A method for preparing a uv light-cured wear-resistant powder coating for wood flooring

Abstract

This invention discloses a method for preparing a UV-curable wear-resistant powder coating for wood flooring, relating to the field of powder coating technology. The method includes: weighing 45-60 parts of unsaturated polyester resin, 8-12 parts of crystalline unsaturated polyester, 15-22 parts of modified glass powder with surface-grafted unsaturated double bonds, 2-4 parts of stearic acid-modified nano-α-alumina, 0.6-1.2 parts of nano-antimony-doped tin oxide, 3-5 parts of photoinitiator, 1-2 parts of leveling agent, 0.3-0.8 parts of degassing agent, and 0.05-0.1 parts of powder flow drying agent; premixing, melt extruding, and then grinding and sieving to obtain the powder coating. Preparation of the crystalline unsaturated polyester: Adipic acid, maleic anhydride, and 1,6-hexanediol are added in a molar ratio of 1:0.60~0.80:1.15~1.25. Following esterification and polycondensation, glycidyl methacrylate is added to graft methacryloyloxy groups onto the end groups. Then, stepwise temperature-controlled crystallization yields a product with a melting point of 52~58℃, a number-average molecular weight of 2500~4000, and a crystallinity of 15%~35%. This invention achieves rapid leveling at ultra-low temperatures, producing a wear-resistant and transparent coating suitable for heat-sensitive wood flooring.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology and discloses a method for preparing a UV-curable wear-resistant powder coating for wood flooring. Background Technology

[0002] UV-curable powder coatings have garnered widespread attention in the wood coating industry due to their environmentally friendly characteristics, including 100% solids content, zero VOC emissions, rapid curing, and powder recyclability. Especially for heat-sensitive substrates like wood flooring, UV-curable powder coatings can effectively avoid substrate deformation problems caused by traditional high-temperature curing (180~210℃) while ensuring coating performance, thus becoming an important development direction for environmentally friendly wood flooring coatings.

[0003] Currently, existing UV-cured powder coatings for wood flooring typically use conventional unsaturated polyester resins and physically blended wear-resistant fillers. These coatings have high infrared leveling temperatures and long leveling times, which makes wood flooring prone to deformation. Furthermore, it is difficult to balance wear resistance and leveling properties, resulting in insufficient wear resistance and durability of the coating. Summary of the Invention

[0004] In view of this, this application provides a method for preparing a UV-curable abrasion-resistant powder coating for wood flooring, so as to achieve rapid leveling under ultra-low temperature conditions of 70~85℃, while improving the abrasion resistance and adhesion of the coating and avoiding thermal deformation of wood flooring.

[0005] To achieve the above objectives, the following technical solution is adopted: This application discloses a method for preparing a UV-curable abrasion-resistant powder coating for wood flooring, comprising the following steps: S1: Weigh out 45-60 parts of unsaturated polyester resin, 8-12 parts of crystalline unsaturated polyester, 15-22 parts of modified glass powder with surface grafted unsaturated double bonds, 2-4 parts of stearic acid surface-modified nano-α-alumina, 0.6-1.2 parts of nano-antimony-doped tin oxide, 3-5 parts of photoinitiator, 1-2 parts of leveling agent, 0.3-0.8 parts of degassing agent, and 0.05-0.1 parts of powder flow desiccant; S2: Add the weighed components to the mixing tank, stir slowly at 20Hz for 3 minutes, and then stir rapidly at 40Hz for 60 seconds to obtain the premix. S3: Add the premixed material into the extruder, and melt-extrude it at a screw speed of 30~45Hz at temperatures of 90~95℃ in Zone I, 95~105℃ in Zone II, and 90~95℃ in Zone III to obtain sheet material; S4: After cooling and crushing the sheet material, it is fed into a grinding mill for grinding. The powder is passed through a 200~220 mesh sieve, and the powder particle size D50 is controlled to be 30~35μm. A powder flow desiccant is added during the grinding process to obtain a UV-curable wear-resistant powder coating. The preparation process for crystalline unsaturated polyester is as follows: A1: In a reaction vessel, adipic acid, maleic anhydride, and 1,6-hexanediol are added in a molar ratio of 1:0.60~0.80:1.15~1.25. Then, 0.05%~0.1% of p-toluenesulfonic acid and 0.01%~0.03% of hydroquinone are added according to the total mass of the three. After purging the reaction vessel with nitrogen to replace the air, the temperature is raised to 120~140℃ and maintained for 30 minutes. The temperature is then raised to 160~180℃ and maintained for 2.5~3.5 hours. The water generated during the esterification reaction is collected, and a sample is taken to test the acid value to 30~40 mg KOH / g to obtain the esterification product. A2: The esterification product obtained from A1 is heated to 190~210℃, while the pressure is gradually reduced to -0.09~-0.095MPa. The reaction is carried out for 1.5~2.5 hours until the acid value is ≤10mgKOH / g, to obtain the condensation product; the condensation product is cooled to 160~180℃, and 1%~3% of glycidyl methacrylate is added. The mixture is kept warm and stirred for 1~1.5 hours to graft methacryloyloxy groups onto the polyester chain ends; A3: The product obtained in A2 is cooled to 90-110℃ at a rate of 1-2℃ / min, and stirred for 30-60 minutes to generate uniform crystal nuclei; then cooled rapidly to room temperature at a rate of 3-5℃ / min, and pulverized through a 20-mesh sieve to obtain a crystalline unsaturated polyester with a melting point of 52-58℃, a number average molecular weight of 2500-4000, and a crystallinity of 15%-35%.

