Water-based polyurethane finish applied to metal and preparation method thereof

Abstract

This application relates to the technical field of metal protective coatings, specifically disclosing a waterborne polyurethane topcoat for metals and its preparation method. The waterborne polyurethane topcoat for metals includes component A and component B. Component A, by weight, comprises the following raw materials: 75-85 parts of an acrylic solution with a solid content of 45%, 5-8 parts of deionized water, 0.8-1.2 parts of dispersant, 0.4-0.6 parts of defoamer, 15-25 parts of rutile titanium dioxide, 5-8 parts of film-forming aid, 3.5-5.5 parts of leveling agent, 2-4 parts of wax paste, and 0.2-0.5 parts of nano-alumina. Component B, by weight, comprises the following raw materials: 85-90 parts of polyurethane curing agent and 10-15 parts of propylene glycol methyl ether acetate. This application helps improve the surface smoothness of the waterborne polyurethane topcoat film applied to metals.

Description

Technical Field

[0001] This invention relates to the technical field of metal protective coatings, and in particular to a water-based polyurethane topcoat for use on metals and its preparation method. Background Technology

[0002] In metal protective coating systems, the topcoat, as the outermost coating, not only needs to provide excellent decoration, but also needs to have excellent weather resistance, chemical resistance, abrasion resistance, mechanical properties, and long-lasting anti-corrosion protection.

[0003] In related technologies, a water-based topcoat for the metal shell of an automotive model is disclosed, comprising component A and component B. Component A includes an acrylic aqueous dispersion, additives, powder, and deionized water. The acrylic aqueous dispersion has a hydroxyl value of 3% and a solid content of 44%. By weight, the acrylic aqueous dispersion comprises 65-78 parts. The additives consist of 4-6 parts film-forming aid, 0.2-0.3 parts neutralizer, 0.2-0.3 parts defoamer, 0.5-0.6 parts leveling agent, and 0.6-0.8 parts [unclear - possibly a component name or ingredient]. The mixture consists of a powder and 0.3-0.4 parts of a substrate wetting agent; the powder consists of 2-2.5 parts of titanium dioxide and 9-12 parts of red pigment; and deionized water consists of 8-15 parts. Component B consists of 70-78 parts of polyurethane curing agent and 20-23 parts of environmentally friendly co-solvent. The ratio of -NCO in the polyurethane curing agent to -OH in the acrylic aqueous dispersion is 1.9-2.1:1. Component A and component B are used in combination at a mass ratio of 5:1. The polyurethane curing agent is Bayer N3390.

[0004] However, metal products generally have high requirements for surface smoothness. The water-based topcoat mentioned above contains a high content of solid powder particles such as pigments, which may result in poor smoothness of the paint film. Summary of the Invention

[0005] To improve the smoothness of the surface of metal paint film, this application provides a water-based polyurethane topcoat for use on metal and a preparation method thereof.

[0006] Firstly, this application provides a water-based polyurethane topcoat for use on metals, employing the following technical solution: A waterborne polyurethane topcoat for use on metals, comprising component A and component B. Component A, by weight, comprises the following raw materials: 75-85 parts of an acrylic solution with a solid content of 45%, 5-8 parts of deionized water, 0.8-1.2 parts of dispersant, 0.4-0.6 parts of defoamer, 15-25 parts of rutile titanium dioxide, 5-8 parts of film-forming aid, 3.5-5.5 parts of leveling agent, 2-4 parts of wax paste, and 0.2-0.5 parts of nano-alumina. Component B, by weight, comprises the following raw materials: 85-90 parts of polyurethane curing agent and 10-15 parts of propylene glycol methyl ether acetate.

[0007] In one specific implementation, the film-forming aid comprises dipropylene glycol methyl ether and dipropylene glycol butyl ether in a weight ratio of (3-4):(2-3).

[0008] In one specific implementation, the leveling agent comprises polyether-modified silicone, acetylenic diol, and fluorocarbon-modified polyacrylate in a weight ratio of (3-6):(1-3):(0.5-1.5).

[0009] In one specific implementation scheme, the wax slurry comprises 20-30 parts PTFE wax, 20-30 parts polyethylene wax, 5-10 parts emulsifier, 1-2 parts anti-settling agent, 0.5-1 part defoamer, and 130-150 parts deionized water.

