Method for preparing a superhydrophobic powder coating, corresponding powder coating and superhydrophobic coating

Abstract

The application belongs to the technical field of new materials, and provides a method for preparing super-hydrophobic powder coating, steps of which comprise: (1) uniformly mixing thermosetting powder coating resin, its curing agent and hydrophobic particles by high-speed stirrer, extruding by extruder and roll-cooling to form paint sheet; (2) blending the paint sheet with hydrophobic nano-particles, crushing and screening by a crusher, and obtaining the mixed powder as the wear-resistant super-hydrophobic coating material. Meanwhile, the application also provides the powder coating prepared by the method, and the wear-resistant super-hydrophobic coating with hydrophobic armor structure prepared by electrostatic spraying and curing of the powder coating. The coating has the hydrophobic armor structure, and has stronger wear resistance and lower thickness dependence than ordinary sprayed coating; compared with the coating needing to engrave the armor structure, the process is simpler, the cost is greatly reduced, and the construction is convenient.

Description

Technical Field

[0001] This patent belongs to the field of new materials technology and relates to wear-resistant superhydrophobic coating materials. Specifically, it relates to a method for preparing superhydrophobic powder coatings, the powder coatings prepared by the method, and the wear-resistant superhydrophobic coatings made by applying the powder coatings. Background Technology

[0002] Superhydrophobic coatings are a new type of biomimetic material with excellent self-cleaning, antifouling, anti-icing, and antibacterial properties, and have broad application prospects in marine wind power systems, communication facilities, ocean shipping, bridge structures, and building facades. However, a common problem with superhydrophobic coatings is their poor wear resistance, which severely restricts their practical application.

[0003] Fabricating superhydrophobic surfaces typically requires meeting two conditions: low surface energy and a micro / nano-level rough structure. Structure is a key factor influencing the wear resistance of the coating. Currently reported wear-resistant superhydrophobic coatings fall into two categories: one is a self-similar structure where the surface and internal structure and composition of the coating are identical. [1] The coating can be prepared by simple spraying and, after wear, exposes a new surface similar to the old surface, maintaining its superhydrophobic properties. However, such coatings are usually dominated by a nanoscale rough structure with loose internal connections, resulting in a high wear rate. Therefore, they can only be applied in the form of thick coatings or even bulk coatings.

[0004] Another type is armor. [2] The structure of the coating can utilize a robust, micron-scale armor-like framework to protect the fragile nanostructure from damage caused by friction. However, the armor structure itself is made of hydrophilic metallic materials, which, in addition to being susceptible to corrosion, are easily worn and deformed under external forces. This leads to a rapid increase in the hydrophilic area of ​​the coating surface, significantly reducing the coating's hydrophobicity. Furthermore, this armor requires separate fabrication, which is complex and expensive, hindering industrial application and widespread adoption. Therefore, developing powder coatings with superior performance is essential.

[0005] [1]M. Liu, Y. Luo, and D. Jia, “Facile, solvent-free fabrication of arobust 3-dimensional continuous superhydrophobic coating with wettabilitycontrol and abrasionhealing,” Chemical Engineering Journal, vol. 368, pp. 18–28, Jul. 2019. [2] D. Wang etal., "Design of robust superhydrophobic surfaces," Nature, vol. 582, p.55, 2020. Summary of the Invention

[0006] The present invention aims to provide a method for preparing superhydrophobic powder coatings, a coating material prepared by the method, and a wear-resistant superhydrophobic coating made by applying the coating material.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing superhydrophobic powder coatings, comprising the following steps: (1) The film-forming substance is mechanically blended with hydrophobic particles to form a film, wherein the film-forming substance is a thermosetting powder coating resin and a corresponding curing agent; (2) After crushing the paint flakes, add hydrophobic nanoparticles and mix evenly, or send the paint flakes and hydrophobic nanoparticles into a crusher together for crushing and mixing. The mixed powder obtained by sieving is the superhydrophobic powder coating.

[0008] Further, in step (1), the hydrophobic particles are fluoropolymer particles with hydrophobicity or inorganic nanoparticles modified by hydrophobicity, with a particle size of 0.2 to 30 μm, and the amount added is 5 to 25% of the weight of the film-forming substance.

[0009] The fluororesin particles are selected from one or more of polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA), and fluorinated ethylene propylene copolymer (FEP).

