Electrostatic spraying high-durability super-hydrophobic coating and preparation method thereof

Abstract

The invention discloses an electrostatic spraying high-durability super-hydrophobic coating and a preparation method thereof, the electrostatic spraying high-durability super-hydrophobic coating is a polyester / PFA / SiO2 composite coating, and a three-dimensional porous frame structure is constructed on the surface of the polyester / PFA / SiO2 composite coating; in the three-dimensional porous frame structure, cured polyester forms a supporting frame, and the supporting frame is filled with PFA and SiO2 particles; the pore diameter of the supporting frame is randomly distributed, the size is 100-300 microns, and the first-stage roughness of the surface of the coating is formed; the second-level roughness is formed by gathering PFA and SiO2 particles, the gathering size of the SiO2 particles is 50-200 nanometers, the gathering size of the PFA particles is 10-60 micrometers, and the gathering size of the SiO2 particles and the gathering size of the PFA particles are both smaller than the pore diameter of the frame. The invention has the characteristics of simple preparation method, low cost and high durability.

Description

Technical Field

[0001] The present invention relates to the technical field of superhydrophobic coatings, and specifically relates to an electrostatic spraying high-durability superhydrophobic coating and a preparation method thereof. Background Art

[0002] A superhydrophobic surface refers to a surface with a water contact angle greater than 150° and a rolling angle less than 10°. Due to its unique waterproof, anti-fouling, self-cleaning and other properties, superhydrophobic coatings have shown great application potential in many fields.

[0003] Existing superhydrophobic technologies still have some deficiencies, which limit their wider application.

[0004] For example, in the patent with publication number: CN114682922, a method for regulating the stress and texture morphology of an aluminum alloy superhydrophobic surface prepared by laser etching is disclosed. Its preparation process is complex, the cost is high, and it is difficult to achieve large-area preparation. In addition, the durability of some coatings is insufficient, especially the long-term stability in harsh environments is poor, and it is easily affected by factors such as wear and corrosion, resulting in a decline in hydrophobic performance. Summary of the Invention

[0005] In order to overcome the above technical problems, the purpose of the present invention is to provide an electrostatic spraying high-durability superhydrophobic coating and a preparation method thereof, which have the characteristics of simple preparation method, low cost and high durability.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] An electrostatic spraying high-durability superhydrophobic coating is a polyester / PFA / SiO2 composite coating, and a three-dimensional porous framework structure is constructed on the surface of the polyester / PFA / SiO2 composite coating;

[0008] In the three-dimensional porous framework structure, the cured polyester constitutes a support framework, and PFA and SiO2 particles are filled inside the support framework;

[0009] The pore diameters of the support framework are randomly distributed, with sizes of 100 - 300 microns, constituting the first-level roughness of the coating surface; the main function of this roughness is to break the continuity of droplets and improve wear resistance, while reducing the solid-liquid contact area;

[0010] The second-level roughness is formed by the aggregation of PFA and SiO2 particles, where the aggregation size of SiO2 particles is 50 - 200 nanometers, and the aggregation size of PFA particles is 10 - 60 microns, and both are smaller than the pore diameter of the framework.

[0011] The agglomeration of the PFA particles and the SiO2 particles forms a surface structure with micron-scale protrusions, presenting a randomly distributed rough morphology. The PFA particles play a role in supporting the droplets, reducing the contact area between the droplets and the coating surface, thereby endowing the coating with superhydrophobic properties. The SiO2 particles are distributed around the PFA particles, further enhancing the mechanical properties of the coating.

[0012] A preparation method of an electrostatic spraying highly durable superhydrophobic coating includes the following steps;

[0013] Step (1) Substrate pretreatment process: First, polish the stainless steel substrate with 60 - 800# sandpaper, then perform ultrasonic cleaning with ethanol for 10 - 60 min, then thoroughly rinse with deionized water, and perform drying treatment;

[0014] Step (2) Powder mixing process: Mix polyester powder, PFA powder, and SiO 2 powder into polyester / PFA / SiO 2 powder. The weight percentage of the PFA powder in the mixed powder is 12%, and the weight percentage of the SiO 2 powder is 1% - 4%, and the rest is polyester powder;

[0015] Step (3) Through an electrostatic spraying device, evenly spray the polyester / PFA / SiO 2 powder onto the surface of the substrate treated in step (1), and then place it in a furnace for heating and curing to obtain a superhydrophobic coating.

[0016] Furthermore, in the step (1), the substrate is metal, glass, ceramic, fabric, wood or plastic.

