A water-based anti-scratch coating for stainless steel speaker mesh, its preparation method and coating method

Abstract

This invention discloses a water-based anti-scratch coating for stainless steel speaker grilles, its preparation method, and its application method, belonging to the technical field of water-based anti-scratch coatings for stainless steel speaker grilles. The coating consists of component A and component B. Component A includes hydroxyl-free waterborne polyurethane resin, high-hydroxyl waterborne polyurethane resin, film-forming aid, defoamer, wetting agent, dispersant, thickener, pH adjuster, matting agent, wax powder, and deionized water. Component B is a water-dispersible isocyanate curing agent. This invention solves the problems of high curing temperature, poor scratch resistance, and poor water resistance in existing technologies, achieving low-temperature curing at 80℃, passing the 10N Newton pen scratch resistance test, and achieving an adhesion grade ≤1 at 100℃ boiling water and 90℃ / 95% humidity, without the need for additional adhesion promoters.

Description

Technical Field

[0001] This invention belongs to the technical field of water-based anti-scratch coatings for stainless steel horn mesh, specifically relating to a water-based anti-scratch coating for stainless steel horn mesh and its preparation and application methods. Background Technology

[0002] Stainless steel speaker grilles are widely used in automotive audio systems, smart home devices, and other fields. Current mainstream production processes (such as electroplating and corrosion passivation) suffer from long production cycles, high energy consumption, and high costs; while chemical coating methods have drawbacks such as poor durability and weak scratch resistance. To reduce energy consumption and costs, single-coat painting has become an alternative, but it faces the following technical bottlenecks in the application of stainless steel speaker grilles:

[0003] Film formation defects and thickness limitations:

[0004] The porous structure of stainless steel speaker mesh and the inherent tension of the coating cause thick edges to easily form during film formation, severely affecting the appearance. Therefore, the coating thickness needs to be strictly controlled, but thin coatings are insufficient to meet protective requirements.

[0005] Key drawbacks of existing single-coat solutions:

[0006] High curing temperature: Existing technologies require curing at temperatures above 150℃, which places high demands on equipment energy consumption and cost;

[0007] Film brittleness: Under limited thickness, stress cannot be dispersed through deformation, resulting in insufficient scratch resistance;

[0008] Poor water resistance: It cannot meet the requirements of adhesion grade ≤1 after boiling in water at 100℃ for 2 hours and adhesion grade ≤1 after 72 hours at 90℃ / 95% humidity;

[0009] Dependent on additives: Additional adhesion promoters need to be added to improve the bonding strength.

[0010] The contradiction caused by the characteristics of the substrate:

[0011] Stainless steel has high hardness and cannot deform to disperse stress. Thin coatings are easily damaged in scratch resistance tests, while increasing the thickness is limited by appearance defects.

[0012] It is evident that existing single-coat solutions, due to their high curing temperature, brittle film, insufficient water resistance, and reliance on adhesion promoters, cannot simultaneously meet the low-energy production requirements and high protective performance requirements (scratch resistance, damp heat resistance, and elimination of thick edge defects) of stainless steel speaker grilles. Summary of the Invention

[0013] The purpose of this invention is to provide a water-based anti-scratch coating for stainless steel speaker grilles, its preparation method, and its coating method. This solution addresses the problems of high curing temperature, poor scratch resistance, and poor adhesion to boiling water and hydrolysis in current water-based stainless steel single-coating solutions, thereby solving at least one of the technical problems mentioned in the background art.

[0014] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0015] In a first aspect, embodiments of the present invention provide a water-based anti-scratch coating for stainless steel speaker mesh, comprising component A and component B;

[0016] Component A, by weight, comprises 65-80 parts of hydroxyl-free waterborne polyurethane resin, 5-15 parts of high-hydroxyl waterborne polyurethane resin, 1-6 parts of film-forming aid, 5-15 parts of deionized water, 0.5-1 part of wetting agent, 0.5-1 part of dispersant, 0.1-0.5 parts of leveling agent, 0.1-0.3 parts of defoamer, 0.1-0.3 parts of thickener, 0.1-0.3 parts of pH adjuster, 4-6 parts of matting agent, and 2-4 parts of wax powder.

[0017] Component B is a water-dispersible isocyanate curing agent.

