JP2022165167A - Method for producing white paperboard - Google Patents

Abstract

To provide a method for producing a white paperboard which can give a white paperboard having a sufficiently high surface whiteness and resistance to ruled cracking, and also resistance to swelling during drying.SOLUTION: The present invention discloses a method for producing a white paperboard at least comprising a surface layer, a subsurface layer, a middle layer and a back layer. The surface layer is made using a paper stock therefor, the paper stock comprising a slurry of a surface-layer pulp material containing deinking pulp and/or bleached pulp with calcium carbonate of 5-12 pts.mass added relative to the surface-layer pulp material 100 pts.mass. The subsurface layer is made using a paper stock therefor, the paper stock comprising a slurry of a subsurface-layer pulp material containing old magazine-derived deinking pulp with calcium carbonate of 3-8 pts.mass added relative to the subsurface-layer pulp material 100 pts.mass.SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing white paperboard.

A white paperboard having at least a surface layer, a lower surface layer and a middle layer is known. Waste paper pulp with low whiteness is used for the middle layer of white paperboard from the viewpoint of low cost and resource saving. In order to conceal the color of this middle layer, the surface layer of the white paperboard is required to have concealability. However, since there is a cost problem when trying to hide the color of the middle layer only with the surface layer, pulp with a relatively high degree of whiteness is also used for the surface and lower layers immediately below the surface layer (Patent Document 1).
Patent Document 1 proposes adding a pigment such as talc to the surface layer or the lower surface layer in an amount of 10% by weight or more based on the pulp in order to improve the surface whiteness of white paperboard. In addition, in Patent Document 1, the Canadian standard freeness of the surface layer, etc. is set within a specific numerical range in order to prevent creases on the surface even if 10% by weight or more of the pigment is blended in the surface layer, etc. . Here, the term "crease on the ruled line" refers to a phenomenon in which the surface of the white paperboard is cracked when the white paperboard is folded after the white paperboard is folded.

JP-A-6-41896

In recent years, it has become more difficult to obtain high-quality pulp raw materials than before, and it is sometimes necessary to use pulp raw materials with insufficient whiteness for use in white paperboard. Therefore, even when a pulp raw material with a low degree of whiteness is used, it is desired to reliably conceal the color of the middle layer and further improve the degree of surface whiteness.
However, according to the studies of the present inventors, even if the amount of the pigment used in the surface layer is increased for the purpose of further improving the surface whiteness, the effect of improving the surface whiteness eventually saturates. In addition, there is a problem that as the amount of pigment used increases, cracks in the ruled lines of the white paperboard become more likely to occur.

In addition, in the white paperboard with a pigment added to the lower surface layer described in Patent Document 1, there is also a problem that voids are formed between the lower surface layer and the middle layer during drying, causing the white paperboard to swell. Blistered white paperboard may cause problems such as delamination during printing.
To provide a method for producing a white paperboard which has a sufficiently high degree of surface whiteness, produces white paperboard which is less prone to creases, and is less likely to blister during drying.

The present invention has the following aspects.
[1] A method for producing white paperboard having at least a surface layer, a lower surface layer, a middle layer, and a back layer, wherein the surface layer pulp material 100 is added to a surface layer pulp material slurry containing at least one of deinked pulp and bleached pulp. A surface layer paper stock obtained by adding 5 to 12 parts by mass of calcium carbonate to the mass parts is used to make the surface layer, and a slurry of pulp raw material for the surface lower layer containing deinked pulp derived from waste magazine paper. A white paperboard, characterized in that the lower surface layer is made using a surface lower layer paper material obtained by adding 3 to 8 parts by mass of calcium carbonate to 100 parts by mass of the pulp raw material for the lower surface layer. manufacturing method.
[2] The method for producing white paperboard according to [1], wherein the amount of calcium carbonate added to 100 parts by mass of the pulp material for the surface layer is larger than the number of parts added of calcium carbonate to 100 parts by mass of the pulp material for the lower surface layer.
[3] The method for producing white paperboard according to [1] or [2], wherein the calcium carbonate added to the slurry of the pulp raw material for the surface lower layer is light calcium carbonate.
[4] The white plate of [3], wherein the particle size distribution of the light calcium carbonate added to the slurry of the pulp raw material for the surface lower layer has peaks between 0.1 μm and 1 μm and between 1 μm and 10 μm. Paper manufacturing method.
[5] The method for producing white paperboard according to any one of [1] to [4], wherein the calcium carbonate added to the slurry of the pulp material for the surface layer is light calcium carbonate.
[6] The white paperboard of [5], wherein the particle size distribution of the light calcium carbonate added to the slurry of the pulp raw material for the surface layer has peaks between 0.1 μm and 1 μm and between 1 μm and 10 μm. manufacturing method.
[7] The method for producing white paperboard according to any one of [1] to [6], wherein the surface of the surface layer is coated with a pigment coating liquid containing a pigment and a binder.
[8] The white paperboard of any one of [1] to [7], wherein a calcium carbonate dispersion in which calcium carbonate is dispersed in water is added to each of the surface layer pulp material slurry and the surface lower layer pulp material slurry. Production method.

