Wear-resistant coating for color-coated aluminum plate strip and preparation method of wear-resistant coating

Abstract

The invention discloses a wear-resistant coating for a color-coated aluminum plate strip and a preparation method of the wear-resistant coating, and relates to the technical field of metal material surface treatment. After a base material is subjected to oil removal, acid pickling and phytic acid-silane composite passivation pretreatment, the base material is sequentially coated with a bottom coating and a surface coating and cured; the bottom coating is prepared by dispersing and stirring a nano aluminum oxide and nano zirconium oxide compound filler, resin and a solvent, and the mechanical property is synergistically improved through a rigid filler framework and toughness buffering; the surface coating comprises graphene-polytetrafluoroethylene composite microspheres, resin and a curing agent, a reinforcing-lubricating network is formed through sanding dispersion, and the resin and the curing agent are subjected to a cross-linking reaction in the curing process to construct a compact coating structure. According to the method, through collaborative design of the bottom coating and the surface coating, the wear resistance, the salt fog resistance and the adhesive force of the color-coated aluminum plate strip are improved.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for metal materials, and in particular to a wear-resistant coating for color-coated aluminum sheets and strips and its preparation method. Background Technology

[0002] Color-coated aluminum sheets and strips, due to their combination of decorative and protective properties, are widely used in building exterior walls, appliance panels, transportation, and other fields. The wear resistance of their surface coatings directly affects the product's service life. In existing technologies, coatings for color-coated aluminum sheets and strips typically employ a two-layer system of a primer and a topcoat. The primer layer often uses epoxy resin or polyester resin as the film-forming substance, combined with inorganic wear-resistant fillers such as alumina and silica, primarily serving to ensure substrate adhesion and provide initial wear resistance. The topcoat layer often uses polyester or fluorocarbon resin, with added pigments such as titanium dioxide and conventional wear-resistant additives to enhance weather resistance and surface hardness.

[0003] However, in existing coating systems, the rigid support of the base layer and the wear resistance of the top layer lack synergistic design: the combination of a single resin and conventional inorganic fillers in the base layer is difficult to form a stable rigid skeleton to resist deep wear; the lubricity and mechanical strength of traditional wear-resistant fillers (such as ordinary silica and glass microspheres) in the top layer are insufficient, and after long-term friction, filler detachment or resin matrix wear is likely to occur, resulting in poor overall wear resistance and durability of the coating. Especially in high-frequency friction or harsh environments, the coating is prone to scratches, exposure of the substrate, or even peeling, which cannot meet the usage requirements of high wear resistance scenarios. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a wear-resistant coating for color-coated aluminum sheets and strips and its preparation method, so as to solve one or more problems in the prior art.

[0005] To achieve the above objectives, the first technical solution of the present invention is as follows: A wear-resistant coating for color-coated aluminum sheets and strips includes a primer and a topcoat. The primer comprises, by weight, 45-55 parts epoxy-modified silicone resin, 8-10 parts nano-alumina, 5-7 parts nano-zirconia, 25-35 parts mixed solvent, and 2.6-3.9 parts additives. The topcoat comprises, by weight, 40-50 parts polyester-modified polyamide resin, 7-9 parts graphene-PTFE composite microspheres, 10-14 parts titanium dioxide, 0.5-1 part weather-resistant additive, 5-7 parts hexamethylene diisocyanate trimer curing agent, and 20-30 parts mixed solvent. The graphene-PTFE composite microspheres have a particle size of 5-10 μm, and the hexamethylene diisocyanate trimer curing agent has an isocyanate content of 20-22%.

[0006] Specifically, the mixed solvent in the base coating includes 15-25 parts xylene and 8-12 parts butyl acetate by weight, and the additives include 1.5-2 parts dispersant, 0.3-0.7 parts defoamer and 0.8-1.2 parts leveling agent. The dispersant is a polycarboxylate dispersant, the defoamer is an organosilicon defoamer, and the leveling agent is a polyether-modified siloxane leveling agent.

[0007] Specifically, the graphene-polytetrafluoroethylene composite microspheres in the surface coating are prepared by weight of 0.4-0.6 parts of graphene oxide, 14-16 parts of polytetrafluoroethylene emulsion with a solid content of 50%, 78-82 parts of deionized water, and 0.3-0.5 parts of hexadecyltrimethylammonium bromide. The graphene-polytetrafluoroethylene composite microspheres have a moisture content ≤0.3% after drying, and the drying conditions are a temperature of 55-65℃, a vacuum degree of -0.10 to -0.08MPa, and a time of 10-14h.

[0008] Specifically, the weather-resistant additives in the topcoat include 0.4-0.6 parts by weight of ultraviolet absorber and 0.2-0.4 parts by weight of hindered amine light stabilizer. The ultraviolet absorber is benzotriazole ultraviolet absorber 327, and the hindered amine light stabilizer is hindered amine light stabilizer 770.

[0009] To ensure the completeness of the technical effect, this invention also includes a second technical solution that is nested and coordinated with the first solution, which is a method for preparing wear-resistant coatings, based on the first technical solution for wear-resistant coatings for color-coated aluminum sheets and strips: (1) Substrate pretreatment: Degreasing, pickling and phytic acid-silane composite passivation are performed in sequence. The phytic acid-silane composite passivation solution includes 15-17 parts of phytic acid, 4-6 parts of γ-glycidyl etheroxypropyltrimethoxysilane, 970-980 parts of deionized water and 3-5 parts of acetic acid by mass, and the pH is 4.0-5.0.

[0010] (2) Preparation of the base coating: Mix the mixed solvent, additives and nanofillers, stir at 1500-2000 r / min for 30-40 min, add epoxy modified silicone resin, stir at 500-600 r / min for 20-30 min to obtain the base coating.

[0011] (3) Preparation of topcoat: Prepare graphene-polytetrafluoroethylene composite microspheres. Mix the mixed solvent, additives, titanium dioxide and the composite microspheres, stir at 1500-2000 r / min for 40-50 min, add polyester modified polyamide resin and hexamethylene diisocyanate trimer curing agent, stir at 600-700 r / min for 15-25 min to obtain the topcoat.