[0006] Preferably, the modified glass powder with surface-grafted unsaturated double bonds has a grafting rate of 1.5~3.0wt%, a water contact angle of 90°~115°, and a median particle size D50=15±2μm.

[0007] Preferably, the primary particle size retention rate of the stearic acid-modified nano-α-alumina is ≥90%, the activation degree is 95%~99%, the modified aggregate D90 is ≤150nm, and the free stearic acid residue is ≤0.5wt%.

[0008] Preferably, the mass ratio of SnO2 to Sb2O3 in the antimony-doped tin oxide nanoparticles is 90:10 to 95:5, the primary particle size is 20±10 nm, and the primary particle size retention rate is ≥90%.

[0009] Preferably, a verification step is included between steps S3 and S4: V1: Take the middle part of the extruded sheet material, grind it with a small mill and pass it through a 200~250 mesh sieve, and control the particle size D50=30~35μm; V2: The sieved powder is electrostatically sprayed onto the pre-treated wooden board with a thickness of 50~70μm. It is then heated to 80~100℃ by infrared light for 2~3 minutes to level, and then cured by UV light for 5~10 seconds. After natural cooling, the transparency, leveling, impact strength, adhesion or abrasion resistance of the coating are tested. V3: If all test results are qualified, proceed to step S4; if any one of them is unqualified, repeat steps S2 and S3 until the test is qualified.

[0010] Preferably, the photoinitiator is a mixture of 2-hydroxy-2-methyl-1-phenylpropanone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in a mass ratio of 1:1.

[0011] Preferably, the glass transition temperature (Tg) of the unsaturated polyester resin is ≥48℃.

[0012] Preferably, the leveling agent is P-64F acrylic leveling agent, and the degassing agent is smokeless crystalline benzoin.

[0013] Preferably, in step S3, the temperature of zone I of the extruder is 92°C, the temperature of zone II is 100°C, and the temperature of zone III is 92°C.

[0014] Preferably, the modified glass powder with surface-grafted unsaturated double bonds is prepared by surface grafting modification of 800-1250 mesh glass powder.

[0015] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention include at least the following: This invention prepares a crystalline unsaturated polyester with a specific melting point of 52-58℃ and a crystallinity of 15%-35%, and grafts methacryloxy groups onto its end groups, causing it to melt near its melting point during infrared heating and significantly reducing the viscosity of the system. Simultaneously, the selective absorption of near-infrared wavelengths by nano-antimony-doped tin oxide allows the coating surface to level rapidly within 60-90 seconds at 70-85℃, effectively preventing deformation of wood flooring due to prolonged high-temperature heating. Furthermore, the modified glass powder grafted with unsaturated double bonds and stearic acid-modified nano-α-alumina form a multi-scale chemically bonded wear-resistant system, significantly improving the wear resistance and adhesion of the coating while ensuring leveling properties. In addition, the synergistic design of the powder coating components gives the coating excellent transparency, hardness, and storage stability, achieving a balance between low-temperature efficiency and high wear resistance in wood flooring coating. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 A flowchart of the method provided by the present invention; Figure 2 This is a flowchart of the preparation process of crystalline unsaturated polyester provided by the present invention; Figure 3 This is a flowchart of the detection process provided by the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] In this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0020] Example 1 During their research on UV-curable powder coatings for wood flooring, the inventors discovered that conventional unsaturated polyester resins in existing technologies typically employ an amorphous structure. While their glass transition temperature (Tg) ensures room-temperature powder storage, the melt flow rate exhibits a gradually changing linear relationship with temperature. Under infrared heating conditions, the viscosity of amorphous resins decreases slowly with increasing temperature, requiring the coating surface to be heated to above 100°C to achieve a sufficiently low melt viscosity for complete leveling. However, wood flooring, being a heat-sensitive substrate, will experience fiber shrinkage and warping deformation when exposed to temperatures above 80°C for extended periods. Therefore, conventional resin systems cannot achieve leveling while ensuring the dimensional stability of the wood flooring.

[0021] Meanwhile, existing technologies commonly employ physical blending to add abrasion-resistant fillers (such as ordinary glass powder and alumina) to coatings. These fillers are only bonded to the resin matrix by van der Waals forces or mechanical interlocking, resulting in weak interfacial adhesion. To achieve sufficient abrasion resistance, a high filler content is often required, but this significantly increases the system's melt viscosity, further deteriorating leveling properties and creating a vicious cycle of "increased abrasion resistance → decreased leveling properties → higher temperature required for leveling → increased risk of wood flooring deformation." Furthermore, traditional infrared heating processes use broadband light sources and lack specific design considerations for the infrared absorption characteristics of the coating. Most of the infrared energy is absorbed by the wood flooring substrate rather than the coating itself, leading to rapid temperature rise in the substrate and slow temperature rise in the coating. This not only results in low energy utilization but also exacerbates the risk of thermal deformation in wood flooring.

