Application of fluorine-free silane double-nanometer gradient composite coating on filter screen of oil fume purification device and preparation method thereof

Abstract

The application discloses application of a fluorine-free silane double-nano gradient composite coating to a filter screen of an oil fume purification device and a preparation method thereof, and belongs to the technical field of surface coatings. The coating is composed of a bottom anchoring nano layer and a surface functional nano layer attached to the surface of a stainless steel filter screen base material to form a gradient structure. The bottom coating liquid contains a fluorine-free alkyl silane coupling agent and nano silicon dioxide, and the surface coating liquid contains long-chain fluorine-free modified silane and hydrophobic nanoparticles. In the preparation, the bottom layer is first sprayed on the surface of the pretreated filter screen and pre-solidified, then the surface layer is sprayed and subjected to segmented gradient temperature solidification. The coating utilizes the double-nano gradient structure and the low-surface-energy surface layer to change the filter screen surface from lipophilic and hydrophilic to oleophobic and hydrophobic, so that oil and water can quickly slide off to avoid hole blocking, and meanwhile, the bottom anchoring structure ensures that the coating is firmly combined with the wire screen base material, and the coating has the advantages of long-acting self-cleaning, high adhesion, environmental protection, fluorine-free and the like, and is suitable for large-scale coating production of the filter screen of the household and commercial oil fume purification devices.

Description

Technical Field

[0001] This invention belongs to the field of surface coating technology, specifically relating to the application and preparation method of a fluorine-free silane dual nanogradient composite coating on the filter screen of an oil fume purification device. The coating of this invention endows the filter screen of the oil fume purification device with excellent hydrophobic and oleophobic properties, allowing oil and water droplets to quickly slide off the filter screen surface, effectively preventing oil adhesion and mesh clogging, and achieving the self-cleaning function of the filter screen. Background Technology

[0002] The pre-filter (commonly known as the oil filter) of a fume purification device (such as a household range hood and a commercial integrated stove) is the first line of defense against grease, water vapor, and particulate matter in cooking fumes. Its performance directly affects the fume extraction efficiency, equipment lifespan, and user cleaning experience.

[0003] Currently, the filters in oil fume purification devices mainly face the following technical problems in practical use: 1. Contaminant adhesion leads to filter clogging and performance degradation: When high-temperature, oily exhaust fumes from cooking pass through a metal filter, oil droplets and water vapor adhere to the filter mesh surface due to impact. Because conventional stainless steel and other metal substrates have high wettability to grease and water, contaminants easily spread, accumulate, and gradually harden on the filter surface. With prolonged use, the effective opening rate of the filter decreases significantly, wind resistance increases sharply, resulting in a significant decline in fume extraction efficiency, accompanied by increased energy consumption and noise. 2. Difficult filter cleaning and high maintenance costs: Once grease and mixed contaminants solidify on the filter surface, they are difficult to remove through conventional rinsing. Users typically need to frequently disassemble the filter, soak it in strong alkaline cleaning agents for extended periods, or use high-temperature steam to rinse it. This is not only labor-intensive and time-consuming, but repeated chemical cleaning also accelerates the corrosion of the metal filter, shortens its lifespan, and increases user costs. 3. Limitations of existing surface treatment technologies: To improve the anti-adhesion performance of the filter, some existing technologies attempt to coat the filter surface with hydrophobic and oleophobic coatings. For example, Chinese patent CN218687406U discloses a range hood filter with a polysilazane coating, which reduces surface energy through a ceramicized coating formed by the curing of polysilazane to reduce oil fume adhesion; Chinese patent CN2709828Y discloses a non-stick oil filter, which sets a non-stick oil coating on the surface of a stainless steel filter to achieve oil droplet separation. However, existing coating technologies still have obvious application defects. Fluorine-containing coatings (such as PTFE) have excellent low surface energy characteristics, but they may pyrolyze and release persistent organic pollutants such as perfluorooctanoic acid (PFOA) in high-temperature cooking environments (>260℃), posing health risks and failing to meet increasingly stringent environmental regulations; while ceramicized coatings such as polysilazane have a certain oleophobic effect, their high hardness and poor flexibility, and the large difference in thermal expansion coefficients with the metal mesh substrate, make them prone to cracking, peeling, or even large-area flaking under the frequent hot and cold cycles and airflow shearing in oil fume environments, leading to a rapid loss of anti-sticking effect. More importantly, existing fluorine-free nanocomposite coatings with similar composition or structure are mostly used in scenarios with static or high hardness requirements, such as protective films for electronic devices or wear-resistant parts for industrial machinery (e.g., an anti-oxidation, scratch-resistant, and environmentally friendly protective film disclosed in Chinese patent CN107323021A, which is applied in the field of screen protection for electronic products). Their design concept and performance indicators are not developed for the dynamic self-cleaning needs of metal filters under the scouring of high-temperature oily airflow. Currently, there is a lack of technical solutions for applying environmentally friendly coatings with strong adhesion, high flexibility, and long-lasting oil and water slippage properties specifically to the filter screen of oil fume purification devices, which is a specific substrate and working environment.

