Water-resistant aluminum material powder coating and preparation method thereof

Abstract

The application discloses a kind of boiling water-resistant aluminum material powder coating and preparation method thereof, it is related to the technical field of powder coating.Boiling water-resistant aluminum material powder coating, including binder 135-160 parts, curing agent 5-16 parts, benzoin 0.3-0.6 parts, leveling agent 0.8-1.2 parts, dispersing agent 1.6-2.6 parts and pigment filler 50-80 parts. Among them, binder includes carboxyl-terminated polyester resin, epoxy propyl methacrylate and carboxyl acrylic resin, by mixing epoxy propyl methacrylate and a small amount of carboxyl acrylic resin in carboxyl-terminated polyester resin to form binder, not only can effectively improve the boiling water resistance of powder coating, and can make powder coating maintain good weather resistance, at the same time can improve the surface hardness of coating, and further improve the wear resistance and scratch resistance of coating, thereby it is beneficial to improve the service life of powder coating when applied outdoors, make powder coating more suitable for surface treatment of outdoor aluminum profile.

Description

Technical Field

[0001] This invention relates to the technical field of powder coatings, and in particular to a water-resistant aluminum powder coating and its preparation method. Background Technology

[0002] Aluminum profiles are a primary structural material for doors, windows, and curtain walls, and are widely used worldwide. However, because untreated aluminum alloy extruded profiles have a monotonous appearance and are prone to corrosion, surface treatment is generally applied to meet the requirements of high decorative value and strong weather resistance in building materials. Based on the processing method, aluminum profile surface treatment technologies can be classified into three main categories: anodizing, anodizing followed by electrophoresis, and powder coating. Powder coating, in particular, is a surface treatment method that uses powder coating to form a protective layer on the aluminum profile. Due to its simple processing, low cost, and the resulting durable and chemically resistant coating, powder coating currently holds a significant share of the aluminum profile surface treatment market.

[0003] However, since aluminum profiles are often used for outdoor coating and decoration, and are frequently exposed to sun and rain, some powder coatings with poor water resistance and weather resistance are prone to various problems such as loss of gloss, coating bubbles, and large color differences under prolonged direct sunlight or rain erosion. These problems can seriously affect the service life of the powder coating and aluminum profiles. Therefore, improving the formulation of powder coatings to further enhance their water resistance and weather resistance is of great significance for the surface treatment of aluminum profiles. Summary of the Invention

[0004] In order to improve the water resistance of powder coatings and further extend their service life when applied outdoors, this application provides a water-resistant aluminum powder coating and its preparation method.

[0005] Firstly, the water-resistant aluminum powder coating provided in this application adopts the following technical solution: A water-resistant powder coating comprises the following raw materials in parts by weight: Adhesive: 135-160 parts; Hardener: 5-16 parts; Benzoin: 0.3-0.6 parts; Leveling agent: 0.8-1.2 parts; Dispersant: 1.6-2.6 parts; Pigments and fillers: 50-80 parts; The adhesive comprises carboxyl-terminated polyester resin, glycidyl methacrylate, and carboxyl acrylate resin, wherein the weight ratio of the carboxyl-terminated polyester resin, the glycidyl methacrylate, and the carboxyl acrylate resin is 10:(2.5-4):(0.1-1), and the acid value of the carboxyl-terminated polyester resin is 40-60 mgKOH / g. The curing agent includes either triglycidyl isocyanurate or β-hydroxyalkylamide.

[0006] By adopting the above technical solution, mixing glycidyl methacrylate and a small amount of carboxyl acrylic resin into the carboxyl-terminated polyester resin not only improves the water resistance of the powder coating, allowing the coating surface to maintain a certain gloss after prolonged immersion in boiling water and exhibiting a high gloss retention rate, but also allows the carboxyl acrylic resin to compensate for the reduced weather resistance caused by the addition of glycidyl methacrylate, thus contributing to the powder coating's excellent weather resistance. Simultaneously, it also increases the surface hardness of the coating, improving its wear and scratch resistance. Therefore, it can further extend the service life of the powder coating when used outdoors, making it more suitable for surface treatment of outdoor aluminum profiles.

