Water-based paint for automobiles as well as preparation method and coating process of water-based paint

Abstract

The invention relates to the technical field of coatings, in particular to a water-based coating for an automobile as well as a preparation method and a coating process of the water-based coating. Comprising the following raw materials in parts by weight: 20-40 parts of a water-based modified acrylic dispersion A, 5-15 parts of a water-based modified acrylic dispersion B, 3-13 parts of deionized water, 0.03-0.15 part of an auxiliary agent, 0.05-0.15 part of a rheological auxiliary agent, 1-3 parts of an ultraviolet light absorber, 2-12 parts of a coalescing agent, 4-10 parts of melamine resin, 0.3-0.7 part of a catalyst, 0.5-3 parts of a cosolvent, 0.1-0.5 part of a wetting agent, 20-35 parts of color paste and 0.05-0.15 part of a dispersing agent. And 5-10 parts of ethylene glycol butyl ether. The water-based paint provided by the invention has good film-forming property, enhanced weather resistance, improved coating hardness and wear resistance, and good construction performance; under a water-based system, a single-coating vehicle body coating process is used, the vehicle body performance of a commercial vehicle is achieved, and the problems of weather resistance, covering, adhesive force and the like of a product under the single-coating process are solved.

Description

Technical Field

[0001] The invention relates to the technical field of coatings, and in particular to a water-based coating for automobiles and a preparation method and a coating process thereof. Background Art

[0002] The requirements for coatings in the automotive aftermarket are different from those in the automotive premarket, which is caused by the different application scenarios of coatings in the automotive premarket and the automotive aftermarket. In the automotive premarket, after the vehicle is sprayed with paint, it is baked at a temperature above 100°C, which has relatively high technical requirements. In addition, since automobiles are limited by cost factors and the difference in usage scenarios with passenger cars, commercial vehicle painting considers the use of low-cost solutions. Some spraying parts adopt a single-coating process, that is, white body + pretreatment + electrophoresis + single-coating MONOCOAT products, eliminating the construction and use of two coatings of primer and varnish, and the performance meets the requirements of general commercial vehicle technical agreements, such as paint film hardness, paint film impact resistance, paint film weather resistance, etc. Traditional MONOCOAT single-coating products are mainly solvent-based products. With the upgrading of the industry and the improvement of environmental protection requirements, some customers require a switch from solvent-based to water-based. Therefore, the single-coating process under the water-based system faces many performance challenges such as appearance, hiding, and adhesion. Summary of the invention

[0003] In order to overcome the shortcomings and deficiencies in the prior art, the purpose of the present invention is to provide a water-based automotive coating, which realizes the transition from solvent-based to water-based, and also improves the hiding performance of similar products from 36 microns to 30 microns. When combined with an electrophoretic substrate (RA≤0.3), the appearance can be improved by LW≤15; SW≤25; DOI≥85. Because the single-coat MONOCOAT process does not contain a varnish coating and lacks the weathering effect provided by the varnish layer, the product can achieve an artificial accelerated aging test result of Δ≤3.0 under 1200H by adding a weathering agent, the surface pencil hardness reaches HB, the 20° gloss ≥85, and the adhesion level 0.

[0004] The invention aims to provide a method for preparing a water-based paint for automobiles, which has the advantages of simple operation, convenient control, high production efficiency, low production cost and is suitable for large-scale production.

[0005] The purpose of the present invention is to provide a coating process for automobile water-based paint. Under the water-based system of the water-based paint, a single-coat body painting process is used to achieve commercial vehicle body performance and solve the problems of product weather resistance, hiding power, adhesion, etc. under the single-coat process.

[0006] The objective of the present invention is achieved by the following technical scheme: a water-based paint for automobiles, comprising the following raw materials in parts by weight: 20-40 parts of a water-based modified acrylic dispersion A, 5-15 parts of a water-based modified acrylic dispersion B, 3-13 parts of deionized water, 0.03-0.15 parts of an additive, 0.05-0.15 parts of a rheological additive, 1-3 parts of an ultraviolet absorber, 2-12 parts of a film-forming additive, 4-10 parts of a melamine resin, 0.3-0.7 parts of a catalyst, 0.5-3 parts of a cosolvent, 0.1-0.5 parts of a wetting agent, 20-35 parts of a color paste, 0.05-0.15 parts of a dispersant, and 5-10 parts of ethylene glycol butyl ether.

