High-wear-resistance cathode electrophoretic coating and preparation method thereof

Abstract

The invention relates to the field of electrophoretic paint, in particular to high-wear-resistance cathode electrophoretic paint and a preparation method thereof. According to the invention, a plurality of high-wear-resistance fillers are innovatively introduced to achieve a synergistic effect and are subjected to organic-inorganic hybridization enhancement with special modified cathode electrophoresis resin, and a filler system, a resin structure and a curing mechanism are reasonably optimized, so that a novel coating with high wear resistance, excellent corrosion resistance and good electrophoresis stability is developed; and the wear resistance of the traditional cathode electrophoretic paint is improved.

Description

Technical Field

[0001] The present invention relates to the field of electrophoretic coatings, and particularly to a highly wear-resistant cathodic electrophoretic coating and a preparation method thereof. Background Art

[0002] Cathodic electrophoretic coatings are widely used in the protection of various metal workpieces due to their excellent anti-corrosion performance, uniform coating ability, environmental friendliness, and low VOC emissions. However, traditional cathodic electrophoretic coatings mainly focus on anti-corrosion performance, with relatively low wear resistance and hardness. The coating is prone to wear in high-friction and high-impact environments, affecting its service life.

[0003] Currently, common methods to improve the wear resistance of cathodic electrophoretic coatings include:

[0004] 1. Increasing the coating thickness - but this will increase energy consumption and cost, and is not conducive to lightweight design;

[0005] 2. Changing the resin system - this may affect the uniformity and adhesion of the coating, and high-hardness coatings are often prone to cracking;

[0006] 3. Introducing fillers for reinforcement - ordinary fillers are difficult to disperse evenly and are prone to precipitation under actual working conditions, which may affect the electrophoretic stability. Summary of the Invention

[0007] The present invention aims to provide a highly wear-resistant cathodic electrophoretic coating and a preparation method thereof. The specific scheme is as follows:

[0008] A highly wear-resistant cathodic electrophoretic coating comprises the following components: a resin system, a curing agent, a highly wear-resistant filler, pigments, a solvent, and other additives. The resin system includes a modified cathodic electrophoretic epoxy resin and a modified polyurethane auxiliary resin. The resin system also includes an amine-modified resin or a phenolic resin. The curing agent is one or both of a blocked isocyanate curing agent and an amino resin curing agent. The highly wear-resistant filler includes nano-silica and ultra-fine corundum, and the D50 of the nano-silica is ≤ 100 nm.

[0009] The highly wear-resistant filler also includes boron nitride and polytetrafluoroethylene.

[0010] The highly wear-resistant filler also includes one or more of stainless steel fibers, nano-silicon carbide, or tungsten carbide.

[0011] The particle size D50 of the highly wear-resistant filler is ≤ 500 nm. With the synergistic effect of a variety of inorganic ultra-fine powder fillers (D50 ≤ 500 nm) and combined with ultra-fine powder dispersion technology, it ensures the uniform dispersion of the filler in the water-based resin system and forms a dense microstructure with the resin network after curing, improving the wear resistance and coating stability.

[0012] The modified polyurethane auxiliary resin is an aqueous polyurethane dispersion containing hydroxyl or carboxyl functional groups. Specifically, it meets the following conditions:

[0013] 1. Molecular weight control: The weight-average molecular weight (Mw) ranges from 15,000 to 50,000, and the molecular weight distribution index (PDI) ≤ 2.0 to ensure the formation of an interpenetrating network structure with epoxy resin; by controlling the upper limit of the molecular weight (50,000), coating defects caused by differences in resin migration rates during electrophoresis are avoided; the lower limit (15,000) ensures effective encapsulation with nano-fillers (such as SiO with D50 ≤ 100 nm).

[0014] 2. Functional group content: The hydroxyl value is 80 - 150 mg KOH / g to provide sufficient crosslinking sites; functional group matching: The molar ratio of the hydroxyl group to the -NCO group of the blocked isocyanate curing agent is 1:0.8 - 1.2 to ensure complete crosslinking.

[0015] 3. Containing quaternary ammonium salt groups (0.5 - 1.2 mmol / g) to endow the resin with cathodic electrophoresis characteristics; the content of quaternary ammonium salt directly affects the electrophoresis deposition efficiency.

[0016] The modified cathodic electrophoretic epoxy resin is a modified bisphenol A epoxy resin or acrylic resin.

[0017] The weight ratio of its material addition is as follows: resin system 38 - 45, curing agent 8 - 20, high wear-resistant filler 7 - 15, pigment 2 - 10, solvent 5 - 10, and other additives 1.

