Transparent powder coating for low-temperature-resistant aluminum hub as well as preparation method and application of transparent powder coating

Abstract

The invention belongs to the technical field of coatings, and particularly relates to transparent polyester resin for a low-temperature-resistant aluminum hub as well as a preparation method and application of the polyester resin. The transparent powder coating for the low-temperature-resistant aluminum hub is prepared from the following raw materials: acrylic modified polyester resin, a curing agent, a plasticizer, a flexibilizer and an adhesion enhancer. The low-temperature high-toughness acrylic acid modified polyester resin is adopted, and the flexibilizer, the plasticizer and the silane coupling agent are cooperatively introduced, so that the powder coating shows excellent flexibility, impact toughness, stone impact resistance and adhesive force at normal temperature and in an extremely cold environment of-40 DEG C, and low-temperature cold brittleness and falling are effectively avoided; meanwhile, the coating has high leveling performance, high transparency, high corrosion resistance and high weather resistance, and the coating requirement of the aluminum hub can be better met.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coatings, and particularly relates to a transparent powder coating for low-temperature-resistant aluminum wheel hubs as well as a preparation method and application thereof. BACKGROUND

[0002] The special geographical and climatic conditions in extremely cold regions impose extremely stringent requirements on the performance of various industrial products and parts. As a key part of vehicles such as automobiles, aluminum wheel hubs face many challenges in the use scenario in extremely cold regions. In particular, in extremely low temperature environments (-40℃), the transparent topcoat of the aluminum wheel hub is prone to brittleness, and the mechanical properties decrease significantly, which not only affects the service life, but also may cause safety hazards. This problem is particularly prominent in major extremely cold regions around the world, seriously restricting the export competitiveness of aluminum wheel hub products.

[0003] Therefore, it is of great significance to provide a transparent powder coating for aluminum wheel hubs that still has good flexibility, adhesion and stone impact resistance performance under the condition of extremely low temperature of -40℃, and can adapt to extremely cold environments. SUMMARY

[0004] The present application aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative. Specifically, the present application provides a powder coating that still has good flexibility, adhesion and stone impact resistance performance under the condition of extremely low temperature of -40℃, and meets the requirements of high transparency, high leveling property and high weather resistance.

[0005] The inventive concept of the present application: the preparation raw materials of the powder coating of the present application include acrylic modified polyester resin, curing agent, plasticizer, toughening agent, adhesion enhancer. The present application uses acrylic resin prepolymer and polyester prepolymer to prepare acrylic modified polyester resin, and through the joint action of acrylic modified polyester resin, curing agent, plasticizer, toughening agent and adhesion enhancer, the coating formed by the powder coating still has good flexibility, adhesion and stone impact resistance performance under the condition of extremely low temperature of -40℃, and meets the requirements of high transparency, high leveling property and high weather resistance.

[0006] Therefore, the first aspect of the present application provides a transparent powder coating for low-temperature-resistant aluminum wheel hubs.

[0007] Specifically, the preparation raw materials of the transparent powder coating for low-temperature-resistant aluminum wheel hubs include acrylic modified polyester resin, curing agent, plasticizer, toughening agent and adhesion enhancer.

[0008] Preferably, the raw materials for preparing the transparent powder coating for low-temperature-resistant aluminum wheel hub include 90-100 parts of acrylic modified polyester resin, 3-10 parts of curing agent, 0.5-1.5 parts of plasticizer, 1-3 parts of toughening agent, and 0.3-0.8 parts of adhesion enhancer, in terms of mass fraction.

[0009] Preferably, the raw materials for preparing the transparent powder coating for low-temperature-resistant aluminum wheel hub further include at least one of leveling agent, degassing agent, ultraviolet absorber, and light stabilizer.

[0010] Preferably, the raw materials for preparing the transparent powder coating for low-temperature-resistant aluminum wheel hub further include leveling agent, degassing agent, ultraviolet absorber, and light stabilizer; and the raw materials for preparing the transparent powder coating for low-temperature-resistant aluminum wheel hub include 90-100 parts of acrylic modified polyester resin, 3-10 parts of curing agent, 0.5-1.5 parts of plasticizer, 1-3 parts of toughening agent, 0.3-0.8 parts of adhesion enhancer, 1-3 parts of leveling agent, 0.5-1.5 parts of degassing agent, 0.5-1.5 parts of ultraviolet absorber, and 0.3-1 parts of light stabilizer, in terms of mass fraction.

[0011] Preferably, the mass ratio of the acrylic modified polyester resin to the curing agent is 1: (0.05-0.09); further preferably, the mass ratio of the acrylic modified polyester resin to the curing agent is 1: (0.055-0.083).