[0007] The water-based coating of the present invention has good film-forming properties, enhanced weather resistance, improved coating hardness and wear resistance, and good construction performance. Among them, the use of specific water-based modified acrylic dispersion A (such as 3AB92W Tongde resin water-based modified acrylic dispersion) and water-based modified acrylic dispersion B (Tongde 3AB91W water-based modified acrylic dispersion) with different number average molecular weight ranges (40,000-80,000 and 70,000-120,000, respectively) helps to form a suitable polymer network structure during the film-forming process, so that the coating can form a uniform film, improve the hardness, chemical resistance, integrity and appearance quality of the coating; the added ultraviolet absorber (2-hydroxy-4-methoxybenzophenone) can effectively absorb ultraviolet rays and reduce the damage of ultraviolet rays to the coating, thereby improving the weather resistance of the coating, delaying the aging and fading of the coating, and extending the service life of the automotive exterior coating; the melamine resin (composed of CYMEL303 LF highly methylated monomer melamine and CYMEL The addition of 325 methyl etherified high imino melamine (composed in a specific mass ratio) can undergo cross-linking reactions with other ingredients during the curing process, which helps to improve the hardness and wear resistance of the coating and better resist damage from external friction, scratches, etc.

[0008] Preferably, the number average molecular weight of the water-based modified acrylic dispersion A is 40,000-80,000; the water-based modified acrylic dispersion A adopts 3AB92W Tongde resin water-based modified acrylic dispersion.

[0009] Preferably, the number average molecular weight of the water-based modified acrylic dispersion B is 70,000 to 120,000; the water-based modified acrylic dispersion B is Tongde 3AB91W water-based modified acrylic dispersion.

[0010] The aqueous modified acrylic dispersion A and the aqueous modified acrylic dispersion B used in the present invention can achieve a baking polymerization reaction.

[0011]

[0012] Preferably, the ultraviolet absorber is at least one of 2-hydroxy-4-methoxybenzophenone, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, and ultraviolet absorber Tinuvin 400DW.

[0013] Preferably, the film-forming aid is at least one of diethylene glycol butyl ether, dodecyl alcohol ester, dipropylene glycol monobutyl ether, tripropylene glycol n-butyl ether, and propylene glycol methyl ether acetate.

[0014] Preferably, the melamine resin is methyl-etherified monomeric melamine and methyl-etherified high-imino melamine.

[0015] Preferably, the co-solvent is at least one of isooctyl alcohol, n-butanol, and propylene glycol dibutyl ether.

[0016] Preferably, the color paste is composed of white paste and black paste in a mass ratio of 2-3:0.008-0.012.

[0017] The film-forming aid (butyl diglycol) used in the present invention can reduce the minimum film-forming temperature of the coating, so that the coating can form a continuous and uniform film at a lower temperature. It improves the film-forming performance of the coating by interacting with the main components such as the water-based modified acrylic dispersion; the cosolvent (isooctanol) can adjust the solubility and volatility of the coating, and synergize with deionized water to optimize the viscosity of the coating, making it easier to apply and apply; the rheological aid can control the rheological properties of the coating, such as the change law of viscosity with shear force, to ensure the stability and operability of the coating during storage, transportation and construction; the dispersant helps the pigment ( White paste and black paste) are evenly dispersed in the coating system to prevent pigment agglomeration and ensure the uniformity of coating color; wetting agent can reduce the interfacial tension between coating and car surface, make coating better wet car surface and improve the adhesion between coating and substrate; mode of action of UV absorber: UV absorber (2-hydroxy-4-methoxybenzophenone) contains a specific conjugated system in its molecular structure. When exposed to ultraviolet rays, it can absorb the energy of ultraviolet rays and dissipate the energy in the form of heat energy through the energy transfer process within the molecule, thereby avoiding the direct effect of ultraviolet rays on the polymer components in the coating and playing a role in protecting the coating.

