Magnesium alloy base composite coating for vehicle-mounted central control large screen and preparation method and application of magnesium alloy base composite coating

Abstract

The invention belongs to the technical field of magnesium alloy base material coating materials, and discloses a vehicle-mounted center control large screen magnesium alloy base composite coating and a preparation method and application thereof.The composite coating is constructed through a double-layer system of a bottom coating and a surface coating, the aluminum zinc phosphate hydrate and the mica powder functional filler are matched, and a pyrazole blocked isocyanate curing agent is adopted to realize high crosslinking; the surface coating is synergistically cured by high molecular weight thermosetting acrylic resin and a methyl etherified high imino melamine cross-linking agent, and is compounded with aluminum paste, mica powder and the like, so that excellent decorative property and protective property are realized, and the composite paint coating has the characteristics of excellent boiling resistance, salt fog resistance, wear resistance, scratch resistance and the like.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy substrate coating materials technology, specifically to a composite coating for a magnesium alloy base of an in-vehicle central control screen, its preparation method, and its application. Background Technology

[0002] Magnesium alloys are a class of lightweight alloy materials composed of magnesium as the matrix and incorporating elements such as aluminum, zinc, manganese, and rare earth elements. Represented by AZ91D magnesium alloy, they exhibit excellent properties in terms of structural strength, specific strength, specific stiffness, vibration damping, thermal conductivity, and electromagnetic shielding, thus being widely used in electronic product housings and lightweight automotive components. However, magnesium alloys have a low thermodynamic standard electrode potential of -2.36V and are highly reactive, making them highly susceptible to corrosion in humid environments and salt spray conditions. This severely restricts the reliable use of magnesium alloys in harsh environments such as humidity and salt spray.

[0003] Therefore, to leverage the lightweight advantages of magnesium alloys and ensure their long-term service stability, appropriate surface protection treatment is necessary. Common processes include chemical conversion coating, anodizing, electroplating, coating with organic coatings, or metal / ceramic composite coatings. In the prior art, a typical method is to first perform chemical phosphate conversion treatment and then apply an organic coating on top. The invention patent with application number CN200610019324.5 discloses a method for phosphate surface modification treatment of magnesium alloys. Through steps such as degreasing, pickling, alkali washing, chemical film formation, and sealing, a phosphate chemical conversion film layer is formed on the surface of the magnesium alloy, effectively improving the corrosion resistance and coating adhesion of the magnesium alloy. Although the above technical solutions have improved corrosion protection, there are still shortcomings. On the one hand, the phosphate conversion film itself is usually thin and fragile, making it difficult to simultaneously meet multiple requirements such as scratch resistance, friction resistance, salt spray resistance, and decorative properties. On the other hand, if only a conventional organic coating is applied afterward, the interfacial bonding force between the coating and the magnesium alloy substrate, the coating density, and the long-term stability are often insufficient for high-durability applications, especially under boiling conditions, where peeling is likely to occur.

[0004] Therefore, a new composite coating system is urgently needed for magnesium alloys, which should have the properties of salt spray resistance, water boiling resistance, and wear and scratch resistance to meet the high requirements of automotive products for long-term weather resistance and durability. Summary of the Invention

[0005] The purpose of this invention is to provide a composite coating for a magnesium alloy base of a vehicle central control screen and its preparation method. By constructing a coating system suitable for magnesium alloy substrates, the final coating's resistance to boiling water, wear resistance, and service stability are improved.

[0006] Another objective of this invention is to provide an application of a composite coating for a magnesium alloy base of a vehicle central control screen.

