One-step preparation of micro-nano double-layer structure super-hydrophobic ptf e coating

Abstract

The application discloses a one-step preparation method of super-hydrophobic PTFE with micro-nano double-layer structure and concretely relates to the field of thermal spraying processes, and comprises the following steps: step 1, sand blasting treatment is performed on the surface of a workpiece to roughen the surface; step 2, a direct current plasma spray gun is started without injecting PTFE emulsion, and pure flame flow is used to scan the surface of the workpiece to preheat; and step 3, after preheating, PTFE emulsion is injected into the flame flow to spray the surface of the workpiece and prepare a micro-nano double-layer structure super-hydrophobic PTFE coating. The application uses PTFE emulsion as raw material and uses direct current plasma spraying to prepare a micro-nano double-layer structure super-hydrophobic PTFE coating, and realizes one-step rapid preparation of the super-hydrophobic PTFE coating. The method does not need PTFE curing and sintering treatment in the prior art and does not need any etching post-treatment process, and the coating forms a micro-nano double-layer surface structure after preparation.

Description

Technical Field

[0001] This application relates to the field of thermal spraying technology, specifically a one-step preparation method for a micro-nano bilayer structure superhydrophobic PTFE coating. Background Technology

[0002] Superhydrophobic surfaces are defined as surfaces with a contact angle greater than 150° and a roll-off angle less than 10°. They have significant application potential in antifouling, corrosion resistance, self-cleaning, underwater drag reduction, and oil-water separation. The superhydrophobic properties of solid surfaces mainly originate from the synergistic effect of the surface's micro / nano bilayer structure and low surface energy materials. The key to preparing superhydrophobic coatings is to construct a micro / nano bilayer surface structure using low surface energy materials; that is, the coating surface structure must have micron-sized structures, and nano-sized structures must be distributed within these micron-sized structures.

[0003] Polytetrafluoroethylene (PTFE) is a commonly used low surface energy polymer material in industrial production and can be used to prepare hydrophobic coatings. Currently, the common method for preparing PTFE hydrophobic coatings involves spraying, dipping, or brushing PTFE emulsion onto the workpiece surface, followed by drying and curing (generally at 80-100℃ for 10-20 minutes), and finally sintering (generally at 350-380℃ for 20-30 minutes). This process is complex, involves many steps, and is time-consuming. Furthermore, the resulting PTFE coating has a flat surface and a maximum contact angle of approximately 120°, failing to achieve superhydrophobic properties. To fabricate micro / nano bilayer structures on this coating, further processing using techniques such as template imprinting, laser etching, and plasma etching is required, significantly increasing the cost and difficulty of the preparation.

[0004] Existing methods for preparing PTFE coatings using powder plasma spraying involve injecting PTFE powder into a plasma stream. After being heated and accelerated, the powder impacts the substrate surface to form the coating. The biggest drawback of this method is its inability to form micro / nano bilayer structures.

[0005] Given the limitations of existing PTFE coating preparation processes, such as complexity and difficulty in one-step fabrication of micro / nano bilayer structures, this invention uses PTFE emulsion as raw material to prepare a superhydrophobic PTFE coating with a convex micro / nano bilayer structure in one step using DC plasma spraying technology. This process requires no additional post-processing and has significant economic and engineering value. Summary of the Invention

[0006] Given the limitations of existing superhydrophobic PTFE coating preparation processes, this application provides a one-step method for preparing a micro / nano bilayer structure superhydrophobic PTFE coating. During plasma spraying, PTFE emulsion is injected into a high-temperature plasma stream, allowing it to spontaneously complete the curing and sintering process within the high-temperature flame. This eliminates the need for additional curing and sintering treatments after spraying, enabling the rapid one-step preparation of a superhydrophobic PTFE coating with a convex micro / nano bilayer structure.

[0007] A one-step method for preparing a superhydrophobic PTFE coating with a micro / nano bilayer structure includes the following steps:

[0008] Step 1: Sandblast the workpiece surface to increase its roughness, then clean the workpiece surface with compressed air before mounting the workpiece on the fixture.

[0009] Step 2: Start the DC plasma spray gun and preheat the workpiece surface by scanning it with a pure plasma flame without injecting PTFE emulsion.

