Middle core base paper, cardboard sheet, and manufacturing method of middle core base paper

Abstract

To provide a middle core base paper having excellent compression strength and wettability, a cardboard sheet using this middle core base paper, and a manufacturing method of a middle core base paper.SOLUTION: Disclosed herein are: a middle core base paper having a coating layer on at least one surface of a paper substrate, wherein the coating layer includes starch and lignin; a cardboard sheet including this middle core base paper; and a manufacturing method of a middle core base paper by applying a coating liquid for a middle core base paper that includes starch and lignin in a sum total of 18 mass% or over and has a B type viscosity of 100 mPa s or under.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a corrugated cardboard sheet having the corrugated cardboard, and a method for manufacturing the corrugated cardboard. [Background technology]

[0002] Corrugated cardboard is a basic industrial material used for packaging and transporting various goods because it is lightweight, inexpensive, and strong. Generally, corrugated cardboard is manufactured by laminating core paper and liner together using a corrugator. Due to its intended use, corrugated cardboard requires high strength, and in order to increase the strength of corrugated cardboard, the core paper in particular must have high compressive strength. Furthermore, core base paper generally contains a high content of recycled paper pulp, but recycled paper pulp has low water absorption and its shape varies widely, which tends to result in a high density of the paper surface. The core base paper is required to have strong adhesive strength with the liner, but core base paper with a high content of recycled paper pulp has low hydrophilicity, so it is required to improve the wettability of the size liquid.

[0003] It is known that coating (external addition) of starch can improve compressive strength by fixing the fiber bonds between pulp. However, the viscosity of starch increases with concentration, reducing its coatability. Therefore, increasing the amount of starch applied (dry coating amount) requires increasing the amount of coating solution (wet coating amount), which increases the energy cost required for drying. Furthermore, when the starch coating solution is low in concentration, more starch penetrates into the interior and less remains on the paper surface, preventing the expected improvement in hydrophilicity due to starch.

[0004] For this reason, it has been proposed to apply a low-viscosity starch. For example, Patent Document 1 proposes a method for producing a reinforced core that improves compressive strength without impairing adhesion or disintegration properties, in which an aqueous suspension of starch to which inorganic acid and urea have been added is passed through a continuous gelatinization device to reduce the viscosity of the starch paste through thermochemical modification, and the resulting starch paste is applied to the surface of the core raw paper. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-026494 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a corrugated cardboard sheet using this corrugated cardboard, and a method for manufacturing the corrugated cardboard. [Means for solving the problem]

[0007] The means for solving the problems of the present invention are as follows. 1. A paper substrate having a coating layer on at least one side thereof; The core raw paper, wherein the coating layer contains starch and lignin. 2. The core raw paper according to 1., wherein the lignin is lignin sulfonate. 3. The core raw paper according to 1. or 2., wherein the mass ratio of starch to lignin (starch:lignin) in the coating layer is 30:70 to 99:1. 4. The core raw paper according to any one of 1. to 3., characterized in that the water contact angle (3.5 μl, 1 second) is 70 degrees or less. 5. The coating amount (solid content) of the coating layer on one side is 1 g / m 2 The core raw paper according to any one of 1. to 4., characterized in that: 6. A cardboard sheet comprising the core raw paper according to any one of 1. to 5. 7. Contains a total of 18% by mass or more of starch and lignin, A method for producing core raw paper, characterized by applying a coating liquid for core raw paper having a B-type viscosity of 100 mPa·s or less. [Effects of the Invention]

[0008] The core raw paper of the present invention has excellent compressive strength and wettability. The corrugated cardboard sheet of the present invention has excellent strength because the core raw paper has excellent compressive strength. Furthermore, the corrugated cardboard sheet of the present invention has excellent wettability with adhesives, so the core raw paper and the liner are firmly bonded together. A coating solution containing both starch and lignin has a lower viscosity than a coating solution containing only starch, allowing it to be applied at a high concentration. Because a high-concentration coating solution requires a small amount of water, the production method of the present invention can reduce the energy cost required for drying. DETAILED DESCRIPTION OF THE INVENTION

[0009] · Core base paper The present invention provides a paper substrate having a coating layer on at least one surface thereof, The present invention relates to a core raw paper in which the coating layer contains starch and lignin. In this specification, the expression "A to B" (A and B are numerical values or ratios) means a numerical range including A and B.

[0010] (Paper base material) The paper substrate can be any paper used as a paperboard such as core raw paper without any particular restrictions, but it is preferably a multi-layer paper made from a paper material containing recycled paper pulp. The basis weight of the paper substrate is not particularly limited, but is preferably 80 to 220 g / m 2 is preferred, and 83 g / m 2 More preferably, 85 g / m 2 More preferably, 210 g / m 2 Less than 200 g / m is more preferable. 2 The following is more preferable: In the case of multi-layer paper, the basis weight of each layer may be the same or different.