[0007] This invention provides a composite coating for a magnesium alloy base of a vehicle-mounted central control screen. The composite coating comprises a base coat and a top coat, wherein the base coat is prepared from the following raw materials in the indicated mass percentages:

[0008] Solvent-based resin-free carbon black paste 10~20%;

[0009] Phosphate-modified saturated polyester 45-65%;

[0010] 3-9% pyrazole-blocked isocyanate curing agent;

[0011] Cyclosilyl alcohol adhesion promoter 0.5~3%;

[0012] Acrylic leveling agent 0.1~0.5%;

[0013] 1-4% hydrophobic silica matting agent;

[0014] 5-10% aluminum zinc phosphate hydrate;

[0015] 5-10% mica powder;

[0016] Diluent 5~10%;

[0017] The topcoat coating is prepared from the following raw materials in the indicated mass percentages:

[0018] Solvent-based resin-free carbon black paste: 10-20%;

[0019] Aluminum silver paste 1.00~3.00%;

[0020] Thermosetting acrylic resin 40.00~50.00%;

[0021] Methyl etherified high-imino melamine crosslinking agent 10.00~20.00%;

[0022] Acrylic leveling agent 0.1~0.5%;

[0023] Pyrazole-blocked isocyanate curing agent 0~6%;

[0024] 3-5% hydrophobic silica matting agent;

[0025] Mica powder 5-8%;

[0026] Diluent 5-11%.

[0027] The solvent-based resin-free carbon black paste is prepared from the following raw materials in the indicated mass percentages:

[0028] Propylene glycol methyl ether acetate 40-60%;

[0029] Butyl acetate 10-20%;

[0030] Polyurethane dispersant 15~25%;

[0031] Carbon black 10~20%.

[0032] The polyurethane dispersant is Huihong Chemical HP-1471.

[0033] The pyrazole-blocked isocyanate curing agent is Innospire Trixene® BI7982.

[0034] The aluminum paste is Xuyang aluminum pigment WHS3014.

[0035] The methyl etherified high-imino melamine crosslinking agent is model number Zanxin Resin CYMEL 325.

[0036] The mica powder is Greene New Material GD-1.

[0037] The aluminum zinc phosphate hydrate is STENICPHOS® ZA from Dingrui New Materials.

[0038] The acrylate leveling agent is BYK-354 from BYK Chemicals.

[0039] The cyclosilane alcohol adhesion promoter is Nochert PAE-206.

[0040] The hydrophobic silica matting agent is Lingwei Technology SCW-3.

[0041] The diluent is prepared from the following raw materials in the indicated mass percentages:

[0042] Propylene glycol methyl ether acetate 10.00~30.00%;

[0043] Butyl acetate 10.00~30.00%;

[0044] Cyclohexanone 20.00~40.00%;

[0045] Methyl isobutyl ketone 20.00~40.00%.

[0046] The method for preparing the phosphate-modified saturated polyester includes the following steps:

[0047] Dicarboxylic acid, phosphorus-containing monomers, and diols are added to a reaction vessel, nitrogen gas is introduced for protection, an esterification catalyst is added, and the mixture is stirred and heated to 180-200°C under normal pressure to carry out the esterification reaction until the acid value drops to 10-15 mg KOH / g. Then the temperature is raised to 230-245°C, and the pressure is gradually reduced to a vacuum degree ≤500 Pa to carry out the polycondensation reaction until the acid value is 2-5 mg KOH / g to obtain the phosphate-modified saturated polyester.

[0048] The dicarboxylic acid is one or more of terephthalic acid or adipic acid; the diol is one or more of 1,4-butanediol, neopentyl glycol or 1,6-hexanediol; the phosphorus-containing monomer is one or more of bis(2-hydroxyethyl) phosphate or bis(2-hydroxyethyl) phenylphosphonate.

[0049] The esterification catalyst is one or more of tetrabutyl titanate or isopropyl titanate, and the amount used is 0.01~0.1 wt% of the total mass of dicarboxylic acid and diol.

[0050] The molar ratio of the dicarboxylic acid, phosphorus-containing monomer, and diol is 20:1~3:22~26.

[0051] This invention provides a method for preparing the composite coating for the magnesium alloy base of the in-vehicle central control screen, the method comprising the following steps:

[0052] 1) Mix the raw materials of the primer coating to obtain the primer coating;

[0053] 2) Mix the raw materials of the topcoat coating to obtain the topcoat coating.

