High-film-thickness transparent paint spraying process for aluminum alloy wheel

Abstract

The invention belongs to the technical field of coating, and relates to an aluminum alloy wheel high-film-thickness transparent paint spraying process which comprises the following steps: S1, pretreating a base material; s2, powder coating spraying and curing; and S3, primer, colored paint and high-film-thickness clear paint are sprayed in a layered mode, the construction viscosity of the clear paint is 18-24 s, the clear paint is painted for 4 cups at the temperature of 25 DEG C, the dry film thickness of the high-film-thickness clear paint is larger than or equal to 60 micrometers, and the baking temperature is 140-150 DEG C. The process disclosed by the invention has the following beneficial effects: the protection performance is improved: the film thickness is more than or equal to 60 microns, and the scratch resistance, acid rain resistance and chemical corrosion resistance of the transparent paint are obviously superior to those of common transparent paint; according to the appearance, the glossiness is improved by 40%, the fullness is improved by 35%, and surface micro-defects are effectively filled; the weather resistance is prolonged by 3-5 years, and cracking and falling are avoided. The cost advantage is that the material cost is reduced by 50-65% compared with that of transparent powder; no newly-added equipment is needed, and production line transformation cost is saved. The process is compatible with an existing coating line, and the mass production yield is larger than or equal to 98%.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and relates to the surface coating process of automotive aluminum alloy wheels, and particularly to a high film thickness transparent paint spraying process for aluminum alloy wheels. Background Technology

[0002] There are generally two ways to paint the outermost layer of the car wheel surface: one is to use clear varnish, which is economical, but ordinary clear varnish has many disadvantages; the other is to use clear powder, which can avoid the disadvantages of ordinary clear varnish, but clear powder is more expensive, costing 2-3 times more than clear varnish.

[0003] The main shortcomings of existing technologies include:

[0004] Ordinary transparent paint: thin dry film thickness (usually <40μm), with problems such as weak coverage, poor corrosion / abrasion resistance, low gloss, and easy aging and discoloration. For example, it has weak scratch resistance (<500g·cm), salt spray resistance <480h, and 60° gloss <85GU.

[0005] Transparent powder: Excellent performance (salt spray resistance >1200h, gloss >95GU), but the cost is too high, with a unit price of 2.5-3.2 times that of transparent paint, which restricts its large-scale application.

[0006] This invention discloses a coating solution that combines high protection, excellent appearance, and low cost, while achieving transparent powder-level performance on existing coating lines and controlling material costs to within 1.5 times that of transparent paint, and is compatible with existing production lines. Summary of the Invention

[0007] To address the problems of poor protection and short lifespan caused by insufficient transparent paint film thickness in existing technologies, and to avoid the high cost of transparent powder, the present invention aims to disclose a high film thickness transparent paint spraying process for aluminum alloy wheels. By optimizing the coating structure and construction process, transparent powder-level protective performance can be achieved at a low cost.

[0008] Technical solution

[0009] A high-film-thickness transparent paint spraying process for aluminum alloy wheels includes the following steps:

[0010] S1. Substrate pretreatment;

[0011] S2. Powder coating spraying and curing;

[0012] S3. Apply primer, color paint and high film thickness transparent paint in layers. The high film thickness transparent paint has an application viscosity of 18-24s, is applied at Forte 4 cup at 25℃, and has a dry film thickness of ≥60μm. The baking temperature is 140-150℃.

[0013] In a preferred embodiment of the present invention, S1, the substrate pretreatment includes grinding the surface of the aluminum wheel → hot water washing → degreasing → water washing → acid washing → pure water washing → passivation → pure water washing → drying.

[0014] In a preferred embodiment of the present invention, S2, the powder coating spraying and curing process involves spraying the powder coating → baking and curing → powder grinding → dust removal and cleaning.

[0015] Furthermore, the baking and curing parameters are 140-150℃ for 20-30 minutes.

[0016] In a preferred embodiment of the present invention, in S3, the layered spraying of primer, color paint and high film thickness transparent paint forms a three-layer coating structure, namely primer layer, color paint layer and high film thickness transparent paint layer.

