Fluorine-free heat-resistant solid super-hydrophobic coating and preparation method thereof

Abstract

The invention relates to a fluorine-free heat-resistant solid super-hydrophobic coating and a preparation method thereof.The coating comprises a double-layer composite structure formed by depositing core-shell structure microspheres on the surface of a bis (3-aminopropyl) terminated polydimethylsiloxane bonding layer and heating and curing the core-shell structure microspheres, hydrophilic nanoscale silicon dioxide serves as a shell layer of the core-shell structure microspheres, and the core-shell structure microspheres are coated with the hydrophilic nanoscale silicon dioxide. The core-shell structure microspheres are coated and loaded on the surfaces of the micron-sized wax microspheres, the core-shell structure microspheres provide roughness and hydrophobicity, the silicon dioxide coated on the surfaces of the core-shell structure microspheres further increases hardness and roughness, the wax of the wax microspheres reversely coats the shell layer during heating to prepare the coating, and after abrasive paper abrasion, gauze abrasion, sand impact, water impact and heat resistance tests, the coating has good heat resistance. Results show that the coating has excellent hydrophobic stability, durability, self-cleaning performance and self-repairing performance, the preparation method is simple and environmentally friendly, fluorine and VOC emission is avoided, the coating can be suitable for the fields of building outer walls, automobile hub surfaces and the like, and the antifouling rate of the self-cleaned automobile hub surfaces can reach 99% preferably.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating materials, and in particular relates to a fluorine-free heat-resistant solid super-hydrophobic coating and a preparation method thereof. Background Art

[0002] Due to its unique surface hydrophobic properties, superhydrophobic coatings have broad application value in many fields such as construction and building materials, transportation, electronics and medical care, industry and manufacturing. For example, automobile wheels, as key components of automobiles, are exposed to rain, mud, brake dust containing metal particles such as Fe / Cu, NaCl / CaCl2 snow melting agents, and mixed oil and dirt pollutants during driving. The use of traditional coatings is prone to form an adhesive dirt layer, which can easily increase wind resistance due to pollutants, affect the endurance of electric vehicles and lead to a decrease in aerodynamic efficiency, cause high-speed vibration due to uneven dirt distribution, and lead to dynamic imbalance, as well as accelerated pitting corrosion of aluminum alloy / magnesium alloy wheels due to the electrolyte liquid film. Therefore, researchers are looking for a special functional surface with self-cleaning and high anti-fouling rate to prevent damage to the surface of automobile wheels and reduce maintenance costs.

[0003] Existing super-hydrophobic coatings are prepared using sol-gel, layer-by-layer assembly, and spray coating methods. However, the following technical problems and causes exist:

[0004] (1) The preparation method is not environmentally friendly and has high cost: In the existing technology, super-hydrophobic coatings are prepared by methods such as modification with fluorinated polymers or silanes and fluorinating agents. This not only brings about fluorine pollution and VOC emission problems, but also the cost of these materials themselves is relatively high, which increases the economic burden of preparing super-hydrophobic coatings and is not conducive to large-scale commercial applications.

[0005] (2) Insufficient heat resistance and stability: Materials with low melting points are used in the coating. For example, patent CN119823644A discloses a fluorine-free transparent self-cleaning solid lubricating coating and its preparation method, in which wax micropowder is used to provide roughness and hydrophobicity. A wax-based suspension including wax micropowder, hydrophobic adhesive and hydrophilic nano-silica is sprayed on the surface of the substrate to prepare the coating. Although the coating has transparency, it still has certain limitations in terms of heat resistance and stability, which restricts its application in some high-temperature environments. For example, in automobile wheel applications, hydrophobic coatings based on low-melting-point materials may not be able to maintain their stable performance.

[0006] (3) Poor hydrophobicity and antifouling properties: The hydrophobicity of superhydrophobic coatings mainly depends on the low surface energy substances on the surface. Due to the improper selection and proportion of low surface energy substances, the single scale structure, insufficient roughness, etc., the hydrophobicity of the coating is not strong enough to effectively reduce the pollution after sewage flushing, or form a hydrophobic barrier to prevent water from contacting the substrate. For example, due to insufficient hydrophobicity and antifouling properties, pollutants are difficult to remove and cannot meet the antifouling and anti-corrosion requirements of automobile wheels in complex use environments.

