A method for improving the interlayer bonding strength of a boxboard by web compound forming

Abstract

The application discloses a web composite forming method for improving the interlayer bonding strength of boxboard, and comprises the following steps: step one, pulp property detection and grading control, step two, white water pretreatment and intelligent dilution water concentration adjustment, step three, pulp pre-dispersion and chest roller shaking forming, step four, composite surface micro-roughening treatment of the wet paper web, step five, interlayer modified starch atomization spraying, step six, multi-layer wet paper web compounding and bonding dryness control, step seven, stepwise vacuum dewatering, and step eight, wet paper web setting and subsequent conveying; the application realizes accurate adaptation of each process link to the pulp property, eliminates the uneven forming problem caused by the pulp property fluctuation from the raw material end, lays a uniform forming foundation for the improvement of the interlayer bonding strength, simultaneously effectively disperses the fiber flocculation group through pre-dispersion treatment, reduces the fiber longitudinal arrangement, makes the fiber distribution in the paper web more uniform, and improves the effectiveness of the interlayer fiber entanglement.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a method for composite forming of wire mesh to improve the interlayer bonding strength of corrugated cardboard. Background Technology

[0002] Against the backdrop of high-quality and green development in the paper industry, corrugated board, as a core category of packaging paper, has interlayer bond strength as a key physical performance indicator. Insufficient interlayer bond strength can easily lead to problems such as delamination, dusting, and decreased burst strength during processing, transportation, and use, seriously affecting product quality. The forming section (wire section) is the core link in corrugated board production. It not only determines the uniformity of paper web forming but is also a key process affecting interlayer bond strength. At the same time, the forming section is also a major energy-consuming unit of the paper machine. The dual demands of energy saving and carbon reduction as well as performance improvement place higher requirements on the wire section composite forming process.

[0003] In existing corrugated board wire bonding processes, the paper layer bonding dryness is typically controlled between 10% and 14%. If the dryness is too low within this range, speed fluctuations can easily damage the paper layer bonding, while if the dryness is too high, it directly reduces interlayer bonding strength, creating a difficult-to-reconcile process contradiction. In the pulp thickening stage, white water from under the wire is often used directly for dilution without pretreatment. This leads to unstable thickening concentrations due to impurities and pH fluctuations in the white water, resulting in poor paper web uniformity and indirectly affecting interlayer bonding. Furthermore, the shaking process in the breast roll forming stage only performs basic vibration adjustments without adapting to the pulp characteristics, resulting in a high proportion of longitudinal fiber alignment and significant flocculation. This results in a loose internal structure of the paper web and a weak foundation for fiber entanglement in the interlayer bonding. The interlayer starch spraying often uses unmodified ordinary starch, which has weak bonding force between starch molecules and fibers, resulting in insignificant bridging and difficulty in effectively filling interlayer pores. Vacuum control during dewatering is often crude, leading to over-suction and significant loss of fine fibers and fillers. This not only reduces raw material utilization but also undermines the material basis for interlayer bonding in the paper web. Furthermore, crude vacuum control results in high energy consumption in the forming section. In addition, existing processes do not specifically treat the wet paper web composite surface, limiting the interlayer contact area and further restricting the improvement of interlayer bonding strength.

