Scratch-resistant thin coating type powder coating plate and preparation method thereof

Abstract

The invention discloses an anti-scraping thin coating type powder coating plate and a preparation method thereof, and relates to the technical field of coating materials and metal surface treatment. According to the scheme, the method comprises the following steps: forming a film on the surface of a degreased, alkali-washed and passivated metal substrate by adopting an interface modification liquid containing a silane coupling agent KH-590; and performing melt extrusion on a powder coating prepared from a hydroxyl-terminated polyether-ether-ketone / bisphenol A type epoxy silane grafted composite resin matrix, a triglycidyl isocyanurate / caprolactam composite curing agent and a titanate modified nano composite filler, and then performing electrostatic spraying and curing to obtain a coated plate with a dry film thickness of 20-40 [mu] m, wherein the powder coating is prepared from the hydroxyl-terminated polyether-ether-ketone / bisphenol A type epoxy silane grafted composite resin matrix, the triglycidyl isocyanurate / caprolactam composite curing agent and the titanate modified nano composite filler. The invention has the following beneficial effects: the interface modification layer and the silicon-containing grafted resin cooperate to improve the interface bonding force, boiling resistance and salt spray resistance; the multi-scale hard filler constructs a reinforced skeleton in the film, so that the scratch resistance is improved while the mechanical property is maintained, and thin coating and powder saving are realized under the condition of ensuring the decoration and durability.

Description

Technical Field

[0001] This invention relates to the field of coating materials and surface treatment technology for metal sheets, and particularly to a scratch-resistant and thin-film powder-coated sheet and its preparation method. Background Technology

[0002] Powder coatings, as a solvent-free and recyclable solid coating material, have been widely used in the surface treatment of metal sheets, including the casings of household appliances, office furniture, architectural decorative panels, and the outer cladding of industrial equipment, since their introduction. Compared with traditional solvent-based coatings, powder coatings have significant advantages in terms of volatile organic compound emissions, single-pass powdering efficiency, film thickness control, and weather and corrosion resistance, making them particularly suitable for continuous coating production of coiled steel sheets, steel furniture panels, and electrical sheet metal parts. Industrially, electrostatic spraying combined with high-temperature curing processes is commonly used to obtain coatings with a dry film thickness typically of 50–150 μm, ensuring sufficient shielding protection and a certain degree of mechanical protection for the substrate. In recent years, with the continuous increase in demand for energy conservation, emission reduction, material saving, and product lightweighting, powder coatings are developing towards thinner coatings while maintaining protective performance. The aim is to achieve scratch resistance, wear resistance, and appearance performance similar to or even better than traditional thick coatings at lower coating thicknesses, for use in various metal sheet applications subject to frequent contact, friction, and cleaning.

[0003] However, regarding the goals of "thin coating" and "high scratch resistance," existing technologies largely extend the traditional thick coating approach in terms of formulation design and coating structure. This leads to significant shortcomings when the film thickness decreases to approximately 20–40 μm. On one hand, existing powder coatings typically improve surface hardness and scratch resistance by increasing resin crosslinking density or introducing resin systems with higher hardness. While this approach can improve scratch marks to some extent at conventional thicknesses, in thin coatings, the effective load-bearing volume decreases, internal stress becomes more concentrated, and highly crosslinked, high-modulus systems often lead to a decrease in overall coating toughness. This makes the coating prone to microcracks or edge cracking during subsequent bending, stamping, and flanging processes, thus weakening its actual scratch resistance. On the other hand, existing technologies generally employ the addition of inorganic rigid fillers, microcrystalline particles, or nanoscale particles to enhance the scratch resistance of the coating surface. While these particles can achieve a relatively uniform distribution in thick film systems through sufficient resin encapsulation and leveling processes, in thin film systems, due to the limited coating thickness and shortened flow time, particles are more likely to accumulate on the surface or in localized areas, causing localized roughness, uneven gloss, or even protrusions. This not only affects the appearance but also creates new stress concentration sources, making them more prone to localized peeling due to scratches and wear in actual use. Furthermore, conventional powder coating of metal sheets relies heavily on traditional pretreatment methods such as phosphating, chromium salts, or simple inorganic conversion films. These interface treatment technologies are mainly designed for medium-thickness coatings, assuming that the coating body has a large thickness and buffer space to compensate for localized interface defects. When the dry film thickness decreases to 20–40 μm, the impact of interface defects on overall performance is amplified. Even if the coating body hardness is increased, if the interface bonding is insufficient, peeling, bulging, or peeling along the interface can still easily occur at the scratched area after scratching or repeated bending. Existing powder coating systems face several challenges under thin-film conditions, including reduced powder application rate during electrostatic spraying, insufficient coverage at edges and corners, and excessive leveling during curing leading to further film thinning. These issues exacerbate the conflict between coating thickness control and scratch resistance. Generally, existing technologies focus on localized optimization using single formulation parameters, single functional fillers, or single process conditions. While these methods can meet general corrosion and decorative requirements under traditional thick-film conditions, achieving high scratch resistance, good adhesion, processability, and surface smoothness simultaneously under thin-film conditions remains challenging. When attempting to directly "compress" traditional thick-film powder formulations for thin-film applications, those skilled in the art often encounter a series of problems, such as decreased scratch resistance, brittle coatings, interface failures, and a narrowed process window.

[0004] Against this backdrop, the industry has imposed more stringent and comprehensive performance requirements on thin-film powder coatings used on sheet metal. On the one hand, in high-contact applications such as appliance panels, office furniture panels, interior decorative panels, and metal cladding for public facilities, the coating needs to provide sufficient scratch resistance and surface abrasion resistance while maintaining a dry film thickness of approximately 20–40 μm. This prevents significant scratches and coating damage caused by friction from keys, stationery, and shoe soles during daily use. On the other hand, for sheets requiring subsequent bending, stamping, and bonding, the thin-film powder coating must also maintain stable adhesion and a certain degree of flexibility with the metal substrate, preventing cracking, peeling, and edge paint loss under multiaxial stress. Simultaneously, while meeting environmental regulations and energy conservation requirements, the coating process aims to maintain conventional electrostatic spraying and short-time curing conditions to reduce energy consumption and production costs. Therefore, there is an urgent need in this field for a powder-coated plate and its preparation method that can still achieve high scratch resistance, excellent interfacial bonding and processing adaptability in the low film thickness range, so as to realize a reliable transformation of powder coating from traditional thick coating to thin coating while ensuring the long-term protective and decorative effect of metal plates. Summary of the Invention

[0005] To achieve the above-mentioned objectives and address the aforementioned technical problems, this invention provides a scratch-resistant and thin-film powder-coated plate and its preparation method, as well as a matching powder coating.