[0018] The present invention also provides a method for preparing a water-based coating for automobiles, comprising the following steps:

[0019] S1. Add the aqueous modified acrylic acid dispersion A and the aqueous modified acrylic acid dispersion B into a reaction device according to parts by weight, and stir at a rate of 200-300 r / min until the mixture is uniformly mixed to obtain a mixture A for standby use;

[0020] S2. According to parts by weight, half of the total amount of deionized water and the additives are added to the mixture A in sequence and mixed evenly, and the pH of the materials in the reaction device is adjusted to 8.4-8.6. In a dispersed state, the rheological additive is added, and the mixture is stirred at a rate of 300-400 r / min for 5-10 min to obtain a mixture B for standby use;

[0021] S3, according to weight portions, the remaining deionized water, ultraviolet absorber, ethylene glycol butyl ether are added to another reaction unit, stirred at a rate of 250-350r / min for 10-20min to obtain a mixture C, and then the mixture C is added to the mixture B, and stirred at a rate of 50-100r / min until uniform, then the melamine resin is added, and the stirring speed is increased to 400-500r / min after the materials are added, and continued for 15-30min to obtain a mixture D for standby use;

[0022] S4, according to the weight parts, the film-forming aid, the cosolvent and the catalyst are added to the reaction device in sequence, stirred at a rate of 200-300r / min for 10-20min, and added to the mixture D after the dispersion state is qualified visually, and then the wetting agent is added and stirred at a rate of 300-400r / min for 10-20min, and then the pH value of the reaction system is adjusted to 8.2-8.6 and the viscosity DIN4#40-60S to obtain a mixture E for standby use;

[0023] S5. According to parts by weight, mix the color paste and dispersant and add them to the mixture E. Stir at a rate of 400-500 r / min for 10-20 min. Finally, adjust the product to the factory viscosity and factory solid content requirements to obtain a water-based paint for automobiles.

[0024] The present invention also proposes a coating process for automobile water-based paint, wherein the water-based paint is directly coated on the surface of the vehicle body by adopting a single coating process, and the single coating process comprises the following steps: a steel plate is selected as the base material of the vehicle body panel, and the water-based paint is sprayed in a painting workshop according to the required color. The pre-treatment electrophoretic line adopts a hanging plate method, and the electrophoretic coating film is controlled to be 18um-20um. After the electrophoretic coating film is completed, it is dried, and then after spraying the water-based paint, it is hung on a plate for baking, first at 80-85°C for pre-baking for 7-10min, and then baked at 140-145°C for 20-30min to complete the coating of the automobile water-based paint.

[0025] The beneficial effects of the present invention are as follows: the automotive water-based paint of the present invention realizes the transfer from solvent-based to water-based, and further improves the hiding performance of similar products in the past from 36 microns to 30 microns. When combined with an electrophoretic substrate (RA≤0.3), the appearance can be improved by LW≤15; SW≤25; DOI≥85. Because the single-coat MONOCOAT process does not contain a varnish coating and lacks the weather resistance effect provided by the varnish layer, the product can achieve an artificial accelerated aging test result of Δ≤3.0 under 1200H by adding a weathering agent, the surface pencil hardness reaches HB, the 20° gloss is ≥85, and the adhesion is level 0.

[0026] The method for preparing the water-based paint for automobiles of the present invention has the advantages of simple operation, convenient control, high production efficiency and low production cost, and is suitable for large-scale production.

[0027] The coating process of the water-based paint for automobiles of the present invention uses a single-coat vehicle body painting process under a water-based system to achieve commercial vehicle body performance and solve the problems of product weather resistance, hiding power, adhesion, etc. under the single-coat process. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments, and the contents mentioned in the implementation modes are not intended to limit the present invention.

[0029] Example 1

[0030] A water-based paint for automobiles comprises the following raw materials in parts by weight: 20 parts of water-based modified acrylic dispersion A, 5 parts of water-based modified acrylic dispersion B, 3 parts of deionized water, 0.03 parts of an additive, 0.05 parts of a rheological additive, 1 part of an ultraviolet absorber, 2 parts of a film-forming additive, 4 parts of a melamine resin, 0.3 parts of a catalyst, 0.5 parts of a cosolvent, 0.1 parts of a wetting agent, 20 parts of a color paste, 0.05 parts of a dispersant, and 5 parts of ethylene glycol butyl ether.

[0031] The number average molecular weight of the water-based modified acrylic dispersion A is 40,000-80,000; the water-based modified acrylic dispersion A adopts 3AB92W Tongde resin water-based modified acrylic dispersion.

[0032] The number average molecular weight of the water-based modified acrylic dispersion B is 70,000 to 120,000; the water-based modified acrylic dispersion B adopts Tongde 3AB91W water-based modified acrylic dispersion.

[0033] The ultraviolet absorber is 2-hydroxy-4-methoxybenzophenone.

