Waterborne coating for magnesium alloy robot shell as well as preparation method and coating method of waterborne coating

Abstract

The invention discloses water-based paint for a magnesium alloy robot shell and a preparation method and a coating method of the water-based paint, and relates to the technical field of paints.The water-based paint for the magnesium alloy robot shell comprises 55-80 parts of modified epoxy dispersoid and 1-10 parts of adhesion promoter; wherein the modified epoxy dispersoid is used as a main film forming substance, and the compatibility and reaction activity of the modified epoxy dispersoid and the surface of the magnesium alloy can be improved through chemical modification, so that the adhesion performance of the coating is enhanced; the adhesion promoter comprises modified molybdate, a rare earth compound, an amine derivative and a heterocyclic compound; the modified molybdate can form a stable complex or deposition layer; the rare earth compound can form a uniform and compact oxide layer on the surface of the magnesium alloy; the amine derivative can generate a three-dimensional network structure; the heterocyclic compound can increase the affinity between the coating and the base material; therefore, the technical problem of poor binding force between the water-based paint and the magnesium alloy is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coatings, in particular to a water-based coating for magnesium alloy robot shells, a preparation method and a coating method thereof. BACKGROUND

[0002] In the outdoor application of robots, they often work in high humidity environments or contact with various liquids, etc. The surface is prone to electrochemical corrosion, which affects the mechanical properties and service life of the material. In order to improve the corrosion resistance, the conventional magnesium alloy water-based coating generally uses an epoxy resin dispersion.

[0003] However, the epoxy resin mainly relies on physical adsorption to adhere to the surface of the magnesium alloy, lacks effective chemical bonding, and the adhesion of the coating is limited, usually not more than 5 MPa. When subjected to external forces (for example, the shell, skeleton, mechanical arm and joint transmission structure of the robot often need to bear a large stress and complex dynamic load, especially the stress generated during the movement of the mechanical arm, collision, etc.), the coating is prone to fall off, thereby losing the protective effect.

[0004] Therefore, the magnesium alloy water-based coating in the related art has poor adhesion to magnesium alloy, resulting in poor corrosion resistance and durability, which cannot meet the requirements of high performance and long service life of materials in the field of unmanned aerial vehicles. SUMMARY

[0005] The main purpose of the present application is to provide a water-based coating for magnesium alloy robot shells, a preparation method and a coating method thereof, which aims to solve the technical problem that the magnesium alloy water-based coating has poor adhesion to magnesium alloy, resulting in poor corrosion resistance and durability, which cannot meet the requirements of high performance and long service life of materials in the field of unmanned aerial vehicles.

[0006] To achieve the above-mentioned purpose, the present application provides a water-based coating for magnesium alloy robot shells, which comprises component A, wherein the component A comprises:

[0007] 55-80 parts of a modified epoxy dispersion, 1-10 parts of an adhesion promoter, wherein the adhesion promoter comprises a modified molybdate, a rare earth compound, an amine derivative and a heterocyclic compound.

[0008] In an embodiment, the component A further comprises:

[0009] 1-10 parts of a salt mist resistant filler, 1-10 parts of a nanosheet filler, wherein the components of the salt mist resistant filler include a modified tripolyphosphate compound and a modified aluminum zinc phosphomolybdate compound.

[0010] In an embodiment, the component A further comprises:

[0011] 1-10 parts of a rheological aid, wherein the components of the rheological aid include a polyurea compound, a modified inorganic salt, and a modified polyurethane.

[0012] In an embodiment, the component A further includes:

[0013] 1-10 parts of a defoaming agent, 1-10 parts of a hydroxyl-containing silicone polymer, and 1-10 parts of a substrate wetting agent, wherein the components of the defoaming agent include a modified silicone and a modified acrylic acid.

[0014] In an embodiment, the water-based paint for the magnesium alloy robot shell further includes a component B, and the component B includes:

[0015] 1-30 parts of a modified water-based amine polymer.

[0016] In addition, to achieve the above object, the application further provides a preparation method of the water-based paint for the magnesium alloy robot shell according to any one of the above, and the preparation method includes:

[0017] The modified epoxy dispersion and the hydroxyl-containing silicone polymer are added to a high-speed dispersion machine, and stirred by the high-speed dispersion machine at a first rotating speed for 10-20 min;

[0018] The nanosheet filler, the salt mist resistant filler, and the adhesion promoter are sequentially added to the high-speed dispersion machine, and continue to be stirred by the high-speed dispersion machine at the first rotating speed for 25-35 min;

[0019] The substrate wetting agent, the rheological aid, and the defoaming agent are added to the high-speed dispersion machine, and continue to be stirred at a second rotating speed for 5-15 min, wherein the second rotating speed is less than the first rotating speed;

[0020] The color paste is added to the high-speed dispersion machine, and continues to be stirred until uniform, and then is aged after being placed for a preset time, to obtain the component A;

[0021] The component A is mixed with a component B to obtain the water-based paint for the magnesium alloy robot shell, and the component B includes a modified water-based amine polymer.

[0022] In addition, to achieve the above object, the application further provides a painting method of the water-based paint for the magnesium alloy robot shell according to any one of the above, and the painting method includes:

[0023] The water-based paint is sprayed on the surface of the magnesium alloy substrate based on preset spraying parameters by using an air-assisted airless spraying technology;

[0024] The magnesium alloy substrate after the spraying is completed is baked at a temperature of 80-120°C for 20-30 min, to complete the painting.

[0025] In one embodiment, the preset spraying parameters include: a spraying pressure of 0.3-0.8 MPa and a nozzle diameter of 0.8-2.5 mm.