[0004] Although some technologies have attempted to improve the interlayer bonding strength of corrugated cardboard through single process optimization, such as adjusting the amount of starch spraying and optimizing the dehydration rhythm, a full-process coordinated control system for pulp thickening, forming, modification, dehydration, and compounding has not been formed. This makes it difficult to fundamentally solve the problems of low interlayer bonding strength and easy delamination, and at the same time, it cannot meet the industry's development needs for energy conservation, carbon reduction, and efficient utilization of raw materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for composite forming of wire mesh to improve the interlayer bonding strength of cardboard, so as to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for composite forming of wire mesh to improve the interlayer bonding strength of corrugated cardboard, comprising the following steps: Step 1: Pulp Characteristics Testing and Grading Control: Test the mass concentration, freeness, and wet weight of the mixed softwood pulp and hardwood pulp used in corrugated board production. Based on the test results, divide the pulp into three grades: high, medium, and low, and preset the corresponding process parameters for each grade. Step 2: Pretreatment of under-mesh white water and intelligent concentration adjustment of dilution water: The under-mesh white water is pretreated by sequentially filtering with an 800-1000 mesh filter, removing impurities and settling for 30-40 minutes, and adjusting the pH value to 6.5-7.5. The pretreated white water is used as concentration water, and cationic polyacrylamide and bentonite are added. It is then mixed with the graded slurry and the slurry mass concentration is stabilized at 0.8%-1.2%. Step 3, Pulp Pre-dispersion and Breast Roll Shaking Forming: After the thickened pulp is ultrasonically micro-dispersed, it is transported to the headbox, and after being distributed, it enters the breast roll shaking and forming to obtain a single-layer wet paper web; Step 4: Micro-roughening treatment of the composite surface of wet paper web: The composite contact surface of the single-layer wet paper web is micro-roughened for 3s-5s using a low-pressure airflow of 0.1MPa-0.2MPa to form a micro-pit structure on the composite surface. Step 5: Interlayer modified starch atomization spraying: Prepare a modified starch solution with a mass concentration of 3.0%-5.0%, and spray it evenly onto the micro-roughened composite surface of the wet paper web using an atomization spraying method, with a spraying rate of 5 g / m². 2 -10g / m 2 ; Step 6: Multi-layer wet paper web lamination and bonding dryness control: The multi-layer wet paper web after starch spraying is conveyed to the lamination roll for lamination, and the bonding dryness of the paper layers is controlled at 12%-15%; Step 7, Stepped vacuum dewatering: Using a variable frequency vacuum system, the vacuum level is adjusted in three stages (low, medium, and high) according to the change in the wetness of the paper after lamination to carry out stepped dewatering; Step 8, Wet Paper Web Shaping and Subsequent Conveying: The dehydrated composite wet paper web is subjected to low-pressure shaping, then peeled off from the forming wire and conveyed to the subsequent process.

[0007] Further, step one specifically involves: selecting a mixed pulp of softwood pulp and hardwood pulp for corrugated board production, and testing three core indicators of the pulp: mass concentration, freeness, and wet weight. The mass concentration is tested within the range of 2.0%-4.0%, the freeness within the range of 30°SR-55°SR, and the wet weight within the range of 3.0g-8.0g. Based on the test results, the pulp is divided into three grades: high, medium, and low. High-grade pulp has a mass concentration ≥3.0%, freeness ≥45°SR, and wet weight ≥6.0g; medium-grade pulp has a mass concentration of 2.5%-3.0%, freeness 35°SR-45°SR, and wet weight 4.0g-6.0g; and low-grade pulp has a mass concentration of 2.0%-2.5%, freeness 30°SR-35°SR, and wet weight 3.0g-4.0g. For different grades of pulp, corresponding dilution water concentration, pre-dispersion treatment time, and vacuum dewatering stage parameters are preset.

[0008] Further, step two specifically involves: pre-treatment of the white water under the filter screen, including filtration, impurity removal and sedimentation, and pH adjustment. The filtration uses an 800-1000 mesh filter to remove coarse fiber impurities from the white water, and the sedimentation time is 30-40 minutes. The pH of the white water is adjusted to 6.5-7.5 using a food-grade weak acid or weak alkali. The pre-treated white water is then mixed with the slurry from step one, and a retention and filter aid is added. This retention and filter aid is a composite system of cationic polyacrylamide and bentonite, with the cationic polyacrylamide added at 0.02‰-0.05‰ (relative to the oven-dry weight of the slurry) and the bentonite added at 0.5‰-1.0‰ (relative to the oven-dry weight of the slurry). Through online detection of the slurry concentration and control of the thickening water flow rate, the mass concentration of the mixed slurry is stabilized at 0.8%-1.2%, with concentration fluctuations controlled within ±0.05%.

[0009] Furthermore, step three specifically involves: based on the slurry grading results from step one, performing ultrasonic micro-dispersion treatment on the thickened slurry. The ultrasonic treatment time is 15 minutes for high-grade slurry, 12 minutes for medium-grade slurry, and 10 minutes for low-grade slurry. The power density of the ultrasonic treatment is 0.3 W / cm³. 3 -0.5W / cm 3 The pre-dispersed pulp is transported to the headbox, and after being distributed in the headbox, it enters the breast roll vibratory forming stage. A vibratory device causes the breast roll to reciprocate and vibrate the pulp, ensuring a uniform transverse distribution of fibers on the forming wire and reducing the proportion of fibers arranged longitudinally. The basis weight deviation of the formed single-layer wet paper web is controlled within ±3g / m². 2 Within.

