JP7611869B2 - Coated white paperboard - Google Patents

Description

The present invention relates to coated white paperboard. More specifically, the present invention relates to coated white paperboard that has low density and excellent suitability for gravure printing.

Known types of white paperboard include high-quality white paperboard, which uses bleached chemical pulp on both sides and has a pigment coating on both sides; special white paperboard, which uses bleached chemical pulp or high-quality recycled paper pulp on both sides and is white on both sides, with a pigment coating on one side to improve the printing effect; and coated white board. Coated white board, a type of coated white paperboard, is widely used as boxes for packaging goods, such as detergent boxes, tissue paper boxes, photographic film boxes, confectionery boxes, and over-the-counter medicine boxes. It is also used for purposes other than packaging, such as book covers and picture books.

Coated whiteboard generally consists of at least three layers, a top layer, a bottom layer, and a bottom layer, or at least four layers, a top layer, a bottom layer, a middle layer, and a bottom layer, and uses a large amount of recycled paper. The top layer, which requires high whiteness, is provided with a pigment coating, the bottom layer is made of paper that is mainly made of recycled paper pulp with a relatively high whiteness, and the middle and bottom layers are made mainly of recycled paper pulp with a relatively low whiteness. These whiteboards are mainly printed on the surface, and are often used after being processed for packaging. In recent years, even low-grade coated whiteboards are used for elaborate printing such as gravure printing, so gravure printing suitability is also required.

One example of a ball that has improved suitability for gravure printing is a coated white ball that has been treated with a super calendar to improve its smoothness (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 11-61690

However, with the configuration of Patent Document 1, it is difficult to obtain sufficient suitability for gravure printing. In gravure printing, the amount of ink transferred is adjusted by the depth and shape of the intaglio part of the gravure roll that measures the ink, but this requires both smoothness and cushioning of the paper. However, when only the smoothness is improved by super calendaring, as in the case of the coated white ball described in Patent Document 1, the density becomes too high and the cushioning is lost.

The present invention was made to solve these problems, and its purpose is to provide a coated white paperboard that has low density and excellent suitability for gravure printing.

Other objects and advantages of the present invention will be readily apparent to those skilled in the art by reading the following description.

After extensive research into coated white paperboard, the inventors of the present application have found that the following configuration can achieve the above objectives. That is, the coated white paperboard of the present invention is a coated white paperboard having a base paper for coated white paperboard having at least three layers, a surface layer, a subsurface layer, and a back layer, and a pigment coating layer applied to the surface layer, characterized in that the surface layer does not contain a sizing agent, and the subsurface layer does contain a sizing agent. With this configuration, the surface layer does not contain a sizing agent, resulting in excellent ink absorbency, and the subsurface layer has sizing and cushioning properties, resulting in a coated white paperboard that is excellent in suitability for gravure printing.

In a preferred embodiment of the present invention, the sizing agent is preferably a fatty acid-based sizing agent. By using such a configuration, it is possible to obtain the desired absorbency of the pigment paint even if the raw material is waste paper pulp.

In a preferred embodiment of the present invention, the amount of the sizing agent is preferably 0.1 to 0.8% by mass relative to 100% by mass of pulp. This configuration provides appropriate sizing properties, making it possible to produce a coated white paperboard with better suitability for gravure printing.

In a preferred embodiment of the present invention, the pigment coating layer is two or more layers, and it is preferable that the thickness of the bottommost coating layer in contact with the surface layer is 2 μm or more. When two or more pigment coating layers are provided, the topmost coating layer that forms the outer surface is the topmost coating layer, and the bottommost coating layer in contact with the surface layer is the bottommost coating layer. With this configuration, a moderate anchor effect is obtained by covering the coated white paperboard base paper with the bottommost coating layer, and the gravure suitability of the topmost coating layer surface is favorable.

In a preferred embodiment of the present invention, the PPS measurement value of the pigment coating layer surface is preferably 1.5 μm or less. With this configuration, the pigment coating layer surface has high smoothness, resulting in a coated white paperboard with better suitability for gravure printing.

In a preferred embodiment of the present invention, the surface layer pulp, which is the raw material for the surface layer, preferably has a disintegrated freeness of 200 to 500 ml CSF. This configuration makes it possible to produce a coated white paperboard with excellent paper strength and operability.

