Water-based midcoat for automotive finishing having improved overcoatability with oil varnish, and method of preparation and use thereof

Abstract

The application discloses a water-based midcoat for automobile coating with improved recoat effect between oil varnish, and a preparation method and application thereof. In the water-based midcoat, the raw materials for forming the water-based midcoat comprise the following components in parts by weight: 15-25 parts of a thermosetting water-based polyurethane resin, 10-20 parts of a water-based aliphatic polyurethane resin, 3-7 parts of an acrylic resin, 1-5 parts of an acrylic modified polyurethane resin, 4-10 parts of an amino resin, 1-3 parts of a hydrophobic polyester resin, 10-25 parts of a pigment filler, 0.5-1.5 parts of an aluminate coupling agent, 0.2-5 parts of an organic solvent and 4-17 parts of deionized water. The water-based midcoat can be used to improve the recoat adhesion between the water-based midcoat and the oil varnish in the automobile coating process, and meanwhile, the obtained coating has good appearance, high-pressure water resistance, anti-sagging property and anti-pinholing property.

Description

Technical Field

[0001] This invention relates to the field of coatings for automotive painting. More specifically, it relates to a water-based intermediate coat for automotive painting that provides improved recoating performance with oil-based clear coats, its preparation method, and its application. Background Technology

[0002] In the automotive coatings industry, good adhesion between coating layers is fundamental for coatings to perform their functions effectively and to leverage their superior mechanical properties. Adhesion is mainly formed by the interaction between the polar groups of the polymer in the paint film and the polar groups in the substrate; however, the adhesion ability of coatings varies depending on the substrate.

[0003] In practical applications, especially during recoating, the coating process of using oil-based clear coats with water-based intermediate coats is common. However, severe delamination problems between water-based intermediate coats and oil-based clear coats are also frequently encountered. This phenomenon directly affects the adhesion and stability of the coating during recoating (such as resistance to high-pressure water jets, resistance to damp heat, anti-sagging, and anti-pinhole properties). Therefore, it is crucial to improve the adhesion and stability between water-based intermediate coats and oil-based clear coats during recoating and to address the problem of poor wetting.

[0004] Traditionally, methods to improve the adhesion between water-based intermediate coats and oil-based varnishes involve using organic co-solvents such as N-methylpyrrolidone (NMP) and N-ethylpyrrolidone (NEP). This is because the highly polar solvents NMP and NEP have excellent dissolving power and are often used to improve adhesion. However, the strong penetrating power of NMP and NEP is a double-edged sword. While they can significantly improve the adhesion between coatings, they can easily carry harmful substances into the human body through the skin, leading to poisoning.

[0005] Several methods exist for improving the adhesion between paint and clear coat during recoating: 1) Physical improvement: sanding the clear coat substrate to increase its surface roughness; 2) Chemical improvement: modifying the paint formulation by adding substances containing polar functional groups to increase the polarity of the automotive paint. Among these, physical improvement methods involve more complex substrate surface treatment processes, higher scrap rates, and higher labor costs. Existing chemical improvement methods, such as flame treatment, use high-temperature gases or flames to enhance substrate polarity, but this method poses safety risks, is complex to operate, lacks stability, and is easily affected by the operating environment and substrate condition, resulting in a short-lived adhesion improvement effect. Corona treatment generates polar groups through discharge, which can increase surface energy, but the operation is cumbersome and inefficient. Summary of the Invention

[0006] Based on the above facts, the purpose of this invention is to provide a water-based intermediate coat for automotive coating that improves recoating performance with oil-based clear coats, its preparation method, and its application. This water-based intermediate coat effectively improves the recoating adhesion between the water-based intermediate coat and the oil-based clear coat during automotive coating, while also resulting in a coating with good appearance, resistance to high-pressure water jetting, anti-sagging, and anti-pinhole properties.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] On one hand, the present invention provides a water-based intermediate coat for automotive coating that has an improved recoating effect with oil-based clear coats. The raw materials forming this water-based intermediate coat, by weight, contain the following components:

[0009] 15-25 parts thermosetting waterborne polyurethane resin, 10-20 parts waterborne aliphatic polyurethane resin, 3-7 parts acrylic resin, 1-5 parts acrylic modified polyurethane resin, 4-10 parts amino resin, 1-3 parts hydrophobic polyester resin, 10-25 parts pigments and fillers, 0.5-1.5 parts aluminate coupling agent, 0.2-5 parts organic solvent and 4-17 parts deionized water.

[0010] Furthermore, the hydrophobic polyester resin has a hydroxyl value of 80-120 mgKOH / g and a weight-average molecular weight of 5000-8000 g / mol.

[0011] Furthermore, the aluminate coupling agent is an isopropoxy aluminate coupling agent.

[0012] Furthermore, the aluminate coupling agent is selected from one or more of SG-Al 821, DL-411 and LK-AL18.

[0013] Furthermore, the mass ratio of the hydrophobic polyester resin to the aluminate coupling agent is (1-1.5):1.

[0014] Furthermore, the thermosetting waterborne polyurethane resin is selected from Changxing's thermosetting waterborne polyurethane VK 563 and / or VK 5516.

[0015] Furthermore, the waterborne aliphatic polyurethane resin is selected from... TW1236 / 40WANEP resin and / or Bayhydrol U XP 2750 resin.

[0016] Furthermore, the acrylic resin is selected from setaqua 6803, One or more of PU 1035W and Lacper 4702.

[0017] Furthermore, the acrylic-modified polyurethane resin is selected from... TW 6466 / 36WA resin and / or VTW 6462 36WA resin.

[0018] Furthermore, the amino resin is composed of 2-5 parts of methyl etherified high-imino melamine resin and 2-5 parts of highly methyl etherified monomeric melamine resin.

[0019] Furthermore, the raw material also contains 10-16 parts of thickener, wherein the thickener contains 0-1 parts of alkali-swellable thickener and 10-15 parts of inorganic associative thickener.

[0020] Furthermore, the organic solvent contains 0-4 parts of high-boiling-point olefin solvent and 0.2-1 parts of alcohol ether solvent.

[0021] Furthermore, the boiling point of the high-boiling-point olefin solvent is ≥170℃.

[0022] Furthermore, the raw materials also contain 2-3.5 parts of pH adjuster, 0.5-1 part of dispersant, 0-1 part of substrate wetting agent and 2-5 parts of organic defoamer.

[0023] Furthermore, the organic defoamer comprises 0-1 parts of an organic acetylenic diol defoamer and 2-4 parts of a high-boiling-point defoamer.

[0024] Furthermore, the boiling point of the high-boiling-point defoamer is ≥170℃.

[0025] In another aspect, the present invention provides a method for preparing the water-based intermediate coating as described above, the method comprising the following steps:

[0026] Under stirring conditions, materials containing part of thermosetting waterborne polyurethane resin, part of aluminate coupling agent, part of organic solvent, part of deionized water, and all pigments and fillers are mixed and milled to obtain milled slurry.

[0027] Under stirring conditions, the sand slurry is mixed with the remaining materials to obtain the water-based intermediate coating.

[0028] In another aspect, the present invention provides the application of the water-based intermediate coating as described above in automotive coating.

[0029] Furthermore, the water-based intermediate coat is used in a recoating process in conjunction with an oil-based varnish.

[0030] Furthermore, the application includes the following steps:

[0031] An electrophoretic coating, a water-based intermediate coat, a water-based color paint, and an oil-based clear varnish are sequentially applied to a substrate to obtain a coating structure.

[0032] Furthermore, the application also includes repeating the steps of applying water-based intermediate coat, water-based color paint and oil-based varnish to the obtained coating structure in sequence.

