A low temperature curing powder coating and a method for its preparation

Abstract

This invention relates to the field of powder coating preparation technology, specifically to a low-temperature curing powder coating and its preparation method. The low-temperature curing powder coating comprises 50-60 parts of resin, 3.5-4.5 parts of low-temperature curing agent, 1-2 parts of defoamer, 1-2 parts of antioxidant, 30-40 parts of modified filler, and 2.5-3.5 parts of pigment. The modified filler has a core-shell structure, with a thermally conductive core and a thermally conductive porous shell and a dense thin shell. This invention achieves a synergistic effect of thermal conductivity, sound insulation, corrosion resistance, and high-temperature thermal shock resistance by constructing a three-layer core-shell structure of thermally conductive core-thermally conductive porous shell-dense thin shell. By introducing thermally conductive filler into the middle shell, the heat absorbed by the thermally conductive core is first transferred to the nano-thermally conductive filler in the middle shell, and then rapidly transferred to the silicone resin matrix through the continuous thermally conductive network of the interlocking thermally conductive fillers, and finally discharged to the outside of the coating, achieving efficient heat dissipation. Through the thermally conductive porous shell and the dense thin shell, a double-layer sound insulation system of porous sound absorption and dense reflection is formed, improving the noise reduction coefficient of the coating.

Description

Technical Field

[0001] This invention relates to the field of powder coating preparation technology, specifically to a low-temperature curing powder coating and its preparation method. Background Technology

[0002] Powder coatings are solid powder synthetic resin coatings composed of solid resins, pigments, fillers, and additives. They are environmentally friendly coatings that do not contain any organic solvents. Low-temperature curing powder coatings are an important branch of the powder coating field. The core definition is thermosetting powder coatings that complete the curing reaction within a temperature range of 140℃-160℃. Compared with traditional powder coatings that require high temperatures above 180℃ for curing, their core advantages are significantly reduced energy consumption, reduced thermal damage to the substrate, and better environmental performance.

[0003] Low-temperature curing powder coatings, with their low-temperature curing advantage, are widely used in coating heat-sensitive substrates and large equipment, such as high-speed trains, aircraft, and ships. During operation, high-speed train braking components generate a large amount of heat due to friction, with instantaneous temperatures exceeding 200°C, accompanied by significant vibration and noise. If the coating's thermal conductivity is insufficient, heat accumulation and accelerated component aging will occur, affecting braking safety. Poor sound insulation will exacerbate noise pollution and reduce passenger comfort. Furthermore, high-speed train braking components are mostly made of metal substrates, and conventional high-temperature curing powder coatings (curing temperature ≥180°C) easily lead to substrate deformation and performance degradation. Therefore, integrated powder coatings with low-temperature curing (140-150°C), high thermal conductivity, high sound insulation, and strong corrosion resistance have become a core industry requirement.

[0004] However, existing powder coatings tend to focus on improving a single property, such as thermal conductivity or corrosion resistance. Regarding thermal conductivity optimization, existing technologies disclose that nano-alumina, nano-silicon nitride, and nano-carbon nanotubes can improve the thermal conductivity of powder coatings. Regarding corrosion resistance optimization, existing technologies disclose the introduction of rust-inhibiting fillers, such as aluminum tripolyphosphate, into low-temperature curing powder coatings to improve corrosion resistance, and also disclose the introduction of fillers, such as silica powder, precipitated barium, wollastonite, or graphene, to improve salt spray resistance. These approaches are insufficient to meet the integrated requirements of low-temperature curing, thermal conductivity, sound insulation, and corrosion resistance for high-speed rail braking components. Therefore, this invention provides a low-temperature curing powder coating suitable for high-speed rail braking scenarios that combines multiple properties, along with its preparation method. Summary of the Invention

[0005] To address the above problems, the present invention provides a low-temperature curing powder coating comprising the following raw materials by weight: 50-60 parts resin, 3.5-4.5 parts low-temperature curing agent, 1-2 parts defoamer, 1-2 parts antioxidant, 30-40 parts modified filler, and 2.5-3.5 parts pigment.

[0006] The modified filler has a core-shell structure, with a thermally conductive core and a thermally conductive porous shell and a dense thin shell. The thermally conductive core is ultrasonically stirred and dispersed in an ethanol aqueous solution, and then surface activated with a silane coupling agent in a weak acid environment. After filtration, washing, and vacuum drying, the activated thermally conductive core is obtained.