[0018] A preparation method of a high wear-resistant cathodic electrophoretic coating is as follows:

[0019] (1) Preparation of resin solution: Mix the resin system, curing agent, solvent, and additives in proportion and stir evenly to obtain a resin solution;

[0020] (2) Neutralization and dispersion: Add lactic acid in an aqueous medium to adjust the pH, and mix it with the resin obtained in step (1) to form a stable emulsion;

[0021] (3) Dispersion and grinding of filler: Add high wear-resistant filler to the emulsion in step (2) under high-speed stirring and continuously grind to obtain a filler dispersion;

[0022] (4) Preparation of electrophoretic paint: Add deionized water to the filler dispersion in step (3), adjust the solid content to an appropriate range, and filter to obtain a uniform and stable working solution of cathodic electrophoretic coating;

[0023] (5) Electrophoretic deposition: Voltage 150 - 300 V, time 1 - 3 min to ensure uniform deposition;

[0024] (6) Curing: Cure at 100 - 180°C for 20 - 60 min to form a highly wear-resistant coating.

[0025] The neutralizing agent includes lactic acid, acetic acid, or formic acid.

[0026] In the step of dispersing and grinding the filler, a combined process of ultrasonic dispersion, high-speed shearing, and ball milling is adopted.

[0027] In the present invention, by innovatively introducing a variety of highly wear-resistant fillers to act synergistically and performing organic-inorganic hybridization enhancement with a special modified cathodic electrophoretic resin, through reasonably optimizing the filler system, resin structure, and curing mechanism, a new type of coating with both high wear resistance, excellent corrosion resistance, and good electrophoretic stability is developed, improving the wear resistance of traditional cathodic electrophoretic coatings. In the present invention, fillers with high hardness (such as corundum and silicon carbide) are used to greatly increase the hardness of the coating, which is increased to 4H - 6H, so as to better resist mechanical damage and reduce scratches and wear. Through the optimization of fillers such as silicon nitride and ultra-high molecular weight polyethylene, the impact resistance of the coating is increased by more than 40%, reducing the risk of peeling and cracking. The optimized resin system and uniform dispersion of the fillers in the present invention enable the coating to form a dense network structure, preventing the penetration of corrosion media such as water and oxygen, and significantly improving the corrosion resistance. In the present invention, boron nitride and polyethylene fillers with good lubricity are added to reduce the friction coefficient to 0.2 - 0.3, reduce mechanical wear, and extend the service life of the equipment.

[0028] The curing agent of the present invention is a blocked isocyanate curing agent, which cures at 100 - 180°C to form a high-strength crosslinked structure, improving the wear resistance and hardness of the coating; the amino resin curing agent improves the weather resistance and scratch resistance of the coating. By controlling the curing temperature and time, the curing agent is evenly distributed in the coating, improving the stability of the coating.

[0029] The filler of the present invention is the biggest innovation point of this application and has the following advantages:

[0030] Nano-silica: After the surface of nano-silica is modified with a silane coupling agent, its silanol groups undergo a condensation reaction with the epoxy groups of the epoxy resin to form stable Si-O-C covalent bonds, enhancing the interfacial bonding force between the filler and the resin. At the same time, the "pinning effect" of the nano-particles inhibits crack propagation.

[0031] Ultra-fine corundum: The surface hydroxyl groups form a hydrogen bond network with the amino groups of the polyurethane auxiliary resin. At the same time, its high hardness (Mohs hardness 9.0) acts as a rigid support framework in the coating, dispersing external stress and reducing local wear.

[0032] Boron nitride (BN) and polytetrafluoroethylene (PTFE): The layered structure of BN is exfoliated into microflakes during friction, which synergizes with the low surface energy property of PTFE to form a continuous lubricating film on the coating surface, reducing the friction coefficient to 0.2 - 0.3. At the same time, it binds to the resin matrix through van der Waals forces to prevent the lubricating phase from falling off.

[0033] Stainless steel fibers: Form a three-dimensional reinforcement structure by physically interpenetrating the resin network, enhancing the impact resistance of the coating. Its passivated surface and the chemical inertness of the resin synergistically inhibit electrochemical corrosion.

[0034] That is, the applicant summarizes that the fillers of the present invention have the following effects:

[0035] Hardness gradient effect: Ultra-fine corundum (Mohs hardness 9.0) and nano-silicon carbide (Mohs hardness 9.5) form a hardness gradient. During friction, the high-hardness silicon carbide bears wear preferentially to protect the resin matrix;

[0036] Self-lubrication synergy: The layered lubricating film of boron nitride (BN) and polytetrafluoroethylene (PTFE) reduces the interfacial shear force, while the extremely high hardness of tungsten carbide (WC) (Mohs hardness 9.0) reduces abrasive wear through microscopic "plowing" action;

[0037] Crack inhibition mechanism: Nano-silica enhances the interfacial bonding through covalent bonds, and its size effect (D50 ≤ 100nm) can block the propagation path of microcracks, improving the toughness of the coating. Detailed implementation mode

[0038] Example 1

[0039] Resin system (40%): Modified bisphenol A epoxy resin (25%); Modified polyurethane auxiliary resin (10%); Amine-modified resin (5%). The modified polyurethane auxiliary resin is an aqueous polyurethane dispersion containing hydroxyl or carboxyl functional groups.

