A waterborne single-coat skin finish bake paint for metal substrates and a method of making the same

Abstract

The application discloses a water-based single-coat skin-feeling baking varnish for metal substrates, which is prepared by mixing different types of water-based polyurethane dispersions in a certain proportion, adding water-based blocked isocyanate resins and methyl etherified melamine resins, and then adding water-based color paste, water-based additives, film-forming additives and acidic catalysts according to a certain process technology. The single-coat skin-feeling baking varnish has good adhesion and hand feeling effect on different types of metal substrates, and is superior or equivalent to the currently used oil-based or water-based double-coat skin-feeling baking varnish. The single-coat skin-feeling baking varnish saves processes and materials, and solves the problems of the oil-based or double-coat skin-feeling baking varnish, such as stickiness caused by heating, easy peeling, and decline of skin feeling effect, and is more environmentally friendly and safe.

Description

Technical Field

[0001] This invention relates to a water-based single-coat skin-feel baking paint for metal substrates and its preparation method, belonging to the field of water-based coating technology. Background Technology

[0002] Currently, skin-feel baking paint products used on metal substrates are mainly double-coat oil-based baking paints or double-coat water-based baking paints. In order to ensure coating performance and feel effect, two layers of coating are required. The first layer is a primer applied to the metal substrate to provide adhesion and color effect to the metal substrate. The second layer is a skin-feel clear coat applied on top of the primer to provide feel effect.

[0003] Double-coated oil-based baking paint has the following disadvantages: (1) It is not environmentally friendly and causes great pollution, and is a technology that is restricted from development by the state;

[0004] (2) Two coatings are involved in two products, the process is complex, the production efficiency is low, and there is a risk of mismatch between the coatings, which affects the yield rate; (3) Oil-based skin-feel varnish will become sticky when heated in summer, and the skin-feel effect will decrease or be lost. Although double-coat water-based baking paint is more environmentally friendly, it involves two coatings, two products, the process is complex, the production efficiency is low, and there is a risk of mismatch between the coatings, which affects the yield rate. Summary of the Invention

[0005] Addressing the technical shortcomings of current products, a water-based single-coat skin-feel baking paint for metal substrates and its preparation method have been designed through formula development. This single-layer coating achieves excellent film performance and a superior skin-feel effect, simplifying the construction process, saving coating materials, and improving yield. While ensuring excellent adhesion to the metal substrate, it provides excellent coating performance and a superior skin-feel effect. High-end mobile phones, computers, intelligent robots, and other information products, as well as equipment in the energy storage, solar, and wind power sectors, have increasingly higher requirements for metals. Single-coat metals offer superior protection against aging, durability, reliability, and process advantages. The single coating prevents coating peeling, has excellent properties of seamless integration with the metal, and significantly reduces manufacturing costs. It can meet these new demands and has a broad market prospect.

[0006] The first objective of this invention is to provide a water-based single-coat skin-feel baking paint formulation for metal substrates, wherein the water-based single-coat skin-feel baking paint, by weight, comprises...

[0007] 10-50 parts of hydroxyl-containing aqueous polyurethane dispersion;

[0008] 10-50 parts of hydroxyl-free aqueous polyurethane dispersion;

[0009] 1-15 parts of a blocked isocyanate resin suitable for use in aqueous systems;

[0010] 1-15 parts of methylated melamine resin that can be used in water-based systems;

[0011] 5-10 parts deionized water;

[0012] 3-20 parts pigment;

[0013] 0-20 parts of filler;

[0014] 0.5-6 parts of aqueous dispersant;

[0015] 0.1-0.5 parts of water-based defoamer;

[0016] 0.1-0.5 parts of water-based wetting agent;

[0017] 0.1-0.5 parts of water-based thickener;

[0018] Catalyst 0.1-0.5 parts;

[0019] Add 3-5 parts of cosolvent.

[0020] Optionally, the pigment includes any one or more combinations of inorganic and organic pigments such as carbon black, iron oxide, bismuth vanadate, titanium dioxide, phthalocyanine, azo, isoindoline, pyrrolidone, quinacridone, and benzimidazolone, with environmentally friendly pigments being preferred;

[0021] Optionally, the filler includes any one or more combinations of natural fillers or artificial synthetic fillers such as barium sulfate, calcium carbonate, talc powder, feldspar powder, mica powder, silica powder, wollastonite powder, bentonite, and kaolin, with environmentally friendly fillers being preferred.

