JP7260328B2 - Multilayer paperboard and method for producing same - Google Patents

Description

The present invention relates to multi-layer paperboard and methods of making same. More particularly, the present invention relates to a technology for manufacturing multi-layer paperboard using waste paper pulp that has undergone heat dispersion treatment.

In recent years, waste paper pulp has come to be widely used for paper and paperboard, and it is becoming difficult to obtain waste paper. Therefore, waste paper pulp is prepared from low-grade waste paper such as waste magazine paper as a raw material, and is recycled as a resource. In addition, waste paper derived from gypsum board, which has not been used in the past, adhesives contained in labels, stickers, packing tapes, etc., and adhesive waste magazine paper such as hot-melt magazine spine glue can be used as raw materials for waste paper pulp. A proposal has been made for

For example, Patent Literature 1 proposes to produce waste paper pulp using gypsum board as a raw material by performing a dehydration and concentration step after a screening step. Further, Patent Document 2 proposes a technique for producing used paper pulp containing less sticky foreign matter from insufficiently sorted used paper raw materials.

In general, it is difficult to remove heat-sensitive foam capsules and sublimation ink from waste paper containing heat-sensitive foam capsules and sublimation ink. classified as goods.

Thermal foaming capsules are used for three-dimensional copying such as Braille, and waste paper containing thermal foaming capsules is, of course, discharged from printing factories, and both thermal foaming capsules and their printers are generally available on the market. Therefore, emissions from general households are not zero. The thermally foamed capsules cannot be visually sorted before the capsules are foamed, and their sorting is extremely difficult. If the heat-sensitive foam capsules are mixed with the waste paper pulp, the heat-sensitive foam capsules will expand due to the heat in the drying process of the paper machine, and large projections will occur on the paper surface, resulting in serious defects in the paper. For example, in multi-layered white paperboard, linerboard, corrugated paperboard, and other multi-layered paper, even if it is not blended in the surface layer or back layer but only in the middle layer, protrusions will occur on the surface of the paper, causing problems. .

Sublimation ink is ink used for sublimation transfer paper, textile printing paper, and the like, and is transferred to a printing material such as cloth by heating. If the sublimation ink contained in the sublimation transfer paper or the printing paper mixes with the waste paper pulp, it can cause sublimation spots. That is, when sublimation ink is mixed into paper, it cannot be detected immediately after papermaking, but the ink sublimes with time and causes spots (sublimation spots). For example, even if it is blended only in the middle layer of the above paperboard or other multi-layered paper, sublimation spots will appear on the surface of the surface layer or the back layer over time, resulting in poor appearance.

In Patent Document 3, foreign substances such as sublimation transfer paper, microorganisms, microbial transformations, foam sheets, and adhesive foreign substances in waste paper are analyzed, and depending on the results, the target waste paper is not used as a raw material, or the target It has been proposed to remove the sublimation transfer paper from waste paper (heap of waste paper) and then use it as a raw material. Further, Patent Document 4 proposes heating and dispersing waste paper slurry at a temperature of 85° C. or higher in order to produce waste paper pulp from waste paper containing thermosensitive foam capsules and sublimation ink.

JP 2009-057645 A JP 2013-159865 A JP 2016-056488 A JP 2018-009263 A

As described above, the present applicant uses a hot disperser or the like to heat and disperse waste paper slurry at a temperature of 85 ° C. or higher even when waste paper containing heat-sensitive foam capsules, sublimation ink, etc. is used as a raw material. It was found that high-quality waste paper pulp can be obtained by doing so (Patent Document 4).

However, it has been found that when waste paper pulp that has undergone heating and dispersion treatment using a hot disperser or the like is used for multi-layer paperboard, so-called creasing problems tend to occur. Paperboard creasing trouble means that the liner on the front side of the paperboard that is folded when the paperboard is folded breaks, and is also called crease cracking. In mild cases, the surface layer of the paperboard is cracked, and in severe cases, the entire paperboard layer may crack. If paperboard has crease problems, it cannot be repaired or repaired, so it loses its commercial value and ends up being disposed of as a defective product.

The problem of creasing in paperboard is thought to be related to the strength of the paperboard surface layer, but simply increasing the strength of the paperboard surface layer is not enough. It is necessary to take countermeasures. In addition, creasing troubles often occur during the dry season in winter, and there is also an idea that the moisture content and elongation of the paperboard are related to creasing troubles.

Several countermeasures have been proposed for the paperboard creasing problem. For example, Japanese Patent Application Laid-Open No. 2005-264404 discloses that the freeness of the pulp raw material used for the paperboard surface layer is adjusted to 250 to 600 ml and the basis weight of the paperboard surface layer is set to 20 to 35 g/m ² to reduce creases. It has been proposed to produce paperboard. In addition, Japanese Patent Application Laid-Open No. 2006-176921 discloses that a white liner containing 50% or more waste paper pulp is added with a paper strength enhancer mainly composed of starch in the surface layer and the lower surface layer, and the ash content of the surface layer and the lower surface layer is reduced to 15. % or more, it is proposed to suppress the occurrence of crease crack trouble. Furthermore, Japanese Patent Application Laid-Open No. 2001-262496 discloses that by adding an amphoteric surfactant having at least one linear and/or branched hydrocarbon group having 8 to 24 carbon atoms, paperboard creases can be prevented. There have been proposed techniques for suppressing

However, the problem of crease cracking, which tends to occur when using waste paper pulp subjected to heating and dispersion treatment, is a phenomenon that the present inventors discovered for the first time, and no effective countermeasures are known.
In view of such circumstances, it is an object of the present invention to provide a technique for suppressing creasing troubles in multi-layered paperboard manufactured using waste paper pulp subjected to heat dispersion treatment.

The inventors of the present invention have made intensive studies on the above-mentioned problems, and have found that cracking problems can be effectively eliminated by reducing the delamination strength of multi-layer paperboard to a certain value or less for multi-layer paperboard manufactured from waste paper pulp that has undergone heat dispersion treatment. The present inventors have found that it is possible to effectively suppress the noise, and have completed the present invention.