[0017] In a preferred embodiment of the present invention, S3 includes two modes:

[0018] Full coating process: Apply primer → leveling → color paint → leveling → high film thickness clear varnish → low temperature leveling → curing in sequence;

[0019] Glossy finish mode: After the primer / color paint has cured, the wheel surface is precision machined or high-precision polished to obtain a high-gloss finish. After pretreatment cleaning, a high-film-thickness transparent paint is sprayed on.

[0020] Further, the process parameters for the full coating mode:

[0021] Primer application: viscosity 14-20s, Ford cup 4, 25℃, film thickness 15-20μm;

[0022] Leveling: 40-70℃, 5-8 min;

[0023] Spray paint: viscosity 14-20s, Ford cup 4, 25℃, film thickness 15-20μm;

[0024] Leveling: 40-70℃, 5-8 min;

[0025] High film thickness transparent varnish spraying: viscosity 18-24s, Coat 4 cup, 25℃, dry film thickness ≥60μm;

[0026] Low temperature leveling: 20-40℃, 5-8 min;

[0027] Curing: 140-150℃, 20-30min.

[0028] Further details regarding the process parameters for the glossy finish mode:

[0029] Primer → Leveling → Color paint → Leveling → Curing (parameters same as full coating) → Gloss finish → Pretreatment cleaning → Spraying high film thickness transparent varnish (parameters same as full coating) → Leveling → Curing.

[0030] In a preferred embodiment of the present invention, the glossy finish is achieved by precision machining the cured wheel to obtain a high-gloss surface.

[0031] In a preferred embodiment of the present invention, the pretreatment cleaning involves thoroughly cleaning the polished surface after finishing with a mild degreaser and pure water to remove oil and processing debris, ensuring the surface is clean and dry.

[0032] Key parameter requirements: Clear varnish application viscosity 18-24s, Forte 4 cup, 25℃; baking temperature 140-150℃; dry film thickness must be ≥60μm.

[0033] The advantages of high film thickness transparent varnish are as follows:

[0034] (1) Dry film thickness: High film thickness transparent paint has a larger dry film thickness, which can form a thicker paint film on the surface of the object, better cover the surface of the object, and provide a more effective protective barrier;

[0035] (2) Protective performance: Due to its thicker film layer, high-film-thickness transparent varnish has stronger resistance to scratches, abrasion, and corrosion. In harsh environments, it can better prevent objects from being corroded by acid rain, chemicals, etc.

[0036] (3) Appearance: High film thickness transparent paint has better gloss and fullness, which can make the surface of the coated object brighter and have a stronger visual impact. Moreover, while having high transparency, it can better fill the small imperfections on the surface of the object, making the surface of the object smoother.

[0037] (4) Durability: Due to the advantage of film thickness, high film thickness transparent paint has better durability and is less prone to problems such as paint film peeling and cracking, and can maintain performance and appearance for a long time;

[0038] (5) The application of high film thickness transparent paint technology has a great advantage in seizing the market at low cost while meeting customer needs;

[0039] (6) The widespread application of high film thickness transparent paint on wheels also reflects technological strength.

[0040] Beneficial effects

[0041] The process disclosed in this invention improves protective performance: film thickness ≥60μm, significantly superior to ordinary transparent paint in terms of scratch resistance, acid rain resistance, and chemical corrosion resistance; appearance: gloss increased by 40%, fullness increased by 35%, effectively filling surface micro-imperfections; lifespan: weather resistance extended by 3-5 years, with no cracking or peeling. Cost advantages: material costs are reduced by 50-65% compared to transparent powder; no new equipment is required, saving production line modification costs. The process is compatible with existing coating lines, with a mass production yield of ≥98%, demonstrating industrialization value. Attached Figure Description

[0042] Figure 1 A schematic diagram of the process flow of this invention. Detailed Implementation

[0043] The present invention will be described in detail below with reference to embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0044] Example 1

[0045] Full paint scheme

[0046] Substrate pretreatment: The aluminum alloy wheel hub undergoes degreasing, pickling, and passivation pretreatment;

[0047] Powder coating spraying and curing: Spray epoxy powder coating and cure at 150℃ for 25 minutes;

[0048] After sanding and dust removal, black primer is sprayed with a film thickness of 18μm and a viscosity of 16s.