[0006] The powder-coated plate includes a substrate, an interface modification layer covering the surface of the substrate, and a powder coating covering the interface modification layer. The interface modification layer is obtained by film formation from an interface modification liquid, and the powder coating is formed by curing powder coating material. The dry film thickness of the powder coating is 20-40 μm.

[0007] By setting an interface modification layer with a specific composition and thickness range on the surface of a metal substrate, and combining it with a powder coating system containing a specific composite resin matrix, composite curing agent and composite filler, high scratch resistance and good adhesion can still be obtained within a low film thickness range, while taking into account the flow leveling and machinability during thin-coat application. Preferably, the substrate is at least one of cold-rolled substrate, hot-rolled substrate, aluminum alloy plate, magnesium alloy plate or galvanized substrate.

[0008] Preferably, the thickness of the substrate is controlled to be 0.2-2.0mm to suit the application scenarios of thin sheet materials such as home appliance panels, office furniture panels and decorative panels.

[0009] Preferably, the interface modification liquid comprises: 5-8% by mass of silane coupling agent KH-590, 30-40% ethanol, and the balance being deionized water; the dry film thickness of the interface modification layer is 5-10 μm.

[0010] Specifically, the interface modification solution is prepared by weighing 5-8% silane coupling agent KH-590, 30-40% ethanol, and deionized water by mass percentage. First, the ethanol and deionized water are mixed evenly, and then the silane coupling agent KH-590 is slowly added dropwise at 25-30℃. The mixture is stirred and hydrolyzed for 1.5-3.5 hours to obtain a transparent and uniform interface modification solution.

[0011] Preferably, in the interface modification layer treatment step, the pretreated substrate is immersed in the interface modification solution and coated using a dip-coating method, preferably with a dip-coating speed of 5-8 cm / min; after removal, it is placed in an oven and dried at 100-120℃ for 3-5 min to allow the interface modification solution to form a film, thus obtaining an interface modification layer. The dry film thickness of this interface modification layer is controlled at 5-10 μm. This interface modification layer facilitates the formation of an organic-inorganic synergistic transition interface between the metal substrate and the powder coating, thereby improving the interface stability of the thin coating under bending and scratching conditions.

[0012] Preferably, the powder coating comprises, by weight, 45-60 parts of composite resin matrix; 8-15 parts of composite curing agent; 18-28 parts of composite filler; and 3-8 parts of functional additives.

[0013] Preferably, 2-5% pigment can be used as the coloring and covering component.

[0014] Preferably, the functional additives include 1-3 parts of acrylate leveling agent, 0.5-2 parts of hindered amine light stabilizer, 0.5-1.5 parts of antioxidant 1010, 0.5-1 parts of silicone defoamer, and 0.5-1 parts of benzoin degassing agent.

[0015] Preferably, the pigments are weather-resistant organic pigments (such as azo and phthalocyanine pigments) and / or inorganic pigments (such as titanium dioxide, iron oxide red pigment, and carbon black).

[0016] Preferably, the composite resin matrix is ​​a graft product of hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin, wherein the mass ratio of hydroxyl-terminated polyether ether ketone to bisphenol A type epoxy resin is 1:(2-5), and 5-8% γ-glycidoxypropyltrimethoxysilane is added to the total mass of hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin for grafting, with a grafting rate of 10-20%.

[0017] Preferably, the composite curing agent is composed of a mixture of triglycidyl isocyanurate and caprolactam, wherein the mass ratio of triglycidyl isocyanurate to caprolactam is (2-5):1.

[0018] Preferably, the composite filler is composed of nano-silicon nitride, nano-titanium dioxide, nano-diamond, and titanium boride in a mass ratio of (1:3:1:3) to (1:6:1:6), wherein the particle size of nano-silicon nitride, nano-titanium dioxide, and nano-diamond is 15-40 nm, and the particle size of titanium boride is 0.8-2 μm; the composite filler is surface modified by a titanate coupling agent, and the amount of titanate coupling agent added is 2-3% of the total mass of the filler.

[0019] Preferably, nano-silicon nitride, nano-titanium dioxide, nano-diamond, and titanium boride are weighed in a mass ratio of 1:3:1:3 to 1:6:1:6 and dispersed in a 1:1 volume ratio ethanol-water mixed solution. The dispersion is ultrasonically dispersed for 30-40 min (power 300-400W). The pH of the system is adjusted to 8.0-9.0 with ammonia. Titanium ester coupling agent (2-3% of the total mass of the four inorganic fillers) is slowly added. The temperature is raised to 60-80℃ and stirred for 3-5 h. After the reaction, the mixture is centrifuged at 8000-10000 r / min for 10-15 min, washed with ethanol 3-4 times, vacuum dried at 85-100℃ for 4-6 h, and finally placed in a muffle furnace and calcined at 450-500℃ for 2-4 h (heating rate 5-10℃ / min). After cooling, the composite filler is obtained by grinding. The composite filler can improve the surface scratch resistance in thin coatings through the synergistic effect of multi-scale rigid particles. At the same time, after modification with titanate coupling agent, its interfacial compatibility with the resin matrix is ​​improved, reducing stress concentration and particle agglomeration under thin film conditions.

