JP6954259B2 - White paperboard and coating white paperboard - Google Patents

Description

The present invention relates to white paperboard. More specifically, the present invention relates to a multi-layered white paperboard having excellent rigidity and smoothness.

In the white paperboard composed of multi-layer papermaking having a surface layer, a middle layer, and a back layer, each layer is independently formed into a paper layer and is made together. The white paperboard includes a coating type in which a pigment coating layer is provided on the surface of the surface layer or both the surface layer and the back layer, and a non-coating type in which the pigment coating layer is not provided.
White paperboard is generally used for paper containers (boxes, blister packs, etc.), paper products (sample book mounts, albums, etc.), publishing (magazines, books, etc.), commercial printing (catalogs, pamphlets, etc.), etc. ing.

White paperboard is required to have printability, especially offset printing. In order to obtain printability, it is important to improve the smoothness of the surface layer in both the coated type and the non-coated type.
White paperboard is also required to have a certain degree of bulkiness. Therefore, Patent Document 1 proposes to obtain a bulky and smooth coating type white paperboard by containing a specific ester compound (Patent Document 1).

Japanese Patent No. 3041300

When white paperboard is used for packaging containers, high rigidity is required in addition to printability. In order to increase the rigidity, it is conceivable to increase the basis weight and increase the thickness. This is because the rigidity is proportional to the cube of the thickness.
In Patent Document 1, both bulkiness and smoothness are achieved, but the basis weight of the obtained white paperboard is less than ^{350 g / m 2.} In order to obtain further rigidity, it is required to secure a thickness with a basis weight of ^{500 g / m 2 or more.}
However, when the basis weight is further increased, it becomes more difficult to secure the smoothness of the surface layer, and it becomes difficult to secure the printability.

Therefore, in the case of white paperboard having a basis weight of 500 g / m ² or more, calendar processing is performed to smooth the surface layer. However, since the thickness is reduced by the calendar processing, high rigidity cannot be obtained even though the basis weight is increased.
Therefore, it is necessary to further increase the basis weight so that the thickness is sufficient even after the calendar processing.
However, if the basis weight is increased unnecessarily, not only the cost increases due to the increase in raw materials, but also the dehydration load of the wire increases, which makes it difficult to adjust the formation and causes an adverse effect such as an increase in waste paper.
In view of the above circumstances, it is an object of the present invention to obtain a white paperboard having high rigidity and surface smoothness without increasing the basis weight.

In order to achieve the above problems, the present invention has adopted the following configuration.
[1] A multi-layer paperboard that has a surface layer, one or more middle layers, and a back layer.
The total basis weight of the white paperboard is 500 to 570 ^{g / m 2} , and the density is 0.80 g / m ³ or less.
A white paperboard characterized in that at least one of the middle layers has an application amount of 50 to 100 g / m ² and a formation index of 5.0 (od) or less.
[2] The middle layer, which is not in contact with either the surface layer or the back layer, has an application amount of 50 to 100 g / m ² and a formation index of 5.0 (od) or less. The white paperboard according to [1].
[3] At least the middle layer in contact with the surface layer has an application amount of 50 to 100 g / m ² and a formation index of 5.5 (od) or less, [1] or [2]. White paperboard described in.
[4] In the middle layer, all the layers have an application amount of 50 to 150 g / m ² , and the formation index is 6.5 (od) or less, [1] to [ 3] The white paperboard according to any one of the items.
[5] A coated white paperboard provided with a pigment coating layer on at least one surface of the white paperboard according to any one of [1] to [4].

In the present invention, in a white paperboard having a large basis weight, the amount of the middle layer fixed within a certain range from the operability such as dehydration load and the formation index of the middle layer measured by the image analysis method are measured on the surface of the white paperboard. It was made by finding that it correlates with dehydration.
The white paperboard of the present invention has high rigidity and is excellent in surface smoothness required for printability.

[White paperboard]
The white paperboard in the present invention is a multi-layer papermaking in which a surface layer, a middle layer, and a back layer are laminated. The surface layer is the layer arranged on the outermost side in the base paper of multi-layer paper making, the back layer is the layer arranged on the back side (opposite side to the front layer), and the middle layer is the surface layer and the back layer. It is a layer arranged between. The middle layer is usually formed of multiple layers. The middle layer in contact with the surface layer may be a lower surface layer using a paper material having a higher quality than the other middle layers. Further, the middle layer in contact with the back layer may be a back lower layer using a paper material having a higher quality than the other middle layers.