[0022] Therefore, this application provides a method for preparing a UV-curable abrasion-resistant powder coating for wood flooring, such as... Figure 1 , Figure 2 and Figure 3 As shown, the method includes: S1: Weigh the raw materials Weigh out 45-60 parts of unsaturated polyester resin, 8-12 parts of crystalline unsaturated polyester, 15-22 parts of modified glass powder with surface grafted unsaturated double bonds, 2-4 parts of stearic acid surface-modified nano-α-alumina, 0.6-1.2 parts of nano-antimony-doped tin oxide, 3-5 parts of photoinitiator, 1-2 parts of leveling agent, 0.3-0.8 parts of degassing agent, and 0.05-0.1 parts of powder flow desiccant.

[0023] S2: Premix Add the weighed components to the mixing tank and stir slowly at 20 Hz for 3 minutes, then stir rapidly at 40 Hz for 60 seconds to obtain the premix.

[0024] S3: Melt extrusion The premixed material is added to a twin-screw extruder, and three heating zones, I, II, and III, are set sequentially along the material conveying direction. The temperature of zone I is 90~95℃, the temperature of zone II is 95~105℃, and the temperature of zone III is 90~95℃. The material is melted and extruded at a screw speed of 30~45Hz to obtain flakes.

[0025] Furthermore, the temperature in Zone I is 92℃, the temperature in Zone II is 100℃, and the temperature in Zone III is 92℃. This temperature distribution allows the premix to gradually soften, fully melt and mix, and protect the heat-sensitive components.

[0026] S4: Grinding and Sieving After the sheet material is cooled and crushed, it is fed into a grinding mill for grinding and passed through a 200~220 mesh sieve. The powder particle size D50 is controlled to be 30~35μm. A powder flow desiccant is added during the grinding process to obtain a UV-curable wear-resistant powder coating.

[0027] The preparation process of crystalline unsaturated polyester is as follows: Figure 2 As shown, it includes: A1: Esterification reaction In a reaction vessel, adipic acid, maleic anhydride, and 1,6-hexanediol are added in a molar ratio of 1:0.60~0.80:1.15~1.25. Then, 0.05%~0.1% of p-toluenesulfonic acid and 0.01%~0.03% of hydroquinone are added according to the total mass of the three. After purging the reaction vessel with nitrogen to replace the air, the temperature is raised to 120~140℃ and maintained for 30 minutes. The temperature is then raised to 160~180℃ and maintained for 2.5~3.5 hours. The water generated during the esterification reaction is collected, and a sample is taken to test the acid value to 30~40 mg KOH / g, yielding the esterification product.

[0028] A2: Polycondensation and end-group grafting The esterified product obtained from A1 is heated to 190-210℃ while gradually reducing the pressure to -0.09 to -0.095 MPa, and reacted for 1.5-2.5 hours until the acid value is ≤10 mg KOH / g, yielding the condensation product. The condensation product is then cooled to 160-180℃, and 1%-3% (by mass) of glycidyl methacrylate (GMA) is added. The mixture is kept at this temperature and stirred for 1-1.5 hours to graft methacryloyloxy groups onto the polyester chain ends. This end-group grafting step allows the crystalline unsaturated polyester to copolymerize with the unsaturated polyester resin during subsequent UV curing, preventing the migration and precipitation of crystalline components.

[0029] A3: Stepwise temperature-controlled crystallization The product obtained from A2 is cooled to 90-110℃ at a rate of 1-2℃ / min and stirred for 30-60 minutes to ensure uniform crystal nucleation. Then, it is rapidly cooled to room temperature at a rate of 3-5℃ / min, pulverized, and passed through a 20-mesh sieve to obtain a crystalline unsaturated polyester with a melting point of 52-58℃, a number-average molecular weight of 2500-4000, and a crystallinity of 15%-35%. Stepwise temperature-controlled crystallization, compared to natural cooling, allows for precise control of crystallinity between 15% and 35%. If the crystallinity is too low (<15%), insufficient viscosity reduction during infrared heating and increased leveling temperature will occur; if the crystallinity is too high (>35%), the powder becomes brittle and the spray coating flowability deteriorates.

[0030] Furthermore, to confirm the structural characteristics of the crystalline unsaturated polyester of this application, the products prepared in the examples were analyzed by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC).

[0031] FTIR spectra show a strong C=O stretching vibration peak (ester bond) at 1720 cm⁻¹, a moderate-intensity C=C stretching vibration peak at 1635 cm⁻¹ (from the terminal double bond introduced by GMA and the residual maleic anhydride double bond), antisymmetric and symmetric stretching vibration peaks of -CH₂- at 2950-2850 cm⁻¹, and a characteristic COC absorption peak at 1200-1250 cm⁻¹. Unmodified unsaturated polyesters do not exhibit this absorption at 1635 cm⁻¹, confirming that the methacryloxy group has been successfully grafted to the polyester chain ends.

