Method for improving the retention of white card and white card

Abstract

The present application relates to the technical field of papermaking, in particular to a method for improving the retention rate of white cardboard and white cardboard. The following steps are combined: a high-concentration grinding step: the mechanical pulp used for white cardboard production is treated by high-concentration grinding to reduce the generation of fine fibers and enhance the fiber bonding capacity; a charge adjusting step: a charge adjusting agent such as aluminum sulfate is added to the pulp to neutralize anionic impurities and ensure the efficiency of chemicals; a micro-particle flocculation step: a multi-component micro-particle retention system composed of cationic starch, high molecular weight polymer flocculants and silica sol is added to the charge-adjusted pulp to efficiently flocculate and retain fine components. Through the synergistic effect of source physical control, process chemical environment optimization and terminal efficient capture, the present application can improve the comprehensive retention rate of white cardboard to more than 88%, the core layer retention rate to more than 90%, significantly reduce the production cost, improve the paper quality and the running stability of the paper machine.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a method for improving the retention rate of white cardboard and white cardboard. Background Technology

[0002] White cardboard, as a high-end packaging material, is widely used in packaging boxes for cosmetics, pharmaceuticals, and electronic products, as well as in printed materials such as business cards, certificates, and invitations. Its market demand is huge, and quality requirements are becoming increasingly stringent. In a fiercely competitive market, paper manufacturers face the dual pressure of continuously reducing production costs and improving product quality and stability. Among these factors, wet end retention rate is one of the key indicators for measuring the resource utilization efficiency and system operating status of the papermaking process.

[0003] In the production process of white cardboard, the core step, and also the main point of raw material loss, is the conveying of pulp from the headbox to the forming wire for dewatering and forming. Besides fibers, the pulp contains a large amount of filler (calcium carbonate) added to impart specific properties to the paper (opacity, whiteness, smoothness), as well as fine fibers generated during the refining process. These fine components, due to their small size, large specific surface area, and weak binding force with fibers, easily pass through the forming wire during rapid dewatering and are lost with the white water. This phenomenon leads to several adverse effects: First, there are direct economic losses. The loss of fine components means a decrease in the utilization rate of raw materials (wood pulp and fillers), an increase in raw material consumption per ton of paper, and a direct increase in production costs. To compensate for the loss, companies have to add excessive amounts of fillers and chemicals, further exacerbating cost pressures.

[0004] Secondly, there is the issue of product quality fluctuations. The uniform distribution of fine particles within the paper sheet is crucial to the paper's physical properties, such as density, burst strength, and interlayer bonding strength. Excessive loss can lead to a loose paper structure, reduced physical strength, and potentially increased surface-to-surface differences, affecting the final product's quality stability and printability.

[0005] Secondly, there is a negative impact on the production system. Lost microparticles enter the white water recycling system, leading to increased white water concentration and increasing the load on white water recovery and treatment. High-concentration white water easily produces sediment in pipes, storage towers, and other equipment, fostering microbial growth and forming "anionic waste." This anionic waste neutralizes and consumes subsequently added cationic functional chemicals (retention aids, sizing agents, dry strength agents), significantly reducing their efficiency and resulting in ineffective waste. Simultaneously, system instability can easily trigger production accidents such as paper machine breakage, severely impacting production efficiency.

[0006] To address these issues, existing technologies typically employ various methods. The most basic is a closed-loop white water recycling system, which reuses white water rich in fine particles for pulp dilution. However, this only alleviates losses to a certain extent and cannot fundamentally solve the problem, potentially leading to the accumulation of contaminants in the system and deteriorating the operating environment. A more effective method is to add chemical retention aids at the wet end. Traditional retention aid systems, such as single cationic polyacrylamide (CPAM), flocculate fine particles through a "bridging" effect. However, their efficiency drops significantly in systems with high anionic waste content. In recent years, microparticle retention aid systems ("cationic starch + PAM + silica sol") have become more widely used. They improve retention through a more complex flocculation mechanism, but their performance is still limited by the original state of the pulp and the chemical environment. Furthermore, traditional pulping processes, especially low-to-medium concentration refining methods, while increasing pulp freeness, easily cut fibers, generating a large number of fine fibers that are unfavorable for retention, thus increasing the difficulty of subsequent retention work from the source.