[0007] Optionally, the weight ratio of the carboxyl-terminated polyester resin, the glycidyl methacrylate, and the carboxyl acrylic resin is 10:(3.5-3.7):(0.3-0.5).

[0008] By adopting the above technical solution, when the mixing weight ratio of terminal carboxyl polyester resin, epoxy methacrylate, and carboxyl acrylic resin in the adhesive is in the range of 10:(3.5-3.7):(0.3-0.5), not only can the water resistance of the powder coating be improved by an appropriate amount of epoxy methacrylate, but also the weather resistance and surface hardness of the powder coating can be improved by an appropriate amount of carboxyl acrylic resin. This prevents the addition of epoxy methacrylate from affecting the weather resistance of the powder coating, which is beneficial to giving the powder coating better comprehensive performance. Therefore, the powder coating is more suitable for the surface treatment of outdoor aluminum profiles.

[0009] Optionally, the acid value of the carboxylated acrylic resin is 50-53.5 mg KOH / g.

[0010] By adopting the above technical solution, the acid value of the carboxyacrylic resin is controlled within the range of 50-53.5 mgKOH / g, which is beneficial to give the powder coating good weather resistance and surface hardness. At the same time, it can also prevent the curing reaction of the carboxyl-terminated polyester resin from being affected by the excessively high acid value of the carboxyacrylic resin, so that the adhesive can be fully cured.

[0011] Optionally, the carboxyl-terminated polyester resin is a stearic acid-modified carboxyl-terminated polyester resin, and the modification steps of the stearic acid-modified carboxyl-terminated resin include: Carboxyl-terminated polyester resin and stearic acid were mixed and dissolved using N,N-dimethylformamide. Then, p-benzenesulfonic acid was added, and the mixture was heated to 125-135℃ for 3-4 hours. The reaction was then continued under vacuum for 12-18 hours. After cooling to room temperature, the pH was adjusted to 4.5-7. The mixture was then precipitated and filtered using ethanol. The filter residue was vacuum dried and then pulverized and ground at high speed to obtain stearic acid-modified carboxyl-terminated polyester resin.

[0012] By adopting the above technical solution, stearic acid can fully react with the residual hydroxyl groups in the carboxyl-terminated polyester resin through esterification, thereby reducing the impact of the hydroxyl groups in the carboxyl-terminated polyester resin on the water resistance of the coating and further improving the water resistance of the powder coating. Secondly, after modifying the carboxyl-terminated polyester resin with stearic acid, long-chain stearic acid groups are introduced into the carboxyl-terminated polyester resin, which can effectively reduce the melt viscosity of the powder coating, thereby improving the flowability of the powder coating during melt curing and enabling the powder coating to form a uniform and smooth powder coating.

[0013] Optionally, the curing agent includes β-hydroxyalkylamide.

[0014] By adopting the above technical solution, in the adhesive system of carboxyl-terminated polyester resin-glycidyl methacrylate-carboxylic acid resin, using β-hydroxyalkylamide as a curing agent not only requires a smaller addition amount, but also results in a coating with better weather resistance, color uniformity, and surface hardness. Furthermore, β-hydroxyalkylamide has a toxicity rating close to non-toxic and non-irritating, making it more environmentally friendly than using triglycidyl isocyanurate as a curing agent, thus meeting the environmental policy requirements of many countries.

[0015] Optionally, the curing agent further includes dicyandiamide, and the weight ratio of the β-hydroxyalkylamide to the dicyandiamide is 1:(0.08-0.12).

[0016] By adopting the above technical solutions, not only can the water resistance of powder coatings be improved, but also the weather resistance of powder coatings can be enhanced, which is beneficial to improving the service life of powder coatings when applied outdoors.

[0017] Optionally, the dispersant is a mixture of silane coupling agent KH550 and silane coupling agent KH570, wherein the weight ratio of the silane coupling agent KH550 to the silane coupling agent KH570 is (0.22-0.3):1.

