Aluminum alloy hub self-repairing coating and preparation method

Abstract

The invention discloses an aluminum alloy hub self-repairing coating and a preparation method, the self-repairing coating comprises polyurethane and nanocapsules uniformly dispersed in a polyurethane matrix, the nanocapsules comprise shells and repairing agents located in the shells, the shells are made of silicon dioxide, the repairing agents are siloxane repairing agents, and the diameter of the nanocapsules is 50-200 nm. The self-repairing coating is formed on the aluminum alloy hub through spraying, and repairing can be conducted when microcracks are generated on the coating due to external force.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy wheels, and more particularly to a self-repairing coating for an aluminum alloy wheel and a preparation method thereof. Background Art

[0002] Aluminum alloy wheels are widely used due to their lightweight and high strength, but their surfaces are susceptible to scratches and corrosion. Existing technologies have the following drawbacks: 1. Traditional coating processes (such as chromium-free passivation) only improve corrosion resistance but cannot repair scratches; 2. Multi-color coating technology focuses on aesthetics but lacks functional breakthroughs; 3. Environmental protection is insufficient, as some processes still use harmful chemicals. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an aluminum alloy wheel hub self-repairing coating and a preparation method thereof.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] The invention discloses a self-repairing coating for an aluminum alloy wheel hub, comprising polyurethane and nanocapsules uniformly dispersed in a polyurethane matrix. The nanocapsules comprise an outer shell and a repairing agent located in the outer shell. The outer shell is made of silicon dioxide, and the repairing agent is a siloxane repairing agent.

[0006] Furthermore, the diameter of the nanocapsules is 50-200 nm.

[0007] Furthermore, the shell has a thickness of 10-20 nm.

[0008] Furthermore, the proportion of the repair agent in the nanocapsule is 70%-80%.

[0009] Furthermore, the viscosity of the repair agent is ≤100 cP.

[0010] The method for preparing a self-repairing coating comprises the following steps:

[0011] Nanocapsule preparation:

[0012] The siloxane repair agent and the silica precursor are mixed by emulsification, an emulsifier is added, and the mixture is stirred at high speed to form a nano-scale oil-in-water emulsion;

[0013] Through the sol-gel method, under the action of an acidic catalyst, the reaction is carried out at 60°C for 4-6 hours; the silica precursor is hydrolyzed to generate silicic acid, which is condensed to form a silica shell that wraps the repair agent;

[0014] The emulsion was converted into solid nanocapsules by spray drying and sieving to control the size;

[0015] Coating preparation:

[0016] The nanocapsules are mixed with polyurethane resin at a ratio of 3% to 10%, a silane coupling agent is added as a dispersant, and the mixture is processed in a disperser for 20 to 30 minutes to form a coating;

[0017] Performing chromium-free passivation treatment on the aluminum alloy wheel hub to form a primer layer on the surface of the aluminum alloy wheel hub, and applying paint on the primer layer on the surface of the aluminum alloy wheel hub through a spraying device;

[0018] The polyurethane is completely cross-linked and cured by heating to form a topcoat layer on the aluminum alloy wheel hub.

[0019] Furthermore, during the temperature-raising curing process, the temperature is raised to 120-150° C., and the curing time is 20-30 minutes.

[0020] Furthermore, a clear varnish layer is coated on the topcoat layer.

[0021] The beneficial effects of the present invention are as follows: external force causes microcracks in the coating, stress concentration at the crack tip causes the shell of the nanocapsule to rupture, the repair agent is released, and the silicone repair agent flows out of the ruptured capsule to fill the crack. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a structure of the coating in this embodiment;

[0023] Figure 2 is a cross-sectional view of the nanocapsule in this embodiment;

[0024] Figure 3 Schematic diagram of a structure of the spraying device in this embodiment;

[0025] Figure 4 is a cross-sectional view of the spraying device in this embodiment;

[0026] Figure 5 is a cross-sectional view of the clamping member in this embodiment;

[0027] Figure 6 for Figure 5 A magnified schematic diagram of point A in the middle;

[0028] Figure 7 Schematic diagram of the internal structure of the chassis in this embodiment;

[0029] Figure 8 for Figure 7 Enlarged schematic diagram of point A in the middle.