[0007] In summary, existing technologies often focus on optimizing single steps, lacking a systematic and synergistic solution encompassing raw material processing, chemical environment control, and retention system execution. This makes it difficult to achieve low-cost, high-efficiency, and high-stability production goals while meeting the high-quality requirements of white cardboard. Therefore, developing a technological solution that can systematically address these issues has significant practical and commercial value. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method to improve the retention rate of white cardboard. By organically combining front-end physical treatment, mid-end chemical environment optimization and back-end high-efficiency flocculation technology, this invention aims to systematically solve the problems of high raw material costs, unstable product quality and low paper machine operating efficiency caused by the loss of fine fibers and fillers.

[0009] Another objective of this invention is to provide a white cardboard that significantly reduces fiber and filler consumption per ton of paper by greatly improving retention rate, thereby directly reducing raw material costs.

[0010] This invention is achieved using the following technical solution: The method for improving the retention rate of white cardboard includes the following steps in synergistic combination: a) High-consistency pulping step: The mechanical pulp used in the production of white cardboard is subjected to high-consistency pulping treatment with a pulping concentration of 30%-35%; b) Charge conditioning step: Add charge conditioner to the subsequent slurry to stabilize the cation requirement of the slurry within the range of -200 μeq / L to 200 μeq / L; c) Microparticle flocculation step: A multi-component microparticle retention aid system is added to the charge-regulated slurry, the retention aid system comprising a cationic polymer, a high molecular weight polymer flocculant and microparticles, to flocculate and retain fine components.

[0011] Specifically, the high-concentration pulping step optimizes the pulp from a physical source. Traditional pulping methods use lower concentrations, where fibers are primarily subjected to shearing forces between the pulping discs, easily breaking them and generating numerous fine fibers. This invention, however, uses a high concentration of 30%-35% for pulping. At this concentration, the pulp is semi-solid, and the inter-fiber interaction forces (friction, compression, and kneading) are far greater than the shearing action of the pulping discs. This "fiber-to-fiber" method effectively promotes fiber bifurcation (i.e., the formation of fine bifurcations on the fiber surface), increasing the fiber's specific surface area and bonding capacity, while maximizing the preservation of the original fiber length and strength, significantly reducing the generation of fragmented and fine fibers. This is equivalent to reducing the difficult elements that need to be "retained" at the source and enhancing the fiber web's own mechanical retention capacity for fine components, creating a highly favorable physical basis for subsequent chemical retention steps.

[0012] The charge conditioning step involves precise pretreatment of the pulp's chemical environment. The wet end of papermaking inevitably contains a large amount of negatively charged soluble and colloidal substances (collectively referred to as "anionic waste"). These substances preferentially react with subsequently added positively charged additives (such as cationic starch and CPAM), resulting in ineffective consumption of the additives. This invention, by adding a charge conditioner, actively and precisely controls the system's cation demand (PCD, i.e., the amount of cationic charge required to neutralize all negative charges in the system) within a narrow, near-neutral range (-200 to +200 μeq / L). This effectively "clears the way" for subsequent chemicals, ensuring that various cationic chemicals can efficiently act on the target materials (fibers and fillers) instead of being wasted by anionic waste, thereby guaranteeing the stability and economy of the entire chemical system.

[0013] The microparticle flocculation step is the final step in achieving high-efficiency retention. A multi-component microparticle retention aid system is introduced into the slurry after physical optimization and chemical pretreatment. This system forms fine and robust flocs through the synergistic effect of various chemicals. First, cationic polymers (such as cationic starch) adsorb onto the negatively charged fiber and filler surfaces, performing initial charge neutralization and flocculation. Then, high molecular weight polymer flocculants (such as PAM) bridge these initial flocs into larger flocs. Finally, microparticles with opposite charges (such as silica sol) are added and adsorb onto the floc surface through electrostatic attraction, making the floc structure more compact, increasing shear stability, and simultaneously increasing the porosity between fibers, thus improving water filtration capacity.

[0014] These three steps are interconnected and work synergistically: high-concentration pulping reduces the burden at the source, charge regulation creates the best working environment for chemicals, and the microparticle system efficiently completes the final capture task.