[0010] The hydrophobically modified inorganic nanoparticles are selected from one or more of silicon nitride, silicon carbide, silicon dioxide, titanium dioxide, aluminum oxide, aluminum nitride, magnetite powder, iron phosphate powder, iron-titanium powder, and glass beads. The hydrophobic modifier is selected from one or more of alkylchlorosilane, alkylbromosilane, fluoroalkylchlorosilane, fluoroalkylsiloxane, and silazane.

[0011] Further, the hydrophobic nanoparticles in step (2) are any one or a combination of hydrophobic silica, hydrophobic aluminum oxide, and hydrophobic titanium dioxide prepared by vapor phase method; the particle size of the hydrophobic nanoparticles is 20-200 nm; and the amount added is 0.2-2% of the total weight of the film-forming material and the hydrophobic particles.

[0012] As a preferred embodiment, the film-forming substance in step (1) is selected from one or more of carboxylated polyesters, hydroxyl polyesters, epoxy resins, polyacrylates, and fluorocarbon resins; wherein, the A component of the fluorocarbon resin bicomponent resin is a copolymer of chlorofluoroethylene and vinyl ester / ether (FEVE), and the B component is a blocked isocyanate.

[0013] In step (1), the specific operation of mechanical blending is as follows: the film-forming material and hydrophobic particles are put into a high-speed mixer and mixed evenly, and then extruded and cooled by an extruder to form a film; the extruder temperature is set to 80-120℃; the extrusion speed is 50-500 rpm.

[0014] In step (2), the median particle size of the mixed powder obtained by sieving is 15-70 μm.

[0015] In a second aspect, a wear-resistant superhydrophobic powder coating is prepared by the method described in the first aspect.

[0016] Thirdly, a wear-resistant superhydrophobic coating is formed by spraying the powder coating described in the second aspect onto a substrate using an electrostatic spray gun at a voltage of -30 to -80 kV, followed by baking and curing. The preferred baking temperature is 160 to 220°C, and the time is 5 to 30 minutes.

[0017] The substrate can be a metallic material such as carbon steel plate, stainless steel plate, phosphated iron plate, aluminum plate, or metal mesh, or a non-metallic material such as fiberglass board, wood board, or ceramic. When the substrate is non-metallic, grounding is not required, but preheating is necessary.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses an organic binder and slightly larger hydrophobic particles, which are then mixed and extruded using an extruder to form a hydrophobic composite, providing a hydrophobic framework for the coating. This composite is then blended with a small amount of hydrophobic nanoparticles, pulverized, and sieved. The mixture is then electrostatically sprayed and cured to form a film. Since the nanoparticles and hydrophobic composite particles are only physically blended, they adhere only to the surface of the hydrophobic composite particles, providing nanoscale roughness and low surface energy. Therefore, the hydrophobic armor structure of this coating can protect the fragile nanoscale structure, and even after the armor structure is worn away, new hydrophobic surfaces are still exposed. Compared to ordinary sprayed coatings, this results in stronger wear resistance and lower dependence on coating thickness.

[0019] 2. Compared with coatings that require engraving armor structures, the present invention has a simpler process, significantly reduced costs, convenient construction, and is environmentally friendly, with high production efficiency, and can achieve a high film thickness in one step.

[0020] 3. Compared with the method of directly mixing micron-sized particles and nano-sized particles into the resin matrix, the present invention has stronger hydrophobicity, specifically manifested in a higher water contact angle, a lower roll-off angle, a smaller requirement for nano-additives, and stronger coating wear resistance. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the superhydrophobic coating obtained in Example 1; Figure 2 These are electron micrographs of the water droplet morphology on the surface of the superhydrophobic coating obtained in Example 1 and a schematic diagram of the calculated water contact angle. Figure 3 This is a scanning electron microscope image of the superhydrophobic coating obtained in Example 3; Figure 4 These are electron micrographs of the water droplet morphology on the surface of the superhydrophobic coating obtained in Example 3 and a schematic diagram of the calculated water contact angle. Figure 5 This is a scanning electron microscope image of the superhydrophobic coating obtained in Example 5; Figure 6 These are electron micrographs of the water droplet morphology on the surface of the superhydrophobic coating obtained in Example 5 and a schematic diagram of the calculated water contact angle. Figure 7 This is a scanning electron microscope image of the superhydrophobic coating prepared in proportion. Figure 8 This is an electronic photograph of the water droplet morphology on the surface of the superhydrophobic coating prepared in proportion, and a schematic diagram of the calculated water contact angle. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer and more explicit, the invention is further described in detail below through embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0023] Example 1: A method for preparing superhydrophobic powder coatings, comprising the following steps: (1) Mix 80g of carboxylated polyester resin and triglycidyl isocyanate (TGIC) curing agent powder (film-forming substance) with 20g of PTFE particles (hydrophobic particles) with a median particle size of 1μm in a high-speed mixer, mix evenly, then use an extruder to knead at 100℃, extrude at 200rpm, and then roll and cool to form a film. (2) The paint flakes and 1g of fumed hydrophobic silica nanoparticles with a median particle size of 25nm were fed into a pulverizer for pulverization and mixing. The mixture was then sieved to obtain a mixed powder with a median particle size of 40μm, which is the superhydrophobic powder coating.

