JP5483313B2 - Multilayer paperboard - Google Patents

Description

  The present invention relates to a multilayer paperboard having printability and used as a container box for corrugated cardboard cases and paper containers. More specifically, the present invention has a resistance to crease cracking required for corrugated cardboard sheets and high printing gloss. The present invention relates to a multilayer paperboard which has no ink omission and has stamp printing suitability suitable for both water-based and oil-based inks when used in a cardboard case for fruits and vegetables.

  Conventionally, in multilayer paperboards used for printing applications, acrylic resin and styrene resin, which are difficult to dissolve in ink solvent, are coated on the surface to increase printing gloss, so that ink does not easily penetrate into the paper layer. Things are known. Also known is a coated paper in which a coating layer comprising an inorganic pigment such as clay and a binder is formed on the surface of the base paper.

  Further, for example, Patent Document 1 discloses an offset gravure printing in which an overcoating layer composed of an inorganic pigment containing calcined kaolin, a binder pigment, and a binder resin is provided on an undercoating layer composed of calcium carbonate and a binder resin. A shared white paperboard is disclosed.

  However, the white paperboard described in Patent Document 1 has not fully satisfied gravure printability. In addition, it is used for cosmetic boxes and soap boxes as usage, and it is not used by pasting the core, outer layer, surface layer and multiple papers like cardboard, so when folding the finished sheet, There is a problem that the surface coat layer is cracked. Furthermore, when the white paperboard described in Patent Document 1 is used in a cardboard case for fruits and vegetables that is subjected to stamp printing such as the date of harvest, inspection of the person in charge of harvesting, etc., the stamp printing used for fruits and vegetables is naturally dried. Therefore, the drying speed of the ink and the ink absorbability are poor, the printing surface is easily smudged by rubbing, and there is a problem of soiling the printed matter.

  Further, for example, in Patent Document 2, wet strength, surface processing / printing characteristics are improved by adding a predetermined amount of a sizing agent having a zeta potential within a predetermined range, such as an alkyl ketene dimer, to the coating layer. A white board for printing has been disclosed in which dot loss is prevented and water resistance is improved during offset printing. However, the white paper for printing described in Patent Document 2 is sufficiently dried after printing in a printing method having a forced drying device, so that the print finish is good, but still naturally dried. In the stamp printing used for the fruits and vegetables which is a method, there has been a problem that the printed surface is stained due to rubbing.

Further, for example, in Patent Document 3, a predetermined amount of each of calcined clay, structured kaolin and / or delaminated clay, and organic pigment is blended on the surface of the base paper, and these components are combined as a whole. A coating liner having a coating layer formed by applying 3 to 12 g / m ^{2 of a} coating solution composed of a pigment containing at least wt% and latex is disclosed. Further, for example, Patent Document 4 has a two-layer coating layer containing a pigment and an adhesive as main components, and a predetermined coating solution was applied in an amount of 8 to 25 g / m ² (two layers in total). An offset gravure-printed coated white board is disclosed.

  However, the coated liner or coated white paperboard described in the cited references 3 and 4 is a gravure printing by examining the formulation of the coating liquid, preventing missing dots and improving the blank paper and printing gloss. Since the suitability has been improved, it does not have the suitability for stamp printing used for the fruits and vegetables that are naturally dried, and the problem of smearing of the printed surface due to rubbing cannot be solved. Further, the inventions described in the cited documents 3 and 4 have a problem that ruled cracks are likely to occur when used in corrugated cardboard sheets for fruits and vegetables because the amount of coating liquid is large.

  For example, Patent Document 5 discloses a printing paper board provided with a coating layer made of an acrylic resin or a styrene resin, an organic pigment, and a latex for improving printing gloss and ink adhesion. However, since the acrylic resin is easily dissolved in the ink solvent, the coating layer easily absorbs the ink. For this reason, although the adhesiveness of the ink is improved, there is a problem that it causes a reduction in printing gloss, there is no suitability for stamp printing for fruits and vegetables, and there is no suitability for ruled cracking as corrugated cardboard.

  Furthermore, in order to secure printing gloss, paperboard with a styrene resin coated on the paper surface is known. However, when printing gloss is improved, the ink does not penetrate the paper layer, making it difficult to melt and bond the ink required for ink adhesion. There is a problem of becoming. Although bonding by hydrogen bonding can be considered instead of melt bonding, there is a problem in that since the coating liquid has no hydroxyl group, hydrogen bonding hardly occurs, and the ink adhesion is insufficient and the stamp printing is easily peeled off. In particular, in an ink using a nitrified cotton resin, the adhesive force of the ink is remarkably deteriorated.

  Further, a coated paper in which a coating layer is formed by applying a coating liquid containing an inorganic pigment has been proposed, but such a coating layer has a problem that it is easily peeled off from the base paper. In this respect, since the paperboard (coated paper) disclosed in Patent Document 1 and Patent Document 2 is also a paperboard having a coating layer containing an inorganic pigment on the base paper, the coating layer is easily peeled off from the base paper. There's a problem.

JP-A-6-65898 JP-A-11-269798 Japanese Patent Application Laid-Open No. 11-279989 JP 2002-363877 A JP 2006-322081 A

  The present invention has been made in view of the above-mentioned circumstances, and the object is to have resistance to crease cracking when used for corrugated cardboard, and there is no ink loss due to lack of inorganic matter or fine fibers. Another object of the present invention is to provide a multi-layer paperboard which has a high printing gloss and is suitable for stamp printing particularly in cardboard for fruits and vegetables.

The above object of the present invention comprises a base paper composed of a plurality of layers and a coating layer coated on at least one side of the base paper, and the coating layer comprises at least an overcoating layer and an undercoating coating. The surface layer of the base paper contains 5-60% by weight of softwood pulp and 2-22% by weight of filler, and the top coat layer is made of styrene- coating a latex butadiene, applying a coating solution containing casein, is formed by performing the casting process further, the undercoat coating layer, a coating solution containing a binder resin particles as a main component formed by engineering, sheet gloss of the surface of the topcoat coating layer was measured in accordance with JIS-P8142 is achieved by providing a multi-layer paper making paperboard, characterized in that 80 to 90%.

The above-described object of the present invention are the topcoat coating layer, as a filler, clay, calcium carbonate 60-50% by weight: wherein the contained to form formed by a proportion of 40 to 50 wt% This is accomplished effectively by providing a multilayer paperboard.

  The above-mentioned object of the present invention is achieved more effectively by providing a multilayer paperboard wherein the resin particles are organic resin particles.

  The above-mentioned object of the present invention is achieved more effectively by providing a multilayer paperboard wherein the resin particles have a volume average particle diameter of 150 to 500 nm.

  Furthermore, the object of the present invention is more effective by providing a multi-layer paperboard characterized in that the coating liquid for forming the undercoat coating layer contains an acrylamide resin as a binder. Is achieved.

  According to the multilayer paperboard according to the present invention, the coating layer is formed on at least one side of the base paper composed of a plurality of layers by applying a coating liquid mainly composed of resin particles. It is possible to provide a multilayer paperboard that is suitable for stamp printing having a marking cracking aptitude, such as harvest date and harvester in fruit and vegetable use, at the same time having ruled line breakability and high printing gloss.

It is a manufacturing equipment flow figure of regenerated particles concerning one embodiment of the present invention. It is explanatory drawing of a 2nd combustion furnace (external heat kiln furnace), (a) is a partial cross section front view which shows an internal structure, (b) is the expanded view of the inside.

  Hereinafter, the multilayer paperboard according to the present invention will be described in detail by taking as an example a case where the paper layer of the base paper is composed of two layers, a front surface layer and a back surface layer. The multilayer paperboard according to the present invention is not limited to the following embodiments, and it is needless to say that the configuration can be changed as appropriate without departing from the scope of the claims.

  The multilayer paperboard according to the present invention (hereinafter referred to as “main paperboard”) includes a base paper and a coating layer, and the coating layer is formed on one side of the base paper. A plurality of layers having at least two layers of an undercoat coating layer and an overcoat coating layer formed on the undercoat coating layer are provided.

  The coating liquid for forming the top coat layer (hereinafter referred to as “coating liquid for top coat layer”) contains styrene / butadiene latex (SBR) and casein. Thereby, the glossy surface which is the object of the present invention can be secured, and the combination with the coating liquid for forming the undercoat coating layer described later is also improved. Furthermore, it is more preferable to contain 10 to 30% by mass of styrene / butadiene latex and 9 to 15% by mass of casein because the suitability of the stamp intended by the present invention can be ensured.

  In addition, as a binder for the coating liquid for the topcoat layer, water-soluble polymers such as polyvinyl alcohol (PVA), polyacrylamide (PVA), and starch can be used as long as they contain styrene / butadiene latex (SBR). Resins can also be used.

  The topcoat layer coating solution contains a filler. Examples of the filler include clay, calcium carbonate, titanium, talc, and regenerated particles. Among them, the present inventors have found that the combination of clay and calcium carbonate is more preferable in combination with the undercoat coating layer. When clay and calcium carbonate are used as fillers, the ratio of clay: calcium carbonate is preferably 60-50% by mass: 40-50% by mass. Thereby, the glossy surface targeted by the present invention can be secured more effectively.

Such top coat layer coating solution is applied to the surface of the lower intermediate coating layer, and cast process, to form a topcoat coating layer. Thereby, the glossy surface targeted by the present invention can be secured. Moreover, the coating amount of the coating liquid for top coat layers is 0.5-5.0 g / m < ² >, Preferably it is 1-2 g / m < ² >.