[0018] Optionally, the hydroxyl-free waterborne polyurethane resin is selected from at least one of Runchang Nanxing M462 and Covestro E-123; the high-hydroxyl waterborne polyurethane resin is selected from at least one of Runchang Nanxing 1800 and Sidon 40G04.

[0019] Optionally, the film-forming aid is a mixture of dipropylene glycol methyl ether and dipropylene glycol butyl ether in a mass ratio of 1:1; the defoamer is selected from at least one of TEGO 902W and Foamex 810; and the wetting agent is selected from at least one of EVONIK WETKL 245, TEGO 4100, TEGO Wet KL 245, and BYK-346.

[0020] Optionally, the dispersant is a polyether-modified styrene-maleic anhydride copolymer; the thickener is selected from at least one of Haimings R299 and FX1010; and the pH adjuster is dimethylethanolamine.

[0021] Optionally, the matting powder is precipitated silica with an average particle size of 1.2-3 μm, selected from at least one of Tosoh K-500, E-1011, and SS-50B; the wax powder is unsintered low molecular weight tetrafluoroethylene resin micro powder.

[0022] Optionally, component B includes:

[0023] 45 parts of hydrophilic hexamethylene diisocyanate curing agent;

[0024] 25 parts of lipophilic hexamethylene diisocyanate curing agent;

[0025] 30 parts of co-solvent;

[0026] The hydrophilic isocyanate curing agent is Covestro XP2655, the lipophilic isocyanate curing agent is Covestro N3900, and the cosolvent is propylene glycol methyl ether acetate.

[0027] The present invention also provides a method for preparing the coating, comprising the following steps:

[0028] Preparation of component A:

[0029] (1) Disperse the hydroxyl-free waterborne polyurethane resin at 600-800 rpm for 5 min;

[0030] (2) Add high hydroxyl waterborne polyurethane resin and disperse at 600-800 rpm for 5 min;

[0031] (3) Add the premixed film-forming aid and deionized water, and disperse at 600-800 rpm for 10 min;

[0032] (4) Add wetting agent, dispersant, leveling agent, defoamer, thickener and pH adjuster in sequence, and disperse at 600-800 rpm for 10 min;

[0033] (5) Add matting agent and disperse at 1000-1200 rpm for 90 min;

[0034] (6) Add wax powder and disperse at 1000-1200 rpm for 30 min;

[0035] Preparation of component B:

[0036] (7) Add the lipophilic isocyanate curing agent to the hydrophilic isocyanate curing agent and disperse at 600-800 rpm for 30 min;

[0037] (8) Add a co-solvent and disperse at 600-800 rpm for 15 min.

[0038] The present invention also provides a coating method for the surface of a stainless steel speaker mesh, comprising:

[0039] The A and B components of the coating are mixed with water at a mass ratio of 100:10-25:10-20, sprayed onto a stainless steel substrate, and baked at 80°C for 120 minutes.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1. Existing technologies require high-temperature curing above 150℃, while the coating of this invention can be fully cured by baking at 80℃ for 2 hours, which greatly reduces production energy consumption and equipment costs.

[0042] 2. When the paint film thickness is >20μm, the present invention can pass the 10N Newton pen scratch test (the comparative example can only withstand 5N-8N), effectively solving the problem of easy damage to the paint film caused by the high hardness of stainless steel substrate.

[0043] 3. The present invention was tested by boiling in water at 100℃ for 2 hours and the adhesion was ≤1 level (no bubbling, no peeling); after being placed in an environment of 90℃ / 95% humidity for 72 hours, the adhesion was still ≤1 level (the control group showed bubbling or the adhesion dropped to level 5).

[0044] 4. This invention simplifies the formulation while ensuring adhesion by using the synergistic effect of hydroxyl-free resin and high-hydroxyl resin (hydroxyl-free resin reduces surface tension, while high-hydroxyl resin increases crosslinking density), thus avoiding the risk of water resistance introduced by additives.