According to the method for producing a white paperboard of the present invention, a white paperboard having a sufficiently high surface whiteness and less cracking of ruled lines can be obtained. In addition, according to the method for producing white paperboard of the present invention, swelling is less likely to occur during drying.

In the method for producing white paperboard of the present invention, white paperboard having at least a surface layer, a lower surface layer, a middle layer and a back layer is produced.
The surface layer is the layer that is arranged on the frontmost side of the multi-layered white paperboard, and the back layer is the layer that is arranged on the rearmost side (opposite side to the surface layer). The subsurface layer is the layer immediately below the surface layer. The lower surface layer can also be said to be a layer that contacts the surface layer inside the white paperboard.
In the present invention, an intermediate layer is arranged between the front and lower layers and the back layer. The middle layer may be formed with one layer or with a plurality of layers. However, in order to increase the amount of low-quality waste paper pulp used, it is preferable to form a plurality of layers.

In the white paperboard manufacturing method of the present invention, a surface layer paper material obtained by adding 5 to 12 parts by mass of calcium carbonate with respect to 100 parts by mass of the surface layer pulp material to a slurry of a specific surface layer pulp material is used. , The surface layer is paper-made, and a surface lower layer paper material obtained by adding 3 to 8 parts by mass of calcium carbonate to 100 parts by mass of the lower surface layer pulp raw material to a slurry of a specific lower surface layer pulp raw material is used. It is characterized by papermaking the surface lower layer.
The pulp, the filler such as calcium carbonate, the auxiliary agent for the paper stock, and the basis weight of each layer used in the white paperboard manufacturing method of the present invention will be described below, and the details of the papermaking method will be described in order.

<About pulp>
(surface)
The pulp raw material for the surface layer contains at least one of deinked pulp and bleached pulp having a high degree of whiteness. As the pulp used for the surface layer, pulp other than these can also be used in combination within a range that does not impair the effects of the invention.
Deinked pulp is deinked white waste paper pulp. A bleaching treatment may be performed to increase the degree of whiteness. Waste paper used as a raw material for deinked pulp includes, for example, paper that has been used once but has a small printed portion such as high white, ruled white, extra white, medium white, white manila; card, imitation, colored paper, Kent, Printed matter such as white art and paper that has been colored and used once; Used high-quality waste paper such as coated paper for printing, beverage packs, and office paper; waste paper; general waste paper such as newspapers and magazines; The used paper may be confidential office paper or shredded materials such as tickets. These may be used singly or in combination of two or more.
As the deinked pulp for the surface layer, deinked pulp derived from waste paper with a high degree of whiteness such as fine white/cards, extra white/medium white/white manila, imitation/high quality, etc.; deinked pulp derived from Kent paper is preferable. , Kent paper-derived deinked pulp is particularly preferred.

Examples of bleached pulp include bleached hardwood kraft pulp (LBKP), semi-bleached hardwood kraft pulp (LSBKP), bleached softwood kraft pulp (NBKP), semi-bleached softwood kraft pulp (NSBKP), and bleached chemithermomechanical pulp (BCTMP). Bleached hardwood kraft pulp and bleached softwood kraft pulp are particularly preferably used.
Examples of unbleached pulp include chemical pulp such as softwood unbleached kraft pulp (NUKP), hardwood unbleached kraft pulp (LUKP), hardwood sulfite pulp, softwood sulfite pulp, thermomechanical pulp (TMP), and chemithermomechanical pulp. Mechanical pulps such as pulp (CTMP), chemi ground pulp (CGP), refiner ground pulp (RGP), ground pulp (GP), pressure stone ground pulp (PGW), stone ground pulp (SGP), etc. They can also be used together as long as the effect is not impaired.

