Color Science

🎨 The Paint Master’s Manual: Mixing & Troubleshooting

Target: Zinc Alloy (Complex Shapes).

Standard: 2K Polyurethane (PU) or Epoxy Enamel.

Goal: Zero "Orange Peel," Class 0 Adhesion, Exact Color Match.

Phase I: The Science of Paint Mixing (The "Kitchen")

Rule #1: Never mix by "feeling." Use a scale.

Rule #2: Viscosity is King.

1. Standard 2K Mixing Ratio (Example Data)

For a high-gloss PU Enamel:

• [QLQ Product] Paint Base (Resin): 100 Parts (by weight).

• [Purchase Locally] Hardener (Curing Agent): 50 Parts (or as per QLQ spec).

• [Purchase Locally] Thinner: 40 – 60 Parts (Variable based on viscosity).

2. The Viscosity Standard (Ford Cup #4)

You cannot eyeball this. You must use a stopwatch.

• Matte / Rubber Paint: Target 20 – 24 seconds. (Thicker, needs body).

• Gloss / Metallic Paint: Target 16 – 18 seconds. (Thinner, needs flow).

• Tumble Spraying: Target 14 – 16 seconds. (Must be thin to penetrate holes inside the drum).

3. Pot Life (The "Ticking Clock")

• Once Hardener is added, the chemical reaction starts.

• Standard Pot Life: 4 Hours at 25°C.

• Master's Tip: Never mix more than you can spray in 2 hours. Old paint gets thick $\rightarrow$ causes Orange Peel.

4. Filtration

• Action: Every drop of mixed paint must pass through a 300 Mesh (Paper Filter) before going into the gun cup.

• Reason: Dried skin or dust in the paint = Clogged Gun = Spitting = Rework.

Phase II: Common Production Defects & Solutions (The "Clinic")

Here is the data-driven troubleshooting table for the Spray Room.

Defect 1: Orange Peel (Textured surface like a fruit skin)

• Diagnosis: The paint dried before it could "flow out" flat.

• Root Cause A: Viscosity too High. (e.g., > 25 sec).

  • Fix: Add 5-10% more Thinner. Aim for 18 sec.

• Root Cause B: Thinner Evaporating too Fast. (Using "Summer Thinner" in Winter, or vice versa).

  • Fix: Use [QLQ Product] Retarder Solvent (Slow drying agent) to keep the paint wet longer (add 3-5%).

• Root Cause C: Gun Distance. Spraying too far (> 25cm), paint dries in the air.

  • Fix: Keep gun 15-20cm from the zipper pull.

Defect 2: Sagging / Runs (Curtains)

• Diagnosis: Gravity pulling wet paint down.

• Root Cause A: Viscosity too Low. (e.g., < 14 sec).

  • Fix: Add more Base Resin.

• Root Cause B: Heavy Hand. Application is too thick in one pass.

  • Fix: Apply a "Mist Coat" (Flash off 2 mins) $\rightarrow$ Then a "Full Coat."

• Root Cause C: Flash-off Time. Putting parts in the oven immediately after spraying.

  • Fix: Let parts sit for 5-10 mins (Leveling time) before entering the oven.

Defect 3: Pinholes / Solvent Pop (Tiny bubbles/craters)

• Diagnosis: Gas trapped under the skin of the paint. Common in Zinc Alloy.

• Root Cause A: Die-Cast Outgassing. Zinc is porous. Heat expands trapped air, which bursts through the paint.

  • Fix: Pre-Bake the raw zinc parts at 150°C for 30 mins before painting to drive out the gas.

• Root Cause B: Oven Ramp-up. Heating too fast (Room Temp $\rightarrow$ 150°C instantly). Solvent boils.

  • Fix: Use a "Step Cure": 60°C (10 mins) $\rightarrow$ 120°C (20 mins).

Defect 4: Adhesion Failure (Tape Test Fail)

• Diagnosis: Paint peels off the metal.

• Root Cause A: No Primer/Pre-treatment.

  • Fix: Dip in [QLQ Product] Adhesion Promoter before spraying.

• Root Cause B: Moisture. Condensation on the metal (common in humid mornings).

  • Fix: Ensure parts are warm (40°C) before painting.

• Root Cause C: Under-Curing. Oven temp was 120°C, but hardener needs 150°C.

  • Fix: Calibrate the oven with a thermometer probe, not just the digital display.

Defect 5: Blushing (White Haze/Fog)

• Diagnosis: High humidity causes moisture to trap in the paint.

• Environment: Humidity > 85%.

• Master's Fix: Add [QLQ Product] Anti-Blush Agent (Slow solvent) @ 5%. Raise the spray room temperature.

Phase III: The Master's Seasonality Adjustments (Real Experience)

A paint formula that works in July will FAIL in December. You must adjust the Thinner.

Phase IV: Daily Gun Maintenance (SOP)

End of Shift Ritual:

1. Back-Flush: Block the nozzle with a rag, pull the trigger. Air flows back into the cup, clearing the passage.

2. Needle Cleaning: Remove the needle. Wipe it with solvent. Do not use metal pliers to pull the tip (scratches = distorted spray pattern).

3. Air Cap: Soak in solvent. Use a wooden toothpick to clean the holes. Never use wire (it enlarges the holes and ruins atomization).