Papermaking process for improving the roughness of the paper surface on both sides of a wide web of paperboard and the paperboard produced thereby

Abstract

The application provides a papermaking process method for improving roughness of both sides of wide-format card paper and card paper thereof. The papermaking process method comprises a wire section, a press section, a front drying section, a sizing section, a rear drying section, a hard pressing section, a coating section, a soft pressing section and a winding section. The press section is a multi-roller pressing section, and the edge pressure of the last pressing roller is increased by at least 30%. The papermaking process method for improving roughness of both sides of wide-format card paper provided by the embodiment of the application can improve the roughness of both sides of the card paper of a high-speed wide-format card paper machine, control the flatness of both sides within a target range of less than or equal to 1.55, and reduce printing defects and complaints.

Description

Technical Field

[0001] This application relates to the technical field of cardboard manufacturing processes, specifically to a papermaking process method for improving the roughness of the paper surfaces on both sides of wide-width cardboard and the cardboard thereof. Background Technology

[0002] Current high-speed wide-width paper machines (width ≥ 8.0m) often experience significant paper surface roughness on both sides of the control and transmission lines due to the large width and resulting shrinkage. This roughness can lead to printing defects when customers use paper in these areas. Therefore, improving the paper surface roughness on both sides of the control and transmission lines to avoid its negative impact on printing has become a pressing technical problem.

[0003] Let's take a printing defect as an example: Paper surface roughness is measured using a flatness instrument; the higher the flatness value, the rougher the paper surface. Currently, most customers can accept a flatness of ≤1.55 for printing.

[0004] A horizontal flatness test was conducted on a master roll with a width of 8.1m and a basis weight of 350gsm. The test results showed that the flatness of the paper surface was worst in the 0~0.5m range on both the operating and transmission sides, and the flatness gradually improved towards the middle area. Specifically, the flatness of the operating side (FS) in the 0~0.5m range was 1.70, and the flatness of the transmission side (DS) in the 0~0.5m range was 1.68.

[0005] The main issues raised by printing clients: In cases involving rough 350gsm paper, the roughness of the paper varied significantly between the two sides of the same 740mm wide sample. Printing clients reported noticeable differences when printing on samples of the same size (740 / 840mm), with printing defects appearing at the paper edges due to the rough paper surface. Summary of the Invention

[0006] The first aspect of this application provides a papermaking process method for improving the roughness of the paper surface on both sides of wide-width cardboard. The papermaking process method includes a wire section, a press section, a pre-drying section, a sizing section, a post-drying section, a hard press, a coating section, a soft press, and a winding section. The press section is a multi-roll press, which increases the edge pressure of the last press roll by at least 30%.

[0007] In some optional embodiments, the pressing section includes a three-pressure process, wherein the linear pressure of the third pressure is 800~850KN / m, and the linear pressure of the three-pressure side pressure is ≥95%.

[0008] In some alternative embodiments, the pre-drying includes multiple steam groups with progressively increasing steam pressure.

[0009] In some optional embodiments, the pressure difference between adjacent steam groups is no greater than 50 kPa.

[0010] In some alternative embodiments, the steam pressure of the later steam group is increased by no more than 25% compared to the steam pressure of the earlier steam group.

[0011] In some optional embodiments, during the soft pressing process, the soft pressing light pressure is 60~80 N / m.

[0012] In some alternative embodiments, the temperature during the soft pressing process is 110~130°C.

[0013] In some optional embodiments, the coating segment includes a pre-coat, an intermediate coat, and a top coat; wherein the coating amount of the pre-coat and the intermediate coat is controlled at 16.0 ± 0.5 gsm.

[0014] In some optional embodiments, the latex content in the pre-coat is 14±0.5%, and the latex content in the intermediate coat is 13±0.5%.

[0015] Secondly, embodiments of this application provide a cardboard, which is prepared using the papermaking process described in the above embodiments.