[0012] (4) Coating and curing: Apply the base coat to the pretreated substrate, and apply the top coat after pre-curing. Control the coating environment temperature at 23-27℃ and the relative humidity at 30-50%. The total dry film thickness after curing is 35-45μm, and wear-resistant coating is obtained.

[0013] Specifically, in step (1), the degreasing process uses a mixture of 18-22 parts by weight of sodium silicate, 18-22 parts by weight of sodium carbonate, 4-6 parts by weight of sodium dodecylbenzenesulfonate, and 220-240 parts by weight of deionized water. The degreasing temperature is 53-57℃, the pressure is 0.2-0.3MPa, and the time is 55-65s. The pickling process uses a mixture of nitric acid and hydrofluoric acid, wherein the mass concentration of nitric acid is 7-9% and the mass concentration of hydrofluoric acid is 0.2-0.3%. The pickling temperature is 20-30℃ and the time is 25-35s.

[0014] Specifically, the nanofiller in step (2) is nano alumina and nano zirconium oxide in a mass ratio of 3:2. After mixing, it is milled with zirconium oxide media at a milling speed of 2000-2500 r / min for 50-70 min. The particle size of the milling media is 0.8-1.0 mm and the filling rate is 65-75%. The particle size D50 after milling is ≤2 μm.

[0015] Specifically, the preparation of the graphene-polytetrafluoroethylene composite microspheres in step (3) includes: mixing deionized water and hexadecyltrimethylammonium bromide, stirring at 800-1000 r / min for 10-15 min, adding graphene oxide, sonicating at 600-800 W power and 20-25 kHz frequency for 50-70 min, adding polytetrafluoroethylene emulsion with a solid content of 50% by mass, keeping warm in a water bath at 80-85℃ for 2-3 h, centrifuging and washing 2-3 times, drying and pulverizing through a 400 mesh sieve.

[0016] Specifically, in step (4), the wet film thickness of the base coating is 13-17 μm, the pre-curing temperature is 155-165℃, and the time is 15-17 s. The wet film thickness of the top coating is 18-22 μm, the curing temperature is 175-185℃, and the time is 23-25 ​​s.

[0017] Specifically, the coating environment described in step (4) also includes an electrostatic elimination device with an ion balance of ±5-±10V and an hourly electrostatic value of ≤5kV.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (i) By combining epoxy-modified silicone resin with nano-alumina and nano-zirconia in the base coating, the high adhesion of the resin and the rigid support of the nano-ceramic particles are used to construct the wear-resistant skeleton of the bottom layer; in the top coating, polyester-modified polyamide resin is combined with graphene-polytetrafluoroethylene composite microspheres and hexamethylene diisocyanate trimer curing agent. Relying on the flexibility of the resin, the lubrication and friction reduction properties of the composite microspheres and the cross-linking strengthening effect of the curing agent, a surface wear-resistant system is formed. Through the synergistic gradient structure of "rigid support of the bottom layer and flexible wear resistance of the surface layer", the overall wear resistance of the coating is improved.

[0019] (ii) The substrate pretreatment adopts a phytic acid-silane composite passivation process. Phytic acid forms a chelate film with the metal substrate, and silane provides molecular-level cross-linking sites. The two chemically bond with the polar groups of epoxy-modified silicone resin in the base coating. At the same time, nano-alumina and nano-zirconia fill the micro-pits on the substrate surface. Through the interface synergy of "passivation layer chemical anchoring - nanoparticle physical filling", the interface defects between the coating and the substrate are reduced, and the coating adhesion and anti-peel performance are improved.

[0020] (III) In the topcoat, the graphene-polytetrafluoroethylene composite microspheres are structurally combined with graphene sheets and polytetrafluoroethylene microspheres. The two-dimensional sheets of graphene enhance the mechanical strength of the microspheres, while the low surface energy of polytetrafluoroethylene gives the microspheres lubricating properties. The two form a bifunctional dispersion system of "reinforcing phase-lubricating phase" in the topcoat resin. It can both transfer stress through the graphene sheets to resist frictional loads and reduce the surface friction coefficient through the polytetrafluoroethylene microspheres, thus synergistically improving the wear resistance and durability of the coating.

[0021] (iv) In the preparation process, the nanofiller of the bottom coating is dispersed by zirconium oxide medium sand milling to ensure that the nano alumina and nano zirconium oxide are uniformly distributed to avoid agglomeration; the coating and curing adopts a step-by-step process of pre-curing the bottom coating and curing the top coating. The pre-curing controls the partial cross-linking of the bottom coating to adapt to the top coating coating, avoiding stress concentration caused by rapid and complete cross-linking inside the coating. Through the synergistic process of "uniform dispersion-step curing", the microstructure density and macroscopic mechanical stability of the coating are improved. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to exemplary embodiments.

[0023] In the field of color-coated aluminum sheet and strip coatings, to meet the need for improved wear resistance, the industry typically adopts a two-layer coating system consisting of a base coat and a top coat. The base coat usually uses epoxy resin or polyester resin as the main film-forming material, combined with inorganic wear-resistant fillers such as alumina and silica. This aims to improve the wear resistance of the underlying layer through the adhesion of the resin and the rigidity of the inorganic fillers. The top coat typically uses polyester resin or fluorocarbon resin, with added pigments such as titanium dioxide and common wear-resistant additives (such as glass microspheres and conventional silica particles) to balance surface decoration and initial wear resistance.

[0024] However, such conventional solutions have significant shortcomings: on the one hand, the simple mixing of a single resin and conventional inorganic fillers in the base coating makes it difficult to form a structurally stable rigid support skeleton, resulting in limited wear resistance of the underlying layer; on the other hand, the mechanical strength and lubrication performance of traditional wear-resistant fillers in the top coating are not well matched, and under long-term friction, filler detachment or resin matrix wear is likely to occur, resulting in poor overall wear resistance of the coating. Especially in high-frequency friction or complex environments, the coating is prone to scratches, exposure of the substrate, or even peeling, which cannot meet the usage requirements of high wear resistance scenarios.

[0025] This invention relates to a wear-resistant coating for color-coated aluminum sheets and strips and its preparation method. The aim is to improve the wear resistance of the surface coating of color-coated aluminum sheets and strips by optimizing the coating system composition and preparation process, thereby meeting the long-term wear-resistant reliability requirements of materials in fields such as construction, home appliances, and transportation. The technical solution of this invention is described in detail below with reference to specific process steps.