[0010] Furthermore, step four specifically involves: using a low-pressure airflow to micro-roughen the composite contact surface of the single-layer wet paper web, with an airflow pressure of 0.1MPa-0.2MPa, an angle of 45°-60° between the airflow and the paper web surface, and a treatment time of 3s-5s; after the micro-roughening treatment, the composite surface of the wet paper web forms a depth of 5μm-10μm and a distribution density of 80 particles / cm. 2 -100 pieces / cm 2 The micro-dimpled structure does not damage the overall forming structure of the wet paper web.

[0011] Further, step five specifically involves: preparing a modified starch solution by first mixing corn starch with deionized water to prepare a starch suspension with a mass concentration of 3.0%-5.0%. The starch suspension is then heated to 50℃-60℃, and 0.5%-1.0% (by dry weight of starch) of a biological enzyme is added for enzymatic hydrolysis for 60-90 minutes. After hydrolysis, 0.3%-0.6% (by dry weight of starch) of hydroxypropyl methylcellulose ether is added, and the mixture is stirred for 30-40 minutes to obtain the modified starch solution. The modified starch solution is then uniformly sprayed onto the micro-roughened composite surface of the wet paper web using an atomizing spray head. The droplet size of the atomized spray is 20μm-50μm, and the spray volume of the starch solution is 5g / m². 2 -10g / m 2 (Based on oven-dried starch), the spray coverage reaches 100% and there is no liquid accumulation.

[0012] Furthermore, step six specifically involves: feeding the multi-layer wet paper webs that have undergone starch spraying to the composite rollers for roll pressing and lamination according to the layered structure design of the linerboard. The roll pressing pressure of the composite rollers is 0.3MPa-0.5MPa, and the synchronization deviation between the roller speed and the forming wire speed is controlled within ±0.5m / min. By adjusting the parameters of the preceding dewatering process, the bonding dryness during the lamination of the multi-layer wet paper webs is precisely controlled at 12%-15%, thus resolving the process contradiction that excessively low dryness can easily damage the forming process, while excessively high dryness can reduce the interlayer bonding strength.

[0013] Furthermore, step seven specifically involves: using a frequency conversion vacuum system to perform three-stage stepped vacuum dewatering on the composite wet paper web. During the dewatering process, the paper web dryness is monitored in real time, and the vacuum stage is switched according to the dryness changes. The low vacuum stage is for a wet paper web dryness of 12%-16%, with the vacuum level controlled between -0.02MPa and -0.04MPa, achieving initial and gentle dewatering and avoiding the loss of fine fibers. The medium vacuum stage is for a wet paper web dryness of 16%-20%, with the vacuum level controlled between -0.04MPa and -0.06MPa, enhancing dewatering efficiency and improving paper web dryness. The high vacuum stage is for a wet paper web dryness of 20%-24%, with the vacuum level controlled between -0.06MPa and -0.08MPa, achieving precise and deep dewatering so that the wet paper web reaches the required dryness for peeling. Throughout the dewatering process, the vacuum level is adjusted smoothly without abrupt changes.

[0014] Furthermore, step eight specifically involves: conveying the composite wet paper web that has undergone stepped dewatering to a setting roller for low-pressure setting. The setting roller has a pressure of 0.1MPa-0.2MPa and a setting time of 5s-8s. Low-pressure setting allows for more complete hydrogen bonding between starch molecules and fibers, enhancing the physical entanglement and chemical bonding between layers. After setting, the wet paper web is peeled off from the forming wire and conveyed to the press section for subsequent dewatering. During the peeling process, the wet paper web exhibits no delamination or tearing.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention achieves precise matching between each process step and the pulp characteristics through pulp characteristic detection and graded control. It eliminates the problem of uneven forming caused by pulp characteristic fluctuations from the raw material end, laying a uniform forming foundation for improving interlayer bonding strength. At the same time, the pre-dispersion treatment effectively breaks up fiber flocs, reduces the longitudinal arrangement of fibers, makes the fiber distribution inside the paper web more uniform, and improves the effectiveness of interlayer fiber entanglement.

[0016] This invention provides a systematic pretreatment of white water from the wire mesh and adds retention and filtration aids, which not only enables the resource recycling of white water from the wire mesh, meeting the requirements of green production, but also improves the stability of dilution water concentration, effectively increases the retention rate of fine fibers and fillers, reduces raw material loss, and supplements the material basis for interlayer bonding. At the same time, the combined use of retention and filtration aids also indirectly optimizes the pore structure of the paper web, which is conducive to the penetration and binding of starch molecules.

