Low-temperature curing powder coating and preparation method thereof

Abstract

The invention relates to the technical field of powder coatings, in particular to a low-temperature curing powder coating and a preparation method thereof.The preparation method comprises the steps that a low-temperature curing polyurethane oligomer, a curing agent, nanometer titania, a flatting agent and polyethylene wax are evenly mixed, and a premix is obtained; and carrying out melt extrusion, grinding and sieving on the premix, and uniformly mixing the premix with the modified microcapsules to prepare the low-temperature curing powder coating. The low-temperature curing polyurethane oligomer and the modified microcapsule are matched for use, so that the prepared coating film has relatively low curing temperature and also has good antibacterial property and self-healing property, and the overall quality of the coating film is improved; moreover, the obtained powder coating can be cured at a relatively low temperature, energy conservation is better realized in actual use, meanwhile, the mass loss of the modified microcapsule at the temperature is very small, and the quality of a formed coating film is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of powder coatings, in particular to a low-temperature curing powder coating and a preparation method thereof. Background Art

[0002] Powder coating and painting are technologies and processes that have developed rapidly in recent years. Powder coating is made of resin matrix and curing agent as film-forming substances, supplemented by fillers, pigments and functional additives. Unlike general coatings, it does not use solvents or water as dispersants, but uses air as a dispersion medium. It has the characteristics of being solvent-free, pollution-free, recyclable, energy-saving and environmentally friendly, and is widely used in the fields of automotive decoration, shipbuilding industry, etc.

[0003] Patent application number 202410752629.5 discloses a high-performance low-temperature curing powder coating and a preparation method thereof, and the obtained powder coating can be cured at about 110°C; Patent application number 202311856633.8 discloses a low-temperature powder coating and a preparation method thereof, and the obtained powder coating can be cured at about 140°C, both of which have the characteristics of low-temperature curing. However, some application scenarios of powder coatings are often more complicated, and the powder coatings in the above patents are relatively simple in function and difficult to adapt to the use of complex scenarios. Based on this, a low-temperature curing powder coating and a preparation method thereof are proposed. Summary of the invention

[0004] In order to address the deficiencies in the prior art, the present invention provides a low-temperature curing powder coating and a method for preparing the same. By using a low-temperature curing polyurethane oligomer and a modified microcapsule in combination, the prepared coating film has good antibacterial and self-healing properties while having a lower curing temperature, thereby improving the overall quality of the coating film.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a low-temperature curing powder coating, comprising the following raw materials in parts by weight: 60-70 parts of low-temperature curing polyurethane oligomer, 8-15 parts of modified microcapsules, 4-8 parts of curing agent, 5-10 parts of nano titanium dioxide, 2-5 parts of leveling agent, and 0.2-0.5 parts of polyethylene wax.

[0006] Preferably, the curing agent is selected from isophorone diisocyanate and diphenylmethane diisocyanate; and the leveling agent is selected from leveling agent GLP588 and leveling agent GLP788.

[0007] Preferably, the preparation method of the low-temperature curing polyurethane oligomer is as follows: S11, toluene-2,4-diisocyanate and dimethyl sulfoxide are mixed, dibutyltin dilaurate, hydroxyethyl methacrylate and hydroquinone are added with stirring, and the mixture is reacted at 30-40°C for 2.5-3h to obtain an intermediate solution; S12, pentaerythritol is added to the intermediate solution, and the mixture is reacted at 60-70°C for 2-2.5h to obtain a mixture; S13, the mixture is added to deionized water to generate a precipitate, and the mixture is crushed, filtered and dried to obtain a low-temperature curing polyurethane oligomer.

[0008] Preferably, in step S11, the mass ratio of toluene-2,4-diisocyanate, hydroxyethyl methacrylate and dimethyl sulfoxide is (3-4): (2-3): (9-11); the amount of dibutyltin dilaurate added is 0.3-0.5% of the total mass of the intermediate solution; and the amount of hydroquinone added is 0.5-1% of the total mass of the intermediate solution.

[0009] Preferably, in step S12, the amount of pentaerythritol added is 5-8% of the total mass of the intermediate solution.