[0020] The present invention also provides a method for preparing a scratch-resistant and thin-film powder-coated plate, comprising the following steps: S1, Substrate pretreatment: Select a substrate, and after degreasing, alkaline washing and passivation treatment, dry it to obtain a pretreated substrate; S2, Preparation of interface-modified liquid and powder coating raw materials: S2a, preparation of interface-modified liquid; S2b is used to prepare a composite resin matrix. S2c, preparation of composite curing agent; S2d, preparation of composite fillers; S3, Interface modification layer treatment: The pretreated substrate is coated with the interface modification liquid and dried to form an interface modification layer; S4, Powder coating preparation: The raw materials for the powder coating are mixed, and the powder coating is obtained by melt extrusion, cooling, crushing and grinding; S5, Electrostatic spraying and curing: The powder coating is sprayed onto the surface of the substrate that has undergone interface modification treatment using an electrostatic spraying method, and then cured by heating to obtain a powder-coated plate.

[0021] Preferably, the substrate is pretreated before preparation, including degreasing, alkaline washing, and passivation in sequence: For degreasing, an alkaline degreasing agent at 50-60℃ is used, corresponding to a sodium hydroxide mass fraction of 3-5%, a sodium carbonate mass fraction of 2-4%, and a surfactant mass fraction of 0.5-1%, for 10-15 minutes to remove surface oil; for alkaline washing, a sodium hydroxide solution at 40-50℃ (mass fraction 5-8%) is used for 5-8 minutes to remove the oxide layer; for passivation, a chromate passivation solution at 20-30℃ (chromic anhydride mass fraction 2-3%, phosphoric acid mass fraction 1-2%) is used for 3-5 minutes to form a dense passivation film. Finally, the substrate is rinsed clean with deionized water and dried to obtain the pretreated substrate. This pretreatment provides a clean and appropriately active surface for the subsequent interface modification layer.

[0022] Preferably, in step S2a, the interface modification liquid raw material is hydrolyzed by mixing ethanol and deionized water evenly and slowly adding silane coupling agent KH-590 to obtain a transparent and uniform interface modification liquid. The hydrolysis temperature is 25-30℃ and the hydrolysis time is 1.5-3.5h. Preferably, in step S2b, hydroxyl-terminated polyetheretherketone (PEEK) and bisphenol A type epoxy resin (preferably with an epoxy value of 0.20-0.25 eq / 100g and a number-average molecular weight of 1200-1800) are weighed at a mass ratio of 1:3 and added to a reaction vessel. The mixture is stirred and melted at 120-140°C for 30-40 minutes. Then, γ-glycidyl etheroxypropyltrimethoxysilane is added, with the amount being 5-8% of the total mass of the hydroxyl-terminated PEEK and bisphenol A type epoxy resin. The temperature is raised to 150-160°C and maintained for 2-3 hours. The grafting reaction is monitored by infrared spectroscopy, and the grafting rate is controlled to be 10-20%. After the reaction, the mixture is cooled and pulverized to obtain the composite resin matrix. Through the above grafting design, rigid segments and silicon-containing functional groups can be introduced into the resin system, achieving comprehensive control over the coating hardness, flexibility, and compatibility with the interface modification layer.

[0023] Preferably, in step S2c, triglycidyl isocyanurate and caprolactam are weighed at a mass ratio of 3:1, added to a mixer, and stirred and mixed at 60-70°C for 15-20 minutes to ensure that the two are fully mixed and homogeneous before cooling to obtain a composite curing agent.

[0024] Preferably, in step S2d, nano-silicon nitride, nano-titanium dioxide, nano-diamond, and titanium boride are weighed in a mass ratio of 1:3:1:3 to 1:6:1:6 and dispersed in a 1:1 volume ratio ethanol-water mixed solution. The dispersion is ultrasonically carried out for 30-40 min (power 300-400W). The pH of the system is adjusted to 8.0-9.0 with ammonia water, and titanate coupling agent (2-3% of the total mass of the four inorganic fillers) is slowly added. The temperature is raised to 60-80℃ and stirred for 3-5 h. After the reaction, the mixture is centrifuged at 8000-10000 r / min for 10-15 min, washed with ethanol 3-4 times, vacuum dried at 85-100℃ for 4-6 h, and finally placed in a muffle furnace and calcined at 450-500℃ for 2-4 h (heating rate 5-10℃ / min). After cooling, the composite filler is obtained by grinding. The composite filler can improve the surface scratch resistance in thin coatings through the synergistic effect of multi-scale rigid particles. At the same time, after modification with titanate coupling agent, its interfacial compatibility with the resin matrix is ​​improved, reducing stress concentration and particle agglomeration under thin film conditions.

[0025] Preferably, in step S3, the interface modification liquid is coated by a lifting method, which facilitates precise control of the thickness and uniformity of the interface modification layer; the lifting speed is controlled at 5-8 cm / min; after removal, it is placed in an oven and dried at 100-120℃ for 3-5 min to form an interface modification layer with a dry film thickness of 5-10 μm. Preferably, in step S4, the grinding is carried out under inert gas protection, the grinding temperature is not higher than 35°C, and the resulting powder coating has a particle size distribution of 15-45μm, with particles of 20-35μm accounting for no less than 90%, so as to obtain good thin-coat coverage and surface smoothness during electrostatic spraying; in step S5, the curing temperature is 180-260°C and the curing time is 2-8min. By adjusting the curing temperature and time, production efficiency and energy consumption control can be taken into account while ensuring full cross-linking of the coating.