[0026] In one embodiment, prior to the step of spraying the water-based coating onto the surface of the magnesium alloy substrate based on preset spraying parameters, the method further includes:

[0027] The magnesium alloy substrate is immersed in an alkaline solution for 3-10 minutes, wherein the alkaline solution comprises NaOH with a concentration of 5-10 g / L and Na2SiO3 with a concentration of 2-5 g / L.

[0028] The magnesium alloy substrate after alkaline treatment is immersed in an acidic solution for 30-120 seconds, wherein the acidic solution comprises citric acid at a concentration of 5-10 g / L and lactic acid at a concentration of 2-5 g / L.

[0029] The magnesium alloy substrate after acid treatment is passivated in a special passivation solution for magnesium alloy for 10-120 seconds to form a dense conversion film on the surface of the magnesium alloy substrate.

[0030] The magnesium alloy substrate with a dense conversion film on its surface is placed in a forced-air drying oven at a temperature of 135-170℃ for 15-30 minutes to complete the pretreatment of the magnesium alloy substrate.

[0031] In one embodiment, the magnesium alloy passivation solution comprises: 10-50 g / L phosphoric acid, 5-50 g / L calcium dihydrogen phosphate, 1-10 g / L sodium silicate, 0.1-1 g / L dodecyl dimethylamine hydantoin, and 1-15 g / L chlorogenic acid; the passivation temperature for the acid-treated magnesium alloy substrate is 35-55°C.

[0032] One or more technical solutions proposed in this application have at least the following technical effects:

[0033] This application presents an aqueous coating for a magnesium alloy robot shell comprising 55-80 parts of a modified epoxy dispersion and 1-10 parts of an adhesion promoter. The modified epoxy dispersion, as the main film-forming substance, improves compatibility and reactivity with the magnesium alloy surface through chemical modification compared to traditional epoxy resins, thereby enhancing the coating's adhesion performance. The adhesion promoter includes modified molybdates, rare earth compounds, amine derivatives, and heterocyclic compounds. The modified molybdates can form a protective film on the magnesium alloy surface, preventing corrosive media such as water and oxygen from contacting the magnesium alloy surface, thus slowing down the corrosion process. Simultaneously, it reacts chemically with the magnesium alloy surface to form stable complexes or... The deposition layer enhances the adhesion between the coating and the substrate; rare earth compounds can form a uniform and dense oxide layer on the magnesium alloy surface, which can effectively increase the surface roughness and the number of active sites, providing more adhesion sites for the coating; amine derivatives contain active hydrogen atoms, which can undergo ring-opening addition reactions with the epoxy groups in the modified epoxy dispersion, promoting resin cross-linking and curing, generating a three-dimensional network structure, thereby forming a denser and tougher coating film; heterocyclic compounds contain heteroatoms such as N, O, and S, which can form special interactions with the magnesium alloy surface, such as through coordination bonds, hydrogen bonds, or other forms of weak interactions, to increase the affinity between the coating and the substrate.

[0034] Based on the above, this application can improve the bonding force between water-based coatings and magnesium alloys, thereby improving corrosion resistance and durability, so as to meet the requirements of the UAV field for high-performance and long-life materials. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the first process of the preparation method of the water-based coating for the magnesium alloy robot shell of this application;

[0038] Figure 2 This is a schematic diagram of the second process of the coating method for the magnesium alloy robot shell using water-based coatings according to this application.

[0039] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0040] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.

[0041] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0042] Based on this, this embodiment provides an aqueous coating for a magnesium alloy robot shell. By weight, the aqueous coating for the magnesium alloy robot shell includes component A, which comprises:

[0043] 55-80 parts modified epoxy dispersion, 1-10 parts adhesion promoter, wherein the adhesion promoter includes modified molybdate, rare earth compound, amine derivative and heterocyclic compound.

[0044] It should be noted that the magnesium alloy substrate can be a lightweight and highly corrosion-resistant magnesium alloy component such as a robot shell, robot skeleton, robotic arm, or joint transmission structure.

[0045] Modified epoxy dispersions can be modified epoxy dispersions containing phosphate groups; modified epoxy dispersions containing phosphate groups can form stronger chemical bonds with magnesium alloy surfaces; phosphate groups have strong reactivity and can react with magnesium alloy ions on the magnesium alloy surface to form stable complexes or covalent bonds, thereby significantly improving the adhesion between the coating and the substrate.

[0046] Meanwhile, the modified epoxy dispersion can also improve the barrier effect and chemical resistance of the coating, further protecting the magnesium alloy from external environmental corrosion.

[0047] By incorporating adhesion promoters including modified molybdates, rare earth compounds, amine derivatives, and heterocyclic compounds, the adhesion promoters can enhance the bonding strength between water-based coatings and magnesium alloys from different angles. Specifically:

[0048] Modified molybdates can form a protective film on the surface of magnesium alloys. This film can block corrosive media such as water and oxygen from contacting the magnesium alloy surface, thereby slowing down the corrosion process. For example, modified molybdates can react with magnesium alloy ions on the surface of magnesium alloys to generate a dense passivation film (such as MoO4). 2- With Mg 2+The resulting composite oxide layer effectively seals surface active sites; this passivation film can reduce pitting corrosion by more than 90%, greatly improving the corrosion resistance of magnesium alloys in harsh environments. Conventional coatings cannot effectively seal the surface active sites of magnesium alloys, making them prone to pitting corrosion in humid or electrolyte environments, affecting the long-term stability of the material. Simultaneously, it reacts chemically with the magnesium alloy surface to form stable complexes or deposits, thereby enhancing the adhesion between the coating and the substrate.

[0049] Rare earth compounds can form a uniform and dense oxide layer on the surface of magnesium alloys. This oxide layer can effectively increase the surface roughness and the number of active sites, providing more adhesion sites for the coating and thus enhancing the adhesion between the coating and the substrate.