The present invention includes, but is not limited to, the following aspects.
(1) A multi-layer paperboard containing waste paper pulp produced by heating and dispersing a waste paper slurry at a temperature of 85° C. or higher, and having an interlaminar peel strength of 1560 kPa or less as measured using a bursting strength tester.
(2) The multilayer paperboard according to (1), which has a basis weight of 100 g/m ² or more and 700 g/m ² or less.
(3) The multilayer paperboard according to (1) or (2), which has 4 or more but 10 or less paper layers.
(4) The multilayer paperboard according to any one of (1) to (3), which is a coated white paperboard having a pigment coating layer.
(5) A method for producing a multi-layer paperboard having an interlaminar peel strength of 1560 kPa or less as measured using a bursting strength tester, wherein the paper contains waste paper pulp produced by heating and dispersing a waste paper slurry at a temperature of 85° C. or more. The above method comprising the step of making multi-layer paperboard from the material.
(6) The method according to (5), wherein a hot disperser is used to heat and disperse.

According to the present invention, it is possible to effectively suppress creasing troubles in multi-layered paperboard manufactured using waste paper pulp obtained by heating and dispersing waste paper raw materials such as waste magazine paper. The details of the reason why such an excellent effect is produced by the present invention are not clear, and the present invention is not bound by the following speculation, but the heating and dispersion treatment advances the refinement of the pulp fibers, and the fine fibers are reduced. It is thought that the ease of tangling in the paperboard is related to the creasing problem, and it is speculated that it is effective to maintain the delamination strength below a certain value against such type of creasing problem. be done.

In addition, according to the present invention, high-quality multi-layer paperboard can be produced using waste paper raw materials that may contain heat-sensitive foam capsules and sublimation ink, so the present invention is excellent from the viewpoint of environmental protection.

The multi-layer paperboard according to the present invention contains waste paper pulp produced by heating and dispersing waste paper slurry at a temperature of 85° C. or higher, and has an interlaminar peel strength of 1560 kPa or less as measured using a burst strength tester.

Heat Dispersed Waste Paper Pulp The multi-layered paperboard according to the present invention includes waste paper pulp produced by heating and dispersing a waste paper slurry at a temperature of 85° C. or higher.

(Recycled paper raw material)
In the present invention, waste paper such as waste magazine paper can be used as a raw material for waste paper pulp. Waste paper is generally classified into waste newspaper, waste cardboard, waste magazine, waste paper of fine quality, etc. Waste paper raw material of the present invention is not particularly limited, and various waste paper raw materials can be used. Waste magazine paper can be used without any particular restrictions as long as it is printed on a base material including paper. printed matter, printed matter printed on uncoated paper, and the like. Specifically, for example, newsprint, medium-quality paper, fine paper, coated paper, lightly coated paper, thermal recording paper, carbonless paper, colored fine paper, PPC paper (toner printing paper), paper containers, stickers, The present invention can be applied to waste paper including labels, forms, corrugated board, white paperboard, etc. The printed matter may be glossy printed matter or surface-treated printed matter such as OP varnish or UV clear coat.

Waste paper used as a raw material for waste paper pulp may be waste paper that has not been printed or waste paper that has been printed. can be done. Examples of methods of printing applied to printed matter include relief printing such as flexographic printing, intaglio printing such as gravure printing, lithographic printing such as offset printing, stencil printing such as screen printing (silk printing), and static printing using static electricity. Electric printing (toner printing), UV ink, hybrid UV ink, UV printing using highly sensitive UV ink, inkjet printing and laser printing widely used in personal computer printers, etc. can be mentioned. Also, the printed ink (ink) is not particularly limited, and a printed matter printed with a coloring material used in various printing methods can be used. In particular, in the present invention, it is possible to produce excellent waste paper pulp even if waste paper containing thermal foaming ink or sublimation ink is used as a raw material for waste paper.

In the present invention, waste paper pulp means pulp produced from waste paper, and may or may not be deinked. In the case of multi-layer paperboard (multi-layer paperboard), if the ink peeled off from the waste paper is not visible on the surface of the paperboard (back layer), it does not pose a quality problem. may not be de-inked.

In the present invention, deinked pulp (DIP) means pulp produced from used paper by removing printing ink and the like and regenerated. Generally, deinked pulp is obtained by deinking a printed material into a slurry and removing the ink using mechanical stress or a chemical such as a deinking agent. Examples of printed materials that can be used as raw materials include newspapers, flyers, magazines, books, office paper, sealed letters, thermal paper, carbonless paper, corrugated cardboard, white paperboard, and other printed paper produced by copiers and OA equipment. Adhesives, adhesives, adhesive tapes, sticky substances such as magazine spine paste, and printed matter including coatings and laminates such as resins can also be used as the printed matter of the present invention. Prints may also contain inorganic particles called ash. Ash refers to inorganic particles in general, and is a substance that remains when paper is incinerated, such as fillers and pigments that have been added or coated during the production of paper. Examples include, but are not limited to, calcium carbonate, talc, kaolin, and titanium dioxide.

When deinking the waste paper pulp according to the present invention, a known deinking device or deinking agent can be used. Examples of equipment used in the deinking process include a floatator. Examples of deinking agents include known surfactants, nonionic surfactants such as fatty acid salts, higher alkyl sulfates, alkylbenzene sulfonates, higher alcohols, alkylphenols, and alkylene oxide adducts of fatty acids; Examples include, but are not limited to, ionic surfactants, cationic surfactants, amphoteric surfactants, organic solvents, proteins, enzymes, natural polymers, and synthetic polymers. Naturally, both single-component and mixtures of two or more components can be used as deinking agents. For example, in one embodiment of producing deinked pulp, defibering treatment in which waste paper is defiberized by adding alkaline chemicals, surfactants, etc., ink stripping treatment in which ink is stripped from pulp under mechanical shear and alkaline conditions, A flotation treatment and/or a washing treatment, etc., can be performed to remove the ink separated from the pulp. Further, for example, after dehydrating the pulp to adjust the pulp concentration to 18 to 35% by weight, alkaline chemicals, surfactants, etc. are added to further strip the ink from the pulp (alkali immersion treatment or aging treatment), Ink may be removed from the pulp by a second flotation treatment or washing treatment. Further, a dust removing step (foreign matter removing step) may be provided to remove foreign matter.