[0030] Figure numerals: 1, wheel hub; 2, primer layer; 3, topcoat layer; 4, varnish layer; 5, housing; 6, repair agent; 7, driving gear; 8, driven gear; 9, crossbeam; 10, moving plate; 11, clamping mechanism; 12, linkage member; 13, conveying roller; 14, stopper; 15, support rail; 16, notch; 17, linear drive 1; 18, mounting plate; 19, rotating motor; 20, rotating shaft; 21, clamping member; 22, connecting arm; 23, linkage seat; 24, guide bar; 25, moving seat; 26, trigger lever; 27, gear lever; 28, spray pump; 29, spray gun; 30, paint box; 31, feed pipe; 32 , drag chain; 33, linear drive 2; 34, positioning rod; 35, middle hole; 36, driving rod; 37, opening; 38, tightening block; 39, protrusion; 40, guide groove; 41, driving block; 42, spring 1; 43, positioning ring; 44, driving head; 45, abutment slope; 46, mounting hole; 47, linkage block; 48, spring 2; 49, guide hole; 50, guide slope; 51, spring 3; 52, driving slope; 53, stepped hole; 54, movable block; 55, spring 4; 56, transmission slope; 57, chassis; 58, side panel; 59, end panel; 60, top panel; 61, screw; 62, screw motor. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] like Figure 1-Figure 2 The self-repairing coating for aluminum alloy wheels is shown in Figure 1. It includes polyurethane and nanocapsules uniformly dispersed within a polyurethane matrix. The polyurethane matrix has been surface-modified to ensure uniform dispersion of the nanocapsules without affecting the coating's transparency and mechanical properties. The nanocapsules have a diameter of 50-200 nm.

[0033] The nanocapsule consists of an outer shell 5 and a healing agent 6 located within it. The outer shell 5 is made of silica, which offers high mechanical strength, chemical stability, and transparency, protecting the internal healing agent 6 from environmental influences. The outer shell 5 has a thickness of 10-20 nm. The healing agent 6 is a low-viscosity silicone with a viscosity of ≤100 cP, such as a hydroxyl-containing silicone. It exhibits fluidity, rapid curing, and compatibility with the coating substrate. The healing agent 6 accounts for 70%-80% of the nanocapsule.

[0034] A method for preparing a self-repairing coating for an aluminum alloy wheel hub comprises the following steps:

[0035] Nanocapsule preparation:

[0036] The siloxane repair agent is mixed with a silica precursor such as ethyl orthosilicate by an emulsification method, and an emulsifier Span-80 is added, and the mixture is stirred at high speed to form a nano-scale water-in-oil emulsion. The mixture is reacted at 60°C for 4-6 hours under the action of an acidic catalyst such as hydrochloric acid by a sol-gel method. The silica precursor is hydrolyzed to generate silicic acid, which is polycondensed to form a silica shell 5 that encapsulates the repair agent 6. The thickness of the shell 5 is ensured to be consistent by adjusting the reaction temperature and catalyst concentration. The emulsion is converted into solid nanocapsules by spray drying, and the size is controlled by screening. Nanocapsules of 50-200 nm are retained.

[0037] Coating preparation:

[0038] Nanocapsules are mixed with polyurethane resin at a mass ratio of 3% to 10%, and a silane coupling agent is added as a dispersant. The mixture is then dispersed in a high-shear disperser at a speed of 8,000 to 12,000 rpm for 20 to 30 minutes to ensure uniform dispersion of the capsules, thereby forming a coating. A chromium-free passivation treatment is then performed on the aluminum alloy wheel hub 1 to form a primer layer 2, i.e., a chromium-free passivation layer, on the surface of the aluminum alloy wheel hub 1. This layer has excellent corrosion resistance and improves the adhesion of subsequent coatings. The coating is then applied to the primer layer 2 on the surface of the aluminum alloy wheel hub 1 via a spraying device. Specifically, an electrostatic spraying process is employed, with a voltage of 10 to 20 kV, a spraying distance of 20 to 30 cm, and a coating thickness of 20 to 30 μm. The coating is then cured by heating to 120 to 150°C for 20 to 30 minutes. This allows the polyurethane to fully crosslink and cure, forming a transparent topcoat layer 3 on the aluminum alloy wheel hub 1. A clearcoat layer 4 is then applied over the topcoat layer 3 to provide protection.