[0007] (4) Lack of self-repairing function and poor durability: The structure and composition of existing super-hydrophobic coatings do not have the ability to reconstruct the hydrophobic microstructure or restore the low surface energy state under certain conditions. When the existing coatings are physically worn, they cannot restore their hydrophobic properties by themselves. For example, when a car wheel is driving, some coatings are scratched or worn, and the micro-nanostructure of the damaged part is destroyed. It is impossible to restore it to the original super-hydrophobic state through simple treatment. As a result, the hydrophobic properties are easily attenuated or even lost, which makes it impossible to meet the requirements of high dynamic load and complex environment applications, and the maintenance cost increases. Summary of the Invention

[0008] The present invention aims to solve at least one of the above-mentioned technical problems to a certain extent. The present invention provides a fluorine-free heat-resistant solid super-hydrophobic coating and a preparation method thereof. The coating has good self-cleaning, hydrophobic, heat-resistant, stable, durable and self-repairing properties. The preparation method is simple and environmentally friendly, and it is fluorine-free and VOC-free, making it suitable for multiple fields such as building exterior walls and automobile wheel hub surfaces, and has broad commercial application prospects.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] The first aspect of the present invention is to provide a fluorine-free, heat-resistant, solid-state super-hydrophobic coating, comprising a double-layer composite structure formed by depositing core-shell structured microspheres on the surface of an adhesive layer, heating, and curing; the core-shell structured microspheres are formed by hydrophilic nano-scale silica as a shell layer, which is coated on the surface of micron-scale wax microspheres; when heated, the wax of the wax microspheres reversely covers the shell layer.

[0011] The mechanisms of the above-mentioned solid-state superhydrophobic coating include:

[0012] The solid-state superhydrophobic coating is designed with fluorine-free materials and innovatively introduces micron-sized wax microspheres with a surface coated with hydrophilic nano-sized silica as functional fillers: at the micron scale, the micron-sized wax microspheres give the coating the necessary surface roughness, which is conducive to constructing the microstructure required for superhydrophobicity; at the nanoscale, the hydrophilic nano-sized silica particles loaded on the surface of the micron-sized wax microspheres not only further increase the surface roughness, but also significantly improve the overall hardness of the coating due to their excellent mechanical properties. The synergistic effect of the micron-nano composite structure, combined with the hydrophobic properties of the wax substance itself, forms a double-layer composite structure, which enables the prepared coating to exhibit excellent solid-state superhydrophobic performance, stability and anti-fouling properties.

[0013] In addition, the coating also exhibits good heat resistance: its mechanism is mainly due to the thermal stability of the core-shell structure microspheres and silica. Compared with Fischer-Tropsch wax, silica has a higher melting point. Under high temperature conditions, when the wax melts, its fluidity is effectively restricted by the silica densely coated on the surface, avoiding the severe destruction or disintegration of the coating structure and the disadvantage of insufficient heat resistance caused by the relatively low melting point of the wax. At the same time, when heated, the molten wax will spontaneously seep out and coat the original hydrophilic nano-scale silica shell. This During the process, the hydrophilic silica originally exposed on the outer surface is "anti-coated" by the inner layer of hydrophobic wax, thereby realizing a dynamic transformation from a hydrophilic to a hydrophobic state, reflecting its application potential as a heat-resistant, fluorine-free solid super-hydrophobic coating; in addition, the addition of core-shell structured microspheres gives this coating a self-repairing function. After wear, the wax on the surface of the core-shell structure is worn away, and the wax in the core-shell structured microspheres can be melted again by high-temperature heating, and the silica is anti-coated again, realizing "anti-coating" again, and the hydrophobic properties of the coating will be restored.

[0014] The wax microspheres are used to provide a certain roughness and hydrophobicity to the solid super-hydrophobic coating. However, in order to further avoid the poor thermal stability of the prepared solid super-hydrophobic layer due to excessive wax microspheres, and the high silica content due to too few wax microspheres, the prepared solid super-hydrophobic layer has poor hydrophobicity. At the same time, in order to take into account the hydrophilic nano-scale silica to increase the hardness, roughness and wrapping effect of the coating, and further avoid the loss of hydrophobicity of the coating due to excessive hydrophilic nano-scale silica, in the preferred technical solution, the weight ratio of the wax microspheres to silica is: (0.3~4): (0.3~1.4). Taking into account the hydrophobicity and thermal stability of the coating, it can be further preferably (0.8~1.2): (0.3~1.4); taking into account the hydrophobicity and thermal stability of the coating, it can be further preferably (0.8~1.2): (0.6~0.8).