[0010] Step 3: After preheating, inject PTFE emulsion into the plasma flame. After the flame stabilizes, spray it along the predetermined path to prepare a superhydrophobic PTFE coating with a micro-nano bilayer structure.

[0011] This application proposes for the first time a method for preparing a superhydrophobic PTFE coating with a micro / nano bilayer structure in one step using plasma spraying. During plasma spraying, a PTFE emulsion is transported into a high-temperature, high-speed plasma stream. The PTFE is atomized into tiny droplets in the stream, and the solvent in the droplets evaporates rapidly, forming tiny PTFE particles. These PTFE particles are heated in the stream and impact the workpiece surface in a molten / semi-molten state, forming a convex-shaped micro / nano bilayer structure superhydrophobic PTFE coating. Compared to the traditional "spraying / dipping / brushing-curing-sintering" process, the PTFE emulsion completes the "curing-sintering" process in the high-temperature stream during plasma spraying, achieving one-step preparation of the PTFE coating on the workpiece surface. This eliminates the need for subsequent curing and sintering after spraying, allowing the PTFE coating to exhibit a micro / nano bilayer structure in a single step, resulting in a superhydrophobic PTFE coating with a micro / nano bilayer structure. Many existing technologies require a traditional "spraying / dipping / brushing-curing-sintering" process to prepare a PTFE coating, followed by post-processing techniques such as plasma etching and laser etching to create microstructures on the PTFE coating. Compared to existing technologies, the one-step method for preparing a PTFE coating with a micro / nano bilayer structure described in this invention significantly improves preparation efficiency and saves costs.

[0012] Furthermore, the spray gun used is a DC plasma spray gun, meaning that the spraying process employed is DC plasma spraying. Of course, other plasma spraying processes, such as inductively coupled plasma spraying, can also be used.

[0013] Furthermore, the concentration of the PTFE emulsion is 20% to 60%.

[0014] Furthermore, the horizontal distance from the liquid nozzle outlet to the DC plasma spray gun is 20-50 mm, and the vertical distance from the DC plasma spray gun axis is 5-10 mm.

[0015] Furthermore, the delivery rate of the PTFE emulsion is 10-40 grams per minute.

[0016] Furthermore, the spraying distance is 60~100 mm.

[0017] Furthermore, the preheating path and spraying path are in an "arch" shape, with a spacing of 1 to 5 millimeters.

[0018] Furthermore, the surface of the superhydrophobic PTFE coating with a convex-shaped micro-nano bilayer structure has a micron-sized convex-shaped structure with obvious gaps between the convex-shaped structures, and the surface of the convex-shaped structure has submicron / nano-sized particles.

[0019] Furthermore, the micro-nano bilayer structure is a micron-sized sheet-like structure formed on the surface of a superhydrophobic PTFE coating, with obvious gaps between the sheet-like structures, and the surface of the sheet-like structure has submicron / nano-sized particles.

[0020] Furthermore, the method allows for the formation of a micro-nano bi-level structure immediately after step 3 is completed, without any post-processing.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention innovatively proposes a one-step DC plasma spraying method for preparing superhydrophobic PTFE coatings with a micro / nano bilayer structure. This method combines liquid PTFE emulsion with plasma spraying equipment, requiring no post-treatment processes. A micro / nano bilayer surface structure is formed immediately after spraying, and the coating exhibits superhydrophobic properties. Compared to other PTFE coating preparation processes, this method enables one-step, rapid, large-area, and high-volume preparation of superhydrophobic PTFE coatings with a micro / nano bilayer structure. Attached Figure Description

[0023] Figure 1 A schematic diagram of the coating preparation process using DC plasma spraying;

[0024] Figure 2 This is a schematic diagram of the spraying path;

[0025] Figure 3 The image shows the surface microstructure of the PTFE coating in Example 1, where (a) is a low-magnification surface microstructure showing a micron-sized convex hull structure; and (b) is a high-magnification surface microstructure showing the nanostructure of the convex hull surface.

[0026] Figure 4 The water contact angle of the PTFE coating in Example 1;

[0027] Figure 5 The image shows the surface microstructure of the PTFE coating in Example 2, where (a) is a low-magnification surface microstructure showing a micron-sized lamellar structure; and (b) is a high-magnification surface microstructure showing a nanostructure of the lamellar surface.

[0028] Figure 6 The water contact angle of the PTFE coating in Example 2.

