JP5374194B2 - Coated paper for gravure printing and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide coated paper for gravure printing having excellent whiteness and gravure printing suitability, and to provide a method for producing the coated paper with high productivity. <P>SOLUTION: The method for producing the coated paper for gravure printing includes: a papermaking step of forming a sheet of base paper; a coating step of carrying out coating of a coating liquid containing a pigment and adhesive, and providing a pigment-coated layer; and a step of treating the surface of the pigment-coated layer, wherein the steps are continuously performed with an on-machine coater. In the method for producing the coated paper, the whiteness of the coated paper is &ge;80%. The method includes: carrying out the coating of the coating liquid containing, in 100 pts.wt. of the pigment, 10-30 pts.wt. of a phyllosilicate mineral having a volume distribution-average particle diameter of 4.0-20 &mu;m measured by a laser diffraction method, and 70-90 pts.wt. of calcium carbonate having a volume distribution-average particle diameter of 0.2-1.0 &mu;m measured by the laser diffraction method; and providing the pigment-coated layer. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a gravure printing coated paper having both excellent white paper appearance and printability and a method for producing the same.

  Gravure printing is an intaglio printing method that transfers ink for the concave part of a plate under pressure, and has excellent gradation reproducibility, so it can be used for commercial printing such as magazines, catalogs, brochures, etc. Widely used. In particular, gravure printing paper used in the commercial printing field is required to have a low price and excellent printability in order to reduce the cost of the paper itself.

  Since gravure printing is intaglio printing, a harder plate is used compared to offset printing. For this reason, there is a case where a speckle phenomenon occurs in which the printing plate surface is hardly adhered to the paper at the time of gravure printing and the halftone dots are not normally transferred. When there are many speckles, the print quality is lowered. In order to suppress the generation of speckles, it is important to increase the adhesion between the gravure printing plate and the paper. From the surface of the paper, it is generally effective to increase the smoothness and elasticity of the coated paper. It is.

  And as a method of improving the smoothness of the coated paper surface from the viewpoint of coating formulation, a layered silicate mineral pigment (delaminate clay, talc, etc.) with a high aspect ratio is blended in the coating layer formation. Has been proposed (Patent Document 1). However, if a large amount of pigment having a high aspect ratio is blended in the coating layer composition, the viscosity of the coating solution increases, so that it is difficult to handle during preparation, which tends to cause coating defects such as streak and scratch. For this reason, it is the present situation that the solid content concentration of the paint for providing the coating layer cannot be so high, and as a result of applying the paint with high moisture, it is necessary to ensure a long drying time of the paper, and at high speed Not suitable for operation. In addition, pigments such as delaminated clay and talc with a high aspect ratio are suitable for low-gloss white paper applications such as matte coated paper (Patent Document 2). Since the expression is deteriorated, it has been difficult to use it on glossy coated paper that requires white paper glossiness. Furthermore, these pigments have low whiteness, and the whiteness of the paper decreases when the blending amount is increased. Therefore, it is difficult to use these pigments on paper having high whiteness.

  Also known is a method in which calcined clay is used in combination with other pigments for the purpose of preventing speckle generation and improving opacity. However, since the fired clay is inferior in fluidity, the viscosity of the coating liquid is increased, which is liable to cause coating defects such as streak and scratch, and the workability in the coating process is deteriorated. For this reason, even when calcined clay is used, the solids viscosity of the paint cannot be increased so much that, as a result, it is necessary to maintain a long drying time after coating, and there is a limit to high-speed operation. .

  Furthermore, a method for imparting high white paper gloss, speckle prevention effect, opacity, etc. using an organic pigment such as plastic pigment is known (Patent Document 3). However, organic pigments are expensive compared to inorganic pigments, resulting in high costs. In addition, coating liquids containing organic pigments tend to increase in viscosity under high shearing force, and can cause streaks, scratches, etc. It is easy to cause poor work. For this reason, it is the present condition that solid content concentration of a paint cannot be made very high, As a result, it is necessary to keep the drying time after coating long, and there was a problem that it was not suitable for high-speed operation.

  Furthermore, in order to prevent speckle, there is a method of simply increasing the coating amount to increase the smoothness. However, this method increases the cost, and the moisture brought in by the paint increases. Therefore, it is necessary to keep the drying time after coating long, which is not suitable for high-speed operation.

