JP2015193949A - coated white paperboard - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated white paperboard concealing a dust and an unevenness in white color derived from a base paper, the paperboard which is excellent in white paper surface feel.SOLUTION: The coated white paperboard has a coating layer in at least one side of a multiple layer-papermade base paper. In the coated white paperboard, the coating layer contains one or more pigment coated layer(s) provided by curtain coating; the base paper contains a surface layer adjacent to the coating layer, a front lower-layer adjacent to one side of the surface layer opposite to the coated side of the surface layer, and another layer. When the coated white paperboard is divided into a divided layer 1 containing the coating layer, the surface layer, and the front lower-layer and a divided layer 2 containing another layer, a difference in the ISO whiteness between both sides of the divided layer 1 is 2.0 point or more.

Description

  The present invention relates to a coated white board comprising a base paper blended with waste paper pulp and a pigment coating layer provided by curtain coating.

  White paperboard is usually classified into white balls and manila balls, and manila balls are further classified into high-quality white paperboards and special white paperboards. White balls and Manila balls are classified into coating type and non-coating type. White paper base paper is usually produced by multi-layered paper with 2 to 9 layers, and the demand for environmental efforts and cost reduction is increasing. For example, in white balls, bleached pulp or deinked pulp, or bleached waste paper pulp with high whiteness is used for the surface layer, and lower whiteness and cheaper deinked pulp and deinking are used for the middle layer and the back layer. Used paper pulp is not used. The proportion of waste paper pulp is increasing year by year, and almost 100% of waste paper pulp is blended with low-grade white paperboard. In such a situation, problems with the base paper accompanying an increase in the ratio of used paper include an increase in the occurrence of defects such as dust and black spots, and white unevenness. In order to remove foreign matters such as dust, measures to strengthen the deinking process and dust removal process have been taken, and the problem of dust has been greatly improved by the progress of deinking technology and dust removal equipment, but it can still be completely removed Not so much. The stronger the deinking process and dust removal process, the worse the yield and the economical disadvantage. Therefore, at present, deinking and dust removal processes are not performed above a certain level. On the other hand, white paperboard is often used as a container for foodstuffs, pharmaceuticals, cosmetics, and the like, and particularly for coated white paperboard, there is an increasing demand for improvement in appearance and printability from the viewpoint of visualization.

  One of the appearances is white unevenness. White unevenness is defined as the standard deviation of whiteness in a minute area. Even if the whiteness is high, if the white unevenness is inferior, the surface feel is poor, and the unevenness is further emphasized particularly in the halftone dot portion of the printed material, so that the value as the printed material is inferior. When the difference between the whiteness of the base paper and the whiteness of the coating layer is large, the whiteness unevenness is particularly remarkable when the coating unevenness of the coating layer is inferior. Therefore, in order to reduce whiteness by bringing the whiteness of the coating layer and the base paper closer, the opacity of the pigment coating layer provided by the curtain coating method is set to 50% or more, and the outermost layer of the multilayer base paper and its direct A method of increasing the whiteness difference of the lower layer to more than 12% or a method of adding a black dye to the coating pigment to make the whiteness of the base paper and the whiteness of the coating layer within 6% are proposed. (Patent Documents 1 and 2). Further, as a method for making the white unevenness of the base paper inconspicuous, a proposal has been made to define the difference in whiteness between the surface layer and the surface layer in the multilayer papermaking within a certain range (Patent Document 3).

  It is generally known to use a roll transfer coating method or an air knife coating method in place of the blade coating method that is normally used as an improvement in white unevenness by the coating method. The blade coating method has a feature that the surface after coating is flattened regardless of the unevenness of the base paper, so that the smoothness of the coating surface is high, but the coating amount is uneven and white unevenness is likely to occur. On the other hand, the roll transfer coating method and the air knife coating method have an advantage that white unevenness is not noticeable because the coating amount is uniform compared to the blade coating method.

  In addition to this, while using the above-mentioned waste paper pulp multi-blend paper, as a technology to make the dust inconspicuous efficiently and improve the whiteness and printability, the coating amount to be applied to the surface is increased, the concealability A method of blending a large amount of organic pigments such as high-titanium dioxide, structured kaolin, and plastic pigment has been proposed (Patent Documents 4 and 5).