[0040] Curing agent (15%): Blocked isocyanate curing agent (15%);

[0041] High wear-resistant filler (13%): Nano-silica (6%); Ultra-fine corundum (7%).

[0042] Pigment (3%): Carbon black (3%);

[0043] Solvent (10%): Ethylene glycol monobutyl ether (10%);

[0044] Auxiliary agent (1%): Dispersant (0.4%), leveling agent (0.3%), defoaming agent (0.3%); Pure water (several)

[0045] Preparation method:

[0046] Preparation of resin solution: Mix modified bisphenol A epoxy resin, special modified polyurethane auxiliary resin, amine-modified resin, blocked isocyanate curing agent, ethylene glycol monobutyl ether, dispersant, leveling agent, and defoaming agent in proportion and stir evenly.

[0047] Neutralization and dispersion: Add lactic acid to the aqueous medium to adjust the pH, mix it with the resin solution to form a stable emulsion.

[0048] Dispersion and grinding of fillers: Under high-speed stirring conditions, add nano-silica, ultra-fine corundum, and nano-silicon carbide to the emulsion, continuously grind it, and use ultrasonic dispersion + high-speed shearing + ball milling to ensure uniform dispersion of the fillers and obtain a filler dispersion liquid.

[0049] Preparation of electrophoretic paint: Add the filler dispersion liquid to deionized water, adjust the solid content to an appropriate range, and filter it to obtain a uniform and stable working solution of cathodic electrophoretic coating.

[0050] Electrophoretic deposition: Voltage 200V, time 2min, ensure uniform deposition.

[0051] Curing: Cure at 150°C for 30min to form a highly wear-resistant coating.

[0052] Examples 2-5 and comparative examples

[0053] Examples 2-5 and the comparative examples are the same as Example 1 in other aspects, except for the differences shown in the following table:

[0054]

[0055]

[0056] Performance comparison analysis table

[0057]

[0058] Example 6 (high lubrication)

[0059] Resin system (45%): Modified bisphenol A epoxy resin (28%); Polyurethane resin (12%); Amine-modified resin (5%).

[0060] Curing agent (8%): Blocked isocyanate curing agent (8%);

[0061] Highly wear-resistant filler (7%): Nano-silica (2%); Boron nitride (2%); Polytetrafluoroethylene (3%).

[0062] Pigment (10%): Titanium dioxide (10%);

[0063] Solvent (5%): Propylene glycol monomethyl ether (5%);

[0064] Auxiliaries (1%): Dispersant (0.4%), fluorine-containing leveling agent (0.4%), defoamer (0.2%);

[0065] Pure water (24%).

[0066] Preparation method:

[0067] Preparation of resin solution: Mix modified bisphenol A epoxy resin, special modified polyurethane auxiliary resin, amine-modified resin, blocked isocyanate curing agent, ethylene glycol monobutyl ether, dispersant, leveling agent, and defoamer in proportion and stir evenly;

[0068] Neutralization and dispersion: Add formic acid to adjust the pH in an aqueous medium, mix with the resin solution to form a stable emulsion;

[0069] Dispersion and grinding of fillers: Add nano-silica, ultra-fine corundum, and polytetrafluoroethylene to the emulsion under high-speed stirring, continuously grind, and use ultrasonic dispersion + high-speed shearing + ball milling to ensure uniform dispersion of the fillers and obtain a filler dispersion;

[0070] Formulation of cathodic electrophoretic paint: Add the filler dispersion to deionized water, adjust the solid content to an appropriate range, and filter to obtain a uniform and stable working solution of cathodic electrophoretic coating;

[0071] Electrophoretic deposition: Voltage 180V, time 2.5min, ensure uniform deposition;

[0072] Curing: Cure at 160°C for 25min to form a highly wear-resistant coating.

[0073] Example 7 (high weather resistance)

[0074] Resin system (38%): Modified acrylic resin (20%); Polyurethane resin (13%); Phenolic modified resin (5%).

[0075] Curing agent (20%): Amino resin curing agent (20%);

[0076] Highly wear-resistant fillers (15%): Ultra-fine corundum (6%); Silicon nitride (5%); Ultra-high molecular weight polyethylene (4%).

[0077] Pigment (2%): Iron oxide red (2%);

[0078] Solvent (10%): Diethylene glycol monobutyl ether (10%);

[0079] Auxiliaries (1%): Dispersant (0.5%), leveling agent (0.3%), ultraviolet absorber (0.2%);

[0080] Pure water (19%).

