Corrugated-cardboard base paper and method for producing corrugated-cardboard base paper

Abstract

The present invention addresses the problem of providing corrugated-cardboard base paper in which generation of paper dust is suppressed, and in which occurrence of paper breakage is suppressed during production. The present invention relates to corrugated-cardboard base paper comprising pulp fibers and a thermoplastic resin. The content of the thermoplastic resin is 50–3000 ppm, and the kink index of the pulp fibers is 2400(1 / m) or higher. The present invention also relates to a method for producing the corrugated-cardboard base paper comprising the pulp fibers and the thermoplastic resin. The content of the thermoplastic resin is 50–3000 ppm, and the kink index of the pulp fibers is 2400(1 / m) or higher.

Description

Corrugated board base paper and method for manufacturing corrugated board base paper

[0001] The present invention relates to a cardboard linerboard and a method for manufacturing the cardboard linerboard.

[0002] In recent years, due to environmental concerns, efforts to eliminate plastic have been accelerating worldwide. As a result, many products are being converted to paper, and there is also a demand for recycled paper products. For example, recycled base paper is being produced using recycled paper such as cardboard, magazines, and copy paper.

[0003] On the other hand, when it comes to recycling paper products, paper products containing plastic are treated as prohibited waste paper, so many are disposed of without being recycled. However, in recent years, the need to recycle paper products containing plastic has increased, and technological advances have led to the advancement of recycling of paper-plastic composite products.

[0004]

[0003] Meanwhile, cardboard cases are often used for transporting products and the like. When products are placed in the cardboard case and transported, paper dust may be generated from the inner surface of the cardboard case due to contact between the inner surface of the cardboard case and the products contained therein. To solve this problem, for example, Patent Document 1 discloses a cardboard liner in which a surface layer is formed by printing a solution containing a synthetic resin and a lubricant on at least one side of a base paper.

[0005] Japanese Patent Application Laid-Open No. 2013-2009

[0006] However, the cardboard liner described in Patent Document 1 has a problem in that it cannot sufficiently suppress paper dust generated from inside the liner when forming the score lines or cutting the cardboard liner. Furthermore, when producing the cardboard liner, paper breakage may occur, which may deteriorate operability.

[0007] Therefore, in order to solve these problems of the conventional technology, the present inventors have conducted research with the aim of providing a base paper for corrugated cardboard in which the generation of paper dust is suppressed and the occurrence of paper cuts during production is suppressed.

[0008] Examples of specific embodiments of the present invention are given below.

[0009] [1] A corrugated cardboard base paper containing pulp fibers and a thermoplastic resin, the content of the thermoplastic resin being 50 to 3000 ppm, and the kink index of the pulp fibers being 2400 (1 / m) or more. [2] The corrugated cardboard base paper according to [1], in which the geometric mean of the tensile modulus of elasticity in the machine direction and the tensile modulus of elasticity in the cross direction is 1.2 GPa or more. [3] A corrugated cardboard base paper having a basis weight of 80 g / m ２ More than 400g / m ２ [4] The corrugated board base paper according to any one of [1] to [3], which has two or more paper layers. [5] The corrugated board base paper according to [1] or [2], which has a basis weight per paper layer of 200 g / m or less. ２ [6] The corrugated board base paper according to any one of [1] to [5], wherein the thermoplastic resin is a polyolefin resin. [7] The corrugated board base paper according to any one of [1] to [6], which contains pulp fibers and a thermoplastic resin derived from laminated recycled paper. [8] A corrugated cardboard sheet comprising the corrugated board base paper according to any one of [1] to [7]. [9] A method for producing corrugated board base paper, which contains pulp fibers and a thermoplastic resin, wherein the thermoplastic resin content is 50 to 3000 ppm, and the kink index of the pulp fibers is 2400 (1 / m) or more.

[10] A method for producing corrugated board base paper according to [9], which comprises the steps of: defibrating pulp fibers from laminated recycled paper having a paper base material containing pulp fibers and a thermoplastic resin layer, to obtain a pulp slurry containing pulp fibers and a thermoplastic resin; and making paper from the pulp slurry.

[11] The method for producing cardboard base paper according to

[10] , wherein the pulp fiber disintegration temperature in the step of obtaining a pulp slurry is 10 to 60°C.

[12] The method for producing cardboard base paper according to

[10] or

[11] , further comprising a step of crushing and washing laminated waste paper before the step of producing a pulp slurry.

[13] The method for producing cardboard base paper according to any of

[10] to

[12] , further comprising a drying step after the step of producing a pulp slurry.

[14] The method for producing a cardboard sheet, comprising a step of subjecting the cardboard base paper according to any of [1] to [7] to a corrugator treatment.

[0010] The present invention will be described in detail below. The following description may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined arbitrarily.

[0011] (Corrugated cardboard base paper) This embodiment relates to a corrugated cardboard base paper containing pulp fibers and a thermoplastic resin, with a thermoplastic resin content of 50 to 3000 ppm and a kink index of the pulp fibers of 2400 (1 / m) or more. In this embodiment, by setting the thermoplastic resin content within the above range and the kink index of the pulp fibers within the above range, it is possible to produce corrugated cardboard base paper that generates less paper dust during the manufacturing process and use and that suppresses the occurrence of paper breaks during manufacturing. Note that in this embodiment, corrugated cardboard base paper includes both liner base paper and core base paper. Furthermore, the effects of this embodiment are preferably exhibited in both liner base paper and core base paper.

[0012] The kink index of pulp fibers is an index for evaluating the degree of bending of pulp fibers contained in the base paper for corrugated cardboard. A higher kink index indicates that the fibers are more bent and more entangled with each other. In this embodiment, by setting the kink index of pulp fibers to the above-mentioned lower limit or higher, it is possible to prevent pulp fibers from falling off from the base paper for corrugated cardboard, thereby suppressing the generation of paper dust. In addition, in this embodiment, by setting the content of thermoplastic resin to the above-mentioned lower limit or higher, the thermoplastic resin is appropriately bound to a portion of the pulp fibers, thereby more effectively preventing the falling off of paper dust.

[0013] Furthermore, in this embodiment, by setting the content of the thermoplastic resin within the above range, it is possible to suppress the shedding of paper powder and the occurrence of paper breaks during production. By setting the content of the thermoplastic resin to the above upper limit or less, the bonds between the pulp fibers are maintained, and as a result, the occurrence of paper breaks during production can be suppressed and operability can be improved.

[0014] The corrugated board base paper of this embodiment preferably has two or more paper layers. The number of paper layers constituting the corrugated board base paper may be two or more, three or more, or four or more. The upper limit of the number of paper layers constituting the corrugated board base paper is not particularly limited, but from the viewpoint of handleability, it is preferable that the number be, for example, 10 or less.

[0015] <Thermoplastic Resin> The thermoplastic resin contained in the corrugated cardboard base paper of this embodiment may be either a natural resin or a synthetic resin, and examples thereof include starch derivatives, casein, shellac, polyvinyl alcohol and its derivatives, acrylic resins, ionomer resins, maleic acid resins, urethane resins, polyester resins (polyethylene terephthalate, etc.), styrene-butadiene resins, vinyl chloride resins, polyolefin resins, ethylene-vinyl alcohol copolymers, ethylene-acrylic acid copolymers (EAA), ethylene-methacrylic acid copolymers (EMAA), ethylene-methyl methacrylate copolymers (EMMA), styrene-acrylic copolymers, and polyamide resins (nylon, etc.). Among these, the thermoplastic resin is preferably a polyolefin resin, and examples of polyolefin resins include polyethylene, polypropylene, and ethylene-α-olefin copolymers (ethylene-propylene copolymers, etc.). The polyolefin resin is preferably polyethylene or polypropylene, with polyethylene being particularly preferred. As the polyethylene, it is preferable to use high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), or linear low density polyethylene (LLDPE), and it is more preferable to use low density polyethylene (LDPE) or linear low density polyethylene (LLDPE).

[0016] The density of the polyolefin resin is 0.900 g / cm ３ It is preferable that the density is 0.910 g / cm or more. ３ The density of the polyolefin resin is more preferably 0.970 g / cm or more. ３ Preferably, it is 0.950 g / cm or less. ３ More preferably, it is 0.930 g / cm or less. ３ The melting point of the polyolefin resin is preferably 85°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher. The melting point of the polyolefin resin is preferably 170°C or lower, more preferably 150°C or lower, and even more preferably 130°C or lower.

