A method for preparing a high-strength containerboard, containerboard and use

Abstract

This invention relates to the field of papermaking technology, specifically to a method for preparing high-strength linerboard, the linerboard itself, and its applications. The method includes the following steps: crushing waste cardboard boxes into coarse pulp, passing it through a high-consistency desander, a coarse screen, and a low-consistency desander to remove impurities, followed by enzymatic hydrolysis with a compound desander enzyme. The pulp is then separated into short fibers, medium fibers, and long fibers by a grading screen, and these fibers are then fed into a paper feeder for the preparation of high-strength linerboard. The compound desander enzyme is composed of modified laccase, xylanase, and pectinase in a mass ratio of 3-5:2-4:1-2. After treatment with the compound desander enzyme, the coarse pulp of this invention uses long fibers, medium fibers, and short fibers as the core layer, bottom layer, and top layer pulp, respectively. The resulting linerboard exhibits a ring crush strength > 8.5 N·m / g and a bursting index > 3.70 kPa·m. 2 / g, fiber tailings rate <1%, which improves the strength of the linerboard while reducing the fiber tailings rate and lowering production costs.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a method for preparing high-strength linerboard, the linerboard itself, and its applications. Background Technology

[0002] As a core raw material in the packaging industry, linerboard's ring crush strength and bursting strength are key indicators for measuring packaging performance. Currently, linerboard production heavily relies on recycled waste pulp to reduce raw material costs and resource consumption. However, after multiple recycling processes, recycled waste paper suffers from problems such as shortened fiber length, thinned cell walls, uneven lignin and hemicellulose residues, and reduced fiber surface active groups, resulting in weak inter-fiber bonding and poor interweaving properties.

[0003] To improve paper strength, existing technologies typically employ two approaches: one is to add expensive dry strength agents (such as cationic polyacrylamide or modified starch) or incorporate high-quality virgin wood pulp. While this can improve strength, it significantly increases production costs and weakens the product's market competitiveness. The other approach involves traditional mechanical refining and chemical cooking processes for fiber modification. However, these processes are complex, energy-intensive, prone to excessive damage to the fiber's main strength, and have poor adaptability to different qualities of waste paper pulp, making it impossible to balance cost control with improved paper performance.

[0004] Chinese invention patent application CN105780564A discloses a process for producing high-strength linerboard from waste cardboard boxes. The process involves breaking down waste cardboard boxes into pulp in a pulper, pumping the pulp through a filter enzyme treatment, then passing it through a high-consistency separator, a coarse screen, and a low-consistency separator to remove impurities. The pulp is then separated into short-fiber, medium-fiber, and long-fiber grades through a grading screen. The short-fiber pulp is concentrated, and after adding bleaching water, it is fed into the paper machine. The medium-fiber pulp is concentrated using a multi-disc concentrate, the filter enzyme is inactivated, and after adding bleaching water, it is fed into the paper machine. The long-fiber pulp is finely screened, concentrated using a multi-disc concentrate, the filter enzyme is inactivated, and after adding bleaching water, it is fed into the paper machine. Using 100% waste cardboard boxes as raw material, the high-strength linerboard produced has a burst strength ≥3.0 kPa•m. 2 / g, flexural strength ≥60 cycles. However, the bursting strength of the above-mentioned patent needs further improvement.

[0005] Chinese invention patent application CN109811585A discloses a method for improving the strength of linerboard. The method involves adding γ-valerol to fully soaked and dispersed waste paper pulp, washing the treated pulp with hot water, and then forming paper. The amount of γ-valerol is 0.5-1 g / g oven-dry pulp, and the treatment conditions are: liquor ratio 1:8-12, temperature 60-100℃, and treatment time 1-3 hours. Using γ-valerol to treat waste paper pulp fibers can effectively enhance the bonding force between fibers, ultimately improving the strength of the paper produced from waste paper pulp. However, the strength of the linerboard obtained by this patent still needs further improvement.