[0015] In a preferred technical solution, the particle size of the wax microspheres is 5 to 20 μm, and they can be dispersed directly by mechanical stirring, which is beneficial to reducing process costs.

[0016] In order to further improve the thermal stability of the solid superhydrophobic coating, in the preferred technical solution, the wax microspheres are Fischer-Tropsch wax microspheres. Fischer-Tropsch wax has a higher melting point and greater hardness than wax materials such as paraffin wax. The melting point is further improved through the thermophysical properties of the material itself. At the same time, compared with wax materials such as microcrystalline wax, it has low viscosity and excellent fluidity at high temperatures, which is more conducive to spontaneous exudation and re-coating with a silica shell in a molten state.

[0017] In a preferred technical solution, the particle size of the silicon dioxide is ≤20 nm, which is conducive to uniform attachment to the surface of the wax microspheres. In order to further control material costs, it can be further preferably 10 to 20 nm.

[0018] In a preferred technical solution, the adhesive layer is bis(3-aminopropyl)-terminated polydimethylsiloxane, which has a certain adhesive strength and is more conducive to the uniform deposition of core-shell structure microspheres.

[0019] A second aspect of the present invention is to provide a method for preparing a fluorine-free heat-resistant solid super-hydrophobic coating, the preparation method comprising:

[0020] Preparation of core-shell structure microspheres: micron-sized wax microspheres and hydrophilic nano-sized silica are uniformly dispersed in a solvent to prepare a wax-based suspension, and the solvent is evaporated from the wax-based suspension to prepare core-shell structure microspheres;

[0021] Preparing a bonding layer: uniformly dispersing the bonding material on the surface of the substrate to prepare a bonding layer;

[0022] Preparing a wax-based solid hydrophilic coating: depositing the core-shell structured microspheres on the surface of the bonding layer to prepare a wax-based solid hydrophilic coating;

[0023] Preparation of a solid super-hydrophobic coating: heating and curing the wax-based solid hydrophilic coating to form a solid super-hydrophobic coating with a double-layer composite structure.

[0024] In a preferred technical solution, when preparing a wax-based suspension, the solvent is anhydrous ethanol, micron-sized wax microspheres are added to the anhydrous ethanol, and then hydrophilic nano-scale silica is added. Anhydrous ethanol is a polar organic solvent with low viscosity. The polarity of anhydrous ethanol can control the dispersion stability of the wax microspheres by adjusting the weight concentration. For the subsequently added hydrophilic nano-silica, the polarity of anhydrous ethanol can improve its dispersibility in the system through hydrogen bonding, avoiding agglomeration of nanoparticles. The fast volatilization rate of anhydrous ethanol is conducive to the rapid evaporation of the solvent of the wax-based suspension. At the same time, taking into account the hydrophobicity and thermal stability of the coating, preferably, when preparing the wax-based suspension, the weight concentration of the wax microspheres in the solvent is 0.3wt% to 4wt%, and the weight concentration of the silica in the solvent is 0.3wt% to 1.4wt%.

[0025] The construction of the core-shell structure microspheres depends on the uniform dispersion of micron-sized wax microspheres and nano-sized silica in a solvent to achieve uniform loading of silica on the surface of the wax microspheres. In the preferred technical solution, when preparing the wax-based suspension, stirring and dispersion are adopted at room temperature. Considering that if the stirring time is insufficient, the nano-silica cannot effectively coat the surface of the wax microspheres, resulting in an incomplete core-shell structure, and in the subsequent high-temperature environment, the wax that is not effectively coated is prone to significant melting and flow, thereby weakening the morphological stability and hydrophobic properties of the coating; on the contrary, although excessively long stirring time helps to achieve uniform coating, it will significantly increase the time cost of the preparation process, which is not conducive to large-scale application and actual production. Therefore, it is preferred to control the stirring speed to 900 r / min and the stirring time to 0.5h~3h, which can achieve the adhesion of hydrophilic nano-sized silica to the surface of the micron-sized wax microspheres. Taking into account the hydrophobic stability of the coating and the time cost of preparation, it can be further preferably 1h~2h, and fixed-speed magnetic stirring is preferably used.

[0026] In a preferred technical solution, when preparing core-shell structured microspheres, the wax-based suspension is placed in an oven at 50-70° C. to evaporate the solvent, thereby preventing the wax microspheres from melting when the temperature is too high.

