JP6034032B2 - Coated white paperboard and method for producing the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a coated white board having a pigment coating layer on a base paper mixed with used paper, and more particularly to a coated white board having high whiteness, little white unevenness, high white paper and high printing gloss, and a method for producing the same.

  The base paper of coated white paperboard is usually manufactured by multi-layer papermaking, and the surface layer uses a lot of expensive bleached chemical pulp with high whiteness. Often used are deinked and undeinked waste paper pulp. The reason why the bleached chemical pulp is used for the surface layer is to keep the white unevenness on the surface of the coated white paperboard well and make it difficult to see foreign matters such as dust contained in the used paper pulp from the surface. In addition, the use of waste paper pulp for the lower and middle layers is from the viewpoint of environmental and cost reduction.

  In recent years, demands for environmental efforts and cost reductions are increasing, and the usage rate of waste paper pulp tends to increase. Along with this, the problem that white unevenness and foreign matters such as dust become conspicuous on the surface of the coated white paperboard is increasing. In order to remove foreign matters such as dust, it is necessary to enhance the deinking and dust removal treatment, but the yield becomes worse as the treatment is enhanced. In addition, as an improvement method using a coating solution, there is a method of increasing the coating amount. However, if the coating amount is too large, the operability is lowered, such as poor drying during coating, and printing unevenness due to binder migration. A new problem will occur.

  For example, Patent Documents 1 and 2 disclose a method for producing white paperboard by using a pigment with high concealability in the coating liquid. However, pigments with high hiding properties are expensive, and the advantage of reducing the cost by increasing the usage rate of waste paper pulp is lost.

  From the viewpoint of the paper layer structure, Patent Document 3 discloses a method for improving whiteness unevenness by making the difference in whiteness between the surface layer and the surface layer lower than a certain level. However, in this method, the usage rate of waste paper pulp cannot be increased beyond a certain level due to the definition of whiteness difference.

  Furthermore, as an improvement by the coating method, a method using a roll transfer coating method or an air knife coating method instead of the normally used blade coating method is known. This is because, in the blade coating method, the surface after coating is flattened regardless of the unevenness of the base paper, and the smoothness of the coating surface is high, but the coating amount is non-uniform. In contrast, the roll transfer coating method and the air knife coating method are more uniform than the blade coating method, and the white unevenness is not noticeable. However, the roll coating method tends to generate a coating pattern peculiar to a roll called orange peel or the like. 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 another coating method, Patent Document 4 discloses a method of making white unevenness and dust inconspicuous without performing coating defects as in the roll coating method by performing curtain coating.

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

  In general, curtain coating is a pre-metering type coating method that does not scrape off the coating liquid during coating, so a uniform coating layer can be applied even if there is some unevenness on the base paper. Therefore, it is considered that white unevenness hardly occurs. Curtain coating does not scrape off with a blade, and the coating layer formed as a curtain film is placed on the base paper, so there are many voids in the coating layer, which is preferable in terms of light scattering and whiteness. It is said.

However, since the coating layer obtained by curtain coating has many voids, there arises a problem that the ink setting becomes faster and the printing glossiness is lowered.
For such a problem, the use of a pigment that can provide a dense coating layer can reduce the voids of the coating layer and slow the ink setting, but the excellent point of curtain coating The bulkiness of the coating layer is lost, and eventually the scattering properties are reduced.

  In view of such a situation, the object of the present invention is to maintain a high light scattering property by a coating layer having a large volume and a lot of voids characteristic of curtain coating, while having an appropriate ink setting property and printing gloss. It is to provide a technique for producing a coated white board having a good degree by curtain coating.

  As a result of intensive studies to solve the above problems, the present inventors have applied a plurality of coating layers simultaneously with a single curtain film, and an overcoat layer that is the outermost layer provided by this curtain coating By making the coating amount of the undercoat layer within a certain range, even when a base paper having a low whiteness of 40 to 70% is used, a white board with excellent whiteness and white unevenness and high printing gloss Has been found to be able to be produced efficiently, and the present invention has been completed.

That is, although not limited thereto, the present invention includes the following inventions.
(1) A method for producing coated white paperboard, comprising forming one curtain film from two or more types of coating liquids, and forming two or more coating layers on the base paper through the base paper through the curtain film. The above method, wherein the whiteness of the base paper is 40 to 70% and the coating amount of the undercoat layer is 10 to 25 g / m ² per side.
(2) The method according to (1), wherein the coating amount of the top coat layer, which is the outermost layer, is ² to 8 g / m ² per side.
(3) The method according to (1) or (2), wherein the total coating amount of the overcoat layer and the undercoat layer is 15 to 30 g / m ² per side.
(4) The method according to any one of (1) to (3), wherein the ratio between the coating amount of the overcoat layer and the coating amount of the undercoat layer is 1: 3 to 1: 8.
(5) As a pigment for the undercoat layer, the average particle size (D50) is 0.3 to 0.8 μm, and the particle size (D75) at 75 cumulative mass% and the particle at 25 cumulative mass% of the particle size distribution curve by the sedimentation method. The method according to any one of (1) to (4), wherein 20 wt% or more of light calcium carbonate having a diameter (D25) ratio (D75 / D25) of 1.5 to 3.5 is used.
(6) A blue / purple color material is contained in at least one of the base paper layer, the overcoat layer, and the undercoat layer, and the hue of the paper in the measurement including ultraviolet rays according to JIS P 8150, and the b ^* value is −10 or more and −0 The method according to any one of (1) to (5), which is less than .5.
(7) Coated white paperboard produced by the method according to any one of (1) to (6).