[0081] Preparation method:

[0082] Preparation of resin solution: Mix modified acrylic resin, special modified polyurethane auxiliary resin, phenolic modified resin, amino resin curing agent, propylene glycol methyl ether, dispersant, leveling agent, and defoaming agent in proportion and stir evenly.

[0083] Neutralization and dispersion: Add acetic acid to the aqueous medium to adjust the pH, mix it with the resin solution to form a stable emulsion.

[0084] Dispersion and grinding of fillers: Under high-speed stirring conditions, add ultra-fine corundum, silicon nitride, and ultra-high molecular weight polyethylene to the emulsion, continuously grind it, and use ultrasonic dispersion + high-speed shearing + ball milling to ensure uniform dispersion of the fillers and obtain a filler dispersion liquid.

[0085] Preparation of electrophoretic paint: Add the filler dispersion liquid to deionized water, adjust the solid content to an appropriate range, and filter it to obtain a uniform and stable working solution of cathodic electrophoretic coating.

[0086] Electrophoretic deposition: Voltage 150V, time 3min, ensure uniform deposition.

[0087] Curing: Cure at 120°C for 40min to form a highly wear-resistant coating.

[0088] Performance:

[0089]

[0090]

[0091] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A highly wear-resistant cathodic electrophoretic coating, characterized in that, It comprises the following components: resin system, curing agent, highly wear-resistant filler, pigment, solvent and other additives. The resin system includes modified cathodic electrophoretic epoxy resin and modified polyurethane auxiliary resin, and the resin system further includes amine-modified resin or phenolic-modified resin; the curing agent is one or both of blocked isocyanate curing agent and amino resin curing agent, the highly wear-resistant filler includes nano-silica and superfine corundum, and the D50 of the nano-silica is ≤100 nm.

2. The highly wear-resistant cathodic electrophoretic coating according to claim 1, characterized in that: The highly wear-resistant filler further includes boron nitride and polytetrafluoroethylene.

3. A highly wear-resistant cathodic electrophoretic coating according to any one of claims 1 or 2, characterized in that: The highly wear-resistant filler further includes one or more of stainless steel fiber, nano-silicon carbide or tungsten carbide.

4. A highly wear-resistant cathodic electrophoretic coating according to claim 1, characterized in that: The particle size D50 of the highly wear-resistant filler is ≤500 nm.

5. The highly wear-resistant cathodic electrophoretic coating according to claim 1, wherein: The modified cathodic electrophoretic epoxy resin is modified bisphenol A epoxy resin or acrylic resin.

6. The high wear-resistant cathodic electrophoretic coating according to claim 1, wherein: The modified polyurethane auxiliary resin is an aqueous polyurethane dispersion containing hydroxyl or carboxyl functional groups, with a weight average molecular weight range of 15,000 - 50,000, a molecular weight distribution index (PDI) ≤2.0, a hydroxyl value of 80 - 150 mg KOH / g, and a quaternary ammonium salt group content of 0.5 - 1.2 mmol / g.

7. A highly wear-resistant cathodic electrophoretic coating according to claim 1, characterized in that, Their addition weight ratios are as follows: resin system 38 - 45, curing agent 8 - 20, highly wear-resistant filler 7 - 15, pigment 2 - 10, solvent 5 - 10 and other additives 1.

8. A preparation method of the high wear-resistant cathodic electrophoretic coating as described in claim 1, characterized in that, The specific scheme is as follows: (1) Resin solution preparation: Mix the resin system, curing agent, solvent and additives in proportion and stir evenly to obtain a resin solution; (2) Neutralization and dispersion: Add lactic acid in an aqueous medium to adjust the pH, and mix with the resin obtained in step (1) to form a stable emulsion; (3) Filler dispersion and grinding: Under high-speed stirring conditions, add the highly wear-resistant filler to the emulsion in step (2) and continuously grind to obtain a filler dispersion; (4) Electrophoretic paint formulation: Add deionized water to the filler dispersion in step (3), adjust the solid content to an appropriate range, and filter to obtain a uniform and stable cathodic electrophoretic coating working solution; (5) Electrophoretic deposition: Voltage 150 - 300 V, time 1 - 3 min to ensure uniform deposition; (6) Curing: Cure at 100 - 180 °C for 20 - 60 min to form a highly wear-resistant coating.

9. The preparation method of a highly wear-resistant cathodic electrophoretic coating according to claim 8, characterized in that: The neutralizing agent includes lactic acid, acetic acid or formic acid.

10. The preparation method of a highly wear-resistant cathodic electrophoretic coating according to claim 8, wherein: In the filler dispersion and grinding step, a combined process of ultrasonic dispersion, high-speed shearing and ball milling is adopted.

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