Preparation and application of multifunctional water-based primer

Abstract

The invention discloses preparation of a multifunctional water-based primer which comprises 40-55 parts of water-based acrylic resin, 20-30 parts of water-based organic silicon resin, 5-10 parts of deionized water, 1-5 parts of a solvent, 8-12 parts of amino resin, 0.3-1 part of a catalyst, 0.3-1.5 parts of a wetting agent, 0.3-1.5 parts of a flatting agent, 0.3-1 part of a defoaming agent and 0.5-1.5 parts of a water-based thickening agent. The preparation method comprises the following steps: mixing the deionized water and the solvent to obtain a first mixed solution; mixing water-based acrylic resin and water-based organic silicon resin to obtain a second mixed solution; mixing the first mixed solution with the second mixed solution to obtain a third mixed solution; mixing amino resin with the third mixed solution to obtain a fourth mixed solution; and mixing and filtering the catalyst, the wetting agent, the flatting agent, the defoaming agent, the water-based thickening agent and the fourth mixed solution. According to the multifunctional water-based primer provided by the invention, the defect that different coating materials are needed for different metal substrates is overcome, the requirements of better bending resistance, impact resistance, high temperature resistance and environmental measurement resistance are met simultaneously according to the requirements of coatings, and the research and development cost and the downstream application cost are saved.

Description

Technical Field

[0001] The invention relates to the technical field of coatings, and in particular to the preparation and application of a multifunctional water-based primer. Background Art

[0002] At present, with the rapid iteration and update of products in the field of electronic consumer products, the substrates and functional requirements of the corresponding products are constantly changing. The constantly changing substrates mean that coating materials need to be constantly updated. The continuous iteration of coating products requires a large investment in R&D and application costs. The market urgently needs a multifunctional coating material that can simultaneously meet the requirements of providing protection and decoration for a variety of metal substrates, which can not only meet the adhesion requirements for different metal substrates, but also have good wear resistance, and can withstand various environmental tests and high temperature resistance. Summary of the invention

[0003] In order to solve the technical problems in the background technology, the present invention provides a preparation and application of a multifunctional water-based primer, and the specific technical scheme is as follows:

[0004] A preparation of a multifunctional water-based primer, the multifunctional water-based primer comprises the following components: by weight, 40-55 parts of water-based acrylic resin, 20-30 parts of water-based silicone resin, 5-10 parts of deionized water, 1-5 parts of solvent, 8-12 parts of amino resin, 0.3-1 part of catalyst, 0.3-1.5 parts of wetting agent, 0.3-1.5 parts of leveling agent, 0.3-1 part of defoaming agent, 0.5-1.5 parts of water-based thickener, and the preparation of the multifunctional water-based primer specifically comprises the following steps:

[0005] Step 1: Mix deionized water and solvent and disperse them evenly to obtain a first mixed solution;

[0006] Step 2: Mix the water-based acrylic resin and the water-based silicone resin and disperse them evenly to obtain a second mixed solution;

[0007] Step 3: Mix the first mixed solution and the second mixed solution and disperse them evenly to obtain a third mixed solution;

[0008] Step 4: mixing the amino resin and the third mixed solution and dispersing them evenly to obtain a fourth mixed solution;

[0009] Step 5: Mix and evenly disperse the catalyst, wetting agent, leveling agent, defoaming agent, water-based thickener and the fourth mixed liquid, and obtain a first filtrate after filtering. The first filtrate is the multifunctional water-based primer.

[0010] Preferably, the components of the multifunctional water-based primer further include 2 to 6 parts of matting powder, and the matting powder is added to the fourth mixed liquid in step 5.

[0011] Preferably,

[0012] In step 3, the first mixed solution and the second mixed solution are mixed in a manner of: slowly adding the first mixed solution to the second mixed solution;

[0013] In step 4, the amino resin and the third mixed liquid are mixed in a manner of: slowly adding the amino resin into the third mixed liquid.

[0014] Preferably, the first mixed solution and the amino resin are added dropwise.

[0015] Preferably, the dispersion method is stirring dispersion.

