The art of refinishing plastics parts can be daunting. Vehicle parts can be made from an array of individual plastics, from ABS and PP, to PVC, or a myriad of combined plastic compounds. To help refinishers chose the right product and process for the right plastic part and to avoid flaws in their repairs, the experts at Standox, one of the premium refinish brands of Axalta, a leading global supplier of liquid and powder coatings, share some helpful insights and practical advice.
Know your plastics
Before starting to work on a plastic part, the refinisher should thoroughly inspect the part and categorise it in one of the following:
Painted old part
Unpainted old part
Uncoated new part
Coated new part
Primed new part.
The repair process will differ for each option, so this is a vital stage of the job.
Getting the paint to adhere on plastics
While all plastic parts need to be thoroughly cleaned before the repair is started, this is particularly true for uncoated new parts. The release agent used to free plastic parts from the mould when manufactured will also release the refinisher’s paint from the plastic, so it is vital that this release agent should be fully removed before the job begins. There are three types of release agent – internal, external and release paints. Firstly, these need to be warmed up (conditioned), being careful to support the part to avoid deformation. The part then needs to be cleaned repeatedly with a pad, brush and fresh cleaning agent, such as the Standox Silicone Remover 6600 or Standoflex Plastic Cleaner 6500. After cleaning, it is essential that the cleaning agent be fully evaporated before further processing.
Major damage such as cracks or deep scratches must be repaired initially with special plastic repair kits, provided that the effort required does not exceed the cost of a new part. Standoflex Plastic Primer U3060 and Standoflex Plastic Stopper U1030 can be applied to the damaged area after sanding and cleaning, followed by a suitable elastified Standox VOC filler like Standox VOC Pro Filler U7530 or Standoflex 2K Plastic Primer Surfacer U3200, which is applied after flash off. Following the application of the Standohyd Plus or Standoblue Basecoat, use elastified Standocryl VOC Clears or elastified VOC Topcoats.
If the complex part structure of a load-bearing carbon fibre part is damaged, the part must be replaced. Failure to do so may lead to an increased safety risk.
A flawless finish
The most common problems encountered when repairing plastics are:
- Orange peel – caused by unsuitable solvent combinations
- Poor adhesion – caused by insufficient cleaning or unsuitable adhesion promoters
- Pinholes – caused when the paint is applied too soon
- Lifting – caused by improper isolation and/or through-sanding.
- By following this checklist, flaws can be avoided, and a perfect finish will be achieved:
- Adequate preparation – conditioning and cleaning.
- Using the right cleaning agents – highly corrosive cleaning agents can damage plastics and lead to cracks.
- Avoid applying the coating too soon after cleaning – this can cause a build-up of vapour pressure between the plastic and the coating, reducing adhesion.
- Using the right coupling agents – each type of plastic has its own specific requirements.
- Using enough plasticiser – fillers, topcoats and clearcoats must contain the right amount of plasticiser to avoid the part cracking under mechanical strain.
Standox has a Standothek guide entitled How to refinish plastics, which contains further detailed information and advice. It can be downloaded from the Services and Training section of the Standox website at www.standox.co.za.