Thus, 10-30 mass% (mass% with respect to 100 mass% of filler) of styrene / butadiene-based latex, 9-15 mass% (mass% with respect to 100 mass% of filler) of casein, clay and calcium carbonate are blended. There 60-50 wt%: the coating liquid for overcoat coating layer containing as a 40 to 50 wt%, was coated on the surface of the undercoat coating layer, by casting process, to obtain high print gloss be able to. As a result, it becomes easy to obtain a main paperboard having high glossiness and suitable for box making and processing for corrugated cardboard. More specifically, the blank paper glossiness of the surface of the top coat layer measured according to JISP8142 can be set to 80 to 90%, and the present paperboard has a high printing glossiness.

  Next, the undercoat coating layer formed on one side (surface layer) of the base paper will be described. In addition, although this undercoat coating layer may be formed only on the single side | surface (surface layer) of a base paper by the use of this paperboard, you may form on both surfaces.

  The coating liquid for forming the undercoat coating layer (hereinafter referred to as “undercoat layer coating liquid”) contains resin particles as the main component. Resin particles have a lower hardness than fillers, elasticity of the particles, and easy deformation of the particles themselves, so that the resistance to ruled cracking of the undercoat coating layer can be improved and gloss is also provided. . Therefore, it is preferable to the filler in that both the printability and the resistance to ruled cracks can be satisfied in a balanced manner. That is, by using resin particles as the main component of the coating solution for the undercoat layer in this way, the flexibility of the entire coating layer including the topcoat coating layer can be secured, and the resistance to bending stress of the surface layer can be ensured. By improving, by significantly reducing the occurrence of cracks in the topcoat layer, by forming the topcoat layer on the undercoat layer using the above-described topcoat layer coating solution, High print gloss can be obtained. In addition, by having resin particles as the main component in this way, the paperboard having the high printing glossiness that is the most effective object of the present invention within the range of the blending amount of the binder and filler specified in the above-mentioned top coat layer. I also found that it can provide.

  Organic resin particles are used as such resin particles, and spherical or hollow plastic pigments (PP) are particularly suitable. That is, the plastic pigment is more flexible than the filler and has a heat-melting property, which makes it possible to more easily obtain a multilayer paperboard having excellent resistance to cracking and high printing gloss. .

  Such resin particles include 5-18% by weight of conjugated diene monomer, 0.25-4% by weight of itaconic acid, 0.25-6% by weight of acrylic acid, and other copolymerizable with these. What is obtained by emulsion copolymerization of a monomer mixture composed of 72 to 94.5% by weight of monomer is used.

  Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, chloroprene, and the like. It is done. Of these, 1,3-butadiene is preferred. These can be used alone or in combination of two or more. Moreover, the usage-amount of a conjugated diene monomer is 5-18 weight% of all the monomers, Preferably it is 8-16 weight%. If this amount is small, the paperboard is inferior in glossiness of white paper, and conversely if it is large, the paperboard is inferior in blocking resistance.

  The amount of itaconic acid used is 0.25 to 4% by weight, preferably 0.5 to 3% by weight of the total monomer. Itaconic acid can also be used as an alkali metal salt or an ammonium salt. If the amount of itaconic acid is small, the mechanical stability of the coating solution for the undercoat layer is inferior. On the other hand, if the amount of itaconic acid is large, the glossiness of the white paper of the main board after the coating solution for the topcoat layer is inferior.

  The amount of acrylic acid used is 0.25 to 6% by weight, preferably 0.5 to 5% by weight of the total monomer. Acrylic acid can also be used as an alkali metal salt or an ammonium salt. When the amount of acrylic acid used is small, the mechanical stability of the coating solution for the undercoat layer is inferior. On the other hand, when the amount is large, the viscosity of the latex of the coating solution for the undercoat layer increases, making it difficult to handle and the overcoat layer. The inferior white paper gloss of the paperboard after the coating liquid is applied.

  Examples of other monomers copolymerizable with conjugated diene monomer, itaconic acid and acrylic acid include, for example, aromatic vinyl monomers, ethylenically unsaturated nitrile monomers, ethylenically unsaturated carboxylic acid ester monomers. And an ethylenically unsaturated carboxylic acid amide monomer excluding itaconic acid and acrylic acid, and a crosslinkable monomer.

  Examples of the aromatic vinyl monomer include styrene, α-methyl styrene, p-methyl styrene, hydroxymethyl styrene and the like, and styrene is particularly preferable.

  Examples of the ethylenically unsaturated nitrile monomer include acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, α-cyanoethylacrylonitrile, and (meth) acrylonitrile is particularly preferable.

  Examples of the ethylenically unsaturated carboxylic acid ester monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and (meth) acrylic acid-2. -Ethylhexyl, trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate, methoxymethyl (meth) acrylate, ethoxyethyl (meth) acrylate, methoxyethoxyethyl (meth) acrylate, (meth) acrylic Ethylenically unsaturated monocarboxylic acid ester monomers such as cyanomethyl acid, 2-cyanoethyl (meth) acrylate, hydroxyethyl acrylate, glycidyl methacrylate; ethylenic acid such as dibutyl maleate, dibutyl fumarate, diethyl maleate Saturated polycarboxylic acid ester Body; and the like. Among these, ethylenically unsaturated monocarboxylic acid ester monomers can be preferably used.

  Examples of the ethylenically unsaturated carboxylic acid amide monomer include (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethylol (meth) acrylamide, and the like.

  Examples of ethylenically unsaturated acid monomers excluding itaconic acid and acrylic acid include unsaturated monocarboxylic acids excluding acrylic acid such as methacrylic acid and crotonic acid; itaconic acids such as fumaric acid, maleic acid and butenetricarboxylic acid Unsaturated polyvalent carboxylic acids except for: ethylenically unsaturated polyvalent carboxylic acids such as monoethyl maleate and monomethyl itaconate; vinyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid, (meth) allyl sulfonic acid , Sulfonic acid group-containing monomers such as (meth) acrylic acid-2-ethyl sulfonate and acrylamide-2-hydroxypropane sulfonic acid; (meth) acrylic acid-3-chloro-2-phosphate propyl, (meth) Acrylic acid-2-ethyl phosphate, 3-allyloxy-2-hydroxypropane phosphorus Phosphoric acid group-containing monomers such as; and the like. These can also be used as an alkali metal salt or an ammonium salt, and these monomers can be used alone or in combination of two or more.

  Examples of the crosslinkable monomer include di (meth) acrylates such as polyethylene glycol di (meth) acrylate and polypropylene glycol di (meth) acrylate; trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate Poly (meth) acrylates such as divinylbenzene and the like.

  These other monomers can be used alone or in combination of two or more. Of these other monomers, aromatic vinyl monomers, ethylenically unsaturated nitrile monomers, ethylenically unsaturated carboxylic acid ester monomers, and ethylenically unsaturated carboxylic acid amide monomers are preferably used. Is done. In addition, the usage-amount of the ethylenically unsaturated acid monomer except for itaconic acid and acrylic acid is preferably 2% by weight or less, more preferably 1% by weight or less, and particularly preferably not used. .

  The usage-amount of another monomer is 72-94.5 weight% of all the monomers, Preferably it is 76-91 weight%. If the amount used is small, the blocking resistance of the board after coating the coating liquid for the topcoat layer is inferior, and conversely if it is large, the glossiness of the blank paper on the board after coating the coating liquid for the topcoat layer is poor. .

  The weight ratio of itaconic acid and acrylic acid is preferably in the range of 1: 1 to 1: 3. If both are used in this range, a coating solution for the undercoat layer excellent in mechanical stability can be obtained, and the viscosity of the coating solution for the undercoat layer can be kept low, so it is also suitable for high-speed coating. it can.

  The volume average particle diameter of the resin particles is 150 to 500 nm, preferably 180 to 320 nm. As a result, the present paperboard is superior in the balance between the white paper gloss and the surface strength. The volume average particle size can be controlled to a desired value by adjusting the amount of emulsifier and polymerization initiator used, or by adjusting the particle size of the seed latex and the amount used. When the volume average particle diameter of the resin particles is less than 150 nm, when the calender treatment is performed after coating the undercoat layer coating solution, the thickness of the undercoat layer becomes too thin, and the cushioning property of the undercoat layer is reduced. As a result, the image becomes dull during gravure printing. On the other hand, when the particle diameter of the resin particles exceeds 500 nm, when the calendar treatment is performed after the coating liquid for the undercoat layer is applied, the undercoat coating layer is difficult to be crushed, so that it may be difficult to obtain surface flatness. For this reason, when the coating liquid for topcoat layers is coated on such an undercoat coating layer, it causes a printing blur at the time of carrying out gravure printing on this board.

  The resin particles preferably have an insoluble content of tetrahydrofuran of 40% by weight or more and 50 to 95% by weight. If the amount of this tetrahydrofuran-insoluble component is small, the reason is not clear, but the blocking resistance of the present paperboard after coating with the topcoat layer coating solution tends to decrease. On the other hand, if the amount is too large, the glossiness of the white paper of the main board after coating the coating liquid for topcoat layer tends to be lowered.

  Furthermore, the glass transition temperature of the resin particles is 30 to 95 ° C, preferably 50 to 80 ° C. When the glass transition temperature is within this range, an undercoat coating layer can be obtained in which the main paperboard after coating the coating solution for the topcoat layer is excellent due to a balance between white paper gloss and blocking resistance.