[0017] The content of thermoplastic resin contained in the cardboard base paper is preferably 50 ppm or more, more preferably 100 ppm or more, even more preferably 150 ppm or more, even more preferably 200 ppm or more, even more preferably 250 ppm or more, and particularly preferably 300 ppm or more. The content of thermoplastic resin is preferably 3000 ppm or less, more preferably 2500 ppm or less, even more preferably 2000 ppm or less, even more preferably 1500 ppm or less, and even more preferably 1000 ppm or less. By setting the content of thermoplastic resin at or above the lower limit, the thermoplastic resin is appropriately bonded to a portion of the pulp fibers, thereby suppressing the generation of paper dust during the manufacturing process and use. On the other hand, by setting the content of thermoplastic resin at or below the upper limit, the occurrence of paper breaks during manufacturing can be suppressed, improving operability.

[0018] The content of thermoplastic resin contained in the cardboard base paper can be controlled by adjusting the content of thermoplastic resin contained in the pulp slurry when producing the cardboard base paper. For example, a predetermined amount of thermoplastic resin may be added to the pulp slurry. Furthermore, as described below, the content of thermoplastic resin may be controlled by appropriately controlling the type and content of thermoplastic resin-containing waste paper used as a recycled raw material (e.g., thermoplastic resin-laminated waste paper, waste paper containing a thermoplastic resin sheet, or waste paper coated with a thermoplastic resin). In this embodiment, the thermoplastic resin contained in the cardboard base paper is preferably a thermoplastic resin derived from thermoplastic resin-containing waste paper.

[0019] The content of thermoplastic resin in cardboard base paper can also be controlled by adjusting the waste paper concentration during disintegration of the thermoplastic resin-containing waste paper. For example, in the disintegration process, the higher the concentration of the thermoplastic resin-containing waste paper, the larger the foreign matter (e.g., pieces of thermoplastic resin) remains and separates from the pulp fibers, making it easier to remove these foreign matter in the dust removal process. However, the lower the concentration of the thermoplastic resin-containing waste paper, the finer the foreign matter fragments become, making them more difficult to remove in the dust removal process. For this reason, it is preferable to determine the disintegration conditions so that the waste paper concentration during disintegration of the thermoplastic resin-containing waste paper is within an appropriate range.

[0020] In this embodiment, the corrugated cardboard base paper may have two or more paper layers. In such a case, the thermoplastic resin may be contained in all of the two or more paper layers, or only in one of the layers. It is particularly preferable that the corrugated cardboard base paper has three or more paper layers. In this case, the thermoplastic resin may be contained in all layers, but it is particularly preferable that the thermoplastic resin be contained in the middle layer. In a paper layer containing a thermoplastic resin, the thermoplastic resin is preferably uniformly dispersed throughout the entire paper layer. For example, when the paper layer is divided into three equal parts in the thickness direction, it is preferable that the thermoplastic resin content in the three regions is within ±10%.

[0021] The thermoplastic resin content of cardboard base paper is measured using an extraction process to separate the thermoplastic resin contained in the cardboard base paper, as described below, and an analysis process to quantify the thermoplastic resin content using pyrolysis GC / MS. In the extraction process, cardboard base paper is sampled and the thermoplastic resin in the cardboard base paper is extracted using a high-speed solvent extraction device (Buchi, E-916). The extraction conditions are an extraction temperature of 180°C, an extraction pressure of 150 bar, and an extraction solvent of xylene (special grade, Wako Pure Chemical Industries). The extraction device is set up, and two extraction cycles of extract are collected. After extraction, the solvent is removed using a rotary evaporator (water bath 60°C), and the sample is dried at 105°C for 12 hours to fully dry the cardboard base paper, thereby obtaining the thermoplastic resin in the cardboard base paper. In the subsequent analysis process, an appropriate amount of xylene is added to the extracted thermoplastic resin to achieve a concentration of 2-5 mg / ml, and the solution is dissolved at 130°C for 2 hours, with stirring during the process. Next, the xylene solution of the extract dissolved in the Eco Cup whose tare weight has been measured is placed in such a way that the extract amount is 50 to 200 μg, and the solvent is evaporated at 105°C for 2 hours, and the amount of the extract to be analyzed is measured. The extract is measured using a pyrolysis GC / MS (Shimadzu Corporation GC / MS-QP2010) to quantify the amount of thermoplastic resin. When the thermoplastic resin is polyethylene, the pyrolysis GC / MS measurement conditions are as follows: Polyethylene standard: (Tosoh 07C03C, LDPE) Column: HP-5MS (length: 30 m, inner diameter: 0.250 mm, thickness: 0.25 μm) Analysis conditions: pyrolysis temperature = 600°C, injection port temperature = 320°C, split ratio = 1:60, interface temperature = 280°C, GC column temperature conditions = 40°C (hold for 3 minutes) → 10°C / min → 325°C (hold for 15 minutes), ion source temperature = 200°C Detection: m / z 29-600 (quantitation was calculated using the mass chromatogram area value of 1,19-eicosadiene (C20) at m / z 82)

[0022] The above analytical method is an analytical method when the thermoplastic resin is polyethylene, but when quantifying the content of a thermoplastic resin other than polyethylene, the analysis can be performed in the same manner by appropriately changing the standard, analytical conditions, and quantitative m / z.

[0023] <Pulp Fiber> The cardboard base paper of this embodiment contains pulp fiber. The content of pulp fiber contained in the cardboard base paper is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. The upper limit of the content of pulp fiber contained in the cardboard base paper is the remainder excluding the thermoplastic resin.

[0024] Pulp fibers include fibers made from wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include chemical pulps such as hardwood pulp (hardwood kraft pulp (LKP)), softwood pulp (softwood kraft pulp (NKP)), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP). Other examples include semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP), and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include cotton-based pulps such as cotton linter and cotton lint, non-wood pulps such as hemp, straw, and bagasse, and cellulose, chitin, and chitosan isolated from sea squirts and seaweed. The deinked pulp may be made from recycled paper. The pulp may be one of the above-mentioned types alone or a mixture of two or more types.

[0025] The pulp fibers preferably include softwood pulp fibers and hardwood pulp fibers, and for example, it is more preferable to use a combination of softwood kraft pulp (NKP) fibers and hardwood kraft pulp (LKP) fibers. In this embodiment, it is also preferable to use deinked pulp fibers in combination as pulp fibers, and it is preferable to include deinked pulp fibers made from recycled paper.

[0026] The corrugated cardboard base paper of this embodiment preferably contains softwood pulp fibers and hardwood pulp fibers. Here, where N is the content (parts by mass) of softwood pulp fibers relative to the total pulp mass, and L is the content (parts by mass) of hardwood pulp fibers relative to the total pulp mass, N:L is preferably 0:100 to 40:60, more preferably 0:100 to 20:80, and even more preferably 0:100 to 10:90. The content of each pulp fiber can be measured according to JIS P 8120:1998.

[0027] The kink index of the pulp fibers contained in the corrugated cardboard base paper of this embodiment is preferably 2400 (1 / m) or more, more preferably 2500 (1 / m) or more, and even more preferably 2600 (1 / m) or more. The kink index of the pulp fibers is preferably 4000 (1 / m) or less, more preferably 3700 (1 / m) or less, and even more preferably 3400 (1 / m) or less. By setting the kink index of the pulp fibers to the above-mentioned lower limit or more, the degree of bending of the pulp fibers can be increased, thereby preventing the pulp fibers from falling out of the corrugated cardboard base paper, and as a result, the generation of paper dust can be more effectively suppressed. Furthermore, by setting the kink index of the pulp fibers to the above-mentioned upper limit or less, a decrease in the strength of the corrugated cardboard base paper can be suppressed.