[0015] Preferably, the charge control agent is aluminum sulfate. Aluminum sulfate is a low-cost and highly effective charge control agent. When its addition amount is controlled at 0-10 kg / ton of slurry, and the addition amount of aluminum sulfate is greater than 0 and not more than 10 kg / ton of slurry, and the slurry pH is under acidic conditions of 4.4-4.8, aluminum sulfate will hydrolyze to form a polynuclear aluminum compound. This compound has a high cationic charge density, which can strongly adsorb and neutralize anionic waste in the system, and efficiently stabilize the PCD value within the target range. The effect is particularly good when the PCD is stabilized at around -150 ueq / L, which proves the necessity and effectiveness of precise control.

[0016] In step c), the cationic polymer is cationic starch, the high molecular weight polymer flocculant is polyacrylamide, and the microparticles are silica sol.

[0017] The amount of cationic starch used is 5-20 kg / ton of slurry.

[0018] The amount of polyacrylamide added to different pulp layers of white cardboard is: 300-400 ppm for the top layer, 300-450 ppm for the core layer, and 100-250 ppm for the bottom layer.

[0019] The amount of silica sol used is 2-8 kg / ton of slurry.

[0020] The white cardboard has a three-layer structure, including a surface layer, a core layer, and a bottom layer; the high-consistency pulping treatment in step a) is mainly applied to the mechanical pulp used in the core layer.

[0021] White cardboard typically has a three-layer structure (face, core, and bottom). The core layer, to increase stiffness and thickness, usually uses a large amount of mechanical pulp. Mechanical pulp, having undergone mechanical processing, already has a high content of fine components, making its preservation both crucial and challenging. Therefore, applying the high-concentration refining treatment in step a) primarily to the mechanical pulp used in the core layer is an optimization measure tailored to the structural characteristics of white cardboard, precisely addressing the core issue.

[0022] By implementing the method of this invention, a comprehensive retention rate of over 88% can be achieved for white cardboard, which is a very high industry standard. In particular, the core layer retention rate can reach over 90%, which is crucial for improving the physical properties of the paper and reducing costs. Simultaneously, a high retention rate means that more filler is retained in the paper sheet, allowing the ash content of the finished paper to be stably increased to 24%-26%, which significantly reduces the consumption of fiber raw materials without sacrificing or even improving physical properties. Furthermore, this invention can also achieve an interlayer bonding strength of ≥150 J / m² in the finished paper.2 The invention achieves a series of performance improvements, including folding endurance of ≥20 cycles and flatness grade ≤2. These technical indicators collectively demonstrate the significant advancement and practical value of the method described in this invention.

[0023] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention is the first to organically combine physical source control (high-concentration pulping), chemical environment optimization (charge regulation), and efficient chemical execution (microparticle flocculation) to form a complete synergistic effect system. This systematic solution overcomes the limitations of single-point optimization in existing technologies, and significantly improves the overall retention rate of fine particles to over 88%, with technical effects far exceeding the simple superposition of existing technologies.

[0024] (2) By significantly improving the retention rate, the consumption of fiber and filler per ton of paper is significantly reduced, directly lowering raw material costs. Simultaneously, the charge regulation step improves the utilization efficiency of chemicals, reduces the ineffective consumption of chemicals such as retention aids, and further reduces chemical costs. It is estimated that raw material costs can be reduced by 2%, resulting in considerable economic benefits.

[0025] (3) High retention rate means that the load on the white water system is greatly reduced, the system cleanliness is improved, and the occurrence of sediment and paper breakage is reduced, thereby improving the operating stability and production efficiency of the paper machine. In addition, the optimized flocculation structure improves the filtration performance of the pulp and has the potential to increase the paper machine speed and output.

[0026] (4) While improving retention rate and reducing cost, this invention can also improve the physical properties of paper, such as interlayer bonding strength, folding endurance, and flatness, making the product quality more stable and excellent, thereby enhancing the product's competitiveness in the market.

[0027] (5) By reducing the consumption of raw materials and chemicals, the present invention reduces the energy and material consumption per unit product, reduces the load on wastewater treatment and carbon emissions, and conforms to the industry's general direction of green manufacturing and sustainable development. Detailed Implementation

[0028] The technical solution 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.

[0029] This invention provides a method for improving the retention rate of fine components in white cardboard production. The method synergistically combines the following steps: a) a high-consistency refining step: subjecting the mechanical pulp used in white cardboard production to a high-consistency refining process with a pulping concentration of 30%-35%; b) a charge conditioning step: adding a charge conditioner to the subsequent pulp to stably control the cationic demand (PCD) value of the pulp within the range of -200 μeq / L to 200 μeq / L; c) a microparticle flocculation step: adding a multi-component microparticle retention aid system to the charge-conditioned pulp, the retention aid system comprising a cationic polymer, a high molecular weight polymer flocculant, and microparticles to flocculate and retain fine components.