[0017] Furthermore, in the step (2), the PFA is in powder form and the particle size range is between 10 nm and 80 μm; preferably, the PFA is in powder form and the particle size range is between 100 nm and 800 nm. The coating prepared with 100 nm - 800 nm PFA powder has a higher contact angle, and has a dual-scale structure and better wear resistance.

[0018] Furthermore, in the step (2), the SiO 2 is in powder form and the particle size range is between 10 nm and 200 nm; preferably, the SiO 2 is in powder form and the particle size range is between 30 nm and 50 nm. Since the surface energy of the SiO 2 material is higher than that of the PFA, using SiO 2 powder with a relatively smaller particle size than the PFA can avoid the protruded structure being SiO 2 powder, thus affecting the superhydrophobicity of the coating.

[0019] Furthermore, in the step (2), the mixing time of the powder mixer is 1 - 300 min; preferably, the mixing time of the powder mixer is 60 - 80 min. This allows the powder to be fully mixed while preventing the powder from being broken by the powder mixer and affecting its particle size.

[0020] Furthermore, in the step (3), the spraying voltage is 30 - 90 kV, the current is 10 - 60 μA, and the spraying distance is 10 - 80 cm; preferably, the spraying voltage is 60 kV, the current is 30 μA, and the spraying distance is 15 - 30 cm. This enables the powder to be evenly sprayed onto the substrate surface. Excessively high voltage and current can cause the coating to break down, while too low voltage and current can lead to uneven spraying on the coating surface and defects.

[0021] Furthermore, in the step (3), the thickness of the superhydrophobic coating is 10 μm - 300 μm.

[0022] Furthermore, in the step (3), the heating and curing temperature is 150 - 250 °C, and the curing time is 10 - 60 min; preferably, the sintering and curing temperature is 180 - 210 °C, and the curing time is 15 - 25 min. The selected sintering temperature is lower than the melting points of PFA and SiO 2 and is within the curing temperature range of the polyester, enabling the polyester to be fully cured.

[0023] Advantages of the present invention:

[0024] The present invention adopts electrostatic powder spraying technology. The coating prepared by this preparation method is uniform, and the preparation method is simple. There is no requirement for the shape of the substrate, and large-scale preparation can be achieved;

[0025] By adjusting the particle sizes and mixing ratios of PFA powder and SiO 2 powder, the present invention can prepare a coating with both superhydrophobicity and wear resistance;

[0026] Through the electrostatic spraying process, the polyester / PFA / SiO 2 mixed powder is evenly sprayed onto the substrate surface. After sintering, the sintering and curing temperature range of the polyester is reached, while the melting points of PFA and SiO 2 are not reached. The cured polyester layers and cures PFA particles and SiO 2 particles on the substrate surface, greatly enhancing the bonding force of the coating and endowing the coating with excellent durability. Even if the outer layer is worn, the internal layer can still maintain good hydrophobicity.

[0027] The SiO 2 powder used in the coating prepared by the present invention has excellent mechanical properties and can improve the mechanical stability of the coating. Brief Description of the Drawings

[0028] Figure 1 Shows the relationship between the contact angle and the change in the PFA weight percentage.

[0029] Figure 2 SEM image of the thermosetting polyester / PFA composite coating prepared for Case 4.

[0030] Figure 3 Element distribution map of the surface of the thermosetting polyester / PFA composite coating prepared for Case 4.

[0031] Figure 4 Shows the relationship between the contact angle and the change in the SiO 2 weight percentage when the PFA weight percentage is 12%.

[0032] Figure 5 Shows the SEM image of the thermosetting polyester / PFA / SiO 2 composite coating prepared in Example 7.

[0033] Figure 6 In (a), it is a schematic diagram of the wear experiment of the thermosetting polyester / PFA / SiO2 composite coating prepared in Example 7, and (b) is the effect of the wear distance on the contact angle of the composite coating. Detailed Description of the Invention

[0034] The present invention will be further described in detail below with reference to the accompanying drawings.