[0028] In this specification, the kink index of the pulp fibers is the kink index of the pulp fibers contained in a pulp slurry obtained by defibrating the pulp fibers in accordance with JIS P 8220-1:2012. Specifically, defibration is performed in accordance with JIS P 8220-1:2012 to obtain a pulp slurry containing 2% by mass of base paper for corrugated board. The pulp slurry is then adjusted to a solids concentration of 0.1% by mass, and the pulp solids concentration is calculated in accordance with JIS P 8225:2003. Next, the defibrated slurry is adjusted to a solids concentration of 0.004% by mass and a volume of 500 g, and the amount of the sample taken is recorded. The solids concentration and the amount of the sample taken are then used to calculate the dry weight of the sample. The obtained slurry is used to measure the "kink index" using a fiber length measuring instrument (Valmet FS-5 with UHD base unit, manufactured by Valmet). The kink index (1 / m) in this specification is Kibblewhite's kink index calculated by the following formula (1): The kink index is calculated by weighting the number of kinks in each angle range according to the increase in angle and dividing the weighted result by the sum of the fiber lengths.

[0029]

[0030] The symbols in formula (1) represent the following: １ n = number of kinks (bends) of 21° or more and 45° or less in the measurement sample ２ n = number of kinks (bends) between 46° and 90° in the measurement sample ３ L = Number of kinks (bending angles) between 91° and 180° in the measurement sample ｃ = Sum of fiber lengths of measurement samples (m)

[0031] The kink index can be adjusted by appropriately controlling the treatment temperature during pulp disintegration and the conditions for crushing and washing the laminated waste paper before disintegrating the pulp. Specifically, the kink index of the pulp fibers can be controlled within a desired range by adopting the disintegration temperature and crushing and washing conditions described below.

[0032] <Optional Components> The corrugated cardboard base paper of this embodiment may contain optional components. Examples of optional components include dry strength agents, wet strength agents, sizing agents, aluminum sulfate, retention aids, freeness improvers, bulking agents, coloring dyes, coloring pigments, fluorescent whitening agents, pH adjusters, pitch control agents, preservatives, slime control agents, and softeners. Examples of dry strength agents include cationized starch, polyacrylamide (PAM), and carboxymethyl cellulose (CMC). Examples of wet strength agents include polyamide epichlorohydrin, urea, melamine, and thermally crosslinkable polyacrylamide. Examples of sizing agents include rosin-based, alkyl ketene dimer-based, and alkenyl succinic anhydride-based sizing agents. The optional components may be used alone or in combination of two or more. However, the content of the optional components is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, and even more preferably 4% by mass or less, relative to the total mass of the cardboard base paper.

[0033] <Physical Properties> The geometric mean of the longitudinal tensile modulus and the transverse tensile modulus of the corrugated cardboard base paper of this embodiment is preferably 1.2 GPa or more, more preferably 1.4 GPa or more, even more preferably 1.6 GPa or more, even more preferably 1.8 GPa or more, and particularly preferably 2.0 GPa or more. The upper limit of the geometric mean of the longitudinal tensile modulus and the transverse tensile modulus of the corrugated cardboard base paper is not particularly limited, but is preferably 5.0 GPa or less, for example. By setting the geometric mean of the longitudinal tensile modulus and the transverse tensile modulus of the corrugated cardboard base paper to the above-mentioned lower limit or more, the generation of paper dust can be more effectively suppressed. Furthermore, by setting the geometric mean of the longitudinal tensile modulus and the transverse tensile modulus of the corrugated cardboard base paper to the above-mentioned lower limit or more, the strength required for corrugated cardboard applications is easily exhibited, and the cardboard base paper is preferably used for packaging applications, for example. When measuring the tensile modulus of elasticity of the cardboard base paper, the cardboard base paper is conditioned for 24 hours in a humidity-controlled environment specified in JIS P 8111:1998, and the tensile modulus of elasticity in the machine direction and the cross direction is measured in accordance with JIS P 8113:2006.

[0034] The generation of paper dust is suppressed in the corrugated cardboard base paper of this embodiment. The degree of paper dust generation can be evaluated by calculating the white area ratio using the following evaluation method. Specifically, the corrugated cardboard base paper is cut into pieces 10 cm long and 10 cm wide, and each layer is carefully peeled off by hand to separate the pieces. An adhesive film (NEION PET75-H120(10) manufactured by Nichiei Shinka Co., Ltd.) is attached to the peeling surface of the separated corrugated cardboard base paper on a metal roll with a diameter of 7 cm and a weight of 10 kg. The roll is then rolled twice at a speed of 60 bpm over the peeling surface of the corrugated cardboard base paper to adhere the paper dust to the adhesive film. The adhesive film is scanned at a size of 5 x 5 cm and an image quality of 400 dpi, and the entire piece is binarized into white and black areas. The white areas are considered to be paper dust, and the white area ratio (%) is calculated. When the corrugated board base paper is single-ply, any tape larger than the corrugated board base paper is applied to both surfaces, the tape is then peeled off, and the white area ratio (%) of the peeled surface of the corrugated board base paper that is split into two is measured. The white area ratio is preferably 3.50% or less, more preferably 3.00% or less, even more preferably 2.50% or less, even more preferably 2.00% or less, still more preferably 1.50% or less, and particularly preferably 1.00% or less.

[0035] The thickness of the cardboard base paper (total thickness of the paper layers) is preferably 50 μm or more, more preferably 75 μm or more, and even more preferably 100 μm or more. The thickness of the cardboard base paper (total thickness of the paper layers) is preferably 400 μm or less, more preferably 370 μm or less, even more preferably 350 μm or less, and particularly preferably 300 μm or less. By keeping the thickness of the cardboard base paper within the above range, it is possible to achieve the strength required for cardboard applications while also improving ease of handling. The thickness of the cardboard base paper is measured in accordance with JIS P 8118:2014 using cardboard base paper that has been conditioned in a humidity-controlled environment as specified in JIS P 8111:1998.

[0036] The basis weight of the cardboard base paper (total basis weight of the paper layers) is 80 g / m ２ It is preferable that the weight is 90 g / m or more.２ More preferably, it is 100 g / m or more. ２ It is more preferable that the basis weight of the base paper for corrugated board (total basis weight of the paper layers) is 400 g / m or more. ２ Preferably, the weight is 350 g / m or less. ２ More preferably, it is 300 g / m or less. ２ More preferably, it is 250 g / m or less. ２ More preferably, it is 200 g / m or less. ２ It is particularly preferable that the basis weight is within the above range. By setting the basis weight within the above range, sufficient strength can be obtained during use and the generation of paper dust can be more effectively suppressed. The above basis weight is a value measured in accordance with JIS P 8124:2011 using a corrugated cardboard base paper that has been conditioned in a humidity-controlled environment specified in JIS P 8111:1998.

[0037] The basis weight of each layer of cardboard base paper is 10 g / m ２ It is preferable that the content is 13 g / m or more. ２ More preferably, it is 15 g / m or more. ２ The basis weight per layer of the cardboard base paper is more preferably 200 g / m or more. ２ Preferably, the weight is 180 g / m or less. ２ More preferably, it is 160 g / m or less. ２ By setting the basis weight per layer of the cardboard base paper within the above range, sufficient strength can be obtained during use and the generation of paper dust can be more effectively suppressed.

[0038] The density of the cardboard base paper is 0.60 g / cm ３ It is preferable that the density is 0.65 g / cm or more. ３ More preferably, it is 0.70 g / cm or more. ３ More preferably, it is 0.75 g / cm or more. ３ It is more preferable that the value is 0.80 g / cm or more. ３ It is particularly preferable that the density of the cardboard base paper is 0.90 g / cm or more. ３By setting the density within the above range, sufficient strength can be obtained during use, and the generation of paper dust can be more effectively suppressed. The density of the cardboard base paper is calculated using the following formula from the basis weight and paper thickness measured as described above, in accordance with JIS P 8118:2014. Density (g / cm ３ )=Basic weight (g / m ２ ) / Paper thickness (μm)

[0039] <Recycled Raw Materials> The cardboard base paper of this embodiment is preferably manufactured using recycled raw materials. That is, the cardboard base paper of this embodiment is cardboard base paper containing recycled raw materials (recycled cardboard base paper). Here, the recycled raw material constituting the cardboard base paper of this embodiment is preferably waste paper, and the waste paper preferably includes thermoplastic resin-containing waste paper (for example, thermoplastic resin-laminated waste paper, waste paper containing a thermoplastic resin sheet, or thermoplastic resin-coated waste paper), more preferably includes laminated waste paper (thermoplastic resin-laminated waste paper) having a paper base material containing pulp fibers and a thermoplastic resin layer, and particularly preferably includes laminated waste paper (thermoplastic resin-laminated waste paper) derived from liquid containers. Note that examples of liquid containers include beverage containers, liquid seasoning containers, detergent containers, etc., and specifically include paper cup containers, paper cups, milk cartons, aseptic containers, etc.

