Outdoor coating with high weather resistance and low surface energy and preparation method thereof

Abstract

The invention relates to the technical field of coatings, in particular to a high-weather-resistance and low-surface-energy outdoor coating and a preparation method thereof. The coating is prepared by taking acrylic resin containing hydroxyl and carboxyl as a matrix and combining with a composite curing agent (internal blocked isocyanate and pyrazole blocked isocyanate containing methacrylic acid groups are synergistic), a molecular-level fluorosilicone functional graft, a modifier mixture, a flatting agent, polyethylene wax, 4-dimethylaminopyridine and the like. According to the present invention, by using the multi-step curing and multi-element catalysis control strategy, the collaborative optimization of the surface energy control and the body cross-linking is achieved, and the coating forms the interface gradient structure after the two-stage curing, such that the excellent hydrophobic and oleophobic properties, the excellent artificial aging resistance, the excellent adhesion, the excellent mechanical toughness and the good fingerprint pollution resistance are provided. According to the technology, the long-term weather resistance and the surface easy-cleaning property of the outdoor coating are obviously improved, and the technology has an important value in the field of high-performance outdoor protective coatings.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coating technology, and particularly relates to a high-weather-resistant and low-surface-energy outdoor coating and a preparation method thereof. BACKGROUND

[0002] Outdoor coatings, as an important protective layer of buildings, vehicles and various facilities, face multiple challenges such as ultraviolet radiation, temperature and humidity changes, acid rain corrosion, and pollutant deposition in long-term outdoor environment. Although traditional outdoor coatings have developed in basic protection performance, there are still significant technical bottlenecks in the synergistic realization of low surface energy characteristics and high weather resistance.

[0003] In the prior art, in order to realize the low surface energy characteristics of the coating, a surface modification strategy of fluorine-containing or silicon-containing additives is often used. Fluorine-containing compounds are widely used due to their extremely low surface tension, but the migration stability of fluorides is insufficient, and the surface enrichment layer is prone to loss in long-term outdoor environment, resulting in the attenuation of hydrophobic and oleophobic properties. Although the silicon-containing modifier has good flexibility and certain surface energy reduction effect, its oleophobicity is limited, and the compatibility problem with the coating matrix often leads to phase separation, affecting the uniformity and durability of the coating.

[0004] In terms of curing system, traditional thermosetting powder coatings mostly use polyester-epoxy, polyester-isocyanate and other curing mechanisms. However, these curing systems have the problems of narrow curing temperature window and unadjustable curing rate, which makes it difficult to provide sufficient time window for the migration and directional arrangement of surface low-energy segments. Especially in the leveling process of powder coating, the interface migration of surface energy modifier and the crosslinking curing of matrix resin often proceed synchronously, causing the interface rearrangement to be completed before the body phase network is cured and fixed, and finally forming a discontinuous surface gradient structure, which is unstable in low surface energy effect.

[0005] Although the existing isocyanate curing system can provide excellent mechanical properties and chemical resistance, the traditional blocked isocyanate usually uses a single blocking agent, and the deblocking temperature is relatively fixed, lacking precise control ability of the curing process. This leads to a lack of effective time sequence control between the steps of coating melting, leveling, surface rearrangement and body phase crosslinking, making it difficult to realize the synergistic optimization of surface functionalization and body phase performance.

[0006] In addition, the existing technology mostly uses physical mixing in the fluorine-silicon synergistic modification, and there is a lack of effective chemical connection between the fluorine-containing component and the silicon-containing component, which is prone to phase separation and uneven distribution. Such physical mixing system has poor stability during coating processing and curing, and the surface modification effect is not durable. Even if a certain hydrophobic and oleophobic effect can be obtained initially, the surface functional layer is prone to peeling or migration failure due to the insufficient binding force between the components in long-term outdoor exposure.

[0007] In view of the current technical situation, the field of outdoor coatings urgently needs to solve the problem of simultaneous realization of low surface energy and high weather resistance, break through the technical bottleneck of mismatching of interface rearrangement and bulk curing timing, and develop a new coating system that can accurately regulate the formation process of surface gradient structure. SUMMARY

[0008] Therefore, the purpose of the present application is to provide a high-weather-resistant and low-surface-energy outdoor coating and a preparation method thereof, so as to realize the synergistic improvement of low surface energy and high weather resistance of outdoor coatings and avoid the performance degradation caused by the timing conflict of interface rearrangement and bulk curing.

[0009] To achieve the above purpose, the present application provides a high-weather-resistant and low-surface-energy outdoor coating, which is prepared from the following components in parts by weight: a hydroxyl and carboxyl-containing acrylic resin 270-290 parts, a composite curing agent mixture 115-135 parts, a fluorosilicon functional graft 20-26 parts, a modifier mixture 20-24 parts, a leveling agent 4-6 parts, polyethylene wax 2.5-3.5 parts, and 4-dimethylaminopyridine 0.8-1.2 parts.

[0010] Preferably, the leveling agent is MODAFLOW Powder 2000.

[0011] Preferably, the polyethylene wax is Ceridust 3620.