  In addition to the resin particles described above, the undercoat layer coating liquid preferably contains an acrylamide resin such as Haricoat G50 as a binder. Acrylamide-based resins have an appropriate film-forming property, are flexible, and have good ink deposition properties. Therefore, in this way, when the base paper of the present paperboard has an intermediate layer by containing the acrylamide resin and the resin particles in combination in the undercoat layer coating liquid, the adhesive foreign matter derived from the raw material of the intermediate layer The effect of preventing the protrusion is exhibited, and the effect of preventing ruled cracks is also increased. As the binder, in addition to the acrylamide resin, a styrene resin, an acrylic resin, a latex, a polyvinyl resin such as PVA, a resin such as starch, and the like can be used. This is the best combination.

  In addition, the compounding quantity of this acrylamide-type resin is 6-12 mass% of acrylamide-type resin with respect to 100 mass% of resin particles of the coating liquid for undercoat in conversion of solid content, Preferably it is 8-10 mass%. . When the blending ratio of the acrylamide resin is less than 6% by mass, it is difficult to fix the resin particles to the base paper, and the undercoat coating layer is easily damaged by rubbing. In addition, if the blending ratio of acrylamide exceeds 12% by mass, the undercoat coating layer itself becomes soft and tends to become hard, so the problem of insufficient resistance to bending stress of the undercoat coating layer is likely to occur. As a result, it becomes difficult to satisfy the resistance to ruled cracking of the present paperboard.

Further, the coating amount per side of the coating solution for the undercoat layer mainly composed of such resin particles is 0 in the dry state of the undercoat coating layer (the state of the undercoat coating layer formed on the base paper). 5 to 5.0 g / m ² . As a result, the gap between the pulp fibers in the surface layer of the base paper in contact with the undercoat coating layer can be sealed, and the glossiness of the white paper of the main paperboard and the smoothing of the printing surface can be achieved. In addition, since the thickness of the undercoat coating layer does not become too thick, the ink easily penetrates into the base paper, and the ink adhesion is improved. If the coating amount of the undercoat layer coating solution is less than 0.5 g / m ² , the effect of sealing the pulp fibers on the surface layer of the base paper cannot be exhibited, and it is difficult to obtain high printing gloss. Become. In addition, in the drying process when applying the coating liquid for the topcoat layer, the thermal adhesion between the resin particles in the undercoat layer and the binder component in the topcoat layer becomes insufficient, and the glossiness of the paperboard is reduced. It becomes difficult to obtain a desired value. On the other hand, if the coating amount of the coating solution for the undercoat layer exceeds 5.0 g / m ² , the thickness of the undercoat coating layer becomes too thick and resistance to bending stress of the surface layer of the base paper cannot be obtained. , Tend to be inferior in resistance to ruled cracks.

As described in detail above, resin particles (particularly plastic pigments) having a volume average particle diameter of 150 to 500 nm are the main components, and an acrylamide resin as a binder is 8 to 10 masses with respect to 100 mass% of the resin particles. % Of the coating solution for the undercoat layer applied on one side of the base paper by combining it with the above-described topcoat layer by applying 0.5 to 5.0 g / m ² on one side of the base paper. It is possible to impart ruled line breakability and high printing gloss more effectively.

  Next, the base paper of this paperboard will be described. The base paper of this paperboard is composed of two paper layers, a front surface layer and a back surface layer. The object of the present invention can be achieved as long as it has at least two layers.

  The surface layer in contact with the undercoat coating layer of the base paper of this paperboard contains 5 to 60% by weight, preferably 10 to 50% by weight, of softwood pulp in the raw material pulp. Thereby, the binding of the pulp fibers in the surface layer is strong, and it is possible to satisfy the resistance to ruled cracks necessary for corrugated cardboard applications, and the loss of fine fibers and inorganic substances is prevented. When the blending amount of the softwood pulp is less than 5% by weight, the long fiber pulp is less likely to cause ruled cracks, and it becomes difficult to ensure the resistance to ruled cracks necessary for corrugated cardboard applications. On the other hand, if it exceeds 60% by weight, the amount of long fiber pulp is too large, so that the surface layer cannot be made uniform (cannot be flattened), which causes printing failure.

  Further, a filler may be internally added to the raw material pulp of the surface layer. The blending amount of the filler at that time is 2 to 22% by weight, preferably 6 to 12% by weight. If the blending amount of the filler is less than 2% by weight, the gap between the pulp fibers is not sufficient, leading to a decrease in glossiness of the blank paper. On the other hand, if the blending amount exceeds 22% by weight, the lack of inorganic matter during printing In addition to the occurrence of ink loss and printing failure, the fiber bond is lowered, so that the paper strength is reduced and ruled cracks are likely to occur. Examples of the filler to be internally added include clay, calcium carbonate, talc, and regenerated particles. Among them, the regenerated particles are preferable because the base paper of the present invention can be provided. The regenerated particles will be described later.

  Raw pulp of layers other than the surface layer is not particularly limited, but generally, the main raw material is white balls made from shredded paper, newspapers, magazines, etc., which are generated at the time of paper container manufacturing, Raw material pulp to be used is used. In addition, when the base paper is provided with an intermediate layer to have three or more layers, the intermediate layer raw material pulp is suitably used by appropriately blending the upper white waste paper and the middle white waste paper comprising the white loss of the coated paper. It is done.

  The raw material pulp as described above is a base of the paperboard having two paper layers of a front surface layer and a back surface layer through a known paper making process, for example, a wire part, a press part, a dryer part, a size press, a calendar part, and the like. Paper is formed. In particular, softwood pulp is soft and easily crushed when calendered. Therefore, before applying the coating solution for the primer layer on the surface layer of the base paper (before forming the primer coating layer), In order to coat the coating layer uniformly and smoothly, it is preferable to surface-treat the base paper with a calendar part.

  The papermaking method for the base paper of the present paperboard is not particularly limited, and any of an acidic papermaking method, a neutral papermaking method, and an alkaline papermaking method may be used. Also, since the paper machine is not particularly limited, for example, various known paper machines such as a long net paper machine, a twin wire paper machine, a circular net paper machine, and a short net combination machine can be used. it can.

The basis weight of the base paper is preferably 100 to 500 g / m ² . When the basis weight is less than 100 g / m ² , there is a problem that the compressive strength of the case is low when the multilayer paperboard is used for corrugated cardboard, and when it exceeds 500 g / m ² , the paper thickness increases, When the multi-layer paperboard is bent, the surface stress becomes too strong, and the problem that the surface coating layer of the undercoat coating layer and the base paper is likely to crack.

In addition, when providing the undercoat coating layer on the surface layer of the base paper, adjusting the paper density of the base paper of the main paperboard to 0.48 to 0.98 g / cm ³ , the base paper of the undercoat layer coating liquid can be obtained. It was found that the absorption balance of was the best. Thereby, even if it is the coating amount of the range of 0.5-5.0 g / m < ² > as above-mentioned in undercoat coating liquid, the objective of this application can be achieved.

  Further, it is preferable that the base paper of the present paperboard is pressure-contacted with a mirror-finished drier after the pressing step, and particularly pressure-dried to a large-diameter drier such as a Yankee drier. Furthermore, it becomes more preferable that the wet paper web moisture of the base paper before press contact is 45% to 53%. If it is less than 45%, the absolute amount of moisture present on the surface decreases, only the surface layer becomes overdried, and the unevenness of the base paper surface of the base paper before applying the coating liquid for the undercoat layer increases. It is difficult to solve the problem with the coating amount of the above-described undercoat layer coating solution. On the other hand, if it exceeds 53%, the amount of absolute water distributed on the surface layer increases and the amount of water vapor evaporated from the surface layer increases, so that the contact between the mirror surface and the base paper becomes insufficient, and a good surface layer can be obtained. It becomes difficult.

  In addition, after making the base paper, in the secondary processing, undercoat liquid is applied by an undercoat machine such as a printing machine, bar coater, rod coater, air knife, etc. to form an undercoat coating layer, and this multilayer paperboard is formed. It is also possible.

  In the above-described embodiment, an explanation has been given of a multilayer paperboard in which an undercoat coating layer is provided on one surface of a base paper on a surface layer, and further an overcoat coating layer is provided on the undercoat coating layer. If the back surface layer is made of the same material as the front surface layer, it is also possible to make a multi-layer paperboard having a base coat layer and a top coat layer on both sides of the base paper. In that case, it is preferable to provide an intermediate layer between the front surface layer and the back surface layer. The composition of the undercoat layer coating solution and the topcoat layer coating solution, the coating amount, the basis weight of the base paper, and the paper density are determined when the undercoat coating layer and the topcoat coating layer are provided only on one side of the base paper. It is the same.

  Next, regenerated particles that are fillers that can be internally added to the base paper of the present paperboard will be described. The method for producing regenerated particles used in the present invention is a deinking process of a used paper processing facility for producing used paper pulp, with the deinking floss separated from the pulp fibers as the main material, dehydrating and drying the main material, Recycled particles are obtained through each step of combustion and pulverization, and the drying and combustion step is a first combustion furnace (internal heat kiln furnace) to which the raw material after dehydration is dried and burned in series. And a second combustion furnace after the deinking floss burned in the first combustion furnace is burned again, and has at least two stages of combustion processes, and then pulverized to obtain regenerated particles .

  More specifically, the combustion process is performed in the first combustion furnace at a temperature of 300 to 500 ° C. so that the oxygen concentration in the first combustion furnace (internal heat kiln furnace) is 0.2 to 20%. Furthermore, a 2nd combustion furnace performs a combustion process on the combustion thing from a 1st combustion furnace at the temperature of 550-780 degreeC.

  However, the deinking floss separated from the pulp fiber in the deinking process of the used paper processing equipment for producing the used paper pulp, which is the main raw material of the regenerated particles to be used in the present invention, contains inorganic fine particles and is also used paper. It contains many fine fibers that are difficult to use as pulp, latex that is an organic polymer frequently used in coated paper, and ink components applied by printing. For this reason, in the combustion process of the combustion process, since the deinking floss itself generates a combustion reaction (oxidation) and burns, heat is generated more than the heat treatment with hot air, and there is a problem that causes excessive combustion of the raw material. did.

