High and low temperature resistant water-based intermediate paint for vehicle body and preparation and coating method thereof

Abstract

The application belongs to the technical field of coatings, and particularly discloses a water-based intermediate paint for a vehicle body, which is resistant to high-low temperature cycles, and a preparation method and a coating method thereof. The water-based intermediate paint is prepared from a water-based intermediate paint composition. According to mass fractions, the water-based intermediate paint composition comprises the following components: deionized water 40-60 parts; a rheological agent 0.1-1 part; an organic amine 0.5-1.5 parts; an acrylic-polyurethane hybrid resin 6-16 parts; a polyester polyol 3-10 parts; a cosolvent 1-5 parts; an amino resin 3-10 parts; a multifunctional epoxy resin 1-6 parts; a pigment paste 10-25.2 parts; a filler paste 2-8 parts; a catalyst 0.01-1 part; a wetting agent 0.1-1 part; an ultraviolet light absorber 0.5-1.5 parts; and a thickening agent 0.1-1 part. The water-based intermediate paint of the application can still maintain excellent adhesion, excellent mechanical properties and long durability under extreme high-low temperature and high humidity cycle conditions.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to a water-based intermediate paint for automotive bodies that is resistant to high and low temperature cycling, and a method for its preparation and application. Background Technology

[0002] Automotive body coating systems are multi-layered composite structures, typically including an electrophoretic primer layer, an intermediate coat layer, a color coat layer, and a clear coat layer. Among these, the intermediate coat layer plays a crucial role in connecting the upper and lower layers. It not only needs to provide a smooth and even base for the topcoat to ensure the final appearance, but also needs to possess excellent mechanical properties (such as hardness, flexibility, and stone chip resistance), excellent adhesion (including interlayer adhesion with the underlying electrophoretic primer and the upper color coat layer), and long-term reliable resistance to environmental aging (such as water resistance, corrosion resistance, and temperature change resistance).

[0003] With increasingly stringent global environmental regulations, reducing volatile organic compound (VOC) emissions has become an irreversible trend in the automotive coatings industry. Waterborne coatings, with water as the primary dispersion medium and extremely low VOC content, have become the preferred alternative to traditional solvent-based coatings. In the automotive coating field, the promotion of compact and energy-saving coating processes such as "3C1B" (three coats, one bake) and "B1B2" (wet-on-wet primer and base coat) has also placed higher demands on waterborne intermediate coats: they must achieve comprehensive performance comparable to or even better than traditional solvent-based products in a shorter process and at a lower baking temperature.

[0004] However, in actual use, especially in harsh regions with large temperature differences between day and night and extreme cold or hot and humid climates, the vehicle body coating continuously experiences drastic and repeated temperature and humidity cycles. For example, from the high temperatures of summer daytime sun exposure (reaching above 80°C) to the extreme cold of winter nights (reaching below -40°C), accompanied by high humidity environments caused by rain, snow, and condensation. This "climate cycle" leads to complex thermal expansion / contraction stress and moisture expansion / contraction stress within the coating and between the coating and different substrate materials. When these stresses accumulate and exceed the coating's cohesive strength or interlayer bonding force, coating failure occurs, manifesting as microcracks, blistering, peeling, and loss of gloss, severely damaging the vehicle's long-term protective performance and aesthetic appearance.

[0005] To address this challenge, existing technologies have proposed various solutions, but each has its own limitations:

[0006] Patent CN102086339B discloses a water-based automotive intermediate paint using water-soluble polyester and emulsion-type polyester resin as base materials, combined with a specific amino resin, focusing on stone impact resistance and lower baking temperature. Patent CN102977752B uses a physical blend of coconut oil acid-modified polyester resin and acrylic emulsion to improve appearance and water resistance. Patent CN109181433A combines a water-based acrylic polyol dispersion with a polyurethane dispersion to achieve versatility for both wet-on-wet and dry-on-wet application. However, a common drawback of these solutions is that, whether polyester / acrylic or acrylic / polyurethane, the resin components are mostly physically mixed. Due to the thermodynamic incompatibility of different resin segments, phase separation easily occurs during curing, forming a microscopically heterogeneous "island structure." Under severe high and low temperature cycling, the large difference in thermal expansion coefficients between different phase regions can easily lead to stress concentration at the interface, which becomes a weak point for coating cracking or interlayer delamination, resulting in insufficient resistance to extreme temperature cycling.

[0007] Patent CN104059533B discloses a coating suitable for intermediate coating reduction processes, which combines a core / shell microgel resin, a polyurethane aqueous dispersion, and a polyester resin. This approach improves coating performance to some extent through resin morphology design. However, it lacks strong chemical bonding bridges between components and does not address key crosslinking components that simultaneously strengthen the internal network and interfacial adhesion of the coating. Therefore, the long-term durability of the coating, especially its adhesion retention and crack resistance under harsh weather conditions, still needs significant improvement.

[0008] Existing technologies generally use amino resins as the main crosslinking agent, reacting with the hydroxyl groups and other groups of the resin. However, relying solely on this type of crosslinking results in limited network strength and insufficient contribution to improving the chemical bonding adhesion between the coating and the cathodic electrophoretic primer. Meanwhile, the addition of conventional fillers (such as titanium dioxide and barium sulfate) mainly serves to color, thicken, and reduce costs; their morphology and function are not specifically designed, making it difficult to actively improve the coating's impermeability and stress dissipation capacity.

[0009] Currently, existing waterborne intermediate coatings often exhibit the following technical defects when facing the challenges of extreme climate cycles, which constitute the core pain points that the industry urgently needs to address: (1) Insufficient toughness of the resin system and poor resistance to stress cracking: Many waterborne intermediate coatings use pure acrylic emulsion or simple physical blends of acrylic resin and polyurethane resin as film-forming substances. Pure acrylic resin chain segments are relatively rigid and have limited flexibility; while simple physical blends are prone to phase separation during curing due to the thermodynamic incompatibility between acrylic and polyurethane resins and the lack of effective chemical bonding, forming a non-uniform "island structure" at the microscale. Under severe high and low temperature cycles, the difference in thermal expansion coefficients between different phase regions is huge, and stress concentration is easily generated at the interface, leading to cohesive cracking (microcracks) in the coating itself, which manifests as a decrease in impact resistance and bending performance. (2) Interlayer adhesion, especially after aging, is severely weakened: Existing technologies often rely on the polar groups (such as hydroxyl and carboxyl groups) contained in the resin itself to form physical adsorption or limited hydrogen bonding with the substrate or topcoat. This bonding force may meet the standard in the initial state, but after long-term exposure to humid heat and cold cycles, the interface is easily weakened by stress and water penetration, resulting in a significant decrease in adhesion and causing interlayer peeling. There is a lack of "bridging" components that can build strong and durable chemical bonds between coatings and between coatings and substrates. (3) The coating has weak anti-permeability and stress dissipation ability: If the filler system in the traditional formulation is not designed properly, such as using only ordinary extender pigments, it mainly plays the role of thickening and reducing costs, and it is difficult to effectively improve the density of the coating. Water vapor and corrosive media (such as salt) can easily penetrate along the interface between filler and resin or the defect path inside the coating, which directly causes blistering and corrosion on the one hand, and exacerbates the swelling stress caused by humidity changes on the other hand. At the same time, the coating lacks a microstructure that can actively buffer and dissipate heat stress, and the stress has nowhere to be released, eventually leading to damage. (4) It is difficult to balance the overall performance: Increasing the crosslinking density often comes at the cost of sacrificing flexibility, while increasing flexibility may lead to a decrease in hardness and solvent resistance. Existing technical solutions often compromise on one aspect while failing to maintain excellent cross-cut adhesion, stone impact resistance, water resistance, salt spray resistance, and appearance stability simultaneously under harsh climate cycling tests.