The basis weight of the entire white paperboard of the present invention is 500~570g / ^{m 2,} is preferably 520~570g / ^{m 2,} and more preferably 550~565g / ^{m 2.} When the basis weight of the entire white paperboard is 500 g / m ² or more, it is possible to secure a thickness capable of obtaining sufficient rigidity. Further, if it is 570 g / m ² or less, the cost increase due to the increase in raw materials is avoided, and the dehydration load of the wire is not excessive.
The basis weight of the entire white paperboard is the total weight per unit area including the surface layer, the middle layer, and the back layer. In a coated white paperboard in which a pigment coating layer is provided on at least one surface of the white paperboard, the basis weight of the entire white paperboard does not include the weight of the pigment coating layer.

The density of the entire white paperboard of the present invention is 0.80 g / ^{m 3} or less, preferably 0.75~0.80g / ^{m 3,} a 0.77~0.79g / ^{m 3} Is more preferable.
A density of 0.80 g / m ³ or less means that the calendar has not been subjected to high pressure calendar processing.
The calendar processing preferably performs the calendar linear pressure at 30 kN / m or less, and more preferably at 20 kN / m or less. On the other hand, it is preferable to perform the calendar linear pressure at 5 kN / m or more. Moreover, it is preferable not to perform the calendar processing unless the effect of the present invention is impaired.

It is not calendared with high pressure and has a low density, so even if the total basis weight of the white paperboard is 570 g / m ² or less, a thickness that can obtain sufficient rigidity is secured. can.
The density of the entire white paperboard is the weight per unit volume of the surface layer, the middle layer, and the back layer. In a coated white paperboard in which a pigment coating layer is provided on at least one surface of the white paperboard, the density of the entire white paperboard does not depend on the density of the pigment coating layer.

The total thickness of the white paperboard of the present invention is preferably 65 to 75 μm, more preferably 68 to 73 μm, and even more preferably 70 to 71 μm.
The thickness of the entire white paperboard is the total thickness of the surface layer, the middle layer, and the back layer. In a coated white paperboard in which a pigment coating layer is provided on at least one surface of the white paperboard, the thickness of the entire white paperboard does not include the thickness of the pigment coating layer.

The rigidity (longitudinal direction) of the entire white paperboard of the present invention is preferably 60 to 70 mN · m, more preferably 62 to 68 mN · m, and even more preferably 63 to 65 mN · m. ..
When the rigidity of the entire white paperboard is 60 mN · m or more, the handleability as a packaging container can be improved.
The larger the thickness of the entire white paperboard, the easier it is to increase the rigidity of the entire white paperboard. In addition, the higher the basis weight, the easier it is to increase the rigidity of the entire white paperboard.
The rigidity of the entire white paperboard is the rigidity obtained by laminating the surface layer, the middle layer, and the back layer. In a coated white paperboard in which a pigment coating layer is provided on at least one surface of the white paperboard, the rigidity of the entire white paperboard is the rigidity before the pigment coating layer is provided.

Further, the Oken-type smoothness of the surface layer surface of the white paperboard of the present invention is preferably 150 to 500 seconds, more preferably 200 to 400 seconds, and further preferably 210 to 300 seconds.
If the surface layer surface of the white paperboard has a smoothness of 150 seconds or more, it is easy to obtain sufficient printability. Further, even in a coated white paperboard in which a pigment coating layer is provided on the surface of the surface layer, sufficient printability can be easily obtained.

Further, the bokeh index obtained by the following method on the surface layer surface of the white paperboard of the present invention is preferably 1.50 to 2.20 μm, more preferably 1.7 to 2.2 μm. It is more preferably 0 to 2.2 μm.
When the unevenness index on the surface layer surface of the white paperboard is 2.2 μm or less, sufficient printability can be easily obtained. Further, even in a coated white paperboard in which a pigment coating layer is provided on the surface of the surface layer, sufficient printability can be easily obtained.
(Bokotsuki index)
The surface unevenness of the surface layer of the white paperboard is acquired as a 3D image, the acquired 3D image is frequency-analyzed, and the standard deviation of the unevenness variation component having a period of 2 to 10 mm is used as the bump index.

