JP6341018B2 - Coated white paperboard - Google Patents

Description

  The present invention relates to coated white paperboard.

  Conventional coated white paperboard usually has two coated layers containing pigment and adhesive as the main components on one side of the base paper of the whiteboard made by combining, sheet-fed flat offset printing and gravure Printability is required for both printing, but poor smoothness due to poor whiteboard paper formation due to the composition, resulting in adhesion of the coating layer to the plate during gravure printing (cushioning), etc. For this reason, it did not necessarily have good gravure printability. Further, if the coating layer has smoothness and cushioning properties in order to solve these problems, generally, when offset printing is performed, printing troubles such as piling often occur. In this regard, for example, in the field of general printing paper such as art paper and coated paper, there is a complete distinction between offset printing and gravure printing. When each paper is printed by a different printing method, printing as described above is performed. Trouble occurs. In particular, between paper for offset printing and gravure printing, in order to improve the anti-piling property, increasing the amount of adhesive to improve the printing strength will improve the ink drying (ink setting) during printing. There is a problem that optical characteristics such as whiteness and concealment properties are deteriorated.

  The coated white paperboard used for processing paper containers is different from general printing coated papers for printing and publishing applications, and is required to have paper container processing suitability in addition to printability. As surface processing for surface cosmetics and surface protection, varnish processing, press coating processing, film laminating processing, etc., and further as box making processing, stamping processing, ruled line processing, gluing processing, etc. are performed, so the above printing In addition to suitability, these various types of post-processing suitability are also required for coated white paperboard.

  As for surface processing of coated white paperboard, there are various surface processing methods such as varnishing, press coating and film laminating as described above. Of these, coater for varnish and UV drying equipment are installed after the printer. Inline varnish (UV varnish) processing is used because paper containers can be produced more efficiently by continuously varnishing the coated white paperboard after printing as it is, and it is economically superior. Increasing 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.

  In response to the above problems, at least one pigment selected from calcined clay, structured kaolin, and delaminated clay as an undercoat layer is used as an offset and gravure-printed coated white board, and the solid content is 30 to 70 per total pigment. A polymer latex containing 5% by weight of a polymer latex having a glass transition temperature of −50 to −5 ° C. as an adhesive and having a solid content of 5 to 25% by weight relative to the total pigment, and having a glass transition temperature of 0 as an adhesive for the overcoat layer There has been proposed a coated white paperboard containing 3 to 30% by weight of a polymer latex having a solid content relative to the pigment of 3 ° C. or higher (see Patent Document 1). However, when containing 30 to 70% by weight of calcined clay or the like like the above coated white paperboard, it causes an increase in the viscosity of the paint, so it is necessary to set the paint concentration low when coating with the coating device, As the coating concentration decreases, the coverage and smoothness of the coating layer decrease, and the missing dots for gravure printing may deteriorate. 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.

Further, as a coated paper for printing having excellent smoothness, a particle size (D ₇₅ ) corresponding to 75% by mass of a particle size distribution curve and a particle size (D ₂₅ ) corresponding to 25% by mass are applied to the top coating layer. The heavy calcium carbonate having a ratio of D ₇₅ / D ₂₅ in the range of 1.5 to 3.3 is contained in an amount corresponding to 10 to 90% by mass of the total pigment contained in the overcoat layer. Has been proposed (see Patent Document 2). Furthermore, the particle diameter corresponding to 75% by mass of the particle size distribution curve (D ₇₅ ) and the particles corresponding to 25% by mass are in the range of 1.0 to 3.5 μm as the pigment in the undercoat coating layer. It has been proposed to contain 50 parts by mass or more of light calcium carbonate having a ratio of D ₇₅ / D ₂₅ in the range of 1.5 to 4.0 with respect to the diameter (D ₂₅ ) (see Patent Document 3).

  However, since the smoothness of the surface by the calendar pressure treatment is limited due to the need to maintain the paper thickness with respect to the strength development of the paper container, compared to general gravure coated paper for printing and publishing applications, In coated white paperboard that tends not to exhibit smoothness, it is difficult to obtain sufficient gravure printing suitability only by improving smoothness expression with a pigment having a characteristic particle size distribution as in the above technique.

  As an adhesive for the top coat layer, it has been proposed to contain a copolymer latex having an average particle size of 80 to 120 nm (Patent Document 4). However, if the average particle diameter of the latex of the top coat layer is only specified, sufficient cushioning properties cannot be obtained, and there is a possibility that the missing dots (missing halftone dots) of gravure printing will deteriorate.

  Various proposals have been made to improve the quality of coated white paperboard as described above, but various aptitudes such as printing suitability, varnishing suitability, and post-processing suitability in paper container processing, as well as the surface of the surface causing stains, etc. The present condition is that the result which fully satisfies gravure printing aptitude and varnishing aptitude is not obtained without stickiness.