  According to the present invention, while maintaining a high light scattering property due to a bulky and void-rich coating layer characteristic of curtain coating, it has an appropriate ink setting property, and white unevenness and printing glossiness are good. Coated white paperboard can be produced by curtain coating.

L ^* a ^* b ^* Hue change after colorant addition in hue system

  The present invention relates to a coated white paperboard and a method for producing the same. In the present invention, the coated white paperboard is one in which a pigment coating layer is provided on one side or both sides of a base paper, and at least used paper pulp is blended.

Base Paper In the present invention, a white paperboard is produced using a base paper having a low whiteness. The whiteness of the base paper used in the present invention is 40 to 70%, preferably 50 to 70%, and more preferably 53 to 68%. According to the present invention, it is possible to produce a white paperboard excellent in whiteness and white unevenness even when such a relatively low whiteness base paper is used. The whiteness refers to the whiteness of the base paper surface on the side where the coating layer is provided. The lower the whiteness of the base paper, the higher the whiteness increase rate of the white paperboard after curtain coating compared to the same amount of coating. For this reason, it is advantageous in terms of cost to use a low whiteness base paper containing a large amount of waste paper pulp or containing pulp that has not been deinked, and the environmental load is also low.

  The base paper used in the present invention is not particularly limited as long as waste paper pulp is blended, and bleached chemical pulp, unbleached chemical pulp, and the like can be used, for example. Used paper pulp may or may not be deinked, and deinked pulp includes high-quality paper, medium-quality paper, low-grade paper, newspaper, flyers, magazines, etc. It is possible to use deinked pulp and the like.

  As the base paper used in the present invention, those generally used for the base paper of coated white paperboard can be used without exception, and the above-mentioned various pulps may be mixed, or the same pulp may be used. Further, one or more layers of different pulps may be stacked. For example, a pulp having a low whiteness can be used for the middle layer, and a pulp having a higher whiteness can be used for the front layer and the back layer, or a plurality of layers of the same pulp can be stacked. According to the present invention, even if the same low-whiteness pulp as used for the middle layer and the back layer is used for the outermost layer, there is no whiteness unevenness, and a coated whiteboard with high whiteness can be obtained. The whiteness difference between the outermost surface layer of the base paper and the pulp immediately below it may be within 10% (points), but the whiteness difference may be more than 10%. The point mentioned here indicates a difference in whiteness. For example, when the ISO whiteness of the surface layer is 80% and the ISO whiteness of the immediately lower layer is 68%, it is 12 points lower.

  Further, in the present invention, since the desired effect is obtained even if the smoothness of the base paper is low, a base paper having a low smoothness may be used. However, a range in which a paint pool called paddling during curtain coating does not occur Thus, a base paper having high smoothness can be used. In order to improve the smoothness of the base paper, a pre-calender or the like may be performed before curtain coating. Furthermore, 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. This pre-coated base paper may be subjected to curtain coating without undergoing a drying step, that is, with the paint on the base paper wet. Thus, the state of the base paper after pre-coating before being used for curtain coating is not limited.

Preparation of coating liquid In the present invention, one curtain film is formed from two or more kinds of coating liquids, and two or more coating layers are formed on the base paper through the curtain film. A work layer is formed by curtain coating. In the present specification, out of two or more outermost coating layers formed by curtain coating, the outermost coating layer is the topcoat layer, and the coating liquid for forming the topcoat coating layer is the topcoat coating solution. There is. A layer adjacent to the outermost layer and closer to the base paper is referred to as an undercoat coating layer, and a coating solution for forming the undercoat coating layer is referred to as an undercoat coating solution.

  In this invention, water and a required component are mixed and a coating liquid is adjusted. In the preparation of the coating liquid, ordinary mixing means such as a mixer may be used. Each component will be described below. In the present invention, one curtain film is formed from two or more kinds of coating liquids.