[0016] Preferably,

[0017] The water-based acrylic resin is a carboxyl water-based acrylic resin and / or a phosphate group-modified water-based acrylic resin;

[0018] The water-based organosilicon resin is an organosilicon semi-emulsion and / or an water-based organosiloxane modified emulsion;

[0019] The amino resin is one or more of a fully methyl etherified amino resin, a mixed etherified amino resin, and a partially etherified high-imino resin;

[0020] The catalyst is a blocked acid catalyst, and the deblocking temperature of the blocked acid catalyst is 80 to 130° C.;

[0021] The solvent is one or more of diethylene glycol butyl ether, ethylene glycol butyl ether, dipropylene glycol butyl ether and propylene glycol butyl ether;

[0022] The wetting agent is BYK 349, BYK 346, Digo Wet 245 and One or more of Wet270;

[0023] The leveling agent is BYK 333, BYK 3760, Digo Glide 406 and One or more of Glide410;

[0024] The defoaming agent is BYK 3481, BYK 024, Foamex 810 and One or more of Foamex825;

[0025] The matting agent is one or more of Tosoh E-220A, Tosoh E-1011, Grace C803, Grace SYLOID 7000 and Evonik ACEMATT TS100;

[0026] The aqueous thickener is Digo ViscoPlus 3030, One or more of ViscoPlus 3060, Hemmings RHEOLATE 299 and RHEOLATE FX 1010.

[0027] Preferably, the preparation method of the phosphate group-modified waterborne acrylic resin specifically comprises the following steps:

[0028] Step 10: Mix acrylate, phosphate and alcohol ether solvents in a mass ratio of 1:(0.8-1):(8-10) and disperse them evenly, and heat to 100° C. to obtain a process solution;

[0029] Step 20: Add the initiator at a mass ratio of m 引发剂 :m 过程溶液 =1:(35-40) Add to the process solution and stir to disperse evenly;

[0030] Step 30: Cooling to 50-60° C., adding an alkaline regulator, adjusting the pH to 7.5-8.5, and dispersing evenly to obtain the phosphate group-modified waterborne acrylic resin.

[0031] The present invention also provides an application of a multifunctional water-based primer, wherein the multifunctional water-based primer prepared by any of the preparation methods described above is coated on a metal substrate to form a paint film.

[0032] Preferably, the metal substrate is made of aluminum alloy, magnesium alloy, stainless steel, iron, zinc alloy, copper or nickel.

[0033] Preferably, the coating on the metal substrate to form a paint film specifically comprises the following steps:

[0034] Step 100: mixing the multifunctional water-based primer and deionized water, and dispersing them evenly to obtain a dispersion;

[0035] Step 200: filtering the dispersion through a 150-300 mesh filter cloth to obtain a second filtrate;

[0036] Step 300: spraying the second filtrate onto a metal substrate;

[0037] Step 400: pre-bake the sprayed metal substrate at 60-80° C. for 5-15 minutes, then adjust the temperature to 140-170° C. and bake for 25-35 minutes.

[0038] The multifunctional water-based primer prepared by the preparation method provided by the present invention solves the problem that different metal substrates require different coating materials, and the coating needs to simultaneously meet the requirements of good bending resistance, impact resistance, high temperature resistance, and environmental testing resistance. By using only one coating material to meet the requirements of more than 90% of metal substrates on the market for coating protection and decorative functions, the research and development costs and downstream application costs are saved. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0040] The present embodiment provides a preparation of a multifunctional water-based primer, which includes the following components: by weight, 40 to 55 parts of water-based acrylic resin, 20 to 30 parts of water-based silicone resin, 5 to 10 parts of deionized water, 1 to 5 parts of solvent, 8 to 12 parts of amino resin, 0.3 to 1 part of catalyst, 0.3 to 1.5 parts of wetting agent, 0.3 to 1.5 parts of leveling agent, 0.3 to 1.5 parts of defoaming agent, and 0.5 to 1.5 parts of water-based thickener. The preparation of the multifunctional water-based primer specifically includes the following steps:

[0041] Step 1: Mix deionized water and solvent and disperse them evenly to obtain a first mixed solution.

[0042] Step 2: Mix the water-based acrylic resin and the water-based silicone resin, and disperse them evenly to obtain a second mixed solution.

[0043] Step 3: Mix the first mixed solution and the second mixed solution, and disperse them evenly to obtain a third mixed solution.

[0044] Step 4: Mix the amino resin and the third mixed solution, and disperse them evenly to obtain a fourth mixed solution.