JP 2002-363877 A JP 2004-003057 A JP 2009-221613 A JP2012-122166A

  The present invention is compatible with various qualities of printing suitability and post-processing suitability required for coated white paperboard, especially with less misting dots for gravure printing as printing suitability, suppressing stickiness, and varnishing as post-working suitability. The main object is to provide a coated white paperboard having excellent glossiness.

  As a result of intensive studies in view of the above-described conventional technology, the present inventors have solved the above-described problems. That is, the present invention relates to the following coated white paperboard.

  Item 1: In coated white paperboard having a coating layer containing a pigment and an adhesive on the surface of the base paper, the coating layer has an undercoat layer on the side close to the base paper and is overcoated on the side far from the base paper A pigment having a multilayer structure having at least two layers, wherein a styrene-butadiene copolymer latex is used as an adhesive in the topcoat layer, and the content of the styrene-butadiene copolymer latex is contained in the topcoat layer The solid content is 9 to 25 parts by mass with respect to 100 parts by mass, the average particle size of the styrene-butadiene copolymer latex is 75 to 150 nm, and the glass transition temperature is −50 to −20 ° C. Coated white paperboard.

  Item 2: The undercoat layer is formed by a coating method using a rod coater, and the overcoat layer is formed by either a coating method using a blade coater or a coating method using an air knife coater. Coated white paperboard.

  Item 3: The coated white paperboard according to Item 1 or 2, comprising heavy calcium carbonate having an average particle size of 0.5 to 1.2 μm as a pigment of the topcoat layer in an amount of 50% by mass or more of the pigment of the topcoat layer. .

  Item 4: The coated white paperboard according to any one of Items 1 to 3, which contains kaolin having an average particle size of 1.2 μm or less as a pigment of the topcoat layer.

  Item 5: The coated white paperboard according to any one of Items 1 to 4, wherein the undercoat layer is a coating layer closest to the base paper, and the overcoat layer is a coating layer farthest from the base paper.

  The coated white paperboard of the present invention has few missing dots for gravure printing, is excellent in varnish glossiness, and suppresses stickiness.

  The coating layer in the present invention is provided on the surface of the base paper and contains a pigment and an adhesive. The coating layer has a multilayer structure of at least two layers having an undercoat layer on the side close to the base paper and an overcoat layer on the side far from the base paper.

  In the present invention, styrene-butadiene copolymer latex is used as an adhesive in the overcoat layer. The content of the styrene-butadiene copolymer latex is 9 to 25 parts by mass in solid content with respect to 100 parts by mass of the pigment contained in the topcoat layer. If it is less than 9 parts by mass, the cushioning property, deformability, surface strength, and varnishing suitability of the overcoat layer are lowered, the gravure printing suitability is lowered, missing dots are increased, and the varnish gloss is lowered. On the other hand, when it exceeds 25 parts by mass, the smoothness and ink drying property of the topcoat layer are lowered, and as a result, the gravure printing suitability is lowered. The content is preferably 10 parts by mass or more. On the other hand, 20 parts by mass or less is preferable.

  The average particle diameter of the styrene-butadiene copolymer latex used for the topcoat layer is 75 to 150 nm. When the average particle size is less than 75 nm, the latex is likely to migrate during drying after coating the latex-containing topcoat layer coating solution. When migration occurs, components other than the latex of the overcoat layer coating solution penetrate into the undercoat layer, and a uniform coating layer is not formed. Thereby, the cushioning property, the deformability, and the smoothness of the overcoat layer are deteriorated, the gravure suitability is deteriorated, and the number of missing dots is increased. In addition, the stickiness may worsen and stains may occur. On the other hand, when the average particle diameter exceeds 150 nm, the absorbability is improved due to an increase in the voids of the coating layer, and the suitability for varnish processing is deteriorated. Thereby, there exists a possibility that varnish gloss may fall. The average particle diameter is preferably 85 to 140 nm, more preferably 85 to 120 nm, and still more preferably 85 to 110 nm.

  The glass transition temperature of the styrene-butadiene copolymer used for the topcoat layer is −50 to −20 ° C. If the glass transition temperature is less than −50 ° C., the stickiness is deteriorated, which may cause dirt or operability. On the other hand, when the glass transition temperature exceeds −20 ° C., the cushioning property of the overcoat layer is deteriorated, and the gravure suitability may be deteriorated. The glass transition temperature is preferably −50 to −25 ° C., more preferably −50 to −30 ° C., and still more preferably −42 to −32 ° C.