[0010] Preferably, the preparation method of the modified microcapsules is as follows: S21, linseed oil, nano zinc oxide and formamide are mixed, and stirred at 55-60°C for 1.5-2h, followed by adding sodium dodecylbenzene sulfonate and continuing to stir for 2.5-3h to obtain an emulsion; S22, calcium chloride solution is added to the emulsion, and stirred at 55-60°C for 2.5-3h, followed by dropwise addition of sodium carbonate solution, stirring to form a precipitate, and filtering, washing and drying to obtain functional microcapsules; S23, surface modification of the functional microcapsules is performed with a silane coupling agent to obtain modified microcapsules.

[0011] Preferably, in step S21, the mass ratio of the linseed oil, sodium dodecylbenzene sulfonate and formamide is (3-5): (0.5-1): (90-100); and the amount of the nano zinc oxide added is 5-10% of the total mass of the emulsion.

[0012] Preferably, in step S22, the calcium chloride solution is prepared by dissolving calcium chloride in formamide; the sodium carbonate solution is prepared by dissolving sodium carbonate in formamide; the mass fraction of the calcium chloride solution is 15%; and the mass fraction of the sodium carbonate solution is 12%.

[0013] Preferably, in step S22, the amount of calcium chloride solution added is 20-30% of the total mass of the emulsion; the amount of sodium carbonate solution added is 25-35% of the total mass of the emulsion.

[0014] The present invention also provides a method for preparing a low temperature curing powder coating, comprising the following steps: (1) uniformly mixing a low-temperature curing polyurethane oligomer, a curing agent, nano titanium dioxide, a leveling agent and polyethylene wax to obtain a premix; (2) The premix is ​​melt-extruded, ground and sieved, and then evenly mixed with the modified microcapsules to obtain a low-temperature curing powder coating.

[0015] The present invention provides a low-temperature curing powder coating and a preparation method thereof, which has the following beneficial effects compared with the prior art: The present invention uses a low-temperature curing polyurethane oligomer and a modified microcapsule in combination, so that the prepared coating has a low curing temperature and good antibacterial and self-healing properties, thereby improving the overall quality of the coating; moreover, the obtained powder coating can be cured at about 120°C, which can better achieve energy saving in actual use. At the same time, the mass loss of the modified microcapsule at this temperature is also very small, thereby ensuring the quality of the formed coating.

[0016] The present invention uses pentaerythritol as the core, which contains multiple hydroxyl functional groups and has a relatively symmetrical structure. The glass transition temperature of the low-temperature curing polyurethane oligomer obtained with pentaerythritol as the core can reach 58.4°C, and can be better applied to low-temperature curing powder coatings.

[0017] The present invention uses linseed oil as the core material, calcium carbonate as the main wall material and doped with nano zinc oxide, so that the modified microcapsules have good antibacterial properties; at the same time, when cracks are generated in the coating film under the action of external force, the microcapsules rupture, the linseed oil inside flows out and contacts with oxygen, and the linolenic acid undergoes a cross-linking and curing reaction to achieve the healing of the cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 This is the infrared spectrum of the low temperature curing polyurethane oligomer in Example 3 of the present invention. DETAILED DESCRIPTION

[0019] The following examples are used to explain the implementation methods of the present application in detail, so that the implementation process of how the present application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0020] Example 1

[0021] The preparation method of low temperature curing polyurethane oligomer is as follows: S11, toluene-2,4-diisocyanate and dimethyl sulfoxide are mixed, dibutyltin dilaurate, hydroxyethyl methacrylate and hydroquinone are added with stirring, and the mixture is reacted at 30° C. for 3 h to obtain an intermediate solution; The mass ratio of the above-mentioned toluene-2,4-diisocyanate, hydroxyethyl methacrylate and dimethyl sulfoxide is 3:2:9; the amount of dibutyltin dilaurate added is 0.5% of the total mass of the intermediate solution; and the amount of hydroquinone added is 1% of the total mass of the intermediate solution.

[0022] S12, adding pentaerythritol to the intermediate solution, reacting at 70° C. for 2 hours to obtain a mixture; wherein the amount of pentaerythritol added is 8% of the total mass of the intermediate solution.