In a preferred embodiment of the present invention, the density of the coated white paperboard may be 0.77 to 0.87 g/cm ^3. With this configuration, the coated white paperboard can have better suitability for gravure printing.

The present invention can also be seen as an invention of base paper for coated white paperboard.

The coated white paperboard base paper of the present invention has at least three layers, a surface layer, a subsurface layer, and a back layer, and is characterized in that the surface layer does not contain a sizing agent, and the subsurface layer contains a sizing agent. With this configuration, a coated white paperboard base paper with excellent coating suitability for the pigment coating layer can be obtained.

The present invention makes it possible to provide a coated white paperboard that has low density and excellent suitability for gravure printing.

FIG. 1 is a diagram showing a schematic diagram of an example of the configuration of a coated white paperboard. 1 is a table showing the physical properties of coated white paperboard obtained in the examples and comparative examples.

Next, the present invention will be described in detail with reference to an embodiment, but the present invention should not be interpreted as being limited to these descriptions. Various modifications of the embodiment may be made as long as the effects of the present invention are achieved.

The coated white paperboard according to this embodiment has a base paper for coated white paperboard, which has at least three layers, a surface layer, a lower surface layer, and a back layer, and a pigment coating layer applied to the surface layer. An example of the structure of the coated white paperboard according to the present invention is shown in FIG. 1. In the figure, 1 is a coated white paperboard, 10 is a base paper for coated white paperboard (hereinafter, sometimes referred to as a base paper), 11 is a surface layer, 12 is a lower surface layer, 13 is a back layer, 13a is an upper back layer, 13b is a lowermost back layer, 14 is a pigment coating layer, 14a is a topmost coating layer, and 14b is a bottommost coating layer. Also, the thickness of each layer in FIG. 1 is not proportional to the actual thickness.

Figure 1(a) shows an example of a structure in which one pigment coating layer 14 is provided on a four-layer coated white board base paper 10 in which the surface layer 11 is a one-layer structure, the undersurface layer 12 is a one-layer structure, and the back layer 13 is a two-layer structure. Figure 1(b) shows an example of a structure in which two pigment coating layers 14 are provided on a five-layer coated white board base paper 10 in which the surface layer 11 is a one-layer structure, the undersurface layer 12 is a one-layer structure, and the back layer 13 is a three-layer structure. In the example of Figure 1(a), the back layer 13 is composed of two layers of the same structure, and in the example of Figure 1(b), the bottom layer 13b on the back side of the back layer 13 is composed of a different structure from the top layer 13a on the inside.

In the present invention, the surface layer preferably has a coating suitability for the pigment coating layer, a certain degree of whiteness and opacity, and does not contain impurities. The pulp used for the surface layer is preferably a pulp with a relatively high whiteness, and examples of such pulp include high-quality waste paper such as white paper, ruled white paper, card, imitation paper, colored paper, Kent, white art, and milk carton, or fresh pulp. When high-quality waste paper is used, in order to remove impurities and ensure whiteness, it is preferable to perform kneading to reduce the ink and impurities, deinking with a floater, and bleaching and washing with hydrogen peroxide and FAS. In addition, if the opacity is insufficient, it is preferable to appropriately supplement it with a filler.

The disintegrated freeness of the surface layer pulp is preferably in the range of CSF 200 to 500 ml, and more preferably 250 to 400 ml. If the CSF is less than 200 ml, not only will the density increase, but drainage in the wire part will deteriorate, and there is a risk that the wet sheet will collapse during pressurized water squeezing in the press part in the next process, making production impossible. On the other hand, if the CSF exceeds 500 ml, the inter-fiber bonds will be weak, and the paper strength will decrease, making it unlikely that it will be able to withstand printing. In addition, when processing into boxes, there is a risk that the weak bending strength of the surface layer will make the crease lines more likely to crack. In addition, the disintegrated freeness of the pulp of each layer in the present invention is determined by separating the base paper into each layer, adjusting the solid concentration to 1% by mass using a Tappi disintegrator (based on JIS P 8220:1998 "Pulp - Disintegration method"), disintegrating the slurry for 25 minutes, and measuring the slurry with a Canadian Standard Freeness Tester (based on JIS P 8121:1995 "Test method for freeness of pulp").

