A high gloss black paint for electrostatic spray process and a method for preparing the same

Abstract

The application relates to the paint field and particularly discloses a one-coat high-gloss black paint for an electrostatic spraying process and a preparation method thereof; the one-coat high-gloss black paint for the electrostatic spraying process comprises the following raw materials in parts by weight: 20-30 parts of polyester resin, 30-40 parts of acrylic resin, 15-20 parts of amino resin, 1-3 parts of leveling wetting agent, 18-22 parts of diluent, 1-3 parts of ultraviolet absorber, 1-3 parts of light stabilizer and 2-4 parts of color paste; the amino resin is modified by alkyd resin; the one-coat high-gloss black paint prepared by the application can be suitable for electrostatic spraying, meanwhile, the paint film surface has good gloss and flatness, the pinhole and orange peel phenomena are reduced, and the one-coat high-gloss black paint has better chemical resistance compared with a two-coat process.

Description

Technical Field

[0001] This application relates to the field of coatings, and in particular to a one-coat high-gloss black paint for electrostatic spraying processes and a method for preparing the same. Background Technology

[0002] Black, as a traditional color, evokes feelings of solemnity, nobility, and seriousness. For sedans, the higher the luxury level, the more limited the color, with black being the most common. The higher the blackness and the more blue it appears, the more upscale the car seems. With the rapid development of the automotive industry and the upgrading of consumer preferences, car body colors are becoming increasingly diverse, highlighting fashionable and personalized trends. Correspondingly, the requirements for the blackness of black sedan bodies are also becoming increasingly stringent.

[0003] Currently, automotive coatings mainly consist of electrophoresis, intermediate coating, and topcoat. The topcoat primarily comprises color paint and clear varnish. Color paint provides different colors to the car body, while the clear varnish provides high gloss, aesthetics, and protection. These coatings require at least two coats to achieve the corresponding performance requirements, resulting in a high defect rate and severe orange peel texture. Furthermore, manual spraying is inefficient and yields low paint utilization. Summary of the Invention

[0004] In order to improve the utilization rate and film problems of existing coatings, this application provides a one-coat high-gloss black paint for electrostatic spraying process and its preparation method.

[0005] In a first aspect, this application provides a one-coat high-gloss black paint for electrostatic spraying processes, employing the following technical solution:

[0006] A high-gloss black paint for electrostatic spraying process comprises the following raw materials in parts by weight: 20-30 parts polyester resin, 30-40 parts acrylic resin, 15-20 parts amino resin, 1-3 parts leveling and wetting agent, 18-22 parts diluent, 1-3 parts ultraviolet absorber, 1-3 parts light stabilizer, and 2-4 parts color paste; wherein the amino resin is modified with alkyd resin.

[0007] By adopting the above technical solutions, polyester resin can improve the flexibility and adhesion of the paint film while maintaining a good gloss, and it can cross-link and cure with amino resin. Acrylic acid can improve the hardness and fast drying of the paint film, cross-link with amino resin, improve the leveling of the coating, and reduce the orange peel phenomenon. Amino resin can improve the cross-linking strength in the coating system, improve the hardness and gloss of the paint film, while alkyd resin can reduce the brittleness of amino resin, improve the hardness and weather resistance of the paint film, improve the leveling of the coating, and reduce the occurrence of pinholes and craters in the coating. The coating prepared by the cross-linking of polyester resin, acrylic resin, and amino resin is suitable for electrostatic spraying, has a high paint utilization rate and reduces paint loss. At the same time, the use of a single-component one-coat process can improve coating efficiency, reduce the orange peel phenomenon of the paint film, and maintain a good paint film appearance.

[0008] Preferably, the alkyd resin is soybean oil alkyd resin, the acid value of the soybean oil alkyd resin is 8-20 mg KOH / g, and the oil length of the soybean oil alkyd resin is 31-37%.