[0022] Optionally, the aqueous dispersant includes any one or more combinations of ionic, nonionic, controlled radical, or polymeric dispersants, preferably polymeric dispersants.

[0023] Optionally, the water-based defoamer includes any one or more combinations of silicone defoamers and non-silicone defoamers, preferably silicone defoamers.

[0024] Optionally, the aqueous wetting agent includes any one or more combinations of silicone wetting agents or non-silicone wetting agents, preferably silicone wetting agents.

[0025] Optionally, the water-based thickener includes any one or more combinations of clay-based thickeners, acrylic thickeners, polyamide thickeners, or polyurethane thickeners, preferably polyurethane thickeners.

[0026] Optionally, the catalyst includes any one or more combinations of p-toluenesulfonic acid and dodecyl toluenesulfonic acid, preferably p-toluenesulfonic acid catalyst.

[0027] Optionally, the co-solvent includes any one or more combinations of alcohols, esters, and ethers that can be used in water-based coating systems, preferably ethers with good water solubility and a boiling point above 100°C.

[0028] Optionally, the hydroxyl-containing aqueous polyurethane dispersion comprises any one or more combinations of acrylic polyurethane dispersion, polyether polyurethane dispersion, polyester polyurethane dispersion, and polycarbonate polyurethane dispersion, preferably polyester polyurethane dispersion.

[0029] Optionally, the hydroxyl-free aqueous polyurethane dispersion comprises any one or more combinations of acrylic polyurethane dispersion, polyether polyurethane dispersion, polyester polyurethane dispersion, and polycarbonate polyurethane dispersion, preferably acrylic polyurethane dispersion.

[0030] Optionally, the blocked isocyanate resin that can be used in aqueous systems includes any one or more combinations of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate, preferably a blocked hexamethylene diisocyanate resin.

[0031] Optionally, the methyl etherified melamine resin that can be used in aqueous systems comprises any one or more combinations of highly methyl etherified melamine resin and partially methyl etherified melamine resin, preferably highly methyl etherified melamine resin.

[0032] Another object of the present invention is to provide a method for preparing a water-based single-coat skin-feel baking paint for metal substrates, comprising the following steps:

[0033] Mixing different types of waterborne polyurethane dispersions;

[0034] Then add the corresponding blocked isocyanate resin that can be used in water-based systems and the methylated melamine resin that can be used in water-based systems;

[0035] Finally, water-based pigments, water-based additives, film-forming aids, and acidic catalysts are added to prepare a water-based single-coat skin-feel baking paint for metal substrates. The paint is evenly applied to unpolished metal substrates and baked at 120-200℃ to form a coating with excellent adhesion and skin feel.

[0036] Mixing different types of waterborne polyurethane dispersions;

[0037] Then add the corresponding blocked isocyanate resin that can be used in water-based systems and the methylated melamine resin that can be used in water-based systems;

[0038] Finally, water-based pigments, water-based additives, film-forming aids, and acidic catalysts are added to prepare a water-based single-coat skin-feel baking paint for metal substrates. The paint is evenly applied to unpolished metal substrates and baked at 120-200℃ to form a coating with excellent adhesion and skin feel.

[0039] Optionally, the steps include:

[0040] 1) Divide the deionized water into two parts, namely deionized water A and deionized water B;

[0041] 2) Add deionized water A, water-based dispersant, and water-based defoamer to the dispersion tank, mix well to form a mixture;

[0042] 3) Add pigments and fillers to the mixture, mix thoroughly, and prepare a premixed slurry;

[0043] 4) Grind the premixed slurry to a fineness of less than 20 micrometers using a grinding device to obtain an aqueous color paste;

[0044] 5) Add hydroxyl-containing waterborne polyurethane dispersion, hydroxyl-free waterborne polyurethane dispersion, blocked isocyanate resin that can be used in waterborne systems, methylated melamine resin that can be used in waterborne systems, cosolvent and catalyst to the paint mixing tank, disperse at high speed for 10 minutes, and then add the color paste from step 3), disperse at high speed until uniform.

[0045] 6) Add the water-based wetting agent, water-based thickener, and deionized water B to the mixture obtained in step 4), and disperse evenly.

[0046] Filtering and packaging yields a water-based single-coat skin-feel baking paint.

[0047] When using this product, deionized water is added to adjust the viscosity to the required application temperature. The product is then applied to a metal substrate and baked at 120-200℃, preferably 150-180℃, to form a film.