[0040] The proportion of thermoplastic resin-containing waste paper relative to the total mass of recycled raw materials used in the manufacture of cardboard base paper in this embodiment is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 2.5% by mass or more, and particularly preferably 3.0% by mass or more. The proportion of thermoplastic resin-containing waste paper is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and particularly preferably 20% by mass or less.

[0041] In the thermoplastic resin-containing waste paper, it is preferable that the thermoplastic resin is not printed. By using such thermoplastic resin-containing waste paper, it is possible to effectively increase the adhesiveness of the thermoplastic resin to the pulp fibers in the cardboard base paper.

[0042] The recycled raw material constituting the cardboard base paper of this embodiment preferably contains thermoplastic resin-containing waste paper, and in this case, the cardboard base paper contains pulp fibers derived from thermoplastic resin-containing waste paper and thermoplastic resin derived from thermoplastic resin-containing waste paper. In particular, the cardboard base paper preferably contains pulp fibers derived from laminated waste paper and thermoplastic resin derived from laminated waste paper.

[0043] The content of thermoplastic resin contained in the thermoplastic resin-containing waste paper is preferably 1% by mass or more, more preferably 5% by mass or more, and particularly preferably 10% by mass or more. The content of thermoplastic resin contained in the thermoplastic resin-containing waste paper is preferably 40% by mass or less, more preferably 30% by mass or less, and particularly preferably 20% by mass or less.

[0044] The thermoplastic resin-containing waste paper preferably contains softwood pulp fibers and hardwood pulp fibers in addition to the thermoplastic resin. If the content of softwood pulp fibers relative to the total pulp mass contained in the thermoplastic resin-containing waste paper is N (parts by mass) and the content of hardwood pulp fibers relative to the total pulp mass is L (parts by mass), then the ratio N:L is preferably 0:100 to 40:60, more preferably 0:100 to 20:80, and even more preferably 0:100 to 10:90.

[0045] The cardboard base paper of this embodiment may further contain deinked pulp fibers or recycled cardboard pulp fibers made from recycled paper. Examples of deinked pulp include recycled paper pulp (Kent recycled paper pulp) made from scraps of coated printing paper generated in bookbinding and printing factories, etc., recycled magazine pulp, recycled flyer pulp, recycled newspaper pulp, recycled office paper pulp, recycled communication paper pulp, recycled cardboard pulp, and recycled paper pulp from folding cartons.

[0046] The recycled raw material constituting the cardboard base paper may be a combination of thermoplastic resin-free waste paper that does not contain thermoplastic resin and thermoplastic resin-containing waste paper. In this case, the proportion of thermoplastic resin-free waste paper relative to the total mass of the recycled raw material used to manufacture the cardboard base paper of this embodiment is preferably 99% by mass or less, more preferably 98% by mass or less, even more preferably 97% by mass or less, even more preferably 95% by mass or less, and particularly preferably 90% by mass or less. Furthermore, the proportion of thermoplastic resin-free waste paper is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more.

[0047] It is preferable that all of the pulp fibers contained in the cardboard base paper of this embodiment are pulp fibers derived from recycled materials. Thus, the cardboard base paper of this embodiment is preferably 100% recycled cardboard base paper.

[0048] (Method for manufacturing corrugated cardboard base paper) This embodiment relates to a method for manufacturing corrugated cardboard base paper containing pulp fibers and a thermoplastic resin, with the thermoplastic resin content being 50 to 3000 ppm and the pulp fibers having a kink index of 2400 (1 / m) or more. The method for manufacturing corrugated cardboard base paper of this embodiment may include a step of adding the thermoplastic resin to a pulp slurry containing pulp fibers so that the thermoplastic resin content is 50 to 3000 ppm.

[0049] The method for producing cardboard base paper of this embodiment preferably includes a step of defibrating pulp fibers from laminated waste paper having a paper base material containing pulp fibers and a thermoplastic resin layer to obtain a pulp slurry containing pulp fibers and a thermoplastic resin, and a step of making a paper from the pulp slurry.Of these, the method for producing cardboard base paper of this embodiment more preferably includes a step of defibrating pulp fibers from laminated waste paper derived from liquid containers containing thermoplastic resin and pulp fibers to obtain a pulp slurry containing thermoplastic resin and pulp fibers, and a step of making a paper from the pulp slurry.

[0050] In the manufacturing method of this embodiment, it is preferable to disperse a predetermined amount of thermoplastic resin in the pulp slurry. For example, a pulp slurry containing pulp fibers and thermoplastic resin can be obtained by crushing thermoplastic resin-containing waste paper used as a recycled raw material and dispersing the crushed waste paper in the pulp slurry. In this case, the content of the thermoplastic resin can be controlled by appropriately controlling the type and content of the thermoplastic resin-containing waste paper used as a recycled raw material.

[0051] In the process of defibrating pulp fibers from laminated recycled paper having a paper base material containing pulp fibers and a thermoplastic resin layer to obtain a pulp slurry containing pulp fibers and a thermoplastic resin, the defibration temperature is preferably 10°C or higher, more preferably 15°C or higher, and even more preferably 20°C or higher. The defibration temperature is preferably 60°C or lower, and more preferably 55°C or lower. By setting the defibration temperature within the above range, it becomes easy to control the kink index of the pulp fibers within a desired range. This makes it possible to prevent pulp fibers from falling off during the manufacturing process or use, thereby more effectively reducing the generation of paper dust.

[0052] In the process of disintegrating pulp fibers from laminated waste paper having a paper base material containing pulp fibers and a thermoplastic resin layer to obtain a pulp slurry containing pulp fibers and a thermoplastic resin, the concentration of the laminated waste paper at the time of disintegration is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more. Furthermore, the concentration of the laminated waste paper at the time of disintegration is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. In the disintegration process, the higher the concentration of the laminated waste paper, the larger the foreign matter (e.g., pieces of thermoplastic resin) that separates from the pulp fibers, making these foreign matter easier to remove in the dust removal process. However, the lower the concentration of the laminated waste paper, the smaller the foreign matter pieces become, making them more difficult to remove in the dust removal process. Therefore, by maintaining the waste paper concentration of the laminated waste paper at the time of disintegration within the above range, it becomes easier to control the thermoplastic resin content in the corrugated board base paper within the desired range.

[0053] In the step of obtaining the pulp slurry, in addition to the pulp fibers and the thermoplastic resin, optional components may be mixed into the pulp slurry. As the optional components, the optional components described above can be appropriately used.

[0054] The process for obtaining the pulp slurry may include a step of bleaching the pulp fiber raw material. As the bleaching agent used in the bleaching step, known bleaching agents such as oxygen bleaching agents and chlorine bleaching agents can be used.

[0055] The process for obtaining the pulp slurry may include a process for beating the pulp fibers. In the beating process, for example, a double-disc refiner or the like may be used for beating treatment. During the beating treatment, for example, the laminated waste paper pulp fibers and the other waste paper pulp fibers may be beaten separately or may be mixed and then beaten.

[0056] In conventional technology, when a thermoplastic resin is incorporated into a cardboard base paper, it tends to become a foreign substance, which often reduces the quality of the cardboard base paper, such as its strength. Therefore, when a cardboard base paper is manufactured using recycled raw materials, the thermoplastic resin is separated and removed. In this embodiment, for example, by selectively using recycled raw materials in which the thermoplastic resin is not printed, the thermoplastic resin does not become a foreign substance and can be bound to part of the pulp fibers, thereby maintaining the quality of the cardboard base paper.

[0057] Examples of paper machines for making paper from the pulp slurry include Fourdrinier paper machines, gap former paper machines, cylinder paper machines, and short wire paper machines.

[0058] A papermaking machine that makes pulp slurry generally includes a wire part, a press part, a dryer part, a calender part, and a reel part. The wire part is a process in which the supplied slurry is dehydrated and formed into a sheet. In the wire part, the pulp slurry is supplied to a head box, where a single-layer or multi-layer sheet that will become the base paper for the corrugated board can be formed. In the head box, the component blend ratios of the pulp slurry that form each layer can be made different. This allows the properties of each layer that makes up the corrugated board base paper to be different.