[0010] In one specific implementation, the method for preparing the wax paste includes the following steps: The emulsifier, anti-settling agent, defoamer and deionized water are mixed evenly to obtain a slurry, and the slurry is divided into two portions. Add PTFE wax to the first slurry, heat to 80℃, and stir evenly to obtain PTFE wax liquid. Add polyethylene wax to the second slurry and stir evenly to obtain polyethylene wax liquid. Mix the PTFE wax liquid and polyethylene wax liquid evenly to obtain wax slurry.

[0011] In one specific feasible implementation, the particle size of PTFE wax is 1-5 μm, and the particle size of polyethylene wax is 8-10 μm.

[0012] In one specific feasible implementation, the particle size of nano-alumina is 10-20 nm.

[0013] Secondly, this application provides a method for preparing a waterborne polyurethane topcoat for use on metals, which adopts the following technical solution: A method for preparing a waterborne polyurethane topcoat for use on metals includes the following steps: According to the proportion of component A, under stirring, dispersant, defoamer, film-forming aid and leveling agent are added to deionized water and stirred evenly. Rutile titanium dioxide, acrylic solution, wax paste and nano alumina are added in sequence. After each addition, the mixture is dispersed evenly, defoamed and sieved to obtain component A. According to the formulation of component B, the polyurethane curing agent and propylene glycol methyl ether acetate are mixed evenly to obtain component B; Mix component A and component B at a weight ratio of (3.5-4.5):1 to obtain a water-based polyurethane topcoat for use on metals.

[0014] In summary, this application has the following beneficial effects: 1. This application achieves the effect of improving the smoothness of the paint film surface of waterborne polyurethane topcoat applied to metals by using a specific ratio of acrylic solution, wax paste, nano alumina and other additives, through the synergistic effect of each component.

[0015] 2. In this application, dipropylene glycol methyl ether and dipropylene glycol butyl ether are preferably used in a weight ratio of (3-4):(2-3), polyether-modified organosilicon, acetylacetonate and fluorocarbon-modified polyacrylate in a weight ratio of (3-6):(1-3):(0.5-1.5), and the nano-alumina has a particle size of 10-20nm, which helps to further improve the smoothness of the paint film surface of waterborne polyurethane topcoat applied to metals. Detailed Implementation

[0016] Unless otherwise specified, all raw materials used in this application were commercially available. Acrylic acid solution was purchased from Shandong Ruifeng New Materials Co., Ltd. Dispersant was BYK-2159. Defoamer was BYK-014. Polyether-modified silicone was Evonik Tegofoamx 825. Nano-alumina was purchased from Beijing Deco Island Gold Technology Co., Ltd. PTFE wax was purchased from Zhejiang Juhua Co., Ltd. Polyethylene wax was purchased from Wuhan Xindongyi Chemical Co., Ltd. Emulsifier was Tween T40. Anti-settling agent was Qiyuan New Materials FC3420. Fluorocarbon-modified polyacrylate was YC388. Alkyne diol was Evonik Surfynol 104E tetramethyldecylene.

[0017] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0018] Example Example 1 This embodiment provides a waterborne polyurethane topcoat for use on metals, comprising component A and component B in a weight ratio of 4:1.

[0019] Component A comprises the following raw materials: 80 kg of acrylic acid solution with a solid content of 45%, 6.5 kg of deionized water, 1 kg of dispersant, 0.5 kg of defoamer, 20 kg of rutile titanium dioxide, 6.5 kg of dipropylene glycol methyl ether, 4.5 kg of polyether-modified silicone, 3 kg of wax paste, and 0.35 kg of nano-alumina. The particle size of the nano-alumina is between 10-20 nm.

[0020] The wax paste is prepared according to the following steps: Weigh the following raw materials: 25 kg PTFE wax, 25 kg polyethylene wax, 7.5 kg emulsifier, 1.5 kg anti-settling agent, 0.8 kg defoamer, and 140 kg deionized water. The particle size of PTFE wax is between 1-5 μm, and the particle size of polyethylene wax is between 8-10 μm.