[0012] Further, the composite curing agent mixture is prepared from the following components in parts by weight: an internal blocked isocyanate curing agent 85-105 parts, a pyrazole blocked isocyanate containing a methacrylic group 25-30 parts, and fumed silica 5-6 parts.

[0013] Preferably, the internal blocked isocyanate curing agent is VESTAGON BF 1540.

[0014] Preferably, the fumed silica is AEROSIL 200.

[0015] Further, the pyrazole blocked isocyanate containing a methacrylic group is prepared by the following steps: S1: reacting hexamethylene diisocyanate trimer with 4-hydroxymethyl-3,5-dimethylpyrazole in acetone at 38-42°C for 3.0-3.5h to obtain a pyrazole blocked isocyanate prepolymer; S2: adding triethylamine and methacryloyl chloride to the pyrazole blocked isocyanate prepolymer prepared in step S1, reacting at 48-52°C for 1.5-2.5h, and removing the solvent by reduced pressure distillation to obtain a pyrazole blocked isocyanate containing a methacrylic group.

[0016] Preferably, the weight ratio of the hexamethylene diisocyanate trimer, 4-hydroxymethyl-3,5-dimethylpyrazole, triethylamine and methacryloyl chloride is 35-48:25-35:1.6-2.4:6.4-9.6.

[0017] Preferably, the model of the hexamethylene diisocyanate trimer is Desmodur N 3300A.

[0018] Further, the fluorosilicon functional graft is prepared by free radical grafting reaction of side chain mercapto-modified polydimethylsiloxane and perfluorooctyl ethyl acrylate under initiation of azobisisobutyronitrile.

[0019] Preferably, the model of the side chain mercapto-modified polydimethylsiloxane is KF-2001.

[0020] Preferably, the weight ratio of the side chain mercapto-modified polydimethylsiloxane, perfluorooctyl ethyl acrylate and azobisisobutyronitrile is 13-17:10-14:0.8-1.2.

[0021] Further, the modifier mixture is prepared from the following components in parts by weight: tris(pentafluorophenyl)borane 1.8-2.5 parts, perfluoropolyether diol 8-9 parts and hydrogen-containing polydimethylsiloxane 12-13 parts.

[0022] Preferably, the number average molecular weight of the perfluoropolyether diol is 1000 g / mol.

[0023] Preferably, the model of the hydrogen-containing polydimethylsiloxane is DOWSIL SH 1107 Fluid.

[0024] Preferably, the hydroxyl and carboxyl containing acrylic resin is prepared by polymerization of methyl methacrylate, n-butyl acrylate, hydroxyethyl methacrylate and acrylic acid under initiation of benzoyl peroxide and dodecyl mercaptan.

[0025] Preferably, the weight ratio of the methyl methacrylate, n-butyl acrylate, hydroxyethyl methacrylate, acrylic acid, benzoyl peroxide and dodecyl mercaptan is 90-110:55-65:35-45:8-12:2.5-3.5:1.6-2.4.

[0026] Preferably, the particle size D50 of the coating is 30-34 μm.

[0027] Further, the application also provides a preparation method of the high-weather-resistant, low-surface-energy outdoor coating, comprising the following steps: (1) Preparation of acrylic resin containing hydroxyl and carboxyl: xylene, methyl methacrylate, n-butyl acrylate, hydroxyethyl methacrylate, acrylic acid are mixed, heated to 78-82℃, benzoyl peroxide and dodecyl mercaptan solution in xylene are added, and the reaction is carried out for 3.5-4.5h, and the acrylic resin is obtained by removing the solvent; (2) Preparation of composite curing agent mixture: internal blocked isocyanate curing agent, methacrylic acid group-containing pyrazole blocked isocyanate, fumed silica are mixed at high speed of 1800-2200rpm for 8-12min; (3) Preparation of fluorosilicon functional grafting: side chain mercapto-modified polydimethylsiloxane, perfluorooctyl ethyl acrylate, toluene and azobisisobutyronitrile are heated to 72-78℃ under nitrogen protection for 3.0-3.5h; (4) Preparation of modifier mixture: tris (pentafluorophenyl) borane, perfluoropolyether diol, hydrogen-containing polydimethylsiloxane are mixed, stirred at room temperature for 50-70min, heated to 75-85℃ for 40-50min; (5) Preparation of powder coating: the acrylic resin containing hydroxyl and carboxyl, the composite curing agent mixture, the fluorosilicon functional grafting, the modifier mixture, the leveling agent, the polyethylene wax and 4-dimethylamino pyridine are mixed, and then sent into a double screw extruder for extrusion, cooling, crushing and sieving to obtain the high weather resistance, low surface energy outdoor coating.

[0028] Preferably, the temperature of the extrusion in step (5) is set to zone 1 80-90℃, zone 2 90-100℃, zone 3 80-90℃, and the screw rotation speed is 30-40rpm.