In the present invention, the undersurface layer preferably has sizing properties and a certain degree of whiteness, and does not contain impurities. The whiteness of the undersurface layer is preferably intermediate between that of the surface layer and the back layer, and if the whiteness of the undersurface layer is too low, there is a risk that color unevenness will be visually observed through the coating layer and the surface layer. As an example, it is preferable that the whiteness of each layer is about 70 to 80% for the surface layer, 50 to 60% for the undersurface layer, and about 45% for the back layer.

The underside layer is mainly made of recycled paper pulp, but considering the effect of whiteness on the surface of the coated whiteboard, it is preferable to use recycled paper pulp with a relatively high whiteness. This structure can prevent uneven whiteness on the surface of the coated whiteboard due to transparency. In the coated whiteboard according to this embodiment, the raw material of the recycled paper pulp used for the underside layer is not particularly limited, but examples include high-quality recycled paper such as white paper, ruled white paper, card, imitation, colored paper, Kent, white art, and milk carton, and medium-quality recycled paper such as newspapers, magazines, cut paper, medium-quality waste paper, brown imitation, cardboard, mount paper and ground paper, and cardboard. If necessary, it is preferable to bleach the paper with hydrogen peroxide or the like, deink the paper with a floater, and refine the ink and impurities by kneading.

In the coated whiteboard according to this embodiment, a sizing agent is not blended in the surface layer, but is blended in the undersurface layer. In order to improve gravure suitability, cushioning and surface smoothness are necessary, and the sizing agent contributes to cushioning. When providing a pigment coating layer on the surface of the base paper, it is necessary to blend a sizing agent in the base paper to prevent excessive penetration of the coating liquid into the base paper. The layer containing the sizing agent has the inhibitory effect of the sizing agent on the interfiber bonds, and becomes a bulkier layer than when the sizing agent is not blended. By making the layer containing the sizing agent a bulkier layer, the cushioning of the entire coated whiteboard paper is improved, and it is expected that the suitability for gravure printing will be improved. However, if a sizing agent is blended in the surface layer to increase the bulk, the smoothness of the surface layer will be impaired, and as a result, the suitability for gravure printing will be impaired. Another problem is that if a sizing agent is included in the surface layer, the coating liquid will be less likely to penetrate into the surface layer when the pigment coating layer is provided, and the adhesive components in the pigment coating layer will be distributed in large amounts on the surface of the pigment coating layer. This reduces the ink setting properties, ultimately resulting in poor suitability for gravure printing.

In the present invention, therefore, no sizing agent is blended in the surface layer, but in the subsurface layer. This configuration enhances the cushioning of the entire coated white ball without impairing the smoothness or ink setting of the surface layer, improving suitability for gravure printing. Examples of sizing agents used here include fatty acid-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), reinforced rosin sizing agents, and rosin emulsion sizing agents. Of these, fatty acid-based sizing agents are particularly preferred, as they exhibit a sizing effect on the papermaking machine and are not easily affected by the papermaking pH.

The content of sizing agent in the undersurface layer is preferably in the range of 0.1 to 0.8% by mass relative to the pulp, and more preferably in the range of 0.2 to 0.6% by mass. If the content is less than 0.1% by mass, the water-soluble components of the coating liquid for the pigment coating layer will penetrate too much into the base paper, resulting in powder falling off from the surface of the pigment coating layer. Conversely, if the content exceeds 0.8% by mass, the high sizing of the undersurface layer may cause too much of the water-soluble components of the coating liquid for the pigment coating layer to remain on the surface of the base paper, resulting in low ink absorbency and reduced suitability for gravure printing.

In the present invention, the back layer does not need to have whiteness, but the purpose is to reduce the amount of impurities in the layer that comes into contact with the surface of the coated white paperboard, and to cover the basis weight when a certain basis weight is required for the entire coated white paperboard. In the coated white paperboard according to this embodiment, for example, when it is made into a coated white board, it is preferable to use recycled paper pulp for the back layer. There is no limit to the recycled paper pulp used, but in order to prevent the inclusion of sticky foreign matter, it is preferable to perform a dust removal process, and further a kneading process. The most preferable order is to perform the kneading process after the dust removal process. This is because when the coated white paperboard is made into a rolled product or a flat product form, the front and back of the coated white paperboard come into contact, and if sticky foreign matter gets mixed in the back layer, the surface may be contaminated by the transfer of the sticky foreign matter, causing problems. In addition, when a pigment coating layer is not provided on the back side, it is preferable not to increase the whiteness too much in order to make the impurities less noticeable, and it is also preferable not to perform a process to increase the whiteness, such as deinking or bleaching.