  Examples of other adhesives that can be contained in the overcoat layer in the present invention include various starches such as oxidized starch, cationized starch, and esterified starch, synthetic resin adhesives such as polyvinyl alcohol, casein, soy protein, and synthetic protein. Proteins, water-soluble adhesives such as cellulose derivatives such as carboxymethylcellulose and methylcellulose, conjugated diene polymer latexes such as methylmethacrylate-butadiene copolymer, acrylic acid ester and / or methacrylic acid ester polymer or copolymer An acrylic acid polymer latex such as a polymer, a vinyl polymer latex such as an ethylene-vinyl acetate copolymer, or an alkali solubility obtained by modifying these various polymer latexes with a functional group-containing monomer such as a carboxy group or Non-alkali soluble polymer latex That.

  When latex and a water-soluble adhesive are used in combination in the topcoat layer, the content of the water-soluble adhesive is preferably 3 parts by mass or less with respect to 100 parts by mass of the total pigment contained in the topcoat layer. It is particularly preferable to do this. When the content of the water-soluble adhesive in the topcoat layer is 3 parts by mass or less with respect to the total pigment contained in the topcoat layer, the cushioning property and smoothness of the topcoat layer can be improved and the gravure printing suitability can be improved. In addition, localization of the water-soluble adhesive due to binder migration during coating to drying can be suppressed, and ink drying can be improved.

  The pigment that can be contained in the overcoat layer in the present invention is not particularly limited. For example, heavy calcium carbonate, light calcium carbonate, titanium dioxide, calcium sulfite, gypsum, barium sulfate, talc, kaolin, clay, calcined kaolin, white carbon , Amorphous silica, deramikaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bentonite, sericite, paper sludge, deinking In addition to inorganic pigments such as regenerated particles using floss as a raw material, organic pigments such as urea formalin resin fine particles and fine hollow particles can be used. These can be used singly or in combination of two or more.

  Among these, heavy calcium carbonate is inexpensive and frequently used as a white pigment in addition to high whiteness. The finer the particle diameter, the better the white paper gloss and smoothness. Moreover, since varnish suitability is superior to light calcium carbonate, it is preferable to use heavy calcium carbonate having an average particle diameter of 0.5 to 1.2 μm in the overcoat layer. More preferably, it is 0.6-1.0 micrometer, More preferably, it is 0.7-0.9 micrometer. By setting the average particle size to 1.2 μm or less, smoothness can be improved, and gravure suitability and varnish suitability can be improved. On the other hand, when the thickness is 0.5 μm or more, the required amount of adhesive can be suppressed, and suitability for varnish and printing gloss can be improved.

  The heavy calcium carbonate is preferably 50% by mass or more of the total pigment contained in the overcoat layer. More preferably, it is 55 mass% or more, and still more preferably 60 mass% or more. By setting it as 50 mass% or more, whiteness can be improved and varnish suitability can be improved.

  In the present invention, it is preferable that the overcoat layer further contains kaolin having an average particle size of 1.2 μm or less as a pigment. Thereby, ink setting property can be improved and workability | operativity can be improved. The lower limit of the average particle diameter is not particularly limited, but it is preferably 0.2 μm or more as a commercially available product without causing a problem such as formation of secondary aggregates. The average particle diameter in the present invention is a particle diameter measured by a light scattering method and having a cumulative mass of 50%.

  The undercoat layer in the present invention may be adjacent to the topcoat layer or may be adjacent to the surface of the base paper. In the present invention, it is preferable that the undercoat layer is a coating layer closest to the base paper, and the topcoat layer is a coating layer farthest from the base paper. Thereby, the effect of this invention can be exhibited without regret. Moreover, the coating layer in this invention may be formed also in the back surface of the base paper if needed.

  The pigment of the undercoat layer in the present invention is not particularly limited. For example, heavy calcium carbonate, light calcium carbonate, titanium dioxide, calcium sulfite, gypsum, barium sulfate, talc, kaolin, clay, calcined kaolin, white carbon, non-carbon Crystalline silica, delaminated kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bentonite, sericite, paper sludge, deinking floss In addition to inorganic pigments such as regenerated particles as raw materials, organic pigments such as urea formalin resin fine particles and fine hollow particles can be used. These can be used singly or in combination of two or more.

  The adhesive contained in the undercoat layer in the invention is not particularly limited, but it is preferable to use a copolymer latex. The glass transition temperature of the copolymer latex is preferably in the range of -40 to 5 ° C. By setting the glass transition temperature of the copolymer latex in the undercoat layer to −40 ° C. or higher, there is no possibility that the copolymer latex becomes too soft and the coating layer strength in offset printing deteriorates. Moreover, stickiness can be suppressed. On the other hand, when the temperature is 5 ° C. or less, the cushioning property and deformability of the undercoat layer necessary for obtaining sufficient gravure printing suitability can be obtained. The glass transition temperature is more preferably −30 to 5 ° C., further preferably −30 to 0 ° C., and particularly preferably −25 to 0 ° C.