[0035] An electrostatic spraying highly durable superhydrophobic coating. The present invention designs a combination of a micro-nano hierarchical structure and an organic-inorganic composite framework, and successfully realizes the synergistic optimization of superhydrophobic performance and mechanical durability. As Figure 2 shown, by adjusting the mixing ratio of the polyester powder and the PFA powder, a micro-protruding surface structure is sprayed and constructed on the substrate. This special protruding structure can effectively reduce the contact area between the water droplet and the coating surface. Combined with the inherently ultra-low surface energy property of the PFA material (surface energy < 12 mN / m), the combined action of these two factors endows the coating with excellent superhydrophobic performance. At this time, there is still room for improvement in the surface hardness and wear resistance of the coating. Therefore, SiO2 powder with excellent mechanical properties is introduced, as Figure 5 shown. After sintering treatment, a three-dimensional porous framework structure is formed on the surface. In this structure, the cured polyester forms the framework, and its Vickers hardness is increased by about 3.2 times (189 Hv) compared with pure PFA, and it has excellent wear resistance. The framework is filled with PFA and SiO2 particles, and at the same time, the SiO2 powder also helps to improve the hardness and wear resistance inside the framework, so that the coating has both superhydrophobicity and excellent wear resistance.

[0036] Comparative Case 1

[0037] This embodiment provides a method for preparing a superhydrophobic coating, which includes the following steps:

[0038] (1) Substrate pretreatment process: First, polish the stainless-steel substrate with 60# sandpaper, then perform ultrasonic cleaning with ethanol for 30 min, then thoroughly rinse with deionized water, and perform drying treatment;

[0039] (2) Powder mixing process: Uniformly mix polyester powder and PFA powder through a powder mixer, and the weight percentage of the PFA powder is 3%.

[0040] (3) Through an electrostatic spraying device, uniformly spray the mixed powder onto the surface of the substrate. The spraying voltage is 60 kV, the current is 30 μA, and the spraying distance is 15 - 30 cm. Then place it in a furnace at 200 °C for heating and curing for 20 min to obtain a thermosetting polyester / PFA composite superhydrophobic coating.

[0041] Performance testing: Use a paint film thickness gauge to measure the coating thickness; measure the contact angle of the coating surface in air using 5 μL of deionized water on a contact angle analyzer (Dataphysics - OCA20, Germany); test the adhesion using the cross - cut method (ISO 2409:2020); test the abrasion resistance using the method of sandpaper polishing, with a 200 g weight, 400 - mesh sandpaper, and 10 cm of friction as one cycle.

[0042] The performance test results are as follows:

[0043] Coating thickness: ~121 nm;

[0044] Contact angle: 116.3°;

[0045] Rolling angle: 39.6°;

[0046] Adhesion test (ISO 2409:2020): The highest level is 0;

[0047] Abrasion resistance (polishing with 4632 Pa pressure, 400# sandpaper, and 10 cm of friction as one cycle): 128 cycles.

[0048] Comparative case 2

[0049] This embodiment provides a method for preparing a superhydrophobic coating, the steps of which are generally similar to those of Embodiment 1. The difference is that the weight percentage of PFA is 6%.

[0050] The performance testing method is the same as that of Embodiment 1, and the performance test results are as follows:

[0051] Coating thickness: ~138 nm;

[0052] Contact angle: 137.3°;

[0053] Rolling angle: 23.4°;

[0054] Adhesion test (ISO 2409:2020): Grade 0 (highest);

[0055] Abrasion resistance (using a pressure of 4632 Pa, sandpaper grit 400#, and 10 cm of abrasion per cycle): 101 cycles.

[0056] Comparative Example 3

[0057] This example provides a method for preparing a superhydrophobic coating. The steps are generally similar to those of Example 1, except that the weight percentage of PFA is 9%.

[0058] The performance test method is the same as that of Example 1, and the performance test results are as follows:

[0059] Coating thickness: ~167 nm;

[0060] Contact angle: 158.1°;

[0061] Rolling angle: 9.6°;

[0062] Adhesion test (ISO 2409:2020): Grade 0 (highest);

[0063] Abrasion resistance (using a pressure of 4632 Pa, sandpaper grit 400#, and 10 cm of abrasion per cycle): 96 cycles.

[0064] Comparative Example 4

[0065] This example provides a method for preparing a superhydrophobic coating. The steps are generally similar to those of Example 1, except that the weight percentage of PFA is 12%. Its contact angle is as Figure 1 shown. The scanning electron microscope image of the thermosetting polyester / PFA composite coating prepared in Example 4 is as Figure 2 shown, and the surface element distribution is as Figure 3 shown.

[0066] The performance test method is the same as that of Example 1, and the performance test results are as follows:

[0067] Coating thickness: ~174 nm;

[0068] Contact angle: 162.3°;

[0069] Rolling angle: 4.3°;

[0070] Adhesion test (ISO 2409:2020): Grade 0 (highest);

[0071] Abrasion resistance (under a pressure of 4632 Pa, polished with 400# sandpaper, 10 cm of friction as one cycle): 101 cycles.