[0007] The activated thermally conductive core was dispersed in deionized water to prepare a suspension with a concentration of 180-220 g / L. The middle shell precursor liquid was slowly added dropwise to the suspension while stirring at a speed of 600-800 rpm. After the addition was completed, the mixture was stirred at a constant temperature of 40-50℃ for 1-2 hours to allow the middle shell to initially coat the surface of the thermally conductive core. The system was then heated to 75-85℃ while continuing to stir and solidified at a constant temperature for 1.5-2.5 hours. After that, stirring was stopped and the system was allowed to cool naturally to room temperature. The mixture was then filtered, washed, and vacuum dried to obtain the thermally conductive and sound-insulating composite particles.

[0008] The thermally conductive and sound-insulating composite particles were dispersed in an ethanol solution to prepare a dispersion with a concentration of 300-360 g / L. A dense thin-shell liquid was slowly added dropwise to the dispersion while stirring at a speed of 600-800 rpm. After the addition was complete, stirring was continued for 1 hour. Then, the temperature was raised to 60℃ and pre-cured at a constant temperature for 1-2 hours. After that, it was cured at a constant temperature of 90-110℃ for 0.5-1.5 hours. After naturally cooling to room temperature, it was passed through a 200-mesh sieve to obtain the modified filler.

[0009] Preferably, the resin is one of epoxy resin, polyester resin, or epoxy-polyester mixed resin, the low-temperature curing agent is one of 2-methylimidazole and 2-ethyl-4-methylimidazole, the defoamer is an organosilicon defoamer, and the antioxidant is a hindered phenolic antioxidant.

[0010] Preferably, the heat-conducting core is one of micron-sized α-Al2O3 or MgO, and the particle size of the heat-conducting core is 5-20 μm.

[0011] Preferably, the concentration of the ethanol aqueous solution is 80-90%, the volume-to-mass ratio of the ethanol aqueous solution to the heat-conducting core is 1L:(80-120)g, the amount of silane coupling agent added is 1-2% of the mass of the heat-conducting core, and the silane coupling agent is one of KH-550 and KH-560.

[0012] Preferably, the conditions for ultrasonic stirring and dispersion of the heat-conducting core are: ultrasonic power of 250-350W, ultrasonic time of 20-40min, stirring speed of 400-600rpm, initial dispersion by stirring for 10min, followed by simultaneous stirring and ultrasonication.

[0013] Preferably, the pH of the solution is adjusted to 4.0-5.5 using dilute hydrochloric acid in a weakly acidic environment, the activation reaction time is 2-3 hours, the temperature is 50-60℃, and the stirring speed is 700-900 rpm.

[0014] Preferably, the intermediate shell precursor liquid comprises the following raw materials by weight: 60-70 parts of silicone resin, 10-15 parts of thermally conductive filler, 5-8 parts of pore-forming agent, 12-16 parts of curing agent, and 0.5-1.5 parts of deionized water. The thermally conductive filler is nano-alumina or nano-magnesium oxide, the pore-forming agent is PEG-4000, the curing agent is MTHPA, and the silicone resin is preferably methylphenyl silicone resin.

[0015] Preferably, the dense thin-shell liquid comprises 45-48 parts of epoxy resin, 0.5-1.5 parts of leveling agent, and 1.5-2.5 parts of low-temperature curing agent, with the total weight of all components being 50 parts, and the leveling agent being an acrylic leveling agent.

[0016] Preferably, the mass ratio of the thermally conductive core to the middle shell precursor liquid is (72-88):100, and the mass ratio of the thermally conductive and sound-insulating composite particles to the dense thin-shell liquid is 100:(45-50).

[0017] Preferably, the mass ratio of the thermally conductive core to the intermediate shell precursor liquid is 4:5, and the mass ratio of the thermally conductive and sound-insulating composite particles to the dense thin-shell liquid is 2:1.

[0018] Preferably, a method for preparing a low-temperature curing powder coating includes the following steps: S1, adding α-Al2O3 to an 80%-90% ethanol aqueous solution, ultrasonically stirring and dispersing to obtain a solution with a concentration of 80-120 g / L; adding a silane coupling agent to the solution, the amount of silane coupling agent added being 1-2% of the mass of α-Al2O3; adjusting the pH value of the solution to a suitable range of 4.0-5.5 with dilute hydrochloric acid; heating to 50-60℃; stirring at 700-900 rpm for 2-3 h; filtering; washing with deionized water 2-4 times; placing the washed particles in a vacuum drying oven; vacuum drying at 55-65℃ for 3-5 h; vacuum degree being -0.07~-0.09 MPa; to obtain surface-activated micron-sized α-Al2O3.