[0034] The film-forming aid is diethylene glycol butyl ether.

[0035] The melamine resin comprises methyl-etherified monomer melamine and methyl-etherified high-imino melamine, wherein the methyl-etherified monomer melamine and the methyl-etherified high-imino melamine are composed in a mass ratio of 5-8:1; the methyl-etherified monomer melamine adopts CYMEL303 LF highly methyl-etherified monomer melamine, and the methyl-etherified high-imino melamine adopts CYMEL 325 methyl-etherified high-imino melamine.

[0036] The cosolvent is isooctyl alcohol.

[0037] The color paste is composed of white paste and black paste in a mass ratio of 2:0.008.

[0038] The automotive water-based paint is prepared by the following steps:

[0039] S1. Add water-based modified acrylic acid dispersion A and water-based modified acrylic acid dispersion B into a reaction device according to weight parts, and stir at a rate of 200 r / min until the mixture is uniformly mixed to obtain a mixture A for standby use;

[0040] S2. According to parts by weight, half of the total amount of deionized water and the additives are added to the mixture A in sequence and mixed evenly, and the pH of the materials in the reaction device is adjusted to 8.4. In a dispersed state, the rheological additive is added, and the mixture is stirred at a rate of 300 r / min for 10 min to obtain a mixture B for standby use;

[0041] S3, according to weight portions, the remaining deionized water, ultraviolet absorber, ethylene glycol butyl ether are added to another reaction unit, stirred at a rate of 250r / min for 20min, to obtain a mixture C, then the mixture C is added to the mixture B, and stirred at a rate of 50r / min until uniform, then the melamine resin is added, and the stirring speed is increased to 400r / min after the materials are added, and continued for 30min to obtain a mixture D, which is reserved;

[0042] S4, according to the weight parts, the film-forming aid, the cosolvent and the catalyst are added to the reaction device in sequence, stirred at a rate of 200r / min for 20min, and added to the mixture D after the dispersion state is qualified visually, and then the wetting agent is added and stirred at a rate of 300r / min for 20min, and then the pH value of the reaction system is adjusted to 8.2 and the viscosity DIN4#40-60S to obtain a mixture E for standby use;

[0043] S5. According to parts by weight, mix the color paste and dispersant and add them to the mixture E. Stir at a rate of 400 r / min for 10 min. Finally, adjust the product to the factory viscosity and factory solid content requirements to obtain a water-based paint for automobiles.

[0044] A coating process for automobile water-based paint, wherein the water-based paint is directly coated on the surface of a vehicle body by adopting a single coating process, and the single coating process comprises the following steps: a steel plate is selected as a base material of a vehicle body panel, and water-based paint is sprayed in a painting workshop according to the required color, a hanging plate method is adopted in a pre-treatment electrophoresis line, and the electrophoretic coating film is controlled at 18um, and a drying treatment is performed after the electrophoretic coating film is completed, and then the water-based paint is sprayed and then hung on a plate for baking, first at 80°C for 7 minutes, and then baked at 140°C for 30 minutes to complete the coating of the automobile water-based paint.

[0045] Example 2

[0046] A water-based paint for automobiles comprises the following raw materials in parts by weight: 30 parts of water-based modified acrylic dispersion A, 10 parts of water-based modified acrylic dispersion B, 7 parts of deionized water, 0.08 parts of an additive, 0.08 parts of a rheological additive, 2 parts of an ultraviolet absorber, 7 parts of a film-forming additive, 6 parts of a melamine resin, 0.5 parts of a catalyst, 2 parts of a cosolvent, 0.3 parts of a wetting agent, 25 parts of a color paste, 0.08 parts of a dispersant, and 8 parts of ethylene glycol butyl ether.

[0047] The number average molecular weight of the water-based modified acrylic dispersion A is 40,000-80,000; the water-based modified acrylic dispersion A adopts 3AB92W Tongde resin water-based modified acrylic dispersion.

[0048] The number average molecular weight of the water-based modified acrylic dispersion B is 70,000 to 120,000; the water-based modified acrylic dispersion B adopts Tongde 3AB91W water-based modified acrylic dispersion.

[0049] The ultraviolet absorber is ultraviolet absorber Tinuvin 400DW.

[0050] The film-forming aid is diethylene glycol butyl ether.

