Process method for improving cleanliness of papermaking coating system

Abstract

The invention relates to the technical field of papermaking, in particular to a process method for improving cleanliness of a papermaking coating system. The method aims at solving the problems that in the prior art, coating crust is difficult to remove, and product quality defects are caused by low impurity filtering efficiency. The method comprises the following steps: a) a system cleaning step: before the coating machine works, carrying out circulating cleaning on a coating system by using string washing water containing a cleaning agent, and controlling the temperature of the string washing water to be 50-60 DEG C and the pH value to be 11-13 in the cleaning process; and b) an automatic filtering step: when the coating machine works, filtering the coating by adopting an automatic deslagging and cleaning filter system, and automatically triggering a deslagging and cleaning program by monitoring a pressure difference value of an inlet and an outlet of a filter or according to a preset time interval. According to the method, the smoothness and glossiness of the coated white board paper can be greatly improved, the production efficiency and the product percent of pass are improved, and remarkable economic and environment-friendly benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a process method for improving the cleanliness of papermaking coating systems. Background Technology

[0002] In the modern papermaking industry, coated whiteboard paper, as a high-end packaging material, directly affects the market value and competitiveness of the final product due to its surface quality, such as smoothness, gloss, and printability. The coating process is the core link that determines the final quality of coated whiteboard paper, and the cleanliness of the coating material used is a prerequisite for ensuring the stable operation of the coating process and excellent product quality.

[0003] The coatings used for whiteboard paper are typically complex suspensions, primarily composed of pigments such as calcium carbonate and kaolin, as well as adhesives like latex. In continuous production processes, the coating flows and is stored for extended periods in pipelines, storage tanks, and the coating machine's circulation system. Due to the chemical and physical properties of the coating, its components tend to aggregate and solidify on the inner walls of the equipment, especially in areas with slower flow rates or temperature variations, forming hard crusts or lumps.

[0004] Once these crusts or clumps detach during production, they enter the coating supply system as impurities. These impurities cause a sharp increase in the coating's residue levels. If not effectively filtered, they are carried along with the coating to the coating head, ultimately causing serious quality defects on the paper surface, such as "dossier marks," "streaks," "spots," and "holes." These defects not only lead to product downgrading or scrapping, increasing the defect rate and production costs, but also seriously affect the continuity and stability of production.

[0005] To solve the above problems, existing technologies typically employ two methods: Chemical cleaning: During shutdowns or refueling, chemical cleaning agents are used to circulate and clean the coating system (series cleaning) to dissolve and peel off the coating skin from the inner walls of the equipment. However, existing cleaning processes have significant shortcomings. First, the selection of cleaning agents is often arbitrary, without optimization for the complex components in the coating such as calcium carbonate, kaolin, and latex, resulting in poor cleaning effects. Second, the control of cleaning process parameters is rudimentary; often, only a certain cleaning agent is used, ignoring the synergistic effect between key process parameters such as cleaning temperature and pH value and the performance of the cleaning agent. This "one-size-fits-all" cleaning method cannot thoroughly remove stubborn coating skin, has low cleaning efficiency, and may even cause corrosion to the equipment or affect the rheological properties of subsequent coatings due to inappropriate pH values ​​or temperatures.

[0006] Physical filtration: Filters are typically installed before the paint is delivered to the coating head to intercept impurities. However, traditional processes generally rely on manual, periodic disassembly and cleaning of these filters. This method has several drawbacks: Inefficient and untimely: Manual cleaning relies on the experience and sense of responsibility of the operators, and cannot be cleaned in a timely manner according to the actual blockage of the filter. This often leads to excessive accumulation of impurities in the filter, increasing the risk of the filter being "punctured".

[0007] Poor stability: The cleaning standards and effects vary among different operators, and there is a great deal of human influence. It is difficult to ensure that each cleaning is thorough and meets the standards, resulting in large fluctuations in the cleanliness of the coating.

[0008] Increased risk of downtime: When the filter is severely clogged, an emergency shutdown may be required, disrupting the production schedule and reducing the overall operating efficiency of the paper machine.