[0010] Therefore, developing a water-based intermediate coat that can fundamentally solve the above-mentioned defects, maintain excellent adhesion, superior mechanical properties, and long-term durability under extreme high and low temperature and high humidity cycling conditions, and comply with environmental regulations, has become a pressing technical challenge for those skilled in the art. This invention is an innovative solution proposed to address this urgent need. Summary of the Invention

[0011] In view of the above-mentioned problems, the present invention provides a water-based intermediate paint for automotive bodies that is resistant to high and low temperature cycling, as well as a method for its preparation and application. The water-based intermediate paint of the present invention maintains excellent adhesion, superior mechanical properties, and long-term durability under extreme high and low temperature and high humidity cycling conditions, and also meets environmental protection requirements.

[0012] To address the aforementioned problems, this invention provides a water-based intermediate paint for automotive applications that is resistant to high and low temperature cycling. The water-based intermediate paint comprises the following components by weight:

[0013] Deionized water: 40-60 parts; rheology modifier: 0.1-1 parts; organic amine: 0.5-1.5 parts; acrylic-polyurethane hybrid resin: 6-16 parts; polyester polyol: 3-10 parts; cosolvent: 1-5 parts; amino resin: 3-10 parts; multifunctional epoxy resin: 1-6 parts; pigment paste: 10-25.2 parts; filler paste: 2-8 parts; catalyst: 0.01-1 parts; wetting agent: 0.1-1 parts; ultraviolet light absorber: 0.5-1.5 parts; thickener: 0.1-1 parts;

[0014] Wherein, the multifunctional epoxy resin is an epoxy resin with an epoxy equivalent of less than 250 g / eq and a functionality ≥3; the acrylic-polyurethane hybrid resin is a core-shell structured hybrid resin prepared by seed emulsion polymerization; the polyurethane segments and acrylic segments in the hybrid resin are covalently linked by urethane bonds; the preparation method of the acrylic-polyurethane hybrid resin includes the following steps:

[0015] S1. In the presence of an emulsifier, add a monomer mixture containing butyl acrylate (BA) and acrylic acid (AA), stir until homogeneous, add an initiator, and carry out a polymerization reaction at 70-75℃ to obtain a seed emulsion with a particle size of 20-30nm.

[0016] S2. A monomer pre-emulsion containing methacrylic acid (MAA), methyl methacrylate (MMA), styrene (St), isooctyl acrylate (2-EHA) and hydroxyl acrylate is added dropwise to the seed emulsion along with an initiator and reacted at 80°C to form a core layer emulsion with a particle size of 30-50 nm.

[0017] S3. A polyurethane prepolymer mixture containing isophorone diisocyanate (IPDI), polyether polyol (PPG) and diol is added dropwise to the core layer emulsion, and an initiator is added during the polymerization process. The reaction is carried out at 80°C until the characteristic peak of the isocyanate group disappears, forming the acrylic-polyurethane hybrid resin emulsion.

[0018] S4. After cooling, the resin is neutralized with organic amines and filtered to obtain an acrylic-polyurethane hybrid resin.

[0019] Preferably, the filler slurry contains talc powder, and the mass content of the talc powder in the filler slurry is 30-40%.

[0020] Preferably, the filler slurry is made of the following components by mass percentage: 55-65% deionized water, 0.5-1.5% organic amine, 0.5-1.5% activator, 2.0-3.0% dispersant, and 30-40% talc.

[0021] Preferably, the rheology modifier is selected from at least one of synthetic lithium saponite, organically modified bentonite, lithium montmorillonite, and attapulgite; and / or,

[0022] The co-solvent is selected from at least one of n-butanol, isooctyl alcohol, propylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol monobutyl ether, dipropylene glycol methyl ether, dipropylene glycol butyl ether, and 3-methoxy-3-methyl-1-butanol; and / or,

[0023] The catalyst is a sulfonic acid catalyst.

[0024] Preferably, the method for preparing the water-based intermediate paint for vehicle bodies that is resistant to high and low temperature cycling includes the following steps:

[0025] (1) Deionized water, rheology modifier and first part organic amine are mixed to obtain a first mixture; wherein the organic amine is composed of a first part organic amine and a second part organic amine;

[0026] (2) Add acrylic-polyurethane hybrid resin and polyester polyol to the first mixture, mix evenly, then add cosolvent, amino resin and multifunctional epoxy resin, mix evenly to obtain the second mixture;

[0027] (3) Add pigment paste, filler paste, catalyst, wetting agent and ultraviolet light absorber to the second mixture, mix evenly to obtain the product;

[0028] (4) Adjust the pH of the product obtained in step (3) to 7.8-8.8 with the organic amine from the second part;

[0029] (5) Add a thickener to the product obtained in step (4) and optionally add deionized water to adjust the viscosity of the product to 100-140 cP, filter, and the product is obtained.

[0030] Based on the same inventive concept, the present invention also provides a coating method, which includes the following steps: applying the above-mentioned water-based intermediate paint for car bodies that is resistant to high and low temperature cycles or the water-based intermediate paint for car bodies that is resistant to high and low temperature cycles prepared by the above-mentioned preparation method to a cleaned electrophoretic plate, and sequentially performing flash drying or pre-drying, applying color paint, applying clear varnish, leveling and baking curing steps to form a composite coating; wherein, the baking curing conditions are to maintain at 140°C for 20-40 minutes.

[0031] Preferably, the coating method is the "3C1B" process or the "B1B2" process.

[0032] The mechanism of action of the acrylic-polyurethane hybrid resin of the present invention:

[0033] The acrylic-polyurethane hybrid resin of this invention is prepared by a stepwise core-shell emulsion polymerization method. First, hydroxyl-containing acrylate copolymer seeds and cores are synthesized. Then, isophorone diisocyanate (IPDI) and polyether polyol (PPG) are polymerized in situ on their surface. Simultaneously, the -NCO groups of IPDI react with the side hydroxyl groups on the core polymer chain to form urethane (-NHCOO-) covalent bonds. This chemical bonding tightly connects the acrylic resin and polyurethane at the molecular scale, effectively suppressing macroscopic phase separation while allowing the formation of microphase-separated structures at the nanoscale. The rigid segments from methyl methacrylate and styrene, together with the hard segments of polyurethane from IPDI / HDO, synergistically form a hard phase region, providing strength and hardness for the waterborne intermediate coating. The flexible segments from butyl acrylate and isooctyl acrylate, together with the soft segments of polyether, form a soft phase region, providing toughness and deformation capability for the waterborne intermediate coating. The two phases are tightly bound together through covalent bonds, hydrogen bonds, and physical entanglement, achieving an excellent balance between rigidity and elasticity in the waterborne intermediate coating. The key reaction formula involved in the acrylic-polyurethane hybrid resin of the present invention is as follows:

[0034] (1) Seed emulsion polymerization (acrylate copolymerization):

[0035] ;

[0036] (2) Core-layer polymerization (acrylate copolymerization):

[0037] ;

[0038] (3) Formation of the shell polyurethane and core-shell bonding:

[0039] Polyurethane synthesis:

[0040] Where R represents an IPDI residue and ~ represents a PPG or HDO chain segment;

[0041] Core-shell chemical bonding:

[0042] ;

[0043] Free radical grafting:

[0044] .

[0045] The mechanism of action of the multifunctional epoxy resin of the present invention:

[0046] The multifunctional epoxy resin in this invention acts as a key "stereobridging and network reinforcing agent," and its mechanism of action goes beyond simply providing a single crosslinking point. Its core innovation lies in the fact that, within a specific curing temperature range (140°C for 20-40 minutes) during the application of the waterborne intermediate paint system (such as B1B2, 3C1B, etc.), its epoxy groups (-CH(O)CH-) can undergo efficient ring-opening addition reactions with multiple functional groups possessing sufficient reactivity at this temperature, thereby constructing a powerful "three-in-one" chemical crosslinking network.

