Professional Zinc Alloy Surface Finishing Solutions

Electrophoresis

Ⅰ. Core Definition & Objectives

Definition: E-Coat (Cathodic Electrophoretic Lacquer) is a high-end coating process that uses electricity to uniformly deposit a polymer film on metal surfaces, ensuring full coverage without dead corners. Application Objects: Luxury buckles, bag locks, zipper pulls. Core Indicators: Film thickness 10-15 microns, hardness 4H, crystal clear or deep black finish, 48-hour salt spray resistance, and zero drip marks.

Ⅱ. Core Process Workflow (SOP)

1.Pre-Treatment (Clean Base Preparation)

Process: Plating → Rinsing → Chrome-Free Passivation → Pure DI Water Rinsing. Critical Requirement: Conductivity of the final rinse water entering the E-Coat tank must be < 20µS. Contaminated water will ruin the E-Coat bath.

2.E-Coating (Soft Start Voltage Curve)

0-10 Seconds: 0V → 30V (gradual voltage increase). 10-40 Seconds: Maintain 40-60V (film thickness build-up). 40-45 Seconds: Reduce to 0V (stable completion).

3.Ultra-Filtration (UF) Rinsing (Recycle Loop)

UF Rinse 1: Removes excess paint, which flows back to the main tank (saves 95% of paint). UF Rinse 2: Final cleaning.

4.Dehydration (Air Knife)

Operation: High-pressure clean air blows off water droplets. Goal: Prevent water spots during baking.

5.Curing (Oven)

Pre-Heat (Flash-off): 10 minutes at 80℃ (solvent evaporation). Full Cure: 30 minutes at 160℃ (for clear coats) or 140℃ (for low-temperature coats). Note: Insufficient temperature results in soft films (fails acetone rub test).

6.Final product

Ⅲ. Key Operational Points

1.Anolyte Balance (The "Kidney")

Issue: Excess acid is generated during coating; pH < 5.0 causes resin dissolution and rough films. Solution: Use anolyte cells (membrane boxes around anodes). Maintenance: Flush the anolyte system daily and check the conductivity of anolyte fluid to remove excess acid.

2.Racking Angle (The "Tear Drop")

Issue: Liquid E-Coat drips due to gravity, forming thick drops at part bottoms. Solution: Rack parts at a tilted (diamond) angle to direct drainage to a sharp point instead of flat edges. Advanced Option: High-end lines use high-voltage grids post-tank for electrostatic detearing.

3.Solvent Balance (Prevent Orange Peel)

Principle: Solvents promote melting and flowing of plastic particles during baking. Low Solvent: Rough, sand-like finish. High Solvent: Orange peel or sagging. Action: Add [QLQ] Leveling Solvent based on refractometer (Brix) readings.

Ⅳ. Common Defects & Quick Solutions

Pinholes/Craters

Core Cause: Excess voltage, silicon contamination, low pH Solution: Adopt soft start, add [QLQ] Anti-Crater Additive, check anolyte system

Orange Peel

Core Cause: High solid content, excess voltage, rapid drying Solution: Add DI water, reduce voltage, add high-boiling solvent

Water Spots

Core Cause: Contaminated final rinse water Solution: Ensure DI water conductivity < 5µS, enhance air drying

Yellowing

Core Cause: Overhigh oven temperature, over-curing Solution: Calibrate oven, maintain temperature < 165℃

Poor Adhesion

Core Cause: Passivation failure Solution: Reactivate the underlying plating before E-Coating

Roughness

Core Cause: Bath instability, tank contamination Solution: Adjust pH, filter the bath with a 10-micron bag

Ⅴ. Cost Control & Efficiency Tips

1.UF Recycling: Recovers 98% of paint (saves $50,000/year). Never let UF membranes dry out; clean weekly to prevent clogging.

2.Energy Management: Run ovens at full capacity to halve the cost per piece.

3.Gloss/Matte Management: Use two separate small tanks (one for gloss, one for matte) on sliding rails instead of a single large tank; avoid mixing powders to convert gloss to matte.

Ⅵ. Key Operating Parameters

Temperature

Range:26-32℃ Target Value:29±1℃ (strict control required)

pH Value

Range:5.5-6.5 Target Value:6.0 (acidic)

Voltage

Range:20-100V Target Value:Soft start mode (see Part III)

E-Coating Time

Range:30-60 Seconds Target Value:45 Seconds

Anode System

Range:- Target Value:SS 316 plates + anolyte cells (membrane boxes)

Circulation Speed

Range:- Target Value:4-6 turnovers/hour (prevents sedimentation)

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