Lion King UV Spray Vacuum Coating Line: Step-by-Step Process for PP Phone Case Coating

How does a UV Spray Vacuum coating line work?

Here I explain it by an example, the step by step process for PP Phone Case Coating.

PP (polypropylene) phone cases are widely used in consumer electronics but pose unique coating challenges—low surface adhesion, sensitivity to high temperatures, and demand for scratch-resistant, aesthetic finishes (e.g., metallic, gradient). Lion King’s UV Spray Vacuum Coating Line addresses these via a customized process flow, integrating PP-specific pre-treatments, PVD aluminum vacuum coating, and multi-layer UV curing to deliver premium, durable PP phone case coatings. Below is the detailed step-by-step process, aligned with user-specified operations.

1. PP Phone Case Pre-Treatment: Lay the Foundation for Adhesion & Cleanliness

Pre-treatment targets PP’s low surface energy and removes contaminants—critical for preventing coating peeling, dust defects, and uneven film formation on phone cases.

• Step 1.1: PP-Specific Vacuum-Compatible Cleaning

Load PP phone cases (typically 150–200 mm in length, 70–90 mm in width) onto Lion King’s PP-adapted fixtures (soft rubber clamps to avoid scratching the case’s raw surface). The fixtures enter Lion King’s pre-vacuum cleaning module:

◦ For mold release agents (common on PP phone cases): Use ultrasonic cleaning in a sealed tank (deionized water + non-ionic detergent, 40–50°C) for 3–5 minutes. The ultrasonic frequency (40 kHz) is optimized to remove residues without damaging PP’s structure.

◦ For surface oils/fingerprints: Follow with high-pressure clean air jets (filtered to Class 100 standards, pressure 0.2–0.3 MPa) to blow away loosened contaminants. A final wipe with Lion King’s VOC-free solvent (isopropyl alcohol diluted to 70%) ensures no residue—critical for preventing vacuum chamber contamination later.

• Step 1.2: Electrostatic Dust Removal (PP-Specific)

PP phone cases easily accumulate static electricity (due to low conductivity), attracting air-borne dust. They pass through Lion King’s electrostatic dedusting module:

◦ High-voltage negative ion nozzles: Deliver a 12–15 kV ion field to neutralize static charges on the phone case’s curved edges (e.g., camera bump, side buttons) and flat back surface.

◦ Low-pressure air curtain: Blows neutralized dust into a HEPA filter (99.97% filtration efficiency for particles >0.3 μm). This step reduces dust-related defects (e.g., tiny bumps on the coating) by 95%—essential for PP phone cases’ high-gloss/metallic finishes.

• Step 1.3: PP Prime Coating & Low-Temperature Drying

PP’s low surface adhesion requires a specialized prime coat to bond with subsequent layers. The phone cases enter Lion King’s prime spray booth (connected to the pre-vacuum line):

◦ Prime coat type: Lion King’s custom PP primer (acrylic-based, low-VOC, vacuum-stable) – formulated to penetrate PP’s surface and form a polar bonding layer.

◦ Spray parameters: Controlled via Lion King’s PLC system (stored in a "PP Phone Case Prime" recipe):

▪ Spray guns: 2 guns (positioned to cover front/back of the case, avoiding button cutouts).

▪ Pressure: 0.3–0.4 MPa; distance: 18–20 cm; conveyor speed: 2 m/min.

▪ Coating thickness: 8–10 μm (thin enough to avoid hiding the case’s texture, thick enough for adhesion).

◦ Drying: Cases move to a low-temperature drying tunnel (60–65°C, 1.5–2 minutes) – Lion King’s design uses uniform hot-air circulation to avoid PP deformation. The goal: 90% solvent volatilization, verified by a moisture sensor (surface moisture <0.5%).

2. Base Coating for PP Phone Cases: Color Foundation & Vacuum Curing

The base coat sets the phone case’s core color (e.g., black, white, or pastel) and prepares the surface for PVD aluminum coating.

• Step 2.1: Base Coat Formulation & Vacuum Degassing

Lion King’s base coat for PP phone cases is tailored for:

◦ Color consistency: Pigment dispersion (e.g., carbon black for matte black cases) mixed at 1000–1200 rpm in a vacuum-sealed disperser (avoids air bubbles).

◦ Vacuum sprayability: Viscosity adjusted to 18–22 cP (via Lion King’s rotational viscometer) using TMPTA monomer (vacuum-stabilized).