[0024] The prepared superhydrophobic powder coating was sprayed onto a grounded carbon steel plate using an electrostatic spray gun at a voltage of -50kV, and cured in an oven at 200 degrees Celsius for 15 minutes. After cooling indoors, a superhydrophobic coating with a thickness of 80μm was obtained.

[0025] Characterized by scanning electron microscopy, such as Figure 1 As shown, the coating surface has a micron-scale skeleton structure, with 1-2μm particles semi-embedded in the inner surface layer of the skeleton (polytetrafluoroethylene particles), and nano-scale particles (hydrophobic silica) densely distributed on the outer surface layer.

[0026] like Figure 2 As shown, the resulting coating has a water contact angle of 163° and a roll-off angle of 3°.

[0027] When rubbed 100 times under a pressure of 9.8 kPa with P220 sandpaper, the contact angle was 155° and the thickness became 35 μm, demonstrating good wear resistance.

[0028] Example 2: A method for preparing superhydrophobic powder coatings, comprising the following steps: (1) 90g of a mixture of hydroxyl polyester resin and caprolactam-blocked isophorone diisocyanate curing agent (film-forming substance) and 10g of hexamethyldisilazane modified silicon carbide particles (hydrophobic particles) with a median particle size of 2μm were put into a high-speed mixer and mixed evenly. Then, the mixture was kneaded at 90°C using an extruder and extruded at 300rpm. Finally, the mixture was rolled and cooled to form a film. The hexamethyldisilazane-modified silicon carbide particles were obtained by dispersing 20g of silicon carbide particles in 100g of toluene, then adding 0.2g of hexamethyldisilazane, stirring for 4 hours, and washing and drying with acetone.

[0029] (2) The paint flakes and 2g of vapor-phase hydrophobic titanium dioxide nanoparticles with a median particle size of 40nm were fed into a pulverizer for pulverization and mixing. The mixture was then sieved to obtain a mixed powder with a median particle size of 35μm, which is the superhydrophobic powder coating.

[0030] The prepared superhydrophobic powder coating was sprayed onto a heated glass fiber plate at a voltage of -45kV using an electrostatic spray gun, and cured in an oven at 200 degrees Celsius for 15 minutes. After cooling indoors, a superhydrophobic coating with a thickness of 60μm was obtained.

[0031] The tested coating showed a water contact angle of 162° and a roll-off angle of 4°. After rubbing it 1000 times with P1000 sandpaper under a pressure of 2.0 kPa, the contact angle became 155° and the thickness increased to 30 μm.

[0032] Example 3: A method for preparing superhydrophobic powder coatings, comprising the following steps: (1) Mix 95g of FEVE resin and caprolactam-blocked isophorone diisocyanate curing agent (film-forming substance) with 5g of perfluorooctyltrimethoxysilane modified alumina particles (hydrophobic particles) with a median particle size of 0.8μm in a high-speed mixer, mix evenly, then use an extruder to knead at 110℃, extrude at 100rpm, and then roll-press and cool to form a film; The perfluorooctyltrimethoxysilane-modified aluminum oxide particles are obtained by dispersing 10g of aluminum oxide particles in 100g of ethanol (5%) aqueous solution, then adding 0.1g of perfluorooctyltrimethoxysilane, stirring for 24 hours, and then washing and drying with water.

[0033] (2) The paint flakes are crushed and sieved to obtain powder with a median particle size of 20 μm, and then mixed with 0.5 g of vapor-phase hydrophobic aluminum oxide with a particle size of 75 nm by high-speed stirring to obtain superhydrophobic powder coating.

[0034] The prepared superhydrophobic powder coating was sprayed onto a grounded 304 stainless steel plate using an electrostatic spray gun at a voltage of -30kV, and cured in an oven at 200 degrees Celsius for 15 minutes. After cooling indoors, a superhydrophobic coating with a thickness of 60μm was obtained.