[0026] I. Substrate Pretreatment To ensure a tight bond between the coating and the aluminum sheet / strip substrate, the substrate needs to undergo multiple pretreatment steps, including degreasing, pickling, and composite passivation.

[0027] The degreasing treatment uses an alkaline degreasing agent, the formulation of which, by weight, includes 18-22 parts sodium silicate, 18-22 parts sodium carbonate, 4-6 parts sodium dodecylbenzenesulfonate, and 220-240 parts deionized water. During treatment, the aluminum strip is immersed in the degreasing agent, with the temperature controlled at 53-57℃, the pressure at 0.2-0.3 MPa, and the treatment time at 55-65 seconds, to remove grease, dirt, and other organic impurities from the substrate surface, thus avoiding interference with subsequent coating adhesion.

[0028] Pickling treatment uses a mixed acid solution of nitric acid and hydrofluoric acid, where the mass concentration of nitric acid is 7-9% and the mass concentration of hydrofluoric acid is 0.2-0.3%. The degreased substrate is placed in this mixed acid solution and treated at 20-30℃ for 25-35 seconds. The slight etching effect of the acid solution removes the oxide scale and residual impurities on the surface of the substrate, while forming a micro-rough surface, which enhances the mechanical adhesion between the coating and the substrate.

[0029] Phytic acid-silane composite passivation is a key step in improving interfacial bonding strength. The passivation solution, by weight, comprises 15-17 parts phytic acid, 4-6 parts γ-glycidyl etheroxypropyltrimethoxysilane, 970-980 parts deionized water, and 3-5 parts acetic acid. The pH of the passivation solution is adjusted to 4.0-5.0 using acetic acid. During treatment, the acid-washed substrate is immersed in the passivation solution. The polyhydroxyl groups in the phytic acid molecules form a stable chelate film with the metal ions on the surface of the metal substrate. The silane molecules, through hydrolysis, generate silanol groups that cross-link with the substrate surface and phytic acid molecules, constructing a composite passivation layer on the substrate surface that combines chemical anchoring and physical barrier functions. This effectively improves the adhesion and peel resistance of subsequent coatings.

[0030] II. Preparation of the base coating The primer layer, as the bottom layer of the coating system, mainly serves as a rigid support and facilitates substrate adhesion. Its formulation and preparation process are as follows: The primer coating formulation, by weight, comprises: 45-55 parts epoxy-modified silicone resin, 8-10 parts nano-alumina, 5-7 parts nano-zirconia, 25-35 parts mixed solvent, and 2.6-3.9 parts additives. The epoxy-modified silicone resin combines the high adhesion of epoxy resin with the high temperature resistance and chemical resistance of silicone resin, providing a basic film-forming framework for the primer coating. The nano-alumina and nano-zirconia (in a 3:2 mass ratio) act as inorganic wear-resistant fillers, enhancing the hardness and scratch resistance of the primer coating through a particle reinforcement effect. The mixed solvent consists of 15-25 parts xylene and 8-12 parts butyl acetate, used to adjust the viscosity of the base coating to suit the coating process; the additives include 1.5-2 parts dispersant (polycarboxylate, used to promote uniform dispersion of nanofillers), 0.3-0.7 parts defoamer (organosilicon, to eliminate bubbles generated during preparation) and 0.8-1.2 parts leveling agent (polyether modified siloxane, to improve coating leveling to avoid defects such as pinholes and orange peel).

[0031] The specific preparation process of the primer coating is as follows: First, the mixed solvent, additives, nano-alumina, and nano-zirconia are mixed and placed in a high-speed dispersion device, stirred at 1500-2000 r / min for 30-40 min to allow the additives to fully play their role and initially disperse the nanofillers; then, the mixture is transferred to a sand mill, using zirconia media with a particle size of 0.8-1.0 mm (filling rate 65-75%), and sand milled at 2000-2500 r / min for 50-70 min to ensure that the particle size D50 of the nanofillers is ≤2μm, avoiding uneven coating performance caused by particle agglomeration; finally, epoxy-modified silicone resin is added to the sand-milled dispersion, and stirred at 500-600 r / min for 20-30 min to fully mix the resin with the dispersion system, obtaining a uniform and stable primer coating.

[0032] III. Preparation of Topcoat As the surface structure of the coating system, the topcoat layer needs to possess both wear resistance and weather resistance. Its formulation design and the preparation of the core functional microspheres are the key to this invention, as detailed below: (a) Topcoat Formulation The topcoat formulation, by weight, includes: 40-50 parts polyester-modified polyamide resin, 7-9 parts graphene-PTFE composite microspheres, 10-14 parts titanium dioxide, 0.5-1 parts weather-resistant additive, 5-7 parts hexamethylene diisocyanate trimer curing agent, and 20-30 parts mixed solvent. Among them, polyester-modified polyamide resin has good flexibility and weather resistance, which can buffer frictional stress and resist environmental aging; titanium dioxide, as a white pigment, provides hiding power and decoration; the weather-resistant additive is composed of ultraviolet absorber (benzotriazole 327, 0.4-0.6 parts) and hindered amine light stabilizer (hindered amine 770, 0.2-0.4 parts), which synergistically delay coating aging by absorbing ultraviolet rays and capturing free radicals; hexamethylene diisocyanate trimer curing agent (isocyanate content 20-22%) can undergo cross-linking reaction with the hydroxyl groups in polyester-modified polyamide resin to form a three-dimensional network structure, thereby improving the mechanical strength and chemical stability of the coating; the mixed solvent is used to adjust the viscosity of the topcoat, and its composition is similar to that of the bottomcoat mixed solvent. The ratio of xylene to butyl acetate can be adjusted according to the coating process requirements.