[0026] Preferably, each component is fed into a high-speed mixer, with the rotation speed controlled at 500-800 r / min and the temperature at 40-50℃, and mixed for 10-20 min to obtain a premix. The premix is ​​then fed into a twin-screw extruder for melt extrusion, with the extrusion temperature controlled in segments: zone 1 95-115℃, zone 2 100-120℃, and zone 3 100-115℃, and the screw speed at 260-400 r / min. The extrudate is cooled to room temperature by a cooling roller (20-30℃) and broken into 5-10 mm particles. It is then ground under the protection of an inert gas (such as nitrogen or argon), with the grinding temperature controlled not to exceed 35℃. After being sieved through a 150-200 mesh sieve, a powder coating is obtained. This invention also provides a powder coating, characterized in that it comprises, by weight parts: 45-60 parts of a composite resin matrix; 8-15 parts of a composite curing agent; 18-28 parts of a composite filler; and 3-8 parts of a functional additive. The composite resin matrix is ​​a grafted product of hydroxyl-terminated polyetheretherketone (PEEK) and bisphenol A type epoxy resin, wherein the mass ratio of PEEK to bisphenol A type epoxy resin is 1:(2-5). Grafting is performed by adding 5-8% γ-glycidoxypropyltrimethoxysilane to the total mass of PEEK and bisphenol A type epoxy resin, with a grafting rate of 10-20%. The curing agent is composed of a mixture of triglycidyl isocyanurate and caprolactam, with a mass ratio of triglycidyl isocyanurate to caprolactam of (2-5):1. The composite filler is composed of nano-silicon nitride, nano-titanium dioxide, nano-diamond, and titanium boride in a mass ratio of (1:3:1:3)-(1:6:1:6), wherein the particle size of nano-silicon nitride, nano-titanium dioxide, and nano-diamond is 15-40 nm, and the particle size of titanium boride is 0.8-2 μm. The composite filler is surface modified by a titanate coupling agent, and the amount of titanate coupling agent added is 2-3% of the total mass of the filler.

[0027] The beneficial effects of the technical solution provided by this invention are as follows: The interface modification layer prepared by the silane coupling agent KH-590 in this invention effectively improves the bonding force between the substrate and the coating, and solves the problem of easy coating peeling. A composite resin matrix of hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin is used, and modified with silane grafting, combined with a composite curing agent of triglycidyl isocyanurate and caprolactam, so that the coating has excellent mechanical properties and chemical resistance. The composite filler adopts a multi-level composite system of nano-diamond, nano-titanium dioxide, nano-silicon nitride and titanium boride, and undergoes surface modification treatment, which significantly improves the scratch resistance and wear resistance of the coating, without affecting the processing performance of the coating. The powder coating of this invention has a dry film thickness of only 20-40 μm, which is significantly thinner than traditional coatings, reducing material consumption and cost while maintaining excellent performance. The preparation process of this invention is stable and controllable, applicable to a variety of substrates, and can be widely used in fields such as construction, home appliances, and automobiles, showing good prospects for industrialization. Attached Figure Description

[0028] Figure 1 This is a powder SEM image of Example 1 of the present invention; Figure 2 This is a SEM image of the powder-coated plate surface in Embodiment 1 of the present invention; Figure 3 This is a cross-sectional view of the powder-coated plate of Embodiment 1 of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] Example 1 1. Substrate pretreatment (S1) Cold-rolled steel sheet with a thickness of 0.8 mm was selected as the base material. The material underwent degreasing, alkaline washing, and passivation treatments sequentially, as detailed below: 1) Defatting: Degreasing solution formula (mass fraction): sodium hydroxide 4%, sodium carbonate 3%, nonionic surfactant 0.8%, balance deionized water; Degreasing temperature: 55℃; soaking time: 12min; rinse thoroughly with deionized water after treatment.

[0031] 2) Alkali washing: The alkaline washing solution was a sodium hydroxide solution with a sodium hydroxide mass fraction of 6%; the alkaline washing temperature was 45℃; and the soaking time was 6 minutes. After treatment, rinse thoroughly with deionized water.

[0032] 3) Passivation: The passivation solution is a chromate passivation solution (mass fraction: 2.5% chromium anhydride, 1.5% phosphoric acid, balance deionized water); Passivation temperature: 25℃; Immersion time: 4 min; After passivation, the steel sheet is rinsed with deionized water and dried with hot air at 60°C to obtain a clean and uniformly passivated pretreated cold-rolled steel sheet.

[0033] 2. Preparation of interface modification solution (S2a) When preparing the interface modification solution, take the following by mass percentage: Silane coupling agent KH-590: 6%; Ethanol: 35%; The remainder is deionized water.

[0034] The specific steps are as follows: 1) Mix ethanol and deionized water thoroughly; 2) At 28℃, slowly add silane coupling agent KH-590 dropwise while stirring. 3) Maintain 28℃ and stir for 2.5h until the system is a transparent and homogeneous solution, which is the interface modified solution.

[0035] 3. Preparation of the composite resin matrix (S2b) Weigh out hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin at a mass ratio of 1:3, wherein the epoxy value of the bisphenol A type epoxy resin is 0.22 eq / 100g and the number average molecular weight is approximately 1500.

[0036] The specific steps are as follows: 1) Add hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin to a stirred reactor and melt mix at 130°C for 35 minutes until a homogeneous melt system is formed; 2) Add 7% γ-glycidoxypropyltrimethoxysilane to the total resin mass mentioned above, and continue heating to 155℃; 3) The reaction was carried out at 155℃ for 2.5 hours, and the grafting rate was controlled to be approximately 15%. 4) After the reaction is complete, cool to room temperature, pulverize the solidified material, and obtain the composite resin matrix of the present invention.

[0037] 4. Preparation of composite curing agent (S2c) Weigh out triglycidyl isocyanurate and caprolactam in a mass ratio of 3:1: 1) Add both to the mixer; 2) Stir at 65℃ for 18 minutes until a homogeneous mixture is formed; 3) Cool to room temperature to obtain the composite curing agent.

[0038] 5. Preparation of composite fillers (S2d) Weigh out the following quantities in a mass ratio of 1:4:1:4: Nano-silicon nitride (particle size approximately 25 nm); nano-titanium dioxide (particle size approximately 25 nm); nano-diamond (particle size approximately 25 nm); titanium boride (particle size approximately 1.2 μm).