JP 2009-41131 A JP-A-1-97295 JP 2005-298998 A JP-A-6-166991 JP 2003-306882 A

The prior art has the following problems.
The techniques disclosed in Patent Documents 1 and 3 define the difference in whiteness between the surface layer and the surface layer in the multilayer paper in order to make the white unevenness of the base paper inconspicuous, but the white color between the coated surface and the base paper It has not yet solved white unevenness due to the degree difference.
In the technique disclosed in Patent Document 2, white unevenness due to the difference in whiteness between the coated surface and the base paper can be eliminated, but in order to reduce the difference in whiteness between the base paper and the coating layer, When black pigment is added, there arises a problem that the overall whiteness is lowered.
When the roll coating method is adopted instead of the blade coating method in order to improve white unevenness, a roll-specific coating pattern called orange peel or the like is likely to occur. In addition, in the air knife coating method, the viscosity of the coating solution must be lowered in principle, so if the solid content concentration is lowered, the moisture of the coating solution will soak into the base paper and the base paper will swell. Occurs and surface smoothness deteriorates. The energy required for drying also increases.
As disclosed in Patent Documents 4 and 5, highly concealed titanium dioxide and plastic pigments that increase the amount of coating on the surface in order to make the dust less noticeable and improve whiteness and printability. When a large amount of organic pigments such as these are blended, not only will the cost increase, but the physical properties of the paints differ greatly from those of general coating pigments, and the physical properties of the paint may change significantly.

  In view of such a situation, the present invention is a coated white board comprising a base paper blended with waste paper pulp and a pigment coating layer, concealing dust and white unevenness derived from the base paper, and excellent in the sense of white paper An object is to provide a coated white paperboard.

  As a result of earnest research, the inventor provided a pigment coating layer containing a specific pigment by curtain coating, which is characterized by contour coating, on white paperboard with a lot of dust and noticeable white unevenness. As a result, the present invention has been completed.

That is, the said subject is solved by the following this invention.
[1] A coated white board having a coating layer on at least one side of a multi-layer base paper,
The coating layer includes one or more pigment coating layers provided by curtain coating,
The base paper consists of a surface layer adjacent to the coating layer, a surface lower layer adjacent to the side opposite to the coating surface of the surface layer, and other layers other than that,
When the coated white paperboard is divided into the divided layer 1 composed of the coating layer, the surface layer, and the lower layer, and the divided layer 2 composed of the other layer, the difference in ISO whiteness between both surfaces of the divided layer 1 is 2.0 points or more,
Coated white paperboard.
[2] The coated white paperboard according to [1], wherein the surface layer contains waste paper pulp.
[3] The coated white paperboard according to [1] or [2], wherein the ratio of the used paper pulp is 50 parts by weight or more with respect to 100 parts by weight of the total pulp of the base paper.
[4] The coated white paperboard according to any one of [1] to [3], wherein the pigment coating layer provided by the curtain coating contains light calcium carbonate.
[5] The coating layer includes two or more pigment coating layers provided by curtain coating, or two or more pigment coating layers provided by curtain coating and other coating methods. , [1] to [4].
[6] The coated white paperboard according to any one of [1] to [5], wherein the front and lower layers do not contain chemical pulp.
[7] The coated white paperboard according to any one of [1] to [6], wherein the total coating amount of the pigment coating layer provided by the curtain coating is 15 g / m ² or more per side.

  According to the present invention, coated white paperboard that conceals dust and white unevenness derived from the base paper and has an excellent white paper feel can be provided.

It is sectional drawing of the coated white paperboard of this invention.

Hereinafter, the present invention will be described in detail. In the present invention, “X to Y” includes values at both ends, that is, X and Y.
In the present invention, the coated white paperboard has a pigment coating layer on at least one side of the multi-layer base paper. It is preferable that waste paper pulp is blended in at least one layer of the base paper.

(1) Base paper The base paper used in the present invention preferably contains at least waste paper pulp. Pulp other than waste paper pulp is not particularly limited, and chemical pulp such as kraft pulp and sulfite pulp; mechanical pulp such as thermomechanical pulp and pressurized groundwood pulp; semi-chemical pulp such as chemical thermomechanical pulp can be used. According to the present invention, since white unevenness such as dust derived from base paper can be concealed, base paper containing a large amount of waste paper pulp can be used. Therefore, it is advantageous in terms of cost and the environmental load is reduced. Used paper pulp includes high-quality paper, medium-quality paper, newspapers, leaflets, magazines, and other sorted waste paper, corrugated wastepaper, and undeinked wastepaper pulp made from unsorted wastepaper mixed with these. it can. The amount of the used paper pulp is 50% by weight or more, preferably 80% by weight or more based on the total pulp.