[0033] The beneficial effects of this invention are as follows:

[0034] In the water-based intermediate coating provided in this invention, through formulation improvements, the combination of aluminate coupling agent and hydrophobic polyester resin in the formulation can effectively solve the technical problems of easy delamination and poor adhesion between water-based intermediate coatings and oil-based clear coats. The preferred aluminate coupling agent is an isopropoxy aluminate, which can bond with inorganic fillers containing hydroxyl, carboxyl, or surface-adsorbed water, forming an organic molecular layer on the surface of inorganic fillers such as barium sulfate. This improves the compatibility between the filler and the organic polymer. Simultaneously, this molecular layer can chemically react with the organic resin or form an entangled structure, thereby significantly improving adhesion during recoating. The preferred hydrophobic polyester resin provides good miscibility and a stronger interlayer chemical bond with the clear coat substrate. Furthermore, the preferred hydrophobic polyester resin contains a large number of ester groups, providing both good adhesion and toughness to the coating. In addition, the hydrophobic polyester resin can also improve the leveling and wetting properties of the intermediate coating system.

[0035] The water-based intermediate coating preparation process and coating process provided in this invention are simple and efficient, and are suitable for industrial production. Attached Figure Description

[0036] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0037] Figure 1 The images show actual paint films after recoating the water-based intermediate coat in Example 1 and Comparative Example 7.

[0038] Figure 2 The images show the appearance of the paint film after high-pressure water rinsing of the water-based intermediate coating of Example 1 and Comparative Example 7. Detailed Implementation

[0039] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0040] In actual automotive painting processes, especially during recoating, the combination of oil-based clear coat and water-based intermediate coat is a common practice. However, severe delamination between the water-based intermediate coat and the oil-based clear coat is frequently encountered, directly affecting the recoating adhesion and stability of the coating. This is because, during recoating, the water-based intermediate coat and oil-based clear coat are inherently immiscible. The clear coat has a smooth surface, low surface energy, and relatively few polar groups. Especially at low temperatures, the mobility and permeability of the polymer resin chains decrease, and the entanglement between molecular chains weakens, resulting in poor adhesion between coatings, leading to paint film peeling and poor recoating adhesion. Therefore, to improve the recoating adhesion between water-based intermediate coats and oil-based clear coats in automotive painting, and to impart good appearance, high-pressure water jet resistance, anti-sagging, and anti-pinhole properties to the coating, one specific embodiment of this invention provides a water-based intermediate coat for automotive painting that has improved recoating performance with oil-based clear coats. The raw materials forming this water-based intermediate coat, by weight, contain the following components:

[0041] 15-25 parts thermosetting waterborne polyurethane resin, 10-20 parts waterborne aliphatic polyurethane resin, 3-7 parts acrylic resin, 1-5 parts acrylic modified polyurethane resin, 4-10 parts amino resin, 1-3 parts hydrophobic polyester resin, 10-25 parts pigments and fillers, 0.5-1.5 parts aluminate coupling agent, 0.2-5 parts organic solvent and 4-17 parts deionized water.

[0042] In this embodiment, based on different resin combinations, a certain amount of aluminate coupling agent and small molecule high hydroxyl hydrophobic polyester resin are further compounded to effectively solve the problem of poor adhesion between water-based intermediate coat and oil-based clear coat. At the same time, the resulting coating has good appearance, high pressure water flushing resistance, anti-sagging (≥55cm) and anti-pinhole (≥50cm).

[0043] In some examples, the hydrophobic polyester resin has a hydroxyl value of 80-120 mg KOH / g and a weight-average molecular weight of 5000-8000 g / mol. When used in conjunction with an aluminate coupling agent, the hydrophobic polyester resin effectively improves the bonding between the intermediate coat and the clear coat, thereby improving the recoating adhesion of the coating film, as well as its toughness, leveling, and wetting properties. In some specific examples, the hydrophobic polyester resin includes, but is not limited to, a hydrophobic polyester resin solution selected from, for example, PRS-1045 hydrophobic polyester resin solution from Nippon Paint Co., Ltd.