[0009] By adopting the above technical solution, using alkyd resins with a shorter oil content of 31-37% can maintain both good molecular chain rigidity and strong polarity, ensuring good miscibility with amino resins and improving the reaction rate of both. Simultaneously, controlling the oil content of the alkyd resin within a suitable range can reduce the occurrence of cratering in the paint film. Excessively short oil content can lead to excessively strong polarity in the alkyd resin, reducing the surface finish of the paint film.

[0010] Preferably, the soybean oil alkyd resin comprises the following raw materials in parts by weight: 40-45 parts soybean oil, 36-42 parts trimethylolpropane, 0.01-0.05 parts lithium hydroxide, 40-45 parts phthalic anhydride, 0.5-1.5 parts maleic anhydride, 1-3 parts benzoic acid, 0.5-1 part p-toluenesulfonic acid, and 50-55 parts solvent.

[0011] By employing the above technical solution, trimethylolpropane is used, utilizing its three primary hydroxyl groups to enhance reactivity. The addition of phthalic anhydride and maleic anhydride promotes the formation of more branches on the main chain of the prepared soybean oil alkyd resin, resulting in a more uniform distribution of active groups and improving the cross-linking reaction between the soybean oil alkyd resin and amino resins. Benzoic acid shortens the soybean oil alkyd resin and closes its end groups, enabling the formation of a three-dimensional structure in the coating system. Simultaneously, its benzene ring enhances the light stability and hardness of the paint film. Toluenesulfonic acid accelerates the reaction and lowers the baking temperature of the coating.

[0012] Preferably, the preparation method of the soybean oil alkyd resin includes the following specific steps: mixing soybean oil, trimethylolpropane, and lithium hydroxide, introducing carbon dioxide, heating to carry out an alcoholysis reaction, cooling after the reaction, adding phthalic anhydride, maleic anhydride, solvent, p-toluenesulfonic acid, and benzoic acid, and continuing to heat to carry out an esterification reaction, and obtaining soybean oil alkyd resin when the acid value reaches the qualified level.

[0013] Preferably, the alcoholysis reaction temperature is 230-250℃, the esterification reaction temperature is 220-240℃, and the temperature is lowered to less than 180℃.

[0014] Preferably, the diluent is at least one of xylene, diacetone alcohol, butyl acetate, and n-butanol.

[0015] Preferably, the ultraviolet absorber is a benzotriazole ultraviolet absorber, and the light stabilizer is a hindered amine light stabilizer.

[0016] Secondly, this application provides a method for preparing a single coat of high-gloss black paint for electrostatic spraying, using the following technical solution:

[0017] A method for preparing a single coat of high-gloss black paint for electrostatic spraying includes the following specific steps:

[0018] Alkyd resin and amino resin are pre-dispersed at high speed to obtain alkyd modified amino resin. Then, alkyd modified amino resin, polyester resin, acrylic resin, leveling and wetting agent, diluent, ultraviolet absorber, light stabilizer and color paste are mixed to obtain a one-coat high-gloss black paint for electrostatic spraying process.

[0019] By adopting the above technical solution, the prepared coating is suitable for electrostatic spraying, reducing coating loss, and is also applicable to one-coat processes, improving coating efficiency. The synergistic effect of the various components reduces orange peel texture on the paint film surface and improves film smoothness.

[0020] Preferably, the mass ratio of alkyd resin to amino resin is (0.5-0.8):1.

[0021] In summary, this application has the following beneficial effects:

[0022] 1. Because this application uses polyester resin, amino resin, and acrylic resin to crosslink with each other, it improves the flexibility, adhesion, and hardness of the paint film, maintains a good gloss on the paint film surface, and reduces the orange peel phenomenon of the paint film. Alkyd resin reduces the brittleness of amino resin, improves the leveling properties of the coating, and reduces the occurrence of pinholes and craters in the coating.

[0023] 2. In this application, alkyd resin with a shorter oil length of 31-37% is used, which can maintain the good molecular chain rigidity and strong polarity of alkyd resin, and can have good miscibility with amino resin, reduce the phenomenon of cratering in the paint film, and improve the surface smoothness of the paint film. Detailed Implementation

[0024] The present application will be further described in detail below with reference to the embodiments.

[0025] All raw materials used in the examples are commercially available.