Undercoat Coating Liquid In the present invention, the undercoat coating liquid comprises a pigment and an adhesive (binder). Adhesives are not particularly limited. For example, various copolymers such as styrene / butadiene, styrene / acryl, ethylene / vinyl acetate, butadiene / methyl methacrylate, vinyl acetate / butyl acrylate, polyvinyl alcohol, and maleic anhydride. Synthetic adhesives such as acid copolymers and acrylic acid / methyl methacrylate copolymers; proteins such as casein, soy protein, synthetic proteins; oxidized starch, positive starch, urea phosphated starch, hydroxyethyl etherified Examples include etherified starch such as starch, starches such as dextrin; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose. In the present invention, a synthetic adhesive having a low viscosity increase of the paint is suitable. Further, polyvinyl alcohol having a low degree of polymerization (degree of polymerization of 1000 or less, for example, a degree of polymerization of about 500) is preferably used in combination because the adhesion effect can be enhanced without significantly increasing the viscosity.
The undercoating liquid can contain a pigment that is usually used in curtain coating liquids. In the present invention, from the viewpoint of whiteness and white unevenness of the white paperboard, it is possible to form a primer layer having many voids by using a pigment having a small average particle diameter and a sharp particle size distribution as a pigment for the primer layer. preferable. For example, the average particle diameter (D50) is 0.2 to 0.8 μm, preferably 0.2 to 0.4 μm. In addition, a light carbonic acid having a ratio (D75 / D25) of a particle size (D75) at 75 cumulative mass% to a particle size (D25) at 25 cumulative mass% of a particle size distribution curve by a sedimentation method is 1.5 or more and less than 3.5 Calcium is preferably used, and the amount used is not particularly limited, but is preferably 10% by weight or more, more preferably 20% by weight or more, and the effect becomes remarkable when 20% by weight to 50% by weight is used. 40% by weight or more, 50% by weight or more, and even 60% by weight or more can be used. However, if the amount exceeds 50% by weight, the surface strength of the coated paper for printing tends to be weak (however, the adhesive By increasing the amount, the surface strength can be improved).
In addition to the above pigment, a pigment having an average aspect ratio of 30 to 60, such as delaminated kaolin, can be used in combination in the undercoat coating layer. A pigment having an average aspect ratio of 30 to 60 further improves white unevenness and water retention. This is presumed to be because dehydration is suppressed and water retention is improved by filling a gap between calcium carbonate having a sharp particle size distribution (D75 / D25) of 1.5 or more and less than 3.5 with a flat pigment. Is done. The amount of the pigment having an average aspect ratio of 30 to 60 is not particularly limited, but can be 10% by weight or more and 40% by weight or less.

  The solid content concentration of the undercoat coating liquid is preferably 40 to 75% by weight, more preferably 50 to 70% by weight, and further preferably 60 to 70% by weight. When the solid content concentration of the undercoat coating liquid is less than 40% by weight, the volume change of the coating layer during coating drying becomes large, resulting in poor surface smoothness after coating. On the other hand, when it is more than 75% by weight, the fluidity of the coating liquid is deteriorated, and it becomes difficult to form a uniform curtain film.

  The B-type viscosity of the undercoat coating solution is preferably in the range of 100 to 2000 mPa · s so as to form a uniform and stable curtain film and to be suitable for delivering the coating solution. When it is 100 mPa · s or less, the moisture in the paint soaks into the base paper excessively and the base paper swells, so that the surface smoothness after coating decreases. The energy required for drying also increases. On the other hand, if it is greater than 2000 mPa · s, the fluidity of the paint is inferior and it becomes difficult to form a stable curtain film.

  The surface tension of the undercoat coating solution is preferably 40 mN / m or less, more preferably 35 mN / m or less, and 30 mN / m or less in order to produce a uniform and stable curtain film even at a small flow rate. Further preferred.

Topcoat coating liquid The topcoat coating liquid used in the present invention comprises a pigment and an adhesive as in the case of the undercoat coating liquid. A pigment is not restrict | limited, The pigment conventionally used for coated paper can be used. Examples include inorganic pigments such as kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, and satin white, and organic pigments such as plastic pigments. Organic / inorganic composite pigments can be used. Among them, heavy calcium carbonate, acicular light calcium carbonate, satin white, fine kaolin, fine delamikaolin and titanium dioxide having high whiteness are preferable. These pigments can be used alone, but if necessary, two or more kinds may be mixed and used. As a combination, a combination of heavy calcium carbonate and another pigment having high whiteness is preferable.

  In the present invention, it is preferable to use a pigment having a relatively broad particle size distribution in the topcoat coating solution, thereby adjusting only the void structure on the very surface layer of the coated white paperboard, which has a large effect on the ink setting properties. be able to. The average particle diameter (D50) is 0.5 to 1.0 μm, and the ratio of the particle diameter (D75) at 75 cumulative mass% to the particle diameter (D25) at 25 cumulative mass% (D75 / By using calcium carbonate with D25) of 3.5 or more and 5.0 or less, a dense coating layer is formed, and the ink setting property of white paperboard is prevented from becoming too fast, and the printing gloss is improved. Tend to. The average particle diameter (D50) is 0.5 to 1.0 μm, and the ratio of the particle diameter (D75) at 75 cumulative mass% to the particle diameter (D25) at 25 cumulative mass% (D75 / The amount of calcium carbonate having D25) of 3.5 or more and 5.0 or less is not particularly limited.