  The base paper used in the present invention is a multilayer paper base paper, and generally used for coated white paperboard can be used without exception. The base paper may be a mixture of the above various pulps or may be the same pulp. In the present invention, in the multi-layer paper, the outermost layer on the side on which the pigment is applied is referred to as the surface layer, the second layer from the coated surface toward the opposite side is referred to as the lower layer, and the other layers are referred to as other layers. Of the other layers, the outermost surface is also called the back layer, and the other is also called the middle layer. Moreover, the layer which comprises a middle layer may be called the 3rd layer and the 4th layer from the surface coated using a curtain coating system. For example, in the case of base paper with three or more layers, you can use pulp with low whiteness for the middle layer and pulp with higher whiteness for the front and back layers, or the same pulp for all layers A plurality of layers can be stacked. However, according to the present invention, even when a pulp having low whiteness is used for the surface layer and the lower layer, the white layer is not uneven and white coated paper having high whiteness is obtained. Therefore, the effect of the present invention can be obtained more remarkably. Further, from the viewpoint of environmental consideration and cost, the surface layer preferably contains 30% by weight or more of waste paper pulp, and more preferably 50% by weight or more. For the above reasons, it is preferable to use 100% by weight of used paper pulp without containing chemical pulp such as kraft pulp and sulfite pulp in the lower layer, and 20% by weight or more of the used paper pulp is deinked. More preferably, the waste paper pulp is not used. Conventionally, chemical pulp having high whiteness is usually used for the front and lower layers, but in the present invention, coated white paperboard having high whiteness can be obtained even if the front and lower layers do not contain chemical pulp. The middle layer preferably uses 100% by weight of waste paper pulp, and 80% by weight or more of the waste paper pulp may be used without deinking.

  The base paper usually contains a filler. Such filler is not particularly limited, for example, diatomaceous earth, talc, kaolin, calcined kaolin, delaminated kaolin, heavy calcium carbonate, light calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, Amorphous silica, calcium sulfite, gypsum, white carbon, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, paper sludge, inorganic fillers such as regenerated inorganic particles from deinking floss, urea-formalin resin, Organic fillers such as polystyrene resin, vinyl chloride resin, melamine resin, phenol resin, and plastic hollow particles, and fillers contained in waste paper and broke can be used alone or in combination of two or more. The blending ratio of the filler to the base paper (base paper ash content) is preferably 10% by weight or more.

  In addition, a coagulant aid, a paper strength enhancer, a tinting dye / pigment, and a sizing agent can be used in the base paper layer according to the desired quality. Moreover, in order to improve the operability at the time of papermaking, a yield improver, a drainage improver, and an antifoaming agent can be used as appropriate.

The paper making method of the base paper in the present invention is not particularly limited, and a long paper machine including a top wire, an on-top former, a gap former, a round paper machine, a paperboard using a long paper machine and a round paper machine in combination. It can be performed using a paper machine, a Yankee dryer machine, a hybrid paper machine combining these, or the like, and two or more layers may be combined to form a base paper. The pH during papermaking may be acidic, neutral or alkaline, but neutral or alkaline is preferred. The paper making speed is not particularly limited. In addition, the base weight of the base paper in white paperboard is about 150-700 g / m < ² > normally. Further, when the coated paper is produced according to the present invention, the base paper may be smoothed in advance during the coating process by an online soft calendar, an online chilled calendar, or the like.

  In the present invention, the method for drying the base paper is not limited. For example, various methods such as a steam heating cylinder, a heated hot air air dryer, a gas heater dryer, an electric heater dryer, and an infrared heater dryer may be used alone or in combination.

  In the present invention, since the desired effect can be obtained even if the smoothness of the base paper is low, a base paper with low smoothness may be used, but within a range where no paint pool called paddling occurs during curtain coating. Highly smooth base paper can be used. In order to improve the smoothness of the base paper, a pre-calender treatment or the like may be performed before curtain coating. Further, as a means for improving the smoothness of the base paper, a clear paint or a paint containing a pigment containing starch as a main component can be applied to the base paper before curtain coating. The coated base paper may be subjected to curtain coating without undergoing a drying step, that is, in a state where the paint on the base paper is applied. Thus, the state of the base paper before being used for curtain coating is not limited.

(2) Curtain coating liquid In the present invention, one curtain film is formed from one or two or more kinds of coating liquids, and the curtain film is passed through the base paper to form one or more layers of curtain coating on the base paper. A pigment coating layer is formed. In order to improve the concealability of the base paper, the pigment coating layer of the present invention is preferably composed of two or more coating solutions. For the above reasons, it is preferable to form two or more pigment coating layers. For example, after performing blade coating, curtain coating may be performed to form a pigment coating layer, or two or more pigment coating layers may be formed by curtain coating. At this time, two or more pigment coating layers may be provided with the same coating liquid, or each pigment coating layer may be provided with different coating liquids. The curtain coating layer includes an outermost coating layer that is the outermost layer of the coated white paperboard. When there are two or more pigment coating layers, the outermost coating layer is also referred to as a top coating layer, and the coating liquid that forms the top coating layer is also referred to as a top coating liquid. Moreover, the coating layer adjacent to the base paper is also referred to as an undercoat coating layer, and the coating liquid for forming the undercoat coating layer is also referred to as an undercoat coating liquid.