[0009] In summary, existing technologies lack a systematic solution that combines efficient chemical cleaning with intelligent physical filtration to address the cleanliness issue of coating systems. There is an urgent need for an innovative process technology to effectively remove coating skins and continuously and efficiently intercept coating impurities, thereby fundamentally improving the cleanliness of coating systems and ensuring product quality and production efficiency. Summary of the Invention

[0010] In view of the shortcomings of the prior art, the purpose of this invention is to provide a process method to improve the cleanliness of paper coating systems, so as to achieve efficient and thorough removal of stubborn skins composed of calcium carbonate, kaolin, latex and other materials in the coating system, while avoiding negative impacts on equipment and coating performance.

[0011] This invention is achieved using the following technical solution: The aforementioned process for improving the cleanliness of a paper coating system, applied to the production of coated whiteboard paper, includes the following steps: a) System cleaning step: The coating system is cleaned before or during non-operation of the coating machine. This step includes: The piping and / or tanks of the coating system are circulated and cleaned using a flushing solution containing cleaning agents; and... During the circulating cleaning process, the water temperature of the washing water is controlled at 50-60℃, and its pH value is controlled at 11-13; b) Automatic filtration step: During the operation of the coating machine, an automatic slag removal and filter cleaning system is used to continuously or intermittently filter the coating. This step includes: By monitoring the pressure difference between the inlet and outlet of the filter, or according to a preset time interval, the filter can be automatically triggered and started to remove impurities trapped in it.

[0012] Step a) "System Cleaning Step" aims to remove stubborn scale from its source. This invention has found that simply using a cleaning agent or simply controlling temperature / pH has limited effectiveness. The key lies in the synergistic effect of these three factors: the specific cleaning agent is fully activated at a temperature of 50-60°C, while the strongly alkaline environment of 11-13 effectively saponifies and disperses organic components such as latex in the paint, and works synergistically with the acidic cleaning agent (or its decomposition products) to remove inorganic pigment scale such as calcium carbonate. This combination of "cleaning agent + temperature + pH" constitutes the key technology for highly efficient chemical cleaning, enabling rapid decomposition and peeling of stubborn scale, far superior to the single-treatment methods of existing technologies.

[0013] Step b) "Automatic Filtration Step" aims to solve the problem of impurities continuously generated during the production process. This invention abandons unreliable manual cleaning and adopts an automated system. This system is automatically triggered by two logics: "Pressure Differential Monitoring" is a responsive logic; when the filter becomes clogged due to impurity accumulation and the inlet-outlet pressure difference increases to a set value, the system immediately responds to perform slag discharge and cleaning, ensuring smooth coating flow; "Preset Time Interval" is a preventative logic; even if the pressure difference does not reach the threshold, the system will periodically perform self-cleaning to prevent the slow accumulation and caking of impurities. The combination of these two logics ensures that the filtration system is always in a highly efficient and clean working state, achieving intelligent and continuous management of impurities.

[0014] As a preferred embodiment, comparative experiments revealed that the cleaning agent AMAZON1797 exhibits the best decomposition and dissolution effects on the paint skin containing calcium carbonate, kaolin, and latex, which is the target of this invention. Therefore, when implementing step a), AMAZON1797 is preferentially selected as the cleaning agent to achieve the best cleaning effect.

[0015] In the automatic filtration step b), the automatic slag discharge and filter cleaning system is equipped with a pressure sensor. When the pressure difference between the filter inlet and outlet reaches a preset threshold, the slag discharge and / or cleaning procedure is automatically initiated. The preset pressure difference threshold is 0.1 MPa. The system monitors pressure data in real time by installing high-precision pressure sensors at the filter inlet and outlet. When the pressure difference detected by the sensor reaches or exceeds a preset threshold (e.g., preferably 0.1 MPa), the control system (such as a PLC) automatically executes the slag discharge and cleaning procedure. The 0.1 MPa threshold strikes a balance between ensuring normal paint supply and indicating that a considerable amount of impurities have accumulated in the filter, enabling timely and necessary cleaning.

[0016] In the automatic filtration step b), the preset time interval is 2 hours. As a supplementary or independent control method, the system can be set to a fixed time period, for example, every 2 hours, automatically starting a cleaning program regardless of whether the pressure difference reaches the threshold. This preventative maintenance can effectively prevent impurities from caking on the filter element due to prolonged residence, further improving the reliability of the system.