[0004] In summary, there is an urgent need in this field for a coating application solution that can firmly adhere to the metal filter substrate, has a long-lasting self-cleaning and anti-clogging function, and is safe and environmentally friendly, so as to fundamentally solve the technical pain points of existing fume purification devices where the filters are prone to clogging and difficult to clean. Summary of the Invention

[0005] This invention provides an application of a fluorine-free silane dual nanogradient composite coating on the filter screen of an oil fume purification device and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The application of a fluorine-free silane dual nanogradient composite coating on the filter screen of an oil fume purification device, the coating comprising a bottom anchoring nanolayer attached to the surface of the filter screen substrate of the oil fume purification device and a surface functional nanolayer attached to the surface of the bottom anchoring nanolayer.

[0007] The bottom anchoring nanolayer is formed by coating and curing a bottom coating liquid containing a fluorine-free alkyl silane coupling agent and nano-silica; the surface functional nanolayer is formed by coating and curing a surface coating liquid containing a long-chain fluorine-free modified silane and hydrophobic nanoparticles.

[0008] The underlying anchoring nano-coating liquid comprises, by weight: 10-15 parts of fluorine-free alkyl silane coupling agent, 5-8 parts of nano silica, 0.5-1.0 parts of acidic catalyst, and 76-82.5 parts of organic solvent.

[0009] The surface functional nano-coating liquid comprises, by weight: 8-12 parts of long-chain fluorine-free modified silane, 7-10 parts of hydrophobic nanoparticles, 1-2 parts of organosilicon dispersant, and 76-83 parts of organic solvent.

[0010] The present invention also provides a method for applying the above-mentioned coating to the filter screen of an oil fume purification device, comprising the following steps: S1: Preparation of coating liquids, including preparation of bottom anchoring nano coating liquid and surface functional nano coating liquid; S2: Pretreatment of filter substrate, which involves degreasing, activating and drying the filter of the fume purification device. S3: Coating and pre-curing of the bottom anchoring nano-layer: The bottom anchoring nano-coating liquid is coated onto the surface of the filter substrate and pre-cured. S4: Coating and overall gradient curing of the surface functional nano-layer: The surface functional nano-coating liquid is coated on the pre-cured bottom surface and cured by segmented gradient heating to obtain the finished product.