  When there are two curtain coating layers, the top coating layer, the coating liquid for forming the top coating layer, the outermost coating layer provided by the curtain coating method among the top coating layers. Also called top coating solution. Of the topcoat coating layers, a layer adjacent to the top coating layer and closer to the base paper is also referred to as a precoating layer, and a coating liquid for forming the precoating layer is also referred to as a precoating liquid. Further, the coating layer adjacent to the topcoat coating layer and the base paper and provided by a coating method other than the curtain coating method is an undercoat coating layer, and the coating liquid for forming the undercoat coating layer is an undercoat coating solution. Also called. The coating liquid for forming each coating layer may be a different coating liquid, or the same coating liquid may be used for two or more layers.

  In the present invention, necessary components such as pigments and adhesives are mixed with water to adjust the coating liquid. In the preparation of the coating liquid, ordinary mixing means such as a mixer may be used. Each component contained in the coating liquid will be described below.

  The pigment used in the coating liquid need not be special, but conventionally known and publicly available are diatomaceous earth, talc, kaolin, calcined kaolin, delaminated kaolin, heavy calcium carbonate, light calcium carbonate, carbonate Magnesium, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, calcium sulfite, gypsum, white carbon, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, paper sludge, deinking floss Inorganic fillers such as regenerated inorganic particles, organic fillers such as urea-formalin resin, polystyrene resin, vinyl chloride resin, melamine resin, phenol resin, and plastic micro hollow particles can be used. However, in order to obtain high concealability and smoothness, delaminated kaolin may be contained in any one of the pigment coating layers. The content ratio of the delaminated kaolin is preferably 20 parts by weight or more, more preferably 50 parts by weight or more in 100 parts by weight of the pigment. Moreover, in order to improve the concealability, it is preferable that any one of the pigment coating layers contains light calcium carbonate. The ratio of the light calcium carbonate contained is preferably 20 parts by weight or more, more preferably 50 parts by weight or more, in 100 parts by weight of the pigment. In particular, since the undercoat coating layer is required to have high concealability and high smoothness, it is preferable to contain delaminated kaolin. Further, since the top coat layer is required to have high concealability and high whiteness, it is preferable to contain light calcium carbonate.

  The adhesive is not particularly limited, and an adhesive conventionally used for coated paper can be used. Examples of adhesives include styrene / butadiene, styrene / acrylic, ethylene / vinyl acetate, butadiene / methyl methacrylate, vinyl acetate / butyl acrylate, and other copolymers, polyvinyl alcohol, maleic anhydride copolymer And synthetic adhesives such as acrylic acid / methyl methacrylate copolymers; proteins such as casein, soy protein, synthetic protein; oxidized starch, positive starch, urea phosphated starch, hydroxyethyl etherified starch, etc. Conventional adhesives for coated paper such as starches such as etherified starch and dextrin; cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, and hydroxymethylcellulose are included. One or more types of adhesives can be appropriately selected and used.

  The blending ratio of the pigment and the adhesive in the coating solution for forming each coating layer in the present invention is appropriately adjusted within a range where a desired pigment coating solution is obtained. Usually, the solid content ratio is preferably 5 to 30 parts by weight, more preferably 8 to 20 parts by weight with respect to 100 parts by weight of the pigment. When the amount is less than 5 parts by weight, the coating layer strength becomes weak, paper dust is generated, and the printing strength may be inferior. On the other hand, when the amount is more than 30 parts by weight, the gap between the pigment particles in the coating layer is filled with the adhesive, and the light scattering property of the coating layer is inferior, so that the opacity is inferior and the cost may increase.

  In the coating liquid for forming each coating layer of the present invention, in addition to the pigment and the adhesive, if necessary, a dispersant, a viscosity improver, a water retention agent, an antifoaming agent, a water resistant agent, a fluorescent dye, Various auxiliaries blended into ordinary coated paper pigments such as colored dyes, colored pigments, surfactants, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers and metal salts can be used as appropriate.

  The solid concentration of the coating liquid is preferably 58% by weight or more, and more preferably 62% by weight or more. When the solid content is lower than 58% by weight, the quality of the coated paper may deteriorate due to excessive penetration of the coating liquid into the base paper. On the other hand, the upper limit of the solid content concentration is not particularly limited, but is preferably 75% by weight or less and more preferably 70% by weight or less in consideration of liquid feeding properties.