[0059] In the manufacturing method of this embodiment, it is preferable to further include a step of crushing and washing the laminated waste paper containing pulp fibers and thermoplastic resin before the step of disintegrating the waste paper to obtain a pulp slurry. In the crushing and washing step, a crushing and washing machine is used, and a crushing step of crushing the laminated waste paper into small pieces using rotary blades and a washing step of washing the crushed laminated waste paper with wash water are carried out consecutively. For example, this can be carried out using a crushing and washing machine (Paper Container Recycling Machine PPRS, manufactured by A-Tech Co., Ltd.). As the rotary blades used in the crushing step, it is preferable to use uniaxial or biaxial rotary blades, and it is more preferable to use biaxial rotary blades. Furthermore, the crush size can be adjusted by changing the number of rotary blades (number of hooks), and increasing the number of hooks allows for smaller crushing. From the viewpoint of improving the efficiency of the disintegration process, the crush size is set to 20 cm. ２ ~400cm ２ It is preferable to adjust it so that

[0060] Examples of the washing water used in the washing step of the shredding and washing step include water, hot water, caustic soda water, ozone water, hydrogen peroxide water, sodium hypochlorite water, etc., and the water can be changed as appropriate. From the viewpoint of removing stains from laminated waste paper, it is preferable to use any of hot water, caustic soda water, ozone water, hydrogen peroxide water, and sodium hypochlorite water, and from the viewpoint of efficiently removing thermoplastic resin from laminated waste paper, it is preferable to use caustic soda water. The flow rate of the washing water can be adjusted to any amount, but it is preferable to use a flow rate of 0.1 m ３ / h or more, and 0.5 m ３ / h or more is more preferable, and 1.0 m ３ / h or more. ３ / h or less. After crushing and washing, the crushed pieces may be baled using a compressor.

[0061] In the manufacturing method of this embodiment, the inclusion of such a crushing and washing step makes it easy to control the kink index of the pulp fibers within a desired range, thereby preventing the pulp fibers from falling off during the manufacturing process and use, and as a result, more effectively reducing the generation of paper dust.

[0062] In the manufacturing method of this embodiment, it is preferable to further include a dust removal step after the step of disintegrating waste paper to obtain a pulp slurry. The dust removal step is a step of removing foreign matter and the like as removed components from the pulp slurry after the disintegration step. Here, foreign matter refers to components derived from layers other than the paper base layer of laminated waste paper, which have a particularly high specific gravity. Furthermore, the removed components refer to all components removed in the dust removal step, including components derived from layers other than the paper base layer of laminated waste paper as well as some laminated waste paper pulp derived from the paper base layer.

[0063] The dust removal step preferably includes a step of removing foreign matter from the pulp slurry after the defibration step by centrifugal separation and a step of removing foreign matter from the pulp slurry after the defibration step by screening.

[0064] The process of removing foreign matter by centrifugation uses a cleaner to remove large foreign matter, mainly those generated after the pulping process. The cleaner is cone-shaped and, using the principles of centrifugation, can remove foreign matter with a higher specific gravity than pulp fibers, such as sand and metal particles. Examples of cleaners used in the process of removing foreign matter by centrifugation include heavy foreign matter cleaners and low-concentration Rameau cleaners, which are effective in efficiently removing foreign matter with a higher specific gravity than pulp fibers. In the process of removing foreign matter by centrifugation, the concentration of the pulp slurry is preferably 0.5% by mass or more and 5.0% by mass or less, more preferably 0.8% by mass or more and 4.0% by mass or less, and even more preferably 1.0% by mass or more and 3.0% by mass or less, from the viewpoints of efficiently removing foreign matter and reducing dust in the resulting waste paper pulp.

[0065] The step of removing foreign matter by screening is carried out for the purpose of removing foreign matter after the step of removing foreign matter by centrifugation. As the screen used for screening, for example, a basket-type screen having holes or slits with a predetermined opening area can be used. Alternatively, a slit screen can be used. Either a coarse or fine screening screen can be used. In the step of removing foreign matter by screening, from the viewpoint of efficiently removing foreign matter, it is preferable to perform a fine screening process after the coarse screening process. As the coarse screening screen, a round hole screen or a slit screen is preferred, and a round hole screen is more preferred. The diameter of the round holes in the round hole screen is preferably 0.5 mm or more and 2.5 mm or less, more preferably 0.8 mm or more and 2.0 mm or less. The slit width of the slit screen is preferably 0.25 mm or more and 0.5 mm or less. From the viewpoint of efficiently removing foreign matter, the slit width of the fine screening screen is preferably 0.10 mm or more and 0.25 mm or less, more preferably 0.10 mm or more and 0.20 mm or less, and even more preferably 0.10 mm or more and 0.18 mm or less.

[0066] The solids concentration of the pulp slurry in the coarse screening treatment is preferably 1.0% by mass to 5.0% by mass, more preferably 1.5% by mass to 4.0% by mass, and even more preferably 2.0% by mass to 3.0% by mass, from the viewpoint of efficiently removing foreign matter. The solids concentration of the pulp slurry in the fine screening treatment is preferably 0.2% by mass to 5.0% by mass, more preferably 0.5% by mass to 3.5% by mass, and even more preferably 0.8% by mass to 3.0% by mass, from the viewpoint of efficiently removing foreign matter.

[0067] In the manufacturing method of this embodiment, if necessary, a deinking step of deinking the pulp slurry may be included after the dust removal step and before the washing step described below. The deinking step removes the ink contained in the printing layer from the pulp slurry, as well as coarse inorganic foreign matter. The deinking step may be performed using a flotator or the like.

[0068] When the deinking treatment is carried out using a flotator, the solids concentration of the pulp slurry is preferably 0.5% by mass or more and 2.0% by mass or less, and more preferably 0.5% by mass or more and 1.3% by mass or less.

[0069] In the deinking step, a deinking agent may be further added immediately before treatment with the flotator. The deinking agent used immediately before treatment with the flotator is preferably one with strong ink coagulation properties, and in the case of fatty acids, examples include DI-254 (oleic acid) and DI-268 manufactured by Kao Corporation, and K-4004-D manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. Examples of fatty acid derivative-based agents include DIY-23543 manufactured by Kao Corporation, and Paper Aid W and Daihope 1000 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. Examples of higher alcohol-based agents include DI-7020 manufactured by Kao Corporation. When a deinking agent is added in the deinking step, the amount of the deinking agent added is preferably 0.01 parts by mass or more and 0.5 parts by mass or less, more preferably 0.03 parts by mass or more and 0.3 parts by mass or less, per 100 parts by mass of the solids content of the pulp slurry.

[0070] In the production method of this embodiment, it is further preferable to include a washing step of washing the pulp slurry after the dust removal step. The washing step further removes foreign matter and the like from the pulp slurry. The washing step may be performed alternately and repeatedly as needed, with washing of the pulp slurry and dewatering of the pulp slurry.

[0071] Examples of equipment used in the washing step include washing equipment such as a DNT washer, a compact washer, a fall washer, a variosplit, an SP filter, a DP Cosmo, a gap washer, and a disc filter, with a disc filter being preferred. In washing the pulp slurry, the solids concentration of the pulp slurry is preferably 0.5% by mass or more and 5.0% by mass or less, more preferably 1.0% by mass or more and 3.0% by mass or less, from the viewpoint of efficiently removing foreign matter in the pulp slurry.

[0072] In the manufacturing method of this embodiment, a dewatering step may be included after the washing step, in which the pulp slurry is dewatered to obtain recycled paper pulp. The dewatering step improves the handleability of the resulting recycled paper pulp, making it easier to incorporate the recycled paper pulp into raw pulp when producing paper products using the recycled paper pulp. Examples of equipment used to dewater the pulp slurry in the dewatering step include a double nip thickener, a drum thickener, a disc thickener, and a valveless thickener, with a disc thickener being preferred.

[0073] The manufacturing method of this embodiment preferably further includes a drying step after the step of making paper from the pulp slurry. In the drying step, the pulp sheet obtained in the papermaking step is dried by heating. The drying step is preferably, for example, a step of blowing hot air toward the wet paper.