  Such excessive combustion (1) yellowing of the raw material due to high-temperature combustion causes a decrease in whiteness, (2) hard material such as gehlenite is likely to occur due to melting of the raw material, and the degree of wire wear in papermaking equipment (3) In order to form agglomerates by melting the raw material, the pulverization energy is increased and the processing efficiency is lowered in the subsequent fine pulverization step. Since it is melted first, the combustion reaction (oxidation reaction) does not proceed to the inside of the raw material, and organic matter (carbon) remains, resulting in problems such as a decrease in whiteness.

  Therefore, as a means for solving such problems, paying attention to measures for controlling excessive combustion, and as a result of intensive studies, the combustion process is composed of at least two stages of a first combustion furnace and a second combustion furnace, Combustion temperature (combustible gas) generated by gasification of organic components contained in the deinking floss without burning the main deinking floss as the main raw material. It has been found that the above problem can be solved by keeping only the temperature necessary for the reaction and promoting only the combustion reaction (oxidation reaction) of the organic component gas, leading to the completion of the regenerated particles internally added to the paperboard. It is a thing.

  Moreover, in the 1st combustion furnace, the oxygen concentration 0.2-20% required in order to burn the deinking floss which is a main raw material is ensured. As a result, an in-furnace environment in which combustion is promoted is generated, and thus excessive deinking floss combustion is likely to occur.

  Furthermore, in order to prevent excessive combustion of the deinking floss, it has been found that a measure for increasing the water content of the deinking floss as a main raw material in addition to supplying hot air is effective. More specifically, the deinking floss as the main raw material has a moisture content of 40 to 90%, preferably 40 to 70%, more preferably 45 to 70% after dehydration. It has been found that the supply to the first combustion furnace is suitable for preventing excessive combustion of the deinking floss. That is, by supplying deinking floss as a main raw material into the first combustion furnace in the first combustion process in a high water content state, moisture is evaporated in the first combustion furnace, and thereby the temperature in the first combustion furnace. Decreases. As a result, it is considered that self-combustion of the deinking floss can be suppressed, combustion of only the generated combustion gas (combustible gas) can be promoted, and excessive combustion can be suppressed.

  Furthermore, on the inner wall in the second combustion furnace of the second combustion process, which is a combustion process after the first combustion process, parallel to the spiral lifter and / or the axis center from one end side to the other end side. It is preferable to arrange a parallel lifter, whereby the raw material can be combusted uniformly, and the quality of the regenerated particles can be made uniform.

  That is, as described above, in the first combustion furnace in the first combustion step, the deinking floss as the main raw material is burned at a low combustion temperature of 300 to 500 ° C., and is contained in the raw material from the raw material. It is necessary to burn as much carbon as possible, which causes organic matter to become a combustion gas, burns (oxidizes) this combustion gas to obtain a homogeneous combustion product of the first combustion furnace, and causes a decrease in whiteness. There is. For this reason, it is necessary to burn the raw material slowly, and in order to continuously carry out uniform combustion as much as possible, the most suitable measure is to appropriately control the raw material conveyance speed in the second combustion furnace in the second combustion step. The present inventors have also found that it is possible to adjust the feed speed of the raw material by using a lifter as a means. However, since known lifters are generally manufactured from iron materials, iron content is contained in the raw material as contamination, resulting in a decrease in whiteness due to iron oxidation and a reduction in the quality of regenerated particles. Cause the problem of Therefore, by providing a stainless steel lifter in the second combustion furnace, a technology that can produce high-quality regenerated particles with uniform firing quality, such as no iron oxidation problem and no reduction in whiteness, is found. It was.

  As the structure of the second combustion furnace, either an external heat kiln furnace or an internal heat kiln furnace can be adopted as appropriate. However, in the external heat kiln furnace, the direct flame of the burner is not directly exposed to the raw material, so that the excessive combustion of the raw material can be prevented, the combustion product of the second combustion furnace can have a uniform firing quality, and high whiteness is achieved. There is an advantage that it can be obtained. On the other hand, the internal heat kiln furnace has an advantage that the refractory attached inside has heat insulation and at the same time emits far infrared rays and can be heated with a small amount of heat. Therefore, regarding the structure of the second combustion furnace, either an external heat kiln furnace or an internal heat kiln furnace can be appropriately selected in view of these conditions, but it is optimal to provide a lifter for any of the methods.

  More preferably, an internal heat source is used as the first first combustion furnace, and an external heat source is used as the second second combustion furnace. As these combustion furnaces, various conventionally used furnaces such as a stalker furnace (fixed bed), a fluidized bed furnace, a cyclone furnace, and a kiln furnace can be used. However, as these combustion furnaces have repeatedly studied the production of regenerated particles in the respective combustion furnaces, the following matters have become clear.

  In other words, for the stalker furnace (fixed bed), it is difficult to adjust the degree of combustion of the deinking floss, and the combustion products are not uniform. Not suitable because it occurs. Since air is blown up and burned under the combustion material through the grate, calcium carbonate or the like becomes fly ash and is sent to the exhaust gas facility together with the exhaust gas.

  As for the fluidized bed furnace, since a particulate fluid medium such as silica sand is used as the fluid medium in the furnace, there is a problem that the silica sand is mixed into the regenerated particles and the quality is deteriorated, and the silica sand is used in the present invention. Hardness is higher than regenerated particles, making it difficult to grind uniformly. After the cinnabar sand is mixed in the fluidized bed and burned, the cinnabar sand and the burned material are separated, and the cinnabar sand is returned to the combustion furnace, and only the burned material is taken out. Is difficult. In addition, since the regenerated particles are burned in a state of floating on the cinnabar sand, it is difficult to adjust the degree of combustion, and the quality of the obtained combustion product varies. Furthermore, since the combustion products are burned while passing through a stoker (stepped shape) of the combustion furnace with a predetermined width, the ash is not sufficiently stirred, and variation occurs in combustion in the width direction. Further, since silica sand has a high hardness, there is also a problem that the combustion products are pulverized by friction and collision, and fly ash is discharged out of the system, resulting in a decrease in yield.

  About a cyclone furnace, since a combustion thing passes the inside of a furnace instantly, the fixed carbon in a combustion substance cannot be burned enough, but it leads to the fall of the whiteness of a reproduction | regeneration particle | grain. Furthermore, since the fine particles are not separated by the cyclone and are sent to the exhaust gas treatment process together with the exhaust gas, the yield decreases.

  Therefore, as a result of considering the above problems of each furnace, the combustion furnace used for the production of regenerated particles used in the present invention includes kiln furnace, fluidized bed furnace, stalker furnace, cyclone furnace, semi-dry distillation and negative pressure combustion. Various known combustion furnaces such as a type furnace can be used, but it is particularly preferable to use a kiln furnace. Furthermore, a well-known combustion method such as an indirect heating type combustion furnace using heavy oil or the like as a heat source may be employed as the second external combustion furnace.

  More preferably, a method is used in which the drying step and the combustion step are performed in a series of steps after the raw material has undergone the dehydration step. In this method, as the first combustion furnace of the first combustion step, the combustion time (residence time) is 30 to 90 minutes, preferably 40 to 80 minutes, more preferably 50 to 70 minutes, preferably the main body is placed horizontally. Using an internal heat (direct heating) kiln furnace that rotates around the central axis, the raw material after the dehydration process is dried and the first combustion is performed. Also, as the second combustion furnace of the second combustion process, the combustion time ( Residence time) is 60 minutes or more, preferably 60 to 240 minutes, more preferably 90 to 150 minutes, particularly preferably 120 to 150 minutes, preferably external heat (indirect heating) in which the main body is placed horizontally and rotates around the central axis ) Using a kiln furnace, in particular, an external heat electric furnace whose combustion temperature can be easily adjusted, the combustion product obtained in the first combustion path is burned again.

  As described above, when an internal heat kiln furnace capable of performing drying and combustion in one furnace is used as the first combustion furnace, it is gradually and stably from the supply port to the discharge port of the first combustion furnace. In addition, drying and combustion proceed, and the pulverization of the combustion product can be suppressed. In addition, when an external heat kiln furnace capable of performing drying and combustion in one furnace is used as the second combustion furnace, the combustion product is discharged from the end of the second combustion furnace with a predetermined residence time and discharged at the other end. Since the heat can be discharged from the outlet and the uniform heat is applied to the combustion product by the external heat, the combustion becomes uniform and does not cause variations in combustion. Furthermore, since the combustion product is gently stirred by friction caused by the rotation of the inner wall of the kiln furnace, the pulverization of the combustion product can be further suppressed. As a result, the quality and shape of the final combustion product are stabilized. That is, as described above, the drying process and the combustion process are performed in two stages using at least two combustion furnaces, preferably using an internal heat kiln furnace and an external heat kiln furnace. High regenerated particles can be obtained.

  In addition, since an external heat kiln furnace becomes a structure which provided the heating equipment in the outer side of the kiln furnace, in order to dry and burn a combustion substance indirectly, a lot of heat sources are needed. Therefore, when an external heat kiln furnace is used as the first combustion furnace, the raw material after the dehydration step is in a high water content state as described above, and thus the drying / combustion efficiency is lowered. As a result, the productivity of the regenerated particles is deteriorated and the temperature is difficult to control, so that a large energy cost is required and the effect on the cost becomes extremely low.