[0029] Further, the application also provides a preparation method of high weather resistance, low surface energy outdoor coating, which coats the high weather resistance, low surface energy outdoor coating on the surface of pretreated aluminum alloy substrate by electrostatic spraying, controls the coating thickness to be 55-65μm, and then enters a curing oven for two-stage curing: the first stage is cured at 130-140℃ for 10-14min; the second stage is cured at 160-170℃ for 14-16min, to obtain the high weather resistance, low surface energy outdoor coating.

[0030] The beneficial effects of the application are: Precise construction of interface gradient structure: the methacrylic acid group-containing pyrazole blocked isocyanate in the application is a bifunctional latent unit, which preferentially constructs an interface-oriented low surface energy segment at a lower temperature stage through the Michael addition reaction of mercapto group to carbon-carbon double bond, and then unblocks the isocyanate group at a high temperature stage to form polyurethane crosslinking with the resin main chain, so as to effectively lock the formed surface gradient structure. This step-by-step reaction mechanism avoids the time sequence conflict between interface rearrangement and bulk curing, and ensures the continuity and stability of the surface functional layer.

[0031] Molecular level realization of fluorosilicon synergistic effect: through radical grafting, perfluorooctyl ethyl acrylate is covalently connected with polydimethylsiloxane containing mercapto side chains, and dehydrogenative coupling of hydrogen-containing polydimethylsiloxane is promoted by using tris(pentafluorophenyl)borane, realizing compatibility and synergistic migration of fluorine-containing and silicon-containing components at the molecular level. Compared with a physical mixing system, the fluorosilicon functional grafting material with chemical bonding has better dispersion stability and migration synergy, and can orderly migrate to the surface of the coating during curing and form a stable low surface energy interface.

[0032] Gradient control of the curing window: the composite curing agent mixture widens the open temperature interval by combining internal and external blocked isocyanates, so that the flow, surface rearrangement and bulk curing of the coating during the curing process are effectively staggered in time. This gradient curing mechanism reduces the occurrence of leveling defects, improves the flatness and gloss retention of the coating surface, and ensures sufficient crosslinking of the bulk network.

[0033] Catalytic selective multi-control: 4-dimethylaminopyridine as an alkaline organic catalyst selectively promotes the Michael addition reaction, so that surface-directed crosslinking is quickly completed at a low temperature stage; tris(pentafluorophenyl)borane as a Lewis acid catalyst specifically catalyzes the silicon-hydrogen coupling reaction, improving the interface enrichment driving force of the fluorosilicon component. The synergistic effect of the multi-catalyst system realizes accurate control of different reaction steps and avoids the occurrence of side reactions.

[0034] Balanced optimization of surface energy and mechanical properties: through the time sequence control of the segmented curing process, the surface low surface energy property and the bulk high crosslinking density are simultaneously obtained. The coating has excellent hydrophobic and oleophobic properties and anti-pollution ability, and also maintains good adhesion, flexibility and impact strength, overcoming the problem of mutual restriction of surface functionalization and mechanical properties in traditional technology.

[0035] Long-term maintenance of weathering stability: through chemical anchoring of the interface gradient structure and molecular level compatibility of the fluorosilicon component, the low surface energy property of the coating can still be stably maintained after long-term outdoor exposure. Compared with the traditional physical mixing modification system, the gloss retention rate of the coating after artificial climate aging is significantly improved, the anti-fingerprint pollution ability is persistent and stable, and the performance requirements for long-term use of outdoor coatings are met. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below with reference to specific examples.

[0037] Example 1: (1) 190g xylene, 90g methyl methacrylate, 55g n-butyl acrylate, 35g hydroxyethyl methacrylate and 8g acrylic acid were added sequentially to a four-necked flask equipped with a stirrer, thermometer and reflux condenser. The temperature was raised to 78°C under nitrogen protection. Then 2.5g benzoyl peroxide and 1.6g dodecyl mercaptan were dissolved in 18g xylene to prepare an initiator solution. The solution was added dropwise over 3 hours. The reaction was continued at 88°C for 3.5 hours. After cooling, the solvent was removed by distillation under reduced pressure to obtain an acrylic resin containing hydroxyl and carboxyl groups. (2) Add 35g of hexamethylene diisocyanate trimer (Desmodur N 3300A) and 25g of acetone to a dry four-necked flask equipped with a stirrer and a dropping funnel. Stir under ice bath conditions, then dissolve 8g of 4-hydroxymethyl-3,5-dimethylpyrazole in 16g of acetone to prepare a solution. Add the solution dropwise over 1.2h. Heat the solution to 38℃ and react for 3h to obtain a pyrazole-blocked isocyanate prepolymer solution. (3) Add 1.6g of triethylamine to the pyrazole-blocked isocyanate prepolymer solution obtained in step 2, dissolve 6.4g of methacryloyl chloride in 8g of acetone to prepare a solution under ice bath conditions, add the solution dropwise over 40min, heat to 48℃ and react for 1.5h, remove the solvent by vacuum distillation to obtain pyrazole-blocked isocyanate containing methacrylic acid groups. (4) Add 85g of internally blocked isocyanate curing agent (VESTAGON BF1540), 25g of pyrazole blocked isocyanate containing methacrylate groups and 5g of fumed silica (AEROSIL 200) to a high-speed mixer in sequence, and mix at 1800rpm for 8min to obtain a composite curing agent mixture. (5) Add 13g of side-chain mercapto-modified polydimethylsiloxane (KF-2001), 10g of perfluorooctyl ethyl acrylate, 18g of toluene and 0.8g of azobisisobutyronitrile to a three-necked flask equipped with a stirrer and a condenser. Heat the mixture to 72°C and react for 3h under nitrogen protection. Remove the solvent by vacuum distillation to obtain the fluorosilicone functional graft. (6) Add 1.8g tris(pentafluorophenyl)borane, 8g perfluoropolyether glycol (number average molecular weight 1000g / mol), and 12g hydrogen-containing polydimethylsiloxane (DOWSIL SH 1107 Fluid) to a dry beaker, stir and mix at room temperature for 50min, and then keep warm at 75℃ for 40min to obtain the modifier mixture; (7) In a high-speed mixer, 270 g of acrylic resin containing hydroxyl and carboxyl groups, 115 g of composite curing agent mixture, 20 g of fluorosil functional graft, 20 g of modifier mixture, 4 g of leveling agent (MODAFLOW Powder 2000), 2.5 g of polyethylene wax (Ceridust 3620) and 0.8 g of 4-dimethylaminopyridine were added in sequence, mixed uniformly, and then fed into a twin-screw extruder, with the extrusion temperature set to 80°C for zone 1, 90°C for zone 2, and 80°C for zone 3, and the screw speed set to 30 rpm. After extrusion, the product was cooled, crushed, and sieved to obtain a powder coating with a particle size D50 of 30 μm.

