JP6414356B1 - Manufacturing method of coated paperboard - Google Patents

Abstract

The present invention provides a coated paperboard in which unevenness of whiteness on the back side is not noticeable even if the use ratio of pulp with low whiteness is high, and excellent in printability.
A base paper having at least a surface layer, an intermediate layer, and a back layer is formed, and after forming a back pigment coating layer containing a pigment and a binder on the back layer surface of the base paper, a first calendar treatment is performed,
Next, after a surface pigment coating layer containing a pigment and a binder is formed on the surface of the base paper, a second calendar treatment is performed.
[Selection figure] None

Description

  The present invention relates to a method for producing a coated paperboard. More specifically, the present invention relates to a coated paperboard in which unevenness of whiteness on the back side is not noticeable even when the use ratio of the low whiteness pulp is high and the printability is excellent.

Paperboards composed of multi-layered paper with surface, middle and back layers are generally used for paper containers (boxes, blister packs, etc.), paper products (sample book mounts, albums, etc.), publications (magazines, books, etc.) Used for commercial printing (catalogs, pamphlets, etc.).
In the manufacture of paperboard, in recent years, saving of wood resources and paper recycling have been encouraged from the viewpoint of protecting the global environment, and the use of used wastepaper as a raw material for pulp has been widely performed.

It is known that when used paper is less rigid than virgin pulp, there is a problem that the use of a large amount of used paper works negatively for paper for applications that require rigidity.
In particular, when the surface strength of the paperboard is insufficient, a so-called white spot problem is likely to occur in which a part of the printing is lost due to the dropped fibers.

The coated paperboard is a paperboard provided with a coating layer containing a pigment on the surface for the purpose of imparting printability and the like. Printing on coated paperboard is mainly performed on the surface layer side, but there are also cases where printing is performed on the back surface, and coating with a coating layer containing a pigment on both the surface layer side and the back layer side. Paperboard has also been proposed (Patent Document 1).
According to Patent Document 1, it is said that by providing a coating layer containing a pigment on the back layer side, the printability of the back layer side is improved and the problem of white spots can be solved.

JP 2000-192395 A

However, in recent years, as the percentage of used paper increases, the amount of used paper that is unsuitable for reuse as paper increases. Even if coating layers are provided on both sides as in Patent Document 1, the problem of white spots is solved. Tends to be insufficient. In particular, when the back layer contains pulp derived from a shredded product of office paper, the tendency is strong because it contains fine fibers.
Further, in the middle layer and the back layer, there is a tendency that the use ratio of the low whiteness pulp is increased as in the case of the magazine waste paper pulp. Even if the coating layer is provided on the back layer side as in Patent Document 1, the back layer Unevenness occurs in the whiteness of the side, making it difficult to obtain sufficient printability.
In view of the above circumstances, an object of the present invention is to obtain a coated paperboard that is not conspicuous in unevenness of whiteness on the back side and has excellent printability even if the use ratio of pulp having low whiteness is high.

In order to achieve the above object, the present invention employs the following configuration.
[1] After forming a base paper having at least a surface layer, an intermediate layer, and a back layer, and forming a back pigment coating layer containing a pigment and a binder on the back layer surface of the base paper, a first calendar treatment is performed,
Next, after forming a surface pigment coating layer containing a pigment and a binder on the surface of the base paper, a second calendering process is performed, and the method for producing a coated paperboard is provided.
[2] The method for producing a coated paperboard according to [1], wherein the second calendering process is a kind selected from a soft nip calender and a gloss calender.
[3] The method for producing a coated paperboard according to [1] or [2], wherein the second calendar treatment is performed while supplying moisture to the surface of the back pigment coating layer.
[4] The method for producing a coated paperboard according to any one of [1] to [3], wherein the coating amount of the back pigment coating solution is less than the coating amount of the surface pigment coating solution.
[5] The method for producing a coated paperboard according to any one of [1] to [4], wherein the coating amount of the back pigment coating solution is 0.1 to 7.5 g / m ² .
[6] The method for producing a coated paperboard according to any one of [1] to [5], wherein the coating amount of the surface pigment coating solution is 5 to 30 g / m ² .
[7] The method for producing a coated paperboard according to any one of [1] to [6], wherein the back surface pigment coating solution is applied with a size press.

  According to the method for producing a coated paperboard of the present invention, even when the use ratio of low whiteness pulp is high, unevenness of the whiteness of the surface is suppressed, and a coated paperboard having excellent printability on the back surface can be obtained. .

[Production method]
The present invention forms a base paper having at least a surface layer, an intermediate layer, and a back layer, and after forming a back pigment coating layer containing a pigment and a binder on the back layer surface of the base paper, performs a first calendar treatment, Next, after the surface pigment coating layer containing a pigment and a binder is formed on the surface of the base paper, a second calendering process is performed.