(Surface layer)
The pulp material for the lower surface layer includes deinked pulp derived from used magazine paper. Pulp other than deinked pulp derived from used magazine paper can also be used as the pulp for the lower surface layer, as long as the effects of the invention are not impaired.
The pulp used for the surface and lower layers is composed of pulp having a lower degree of whiteness than the pulp of the surface layer and a higher degree of whiteness than the pulp of the middle layer. As the pulp constituting the lower surface layer, deinked pulp derived from waste paper, which is lower grade than that of the surface layer, that is, deinked pulp derived from waste paper containing a large amount of medium-quality fibers can be preferably used. For example, deinked pulp derived from newspapers, color, balls and the like is preferred.

(middle class)
Pulp used for the middle layer is generally the lowest grade pulp among the layers constituting the white paperboard. For example, disaggregated pulp such as newspapers, magazines, tickets, medium-quality rolls, tea imitations, corrugated cardboard, mounts, coupons, and balls can be mentioned.
The middle layer may be formed with one layer or with a plurality of layers. However, in order to increase the amount of low-quality waste paper pulp used, it is preferable to form the middle layer with a plurality of layers. When the middle layer is composed of a plurality of layers, the pulp constituting each layer of the middle layer may be the same or different.

(lower back layer)
In the method for producing white paperboard of the present invention, a lower back layer may be provided between the back layer and the middle layer. A lower backing layer is disposed between the backing layer and the middle layer. The lower back layer can also be said to be a layer that contacts the back layer inside the white paperboard.
The pulp constituting the lower back layer has a higher degree of whiteness than the pulp of the middle layer and a lower degree of whiteness than the pulp of the back layer. The pulp used for the surface and bottom layers may be used for the back and bottom layers, but usually low grade waste paper compared to the surface layer, that is, waste paper containing a large amount of medium-density fibers is used. For example, it is common to use unbleached deinked waste paper pulp such as newspapers, magazines, colored papers, balls, and the like.

(back layer)
The back layer is not required to be as white as the surface layer, but since it is visible to the human eye, pulp with a higher whiteness than that of the middle layer is usually used. The backing layer may comprise pulp from shredded material such as office paper. Pulp obtained by defibrating shredded materials such as office paper has a relatively high degree of whiteness even without deinking and bleaching, so it is preferably blended in the backing layer. If the whiteness of the surface layer is required, the lower back layer should be the same as the front and lower layers, and the back layer should be the same as the front layer.

<About calcium carbonate and other fillers>
The surface layer stock is obtained by adding calcium carbonate to the slurry of the pulp raw material for the surface layer. The amount of calcium carbonate added to the surface layer pulp material slurry is 5 to 12 parts by mass, preferably 8 to 11 parts by mass, per 100 parts by mass of the surface layer pulp material. If the amount of calcium carbonate added is at least the above lower limit, the blackness of the middle layer can be sufficiently concealed. If the amount of calcium carbonate to be added is equal to or less than the above upper limit, crease cracks in the white paperboard are less likely to occur.
The surface layer stock is obtained by adding calcium carbonate to a slurry of pulp material for the surface and lower layers. The amount of calcium carbonate added to the slurry of the lower surface layer pulp material is 3 to 8 parts by mass, preferably 5 to 7 parts by mass, per 100 parts by mass of the lower surface layer pulp material. If the amount of calcium carbonate added is at least the above lower limit, the darkness of the middle layer can be sufficiently hidden. In addition, swelling during manufacturing can be suppressed. If the amount of calcium carbonate to be added is equal to or less than the upper limit, swelling during production can be suppressed.
In particular, when the number of parts of calcium carbonate added to 100 parts by mass of the pulp material for the surface layer is greater than the number of parts of calcium carbonate added to 100 parts by mass of the pulp material for the surface and lower layers, the concealing property of the intermediate layer, the effect of suppressing crease cracks, and the effect of suppressing cracks during production It is preferable because it is excellent in all the control of swelling.

