A pfas-free, environmentally friendly, sand-textured powder coating composition and a method for its preparation

Abstract

The present application provides a PFAS-free environment-friendly sand-textured powder coating composition and a preparation method thereof, and belongs to the technical field of powder coating. The polyester resin is used as the main film-forming material, and the carboxyl-terminated polyester resin, hydroxyl-terminated polyester resin, bio-based epoxy resin, hydrophobically modified microcrystalline cellulose, porous microspheres, pigments and fillers, and fluorine-free additives are contained. The hydrophobically modified microcrystalline cellulose is melt-extruded into the base powder, the porous microspheres are adsorbed on the surface of the base powder particles through low-shear dry mixing after the base powder is prepared, the carboxyl-terminated polyester resin reacts with the epoxy group to form preliminary cross-linking shrinkage during the curing process, the hydroxyl-terminated polyester resin fills the micro-pores through subsequent reaction with the epoxy group, the hydrophobically modified microcrystalline cellulose constructs the raised sand-textured skeleton, and the porous microspheres form controllable micro-pits, so that the gradient sand-textured structure is obtained, and the present application is suitable for surface coating of metal furniture, outdoor guardrails, traffic facilities and instrument and meter housings.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology, specifically to a PFAS-free environmentally friendly sand-textured powder coating composition and its preparation method. Background Technology

[0002] Currently, research on fluorine-free textured powder coatings mainly focuses on replacing traditional fluorinated texture agents through physical fillers or resin modification to balance environmental protection and surface texture effects. However, existing solutions often fail to simultaneously satisfy texture uniformity, coating flexibility, impact resistance, and gradient structure stability during long-term use. Moreover, most methods rely on single-component texture creation, resulting in poor texture controllability or decreased mechanical properties.

[0003] To address the aforementioned issues, CN121991578A proposed a high-weather-resistant fluorine-free sand-textured powder coating and its preparation method. This method involves preparing flame-retardant additives, core-shell alumina composite materials, and eugenol-modified cellulose nanocrystals, which are then compounded with organosilicon-modified polyester to improve the coating's flame retardancy, UV resistance, and high-temperature resistance. However, while introducing multiple functional components, it lacks a specific design for the sand-textured structure. The modified cellulose nanocrystals, in nanofiber form, primarily fill the gaps in the cross-linked network to enhance heat resistance, but cannot serve as a rigid framework for constructing the sand texture. Simultaneously, the alumina composite material, with nano-alumina as the core and quaternized alkali lignin as the shell, improves dispersibility but lacks a post-mixing adhesion process using porous microspheres, making it impossible to form controllable micro-pits on the coating surface. Therefore, the three-dimensionality and uniformity of the sand texture depend on a single fluorine-free sand-texturing agent, making it difficult to achieve a gradient structure. CN121975409A proposes a fluorine-free, environmentally friendly, stain-resistant, anti-slip, and textured powder coating and its preparation method. It synthesizes a branched, carboxyl-terminated polyester containing polydimethylsiloxane segments and crosslinks it with bisphenol A type epoxy resin. Modified nano-zinc oxide and PDMS-coated silica are added simultaneously to achieve low surface energy stain resistance, antibacterial properties, and anti-slip properties. Although it utilizes the hydrophobicity of PDMS and the texture-forming function of the texture agent, the texture formation relies solely on the physical obstruction of the wax powder and the steric hindrance caused by the branched structure of the resin. It does not introduce non-melting, hard skeleton particles, and all components are melt-extruded. The nano-zinc oxide and silica are embedded within the coating, preventing the formation of micro-pits on the surface. This results in limited texture depth and tactile control, and the coating's flexibility and impact resistance are also limited due to the lack of a gradient buffer structure.

[0004] In summary, existing fluorine-free sand-textured powder coating technologies lack a two-component system capable of synergistically controlling the raised skeleton and micro-dimples, and it is difficult to simultaneously achieve coating flexibility and impact resistance. Therefore, there is an urgent need to develop a PFAS-free environmentally friendly sand-textured powder coating composition and its preparation method that utilizes the synergistic effect of modified microcrystalline cellulose and porous silica microspheres, combined with the difference in reaction rates of the two resins and a post-mixing process, to form a gradient sand-textured structure with a hard skeleton at the bottom and micro-dimples at the top. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a PFAS-free environmentally friendly sand-textured powder coating composition and its preparation method. This invention uses polyester resin as the main film-forming substance and includes carboxyl-terminated polyester resin, hydroxyl-terminated polyester resin, bio-based epoxy resin, hydrophobically modified microcrystalline cellulose, porous microspheres, pigments and fillers, and fluorine-free additives. The hydrophobically modified microcrystalline cellulose is melt-extruded into the base powder. After the base powder is prepared, the porous microspheres are adsorbed onto the surface of the base powder particles via a low-shear dry mixing method. During the curing process, the carboxyl-terminated polyester resin reacts with epoxy groups to form preliminary cross-linking shrinkage. The hydroxyl-terminated polyester resin then reacts with the epoxy groups to fill the micropores. The hydrophobically modified microcrystalline cellulose constructs a raised sand-textured framework, and the porous microspheres form controllable micro-pits, thereby obtaining a gradient sand-textured structure. This invention solves the technical problems of persistent environmental pollution and biotoxicity risks associated with PFAS in traditional coatings, the reliance on fluorine-containing additives to control surface energy to obtain texture in traditional sand-textured coatings, and the high brittleness and excessive surface roughness of the coating film caused by the use of inorganic coarse fillers in fluorine-free solutions.

[0006] This invention proposes a PFAS-free environmentally friendly sand-textured powder coating composition, comprising the following raw materials by weight: 55-75 parts of carboxyl-terminated polyester resin, 15-35 parts of hydroxyl-terminated polyester resin, 10-20 parts of bio-based epoxy resin, 3-12 parts of hydrophobically modified microcrystalline cellulose, 0.8-5 parts of porous microspheres, 3-16 parts of pigments and fillers, 0.3-1.0 parts of fluorine-free leveling agent, 0.2-0.8 parts of benzoin, 0.1-0.4 parts of epoxy reaction catalyst, 0.5-1.0 parts of ethylene bis-stearamide wax, 0.05-0.4 parts of antioxidant, and 0.05-0.4 parts of hindered amine light stabilizer.

