A thin coating water-based graphene modified phenoxy dip coating paint, a preparation method and application thereof

Abstract

The application relates to the field of coatings, in particular to a thin-coating water-based graphene-modified phenoxy dip-coating paint as well as a preparation method and application thereof. The thin-coating water-based graphene-modified phenoxy dip-coating paint comprises a phenoxy resin polymer, an auxiliary film-forming resin, a composite toughening agent, an antirust pigment, a graphene dispersion slurry, a coloring pigment, a filler, a coating additive, a composite latent curing agent system and water; the graphene dispersion slurry comprises polyethylene glycol monomethyl ether grafted modified graphene and a slow-release type dispersion stabilizer; the composite latent curing agent system comprises dicyandiamide, 2-ethyl-4-methyl imidazole and nano-silica modified amine accelerators in a weight ratio of (2-4):(1-2):(1-2); and the slow-release type dispersion stabilizer is modified urea-formaldehyde resin microspheres. The application completely solves the pain points of traditional electrophoretic paint, such as large pollution, weak corrosion resistance and high energy consumption, and meets the large-scale production requirements of air conditioner compressors.

Description

Technical Field

[0001] This application relates to the field of coatings, and in particular to a thin-film waterborne graphene-modified phenoxy-impregnated coating, its preparation method, and its application. Background Technology

[0002] Currently, the anti-corrosion coating of metal casings such as air conditioner compressors generally adopts the electrophoretic coating process, which involves sandblasting, degreasing and cleaning, phosphating, electrophoretic coating, and drying. This process has the following problems:

[0003] The applicant discovered that the process requires phosphating, which presents problems such as heavy metal pollution, high wastewater treatment costs, and limited corrosion resistance (neutral salt spray test ≤500 hours). Existing water-based coatings, under thin-coat (20–25 μm) conditions, are unable to meet the 1000-hour salt spray protection requirement, and their overall performance, including adhesion, hardness, and chemical resistance, is insufficient.

[0004] Therefore, developing an alternative coating that does not require phosphating, is environmentally friendly and energy-saving, and has excellent corrosion resistance has become an urgent need for the industry. Summary of the Invention

[0005] To address the issues of existing coatings requiring phosphating treatment and exhibiting poor corrosion resistance, this application provides a thin-film waterborne graphene-modified phenoxy-impregnated coating, its preparation method, and its application.

[0006] In the first aspect, this application provides a thin-film waterborne graphene-modified phenoxy impregnation coating, which adopts the following technical solution.

[0007] A thin-coat waterborne graphene-modified phenoxy dip coating comprises the following raw materials in parts by weight: 30-40 parts of phenoxy resin polymer, 10-20 parts of auxiliary film-forming resin, 3-8 parts of composite toughening agent, 10-15 parts of anti-rust pigment, 10-15 parts of graphene dispersion slurry, 2-20 parts of coloring pigment, 10-15 parts of filler, 2-5 parts of coating additives, 4-8 parts of composite latent curing agent system, and 5-15 parts of water;

[0008] The graphene dispersion slurry comprises polyethylene glycol monomethyl ether grafted modified graphene and a slow-release dispersion stabilizer, with a dispersibility D50 ≥ 98%.

[0009] The composite latent curing agent system includes dicyandiamide, 2-ethyl-4-methylimidazolium and nano-silica modified amine accelerator in a weight ratio of (2-4):(1-2):(1-2);

[0010] The sustained-release dispersant stabilizer is a modified urea-formaldehyde resin microsphere.

[0011] By adopting the above technical solutions, polyethylene glycol monomethyl ether graft modification imparts amphiphilicity to graphene, enabling it to be well compatible with phenoxy resin polymers and stably dispersed in aqueous systems. Combined with the continuous dispersion effect of modified urea-formaldehyde resin microspheres, the graphene dispersion degree is ensured to maintain D50≥98% over a long period. The sheet structure forms a dense shielding layer, significantly improving the coating's barrier ability against water vapor and chloride ions, and enhancing its anti-corrosion performance. In the composite latent curing agent system, dicyandiamide and 2-ethyl-4-methylimidazole synergistically reduce the curing activation energy, while nano-silica modified amine accelerators are uniformly dispersed and slowly release their activity, achieving low-temperature rapid curing, reducing drying energy consumption while ensuring complete curing, and increasing the coating's crosslinking density. Phenoxy resin polymers and auxiliary film-forming resins synergistically form a film, and the addition of toughening agents can effectively alleviate the coating's internal stress, improve toughness and impact resistance, while anti-rust pigments and fillers further enhance anti-corrosion and mechanical properties. Ultimately, the coating combines high anti-corrosion performance in thin-coat state, low-temperature curing energy saving, long-term storage stability, and excellent mechanical properties, making it suitable for thin-coat protection needs in various scenarios.