In the present invention, the back layer may be two or more layers depending on the required basis weight. When the back layer is two or more layers, two or more layers of the same composition may be provided, or two or more layers of different raw material compositions may be provided. When providing multiple back layers with different raw material compositions, it is preferable to use mainly medium-quality waste paper for the upper back layer (see FIG. 1(b) 13a) that is not exposed on the back side even though it is a back layer, and not to perform kneading, deinking, bleaching, etc. for refining impurities. By eliminating unnecessary processing, it is possible to avoid using unnecessary energy and to suppress the release of alkali elution and ash from waste paper pulp into the environment, which is preferable from the environmental and cost perspectives. The bottom layer of the back layer (see FIG. 1(b) 13b) that is exposed on the back side may be configured in the same way as when the back layer is provided as a single layer.

In addition to the above, the pulp used in each layer may be fresh pulp such as bleached hardwood sulfite pulp (LBSP), bleached hardwood kraft pulp (LBKP), bleached softwood sulfite pulp (NBSP), bleached softwood kraft pulp (NBKP), mechanical pulp (GP, TMP, BCTMP), etc., which may be used as appropriate depending on the purpose. Note that "fresh pulp" here does not refer to recycled waste paper, but is pulp made directly from wood or non-wood materials, and is also called virgin pulp.

In the coated white paperboard according to this embodiment, fillers may be blended into each layer. Examples of fillers that may be used include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, calcined clay, titanium dioxide, and aluminum hydroxide. Among fillers, light calcium carbonate and heavy calcium carbonate are excellent in improving whiteness and opacity, so when a low-whiteness DIP (De-Inked Pulp) is used in the back layer, it is preferable to blend these fillers in the surface layer to improve the whiteness and opacity of the surface layer.

In the coated white paperboard according to this embodiment, in addition to the pulp, filler and sizing agent, various auxiliary agents such as aluminum sulfate, cationic starch or polyacrylamide-based internal paper strength enhancers, retention improvers, drainage improvers, bulking agents, colored dyes, colored pigments, fluorescent brighteners, fluorescent decolorizing agents or pitch control agents may be blended in each layer to the extent that the intended effect of the present invention is not impaired.

In the coated white paperboard according to this embodiment, various papermaking aids can be applied to the surface of the front layer and/or back layer to the extent that the intended effect of the present invention is not impaired. For example, starches, paper strength agents such as polyvinyl alcohol and polyacrylamide, various dyes, and fluorescent dyes can be used. There are no particular limitations on the application method, and known application machines such as a type equipped with a pond such as a size press, a film metering type such as a gate roll size press or a shim sizer, a rod coater, or an air knife coater can be used.

The basis weight of each layer is not particularly limited, but it is preferable that the surface layer has a basis weight of 15 to 80 g/ ^m2 , more preferably 30 to 60 g/ ^m2 , and the undersurface layer has a basis weight of 15 to 80 g/ ^m2 , more preferably 20 to 60 g/ ^m2 . If the basis weight of the surface layer is too large or the basis weight of the undersurface layer is too small, the effect of the present invention, which is achieved by not incorporating a sizing agent in the surface layer but incorporating a sizing agent in the undersurface layer, may be poor. The basis weight of the back layer is not particularly limited, and is, for example, 10 to 500 g/ ^m2 , and the back layer may be composed of multiple layers.

In the coated white paperboard according to this embodiment, a pigment coating layer containing a pigment and an adhesive is provided on the surface of the surface layer. Two or more pigment coating layers may be provided as necessary. When two or more pigment coating layers are provided, the uppermost coating layer that becomes the outer surface is referred to as the uppermost coating layer, and the lowermost coating layer that contacts the surface layer is referred to as the lowermost coating layer. The pigments used in the pigment coating layer are preferably refined natural mineral pigments such as kaolin, heavy calcium carbonate (ground calcium carbonate), light calcium carbonate, and organic pigments. These may be used alone or in combination of two or more. The other pigments are not particularly limited, and for example, at least one of talc, satin white, lithopone, titanium dioxide, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate, and calcined kaolin can be used.