[0048] Optionally, the different types of waterborne polyurethane dispersions are hydroxyl-containing waterborne polyurethane dispersions and hydroxyl-free waterborne polyurethane dispersions.

[0049] Optionally, the hydroxyl-containing aqueous polyurethane dispersion and the hydroxyl-free aqueous polyurethane dispersion are mixed and formulated at a ratio of 1:5 to 5:1 according to different skin feel and adhesion requirements.

[0050] Optionally, two crosslinking resins are added: a blocked isocyanate resin suitable for aqueous systems and a methylated melamine resin suitable for aqueous systems. The amount of the blocked isocyanate resin suitable for aqueous systems is calculated based on the hydroxyl content in the hydroxyl-containing polyester polyurethane dispersion, while the amount of the methylated melamine resin suitable for aqueous systems is calculated based on the solid content of all polyurethane dispersions.

[0051] Optionally, the acidic catalyst is preferably an aqueous, closed-type acidic catalyst, and the amount added is 0.05%-1% of the total formulation, depending on the baking temperature.

[0052] Optionally, the coating substrate is an unpolished metal substrate, including but not limited to stainless steel, carbon steel, copper, and aluminum.

[0053] Optionally, the baking temperature of the coating is suitable for 120-200℃, which results in better paint film performance. Other baking temperatures can also form a film, but the performance will differ from that of baking at 120-200℃.

[0054] This invention has one or more of the following beneficial effects:

[0055] 1. The water-based single-coat skin-feel baking paint of the present invention can be used on different metal substrates, does not require polishing, and has excellent adhesion and excellent skin-feel effect after film formation.

[0056] 2. The water-based single-coat skin-feel baking paint of the present invention is a water-based product with low solvent content, no fire risk, and is an environmentally friendly and safe product.

[0057] 3. The water-based single-coat skin-feel baking paint of the present invention has high coating efficiency, no matching problems between coating layers, and high yield rate compared with the two-coat scheme.

[0058] 4. The preparation process of the present invention is simple, easy to operate, has low production cost, and high production efficiency. Detailed implementation method:

[0059] To better understand the present invention, specific examples are used below to illustrate the technical solution of the present invention in detail, but the present invention is not limited thereto.

[0060] All raw materials used in this invention are commercially available products.

[0061] The hydroxyl-containing aqueous polyurethane dispersion is an aqueous polyester polyurethane dispersion resin. As a film-forming substance, the hydroxyl content (to solids) is 1.7%, and the solid content is 41%.

[0062] The hydroxyl-free aqueous polyurethane dispersion is an aqueous acrylic polyurethane dispersion resin, which serves as a film-forming substance with a solid content of 32%.

[0063] The blocked isocyanate resin that can be used in aqueous systems is a blocked hexamethylene diisocyanate resin. As a crosslinking reaction resin, it has an NCO content (for the form of supply) of 5% and a solid content of 40%.

[0064] The methylated melamine resin that can be used in aqueous systems is a highly methylated melamine resin, which serves as a crosslinking reaction resin and has a solid content of 98%.

[0065] The pigment is rutile titanium dioxide, which is used as the main coloring pigment and has a solid content of 100%.

[0066] The pigment is medium-pigment carbon black powder, used as a secondary coloring pigment, with a solid content of 100%.

[0067] The filler is precipitated barium sulfate, which is used as a bulk filler and has a solid content of 100%.

[0068] The aqueous dispersant is an acrylate copolymer containing pigment affinity groups, used as an auxiliary agent for wetting and dispersing pigments and fillers, with an active ingredient content of 40%.

[0069] The water-based defoamer is a mixture of polyether siloxane copolymer and hydrophobic particles, and as a defoaming aid, the active ingredient content is 20%.

[0070] The aqueous wetting agent is a polyether-modified siloxane solution, used as an additive to wet the substrate, with an active ingredient content of 52%.

[0071] The aqueous thickener is a nonionic polyurethane solution, used as an anti-settling and thickening agent, with an active ingredient content of 40%.

[0072] The catalyst is an amino-blocked p-toluenesulfonic acid solution, which serves as an auxiliary agent for the catalytic reaction, and the active ingredient content is 25%.

[0073] The cosolvent is dipropylene glycol methyl ether, which is used as a film-forming aid. Its CAS number is 34590-94-8 and its boiling point is 190°C.

