Paperboard and preparation method thereof

Abstract

The invention provides a paperboard and a preparation method thereof. The preparation method comprises the steps that paper pulp is prepared, the paper pulp comprises core layer paper pulp, face lining layer paper pulp, face layer paper pulp and bottom layer paper pulp, and microfibrillated cellulose and chemical pulp are added to at least one of the face lining layer paper pulp and the bottom layer paper pulp to be ground together before grinding; making raw paper from the paper pulp; and coating surface glue on the surface of the surface layer of the body paper. According to the preparation method of the paperboard provided by the embodiment of the invention, the adding point of the MFC applied to the high-speed paper machine system is determined, the influence on the paper machine system is reduced, and dehydration of the pulp and operation of the paper machine are ensured. By combining the papermaking characteristics of a multi-layer paper machine, the surface lining layer and the bottom layer applied to the paper sheets can effectively improve the interlayer bonding strength between the paper sheets, improve TV-16, reduce the use amount of spraying starch in the conventional process or cancel the spraying starch, and improve the operation of the paper machine.

Description

Technical Field

[0001] The present application relates to the technical field of papermaking, and in particular to a paperboard and a preparation method thereof. Background Art

[0002] Cardboard is formed by the interweaving of fibers. Multi-layered whiteboard lacks interweaving between layers, so to improve the bonding between the sheets, a starch layer is often sprayed between them. The starch absorbs water, swells within the paper, and gelatinizes at high temperatures, creating a tighter bond between the layers. This makes high-weight paperboard less prone to blistering and delamination during the printing process. However, high-speed paper machines currently face two major challenges when producing high-weight paperboard. First, the high fiber basis weight of high-weight paperboard makes dehydration difficult. Second, the sprayed starch used between the layers of paper is difficult to fully gelatinize on high-speed machines due to the insufficient water and time required for swelling and gelatinization, resulting in a less pronounced reinforcing effect. Furthermore, when sprayed starch is used in large quantities, it tends to accumulate on the spray rods, causing holes and breaks in the paper, impacting machine efficiency.

[0003] Microfibrillated cellulose (MFC) is a one-dimensional nanoscale cellulose material made from plant fibers through mechanical defibrination. Its width is less than 100nm, but its length can reach 2-200um. Since MFC has a large specific surface area and abundant surface hydroxyl groups, it can increase the electrostatic repulsion between fibers after being added to the pulp, which is beneficial to the dispersion of fibers and fillers in the papermaking process. During the dehydration and forming of the pulp, the high hydroxyl content on the surface of MFC can improve the ability of hydrogen bonding between fibers and enhance the strength of the paper sheet. Studies on the effect of MFC on the drainage performance and strength of bleached softwood kraft pulp have shown that the application of MFC will reduce the drainage performance of the pulp, but will significantly enhance the tensile strength of the paper.

[0004] During the pulping and bleaching process, a large number of carboxyl and carbonyl groups are generated on the fiber surface, making the fiber surface negatively charged. This not only causes electrostatic repulsion between long and fine fibers, but also hinders the formation of larger flocs, affecting the drainage performance and filler retention of the pulp. Cationic retention and drainage aids are generally added to improve the drainage performance of the pulp, enhance the retention of fine components and fillers, and improve paper strength. Therefore, numerous studies have shown that by introducing positive charges onto the fiber surface through chemical modification to impart a certain degree of positive charge to the fiber, the problems of salt accumulation and charge reversal caused by typical cationic additives can be eliminated. Furthermore, these additives offer advantages such as high fine fiber and filler retention, improved drainage performance, and significantly improved paper strength.

[0005] Cationization of microfibrillated cellulose can enhance its retention and sheet strength through its charge. However, industrial applications, particularly on large, high-speed paper machines, still suffer from low MFC retention, which impacts dehydration and hinders efficiency gains. Therefore, the application of MFC on high-speed paper machines and the design of paper products that meet both paperboard quality requirements and maximize machine efficiency have become pressing challenges. Summary of the Invention

[0006] A first aspect of an embodiment of the present application provides a method for preparing paperboard, the method comprising:

[0007] Prepare pulp, the pulp comprising core pulp, lining pulp, surface pulp and bottom pulp, wherein at least one of the lining pulp and the bottom pulp is refined together with chemical pulp by adding microfibrillated cellulose before refining;

[0008] Making pulp into base paper;

[0009] Apply surface glue on the surface of the base paper.