[0035] The surface morphology of the obtained coating, as characterized by scanning electron microscopy, is as follows: Figure 3 As shown, there are many protrusions in the depressions on the coating surface.

[0036] like Figure 4 As shown, the water contact angle of the coating is 163° and the roll-off angle is 4°.

[0037] When rubbed 100 times with P80 sandpaper under a pressure of 5.0 kPa, the contact angle is 152° and the thickness becomes 22 μm.

[0038] Example 4: A method for preparing superhydrophobic powder coatings, comprising the following steps: (1) 80g of a mixture of epoxy resin and carboxylated polyester curing agent for powder coating (film-forming substance) and 20g of 1H,1H,2H,2H-perfluorododecyltrichlorosilane modified glass microspheres (hydrophobic particles) with a median particle size of 5μm were put into a high-speed mixer and mixed evenly. Then, the mixture was kneaded in an extruder at 100℃, extruded at 250rpm, and then rolled and cooled to form a film. The 1H,1H,2H,2H-perfluorododecyltrichlorosilane modified glass microspheres were prepared by dispersing 30g of glass microspheres in 100g of toluene, followed by slowly adding 3g of a toluene solution containing 5% 1H,1H,2H,2H-perfluorododecyltrichlorosilane, stirring the reaction for 24 hours, and then washing and drying with toluene.

[0039] (2) The paint flakes and 1.5g of fumed hydrophobic silica nanoparticles with a median particle size of 50nm were fed into a pulverizer for pulverization and mixing. The mixture was then sieved to obtain a mixed powder with a median particle size of 45μm, which is the superhydrophobic powder coating.

[0040] The prepared superhydrophobic powder coating was sprayed onto a grounded aluminum plate using an electrostatic spray gun at a voltage of -60kV, cured in an oven at 200 degrees Celsius for 10 minutes, and then cooled indoors to obtain a superhydrophobic coating with a thickness of 60μm.

[0041] The tested coating showed a water contact angle of 156° and a roll-off angle of 5°. After rubbing with P80 sandpaper under a pressure of 20.0 kPa for 50 cycles, the contact angle became 153° and the thickness increased to 30 μm.

[0042] Example 5: A method for preparing superhydrophobic powder coatings, comprising the following steps: (1) 75g of a mixture of acrylic resin and dodecanoic acid curing agent (film-forming substance) for powder coating and 25g of FEP particles (hydrophobic particles) with a median particle size of 2μm were put into a high-speed mixer and mixed evenly. Then, the mixture was kneaded at 100°C using an extruder and extruded at 250rpm. Then, the mixture was rolled and cooled to form a film. (2) The paint flakes and 0.2g of fumed hydrophobic silica with a median particle size of 50nm were fed into a pulverizer for pulverization and mixing. The mixture was then sieved to obtain a mixed powder with a median particle size of 40μm, which is the superhydrophobic powder coating.

[0043] The prepared superhydrophobic powder coating was sprayed onto a grounded carbon steel plate using an electrostatic spray gun at a voltage of -60kV, and cured in an oven at 200 degrees Celsius for 15 minutes. After cooling indoors, a superhydrophobic coating with a thickness of 50μm was obtained.

[0044] The surface morphology of the obtained coating, as characterized by scanning electron microscopy, is as follows: Figure 5 As shown, the coating surface has many raised peaks.

[0045] like Figure 6 As shown, the water contact angle of the resulting coating is 158° and the roll-off angle is 7°.

[0046] When rubbed 50 times with P220 sandpaper under a pressure of 10.0 kPa, the contact angle is 152° and the thickness becomes 22 μm.

[0047] Comparative example: A method for preparing superhydrophobic powder coatings, comprising the following steps: (1) Mix 80g of carboxylated polyester resin and triglycidyl isocyanate (TGIC) curing agent (film-forming substance) with 20g of PTFE particles (hydrophobic particles) with a median particle size of 1μm and 1g of fumed hydrophobic silica nanoparticles with a median particle size of 25 nm in a high-speed mixer and mix evenly. Then, use an extruder to knead at 100°C, extrude at 200rpm, and then roll-press and cool to form a film. (2) The paint flakes are fed into a pulverizer for pulverization and mixing, and then sieved to obtain a mixed powder with a median particle size of 40 μm, which is the superhydrophobic powder coating.

[0048] The prepared superhydrophobic powder coating was sprayed onto a grounded carbon steel plate using an electrostatic spray gun at a voltage of -50kV, and cured in an oven at 200 degrees Celsius for 15 minutes. After cooling indoors, a superhydrophobic coating with a thickness of 80μm was obtained.