[0039] After curing, the scratch test showed that the repair efficiency reached 92% within 30 minutes, and there was no corrosion after 480 hours of salt spray test.

[0040] Mechanical scratches can cause microcracks in the coating, with stress concentration at the crack tips rupturing the nanocapsule shells 5. In corrosive environments, local pH changes, such as acidic corrosion, can trigger the rupture of some nanocapsules. This rupture releases the internal repair agent 6, allowing the siloxane repair agent to flow out of the ruptured capsules and fill the cracks. The hydroxyl groups in the siloxane react with moisture in the air to form a three-dimensional network structure. The reaction equation is: Si-OH + H₂O → Si-O-Si + H₂O. The cured repair layer seamlessly bonds with the original coating, creating a smooth surface and restoring both its appearance and protective properties.

[0041] Repair Efficiency: ≥90% repair efficiency within 30 minutes. Durability: After a single repair, the coating's salt spray resistance returns to 95% of its original state. Appearance: For scratches ≤50μm deep, no visible marks remain on the repaired surface. Extended Wheel Life: The self-repair function reduces the spread of corrosion caused by scratches, increasing service life by 50%. Reduced Maintenance Costs: No frequent repainting or wheel replacement is required.

[0042] The spraying device includes a chassis 57 and a conveyor mechanism. The conveyor mechanism is located on either side of the chassis 57, providing feed and discharge functions. The wheel hub 1 enters the chassis 57 for spraying. The conveyor mechanism includes several conveyor rollers 13, which are driven by an external mechanism for synchronous rotation. A stopper 14 is installed on the feed side of the chassis 57. This block 14 blocks and positions the incoming wheel hub 1, allowing the clamping mechanism 11 to accurately grip the wheel hub 1 while preventing it from falling off the conveyor rollers 13 and into the drive gear 7.

[0043] The chassis 57 includes two parallel side panels 58, two end panels 59 connected between the side panels 58, a top panel 60 connected to the upper portion of the side panels 58, a support rail 15 provided on the upper portion of the top panel 60, a movable plate 10 slidably provided on the support rail 15, a clamping mechanism 11 mounted on the movable plate 10, and a driving mechanism provided on the top panel 60, capable of driving the movable plate 10 to move along the support rail 15. A notch 16 is provided on the upper portion of the end panel 59 for the wheel hub 1 to pass through.

[0044] The ends of the support rails 15 extend beyond the top plate 60 and are connected to the crossbeams 9. The drive mechanism includes a screw 61 that rotates between the two crossbeams 9, and the movable plate 10 is mounted on the screw 61. A screw motor 62 rotates the drive gear 7, which, through the meshing driven gear 8, drives the screw 61, thereby driving the movable plate 10 along the support rails 15. During movement, the movable plate 10, through the clamping mechanism 11, picks up the wheel hub 1 delivered by the conveyor mechanism and places it into the chassis 57 for spraying. The finished wheel hub 1 is then placed on the conveyor mechanism at the discharge point.

[0045] A guide bar 24 is connected between the two end plates 59. The guide bar 24 is parallel to the support rail 15. A moving seat 25 is slidably provided on the guide bar 24. A spraying mechanism is installed on the moving seat 25. A linkage member 12 is installed on the moving plate 10. The moving plate 10 can drive the moving seat 25 to move through the linkage member 12, so that the spraying mechanism moves with the transportation of the wheel hub 1, so that spraying is carried out synchronously during the feeding process, which can reduce the waiting time in spraying and speed up the overall processing efficiency.