[0012] Preferably, the acrylic modified polyester resin has an acid value of 45-66 mgKOH / g, a glass transition temperature (Tg) of 35-44℃, and a softening point of 70-82℃.

[0013] In particular, the acrylic modified polyester resin is a low-temperature high-toughness acrylic modified polyester resin.

[0014] Preferably, the transparent powder coating for low-temperature-resistant aluminum wheel hub has a D50 particle size of 25-35 μm; further preferably, the transparent powder coating for low-temperature-resistant aluminum wheel hub has a D50 particle size of 26-29 μm.

[0015] Preferably, the curing agent includes triisocyanurate (TGIC).

[0016] Preferably, the plasticizer includes at least one of cyclohexane 1,2-dicarboxylic acid diisononyl ester, dibutyl sebacate, dioctyl sebacate, and diisooctyl sebacate.

[0017] Preferably, the toughening agent includes at least one of polyvinyl butyral (PVB) and thermoplastic polyester elastomer (TPEE).

[0018] Preferably, the adhesion enhancer includes silane coupling agent.

[0019] Preferably, the silane coupling agent comprises at least one of 3-aminopropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, gamma-aminopropylmethyldimethoxysilane.

[0020] Preferably, the leveling agent is a polyether modified polydimethylsiloxane leveling agent.

[0021] Further preferably, the leveling agent comprises at least one of BYK-360P, BYK-364P, BYK-3902P produced by BYK.

[0022] Preferably, the degassing agent comprises benzoin (benzoin).

[0023] Preferably, in the preparation raw material of the transparent powder coating for low-temperature-resistant aluminum wheel hub, the ultraviolet absorber comprises a benzotriazole ultraviolet absorber.

[0024] Further preferably, in the preparation raw material of the transparent powder coating for low-temperature-resistant aluminum wheel hub, the ultraviolet absorber comprises at least one of Tinuvin® 328, Tinuvin® 234, Tinuvin® 477 produced by BASF, Germany, and SONGSORB® CS 400 produced by SONGWON.

[0025] Preferably, the light stabilizer comprises a hindered amine light stabilizer.

[0026] Further preferably, the light stabilizer comprises at least one of Chimassorb® 944, Tinuvin® 292 produced by BASF, Germany, Hostavin® N30P produced by Clariant, and SONGSORB® CS 292 produced by SONGWON.

[0027] Preferably, the preparation raw material of the acrylic modified polyester resin comprises an acrylic resin prepolymer, a polyester prepolymer, an esterification catalyst, a filler, and an ultraviolet absorption auxiliary agent.

[0028] Preferably, in terms of mass fraction, the preparation raw material of the acrylic modified polyester resin comprises 300-350 parts of an acrylic resin prepolymer, 400-500 parts of a polyester prepolymer, 3-7 parts of an esterification catalyst, 5-15 parts of a filler, and 20-40 parts of an ultraviolet absorption auxiliary agent.

[0029] Preferably, in the preparation raw material of the acrylic modified polyester resin, the esterification catalyst comprises monobutyl tin acid.

[0030] Preferably, in the preparation raw material of the acrylic modified polyester resin, the filler comprises nano-silicon dioxide.

[0031] Preferably, the anti-ultraviolet absorption aid in the raw material for preparing the acrylic resin prepolymer comprises 2-hydroxy-4-n-octyloxybenzophenone (UV-531).

[0032] Preferably, the raw material for preparing the acrylic resin prepolymer comprises methacrylic acid, methyl methacrylate, butyl methacrylate, isooctyl acrylate, an initiator, a chain transfer agent, a free radical trapping agent, a solvent and an adsorbent.

[0033] Preferably, the raw material for preparing the acrylic resin prepolymer comprises, in terms of mass fraction, 250-350 parts of methacrylic acid, 350-450 parts of methyl methacrylate, 150-250 parts of butyl methacrylate, 30-50 parts of isooctyl acrylate, 10-20 parts of an initiator, 5-15 parts of a chain transfer agent, 10-20 parts of a free radical trapping agent, 400-600 parts of a solvent and 8-12 parts of an adsorbent.

[0034] Preferably, the initiator in the raw material for preparing the acrylic resin prepolymer comprises di-tert-butyl peroxide.

[0035] Preferably, the chain transfer agent in the raw material for preparing the acrylic resin prepolymer comprises n-dodecyl mercaptan.

[0036] Preferably, the free radical trapping agent in the raw material for preparing the acrylic resin prepolymer comprises butylated hydroxytoluene.

[0037] Preferably, the solvent in the raw material for preparing the acrylic resin prepolymer comprises xylene.