[0033] (II) Preparation of graphene-polytetrafluoroethylene composite microspheres Graphene-PTFE composite microspheres are the core functional component for achieving high wear resistance in surface coatings. They combine the mechanical reinforcing properties of graphene with the low-friction characteristics of PTFE. The specific preparation steps are as follows: Dispersion preparation: By mass, 78-82 parts of deionized water and 0.3-0.5 parts of hexadecyltrimethylammonium bromide are added to a reaction vessel and stirred at 800-1000 r / min for 10-15 min to completely dissolve the hexadecyltrimethylammonium bromide and form a uniformly dispersed surfactant solution; then 0.4-0.6 parts of graphene oxide are added and ultrasonically treated at 600-800W power and 20-25kHz frequency for 50-70 min. The cavitation effect of ultrasound is used to peel off the graphene oxide sheets and uniformly disperse them in water to form a stable graphene oxide dispersion.

[0034] Construction of composite microspheres: Slowly add 14-16 parts of polytetrafluoroethylene emulsion (50% by weight solid content) to the above dispersion. After the addition is completed, place the reaction vessel in a water bath at 80-85℃ and keep it warm for 2-3 hours. Under the action of surfactant, the polytetrafluoroethylene particles self-assemble with the graphene oxide sheets to form a composite microsphere structure with polytetrafluoroethylene as the core and graphene as the shell.

[0035] Post-processing: The reaction product was centrifuged (centrifugation speed 3000-4000 r / min, time 10-15 min). The obtained solid was washed with deionized water 2-3 times to remove residual surfactant. Then it was dried at 55-65℃ and vacuum degree -0.10 to -0.08 MPa for 10-14 h (controlling the moisture content ≤0.3%). After drying, it was mechanically crushed and passed through a 400-mesh sieve to obtain graphene-polytetrafluoroethylene composite microspheres with a particle size of 5-10 μm.

[0036] (III) Topcoat preparation process The mixed solvent, weather-resistant additive, titanium dioxide, and the graphene-polytetrafluoroethylene composite microspheres prepared above are added to a dispersion device and stirred at 1500-2000 r / min for 40-50 min to fully disperse the solid particles. Then, polyester-modified polyamide resin and hexamethylene diisocyanate trimer curing agent are added and stirred at 600-700 r / min for 15-25 min to ensure that the resin and curing agent are uniformly mixed and pre-crosslinked, thus obtaining a topcoat that can be directly applied.

[0037] IV. Coating and Curing Coating and curing are crucial steps in forming a complete coating system from the primer and topcoat. It is essential to strictly control the coating parameters and curing conditions to ensure stable coating performance.

[0038] The coating environment must meet the requirements of a temperature of 23-27℃ and a relative humidity of 30-50%, and be equipped with an electrostatic elimination device (ion balance ±5-±10V, static electricity value monitored ≤5kV per hour) to avoid coating defects (such as pinholes and craters) caused by static electricity.

[0039] The base coat is applied by roller coating or spraying, with the wet film thickness controlled at 13-17μm. After coating, a pre-curing treatment is performed: baking at 155-165℃ for 15-17s to partially cross-link the base coat and form a bottom layer structure with a certain strength. This not only avoids the dissolution of the bottom layer during the subsequent top coat application, but also provides a good adhesion substrate for the top coat.

[0040] The topcoat is applied after the base coat has pre-cured, using either roller coating or spraying, with a wet film thickness controlled at 18-22 μm. It is then cured at 175-185℃ for 23-25 ​​seconds to allow the resin and hardener in the topcoat to fully cross-link, forming a dense, wear-resistant surface structure. The final total dry film thickness is controlled at 35-45 μm. Through the synergistic effect of the rigid support of the base coat and the flexible wear resistance of the topcoat, the overall coating achieves high wear resistance.

[0041] Through the above-mentioned substrate pretreatment, base coating preparation, top coating preparation and coating curing process, a color-coated aluminum strip with excellent wear resistance can be obtained. The bottom layer is constructed with epoxy-modified silicone resin and nano-ceramic particles to form a rigid support skeleton, and the surface layer relies on the "enhancement-lubrication" synergistic effect and cross-linked network structure of graphene-polytetrafluoroethylene composite microspheres to achieve a significant improvement in the wear resistance and durability of the coating, which can meet the long-term use requirements in high friction environments.

[0042] To verify the synergistic effects of the nanofiller ratio in the base coating, the amount of composite microspheres added in the top coating, and the curing temperature on the coating performance of color-coated aluminum sheets and strips in this scheme, a comparative experiment was designed using the controlled variable method. Based on current national standards, the wear resistance, adhesion, and salt spray resistance of the coatings under different parameter combinations were systematically evaluated. The specific experimental design is as follows: I. Testing Standards and Methods Abrasion resistance test: According to ASTM D4060-2021 "Taber wear method", CS-10 grinding wheel, 1kg load, 1000 wear cycles, record the Taber wear amount (mg / 1000 cycles).

[0043] Adhesion test: According to GB / T 5210-2020 "Paints and Varnishes - Pull-off test" (currently valid), a pull-out head with a diameter of 50 mm is used to pull the coating at a uniform speed of 10 mm / min to determine the maximum force (unit: MPa) that the coating peels off from the substrate.

[0044] Salt spray resistance test: According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test" (currently valid), a 5% NaCl solution was used, pH 6.5-7.2, temperature 35℃, and continuous spraying was performed. The time (unit: hours) when 5% rust spots appeared on the coating was recorded.

[0045] Experimental Design 2.1, (1) Sample preparation control Uniform substrate: All use 3003 series aluminum alloy sheets (0.5mm thickness, 300mm×300mm size), and the passivation film weight is tested after pretreatment (80-120mg / m³). 2 ); Coating preparation control: After sanding, the particle size of both the primer and topcoat was measured using a laser particle size analyzer (Mastersizer3000). The primer D50≤2μm and the topcoat D90≤8μm can be applied. Coating environment control: The temperature and humidity are controlled by a constant temperature and humidity unit at 25±2℃ and 45-55%, respectively. Static electricity elimination device (ion balance ±5V) is used, and parameters are recorded every hour.

[0046] (2) Detection operation details Taber wear test: After the sample is fixed, it is pre-ground 50 times with a CS-10 grinding wheel (to remove the surface floating layer), and then formally worn for 1000 times. After each wear, it is weighed with a balance with an accuracy of 0.1mg to calculate the wear amount. Pull-out adhesion test: The pull-out head was bonded to the coating with epoxy adhesive (shear strength ≥20MPa), and tested after curing for 24 hours. The average value of 3 points was taken. Salt spray resistance test: The sample was placed at a 15° angle and sprayed at a pressure of 0.07 MPa. The corrosion of the coating was observed daily, and the time when 5% of the corrosion spots appeared was recorded.