"Base paper"
The base paper in the present invention is a multilayer papermaking in which at least a surface layer, a middle layer, and a back layer are laminated. The surface layer is the layer that is arranged on the most front side in the base paper of the multilayer paper making, the back layer is the layer that is arranged on the most back side (opposite side to the surface layer), and the middle layer is the surface layer and the back layer. It is a layer arrange | positioned between. A surface lower layer may be provided between the surface layer and the middle layer. A back lower layer may be provided between the back layer and the middle layer. Each layer may be formed by a single layer or a plurality of layers, but in order to increase the amount of low-quality waste paper pulp used, it is preferable to form the middle layer by a plurality of layers. Each of these paper layers is laminated by multilayer papermaking.

  A known multilayer paper machine can be used for multilayer paper making. For example, a combination of wire parts such as a round net type, a long net type, a short net type, an inclined type, a twin wire type, etc., a long net pattern, a short net pattern, a short net pattern combination, a long net pattern There are combinations. Among these, the use of short netting is preferable from the viewpoint of improving the yield of waste paper pulp containing a large amount of fine fibers.

  The base paper in the present invention is mainly composed of pulp, and 70% or more of all pulp components constituting the base paper are preferably waste paper pulp. The ratio of waste paper pulp in the total pulp components is more preferably 75 to 100% by mass, and further preferably 80 to 95% by mass.

In the present invention, the used paper pulp is a pulp obtained by recycling used paper.
As used paper, for example, white paper and ruled white paper that has been used once, but has few printed parts, printed matter such as cards, imitations, color, Kent, white art, and colored paper that has been used once, Used high-quality used paper such as coated paper for printing, beverage packs, office paper, etc.Furthermore, medium-quality used paper such as tickets / medium anti-old / Kent Manila, general medium-sized used paper such as newspapers / magazines / miscellaneous paper, Examples include tea-based waste paper such as cut tea, plain tea, miscellaneous bags, and cardboard. Used paper such as office paper and tickets having confidentiality may be a shredder processed product.
As the waste paper pulp, a disintegrated pulp obtained by disaggregating used paper, an unbleached deinked pulp subjected to a disaggregating process and a deinking process, a bleached deinked pulp subjected to a bleaching process after the deinking process, and the like can be appropriately used.

  Examples of so-called virgin pulp that is not waste paper pulp include, for example, softwood unbleached kraft pulp (NUKP), hardwood unbleached kraft pulp (LUKP), softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), and hardwood half bleached Kraft pulp (LSBKP), softwood semi-bleached kraft pulp (NSBKP), hardwood sulfite pulp, softwood sulfite pulp and other chemical pulp, thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemiground pulp (CGP), refiner Examples include mechanical pulps such as ground pulp (RGP), ground pulp (GP), pressed stone ground pulp (PGW), and stone ground pulp (SGP).

The pulp constituting the base paper is preferably 70% or more of waste paper pulp as a whole, but the blending ratio of waste paper pulp can be appropriately adjusted for each layer according to the role of each layer. Moreover, the kind of used paper pulp used for each layer can also be suitably selected according to the role of each layer for every layer.
In any layer, two or more kinds of used paper pulp may be mixed and used. Moreover, when using virgin pulp, you may mix and use 2 or more types of virgin pulp.
Hereinafter, although the normal pulp composition etc. in each layer are demonstrated, this invention is not limited to the following normal pulp composition etc.

  For the surface layer, pulp with high whiteness is usually used. For example, the above virgin pulp and waste paper deinked pulp can be mainly used. As the used paper, used paper with high whiteness such as upper white / card, extra white / middle white / white Manila, imitation / color, etc. can be preferably used.

The basis weight of the surface layer is preferably set to 15~90g / ^{m 2,} and more preferably a 25~70g / ^{m 2.} The basis weight of each layer constituting the base paper can be measured according to JIS P8124.
If the basis weight of the surface layer is at least the preferred lower limit, the colored foreign matter in the middle layer can be sufficiently concealed. Further, if the basis weight of the surface layer is not more than the preferred upper limit value, sufficient paper layer strength can be obtained.

  When providing a surface lower layer, the pulp which comprises a surface lower layer uses the pulp whose whiteness is higher than the pulp of a middle layer, and whiteness is lower than the pulp of a surface layer. Although the pulp used for the surface layer may be used for the surface layer, usually, low-grade waste paper compared to the surface layer, that is, waste paper containing a lot of medium fibers is used. For example, deinked waste paper pulp such as newspapers, magazines, colors, and balls is generally used.

Table lower basis weight is preferably in a 15~90g / ^{m 2,} and more preferably a 25~75g / ^{m 2.}
If the basis weight of the surface lower layer is equal to or more than the preferred lower limit value, the colored foreign matter in the middle layer can be sufficiently concealed together with the surface layer. Further, if the basis weight of the front and lower layers is not more than the preferred upper limit value, sufficient paper layer strength can be obtained.