[0051] The melamine resin comprises methyl-etherified monomer melamine and methyl-etherified high-imino melamine, wherein the methyl-etherified monomer melamine and the methyl-etherified high-imino melamine are composed in a mass ratio of 7:1; the methyl-etherified monomer melamine adopts CYMEL303 LF highly methyl-etherified monomer melamine, and the methyl-etherified high-imino melamine adopts CYMEL 325 methyl-etherified high-imino melamine.

[0052] The co-solvent is n-butanol.

[0053] The color paste is composed of white paste and black paste in a mass ratio of 2.5:0.010.

[0054] The automotive water-based paint is prepared by the following steps:

[0055] S1. Add water-based modified acrylic acid dispersion A and water-based modified acrylic acid dispersion B into a reaction device according to weight parts, and stir at a rate of 250 r / min until the mixture is uniformly mixed to obtain a mixture A for standby use;

[0056] S2. According to parts by weight, half of the total amount of deionized water and the additives are added to the mixture A in sequence and mixed evenly, and the pH of the materials in the reaction device is adjusted to 8.5. In a dispersed state, the rheological additive is added, and the mixture is stirred at a rate of 350 r / min for 8 minutes to obtain a mixture B for standby use;

[0057] S3, according to weight portions, the remaining deionized water, ultraviolet absorber, ethylene glycol butyl ether are added to another reaction unit, stirred at a rate of 300r / min for 15min, to obtain a mixture C, then the mixture C is added to the mixture B, and stirred at a rate of 80r / min until uniform, then the melamine resin is added, and the stirring speed is increased to 450r / min after the materials are added, and continued for 20min to obtain a mixture D for standby use;

[0058] S4, according to weight parts, add film-forming aid, cosolvent and catalyst to the reaction device in sequence, stir at a rate of 250r / min for 15min, add to mixture D after the dispersion state is qualified visually, then add wetting agent and stir at a rate of 350r / min for 15min, then adjust the pH value of the reaction system to 8.4 and the viscosity DIN4#40-60S to obtain mixture E for standby use;

[0059] S5. According to parts by weight, mix the color paste and dispersant and add them to the mixture E. Stir at a rate of 450 r / min for 15 min. Finally, adjust the product to the factory viscosity and factory solid content requirements to obtain a water-based paint for automobiles.

[0060] A coating process for automobile water-based paint, wherein the water-based paint is directly coated on the surface of a vehicle body by adopting a single coating process, and the single coating process comprises the following steps: a steel plate is selected as a base material of a vehicle body panel, and a water-based paint is sprayed in a painting workshop according to the required color. A pre-treatment electrophoretic line adopts a hanging plate method, and the electrophoretic coating film is controlled to be 18um-20um. After the electrophoretic coating film is completed, a drying treatment is performed, and then after spraying the water-based paint, the hanging plate is baked, first at 83°C for 8 minutes, and then baked at 143°C for 25 minutes to complete the coating of the automobile water-based paint.

[0061] Example 3

[0062] A water-based paint for automobiles, comprising the following raw materials in parts by weight: 28 parts of water-based modified acrylic dispersion A, 12 parts of water-based modified acrylic dispersion B,

[0063] 10 parts of deionized water, 0.13 parts of additives, 0.13 parts of rheological additives, 2 parts of ultraviolet absorbers, 10 parts of film-forming additives, 8 parts of melamine resin, 0.6 parts of catalysts, 2.7 parts of cosolvents, 0.4 parts of wetting agents, 28 parts of color pastes, 0.15 parts of dispersants, and 8 parts of ethylene glycol butyl ether.

[0064] The number average molecular weight of the water-based modified acrylic dispersion A is 40,000-80,000; the water-based modified acrylic dispersion A adopts 3AB92W Tongde resin water-based modified acrylic dispersion.

[0065] The number average molecular weight of the water-based modified acrylic dispersion B is 70,000 to 120,000; the water-based modified acrylic dispersion B adopts Tongde 3AB91W water-based modified acrylic dispersion.

[0066] The ultraviolet absorber is composed of 2-hydroxy-4-methoxybenzophenone and ultraviolet absorber Tinuvin 400DW in a mass ratio of 1:1.

[0067] The film-forming aid is composed of diethylene glycol butyl ether, tripropylene glycol n-butyl ether and propylene glycol methyl ether acetate in a mass ratio of 0.8:0.4:0.7.