  The average particle diameter of the copolymer latex in the undercoat layer is preferably about 97 to 300 nm. More preferably, it is about 110-300 nm, More preferably, it is about 125-250 nm. By setting the average particle size of the copolymer latex of the undercoat layer to 97 nm or more, the cushioning property, deformability, and smoothness of the undercoat layer can be improved, and the gravure printing suitability can be improved. On the other hand, by setting the thickness to 300 nm or less, the coating layer strength can be improved.

  The copolymer latex in the undercoat layer is not particularly limited. For example, conjugated diene polymer latex such as styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer, acrylate ester and / or methacrylate ester. Acrylic acid polymer latex such as polymer or copolymer, vinyl polymer latex such as ethylene-vinyl acetate copolymer, or these various polymer latexes with functional group-containing monomers such as carboxy groups One or more types of modified alkali-soluble or non-alkali-soluble polymer latexes can be selected and used. From the viewpoint of improving the gravure printability, it is preferable to use a styrene-butadiene copolymer latex.

  Although content of said polymer latex in an undercoat layer is not specifically limited, About 9-25 mass parts is preferable by solid content with respect to 100 mass parts of pigments contained in an undercoat layer. By setting it as 9 mass parts or more, the cushioning property of a undercoat layer, a deformability, smoothness, and the coating layer intensity | strength can be improved and gravure printing aptitude can be improved. Thereby, the effect which improves offset printing intensity is also acquired. On the other hand, by setting it to 25 parts by mass or less, the smoothness of the undercoat layer and the ink drying property can be improved, and as a result, the gravure printing suitability can be improved. The content is preferably 10 parts by mass or more. On the other hand, 20 parts by mass or less is preferable.

  As an adhesive other than latex in the undercoat layer, one or more kinds of starches such as polyvinyl alcohol, oxidized starch, cationized starch, esterified starch and dextrin are impaired as a water-soluble adhesive. The content of the water-soluble adhesive at that time is preferably 3 parts by mass or less with respect to 100 parts by mass of the total pigment contained in the undercoat layer, and 0 mass by mass. It is particularly preferable to use parts. By setting the total amount of the water-soluble adhesive in the undercoat layer to 3 parts by mass or less, the cushioning property of the undercoat layer can be improved and the gravure printing suitability can be improved.

  In the present invention, it is preferable to use a styrene-butadiene copolymer latex having a low glass transition temperature for the topcoat layer and a styrene-butadiene copolymer latex having a high glass transition temperature for the undercoat layer. By using a styrene-butadiene copolymer latex with different glass transition temperatures as an adhesive, and having a multilayer structure of an overcoat layer and an undercoat layer, cushioning properties, deformability, smoothness, and coating layer strength are further improved. Can be increased. The difference in glass transition temperature between the low glass transition temperature styrene-butadiene copolymer latex and the high glass transition temperature styrene-butadiene copolymer latex is preferably in the range of 5 to 50 ° C, and 10 to 50 ° C. The range of 20-50 degreeC is more preferable.

  The coating layer in the present invention can be formed, for example, by coating and drying using a coating liquid containing water as a dispersion medium. For example, the overcoat layer can be formed on the undercoat layer using a coating solution for an overcoat layer containing a specific latex, heavy calcium carbonate, light calcium carbonate, kaolin, and other adhesives as required. The undercoat layer can be formed on the base paper using an undercoat layer coating solution containing a pigment and an adhesive. In the coating liquid, if necessary, pH adjusters such as dispersants, caustic soda, ammonia water, antifoaming agents, preservatives, fluorescent dyes, mold release agents, dyes, water resistance agents, flow modifiers, color pigments, etc. Can be contained as appropriate.

  The topcoat layer coating solution and the undercoat layer coating solution are not particularly limited, and can be applied by a coating method using a coating apparatus generally used for producing coated paper. Examples of the coating apparatus include blade coaters, rod coaters, air knives, roll coaters, reverse roll coaters, bar coaters, curtain coaters, die slot coaters, gravure coaters, champlex coaters, 2 roll size press coaters, and gate roll size presses. Examples thereof include a coater and a film metering size press coater. Moreover, it can coat on the base paper which comprises white paperboard by an on-machine system or an off-machine system irrespective of a coating apparatus.

  As a coating method for forming the undercoat layer, it is possible to form a coating layer having a certain thickness (so-called contour coating) relatively in a form along the unevenness of the surface of the base paper. Therefore, a coating method using a rod coater, an air knife coater, a curtain coater, or the like is preferable because a coating layer having a certain cushioning property can be easily obtained and high-concentration coating and high-speed coating are possible. Among these, it is preferable to form by a coating method using a rod coater from the viewpoint of obtaining a relatively high smooth coating surface.