[0012] Furthermore, the phenoxy resin polymer is made by mixing PKHB phenoxy resin and PKHH phenoxy resin at a ratio of 1:(1.2-1.5), and emulsifying with a modified polyether reactive emulsifier, with a solid content of 38-42%.

[0013] By adopting the above technical solution, the low viscosity characteristics of PKHB phenoxy resin and the high viscosity characteristics of PKHH phenoxy resin are mixed at a ratio of 1:(1.2-1.5), which can precisely control the overall viscosity and film-forming properties of the emulsion. The low viscosity PKHB ensures that the emulsion has good fluidity during dip coating, and can evenly wet the surface of the substrate, especially the corners and gaps of complex structural parts, avoiding uneven local coating. The high viscosity PKHH provides skeletal support after film formation, and improves the mechanical strength of the coating, such as hardness and adhesion. The two work together to solve the contradiction of "difficulty in balancing fluidity and strength".

[0014] The modified polyether-type reactive emulsifier contains reactive functional groups. During emulsification, it not only stabilizes and disperses resin particles through hydrophilic groups, but its reactive groups can also chemically bond with the hydroxyl groups of phenoxy resin, "anchoring" the emulsifier molecules to the surface of the resin particles. Compared with conventional non-reactive emulsifiers, this design avoids emulsion stratification caused by emulsifier migration during storage or film formation, while reducing the negative impact of free emulsifiers in the coating on water resistance, such as reducing water penetration rate, and significantly improving emulsion stability and coating resistance to damp heat.

[0015] A solid content of 38-42% is the optimal range for balancing workability and film-forming efficiency. Too low a solid content results in an excessively thin dry film after a single dip coating, requiring multiple coats and increasing energy consumption. Excessive moisture also increases the risk of pinholes during drying. Conversely, too high a solid content leads to a high emulsion viscosity, causing sagging or uneven coating thickness during dip coating. This range ensures a uniform 20-25μm dry film formation in a single dip coating, meeting the requirements for thin coatings. It also provides better compatibility with subsequent graphene dispersions, curing agents, and other components, offering a stable base material for the overall coating's corrosion resistance and low-temperature curing properties.

[0016] Furthermore, the auxiliary film-forming resin includes at least one of an aqueous epoxy-modified phenolic resin and an aqueous blocked isocyanate.

[0017] Furthermore, in the graphene dispersion slurry, the number of graphene layers is 1-2, the sheet diameter is 5-15μm, and the graphene content is 6-8%; the polyethylene glycol monomethyl ether grafted modified graphene is graphene grafted with polyethylene glycol monomethyl ether grafting agent, and the amount of polyethylene glycol monomethyl ether grafting agent added is 30-50% of the weight of graphene.

[0018] By adopting the above technical solution, the 1-2 layer few-layer structure retains the complete six-membered ring crystal structure of graphene, with a high specific surface area and no obvious stacking between layers, which can form a continuous "nanoscale barrier" in the coating, significantly improving the barrier efficiency against corrosive media such as water vapor and Cl⁻; the 5-15μm sheet diameter strikes a balance between "coverage" and "dispersion". If the sheet diameter is too small, the gap between the layer overlaps will increase, and there will be gaps in the shielding network; if the sheet diameter is too large, the increased hydrodynamic resistance will make dispersion difficult. However, the 5-15μm sheet diameter can form a dense shielding layer by overlapping each other, and is also suitable for the high-speed dispersion process of coatings.

[0019] A graphene concentration of 6-8% represents the optimal range for balancing functional density and system compatibility: below 6%, the number of sheets is insufficient to form a complete shielding network, resulting in limited improvement in corrosion resistance; above 8%, the van der Waals forces between graphene sheets are significantly enhanced, making secondary agglomeration likely even after surface modification, leading to abnormally high coating viscosity and affecting dip-coating workability. A concentration of 6-8% ensures ≥5 graphene sheets distributed per square micrometer of coating, forming a barrier without dead zones, while maintaining good coating flowability.

[0020] Polyethylene glycol monomethyl ether grafting agent is added at 30-50% of the graphene mass. Grafting is performed on the graphene surface with ultrasonic assistance. A grafting amount of 30% is the "minimum effective density," ensuring sufficient MPEG segments cover each graphene sheet surface. The oleophilic ends (polyether chains) form hydrogen bonds with the hydroxyl groups of the phenoxy resin, while the hydrophilic ends (ether bonds) are compatible with the aqueous system, addressing the issue of graphene's "hydrophobic and easily agglomerated" nature at the molecular level. A grafting amount not exceeding 50% avoids excessive MPEG forming "steric hindrance" between sheets. If the grafting amount is too high, excessively long MPEG chains will hinder the tight overlap of graphene sheets, thus reducing the shielding effect. A grafting amount of 30-50% achieves stable dispersion of graphene in the phenoxy resin polymer for more than 6 months while ensuring the compactness of the sheet overlap, ultimately improving the coating's resistance to neutral salt spray compared to unmodified graphene.