[0017] This invention performs targeted micro-roughening treatment on the wet paper web before lamination, increasing the physical contact area between layers without damaging the paper web shape. This allows for more complete entanglement of fibers between layers. Combined with the modified starch solution sprayed by atomization, a dual interlayer bonding system of physical roughening and chemical bridging is formed. The film-forming properties and fiber bonding strength of the modified starch molecules are greatly improved, enabling the formation of a denser bridging structure between fibers. This fully fills the interlayer pores and significantly enhances the hydrogen bonding force between fibers, fundamentally improving the interlayer bonding strength of the linerboard and solving the technical problem of easy delamination.

[0018] The stepped vacuum dewatering process adopted in this invention allows for precise and smooth vacuum adjustment based on the changes in the dryness of the wet paper web after lamination. This avoids the problem of excessive suction caused by traditional extensive dewatering, effectively reducing the loss of fine fibers and fillers. At the same time, the segmented control of the frequency conversion vacuum system significantly reduces the vacuum energy consumption of the forming section, achieving the industry's requirements for energy conservation and carbon reduction. Furthermore, the stepped dewatering process makes the paper web dewatering process gentler, the internal structure of the paper web denser, and further improves the stability of interlayer bonding. Attached Figure Description

[0019] Figure 1 This is a flowchart of the forming method of the present invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1 This invention provides a method for composite forming of wire mesh to improve the interlayer bonding strength of corrugated cardboard, comprising the following steps: Step 1: Pulp Characteristic Testing and Grading Control: The mass concentration, freeness, and wet weight of the mixed softwood and hardwood pulp used in corrugated board production are tested. Based on the test results, the pulp is divided into three grades: high, medium, and low, and the corresponding process parameters for each grade are preset. Specifically: The mixed softwood and hardwood pulp used in corrugated board production is selected, and the three core indicators of pulp mass concentration, freeness, and wet weight are tested. The pulp mass concentration testing range is 2.0%-4.0%, the freeness testing range is 30°SR-55°SR, and the wet weight testing range is 3.0g- 8.0g; Based on the test results, the slurry is divided into three grades: high, medium, and low. High-grade slurry has a mass concentration ≥3.0%, a knockout degree ≥45°SR, and a wet weight ≥6.0g; medium-grade slurry has a mass concentration of 2.5%-3.0%, a knockout degree of 35°SR-45°SR, and a wet weight of 4.0g-6.0g; low-grade slurry has a mass concentration of 2.0%-2.5%, a knockout degree of 30°SR-35°SR, and a wet weight of 3.0g-4.0g. For different grades of slurry, corresponding dilution water concentration, pre-dispersion treatment time, and vacuum dewatering stage parameters are preset. Step Two: Pretreatment of Under-Net White Water and Intelligent Concentration Adjustment of Dilution Water: The under-net white water undergoes pretreatment sequentially, including filtration through an 800-1000 mesh screen, 30-40 minutes of impurity removal and sedimentation, and pH adjustment to 6.5-7.5. This pretreated white water is then used as concentration water, with the addition of cationic polyacrylamide and bentonite. This is then mixed with the graded slurry, and the slurry concentration is stabilized at 0.8%-1.2%. Specifically, the under-net white water undergoes pretreatment operations including filtration, impurity removal and sedimentation, and pH adjustment. Filtration uses an 800-1000 mesh screen to remove coarse fiber impurities from the white water, and the sedimentation time is 30-40 minutes. For 0 minutes, the pH of the white water is adjusted to 6.5-7.5 using food-grade weak acid or weak alkali. The pretreated white water is then mixed with the slurry from step one after grading, and a retention and filtration aid is added. The retention and filtration aid is a composite system of cationic polyacrylamide and bentonite, with the cationic polyacrylamide added at 0.02‰-0.05‰ (relative to the oven-dry weight of the slurry) and the bentonite added at 0.5‰-1.0‰ (relative to the oven-dry weight of the slurry). By online detection of the slurry concentration and control of the concentration water flow rate, the mass concentration of the mixed slurry is stabilized at 0.8%-1.2%, and the concentration fluctuation deviation is controlled within ±0.05%. Step 3: Pulp Pre-dispersion and Breast Roll Shaking Forming: After ultrasonic micro-dispersion, the thickened pulp is transported to the headbox, distributed, and then shaken on the breast roll to obtain a single-layer wet paper web. Specifically, based on the pulp grading results from Step 1, the thickened pulp undergoes ultrasonic micro-dispersion. The ultrasonic treatment time is 15 minutes for high-grade pulp, 12 minutes for medium-grade pulp, and 10 minutes for low-grade pulp. The power density of the ultrasonic treatment is 0.3 W / cm³.3 -0.5W / cm 3 The pre-dispersed pulp is transported to the headbox, and after being distributed