[0072] It can be seen from Figure 2 that the surface structural characteristics of the composite coating are jointly composed of spherical and irregular morphologies. Given that the curing temperature is set at 200 °C, which is the curing temperature of thermosetting polyester, while the melting temperature of PFA is 380 °C, the observed particle agglomeration phenomenon on the surface should be attributed to the unmelted PFA powder particles, which are fixed on the substrate surface by the molten thermosetting polyester curing agent.

[0073] It can be seen from Figure 3 that the distribution of surface elements C, F, and O shows overall uniformity, which ensures the uniformity of powder mixing and stable powder supply during electrostatic spraying, thus guaranteeing the stability of the coating preparation process and the consistency of coating composition and performance.

[0074] Comparative case 5

[0075] This example provides a method for preparing a superhydrophobic coating, the steps of which are generally similar to those of Example 1, except that the weight percentage of PFA is 15%.

[0076] The performance test method is the same as that of Example 1, and the performance test results are as follows:

[0077] Coating thickness: ~194 nm;

[0078] Contact angle: 161.6°;

[0079] Rolling angle: 4.2°;

[0080] Adhesion test (ISO 2409:2020): Grade 0 (highest level);

[0081] Abrasion resistance (under a pressure of 4632 Pa, polished with 400# sandpaper, 10 cm of friction as one cycle): 71 cycles.

[0082] Example 6

[0083] This example provides a method for preparing a superhydrophobic coating, which includes the following steps:

[0084] (1) Substrate pretreatment process: First, polish the stainless steel substrate with 60# sandpaper, then perform ultrasonic cleaning with ethanol for 30 min, then thoroughly rinse with deionized water, and perform drying treatment;

[0085] (2) Powder mixing process: Uniformly mix polyester powder, PFA powder, and SiO 2 powder through a powder mixer. The weight percentage of the PFA powder is 12%, and SiO2 The weight percentage of the powder is 2%.

[0086] (3) Through an electrostatic spraying device, the mixed powder is evenly sprayed onto the surface of the substrate. The spraying voltage is 60 kV, the current is 30 μA, and the spraying distance is 15 - 30 cm. Subsequently, it is placed in a furnace at 200 °C and heated and cured for 20 min to obtain a thermosetting polyester / PFA composite superhydrophobic coating.

[0087] The performance test method is the same as that in Example 1, and the performance test results are as follows:

[0088] Coating thickness: ~203 nm;

[0089] Contact angle: 159.6°;

[0090] Rolling angle: 8.1°;

[0091] Adhesion test (ISO 2409:2020): Grade 0 (highest level);

[0092] Abrasion resistance (with a pressure of 4632 Pa, polished with 400# sandpaper, and 10 cm of friction as one cycle): 120 cycles.

[0093] Example 7

[0094] This example provides a method for preparing a superhydrophobic coating. Its steps are generally similar to those in Example 6, except that the weight percentage of SiO 2 powder is 4%.

[0095] The performance test method is the same as that in Example 1, and the performance test results are as follows:

[0096] Coating thickness: ~197 nm;

[0097] Contact angle: 162.2°;

[0098] Rolling angle: 4.6°;

[0099] Adhesion test (ISO 2409:2020): Grade 0 (highest level);

[0100] The coating material used in the present invention is a composite system of a thermosetting polyester matrix and a double filler (PFA / SiO 2 ). The curing temperature of this composite system is set at 200 °C, which is within the curing temperature range of the thermosetting polyester, while neither the PFA nor the SiO 2 powder reaches its respective melting point. Observation Figure 5From the microstructures shown, it can be found that unfused PFA and SiO2 powders are embedded in the pore structure of the thermosetting polyester. Among them, the PFA powder endows the coating with superhydrophobic properties due to its low surface energy characteristics; while silica, as a hard filler, its excellent mechanical properties contribute to improving the hardness and wear resistance of the coating.

[0101] Wear resistance tests were carried out on the double-filler composite coating, as Figure 6 shown. The contact angle of the coating remained relatively stable during the change of the wear distance, indicating the excellent wear resistance of the coating.

[0102] Example 8

[0103] This example provides a preparation method of a superhydrophobic coating. Its steps are roughly similar to those of Example 6. The difference is that the weight percentage of SiO 2 powder is 6%. Its contact angle is as Figure 2 shown. The scanning electron microscope image of the thermosetting polyester / PFA composite coating prepared in Example 8 is as Figure 2 shown, and the surface element distribution is as Figure 3 shown.