[0074] The deionized water is used as the main diluent.

[0075] Commercially available sample 1: A commercially available double-coat oil-based skin-feel baking paint product for metal substrates, as a comparative example, including primer and clear coat.

[0076] Commercially available sample 2: A commercially available double-coat water-based skin-feel baking paint product for metal substrates, as a comparative example, including primer and clear coat.

[0077] Test substrates: 304 stainless steel plate, cold-rolled steel plate, and aluminum plate were used as test substrates.

[0078] Example 1

[0079] Components Proportion Deionized water A 5 copies Main pigments 13 copies Secondary pigments 0.5 copies filler 1.5 copies Aqueous dispersants 1 copy Water-based defoamer 0.3 copies Water-based wetting agents 0.3 copies Water-based thickener 0.2 copies catalyst 0.2 copies Cosolvent 3 copies Hydroxyl-containing aqueous polyurethane dispersion 15 copies Hydroxyl-free waterborne polyurethane dispersion 45 copies Blocked isocyanate resins suitable for use in water-based systems 7.7 copies Highly methylated melamine resins suitable for water-based systems 4.1 copies Deionized water B 3.2 copies

[0080] The preparation method of Example 1 is as follows:

[0081] 1) Divide the deionized water into two parts, namely deionized water A and deionized water B;

[0082] 2) Add deionized water A, water-based dispersant, and water-based defoamer to the dispersion tank, mix well to form a mixture;

[0083] 3) Add pigments and fillers to the mixture, mix thoroughly, and prepare a premixed slurry;

[0084] 4) Grind the premixed slurry to a fineness of less than 20 micrometers using a grinding device to obtain an aqueous color paste;

[0085] 5) Add hydroxyl-containing waterborne polyurethane dispersion, hydroxyl-free waterborne polyurethane dispersion, blocked isocyanate resin that can be used in waterborne systems, methylated melamine resin that can be used in waterborne systems, cosolvent and catalyst to the paint mixing tank, disperse at high speed for 10 minutes, and then add the color paste from step 3), disperse at high speed until uniform.

[0086] 6) Add the water-based wetting agent, water-based thickener, and deionized water B to the mixture obtained in step 4), and disperse evenly.

[0087] After filtration and packaging, a water-based single-coat skin-feel baking paint is obtained.

[0088] When using, add deionized water to adjust to the application viscosity, apply to the metal substrate, and bake at 120-200℃ to form a film.

[0089] Baking at 150-180℃ is preferred.

[0090] According to the production process, the finished paint is prepared and sprayed onto unpolished 304 stainless steel plate, cold-rolled steel plate, copper plate and aluminum plate respectively. After baking at 160℃ for 30 minutes and curing for 24 hours, the performance is tested. Then, it is placed in a 50℃ oven for heat storage for 1 month before testing the performance again.

[0091] Example 2

[0092]

[0093]

[0094] The manufacturing process of Example 2 is similar to that of Example 1, and will not be described in detail here.

[0095] According to the production process, the finished paint is prepared and sprayed onto unpolished 304 stainless steel plate, cold-rolled steel plate, copper plate and aluminum plate respectively. After baking at 160℃ for 30 minutes and curing for 24 hours, the performance is tested. Then, it is placed in a 50℃ oven for heat storage for 1 month before testing the performance again.

[0096] Comparative Example 1

[0097] The varnish of commercially available sample 1 was sprayed onto unpolished 304 stainless steel plate, cold-rolled steel plate, copper plate, and aluminum plate, respectively. After baking at 160°C for 30 minutes and curing for 24 hours, the performance was tested. Then, it was placed in a 50°C oven for heat storage for 1 month before the performance was tested again.

[0098] Comparative Example 2

[0099] The varnish of commercially available sample 2 was sprayed onto unpolished 304 stainless steel plate, cold-rolled steel plate, copper plate, and aluminum plate, respectively. After baking at 160°C for 30 minutes and curing for 24 hours, the performance was tested. Then, it was placed in a 50°C oven for heat storage for 1 month before the performance was tested again.

[0100] Comparative Example 3

[0101] The primer of commercially available sample 1 was sprayed onto unpolished 304 stainless steel plate, cold-rolled steel plate, copper plate and aluminum plate respectively, baked at 120°C for 10 minutes, cooled to room temperature, and then sprayed with the clear varnish of commercially available sample 1. It was baked at 160°C for 30 minutes, cured for 24 hours and then tested for performance. Then it was placed in a 50°C oven for heat storage for 1 month and then tested for performance.