[0011] Compared to existing technologies, this invention creatively applies a fluorine-free silane dual nanogradient composite coating to the filter screen of an oil fume purification device, achieving significant and synergistic benefits in multiple aspects: This invention is the first to apply this specific coating system to the surface of an oil fume filter. Utilizing its dual nano-gradient structure and low surface energy surface layer, the surface of the filter's metal mesh changes from oleophilic and hydrophilic to oleophobic and hydrophobic. During cooking, condensed oil and water droplets cannot spread on the coating surface but quickly form spheres and slide rapidly into the oil tank due to gravity. This fundamentally prevents oil and water from stagnating and hardening in the filter pores, ensuring the filter remains unobstructed during use and significantly extending its effective lifespan. Simultaneously, the gradient structure design of the bottom anchoring and surface layer functions in this invention, through the formation of a stable chemical bond between the bottom fluorine-free silane coupling agent and the stainless steel substrate, combined with a gradient curing process, releases the thermal stress between the coating and the metal mesh. This allows the coating to firmly adhere to the complex and easily deformable mesh surface, remaining resistant to peeling and cracking even under long-term alternating hot and cold temperatures and high-speed airflow impact. Its adhesion and durability far exceed those of simple anti-stick coatings in existing technologies, completely overcoming the predicament of traditional filter coatings being prone to peeling and failure. Based on this, after applying the coating of this invention, the small amount of floating dust or dry particles remaining on the filter screen can be removed simply by rinsing with water or wiping lightly, completely eliminating the tedious process of soaking in strong alkaline chemicals and high-intensity scrubbing. This significantly reduces the user's cleaning labor intensity and maintenance costs, and also avoids mechanical damage to the filter screen and equipment caused by frequent disassembly and assembly. Furthermore, the coating of this invention is completely free of fluorine and exhibits excellent thermochemical stability throughout the entire cooking temperature range, posing no risk of releasing harmful substances. It combines the dual advantages of high-efficiency self-cleaning and environmental safety. Simultaneously, the coating has a nano-composite thin-layer structure, which hardly changes the original porosity and ventilation area of ​​the filter screen, fully ensuring the airflow and collection efficiency of the fume purification device while achieving self-cleaning functionality. In summary, this invention successfully crosses over from other fields to the specific scenario of fume purification filters by optimizing the formula and process, providing a new and feasible technical path for the design of self-cleaning filters in range hoods and fume purification equipment, and possessing extremely high industrial application value. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto. All parts mentioned in the embodiments are parts by weight, and all percentages are weight percentages.

[0013] Example 1 A method for coating a basic, general-purpose, fluorine-free silane dual-nano composite coating onto the filter screen of an oil fume purification device includes the following steps: S1: Preparation of coating liquid Preparation of S1-1 Underlying Anchoring Nano-Coating Liquid: By weight, take 12 parts of methyltriethoxysilane (fluorine-free alkylsilane coupling agent), 5 parts of nano silica (average particle size 15-25 nm), 0.5 parts of glacial acetic acid (acidic catalyst), and 82.5 parts of anhydrous isopropanol.

[0014] Anhydrous isopropanol was added to a reaction vessel equipped with a stirrer. Nano-silica powder was slowly added while stirring, and the mixture was stirred and dispersed at 300–500 rpm for 10 minutes. Then, methyltriethoxysilane was slowly added dropwise, and stirring continued for 5 minutes after the addition was complete. Finally, glacial acetic acid was added to adjust the pH of the system to 4.0–5.0, and the mixture was continuously stirred and hydrolyzed at 200–300 rpm for 45 minutes at 20–30°C. After hydrolysis, the mixture was allowed to stand for 2 hours for later use, yielding the bottom anchoring nano-coating solution.

[0015] Preparation of S1-2 surface functional nano-coating liquid: By weight, take 9 parts of octyltriethoxysilane (long-chain fluorine-free modified silane), 7 parts of hydrophobic nano silica (average particle size 20-30 nm, surface treated with hexamethyldisilazane hydrophobic modification), 1 part of organosilicon dispersant (BYK-9076), and 83 parts of anhydrous ethanol and isopropanol mixed solvent (volume ratio 1:1).

[0016] Add the mixed solvent to a high-speed dispersion tank, add the organosilicon dispersant, and stir to dissolve at a speed of 400-600 r / min. While stirring, slowly add hydrophobic nano-silica powder. After the addition is complete, increase the speed to 1500-2000 r / min and stir at high speed for 15 min. Then transfer to an ultrasonic dispersion device and ultrasonically disperse at a frequency of 40 kHz and a power of 300 W for 30 min. Finally, slowly add octyltriethoxysilane and continue stirring at a speed of 200-300 r / min for 15 min to obtain the surface functional nano-coating liquid, which is then sealed and stored for later use.