[0049] Leveling at 65℃ for 6 minutes → Spraying metallic paint, film thickness 17μm, viscosity 18s, Forecast cup 4, 25℃ → Leveling at 65℃ for 6 minutes;

[0050] High film thickness transparent varnish spraying: viscosity 18-24s, Forward 4 cup, 25℃, dry film thickness ≥60μm → leveling at 30℃ for 7min → baking at 145℃ for 25min to cure.

[0051] Test results:

[0052] No corrosion after >1000h salt spray test; gloss (60°) reaches 95 GU; film thickness 65.3μm;

[0053] The material cost is 58% lower than that of the transparent powder process.

[0054] Example 2

[0055] Glossy mode

[0056] Substrate pretreatment: Same as in Example 1;

[0057] Powder coating application and curing: Same as in Example 1;

[0058] Primer and color coat spraying and curing (preparation of glossy substrate):

[0059] After sanding and dust removal, spray black primer: viscosity 16s, Forecast cup 4, 25℃, film thickness controlled at 18μm;

[0060] Leveling at 65℃ for 6 minutes → Spraying metallic paint, film thickness 17μm, viscosity 18s, Ford cup 4, 25℃ → Leveling at 65℃ for 6 minutes → Curing: 145℃, 25 minutes (this step completes the coating curing before gloss finishing).

[0061] Gloss finish: The cured wheels are precision machined to obtain a high-gloss surface;

[0062] Pre-treatment cleaning after glossing: Use a mild degreaser and pure water to thoroughly clean the glossy surface after finishing to remove oil and processing debris, and ensure that the surface is clean and dry (this step is crucial to ensuring the adhesion of the clear coat).

[0063] High film thickness transparent varnish spraying: application viscosity 20s, Coat-4 cup, 25℃; target dry film thickness ≥60μm (actual measurement 62μm) → leveling at 30℃ for 7min → curing at 145℃ for 25min.

[0064] Test results:

[0065] Salt spray test (ISO 9227) >1100h: No substrate corrosion or paint film blistering.

[0066] Gloss (60° GU, ASTM D523): 98 GU (The combination of glossy finish and high film thickness clear coat has a significant effect).

[0067] Film thickness measurement (dry film): 62.1 μm.

[0068] Scratch resistance (ASTM D3363 or equivalent) >1100 g·cm.

[0069] QUV-B accelerated aging (ASTM G154): After 1500h, the gloss retention rate is >90%, with no cracking, powdering, or peeling.

[0070] Appearance: The paint film has extremely high fullness and the surface is extremely glossy like a mirror, effectively concealing the very fine tool marks that may be produced during precision machining.

[0071] The material cost is 60% lower than that of the transparent powder process.

[0072] Example 3

[0073] Full paint scheme (different colors / parameters)

[0074] Substrate pretreatment: Same as in Example 1;

[0075] Powder coating application and curing: Same as in Example 1;

[0076] After sanding and dust removal, apply primer (gray): viscosity 18s, Forecast cup 4, 25℃, film thickness controlled at 16μm;

[0077] Leveling at 60℃ for 7 minutes → Spraying color paint (pearl white): viscosity 16s, Forecast cup 4, 25℃, film thickness control 19μm → Leveling at 60℃ for 7 minutes;

[0078] High film thickness transparent varnish spraying: viscosity 22s, Forecast cup 4, 25℃, target dry film thickness ≥60μm (actual measured 61μm → 35℃ low temperature leveling 6min → curing: 142℃, 28min).

[0079] Test results:

[0080] Salt spray test (ISO 9227) >1050h No defects.

[0081] Gloss (60° GU, ASTM D523): 96 GU.