[0102] Comparative Example 4

[0103] The primer of commercially available sample 2 was sprayed onto unpolished 304 stainless steel plate, cold-rolled steel plate, copper plate, and aluminum plate, respectively. It was baked at 120°C for 10 minutes, cooled to room temperature, and then the clear varnish of commercially available sample 2 was sprayed on. It was baked at 160°C for 30 minutes and cured for 24 hours before performance testing. Then it was placed in a 50°C oven for heat storage for 1 month before performance testing.

[0104] Performance test results:

[0105]

[0106] *The test results are based on GB / T 9286-1998, where level 0 is the best with no peeling and level 5 has a relatively high degree of peeling.

[0107] The embodiments of the present invention and comparative examples of commercially available samples, through testing the adhesion and feel effects before and after heat storage on different substrates, lead to the following conclusions:

[0108] 1. The adhesion of Examples 1 and 2 before and after heat storage on different substrates was qualified. In Example 1, increasing the proportion of hydroxyl-free waterborne polyurethane dispersion can significantly improve the feel effect; in Example 2, increasing the proportion of hydroxyl-containing waterborne polyurethane dispersion can significantly improve the adhesion to different metal substrates.

[0109] 2. Comparative Examples 1 and 2 exhibit excellent tactile feel, but lack adhesion to various metal substrates. After heat treatment, the paint film in Comparative Example 1 becomes sticky, losing its tactile feel; in Comparative Example 2, the paint film does not become sticky after heat treatment, and the tactile feel is significantly improved.

[0110] 3. Comparative Examples 3 and 4 exhibit excellent tactile feel and good adhesion to various metal substrates. After heat treatment, the paint film in Comparative Example 3 became sticky, significantly reducing the tactile feel, and its adhesion to the aluminum plate was unsatisfactory. In contrast, the paint film in Comparative Example 4 did not become sticky after heat treatment, exhibiting a noticeable tactile feel and satisfactory adhesion.

[0111] Experiments have shown that this invention has excellent adhesion and a good feel on different metal substrates, making it a water-based single-coat skin-feel baking paint suitable for various metal substrates.

[0112] All the raw materials listed in this invention, as well as the upper and lower limits and ranges of the raw materials and the upper and lower limits and ranges of the process parameters, can realize this invention. Examples are not listed one by one here.

[0113] The above description is merely a preferred embodiment of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

[0114] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope defined in the claims.

Claims

1. A water-based single-coat skin-feel baking paint for metal substrates, characterized in that, The water-based single-coat skin-feel baking paint comprises, by weight parts: 10-50 parts of hydroxyl-containing aqueous polyurethane dispersion; 10-50 parts of hydroxyl-free aqueous polyurethane dispersion; 1-15 parts of a blocked isocyanate resin suitable for use in aqueous systems; 1-15 parts of methylated melamine resin that can be used in water-based systems; 5-10 parts deionized water; 3-20 parts pigment; 0-20 parts of filler; 0.5-6 parts of aqueous dispersant; 0.1-0.5 parts of water-based defoamer; 0.1-0.5 parts of water-based wetting agent; 0.1-0.5 parts of water-based thickener; Catalyst 0.1-0.5 parts; Add 3-5 parts of cosolvent.

2. The water-based single-coat skin-feel baking paint as described in claim 1, characterized in that, The pigments include any one or more combinations of carbon black, iron oxide, bismuth vanadate, titanium dioxide, phthalocyanine, azo, isoindoline, pyrrolidone, quinacridone, and benzimidazolone.