The middle layer is usually composed of a plurality of layers, but may be a single layer. When the middle layer is composed of a plurality of layers, the pulp constituting each layer may be all the same or different.
Since the middle layer is a layer sandwiched at least between the front layer and the back layer, usually the lowest pulp among the layers constituting the base paper is generally used. For example, disintegrated pulps such as newspapers, magazines, tickets, medium-sized antiquity, tea imitation, corrugated cardboard, mounts, ground cards, balls, and the like can be mentioned.
The total basis weight of the middle layer is appropriately adjusted according to the thickness required for the application of the coated paperboard, but the basis weight per layer is preferably 15 to 90 g / m ^2, and preferably 25 to 75 g. / M ² is more preferable.

  When providing a back lower layer, the pulp which comprises a back lower layer uses the pulp whose whiteness is higher than the pulp of a middle layer, and whiteness is lower than the pulp of a back layer. For the back and bottom layers, the surface layer and the pulp used for the top and bottom layers may be used. Usually, however, waste paper that is lower in comparison with the surface layer, that is, waste paper containing a lot of medium fibers is used. For example, unbleached waste paper pulp such as newspapers, magazines, colors and balls is generally used.

The basis weight of the lower back is preferably in a 15~90g / ^{m 2,} and more preferably a 25~75g / ^{m 2.}
If the basis weight of the back lower layer is equal to or more than the preferred lower limit, the colored foreign matter in the middle layer can be sufficiently concealed together with the back layer. Moreover, if the basis weight of the back lower layer is not more than the preferable upper limit value, sufficient paper layer strength can be obtained.

For the back layer, whiteness as high as the surface layer is not required, but in order to touch human eyes, pulp having whiteness higher than that of the middle layer is usually used. You may include the pulp derived from the waste paper gypsum board collect | recovered in the state which peeled off the gypsum from the paper used for the shredder processed material, such as office paper, and the paper used for the gypsum board.
When at least one kind of pulp selected from the group consisting of pulp derived from a shredder processed product and pulp derived from waste gypsum board is used as the waste paper pulp constituting the base paper, it is preferably blended in this backing layer. This is because these pulps have a relatively high whiteness even without deinking or bleaching.

However, since the pulp obtained by disaggregating the shredder-treated product such as office paper is collected in a finely cut state, the obtained pulp is a pulp having a lot of fine fibers. In addition, because of its shape, it is difficult to blend in water during the disaggregation treatment, and thus it is difficult to mix in a large amount. Pulp derived from waste gypsum board is also a pulp with many fine fibers.
Therefore, when using at least one kind of pulp selected from the group consisting of pulp derived from shredded products and pulp derived from waste gypsum board as the back layer, these pulps are 2 to 40% by mass of the pulp constituting the back layer. It is preferable that it is 3 to 30% by mass.

The basis weight of the backing layer is preferably in a 15~90g / ^{m 2,} and more preferably a 25~70g / ^{m 2.} The basis weight of the middle layer is appropriately adjusted according to the thickness required by the application of the coated paperboard.
If the basis weight of the back layer is not less than the preferred lower limit value, the colored foreign matter in the middle layer can be sufficiently concealed. In addition, if the basis weight of the back layer is equal to or less than the preferable upper limit value, sufficient paper layer strength can be obtained.

  In the manufacturing method of this invention, it is preferable to make the basic weight of a surface layer smaller than the basic weight of a surface layer, and to make the basic weight of a surface layer lower than the basic weight of a middle layer. More preferably, the basis weight of the front and lower layers is equal to or less than the basis weight per layer of the multi-layered middle layer. By reducing the basis weight of the surface layer and the lower layer and increasing the basis weight of the middle layer, the blending amount of the base paper of the disaggregated waste paper can be increased.

  The above-described pulp slurry composition used for each layer from the surface layer to the back layer, if necessary, paper strength enhancer, water resistant agent, water repellent, foamable microcapsule, sizing agent, dye, Yield improver, filler, pH adjuster, slime control agent, thickener, preservative, fungicide, antibacterial agent, flame retardant, antiseptic, rodenticide, insect repellent, moisturizer, freshness retainer, oxygen scavenger , Microcapsules, foaming agents, surfactants, electromagnetic shielding materials, antistatic agents, rust inhibitors, fragrances, deodorants and the like can be selected and blended. These can be used in combination.

"Back side pigment coating layer"
In the production method of the present invention, first, a back surface coating liquid containing a pigment and a binder is applied to the back layer side of the base paper and dried to form a back surface pigment coating layer.
The back side pigment coating layer has the pigment fixed to the back side of the base paper with a binder, and part of the binder penetrates into the inside of the base paper, preventing fine fibers from falling off the back side. It is thought to do.
In addition, after forming the surface pigment coating layer first, when the back pigment coating layer is formed, the water used in the coating liquid for the back pigment coating layer penetrates into the inside of the base paper, the middle layer, etc. Since the colored component contained in the used paper pulp used for is transferred to the surface side of the base paper and the whiteness on the surface side is lowered, it is not suitable.