[0029] In the diagram: 1. PTFE emulsion; 2. Peristaltic pump; 3. DC plasma spray gun; 4. Liquid nozzle; 5. Plasma flame; 6. Workpiece; 7. Spraying start point; 8. Lane spacing; 9. Spraying path. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments. To better illustrate the coating preparation method of this application, the liquid plasma spraying method described in this application is explained below. For example... Figure 1 As shown, during the plasma spraying process, PTFE emulsion 1 is transported by peristaltic pump 2 and sprayed into the plasma flame 5 generated by DC plasma spray gun 3 through liquid nozzle 4. After the plasma flame 5 stabilizes, DC plasma spray gun 3... Figure 2The spraying path shown moves in a "bow-shaped" motion to spray the surface of workpiece 6. The detailed process is as follows: The DC plasma spray gun 3 starts from the spraying starting point 7 outside the workpiece 6, first completing one layer of PTFE material spraying, then moving down one pass spacing 8 to spray the next layer of PTFE material. After each layer is sprayed, it continues to move down one pass spacing 8 until the entire surface of workpiece 6 is sprayed, thus completing the first layer of coating. The DC plasma spray gun 3 returns to the spraying starting point 7 and repeats the above trajectory to spray another layer, thus cycling until the predetermined number of coating layers is reached, ultimately forming a superhydrophobic PTFE coating with a micro-nano dual-layer structure. The PTFE coating formed in this application has a micro-nano bilayer structure, which consists of micron-sized convex / lamellar structures on the surface of the PTFE coating, with significant gaps between them, and submicron / nano-sized particles on the surface of the convex / lamellar structures; that is, the first layer is a micron-sized convex / lamellar structure, and the second layer is a convex / lamellar structure with submicron / nano-sized particles on its surface. The gap-distributed convex / lamellar structures and the submicron / nano-sized particles on their surface give the PTFE coating superior superhydrophobic properties.

[0031] Furthermore, to more clearly illustrate the formation of the micro / nano bilayer structure in this application, the coating deposition principle of the method described in this application is explained. When the PTFE emulsion is injected into the plasma stream, it is atomized into numerous tiny droplets under the action of the high-speed stream. These droplets then undergo solvent evaporation and internal particle aggregation, forming extremely small molten or partially molten microparticles. When the plasma stream carrying a large number of microparticles comes into contact with the substrate, the stream is deflected by the substrate, forming a deflected stream parallel to the substrate surface near the substrate. Because the microparticles carried in the stream are very small in size and mass, they are easily affected by the deflected stream during the deposition process (i.e., when colliding with the substrate), forming an inclined deposition trajectory and impacting the substrate surface at an inclined angle. As the spraying process proceeds, because the impact of the microparticles is inclined, the microparticles only impact one side of the previously deposited coating and cannot impact the other side. This results in the coating on one side continuously accumulating and increasing, while the other side forms voids due to the lack of particle impact. Therefore, under this effect, micron-sized structures and gaps gradually form. The above theory can also explain why traditional plasma spraying using powder as raw material cannot prepare micro-nano bilayer structures. Traditional plasma spraying uses large-size powder (particle size 20~100 micrometers) as raw material. Due to the large mass of the large-size powder, it is not affected by the deflection of the flame when impacting the substrate, and all of it impacts the substrate surface at a perpendicular angle, ultimately forming a flat coating morphology.

[0032] Example 1

[0033] (1) Sandblast the surface of workpiece 6, then use compressed air to blow away the residual sandblasting particles on the surface of the workpiece, and then install the workpiece on the fixture.

[0034] (2) Start the DC plasma spray gun 3 to generate plasma flame 5. Without injecting PTFE emulsion 1, move the DC plasma spray gun 3 from the spraying starting point 7 along the spraying path 9 to scan the surface of the workpiece 6 for preheating. The main process parameters of the preheating stage include: the plasma gas input to the DC plasma spray gun 3 is 30 standard liters per minute of argon and 5 standard liters per minute of hydrogen; the power of the DC plasma spray gun 3 is 24 kilowatts; the moving speed of the DC plasma spray gun 3 relative to the workpiece 6 is 1 meter per second; the channel spacing 8 is 5 millimeters; the distance between the DC plasma spray gun 3 and the workpiece 6 is 100 millimeters; and the number of scanning layers is 5 layers.