[0074] The drying temperature in the drying step is preferably 80°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher. The drying temperature is preferably 160°C or lower, and more preferably 140°C or lower. The papermaking speed in the drying step is preferably 400 m / min or higher, and more preferably 500 m / min or higher. The papermaking speed in the drying step is preferably 1200 m / min or lower. By providing such a drying step, the thermoplastic resin melts and is appropriately bound to a portion of the pulp fibers, thereby suppressing the shedding of paper powder.

[0075] The manufacturing method of this embodiment may further include a calendering step after the drying step. The calendering step is carried out in a calender part, in which the surface of the dried sheet is stretched while being pressed to smooth the surface of the sheet.

[0076] The manufacturing method of this embodiment may include a step of winding the corrugated cardboard base paper to form a roll (winding). In the end processing section of the winding, it is preferable to glue the end of the long corrugated cardboard base paper discharged from the winding section along the width direction to prevent the long corrugated cardboard base paper from unwinding.

[0077] (Corrugated cardboard sheet) The corrugated cardboard base paper of this embodiment is used for a corrugated cardboard sheet. The corrugated cardboard sheet includes a liner base paper and a corrugated core base paper, and the liner base paper is disposed on one or both sides of the core base paper. In this embodiment, the corrugated cardboard base paper can be used as both the liner base paper and the core base paper.

[0078] The corrugated cardboard sheet may be a single-faced cardboard sheet in which liner paper is placed on only one side of the corrugated cardboard core, or a double-faced cardboard sheet in which liner paper is placed on both sides of the corrugated cardboard core. Furthermore, the corrugated cardboard sheet may be a laminate of multiple layers of corrugated cardboard core and liner paper, such as a double-faced cardboard sheet (a cardboard sheet in which the corrugation crest of a single-faced cardboard sheet is attached to one side of a double-faced cardboard sheet) or a quadruple-faced cardboard sheet (a cardboard sheet in which the corrugation crest of a single-faced cardboard sheet is attached to one side of a double-faced cardboard sheet). Examples of thicknesses of the corrugated cardboard sheet include A-flute, B-flute, C-flute, E-flute, F-flute, G-flute, W-flute, two-ply AA-coated, and three-ply AAA-coated. The corrugated cardboard base paper of this embodiment can be used for cardboard sheets as well as thick paper (coated cardboard).

[0079] A known method for manufacturing a cardboard sheet can be applied to the manufacturing method of a cardboard sheet that can use the cardboard base paper of this embodiment, and for example, the cardboard sheet can be manufactured by performing a corrugator process in which core base paper and liner base paper are bonded together with an adhesive.

[0080] Examples of adhesives used to bond the liner paper to the core raw paper include synthetic resins such as starch, polyethylene resin, polypropylene resin, polyamide resin, polyester resin, ethylene / unsaturated carboxylic acid copolymer, styrene / butadiene copolymer, butadiene / acrylonitrile copolymer, styrene / butadiene / acrylonitrile copolymer, polyvinyl acetate resin, ethylene / vinyl acetate copolymer, polyacrylic acid ester copolymer, styrene / acrylic acid ester copolymer, etc. The adhesive may be applied to the flute top of the core raw paper or to the backing layer of the liner paper, and the core raw paper and the liner raw paper may be overlapped and bonded together by applying pressure and heat, or the adhesive may be formed as a film and placed between the core raw paper and the backing layer of the liner paper, and the core raw paper and the liner raw paper may be bonded together by applying pressure and heat.

[0081] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Furthermore, the operations in the examples and comparative examples were carried out under conditions of 23±1°C and a relative humidity of 50±2%, unless otherwise specified.

[0082] Example 1 [Production of Laminated Wastepaper Pulp] (Crushing and Washing Process) As laminated wastepaper, packaging material for aseptic containers (LDPE layer / printing layer / paper base layer / LDPE layer / aluminum foil / EMMA adhesive resin layer / LLDPE layer, pulp composition of the paper base layer: N:L=10:90, basis weight: 283 g / m) was used. ２ ) was used, and a crushing and washing machine (manufactured by A-Tech, paper container recycling device PPRS, number of hooks: 6, washing water: caustic soda water, flow rate 1.5 m ３ / h) at 20 cm ２ More than 400cm ２ The following size (average size: 67cm ２) and washed. (Disintegration Step) 100 kg of the shredded and washed laminated waste paper and water were charged into a high-concentration pulper (AHP Helidisc Pulper, manufactured by Aikawa Iron Works Co., Ltd.), and disintegration treatment was carried out under conditions of a laminated waste paper concentration of 20% by mass, a treatment time of 30 minutes, a treatment temperature of 50°C, and a pH of 6, to obtain a laminated waste paper pulp slurry. (Dust Removal Step) The pulp slurry after the disintegration step was adjusted to a solids content of 2.5% by mass, and then treated with a heavy foreign matter cleaner (FC100, manufactured by Aikawa Iron Works Co., Ltd.), and further treated with a coarse screening screen (MaxFlow-1, Model 1000, round holes 1.2 mm, manufactured by Aikawa Iron Works Co., Ltd.). The pulp slurry after the coarse screening process was adjusted to a solids content of 1.0% by mass and treated with a fine screening screen (MaxFlow-1, Model 1000, slit 0.15 mm, manufactured by Aikawa Iron Works Co., Ltd.). The pulp slurry after the fine screening process was treated with a low-concentration Rameau Cleaner (Bicone 150, manufactured by Aikawa Iron Works Co., Ltd.). (Washing process, dewatering process) The slurry after the dust removal process was washed using a disc filter (DF520, manufactured by IHI Voith Paper Technology Co., Ltd.) and then dewatered using a disc thickener (EFK1310, manufactured by IHI Voith Paper Technology Co., Ltd.) to obtain laminated recycled paper pulp.

[0083] [Preparation of base paper for corrugated cardboard] (Preparation of surface layer paper stock) Waste corrugated cardboard paper was used as raw material pulp and was disintegrated under conditions of a waste paper concentration of 4% by mass, a treatment time of 15 minutes, a treatment temperature of 50°C, and a pH of 6, to obtain a waste corrugated cardboard pulp slurry. To 100 parts by mass of pulp (solid content) in this pulp slurry, 0.35 parts by mass of a sizing agent (product name: Sizepine N-817, manufactured by Arakawa Chemical Industries, Ltd.) and 2.5 parts by mass of aluminum sulfate were added to prepare a surface layer (first layer) paper stock (pulp slurry). (Preparation of Middle Layer Stock) A pulp slurry was obtained by disintegrating recycled corrugated cardboard pulp as the raw material pulp under conditions of a waste paper concentration of 4% by mass, a treatment time of 15 minutes, a treatment temperature of 50°C, and a pH of 6. This slurry was then blended with a laminated recycled cardboard pulp slurry obtained by adding water to the laminated recycled cardboard pulp obtained above, with a laminated recycled cardboard pulp concentration of 4% by mass, in a mass ratio of 95:5. A middle layer (second and third layer) stock (pulp slurry) was prepared by adding 1.5 parts by mass of aluminum sulfate to 100 parts by mass of pulp (solid content) in this pulp slurry. (Preparation of Back Layer Stock) A pulp slurry was obtained by disintegrating recycled corrugated cardboard pulp as the raw material pulp under conditions of a waste paper concentration of 4% by mass, a treatment time of 15 minutes, a treatment temperature of 50°C, and a pH of 6. A back layer (fourth layer) paper material (pulp slurry) was prepared by adding 1.0 part by mass of aluminum sulfate to 100 parts by mass of pulp (solid content) in this pulp slurry.

[0084] (Production of base paper for corrugated cardboard) Using the paper materials for each layer prepared above, a surface layer (first layer) was made to have a basis weight of 57 g / m ２ , the basis weight of the middle layer (second layer) is 45 g / m ２ , the basis weight of the middle layer (third layer) is 140 g / m ２ , the basis weight of the back layer (fourth layer) is 41 g / m ２ The four layers were combined and made into paper using a short wire paper machine, with a basis weight of 283 g / m ２ The amount of laminated recycled paper pulp in the middle layer paper material was {100 / (100+1.5)}×{5 / (95+5)}×100=4.9% by mass, and the amount of laminated recycled paper pulp in the obtained cardboard base paper was {(45 g / m ２ +140g / m ２)×4.9% by mass} / 283g / m ２ In the papermaking process, the paper was dried in a multi-cylinder dryer at a speed of 750 m / min and a temperature of 125° C., and then wound up to a total length of 5000 m.