[0044] For example, the aluminate coupling agent is preferably an isopropoxy aluminate coupling agent.

[0045] In this embodiment, the aluminate coupling agent interacts with the film-forming resin and pigments and fillers, which not only improves the wettability and dispersibility of the coating at the physical level, but also enhances the compatibility of the coating interface at the chemical level. This further improves the recoating effect of the obtained coating, increases the recoating adhesion, and shortens the grinding time, improves the fineness and brightness, and reduces the viscosity during recoating.

[0046] In some examples, the aluminate coupling agent includes, but is not limited to, one or more of the following: SG-Al 821 aluminate coupling agent from Nanjing Shuguang Chemical Group Co., Ltd., DL-411 aluminate coupling agent from Jiangsu Jufeng Chemical Technology Co., Ltd., and LK-AL18 aluminate coupling agent from Guangdong Longkai Chemical Co., Ltd.

[0047] In some preferred examples, the mass ratio of the hydrophobic polyester resin to the aluminate coupling agent is (1-1.5):1. In this case, the coating obtained by combining the two has better recoating adhesion and high-pressure water flushing resistance.

[0048] In this embodiment, the thermosetting waterborne polyurethane resin, as the main film-forming substance of the coating film, is required to possess certain flexibility, excellent adhesion, mechanical properties, and weather resistance. In some examples, the thermosetting waterborne polyurethane resin is selected from Changxing's thermosetting waterborne polyurethane VK 563 or VK 5516. TW 6431 / 45WA.

[0049] In this embodiment, the waterborne aliphatic polyurethane resin exhibits good pigment compatibility and can provide extremely high flexibility, low-temperature stone-impact performance, or excellent weather resistance and gloss. For example, the waterborne aliphatic polyurethane resin is selected from Zhanxin Company. TW1236 / 40WANEP resin and / or Covestro's Bayhydrol U XP 2750 resin.

[0050] In this embodiment, the acrylic resin can exist in the form of a resin or an emulsion. The acrylic resin can react with amino resins to give the paint film better appearance and performance. Exemplarily, the acrylic resin includes, but is not limited to, Setaqua 6803 selected from Zhanxin Company and BASF... One or more of PU 1035W and Wanhua Chemical's Lacper 4702.

[0051] In this embodiment, the acrylic-modified polyurethane resin can exist in the form of a resin or an emulsion. The acrylic-modified polyurethane resin can provide excellent coating appearance, superior mechanical properties and wet adhesion, and very good outdoor durability; it offers higher flexibility, better wet adhesion, and lower pinhole tendency; it can generate transparent and crack-free films without the addition of any solvents or coating additives, or it can have good pigment wetting properties, excellent film-forming properties, interlayer adhesion, and impact resistance. For example, the acrylic-modified polyurethane resin includes, but is not limited to, those selected from Zhanxin Company. TW 6466 / 36WA resin and / or VTW 6462 36WA resin.

[0052] In this embodiment, the amino resin can react with other resins to give the paint film a good appearance and crosslinking density. Exemplary amino resins are preferably methyl etherified amino resins, such as one or more of CYMEL327, CYMEL370, and CYMEL303LF from Zhanxin Company. In some preferred examples, the amino resin is composed of 2-5 parts of methyl etherified high-imino melamine resin (e.g., CYMEL327) and 2-5 parts of highly methyl etherified monomeric melamine resin (e.g., CYMEL303LF).

[0053] In some examples, the raw material also contains 10-16 parts of a thickener, which includes 0-1 parts of an alkali-swellable thickener and 10-15 parts of an inorganic associative thickener.

[0054] In some preferred examples, the thickener contains 0.2-0.7 parts of alkali-swellable thickener and 10-15 parts of inorganic associative thickener.