[0035] (3) Start the peristaltic pump 2 and inject the PTFE emulsion 1 into the plasma flame 5 through the nozzle 4. Adjust the speed of the peristaltic pump 2 to keep the delivery rate of the PTFE emulsion 1 at about 40 grams per minute. After the plasma flame 5 stabilizes, move the DC plasma spray gun 3 from the spraying starting point 7 along the spraying path 9 to spray the surface of the workpiece 6. The main process parameters of the spraying stage include: the concentration of PTFE emulsion 1 is 60%; the horizontal distance from the outlet of the liquid nozzle 4 to the DC plasma spray gun 3 is 20 mm, and the vertical distance from the outlet of the DC plasma spray gun 3 to the axis of the DC plasma spray gun 3 is 5 mm; the plasma gas input into the DC plasma spray gun 3 is 40 standard liters per minute of argon and 10 standard liters per minute of hydrogen, and the power of the DC plasma spray gun 3 is 32 kilowatts; the moving speed of the DC plasma spray gun 3 relative to the workpiece 6 is 0.5 meters per second, the channel spacing 8 is 3 mm, the distance between the DC plasma spray gun 3 and the workpiece 6 is 60 mm; and the number of sprayed layers is 20.

[0036] The microstructure of the PTFE coating sprayed according to the parameters described in Example 1 is as follows: Figure 3 As shown. Surface microstructure image at low magnification ( Figure 3 a) The coating surface exhibits a spherical convex-bump structure with a diameter of approximately 200 micrometers. There are obvious gaps between these convex-bump structures, and some of them connect to form larger micrometer-sized island structures; high-magnification image of the surface microstructure ( Figure 3 (b) The surface of the micron-sized convex structure is also covered with irregularly shaped submicron / nano-sized particles. This micron-sized convex structure and the submicron / nano-sized particles on its surface combine to form a micro / nano bilayer structure. The sprayed PTFE coating exhibits superhydrophobic properties without the curing and sintering processes required in traditional technologies, with a water contact angle of 164°. Figure 4As shown. The microstructure and water contact angle of the coating in Example 1 confirm that the method described in this application can achieve one-step preparation of micro / nano bilayer superhydrophobic PTFE coatings without any post-processing.

[0037] Example 2

[0038] Compared to Example 1, the main changes in process parameters in Example 2 include: a lower PTFE emulsion concentration (i.e., less PTFE in the same mass of PTFE emulsion), a smaller feed rate, a PTFE injection position further away from the flame outlet, a lower spray gun power, a higher spray gun moving speed relative to the workpiece, and a larger distance between the spray gun and the workpiece. The purpose of these parameter changes is to reduce the melting degree of the PTFE emulsion, thereby allowing for comparison with the coating in Example 1.

[0039] (1) Sandblast the surface of workpiece 6, then use compressed air to blow away the residual sandblasting particles on the surface of the workpiece, and then install the workpiece on the fixture.

[0040] (2) Start the DC plasma spray gun 3 to generate plasma flame 5. Without injecting PTFE emulsion 1, move the DC plasma spray gun 3 from the spraying starting point 7 along the spraying path 9 to scan the surface of the workpiece 6 for preheating. The main process parameters of the preheating stage include: the plasma gas input to the DC plasma spray gun 3 is 30 standard liters per minute of argon and 5 standard liters per minute of hydrogen; the power of the DC plasma spray gun 3 is 24 kilowatts; the moving speed of the DC plasma spray gun 3 relative to the workpiece 6 is 1 meter per second; the channel spacing 8 is 3 millimeters; the distance between the DC plasma spray gun 3 and the workpiece 6 is 80 millimeters; and the number of scanning layers is 5.