[0017] S2: Substrate Pretreatment The stainless steel filter screen (material: 304 stainless steel, wire diameter: 0.3–0.5 mm, mesh size: 20–40 mesh) from Merck commercial indoor direct-exhaust fume hoods was selected as the coating substrate. The pretreatment steps are as follows: (1) Alkaline washing and degreasing: Use a sodium hydroxide aqueous solution with a mass fraction of 5% to 8% to spray and clean the surface of the stainless steel filter screen for 10 to 15 minutes at a temperature of 60 to 70°C; (2) Rinse with deionized water: Rinse under high pressure at room temperature for 2-3 minutes until the surface pH test paper shows neutrality; (3) Acid washing and activation: Spray the citric acid aqueous solution with a mass fraction of 3% to 5% at room temperature for 1 to 2 minutes; (4) Secondary deionized water rinse: Rinse thoroughly to remove residual acid; (5) Hot air drying: Dry with hot air at 80-100℃ for 10-15 minutes, and then cool to room temperature for later use.

[0018] S3: Coating and pre-curing of the bottom anchoring nanolayer An air-assisted, airless spraying method was used to uniformly spray the prepared S1-1 base anchoring nano-coating liquid onto the surface of the stainless steel filter screen treated with S2. Considering the large specific surface area of ​​the filter screen mesh structure, a cross-reciprocating spraying path was adopted during spraying. The spray gun nozzle diameter was 1.0–1.2 mm, the spraying pressure was 0.3–0.5 MPa, the distance between the spray gun and the filter screen surface was 15–25 cm, and the gun travel speed was 35–45 cm / s. The ambient temperature was controlled at 20–28℃, and the relative humidity was controlled at 40%–60%.

[0019] After spraying, let it stand at room temperature for 8 minutes, then transfer it to a forced-air drying oven and pre-cur it at 70°C for 20 minutes. Remove it and let it cool naturally to room temperature to obtain the bottom anchoring nano-layer.

[0020] S4: Coating of the surface functional nanolayer and overall gradient curing On the surface of the pre-cured S3 anchoring nano-layer, the surface functional nano-coating liquid prepared in S1-2 is applied using an air-assisted airless spraying method. A cross-spraying path is used during spraying to avoid excessive paint accumulation at the mesh openings, which could cause clogging, ensuring uniform coating coverage of the filament surface and maintaining unobstructed mesh openings. The spraying process parameters are: spray gun nozzle diameter 0.8–1.0 mm, spraying pressure 0.25–0.4 MPa, distance between the spray gun and the filter surface 20–25 cm, gun travel speed 40–50 cm / s, and environmental temperature and humidity control conditions are the same as for S3.

[0021] After spraying, allow the coating to stand at room temperature for 12 minutes, then transfer it to a forced-air drying oven for staged gradient temperature curing. First stage: Increase the temperature from room temperature to 80℃ at a rate of 2-3℃ / min, and keep it at that temperature for 15 minutes to cure. Second stage: Increase the temperature from 80℃ to 110℃ at a rate of 2℃ / min, and hold for 15 minutes to cure. The third stage: the temperature is increased from 110℃ to 130℃ at a rate of 1.5℃ / min, and then kept at that temperature for 30 minutes to cure.

[0022] After curing, the filter screen is taken out after being naturally cooled to below 60°C in the oven and then cooled to room temperature to obtain the finished fluorine-free silane double nanocomposite coating filter screen. The total coating thickness is about 5 to 8 μm.

[0023] Example 2 A method for applying a wear-resistant, reinforced, fluorine-free silane dual-nano composite coating to a filter screen of an oil fume purification device includes the following steps: S1: Preparation of coating liquid Preparation of S1-1 Underlying Anchoring Nano-Coating Liquid: By weight, take 10 parts of methyltriethoxysilane, 5 parts of nano silica (average particle size 15-25 nm), 3 parts of nano alumina (average particle size 20-30 nm, α phase), 0.6 parts of glacial acetic acid, and 81.4 parts of anhydrous isopropanol.