[0046] The clamping mechanism 11 comprises a lifting and rotating mechanism, the lifting and rotating mechanism is drivingly connected with the clamping piece 21, the lifting and rotating mechanism comprises a linear actuator 17 installed on the moving plate 10, the linear actuator 17 is drivingly connected with a mounting plate 18, the lower part of the mounting plate 18 is installed with a rotating motor 19, the rotating motor 19 is drivingly connected with a rotating shaft 20, the rotating shaft 20 passes through the moving plate 10 and is arranged, and the clamping piece 21 is installed at the lower end of the rotating shaft 20. The clamping piece 21 comprises a linear actuator 33, the lower part of the linear actuator 33 is installed with a positioning rod 34, the inside of the positioning rod 34 is provided with a middle hole 35, the linear actuator 33 is drivingly connected with a driving rod 36, the driving rod 36 is located in the middle hole 35, the lower end of the driving rod 36 is connected with a driving head 44, the lower part of the driving head 44 is in the shape of a circular truncated cone and the diameter of the lower end is smaller. Four openings 37 are arranged on the outer periphery of the positioning rod 34, the four openings 37 are uniformly distributed, and the openings 37 are communicated with the outer periphery of the positioning rod 34 and the middle hole 35. A pressing block 38 is slidingly arranged in the opening 37, the inside of the pressing block 38 is connected with a driving block 41, and the upper part of the driving block 41 is provided with an abutting inclined surface 45. The two driving blocks 41 are connected with a spring 42. Under the action of the spring 42, the pressing block 38 has a tendency to move inward, so that the abutting inclined surface 45 on the driving block 41 abuts against the outer periphery of the driving head 44.

[0047] The driving mechanism drives the movable plate 10 to move, so that the clamping mechanism 11 reaches the feed point outside the chassis 57. The linear drive 17 drives the mounting plate 18 to move downward, driving the clamping member 21 to descend. The positioning rod 34 is inserted into the axial hole of the wheel hub 1. The positioning rod 34 descends until the positioning ring 43 abuts the upper end surface of the axial hole. The linear drive 2 33 drives the driving rod 36 to move downward. In the process of the driving head 44 descending against the abutting inclined surface 45 on the driving block 41, the driving block 41 pushes the clamping block 38 out of the opening 37, so that the outer periphery of the clamping block 38 contacts and abuts the inner wall of the axial hole of the wheel hub 1, thereby completing the clamping and fixing of the wheel hub 1. A protrusion 39 is provided at the lower position of the outer side of the clamping block 38. The protrusion 39 extends out of the axial hole of the wheel hub 1 to support the lower end of the axial hole of the wheel hub 1, which can more effectively fix the wheel hub 1. The linear actuator 17 then drives the mounting plate 18 upward, driving the hub 1 on the clamping member 21 to move upward, so that the position of the hub 1 corresponds to the height of the spray gun 29 in the spraying mechanism. When the driving mechanism drives the movable plate 10 to move into the end plate 59, the rim portion of the hub 1 is located within the coverage space of the spray gun 29. At this time, the driving mechanism drives the movable plate 10 to move, driving the hub 1 on the clamping member 21 to move within the end plate 59. The spraying mechanism can move synchronously with the hub 1, and the spraying mechanism sprays the surface of the hub 1 at the same time. After moving to the other end of the end plate 59, the spraying mechanism stops moving. The movable plate 10 continues to drive the hub 1 on the clamping member 21 to move, so that the hub 1 leaves the coverage area of ​​the spray gun 29 and reaches outside the end plate 59. The linear actuator 17 drives the mounting plate 18 downward, driving the hub 1 on the clamping member 21 to descend. The clamping member 21 releases the clamping and fixing of the wheel hub 1 , so that the wheel hub 1 on the clamping member 21 falls onto the conveying roller 13 at the discharge location.

[0048] The positioning ring 43 can not only be used for positioning, but also can shield the upper end of the shaft hole of the wheel hub 1 to prevent paint from entering the shaft hole during spraying.

[0049] A guide slot 40 is defined in the sidewall of the opening 37. The length of the guide slot 40 is less than the width of the opening 37. A stopper is provided on the driving block 41 to cooperate with the guide slot 40. The stopper of the driving block 41 is located within the guide slot 40. The cooperation of the stopper of the driving block 41 not only guides the movement of the abutting block 38 within the opening 37 but also limits the position of the abutting block 38 to prevent it from falling off the positioning rod 34.