[0016] The papermaking process method for improving the roughness of the paper surface on both sides of wide-width cardboard provided in this application embodiment can improve the problem of roughness on both sides of the operating and transmission sides of high-speed wide-width white cardboard machines, control the flatness of both sides of the operating and transmission sides within the target range of ≤1.55, and reduce printing defects and customer complaints. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of an embodiment of the papermaking process for improving the roughness of the paper surface on both sides of wide-width cardboard, as described in this application. Figure 2 This is a line graph showing the flatness test data for 350gsm horizontal paper. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0020] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movement of components in a specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. 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 may optionally include steps or units not listed, or may optionally include other steps or components inherent to these processes, methods, products, or devices.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] In previous production processes, it was found that the roughness of the paper surface on both sides of the banner was not affected by a single factor, which increased the difficulty of improving the roughness of the paper surface on both sides of the banner. Currently, the main improvement is to simultaneously improve two aspects: paper web shrinkage and paper surface finishing, so as to control the paper surface roughness within an effective range, which can fully meet the printing needs of customers.

[0023] The main problems with the existing process are: ① The pressure of the three-sided pressing line in the pressing section is too low; ② Excessive steam pressure in the first 1-3 drying stages caused the paper web to become rough due to rapid drying as it entered the pre-drying section; ③ Insufficient coating amount results in a rough paper surface that cannot be filled; ④ Soft pressing and low temperature cannot effectively modify the paper surface.

[0024] Data related to the roughness of the paper surfaces on both sides of the raw paper handling process: FS (operating side): 0-0.2m, roughness 1.70; DS (transmission side): 0-0.2m, roughness 1.68; The technical problem solved by the technical solution in this application embodiment is as follows: Based on the analysis of existing technologies, the inventive point of this invention is determined, that is, the technical problem to be solved by this invention is: by optimizing process parameters such as edge pressure of the press section, steam gradient of the pre-drying cylinder, coating amount and coating formulation, soft pressing, and temperature, the problem of roughness on both sides of the paper surface of the high-speed wide-width white cardboard machine is improved, and the flatness on both sides of the press is controlled within the target range of ≤1.55, thereby reducing customer complaints about printing defects.

[0025] Please refer to the following: Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the papermaking process for improving the roughness of the paper surface on both sides of wide-width cardboard, as described in this application. The papermaking process includes, but is not limited to, the following steps: wire section S101, press section S102, pre-drying S103, sizing S104, post-drying S105, hard pressing S106, coating section S107, soft pressing S108, and winding S109. In this embodiment, the improvements will be mainly described; other processes are within the understanding of those skilled in the art and will not be elaborated upon here. Overall technical solution: By simultaneously optimizing the edge pressure of the press section, the steam gradient of the pre-drying cylinder, the coating amount and coating formulation, and the light pressing pressure and temperature of the soft pressing, the flatness of both sides of the paper is ultimately controlled within the target range of ≤1.55, thereby reducing customer complaints about printing defects.

[0026] The first step is to adjust the process of pressing the edge of the pressing section. 1. Increasing the overall linear pressure of the press section can reduce and evenly compress the gaps between fibers, making the paper denser and smoother. However, if the overall linear pressure is increased too much, the surface fibers will be crushed and broken, making them prone to sticking to the rolls and falling off, which will actually worsen the smoothness and even increase the risk of paper breaks. In particular, many rolls on paper machines are designed with medium to high pressure, and if the pressure is increased too much, problems are more likely to occur in the middle zone of the paper machine.

[0027] In this embodiment, the pressing section S102 is a multi-roller pressing unit, increasing the edge pressure of the last pressing roller by at least 30%. Specifically, the pressing section S102 may include a three-pressing process, wherein the linear pressure of the third press is 800~850KN / m, specifically 800KN / m, 810KN / m, 820KN / m, 830KN / m, 840KN / m, and 850KN / m, etc. The linear pressure of the three-press edge pressure is ≥95%.