[0047] (1) Constructing a composite reinforcing network within the intermediate paint:

[0048] During the curing process, multifunctional epoxy resins react simultaneously with multiple functional groups in the intermediate varnish matrix:

[0049] Reaction with hydroxyl groups (-OH): It reacts with hydroxyl groups on the molecular chains of acrylic-polyurethane hybrid resins and polyester polyols to generate stable ether bonds (-COC-), which is the core of chain extension and increasing network crosslinking density;

[0050] Reaction with carboxyl groups (-COOH): It reacts with carboxyl groups in components such as polyester resin to form ester bonds (-COO-), which further enriches the chemical bond types of the cross-linked network and improves its density;

[0051] Synergistic crosslinking with amino resins: The epoxy groups can also react with primary / secondary amino groups (-NH2 / -NH-) released during the curing process of amino resins (such as melamine resin) or contained in the system to generate β-hydroxyamine structures. This reaction enables the crosslinking network of epoxy resin to form chemical interpenetration and synergistic reinforcement with the inherent crosslinking network of amino resin, avoiding the performance shortcomings of a single crosslinking system, thereby endowing the coating with more balanced and excellent toughness, hardness and hydrolysis resistance.

[0052] (2) Achieving chemical anchoring with the underlying electrophoretic paint:

[0053] Under the same curing conditions (140℃ for 20-40 minutes), the epoxy groups of multifunctional epoxy resins can diffuse to the interface and undergo the same chemical reactions as described above with the abundant hydroxyl and amino groups on the surface of the cathodic electrophoretic coating. This forms a strong covalent bond "molecular bridge" between the intermediate coat and the electrophoretic primer. The strength of this interfacial chemical bond is far higher than that of physical adsorption or hydrogen bonding, which is the key to fundamentally solving the problem of interlayer adhesion failure of coating systems under environmental stress.

[0054] (3) Provides a reactive interface with the top coating:

[0055] After the intermediate coat has cured through the above process, some active epoxy groups or newly generated hydroxyl groups may remain on its surface. During the subsequent wet-on-wet application of color paint and clear coat and co-baking, these active groups can further react with the corresponding functional groups in the topcoat system, thereby strengthening the interfacial bonding between the intermediate coat and the topcoat and improving the overall integration of the coating system.

[0056] In summary, this invention, by introducing a multifunctional epoxy resin, simultaneously drives a multi-faceted chemical reaction with its internal matrix (-OH, -COOH), internal crosslinking agent (-NH-), and external interface (primer active groups) under defined curing conditions. This is not a simple superposition of crosslinking densities, but rather the construction of a three-dimensional interpenetrating chemical network characterized by "lateral reinforcement and vertical bridging."

[0057] Lateral reinforcement: By forming synergistic crosslinks with hydroxyl, carboxyl and amino resins inside the intermediate paint, a dense, tough and hydrolysis-resistant composite network is constructed, which significantly improves the bulk mechanical properties of the coating.

[0058] Longitudinal bridging: By forming covalent bonds with the active groups of the upper and lower coatings (electrophoretic primer and topcoat), the traditional physically superimposed multilayer coatings are transformed into a chemically bonded whole, which greatly enhances the interlayer adhesion and system integrity.

[0059] This three-dimensional bridging design is the core chemical basis for overcoming the defects of water-based intermediate paints that are prone to cracking and peeling under extreme climate changes due to weak interfacial bonding and fragile network. It is also one of the key innovations that distinguishes it from the simple physical blending or single crosslinking system in the existing technology.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0061] (1) The acrylic-polyurethane hybrid resin prepared by chemical synthesis in this invention simultaneously introduces rigid acrylic segments and flexible polyurethane segments (containing -O- ether bonds) into the molecular chain, and achieves covalent connection through urethane bonds (-NHCOO-), forming a uniform "rigid-tough interpenetrating" network. When the temperature changes drastically, the flexible segments can efficiently absorb expansion / contraction stress through conformational changes, while the rigid segments suppress excessive deformation, thereby actively buffering thermal stress at the matrix level and avoiding brittle cracking caused by excessive rigidity, as in Comparative Example 1 (pure acrylic acid). Secondly, the addition of multifunctional epoxy resin reacts with the active groups (-OH, -COOH) of the hybrid resin and polyester polyol to form a high-strength, high-density three-dimensional cross-linked network. This network is not only robust itself, but also "locks in" and strengthens the aforementioned stress dissipation mechanism. Simultaneously, it chemically bonds the coating to the substrate with strong bridging, effectively suppressing interlayer delamination and blistering caused by interfacial slippage or insufficient cohesive strength (a defect observed in both the physical blend of Comparative Example 2 and the epoxy-free resin of Comparative Example 3). Finally, the flake-like talc powder in the self-made filler slurry is arranged in parallel within the coating. The interface between its flakes and the resin matrix serves as an additional micro-stress buffer point, further dissipating in-plane stress through micro-slippage and preventing stress accumulation that could lead to microcracks. These three factors synergistically endow the coating with a dynamic environmental adaptability similar to "elastic armor," fundamentally solving the problem of cracking and blistering failure under extreme weather conditions and achieving excellent dynamic environmental stability.

[0062] (2) The acrylic-polyurethane hybrid resin of the present invention provides an ideal matrix that combines rigidity and elasticity, overcoming the problems of interface fragility and internal stress concentration caused by phase separation in simple physical mixing (Comparative Example 2), and laying a uniform and tough foundation for excellent mechanical properties. On this basis, the multifunctional epoxy resin plays a dual role as a "network reinforcing agent" and a "chemical anchoring agent". The three-dimensional cross-linked network formed during the curing process greatly enhances the cohesive strength and deformation recovery ability of the coating, which is the key to obtaining high hardness and stone impact resistance. More importantly, its epoxy groups can react with the active groups on the substrate surface to form a strong covalent bond between the coating and the metal substrate, thereby achieving a long-lasting and strong adhesion that far exceeds physical adsorption and hydrogen bonding. This reinforcement from the inside out makes it difficult for the coating to peel off from the substrate or break even after deformation. Ultimately, it endows the coating with excellent toughness and adhesion while maintaining high hardness, achieving a breakthrough balance of comprehensive mechanical properties.

[0063] (3) The polymer network constructed by the acrylic-polyurethane hybrid resin and multifunctional epoxy resin in this invention has extremely high crosslinking density and continuity, which greatly reduces the porosity and permeability of the coating itself, and chemically blocks the rapid penetration of water, oxygen and corrosive ions. On the other hand, the directional arrangement of flake talc powder inside the coating constructs a tortuous "maze-like" physical barrier, forcing the corrosive medium to take a longer route to reach the substrate surface, thereby significantly delaying the corrosion process and aging reaction (as shown in Comparative Example 4, which lacks this barrier, its moisture resistance decreased and discoloration occurred). At the same time, the excellent adhesion as mentioned above ensures that the protective system will not create new corrosion channels due to cracking or peeling under long-term environmental stress. This synergy of "active defense (anti-permeability) + passive reinforcement (strong adhesion)" constitutes the cornerstone of the long-term protection of the coating. Attached Figure Description

[0064] Figure 1 The infrared spectrum of the acrylic-polyurethane hybrid resin prepared in Example 1 of this invention;

[0065] Figure 2 The images show SEM images of the cross-sections of the water-based intermediate paint prepared in Example 1 and Comparative Example 1 after curing; where (a) is an SEM image of the cross-section of the water-based intermediate paint prepared in Example 1 after curing; and (b) is an SEM image of the cross-section of the water-based intermediate paint prepared in Comparative Example 1 after curing. Detailed Implementation

[0066] To make the present invention easier to understand, specific embodiments are described below to further illustrate the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved herein can be purchased commercially or obtained by known methods.