[0038] Preferably, the adsorbent in the raw material for preparing the acrylic resin prepolymer comprises molecular sieves.

[0039] Preferably, the raw material for preparing the polyester prepolymer comprises an alcohol compound, an acid compound, a catalyst, an alicyclic polyester diol and an antioxidant.

[0040] Preferably, the raw material for preparing the polyester prepolymer comprises, in terms of mass fraction, 430-600 parts of an alcohol compound, 680-920 parts of an acid compound, 3-7 parts of a catalyst, 5-20 parts of an antioxidant and 20-40 parts of an alicyclic polyester diol.

[0041] Preferably, the alcohol compound in the raw material for preparing the polyester prepolymer comprises neopentyl glycol and trimethylolpropane.

[0042] Preferably, the alcohol compound comprises, in terms of mass fraction, 350-450 parts of neopentyl glycol and 80-120 parts of trimethylolpropane.

[0043] Preferably, the acid compound comprises terephthalic acid, isophthalic acid, and adipic acid in the raw materials for preparing the polyester prepolymer.

[0044] Preferably, the acid compound comprises terephthalic acid 450-550 parts by mass, isophthalic acid 150-250 parts by mass, and adipic acid 80-120 parts by mass.

[0045] Preferably, the alicyclic polyester diol comprises polyhexanedioic acid-1,4-cyclohexanedimethanol diol in the raw materials for preparing the polyester prepolymer.

[0046] Preferably, the catalyst comprises monobutyl tin oxide in the raw materials for preparing the polyester prepolymer.

[0047] Preferably, the antioxidant comprises tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester (Irganox 1010 antioxidant) in the raw materials for preparing the polyester prepolymer.

[0048] The second aspect of the present application provides a preparation method of the transparent powder coating for low-temperature-resistant aluminum wheel hubs according to the first aspect of the present application.

[0049] Specifically, the preparation method of the transparent powder coating for low-temperature-resistant aluminum wheel hubs comprises the following steps: The raw materials of the powder coating are mixed, extruded, tabletized, cooled, and crushed to obtain the powder coating.

[0050] Preferably, the extrusion device is a double-screw extruder.

[0051] Preferably, the temperature of the first zone of the double-screw extruder is 80-95°C, and the temperature of the second zone is 85-100°C.

[0052] Further preferably, the temperature of the first zone of the double-screw extruder is 83-90°C, and the temperature of the second zone is 90-96°C.

[0053] Preferably, the preparation method of the acrylic-modified polyester resin comprises the following steps: the raw materials of the acrylic-modified polyester resin are mixed and reacted to obtain the acrylic-modified polyester resin.

[0054] Preferably, the temperature of the reaction is 240-260°C, and the reaction time is 1.5-2.5h in the preparation process of the acrylic-modified polyester resin.

[0055] Preferably, the preparation process of the acrylic-modified polyester resin further comprises a vacuumizing process after the reaction.

[0056] Preferably, the preparation method of the acrylic-modified polyester resin comprises the following steps: Acrylic resin prepolymer, polyester prepolymer, and esterification catalyst are mixed, and sufficient nitrogen gas is introduced. The mixture is heated to 140-160℃, stirred, and gradually heated to 240-260℃ for 1.5-2.5 hours. After adding the acrylic resin prepolymer, polyester prepolymer, and esterification catalyst, the mixture is stirred at 140-160℃ and 300-400 r / min for 20-40 minutes. The stirring speed is then maintained, and filler is added. During the reaction, 3-7 parts of UV absorber are added every 20-40 minutes. After the reaction is completed, a vacuum is applied for 0.4-0.6 hours, controlling the vacuum degree to -0.090~-0.100 MPa to ensure complete removal of small molecules. After releasing the vacuum, the mixture is cooled and discharged to obtain acrylic modified polyester resin.

[0057] Specifically, the acrylic-modified polyester resin is a low-temperature, high-toughness acrylic-modified polyester resin.

[0058] Specifically, the purpose of adding fillers is to improve the mechanical properties and weather resistance of the resin; the purpose of UV absorbers is to improve the weather resistance and UV resistance of the resin; and the purpose of vacuuming under negative pressure is to remove residual small molecules from the system.

[0059] Preferably, the method for preparing the acrylic resin prepolymer includes the following steps: mixing the raw materials for preparing the acrylic resin prepolymer, reacting them, and obtaining the prepolymer.