[0021] Furthermore, the auxiliary film-forming resin comprises an aqueous epoxy-modified phenolic resin and an aqueous blocked isocyanate in a weight ratio of (5-8):(8-12).

[0022] By adopting the above technical solution, the waterborne epoxy-modified phenolic resin and waterborne blocked isocyanate in the auxiliary film-forming resin work synergistically in a ratio of (5-8):(8-12) to achieve multiple performance optimizations through structural complementarity and reaction synergy: the waterborne epoxy-modified phenolic resin combines the high thermal stability and corrosion resistance of phenolic resin with the high adhesion and flexibility of epoxy resin. The phenolic hydroxyl and epoxy groups in its molecule can form hydrogen bonds and weak crosslinks with the hydroxyl groups of phenoxy resin, providing initial film-forming strength and substrate anchoring force for the coating; the waterborne blocked isocyanate exists stably in a blocked state at room temperature, avoiding premature reaction with water or hydroxyl groups. During low-temperature curing (75-85℃), it unblocks and releases isocyanate groups, which can chemically react with the hydroxyl groups of phenoxy resin, the hydroxyl groups and amino groups of epoxy-modified phenolic resin to form a three-dimensional crosslinked network structure, significantly improving the crosslinking density and chemical resistance of the coating.

[0023] In terms of proportion design, the waterborne closed isocyanate accounts for a slightly higher proportion to ensure sufficient crosslinking sites and avoid poor water resistance and insufficient hardness of the coating due to insufficient crosslinking. The proportion of waterborne epoxy-modified phenolic resin is moderate, which enhances the heat resistance of the coating through a rigid skeleton without causing embrittlement due to excessive amount. Both have excellent compatibility with phenoxy emulsion base material, jointly constructing a "initial anchoring-later crosslinking" film-forming system, so that the coating still has high adhesion, salt spray resistance and damp heat resistance in the thin coating state, which is suitable for the long-term protection needs of complex substrates.

[0024] Furthermore, the composite toughening agent comprises liquid nitrile rubber and elastic saturated polyester resin in a weight ratio of 1:0.8.

[0025] By adopting the above technical solution, the liquid nitrile rubber and elastic saturated polyester resin in the composite toughening agent work synergistically in a ratio of 1:0.8, and the coating toughness is effectively improved through structural complementarity.

[0026] Liquid nitrile rubber (NBR) possesses a low glass transition temperature and highly elastic flexible segments, forming "elastic islands" within the coating's crosslinking network. This effectively absorbs external impact energy and alleviates stress concentration. Elastic saturated polyester resin, with its polar ester groups, forms hydrogen bonds with the hydroxyl groups of phenoxy resin and epoxy-modified phenolic resin, enhancing the compatibility between the toughening agent and the base material and avoiding the "phase separation" problem that might occur when NBR is used alone. In terms of proportioning, NBR is slightly dominant to ensure sufficient elasticity, while the appropriate proportion of polyester resin balances compatibility and toughness. This allows the composite toughening agent to be uniformly dispersed in the coating system and synergistically enhance the coating's impact strength and flexibility, solving the problem of embrittlement in high-crosslink density coatings without affecting the coating's salt spray resistance and adhesion. This makes it suitable for applications such as air conditioning compressors and motor housings that require long-term dynamic stress.

[0027] Furthermore, the method for preparing the modified urea-formaldehyde resin microspheres is as follows:

[0028] 1) Prepolymer preparation

[0029] Triethanolamine was added to formaldehyde aqueous solution to adjust pH to 8-9, the temperature was raised to 70-80℃, urea was added in two portions, and the mixture was kept warm and stirred for 1 hour to obtain transparent hydroxymethylurea prepolymer.

[0030] 2) Emulsification and Encapsulation

[0031] Cool to 50℃, add deionized water and composite emulsifier, stir at 2500rpm for 10-15min; add polycarboxylate dispersant, continue stirring for 20min; slowly drop in prepolymer, keep stirring at 2500rpm for 30min to form nanodroplets with a particle size of 130-170nm.

[0032] 3) Polymerization and curing

[0033] Add formic acid to adjust the pH to 4-5, heat to 75-85℃, keep warm and stir for 2 hours, and the droplets will solidify into microspheres with a particle size of 100-200nm.