[0045] Step 5: Mix and evenly disperse the catalyst, wetting agent, leveling agent, defoaming agent, water-based thickener and the fourth mixed liquid, and obtain a first filtrate after filtering. The first filtrate is a multifunctional water-based primer.

[0046] Among them, water-based paint is widely used on metal substrates in the 3C field. In the 3C field, water-based acrylic resin is usually used as the main resin of metal paint. Paint prepared with water-based acrylic resin as the main resin generally has good impact resistance and bending resistance on metal substrates in addition to good adhesion. However, when simulating high temperature tests (300°C and above), adhesion deterioration and discoloration problems are prone to occur. Water-based organic resins have good high temperature resistance and aging resistance, and can be combined with water-based acrylic resins to improve the high temperature resistance and aging resistance of the paint film. Combining the two, the paint prepared in an appropriate proportion can have the advantages of both resins. When an amino resin is added in an appropriate proportion, the prepared paint film not only has good flexibility, but also has good high temperature resistance and aging resistance. Compared with water-based acrylic resins, water-based silicone resins can form stronger chemical bonds with the surface of the metal substrate after hydrolysis and curing, giving the paint film better adhesion strength, and further enhancing the water-boiling adhesion between the paint film and the metal substrate. It has good water boiling resistance on metal substrates such as aluminum alloy, magnesium alloy, various types of stainless steel, iron, zinc alloy, copper and nickel, and can solve the problem of adhesion firmness of various substrates. The prepared water-based paint can not only be used for a variety of metal substrates, but also has good performance after curing, and has a wide range of application prospects in 3C and industrial fields.

[0047] The multifunctional water-based primer prepared by the preparation method provided in this embodiment solves the problem that different metal substrates require different coating materials, and the coating needs to simultaneously meet the requirements of good bending resistance, impact resistance, high temperature resistance, and environmental testing resistance. By using only one coating material to meet the requirements of more than 90% of metal substrates on the market for coating protection and decorative functions, R&D costs and downstream application costs are saved.

[0048] Furthermore, the components of the multifunctional water-based primer also include 2 to 6 parts of matting powder, and the matting powder is added to the fourth mixed liquid in step 5.

[0049] Furthermore, in step 3, the first mixed liquid and the second mixed liquid are mixed in a manner of: slowly adding the first mixed liquid into the second mixed liquid.

[0050] In step 4, the amino resin and the third mixed liquid are mixed in the following manner: the amino resin is slowly added to the third mixed liquid.

[0051] Furthermore, the first mixed solution and the amino resin are added dropwise.

[0052] Furthermore, the dispersion method is stirring dispersion.

[0053] Furthermore, the water-based acrylic resin is a carboxyl water-based acrylic resin and / or a phosphate group-modified water-based acrylic resin.

[0054] The water-based silicone resin is a silicone semi-emulsion and / or a water-based silicone modified emulsion.

[0055] The amino resin is one or more of fully methyl etherified amino resin, mixed etherified amino resin and partially etherified high imino resin.

[0056] The catalyst is a blocked acid catalyst, and the deblocking temperature of the blocked acid catalyst is 80-130°C.

[0057] The solvent is one or more of diethylene glycol butyl ether, ethylene glycol butyl ether, dipropylene glycol butyl ether and propylene glycol butyl ether.

[0058] Wetting agents include BYK 349, BYK 346, and Digo Wet 245 and One or more of Wet 270.

[0059] Leveling agents include BYK 333, BYK 3760, and Digo Glide 406 and One or more of Glide410.

[0060] The defoamers are BYK 3481, BYK 024, Foamex 810 and One or more of Foamex825.

[0061] The matting agent is one or more of Tosoh E-220A, Tosoh E-1011, Grace C803, Grace SYLOID 7000 and Evonik ACEMATT TS100.

[0062] Water-based thickener is Digo ViscoPlus 3030, One or more of ViscoPlus 3060, Hemmings RHEOLATE 299 and RHEOLATE FX 1010.

[0063] Furthermore, the preparation method of the water-based acrylic resin modified with phosphate groups specifically comprises the following steps:

[0064] Step 10: Mix acrylate, phosphate and alcohol ether solvents in a mass ratio of 1:(0.8-1):(8-10) and disperse them evenly, and heat them to 100° C. to obtain a process solution.