[0018] By adopting the above technical solution, since the binder includes not only carboxyl-terminated polyester resin, but also glycidyl methacrylate and carboxyl acrylic resin, the use of silane coupling agent KH550 as an aminosilane and silane coupling agent KH570 as an acyloxysilane mixed together at a weight ratio of (0.22-0.3):1 is beneficial to improve the dispersion performance of pigments and fillers in the binder, so that the pigments and fillers can be uniformly dispersed in the coating.

[0019] Optionally, the pigments and fillers include bentonite, barium sulfate, rutile titanium dioxide, and inorganic pigments, wherein the weight ratio of the bentonite, barium sulfate, rutile titanium dioxide, and inorganic pigments is 1:(22.5-35):(1.5-3.5):(0.5-0.8).

[0020] By adopting the above technical solutions, bentonite has good heat resistance and is also conducive to improving the smoothness and fineness of the powder coating; barium sulfate can increase the water resistance and leveling of the coating, which is not only conducive to improving the coating's resistance to boiling water, but also conducive to the formation of a smooth and flat coating surface in the powder coating; rutile titanium dioxide can improve the hiding power and weather resistance of the coating, and can also improve the color retention rate of inorganic pigments; inorganic pigments have the characteristics of being sun-resistant, heat-resistant, weather-resistant, and having strong hiding power. When the mixing weight ratio of bentonite, barium sulfate, rutile titanium dioxide, and inorganic pigments is in the range of 1:(22.5-35):(1.5-3.5):(0.5-0.8), it is conducive to forming a powder coating with good resistance to boiling water and weather resistance, uniform color, gloss, and high color retention rate.

[0021] Optionally, the leveling agent is a polyether-modified organosilicon compound.

[0022] By adopting the above technical solution, polyether-modified organosilicon compounds can be fully mixed in the binder system of carboxyl-terminated polyester resin-glycidyl methacrylate-carboxylic acid resin, which can effectively improve the melt flowability of powder coatings, thereby helping to form a uniform and smooth coating.

[0023] Secondly, the preparation method of a water-resistant aluminum powder coating provided in this application adopts the following technical solution: A preparation method of a water-resistant aluminum powder coating includes the following steps: S1. The carboxyl-terminated polyester resin and the glycidyl methacrylate are stirred and mixed at 130-150°C in a certain proportion. After the mixture is uniform, the carboxyl acrylate resin is added after the temperature is raised to 160-175°C. The temperature is maintained and the mixture is stirred and mixed. After the mixture is uniform, it is extruded and granulated to obtain the binder. S2. After uniformly mixing the binder, curing agent, benzoin, leveling agent, dispersant, pigments and fillers, the mixture is melt-extruded, pressed into sheets, crushed, and sieved to obtain a powder coating.

[0024] By adopting the above technical solution, the preparation of powder coatings has the characteristics of simple steps and convenient operation, and at the same time, it is conducive to the full mixing of the binder, so that the coating formed by the powder coating can be cured uniformly.

[0025] In summary, the technical solution of this application has at least one of the following beneficial effects: 1. By mixing glycidyl methacrylate and a small amount of carboxyl acrylic resin into end-carboxyl polyester resin, it is not only beneficial to improve the water resistance of powder coating, but also to maintain good weather resistance. At the same time, it is beneficial to improve the surface hardness of the coating, further improve the wear and scratch resistance of the coating, and improve the service life of the powder coating when applied outdoors.

[0026] 2. By using a mixture of β-hydroxyalkylamide and dicyandiamide as a curing agent, not only can the water resistance of powder coatings be improved, but also the powder coatings can have good weather resistance, which is beneficial to improving the service life of powder coatings when used outdoors. Detailed Implementation

[0027] The present application will be further described in detail below with reference to embodiments and comparative examples. Example

[0028]

Example 1

[0029] Specifically, the binder comprises a mixture of three substances: carboxyl-terminated polyester resin, glycidyl methacrylate, and carboxyl acrylate resin. The weight ratio of these three substances is 10:3:1, meaning the amount of carboxyl-terminated polyester resin added is 100 kg, glycidyl methacrylate added is 30 kg, and carboxyl acrylate resin added is 10 kg. Specifically, the carboxyl-terminated polyester resin is purchased from Huachang Chemical Co., Ltd., with an acid value of 58.1 mg KOH / mg; the carboxyl acrylate resin has an acid value of 44.2 mg KOH / mg.