[0024] Anhydrous isopropanol was added to the reaction vessel, and nano-silica and nano-alumina mixed filler were added slowly and sequentially while stirring. The mixture was stirred and dispersed at 400-600 r / min for 15 min. Then, methyltriethoxysilane was slowly added dropwise, and stirring was continued for 5 min. Finally, glacial acetic acid was added to adjust the pH of the system to 4.0-5.0, and the mixture was continuously stirred and hydrolyzed at 200-300 r / min at 20-30℃ for 50 min. After hydrolysis, the mixture was allowed to stand and mature for 2.5 h for later use, which yielded the bottom anchoring nano-coating liquid.

[0025] Preparation of S1-2 surface functional nano-coating liquid: By weight, take 8 parts of dodecyltriethoxysilane (long-chain fluorine-free modified silane, carbon chain length C12), 8 parts of hydrophobic nano silica (average particle size 20-30 nm, surface hydrophobically modified with octylsilane), 2 parts of hydrophobic nano titanium dioxide (average particle size 15-25 nm, surface hydrophobically modified with stearic acid), 1.2 parts of organosilicon dispersant (BYK-9076), and 80.8 parts of anhydrous ethanol and isopropanol mixed solvent (volume ratio 1:1).

[0026] Add the mixed solvent to a high-speed dispersion tank, add the organosilicon dispersant, and stir to dissolve at 400-600 r / min. While stirring, slowly add the mixed powder of hydrophobic nano-silica and hydrophobic nano-titanium dioxide. After the addition is complete, increase the speed to 1800-2200 r / min and stir at high speed for 20 min. Then transfer to an ultrasonic dispersion device and ultrasonically disperse at a frequency of 40 kHz and a power of 350 W for 40 min. Finally, slowly add dodecyltriethoxysilane and continue stirring at 200-300 r / min for 20 min to obtain the surface functional nano-coating liquid, which is then sealed and stored for later use.

[0027] S2: Substrate Pretreatment Stainless steel filter mesh (material: 201 stainless steel, wire diameter: 0.4–0.6 mm, mesh size: 16–30 mesh) from Merck commercial indoor direct-exhaust fume hoods was selected as the coating substrate. The pretreatment steps are as follows: (1) Alkaline washing and degreasing: Use a sodium hydroxide aqueous solution with a mass fraction of 5% to 8% to spray and clean the surface of the stainless steel filter screen for 10 to 15 minutes at a temperature of 60 to 70°C; (2) Rinse with deionized water: Rinse under high pressure at room temperature for 2-3 minutes until the surface pH test paper shows neutrality; (3) Acid washing and activation: Spray the citric acid aqueous solution with a mass fraction of 3% to 5% at room temperature for 1 to 2 minutes; (4) Secondary deionized water rinse: Rinse thoroughly to remove residual acid; (5) Hot air drying: Dry with hot air at 80-100℃ for 10-15 minutes, and then cool to room temperature for later use.

[0028] S3: Coating and pre-curing of the bottom anchoring nanolayer An air-assisted, airless spraying method was used to uniformly spray the prepared S1-1 base anchoring nano-coating liquid onto the surface of the stainless steel filter screen treated with S2. Considering the characteristics of the filter screen's mesh structure, a cross-reciprocating spraying path was adopted during spraying. The spray gun nozzle diameter was 1.0–1.2 mm, the spraying pressure was 0.3–0.5 MPa, the distance between the spray gun and the filter screen surface was 15–25 cm, and the gun travel speed was 35–45 cm / s. The ambient temperature was controlled at 20–28℃, and the relative humidity was controlled at 40%–60%.

[0029] After spraying, let it stand at room temperature for 10 minutes, then transfer it to a forced-air drying oven and pre-cur it at 75°C for 25 minutes. Remove it and let it cool naturally to room temperature to obtain the bottom anchoring nano-layer.

[0030] S4: Coating of the surface functional nanolayer and overall gradient curing On the surface of the pre-cured anchoring nano-layer of S3, the surface functional nano-coating liquid prepared in S1-2 is applied using an air-assisted airless spraying method. A cross-spraying path is used during spraying to avoid excessive paint accumulation at the mesh openings, which could cause clogging. The spraying process parameters are: spray gun nozzle diameter 0.8–1.0 mm, spraying pressure 0.25–0.4 MPa, distance between the spray gun and the filter surface 20–25 cm, gun travel speed 40–50 cm / s, and environmental temperature and humidity control conditions are the same as for S3.