[0055] For example, the alkali-swellable thickener is a non-associative polyacrylate alkali-swellable emulsion, which has a good thickening effect. When combined with an inorganic associative thickener, it can achieve a stable thickening effect on resins, particles, and water. Exemplary alkali-swellable thickeners include, but are not limited to, one or both of Rohm and Haas's ASE 60 and Ciba's Viscalex HV-30. For example, the alkali-swellable thickener in the raw materials includes, but is not limited to, 0.2-0.5 parts, 0.4-0.5 parts, etc.

[0056] The inorganic associative thickener is a high-performance thickener that provides thermal stability of viscosity and good thixotropy. For example, the inorganic associative thickener includes, but is not limited to, lithium magnesium silicate (e.g., BYK's Laponite RD) and montmorillonite clay rheology modifiers (e.g., Hemings' BENTONE LT). For example, the inorganic associative thickener in the raw material includes, but is not limited to, 10-12 parts or 11-12 parts.

[0057] In some examples, the organic solvent contains 0-4 parts of high-boiling-point olefin solvent and 0.2-1 parts of alcohol ether solvent.

[0058] The high-boiling-point olefin solvent can be used to prevent surface defects such as pinholes, orange peel, bubbling, and pores, and to prevent boiling marks, achieving excellent leveling properties. For example, the high-boiling-point olefin solvent has a boiling point ≥170°C. Exemplary high-boiling-point olefin solvents include, but are not limited to, BYK-WS from BYK Corporation and SHELLSOL TK from Shell Corporation.

[0059] For example, the alcohol ether solvent can help the paint film form. Examples of alcohol ether solvents include, but are not limited to, one or more of diethylene glycol butyl ether, dipropylene glycol methyl ether, dipropylene glycol butyl ether, and ethylene glycol isooctyl ether.

[0060] In some examples, the raw materials also contain 2-3.5 parts of pH adjuster, 0.5-1 part of dispersant, 0-1 part of substrate wetting agent and 2-5 parts of organic defoamer.

[0061] In some examples, the pH adjuster includes, but is not limited to, dimethylethanolamine (DMEA), such as dimethylethanolamine produced by Shandong Jiawei Chemical Co., Ltd. The exemplary amounts of the pH adjuster added to the raw materials include, but are not limited to, 3-3.5 parts, 3-3.2 parts, and 2-3.2 parts.

[0062] Dispersants exhibit excellent dispersion stability, superior anti-floating and anti-blooming properties, and viscosity-reducing abilities for both inorganic and organic pigments. In some examples, the dispersants include, but are not limited to, for example, BYK's Dispersant 192 and Eucalyptus's... One or more of the SPERSE series 688W and 685U.

[0063] For example, the organic defoamer comprises 0-1 parts of an acetylenic diol defoamer and 2-4 parts of a high-boiling-point defoamer. The organic defoamer helps eliminate bubbles generated during film formation. In some examples, the high-boiling-point defoamer has a boiling point ≥170°C. In some specific examples, the acetylenic diol defoamer includes, but is not limited to, Evonik's TEGO 805N. In some specific examples, the high-boiling-point defoamer includes, but is not limited to, products selected from BYK-WA.

[0064] For example, the substrate wetting agent is one or more of the following: acetylenic diol products (e.g., Evonik's BETTERSOL 440; function: BETTERSOL 440 is an ethylene oxide addition-modified acetylenic diol product. The product has multifunctional characteristics of wetting, defoaming, and dispersing. BETTERSOL 440 exhibits excellent dynamic migration in the system, providing excellent dynamic wetting, spreading, and leveling effects without affecting recoating) and silicone products (e.g., BYK-346 leveling agent (which combines anti-cratering and leveling properties. It can enhance coating gloss and improve long-wave leveling effects; slightly reduce surface tension without affecting recoating and interlayer adhesion. This additive also has defoaming function and good thermal stability)... The exemplary amount of substrate wetting agent added to the raw materials includes, but is not limited to, 0.1-0.5 parts, 0.3-0.5 parts, 0.3-0.4 parts, etc.

