One-step preparation method of super-hydrophobic PTFE (Polytetrafluoroethylene) coating with micro-nano double-layered structure

Abstract

The invention discloses a one-step preparation method of super-hydrophobic PTFE (Polytetrafluoroethylene) with a micro-nano double-layered structure, and particularly relates to the field of thermal spraying processes, which comprises the following steps: step 1, performing sand blasting treatment on the surface of a workpiece to roughen the surface of the workpiece; 2, under the condition that PTFE emulsion is not injected, a direct-current plasma spray gun is started, and the surface of the workpiece is scanned through pure flame flow for preheating; and 3, after preheating is completed, PTFE emulsion is injected into flame flow, the surface of the workpiece is sprayed, and the super-hydrophobic PTFE coating of the micro-nano double-layer structure is prepared. According to the method, the PTFE emulsion is used as a raw material for the first time, the super-hydrophobic PTFE coating with the micro-nano double-layered structure is prepared through direct-current plasma spraying, and one-step rapid preparation of the super-hydrophobic PTFE coating is achieved. According to the method, PTFE curing and sintering treatment in the prior art are not needed, any etching post-treatment process is also not needed, and the micro-nano double-layer surface structure is formed after the coating is prepared.

Description

Technical Field

[0001] The present application relates to the field of thermal spraying technology, and specifically to a one-step preparation method of a micro-nano double-layer structured super-hydrophobic PTFE coating. Background Art

[0002] A superhydrophobic surface refers to a surface with a contact angle greater than 150° and a rolling angle less than 10°. It has great application potential in the fields of antifouling, anticorrosion, self-cleaning, underwater drag reduction, and oil-water separation. The superhydrophobic property of solid surfaces mainly comes from the synergistic effect of the micron / nano double-layer structure on the surface and the low surface energy material. The key to preparing a superhydrophobic coating is to use low surface energy materials to construct a micro-nano double-layer surface structure, that is, the coating surface structure must have a micron-sized structure, and the nano-sized structure must also be distributed on the micron structure.

[0003] Polytetrafluoroethylene (PTFE) is a low surface energy polymer material commonly used in industrial production and can be used to prepare hydrophobic coatings. The currently commonly used method for preparing PTFE hydrophobic coatings is to spray, dip, or brush PTFE emulsion onto the surface of the workpiece, then dry and solidify it (generally at 80-100°C for 10-20 minutes), and finally sinter it (generally at 350-380°C for 20-30 minutes) to obtain the PTFE coating. It can be seen that the existing preparation process is complicated, has many steps, and is time-consuming. In addition, the surface of the prepared PTFE coating is flat, and the maximum contact angle is about 120°, which cannot achieve super-hydrophobic properties. In order to prepare a micro-nano double-layer structure on it, the PTFE coating needs to be further processed using template imprinting, laser etching, plasma etching and other processes, which greatly increases the preparation cost and difficulty.

[0004] The existing method of preparing PTFE coating using powder plasma spraying is to inject PTFE powder as raw material into the plasma flame flow, and after the powder is heated and accelerated, it hits the surface of the substrate to form a coating. The biggest disadvantage of this method is that it cannot form a micro-nano double-layer structure.

[0005] In view of the limitations of the prior art that the preparation process of PTFE coating is complicated and it is difficult to prepare a micro-nano double-layer structure in one step, the present invention uses PTFE emulsion as raw material and prepares a super-hydrophobic PTFE coating with a convex hull-shaped micro-nano double-layer structure in one step through DC plasma spraying technology, without the need for any additional post-processing process, which has important economic value and engineering significance. Summary of the invention

[0006] In view of the limitations of the preparation process of super-hydrophobic PTFE coating in the prior art, the present application provides a one-step preparation method of a micro-nano double-layer structure super-hydrophobic PTFE coating. In the plasma spraying process, by injecting PTFE emulsion into a high-temperature plasma flame flow, the PTFE emulsion spontaneously completes the curing and sintering process in the high-temperature flame flow, and no additional curing and sintering treatment is required after the spraying is completed, so that a one-step rapid preparation of a super-hydrophobic PTFE coating with a convex micro-nano double-layer structure can be achieved.