[0006] Furthermore, during the waste paper pulp dismantling process, a large number of undismantled fiber clumps and small paper pieces with a size of <10 mm are difficult to fully dismantle under conventional dismantling methods and are often discharged as tailings, resulting in a waste of fiber resources and affecting the overall uniformity of the pulp. Therefore, developing a low-cost, high-efficiency, and highly adaptable waste paper pulp modification method to achieve efficient fiber dismantling and simultaneous improvement of strength properties has become an urgent technical challenge to be solved in the corrugated board production industry. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for preparing high-strength linerboard, the linerboard itself, and its applications. After treatment with a compound desiccant, the coarse pulp is separated into long, medium, and short fibers, which are used as the core, bottom, and top layers of pulp, respectively. The resulting linerboard exhibits a ring crush strength > 8.5 N·m / g and a bursting index > 3.70 kPa·m. 2 / g, fiber tailings rate <1%. This method improves the strength of linerboard while reducing the fiber tailings rate and lowering production costs.

[0008] This invention is achieved through the following technical solution: The first aspect of this invention relates to a method for preparing high-strength linerboard, comprising the following steps: crushing waste cardboard boxes into coarse pulp, passing it through a high-consistency desander, a coarse screen, and a low-consistency desander to remove impurities, followed by enzymatic hydrolysis with a compound desander enzyme, and then separating the pulp into short fibers, medium fibers, and long fibers through a grading screen. These fibers are then fed into a paper feeder for the preparation of high-strength linerboard. The compound disintegrant is composed of modified laccase, xylanase, and pectinase in a mass ratio of 3-5:2-4:1-2.

[0009] In some embodiments of the present invention, the concentration of the coarse slurry is 8%-12%.

[0010] In some embodiments of the present invention, the impurity removal process of entering the high-consistency slag remover, coarse screen, and low-consistency slag remover is as follows: the slurry treated with compound decomposition enzyme is diluted with clean water to a concentration of 4-5%, enters the high-consistency slag remover, and removes stones and iron nails by centrifugal force and gravity. After being diluted with clean water to a concentration of 3%, it enters the coarse screen, where slurry blocks and plastic fragments are discharged. Then, the slurry is diluted with clean water to a concentration of 2%, enters the low-consistency slag remover, and removes mud and sand from the slurry by gravity and centrifugal force.

[0011] In some embodiments of the present invention, the process of treating the pulp with the composite disintegrant is as follows: the pulp temperature is adjusted to 45-60℃ and the pH value to 6.5-8.0, 0.15%-0.35% of the weight of oven-dried waste paper is added to the composite disintegrant, and enzymatic hydrolysis is performed for 25-45 minutes to obtain the disintegrant pulp.

[0012] In some embodiments of the present invention, the average length of the short fibers is less than 0.5 mm, the average length of the medium fibers is between 0.5 and 1 mm, and the average length of the long fibers is greater than 1 mm.

[0013] In some embodiments of the present invention, the processing specifically involves: concentrating, pressing, and dispersing short fiber pulp using a multi-disc press to obtain surface pulp; concentrating, pressing, and dispersing long fiber pulp using a multi-disc press to obtain core pulp; and concentrating, pressing, and dispersing medium fiber pulp using a multi-disc press to obtain bottom pulp.

[0014] In some embodiments of the present invention, the dispersion treatment is to dilute the pulp with turbid water after multi-disc concentration and pressing, wherein the concentrations of the top layer pulp, bottom layer pulp and core layer pulp are independently selected from 3.5% to 4.5%.

[0015] In some embodiments of the present invention, the source of the turbid white water is: the slurry obtained after multi-disc concentration is recycled into the slurry mixing tank for slurry mixing, and the white water obtained is classified according to concentration as follows: turbid white water, SS≥300mg / L; clear white water, 60mg / L<SS<300mg / L; ultra-clear white water, 30mg / L≤SS≤60mg / L; and ultra-filtered water, 10mg / L<SS<30mg / L.

[0016] A second aspect of the present invention relates to linerboard prepared using the above-described preparation method.

[0017] In some embodiments of the present invention, the ring crush strength of the linerboard is >8.5 N·m / g, and the bursting strength index is >3.70 kPa·m. 2 / g, fiber tailings rate <1%.

[0018] A third aspect of the present invention relates to the application of the linerboard prepared by the above-described preparation method in the preparation of high-strength cartons.