[0030] Specifically, the curing agent is triglycidyl isocyanurate; the leveling agent is a polyether-modified organosilicon compound, specifically brand BYK-320; the dispersant is a mixture of silane coupling agents KH550 and KH570, with a weight ratio of 0.22:1, meaning the amount of silane coupling agent KH550 added is 0.4 kg and the amount of silane coupling agent KH570 added is 1.8 kg; the pigments and fillers include 2 kg of bentonite, 54 kg of barium sulfate, 6 kg of titanium dioxide, and 1.2 kg of inorganic pigment, specifically cobalt blue with a particle size range of 20-30 nm.

[0031] The preparation method of a water-resistant aluminum powder coating in this embodiment includes the following steps: S1. Add carboxyl-terminated polyester resin and glycidyl methacrylate to a reactor, heat to 140°C, and stir for 20 minutes at a speed of 200 r / min. Then raise the reactor temperature to 170°C, add carboxyl acrylic resin, and continue stirring for 30 minutes at a speed of 400 r / min. Finally, transfer the uniformly mixed material to a screw extruder for extrusion granulation to obtain the binder. S2. Add various raw materials such as binder, curing agent, benzoin, leveling agent, dispersant and pigments to the reactor and stir for 30 minutes at a temperature of 120℃ and a stirring speed of 400r / min. Then transfer the uniformly mixed material to a screw extruder, control the screw speed at 15r / min and the extrusion temperature at 145℃ for melt extrusion, tableting, crushing and sieving to obtain powder coating.

[0032]

Example 2

[0033] Specifically, the binder comprises a mixture of three substances: carboxyl-terminated polyester resin, glycidyl methacrylate, and carboxyl acrylate resin. The weight ratio of these three resins is 10:2.5:0.3, meaning the amount of carboxyl-terminated polyester resin added is 125 kg, glycidyl methacrylate added is 31.25 kg, and carboxyl acrylate resin added is 3.75 kg. Specifically, the carboxyl-terminated polyester resin is purchased from Huachang Chemical, with an acid value of 58.1 mg KOH / mg; the carboxyl acrylate resin has an acid value of 44.2 mg KOH / mg.

[0034] Specifically, the curing agent is β-hydroxyalkylamide; the leveling agent is a polyether-modified organosilicon compound, specifically brand BYK-320; the dispersant is a mixture of silane coupling agents KH550 and KH570, with a weight ratio of 0.3:1, meaning the amount of silane coupling agent KH550 added is 0.6 kg and the amount of silane coupling agent KH570 added is 2 kg; the pigments and fillers include 2 kg of bentonite, 70 kg of barium sulfate, 7 kg of titanium dioxide, and 1 kg of inorganic pigment, specifically cobalt blue with a particle size range of 20-30 nm.

[0035] In addition, the preparation method of a water-resistant aluminum powder coating in this embodiment includes the following steps: S1. Add carboxyl-terminated polyester resin and glycidyl methacrylate to a reactor, heat to 130°C, and stir for 30 minutes at a speed of 200 r / min. Then raise the reactor temperature to 175°C, add carboxyl acrylic resin, and continue stirring for 20 minutes at a speed of 400 r / min. Finally, transfer the uniformly mixed material to a screw extruder for extrusion granulation to obtain the binder. S2. Add various raw materials such as binder, curing agent, benzoin, leveling agent, dispersant and pigments to the reactor and stir for 30 minutes at a temperature of 120℃ and a stirring speed of 400r / min. Then transfer the uniformly mixed material to the screw extruder, control the screw speed at 15r / min and the extrusion temperature at 140℃ for melt extrusion, tableting, crushing and sieving to obtain powder coating.