Calcium carbonate may be added to the pulp slurry in the form of powder, or may be added to the pulp slurry in the form of a calcium carbonate dispersion in which calcium carbonate is dispersed in water. preferably. This makes it possible to add a fixed amount, and it is easy to suppress fluctuations in the amount to be added.
The calcium carbonate dispersion is preferably added to each of the slurry of the pulp material for the surface layer and the slurry of the pulp material for the lower surface layer. In this case, the calcium carbonate dispersion prepared in the same batch is divided into two or more, and the same calcium carbonate dispersion is used to add a predetermined amount of calcium carbonate to the slurry of the pulp material for the surface layer and the pulp material for the surface lower layer. Add to each of the slurries.
When adding as a calcium carbonate dispersion, a dispersant may be added to the calcium carbonate dispersion in order to obtain good dispersibility. Dispersants include anionic surfactants and the like.

Calcium carbonate is not particularly limited. As calcium carbonate, light calcium carbonate and heavy calcium carbonate may be used, and light calcium carbonate is preferred.
The volume-based average primary particle diameter D ₅₀ of precipitated calcium carbonate is preferably 0.2 to 10 μm, more preferably 1 to 5 μm, even more preferably 2 to 3 μm.
Here, the primary particle size refers to a particle size measured after an aqueous dispersion of light calcium carbonate is dropped into the circulation system of a laser diffraction particle size distribution analyzer and then subjected to ultrasonic treatment. The volume-based average primary particle diameter _D50 is the 50% volume-based primary particle diameter.

Light reflection is more likely to occur within the surface layer of the white paperboard, and the surface whiteness of the white paperboard is further improved. It is preferable to have peaks between and respectively. The particle size distribution of precipitated calcium carbonate can be obtained, for example, with a laser diffraction particle size distribution analyzer, but is not particularly limited.

Other fillers may be blended in the surface layer and the lower surface layer as long as the effect of the invention is not impaired. Other fillers include known fillers such as clay, clay, calcined clay, talc, titanium oxide and silica. Since the lower surface layer contains a filler derived from a waste paper material, the amount of calcium carbonate to be added may be adjusted within the above addition range in consideration of the content of the filler.

<About auxiliary agents>
If necessary, a paper strength agent, aluminum sulfate, and other auxiliary agents may be added to the stock used for making each layer.
The composition of the stock used for making paper for each layer can be appropriately changed in consideration of the quality required for the white paperboard, convenience in manufacturing, and the like. For example, the ratio of deinked pulp and bleached pulp to the total pulp in the stock are not particularly limited. It is appropriately adjusted in consideration of which layer the stock is to be used for forming.

A paper strength agent is a papermaking chemical for giving strength to paper products. Strength agents are divided into wet strengthening agents and dry strengthening agents. The paper strength agent is preferably a dry paper strength agent in order to improve internal strength, surface strength and interlaminar strength.

Among the dry paper strength agents, it is preferable to use a polyacrylamide-based paper strength agent for the effect of developing strength and improving the yield of pulp. The proportion of the polyacrylamide-based paper strength agent in the paper strength agent used in the stock is preferably 0.1% or more, more preferably 0.4% or more, and particularly preferably only the polyacrylamide-based paper strength agent.

The polyacrylamide-based paper strength agent is not particularly limited, and any of anionic, amphoteric and cationic agents can be used. Among these, an amphoteric polyacrylamide-based paper strength agent is preferable because of its wide fixing area.

Examples of paper strength agents other than polyacrylamide-based paper strength agents include natural paper strength agents such as starch and vegetable gums, polyvinyl alcohol resins, styrene-butadiene latex, urea-formaldehyde resins, melanin resins, polyamide resins, and ketone resins. , polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, polyamide epoxy resins, glycerol polyglycidyl ether resins, polyethyleneimine resins and other synthetic paper strength agents. These can be used singly or in combination.
Among these, starches, polyvinyl alcohol resins, and styrene-butadiene latex are preferred, and starches are particularly preferred. Examples of starches include oxidized starch, esterified starch such as urea phosphate esterified starch, enzyme-modified starch, etherified starch such as hydroxyethyl etherified starch, and the like, and these can be used alone or in combination. can do. Among them, it is preferable to use oxidized starch.