[0068] The melamine resin comprises methyl-etherified monomer melamine and methyl-etherified high-imino melamine, wherein the methyl-etherified monomer melamine and the methyl-etherified high-imino melamine are composed in a mass ratio of 5-8:1; the methyl-etherified monomer melamine adopts CYMEL303 LF highly methyl-etherified monomer melamine, and the methyl-etherified high-imino melamine adopts CYMEL 325 methyl-etherified high-imino melamine.

[0069] The co-solvent is composed of isooctyl alcohol and n-butanol in a mass ratio of 1:1.

[0070] The color paste is composed of white paste and black paste in a mass ratio of 2.8:0.012.

[0071] The automotive water-based paint is prepared by the following steps:

[0072] S1. Add water-based modified acrylic acid dispersion A and water-based modified acrylic acid dispersion B into a reaction device according to weight parts, and stir at a rate of 290 r / min until the mixture is uniformly mixed to obtain a mixture A for standby use;

[0073] S2. According to parts by weight, half of the total amount of deionized water and the additives are added to the mixture A in sequence and mixed evenly, and the pH of the materials in the reaction device is adjusted to 8.6. In a dispersed state, the rheological additive is added, and the mixture is stirred at a rate of 380 r / min for 8 minutes to obtain a mixture B for standby use;

[0074] S3, according to weight portions, the remaining deionized water, ultraviolet absorber, ethylene glycol butyl ether are added to another reaction unit, stirred at a rate of 320r / min for 18min, to obtain a mixture C, then the mixture C is added to the mixture B, and stirred at a rate of 90r / min until uniform, then the melamine resin is added, and the stirring speed is increased to 490r / min after the materials are added, and continued for 27min to obtain a mixture D, which is standby;

[0075] S4, according to the weight parts, the film-forming aid, the cosolvent and the catalyst are added to the reaction device in sequence, stirred at a rate of 280r / min for 18min, and added to the mixture D after the dispersion state is qualified visually, and then the wetting agent is added and stirred at a rate of 380r / min for 18min, and then the pH value of the reaction system is adjusted to 8.5 and the viscosity DIN4#40-60S to obtain a mixture E for standby use;

[0076] S5. According to parts by weight, the color paste and dispersant are mixed and added to the mixture E. The mixture is stirred at a rate of 480 r / min for 18 min. Finally, the product is adjusted to the factory viscosity and factory solid content requirements to obtain a water-based paint for automobiles.

[0077] A coating process for automobile water-based paint, wherein the water-based paint is directly coated on the surface of a vehicle body by adopting a single coating process, and the single coating process comprises the following steps: a steel plate is selected as a base material of a vehicle body panel, and a water-based paint is sprayed in a painting workshop according to the required color. A pre-treatment electrophoretic line adopts a hanging plate method, and the electrophoretic coating film is controlled to be 18um-20um. After the electrophoretic coating film is completed, a drying treatment is performed, and then after spraying the water-based paint, the hanging plate is baked, first at 84°C for 8 minutes, and then baked at 144°C for 28 minutes to complete the coating of the automobile water-based paint.

[0078] Example 4

[0079] A water-based paint for automobiles comprises the following raw materials in parts by weight: 40 parts of water-based modified acrylic dispersion A, 15 parts of water-based modified acrylic dispersion B, 13 parts of deionized water, 0.15 parts of additives, 0.15 parts of rheological additives, 3 parts of ultraviolet absorbers, 12 parts of film-forming additives, 10 parts of melamine resins, 0.7 parts of catalysts, 3 parts of cosolvents, 0.5 parts of wetting agents, 35 parts of color pastes, 0.15 parts of dispersants, and 10 parts of ethylene glycol butyl ether.

[0080] The number average molecular weight of the water-based modified acrylic dispersion A is 40,000-80,000; the water-based modified acrylic dispersion A adopts 3AB92W Tongde resin water-based modified acrylic dispersion.

[0081] The number average molecular weight of the water-based modified acrylic dispersion B is 70,000 to 120,000; the water-based modified acrylic dispersion B adopts Tongde 3AB91W water-based modified acrylic dispersion.

[0082] The ultraviolet absorber is 2-(2'-hydroxy-5'-methylphenyl)benzotriazole.

[0083] The film-forming aid is dipropylene glycol monobutyl ether.