  On the other hand, as a method for improving the smoothness of the coated paper surface and imparting white paper gloss from the viewpoint of manufacturing equipment, a high linear pressure pressurizing process using a super calendar is generally performed. However, the surface treatment by the supercalender increases the smoothness and the glossiness of the blank paper, but at the same time the density of the coated paper increases and the opacity and rigidity of the coated paper are lost. In particular, when the opacity is insufficient, the printed pattern is transmitted and affects the printed pattern on the back surface, and the quality of the blank paper on the back surface is impaired. In addition, a method of lowering the linear pressure of the pressure treatment is conceivable so as not to reduce the opacity and rigidity, but the smoothness of the paper decreases due to the decrease of the linear pressure and the speckle during gravure printing increases. At present, the pressure treatment cannot be simply reduced. Furthermore, cotton rolls used in conventional supercalenders are limited in terms of speeding up coated paper production because they are inferior in heat resistance due to problems of internal heat generation, and inferior in pressure resistance and durability. The maximum speed that can be operated was about 800 m / min.

  Further, as another method for improving the smoothness of the coated paper surface from the viewpoint of production equipment, there is a surface treatment by a high temperature soft nip calender that performs a high temperature treatment using a resin roll having high heat resistance. Surface treatment with a high-temperature soft nip calender can maintain high density of blank paper at low linear pressure compared to super calender treatment, so that the density of coated paper can be kept low, and high opacity and rigidity can be obtained. It is done. In addition, since the roll has high heat resistance, it has high durability and can be operated at high speed. However, it is difficult to improve the smoothness by surface treatment with a high-temperature soft nip calender, and there is a problem that the gravure printing quality is lowered due to an increase in speckle.

JP 2002-88679 A JP 2000-199198 A JP-A-1-20396

  From the background as described above, it has been desired to develop a coated paper for gravure printing having low density, high whiteness, and excellent gravure printing suitability, and a method for producing it at high speed.

  In view of such a situation, an object of the present invention is to provide a gravure-coated paper having high whiteness and excellent gravure printability, and a method for efficiently producing the same.

  As a result of diligent research on the above problems, the present inventors have obtained a layered silicate mineral having a volume distribution average particle diameter (volume frequency 50% particle diameter) measured by a laser diffraction method of 4.0 to 20 μm as a pigment. Pigment coating is carried out using a pigment coating solution containing 70 to 90 parts by weight of calcium carbonate having 10 to 30 parts by weight of 100 parts by weight of pigment and a volume distribution average particle size of 0.2 to 1.0 μm. It has been found that by providing a working layer, a coated paper for gravure printing having high whiteness, white paper glossiness, and opacity, having suppressed speckles and having excellent gravure printing suitability can be obtained. In addition, the present invention can cope with high-speed operation and can continuously perform papermaking, coating, and surface treatment online, so that it is possible to produce excellent coated paper for gravure printing with high operability. It is.

  Although not limited to the following, the present invention includes the following inventions.

(1) A paper making process for making a base paper, a coating process for applying a coating liquid containing a pigment and an adhesive to provide an outermost pigment coating layer of 5 to 15 g / m ² per side, and a pigment A surface treatment of the coating layer, and these steps are continuously performed using an on-machine coater. The whiteness of the coated paper is 80% or more. 10 to 30 parts by weight of a layered silicate mineral having a volume distribution average particle diameter measured by laser diffraction method of 4.0 to 20 μm and a volume distribution average particle diameter of 0 in 100 parts by weight of pigment. The said method of coating the coating liquid containing 70-90 weight part of calcium carbonate which is .2-1.0 micrometer, and providing a pigment coating layer.

  (2) The operation speed is 1300 m / min or more, the coating process is performed using a blade-type on-machine coater, and the surface treatment process is performed using a thermal soft calender composed of a metal roll and an elastic roll. The manufacturing method of the coated paper for gravure printing as described in (1) performed by 6 nips or more.

  (3) The pre-calendar treatment of the base paper is performed under the condition where the treatment linear pressure is 30 kN / m to 100 kN / m before the coating step, the coated paper for gravure printing according to (1) or (2) Production method.

(4) A gravure coated paper having a pigment coating layer on the base paper and having a whiteness of 80% or more, measured by laser analysis / scattering method in 100 parts by weight of the pigment constituting the coating layer 10 to 30 parts by weight of a layered silicate mineral having a volume distribution average particle size of 4.0 to 20 μm, and a carbonic acid having a volume distribution average particle size of 0.2 to 1.0 μm measured by a laser analysis / scattering method The said gravure coated paper containing 70 to 90 parts by weight of calcium and having an outermost pigment coating layer of 5 to 15 g / m ² per side.

  According to the present invention, a coated paper for gravure printing having excellent printability and high white paper appearance can be obtained. In addition, according to the present invention, paper making, coating, and surface treatment can be continuously performed on-line, so that a coated paper for gravure printing having excellent printability and high white paper appearance is manufactured with extremely high productivity. Is possible.