  Further, when an internal heat kiln furnace is used as the second combustion furnace, the combustion heat is transferred to the internal heat kiln furnace unless a large amount of dilution air is introduced in the combustion of the remaining carbon of the combustion product obtained in the first combustion furnace. It is difficult to convey uniformly inside the furnace, and it is difficult to adjust the temperature in the furnace. The problem occurs. Furthermore, a heavy oil burner is usually used for heating the internal heat kiln furnace, but particles with low whiteness such as heavy oil combustion residual carbon and sulfur oxide are generated, resulting in a decrease in whiteness and variations in the resulting regenerated particles. And it becomes difficult to obtain uniform quality.

  Furthermore, the internal heat kiln furnace or the external heat kiln furnace used as the preferred first combustion furnace and the second combustion furnace is a hexagonal or octagonal internal refractory instead of a circumferential shape. Can be lifted and stirred without slipping. However, in reality, since the kiln furnace is cylindrical, it is optimal to provide a lifter for stirring the combusted material because the raw material can be uniformly burned and the quality can be made uniform. This is also considered to be related to intentionally burning the entire raw material at a low temperature of 300 to 500 ° C. in the first combustion furnace.

Next, an example of a method for producing regenerated particles used for the present paperboard will be described with reference to the drawings.
〔Overview〕
FIG. 1 is a manufacturing equipment flow diagram according to an embodiment of recycled particles internally added to the base paper of the present paperboard. As will be described below, the production process of the regenerated particles includes a dehydration process, a drying / combustion process, and a pulverization process. In addition to this, the deinking floss aggregation process or granulation process, and each process A classification step or the like may be provided between them. This equipment is equipped with various sensors, and controls the state of the combustibles and equipment, the processing speed, and the like.

  The deinking floss separated from the pulp fiber in the deinking process for producing the waste paper pulp not shown is subjected to various operations, and the moisture content is 40 to 90%, preferably 45 to 70 by a known dehydration equipment not shown. %, More preferably 50 to 60% high water content. Furthermore, it is desirable that the raw material 10 after such dehydration is pulverized by a pulverizer (or pulverizer) (not shown) so as to have a particle diameter of 40 mm or less.

  The raw material 10 is cut out from the storage tank 12, and is charged from the first combustion furnace 14 from one side of the first combustion furnace 14 which is an internal heat kiln furnace in which the main body is placed horizontally and rotates around the central axis by the charging machine 15. Is charged. Further, an exhaust gas chamber 16 is provided on one side of the first combustion furnace 14, and an exhaust chamber 18 is provided on the other side. The hot air passes through the discharge chamber 18, is blown from the other side of the first combustion furnace 14, is charged from the one side, and is sequentially transferred to the other side as the first combustion furnace 14 rotates. Drying and burning are performed.

  Here, it is desirable that the hot air blown into the first combustion furnace 14 has an oxygen concentration of 0.2 to 20%. The furnace temperature is 300 to 500 ° C, preferably 400 to 500 ° C, more preferably 400 to 450 ° C. Hot air is blown from a hot air generating furnace 20 provided with a burner 20A.

  From the exhaust gas chamber 16, exhaust gas subjected to drying and combustion is sent into the recombustion chamber 22. The fine powder of the combustion material contained in the exhaust gas is discharged from the lower part of the exhaust gas chamber 16 and reused. The exhaust gas is recombusted by the burner in the recombustion chamber 22, precooled by the precooler 24, passed through the heat exchanger 26, and discharged from the chimney 30 by the induction fan 28. Here, after raising the temperature of the outside air, the heat exchanger 26 is sent to the hot air generating furnace 20 and used for the hot air blown from the first combustion furnace 14 to recover the heat of the exhaust gas from the exhaust gas chamber 16. It is like that. The treatment of exhaust gas is effective for removing harmful substances contained in the exhaust gas.

  Combustion products that have undergone drying and combustion treatment in the first combustion furnace 14 are charged into a second combustion furnace 32 that is an external heat kiln furnace in which the main body is placed horizontally and rotates around the central axis. The particle size of the combusted material to be charged is preferably 40 mm or less. As a heat source in the second combustion furnace 32, it is preferable to use an electric adjustment that allows easy temperature control in the second combustion furnace 32 and easy temperature control in the longitudinal direction. Therefore, it is desirable to be an external heating type combustion furnace in which the combustion product obtained from the first combustion furnace 14 indirectly is burned again by an electric heater.

  In the second combustion furnace 32, the oxygen concentration is 5 to 20%, preferably 10 to 20%, more preferably 10 to 15% by an air or oxygen supply mechanism (not shown) for adjusting the oxygen concentration. To burn. As temperature, it is 550-780 degreeC, Preferably it is 600-750 degreeC. The residence time in the second combustion furnace 32 is 60 minutes or longer, preferably 60 to 240 minutes, more preferably 90 to 150 minutes, and particularly preferably 120 to 150 minutes, in order to completely burn the remaining carbon. .

  The combusted material that has been burned is cooled by a cooler 34, and then sorted by a particle size sorter 36 such as a vibration sieve, and adjusted to a target particle size in a grinding process using a wet grinding machine or the like. The burned product is temporarily stored in the combusted product silo 38 and is sent to the application destination of the pigment and filler.

  In addition, although the case where deinking floss was used as a raw material was illustrated, the combustion material which used as a raw material what mixed papermaking sludges, such as papermaking sludge in a papermaking process, with deinking floss as a main raw material may be sufficient. .

As mentioned above, although the outline | summary of the manufacturing process of regenerated particle was demonstrated, the detail and an application example are demonstrated below.
〔material〕
In the used paper pulp manufacturing process, in order to continuously produce used paper pulp of stable quality, used paper is selected and selected, and used paper of a certain quality is used. For this reason, the types, ratios, and amounts of inorganic substances brought into the used paper pulp manufacturing process are basically constant. Moreover, even when plastics such as vinyl and film, which cause fluctuations in unburned materials in the method for producing regenerated particles, are contained in the waste paper, these foreign matters are not before the deinking process to obtain deinking floss. Can be removed in stages. Accordingly, the deinking floss is a raw material for producing regenerated particles having extremely stable quality as compared with paper sludge generated in other processes such as a factory drainage process and a papermaking raw material preparation process.

  The deinking floss referred to in the present specification refers to what is separated from the pulp fiber in the deinking process for removing ink adhering to the used paper in the used paper processing process for producing the used paper pulp.

[Dehydration process]
For further dehydration of the deinking floss, known dehydration means can be used as appropriate. In one example of this embodiment, the deinking floss is dehydrated by separating water from the deinking floss by a dehydrating means such as a screen. In the screen, it is preferable that the deinking floss dehydrated to 90 to 97% is sent to, for example, a screw press and further dehydrated to a predetermined moisture.

  If the moisture content of the raw material 10 after dehydration exceeds 70%, the temperature of the drying / combustion treatment in the first combustion furnace 14 will be lowered, the energy loss for heating will be great, and the non-uniform combustion of the raw material 10 will occur. It becomes easy and it becomes difficult to advance uniform combustion. Further, there are problems that the moisture in the exhaust gas to be discharged increases, the recombustion treatment efficiency is reduced in dioxin countermeasures, and the load on the exhaust gas treatment facility is increased. Moreover, when the moisture content of the raw material 10 after dehydration is as low as less than 40%, it causes excessive combustion of the deinking floss.

  As has been clarified in the above description, if dewatering of the deinking floss is performed in a multi-stage process and abrupt dewatering is avoided, the outflow of inorganic substances can be suppressed and there is no possibility that the deinking floss flock becomes too hard. In the dehydration treatment, an auxiliary agent for improving the dehydration efficiency such as an aggregating agent for aggregating the deinking floss may be added, but it is preferable to use an aggregating agent that does not contain iron. When iron is contained, it causes a problem of lowering the whiteness of the regenerated particles due to oxidation of iron.

  The deinking process of deinking floss is preferably adjacent to the manufacturing process of regenerated particles used for the paperboard in terms of production efficiency. It can also be transported, and it is transported to a fixed amount feeder by a transport means such as a truck or a belt conveyor, and supplied to the drying / combustion process from this constant amount feeder.

  In the operation of supplying the raw material 10 after dehydration to the first combustion furnace 14, the average particle diameter is reduced to 40 mm or less, preferably 3 to 30 mm, more preferably 5 to 20 mm by a pulverizer (or pulverizer). To be adjusted. Furthermore, it is more preferable to grind so that the ratio of an average particle diameter of 50 mm or less may be 70% by weight or more. In order to achieve a combustion treatment that does not cause a heat change of the calcium carbonate contained in the deinking floss, it is preferable that the average particle diameter of the raw material is uniform. However, if the average particle diameter is less than 3 mm, overcombustion tends to occur. This is because if it exceeds 40 mm, there is a problem that it is difficult to uniformly burn the raw material core.

  The ratio between the average particle size and the particle size was measured using a sample solution sufficiently dispersed by a stirring type disperser. The particle diameter in each combustion process was measured with a metal plate sieve based on JIS Z8801-2: 2000.

[First combustion process] (Drying and combustion process)
The raw material 10 is cut out from the storage tank 12 and supplied to the first combustion furnace. The first combustion furnace has an internal heat kiln furnace system in which a main body is placed horizontally and rotates around a central axis, and is charged from one side of the internal heat kiln furnace 14 by a charging machine 15. The internal heat kiln furnace heating means feeds hot air generated in the hot air generation furnace from the discharge port side of the internal heat kiln furnace 14 so as to counter-flow with the flow of the dehydrated product. An exhaust gas chamber 16 is provided on one side of the internal heat kiln furnace 14, and an exhaust chamber 18 is provided on the other side. Hot air is blown from the other side of the internal heat kiln furnace 14 through the discharge chamber 18, charged from the one side, and sequentially transferred to the other side as the internal heat kiln furnace 14 rotates. It is designed to dry and burn.