  Furthermore, it is preferable that the coating liquid for undercoat layers contains polycarboxylic acid sodium salt as a dispersing agent. Thereby, the coating liquid before coating can suppress thickening with time and can stably adjust the B-type viscosity within a preferable range. Although it does not specifically limit as content of a dispersing agent, The range of 0.01-0.3 part is preferable with respect to 100 mass parts of all the pigments.

  As the coating method of the topcoat layer, it is possible to form a coating layer having a relatively high smooth coating surface (so-called flat coating), which makes it easy to obtain high gravure printability and high Concentration coating, high-speed coating with a blade coater, or air knife coating system with excellent blank surface feel, no equipment wear, etc. when coating and weighing, and stable operation for a long time It is preferable to form any of these.

The solid content concentration of the undercoat layer coating solution and the overcoat layer coating solution in the present invention can be selected in the range of 10 to 75%. Regarding the coating amount of each coating layer, it is preferable to appropriately adjust the solid content concentration according to the coating method so that the dry weight per side is in the range of 0.5 to 20 g / m ² , and further undercoat The coating amount of the layer is 5 to 15 g / m ² as the dry weight per side, the coating amount of the top coat layer is 3 to 15 g / m ² as the dry weight per side, and the coating of the undercoat layer and the top coat layer It is more preferable to adjust the total amount to be in the range of 8 to 25 g / m ² as a dry weight per side.

By setting the coating amount of the undercoat layer to 5 g / m ² or more as the dry weight per side, the surface of the base paper can be sufficiently covered, and the desired smoothness in the present invention can be obtained, which is preferable. On the other hand, by setting it to 15 g / m ² or less, there is no possibility of causing a crack in the coating layer when a box is put in a ruled line during box making. In addition, with respect to the overcoat layer, by setting the dry weight per side to 3 g / m ² or more, the surface of the undercoat layer can be sufficiently covered, and there is no risk of causing ink transfer failure, and offset printing and gravure printing. Both can improve printability. On the other hand, by setting it to 15 g / m ² or less, similarly to the case of the undercoat layer, there is no possibility of causing a crack in the coating layer when forming a box with a ruled line during box making.

  In the present invention, coating is preferably performed using an undercoat layer coating solution having a solid content concentration of 50 to 70% and a B-type viscosity of 400 mPa · s or less. More preferably, it is 300 mPa · s or less. Thereby, the coating suitability by a rod coater can be improved. The coating solution for the undercoat layer in the present invention is not particularly limited, but preferably contains a specific calcium carbonate and latex, so that the solid content of the coating solution usually tends to increase due to selective absorption as the coating progresses. Concentration and viscosity can be stably maintained within the above ranges, and the operability is remarkably improved and more excellent effects are obtained by gravure printing suitability.

  In the present invention, a pigment coating layer is provided on the surface (back surface) opposite to the surface of the base paper coated with the undercoat layer and the topcoat layer for the purpose of improving printability, offset printing workability, and punching workability. Also good.

The white paperboard base paper in the present invention is made by combining two or more paper layers. That is, the base paper has a multilayer structure including at least a surface layer having a relatively high whiteness and a back layer having a relatively low whiteness. However, since the rice paper weight of white paperboard is often 200 g / m ² or more, a structure of three or more layers in which an intermediate layer is present between the surface layer and the back layer is usually used. It is composed of 4 layers or more of middle layer (1 layer or more) / back layer. However, the layer structure of the base paper is not limited to these. The overcoat layer and undercoat layer in the present invention are provided with the surface layer side as the surface.

  For the surface layer, pulp with high whiteness is usually used. For example, bleached chemical pulp obtained by kraft pulping, sulphite pulping, alkali pulping of conifers or hardwoods, or cotton pulp, linter pulp, waste paper pulp, and the like. Examples of the used paper pulp include pulp prepared from used paper such as upper white / card, extra white / middle white / white Manila, imitation / color, newspaper, magazine, cutting / medium anti-old, etc. It is not limited as used paper. These waste papers may be used as they are after the disaggregation and dust removal treatments, but can be used as waste paper pulp after passing through the steps of deinking, bleaching, ink dispersion, washing, etc., if necessary.

  The base paper has a front and lower layer as necessary. The pulp used for the above-mentioned surface layer is used for the surface layer, unbleached chemical pulp obtained by kraft pulping, sulfite pulping, alkali pulping, etc., or GP (ground pulp). Mechanical pulp such as TMP (thermomechanical pulp) and waste paper pulp can be used. As the used paper pulp, pulp prepared from tea imitation, corrugated cardboard, backing paper / sheet certificate, balls, etc. can be used in addition to the used paper used for the surface layer. Usually, however, used paper that is lower in quality than the surface layer, that is, used paper containing a large amount of medium fiber is used. For example, deinked waste paper such as newspapers, magazines, white / middle white, and balls is generally used, but the present invention is not limited to using these.