  In the overcoating and undercoating liquids of the present invention, the dynamic surface tension of the coating liquid can be adjusted using a surfactant. The surfactant includes an anionic surfactant, a cationic surfactant, and a nonionic surfactant. In the present invention, an anionic surfactant is preferable. The cationic surfactant tends to aggregate the pigment in the coating solution. Further, the nonionic surfactant is difficult to give sufficient wettability to the coating solution. Examples of the anionic surfactant include sulfonic acid surfactants, sulfate ester surfactants, and carboxylic acid surfactants. Among these, sulfonic acid-based surfactants are preferable and alkylsulfosuccinic acid is particularly preferable because the wettability of the coating liquid can be improved. In a preferred embodiment, these surfactants are used in the range of about 0.1 to 2 parts by weight, more preferably about 0.2 to 1 part by weight per 100 parts by weight of the pigment.

  In this invention, it is preferable to mix | blend an adhesive agent (binder) with topcoat coating liquid. 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. In a preferred embodiment, these adhesives are used in the range of about 5 to 50 parts by weight, more preferably about 8 to 30 parts by weight per 100 parts by weight of the pigment. Synthetic adhesives are preferred because they do not raise the paint significantly.

In the topcoat and undercoat coating liquids of the present invention, if necessary, they are blended with ordinary pigments for coated paper, such as dispersants, thickeners, water retention agents, antifoaming agents, water resistance agents, and colorants. Various auxiliaries can be used as appropriate.
The solid content concentration of the top coating liquid is preferably 40 to 75% by weight, more preferably 50 to 70% by weight, and still more preferably 60 to 70% by weight. When the solid content concentration of the topcoat coating liquid is less than 40% by weight, the volume change of the coating layer during coating drying increases, resulting in poor surface smoothness after coating. On the other hand, when it is more than 75% by weight, the fluidity of the coating liquid is deteriorated, and it becomes difficult to form a uniform curtain film.

  The B-type viscosity of the top coating liquid is preferably in the range of 100 to 2500 mPa · s so as to be suitable for forming a uniform and stable curtain film and for delivering the coating liquid. When it is 100 mPa · s or less, the moisture in the paint soaks into the base paper excessively and the base paper swells, so that the surface smoothness after coating decreases. The energy required for drying also increases. On the other hand, if it is greater than 2500 mPa · s, the fluidity of the paint is poor and a stable curtain film cannot be formed.

  The surface tension of the coating solution is preferably 40 mN / m or less, more preferably 35 mN / m or less, and even more preferably 30 mN / m or less in order to produce a uniform and stable curtain film even at a small flow rate.

Curtain coating In the present invention, curtain coating is a coating method in which a coating liquid is flowed down in a curtain shape to form a film, and a base paper is passed through the film to provide a coating layer on the base paper. Curtain coating is a contour coating in which a coating layer is formed along a base paper, and has a characteristic that the coating amount can be easily controlled because of a so-called pre-weighing system.

  The coated white paperboard of the present invention is produced by applying two or more layers on both sides or one side of a base paper by curtain coating. In the present invention, one curtain film is formed from a plurality of coating liquids, a base paper is passed through the curtain film, and two or more coating layers are curtain-coated on the base paper. When curtain coating is performed by forming multiple curtain films from multiple coating liquids, the curtain film becomes thin and unstable as a film, so the film state cannot be maintained until the curtain film falls on the base paper. Although it may not be possible to apply properly, if one curtain film is formed from multiple coating solutions and multiple coating layers are applied simultaneously, the curtain film becomes thicker and stable as a film. Can be applied stably.

In the present invention, it is necessary that the coating amount of the topcoat layer, which is the outermost layer, is ² to 8 g / m ² , and the coating amount of the undercoat layer is 10 to 25 g / m ² . In this way, by increasing the coating amount of the undercoat layer relative to the outermost coat layer, the concealability of the undercoat layer is increased, and the whiteness and white unevenness of the white paperboard are reduced even when the base paper is low in whiteness. In addition to improving the ink setting property, only the surface layer portion of the white paperboard which has a great influence on the ink setting property and the printing quality can be made into a structure suitable for printing.
In the present invention, the ratio of the coating amount of the overcoat layer and the undercoat layer is preferably 1: 1.1 to 1:10, more preferably 1: 2 to 1: 9, and still more preferably 1: 3 to 1: 8. 1: 5 to 1: 8 is even more preferable.
In the present invention, in addition to the coating layer provided by curtain coating as described above, it is also possible to provide an additional coating layer using a coating device other than the curtain coating device, for example, Curtain coating may be performed after blade coating. However, it is necessary to make the top coat layer formed by the curtain coating of the present invention the outermost coat layer. Moreover, you may perform wet on wet coating which performs upper layer coating, without drying a lower layer coating part.

