Paperboard

Abstract

To provide paperboard that is superior in strength, is hard to collapse, hardly generates cracking on a ruled line, and is suitable for being used in bending processing even though employing used paper pulp.SOLUTION: Multi-layered paper-made paperboard has a blending ratio of used paper pulp to the whole pulp of 65 mass% or more, a basis weight of 350 g / m2 or more, and Taber stiffness of 20-55 mN m vertically and 8-23 mN m horizontally. Accordingly, since the paperboard, even though the used paper pulp is employed, is superior in strength, is hard to collapse, and hardly generates cracking on a ruled line, the paperboard is suitable for being used in bending processing and is suitable for being transported in a vacuum suction method.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a paperboard, and in particular to a paperboard that can be suitably used for liners for corrugated cardboard, box making, laminated paper, and the like. [Background technology]

[0002] Corrugated cardboard is lightweight and inexpensive, and is therefore used to package a variety of items. For example, when used to package heavy items such as precision machinery, it is required to be strong enough to withstand the weight of the packaged heavy items and the weight when the cardboard is stacked. Generally, cardboard is manufactured by laminating a liner to one or both sides of a corrugated core using a corrugator. For cardboard used to package heavy items, a high level of strength is required for the liner. As a liner for such cardboard for packaging heavy items, cardboard with a basis weight of 400 g / m, which has traditionally been manufactured using only kraft pulp (KP) as the raw pulp, has been used. 2 In this way, paperboard that uses 100% kraft pulp as the raw pulp is strong and less prone to line cracks (breaks that occur from the lines (shallow grooves) given to the base paper), making it suitable for use as a liner for cardboard used to pack heavy items.

[0003] However, paperboard using 100% by mass of kraft pulp as the raw material pulp has high raw material costs, and there is a limit to how much cost can be reduced when such paperboard is used to manufacture corrugated cardboard for packaging heavy items, or for making boxes and interleaving paper.

[0004] In order to solve this problem, the blending ratio of kraft pulp is reduced and the blending ratio of recycled paper pulp is increased to reduce the raw material cost. 2 The following discloses a multi-layer paperboard having a thickness of 0.75 mm or more, the surface layer of which is made from a pulp that contains at least 20% by mass of softwood-based chemical pulp and recycled paper pulp (Patent Document 1).

[0005] The applicant also developed a paperboard with a basis weight of 350 g / m2 that is compatible with automated processes in cardboard manufacturing, box making, etc., such as the paperboard conveying process using a vacuum suction pad, despite the high recycled paper pulp content. 2 The above-mentioned thick paperboard has been proposed (Patent Document 2). However, as the air resistance and recycled paper pulp content rate of thick paperboard have both been increased, the risk of creasing problems in paperboard has also increased. The cause of creasing problems is thought to be related to the paper density and the strength of the surface layer of the paperboard, but simply increasing the strength of the surface layer of the paperboard is not enough; measures must be taken by comprehensively considering various factors such as the flexibility of the surface layer and its combination with the lower layer. In addition, creasing problems occur frequently in the dry winter season, and it is thought that the moisture content and elongation of the paperboard are related to creasing problems. Thus, in the case of thick paperboard, there has been a demand for providing a paperboard that has excellent strength, is less prone to line cracking, and is also adaptable to automation while maintaining a high recycled paper content. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-206073 A [Patent Document 2] JP 2020-020065 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances, and its object is to provide a paperboard which uses recycled paper pulp but has excellent strength and is not easily crushed even when heavy items are packed in it, is less likely to break at the creases when folded, and is suitable for transport using a vacuum suction method. [Means for solving the problem]

[0008] The paperboard according to the present invention for solving the above problems includes, but is not limited to, the following aspects. (1) Multi-layered paperboard, with recycled paper pulp content of 65% or more by mass and a basis weight of 350 g / m 2 and wherein the Taber stiffness is 20 to 55 mN·m vertically and 8 to 23 mN·m horizontally. (2) Specific compressive strength is 180N m 2 / g or more. (3) The paperboard according to (1) or (2), characterized in that the breaking elongation in the transverse direction perpendicular to the papermaking direction is 2.8% or more. (4) The paperboard according to any one of (1) to (3), characterized in that the breaking elongation in the machine direction parallel to the papermaking direction is 1.3% or more. (5) The paperboard according to any one of (1) to (4), characterized in that the air resistance is 150 seconds or more. (6) The paperboard according to any one of (1) to (5), characterized in that it is a paperboard made of four or more layers. (7) The paperboard according to any one of (1) to (6), which is a liner for corrugated cardboard. (8) The paperboard according to any one of (1) to (6), which is a paperboard for making boxes. (9) The paperboard according to any one of (1) to (6), which is a paperboard for laminated paper. Effect of the Invention