[0017] The automatic slag discharge and cleaning filter system uses filter elements with increased filtration area to improve filtration efficiency.

[0018] The filter element is made of stainless steel fiber sintered felt.

[0019] The filter element adopts a folded or multi-layer composite structure.

[0020] By comprehensively implementing steps a) and b) above, the present invention can stably control the residue content in coatings at a level of ≤300ppm. This indicator is far superior to the prior art (the original average value was higher than 400ppm), which is a direct quantitative manifestation of the technological progress of the present invention and a guarantee for a fundamental improvement in product quality.

[0021] Because this invention fundamentally improves the cleanliness of the coating, the resulting coated whiteboard paper will differ in physical properties (such as fewer surface defects, higher smoothness and gloss) from products produced using conventional processes.

[0022] Compared with the prior art, the beneficial effects of the present invention are: (1) The most direct effect of this invention is to significantly reduce the impurity content in the coating, reducing the average residue on the coating sieve from 400-500 ppm to ≤300 ppm. This fundamentally eliminates paper defects such as scraper marks, color spots, and holes caused by coating impurities, greatly improving the product qualification rate. According to implementation data, after adopting this process, the surface smoothness (PPS) of coated whiteboard paper can be reduced from 0.75 μm to about 0.6 μm, an increase of about 20%; the gloss can be increased from 47.5% to about 50%, an increase of about 5-6%. The improvement in product appearance and printing performance greatly enhances its market competitiveness.

[0023] (2) The automatic slag discharge and filter cleaning system replaces the cumbersome and inefficient manual cleaning, realizing 24 / 7 unattended operation and intelligent maintenance of the filtration process. This greatly reduces unplanned downtime caused by filter clogging. According to statistics, the number of paper machine downtimes caused by impurities per month has been reduced from 5-8 times to 1-2 times. At the same time, the automated cleaning process is fast and thorough, and the filtration efficiency is more than 30% higher than that of traditional manual cleaning, ensuring the continuity and stability of the production process and improving the overall operating efficiency of the paper machine.

[0024] (3) Improved product quality and production efficiency directly translate into considerable economic benefits. A lower defect rate means a significant reduction in non-conforming products (approximately 200 tons per month), directly saving substantial costs in raw materials, water, electricity, steam, and other energy sources. Calculations show that this alone can generate an annualized economic benefit of 6 million yuan. Furthermore, the automation system reduces reliance on manual labor, saving on labor costs.

[0025] (4) This invention reduces the generation of defective products, thereby reducing resource consumption and environmental pollution during waste disposal. The conservation of resources such as water, electricity, and steam also aligns with the national policy guidelines of "energy conservation and emission reduction" and "green production." This invention helps enterprises achieve a balance between economic, social, and environmental benefits, promoting the sustainable development of the paper industry. Detailed Implementation

[0026] 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.

[0027] This invention provides a process method to improve the cleanliness of a paper coating system. Its core lies in the systematic combination of optimized chemical cleaning steps and intelligent physical filtration steps to solve the problems of skinning and impurities in the coating system during the production of coated whiteboard paper.

[0028] In this invention, the process includes a system cleaning step a) and an automatic filtration step b). The system cleaning step a) aims to remove stubborn crusts adhering to the inner walls of the coating system (such as pipes and tanks). This invention has found that the effective removal of coating crusts depends on the synergistic effect of the cleaning agent, temperature, and pH value. Therefore, in the circulating cleaning process, the temperature of the wash water is strictly controlled at 50℃-60℃, and the pH value is controlled within a strongly alkaline range of 11-13. Under these conditions, the chemical activity of the cleaning agent is fully activated, and the strongly alkaline environment can effectively saponify, disperse, and dissolve organic adhesive components such as latex in the coating, thereby working synergistically with the cleaning agent to efficiently break down the complex crusts composed of inorganic pigments such as calcium carbonate and kaolin, as well as organic matter. Preferably, the cleaning agent is AMAZON 1797, which exhibits the best cleaning effect on the coating crusts targeted by this invention under the above-mentioned temperature and humidity conditions.