[0085] Example 2 Base paper for corrugated cardboard was obtained in the same manner as in Example 1, except that in the (disintegration step) of [Manufacturing laminated recycled paper pulp], the disintegration treatment was carried out under the condition that the laminated recycled paper concentration was 18% by mass.

[0086] Example 3 Base paper for corrugated cardboard was obtained in the same manner as in Example 1, except that in the (disintegration step) of [Manufacturing laminated recycled paper pulp], the disintegration treatment was carried out under the condition of a laminated recycled paper concentration of 16% by mass.

[0087] Example 4 Cardboard base paper was obtained in the same manner as in Example 1, except that in the (defibration step) of [Manufacturing laminated recycled paper pulp], defibration treatment was carried out at a treatment temperature of 35°C, and in [Preparation of cardboard base paper], the recycled cardboard was also defibrated at a treatment temperature of 35°C.

[0088] Example 5 Cardboard base paper was obtained in the same manner as in Example 1, except that in the (defibration step) of [Manufacturing laminated recycled paper pulp], defibration treatment was carried out at a treatment temperature of 20°C, and in [Preparation of cardboard base paper], the recycled cardboard was also defibrated at a treatment temperature of 20°C.

[0089] Example 6 Base paper for corrugated cardboard was obtained in the same manner as in Example 2, except that the crushing and washing step in [Production of laminated recycled paper pulp] was not carried out.

[0090] Example 7 A corrugated cardboard base paper was obtained in the same manner as in Example 1, except that in the (preparation of the middle layer paper material) of [Preparation of Corrugated Cardboard Base Paper], a pulp slurry in which a corrugated cardboard waste paper pulp slurry and a laminated waste paper pulp slurry were blended in a mass ratio of 85:15 was used. The blending ratio of laminated waste paper pulp in the middle layer paper material was {100 / (100+1.5)}×{15 / (85+15)}×100=14.8 mass%, and the blending amount of laminated waste paper pulp in the obtained corrugated cardboard base paper was {(45 g / m ２ +140g / m ２)×14.8% by mass} / 283g / m ２ = 9.7% by mass.

[0091] <Example 8> Aseptic container packaging material (LDPE layer / printing layer / paper base layer / LDPE layer / aluminum foil / EMMA adhesive resin layer / LLDPE layer, pulp blend of paper base layer N:L=50:50, basis weight 283 g / m) was used as laminated recycled paper. ２ A base paper for corrugated cardboard was obtained in the same manner as in Example 7, except that the above-mentioned cellulose acetate sheet was used instead of the above-mentioned cellulose acetate sheet.

[0092] <Example 9> Aseptic container packaging material (LDPE layer / printing layer / paper base layer / LDPE layer / aluminum foil / EMMA adhesive resin layer / LLDPE layer, pulp composition of the paper base layer N:L=100:0, basis weight 283 g / m) was used as laminated recycled paper. ２ A base paper for corrugated cardboard was obtained in the same manner as in Example 7, except that the above-mentioned cellulose acetate sheet was used instead of the above-mentioned cellulose acetate sheet.

[0093] Example 10 In the production of base paper for corrugated cardboard, the basis weight of the surface layer (first layer) was 53 g / m ２ , the basis weight of the middle layer (second layer) is 67 g / m ２ , the basis weight of the middle layer (third layer) is 92 g / m ２ , the basis weight of the back layer (fourth layer) is 71 g / m ２ A base paper for corrugated cardboard was obtained in the same manner as in Example 1, except that the temperature was set to 100°C.

[0094] Example 11 In the manufacture of base paper for corrugated cardboard, the basis weight of the surface layer (first layer) was 24 g / m ２ , the basis weight of the middle layer (second layer) is 20 g / m ２ , the basis weight of the middle layer (third layer) is 59 g / m ２ , the basis weight of the back layer (fourth layer) is 17 g / m ２ The four layers were combined to form a paper with a basis weight of 120 g / m ２ A base paper for corrugated cardboard was obtained in the same manner as in Example 1, except that:

[0095] Example 12 In the manufacture of cardboard base paper, the basis weight of the surface layer (first layer) was 22 g / m ２ , the basis weight of the middle layer (second layer) is 29 g / m ２ , the basis weight of the middle layer (third layer) is 39 g / m ２ , the basis weight of the back layer (fourth layer) is 30 g / m ２The four layers were combined to form a paper with a basis weight of 120 g / m ２ A base paper for corrugated cardboard was obtained in the same manner as in Example 1, except that:

[0096] Example 13: In the disintegration step of [Manufacturing laminated recycled paper pulp], disintegration was carried out under conditions of a laminated recycled paper concentration of 8% by mass, and in the preparation of the middle layer paper material of [Preparation of corrugated board base paper], a pulp slurry prepared by blending a corrugated board recycled paper pulp slurry and a laminated recycled paper pulp slurry at a mass ratio of 70:30 was used. The blending ratio of laminated recycled paper pulp in the middle layer paper material was {100 / (100+1.5)}×{30 / (70+30)}×100=29.6% by mass, and the blending amount of laminated recycled paper pulp in the obtained corrugated board base paper was {(45 g / m ２ +140g / m ２ )×29.6% by mass} / 283g / m ２ = 19.3 mass%.

[0097] Comparative Example 1 In the manufacture of cardboard base paper (preparation of middle layer paper material), 100% recycled cardboard pulp slurry was used, and 1.5 parts by mass of aluminum sulfate and 0.2 parts by mass of a dry strength agent (trade name: Polystron 117, manufactured by Arakawa Chemical Industries, Ltd.) were added per 100 parts by mass of pulp (solid content) in the pulp slurry, but cardboard base paper was obtained in the same manner as in Example 1. The cardboard base paper of Comparative Example 1 had a blending rate of laminated recycled paper pulp of 0%.

[0098] Comparative Example 2 Base paper for corrugated cardboard was obtained in the same manner as in Example 13, except that in the (disintegration step) of [Manufacturing laminated recycled paper pulp], the disintegration treatment was carried out under the condition that the laminated recycled paper concentration was 3% by mass.

[0099] Comparative Example 3 Cardboard base paper was obtained in the same manner as in Example 1, except that in the (defibration step) of [Manufacturing laminated recycled paper pulp], defibration treatment was carried out at a treatment temperature of 65°C, and in [Preparation of cardboard base paper], the recycled cardboard was also defibrated at a treatment temperature of 65°C.

[0100] <Measurement and Evaluation Methods> (Basis Weight) The corrugated cardboard base paper obtained in the Examples and Comparative Examples was conditioned for 24 hours in a humidity-controlled environment specified in JIS P 8111:1998. The basis weight of the conditioned corrugated cardboard base paper was measured in accordance with JIS P 8124:2011. When measuring the basis weight per layer of the corrugated cardboard base paper, the cardboard base paper was pre-treated by immersing it in hot water at 40°C for 6 hours, carefully peeling each layer by hand, and drying it in a dryer set at 105°C for 30 minutes. Thereafter, after 24 hours of humidity control in a humidity-controlled environment specified in JIS P 8111:1998, the basis weight per layer of the conditioned corrugated cardboard base paper was measured in accordance with JIS P 8124:2011.

[0101] (Thickness) The cardboard base papers obtained in the examples and comparative examples were conditioned for 24 hours in a humidity-controlled environment specified in JIS P 8111: 1998. The thickness of the cardboard base paper after humidity conditioning was measured in accordance with JIS P 8118: 2014.

[0102] (Density) From the measured basis weight and thickness, the basis weight (g / m ２ The density was calculated using the formula: 1 / thickness (μm).

[0103] (Tensile Modulus of Elasticity) The corrugated cardboard base paper obtained in the Examples and Comparative Examples was conditioned for 24 hours in a humidity-controlled environment specified in JIS P 8111:1998. The tensile modulus of the corrugated cardboard base paper after humidity conditioning was measured in accordance with JIS P 8113:2006. The tensile modulus was measured in the machine direction (papermaking direction, MD direction) and the cross direction (direction perpendicular to the papermaking direction, CD direction). The test was performed using a horizontal tensile tester (manufactured by Lorentzen & Wattre, CODE SE-064), and the geometric mean value of the obtained machine direction tensile modulus and cross direction tensile modulus was calculated.