[0021] Mix the emulsifier, anti-settling agent, defoamer and deionized water, stir until uniform to obtain a slurry, and divide the slurry into two portions.

[0022] PTFE wax is added to the first slurry, heated to 80°C, and stirred evenly to obtain PTFE wax liquid; polyethylene wax is added to the second slurry and stirred evenly to obtain polyethylene wax liquid; the PTFE wax liquid and polyethylene wax liquid are mixed evenly to obtain wax slurry.

[0023] Component B comprises the following raw materials: 88 kg of polyurethane curing agent and 12 kg of propylene glycol methyl ether acetate. The polyurethane curing agent and propylene glycol methyl ether acetate are mixed evenly to obtain component B.

[0024] This embodiment also provides a method for preparing a waterborne polyurethane topcoat for use on metals, comprising the following steps: According to the proportion of component A, the dispersant, defoamer, film-forming aid, and leveling agent are added to deionized water under stirring and stirred evenly. Rutile titanium dioxide, acrylic solution, wax paste, and nano alumina are added in sequence, and the mixture is dispersed evenly after each addition. The mixture is then defoamed and sieved to obtain component A.

[0025] According to the formulation of component B, the polyurethane curing agent and propylene glycol methyl ether acetate are mixed evenly to obtain component B.

[0026] Component A and component B are mixed evenly at a weight ratio of 4:1 to obtain a water-based polyurethane topcoat for use on metals.

[0027] Example 2 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, the weight ratio of component A to component B is 3.5:1.

[0028] Example 3 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metal, the weight ratio of component A to component B is 4.5:1.

[0029] Example 4 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, component A includes the following raw materials: 75 kg of acrylic solution with a solid content of 45%, 5 kg of deionized water, 0.8 kg of dispersant, 0.4 kg of defoamer, 15 kg of rutile titanium dioxide, 5 kg of film-forming aid, 3.5 kg of leveling agent, 2 kg of wax paste, and 0.2 kg of nano-alumina.

[0030] Example 5 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, component A includes the following raw materials: 85 kg of acrylic solution with a solid content of 45%, 8 kg of deionized water, 1.2 kg of dispersant, 0.6 kg of defoamer, 25 kg of rutile titanium dioxide, 8 kg of film-forming aid, 5.5 kg of leveling agent, 4 kg of wax paste, and 0.5 kg of nano-alumina.

[0031] Example 6 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, component B includes the following raw materials: 85 kg of polyurethane curing agent and 15 kg of propylene glycol methyl ether acetate.

[0032] Example 7 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, component B includes the following raw materials: 90 kg of polyurethane curing agent and 10 kg of propylene glycol methyl ether acetate.

[0033] Example 8 The only difference between this embodiment and Example 1 is that the wax paste is prepared according to the following steps: Weigh the following raw materials: 20 kg PTFE wax, 30 kg polyethylene wax, 5 kg emulsifier, 1 kg anti-settling agent, 0.5 kg defoamer, and 130 kg deionized water. The particle size of PTFE wax is between 1-5 μm, and the particle size of polyethylene wax is between 8-10 μm.

[0034] Mix the emulsifier, anti-settling agent, defoamer and deionized water, stir until uniform to obtain a slurry, and divide the slurry into two portions.

[0035] PTFE wax is added to the first slurry, heated to 80°C, and stirred evenly to obtain PTFE wax liquid; polyethylene wax is added to the second slurry and stirred evenly to obtain polyethylene wax liquid; the PTFE wax liquid and polyethylene wax liquid are mixed evenly to obtain wax slurry.

[0036] Example 9 The only difference between this embodiment and Example 1 is that the wax paste is prepared according to the following steps: Weigh the following raw materials: 30 kg PTFE wax, 20 kg polyethylene wax, 10 kg emulsifier, 2 kg anti-settling agent, 1 kg defoamer, and 150 kg deionized water. The particle size of PTFE wax is between 1-5 μm, and the particle size of polyethylene wax is between 8-10 μm.

[0037] Mix the emulsifier, anti-settling agent, defoamer and deionized water, stir until uniform to obtain a slurry, and divide the slurry into two portions.