[0054] In steps 1) and 2) of the above preparation method, the temperature of the mixing process is 30~40℃.

[0055] This invention provides the application of the aforementioned composite coating for the magnesium alloy base of the vehicle central control screen in the preparation of the coating for the magnesium alloy base of the vehicle central control screen.

[0056] A method for preparing a magnesium alloy base coating for a vehicle-mounted central control screen, the method comprising the following steps:

[0057] a. The magnesium alloy base of the vehicle central control screen is subjected to degreasing, pickling, alkaline washing and micro-arc oxidation treatment in sequence to obtain the surface-treated workpiece;

[0058] b. Spray the base coating of the composite coating of the vehicle central control screen magnesium alloy base as described in claim 1 onto the surface-treated workpiece, and then spray the top coating of the composite coating of the vehicle central control screen magnesium alloy base as described in claim 1 to obtain the sprayed workpiece.

[0059] c. After spraying, the workpiece is leveled and then baked.

[0060] In step a of the above method, the degreasing treatment refers to soaking the sample in a 5-10% sodium hydroxide aqueous solution at a temperature of 50-60°C for 5-10 minutes.

[0061] In step a of the above method, the pickling treatment refers to soaking in a sulfuric acid aqueous solution with a mass fraction of 10-15% for 3-5 minutes at room temperature.

[0062] In step a of the above method, the alkaline washing treatment uses a sodium carbonate aqueous solution with a mass fraction of 5-8%, and soaks the sample for 3-5 minutes at a temperature of 40-50℃.

[0063] In step a of the above method, the micro-arc oxidation process involves a processing voltage of 300-350V and a processing time of 5-8 minutes.

[0064] In step b of the above method, the spray gun pressure for the spraying treatment is 0.3-0.4 MPa, the spraying distance is 15-20 cm, the number of spraying times is 2-3, and the wet film thickness of each spraying is controlled at 20-25 μm.

[0065] In step c of the above method, the baking temperature is 150°C and the baking time is 60 min.

[0066] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0067] 1. This invention significantly improves the adhesion of the coating by using phosphate-modified saturated polyester in the base coating layer. The oxygen atoms or hydroxyl groups with high electron cloud density in the phosphate groups react with the metal cations on the magnesium alloy surface to form strong chemical bonds (PO-Mg).

[0068] 2. Compared to the inorganic conversion film formed by traditional phosphoric acid treatment, although the inorganic conversion film passivates the magnesium alloy surface, moisture can still penetrate through the intergranular gaps of the inorganic film under high-temperature boiling conditions, inducing the hydrogen evolution reaction of the magnesium alloy (Mg + 2H2O = Mg(OH)2 + H2). The resulting hydrogen pressure directly pushes up the loose inorganic film, leading to large-area peeling. The synergistic effect of the phosphate ester modified resin and the pyrazole blocked isocyanate curing agent in the primer system of this invention forms a three-dimensional network with extremely high cross-linking density at high temperature. This network can effectively block the micropores of the substrate surface treatment layer and prevent the microscopic penetration of water molecules. At the same time, the phosphate ester groups have a certain interfacial passivation effect in humid environments, which can inhibit the hydrogen evolution reaction of magnesium alloy and solve the problems of blistering and peeling that easily occur in magnesium alloy coatings under boiling conditions.

[0069] 3. The coating is made of a combination of aluminum zinc phosphate hydrate and mica powder. The layered structure of mica powder effectively extends the penetration path of corrosive media. The aluminum zinc phosphate hydrate provides long-lasting chemical rust inhibition. Combined with high molecular weight thermosetting acrylic resin, the final coating is both wear-resistant and scratch-resistant, meeting the requirements of long-term reliability and visual quality of the in-vehicle central control screen base. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. 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.

[0071] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0072] The solvent-based resin-free carbon black pastes used in the following examples and comparative examples were prepared by mixing the following raw materials in the indicated weight percentages:

[0073] 50% propylene glycol methyl ether acetate;

[0074] 15% butyl acetate;

[0075] Huihong Chemical HP-1471 polyurethane dispersant 20%;

[0076] Carbon black 15%.