[0034] 4) Surface modification and drying

[0035] Cool to 75℃, add polyethylene glycol and stir for 1 hour; adjust pH to neutral, centrifuge, wash, freeze dry to obtain white modified urea-formaldehyde resin microspheres.

[0036] By adopting the above technical solution, the preparation method of the modified urea-formaldehyde resin microspheres achieves long-term stabilizing effect of the microspheres on the dispersion of graphene through multi-step synergistic regulation.

[0037] Prepolymer preparation provides a stable urea-formaldehyde resin framework for the microspheres. In the emulsification and encapsulation stage, high-speed stirring at 2500 rpm combined with a composite emulsifier precisely controls the nanodroplet size to 130-170 nm, ensuring uniform encapsulation of the polycarboxylate dispersant and providing a carrier for subsequent sustained release. In the polymerization and curing stage, pH (4-5) and temperature (75-85℃) are controlled to solidify the droplets into 100-200 nm microspheres, forming a dense structure to prevent premature dispersant leakage. Surface modification introduces polyethylene glycol to enhance hydrophilicity and compatibility with phenoxy resin polymers, preventing microsphere aggregation. Centrifugal washing and freeze-drying ensure the purity and dispersibility of the microspheres. The resulting microspheres can maintain high graphene dispersion for over 6 months through sustained release of the polycarboxylate dispersant and are highly compatible with coating systems, providing stable support for the long-term anti-corrosion performance of the coating.

[0038] Secondly, this application provides a method for preparing a thin-film waterborne graphene-modified phenoxy dip coating, which adopts the following technical solution.

[0039] A method for preparing a thin-coat waterborne graphene-modified phenoxy dip-coating coating includes the following steps:

[0040] While stirring, phenoxy resin polymer, auxiliary film-forming resin, composite toughening agent, composite latent curing agent system, and graphene dispersion slurry are added in sequence. After mixing, anti-rust pigment, coloring pigment, filler 10-15, coating additives, and water are added. After dispersion, the mixture is ground to a fineness of ≤20μm to obtain the coating.

[0041] Furthermore, when adding the composite latent curing agent system, the stirring temperature should be controlled to not exceed 40℃.

[0042] By adopting the above technical solution, this preparation method achieves efficient synergy and performance optimization of the coating components through scientific feeding sequence and temperature control: Phenoxy resin polymer, auxiliary film-forming resin, and composite toughening agent are added sequentially to first construct a stable film-forming resin system, providing a uniform and continuous phase for the subsequent dispersion of functional components; then, the temperature is controlled at ≤40℃ when adding the composite latent curing agent system to avoid premature activation of the latent curing agent at room temperature, preventing premature cross-linking of the resin that could lead to coating gelation or performance degradation, and ensuring the storage stability of the coating; subsequently, graphene dispersion slurry, coloring pigments, and other components are added, which can be uniformly dispersed in the already formed resin system. Combined with grinding to a fineness of ≤20μm, graphene sheet agglomeration and pigment / filler sedimentation are avoided, ensuring the coating's shielding properties and uniform appearance. The overall process takes into account the compatibility and controllable reaction of each component, ultimately giving the coating the characteristics of low-temperature rapid curing, long-term storage stability, and excellent coating performance, making it suitable for the needs of industrial dip coating production.

[0043] Thirdly, this application provides an application of a thin-film waterborne graphene-modified phenoxy impregnation coating, which adopts the following technical solution.

[0044] An application of a thin-film waterborne graphene-modified phenoxy dip coating for use in air conditioning compressors, wherein the coating is dried at 75-85℃ for 25-30 minutes after dip coating, resulting in a dry film thickness of 20-25μm.

[0045] By adopting the above technical solution, when this thin-film waterborne graphene-modified phenoxy impregnation coating is applied to air conditioning compressors, it achieves efficient protection and production optimization of the compressor substrate through suitable coating and drying processes and synergistic performance: the low-temperature drying condition of 75-85℃ significantly reduces energy consumption compared to the high-temperature drying of traditional electrophoretic paint (above 120℃), while avoiding thermal stress damage to the compressor substrate caused by high temperature. Furthermore, the short drying time improves production line efficiency, adapting to the needs of large-scale compressor production; the 20-25μm dry film thickness meets the "thin coating" requirement, reducing coating usage to lower costs, and also allows for... The dense shielding network of graphene sheets, the anti-corrosion effect of rust-preventing pigments, and the high adhesion of the resin system effectively block corrosive media such as water vapor and oil stains in the humid, hot, and vibrating environment where the compressor operates for a long time, preventing the substrate from rusting and ensuring the normal operation of the compressor under harsh conditions. In addition, the coating does not require phosphating pretreatment and can be directly applied to form a stable coating, reducing the discharge of phosphating wastewater containing heavy metals, which meets the green production requirements of the air conditioning manufacturing industry. At the same time, the coating has strong adhesion to the compressor's metal substrate and is not prone to cracking or peeling due to vibration during long-term operation, further extending the compressor's service life and reducing maintenance costs.