[0039] Preparation steps: 1) The above four powders are added to an ethanol-water mixed solution in a mass ratio of 1:1; 2) The mixture was ultrasonically dispersed at an ultrasonic power of 350W for 35 minutes to obtain a uniformly dispersed slurry; 3) Adjust the pH of the system to 8 using ammonia; 4) Slowly add titanate coupling agent, the amount of titanate coupling agent added is 2.5% of the total mass of the four inorganic fillers, and mechanically stir the reaction at 70℃ for 4 hours to carry out surface modification; 5) After the reaction is complete, centrifuge at 9000 r / min for 12 min, discard the supernatant, and wash the obtained solid phase three times with ethanol. 6) Vacuum dry at 95℃ for 5 hours to remove most of the solvent; 7) Place the dried powder in a muffle furnace and calcine it at 480℃ for 3 hours with a heating rate of 8℃ / min, then allow it to cool naturally to room temperature; 8) Finally, the composite filler modified with titanate coupling agent is ground to a suitable particle size using an air jet mill.

[0040] 6. Preparation of powder coatings (S4) In this embodiment, the powder coating comprises, by mass parts: 52 parts of composite resin matrix; 12 parts of composite curing agent; 24 parts of composite filler; 6 parts of functional additives; 4 parts of pigment.

[0041] The functional additives consist of: Acrylic leveling agent: 2 parts; hindered amine light stabilizer: 1 part; antioxidant 1010: 1 part; silicone defoamer: 0.7 parts; benzoin degassing agent: 0.8 parts.

[0042] Titanium dioxide was selected as the pigment.

[0043] Preparation steps: 1) Add the composite resin matrix, composite curing agent, composite filler, functional additives and pigments into a high-speed mixer in the above proportions; 2) Control the mixing temperature at 45℃ and the rotation speed at 700r / min, mix for 15min to obtain a uniform premix; 3) The premix is ​​fed into a twin-screw extruder for melt extrusion, with the extrusion temperature segmented as follows: Zone 1: 105℃; Zone 2: 110℃; Zone 3: 110℃; Screw speed: 320r / min; 4) The extrudate is cooled to room temperature by a cooling roller at 25°C and then broken into thin flakes of about 5-10 mm. 5) Put the particles into the crushing equipment and grind them under nitrogen protection. The grinding temperature should not exceed 30℃. 6) The ground product is sieved through a 180-mesh sieve to obtain powder coating with the target particle size.

[0044] The resulting powder coating has a particle size distribution range of 15-45μm, with an average particle size of about 28μm. Among them, particles with a particle size of 20-35μm account for no less than 90%, which is beneficial for uniform powder application and smooth film formation under thin coating conditions.

[0045] 7. Interface modification layer treatment and spray curing (S3, S5) 1) Interface modification layer processing (S3) The pretreated cold-rolled steel sheet was completely immersed in the aforementioned interface modification solution and left to stand for 2 minutes. The coating is applied using a lifting method, with the lifting speed controlled at 6 cm / min. Immediately after lifting, place the mixture in an oven at 110℃ for 4 minutes to dry, allowing the interface modification liquid to form a film and obtain the interface modification layer. The measured thickness of the dry film of the interface-modified layer was approximately 7 μm.

[0046] 2) Electrostatic spraying and curing (S5) The powder coating described above was applied to the surface of a cold-rolled steel sheet with an interface modification layer using conventional electrostatic spraying equipment. Spraying parameters: Electrostatic voltage: 70kV; atomizing air pressure: 0.3MPa; distance between nozzle and workpiece: 30cm; after spraying, the workpiece is sent into a hot air circulating curing oven and cured at 200℃ for 4min. After curing, the material is allowed to cool naturally to room temperature to obtain the scratch-resistant and thin-film powder-coated plate of the present invention.

[0047] The dry film thickness of the powder coating was measured to be approximately 30 μm using a film thickness gauge. Example 2 Prepared using the same method as in Embodiment 1, except that... Preparation of interface modification liquid (S2a) Take by mass percentage: silane coupling agent KH-590: 5.0%; ethanol: 30.0%; Specific preparation steps: (1) Mix ethanol and deionized water thoroughly; (2) Add silane coupling agent KH-590 slowly dropwise at 25℃ while stirring; (3) Maintain a temperature of 25°C and stir for 1.5 hours until the system is a transparent and homogeneous solution, which is the interface modified solution.

[0048] Interface modification layer processing (S3) The pretreated cold-rolled steel sheet was completely immersed in the above interface modification liquid and left to stand for 2 minutes. The coating was then applied by a lifting method with a lifting speed of 5 cm / min. Immediately after lifting, the mixture was placed in a 100℃ oven for 3 minutes to allow the interface modification liquid to form a film. The thickness of the dry film of the interface modification layer was measured to be approximately 5 μm.

[0049] Electrostatic spraying and curing (S5) After curing and natural cooling to room temperature, the dry film thickness of the coating was measured to be approximately 28-30 μm using a film thickness gauge.

[0050] Example 3 Prepared using the same method as in Embodiment 1, except that... Preparation of interface modification liquid (S2a) By mass percentage: Silane coupling agent KH-590: 8.0%; Ethanol: 40.0%; Specific preparation steps: (1) Mix ethanol and deionized water thoroughly; (2) Add silane coupling agent KH-590 slowly dropwise at 30℃ while stirring; (3) Maintain stirring at 30°C for 3.5 hours until the system is a transparent and homogeneous solution, which is the interface modified solution.

[0051] Interface modification layer processing (S3) The pretreated cold-rolled steel sheet was completely immersed in the above interface modification liquid and left to stand for 2 minutes. The coating was then applied by a lifting method with the lifting speed controlled at 8 cm / min. Immediately after lifting, the mixture was placed in a 100℃ oven for 3 minutes to allow the interface modification liquid to form a film. The thickness of the dry film of the interface modification layer was measured to be approximately 10 μm.

[0052] Electrostatic spraying and curing (S5) The spraying and curing conditions were the same as in Example 1, and the dry film thickness of the cured coating was approximately 30 μm.

[0053] Example 4 Prepared using the same method as in Embodiment 1, except that... Preparation of composite fillers (S2d) Weigh out the following quantities in a mass ratio of 1:6:1:6: Nano-sized silicon nitride (particle size approximately 25 nm); Nano titanium dioxide (particle size approximately 25 nm); Nanodiamonds (particle size approximately 25 nm); Titanium boride (particle size approximately 2.0 μm).