The amount of the paper strength agent added is preferably 0.1 to 1.5% by mass, more preferably 0.4 to 1.0% by mass, based on 100% by mass of the solid content of the pulp slurry.
When the addition amount of the paper strength agent is equal to or more than the lower limit, it is possible to more reliably suppress the formation of precipitates. In addition, when it is equal to or less than the above upper limit, it is possible to suppress the deterioration of drainage due to over-aggregation.

Aluminum sulfate is the common name for aluminum sulfate. Aluminum sulfate is a representative inorganic flocculant. By adding aluminum sulfate, even when waste paper pulp is used, it is possible to suppress the dropping of fine fibers in the wire part and improve the yield of the pulp slurry.

The amount of aluminum sulfate added is preferably 0.1 to 2.0% by mass, more preferably 0.4 to 1.0% by mass, based on 100% by mass of the solid content of the pulp slurry.
When the addition amount of aluminum sulfate is equal to or more than the above lower limit, it is easy to obtain the effect of improving the yield of the pulp slurry. In addition, when the content is equal to or less than the upper limit, it is possible to more reliably suppress the formation of precipitates.

Other auxiliary agents include paper strength agents, water resistance agents, water repellents, foaming microcapsules, sizing agents, dyes, fillers, pH adjusters, slime control agents, thickeners, preservatives, and antifungal agents. , antibacterial agents, flame retardants, rodenticides, insect repellents, moisturizers, freshness agents, oxygen absorbers, microcapsules, foaming agents, surfactants, electromagnetic shielding materials, antistatic agents, rust inhibitors, fragrances, deodorants agents and the like. These may be used individually by 1 type, and may use 2 or more types together.

<Regarding basis weight>
The basis weight of the surface layer is preferably 15-90 g/m ² , more preferably 25-70 g/m ² . The basis weight of each layer can be measured according to JIS P8124. If the basis weight of the surface layer is at least the above lower limit, the darkness of the middle layer can be sufficiently hidden. Further, when the basis weight of the surface layer is equal to or less than the upper limit, swelling during papermaking can be suppressed.

The basis weight of the surface lower layer is preferably 15 to 70 g/m ² , more preferably 20 to 60 g/m ² and even more preferably 25 to 55 g/m ² . If the basis weight of the surface and bottom layers is at least the above lower limit, the darkness of the middle layer can be sufficiently concealed together with the surface layers. When the basis weight of the surface and bottom layer is equal to or less than the upper limit, swelling during papermaking can be suppressed.
In the white paperboard of the present invention, the basis weight of the lower surface layer is preferably larger than the basis weight of the surface layer because cracks on the surface of the white paperboard can be suppressed.

The total basis weight of the middle layer is appropriately adjusted according to the thickness required by the use of the white paperboard. The basis weight per layer of the intermediate layer is, for example, preferably 15 to 90 g/m ² , more preferably 25 to 75 g/m ² .

When forming the lower back layer, its basis weight is preferably 15 to 90 g/m ² , more preferably 25 to 75 g/m ² . If the basis weight of the lower back layer is at least the above lower limit, the colored foreign matter in the middle layer can be sufficiently concealed together with the back layer.

The basis weight of the backing layer is preferably 15-90 g/m ² , more preferably 25-70 g/m ² . If the basis weight of the back layer is at least the above lower limit, colored foreign matter in the middle layer can be sufficiently concealed. Further, when the basis weight of the backing layer is equal to or less than the above upper limit, sufficient strength of the paper layer can be obtained.

<About the papermaking method>
The papermaking method for forming each layer is not particularly limited. It is preferable to use a paper machine having at least a wire part, a press part and a dryer part. Also, a size press may be performed in the dryer part. A paper machine having a calendering part (pre-calendering) after the dryer part may also be used. When laminating each layer, an adhesive such as starch can be used between each layer. The adhesive can be applied by a spray method or the like.

As the wire part, a known multistage wire part can be used as appropriate. A multistage wire part has at least two or more wire part portions.
Types of wire parts generally used for papermaking include a circular net type, a fourdrinier type, a short net type, an inclined type, and a twin wire type.
In a multistage wire part, these methods can be combined in multiple stages. Examples include fourdrinier mesh, short mesh mesh, short mesh combination, fourdrinier mesh combination, and the like.