[0038] PTFE wax is added to the first slurry, heated to 80°C, and stirred evenly to obtain PTFE wax liquid; polyethylene wax is added to the second slurry and stirred evenly to obtain polyethylene wax liquid; the PTFE wax liquid and polyethylene wax liquid are mixed evenly to obtain wax slurry.

[0039] Example 10 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, dipropylene glycol methyl ether is replaced with a mixture of dipropylene glycol methyl ether and dipropylene glycol butyl ether in an equal weight ratio of 3.5:2.5.

[0040] Example 11 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, dipropylene glycol methyl ether is replaced with a mixture of dipropylene glycol methyl ether and dipropylene glycol butyl ether in an equal weight ratio of 1:1.

[0041] Example 12 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, dipropylene glycol methyl ether is replaced with a mixture of dipropylene glycol methyl ether and dipropylene glycol butyl ether in an equal weight ratio of 2:1.

[0042] Example 13 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, the polyether-modified organosilicon is replaced with a mixture of polyether-modified organosilicon, acetylacetonate and fluorocarbon-modified polyacrylate in an equal weight ratio of 4.5:2:1.

[0043] Example 14 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, the polyether-modified organosilicon, acetylation diol and fluorocarbon-modified polyacrylate in equal weight ratios of 3:1:1.5 are used to replace the polyether-modified organosilicon.

[0044] Example 15 The only difference between this embodiment and Embodiment 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metals, the polyether-modified organosilicon, acetylation diol and fluorocarbon-modified polyacrylate in equal weight ratios of 6:3:0.5 are used to replace the polyether-modified organosilicon.

[0045] Example 16 The only difference between this embodiment and Embodiment 1 is that the particle size of the nano-alumina is between 4-8 nm.

[0046] Example 17 The only difference between this embodiment and Embodiment 1 is that the particle size of the nano-alumina is between 22-30 nm.

[0047] Comparative Example Comparative Example 1 The only difference between this comparative example and Example 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metal, the weight ratio of component A to component B is 3:1.

[0048] Comparative Example 2 The only difference between this comparative example and Example 1 is that, in the raw materials and preparation method of the waterborne polyurethane topcoat applied to metal, the weight ratio of component A to component B is 5:1.

[0049] Comparative Example 3 The only difference between this comparative example and Example 1 is that, in the raw materials of component A, an equal amount of deionized water is used to replace dipropylene glycol methyl ether.

[0050] Comparative Example 4 The only difference between this comparative example and Example 1 is that, in the raw materials of component A, an equal amount of deionized water is used to replace the polyether-modified organosilicon.

[0051] Comparative Example 5 The only difference between this comparative example and Example 1 is that, in the raw materials of component A, an equal amount of deionized water is used to replace the wax paste.

[0052] Comparative Example 6 The only difference between this comparative example and Example 1 is that, in the raw materials of component A, an equal amount of rutile titanium dioxide is used to replace nano-alumina.

[0053] Performance testing The following performance tests were conducted on Examples 1-17 and Comparative Examples 1-6: A 120mm × 50mm × 0.3mm tinplate was lightly sanded unidirectionally (along the long side) with 400#-600# wet sandpaper to remove the oxide layer and minor scratches. After cleaning and drying, the substrate was obtained. The water-based polyurethane topcoat for metals prepared in each embodiment and comparative example was sprayed onto the surface of the substrate. The samples were placed horizontally under standard conditions and allowed to level for 20 minutes. After drying, a dry film with a thickness of 30±2μm was obtained. Five different areas were randomly selected on the surface of the paint film for measurement. Within the sampling length, the average absolute distance from each point on the contour to the centerline was calculated, denoted as Ra. The smaller the Ra value, the higher the smoothness. The DOI value of the paint film was measured using a DOI (Distinctness of Reflectance) meter. The higher the DOI value, the better the surface smoothness.

[0054] The test results are shown in Table 1.

[0055] Table 1 As can be seen from Example 1 and Comparative Examples 1-6, and in conjunction with Table 1, compared to Example 1, the Ra values ​​of Comparative Examples 1-6 are all significantly larger, and the DOI values ​​are all significantly smaller. This indicates that using the raw material ratio and preparation method of Example 1 helps to improve the surface smoothness of the waterborne polyurethane topcoat applied to metals.