[0045] 5. Low gloss of this invention: gloss can be as low as 0.4° (comparative examples are generally >30°), meeting the requirements for matte finish; Improved weather resistance: the combination of high-boiling-point film-forming aids (DPM / DPNB) delays moisture evaporation and reduces stress cracking; Process adaptability: the two-component design (A / B components) ensures construction stability and avoids defects such as sagging and pinholes. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] The terms "first," "second," etc., used in the specification and claims of this invention are used to distinguish similar objects, not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate, and the objects distinguished by "first," "second," etc., are generally of the same class, not limited in number; for example, the first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0048] The following detailed description of the water-based anti-scratch coating for stainless steel speaker mesh, its preparation method, and its coating method provided in this invention will be illustrated through specific embodiments and application scenarios.

[0049] This invention provides a water-based anti-scratch coating for stainless steel speaker grilles, comprising component A and component B;

[0050] Component A, by weight, comprises 65-80 parts of hydroxyl-free waterborne polyurethane resin, 5-15 parts of high-hydroxyl waterborne polyurethane resin, 1-6 parts of film-forming aid, 5-15 parts of deionized water, 0.5-1 part of wetting agent, 0.5-1 part of dispersant, 0.1-0.5 parts of leveling agent, 0.1-0.3 parts of defoamer, 0.1-0.3 parts of thickener, 0.1-0.3 parts of pH adjuster, 4-6 parts of matting agent, and 2-4 parts of wax powder.

[0051] Component B is a water-dispersible isocyanate curing agent.

[0052] Specifically, the hydroxyl-free waterborne polyurethane resin is selected from at least one of Runchang Nanxing M462 and Covestro E-123; the high-hydroxyl waterborne polyurethane resin is selected from at least one of Runchang Nanxing 1800 and Sidon 40G04.

[0053] It should be noted that hydroxyl-free waterborne polyurethane resin cannot react with isocyanates to form chemical crosslinks during film formation. After curing, it has low cohesion and a rougher surface, thus achieving a matte finish. Using it as the main resin can reduce the amount of matting powder added to the formulation, thereby avoiding gaps caused by the resin's inability to effectively encapsulate the powder due to excessive filler content, which would lead to a decrease in water resistance. The high-hydroxyl waterborne polyurethane resin used in this invention contains abundant hydroxyl groups that can react with isocyanates to form crosslinks. Adding a small amount of high-hydroxyl resin to the base material can significantly improve the strength of the paint film, thereby improving scratch resistance. However, hydroxyl groups are hydrophilic groups, and excessive addition will lead to a decrease in the water resistance of the paint film, affecting its resistance to boiling and hydrolysis.

[0054] The film-forming aid is a mixture of dipropylene glycol methyl ether and dipropylene glycol butyl ether in a mass ratio of 1:1. The boiling points of the two solvents are 188°C and 231°C, respectively. The addition of the high-boiling-point solvent can effectively slow down the rate of water evaporation, reduce stress cracking caused by rapid shrinkage, and temporarily lower the glass transition temperature of the resin. The volatilization gradient formed by the two solvents with different boiling points can prolong the open period of the paint film, ensure that water evaporation and gas generated by the reaction are fully released, and avoid residual bubbles in the paint film that cause appearance problems.

[0055] The defoamer is selected from at least one of TEGO 902W and Foamex 810. The water-based defoamer of the present invention is a polysiloxane, which has a good defoaming effect on both large and micro bubbles generated by the stirring and dispersion process and the dispersion process of matting powder during the coating preparation process, so as to avoid appearance problems such as pinholes and depressions on the paint film surface due to the presence of bubbles during construction.

[0056] The wetting agent is selected from at least one of EVONIK WET KL 245, TEGO 4100, TEGO Wet KL 245, and BYK-346. Its composition is polyether-modified siloxane. After being added to the liquid, it accumulates on the liquid surface, significantly reducing the surface tension of the liquid. Its amphiphilic structure causes it to be oriented at the liquid-solid interface, reducing the interfacial energy difference and achieving efficient wetting.

[0057] The dispersant is a polyether-modified styrene-maleic anhydride copolymer, which effectively disperses pigments and components through steric hindrance.

[0058] The thickener is selected from at least one of Haimings R299 and FX1010. Its composition is polyether polyurethane, which can provide strong medium and low shear thickening as well as good leveling and anti-sagging properties, avoiding sagging during construction and resulting in uneven film thickness of the coating.