[0032] DSC analysis: Heating rate was 10℃ / min, nitrogen atmosphere. The product exhibited a sharp endothermic melting peak (Tm) in the 52-58℃ range, with a melting enthalpy ΔHm of 20.25~47.25 J / g. Based on the crystallinity calculation formula (crystallinity = ΔHm / ΔH° × 100%, where ΔH° is the theoretical melting enthalpy of 100% crystalline polyester, taken as 135 J / g), the crystallinity was calculated to be 15~35%. Amorphous unsaturated polyesters only showed a glass transition (Tg) on ​​the DSC curve, without a melting peak.

[0033] like Figure 3 As shown, verification steps V1~V3 are also included between steps S3 and S4: V1: Take the middle part of the extruded sheet material, grind it with a small mill and pass it through a 200~250 mesh sieve, and control the particle size D50=30~35μm; V2: The sieved powder is electrostatically sprayed onto the pre-treated wooden board with a thickness of 50~70μm. It is then heated to 70~85℃ by infrared light for 2~3 minutes to level, and then cured by UV light for 5~10 seconds. After natural cooling, the transparency, leveling, impact strength, adhesion or abrasion resistance of the coating are tested. V3: If all test results are qualified, proceed to step S4; if any one of them is unqualified, repeat steps S2 and S3 until the test is qualified.

[0034] The core technology of this application lies in utilizing the synergistic effect of the "melting point switch" effect of crystalline unsaturated polyester and the "selective infrared absorption" of antimony-doped tin oxide nanoparticles to achieve rapid leveling at ultra-low temperatures. Crystalline unsaturated polyester is crystalline at room temperature, with a non-stick powder surface and stable storage; when heated to its melting point (52~58℃) by infrared radiation, the crystalline region melts, and the viscosity of the system decreases sharply. According to the Flory-Huggins theory, the relationship between the viscosity (η) and temperature (T) of a semi-crystalline polymer near the melting point Tm satisfies: in: Indicates temperature as Melt viscosity at that time; Indicates the pre-exponential factor (constant); Indicates the activation energy of the flow; This represents the ideal gas constant (8.314 J / (mol·K)). Indicates absolute temperature; From the above formula, it can be seen that when the temperature Exceeding the melting point At this temperature, the viscosity decreases exponentially, thus achieving the leveling effect required by traditional powder coatings at temperatures above 100°C at 70-85°C.

[0035] Furthermore, the glass transition temperature (Tg) of the unsaturated polyester resin ≥ 48℃ ensures that the powder does not clump when stored at room temperature.

[0036] Antimony-doped tin oxide (ATO) nanoparticles exhibit strong absorption characteristics in the near-infrared band (1.4~1.8 μm), and the relationship between its absorption rate and Sb doping amount can be expressed as: in: Indicates wavelength as The absorption coefficient at that time; Indicates the mole fraction of antimony (Sb) doping; Indicates the free carrier concentration; This represents carrier mobility (wavelength-dependent).

[0037] By controlling the SnO2:Sb2O3 mass ratio to 90:10~95:5 (the absorption efficiency is insufficient if the Sb doping amount is less than 10%, and it is easy to form impurities and increase costs if it is higher than 5%), the absorption peak is matched with the infrared light source band, and the energy utilization rate is improved by more than 30%.

[0038] Furthermore, the primary particle size of ATO is controlled at 20±10nm with a retention rate of ≥90%, which can both ensure the nanoscale effect and avoid the modification process from damaging its structure.

[0039] Regarding wear resistance, the glass powder (KH570 modified) with surface-grafted unsaturated double bonds forms Si-O-Si covalent bonds through a condensation reaction, and its grafting rate is: in: This indicates the quality of the KH570 organic layer grafted onto the surface of the glass powder via chemical bonds; This indicates the quality of the glass powder before modification.

[0040] This application controls If the concentration is below 1.5%, the C=C double bond density will be insufficient, the chemical anchoring effect will be poor, and the filler will be easy to fall off; if it is above 3.0%, the organic layer will be too thick and will shield the hardness of the glass powder, reducing the wear resistance of the coating.

[0041] Furthermore, the water contact angle of the glass powder grafted with unsaturated double bonds is 90°~115°, ensuring that the modified glass powder has moderate compatibility with the resin (below 90°, the hydrophobicity is insufficient and it is easy to agglomerate; above 115°, it is excessively hydrophobic and may separate into phases). The median particle size D50=15±2μm forms a multi-scale filling with the powder coating base particle size of 30~35μm (too coarse will affect the smoothness, too fine will easily agglomerate).

[0042] Stearic acid-modified nano-α-Al₂O₃ is monolayer coated via esterification reaction, with increased activation. Defined as: in: This indicates the mass of modified nano-α-Al2O3 that floats on the water surface after being left to stand. This represents the total mass of the modified nano-α-Al2O3.