[0030] In this invention, the high-consistency pulping step involves treating the mechanical pulp used in white cardboard production, preferably the bleached chemithermomechanical pulp used in the core layer pulp, with a high-consistency pulping concentration of 30%-35%. This step promotes fiber fibrillation by enhancing the friction, compression, and kneading action between the pulps, while significantly reducing fiber cutting, thereby reducing the generation of fine fibers at the source. This physical pretreatment method not only preserves the length and strength of the fibers but also strengthens the mechanical retention of the fiber web, creating a highly favorable physical basis for subsequent chemical retention steps.

[0031] In this invention, the charge adjustment step involves adding a charge regulator to stably control the cation demand (PCD) value of the slurry within a preferred range of -200 μeq / L to 200 μeq / L. Preferably, the charge regulator is aluminum sulfate, and its addition amount is preferably 0-10 kg / ton of slurry. More preferably, aluminum sulfate is added when the slurry pH is 4.4-4.8. The resulting polynuclear aluminum compound with a high cation charge density can strongly adsorb and neutralize anionic waste in the system, ensuring that subsequent cationic chemicals (such as retention aids) can act efficiently on the target fibers and fillers, avoiding ineffective consumption, thereby ensuring the stable operation of the entire wet-end chemical system.

[0032] In this invention, the microparticle flocculation step involves constructing a multi-component retention and filtration aid system in the slurry that has undergone the aforementioned physical optimization and chemical pretreatment. Preferably, this system consists of "cationic starch + polyacrylamide (PAM) + silica sol".

[0033] The cationic starch, as a cationic polymer, is preferably used at a dosage of 5-20 kg / ton of slurry.

[0034] The polyacrylamide (PAM) used as a high molecular weight polymer flocculant is finely controlled according to the different pulp layers of the white cardboard, preferably: 300-400 ppm for the top layer, 300-450 ppm for the core layer, and 100-250 ppm for the bottom layer. In this invention, commercially available high-performance retention aids, such as solid retention aids from the Askemo brand, can be used.

[0035] The silica sol, as microparticles, is preferably used at a dosage of 2-8 kg / ton of slurry.

[0036] This microparticle system promotes the firm aggregation of fine fibers and fillers on the fiber surface through the initial flocculation of cationic starch, the reinforcing bridging of PAM, and the refining and strengthening effect of silica sol on flocs, thereby significantly improving the retention rate of fine components and improving the filtration performance of the slurry.

[0037] In a preferred embodiment of the present invention, the method is applied to the production of three-layer white cardboard, which includes a top layer, a core layer, and a bottom layer. The high-consistency refining step is primarily applied to the mechanical pulp used in the core layer, a key step in precisely addressing the retention rate issue.

[0038] The method for improving the retention rate of white cardboard provided by this invention organically combines front-end physical treatment (high-consistency pulping), mid-end chemical environment optimization (charge regulation), and back-end high-efficiency flocculation technology (microparticle flocculation), achieving a synergistic effect of "source burden reduction - environmental protection - high-efficiency capture". This method requires no modification to existing paper machine hardware, is low-cost, and easy to implement. While significantly improving the retention rate and reducing production costs, it also improves paper quality and enhances production stability.

[0039] To further illustrate the present invention, detailed descriptions are provided below through the following embodiments and comparative examples. The raw materials used in the following embodiments of the present invention are all commercially available products or prepared according to conventional methods in the art. Unless otherwise stated, all embodiments and comparative examples are based on the white cardboard production baseline process described below, differing only in specified key parameters.

[0040] To better understand the implementation of this invention, a typical white cardboard production process based on the embodiments and comparative examples is first introduced. Unless otherwise specifically stated in the embodiments or comparative examples, the following process flow and basic parameters are followed. The core improvements of this invention are mainly reflected in specific steps of this process.

[0041] The implementation of this invention requires no changes to existing paper machine hardware, only optimization of the manufacturing process, thus resulting in lower costs and ease of implementation on existing production lines.