[0028] 2. To address the issue of poor paper web flatness on both sides of the press section, the overall linear pressure of the press section is not increased; only the edge pressure is improved. Simultaneously, research was conducted on which pressure zone in a three-pressure press (for paper machines with three shoe pressures in the press section) is most effective in improving flatness. The test results are as follows: ① First pressure: Line pressure is maintained at 850KN / m, edge pressure is changed from 65% to 95%, and the flatness improvement is not obvious; ② Second pressure: Line pressure is maintained at 850KN / m, and edge pressure is changed from 65% to 95%, with no significant improvement in flatness; ③ Three pressures: Line pressure is maintained at 850KN / m, and edge pressure is increased from 65% to 95%, resulting in a significant improvement in flatness.

[0029] Process conditions for edge pressing: Maintain the same line pressing, increase the edge pressing of the three pressing (increase by ≥30%), which helps to improve the flatness of both sides of the transmission.

[0030] Secondly, the steam pressure of the pre-drying S103 needs to be adjusted. 1. Reasons for process adjustment When the paper web enters the pre-drying section from the press, its dryness is about 45% to 55%, with high moisture content, low strength, and weak fiber bonding. If the steam rises too quickly, it can easily lead to uneven dehydration of the web, with faster shrinkage at the edges and slower shrinkage in the middle, forming waves. This results in poor flatness of the paper surface on both sides of the conveyor due to shrinkage, especially the steam pressure distribution of the first 1 to 3 drying cylinders in the pre-drying section, which has a significant impact.

[0031] 2. Gradient heating design ①The main purpose of gradient temperature increase: Low temperature at the beginning: slowly evaporates surface water, allowing the fibers to gradually shrink and bond together, establishing initial strength; High temperature in the later stage: After the paper web strength is improved, the internal water evaporates quickly, and the drying is completed efficiently.

[0032] ② The principle of gradient temperature control: The steam pressure should be gentle at the beginning, stable in the middle, and steadily increase at the end, without steep rises or abrupt changes. The steam pressure of the first three groups should gradually increase from low to high, and the pressure difference between adjacent steam groups should not exceed 50 kPa. That is, the steam pressure between groups should be ≤50 kPa, and the increase in steam pressure in the later group should not exceed 25% compared to the previous group.

[0033] Pre-drying process conditions: Steam pressure increases from low to high, and the increase in steam pressure in the second group is ≤25% compared to the first group.

[0034] Next is the adjustment of the soft calendering S108 process. Soft calendering is a key process in modern papermaking for controlling paper surface properties such as smoothness, gloss, and evenness. Linear load and temperature are two of the most critical control parameters.

[0035] Unlike traditional hard calendering (which uses two metal rollers), soft calendering consists of a heated hard roller (usually a metal roller that can be heated) and a soft roller (made of composite materials such as polymers, wool, or cotton). The elastic deformation of the soft roller allows for a wider pressure zone and a more uniform pressure distribution, enabling a smoother paper surface more effectively without excessively reducing paper thickness (i.e., without sacrificing bulk).

[0036] 1. Core Parameter Definition Linear pressure: The pressure exerted per unit width of the calendering zone, usually expressed in kN / m, representing the mechanical pressure intensity of the calendering operation.

[0037] Temperature: Specifically refers to the surface temperature of the hot roller, usually measured in °C. Heat causes physical and chemical changes in the paper components (mainly fibers, fillers, and sizing agents), making them easier to flatten.

[0038] 2. The influence and mechanism of parameters on paper surface roughness (1) Line pressure ① Mechanical Deformation and Rheology: Line pressing directly applies mechanical force, forcing the raised parts of the paper surface (such as fiber bundles, fiber ends, and filler clumps) to undergo plastic deformation and creep. The elasticity of the soft roller allows it to "wrap" and press into the pits on the paper surface, while simultaneously applying pressure to the raised parts, causing them to be flattened, spread out, and fill into the surrounding valleys, thereby achieving homogenization of the entire surface. This process is similar to "ironing," but it is mainly the action of mechanical force.

[0039] ② Reduce porosity and compress thickness: Pressure makes the bonds between fibers tighter, reduces the micropores on the paper surface, thereby reducing roughness and making the surface more "closed".