Oken-type smoothness represents smoothness by the time it takes for air to leak from the gap between the measuring head and the test piece. During the test, a constant pressure is applied to the test piece and the measuring ring to press them, so the evaluation is performed under pressure.
On the other hand, the Bokotsuki index is an evaluation in a state where no pressure is applied because the height of the 3D image obtained optically in a non-contact manner is quantified to represent the unevenness of the surface. Therefore, the surface smoothness can be evaluated in a state closer to the situation at the time of printing.

In addition, while the Oken method targets everything from micro-roughness to macro-roughness, the Bokotsuki index allows the measurement area to be limited. In the present invention, the unevenness variation component having a period of 2 to 10 mm, which is considered to easily affect the printability, is evaluated.
A specific method for obtaining the Bokotsuki index will be described in detail in Examples.

The white paperboard in the present invention is mainly composed of pulp containing used paper pulp.
Recycled paper pulp is pulp obtained by reusing used paper.
As used paper, for example, paper that has been used once but has few printed parts, such as top white and ruled white, printed matter such as cards, imitation, color top, Kent, and white art, and colored paper that has been used once. Used high-quality waste paper such as coated paper for printing, beverage packs, office paper, business-related medium-quality waste paper such as tickets, medium-quality anti-old paper, and Kent Manila, general medium-quality waste paper such as newspapers, magazines, and miscellaneous paper. Examples include cut tea, plain tea, miscellaneous bags, and used tea-based paper such as cardboard. Recycled paper such as office paper and tickets having confidentiality may be shredded products.
As the used paper pulp, unbleached pulp obtained by disintegrating the used paper, unbleached deinked pulp subjected to the disintegration treatment and deinking treatment, bleached deinking pulp subjected to the deinking treatment and then bleaching treatment, and the like can be appropriately used.

Examples of so-called virgin pulp that is not used paper pulp include coniferous unbleached kraft pulp (NUKP), broadleaf unbleached kraft pulp (LUKP), coniferous bleached kraft pulp (NBKP), broadleaf bleached kraft pulp (LBKP), and broadleaf bleached kraft pulp (LBKP). Chemical pulp such as kraft pulp (LSBKP), coniferous semi-bleached kraft pulp (NSBKP), broadleaf tree sulfite pulp, coniferous sulfite pulp, thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemigrand pulp (CGP), refiner Examples thereof include mechanical pulp such as ground pulp (RGP), ground pulp (GP), pressurized stone ground pulp (PGW), and stone ground pulp (SGP).

The blending ratio of the used paper pulp can be appropriately adjusted for each layer according to the role of each layer. Further, the type of used paper pulp used for each layer can be appropriately selected for each layer according to the role of each layer.
In any layer, two or more kinds of used paper pulp may be mixed and used. When virgin pulp is used, two or more kinds of virgin pulp may be mixed and used. Further, virgin pulp and used paper pulp may be mixed and used.
Hereinafter, the ordinary pulp composition and the like in each layer will be described, but the present invention is not limited to the following ordinary pulp composition and the like.

Pulp with high whiteness is usually used for the surface layer. For example, the above-mentioned virgin pulp and deinked pulp of used paper can be mainly used. As the used paper, it is preferable to use used paper having a high degree of whiteness such as fine white / card, special white / medium white / white Manila, and imitation / color.

The surface layer of the marked amount is preferably set to 70~150g / ^{m 2,} and more preferably to 80-100 g / ^{m 2.} The amount to be applied is the weight per unit area of the paper charge of each layer.
When the amount of the surface layer is not more than the preferable lower limit value, the blackness of the middle layer can be sufficiently concealed. Further, if the amount of the surface layer attached is not more than the preferable upper limit value, the cost increase due to the increase in raw materials and the dehydration load of the wire can be effectively suppressed.

The back layer is not required to have the same whiteness as the surface layer, but since it is visible to the human eye, pulp having a higher whiteness than the middle layer is usually used. Pulp derived from a shredder-treated product such as office paper may be included. Pulp obtained by dissociating a shredder-treated product such as office paper has a relatively high whiteness without being deinked or bleached, and therefore is preferably blended in the back layer. Pulp obtained by dissociating a shredder-treated product such as office paper can increase the whiteness, but due to its shape, it is difficult to be compatible with water during the dissociation treatment, so that it is difficult to mix it in a large amount. Therefore, it is preferable to use 3 to 40% by mass, preferably 3 to 30% by mass, per pulp of the back layer.