[0056] This is likely because the acrylic solution provides the film-forming base, and its low viscosity and low surface tension facilitate leveling. The PTFE wax in the wax paste provides a long-lasting, dry, and smooth feel. The combination of polyethylene wax and PTFE wax enhances abrasion resistance and anti-tack properties. Nano-alumina fills microscopic defects, resulting in a unique ceramic texture and increased hardness. Other additives and deionized water adjust viscosity, ensure stable pigment dispersion, and improve film formation. Therefore, through the synergistic effect of these components, the smoothness of the paint film surface in waterborne polyurethane topcoats applied to metals is improved.

[0057] As can be seen from Examples 1-17 and Table 1, the Ra values ​​of Examples 1-17 are all relatively small and the Ra values ​​of Examples 2-17 are relatively large. This indicates that the raw material ratios and preparation methods of Examples 1-17 are helpful in improving the smoothness of the paint film surface of waterborne polyurethane topcoats applied to metals.

[0058] Based on Examples 1-17 and Table 1, it can be seen that by comparing the test data of each example, using dipropylene glycol methyl ether and dipropylene glycol butyl ether in a weight ratio of (3-4):(2-3), polyether-modified organosilicon, acetylacetonate and fluorocarbon-modified polyacrylate in a weight ratio of (3-6):(1-3):(0.5-1.5), and nano-alumina with a particle size of 10-20 nm, helps to further improve the smoothness of the paint film surface of waterborne polyurethane topcoat applied to metals.

[0059] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A water-based polyurethane topcoat for use on metals, characterized in that, The product comprises two components, A and B, in a weight ratio of (3.5-4.5):

1. Component A, by weight, includes the following raw materials: 75-85 parts of an acrylic acid solution with a solid content of 45%, 5-8 parts of deionized water, 0.8-1.2 parts of dispersant, 0.4-0.6 parts of defoamer, 15-25 parts of rutile titanium dioxide, 5-8 parts of film-forming aid, 3.5-5.5 parts of leveling agent, 2-4 parts of wax paste, and 0.2-0.5 parts of nano-alumina. Component B, by weight, includes the following raw materials: 85-90 parts of polyurethane curing agent, and 10-15 parts of propylene glycol methyl ether acetate. The film-forming aid includes... The wax slurry comprises dipropylene glycol methyl ether and dipropylene glycol butyl ether in a weight ratio of (3-4):(2-3), and the leveling agent comprises polyether-modified silicone, acetylation glycol and fluorocarbon-modified polyacrylate in a weight ratio of (3-6):(1-3):(0.5-1.5), and the nano-alumina has a particle size of 10-20 nm; the wax slurry comprises the following raw materials in parts by weight: 20-30 parts PTFE wax, 20-30 parts polyethylene wax, 5-10 parts emulsifier, 1-2 parts anti-settling agent, 0.5-1 parts defoamer and 130-150 parts deionized water; the PTFE wax has a particle size of 1-5 μm and the polyethylene wax has a particle size of 8-10 μm.

2. The waterborne polyurethane topcoat for metals according to claim 1, characterized in that, The method for preparing the wax paste includes the following steps: The emulsifier, anti-settling agent, defoamer and deionized water are mixed evenly to obtain a slurry, and the slurry is divided into two portions. Add PTFE wax to the first slurry, heat to 80℃, and stir evenly to obtain PTFE wax liquid. Add polyethylene wax to the second slurry and stir evenly to obtain polyethylene wax liquid. Mix the PTFE wax liquid and polyethylene wax liquid evenly to obtain wax slurry.

3. A method for preparing a waterborne polyurethane topcoat for metals according to any one of claims 1-2, characterized in that, Includes the following steps: According to the proportion of component A, under stirring, dispersant, defoamer, film-forming aid and leveling agent are added to deionized water and stirred evenly. Rutile titanium dioxide, acrylic solution, wax paste and nano alumina are added in sequence. After each addition, the mixture is dispersed evenly, defoamed and sieved to obtain component A. According to the formulation of component B, the polyurethane curing agent and propylene glycol methyl ether acetate are mixed evenly to obtain component B; Mix component A and component B at a weight ratio of (3.5-4.5):1 to obtain a water-based polyurethane topcoat for use on metals.

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