[0007] This invention also proposes a method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition, the specific technical solution of which is as follows: Step 1: Mix carboxyl-terminated polyester resin, hydroxyl-terminated polyester resin, bio-based epoxy resin, hydrophobically modified microcrystalline cellulose, pigments and fillers, fluorine-free leveling agent, benzoin, epoxy reaction catalyst, ethylene bis-stearamide wax, antioxidant and light stabilizer and let them equilibrate. Then add them together to a mixer for mixing to obtain a premix.

[0008] Step 2: Add the premixed material to a twin-screw extruder for melt extrusion. After extrusion, the material is cooled by tableting and then crushed by a crusher.

[0009] Step 3: The crushed material is fed into a crushing equipment for crushing and then classified by a grading equipment to collect the base powder that meets the requirements.

[0010] Step 4: Pre-dry the porous microspheres, then add the dried porous microspheres to the base powder, dry mix them in a low-shear mixer and sieve them to obtain a PFAS-free environmentally friendly sand texture powder coating composition.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By combining fluorine-free cellulose with microspheres and controlling the reaction rate of dual resins, the same sand texture effect as traditional sand texture powder coatings is achieved without introducing any fluorocarbon bonds. The prepared products will not produce perfluorinated persistent organic pollutants throughout their entire life cycle, thus meeting environmental protection requirements.

[0012] 2. Two types of texture builders with different properties are used in synergy. The hydrophobic modified microcrystalline cellulose has good compatibility with polyester resin after fluorine-free modification. It forms a raised sand texture skeleton in the lower layer of the coating, which disperses stress to a certain extent and prevents crack propagation. The porous microspheres form controllable micro-pits by adsorbing low molecular weight components during the curing process, which improves the surface feel of the coating.

[0013] 3. The resulting coating surface has a uniformly distributed micron-level pit structure with rounded edges and moderate opening size, which allows contaminants to only loosely adhere to the top of the surface protrusions and prevents them from embedding into the coating to form stubborn stains. In daily cleaning, surface dirt can be thoroughly removed by using a damp cloth with a neutral detergent, without the need for fluorinated detergents or high-pressure washing equipment. The micro-pit structure can also effectively inhibit the continuous spread and adhesion of contaminants on the coating surface, significantly reducing the ability of dirt to remain. Attached Figure Description

[0014] Figure 1 Here are SEM images of the powder particles in Example 1, where a is the surface morphology of the base powder and b is the surface morphology of the final coating powder. Figure 2 This is the EDS surface distribution diagram of the final coating powder in Example 1; Figure 3 The images show the SEM morphology of the coating samples of the examples and comparative examples, where a is the cross-sectional morphology of Example 1, b is the surface morphology of Example 1, c is the surface morphology of Comparative Example 1, d is the surface morphology of Comparative Example 2, and e is the surface morphology of Comparative Example 3. Figure 4 These are height diagrams of the three-dimensional morphology of the coatings in the examples and comparative examples, where a is the height diagram of Example 1, b is the height diagram of Comparative Example 1, c is the height diagram of Comparative Example 2, and d is the height diagram of Comparative Example 3. Detailed Implementation

[0015] The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as detailed in the claims.

[0016] This invention proposes a method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition, the specific technical solution of which is as follows: 1. Raw material premixing Polyester resin, hydrophobically modified microcrystalline cellulose, and additives are premixed in a mixer to obtain a mixture. Carboxyl-terminated and hydroxyl-terminated polyester resins are polymers constituting the main framework of the coating film, possessing natural hydrophobicity. Bio-based epoxy resin is added as a crosslinking agent. When the coating is heated and cured for spraying, multiple epoxy groups on its molecules simultaneously undergo ring-opening addition reactions with the end groups of the two polyester resins, thereby connecting the linear polyester molecular chains into a three-dimensional network. Simultaneously, the long fatty acid chains in the crosslinking agent molecules provide flexible segments, preventing the coating film from becoming too brittle. Furthermore, the reaction rate between carboxyl and epoxy groups is faster than that between hydroxyl and epoxy groups. This kinetic difference results in a shrinkage followed by filling effect during curing, synergistically forming a textured surface with the hydrophobically modified microcrystalline cellulose and porous silica microspheres. The hydrophobically modified microcrystalline cellulose is a crystalline cellulose with a fluorine-free surface chemical modification, maintaining its original rod-shaped or block-shaped morphology. Its particle hardness is much higher than that of the resin, and it hardly undergoes any deformation during mixing. These raw materials and additives are fed into a mixer for mixing. Particles of different sizes and densities collide and exchange positions randomly in the turbulent flow. At the same time, the relative motion between the edge of the agitator and the material generates a shear field, causing the fine powder to adhere evenly to the surface of the larger resin particles. Furthermore, because the size of the hydrophobically modified microcrystalline cellulose particles is between that of resin particles and pigments / fillers, they are uniformly suspended in the mixed system under mechanical force.

[0017] During the mixing process, friction between particles and between particles and the container wall generates static electricity. This static electricity facilitates the adhesion of fine particles to the surface of coarse particles, forming an adhesive mixture, which helps to uniformly disperse small doses of additives in the subsequent melt extrusion stage. Since all components are solids at room temperature and do not undergo chemical reactions, premixing is a purely physical process that can construct a macroscopically homogeneous solid mixture without changing any of the original particle size and morphology, thus providing a stable feed composition for the next step of melt extrusion.

[0018] 2. Extrusion crushing The mixture is heated and melted, then pressed into thin sheets and broken up. The solid particles in the premix still coexist as independent particles at the microscale; there is no molecular-level contact between the resin and the crosslinking agent. The melt extrusion step, through the combined action of heat and shear force, transforms the discrete particle system into a continuous, homogeneous melt. In the melting and mixing sections, the kneading blocks and reverse thread elements installed on the screw exert strong shear and stretching forces on the melt, not only creating relative motion between the molten resin and unmelted solid additives, but also breaking up agglomerated particles and dispersing them uniformly into the continuous resin phase. The bio-based epoxy resin also melts under heating conditions, forming a miscible homogeneous system with the polyester resin. Other small-molecule additives are also completely dissolved in the resin and distributed in a molecular state. Meanwhile, the hydrophobically modified microcrystalline cellulose retains its original particle morphology. In the strong shear flow field, these hard particles are encapsulated by the melt and uniformly dispersed, with each particle completely wetted by the continuous resin phase.

[0019] Because the material has a short residence time in the barrel, although the temperature reaches the resin's melting temperature, it is still below the significant starting temperature of the curing reaction. Therefore, carboxyl-terminated polyester resins and hydroxyl-terminated polyester resins do not undergo chemical crosslinking with the epoxy crosslinking agent. When the melt is extruded into the tableting and cooling unit, the melt temperature rapidly drops below the resin's glass transition temperature. The resin re-solidifies from a viscous flow state into a glassy sheet, causing the uniformly dispersed structure established during melt mixing to be instantly frozen into a brittle sheet.

