PVDF (Polyvinylidene Fluoride) covering film of electrode plate and preparation method thereof

Abstract

The invention provides a PVDF (Polyvinylidene Fluoride) covering film of an electrode plate and a preparation method thereof, and relates to the technical field of electrostatic dust collection. The preparation method comprises the following steps: step 1, preparing a PVDF emulsion; 2, pretreating the electrode plate; 3, coating the PVDF emulsion on the surface of the electrode plate; and 4, drying and hot-pressing the coated electrode plate to obtain the PVDF film covering the surface of the electrode plate. According to the method, a relatively wide large-ventilation-quantity electrode plate is coated with a film by adopting a water-based film coating process, so that the problems in the prior art are solved; meanwhile, the PVDF material is improved, surface charge accumulation is reduced, the safety is improved, the wear resistance of the coated electrode plate is improved, the coated electrode plate can be well applied to a dry type self-cleaning electrostatic dust collector provided with a scraping brush, and the effects of wear resistance, safety and difficulty in sparking are achieved; the prepared PVDF film has the advantages that the film bubble rate is reduced, the wear resistance of the PVDF film of the electrode plate is improved, and the product percent of pass is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of electrostatic dust removal, and in particular to a PVDF coating for an electrode plate and a preparation method thereof. Background Art

[0002] Electrostatic precipitators are increasingly used in industrial dust removal, achieving ever-increasing dust removal efficiency. Their operating principle is to use a high-voltage electric field to ionize flue gas, charging the dust particles in the airflow and separating them from the airflow. The negative electrode, made of metal wires of varying cross-sectional shapes, is called the discharge electrode. The positive electrode, made of metal plates of varying geometric shapes, is called the dust collecting electrode.

[0003] Traditional electrode plates are typically made of metal, purifying air through high-voltage electrostatic attraction of charged particles in the air. Electrostatic precipitators apply high voltage to metal electrode plates to generate an electric field, attracting oppositely charged dust particles. Electrode plate design is dependent on airflow: at the same voltage, greater airflow requires wider electrode plates. However, metal materials are prone to breakdown under high-voltage conditions, especially when heavy dust accumulation occurs.

[0004] To address and mitigate high-voltage breakdown, existing technologies use heat-shrinkable films made of materials like PVDF to wrap the electrode plates. While this improves voltage resistance to some extent, in high-air-volume applications, the dust-collecting electrode plates are deep and wide, and the heat-shrinking process can easily cause bubbles or wrinkles in the film, seriously impacting product quality and yield. Furthermore, electrostatic precipitators typically require self-cleaning brushes to reduce maintenance costs, but traditional PVDF films lack the wear resistance to withstand the long-term demands of scraping.

[0005] For example, prior art CN108372028A discloses a coated electrode plate for an electrostatic precipitator. This involves uniformly spraying a non-stick coating, typically a corrosion-resistant polymer coating, onto the surface of the dust collecting electrode plate. The coated electrode plate effectively prevents corrosion and scaling, ensuring stable operation of the electric field. However, no effective solution has been proposed for improving the relevant performance of this coating. CN118326462A discloses a composite coating structure suitable for an electrostatic precipitator cathode plate. The composite coating structure comprises a nickel-based coating skeleton parallel to the cathode plate substrate and a nickel deposit disposed on the nickel-based coating skeleton. The composite coating structure utilizes a composite electrodeposition process and a plasma flame heat treatment process. The nickel-based coating skeleton is electrodeposited onto the cathode plate substrate using a deposition liquid. Nickel is then formed onto the nickel-based coating skeleton to form a nickel deposit. The surface of the nickel deposit is etched to introduce a fluoropolymer. The fluoropolymer-introduced nickel deposit is then treated with a plasma flame. When mirror reflection occurs, the flame is moved to an outer adjacent area until the entire outer surface of the cathode plate substrate is completed, thereby producing the composite coating structure. The preparation process of the electrode plate is complicated, and the prepared coating has certain limitations.

[0006] Therefore, there is an urgent need to develop a preparation method for a new PVDF coating suitable for electrode plates to solve the problems existing in the prior art. Summary of the Invention

[0007] Based on this, the present invention provides a PVDF coating for an electrode plate and a preparation method thereof, which is suitable for improving the defects of the coating process of the electrode plate, while improving the wear resistance of the coating, and meeting the use requirements of a large air volume electrostatic precipitator. The preparation method adopts an aqueous coating process to coat a wider large air volume electrode plate, solving the problems existing in the prior art; at the same time, the preparation method provided by the present invention improves the PVDF material, reduces surface charge accumulation, improves safety, and improves the wear resistance of the coated electrode plate, so that the prepared electrode plate can be better used in a dry self-cleaning electrostatic precipitator equipped with a scraper, achieving the effects of anti-wear, safety and non-flammability; in addition, the prepared PVDF coating has the advantages of reducing the coating bubble rate, improving the wear resistance of the PVDF coating of the electrode plate, and improving the product qualification rate.

[0008] In a first aspect, the present invention provides a method for preparing a PVDF coating for an electrode plate, comprising the following steps: Step 1: preparing PVDF emulsion; Step 2: Pre-treating the electrode plate; Step 3: Apply PVDF emulsion on the surface of the electrode plate; Step 4: Dry and hot-press the coated electrode plate to obtain a PVDF film covering the surface of the electrode plate.

[0009] The PVDF emulsion provided by the present invention forms a stable coating liquid by formulating resin components and dispersants, which can be achieved specifically by multi-component mixing and pH adjustment, and is used to provide a coating material with suitable rheological properties. Pretreatment of electrode plates refers to surface cleaning and activation treatment of the metal substrate, which can be achieved specifically by degreasing cleaning and plasma treatment, and is used to enhance the interfacial bonding between the PVDF film layer and the substrate. The coating process refers to the operation of uniformly covering the surface of the substrate with a liquid emulsion, which can be achieved specifically by roller coating equipment, and is used to form a wet film layer with controllable thickness. Drying and hot pressing refers to the completion of film curing through the synergistic effect of temperature gradient and pressure, which can be achieved specifically by segmented heating and roller pressing devices, and is used to eliminate internal defects of the coating and obtain a dense structure.