[0050] The N and S coordinating atoms in amine derivatives (e.g., imidazoline, benzotriazole, etc.) can interact with magnesium alloy ions (such as Mg) on ​​the surface of magnesium alloys. 2+ Amine derivatives undergo complexation reactions to form stable chemical bonds. Furthermore, due to the high surface tension of magnesium alloy substrates, ordinary coatings struggle to fully wet them, affecting adhesion. Amine derivatives, containing active hydrogen atoms, can undergo ring-opening addition reactions with the epoxy groups in the modified epoxy dispersion, promoting resin cross-linking and curing to generate a three-dimensional network structure, thus forming a denser and tougher coating film. Simultaneously, amine derivatives possess excellent polar head group structures, reducing interfacial tension between the coating and substrate, improving wettability and spreadability, thereby improving the contact state between the coating and substrate, resulting in tighter interfacial bonding and further enhancing adhesion and overall coating quality.

[0051] Heterocyclic compounds containing heteroatoms such as N, O, and S can form special interactions with the magnesium alloy surface, such as through coordination bonds, hydrogen bonds, or other forms of weak interactions, to increase the affinity between the coating and the substrate.

[0052] In summary, the synergistic effect of modified molybdates, rare earth compounds, amine derivatives, and heterocyclic compounds not only enhances initial adhesion but also forms a more stable cross-linked network after coating curing, improving the coating's resistance to aging, temperature changes, and chemicals. Furthermore, the adhesion promoter in this embodiment is applicable to different surface materials (e.g., imidazoline is suitable for magnesium alloys, and rare earth compounds can enhance polymer interfacial bonding), improving the compatibility of waterborne coatings with composite substrates (e.g., magnesium alloy + aluminum alloy + plastic).

[0053] Based on the above, the modified epoxy dispersion and the adhesion promoter produce a synergistic effect, resulting in an adhesion between the coating and the substrate greater than 10 MPa. Furthermore, due to the formation of strong interfacial chemical bonds, the coating can be effectively prevented from peeling off even under external forces or environmental stress, thus improving the coating's durability and protective performance.

[0054] In this embodiment, component A further includes:

[0055] 1-10 parts salt spray resistant filler, 1-10 parts nanosheet filler, wherein the salt spray resistant filler comprises modified tripolyphosphate compounds and modified aluminum zinc phosphomolybdate compounds.

[0056] It should be noted that ordinary epoxy resin coatings have high porosity and are prone to corrosive media penetration during salt spray testing, with a salt spray resistance time typically ≤500 hours.

[0057] This embodiment provides immediate protection and long-lasting self-healing capabilities by adding salt spray resistant fillers containing modified tripolyphosphate and modified aluminum zinc phosphomolybdate, thus maintaining a high level of corrosion resistance in complex salt spray environments.

[0058] Specifically, tripolyphosphates can release PO4. 3- Ions, these PO4 3- Ions can react with Mg on the surface of magnesium alloys 2+ The combination forms a sparingly soluble magnesium phosphate (such as Mg3(PO4)2) passivation film. This passivation film has good stability and corrosion resistance, and can effectively prevent corrosive media such as oxygen, moisture and chloride ions from contacting the substrate surface, thereby inhibiting the anodic reaction (Mg→Mg). 2+ +2e - This process helps prevent oxidation and corrosion of magnesium alloy substrates. Furthermore, through organic modification, the dispersibility and compatibility of tripolyphosphates in the resin system can be improved, avoiding the agglomeration of inorganic particles and making the coating more uniform and dense. The modified tripolyphosphates can also better combine with other components (such as hyperbranched microgels) to jointly build a more robust physical barrier, further delaying the penetration path of corrosive media.

[0059] In addition, aluminum zinc phosphomolybdate materials contain Al 3+ and Zn 2+ These can deposit a dense oxide or hydroxide protective layer on the surface of magnesium alloys. This protective film not only blocks the intrusion of external corrosive agents but also repairs locally damaged areas, providing a continuous protective effect; molybdate ions (MoO4) 2- ) in Mo 6+ It exhibits strong redox properties, preferentially initiating reduction reactions at the cathode, consuming dissolved oxygen in the solution, and reducing the occurrence of cathode reactions (O2 + 4e). - +2H₂O→4OH⁻ -This achieves cathodic protection. Furthermore, by modifying zinc aluminum phosphomolybdate, its release rate within the coating can be controlled, ensuring the continuous release of effective corrosion-inhibiting ions throughout its service life and extending the coating's effective protection time.

[0060] In summary, PO4 3- Al 3+ Zn 2+ Mo 6+ The chemical barrier formed by various corrosion-inhibiting ions not only creates a physical barrier within the coating but also generates a stable passivation film at the interface, significantly improving the overall corrosion resistance of the coating through this dual protection. Furthermore, a synergistic effect exists; for example, PO4... 3- The resulting passivation film provides a better adhesion substrate for ions from other magnesium alloy substrates, while Al 3+ Zn 2+ The resulting protective layer further strengthens this barrier. 6+ The cathodic protection provided reduces the corrosion tendency of the entire system.

[0061] Experimental data shows that when the amount of salt spray resistant filler is less than 1 part, the release of corrosion-inhibiting ions is insufficient, making it difficult to form an effective protective layer; when the amount of salt spray resistant filler is more than 10 parts, it leads to filler agglomeration and poor dispersibility, affecting the density and mechanical properties of the coating. Therefore, in this embodiment, the preferred amount of salt spray resistant filler is 1-10 parts.