[0020] 3. Crushing and grading The fragments are ground into powder and then graded and screened to obtain base powder with a suitable particle size. Since the flakes obtained after melt extrusion and cooling are in the millimeter to centimeter range, while the electrostatic spraying process of coatings requires the particle size distribution of powder coatings to be in the tens of micrometers range, particles that are too large cannot pass through the delivery pipeline of the electrostatic spray gun and have poor charge capacity, making it difficult to adhere to the workpiece surface. However, powders that are too small are easy to disperse, causing material waste and environmental pollution, and their low bulk density leads to uneven coating thickness. Therefore, it is necessary to pulverize the extruded and cooled flakes into micrometer-sized powder.

[0021] The crushing and classification of particles are carried out in a cycle within the same equipment. When the powder is carried by the airflow into the rotating classifying wheel area, the particles are subjected to two opposing forces: the drag force exerted by the airflow and the centrifugal force generated by the rotation of the classifying wheel. Coarse particles are repeatedly impacted until their size is reduced below a critical value. By utilizing the mechanical properties of brittle fracture in solids, continuous thin sheets are discretized into particles. Then, the size-dependent force behavior of the particles in fluid dynamics is used to achieve particle size screening, thereby obtaining a narrow-distribution powder that meets the requirements of electrostatic spraying processes.

[0022] 4. Post-mixing screening The dried porous microspheres are mixed with the base powder at low speed and sieved to obtain the desired powder coating composition. The function of the porous microspheres is to form micro-pits on the coating surface. This requires that the microspheres be located on the surface of the coating rather than embedded inside during spray curing. If the microspheres are melt-extruded together with other components, the molten resin will penetrate into the channels and encapsulate the microspheres. In this way, after cooling, the microspheres will be located inside the particles and remain inside the coating after spray curing. Therefore, the microspheres must be attached to the particle surface after the base powder is applied. Since high shear can destroy the thin-walled pore structure of the microspheres, and frictional heat may soften and stick the surface of the base powder particles, causing the microspheres to embed rather than adhere, a low-shear method is required for post-mixing. Under low shear, the particle collision energy is small, and the microspheres adhere to the surface of the base powder through van der Waals forces and electrostatic forces, without embedding inside. This results in the microspheres gradually forming a discontinuous load layer on the surface of the base powder particles, thus forming a base powder-surface porous microsphere composite powder.

[0023] Because the nanopores of porous microspheres exhibit capillary coagulation, they spontaneously adsorb water vapor from the air and condense into liquid water. Without prior drying, this water vaporization and expansion during spray curing can rupture the molten coating, forming bubbles or pinholes. Drying desorbs water molecules and reduces surface hydrophilicity, minimizing the risk of re-hygroscopic absorption. During post-mixing, microsphere aggregates or residual coarse particles may form. These larger-than-mesh particles are retained during sieving, allowing individual base powder particles and their attached microspheres to pass through the screen, preventing agglomerates from clogging the spray gun or causing coating bumps.

[0024] The following specific examples and comparative examples further illustrate the PFAS-free environmentally friendly sand texture powder coating composition of the present invention. Table 1 shows the specific information of the raw materials used in the examples.

[0025] Table 1 Raw Material Information Table

[0026] Example 1

[0027] S1: Take 60 parts by weight of carboxyl-terminated polyester resin, 27 parts by hydroxyl-terminated polyester resin, 13 parts by weight of bio-based epoxy resin, 8 parts by weight of hydrophobically modified microcrystalline cellulose treated with octyltriethoxysilane, 6 parts by weight of precipitated barium sulfate, 3 parts by weight of rutile titanium dioxide, 1 part by weight of carbon black, 0.8 parts by weight of fluorine-free leveling agent, 0.5 parts by weight of benzoin, 0.2 parts by weight of 2-methylimidazole, 0.6 parts by weight of ethylene bis-stearamide wax, 0.3 parts by weight of antioxidant 1010, and 0.3 parts by weight of hindered amine light stabilizer HALS 292. Equilibrate all raw materials at 25℃ and 55% relative humidity for 12 hours. Then put them all into a high-speed mixer and stir at 900 rpm for 4 minutes, alternating the stirring direction every 30 seconds. After mixing, stop the machine and let it stand for 30 seconds to dissipate static electricity to obtain the premix.

[0028] S2: The premix obtained in S1 is continuously fed into a twin-screw extruder. The feed screw speed is set to 25 rpm, the length-to-diameter ratio of the extruder screw is 38:1, the main screw speed is 300 rpm, and the temperature control of each section of the barrel is as follows: Zone 1 85℃, Zone 2 95℃, Zone 3 105℃, Zone 4 110℃, Zone 5 110℃, and Die head 105℃. The total residence time of the material in the barrel is 75s. The extruded strip is 30mm wide and 2mm thick. The strip is then immediately cooled by a twin-roller tablet press. 10℃ cooling water is circulated inside the cooling rollers, and the distance between the upper and lower rollers is 1.0mm. The tablets are then fed into a hammer mill for crushing. The screen aperture of the crusher is 8mm, and the hammer linear velocity is 25m / s, resulting in the crushed material.

[0029] S3: The material crushed in S2 is fed into the air classifier mill at a rate of 30 kg / h via a vibrating feeder. The feeder vibration frequency is 50 Hz, the grinding disc speed is 8500 rpm, the air inlet temperature of the grinding chamber is 10℃, the classifier speed is 6500 rpm, and the negative pressure of the grinding chamber is -800 Pa. The powder obtained after crushing and classifying is passed through a double-layer vibrating screen. The upper screen is a 120-mesh screen and the lower screen is a 1250-mesh screen. After sieving, the powder that does not pass through the upper screen is fed back into the crusher for re-crushing and classification until all the material passes through the upper screen. The powder that does not pass through the lower screen is taken as qualified base powder.

[0030] S4: Weigh 3.5 parts of porous silica microspheres and place them in a vacuum drying oven. Dry them at -0.09MPa and 80℃ for 3 hours until the moisture content is no more than 0.3%. After cooling, take them out and seal them. Add the qualified base powder obtained in S3 and the dried porous silica microspheres together to a V-type low-shear mixer. Mix at 20rpm for 15 minutes, stopping the machine every 5 minutes and eliminating static electricity by grounding and ionizing. After mixing, pass the powder through a 180-mesh ultrasonic vibrating sieve with a vibration frequency of 25kHz and an amplitude of 0.8mm. Take the sieve material, seal it and store it for later use. This is the desired powder coating composition.