  The base paper has a middle layer as required. Although all the pulp that can be used for the front layer, front surface lower layer, and back layer can be used for the middle layer, since the middle layer is a layer that is sandwiched at least between the front layer and the back layer, it is usually a base paper of white paperboard In general, the lowest pulp is used among the paper layers constituting the sheet. For example, a newspaper, a magazine, a ticket, a medium quality antiquity, tea imitation, cardboard, a mount, a ground ticket, a ball, etc. are mentioned. These waste papers are generally used as they are after disaggregation and dust removal treatment, but may be used after passing through each process such as deinking, bleaching, ink dispersion, and washing, as necessary. However, the present invention is not limited to those using these raw materials.

  For the back layer, it is possible to use all the pulp used for the surface layer, front surface lower layer, middle layer, but usually newspapers, magazines, tickets, medium-sized antiko, tea imitation, corrugated cardboard, mount, land ticket, Waste paper such as balls is used as it is after disaggregation and dust removal treatment. Of course, after the disaggregation and dust removal treatment, steps such as deinking, bleaching, and ink dispersion can be arbitrarily added as necessary, but the present invention is limited to those using these treatments. It is not something.

  In the pulp slurry composition used for each layer from the surface layer to the back layer, a paper strength enhancer, a water resistance agent, a water repellent, a foamable microcapsule, a sizing agent, a dye, Yield improver, filler, pH adjuster, slime control agent, thickener, preservative, antifungal agent, antibacterial agent, flame retardant, antiseptic, rodenticide, insect repellent, moisturizer, freshness retainer, oxygen scavenger , Microcapsules, foaming agents, surfactants, electromagnetic shielding materials, antistatic agents, rust inhibitors, fragrances, deodorants and the like can be selected and blended. These can be used in combination.

  The base paper used for the white paperboard of the present invention can of course be obtained by hand-drawing, but is usually made by a multi-stage paper machine equipped with at least two wire parts. As a single wire type, there are a circular net type, a long net type, an inclined type, a twin wire type, and the like, and a wire part in which methods generally used for papermaking are combined in multiple stages is usually used. For example, there are a long mesh patterning, a short mesh patterning, a short mesh pattern combination, a long mesh pattern combination, and the like. Also, as a drying method, a method generally used for papermaking, for example, a Yankee dryer, a multi-cylinder dryer, etc., is used, but a multi-cylinder dryer is more preferable in view of the fact that white paperboard is generally thick. .

  In the present invention, before forming the undercoat layer, after forming the undercoat layer, or after completing the formation of the overcoat layer, smoothing is performed using a machine calendar, a soft calendar, a super calendar, or the like. Can be applied. From the viewpoint of improving smoothness, it is preferable after the overcoat layer is formed. As described above, the smoothness of the coated white paperboard is improved by applying the smoothing treatment to the coated whiteboard paper after coating, thereby improving the gravure printing suitability.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “part” and “%” in the examples indicate “part by mass” and “% by mass”, respectively.

(Average pigment particle size)
A pigment dilution solution having a solid content concentration of about 10% was prepared, and the pigment particle size distribution was measured by a light scattering method using Microtrack HRAX-100 manufactured by Nikkiso Co., Ltd. From the obtained pigment particle size distribution, the particle size distribution curve The particle diameter corresponding to 50 cumulative mass% was taken as the average particle diameter.

(Latex particle size)
The Brownian motion of copolymer latex (emulsion particles) in water of each copolymer latex is observed by dynamic laser light scattering method, and the temporal fluctuation of the scattered light intensity (fluctuation of the number of photons in the scattered light) is accurately measured. We analyzed by the photon correlation method to obtain the diffusion coefficient by grasping with various time scales. The unit of average particle diameter was “nm”.

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

Example 1 (Reference Comparative Example)
(Preparation of base paper)
Imitation / colored waste paper pulp containing Kent waste paper on the surface layer of the first layer which is the surface of the base paper, deinked waste paper pulp on the bottom layer of the second layer, middle layer of the third layer, middle layer of the fourth layer, In addition, the back layer of the fifth layer which is the back surface is made of undeinked waste paper pulp, made into 5 layers, machine calendered, and a base for coated white paperboard with a weight of 290 g / m ² I got paper.

(Preparation of coating solution for undercoat layer)
As pigments, 40 parts of kaolin A (trade name: HT-GAS, manufactured by BASF, average particle size 3.12 μm) and heavy calcium carbonate A (trade name: Carbital 60, manufactured by Imeris Co., Ltd., average particle size of 1.77 μm) ) 60 parts were used, and 0.25 parts of sodium polyacrylate was added as a dispersant to 100 parts of the pigment, and a pigment dispersion having a solid content of 70% was prepared using a Coreless disperser. Next, 4 parts of oxidized starch (trade name: Oji Ace Y, manufactured by Oji Cornstarch Co., Ltd.), styrene-butadiene copolymer latex A (trade name: product name: as solid content conversion with respect to 100 parts of pigment with respect to this pigment dispersion. 10 parts of PB4460 (manufactured by JSR Corporation, glass transition temperature -5 ° C., average particle diameter 165 nm) were added to finally obtain a coating solution for an undercoat layer having a solid content concentration of 62%.