In the present invention, a process other than the deinking process, in which the ink adhering to the pulp fibers is peeled off by applying a mechanical shear, is referred to as a "deinking process", and the peeled ink is removed from the system. The removing process is sometimes called an "ink removing process".

(heat dispersion treatment)
A slurry of waste paper pulp may be prepared by a general defibering treatment. That is, it is sufficient to disaggregate waste paper raw materials in water to form a slurry, and a disaggregator called a pulper is usually used for the disaggregation treatment. As the pulper, for example, a low-concentration pulper that processes at a dry solid concentration of 3 to 5% by mass, a medium-concentration pulper that processes at a dry solids concentration of 5 to 18% by mass, and a dry solids concentration of 18 to 25% by mass. A high-concentration pulper and the like are included. In addition, in the present invention, known devices such as a kneading pulper can be used without limitation.

In a preferred embodiment of the present invention, for example, a pulp slurry having a solid content concentration of 5 to 18% by mass can be prepared from a waste paper raw material using a medium consistency pulper. The temperature during the disintegration treatment is not particularly limited, but may be, for example, 5° C. or higher and 60° C. or lower, preferably 6° C. or higher and 50° C. or lower, more preferably 7° C. or higher and 40° C. or lower.

The waste paper pulp according to the present invention is produced by heating and dispersing waste paper slurry at a temperature of 85° C. or higher. Heating dispersion treatment includes, for example, hot disperser, conid disc, deflaker, finer, conifer, top finer, conical flaker, power finer, refiner, double disc refiner, beater, kneader, disperser, New Taizen, etc. The pulp slurry is subjected to mechanical dispersion treatment by heating to a temperature of 85° C. or higher. Considering the effect, efficiency, energy saving, etc. of contraindicated products such as thermal foaming ink and sublimation ink, it is desirable to perform processing at 88 to 130°C, more preferably 90 to 120°C, and 93°C. Above 110° C. or below is more desirable. Heating to 85° C. or higher and applying a mechanical dispersion treatment facilitates effective reduction of spots originating from contraindicated products.

When waste paper pulp is produced from waste magazine paper containing sublimation ink, even if the temperature in the slurry dispersing process is normal temperature or higher (approximately 20° C. or higher), the spots contained in the waste paper pulp are reduced. It is preferable that the temperature in the step of heating and dispersing the slurry is 85° C. or higher because the effect of reducing spots is enhanced.

In addition, when waste paper pulp is produced from waste magazine paper containing conspicuous colored foreign matter such as red undissociated fragments, even if the temperature in the slurry dispersing process is normal temperature or higher, the number of foreign substances contained in the waste paper pulp is reduced. be able to. For example, it is possible to reduce dirt derived from red undissociated fragments with a diameter of 100 μmm or more by 60% or more, or reduce dirt with a diameter of 500 μmm or more by 80% or more. This is desirable because it enhances the effect of reducing foreign matter.

In the heating and dispersing step according to the present invention, the used paper slurry is heated and mechanically dispersed. In this heating and dispersing step, foreign matters such as thermal foaming ink and sublimation ink are made finer.

In the heating dispersion step according to the present invention, the concentration of the waste paper slurry is preferably 15% by mass or more and 40% by mass or less, more preferably 20% by mass or more and 39% by mass or less, and 25% by mass or more and 38% by mass or less. is more preferable, and 28% by mass or more and 36% by mass or less is even more preferable.

(Foreign matter removal process)
In the present invention, foreign matter may be removed using a cleaner or the like for the purpose of removing foreign matter contained in the used paper slurry after the defibration step. A general cleaner has a conical shape, and can remove foreign matter, such as sand and metal grains, which have a higher specific gravity than pulp fibers, according to the principle of centrifugal separation. From the viewpoint of productivity and disintegration, the raw material concentration in the foreign matter removal step is preferably 1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 8% by mass or less, in terms of dry solid content. Since it is preferable, the foreign matter removal step may be performed after diluting or concentrating with water, if necessary.

In the present invention, a dust removal step using a screen or the like may be provided in addition to removing foreign matter using a cleaner. The dust removal step can be performed using a known device, for example, a rough screen or a fine screen can be used.

As the rough selection screen, for example, a basket type screen having holes or slits with a predetermined opening area is used. The coarse selection screen differs from the fine selection screen described later in the size of the screen holes, and the coarse selection screen uses a round hole screen (1.5 to 2.5 mmΦ) or a slit screen (0.18 to 0.25 mm slit). be done.

From the viewpoint of improving the dust removal effect, the selective screen preferably has a slit width of 0.10 mm or more and 0.25 mm or less. The upper limit of the slit width is more preferably 0.20 mm, still more preferably 0.15 mm, and particularly preferably 0.13 mm. If the slit width of the screening screen is too wide, it will be difficult to sufficiently reduce the content of sticky contaminants. On the other hand, if the slit width is too narrow, the yield of waste paper pulp will decrease.

The dust removal process may be performed a plurality of times, but if the cleaning dust removal process is performed too many times, the yield of waste paper pulp will decrease, so it is preferable to perform the dust removal process one to three times. When the cleaning and dust removal step is performed several times, it is preferable to perform the steps successively.

(Dilution process/dehydration process)
In the present invention, a step of diluting or dehydrating (concentrating) the used paper slurry can be provided.

In the dilution step, the waste paper slurry can be diluted to a concentration suitable for processing. Depending on the equipment used, for example, the dry solid content concentration of the slurry after the dilution step is preferably 0.5% by mass or more and 5% by mass or less, and 0.5% by mass or more and 4.0% by mass or less. It is more preferable that the content is 0.5% by mass or more and 3.0% by mass or less, but the lower limit of the slurry concentration may be 1.0% by mass or 1.5% by mass. When the dry solid content concentration of the slurry is 0.5% by mass or more, it may be possible to efficiently remove foreign matter. Clogging of the screen can be prevented by setting the dry solid concentration of the slurry after the dilution step to 5% by mass or less. In the dilution step, it is preferable to use clean water containing no foreign matter so as not to refine the sticky foreign matter grown in the dehydration and concentration step.