With the amount of the back layer is preferably in a 30 to 80 g / ^{m 2,} and more preferably set to 40 to 50 g / ^{m 2.}
When the amount of the back layer is not more than the preferable lower limit value, the colored foreign matter in the middle layer can be sufficiently concealed. Further, if the amount of the back layer attached is not more than the preferable upper limit value, the cost increase due to the increase in raw materials and the dehydration load of the wire can be effectively suppressed.

The middle layer is usually composed of a plurality of layers. The pulp constituting each layer of the middle layer may be the same or different.
Since the middle layer is a layer sandwiched between the surface layer and the back layer, pulp lower than the surface layer and the back layer is usually used. Examples include dissociated pulp from newspapers, magazines, tickets, medium-sized antiques, tea imitations, cardboard, mounts, ground tickets, balls, and the like.

Of the middle layers, when the middle layer in contact with the surface layer is used as the lower surface layer and pulp having a higher whiteness than the pulp of the other middle layers is used, the pulp used for the above surface layer may be used for the lower surface layer. Usually, used paper having a lower quality than the surface layer, that is, used paper containing a large amount of medium fibers is used. For example, deinked recycled paper pulp such as newspapers, magazines, colors, and balls is generally used.

Further, when using a pulp having a higher whiteness than the pulp of the other middle layers by using the middle layer in contact with the back layer as the back lower layer of the middle layers, the pulp used for the back layer is used for the back lower layer. Although it may be used, waste paper having a lower quality than that of the back layer, that is, waste paper containing a large amount of medium fibers is usually used.
For example, deinked recycled paper pulp such as newspapers, magazines, colors, and balls is generally used.

At least one of the middle layers has an application amount of 50 to 100 g / m ² . At least one layer of attached amount of middle is preferably in a 60~80g / ^{m 2,} and more preferably a 65~70g / ^{m 2.} The formation of the middle layer with an application amount of 100 g / m ^{2 or less tends to be good.}

At least one of the middle layers has an application amount of 50 to 100 g / m ² , and the formation index obtained by the following method is 5.0 (od) or less.
(Constitution index)
The transmitted image of each layer peeled off for each layer is acquired by a flat scanner, the acquired transmitted image is frequency-analyzed, and the standard deviation of the optical density fluctuation component having a period of 2 to 10 mm is used as the formation index.

The reason why the formation index is obtained based on the optical density fluctuation component having a period of 2 to 10 mm is that the flock size, which is visually unsatisfactory, is 2 to 10 mm.
The specific method of obtaining the formation index will be described in detail in the examples.
The smaller the value of the formation index, the better the formation. That is, the smaller the formation index, the better, but it is difficult to set it to zero, and in consideration of manufacturing efficiency and the like, it must be a certain value or more.

In order to reduce the formation index, it is preferable to reduce the amount of water applied during papermaking to reduce the amount of water brought in during papermaking.
Further, it is preferable that the concentration of the inlet is low. The inlet concentration for forming the middle layer is preferably 0.1 to 1.0% by mass, more preferably 0.5 to 0.8% by mass.
Further, it is preferable that the papermaking speed is slow. The papermaking speed is preferably 150 to 200 m / min, more preferably 160 to 180 m / min.

Further, the formation index can be adjusted by adjusting the blending amount of the internal chemicals such as the aluminum sulfate band, the acidic rosin sizing agent, and the PAM-based yield improving agent. The aluminum sulfate band preferably has a solid content of 0.2 to 5.0 parts by mass, more preferably 0.5 to 5.0 parts by mass with respect to 100 parts by mass of pulp. The acidic rosin sizing agent is preferably 0.05 to 3.0 parts by mass, more preferably 0.5 to 1.0 parts by mass. The cationized starch is preferably 0.2 to 3.0 parts by mass, more preferably 0.5 to 1.0 parts by mass. The PAM-based yield improver is preferably 10 to 1000 ppm, more preferably 100 to 500 ppm.

At least one of the middle layers preferably has an application amount of 50 to 100 g / m ² and a formation index of 1.0 to 5.0 (od), preferably 4.0 to 5.0. (O.d.) is more preferable.
If there is a middle layer with a good formation, the smoothness of the surface layer tends to be good even if the calendering pressure is low.