[0029] In this invention, the automatic filtration step b) aims to continuously and efficiently intercept and remove impurities from the coating during the production process. This invention abandons the traditional, inefficient manual cleaning method and employs an automatic slag discharge and filter cleaning system. This system has an intelligent triggering mechanism, that is, it automatically starts the slag discharge and cleaning program by monitoring the pressure difference between the filter inlet and outlet in real time, or according to a preset time interval. Pressure difference triggering is a responsive maintenance method; when impurities accumulate and the pressure difference reaches a preset threshold (preferably 0.1 MPa), the system immediately self-cleans, ensuring a smooth coating supply. Time interval triggering is a preventative maintenance method; for example, it is set to automatically clean every 2 hours, and manually clean it every 48 hours to check the integrity of the filter screen and whether it needs replacement, effectively preventing impurities from remaining on the filter element for a long time, leading to caking and decreased filtration efficiency.

[0030] To further improve the filtration effect, the present invention preferably optimizes the structure of the automatic filter. The filter element can adopt a pleated or multi-layer composite structure to increase the filtration area within a limited space, thereby increasing the flow rate and extending the working cycle. The filter element is preferably made of stainless steel fiber sintered felt, which is corrosion-resistant, high-strength, and has excellent backwashing and regeneration performance, and can adapt to the strongly alkaline cleaning environment and frequent automatic cleaning requirements of the present invention. By implementing the complete process of the present invention, the residue in the coating can be stably controlled at ≤300ppm, which is significantly better than the existing technology.

[0031] To further illustrate the present invention, the following detailed description is provided through the examples and comparative examples.

[0032] Example 1 Process: This embodiment fully applies the method of the present invention.

[0033] Step a) System cleaning: During shutdown, prepare flushing water using AMAZON1797 cleaning agent. After starting the circulation pump, control the water temperature at 55℃ using the heating device and online sensor, and simultaneously control the pH value at 12 using the automatic dosing pump. Circulate the flushing water under these conditions for 10 hours.

[0034] Step b) Automatic filtration: During production, an automatic slag discharge and filter cleaning system is used. The filter element is a pleated structure made of stainless steel fiber sintered felt. The PLC control system is set with a pressure difference trigger threshold of 0.1 MPa and a time trigger interval of 2 hours.

[0035] After system cleaning, the inner wall is smooth. During production, the automatic filtration system operates stably, automatically initiating the cleaning program every 2 hours on average when the pressure difference reaches the threshold. Multiple batches of tests showed that the residue content of the coating material on each coating head remained consistently between 197 ppm and 272 ppm, far below the target value of 300 ppm. The quality of the final product was significantly improved, with an average smoothness (PPS - positive) of 0.59 μm and an average gloss of 49.5%. The paper machine operated smoothly, and the number of downtimes due to impurities was reduced to once a month.

[0036] Example 2 Process: Basically the same as Example 1, except that: Step a) System cleaning: To verify the effectiveness of the parameter range, the water temperature was controlled at the lower limit of 50℃ and the pH value was controlled at the lower limit of 11.

[0037] Step b) Automatic filtering: mainly relies on time-triggered logic, set to automatically clean once every 2 hours.

[0038] The system achieved good cleaning results. Although the cleaning rate was slightly slower than in Example 1, it still effectively removed the crust. During production, the residue on the paint sieve was consistently controlled within the range of 220 ppm to 280 ppm. The final product quality was comparable to that of Example 1, demonstrating that the lower limit of the parameter range defined in this invention also possesses excellent technical effects.

[0039] Example 3 Process: Basically the same as Example 1, except that: Step a) System cleaning: To verify the effectiveness of the parameter range, the water temperature was controlled at the upper limit of 60℃ and the pH value was controlled at the upper limit of 13.

[0040] Step b) Automatic filtration: The filter element adopts a multi-layer composite structure and mainly relies on pressure difference triggering logic.

[0041] At 60℃ and pH 13, the skin decomposes very quickly, resulting in extremely high cleaning efficiency. During production, the use of a multi-layer composite filter element with higher filtration efficiency slows down the pressure difference rise, extending the automatic cleaning interval to approximately 9 hours. The paint residue is stably controlled within the range of 180ppm to 250ppm, demonstrating excellent performance. This proves that the upper limit of the parameter range defined in this invention and different filter structures can all achieve the objectives of this invention.