[0031] Example 2

[0032] The difference from the preparation method in Example 1 is as follows: S1: Take 55 parts of carboxyl-terminated polyester resin, 15 parts of hydroxyl-terminated polyester resin, 20 parts of bio-based epoxy resin, 3 parts of hydrophobically modified microcrystalline cellulose, 1.8 parts of precipitated barium sulfate, 0.9 parts of rutile titanium dioxide, 0.3 parts of carbon black, 0.3 parts of fluorine-free leveling agent, 0.2 parts of benzoin, 0.1 parts of 2-methylimidazole, 0.5 parts of ethylene bis-stearamide wax, 0.05 parts of antioxidant 1010, and 0.05 parts of hindered amine light stabilizer HALS 292; S4: Weigh 0.8 parts of porous silica microspheres, and the remaining steps are the same.

[0033] Example 3

[0034] The difference from the preparation method in Example 1 is as follows: S1: Take 75 parts of carboxyl-terminated polyester resin, 15 parts of hydroxyl-terminated polyester resin, 10 parts of bio-based epoxy resin, 12 parts of hydrophobically modified microcrystalline cellulose, 9.6 parts of precipitated barium sulfate, 4.8 parts of rutile titanium dioxide, 1.6 parts of carbon black, 1.0 part of fluorine-free leveling agent, 0.8 parts of benzoin, 0.4 parts of 2-methylimidazole, 1.0 part of ethylene bis-stearamide wax, 0.4 parts of antioxidant 1010, and 0.4 parts of hindered amine light stabilizer HALS 292; S4: Weigh 5 portions of porous silica microspheres, and the remaining steps are the same.

[0035] Example 4

[0036] The difference from the preparation method in Example 1 is as follows: S1: Balancing time is 8 hours, mixer speed is 850 rpm, and mixing time is 3 minutes; S2: The feed screw speed is 20 rpm, the extruder screw speed is 280 rpm, and the internal water temperature of the cooling roller is 0℃; S3: The feeder speed is 25kg / h, the crushing disc speed is 8000rpm, and the classifying wheel speed is 6000rpm; S4: The vacuum drying temperature is 70℃, the mixer speed is 10rpm, the mixing time is 12min, and the machine is stopped every 3min. All other steps are the same.

[0037] Example 5

[0038] The difference from the preparation method in Example 1 is as follows: S1: Balancing time is 15 hours, mixer speed is 1000 rpm, and mixing time is 6 minutes; S2: The feed screw speed is 35 rpm, the extruder screw speed is 350 rpm, and the internal water temperature of the cooling roller is 15℃; S3: The feeder speed is 40kg / h, the crushing disc speed is 9500rpm, and the classifying wheel speed is 7500rpm; S4: The vacuum drying temperature is 90℃, the mixer speed is 25rpm, the mixing time is 20min, and the machine is stopped every 8min. All other steps are the same.

[0039] Example 6

[0040] The difference from the preparation method in Example 1 is as follows: S1: Replace 2-methylimidazole with 2-ethyl-4-methylimidazole, replace antioxidant 1010 with antioxidant 245, and the rest of the steps are the same.

[0041] Example 7

[0042] The difference from the preparation method in Example 1 is as follows: S1: Replace antioxidant 1010 with antioxidant 3114, and the rest of the steps are the same.

[0043] Example 8

[0044] The difference from the preparation method in Example 1 is as follows: S4: Replace the porous silica microspheres with an equal mass of porous ceramic microspheres, and the remaining steps are the same.

[0045] Comparative Example 1 The difference from the preparation method in Example 1 is as follows: S1: Remove microcrystalline cellulose, and the missing mass is made up by precipitating barium sulfate. The remaining steps are the same.

[0046] Comparative Example 2 The difference from the preparation method in Example 1 is as follows: S4: Remove the porous silica microspheres. The missing mass is replenished by precipitated barium sulfate. The remaining steps are the same.

[0047] Comparative Example 3 The difference from the preparation method in Example 1 is as follows: S1: Replace the microcrystalline cellulose and porous silica microspheres with an equal mass of coarse-grained quartz powder, and the remaining steps are the same.

[0048] Comparative Example 4 The difference from the preparation method in Example 1 is as follows: S2: The premix obtained in S1 is not melt-extruded or tableted and is directly used as base powder for crushing and grading. All other steps are the same.

[0049] Comparative Example 5 The difference from the preparation method in Example 1 is as follows: S2: The melt-extruded strip is not cooled by a two-roller tablet press, but is instead allowed to cool and solidify naturally at room temperature. All other steps are the same.

[0050] Comparative Example 6 The difference from the preparation method in Example 1 is as follows: S4: Use only a 120-mesh sieve to sieve the powder, and finally select the sieve-underfill material as the final sample. All other steps are the same.

[0051] Comparative Example 7 The difference from the preparation method in Example 1 is as follows: S1: Replace 0.4 parts of the modified microcrystalline cellulose with PTFE wax, and the remaining steps are the same.

[0052] Experimental Example 1 According to T / CSTM 00222-2020 "Determination of Fluorine Content in Powder Coatings", 1 g of each of the powder coating samples prepared in Examples 1-8 and Comparative Examples 1-7 were weighed, 20 mL of N,N-dimethylformamide was added, and the mixture was heated in a 60℃ water bath for 30 min. After cooling, the mixture was centrifuged at 4000 rpm for 10 min. 1 mL of the supernatant was taken and dropped onto 1 cm × 1 cm ashless filter paper. After evaporating the solvent, the mixture was placed in an oxygen bomb. 20 mL of 0.01 mol / L NaOH absorption solution was added to the oxygen bomb, and then 3.0 MPa of oxygen was introduced. The mixture was then ignited and allowed to stand for 30 min before the gas was released and the bomb was opened. The absorption solution was transferred to a 100 mL volumetric flask and diluted to volume with primary water. Then, 20 mL of the absorption solution was transferred to a plastic beaker, and 20 mL of total ionic strength adjustment buffer was added. The potential value was measured under magnetic stirring, and the total fluorine content in the sample was calculated according to the fluoride ion concentration standard curve.