In the present invention, the coating amount of the curtain coating layer is a total of each layer, preferably 10 to 30 g / m ² , more preferably 15 to 30 g / m ² , more preferably ²⁰ to 25 g / m ² in terms of dry weight per side. preferable. When the coating amount is less than 10 g / m ² , the coating layer becomes thin and the whiteness and whiteness unevenness of the white paperboard cannot be sufficiently improved. On the other hand, if the coating amount of one layer exceeds 30 g / m ² , it is not preferable because the operability is deteriorated, for example, the drying property at the time of coating is deteriorated, or printing unevenness due to binder migration is caused. The coating amount is preferably 15 to 25 g / m ² per side, and more preferably ^{20 to} 25 g / m ² . In particular, when the whiteness of the base paper is low, the whiteness of the product can be made a sufficient value by increasing the coating amount.

  Moreover, in this invention, the well-known apparatus used for curtain coating can be used. What is known as the shape of the curtain coating apparatus is a slot type curtain coating apparatus that directly forms a curtain film by discharging the coating liquid downward from the die, and discharging the coating liquid upward from the die, There is a slide-type curtain coating apparatus that flows while forming a coating liquid film on a slope on a die, and then forms a curtain film by free-falling after leaving the die. Any device may be used in the present invention.

The coating speed of the present invention is not particularly limited, but is generally about 100 m / min to 800 m / min. When the coating speed is high, craters tend to occur.
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, the coated white paperboard after production is finished by adjusting so that the water content 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.
Blue / Purple Material In the present invention, one or more color materials selected from the group consisting of purple pigments, purple dyes, blue pigments, and blue dyes (referred to herein as blue-violet materials) The color tone of the coated white paperboard is the hue of the paper in the measurement including ultraviolet rays according to JIS P 8150, and the b ^* value is -10 or more and less than -0.5. Is preferred. By doing in this way, the whiteness of white paperboard can be improved, and the whiteness nonuniformity of white paperboard can be improved by improving the opacity of the layer which added the color material.

  In the coated white paperboard of the present invention, the blue-violet material is contained in at least one of the base paper layer, the topcoat layer, and the undercoat layer, but may be contained in all layers. In general, opacity and whiteness are affected by reflection of light within the paper surface or within the paper layer and absorption within the paper layer. The opacity defined in JIS P 8149 is a value representing the single sheet luminous reflectance R0 as a ratio to the intrinsic luminous reflectance R∞ in the same sample, and is the Z-axis direction (thickness direction) of the coated white paperboard ) Is hardly affected even if the color material is present anywhere. On the other hand, the whiteness defined in JIS P 8148 is the reflectance (inherent reflectance) of a sample in which a sufficient number of samples are stacked so that there is no change in the measured reflectance, and is affected by the pigment contained in the outermost layer. Receive. For this reason, when the color material is present in a plurality of layers, the effect of the present invention can be efficiently obtained by increasing the ratio of the color material present in the coating layer that is the outermost layer. However, when a color material is included only in the coating layer that is the outermost layer, or when a large amount of color material is included in the outermost layer, the bluish white becomes stronger and the apparent whiteness may decrease. In the present invention, it is preferable that the blue-violet material is present in a plurality of layers in order to stabilize the color tone.

  The base paper used in the present invention may be a single-layer paper or a multi-layer paper, but when the base paper contains a blue-violet material, the base paper includes any one or more of a plurality of layers constituting the base paper. What is necessary is just to contain a coloring material. In order for the coloring material to be present in the base paper layer, the base paper may be made from the papermaking raw material containing the coloring material. The method for producing the base paper of the present invention is not particularly limited, and can be performed by a known method using known raw materials.

  In the present invention, it is more preferable that the base paper contains a blue / purple dye. As described above, since the dye is dyed on fibers, pigments, and the like, the base paper is easily dyed. Moreover, although a dye may cause discoloration with time, such discoloration can be suppressed by including the dye in the innermost base paper layer. Furthermore, when many deinked pulps are used in the present invention, even if discoloration occurs due to a dye, the apparent whiteness does not decrease so much.

In the present invention, the hue of the base paper is measured with the dye according to the method of JIS P 8150 including ultraviolet rays, and the b ^* value is −10 or more and less than −0.5, more preferably −3.0 or more and −0.5. When adjusted to less than, the effects of the present invention are more easily achieved.

The a ^* value of the base paper layer is not particularly limited because it does not greatly contribute to the whiteness or opacity of the white paperboard, but is usually preferably −1 or more and less than 7, more preferably −1 or more and less than 5, and −1. More preferably less than 3. If it is out of the range, the color of the white paperboard may not appear white, which is not preferable.

  The addition amount of the colorant in the base paper is not particularly limited. For example, the basic dye is 0.001 to 0.01% by weight and the direct dye is 0.015 to 0.005% based on the absolute dry weight of the whole pulp. It may be 15% by weight.

  In particular, when the proportion of the deinked pulp contained in the base paper is high, a lot of mechanical pulp or the like derived from the deinked pulp is contained, so that a yellowish color is likely to occur. Therefore, by adjusting the coated white paperboard to a specific color tone using the blue-purple material according to the present invention, excessive bluishness can be suppressed, and the yellowish color resulting from containing a lot of mechanical pulp is efficiently used. Can be suppressed and high whiteness can be achieved. Moreover, when using deinked pulp, it is preferable to make the ratio of the blue-violet material which exists in a base paper layer higher than another layer.