[0067] It should be noted that in this invention, in descriptions like "EX-614B (Shanghai Meiyingrei)," "EX-614B" refers to the model number, and "Shanghai Meiyingrei" refers to the manufacturer. The same applies to EX-500 (Shanghai Meiyingrei), EX-421 (Shanghai Meiyingrei), SETAQUABE270 (Zhanxin Allnex), HydroTech ZHLPE90 (Zhimo New Materials), Cymel 303LF (Zhanxin Allnex), Cymel 350 (Zhanxin Allnex), Cymel 370 (Zhanxin Allnex), Cymel 327 (Zhanxin Allnex), Cymel 328 (Zhanxin Allnex), Cymel 325 (Zhanxin Allnex), Cymel 380 (Zhanxin Allnex), etc.

[0068] It should be noted that in this invention, BYK-346, BYK-348, TEGO Wet 270, Wet 280, Wet 500, Dynol 607, Surfynol 104E, LAPONITE-RD, Bentone LT, BENTONE DE, Bentone AD, TINUVIN1130, TINUVIN 479-DW, INUVIN 292, TINUVIN 123-DW, BYK 425, Rheolate 299, TEGOViscoPlus 3030, DeuRheo WT-108F, Rheovis AS1130, ACRYSOL ASE-60, ACRYSOL TT-935, etc., all refer to model numbers.

[0069] The following problems exist with water-based intermediate paints on the market: (1) insufficient toughness of the resin system and poor resistance to stress cracking; (2) severe attenuation of interlayer adhesion, especially after aging; (3) weak coating impermeability and stress dissipation ability; and (4) difficulty in balancing overall performance. This invention provides a water-based intermediate paint for automotive bodies that is resistant to high and low temperature cycling, as well as its preparation and application methods. The water-based intermediate paint of this invention maintains excellent adhesion, superior mechanical properties, and long-term durability under extreme high and low temperature and high humidity cycling conditions, and meets environmental protection requirements.

[0070] In some embodiments, an aqueous intermediate paint composition, by weight, comprises the following components: 40-60 parts deionized water; 0.1-1 parts rheology modifier; 0.5-1.5 parts organic amine; 6-16 parts acrylic-polyurethane hybrid resin; 3-10 parts polyester polyol; 1-5 parts cosolvent; 3-10 parts amino resin; 1-6 parts multifunctional epoxy resin; 10-25.2 parts pigment paste; 2-8 parts filler paste; 0.01-1 part catalyst; 0.1-1 part wetting agent; 0.5-1.5 parts ultraviolet absorber; and 0.1-1 part thickener; wherein the acrylic-polyurethane hybrid resin is a core-shell hybrid resin prepared by seed emulsion polymerization; and the polyurethane segments and acrylic segments in the hybrid resin are covalently linked by urethane bonds.

[0071] In some embodiments, the pigment paste includes a white paste and a black paste; in the water-based intermediate paint composition, the white paste is 10-25 parts by mass and the black paste is 0.01-0.2 parts by mass.

[0072] For example, the white paste is at least one of YWT-101 (Matsui) and YWT-106 (Matsui).

[0073] For example, the black paste is at least one of YWT203 (Matsui) and YWT204 (Matsui).

[0074] In some embodiments, the preparation method of the acrylic-polyurethane hybrid resin includes the following steps:

[0075] S1. In the presence of an emulsifier, add a monomer mixture containing butyl acrylate and acrylic acid, stir until homogeneous, add an initiator, and carry out a polymerization reaction at 70-75℃ to obtain a seed emulsion with a particle size of 20-30nm;

[0076] S2. A monomer pre-emulsion containing methacrylic acid, methyl methacrylate, styrene, isooctyl acrylate and hydroxyl acrylate is added dropwise to the seed emulsion along with an initiator, and the mixture is reacted at 80°C to form a core layer emulsion with a particle size of 30-50 nm.

[0077] S3. A polyurethane prepolymer mixture containing isophorone diisocyanate, polyether polyol and diol is added dropwise to the core layer emulsion, and an initiator is added during the polymerization process. The reaction is carried out at 80°C until the characteristic peak of the isocyanate group disappears, forming the acrylic-polyurethane hybrid resin emulsion.

[0078] S4. After cooling, the resin is neutralized with organic amines and filtered to obtain an acrylic-polyurethane hybrid resin.

[0079] In some embodiments, in step S1, the emulsifier comprises sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) in a mass ratio of 1:1.

[0080] For example, in step S1, the initiator is ammonium persulfate (APS).

[0081] In some embodiments, in step S2, the hydroxy acrylate includes at least one of hydroxyethyl acrylate (HEA) and hydroxypropyl acrylate (HPA).

[0082] In some embodiments, in step S2, the monomer preemulsion contains an emulsifier and water.

[0083] In some embodiments, in step S2, the monomer pre-emulsion contains an emulsifier and water, the emulsifier being the same as that used in step S1.

[0084] In some implementations, a catalyst is also required in step S2.

[0085] For example, in step S2, the catalyst is dibutyltin dilaurate (DBTDL).

[0086] In some implementations, a co-solvent needs to be added in step S2.

[0087] For example, in step S2, the cosolvent is propylene glycol methyl ether (PM).

[0088] For example, in step S3, the diol is 1,6-hexanediol (HDO).

[0089] For example, in step S3, the initiator is ammonium persulfate (APS).

[0090] For example, in step S4, the organic amine is N,N-dimethylethanolamine (DMEA).

[0091] In some embodiments, the multifunctional epoxy resin is an epoxy resin with an epoxy equivalent of less than 250 g / eq and a functionality of ≥3.

[0092] For example, the multifunctional epoxy resin is at least one of EX-614B (Shanghai Maingrui), EX-500 (Shanghai Maingrui), and EX-421 (Shanghai Maingrui).

[0093] For example, the polyester polyol is at least one of SETAQUA BE270 (Allnex) and HydroTech ZHLPE90 (Zhimo New Materials).

[0094] For example, the amino resin is at least one of Cymel 303LF (Allnex), Cymel 350 (Allnex), Cymel 370 (Allnex), Cymel 327 (Allnex), Cymel 328 (Allnex), Cymel 325 (Allnex), and Cymel 380 (Allnex).

[0095] For example, the wetting agent is at least one of BYK-346, BYK-348, TEGO Wet 270, Wet 280, Wet 500, Dynol607, and Surfynol 104E.

[0096] In some embodiments, the filler slurry contains talc powder, and the talc powder in the filler slurry has a mass content of 30-40%.

[0097] In some embodiments, the preparation method of the acrylic-polyurethane hybrid resin includes the following steps:

[0098] S1. In the presence of deionized water and an emulsifier, a monomer mixture containing butyl acrylate and acrylic acid is added, stirred until homogeneous, and then an initiator is added. The polymerization reaction is carried out at 70-75℃ to obtain a seed emulsion with a particle size of 20-30 nm. The emulsion comprises, by mass parts: 30-50 parts deionized water; 0.2-0.3 parts emulsifier (composed of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate in a mass ratio of 1:1); 3-8 parts butyl acrylate; 0.5-1.5 parts acrylic acid; and 0.1-0.2 parts initiator.