[0046] In summary, this application has the following beneficial effects:

[0047] This coating achieves comprehensive performance of "salt spray resistance ≥1100h and adhesion ≥16.5MPa" under thin coating conditions (20-25μm) by combining technologies such as synergistic mixed resin, modified graphene shielding, energy-saving composite curing agent, and stabilizing urea-formaldehyde microspheres. It completely solves the pain points of traditional electrophoretic paints such as "high pollution, weak corrosion resistance, and high energy consumption" and is suitable for the large-scale production needs of air conditioning compressors. Detailed Implementation

[0048] The present application will be further described in detail below with reference to the embodiments.

[0049] Example of raw material and intermediate preparation

[0050] raw material

[0051] It should be noted that: in the following examples, unless otherwise specified, the conditions shall be in accordance with conventional conditions or the manufacturer's recommended conditions; and the raw materials used in the following examples, unless otherwise specified, shall be from commercially available sources.

[0052] Urea, analytical grade;

[0053] PKHB phenoxy resin, Mw≈45000, hydroxyl value 65 mgKOH g -1 ;

[0054] PKHH phenoxy resin, Mw≈60000, hydroxyl value 70 mgKOH g -1 ;

[0055] Modified polyether reactive emulsifier, epoxy equivalent 450-500 g eq -1 Nonionic-reactive type;

[0056] Waterborne epoxy-modified phenolic resin, with a solid content of 42% and an epoxy value of 0.12 mol / 100 g;

[0057] Aqueous blocked isocyanate with NCO content of 6.2% and deblocking temperature of 75℃;

[0058] Liquid nitrile rubber, acrylonitrile content 33%, Mw 3500;

[0059] Elastic saturated polyester resin, hydroxyl value 55 mgKOH g -1 Tg -15 ℃;

[0060] Zinc aluminum phosphate anti-rust pigment, ZnO·AlPO4, average particle size 3 μm;

[0061] Graphene powder, with ≤2 layers, a sheet diameter of 5-15 μm, and C ≥98%;

[0062] Polyethylene glycol monomethyl ether, MPEG-750, hydroxyl value 75 mgKOH g -1 ;

[0063] Dicyandiamide, electronic grade, content ≥99.5%;

[0064] 2-Ethyl-4-methylimidazolium, color ≤50 Hazen, moisture ≤0.2%;

[0065] Nano-silica modified amine accelerator, particle size 20 nm, amine value 180 mgKOH g -1 ;

[0066] Polycarboxylate dispersant, solid content 40%, acid value 60 mgKOH g -1 ;

[0067] Polyethylene glycol, PEG-400, industrial grade.

[0068] Preparation Example

[0069] Preparation Example 1

[0070] A modified urea-formaldehyde resin microsphere is prepared by the following method:

[0071] 1) Prepolymer preparation

[0072] Add 30 kg of 37% formaldehyde aqueous solution to the reactor and stir at 600 rpm. Then add triethanolamine to adjust the pH to 8, raise the temperature to 75°C, and add 12 kg of urea in two portions, with an interval of 15 min between each addition. Keep the mixture warm and stir for 1 hour until the solution becomes transparent and viscous, thus obtaining hydroxymethylurea prepolymer.

[0073] 2) Emulsification and Encapsulation

[0074] The compound emulsifiers include Tween 80 and Span 80. The temperature is lowered to 50°C, 60 kg of deionized water is added, the stirring speed is increased to 2500 rpm, 1.5 kg of Tween 80 and 1 kg of Span 80 are added in sequence, and the mixture is stirred for 10 min until the emulsifiers are completely dissolved.

[0075] Slowly add 2.5 kg of polycarboxylate dispersant and continue stirring for 20 minutes to ensure that the dispersant is evenly dispersed in the aqueous phase.

[0076] While maintaining a speed of 2500 rpm, slowly add the hydroxymethylurea prepolymer dropwise into the system at a rate of 1 mL / min. After the dropwise addition is complete, continue stirring for 30 min to form a stable nanoscale prepolymer emulsion with a particle size of 130-170 nm.

[0077] 3) Polymerization and curing

[0078] Add formic acid dropwise to the emulsified system, adjust the pH to 4, and heat to 80°C;

[0079] Keep warm and stir for 2 hours. During this time, the urea-formaldehyde prepolymer crosslinks and solidifies under acidic conditions, gradually forming solid microspheres. Take samples every 30 minutes and use a laser particle size analyzer to detect the particle size (controlled within 100-200nm). If the particle size is too large, the stirring speed can be increased appropriately (maximum 3500rpm). If the particle size is too small, the stirring speed can be reduced (minimum 1800rpm).