[0027] In a preferred technical solution, when preparing core-shell structured microspheres, the core-shell structured microspheres are obtained by evaporating the solvent and then grinding to obtain the core-shell structured microspheres, which can obtain powdered core-shell structured microspheres, and is conducive to high-density powder accumulation treatment of the core-shell structured microspheres on the surface of the bonding layer, thereby realizing full coverage thick layer construction.

[0028] In the preferred technical solution, when preparing the bonding layer, a glue spreader is used to disperse the bonding material, and the speed of the glue spreader is controlled to 5000-6000rpm, the acceleration is 1000rpm / s, and the time is 30s, which is used to evenly spread the bonding material applied to the substrate into a thin film and control the coating thickness.

[0029] In a preferred technical solution, when preparing the adhesive layer, the surface of the substrate is cleaned with anhydrous ethanol and then dried with air, which can prevent stains from affecting the adhesion of the adhesive material to the substrate.

[0030] In a preferred technical solution, when preparing a wax-based solid hydrophilic coating, the core-shell structure microspheres are evenly sprinkled on the surface of the adhesive layer using a filter cloth, and then flattened with a roller to ensure full contact between the core-shell structure microspheres and the substrate, and the high-density core-shell structure microsphere powder is evenly applied to the surface of the adhesive layer to achieve full coverage thick layer construction.

[0031] In a preferred technical solution, when preparing a solid super-hydrophobic coating, the wax-based solid hydrophilic coating is placed in an oven at 110°C to 120°C and heated and dried, preferably for 60 minutes, to promote the wax to fully melt and encapsulate the silica, so that the coating is transformed from hydrophilic to hydrophobic.

[0032] The third aspect of the present invention is to provide an application of a fluorine-free heat-resistant solid super-hydrophobic coating, including applying the solid super-hydrophobic coating to the exterior walls of buildings and the surfaces of automobile wheels, with the exterior walls of buildings and the surfaces of automobile wheels serving as substrates.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The solid super-hydrophobic coating of the present invention does not require modification with silane and fluorinating agent, and can be prepared using a fluorine-free method, which is fluorine-free and VOC-free, making the preparation simple and environmentally friendly, helping to reduce production costs, and having a wider commercial application prospect.

[0035] (2) The solid super-hydrophobic coating of the present invention successfully avoids the disadvantage of the wax melting point by constructing a core-shell structure microsphere formed by hydrophilic nano-scale silica as a shell layer and coating the surface of micron-scale wax microspheres. The heat resistance of the prepared solid super-hydrophobic coating is improved, the stability is better, and its application field is broadened.

[0036] (3) The solid super-hydrophobic coating of the present invention is a double-layer composite structure formed by depositing core-shell structure microspheres on the surface of the bonding layer and heating and curing. The core-shell structure microspheres are provided with a certain roughness and hydrophobicity by Fischer-Tropsch wax, and the hydrophilic nano-scale silica is used as a shell layer to cover the surface of the wax microspheres loaded on the micron scale. The wax is melted and the silica is wrapped back by the high temperature during heating, thereby realizing the transformation of the hydrophilicity of the coating to the hydrophobicity. Compared with the coating prepared by electrostatic spraying and other methods, the physical stability is better, and the excellent hydrophobicity can still be maintained after sandpaper wear, gauze wear, sand impact and water impact. At the same time, the coating has good self-cleaning and anti-fouling properties.

[0037] (4) The solid super-hydrophobic coating of the present invention has a self-repairing function. After being physically worn, the wax in the core-shell structure can be melted again by high-temperature heating to achieve "reverse coating" again, thereby restoring its hydrophobic properties.

[0038] (5) The solid super-hydrophobic coating of the present invention is applied in application fields such as building exterior walls and automobile wheel hub surfaces. It can effectively reduce the pollution of building exterior walls or automobile wheel hubs after sewage flushing, and can also effectively isolate water and oxygen, delaying the oxidation corrosion of the metal substrate of the wheel hub. Moreover, after testing, the anti-fouling rate of the automobile wheel hub after self-cleaning can preferably reach 99%. Its excellent self-cleaning, hydrophobicity and durability lay the foundation for achieving wider commercial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0040] Figure 1is a SEM image of the Fischer-Tropsch wax microspheres used in the present invention;

[0041] Figure 2 is a SEM image of the core-shell structured microspheres prepared in Example 1 of the present invention;

[0042] Figure 3 TEM image of the core-shell structured microspheres prepared in Example 1 of the present invention;