[0038] Coating preparation: The powder coating was applied to the surface of a pretreated aluminum alloy substrate using electrostatic spraying, with the coating thickness controlled at 55 μm, and then subjected to two-stage curing in a curing oven: the first stage was curing at 130°C for 10 min, and the second stage was curing at 160°C for 14 min, to obtain a high-weather-resistant, low-surface-energy outdoor coating.

[0039] Example 2: (1) In a four-necked flask equipped with a stirrer, thermometer and reflux condenser, 200 g of xylene, 100 g of methyl methacrylate, 60 g of n-butyl acrylate, 40 g of hydroxyethyl methacrylate and 10 g of acrylic acid were added in sequence, heated to 80°C under nitrogen protection, then 3 g of benzoyl peroxide and 2 g of dodecyl mercaptan were dissolved in 20 g of xylene to prepare an initiator solution, which was added dropwise within 3 h, and the reaction was continued at 90°C for 4 h. After cooling, the solvent was removed by distillation under reduced pressure to obtain an acrylic resin containing hydroxyl and carboxyl groups; (2) In a dry four-necked flask equipped with a stirrer and dropping funnel, 40 g of hexamethylene diisocyanate trimer (Desmodur N 3300A) and 30 g of acetone were added, stirred under ice bath conditions, then 10 g of 4-hydroxymethyl-3,5-dimethylpyrazole was dissolved in 20 g of acetone to prepare a solution, which was added dropwise within 1 h, and the temperature was raised to 40°C for 3 h to obtain a pyrazole-enclosed isocyanate prepolymer solution; (3) To the pyrazole-enclosed isocyanate prepolymer solution obtained in step 2, 2 g of triethylamine was added, 8 g of methacryloyl chloride was dissolved in 10 g of acetone to prepare a solution under ice bath conditions, which was added dropwise within 30 min, and the temperature was raised to 50°C for 2 h. The solvent was removed by distillation under reduced pressure to obtain a pyrazole-enclosed isocyanate containing methacrylic acid groups; (4) In a high-speed mixer, 90 g of internal blocked isocyanate curing agent (VESTAGON BF1540), 25 g of pyrazole-enclosed isocyanate containing methacrylic acid groups and 5 g of fumed silica (AEROSIL 200) were added in sequence, mixed at 2000 rpm for 10 min to obtain a composite curing agent mixture; (5) In a three-necked flask equipped with a stirrer and a condenser, 15 g of side chain mercapto-modified polydimethylsiloxane (KF-2001), 12 g of perfluoro-octyl ethyl acrylate, 20 g of toluene and 1 g of azobisisobutyronitrile were added, and the mixture was heated to 75°C under nitrogen protection for 3 h. The solvent was removed by distillation under reduced pressure to obtain a fluorosilicon functional graft; (6) In a dry beaker, 2 g of tris(pentafluorophenyl)borane, 8 g of perfluoropolyether glycol (number average molecular weight 1000 g / mol), and 12 g of hydrogen-containing polydimethylsiloxane (DOWSIL SH 1107 Fluid) were added, and the mixture was stirred at room temperature for 60 min, and then was heated at 80°C for 45 min to obtain a modifier mixture; (7) In a high-speed mixer, 280 g of an acrylic resin containing hydroxyl and carboxyl groups, 125 g of a composite curing agent mixture, 23 g of a fluorosilicon functional graft, 22 g of a modifier mixture, 5 g of a leveling agent (MODAFLOW Powder 2000), 3 g of a polyethylene wax (Ceridust 3620), and 1 g of 4-dimethylaminopyridine were sequentially added, and the mixture was uniformly mixed and then was fed into a twin-screw extruder. The extrusion temperature was set to 85°C for zone 1, 95°C for zone 2, and 85°C for zone 3. The screw rotation speed was 35 rpm. After extrusion, the product was cooled, crushed, and sieved to obtain a powder coating with a particle size D50 of 32 μm.