[0050] The spraying operation needs to be controlled within the chassis 57, requiring the spraying mechanism to move within the chassis 57. The clamping mechanism 11 needs to move beyond the chassis 57 because it needs to feed and discharge the wheel hub 1. The linkage 12 and the movable seat 25 cooperate to achieve linkage as required, and can control whether the movable seat 25 moves with the movable plate 10. The movable seat 25 is driven to move only when the movable plate 10 moves within the chassis 57.

[0051] The linkage 12 comprises a connecting arm 22 connected at the end of the moving plate 10, a linkage seat 23 connected at the lower part of the connecting arm 22, a mounting hole 46 formed at the side of the linkage seat 23 facing the moving seat 25, a linkage block 47 mounted in the mounting hole 46, a spring 48 connected between the inner end of the linkage block 47 and the inner wall of the mounting hole 46, and a guide hole 49 formed at the side plate 58 near the side of the linkage seat 23, through which the linkage block 47 extends into the case 57. The spring 48 is in a normal state, so that the end of the linkage block 47 is arranged beyond the linkage seat 23.

[0052] The guide slope 50 is arranged at the position of the side plate 58 at both ends of the guide hole 49, which guides the linkage block 47 separated from the stepped hole 53, so that the end of the linkage block 47 moves to the outside of the side plate 58 during the movement of the linkage seat 23.

[0053] The stepped hole 53 is formed in the moving seat 25, the large diameter section of the stepped hole 53 is arranged near the linkage seat 23, the movable block 54 is arranged in the large diameter section of the stepped hole 53, the trigger lever 26 is connected at the end of the movable block 54 away from the linkage seat 23, the trigger lever 26 extends out of the moving seat 25, and the transmission slope 56 is arranged at both sides of the end of the trigger lever 26 extending out of the moving seat 25. The spring 55 is sleeved on the trigger lever 26, one end of the spring 55 is connected with the step of the stepped hole 53, and the other end of the spring 55 is connected with the end of the movable block 54. The spring 55 is in a normal state, so that the end of the movable block 54 near the linkage seat 23 is located in the stepped hole 53, and is a certain distance away from the end surface of the moving seat 25 near the linkage seat 23.

[0054] The stop lever 27 is mounted at the inner side of the two end plates 59, and the driving slope 52 is arranged at the side of the stop lever 27 facing the linkage seat 23. The spring 51 is mounted at the inner side of the two end plates 59, and the position of the spring 51 corresponds to that of the moving seat 25. During the movement of the moving seat 25 and the linkage seat 23 to the position near the end plate 59, the spring 51 is compressed, so that the spring 51 is contracted. When the linkage seat 23 drives the moving seat 25 to move to the position near the end plate 59, the transmission slope 56 of the trigger lever 26 contacts with the driving slope 52 of the stop lever 27, the stop lever 27 drives the trigger lever 26 through the cooperation of the driving slope 52 and the transmission slope 56. The trigger lever 26 drives the movable block 54 to move. When the end of the trigger lever 26 reaches the plane of the stop lever 27 through the top end of the driving slope 52, the end of the movable block 54 is flush with or slightly beyond the end surface of the moving seat 25, so that the end of the linkage block 47 is separated from the stepped hole 53, and the linkage between the moving seat 25 and the linkage seat 23 is disconnected. During the subsequent movement of the linkage seat 23, the end of the linkage block 47 moves along the guide slope 50, so as to reach the outside of the side plate 58. The moving seat 25 stops.

[0055] When the moving seat 25 moves to the designated position, i.e. the end of the trigger lever 26 reaches the plane of the stop lever 27, the movable block 54 is flush with or slightly beyond the end face of the moving seat 25 at one end close to the linkage seat 23, and the linkage block 47 is pushed out of the stepped hole 53. The spring 51 can push the moving seat 25 outward by a certain distance, so that the end of the trigger lever 26 returns to the driving slope 52 on the stop lever 27. At this time, the movable block 54 moves away from the linkage seat 23 due to the effect of the stepped hole 53, so that the end of the movable block 54 is away from the end of the moving seat 25 by a certain distance, leaving enough space for the end of the linkage block 47 to be inserted. When the linkage seat 23 moves back subsequently, the end of the linkage block 47 can be smoothly inserted into the stepped hole 53, so as to accurately drive the moving seat 25 to move.