[0042] Comparative Example 1 Process: In the production process of coated whiteboard paper, the cleaning and filtration of the coating system are carried out using traditional methods.

[0043] System cleaning: When shutting down, use a commercially available cleaning agent to circulate and clean the paint system for 2 hours at room temperature (about 25°C) and without adjusting the pH value (neutral or weakly alkaline).

[0044] Paint filtration: During the production process, ordinary mesh filters with standard pore size are used, which rely on manual disassembly, inspection and manual cleaning once per shift (8 hours).

[0045] Post-cleaning inspection revealed stubborn scale residue remaining at pipe bends and at the bottom of the tank. During production, the coating residue level fluctuated significantly, averaging as high as 480 ppm. Due to untimely or incomplete manual cleaning, an average of six emergency shutdowns per month were required due to filter clogging leading to paper defects such as doctor blade marks. The produced coated white cardboard had a high defect rate, with an average surface smoothness (PPS - positive) of 0.78 μm and an average gloss of 47.2%.

[0046] Comparative Example 2 Process: System cleaning: The system cleaning steps in Example 1 of this invention were adopted. Specifically, AMAZON 1797 cleaning agent was used to circulate and clean the coating system for 2 hours at a water temperature of 55°C and a pH of 12.

[0047] Paint filtration: The manual filter cleaning method used in Comparative Example 1 is still employed.

[0048] Post-cleaning inspection revealed a clean system interior with no significant skin residue. Initially, paint residue was low, approximately 350 ppm. However, as production continued, the filtration system remained manual, leading to delayed impurity removal. After 4-5 hours of operation, residue gradually rose to over 400 ppm, posing a risk of scraper marks. This indicates that optimizing chemical cleaning alone cannot consistently guarantee paint cleanliness during production.

[0049] In summary, the process method provided by this invention systematically solves the problem of paint cleanliness from both the source and process aspects by combining optimized chemical cleaning with intelligent automatic filtration. Compared with the prior art, it has significant technological progress and beneficial effects.

[0050] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A process for improving the cleanliness of a paper coating system, characterized in that, This includes applications in the production of coated whiteboard paper, characterized by comprising the following steps: a) System cleaning step: The coating system is cleaned before or during non-operation of the coating machine. This step includes: The piping and / or tanks of the coating system are circulated and cleaned using a flushing solution containing cleaning agents; and... During the circulating cleaning process, the water temperature of the washing water is controlled at 50-60℃, and its pH value is controlled at 11-13; b) Automatic filtration step: During the operation of the coating machine, an automatic slag removal and filter cleaning system is used to continuously or intermittently filter the coating. This step includes: By monitoring the pressure difference between the filter inlet and outlet, or according to a preset time interval, the filter can be automatically triggered and started to remove impurities trapped in it.

2. The process method for improving the cleanliness of a paper coating system according to claim 1, characterized in that, The cleaning agent in step a) is AMAZON1797.

3. The process method for improving the cleanliness of a paper coating system according to claim 1, characterized in that, In step b), the automatic slag discharge and filter cleaning system is equipped with a pressure sensor. When the pressure difference between the inlet and outlet of the filter reaches a preset threshold, the slag discharge and / or cleaning program is automatically started.

4. The process method for improving the cleanliness of a paper coating system according to claim 3, characterized in that, The preset pressure difference threshold is 0.1 MPa.

5. The process method for improving the cleanliness of a paper coating system according to claim 1, characterized in that, In the automatic filtering step b), the preset time interval is 2 hours.

6. The process method for improving the cleanliness of a paper coating system according to claim 1, characterized in that, The automatic slag discharge and cleaning filter system uses filter elements with increased filtration area to improve filtration efficiency.

7. The process method for improving the cleanliness of a paper coating system according to claim 6, characterized in that, The filter element is made of stainless steel fiber sintered felt.

8. The process method for improving the cleanliness of a paper coating system according to claim 6, characterized in that, The filter element adopts a folded or multi-layer composite structure.