[0019] S2. Add the surface-activated micron-sized α-Al2O3 to deionized water and stir at 1000-1400 rpm for 15-25 min to form a suspension with a concentration of 180-220 g / L.

[0020] 60-70g of silicone resin, 10-15g of thermally conductive filler, 5-8g of pore-forming agent, 12-16g of curing agent, and 0.5-1.5g of deionized water are placed in a beaker and stirred at 1000rpm for 30min to obtain a shell precursor solution. The shell precursor solution is slowly added dropwise to the suspension at a dropping rate of 8-12g / min while stirring. The mixture is stirred at 600rpm for 2h at 40-50℃ to initially coat the thermally conductive core. The system is heated to 75-85℃ while continuing to stir and is kept at this temperature for 1.5-2.5h. After that, stirring is stopped, and the system is allowed to cool naturally to room temperature. The mixture is then filtered and washed 3-5 times with hot water at 80-90℃ to completely remove the pore-forming agent. The washed particles are placed in a vacuum drying oven at a vacuum degree of -0.07~-0.09MPa and vacuum dried at 50-60℃ for 5-7h to obtain thermally conductive and sound-insulating composite particles.

[0021] S3. Disperse the thermally conductive and sound-insulating composite particles in a 95% ethanol solution and stir at 500-700 rpm for 10-20 min to prepare a dispersion with a concentration of 300-360 g / L. Weigh 45-48 g of epoxy resin, 0.5-1.5 g of leveling agent, and 1.5-2.5 g of low-temperature curing agent and place them in a beaker. Stir at 800-1000 rpm for 15-25 min to obtain a dense thin-shell liquid. Slowly add 50 g of the dense thin-shell liquid to the dispersion at a dropping rate of 4-6 g / min while stirring. Stir at 600-800 rpm and continue stirring at 30-40℃ for 1 h to allow the epoxy resin to uniformly wet and spread on the surface of the thermally conductive and sound-insulating composite particles, forming an ultra-thin and dense coating layer. Continue stirring to raise the system temperature to a suitable range of 60℃ and cure at a constant temperature for 1-2 h to obtain pre-cured composite particles.

[0022] S4. Place the pre-cured composite particles in an oven and cure at a constant temperature of 90-110℃ for 0.5-1h. After curing, allow them to cool naturally to room temperature and pass them through a 200-mesh sieve to obtain the modified filler.

[0023] The dense thin shell adopts a partial curing process, which allows the dense thin shell to retain a certain number of active epoxy groups. In the final powder coating curing stage, the active groups remaining in the epoxy resin shell undergo a cross-linking reaction with the low-temperature curing agent in the matrix resin to form a chemical bonding interface, thereby ensuring the integrated bonding of the modified filler and the matrix resin.

[0024] S5. Mix 30-40g of modified filler, 50-60g of epoxy resin, 3.5-4.5g of low-temperature curing agent, 1-2g of defoamer and 1-2g of antioxidant, and 2.5-3.5g of pigment. Stir at 2000rpm for 15min. Feed the mixture into a twin-screw extruder. Set the extruder temperature as follows: Zone I 75-85℃, Zone II 80-90℃, Zone III 85-95℃, Zone IV 85-95℃. Screw speed 900-1100rpm. The length-to-diameter ratio of the twin-screw extruder is 36:1. The feed rate is 15-20kg / h. After extrusion and cooling, coarsely pulverize and finely pulverize the mixture, and sieve to obtain a low-temperature curing powder coating. Coarse pulverization is performed using a hammer mill to pulverize to a particle size ≤5mm. Fine pulverization is performed using an air jet mill. The particle size range of the finished powder coating is 30-90μm.

[0025] Preferably, the heating rate of all vacuum drying processes is 3-5℃ / min, and the temperature is kept constant after the temperature rises from room temperature to the set temperature. The vacuum degree is maintained at -0.07~-0.09MPa throughout the process, and the gas is released once every 1 hour during the drying process.

[0026] The present invention has at least one of the following technical effects: by constructing a three-layer core-shell structure of thermally conductive core-thermally conductive porous shell-dense thin shell, the present invention achieves a synergistic effect of thermal conductivity, sound insulation, corrosion resistance and high temperature thermal shock resistance.

[0027] This invention introduces thermally conductive fillers into the middle shell. The heat absorbed by the thermally conductive core is first transferred to the nano-thermally conductive fillers in the middle shell, and then rapidly transferred to the silicone resin matrix through the continuous thermally conductive network of the interlocking thermally conductive fillers, and finally discharged to the outside of the coating, thus achieving efficient heat dissipation.