[0047] 2.2 Variable Settings (based on the technical parameter limits of this solution): Variable 1: The ratio of nanofiller in the base coating (nano alumina: nano zirconium oxide, mass ratio), with a limited range of 1.14:1 to 2:1; Variable 2: The amount of composite microspheres added to the surface coating (graphene-PTFE composite microspheres, parts by mass), limited to 7-9 parts; Variable 3: Curing temperature (topcoat curing stage, °C), limited range 175~185 °C.

[0048] Experimental group division (10 groups, each group had 3 parallel experiments and the average value was taken): Examples 1 to 5: All variables are within the specified range; Comparative examples one through four: a single variable exceeds the limit, the rest are consistent with the regular group; Comparative Example 5: Using existing technology (1:1 filler ratio for the base coating, no composite microspheres, curing temperature 160℃).

[0049] III. Experimental Data and Weighted Scoring Based on the benchmark index as the full score, the comprehensive score is calculated according to the following weighting: "Abrasion resistance 40% + Adhesion 30% + Salt spray resistance 30%", as follows:

[0050] Experimental plan: Example 1 1. Raw material usage (all are parts by mass, and the total of all components in the system meets the proportional coordination requirements) Base coating system (total mass parts 100): 45 parts epoxy-modified silicone resin, 9 parts nano-alumina (particle size 50nm, hydrophilic), 6 parts nano-zirconia (particle size 30nm, hydrophilic), 25 parts xylene, 12 parts butyl acetate, 1.5 parts polycarboxylate dispersant, 0.5 parts silicone defoamer, 1 part polyether-modified siloxane leveling agent; Top coating system (total mass parts 100): 45 parts polyester-modified polyamide resin, 7 parts graphene-PTFE composite microspheres (particle size 5-8μm, moisture content 0.2%), 10 parts titanium dioxide (model R902), benzotriazole ultraviolet absorber (U V-327) 0.4 parts, hindered amine light stabilizer (HALS-770) 0.2 parts, hexamethylene diisocyanate trimer curing agent 5 parts (isocyanate content 21%), xylene 20 parts, butyl acetate 12.4 parts; Substrate pretreatment agents: degreasing agent (sodium silicate 20 parts, sodium carbonate 20 parts, sodium dodecylbenzenesulfonate 5 parts, deionized water 230 parts), pickling solution (nitric acid 8%, hydrofluoric acid 0.25%, deionized water 91.75%), phytic acid-silane composite passivation solution (phytic acid 16 parts, γ-glycidyl etheroxypropyltrimethoxysilane 5 parts, deionized water 975 parts, acetic acid 4 parts, pH 4.5).

[0051] 2. Preparation method (1) Substrate pretreatment: Select 3003 series aluminum alloy plate (thickness 0.5mm, size 300mm×300mm), firstly perform degreasing treatment - immerse the substrate in degreasing agent, control the temperature 55℃, pressure 0.2MPa, treatment time 60s, to remove surface grease and dirt; then perform pickling treatment - place the degreased substrate in pickling solution, temperature 25℃, treatment time 30s, to remove surface oxide scale and form micro-rough surface; finally perform phytic acid-silane composite passivation treatment - use roller coating to coat the passivation solution on the substrate surface, wet film thickness 7μm, then dry at 60℃ for 90s, forming a film weight of 100mg / m 2 The passivation film.

[0052] (2) Preparation of the base coating: First, xylene and butyl acetate were added to the dispersion tank and stirred at 600 r / min for 5 min to make the solvent mix evenly. Then, polycarboxylate dispersant, organosilicon defoamer and polyether modified siloxane leveling agent were added, and the speed was adjusted to 800 r / min and stirred for 10 min until the additives were completely dissolved. Next, nano alumina and nano zirconium oxide were added, and the speed was increased to 1800 r / min and stirred for 35 min for preliminary dispersion. Then, the mixture was transferred to a sand mill, and zirconium oxide media with a particle size of 0.8 mm (filling rate of 70%) was selected and sand milled at 2000 r / min for 60 min to ensure that the particle size of the nano filler D50 ≤ 2 μm. Finally, epoxy modified organosilicon resin was added, the speed was adjusted to 550 r / min and stirred for 25 min to obtain a uniform and stable base coating.

[0053] (3) Preparation of topcoat: First, xylene and butyl acetate were added to the dispersion tank and stirred at 600 r / min for 5 min; then UV-327 and HALS-770 were added, the speed was adjusted to 800 r / min, and stirred for 10 min until the weather-resistant additives were dissolved; then titanium dioxide and graphene-polytetrafluoroethylene composite microspheres were added, the speed was increased to 1800 r / min, and stirred for 45 min; then the mixture was transferred to a sand mill and sand milled at 1800 r / min for 45 min to ensure that the particle size D90 of the system was ≤8 μm; finally, polyester modified polyamide resin and hexamethylene diisocyanate trimer curing agent were added, and stirred at 600 r / min for 15 min under nitrogen protection to obtain the topcoat.

[0054] (4) Coating and curing: The base coating is applied to the surface of the pretreated substrate by roller coating, and the wet film thickness is controlled at 15μm. Then the substrate is sent into the oven and pre-cured at 160℃ for 16s. After pre-curing, it is cooled to room temperature and then the top coating is applied by roller coating, and the wet film thickness is controlled at 20μm. Finally, the substrate is sent into the oven and cured at 175℃ for 24s. After curing, it is cooled to below 40℃ by water-cooled roller to obtain a color-coated aluminum strip with a total dry film thickness of 38μm.

[0055] 3. Performance Results The coating exhibits good abrasion resistance, with a Taber abrasion rate of 0.68 mg / 1000 cycles, adhesion of 6.8 MPa, and salt spray resistance of 650 hours, effectively resisting surface damage caused by daily friction. It also demonstrates strong adhesion, making it less prone to coating peeling during tensile testing. Furthermore, its excellent salt spray resistance allows it to maintain surface integrity for extended periods in corrosive environments, meeting the needs of medium- to high-abrasion-resistance applications.

