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CN-121673932-B - High-low temperature cycle resistant water-based intermediate paint for vehicle body and preparation and coating methods thereof

CN121673932BCN 121673932 BCN121673932 BCN 121673932BCN-121673932-B

Abstract

The invention belongs to the technical field of coatings, and particularly discloses a high-low temperature cycle resistant water-based intermediate paint for a vehicle body and a preparation and coating method thereof. The aqueous intermediate paint is prepared from the following aqueous intermediate paint composition. The water-based intermediate paint composition comprises, by mass, 40-60 parts of deionized water, 0.1-1 part of a rheological agent, 0.5-1.5 parts of organic amine, 6-16 parts of acrylic acid-polyurethane hybrid resin, 3-10 parts of polyester polyol, 1-5 parts of a cosolvent, 3-10 parts of amino resin, 1-6 parts of polyfunctional epoxy resin, 10-25.2 parts of pigment slurry, 2-8 parts of filler slurry, 0.01-1 part of a catalyst, 0.1-1 part of a wetting agent, 0.5-1.5 parts of an ultraviolet light absorber and 0.1-1 part of a thickener. The water-based intermediate paint can still keep excellent adhesive force, excellent mechanical property and long-term durability under the extremely high and low temperature and high humidity circulating condition.

Inventors

  • ZHANG WEI
  • XIANG BO
  • YANG KANG
  • GE HUAFEI
  • ZENG YI
  • LIU YALI

Assignees

  • 湖南松井先进表面处理与功能涂层研究院有限公司

Dates

Publication Date
20260508
Application Date
20260209

Claims (6)

  1. 1. The weather-resistant alternating-cycle water-based intermediate paint for the vehicle body is characterized by comprising the following components in parts by weight: 40-60 parts of deionized water; 0.1-1 part of rheological agent; 0.5-1.5 parts of organic amine; 6-16 parts of acrylic acid-polyurethane hybrid resin; 3-10 parts of polyester polyol; 1-5 parts of cosolvent; 3-10 parts of amino resin; 1-6 parts of polyfunctional epoxy resin; Pigment paste 10-25.2 parts; 2-8 parts of filler slurry; 0.01-1 part of catalyst; 0.1-1 part of wetting agent; 0.5-1.5 parts of ultraviolet light absorber; 0.1-1 part of thickener; The filler slurry comprises talcum powder, wherein the mass content of the talcum powder in the filler slurry is 30-40%, the polyfunctional epoxy resin is epoxy resin with the epoxy equivalent of less than 250g/eq and the functionality of more than or equal to 3, the acrylic acid-polyurethane hybrid resin is hybrid resin with a core-shell structure prepared by a seed emulsion polymerization method, a polyurethane chain segment in the hybrid resin is covalently connected with an acrylic acid chain segment through a carbamate bond, and the preparation method of the acrylic acid-polyurethane hybrid resin comprises the following steps: S1, adding a monomer mixture containing butyl acrylate and acrylic acid in the presence of an emulsifier, uniformly stirring, adding an initiator, and performing polymerization reaction at 70-75 ℃ to obtain seed emulsion with the particle size of 20-30 nm; S2, monomer pre-emulsion containing methacrylic acid, methyl methacrylate, styrene, isooctyl acrylate and hydroxyl acrylate is added into the seed emulsion together with an initiator in a dropwise manner, and the mixture reacts at 80 ℃ to form a nuclear layer emulsion with the particle size of 30-50 nm; S3, dripping a polyurethane prepolymer mixture containing isophorone diisocyanate, polyether polyol and diol into the core layer emulsion, adding an initiator in the polymerization process, and reacting at 80 ℃ until the characteristic peak of isocyanate groups disappears to form the acrylic acid-polyurethane hybrid resin emulsion; s4, neutralizing by adopting organic amine after cooling, and filtering to obtain acrylic acid-polyurethane hybrid resin; under the condition of coating, baking and curing, the epoxy groups of the polyfunctional epoxy resin react with active groups in the acrylic acid-polyurethane hybrid resin, the polyester polyol and the amino resin to construct a composite reinforced network in the intermediate paint, and react with the active groups of the primer and/or the finish paint to form chemical bonding, wherein the condition of baking and curing is that the temperature is 140 ℃ and the temperature is kept for 20-40min.
  2. 2. The weather-resistant circulating water-based intermediate paint for vehicle bodies according to claim 1, wherein the filler slurry is prepared from, by mass, 55-65% of deionized water, 0.5-1.5% of organic amine, 0.5-1.5% of an active agent, 2.0-3.0% of a dispersing agent and 30-40% of talcum powder.
  3. 3. The weather-resistant, alternating cycle water-based intermediate paint for vehicle bodies according to claim 1 or 2, wherein the rheological agent is at least one selected from laponite, organomodified bentonite, hectorite, attapulgite, and/or, The cosolvent is selected from at least one of n-butanol, isooctanol, propylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol monobutyl ether, dipropylene glycol methyl ether, dipropylene glycol butyl ether, 3-methoxy-3-methyl-1-butanol, and/or, The catalyst is a sulfonic acid catalyst.
  4. 4. A process for the preparation of a weather-resistant, cycle-on-cycle water-based intermediate paint for vehicle bodies according to any one of claims 1 to 3, characterized in that it comprises the following steps: (1) Mixing deionized water, a rheological agent and a first part of organic amine to obtain a first mixture, wherein the organic amine consists of the first part of organic amine and a second part of organic amine; (2) Adding acrylic acid-polyurethane hybrid resin and polyester polyol into the first mixture, uniformly mixing, adding cosolvent, amino resin and polyfunctional epoxy resin, and uniformly mixing to obtain a second mixture; (3) Adding pigment slurry, filler slurry, catalyst, wetting agent and ultraviolet light absorber into the second mixture, and uniformly mixing to obtain a product; (4) Adjusting the pH of the product from step (3) to 7.8-8.8 with a second portion of an organic amine; (5) And (3) adding a thickening agent into the product obtained in the step (4), optionally adding deionized water, adjusting the viscosity of the product to 100-140cP, and filtering to obtain the product.
  5. 5. A coating method is characterized by comprising the steps of applying the weather-resistant circulating water-based intermediate paint for a vehicle body or the weather-resistant circulating water-based intermediate paint for a vehicle body, which is prepared by the preparation method according to any one of claims 1-3, to an wiped electrophoretic plate, and sequentially performing the steps of flash drying or pre-drying, shi Tuse paint, varnish application, leveling and baking curing to form a composite coating, wherein the baking curing condition is that the temperature is 140 ℃ and the temperature is kept for 20-40min.
  6. 6. The coating method according to claim 5, wherein the coating method is a "3C1B" process or a "B1B2" process.