  The present invention relates to a coated paper for gravure printing and a method for producing the same. The coated paper for gravure printing of the present invention is particularly excellent in gravure printing suitability and generates less speckle and the like. Moreover, the coated paper for gravure printing of the present invention has a high whiteness, and therefore has an excellent white paper appearance. Specifically, the coated paper has a whiteness of 80% or more. Furthermore, in the present invention, by providing a coating layer using a specific pigment and performing a surface treatment under specific conditions using a soft calender, it is possible to obtain a coated paper for gravure printing with a high blank glossiness. In a preferred embodiment, the blank paper gloss is 50% or more, and in a more preferred embodiment, the blank paper gloss is 60% or more.

From the viewpoint of gravure printing suitability, the smoothness of the coated paper for gravure printing of the present invention preferably has a Parker print surface roughness value (hard packing: 1000 kPa) of 1.6 μm or less, and 1.3 μm or less. Is more preferable. Moreover, according to this invention, it can respond also to the low basic weight coated paper, The basic weight of the printing coated paper of this invention becomes like this. Preferably it is 70 g / m < ² > or less, More preferably, it is 35-60 g. / M ² .

The coated paper for gravure printing according to the present invention achieves high opacity and rigidity by maintaining the coated paper at a low density by using a specific pigment or by surface treatment under a specific condition using a soft calender. ing. The density of coated printing paper of the present invention is 1.20 g / ^{m 3} or less in a preferred embodiment, is in a more preferred embodiment 1.15 g / ^{m 3} or less. Moreover, the rigidity (ISO bending stiffness) of the coated paper for printing of the present invention is 400 μNm or more in a preferred embodiment, and 450 μNm or more in a more preferred embodiment. The advantages of the present invention are particularly high in the production of coated paper for gravure printing having these opacity and stiffness.

  In the present invention, not only the paper making process and the coating process, but also the surface treatment process can be continuously performed online, so that the coated paper for gravure printing can be manufactured at a high speed, thereby improving productivity. Can do. In the present invention, the high-speed operation means an operation condition at 1300 m / min or more, and according to the present invention, the operation is preferably at least 1500 m / min, more preferably at least 1600 m / min to 1800 m / min to 2500 m / min. Is also possible.

Papermaking Coated base paper used in the present invention includes pulp slurries made from paper pulp such as chemical pulp, waste paper pulp, and mechanical pulp, and fillers usually used in the papermaking process as necessary, such as talc, kaolin, and heavy carbonate. Paper is made by adding calcium, light calcium carbonate, titanium dioxide and the like, and further adding chemicals such as a paper strength enhancer, a sizing agent, an antifoaming agent and a colorant.

  The paper making method is not particularly limited. Acid paper, neutral paper, alkaline paper making using a long net machine including a top wire, a round net machine, a paperboard machine using the two, a Yankee dryer machine, etc. It may be any of the base papers made in step 1. Moreover, the base paper which applied the adhesive agents, such as starch and polyvinyl alcohol, using a size press, a gate roll coater, and a pre metering size press can be used. However, in the present invention, a base paper not subjected to clear coating is preferable. The surface of the base paper is hardened by applying a surface treatment agent based on water-soluble polymers such as starch to the coated base paper (size press), so that minute irregularities are less likely to be crushed in the subsequent surface treatment process. , Smoothness is reduced.

  Mechanical pulp can be used as a pulp raw material for the coated base paper of the present invention. In addition to mechanical pulp, various types of pulp can be used depending on the application. For example, it is commonly used as a papermaking raw material for printing paper such as deinked pulp (DIP), softwood kraft pulp (NKP), and hardwood kraft pulp (LKP). The pulp used in the above can be appropriately used alone or in combination. Examples of the mechanical pulp include groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemiground pulp (CGP), semi-chemical pulp (SCP), and the like. . As the deinked pulp, it is possible to use deinked pulp made from selected waste paper such as high quality paper, medium quality paper, lower grade paper, newspaper, flyers, magazines, etc., or unselected waste paper mixed with these.

  As the filler for the coated base paper of the present invention, known ones can be arbitrarily used as necessary. For example, heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate / silica composite, kaolin, baking Kaolin, deramikaolin, talc, etc. can be used alone or in combination. The filler content in the paper is preferably 1 to 40% by weight, more preferably 10 to 35% by weight.

  As internal chemicals used in the production of the coated base paper of the present invention, chemicals such as dry paper strength improver, wet paper strength improver, drainage improver, dye, neutral sizing agent are used as necessary. Also good. Examples of the dry paper strength improver include polyacrylamide and cationized starch, and examples of the wet paper strength improver include polyamidoamine epichlorohydrin. These chemicals are added within a range that does not affect the formation and operability. Examples of neutral sizing agents include alkyl ketene dimers, alkenyl succinic anhydrides, and neutral rosin sizing agents.