in the headbox, it enters the breast roll vibratory forming stage. A vibratory device causes the breast roll to reciprocate and vibrate the pulp, ensuring a uniform transverse distribution of fibers on the forming wire and reducing the proportion of fibers arranged longitudinally. The basis weight deviation of the formed single-layer wet paper web is controlled within ±3g / m². 2 within; Step 4: Micro-roughening treatment of the composite surface of wet paper web: A low-pressure airflow of 0.1MPa-0.2MPa is used to micro-roughen the composite contact surface of the single-layer wet paper web for 3-5 seconds, forming a micro-pit structure on the composite surface. Specifically, a low-pressure airflow of 0.1MPa-0.2MPa is used to micro-roughen the composite contact surface of the single-layer wet paper web, with the airflow pressure at 45°-60° angle to the paper web surface, and the treatment time at 3-5 seconds. After micro-roughening treatment, the composite surface of the wet paper web has a depth of 5μm-10μm and a distribution density of 80 pits / cm². 2 -100 pieces / cm 2 The micro-dimpled structure does not damage the overall forming structure of the wet paper web; Step 5: Interlayer modified starch atomization spraying: Prepare a modified starch solution with a mass concentration of 3.0%-5.0%, and spray it evenly onto the micro-roughened composite surface of the wet paper web using an atomization spraying method, with a spraying rate of 5 g / m². 2 -10g / m 2 Specifically, the modified starch solution is prepared by first mixing corn starch with deionized water to form a starch suspension with a mass concentration of 3.0%-5.0%. The starch suspension is then heated to 50℃-60℃, and 0.5%-1.0% (by dry weight of starch) of a biological enzyme is added for enzymatic hydrolysis for 60-90 minutes. After hydrolysis, 0.3%-0.6% (by dry weight of starch) of hydroxypropyl methylcellulose ether is added, and the mixture is stirred for 30-40 minutes to obtain the modified starch solution. The modified starch solution is then uniformly sprayed onto the micro-roughened composite surface of the wet paper web using an atomizing spray head. The droplet size of the atomized spray is 20μm-50μm, and the spray rate of the starch solution is 5g / m². 2 -10g / m 2 (Based on oven-dried starch), the spray coverage reaches 100% with no liquid accumulation; Step Six: Multi-layer Wet Paper Web Lamination and Bond Dryness Control: The multi-layer wet paper web after starch spraying is conveyed to the laminating roller for lamination, and the bond dryness of the paper layers is controlled at 12%-15%. Specifically, the multi-layer wet paper web after starch spraying is conveyed sequentially to the laminating roller for lamination according to the layered structure design of the linerboard. The laminating roller pressure is 0.3MPa-0.5MPa, and the synchronization deviation between the roller speed and the forming wire speed is controlled within ±0.5m / min. By adjusting the preceding dewatering process parameters, the bond dryness during multi-layer wet paper web lamination is precisely controlled at 12%-15%, resolving the process contradiction that too low dryness easily damages the forming and too high dryness reduces the interlayer bonding strength. Step 7, Stepped Vacuum Dewatering: A variable frequency vacuum system is used to perform stepped dewatering by adjusting the vacuum level in three stages (low, medium, and high) according to the changes in the dryness of the wet paper web after lamination. Specifically, the variable frequency vacuum system is used to perform three-stage stepped vacuum dewatering on the laminated wet paper web. During the dewatering process, the dryness of the paper web is monitored in real time, and the vacuum stage is switched according to the changes in dryness. The low vacuum stage is when the dryness of the wet paper web is 12%-16%, and the vacuum level is controlled between -0.02MPa and -0.04MPa to achieve initial gentle dewatering. Dehydration is performed to prevent the loss of fine fibers; the medium vacuum section is for a wet paper web dryness of 16%-20%, with the vacuum level controlled between -0.04MPa and -0.06MPa to enhance dehydration efficiency and improve paper web dryness; the high vacuum section is for a wet paper web dryness of 20%-24%, with the vacuum level controlled between -0.06MPa and -0.08MPa to achieve precise and deep dehydration, ensuring that the wet paper web reaches the required dryness for peeling; throughout the entire dehydration process, the vacuum level is adjusted smoothly without abrupt changes. Step 8, Wet Paper Web Setting and Subsequent Conveying: The dehydrated composite wet paper web undergoes low-pressure setting, then is peeled off from the forming wire and conveyed to the subsequent process. Specifically, the composite wet paper web that has undergone stepped dehydration is conveyed to the setting roller for low-pressure setting. The roller pressure of the setting roller is 0.1MPa-0.2MPa, and the setting time is 5s-8s. Low-pressure setting allows for more complete hydrogen bonding between starch molecules and fibers, strengthening the physical entanglement and chemical bonding effect between layers. After setting, the wet paper web is peeled off from the forming wire and conveyed to the press section for subsequent dehydration. During the peeling process, there is no delamination or tearing of the wet paper web.