[0062] Because ordinary epoxy resin coatings have insufficient penetration, the resulting coating thickness is usually ≤15μm and the film application speed is <5μm / min, which cannot meet the protection requirements of high-requirement application scenarios such as subway grilles. This embodiment uses nanosheet fillers (such as graphene or boron nitride), which utilize their excellent planar structure to form a "maze"-like path in the coating. This structure can significantly extend the path length of corrosive media (such as chloride ions in salt spray) to penetrate the substrate by more than 3 times. It can also be better dispersed in the coating during electrophoresis, increasing the coating thickness and improving its uniformity.

[0063] Compared to traditional fillers, nanosheet fillers, due to their extremely small size and good dispersibility, can more effectively fill the micropores in the coating, thereby increasing the overall film thickness.

[0064] To achieve the required film thickness and uniformity, this embodiment also adds 1-10 parts of anionic mineral-modified rheology modifier to ensure that the coating can be uniformly and quickly applied during electrophoresis. The use of anionic mineral-modified rheology modifier can significantly improve the rheological properties of the coating, giving it better flowability and smoothness during application, which helps to achieve a uniform film thickness distribution. By adjusting the viscosity and thixotropy of the coating, the anionic mineral-modified rheology modifier can promote faster coating application, increasing the coating speed to over 5 μm / min, meeting the needs of applications such as subway grilles.

[0065] In this embodiment, component A further includes:

[0066] 1-10 parts of rheology modifier, wherein the components of the rheology modifier include polyurea compounds, modified inorganic salts, and modified polyurethanes.

[0067] It should be noted that the mismatch in coefficients of thermal expansion is one of the main reasons why coatings develop internal stress and eventually detach during temperature changes (such as from -40℃ to 80℃). Introducing rheology modifiers, especially those that increase coating flexibility, can alleviate this stress concentration to some extent. Specifically:

[0068] Polyurea compounds are typically formed by the reaction of isocyanates with polyamines. Their structure is rich in urethane bonds (-NHCOO-) and urea bonds (-NHCONH-), which endow the materials with excellent mechanical properties and chemical resistance. Furthermore, polyureas exhibit high elongation at break, effectively absorbing deformation energy caused by temperature changes and reducing internal stress accumulation.

[0069] Modified inorganic salts are inorganic fillers that have undergone surface treatment or chemical modification, such as silicates and aluminates. Modified inorganic salts can not only regulate the rheological behavior of coatings but also improve their hardness and wear resistance. They react with modified epoxy dispersions through ionic bonds or other means to form physical cross-linking points, thereby enhancing the stability of the coating's internal structure. The metal ions in the modified inorganic salts (e.g., Zn)... 2+ Al 3+ These substances can coordinate and complex with organic molecules in adhesion promoters (such as amine derivatives, heterocyclic compounds, etc.), which helps to improve the adhesion between the coating and the substrate.

[0070] Modified polyurethanes optimize their properties by introducing special functional groups into their main chain or side chains. For example, introducing hydrophilic groups can improve their dispersibility and compatibility in aqueous environments; while introducing rigid segments can enhance the material's hardness and heat resistance.

[0071] In modified polyurethanes, soft segments (such as polyether or polyester segments) provide elastic resilience, while hard segments (such as diisocyanate units) contribute strength and rigidity. This combination allows the coating to possess both the necessary flexibility to cope with dimensional changes caused by thermal cycling and sufficient rigidity to maintain shape stability.

[0072] By adding rheology modifiers to adjust the coating flexibility, no peeling occurred after 10 cycles of thermal exchange at temperatures ranging from -40℃ to 80℃.

[0073] In this embodiment, component A further includes:

[0074] 1-10 parts of defoamer, 1-10 parts of hydroxyl-containing siloxane polymer, and 1-10 parts of substrate wetting agent, wherein the components of the defoamer include modified organosilicon and modified acrylic acid.

[0075] In water-based coatings, especially when applied in high-humidity environments, the rate of paint film defects (such as sagging, blistering, and flash rust) exceeds 30%. These defects compromise the density and protective properties of the coating, making the magnesium alloy substrate more susceptible to corrosion failure during use.

[0076] Defoamers effectively reduce the surface tension of coating systems, thereby quickly breaking down existing foam films. Modified silicones and modified acrylics can efficiently eliminate bubbles without affecting other coating properties and without causing surface defects such as pinholes or fisheyes.

[0077] Specifically, the molecular structure of modified organosilicon (longer Si-O bond length and larger bond angle) results in lower surface energy, allowing it to spread effectively on liquid surfaces and thus disrupt foam stability. Modified organosilicon also possesses good thermal stability and chemical inertness, making it suitable for long-term use. Modified acrylic acid enhances the compatibility of defoamers with coatings, avoiding surface defects caused by incompatibility.

[0078] Experimental data show that the above-mentioned defoamer and wetting agent work synergistically to reduce both the sagging rate and foaming rate to less than 5%.

[0079] To enhance the coating's weather resistance, water resistance, and adhesion, especially under long-term outdoor use conditions, this embodiment also adds 1-10 parts of a hydrogen-containing siloxane polymer. The Si-H bonds in the hydrogen-containing siloxane polymer can react with moisture in the air to generate Si-OH bonds, which then crosslink to form a dense protective layer, providing excellent water resistance and weather resistance, suitable for applications in outdoor exposure environments. The hydrogen-containing siloxane polymer can enhance the adhesion between the coating and the substrate through chemical bonding or other interactions, especially on magnesium alloy substrates. Its hydrophilic end groups can form stable bonding points with the magnesium alloy substrate surface, improving the coating's long-lasting adhesion performance.

[0080] Substrate wetting agents reduce the surface tension of liquids, allowing paints or coatings to spread better on the substrate surface and improving the wettability of the paint to the substrate. This ensures uniform coating distribution and reduces surface defects such as pinholes and fisheyes.