[0026] Example

[0027] Example 1

[0028] This embodiment provides a one-coat high-gloss black paint for electrostatic spraying, comprising the following raw materials in parts by weight: 25 kg polyester resin, 35 kg acrylic resin, 18 kg amino resin, 2 kg leveling and wetting agent, 20 kg diluent, 2 kg UV absorber, 2 kg light stabilizer, and 3 kg color paste. The amino resin is modified with alkyd resin. The diluent is n-butanol. The polyester resin has a weight-average molecular weight of 18200 and a hydroxyl OH value of 68 mgKOH / g. The acrylic resin is purchased from Setalux 1766VB-64 from Zhanxin Company, the amino resin from Suzhou Hetai Chemical Company 27-585, the leveling and wetting agent is TEGO-2100 from Dedigo, the UV absorber is THASORB UV-234 from Tianjin Lianlong New Material Co., Ltd., and the light stabilizer is RIASORB from Tianjin Lianlong New Material Co., Ltd. UV-292, the color paste is a common commercially available black color paste; the alkyd resin selected is DSM Novalkyd252 alkyd resin, with an oil length of 46% and a hydroxyl OH value of 130mgKOH / g.

[0029] The preparation method of a single coat of high-gloss black paint for electrostatic spraying includes the following specific steps:

[0030] Alkyd resin and amino resin are pre-dispersed at high speed for 10 minutes at a speed of 2000 r / min. The mass ratio of alkyd resin to amino resin is 0.6:1 to obtain alkyd modified amino resin. Then, alkyd modified amino resin, polyester resin, acrylic resin, leveling and wetting agent, diluent, ultraviolet absorber, light stabilizer and color paste are mixed to obtain a one-coat high-gloss black paint for electrostatic spraying process.

[0031] Example 2

[0032] The difference between Example 2 and Example 1 is that the amount of polyester resin used in the raw material for the electrostatic spraying process is 20 kg, acrylic resin is 40 kg, amino resin is 15 kg, leveling and wetting agent is 1 kg, diluent is 18 kg, ultraviolet absorber is 1 kg, light stabilizer is 3 kg, and color paste is 2 kg.

[0033] Example 3

[0034] The difference between Example 3 and Example 1 is that the amount of polyester resin used in the raw material for the electrostatic spraying process is 30 kg, the amount of acrylic resin is 30 kg, the amount of amino resin is 20 kg, the amount of leveling and wetting agent is 3 kg, the amount of diluent is 22 kg, the amount of ultraviolet absorber is 3 kg, the amount of light stabilizer is 1 kg, and the amount of color paste is 4 kg.

[0035] Example 4

[0036] The difference between Example 4 and Example 1 is that the alkyd resin in the high-gloss black paint raw material used in the electrostatic spraying process is soybean oil alkyd resin. The soybean oil alkyd resin comprises the following raw materials in parts by weight: 43 kg soybean oil, 39 kg trimethylolpropane, 0.03 kg lithium hydroxide, 43 kg phthalic anhydride, 1 kg maleic anhydride, 2 kg benzoic acid, 0.8 kg p-toluenesulfonic acid, and 53 kg solvent. The soybean oil is salad soybean oil, the solvent is xylene, and the trimethylolpropane is Perstorp 39 from Switzerland.

[0037] The preparation method of a single coat of high-gloss black paint for electrostatic spraying includes the following specific steps:

[0038] S1: Mix soybean oil, trimethylolpropane, and lithium hydroxide, introduce carbon dioxide, and heat to 240℃ for alcoholysis reaction for 2 hours. After the reaction, cool down to 180℃, add phthalic anhydride, maleic anhydride, and solvent, and reflux for 2 hours. Then add p-toluenesulfonic acid and benzoic acid and continue heating to 230℃ for esterification reaction. After the acid value reaches the qualified level, cool down to obtain soybean oil alkyd resin with an acid value of 15 mg KOH / g and an oil length of 34%.