[0009] The paperboard according to the present invention is as described above, and has excellent strength, is not easily crushed even when heavy objects are packed in it, and is also less likely to break at the creases when folded. In addition, the paperboard according to the present invention has a high air resistance, which makes it suitable for transport using a vacuum suction method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The paperboard according to the present invention is a multi-layer paperboard, in which the blending ratio of recycled paper pulp to the total pulp is 65% by mass or more, and the basis weight is 350 g / m2 The paperboard according to the present invention has excellent strength and is also less susceptible to cracking along its creases, and is therefore able to maintain its strength even after bending. In this specification, the expression "A to B" (A and B are numerical values) means a numerical range including the values ​​of A and B, that is, A or more and B or less.

[0011] The paperboard according to the present invention is composed of a surface layer, one or more middle layers, and a back layer, and the total number of layers can be appropriately set to 4 or more depending on the basis weight of the paperboard. The paperboard according to the present invention has a recycled paper pulp content of 65% by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, and most preferably 80% by mass or more of the total pulp. There is no particular upper limit to the recycled paper pulp content of the total pulp, and pulps other than recycled paper pulp may or may not be included. Such a high recycled paper pulp content makes it possible to reduce the cost of raw pulp. The surface layer may or may not contain recycled paper pulp, may contain kraft pulp as a pulp other than recycled paper pulp, or may be entirely made of kraft pulp. In the middle layer and back layer, the recycled paper pulp content can be 70% by mass or more of the total pulp, preferably 80% by mass or more, more preferably 90% by mass or more, and can also be 100% by mass (consisting only of recycled paper-derived pulp).

[0012] The paperboard according to the present invention has a basis weight of 350 g / m 2 More than 370g / m 2 More preferably, 400 g / m 2 More preferably, 420 g / m 2 The upper limit of the basis weight is not particularly limited as long as it can be produced by a papermaking machine, but it is preferably 600 g / m 2 Less than 550g / m 2 More preferably, 500 g / m or less 2The basis weight can be set appropriately according to the application within the following ranges: 2 If it is less than this, the strength may be insufficient when used as a liner for cardboard for packaging heavy items, which is one of the uses of the paperboard according to the present invention. The basis weight ratio (basis weight distribution) of each layer is not particularly limited, but it is preferable that the surface layer accounts for 16 to 20 mass% of the total in order to simultaneously suppress cracking at the creases and maintain the bursting strength.

[0013] Furthermore, the paperboard according to the present invention preferably has a Taber stiffness in the longitudinal direction parallel to the papermaking direction of 20 to 55 mN·m, and a Taber stiffness in the transverse direction perpendicular to the papermaking direction of 8 to 23 mN·m. With a Taber stiffness within the above ranges, the paperboard is less likely to break at the creases when bent, allowing for reliable bending, and also enabling the paperboard to maintain its shape when used as a box. The Taber stiffness in the longitudinal direction is more preferably 22 to 50 mN·m. The Taber stiffness in the transverse direction is more preferably 9 to 22 mN·m.

[0014] The paperboard of the present invention has a specific compressive strength of 180 N·m 2 / g or more, and 188 N·m 2 / g or more is preferable, and 195 N·m 2 / g or more. The specific compressive strength of the paperboard is preferably 180 N m 2 / g or more, the material is less likely to be crushed and can be suitably used, for example, as a liner for cardboard for packaging heavy items.

[0015] The paperboard according to the present invention preferably has a breaking elongation of 2.8% or more in the transverse direction perpendicular to the papermaking direction. Also, the breaking elongation of the paperboard according to the present invention preferably has a breaking elongation of 1.3% or more in the longitudinal direction parallel to the papermaking direction. Because of such a large breaking elongation in the load direction, for example, when used as a cardboard liner, it is possible to produce a cardboard box that is not easily broken even when packaging heavy items. Also, because of the large breaking elongation in the load direction, it can be used for box making, as a laminated interleaving paper, and can be preferably used as a cardboard box using the paperboard as it is, a partition that can withstand external pressure and wind pressure, a paper board material for various signs, etc.