Further, in the present invention, a dehydration and concentration step can be provided, and for example, the dehydration and concentration is performed so that the solid content concentration of the raw slurry becomes 8 to 40%. Examples of the equipment include a pressurized dehydrator such as a screw press. In the dehydration and concentration step, the slurry is dehydrated and concentrated so that the dry solid content concentration of the slurry is increased, for example, 8% by mass or more, 10% by mass or more, or further 15% by mass or more. Can be concentrated. However, dehydration and concentration to an excessively high concentration is not only technically difficult, but also requires an excessive amount of power consumption for dehydration and concentration, which is not preferable. Therefore, the dry solid content concentration of the slurry after the dehydration and concentration step is more preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

In the dehydration and concentration step, the device for concentrating the slurry is not particularly limited, but it is preferable to use a pressurized dehydrator such as a screw press. The uniaxial screw press includes V45LM-H type manufactured by Aikawa Iron Works Co., Ltd., Valmet, and Optimum Screw Press manufactured by AFT. Twin press and twin wire type dehydrators include the twin screw press of Ishigaki Co., Ltd. and the twin wire press of Maruishi Seisakusho.

In the dehydration and concentration step, a polymer flocculant may be added to the slurry. As a result, even low-concentration slurries that cannot be sufficiently squeezed by mechanical force alone can be raised to the target dry solid content concentration relatively instantly with a normal pressurized dehydrator. When adding a polymer flocculant, it is added before processing with a dehydrator or during processing with a dehydrator. It is preferable that the pulp or the like in the slurry is sufficiently immersed in the polymer flocculant before being treated with the dehydrator. The addition rate of the polymer flocculant depends on the dry solid content concentration of the slurry and equipment, but is preferably 0.005% by mass or more and 0.05% by mass or less relative to the dry solid content of the slurry. More preferably, it is 0.01% by mass or more and 0.04% by mass or less. If the addition rate is low, a sufficient concentration effect cannot be obtained. If the addition rate is too high, the dry solid content concentration of the slurry after the dehydration and concentration process may exceed the target dry solid content concentration, and excessive production costs are incurred, which is not practical.

As for the polymer flocculant, there are no particular restrictions as long as the dry solid content concentration can be increased to the target concentration in the dehydration and concentration process, but an acrylic acid ester-based cationic polymer flocculant can most efficiently increase the dry solid content concentration. Therefore, it is preferable. Examples of cationic polyacrylic acid esters include C-525M and C-500N manufactured by MT Aquapolymer, Hi Holder 725 and High Form K162 manufactured by Kurita Water Industries.

(Washing process)
In the present invention, a step of washing the waste paper pulp may be provided. By performing pulp washing treatment, ash content can be reduced, and in general, washing with a DNT washer, compact washer, fall washer, vario split, SP filter, DP Cosmo, gap washer, etc. is performed in the heating and dispersing process. It is possible to wash away the finely divided foreign matter.

Since the pulp washing process improves as the dry solids concentration decreases, it is preferable to dilute the slurry before the pulp washing process. The dry solid content concentration of the slurry before the pulp washing treatment is preferably 0.5% by mass or more and 5% by mass or less, more preferably 1% by mass or more and 4% by mass or less, and 1% by mass or more and 3 % by mass or less is more preferable.

The flow of the method for producing waste paper pulp of the present invention is not particularly limited. Considering the effect of reducing the load of hot dispersers, etc. in the process, it may or may not be performed), dust removal process by selective screen, dehydration (concentration) process by screw press, heating dispersion by hot disperser A treatment step can be mentioned. Further, a cleaning step may be appropriately introduced into the above flow, each of the above steps may be omitted, or the order may be changed.

Manufacture of multi-layer paperboard In the present invention, the waste paper pulp subjected to the heating and dispersion treatment as described above is used to manufacture multi-layer paperboard. The papermaking method is not particularly limited, and multilayer paperboard can be produced by a generally known method. According to the present invention, it is possible to produce multi-layered paperboard in which the occurrence of creasing trouble is suppressed even though waste paper raw materials such as waste magazine paper are used. is also extremely good.

The multilayer paperboard according to the present invention is required to have an appropriate range of delamination strength. The upper limit of the delamination strength is 1560 kPa or less, preferably 1500 kPa or less, more preferably 1450 kPa or less, and still more preferably 1400 kPa or less. The lower limit of the delamination strength is preferably 800 kPa or more, more preferably 900 kPa or more, still more preferably 1000 kPa or more, and may be 1100 kPa or more. By adjusting the delamination strength of the multi-layered paperboard to such a range, it is possible to suppress the problem of creasing of the multi-layered paperboard. If the delamination strength is too high, there is little variation in compression on the inner side of the fold during folding, and an excessive tensile load is applied to the surface layer, increasing the risk of creasing. Further, if the delamination strength is too low, the risk of delamination on the paper surface when the paper is separated from the blanket increases when a printing method using high-viscosity ink such as UV printing is applied.

In the present invention, the method for adjusting the delamination strength is not particularly limited, and the type of raw material pulp, the freeness of the raw material pulp, the basis weight of each layer, the amount of starch added between the layers, etc. may be adjusted as appropriate. May be combined. For example, the delamination strength of the multi-layer paperboard can be lowered by using raw material pulps of different types and freeness for each layer, or by increasing the basis weight of the surface layer side than that of the back layer side. In addition, the delamination strength can be lowered by increasing the freeness of the raw material pulp or by reducing the binder applied between the layers.