[0065] In this embodiment, the pigments and / or fillers include pigments and / or fillers.

[0066] For example, the pigments include, but are not limited to, titanium dioxide (e.g., rutile titanium dioxide, specifically DuPont R-902 (with good dispersibility and whiteness), or Lomon R-996 (with good dispersibility)), and carbon black (e.g., Orion high-pigment channel carbon black Black 4 (with advantages such as high blackness, high gloss, and good dispersibility)). The exemplary amount of the pigments added to the raw materials includes, but is not limited to, 6-15 parts.

[0067] For example, the filler may include, but is not limited to, barium sulfate (fineness ≤ 5 μm), such as: Lianzhuang precipitated barium sulfate (Xiangxing) 1250 mesh, etc. The exemplary amounts of fillers added to the raw materials may include, but are not limited to, 4-10 parts, 4-8 parts, etc.

[0068] For example, the content of deionized water in the raw materials includes, but is not limited to, 4-10 parts, 12-17 parts, etc.

[0069] For example, in the water-based intermediate coating, the total weight of the raw materials is 100 parts.

[0070] According to another specific embodiment of the present invention, a method for preparing the aforementioned water-based intermediate coating is provided, the method comprising the following steps:

[0071] Under stirring conditions, materials containing part of thermosetting waterborne polyurethane resin, part of aluminate coupling agent, part of organic solvent, part of deionized water, and all pigments and fillers are mixed and milled to obtain milled slurry.

[0072] Under stirring conditions, the sand slurry is mixed with the remaining materials to obtain the water-based intermediate coating.

[0073] In some preferred embodiments, the method for preparing the aqueous intermediate coating includes the following steps:

[0074] 1) According to the indicated raw material ratio, under stirring conditions at a speed of 500-800 r / min, add 1 / 3-1 / 2 weight of thermosetting waterborne polyurethane resin, 1 / 3 weight of pH adjuster, 1 / 3-1 / 2 weight of deionized water, all dispersant, all organic defoamer, 1 / 3-1 / 2 weight of aluminate coupling agent, 1 / 2 weight of alcohol ether solvent, and 1 / 3-1 / 2 weight of high-boiling-point olefin solvent into the reactor in sequence. After stirring thoroughly for 30 min, test the fineness to be <5μm. Add all pigments and fillers, increase the speed to 1000-1500 r / min, and stir at high speed for 30 min. Then transfer to a sand mill for sand milling for 2 h and test the fineness. Stop sand milling when the fineness is <5μm. Filter to obtain sand mill slurry.

[0075] 2) According to the raw material ratio, under the stirring condition of 400-500r / min for grinding slurry, the remaining thermosetting waterborne polyurethane resin, acrylic modified polyurethane resin, waterborne aliphatic polyurethane resin, acrylic resin, aluminate coupling agent, alkali swelling thickener, inorganic associative thickener, amino resin, high boiling point olefin solvent, alcohol ether solvent, substrate wetting agent, hydrophobic polyester resin, remaining deionized water and pH adjuster are added in sequence to adjust to a suitable viscosity and pH value, and then diluted to a suitable application viscosity before use.

[0076] According to yet another specific embodiment of the present invention, the application of the water-based intermediate coating as described above in automotive painting is provided.

[0077] For example, the application includes the following steps:

[0078] Electrophoretic paint, water-based intermediate coat, water-based color paint, and oil-based varnish are sequentially applied to the substrate to obtain a coated structure.

[0079] Preferably, the application further includes repeating the steps of applying water-based intermediate coat, water-based color paint and oil-based varnish to the obtained coating structure in sequence.