In the coated white paperboard according to this embodiment, examples of adhesives used in the pigment coating layer include various copolymer latexes such as styrene-butadiene, acrylic, polyvinyl acetate, or ethylene-vinyl acetate, polyvinyl alcohol, modified polyvinyl alcohol, polyacrylamide, urea or melamine/formalin resin, polyethyleneimine, or polyamidepolyamine/epichlorohydrin. Further examples include starch purified from natural plants, hydroxyethylated starch, oxidized starch, etherified starch, phosphate esterified starch, enzyme-modified starch, or cold water-soluble starch obtained by flash drying thereof, natural polysaccharides such as dextrin, mannan, chitosan, arabinogalactan, glycogen, inulin, pectin, hyaluronic acid, carboxymethylcellulose, and hydroxyethylcellulose, or oligomers or modified forms thereof. Other examples include natural proteins such as casein, gelatin, soybean protein, and collagen, or modified forms thereof, and synthetic polymers or oligomers such as polylactic acid and peptides. These may be used alone or in combination of two or more.

When two or more pigment coating layers are provided, the topmost coating layer, which is the outer surface, needs to be strong, and it is preferable to use styrene-butadiene copolymer latex (SBR). Specifically, when two or more pigment coating layers are provided, the topmost coating layer preferably contains 10 parts by mass or more of SBR per 100 parts by mass of pigment, and more preferably 12 parts by mass or more. There are no particular restrictions on the amount of SBR used in coating layers other than the topmost coating layer, but even if SBR is used, it is preferable to use a smaller amount than in the topmost coating layer.

In addition, when two or more pigment coating layers are provided, it is preferable that the top coating layer has a strength suitable for box-making. If the strength of the top coating layer is insufficient during box-making, it may crack when bent, and the function of the box may not be maintained. In order to make the top coating layer less likely to crack when bent, it is preferable to minimize the amount of starch-based adhesive blended. Specifically, the content of starch-based adhesive in the top coating layer of the pigment coating layer is preferably 1 part by mass or less per 100 parts by mass of pigment, and more preferably 0.5 parts by mass or less. There are no particular restrictions on the amount of starch-based adhesive blended for coating layers other than the top coating layer, but although not as strict as for the top coating layer, it is preferable that the amount of starch-based adhesive blended for the other coating layers is not too large.

In the coated white paperboard according to this embodiment, the paint for the pigment coating layer may contain various commonly used auxiliary agents such as dispersants, defoamers, water-resistant agents, coloring dyes, coloring pigments, and thickeners, or cationized versions of these various auxiliary agents, as necessary.

In the coated white paperboard according to this embodiment, the method of applying the coating liquid for the pigment coating layer is not particularly limited, and various methods such as various film transfer coaters such as a metering size press and a sim sizer, an air knife coater, a rod coater, a blade coater, a direct fountain coater, a spray coater, and a curtain coater are appropriately used. Here, it is preferable to use a scraping method, such as a rod coater or a blade coater, for coating the pigment coating layer, which is the bottom layer. By increasing the smoothness of the base, the smoothness of the final top layer can be improved, and as a result, suitability for gravure printing with fewer missed dots can be easily obtained.

In the coated white paperboard according to this embodiment, the thickness of the pigment coating layer is preferably 3 to 20 μm, and more preferably 8 to 17 μm. If the desired coating amount is not achieved with one coating, coating may be repeated two or more times. If the thickness of the pigment coating layer is less than 3 μm, the rate of missed dots during gravure printing will deteriorate, and the desired print gloss may not be achieved. On the other hand, if the thickness of the pigment coating layer exceeds 20 μm, the strength of the coating layer will decrease, and paper dust or powder falling will occur during punching or box making, which may cause serious problems.