[0016] The paperboard according to the present invention has an air resistance of preferably 150 seconds or more, more preferably 175 seconds or more, and even more preferably 200 seconds or more. There is no particular upper limit, but it is preferably 400 seconds or less, more preferably 350 seconds or less. The paperboard according to the present invention, which has an air resistance of 150 seconds or more, can reduce the suction pressure when transported by a vacuum suction pad, thereby improving workability and energy saving. Thus, the paperboard according to the present invention has both the same level of strength as conventional liner paperboard made only from kraft pulp, and good transportability, despite having a high blending rate of recycled paper pulp and a high content of short fibers.

[0017] Since the paperboard according to the present invention has a high basis weight, it is manufactured by combining multiple layers using a cylinder paper machine or a fourdrinier multi-layer paper machine. The strength of the paperboard can also be improved by adjusting the papermaking conditions for the multiple layers. Examples of such papermaking conditions include lowering the Canadian Standard Freeness (CSF) of the raw pulp to about 200 to 600 ml, changing the basis weight distribution of each layer to increase the basis weight of the surface layer and / or back layer, and adjusting the strength enhancer blending ratio of each layer to blend more strength enhancer in the surface layer and / or back layer than in other layers. The wire part is preferably equipped with a shaking device. The shaking device is a device that slides the breast roll of the wire part in a direction perpendicular to the flow direction of the paper material (also called the machine width direction). By using the shaking device, the basis weight is made uniform (the formation is improved), and the bursting strength is improved.

[0018] A coating layer can also be provided on the surface of the paperboard. When providing a coating layer, for example, a two-roll size press, a metering size press, a gate roll coater, a spray, or other device can be used. As the coating layer, for example, a hydrophobic layer, a starch layer, a pigment coating layer, or the like can be provided. The hydrophobic layer can be formed, for example, by coating a coating liquid containing hydrophobic silica fine particles, coating a hydrophobic resin emulsion, or coating a coating liquid containing a polymer filler having a hydrophobic functional group.

[0019] In the papermaking of the paperboard according to the present invention, recycled paper pulp is blended in an amount of 65% by mass or more with respect to the total pulp as the raw material pulp. Examples of recycled paper pulp that can be used include recycled cardboard paper, recycled white paper, extra white paper, medium white paper, white damaged paper, and other unprinted recycled paper pulp, recycled paper printed on fine paper, fine coated paper, medium quality paper, medium quality coated paper, and recycled paper, and pulp (DIP) obtained by disintegrating and deinking recycled paper such as discarded confidential documents, recycled magazines, and recycled newspapers.

[0020] Examples of raw material pulps other than recycled paper pulp include various pulps derived from wood fibers, such as bleached softwood kraft pulp (NBKP), bleached hardwood kraft pulp (LBKP), unbleached softwood kraft pulp (NUKP), unbleached hardwood kraft pulp (LUKP), groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP), as well as non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, etc. The Canadian standard freeness of the pulp used in each layer is preferably about 200 to 600 ml, more preferably about 250 to 550 ml, and even more preferably about 300 to 520 ml. The Canadian standard freeness of the pulp used in each layer may be the same or different, but from the viewpoint of achieving both dewaterability and fiber yield in the wire part and press part during papermaking, the freeness of the pulp for the back layer is preferably lower than the freeness of the pulp for the surface layer and the pulp for the middle layer. For example, the freeness of the pulp for the back layer is set to about 200 to 450 ml, and the freeness of the pulp for the back layer is preferably 10 ml or more lower than the pulp for the surface layer and the pulp for the middle layer, and more preferably 20 ml or more lower.