[0080] 4) Surface modification and drying

[0081] After polymerization, the temperature was lowered to 75°C, 1 kg of polyethylene glycol was added, the stirring speed was reduced to 1000 rpm, and the reaction was maintained at this temperature for 1 hour. After the reaction was completed, the pH of the system was adjusted to 7 with deionized water, stirring was stopped, and a modified urea-formaldehyde resin microsphere dispersion was obtained.

[0082] Transfer the microsphere dispersion to a centrifuge at 9000 rpm for 25 min, discard the supernatant, and wash the precipitate repeatedly with deionized water 4 times (discarding the supernatant after each centrifugation) until the supernatant is clear.

[0083] The washed microsphere precipitate was placed in a freeze dryer at -45°C and a vacuum of 6 Pa for 14 hours to obtain white powdery modified urea-formaldehyde resin microspheres.

[0084] Preparation Example 2

[0085] A graphene dispersion slurry, the preparation method of which is as follows:

[0086] 7 kg of graphene powder, 3 kg of polyethylene glycol monomethyl ether, and 80 kg of deionized water were added to an ultrasonic disperser (350W) and ultrasonically dispersed at 28°C for 30 min. Then, 0.5 kg of the modified urea-formaldehyde resin microspheres obtained in Preparation Example 1 were added and stirred at 600 rpm for 12 min. The dispersion degree D50 was measured to be 98.5%, and a graphene dispersion slurry with a graphene content of 7.7% was obtained.

[0087] Preparation Example 3

[0088] A graphene dispersion slurry, the preparation method of which is as follows:

[0089] 7 kg of graphene powder, 3 kg of polyethylene glycol monomethyl ether, and 80 kg of deionized water were added to an ultrasonic disperser (350W) and ultrasonically dispersed at 28°C for 30 min to obtain a graphene dispersion slurry with a graphene content of 7.7%.

[0090] Preparation Example 4

[0091] A phenoxy resin polymer, the preparation method of which is as follows:

[0092] 10 kg of PKHB phenoxy resin and 13 kg of PKHH phenoxy resin were added to a reaction vessel; the temperature was raised to 80°C, 4 kg of modified polyether reactive emulsifier was added, and the mixture was stirred at 900 rpm for 35 min to emulsify; 23 kg of deionized water was added, and the solid content was adjusted to 40% to obtain the phenoxy resin polymer.

[0093] Example

[0094] Examples 1-3

[0095] A thin-film waterborne graphene-modified phenoxy impregnation coating, the preparation method of which is as follows:

[0096] S1. According to the proportions in Table 1, add phenoxy resin polymer to the mixing tank and stir at 1300 rpm; then add auxiliary film-forming resin and composite toughening agent in sequence and stir for 18 min.

[0097] S2. Cool to 35℃, add the composite latent curing agent system, and stir at 1000 rpm for 10 min;

[0098] S3. Add graphene dispersion slurry, heat to 42℃, and stir at 2200 rpm for 28 min;

[0099] S4. Add rust-preventive pigments, coloring pigments, and fillers, and continue stirring for 20 minutes; add coating additives and deionized water, and stir for 10 minutes;

[0100] S5. Grind the coating to a fineness of 18μm using a sand mill to obtain the finished coating product.

[0101] Table 1. Raw material ratios for Examples 1-3 (kg)

[0102]

[0103] The phenoxy resin polymer was derived from Preparation Example 4. The auxiliary film-forming resin included a waterborne epoxy-modified phenolic resin and a waterborne blocked isocyanate in a weight ratio of 6:10. The composite toughening agent included liquid nitrile rubber and elastic saturated polyester resin in a weight ratio of 1:0.8. The anti-rust pigment was zinc aluminum phosphate. The graphene dispersion slurry was derived from Preparation Example 2. The coloring pigment was titanium dioxide. The filler was mica powder. The coating additives included EGO755 wetting and dispersing agent, TEGO4100 wetting agent, TEGO810 defoamer, and TEGO410 leveling agent in a weight ratio of 1:1:1:1. The composite latent curing agent system included dicyandiamide, 2-ethyl-4-methylimidazolium, and nano-silica-modified amine accelerator in a weight ratio of 3:1.5:1.5.

[0104] Example 4

[0105] Unlike Example 2, the graphene dispersion slurry in Example 4 was derived from Preparation Example 3.

[0106] Example 5

[0107] Unlike Example 2, the composite latent curing agent system in Example 5 includes dicyandiamide, 2-ethyl-4-methylimidazole and nano-silica modified amine accelerator in a weight ratio of 2:2:1.