  That is, in this drying / combustion process, the dehydrated product is dried and burned gently from the supply port to the discharge port by drying and burning in an internal heat kiln furnace in which the main body is placed horizontally and rotates around the central axis. Combustion of organic components can be performed, pulverization of combustibles can be suppressed, and the degree of combustion of dehydrated products having various properties such as formation of aggregates, hard and soft, and particle alignment can be stably performed. In addition, the drying can be divided into separate steps and a blow-up type dryer can be inserted.

  Here, the hot air blown into the internal heat kiln furnace 14 has an oxygen concentration of 0.2 to 20%, preferably 1 to 17%, more preferably 7 to 15%.

  Since the oxygen concentration is consumed by the combustion (oxidation) of the raw material, the oxygen concentration varies depending on the state of combustion. If the oxygen concentration is excessively low, it is difficult to achieve sufficient combustion. Oxygen in the combustion furnace is consumed due to the combustion of raw materials and the like, and the oxygen concentration decreases.However, the oxygen concentration is reduced by blowing or exhausting oxygen-containing gas such as air by a hot air generator for combustion. Further, the temperature in the combustion furnace can be finely adjusted by blowing or exhausting the oxygen-containing gas, and the raw material can be burned uniformly without unevenness.

  The furnace temperature of the first combustion furnace is 300 to 500 ° C, preferably 400 to 500 ° C, more preferably 400 to 450 ° C. In the first combustion furnace, it is preferable to combust at a combustion temperature range of 300 to 500 ° C. for the purpose of slowly burning an easily combustible organic substance and suppressing the formation of residual carbon that is difficult to burn. When the temperature is excessively low, the organic matter is not sufficiently combusted. When the temperature is excessively high, overcombustion occurs, and calcium oxide is easily generated due to decomposition of calcium carbonate. Furthermore, when the furnace temperature exceeds 500 ° C, the drying and combustion progress locally before the particle alignment of the combustibles with various properties such as hard and soft proceeds, so the unburned rate on the particle surface and inside It becomes difficult to make the difference between them small and uniform.

Hot air is blown from a hot air generating furnace 20 provided with a burner 20A.
From the exhaust gas chamber 16, exhaust gas subjected to drying and combustion is sent into the recombustion chamber 22. The fine powder is discharged from the lower part of the exhaust gas chamber 16 and is mixed with the raw material and reused.

  The exhaust gas is recombusted by the burner in the recombustion chamber 22, precooled by the precooler 24, passed through the heat exchanger 26, and discharged from the chimney 30 by the induction fan 28. Here, after raising the temperature of the outside air, the heat exchanger 26 is sent to the hot air generating furnace 20 and is used for hot air blown from the internal heat kiln furnace 14 to recover the heat of the exhaust gas from the exhaust gas chamber 16. It is like that.

  The first combustion furnace preferably burns with a residence time of 30 to 90 minutes under the above conditions in order to slowly burn the easily combusted organic matter contained in the deinking floss and suppress the formation of residual carbon. Is preferred. The range of 40 to 80 minutes is more preferable from the viewpoint of combustion of organic matter and production efficiency, and the range of 50 to 70 minutes is particularly preferable from the viewpoint of ensuring constant quality. If the combustion time is less than 30 minutes, sufficient combustion is not performed and the proportion of remaining carbon increases. When the combustion time exceeds 90 minutes, thermal decomposition of calcium carbonate occurs due to overcombustion of the raw material, and the obtained regenerated particles become extremely hard.

  In particular, it is dried and burned so that the unburned rate of the burned product supplied in the second combustion step of the next step is 2 to 20% by mass, preferably 5 to 17% by mass, more preferably 7 to 12% by mass. .

  By setting the unburnt rate to 2 to 20% by mass, the combustion in the second combustion process can be efficiently performed in a short time, and the hardness is low and the whiteness is 80% by stable heating in the external heating furnace. As described above, a combustion product having a high whiteness of at least 70% can be obtained. If the unburned material is less than 2% by mass, the energy cost in the first combustion furnace is high, and the hardness of the combustion material may be relatively high. There is a case where quality deterioration such as deterioration occurs.

[Second combustion process]
Combustion products that have undergone drying and combustion treatment in the internal heat kiln furnace 14 are loaded into an external heat kiln furnace 32 that corresponds to a second combustion furnace having an external heat jacket 31 that rotates horizontally about the central axis through a transfer channel. Entered.

  In this combustion furnace, the combustion product is heated by external heat and controlled by the lifter provided on the inner wall of the kiln furnace to control the conveyance of the raw material in the combustion furnace and burn slowly. To burn.

  In the combustion in the second combustion furnace, the residual organic matter that could not be combusted in the first combustion furnace, such as residual carbon, is burned, so that the particle diameter is adjusted to be smaller than the particle diameter of the raw material supplied in the first combustion furnace. It is preferable to use a combustion product. The particle size of the burned product after the drying / combustion step is adjusted so that the average particle size is 10 mm or less, preferably 1 to 8 mm, more preferably 1 to 5 mm.

  If the average particle diameter at the entrance of the second combustion furnace is less than 1 mm, there is a risk of overcombustion, and if the average particle diameter exceeds 10 mm, the remaining carbon is difficult to burn and combustion may not proceed to the core. The problem is that the whiteness of the regenerated particles is reduced. In order to ensure stable production in the second combustion furnace, it is preferable to adjust the particle size so that the combustion product having an average particle size of 1 to 8 mm is 70% or more. Therefore, it is useful for practical application in terms of uniforming the quality of the regenerated particles obtained. Further, when the classification is performed after drying as in this embodiment, the combustion product of small-diameter particles can be surely removed, and the processing efficiency is improved.

  As an external heat source in the external heat kiln furnace 32, an electric heating type electric furnace in which temperature control in the external heat kiln furnace 32 is easy and temperature control in the longitudinal direction is easy is preferable. A kiln furnace 32 is desirable.

  By using electricity for the external heat, it becomes possible to finely adjust the temperature and control the internal temperature uniformly, control the degree of combustion of dehydrated products with various properties such as formation of aggregates, hard and soft, and granulation Alignment can be performed stably.

  Furthermore, the electric furnace can be provided with a temperature gradient arbitrarily by providing a plurality of electric heaters in the flow direction of the furnace, and can maintain the temperature of the combustion product for a certain period of time. Residual organic content in the combustion product that has passed through one combustion furnace, especially residual carbon, can be brought to zero as much as possible without causing decomposition of calcium carbonate in the second combustion furnace. Regenerated particles with whiteness can be obtained.

  In the external heat kiln furnace 32, the oxygen concentration is set to 5 to 20%, preferably 10 to 20%, more preferably 10 to 15%. The oxygen concentration can be controlled by controlling the amount of oxygen or air input to the second firing furnace by an appropriate means (illustration of a specific form is omitted). If the oxygen concentration in the external heat kiln furnace is less than 5%, there arises a problem that the combustion of the remaining carbon which is difficult to burn does not proceed. On the other hand, when the oxygen concentration exceeds 20%, the oxidation of calcium carbonate proceeds and tends to change to calcium oxide. For this reason, it becomes easy to elute in water, and there exists a possibility that scale dirt may generate | occur | produce in papermaking type | system | group.

  The combustion temperature of the second combustion furnace is 550 to 780 ° C, preferably 600 to 750 ° C. As described above, since the second combustion furnace needs to burn residual organic matter, particularly residual carbon, that could not be burned in the first combustion furnace 14, it can be burned at a higher temperature than the first combustion furnace 14. preferable. Therefore, if the combustion temperature of the second combustion furnace is less than 550 ° C., it is difficult to sufficiently burn the residual organic matter. On the other hand, if the combustion temperature exceeds 780 ° C., the oxidation of calcium carbonate in the combustion product Advances and the problem that the particles become hard arises.

  The residence time is 60 minutes to 240 minutes, preferably 90 minutes to 150 minutes, and more preferably 120 minutes to 150 minutes. That is, it is preferable that the residence time is 60 minutes or more from the viewpoint of stable production of combustion products, while the residence time is 240 minutes or less from the viewpoint of preventing overcombustion and ensuring production. In particular, the remaining carbon must be burnt slowly at a high temperature that does not cause the decomposition of calcium carbonate as much as possible. However, if the residence time is less than 60 minutes, the remaining carbon is burnt in a short time. On the other hand, when it exceeds 240 minutes, the problem that calcium carbonate decomposes occurs.

  The particle size of the combustion product discharged from the external heat kiln furnace 32 is adjusted to 10 mm or less, preferably the average particle size is 1 to 8 mm, more preferably 1 to 5 mm.

  The regenerated particles whose combustion has been completed are preferably aggregates (regenerated particle aggregates), and after being cooled by the cooler 34, those having a target particle size are combusted by a particle size sorter 36 such as a vibration sieve. It is temporarily stored in the silo 38 and sent to the application destination of the pigment and filler.

  In addition, although the case where the deinking froth was used as the raw material 10 was illustrated, it may be a combustion product obtained by appropriately mixing other papermaking sludge such as papermaking sludge in the papermaking process with the deinking floss as the main raw material.

[Crushing process]
In the method for producing regenerated particles based on the present embodiment, if necessary, a known dispersion / pulverization step is further provided, and a pigment for coating and a filler for internal addition are prepared by appropriately finely pulverizing to a necessary particle size. Can be used as

  In one example, the particles obtained after combustion are pulverized using a dry pulverizer such as a jet mill or a high-speed rotary mill, or a wet pulverizer such as an attritor, a sand grinder, or a ball mill. The optimum particle size for the regenerated particle filler and pigment application of the present embodiment is preferably an average particle size of 2 to 5 μm.