[0036]

Example 3

[0037] Specifically, the binder comprises a mixture of three substances: carboxyl-terminated polyester resin, glycidyl methacrylate, and carboxyl acrylate resin. The weight ratio of these three resins is 10:4:1, meaning the amount of carboxyl-terminated polyester resin added is 90 kg, glycidyl methacrylate added is 36 kg, and carboxyl acrylate resin added is 9 kg. Specifically, the carboxyl-terminated polyester resin is purchased from Huachang Chemical Co., Ltd., with an acid value of 58.1 mg KOH / mg; the carboxyl acrylate resin has an acid value of 53.5 mg KOH / mg.

[0038] Specifically, the curing agent is a mixture of β-hydroxyalkylamide and dicyandiamide, and the weight ratio of β-hydroxyalkylamide to dicyandiamide is 1:0.24, that is, the amount of β-hydroxyalkylamide added is 4.52 kg and the amount of dicyandiamide added is 1.08 kg.

[0039] Specifically, the leveling agent is a polyether-modified organosilicon compound, specifically brand BYK-320; the dispersant is a mixture of silane coupling agents KH550 and KH570, with a weight ratio of 0.25:1, meaning the amount of silane coupling agent KH550 added is 0.4 kg and the amount of silane coupling agent KH570 added is 1.6 kg; the pigments and fillers include 2 kg of bentonite, 45 kg of barium sulfate, 3 kg of titanium dioxide, and 1.6 kg of inorganic pigment, specifically cobalt blue with a particle size range of 20-30 nm.

[0040] In addition, the preparation method of a water-resistant aluminum powder coating in this embodiment includes the following steps: S1. Add carboxyl-terminated polyester resin and glycidyl methacrylate to a reactor, heat to 150°C, and stir for 20 minutes at a speed of 200 r / min. Then raise the reactor temperature to 160°C, add carboxyl acrylic resin, and continue stirring for 25 minutes at a speed of 400 r / min. Finally, transfer the uniformly mixed material to a screw extruder for extrusion granulation to obtain the binder. S2. Add various raw materials such as binder, curing agent, benzoin, leveling agent, dispersant and pigments to the reactor and stir for 30 minutes at a temperature of 120℃ and a stirring speed of 400r / min. Then transfer the uniformly mixed material to the screw extruder, control the screw speed at 15r / min and the extrusion temperature at 140℃ for melt extrusion, tableting, crushing and sieving to obtain powder coating.

[0041]

Example 4

[0042] In this embodiment, the weight ratio of carboxyl-terminated polyester resin, glycidyl methacrylate, and carboxyl acrylic resin is 10:3.5:0.5, that is, the amount of carboxyl-terminated polyester resin added is 100 kg, the amount of glycidyl methacrylate added is 35 kg, and the amount of carboxyl acrylic resin added is 5 kg.

[0043]

Example 5

[0044] In this embodiment, the weight ratio of carboxyl-terminated polyester resin, glycidyl methacrylate, and carboxyl acrylic resin is 10:3.7:0.3, that is, the amount of carboxyl-terminated polyester resin added is 100 kg, the amount of glycidyl methacrylate added is 37 kg, and the amount of carboxyl acrylic resin added is 3 kg.

[0045]

Example 6

[0046] In this embodiment, the weight ratio of carboxyl-terminated polyester resin, glycidyl methacrylate, and carboxyl acrylic resin is 10:39:0.1, that is, the amount of carboxyl-terminated polyester resin added is 100 kg, the amount of glycidyl methacrylate added is 39 kg, and the amount of carboxyl acrylic resin added is 1 kg.

[0047]

Example 7

[0048] In this embodiment, the acid value of the carboxyacrylate resin in the adhesive is 53.5 mg KOH / mg.

[0049]

Example 8

[0050] In this embodiment, the acid value of the carboxyacrylate resin in the adhesive is 68.9 mg KOH / mg.