[0042] The following is the technical solution of the present invention: 1. Main process flow: Pulping → Grinding → Pulping → Dilution → Web forming → Pressing → Pre-drying → Surface sizing → Post-drying → Hard calendering → Multiple coatings → Soft calendering → Curling → Rewinding → Slitting → Warehousing.

[0043] 2. Detailed description of each step: (1) Pulping: Use the white water separated during the wire mesh forming process as pulping water, and control the pulp concentration to 5%.

[0044] (2) Pulping: The coarse pulp is passed through a pressure screen to remove large particles of impurities and then enters a slag remover for secondary purification to reduce subsequent grinding losses. Subsequently, the pulp enters a thickening tank to adjust the pulp concentration, and then passes through a conical mill for grinding.

[0045] Model of softwood / broadwood pulp refiner: 3XRF-4; Specific energy consumption: 350kWh / t (softwood pulp) / 160kWh / t (broadwood pulp); Freeness variation: 700-750ml→300ml (softwood pulp) / 625-675ml→350ml (broadwood pulp).

[0046] Model of chemical pulp refiner: 2XRF-4; Specific energy consumption: 70kWh / t; Freeness change: 500ml→425ml.

[0047] One of the core steps of this invention is to grind the mechanical pulp (chemimechanical pulp) at a high concentration of 30-35% in this step.

[0048] (3) Pulp preparation: Slurry mix ratio: The surface layer uses 25% bleached softwood chemical pulp (NBKP) + 75% bleached hardwood chemical pulp (LBKP); the bottom layer uses 15% NBKP + 85% LBKP; the core layer uses 64% bleached thermomechanical chemical pulp (BCTMP) + 36% bleached chemical pulp (BK).

[0049] Chemical additions: After mixing the slurry according to the specified ratio, add a portion of cationic starch (concentration 1.0-1.5%). Add AKD sizing agent (core layer dosage 4.5-7 kg / t), dry strength agent (5-20 kg / t), and filler (40-80 kg / t) according to the slurry requirements.

[0050] The second core step of this invention is to dynamically adjust the amount of aluminum sulfate used in this step so that the PCD value of the slurry is stabilized within the target range of -200 to 200ueq / L.

[0051] (4) Dilution: The surface layer and bottom layer were diluted from (3.2±0.2)% to (0.3±0.05)% after mixing; the core layer was diluted from (3.7±0.2)% to (1.0±0.2)% after mixing.

[0052] Microparticle system construction: The third core step of this invention is completed in this stage. The remaining cationic starch, AKD, and filler (GCC) are added sequentially before the three-layer slurry pump. A high molecular weight polymer flocculant (such as Askemo solid retention aid, CPAM) is added after the slurry pump, and microparticles (such as silica sol) are added after the pressure screen.

[0053] (5) Forming on the wire: The pulp enters the three-layer headbox, and after being distributed, it is dewatered on the forming wire. The three layers of pulp, namely the face, core and bottom, are sequentially combined to form the base paper, which then enters the press section.

[0054] (6) Pressing: The base paper is successively passed through two boot presses and one gloss press to dehydrate to a dryness of 45-48%.

[0055] (7) Pre-drying: The temperature of the drying cylinder is steadily increased from 40 / 50℃ to 130 / 140℃, so that the dryness of the base paper is increased to 93-94%.

[0056] (8) Surface sizing: Enzymatically converted cassava starch was used as the surface sizing agent, with a sizing amount of 4.3 ± 0.5 g / m² on the front side. 2 The amount of adhesive applied on the reverse side is 2.5 ± 0.5 g / m². 2 .

[0057] (9) Drying: Temperature 100-120℃ to fully mature the sizing agent.

[0058] (10) Hard calendering: Temperature 110-130℃, pressure 5-20kN / m, to modify the paper surface and reduce roughness.

[0059] (11) Coating: Perform pre-coating sequentially (11.5-13 g / m²). 2 ), intermediate coat (10.5g / m 2 Topcoat (14-15g / m²) 2 ), back coating (15g / m 2 ).

[0060] (12) Soft calendering: Soft calendering is performed on the front and back sides respectively to improve gloss, smoothness and reduce the difference between the two sides. Front side temperature 110-130℃, pressure 15-25kN / m; back side temperature ≤75℃, pressure 0kN / m.

[0061] (13) Curling, rewinding, and slitting: Cutting into different specifications according to customer needs.