To reduce the rate of missed dots, which is important in gravure printing, it is preferable to form the pigment coating layer in two or more layers rather than in one layer. By forming two or more pigment coating layers, the bottommost coating layer exerts an anchor effect, improving the smoothness of the surface of the topmost pigment coating layer and reducing the rate of missed dots. When forming two or more pigment coating layers, the thickness of the bottommost pigment coating layer is preferably 2 μm or more, and more preferably 3 μm or more. If it is less than 2 μm, it is not possible to sufficiently fill the recesses present on the surface of the base paper, and the effect of reducing the rate of missed dots is poor. On the other hand, if it exceeds 15 μm, the strength of the coating layer decreases, and paper dust or powder falling is likely to occur during punching or box making.

In the coated white paperboard according to this embodiment, a coating liquid called a backing liquid or anti-curling liquid (hereinafter referred to as backing liquid or anti-curling liquid) may be applied to the surface of the back layer in order to prevent curling. The backing liquid may be an aqueous solution of a known water-soluble polymer such as starch, polyvinyl alcohol, or polyacrylamide. In addition to the water-soluble polymer, the backing liquid may also contain a sizing agent, a colorant, or a fluorescent dye as an auxiliary. There is no particular limitation on the method for applying the backing liquid, but known coaters such as a film metering type such as a Sim Sizer, a rod coater, a blade coater, or an air knife coater may be used.

The coated white board according to this embodiment may be subjected to a calendaring process to improve smoothness, a luster press process to increase gloss, or other processes depending on the application.

The coated white paperboard according to this embodiment preferably has a density of 0.77 to 0.87 g/ ^cm3 , and more preferably 0.81 to 0.86 g/ ^cm3 . If the density is less than 0.77 g/ ^cm3 , not only will the paper peel off due to a decrease in printing strength, but the stiffness of the coated white paperboard itself will decrease, which may reduce workability such as transportation. In addition, if the paper becomes too bulky, it will tend to have low smoothness, which may worsen the rate of missed dots during gravure printing. On the other hand, if the density exceeds 0.87 g/ ^cm3 , the paper will tend to have poor cushioning properties, which may worsen the rate of missed dots during gravure printing. In addition, the paper will be relatively heavy, which is unfavorable for the environment as it requires a large amount of energy to transport.

In the coated whiteboard according to this embodiment, the PPS measurement value of the pigment coating layer surface is preferably 1.5 μm or less, more preferably 1.3 μm or less, and even more preferably 1.1 μm or less. There is no particular limit to the lower limit of the PPS measurement value, but if calendaring is performed to reduce the PPS measurement value, the density increases, the cushioning properties are impaired, and there is a risk of impairing suitability for gravure printing. Therefore, it is preferable that the PPS measurement value is 0.5 μm or more. The PPS measurement value is an index of smoothness, and if this value is within the above range, it is easy to reduce the rate of missed dots during gravure printing. Note that the clamping pressure and packing material can be selected for PPS, and in this invention, the conditions of clamping pressure of 1000 kPa and use of hard packing are selected as conditions that are likely to correlate with suitability for gravure printing. In addition to calendaring, the PPS measurement value of the pigment coating layer surface can also be adjusted by changing the composition of the pigment coating layer. In general, it is easier to increase the PSS measurement value by increasing the amount of coating or by increasing the amount of flat pigment used as a pigment.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of parts added is a value calculated as the solid content.

The following evaluations were carried out on the coated white paperboards of the Examples and Comparative Examples. The evaluation results are shown in Figure 2. The evaluation methods are as follows:

<Evaluation of suitability for gravure printing: PPS smoothness measurement>
Measurements were made according to JIS P8151:04 Paper and paperboard - Surface roughness and smoothness test method (air leak method) - Print surf tester method, with a clamp pressure of 1000 kPa and hard packing.

<Density>
Measurements were made in accordance with JIS P8118:14 Paper and paperboard -- Test methods for thickness, density and specific volume.