[0040] (2) Temperature ① Thermoplastic softening: The main components of paper (cellulose, hemicellulose, lignin) and added chemical raw materials (such as starch and latex) are all thermoplastic materials. Heating them above the glass transition temperature enhances the mobility of molecular chain segments, and the material changes from a glassy state to a highly elastic state, becoming soft and malleable, and can undergo permanent deformation under less mechanical force.

[0041] ② Moisture evaporation and redistribution: Water vapor can exist briefly between fibers to act as a lubricant and reduce friction between fibers; heat activates the bound water in the fiber cell walls, and water molecules act as plasticizers to further soften the fibers and enhance their plasticity.

[0042] ③ Latex melting and leveling (for coated paper): Heating melts and aggregates the latex particles (such as SBR, acrylic ester) in the coating on the coated paper surface, forming a continuous film that flows and fills the tiny pores in the coating layer, greatly improving surface smoothness and gloss. This is key to achieving high print quality.

[0043] Therefore, the soft calendering process of a paper machine is essentially a coupling effect of "heat" and "force" to cause controllable and selective plastic rheology in the surface layer of the paper, thereby optimizing the overall performance of the paper as much as possible while meeting the roughness requirements.

[0044] 3. Process testing and condition determination Tests showed that increasing the linear pressure of the soft calender from the conventional 20 N / m to 60-80 N / m resulted in a gradual improvement in paper surface smoothness. However, when the linear pressure was increased to 80-100 N / m, the paper surface smoothness did not improve further. Similarly, increasing the soft calendering temperature from 50℃ to 130℃ resulted in a gradual improvement in paper surface smoothness. However, when the temperature was increased to 130-150℃, the paper surface smoothness did not improve further.

[0045] Therefore, the soft calendering process conditions in this application embodiment are: soft calendering pressure of 60~80 N / m, specifically 60 N / m, 62 N / m, 65 N / m, 70 N / m, 75 N / m, 80 N / m, etc., and temperature of 110~130℃, specifically 110℃, 115℃, 118℃, 120℃, 125℃, 130℃, etc.

[0046] Finally, the coating amount process is adjusted. 1. The effect of coating amount on paper surface roughness The surface of the base paper is composed of interwoven fibers, resulting in an uneven surface with numerous pores and irregularities. Coating essentially involves uniformly applying a liquid coating composed of pigments, adhesives, and other additives to the surface of the base paper. Low coating: The coating can only partially cover the fibers and pores on the surface of the base paper, leaving many smaller bumps and fiber tips exposed, and the surface remains relatively rough. High coating coverage: More coating can more completely cover all irregularities on the surface of the base paper, forming a thicker and more continuous coating, effectively "smoothing" the unevenness of the bottom layer and significantly reducing roughness.

[0047] However, increasing the coating amount can weaken the coating strength and easily lead to problems such as ink splattering and peeling. Therefore, it is necessary to optimize the coating formulation.

[0048] 2. Laboratory tests: The effects of different coating amounts and latex fractions on ink bursting during reversal are shown in the table below.

[0049]

[0050] 3. Test Conclusions and Process Conditions ① Control of front coating amount: pre-coating amount 16.0±0.5gsm, intermediate coating amount 16.0±0.5gsm, top coating amount 13.0±0.5gsm. As the pre-coating and intermediate coating amounts increase, the ink bursting effect of reverse folding becomes significantly worse without adjusting the latex amount. ②After the coating amount is increased, the latex content in the pre-coat / intermediate coating formulation changes from 12.0 / 11.0% to 14.0 / 13.0%, and the reverse ink burst can be achieved at the same level as before the coating amount was increased.

[0051] Therefore, the process conditions for coating amount and latex usage in this embodiment are as follows: the coating amount of both pre-coat and intermediate coat is controlled at 16.0±0.5gsm, the latex content in the pre-coat is 14±0.5%, and the latex content in the intermediate coat is 13±0.5%.

[0052] The experimental parameters for several specific embodiments are shown in the table below.