(3) Curtain coating With curtain coating, a coating layer is formed on a base paper by forming one or two or more coating liquids in a curtain shape to form a film and passing the base paper through the film. It is a coating method. Curtain coating is a contour coating in which a coating layer is formed along the base paper, and even if there is some unevenness on the base paper, a uniform coating layer can be applied and white unevenness is unlikely to occur. It is believed that. Also, compared to contact coating methods such as blade coating, where the coating liquid is scraped off with a blade, the coating layer formed by curtain coating, which is a non-contact coating method, has more voids and light. It is preferable in terms of scattering properties and whiteness. Furthermore, curtain coating is a non-contact type coating method, and the load applied to the base paper is small and the paper breakage can be suppressed, so that the productivity is excellent.

  In the present invention, at least one side of the base paper is coated with a single layer or multiple layers by curtain coating. As described above, in the multilayer coating, it is possible to use a coating apparatus other than the curtain coating apparatus for coating any layer, for example, lot (bar) coating or blade coating. The curtain coating may be performed later, or the blade coating may be performed after the curtain coating. In order to obtain high smoothness, it is preferable to perform blade coating after bar coating. In order to obtain higher smoothness, it is preferable to perform blade coating on the outermost layer after curtain coating. Moreover, you may perform wet on wet coating which performs upper layer coating, without drying a lower layer coating part.

The total coating amount of each coating solution in the present invention is preferably ² to 50 g / m ² , more preferably 5 to 50 g / m ² in terms of solid content per one side. If the coating amount is less than 5 g / m ² , the unevenness on the surface of the paper substrate cannot be sufficiently covered, and the acceptability of the printing ink may be significantly reduced. In order to improve the concealability of the base paper, it is more preferably 15 g / m ² or more. On the other hand, when the coating amount is more than 50 g / m ^2, it is preferable for improving the concealing property, but the operability is lowered due to the deterioration of the drying property at the time of coating, and cracks at the ruled line portion occur in the post-processing step. This is not preferable because problems are likely to occur. Even when the coating layer is composed of multiple layers, the coating amount is preferably 50 g / m ² or less per side. In addition, in order to improve the concealability of the base paper and to obtain a coated white board with less haze, the total coating amount of the pigment coating layer formed by curtain coating, which is contour coating, must be solid per side. It is preferably 15 g / m ² or more per minute.

Coated white board paper having a basis weight of the present invention is not particularly limited, is generally about 150 to 800 g / ^{m 2.}

  Moreover, in this invention, the well-known apparatus used for curtain coating can be used. For example, a pump for feeding the coating liquid, a defoaming device for degassing the coating liquid, and the like can be used.

  In the present invention, a pigment coating layer may be provided on one side of the base paper by curtain coating, but a clear coating layer or a pigment coating layer may be provided on the other side (also referred to as “back side” for convenience). Good. By providing a coating layer on the other surface, rigidity can be improved or curling can be suppressed. In the coating liquid for forming the back coating layer, if necessary, conventionally known and publicly used pigments and binders, and dispersants, viscosity improvers, water retention agents, antifoaming agents, water resistance agents, fluorescent dyes, Various auxiliaries blended in normal coating liquids such as colored dyes, colored pigments, surfactants, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, metal salts, and the like can be used as appropriate.

The coating amount of the clear or pigment coating layer on the back of the base paper is not particularly limited, but is generally 0.1 to 5 g / m ² in terms of solid content on one side.

  Moreover, the coating method and drying method of a back surface coating layer are not restrict | limited. For example, using a known size press apparatus, for example, a 2-roll type, a 3-roll type, a gate roll type, a film transfer type, a calendar type, or a coater (coating machine) such as a curtain coater, a spray coater, or a blade coater. After the application, various drying processes such as a steam heating cylinder, a heated hot air air dryer, a gas heater dryer, an electric heater dryer, and an infrared heater dryer may be used alone or in combination, or the drying process may not be performed.

  The coated white paperboard of the present invention is produced through a normal drying step after providing a coating layer on the base paper, but may be smoothed in a surface treatment step or the like as necessary. In a preferred embodiment, it is finished by adjusting so that the water content of the coated paper after production is about 3 to 10% by weight, more preferably about 4 to 8% by weight. For smoothing processing, a smoothing processing device such as a normal super calendar, gloss calendar, soft calendar, thermal calendar, shoe calendar, or the like can be used. The smoothing apparatus is appropriately used on-machine or off-machine, and the form of the pressure device, the number of pressure nips, heating, and the like are also adjusted as appropriate.

  The coating speed is not particularly limited, but is generally about 100 to 800 m / min. If the coating speed is excessively high, craters tend to occur.