[0011] [Raw pulp] The pulp raw material for the core raw paper produced in the present invention preferably contains a large amount of recycled paper pulp. In the core raw paper of the present invention, the recycled paper pulp content of the total pulp is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and may be 90% by mass or more. Pulps other than recycled paper pulp are not particularly limited, and pulps generally used as papermaking raw materials, such as ground pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), deinked pulp (DIP), softwood kraft pulp (NKP), and hardwood kraft pulp (LKP), can be used.

[0012] Examples of waste paper pulp that can be used include waste cardboard, unprinted waste paper such as white, extra white, medium white, and white damage, which are scraps, broken sheets, and width-reduced waste paper generated in bookbinding plants, printing factories, cutting shops, etc.; waste paper printed on high-quality paper, high-quality coated paper, medium-quality paper, medium-quality coated paper, and wood-burning paper using lithographic, letterpress, or intaglio printing methods, electrophotographic, thermal, thermal transfer, pressure-sensitive recording, inkjet recording, or carbon paper; waste paper written on with water-based or oil-based inks or pencils; pulp obtained by disintegrating and deinking waste newspaper (hereinafter sometimes referred to as DIP); papermaking sludge; and wastewater scum from papermaking factories. These can be used alone or in combination of two or more types. Among recycled paper pulps, low-grade recycled paper such as recycled magazine paper has low strength, but the core raw paper of the present invention has excellent compressive strength, so it is possible to blend 5% or more by mass of recycled magazine paper with the total pulp.

[0013] The paper substrate may contain fillers and internal papermaking additives. Any known filler can be used without any particular limitation. Examples of the filler include inorganic fillers such as calcium carbonate (e.g., heavy calcium carbonate, light calcium carbonate), titanium oxide, clay, silica, talc, kaolin, calcined kaolin, delaminated kaolin, magnesium carbonate, barium carbonate, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, titanium oxide, and bentonite; organic fillers such as urea-formalin resin, polystyrene resin, melamine resin, phenolic resin, and hollow microparticles; and recycled fillers made from papermaking sludge, deinking froth, and the like, and these can be used alone or in combination of two or more.

[0014] The papermaking additives are not particularly limited, and known additives can be used alone or in combination of two or more. Examples of papermaking additives include retention aids, drainage aids, coagulants, aluminum sulfate, bentonite, silica, sizing agents, dry strength agents, wet strength agents, bulking agents, fillers, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, UV inhibitors, anti-fading agents, pitch control agents, and slime control agents. When the paper substrate has a low basis weight, for example, 140 g / m 2 In the following cases, it is preferable to add an internal paper strength agent. As the internal paper strength agent, polyacrylamide (PAM) is preferable. The amount added is preferably 0.1 to 5.0% by mass, more preferably 0.2 to 2.0% by mass, based on the pulp.

[0015] (coating layer) The coating layer is provided on at least one side of the paper substrate, and preferably on both sides. The coating layer contains starch and lignin and may contain various auxiliaries that are commonly blended into coating solutions in the papermaking field, such as dispersants, thickeners, water retention agents, antifoaming agents, waterproofing agents, and colorants. "starch" As the starch, any starch known in the papermaking field can be used without any particular limitation, and examples thereof include raw starch, oxidized starch, esterified starch, cationized starch, enzyme-modified starch, aldehyde starch, hydroxyethylated starch, hydroxypropylated starch, dextrin, etc. The raw material of the starch is also not particularly limited, and examples thereof include corn, potato, tapioca, etc.

[0016] "Lignin" The lignin used in the present invention is not particularly limited, and may be one or a combination of two or more of lignosulfonic acid, kraft lignin, and their salts and modified products, as well as millwood lignin (MWL), explosive lignin, and lignin extracted from wood with an organic solvent. Among these, lignosulfonates are preferred due to their excellent solubility in water. Commercially available lignosulfonates may also be used, such as Sanex P201 (calcium lignosulfonate), Sanex P321 (magnesium lignosulfonate), Sanex P252 (sodium lignosulfonate), and Sanex M100 (magnesium lignosulfonate), all manufactured by Nippon Paper Industries Co., Ltd.

[0017] However, since lignin does not adhere to the paper, when water adheres to the paper, the lignin migrates to the water, causing discoloration of the paper. The core raw paper of the present invention is used while sandwiched between liners, so there is little possibility of water adhering to the paper, and even if discoloration occurs, it is unlikely to be a problem.

[0018] The mass ratio of starch to lignin in the coating layer (starch:lignin, total 100) is preferably 30:70 to 99:1 from the viewpoint of coatability (viscosity) and strength development. If the amount of starch exceeds this range, the viscosity of the coating solution may increase, which may reduce coatability and may result in little improvement in wettability. Although the strength and wettability tend to improve with an increase in lignin content, if the amount of lignin exceeds this range, the effect saturates and there is little further improvement. Furthermore, lignin is more expensive than starch, resulting in high costs. The mass ratio of starch to lignin is more preferably 40:60 to 98:2, even more preferably 50:50 to 97:3, even more preferably 60:40 to 96:4, and even more preferably 70:30 to 95:5.