As the press part, a known press machine can be used as appropriate, but a shoe press is preferably included. It is also preferable to combine a roll press and a shoe press. When a shoe press is used, water can be sufficiently squeezed in the press part, so it is easy to control the amount of water when size-pressing in the dryer part.

A known drier can be appropriately used as the drier part. For example, a non-contact dryer such as a cylinder dryer that contacts and heats the white paperboard in a wet state, an infrared dryer, a hot air dryer, or the like can be used alone or in combination.

<About the pigment coating layer>
In the method for producing white paperboard of the present invention, a pigment coating layer containing a pigment and a binder may be provided on the surface of the surface layer.
Examples of pigments include those commonly used in the field of coated paper production, such as kaolin, calcium carbonate (heavy calcium carbonate, light calcium carbonate), titanium dioxide, aluminum hydroxide, silica, satin white and talc. Among these, calcium carbonate is preferable because it exhibits excellent printability.

A water-based adhesive is preferable as the binder. Water-based adhesives include starches such as oxidized starch, phosphate esterified starch, hydroxyethyl etherified starch, dextrin, enzyme-modified starch, water-soluble starch; styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer. latexes, latexes such as conjugated diene copolymer latexes such as styrene-methyl methacrylate-butadiene copolymer latexes, acrylic copolymer latexes such as acrylic acid ester and/or methacrylic acid ester copolymer latexes; casein; , gelatin, soybean protein and other proteins; various polyvinyl alcohols, various polyacrylamides, synthetic resin adhesives such as melamine resin; and various cellulose derivatives such as carboxymethyl cellulose. One or more of these adhesives can be used as the binder.

Among these, a latex having a glass transition temperature of −50 to 30° C. as measured by Vibron viscoelasticity is preferred because it increases the flexibility of the coated surface and improves the resistance to bending and cracking. More preferably, the latex has a glass transition temperature of -50 to 0°C.
It is also preferred to incorporate starch with the latex. The combination of latex and starch balances the fixation of fine fibers within the backing layer and the surface strength of the surface of the backing layer.
The weight ratio of latex to starch is preferably from 100:0 to 5:50.

Pigment coating liquid, if necessary, a dispersing agent, sodium hydroxide, a pH adjuster such as aqueous ammonia; an antifoaming agent; a fluorescent dye; It may further contain one or more of preservatives, dyes, color pigments, and the like.
A pigment coating layer may also be provided on the surface of the back layer.

When the pigment coating layer is provided on the surface of the surface layer of white paperboard, the coating layer is provided by applying a pigment coating liquid to the surface of the surface layer. Next, the coating layer is dried to form a pigment coating layer on the surface of the surface layer.
The pigment coating liquid preferably contains 2 to 50 parts by mass, more preferably 5 to 25 parts by mass, of the binder with respect to 100 parts by mass of the pigment.
If the proportion of the binder is at least the above lower limit, the strength of the pigment coating layer tends to be sufficient. In addition, if the ratio of the binder is equal to or less than the above upper limit value, the ink drying property is excellent and the suitability for box-making is also excellent.
The coating amount of the pigment coating liquid is preferably 5 to 50 g/m ² , preferably 8 to 40 g/m ² , more preferably 10 to 35 g/m ² in terms of dry mass.

The pigment coating liquid may be applied in multiple times. When the pigment coating liquid is applied a plurality of times, for example, two times, the first coating liquid (undercoat layer) and the second coating liquid (topcoat layer) may be the same or different.
The pigment coating liquid may be applied directly to the surface layer, or may be applied via a coating film of a size press liquid applied to the surface layer. Before applying the pigment coating liquid, the surface layer surface may be smoothed by pre-calendering. The pigment coating liquid may be applied only once or may be applied multiple times. In particular, it is preferable to apply the pigment coating liquid for the undercoat layer and the pigment coating liquid for the topcoat layer to sequentially form the undercoat layer and the topcoat layer.
By applying the pigment coating liquid, it is possible to improve the printability of the surface layer side and increase the degree of whiteness.

The coater may be either on-machine or off-machine, but is preferably on-machine using a known coater part attached to the paper machine. Examples of coating equipment for the coater part include blade coaters, air knife coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, slot die coaters, gravure coaters, champlex coaters, brush coaters, slide bead coaters, two-roll or A metering blade type size press coater, a bill blade coater, a short dwell coater, a gate roll coater, a calender nip coater, and the like are appropriately used.
Among these, a rod metering coater and a curtain coater are preferable because the coating amount is constant and a coating layer with suppressed coating unevenness can be obtained. The applied coating layer is dried with a known drying device to form a pigment coating layer. The paper machine may have multiple coater parts. In this case, the coating layer can be applied in a plurality of times.