[0010] In some optional embodiments, in the step of preparing the pulp, microfibrillated cellulose is added to each of the surface lining pulp and the bottom layer pulp before refining, and the pulp is refined together with the broadleaf chemical pulp.

[0011] In some optional embodiments, the core layer pulp comprises 40%-60% mechanical pulp, 10%-30% hardwood pulp, 20%-30% broke pulp and 0.2-1% microfibrillated cellulose.

[0012] In some optional embodiments, the facing layer pulp and the bottom layer pulp both comprise 20-30% softwood pulp and 70-80% hardwood pulp, wherein microfibrillated cellulose is refined together with the hardwood pulp and the microfibrillated cellulose is contained in the 70-80% hardwood pulp.

[0013] In some optional embodiments, the amount of microfibrillated cellulose added to the facing layer pulp and the bottom layer pulp is 0.2-1.0% of the absolute dry fiber amount of the pulp, respectively; and the aspect ratio of the microfibrillated cellulose is ≥5000.

[0014] In some optional embodiments, the hardwood pulp is refined and mixed with the softwood pulp, and then a strong cationic PAC and a cationic retention aid are added.

[0015] In some optional embodiments, the addition amount of the strong cationic PAC is 0.2-0.4% of the absolute dry weight of the pulp, and the addition amount of the cationic retention aid is 200-300 ppm.

[0016] In some optional embodiments, while adding the cationic retention aid, 2-4 kg / ton of pulp silica sol retention aid is also added.

[0017] In some optional embodiments, the PCD of the modified pulp is: +100,000 to +300,000 ueq / L, solid content is 6-8%, and viscosity is: 400-800 cps.

[0018] In a second aspect, an embodiment of the present application provides a cardboard, which is prepared using the preparation method described in the above embodiment.

[0019] The paperboard manufacturing method provided in the examples of this application identifies the point at which MFC is added to a high-speed paper machine system, minimizing its impact on the machine system and ensuring pulp dehydration and machine operation. In light of the papermaking characteristics of multi-layer paper machines, it was discovered that applying MFC to the facing and backing layers of paper sheets can effectively improve interlayer bonding strength, enhance TV-16, reduce or eliminate the amount of starch spraying used in conventional processes, and improve machine operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 This is a schematic diagram of the overall structure of an embodiment of a method for preparing paperboard of the present application;

[0022] Figure 2 This is a schematic diagram of the stacking structure of an embodiment of the paperboard of the present application;

[0023] Figure 3 It is the slurry freeness curve;

[0024] Figure 4 It is the cohesion curve of slurry;

[0025] Figure 5 It is the folding endurance curve of slurry. DETAILED DESCRIPTION

[0026] The present application will be further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only intended to illustrate the present application and are not intended to limit the scope of the present application. Similarly, the following examples are only some examples of the present application and not all examples. All other examples obtained by those of ordinary skill in the art without creative work are intended to fall within the scope of protection of this application.

[0027] The terms "first", "second" and "third" in the embodiments of the present application are used only for descriptive purposes and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second" and "third" may explicitly or implicitly include at least one of such features. In the description of the present application, "multiple" means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined. All directional indications in the embodiments of the present application (such as up, down, left, right, front, back...) are only used to explain the relative positional relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. The terms "including" and "having" in the embodiments of the present application and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally also includes steps or units that are not listed, or optionally also includes other steps or components inherent to these processes, methods, products or devices.

[0028] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0029] The present invention provides a paperboard manufacturing process using microfibrillated cellulose (MFC), which reduces or even eliminates the use of starch spraying and designs a novel multi-layer paperboard manufacturing process. When improving the strength of traditional multi-layer paperboard, the core layer is typically the weakest due to the addition of chemical mechanical pulp and fillers. The core layer also has the highest basis weight in the multi-layer paperboard. Using MFC to improve the core layer's strength increases costs significantly. The present invention adds MFC to adjacent layers of the core layer of multi-layer web-made paperboard, such as the liner or bottom layer. This improves the bonding strength between the paperboard sheets and improves the TV-16 of the paperboard, thereby reducing or even eliminating the use of starch spraying and improving paper machine operation. Furthermore, the invention explores the point at which MFC can be added. MFC can be ground together with chemical pulp or added to a thickened chemical pulp stock to ensure thorough mixing. This addresses the issues of microfibrillated cellulose mismatching with the wet-end system of large paper machines, impacting dewatering efficiency, and lacking a significant strengthening effect.