[0049] Characterized by scanning electron microscopy, such as Figure 7 As shown, the coating surface has a micron-scale skeleton structure, with 1-2μm particles semi-embedded in the inner surface layer of the skeleton (polytetrafluoroethylene particles), while the outer surface layer has fewer nano-scale particles (hydrophobic silica).

[0050] like Figure 8 As shown, the resulting coating has a water contact angle of 156° and a roll-off angle of 9°.

[0051] When rubbed 100 times with P220 sandpaper under a pressure of 9.8 kPa, the contact angle decreased to 138°, the superhydrophobicity was lost, and the thickness became 30 μm.

[0052] It is evident that by simultaneously adding micron-sized hydrophobic particles and nano-sized hydrophobic particles without using the stepwise mixing method of this invention, the resulting coating still possesses hydrophobic properties, but it affects the distribution of these two types of particles in the system, thereby reducing the hydrophobicity and wear resistance of the coating.

[0053] The foregoing has described preferred embodiments of the present invention. However, it should be understood that the invention is not limited to the content disclosed herein. Any non-substantial improvements made using the inventive concept and technical solution, or any application of the inventive concept and technical solution to other situations, are within the protection scope of the present invention.

Claims

1. A process for the preparation of a superhydrophobic powder coating, characterized in that, Includes the following steps: (1) The film-forming substance and hydrophobic particles are mechanically blended to form a film. The film-forming substance is a thermosetting powder coating resin and a corresponding curing agent. The hydrophobic particles are fluoropolymer particles with hydrophobicity or inorganic nanoparticles modified by hydrophobicity, with a median particle size of 0.2 to 30 μm. The amount of hydrophobic particles added is 5 to 25% of the weight of the film-forming substance. The specific operation of mechanical blending is as follows: the film-forming substance and hydrophobic particles are put into a high-speed mixer and mixed evenly. Then, the mixture is extruded through an extruder and cooled by roller pressing to form a film. The temperature of the extruder is set to 80 to 120°C. (2) After crushing the paint flakes, add hydrophobic nanoparticles and mix evenly, or send the paint flakes and hydrophobic nanoparticles into a crusher together for crushing and mixing. The mixed powder obtained by sieving is the superhydrophobic powder coating. The median particle size of the hydrophobic nanoparticles is 20-200 nm, and the amount added is 0.2-2% of the total weight of the film-forming substance and the hydrophobic particles.

2. The method for preparing superhydrophobic powder coatings as described in claim 1, characterized in that, The fluororesin particles are selected from one or more of polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA), and fluorinated ethylene propylene copolymer (FEP).

3. The method for preparing superhydrophobic powder coatings as described in claim 1, characterized in that, The hydrophobically modified inorganic nanoparticles are selected from one or more of silicon nitride, silicon carbide, silicon dioxide, titanium dioxide, aluminum oxide, aluminum nitride, magnetite powder, iron phosphate powder, iron-titanium powder, and glass beads. The hydrophobic modifier is selected from one or more of alkylchlorosilane, alkylbromosilane, fluoroalkylchlorosilane, fluoroalkylsiloxane, and silazane.

4. The method for preparing superhydrophobic powder coatings as described in claim 1, characterized in that, The hydrophobic nanoparticles in step (2) are any one or a combination of hydrophobic silicon dioxide, hydrophobic aluminum oxide, and hydrophobic titanium dioxide prepared by the gas phase method.

5. The method for preparing superhydrophobic powder coatings as described in claim 1, characterized in that, The film-forming substance in step (1) is selected from one or more of carboxylated polyesters, hydroxyl polyesters, epoxy resins, polyacrylates, and fluorocarbon resins; wherein, the fluorocarbon resin is a two-component resin, whose component A is FEVE and component B is a blocked isocyanate.

6. The method for preparing superhydrophobic powder coatings according to any one of claims 1-5, characterized in that, In step (1), the extrusion speed is 50 to 500 rpm.

7. The method for preparing superhydrophobic powder coatings as described in claim 1, characterized in that, In step (2), the median particle size of the mixed powder obtained by sieving is 15-70 μm.

8. A superhydrophobic powder coating, characterized in that, Prepared by the method of any one of claims 1-7.

9. A superhydrophobic coating, characterized in that, The powder coating described in claim 8 is sprayed onto the substrate using an electrostatic spray gun at a voltage of -30 to -80 kV, and then baked and cured to form a superhydrophobic coating.

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