[0031] After spraying, allow the coating to stand at room temperature for 15 minutes, then transfer it to a forced-air drying oven for staged gradient temperature curing. First stage: Increase the temperature from room temperature to 85℃ at a rate of 2℃ / min, and maintain the temperature for 20 minutes to cure; Second stage: Increase the temperature from 85℃ to 115℃ at a rate of 2℃ / min, and keep it at that temperature for 20 minutes to cure. The third stage: the temperature is increased from 115℃ to 135℃ at a rate of 1.5℃ / min, and then kept at that temperature for 40 minutes to cure.

[0032] After curing, the filter screen is taken out after being naturally cooled to below 60°C in the oven and then cooled to room temperature to obtain a wear-resistant and reinforced fluorine-free silane double nanocomposite coating filter screen with a total coating thickness of about 6 to 10 μm.

[0033] Example 3 A method for applying a high-volume, fluorine-free silane dual-nano composite coating to the filter screen of an oil fume purification device includes the following steps: S1: Preparation of coating liquid Preparation of S1-1 Underlying Anchoring Nano-Coating Liquid: By weight, take 15 parts of methyltriethoxysilane, 8 parts of nano-silica (average particle size 10-20 nm), 1.0 part of glacial acetic acid, and 76 parts of anhydrous isopropanol.

[0034] Anhydrous isopropanol was added to an industrial-grade stainless steel reactor with a jacketed cooling system. Nano-silica powder was slowly added while stirring, and the mixture was stirred and dispersed at 300–500 rpm for 10 minutes. Then, methyltriethoxysilane was slowly added dropwise, and stirring continued for 5 minutes after the addition was complete. Finally, glacial acetic acid was added to adjust the pH of the system to 4.0–5.0. The temperature of the reaction system was controlled within the range of 20–30°C using circulating cooling water in the jacket, and hydrolysis was carried out by continuous stirring at 200–300 rpm for 60 minutes. After hydrolysis, the mixture was allowed to stand for 4 hours for later use, yielding the bottom anchoring nano-coating solution.

[0035] Preparation of S1-2 surface functional nano-coating liquid: By weight, take 12 parts of octyltriethoxysilane, 10 parts of hydrophobic nano-silica (average particle size 20-30 nm), 2.0 parts of organosilicon dispersant (BYK-9076), and 76 parts of anhydrous ethanol and isopropanol mixed solvent (volume ratio 1:1).

[0036] Add the mixed solvent to an industrial-grade preparation tank equipped with high-speed dispersion and online ultrasonic dispersion functions, add the organosilicon dispersant, and stir to dissolve at a speed of 400-600 r / min; while stirring, slowly add hydrophobic nano-silica powder, and after the addition is complete, increase the speed to 1500-2000 r / min and stir at high speed for 15 min; then start the industrial-grade rod ultrasonic vibration system and perform cyclic ultrasonic treatment at a frequency of 28 kHz and a power of 3 kW for 40 min; finally, slowly add octyltriethoxysilane and continue stirring at a speed of 200-300 r / min for 15 min to obtain the surface functional nano-coating liquid, which is then sealed and stored for later use.

[0037] S2: Substrate Pretreatment Stainless steel filters (304 stainless steel, wire diameter 0.3–0.5 mm, mesh size 20–40) from Merck commercial indoor direct-exhaust fume hoods were selected as the coating substrate and underwent continuous pretreatment on the mass production coating line. The pretreatment steps are as follows: (1) Alkaline washing and degreasing: The filter wire is conveyed into the automatic alkaline washing spray section by a suspended chain. It is sprayed and cleaned at 65°C for 12 minutes with a sodium hydroxide solution of 6% by mass to remove rolling oil and processing residues from the surface of the filter wire. (2) Deionized water rinsing: Enter the first deionized water spray cleaning section and spray clean at room temperature and high pressure for 3 minutes; (3) Pickling and activation: Enter the pickling and activation section and spray the screen with a 4% citric acid solution at room temperature for 2 minutes to activate the screen surface and enhance the adhesion of the coating. (4) Secondary deionized water rinse: Enter the second deionized water spray cleaning section and spray clean at room temperature and high pressure for 3 minutes; (5) Hot air drying: Enter the hot air drying tunnel, circulate hot air at 90℃ for 12 minutes, and cool to room temperature after exiting the tunnel for use.