Printing was performed using a halftone gravure plate with a Ministry of Finance Printing Bureau type gravure printability tester (manufactured by Kumagai Riki Kogyo Co., Ltd.), and the missing dots in the 10 to 70% halftone dot area were visually evaluated, and the setting property was evaluated by rubbing the solid area with a finger immediately after printing. The ink used was OGH91 Sumi manufactured by Toyo Ink Mfg. Co., Ltd.
Missing dot evaluation
.circle-solid.: No missing dots, good.
◯: Very few missing dots, good.
△: A few missing dots are observed (lower limit of use).
×: Missing dots are clearly visible. (Not available)
<Setting evaluation>
⊚: Does not come off even when rubbed with fingers. Good.
○: Does not come off even when rubbed with fingers. Good.
△: When rubbed with a finger, a small amount of ink was transferred to the finger (lower limit of use).
×: When rubbed with a finger, the ink stains the finger. (Not for use)

Example 1
<Preparation of base paper>
The surface layer was formed using 90 parts of high-quality recycled paper pulp adjusted to a CSF of 300 ml, 10 parts of softwood bleached kraft pulp (N-BKP) adjusted to a CSF of 500 ml, heavy calcium carbonate (manufactured by Imerys Mineral Japan, product name: Carbital 90) with an ash content of 3 mass% relative to the mass of pulp, and 0.5 parts of aluminum sulfate per 100 mass parts of pulp as a coagulation aid.
The lower surface layer was formed using 100 parts of unbeaten waste paper pulp that had been deinked and bleached from 300 ml of CSF recycled newspaper, 2.0 parts by mass of aluminum sulfate per 100 parts by mass of pulp as a flocculation aid, and 0.4 parts by mass of a fatty acid-based sizing agent (manufactured by Arakawa Chemical Industries, Ltd., product name: Size Pine CA956) per 100 parts by mass of pulp as a sizing agent.
The upper back layer was formed of three layers using 100 parts of unbeaten waste paper pulp obtained by removing dust from waste magazine paper having a CSF of 300 ml, and 2.0 parts by mass of aluminum sulfate as a flocculating aid relative to 100 parts by mass of pulp.
The bottommost back layer was made of 100 parts of unbeaten waste paper pulp obtained by removing dust from waste newspapers with a CSF of 300 ml. The paper was made at a speed of 200 m/min using a short wire combination papermaking machine to obtain a base paper for coated white cardboard with a total basis weight of 310 g/ ^m2 consisting of six layers: one surface layer, one undersurface layer, and four back layers. The basis weight of the surface layer was 40 g/ ^m2 , the basis weight of the undersurface layer was 30 g/ ^m2 , the basis weight of each of the three upper back layers was 70 g/ ^m2 , and the basis weight of the bottommost back layer was 30 g/ ^m2 . In addition to the above-mentioned raw materials, a paper strength agent, polyacrylamide (manufactured by Arakawa Chemical Industries, Ltd., product name: Polystron 619), was added to each of the six layers in an amount of 0.4 part per 100 parts by mass of pulp, and a retention aid (manufactured by Kurita Water Industries, Ltd., product name: HH220) was added to each of the six layers in an amount of 0.03 part per 100 parts by mass of pulp.

<Formation of coating layer on the surface>
A paint for a lowermost coating layer was prepared by dispersing in water 20 parts of kaolin (trade name: Hydrasperse, manufactured by Keimin Co., Ltd.) and 80 parts of wet heavy calcium carbonate (trade name: Carbital 60, manufactured by Imerys Minerals Japan Co., Ltd.) as pigments, 12 parts of SBR (styrene-butadiene rubber) latex (trade name: B-1541, manufactured by Asahi Kasei Chemical Corporation) as adhesives, and 3 parts of urea phosphate esterified starch. Furthermore, 30 parts of kaolin (manufactured by Kadam, product name: Amazon SB) as a pigment, 60 parts of wet heavy calcium carbonate (manufactured by Imerys Minerals Japan, product name: Carbital 90) and 10 parts of titanium oxide (manufactured by DuPont, product name: RPS-Vantage) as a pigment, and 13 parts of SBR-based latex (manufactured by Asahi Kasei Chemical Corporation, product name: B-1541) as an adhesive were dispersed in water to prepare a paint for the uppermost coating layer.
Next, the paint for the bottom coating layer was applied to the surface of the obtained base paper for coated white board with a rod coater so that the coating amount was 8 g/ ^m2 in solid content, and then dried to provide an undercoat layer. Next, the paint for the top coating layer was applied to the bottom coating layer with a rod coater so that the coating amount was 7 g/ ^m2 in solid content, and then dried to form a top coating layer.