  Examples of the pigment generally include pigments and fillers used for coating on paper or paperboard or for internal addition to paper. Specific examples include magnesium carbonates; calcium and magnesium carbonates such as dolomite; kaolin, natural clay, calcined clay, wax, bentonite, feldspar, talc, mica, wollastonite, synthetic silicic acid Silicates such as aluminum and synthetic calcium silicate; Hydrous aluminosilicates such as natural zeolite and synthetic zeolite; Silicates such as diatomaceous earth, quartzite powder, hydrous fine powdered silicic acid (white carbon), anhydrous fine powdered silicic acid; Aluminum such as synthetic aluminum hydroxide Hydrate; Barium sulfate such as barite and blank finks; Calcium sulfate such as gypsum and synthetic calcium sulfite; calcium sulfite; Titanium dioxide such as anatase type titanium dioxide and rutile type titanium dioxide; Lithium aluminum carbonate; It is done. Of these, kaolin, talc, and calcium carbonate are preferable.

  When the back surface coating liquid contains a pigment, the coating layer formed from the back surface coating liquid can be prevented from cracking when the coated paperboard is processed into a box or the like. In particular, kaolin and talc are plate-like pigments, and when used, the number of micro-projections on the back surface is relatively small, and even if the surface and the back surface are rubbed after offset printing, the surface printed layer is hardly roughened. Calcium carbonate and titanium dioxide are white pigments, which are preferable because they can increase the whiteness of the back layer and improve printability. In particular, kaolin as a plate-like pigment and calcium carbonate as a white pigment are preferable pigments.

  The average particle diameter of the pigment is preferably 0.1 to 2.5 μm, and more preferably 0.1 to 1.5 μm. It is preferable that the average particle diameter of the pigment is equal to or more than a preferable lower limit value, because dropping of fine fibers is suppressed. It is preferable that the average particle diameter of other pigments is less than or equal to the preferable upper limit value because micro protrusions can be reduced on the coated surface. In addition, the average particle diameter of the pigment in the present specification means a particle diameter measured by a sedimentation method (Cedigraph) and having a cumulative mass of 50%.

  As the binder, an aqueous adhesive is preferable. Water-based adhesives include oxidized starch, phosphate esterified starch, hydroxyethyl etherified starch, dextrin, enzyme-modified starch, water-soluble starch and the like; styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer Latex such as latex, conjugated diene copolymer latex such as styrene-methyl methacrylate-butadiene copolymer latex, acrylic copolymer latex such as copolymer latex of acrylate ester and / or methacrylate ester; casein Proteins such as gelatin, soybean protein, various polyvinyl alcohols, various polyacrylamides, synthetic resin adhesives such as melamine resins, various cellulose derivatives such as carboxymethylcellulose, etc., one or two of these adhesives that's all Selected and can be used.

Among them, it is preferable to add a latex having a glass transition temperature measured by vibron viscoelasticity of −50 to 30 ° C., because the flexibility of the coated surface is increased and the crease resistance is improved.
In consideration of the second calendar treatment described later, the glass transition temperature of the latex is more preferably −50 to −5 ° C.
Moreover, it is preferable to mix | blend starch with the said latex. When latex and starch are used in combination, it is preferable because the fine fibers in the back layer can be fixed and the surface strength of the surface of the back layer can be balanced.
The mass ratio of latex to starch is preferably 100: 0 to 5:50.

The back pigment coating solution preferably contains 4 to 1000 parts by mass of binder, more preferably 10 to 800 parts by mass with respect to 100 parts by mass of pigment.
If the ratio of the binder is at least the preferred lower limit, it is easy to obtain sufficient interlayer strength, and the punching suitability at the time of box making is also excellent. Moreover, if the ratio of a binder is below a preferable upper limit, it is excellent in the folding property at the time of box making.

  For the back pigment coating liquid, if necessary, a dispersant, a pH adjuster such as sodium hydroxide / ammonia water, an antifoaming agent, a fluorescent dye, a mold release agent, a water resistance agent, a fluidity improver, You may contain 1 or more types, such as a slime control agent, antiseptic | preservative, dye, and a color pigment.

The coating amount of the back pigment coating layer is preferably 0.1~7.5g / ^{m 2,} is preferably 1 to 6 g / ^{m 2,} is 1.5 to 4 g / ^{m 2} Is more preferable. In the present specification, the coating amount means a dry coating amount.
If the coating amount of the back pigment coating layer is at least the preferred lower limit, it is easy to obtain sufficient strength on the back layer side. If the coating amount of the back pigment coating layer is less than or equal to the preferred upper limit value, it is easy to ensure the folding ability during box molding and the paste permeability.

  The coating apparatus for the back surface coating liquid is not particularly limited, and a known coating apparatus can be used, for example, blade coater, air knife coater, roll coater, reverse roll coater, bar coater, curtain coater, slot die coater. For example, a coater, a gravure coater, a champlex coater, a brush coater, a slide bead coater, a two-roll or metering blade type size press coater, a bill blade coater, a short dwell coater, a gate roll coater, a nip coater using a calendar, and the like are appropriately used.