[0060] More preferably, the preparation method of the acrylic resin prepolymer includes the following steps: mixing methacrylic acid, methyl methacrylate, butyl methacrylate, isooctyl acrylate, initiator, and chain transfer agent to obtain a mixture; adding the mixture to a heated solvent, and simultaneously adding a free radical scavenger, heating, reacting, and then continuing to heat, while adding a molecular sieve during the continued heating process, and then drawing a vacuum to obtain the product.

[0061] More preferably, the preparation method of the acrylic resin prepolymer includes the following steps: mixing methacrylic acid, methyl methacrylate, butyl methacrylate, isooctyl acrylate, initiator, and chain transfer agent to obtain a mixture; adding the mixture dropwise to a solvent heated to 110-130°C over 1.5-2.5 hours, adding 3-7 parts of free radical scavenger every 20-40 minutes during the dropwise addition, refluxing at 120-140°C for 2-4 hours, then continuing to heat to 240-260°C to evaporate the solvent, adding an adsorbent during the continued heating process, and finally evacuating under negative pressure, releasing the vacuum, cooling down, and discharging to obtain the acrylic resin prepolymer.

[0062] Preferably, during the preparation of the acrylic resin prepolymer, the negative pressure is... 0.09~ 0.095MPa.

[0063] Preferably, the vacuuming time during the preparation of the acrylic resin prepolymer is 30-60 minutes.

[0064] Specifically, the acrylic resin prepolymer is a low-temperature, high-toughness acrylic resin prepolymer. The addition of a free radical scavenger prevents the monomer from oxidizing at high temperatures; the addition of an adsorbent adsorbs moisture generated during the reaction, improving reaction efficiency; and the vacuum under negative pressure removes unreacted monomers and other small molecules.

[0065] Preferably, the method for preparing the polyester prepolymer includes the following steps: mixing the raw materials for preparing the polyester prepolymer, reacting them, and obtaining the prepolymer.

[0066] More preferably, the method for preparing the polyester prepolymer includes the following steps: mixing an alcohol compound, an acid compound, and a catalyst, heating, and reacting; then adding an alicyclic polyester diol, continuing to heat and react, and adding an antioxidant during the continued heating and reaction process to obtain the prepolymer.

[0067] More preferably, the preparation method of the polyester prepolymer includes the following steps: nitrogen gas is introduced into an alcohol compound, the temperature is raised to the point where the material melts, and the mixture is stirred at a speed of 200-300 r / min. An acid compound and a catalyst are added, and the temperature is raised to 170-190°C for 0.5-1.5 h. Then, an alicyclic polyester diol is added, and the temperature is raised to 240-260°C for 2-4 h. During the reaction, 5-15 parts of antioxidant are added every 0.5-1.5 h to prevent the polyester from oxidizing and degrading at high temperatures. Finally, a vacuum is drawn under negative pressure, and the material is cooled and discharged after the vacuum is released to obtain the prepolymer.

[0068] Preferably, during the preparation of the polyester prepolymer, the negative pressure is... 0.095~ 0.099MPa.

[0069] Preferably, the vacuuming time during the preparation of the polyester prepolymer is 45-90 minutes.

[0070] Specifically, the polyester prepolymer is a low-temperature, high-toughness polyester prepolymer.

[0071] Specifically, the role of alicyclic polyester diols is to introduce flexible aliphatic ethers to improve low-temperature brittleness resistance; the role of antioxidants is to prevent polyester from oxidizing and degrading at high temperatures.

[0072] A third aspect of the present invention provides an aluminum wheel hub.

[0073] Specifically, the aluminum wheel hub includes a coating formed by the transparent powder coating for low-temperature resistant aluminum wheel hubs as described in the first aspect of the present invention.

[0074] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: This invention utilizes acrylic resin prepolymer and polyester prepolymer to prepare acrylic-modified polyester resin. Through the combined action of acrylic-modified polyester resin, curing agent, plasticizer, toughening agent, and adhesion enhancer, the powder coating maintains excellent flexibility, adhesion, and resistance to gravel impact even at extreme low temperatures of -40℃, while simultaneously meeting the requirements of high transparency, high leveling properties, and high weather resistance. This provides a solid technical guarantee for the reliable application of aluminum wheels in extremely cold climates, demonstrating significant practical application value and broad application prospects. Detailed Implementation