  In the present invention, the coated white paperboard is divided into a coating layer including a pigment coating layer, a dividing layer 1 composed of a surface layer and a lower layer of a base paper, and a dividing layer 2 other than that. The difference between the ISO whiteness (UV-in) measured from the construction surface side and the ISO whiteness (UV-in) measured from the surface lower layer side is 2.0 points or more. The difference is preferably 5.0 points or more. The point here indicates a difference in whiteness. For example, when the ISO whiteness of one surface is 80% and the ISO whiteness of the other surface is 78%, the difference is 2 points. is there. As described above, the coated white paperboard of the present invention may have a pigment coating layer by curtain coating on both sides. At this time, there are two layers, a divided layer 1A based on the front surface and a divided layer 1B based on the back surface. In such a case, it is sufficient that either one or both of the divided layer 1A and the divided layer 1B have the difference in whiteness.

  The whiteness measured from the coated surface side of the divided layer 1 is the whiteness of the coated surface, and the whiteness measured from the front lower layer side is the whiteness of the base paper. As described above, the present invention relates to a coated white paperboard that conceals dust and white unevenness derived from a base paper, which is generated when a base paper containing a large amount of waste paper pulp is used, and has an excellent white paper surface feeling. Insufficient concealment of minute color differences such as dust and white unevenness derived from the base paper causes color shading from the base paper to occur on the pigment coated surface, resulting in deterioration of the interfacial surface of the pigment coated surface and whiteness. Incurs a decline. However, if the base paper is uniformly coated and the concealment of defects, etc. is sufficient, the base paper contains a large amount of waste paper pulp, dust and white unevenness, and even if a low whiteness base paper is used, the pigment coated surface A decrease in whiteness can be suppressed.

  In the present invention, the curtain coating method that is contour coating is used, and the whiteness difference is set to 2.0 points or more, thereby concealing the increase in the used paper content of the base paper and the dust and white unevenness derived from the base paper. Thus, it is possible to achieve both high whiteness coated paper and obtain coated white paperboard with excellent white paper surface. In the prior art, there was no idea of dividing the coated white paperboard into the coating layer including the pigment coating layer, the base layer of the base paper, and the split layer 1 consisting of the front and lower layers and the other split layer 2. Moreover, even if the division layer 1 is obtained in the prior art and the whiteness difference is measured, it has been common knowledge that the whiteness difference between the coating layer and the base paper layer is close, so the difference is 2.0 points. Was less than. However, in the present invention, the desired effect was achieved by setting the difference to 2.0 points or more. The reason for this is not limited, but in curtain coating with a high coverage of base paper, by using light calcium carbonate with a high specific scattering coefficient as a coating pigment, the coverage of the base paper can be further improved, so the ratio of used paper is It can be presumed that this is because even if a high-low whiteness base paper is used, a decrease in whiteness of the coated surface can be suppressed. Moreover, it can be inferred that a higher concealment effect can be obtained by providing two or more pigment coating layers.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. Unless otherwise specified, parts and% in this specification represent parts by weight and% by weight, respectively, and numerical ranges include their end points.

(Evaluation method)
(1) Basis weight: Measured according to JIS P 8124.
(2) Paper thickness: Measured according to JIS P 8118.
(3) Density: Determined from basis weight and paper thickness according to JIS P 8118.
(4) Smoothness: According to JIS P8151 “Paper and paperboard—Surface roughness and smoothness test method (air leak method) —Print surf tester method”, the pressure difference of the measuring head is 19.6 ± 0. The smoothness in the case of 1 kPa was measured.
(5) DAV2: A DuPont Appearance Analyzer was used to evaluate the haze of the coated paper surface. The larger the value is, the more slightly the surface of the coated paper is, and the lower the blank paper feel.

(6) Blank paper texture: Using the following criteria, the shading unevenness seen on the coated paper surface was visually evaluated.
4: Unevenness is not conspicuous at all 3: Mild unevenness is observed 2: Unevenness is observed and may cause a problem in practical use 1: Remarkable unevenness is observed and is not suitable for practical use (7) Contaminants: Using the following criteria, impurities derived from the base paper layer found on the coated paper surface were visually evaluated.
4: No foreign matter is seen 3: Some foreign matter is seen 2: Some foreign matter is observed, which may be a problem in practical use 1: Many foreign matters are found, which is not suitable for practical use

(8) Measurement of whiteness The dividing layer 1 was obtained from the coated white paperboard, and the whiteness in the measurement including ultraviolet rays was measured by a method based on JIS P 8150. The measurement sample was prepared according to the following.
A5 size coated white paperboard was prepared and immersed in warm water at 65 ° C. for about 3 hours. Before the sample was dried, it was divided into a divided layer 1 composed of a coating layer, a surface layer and a lower layer, and a divided layer 2 composed of other base paper layers. At this time, care was taken so that the raw paper pulp on the side where the divided layer 2 was in contact did not adhere to the surface lower layer side of the divided layer 1 as much as possible. The split layer 1 was dried for 24 hours at 23 ° C. and 50% using an A4 size metal plate as a weight to prevent drying shrinkage. In the measurement, an A5 size sample was equally folded in three.