[0108] Example 6

[0109] Unlike Example 2, the composite latent curing agent system in Example 6 includes dicyandiamide, 2-ethyl-4-methylimidazole and nano-silica modified amine accelerator in a weight ratio of 4:1:2.

[0110] Example 7

[0111] Unlike Example 2, the phenoxy resin polymer in Example 7 is PKHB phenoxy resin.

[0112] Example 8

[0113] Unlike Example 2, the phenoxy resin polymer in Example 8 is PKHH phenoxy resin.

[0114] Comparative Example

[0115] Comparative Example 1

[0116] Unlike Example 1, in Comparative Example 1, the graphene dispersion slurry was prepared by adding 7 kg of graphene powder and 80 kg of deionized water to an ultrasonic disperser (350W) and ultrasonically dispersing at 28°C for 30 min to obtain a graphene dispersion slurry with a solid content of 6.8%.

[0117] Comparative Example 2

[0118] Unlike Example 1, the composite latent curing agent system in Comparative Example 2 includes dicyandiamide and nano-silica modified amine accelerator in a weight ratio of 3:2.

[0119] Performance testing

[0120] The steel substrate of the air conditioner compressor was sandblasted, degreased and cleaned, and then dip-coated. The dip-coating time was 12s, the lifting speed was 6cm / s, the room temperature was 23±2℃, the RH was 50±5%, and it was dried at 80℃ for 28min. The dry film thickness was 22μm. Then the following performance tests were carried out, and the test results are shown in Table 2.

[0121] The resistance to neutral salt spray was tested in accordance with GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test".

[0122] The adhesion was tested according to GB / T5210-2006 "Paints and Varnishes - Pull-off Adhesion Test".

[0123] The impact strength of the coating was tested according to GB / T 1732-2020 "Test Method for Impact Resistance of Coating Film".

[0124] The resistance to damp heat was tested according to GB / T 1740-2007 "Test Method for Resistance to Damp Heat of Coating Film", and the test conditions were 40℃×95%RH.

[0125] The acid and alkali resistance was tested according to GB / T 9274-1988 "Determination of resistance to liquid media for paints and varnishes" under the test condition of 5% H2SO4.

[0126] The dispersion of graphene after six months of storage was measured using a Malvern Mastersizer 3000 laser particle size analyzer.

[0127] Table 2 Performance Test Results

[0128]

[0129] Note: Commercially available traditional electrophoretic paint requires phosphating treatment and drying at 120℃.

[0130] Examples 1-3 exhibited neutral salt spray resistance ≥1100h, exceeding the 500h resistance of traditional electrophoretic paint by over 120%, and exceeding the 680h resistance of Comparative Example 1 (without modified graphene) by over 61%. The core reason is the dense shielding provided by 1-2 layers of graphene combined with the slow-release dispersion of modified urea-formaldehyde microspheres, which effectively prevents Cl- from being released over a long period. - Permeation; Example 4: Urea-formaldehyde microspheres were used, and the salt spray resistance was reduced to 920h, proving that urea-formaldehyde microspheres can extend the dispersion stability period of graphene and avoid shielding gaps caused by agglomeration; Examples 7-8: Single resins had a salt spray resistance of 980-1020h, which is lower than that of mixed resin systems, demonstrating the synergistic effect of PKHB / PKHH in optimizing film density.

[0131] Examples 1-3 exhibit adhesion ≥16.5 MPa and impact strength ≥57 kg·cm, superior to the 12.0 MPa and 42 kg·cm of traditional electrophoretic paints and the 14.2-15.5 MPa and 50-52 kg·cm of single-resin systems in Examples 7-8. The key lies in the "elastic island" effect of the composite toughening agent; the liquid nitrile rubber absorbs the impact, and the viscosity balance of the mixed resin ensures adhesion.

[0132] After 6 months of storage, the graphene dispersion in Examples 1-3 remained ≥96.3%, while in Example 4, the dispersion of urea-formaldehyde microspheres decreased to 88.2%, and in Comparative Example 1, the dispersion of unmodified urea-formaldehyde microspheres was only 82.5%. This demonstrates that the PEG surface modification and dispersant slow-release function of the modified urea-formaldehyde microspheres effectively solve the problem of graphene hydrophobic aggregation and ensure consistent performance of different batches of coatings.

[0133] Examples 1-3 show resistance to damp heat ≥860h and resistance to 5% H2SO4 ≥500h, which is 56% and 56% higher than the traditional electrophoretic paint's 550h and 320h, respectively. This makes it suitable for humid and hot environments in coastal areas and for compressor oil contamination scenarios, demonstrating the chemical resistance of the three-dimensional cross-linked network of the auxiliary film-forming resin.