  The paper machine used for paper making of the coated base paper of the present invention is not particularly limited, but ordinary paper machines such as an on-top former and a gap former are used. In particular, in the present invention, it is possible to use a gap former type paper machine in which the paper material sprayed from the head box runs between two wires and dehydrates almost evenly from both sides of the wet paper. A base paper having a good surface property is obtained, and paper can be stably produced at a high paper making speed of 1300 m / min or more.

  In the paper making process of the present invention, a paper machine pre-dryer and an after-dryer can use public equipment, and drying conditions are not particularly limited, and can be appropriately set within a normal operating range.

In the present invention, the basis weight of the coated base paper can be set while keeping a balance with the subsequent coating step, for example, the base paper basis weight can be about 30 to 60 g / m ² .

  In the present invention, pre-calendar processing is performed on the base paper before coating by an online soft calendar, online chilled calendar, etc., and smoothing the base paper in advance makes the coating layer after coating uniform. preferable. In this case, the treatment linear pressure is preferably 30 to 100 kN / m, more preferably 50 to 100 kN / m. Moreover, the moisture content of the base paper at the time of pre-calendering is also important, and the moisture content is preferably 3 to 5%. If the moisture content is less than 3.0%, the paper moisture is low, so that it is difficult to obtain sufficient smoothness even if pre-calendar treatment is performed. On the other hand, if it exceeds 5.0%, the water content in the paper is high, so that the base paper is easily crushed by the calendar process, and sufficient smoothness can be obtained, but the opacity and rigidity are liable to decrease because the paper is crushed too much.

Coating In the present invention, 10 to 30 parts by weight of a layered silicate mineral having a volume distribution average particle diameter of 4.0 to 20 μm measured by a laser diffraction method in 100 parts by weight of the pigment constituting the pigment coating layer 70 to 90 parts by weight of calcium carbonate having a volume distribution average particle size of 0.2 to 1.0 μm is used. By using such a pigment, it is possible to obtain excellent white paper gloss and gravure printing characteristics while maintaining high whiteness. Here, the volume distribution average particle diameter in the present invention means a 50% volume frequency particle diameter measured by a laser diffraction method.

  In the present invention, as a coating pigment, 70 to 90 parts by weight of calcium carbonate having a volume distribution average particle diameter measured by a laser diffraction method of 0.2 to 1.0 μm is used. When the calcium carbonate is less than 70 parts by weight, the whiteness is reduced although the glossiness of white paper is improved. By blending 70 parts by weight or more of calcium carbonate, the whiteness can be increased, and good printability and high white paper gloss can be obtained. In particular, in the present invention, a high calcium carbonate content is obtained by setting the volume distribution average particle size measured by laser diffraction of calcium carbonate to be used to 0.2 to 1.0 μm, more preferably 0.2 to 0.7 μm. Can compensate for the reduction in gloss and smoothness.

  In the present invention, a layered silicate mineral having a volume distribution average particle diameter of 4.0 to 20 μm as measured by laser diffraction is used as a coating pigment in a range of 10 to 30 parts by weight in 100 parts by weight of the pigment. Blend in. By using such a layered silicate mineral, it is possible to improve smoothness while minimizing a decrease in whiteness. In addition, since the viscosity of a coating liquid becomes low by mix | blending 70 weight% or more of calcium carbonate, the high solid differentiation of a coating liquid is attained and the operation under high speed is attained. Examples of the layered silicate mineral used in the present invention include pigments such as kaolin, clay and talc. From the viewpoint of smoothness, the volume distribution average particle size of the layered silicate mineral is more preferably 6.0 to 10 μm.

  In the present invention, there is no limitation on the type of other coating pigments, kaolin, clay, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, conventionally used for coated paper, One or more kinds of inorganic pigments such as barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, and satin white, and organic pigments such as plastic pigments can be mixed and used.

In the present invention, specific calcium carbonate can be used as the calcium carbonate of the coating pigment. That is, in the present invention, calcium carbonate obtained by wet pulverization of light calcium carbonate of spindle-shaped calcite crystal, which is an average particle diameter (d50: integration 50) measured by an X-ray transmission type particle size distribution analyzer. (Weight% particle diameter) is 0.2 to 0.5 μm, the BET specific surface area is in the range of 10 to 30 m ² / g, and the following formula measured with an X-ray transmission type particle size distribution analyzer:
Sharpness = (d30 / d70) × 100
[Wherein d30 is a particle size of 30% by weight and d70 is a particle size of 70% by weight]
It is preferable to use calcium carbonate having a sharpness of the particle size distribution represented by When such a calcium carbonate is coated with a pigment, a coated paper for printing excellent in see-through is obtained.