[0082] Film thickness measurement (dry film): 61.5 μm.

[0083] Scratch resistance (ASTM D3363 or equivalent) >1050 g·cm.

[0084] Chemical resistance (after 24 hours of adding gasoline and brake fluid): No discoloration, loss of gloss, or softening marks.

[0085] QUV-A Accelerated Aging (ASTM G154): After 2000 hours, the gloss retention rate is >85%, with no cracking or significant loss of gloss.

[0086] The yield rate of mass production (continuous production of 1000 units) is 99.2%.

[0087] The material cost is 55% lower than that of transparent powder process.

[0088] The embodiments described above are merely specific implementations of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A high-film-thickness transparent paint spraying process for aluminum alloy wheels, characterized in that, Includes the following steps: S1. Substrate pretreatment; S2. Powder coating spraying and curing; S3. Apply primer, color paint and high film thickness transparent paint in layers. The high film thickness transparent paint has an application viscosity of 18-24s, is applied at Forte 4 cup at 25℃, and has a dry film thickness of ≥60μm. The baking temperature is 140-150℃.

2. The high film thickness transparent paint spraying process for aluminum alloy wheels according to claim 1, characterized in that: In S1, the substrate pretreatment includes grinding the surface of the aluminum wheel → hot water washing → degreasing → water washing → pickling → pure water washing → passivation → pure water washing → drying.

3. The high film thickness transparent paint spraying process for aluminum alloy wheels according to claim 1, characterized in that: In S2, the powder coating is sprayed and cured, which involves spraying the powder coating → baking and curing → powder grinding → dust removal and cleaning.

4. The high film thickness transparent paint spraying process for aluminum alloy wheels according to claim 3, characterized in that: The baking and curing parameters are 140-150℃ for 20-30 minutes.

5. The high film thickness transparent paint spraying process for aluminum alloy wheels according to claim 1, characterized in that: In S3, the layered spraying of primer, color paint and high film thickness transparent paint forms a three-layer coating structure, namely primer layer, color paint layer and high film thickness transparent paint layer.

6. The high-film-thickness transparent paint spraying process for aluminum alloy wheels according to claim 1, characterized in that, S3 includes two modes: Full coating process: Apply primer → leveling → color paint → leveling → high film thickness clear varnish → low temperature leveling → curing in sequence; Glossy finish mode: After the primer / color paint has cured, the wheel surface is precision machined or high-precision polished to obtain a high-gloss finish. After pretreatment cleaning, a high-film-thickness transparent paint is sprayed on.

7. The high film thickness transparent paint spraying process for aluminum alloy wheels according to claim 6, characterized in that, The process parameters for the full coating mode are as follows: Primer spraying: viscosity 14-20s, Forecast cup 4, 25℃, film thickness 15-20μm; leveling: 40-70℃, 5-8min; Color paint spraying: viscosity 14-20s, Forecast cup 4, 25℃, film thickness 15-20μm; leveling: 40-70℃, 5-8min; High film thickness transparent varnish spraying: viscosity 18-24s, Forecast cup 4, 25℃, dry film thickness ≥60μm; Low temperature leveling: 20-40℃, 5-8min. Curing: 140-150℃, 20-30min.

8. The high film thickness transparent paint spraying process for aluminum alloy wheels according to claim 6, characterized in that, The process parameters for the glossy finish mode are: primer → leveling → color paint → leveling → curing (parameters same as full coating) → glossy finish processing → pretreatment cleaning → spraying high film thickness transparent paint (parameters same as full coating) → leveling → curing.

9. The high film thickness transparent paint spraying process for aluminum alloy wheels according to claim 8, characterized in that, The bright finish process involves precision machining the cured wheels to obtain a high-gloss surface.

10. The high film thickness transparent paint spraying process for aluminum alloy wheels according to claim 8, characterized in that, The pretreatment cleaning process involves thoroughly cleaning the polished surface after machining with a mild degreaser and pure water to remove oil and machining debris, ensuring the surface is clean and dry.

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