Professional Zinc Alloy Surface Finishing Solutions

Cold Painting

Cold Painting — Air-Dry & UV-Cure Coatings for Heat-Sensitive Substrates

When plastic, zinc alloy or assembled parts can't take oven heat, cold painting is the answer. Self-dry and UV-cure technologies compared.

The Cold Painting Process

Spray → Flash → Cure (UV or air-dry) — no oven, no heat damage

1Understanding Cold Paint vs Baked Paint

Cold paint dries by solvent evaporation or UV polymerization at ambient temperature (20–35 °C). Baked paint needs 80–180 °C for chemical cross-linking. Cold paint is softer but indispensable for heat-sensitive substrates.

Key Parameters

Cold paint dry temp: 20–35 °C

Baked paint cure: 80–180 °C

Substrate limit: Plastic: < 80 °C / Zn alloy: < 120 °C

Before

After

2Self-Dry (Air-Dry) Paint Application

Acrylic or nitrocellulose-based — solvent evaporates in air. Dries to touch in 20–30 min, full hardness in 24 h. VOC content is higher than UV or baked systems. Good for small batches and field touch-up.

Key Parameters

Dry to touch: 20–30 min

Full cure: 24 h

Hardness (pencil): HB–2H

VOC: 400–600 g/L

3UV-Cure Paint — Fast & Hard

100% solids or low-VOC UV formulations polymerize in seconds under UV light. High cross-link density = harder film than air-dry. But: 3D shadows don't cure (line-of-sight limitation). Photoinitiator chemistry matters.

Key Parameters

Cure time: 2–10 s

Hardness (pencil): 2H–4H

VOC: < 50 g/L

Shadow cure: Poor — line of sight

4Drying Time & Hardness Comparison

UV gives the fastest cure-to-handle cycle (seconds) and highest hardness, but only on flat/exposed surfaces. Air-dry is slower but works on any geometry. Baked paint remains the benchmark for chemical resistance.

Key Parameters

Time to handle: UV: 2–10 s / Air: 30–60 min / Bake: 20–30 min

Full hardness: UV: immediate / Air: 24 h / Bake: after cool

Chemical resistance: Bake > UV > Air-dry

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Cold Paint vs Baked Paint — Full Comparison

Hardness, chemical resistance, heat tolerance and throughput

Property	Self-Dry (Air)	UV-Cure	Baked Paint
Cure temperature	20–35 °C	20–40 °C (light only)	80–180 °C
Cure time	24 h full	2–10 s	20–30 min
Hardness (pencil)	HB–2H	2H–4H	H–3H
Chemical resistance	Fair	Good	Excellent
VOC content	400–600 g/L	< 50 g/L	200–400 g/L
Suitable for plastic	Yes	Yes	Limited
Suitable for assembled parts	Yes	Yes	No (heat damages)
Shadow cure	Yes (any shape)	No (line of sight)	Yes (convection)
Equipment cost	Low	Medium-high	High

📌 Cold Painting Cheat Sheet

Air-dry full cure24 h

UV cure time2–10 s

UV hardness2H–4H pencil

Air-dry hardnessHB–2H

Max substrate temp80 °C (plastic) / 120 °C (Zn)

UV VOC< 50 g/L

Air-dry VOC400–600 g/L

💡 Picking the Right Cold Paint SystemFor small plastic parts with simple geometry: UV-cure gives the fastest cycle time and highest hardness. For complex shapes or assembled parts: air-dry acrylic is the safe choice. For medium volumes: a hybrid line with UV for flat surfaces and air-dry for recesses maximizes throughput.

⚠ Never UV-cure assembled electronics or temperature-sensitive insertsUV lamps generate significant heat (60–80 °C at the surface during extended exposure). Some plastic formulations yellow under UV even without heat — always test on actual production parts first. Air-dry is the safest choice for unknown plastic grades.

FAQ

Can cold painting match baked paint adhesion?

Not exactly — cold paint relies on mechanical interlocking and mild solvent etching of the substrate. Adhesion is 50–70% of baked paint levels on metal. Use a CPO (chlorinated polyolefin) adhesion promoter on polypropylene and other low-energy plastics.

Why does my UV paint feel tacky after curing?

Tacky = under-cured. Increase exposure time or UV intensity. Check that the photoinitiator wavelength matches your lamp spectrum. Oxygen inhibition can also cause surface tack — use an inert gas blanket or a higher-intensity lamp.

Can I apply cold paint over a baked primer?

Yes — a baked primer (cured at 160 °C) gives excellent adhesion and chemical resistance, then a cold topcoat allows heat-sensitive colors or effects. This hybrid approach is common for automotive interior parts.

How long does air-dry paint stay potable after mixing?

Most 2K air-dry paints have a pot life of 2–4 hours after mixing hardener. Beyond that, viscosity rises and film quality degrades. Single-component air-dry paints can stay in the pot for 8–24 hours if covered.

Is cold paint as durable for outdoor use?

No — cold paint has lower UV resistance and chemical resistance than baked. For outdoor hardware, specify a baked system if the substrate allows it, or use a UV-stable clear topcoat over the cold color layer.

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Workshop Planning Data

Cold Painting — Data Zinc Alloy Finishing Managers Need

Cold painting uses air-dry or UV-cure coatings for heat-sensitive zinc alloy parts, delivering full color coverage at low bake temperature with short line length and fast changeover.

280 m²Workshop Area

10 peopleTeam Size

90 kWInstalled Power

300-600k pcs/dayDaily Output (10 h)

Quality Inspection & Control

Check item	Method	Acceptance standard
Film thickness	Thickness gauge	30-50 μm total
Color match	Colorimeter	ΔE ≤ 1.0
Adhesion	Cross-cut	ISO 2409 rating 0-1
Hardness	Pencil hardness	≥ HB after full cure
Drying time	Tack-free test	Tack-free ≤ 30 min at 25 °C
Appearance	Visual	No pinholes, runs or fisheyes

Workshop Layout & Floor Area

Zone	Area
Booth + conveyor	100 m²
UV / air-dry tunnel	60 m²
Paint store & mixing	40 m²
QA	25 m²
Utility & lockers	55 m²
Total workshop	280 m²

Manpower & Shift Plan

Role	Headcount
Spray operators	5
QC inspectors	2
Paint technician	1
Supervisor	1
Maintenance	1
Total (2 shifts × 10 h)	10

Power & Utility Demand

Equipment	Demand
Booth extraction	18 kW
UV lamps	24 kW
Air compressor	18.5 kW
Conveyor	9 kW
Paint pumps	6 kW
Lighting & auxiliary	14.5 kW
Installed total	90 kW
Typical running load	≈ 70 kW

Production Flow Chart

PretreatmentClean and dry parts

LoadJigs, trays or barrels

Cold SprayAir-dry / UV paint spray

Flash & CureAmbient or UV cure

InspectFilm, color, adhesion

PackProtect and pack

Daily Capacity — 10-Hour Operating Day

Parameter	Value
Cycle time	20-40 min
Load per batch	50-100 kg
Batches per 10 h day	14-18
Daily output	300,000-600,000 pcs
Monthly output (26 days)	7-15 million pcs

Output Value Estimate

Parameter	Value
Painting fee per piece	USD 0.008-0.02
Daily output value (10 h)	USD 3,000-8,000
Monthly output value	USD 78,000-208,000
Annual output value	USD 940,000-2,500,000