  These may be on-machine coaters or off-machine coaters. Among these, coating by a size press is preferable because fine fibers can be fixed at an early stage. In particular, the rod metering size press and the gate roll size press, once formed a coating liquid film, and then transferred to the base paper, it does not apply a strong pressure during coating, coloring components derived from waste paper pulp Can be suppressed, which is preferable.

"First calendar process"
After forming the back pigment coating layer, a first calendar process is performed. By performing this first calendar treatment, the back pigment coating layer is smoothed and becomes a layer having excellent printability, and at the same time, the surface layer of the base paper is densified to be applied later. Infiltration of the surface pigment coating layer into the surface layer can be prevented.
As the calendar device to be used, a known calendar device can be used, and examples thereof include a super calendar, a gloss calendar, a soft nip calendar, a hard nip calendar, and a shoe calendar. For example, a machine calendar incorporated in a paper machine such as a 6-roll 5-nip, 3-roll 2-nip can be used.

In the first calendar process, the base paper on which the back pigment coating layer is formed may be nipped between the metal roll and the metal roll, or may be nipped between the metal roll and the resin roll.
Further, the first calendar process may be one nip of two rolls, or may be a multistage process. In the case of multiple stages, it may be only the nip between the metal roll and the metal roll, or only the nip between the metal roll and the resin roll, or the nip and metal between the metal roll and the metal roll. There may be both a nip between the roll and the resin roll.

The calendar roll used for the first calendar process may be heated. The heating temperature is preferably 80 to 300 ° C, more preferably 120 to 200 ° C.
The first calendar process is preferably performed by a machine calendar installed after the dryer part because the calendar process can be performed at a high paper surface temperature.
The linear pressure in the first calendar process is preferably 300 kN / m or less, and more preferably 150 kN / m or less. Although it does not specifically limit about a lower limit. It can also be done with the roll's own weight. Excessive linear pressure increases the density of the coated paperboard, making it difficult to obtain sufficient bulk and strength.

"Surface pigment coating layer"
After the first calendar treatment, a surface pigment coating layer is formed on the surface layer side. The surface pigment coating layer can be formed by coating and drying a surface pigment coating solution containing a pigment and a bander. The surface pigment coating layer may be a single layer or multiple layers. In the case of multiple layers, each layer can be configured for different purposes. For example, the undercoat layer can be formed for the purpose of hiding the low whiteness of the base paper, and the overcoat layer can be formed for the purpose of imparting printability.

Examples of the pigment include one or more publicly known pigments used in the general coated paper manufacturing field such as kaolin, heavy calcium carbonate, light calcium carbonate, titanium dioxide, aluminum hydroxide, silica, satin white, and talc. The present invention can be used as appropriate within the above specified range without impairing the effects of the present invention. In particular, calcium carbonate is preferable because it provides excellent printability.
As the binder, known and publicly used binders used in the general coated paper manufacturing field can be used. As a preferable binder, those exemplified for the back pigment coating layer can be used. Particularly preferred is a styrene-butadiene copolymer latex.

The surface pigment coating liquid preferably contains 2 to 50 parts by mass of binder and more preferably 5 to 20 parts by mass with respect to 100 parts by mass of pigment.
If the ratio of a binder is more than a preferable lower limit, the strength of the coating layer of the surface pigment coating layer can be obtained. Moreover, if the ratio of a binder is below a preferable upper limit, ink drying property will be excellent and box-making suitability will also be excellent.
In addition, if necessary, a dispersant, a pH adjuster such as sodium hydroxide or ammonia water, an antifoaming agent, a fluorescent dye, a mold release agent, a water resistance agent, a fluidity improver, a slime control agent, an antiseptic agent In addition, one or more of dyes, coloring pigments and the like may be contained.

  The surface layer side is required to have higher printability and whiteness than the back layer side. Therefore, the coating amount of the surface pigment coating layer is preferably larger than the coating amount of the back pigment coating layer. In other words, the coating amount of the back pigment coating layer is preferably smaller than the coating amount of the surface pigment coating layer.

The coating amount of the surface pigment coating layer is preferably 5 to 50 g / ^{m 2} is preferably 8~45g / ^{m 2,} further preferably 10~35g / ^{m 2.}
When the surface pigment coating layer is applied a plurality of times, for example, twice, the first (undercoat layer) and second (overcoat layer) coating solutions may be the same or different. In particular, it is preferable to apply a surface pigment coating solution for the undercoat layer and a surface pigment coating solution for the topcoat layer, and sequentially form the undercoat layer and the topcoat layer.

The coating device for the surface pigment coating solution is not particularly limited, and a known coating device can be used, for example, blade coater, air knife coater, roll coater, reverse roll coater, bar coater, curtain coater, slot Die coater, gravure coater, champlex coater, brush coater, slide bead coater, two-roll or metering blade type size press coater, bill blade coater, short dwell coater, gate roll coater, nip coater with calendar, etc. are used as appropriate. .
These can be on-machine coaters or off-machine coaters, but when the surface pigment coating layer is formed immediately after the first calendering treatment of the pretreatment, the surface surface is kept in a dense state. It is preferable because it can be applied in a coated state.