  When a blue-violet material is contained in the coating layer by curtain coating, it can be carried out by blending and applying the blue-violet material in the coating liquid. In particular, since curtain coating can form a bulky coating layer as compared with blade coating and the like, the coating layer containing a blue-violet material is formed by curtain coating. The whiteness of the white paperboard and the opacity of the coating layer can be improved to further improve the whiteness unevenness. When a plurality of layers are applied simultaneously by curtain coating, a blue-violet material may be included in any one layer, or a blue-violet material may be included in all coating layers. As described above, since the whiteness is affected by the color material contained in the outermost layer, the color material is preferably contained in the outermost coating layer.

  In the present invention, the color material means a colored pigment or dye other than white. The pigment is a white or colored powder that is insoluble, hardly soluble or dispersed in water, oil, an organic solvent or the like, and includes an inorganic pigment and an organic pigment. In the present invention, any of an inorganic pigment and an organic pigment may be used as the color material. The dye means an organic dye that is dyed onto fibers, pigments, or the like by an appropriate dyeing method among organic dyes having a specific color by selectively absorbing or reflecting visible light. The dye is soluble in a solvent (such as water or an organic solvent). In the present invention, a dye may be used in combination. In the present invention, “use a blue / purple color material” includes a case where both a blue color material and a purple color material are used, and one of them is used. In the present invention, the “blue / purple color material” means “blue and / or purple color material”.

  Examples of the commercially available blue pigment include EMT-Blue DS-18 (manufactured by Toyo Ink Manufacturing Co., Ltd.), and examples of the commercially available purple pigment include SA Violet C12896 (manufactured by Mikuni Dye Co., Ltd.). Is mentioned. A blue pigment alone or a purple pigment alone may be used, but both may be used in combination. In order to improve the opacity, it is preferable to use a purple pigment. Moreover, in this invention, you may add color materials other than blue and purple, such as black, red, and yellow, as needed.

  As the blue pigment and purple pigment, any of inorganic pigments and organic pigments can be used as described above. Specific examples of blue pigments include, for example, ultramarine, azurite, prussian blue, ultramarine, smalto, cobalt blue (cobalt aluminate), cerulean blue (cobalt stannate), cobalt chrome blue, cobalt, aluminum, and silicon. Examples thereof include oxide, cobalt / zinc / silicon oxide, manganese blue, and phthalocyanine. Specific examples of purple pigments include, for example, cobalt violet (cobalt arsenate, cobalt phosphate, cobalt lithium phosphate, hydrous ammonium phosphate, cobalt borate, etc.), purple ultramarine blue, iron oxide purple, manganese violet, mineral Examples thereof include inorganic pigments such as violet, indigoid, quinacridone, oxazine, anthraquinone, carbonium, and xanthene organic pigments.

  In the present invention, by adding a certain amount of the color material to the coated white paperboard and setting the hue within the range described later, the surface color of the coated white paperboard is made pale, the whiteness of appearance is enhanced, and the white Unevenness can be prevented.

When a color material is added in the present invention, the hue of the paper can be changed in the direction shown in FIG. FIG. 1 shows the change in hue of paper that does not contain the color material of the present invention and paper that has been incorporated, based on the L ^* a ^* b ^* color system. When the hue is expressed as 0 ° in the (+) direction of the a ^* value, 180 ° in the (−) direction, b ^* (90) in the (+) direction, and 270 ° in the (−) direction, Assuming that the position of the origin is zero, when a blue color material is added, the hue of the paper after the addition changes to the portion of 210 ° or more and less than 280 ° shown in FIG. When it is added, it indicates that the hue of the paper after the addition changes to a portion of 280 ° to less than 335 ° shown in FIG. 1 as “purple”.

The color material used in the present invention preferably has a total color material amount of 0.4 to 3.5 mg, more preferably 0.9 mg to 3.0 mg per 1 m ^{2 of} coated white paperboard. In general, when the amount is less than 0.4 mg, light absorption by the coloring material is small, and thus the concealability contributing to opacity is insufficient, which is not preferable. In general, when the amount is more than 3.5 mg, the amount of light absorbed by the coloring material is large, which greatly contributes to the improvement in opacity, but the hue is greatly deviated from 0 point, and it is not preferable to feel white. Absent. The total content of the color material can be appropriately adjusted depending on the whiteness of the raw material or the base paper.

The color material may be contained in either the base paper layer or the coating layer of the coated white paperboard. In this case, the total color material amount is a value obtained by adding the color material contents of the respective layers.
Coated white paperboard The ash content of the coated white paperboard produced in the present invention is preferably 10% by weight or more, and more preferably 20% by weight or more. This is because when the ash content is less than 10% by weight, the opacity may not be sufficiently improved.