[0084] The melamine resin comprises methyl-etherified monomer melamine and methyl-etherified high-imino melamine, wherein the methyl-etherified monomer melamine and the methyl-etherified high-imino melamine are composed in a mass ratio of 8:1; the methyl-etherified monomer melamine adopts CYMEL303 LF highly methyl-etherified monomer melamine, and the methyl-etherified high-imino melamine adopts CYMEL 325 methyl-etherified high-imino melamine.

[0085] The cosolvent is isooctyl alcohol.

[0086] The color paste is composed of white paste and black paste in a mass ratio of 3:0.012.

[0087] The automotive water-based paint is prepared by the following steps:

[0088] S1. Add water-based modified acrylic acid dispersion A and water-based modified acrylic acid dispersion B into a reaction device according to weight parts, and stir at a rate of 300 r / min until the mixture is uniformly mixed to obtain a mixture A for standby use;

[0089] S2. According to parts by weight, half of the total amount of deionized water and the additives are added to the mixture A in sequence and mixed evenly, and the pH of the materials in the reaction device is adjusted to 8.6. In a dispersed state, the rheological additive is added, and the mixture is stirred at a rate of 400 r / min for 10 min to obtain a mixture B for standby use;

[0090] S3, according to weight portions, the remaining deionized water, ultraviolet absorber, ethylene glycol butyl ether are added to another reaction unit, stirred at a rate of 350r / min for 20min, to obtain a mixture C, then the mixture C is added to the mixture B, and stirred at a rate of 100r / min until uniform, then the melamine resin is added, and the stirring speed is increased to 500r / min after the materials are added, and continued for 15min to obtain a mixture D for standby use;

[0091] S4, according to the weight parts, the film-forming aid, the cosolvent and the catalyst are added to the reaction device in sequence, stirred at a rate of 300r / min for 10min, and added to the mixture D after the dispersion state is qualified visually, and then the wetting agent is added and stirred at a rate of 400r / min for 10min, and then the pH value of the reaction system is adjusted to 8.6 and the viscosity is DIN4#40-60S to obtain a mixture E for standby use;

[0092] S5. According to parts by weight, mix the color paste and dispersant and add them to the mixture E. Stir at a rate of 500 r / min for 10 min. Finally, adjust the product to the factory viscosity and factory solid content requirements to obtain a water-based paint for automobiles.

[0093] A coating process for automobile water-based paint, wherein the water-based paint is directly coated on the surface of a vehicle body by adopting a single coating process, and the single coating process comprises the following steps: a steel plate is selected as a base material of a vehicle body panel, and water-based paint is sprayed in a painting workshop according to the required color, a pre-treatment electrophoretic line adopts a hanging plate method, and the electrophoretic coating film is controlled to be 18um-20um, and a drying treatment is performed after the electrophoretic coating film is completed, and then the water-based paint is sprayed and then hung on a plate for baking, first pre-baking at 85°C for 7min, and then baking at 145°C for 20min to complete the coating of the automobile water-based paint.

[0094] Comparative Example 1

[0095] The difference between this comparative example and the above-mentioned Example 2 is that: the raw materials of the water-based coating of this comparative example do not contain water-based modified acrylic dispersion B. The rest of the contents of this comparative example are the same as those of Example 2, and will not be repeated here.

[0096] Comparative Example 2

[0097] The difference between this comparative example and the above-mentioned Example 2 is that no melamine resin is added to the raw materials of the water-based coating of this comparative example. The rest of the contents of this comparative example are the same as those of Example 2, and will not be repeated here.

[0098] The performance of the water-based coatings prepared in Example 2 and Comparative Examples 1-2 was tested after film formation, and the results are shown in Table 1:

[0099] Adhesion test, weather resistance and glossiness are tested according to normal national standards and the average value is taken.

[0100] Table 1

[0101]

[0102]

[0103] It can be seen from Example 2 that the water-based coating prepared by the present invention has advantages such as good adhesion, weather resistance and film-forming performance, as well as glossiness.

[0104] From the comparison between Example 2 and Comparative Examples 1-2, it can be seen that under the same conditions, the water-based coating obtained by adding water-based modified acrylic dispersion B and melamine resin to the formula has good adhesion, weather resistance and film-forming properties, as well as glossiness, and has broad market prospects and application value.

[0105] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present invention is within the protection scope of the present invention.