Description

High-low temperature cycle resistant water-based intermediate paint for vehicle body and preparation and coating methods thereof Technical Field The invention relates to the technical field of coating application, in particular to high-low temperature cycle resistant water-based intermediate paint for a vehicle body and a preparation and application method thereof. Background Automotive body coating systems are multi-layer composite structures that typically include an electrocoat primer layer, an intermediate paint layer, a pigmented paint layer, and a clear paint layer. The intermediate paint layer plays a key role in the development, and not only needs to provide a flat and smooth substrate for the top paint to ensure the final appearance effect, but also needs to have excellent mechanical properties (such as hardness, flexibility and stone-strike resistance), excellent adhesion (including interlayer adhesion with the lower electrophoretic primer and the upper colored paint) and long-term reliable environmental aging resistance (such as water resistance, corrosion resistance and temperature denaturation resistance). With increasingly stringent global environmental regulations, the reduction of Volatile Organic Compound (VOC) emissions has become an irreversible trend in the automotive coating industry. The water-based paint takes water as a main dispersion medium, has extremely low VOC content and becomes the first choice for replacing the traditional solvent-based paint. In the field of automobile coating, the popularization of compact energy-saving coating processes such as '3C 1B' (three-coating one-baking) and 'B1B 2' (wet-on-wet of primer and primer) and the like also puts higher requirements on the water-based intermediate paint, namely that the water-based intermediate paint must realize the comprehensive performance which is comparable with or even better than that of the traditional solvent-based product under the condition of shorter flow and lower baking temperature. However, automotive body coatings continue to undergo severe and repeated cycling of temperature and humidity during actual use, especially in severe areas with large diurnal temperature differentials, cold climates, or hot and humid conditions. For example, from summer daytime high temperature insolation (up to 80 ℃ or more) to winter night severe cold (up to-40 ℃ or less), and high humidity environments accompanied by rain, snow, condensation. Such "alternating climate cycles" can result in complex thermal and wet expansion/contraction stresses within the coating and between the coating and the dissimilar substrate. When these stresses accumulate and exceed the cohesive strength or interlayer bonding force of the coating itself, the coating may fail, manifesting as micro-cracks, blisters, flaking, light loss, etc., severely impairing the long-term protective performance and appearance value of the vehicle. To address this challenge, the prior art proposes a number of solutions, but each has respective limitations: Patent number CN102086339B discloses a water-based automotive intermediate paint based on water-soluble polyester and emulsion type polyester resin, in combination with specific amino resin, which is focused on stone-impact resistance and baking temperature reduction. The patent No. CN102977752B adopts coconut acid modified polyester resin and acrylic emulsion to be physically blended, so as to improve the appearance and the water resistance. The patent CN109181433a combines aqueous acrylic polyol dispersions with polyurethane dispersions to achieve wet-on-wet and dry-spray wet construction versatility. However, a common disadvantage of such solutions is that the resin components, whether polyester/acrylic or acrylic/polyurethane, are mostly physically mixed. Because of the thermodynamic incompatibility of different resin chain segments, phase separation easily occurs in the curing process, and a microscopically inhomogeneous 'sea-island structure' is formed. Under severe high-low temperature circulation, stress concentration is easy to occur at the interface due to the large difference of thermal expansion coefficients between different phase regions, and the stress concentration becomes a weak point of coating cracking or interlayer stripping, so that the extreme temperature cycle resistance of the coating is insufficient. Patent CN104059533B discloses a coating suitable for a mid-coat subtractive process, which uses a combination of core/shell microgel resin, polyurethane aqueous dispersion and polyester resin. The scheme improves the film coating performance to a certain extent through the morphological design of the resin. However, there is still a lack of strong chemical bonding bridges between the components and there is no involvement of critical crosslinking components that can simultaneously strengthen the network and interfacial adhesion within the coating. Thus, the long-term durability of the coating, part