[0039] S2: Soybean oil alkyd resin and amino resin are pre-dispersed at high speed for 10 minutes at a speed of 2000 r / min. The mass ratio of soybean oil alkyd resin to amino resin is 0.65:1 to obtain alkyd modified amino resin. Then, alkyd modified amino resin, polyester resin, acrylic resin, leveling and wetting agent, diluent, ultraviolet absorber, light stabilizer and color paste are mixed to obtain a one-coat high-gloss black paint for electrostatic spraying process.

[0040] Example 5

[0041] The difference between Example 5 and Example 4 is that the amount of soybean oil used in the soybean oil alkyd resin raw material is 40 kg, the amount of trimethylolpropane is 36 kg, the amount of lithium hydroxide is 0.01 kg, the amount of phthalic anhydride is 40 kg, the amount of maleic anhydride is 0.5 kg, the amount of benzoic acid is 1 kg, the amount of p-toluenesulfonic acid is 0.5 kg, and the amount of solvent is 50 kg.

[0042] Example 6

[0043] The difference between Example 6 and Example 4 is that the amount of soybean oil used in the soybean oil alkyd resin raw material is 45 kg, the amount of trimethylolpropane is 42 kg, the amount of lithium hydroxide is 0.05 kg, the amount of phthalic anhydride is 45 kg, the amount of maleic anhydride is 1.5 kg, the amount of benzoic acid is 3 kg, the amount of p-toluenesulfonic acid is 1 kg, and the amount of solvent is 55 kg.

[0044] Example 7

[0045] The difference between Example 7 and Example 4 is that the oil length of the soybean oil alkyd resin is adjusted to 31%.

[0046] Example 8

[0047] The difference between Example 8 and Example 4 is that the oil length of the soybean oil alkyd resin is adjusted to 37%.

[0048] Example 9

[0049] The difference between Example 9 and Example 4 is that the oil length of the soybean oil alkyd resin is adjusted to 28%.

[0050] Example 10

[0051] The difference between Example 10 and Example 4 is that the mass ratio of soybean oil alkyd resin to amino resin is 0.5:1.

[0052] Example 11

[0053] The difference between Example 11 and Example 4 is that the mass ratio of soybean oil alkyd resin to amino resin is 0.8:1.

[0054] Comparative Example

[0055] Comparative Example 1

[0056] The difference between Comparative Example 1 and Example 1 is that alkyd resin is not used in the raw materials for the one-coat high-gloss black paint used in the electrostatic spraying process.

[0057] The preparation method of a single coat of high-gloss black paint for electrostatic spraying includes the following specific steps:

[0058] Amino resin, polyester resin, acrylic resin, leveling and wetting agent, diluent, ultraviolet absorber, light stabilizer, and color paste are mixed to obtain a one-coat high-gloss black paint for electrostatic spraying.

[0059] Performance testing

[0060] The following performance tests were conducted on the high-gloss black paint for electrostatic spraying provided in Examples 1-11 and Comparative Example 1 of this application. The specific test results are shown in Table 1.

[0061] Detection methods

[0062] I. Electrostatic spraying effect

[0063] The high-gloss black paint prepared in this application for electrostatic spraying was applied by a robotic electrostatic rotary cup, baked and cooled, with a paint film thickness of 10 μm. The surface was then observed for problems such as orange peel and pinholes.

[0064] II. Gloss

[0065] Referring to GB / T 9754-2007 "Determination of 20°, 60° and 85° Specular Gloss of Paint Films without Metallic Pigments", the surface gloss of the one-coat high-gloss black paint prepared in this application for electrostatic spraying process was tested at 20° after baking and being left at room temperature for 24 hours.

[0066] III. Hardness and Adhesion

[0067] Referring to GB / T 6739-2022 "Determination of Hardness of Paints and Varnishes by Pencil Hair", the hardness of the first coat of high-gloss black paint prepared in this application for electrostatic spraying was tested after baking and leaving it at room temperature for 24 hours. Referring to GB / T9286-2021 "Cross-cut Test of Paints and Varnishes", the adhesion effect of the first coat of high-gloss black paint prepared in this application for electrostatic spraying was tested.