[0010] Furthermore, the preparation process of the PVDF emulsion is as follows: S1: Dissolve PVDF, alumina, and acrylic resin in water to prepare a suspension; S2: A hydrophilic acrylic monomer is mixed with a fluorinated hydrophobic monomer to form a dispersant emulsion with an amphiphilic structure; S3: adding a nonionic surfactant to the emulsion described in S2, stirring and mixing, to obtain a mixed emulsion; S4: adding the mixed emulsion to the suspension and adjusting the pH with alkali to prepare a PVDF emulsion.

[0011] The PVDF emulsion prepared by the present invention should ensure that the coating has the necessary bonding strength and wear resistance.

[0012] Furthermore, the water is warm water with a temperature of 25-60°C, preferably 35-50°C, preferably 43°C, 44°C, 45°C, 46°C, or 47°C.

[0013] Furthermore, the mass ratio of PVDF, alumina, and acrylic resin is 1000:(5-10):(1-5), preferably 1000:7:5. By precisely defining the mass ratio of PVDF, alumina, and acrylic resin, the alumina, acting as an inorganic filler, effectively enhances the mechanical strength of the coating layer, while the acrylic resin, acting as an adhesion promoter, strengthens the interfacial bonding between the organic and inorganic phases. The synergistic effect of the inorganic particles and the resin enhances the mechanical strength, bonding, and insulation properties of the coating. For example, excessive alumina addition can increase film brittleness, while insufficient acrylic resin can compromise interfacial bonding.

[0014] Furthermore, the PVDF has a withstand voltage of up to 40-50 kV / mm, preferably 40 kV / mm, 42 kV / mm, 44 kV / mm, 45 kV / mm, 46 kV / mm, 48 kV / mm, or 50 kV / mm. The particle size is 0.1-0.3 μm, preferably 0.1 μm, 0.2 μm, or 0.3 μm, and the moisture content is less than 0.5%. PVDF resin with a withstand voltage of 40-50 kV / mm is selected for its high insulation properties, which prevents breakdown failure under high-voltage electric fields. A particle size range of 0.1-0.3 μm facilitates the formation of a defect-free, continuous film during the coating process. A moisture content above 0.5% causes rapid evaporation of moisture during the drying process, which can easily form pinhole defects.

[0015] Furthermore, the alumina particle size is 1 to 5 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. The 1 μm alumina particle size maintains the filler's suspension stability while avoiding the roughness of the coating surface caused by excessively large particles. This is achieved by reinforcing the PVDF matrix with alumina particles, which can extend the life of the self-cleaning device and provide support during the scraping and brushing process.

[0016] Furthermore, the weight ratio of the sum of the weights of the PVDF, alumina and acrylic resin to water is 1:(5-10), preferably 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, which can ensure that the suspension has rheological properties suitable for roller coating. For example, when the ratio exceeds the range, sagging caused by low viscosity may occur. Strictly controlling the amount of water can effectively inhibit the generation of bubbles during the drying process after coating.

[0017] Furthermore, in S1, the stirring speed during the preparation of the suspension is 200-400 rpm, preferably 200 rpm, 250 rpm, 300 rpm, 350 rpm, and 400 rpm. The suspension achieves uniform dispersion of PVDF and alumina by controlling the dissolution temperature and stirring speed, avoiding coating defects caused by particle agglomeration, balancing the dispersion effect and the risk of bubble generation, and ensuring leveling during the coating process. The stirring speed can fully disperse the agglomerated particles while avoiding excessively high rotation speeds that cause air to be entrained and form a bubble source.

[0018] Furthermore, the mass ratio of the hydrophilic acrylic monomer to the fluorinated monomer (hydrophobic monomer) is (4-6):(1-3), preferably 5:3. This ratio of hydrophilic to hydrophobic components balances the dispersion stability of the emulsion with the hydrophobic properties after film formation through the amphiphilic structure, allowing the dispersant to form a stable interface in the PVDF emulsion and avoid phase separation during the coating process. In the emulsion system, the dispersant can effectively adsorb on the surface of the PVDF particles to form a stable dispersion, while also ensuring the fluidity and wettability of the emulsion during the coating process, avoiding coating defects caused by uneven dispersion.

[0019] Furthermore, the hydrophilic acrylic monomer is selected from any one or more combinations of acrylic acid or acrylic acid derivatives.

[0020] Furthermore, the acrylic acid derivative is selected from any one or more combinations of 2-methacryloyloxyethyl phosphorylcholine, 3-sulfopropyl methacrylate potassium salt, methacryloyloxyethyl trimethylammonium chloride, methacryloylethyl sulfobetaine or methacrylate carboxybetaine, and its polar groups (such as sulfonic acid groups or betaine groups) form strong chemical bonds on the pretreated electrode plates through ionic bonds or hydrogen bonds with the surface of the metal electrode plates, thereby enhancing the adhesion of the coating.

[0021] Furthermore, the fluorine-containing monomer is selected from one or more of tetrafluoroethylene, chlorotrifluoroethylene, perfluoroalkyl vinyl ether, vinylidene fluoride, and hexafluoropropylene. The fluorocarbon chain of the fluorine-containing monomer forms a low surface energy area through hydrophobic effect, which not only reduces the deposition of dust particles on the surface of the film, but also improves the wear resistance of the film through the rigid structure of the molecular chain.

[0022] Furthermore, the nonionic surfactant is polyoxyethylene lauryl ether, which is used to reduce the interfacial tension of the dispersant emulsion and enhance the leveling properties of the emulsion during the coating process. The addition of the nonionic surfactant further optimizes the rheological properties of the emulsion, adapting its viscosity to the dynamic film-forming requirements of the roller coating process. The molecular structure of polyoxyethylene lauryl ether contains both hydrophilic polyoxyethylene segments and hydrophobic lauryl segments, which can effectively adsorb at the interface between the dispersant emulsion and the suspension, reducing the interfacial energy difference between the two phases, thereby suppressing bubbles or wrinkles caused by phase separation during the coating process.