[0059] The pH adjuster is dimethylethanolamine, which is a polyether-modified styrene-maleic anhydride copolymer. It effectively disperses pigments and components through steric hindrance. The pH adjuster can react with the carboxyl groups in polyurethane to control the pH of the system at 8.0-9.5, preventing resin flocculation under acidic conditions and ensuring that the spraying equipment will not corrode under acidic or alkaline conditions. At the same time, the presence of amino groups can act as nucleophiles to attack the carbonyl carbon on the isocyanate, forming a transition state to accelerate the reaction between isocyanate and hydroxyl groups (from high-hydroxyl polyurethane resin and water), thus shortening the surface drying time.

[0060] The matting agent is precipitated silica with an average particle size of 1.2-3 μm, selected from at least one of Tosoh K-500, E-1011, and SS-50B. Its composition is silica obtained by precipitation method with an average particle size of 1.2-3 μm. Due to its small particle size, it can be evenly distributed in the coating, making the paint film smooth, delicate, and with uniform gloss. Furthermore, its compact distribution can improve the surface hardness of the paint film, which is beneficial to improving scratch resistance.

[0061] The wax powder is unsintered low molecular weight tetrafluoroethylene resin micro powder. Its composition is unsintered low molecular weight tetrafluoroethylene resin micro powder. Due to its large specific surface area and high oil absorption, it is difficult to settle and float on the surface of the paint film when dispersed in liquid. Its particles are soft and easily deformable, which can effectively disperse external impact and improve the wear resistance and scratch resistance of the paint film.

[0062] Component B includes:

[0063] 45 parts of hydrophilic hexamethylene diisocyanate curing agent;

[0064] 25 parts of lipophilic hexamethylene diisocyanate curing agent;

[0065] 30 parts of co-solvent;

[0066] The hydrophilic isocyanate curing agent is Covestro XP2655, which is a hydrophilic hexamethylene diisocyanate; the lipophilic isocyanate curing agent is Covestro N3900, which is a lipophilic hexamethylene diisocyanate used to improve the water resistance of the paint film, with an overall NCO of 14.5-16.5%, good dispersibility in water, easier to disperse evenly when stirred, and better consistency of the resulting coating reaction; the co-solvent is propylene glycol methyl ether acetate, which has low odor and low volatility, and can effectively dilute the isocyanate, making it easier to disperse evenly when mixed with component A.

[0067] The present invention also provides a method for preparing the coating, comprising the following steps:

[0068] Preparation of component A:

[0069] (1) Disperse the hydroxyl-free waterborne polyurethane resin at 600-800 rpm for 5 min;

[0070] (2) Add high hydroxyl waterborne polyurethane resin and disperse at 600-800 rpm for 5 min;

[0071] (3) Add the premixed film-forming aid and deionized water, and disperse at 600-800 rpm for 10 min;

[0072] (4) Add wetting agent, dispersant, leveling agent, defoamer, thickener and pH adjuster in sequence, and disperse at 600-800 rpm for 10 min;

[0073] (5) Add matting agent and disperse at 1000-1200 rpm for 90 min;

[0074] (6) Add wax powder and disperse at 1000-1200 rpm for 30 min.

[0075] It should be noted that the waterborne polyurethane resin used in this invention is mainly composed of hydroxyl-free polyurethane resin combined with a small amount of high-hydroxyl polyurethane resin. When there is too much powder in the coating and the resin cannot completely coat it, water molecules will penetrate during boiling and hydrolysis tests, causing a decrease in the adhesion of the paint film to the substrate surface, and even causing blistering due to the expansion of water molecules. Because hydroxyl-free resin has low cohesion during curing, its paint film surface is rough, which can significantly reduce the amount of matting powder added, thus resulting in good water resistance. Introducing a small amount of high-hydroxyl resin into the base material and mechanically mixing it evenly with hydroxyl-free amino resin can significantly improve the hardness of the paint film and enhance its scratch resistance when the hydroxyl groups react with isocyanates to form a cross-linked network.

[0076] Preparation of component B:

[0077] (7) Add the lipophilic isocyanate curing agent to the hydrophilic isocyanate curing agent and disperse at 600-800 rpm for 30 min;

[0078] (8) Add a co-solvent and disperse at 600-800 rpm for 15 min.