"Second calendar process"
After forming the surface pigment coating layer, a second calendar treatment is performed. By performing this second calendering treatment, the surface pigment coating layer is smoothed to become a layer excellent in printability, and at the same time, the pigment coating layer on the back surface is further smoothed. Since the back surface pigment coating layer is calendered twice even with a small coating amount, printability is improved as compared with the prior art.

As a calendar to be used, a known calendar device can be used. For example, a super calendar, a gloss calendar, a soft nip calendar, a hard nip calendar, a shoe calendar, etc. can be used. You may combine these apparatuses.
Of these, a gloss calender and a soft nip calender using a heating roll are preferable from the effect of increasing the smoothness of the surface pigment coating layer. In particular, it is preferable from the balance between the density and smoothness of the coated paper board from which a soft nip calender is obtained.

The soft nip calender is a calender provided with a heated metal roll and an elastic roll. The metal roll is preferably heated to 80 to 300 ° C, more preferably 120 to 200 ° C.
The linear pressure of the soft nip calendar in the second calendar process is preferably 3 to 180 kN / m, and more preferably 5 to 50 kN / m.

The second calendering process may be one nip of two rolls, or may be a multistage process. When processing one nip with a soft nip calender, the surface pigment coating layer is processed so as to contact the metal roll.
In the present invention, since the back pigment coating layer has already been smoothed by the first calendering process, the surface pigment coating layer that has not been smoothed is smoothed. The surface pigment coating layer in contact with the heated metal roll can obtain excellent smoothness and gloss.

Even when a 1-nip process is performed with a soft nip calender, the smoothness of the back pigment coating layer is also improved to some extent. This is because pressure is also applied to the back surface from the elastic roll of the soft nip calender.
In addition, the paper surface temperature on the back surface side is not as high as that on the front surface side. Therefore, for example, when a latex having a glass transition temperature of −50 to −5 ° C. is used as the binder of the back surface pigment coating layer, the coating layer is slightly present. It is thought that it is plasticized and smoothed.
When the second calendering process is performed with a plurality of soft nip calenders, the back pigment coating layer is treated so as to be in contact with the metal roll, and then the front pigment coating layer is treated so as to be in contact with the metal roll. Is preferred.

  Moreover, it is also preferable to perform a 2nd calendar process, supplying a water | moisture content to the back surface pigment coating layer surface. Examples of a method for performing the calendar treatment while supplying moisture to the surface of the back pigment coating layer include a method of imparting moisture by forming a water film on a calender roll and pressing it onto the surface of the back pigment coating layer. It is done. Moreover, you may give directly to the surface of a back surface pigment coating layer using spray etc. When the calendar treatment is performed while supplying moisture to the surface of the back pigment coating layer, the surface of the coating layer is pressed in a wet state, so that a smoother coated surface can be obtained. In this case, both surfaces can be dried with a cylinder dryer or the like after the calendar process.

Calendering while supplying moisture can be done with a nip between a metal roll and a metal roll, with a nip between a metal roll and a resin roll, or with a nip between a metal roll and an elastic roll. (Soft nip calender) is also acceptable.
A soft nip calender may be further performed after performing a calendering process with a nip between a metal roll and a metal roll or between a metal roll and a resin roll while supplying moisture.

The amount of moisture supplied depends on whether or not soft nip calendering is performed after calendering while supplying moisture, and whether or not there is a drying facility after the second calendering and its capability, but it is in a wet state. And preferably about ² to 12 g / m ² . If water is supplied excessively, not only will drying equipment be required, but water will penetrate into the base paper, and the colored components of the waste paper pulp used for the middle layer will move to the surface layer, resulting in surface whiteness. Will be lowered.
When supplying water, not only water but water containing a paper strength agent such as polyacrylamide or polyvinyl alcohol may be supplied. If water containing a paper strength agent is supplied, the effect of preventing fine fibers from falling off can be further enhanced.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example. In addition,% is the mass% unless there is particular notice. Further, the “parts” of the raw materials other than the medium are parts by mass not including the dispersion medium unless otherwise specified.

[Example 1]
"Preparation of surface pigment coating solution (for undercoat layer)"
As a pigment, 100 parts of heavy calcium carbonate (trade name: FMT-OP, manufactured by Phimatech, average particle diameter 0.6 μm), and as a binder, oxidized starch (trade name: Oji Ace Y, manufactured by Oji Cornstarch) 3 parts, 14 parts of styrene-butadiene copolymer latex (trade name: T2548A, manufactured by JSR, glass transition temperature -34 ° C., average particle diameter 140 nm), a trace amount of sodium polyacrylate and water as a dispersant A surface pigment coating liquid (for undercoat layer) having a solid content concentration of 62% was prepared.