[0028] The middle shell of this invention is a thermally conductive porous shell, and the outer layer is a dense thin shell, forming a double-layer sound insulation system with porous sound absorption and dense reflection. That is, the sound waves are first absorbed by the thermally conductive porous shell, most of the energy is absorbed, and the remaining small amount of sound waves are reflected by the dense thin shell and then absorbed again by the porous shell. The noise reduction coefficient is improved, and the sound insulation effect is improved accordingly. The pores of the thermally conductive porous shell are closed micron-level pores, and the nano-thermal conductive filler forms a continuous thermally conductive network between the pores, which cancels the thermal insulation effect of the air in the pores. This makes the porous shell have both thermal conductivity and sound insulation properties without significant loss of thermal conductivity.

[0029] This invention encapsulates a thermally conductive porous shell with a dense thin shell, which not only prevents the porous structure from being invaded by corrosive media and improves the corrosion resistance of the coating, but also forms a dense reflective layer to improve the sound insulation effect. At the same time, the dense thin shell adopts a partial curing process, in which the epoxy resin of the dense thin shell forms a chemical bond with the matrix resin, enhancing the bonding force between the modified filler and the resin. Detailed Implementation

[0030] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to limit the scope of protection of the invention to these embodiments. All equivalent transformations or simple substitutions made based on the substantive content of this application should fall within the scope of protection of this application. For parameter ranges not mentioned, intermediate values ​​are selected. Furthermore, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0031] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0032] Example 1 S1. Take 900 mL of ethanol and 100 mL of deionized water and mix them at a stirring speed of 600 rpm for 10 min to obtain an ethanol aqueous solution with a concentration of 90%. Take 100 g of α-Al2O3 and add it to the ethanol aqueous solution. First, stir at a speed of 500 rpm for 10 min, and then sonicate at an ultrasonic power of 300 W for 30 min while continuing to stir to ensure that α-Al2O3 is uniformly dispersed in the ethanol aqueous solution to obtain a solution with a concentration of 100 g / L.

[0033] 1.5 g KH-550 was added to the solution, and the pH of the system was adjusted to 5.0 with dilute hydrochloric acid. The temperature was raised to 55 °C, and the mixture was stirred at 800 rpm for 2 h to activate the α-Al2O3 surface. The solution was then filtered and washed three times with deionized water to remove unreacted impurities and silane coupling agent. The washed particles were then vacuum dried at 60 °C for 4 h at a vacuum degree of -0.08 MPa to obtain surface-activated micron-sized α-Al2O3.

[0034] S2. Weigh 80g of surface-activated micron-sized α-Al2O3, add 400mL of deionized water, and stir at 1200rpm for 20min to form a suspension with a concentration of 200g / L.

[0035] Take 65g of methylphenyl silicone resin, 12g of nano alumina, 8g of PEG-4000, 14g of MTHPA, and 1g of deionized water and place them in a beaker. Stir at 1000rpm for 30min to obtain the shell precursor solution. Slowly add 100g of the shell precursor solution to the suspension at a dropping rate of 10g / min while stirring. Stir at 600rpm for 2h at 45℃ to initially coat the thermally conductive core. Continue stirring and raise the system temperature to 80℃, then keep it at that temperature for 2h. After that, stop stirring and allow the system to cool naturally to room temperature. Filter the mixture and wash it 3-5 times with hot water at 80-90℃ to completely remove PEG-4000. Place the washed particles in a vacuum drying oven and vacuum dry at 55℃ for 6h at a vacuum degree of -0.08MPa to obtain thermally conductive and sound-insulating composite particles.

[0036] On the one hand, after micron-sized α-Al2O3 is activated by KH-550, one end forms a stable Si-O-Al chemical bond with the hydroxyl groups on the surface of α-Al2O3, and the other end reacts with methylphenyl organosilicon resin to form a chemical bond, realizing the chemical bonding between the inorganic heat-conducting core and the organic resin shell, providing the main force for the core-shell bonding; at the same time, after activation, the surface of α-Al2O3 changes from hydrophilic to hydrophobic, improving its compatibility with hydrophobic organosilicon resin, and further enhancing the tightness of the core-shell bonding through van der Waals forces. The two work together to achieve a firm coating of the heat-conducting core and the heat-conducting porous shell.