[0040] Coating preparation: The powder coating was applied to the surface of a pretreated aluminum alloy substrate by electrostatic spraying, and the coating thickness was controlled at 60 μm. Then the coating was subjected to two-stage curing in a curing oven: the first stage was at 135°C for 12 min, and the second stage was at 165°C for 15 min to obtain a high-weather-resistant, low-surface-energy outdoor coating.

[0041] Example 3: (1) In a four-necked flask equipped with a stirrer, a thermometer, and a reflux condenser, 210 g of xylene, 110 g of methyl methacrylate, 65 g of n-butyl acrylate, 45 g of hydroxyethyl methacrylate, and 12 g of acrylic acid were sequentially added. The mixture was heated to 82°C under nitrogen protection. Then, 3.5 g of benzoyl peroxide and 2.4 g of dodecyl mercaptan were dissolved in 22 g of xylene to prepare an initiator solution. The initiator solution was added dropwise over 3 h. The reaction was continued at 92°C for 4.5 h. After cooling, the solvent was removed by distillation under reduced pressure to obtain an acrylic resin containing hydroxyl and carboxyl groups; (2) In a dry four-necked flask equipped with a stirrer and a dropping funnel, 45 g of hexamethylene diisocyanate trimer (Desmodur N 3300A) and 35 g of acetone were added and stirred under ice bath conditions. Then, 12 g of 4-hydroxymethyl-3,5-dimethylpyrazole was dissolved in 24 g of acetone to prepare a solution. The solution was added dropwise over 0.8 h. The reaction was carried out at 42°C for 3.5 h to obtain a pyrazole-capped isocyanate prepolymer solution. (3) To the solution of pyrazole blocked isocyanate prepolymer from step 2, 2.4 g of triethylamine was added, and 9.6 g of methacryloyl chloride was dissolved in 12 g of acetone under ice bath condition, and the solution was added dropwise within 25 min. The temperature was raised to 52 °C and reacted for 2.5 h. The solvent was removed by distillation under reduced pressure to obtain a pyrazole blocked isocyanate containing methacrylic acid group; (4) 105 g of internal blocked isocyanate curing agent (VESTAGON BF1540), 30 g of pyrazole blocked isocyanate containing methacrylic acid group, 6 g of fumed silica (AEROSIL 200) were sequentially added into a high-speed mixer and mixed at 2200 rpm for 12 min to obtain a composite curing agent mixture; (5) A three-necked flask equipped with a stirrer and a condenser was charged with 17 g of side-chain mercapto-modified polydimethylsiloxane (KF-2001), 14 g of perfluoro-octyl ethyl acrylate, 22 g of toluene and 1.2 g of azobisisobutyronitrile. The temperature was raised to 78 °C under nitrogen protection and reacted for 3.5 h. The solvent was removed by distillation under reduced pressure to obtain a fluorosilicon functional graft; (6) A dry beaker was charged with 2.5 g of tris(pentafluorophenyl)borane, 9 g of perfluoropolyether diol (number average molecular weight 1000 g / mol), 13 g of hydrogen-containing polydimethylsiloxane (DOWSIL SH 1107 Fluid). The mixture was stirred at room temperature for 70 min, and then incubated at 85 °C for 50 min to obtain a modifier mixture; (7) A high-speed mixer was sequentially charged with 290 g of acrylic resin containing hydroxyl and carboxyl groups, 135 g of composite curing agent mixture, 26 g of fluorosilicon functional graft, 24 g of modifier mixture, 6 g of leveling agent (MODAFLOW Powder 2000), 3.5 g of polyethylene wax (Ceridust 3620) and 1.2 g of 4-dimethylaminopyridine. After uniform mixing, the mixture was fed into a twin-screw extruder, with the extrusion temperature set at 90 °C for zone 1, 100 °C for zone 2, and 90 °C for zone 3, and the screw rotation speed set at 40 rpm. After extrusion, the product was cooled, broken and sieved to obtain a powder coating with a particle size D50 of 34 μm.

[0042] Coating preparation: The powder coating was applied to the surface of a pretreated aluminum alloy substrate by electrostatic spraying, with the coating thickness controlled at 65 μm. The coating was then subjected to two-stage curing in a curing oven: the first stage was at 140 °C for 14 min, and the second stage was at 170 °C for 16 min, to obtain a high-weather-resistant, low-surface-energy outdoor coating.

[0043] Comparative Example 1: Comparative Example 1 differs from Example 2 in that the methacryl group containing pyrazole blocked isocyanate is not used, but 25 g of pyrazole blocked isocyanate (without methacryl group) is directly used, and the rest of the conditions are the same as Example 2.