[0019] From the viewpoint of wettability of the paste, the coating layer preferably has a water contact angle (3.5 μl, 1 second) of 70 degrees or less, more preferably 68 degrees or less, even more preferably 66 degrees or less, even more preferably 64 degrees or less, even more preferably 62 degrees or less, and even more preferably 60 degrees or less.

[0020] The coating machine used to apply the coating liquid containing starch and lignin to the paper substrate is not limited, and examples thereof include a two-roll size press, a gate roll coater, a rod metering size press, a blade coater, a bar coater, a spray coater, an air knife coater, and a curtain coater. The viscosity of the coating liquid can be adjusted appropriately depending on the coating machine used.

[0021] The coating solution containing starch and lignin for forming the coating layer of the present invention has a lower viscosity than a conventional coating solution containing starch but not lignin, even at the same concentration. That is, by using starch and lignin in combination, the coating solution used in the present invention can have a low viscosity despite its high concentration. The coating fluid used in the present invention preferably contains a total of 18% by mass or more of starch and lignin and has a B-type viscosity of 100 mPa·s or less. Because the coating fluid contains a total of 18% by mass or more of starch and lignin and has a B-type viscosity of 100 mPa·s or less, it is easy to apply a highly concentrated coating fluid using various coating machines. The B-type viscosity of the coating fluid is more preferably 90 mPa·s or less. The upper limit of the total concentration of starch and lignin in the coating fluid is not particularly limited, but is about 40% by mass.

[0022] The coating amount (solid content) per side of the coating layer is 1g / m 2 The coating weight is preferably 1 g / m or more. 2 By satisfying the above criteria, higher strength and improved wettability can be expected. The coating amount (solid content) per side of the coating layer is 1.2 g / m 2 More preferably, 1.5 g / m 2 More preferably, 2 g / m 2 More preferably, 2.5 g / m 2 The upper limit of the coating amount (solid content) per one side of the coating layer is not particularly limited, but it is preferably 6 g / m 2 Above that, the effect becomes saturated.

[0023] The core raw paper of the present invention can be fluted using a known corrugator. Any known corrugation process can be used, such as A flute, B flute, C flute, E flute, F flute, G flute, AAA flute, and AA flute.

[0024] ·Corrugated cardboard sheets The corrugated cardboard sheet of the present invention has the above-mentioned core raw paper. In the corrugated cardboard sheet of the present invention, the liner to be bonded to the core raw paper is not particularly limited, and known liners can be used. Multi-layer paperboard is generally used as the liner, and recycled paper pulp or kraft pulp is the main raw material. Since strength and weather resistance are required for the liner, a paper strength enhancer such as polyacrylamide or modified starch may be added, and a sizing agent or water repellent may be used to prevent moisture absorption. Depending on the application, the surface opposite to the side to which the core is bonded (surface layer) may be coated with a pigment or the like to improve printability, or may be laminated or coated with a water-resistant or waterproofing agent to impart waterproofing properties.

[0025] The corrugated cardboard sheet of the present invention has excellent wettability and therefore excellent adhesiveness, and therefore has superior adhesive strength between the liner and the corrugated cardboard sheet compared to corrugated cardboard sheets using conventional starch-coated corrugated cardboard sheets. [Example]

[0026] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and % in the examples represent parts by mass and % by mass, respectively. "Preparation of paper substrate" Made from recycled cardboard and magazine paper, with a target basis weight of 120g / m2 and a four-layer construction. 2 The pulp content of each layer of this four-layered core paper was 90% by mass of recycled corrugated cardboard and 10% by mass of recycled magazine paper (CSF 400 ml when mixed). 0.4% by mass of polyacrylamide and 0.3% by mass of aluminum sulfate were added to the paper stock.

[0027] "Preparation of coating liquid" A coating solution was prepared by blending lignin (trade name: Sunex M-100, manufactured by Nippon Paper Industries Co., Ltd.) and starch (trade name: MS#3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) in the mass ratio (bone dry) shown in Table 1 below. The concentration and Brookfield viscosity of the coating solution are shown in Table 1. "Creating core paper" Each coating liquid was applied to both sides of the paper substrate using a size press and dried to obtain core raw paper. In Comparative Example 1, a paper substrate that had not been coated with any coating liquid was used as the core raw paper.