[0056] Example 2 1. Core Variables (Different from Example 1) Base coating: 9 parts nano-Al2O3, 6 parts nano-ZrO2 (mass ratio 3:2) Topcoat: 8 parts graphene-PTFE composite microspheres, curing temperature 180℃ 2. Performance Results The coating exhibits the best overall performance, with a Taber abrasion rate of 0.52 mg / 1000 cycles, an adhesion of 7.5 MPa, and a salt spray resistance of 780 hours. It maintains surface integrity even under high-frequency friction. It has extremely strong adhesion and can withstand high tensile loads. It also has excellent salt spray resistance and shows no significant rust in long-term corrosive environments, meeting the requirements for high wear resistance and high protection scenarios.

[0057] Example 3 1. Core Variables (Different from Example 1) Base coating: 10 parts nano-Al2O3, 5 parts nano-ZrO2 (mass ratio 2:1) Topcoat: 9 parts graphene-PTFE composite microspheres, curing temperature 185℃ 2. Performance Results The coating exhibits good wear resistance, with a Taber wear rate of 0.58 mg / 1000 cycles, an adhesion of 7.2 MPa, and a salt spray resistance of 720 hours. No obvious scratches are observed under normal friction conditions. It also demonstrates strong adhesion, with no peeling under normal external forces. Furthermore, it exhibits excellent salt spray resistance, maintaining its integrity for a long time in moderately corrosive environments, thus meeting the requirements for medium-to-high wear resistance scenarios.

[0058] Example 4 1. Core Variables (Different from Example 1) Base coating: 9 parts nano-Al2O3, 6 parts nano-ZrO2 (mass ratio 3:2) Topcoat: 8 parts graphene-PTFE composite microspheres, curing temperature 185℃ 2. Performance Results The coating exhibits good wear resistance, with a Taber wear rate of 0.61 mg / 1000 cycles, an adhesion of 7.0 MPa, and a salt spray resistance of 700 hours. It shows no damage from daily friction. The coating has strong adhesion and remains stable under normal external forces. It also demonstrates good salt spray resistance and excellent surface condition in mildly corrosive environments, meeting the requirements of typical wear-resistant scenarios.

[0059] Example 5 1. Core Variables (Different from Example 1) Base coating: 9 parts nano-Al2O3, 5 parts nano-ZrO2 (mass ratio 1.8:1) Topcoat: 7 parts graphene-PTFE composite microspheres, curing temperature 175℃ 2. Performance Results The coating's abrasion resistance meets general requirements, with a Taber abrasion rate of 0.63 mg / 1000 cycles, adhesion of 6.7 MPa, and salt spray resistance of 680.50 hours. It exhibits no significant wear under light to moderate friction. The coating has good adhesion, and there is no peeling during normal use. Its salt spray resistance meets basic protection requirements, and the surface remains intact in mildly corrosive environments.

[0060] Comparative Example 1 1. Core Variables (Different from Example 1) Base coating: 7 parts nano-Al2O3 and 7 parts nano-ZrO2 (mass ratio 1:1, exceeding the conventional range). Topcoat: 8 parts graphene-PTFE composite microspheres, curing temperature 180℃ 2. Performance Results The coating exhibits reduced abrasion resistance, with a Taber abrasion rate of 0.95 mg / 1000 cycles, adhesion of 5.5 MPa, and salt spray resistance of 530 hours. It is prone to scratches under moderate friction. The adhesion is weakened, and there is a risk of peeling under external force. The salt spray resistance is reduced, and the surface remains intact for a shorter time in corrosive environments, only meeting the requirements for mild abrasion resistance and low protection scenarios.

[0061] Comparative Example 2 1. Core Variables (Different from Example 1) Base coating: 9 parts nano-Al2O3, 6 parts nano-ZrO2 (mass ratio 3:2) Topcoat: 10 parts graphene-PTFE composite microspheres (outside the conventional range), curing temperature 180℃ 2. Performance Results The coating exhibits reduced abrasion resistance, with a Taber abrasion rate of 0.88 mg / 1000 cycles, adhesion of 5.8 MPa, and salt spray resistance of 590 hours. Microsphere agglomeration exacerbates localized frictional damage. Adhesion is slightly reduced, and there are weak areas within the coating. Salt spray resistance is weakened, and corrosive media can easily penetrate the agglomerated areas, only meeting the basic requirements for low abrasion resistance scenarios.

[0062] Comparative Example 3 1. Core Variables (Different from Example 1) Base coating: 9 parts nano-Al2O3, 6 parts nano-ZrO2 (mass ratio 3:2) Topcoat: 8 parts graphene-PTFE composite microspheres, curing temperature 165℃ (outside the conventional range) 2. Performance Results The coating exhibits decreased abrasion resistance, with a Taber abrasion amount of 0.92 mg / 1000 cycles, adhesion of 5.2 MPa, and salt spray resistance of 550 hours. Insufficient cross-linking leads to low hardness and easy wear. The adhesion is significantly weakened, and the bonding strength between the coating and the substrate is insufficient. The salt spray resistance is poor, and the coating density is insufficient, meaning it can only be used for a short period in a dry, non-corrosive environment.

[0063] Comparative Example 4 1. Core Variables (Different from Example 1) Base coating: 9 parts nano-Al2O3, 6 parts nano-ZrO2 (mass ratio 3:2) Topcoat: 8 parts graphene-PTFE composite microspheres, curing temperature 195℃ (outside the conventional range) 2. Performance Results The coating's abrasion resistance decreased, with a Taber abrasion of 0.90 mg / 1000 cycles, adhesion of 5.0 MPa, and salt spray resistance of 560 hours. Excessive cross-linking resulted in low toughness and easy cracking. The adhesion was significantly weakened, and the coating had high internal stress, making it prone to cracking and peeling. The salt spray resistance decreased, and the resin pyrolysis damaged the structure, failing to meet the requirements for long-term use.