[0019] The beneficial effects of this invention are as follows: After the crude pulp of this invention is treated with a composite disintegrant consisting of modified laccase, xylanase, and pectinase in a mass ratio of 3-5:2-4:1-2, long fibers, medium fibers, and short fibers are separated and used as the core layer, bottom layer, and top layer pulp, respectively. The resulting linerboard has a ring crush strength > 8.5 N·m / g and a bursting index > 3.70 kPa·m. 2 / g, fiber tailings rate <1%. This method improves the strength of linerboard while reducing the fiber tailings rate and lowering production costs. Detailed Implementation

[0020] To clarify the purpose, technical solution, and advantages of this invention, the following detailed description is provided in conjunction with specific embodiments. To facilitate understanding of the technical means, creative features, and achieved objectives and effects of this invention, the following detailed description further clarifies the invention in conjunction with specific embodiments. However, these embodiments are merely preferred embodiments and not exhaustive. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the scope of protection of this invention. In the following embodiments, unless otherwise specified, the operating methods used are conventional operating methods, the equipment used is conventional equipment, and the equipment materials used in each embodiment are the same. This invention does not limit the source of the raw materials used. Unless otherwise specified, the raw materials used in this invention are all commercially available products in this technical field, with a purity of 98% or higher.

[0021] Example 1 A method for preparing high-strength corrugated board includes the following steps: (1) Shred waste cardboard boxes into coarse pulp with a concentration of 10%; (2) The slurry is diluted to 4.5% with clean water and enters the high-consistency slag remover; then diluted to 3% and enters the coarse screen; then diluted to 2% and enters the low-consistency slag remover to remove impurities; (3) Adjust the pulp temperature to 52℃ and pH value to 7.2, add 0.25% of the weight of oven-dried waste paper of compound disintegrant (modified laccase: xylanase: pectinase = 4:3:1.5, mass ratio), and enzymatically hydrolyze for 35 min; (4) Grading by grading sieve: short fibers < 0.5 mm, medium fibers 0.5-1 mm, long fibers > 1 mm; (5) Short fibers are concentrated, pressed, and diluted with turbid water to 4.0% to obtain surface pulp; medium fibers are concentrated, pressed, and diluted with turbid water to 4.0% to obtain bottom pulp; long fibers are concentrated, pressed, and diluted with turbid water to 4.0% to obtain core pulp. (6) The surface layer, bottom layer and core layer pulp are fed into the paper feeder to form high-strength boxboard.

[0022] Example 2 The difference from Example 1 is that the amount of compound dehydrogenase used is 0.18%, and the rest is the same as in Example 1.

[0023] Example 3 The difference from Example 1 is that the mass ratio of modified laccase, xylanase, and pectinase is 3:2:1, and the amount of compound disintegrant is 0.30%, while the rest is the same as in Example 1.

[0024] Comparative Example 1 The only difference from Example 1 is that no compound decomposition enzyme is added for enzymatic hydrolysis; instead, mechanical decomposition, slag removal, grading, and papermaking are performed.

[0025] Comparative Example 2 Only 0.25% modified laccase was added; xylanase and pectinase were not added. The rest was the same as in Example 1.

[0026] Comparative Example 3 Only 0.25% xylanase was added, without adding modified laccase or pectinase, and the rest was the same as in Example 1.

[0027] Comparative Example 4 The compound disintegrant does not contain pectinase and consists only of modified laccase and xylanase, wherein the ratio of modified laccase to xylanase is 4:3 (excluding pectinase), and the total amount used is 0.25%, and the rest is the same as in Example 1.

[0028] Comparative Example 5 The modified laccase in Example 1 was replaced with an equal amount of cellulase; that is, the complex enzyme in Comparative Example 6 was replaced with a mixture of cellulase, xylanase, and pectinase in a mass ratio of 4:3:1.5. Everything else was the same as in Example 1.

[0029] Comparative Example 6 The xylanase in Example 1 was replaced with an equal amount of hemicellulase, i.e., the complex enzyme in Comparative Example 7 consisted of modified laccase, hemicellulase, and pectinase in a mass ratio of 4:3:1.5. The rest was the same as in Example 1.

[0030] Comparative Example 7 The enzymatic hydrolysis is the same as in Example 1, but without grading. Long / medium / short fibers are mixed, directly concentrated, diluted to 4.0%, and then printed on the wire without separating the core / bottom / top layer.

[0031] Performance testing methods 1) Ring crush strength (N) m / g): According to GB / T 2679.8, transverse samples were tested using a ring crusher, with 10 samples per group, and the average value was taken.

[0032] 2) Bursting index (kPa) m² / g): The index was determined and calculated using a bursting strength tester according to GB / T 465.1. Ten samples were collected in each group, and the average value was taken.