[0038] S3: Coating and pre-curing of the bottom anchoring nanolayer A robotic, automated, air-assisted, airless spraying system was used to uniformly spray the prepared S1-1 base anchoring nano-coating liquid onto the surface of the stainless steel filter screen treated with S2, employing a cross-reciprocating spraying path. Considering the large specific surface area of ​​the filter screen mesh structure, the spray gun speed was appropriately increased to 45–50 cm / s, and a cross-reciprocating path was used to avoid excessive paint accumulation at the mesh openings, which could cause clogging. This ensured uniform coating coverage of the wire surface and that the mesh openings remained unobstructed. The spraying process parameters were: spray gun nozzle diameter 1.0–1.2 mm, spraying pressure 0.3–0.5 MPa, distance between the spray gun and the filter screen surface 15–25 cm, and spray gun speed 45–50 cm / s; ambient temperature was controlled at 20–28℃, and relative humidity at 40%–60%.

[0039] After spraying, the coating is conveyed to the leveling section by a suspended chain and leveled in a constant temperature and humidity environment of 25℃ (50% relative humidity) for 10 minutes. Then it enters the tunnel-type pre-curing oven and is kept at 75℃ for 20 minutes for curing. After exiting the oven, it is forced to cool to room temperature to obtain the bottom anchoring nano-layer.

[0040] S4: Coating of the surface functional nanolayer and overall gradient curing On the surface of the pre-cured S3 anchor nano-layer, a surface functional nano-coating liquid prepared in S1-2 is applied using a robotic automated air-assisted airless spraying system. A cross-reciprocating spraying path is used to avoid excessive paint accumulation at the mesh openings, which could cause clogging. The spraying process parameters are: spray gun nozzle diameter 0.8–1.0 mm, spraying pressure 0.25–0.4 MPa, distance between the spray gun and the filter surface 20–25 cm, gun travel speed 45–50 cm / s, and environmental temperature and humidity control conditions are the same as for S3.

[0041] After spraying, the coating enters the leveling section and is left to level for 15 minutes in a constant temperature and humidity environment of 25℃ (50% relative humidity); then it enters a three-stage continuous tunnel curing oven for segmented gradient temperature curing. First stage: Increase the temperature from room temperature to 80℃ at a rate of 2-3℃ / min, and keep it at that temperature for 15 minutes to cure. Second stage: Increase the temperature from 80℃ to 110℃ at a rate of 2℃ / min, and hold for 15 minutes to cure. The third stage: the temperature is increased from 110℃ to 130℃ at a rate of 1.5℃ / min, and then kept at that temperature for 30 minutes to cure.

[0042] The three drying ovens are connected by a transition section, with a total curing time of 60 minutes. After curing, the filter is cooled to room temperature in a forced air cooling section, resulting in the finished coated filter. After passing inspection, it is transferred to the packaging process, whereby the coated filter is assembled with the main body of the fume hood.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. The application of a fluorine-free silane dual nanogradient composite coating on the filter screen of an oil fume purification device, characterized in that, The coating includes a bottom anchoring nanolayer attached to the surface of the filter substrate of the fume purification device and a surface functional nanolayer attached to the surface of the bottom anchoring nanolayer. The underlying anchoring nanolayer is formed by coating and curing an underlying coating liquid containing a fluorine-free alkyl silane coupling agent and nano silica. The surface functional nanolayer is formed by coating and curing a surface coating liquid containing long-chain fluorine-free modified silane and hydrophobic nanoparticles.

2. The application according to claim 1, characterized in that, The underlying anchoring nano-coating liquid comprises, by weight: 10-15 parts of fluorine-free alkylsilane coupling agent, 5-8 parts of nano-silica, 0.5-1.0 parts of acidic catalyst, and 76-82.5 parts of organic solvent; the fluorine-free alkylsilane coupling agent is methyltriethoxysilane, the average particle size of the nano-silica is 10-25 nm, the acidic catalyst is glacial acetic acid, and the organic solvent is anhydrous isopropanol.