[0075] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0076] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0077] The raw materials and equipment used in Examples 1-3 and Comparative Examples 1-4 are as follows: Twin-screw extruder: JFY-30 crawler-type twin-screw extruder; Triglycidyl isocyanurate: Anshan Runde Fine Chemical Co., Ltd.; Leveling agent: BYK Chemicals, BYK-3902P; Degassing agent: Benzoin, Miwon Specialty Chemical Co., Ltd.; Adhesion enhancer: 3-aminopropyltrimethoxysilane, Guangdong Fangzhou Chemical Co., Ltd., brand name KH-540; Plasticizer: Diisononyl cyclohexane 1,2-dicarboxylate, BASF (Germany), brand name Hexamoll® Dinch; Toughening agent: Polyvinyl butyral (PVB), Solutia, USA, brand name Butvar B-76; UV absorber: BASF (Germany), Tinuvin® 328; Light stabilizer: BASF (Germany), Tinuvin® 292; GMA acrylic resin Almatex PD-7610: Mitsui Chemicals Co., Ltd. (Japan); Dodecanoic acid: Shanghai Kaisai Biotechnology Co., Ltd.; Polyester resin NH-3307: Qingtian Materials Technology Co., Ltd.

[0078] The raw materials and dosages for the preparation of transparent powder coatings for low-temperature resistant aluminum wheel hubs in Examples 1-3 are shown in Table 1.

[0079] Table 1: Raw materials and dosage (parts by mass) for the preparation of transparent powder coatings for low-temperature resistant aluminum wheel hubs in Examples 1-3

[0080] Example 1 This embodiment provides a transparent powder coating for low-temperature resistant aluminum wheel hubs, the raw material components and dosages of which are shown in Table 1.

[0081] This embodiment also provides a method for preparing a transparent powder coating for low-temperature resistant aluminum wheel hubs, the steps of which are as follows: Add all raw material components to a mixing cylinder, mix thoroughly, and crush for 6 minutes to obtain a mixture. Feed the mixture into a twin-screw extruder for extrusion. The heating temperature of the first zone of the twin-screw extruder is 85℃, and the heating temperature of the second zone is 93℃. The extruded material is then fed into a tablet press for tableting, followed by cooling, crushing, sieving, and packaging to obtain a transparent powder coating (D) for low-temperature resistant aluminum wheels. 50 (Particle size: 28 μm).

[0082] The preparation process of the low-temperature, high-toughness acrylic-modified polyester resin is as follows: (1) Synthesis of low-temperature high-toughness acrylic resin prepolymer: In a 2000mL glass four-necked flask equipped with heating, electric stirrer, thermometer, feeding port and fractionation condenser, 450 parts of xylene were added, heated to 120℃ and kept constant temperature, while sufficient nitrogen was introduced to remove oxygen; 320 parts of methacrylic acid, 380 parts of methyl methacrylate, 190 parts of butyl methacrylate, 40 parts of low-temperature toughness monomer isooctyl acrylate, 15 parts of di-tert-butyl peroxide as initiator and 8 parts of n-dodecyl mercaptan as chain transfer agent were mixed evenly to obtain a mixture; the mixture was placed in a constant pressure dropping funnel, the container holding the mixture was washed with a small amount of xylene, and the washed liquid was added to the dropping funnel. In a flask, the mixture was uniformly added dropwise over 1.5 hours. During the dropwise addition, 4 parts of butylated hydroxytoluene (BHT) were added every 25 minutes, for a total of 12 parts of BHT, to prevent the monomer from oxidizing at high temperatures. The mixture was then heated to 125°C and refluxed for 2.5 hours. After the reaction was completed, the temperature was gradually increased to 260°C to evaporate the solvent. During the solvent evaporation process at 260°C, 10 parts of molecular sieve were added to adsorb the water generated during the reaction and improve the reaction efficiency. After the reaction was completed, the mixture was evacuated for 0.8 hours to remove residual small molecules under negative pressure. The vacuum degree was controlled at -0.092 MPa. After the vacuum was released, the mixture was cooled and discharged to obtain a low-temperature, high-toughness acrylic resin prepolymer. (2) Synthesis of low-temperature high-toughness polyester prepolymer: In a 2000mL glass four-necked flask equipped with heating, electric stirrer, thermometer, feeding port and fractionation condenser, 370 parts of neopentyl glycol and 90 parts of trimethylolpropane were added as alcohols. Sufficient nitrogen gas was introduced, and the temperature was raised to melt the material. The mixture was stirred at a speed of 300r / min. Then, 490 parts of terephthalic acid, 160 parts of isophthalic acid, 90 parts of adipic acid and 6 parts of... Monobutyltin oxide was used as a catalyst, and the temperature was further increased to 180°C and reacted for 1 hour. Then, 25 parts of poly(1,4-cyclohexanediethanol adipate) diol were added to introduce flexible aliphatic ethers and improve low-temperature brittleness resistance. Subsequently, the temperature was gradually increased to 250°C and reacted for 3 hours until 98% of the esterified water was discharged. During the reaction, 6 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010 antioxidant) were added every hour, for a total of 18 parts, to prevent the polyester from oxidative degradation at high temperatures. After the reaction was completed, a vacuum was applied for 1 hour to remove residual small molecules in the system under negative pressure. The vacuum degree was controlled at -0.096 MPa. After the vacuum was released, the material was cooled and discharged to obtain a low-temperature, high-toughness polyester prepolymer. (3) Synthesis of low-temperature, high-toughness acrylic-modified polyester resin: In a 1000 mL four-necked glass flask equipped with a heater, electric stirrer, thermometer, feed port, and fractionation condenser, 350 parts of acrylic resin prepolymer, 450 parts of polyester prepolymer, and 6 parts of esterification catalyst monobutylstannic acid were added. Sufficient nitrogen gas was introduced, and the temperature was raised to 145 °C. Stirring was started, and then the temperature was gradually raised to 260 °C for 2 h. After adding acrylic resin prepolymer, polyester prepolymer, and esterification catalyst, the mixture was first stirred at 160 °C at a speed of 360 r / min for 25 min, and then kept at 160 °C for 2 h. While maintaining the stirring speed, 10 parts of nano-silica were added to improve the mechanical properties and weather resistance of the resin. During the reaction, 5 parts of 2-hydroxy-4-n-octyloxybenzophenone (UV-531) were added every 20 minutes, for a total of 30 parts of UV-531, to improve the weather resistance and UV resistance of the resin. After the reaction was completed, a vacuum was applied for 0.6 hours to remove residual small molecules in the system under negative pressure. The vacuum degree was controlled at -0.095 MPa to ensure complete removal of small molecules. After the vacuum was released, the material was cooled and discharged to obtain a low-temperature, high-toughness acrylic modified polyester resin.