[0007] A one-step preparation method for preparing a super-hydrophobic PTFE coating with a micro-nano double-layer structure comprises the following steps: Step 1: Sandblast the workpiece surface to increase the roughness of the workpiece surface, then use compressed air to clean the workpiece surface and install the workpiece on the fixture; Step 2: Start the DC plasma spray gun and use the pure plasma flame flow to scan the workpiece surface for preheating without injecting PTFE emulsion.

[0008] Step 3: After the preheating is completed, PTFE emulsion is injected into the plasma flame flow. After the flame flow is stabilized, spraying is performed along a predetermined path to prepare a super-hydrophobic PTFE coating with a micro-nano double-layer structure.

[0009] The present application proposes for the first time a method for preparing a super-hydrophobic PTFE coating with a micro-nano double-level structure by a plasma spraying process in one step. In the plasma spraying process, a PTFE emulsion is transported to a high-temperature, high-speed plasma flame flow. PTFE is atomized into tiny droplets in the flame flow, and the solvent in the droplets evaporates rapidly to form tiny PTFE particles. The PTFE particles are heated in the flame flow, and impact the workpiece surface with a molten / semi-molten state, forming a convex hull-shaped micro-nano double-level structure super-hydrophobic PTFE coating. Compared to traditional "spraying / dip coating / brush coating-curing-sintering" process, in the plasma spraying process, PTFE emulsion completes the "curing-sintering" process in the high-temperature flame flow, and a one-step preparation of the workpiece surface PTFE coating is achieved, and there is no need to perform curing and sintering treatment after spraying is completed, so that the PTFE coating can be prepared in one step while the PTFE coating is presented with a micro-nano double-level structure, i.e., a super-hydrophobic PTFE coating with a micro-nano double-level structure is prepared in one step. Many existing technologies require the preparation of PTFE coatings through the traditional "spraying / dipping / brushing-curing-sintering" process, and then combined with post-processing processes such as plasma etching and laser etching to prepare microstructures on the PTFE coatings. Compared with the existing technologies, the one-step preparation method of the PTFE coating with a micro-nano double-layer structure described in the present invention greatly improves the preparation efficiency and saves costs.

[0010] Furthermore, the spray gun used is a DC plasma spray gun, that is, the spraying process adopted is a DC plasma spraying process. Of course, other plasma spraying processes, such as an inductively coupled plasma spraying process, etc., may also be adopted.

[0011] Furthermore, the concentration of the PTFE emulsion is 20% to 60%.

[0012] Furthermore, the horizontal distance between the liquid material nozzle outlet and the DC plasma spray gun is 20 to 50 mm, and the vertical distance between the liquid material nozzle outlet and the DC plasma spray gun axis is 5 to 10 mm.

[0013] Furthermore, the delivery rate of the PTFE emulsion is 10 to 40 grams per minute.

[0014] Furthermore, the spraying distance is 60 to 100 mm.

[0015] Furthermore, the preheating path and the spraying path are in a "bow shape" with a path spacing of 1 to 5 mm.

[0016] Furthermore, the surface of the convex-hull micro-nano double-layer structure super-hydrophobic PTFE coating has micron-sized convex-hull structures, there are obvious gaps between the convex-hull structures, and the surface of the convex-hull structures has submicron / nano-sized particles.

[0017] Furthermore, the micro-nano double-layer structure is a micron-sized lamellar structure formed on the surface of the super-hydrophobic PTFE coating, there are obvious gaps between the lamellar structures, and the surface of the lamellar structure has submicron / nano-sized particles.