[0044] Comparative Example 2: Comparative Example 2 differs from Example 2 in that the fluoro-silicon functional graft is not used, but a physical mixture of 15 g of polydimethylsiloxane and 8 g of perfluoro-octyl ethyl acrylate is added respectively, and the rest of the conditions are the same as Example 2.

[0045] Comparative Example 3: Comparative Example 3 differs from Example 2 in that the tris(pentafluorophenyl)borane catalyst is not used, but no catalyst is added in the modifier mixture, and 8 g of perfluoropolyether diol and 12 g of hydrogen-containing polydimethylsiloxane are directly mixed, and the rest of the conditions are the same as Example 2.

[0046] Comparative Example 4: Comparative Example 4 differs from Example 2 in that the stepwise curing process is not used, but a single-stage curing process is used to cure at 165°C for 25 minutes, and the rest of the conditions are the same as Example 2.

[0047] Comparative Example 5: Comparative Example 5 differs from Example 2 in that the composite curing agent mixture is not used, but only 115 g of internal blocked isocyanate curing agent (VESTAGON BF 1540) is used, and the rest of the conditions are the same as Example 2.

[0048] Comparative Example 6: Comparative Example 6 differs from Example 2 in that the 4-dimethylamino pyridine catalyst is not used, but no DMAP catalyst is added during the powder coating preparation process, and the rest of the conditions are the same as Example 2.

[0049] Performance Test: Contact Angle Test: A contact angle measuring instrument was used to measure the static contact angle of deionized water and diiodomethane on the surface of the coating at room temperature 25±2°C and relative humidity 50±5%. Five different positions of each sample were tested, and the average value was taken. The results are shown in Table 1.

[0050] Artificial Weathering Resistance Test: The test was carried out according to GB / T 1865-2009 standard, using a xenon lamp aging test box (model Q-SUN Xe-3), setting the irradiance to 0.55 W / m 2 (340 nm), black mark temperature 63±3°C, relative humidity 50±10%, continuous irradiation mode, and sampling at 3000h for gloss testing, using a 60° gloss meter to determine the gloss retention rate. The results are shown in Table 1.

[0051] Adhesion and mechanical property test: The adhesion of the coating was determined according to the GB / T 9286-2021 standard, a 2mm x 2mm square grid network was drawn on the surface of the coating using an adhesion tester, a total of 100 small squares, then 3M tape was attached and quickly removed at a 45° angle, and the number of falling squares was graded, with 0 being the best; at the same time, the impact strength was determined according to GB / T 1732-2020, using an impact tester, the impact height was from 10 cm, increasing by 10 cm each time until the coating cracked or peeled off, and the flexibility test was carried out according to GB / T 6742-2007, using cylindrical shafts of different diameters for bending tests.

[0052] Fingerprint resistance test: The artificial fingerprint contamination test used a standard artificial sebum solution prepared according to ASTM D4265-14, a standard fingerprint imprinter was used to apply a standard pressure of 0.5kg / cm 2 on the surface of the coating, with a contact time of 2 seconds, forming a standard fingerprint contamination area, the fingerprint visibility evaluation was observed under 10x magnification using an optical microscope, combined with a digital image analysis system to measure the contrast of the fingerprint profile, the results are shown in Table 1.

[0053] Table 1 Performance test results

[0054] Data analysis: From the data of Examples 1-3 in Table 1, it can be seen that the coating prepared by the present application has a combination of performance in hydrophobic and oleophobic, artificial aging resistance, adhesion and mechanical toughness, and fingerprint inhibition, which reflects the characteristics of surface energy control and bulk crosslinking synergy. Based on the overall trend reflected by the data, it can be inferred that the technical effect comes from the following mechanism coupling: the methyl methacrylate group-containing pyrazole blocked isocyanate as a bifunctional latent unit preferentially participates in the Michael addition of mercapto to carbon-carbon double bond at a lower temperature stage, and first constructs an interface-oriented low surface energy segment; then at a higher temperature stage, the isocyanate group is unblocked, and forms a polyurethane crosslinking with the hydroxyl or carboxyl in the acrylic resin, and then fixes the surface gradient formed. The fluorosilicon functional graft connects perfluoroalkyl acrylate and polydimethylsiloxane containing mercapto in the side chain with a covalent bond through free radical grafting, at the same time, tris(pentafluorophenyl)borane promotes the coupling of hydrogen-containing polydimethylsiloxane, so that the fluorine-containing and silicon-containing components are compatible and synergistically migrated at the molecular level. The mixed curing agent mixture widens the unblocking temperature range, so that the flow, surface rearrangement and bulk curing are effectively staggered in time, thereby reducing the leveling defects and improving the aging resistance stability.