[0033] 3) Fiber tailings rate (%): After enzymatic hydrolysis and screening, collect unbroken fiber clumps / paper pieces >10 mm, dry and weigh them. Tailings rate = dry weight of tailings / dry weight of raw materials × 100%.

[0034] The test results are shown in Table 1.

[0035] Table 1: Comparison Results of Corrugated Board Properties

[0036] As shown in Table 1, the ring crush strength of Examples 1-3 of the present invention is all >8.5 N. m / g and bursting index are both >3.70kPa m 2 / g and fiber tailings rate are both <1%, achieving the invention objective. Comparative Example 1 (no enzyme) has the lowest strength and the highest tailings rate; single enzyme (Comparative Examples 2 and 3) or pectinase-deficient (Comparative Example 4) are significantly less effective than the compound enzyme; when one enzyme in the compound disintegrant is replaced with another type of enzyme (Comparative Examples 5 and 6), the overall performance of the linerboard is reduced compared to the examples; the strength of ungraded (Comparative Example 7) is significantly reduced, proving that graded and layered papermaking is crucial for improving strength.

[0037] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing high-strength corrugated board, characterized in that, Includes the following steps: Waste cardboard boxes are shredded into coarse pulp, which then passes through a high-consistency desander, a coarse screen, and a low-consistency desander to remove impurities. After enzymatic hydrolysis by a compound desander enzyme, the pulp is separated into short fibers, medium fibers, and long fibers by a grading screen. These fibers are then fed into separate paper feeders for the production of high-strength linerboard. The compound disintegrant is composed of modified laccase, xylanase, and pectinase in a mass ratio of 3-5:2-4:1-2.

2. The preparation method according to claim 1, characterized in that, The concentration of the coarse slurry is 8%-12%.

3. The preparation method according to claim 1, characterized in that, The impurity removal process, including the high-consistency slag remover, coarse screen, and low-consistency slag remover, involves the following steps: After treatment with compound decomposition enzyme, the slurry is diluted with clean water to a concentration of 4%-5% and then enters the high-consistency slag remover. Stones and iron nails are removed by centrifugal force and gravity. After further dilution with clean water to a concentration of 3%, the slurry enters the coarse screen, where slurry lumps and plastic fragments are removed. Finally, the slurry is diluted with clean water to a concentration of 2% and then enters the low-consistency slag remover, where mud and sand are removed by gravity and centrifugal force.

4. The preparation method according to claim 1, characterized in that, The process of treating the pulp with the compound disintegrant is as follows: the pulp temperature is adjusted to 45-60℃ and the pH value to 6.5-8.0, 0.15%-0.35% of the weight of the oven-dried waste paper is added to the compound disintegrant, and the pulp is hydrolyzed for 25-45 minutes to obtain the disintegrant pulp.

5. The preparation method according to claim 1, characterized in that, The average length of the short fibers is less than 0.5 mm, the average length of the medium fibers is between 0.5 and 1 mm, and the average length of the long fibers is greater than 1 mm.

6. The preparation method according to claim 1, characterized in that, The specific processing involves: concentrating, pressing, and dispersing short fiber pulp using a multi-disc press to obtain surface pulp; concentrating, pressing, and dispersing long fiber pulp using a multi-disc press to obtain core pulp; and concentrating, pressing, and dispersing medium fiber pulp using a multi-disc press to obtain bottom pulp.

7. The preparation method according to claim 1, characterized in that, The dispersion treatment involves thickening and pressing the pulp with multi-disc concentrate, followed by dilution with turbid water, wherein the concentrations of the top layer pulp, bottom layer pulp, and core layer pulp are independently selected from 3.5% to 4.5%.

8. The preparation method according to claim 7, characterized in that, The source of the turbid white water is as follows: the slurry obtained after multi-disc concentration is recycled into the slurry mixing tank for mixing, and the white water obtained is classified according to concentration as follows: turbid white water, SS≥300mg / L; clear white water, 60mg / L<SS<300mg / L; ultra-clear white water, 30mg / L≤SS≤60mg / L; and ultra-filtered water, 10mg / L<SS<30mg / L.

9. A type of linerboard prepared by the preparation method according to any one of claims 1-8, characterized in that, The ring crush strength of the linerboard is >8.5 N·m / g, and the bursting strength index is >3.70 kPa·m. 2 / g, fiber tailings rate <1%.

10. The application of a linerboard prepared by the preparation method according to any one of claims 1-8 or the linerboard according to claim 9 in the preparation of high-strength cartons.

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