[0083] Example 2 This embodiment provides a transparent powder coating for low-temperature resistant aluminum wheel hubs, the raw material components and dosages of which are shown in Table 1.

[0084] This embodiment also provides a method for preparing a transparent powder coating for low-temperature resistant aluminum wheel hubs, the steps of which are as follows: The raw material components are added to a mixing cylinder in the specified proportions, thoroughly mixed, and crushed for 7 minutes to obtain a mixture. This mixture is then fed into a twin-screw extruder for extrusion. The heating temperature of the first zone of the twin-screw extruder is 86℃, and the heating temperature of the second zone is 94℃. The extruded material is then fed into a tablet press for tableting, followed by cooling, crushing, sieving, and packaging to obtain a transparent powder coating (D) for low-temperature resistant aluminum wheels. 50 (Particle size: 27 μm).

[0085] The preparation process of the low-temperature, high-toughness acrylic-modified polyester resin is the same as in Example 1.

[0086] Example 3 This embodiment provides a transparent powder coating for low-temperature resistant aluminum wheel hubs, the raw material components and dosages of which are shown in Table 1.

[0087] This embodiment also provides a method for preparing a transparent powder coating for low-temperature resistant aluminum wheel hubs, the steps of which are as follows: The raw material components are added to a mixing cylinder in the specified proportions, thoroughly mixed, and crushed for 8 minutes to obtain a mixture. This mixture is then fed into a twin-screw extruder for extrusion. The heating temperature of the first zone of the twin-screw extruder is 85℃, and the heating temperature of the second zone is 95℃. The extruded material is then fed into a tablet press for tableting, followed by cooling, crushing, sieving, and packaging to obtain a transparent powder coating (D) for low-temperature resistant aluminum wheels. 50 (Particle size: 29 μm).

[0088] The preparation process of the low-temperature, high-toughness acrylic-modified polyester resin is the same as in Example 1.

[0089] Comparative Example 1 The only difference between Comparative Example 1 and Example 2 is that Comparative Example 1 uses 85 parts of GMA acrylic resin Almatex PD-7610 to replace the low-temperature high-toughness acrylic modified polyester resin of Example 2, and 15 parts of dodecanoic acid to replace the triglycidyl isocyanurate of Example 2. The rest is the same as Example 2.

[0090] Comparative Example 2 The only difference between Comparative Example 2 and Example 2 is that Comparative Example 2 uses an equal amount of polyester resin NH-3307 to replace the low-temperature high-toughness acrylic modified polyester resin in Example 2; otherwise, they are the same as in Example 2.

[0091] Comparative Example 3 The only difference between Comparative Example 3 and Example 3 is that Comparative Example 3 uses dibutyl phthalate (DBP) plasticizer to replace the plasticizer diisononyl cyclohexane 1,2-dicarboxylate in Example 3 in an equal amount, and uses core-shell silicone elastomer micro powder (overseas electric TP901A) to replace the polyvinyl butyral (PVB) in Example 3 in an equal amount. All other aspects are the same as Example 3.