[0081] Specifically, the substrate wetting agent can be a silicone-based wetting agent or a nonionic wetting agent. Due to the unique molecular structure of silicone-based wetting agents (e.g., modified polydimethylsiloxane) (longer Si-O bond length and larger bond angle), they have extremely low surface energy, which makes them very effective in reducing the surface tension of the coating system and helps improve the spreadability of the coating on complex or difficult-to-wet substrates. For highly reactive metals such as magnesium alloys, the use of silicone-based wetting agents can help form a more uniform coating and reduce surface defects such as pinholes and fisheyes.

[0082] In addition, component A may also include 50-100 parts of color paste, which provides color and decoration without affecting the coating performance.

[0083] In this embodiment, the water-based coating for the magnesium alloy robot shell further includes component B, which comprises 1-30 parts of a modified water-based amine polymer.

[0084] In this embodiment, a waterborne epoxy-amine curing system is constructed using a modified epoxy dispersion and a modified waterborne amine polymer. This system offers significant advantages over existing technologies in terms of environmental friendliness, application adaptability, and coating performance (adhesion, flexibility, corrosion resistance). Specifically:

[0085] By introducing modified waterborne amine polymers as curing agents and combining them with modified epoxy dispersions to construct an all-waterborne system, no organic solvents are needed, significantly reducing VOC (volatile organic compounds) emissions. The modified waterborne amine polymers and modified epoxy dispersions have higher reactivity, enabling cross-linking and curing at room temperature, saving energy, and making them suitable for outdoor and on-site construction.

[0086] Modified waterborne amine polymers can be waterborne amine polymers with the introduction of flexible segments (such as polyethers and aliphatic chains) and polar groups (such as hydroxyl and carboxyl groups). Flexible segments can alleviate the brittleness problem of modified epoxy dispersions after curing and improve impact resistance and bending performance, while polar groups can enhance the interfacial bonding force with a variety of complex substrates such as magnesium alloys and plastics.

[0087] It should be noted that the above-mentioned 55-80 parts of modified epoxy resin, 20-35 parts of phosphate ester polymer modified epoxy resin, 1-10 parts of hyperbranched modified resin microgel, 1-10 parts of salt spray resistant filler, 1-10 parts of nanosheet filler, 1-10 parts of anionic mineral modified rheology modifier, 1-10 parts of hydrogen-containing siloxane polymer and 50-100 parts of color paste are mixed and stirred to uniformly disperse the components, thus obtaining component A.

[0088] Component A and component B are mixed only when needed to obtain the water-based coating for the magnesium alloy robot shell.

[0089] In one feasible embodiment, the mixture may consist of 60 parts modified epoxy resin, 30 parts phosphate ester polymer modified epoxy resin, 5 parts hyperbranched modified resin microgel, 5 parts salt spray resistant filler, 5 parts nanosheet filler, 5 parts anionic mineral modified rheology modifier, 5 parts hydrogen-containing siloxane polymer, and 80 parts...

[0090] The color paste is mixed and stirred to ensure uniform dispersion of all components, resulting in water-based coating component A for the magnesium alloy robot shell. Component A is only mixed with 20 parts of modified water-based amine polymer component B before use to obtain the water-based coating for the magnesium alloy robot shell, thus preventing premature cross-linking between the modified water-based amine polymer and component A.

[0091] In this embodiment, 55-80 parts of modified epoxy dispersion, 1-10 parts of adhesion promoter, 1-10 parts of salt spray resistant filler, 1-10 parts of nanosheet filler, 1-10 parts of rheology modifier, 1-10 parts of defoamer, 1-10 parts of hydroxyl-containing siloxane polymer, 1-10 parts of substrate wetting agent, and 1-30 parts of modified waterborne amine polymer are used to significantly improve the adhesion (≥10MPa) between the waterborne coating and the magnesium alloy substrate of the above-mentioned magnesium alloy robot shell, and achieve salt spray resistance ≥1000 hours and no peeling after 10 cycles of hot and cold alternation, which meets the requirements of the UAV field for high performance and long service life of materials.

[0092] Based on the first embodiment of this application, in the second embodiment of this application, the content that is the same as or similar to that in Embodiment 1 above can be referred to the above description, and will not be repeated hereafter. On this basis, a method for preparing a water-based coating for a magnesium alloy robot shell as described in Embodiment 1 is proposed, referring to… Figure 1 , Figure 1 This is a schematic flowchart of the preparation method of the water-based coating for the magnesium alloy robot shell of this application, wherein the preparation method includes:

[0093] Step S10: Add the modified epoxy dispersion and the hydroxyl-containing siloxane polymer to a high-speed disperser and stir at the first speed for 10-20 minutes.

[0094] In this embodiment, a high-speed disperser is used to rapidly and uniformly shear and disperse macromolecular materials (such as epoxy resin and amine polymers) including modified epoxy dispersion, waterborne amine polymers, and hydroxyl-containing siloxane polymers at a first rotation speed (1000-2000 r / min, preferably 1500 r / min). This facilitates the formation of a stable emulsion system, improves the compatibility of subsequent fillers and additives, and avoids gel points or phase separation caused by excessively high local concentrations. Simultaneously, thorough mixing is ensured without excessive shearing that damages polymer chains, and the time is controlled within 10-20 minutes (preferably 15 minutes) to avoid generating excessive bubbles.

[0095] Step S20: The nanosheet filler, salt spray resistant filler and adhesion promoter are added to the high-speed disperser in sequence, and the mixture is stirred at the first speed for 25-35 minutes.