[0037] PEG-4000 exhibits good thermal compatibility with methylphenyl silicone resin. During the preparation of the mid-shell precursor solution, PEG-4000 is uniformly distributed in the silicone resin matrix in a molecularly dispersed state. Moreover, PEG-4000 and silicone resin are only physically mixed without chemical bonding, and no phase separation or aggregation occurs. When washed with hot water at 80-90℃, the hydrophilic end groups of PEG-4000 form hydrogen bonds with water molecules and dissolve rapidly, completely precipitating out of the mid-shell and leaving continuous porous cavities without damaging the cross-linked skeleton of the silicone resin.

[0038] S3. Disperse 100g of thermally conductive and sound-insulating composite particles in 300mL of 95% ethanol solution and stir at 600rpm for 15min to prepare a dispersion. Weigh 47g of epoxy resin, 1g of BYK-361N, and 2g of 2-methylimidazole and place them in a beaker. Stir at 900rpm for 20min to obtain a dense thin-shell liquid. Slowly add 50g of the dense thin-shell liquid to the dispersion at a dropping rate of 5g / min while stirring at 700rpm. Continue stirring at 35℃ for 1h to allow the epoxy resin to be uniformly wetted and spread on the surface of the thermally conductive and sound-insulating composite particles, forming an ultra-thin and dense coating layer. Continue stirring to raise the system temperature to a suitable range of 60℃ and cure at a constant temperature for 1.5h to obtain pre-cured composite particles. S4. Place all pre-cured composite particles into an oven and cure at 100℃ for 1 hour. After curing, allow them to cool naturally to room temperature and pass them through a 200-mesh sieve to obtain the modified filler. The dense thin shell is pre-cured at 60℃ for 1.5h and then cured at 100℃ for 1h, which partially cures the epoxy resin. The remaining epoxy groups undergo a ring-opening addition reaction with the low-temperature curing agent (2-methylimidazole) during the low-temperature curing stage to form chemical bonds, thereby achieving covalent bonding between the modified filler and the matrix resin.

[0039] S5. Mix 35g of modified filler, 55g of bisphenol A epoxy resin, 4g of 2-methylimidazole, 1.5g of silicone defoamer BYK-066N, 1.5g of hindered phenolic antioxidant 1010, and 3g of titanium dioxide. Stir at 2000rpm for 15min. Feed the mixture into a twin-screw extruder. Set the extruder temperature as follows: Zone I 75-85℃, Zone II 80-90℃, Zone III 85-95℃, Zone IV 85-95℃. Screw speed 1000rpm. After extrusion and cooling, coarsely pulverize and finely pulverize to obtain a low-temperature curing powder coating.

[0040] Example 2 The difference from Example 1 is that the amount of modified filler added is 30g, and the amount of epoxy resin added is 60g.

[0041] Example 3 The difference from Example 1 is that the amount of modified filler added is 40g and the amount of epoxy resin added is 50g.

[0042] Example 4 The difference from Example 1 is that the amount of surface-activated micron-sized α-Al2O3 added is 72g, and the concentration of the suspension is 180g / L.

[0043] Example 5 The difference from Example 1 is that the amount of surface-activated micron-sized α-Al2O3 added is 88g, and the concentration of the suspension is 220g / L.

[0044] Example 6 The difference from Example 1 is that the amount of dense thin-shell liquid used is 45g. Example

[0045] The difference from Example 1 is that the amount of nano-alumina added is 10g, and the amount of organosilicon resin added is 67g.

[0046] Example 8 The difference from Example 1 is that the amount of nano-alumina added is 15g, and the amount of organosilicon resin added is 62g.

[0047] Comparative Example Comparative Example 1 The difference from Example 1 is that no thermally conductive filler is added to the shell precursor solution.

[0048] Comparative Example 2 The difference from Example 1 is that no pore-forming agent is added to the shell precursor solution.

[0049] Comparative Example 3 The difference from Example 1 is that no thermally conductive filler and pore-forming agent are added to the shell precursor liquid.

[0050] Comparative Example 4 The difference from Example 1 is that the modified filler is a single-layer shell and does not undergo the first thermally conductive porous shell coating.

[0051] Comparative Example 5 The difference from Example 1 is that the modified filler is a single-layer shell and does not undergo a second dense thin-shell coating.

[0052] Using an electrostatic spraying process, the powder coatings prepared in Examples 1-8 and Comparative Examples 1-5 were uniformly sprayed onto the surface of a substrate (alloy steel for high-speed rail braking components) to prepare coating samples with a coating thickness of 80 μm (within ±5 μm). The sample size was 100 mm × 100 mm, and a total of 13 samples were prepared.