[0021] In the papermaking of the paperboard according to the present invention, a conventional strength agent such as polyacrylamide (PAM) or modified starch may be used as necessary to improve the strength of the paperboard. When the strength agent is added internally, it is added so that the total amount of the strength agent is 0.2% by mass or more, preferably 0.4% by mass or more, and more preferably 0.6% by mass or more, based on the total amount of the paperboard. There is no particular upper limit to the blending rate of the strength agent, but it is preferable to add it internally so that the blending rate is preferably 2.0% by mass or less, more preferably 1.8% by mass or less, and even more preferably 1.6% by mass or less. The addition rate of the strength agent in each layer of the paperboard made in multiple layers may be the same or different.

[0022] In the papermaking process of the present invention, a sizing agent for preventing moisture absorption or a water repellent agent can be added internally to improve the weather resistance of the paperboard. Examples of sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxymethyl saturated fatty acids, neutral rosin-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA), cationic polymer-based sizing agents, etc. Examples of water repellents include fluorine-based resins, polyamide-based resins, wax emulsions, etc.

[0023] If necessary, known fillers can be added internally. Examples of the fillers include inorganic fillers such as kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, and organic fillers such as urea-formaldehyde resin, polystyrene resin, and phenol resin.

[0024] Furthermore, aluminum sulfate, aluminum chloride, sodium aluminate, basic aluminum compounds, water-soluble aluminum compounds, polyvalent metal compounds, silica sol, etc. may be added internally within the limits that do not affect the quality. In the paperboard of the present invention, the addition rates of auxiliaries such as sizing agents and water repellents and fillers may be the same or different.

[0025] There is no particular restriction on the uses of the paperboard according to the present invention, and it can be used, for example, as a liner for corrugated cardboard, particularly for packaging heavy items, paperboard for making boxes, paperboard for laminated paper, and the like. EXAMPLES

[0026] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0027] [Example 1] Made from recycled cardboard and softwood unbleached kraft pulp (NUKP), this four-ply paper has a basis weight of 375g / m 2 The paperboard was made so that the raw pulp content of each layer of this four-ply paperboard was 100% by mass (CSF 500 ml) for the surface layer, 90% by mass of recycled corrugated cardboard and 10% by mass of NUKP for the back layer (CSF 380 ml when mixed), and 100% by mass (CSF 420 ml) for the middle layer. The recycled paper pulp content of the total pulp was 77% by mass. The paper stock used to make each layer contained 0.4% by mass of polyacrylamide (PAM) as a paper strength agent, 1.5% by mass of aluminum sulfate (solid content equivalent), and 0.3% by mass of a sizing agent.

[0028] [Example 2] Made from recycled cardboard and softwood unbleached kraft pulp (NUKP), this four-ply paper has a basis weight of 400g / m 2 The paperboard was made so that the paperboard was made as follows. The raw pulp content of each layer in this four-ply paperboard was 100% by mass of NUKP (CSF 500ml) for the surface layer, and 100% by mass of recycled corrugated paper for the back and middle layers (CSF: back layer 380ml, middle layer 420ml). The recycled paper pulp content of the total pulp was 83% by mass. The paper stock used to make each layer contained 0.3% by mass of polyacrylamide (PAM) as a paper strength agent, 1.0% by mass of aluminum sulfate (solid content equivalent), and 0.15% by mass of a sizing agent, and a shaking device was operated when making the back layer.

[0029] [Example 3] 4-ply paper with a basis weight of 420g / m 2 The same blending and chemical addition procedures were carried out as in Example 1, except that the paperboard was produced so that the composition was such that the composition satisfies the following criteria: [Example 4] 4-ply paper with a basis weight of 440g / m 2 The same blending and chemical addition procedures were carried out as in Example 2, except that the paperboard was produced so that the composition was such that the composition satisfies the following criteria:

[0030] [Example 5] The surface layer is 50% recycled cardboard and 50% NUKP (CSF 450ml when mixed), the back and middle layers are 100% recycled cardboard (CSF: back layer 380ml, middle layer 420ml), and the 6-ply paper has a basis weight of 440g / m 2 Except for the fact that the paperboard was produced so as to satisfy the above conditions, the same blending and chemical addition were carried out as in Example 1. The blending ratio of recycled paper pulp to the total pulp was 93 mass %.