[0023] Furthermore, the dispersant emulsion in the mixed emulsion accounts for 1-5% of the total system, preferably 2%-3%, 1%, 2%, 3%, 4% or 5%. The combination of the hydrophilic component and the fluorine-containing hydrophobic component in the dispersant emulsion enables the PVDF particles to form a dense and high-pressure resistant continuous film layer after coating, and the specific component proportion avoids excessive dispersant from interfering with the film density. When the dispersant emulsion preferably accounts for 2-3% in the mixed emulsion, it can provide sufficient steric hindrance effect to prevent particle agglomeration, and can also avoid excessive dispersant remaining in the film to form a weak interface layer, affecting the surface smoothness and mechanical properties of the coating.

[0024] Furthermore, the base is ammonia or triethylamine, and the pH is adjusted to 8-9. This weakly alkaline environment can partially dissociate the acid groups in the acrylic resin into acid salts, enhancing its compatibility with PVDF. It also avoids strong alkaline conditions that would cause hydrolysis and cleavage of the PVDF molecular chain, prompting the emulsion system to form a stable micellar structure. The pH adjustment step maintains the solubility of the acrylic resin while preventing strong alkalinity from damaging the PVDF molecular chain structure. It stabilizes the emulsion system through a charge balance mechanism, preventing phase separation during storage or coating.

[0025] Furthermore, the viscosity of the PVDF emulsion is 600-800 cps at 25°C, preferably 600 cps, 650 cps, 700 cps, 750 cps, or 800 cps. The solid content of the PVDF emulsion is 20%-40%, and the tensile strength is 500 kg / cm 2,‌ meeting the requirements of roller coating process. The viscosity of 600~800cps refers to the range of flow resistance of the emulsion at 25°C. It can be achieved by adjusting the solid content or adding rheological additives, so that the emulsion has appropriate fluidity to achieve uniform spreading by roller coating, and prevents excessive sagging from causing uneven film thickness, adapting to the leveling requirements of the roller coating process. The optimized combination of material ratio and process parameters ensures the stability of the coating process. For example, a solid content of 20%~40% ensures that the emulsion has sufficient fluidity while maintaining the necessary solid content to meet the subsequent film formation requirements, so that the water evaporation rate of the coating and the curing rate of the film layer are balanced during drying, reducing stress cracks caused by rapid shrinkage. The specific tensile strength can subsequently ensure that the coating has sufficient mechanical strength, which is achieved through the rigid particle reinforcement effect of PVDF and alumina. The alumina particles are evenly dispersed in the PVDF matrix to form physical cross-linking points, thereby improving the scratch resistance of the coating.

[0026] Furthermore, in step 2, the pretreatment process of the electrode plate includes: a. Cleaning and degreasing: Remove oil and impurities from the electrode plate surface. This can be achieved by using an alkaline degreasing agent combined with ultrasonic cleaning to ensure that the substrate surface meets the industrial standard of cleanliness level 6 and eliminate coating defects caused by contaminants. An alkaline cleaning agent (60°C spray) can also be used to directly remove oil from the electrode plate surface, achieving cleanliness level 6 (ISO 8501-1 standard) and a dyne value ≥72mN / m. b. Mechanical polishing: Mechanically polish the electrode plate to improve PVDF adhesion. Specifically, the electrode plate surface can be treated with sandpaper or sandblasting equipment. Specifically, an abrasive with a particle size of 80-120 mesh can be used for uniform polishing, or 600-mesh sandpaper can be used to polish the surface. The linear speed is 15-20 m / s, and the roughness is controlled to Ra 1.5 μm. By increasing the surface roughness, anchoring sites are provided for subsequent coatings. The surface micromorphology is changed by physical means to form a rough structure that is conducive to coating adhesion. c. Surface Activation: Improve the adhesion of PVDF to the electrode plate by treating the electrode plate with plasma. This can be done using atmospheric pressure plasma equipment in an inert gas environment to introduce hydroxyl or carboxyl active groups on the metal substrate surface, enhancing the chemical bonding between the PVDF material and the substrate. Alternatively, plasma activation can be performed in an argon atmosphere with an argon flow rate of 20 L / min and a power of 100 W for 60 seconds to achieve a contact angle of ≤15°. d. Drying and dehydration: The pre-treated electrode plates are dried. Specifically, a hot air circulation drying oven can be used to dehydrate the plates at 80-120°C for 5-30 minutes. The electrode plates need to be dried to a moisture content of <0.1% to prevent water vapor from escaping and forming bubbles during coating.

[0027] This invention pre-treats the electrode plates to eliminate the effects of contaminants on coating adhesion. The four-stage synergy creates a dual physical and chemical reinforcement mechanism. The combination of mechanical polishing and plasma treatment increases mechanical engagement and strengthens interfacial bonding, while strict moisture control and cleanliness management create ideal conditions for subsequent precision coating.

[0028] Furthermore, in step three, the PVDF emulsion is coated on the surface of the electrode plate. The specific process is: using a three-roll coating structure equipment, controlling the coating temperature, and evenly coating the PVDF emulsion on the surface of the substrate to form a PVDF wet film. Furthermore, the three-roll coating structure equipment adopts a combination of forward coating and reverse coating or a combination of roller coating and blade coating for coating. Furthermore, the three-roll coating structure equipment needs to support dynamic adjustment of the coating thickness and the equipment accuracy is ±1μm. Further, the three-roll coating structure equipment controls the coating temperature to 80~120℃, preferably 80℃, 90℃, 100℃, 110℃ or 120℃. Further, the coating process of the three-roll coating structure equipment controls the speed to 4~6m / min, preferably 4m / min, 5m / min or 6m / min, to avoid uneven thickness and avoid microstructural defects in the film layer. This is achieved using a three-roll coating device coupled with a dynamic adjustment system, a feature that eliminates abnormal electric field distribution caused by uneven thickness.