◦ Dual-stage degassing: First in a low-vacuum tank (10⁻¹ Torr, 3 minutes) to remove large bubbles, then in a high-vacuum tank (10⁻³ Torr, 8 minutes) – matching the main chamber’s pressure to prevent pinholes.

• Step 2.2: Precision Base Coat Spray (PP Phone Case-Sized)

Primed cases enter Lion King’s main vacuum chamber (evacuated to 10⁻³–10⁻⁴ Torr via mechanical/Roots/diffusion pumps). Key spray settings:

◦ 360° rotating fixtures: Lion King’s fixtures spin the phone case at 60 rpm to ensure even coverage on curved edges (e.g., camera bump) – no "shadow areas" common in fixed-spray systems.

◦ Spray guns: 3 guns (positioned 19 cm from the case) with pressure 0.25–0.35 MPa. Conveyor speed: 2.5 m/min (balances coating thickness and efficiency).

◦ Target thickness: 12–15 μm (thick enough for color opacity, thin enough to layer with PVD).

• Step 2.3: UV Curing & Vacuum Cooling (PP Heat Protection)

Immediately after spraying, the chamber’s dual-source UV lamps (Lion King’s design) activate:

◦ LED UV lamps (40 W/cm, 365 nm): Used for PP (heat-sensitive) – cures the base coat in 8–10 seconds (total energy 900–1100 mJ/cm²) without overheating.

◦ Vacuum gradient cooling: Water-cooled plates + low-pressure air circulation lower the case’s temperature from 65–75°C to <35°C in 3 minutes – prevents PP warping (a common issue with traditional hot-air cooling).

3. PVD Aluminum Vacuum Coating: Metallic Finish for PP Phone Cases

Physical Vapor Deposition (PVD) aluminum coating creates the popular metallic effect (e.g., silver, rose gold) on PP phone cases—Lion King’s vacuum technology ensures uniform, thin aluminum layers.

• Step 3.1: PVD Chamber Preparation (Aluminum Target)

The main vacuum chamber remains sealed (pressure maintained at 10⁻⁴–10⁻⁵ Torr, lower than spray coating for PVD). Lion King’s PVD module uses:

◦ Aluminum targets: High-purity (99.99%) aluminum ingots positioned 20–25 cm from the phone cases.

◦ Ion bombardment pre-treatment: Low-energy argon ions (500–800 eV) clean the base coat’s surface for 2 minutes – enhances aluminum adhesion to PP’s base coat.

• Step 3.2: Aluminum Deposition (Metallic Effect Control)

Lion King’s PVD system uses magnetron sputtering to vaporize aluminum:

◦ Sputtering power: 1.5–2 kW (adjusted for desired metallic intensity – higher power for brighter silver, lower for subtle rose gold via alloyed targets).

◦ Deposition rate: 0.5–1 nm/second (controlled via Lion King’s thickness monitor). Target thickness: 50–80 nm (thin enough to retain flexibility, thick enough for uniform metallic sheen).

◦ Case rotation: Fixtures spin at 40 rpm to ensure even aluminum coverage – no "patchy" areas on the phone case’s back or camera bump.

• Step 3.3: In-Vacuum Inspection (PVD Quality Check)

Before venting the chamber, Lion King’s in-line module tests:

◦ Aluminum layer uniformity: Eddy current thickness gauge (deviation ±5 nm).

◦ Surface defects: High-resolution camera (detects pinholes >0.1 μm – critical for metallic finishes, where defects are visible).

4. Post-PVD Treatment: Dust Removal & Mid Coat Spraying

After PVD, the aluminum layer is delicate—additional steps protect it and smooth the surface for the top coat.

• Step 4.1: Post-PVD Electrostatic Dust Removal

The chamber vents to 10⁻¹ Torr (gradient venting to avoid pressure shock), then cases move to a second electrostatic dedusting module:

◦ Low-pressure ion nozzles: 8–10 kV (gentler than pre-PVD to avoid damaging the aluminum layer) neutralize static.

◦ Soft air jets: 0.15–0.2 MPa pressure blows away dust accumulated during venting – ensures the mid coat adheres evenly.