[0096] Furthermore, the nanosheet filler, salt spray resistant filler, and adhesion promoter are added sequentially to the high-speed disperser and stirred for 25-35 minutes (preferably 30 minutes) to ensure that the filler is fully wetted and uniformly dispersed in the resin system. This facilitates the interfacial bonding between the functional filler and the resin. The adhesion promoter needs sufficient time to migrate to the particle surface and react with the metal ions. If the nanosheet filler, salt spray resistant filler, and adhesion promoter are added first, it will affect the dispersion uniformity of the epoxy dispersion, causing agglomeration or sedimentation.

[0097] This step enhances the physical barrier properties of the coating, allowing the adhesion promoter to begin its passivation and anchoring effects, resulting in a significant improvement in the overall corrosion resistance, density, and initial adhesion of the coating.

[0098] Step S30: Add the substrate wetting agent, rheology modifier and defoamer to the high-speed disperser and continue stirring at the second speed for 5-15 minutes, wherein the second speed is less than the first speed;

[0099] Furthermore, the substrate wetting agent, rheology modifier, and defoamer are stirred at a low speed of 5-15 min (preferably 10 min) using a high-speed disperser at a second rotation speed (e.g., 100-400 r / min) to prevent the introduction of new air bubbles, avoid disrupting the already formed stable system, and ensure uniform distribution of the additives without causing them to become ineffective due to prolonged stirring.

[0100] Step S40: Add the color paste to the high-speed disperser and continue stirring until it is uniform. Then let it stand for a preset time to mature and obtain component A.

[0101] Further, the pigment paste is added to the high-speed disperser and stirred until it is uniform, ensuring that the pigment is evenly dispersed and that there is no floating color or blooming. After standing for a preset time (24-60h, preferably 48h) for curing, the components in the coating system can be fully relaxed and balanced, allowing the resin and additives to complete the initial physical / chemical interaction, which is beneficial to eliminate internal stress and improve storage stability.

[0102] Step S50: Mix component A and component B to obtain the water-based coating for the magnesium alloy robot shell, wherein component B includes a modified water-based amine polymer.

[0103] That is, component A and component B (modified waterborne amine polymer) are mixed only during use to obtain the waterborne coating for the magnesium alloy robot shell, so as to avoid premature cross-linking between the modified waterborne amine polymer and component A.

[0104] In this embodiment, the water-based coating for the magnesium alloy robot shell can be prepared by the above preparation method.

[0105] Based on the first embodiment of this application, in the second embodiment of this application, the content that is the same as or similar to that in Embodiment 1 above can be referred to the above description, and will not be repeated hereafter. On this basis, a coating method for a magnesium alloy robot shell using a water-based coating as described in Embodiment 1 is proposed, referring to… Figure 2 , Figure 2 This is a schematic flowchart of the coating method for the magnesium alloy robot shell using water-based coatings according to this application.

[0106] In this embodiment, the coating method includes steps A1-A2:

[0107] Step A1: Using air-assisted airless spraying technology, the water-based coating is sprayed onto the surface of the magnesium alloy substrate based on preset spraying parameters;

[0108] It should be noted that using high pressure to atomize the coating, supplemented by a small amount of compressed air, can improve the atomization effect; it can achieve uniform, continuous, and thin-layer coating, and is suitable for occasions with high requirements for film thickness and appearance; it is suitable for water-based coating systems, reduces splashing loss, and thus improves the paint application rate.

[0109] The preset spraying parameters include: a spraying pressure of 0.3-0.8 MPa and a nozzle diameter of 0.8-2.5 mm. The spraying pressure of 0.3-0.8 MPa can control the atomization degree of the coating. Too high a pressure will easily cause dry spraying, while too low a pressure will result in poor atomization. The nozzle diameter of 0.8-2.5 mm affects the flow rate and atomized particle size, and is adapted to the viscosity characteristics of water-based coatings.

[0110] In one feasible implementation, the preset spraying parameters include: a spraying pressure of 0.6 MPa and a nozzle diameter of 2.0 mm.

[0111] Using the above method, the film thickness can be controlled to 20-30μm, ensuring corrosion resistance while avoiding sagging, which meets the requirements for lightweight protection of magnesium alloys.

[0112] Step A2: Bake the coated magnesium alloy substrate at 80-120℃ for 20-30 minutes to complete the coating process.

[0113] Furthermore, the coated magnesium alloy substrate is baked at 80-120℃ (preferably 100℃) for 20-30 minutes (preferably 25 minutes) to achieve the crosslinking reaction between the epoxy resin and the amine curing agent, and to complete the Si-H addition or condensation reaction of the siloxane component, thereby improving the mechanical strength, chemical resistance, adhesion and weather resistance of the coating.

[0114] A temperature of 80-120℃ can provide enough energy to activate the curing reaction, but too high a temperature may lead to thermal aging; baking for 20-30 minutes ensures that the epoxy-amine system reaches full cross-linking, while perfecting the siloxane network structure and improving density and adhesion.

[0115] The quality of the spraying determines the curing effect. If the sprayed film thickness is uniform, the subsequent curing will be uniform. If there are no bubbles or pinholes on the surface during spraying, there will be no defects after curing. Therefore, the method described in this embodiment can make the coating more uniform and the surface free of defects. It not only fully considers the rheological properties and application sensitivity of water-based coatings, but also takes into account the activity and thermal sensitivity of magnesium alloy substrates.