[0053] Four samples were taken for thermal conductivity testing. The thermal conductivity of the coating was tested using the protective hot plate method (GB / T10294-2008). The heating power Q (W) and the effective area A (m²) of the sample were recorded during thermal steady-state testing. 2 Temperature difference (K) and thickness d (m), substitute them into the formula to calculate the thermal conductivity λ: .

[0054] After the thermal conductivity test, the four samples were divided into two groups for thermal shock resistance test and corrosion resistance test. The thermal shock resistance of the coating was tested according to GB / T 2423.22 (thermal shock). On one hand, the samples were subjected to thermal cycling from -40℃ to 220℃, with each cycle lasting 30 minutes. After 100 cycles, the thermal conductivity of the coating was tested and the thermal conductivity retention rate was calculated. On the other hand, two new samples were subjected to the same thermal cycling test to determine the ultimate thermal shock resistance number of the samples. The ultimate thermal shock resistance number was determined as follows: when the coating showed cracks, blistering, or peeling of ≥0.1mm, it was considered to have failed in thermal shock resistance.

[0055] Existing technologies were used to test thermal conductivity, thermal shock resistance, and corrosion resistance.

[0056] The anti-corrosion performance of the coating was tested by a neutral salt spray test, which was conducted in accordance with the standard GB / T 10125-2021. After the sample was treated in the neutral salt spray test chamber for 500 hours, the thermal conductivity of the coating was retested, and the retention rate of the thermal conductivity was calculated.

[0057] In addition, two new samples were taken and subjected to extreme salt spray resistance test simultaneously. A cross-shaped scratch was made from the center of the sample to the substrate, with a scratch width of 1 mm, which conforms to the standard specification of GB / T 10125-2021. When the rust width on one side of the scratch is ≥3 mm, the coating is judged to have failed. The cumulative test time from the start of the test to the coating failure is the extreme salt spray resistance time. The test was carried out every 200 hours for the first 1000 hours, and every 20 hours after 1000 hours. The results are shown in Table 2 below.

[0058] Table 1. Thermal conductivity of samples corresponding to powder coatings in Examples 1-8 and Comparative Examples 1-5.

[0059] The sound insulation performance (noise reduction coefficient) of the coating was tested using the impedance tube method, according to ISO 10534-2 "Determination of absorption coefficient and acoustic impedance in acoustic impedance tubes". The powder coatings of Examples 1-8 and Comparative Examples 1-5 were sprayed onto a metal circular plate with dimensions matching the inner diameter of the impedance tube. The metal circular plate was made of alloy steel used in high-speed rail braking components. The coating thickness was 80 μm. According to ISO 10534-2, the vertical incident sound absorption coefficient of the coating was measured. The noise reduction coefficient (NRC) was obtained by averaging the sound absorption coefficients at four frequencies: 125, 250, 500, and 1000 Hz. The sound insulation performance was tested using existing technology. The test results are shown in Table 2 below.

[0060] Table 2. Test results of thermal shock resistance, corrosion resistance, and sound insulation performance of Examples 1-8 and Comparative Examples 1-5.

[0061] As shown in Tables 1 and 2, the thermal conductivity of Examples 1-8 is higher than that of Comparative Examples 1 and 3, indicating that adding nanoscale thermally conductive fillers to the middle shell can optimize and improve the overall thermal conductivity of the coating. The thermally conductive fillers form a thermally conductive network in the resin, which can quickly conduct the heat of the thermal core.

[0062] After 100 thermal shocks and 500 hours of salt spray corrosion, the thermal conductivity retention rate of Examples 1-8 remained above 94.8%. In contrast, Comparative Examples 4 and 5, which only used a single-shell coating of the heat-conducting core, showed a significant decrease in thermal conductivity after thermal shock and salt spray corrosion. This indicates that the heat-conducting network constructed by the heat-conducting core-heat-conducting porous shell-dense thin shell has extremely strong structural stability, can resist extreme temperature changes and corrosive media erosion of high-speed rail braking components, and avoids a significant decrease in thermal conductivity due to damage to the coating structure.

[0063] The dense thin shell of Comparative Example 5 was not wrapped, and it only withstood 35 extreme thermal shocks and 200 hours of extreme salt spray, failing before reaching the basic working conditions. Moreover, its thermal conductivity was greatly reduced after salt spray. This indicates that the dense thin shell is the core barrier for the coating to resist the intrusion of corrosive media and alleviate the structural stress under extreme temperature changes, and can prevent the coating from peeling and collapsing under thermal cycling.