[0018] Furthermore, the method is that after step 3 is completed, a micro-nano double-layer structure can be formed without any post-processing process.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a direct current plasma spraying method for preparing a super-hydrophobic PTFE coating with a micro-nano double-layer structure in a step. The method utilizes liquid PTFE emulsion to be combined with a plasma spraying device, without any post-processing process, and a micro-nano double-layer surface structure can be formed after spraying is completed, and the coating has super-hydrophobic performance. Compared with other PTFE coating preparation processes, the method can realize a one-step, fast, large-area, large-batch preparation of a super-hydrophobic PTFE coating with a micro-nano double-layer structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the coating preparation process by DC plasma spraying; Figure 2 Schematic diagram of the spraying path; Figure 3The surface microstructure of the PTFE coating in Example 1, wherein (a) is a low-magnification surface microstructure, showing a micron-sized convex structure; (b) is a high-magnification surface microstructure, showing a nanostructure on the convex surface; Figure 4 is the water contact angle of the PTFE coating in Example 1; Figure 5 The surface microstructure of the PTFE coating in Example 2, wherein (a) is a low-magnification surface microstructure, showing a micron-sized lamellar structure; (b) is a high-magnification surface microstructure, showing a nanostructure of the lamellar surface; Figure 6 is the water contact angle of the PTFE coating in Example 2.

[0021] In the figure: 1. PTFE emulsion; 2. peristaltic pump; 3. DC plasma spray gun; 4. liquid material nozzle; 5. plasma flame flow; 6. workpiece; 7. spraying starting point; 8. pass spacing; 9. spraying path. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with the accompanying drawings and embodiments. In order to better illustrate the coating preparation method of the present application, the liquid plasma spraying method described in the present application is described below. Figure 1 As shown in FIG. 1 , during the plasma spraying process, the PTFE emulsion 1 is transported by the peristaltic pump 2 and sprayed into the plasma flame 5 generated by the DC plasma spray gun 3 through the liquid nozzle 4. After the plasma flame 5 is stabilized, the DC plasma spray gun 3 is operated according to Figure 2The spraying path shown in the figure performs a "bow-shaped" movement to spray the surface of the workpiece 6. The detailed process is as follows: the DC plasma spray gun 3 starts to move from the spraying starting point 7 outside the workpiece 6, first completes the spraying of a layer of PTFE material, and then moves down a path spacing 8 to spray the next layer of PTFE material. After each spraying, it continues to move down a path spacing 8 until the entire surface of the workpiece 6 is sprayed, and the first layer of spraying of the workpiece 6 is completed. The DC plasma spray gun 3 returns to the spraying starting point 7, repeats the above trajectory to spray another layer, and repeats this cycle until the predetermined number of spray layers is reached, and finally forms a super-hydrophobic PTFE coating with a micro-nano double-layer structure. The PTFE coating formed in the present application has a micro-nano double-layer structure, which is a micron-sized convex hull structure / lamellar structure formed on the surface of the PTFE coating, and there are obvious gaps between the convex hull structures / lamellar structures, and the surface of the convex hull structure / lamellar structure has submicron / nano-sized particles; that is, the first level is a micron-sized convex hull structure / lamellar structure, and the second level is a convex hull structure / lamellar structure with submicron / nano-sized particles on the surface. The convex hull structure / lamellar structure with gap distribution and the submicron / nano-sized particles on the surface of the convex hull structure / lamellar structure make the PTFE coating have better superhydrophobic properties.