[0062] The following is a description of some of the raw materials used in the examples and comparative examples: Bleached sulfate softwood pulp, purchased from Arauco Group; Bleached sulfate hardwood pulp, purchased from Asia Pulp & Paper Limited; Cationic starch, produced by Shandong Bohui Co., Ltd. AKD, 374NP, purchased from Kemira (Shanghai) Management Co., Ltd.; Dry strength agent, CH-1406, purchased from Nantong Arakawa Chemical Industry Co., Ltd.; Silica sol, NCC®998, purchased from Zhejiang Jiuben Environmental Protection Technology Co., Ltd. Solid retention aid, AF9510 ES, purchased from Yingde Askemo Chemical Co., Ltd. Liquid filter aid, AF 4820, purchased from Yingde Askemo Chemical Co., Ltd. Aluminum sulfate, purchased from Regit Chemical Co., Ltd. Enzyme, BUZYME 2583, purchased from Buckman Laboratories Chemicals (Shanghai) Co., Ltd.; Cassava starch was purchased from SWI Ltd., Thailand.

[0063] The testing method is as follows: Ash content / retention rate of finished paper (%): Tested according to GB / T 742-2018; Interlayer bond strength (J / m) 2 (The test shall be conducted in accordance with GB / T 26203-2023;) Flexural endurance (cycles): Tested according to GB / T 2679.5-1995; Smoothness (Grade): Take a paper sample with an undamaged coating and observe the surface smoothness with a magnifying glass; Shine a flashlight at a zero angle onto the paper, or shine it on multiple sheets at the same time, and compare the degree of unevenness on the paper surface.

[0064] Example 1: This embodiment fully adopts the technical solution of the present invention, that is, the synergistic application of high-concentration pulping, charge adjustment and microparticle flocculation system.

[0065] The process parameters are as follows: High-consistency mechanical pulp: 33% Aluminum sulfate dosage: 10 kg / ton slurry Retention aid (PAM) dosage: Top coat 300 ppm, core coat 300 ppm, bottom coat 200 ppm Filter aid dosage: 350 ppm Cationic starch dosage: 8 kg / ton slurry Silica sol dosage: 6 kg / ton of slurry.

[0066] Example 2: This embodiment also fully adopts the technical solution of the present invention, but some process parameters are adjusted.

[0067] The process parameters are as follows: Mechanical pulp high-consistency pulping concentration: 30% Aluminum sulfate dosage: 5 kg / ton slurry Retention aid (PAM) dosage: Top coat 400 ppm, core coat 450 ppm, bottom coat 250 ppm Filter aid dosage: 450 ppm Cationic starch dosage: 15 kg / ton slurry Silica sol dosage: 7 kg / ton of slurry.

[0068] Example 3: This embodiment also fully adopts the technical solution of the present invention, but some process parameters are adjusted.

[0069] The process parameters are as follows: Mechanical pulp high-consistency pulping concentration: 35% Aluminum sulfate dosage: 1.5 kg / ton slurry Retention aid (PAM) dosage: Top coat 350 ppm, core coat 400 ppm, bottom coat 150 ppm Filter aid dosage: 400 ppm Cationic starch dosage: 10 kg / ton slurry Silica sol dosage: 4 kg / ton of slurry.

[0070] Comparative Example 1: The process parameters are as follows: High-consistency mechanical pulp: 33% Aluminum sulfate dosage: 10 kg / ton slurry Retention aid (PAM) dosage: 0 ppm for top coat, core, and bottom coat. Filter aid dosage: 0 ppm Cationic starch dosage: 8 kg / ton slurry Silica sol dosage: 6 kg / ton of slurry.

[0071] Comparative Example 2: The process parameters are as follows: High-consistency mechanical pulp: 33% Aluminum sulfate dosage: 0 kg / ton slurry Retention aid (PAM) dosage: Top coat 300 ppm, core coat 300 ppm, bottom coat 200 ppm Filter aid dosage: 350 ppm Cationic starch dosage: 8 kg / ton slurry Silica sol dosage: 6 kg / ton of slurry.

[0072] Comparative Example 3: The process parameters are as follows: Mechanical pulping concentration: 20% (low-consistency pulping) Aluminum sulfate dosage: 10 kg / ton slurry Retention aid (PAM) dosage: Top coat 300 ppm, core coat 300 ppm, bottom coat 200 ppm Filter aid dosage: 350 ppm Cationic starch dosage: 8 kg / ton slurry Silica sol dosage: 6 kg / ton of slurry.