[0065] Step 20: Add the initiator at a mass ratio of m 引发剂 :m 过程溶液 =1:(35~40)Add to the process solution and stir to disperse evenly.

[0066] Step 30: Cool down to 50-60° C., then add an alkaline regulator to adjust the pH to 7.5-8.5, and disperse evenly to obtain a phosphate group-modified water-based acrylic resin.

[0067] This embodiment also provides an application of a multifunctional water-based primer, wherein the multifunctional water-based primer prepared by any of the preparation methods described above is applied on a metal substrate to form a paint film.

[0068] Furthermore, the metal substrate is made of aluminum alloy, magnesium alloy, stainless steel, iron, zinc alloy, copper or nickel.

[0069] Furthermore, coating on a metal substrate to form a paint film specifically includes the following steps:

[0070] Step 100: Mix the multifunctional water-based primer and deionized water, and disperse them evenly to obtain a dispersion.

[0071] Step 200: Filter the dispersion through a 150-300 mesh filter cloth to obtain a second filtrate.

[0072] Step 300: Spray the second filtrate onto the metal substrate.

[0073] Step 400: pre-bake the sprayed metal substrate at 60-80° C. for 5-15 minutes, then adjust the temperature to 140-170° C. and bake for 25-35 minutes.

[0074] Furthermore, the components of the multifunctional water-based primer can be specifically proportioned according to the following table:

[0075]

[0076]

[0077] The following provides several specific examples of component ratios, each of which is prepared according to the following steps:

[0078] Step 1: Mix the weighed deionized water and solvent to prepare a first mixed solution.

[0079] Step 2: Mix the weighed water-based acrylic resin and water-based silicone resin to prepare a second mixed solution.

[0080] Step 3: slowly add the first mixed solution into the weighed second mixed solution, mix them, and prepare a third mixed solution.

[0081] Step 4: slowly add the weighed amino resin into the third mixed solution, mix them, and prepare a fourth mixed solution.

[0082] Step 5: adding the weighed catalyst, wetting agent, leveling agent, defoaming agent, matting powder and water-based thickener to the fourth mixed liquid, mixing them to form a fifth mixed liquid, and filtering them to obtain a multifunctional water-based primer coating.

[0083] The group distribution ratios of each group of embodiments are shown in the following table:

[0084]

[0085] The multifunctional water-based primer prepared in each group of examples was coated on the metal substrate according to the following steps:

[0086] The prepared multifunctional water-based primer was added with 20% deionized water according to weight, stirred evenly, then filtered with a 200-mesh filter cloth, and sprayed on a metal substrate with an automatic spray gun. The sprayed product was pre-baked at 75°C for 15 minutes, and then transferred to 170°C for baking for 35 minutes.

[0087] The test results of coating properties of Examples 1 to 5 and Comparative Examples 1 to 3 are as follows:

[0088]

[0089] It can be seen from Examples 1 to 5 in the above table that when the water-based acrylic resin, the water-based silicone resin and the amino resin are matched in appropriate proportions, the resulting paint films have good conventional adhesion and boiling water adhesion on different metal substrates, and the paint films have good bending resistance, impact resistance, wear resistance, high temperature resistance, aging resistance, high temperature and high humidity resistance, cold and hot cycle resistance and high pencil hardness.