(Preparation of coating solution for topcoat layer)
As pigments, kaolin B (trade name: Kaofine, manufactured by Thiele, average particle size 0.5 μm), 30 parts, heavy calcium carbonate B (trade name: Carbital 90, manufactured by Imeris, average particle size 1.11 μm) 65 Part and 5 parts of titanium dioxide (trade name: KA-100, manufactured by Korea Cosmo Chemical Co., Ltd.), 0.1% of sodium polyacrylate is added to the pigment 100 as a dispersant, and a coreless disperser is used. Thus, a pigment dispersion having a solid content of 68% was prepared. Next, for this pigment dispersion, 2 parts of oxidized starch (trade name: Ace Y, supra) and styrene-butadiene copolymer latex B (trade name: T2548A; 10 parts (manufactured by JSR Corporation, glass transition temperature -34 ° C., average particle diameter 140 nm) were added, respectively, to finally obtain a coating solution for an overcoat layer having a solid content concentration of 60%.

(Preparation of coated white paperboard)
On the surface of the base paper for the coated white paperboard obtained by the preparation of the base paper, the undercoat layer coating solution is applied to a dry weight of 10 g / m ² per side using a rod coater. And dried to form an undercoat layer. On the undercoat layer, a topcoat layer was formed by coating and drying the above-mentioned overcoat layer coating solution using a blade coater so that the dry weight per side was 10 g / m ² . The base paper on which the undercoat layer and the overcoat layer were formed was subjected to a paper feeding process using a soft calender with a metal roll surface temperature of 200 ° C. and 2 nips to obtain a coated white paperboard.

Example 2 (Reference Comparative Example)
In the preparation of the coating solution for the topcoat layer of Example 1, heavy calcium carbonate C (trade name: Carbital 97, manufactured by Imeris Co., Ltd., average particle size 0.87 μm) was used instead of heavy calcium carbonate B. In the same manner as in Example 1, a coated white paperboard was obtained.

Example 3 (Reference Comparative Example)
In the preparation of the coating solution for the overcoat layer of Example 2, instead of the styrene-butadiene copolymer latex B, a styrene-butadiene copolymer latex C (trade name: S2831 (J) -3, manufactured by JSR Corporation, A coated white paperboard was obtained in the same manner as in Example 2 except that the glass transition temperature was −25 ° C. and the average particle size was 120 nm.

Example 4
In the preparation of the coating liquid for the overcoat layer of Example 2, instead of the styrene-butadiene copolymer latex B, a styrene-butadiene copolymer latex D (trade name: S2831 (J) -4, manufactured by JSR Corporation, Coated white paperboard was obtained in the same manner as in Example 2 except that the glass transition temperature was -39 ° C and the average particle size was 90 nm.

Example 5
In the preparation of the coating solution for the overcoat layer of Example 4, a coated white paperboard was obtained in the same manner as in Example 4 except that the amount of the styrene-butadiene copolymer latex D was changed to 20 parts instead of 10 parts. It was.

Example 6 (Reference Comparative Example)
In the preparation of the coating solution for the overcoat layer of Example 2, instead of the styrene-butadiene copolymer latex B, a styrene-butadiene copolymer latex E (trade name: OJ3000H, manufactured by JSR, glass transition temperature-30) Coated white paperboard was obtained in the same manner as in Example 2 except that the average particle diameter was 80 ° C.).

Comparative Example 1
In the preparation of the coating solution for the overcoat layer of Example 4, a coated white paperboard was obtained in the same manner as in Example 4 except that the amount of the styrene-butadiene copolymer latex D was changed to 8 parts instead of 10 parts. It was.

Comparative Example 2
In the preparation of the coating solution for the overcoat layer of Example 2, in place of the styrene-butadiene copolymer latex B, a styrene-butadiene copolymer latex F (trade name: PB9317, manufactured by A & L, glass transition temperature -44). Coated white paperboard was obtained in the same manner as in Example 2 except that the average particle diameter was 160 ° C.

Comparative Example 3
In the preparation of the coating liquid for the overcoat layer of Example 2, in place of the styrene-butadiene copolymer latex B, a styrene-butadiene copolymer latex G (trade name: BA025, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature) A coated white paperboard was obtained in the same manner as in Example 2 except that 12 ° C. and an average particle diameter of 95 nm were used.