[0030] Please also refer to Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the overall structure of an embodiment of the method for preparing paperboard of the present application. Figure 2 Schematic diagram of the stacking structure of an embodiment of the paperboard of the present application; the preparation method of this embodiment includes but is not limited to the following steps.

[0031] Step S100: preparing pulp.

[0032] Please refer to Figure 2 The paperboard in this embodiment includes a surface layer 101, a surface lining layer 102, a core layer 103 and a bottom layer 104 stacked in sequence; wherein, at least one of the surface lining layer pulp and the bottom layer pulp is added with microfibrillated cellulose before refining and refined together with chemical pulp.

[0033] Optionally, in this embodiment, microfibrillated cellulose may be added to both the surface lining pulp and the bottom pulp before refining and refined together with the broadleaf chemical pulp.

[0034] Optionally, the core layer pulp in this embodiment includes 40%-60% mechanical pulp, 10%-30% broadleaf pulp, 20%-30% broke pulp and 0.2-1% microfibrillated cellulose; the surface layer pulp includes 20-30% coniferous pulp and 70-80% broadleaf pulp.

[0035] The facing pulp and the bottom pulp both comprise 20-30% softwood pulp and 70-80% hardwood pulp, wherein microfibrillated cellulose is refined together with the hardwood pulp and the microfibrillated cellulose is contained in the 70-80% hardwood pulp.

[0036] In the embodiment of the present application, the broadleaf pulp L pulp (a pulp product obtained by bleaching broadleaf pulp. Specifically, L pulp is a type of bleached sulfate broadleaf pulp, usually made from broadleaf wood (such as eucalyptus, birch, etc.)) used in the surface lining layer 102 and the bottom layer 104 is added with microfibrillated cellulose during the preparation process. The microfibrillated cellulose is added before the disk grinding of the broadleaf pulp to obtain broadleaf chemical pulp containing microfibrillated cellulose. The chemical pulp containing MFC is then pumped to the paper machine mixing pipe, and the various pulps are mixed in the static mixer of the mixing pipe and then flowed to the paper machine pulp pool. During the flow of the pulp, chemicals from the wet end of papermaking are added, and the MFC is dispersed again through the flow system.

[0037] Optionally, the amount of microfibrillated cellulose added to the surface lining pulp and the bottom pulp is 0.2-1.0% of the absolute dry fiber amount of the pulp; and the aspect ratio of the microfibrillated cellulose is ≥5000.

[0038] MFC is added at the pump inlet of the chemical pulping line's disc refiner or at the pump inlet of the pulp storage tower. The pump suction mixes the MFC with the pulp, which then passes through the disc refiner on the pulping line to produce the MFC-containing chemical pulp. The refining equipment has a specific energy of 180-300, and the refining return is set at 40% to improve pulp circulation.

[0039] Chemical pulp containing MFC is mixed with softwood and hardwood pulps at a pulp concentration of 3.5-4.5%. The pulp passes through a static mixer and is then pumped to a mixing tank for further mixing. After entering the mixing tank, a strong cationic PAC is added at a rate of 0.2-0.4% of the pulp's absolute dry weight. A cationic retention aid (200-300 ppm) and a silica sol retention aid (2-4 kg) are added before the pressure screen pump. This results in a lining or base layer pulp. The modified pulp has a PCD of +100,000 to +300,000 ueq / L, a solids content of 6-8%, and a viscosity of 400-800 cps.

[0040] The white water of the paper machine system is recycled through multiple discs, with 40-50% of the recycled pulp being mixed into the bottom layer and 50-60% being mixed into the surface layer.

[0041] Please continue reading Figure 1 The preparation method in the embodiment of the present application further includes step S200 of making pulp into base paper.

[0042] After the surface layer, lining layer, core layer and bottom layer pulp are put on the screen, the dehydrated wet paper sheets are compounded in multiple layers, pressed and dried to complete the base paper making.

[0043] Step S300: applying a surface glue on the surface of the base paper.

[0044] After gluing, the cardboard is obtained

[0045] The following will introduce the specific experimental parameter comparison.

[0046] 1) Testing of MFC addition points.

[0047]

[0048] 2) Simulate the application of MFC at different addition points

[0049]

[0050]

[0051] From the above experimental data table, it can be seen that the enhancement effect is obvious when MFC and L pulp are mixed first.

[0052] 3) MFC is applied to the bottom layer of paper, dehydration and strength of pulp

[0053] Please also refer to Figures 3 to 5 , Figure 3 is the slurry freeness curve, Figure 4 is the slurry cohesion curve, Figure 5 It is a folding endurance curve of the slurry. It can be seen from the figure that after the application of MFC, the dehydration of the slurry is slightly reduced and the strength is significantly improved.