[0051]

Example 9

[0052] Specifically, the preparation of stearic acid-modified carboxyl-terminated polyester includes the following steps: Carboxyl-terminated polyester resin and stearic acid were mixed and dissolved using excess N,N-dimethylformamide. Then, 0.5% p-benzenesulfonic acid was added, and the mixture was heated to 135°C for 3 hours. The reaction was then continued under vacuum for 12 hours. After cooling to room temperature, the pH was adjusted to 5.5 with dilute sodium hydroxide solution. The mixture was then precipitated with anhydrous ethanol and filtered. The filter residue was then vacuum dried and high-speed pulverized to obtain stearic acid-modified carboxyl-terminated polyester resin.

[0053]

Example 10

[0054] In this embodiment, the curing agent is replaced with β-hydroxyalkylamide, and the amount added is 6 kg.

[0055]

Example 11

[0056] In this embodiment, the amount of β-hydroxyalkylamide added is 4.44 kg, and the amount of dicyandiamide added is 1.56 kg.

[0057] Comparative Example Comparative Example 1 A powder coating differs from [Example 1] in that it does not contain glycidyl methacrylate and carboxyacrylate resin, and replaces glycidyl methacrylate and carboxyacrylate resin in equal amounts with carboxyl-terminated polyester resin.

[0058] Specifically, in this comparative example, the adhesive includes 140 kg of carboxyl-terminated polyester resin.

[0059] Comparative Example 2 A powder coating differs from [Example 1] in that it does not contain glycidyl methacrylate, and replaces glycidyl methacrylate in an equal amount with a carboxyl-terminated polyester resin.

[0060] Specifically, in this comparative example, the adhesive includes 130 kg of carboxyl-terminated polyester resin and 10 kg of carboxyl-terminated acrylic resin.

[0061] Comparative Example 3 A powder coating differs from [Example 1] in that it does not contain carboxyl acrylic resin, and replaces the carboxyl acrylic resin with an equal amount of carboxyl-terminated polyester resin.

[0062] Specifically, in this comparative example, the adhesive includes 110 kg of carboxyl-terminated polyester resin and 30 kg of glycidyl methacrylate.

[0063] Performance test data Sample preparation: Under the same spraying pressure, the powder coatings prepared in Examples 1-11 and Comparative Examples 1-3 were sprayed onto standard test plates preheated in an oven at 180°C using high-voltage electrostatic spraying. The coating thickness was approximately 200 μm, the curing temperature was 200°C, and the curing time was 5 min, thus obtaining the test samples. The standard test plates used for testing were aluminum plates, and pretreated according to GB / T 9271-2008 Standard Test Plates for Paints and Varnishes.

[0064] Aging treatment: The test samples were subjected to an automatic cyclic exposure test according to the provisions of Method A, Cycle No. 1 in Table 3 of GB / T 16422.2-2014 Laboratory Light Source Exposure Test Method for Plastics, with an exposure time of 1000h.

[0065] 1. Boiling Water Resistance Test: A boiling water test was conducted according to section 6.14.1 of GB 5237.4-2004 Aluminum Alloy Building Profiles Part 4: Powder Coated Profiles. The surface condition and gloss loss rate of the coatings for each example and comparative example were recorded after 12 hours of boiling. The gloss loss rate was determined according to GB / T 9754 Determination of 20°, 60° and 85° Specular Gloss of Paint Films Without Metallic Pigments. The test geometric conditions were 60° ± 0.1° gloss loss rate = . The higher the gloss loss rate, the lower the gloss retention rate.

[0066] 2. Color difference value: The color difference of the test samples before and after aging was tested using a colorimeter, referring to GB / T 11186.2 Measurement Methods for Coating Color Part 2: Color Measurement. The color difference value of the test samples before and after aging was calculated, referring to GB / T 11186.3 Measurement Methods for Coating Color Part 3: Color Difference Calculation. A larger color difference value indicates a lower color retention rate and poorer weather resistance.