[0022] Example: This embodiment focuses on the wire mesh composite forming of three-layer boxboard. The pulp used in production is a mixture of softwood pulp and hardwood pulp in a 3:7 ratio. The specific implementation steps are as follows: Step 1: Slurry Characteristic Testing and Grading Control A mixed slurry sample was selected and tested. Its mass concentration was 2.8%, its freeness was 40°SR, and its wet weight was 5.2g. According to the indicators, it belongs to the medium-grade slurry. The preset ultrasonic pre-dispersion time was 12min, the concentration of dilution water was 1.0%, and the vacuum degree of the medium vacuum section of the step dewatering was -0.05MPa.

[0023] Step 2: Pretreatment of white water and intelligent concentration adjustment of dilution water The white water generated by the mesh section is pretreated by first filtering it through a 900-mesh filter to remove coarse fiber impurities, then letting it stand for 35 minutes to remove impurities and allow it to settle. The pH of the white water is then adjusted to 7.0 with dilute citric acid. The pretreated white water is then used as thickening water and mixed with medium-grade slurry. At the same time, 0.03‰ (relative to the oven-dry weight of the slurry) of cationic polyacrylamide and 0.8‰ (relative to the oven-dry weight of the slurry) of bentonite are added. By online detection of the slurry concentration and real-time control of the thickening water flow rate, the mass concentration of the mixed slurry is stabilized at 1.0%, and the concentration fluctuation deviation is controlled within ±0.03%.

[0024] Step 3: Slurry pre-dispersion and breast roller vibration molding The thickened slurry was fed into an ultrasonic micro-dispersing device at a speed of 0.4 W / cm². 3 The power density treatment lasted 12 minutes to fully disperse the fiber flocs in the slurry. The pre-dispersed slurry was then transported to the headbox, where it was evenly distributed by the distributor and then conveyed to the breast roller vibrating forming area. The vibrating device drove the breast roller to reciprocate, ensuring that the fibers were evenly distributed laterally on the forming mesh surface and reducing longitudinal alignment, ultimately achieving a quantitative deviation of ±2g / m. 2 The single-layer wet paper web has no obvious clumps or holes on its surface.

[0025] Step 4: Micro-roughening treatment of wet paper web composite surface The formed single-layer wet paper web is conveyed to the micro-roughening treatment station, where a low-pressure airflow of 0.15 MPa is used to micro-roughen the composite contact surface of the wet paper web at a 50° angle for 4 seconds, forming a micro-roughening effect on the composite surface with a depth of approximately 8 μm and a distribution density of approximately 90 particles / cm. 2 The micro-dimpled structure does not disrupt the overall shape of the wet paper web, but only increases the roughness of the composite surface.

[0026] Step 5: Interlayer modified starch atomized spray Preparation of modified starch solution: Corn starch was mixed with deionized water to prepare a starch suspension with a mass concentration of 4.0%. The suspension was heated to 55°C, and 0.8% (by oven-dry weight) of a biological enzyme was added for enzymatic hydrolysis for 75 min. After hydrolysis, 0.5% (by oven-dry weight) of hydroxypropyl methylcellulose ether was added, and the mixture was stirred continuously for 35 min to obtain a homogeneous modified starch solution. The modified starch solution was then fed into an atomizing spray device, where it was uniformly sprayed onto the micro-roughened composite surface of the wet paper web at a droplet size of 30 μm through the atomizing spray head at a spray rate of 8 g / m². 2 (Based on oven-dry starch), the spray coverage reaches 100%, and there is no starch residue on the paper surface.