[0055] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that Example 2 presents more synergistic performance in terms of hydrophobicity, oleophobicity, weather resistance, adhesion, impact toughness and fingerprint visibility. The differences pointed by the data can be reasonably attributed to the introduction of the methacrylic group-containing pyrazole blocked isocyanate, which introduces a controllable two-stage reaction sequence: first, the surface-oriented low surface energy layer is constructed by Michael addition promoted by basic organic catalyst, and then the deblocked isocyanate group completes the in-situ polyurethane. Comparative Example 1 lacks this reactive side chain, and the interface rearrangement and in-situ curing are more synchronized, which may cause insufficient anchoring of the surface low-energy segment and a decrease in the crosslinking network synergy, thus presenting an unfavorable trend in terms of apparent energy, weather retention and anti-fingerprint, and the adhesion and toughness indicators are also affected.

[0056] Compared with Comparative Example 2, the data of Example 2 shows lower surface energy, better weather resistance maintenance and stronger anti-fingerprint ability, while Comparative Example 2 may show a trend of increasing impact strength due to physical plasticization, but the oil-repellent and durability indicators are obviously limited. This difference can be explained by the different natures of chemical grafting and physical blending: in Example 2, the fluorine-containing and silicon-containing segments form stable covalent connection and molecular-level compatibility through free radical grafting and borane-catalyzed coupling, which enables controllable migration and network locking within the curing window; in Comparative Example 2, only physical mixing of polydimethylsiloxane and perfluoroalkyl monomers occurs, which is prone to phase separation and unstable migration, resulting in apparent improvement in flexibility / impact in the short term, but it is difficult to form stable and sustainable interface structures in terms of low surface energy, gloss retention and fingerprint inhibition.

[0057] Compared with Comparative Example 3, Example 2 is more advantageous in terms of oil-repellency, weather resistance and anti-fingerprint, and the adhesion and mechanical toughness are also balanced. The data difference can be inferred to be due to the key role of tris(pentafluorophenyl)borane: this Lewis acid catalyzes the dehydrogenative coupling between hydrogen-containing polydimethylsiloxane and diol, forming a siloxane bond between the fluorine-containing and silicon-containing soft segments, which not only improves the interface enrichment driving force, but also reduces the later migration loss; without catalyst, the above coupling efficiency is reduced, the continuity and durability of the interface low-energy layer are limited, thus presenting an unfavorable change in terms of oil-repellent retention and gloss maintenance after aging, while the flexibility difference is not significant due to the presence of soft segments in the system.

[0058] Compared with Comparative Example 4, the advantages of Example 2 in gloss retention and surface energy regulation are more obvious, and the fingerprint visibility is also lower. This difference can be explained by the curing path: Example 2 uses a segmented curing, which sequentially unfolds leveling, surface rearrangement and in-situ crosslinking, allowing the fluorine-containing and silicon-containing segments to have enough time to migrate to the interface and be locked by the subsequent polyurethane network; the single-stage curing of Comparative Example 4 brings the gel point forward, and the competition between flow and crosslinking intensifies, the interface structure is not yet stable before being solidified and shaped, which is prone to induce surface defects and low-energy layer discontinuity, ultimately reflecting the simultaneous decline in gloss retention and anti-pollution ability after aging.

[0059] Compared with Comparative Example 5, the data of Example 2 embodies better synergistic combination of hydrophobicity, oleophobicity, weather resistance and anti-fingerprint. The design point of the composite curing agent is the combination of internal and external blocked types, which makes the deblocking and crosslinking window adjustable and matched with the timing of Michael addition, so as to improve the construction efficiency of the interface layer and ensure the sufficient crosslinking of the bulk network. Comparative Example 5 only uses a single internal blocked isocyanate, and the curing window is relatively convergent, which is easy to cause the surface rearrangement to be insufficient before entering the rapid crosslinking stage, the synergy degree of anchoring of the interface low-energy segment and the bulk crosslinking is reduced, and then reflected in the gap of multiple apparent and durability indicators.

[0060] Compared with Comparative Example 6, the advantage of Example 2 in oil repellency and anti-fingerprint is more prominent, and the artificial aging resistance and impact toughness also present a more stable combination, while the adhesion remains at a relatively high level. The data difference can be reasonably attributed to the promotion effect of the basic organic catalyst on the thiol-Michael addition: Example 2 can quickly form interface-oriented crosslinking points and oriented segments at the low temperature stage, providing a surface gradient to be locked for subsequent deblocking polyurethanization; Comparative Example 6 lacks this catalyst, and the Michael addition rate and conversion are limited, the integrity and durability of the interface low-surface-energy structure are insufficient, and thus the low-polarity liquid contact angle and fingerprint visibility fall back, the impact toughness also presents a certain amplitude of decline, while the adhesion remains at a good level due to the formation of the polyurethane network.

[0061] It should be understood by those of ordinary skill in the art that the above discussion of any of the embodiments is only exemplary and is not intended to suggest that the scope of the present application is limited to these examples; under the idea of the present application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in details.