[0043] This application controls The free stearic acid residue is ≤0.5wt%. An activation degree below 95% indicates uneven stearic acid coating and easy agglomeration of nanoparticles; a free stearic acid residue above 0.5wt% inhibits UV-cured free radical polymerization, leading to a decrease in coating crosslinking density. Meanwhile, a primary particle size retention rate ≥90% ensures that the modification process does not damage the original structure of the nanoparticles, and an agglomerate D90 ≤150nm guarantees the dispersibility after modification, avoiding clogging or coating defects during spraying.

[0044] Furthermore, the photoinitiator is a 1:1 mass mixture of 2-hydroxy-2-methyl-1-phenylpropanone (184) and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO). The absorption peaks of 184 are in the near-ultraviolet region (approximately 245 nm, 280 nm, and 330 nm), which is beneficial for surface curing; the absorption peaks of TPO are in the long-wave ultraviolet region (approximately 370–420 nm), which is beneficial for deep curing. The combination of these two ingredients ensures complete curing of the coating from the surface to the bottom.

[0045] Furthermore, P64F acrylic leveling agent was selected, and smokeless crystalline benzoin was chosen as the degassing agent. P64F is an acrylic leveling agent containing carboxyl functional groups, which can rapidly reduce the surface tension of the coating during the infrared leveling stage, promote uniform spreading of the powder after melting, avoid surface defects such as orange peel and pinholes, and has excellent compatibility with unsaturated polyester systems. Smokeless crystalline benzoin decomposes and escapes during heating, effectively removing air bubbles from the coating and preventing pinholes. At the same time, its smokeless properties avoid smoke pollution in the oven and yellowing of the coating. The synergistic use of the two can obtain a smooth, dense, and defect-free coating film.

[0046] Furthermore, the extrusion temperature adopts the preferred values ​​of 92℃ in Zone I, 100℃ in Zone II, and 92℃ in Zone III: the low temperature in Zone I gradually softens the material, the high temperature in Zone II ensures full melting and mixing, and the appropriate cooling in Zone III protects the heat-sensitive photoinitiator and crystalline polyester.

[0047] Furthermore, the glass powder raw material is selected from 800~1250 mesh, corresponding to a median particle size of about 10~18μm, which matches D50=15±2μm. Too coarse (low mesh number) will result in a rough coating surface, while too fine (high mesh number) will increase oil absorption and affect powder flowability.

[0048] Example 2 This embodiment specifies the range of each parameter in Embodiment 1. The specific operating parameters are as follows: Preparation of crystalline unsaturated polyesters (median) 146.1 g (1.0 mol) of adipic acid, 68.6 g (0.7 mol) of maleic anhydride, and 141.8 g (1.2 mol) of 1,6-hexanediol were added to the reactor. 0.32 g of p-toluenesulfonic acid (0.09% of the total monomer mass) and 0.07 g (0.02%) of hydroquinone were also added. After purging with nitrogen, the mixture was heated to 130 °C and held for 30 min, then heated to 170 °C and reacted for 3 h. Approximately 36 mL of esterified water was collected, and the acid value was measured to be 35 mg KOH / g. The product was heated to 200 °C and gradually reduced to -0.095 MPa, reacting for 2 h until the acid value decreased to 8 mg KOH / g. The mixture was then cooled to 170 °C, and 7.2 g of GMA (2% of the condensation product mass) was added. The mixture was stirred and kept at this temperature for 1.2 h. The product was cooled to 100℃ at a rate of 1.5℃ / min and held at that temperature for 45 min. It was then rapidly cooled to room temperature at a rate of 4℃ / min, pulverized, and passed through a 20-mesh sieve to obtain a crystalline unsaturated polyester. DSC measured the melting point to be 55℃, and GPC determined Mn=3200 and crystallinity to be 26%. Preparation of powder coatings (median) Weigh out 525g of unsaturated polyester resin (Tg=50℃), 100g of the above-mentioned crystalline unsaturated polyester, 185g of modified glass powder (grafting rate 2.1%, contact angle 102°, D50=15.2μm), 30g of modified nano α-Al2O3 (primary particle size retention rate 92%, activation degree 97%, D90=135nm, free stearic acid 0.3%), 9g of nano ATO (SnO2:Sb2O3=92:8, primary particle size 18nm, retention rate 91%), 18420g of photoinitiator, 20g of TPO, 15g of P64F, 5g of benzoin, and 0.75g of powder flow desiccant.

[0049] The above materials were processed according to steps S2-S4: premixing (20Hz for 3 min + 40Hz for 60 s), extruder zone I 92℃, zone II 100℃, zone III 92℃, screw speed 40Hz. The material was then ground through a 220-mesh sieve, with a D50 of 32μm.

[0050] Verification and Coating Sampling and testing according to V1-V3: Sprayed onto birch multi-layer solid wood composite flooring, 60μm thickness, infrared light source wavelength 1.5μm, power density 5kW / m², after heating for 75 seconds, the coating surface temperature reached 78℃, and leveling was complete. UV mercury lamp (1000mJ / cm²) curing for 8 seconds. Test results: gloss (60°) 92%, leveling grade (PCI) 8, leveling temperature 78℃, leveling time 75s, impact strength 50cm·kg no cracks, adhesion (cross-cut test) 5B, Taber abrasion (CS-17, 1000 rpm) weight loss 28mg, pencil hardness 2H, no deformation. The product is qualified and will be transferred to mass production for grinding.