[0064] Comparative Example 5 1. Differences in raw material usage and processing techniques The base coating system consists of 50 parts of ordinary filler (talc and calcium carbonate in a 1:1 mass ratio), 40 parts of epoxy-modified silicone resin, 8 parts of xylene, and 2 parts of butyl acetate, without nano-alumina or nano-zirconia. Topcoat system: 90 parts polyester modified polyamide resin, 5 parts hexamethylene diisocyanate trimer curing agent, 3 parts xylene, 2 parts butyl acetate, without graphene-polytetrafluoroethylene composite microspheres and weather-resistant additives; Substrate pretreatment: Phosphating is used only (the phosphating solution is a zinc-based phosphating agent, the treatment temperature is 40℃, and the time is 10min), without the phytic acid-silane composite passivation step; Curing process: The curing temperature of the topcoat is adjusted to 160℃.

[0065] 2. Preparation method (only briefly describe the different steps) The substrate pretreatment only involves degreasing, pickling, and phosphating; the preparation of the base coating does not require a sand milling step, but is simply mixed uniformly by stirring at 500 r / min for 30 min; the preparation of the top coating does not involve the addition of weather-resistant additives or composite microspheres, and is directly applied after mixing; after coating, it is cured at 160℃ for 20 min.

[0066] Performance Results The coating has poor wear resistance, with a Taber wear rate of 1.52 mg / 1000 cycles, an adhesion of 4.2 MPa, and a salt spray resistance of 410 hours. Even under light friction conditions, it is prone to obvious scratches and wear. The adhesion is insufficient, and the coating may peel off due to slight external force. The salt spray resistance is weak, and surface corrosion occurs in a short time. It can only meet the needs of simple scenarios where there is no need for wear resistance and the surface is dry and non-corrosive, which is far inferior to the performance level of this technical solution.

[0067] Experimental results: Table 1. Material Performance Test Results

[0068] IV. Experimental Conclusions The wear resistance, adhesion and salt spray resistance of Examples 1 to 5 are significantly better than those of Comparative Examples 1 to 5. Among them, Example 2 has the best overall performance, which verifies that the synergistic optimization of the nanofiller ratio of the bottom coating, the amount of composite microspheres added to the top coating and the curing temperature within the specified range can significantly improve the coating performance.

[0069] To further clarify the essential reasons for the differences in coating performance in this scheme, it is necessary to analyze the control mechanism of the macroscopic performance of the coating by the filler ratio of the base coating, the amount of composite microspheres added to the top coating, and the curing temperature from the perspective of material microstructure and molecular interaction, combined with the performance trends presented by the experimental data of each group. In this way, the core logic of the performance advantage of the conventional group can be clarified, providing theoretical support for the practicality and reliability of the technical solution.

[0070] From a molecular perspective, the ratio of nano-alumina to nano-zirconia in the base coating affects the coating's mechanical properties through a molecular-level synergy of "rigid skeleton - tough buffer": the hydroxyl groups on the surface of nano-alumina can form stable hydrogen bonds with the epoxy groups in epoxy-modified silicone resin molecules, and its high hardness constructs a rigid support network at the bottom layer, enabling effective transfer of frictional loads; nano-zirconia, with its tetragonal-monoclinic phase transformation characteristics, absorbs energy through volume expansion when subjected to external forces, alleviating stress concentration between molecular chains and preventing crack propagation. When the two are within a specific ratio range, the "point-to-surface" load transfer of alumina and the "stress buffering" of zirconia form optimal synergy, strengthening the wear-resistant foundation of the base layer; if the ratio deviates from this range, either due to insufficient alumina content leading to a weak rigid skeleton, or due to insufficient zirconia content failing to effectively buffer stress, the supporting effect of the base coating on the upper coating will be weakened, ultimately leading to a decrease in overall wear resistance.

[0071] The amount of graphene-PTFE composite microspheres added to the topcoat directly affects their dispersion and functional network construction in the resin matrix: the two-dimensional sheet structure of graphene forms a continuous physical barrier in the resin through π-π stacking and van der Waals forces, hindering the concentration of local loads during friction; the PTFE molecular chain is composed of -CF2-CF2- repeating units, and the high electronegativity of fluorine atoms results in extremely low intermolecular forces, giving the coating excellent self-lubricating properties. When the amount of microspheres added is appropriate, the graphene sheets uniformly coat the surface of the PTFE microspheres to form a "core-shell" structure. The PTFE core reduces the coefficient of friction through low surface energy, while the graphene shell constructs a three-dimensional reinforcing network through sheet overlap, dispersing the friction load to a larger area; if the amount added is too high, the microspheres are prone to agglomeration due to intermolecular hydrophobic interactions, forming stress-weak areas inside the coating. During friction, the microspheres fall off, forming pores, which in turn destroys the continuous wear-resistant structure of the coating, leading to a decline in wear resistance.

[0072] The effect of curing temperature on coating performance is reflected in the progress of molecular crosslinking reaction: the hydroxyl groups of the polyester-modified polyamide resin in the topcoat and the isocyanate groups of the hexamethylene diisocyanate trimer need to undergo an addition reaction at a specific temperature to form stable urethane bonds. If the temperature is too low, the activation energy is insufficient, the collision frequency between isocyanate and hydroxyl groups decreases, the degree of crosslinking is insufficient, and a large number of unreacted free end groups exist between molecular chains, increasing internal defects in the coating and reducing salt spray resistance and adhesion. If the temperature is too high, isocyanate is prone to self-polymerization to form urea or biuret, leading to increased branching of the molecular chains. Simultaneously, the ester bonds in the resin matrix may break due to thermal oxidation, increasing internal stress and reducing toughness in the coating, thus affecting adhesion and wear resistance. Only within a suitable temperature range, the crosslinking reaction is complete without significant side reactions, the molecular chains are arranged in a regular three-dimensional network, and the bond energy and chain segment mobility are balanced. The coating possesses both high density to hinder the penetration of corrosive media and a certain degree of molecular chain flexibility to alleviate frictional stress, ultimately achieving optimized overall performance.