[0067] 3. Pencil Hardness: The test was conducted according to GB / T 6739-2006 "Determination of Hardness of Paints and Varnishes by Pencil Method", and the results were recorded in Table 1 below. The test object was the sample to be tested. The higher the hardness of the paint film, the better its abrasion resistance.

[0068] Table 1 Performance Test Data Based on Examples 1 and Comparative Examples 1-3, and the data in Table 1, it can be seen that mixing glycidyl methacrylate into the carboxyl-terminated polyester resin effectively improves the water resistance of the powder coating. After prolonged immersion in boiling water, the coating surface does not completely lose its gloss and retains a certain gloss rate, but the weather resistance of the powder coating decreases somewhat. This may be because glycidyl methacrylate contains epoxy groups. During the curing of the carboxyl-terminated polyester resin, the epoxy groups in the glycidyl methacrylate undergo ring-opening and cross-linking with the carboxyl-terminated polyester resin, further increasing the curing cross-linking density and improving the density of the formed coating, thereby enhancing the water resistance of the powder coating.

[0069] Adding a small amount of carboxylated acrylic resin not only further improves the water resistance of polyester resin, allowing the coating to maintain a uniform color after prolonged boiling, but also enhances the weather resistance of powder coatings, compensating for the reduced weather resistance caused by the addition of glycidyl methacrylate. Furthermore, it increases the surface strength of the coating, enabling the powder coating to form a powder coating with higher mechanical strength.

[0070] Combining Examples 1 and 4-6 with the data in Table 1, it can be seen that when the mixing weight ratio of the end-carboxyl polyester resin, glycidyl methacrylate, and carboxyl acrylic resin in the binder is in the range of 10:(3.5-3.7):(0.3-0.5), the powder coating exhibits better overall performance, possessing not only higher water resistance and weather resistance but also higher surface hardness. This may be because, with the polyester resin addition amount remaining constant, while increasing the addition amount of glycidyl methacrylate and decreasing the addition amount of carboxyl acrylic resin improves the water resistance of the powder coating, the excessive amount of glycidyl methacrylate can lead to a decrease in the weather resistance of the powder coating, as well as low color retention and decreased hardness, which is detrimental to the long-term outdoor application of the powder coating.

[0071] Based on Examples 5 and 7-8, and the data in Table 1, it can be seen that as the acid value of the carboxyacrylate resin increases, the powder coating exhibits good weather resistance and surface hardness. This is likely because a higher acid value provides more crosslinking reaction sites in the system, allowing for sufficient entanglement and crosslinking with the end-carboxyl polyester resin and glycidyl methacrylate. This enables the glycidyl methacrylate and carboxyacrylate resin to fully function and improve the coating's various properties. However, when the acid value of the carboxyacrylate resin exceeds a certain range, the coating's water resistance decreases significantly. This may be because excessively high acid values ​​in the carboxyacrylate resin can affect the reaction between the curing agent and the end-carboxyl polyester resin, directly impacting the coating's degree of curing.

[0072] Combining Examples 7 and 9 with the data in Table 1, it can be seen that modifying the carboxyl-terminated polyester resin with stearic acid further improves the water resistance of the powder coating. This may be because the carboxyl-terminated polyester resin still contains some hydroxyl groups. After modification with stearic acid, the stearic acid undergoes an esterification reaction with the residual hydroxyl groups in the carboxyl-terminated polyester resin. This not only eliminates the residual hydroxyl groups in the carboxyl-terminated polyester resin, reducing the reaction sites available for water molecule adsorption and decreasing the water molecule penetration capacity, but also introduces long-chain stearic acid groups into the carboxyl-terminated polyester resin. This helps to reduce the melt viscosity of the coating and improve its leveling properties during melting and solidification, allowing the coating to remain uniform and smooth.