[0029] A three-roll coating system consists of three coating rollers. Dynamic control of coating thickness is achieved by adjusting the gap and speed between the rollers. This is achieved by using servo motors to synchronize the rollers, eliminating coating solution buildup and adapting to substrates with varying surface characteristics. Forward or reverse coating refers to a coating method in which the coating rollers rotate in the same or opposite direction as the substrate's travel. This is achieved by adjusting roller steering parameters. This optimizes the coating direction based on the substrate's surface roughness to improve wettability. A combined roller and blade coating process combines roller transfer with blade smoothing. This is achieved by placing an adjustable-gap blade assembly downstream of the rollers. This mechanical limiter eliminates coating thickness fluctuations and improves surface smoothness. Dynamic coating thickness adjustment with an accuracy of ±1μm refers to the ability to monitor wet film thickness in real time during the coating process and adjust equipment parameters accordingly. This is achieved by using a laser thickness gauge coupled with a closed-loop control system. This ensures consistent thickness along the entire length of wide and deep substrates. Controlling the coating temperature in the range of 80~120℃ means segmented temperature control of the coating area, which can be achieved by using an infrared heating module in conjunction with a temperature sensor. Its function is to maintain the optimal flow state of the PVDF emulsion to prevent decomposition of the components. Specifically, the three-roll coating equipment forms a uniform wet film coating on the substrate surface through a combination of rolling and scraping. The forward or reverse rotation of the coating roller is automatically adjusted according to the surface topography of the substrate. For example, reverse coating is used at the edge of the substrate to compensate for surface tension differences. During the coating process, a laser thickness gauge collects wet film thickness data in real time and transmits the deviation signal to the servo motor to dynamically adjust the gap between the rollers and the coating speed. The temperature control module divides the coating area into multiple temperature zones. For example, it sets the temperature at 80°C at the substrate inlet to prevent premature solidification of the solution and increases it to 120°C in the center area to enhance the fluidity of the emulsion. When the coating speed is limited to 4-6 m / min, the balance point between the rheological properties of the PVDF emulsion and the solvent evaporation rate is calculated to ensure that the wet film forms a uniform surface without splashing or sagging defects during the leveling stage.

[0030] Furthermore, the drying adopts segmented drying. Furthermore, the specific process of segmented drying is: 80~100℃ in the initial stage to evaporate water, maintain for 30~45 seconds (preferably 35~40s, 30s, 35s, 40s or 45s), 120~150℃ to maintain for 25~45 seconds (preferably 30~35s, 25s, 30s, 35s, 40s or 45s) in the high temperature stage to promote the melting of PVDF particles to form a continuous film layer, promote rapid drying of the surface, and avoid the generation of bubbles. Segmented drying refers to dividing the drying process into two stages: the initial stage and the high temperature stage. The initial stage adopts the medium temperature condition of 80~100℃, and the gentle temperature increase promotes the gradual evaporation of water to avoid the rapid vaporization that causes the formation of bubbles inside the film layer; the high temperature stage adopts the condition of 120~150℃, and uses the temperature exceeding the melting point of PVDF to promote the full melting of the particles to form a continuous and dense film layer. Furthermore, the hot pressing refers to bonding the PVDF layer to the electrode plate at 130-160°C (preferably 150-155°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, or 160°C) and a pressure of 0.5-1.5 MPa (preferably 1-1.5 MPa, 0.5 MPa, 0.8 MPa, 1 MPa, 1.2 MPa, or 1.5 MPa) for 25-45 seconds (preferably 25-30 seconds, 25s, 30s, 35s, 40s, or 45s). The synergistic effect of temperature and pressure enhances the physical bonding between the PVDF molecular chains and the electrode plate surface, while eliminating any minor wrinkles that may remain during the drying phase.

[0031] In the initial drying stage, the temperature is controlled below the melting point of PVDF, allowing the moisture inside the wet film to evaporate at a controllable rate, preventing moisture retention and the formation of bubbles. Subsequently, in the high-temperature stage, the temperature is raised to exceed the melting point of PVDF, causing the particles to melt and form a continuous film layer without pores. During the hot pressing stage, pressure is applied while maintaining the temperature, allowing the molten PVDF material to fully contact and tightly bond with the surface of the electrode plate. At the same time, the pressure eliminates local unevenness on the surface of the film layer, and the hot pressing process eliminates residual bubbles on the interface. A staged drying process is used to gradually remove the solvent and promote resin melting. Finally, hot pressing is applied to fully cross-link the PVDF molecular chains, forming a dense film layer without bubbles.

[0032] Furthermore, the resulting PVDF coating has a relatively uniform thickness of 21μm ± 1μm, high wear resistance, and is suitable for use with self-cleaning scrapers. Compared to traditional heat shrink processes, the bubble rate is significantly reduced, improving the pass rate and thus ensuring the stability of the plate's electric field. Strict control of thickness deviation within ± 1μm ensures uniform distribution of electric field strength and avoids sudden voltage gradient changes caused by local film thickness differences.

[0033] Furthermore, the PVDF film was tested for bubbles and wrinkles, and no obvious bubbles or uneven surface areas were found.

[0034] Furthermore, the coating thickness of the PVDF coating was measured using a profilometer stylus method, and the average thickness was 21 μm±1 μm.

[0035] Furthermore, the ASTM D968 falling sand abrasion test was used to evaluate the wear resistance of the PVDF coating layer; the falling sand abrasion test results showed a wear resistance value V / T = 6.9 L / μm.

[0036] Furthermore, the electrode plate is a dust collecting electrode plate.

[0037] In a second aspect, the present invention provides a PVDF membrane prepared using the method of the present invention.

[0038] In a third aspect, the present invention provides an electrode plate, the surface of which is adhered with the PVDF film prepared by the present invention.

[0039] In a fourth aspect, the present invention provides an application of an electrode plate having a PVDF coating prepared by the present invention, which is applied to an electrostatic precipitator.

[0040] In a fifth aspect, the present invention provides an application of a PVDF coating on an electrode plate, wherein the PVDF coating is attached to the electrode plate.