[0092] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that Comparative Example 4 uses an equal amount of the adhesion enhancer in Example 1, which is a titanate coupling agent bis(dioctyloxypyrophosphate) ethylene titanate amine salt. Otherwise, it is the same as Example 1.

[0093] Performance testing The aluminum wheel hub was pretreated with a silane-based chromium-free passivation solution (Henkel BONDERITE M-NT 5200). Then, the powder coatings of Examples 1-3 and Comparative Examples 1-4 were applied to the pretreated aluminum wheel hub surface using a high-pressure electrostatic spray gun. The coating thickness was 100 μm. The coatings were cured in a curing oven at 180°C for 20 min to form a coating film. The coating film was then tested.

[0094] The test items and test methods are as follows: Leveling grade: The test panel and the PCI leveling standard panel (Powder Coating Institute) are visually compared under natural diffused light or 5000K fluorescent light, at a distance of 0.5-1m and a 45° viewing angle. The leveling performance of the coating is divided into 1-10 grades. From grade 1 to grade 10, the leveling performance gradually improves, with grade 1 being severe orange peel and grade 10 being mirror finish. Gloss: Tested according to GB / T 9754-2025; T-bend performance: Tested in accordance with GB / T 13448-2019; Adhesion (cross-cut test): Tested according to GB / T 9286-2021; Impact performance: Tested in accordance with GB / T 1732-2020; Copper-accelerated acetic acid salt spray test (CASS) (240h): The test shall be conducted in accordance with GB / T 10125-2021; Neutral salt spray performance (NSS) (1000h): Tested according to GB / T 10125-2021; Impact performance of crushed stone: Tested according to ASTM D3170; Xenon lamp aging performance (2000h): Tested in accordance with GB / T 1865-2009.

[0095] The performance test results of the powder coatings in Examples 1-3 are shown in Table 2, and the performance test results of the powder coatings in Comparative Examples 1-4 are shown in Table 3.

[0096] Table 2: Performance test results of powder coatings in Examples 1-3

[0097] Table 3: Performance test results of powder coatings in Comparative Examples 1-4

[0098] As shown in Table 2, the transparent powder coating for low-temperature resistant aluminum wheel hubs of the present invention still exhibits excellent flexibility (≤2T), adhesion performance (cross-cut ≤1 grade), impact resistance (≥30kg·cm), and stone chip resistance (≥6B) even at extreme low temperatures of -40℃. It also boasts high optical transparency (60° mirror gloss ≥200%), excellent leveling (visual leveling grade ≥7), outstanding weather resistance (gloss retention ≥90% after 2000h xenon lamp aging, color difference ΔE ≤3.0, secondary adhesion ≤1 grade), and high corrosion resistance (single-sided corrosion ≤1.0mm after 240h CASS or 1000h NSS), fully meeting the comprehensive requirements of wheel hub coatings under extremely cold conditions.

[0099] Comparative Example 1 uses an acrylic curing system. Although some indicators meet the standards, its corrosion resistance is weak, and its flexibility, impact toughness and stone impact resistance are significantly reduced at room temperature and -40℃.

[0100] Comparative Example 2 uses unmodified polyester resin, which has poorer flexibility, impact resistance and stone chip resistance than Example 2, and has problems with poor leveling, low gloss and insufficient weather resistance.

[0101] Comparative Example 3 used other types of plasticizers and toughening agents, which significantly deteriorated its flexibility and impact resistance, and worsened its low-temperature adhesion and stone impact resistance, with a particularly prominent low-temperature embrittlement effect.

[0102] Comparative Example 4 replaced the adhesion enhancer in Example 1 with a titanate coupling agent. The performance was acceptable at normal temperatures, but the adhesion was significantly reduced in the extremely cold environment of -40°C, resulting in the risk of cold brittle peeling. At the same time, it produced a hazy shadow and reduced gloss.

[0103] In summary, this invention, by employing a low-temperature, high-toughness acrylic-modified polyester resin and synergistically introducing toughening agents, plasticizers, and adhesion enhancers such as silane coupling agents, enables the powder coating to exhibit excellent flexibility, impact toughness, stone impact resistance, and adhesion in both ambient and extremely cold environments (-40℃), effectively preventing low-temperature brittle peeling. Simultaneously, it also possesses high leveling, high transparency, high corrosion resistance, and high weather resistance, better meeting the coating requirements of aluminum wheel hubs.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A powder coating, characterized in that, The raw materials for preparing the powder coating include acrylic modified polyester resin, curing agent, plasticizer, toughening agent, and adhesion enhancer.