Comparative Example 4
In the preparation of the coating solution for the overcoat layer of Example 2, in place of the styrene-butadiene copolymer latex B, a styrene-butadiene copolymer latex H (trade name: PB0414, manufactured by A & L, glass transition temperature 4 ° C. The coated white paperboard was obtained in the same manner as in Example 2 except that the average particle diameter was 70 nm.

  The coated white paper board thus obtained is conditioned for 6 hours under the conditions in accordance with JIS P8111, then the white paper quality is white paper glossiness and smoothness, the offset printability is print glossiness, the gravure printability is missing dots, and post-processing The following evaluation was performed about UV varnish glossiness and stickiness as suitability (varnish suitability). The results were as shown in Table 1.

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

(Print / surf surface roughness)
The print / surf surface roughness of the coated surface of the coated white paperboard is PPS smooth using a PPS smoothness meter (model 165, manufactured by L & W) using a soft backing and pressurizing to 2 MPa. Measured as degrees.

(Offset printing suitability: printing glossiness)
Using 0.6 cc of printing ink (trade name: FUSION-G black, S type, manufactured by Dainippon Ink & Chemicals, Inc.) on the coated surface of the coated white paperboard using an RI printing machine (Meiji Seisakusho) Printing was performed, and the 60 degree glossiness was measured using a gloss meter (GM-26D, manufactured by Murakami Color Research Laboratory).

(Applicability to gravure printing: missing dots)
Gravure printing is performed on the coated surface of coated white paperboard using a printing bureau type gravure printing tester, and the degree of missing dots (halftone dot missing) at 50% gradation halftone dot is visually observed. It was evaluated with. The fewer missing dots, the better.
○: There are almost no missing dots.
Δ: About ten or more missing dots are recognized, but there is no practical problem.
X: Many missing dots exceeding 20 are recognized, which is a practical problem.

(UV varnish gloss)
After adjusting the UV curable varnish (trade name: Dicure Clear UV1603, manufactured by DIC Graphics) to 10 seconds with Zahn Cup # 4, the coating device with UV curing device (model: SG610UV, manufactured by Duplo) The UV curable varnish was applied to the coated surface of the coated white paperboard and UV cured and dried to perform varnish surface processing. The varnished portion of the obtained coated white paperboard was measured for glossiness using a gloss meter (GM-26D, manufactured by Murakami Color Research Laboratory) with an incident angle of 60 degrees.

(Sticky)
The degree of stickiness of the calender roll in the finishing calender process after coating of the coated white paperboard (roll sticking sound during operation, dirt on the calender surface and coated surface) was evaluated.
◯: There is no roll sticking sound and no calendar surface contamination occurs.
(Triangle | delta): There is almost no tendency for roll sticking, and there is almost no calendar surface dirt.
X: Due to roll adhesion, dirt is generated on the calendar surface and dirt is also generated on the coated surface.

Claims (5)

In coated white paperboard provided with a coating layer containing a pigment and an adhesive on the surface of the base paper, the coating layer has an undercoat layer on the side close to the base paper, and an overcoat layer on the side far from the base paper 100 parts by mass of a pigment having a multilayer structure of at least two layers, wherein a styrene-butadiene copolymer latex is used as an adhesive in the topcoat layer, and the content of the styrene-butadiene copolymer latex is contained in the topcoat layer The solid content is 9 to 25 parts by mass, the average particle size of the styrene-butadiene copolymer latex is 85 to 110 nm, and the glass transition temperature is −50 to −20 ° C. Coated white paperboard. The coated white paperboard of Claim 1 which contains 50 mass% or more of heavy calcium carbonate whose average particle diameter is 0.5-1.2 micrometers as a pigment of the said topcoat layer of the pigment of a topcoat layer. The coated white paperboard of Claim 1 or 2 containing the kaolin whose average particle diameter is 1.2 micrometers or less as a pigment of the said topcoat layer. The coated white paperboard according to any one of claims 1 to 3 , wherein the undercoat layer is a coating layer closest to the base paper, and the topcoat layer is a coating layer furthest from the base paper. A method for producing a coated white paperboard comprising a step of forming a coating layer containing a pigment and an adhesive on the surface of a base paper,
  The coating layer has an undercoat layer on the side close to the base paper, and a multi-layer structure of at least two layers having an overcoat layer on the side far from the base paper, and a styrene-butadiene copolymer latex is bonded to the overcoat layer The content of the styrene-butadiene copolymer latex is 9 to 25 parts by mass with respect to 100 parts by mass of the pigment contained in the overcoat layer, and is an average of the styrene-butadiene copolymer latex. The particle diameter is 85 to 110 nm, and the glass transition temperature is −50 to −20 ° C.,
  The undercoat layer is formed by a coating method using a rod coater, and the overcoat layer is formed by either a coating method using a blade coater or a coating method using an air knife coater. A method for producing white paperboard.