[0073] The test data for Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0074] Table 1: Test data of Examples 1-3 and Comparative Examples 1-3

[0075] As shown in Table 1, compared with Example 1 and Comparative Example 1, both used high-consistency pulp and aluminum sulfate, but Comparative Example 1 lacked retention aids and filter aids, resulting in significantly lower retention rates and paper ash content compared to Example 1. This demonstrates that the microparticle retention aid system is an indispensable part of achieving high retention rates. Comparing Example 1 and Comparative Example 2, both used high-consistency pulp and a complete set of retention and filter aids, but Comparative Example 2 did not add aluminum sulfate for charge adjustment, resulting in significantly lower retention rates and ash content compared to Example 1. This indicates that without effective charge pretreatment, the efficiency of the retention aid system will be greatly reduced, demonstrating the criticality of the charge adjustment step. Comparing Example 1 and Comparative Example 3, both used a complete set of chemicals, but Comparative Example 3 used low-consistency pulp, resulting in significantly lower retention rates and ash content compared to Example 1. This strongly demonstrates that high-consistency pulp improves pulp properties and reduces fine particles from a physical source, creating a crucial prerequisite for subsequent chemical retention aids. The results of Example 1 are not a simple linear summation of the effects of the comparative examples. The absence of any single key step results in low retention rates and paper ash content. However, when all three steps work synergistically, the core layer retention rate jumps to 91%, and the paper ash content reaches 24.5%. Simultaneously, various physical properties such as interlayer bonding strength, folding endurance, and flatness all experience a qualitative leap. This dramatic performance improvement is unpredictable by those skilled in the art through simple combinations of existing technologies, demonstrating the inventiveness of this invention. Examples 1, 2, and 3 employed different parameter combinations, and the results show that they all achieved significantly superior performance compared to the comparative examples, with all indicators remaining at very high levels. This proves that the technical solution of this invention does not rely on a single, demanding parameter point, but rather can stably demonstrate its advantages within a reasonable process window, exhibiting good industrial applicability and robustness.

Claims

1. A method of improving the retention of a white paperboard, characterized by, The method combines the following steps in a coordinated manner: a) High-consistency pulping step: The mechanical pulp used in the production of white cardboard is subjected to high-consistency pulping treatment with a pulping concentration of 30%-35%; b) Charge conditioning step: Add charge conditioner to the subsequent slurry to stabilize the cation requirement of the slurry within the range of -200 μeq / L to 200 μeq / L; c) Microparticle flocculation step: A multi-component microparticle retention aid system is added to the charge-regulated slurry, the retention aid system comprising a cationic polymer, a high molecular weight polymer flocculant and microparticles, to flocculate and retain fine components.

2. The method of improving the retention of white paper according to claim 1, characterized in that, The charge regulator in step b) is aluminum sulfate.

3. The method of improving the retention of white paper according to claim 2, characterized in that, The amount of aluminum sulfate added is greater than 0 and not more than 10 kg / ton of slurry, and the pH value of the slurry is controlled within the range of 4.4-4.8 when aluminum sulfate is added.

4. The method of improving the retention of white paper according to claim 1, characterized in that, In step c), the cationic polymer is cationic starch, the high molecular weight polymer flocculant is polyacrylamide, and the microparticles are silica sol.

5. The method of improving the retention of white paper according to claim 4, characterized in that, The amount of cationic starch used is 5-20 kg / ton of slurry.

6. The method for improving the retention rate of white cardboard according to claim 4, characterized in that, The amount of polyacrylamide added to different pulp layers of white cardboard is: 300-400 ppm for the top layer, 300-450 ppm for the core layer, and 100-250 ppm for the bottom layer.

7. The method for improving the retention rate of white cardboard according to claim 4, characterized in that, The amount of silica sol used is 2-8 kg / ton of slurry.

8. The method for improving the retention rate of white cardboard according to claim 1, characterized in that, The white cardboard has a three-layer structure, including a surface layer, a core layer, and a bottom layer; the high-consistency pulping treatment in step a) is applied to the mechanical pulp used in the core layer.

9. A type of white cardstock, characterized in that, It is prepared by any of the methods for improving the retention rate of white cardboard as described in claims 1-8 above.

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