Among the middle layers, the middle layer (hereinafter referred to as "intermediate layer"), which does not contact either the surface layer or the back layer, has an application amount of 50 to 100 g / m ² and a formation index of 5.0 (od). .) The following is preferable.
With the amount of the intermediate layer is preferably in a 60~80g / ^{m 2,} and more preferably a 65~70g / ^{m 2.}
Further, the intermediate layer preferably has an applied amount of 50 to 100 g / m ² , or the above-mentioned preferable range, and a formation index of 1.0 to 5.0 (od), preferably 4.0. It is more preferably ~ 5.0 (od).
Among the middle layers, if the formation of the middle layer is particularly good, the smoothness near the center in the thickness direction of the white paperboard can be obtained, so that the smoothness of the surface layer tends to be even better even if the calendering pressure is low. it is conceivable that.
The formation of the intermediate layer is preferably adjusted by setting the amount of application to a relatively small range even in the middle layer.

Among the middle layers, the middle layer in contact with the surface layer preferably has an application amount of 50 to 100 g / m ² and a formation index of 5.5 (od) or less.
With the amount of middle in contact with the surface layer is preferably set to 60 to 90 g / ^{m 2,} more preferably to 70~90g / ^{m 2,} and even more preferably from 80~85g / ^{m 2.}
Further, in the middle layer in contact with the surface layer, the amount applied is ^{preferably 50 to 100 g / m 2} , or the above-mentioned preferable range, and the formation index is preferably 1.0 to 5.5 (od). It is more preferably .0 to 5.5 (od).
Among the middle layers, if the formation of the middle layer in contact with the surface layer is particularly good, the smoothness of the surface layer tends to be further improved even if the pressure of the calendar processing is low.

Further, it is preferable that all the middle layers have an application amount of 50 to 150 g / m ² and the formation index of 6.5 (od) or less.
It is more preferable that all the middle layers have an application amount of 50 to 110 g / m ² and the formation index of 6.4 (od) or less.
If the formation of all the middle layers reaches a certain level, the smoothness of the surface layer tends to be better even if the pressure of the calendar processing is low.

The total amount of the middle layer is the amount required for the total basis weight of the white paperboard to be ^{500 to 570 g / m 2.}
The number of layers of the middle layer and the amount of each layer of the middle layer are determined so that the total amount of the middle layer is the amount required for the total basis weight of the white paperboard to be ^{500 to 570 g / m 2.}
The number of layers in the middle layer is preferably 3 to 10 layers, more preferably 6 to 8 layers.

As described above, high-quality paper materials are usually used for the front layer and the back layer, so that the texture tends to be good.
The formation index of the surface layer is preferably 0.5 to 3.0 (od), more preferably 1.0 to 2.0 (od).
The formation index of the back layer is preferably 0.5 to 5.0 (od), more preferably 2.0 to 3.0 (od).

The pulp slurry composition used for each layer from the surface layer to the back layer may contain, as necessary, a paper strength enhancer, a water resistant agent, a water repellent, an effervescent microcapsule, a sizing agent, a dye, and the like. Yield improver, filler, pH adjuster, slime control agent, thickener, preservative, fungicide, antibacterial agent, flame retardant, antiseptic, antiseptic, insect repellent, moisturizer, freshness preservative, oxygen scavenger , Microcapsules, foaming agents, surfactants, electromagnetic shielding materials, antistatic agents, rust preventives, fragrances, deodorants and the like can be selected and blended. These can be used in combination of two or more.

The white paperboard of the present invention is not particularly limited as long as multi-layer papermaking can be performed, and for example, a long net machine including a top wire, a short net machine, a circular net machine, and two or more of these are used in combination. You can use the machine etc.
As the adhesive used for pasting, starch, PVA, latex, cellulose derivative and the like can be used.
The inlet density and papermaking speed should be adjusted so that the formation of each layer is sufficient.

The press pressure at the time of papermaking and the calendar line pressure after papermaking can be adjusted so that ^{the density of the entire white paperboard is 0.8 g / m 3 or less.}
As the calendar device, a machine calender, a soft calender, a Yankee dryer, or the like can be used.

[Painted white paperboard]
The coated white paperboard of the present invention is provided with a pigment coating layer on at least one surface of the white paperboard of the present invention. When the pigment coating layer is provided on only one surface, it is preferably provided on the surface of the surface layer.
The pigment coating layer is formed by applying a pigment coating liquid to at least one surface. The pigment coating liquid contains a pigment and a binder.