[0041] In existing technologies, electrostatic precipitators are generally made of metal and combined with high-voltage electrostatic adsorption to absorb charged particles. Metal materials are prone to breakdown under high pressure, and subsequent improvements have adopted a heat shrink process to wrap PVDF materials to improve pressure resistance. However, in high-air volume applications, the increased size of the dust collecting electrode plates makes it difficult to avoid the formation of wrinkles and bubbles in the film layer during the heat shrink process, significantly increasing the rework rate. At the same time, the self-cleaning scraper device places higher demands on the wear resistance of the coating. The PVDF film layer prepared by traditional processes cannot meet the long-term scraping requirements.

[0042] The inventors of this application discovered that the heat shrink process is limited by the uneven distribution of thermal stress in the material. When heated, wide electrode plates are prone to localized shrinkage differences, leading to surface defects. By analyzing the feasibility of coating processes, they proposed using liquid PVDF emulsions, particularly water-based emulsions, as an alternative to solid heat shrink film. Based on the material's bonding properties and the coating and forming mechanism, they redesigned the composition and preparation process of the PVDF emulsion. This, combined with substrate pretreatment and a staged drying and hot pressing process, resulted in a complete wet coating technology system.

[0043] Beneficial effects: Compared to existing technologies, this invention achieves in-situ conversion of liquid materials into solid films through wet coating, avoiding stress concentration during thermal shrinkage. While film formation in existing technologies is limited by the thermal shrinkage of the material, this invention directly controls film thickness and uniformity through adjustment of coating and drying process parameters, making it more suitable for processing wide-width electrode plates.

[0044] The existing technology relies on the heat shrinkage of PVDF materials to directly wrap the electrode plates, but the wide electrode plates are easily heated due to uneven heating, which can lead to wrinkles or bubbles. The present invention constructs an emulsion system in steps to form a stable dispersion state before coating, thereby avoiding the film-forming defects of the heat shrinkage process. In the existing technology, it is difficult for a single dispersant to take into account both the dispersibility of PVDF and the voltage resistance of the film, while the amphiphilic structure dispersant of the present invention achieves uniform particle distribution and film-forming interface optimization through chemical bonding. The present application solves the problem of dispersion stability of PVDF emulsion when coating wide electrode plates, and achieves a film-forming effect with uniform film thickness and no bubbles; the synergistic effect of aluminum oxide and acrylic resin in the emulsion improves the mechanical strength of the film layer, enabling it to withstand repeated friction of the self-cleaning scraper and reduce the maintenance frequency; the introduction of amphiphilic monomers as dispersants enhances the high-voltage breakdown resistance of the film, adapting to the high-voltage electric field environment of the electrostatic precipitator plate.

[0045] Existing technologies typically employ a single hydrophilic or hydrophobic structure, making it difficult to simultaneously meet coating adhesion and stain resistance requirements. This invention, through the precise proportioning of amphiphilic monomers, creates a dual-functional interface within the PVDF emulsion. This ensures the emulsion spreads and penetrates the metal substrate while also forming a protective layer through the fluorocarbon chains, overcoming the problem of film wear caused by airflow scouring in high-airflow environments.

[0046] The existing technology only shrinks and adheres the PVDF material by heating, and lacks a substrate pretreatment step, which makes the coating prone to bubbles, wrinkles and insufficient adhesion. The present invention introduces a multi-stage pretreatment process to establish a clean, rough and chemically active substrate surface before coating, fundamentally solving the problem of insufficient interfacial bonding strength, while eliminating the bubble defects caused by residual moisture. The present application effectively solves the problems of bubble generation, surface wrinkles and insufficient adhesion in the PVDF coating process under high air volume scenarios, and significantly improves the qualified rate of finished coating products. The pretreatment process of the present application enables the PVDF film layer to form a stable bonding interface with the substrate, improves the electric field stability, and at the same time enhances the wear resistance of the coating surface to meet the long-term use requirements of the self-cleaning scraper.

[0047] Existing coating technologies rely on the stress generated by thermal shrinkage of the material to achieve coating, which can easily lead to wrinkles and bubbles on wide and deep substrates due to uneven shrinkage. This invention, however, employs active coating control, directly forming a wet film of predetermined thickness through mechanical limiting and dynamic adjustment, avoiding the shrinkage stress dependency of heat shrink processes. Existing coating equipment often uses a single roller or scraper, making it difficult to eliminate coating edge buildup. However, the three-roller combination coating significantly improves coating uniformity by synergizing the coating transfer process with secondary leveling by the scraper.

[0048] This application achieves uniform PVDF coating of wide and deep dust collecting electrode plates in high-volume electrostatic precipitators, eliminating the bubbles and wrinkles caused by traditional heat shrink processes. Dynamic thickness adjustment and temperature control work together to ensure stable coating thickness along the length of the substrate, thus meeting the requirements for uniform electric field distribution in high-voltage environments. The matching design of coating speed and equipment accuracy effectively avoids coating thickness deviations caused by speed fluctuations, ensuring surface flatness for the reliable operation of the subsequent self-cleaning scraper.

[0049] The existing technology uses a one-time high-temperature treatment, which leads to an imbalance between the water evaporation rate and the material melting rate, and is prone to bubbles and wrinkles. However, the segmented drying method of this application balances the water evaporation and melting processes by controlling the temperature window and duration in stages. The hot pressing process further eliminates microscopic defects and improves the film flatness and interface bonding strength. This application solves the problems of high bubble rate and uneven surface of the coating layer caused by improper temperature control in traditional processes. While ensuring the bonding strength between the PVDF coating and the electrode plate, it reduces the rework rate in the production process, thereby improving the electric field stability of the electrostatic dust removal plate and meeting the wear resistance requirements of the self-cleaning scraper.