[0031] [Comparative Example 1] The same procedure as in Example 4 was used except that no recycled cardboard was used and only unbleached softwood kraft pulp (NUKP, CSF 500ml) was used, resulting in a four-ply paper with a basis weight of 445g / m. 2 The paperboard was made so that the

[0032] [Physical property measurements] The paperboards of the Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1. (Basic weight) Measurements were performed in accordance with JIS P 8124. (Thickness) Measurements were performed in accordance with JIS P 8118 and JIS P 8124. (density) It was calculated from the basis weight and thickness measured in accordance with JIS P 8118 and JIS P 8124.

[0033] (Burst strength, burst strength index) According to JIS P 8131, pressure was applied from the surface side of the paper to measure the bursting strength, and the bursting strength index was calculated by dividing the bursting strength by the basis weight. (Taber fear) The measurements were made in the machine direction (vertical) and width direction (horizontal) of the paper in accordance with JIS P8125. (Compressive strength, specific compressive strength) The compressive strength was measured by the ring crush method in accordance with JIS P 8126, and the specific compressive strength was calculated by dividing the compressive strength by the basis weight.

[0034] (Tensile elongation at break) According to JIS P8113, the paper strip was pulled under certain conditions, and the strength and elongation until breakage were measured. The elongation was expressed as a percentage of the initial test length. (Air resistance) The measurements were made from the surface side using an Oken type smoothness and air permeability tester in accordance with JIS P 8117. (Evaluation of crease cracks in the flow direction) Each sample was cut to 50 mm in the machine direction (vertical) and 100 mm in the width direction (horizontal), and conditioned for one day so that the paper moisture content was 6%. The center of the width direction of the surface layer of the conditioned sample was colored with an oil-based pen to make it easier to see whether or not cracks would occur at the creases when folded, and then a crease 50 mm long (the same as the machine direction of the paper) was made in the center of the width direction so that the surface layer side was folded at a mountain angle of 180° in the machine direction of the paper, and the presence or absence of cracks at the creases was confirmed.

[0035] The results are shown in Table 1. [Table 1]

[0036] The paperboards obtained in the Examples had smaller Taber stiffness values ​​than the paperboards obtained in the Comparative Examples, which made them less susceptible to crease cracking, making them suitable for processing with a low risk of crease cracking during bending.

[0037] The paperboards obtained in the Examples had the same burst strength ratio as the paperboards obtained in the Comparative Examples, but had higher compression strength ratios. Therefore, the paperboards obtained in the Examples are less prone to crushing and can be used for practical purposes, for example, as liners for cardboard used in packaging heavy items.

[0038] In addition, the paperboard obtained in the Examples has a larger breaking elongation than the paperboard obtained in the Comparative Examples. As a result, for example, when used as a cardboard liner, it is possible to produce cardboard boxes that are less likely to break even when packaging heavy items.

[0039] The paperboard obtained in the examples has a higher air resistance than the paperboard obtained in the comparative examples, which allows the suction pressure to be lowered when transported using a vacuum suction pad, improving workability and enabling energy savings. [Industrial Applicability]

[0040] The paperboard of the present invention is as described above, has excellent strength and is resistant to crushing, is less likely to break at the creases, and is suitable for applications that require folding processing. Therefore, it is particularly suitable for use in a variety of applications such as liners for corrugated cardboard, box making, and laminated interleaf paper, and has great industrial applicability.

Claims

1. A multi-layered paperboard, in which the blending rate of recycled paper pulp in the total pulp is 65% by mass or more, and the basis weight is 350 g / m ２ The paperboard is characterized in that it has a Taber stiffness of 20 to 55 mN·m vertically and 8 to 23 mN·m horizontally, and a breaking elongation of 2.8% or more in the horizontal direction perpendicular to the papermaking direction.

2. Specific compressive strength is 180N・m ２ 2. The paperboard of claim 1, wherein the elastic modulus is 1 / g or more.

3. 3. The paperboard according to claim 1, characterized in that the breaking elongation in the machine direction parallel to the papermaking direction is 1.3% or more.

4. 4. The paperboard according to claim 1, wherein the paperboard has an air resistance of 150 seconds or more.

5. 5. The paperboard according to claim 1, which is a multi-layer paperboard having four or more layers.

6. 6. The paperboard of any one of claims 1 to 5, which is a liner for corrugated board.

7. 6. The paperboard of any one of claims 1 to 5, which is a box-making paperboard.

8. 6. The paperboard of claim 1, which is a paperboard for laminating.

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