[0023] S13. The mixture is added into deionized water to generate a precipitate, which is crushed, filtered and dried to obtain a low-temperature curing polyurethane oligomer having a glass transition temperature of 56.5° C. and is stored at 40° C. for 3 months without agglomeration.

[0024] Example 2

[0025] The preparation method of low temperature curing polyurethane oligomer is as follows: S11, toluene-2,4-diisocyanate and dimethyl sulfoxide are mixed, dibutyltin dilaurate, hydroxyethyl methacrylate and hydroquinone are added with stirring, and the mixture is reacted at 40° C. for 2.5 hours to obtain an intermediate solution; The mass ratio of the above-mentioned toluene-2,4-diisocyanate, hydroxyethyl methacrylate and dimethyl sulfoxide is 4:3:11; the amount of dibutyltin dilaurate added is 0.3% of the total mass of the intermediate solution; and the amount of hydroquinone added is 0.5% of the total mass of the intermediate solution.

[0026] S12, adding pentaerythritol to the intermediate solution, reacting at 60° C. for 2.5 hours to obtain a mixture; wherein the amount of pentaerythritol added is 5% of the total mass of the intermediate solution.

[0027] S13. The mixture is added into deionized water to generate a precipitate, which is crushed, filtered and dried to obtain a low-temperature curing polyurethane oligomer having a glass transition temperature of 57.6° C. and is stored at 40° C. for 3 months without agglomeration.

[0028] Example 3

[0029] The preparation method of low temperature curing polyurethane oligomer is as follows: S11, toluene-2,4-diisocyanate and dimethyl sulfoxide were mixed, dibutyltin dilaurate, hydroxyethyl methacrylate and hydroquinone were added with stirring, and the mixture was reacted at 35° C. for 2.7 h to obtain an intermediate solution; The mass ratio of the above-mentioned toluene-2,4-diisocyanate, hydroxyethyl methacrylate and dimethyl sulfoxide is 3.5:2:10; the amount of dibutyltin dilaurate added is 0.4% of the total mass of the intermediate solution; and the amount of hydroquinone added is 0.6% of the total mass of the intermediate solution.

[0030] S12, adding pentaerythritol to the intermediate solution, reacting at 65° C. for 2.2 hours to obtain a mixture; wherein the amount of pentaerythritol added is 7% of the total mass of the intermediate solution.

[0031] S13. The mixture is added into deionized water to generate a precipitate, which is crushed, filtered and dried to obtain a low-temperature curing polyurethane oligomer having a glass transition temperature of 58.4° C. and is stored at 40° C. for 3 months without agglomeration.

[0032] Example 4

[0033] The preparation method of the modified microcapsules is as follows: S21, mixing linseed oil, nano zinc oxide and formamide, stirring at 55° C. for 2 h, then adding sodium dodecylbenzene sulfonate and continuing stirring for 2.5 h to obtain an emulsion; The mass ratio of the linseed oil, sodium dodecylbenzene sulfonate and formamide is 3:0.5:90; the added amount of nano zinc oxide is 10% of the total mass of the emulsion.

[0034] S22, adding 15wt% calcium chloride solution to the emulsion, maintaining stirring at 55°C for 3h, then dropping 12wt% sodium carbonate solution, stirring to form a precipitate, filtering, washing, and drying to obtain functional microcapsules; The calcium chloride solution is prepared by dissolving calcium chloride in formamide; the sodium carbonate solution is prepared by dissolving sodium carbonate in formamide; the amount of calcium chloride solution added is 20% of the total mass of the emulsion; the amount of sodium carbonate solution added is 25% of the total mass of the emulsion.

[0035] S23. The functional microcapsules were surface modified by using silane coupling agent KH-550 to obtain modified microcapsules. When the modified microcapsules were baked at 120° C. for 10 min, the mass loss was 2.05%.

[0036] Example 5

[0037] The preparation method of the modified microcapsules is as follows: S21, mixing linseed oil, nano zinc oxide and formamide, stirring at 60° C. for 1.5 h, then adding sodium dodecylbenzene sulfonate and continuing stirring for 3 h to obtain an emulsion; The mass ratio of the linseed oil, sodium dodecylbenzene sulfonate and formamide is 5:1:100; the added amount of nano zinc oxide is 5% of the total mass of the emulsion.