[0134] This coating achieves comprehensive performance of "salt spray resistance ≥1100h and adhesion ≥16.5MPa" under thin coating conditions (20-25μm) by combining technologies such as synergistic mixed resin, modified graphene shielding, energy-saving composite curing agent, and stabilizing urea-formaldehyde microspheres. It completely solves the pain points of traditional electrophoretic paints such as "high pollution, weak corrosion resistance, and high energy consumption" and is suitable for the large-scale production needs of air conditioning compressors.

[0135] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A thin-film waterborne graphene-modified phenoxy dip coating material, characterized by, The coating comprises the following raw materials by weight: phenoxy resin polymer 30-40 parts, auxiliary film-forming resin 10-20 parts, composite toughening agent 3-8 parts, anti-rust pigment 10-15 parts, graphene dispersion slurry 10-15 parts, coloring pigment 2-20 parts, filler 10-15 parts, coating additive 2-5 parts, composite latent curing agent system 4-8 parts, and water 5-15 parts. The graphene dispersion slurry comprises polyethylene glycol monomethyl ether grafted graphene and slow-release dispersion stabilizer, and the dispersion degree D50 is greater than or equal to 98%. The phenoxy resin polymer is obtained by mixing PKHB phenoxy resin and PKHH phenoxy resin at a molar ratio of 1: (1.2-1.5), emulsifying by a modified polyether reactive emulsifier, and having a solid content of 38-42%. The composite latent curing agent system comprises dicyandiamide, 2-ethyl-4-methyl imidazole and nano-silica modified amine accelerant at a weight ratio of (2-4):(1-2):(1-2). The slow-release dispersion stabilizer is modified urea-formaldehyde resin microspheres. The preparation method of the modified urea-formaldehyde resin microspheres is as follows: 1) Preparation of prepolymer Add triethanolamine to formaldehyde aqueous solution to adjust pH to 8-9, heat to 70-80℃, add urea in two portions, and keep stirring for 1h to obtain transparent methylol urea prepolymer; 2) Emulsification and wrapping Cool to 50℃, add deionized water and composite emulsifier, and stir at 2500rpm for 10-15min; add polycarboxylate dispersant, and continue stirring for 20min; slowly drop the prepolymer, keep stirring at 2500rpm for 30min, form nano droplets, and the particle size is 130-170nm; 3) Polymerization and curing Drop formic acid to adjust pH to 4-5, heat to 75-85℃, and keep stirring for 2h, the droplets are cured into microspheres, and the particle size is 100-200nm; 4) Surface modification and drying Cool to 75℃, add polyethylene glycol and stir for 1h; adjust pH to neutral, centrifuge, wash, freeze-dry, and obtain white modified urea-formaldehyde resin microspheres.

2. A thin film waterborne graphene-modified phenoxy dip coating paint according to claim 1, characterized in that, The auxiliary film-forming resin comprises at least one of water-based epoxy modified phenolic resin and water-based blocked isocyanate.

3. A thin film waterborne graphene-modified phenoxy dip coating paint according to claim 1, characterized in that, In the graphene dispersion slurry, the number of graphene layers is 1-2, the flake diameter is 5-15μm, and the content of graphene is 6-8%; the polyethylene glycol monomethyl ether grafted graphene is grafted with polyethylene glycol monomethyl ether grafting agent, and the addition amount of the polyethylene glycol monomethyl ether grafting agent is 30-50% of the weight of graphene.

4. A thin-film water-borne graphene-modified phenoxy dip coating paint according to claim 2, characterized in that, The auxiliary film-forming resin comprises water-based epoxy modified phenolic resin and water-based blocked isocyanate at a weight ratio of (5-8):(8-12).

5. A thin film waterborne graphene-modified phenoxy dip coating paint according to claim 1, characterized in that, The composite toughening agent comprises liquid nitrile rubber and elastic saturated polyester resin at a weight ratio of 1:0.

8.

6. A process for the preparation of a thin waterborne graphene-modified phenoxy dip coating according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: In a stirring state, sequentially add phenoxy resin polymer, auxiliary film-forming resin, composite toughening agent, composite latent curing agent system, and graphene dispersion slurry, then add anti-rust pigment, coloring pigment, filler, coating additive, and water after mixing, disperse, grind to a fineness of less than or equal to 20μm, and obtain the coating.

7. A method of preparing a thin coating waterborne graphene-modified phenoxy dip coating paint according to claim 6, characterized in that, When the composite latent curing agent system is added, the stirring temperature is controlled to be not higher than 40℃.

8. Use of a thin-film waterborne graphene-modified phenoxy dip coating according to any one of claims 1 to 5, characterized in that Applied to air conditioner compressor, dip-coated and dried at 75-85℃ for 25-30min, dry film thickness 20-25μm.

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