[0080] The technical solution of the present invention will be described below with reference to some specific embodiments:

[0081] Example 1

[0082] A water-based intermediate coat for automotive coating that provides improved recoating performance with oil-based clear coats is shown in Table 1 below.

[0083] The preparation method of this water-based intermediate coating includes the following steps:

[0084] Step a: According to the raw material ratio shown, under stirring conditions at a speed of 500-800 r / min, add 1 / 3-1 / 2 weight of thermosetting waterborne polyurethane resin, 1 / 3 weight of pH adjuster, 1 / 3-1 / 2 weight of deionized water, all dispersant, all organic defoamer, 1 / 3-1 / 2 weight of aluminate coupling agent, 1 / 2 weight of alcohol ether solvent, and 1 / 3-1 / 2 weight of high-boiling-point olefin solvent into the reactor in sequence. After stirring thoroughly for 30 min, test the fineness to be <5μm. Add all pigments and fillers, increase the speed to 1000-1500 r / min, and stir at high speed for 30 min. Then transfer to a sand mill for sand milling for 2 h. Test the fineness until it is <5μm, then stop sand milling. After filtration, obtain the sand mill slurry.

[0085] Step b: According to the raw material ratio, under the stirring condition of 400-500r / min for grinding slurry, the remaining thermosetting waterborne polyurethane resin, acrylic modified polyurethane resin, waterborne aliphatic polyurethane resin, acrylic resin, aluminate coupling agent, alkali swelling thickener, inorganic associative thickener, amino resin, high boiling point olefin solvent, alcohol ether solvent, substrate wetting agent, hydrophobic polyester resin, remaining deionized water and pH adjuster are added in sequence to adjust to a suitable viscosity and pH value, and then diluted to a suitable application viscosity before use.

[0086] Comparative Examples 1-9

[0087] A water-based intermediate coat for automotive coating has the formulation shown in Table 1 or Table 2 below. The preparation method is the same as in Example 1.

[0088] Table 1

[0089]

[0090]

[0091] Table 2

[0092]

[0093] Examples 2-5

[0094] A water-based intermediate coat for automotive coating has the following formulation, as shown in Table 3. The preparation method is the same as in Example 1.

[0095] Table 3

[0096]

[0097] Performance testing

[0098] The water-based intermediate coats obtained in the above embodiments and comparative examples were used as intermediate coats, and dry films were prepared according to the standard automotive paint recoating process. The specific preparation methods and conditions are as follows:

[0099] Single coating: Select a qualified steel plate with an electrophoretic coating, spray a water-based intermediate coat onto the steel plate according to the required film thickness, dehydrate the intermediate coat at 80℃ for 5 minutes, and then cure it at 145℃ for 25 minutes. Spray a color paint onto the intermediate coat according to the required film thickness, dehydrate the color paint at 80℃ for 5 minutes, and then spray a clear varnish according to the required film thickness. The clear varnish is cured at 145℃ for 25 minutes.

[0100] Recoating: Spray a water-based intermediate coat on the coating obtained by the above single coat as required. Dehydrate the intermediate coat at 80℃ for 5 minutes and then cure it at 145℃ for 25 minutes. Spray a color paint on the intermediate coat to the required film thickness. Dehydrate the color paint at 80℃ for 5 minutes. Then spray a clear varnish to the required film thickness and cure it at 145℃ for 25 minutes.

[0101] The results are shown in Tables 4-6 below. Figure 1 and Figure 2 As shown.

[0102] in, Figure 1 The figures show actual images of the paint films after recoating the water-based intermediate coat in Example 1 and Comparative Example 7, respectively. As can be seen from the figures, the recoating result in Example 1 was OK; however, the paint film in Comparative Example 7 showed peeling, indicating poor adhesion.

[0103] Figure 2 The figures show the appearance of the paint film after high-pressure water rinsing for Example 1 and Comparative Example 7, respectively. As can be seen from the figures, the paint film in Example 1 did not peel off after high-pressure water rinsing, which is considered OK; however, the paint film in Comparative Example 7 peeled off after high-pressure water rinsing, which is considered NG.

