Mobile Phone Case Coating Line

Mobile phone case coating is a critical manufacturing process for achieving the desired appearance (such as matte, high-gloss, gradient, and iridescent effects) and protective properties (such as scratch resistance and corrosion resistance). This process requires balancing aesthetic appeal, protective performance, mass production efficiency and cost control.

Phone Case Coating Process Overview

The process begins with the “bare case” followed by pre-treatment, primer coating, color coating, and topcoat coating, cooling and final inspection to produce the finished product. The entire process must be conducted in a controlled environment to ensure yield and consistency.

Pre-treatment

The first step, including ultrasonic cleaning (50-60℃ weak alkaline solution, 28kHz ultrasonic vibration for 120 seconds), deionized water rinsing (resistivity ≥10MΩ·cm), and drying and activation (80℃ hot air drying for 5 minutes, combined with plasma surface activation), aims to remove mold release agents, fingerprints, and other impurities, increasing the surface energy to above 45 dyn/cm, laying the foundation for coating adhesion.

Primer Coating

A two-component polyurethane primer (main agent:hardener = 4:1) is applied using an air spray gun (such as the W-101 type, 1.0mm nozzle), with an air pressure of 0.35MPa and a distance of 20-25cm, controlling the film thickness to 8-12μm. After spraying, it is pre-baked at 60℃ for 10 minutes to form a uniform adhesive layer.

Color Coating

This achieves the core visual effects (such as gradient and metallic texture). For example, gradient colors use a “dual-gun cross-spraying method,” where a PLC controls the movement speed (0.8m/s) and paint output (dynamic adjustment of light and dark colors) of two spray guns to create a natural transition. Metallic texture or chameleon effects rely on special pigments (such as chameleon pigments that achieve angle-dependent color changes through light reflection).

Topcoat Coating

As a protective layer, hydroxy acrylic topcoat (containing nano-silica) is commonly used to improve hardness (≥2H pencil hardness) and weather resistance. The spraying environment humidity needs to be controlled at 50±5% (to prevent whitening), with a film thickness of 20-25μm. This is followed by baking at 80℃ for 30 minutes to ensure sufficient cross-linking of the coating.

Cooling and Final Inspection: After baking, the casing is slowly cooled through a tunnel-type cooling line (15℃ cold air, 5 minutes) to prevent coating cracking. Finally inspect over appearance, film thickness (e.g., color difference ΔE≤0.5), and performance tests (e.g., adhesion ≥4B, abrasion resistance 5000 cycles without substrate exposure) are conducted to ensure compliance with standards.

Key Control Points

Coating Formulation and Environment: The mixing ratio error of the two-component coating must be ≤±2%, verified using an electronic scale; the spraying workshop needs to meet Class 10,000 cleanliness standards (≥0.5μm particles per cubic meter ≤10,000), with regular filter replacement and cleanliness monitoring.

Baking Process: The baking curve (e.g., topcoat 120℃ × 30 minutes) is critical; temperature or time deviations will affect coating durability (e.g., too low a temperature can lead to a 50% reduction in abrasion resistance).

Equipment and Personnel: The combination of an automatic painting machine and spray gun improves spraying stability and coating utilization rate (up to 70%); personnel must pass sufficient technical training (theory, simulation, on-the-job training, and assessment), focusing on parameter control.

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