Painting plastics – the most common problems and how to solve them

Painting plastics seems to be a simple process. So why do many well-known companies, including large corporations, outsource this service instead of providing it in-house? In the article below you will find the answer to this question, including the most common defects in the process of painting plastics and how to solve them.

Painting plastic parts – why isn’t it so easy?

At first glance, painting plastic components involves spraying the part with paint and letting it dry. In reality, however, it is a multi-stage process that requires specialized knowledge and long experience.

Before painting, several factors should be analyzed, the most important of which are:

  • determining the type of plastic – this affects adhesion, drying temperature, the use of additional processes before painting, and even the way of assembling the part in the process,
  • determining the customer’s requirements regarding the resistance of the coating – influence on the selection of paint material and the drying process,
  • indication of the surface to be painted – this determines the method of fastening and the possible selection of masking as well as the method of applying the varnish,
  • understanding the target visual and tactile effect that the client would like to achieve – we adapt not only the appropriate varnishing materials, but also select the number of layers and technological parameters of varnishing and drying.

Then we prepare for painting trials:

  • we order varnishes or select them from those already used in production,
  • we determine the method of assembling the parts,
  • we pass the client’s requirements to the team responsible for testing,
  • we define the process diagram and technological details for each of these processes,
  • after testing and seasoning the coating, we check the compliance of the obtained effect with the requirements and send the painted parts to the customer for evaluation.

After accepting the results of the tests and commercial conditions, we can start the first trial production, before which a process sheet is created, and the entire team involved in production is trained in every aspect of the project. The further process will be described in another blog post.

The process of painting plastic is subject to many environmental and health and safety requirements. It is extremely important to establish and comply with high standards of occupational health and safety – from protective clothing to appropriate working conditions (well-ventilated painting booths, air treatment systems, effective and multi-stage filtration, etc.). Permits for the emission of VOCs into the atmosphere are also required and will only be issued if strict requirements are met. For this reason, many corporations refrain from establishing an industrial painting department within the company and outsource such services to specialized paint shops – such as ours.

The most common problems when painting plastics

Painting plastic involves many risks. The most popular include:

  • lack of adhesion – plastics with low surface tension require surface activation by e.g. plasma, flame treatment, the use of a primer or the selection of paint created specifically for a given type of material. Lack of adhesion of the paint coating may also occur on a seemingly safe material (e.g. ABS) if it is greasy.
  • deformation of parts – the selection of fastening, flame and drying temperature to the type and shape of the material has a key impact on the possible occurrence of this problem. For example, thin-walled ABS is very susceptible to deformation even at a temperature lower than the flowing temperature of this material. Blow molded plastics cannot withstand strong flames (like PET). Too high drying temperature, even if the part is properly attached, will damage most materials that have a low melting point.
  • visibility of defects – many paint coatings will not cover injection defects, e.g. flow lines, injection point, streaks, weld lines, etc. The selection of an additional layer of filler primer or an appropriate target coating that hides defects (such as structural or soft-touch coatings) may allow to cover most defects.
  • lack of printability – customers often order printing on a ready-made varnish coating. Painting the material should therefore take into account the selection of varnishes that will constitute a good base for e.g. pad printing, screen printing or hot-stamping.
  • too poor coverage – it is recommended that the color of the material be as close as possible to the color of the target paint coating. If this is not possible, we choose paints with the highest pigment saturation or use two-layer varnishing – e.g. wet on wet varnishing.
  • stains, streaks, orange peel – the viscosity of the varnish is key here. Too viscous (i.e. a slow-flowing varnish) gives an orange peel effect. Too low viscosity causes the varnish to flow too quickly, which is a common cause of streaks.

Painting plastics is a complicated process for novices. Only many years of experience in wet painting services and contact with hundreds of projects allow for professional and repeatable painting of materials. We invite you to cooperate.

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