[0116] In this embodiment, before the step of spraying the water-based coating onto the surface of the magnesium alloy substrate based on preset spraying parameters, the following may also be performed:

[0117] The magnesium alloy substrate is immersed in an alkaline solution for 3-10 minutes, wherein the alkaline solution comprises NaOH at a concentration of 5-10 g / L and Na2SiO3 at a concentration of 2-5 g / L; the alkaline-treated magnesium alloy substrate is then immersed in an acidic solution for 30-120 seconds, wherein the acidic solution comprises citric acid at a concentration of 5-10 g / L and lactic acid at a concentration of 2-5 g / L; the acid-treated magnesium alloy substrate is then passivated in a magnesium alloy-specific passivation solution for 10-120 seconds to form a dense conversion film on the surface of the magnesium alloy substrate; the magnesium alloy substrate with the dense conversion film on its surface is then placed in a forced-air drying oven at a temperature of 135-170℃ for 15-30 minutes to complete the pretreatment of the magnesium alloy substrate.

[0118] Conventional magnesium alloy electrophoretic coating generally uses ordinary epoxy resin coatings and relies on traditional phosphating / chromate pretreatment processes to improve the surface condition of the substrate, thereby enhancing the adhesion between the coating and the substrate. This type of pretreatment process forms a dense conversion film (such as a phosphate or chromate film) on the magnesium alloy surface, providing a certain degree of physical anchoring and interfacial stability for the subsequent epoxy resin coating.

[0119] However, the traditional phosphating / chromate pretreatment process is complex and involves multiple steps, which not only increases production costs but also causes environmental pollution problems due to the high toxicity and carcinogenicity of hexavalent chromium compounds.

[0120] In this embodiment, the magnesium alloy substrate is immersed in an alkaline solution for 3-10 minutes (preferably 5 minutes). Since the alkaline solution usually contains strong alkali (such as sodium hydroxide or sodium carbonate) and surfactants, it can effectively remove grease, organic contaminants and mild oxides from the magnesium alloy surface. At the same time, the alkaline treatment can slightly corrode the magnesium alloy surface to generate a thin magnesium alloy hydroxide film, which helps to form a denser conversion film more uniformly during the subsequent acid treatment.

[0121] The alkaline solution comprises 5-10 g / L NaOH and 2-5 g / L Na₂SiO₃, preferably 7 g / L NaOH and 3 g / L Na₂SiO₃. The 5-10 g / L NaOH helps decompose and remove grease and other organic contaminants from the magnesium alloy surface, while also slightly dissolving the oxide layer and mild contaminants, forming a magnesium alloy hydroxide film that improves the adhesion between the subsequent conversion film and the substrate. The 2-5 g / L Na₂SiO₃ has emulsifying and dispersing capabilities, further improving the cleaning performance of the alkaline washing solution and helping to remove stubborn stains. Simultaneously, the formed silicate film can protect the magnesium alloy surface from excessive corrosion to some extent, providing protection for subsequent acid washing.

[0122] Furthermore, the magnesium alloy substrate after alkaline treatment is immersed in an acidic solution for 30-120 seconds (preferably 60 seconds). Since the acidic solution (such as nitric acid or ammonium bifluoride solution) can slightly dissolve the surface of the magnesium alloy, it produces tiny pits and irregular structures, increasing the surface area and thus enhancing the mechanical bonding force between the subsequent conversion film and the substrate. At the same time, it removes alkaline substances and other impurities that may remain during the alkaline washing process, ensuring surface cleanliness.

[0123] The acidic solution comprises citric acid at a concentration of 5-10 g / L and lactic acid at a concentration of 2-5 g / L, preferably citric acid at a concentration of 8 g / L and lactic acid at a concentration of 4 g / L. The mild organic acid properties of the 5-10 g / L citric acid can effectively remove the oxide layer and residual alkaline substances on the surface without severely damaging the magnesium alloy substrate, while generating a micro-pit structure to increase the surface area. The 2-5 g / L lactic acid can work together with the citric acid to further optimize the etching effect during the pickling process, ensuring uniform surface treatment, thereby facilitating the smooth progress of the chemical reaction during subsequent conversion coating treatment and improving the quality and adhesion of the conversion coating.

[0124] The magnesium alloy passivation solution comprises: 10-50 g / L phosphoric acid, 5-50 g / L calcium dihydrogen phosphate, 1-10 g / L sodium silicate, 0.1-1 g / L dodecyl dimethylamine hydantoin, and 1-15 g / L chlorogenic acid. The passivation temperature for the acid-treated magnesium alloy substrate is 35-55°C, so that the formed dense conversion film has good corrosion resistance and can also provide excellent interfacial adhesion, supporting the adhesion of subsequent coatings.

[0125] Furthermore, at high temperatures, moisture and other volatile components in the conversion film evaporate, resulting in a denser and more robust film structure. Appropriate heat treatment helps promote the formation of chemical bonds within the conversion film and between it and the substrate surface, further enhancing the film's stability and durability. Ensure the magnesium alloy substrate is completely dry before entering the electrophoresis tank to avoid problems such as decreased electrophoretic quality or the formation of bubbles due to residual moisture.

[0126] A temperature range of 135-170℃ (e.g., 150℃) can effectively complete the dehydration and polycondensation reactions without causing excessive oxidation or ablation of the magnesium alloy substrate. Furthermore, 10-30 minutes is sufficient for the entire conversion film system to complete the dehydration, polycondensation, and densification process. Too short a time will result in incomplete curing of the film, affecting corrosion resistance and adhesion, while too long a time may lead to carbonization of the silane coupling agent and brittle cracking of the film, thus reducing performance.

[0127] Experimental data show that the magnesium alloy substrate obtained by the above coating method can achieve the following properties:

[0128] Adhesion: ≥10MPa (≤5MPa for conventional process pull-off test).

[0129] Salt spray resistance: No white rust after 1000 hours of neutral salt spray test (≤500 hours for conventional processes).

[0130] Thermal cycling: 10 cycles of -40℃ to 80℃, no coating peeling.