[0054] The specific steps are as follows: (1) The above powder was put into a mixed solution of ethanol / deionized water in a volume ratio of 1:1 and ultrasonically dispersed for 40 min at an ultrasonic power of 400W. (2) Adjust the pH of the system to 9.0 using ammonia; (3) Slowly add titanate coupling agent, the amount of which is 3.0% of the total mass of the four inorganic fillers, and mechanically stir the reaction at 80℃ for 5 hours; (4) Centrifuge at 10000r / min for 15min, discard the supernatant, and wash with ethanol 3 times; (5) Vacuum dry at 100℃ for 6 hours; (6) The dried powder was calcined in a muffle furnace at 500°C for 4 hours with a heating rate of 10°C / min. After naturally cooling to room temperature, it was ground to a suitable particle size by an air jet mill to obtain the composite filler.

[0055] Example 5 Prepared using the same method as in Embodiment 1, except that... Preparation of composite resin matrix (S2b) (1) Weigh hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin at a mass ratio of 1:5. The epoxy resin has an epoxy value of 0.25 eq / 100g and a number average molecular weight of about 1800. (2) Add both to the reactor and melt-mix at 140°C for 40 min to obtain a homogeneous melt system; (3) Add 8% γ-glycidoxypropyltrimethoxysilane based on the total resin mass; (4) Heat to 160℃ and keep the temperature for 3 hours. Monitor the changes in the characteristic peaks of the grafting reaction by infrared spectroscopy and control the grafting rate to be about 19-20%. (5) After the reaction is complete, cool to room temperature and crush the solidified material to obtain the composite resin matrix.

[0056] Example 6 Prepared using the same method as in Embodiment 1, except that... Substrate and Pretreatment A 0.7mm thick aluminum alloy sheet was selected as the substrate and subjected to degreasing, alkaline washing, and passivation treatments in sequence. Degreasing: The degreasing solution formula (mass fraction) is 3% sodium hydroxide, 2% sodium carbonate, 0.5% nonionic surfactant, and the balance is deionized water; the degreasing temperature is 50℃, the soaking time is 10min, and the solution is rinsed with deionized water after treatment; Alkaline washing: Use an alkaline washing solution with a sodium hydroxide mass fraction of 5%, an alkaline washing temperature of 40℃, a soaking time of 5 minutes, and rinse thoroughly with deionized water after treatment; Passivation: The passivation solution is a chromate passivation solution (mass fraction: 2.0% chromium anhydride, 1.0% phosphoric acid, and the balance is deionized water). The passivation temperature is 22℃, the soaking time is 3min, and then it is rinsed with deionized water and dried with hot air at 60℃ to obtain a pretreated aluminum alloy plate.

[0057] Interface modification layer The composition and preparation conditions of the interface modification liquid are the same as those in Example 1, namely, KH-590 is 6.5%, ethanol is 35%, and the balance is deionized water, which is hydrolyzed at about 28°C for about 2.5 hours.

[0058] The pretreated aluminum alloy plate was immersed in the interface modification solution for about 2 minutes, coated by a lifting method at a lifting speed of 6 cm / min, and then dried in an oven at 110℃ for 4 minutes to obtain an interface modification layer with a dry film thickness of about 7 μm.

[0059] Powder coatings and coating curing The composition and preparation method of the composite resin matrix, composite curing agent, and composite filler, as well as the formulation and preparation process of the powder coating, are the same as in Example 1. The particle size distribution of the obtained powder coating is 15-45μm, of which particles of 20-35μm account for no less than 90%.

[0060] Electrostatic spraying is used for coating: spraying voltage 70kV, atomizing air pressure 0.3MPa, distance between spray gun and workpiece 30cm, powder application amount is controlled by adjusting the number of reciprocating strokes and workpiece running speed, so that the coating thickness after curing is close to the lower limit of the scope of this invention.

[0061] The curing conditions were 190℃ for 6 minutes. After curing, the powder coating was allowed to cool naturally to room temperature, and the dry film thickness was measured to be approximately 22-24 μm using a film thickness gauge.

[0062] Example 7 Prepared using the same method as in Embodiment 1, except that... Electrostatic spraying and curing conditions The same electrostatic spraying equipment and parameters as in Example 1 were used: spraying voltage 70kV, atomizing air pressure 0.3MPa, and distance between the spray gun and the workpiece 30cm. By increasing the number of spraying cycles and appropriately reducing the workpiece running speed, the powder application was increased, resulting in a dry film thickness of approximately 40μm after curing.

[0063] The curing conditions were adjusted to 230℃ for 3 minutes. After curing, the film was allowed to cool naturally to room temperature. The film thickness test results showed that the dry film thickness of the powder coating was approximately 38-40 μm.

[0064] Comparative Example 1: Prepared using the same method as in Example 1, except that: Interface modification layer processing (S3): In this comparative example, after completing the substrate pretreatment (S1) in Example 1, the steps of preparing the interface modification liquid (S2a) and treating the interface modification layer (S3) are omitted. That is, the pretreated cold-rolled steel sheet is not immersed in KH-590 interface modification liquid, nor is the pull coating and drying film formation treatment performed.

[0065] After the pre-treatment, the surface of the cold-rolled steel sheet is dried and then directly enters the electrostatic spraying step (S5).

[0066] Powder coating preparation and spray curing: The formulations and preparation processes of the composite resin matrix, composite curing agent, composite filler and functional additives, and pigments are the same as in Example 1; The electrostatic spraying and curing conditions (200℃×4min) were the same as in Example 1, and the dry film thickness of the cured coating was approximately 30μm.

[0067] Comparative Example 2: Prepared using the same method as in Example 1, except that: Preparation of interface-modified liquid (S2a): The following percentages by mass are used: silane coupling agent KH-590: 3.0%; ethanol: 25.0%; the remainder is deionized water. The preparation steps are the same as in Example 1: first, ethanol and deionized water are mixed, KH-590 is slowly added dropwise at 25°C, and the mixture is stirred and hydrolyzed for 2.5 h to obtain the interface modified solution.