[0053] Weigh 2g of each of the powder coating samples prepared in Examples 1-8 and Comparative Examples 1-7 into 50mL polypropylene centrifuge tubes, add 10mL of methanol, extract by sonication for 30min, centrifuge at 5000rpm for 10min, then take 1mL of supernatant and filter it through a 0.22μm polypropylene filter membrane. Inject the filtrate into a liquid chromatography-tandem mass spectrometer. The chromatographic column is a C18 column, the mobile phase is 2mmol / L ammonium acetate aqueous solution and methanol, gradient elution is performed, the flow rate is 0.3mL / min, the injection volume is 10μL, and the mass spectrometry is performed in electrospray negative ion mode with multiple reaction monitoring mode to detect the content of various PFAS substances in the sample.

[0054] Table 2 Performance of Examples and Comparative Samples

[0055] As shown in Table 2, the total fluorine content in the samples of Examples 1-8 and Comparative Examples 1-6 is extremely low, and the total fluorine content of the Example samples is also lower than that of the Comparative Examples. The increased filler content in Comparative Examples 1-3 leads to the introduction of trace fluorine impurities. In Comparative Example 4, the insufficient contact between resin and filler in the unextruded material also introduces trace impurities to some extent. Comparative Examples 5 and 6 are due to the slow natural cooling process or the inclusion of some ultrafine powder in the base powder, resulting in an excessively large specific surface area and adsorption of fluorine from the environment. However, overall, the PFAS content of Examples 1-8 and Comparative Examples 1-6 is still below the detection limit, indicating that the overall process can still follow the PFAS-free standard. In contrast, Comparative Example 7, due to the replacement of some raw materials with PTFE resin, i.e., the raw material of conventional sand-textured powder coatings, has a significantly increased total fluorine content. At the same time, the PFAS content detection results exceed the upper limit of market requirements for PFAS, further illustrating the necessity of the process of this invention.

[0056] Experimental Example 2 The powder coating samples prepared in Examples 1-8 and Comparative Examples 1-7 were electrostatically sprayed onto the treated tinplate using a spray gun. The spraying voltage was 70 kV, the spraying air pressure was 0.5 MPa, and the coating thickness was controlled at 70 μm. After spraying, the samples were placed in a hot air circulating oven and cured at 180°C for 15 min. After removal, they were allowed to cool naturally to room temperature. Subsequently, the samples were placed in an environment of 25°C and 55% relative humidity. A contact roughness tester with a stylus tip radius of 5 μm and a measuring force of 0.75 mN was used, with a sampling length of 2.5 mm and an evaluation length of 5 mm. For each sampling length, the stylus is placed on the sample surface and driven to move at a constant speed along the evaluation length. The sampling interval is no more than 2.5 μm. After filtering with a Gaussian filter, five different positions are selected on each sample for measurement. The arithmetic mean deviation value Ra and the maximum profile height Rz of each position are recorded. The average value of the five positions is taken as the average Ra and average Rz of the sample. Then, the standard deviation of the Ra values ​​at the five positions is calculated. According to the formula texture height variation coefficient CV = Ra standard deviation / Ra average value × 100%, the surface roughness after powder coating spraying and curing is evaluated.

[0057] Table 3 Performance of Examples and Comparative Samples

[0058] As can be seen from Table 3, the average Ra and average Rz of the sample in the examples are within a moderate range, indicating that the present invention can form a sand textured surface with appropriate depth, anti-slip properties and tactile comfort through the synergistic effect of the cellulose hard skeleton and microsphere micro-pits. At the same time, the texture height variation coefficient is small, indicating that the sand texture formed by the sample is uniform and delicate.

[0059] Comparative Example 1, without the addition of modified microcrystalline cellulose, relied solely on porous silica microspheres to construct the texture. The average Ra and average Rz were both low, the sand texture was too smooth, resulting in insufficient anti-slip effect, and the texture uniformity was significantly reduced.

[0060] Comparative Example 2 did not add porous silica microspheres, and only relied on modified microcrystalline cellulose to form a raised skeleton. The average Ra and average Rz were similar to those of the Example, but the texture height variation coefficient was large. The lack of micro-dimple control resulted in a single surface undulation and poor texture uniformity.

[0061] Comparative Example 3 used coarse-grained quartz powder to replace the two building agents. The quartz powder had a wide particle size distribution and sharp shape, and the average Ra and average Rz were significantly higher. The sand texture was too coarse and sharp, felt rough and hard, and easily hid dirt. At the same time, the texture distribution was extremely uneven.

[0062] Comparative Example 4 did not undergo melt extrusion; the premix was directly crushed and graded. The crosslinking agent and resin did not achieve molecular-level mixing, resulting in huge local differences in crosslinking density during curing. The average Ra and average Rz were high, and the texture height variation coefficient was the worst, with uneven and disordered sand texture.

[0063] Comparative Example 5: The extruded strip was naturally cooled instead of being rapidly cooled during tableting. The slow crystallization of the resin led to inconsistent local shrinkage, with higher average Ra and average Rz, and a larger coefficient of variation in texture height. The sand texture showed irregular mottled patterns and poor uniformity.

[0064] In Comparative Example 6, after pulverization, only a single-layer sieve was used without a lower sieve to retain fine powder. A large amount of ultrafine powder was mixed into the base powder. The fine powder melted and flowed quickly, destroying the overall texture consistency. The average Ra and average Rz were close to those of the Example, but the texture height variation coefficient increased significantly, and the uniformity of the sand texture decreased.

[0065] Comparative Example 7 replaced some of the modified microcrystalline cellulose with PTFE wax. The average Ra and average Rz were similar to those of the Example, but the coefficient of variation of texture height was slightly higher than that of the Example. Although the fluorinated wax helped to form texture, the reduction of cellulose resulted in a slightly weaker skeleton, which led to slightly poorer uniformity.

[0066] Experiment Example 4 According to GB / T 1732-2020 "Test Method for Impact Resistance of Coating Film", the cured coating samples of Examples 1-8 and Comparative Examples 1-7 were conditioned for 16 hours at 25°C and 55% relative humidity. The coating surface was placed flat on the anvil of the impact tester with the coating surface facing upward. The weight of the tester was 1 kg, the diameter of the steel ball of the punch was 8 mm, the penetration depth was 2 mm, and the guide height was 0-100 cm. The weight was raised to the initial height of 50 cm and allowed to fall freely to impact the punch. The film layer was checked for cracks or peeling. If damage occurred, the height was reduced by 1 cm and the test was repeated. Otherwise, it was increased by 5 cm until the maximum height that did not cause damage was obtained in three consecutive tests. This height was recorded and used as the normal impact strength of the sample.