<Application of anti-curl solution to back layer>
Next, a 1% paste solution of oxidized starch (manufactured by Nippon Shokuhin Kako Co., Ltd., product name: MS#3800) was applied to the surface of the bottom layer of the back layer of the coated white board base paper on which the bottom and top coating layers were formed, using a rod coater to a solid content of 0.1 g/ ^m2 , and then dried.

<Smoothing processing>
Next, a calendaring treatment was carried out at a linear pressure of 50 kg/cm, and then the surface was treated with a luster press at 80 kg/cm and 140° C. to obtain a coated white paperboard according to Example 1.

Example 2
A coated white paperboard according to Example 2 was obtained in the same manner as in Example 1, except that the addition ratio of the fatty acid-based sizing agent used in the undersurface layer was changed from 0.4 parts to 0.2 parts.

Example 3
A coated white paperboard according to Example 3 was obtained in the same manner as in Example 1, except that the addition ratio of the fatty acid-based sizing agent used in the undersurface layer was changed from 0.4 parts to 0.6 parts.

Example 4
A coated white paperboard according to Example 4 was obtained in the same manner as in Example 1, except that the fatty acid-based sizing agent used in the lower surface layer was changed to a rosin emulsion sizing agent (Size Pine NT78, manufactured by Arakawa Chemical Industries Co., Ltd.).

Example 5
A coated white paperboard according to Example 5 was obtained in the same manner as in Example 1, except that the smoothing process was performed at a line pressure of 50 kg/cm to 100 kg/cm, and the basis weight of the back layer and upper layer was changed from 70 g/ ^m2 to 75 g/ ^m2 .

Example 6
A coated white paperboard according to Example 6 was obtained in the same manner as in Example 1, except that the line pressure during the smoothing process was changed from 50 kg/cm to 20 kg/cm, and the basis weight of the back layer and upper layer was changed from 70 g/ ^m2 to 65 g/ ^m2 , respectively.

(Comparative Example 1)
A coated white paperboard according to Comparative Example 1 was obtained in the same manner as in Example 1, except that 0.4 parts of the fatty acid-based sizing agent used in the subsurface layer was added to the surface layer.

As is clear from Figure 2, the coated white paperboards of Examples 1 to 6 all had low PPS values and were excellent in suitability for gravure printing. In contrast, the coated white paperboard of Comparative Example 1 used a sizing agent in the surface layer as well, which caused resins such as latex to be localized on the surface, resulting in poor ink absorption and making the paper unsuitable for practical use in terms of both missing dot evaluation and setting properties.

REFERENCE SIGNS LIST 1 Coated white paperboard 10 Base paper for coated white paperboard 11 Surface layer 12 Surface lower layer 13 Back layer 13a Back upper layer 13b Back lowermost layer 14 Pigment coating layer 14a Top coating layer 14b Bottom coating layer

Claims (7)

A coated white paperboard having a base paper for coated white paperboard having at least three layers, i.e., a surface layer, a subsurface layer, and a back layer, and a pigment coating layer applied to the surface layer,
The coated white paperboard has two or more pigment coating layers, the uppermost coating layer of the pigment coating layers contains 10 parts by mass or more of styrene-butadiene copolymer latex (SBR) per 100 parts by mass of pigment, the surface layer does not contain a sizing agent, and the undersurface layer contains a sizing agent. The coated white paperboard according to claim 1, characterized in that the sizing agent is a fatty acid-based sizing agent. The coated white paperboard according to claim 2, characterized in that the amount of the sizing agent is 0.1 to 0.8% by mass relative to 100% by mass of pulp. 4. The coated white paperboard according to claim 1, wherein the thickness of the lowermost coating layer in contact with the surface layer among the pigment coating layers is 2 μm or more. 2. The coated white paperboard according to claim 1, wherein the PPS measurement value of the surface of the uppermost coating layer is 1.5 μm or less. The coated white paperboard according to claim 1, characterized in that the disintegrated freeness of the surface layer pulp, which is the raw material for the surface layer, is 200 to 500 ml CSF. 2. The coated white paperboard according to claim 1, characterized in that it has a density of 0.77 to 0.87 g/cm ³ .

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