Hue of the coating white paperboard produced in the present invention is ^preferably the ^{b *} value is adjusted to less than -15 -0.5 in the measurement containing the ultraviolet defined in JIS P 8150, ^{b *} value It is more preferably −6 or more and less than −1, and a b ^* value is further preferably −4 or more and less than −2. Thus, by making b ^* value comparatively low, while the whiteness of the appearance of the coated white paperboard can be enhanced, white unevenness can be improved. Further, the a ^* value in the same measurement is not particularly limited because it does not greatly contribute to the whiteness and opacity of the coated white paperboard, but is usually preferably −1 or more and less than 7, more preferably −1 or more and less than 5. Preferably, it is more preferably −1 or more and less than 3. If it is out of the range, the color of the coated white paperboard may not appear white, which is not preferable.

  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, in this specification, “part” and “%” respectively represent “part by weight” and “% by weight”, and the numerical range is described as including the end points.

(Evaluation method)
Whiteness: Whiteness: Measured according to JIS P8148 “Paper, paperboard and pulp—Method for measuring ISO whiteness (diffuse blue light reflectance)”.
-White unevenness: Evaluated visually by 4 steps according to the following criteria.
A: Unevenness is not noticeable. ○: Mild unevenness is observed. Δ Unevenness is recognized, which may cause a problem in practical use. X: Remarkable unevenness was recognized and not suitable for practical use. Blank paper glossiness: Measured according to JIS P8142 “Paper and paperboard—Measurement method of 75 ° specular gloss”.
・ Glossiness of printing: Using a four-color sheet-fed printing machine (R304) manufactured by Roland, with a sheet-fed process printing ink (manufactured by Toyo Ink: NEX-M) at a printing speed of 8000 sheets / hour, a solid density (ink / indigo) /Red/Yellow=1.85/1.60/1.50/1.40). After leaving the printed matter for about 10 hours, the gloss of the black solid print portion was measured in accordance with JIS P8142 “Paper and paperboard—Method of measuring 75 degree specular gloss”.

Example 1
(Base paper)
75% whiteness using pulp blended at a rate of 100% deinked waste paper, surface layer of 40g / m ² of rice tsubo, 55% whiteness using pulp blended with 100% magazine waste paper not deinked, rice Using the same pulp as the middle layer and middle layer of 210g / m ² , each of the back layers of 45% whiteness and 40g / m ² is prepared, pressed and dried, and 290g / m ^2. A coated white paperboard m ² was obtained. The whiteness of the base paper was 67%. The paper making speed was 300 m / min.

(Undercoating liquid)
Spindle-shaped light calcium carbonate (Okutama Kogyo Co., Ltd., TP-221-70GS, D50 = 0.5 μm, D75 / D25 = 2.5) 45 parts, Delaminated Kaolin (Imerys, Contour 1500, average aspect ratio 50) ) After preparing a pigment slurry consisting of 15 parts heavy calcium carbonate (Fimatech, FMT97, D50 = 0.7 μm, D75 / D25 = 3.8) 40 parts, Add 14 parts of butadiene copolymer latex (ALB1735, manufactured by Asahi Kasei Chemical Co., Ltd.), 0.5 part of PVA (polyvinyl alcohol, POVAL 105, manufactured by Kuraray Co., Ltd.), 0.5 part of surfactant (Newcol 291-PG, manufactured by Nippon Emulsifier Co., Ltd.) did. Further, when water was added to adjust the B-type viscosity at 30 ° C. and 60 rpm to 1000 mPa · s, the solid content concentration was 65% and the static surface tension was 30 mN / m.

(Top coating liquid)
50 parts heavy calcium carbonate (Fimatec, FMT97, D50 = 0.7 μm, D75 / D25 = 3.8), 50 parts delaminated kaolin (Imerys, Contour Xtreme, average aspect ratio 35) After preparing the pigment slurry, 14 parts of styrene / butadiene copolymer latex (ALB1443, manufactured by Asahi Kasei Chemical Co., Ltd.) and 0.5 part of surfactant (Newcol 291-PG, manufactured by Nippon Emulsifier Co., Ltd.) are added to 100 parts of pigment. Further, when water was 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.

(Coating)
The above coating solution was simultaneously coated with two layers using a slot type curtain coating apparatus and dried. Amount of coating is undercoat coating solution at a weight after drying of 20 g / ^{m 2,} topcoat coating solution is 4g / ^{m 2,} the basis weight of the coated white paperboard was 314 g / ^{m 2.} The coating speed was 300 m / min, the same as the papermaking speed, since 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, which was the same as the papermaking speed and the coating speed, because it was performed consistently with the papermaking and coating by on-machine.

Example 2
In Example 1, a coated white paperboard was obtained in the same manner as in Example 1 except that the surface layer of the base paper was changed to 100% magazine waste paper that was not deinked. The whiteness of the base paper was 55%.

Example 3
In Example 1, a coated white paperboard was obtained in the same manner as in Example 1, except that the coating amount of the undercoat coating solution was changed to 16 g / m ² and the coating amount of the topcoat coating solution was changed to 8 g / m ^2. It was.

Example 4
In Example 1, except that the spindle-shaped light calcium carbonate of the undercoat coating solution was changed to heavy calcium carbonate (manufactured by PMMA Tech, FMT97, D50 = 0.7 μm, D75 / D25 = 3.8). In the same manner as in No. 1, coated white paperboard was obtained. The solid content concentration of the coating solution was 66%.

