Surface Treatment to Make CNC Machined Plastic Parts More Durable and Aesthetic
Introduction
Plastic is a versatile material in CNC machining, used across industries from consumer electronics to medical devices. However, uncoated plastic parts often lack the durability, UV resistance, and surface finish required for demanding environments or premium products.
Applying proper surface treatments to CNC-machined plastic parts enhances mechanical strength, chemical resistance, and thermal stability and improves the visual appeal and branding potential. This blog explores eight commonly used surface finishing processes that boost performance and aesthetics for plastic components.
Surface Treatment Technologies for Plastic Components
Scientific Principles & Industrial Standards
Definition: Surface treatments for plastics involve modifying the outer layer of a part through mechanical, chemical, or deposition processes to increase functionality—such as scratch resistance, adhesion, gloss, or non-stick properties—without altering the base polymer structure.
Governing Standards:
ASTM D3359: Adhesion testing for coated plastic substrates.
ISO 2409: Cross-cut test for paint or coating adhesion.
ASTM D1003: Haze and transparency for optical plastics.
Process Function and Cases
Performance Dimension | Technical Parameters | Application Cases |
|---|---|---|
Surface Protection | - UV coating: 60–80 µm - Painting: up to 100 µm - Teflon: 25–30 µm/layer | Phone cases, automotive dashboards, appliance panels |
Visual Enhancement | - Chrome plating: Ra ≤ 0.1 µm, high gloss - Brushing: matte lines with #400 grit - Polishing: Ra ≤ 0.2 µm | Cosmetic packaging, lighting covers, speaker housings |
Chemical Resistance | - Teflon: pH 1–14 resistance, 260°C stable - UV coating: resists yellowing under UV-C radiation | Lab enclosures, chemical reservoirs, food-grade trays |
Electrical/Decorative Finishes | - Electroplating: ABS and PC-ABS compatible - Anodizing (for aluminum-filled plastics): uniform oxide layer | Housings for electronics, touch interfaces, fashion accessories |
Surface Treatment Process Classification
Technical Specification Matrix
Treatment Type | Key Parameters & Metrics | Advantages | Limitations |
|---|---|---|---|
- Thickness: 60–80 µm - Cure: UV 365–400 nm lamp for 3–5 sec | - Fast curing, scratch resistant - Optical clarity | - Surface must be clean and static-free | |
- Thickness: 50–100 µm - Spray or dip coat, baked @ 80–120°C | - Wide color flexibility - UV and abrasion protection | - Prone to peeling if surface not primed | |
- Multi-layer: Cu/Ni/Cr - ABS pre-treatment with etching & seeding | - Metallic appearance - Enhanced wear resistance | - Limited to electroplatable plastics | |
- Oxide thickness: 5–25 µm - Only for aluminum-filled polymers | - Corrosion resistance - Matte and colorable finish | - Only applies to specific composite plastics | |
- Layer: 0.5–2 µm - Applied via electroless or electrolytic process | - High reflectivity and abrasion resistance | - Requires strong adhesion layers | |
- Friction: 0.05–0.20 - Thermal range: –200°C to 260°C | - Chemical, heat, and stain resistant - Easy cleaning | - Requires grit blasting and primer | |
- Achievable Ra: ≤ 0.2 µm - Buffing with diamond or alumina compounds | - Improves optical clarity - Removes tool marks | - Only suitable for thermoplastics like PC, PMMA | |
- Grit: #320–#600 - Linearity control critical | - Aesthetic matte texture - Reduces glare | - Must be sealed to prevent contamination |
Selection Criteria & Optimization Guidelines
UV Coating
Selection Criteria: Ideal for plastic parts needing scratch resistance and UV protection, such as mobile device casings and automotive interiors.
Optimization Guidelines:
Clean the surface with ionized air before coating.
Apply evenly via spray or roll coat.
Cure under a high-intensity UV lamp (365–400 nm, 5 seconds).
Painting
Selection Criteria: Suitable for branding, color-coding, or decorative applications across large or uniquely shaped parts.
Optimization Guidelines:
The surface roughness Ra < 0.6 µm for proper adhesion.
Use a primer for improved durability.
Cure with heat or UV depending on the paint formulation.
Electroplating
Selection Criteria: Used for cosmetic and functional enhancement of ABS, PC-ABS, or conductive-filled plastics.
Optimization Guidelines:
Etch with chromic acid, then apply palladium seeding.
Apply successive Cu/Ni/Cr layers with current control.
Measure thickness with XRF (±0.1 µm accuracy).
Anodizing
Selection Criteria: Limited to aluminum-filled polymers or metal-plastic hybrid structures used in high-touch or corrosion-prone applications.
Optimization Guidelines:
Mask non-conductive surfaces.
Use Type II anodizing at 18–24 V, 20–25°C.
Dye for color, then seal at 95°C in DI water.
Chrome Plating
Selection Criteria: Applied to decorative or mechanical plastic components for mirror-finish and wear resistance.
Optimization Guidelines:
Precondition with electroless nickel for base adhesion.
Plate chrome at 25–30 A/dm², 50–55°C.
Polish post-plating for optical gloss.
Teflon Coating
Selection Criteria: Recommended for components exposed to high-friction or aggressive chemical environments.
Optimization Guidelines:
Grit blast plastic surface to Ra ~1.0 µm.
Apply primer layer before Teflon (PTFE, FEP).
Bake at 280–370°C, depending on coating type.
Polishing
Selection Criteria: Used for display panels, lenses, or parts requiring clarity and gloss, especially in PC, PMMA, or acrylic.
Optimization Guidelines:
Wet sand to 1,000–3,000 grit, then buff.
Polish with cerium oxide for PMMA or alumina slurry for PC.
Final Ra ≤ 0.1 µm for optical surfaces.
Brushing
Selection Criteria: Ideal for achieving uniform matte finishes in casings, bezels, or industrial controls.
Optimization Guidelines:
Brush with #400–#600 grit ina single direction.
Use jigs to maintain brushing uniformity.
Apply topcoat or UV sealant to prevent residue adhesion.
Material-Coating Compatibility Chart
Plastic Material | Recommended Surface Treatment | Performance Gain | Industrial Validation Data |
|---|---|---|---|
Electroplating + Chrome | Metal-like finish, 3× wear resistance | Automotive knobs, decorative handles | |
UV Coating + Polishing | Scratch resistance, optical clarity | Smartphone covers, light diffusers | |
Polishing | Improved smoothness for seals/sliders | Non-stick gaskets, labware | |
Painting + Brushing | Decorative matte with brand colors | Cosmetic packaging, signage panels | |
Chrome Plating | Enhanced strength and metallic shine | Automotive vents, display bezels |
Comprehensive Process Control and Quality Assurance
Preparation and Quality Standards
Pre-Treatment: Surfaces must be clean, dry, and roughened or chemically primed for best adhesion.
Process Control: Film thickness, cure time, adhesion strength, and gloss level are monitored in real-time.
Post-Treatment: Quality tests include tape adhesion (ASTM D3359), hardness (pencil or nanoindentation), visual inspection, and chemical resistance trials.
Expert Insights and Common Inquiries
Can electroplating be done on all plastic materials?
Which surface finish offers the best UV resistance for outdoor plastic components?
What’s the best option for plastic parts used in medical environments?
Can Teflon coating improve the lifespan of sliding plastic parts?
Is anodizing possible on pure polymer-based parts?