[Example 1]
(Base paper 1)
Using 100% deinked waste paper pulp with a surface layer of 33 g / m ² basis weight, 100% used waste paper pulp with a basis weight of 36 g / m ² and 100% basis paper without deinking Then, the 4th to 7th layers were each made and made, pressed and dried to obtain a coated white board base paper of 294 g / m ² .

(Coating fluid A)
After preparing a pigment slurry comprising 50 parts of spindle-shaped light calcium carbonate (D50 = 0.5 μm, D75 / D25 = 2.5) and 50 parts of delaminated kaolin (average aspect ratio 50), Then, 16.5 parts of styrene / butadiene copolymer latex and 0.2 parts of a surfactant were added. Water was further added to adjust the B-type viscosity at 30 ° C. and 60 rpm to 1000 mPa · s to obtain a coating liquid A having a solid content concentration of 65% and a static surface tension of 30 mN / m.

(Coating fluid B)
After preparing a pigment slurry consisting of 85 parts of heavy calcium carbonate (D50 = 0.7 μm, D75 / D25 = 3.8) and 15 parts of titanium oxide, 11 parts of styrene / butadiene copolymer latex with respect to 100 parts of pigment. In addition, 0.2 part of a surfactant was added, water was further added to adjust the B-type viscosity at 60 rpm to 1000 mPa · s, the solid content concentration was 63%, and the static surface tension was 30 mN / m. A coating liquid B was obtained.

(Coating)
The above coating liquid A is applied to the base paper 1 as an undercoat coating layer by a bent blade coating method, and the coating liquids A and B are applied so that the coating liquid B becomes the outermost layer without passing through a drying step. Two-layer coating was simultaneously performed with a curtain coating apparatus and dried. For the curtain coating layer, the coating liquid A layer was a pre-coating layer, and the coating liquid B layer was a top coating layer. Amount of coating is subbing coating layer 10 g / ^{m 2} in weight after drying, the pre-coating layer 12 g / ^{m 2,} the top coating layer is 5 g / ^{m 2,} the basis weight of the coated white board paper It was 324 g / m ² . The coating speed was 300 m / min, which was the same as the papermaking speed because it was performed consistently with the papermaking by on-machine.

(Finishing process)
The coated white paperboard obtained was calendered to obtain a coated white paperboard. The processing speed was 300 m / min, the same as the papermaking speed and the coating speed, because the papermaking and coating were performed consistently by on-machine. Moreover, the clear coating of the coating liquid which consists of PVA2% and PAM1% was performed to the back surface of the coating surface of the obtained coated white paperboard. The coating amount of clear coating was 1 g / m ² .

[Example 2]
(Base paper 2)
A coated white paperboard base paper was obtained in the same manner as base paper 1 except that the pulp of the front and lower layers of base paper 1 was changed to 100% deinked waste paper pulp.

A coated white paperboard having a basis weight of 322 g / m ² was obtained in the same manner as in Example 1 except that the base paper of Example 1 was changed to base paper 2.

[Example 3]
(Base paper 3)
A coated white paperboard base paper was obtained in the same manner as the base paper 1, except that the surface layer pulp of the base paper 1 was LBKP 40%, deinked waste paper pulp 60%, and the bottom layer pulp was deinked waste paper pulp 100%.

A coated white paperboard having a basis weight of 324 g / m ² was obtained in the same manner as in Example 1 except that the base paper of Example 1 was changed to base paper 3.

[Example 4]
(Base paper 4)
A coated white paperboard base paper was obtained in the same manner as the base paper 1 except that the surface layer of the base paper 1 was LBKP 100% and the base layer was 100% deinked waste paper pulp.

A coated white paperboard having a basis weight of 323 g / m ² was obtained in the same manner as in Example 1 except that the base paper of Example 1 was changed to base paper 4.

[Example 5]
(Coating fluid C)
Except that the pigment of the coating liquid B was changed to 100 parts by weight of heavy calcium carbonate, the B-type viscosity at 30 ° C. and 60 rpm was adjusted to 1000 mPa · s in the same manner as the coating liquid B, and the solid content concentration Of 65% and a static surface tension of 30 mN / m.

A coated white paperboard having a basis weight of 318 g / m ² was obtained in the same manner as in Example 1 except that the pre and top curtain coating layers were changed to the coating liquid C in Example 1.

[Example 6]
In Example 1, except that the undercoat coating layer was not provided by the vent blade coating method by the coating liquid A, and the coating amount of the top coating layer by the curtain coating method was 15 g / m ^2. In the same manner as in No. 1, coated white paperboard was obtained.