The multi-layered paperboard according to the present invention preferably has anisotropy in the machine direction (MD direction) and width direction (CD direction) adjusted within a certain range. In general, paper manufactured using a paper machine has significantly different tensile strengths in the MD and CD directions. On the other hand, creasing trouble occurs when excessive tensile strength is applied to the surface layer during folding, so it is desirable to increase the tensile strength of the multi-layered paperboard. Therefore, in order to obtain paper that can withstand folding in both the MD and CD directions, it is necessary to keep the tensile strength in both the MD and CD directions at a certain level or higher. Therefore, it is effective to adjust the aspect ratio within a certain range. As for the compressive strength, the ratio of the compressive strength in the MD direction to the compressive strength in the CD direction (compressive strength in the MD direction/compressive strength in the CD direction) is preferably 1.34 or less. As for the tensile strength, the ratio of the tensile strength in the MD direction to the tensile strength in the CD direction (tensile strength in the MD direction/tensile strength in the CD direction) is preferably 2.12 or less. As for the taper stiffness, the ratio of the taper stiffness in the MD direction to the taper stiffness in the CD direction (taper stiffness in the MD direction/taper stiffness in the CD direction) is preferably 2.20 or less.

In addition, the multilayer paperboard according to the present invention can have a coefficient of static friction of 0.50 or less, and may be 0.48 or less, in order to obtain good slipperiness during processing. If the coefficient of static friction is too high, the printed surface will be rubbed and smeared, and the slipperiness will be poor, making it easy for transport failures such as double feeding to occur. However, if the coefficient of static friction is too low, there is a possibility that troubles such as collapsing of boxes may occur when the boxes are loaded. The coefficient of static friction can be obtained by appropriately adjusting, for example, pre-calendering treatment, calendering (finishing treatment) conditions after providing the coating layer, formulation and layer composition of the coating layer, coating amount, etc., and by combining these good too.

In the papermaking method of the present invention, it is not necessary to use only the heat-dispersed waste paper pulp, and paper may be produced from a stock containing other pulps in an arbitrary ratio.

Pulp used in combination in the present invention includes, for example, deinked pulp (DIP), softwood or hardwood kraft pulp (NKP or LKP), mechanical pulp using softwood or hardwood, such as groundwood pulp (GP), refiner groundwood pulp ( RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemigrand pulp (CGP), semi-chemical pulp (SCP), defibered corrugated paper pulp, coated paper, base paper for coating, and other Papermaking may be performed by using a coat brok obtained by defibrating waste paper containing paper, and a mixture of two or more of these pulps.

Further, in the present invention, chemicals and fillers may be added when paper is made. Chemicals to be added include rosin emulsions, neutral rosins, alkyl ketene dimers, alkenyl succinic anhydrides, sizing agents such as styrene/acrylic copolymers, cationic, amphoteric and anionic polyacrylamides, polyvinylamines, poly Resins containing acrylic acid, dry paper strength agents such as guar gum, cationic, amphoteric, and anionic modified starch, wet paper strength agents such as polyamidoamine epichlorohydrin, carboxymethyl cellulose, drainage improvers, Colorants, dyes, fluorescent dyes, coagulants, bulking agents, retention agents and the like can be mentioned. The filler is not particularly limited as long as it is particles generally called inorganic fillers and organic fillers. Specifically, inorganic fillers include calcium carbonate (light calcium carbonate, heavy calcium carbonate, synthetic calcium carbonate), magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay ( kaolin, calcined kaolin, delaminated kaolin), talc, zinc oxide, zinc stearate, titanium dioxide, silica made from sodium silicate and mineral acids (white carbon, silica/calcium carbonate complex, silica/titanium dioxide complex) . As the calcium carbonate-silica composite, amorphous silica such as white carbon may be used in combination with calcium carbonate and/or light calcium carbonate-silica composite. Among these, calcium carbonate and light calcium carbonate-silica composites, which are representative fillers in neutral papermaking and alkaline papermaking, are preferably used.

Specific examples of the multi-layered paperboard according to the present invention include white paperboard including high-grade white paperboard, special white paperboard, and white board, linerboard, core base paper, paper tube base paper, building material base paper, paper container base paper, and the like. be able to. According to the present invention, foreign substances that become spots are made finer, and a product having a particularly good appearance can be obtained. Therefore, the present invention can be particularly preferably applied to manufacture white paperboard. Among white paperboards, it is particularly suitable for printing boxes (medical products, cosmetics, soaps, cigarettes, caramel, curry, etc.). The waste paper pulp obtained by the production method of the present invention can be appropriately blended into at least one of the surface layer, middle layer, and back layer of multi-layer paperboard.

Multilayer paperboard according to the present invention can be made using pulp with a low brightness (low white pulp). As already mentioned, the blending of pulp other than the heat-dispersed waste paper pulp is not particularly limited, and various pulps can be used.

The content of waste paper pulp in the base paper surface layer of the present invention can be 90 parts by weight or more, more preferably 95 weight % or more of the total pulp. Whole waste paper pulp may be used. In addition, the ISO brightness of the used paper pulp is preferably 65% or less, more preferably 60% or less, from the viewpoint of cost. As the low whiteness waste paper pulp, magazine waste paper pulp is preferable, and unbleached waste paper pulp with low whiteness may also be used. Naturally, heat-dispersed waste paper pulp can be used.

The multi-layer paperboard according to the invention can be provided with a pigment coating. For example, in the case of four-layer paper, the outermost layer of the surface to be coated with the pigment is called the surface layer, the second layer is called the front and lower layer, the rearmost layer is called the back layer, and the other layer is called the middle layer. In addition, the layers constituting the intermediate layer are sometimes called the third layer and the fourth layer counting from the pigment-coated surface. These layers may have different pulp formulations, or multiple layers may be stacked with the same pulp in all layers.

The number of layers of the multi-layered paperboard according to the present invention is not particularly limited, but for example, it preferably has 2 to 10 layers, more preferably 3 to 9 layers. The basis weight of each layer is not particularly limited, but the basis weight of the surface layer in contact with the pigment coating layer is, for example, 20 g/m ² or more and 100 g/m ² or less, and may be 20 g/m ² or more and 70 g/m ² or less. , 25 g/m ² or more and 50 g/m ² or less.