Claims

1. A water-based paint for automobiles, characterized in that: The invention comprises the following raw materials in parts by weight: 20-40 parts of water-based modified acrylic dispersion A, 5-15 parts of water-based modified acrylic dispersion B, 3-13 parts of deionized water, 0.03-0.15 parts of additives, 0.05-0.15 parts of rheological additives, 1-3 parts of ultraviolet absorbers, 2-12 parts of film-forming additives, 4-10 parts of melamine resins, 0.3-0.7 parts of catalysts, 0.5-3 parts of cosolvents, 0.1-0.5 parts of wetting agents, 20-35 parts of color pastes, 0.05-0.15 parts of dispersants and 5-10 parts of ethylene glycol butyl ether.

2. A water-based paint for automobiles according to claim 1, characterized in that: The number average molecular weight of the aqueous modified acrylic dispersion A is 40,000-80,000.

3. The water-based paint for automobiles according to claim 1, characterized in that: The number average molecular weight of the aqueous modified acrylic dispersion B is 70,000 to 120,000.

4. The water-based paint for automobiles according to claim 1, characterized in that: The ultraviolet absorber is at least one of 2-hydroxy-4-methoxybenzophenone, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, and ultraviolet absorber Tinuvin 400DW.

5. The water-based paint for automobiles according to claim 1, characterized in that: The film-forming aid is at least one of diethylene glycol butyl ether, dodecyl alcohol ester, dipropylene glycol monobutyl ether, tripropylene glycol n-butyl ether, and propylene glycol methyl ether acetate.

6. The water-based paint for automobiles according to claim 1, characterized in that: The melamine resin is methyl etherified monomeric melamine and methyl etherified high-imino melamine.

7. The water-based paint for automobiles according to claim 1, characterized in that: The co-solvent is at least one of isooctyl alcohol, n-butanol and propylene glycol dibutyl ether.

8. The water-based paint for automobiles according to claim 1, characterized in that: The color paste is composed of white paste and black paste in a mass ratio of 2-3:0.008-0.

012.

9. A method for preparing a water-based coating for automobiles as claimed in any one of claims 1 to 8, characterized in that: The steps include: S1. Add the aqueous modified acrylic acid dispersion A and the aqueous modified acrylic acid dispersion B into a reaction device according to parts by weight, and stir at a rate of 200-300 r / min until the mixture is uniformly mixed to obtain a mixture A for standby use; S2. According to parts by weight, half of the total amount of deionized water and the additives are added to the mixture A in sequence and mixed evenly, and the pH of the materials in the reaction device is adjusted to 8.4-8.

6. In a dispersed state, the rheological additive is added, and the mixture is stirred at a rate of 300-400 r / min for 5-10 min to obtain a mixture B for standby use; S3, according to weight portions, the remaining deionized water, ultraviolet absorber, ethylene glycol butyl ether are added to another reaction unit, stirred at a rate of 250-350r / min for 10-20min to obtain a mixture C, and then the mixture C is added to the mixture B, and stirred at a rate of 50-100r / min until uniform, then the melamine resin is added, and the stirring speed is increased to 400-500r / min after the materials are added, and continued for 15-30min to obtain a mixture D for standby use; S4, according to the weight parts, the film-forming aid, the cosolvent and the catalyst are added to the reaction device in sequence, stirred at a rate of 200-300r / min for 10-20min, and added to the mixture D after the dispersion state is qualified visually, and then the wetting agent is added and stirred at a rate of 300-400r / min for 10-20min, and then the pH value of the reaction system is adjusted to 8.2-8.6 and the viscosity DIN4#40-60S to obtain a mixture E for standby use; S5. According to parts by weight, mix the color paste and dispersant and add them to the mixture E. Stir at a rate of 400-500 r / min for 10-20 min. Finally, adjust the product to the factory viscosity and factory solid content requirements to obtain a water-based paint for automobiles.

10. A coating process for a water-based paint for automobiles according to any one of claims 1 to 8, characterized in that: The water-based paint is directly applied to the surface of the vehicle body by adopting a single coating process, and the single coating process includes the following steps: a steel plate is selected as the base material of the vehicle body panel, and the water-based paint is sprayed in a painting workshop according to the required color. The pre-treatment electrophoretic line adopts a hanging plate method, and the electrophoretic coating film is controlled to be 18um-20um. After the electrophoretic coating film is completed, it is dried, and then the water-based paint is sprayed and then hung on the plate for baking. It is pre-baked at 80-85°C for 7-10min, and then baked at 140-145°C for 20-30min to complete the coating of the automobile water-based paint.

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