[0064] The noise reduction coefficients of Comparative Examples 2 and 3 were all poor, proving that the porous structure formed by the porogen (PEG-4000) in the middle shell is the core carrier of the porous sound absorption structure. Without the porogen, effective sound absorption cannot be achieved. Comparative Example 4 was not wrapped with a middle shell, so it had neither resin insulation nor porous sound absorption, and its sound insulation effect was the worst.

[0065] The amount of modified filler added in Examples 1-3 varies. It can be seen that within the range of 30-40 parts, a moderate increase in the amount of modified filler added leads to an overall optimization trend in the core properties of the coating, such as thermal conductivity and thermal shock resistance. However, there are slight fluctuations due to operational errors. The modified filler of this invention has a three-layer core-shell structure. The modified filler is the core foundation for the coating to achieve multi-performance synergy. As long as the core structure is not changed, only a small adjustment to a single parameter within the range can ensure excellent coating performance.

[0066] Comparative Examples 4 and 5 did not undergo thermal conductivity testing after salt spray because the coatings failed prematurely.

[0067] This invention uses a silane coupling agent to activate the surface of the heat-conducting core, while the dense thin shell forms a covalent bond with the matrix resin, which can ensure that the adhesion between the coating and the substrate meets the GB / T 9286-1998 Grade 0 requirements and meets the actual application needs of high-speed rail braking components.

[0068] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0069] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A low-temperature curing powder coating, characterized in that, Raw materials comprising the following weight components: 50-60 parts resin, 3.5-4.5 parts low-temperature curing agent, 1-2 parts defoamer, 1-2 parts antioxidant, 30-40 parts modified filler, and 2.5-3.5 parts pigment; The modified filler has a core-shell structure, with a thermally conductive core and a thermally conductive porous shell and a dense thin shell. The thermally conductive core is ultrasonically stirred and dispersed in an ethanol aqueous solution, and then surface activated with a silane coupling agent in a weak acid environment. The activated thermally conductive core is obtained by filtration, washing, and vacuum drying. The activated thermally conductive core was dispersed in deionized water to prepare a suspension with a concentration of 180-220 g / L. The middle shell precursor liquid was slowly added dropwise to the suspension while stirring. After the addition was completed, the system was continuously stirred at a constant temperature of 40-50℃ for 1-2 hours. The system was then heated to 75-85℃ while stirring, and solidified at a constant temperature for 1.5-2.5 hours. After that, stirring was stopped, and the system was allowed to cool naturally to room temperature. The system was then filtered, washed, and vacuum dried to obtain thermally conductive and sound-insulating composite particles. Thermally conductive and sound-insulating composite particles were dispersed in an ethanol solution to prepare a dispersion with a concentration of 300-360 g / L. Dense thin-shell liquid was slowly added dropwise to the dispersion while stirring. After the addition was completed, stirring was continued for 1 hour. Then the temperature was raised to 60℃ and pre-cured at a constant temperature for 1-2 hours. After that, it was cured at a constant temperature of 90-110℃ for 0.5-1.5 hours. After naturally cooling to room temperature, it was passed through a 200-mesh sieve to obtain the modified filler.

2. The low-temperature curing powder coating according to claim 1, characterized in that... The resin is one of epoxy resin, polyester resin, or epoxy-polyester mixed resin; the low-temperature curing agent is one of 2-methylimidazole or 2-ethyl-4-methylimidazole; the defoamer is an organosilicon defoamer; and the antioxidant is a hindered phenolic antioxidant.

3. The low-temperature curing powder coating according to claim 1, characterized in that... The heat-conducting core is either micron-sized α-Al₂O₃ or MgO.

4. The low-temperature curing powder coating according to claim 1, characterized in that... The concentration of the ethanol aqueous solution is 80-90%, the volume-to-mass ratio of the ethanol aqueous solution to the heat-conducting core is 1L:(80-120)g, the amount of silane coupling agent added is 1-2% of the mass of the heat-conducting core, and the silane coupling agent is one of KH-550 and KH-560.

5. The low-temperature curing powder coating according to claim 1, characterized in that... The conditions for ultrasonic stirring and dispersion of the heat-conducting core are: ultrasonic power 250-350W, ultrasonic time 20-40min, and stirring speed 400-600rpm.