Further, when using the above calcium carbonate in the present invention, it is preferable to use a calcite crystal in which spindle-shaped primary particles aggregate to form rosette-shaped secondary particles as light calcium carbonate before pulverization. The average particle diameter (d50) measured by the previous light calcium carbonate X-ray transmission particle size distribution analyzer is 1.4 to 3.0 μm, and the BET specific surface area is 4 to 12 m ² / g. preferable.

  As an adhesive used for pigment coating in the present invention, copolymer latex is used alone or in combination of several kinds, but other adhesives such as starch are used in combination as long as the object of the present invention is not impaired. can do. As the copolymer latex, not only rubber latex but also synthetic resin emulsion can be used, conjugated diene copolymer latex such as styrene / butadiene copolymer, methacrylate / butadiene copolymer, acrylic acid ester and Or a vinyl polymer latex such as a polymer or copolymer of a methacrylic acid ester, or an alkali-soluble, alkali-swellable or alkali-insoluble polymer latex obtained by modifying these various polymer latexes with a carboxyl group or the like One or more kinds of various synthetic resin polymers called binder pigments are appropriately selected and used. The copolymer latex is preferably used in an amount of 3 to 10 parts by weight based on 100 parts by weight of the pigment as a solid content. Coated paper produced with a copolymer latex of less than 3 parts by weight is not preferred for gravure printing because the surface strength of the coating layer tends to be weak. In addition, the coated paper produced with an amount of copolymer latex exceeding 10 parts by weight tends to increase the speckle during gravure printing because the coating layer becomes hard, cushioning properties become insufficient, and gravure printing tends to increase. It is not preferable.

  Examples of adhesives other than latex include proteins such as casein, soybean protein, and synthetic proteins; synthetic resin adhesives such as polyvinyl alcohol, olefin / maleic anhydride resin, and melamine resin; oxidized starch, positive starch, urea Select one or more types of normal coating adhesives such as phosphate esterified starch, etherified starch such as hydroxyethyl ether starch, starches such as dextrin; carboxymethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, cellulose derivatives, etc. May be used.

  Additives to be blended as necessary in the pigment coating layer of the present invention include dispersants, thickeners, water retention agents, defoaming agents, water resistance agents, colorants, etc. Various auxiliary agents can be used as appropriate.

  In the present invention, the method for preparing the pigment coating liquid is not particularly limited, but in a preferred embodiment, the solid content concentration of the coating liquid is about 30 to 68% by weight.

  In the present invention, the adjusted coating liquid is applied to a coated base paper using a blade coater, bar coater, roll coater, air knife coater, reverse roll coater, curtain coater, size press coater, gate roll coater, or One layer or two or more layers can be coated on one side or both sides of the base paper by a coating machine or the like in which a paint such as OptiSpray is directly sprayed onto the base paper by a spray nozzle. Among these, in consideration of image reproducibility after printing, a blade system such as a flooded nip type blade coater, a jet fountain type blade coater, a short dwell time application type blade coater, etc. is preferable, especially smoothness after coating, etc. From the viewpoint of quality, it is preferable to employ a jet fountain blade coater. The reason is considered that the blade method as leveling coating can increase the smoothness after coating as compared with the film transfer method and curtain method as contour coating.

  In particular, after coating with a blade type coater, surface treatment is performed at 6 nips or more using a thermal soft calender composed of metal rolls and elastic rolls, especially under high-speed operation conditions where the operation speed is 1300 m / min or more. The coated paper for gravure printing can be manufactured stably.

In the coated paper for gravure printing of the present invention, the weight of the outermost pigment coated layer is about 5 to 15 g / m ² per side. By setting the coating amount within this range, it becomes possible to efficiently produce high-quality gravure-coated paper. On the other hand, when the coating amount is less than 5 g / m ² , the base paper is coated. When the coating amount is more than 15 g / m ² , the basis weight of the base paper becomes light, so that the frequency of sheet cutting in the paper making process increases, and in the coating process, coating defects such as streaks and scratches occur. In addition, high-speed operability is impaired due to an increase in drying load. In a preferred embodiment, the coating amount of the outermost pigment coating layer is 5 to 13 g / m ² per side, more preferably 5 to 10 g / m ² , and further preferably 7 to 9 g / m ² . In addition, the pigment coating layer may be one or plural.

  In the present invention, as a method for drying the wet coating layer, various methods such as a steam heating cylinder, an electric heater dryer, an infrared heater dryer, and a high-frequency heater dryer are used alone or in combination.

Surface Treatment The coated paper for gravure printing of the present invention comprises a step of surface-treating the pigment coating layer after the paper making step and the coating step. In particular, in the present invention, smoothness is improved without excessively densifying the coated paper by performing surface treatment under specific conditions using an on-line soft calendar composed of a metal roll and an elastic roll. Thus, a coated paper for gravure printing that is less likely to cause speckle can be produced with high productivity. In a preferred embodiment of the present invention, the surface treatment of the coated paper is performed under a condition of 6 nips or more using a hot nip (heat) soft calender composed of a metal roll and an elastic roll.

  In the surface treatment of the present invention, the surface treatment is preferably performed under conditions of 6 nips or more. In general, in the case of gravure coated paper, increasing the calendar load to improve smoothness increases the density of the coated paper, leading to a decrease in opacity and stiffness, and also causes paper breakage. It becomes easy and decreases productivity. In the present invention, a calender load is dispersed by surface treatment using a soft nip calender under conditions of 6 nips or more, and an increase in density that affects opacity can be suppressed while obtaining target smoothness. In particular, by surface treatment with a thermal soft calender of at least 6 nips or more, even on low basis weight coated paper, on-machine production of gravure printing coated paper is possible under high-speed operating conditions without loss of quality. It becomes possible to do. On the other hand, in the case of 5 nips or less, high blank paper glossiness can be obtained by high-temperature treatment, but the roll linear pressure can be increased in order to obtain high smoothness necessary for gravure printing quality due to the small number of treatments. Necessary, and the opacity and stiffness tend to decrease. By performing processing of 6 nips or more, high smoothness can be obtained while suppressing increase in density due to calendar processing even at low linear pressure, and opacity and rigidity can be made higher than conventional gravure coated paper. it can. There is no upper limit on the number of nips, and high blank paper glossiness, smoothness and opacity can be obtained even when the number of treatments is 10 nips or more, but since there are no significant differences in quality, it is preferably 6-8 nips is there.

  Generally, when surface treatment is performed using an online thermal soft calender composed of a metal roll and an elastic roll after the coating layer is provided, the surface temperature of the metal roll and the nip pressure of the calender have a large effect on the density. Density is an important factor because it greatly contributes to gloss and opacity.

  In the surface treatment of the present invention, the surface temperature of the metal roll is preferably 100 ° C. or higher and 300 ° C. or lower, and more preferably 130 ° C. or higher and 250 ° C. or lower. If the water content of the coated paper is appropriate, the coated layer can be smoothed with a low nip pressure or a short nip residence time by using a metal roll heated to 100 ° C. or higher. The opacity can be improved while keeping the density of the film low. Furthermore, by heating the surface of the metal roll to 100 ° C or higher, coated paper with good smoothness can be processed at a higher speed than conventional supercalenders, and rewinding frame changes, etc. are omitted. Therefore, it can be produced efficiently and has excellent operability.

  Moreover, as a preferable condition when using a high temperature soft nip calender, for example, the Shore D hardness of the elastic roll is preferably 80 to 100, and more preferably 85 to 97. The linear pressure of the soft calendar is preferably about 30 to 500 kg / cm. The pre-calendar coating moisture is preferably 3 to 12%, but more preferably 4 to 8% in order to achieve both smoothness and operability.

  The material of the elastic roll used in pair with the metal roll of the soft calender is not particularly limited, but generally at high temperature and high pressure such as modified urethane resin, epoxy resin, polyamide resin, phenol resin, polyether resin, polyacrylate resin, etc. A resin roll exhibiting durability is preferably used.

  The type of soft calender used in the present invention is preferably 6 stacks or more with two tandem type rolls in consideration of easy paper passing and space saving. The tandem type is a soft calendar of a type in which two rolls obtained by overlapping a pair of metal rolls and elastic rolls are arranged in parallel.

As described above, the gravure coated paper of the present invention achieves high whiteness and high printability and white paper gloss by blending a specific pigment into the pigment coating layer. . The effect of the coated paper for gravure printing of the present invention is particularly remarkable when the density is 1.20 g / m ³ or less and the glossiness of blank paper is 50% or more. In the present invention, papermaking, coating, and surface treatment are continuously performed online, so that productivity can be improved.

  EXAMPLES Hereinafter, although an Example of this invention is given and this invention is demonstrated further in detail, this invention is not limited at all by these. Unless otherwise specified, in the present specification, “part” and “%” respectively represent “part by weight” and “% by weight”, and the numerical range is described as including the end points.