[0067] According to GB / T 9286-2021 "Cross-cut Test for Paints and Varnishes", the cured coating samples of Examples 1-8 and Comparative Examples 1-7 were conditioned for 24 hours at 25°C and 55% relative humidity. A 2mm multi-blade cutting tool was selected, and the tool was placed vertically on the coating surface to make 6 parallel cuts at a speed of 20mm / s. The cut length was not less than 20mm. After rotating the sample 90°, 6 more cuts were made, forming 36 squares. The squares were then lightly brushed along the diagonal. Brush five times to remove debris. Take a 25mm wide transparent pressure-sensitive tape with an adhesion strength of 600g / 25mm and apply it to the grid area. Roll it back and forth twice with a 500g rubber roller at a speed of 10mm / s. After standing for 1 minute, hold the free end of the tape at a 60° angle to the sample and quickly peel it off within 0.5~1.0s. Repeat this process at three different locations. Observe the peeling area with a 10x magnifying glass and rate it from 0 to 5, with 0 being the best and 5 being the worst.

[0068] Seal the back and edges of the sample with water-resistant epoxy, exposing the front coating. Hang the sample vertically in boiling deionized water, maintaining a water temperature of about 100°C and a water level at least 30 mm above the top edge of the sample for 2 hours. After removal, use lint-free paper to dry the surface of the sample and place it at 25°C for 1 hour. Then, retest the adhesion using the chemical grid method.

[0069] Table 4 Mechanical properties of the examples and comparative samples

[0070] As can be seen from Table 4, the positive impact strength, adhesion and water resistance of the sample of the example are better than those of the comparative example, indicating that the present invention can form a gradient structure coating film with both impact resistance and strong adhesion through the synergistic effect of cellulose hard skeleton and microsphere micro-pits and the cross-linking mechanism of double resin shrinkage followed by filling.

[0071] Comparative Example 1, without the addition of modified microcrystalline cellulose, relies solely on porous silica microspheres to form micropits. Lacking a raised skeleton for support, the coating cannot disperse stress during impact, leading to rapid crack propagation and a significant decrease in normal impact strength. At the same time, the lack of a skeleton weakens the interfacial bonding between the coating and the substrate, resulting in poor adhesion. After boiling, water can more easily penetrate from the interface, further deteriorating the adhesion.

[0072] Comparative Example 2 did not add porous silica microspheres. It relied solely on modified microcrystalline cellulose to provide bulges without the buffer of micro-pits. The impact energy was concentrated and transferred to the inside of the coating, resulting in brittle fracture. The normal impact strength was lower than that of the Example, and there was no micro-pit anchoring effect on the surface, resulting in poor adhesion. Furthermore, the stress release inside the coating after boiling further weakened the interfacial bonding.

[0073] Comparative Example 3 uses coarse-grained quartz powder to replace the two building agents. The sharp edges of the quartz powder become stress concentration points under impact, inducing cracks and significantly reducing the normal impact strength. At the same time, the quartz powder has poor compatibility with the resin, and the interface defects lead to poor adhesion. After boiling in water, water penetrates along the defects, causing the coating to blister and fall off, and the water resistance is severely reduced.

[0074] Comparative Example 4 did not undergo melt extrusion, and the crosslinking agent and resin did not achieve molecular-level mixing. After curing, the crosslinking density was extremely uneven in some areas, the overall strength of the coating was low, and there were many fragile areas. The normal impact strength was the lowest among the comparative examples, and the adhesion was very poor due to incomplete crosslinking. After boiling in water, the uncrosslinked areas preferentially absorbed water and swelled, resulting in large-area peeling of the coating.

[0075] Comparative Example 5: The extruded strip cooled naturally, and the resin crystallized slowly, resulting in microcracks and stress concentration points inside the coating. During impact, the cracks expanded rapidly along the grain boundaries, resulting in extremely poor normal impact strength. At the same time, the uneven crystallization made the coating weakly bonded to the substrate, resulting in extremely poor adhesion. After boiling in water, the microcracks became moisture channels, causing the adhesion to be almost completely lost.

[0076] Comparative Example 6: After pulverization, only a single-layer sieve was used. A large amount of ultrafine powder was mixed into the base powder. The fine powder melted and flowed too quickly, resulting in local areas that were too thin on the coating surface. These areas broke first upon impact, reducing the normal impact strength. In addition, the fine powder adsorbed environmental impurities and contaminated the interface, resulting in poor adhesion. After boiling in water, the contaminant interface accelerated the penetration of water molecules, causing the coating to peel off.

[0077] Comparative Example 7 replaced some of the modified microcrystalline cellulose with PTFE wax. Although the fluorinated wax can reduce surface friction, it weakens the supporting effect of the cellulose skeleton. The insufficient skeleton strength during impact resulted in a lower normal impact strength than all examples. At the same time, the fluorinated component has poor compatibility with polyester resin, weakening the interfacial bonding force and resulting in poor adhesion. After boiling in water, the interface with poor compatibility is more easily attacked by water molecules, and the water resistance is significantly worse than that of the examples.

[0078] Experiment Example 4 According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", the back and edges of the cured coating samples of Examples 1-8 and Comparative Examples 1-7 were sealed. Lines were scribed on the coating surface down to the metal substrate, with a scribing width of 0.5-1.0 mm. A 50 g / L NaCl solution was used as the test solution. The samples were exposed in a salt spray chamber at 35°C for 500 h. After the exposure, the salt deposits were washed with flowing deionized water and dried at room temperature for 2 h. The single-sided corrosion expansion width at the scribing point was measured, and the blistering, rusting, cracking, and peeling in the unscribing area were recorded.

[0079] According to GB / T 23987.3-2025 "Laboratory Light Source Exposure Methods for Paints and Varnishes - Part 3: Fluorescent Ultraviolet Lamps", the cured coating samples of Examples 1-8 and Comparative Examples 1-7 were exposed to fluorescent ultraviolet lamps using UVA-340 lamps. The initial 8-hour ultraviolet irradiation was performed at a blackboard temperature of 60°C and an irradiance of 0.89 W / m². 2 The samples were then subjected to 4 hours of condensation at a blackboard temperature of 50°C. This constituted one cycle, with a total exposure time of 500 hours. The 60° gloss of the samples was tested before and after exposure, and the gloss retention rate was calculated.