"Preparation of surface pigment coating solution (for topcoat layer)"
As pigments, 5 parts of heavy calcium carbonate (trade name: FMT-OP, supra), 90 parts of kaolin (trade name: Ultra White 90, manufactured by BASF, average particle size 0.32 μm), and titanium dioxide ( 5 parts of trade name: KA-100, manufactured by Korea Cosmo Chemical Co., Ltd., 2 parts of oxidized starch (trade name: Ace Y, supra) and styrene-butadiene copolymer latex (trade name: trade name: Korea Cosmo Chemical Co., Ltd.) 16 parts of B1840, manufactured by Asahi Kasei Chemicals Corporation, average particle size 95 nm), and using a trace amount of sodium polyacrylate and water as a dispersant, a surface pigment coating liquid (for topcoat layer) having a solid content concentration of 62% is prepared. did.

"Preparation of back side pigment coating solution"
As pigment, 70 parts of kaolin (trade name: Ultra White 90, supra) and 30 parts of heavy calcium carbonate (trade name: FMT-OP, supra) are used, and oxidized starch (trade name: trade name: 3 parts of Oji Ace Y, supra) and 14 parts of styrene / butadiene copolymer latex (trade name: T2548A, supra) were added, respectively, and finally the back side pigment coating solution with a solid content concentration of 26% Got.

"Manufacture of coated paperboard"
In the wire part of a paper machine, the surface pulp is 30 g / m ² , the lower layer pulp is 40 g / m ² , the middle layer pulp is 150 g / m ² , and the back layer pulp is 50 g / m ² . and papermaking each m ^2, and the to cause抄合, and dewatering process in the press part, to obtain a base paper in a wet state of basis weight 270 g / m ^2.
As the pulp for the surface layer, 80% pulp obtained by deinking fine waste paper (printed and collected from bookbinding companies) and 20% hardwood bleached kraft pulp were mixed, and a pulp having a whiteness of 85% was used. .
As the pulp for the front and lower layers, deinked magazine waste paper pulp having a chromaticity of 65% was used.
As the middle layer pulp, magazine waste paper pulp having a whiteness of 40% was used.
As the back layer pulp, used was a pulp having a whiteness of 53%, blended in a ratio of 45% newspaper waste paper pulp, 35% magazine waste paper pulp, and 20% pulp derived from shredded office waste paper.

Then, after drying to some extent in the pre-dryer part of the dryer part, using a rod metaling type size press, the back surface pigment coating solution is applied to the back layer surface so that the coating amount is 4 g / m ^2. Worked.
Then, the drying process was carried out with an after-dryer part, and then the first calendar process was carried out with a machine calendar (linear pressure 35 kN / m). A soft nip calender was used as the machine calendar subjected to the first calendar process.

Next, the surface pigment coating solution (for the undercoat layer) is applied with a rod blade coater so that the coating amount is 10 g / m ² , dried with a drier, and further the surface pigment coating solution (overcoat layer). Was coated with a rod blade coater so that the coating amount was 10 g / m ² and dried with a dryer.
Then, the 2nd calendar process was performed and the coated paperboard of Example 1 was obtained. As the second calendering treatment, a soft nip calender was used, and the surface pigment coating layer side was passed through so that the surface temperature of the roll was in contact with a metal roll heated to 200 ° C. (linear pressure 35 kN / m).

[Comparative Example 1]
The back side pigment coating solution is not applied with a size press, but is applied to the back layer surface of the base paper using a rod blade coater after machine calendering, and then the surface pigment coating solution (for the undercoat layer), surface A coated paperboard of Comparative Example 1 was obtained in the same manner as in Example 1 except that the pigment coating solution (for the topcoat layer) was coated.

[Comparative Example 2]
The surface pigment coating layer (for the undercoat layer and the top coat layer) is applied to the surface of the base paper using a rod blade coater after machine calendering treatment, without applying the back side pigment coating solution with a size press. After forming the pigment coating layer, the coated paperboard of Comparative Example 2 was obtained in the same manner as in Example 1 except that the back pigment coating solution was coated on the back layer surface of the base paper using a rod blade coater. It was.

[Example 2]
The coated paperboard of Example 2 was used in the same manner as in Example 1 except that a pulp having a whiteness of 48% was blended in a ratio of 50% newspaper wastepaper pulp and 50% magazine wastepaper pulp as the back layer pulp. Obtained.

[Example 3]
The second calendering process was changed to the following conditions, and after the second calendering process, the coated paperboard of Example 3 was treated in the same manner as in Example 2 except that both sides were dried with two cylinder dryers. Obtained.
"Calendar processing conditions"
Water was supplied to the bottom roll using a calendar with three metal rolls. Pass the paper through the nip between the top roll and the second roll from the top so that the surface pigment coating layer is in contact with the second roll from the top, and then between the second roll from the top and the bottom roll. The paper was passed through the nip so that the back pigment coating layer was in contact with the bottom roll. The linear pressure at each nip was 20 kN / m. The amount of water supplied to the surface of the back side pigment coating layer was 8 g / m ² .