[0051] Preparation of crystalline unsaturated polyesters (lower limit value) Adipic acid 146.1g, maleic anhydride 58.8g (0.6mol), 1,6-hexanediol 135.9g (1.15mol), catalyst 0.18g (0.05%), polymerization inhibitor 0.036g (0.01%). Esterification: 125℃ for 30min → 165℃ for 2.5h, acid value 38mgKOH / g. Condensation: 195℃, -0.09MPa, 1.5h, acid value 9.5mgKOH / g. GMA addition: 1%. Cooling crystallization: 1℃ / min to 95℃, hold for 30min, then rapidly cool at 3℃ / min. Product melting point 52℃, Mn=2600, crystallinity 16%.

[0052] Preparation of powder coatings (lower limit of formulation) The composition includes: 450g unsaturated polyester resin, 80g crystalline polyester, 150g modified glass powder, 20g modified nano-Al₂O₃, 6g nano-ATO, 30g photoinitiator (184:TPO=1:1), 10g P64F, 3g benzoin, and 0.5g flowable desiccant. Extrusion temperatures are: Zone I 90℃, Zone II 95℃, Zone III 90℃; screw speed 32Hz. Grinding D50 = 33μm.

[0053] Coating verification Infrared heating: 1.4μm, 4.5kW / m², 90 seconds, coating surface temperature 72℃; UV LED lamp (3000mJ / cm²) curing for 10 seconds. Test results: Adhesion 4B, Taber weight loss 42mg, pencil hardness H, leveling time 95 seconds, leveling temperature 75℃, no deformation of the wood board. It still meets the usage requirements, proving the boundary values ​​are effective.

[0054] Comparative Example 1 non-crystalline unsaturated polyester In this formulation, the crystalline unsaturated polyester is replaced with an equal amount of unsaturated polyester resin (i.e., a total of 615g of unsaturated polyester resin), and the rest is the same as in the aforementioned preferred embodiment. Powder coatings are prepared using the same process.

[0055] Coating test: Infrared heating to 95℃ was required for barely leveling, taking 150 seconds. The temperature on the back of the wood panel reached 58℃, resulting in slight warping (deformation 0.8mm / 300mm). Taber weight loss was 65mg, and adhesion was 3B. The results indicate that the lack of crystalline unsaturated polyester prevents rapid low-temperature leveling, and significantly reduces abrasion resistance and adhesion.

[0056] Comparative Example 2 No nano-ATO and no stepwise temperature-controlled crystallization The nano-ATO was removed from the formulation, while the rest remained the same as in the aforementioned preferred embodiment. In the preparation of the crystalline unsaturated polyester, the GMA grafting of A2 and the stepwise temperature-controlled crystallization of A3 were removed (and replaced with natural cooling), resulting in a product with a melting point of 49°C and a crystallinity of 12%.

[0057] Coating test: Infrared heating (1.5μm, 5kW / m²) requires 100 seconds for the coating surface temperature to reach 80℃, resulting in incomplete leveling and orange peel appearance. Taber weight loss was 58mg, adhesion was 3B, and pencil hardness was HB. The reasons are: lack of ATO leading to low infrared absorption efficiency, and the absence of stepwise temperature-controlled crystallization resulting in insufficient crystallinity and a low melting point of the crystalline polyester, making it impossible to effectively reduce viscosity at 70-85℃.

[0058] The following table compares the performance indicators of Example 2 (median and boundary parameters) with those of Comparative Example 1 and Comparative Example 2: Table 1 It should be noted that all performance parameters in this application were tested using the following methods: Leveling temperature and leveling time: The surface temperature of the coating was monitored in real time using an infrared thermal imager (FLIRE60). The time required for the surface temperature of the coating to reach a stable value and the stable value were recorded. At the same time, the temperature and time when the coating was completely leveled (uniform surface without orange peel) were observed visually.

[0059] Wood board deformation: Place a 300mm long wood floor on a level surface and use a feeler gauge to measure the maximum warping height difference (mm) between the two ends and the middle before and after curing.

[0060] Taber weight loss: Referring to GB / T1768-2006 "Determination of Abrasion Resistance of Paints and Varnishes - Rotating Rubber Grinding Wheel Method", a Taber 5135 abrasion tester with a CS-17 grinding wheel was used. After a load of 1000g and 1000 revolutions, the weight loss (mg) was calculated. Adhesion: Referencing GB / T9286-2021 "Paints and Varnishes Cross-cut Test", the adhesion was determined by cross-cutting with a cross-cutting tool followed by peeling with 3M tape. The rating was 0-5B. Pencil hardness: Refer to GB / T6739-2022 "Determination of paint film hardness by pencil method for paints and varnishes", use a Mitsubishi standard pencil, scratch the paint film at a 45° angle and a 750g load, and record the highest hardness value that is not broken.

[0061] Storage stability: Place the powder coating in a 40℃ constant temperature drying oven for 7 days. After taking it out, observe the clumping situation and sieve it through a 120-mesh sieve, and record the residue.