[0080] According to GB / T 23989-2009 "Determination of Solvent Resistance of Coatings", MEK solvent resistance was tested on the cured coating samples of Examples 1-8 and Comparative Examples 1-7. Degreased cotton was soaked in methyl ethyl ketone (MEK) to fully wet the sample without dripping. The sample was wiped back and forth along the same path on the sample surface under a load of about 1000g. One back and forth motion was counted as one double wipe. MEK was added every 25 back and forth motions. The number of double wipes was recorded when the sample showed signs of exposure, softening, or loss of gloss.

[0081] Table 5. Durability of the Examples and Comparative Samples

[0082] As can be seen from Table 5, the durability of the sample from the examples is better than that of the comparative examples, indicating that the present invention can form a dense gradient cross-linked structure by combining fluorine-free cellulose with microspheres and controlling the reaction rate of the two resins, which can effectively block the penetration of corrosive media and maintain long-term weather resistance.

[0083] Comparative Example 1, without the addition of modified microcrystalline cellulose, relied solely on porous silica microspheres to form micropits, resulting in insufficient coating density. The corrosion spread width at the salt spray underline was significantly increased, and a small amount of blistering appeared in the un-underlined area. After UV aging, the gloss retention rate decreased significantly, and the solvent resistance was poor when wiping with MEK.

[0084] Comparative Example 2 did not add porous silica microspheres, and relied solely on modified microcrystalline cellulose to provide a raised skeleton. The coating lacked the physical barrier of the micro-pit layer, making it easier for corrosive media to penetrate. The salt spray corrosion spread width and blistering degree were inferior to those of the Example, and the UV resistance and solvent resistance were also significantly reduced.

[0085] Comparative Example 3 used coarse-grained quartz powder to replace the two building agents. The poor compatibility between quartz powder and resin resulted in a large number of interface defects inside the coating. Under salt spray, corrosion spread rapidly along the interface, the corrosion width at the scribing area increased significantly, and blistering was severe in the unscribing area. After UV aging, the gloss retention rate was very low, and the coating easily softened and lost its gloss when wiped with MEK.

[0086] Comparative Example 4 did not undergo melt extrusion, the crosslinking agent and resin did not achieve molecular-level mixing, the coating crosslinking density was extremely uneven and there were many weak areas, the corrosion expansion width at the salt spray underline was the largest among the comparative examples, and a large number of bubbles appeared in the un-underlined area, the gloss retention rate was the lowest after UV aging, and the solvent resistance was extremely poor when wiping with MEK.

[0087] Comparative Example 5: The extruded strip was naturally cooled instead of being rapidly cooled during tableting. The resin crystallized slowly, causing microcracks to form inside the coating. Under salt spray, the corrosive medium rapidly penetrated along the microcracks. The corrosion spread at the scribe line was very wide, and blistering occurred in the unscribe line area. The UV aging and MEK wiping performance were significantly worse than those of the Example.

[0088] Comparative Example 6: After pulverization, only a single-layer sieve was used. A large amount of ultrafine powder was mixed into the base powder. The fine powder melted and flowed too quickly, resulting in localized thin coatings with microscopic defects. The salt spray corrosion spread width increased significantly and a small amount of blistering occurred. The UV resistance and solvent resistance both decreased.

[0089] Comparative Example 7 replaced some of the modified microcrystalline cellulose with PTFE wax. Although the fluorinated wax helped to form texture, the weakening of the cellulose skeleton led to a decrease in the density of the coating. The salt spray corrosion spread width was slightly higher than that of the example and slight edge blistering occurred. The UV resistance and solvent resistance were lower than those of the example but better than other comparative examples.

[0090] Experimental Example 5 Take 20 mg each of the base powder and the final coating powder from Example 1, dry them, and sprinkle them onto an aluminum SEM sample stage with conductive adhesive. Use a syringe to blow away loose large agglomerates, and then spray a 4-6 nm thick Pt conductive layer for SEM detection. Take another 20 mg of the final coating powder from Example 1, dry it, sprinkle it onto the conductive adhesive, do not spray a conductive layer, and use low vacuum mode for EDS detection.

[0091] Figure 1a and b are SEM scans of the base powder and the final coating powder in Example 1, respectively. It can be seen that the edges of the base powder particles are brittle and fractured, the surface is relatively continuous, there are no near-spherical porous microspheres attached, and the texture of resin composite particles formed by pigments, fillers and microcrystalline cellulose is visible in some areas. On the other hand, the surface of the final coating powder is distributed with a large number of small near-spherical particles, and these microspheres are adsorbed on the larger irregular base powder surface in a discontinuous dot-like and island-like manner. These microspheres, which maintain an independent spherical shape and are partially embedded on the powder surface but are not continuously embedded by the resin, indicate the success of the post-mixing surface loading.

[0092] Figure 2 The EDS surface distribution diagram of the final coating powder in Example 1 shows that the Si signal in the EDS mainly corresponds to the near-spherical deposits on the powder surface, which originate from porous silica microspheres enriched on the particle surface; the O signal comes from silica, barium sulfate, titanium dioxide and organic oxygen-containing resin, so the range is relatively wide; the Ba signal corresponds to precipitated barium sulfate, and the Ti signal corresponds to rutile titanium dioxide, which shows a relatively uniform dotted distribution in the particle bulk phase; the C signal represents the organic resin matrix and bio-based components.

[0093] Experimental Example 6 After curing, the coating samples from the examples and comparative samples were cut into 10mm × 10mm pieces. These pieces were immersed in liquid nitrogen for 15 minutes and then quickly broken perpendicular to the coating direction using pre-cooled tweezers. The broken side was mounted face up on a cross-section sample holder and fixed with conductive adhesive. A small amount of conductive paste was applied to the edge of the sample, followed by a 5-8nm thick Pt conductive layer to characterize the cross-sectional morphology of the coating. Next, a 10mm × 10mm sample was cut from the center of the cured coating sample. Dust was removed using low-pressure nitrogen. The sample was fixed on an aluminum stage and then sprayed with a 4-6nm thick Pt conductive layer to characterize the surface morphology of the coating. A 20mm × 20mm sample was cut from each cured coating sample. Dust was removed using a dust-free airflow, and a three-dimensional height map of the sample was obtained using a laser confocal microscope. Each field of view had an area of ​​1000μm × 1000μm, with the average plane as the zero height point.