[Example 4]
In the second calendar treatment, a coated paperboard of Example 4 was obtained in the same manner as in Example 3 except that a 0.1% aqueous solution of polyvinyl alcohol was used instead of water.

[Blank 1]
In the same manner as in Example 1, a wet base paper of 270 g / m ² was obtained. Then, the blank 1 which performed the 1st calendar process, the surface pigment coating layer, and the 2nd calendar process was prepared like Example 1 except not having performed size press.

[Blank 2]
A blank 2 was obtained in the same manner as the blank 1 except that a pulp with a whiteness of 48%, which was blended at a ratio of 50% newspaper waste paper pulp and 50% magazine waste paper pulp, was used as the back layer pulp.

[Evaluation method]
The following evaluation was performed about the coated paperboard of each Example and the comparative example. The results are shown in Table 1.

"Back side inking"
The obtained coated paperboard was cut with a cutter to obtain a lithographic sample of 15 cm × 20 cm. Using a color developing device (a device generally used as an RI printing machine in the field of paper pulp) specified in JIS-K5701 (a test method for lithographic and relief printing inks), TK high echo (black) (Toyo) Ink Co., Ltd. (0.5 cc) was taken, kneaded for 2 minutes, transferred to the back side of the sample and allowed to stand for 1 hour. In addition, Example 1 and specific nuclear examples 1 and 2 were compared with Blank 1 and Examples 2 to 4 were compared with Blank 2.
A: Very good compared to blank.
○: Good compared with blank.
Δ: Slightly better than blank.
×: Level equivalent to blank.

"White spot resistance"
The obtained coated paperboard was cut with a cutter to obtain a lithographic sample. Using a sheet-fed offset printing machine, 1050 sheets of solid printing on the back side of the above flat sample were continuously performed, and the amount of white spots in the solid printing part from the 1000th sheet to the 1050th sheet was determined as follows. Evaluated by criteria.
A: There is no white spot.
○: Slight white spots are recognized, but there is no practical problem.
(Triangle | delta): There exists a white spot and a problem arises depending on a use.
X: White spots are very conspicuous and have practical problems.

"Unevenness of surface whiteness"
The degree of whiteness unevenness on the back of the coated paperboard obtained was visually evaluated.
A: Uniform and no whiteness unevenness.
○: Some whiteness unevenness is recognized, but there is no practical problem.
(Triangle | delta): Whiteness nonuniformity is conspicuous and there is a problem in practical use.
X: Unevenness in whiteness is very conspicuous.

"Surface quality on the back"
The quality of the paper surface on the back surface side of the coated paper board obtained was visually confirmed and evaluated according to the following criteria.
A: Excellent smoothness, gloss and whiteness.
○: One of smoothness, glossiness, and whiteness is slightly inferior, but there is no practical problem.
Δ: Two of the smoothness, glossiness, and whiteness are slightly inferior, but there is no practical problem.
X: One or more of smoothness, glossiness, and whiteness are inferior, and there is a problem in practical use.

As shown in Table 1, all of the coated paperboards of the examples were excellent in ink inking on the back surface, white spots were suppressed, and white unevenness on the surface was not noticeable.
On the other hand, white spots occurred in Comparative Example 1 in which the calendar processing on the back layer side was performed only with the soft nip calendar which is the second calendar processing. This is considered to be because the calendar treatment of the coating layer on the back layer side was not sufficient.

  Further, in Comparative Example 2 in which the surface pigment coating layer was provided before the back pigment coating layer, although the ink inking property and white spot resistance on the back surface were good, the white unevenness on the surface was conspicuous. . This is presumably because the colored component contained in the middle layer or the like has moved to the front side due to moisture when the back pigment coating layer is applied.

Claims (7)

After forming a base paper having at least a surface layer, an intermediate layer, and a back layer, and forming a back pigment coating layer containing a pigment and a binder only on the back layer surface of the base paper, a first calendar treatment is performed,
Next, after forming a surface pigment coating layer containing a pigment and a binder on the surface of the base paper, a second calendering process is performed, and the method for producing a coated paperboard is provided.   The manufacturing method of the coated paperboard of Claim 1 whose said 2nd calendar process is 1 type chosen from a soft nip calender and a gloss calendar.   The manufacturing method of the coated paperboard of Claim 1 or 2 which performs said 2nd calendar process, supplying a water | moisture content to the back surface pigment coating layer surface. The coating amount of the back surface pigment coating layer, the less than the coating weight of the surface pigment coating layer, the manufacturing method of the coated board according to any one of claims 1 to 3. The manufacturing method of the coated paperboard as described in any one of Claims 1-4 whose coating amount of the said back surface pigment coating layer is 0.1-7.5 g / m < ² >. The manufacturing method of the coated paperboard as described in any one of Claims 1-5 whose coating amount of the said surface pigment coating layer is 5-30 g / m < ² >. The manufacturing method of the coated paperboard as described in any one of Claims 1-6 which performs coating of the said back surface pigment coating layer with a size press.