp are added, and after alkali extraction under conditions of pulp concentration 10%, 60 ° C. for 90 minutes, washing treatment is performed in the washing step. did. Finally, 0.2% chlorine dioxide per mass of dry pulp was added, and after bleaching chlorine dioxide under the conditions of 10% pulp density, 70 ° C., 120 minutes, washing treatment was performed in the washing step, and bleached pulp A Got. The bleached pulp A 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 length weighted average fiber length and fiber width of bleached pulp A were measured using a fiber length distribution measuring device (model name: Fiber Lab, manufactured by Metso Automation Co., Ltd.).

(Preparation of base paper)
100% pulp slurry consisting of raw pulp obtained by beating bleached pulp A to CSF 450ml, light calcium carbonate (trade name: Tama Pearl TP-121, manufactured by Okutama Kogyo Co., Ltd.) as a filler so that the base paper ash content becomes 10% After addition to the total solid content of the pulp slurry, 0.5% aluminum sulfate, cationic starch (trade name: Ace K100, manufactured by Oji Cornstarch) 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)
Sodium kaleacrylate (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) as a dispersant is added to an aqueous solution in which 0.1 part of kaolin to be dispersed is added to finely divided kaolin (trade name Hydra Gloss 90, manufactured by Huber). ) 50 parts of an average particle diameter of 0.9 μm, D ₇₅ / D ₂₅ of 2.4 heavy calcium carbonate (trade name: Supercoat-95, manufactured by Pfematech Co., Ltd.) 50 parts is added and dispersed with a Coreless disperser Thus, a pigment slurry was prepared. To 100 parts of the pigment slurry, 3 parts of oxidized starch (trade name: Oji Ace A, manufactured by Oji Cornstarch Co., Ltd.), styrene-butadiene copolymer latex (trade name: OJ-2000, manufactured by JSR) 7 Then, an antifoaming agent and a dye were sequentially added as an auxiliary agent to finally prepare a pigment coating solution for a coating layer having a solid content concentration of 63%.

(Create coated paper for printing)
Using a blade coater that supplies the coating liquid obtained in the jet fountain method to the above-obtained base paper (basis weight 53 g / m ² ), the dry coating amount per side is 11 g / m. ^The coating layer was formed on both sides by coating and drying so as to be ² . 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 of paper were passed through each so as to contact with each other 4 times to obtain a coated paper for printing having a basis weight of 75 g / m ² .

Example 2
A coated paper for printing was obtained under the same conditions as in Example 1 except that the pigment composition of Example 1 was 100 parts of heavy calcium carbonate (trade name: Supercoat-95, supra). It was.

Example 3
The heavy calcium carbonate in Example 1 was changed to heavy calcium carbonate having an average particle size of 1.5 μm and D ₇₅ / D ₂₅ of 4.2 (trade name: Hydrocurve 60, manufactured by Bihoku Powdered Industries Co., Ltd.). A coated paper for printing was obtained under the same conditions as in Example 1 except for the above.

Example 4
Using a blade coater that supplies the coating liquid of Example 2 to the base paper of Example 1 for the undercoating and supplies the coating liquid by the jet fountain method, the dry coating amount per side becomes 11 g / m ^2. Using a blade coater that supplies the coating liquid by the jet fountain method, using the pigment coating liquid of Example 1 as a pigment coating liquid for top coating, and forming a coating layer on both sides by coating The coating was applied so that the dry coating amount per side was 5 g / m ² and dried to form two coating layers 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 5
In Example 4, a heavy calcium carbonate topcoat pigment coating solution, the average particle diameter of _{0.9μm, D} 75 _/ D ₂₅ is heavy calcium carbonate 4.2 (trade name: FMT95, Phi Matec Co. The coated paper for printing was obtained on the same conditions as Example 4 except having changed into (1).

Comparative Example 1
In preparation of the pulp of Example 1, bleached pulp B 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. In the production of the base paper of Example 1, a coated paper for printing was obtained in the same manner as in Example 1 except that bleached pulp A was changed to bleached pulp B. The bleached pulp B 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
The heavy calcium carbonate pigment coating solution, the average particle diameter _{3.1μm, D} 75 _/ D ₂₅ is heavy calcium carbonate 4.5 (trade name: Softon 1500, Bihoku Funka Kogyo Co., Ltd.) except for using A coated paper for printing was obtained under the same conditions as in Example 1.

Comparative Example 3
A coated paper for printing was obtained under the same conditions as in Example 4 except that the bleached pulp B obtained in Comparative Example 1 was used.

  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. The following evaluation test was performed in an environment of 23 ° C. and a relative humidity of 50%.

(Coated paper smoothness)
JAPAN TAPPI No. According to 5-2, it was measured with a Oken type smoothness tester.

(Whiteness of coated paper)
It measured by the method of JISP8148 using the spectral whiteness colorimeter (made by Suga Test Instruments company).

(Print smoothness)
Using an RI printer (Meiji Seisakusho), printing is performed using 0.2 cc of printing ink (Values-G type, manufactured by Dainippon Ink & Chemicals, Inc.), and the transfer uniformity (print smoothness) of the ink is visually observed. Observed and evaluated.
A: Particularly excellent in printing smoothness.
○: Excellent printing smoothness.
(Triangle | delta): It is inferior to printing smoothness.
X: The printing smoothness is considerably inferior.

  As can be seen from Table 1, by the production method of the present invention, a coated paper for printing excellent in whiteness, smoothness and printing smoothness of white paper could be obtained.

Claims (6)

In a method for producing a coated paper for printing in which at least one coating layer containing a pigment and an adhesive is provided on at least one side of a base paper, 50% or more of bleached pulp used for the base paper is made of eucalyptus or acacia. A pulp produced by a kraft cooking method in which a cooking liquor is dividedly added and further produced in a multi-stage bleaching process including an ozone bleaching stage, the bleached pulp comprising the bleached pulp A process of forming wet paper with a gap former type wire part, in which the paper stock is ejected from the head box between two looped wires and dehydrated with a forming roll to form a paper layer. The water-making process, the paper-making process for drying wet paper in the dryer part, the process for coating the coating liquid with the blade method, and the combination of metal roll and elastic roll And a step of treating flattened by calendering consisting Align, and the coating layer formed in the step of coating Engineering, average particle diameter (D ₅₀₎ measured by sedimentation method is 0.5~2.5μm The manufacturing method of the coated paper for printing characterized by containing 50 mass% or more of heavy calcium carbonate in the range. The coating layer has at least two layers, and the outermost coating layer contains 50% by mass of heavy calcium carbonate having an average particle diameter (D ₅₀ ) measured by a precipitation method in the range of 0.5 to 1.2 μm. It contains above, The manufacturing method of the coated paper for printing of Claim 1 characterized by the above-mentioned. The heavy calcium carbonate contained in the outermost coating layer has a particle size (D ₇₅ ) corresponding to ₇₅ cumulative mass% and a particle size (D ₂₅ ) corresponding to 25 cumulative mass% of the particle size distribution curve by the precipitation method. The ratio (D ₇₅ / D ₂₅ ) to the range of 1.5 to 3.3 is a method for producing a coated paper for printing according to claim 1 or 2.   The method for producing a coated paper for printing according to any one of claims 1 to 3, wherein in the blade-type coating process, a method of supplying a coating liquid is a jet fountain system.   The manufacturing method of the coated paper for printing of any one of Claim 1 to 4 with which the calendar | calender which consists of a combination of the said metal roll and an elastic roll is comprised from three or more rolls and two or more nips.   The manufacturing method of the coated paper for printing of any one of Claim 1 to 5 in which the roll of the said calendar is inclined.