Pigments used in the pigment coating liquid include fired clay, ordinary clay such as structured kaolin and delaminated clay, heavy calcium carbonate, light calcium carbonate, titanium dioxide, aluminum hydroxide, silica, satin white, and talc. , One or more of publicly known and public pigments used in the field of general coated paper manufacturing such as plastic pigments can be appropriately used.

Examples of the binder include conjugated diene polymer latex such as styrene / butadiene copolymer, methyl methacrylate / butadiene copolymer, acrylic acid ester and / or methacrylic acid ester polymer or acrylic acid polymer such as copolymer. Vinyl-based polymer latex such as latex, ethylene / vinyl acetate copolymer, or alkali-soluble or non-alkali-soluble polymer latex obtained by modifying these various polymer latex with a functional group-containing monomer such as a carboxy group. , Casein, soybean protein, synthetic protein and other proteins, polyvinyl alcohol, olefin / maleic anhydride resin, melamine resin and other synthetic resin adhesives, cationic starch, oxidized starch, thermochemically modified starch and other starches, carboxymethyl cellulose , A cellulose derivative such as hydroxyethyl cellulose, and the like, and are used alone or in combination of two or more. The amount of the binder used is about 5 to 40 parts by mass with respect to 100 parts by mass of the pigment.

Pigment coating liquids include dispersants, caustic sodas, pH adjusters such as aqueous ammonia, defoamers, preservatives, fluorescent dyes, mold release agents, dyes, water resistant agents, flow modifiers, and coloring, if necessary. Pigments and the like can be added as appropriate.

Regarding the pigment coating layer, two layers, an undercoat layer and an overcoat layer, are generally formed on the surface layer, but the undercoat layer has a dry weight of 5 to 15 g / m ² , and the topcoat layer has a dry weight of 3 to 15 g / m. It is desirable that the total amount of the undercoat and topcoat applied is m ² and the dry weight is in the range of 8 to ^{25 g / m 2.}

The coating device for forming the pigment coating layer is not particularly limited, and for example, an air knife coater, a blade coater, a rod coater, a bar coater and a gate roll coater, a roll coater such as a size press, a bill blade coater, a velvapa coater, etc. Are preferably used in combination, but a rod coater is preferably used for forming the undercoat layer, and a blade coater is preferably used for forming the topcoat layer.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples. In addition,% is mass% unless otherwise specified, and part is mass part unless there is particular notice.

[Paper charges]
Paper materials for each layer were prepared according to the formulations shown below (both solid content).
(1st layer: surface layer)
Hardwood bleached kraft pulp (LBKP) (freeness 350 mL): 100 parts Internal filler (charcoal cal): 15 parts Sulfate band: 5 parts Acid rosin sizing agent: 0.5 parts Cationicized starch: 0.5 parts PAM-based yield improvement Agent: 100ppm
Inlet concentration: 0.5%

(2nd layer: middle layer, which is the lower layer)
Deinked recycled paper pulp: 100 parts Sulfate band: 5 parts Acid rosin sizing agent: 0.5 parts Cationicized starch: 0.5 parts PAM-based yield improver: 100 ppm
Inlet concentration: 0.5%

(3rd to 5th layers: middle layer, which is an intermediate layer)
Uninked recycled paper pulp: 100 parts Sulfate band: 5 parts Acid rosin sizing agent: 0.5 parts Catylated starch: 0.5 parts PAM-based yield improver: 100 ppm
Inlet concentration: 0.5%

(6th layer: middle layer, which is the lower back layer)
Deinked recycled paper pulp: 100 parts Sulfate band: 5 parts Acid rosin sizing agent: 0.5 parts Cationicized starch: 0.5 parts PAM-based yield improver: 100 ppm
Inlet concentration: 0.5%

(7th layer: back layer)
Mixed pulp with a mass ratio of 50:50 between deinked recycled paper pulp and bleached kraft pulp: 100 parts Sulfate band: 5 parts Acid rosin sizing agent: 0.5 parts Cationicized starch: 0.5 parts PAM-based yield improver: 100ppm
Inlet concentration: 0.5%

[Creating white paperboard]
The seven layers using the paper material of each of the above layers were pasted together so as to have the amounts shown in Table 1, and white paperboards of each Example and Comparative Example were prepared. Interlayer starch was used for adhesion of each layer.
A paper machine was used for paper making, and after the paper was made, it was processed with a machine calendar. The papermaking conditions of each Example and Comparative Example are as shown in Table 1.