[0131] The performance testing method is as follows:

[0132] Adhesion: The adhesion was tested using the pull-off method, in accordance with GB / T5210-2006.

[0133] Salt spray resistance: The coating's resistance to chloride ion corrosion is evaluated by testing according to GB / T 1771-2007 (neutral salt spray NSS).

[0134] Thermal cycling: The test was conducted in a high and low temperature test chamber under the following conditions: 80±2℃, maintained at RH95±5% for 4 hours, then cooled to -40℃ at a rate of 1℃ / min, maintained at -40±2℃ for 4 hours, then cooled to 80℃ at a rate of 1℃ / min with RH95%. Each cycle lasted 12 hours. After 10 cycles, the samples were removed and visually inspected. The samples were required to show no blistering, cracking, or peeling.

[0135] The preparation method provided in this application significantly improves the coating's adhesion, salt spray resistance, thermal shock resistance, and application flexibility. Simultaneously, dynamic voltage control technology avoids breakdown problems in magnesium alloys due to current overload during electrophoresis. The pretreatment process uses zirconate titanate conversion instead of traditional phosphating, eliminating heavy magnesium alloy pollution, achieving green manufacturing, and combining excellent interfacial adhesion and corrosion resistance.

[0136] It should be noted that the above examples are only for understanding this application and do not constitute a limitation on the preparation method and coating method of the water-based coating for the magnesium alloy robot shell of this application. Any simple modifications based on this technical concept are within the protection scope of this application.

Claims

1. A water-based coating for a magnesium alloy robot shell, characterized in that, By weight, the water-based coating for the magnesium alloy robot housing includes component A, which comprises: 55-80 parts modified epoxy dispersion, 1-10 parts adhesion promoter, wherein the adhesion promoter includes modified molybdate, rare earth compound, amine derivative and heterocyclic compound.

2. The water-based coating for the magnesium alloy robot shell as described in claim 1, characterized in that, Component A further includes: 1-10 parts salt spray resistant filler, 1-10 parts nanosheet filler, wherein the salt spray resistant filler comprises modified tripolyphosphate compounds and modified aluminum zinc phosphomolybdate compounds.

3. The water-based coating for the magnesium alloy robot shell as described in claim 1, characterized in that, Component A further includes: 1-10 parts of rheology modifier, wherein the components of the rheology modifier include polyurea compounds, modified inorganic salts, and modified polyurethanes.

4. The water-based coating for the magnesium alloy robot shell as described in claim 1, characterized in that, Component A further includes: 1-10 parts of defoamer, 1-10 parts of hydroxyl-containing siloxane polymer, and 1-10 parts of substrate wetting agent, wherein the components of the defoamer include modified organosilicon and modified acrylic acid.

5. The water-based coating for the magnesium alloy robot shell as described in claim 1, characterized in that, The water-based coating for the magnesium alloy robot shell further includes component B, which comprises: 1-30 parts modified waterborne amine polymer.

6. A method for preparing an aqueous coating for a magnesium alloy robot shell as described in any one of claims 1 to 5, characterized in that, The preparation method includes: The modified epoxy dispersion and the hydroxyl-containing siloxane polymer were added to a high-speed disperser and stirred at the first speed for 10-20 minutes. The nanosheet filler, salt spray resistant filler and adhesion promoter are added to the high-speed disperser in sequence, and the mixture is stirred at the first speed for 25-35 minutes. Add the substrate wetting agent, rheology modifier and defoamer to the high-speed disperser and continue stirring at the second speed for 5-15 minutes, wherein the second speed is less than the first speed. Add the color paste to the high-speed disperser and continue stirring until it is uniform. Let it stand for a preset time to mature and obtain component A. Component A and component B are mixed to obtain the water-based coating for the magnesium alloy robot shell, wherein component B includes a modified water-based amine polymer.

7. A method for applying a water-based coating to a magnesium alloy robot shell as described in any one of claims 1 to 5, characterized in that, The coating method includes: Air-assisted airless spraying technology is used to spray the water-based coating onto the surface of the magnesium alloy substrate based on preset spraying parameters; The coated magnesium alloy substrate is baked at 80-120℃ for 20-30 minutes to complete the coating process.

8. The method as described in claim 7, characterized in that, The preset spraying parameters include: a spraying pressure of 0.3-0.8 MPa and a nozzle diameter of 0.8-2.5 mm.

9. The method as described in claim 7, characterized in that, Prior to the step of spraying the water-based coating onto the surface of the magnesium alloy substrate, the method further includes: The magnesium alloy substrate is immersed in an alkaline solution for 3-10 minutes, wherein the alkaline solution comprises NaOH with a concentration of 5-10 g / L and Na2SiO3 with a concentration of 2-5 g / L. The magnesium alloy substrate after alkaline treatment is immersed in an acidic solution for 30-120 seconds, wherein the acidic solution comprises citric acid at a concentration of 5-10 g / L and lactic acid at a concentration of 2-5 g / L. The magnesium alloy substrate after acid treatment is passivated in a special passivation solution for magnesium alloy for 10-120 seconds to form a dense conversion film on the surface of the magnesium alloy substrate. The magnesium alloy substrate with a dense conversion film on its surface is placed in a forced-air drying oven at a temperature of 135-170℃ for 15-30 minutes to complete the pretreatment of the magnesium alloy substrate.

10. The method as described in claim 9, characterized in that, The magnesium alloy passivation solution comprises: 10-50 g / L phosphoric acid, 5-50 g / L calcium dihydrogen phosphate, 1-10 g / L sodium silicate, 0.1-1 g / L dodecyl dimethylamine hydantoin, and 1-15 g / L chlorogenic acid. The passivation temperature for magnesium alloy substrates after acid treatment is 35-55℃.

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