[0073] The technical features described above can be combined in any way. For the sake of brevity, not all possible combinations of the technical features described above are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A wear-resistant coating for a color-coated aluminum sheet, characterized by: The coating includes a base coat and a top coat; the base coat includes, by mass fraction, 45-55 parts of an epoxy-modified silicone resin, 8-10 parts of nano-alumina, 5-7 parts of nano-zirconia, 25-35 parts of a mixed solvent, and 2.6-3.9 parts of an additive; the top coat includes, by mass fraction, 40-50 parts of a polyester-modified polyamide resin, 7-9 parts of graphene-polytetrafluoroethylene composite microspheres, 10-14 parts of titanium white, 0.5-1 part of a weather-resistant additive, 5-7 parts of a hexamethylene diisocyanate trimer curing agent, and 20-30 parts of a mixed solvent; the graphene-polytetrafluoroethylene composite microspheres have a particle size of 5-10 μm, and the hexamethylene diisocyanate trimer curing agent has an isocyanate content of 20-22%.

2. The abrasion resistant coating for a color coated aluminum sheet as claimed in claim 1, wherein: The mixed solvent in the base coat includes, by mass fraction, 15-25 parts of xylene and 8-12 parts of butyl acetate, and the additive includes 1.5-2 parts of a dispersant, 0.3-0.7 parts of an antifoaming agent, and 0.8-1.2 parts of a leveling agent; the dispersant is a polycarboxylate dispersant, the antifoaming agent is a silicone antifoaming agent, and the leveling agent is a polyether-modified siloxane leveling agent.

3. The abrasion resistant coating for a color coated aluminum sheet as claimed in claim 1, wherein: The graphene-polytetrafluoroethylene composite microspheres in the top coat are prepared from, by mass fraction, 0.4-0.6 parts of graphene oxide, 14-16 parts of polytetrafluoroethylene emulsion with a mass solid content of 50%, 78-82 parts of deionized water, and 0.3-0.5 parts of cetyltrimethylammonium bromide, and the graphene-polytetrafluoroethylene composite microspheres have a water content of ≤0.3% after drying under conditions of a temperature of 55-65 ℃, a vacuum degree of -0.10 to -0.08 MPa, and a time of 10-14 h.

4. The abrasion resistant coating for a colored aluminum sheet as set forth in claim 1, wherein the abrasion resistant coating is formed by applying a primer layer, a base layer, and a top layer in this order on the surface of the aluminum sheet. The weather-resistant additive in the top coat includes, by mass fraction, 0.4-0.6 parts of an ultraviolet absorber and 0.2-0.4 parts of a hindered amine light stabilizer; the ultraviolet absorber is benzotriazole ultraviolet absorber 327, and the hindered amine light stabilizer is hindered amine light stabilizer 770.

5. A method for preparing a wear-resistant coating, based on the wear-resistant coating for a colored aluminum plate strip according to any one of claims 1-4, characterized in that: (1) substrate pretreatment: sequentially performing oil removal, pickling, and phytic acid-silane composite passivation; the phytic acid-silane composite passivation solution includes, by mass fraction, 15-17 parts of phytic acid, 4-6 parts of γ-glycidoxypropyltrimethoxysilane, 970-980 parts of deionized water, and 3-5 parts of acetic acid, and has a pH of 4.0-5.0; (2) base coat preparation: mixing a mixed solvent, an additive, and nano-filler, stirring at a speed of 1500-2000 r / min for 30-40 min, adding an epoxy-modified silicone resin, and stirring at a speed of 500-600 r / min for 20-30 min to obtain a base coat. (3) surface coating preparation: prepare graphene-polytetrafluoroethylene composite microspheres, mix the mixed solvent, additive, titanium dioxide and the composite microspheres, stir at a speed of 1500-2000 r / min for 40-50 min, add polyester modified polyamide resin and hexamethylene diisocyanate trimer curing agent, stir at a speed of 600-700 r / min for 15-25 min, and obtain the surface coating; (4) coating and curing: the base coating is coated on the pretreated substrate, and the surface coating is coated after pre-curing, the coating environment temperature is controlled at 23-27℃, the relative humidity is controlled at 30-50%, and the total dry film thickness after curing is 35-45μm, thereby obtaining the wear-resistant coating.

6. The method of claim 5, wherein the abrasion-resistant coating is prepared by: In step (1), the oil removal uses a mixed solution of sodium silicate 18-22 parts by mass, sodium carbonate 18-22 parts by mass, sodium dodecylbenzenesulfonate 4-6 parts by mass, and deionized water 220-240 parts by mass, the oil removal temperature is 53-57℃, the pressure is 0.2-0.3 MPa, and the time is 55-65 s; the pickling uses a mixed acid solution of nitric acid and hydrofluoric acid, the mass concentration of nitric acid is 7-9%, the mass concentration of hydrofluoric acid is 0.2-0.3%, the pickling temperature is 20-30℃, and the time is 25-35 s.

7. The method of claim 5, wherein the abrasion resistant coating is prepared by: In step (2), the nano filler is nano aluminum oxide and nano zirconium oxide, the ratio by mass is 3:2, and after mixing, the medium zirconium oxide is sand ground, the sand grinding speed is 2000-2500 r / min, the time is 50-70 min, the sand grinding medium particle size is 0.8-1.0 mm, the filling rate is 65-75%, and the particle size D50≤2μm after sand grinding.

8. The method of claim 5, wherein the wear resistant coating is prepared by: In step (3), the preparation of graphene-polytetrafluoroethylene composite microspheres includes: mixing deionized water and cetyltrimethylammonium bromide, stirring at a speed of 800-1000 r / min for 10-15 min, adding graphene oxide, ultrasonicating at a power of 600-800 W and a frequency of 20-25 kHz for 50-70 min, adding polytetrafluoroethylene emulsion with a mass solid content of 50%, incubating in a water bath at 80-85℃ for 2-3 h, washing 2-3 times after centrifugal separation, drying, and crushing through a 400 mesh sieve.

9. The method of claim 5, wherein the wear resistant coating is prepared by: In step (4), the wet film thickness of the base coating is 13-17μm, the pre-curing temperature is 155-165℃, and the time is 15-17 s; the wet film thickness of the surface coating is 18-22μm, the curing temperature is 175-185℃, and the time is 23-25 s.

10. The method of claim 5, wherein the abrasion resistant coating is prepared by: In step (4), the coating environment also includes an electrostatic elimination device, the ion balance degree is ±5-±10 V, and the static value is monitored every hour≤5 kV.

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