[0068] Interface modification layer processing (S3): The pretreated cold-rolled steel sheet was immersed in the above interface modification solution for 2 minutes. The coating is applied using a lifting method, with the lifting speed controlled at 4 cm / min. After being lifted, the film was dried in a 90℃ oven for 2 minutes, and the thickness of the dry film of the interface modified layer was measured to be approximately 3 μm.

[0069] The remaining steps (composite resin matrix, composite curing agent, composite filler, powder coating preparation, spraying and curing conditions, etc.) are the same as in Example 1, and the dry film thickness of the cured coating is about 30 μm.

[0070] Comparative Example 3: Prepared using the same method as in Example 1, except that: Composition and preparation of composite fillers (S2d): In this comparative example, nano-silicon nitride, nano-titanium dioxide, nano-diamond and titanium boride were not used, nor was surface modification with titanate coupling agent performed. A conventional inorganic packing system is adopted, specifically: Titanium dioxide (TiO2, average particle size approximately 0.3–0.5 μm); Barium sulfate (BaSO4, average particle size approximately 1–3 μm); Weigh titanium dioxide and barium sulfate at a mass ratio of 1:2, mix them evenly, and use them as fillers without ultrasonic dispersion, pH adjustment, or titanate coupling agent treatment.

[0071] Powder coating formulation (S4): The total amount of filler remains unchanged at 24 parts, that is, the composite nanofiller of Example 1 is replaced by the above-mentioned mixture of titanium dioxide and barium sulfate in equal amounts; The mixing, extrusion, cooling, crushing, grinding, and sieving conditions were the same as in Example 1, so that the powder particle size distribution was maintained at 15–45 μm.

[0072] The interface modification layer (S3) and electrostatic spraying / curing (S5) are the same as in Example 1, and the dry film thickness of the coating after curing is about 30 μm.

[0073] Comparative Example 4: Prepared using the same method as in Example 1, except that: Electrostatic spraying parameter adjustment (S5): By increasing the workpiece running speed and reducing the number of spraying cycles, the amount of powder applied per unit area can be significantly reduced, resulting in a thinner coating.

[0074] The curing conditions remain unchanged: The curing oven temperature was maintained at 200℃, and the curing time was 4 min, the same as in Example 1; After curing and natural cooling to room temperature, the dry film thickness of the powder coating is approximately 15 μm.

[0075] Experimental test: 1. Coating film thickness Film thickness was measured using a film thickness gauge, according to GB5237, requiring that the area of ​​a single point (local thickness) on the profile be ≤1 cm². 2 The average value obtained from three or more measurements.

[0076] 2. Flexibility test The flexibility is tested using a T-bend tester: one bend is 0T, two bends are 1T, and so on. The product is considered qualified if it does not crack after being flattened after bending.

[0077] 3. Boiling water test A pressure cooker was used to perform a boiling test; the test pressure was 0.9-1.1 MPa; the test time was 2 hours; after boiling, there should be no bubbling or peeling.

[0078] 4. Hardness test After the stroller has passed by, erase it with an eraser to ensure there are no scratches.

[0079] 5. Impact test The coating should not crack after being tested using a GB / T 1732 impact tester, including both reverse and forward impacts.

[0080] 6. Salt spray test Conditions: 5% NaCl solution, 500h; cross-cut test required; area beyond 2mm is the post-test judgment area, no corrosion observed; copper accelerated acetic acid test (CASS), 120h.

[0081] 7. Particle size test Particle size analyzer 8. Scratch resistance test The loaded trolley was rolled back and forth on the test board 20 times (the distance was about 30 cm and the speed was about 0.3–0.5 m / s). After rolling, let it stand for 10 minutes, then wipe the surface with a lint-free cloth moistened with anhydrous ethanol. evaluate: Grade A: No obvious scratches, and the marks can be completely erased; Grade B: Minor scratches, barely noticeable to the naked eye; Grade C: Visible scratches / damage.

[0082] 9. Adhesion The GBT9286 standard is adopted.

[0083] Table 1 Test Data

[0084] A comprehensive analysis of Table 1 and the corresponding test results shows that, under similar or lower film thickness conditions, the embodiments of the present invention generally achieve excellent bending resistance, water boiling adhesion, impact toughness, salt spray / CASS corrosion resistance, and scratch resistance. In contrast, the comparative examples, when lacking an interface modification layer, with interface layer thickness and silane content deviating from the set range, omitting a specific nanocomposite filler system, or reducing the film thickness below the invention's range, all exhibit significant failures or reductions in one or more key indicators: The embodiments showed no cracking during T-bend tests, no cracks or peeling during impact resistance, no blistering or peeling after boiling, minimal rust spread at the scribing points in salt spray and CASS tests with slight gloss loss, and scratch resistance grades mostly A. This indicates that the "cold-rolled / aluminum substrate pretreatment + KH-590 interface modification layer + composite resin matrix formed by grafting PEEK terminal hydroxyl groups with epoxy + multi-scale nano / micro composite filler treated with titanate coupling agent + 20–40μm" properties demonstrate the superior performance of the invention. The synergistic system of "thin coating, thick film" forms a stable organic-inorganic transition layer at the metal / coating interface and constructs a micro-skeleton structure within the coating that combines rigid support and stress buffering, thus maintaining good flexibility and impact resistance while ensuring hardness and scratch resistance. In contrast, Comparative Example 1, without the interface modification layer, first exhibited blistering, peeling, and large-area corrosion in the boiling water and salt spray / CASS tests, and was also prone to cracking during T-bending and impact processes, indicating that without the silane interface layer, the interfacial bonding of the coating in the thin film state becomes a weak link. Comparative Example 2, although retaining the interface layer, had significantly lower silane content and film thickness, resulting in insufficient interfacial density and chemical bonding, allowing the corrosive medium to spread rapidly along the scribing lines, and making it more prone to cracking during bending. Comparative Example 3... After replacing the filler with conventional TiO2 / BaSO4 without coupling modification, the coating exhibited continuous pitting and blistering in salt spray / CASS, and its scratch resistance rating dropped to C. This reflects the crucial role of the hard phase network composed of nano-silicon nitride / titanium dioxide / nano-diamond and titanium boride, as well as the titanate coupling modification, in improving the thin coating's resistance to micro-cutting and inhibiting corrosion channels. Comparative Example 4, even with the formulation unchanged, showed large-area blistering, severe corrosion, and impact spalling after the film thickness was reduced below the invention's range, indicating that it is difficult to form a continuous and dense protective and load-bearing structure below a certain film thickness. The embodiments formed a comprehensive performance platform of "high flexibility + high adhesion + high corrosion resistance + high scratch resistance" across multiple performance dimensions, while the comparative examples showed performance "collapse" after removing or weakening any key technical feature. Both mechanistic and experimental evidence demonstrate that the parameter combination and structural design of this invention play a decisive role in solving the technical problem of simultaneously achieving high scratch resistance and long-term service stability under thin coating conditions, and this cannot be expected through simple optimization of existing technologies.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An anti-scratch and thin-coat powder coated panel, characterized in that, It comprises: a substrate; an interface modification layer covering the surface of the substrate; a powder coating layer covering the interface modification layer; wherein the interface modification layer is formed by film-forming of an interface modification liquid; the powder coating layer is formed by curing of a powder coating material, and the dry film thickness of the powder coating layer is 20-40 μm.

2. The powder coating panel according to claim 1, wherein: the substrate is at least one of a cold-rolled substrate, a hot-rolled substrate, an aluminum alloy panel, a magnesium alloy panel or a galvanized substrate.

3. The powder coating panel according to claim 2, wherein: the interface modification liquid comprises: 5-8% of silane coupling agent KH-590, 30-40% of ethanol and the rest of deionized water by mass of the interface modification liquid; the dry film thickness of the interface modification layer is 5-10 μm.

4. The powder coating panel according to claim 3, wherein: the powder coating material comprises, by mass fraction: 45-60 parts of a composite resin matrix; 8-15 parts of a composite curing agent; 18-28 parts of a composite filler; 3-8 parts of a functional additive.

5. The powder coating panel according to claim 4, wherein: the composite resin matrix is a graft product of hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin, the mass ratio of the hydroxyl-terminated polyether ether ketone to the bisphenol A type epoxy resin is 1: (2-5), 5-8% of γ-glycidoxypropyltrimethoxysilane is added to the total mass of the hydroxyl-terminated polyether ether ketone and the bisphenol A type epoxy resin for grafting, and the grafting rate is 10-20%.

6. The powder coating panel according to claim 4, wherein: the composite curing agent is composed of a mixture of isocyanuric acid triglycidyl ester and caprolactam, the mass ratio of isocyanuric acid triglycidyl ester to caprolactam is (2-5):

1.

7. The powder coating panel according to any one of claim 4, wherein: the composite filler is composed of nano-silicon nitride, nano-titanium dioxide, nano-diamond and titanium boride in a mass ratio of (1:3:1:3)-(1:6:1:6), wherein the particle size of the nano-silicon nitride, the nano-titanium dioxide and the nano-diamond is 15-40 nm, and the particle size of the titanium boride is 0.8-2 μm; the composite filler is surface-modified by a titanate coupling agent, and the addition amount of the titanate coupling agent is 2-3% of the total mass of the filler.

8. A process for the production of a scratch-resistant and thin-coat powder-coated panel according to any one of claims 1 to 7, characterized in that, It comprises the following steps: S1, substrate pretreatment: select a substrate, after degreasing, alkaline washing and passivation treatment, dry the pretreated substrate; S2, preparation of interface modification liquid and powder coating material raw materials: S2a, preparation of interface modification liquid; S2b, preparation of a composite resin matrix; S2c, preparation of a composite curing agent; S2d, preparation of a composite filler; S3, interface modification layer treatment: coat the pretreated substrate with the interface modification liquid and dry it to form an interface modification layer; S4, powder coating material preparation: mix the raw materials of the powder coating material, melt extrude, cool, crush and grind to obtain the powder coating material; S5, electrostatic spraying and curing: use electrostatic spraying to spray the powder coating material on the surface of the substrate treated by the interface modification, and after heating and curing, obtain a powder coating panel.

9. The preparation method according to claim 8, characterized in that: in step S2a, the interface modification liquid raw material is hydrolyzed, the hydrolysis temperature is 25-30℃, and the hydrolysis time is 1.5-3.5h; in step S3, the interface modification liquid is coated by pulling mode; in step S4, the grinding is carried out under inert gas protection, the grinding temperature is not higher than 35℃, the obtained powder coating particle size distribution is 15-45μm, and the proportion of particles with particle size of 20-35μm is not less than 90%; in step S5, the curing temperature is 180-260℃, and the curing time is 2-8min.

10. A powder coating, characterized in that, by mass fraction comprising: composite resin matrix 45-60 parts; composite curing agent 8-15 parts; composite filler 18-28 parts; functional additives 3-8 parts, the composite resin matrix is the graft product of hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin, the mass ratio of hydroxyl-terminated polyether ether ketone to bisphenol A type epoxy resin is 1:(2-5), 5-8% γ-glycidyl ether propyl trimethoxysilane is added to the total mass of hydroxyl-terminated polyether ether ketone and bisphenol A type epoxy resin for grafting, and the grafting rate is 10-20%, the composite curing agent is composed of isocyanuric acid triglycidyl ester and caprolactam, the mass ratio of isocyanuric acid triglycidyl ester to caprolactam is (2-5):1, the composite filler is composed of nano silicon nitride, nano titanium dioxide, nano diamond and titanium boride in a mass ratio of (1:3:1:3)-(1:6:1:6), wherein the particle size of nano silicon nitride, nano titanium dioxide and nano diamond is 15-40nm, and the particle size of titanium boride is 0.8-2μm; the composite filler is surface modified by titanate coupling agent, and the addition amount of the titanate coupling agent is 2-3% of the total mass of the filler.

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