[0104] (Thermoplastic Resin Amount) The thermoplastic resin content was measured by an extraction process to separate the thermoplastic resin contained in the cardboard base paper and an analysis process to quantify the thermoplastic resin using pyrolysis GC / MS. [Extraction Process] 3 to 5 g of dry weight of the cardboard base paper obtained in the Examples and Comparative Examples was sampled and placed in an extraction cell (20 ml container). Next, the thermoplastic resin from the cardboard base paper was extracted using a high-speed solvent extractor (machine: Buchi, E-916). The extraction conditions were an extraction temperature of 180°C, an extraction pressure of 150 bar, and an extraction solvent of xylene (special grade, Wako Pure Chemical Industries). A 100 ml vial (Maruem, Mighty Vial No. 8) was placed in the extractor, and two extraction cycles of extract were collected. After extraction, the solvent was removed using a rotary evaporator (water bath 60°C), and the sample was dried at 105°C for 12 hours to fully dry, thereby obtaining the thermoplastic resin in the cardboard base paper. [Analysis Process] An appropriate amount of xylene was added to the dried thermoplastic resin in the vial extracted above to a concentration of 2-5 mg / ml, and the mixture was dissolved at 130°C for 2 hours with stirring. Next, the xylene solution of the extracted extract, whose tare weight had been measured, was placed in an eco-cup so that the extract amount was 50-200 μg. The solvent was evaporated at 105°C for 2 hours, and the analytical sample amount of the extract was measured. The amount of thermoplastic resin in the obtained extract was quantified using a pyrolysis GC / MS (Shimadzu Corporation GC / MS-QP2010). The amount of thermoplastic resin in the extracted material was calculated from the amount of thermoplastic resin. The pyrolysis GC / MS measurement conditions were as follows: Polyethylene standard: (Tosoh 07C03C, LDPE) Column: HP-5MS (length: 30 m, inner diameter: 0.250 mm, thickness: 0.25 μm) Analysis conditions: pyrolysis temperature = 600°C, injection port temperature = 320°C, split ratio = 1:60, interface temperature = 280°C, GC column temperature conditions = 40°C (hold for 3 minutes) → 10°C / min → 325°C (hold for 15 minutes), ion source temperature = 200°C Detection: m / z 29-600 (quantitation was calculated from the mass chromatogram area value of 1,19-eicosadiene (C20) at m / z 82)

[0105] (Kink Index) The corrugated cardboard base paper obtained in the Examples and Comparative Examples was cut into 4 cm square pieces, immersed in ion-exchanged water, and adjusted to a corrugated cardboard base paper content of 2% by mass. The pieces were then soaked for 24 hours. After 24 hours of soaking, the pulp was defibrated into fibers using a standard defibrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) in accordance with JIS P 8220-1:2012 until no undefibrated fibers remained. The defibrated slurry (pulp fiber dispersion) was adjusted to a solids concentration of 0.1% by mass, and the pulp solids concentration was calculated in accordance with JIS P 8225:2003. The defibrated slurry was adjusted to a solids concentration of 0.004% by mass, and 500 g of slurry was obtained. The amount of the sample taken was recorded. The dry weight of the sample was calculated using the solids concentration and the amount of the slurry taken. The resulting slurry was used to measure the "kink index" using a fiber length measuring machine (model Valmet FS-5 with UHD base unit, manufactured by Valmet Co., Ltd.).

[0106] The kink index (1 / m) is Kibblewhite's kink index calculated by the following formula (1). The kink index was calculated by weighting the number of kinks in each angle range according to the increase in angle and dividing the result by the sum of the fiber lengths. The measurement was performed in accordance with ISO 16065-2:2014. The instrument was also capable of detecting and measuring each fiber individually using an attached camera, and images were taken within a measurement cell with a depth of field of 0.5 mm. Fibers with fiber lengths of 0.01 mm or more and 10.00 mm or less were photographed using the instrument.

[0107]

[0108] The symbols in formula (1) represent the following: １ n = number of kinks (bends) of 21° or more and 45° or less in the measurement sample ２ n = number of kinks (bends) between 46° and 90° in the measurement sample ３ L = Number of kinks (bending angles) of 91° or more and 180° or less in the measurement sample ｃ = Sum of fiber lengths of measurement samples (m)

[0109] (Paper Dust) The corrugated cardboard base paper obtained in the Examples and Comparative Examples was conditioned for 24 hours in a humidity-controlled environment specified in JIS P 8111:1998. After conditioning, the corrugated cardboard base paper was cut into 10 cm x 10 cm pieces, and each layer was carefully peeled off by hand to separate into four pieces. An adhesive film (PET75-H120(10) manufactured by Nichiei Shinka Co., Ltd.) was attached to a 7 cm diameter, 10 kg weight metal roll on the release surface of each divided corrugated cardboard base paper. The roll was rolled twice at a speed of 60 bpm over the release surface, causing paper dust to adhere to the adhesive film. The adhesive film was scanned at a size of 5 cm x 5 cm and an image resolution of 400 dpi. The entire image was binarized into white and black areas, and the white area was considered to be paper dust. The white area ratio (%) was calculated. The remaining release surfaces were evaluated in the same manner. The average white area ratio of the six surfaces was calculated, and the paper dust was evaluated according to the following criteria. [Evaluation criteria] A: White area ratio is 1.00% or less B: White area ratio is more than 1.00% and 2.50% or less C: White area ratio is more than 2.50% and 3.50% or less D: White area ratio is more than 3.50%

[0110] (Operability) In the examples and comparative examples, the frequency of paper breaks was counted when a total length of 5000 m of base paper for corrugated cardboard was wound up, and the operation was evaluated according to the following criteria. [Evaluation criteria] A: No paper breaks occurred. B: Paper breaks occurred once. C: Paper breaks occurred two or more times.

[0111]

[0112]

[0113] In the examples, the generation of paper dust was suppressed and the operability was good.

Claims

1. A base paper for corrugated cardboard, comprising pulp fiber and a thermoplastic resin, wherein the content of the thermoplastic resin is 50 to 3000 ppm, and the kink index of the pulp fiber is 2400 (1 / m) or more.

2. The corrugated board base paper according to claim 1, wherein the geometric mean of the tensile modulus in the machine direction and the tensile modulus in the cross direction is 1.2 GPa or more.

3. Basis weight: 80 g / m ２ More than 400g / m ２ The cardboard base paper according to claim 1, wherein:

4. The cardboard base paper according to claim 1, which has two or more paper layers.

5. The basis weight of each paper layer is 200 g / m ２ The cardboard base paper according to claim 4, wherein:

6. The cardboard base paper according to claim 1, wherein the thermoplastic resin is a polyolefin resin.

7. The cardboard base paper according to claim 1, which contains pulp fibers and a thermoplastic resin derived from laminated recycled paper.

8. A corrugated board sheet comprising the corrugated board base paper according to any one of claims 1 to 7.

9. A method for producing base paper for corrugated cardboard, comprising pulp fiber and a thermoplastic resin, wherein the content of the thermoplastic resin is 50 to 3000 ppm, and the kink index of the pulp fiber is 2400 (1 / m) or more.

10. A method for manufacturing base paper for corrugated cardboard according to claim 9, comprising the steps of: defibrating pulp fibers from laminated recycled paper having a paper base material containing pulp fibers and a thermoplastic resin layer to obtain a pulp slurry containing pulp fibers and a thermoplastic resin; and making paper from the pulp slurry.

11. The method for producing cardboard base paper according to claim 10, wherein the pulp fiber disintegration temperature in the step of obtaining the pulp slurry is 10 to 60°C.

12. The method for manufacturing base paper for corrugated cardboard according to claim 10, further comprising a step of crushing and washing the laminated waste paper before the step of making paper from the pulp slurry.

13. The method for manufacturing cardboard base paper according to claim 10, further comprising a drying step after the step of making paper from the pulp slurry.

14. A method for producing a corrugated cardboard sheet, comprising a step of subjecting the cardboard base paper according to any one of claims 1 to 7 to corrugation.

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