• Step 4.2: Mid Coat Spraying (Aluminum Layer Protection)

Lion King’s mid coat (clear acrylic-UV blend) acts as a barrier between PVD aluminum and the top coat, smoothing minor imperfections:

◦ Spray parameters: PLC recipe "PP Phone Case Mid Coat" – 2 guns, pressure 0.3 MPa, distance 20 cm, thickness 10–12 μm.

◦ Drying: Low-vacuum baking (10⁻² Torr, 60°C, 2 minutes) – volatilizes solvent without aluminum oxidation.

◦ UV curing: LED lamps (35 W/cm) cure in 7–9 seconds (energy 800–1000 mJ/cm²) – maintains the aluminum’s metallic luster.

5. Top Coat Spraying: Scratch Resistance for PP Phone Cases

The top coat is the final layer, providing daily scratch protection (critical for phone cases) and enhancing gloss/matte effects.

• Step 5.1: Top Coat Formulation (PP Durability Focus)

Lion King’s top coat for PP phone cases includes:

◦ Scratch-resistant additives: 10% nano-silica (20–30 nm particle size) for 4H pencil hardness (tested per ISO 15184).

◦ UV stability: Benzophenone-based UV absorbers (prevents color fading from sunlight).

◦ Vacuum degassing: Same dual-stage process as base coat – ensures no bubbles.

• Step 5.2: Top Coat Spray & Gradient Baking

Cases return to the main vacuum chamber (10⁻³ Torr):

◦ Spray: 3 guns, pressure 0.3–0.4 MPa, distance 21 cm, thickness 15–18 μm (thicker for better scratch resistance).

◦ Gradient baking: Chamber temperature rises from 55°C to 65°C over 3 minutes (avoids PP warping) – allows the top coat to level (reduces brush marks).

• Step 5.3: Final UV Curing (Full Hardness)

◦ Mercury-LED hybrid lamps: For maximum hardness – mercury lamps (80 W/cm) cure the inner layer (5 seconds), LED lamps (45 W/cm) cure the surface (6 seconds) – total energy 1300–1500 mJ/cm².

◦ Final cooling: Vacuum-cooled to <30°C in 4 minutes – ready for unloading.

6. Unloading, Inspection & Packing (PP Phone Case Final Steps)

• Step 6.1: Automated Unloading (Cleanroom-Controlled)

Cases are unloaded via Lion King’s Class 1000 cleanroom conveyor (anti-static belt) – operators wear lint-free gloves to avoid fingerprints.

• Step 6.2: PP Phone Case-Specific Inspection

2% of cases are sampled for offline tests (Lion King’s quality protocol):

◦ Adhesion: Cross-cut test (ISO 2409) – 1 mm × 1 mm squares, no more than 2 squares peeling (stricter than industry standards for phone cases).

◦ Scratch resistance: Pencil hardness test (4H, no visible scratches).

◦ Metallic finish consistency: Colorimeter (ΔE < 1.0 – ensures no batch-to-batch color variation).

◦ Drop test: 1.2 m drop onto concrete (simulates daily use) – no coating chipping.

• Step 6.3: Anti-Static Packing (Consumer Electronics Standard)

Qualified cases are packed in:

◦ Anti-static film: Wrapped individually to prevent static damage (critical for phone case storage/transport).

◦ Foam-lined cartons: 10 cases per carton (separated by foam inserts to avoid scratching).

◦ Storage guidelines: 15–25°C, humidity <55% (Lion King’s label included) – prevents coating yellowing.

Core Advantages for PP Phone Case Coating

1. PP Adhesion Solution: Custom primer + PVD ion pre-treatment solves PP’s low adhesion issue – coating peeling rate <0.1%.

2. Metallic Finish Excellence: PVD aluminum + clear mid coat delivers uniform, scratch-resistant metallic effects (popular with consumers).

3. Heat Protection: LED UV curing + vacuum gradient cooling prevents PP warping – 100% case dimensional stability.

4. Eco-Efficiency: Zero VOCs (UV paints) + 40% paint recovery (vacuum cyclone separator) – meets EU REACH for consumer electronics.

5. High Throughput: 300–400 PP phone cases per hour – ideal for large-scale production (e.g., phone accessory brands).

7. Troubleshooting: Lion King’s Vacuum-Based Solutions (User-Specified Focus)

User-specified troubleshooting (environmental control, defect resolution) is addressed via Lion King’s vacuum coating line design—targeting common issues like matte finish, dust, and weak paint film: