JP5625655B2 - Coated white paperboard - Google Patents

Description

  The present invention relates to coated white paperboard, and more specifically, it balances both the printability and post-processing suitability required for coated whiteboard, and in particular, reduces misdots in gravure printing as printability and varnish as post-processing suitability. The present invention relates to a coated white paperboard excellent in gloss development and boxing suitability.

  Coated white paperboard is mainly used in paper containers such as cosmetic boxes, confectionery boxes, soap boxes, etc., and after printing on the paper surface by various printing methods to appeal the enclosed products, It is processed into a paper container. The coated white paperboard used for processing in paper containers is different from general printing coated paper for printing and publishing applications, and is required to have paper container processing suitability in addition to printability. Among these, since printing is performed by various printing methods such as sheet-fed lithographic offset printing, gravure printing, flexographic printing, etc., quality suitability for each printing method is required for coated white paperboard. In addition, the processing of paper containers includes surface finishing for surface cosmetics and surface protection, varnishing, press coat processing, film laminating processing, etc., and box making, punching, ruled line processing, and gluing. Since processing and the like are performed, in addition to the above printability, these various post-processing suitability are also required for coated white paperboard.

  In such paperboard processing of coated white paperboard, printing of large lot products is possible at high speed using winding, and more efficiently by combining a punching device with the printing line. Gravure printing is often used because paper containers can be produced and are economically superior. However, in coated white paperboard, the smoothing of the surface by the calendar pressurization process is limited because the base paper is a multilayer paper making composition with many used papers and the need to maintain the paper thickness against the development of strength of the paper container Therefore, compared to general gravure coated paper for printing and publishing applications, there is a tendency that smoothness is less likely to occur. For this reason, in gravure printing, misdots (missing gravure halftone dots) occur, There is a problem that the print finish tends to deteriorate.

  In addition, as described above, surface processing of coated white paperboard includes various surface processing methods such as varnishing, press coating, and film laminating. Of these, a varnish coater and UV drying equipment are installed after the printing machine. Inline varnish (UV varnish) processing is used because it is more efficient and economical because it can be installed and continuously varnished onto the coated white paperboard after printing. Increasing number of cases. However, for coated white paperboard, which also requires offset printing suitability, it is necessary to improve the absorption capacity of the coating layer in order to improve offset printing suitability such as ink drying properties and water absorbability. Since the varnish developed on the surface of the coated white paperboard is absorbed, it becomes impossible to form a varnish layer having a sufficient thickness, and this reduces the expression of varnish gloss, resulting in the desired cosmetic effect and surface protection effect. There is a problem that cannot be obtained.

  For this reason, various methods have been proposed. Among these, as a coated printing paper having good halftone dot reproducibility in gravure printing and having good super-calendar stain resistance, the average particle diameter is 0.2 to 0 with respect to 100 parts by weight of paper coating pigment. A method of blending an aqueous latex containing a styrene-butadiene copolymer having a diameter of 0.4 μm, a glass transition temperature of −50 to −10 ° C., and a gel content of 70 to 90% by weight has been proposed (see Patent Document 1). However, although the above technique is effective in improving the gravure printing aptitude, it is difficult to improve various necessary aptitudes such as surface processing aptitude and post-processing aptitude required for coated white paperboard. In addition, as a coated white paperboard that improves coating suitability and cracking, as the undercoat latex, the glass transition temperature obtained by emulsion polymerization by specific monomer composition and blending is in the range of −10 to −45 ° C., specified There has been proposed a method using a water-soluble copolymer obtained by copolymerizing the above monomers and a water retention agent (see Patent Document 2). However, the improvement effect of gravure printing suitability is limited only by improving the undercoat layer latex as described above.

  In addition, in order to obtain a coated paperboard having good coating operability and excellent surface strength, water resistance, ink drying properties, printing gloss, blister pack suitability and pasting properties, the paperboard coating composition can be used. The polymer latex has at least two glass transition points in the range of −100 to 50 ° C., and the difference between the highest glass transition point and the lowest glass transition point is 5 ° C. or more, and the zeta potential on the particle surface A method using a latex having a -100 to -10 mV has been proposed (see Patent Document 3). However, when latex such as the above technique is applied to the entire coating layer, the flexibility and cushioning properties of the coating layer are hindered, and therefore the gravure printing suitability is difficult to improve.

  In addition, as coated white paperboard that is suitable for varnish application immediately after printing with oil-based ink and does not generate unevenness, the pigment of the topcoat layer contains heavy calcium carbonate in an amount of 45% by mass or more of the total pigment, and the coating concentration is 64%. It has been proposed to apply with the above coating solution (see Patent Document 4). However, it is difficult to obtain sufficient gravure printing suitability only by improving the pigment and paint concentration of the overcoat layer as in the above technique.

  Furthermore, as an offset / gravure printing common coated white paperboard, the undercoat layer contains at least one pigment selected from calcined clay, structured kaolin and delaminated clay in an amount of 30 to 70 parts by weight based on the solid content per total pigment. In addition, a copolymer latex having a glass transition temperature of −50 to −5 ° C. as an adhesive is contained in an amount of 5 to 25 parts by weight with respect to the total pigment, and the glass transition temperature is 0 ° C. or more as an adhesive for the overcoat layer. A coated white paperboard containing 3 to 30 parts of copolymer latex in terms of the solid content relative to the total pigment has been proposed (see Patent Document 5). However, in the above method, it is necessary to set the coating concentration low when coating by the coating apparatus, and the coverage and smoothness of the coating layer are lowered as the coating concentration decreases, so that misdots deteriorate. There is a fear. In addition, since a pigment that forms a bulky coating layer such as calcined clay or structured kaolin is used as in the above method, the absorbability of the coating layer increases, and the suitability for varnishing tends to decrease.

  As described above, various methods have been proposed to improve the quality of coated white paperboard, but it has various aptitudes such as printability, varnishing suitability, post-processing suitability, etc., especially gravure printing suitability and varnishing suitability. The current situation is that there is no satisfactory method.

JP 02-139500 A Japanese Patent Application Laid-Open No. 05-287797 Japanese Patent Laid-Open No. 11-060817 JP 2008-231586 A JP 2002-363877 A

  The present invention is compatible with various qualities of printing suitability and post-processing suitability for paper container processing required for coated white paperboard. Especially, it reduces misdots in gravure printing as printability, and develops varnish glossiness as post-processing suitability. It provides excellent coated white paperboard.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a coated white paperboard excellent in gravure suitability and post-processing suitability can be obtained. That is, the present invention provides a coated white board having two coating layers containing a pigment and an adhesive as main components on the surface of the base paper, and is provided adjacent to the base paper among the coating layers. The undercoat coating layer contains, as a pigment, 70% by mass or more of calcium carbonate having a particle content of 2 μm or less of 80 to 95% as a pigment, and a glass transition temperature of −50 to −30 ° C. as an adhesive. The copolymer latex contained therein is contained in an amount of 5 to 20% by mass with respect to the pigment, and the particle content of 2 μm or less is 90% in the topcoat layer provided adjacent to the undercoat layer. containing more than 50% by weight of the total pigment or more pigments, and the average particle size as the adhesive is 80 to 120 nm, and within the glass transition temperature is. 10 to 60 ° C. in the range of -25 to -10 ° C. copolymer lattes with peaks one each to Hex which is a coated white sheet paper, characterized in that it contains 5 to 20% by weight in terms of solid content of the pigment.
It is preferable that 100% by mass of the total pigment contains calcium carbonate having a particle content of 2 μm or less in the undercoat coating layer of 80 to 95%.
It is preferable that the pigment of the topcoat layer contains heavy calcium carbonate having a particle content of 95 to 100% of 2 μm or less and 60% by mass or more of the total pigment of the topcoat layer.
Preferably, the undercoat coating layer is formed by a rod coating method and the topcoat coating layer is formed by a blade coating method.
The undercoat coating layer and the topcoat coating layer are preferably provided on both sides of the base paper.

  According to the present invention, a coated white paperboard having improved gravure halftone reproducibility in a printing process during paper container processing and excellent post-processing suitability such as box making and varnishing can be obtained.

  In the coated white paperboard of the present invention, the undercoat coating layer provided adjacent to the base paper contains 70% by mass or more of calcium carbonate having a particle content of 80 μm or less of 2 μm or less as a pigment, And it is necessary to contain 5-20 mass% by solid content of the copolymer latex having a glass transition temperature in the range of −50 to −30 ° C. as an adhesive. When the pigment and adhesive of the undercoat layer have the above-described configuration, when the plate comes into contact with paper during gravure printing, the effect of the reasonably fine particle size pigment and the adhesive having a low glass transition point is applied to the undercoat layer. By providing cushioning properties and making the undercoat layer easily deformed, the adhesion between the paper surface and the plate is improved and excellent gravure halftone reproducibility is exhibited. Moreover, it has the effect of improving the coating layer strength with respect to the offset printability.

  In the present invention, the pigment used in the undercoating layer for the above-described effect of the undercoating layer is an irregular and block-like particle shape that hardly inhibits the cushioning and deformability of the undercoating layer. Calcium carbonate having the following particle shape, particularly heavy calcium carbonate is preferred. Calcium carbonate is also preferred because it is the cheapest of the pigments used in the paper coating field. In contrast, pigments used in the paper coating field include kaolin and talc with strong flatness, light calcium carbonate and satin white with strong acicular and columnar properties, etc. However, a pigment having such a strong shape characteristic may impair the cushioning properties and deformability of the undercoat coating layer. In addition, the pigment having strong shape characteristics as described above is expensive in terms of price.

  The particle size of the calcium carbonate in the undercoat layer is such that the cushioning property, deformability, and smoothness of the undercoat layer are difficult to inhibit. The particle content of 2 μm or less is 80 to 95%, and the particle size is 2 μm or less. It is particularly preferable that the rate is 90 to 95%. When the particle size of the calcium carbonate in the undercoat layer is coarse such that the particle content of 2 μm or less is less than 80%, the surface smoothness of the undercoat layer decreases, and this decrease in smoothness is the smoothness of the overcoat layer. Therefore, there is a fear that sufficient gravure halftone dot reproducibility cannot be obtained and offset printing suitability may be deteriorated. On the other hand, when the particle content of 2 μm or less of the calcium carbonate particle size of the undercoat layer exceeds 95%, the coating layer strength may be lowered in the offset printability.

  In addition, since it is important that the particle size distribution of the calcium carbonate in the undercoat layer includes a large amount of pigment particles that effectively work for forming the coating layer and expressing smoothness, the content of coarse particles and fine particles is small. A type having a large particle size in the vicinity of the average particle size (a type having a narrow particle size distribution) is preferable. When the calcium carbonate in the undercoat layer contains a large amount of coarse particles, the cushioning property, deformability and smooth expression of the undercoat layer may be impaired. On the other hand, if the calcium carbonate in the undercoat layer contains a large amount of fine components, the fine components will sink into the gaps between the pulp fibers of the base paper of the paperboard. In addition, the coating layer strength in offset printing may be deteriorated.

  The blending amount of the above calcium carbonate in the undercoat layer is preferably 70% by mass or more of the total pigment blended in the undercoat coating layer as a formulation that does not hinder the cushioning property, deformability, and smoothness of the undercoat layer. 100% by mass is particularly preferable. When the calcium carbonate content in the undercoat layer is less than 70% by mass, the cushioning properties, deformability and smoothness of the undercoat layer are hindered due to the influence of the particle shape and particle size of other pigments to be added. There is a fear.

  Here, the pigment that can be used in combination with the above calcium carbonate in the undercoat layer is a pigment other than the calcium carbonate defined by the present invention, such as ordinary clay, heavy calcium carbonate, light calcium carbonate, titanium dioxide, aluminum hydroxide, One or more publicly known pigments used in the general coated paper manufacturing field such as silica, satin white, talc and the like can be appropriately used within a range not impairing the effects of the present invention.

  Furthermore, the copolymer latex used as an adhesive for the undercoat layer in the present invention has a glass transition temperature of −50 to −30 ° C. in order to develop cushioning properties, deformability, and elasticity in the undercoat layer. Must be in range. When the glass transition temperature of the copolymer latex of the undercoat layer is lower than −50 ° C., the copolymer latex becomes too soft and the coating layer strength in offset printing may be deteriorated. On the other hand, when the glass transition temperature of the copolymer latex of the undercoat layer is higher than −30 ° C., there is a possibility that the cushioning property and the deformability of the undercoat layer necessary for obtaining sufficient gravure printability may not be obtained. .

  The average particle size of the copolymer latex in the undercoat layer is preferably 100 to 300 nm as the average particle size in order to develop cushioning properties, deformability, smoothness, and coating layer strength of the undercoat layer. . When the average particle diameter of the copolymer latex of the undercoat layer is less than 100 nm, the cushioning property, deformability, and smoothness of the undercoat layer may be deteriorated. On the other hand, when the average particle diameter of the copolymer latex of the undercoat layer exceeds 300 nm, the coating layer strength may be deteriorated.

  The copolymer latex in the undercoat layer is not particularly limited as long as the glass transition point and the average particle diameter are within the above ranges, for example, styrene / butadiene copolymer, methyl methacrylate / butadiene copolymer, etc. Conjugated diene polymer latex, acrylic acid polymer latex such as acrylic acid ester and / or methacrylic acid ester polymer or copolymer, vinyl polymer latex such as ethylene / vinyl acetate copolymer, or the like It is possible to select and use one or more kinds of alkali-soluble or non-alkali-soluble polymer latexes obtained by modifying various polymer latexes with a functional group-containing monomer such as a carboxy group.

  The amount of the above-mentioned copolymer latex in the undercoat layer is 5% in terms of solid content of the copolymer latex with respect to the pigment in order to develop the cushioning property, deformability, smoothness, and coating layer strength of the undercoat layer. It is preferable to contain -20 mass%. When the content of the copolymer latex of the undercoat layer is less than 5% by mass in solid content with respect to the pigment, the cushioning property, deformability, smoothness, and coating layer strength of the undercoat layer may be deteriorated. On the other hand, when the blend of the copolymer latex of the undercoat layer exceeds 20% by mass with respect to the pigment, the smoothness of the undercoat layer may be deteriorated.

  As an adhesive other than latex in the undercoat coating layer, one or more kinds of starches such as polyvinyl alcohol, oxidized starch, positive starch, esterified starch, dextrin, etc. are used within the range not impairing the effects of the present invention. It can be appropriately selected and used.

In the coated white paperboard of the present invention, a pigment having a particle content of 2 μm or less as a pigment of 90% or more in the topcoat layer provided adjacent to the undercoat layer in addition to the undercoat layer having the above-described configuration In the range of −25 ° C. to −10 ° C. and 10 ° C. to 60 ° C., respectively , with an average particle diameter of 80 to 120 nm as an adhesive. It is necessary to contain a copolymer latex having a peak at 5 to 20% by mass in solid content with respect to the pigment. If the pigment and adhesive of the topcoat layer have the above configuration, the topcoat layer and the topcoat layer also have cushioning properties due to the effect of the pigment having a moderately fine particle diameter and the adhesive having a low glass transition point. Is provided, and the adhesiveness between the paper surface and the plate is improved by a synergistic effect with the undercoat layer, and excellent gravure halftone dot reproducibility is exhibited. In addition, the effect of an adhesive having a high glass transition temperature partially stabilizes the operability by preventing peeling of the coating layer, fluffing on the back surface, and stickiness in the coating and calendering processes, as well as the pigment particle size. By not making it excessively fine, varnish gloss development in varnish surface processing is improved.

  In the present invention, the particle size of the pigment of the topcoat layer as described above is such that the particle content of 2 μm or less is 90% or more, more preferably the particle content of 2 μm or less is 95 to 100%. There is an effect that it is difficult to inhibit cushioning, deformability and smooth expression. If the particle size of the pigment in the overcoat layer is less than 90%, the coarse particle content is included, the surface smoothness and cushioning properties of the overcoat layer are reduced, and sufficient gravure printing dot reproduction is achieved. There is a risk that sex will not be obtained.

  In addition, the blending of the pigment in the topcoat layer is a composition that hardly inhibits the cushioning property, deformability, and smoothness of the topcoat layer, and the solid content is 50% by mass or more based on the total pigment blended in the topcoat coating layer. 80 mass% or more is more preferable, and 100 mass% is particularly preferable. When the amount of the pigment in the topcoat layer is less than 50% by mass, the cushioning property, deformability, and smoothness of the topcoat layer may be hindered due to the effect of an increase in pigment coarse particles in the topcoat layer.

  Furthermore, the pigment in the overcoat layer is a heavy calcium carbonate having an irregular and block-like particle shape as a particle shape that does not hinder the cushioning and deformability of the overcoat layer, as in the case of the undercoat layer. Is preferably included. Also, heavy calcium carbonate is particularly preferable because it is the cheapest of the pigments used in the paper coating field. In contrast, pigments used in the paper coating field include kaolin and talc with strong flatness, light calcium carbonate and satin white with strong acicular and columnar properties, etc. However, the pigment having such strong shape characteristics may impair the cushioning properties and deformability of the topcoat layer, as in the case of the undercoat layer. In addition, the pigment having a strong shape characteristic as described above is expensive in terms of price.

  Here, the pigment that can be used in combination with the above-mentioned calcium carbonate in the overcoat layer is a pigment other than the calcium carbonate defined by the present invention, such as ordinary clay, heavy calcium carbonate, light calcium carbonate, titanium dioxide, aluminum hydroxide, One or more publicly known pigments used in the general coated paper manufacturing field such as silica, satin white, talc and the like can be appropriately used within a range not impairing the effects of the present invention.

  Furthermore, the copolymer latex used as the adhesive for the topcoat layer in the present invention has an average particle diameter of 80 to 120 nm in order to develop cushioning properties, deformability, smoothness and suitability for varnishing of the topcoat layer. Is necessary. If the average particle size of the copolymer latex of the topcoat layer is less than 80 nm, the latex tends to migrate during coating drying and may penetrate into the undercoat layer, and the cushion of the topcoat layer There is a risk that the property, deformability, and smoothness will deteriorate. On the other hand, when the average particle size of the copolymer latex of the overcoat layer exceeds 120 nm, the suitability for varnish processing may be deteriorated due to the effect of improving the absorbability of the coating layer due to the increase in the coating layer voids.

The glass transition temperature of the copolymer latex in the overcoat layer, if latex having a glass transition temperature of one each and the range of. 10 to 60 ° C. in the range of -25 to -10 ° C., a glass transition The effect of contributing to halftone dot reproducibility during gravure printing by exhibiting elasticity due to the low temperature part, and peeling of the coating layer in the coating and calendar process due to the high glass transition temperature, fluffing on the back surface, In addition, it is possible to achieve two conflicting effects that prevent stickiness and stabilize the operability . Copolymer latex of the upper coating layer, in the case of a type having one of the glass transition temperature of the low glass transition temperature or higher glass transition temperature, can not compatible with the workability gravure printability improving. Moreover, even if it is copolymer latex which has two different glass transition temperatures, when either of two glass transition temperatures is lower than -25 degreeC, the operativity in a coating or a calendar process may deteriorate. When either of the two glass transition temperatures is higher than 60 ° C., the gravure printing suitability is deteriorated due to the decrease in elasticity, the coating layer strength expression is decreased due to poor glass transition, and the varnish processing suitability There is a risk of causing a decline.

  The copolymer latex in the overcoat layer is not particularly limited as long as the glass transition temperature and the average particle diameter are within the above ranges, for example, styrene / butadiene copolymer, methyl methacrylate / butadiene copolymer, etc. Conjugated diene polymer latex, acrylic acid polymer latex such as acrylic acid ester and / or methacrylic acid ester polymer or copolymer, vinyl polymer latex such as ethylene / vinyl acetate copolymer, or the like One kind or two or more kinds of alkali-soluble or non-alkali-soluble polymer latex obtained by modifying various polymer latexes with a functional group-containing monomer such as a carboxy group can be selected and used.

  The amount of the above-mentioned copolymer latex in the topcoat layer is such that the copolymer latex is added to the pigment in order to develop the cushioning properties, deformability, smoothness, coating layer strength, and varnishing suitability of the topcoat layer. It is necessary to contain 5-20 mass% by solid content. When the composition of the copolymer latex of the topcoat layer is less than 5% by mass with respect to the pigment, the cushioning property, deformability, coating layer strength, and varnish processing suitability of the topcoat layer are deteriorated. There is a fear. On the other hand, if the blend of the copolymer latex of the topcoat layer is more than 20% by mass in solid content with respect to the pigment, the smoothness of the topcoat layer may be deteriorated.

  Here, as an adhesive other than latex in the top coat layer, one or more kinds of starches such as polyvinyl alcohol, oxidized starch, positive starch, esterified starch, dextrin, etc. are not impaired. It can be appropriately selected and used within the range.

The base paper used for the coated white paperboard of the present invention is composed of multiple layers of paper layers of two or more layers (generally 5 to 7 layers), and the base weight of the base paper is usually 150. It is about ˜650 g / m ² .

  The pulp to be used for each paper layer of the base paper is not particularly limited. For example, bleached or unbleached chemical pulp, mechanical pulp, and further, for example, magazine waste paper, flyer waste paper, newspaper waste paper, office waste paper, information paper Waste paper pulp such as waste paper, corrugated cardboard, and paper container waste paper is used for deinking as needed, or one or two or more kinds of undeinked waste paper pulp, etc. In the type of coated white paperboard in which the pigment coating layer is provided on one side of the paper, the bleached chemical pulp is applied to the outermost layer (first layer, surface layer) of the base paper on which the coating layer is provided in the base paper having a multilayer structure. It is preferable to use deinked waste paper pulp for the second layer (surface lower layer) adjacent to the surface layer, and undeinked waste paper pulp for the third and subsequent layers (respectively middle layer) and the lowermost layer (back layer). In the case of coated white paperboard of the type in which a pigment coating layer is provided on both sides of the base paper for the purpose of double-sided printing, the exposed chemical pulp is adjacent to the outermost layer (surface layer) on both sides of the base paper, and is adjacent to the lowermost layer on both sides. It is preferable to use deinked waste paper pulp for the second layer (surface lower layer). As described above, undeinked waste paper pulp with low whiteness and gray color is used for the middle layer of the base paper. By improving the whiteness of the base paper by applying ink waste paper pulp, it is possible to make the middle-layer gray that is visible through the surface of the base paper inconspicuous, and to improve the appearance after printing and paper container processing. it can.

  The above base paper contains sizing agents such as sulfuric acid band and rosin, paper strength enhancers such as polyamide and starch, drainage retention improvers, water-proofing agents such as polyamide polyamine epichlorohydrin, and various auxiliary agents such as dyes. It can also be added appropriately by an internal addition method added to the pulp raw material or an external addition method applied to the surface of the base paper by a size press or the like.

  The base paper is preferably subjected to a smoothing process in advance using a machine calendar, a soft calendar, a Yankee dryer or the like before applying the undercoat coating layer. The smoothness of the base paper is improved by applying a smoothing treatment to the base paper before coating as described above, and the smooth expression effect of the coated white paperboard is improved by providing a coating layer on the base paper. Therefore, the gravure printing suitability can be improved.

  As a method for applying the undercoat layer coating solution and the overcoat layer coating solution of the present invention to a base paper, a coating device generally used for producing coated paper can be used, for example, a blade coater, Rod coater, air knife coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, gravure coater, champlex coater, 2 roll size press coater, gate roll size press coater, film metering size press coater, etc. Can be applied to the surface of the multi-layer base paper by an on-machine method or an off-machine method. A coating layer having a certain thickness is formed in a form along the unevenness (so-called contour coating). Are possible, thereby easily coating layer is obtained with a constant cushioning, and high density coating, since it is capable of high-speed coating, coating method using a rod coater is preferred. On the other hand, as a coating method of the top coat layer provided adjacent to the undercoat coat layer, it is possible to form a coating layer having a relatively high smooth coating surface (so-called flat coating). Thus, a coating method using a blade coater is preferred because high gravure printing suitability is easily obtained, and high-concentration coating and high-speed coating are possible.