[0079] The present invention also provides a coating method for the surface of a stainless steel speaker mesh, comprising:

[0080] The A and B components of the coating are mixed with water at a mass ratio of 100:10-25:10-20, sprayed onto a stainless steel substrate, and baked at 80°C for 120 minutes.

[0081] The following detailed description of the water-based anti-scratch coating for stainless steel speaker mesh provided by the present invention, its preparation method, and its coating method are based on specific embodiment 1 and comparative examples 2-7.

[0082] The coating provided in Example 1 includes component A and component B, wherein component A is shown in Table 1 below; and component B is a water-dispersible isocyanate curing agent.

[0083] Table 1 Component A

[0084]

[0085] The coating provided in Comparative Example 2 includes component A and component B, wherein component A is shown in Table 2 below; and component B is a water-dispersible isocyanate curing agent.

[0086] Table 2 Component A

[0087]

[0088] The coating provided in Comparative Example 3 includes component A and component B, wherein component A is shown in Table 3 below; and component B is a water-dispersible isocyanate curing agent.

[0089] Table 3 Component A

[0090]

[0091] The coating provided in Comparative Example 4 includes component A and component B, wherein component A is shown in Table 4 below; and component B is a water-dispersible isocyanate curing agent.

[0092] Table 4 Component A

[0093]

[0094] The coating provided in Comparative Example 5 includes component A and component B, wherein component A is shown in Table 5 below; and component B is a water-dispersible isocyanate curing agent.

[0095] Table 5 Component A

[0096]

[0097] The coating provided in Comparative Example 6 includes component A and component B, wherein component A is shown in Table 6 below; and component B is a water-dispersible isocyanate curing agent.

[0098] Table 6 Component A

[0099]

[0100] The coating provided in Comparative Example 7 includes component A and component B, wherein component A is shown in Table 7 below; and component B is a water-dispersible isocyanate curing agent.

[0101] Table 7 Component A

[0102]

[0103] The components B of Examples 1 and Comparative Examples 2-7 are shown in Table 8 below.

[0104] Table 8 Component A

[0105]

[0106] The components A and B provided in Example 1 and Comparative Examples 2-7 were prepared using the preparation method provided by this invention. The prepared anti-scratch coating component A for stainless steel speaker mesh was mixed with component B and water in a ratio of 100:10-25:10-20. The mixture was sprayed onto a stainless steel substrate and baked at 80°C for 120 minutes to obtain a completely dried anti-scratch coating for stainless steel speaker mesh.

[0107] Tests have shown that the gloss of the fully dried water-based anti-scratch matte black two-component polyurethane coating of this invention can be as low as 0.1-1°, and it meets the following performance requirements: adhesion ≤1 at 100℃ water boiling, adhesion ≤1 at 90℃ / 95% humidity for 72h, and the coating thickness >20μm can pass the 10N Newton pen scratch resistance test. The main performance requirements are shown in Table 9 below.

[0108] Table 9 Performance Table

[0109]

[0110] As can be seen, compared with Comparative Example 2, the amount of high-hydroxyl waterborne polyurethane resin added in Comparative Example 2 is lower than that in Example 1. The crosslinking density is lower during the curing process, the hardness of the paint film is lower, and therefore the critical value for scratch resistance is lower.

[0111] Compared with Comparative Examples 3-4, Example 1 used hydroxyl-free waterborne polyurethane resin as the base material. During the curing process, there was no chemical crosslinking, resulting in lower film strength and a scratch resistance threshold of 4-5N.

[0112] Compared with Comparative Examples 5-7, Example 1, which uses high-hydroxyl waterborne polyurethane resin as the base material, showed a gloss level greater than 15° and could not achieve a matte effect under the same amount of matting powder added. Hydroxyl groups are hydrophilic groups, and the hydroxyl groups that failed to react during the curing process reduced the water resistance of the paint film. In addition, excessive crosslinking caused the paint film to shrink and generate stress, which also affected the adhesion of the coating. The adhesion was significantly reduced after hydrolysis and boiling.