A calendar part may be provided after the coater part, if necessary. By providing a calendar part after the coater part, the pigment coating layer is smoothed.
For the calendering part after the coater part, a known calendering device can be appropriately used, and examples thereof include a super calender, a gloss calender, a soft nip calender, a heat calender, and a shoe calender. These may be used in combination. Among them, a soft nip calender having metal rolls and elastic rolls is preferable because it can smoothen the coating layer while maintaining the thickness of the paper. The calendar part after the coater part can be either on-machine or off-machine.

(Mechanism of action)
In the white paperboard manufacturing method of the present invention described above, since calcium carbonate with a high concealing effect is blended in both the surface layer stock and the surface bottom layer stock, the amount of calcium carbonate in the two layers, the surface layer and the bottom layer, is can be a sufficient amount to hide the color of the middle layer. Therefore, the surface whiteness of the obtained white paperboard is improved. In addition, since it is not necessary to add an excessive amount of pigment only to the surface layer paper material, it is possible to suppress creases in the resulting white paperboard.
In addition, adjusting the amount of calcium carbonate added to the paper material for the lower surface layer makes it easier for steam to pass through the lower surface layer during drying during manufacturing by multi-layer papermaking. Therefore, it is difficult for air to accumulate between the surface lower layer and the middle layer, and the occurrence of swelling is suppressed.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following description.

<Example 1>
A multi-layer paper machine was used to obtain a white paperboard having a top layer, a bottom layer, a middle layer and a back layer. Here, the multilayer paper was made so that the basis weight of the surface layer was 45 g/m ² , the basis weight of the upper and lower layers was 50 g/m ² , the basis weight of the middle layer was 135 g/m ² , and the basis weight of the back layer was 45 g/m ² . I did
As a surface layer paper material, 100 mass of surface pulp material is added to a slurry of surface layer pulp material with a whiteness of 85%, which is a mixture of 80% by mass of deinked pulp obtained by deinking Kent waste paper and 20% by mass of hardwood bleached kraft pulp. part, light calcium carbonate (trade name "Tamapearl TP121-6S", manufactured by Okutama Kogyo Co., Ltd., having peaks between particle sizes of 0.1 to 1 μm and between 1 μm to 10 μm, volume-based average primary particle size 2 to 3 μm) was added in an amount of 9 parts by mass.
As the paper material for the surface layer, light calcium carbonate (trade name "Tamapearl TP121- 6S”, manufactured by Okutama Kogyo Co., Ltd., having peaks between particle sizes of 0.1 to 1 μm and between 1 μm to 10 μm, and having a volume-based average primary particle size of 2 to 3 μm). board.
A slurry of recycled magazine pulp having a whiteness of 40% was used as the middle layer stock.
As the stock for the backing layer, a pulp slurry with a whiteness of 51% was used, which was a mixture of 50% by mass of waste newspaper, 40% by mass of waste magazine paper, and 10% by mass of pulp derived from shredded office waste paper.

<Examples 2 and 3, Comparative Examples 1 to 3>
White paperboard was obtained in the same manner as in Example 1, except that the amount of calcium carbonate was changed as shown in Table 1.

<Evaluation>
"ruled line crack"
The resulting white paperboard was evaluated for crease cracking in accordance with T495 om-82 "Paperboard folding index" standardized as the Tappi standard test method under the condition that the groove width of the recess was about 3.5 times the paper thickness. .
A: No crack occurred.
◯: Slight cracking occurred, but no problem at all.
(triangle|delta): A crack generate|occur|produced.
x: Severe cracking occurred.

"Surface Strength"
On the surface of the surface layer of the obtained white paperboard, printing was performed using Ink Tac 6 (manufactured by Toyo Ink Mfg. Co., Ltd.) using an RI tester (manufactured by Akira Seisakusho Co., Ltd.). The peeled state of fibers per 10 cm ² was visually observed and evaluated according to the following criteria.
(double-circle): There is almost no peeling of a fiber.
◯: There is slight peeling of the fiber.
Δ: Slight peeling of fibers.
x: There is peeling of a fiber.