[0068] Table 1: Performance Test Results Data Table

[0069]

[0070] The performance test results show that the one-coat high-gloss black paint prepared in this application is suitable for electrostatic spraying and has high paint utilization and coating efficiency when using a one-coat process. The amounts of each component in the raw materials of the one-coat high-gloss black paint in Examples 1-2 are different, with Example 1 showing superior overall performance. A comparison between Comparative Example 1 and Example 1 shows that in Comparative Example 1, the amino resin was not modified with alkyd resin. Although the resulting paint film did not have pinholes or orange peel issues, the surface smoothness and gloss of the paint film were significantly reduced, and the hardness was also decreased. This further demonstrates that alkyd resin and amino resin can cross-link with each other, improving the hardness and surface smoothness of the paint film.

[0071] Examples 4-8 show that the soybean oil alkyd resin prepared in Examples 4-8 has better miscibility with the amino resin, further improving the gloss and smoothness of the paint film. A comparison between Example 9 and Example 4 shows that when the oil length of the soybean oil alkyd resin is too short, the crosslinking between the soybean oil alkyd resin and the amino resin is affected, which in turn has a certain negative impact on the surface effect and hardness of the paint film.

[0072] 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 single-coat high-gloss black paint for electrostatic spraying process, characterized in that, The raw materials include the following parts by weight: 20-30 parts polyester resin, 30-40 parts acrylic resin, 15-20 parts amino resin, 1-3 parts leveling and wetting agent, 18-22 parts diluent, 1-3 parts ultraviolet absorber, 1-3 parts light stabilizer, and 2-4 parts color paste; the amino resin is modified with alkyd resin, the alkyd resin is soybean oil alkyd resin, the acid value of the soybean oil alkyd resin is 8-20 mg KOH / g, and the oil length of the soybean oil alkyd resin is 31-37%; the soybean oil alkyd resin includes the following raw materials in parts by weight: 40-45 parts soybean oil, 36-42 parts trimethylolpropane, 0.01-0.05 parts lithium hydroxide, 40-45 parts phthalic anhydride, 0.5-1.5 parts maleic anhydride, 1-3 parts benzoic acid, 0.5-1 part p-toluenesulfonic acid, and 50-55 parts solvent.

2. The high-gloss black paint for electrostatic spraying process according to claim 1, characterized in that, The preparation method of the soybean oil alkyd resin includes the following specific steps: soybean oil, trimethylolpropane, and lithium hydroxide are mixed, carbon dioxide is introduced, and the mixture is heated to carry out an alcoholysis reaction. After the reaction, the mixture is cooled down, and phthalic anhydride, maleic anhydride, solvent, p-toluenesulfonic acid, and benzoic acid are added to continue heating to carry out an esterification reaction. When the acid value reaches the qualified level, soybean oil alkyd resin is obtained.

3. The single-coat high-gloss black paint for electrostatic spraying process according to claim 2, characterized in that, The alcoholysis reaction temperature is 230-250℃, the esterification reaction temperature is 220-240℃, and the temperature is lowered to less than 180℃.

4. The high-gloss black paint for electrostatic spraying process according to claim 1, characterized in that, The diluent is at least one of xylene, diacetone alcohol, butyl acetate, and n-butanol.

5. The high-gloss black paint for electrostatic spraying process according to claim 1, characterized in that, The ultraviolet absorber is a benzotriazole ultraviolet absorber, and the light stabilizer is a hindered amine light stabilizer.

6. A method for preparing a single coat of high-gloss black paint for electrostatic spraying as described in any one of claims 1-5, characterized in that, The specific steps include the following: Alkyd resin and amino resin are pre-dispersed at high speed to obtain alkyd modified amino resin. Then, alkyd modified amino resin, polyester resin, acrylic resin, leveling and wetting agent, diluent, ultraviolet absorber, light stabilizer and color paste are mixed to obtain a one-coat high-gloss black paint for electrostatic spraying process.

7. The method for preparing a single coat of high-gloss black paint for electrostatic spraying according to claim 6, characterized in that, The mass ratio of alkyd resin to amino resin is (0.5-0.8):1.

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