2. The powder coating according to claim 1, characterized in that, The raw materials for preparing the acrylic-modified polyester resin include acrylic resin prepolymer, polyester prepolymer, esterification catalyst, filler, and UV absorber. The raw materials for preparing the acrylic resin prepolymer include methacrylic acid, methyl methacrylate, butyl methacrylate, isooctyl acrylate, initiator, chain transfer agent, free radical scavenger, solvent and adsorbent; The raw materials for preparing the polyester prepolymer include alcohol compounds, acid compounds, catalysts, alicyclic polyester diols, and antioxidants. And / or, the acrylic-modified polyester resin has an acid value of 45-66 mgKOH / g, a glass transition temperature of 35-44℃, and a softening point of 70-82℃.

3. The powder coating according to claim 1, characterized in that, The raw materials for preparing the powder coating, by weight, include 90-100 parts of acrylic modified polyester resin, 3-10 parts of curing agent, 0.5-1.5 parts of plasticizer, 1-3 parts of toughening agent, and 0.3-0.8 parts of adhesion enhancer. And / or, the raw materials for preparing the powder coating also include at least one of leveling agent, degassing agent, ultraviolet absorber and light stabilizer.

4. The powder coating according to claim 3, characterized in that, The raw materials for preparing the powder coating also include leveling agents, degassing agents, ultraviolet absorbers, and light stabilizers; and by mass parts, the raw materials for preparing the powder coating include 90-100 parts of acrylic modified polyester resin, 3-10 parts of curing agent, 0.5-1.5 parts of plasticizer, 1-3 parts of toughening agent, 0.3-0.8 parts of adhesion enhancer, 1-3 parts of leveling agent, 0.5-1.5 parts of degassing agent, 0.5-1.5 parts of ultraviolet absorber, and 0.3-1 parts of light stabilizer.

5. The powder coating according to claim 2, characterized in that, The raw materials for preparing the acrylic modified polyester resin, by mass parts, include 300-350 parts of acrylic resin prepolymer, 400-500 parts of polyester prepolymer, 3-7 parts of esterification catalyst, 5-15 parts of filler, and 20-40 parts of UV absorber. And / or, by mass parts, the raw materials for preparing the acrylic resin prepolymer include 250-350 parts of methacrylic acid, 350-450 parts of methyl methacrylate, 150-250 parts of butyl methacrylate, 30-50 parts of isooctyl acrylate, 10-20 parts of initiator, 5-15 parts of chain transfer agent, 10-20 parts of free radical scavenger, 400-600 parts of solvent and 8-12 parts of adsorbent; And / or, by mass parts, the raw materials for preparing the polyester prepolymer include 430-600 parts of alcohol compounds, 680-920 parts of acid compounds, 3-7 parts of catalyst, 20-40 parts of alicyclic polyester diol, and 5-20 parts of antioxidant.

6. The method for preparing powder coating according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: The powder coating is prepared by mixing the raw materials, extruding, pressing, cooling, and pulverizing.

7. The preparation method according to claim 6, characterized in that, The preparation method of the acrylic modified polyester resin includes the following steps: mixing the raw materials for preparing the acrylic modified polyester resin, reacting them, and obtaining the resin.

8. The preparation method according to claim 7, characterized in that, In the preparation process of the acrylic-modified polyester resin, the reaction temperature is 240-260℃ and the reaction time is 1.5-2.5h; And / or, the method for preparing the acrylic resin prepolymer includes the following steps: mixing the raw materials for preparing the acrylic resin prepolymer, reacting them, and obtaining the prepolymer; And / or, the method for preparing the polyester prepolymer includes the following steps: mixing the raw materials for preparing the polyester prepolymer, reacting them, and obtaining the prepolymer.

9. The preparation method according to claim 8, characterized in that, The method for preparing the acrylic resin prepolymer includes the following steps: mixing methacrylic acid, methyl methacrylate, butyl methacrylate, isooctyl acrylate, initiator, and chain transfer agent to obtain a mixture; adding the mixture to a heated solvent, and simultaneously adding a free radical scavenger, heating, reacting, and then continuing to heat, while adding an adsorbent during the continued heating process, and then evacuating to obtain the product; And / or, the method for preparing the polyester prepolymer includes the following steps: mixing an alcohol compound, an acid compound, and a catalyst, heating, and reacting; then adding an alicyclic polyester diol, continuing to heat and react, and adding an antioxidant during the continued heating and reaction process to obtain the prepolymer.

10. An aluminum wheel hub, characterized in that, The coating formed by the powder coating as described in any one of claims 1-5.

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