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Surface Finishing：What is painting?
Spray Painting Surface
A Complete Practical Guide
Spray painting is one of the most widely used surface finishing processes in industrial and consumer products. It atomizes coating material into fine particles and applies them evenly onto substrates to achieve decoration, protection, abrasion resistance, insulation, and tactile feel. This guide covers fundamentals, workflow, material selection, parameter control, defect troubleshooting, and process comparison — a fully practical reference for production and application.
Spray painting (spray coating) atomizes paint using compressed air, electrostatic force, or airless high pressure, then deposits it uniformly on metals, plastics, silicone, wood, 3D‑printed parts, and more, forming a cured film.
- Extremely rich colors and effects: solid color, metallic, pearl, matte, high‑gloss, rubber‑feel paint, PU high‑gloss, etc.
- Wide compatibility: works with almost all common materials, ideal for curved, complex, and hollow parts
- Controllable film thickness: typically 15–40μm, thin and uniform with fine appearance
- Flexible production: cost‑effective for small batches, multi‑color jobs, and rapid prototyping
Painting involves atomizing paint with a spray gun and applying it evenly to a workpiece surface, followed by curing through air-drying or low-temperature baking
-Deciding Parts&baking/curing temperature by paint type (guideline ranges—follow manufacturer TDS).
Paint coatings are typically cured in four ways:
①Air drying (room temperature),
②low-temperature baking
③medium-temperature baking
④high-temperature baking.
You can tell the manufacturer the following when you don’t know which paint to use:
“I’m not sure which coating to specify — please recommend based on my requirements.”
🌟Key questions / information to provide:
- Where will the part be used? (indoor / outdoor / marine / automotive / electronics)
- Will it need corrosion resistance or salt-spray testing? (Yes / No — required hours)
- Appearance requirements: color, texture, blemish tolerance.
- Gloss level: matte / satin / semi-gloss / high-gloss (specify % or visual sample if possible).
- Substrate material: steel, stainless, aluminum, ABS, PC, PP, etc.
- Maximum allowable baking/assembly temperature or heat-sensitive constraints.
- Durability requirements: abrasion resistance, chemical resistance, UV resistance.
- Production volume & process: prototype, small batch, mass production; manual spray, robotic, powder coat, UV cure.
- Environmental/VOC constraints or preferred technologies (waterborne, powder, low-VOC).
- Budget considerations and acceptable cost vs. performance trade-offs.
- Any required certifications or tests (salt spray, adhesion, impact, color matching).
- Pre-treatment expectations (cleaning, blasting, conversion coating) or if you want them to quote options.
These details are critical inputs that directly determine project specifications and pricing.
🌟Main paint types for spray finishing and typical baking/curing temperatures(typical ranges; follow manufacturer TDS)
——Epoxy
- Use: corrosion-resistant primers, industrial metal parts.
- Cure: 120–180°C (248–356°F) short bake; 80–120°C (176–248°F) longer bake.
- Notes: Excellent corrosion resistance; often requires crosslinker and higher cure.
——Polyurethane (PU)
- Use: high-gloss topcoats, outdoor/weather-resistant surfaces.
- Cure: 80–150°C (176–302°F); common: 80–120°C (176–248°F) for 30–60 min.
- Notes: Good hardness and weatherability.
——Acrylic
- Use: appliances, decorative finishes; available waterborne or solventborne.
- Cure: 60–120°C (140–248°F); waterborne often air-dry or low-temp cure.
- Notes: Good color retention and flow; waterborne reduces VOCs.
——Polyester
- Use: furniture, appliance housings, high-wear surfaces.
- Cure: 100–160°C (212–320°F).
- Notes: Common in powder and 2K systems.
——UV-curable Coatings
- Use: electronics, plastics, high-speed production.
- Cure: UV lamp — no thermal bake required.
- Notes: Fast cure, ideal for heat-sensitive substrates; requires photoinitiators.
——Fluorocarbon / PVDF
- Use: exterior architectural metal, extreme weather resistance.
- Cure: ~150–200°C (302–392°F).
- Notes: Used on pretreated metal panels.
Low-temperature / 2K Fast-cure Systems
- Use: heat-sensitive plastics or assembled parts that cannot be baked hot.
- Cure: as low as 40–80°C (104–176°F) or room-temperature cure (longer time).
- Notes: Depend on hardener/accelerator and correct mix ratio.
——Ceramic Coatings (Ceramic Paint)
- Use: high-temperature resistance, thermal barrier, wear-resistant or decorative finishes on metal and some engineered substrates.
- Process & Cure: often require specific spray application (thin, even coats), followed by high-temperature curing or controlled air-dry plus post-bake depending on formulation; typical cure ranges vary widely—from low-temp air-dry ceramics to high-temp sintering processes (can exceed 250°C for some formulations).
- Notes: Ceramic paints provide excellent heat resistance and hardness; substrate compatibility and exact cure profile depend on product—follow manufacturer guidelines.
Key reminders
- Plastics are heat-sensitive: many plastics (PP, PE, some ABS, PVC) cannot tolerate high bake—use low-temp systems, UV cure, or specially formulated plastic primers.
- Time × temperature trade-off: higher temperature shortens cure time; lower temperature requires longer cure—always follow TDS.
- Safety & performance: follow TDS/SDS; ensure oven airflow and temperature uniformity; control film thickness.
🌟Temperature Selection & Coating Matching
Temperature determines the choice of coating system, which must match the heat resistance of the base material.
The higher the baking temperature, the stronger the coating hardness, adhesion and corrosion resistance, but the higher the energy consumption and equipment requirements.