Example 5
In Example 1, except that the heavy calcium carbonate of the top coating liquid was changed to spindle-shaped light calcium carbonate (Okutama Kogyo Co., Ltd., TP-221-70GS, D50 = 0.5 μm, D75 / D25 = 2.5). Coated white paperboard was obtained in the same manner as in Example 1. The solid content concentration of the coating solution was 62%.
Example 6
Obtained in Example 1, the undercoat coating solution coating amount of 12 g / m ^2, except that the coating amount of overcoat coating solution was changed to 12 g / m ^2, a coated white sheet paper in the same manner as in Example 1 It was.
Comparative Example 1
In Example 1, the undercoat coating solution was applied with a bar blade at a coating amount of 16 g / m ² and dried, and then the top coating solution was applied with a vent blade at an application amount of 8 g / m ^2. A coated white paperboard was obtained in the same manner as in Example 1 except that drying was performed.

Comparative Example 2
In Example 1, the coated white paperboard was prepared in the same manner as in Example 1 except that the coating amount of the undercoat coating solution was 8 g / m ² and the coating amount of the top coating solution was changed to 16 g / m ^2. Obtained.
As can be seen from Table 1, in Example 1, even a base paper with low whiteness using deinked pulp as the surface layer has high whiteness, very little white unevenness, and high white paper and printing gloss. In Example 2, even if the base paper has a lower whiteness using undeinked pulp as the surface layer, the whiteness is sufficiently high and the whiteness unevenness is small as long as the whiteness of the base paper is within an appropriate range. Blank paper and high printing gloss. In Example 3, the whiteness, white unevenness, white paper, and printing glossiness are adjusted within a sufficiently high range by changing the coating amounts of the undercoat coating liquid and the topcoat coating liquid within an appropriate range. Can do. Further, when Example 1 and Example 4 are compared, the whiteness of white paperboard can be improved by 3 points by using calcium carbonate having a sharp particle size distribution in the undercoat coating solution (Example 1). ). Furthermore, when Example 1 and Example 5 are compared, the use of calcium carbonate having a broad particle size distribution in the top coating liquid increases the voids in the outermost coating layer and increases the ink setting property of white paperboard. Excessiveness is suppressed, and the print glossiness is high (Example 1).

  On the other hand, in the comparative example 1, not only the whiteness is greatly reduced but also white unevenness is remarkably generated due to the blade coating method. In Comparative Example 2, the coating amount of the undercoat coating solution and the top coating solution is not within the appropriate range, and the coating amount of the undercoat coating solution that contributes to the improvement in whiteness due to high scattering properties is more than the appropriate range. Therefore, the whiteness is low.

Claims (10)

A method for producing a coated white paperboard comprising: forming one curtain film from two or more types of coating liquids; and forming two or more coating layers on the base paper through the base paper through the curtain film,
The whiteness of the base paper is 40 to 70%, the coating amount of the undercoat layer is 10 to 25 g / m ² per side,
As the pigment for the undercoat layer, the average particle size (D50) is 0.3 to 0.8 μm, the particle size (D75) at 75 cumulative mass% and the particle size (D25) at 25 cumulative mass% of the particle size distribution curve by the sedimentation method. ) Light calcium carbonate having a ratio (D75 / D25) of 1.5 to 3.5,
As the pigment for the topcoat layer, the average particle size (D50) is 0.5 to 1.0 μm, the particle size (D75) at 75 cumulative mass% and the particle size (D25) at 25 cumulative mass% of the particle size distribution curve by the sedimentation method. ), Wherein the ratio (D75 / D25) is from 3.5 to 5.0.   The method according to claim 1, wherein a delaminated kaolin having an average aspect ratio of 30 to 60 is further used as a pigment for the undercoat layer.   The method of Claim 1 or 2 that the coating speed of curtain coating is 100-800 m / min. The method in any one of Claims 1-3 whose coating amount of the topcoat layer which is an outermost layer is 2-8 g / m < ² > per single side | surface. The method according to any one of claims 1 to 4, wherein a total coating amount of the overcoat layer and the undercoat layer is 15 to 30 g / m ² per side.   The method according to any one of claims 1 to 5, wherein the ratio of the coating amount of the topcoat layer to the coating amount of the undercoat layer is 1: 3 to 1: 8.   The method according to claim 1, wherein 20 wt% or more of the light calcium carbonate is used as a pigment for the undercoat layer. A blue / purple color material is contained in at least one of the base paper layer, the overcoat layer, and the undercoat layer, and the hue of the paper in the measurement including ultraviolet rays according to JIS P 8150. The b ^* value is −10 or more and less than −0.5 The method according to claim 1, wherein The method in any one of Claims 1-8 whose b ^* value of a coated white paperboard is -4 or more and less than -0.5.   The method according to any one of claims 1 to 9, wherein the whiteness of the coated white paperboard is 78% or more.