[0094] Figure 3 a is a cross-sectional SEM image of the coating sample in Example 1. It can be seen that the cured coating has a continuous gradient structure along the thickness direction. There are micro-pits and shallow pits on the surface layer near the air interface. The center is a transition zone. There is a relatively dense skeleton support area in the bottom or middle-lower layer. The overall cross-section has no through holes, continuous cracks, large bubbles and substrate interface peeling. Figure 3b is a SEM image of the coating sample surface in Example 1. The sample surface exhibits a sandy texture composed of rounded micro-pits and moderate ridges. The opening size of the micro-pits is roughly matched with the particle size of the porous microspheres, and the pit walls and pit edges should be rounded without sharp cracks or fragmented inorganic particle protrusions. This indicates that the sample in Example 1 does not rely on the sharp mechanical roughness of coarse fillers, but rather on the controlled micron-scale pits formed by the synergy between the microcrystalline cellulose skeleton and porous microspheres. Figure 3 c~e are SEM images of the coating surfaces of comparative examples 1~3, respectively. It can be seen that the surface of the coating of comparative example 1 is relatively flat due to the absence of microcrystalline cellulose, with a limited number of micro-pits and a lack of continuous raised skeleton, indicating that it is difficult to form a supported sand texture layer by relying solely on porous microspheres. The surface of the sample of comparative example 2, without the addition of porous microspheres, shows certain undulations, but the number of micro-pits is insufficient and the pit diameter distribution is discontinuous, indicating that the cellulose skeleton alone cannot form a uniform surface micro-pit. The surface of the sample of comparative example 3 shows sharp protrusions, large peak-to-valley differences, and local accumulation of coarse particles, indicating that although coarse and hard inorganic fillers can improve the apparent roughness, their texture is rough, sharp, and uneven, and cannot replace the rounded and controllable gradient sand texture structure of the present invention.

[0095] Figure 4 a is a three-dimensional morphology height diagram of the coating film of Example 1. It can be seen that the sample of Example 1 exhibits a three-dimensional morphology with uniform and moderate height undulations, uniformly distributed micro-pits, smooth transition between peaks and valleys, and a relatively balanced yellow-green / light blue area in the range of -15~+15μm of the color mark, indicating that the height distribution is concentrated and there are no extreme peaks. Figure 4 b~d are the three-dimensional morphology height diagrams of comparative examples 1~3, respectively. It can be seen that the three-dimensional image of comparative example 1 is generally flat with shallow texture, indicating that the anti-slip feel is insufficient when there is no skeleton. Comparative example 2 has undulations but lacks uniform micro-pits, and the local pits and height differences are unstable. Comparative example 3 has red peaks and blue valleys coexisting, indicating that the height variation is extremely high, indicating that the texture height of the comparative example sample is not uniform.

Claims

1. A PFAS-free environmentally friendly sand-textured powder coating composition, characterized in that: Based on 100 parts by weight of carboxyl-terminated polyester resin, hydroxyl-terminated polyester resin, and bio-based epoxy resin, the coating composition comprises the following components in parts by weight: 55-75 parts of carboxyl-terminated polyester resin, 15-35 parts of hydroxyl-terminated polyester resin, and 10-20 parts of bio-based epoxy resin; the coating composition also comprises the following components in parts by weight: 3-12 parts of hydrophobically modified microcrystalline cellulose, 0.8-5 parts of porous microspheres, 3-16 parts of pigments and fillers, 0.3-1.0 parts of fluorine-free leveling agent, 0.2-0.8 parts of benzoin, 0.1-0.4 parts of epoxy reaction catalyst, 0.5-1.0 parts of ethylene bis-stearamide wax, 0.05-0.4 parts of antioxidant, and 0.05-0.4 parts of hindered amine light stabilizer; the pigments and fillers include pigment carbon black and filler precipitated barium sulfate and rutile titanium dioxide.

2. The PFAS-free environmentally friendly sand-textured powder coating composition according to claim 1, characterized in that: The powder coating composition is a composite powder structure, including a base powder and porous microspheres loaded on the surface of the base powder; the base powder is a composite formed by melt blending the polyester resin, bio-based epoxy resin, modified microcrystalline cellulose, pigments, fillers and additives; in the base powder, the modified microcrystalline cellulose is uniformly dispersed in the form of independent hard particles; the porous microspheres are loaded on the surface of the base powder by physical adhesion.

3. A method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition according to any one of claims 1 to 2, characterized in that, It is prepared by the following method: S1: Mix carboxyl-terminated polyester resin, hydroxyl-terminated polyester resin, bio-based epoxy resin, hydrophobically modified microcrystalline cellulose, pigments and fillers, fluorine-free leveling agent, benzoin, epoxy reaction catalyst, ethylene bis-stearamide wax, antioxidant and light stabilizer and let them stand to equilibrate. Then add them together to a mixer and mix to obtain a premix. S2: The premixed material is added to a twin-screw extruder for melt extrusion. The extruded material is cooled by tableting and then crushed by a crusher. S3: The crushed material is fed into the crushing equipment for crushing and then classified by the grading equipment to collect the base powder that meets the requirements. S4: The porous microspheres are pre-dried, and then the dried porous microspheres are added to the base powder. The mixture is then dry-mixed in a low-shear mixer and sieved to obtain a PFAS-free environmentally friendly sand texture powder coating composition.

4. The method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition according to claim 3, characterized in that: The epoxy reaction catalyst mentioned in S1 is one or more of 2-methylimidazole and 2-ethyl-4-methylimidazole.

5. The method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition according to claim 3, characterized in that: The antioxidant mentioned in S1 is one or more of antioxidant 1010, antioxidant 245, and antioxidant 3114.

6. The method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition according to claim 3, characterized in that: The equilibration time in S1 is 8-15 hours; the mixing speed is 850-1000 rpm, and the mixing time is 3-6 minutes.

7. The method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition according to claim 3, characterized in that: The feed screw speed of the twin-screw extruder mentioned in S2 is 20~35 rpm; the extruder screw speed is 280~350 rpm; and the cooling water temperature during tableting is 0~15℃.

8. The method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition according to claim 3, characterized in that: The feeder speed when the material is fed into the crushing equipment is 25~40 kg / h; the crushing disc speed is 8000~9500 rpm during crushing; and the grading wheel speed is 6000~7500 rpm during grading.

9. The method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition according to claim 3, characterized in that: The porous microspheres mentioned in S4 are one or more of porous silica microspheres and porous ceramic microspheres.

10. The method for preparing a PFAS-free environmentally friendly sand-textured powder coating composition according to claim 3, characterized in that: The drying temperature of S4 is 70~90℃; the mixing rate is 10~25rpm; the mixing time is 12~20min; and the machine is stopped every 3~8min to release static electricity during mixing.

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