[0099] S2. A monomer pre-emulsion containing methacrylic acid, methyl methacrylate, styrene, isooctyl acrylate, and hydroxyl-containing acrylate is added dropwise to the seed emulsion along with an initiator, and reacted at 80°C to form a core layer emulsion with a particle size of 30-50 nm; wherein, by mass parts, methacrylic acid is 1-3 parts, methyl methacrylate is 10-20 parts, styrene is 5-15 parts, isooctyl acrylate is 5-15 parts, hydroxyl acrylate (composed of 1-3 parts hydroxyethyl acrylate and 1-3 parts hydroxypropyl acrylate) is 2-6 parts, and the initiator is 0.3-0.4 parts of ammonium persulfate (APS); the monomer pre-emulsion contains 20-40 parts of deionized water and 1.0-2.0 parts of emulsifier (the emulsifier is composed of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate in a mass ratio of 1:1);

[0100] S3. A polyurethane prepolymer mixture comprising isophorone diisocyanate, polyether polyol, and diol is dropwise added to the core layer emulsion, and an initiator is added during polymerization. The reaction is carried out at 80°C until the characteristic peak of the isocyanate group disappears, forming the acrylic-polyurethane hybrid resin emulsion; wherein, by mass parts, isophorone diisocyanate is 5-15 parts; polyether polyol is 15-30 parts; diol is 0.5-2 parts of 1,6-hexanediol; and initiator is 0.2 parts of ammonium persulfate (APS).

[0101] S4. After cooling, the mixture is neutralized with an organic amine and filtered to obtain an acrylic-polyurethane hybrid resin. The organic amine comprises 0.5-0.9 parts by weight.

[0102] In some embodiments, the filler slurry is made of the following components by mass percentage: 55-65% deionized water, 0.5-1.5% organic amine, 0.5-1.5% activator, 2.0-3.0% dispersant, and 30-40% talc.

[0103] In some embodiments, the method for preparing the filler slurry includes the following steps:

[0104] The first part of deionized water and organic amine are mixed at low speed and room temperature for 5-10 minutes. Then, the activator is added while stirring at medium speed, and the mixture is stirred until homogeneous. Next, the dispersant is added and stirred at medium speed and room temperature until homogeneous. Then, talc powder is added and stirred at medium speed and room temperature until homogeneous. The mixture is then ground (zirconium beads 0.6-1.0 μm, temperature ≤50℃) until the fineness is ≤10 μm, and then grinding is stopped. The second part of deionized water is added to adjust the viscosity to 150-300 cp. The mixture is then filtered and set aside for use. The first and second parts of deionized water constitute the total deionized water.

[0105] In some implementations, the total deionized water comprises, by mass percentage, 85-95% of the first portion and 5-15% of the second portion.

[0106] For example, the low speed mentioned above is 300-500 rpm; and / or, the medium speed mentioned above is 500-800 rpm.

[0107] In some embodiments, the rheology modifier is selected from at least one of synthetic lithium saponite, organically modified bentonite, lithium montmorillonite, and attapulgite; and / or,

[0108] The co-solvent is selected from at least one of n-butanol, isooctyl alcohol, propylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol monobutyl ether, dipropylene glycol methyl ether, dipropylene glycol butyl ether, and 3-methoxy-3-methyl-1-butanol; and / or,

[0109] The catalyst is a sulfonic acid catalyst.

[0110] For example, synthetic lithium saponite is synthetic lithium saponite LAPONITE-RD; organic modified bentonite is organic modified bentonite Bentone LT; lithium montmorillonite is lithium montmorillonite BENTONE DE; and attapulgite is attapulgite MIN-U-GEL 400.

[0111] In some embodiments, the sulfonic acid catalyst is at least one of p-toluenesulfonic acid, dinonylnaphthalenedisulfonic acid, and dodecylbenzenesulfonic acid.

[0112] In some embodiments, the organic amine is at least one of N,N-dimethylethanolamine (DMEA), 2-amino-2-methyl-1-propanol (AMP), and dimethylmethoxypropylamine.

[0113] For example, 2-amino-2-methyl-1-propanol is a 95% aqueous solution, namely AMP-95.

[0114] In some embodiments, the ultraviolet absorber is at least one of benzotriazole ultraviolet absorbers, triazine ultraviolet absorbers, and hindered amine ultraviolet absorbers.

[0115] For example, a benzotriazole UV absorber is TINUVIN 1130.

[0116] For example, a triazine-based ultraviolet absorber is TINUVIN 479-DW.

[0117] For example, the hindered amine ultraviolet absorber is at least one of TINUVIN 292 and TINUVIN 123-DW.

[0118] In some embodiments, the thickener is at least one of polyurethane associative thickeners, alkali-swellable thickeners, etc.

[0119] For example, the polyurethane associative thickener is at least one of BYK 425, Rheolate 299, TEGO ViscoPlus3030, and DeuRheo WT-108F.

[0120] For example, the alkali-swellable thickener is at least one of Rheovis AS1130, ACRYSOL ASE-60, and ACRYSOL TT-935.

[0121] In some embodiments, the present invention also provides a water-based intermediate paint for automotive bodies that is resistant to high and low temperature cycling, which is prepared from any of the water-based intermediate paint compositions described above.

[0122] In some embodiments, a method for preparing a water-based intermediate paint for automotive bodies that is resistant to high and low temperature cycling includes the following steps:

[0123] (1) Deionized water, rheology modifier and first part organic amine are mixed to obtain a first mixture; wherein the organic amine is composed of a first part organic amine and a second part organic amine;

[0124] (2) Add acrylic-polyurethane hybrid resin and polyester polyol to the first mixture, mix evenly, then add cosolvent, amino resin and multifunctional epoxy resin, mix evenly to obtain the second mixture;

[0125] (3) Add pigment paste, filler paste, catalyst, wetting agent and ultraviolet light absorber to the second mixture, mix evenly to obtain the product;

[0126] (4) Adjust the pH of the product obtained in step (3) to 7.8-8.8 with the organic amine from the second part;

[0127] (5) Add a thickener to the product obtained in step (4) and optionally add deionized water to adjust the viscosity of the product to 100-140 cP, filter, and the product is obtained.

[0128] In some implementations, the deionized water in step (1) is 85-95% deionized water; the deionized water in step (5) is 5-15% deionized water.

[0129] In some embodiments, the organic amine comprises, by mass percentage, 85-98% of the first portion and 2-15% of the second portion.

[0130] In some embodiments, the present invention provides a coating method, which includes the following steps: applying the above-mentioned water-based intermediate paint or the water-based intermediate paint prepared by the above-mentioned preparation method to a cleaned electrophoretic plate, and sequentially performing flash drying or pre-drying, applying color paint, applying clear varnish, leveling and baking curing steps to form a composite coating; wherein the baking curing conditions are 140°C for 20-40 minutes.

[0131] In some embodiments, the coating method is a "3C1B" process or a "B1B2" process.

[0132] The following examples and comparative models further illustrate this point.

[0133] Example 1

[0134] (1) A method for preparing a filler slurry, comprising the following steps:

[0135] Based on the total mass of the filler slurry as 100%, 56% deionized water and 0.90% organic amine were mixed at room temperature and low speed (400 rpm) for 8 minutes. Then, 1.00% activator (Lubrizol) was added while stirring at medium speed (600 rpm). After stirring for 90 minutes until homogeneous, 2.60% dispersant (OMG Borchers) was added and stirred at room temperature and medium speed (600 rpm) for 17 minutes until homogeneous. Then, 35% talc was added and stirred at room temperature and medium speed (600 rpm) for 23 minutes until homogeneous. The mixture was then ground (zirconium beads 1.0 μm, temperature 25℃) until the fineness was ≤10 μm and then grinding was stopped. Finally, 4.50% deionized water was added to adjust the viscosity to 200 cp. The mixture was then filtered through a filter screen to obtain the filler slurry.

[0136] (2) A method for preparing an acrylic-polyurethane hybrid resin, comprising the following steps:

[0137] The preparation method of the acrylic-polyurethane hybrid resin includes the following steps:

[0138] S1. In the presence of deionized water and an emulsifier, a monomer mixture containing butyl acrylate and acrylic acid is added, stirred until homogeneous, and then an initiator is added. The polymerization reaction is carried out at 70-75℃ to obtain a seed emulsion with a particle size of 20-30 nm. The emulsion comprises, by mass, 40 parts deionized water; 0.25 parts emulsifier (composed of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate in a mass ratio of 1:1); 5 parts butyl acrylate; 1 part acrylic acid; and 0.15 parts initiator (APS).