"swell"
The resulting white paperboard was subjected to JAPAN TAPPI Paper Pulp Test Method No. 18-1 Paper and Paperboard--Inner Bond Strength Test Method--Part 1: Measured according to Z-axis tensile test.
A: The interlaminar strength exceeds 400 kPa, and no swelling occurs.
◯: The interlaminar strength is 350 kPa or more and 400 kPa or less, and no swelling occurs.
Δ: The interlaminar strength is less than 350 kPa, and blistering occurs.
x: Obvious swelling occurred during production, and production was discontinued.

"Surface surface quality"
The surface quality of the surface layer of the obtained white paperboard was visually observed and evaluated according to the following criteria.
A: Excellent smoothness and excellent surface whiteness.
◯: One of smoothness and surface whiteness is slightly inferior, but there is no practical problem.
Δ: Poor in one of smoothness and surface whiteness, causing practical problems.
x: The surface is rough, and there is a problem in practical use.

In Examples 1 to 3, the evaluation results for cracks in creases, surface strength, interlayer strength, and surface quality of the surface layer surface were all good, and the surface whiteness was sufficiently high. In addition, no cracking of ruled lines occurred, and swelling during drying did not occur.
In Comparative Example 1, a large amount of calcium carbonate was added to the slurry of the pulp raw material for the surface layer, and severe crease cracking occurred. In addition, the surface strength and interlaminar strength decreased, and blistering occurred during drying.
In Comparative Example 2, the amount of calcium carbonate added to the slurry of the pulp raw material for the surface lower layer was small, the surface whiteness was insufficient, and the surface quality of the surface layer surface was insufficient.
In Comparative Example 3, the amount of calcium carbonate added to the slurry of the pulp raw material for the surface layer was small, and the surface quality of the surface layer surface was insufficient.
In Comparative Example 4, the amount of calcium carbonate added to the slurry of the pulp raw material for the surface lower layer was large, and crease cracks occurred, the surface strength was lowered, the surface of the surface layer was rough, and the smoothness was insufficient. . Moreover, swelling occurred at the time of drying.

Claims (8)

A method for producing a white paperboard having at least a surface layer, a surface and bottom layer, a middle layer and a back layer,
Using a surface layer paper stock obtained by adding 5 to 12 parts by mass of calcium carbonate to 100 parts by mass of the surface layer pulp material to a slurry of the surface layer pulp material containing at least one of deinked pulp and bleached pulp 3 to 8 parts by mass of calcium carbonate is added to 100 parts by mass of the pulp raw material for the lower surface layer to a slurry of pulp raw material for the lower surface layer containing deinked pulp derived from waste magazine paper. A method for producing white paperboard, characterized in that the lower surface layer is made into paper using the lower surface layer stock obtained by the above method. 2. The method for producing white paperboard according to claim 1, wherein the amount of calcium carbonate added to 100 parts by mass of the pulp material for the surface layer is larger than the number of parts added of calcium carbonate to 100 parts by mass of the pulp material for the lower surface layer. The method for producing white paperboard according to claim 1 or 2, wherein the calcium carbonate added to the slurry of the pulp raw material for the surface lower layer is light calcium carbonate. 4. The white paperboard according to claim 3, wherein the particle size distribution of the light calcium carbonate added to the slurry of the pulp raw material for the surface lower layer has peaks between 0.1 μm and 1 μm and between 1 μm and 10 μm. manufacturing method. The method for producing white paperboard according to any one of claims 1 to 4, wherein the calcium carbonate added to the slurry of the pulp raw material for the surface layer is light calcium carbonate. 6. The white paperboard according to claim 5, wherein the particle size distribution of the light calcium carbonate added to the slurry of the pulp raw material for the surface layer has peaks between 0.1 μm and 1 μm and between 1 μm and 10 μm. Production method. The method for producing white paperboard according to any one of claims 1 to 6, wherein a pigment coating liquid containing a pigment and a binder is applied to the surface of the surface layer. 8. The manufacture of the white paperboard according to any one of claims 1 to 7, wherein a calcium carbonate dispersion in which calcium carbonate is dispersed in water is added to each of the surface layer pulp raw material slurry and the surface lower layer pulp raw material slurry. Method.