[0028] "Cardboard making" The pulp used was 100% corrugated recycled paper pulp for the back layer, 100% recycled paper pulp for the middle layer, and 70% unbleached kraft pulp and 30% corrugated recycled paper pulp for the surface layer. For the 100% pulp, 0.25% amphoteric starch, 2.0% aluminum sulfate, and 0.22% rosin-based sizing agent were added as paper strength enhancers to the back layer, 0.8% amphoteric starch, 2.0% aluminum sulfate, and 0.12% rosin-based sizing agent were added as paper strength enhancers to the middle layer, and 2.5% aluminum sulfate and 0.45% rosin-based sizing agent were added as paper strength enhancers to the surface layer. The pulp was combined in a mass ratio of 20:65:15 for the back layer:middle layer:surface layer, with a target basis weight of 170 g / m. 2 A liner base paper of the above was produced. From the core base paper and liner base paper obtained in Examples 1, 4, 5, and 8 and Comparative Examples 1, 2, and 4, A-flute cardboard sheets having a thickness of 5 mm were produced.

[0029] (Evaluation method) ·B type viscosity Measurement was carried out using a Brookfield viscometer under the following conditions. Rotor: No. 1 for viscosity below 100 mPa·s No. 2 for viscosity of 100 mPa·s or more Rotation speed: 60 rpm Temperature: 30℃ ·Basic weight The paper base material and core raw paper were measured with reference to JIS P8124. ·Paper thickness Measurements were made on the core raw paper with reference to JIS P8118 and JIS P8124. ·density The density of the core raw paper was calculated from the basis weight and thickness.

[0030] Coating amount A 50mm square test piece was cut into 5mm square pieces, 2ml of α-amylase was added, and the pieces were soaked at 80℃ for 2 hours, then cooled to room temperature. Then, 2ml of glucoamylase was added, and the pieces were soaked at 50℃ for 2 hours, then cooled to room temperature to prepare the samples. The sample obtained above was measured using a biosensor (model: BF5S, manufactured by Oji Scientific Instruments) to determine the amount of starch, and the dry coating amount (solid content) was calculated from the mass ratio of starch to lignin in the coating liquid. The wet coating weight was calculated from the dry coating weight and the coating liquid concentration.

[0031] Compressive strength, specific compressive strength The core raw paper was evaluated in accordance with JIS P8126. ·Contact angle 3.5 μl of pure water was dropped onto the surface of the coating layer, and the contact angle was measured 1 second after the drop using a contact angle measuring device (DAT1100, manufactured by FIBRO System). The measurement was performed five times, and the average value was used as the measured value. ·Operability The surface properties of the paper substrate coated with the coating liquid were evaluated according to the following criteria: ◯ or Δ indicates no practical problems. 〇: No uneven coating △: There is some unevenness in the coating, but it does not cause any problems in practical use. ×: There are many coating irregularities, which is problematic for practical use.

[0032] Adhesion strength of cardboard sheets Measurements were taken of cardboard sheets using an attachment for A-type cardboard, with reference to JIS Z0402.

[0033] [Table 1]

[0034] The core raw papers obtained in Examples 1 to 8 of the present invention had superior compressive strength compared to Comparative Example 1, which was a paper base material without a coating layer, and Comparative Examples 2 to 5, which were coated with starch. The results of Examples 1 to 4 and Comparative Example 2, and the results of Examples 5 to 8 and Comparative Examples 4 and 5, confirmed that when the dry coating amount is the same, the wettability is improved by using lignin and starch in combination, and that the wettability improves as the lignin ratio increases. Comparative Example 3 had excellent wettability, but this was because the high viscosity of the coating liquid resulted in the formation of a starch coating on the surface. Furthermore, the high viscosity of the coating liquid in Comparative Example 3 resulted in poor operability and was unsuitable for practical use. The results of Examples 1 and 4 and Comparative Examples 1 and 2, and the results of Examples 5 and 8 and Comparative Examples 1 and 4 show that the cardboard sheets using the core raw paper of the present invention had superior adhesive strength to the liner compared to cardboard sheets using core raw paper coated with starch.

Claims

1. A coating layer is provided on at least one surface of the paper substrate, The core raw paper, wherein the coating layer contains starch and lignin.

2. 2. The core raw paper according to claim 1, wherein the lignin is a lignin sulfonate.

3. 2. The core raw paper according to claim 1, wherein the mass ratio of starch to lignin (starch:lignin) in the coating layer is 30:70 to 99:

1.

4. 2. The core raw paper according to claim 1, wherein the water contact angle (3.5 μl, 1 second) is 70 degrees or less.

5. The coating amount (solid content) of the coating layer per one side is 1 g / m ２ 2. The core raw paper according to claim 1, wherein the core raw paper is as described above.

6. A corrugated cardboard sheet comprising the core raw paper according to any one of claims 1 to 5.

7. Contains starch and lignin in total at 18% by mass or more, A method for producing core raw paper, comprising applying a coating liquid for core raw paper having a B-type viscosity of 100 mPa·s or less.

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