[0056] Based on the weight of the moving seat 25 and the weight of the mechanism thereon, the moving seat 25 is not easy to change after moving to the corresponding position, which can ensure that the moving seat 25 can continue to move after the linkage seat 23 returns to the position.

[0057] The spraying mechanism includes a spraying pump 28 mounted on the moving seat 25, and a spray gun 29 connected to the spraying pump 28. The spray gun 29 is in a semi-ring shape, and a paint tank 30 is mounted at the lower part of the top plate 60. The paint tank 30 and a supply pipe 31 are connected by the spraying pump 28. The spraying pump 28 pumps the paint stored in the paint tank 30 into the spray gun 29, and the spray gun 29 sprays the surface of the hub 1. The rotating motor 19 can drive the clamping piece 21 to rotate through the rotating shaft 20, thereby driving the hub 1 to rotate, so that the spray gun 29 can spray the entire outer periphery of the hub 1.

[0058] The lower part of the top plate 60 is provided with a drag chain 32, and the supply pipe 31 is mounted on the drag chain 32. The drag chain 32 plays a traction and protection role for the supply pipe 31, avoiding damage caused by bending of the supply pipe 31 during movement with the spraying pump 28.

[0059] The above is only a preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical solutions falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the present application shall also be considered as the protection scope of the present application.

Claims

1. A self-repairing coating for an aluminum alloy wheel hub, characterized in that: The invention comprises polyurethane and nanocapsules uniformly dispersed in a polyurethane matrix. The nanocapsules comprise an outer shell and a repairing agent located in the outer shell. The outer shell is made of silicon dioxide, and the repairing agent is a silicone repairing agent.

2. The aluminum alloy wheel hub self-repair coating according to claim 1, characterized in that: The diameter of the nanocapsule is 50-200 nm.

3. The aluminum alloy wheel hub self-repair coating according to claim 1, characterized in that: The thickness of the shell is 10-20 nm.

4. The aluminum alloy wheel hub self-repair coating according to claim 1, characterized in that: The proportion of the repair agent in the nanocapsule is 70%-80%.

5. The aluminum alloy wheel hub self-repair coating according to claim 1, characterized in that: The viscosity of the repair agent is ≤100 cP.

6. A method for preparing the aluminum alloy wheel self-repairing coating according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Nanocapsule preparation: The siloxane repair agent and the silica precursor are mixed by emulsification, an emulsifier is added, and the mixture is stirred at high speed to form a nano-scale oil-in-water emulsion; Through the sol-gel method, under the action of an acidic catalyst, the reaction is carried out at 60°C for 4-6 hours; the silica precursor is hydrolyzed to generate silicic acid, which is condensed to form a silica shell that wraps the repair agent; The emulsion was converted into solid nanocapsules by spray drying and sieving to control the size; S2. Coating preparation: The nanocapsules are mixed with polyurethane resin at a ratio of 3% to 10%, a silane coupling agent is added as a dispersant, and the mixture is processed in a disperser for 20 to 30 minutes to form a coating; Performing chromium-free passivation treatment on the aluminum alloy wheel hub to form a primer layer on the surface of the aluminum alloy wheel hub, and applying paint on the primer layer on the surface of the aluminum alloy wheel hub through a spraying device; The polyurethane is completely cross-linked and cured by heating to form a topcoat layer on the aluminum alloy wheel hub.

7. The method for preparing a self-repairing coating for an aluminum alloy wheel hub according to claim 6, characterized in that: During the temperature-raising curing process, the temperature is raised to 120-150°C and the curing time is 20-30 minutes.

8. The method for preparing a self-repairing coating for an aluminum alloy wheel hub according to claim 6, characterized in that: A clear coat is applied over the topcoat layer.

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