[0090] It can be seen from Comparative Example 1 and Examples 1 to 5 that when acrylic resin and amino resin are used alone, the obtained paint film has reduced bending resistance, impact resistance, and high temperature resistance, and the high temperature and humidity resistance and hot and cold cycle functions are reduced. This is mainly because the acrylic resin molecular chain has a certain rigidity and exhibits brittleness when subjected to external stress. Since water-based acrylic polymer resin does not have good heat resistance, the general temperature is higher than 300°C, and the polymer chain undergoes oxidation degradation at high temperature, and the paint film gradually turns yellow. It can be seen from Comparative Example 2 and Comparative Example 1 that water-based silicone resin has good high temperature resistance, thanks to the protective effect of inorganic siloxane in the molecular chain segment on the nearby molecular chain segment, so that the polymer chain has good high temperature degradation resistance, and can withstand temperatures above 300°C without yellowing. It can be used with yellowing resin to alleviate the yellowing phenomenon under high temperature conditions and the problem of poor adhesion after high temperature baking, showing good high temperature resistance. The silicon-oxygen bonds in the silicone molecular chain segments rotate freely, giving the molecular chain better flexibility, and the prepared paint film has good bending and impact resistance. But at the same time, the paint film has the disadvantages of poor wear resistance and low hardness. When water-based acrylic resin is used alone, the resistance to cold and hot cycle testing decreases. This is attributed to the fact that acrylic resin usually has a higher Tg point. When subjected to cold and hot shock cycles, the internal stress of the paint film continues to change, resulting in a decrease in adhesion to the substrate and blistering. However, since the siloxane chain segments of silicone resin can rotate freely, when subjected to high and low temperature shocks, the drastic changes in the internal stress of the paint film can be alleviated, ensuring good adhesion between the paint film and the substrate. Therefore, the paint film prepared by combining the characteristics of the two resins can have the excellent characteristics of both resins, giving the paint film better performance.

[0091] From Comparative Example 3 and Examples 4-5, it can be seen that when the amount of amino resin in the system exceeds a certain range, the paint film becomes hard, and the flexibility, impact resistance, adhesion, high temperature and humidity resistance, and cold and hot cycle resistance decrease. This is attributed to the tendency of amino resin to self-crosslink under high temperature conditions, which leads to excessive self-crosslinking of amino resin in the paint film, making the paint film brittle, and reducing flexibility and impact resistance, and adhesion. It needs to be matched with the corresponding resin in a certain proportion to form a paint film with better performance.

[0092] It can be seen from the above Examples 1 to 5 and Comparative Examples 1 to 3 that when the water-based acrylic resin and the water-based silicone resin are mixed in a certain proportion in the system and matched with a corresponding proportion of amino resin, the prepared paint film not only has good conventional adhesion on various metal substrates, but also has good boiling water resistance. The corresponding paint film also has good flexibility, wear resistance and environmental resistance, and has a wide range of application scenarios.

[0093] The paint prepared with water-based acrylic resin as the main resin generally has good impact resistance and bending resistance on the metal substrate in addition to good adhesion; while the paint prepared with water-based organosilicone resin has good high temperature resistance and aging resistance. Through research, the paint prepared by combining the two and preparing them in an appropriate proportion can have the advantages of both resins. The prepared paint film not only has good flexibility, but also has good high temperature resistance and aging resistance. The bending and impact resistance tests of the cured paint film showed that the paint film did not crack when bent 180 degrees, and the paint film did not crack when the impact test was 50kg.cm. Further high temperature resistance tests were carried out, and the paint film did not change color under high temperature baking conditions of 300℃ for 0.5h. Compared with water-based acrylic resin, water-based organosilicone resin can form a strong chemical bond with the surface of the metal substrate after hydrolysis and curing, giving the paint film better adhesion strength, and further enhancing the water boiling adhesion between the paint film and the metal substrate. It has good water boiling resistance on metal substrates such as aluminum alloy, magnesium alloy, various types of stainless steel, iron, zinc alloy, copper and nickel, and can solve the problem of adhesion firmness of various substrates. The prepared water-based paint can not only be used for a variety of metal substrates, but also has good performance after curing, and has a wide range of application prospects in 3C and industrial fields.

[0094] The principles and implementation methods of the present invention are described herein using specific examples, and the description of the above embodiments is only used to help understand the method and core ideas of the present invention. The above are only preferred implementations of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention, which should be within the protection scope of the present invention.

Claims

1. A preparation method of a multifunctional water-based primer, characterized in that: The multifunctional water-based primer comprises the following components: by weight, 40-55 parts of water-based acrylic resin, 20-30 parts of water-based silicone resin, 5-10 parts of deionized water, 1-5 parts of solvent, 8-12 parts of amino resin, 0.3-1 part of catalyst, 0.3-1.5 parts of wetting agent, 0.3-1.5 parts of leveling agent, 0.3-1 part of defoaming agent, and 0.5-1.5 parts of water-based thickener. The preparation of the multifunctional water-based primer specifically comprises the following steps: S1: Mix deionized water and solvent and disperse them evenly to obtain a first mixed solution; S2: mixing the water-based acrylic resin and the water-based silicone resin and dispersing them evenly to obtain a second mixed solution; S3: mixing the first mixed solution and the second mixed solution and dispersing them uniformly to obtain a third mixed solution; S4: mixing the amino resin and the third mixed solution and dispersing them evenly to obtain a fourth mixed solution; S5: Mix the catalyst, wetting agent, leveling agent, defoaming agent, water-based thickener and the fourth mixed liquid and disperse them evenly, and obtain a first filtrate after filtering. The first filtrate is the multifunctional water-based primer.