[0027] Step Six: Multi-layer wet paper web lamination and bonding dryness control The core, surface, and bottom wet paper webs, after starch spraying, are sequentially fed to the composite rollers for lamination according to the three-layer linerboard structure design. The lamination roller pressure is set to 0.4 MPa, and the synchronization deviation between the roller speed and the forming wire speed is controlled within ±0.3 m / min. By adjusting the basic parameters of the preceding dewatering, the bonding dryness during the lamination of the three wet paper webs is precisely controlled at 13.5%, which avoids paper layer displacement and forming damage caused by excessively low dryness, and ensures the basic conditions for interlayer bonding.

[0028] Step 7: Step-by-step vacuum dehydration The composite three-layer wet paper web is conveyed to the frequency conversion vacuum dewatering area, where a three-stage stepped vacuum dewatering process is adopted. The paper web dryness is monitored in real time and the vacuum degree is smoothly adjusted: when the wet paper web dryness is 12%-16%, it is in the low vacuum stage, and the vacuum degree is controlled at -0.03MPa to achieve initial gentle dewatering and reduce the loss of fine fibers and fillers; when the dryness rises to 16%-20%, it switches to the medium vacuum stage, and the vacuum degree is adjusted to -0.05MPa to enhance the dewatering efficiency and quickly increase the paper web dryness; when the dryness reaches 20%-24%, it enters the high vacuum stage, and the vacuum degree is adjusted to -0.07MPa to achieve precise deep dewatering, so that the wet paper web reaches the dryness requirement that can be peeled from the forming wire surface.

[0029] Step 8: Wet paper web setting and subsequent conveying The composite wet paper web, after step-by-step dewatering, is conveyed to the setting roller for low-pressure setting. The setting roller pressure is set to 0.15 MPa, and the setting time is 6 seconds. Low-pressure setting allows starch molecules to fully penetrate into the fiber gaps and form denser hydrogen bonds with the fibers, while also strengthening the physical entanglement effect of the interlayer fibers. After setting, the wet paper web is smoothly peeled from the forming wire. During the peeling process, there is no delamination or tearing of the wet paper web. The wet paper web is then conveyed to the press section for subsequent dewatering processes.

[0030] In this embodiment, the parameters of each link in the entire wire section composite forming process are highly matched, realizing the full-process coordination of pulp thickening, forming, modification, dewatering and compounding. The resulting three-layer boxboard has significantly improved interlayer bonding performance, good paper web uniformity, and the energy consumption of the vacuum system in the forming section is greatly reduced compared with the traditional process, and the retention rate of fine fibers is significantly improved.

[0031] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for composite forming of wire mesh sections to improve the interlayer bonding strength of corrugated cardboard, characterized in that: Includes the following steps: Step 1: Pulp Characteristics Testing and Grading Control: Test the mass concentration, freeness, and wet weight of the mixed softwood pulp and hardwood pulp used in corrugated board production. Based on the test results, divide the pulp into three grades: high, medium, and low, and preset the corresponding process parameters for each grade. Step 2: Pretreatment of under-mesh white water and intelligent concentration adjustment of dilution water: The under-mesh white water is pretreated by sequentially filtering with an 800-1000 mesh filter, removing impurities and settling for 30-40 minutes, and adjusting the pH value to 6.5-7.