<Manufacture of coated paper for printing>
[Example 1]
A pulp slurry containing 15 parts of hardwood kraft pulp (LBKP), 30 parts of softwood kraft pulp (NBKP) and 55 parts of waste paper pulp (DIP) was prepared. A paper stock was prepared by adding 0.5% of a cationic paper strength enhancer to the pulp as an agent.

Using this stock, paper was made with a paper machine having a gap type former at a paper making speed of 1600 m / min to obtain a base paper having a basis weight of 37 g / m ² .

Next, with respect to 100 parts of pigment containing 72 parts of heavy calcium carbonate, 27 parts of delaminated clay and 1 part of organic pigment, 6.5 parts of carboxy-modified styrene-butadiene copolymer latex as an adhesive and non-associative type A coating solution having a solid content concentration of 63% was prepared by blending 0.15 part of an acrylic synthetic water retention agent. This coating solution was dried by applying a pigment on both sides with a jet fountain-applied blade coater at a coating speed of 1600 m / min so that the coating amount was 8.5 g / m ² per side. .

  Subsequently, in the surface treatment process, the surface temperature of the metal roll at the first nip is 90 ° C., the surface temperature of the metal roll at 2 to 6 nip is 130 ° C., 1 to 6 using a heat soft calender of 2 rolls and 6 stacks. Calendering was performed with a linear pressure at the nip of 250 kN / m to obtain a coated paper for gravure printing.

  In this example, since papermaking, coating, and surface treatment were continuously performed online, the coating speed and calendar speed were also 1600 m / min.

[Example 2]
A gravure coated paper was obtained in the same manner as in Example 1 except that the pigment composition of the coating liquid of Example 1 was changed to 82 parts of heavy calcium carbonate and 18 parts of talc.

[Example 3]
About the base paper of Example 1, the coated paper for gravure printing was obtained by the method similar to Example 1 except having implemented the pre-calendar process on the conditions of 38 kN / m before coating.

[Example 4]
About the pigment combination of the coating liquid of Example 1, the coated paper for gravure printing was obtained by the method similar to Example 1 except having used the following grinding | pulverization light calcium carbonate instead of heavy calcium carbonate.

In this example, as calcium carbonate, spindle-shaped primary particles agglomerated to form Rosetta-shaped secondary particles, calcium carbonate of calcite crystal (Okutama Kogyo Co., Ltd .: TP221BM) was made a solid content concentration 20%, After adding 1.5 parts by weight of a polyacrylate dispersant to form a slurry, wet milling is performed using SC Mill Long (manufactured by Mitsui Mining Co., Ltd .: SC Mill 100), which is a multi-pass mill. Was used as a pigment. The pulverized calcium carbonate has an average particle size (d50: 50% by weight particle size) measured by an X-ray transmission particle size distribution analyzer of 0.38 μm, and a volume distribution average particle size (volume frequency 50% particle size). Was 0.23 μm, the BET specific surface area was 22.5 m ² / g, and the sharpness was 62.

Here, the sharpness is the following formula measured with an X-ray transmission type particle size distribution analyzer (Cedigraph 5100, manufactured by Micromeritics):
Sharpness = (d30 / d70) × 100
[Wherein d30 is a particle size of 30% by weight and d70 is a particle size of 70% by weight]
It is a parameter | index which shows the sharpness of a particle size distribution represented by these.

Light calcium carbonate before pulverization (calcite crystal in which spindle-shaped primary particles agglomerate to form rosette-shaped secondary particles) was measured with an X-ray transmission type particle size distribution analyzer of light calcium carbonate before pulverization. The average particle diameter (d50) was 2.2 μm, and the BET specific surface area was 5.9 m ² / g.

[Example 5]
For the coated paper of Example 1, in the surface treatment step, the surface temperature of the metal roll at the first nip is 90 ° C. and the surface temperature of the metal roll at 2 to 4 nips using a 2-roll, 4-stack thermal soft calender. A gravure coated coated paper was obtained in the same manner as in Example 1 except that the calendering was performed at 150 ° C. and the linear pressure at the 1st to 4th nips was 250 kN / m.
[Example 6]
For the base paper of Example 1, for the printing of gravure in the same manner as in Example 1 except that clear starch was applied so that the total amount of both sides of oxidized starch (Nihon Cornstarch SK20) was 0.8 g / m ² . Coated paper was obtained.

[Comparative Example 1]
About the pigment combination of the coating liquid of Example 1, the coated paper for gravure printing was obtained by the method similar to Example 1 except having changed into 100 parts of heavy calcium carbonate.

[Comparative Example 2]
About the pigment combination of the coating liquid of Example 1, the coating paper for gravure printing is obtained by the method similar to Example 1 except having changed into 72 parts of heavy calcium carbonate, 27 parts of fine clay, and 1 part of organic pigments. It was.

[Comparative Example 3]
The base paper of Example 1 was the same as Example 1 except that the basis weight was 27 g / m ² and the coating amount of Example 1 was pigment-coated on both sides so as to be 15.5 g / m ² per side. Thus, a gravure coated paper was obtained.

[Comparative Example 4]
A gravure is obtained in the same manner as in Example 6 except that the pigment composition of the coating liquid of Example 6 is changed to 54 parts of heavy calcium carbonate, 36 parts of delaminated clay, 9 parts of calcined clay, and 1 part of organic pigment. A coated paper for printing was obtained.

<Evaluation method>
The test was conducted based on the evaluation method as shown below.

(1) Whiteness Measured based on JIS P 8123.

(2) Speckle Using a Ministry of Finance gravure printing machine, printing was performed at a printing speed of 40 m / min and a printing pressure of 10 kgf / cm, and the halftone dot missing state on the surface of the obtained printed matter was visually evaluated.
○: Good, Δ: Slightly inferior, ×: Inferior (3) Blank paper glossiness Measured based on JIS P8142.

(4) Opacity Measured based on JIS P 8138.

(5) Density The density was measured based on JIS P 8118.

(6) High-speed operability High-speed operability was visually evaluated. High-speed operability was evaluated from the viewpoints of the difficulty of paper breakage in each process, and the drying process and the occurrence of mist and streaks in the coating process. The evaluation criteria are as follows.
◎ = Very good, ○ = Good, Δ = Slightly poor, × = Poor (7) Volume distribution average particle size of pigment was measured by a laser diffraction particle size distribution analyzer (Malvern, Mastersizer 2000). It is a numerical value of a particle size with a frequency of 50%.

Table 1 shows the evaluation results. As is clear from Table 1, 10 to 30 parts by weight of a layered silicate mineral having a volume distribution average particle diameter of 4.0 to 20 μm as a pigment in 100 parts by weight of pigment and a volume distribution average particle diameter of 0.2 to By providing a coating layer having an outermost coating amount of 5 to 15 g / m ² per side using a coating liquid containing 70 to 90 parts by weight of calcium carbonate of 1.0 μm in 100 weights of pigment. It was confirmed that a coated paper having high whiteness and good gravure printability could be produced without impairing high-speed operability.

Claims (10)

A paper making process for making a base paper,
A coating step of coating a coating liquid containing a pigment and an adhesive, and providing a pigment coating layer of 5 to 15 g / m ² per side on the outermost layer;
A step of surface-treating the pigment coating layer;
A process for producing a coated paper for gravure printing in which the whiteness of the coated paper is 80% or more, wherein these steps are continuously performed using an on-machine coater,
10 to 30 parts by weight of a layered silicate mineral having a volume distribution average particle diameter of 6.0 to 20 μm measured by a laser diffraction method in 100 parts by weight of a pigment, and a volume distribution average particle diameter of 0.2 to 1.0 μm. The said method of coating the coating liquid containing 70-90 weight part of calcium carbonate which is and providing a pigment coating layer. The method of claim 1, wherein the layered silicate mineral comprises talc and / or clay. The method according to claim 1 or 2, wherein the volume distribution average particle diameter of the layered silicate mineral is 6.2 µm or more. The density of the coated paper is 1.10 to 1.20 g / m ³ The method according to claim 1, wherein The method according to any one of claims 1 to 4, wherein the glossiness of the coated paper is 50% or more. The method according to claim 1, wherein the coated paper has a Parker print surface roughness value of 1.6 μm or less. The operation speed is 1300 m / min or more, the coating process is performed using a blade-type on-machine coater, and the surface treatment process is performed using a thermal soft calender composed of a metal roll and an elastic roll. The method according to any one of claims 1 to 6 , which is performed as described above . The method according to any one of claims 1 to 7 , wherein the base paper is precalendered under a condition of a treatment linear pressure of 30 kN / m to 100 kN / m before the coating step. A coated paper for gravure printing having a pigment coating layer on a base paper and having a whiteness of 80% or more,
10 to 30 parts by weight of layered silicate mineral having a volume distribution average particle diameter of 4.0 to 20 μm measured by laser analysis / scattering method in 100 parts by weight of pigment constituting the coating layer, laser analysis / scattering method 70 to 90 parts by weight of calcium carbonate having a volume distribution average particle size of 0.2 to 1.0 μm as measured in Step 1, and the coating amount of the outermost pigment coating layer is 5 to 15 g / m ² per side. The above-mentioned coated paper for gravure printing. The coated paper of Claim 9 manufactured by the method in any one of Claims 1-8.