[0050] The existing technology causes membrane wrinkles in wide-width electrode plates with high airflow rates due to uneven thermal stress distribution. The present invention avoids thermal shrinkage through coating and molding. The existing technology uses pure PVDF material, which has insufficient wear resistance. The present invention improves scratch resistance by adding inorganic particles. The existing technology's process is not sufficiently dehydrated, which easily forms interface bubbles. The present invention reduces the moisture content to less than 0.1% through pre-treatment drying and staged drying, eliminating the conditions for bubble formation at the root.

[0051] The present invention realizes the smooth and wrinkle-free forming of the wide-width electrode plate coating, so that the self-cleaning scraper can still maintain the integrity of the film layer after long-term reciprocating motion. At the same time, it effectively reduces the electric field distortion caused by bubbles and adapts to the structural stability requirements of the dust collecting plate of the large-volume electrostatic dust removal device.

[0052] The present invention provides a PVDF coating for an electrode plate and a preparation method thereof, which effectively reduces coating bubbles and wrinkles through a segmented drying and hot pressing process combined with a specific PVDF emulsion formula and coating parameters, thereby solving the problem of bubbles and wrinkles generated during the coating process of wide-width electrode plates, while improving the wear resistance of the coating, having the advantages of reducing the coating bubble rate, improving wear resistance and product qualification rate, and a low coating bubble rate can prevent local breakdown of the electric field.

[0053] In the preparation process of the present invention, the various components of PVDF emulsion are mixed according to a certain ratio to obtain an aqueous emulsion of PVDF; the electrode plate is pretreated to facilitate the subsequent perfect combination of the electrode plate and the coating emulsion; the electrode plate is coated by a roller coating device to ensure uniform coating; the PVDF coating of the electrode plate prepared by the present invention has higher wear resistance and safety, meets the long-term use requirements of the self-cleaning scraper device, and can be applied to electrostatic precipitators with large ventilation volumes.

[0054] The PVDF coating prepared by the preparation method of the present invention has a thickness of about 21 μm and is relatively uniform. It has high wear resistance and is suitable for configuring a self-cleaning scraper. Compared with the existing technology, the bubble rate is significantly reduced, the qualified rate is improved, and thus the stability of the plate electric field is ensured.

[0055] The present invention can effectively avoid the problems of uneven electric field distribution or local breakdown caused by surface defects in the film layer, ensure the stable operation of the electrostatic precipitator plate under high-voltage environment, and reduce material waste and increased production costs caused by rework. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is an application scenario diagram of the electrode plate.

[0057] Figure 2 This is a diagram showing the position relationship of the PVDF coating in the electrode plate.

[0058] Figure 3 The figure is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0059] Certain embodiments of the present invention are now described in detail, examples of which are illustrated by the accompanying structural formulas and chemical formulae. The present invention is intended to encompass all substitutions, modifications, and equivalent technical solutions, which are all included within the scope of the invention as defined in the claims. Those skilled in the art will recognize that many methods and materials similar or equivalent to those described herein can be used to practice the present invention. The present invention is in no way limited to the methods and materials described herein. In the event that one or more of the combined documents, patents, and similar materials differ from or contradict the present application (including but not limited to defined terms, term applications, described technologies, etc.), the present application shall prevail.

[0060] It will be further appreciated that certain features of the invention, which, for clarity, are described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which, for brevity, are described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

[0061] Unless otherwise specified, all technical terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. All patents and publications related to the present invention are incorporated herein by reference in their entirety.

[0062] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", "further", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, unless they are contradictory.

[0063] In the following description, all numbers disclosed herein are approximate, regardless of whether the word "about" or "approximately" is used. The numerical value of each number may vary by 1%, 2%, 5%, 7%, 8%, 10%, 15%, or 20%. Whenever a number having a value of N is disclosed, any number having a value of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, N+ / -10%, N+ / -15%, or N+ / -20% is expressly disclosed, where "+ / -" means plus or minus.

[0064] The term "and / or" should be understood to mean any one of the options or a combination of any two or more of the options.

[0065] The terms "optional," "optional," or "optionally" mean that the subsequently described event or circumstance may but need not occur.

[0066] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the following examples. The specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention in any way. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion about the concepts of the present disclosure. Such structures and technologies are also described in many publications.

[0067] The reagents used in the present invention can be purchased from the market or prepared by the method described in the present invention.

[0068] The technical solutions of the present invention are illustrated below with examples, and the scope of protection requested by the present invention includes but is not limited to the following embodiments.

[0069] raw material: PVDF powder (Arkema KYNAR 720, voltage resistance 40-50 kV / mm, particle size 0.1-0.3 μm, water content <0.5%), alumina (particle size 1 μm) Acrylic resin (commercially available industrial grade, BASF ACRONAL S760), hydrophilic acrylic monomers (such as methacryloyloxyethyltrimethylammonium chloride, potassium salt of 3-sulfonated propyl methacrylate), fluorinated monomers (such as tetrafluoroethylene, perfluoroalkyl vinyl ether, vinylidene fluoride), nonionic surfactant (polyoxyethylene lauryl ether), deionized water, ammonia (pH adjuster) Equipment: High-speed stirring reactor (temperature control accuracy ±1°C), three-roll coater (accuracy ±1 μm, supports forward / reverse coating combination mode), segmented drying oven (temperature range 80-150°C), hot press (pressure 0.5-1.5 MPa, temperature 130-160°C) Example 1 A coating and preparation method of an electrostatic precipitator electrode plate: Step 1: Preparation of PVDF emulsion Add 30 kg of deionized water to a 50 L reactor and heat to 45°C. Then add 6 kg of PVDF powder (particle size 0.2 μm), 42 g of α-alumina (99.9% purity, 1 μm), and 30 g of acrylic resin in that order. Stir at 300 rpm for 30 minutes to form a suspension. Prepare a dispersant emulsion in another container: 250 g of methacryloyloxyethyltrimethylammonium chloride, 150 g of vinylidene fluoride, and 20 g of polyoxyethylene lauryl ether (HLB = 16.7); The dispersant emulsion was added to the suspension, and ammonia water was added dropwise to adjust the pH to 8.5 to obtain the final emulsion with the following parameters: viscosity: 720 cps (25°C, Brookfield RV#3 / 50 rpm), solid content: 32%, and zeta potential: +35 mV.