[0104] The performance test method is the same as that in Example 1, and the performance test results are as follows:

[0105] Coating thickness: ~224 nm;

[0106] Contact angle: 163.4°;

[0107] Rolling angle: 3.4°;

[0108] Adhesion test (ISO 2409: 2020): The highest level is 0;

[0109] Abrasion resistance (using a pressure of 4632 Pa, sanding with 400# sandpaper, and 10 cm of friction as one cycle): 97 cycles.

[0110] By adjusting the particle size and mixing ratio of the PFA powder and SiO 2 powder. When the weight percentage of the PFA powder in the mixed powder is 12% and the weight percentage of the SiO 2 powder is 3%, a coating with both superhydrophobicity and wear resistance can be prepared;

[0111] In summary, the above-mentioned are only the preferred embodiments of the present invention, and do not impose any limitations on the scope of the present invention. For those skilled in the art of this technology, the modifications of the above embodiments based on the core technology of the present invention should be regarded as within the protection scope of the technical solution of the present invention.

Claims

1. An electrostatically sprayed highly durable super hydrophobic coating, characterized in that: It is a polyester / PFA / SiO2 composite coating, and a three-dimensional porous framework structure is constructed on the surface of the polyester / PFA / SiO2 composite coating; In the three-dimensional porous framework structure, the cured polyester forms a support frame, and the interior of the support frame is filled with PFA and SiO2 particles; The pores of the support frame are randomly distributed with a size of 100-300 μm, which constitute the first level of roughness of the coating surface; The second level of roughness is formed by the aggregation of PFA and SiO2 particles, where the aggregation size of SiO2 particles is 50-200 nanometers, while the aggregation size of PFA particles is 10-60 microns, both of which are smaller than the framework aperture.

2. The electrostatically sprayed highly durable super hydrophobic coating according to claim 1, characterized in that: The agglomeration of the PFA particles and the SiO2 particles forms a surface structure with micron-scale protrusions, presenting a randomly distributed rough morphology. The PFA particles play a role in supporting the droplets, and the SiO2 particles are distributed around the PFA particles.

3. A method for preparing a highly durable super hydrophobic coating by electrostatic spraying, characterized in that: The steps include: Step (1) substrate pretreatment process: first, the stainless steel substrate is polished with sandpaper, then ultrasonically cleaned with ethanol for 10-60 minutes, then thoroughly rinsed with deionized water, and dried; Step (2) powder mixing process: polyester powder, PFA powder and SiO2 powder are mixed into polyester / PFA / SiO2 powder by a powder mixer, wherein the weight percentage of PFA powder accounts for 12% of the mixed powder, the weight percentage of SiO2 powder is 1%-4%, and the rest is polyester powder; Step (3) uses an electrostatic spraying device to evenly spray the polyester / PFA / SiO2 powder onto the surface of the substrate treated in step (1), and then heats and cures it in a furnace to obtain a super-hydrophobic coating.

4. The method for preparing a highly durable super hydrophobic coating by electrostatic spraying according to claim 1, wherein: In the step (1), the substrate is metal, glass, ceramic, fabric, wood or plastic.

5. The method for preparing a highly durable super hydrophobic coating by electrostatic spraying according to claim 1, wherein: In the step (2), the PFA is in the form of powder and has a particle size ranging from 10 nm to 80 μm.

6. The method for preparing a highly durable super hydrophobic coating by electrostatic spraying according to claim 1, wherein: In the step (2), the SiO2 is powder and has a particle size ranging from 10nm to 200nm.

7. The method for preparing a highly durable super hydrophobic coating by electrostatic spraying according to claim 1, wherein: In the step (2), the powder mixer mixes the powder for a time of 1-300 minutes.

8. The method for preparing a highly durable super hydrophobic coating by electrostatic spraying according to claim 1, wherein: In the step (3), the spraying voltage is 30-90 kV, the current is 10-60 μA, and the spraying distance is 10-80 cm.

9. The method for preparing a highly durable super hydrophobic coating by electrostatic spraying according to claim 1, wherein: In the step (3), the thickness of the super hydrophobic coating is 10 μm-300 μm.

10. The method for preparing a highly durable super hydrophobic coating by electrostatic spraying according to claim 1, characterized in that: In the step (3), the heating curing temperature is 150-250° C., and the curing time is 10-60 min.

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