6. The low-temperature curing powder coating according to claim 1, characterized in that... In a weakly acidic environment, adjust the pH of the solution to 4.0-5.5 with dilute hydrochloric acid. The activation reaction time is 2-3 hours, the temperature is 50-60℃, and the stirring speed is 700-900 rpm.

7. The low-temperature curing powder coating according to claim 1, characterized in that... The intermediate shell precursor liquid comprises the following raw materials by weight: 60-70 parts of silicone resin, 10-15 parts of thermally conductive filler, 5-8 parts of pore-forming agent, 12-16 parts of curing agent, and 0.5-1.5 parts of deionized water. The thermally conductive filler is nano-alumina or nano-magnesium oxide, the pore-forming agent is PEG-4000, and the curing agent is MTHPA.

8. The low-temperature curing powder coating according to claim 1, characterized in that... The dense thin-shell liquid comprises 45-48 parts epoxy resin, 0.5-1.5 parts leveling agent, and 1.5-2.5 parts low-temperature curing agent.

9. A low-temperature curing powder coating according to claim 1, characterized in that... The mass ratio of the thermally conductive core to the middle shell precursor liquid is (72-88):100, and the mass ratio of the thermally conductive and sound-insulating composite particles to the dense thin-shell liquid is 100:(45-50).

10. A method for preparing a low-temperature curing powder coating, characterized in that... Includes the following steps: S1. Add α-Al2O3 to an 80%-90% ethanol aqueous solution and disperse by ultrasonic stirring to obtain a solution with a concentration of 80-120 g / L. Add a silane coupling agent to the solution, with the amount of silane coupling agent added being 1%-2% of the mass of α-Al2O3. Adjust the pH of the solution to a suitable range of 4.0-5.5 with dilute hydrochloric acid. Heat the solution to 50-60℃ and stir at 700-900 rpm for 2-3 hours. Filter the solution and wash it 2-4 times with deionized water. Place the washed particles in a vacuum drying oven and vacuum dry them at 55-65℃ for 3-5 hours to obtain surface-activated micron-sized α-Al2O3. S2. Add the surface-activated micron-sized α-Al2O3 to deionized water and stir at 1000-1400 rpm for 15-25 min to form a suspension with a concentration of 180-220 g / L. Weigh 60-70g of silicone resin, 10-15g of thermally conductive filler, 5-8g of pore-forming agent, 12-16g of curing agent, and 0.5-1.5g of deionized water and place them in a beaker. Stir at 1000rpm for 30min to obtain a shell precursor solution. Slowly add the shell precursor solution to the suspension at a dropping rate of 8-12g / min while stirring. Stir at 600rpm for 2h at 40-50℃ to initially coat the thermally conductive core. Continue stirring and raise the temperature of the system to 75-85℃, and cure at a constant temperature for 1.5-2.5h. Then stop stirring and allow the system to cool naturally to room temperature. Filter and wash with hot water 3-5 times to completely remove the pore-forming agent. Place the washed particles in a vacuum drying oven and vacuum dry at 50-60℃ for 5-7h to obtain thermally conductive and sound-insulating composite particles. S3. Disperse the thermally conductive and sound-insulating composite particles in an ethanol solution and stir at 500-700 rpm for 10-20 min to prepare a dispersion with a concentration of 300-360 g / L. Weigh 45-48 g of epoxy resin, 0.5-1.5 g of leveling agent, and 1.5-2.5 g of low-temperature curing agent and place them in a beaker. Stir at 800-1000 rpm for 15-25 min to obtain a dense thin-shell liquid. Slowly add the dense thin-shell liquid dropwise to the dispersion at a dropping rate of 4-6 g / min while stirring. Stir at a stirring speed of 600-800 rpm and continue stirring at 30-40℃ for 1 h to form an ultra-thin and dense coating layer. Continue stirring to raise the system temperature to a suitable range of 60℃ and cure at a constant temperature for 1-2 h to obtain pre-cured composite particles. S4. Place the pre-cured composite particles in an oven and cure them at a constant temperature of 90-110℃ for 0.5-1h. After curing, allow them to cool naturally to room temperature and pass them through a 200-mesh sieve to obtain the modified filler. S5. Mix 30-40g of modified filler, 50-60g of epoxy resin, 3.5-4.5g of low-temperature curing agent, 1-2g of defoamer and 1-2g of antioxidant, and 2.5-3.5g of pigment. Stir at 2000rpm for 15min. Feed the mixture into a twin-screw extruder. After extrusion and cooling, coarsely pulverize and finely pulverize the mixture and sieve to obtain a low-temperature curing powder coating.

Images