Claims

1. A high weatherable, low surface energy outdoor coating characterized in that, prepared from the following components in parts by weight: a hydroxyl and carboxyl containing acrylic resin 270-290 parts, a composite curing agent mixture 115-135 parts, a fluorosilicon functional graft 20-26 parts, a modifier mixture 20-24 parts, a leveling agent 4-6 parts, a polyethylene wax 2.5-3.5 parts and 4-dimethylaminopyridine 0.8-1.2 parts; the composite curing agent mixture is prepared from the following components in parts by weight: an internal blocked isocyanate curing agent 85-105 parts, a methylacryl group containing pyrazole blocked isocyanate 25-30 parts and fumed silica 5-6 parts; the methylacryl group containing pyrazole blocked isocyanate is prepared by the following steps: S1: reacting hexamethylene diisocyanate trimer with 4-hydroxymethyl-3,5-dimethylpyrazole in acetone, reacting at 38-42℃ for 3.0-3.5h to obtain a pyrazole blocked isocyanate prepolymer; S2: adding triethylamine and methacryloyl chloride to the pyrazole blocked isocyanate prepolymer prepared in step S1, reacting at 48-52℃ for 1.5-2.5h, removing the solvent by distillation under reduced pressure to obtain the methylacryl group containing pyrazole blocked isocyanate; the weight ratio of hexamethylene diisocyanate trimer, 4-hydroxymethyl-3,5-dimethylpyrazole, triethylamine and methacryloyl chloride in the step S1 and step S2 is 35-48:25-35:1.6-2.4:6.4-9.6; the fluorosilicon functional graft is prepared by radical grafting reaction of side chain mercapto modified polydimethylsiloxane and perfluorooctyl ethyl acrylate under initiation of azobisisobutyronitrile; the weight ratio of the side chain mercapto modified polydimethylsiloxane, perfluorooctyl ethyl acrylate and azobisisobutyronitrile is 13-17:10-14:0.8-1.2; the modifier mixture is prepared from the following components in parts by weight: tris(pentafluorophenyl)borane 1.8-2.5 parts, perfluoropolyether diol 8-9 parts and hydrogen-containing polydimethylsiloxane 12-13 parts.

2. The high-weatherable, low-surface energy outdoor coating of claim 1, wherein, The leveling agent is MODAFLOW Powder 2000; the polyethylene wax is Ceridust 3620.

3. The high-weatherable, low-surface energy outdoor coating of claim 1, wherein, The internal blocked isocyanate curing agent is VESTAGON BF 1540.

4. The high-weatherable, low-surface energy outdoor coating of claim 1, wherein, The hexamethylene diisocyanate trimer is Desmodur N 3300A.

5. The high-weatherable, low-surface energy outdoor coating of claim 1, wherein, The side chain mercapto modified polydimethylsiloxane is KF-2001.

6. The high-weatherable, low-surface energy outdoor coating of claim 1, wherein, The perfluoropolyether diol has a number average molecular weight of 1000g / mol.

7. The high-weatherable, low-surface energy outdoor coating of claim 1, wherein, The hydrogen-containing polydimethylsiloxane is DOWSIL SH 1107 Fluid.

8. The high-weatherable, low-surface energy outdoor coating of claim 1, wherein, The hydroxyl and carboxyl containing acrylic resin is prepared by polymerization of methyl methacrylate, n-butyl acrylate, hydroxyethyl methacrylate and acrylic acid under initiation of benzoyl peroxide and dodecyl mercaptan.

9. A process for the preparation of a high weatherable, low surface energy outdoor coating according to any one of claims 1 to 8, characterized in that, comprising the following steps: (1) Preparation of acrylic resin containing hydroxyl and carboxyl: xylene, methyl methacrylate, n-butyl acrylate, hydroxyethyl methacrylate, acrylic acid are mixed, heated to 78-82℃, benzoyl peroxide and dodecyl mercaptan solution in xylene is added, reaction for 3.5-4.5h, remove the solvent to obtain acrylic resin; (2) Preparation of composite curing agent mixture: internal blocked isocyanate curing agent, pyrazole blocked isocyanate containing methacrylic acid group, fumed silica are mixed at high speed of 1800-2200rpm for 8-12min; (3) Preparation of fluorosilicon functional graft: side chain mercapto modified polydimethylsiloxane, perfluoro octyl ethyl acrylate, toluene and azobisisobutyronitrile are heated to 72-78℃ under nitrogen protection for 3.0-3.5h; (4) Preparation of modifier mixture: tris (pentafluorophenyl) borane, perfluoro polyether diol, hydrogen-containing polydimethylsiloxane are mixed, stirred at room temperature for 50-70min, heated to 75-85℃ for 40-50min; (5) Preparation of powder coating: hydroxyl and carboxyl containing acrylic resin, composite curing agent mixture, fluorosilicon functional graft, modifier mixture, leveling agent, polyethylene wax and 4-dimethylamino pyridine are mixed, fed into a twin screw extruder, extruded, cooled, broken and sieved to obtain high weather resistance, low surface energy outdoor coating.

10. The method of making a high-weatherable, low-surface energy outdoor coating of claim 9, wherein, The temperature of the extrusion in step (5) is set to zone 1 80-90℃, zone 2 90-100℃, zone 3 80-90℃, screw speed 30-40rpm.

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