[0053]

[0054] Adjustment of test timing for each scheme ① February 5th: The three-pressure line remained unchanged, while the edge pressure changed from 65% to 95%; ② February 25: Before drying, the steam pressure of the three groups was changed from 350 / 220 / 200 kPa to 210 / 260 / 300 kPa; ③ March 6: The latex content of the pre-coat / intermediate coat was increased from 12.0 / 11.0 to 14.0 / 13.0% to reinforce the strength of the coating, and then the application rate of the pre-coat / intermediate coat was increased from 15.0 / 12.0 to 16.0 / 16.0 gsm; ④ April 4: The soft pressing temperature changed from 100 to 110~130℃, and the soft pressing light pressure changed from 2080N / m to 60~80N / m.

[0055] 3. Test Results Through the above improvement measures, the flatness of both sides of the control panel is controlled to ≤1.55, which meets the printing requirements.

[0056] The table below shows a comparison of the improvements before and after:

[0057] Please see Figure 2 , Figure 2 This is a line graph showing the flatness data of 350gsm horizontal paper. As can be seen from the graph, the tracking results of the improvement of the surface feel of the main roll horizontal paper show that the flatness of the paper surface on both sides of FS / DS for 0.2 meters has improved from 1.68~1.70 (red line) to 1.44~1.53 (green line), showing a significant improvement trend.

[0058] The papermaking process method in this application embodiment is improved mainly in the following aspects: 1. Based on the three-pressure line pressure of the pressing section being 800~850KN / m, the side pressure of the three pressure lines is increased (the increase is ≥30%). 2. The steam pressure of the first 1-3 drying groups is adjusted from low to high in a gradient. Compared with the first group, the steam pressure increase of the second group is ≤25%. 3. The application rate of the pre-coat / intermediate coat is 16.0~17.0 gsm, and the latex content in the pre-coat / intermediate coat is 13.0~14.0%; 4. Soft pressing light pressure 60~80N / m, soft pressing temperature 110~130℃.

[0059] The papermaking process method for improving the roughness of the paper surface on both sides of wide-width cardboard provided in this application embodiment can improve the problem of roughness on both sides of the operating and transmission sides of high-speed wide-width white cardboard machines, control the flatness of both sides of the operating and transmission sides within the target range of ≤1.55, and reduce printing defects and customer complaints.

[0060] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. Any equivalent device or equivalent process transformation made based on the content of this application specification and drawings, or direct or indirect application in other related technical fields, are similarly included in the patent protection scope of this application.

Claims

1. A papermaking process for improving the roughness of both sides of wide-width cardboard, characterized in that, The papermaking process includes a wire section, a press section, a pre-drying section, a sizing section, a post-drying section, a hard press, a coating section, a soft press, and a winding section; wherein the press section is a multi-roll press, and the edge pressure of the last press roll is increased by at least 30%.

2. The papermaking process according to claim 1, characterized in that, The pressing section includes a three-press process, with the linear pressure of the third press being 800~850KN / m and the linear pressure of the three-press side press being ≥95%.

3. The papermaking process according to claim 1, characterized in that, The pre-drying process includes multiple steam groups, with the steam pressure of each group increasing in a stepped manner.

4. The papermaking process according to claim 3, characterized in that, The pressure difference between adjacent steam groups should not exceed 50 kPa.

5. The papermaking process according to claim 4, characterized in that, The steam pressure of the adjacent steam group shall not be increased by more than 25% compared with the steam pressure of the previous group.

6. The papermaking process according to claim 1, characterized in that, During the soft pressing process, the soft pressing light pressure is 60~80 N / m.

7. The papermaking process according to claim 6, characterized in that, During the soft pressing process, the temperature is 110~130℃.

8. The papermaking process according to claim 1, characterized in that, The coating section includes a pre-coat, an intermediate coat, and a top coat; wherein the coating amount of the pre-coat and the intermediate coat is controlled at 16.0±0.5gsm.

9. The papermaking process according to claim 8, characterized in that, The latex content in the pre-coat is 14±0.5%, and the latex content in the intermediate coat is 13±0.5%.

10. A type of cardstock, characterized in that, The cardboard is prepared using the papermaking process described in any one of claims 1-9.

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