3. The water-based single-coat skin-feel baking paint as described in claim 1, characterized in that, The filler includes any one or more combinations of barium sulfate, calcium carbonate, talc powder, feldspar powder, mica powder, silica fume, wollastonite powder, bentonite, and kaolin. The aqueous dispersant includes any one or more combinations of ionic, nonionic, and controlled radical types; The water-based defoamer includes any one or more combinations of silicone defoamers and non-silicone defoamers; The aqueous wetting agent includes any one or more combinations of organosilicon wetting agents or non-silicone wetting agents; The water-based thickener includes any one or more combinations of clay-based thickeners, acrylic thickeners, polyamide thickeners, or polyurethane thickeners. The catalyst includes any one or more combinations of p-toluenesulfonic acid and dodecyl toluenesulfonic acid. The co-solvent comprises any one or more combinations of alcohols, esters, and ethers that can be used in water-based coating systems; It includes any one or more combinations of acrylic polyurethane dispersions, polyether polyurethane dispersions, polyester polyurethane dispersions, and polycarbonate polyurethane dispersions. The hydroxyl-free aqueous polyurethane dispersion comprises any one or more combinations of acrylic polyurethane dispersion, polyether polyurethane dispersion, polyester polyurethane dispersion, and polycarbonate polyurethane dispersion. The blocked isocyanate resin that can be used in aqueous systems includes any one or more combinations of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate. The methylated melamine resin that can be used in aqueous systems includes any one or more combinations of highly methylated melamine resin and partially methylated melamine resin.

4. A method for preparing a water-based single-coat skin-feel baking paint as described in any one of claims 1-3, characterized in that, Includes the following steps: Mixing different types of waterborne polyurethane dispersions; Then add the corresponding blocked isocyanate resin that can be used in water-based systems and the methylated melamine resin that can be used in water-based systems; Finally, water-based pigments, water-based additives, film-forming aids, and acidic catalysts are added to prepare a water-based single-coat skin-feel baking paint for metal substrates. The paint is evenly applied to unpolished metal substrates and baked at 120-200℃ to form a coating with excellent adhesion and skin feel.

5. The preparation method according to claim 4, characterized in that: The steps include: 1) Divide the deionized water into two parts, namely deionized water A and deionized water B; 2) Add deionized water A, water-based dispersant, and water-based defoamer to the dispersion tank, mix well to form a mixture; 3) Add pigments and fillers to the mixture, mix thoroughly, and prepare a premixed slurry; 4) Grind the premixed slurry to a fineness of less than 20 micrometers using a grinding device to obtain an aqueous color paste; 5) Add hydroxyl-containing waterborne polyurethane dispersion, hydroxyl-free waterborne polyurethane dispersion, blocked isocyanate resin that can be used in waterborne systems, methylated melamine resin that can be used in waterborne systems, cosolvent and catalyst to the paint mixing tank, disperse at high speed for 10 minutes, and then add the color paste from step 3), disperse at high speed until uniform. 6) Add the water-based wetting agent, water-based thickener, and deionized water B to the mixture obtained in step 4), and disperse evenly. Filtering and packaging yields a water-based single-coat skin-feel baking paint. When using, deionized water is added to adjust to the application viscosity, and the mixture is applied to a metal substrate and baked at 120-200℃ to form a film, preferably at 150-180℃. The different types of waterborne polyurethane dispersions are waterborne polyurethane dispersions containing hydroxyl groups and waterborne polyurethane dispersions without hydroxyl groups.

6. The preparation method according to claim 4, characterized in that: The hydroxyl-containing aqueous polyurethane dispersion and the hydroxyl-free aqueous polyurethane dispersion are mixed and formulated at a ratio of 1:5 to 5:1 according to different skin feel and adhesion requirements.

7. The preparation method according to claim 4, characterized in that: Two types of crosslinking resins are added: a blocked isocyanate resin suitable for aqueous systems and a methylated melamine resin suitable for aqueous systems. The amount of the blocked isocyanate resin suitable for aqueous systems is calculated based on the hydroxyl content in the hydroxyl-containing polyester polyurethane dispersion, while the amount of the methylated melamine resin suitable for aqueous systems is calculated based on the solid content of all polyurethane dispersions. 10-50 parts of hydroxyl-containing aqueous polyurethane dispersion; 10-50 parts of hydroxyl-free aqueous polyurethane dispersion; 1-15 parts of a blocked isocyanate resin suitable for use in aqueous systems; 1-15 parts of methylated melamine resin that can be used in water-based systems.

8. The preparation method according to claim 4, characterized in that: The acidic catalyst is preferably an aqueous, closed-type acidic catalyst, and the amount added is 0.05%-1% of the total formula, depending on the baking temperature.

9. The preparation method according to claim 4, characterized in that: The coating substrate is an unpolished metal substrate, including but not limited to stainless steel, carbon steel, copper, and aluminum.

10. The preparation method according to claim 4, characterized in that: The coating is suitable for baking at 120-200℃, resulting in good film performance. Other baking temperatures can also form a film, but the performance will differ from that of baking at 120-200℃.

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