[Measuring method]
The formation index, addition amount, basis weight, thickness, density, rigidity (longitudinal direction), royal smoothness, and bokotsuki index of each example and comparative example were obtained as follows.
The results of each measurement are shown in Table 1.

(Constitution index)
The white paper sheets of each example and comparative example were peeled off layer by layer, and a transmission image (gray scale) was obtained for each layer with a flat scanner.
The layer was peeled off by impregnating it with a 1% amylase solution at 40 ° C. for 30 minutes to divide the layer.
As a flat scanner, EPSON Scan (Ver.3.04J) was used, and scanning was performed under the conditions of an image size of 10 cm × 10 cm and a resolution of 0.1 mm.

In the obtained transmitted image, the shading of the paper is represented as black where the light does not pass (where the fibers are gathered and the density is high) and white where the light is transmitted.
This image is quantified into a gray scale of 256 gradations, and by frequency analysis (power spectrum is acquired and periodic components of 0.1 mm or more are output as spectral intensities), the target periodic components of 2 to 10 mm are obtained. The power spectrum was extracted, and the standard deviation of the black-and-white level was used as the formation index.

(Amount, basis weight)
The amount to be applied was determined by JIS P8124 for each layer peeled off for the formation index measurement, and the basis weight was determined for the obtained white paperboard.
(density)
The density of the entire white paperboard was determined by JIS P8118.
(thickness)
The thickness of the entire white paperboard was determined by dividing the basis weight of the entire white paperboard by the density of the entire white paperboard.

(Rigidity)
The rigidity (vertical direction) of the entire white paperboard was determined by JIS P8125.
(Oken type smoothness)
The Oken-type smoothness of the surface layer of white paperboard was determined by JIS P8155.

(Bokotsuki index)
The surface unevenness of the surface layer of the white paperboard of each Example and Comparative Example was measured in a non-contact manner, and a 3D image (gray scale) was acquired. A one-shot 3D measurement macroscope VR3200 (Keyence) was used to acquire the 3D image.
In the obtained 3D image, the surface unevenness is represented as black in the concave portion and white in the convex portion.
This image is quantified into a gray scale of 256 gradations, and by frequency analysis (power spectrum is acquired and periodic components of 0.1 mm or more are output as spectral intensities), the target periodic components of 2 to 10 mm are obtained. The power spectrum was extracted, and the standard deviation of the black-and-white level was used as the Bokotsuki index.

As shown in Table 1, the white paperboard of the example in which the amount applied to the third layer is 50 to 100 g / m ² and the formation index is 5.0 (od) or less is the Bokotsuki index. Was low. Moreover, although the basis weight was relatively small, sufficient rigidity was obtained.
On the other hand, in Comparative Example 1 in which the middle layer having a geological index of 5.0 (od) or less does not exist, the Oken-type smoothness was low, but the Bokotsuki index suitable for evaluating printability was high. rice field.
Further, in Comparative Example 2 in which the calendar processing was performed at a high linear pressure to increase the density, although the smoothness was good, sufficient rigidity according to the basis weight was obtained in spite of having a high basis weight. There wasn't.

Claims (5)

It is a multi-layered white paperboard that has a surface layer, one or more middle layers, and a back layer.
The total basis weight of the white paperboard is 500 to 570 ^{g / m 2} , and the density is 0.80 g / m ³ or less.
A white paperboard characterized in that at least one of the middle layers has an application amount of 50 to 100 g / m ² and a formation index of 5.0 (od) or less. Middle layer contacting with one of said surface layer and said backing layer, with weight of 50 to 100 g / ^{m 2,} and the formation index is 5.0 (o.d.) Or less, according to claim 1 The white paperboard described in. The white paperboard according to claim 1 or 2, wherein at least the middle layer in contact with the surface layer has an application amount of 50 to 100 g / m ² and a formation index of 5.5 (od) or less. .. The middle layer is any one of claims 1 to 3, wherein all the layers have an application amount of 50 to 150 g / m ² and the formation index is 6.5 (od) or less. The white paperboard described in item 1. A coated white paperboard provided with a pigment coating layer on at least one surface of the white paperboard according to any one of claims 1 to 4.