[0038] S22, adding 15wt% calcium chloride solution to the emulsion, maintaining stirring at 60°C for 2.5h, then dropping 12wt% sodium carbonate solution, stirring to form a precipitate, filtering, washing, and drying to obtain functional microcapsules; The calcium chloride solution is prepared by dissolving calcium chloride in formamide; the sodium carbonate solution is prepared by dissolving sodium carbonate in formamide; the amount of calcium chloride solution added is 30% of the total mass of the emulsion; the amount of sodium carbonate solution added is 35% of the total mass of the emulsion.

[0039] S23. The functional microcapsules were surface modified by using silane coupling agent KH-560 to obtain modified microcapsules. When the modified microcapsules were baked at 120°C for 10 minutes, the mass loss was 1.82%.

[0040] Example 6

[0041] The preparation method of the modified microcapsules is as follows: S21, mixing linseed oil, nano zinc oxide and formamide, stirring at 58° C. for 1.8 h, then adding sodium dodecylbenzene sulfonate and continuing stirring for 2.7 h to obtain an emulsion; The mass ratio of the linseed oil, sodium dodecylbenzene sulfonate and formamide is 4:0.8:95; the added amount of nano zinc oxide is 8% of the total mass of the emulsion.

[0042] S22, adding 15wt% calcium chloride solution to the emulsion, maintaining stirring at 58°C for 2.6h, then dropping 12wt% sodium carbonate solution, stirring to form a precipitate, filtering, washing, and drying to obtain functional microcapsules; The calcium chloride solution is prepared by dissolving calcium chloride in formamide; the sodium carbonate solution is prepared by dissolving sodium carbonate in formamide; the amount of calcium chloride solution added is 25% of the total mass of the emulsion; the amount of sodium carbonate solution added is 30% of the total mass of the emulsion.

[0043] S23. The functional microcapsules were surface modified by using silane coupling agent KH-570 to obtain modified microcapsules. When the modified microcapsules were baked at 120°C for 10 minutes, the mass loss was 1.79%.

[0044] Example 7

[0045] A low-temperature curing powder coating comprises the following raw materials in parts by weight: 70 parts of low-temperature curing polyurethane oligomer, 8 parts of modified microcapsules, 8 parts of isophorone diisocyanate curing agent, 5 parts of nano titanium dioxide, 5 parts of leveling agent GLP588, and 0.2 parts of polyethylene wax.

[0046] The method for preparing the low temperature curing powder coating comprises the following steps: (1) uniformly mixing a low-temperature curing polyurethane oligomer, an isophorone diisocyanate curing agent, nano titanium dioxide, a leveling agent GLP588 and polyethylene wax to obtain a premix; (2) The premix is ​​melt-extruded, ground and sieved, and then evenly mixed with the modified microcapsules to obtain a low-temperature curing powder coating.

[0047] In this embodiment, the low temperature curing polyurethane oligomer in Example 1 and the modified microcapsule in Example 5 are used.

[0048] Example 8

[0049] A low-temperature curing powder coating comprises the following raw materials in parts by weight: 60 parts of low-temperature curing polyurethane oligomer, 15 parts of modified microcapsules, 4 parts of diphenylmethane diisocyanate curing agent, 10 parts of nano titanium dioxide, 2 parts of leveling agent GLP788, and 0.5 parts of polyethylene wax.

[0050] The method for preparing the low temperature curing powder coating comprises the following steps: (1) uniformly mixing a low-temperature curing polyurethane oligomer, a diphenylmethane diisocyanate curing agent, nano titanium dioxide, a leveling agent GLP788 and polyethylene wax to obtain a premix; (2) The premix is ​​melt-extruded, ground and sieved, and then evenly mixed with the modified microcapsules to obtain a low-temperature curing powder coating.

[0051] In this embodiment, the low temperature curing polyurethane oligomer in Example 2 and the modified microcapsule in Example 4 are used.

[0052] Example 9

[0053] A low-temperature curing powder coating comprises the following raw materials in parts by weight: 65 parts of low-temperature curing polyurethane oligomer, 10 parts of modified microcapsules, 5 parts of isophorone diisocyanate curing agent, 7 parts of nano titanium dioxide, 3 parts of leveling agent GLP788, and 0.4 parts of polyethylene wax.