3. The application according to claim 1, characterized in that, The surface functional nano-coating liquid comprises, by weight: 8-12 parts of long-chain fluorine-free modified silane, 7-10 parts of hydrophobic nanoparticles, 1-2 parts of organosilicon dispersant, and 76-83 parts of organic solvent; the long-chain fluorine-free modified silane is octyltriethoxysilane or dodecyltriethoxysilane, the hydrophobic nanoparticles are hydrophobic nano-silica and / or hydrophobic nano-titanium dioxide, the average particle size of the hydrophobic nano-silica is 20-30 nm, and the organic solvent is a mixture of anhydrous ethanol and isopropanol in a volume ratio of 1:

1.

4. The application according to claim 1, characterized in that, The underlying anchoring nano-coating liquid also contains nano-alumina, the average particle size of which is 20-30 nm; the filter screen of the fume purification device is made of stainless steel, with a wire diameter of 0.3-0.6 mm and a mesh size of 16-40.

5. A method for coating a filter screen of an oil fume purification device with a fluorine-free silane dual nanogradient composite coating as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Preparation of coating liquids, including preparation of bottom anchoring nano coating liquid and surface functional nano coating liquid; S2: Pretreatment of filter substrate, which involves degreasing, activating and drying the filter of the fume purification device. S3: Coating and pre-curing of the bottom anchoring nano-layer: The bottom anchoring nano-coating liquid is coated onto the surface of the filter substrate and pre-cured. S4: Coating and overall gradient curing of the surface functional nano-layer: The surface functional nano-coating liquid is coated on the pre-cured bottom surface and cured by segmented gradient heating to obtain the finished product.

6. The coating method according to claim 5, characterized in that, The pretreatment of the filter substrate in S2 specifically includes the following steps: (1) Alkaline washing and degreasing: using a sodium hydroxide aqueous solution with a mass fraction of 5% to 8% to spray and clean at 60 to 70°C for 10 to 15 minutes; (2) Deionized water rinsing; (3) Acid washing and activation: using a citric acid aqueous solution with a mass fraction of 3% to 5% to spray and clean at room temperature for 1 to 2 minutes; (4) Secondary deionized water rinsing; (5) Hot air drying: drying at 80 to 100°C for 10 to 15 minutes.

7. The coating method according to claim 5, characterized in that, The coating in S3 is applied using an air-assisted airless spraying method, with a spray gun nozzle diameter of 1.0–1.2 mm, a spraying pressure of 0.3–0.5 MPa, a distance of 15–25 cm between the spray gun and the filter screen surface, and a gun travel speed of 35–45 cm / s. A cross-reciprocating spraying path is used during spraying. The pre-curing conditions are 70–75℃ for 20–25 min.

8. The coating method according to claim 5, characterized in that, The coating in S4 adopts an air-assisted airless spraying method, with a spray gun nozzle diameter of 0.8-1.0 mm, a spraying pressure of 0.25-0.4 MPa, a distance of 20-25 cm between the spray gun and the filter screen surface, and a gun travel speed of 40-50 cm / s. During spraying, a cross-reciprocating spraying path is used to avoid excessive accumulation of paint at the mesh openings, which could cause clogging.

9. The coating method according to claim 5, characterized in that, The segmented gradient temperature curing process in S4 specifically involves: First stage: Increase the temperature from room temperature to 80-85℃ at a rate of 2-3℃ / min, and keep it at that temperature for 15-20 minutes to cure. Second stage: Increase the temperature from 80-85℃ to 110-115℃ at a rate of 2℃ / min, and keep it at that temperature for 15-20 minutes to cure. The third stage: the temperature is increased from 110-115℃ to 130-135℃ at a rate of 1.5℃ / min, and then kept at that temperature for 30-40 minutes to cure.

10. The coating method according to claim 5, characterized in that, The total thickness of the coating is 5–10 μm.