  This is considered to be because the bulky effect is improved because the average particle size is larger than that of conventional calcium carbonate. Talc and clay have a larger average particle size than regenerated particles and can be expected to have a bulky effect. However, since they become acidic papermaking, they tend to yellow and are not practical.

  The particle size of the regenerated particles after the pulverization step was measured by a volume average particle size using a particle size distribution measuring device (laser type microtrack particle size analyzer: manufactured by Nikkiso Co., Ltd.).

[Attached process]
In this production facility, in order to obtain more stable quality, it is preferable to classify the particle size of the regenerated particles uniformly in each step, and feed back coarse and fine particles to the previous step. The quality can be further stabilized.

  In addition, it is preferable to granulate the deinked floss that has been subjected to dehydration in the previous stage of the drying process, and it is more preferable to classify the granulated product so that the particle diameter is uniform, The quality can be further stabilized by feeding back the fine granulated particles to the previous process. In granulation, a known granulation facility can be used, and facilities such as a rotary type, a stirring type and an extrusion type are suitable.

  As the raw material 10 of this manufacturing method, it is preferable to remove in advance other than the raw material of the regenerated particles. That is, for example, it is preferable in terms of removal efficiency to remove sand, plastic foreign matters, metals, and the like with a pulper, screen, cleaner, etc., before the deinking process of the used paper pulp manufacturing process. In particular, the iron content is a causative substance that lowers the whiteness of the fine particles due to oxidation of the iron content. Therefore, it is recommended to selectively remove iron to avoid iron contamination. For this reason, each process is designed or lined with a material other than iron to prevent iron from being mixed into the system due to wear, etc., and a high magnetic material such as a magnet is installed in the drying / classifying equipment. It is preferable to remove iron.

  Furthermore, the regenerated particles produced by the method for producing regenerated particles according to the present embodiment have a ratio of calcium, silica and aluminum of 30 to 82: 9 to 35: 9 in terms of oxides in the elemental analysis of fine particles using an X-ray microanalyzer. To 35, preferably 40 to 82: 9 to 30: 9 to 30, more preferably 60 to 82: 9 to 20: 9 to 20.

  By including calcium, silica, and aluminum in a mass ratio of 30 to 82: 9 to 35: 9 to 35 in terms of oxides, the specific gravity is light and excessive aqueous solution absorption can be suppressed. The ratio of unburned matter in the drying / combustion process and the possibility of excessive curing due to sintering in the combustion process can be reduced.

  As a method for adjusting the ratio of the present embodiment, the main point is to adjust the raw material composition in the deinking floss, but in the drying / combustion process and the combustion process, the coating floss and preparation process with a clear origin It is also possible to adjust by means of containing floss in the process by spraying or the like, or means of containing incinerator scrubber lime.

  For example, using deinked floss as the main raw material, neutral papermaking wastewater sludge and coated paper manufacturing wastewater sludge are used to adjust calcium in the recycled particles, and white carbon is used as an opacity improver to adjust silica. Wastewater sludge from the newsprint manufacturing system to which a large amount of is added, and the drainage sludge from the papermaking system that uses sulfuric acid bands such as acidic papermaking system to adjust the aluminum, and the wastewater from the high quality papermaking process that often uses clay Sludge can be used.

In addition, the regenerated particles obtained by the production method as described above have a weight loss (rate) in decomposition (change to calcium oxide) of calcium carbonate that occurs in the vicinity of 700 ° C. in differential thermal analysis using a differential thermothermal gravimetric simultaneous measurement apparatus. By controlling combustion of the deinking froth based on the present embodiment so as to be 50% or more, it is preferable because the progress of oxidation of the calcium component can be suppressed more accurately and the particles can be prevented from becoming hard. .
[About the lifter of the second combustion furnace (external heat kiln furnace)]
As described above together with the reason for adoption, the spiral lifter and / or the parallel lifter parallel to the axial center is formed on the inner wall of the second combustion furnace (external heat kiln furnace) 32 from one end side to the other end side. It is possible to achieve uniform combustion of the raw material 10 and uniform quality.

  For this second combustion furnace (external heat kiln furnace) 32, a known rotary combustion apparatus as shown in FIG. 2 (a) with its internal structure and FIG. Used.

  That is, the second combustion furnace (external heat kiln furnace) 32 is configured to be rotationally driven by a rotational drive means (not shown), and has a charging part 32a at one end and a discharge part ( A combustion burner 20A (not shown) for introducing combustion gas into the cylindrical main body 32b is disposed at the other end. The inner surface of the fireproof wall 32c on the side of the insertion portion 32a of the cylindrical main body 32b has a plurality of spirals (eight in the illustrated example) that are inclined at an inclination angle of 45 ° to 70 ° with respect to the axis of the cylindrical main body 32b. A cylindrical lifter 32d protrudes at equal intervals through a bracket 32e, and a parallel lifter 32f of an appropriate length parallel to the axial center of the cylindrical main body 32b is provided at the other end side in the circumferential direction. A plurality (eight in the illustrated example) are provided at intervals, and a plurality of rows (eight in the illustrated example) bracket 32g are provided in the axial direction.

  The fireproof wall 32c is preferably made of fireproof castable or fireproof brick, and the helical lifter 32d and the parallel lifter 32f are made of metal such as a stainless steel plate having heat resistance, for example. Therefore, durability and strength can be sufficiently secured without using an expensive heat-resistant material, and heat transfer efficiency is higher than that of a refractory lifter, so that the heat efficiency can be further improved. In particular, it is desirable that the spiral lifter 32d and the parallel lifter 32f are arranged in this order from the combusted material input portion 32a side to the discharge side as described above.

  According to the second combustion furnace (external heat kiln furnace) 32 configured as described above, the content charged from the charging portion 32a is firstly fed in an appropriate amount toward the other end side by the spiral lifter 32d. While being lifted and dropped while being fed, the organic components resulting from the raw material 10 efficiently come into contact with the combustion gas (combustible gas) generated by gasification, and subsequently lifted and dropped by the parallel lifter 32f. By repeating the operation, the contents can be efficiently contacted with the combustion gas (combustible gas), so that the contents can be combusted efficiently. In particular, by controlling the amount of the content fed into the parallel lifter 32f by the spiral lifter 32d, the content can be properly lifted and dropped at the parallel lifter 32f, and the content can be burned uniformly and efficiently. Can be done automatically. Further, since there is no fear of damage to the refractory, there is no decrease in the purity of the fired product, and its production capacity can be improved. In the above-described embodiment, the spiral lifter 32d and the parallel lifter 32f are provided side by side, but only one of them may be provided as necessary.

  The regenerated particles obtained as described above have a high whiteness of 75 to 85%, preferably 80 to 85%, and little variation in whiteness. Further, when the regenerated particles obtained by the production method described above are used for the base paper of the present coated paperboard, the whiteness is lower than that in the case of using conventionally known regenerated particles and calcium carbonate which is a commercially available filler. The coated paperboard which is high and bulky and does not peel off during printing can be obtained.

  The regenerated particles obtained by the above-described production method have an average particle size larger than that of conventionally known calcium carbonate (1 to 2 μm), and the regenerated particles are fixed between the fibers, so that the bulk effect is improved. In addition, since the aluminum of the regenerated particles is cationic, the fixing property to the fiber is strong, and since the blending amount can be reduced more than calcium carbonate, the ash content can be lowered, the bulk effect and the surface strength are improved, As a result, it is considered that paper peeling during printing can be reduced.

  In the present paperboard, it is desirable that the content of aluminum oxide is 10 to 35% by mass, preferably 15 to 25% by mass, of the total inorganics including the inorganics brought in from the regenerated particles. When the content of aluminum oxide is less than 10%, the effect of improving fixability is reduced. On the other hand, when the content of aluminum oxide exceeds 35%, the cationicity becomes too strong and reacts with the papermaking chemicals to generate aggregates or black foreign matters such as pitch.

  In the present embodiment, the regenerated particles as described above can be used alone, or such regenerated particles and heavy calcium carbonate, light calcium carbonate, talc, clay, kaolin, ordinarily used as an internal filler. One or more fillers selected from inorganic fillers such as titanium dioxide, synthetic silica and aluminum hydroxide, and synthetic polymer fine particles such as polystyrene resin and urea formaldehyde resin can be used in combination.

  In order to confirm the effect of the multilayer paperboard according to the present invention, the following various samples were prepared, and a test for evaluating the quality of each sample was performed. In addition, in a present Example, the numerical value which shows a mixing | blending, a density | concentration, etc. is a numerical value of the solid content or the mass reference | standard of an active ingredient. Moreover, since the pulp, chemical | medical agent, etc. which are shown in a present Example are only examples, it cannot be overemphasized that this invention is not restrict | limited by these Examples, and can be selected suitably.

  For comparison with 43 types of multilayer paperboards (referred to as “Example 1” to “Example 43”) according to the present invention and these Examples 1 to 43, there are two types. Multi-layer paperboards (referred to as “Comparative Example 1” and “Comparative Example 2”) were prepared in the configurations shown in Tables 1 and 2.