[0113] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0114] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. An aqueous anti-scratch coating for stainless steel horn mesh, characterized by, The A component and the B component are included; The A component includes, by weight parts, 65-80 parts of a hydroxyl-free waterborne polyurethane resin, 5-15 parts of a high-hydroxyl waterborne polyurethane resin, 1-6 parts of a film-forming aid, 5-15 parts of deionized water, 0.5-1 part of a wetting agent, 0.5-1 part of a dispersant, 0.1-0.5 part of a leveling agent, 0.1-0.3 part of an antifoaming agent, 0.1-0.3 part of a thickening agent, 0.1-0.3 part of a pH value regulator, 4-6 parts of an extinction powder, and 2-4 parts of a wax powder; The B component is a water-dispersible isocyanate curing agent; By the ratio combination of the hydroxyl-free waterborne polyurethane resin and the high-hydroxyl waterborne polyurethane resin, the hydroxyl-free waterborne polyurethane resin is used to reduce the surface tension of the paint film and achieve extinction, and the high-hydroxyl waterborne polyurethane resin is used to crosslink with the B component to improve the hardness and scratch resistance of the paint film, so that the paint can meet the requirements of low gloss, high scratch resistance and high boiling water resistance after curing.

2. The waterborne scratch resistant coating for stainless steel horn mesh according to claim 1, characterized in that, The hydroxyl-free waterborne polyurethane resin is selected from at least one of Run Chang Nanxing M462 and Covestro E-123; and the high-hydroxyl waterborne polyurethane resin is selected from at least one of Run Chang Nanxing 1800 and Xidun 40G04.

3. The aqueous scratch resistant coating for stainless steel horn mesh according to claim 1, characterized in that, The film-forming aid is a mixture of dipropylene glycol methyl ether and dipropylene glycol butyl ether with a mass ratio of 1:1; the antifoaming agent is selected from at least one of TEGO 902W and Foamex 810; and the wetting agent is selected from at least one of EVONIK WET KL 245, TEGO 4100, TEGO Wet KL245 and BYK-346.

4. The waterborne scratch resistant coating for stainless steel horn mesh according to claim 1 or 2, characterized in that, The dispersant is a polyether-modified styrene maleic anhydride copolymer; the thickening agent is selected from at least one of Himax R299 and FX1010; and the pH value regulator is dimethyl ethanolamine.

5. The waterborne scratch resistant coating for stainless steel horn mesh according to claim 1, characterized in that, The extinction powder is a precipitated silica with an average particle size of 1.2-3 μm, and is selected from at least one of DOWSIL K-500, E-1011 and SS-50B; and the wax powder is an unsintered low-molecular-weight tetrafluoroethylene resin micro powder.

6. The waterborne scratch resistant coating for stainless steel horn mesh according to claim 1, wherein The B component includes: Hydrophilic hexamethylene diisocyanate curing agent 45 parts; Lipophilic hexamethylene diisocyanate curing agent 25 parts; Co-solvent 30 parts; The hydrophilic hexamethylene diisocyanate curing agent is Covestro XP2655, the lipophilic hexamethylene diisocyanate curing agent is Covestro N3900, and the co-solvent is propylene glycol methyl ether acetate.

7. A process for the preparation of the coating according to any one of claims 1 to 6, characterized in that, The method includes the following steps: Preparation of the A component: (1) Disperse the hydroxyl-free waterborne polyurethane resin at 600-800 rpm for 5 min; (2) Add the high-hydroxyl waterborne polyurethane resin and disperse at 600-800 rpm for 5 min; (3) Add the pre-mixed film-forming aid and deionized water and disperse at 600-800 rpm for 10 min; (4) Add the wetting agent, dispersant, leveling agent, antifoaming agent, thickening agent and pH value regulator in sequence and disperse at 600-800 rpm for 10 min; (5) Add the extinction powder and disperse at 1000-1200 rpm for 90 min; (6) Add wax powder, disperse at 1000-1200 rpm for 30 min; Preparation of B component: (7) Add lipophilic isocyanate curing agent into hydrophilic isocyanate curing agent, disperse at 600-800 rpm for 30 min; (8) Add cosolvent, disperse at 600-800 rpm for 15 min.

8. A method of coating a surface of a stainless steel bellows, characterized by, Comprise: Mix A component, B component and water of the paint according to any one of claims 1-6 at a mass ratio of 100:10-25:10-20, spray on stainless steel substrate, and bake at 80°C for 120 min.

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