[0070] Step 2: Pretreatment of dust collecting electrode plates Cleaning and degreasing: Use alkaline cleaning agent (60℃ spray, such as sodium hydroxide (NaOH) cleaning agent) to remove oil stains on the surface of the electrode plate, with a cleanliness level of 6 (ISO 8501-1 standard) and a dyne value of ≥72mN / m.

[0071] Mechanical polishing: Use 600-grit sandpaper to polish the surface at a linear speed of 15 m / s and a roughness control Ra of 1.5 μm.

[0072] Plasma activation: In an argon atmosphere with an argon flow rate of 20 L / min, the electrode plate surface was treated at a power of 100 W for 60 seconds, with a contact angle of ≤15°.

[0073] Drying and dehydration: Dry with hot air at 80℃ for 5 minutes until the moisture content reaches 0.08%.

[0074] Step 3: PVDF emulsion coating Use a three-roll coater (scrape coating mode, gap accuracy ±1 μm) to coat at a speed of 5 m / min, set the upper roller to 50 μm, the middle roller to 30 μm, and the lower roller to be fixed. Set the coating roller to 90°C and the back roller to 105°C; control the wet film thickness to 20 μm (dry film thickness ≈15 μm).

[0075] Step 4: Drying and hot pressing Staged drying: Initial stage: 85℃ hot air drying for 40 seconds, wind speed is 2.5m / s; High temperature stage: 135℃ treatment for 30 seconds, wind speed is 1.8m / s, to promote PVDF melting and film formation; Hot pressing: hot pressing for 25 seconds at 150°C and 1.5 MPa pressure with a wind speed of 1.8 m / s to make the PVDF film layer and the electrode plate tightly bonded.

[0076] Example 2 The difference from Example 1 is that the fluorine-containing monomer is replaced by a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, and the mass ratio of the two is 1:1.

[0077] Example 3 The difference from Example 1 is that the hydrophilic acrylic monomer is replaced by potassium salt of 3-sulfonate propyl methacrylate.

[0078] Example 4 The difference from Example 1 is that ammonia water is replaced by triethylamine.

[0079] Examples 5-11 The difference from Example 1 is that some experimental parameters are adjusted, as shown in Table 1 below.

[0080] Examples 12-17 The difference from Example 1 is that the coating stage parameters are slightly different, as shown in Table 2 below

[0081] Comparative Example 1 The film-coated electrode plate was prepared using Example 1 of CN118326462A. Effect Example 1: Performance Index (1) Bubble and wrinkle detection Sample preparation: One sample of each of the film-coated electrode plates prepared in Examples 1 to 16 and Comparative Example 1 was randomly selected. The electrode plate dimensions were 390×145 mm in length and width. Detection method: conventional detection Visual inspection: Check from different angles for bubbles or uneven areas. Bubbles tend to accumulate at the edges or seams of the film, so a magnifying glass should be used to assist in observing tiny bubbles.

[0082] Results: The film-coated electrode plates prepared in Examples 1 to 16 had no obvious bubbles or obvious uneven areas on the surface.

[0083] Scraper-assisted detection: Use a plastic scraper (hardness ≤ Shore A60) to gently scrape the film surface at a 45° angle, and judge the presence of bubbles by the resistance and sound.

[0084] Results: The film-coated electrode plates prepared in Examples 1 to 16 had no abnormal noise or resistance in the film scraping test.

[0085] Comparative Example 1: A plurality of tiny bubbles can be seen visually at a ratio of about 1, and rework is required.

[0086] (2) Use the profilometer stylus method to detect coating thickness Step 1: prepare and select one sample of each of the film-coated electrode plates prepared in Examples 1, 2, and 3 and the film-coated electrode prepared in Comparative Example 1, and form a height difference step between the coating and the substrate on the surface of the sample.

[0087] Step 2: Place the sample on the base of the measuring table and adjust the stylus height by the manual knob of the column so that the stylus tip contacts the step area vertically. Step 3: Start the driving device, and slide the stylus at a constant speed along the step direction (the speed is set to 0.1-1mm / s), and record the vertical displacement change.

[0088] Each sample was measured three times to obtain the following thickness data set in Table 3:

[0089] It can be seen that the PVDF coating prepared in the embodiment of the present application has a thickness of about 21 μm and is relatively uniform.

[0090] (3) The wear resistance of the PVDF coating layer was evaluated using ASTM D968 falling sand abrasion test.

[0091] Sample preparation: One sample of each of the film-coated electrode plates prepared in Examples 1 to 3 was selected, and the electrode plate dimensions were 390 × 145 mm in length and width; Test temperature: 23±2℃, relative humidity 50±5%; Equipment calibration: Adjust the verticality of the guide tube to ensure that the center of the sand flow is aligned with the axis of the guide tube, with a deviation of ≤±5°, and adjust the vertical distance between the lower end of the guide tube and the surface of the test plate to 25mm; Select standard sand: 0.25-0.65mm; calibration sand flow rate: 2L flows out in 21-23.5 seconds (about 10g / s); Parameter recording: Record the amount of sand (volume or mass) required to wear through the coating and the corresponding coating thickness; calculate the wear resistance value according to the formula ‌A=V / T‌: ‌A‌: wear resistance coefficient (L / μm or kg / μm); ‌V‌: amount of sand consumed (keep one decimal place); ‌T‌: average coating thickness (μm, keep one decimal place).

[0092] The data and results of the amount of sand required to penetrate a 20μm PVDF film are shown in Table 4:

[0093] As can be seen from Table 4, the wear resistance values ​​obtained by different PVDF film preparation methods and films made from different PVDF emulsions during the falling sand wear test are slightly different, but all are greater than the PVDF film prepared by the traditional method (the V / T obtained in the industry is between 4L / μm and 6.5L / μm).