[Example 7]
(Base paper 5)
A coated white paperboard base paper is obtained in the same manner as the base paper 1 except that the surface layer pulp of the base paper 1 is LBKP 40%, deinked waste paper pulp 60%, and the bottom layer pulp is LBKP 40% and non-deinked waste paper pulp 60%. It was.

In Example 1, the base paper is the base paper 5, the undercoat coating layer is not provided by the blade, the coating liquid A is applied in a single layer by the curtain coating method, and is subjected to a drying process. White paperboard was obtained. The coating amount was 7 g / m ² by weight after drying, and the basis weight of the coated white paperboard was 300 g / m ² . A coated white paperboard was obtained in the same manner as in Example 1 except for the configuration of the coating layer.

[Comparative Example 1]
(Coating fluid D)
After preparing a pigment slurry consisting of 35 parts delaminated kaolin (average aspect ratio 50) and 65 parts heavy calcium carbonate (D50 = 0.7 μm, D75 / D25 = 3.8), 3 parts of urea phosphate starch and 12 parts of styrene / butadiene copolymer latex were added. Further, water was added to adjust the B-type viscosity at 30 ° C. and 60 rpm to 1000 mPa · s to obtain a coating liquid D having a solid content concentration of 65% and a static surface tension of 30 mN / m.

(Coating fluid E)
25 parts of delaminated kaolin (average aspect ratio 50), 25 parts of clay, 5 parts of heavy calcium carbonate (D50 = 0.7 μm, D75 / D25 = 3.8), spindle-shaped light calcium carbonate (D50 = 0.5 μm) D75 / D25 = 2.5) After preparing a pigment slurry consisting of 38 parts and 7 parts of titanium oxide, 5 parts of urea phosphate starch and 14.5 parts of styrene / butadiene copolymer latex were added to 100 parts of pigment. Added. Water was further added to adjust the B-type viscosity at 30 ° C. and 60 rpm to 1000 mPa · s to obtain a coating liquid E having a solid content concentration of 65% and a static surface tension of 30 mN / m.

In Example 1, as the undercoat coating layer, the coating liquid D was applied by the bar coating method, and after passing through the drying step, the coating liquid E was applied by the vent blade coating method as the top coating layer. Coated. Amount of coating is subbing coating layer 8 g / ^{m 2} in weight after drying, a topcoat coating layer 12 g / ^{m 2,} the basis weight of the coated white paperboard was 320 g / ^{m 2.} A coated white paperboard was obtained in the same manner as in Example 1 except for the configuration of the coating layer.

[Comparative Example 2]
(Coating fluid F)
To the pigment slurry consisting of 100 parts of clay, 12 parts of styrene / butadiene copolymer latex and 0.2 part of surfactant are added, and water is further added so that the B-type viscosity at 60 rpm is 1000 mPa · s. When adjusted, a coating solution F having a solid content concentration of 63% and a static surface tension of 30 mN / m was obtained.

In Example 7, except that the base paper is base paper 2, the coating liquid is coating liquid F, the coating amount is 5 g / m ^{2 by} weight after drying, and the basis weight of the coated white paperboard is 310 g / m ² Coated white paperboard was obtained in the same manner as in Example 7.

  As is apparent from the examples, the coated white paperboard of the present invention is less likely to recognize foreign matters and is excellent in white paper texture.

10 coating layer 20 surface layer 22 surface lower layer 24 other layer

Claims (7)

A coated white board having a coating layer on at least one side of a multi-layer base paper,
The coating layer includes one or more pigment coating layers provided by curtain coating,
The base paper consists of a surface layer adjacent to the coating layer, a surface lower layer adjacent to the side opposite to the coating surface of the surface layer, and other layers other than that,
When the coated white paperboard is divided into the divided layer 1 composed of the coating layer, the surface layer, and the lower layer, and the divided layer 2 composed of the other layer, the difference in ISO whiteness between both surfaces of the divided layer 1 is 2.0 points or more,
Coated white paperboard.   The coated white paperboard according to claim 1, wherein the surface layer contains waste paper pulp.   The coated white paperboard of Claim 1 or 2 whose compounding ratio of the said used paper pulp is 50 weight part or more with respect to 100 weight part of total pulp amount of a base paper.   The coated white paperboard according to any one of claims 1 to 3, wherein the pigment coating layer provided by the curtain coating contains light calcium carbonate.   The coating layer includes two or more pigment coating layers provided by curtain coating, or two or more pigment coating layers provided by curtain coating and other coating methods. The coated white paperboard in any one of 1-4.   The coated white paperboard according to any one of claims 1 to 5, wherein the upper and lower layers do not contain chemical pulp. The coated white paperboard according to any one of claims 1 to 6, wherein a total coating amount of the pigment coating layer provided by the curtain coating is 15 g / m ² or more per side.