[0062] The above examples, comparative examples, and Table 1 show that this application, through the specific preparation of crystalline unsaturated polyester (including GMA end-group grafting and stepwise temperature-controlled crystallization) and the synergistic effect of multiple components such as nano-ATO, significantly reduces the leveling temperature and leveling time, avoids wood flooring deformation, and greatly improves the wear resistance, adhesion, and hardness of the coating, demonstrating outstanding substantive features and significant progress.

[0063] Furthermore, to verify the effect of surface-grafted unsaturated double bonds on the wear resistance of glass powder, the modified glass powder in the examples was replaced with an equal amount of ordinary unmodified glass powder (800 mesh, without KH570 surface treatment) of the same particle size, while the other components and processes remained unchanged. Coating test results showed that the coating was basically leveled when heated to 82°C with an infrared heating time of 95 seconds, but the 60° gloss decreased to 78%; the adhesion (cross-cut test) decreased to 3B, the Taber abrasion loss increased to 68mg, and the pencil hardness decreased to HB. Scanning electron microscopy observation showed that ordinary glass powder only physically interlocks with the resin matrix, and the particles detach after wear, leaving a large number of voids; while the modified glass powder with surface-grafted unsaturated double bonds used in this application, through KH570 grafting, introduces C=C double bonds, which undergo free radical copolymerization with the resin during UV curing, forming a chemically bonded interface. The glass powder is firmly anchored in the cross-linked network, and even if the surface resin wears away, the exposed glass powder is not easily detached. Therefore, the chemical bonding of the modified glass powder improves wear resistance by about 59% and adhesion by 2 levels, which is one of the core technical features of this application in achieving a high wear-resistant coating.

[0064] Example 3 This embodiment specifies the upper limit of the parameter range in the above embodiments. The specific operating parameters are as follows: Preparation of crystalline unsaturated polyesters (upper limit value) 146.1 g (1.0 mol) of adipic acid, 78.5 g (0.8 mol) of maleic anhydride, and 147.7 g (1.25 mol) of 1,6-hexanediol were added to the reactor. 0.37 g of p-toluenesulfonic acid (0.10% of the total monomer mass) and 0.11 g (0.03%) of hydroquinone were also added. After purging with nitrogen, the mixture was heated to 140 °C and held for 30 min, then heated to 180 °C and reacted for 3.5 h. Approximately 38 mL of esterified water was collected, and the acid value was measured to be 40 mg KOH / g. The product was heated to 210 °C and gradually reduced to -0.095 MPa, reacting for 2.5 h until the acid value decreased to 9.8 mg KOH / g. The mixture was then cooled to 180 °C, and 11.1 g of GMA (3% of the polycondensation product mass) was added. The mixture was stirred and kept at this temperature for 1.5 h. The product was cooled to 110°C at a rate of 2°C / min, held at that temperature for 60 min, and then rapidly cooled to room temperature at a rate of 5°C / min. It was then pulverized and passed through a 20-mesh sieve to obtain crystalline unsaturated polyester. The melting point was measured to be 58°C by DSC, and Mn was measured to be 3950 by GPC, with a crystallinity of 34%.

[0065] Preparation of powder coatings (formulation upper limit) Weigh out 600g of unsaturated polyester resin (Tg=50℃), 120g of the above-mentioned crystalline unsaturated polyester, 220g of modified glass powder (grafting rate 2.9%, contact angle 113°, D50=16.8μm), 40g of modified nano α-Al2O3 (primary particle size retention rate 91%, activation degree 98%, D90=148nm, free stearic acid 0.45%), 12g of nano ATO (SnO2:Sb2O3=95:5, primary particle size 28nm, retention rate 92%), 25g of photoinitiator 184, 25g of TPO, 20g of P64F, 8g of benzoin, and 1.0g of powder flow desiccant.

[0066] The above materials were processed according to steps S2-S4: premixing (20Hz for 3 min + 40Hz for 60 s), extruder zone I 95℃, zone II 105℃, zone III 95℃, screw speed 45Hz. The material was then ground through a 200-mesh sieve, with D50 = 34μm.

[0067] Verification and Coating Sampling and testing according to V1-V3: Sprayed onto birch multi-layer solid wood composite flooring, 70μm thickness, infrared light source wavelength 1.5μm, power density 5.5kW / m², after heating for 85 seconds, the coating surface temperature reached 84℃, and leveling was complete. UV mercury lamp (1200mJ / cm²) curing for 10 seconds. Test results: 60° gloss 88%, leveling grade PCI 7, leveling temperature 84℃, leveling time 85s, impact strength 50cm·kg no cracks, adhesion (cross-cut test) 5B, Taber abrasion loss 35mg, pencil hardness 2H, no deformation. The product is qualified and will proceed to mass production for grinding.

[0068] Results show that compared with the above examples (median), the leveling temperature of the upper limit formulation is slightly higher (84℃ vs 78℃), the leveling time is slightly longer (85s vs 75s), and the abrasion resistance is slightly lower (weight loss 35mg vs 28mg), but it is still far superior to the comparative example, and the wood board is not deformed, proving that the upper limit range of this application is still valid.

[0069] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0070] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a UV-curable abrasion-resistant powder coating for wood flooring, characterized in that, Includes the following steps: S1: Weigh out 45-60 parts of unsaturated polyester resin, 8-12 parts of crystalline unsaturated polyester, 15-22 parts of modified glass powder with surface grafted unsaturated double bonds, 2-4 parts of stearic acid surface-modified nano-α-alumina, 0.6-1.2 parts of nano-antimony-doped tin oxide, 3-5 parts of photoinitiator, 1-2 parts of leveling agent, 0.3-0.8 parts of degassing agent, and 0.05-0.1 parts of powder flow desiccant; S2: Add the weighed components to the mixing tank, stir slowly at 20Hz for 3 minutes, and then stir rapidly at 40Hz for 60 seconds to obtain the premix. S3: Add the premixed material into the extruder, and melt-extrude it at a screw speed of 30~45Hz at temperatures of 90~95℃ in Zone I, 95~105℃ in Zone II, and 90~95℃ in Zone III to obtain sheet material; S4: After cooling and crushing the sheet material, it is fed into a grinding mill for grinding. The powder is passed through a 200~220 mesh sieve, and the powder particle size D50 is controlled to be 30~35μm. A powder flow desiccant is added during the grinding process to obtain a UV-curable wear-resistant powder coating. The preparation process of the crystalline unsaturated polyester is as follows: A1: In a reaction vessel, adipic acid, maleic anhydride, and 1,6-hexanediol are added in a molar ratio of 1:0.60~0.80:1.15~1.

25. Then, 0.05%~0.1% of p-toluenesulfonic acid and 0.01%~0.03% of hydroquinone are added according to the total mass of the three. After purging the reaction vessel with nitrogen to replace the air, the temperature is raised to 120~140℃ and maintained for 30 minutes. The temperature is then raised to 160~180℃ and maintained for 2.5~3.5 hours. The water generated during the esterification reaction is collected, and a sample is taken to test the acid value to 30~40 mg KOH / g to obtain the esterification product. A2: The esterification product obtained from A1 is heated to 190~210℃, while the pressure is gradually reduced to -0.09~-0.095MPa. The reaction is carried out for 1.5~2.5 hours until the acid value is ≤10mgKOH / g, to obtain the condensation product; the condensation product is cooled to 160~180℃, and 1%~3% of glycidyl methacrylate is added. The mixture is kept warm and stirred for 1~1.5 hours to graft methacryloyloxy groups onto the polyester chain ends; A3: The product obtained in A2 is cooled to 90-110℃ at a rate of 1-2℃ / min, and stirred for 30-60 minutes to generate uniform crystal nuclei; then cooled rapidly to room temperature at a rate of 3-5℃ / min, and pulverized through a 20-mesh sieve to obtain a crystalline unsaturated polyester with a melting point of 52-58℃, a number average molecular weight of 2500-4000, and a crystallinity of 15%-35%.

2. The method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 1, characterized in that, The modified glass powder with surface-grafted unsaturated double bonds has a grafting rate of 1.5~3.0wt%, a water contact angle of 90°~115°, and a median particle size D50=15±2μm.

3. The method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 1, characterized in that, The primary particle size retention rate of the stearic acid-modified nano-α-alumina is ≥90%, the activation degree is 95%~99%, the modified aggregate D90 is ≤150nm, and the free stearic acid residue is ≤0.5wt%.

4. The method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 1, characterized in that, The mass ratio of SnO2 to Sb2O3 in the nano-antimony-doped tin oxide is 90:10~95:5, the primary particle size is 20±10nm, and the primary particle size retention rate is ≥90%.

5. The method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 1, characterized in that, A verification step is also included between steps S3 and S4: V1: Take the middle part of the extruded sheet material, grind it with a small mill and pass it through a 200~250 mesh sieve, and control the particle size D50=30~35μm; V2: The sieved powder is electrostatically sprayed onto the pre-treated wooden board with a thickness of 50~70μm. It is then heated to 80~100℃ by infrared light for 2~3 minutes to level, and then cured by UV light for 5~10 seconds. After natural cooling, the transparency, leveling, impact strength, adhesion or abrasion resistance of the coating are tested. V3: If all test results are qualified, proceed to step S4; if any one of them is unqualified, repeat steps S2 and S3 until the test is qualified.

6. The method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 1, characterized in that, The photoinitiator is a mixture of 2-hydroxy-2-methyl-1-phenylpropanone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in a mass ratio of 1:

1.

7. The method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 1, characterized in that, The glass transition temperature (Tg) of the unsaturated polyester resin is ≥48℃.

8. The method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 1, characterized in that, The leveling agent is P-64F acrylic leveling agent, and the degassing agent is smokeless crystalline benzoin.

9. The method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 1, characterized in that, In step S3, the temperature of zone I of the extruder is 92°C, the temperature of zone II is 100°C, and the temperature of zone III is 92°C.

10. A method for preparing a UV-curable wear-resistant powder coating for wood flooring according to claim 2, characterized in that, The modified glass powder with surface-grafted unsaturated double bonds is prepared by surface grafting modification of 800-1250 mesh glass powder.

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