[0077] The diluents used in the following examples and comparative examples were prepared by mixing the following raw materials in the indicated mass percentages:

[0078] 20% propylene glycol methyl ether acetate;

[0079] Butyl acetate 20%;

[0080] 30% methyl isobutyl ketone;

[0081] Cyclohexanone 30%.

[0082] The preparation methods of the phosphate-modified saturated polyesters used in the following embodiments and comparative examples specifically include the following steps:

[0083] 20 mol adipic acid, 3 mol bis(2-hydroxyethyl) phenylphosphonic acid, and 22 mol neopentyl glycol were added to a reaction vessel under nitrogen protection. 5.21 g tetrabutyl titanate was added, and the mixture was stirred and heated to 200°C under normal pressure to carry out an esterification reaction until the acid value dropped to 15 mg KOH / g. Subsequently, the temperature was raised to 240°C, and the pressure was gradually reduced to a vacuum of 500 Pa to carry out a polycondensation reaction until the acid value was 2 mg KOH / g to obtain the phosphate-modified saturated polyester.

[0084] Examples 1-3

[0085] A composite coating for a magnesium alloy base of a vehicle central control screen includes a base coating and a top coating. In each embodiment, the mass percentage and raw materials of the base coating are shown in Table 1, and the mass percentage and raw materials of the top coating are shown in Table 2.

[0086] The preparation method of the base coating is as follows: the raw materials of the base coating are mixed to obtain the base coating, and the mixing temperature is 30℃.

[0087] The preparation method of the topcoat coating is as follows: the raw materials of the topcoat coating are mixed to obtain the topcoat coating, and the mixing temperature is 30℃.

[0088] Table 1

[0089]

[0090] Table 2

[0091]

[0092] Comparative Examples 1-3

[0093] A magnesium alloy composite coating comprises a base coat and a top coat. The mass percentage and raw materials of the base coat in each comparative example are shown in Table 3, and the mass percentage and raw materials of the top coat are shown in Table 4.

[0094] The preparation methods for the base coat and top coat are the same as those in Examples 1-3.

[0095] Table 3

[0096]

[0097] Table 4

[0098]

[0099] The test results of each embodiment and comparative example are shown in Table 5 below:

[0100] Table 5

[0101]

[0102] Test results of magnesium alloy coatings prepared by phosphate-modified saturated polyester showed that the examples were superior to the comparative examples in all aspects of adhesion, scratch resistance, abrasion resistance, salt spray resistance, and boiling water resistance. All examples achieved a grade 0 adhesion, showed no corrosion after 48 hours of salt spray resistance, and a grade 0 boiling water resistance after 30 minutes. Scratch and abrasion resistance were consistently passed without cracking or discoloration. In contrast, the comparative examples mostly showed a grade 1 adhesion, with some exhibiting cracking, severe discoloration, pitting corrosion, or grade 2-3 boiling water damage. Gloss, color difference, film thickness, and other appearance indicators were comparable across groups with no significant differences. Comparative example 3 improved its boiling water resistance by adding phosphate, but its performance was still inferior to the examples. Overall, the phosphate modification significantly improved the adhesion, corrosion resistance, and mechanical durability of the coating on magnesium alloys, demonstrating stable and excellent performance.

[0103] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0104] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A composite coating for a magnesium alloy base of a vehicle-mounted central control screen, characterized in that, The composite coating for the magnesium alloy base of the in-vehicle central control screen comprises a base coating and a top coating, wherein the base coating is prepared from the following raw materials by mass percentage: Solvent-based resin-free carbon black paste: 10-20%; Phosphate-modified saturated polyester 45-65%; 3-9% pyrazole-blocked isocyanate curing agent; Cyclosilyl alcohol adhesion promoter 0.5~3%; Acrylic leveling agent 0.1~0.5%; 1-4% hydrophobic silica matting agent; 5-10% aluminum zinc phosphate hydrate; 5-10% mica powder; Diluent 5~10%; The topcoat coating is prepared from the following raw materials in the indicated mass percentages: Solvent-based resin-free carbon black paste: 10-20%; Aluminum silver paste 1.00~3.00%; Thermosetting acrylic resin 40.00~50.00%; Methyl etherified high-imino melamine crosslinking agent 10.00~20.00%; Acrylic leveling agent 0.1~0.5%; Pyrazole-blocked isocyanate curing agent 0~6%; 3-5% hydrophobic silica matting agent; Mica powder 5-8%; Diluent 5-11%.