[0139] S2. A monomer pre-emulsion containing methacrylic acid, methyl methacrylate, styrene, isooctyl acrylate, and hydroxyl-containing acrylate is added dropwise to the seed emulsion along with an initiator, and reacted at 80°C to form a core layer emulsion with a particle size of 30-50 nm; wherein, by mass parts, methacrylic acid is 1-3 parts, methyl methacrylate is 15 parts, styrene is 10 parts, isooctyl acrylate is 10 parts, hydroxyl acrylate (composed of 2 parts hydroxyethyl acrylate and 2 parts hydroxypropyl acrylate) is 4 parts, and initiator (APS) is 0.35 parts; the monomer pre-emulsion contains 30 parts deionized water and 1.5 parts emulsifier (the emulsifier is composed of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate in a mass ratio of 1:1);

[0140] S3. A mixture of catalyst, co-solvent, and polyurethane prepolymer containing isophorone diisocyanate, polyether polyol, and diol is dropwise added to the core layer emulsion. An initiator is added during polymerization, and the reaction is carried out at 80°C until the characteristic peak of the isocyanate group disappears, forming the acrylic-polyurethane hybrid resin emulsion. The catalyst, by mass parts, is 0.03 parts of dibutyltin dilaurate (DBTDL); the co-solvent is 10 parts of propylene glycol methyl ether (PM); the isophorone diisocyanate is 10 parts; the polyether polyol is 22 parts; the diol is 1 part of 1,6-hexanediol; and the initiator is 0.2 parts of ammonium persulfate (APS).

[0141] S4. After cooling, the resin is neutralized with an organic amine and filtered to obtain an acrylic-polyurethane hybrid resin. The organic amine is 0.8 parts of N,N-dimethylethanolamine (DMEA).

[0142] (3) A method for preparing a water-based intermediate paint for automotive bodies that is resistant to high and low temperature cycling, comprising the following steps:

[0143] 1) According to the mass fractions, 30 parts of deionized water (part 1), 0.3 parts of rheology modifier and 1.2 parts of organic amine (part 1) are mixed to obtain the first mixture;

[0144] 2) Add 10.8 parts of the acrylic-polyurethane hybrid resin and 5.5 parts of polyester polyol prepared above to the first mixture, mix evenly, then add 4.5 parts of cosolvent (propylene glycol methyl ether), 7 parts of amino resin and 2.9 parts of multifunctional epoxy resin, mix evenly to obtain the second mixture;

[0145] 3) Add 17.1 parts of pigment paste (17 parts of white paste and 0.1 parts of black paste), 3.5 parts of the filler paste prepared above, 0.4 parts of catalyst (dibutyltin dilaurate), 1 part of wetting agent and 1.5 parts of ultraviolet light absorber to the second mixture, mix evenly, and obtain the product (detection fineness ≤10μm).

[0146] 4) Adjust the pH of the product obtained in step (3) to 7.8-8.8 with 0.05 parts of organic amine (part 2);

[0147] 5) Add 0.5 parts thickener to the product obtained in step (4) and add 13.75 parts deionized water (second part) to adjust the viscosity of the product to 100-140 cP, filter, and you will get a water-based intermediate paint for car body that is resistant to high and low temperature cycles.

[0148] Among them, the rheology modifier is synthetic lithium saponite LAPONITE-RD; the polyester polyol is SETAQUA BE270 (Allnex); the amino resin is Cymel 303LF (Allnex); the multifunctional epoxy resin is EX-614B (Shanghai Meiyingeri); the white paste is YWT-101 (Matsui); the black paste is YWT203 (Matsui); the wetting agent is BYK-346; the ultraviolet absorber is benzotriazole ultraviolet absorber TINUVIN 1130; and the thickener is alkali-swellable Rheovis AS 1130.

[0149] Example 2

[0150] The difference between this embodiment and Example 1 is only in the composition of the water-based intermediate paint, namely: 30 parts deionized water (part 1); 0.3 parts rheology modifier; 1.2 parts organic amine (part 1); 6.8 parts acrylic-polyurethane hybrid resin; 5.5 parts polyester polyol; 4.5 parts cosolvent; 7 parts amino resin; 2.9 parts multifunctional epoxy resin; 17.1 parts pigment paste; 3.5 parts filler paste; 0.4 parts catalyst; 1 part wetting agent; 1.5 parts ultraviolet absorber; 0.05 parts organic amine (part 2); 0.5 parts thickener; and 13.75 parts deionized water (part 2). Other steps and parameters are the same as in Example 1. See Table 1 for a detailed comparison.

[0151] Example 3

[0152] The difference between this embodiment and Example 1 is only in the composition of the water-based intermediate paint, namely: 30 parts deionized water (part 1); 0.3 parts rheology modifier; 1.2 parts organic amine (part 1); 14.8 parts acrylic-polyurethane hybrid resin; 5.5 parts polyester polyol; 4.5 parts cosolvent; 7 parts amino resin; 2.9 parts multifunctional epoxy resin; 17.1 parts pigment paste; 3.5 parts filler paste; 0.4 parts catalyst; 1 part wetting agent; 1.5 parts ultraviolet absorber; 0.05 parts organic amine (part 2); 0.5 parts thickener; and 13.75 parts deionized water (part 2). Other steps and parameters are the same as in Example 1. See Table 1 for a detailed comparison.

[0153] Example 4

[0154] The difference between this embodiment and Example 1 is only in the composition of the water-based intermediate paint, namely: 30 parts deionized water (part 1); 0.3 parts rheology modifier; 1.2 parts organic amine (part 1); 10.8 parts acrylic-polyurethane hybrid resin; 5.5 parts polyester polyol; 4.5 parts cosolvent; 7 parts amino resin; 1.3 parts multifunctional epoxy resin; 17.1 parts pigment paste; 3.5 parts filler paste; 0.4 parts catalyst; 1 part wetting agent; 1.5 parts ultraviolet absorber; 0.05 parts organic amine (part 2); 0.5 parts thickener; and 13.75 parts deionized water (part 2). Other steps and parameters are the same as in Example 1. See Table 1 for a detailed comparison.

[0155] Example 5

[0156] The difference between this embodiment and Example 1 is only in the composition of the water-based intermediate paint, namely: 30 parts deionized water (part 1); 0.3 parts rheology modifier; 1.2 parts organic amine (part 1); 10.8 parts acrylic-polyurethane hybrid resin; 5.5 parts polyester polyol; 4.5 parts cosolvent; 7 parts amino resin; 4.5 parts multifunctional epoxy resin; 17.1 parts pigment paste; 3.5 parts filler paste; 0.4 parts catalyst; 1 part wetting agent; 1.5 parts ultraviolet absorber; 0.05 parts organic amine (part 2); 0.5 parts thickener; and 13.75 parts deionized water (part 2). Other steps and parameters are the same as in Example 1. See Table 1 for a detailed comparison.

[0157] Table 1:

[0158]

[0159] Example 6

[0160] The difference between this embodiment and Example 1 is only in the composition of the water-based intermediate paint, namely: 30 parts deionized water (part 1); 0.3 parts rheology modifier; 1.2 parts organic amine (part 1); 10.8 parts acrylic-polyurethane hybrid resin; 5.5 parts polyester polyol; 4.5 parts cosolvent; 7 parts amino resin; 2.9 parts multifunctional epoxy resin; 17.1 parts pigment paste; 1.5 parts filler paste; 0.4 parts catalyst; 1 part wetting agent; 1.5 parts ultraviolet absorber; 0.05 parts organic amine (part 2); 0.5 parts thickener; and 13.75 parts deionized water (part 2). Other steps and parameters are the same as in Example 1. See Table 1 for a detailed comparison.