[0054] The method for preparing the low temperature curing powder coating comprises the following steps: (1) uniformly mixing a low-temperature curing polyurethane oligomer, an isophorone diisocyanate curing agent, nano titanium dioxide, a leveling agent GLP788 and polyethylene wax to obtain a premix; (2) The premix is ​​melt-extruded, ground and sieved, and then evenly mixed with the modified microcapsules to obtain a low-temperature curing powder coating.

[0055] In this embodiment, the low temperature curing polyurethane oligomer in Example 3 and the modified microcapsule in Example 6 are used.

[0056] Comparative Example 1 A low-temperature curing powder coating, the preparation method of which is basically the same as that of Example 9, except that the modified microcapsules therein are replaced by calcium carbonate.

[0057] Comparative Example 2 A low temperature curing powder coating, the preparation method of which is basically the same as that of Example 9, except that the preparation method of the modified microcapsules is as follows: S21. Mix linseed oil and formamide, stir at 58° C. for 1.8 h, then add sodium dodecylbenzene sulfonate and continue stirring for 2.7 h to obtain an emulsion; the mass ratio of the linseed oil, sodium dodecylbenzene sulfonate and formamide is 4:0.8:95.

[0058] S22, adding 15wt% calcium chloride solution to the emulsion, maintaining stirring at 58°C for 2.6h, then dropping 12wt% sodium carbonate solution, stirring to form a precipitate, filtering, washing, and drying to obtain functional microcapsules; The calcium chloride solution is prepared by dissolving calcium chloride in formamide; the sodium carbonate solution is prepared by dissolving sodium carbonate in formamide; the amount of calcium chloride solution added is 25% of the total mass of the emulsion; the amount of sodium carbonate solution added is 30% of the total mass of the emulsion.

[0059] S23, using silane coupling agent KH-570 to perform surface modification on the functional microcapsules to obtain modified microcapsules.

[0060] Comparative Example 3 A low temperature curing powder coating, the preparation method of which is basically the same as that of Example 9, except that the preparation method of the modified microcapsules is as follows: S21, mixing linseed oil, nano zinc oxide and formamide, stirring at 58° C. for 1.8 h, then adding sodium dodecylbenzene sulfonate and continuing stirring for 2.7 h to obtain an emulsion; The mass ratio of the linseed oil, sodium dodecylbenzene sulfonate and formamide is 4:0.8:95; the added amount of nano zinc oxide is 8% of the total mass of the emulsion.

[0061] S22. Add 15 wt % calcium chloride solution to the emulsion, keep stirring at 58° C. for 2.6 h, then dropwise add 12 wt % sodium carbonate solution, stir to form a precipitate, filter, wash and dry to obtain functional microcapsules, and regard the obtained functional microcapsules as modified microcapsules.

[0062] The calcium chloride solution is prepared by dissolving calcium chloride in formamide; the sodium carbonate solution is prepared by dissolving sodium carbonate in formamide; the amount of calcium chloride solution added is 25% of the total mass of the emulsion; the amount of sodium carbonate solution added is 30% of the total mass of the emulsion.

[0063] Quality Inspection The powder coatings in Examples 7-9 and Comparative Examples 1-3 were used as samples for testing: the samples were sprayed on stainless steel plates by electrostatic spraying, and baked at 120° C. for 10 minutes to prepare coating films with a thickness of 100 μm.

[0064] 1. Antibacterial property: The antibacterial property of the coating was tested according to the standard of GB / T 21866-2008. The specific test results are shown in the following table.

[0065] Table 1 Antibacterial properties

[0066] 2. Scratch self-healing and repeated self-healing: Use a scalpel to make a small scratch on the surface of the coating, and self-heal at room temperature until the small crack disappears. After the scratch is self-healed, make another small crack at the same position, repeat the above operation, and observe whether the crack can continue to self-heal. The specific test results are shown in the following table.