[0073] Combining Examples 9 and 10-11 with the data in Table 1, it can be seen that when β-hydroxyalkylamide is used as the curing agent, not only is the amount added less than when triglycidyl isocyanurate is used as the curing agent, but β-hydroxyalkylamide also does not contain epoxy groups, thus improving the weather resistance of the powder coating to some extent. However, the water resistance of the powder coating is not as good as when triglycidyl isocyanurate is used, and the gloss loss rate is higher. When β-hydroxyalkylamide is mixed with dicyandiamide as the curing agent, the overall performance of the powder coating is improved. It not only makes the water resistance of the powder coating close to that when triglycidyl isocyanurate is used alone, but also has the good weather resistance when β-hydroxyalkylamide is used alone.

[0074] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this specific embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A water-resistant aluminum powder coating, characterized in that, Including the following parts by weight of raw materials: Adhesive: 135-160 parts; Hardener: 5-16 parts; Benzoin: 0.3-0.6 parts; Leveling agent: 0.8-1.2 parts; Dispersant: 1.6-2.6 parts; Pigments and fillers: 50-80 parts; The adhesive comprises carboxyl-terminated polyester resin, glycidyl methacrylate, and carboxyl acrylate resin, wherein the weight ratio of the carboxyl-terminated polyester resin, the glycidyl methacrylate, and the carboxyl acrylate resin is 10:(2.5-4):(0.1-1), and the acid value of the carboxyl-terminated polyester resin is 40-60 mgKOH / g. The carboxyl-terminated polyester resin is a stearic acid-modified carboxyl-terminated polyester resin, and the modification steps of the stearic acid-modified carboxyl-terminated resin are as follows: Carboxyl-terminated polyester resin and stearic acid were mixed and dissolved using N,N-dimethylformamide. Then p-toluenesulfonic acid was added, and the mixture was heated to 125-135℃ for 3-4 hours. The reaction was then continued under vacuum for 12-18 hours. After cooling to room temperature, the pH was adjusted to 4.5-7. The mixture was then precipitated and filtered using ethanol. The filter residue was vacuum dried and then pulverized and ground at high speed to obtain stearic acid-modified carboxyl-terminated polyester resin. The curing agent is a composition of β-hydroxyalkylamide and dicyandiamide, wherein the weight ratio of β-hydroxyalkylamide to dicyandiamide is 1:0.24 or 1:0.

35.

2. The water-resistant aluminum powder coating according to claim 1, characterized in that: The weight ratio of the carboxyl-terminated polyester resin, the glycidyl methacrylate, and the carboxyl acrylic resin is 10:(3.5-3.7):(0.3-0.5).

3. The water-resistant aluminum powder coating according to claim 2, characterized in that: The acid value of the carboxylated acrylic resin is 50-53.5 mg KOH / g.

4. The water-resistant aluminum powder coating according to claim 1, characterized in that: The dispersant is a mixture of silane coupling agent KH550 and silane coupling agent KH570, and the weight ratio of the mixture of silane coupling agent KH550 and silane coupling agent KH570 is (0.22-0.3):

1.

5. The water-resistant aluminum powder coating according to claim 1, characterized in that: The pigments and fillers include bentonite, barium sulfate, rutile titanium dioxide, and cobalt blue. The weight ratio of the bentonite, barium sulfate, rutile titanium dioxide, and cobalt blue is 1:(22.5-35):(1.5-3.5):(0.5-0.8), and the particle size of the cobalt blue is in the range of 20-30 nm.

6. The water-resistant aluminum powder coating according to claim 1, characterized in that: The leveling agent is a polyether-modified organosilicon compound.

7. A method for preparing a water-resistant aluminum powder coating, characterized in that, The method for preparing a water-resistant aluminum powder coating according to any one of claims 1-6 comprises the following steps: S1. The carboxyl-terminated polyester resin and the glycidyl methacrylate are stirred and mixed at 130-150°C in a certain proportion. After the mixture is uniform, the carboxyl acrylate resin is added after the temperature is raised to 160-175°C. The temperature is maintained and the mixture is stirred and mixed. After the mixture is uniform, it is extruded and granulated to obtain the binder. S2. After uniformly mixing the binder, curing agent, benzoin, leveling agent, dispersant, pigments and fillers, the mixture is melt-extruded, pressed into sheets, crushed, and sieved to obtain a powder coating.

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