[0161] Example 7

[0162] The difference between this embodiment and Example 1 is only in the composition of the water-based intermediate paint, namely: 30 parts deionized water (part 1); 0.3 parts rheology modifier; 1.2 parts organic amine (part 1); 10.8 parts acrylic-polyurethane hybrid resin; 5.5 parts polyester polyol; 4.5 parts cosolvent; 7 parts amino resin; 2.9 parts multifunctional epoxy resin; 17.1 parts pigment paste; 5.5 parts filler paste; 0.4 parts catalyst; 1 part wetting agent; 1.5 parts ultraviolet absorber; 0.05 parts organic amine (part 2); 0.5 parts thickener; and 13.75 parts deionized water (part 2). Other steps and parameters are the same as in Example 1. See Table 1 for a detailed comparison.

[0163] Comparative Example 1

[0164] The difference between this comparative example and Example 1 is that 10.8 parts of acrylic-polyurethane hybrid resin were replaced with 10.8 parts of acrylic emulsion (Wantipro 0678). Other steps and parameters were the same as in Example 1. See Table 2 for a detailed comparison.

[0165] Table 2:

[0166]

[0167] It should be noted that the "-" in Table 2 indicates that it is not added.

[0168] Comparative Example 2

[0169] The difference between this comparative example and Example 1 is that 10.8 parts of acrylic-polyurethane hybrid resin were replaced with 5.8 parts of acrylic emulsion (Wantipro 0678) and 5 parts of polyurethane dispersion (Bayhydrol UH 2606). Other steps and parameters were the same as in Example 1. See Table 2 for a detailed comparison.

[0170] Comparative Example 3

[0171] The difference between this comparative example and Example 1 is that no multifunctional epoxy resin was added. Other steps and parameters are the same as in Example 1. See Table 2 for a detailed comparison.

[0172] Comparative Example 4

[0173] The difference between this comparative example and Example 1 is that no filler slurry was added. Other steps and parameters are the same as in Example 1. See Table 2 for a detailed comparison.

[0174] Performance testing and results analysis:

[0175] The acrylic-polyurethane hybrid resin prepared in Example 1 was subjected to infrared spectroscopy analysis, and the results are as follows: Figure 1 As shown. By Figure 1 It can be seen that at ~3390cm -1A broad and asymmetric strong peak exists at ~1727 cm⁻¹, which is a superposition of the stretching vibrations of -OH and -NH; -1 The strong peak at 1623 cm⁻¹ is due to the C=O stretching vibration of the carbamate, which is affected by hydrogen bonding; -1 The strong peak at that point is the amide II band of the carbamate, which shifts to a higher wavenumber of 1623 cm⁻¹ due to strong hydrogen bonding. -1 1238cm -1 The strong peak at that point is the ether bond-COC- stretching vibration peak. This indicates that the polyurethane and acrylic segments in this hybrid resin are covalently linked by urethane bonds.

[0176] The cross-sections of the cured water-based intermediate paints prepared in Example 1 and Comparative Example 1 were analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the cross-section of the water-based intermediate paint in Example 1 after curing is extremely uniform, dense and homogeneous, while the cross-section of the water-based intermediate paint in Comparative Example 1 after curing is uneven, with clusters, loose and grooves formed due to phase separation.

[0177] The water-based intermediate paints prepared in Examples 1-7 and Comparative Examples 1-4 were electrostatically sprayed onto the substrates using the 3C1B and B1B2 coating methods. The results are shown in Table 3. Specifically:

[0178] B1B2 process (ambient temperature 22-25℃ / humidity 60-70%): Clean the test panel - apply water-based intermediate paint by robot - flash dry for 2 minutes - apply color paint by robot - dehydrate in constant temperature oven at 80℃ for 5 minutes - apply clear varnish by robot - level for 10 minutes - keep in constant temperature oven at 140℃ for 30 minutes - cool to room temperature.

[0179] 3C1B process (ambient temperature 22-25℃ / humidity 60-70%): Clean the test panel - apply water-based intermediate paint by robot - dehydrate in constant temperature oven at 80℃ for 5 minutes - apply color paint by robot - dehydrate in constant temperature oven at 80℃ for 5 minutes - apply clear varnish by robot - leveling for 10 minutes - maintain at constant temperature oven at 140℃ for 30 minutes - cool to room temperature.

[0180] Table 3:

[0181]

[0182] As shown in Table 3, when the 3C1B process was used for coating, the appearance of the coated products of Examples 1-7 and Comparative Examples 2-4 was normal. When the paint was sprayed on Comparative Example 1, the edge of the test panel showed the substrate. When the B1B2 process was used for coating, the appearance of the coated products of Examples 1-7 and Comparative Examples 1-4 was normal.

[0183] The water-based intermediate paints prepared in Examples 1-7 and Comparative Examples 1-4 were subjected to routine physical property tests, and the results are shown in Table 4 below.

[0184] As shown in Table 4, Comparative Example 1 exhibits the worst impact resistance (35cm) and cupping value (4.2mm), indicating high brittleness and poor deformation resistance in the intermediate paint film. Furthermore, its cross-cut adhesion is grade 1 (worst) and recoating adhesion is grade 2 (worst), suggesting poor stress matching between the rigid resin, substrate, and topcoat, resulting in weak interfacial bonding. Comparative Example 2 also shows lower impact resistance (48cm) and cupping value (5.0mm) compared to most examples, with slightly wrinkled water resistance and only grade 1 recoating adhesion, demonstrating that physically incompatible interfaces remain a performance bottleneck. In contrast, all embodiments of this invention demonstrate excellent impact resistance (≥48cm) and cupping value (≥5.0mm). Example 1, in particular, achieves a high level of combination of 50cm impact resistance and a 5.4mm cupping value, proving that the intermediate paint film of this invention possesses both high toughness and good ductility. Comparative Example 1 demonstrates the inherent defects of a single rigid resin; Comparative Example 2 demonstrates that simple physical mixing cannot achieve a fundamental improvement in performance; while this invention, through chemical hybridization, covalently bonds flexible polyurethane segments (providing toughness) and rigid acrylic segments (providing hardness), forming a uniform "rigid-tough" network at the molecular scale. This fundamentally endows the intermediate coating with excellent bulk strength and toughness (high impact resistance, high cupping), and provides a robust yet flexible matrix for subsequent adhesion and water resistance. Example 3 (highest resin content) showed a slight decrease in pencil hardness to B, but a cupping value as high as 6.0 mm, further confirming that the "hard-flexible" balance can be flexibly adjusted within the system of this invention by modifying the components.

[0185] Table 4:

[0186]

[0187] Furthermore, as shown in Table 4, the recoating adhesion of Comparative Example 1 (lacking a tough substrate) and Comparative Example 3 (lacking epoxy crosslinking) was only grade 2 and grade 1, respectively, significantly worse than the grade 0 of the Example. This indicates that without a tough substrate or strong interlayer chemical crosslinking, the overall adhesion of the coating system will decrease. The water resistance test results of Comparative Example 1 (pure acrylic), Comparative Example 3 (without multifunctional epoxy resin), and Comparative Example 4 (without filler slurry) were "wrinkled," "wrinkled," and "whitened," respectively, all showing obvious defects. Comparative Example 2 (physical blend) only showed "slight wrinkling." Except for a few formulation adjustments (such as "slight whitening" due to slightly less filler in Example 6), the water resistance of most examples of this invention was "no abnormalities." Examples 1, 2, 3, and 7 all performed perfectly.