5. The pretreated white water is used as concentration water, and cationic polyacrylamide and bentonite are added. It is then mixed with the graded slurry and the slurry mass concentration is stabilized at 0.8%-1.2%. Step 3, Pulp Pre-dispersion and Breast Roll Shaking Forming: After the thickened pulp is ultrasonically micro-dispersed, it is transported to the headbox, and after being distributed, it enters the breast roll shaking and forming to obtain a single-layer wet paper web; Step 4: Micro-roughening treatment of the composite surface of wet paper web: The composite contact surface of the single-layer wet paper web is micro-roughened for 3s-5s using a low-pressure airflow of 0.1MPa-0.2MPa to form a micro-pit structure on the composite surface. Step 5: Interlayer modified starch atomization spraying: Prepare a modified starch solution with a mass concentration of 3.0%-5.0%, and spray it evenly onto the micro-roughened composite surface of the wet paper web using an atomization spraying method, with a spraying rate of 5 g / m². 2 -10g / m 2 ; Step 6: Multi-layer wet paper web lamination and bonding dryness control: The multi-layer wet paper web after starch spraying is conveyed to the lamination roll for lamination, and the bonding dryness of the paper layers is controlled at 12%-15%; Step 7, Stepped vacuum dewatering: Using a variable frequency vacuum system, the vacuum level is adjusted in three stages (low, medium, and high) according to the change in the wetness of the paper after lamination to carry out stepped dewatering; Step 8, Wet Paper Web Shaping and Subsequent Conveying: The dehydrated composite wet paper web is subjected to low-pressure shaping, then peeled off from the forming wire and conveyed to the subsequent process.

2. The method for improving the interlayer bonding strength of corrugated cardboard according to claim 1, characterized in that: The mass concentration of the mixed slurry mentioned in step one is measured in the range of 2.0%-4.0%, the freeness is measured in the range of 30°SR-55°SR, and the wet weight is measured in the range of 3.0g-8.0g; for high-grade slurry, the mass concentration is ≥3.0%, the freeness is ≥45°SR, and the wet weight is ≥6.0g; for medium-grade slurry, the mass concentration is 2.5%-3.0%, the freeness is 35°SR-45°SR, and the wet weight is 4.0g-6.0g; and for low-grade slurry, the mass concentration is 2.0%-2.5%, the freeness is 30°SR-35°SR, and the wet weight is 3.0g-4.0g.

3. The method for improving the interlayer bonding strength of corrugated cardboard according to claim 1, characterized in that: In step two, the amount of cationic polyacrylamide added is 0.02‰-0.05‰ relative to the oven-dry weight of the slurry, and the amount of bentonite added is 0.5‰-1.0‰ relative to the oven-dry weight of the slurry. After thickening, the slurry concentration fluctuation deviation is controlled within ±0.05%.

4. The method for improving the interlayer bonding strength of cardboard according to claim 1, characterized in that: The power density of the ultrasonic micro-dispersion treatment in step three is 0.3 W / cm². 3 -0.5W / cm 3 The ultrasonic treatment time is 15 minutes for high-grade pulp, 12 minutes for medium-grade pulp, and 10 minutes for low-grade pulp; the basis weight deviation of the formed single-layer wet paper web is controlled within ±3g / m². 2 Within.

5. The method for improving the interlayer bonding strength of cardboard according to claim 1, characterized in that: In step four, the angle between the low-pressure airflow and the paper surface is 45°-60°, the depth of the micro-pit structure is 5μm-10μm, and the distribution density is 80 pits / cm². 2 -100 pieces / cm 2 .

6. The method for improving the interlayer bonding strength of corrugated cardboard according to claim 1, characterized in that: The modified starch solution mentioned in step five is prepared from corn starch, bio-enzyme, and hydroxypropyl methylcellulose ether. The amount of bio-enzyme added is 0.5%-1.0% of the dry weight of starch, and the amount of hydroxypropyl methylcellulose ether added is 0.3%-0.6% of the dry weight of starch. The droplet size of the atomized spray is 20μm-50μm, and the spray coverage is 100%.

7. The method for improving the interlayer bonding strength of cardboard according to claim 1, characterized in that: In step six, the rolling pressure of the composite roller is 0.3MPa-0.5MPa, and the synchronization deviation between the roller speed and the forming screen speed is controlled within ±0.5m / min.

8. The method for improving the interlayer bonding strength of cardboard according to claim 1, characterized in that: The low vacuum section in step seven is for a wet paper width dryness of 12%-16% and a vacuum degree of -0.02MPa to -0.04MPa; the medium vacuum section is for a wet paper width dryness of 16%-20% and a vacuum degree of -0.04MPa to -0.06MPa; the high vacuum section is for a wet paper width dryness of 20%-24% and a vacuum degree of -0.06MPa to -0.08MPa; the vacuum degree adjustment is a smooth transition.

9. The method for improving the interlayer bonding strength of corrugated cardboard according to claim 1, characterized in that: The low-pressure setting described in step eight uses a setting roller with a setting roller pressure of 0.1MPa-0.2MPa and a setting time of 5s-8s. There is no delamination or tearing during the wet paper web peeling process.

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