A filler may be added internally to the base paper of the present invention. Examples of such fillers include, but are not limited to, diatomaceous earth, talc, kaolin, calcined kaolin, delaminated kaolin, ground calcium carbonate, light calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, and zinc oxide. , Silicon oxide, Amorphous silica, Calcium sulfite, Gypsum, White carbon, Aluminum hydroxide, Calcium hydroxide, Magnesium hydroxide, Zinc hydroxide, Papermaking sludge, Inorganic fillers such as recycled inorganic particles from deinked floss, Urea - Organic fillers such as formalin resins, polystyrene resins, vinyl chloride resins, melamine resins, phenolic resins, hollow plastic microparticles, and fillers contained in waste paper and broken paper are used singly or in combination of two or more as appropriate. The blending ratio of the filler in the base paper (base paper ash content) is preferably 10% by weight or more.

Cohesion aids, paper strength agents, coloring dyes/pigments, and sizing agents can be used in the base paper layer according to the desired quality. In addition, a retention aid, a drainage improver, and an antifoaming agent can be appropriately used in order to improve runnability during papermaking.

The papermaking method of the multi-layer paperboard in the present invention is not particularly limited, and a fourdrinier paper machine including a top wire or the like, an on-top former, a gap former, a cylinder paper machine, or a fourdrinier paper machine and a cylinder paper machine are used in combination. It can be carried out using a paperboard machine, a Yankee dryer machine, or the like. The pH during papermaking may be acidic, neutral or alkaline, preferably neutral or alkaline. The papermaking speed is not particularly limited. The basis weight (basis basis) of the multilayer paperboard is preferably about 100 g/m ² or more and 700 g/m ² or less, more preferably 150 g/m ² or more and 600 g/m ² or less, and still more preferably 200 g. /m ² or more and 500 g/m ² or less, or 300 g/m ² or more and 400 g/m ² or less.

The method of drying the multi-layer paperboard in the present invention is not limited. For example, various methods such as a steam heating cylinder, heated hot air dryer, gas heater dryer, electric heater dryer, infrared heater dryer and the like are used alone or in combination.

(pigment coating)
In the present invention, the multi-layer paperboard may be provided with a pigment coating layer. The pigment coating layer can be provided by a known method.

In a preferred embodiment, the pigment coating layer can be applied by curtain coating. In curtain coating, one curtain film is formed from one or more coating liquids, and a base paper is passed through the curtain film to form one or more curtain coating layers on the base paper. The curtain coating layer preferably includes an outermost coating layer, which is the outermost layer of the coated white paperboard. When there are two or more pigment coating layers, the outermost coating layer is also referred to as a top coating layer, and the coating solution forming the top coating layer is also referred to as a top coating solution. Also, the coating layer adjacent to the base paper is called an undercoat coating layer, and the coating liquid forming the undercoat coating layer is also called an undercoat coating liquid. The coating liquids forming each coating layer may be different coating liquids or the same coating liquid may be used for two or more layers.

In the present invention, it is possible to combine curtain coating with other coating methods. For example, curtain coating may be performed after blade coating or the like, or blade coating may be performed after curtain coating. and so on. Alternatively, wet-on-wet coating may be performed in which the upper layer is applied without drying the lower layer coated portion.

In the present invention, a coating solution is prepared by mixing water with necessary components such as pigments and adhesives. In preparation of the coating liquid, ordinary mixing means such as a mixer may be used. Each component contained in the coating liquid will be described below.

The pigment contained in the coating liquid in the present invention does not need to be special, and a known white pigment can be used. Conventionally known pigments include diatomaceous earth, talc, kaolin, calcined kaolin, delaminated kaolin, ground calcium carbonate, ground calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, and amorphous silica. , Calcium sulfite, Gypsum, White carbon, Aluminum hydroxide, Calcium hydroxide, Magnesium hydroxide, Zinc hydroxide, Papermaking sludge, Inorganic fillers such as recycled inorganic particles from deinked froth, Urea-formalin resin, Polystyrene resin, Chloride It is possible to use organic fillers such as vinyl resins, melamine resins, phenolic resins, plastic fine hollow particles, and the like.

In the present invention, the pigment coating layer preferably contains kaolin. The content of kaolin in the outermost pigment coating layer is preferably 5 parts by weight or more and 60 parts by weight or less, more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the pigment. In order to improve hiding power and whiteness, it is preferable that one of the pigment coating layers contains light calcium carbonate, and more preferably, the outermost pigment coating layer contains light calcium carbonate. is preferred. The content of calcium carbonate is preferably 20 parts by weight or more, more preferably 50 parts by weight or more, based on 100 parts by weight of the pigment.

The adhesive is not particularly limited, and adhesives conventionally used for coated paper can be used. Examples of adhesives include various copolymers such as styrene/butadiene, styrene/acrylic, ethylene/vinyl acetate, butadiene/methyl methacrylate, vinyl acetate/butyl acrylate, polyvinyl alcohol, and maleic anhydride copolymers. Coalescence and synthetic adhesives such as acrylic acid/methyl methacrylate copolymers; Proteins such as casein, soybean protein and synthetic proteins; starches such as etherified starch and dextrin; and ordinary coated paper adhesives such as cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose and hydroxymethyl cellulose. One or more types of adhesives can be appropriately selected and used.

The blending ratio of the pigment and the adhesive in the coating solution forming each coating layer in the present invention is appropriately adjusted within the range in which a desired pigment coating solution can be obtained. In general, the solid content ratio is preferably 5 parts by weight or more and 30 parts by weight or less, more preferably 8 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the pigment. If the amount is less than 5 parts by weight, the strength of the coating layer becomes weak, which causes problems such as generation of paper dust and deterioration of printing strength. On the other hand, when the amount is more than 30 parts by weight, the voids between the pigment particles in the coating layer are filled with the adhesive, and the light scattering properties of the coating layer are poor, resulting in problems such as poor opacity and high cost. be.