[0094] Effect Example 2 The electrode plate covered with PVDF membrane of the present invention was subjected to other tests, and the results are shown in Table 5 below:

[0095] It can be seen that the PVDF coating of the electrode plate prepared by the preparation method of the present invention can effectively avoid the uneven electric field distribution or local breakdown problems caused by surface defects of the film layer, ensure the stable operation of the electrostatic precipitator plate under high-voltage environment, and reduce the material waste and increased production costs caused by rework.

[0096] The methods of the present invention have been described through preferred embodiments. It is apparent that those skilled in the art will be able to modify or appropriately alter and combine the methods and applications described herein within the scope, spirit, and spirit of the present invention to implement and apply the technology of the present invention. Those skilled in the art may refer to the disclosure herein and appropriately modify the process parameters to achieve the desired effect. It is particularly important to note that all similar substitutions and modifications apparent to those skilled in the art are considered encompassed by the present invention.

Claims

1. A method for preparing a PVDF film for an electrode plate, characterized in that: The steps include: Step 1: preparing PVDF emulsion; Step 2: Pre-treating the electrode plate; Step 3: Apply PVDF emulsion on the surface of the electrode plate; Step 4: Drying and hot pressing the coated electrode plate to obtain a PVDF film covering the surface of the electrode plate; The preparation process of the PVDF emulsion is as follows: S1: Dissolve PVDF, alumina, and acrylic resin in water to prepare a suspension; S2: A hydrophilic acrylic monomer is mixed with a fluorinated hydrophobic monomer to form a dispersant emulsion with an amphiphilic structure; S3: adding a nonionic surfactant to the emulsion described in S2, stirring and mixing, to obtain a mixed emulsion; S4: adding the mixed emulsion to the suspension and adjusting the pH with alkali to prepare a PVDF emulsion.

2. The preparation method according to claim 1, characterized in that In S1, the water is warm water with a temperature of 25-60°C; Further preferably, the mass ratio of the PVDF, alumina and acrylic resin is 1000:(5-10):(1-5); Further preferably, the PVDF has a withstand voltage strength of up to 40-50 kV / mm, a particle size of 0.1-0.3 μm, and a water content of less than 0.5%; Further preferably, the particle size of the aluminum oxide is 1 to 5 μm; Further preferably, the weight ratio of the sum of the weights of the PVDF, alumina and acrylic resin to water is 1:(5-10); Further preferably, in S1, the stirring speed during preparation of the suspension is 200-400 rpm.

3. The preparation method according to claim 1, characterized in that: In S2, the mass ratio of the hydrophilic acrylic monomer to the fluorinated monomer and the hydrophobic monomer is (4-6):(1-3); Further preferably, the hydrophilic acrylic monomer is selected from any one or more combinations of 2-methacryloyloxyethyl phosphorylcholine, 3-sulfopropyl methacrylate potassium salt, methacryloyloxyethyl trimethylammonium chloride, methacryloylethyl sulfobetaine or methacrylate carboxybetaine; More preferably, the fluorine-containing monomer is selected from one or more of tetrafluoroethylene, chlorotrifluoroethylene, perfluoroalkyl vinyl ether, vinylidene fluoride, and hexafluoropropylene.

4. The preparation method according to claim 1, characterized in that In S3, the nonionic surfactant is polyoxyethylene lauryl ether, Further preferably, the dispersant emulsion in the mixed emulsion accounts for 1-5% of the total system.

5. The preparation method according to claim 1, characterized in that: The base is ammonia or triethylamine, and the pH is adjusted to 8-9. The viscosity of the PVDF emulsion is 600-800 cps at 25°C, the solid content of the PVDF emulsion is 20%-40%, and the tensile strength is 500 kg / cm 2 .

6. The preparation method according to claim 1, characterized in that: In step 2, the pretreatment process of the electrode plate includes: a. Cleaning and degreasing: remove oil and impurities from the surface of the electrode plate; b. Mechanical polishing: mechanically polishing the electrode plate; c. Surface activation: plasma treatment of the electrode plate; d. Drying and dehydration: The pretreated electrode plates are dried.

7. The preparation method according to claim 6, characterized in that: In step 2, the pretreatment process of the electrode plate includes: a. Cleaning and degreasing: using an alkaline degreasing agent combined with ultrasonic cleaning to ensure that the substrate surface meets the industrial standard of cleanliness level 6; or using an alkaline cleaning agent to directly remove oil stains on the surface of the electrode plate, achieving cleanliness level 6; b. Mechanical polishing: Process the electrode plate surface using sandpaper or sandblasting equipment; c. Surface activation: In an argon atmosphere with an argon flow rate of 20 L / min and a power of 100 W, the electrode surface was treated for 60 seconds, with a contact angle of ≤15°. d. Drying and dehydration: Use a hot air circulation drying oven to dehydrate at 80~120℃ for 5~30 minutes. The electrode plate needs to be dried to a moisture content of <0.1%.

8. The preparation method according to claim 1, characterized in that: In step 3, the PVDF emulsion is coated on the surface of the electrode plate. The specific process is as follows: a three-roll coating structure device is used to control the coating temperature and evenly coat the PVDF emulsion on the surface of the substrate to form a PVDF wet film; Further preferably, the three-roll coating structure equipment adopts a combination of forward coating and reverse coating or a combination of roller coating and blade coating for coating; further preferably, the three-roll coating structure equipment needs to support dynamic adjustment of coating thickness and an equipment accuracy of ±1μm; Further preferably, the three-roll coating structure equipment controls the coating temperature to 80-120°C and the speed to 4-6 m / min; Alternatively, the drying is performed by staged drying; further preferably, the specific process of the staged drying is: evaporating water at 80-100°C for an initial stage, maintaining for 30-45 seconds, and maintaining for 25-45 seconds at 120-150°C; More preferably, the hot pressing refers to bonding the PVDF layer to the electrode at 130-160° C. and a pressure of 0.5-1.5 MPa for 25-45 seconds.

9. An electrode plate, characterized in that: The surface of the film is covered with a PVDF film prepared by the preparation method according to any one of claims 1 to 8.

10. An application of the electrode plate according to claim 9, characterized in that: The electrode plate is applied to an electrostatic precipitator.

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