Painting Plastic – What to Consider When Coating Thermoplastics

What Are the Benefits of Painting Thermoformed Plastic Parts?

There are two ways to achieve the desired surface finish in thermoforming: (1) using pre-colored or pre-treated plastic sheets that already possess the necessary characteristics before the thermoforming process, or (2) post-processing the finished plastic part. The next section explains why pre-treated plastic is not always used.

Here, we first outline the reasons and benefits of painting thermoformed plastic parts as a post-processing step:

1. Painting Plastic for Aesthetics and Brand Identity

Painting your thermoformed plastic parts strengthens brand identity and enhances aesthetics. A high-quality surface immediately improves the perceived value of your product.

You can integrate special effects such as:

• High-gloss finish
• Metallic effects
• Matte or textured finishes

Additionally, full or partial coloration, different colors, or color gradients in all RAL shades are possible.

2. Painting Plastic for Protection Against Environmental Influences

A painted surface acts as a protective layer, shielding thermoformed parts from UV radiation, moisture, and chemicals. Painting plastic extends the lifespan of the parts and increases the efficiency of your production cycle.

3. Painting Plastic for Easier Cleaning and Maintenance

Painted thermoformed plastic parts are easier to clean and maintain. The smooth surface prevents dirt accumulation and simplifies maintenance.

For specific cleaning requirements, feel free to contact us directly or read our post “How to Clean Trays.”

Painting Plastic vs. Pre-Colored Plastic Sheets – Key Reasons for Choosing Paint

Coloring can also be achieved by purchasing pre-colored plastic sheets or films that are extruded in the desired RAL shade. However, specific circumstances and requirements may favor post-processing through painting to achieve the desired surface finish.

In the following cases, pre-colored plastic sheets are usually avoided in favor of painting thermoformed parts:

Minimum Order Quantities (MOQs)

Custom RAL colors require custom extrusion, and most plastic manufacturers impose minimum order quantities. These quantities can be too high to justify custom extrusion for a specific product or order.

Multicolored Parts

If a thermoformed part needs to be multicolored, it cannot be achieved with a pre-colored, extruded sheet. While simple color stripes can be added for product identification, complex color patterns require painting.

Which Plastics Can Be Painted?

Plastics have a lower affinity for paint adhesion compared to metallic surfaces due to properties like surface energy, porosity, and smoothness. Therefore, 2K-PUR paints (two-component polyurethane-based coatings) are commonly used due to their strong adhesion and long-lasting durability.

Plastics That Are Easy to Paint:

• ABS (Acrylonitrile Butadiene Styrene)
• PC (Polycarbonate)
• PMMA (Polymethyl Methacrylate)
• PA (Polyamide)

Plastics That Are Difficult to Paint:

• PE (Polyethylene)
• PP (Polypropylene)
• PVC (Polyvinyl Chloride)
• Other elastic plastics

To improve paint adhesion, pre-treatment methods such as primers, adhesion promoters, or chemical treatments are often required to enhance surface energy.

Learn more about thermoplastic materials and their properties in our Thermoplastic Plastics Webinar.

Special pre-treatments are often carried out to improve the adhesion of coatings to plastics. This may include the use of adhesion promoters, primers, or other chemical treatments to increase the surface energy from a chemical point of view and improve adhesion.

It is important to consider the compatibility between the plastic material and the selected coating system to ensure successful plastic coating.

Painting Plastic: The Coating Process

Before painting, plastics require thorough pre-treatment. Various cleaning and pre-treatment methods include:

Painting Plastic: The Coating Process

Before painting, plastics require thorough pre-treatment. Various cleaning and pre-treatment methods include:

Surface Pre-Treatment Methods:

• CO₂ Cleaning: Compressed carbon dioxide is used in a blasting process to remove contaminants.
• Steam Cleaning: Hot steam cleans plastic parts without leaving residue.
• Flame Treatment: Controlled heat application removes impurities and enhances paint adhesion.
• Low-Pressure Plasma Treatment: Ionized gas interacts with the surface to improve adhesion without leaving residue.

Manual vs. Automated Plastic Painting

Once the plastic parts are cleaned and pre-treated, the next step is choosing between **manual or automated painting.**Masking-free painting techniques can improve precision and efficiency.

The choice between manual and automated painting depends on factors such as production volume, part complexity, and specific coating requirements.

• Robotic Painting: Industrial robots apply coatings precisely, ensuring uniformity on complex geometries.
• Automated Paint Lines: Conveyor systems transport parts through the coating process for efficient high-volume production.
• Spray Coating: Paint is atomized and applied using compressed air or electrostatics.
• Dip Coating: Parts are submerged in paint, ensuring even coverage, followed by excess removal.

Following the painting process, a drying phase hardens the coating, resulting in a durable, high-quality finish. These painted plastic parts are widely used in industries like automotive, electronics, and furniture manufacturing.

Painting Plastic – A Conclusion

Painting thermoformed plastic parts provides numerous advantages, including aesthetic enhancement, environmental protection, and ease of maintenance. By considering material properties and using proper painting techniques, high-quality results can be achieved.

However, proper preparation is key. Do you have questions about the optimal color finish for your thermoformed parts? Contact us via email or call us directly at Tel: +4971919525170.