[0041] (3) Start the peristaltic pump 2 and inject the PTFE emulsion 1 into the plasma flame 5 through the nozzle 4. Adjust the speed of the peristaltic pump 2 to keep the delivery rate of the PTFE emulsion 1 at about 10 grams per minute. After the plasma flame 5 stabilizes, move the DC plasma spray gun 3 from the spraying starting point 7 along the spraying path 9 to spray the surface of the workpiece 6. The main process parameters of the spraying stage include: the concentration of PTFE emulsion 1 is 20%; the horizontal distance from the outlet of the liquid nozzle 4 to the DC plasma spray gun 3 is 50 mm, and the vertical distance from the outlet of the DC plasma spray gun 3 to the axis of the DC plasma spray gun 3 is 10 mm; the plasma gas input to the DC plasma spray gun 3 is 30 standard liters per minute of argon and 5 standard liters per minute of hydrogen; the power of the DC plasma spray gun 3 is 24 kilowatts; the moving speed of the DC plasma spray gun 3 relative to the workpiece 6 is 1 meter per second, the channel spacing 8 is 5 mm, the distance between the DC plasma spray gun 3 and the workpiece 6 is 100 mm; the number of sprayed layers is 20.

[0042] The microstructure of the PTFE coating sprayed according to the parameters described in Example 2 is as follows: Figure 5As shown. Surface microstructure image at low magnification ( Figure 5 a) The coating surface exhibits an irregular, micron-sized lamellar structure, with dimensions ranging from several hundred micrometers. Significant gaps exist between these lamellar structures. Due to the parameters used in Example 2, the PTFE emulsion melting was impaired, and the low PTFE emulsion concentration and small feed rate ultimately resulted in the formation of thinner lamellar structures. (High-magnification image of the surface microstructure) Figure 5 (b) The surface of the micron-sized lamellar structure is also covered with irregularly shaped submicron / nano-sized particles. This micron-sized lamellar structure and the submicron / nano-sized particles on its surface combine to form a micro / nano bilayer structure. The sprayed PTFE coating exhibits superhydrophobic properties without the need for curing and sintering processes found in traditional techniques, with a water contact angle of 152°. Figure 6 As shown. The microstructure and water contact angle of the coating in Example 2 confirm that the method described in this application can achieve one-step preparation of micro / nano bilayer superhydrophobic PTFE coatings without any post-processing.

[0043] Finally, it should be noted that all parts not covered in this invention are the same as or can be implemented using existing technologies. Furthermore, the above embodiments are only used to illustrate the technical solutions of this invention and not to limit it. Although this invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of this invention, and these modifications or equivalent substitutions should not cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of this invention.

Claims

1. A one-step preparation method for a micro / nano bilayer structure superhydrophobic PTFE coating, characterized in that, Includes the following steps: Step 1: Sandblast the surface of the workpiece to increase its roughness, then clean the surface of the workpiece with compressed air before mounting it on the fixture; Step 2: Start the DC plasma spray gun and preheat the workpiece surface by scanning it with a pure flame without injecting PTFE emulsion; Step 3: After preheating, inject PTFE emulsion into the flame stream. After the flame stream stabilizes, spray according to the predetermined spraying path to prepare a micro-nano bilayer structure superhydrophobic PTFE coating. The micro-nano bilayer structure is a micron-sized convex-shaped structure formed on the surface of a superhydrophobic PTFE coating. There are obvious gaps between the convex-shaped structures, and the surface of the convex-shaped structure has submicron / nano-sized particles. Or, The micro-nano bilayer structure is a micron-sized sheet-like structure formed on the surface of a superhydrophobic PTFE coating. There are obvious gaps between the sheet-like structures, and the surface of the sheet-like structure has submicron / nano-sized particles.

2. The one-step preparation method according to claim 1, characterized in that, The spray gun used is a DC plasma spray gun.

3. The one-step preparation method according to claim 2, characterized in that, The concentration of the PTFE emulsion is 20% to 60%.

4. The one-step preparation method according to claim 3, characterized in that, The horizontal distance from the liquid nozzle outlet to the DC plasma spray gun is 20-50 mm, and the vertical distance from the DC plasma spray gun axis is 5-10 mm.

5. The one-step preparation method according to claim 4, characterized in that, In step 3, the PTFE emulsion is delivered at a rate of 10-40 grams per minute.

6. The one-step preparation method according to claim 5, characterized in that, In step 3, the spraying distance is 60~100 mm.

7. The one-step preparation method according to claim 1, characterized in that, Both the preheating path and the spraying path are "bow-shaped", with a spacing of 1 to 5 mm.

8. The one-step preparation method according to any one of claims 1-7, characterized in that, The method is that after step 3 is completed, a superhydrophobic PTFE coating with a micro-nano bilayer structure can be formed without any post-processing.

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