The coating solution for forming each coating layer of the present invention contains, in addition to a pigment and an adhesive, if necessary, a dispersant, a viscosity improver, a water retention agent, an antifoaming agent, a water resistance agent, a fluorescent dye, Various auxiliaries such as coloring dyes, coloring pigments, surfactants, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, metal salts, etc., which are blended in ordinary coated paper pigments, can be appropriately used.

The solid content concentration of the pigment coating liquid is preferably 58% by weight or more, more preferably 62% by weight or more. If the solids content is lower than 58% by weight, the quality of the coated paper may be deteriorated due to excessive penetration of the coating liquid into the base paper. On the other hand, although the upper limit of the solid content concentration is not particularly limited, it is preferably 75% by weight or less, more preferably 70% by weight or less, in consideration of liquid transferability and the like.

The total coating amount of each coating liquid in the present invention is preferably 2 g/m ² or more and 50 g/m ^{2 or} less in terms of dry solid content per side. With such a coating amount, the unevenness of the paper substrate surface can be sufficiently covered, and not only can the receptivity and concealability of the printing ink be improved, but also due to the deterioration of the drying property during coating. It is also possible to avoid problems such as deterioration of operability and occurrence of cracks at ruled lines in post-processing steps. Even when the coating layer is composed of multiple layers, it is preferable to set the coating amount to 2 g/m ² or more and 50 g/m ² or less per side. The coating amount of each coating layer is preferably 5 g/m ² or more, more preferably 10 g/m ² or more. The coating weight of the coating layer is preferably 40 g/m ² or less, more preferably 30 g/m ² or less.

In the present invention, a clear coating layer may be provided on the multi-layered paperboard in order to improve stiffness and suppress curling. Conventionally known binders can be used in the clear coating liquid as needed, and dispersants, viscosity improvers, water retention agents, antifoaming agents, water resistance agents, fluorescent dyes, coloring dyes, coloring pigments, Various auxiliary agents such as surfactants, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, metal salts, etc., which are blended in ordinary coating solutions can be used as appropriate. The coating amount of the clear coating layer is not particularly limited, but is generally about 0.1 g/m ² or more and 5.0 g/m ² or less in terms of solid content per side.

The coating method and drying method of the clear coating layer are not limited. For example, using a known size press device such as 2-roll type, 3-roll type, gate roll type, film transfer type, calender type, and coater (coating machine) such as curtain coater, spray coater, blade coater, etc. After coating, various drying processes such as a steam heating cylinder, heated hot air dryer, gas heater dryer, electric heater dryer, infrared heater dryer may be used alone or in combination, or the drying process may be omitted.

The multilayer paperboard of the present invention may be smoothed by a surface treatment process or the like, if necessary. In a preferred embodiment, the paper is finished after being adjusted so that the water content of the paper after production is about 3% to 10% by weight, more preferably about 4% to 8% by weight. For the smoothing treatment, a normal smoothing treatment apparatus such as a super calender, a gross calender, a soft nip calender, a heat calender, and a shoe calender can be used. You may combine these. In particular, the multi-layer paperboard of the present invention preferably includes a smoothing treatment with a soft nip calender having metal rolls and elastic rolls. The smoothing device is appropriately used on-machine or off-machine, and the form of the pressure device, the number of pressure nips, heating, etc. are also appropriately adjusted. Also in order to improve the smoothness of the surface, it is preferable to carry out the multi-stage nipping with 2 or more and 6 or less nips. The temperature is about 80° C. to 300° C., preferably 90° C. to 250° C., and the linear pressure is about 4 kN/m to 200 kN/m, preferably 4.5 kN/m to 100 kN/m.

In the present invention, for the main purpose of smoothing the base paper, precalendering may be performed before the coating layer is provided on the base paper. Pre-calendering may be carried out by either a method of sandwiching the base paper between metal rolls or a method of sandwiching the base paper between metal rolls and resin rolls. The base paper is nipped by being tightened between the rolls. In the present invention, a roll (hereinafter sometimes referred to as an "induction heating roll") equipped with an induction heating mechanism that allows the temperature to be set freely and heats the roll itself and a heat pipe mechanism that equalizes the temperature of the entire roll surface is provided. It is preferable to use As such a roll, "Jacket Roll (registered trademark)" manufactured by Tokuden Co., Ltd. can be exemplified. The induction heating roll has an induction heating type heat source inside the roll to accurately control a desired roll surface temperature. An induction coil is mentioned as an induction heating method. The induction heating roll also has a heat pipe mechanism that equalizes the temperature of the entire roll surface. As the heat pipe mechanism, there is a jacket chamber provided along the circumferential surface in the vicinity of the roll surface. The conditions for the pre-calendering treatment are not particularly limited, but can be, for example, 80° C. or higher and 300° C. or lower and a linear pressure of about 4 kN/m or higher and 100 kN/m or lower. More preferably, the temperature is 90° C. or higher and 250° C. or lower, and the linear pressure is 4.5 kN/m or higher and 50 kN/m or lower. The base paper to be subjected to the pre-calendering process can be the paper web leaving the dryer part. Although the surface of this paper web is rough, it is considered that the white unevenness is improved because the surface can be smoothed by this process and the texture can be made dense to obtain a predetermined paper thickness.

Also, the coating speed is not particularly limited, but is generally about 100 m/min or more and 800 m/min or less. Craters tend to occur when the coating speed is too high.
In this specification, unless otherwise specified, numerical ranges include their endpoints, and concentrations and the like are described on a weight basis.