[0023] In addition, in order to more clearly state the formation of the micro-nano double-layer structure in the present application, the coating deposition principle in the method described in the present application is described. When the PTFE emulsion is injected into the plasma flame flow, it is atomized into a large number of tiny droplets under the action of the high-speed flame flow, and these droplets undergo processes such as solvent volatilization and internal particle agglomeration of the droplets to form extremely small molten or partially molten particles. When the plasma flame flow carrying a large number of particles contacts the substrate, the flame flow is blocked by the substrate and deflected, and a deflected flame flow parallel to the substrate surface is formed near the substrate. Since the size and mass of the particles carried in the flame flow are very small, they are easily affected by the deflected flame flow during the deposition process (i.e., when colliding with the substrate), forming an inclined deposition trajectory, and hitting the substrate surface at an inclined angle. As the spraying process proceeds, since the impact of the particles is inclined, the particles will only hit one side of the previously deposited coating, and cannot hit the other side, which causes the coating on one side to accumulate and increase continuously, while the other side forms a gap due to the impact of no particles. Therefore, under this action, micron structures and gaps are gradually formed. The above theory can also explain why traditional plasma spraying with powder as raw material cannot produce micro-nano double-layer structures. Traditional plasma spraying uses large-sized powder (particle size 20~100 microns) as raw materials. Due to the large mass of large-sized powder, it will not be affected by the deflected flame flow when it hits the substrate, and all hit the substrate surface at a vertical angle, eventually forming a coating morphology with a flat surface.

[0024] Example 1 (1) The surface of the workpiece 6 is sandblasted, and then the remaining sandblasting particles on the surface of the workpiece are blown away with compressed air, and then the workpiece is mounted on the fixture.

[0025] (2) Start the DC plasma spray gun 3 to generate a plasma flame 5. Without injecting the PTFE emulsion 1, the DC plasma spray gun 3 moves 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 into 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 path spacing 8 is 5 mm, and the distance between the DC plasma spray gun 3 and the workpiece 6 is 100 mm; the number of scanning layers is 5 layers.

[0026] (3) Start the peristaltic pump 2, inject the PTFE emulsion 1 into the plasma flame 5 through the nozzle 4, and 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 is stable, the DC plasma spray gun 3 starts to move 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 the 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 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 path spacing 8 is 3 mm, and the distance between the DC plasma spray gun 3 and the workpiece 6 is 60 mm; the number of spray layers is 20 layers.

[0027] 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 shows a spherical convex hull structure with a diameter of about 200 microns. There are obvious gaps between the convex hull structures, and some of the convex hull structures are connected together to form larger micron-sized island structures; surface microstructure images at high magnification ( Figure 3 b) shows that irregularly shaped submicron / nano particles are distributed on the surface of the micron-sized convex structure. This micron-sized convex structure and the submicron / nano particles on its surface are combined to form a micro-nano double-layer structure. The sprayed PTFE coating can show super hydrophobic properties without the need for curing and sintering in traditional technologies, and its water contact angle is 164°, as shown in Figure 2. Figure 4The microstructure and water contact angle of the coating in Example 1 confirm that the method described in this application can achieve the one-step preparation of micro-nano dual-layer super-hydrophobic PTFE coating without any post-treatment process.

[0028] Example 2 Compared with Example 1, the main changes in the process parameters of Example 2 include: the concentration of PTFE emulsion is reduced (i.e., the content of PTFE is less in the PTFE emulsion of the same mass), the liquid feeding amount is reduced, the PTFE injection position is further away from the flame outlet, the spray gun power is reduced, the movement speed of the spray gun relative to the workpiece is increased, the distance between the spray gun and the workpiece is increased, etc. The purpose of the above parameter changes is to reduce the melting degree of the PTFE emulsion, and then compare with the coating in Example 1.

[0029] (1) The surface of the workpiece 6 is sandblasted, and then the remaining sandblasting particles on the surface of the workpiece are blown away with compressed air, and then the workpiece is mounted on the fixture.

[0030] (2) Start the DC plasma spray gun 3 to generate a plasma flame 5. Without injecting the PTFE emulsion 1, the DC plasma spray gun 3 moves 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 into 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 path spacing 8 is 3 mm, and the distance between the DC plasma spray gun 3 and the workpiece 6 is 80 mm; the number of scanning layers is 5 layers.