[0067] Table 2 Self-healing

[0068] From the above table, we can see that: (1) Compared with Example 9, the coating in Comparative Example 1 has poor antibacterial and self-healing properties because no modified microcapsules are added; (2) Compared with Example 9, the modified microcapsules in Comparative Example 2 have poor antibacterial properties due to the lack of nano zinc oxide, but good self-healing properties; (3) Compared with Example 9, the modified microcapsules in Comparative Example 3 were not surface-modified with a silane coupling agent, which affected the uniform dispersion of the modified microcapsules in the premix and affected the antibacterial and self-healing properties of the coating.

[0069] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low temperature curing powder coating, characterized in that: The invention comprises the following raw materials in parts by weight: 60-70 parts of low-temperature curing polyurethane oligomer, 8-15 parts of modified microcapsules, 4-8 parts of curing agent, 5-10 parts of nano titanium dioxide, 2-5 parts of leveling agent and 0.2-0.5 parts of polyethylene wax.

2. The low temperature curing powder coating according to claim 1, characterized in that: The curing agent is selected from isophorone diisocyanate and diphenylmethane diisocyanate; the leveling agent is selected from leveling agent GLP588 and leveling agent GLP788.

3. The low temperature curing powder coating according to claim 1, characterized in that: The preparation method of the low temperature curing polyurethane oligomer is as follows: S11, mixing toluene-2,4-diisocyanate and dimethyl sulfoxide, adding dibutyltin dilaurate, hydroxyethyl methacrylate and hydroquinone with stirring, and reacting at 30-40° C. for 2.5-3 hours to obtain an intermediate solution; S12, adding pentaerythritol to the intermediate solution, reacting at 60-70° C. for 2-2.5 hours to obtain a mixture; S13, adding the mixture into deionized water to generate a precipitate, and then crushing, filtering and drying to obtain a low-temperature curing polyurethane oligomer.

4. The low temperature curing powder coating according to claim 3, characterized in that: In step S11, the mass ratio of toluene-2,4-diisocyanate, hydroxyethyl methacrylate and dimethyl sulfoxide is (3-4): (2-3): (9-11); The amount of dibutyltin dilaurate added is 0.3-0.5% of the total mass of the intermediate solution; the amount of hydroquinone added is 0.5-1% of the total mass of the intermediate solution.

5. The low temperature curing powder coating according to claim 3, characterized in that: In step S12, the amount of pentaerythritol added is 5-8% of the total mass of the intermediate solution.

6. The low temperature curing powder coating according to claim 1, characterized in that: The preparation method of the modified microcapsule is as follows: S21, mixing linseed oil, nano zinc oxide and formamide, stirring at 55-60° C. for 1.5-2 h, then adding sodium dodecylbenzene sulfonate and continuing stirring for 2.5-3 h to obtain an emulsion; S22, adding calcium chloride solution to the emulsion, maintaining stirring at 55-60° C. for 2.5-3 hours, then dropping sodium carbonate solution, stirring to form a precipitate, filtering, washing, and drying to obtain functional microcapsules; S23, performing surface modification treatment on the functional microcapsules using a silane coupling agent to obtain modified microcapsules.

7. The low temperature curing powder coating according to claim 6, characterized in that: In step S21, the mass ratio of linseed oil, sodium dodecylbenzene sulfonate and formamide is (3-5): (0.5-1): (90-100); The added amount of the nano zinc oxide is 5-10% of the total mass of the emulsion.

8. The low temperature curing powder coating according to claim 6, characterized in that: In step S22, the calcium chloride solution is prepared by dissolving calcium chloride in formamide; the sodium carbonate solution is prepared by dissolving sodium carbonate in formamide; The mass fraction of the calcium chloride solution is 15%; the mass fraction of the sodium carbonate solution is 12%.

9. The low temperature curing powder coating according to claim 6, characterized in that: In step S22, the amount of calcium chloride solution added is 20-30% of the total mass of the emulsion; the amount of sodium carbonate solution added is 25-35% of the total mass of the emulsion.

10. The method for preparing a low temperature curing powder coating according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) uniformly mixing a low-temperature curing polyurethane oligomer, a curing agent, nano titanium dioxide, a leveling agent and polyethylene wax to obtain a premix; (2) The premix is ​​melt-extruded, ground and sieved, and then evenly mixed with the modified microcapsules to obtain a low-temperature curing powder coating.

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