[0188] The water-based intermediate paints prepared in Examples 1-7 and Comparative Examples 1-4 were coated using the B1B2 process described above. A climate cycling test was then conducted, specifically: the temperature was increased from room temperature to 85°C and humidity to 80% over 1 hour; this was maintained at 85°C and 80% humidity for 4 hours; the temperature was decreased from 85°C to -40°C over 2 hours; this was maintained at -40°C for 4 hours; and the temperature was increased to 23°C over 1 hour. (This constitutes one cycle, and a total of 20 cycles were performed.) After the time was up, the test panels were removed, and the appearance, cross-cut test, and stone impact resistance were tested. The results are shown in Table 5.

[0189] Table 5:

[0190]

[0191] As shown in Table 5, after 20 severe climate cycles, the coatings obtained in Examples 1-7 of this invention maintained an "abnormal" appearance, without any fatal defects such as cracking or peeling. Their key protective properties—adhesion (cross-cut test) and mechanical impact resistance (stone impact resistance)—remained at excellent or good levels (cross-cut test grade 0-1, stone impact resistance grade 0.5-2). In contrast, Comparative Examples 1-4 all showed severe or obvious failures, specifically: Comparative Example 1 showed obvious cracking, Comparative Examples 2 and 3 showed blistering, and Comparative Example 4 showed discoloration and cracking. Their functional performance also deteriorated sharply, with adhesion and stone impact resistance dropping to unacceptable levels (cross-cut test grade 1-3, stone impact resistance grade 2-4).

[0192] The water-based intermediate paints prepared in Example 1 and Comparative Examples 1-4 were coated using the B1B2 process described above to obtain the actual vehicle coating system (electrophoretic primer + intermediate paint + color paint + clear coat). The composite coating properties were tested, and the results are shown in Table 6 below.

[0193] Table 6:

[0194]

[0195] As shown in Table 6, the impact resistance of Example 1 of the present invention is 45cm, which is significantly higher than that of Comparative Example 1 (30cm). The higher impact toughness means that the coating is less likely to develop microcracks under external forces such as stone impacts, which is the first line of defense for long-term corrosion protection. Although the corrosion at the scratch of Comparative Example 3 (without multifunctional epoxy resin) is 1.9mm, its water resistance and moisture resistance both show "wrinkling". More importantly, it shows "microbubbles" and decreased adhesion (level 2) in the weathering cycle (system); while Example 1 maintains excellent salt spray resistance (1.2mm), while its water resistance and moisture resistance are normal, and there are no bubbles and the adhesion is level 0 after weathering. Comparative Example 4 (unfilled slurry) showed acceptable salt spray resistance (1.6 mm) and initial appearance, but "micro-cracks" appeared after weather alteration, stone impact resistance decreased (2.0 grade), and moisture resistance showed "discoloration". In contrast, Example 1, with the addition of filler slurry, not only had better salt spray resistance (1.2 mm), but also completely overcame the aforementioned problems of appearance and performance degradation after long-term aging.

[0196] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A water-based intermediate paint for automotive bodies that is resistant to weather cycling, characterized in that, The water-based intermediate paint comprises the following components by weight: Deionized water: 40-60 parts; Rheology modifier: 0.1-1 part; Organic amines: 0.5-1.5 parts; Acrylic-polyurethane hybrid resin: 6-16 parts; Polyester polyol: 3-10 parts; Cosolvent: 1-5 parts; Amino resin: 3-10 parts; Multifunctional epoxy resin: 1-6 parts; Pigment paste: 10-25.2 parts; Filler slurry: 2-8 parts; Catalyst: 0.01-1 part; Wetting agent: 0.1-1 part; Ultraviolet light absorber: 0.5-1.5 parts; Thickener: 0.1-1 part; The filler slurry contains talc powder, and the talc powder content in the filler slurry is 30-40% by mass; the multifunctional epoxy resin is an epoxy resin with an epoxy equivalent of less than 250 g / eq and a functionality of ≥3; the acrylic-polyurethane hybrid resin is a core-shell structured hybrid resin prepared by seed emulsion polymerization; the polyurethane segments and acrylic segments in the hybrid resin are covalently linked by urethane bonds; the preparation method of the acrylic-polyurethane hybrid resin includes the following steps: S1. In the presence of an emulsifier, add a monomer mixture containing butyl acrylate and acrylic acid, stir until homogeneous, add an initiator, and carry out a polymerization reaction at 70-75℃ to obtain a seed emulsion with a particle size of 20-30nm; S2. A monomer pre-emulsion containing methacrylic acid, methyl methacrylate, styrene, isooctyl acrylate and hydroxyl acrylate is added dropwise to the seed emulsion along with an initiator, and the mixture is reacted at 80°C to form a core layer emulsion with a particle size of 30-50 nm. S3. A polyurethane prepolymer mixture containing isophorone diisocyanate, polyether polyol and diol is added dropwise to the core layer emulsion, and an initiator is added during the polymerization process. The reaction is carried out at 80°C until the characteristic peak of the isocyanate group disappears, forming the acrylic-polyurethane hybrid resin emulsion. S4. After cooling, the resin is neutralized with organic amine and filtered to obtain an acrylic-polyurethane hybrid resin; Under the conditions of coating, baking, and curing, the epoxy groups of the multifunctional epoxy resin react with the active groups in the acrylic-polyurethane hybrid resin, polyester polyol, and amino resin to construct a composite reinforcing network inside the intermediate paint, and react with the active groups of the primer and / or topcoat to form chemical bonds; the baking and curing conditions are to maintain at 140°C for 20-40 minutes.

2. The water-based intermediate paint for automotive bodies resistant to weather cycling according to claim 1, characterized in that, The filler slurry is made of the following components by mass percentage: 55-65% deionized water, 0.5-1.5% organic amine, 0.5-1.5% activator, 2.0-3.0% dispersant, and 30-40% talc.

3. The water-based intermediate paint for automotive bodies resistant to weather cycling according to claim 1 or 2, characterized in that, The rheology modifier is selected from at least one of synthetic lithium saponite, organically modified bentonite, lithium montmorillonite, and attapulgite; and / or, The co-solvent is selected from at least one of n-butanol, isooctyl alcohol, propylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol monobutyl ether, dipropylene glycol methyl ether, dipropylene glycol butyl ether, and 3-methoxy-3-methyl-1-butanol; and / or, The catalyst is a sulfonic acid catalyst.

4. The method for preparing a water-based intermediate paint for automotive bodies resistant to weather cycling according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Deionized water, rheology modifier and first part organic amine are mixed to obtain a first mixture; wherein the organic amine is composed of a first part organic amine and a second part organic amine; (2) Add acrylic-polyurethane hybrid resin and polyester polyol to the first mixture, mix evenly, then add cosolvent, amino resin and multifunctional epoxy resin, mix evenly to obtain the second mixture; (3) Add pigment paste, filler paste, catalyst, wetting agent and ultraviolet light absorber to the second mixture, mix evenly to obtain the product; (4) Adjust the pH of the product obtained in step (3) to 7.8-8.8 with the organic amine from the second part; (5) Add a thickener to the product obtained in step (4) and optionally add deionized water to adjust the viscosity of the product to 100-140 cP, filter, and the product is obtained.

5. A coating method, characterized in that, The coating method includes the following steps: applying the water-based intermediate paint for vehicle body with weather-resistant alternating cycle as described in any one of claims 1-3 or the water-based intermediate paint for vehicle body with weather-resistant alternating cycle prepared by the preparation method described in claim 4 to a cleaned electrophoretic plate, and sequentially performing flash drying or pre-drying, applying color paint, applying clear varnish, leveling and baking curing steps to form a composite coating; wherein the baking curing conditions are 140°C for 20-40 minutes.

6. The coating method according to claim 5, characterized in that, The coating method is either the "3C1B" process or the "B1B2" process.

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