The present invention will be described in more detail below with specific examples, but the present invention is not limited to the following specific examples.
Evaluation method
(1) Basis weight: Measured according to JIS P 8124.
(2) Paper thickness and density: Measured according to JIS P8118.
(3) Whiteness: Measured according to JIS P8148.
(4) Compressive strength: Measured according to JIS P 8126:2005.
(5) Tensile strength: Measured according to JIS P 8113:2006.
(6) Taper stiffness: Measured according to JIS P 8125:2000.
(7) Peel strength between layers Using a burst strength tester (Japan TMC, D-111) conforming to JIS P 8131, the peel strength between layers of multi-layer paperboard was measured according to TAPPI UM522. Specifically, a doughnut-shaped sample of multi-layered paperboard with double-sided tape attached was sandwiched between an annular disc and a metal plate without holes, and pressure was applied to measure the maximum pressure at which the multi-layered paperboard was peeled off.
(8) Crease cracking test In order to make it easier to see whether creases have occurred when folding, the part where the crease (folding line) will be colored with a permanent pen in advance, and then a ruled line inserter and extractor will be used to put the sample on the sample. A streak process was applied (depth of recess: 0.4 mm, length: 50 mm, width: 1.5 mm). Next, the sample was folded so that the dent was on the outside, and in the folded state, pressure was applied for 60 seconds using a press (pressure: 3 kgf/cm ² ). After pressurization, the cross section of the folded portion, the peeling state between the base paper layers, and the presence or absence of creases were observed using a microscope.

Manufacture of waste paper pulp by heat dispersion treatment Waste paper pulp was produced from waste magazine paper by heat dispersion treatment.
Using a pulper (ADP-5 type low concentration pulper, manufactured by Aikawa Tekko), the pulp was defibered for 15 minutes at room temperature to obtain a pulp slurry having a dry solid content concentration of 8%. This pulp slurry was treated with a high-concentration cleaner (A strong type high-concentration cleaner, manufactured by Aikawa Iron Works Co., Ltd.) to remove foreign matters. It was then diluted with water to a dry solids concentration of about 1.7% and then dusted using a 0.15 mm slit screen (coarse screening screen).

The pulp slurry after dust removal was put into a fractionator equipped with a basket having a slit with a slit width of 0.10 mm, and classified into a long fiber fraction and a short fiber fraction. Next, after washing the long fiber fraction, it is dehydrated and concentrated so that the dry solid content concentration is 32% at the hot disperser inlet concentration, and then processed using a hot disperser (Konidisc CD22 type, manufactured by Aikawa Tekko). It was subjected to thermal dispersion treatment (treatment temperature: 100° C.) and used for the production of multi-layer paperboard.

Experiment 1: Production and Evaluation of Multilayer Paperboard (1)
A multi-layer coated white paperboard with seven layers (set basis weight: about 270 g/m ² ) was produced according to the following procedure.

100% softwood kraft pulp for the surface layer (1st layer), 100% deinked waste paper pulp (without heat dispersion treatment) for the lower surface layer (2nd layer), middle layers (3rd to 6th layers) 100% waste paper pulp obtained from the above-mentioned waste magazine paper through the heating dispersion treatment process, and 100% waste paper pulp obtained from waste magazine paper without the heat dispersion treatment process for the back layer (7th layer). Then, paperboard base paper was produced by seven-layer papermaking. Each layer was made into paper, combined, pressed and dried to obtain a base paper for multi-layered paperboard (basis weight of base paper: about 251 g/m ² , whiteness of base paper: 54%). The papermaking speed was about 300 m/min, and the basis weight of each layer is shown in the table below. In addition, 0.1 to 0.3% by weight of a drainage improver based on the solid weight of the pulp was blended in the stock of the 2nd to 7th layers. Also, an interlayer binder was sprayed between the 1st to 5th layers to produce base papers with different peel strengths (total amount of interlayer binder applied: 2.4 to 3.5 g/m ² ).

Next, a pigment coating layer was provided on the surface layer of the multilayer paperboard base paper to obtain a coated white paperboard (set coating amount: about 19 g/m ² ). For the pigment coating layer, calcium carbonate was used as the pigment, and 15 parts by weight of latex (binder) was used for 100 parts by weight of the pigment.

Experiment 2: Production and evaluation of multi-layered paperboard Seven-layered multi-layered coated white paperboard (set basis weight: about 315 g/m ² ) was produced in the same manner as in Experiment 1. However, the basis weight of each layer is as follows.

Experiment 3: Production and evaluation of multi-layered paperboard Seven-layered multi-layered coated white paperboard (set basis weight: about 600 g/m ² ) was produced in the same manner as in Experiment 1. However, the basis weight of each layer is as follows.

By producing a multi-layered paperboard adjusted to a delamination strength of 1560 kPa or less based on the present invention, an excellent multi-layered paperboard that is less susceptible to delamination and creasing even when subjected to bending was obtained. By using the multi-layered paperboard of the present invention, it is possible to produce a box that is excellent in strength and appearance while maintaining suitability for box making.

In addition, by suppressing delamination and creases based on the present invention, the amount of various chemicals used to increase surface strength, such as binders and interlayer binders used in pigment coating liquids, can be reduced. It can save money and produce a cheaper and better multi-layer paperboard.

Claims (6)

A multi-layered paperboard containing waste paper pulp produced by heating and dispersing a waste paper slurry at a temperature of 85° C. or higher, and having 2 to 10 paper layers,
A multi-layer paperboard having a delamination strength of 1000 kPa or more and 1560 kPa or less and a basis weight of 200 g/m ² or more and 700 g/m ^{2 or} less as measured using a bursting strength tester. 2. The multi-layer paperboard of claim 1, having a basis weight of from 300 g/m ^<2> to 700 g/m ^<2> . 3. A multi-layer paperboard according to claim 1 or 2, having 4 or more and 10 or less paper layers. The multi-layered paperboard according to any one of claims 1 to 3, which is a coated white paperboard having a pigment coating layer, and the surface layer in contact with the pigment coating layer has a basis weight of 20 g/m ² or more and 100 g/m ² or less . . Multilayered paperboard having an interlaminar peel strength of 1000 kPa or more and 1560 kPa or less , a basis weight of 200 g/m ² or more and 700 g/m ² or less, and having 2 or more and 10 or less paper layers, as measured using a burst strength tester. A manufacturing method comprising:
The above method, comprising the step of making multi-layered paperboard from stock containing waste paper pulp produced by heating and dispersing waste paper slurry at a temperature of 85° C. or higher. 6. The method of claim 5, wherein the warm dispersing is performed using a hot disperser.