Moreover, the solid content concentration of the coating solution for the undercoat layer and the coating solution for the topcoat layer of the present invention is in the range of 10 to 75% by mass, and the coating amount of each coating layer is 0.00 by dry weight per side. It is preferable to adjust the solid content concentration appropriately according to the coating method so as to be in the range of 5 to ²⁰ g / m ² , and the coating amount of the undercoat coating layer is preferably 5 to 15 g / dry weight per side. m ² , the coating amount of the top coating layer is 3 to 15 g / m ² as a dry weight per side, and the total coating amount of both the under coating layer and the top coating layer is 8 as a dry weight per side. It is more preferable to adjust to be in the range of ˜25 g / m ² . If the coating amount of the undercoat coating layer is less than 5 g / m ² as the dry weight per side, the surface of the base paper cannot be sufficiently covered, and the desired smoothness of the present invention may not be obtained. On the other hand, if it exceeds 15 g / m ² , cracking of the coating layer may occur if a box is formed with ruled lines during box making. For the top coat layer, if the dry weight per side is less than 3 g / m ² , the surface of the undercoat layer cannot be sufficiently covered, causing ink transfer failure and the like, and satisfying both offset and gravure printing. Cannot be obtained. On the other hand, if it exceeds 15 g / m ² , as in the case of the undercoating coating layer, there is a risk of causing a cracking of the coating layer when a box is formed with ruled lines during box making.

  In the coated white paperboard of the present invention, it is preferable to apply a smoothing treatment using a machine calender, soft calender, super calender, or the like after coating and drying the overcoat layer coating solution. As described above, the smoothness of the coated white paperboard after coating is improved to improve the smoothness of the coated whiteboard paper and improve the gravure printing suitability.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these ranges. In the examples, “parts” and “%” indicate parts by mass and mass% unless otherwise specified.

(Particle content of 2 μm or less of pigment)
A 0.1% solution of sodium pyrophosphate is added to a single dispersion of each pigment to prepare a pigment diluted dispersion with a solid content concentration of about 4 to 8%, and further dispersed for 5 minutes with an ultrasonic cleaning device. For the pigment diluted dispersion obtained in this way, the pigment particle size distribution was measured by sedimentation using a Cedigraph 5100 (manufactured by Micromeritics, USA), and the cumulative mass% of particles of 2 μm or less was determined. The particle content was determined.

(Latex particle size)
Observe Brownian motion of copolymer latex (emulsion particles) in water by dynamic laser light scattering method, and grasp temporal fluctuation of this scattered light intensity (fluctuation of the number of photons of scattered light) on an accurate time scale. Thus, the photon correlation method for obtaining the diffusion coefficient is analyzed. (Unit of average particle size: nm)

(Glass transition temperature of copolymer latex)
The dry film of the copolymer latex obtained by vacuum drying the copolymer latex at 100 ° C. for 20 hours was measured using a differential scanning calorimeter (DSC: manufactured by Seiko Instruments Inc.).

Example 1
(Preparation of base paper)
Bleached chemical pulp on the surface layer of the first layer of the base paper, deinked waste paper pulp on the lower surface of the second layer, the middle layer of the third layer, the middle layer of the fourth layer, and the back layer of the fifth layer Undeinked waste paper pulp was used to make the paper into 5 layers, and then machine calendering was performed to obtain a base paper for coated white board with a weight of 290 g / m ² .

(Preparation of coating solution for undercoat layer)
As a pigment, 100 parts of heavy calcium carbonate (trade name: Hydrocurve 90, manufactured by Bihoku Flour Industry Co., Ltd.) having a particle content of 2 μm or less of 90% is used, and as a dispersant, 100 parts of pigment is polyacrylic acid. 0.25 part of soda was added, and a pigment dispersion having a solid content of 72% was prepared using a Coreless disperser. Next, 6 parts of oxidized starch (trade name: Oji Ace Y, manufactured by Oji Cornstarch Co., Ltd.) and a glass transition temperature of −44 ° C. and an average particle diameter of 160 nm are converted into a solid content with respect to 100 parts of pigment with respect to this pigment dispersion. Styrene-butadiene copolymer latex (trade name: PB9317, manufactured by Nippon A & L Co., Ltd.) 11 parts (in terms of each solid content) was added, respectively, to finally obtain a coating solution for an undercoat layer having a solid content concentration of 62%. It was.

(Preparation of coating solution for topcoat layer)
As a pigment, 30 parts of kaolin having a particle content of 2 μm or less (90%) (trade name: Kaofine 90, manufactured by US Seal Co., Ltd.), heavy calcium carbonate having a particle content of 2 μm or less, 97% (trade name: Carbital 97) And 64 parts of titanium dioxide (trade name: KA-100, manufactured by Korea Cosmo Chemical Co., Ltd.), and 0.2 parts of sodium polyacrylate with respect to 100 parts of pigment as a dispersant. And a pigment dispersion having a solid content of 68% was prepared using a Coreless disperser. Next, for this pigment dispersion, 1 part of oxidized starch (trade name: Oji Ace Y, supra) and two glass transition temperatures of −13 ° C. and 35 ° C. are converted into solid content for 100 parts of pigment. And 15 parts of styrene-butadiene copolymer latex (trade name: B1840, manufactured by Asahi Kasei Kogyo Co., Ltd.) with an average particle diameter of 95 nm is added (each solid content conversion), and the final solid content concentration is 64%. A layer coating solution was obtained.

(Preparation of coated white paperboard)
A base coat for the above coated white paperboard is coated by using a rod coater to coat the above undercoat layer coating solution so that the dry weight per side is 9 g / m ^2. I got paper. Subsequently, with respect to the obtained undercoat coated paper, using a blade coater, the above-mentioned topcoat layer coating solution was coated and dried so that the dry weight per side was 10 g / m ^2, and the metal roll surface temperature was Was subjected to a paper passing process at 200 ° C. and a 2-nip soft calender to obtain a coated white paperboard.

Example 2
In Example 1, 80 parts of heavy calcium carbonate (trade name: Hydrocurve 90, supra) having a particle content of 2 μm or less and a particle content of 2 μm or less were used as the pigment of the coating liquid for the undercoat layer. Coated white paperboard was obtained in the same manner as in Example 1 except that 20 parts of heavy calcium carbonate (trade name: Hydrocurve 60, manufactured by Bihoku Flour Chemical Co., Ltd.) was 20 parts.

Example 3
In Example 1, 30 parts of kaolin (trade name: Kaofine 90, supra) having a particle content of 2 μm or less and a particle content of 2 μm or less is 90% weight. Coated white paperboard in the same manner as in Example 1 except that 64 parts of calcium carbonate (trade name: Hydrocurve 90, supra) and 6 parts of titanium dioxide (trade name: KA-100, supra) were used. Got.

Example 4
In Example 1, 10 parts of kaolin (trade name: Kaofine 90, supra) having a particle content of 2 μm or less and a particle content of 2 μm or less is 97% weight. The coated white paperboard was prepared in the same manner as in Example 1 except that 84 parts of calcium carbonate (trade name: Carbital 97, supra) and 6 parts of titanium dioxide (trade name: KA-100, supra) were used. Obtained.

Example 5
In Example 1, 54 parts of kaolin (trade name: Kaofine 90, supra) having a particle content of 2 μm or less and a particle content of 2 μm or less was 99% light as the pigment of the coating solution for the topcoat layer. Coated white paperboard in the same manner as in Example 1 except that 40 parts of calcium carbonate (trade name: Tama Pearl TP221GS, manufactured by Okutama Kogyo Co., Ltd.) and 6 parts of titanium dioxide (trade name: KA-100, supra) were used. Got.

Example 6
In Example 1, the white coating sheet was coated in the same manner as in Example 1 except that the solid content concentration of the coating liquid for topcoat layer was 40% and the coating system for the coating liquid for topcoat layer was an air knife system. I got paper.

Example 7
In Example 1, by applying two layers of the undercoat coating layer and the topcoat coating layer to the back surface of the base paper for coated white paperboard in the same manner as the front surface, application of double-sided two-layer coating A coated white paperboard was obtained in the same manner as in Example 1 except that white paperboard was used.

Comparative Example 1
In Example 1, except that the pigment of the coating solution for undercoat layer was 100 parts of heavy calcium carbonate (trade name: Hydrocurve 60, supra) having a particle content of 2 μm or less of 60%, Example 1 Coated white paperboard was obtained in the same manner as above.

Comparative Example 2
In Example 1, 60 parts of heavy calcium carbonate (trade name: Hydrocurve 90, supra) having a particle content of 2 μm or less and a particle content of 2 μm or less was used as the pigment of the coating liquid for the undercoat layer. Coated white paperboard was obtained in the same manner as in Example 1, except that 40 parts of heavy calcium carbonate (trade name: Hydrocurve 60, supra) was 40 parts.

Comparative Example 3
In Example 1, except that the pigment of the coating liquid for undercoat layer was 100 parts of heavy calcium carbonate (trade name: Carbital 97, supra) having a particle content of 2 μm or less of 97%, Coated white paperboard was obtained in the same manner.

Comparative Example 4
In Example 1, the copolymer latex of the coating liquid for undercoat layer is a styrene-butadiene copolymer latex having a glass transition temperature of −20 ° C. and an average particle diameter of 150 nm (trade name: G1475, manufactured by Asahi Kasei Kogyo Co., Ltd.) 11 Coated white paperboard was obtained in the same manner as in Example 1 except that the parts were used.

Comparative Example 5
In Example 1, the copolymer latex of the coating liquid for undercoat layer has two glass transition temperatures of −13 ° C. and 35 ° C., and has an average particle diameter of 95 nm, a styrene-butadiene copolymer latex (trade name) : B1840, supra) A coated white paperboard was obtained in the same manner as in Example 1 except that the amount was 11 parts.

Comparative Example 6
In Example 1, 30 parts of kaolin (trade name: Kaofine 90, supra) having a particle content of 2 μm or less and a particle content of 2 μm or less is 60% weight. Coated white paperboard in the same manner as in Example 1 except that 64 parts of calcium carbonate (trade name: Hydrocurve 60, supra) and 6 parts of titanium dioxide (trade name: KA-100, supra) were used. Got.

Comparative Example 7
In Example 1, 15 parts of styrene-butadiene copolymer latex having a glass transition temperature of −44 ° C. and an average particle diameter of 160 nm (trade name: PB9317, supra) A coated white paperboard was obtained in the same manner as in Example 1 except that.

Comparative Example 8
In Example 1, 15 parts of styrene-butadiene copolymer latex having a glass transition temperature of 12 ° C. and an average particle diameter of 100 nm (trade name: PA4046, manufactured by Nippon A & L Co., Ltd.) A coated white paperboard was obtained in the same manner as in Example 1 except that.

  The coated white paperboards in Examples and Comparative Examples obtained as described above were conditioned for 6 hours under conditions conforming to JISP811, and then printed as smoothness, white paper gloss, and offset printability as the white paper quality of the coated white paperboard. The strength and printing gloss, misdot as gravure printing aptitude, and UV varnish gloss as post-processing aptitude (surface processing aptitude) were evaluated according to the following methods. Moreover, the stickiness of the calender roll in the calendering process after the application of the coated white paperboard was also evaluated as operational stability. Table 1 shows the production conditions and quality evaluation results of the coated white paperboard in each example and comparative example.

(PPS smoothness)
The coated surface of the coated white paperboard is measured according to JIS P8151: 2004 using a pressure type smoothness meter (measuring device: Parker Print Surf, manufactured by Messmer Buchel), and the smoothness when the clamp pressure is 1960 kPa is measured. did. The unit is μm, and the smaller the value, the better the smoothness.

(White paper gloss)
The coated surface of the coated white paperboard was measured according to JIS P8142: 2005.

(Offset printing suitability: printing strength)
The degree of coating layer picking generated when the coated white paperboard was printed using an offset ink with an RI printing machine (manufactured by Meisei Seisakusho) was visually evaluated.
A: Very good.
○: Good.
Δ: Slightly inferior
X: Inferior.

(Offset printing suitability: printing gloss)
Using an offset sheet-fed printing press (Speedmaster 102, manufactured by Heidelberg), offset printing was performed on the coated white paperboard, and the printed gloss of the four-color heavy color portion was measured according to JIS P8142: 2005.

(Applicability to gravure printing: Miss dot)
Gravure printing of coated white paperboard was performed using a Ministry of Finance gravure printing tester, and the degree of halftone dot missing at the 50% gradation halftone dot portion was visually evaluated.
A: There are almost no missing dots.
○: Several missing dots are recognized.
Δ: Missing about 10 halftone dots.
X: A large number of missing halftone dots exceeding 20 are recognized.

(UV varnish gloss)
After adjusting UV curing type varnish (trade name: Daikyu Acryria UV1603, manufactured by DIC Graphics) to 10 seconds with Zahn Cup # 4, a coating device with a UV curing device (model: SG610UV, manufactured by Duplo) After applying the UV curable varnish to the coated white paperboard surface, the varnish surface was processed by UV curing and drying. With respect to the varnished portion of the obtained coated white paperboard, the glossiness at an incident angle of 60 degrees was measured using a gloss meter (GM-26D, manufactured by Murakami Color Research Laboratory).

(Operational stability: stickiness of calendar roll)
The degree of stickiness to the calender roll when calendering the coated white paperboard after coating (sound on the roll during operation, dirt on the calender surface) was evaluated.
○: There is no roll sticking sound and no calendar surface contamination occurs.
X: A tendency of sticking to rolls is recognized, and the surface of the calendar is also stained.

  As is clear from Table 1, Examples 1 to 7, which are coated white paperboards according to the present invention, are both excellent in both gravure printing suitability and UV varnishing suitability, and a sufficient level of offset. It also has printability.

  INDUSTRIAL APPLICABILITY The present invention can be applied to coated white paperboard to reduce misdots in gravure printing as printability, and to improve varnish glossiness and boxing suitability as post-processing suitability.

Claims (5)

In the coated white paperboard having two coating layers containing a pigment and an adhesive as main components on the surface of the base paper, among the coating layers, an undercoat coating layer provided adjacent to the base paper A copolymer containing 70% by mass or more of calcium carbonate having a particle content of 80 to 95% of 2 μm or less as a pigment and a glass transition temperature in the range of −50 to −30 ° C. as an adhesive A latex having a solid content of 5 to 20% by mass with respect to the pigment, and a pigment having a particle content of 2 μm or less of 90% or more as a pigment in the topcoat layer provided adjacent to the undercoat layer. containing more than 50% by weight of the total pigment, and an average particle size as the adhesive is 80 to 120 nm, one of each glass transition temperature to the range of. 10 to 60 ° C. in the range of -25 to -10 ° C. copolymer latex having a peak by Coated white paperboard, characterized in that it contains 5 to 20% by weight in terms of solid content of the pigment.
  2. The coated white paperboard according to claim 1, wherein 100% by mass of the total pigment contains calcium carbonate having a particle content of 2 μm or less in the undercoat coating layer of 80 to 95%.   3. The pigment of the top coat layer contains heavy calcium carbonate having a particle content of 95 to 100% of 2 μm or less, and 60% by weight or more of the total pigment of the top coat layer. Coated white paperboard.   The coated white paperboard according to any one of claims 1 to 3, wherein the undercoat coating layer is formed by a rod coating method and the topcoat coating layer is formed by a blade coating method.   The coated white paperboard according to any one of claims 1 to 4, wherein the undercoat coating layer and the topcoat coating layer are provided on both sides of the base paper, respectively.