ABS Surface Finishing FAQ

1. Thorough cleaning and degreasing: Wash the ABS plastic with warm water and a dishwashing soap that doesn’t contain hand softeners or dedicated wax and grease removers to remove oils. Wipe with isopropyl alcohol to remove remaining oils, mold release agents, or residues.
2. Sanding: Lightly sand the entire surface to be painted using 320 – 400 grit sandpaper. The goal is to create a sort of “mechanical key” for the paint to bind.
3. Dust removal: Clean again to remove sanding dust and wipe with isopropyl alcohol and allow to dry.
4. Apply adhesion promoter: Apply in 1 to 2 light coats to act as a “glue” between the plastic and the paint. Leave for 5 to 10 minutes to dry, or according to the manufacturer’s instructions.

It is a link between the plastic surface and paint, creating a smooth, uniform surface and improving adhesion. Filler primer is applied in multiple thin coats and allowed to dry before sanding with 600-grit sandpaper for the best results. The most popular option for 3D prints is the Rust-Oleum filler primer. Seymour filler primer is often used as an alternative.

It acts as a protective sealer that prevents aggressive solvents in paints (for example, lacquers or polyurethane enamels) from attacking the substrate. Aggressive solvents can cause crazing, cracking, or weakening of the plastic part. It can also be used for sealing to prevent moisture intrusion for parts that will be in a constantly damp environment.

• Spray painting (aerosol): This is best for painting large parts using plastic-specific spray paints. Several layers of light, thin coats are used to achieve the desired result.
• Airbrushing: Best for high-detail work like miniature painting. On the other hand, it allows for fine control and thinner, more precise layers.
• Brush painting: It is best for small touch-ups, repairs, or detailed work.
• Dip coating: This is an industrial method used for high-volume production. The part is dipped into the paint, providing consistent, full coverage for complex shapes.

Avoid high-thinner lacquer paints because they can weaken or crack ABS parts. The table below highlights some of the best paint and primer options for ABS.

ABS is susceptible to yellowing and becoming brittle with frequent exposure to sunlight. A UV-resistant clear coat shields the part from UV damage. In addition to UV protection, a clear coat also serves other purposes, including:

• Surface protection from physical damage, scratches, and abrasion.
• Enhance aesthetics like achieving a high-gloss, satin, or matte finish.
• Improve longevity by protecting the part from environmental damage, especially products intended for outdoor use.

Since ABS is non-conductive, a specialized pretreatment process involving chemical etching and sensitization is used to create a conductive metal base (mostly nickel or copper) before the application of the final, durable electroplating layer.

The detailed steps involved in the process are as follows:

1. Degreasing: This is the removal of surface oils, grease, and contamination using alkaline cleaners.
2. Roughening: A chromium-sulfuric acid solution is used to corrode the ABS, particularly etching the butadiene phase to create microscopic “anchor points” for mechanical adhesion.
3. Neutralization: This is the removal of residual etching chemicals.
4. Activation: Stannous chloride or palladium is used to absorb catalytic metal particles, enabling the ABS to hold the future metal layer.
5. Electroless plating: This is a chemical plating step that deposits a thin, conductive layer of nickel or copper onto the activated ABS without electricity.
6. Electroplating: The traditional process applies copper, nickel, or chrome over the electroless layer to add the desired finish and thickness.

Some of the key industries where ABS electroplating is applied include:

• Automotive industry: Accounts for the largest application of plastic plating for both functional and decorative purposes, including interior and exterior trims, grilles, door handles, and so on.
• Consumer electronics: Plating is used to add a high-end, durable finish to electronic devices and provide an electromagnetic interference shield, e.g., smartphone casings, laptop shells, computer keyboards, etc.
• Medical devices: ABS plating is used to create durable and hygienic surfaces that can withstand harsh cleaning agents. For example, medical instrument housings, equipment casings, and so on.
• Home appliances and plumbing: Mostly used for decorative and premium feel without the weight and cost of solid metal, e.g., faucets, showerheads, washbasin taps, and so on.

The key difference lies in the preparation of the plastics. ABS is easily etched using standard chemical solutions like sulfuric acid or chromic acid, which dissolve the butadiene phase to create microscopic pores where metals will firmly adhere. The pores ensure the plating results on ABS have higher adhesion strength. PC is harder to etch and often requires more aggressive and expensive pre-treatment steps to ensure the metal doesn’t peel off.

• Nickel: Used primarily as a base coat. It provides a bright, wear-resistant, and corrosion-resistant finish.
• Copper: Commonly used because of its excellent conductivity, lower cost, and ability to act as a barrier to prevent blister formation on plastic parts.
• Chrome or chromium: Used mainly for decorative parts to achieve a shiny, metal-like appearance without adding to the weight.
• Gold: Used for both decorative and functional purposes, including high-temperature corrosion resistance and conductivity in electronic components.
• Silver: It is used mainly for decorative purposes but can sometimes play functional roles.
• Palladium: It is frequently used in the activation step of the plating process to facilitate the bonding of other metals.

1. Enhanced aesthetic appeal: Provides a high-end, shiny metallic look for luxury finishes.
2. Wear and corrosion resistance: Protects the ABS plastic underneath from degradation and environmental damage.
3. Surface hardness: Allows manufacturers to create parts that look like metal but are significantly lighter.
4. Enhanced structural integrity: The metal coating enhances the dimensional stability and rigidity of the plastic.
5. Electrical conductivity: Allows the use of cheaper plastic to conduct electricity in electronic components.
6. Cost-effectiveness: Offers a cheaper alternative to heavy, expensive metal parts.

• Acetone vapor polishing: In this technique, acetone vapor is used to melt the outermost layer of the ABS part, allowing the layers to fuse and create a glossy finish. The key advantage is that it instantly removes surface roughness.
• Wet sanding: Best for removing deep scratches or preparing the part for painting. The main advantage is that it allows for precise control over the surface, maintaining sharp edges and geometries.
• Mechanical buffing: Often used after manual sanding to bring a dull ABS surface to a high-gloss, mirror-like finish. It is excellent at removing micro-scratches and achieving high gloss or transparency.

Acetone has a low flash point (-20^oC or -4^oF), making it easily ignitable. The accumulation of acetone vapors increases the risk of explosion. Consequently, the handling must be done in a well-ventilated area with appropriate personal protective equipment (PPE).

Excessive exposure of the ABS part to acetone can lead to over-smoothing or loss of details. The chemical action softens the ABS, which can lead to warping. Directly dipping the part in liquid acetone can leave a white, hazy, or powdery finish instead of the desired glossy finish.

The best result is achieved using acetone vapor smoothing. Place the part in a sealed container with a small amount of acetone on a paper towel. The fumes melt the surface microscopically to give extremely smooth, glass-like gloss. The easiest method to achieve this result is clear coating. Applying a gloss clear coat is a quick way to change the finish without altering the plastic.

To speed up the drying process, place the part in a well-ventilated area and use a fan to accelerate acetone evaporation. Alternatively, you can place it under mild sunlight.