[0104] Table 4

[0105]

[0106] Table 5

[0107]

[0108] Table 6

[0109]

[0110]

[0111] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A water-based intermediate coat for automotive coating that provides improved recoating effect with oil-based clear coats, characterized in that, The raw materials forming this water-based intermediate coating contain the following components, in parts by weight: 15-25 parts thermosetting waterborne polyurethane resin, 10-20 parts waterborne aliphatic polyurethane resin, 3-7 parts acrylic resin, 1-5 parts acrylic modified polyurethane resin, 4-10 parts amino resin, 1-3 parts hydrophobic polyester resin, 10-25 parts pigments and fillers, 0.5-1.5 parts aluminate coupling agent, 0.2-5 parts organic solvent and 4-17 parts deionized water.

2. The water-based intermediate coating according to claim 1, characterized in that, The hydrophobic polyester resin has a hydroxyl value of 80-120 mgKOH / g and a weight-average molecular weight of 5000-8000 g / mol.

3. The water-based intermediate coating according to claim 1, characterized in that, The aluminate coupling agent is an isopropoxy aluminate coupling agent; Preferably, the aluminate coupling agent is selected from one or more of SG-Al 821, DL-411 and LK-AL18.

4. The water-based intermediate coating according to any one of claims 1-3, characterized in that, The mass ratio of the hydrophobic polyester resin to the aluminate coupling agent is (1-1.5):

1.

5. The water-based intermediate coating according to claim 1, characterized in that, The thermosetting waterborne polyurethane resin is selected from Changxing's thermosetting waterborne polyurethane VK 563 and / or VK 5516. Preferably, the waterborne aliphatic polyurethane resin is selected from... TW1236 / 40WANEP resin and / or Bayhydrol U XP 2750 resin; Preferably, the acrylic resin is selected from setaqua 6803, One or more of PU 1035W and Lacper 4702; Preferably, the acrylic-modified polyurethane resin is selected from... TW 6466 / 36WA resin and / or VTW 6462 36WA resin; Preferably, the amino resin is composed of 2-5 parts of methyl etherified high-imino melamine resin and 2-5 parts of highly methyl etherified monomeric melamine resin.

6. The water-based intermediate coating according to claim 1, characterized in that, The raw materials also contain 10-16 parts of thickener, wherein the thickener contains 0-1 parts of alkali-swellable thickener and 10-15 parts of inorganic associative thickener; Preferably, the organic solvent contains 0-4 parts of high-boiling-point olefin solvent and 0.2-1 parts of alcohol ether solvent.

7. The water-based intermediate coating according to claim 1, characterized in that, The raw materials also contain 2-3.5 parts of pH adjuster, 0.5-1 part of dispersant, 0-1 part of substrate wetting agent and 2-5 parts of organic defoamer.

8. The method for preparing the water-based intermediate coating according to any one of claims 1-7, characterized in that, Includes the following steps: Under stirring conditions, materials containing part of thermosetting waterborne polyurethane resin, part of aluminate coupling agent, part of organic solvent, part of deionized water, and all pigments and fillers are mixed and milled to obtain milled slurry. Under stirring conditions, the sand slurry is mixed with the remaining materials to obtain the water-based intermediate coating.

9. The application of the water-based intermediate coating as described in any one of claims 1-7 in automotive coating.

10. The application according to claim 9, characterized in that, The water-based intermediate coat is used in a recoating process in conjunction with an oil-based varnish; Preferably, the application includes the following steps: An electrophoretic coating, a water-based intermediate coat, a water-based color paint, and an oil-based clear varnish are sequentially applied to a substrate to obtain a coating structure. Preferably, the application further includes repeating the steps of applying water-based intermediate coat, water-based color paint and oil-based varnish to the obtained coating structure in sequence.

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