[0054] 4) Adjustment of TV-16 and spray starch dosage for paper

[0055]

[0056] From the above chart, we can see that

[0057] When the MFC bottom layer is applied at a concentration of 0.2-0.4%, the TV-16 on the back side (B) of the cardboard increases by 1-1.5 times. After the white water system circulates, the TV-16 on the front side (T) increases by 1 time. When the MFC addition amount is maintained at 0.4%, the spray starch pressure on the front side decreases from 1.34 to 0.7 bar, and on the back side from 0.87 to 0.28 bar. The strength is equivalent to that before the pilot test.

[0058] The technical solution in the embodiments of the present application involves refining MFC with broadleaf chemical pulp. During the refining process, the physical squeezing action of the grinding disc allows the MFC to be fully dispersed, giving full play to its high specific surface area. The chemical pulp is then divided and broomed during the grinding process, and the surface hydroxyl groups can preferentially combine with the hydroxyl groups or modified cationic groups of the MFC through hydrogen bonding, allowing the MFC to graft onto the chemical pulp fibers and form "tentacles" on the fiber surface to enhance the fiber-to-fiber bonding strength. When paper sheets are pressed and compounded, the small-sized MFC on the fiber surface is closer to the other fibers, and the high-aspect-ratio MFC can entangle with the fibers, easily forming hydrogen bonds with the paper fibers in the core layer, thereby enhancing the bonding strength between the paper sheets and reducing the need for spray starch.

[0059] The paperboard manufacturing method provided in the examples of this application identifies the point at which MFC is added to a high-speed paper machine system, minimizing its impact on the machine system and ensuring pulp dehydration and machine operation. In light of the papermaking characteristics of multi-layer paper machines, it was discovered that applying MFC to the facing and backing layers of paper sheets can effectively improve interlayer bonding strength, enhance TV-16, reduce or eliminate the amount of starch spraying used in conventional processes, and improve machine operation.

[0060] The above descriptions are only some embodiments of the present application and do not limit the scope of protection of the present application. Any equivalent device or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the scope of patent protection of this application.

Claims

1. A method for preparing paperboard, characterized in that: The preparation method comprises: Prepare pulp, the pulp comprising core pulp, lining pulp, surface pulp and bottom pulp, wherein at least one of the lining pulp and the bottom pulp is refined together with chemical pulp by adding microfibrillated cellulose before refining; Making pulp into base paper; Apply surface glue on the surface of the base paper.

2. The preparation method according to claim 1, characterized in that In the step of preparing the pulp, microfibrillated cellulose is added to the surface lining pulp and the bottom layer pulp before refining, and the pulp is refined together with the broadleaf chemical pulp.

3. The preparation method according to claim 1, characterized in that The core layer pulp comprises 40%-60% of mechanical pulp, 10%-30% of broadleaf wood pulp, 20%-30% of broke pulp and 0.2-1% of microfibrillated cellulose.

4. The preparation method according to claim 1, characterized in that The facing layer pulp and the bottom layer pulp both comprise 20-30% of softwood pulp and 70-80% of hardwood pulp, wherein microfibrillated cellulose is refined together with the hardwood pulp and the microfibrillated cellulose is contained in the 70-80% of hardwood pulp.

5. The preparation method according to claim 4, characterized in that The amount of microfibrillated cellulose added to the surface lining pulp and the bottom pulp is 0.2-1.0% of the absolute dry fiber amount of the pulp respectively; the aspect ratio of the microfibrillated cellulose is ≥5000.

6. The preparation method according to claim 5, characterized in that The hardwood pulp is refined and mixed with the softwood pulp, and then a strong cationic PAC and a cationic retention aid are added.

7. The preparation method according to claim 6, characterized in that The addition amount of the strong cationic PAC is 0.2-0.4% of the absolute dry weight of the pulp, and the addition amount of the cationic retention aid is 200-300 ppm.

8. The preparation method according to claim 7, characterized in that While adding the cationic retention aid, 2-4 kg / ton of pulp silica sol retention aid is also added.

9. The preparation method according to claim 8, characterized in that The PCD of the modified pulp is: +100000~+300000ueq / L, solid content is 6-8%, and viscosity is: 400-800cps.

10. A paperboard, characterized in that: The paperboard is prepared by the preparation method according to any one of claims 1 to 9.

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