Mainstream industrial coating: medium temperature (120–140°C) and high temperature (180°C) are the most commonly used; room temperature / low temperature is mostly used for heat-sensitive materials and small-batch production.
1. Room Temperature Cure (Air-Dry / Self-Drying)
Temperature: 15–35°C (natural environment, no heating required)
Mechanism: Solvent evaporation, oxidative crosslinking, reaction with room-temperature curing agents
Mechanism: Solvent evaporation, oxidative crosslinking, reaction with room-temperature curing agents
Typical coatings:
- Nitrocellulose lacquer, alkyd paint, one-component acrylic paint
- Two-component PU / epoxy (room-temperature curing)
- Most water-based paints (air-drying)
Features:
- No baking equipment needed, low cost
- Slow drying (several hours to 24 hours)
- Moderate hardness and chemical resistance
Applications:
Wood products, plastics, small-batch hardware, on-site coating, and paint repair.
Wood products, plastics, small-batch hardware, on-site coating, and paint repair.
2. Low-Temperature Baking (Forced Drying)
Temperature: 60–100°C (mainstream industry standard)
Mechanism: Accelerated solvent evaporation + mild crosslinking
Typical coatings:
Mechanism: Accelerated solvent evaporation + mild crosslinking
Typical coatings:
- Low-temperature acrylic baking paint
- Industrial water-based paints (low-temperature accelerated)
- Some modified alkyd paints
Features:
- Fast drying (30 minutes to 2 hours)
- Low heat resistance requirement for substrates
- Better hardness and adhesion than air-dried coatings
Applications:
Plastics, aluminum alloy, magnesium alloy;
home appliance shells, small hardware parts, automotive interiors.
3. Medium-Temperature Baking
Temperature: 100–150°C
Mechanism: Full resin crosslinking and curing
Mechanism: Full resin crosslinking and curing
Typical coatings:
- Amino baking paint (most widely used)
- Medium-temperature epoxy ester, medium-temperature acrylic paint
- Some water-based baking paints
Features:
- High hardness, good gloss, balanced weather and chemical resistance
- Mainstream for industrial assembly lines
- Low yellowing (suitable for topcoats)
Applications:
Metal parts, general industrial products, agricultural machinery, engineering machinery;
home appliances, instrument housings, topcoats.
4. High-Temperature Baking
Temperature: Above 150°C (commonly 160–220°C)
Mechanism: Deep crosslinking and complete curing
Mechanism: Deep crosslinking and complete curing
Typical coatings:
- Powder coating (180–200°C)
- High-temperature epoxy, epoxy phenolic paint
- Silicone high-temperature paint, high-temperature fluorocarbon paint
- Original automotive electrocoating / topcoat (160–180°C)
Features:
- Extremely high hardness, excellent anti-corrosion, heat resistance, and solvent resistance
- Requires special ovens, high energy consumption
Applications:
Automotive bodies, anti-corrosion pipes, storage tanks, guardrails;
home appliances, hardware, and parts requiring long-term weathering / corrosion protection.
Automotive bodies, anti-corrosion pipes, storage tanks, guardrails;
home appliances, hardware, and parts requiring long-term weathering / corrosion protection.
Hardware Metal Painting
The process requires precise pretreatment (pickling, phosphating, fine sanding) to ensure a contaminant-free surface. After priming and topcoating, the workpiece is baked at a controlled temperature (e.g., 160℃ for 30-60 minutes for automotive finishes) where powder melts and cures into a hard film.
Baking finish delivers a smooth, high-gloss surface with exceptional hardness (up to H grade), wear resistance, and corrosion resistance
Plastic Spray Painting
Ceramic Coatings (Ceramic Paint)
🌟(Metal vs Plastic spray painting) Main differences
1.Substrate chemistry and adhesion mechanisms
- Metal: adhesion relies on mechanical interlocking and chemical bonding; phosphating, conversion coatings, or metal-specific primers are commonly used to enhance adhesion and corrosion resistance.
- Plastic: low and variable surface energy (PP, PE, ABS, PC, etc.); requires surface energy increase (plasma/flame/corona treatment or chemical etching) or use of specialized adhesion primers/coupling agents.
2.Surface pretreatment
- Metal: degreasing, acid/alkaline wash, abrasive blasting, phosphating, or anodizing (for aluminum).
- Plastic: solvent wipe, hot-water/ultrasonic cleaning, flame/plasma/corona treatment, or chemical etching depending on the polymer.
3.Coating types and formulations
- Metal commonly uses: epoxy primers, polyurethane topcoats, polyester, powder coatings, fluorocarbon (PVDF). Emphasis on corrosion protection, hardness, and weatherability.
- Plastic commonly uses: low-temperature 2K systems, flexible PU/acrylics, UV-curable coatings, and plastic-specific primers. Emphasis on flexibility, adhesion, and low-temp/low-stress formulations.
4.Curing temperature and process limits
- Metal: tolerates higher temperatures; high-temperature bakes and powder curing (e.g., ~180°C) are common.
- Plastic: temperature-sensitive; requires low-temperature cure, UV cure, or ambient cure systems.
5.Coating performance requirements
- Metal: greater focus on corrosion resistance, wear resistance, weatherability, and high hardness.
- Plastic: greater focus on flexibility, crack resistance, impact resistance, chemical resistance, and stable appearance (no wrinkling or crazing).
6.Spray parameters and equipment
- Metal: powder coating, electrostatic spray, and electrophoretic deposition (for small hardware) are common in industrial lines.
- Plastic: often uses low-pressure HVLP, UV lines, manual or robotic spray; pay attention to part temperature and preheat limits.
FORMEXFABTECH primarily offers processing services for various product designs, ranging from sample development to mass production. If you are looking for a reliable partner, please feel free to contact us.