[0043] Figure 4 This is a local TEM image of the core-shell structured microspheres prepared in Example 1 of the present invention;

[0044] Figure 5 This is a physical picture of the solid super-hydrophobic coating prepared in Example 1 of the present invention;

[0045] Figure 6 This is the sandpaper abrasion test result of the solid super-hydrophobic coating prepared in Example 8. DETAILED DESCRIPTION

[0046] The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0047] In the following examples and comparative examples, the sources of reagents and testing equipment used include:

[0048] Fischer-Tropsch wax microspheres: melting point 95°C, particle size 5-20 μm, purchased from Dongguan Shanyi Plastic Co., Ltd.; bis(3-aminopropyl)-terminated polydimethylsiloxane, CAS number: 106214-84-0, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; hydrophilic nano-scale silica particles: particle size 10-20 nm, and anhydrous ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd.; the magnetic stirring rotor selected was a type A rotor; glass slides, sandpaper, and flannel were purchased from Henan Anning E-Commerce Co., Ltd.; 12-inch wheel hub: purchased from Liuzhou Gaohang Auto Parts Co., Ltd.; weights: purchased from Shanghai Yanheng Instrument Co., Ltd.; water: laboratory deionized water.

[0049] In the following examples and comparative examples, the coating test method includes:

[0050] (1) Test the hydrophobicity of the solid super-hydrophobic coating of the sample: Use the OCA20 contact angle tester to test the hydrophobicity of the surface of the solid super-hydrophobic coating to obtain the water contact angle WCA and the rolling angle WSA.

[0051] (2) Test the anti-fouling rate of the solid super-hydrophobic coating applied to the wheel hub surface: replace the base glass slide with a 12-inch wheel hub, and construct a functional interface with low surface energy and micro-nano dual structure by attaching the prepared solid super-hydrophobic coating on the surface of the 12-inch wheel hub to test whether the coating can effectively inhibit the adhesion and residue of pollutants; at the same time, under experimental simulation conditions, artificial mud solution is evenly sprayed on the wheel hub surface, and the anti-fouling performance of the coated and uncoated samples under natural drying and artificial rain conditions is compared to obtain the anti-fouling rate after mud and water flushing.

[0052] (3) Test the self-repairing performance of the solid super-hydrophobic coating of the sample: The solid super-hydrophobic coating is subjected to physical wear by sandpaper to reduce its hydrophobicity. The friction distance of 10 cm is counted as 1 time, and the coating is rubbed 4, 8, 12, 16, 20, 24, and 28 times respectively. The hydrophobicity of the super-hydrophobic coating under each friction number is tested to obtain the water contact angle WCA and the rolling angle WSA. At the same time, under the experimental simulation conditions, an artificial mud solution is evenly sprayed on the surface of the solid super-hydrophobic coating after the final wear to obtain the anti-fouling rate after wear. Then, the worn solid super-hydrophobic coating is placed in a 120°C oven for high temperature heating to test whether the hydrophobicity of the solid super-hydrophobic coating after heating can be restored to the original level. Under the experimental simulation conditions, an artificial mud solution is evenly sprayed on the surface of the worn and heated solid super-hydrophobic coating to obtain the anti-fouling rate after heating.

[0053] Example 1:

[0054] A preferred embodiment of the method for preparing the fluorine-free heat-resistant solid super-hydrophobic coating of the present invention comprises the following steps:

[0055] S1. Preparation of core-shell structure microspheres:

[0056] With anhydrous ethanol as solvent, 30 ml of anhydrous ethanol was poured into a 50 mL beaker, and micron-sized Fischer-Tropsch wax microspheres and hydrophilic nano-sized silica were placed into the beaker in sequence. The weight concentration of the Fischer-Tropsch wax microspheres in the solvent was 0.3 wt %. The SEM image of the Fischer-Tropsch wax microspheres is shown in FIG. Figure 1 As shown, the weight concentration of silica in the solvent is 0.7wt%, and at room temperature and a rotation speed of 900r / min, constant speed magnetic stirring is carried out for 2 hours to uniformly disperse Fischer-Tropsch wax microspheres and silica in the solvent to prepare a wax-based suspension, so that silica is attached to the surface of the Fischer-Tropsch wax microspheres. After stirring, the beaker containing the wax-based suspension is placed in a 70°C oven to evaporate the solvent, and finally the beaker is taken out and the contents of the beaker are ground using a mortar to obtain core-shell structure microsphere powder. The SEM image of the core-shell structure microspheres is shown as follows. Figure 2 As shown, the TEM image of the core-shell structure microspheres is as follows Figure 3 As shown, the TEM image of the core-shell structure microspheres is as follows Figure 4As shown, it can be seen that the core-shell structure microspheres are formed by silica as a shell layer, which is wrapped and loaded on the surface of the Fischer-Tropsch wax microspheres.

[0057] S2. Preparation of bonding layer:

[0058] The surface of the base glass slide was cleaned with anhydrous ethanol and then dried with air blast. Bis(3-aminopropyl)-terminated polydimethylsiloxane was evenly coated on the base glass slide using a coating machine at a rotation speed of 6000 rpm, an acceleration of 1000 rpm / s, and a time of 30 s to prepare a bonding layer.

[0059] S3. Preparation of wax-based solid hydrophilic coating:

[0060] The core-shell structure microsphere powder obtained in step S1 is evenly sprinkled on the surface of the bis(3-aminopropyl)-terminated polydimethylsiloxane of the adhesive layer obtained in step S2 through a filter cloth. The powdered core-shell structure microspheres are then flattened and compacted with a roller to ensure full contact between the core-shell structure microspheres and the base glass slide. High-density powder stacking treatment and full-coverage thick layer construction are performed to obtain a wax-based solid hydrophilic coating.

[0061] S4. Preparation of solid super-hydrophobic coating by heating:

[0062] The wax-based solid coating obtained in S3 was placed in an oven at 120°C and dried for 60 minutes to allow the wax of the Fischer-Tropsch wax microspheres to reversely cover the silica in the shell layer, so that the wax-based solid hydrophilic coating was transformed from hydrophilic to hydrophobic. The coating was taken out and cured to obtain a solid super-hydrophobic coating with a double-layer composite structure, as shown in the figure. Figure 5 As shown, the obtained solid superhydrophobic coating is white.

[0063] In order to investigate the effect of wax microsphere concentration on the solid super-hydrophobic coating, the concentration of the Fischer-Tropsch wax microspheres in the solvent in Example 1 was replaced with different concentrations to prepare coatings. The hydrophobicity of each coating was tested and the antifouling performance was tested under the same environment. The results are shown in Table 1 below:

[0064] Table 1. Properties of solid-state superhydrophobic coatings at different wax microsphere weight concentrations

[0065]

[0066] From the comparison results of Examples 1 to 3 with Comparative Examples 1 and 2, it can be seen that the ratio of silica to wax microspheres has a key influence on the hydrophobic properties of the coating: when the proportion of wax microspheres is low, the silica content is relatively high, which is conducive to forming a better coating structure, but will significantly weaken the hydrophobic properties of the coating surface and enhance its hydrophilicity; and when the proportion of wax microspheres is too high, that is, the content of Fischer-Tropsch wax microspheres is relatively large, it is difficult for silica to effectively coat the wax microspheres, resulting in insufficient coating. In a high temperature environment, the Fischer-Tropsch wax that is not fully coated is prone to melting and leveling on the surface, thereby reducing the surface roughness and causing a decrease in hydrophobic properties.

[0067] In addition, the amount of core-shell structured microspheres is the key to determining the self-healing performance of the coating, which further improves the durability of the coating. Therefore, reasonable optimization of the weight ratio of wax microspheres to silica is a key factor in achieving excellent hydrophobic properties: the weight ratio of wax microspheres to silica is (0.3~4): (0.3~1.4), and the weight concentration of wax microspheres in the solvent is preferably 0.3wt%~4wt%. Taking into account the hydrophobicity and thermal stability of the coating, the weight concentration of wax microspheres in the solvent can be further preferably 0.8wt%~1.2wt%.

[0068] Example 4:

[0069] Another preferred embodiment of the method for preparing the fluorine-free heat-resistant solid super-hydrophobic coating of the present invention is different from Example 1 in that: S1, preparing core-shell structure microspheres: the weight concentration of Fischer-Tropsch wax microspheres in the solvent is 1wt%, and constant speed magnetic stirring is performed for 0.5 hours; a solid super-hydrophobic coating with a double-layer composite structure is obtained.

[0070] In order to investigate the effect of the magnetic stirring time on the solid super-hydrophobic coating in step S1, different super-hydrophobic coatings were prepared using different magnetic stirring times in Example 4, and the hydrophobicity of each coating was tested and the antifouling performance was tested under the same environment. The results are shown in Table 2 below:

[0071] Table 2. Properties of solid-state superhydrophobic coatings at different magnetic stirring times

[0072]

[0073] From the comparison results of Examples 4 to 6 with Comparative Examples 3 and 4, it can be seen that the core-shell structure microspheres mainly rely on the physical effect under magnetic stirring conditions to make the nano-scale silica uniformly adhere to the surface of the micron-scale Fischer-Tropsch wax microspheres; therefore, the magnetic stirring time is a key process parameter affecting the quality of the core-shell structure formation: if the stirring time is too short, it is difficult for silica to fully adhere, resulting in incomplete formation of the core-shell structure and weak interfacial bonding force. In the subsequent high-temperature environment, the wax that is not effectively coated is prone to significant melting and flow, thereby affecting its structural stability; and although a stirring time that is too long can improve the adhesion effect, it will significantly increase the time cost, which is not conducive to the industrial promotion and practical application of the process.

[0074] In addition, the amount of core-shell structured microspheres is the key to determining the self-healing performance of the coating, which further improves the durability of the coating. Therefore, the stirring time needs to be reasonably controlled to improve the preparation efficiency while ensuring the stability of the core-shell structure. The stirring time is preferably 0.5h to 3h. Taking into account the hydrophobicity, stability and time cost of the coating, it can be further preferably 1h to 2h.

[0075] Example 7:

[0076] Another preferred embodiment of the method for preparing the fluorine-free heat-resistant solid super-hydrophobic coating of the present invention is different from Example 1 in that: S1, preparing core-shell structure microspheres: the weight concentration of Fischer-Tropsch wax microspheres in the solvent is 1wt%, and the weight concentration of silica in the solvent is 0.3wt%; a solid super-hydrophobic coating with a double-layer composite structure is obtained.

[0077] In order to investigate the effect of hydrophilic nano-scale silica concentration on the solid super-hydrophobic coating, the weight concentration of silica in the solvent in Example 7 was changed to prepare different solid coatings. The hydrophobicity of each coating was tested and the antifouling performance was tested under the same environment. The results are shown in Table 3 below:

[0078] Table 3. Properties of solid superhydrophobic coatings with different silica weight concentrations

[0079]

[0080]

[0081] From the comparison results of Examples 7 to 9 with Comparative Examples 5 and 6, it can be seen that hydrophilic silica, as a key material for constructing core-shell structured microspheres, has a significant effect on the final coating performance. An appropriate amount of silica helps to form a stable and continuous coating layer on the surface of the microspheres, thereby improving the structural integrity and thermal stability; however, when the silica content is too high, although the coating effect is enhanced, the roughness of the coating surface is reduced, its hydrophobic properties are significantly weakened, and it exhibits stronger hydrophilicity; on the contrary, when the content is insufficient, it is difficult for silica to achieve effective coating of the Fischer-Tropsch wax microspheres, resulting in an incomplete core-shell structure and poor thermal stability of the solid super-hydrophobic layer.

[0082] In addition, the amount of core-shell structured microspheres is the key to determining the self-healing properties of the coating. In order to take into account the hydrophilic nano-scale silica to increase the hardness, roughness and wrapping effect of the coating, and further avoid the excessive amount of hydrophilic nano-silica and the loss of hydrophobicity of the coating, the weight ratio of the wax microspheres to silica is: (0.3~4): (0.3~1.4), and the weight concentration of the silica in the solvent is preferably 0.3wt%~1.4wt%. Taking into account the hydrophobicity and anti-fouling rate of the coating, the weight concentration of silica in the solvent can be further preferably 0.6wt%~0.8wt%.

[0083] During the self-repairing performance test of the solid super-hydrophobic coating obtained in Examples 1 to 9, Figure 6 Taking the sandpaper abrasion test results of the prepared solid super-hydrophobic coating under the shown embodiment 8 as an example, at the micron scale, the Fischer-Tropsch wax microspheres give the coating the necessary surface roughness, and at the nanoscale, the nanoscale silica particles loaded on the surface of the microspheres further increase the surface roughness and mechanical properties, and the synergistic effect of the micron-nano composite structure, combined with wax substances and the hydrophobic bonding layer surface, makes the prepared coating show excellent solid-state super-hydrophobicity, and can still maintain excellent hydrophobicity after sandpaper abrasion, and has better stability. At the same time, after wear, high temperature heating can make the wax in the core-shell structure melt again, spontaneously ooze out again and re-coat the nano-silica shell, and realize "anti-coating" again. The hydrophobicity and anti-fouling properties of the coating can be restored.

[0084] As can be seen from the results of Examples 1 to 9, the solid super-hydrophobic coating obtained by the present invention adopts a double-layer composite structure design, has good anti-fouling performance, excellent self-cleaning, hydrophobicity, stability and durability, the preparation method is simple and environmentally friendly, fluorine-free and VOC-free, and a solid super-hydrophobic coating with high anti-fouling rate and durability is obtained using environmentally friendly wax. Although the solid super-hydrophobic coating is white and lacks transparency, it exhibits more excellent comprehensive performance in terms of hydrophobicity and thermal stability, making it suitable for multiple fields such as building exterior walls and automobile wheel hub surfaces, and has broad commercial application prospects.

[0085] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fluorine-free heat-resistant solid super-hydrophobic coating, characterized in that, The invention comprises a double-layer composite structure formed by depositing core-shell structure microspheres on the surface of an adhesive layer, heating and curing; the core-shell structure microspheres are formed by hydrophilic nano-scale silicon dioxide as a shell layer, which is coated on the surface of micron-scale wax microspheres; when heated, the wax of the wax microspheres reversely covers the shell layer.

2. The fluorine-free heat-resistant solid super-hydrophobic coating according to claim 1, wherein The weight ratio of the wax microspheres to silicon dioxide is: (0.3-4): (0.3-1.4).

3. The fluorine-free heat-resistant solid super-hydrophobic coating according to claim 2, wherein The particle size of the wax microspheres is 5 to 20 μm, and the particle size of the silicon dioxide is ≤20 nm.

4. The fluorine-free heat-resistant solid super-hydrophobic coating according to claim 2, wherein The wax microspheres are Fischer-Tropsch wax microspheres.

5. The fluorine-free heat-resistant solid super-hydrophobic coating according to claim 1, wherein The bonding layer is a bis(3-aminopropyl)-terminated polydimethylsiloxane bonding layer.

6. The method for preparing a fluorine-free heat-resistant solid super-hydrophobic coating according to any one of claims 1 to 5, wherein: The preparation method thereof comprises: Preparation of core-shell structure microspheres: micron-sized wax microspheres and hydrophilic nano-sized silica are uniformly dispersed in a solvent to prepare a wax-based suspension, and the solvent is evaporated from the wax-based suspension to prepare core-shell structure microspheres; Preparing a bonding layer: uniformly dispersing the bonding material on the surface of the substrate to prepare a bonding layer; Preparing a wax-based solid hydrophilic coating: depositing the core-shell structured microspheres on the surface of the bonding layer to prepare a wax-based solid hydrophilic coating; Preparation of a solid super-hydrophobic coating: heating and curing the wax-based solid hydrophilic coating to form a solid super-hydrophobic coating with a double-layer composite structure.

7. The preparation method of the fluorine-free heat-resistant solid super-hydrophobic coating according to claim 6, wherein When preparing a wax-based suspension, the weight concentration of the wax microspheres in the solvent is 0.3wt% to 4wt%, and the weight concentration of the silicon dioxide in the solvent is 0.3wt% to 1.4wt%. The wax suspension is dispersed by stirring at room temperature, with a stirring speed of 900 r / min and a stirring time of 0.5h to 3h. The wax-based suspension is placed in an oven at 50-70°C to evaporate the solvent, and finally ground to obtain the core-shell structured microspheres.

8. The preparation method of the fluorine-free heat-resistant solid super-hydrophobic coating according to claim 6, wherein When preparing the bonding layer, a glue spreader is used to disperse the bonding material. The speed of the glue spreader is controlled to be 5000-6000 rpm, the acceleration is 1000 rpm / s, and the time is 30 s.

9. The method for preparing a fluorine-free heat-resistant solid super-hydrophobic coating according to claim 6, wherein When preparing a wax-based solid hydrophilic coating, the core-shell structure microspheres are evenly sprinkled on the surface of the adhesive layer using a filter cloth, and then flattened with a roller to ensure full contact between the core-shell structure microspheres and the substrate. When preparing a solid super-hydrophobic coating, the wax-based solid hydrophilic coating is placed in an oven at 110°C to 120°C for heating and drying.

10. Use of the fluorine-free heat-resistant solid super-hydrophobic coating according to any one of claims 1 to 5, characterized in that: The method includes applying the solid super-hydrophobic coating to the exterior walls of buildings and the surfaces of automobile wheels.

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