2. The preparation of the multifunctional water-based primer according to claim 1, characterized in that: The components of the multifunctional water-based primer also include 2 to 6 parts of matting powder, and the matting powder is added to the fourth mixed liquid in step S5.

3. The preparation of the multifunctional water-based primer according to claim 1 or 2, characterized in that: In step S3, the first mixed liquid and the second mixed liquid are mixed in a manner of: slowly adding the first mixed liquid to the second mixed liquid; In step S4, the amino resin and the third mixed liquid are mixed in a manner of: slowly adding the amino resin into the third mixed liquid.

4. The preparation of the multifunctional water-based primer according to claim 3, characterized in that: The first mixed solution and the amino resin are added dropwise.

5. The preparation of the multifunctional water-based primer according to claim 1 or 2, characterized in that: The dispersion method is stirring dispersion.

6. The preparation of the multifunctional water-based primer according to claim 2, characterized in that: The water-based acrylic resin is a carboxyl water-based acrylic resin and / or a phosphate group-modified water-based acrylic resin; The water-based organosilicon resin is an organosilicon semi-emulsion and / or an water-based organosiloxane modified emulsion; The amino resin is one or more of a fully methyl etherified amino resin, a mixed etherified amino resin, and a partially etherified high-imino resin; The catalyst is a blocked acid catalyst, and the deblocking temperature of the blocked acid catalyst is 80 to 130° C.; The solvent is one or more of diethylene glycol butyl ether, ethylene glycol butyl ether, dipropylene glycol butyl ether and propylene glycol butyl ether; The wetting agent is BYK 349, BYK 346, Digo Wet 245 and One or more of Wet 270; The leveling agent is BYK 333, BYK 3760, Digo Glide 406 and One or more of Glide 410; The defoaming agent is BYK 3481, BYK 024, Foamex 810 and One or more of Foamex825; The matting agent is one or more of Tosoh E-220A, Tosoh E-1011, Grace C803, Grace SYLOID 7000 and Evonik ACEMATT TS100; The aqueous thickener is Digo ViscoPlus 3030, One or more of ViscoPlus 3060, Hemmings RHEOLATE 299 and RHEOLATE FX 1010.

7. The preparation of the multifunctional water-based primer according to claim 6, characterized in that: The preparation method of the phosphate group-modified water-based acrylic resin specifically comprises the following steps: S10: Mix acrylate, phosphate and alcohol ether solvents in a mass ratio of 1:(0.8-1):(8-10) and disperse them uniformly, and heat them to 100° C. to obtain a process solution; S20: The initiator is added at a mass ratio m 引发剂 :m 过程溶液 =1:(35-40) Add to the process solution and stir to disperse evenly; S30: cooling to 50-60° C., adding an alkaline regulator, adjusting the pH to 7.5-8.5, and dispersing evenly to obtain the phosphate group-modified waterborne acrylic resin.

8. Application of a multifunctional water-based primer, characterized in that: The multifunctional water-based primer prepared by the preparation method according to any one of claims 1 to 7 is coated on a metal substrate to form a paint film.

9. The use according to claim 8, characterized in that: The metal substrate is made of aluminum alloy, magnesium alloy, stainless steel, iron, zinc alloy, copper or nickel.

10. The use according to claim 8, characterized in that: The coating on the metal substrate to form a paint film specifically comprises the following steps: S100: mixing the multifunctional water-based primer and deionized water, and dispersing them uniformly to obtain a dispersion; S200: filtering the dispersion through a 150-300 mesh filter cloth to obtain a second filtrate; S300: spraying the second filtrate onto a metal substrate; S400: pre-bake the sprayed metal substrate at 60-80°C for 5-15 minutes, then adjust the temperature to 140-170°C and bake for 25-35 minutes.

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