[Example 1]
Using the following raw materials, a multilayer paperboard having a five-layer structure consisting of a surface layer, three middle layers, and a back layer was obtained according to the following production method.
<Base paper>
・ Surface layer After blending 50% by weight of softwood bleached kraft pulp (NBKP) and 50% by weight of upper white waste paper (dry), the Canadian Standard Freeness (CSF) becomes 400 cc with a double disc refiner. The raw material pulp was adjusted. In this raw material pulp, 8% by mass of regenerated particles as a filler was added in solid content with respect to the weight of the raw material pulp to obtain a raw material pulp slurry. “Regeneration” in Table 1 represents regenerated particles.
-Middle layer The raw material pulp slurry which used as a main component what mix | blended upper white waste paper pulp and middle white waste paper pulp by the weight ratio of 1: 1 was used.
-Back layer A raw material slurry mainly composed of old paper was used.
Yankee with mirror finish after adjusting the water content to 51% after combining the paper layers of the surface layer, 3 layers of the middle layer and the back layer with a circular net paper machine using these raw pulp slurries It dried, pressing on the dryer surface. Further, the press condition of the gloss calendar was changed, and the basis weight of the base paper was adjusted to 210 g / m ² and the paper density was adjusted to 0.98 g / cm ³ to obtain a base paper of a multi-layered paperboard having five layers. .
<Coating liquid for topcoat layer>
Next, as shown in Table 1, a topcoat layer coating solution for forming a topcoat layer was prepared. That is, as a filler, clay (trade name “UW90”, manufactured by Engelhard) is 40% by mass in solid content, and calcium carbonate (trade name “TP-123CS”, manufactured by Okutama Engineering Co., Ltd.) is 60% in solid content. In addition, SBR latex (trade name “L-1388”, manufactured by Asahi Kasei Co., Ltd.) as a binder is 19% by mass in solid content, casein (trade name “casein”, manufactured by Nippon Synthetic Rubber Co., Ltd.). ) With a solid content of 12% by mass to prepare an overcoat layer coating solution.
<Coating liquid for undercoat layer>
Further, as shown in Table 2, as a resin particle, a spherical plastic pigment (trade name “V1004”, manufactured by Nippon Zeon Co., Ltd.) having a volume average particle diameter of 300 nm, which is an organic resin particle, is obtained with a solid content of 100. Undercoat layer coating that forms an undercoat coating layer by blending 10% by mass of an acrylylamide resin (trade name “Haricoat G50”, manufactured by Harima Chemicals Co., Ltd.) as a binder. Make a liquid.
<Formation of topcoat layer and undercoat layer>
The undercoat layer coating solution was applied onto the surface layer of the base paper with a bar coater at a coating amount of 11 g / m ² to form an undercoat layer. Then, on the surface of the undercoat coating layer, the above-mentioned topcoat layer coating solution is applied as follows. After the application at a coating amount of 6 g / m ² , cast processing was performed to obtain the present multilayer paperboard (Example 1).

  Further, Examples 2 to 43 and Comparative Examples 1 to 2 were prepared in the same manner as in Example 1 except that the conditions shown in Tables 1 and 2 were used. In addition, the product name “TP-123CS” manufactured by Okutama Kogyo Co., Ltd. is used as the calcium carbonate (in the table, “charcoal cal”) of the base paper filler in Table 1, and talc manufactured by Nippon Talc Co., Ltd. The trade name “Nanoace D1000” having an average particle diameter of 1.0 μm was used, and the trade name “UW90” manufactured by Engelhard Inc. was used as the clay. Moreover, the product name “PVA405” manufactured by Kuraray Co., Ltd. is used as the PVA of the coating liquid for the overcoat layer, the product name “Haricoat G50” manufactured by Harima Chemicals Co., Ltd. is used as the PAM, and the three crystals are used as starch. The trade name “Coat Master K96F” manufactured by Co., Ltd. was used. Further, “hollow” of the organic resin particles in Table 2 is a hollow plastic pigment, and the trade name “ROPAIKE HP-1055” manufactured by Rohm & Half Co., Ltd. was used. In addition, the trade name “TP-123CS” manufactured by Okutama Kogyo Co., Ltd. was used as the calcium carbonate in Table 2, and the trade name “UW90” manufactured by Engelhard Inc. was used as the clay. Furthermore, the product name “PA5036” manufactured by Nippon A & L Co., Ltd. is used as the SBR in Table 2, the product name “Coat Master K96F” manufactured by Sanki Co., Ltd. is used as the starch, and the product name “Kuraray Co., Ltd.” is used as the PVA. PVA405 "was used.

In addition, “basis weight (g / m ² )” in Table 1 is the total basis weight of the base paper of each sample, and “paper and paperboard—basis weight measuring method” described in JIS-P8124 (1998). It is a value measured according to.

The “paper density (g / cm ³ )” is based on the basis weight of the base paper of each sample and “paper and paperboard—thickness and density test method” described in JIS-P8118 (1998). It is a value calculated from the thickness of the measured base paper.

  Table 3 shows the results of quality evaluation, that is, evaluation of blank paper gloss, ink dropout, ruled cracking, ink adhesion, and stamp suitability for all of these Examples and Comparative Examples. This quality evaluation test was performed under environmental conditions of temperature 23 ± 2 ° C. and humidity 50 ± 2% in accordance with JIS-P8111.

  Here, “white paper gloss (%)” in Table 3 is the white paper glossiness of the surface of the multilayer paperboard as the sample (the surface of the top coat layer), which was measured according to JIS-P8124. This is a value obtained by measuring the glossiness (%) of white paper.

“Ink omission” means that gravure ink NT-2000 manufactured by Sakata Inx Co., Ltd. is used in a gravure printing machine, and each sample is coated with a multi-layer paperboard using a gravure roll with a depth of 100 μm. Solid printing was performed on the layer, and the number of pinholes having a diameter of 0.3 mm or more generated on the topcoat layer of each A4 size sample was confirmed and evaluated with the naked eye. The evaluation criteria were as follows.
A: The number of pinholes is 5 or less.
○: The number of pinholes is 6 to 10.
(Triangle | delta): The number of pinholes is 11-20.
X: The number of pinholes exceeds 20.

“Rule cracking” means that the multi-layer paperboard of each sample printed in the same way as ink missing is cut into A4 size (longitudinal), folded in half with respect to the long side, and a press pressure of 2.0 kg. After pressing for 5 minutes at / m ² , the evaluation was made by checking the presence or absence of cracks in the crease portion with the naked eye. The evaluation criteria were as follows.
(Double-circle): The crack has not generate | occur | produced.
○: Cracks having a total length of less than 15% occur with respect to the crease length.
Δ: Cracks having a total length of 15% or more and less than 30% with respect to the crease length occur.
X: Cracks having a total length of 30% or more with respect to the crease length are generated.

“Ink adhesion” refers to the standard tack grade ink used in the IGT print suitability tester specified in JIS-P8129, using each KRK universal print suitability tester manufactured by Kumagaya Riki Kogyo Co., Ltd. After printing on the surface of the top coat layer of the multi-layer paperboard, which was evaluated by an RI printability test. The evaluation criteria were as follows.
A: No surface fluff or paper peeling is observed.
A: Fluff of 0.5 mm or more or paper peeling is 2 or less.
(Triangle | delta): The fuzz or paper peeling of 0.5 mm or more is 3-5 places.
X: Fluff of 0.5 mm or more and paper peeling are 6 or more places.

Furthermore, “stamp suitability” refers to the evaluation by visually confirming the rubbing state when the surface was wiped off 3 seconds after stamping using a commercially available oil-based and water-based stamp, killer whale stamp and vermilion stamp. is there. The evaluation criteria were as follows.
A: Ink rubbing stains are not generated at all.
A: Almost no ink rubbing stains occur.
(Triangle | delta): The rubbing stain | pollution | contamination of ink has generate | occur | produced.
X: The ink is scraped off.

From Table 3, according to the multi-layer paperboard according to the present invention, all the items of blank paper gloss, ink loss, ruled cracking, and ink adhesion force are free from problems while having flexo printing suitability and gravure printing suitability. It can be seen that the stamp printing suitability as described above can be satisfied, and a multilayer paperboard satisfying the quality required for corrugated cardboard applications can be obtained.

The multilayer paperboard of the present invention is useful in the fields of papermaking and printing as a multilayer paperboard having excellent printing characteristics and low cost.

10 Material 12 Reservoir 14 First Combustion Furnace (Internal Heat Kiln Furnace)
15 Charging machine 16 Exhaust gas chamber 18 Exhaust chamber 20 Hot air generating furnace 22 Recombustion chamber 24 Precooler 26 Heat exchanger 31 External heat jacket 32 Second combustion furnace (external heat kiln furnace)
32b Tubular body 32c Fire wall 32d Spiral lifter 32f Parallel lifter 34 Cooler 36 Particle size sorter 38 Combustion furnace silo

Claims (5)

It comprises a base paper composed of a plurality of layers and a coating layer coated on at least one side of the base paper, and the coating layer comprises at least two layers of a top coat layer and an undercoat coat layer. ,
The surface layer of the base paper contains 5-60% by weight of softwood pulp and 2-22% by weight of filler,
The overcoat coating layer comprises a latex of styrene-butadiene-based, coating a coating solution containing casein, is formed by performing the casting process further,
The undercoat coating layer is formed by applying a coating liquid containing resin particles as a main component and a binder,
A multilayer paperboard having a blank paper glossiness of 80 to 90% on the surface of the topcoat layer measured according to JIS-P8142. Wherein the topcoat coating layer, as a filler, clay and calcium carbonate 60-50% by weight: multilayer according to claim 1, characterized in that the content to form formed by a proportion of 40 to 50 wt% paper making Paperboard.   The multilayer paperboard according to claim 2, wherein the resin particles are organic resin particles.   The multilayer paperboard according to claim 2 or 3, wherein the resin particles have a volume average particle diameter of 150 to 500 nm.   The multilayer paperboard according to any one of claims 1 to 4, wherein the coating liquid for forming the undercoat coating layer contains an acrylamide resin as a binder.

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