[0031] (3) Start the peristaltic pump 2, inject the PTFE emulsion 1 into the plasma flame 5 through the nozzle 4, and 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 is stable, the DC plasma spray gun 3 starts to move 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 the 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 axis of the DC plasma spray gun 3 is 10 mm; the plasma gas input into the DC plasma spray gun 3 is 30 standard liters per minute of argon and 5 standard liters per minute of hydrogen, and 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 path spacing 8 is 5 mm, and the distance between the DC plasma spray gun 3 and the workpiece 6 is 100 mm; the number of spray layers is 20.

[0032] 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 shows irregular micron-sized lamellar structures, the size of the lamellar structures is hundreds of microns, and there are obvious gaps between the lamellar structures. Due to the parameters used in Example 2, the melting degree of the PTFE emulsion is poor, and the PTFE emulsion concentration is low and the liquid delivery volume is small, which ultimately leads to the formation of thin lamellar structures. Surface microstructure pictures at high magnification ( Figure 5 b) shows that irregularly shaped submicron / nano particles are distributed on the surface of the micron-sized lamellar structure. This micron-sized lamellar structure and the submicron / nano particles on its surface are combined to form a micro-nano double-layer structure. The sprayed PTFE coating can show super hydrophobic properties without the need for curing and sintering treatment in traditional technologies, and its water contact angle is 152°, as shown in Figure 2. Figure 6 The microstructure and water contact angle of the coating in Example 2 confirm that the method described in this application can achieve the one-step preparation of micro-nano dual-layer super-hydrophobic PTFE coating without any post-treatment process.

[0033] Finally, it should be noted that the parts not involved in the present invention are the same as the prior art or can be implemented by the prior art. The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention is described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that they can still modify or replace the technical solution of the present invention, and these modifications or replacements cannot make the modified technical solution deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A one-step preparation method of a micro-nano double-layer structure super-hydrophobic PTFE coating, characterized in that: The following steps are involved: Step 1: Sandblast the workpiece surface to increase the roughness of the workpiece surface, then use compressed air to clean the workpiece surface and install it on the fixture; Step 2: Start the DC plasma spray gun and use pure flame flow to scan the workpiece surface for preheating without injecting PTFE emulsion; Step 3: After the preheating is completed, PTFE emulsion is injected into the flame flow. After the flame flow is stabilized, spraying is performed according to a predetermined spraying path to prepare a micro-nano double-layer structure super-hydrophobic PTFE coating.

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 1, characterized in that: The concentration of the PTFE emulsion is 20% to 60%.

4. The one-step preparation method according to claim 1, characterized in that: The horizontal distance between the liquid nozzle outlet and the DC plasma spray gun is 20 to 50 mm, and the vertical distance between the liquid nozzle outlet and the DC plasma spray gun axis is 5 to 10 mm.

5. The one-step preparation method according to claim 1, characterized in that: In step 3, the delivery rate of PTFE emulsion is 10-40 g / min.

6. The one-step preparation method according to claim 1, characterized in that: The spraying distance in step 3 is 60~100 mm.

7. The one-step preparation method according to claim 1, characterized in that: The preheating path and the spraying path are both "bow-shaped", and the path spacing is 1~5 mm.

8. The one-step preparation method according to claim 1, characterized in that: The micro-nano double-layer structure is a micron-sized convex hull structure formed on the surface of the super-hydrophobic PTFE coating, there are obvious gaps between the convex hull structures, and the surface of the convex hull structure has submicron / nano-sized particles.

9. The one-step preparation method according to claim 1, characterized in that: The micro-nano double-layer structure is a micron-sized lamellar structure formed on the surface of the super-hydrophobic PTFE coating, there are obvious gaps between the lamellar structures, and the surface of the lamellar structure has submicron / nano-sized particles.

10. The one-step preparation method according to claim 1, characterized in that: The method is that after step 3 is completed, a super-hydrophobic PTFE coating with a micro-nano double-layer structure can be formed without any post-processing process.

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