2. The composite coating for the magnesium alloy base of the vehicle-mounted central control screen according to claim 1, characterized in that, The solvent-based resin-free carbon black paste is prepared from the following raw materials in the indicated mass percentages: Propylene glycol methyl ether acetate 40-60%; Butyl acetate 10-20%; Polyurethane dispersant 15~25%; Carbon black 10~20%.

3. The composite coating for the magnesium alloy base of the vehicle-mounted central control screen according to claim 1, characterized in that, The diluent is prepared from the following raw materials in the indicated mass percentages: Propylene glycol methyl ether acetate 10.00~30.00%; Butyl acetate 10.00~30.00%; Cyclohexanone 20.00~40.00%; Methyl isobutyl ketone 20.00~40.00%.

4. The composite coating for the magnesium alloy base of the vehicle-mounted central control screen according to claim 1, characterized in that, The method for preparing the phosphate-modified saturated polyester includes the following steps: Dicarboxylic acid, phosphorus-containing monomers, and diols are added to a reaction vessel, nitrogen gas is introduced for protection, an esterification catalyst is added, and the mixture is stirred and heated to 180-200°C under normal pressure to carry out the esterification reaction until the acid value drops to 10-15 mg KOH / g. Then the temperature is raised to 230-245°C, and the pressure is gradually reduced to a vacuum degree ≤500 Pa to carry out the polycondensation reaction until the acid value is 2-5 mg KOH / g to obtain the phosphate-modified saturated polyester.

5. The composite coating for the magnesium alloy base of the vehicle-mounted central control screen according to claim 4, characterized in that, The dicarboxylic acid is one or more of terephthalic acid or adipic acid; the diol is one or more of 1,4-butanediol, neopentyl glycol, or 1,6-hexanediol; the phosphorus-containing monomer is one or more of bis(2-hydroxyethyl) phosphate or bis(2-hydroxyethyl) phenylphosphonate; the molar ratio of the dicarboxylic acid, the phosphorus-containing monomer, and the diol is 20:1~3:22~26.

6. The composite coating for the magnesium alloy base of the vehicle-mounted central control screen according to claim 4 or 5, characterized in that, The esterification catalyst is one or more of tetrabutyl titanate or isopropyl titanate, and the amount used is 0.01~0.1 wt% of the total mass of dicarboxylic acid and diol.

7. A method for preparing a composite coating for a magnesium alloy base of a vehicle-mounted central control screen as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: 1) Mix the raw materials of the primer coating to obtain the primer coating; 2) Mix the raw materials of the topcoat coating to obtain the topcoat coating.

8. The application of the composite coating for the magnesium alloy base of the vehicle central control screen as described in claim 1 in the preparation of the coating for the magnesium alloy base of the vehicle central control screen.

9. A method for preparing a magnesium alloy base coating for a vehicle-mounted central control screen, characterized in that, The method includes the following steps: a. The magnesium alloy base of the vehicle central control screen is subjected to degreasing, pickling, alkaline washing and micro-arc oxidation treatment in sequence to obtain the surface-treated workpiece; b. Spray the base coating of the composite coating of the vehicle central control screen magnesium alloy base as described in claim 1 onto the surface-treated workpiece, and then spray the top coating of the composite coating of the vehicle central control screen magnesium alloy base as described in claim 1 to obtain the sprayed workpiece. c. After spraying, the workpiece is leveled and then baked.

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