More Efficient Coating and Painting on Plastic Parts: A Study on Quality, Cost and Durability

Nowadays, the proportion of plastic parts in coating and painting is steadily increasing. The variety of these parts knows virtually no limits. Meanwhile, customer quality expectations and the volumes of individual orders continue to grow. On one hand, there is cost pressure, while on the other hand more environmentally friendly, more efficient, more flexible and resource-conserving painting processes are being demanded. Today, it is not only the automotive sector that is aiming to use increasingly more plastic parts. There are virtually no sectors left that do not use plastic parts made of macromolecules. Coating is in any case necessary in order to change the appearance of a product, make it attractive, give it resistance to physical and chemical effects, or achieve other special functions. But let us not merely say coating – as application areas are shrinking while color variety is expanding, achieving both economical and lasting results has become extremely important.

How Can We Optimize

Paint contamination and other coating defects result in production scrap and costly rework. Companies specializing in coating plastic parts in particular suffer from these problems. One of the reasons is that plastic undergoes continuous processes that generate dust, from injection molding through polishing. Excessive overspray can also be a contributing factor. Furthermore, many plastic parts used today electrostatically charge themselves and attract dust due to their surface structure. To prevent coating defects and optimize quality, all production stages must be examined closely. First and foremost, the products to be coated must be structurally suitable for coating. For example, a product with fewer curves absorbs paint better. Similarly, rounded edges are coated better than sharp edges. Minimizing polishing processes also improves quality because residue from excessive polishing and particles used to remove injection molding gates often make their way as dust into the paint booth. Likewise, keeping the equipment used clean is extremely important. Over time, accumulations collected from plastics can cause coating defects or dirt contamination during painting.

Cleaning and Activation

While solvents, additives and fillers, fibers, are important for plastic part durability and easy processing, when they reach the part surface they negatively affect paint coverage. Another problem is that many plastic parts have low surface energy. There is currently a trend toward water-based paints. Due to non-multi-stage coating techniques, the primer must be far more durable. That is, surfaces must be cleaned well and even undergo pre-treatment. Dry applications are currently very popular for plastic cleaning. Among these are cleaning with carbon dioxide foam, plasma cleaning, and cleaning with vapor pressure. These applications are both low-cost and space-saving, and are highly preferred from an environmental protection standpoint. The only way to counter electrostatic charging of surfaces is through ionization technology. For difficult-to-coat plastic materials such as polypropylene or polyethylene, where paint adhesion is problematic, surfaces are activated before painting. The most preferred methods are gas phase treatment, atmospheric pressure plasma activation, corona treatment, and surface flame treatment.

Faster Painting Processes

Achieving efficiency gains and reducing part costs requires reducing the number of stages in painting processes. Currently, the most sought-after painting technique is single-coat paints. Systems that enable this are available for both solvent-based and water-based paints. However, using these systems requires surfaces to undergo pre-treatment in any case. Another method for simplifying paint processes is preventing potential losses. For example, losses during spraying and losses that occur when changing paint during application and feeding must be eliminated. To achieve this, electrostatic-assisted spray guns or high-performance sprayers capable of achieving 90% application rates can be used. Application systems that minimize detergent use and paint changeover times provide additional savings. The trend toward robot use and automated applications continues unabated. Robot applications result in significant savings in both material and processing time, while losses in stages are greatly reduced. A positive cost benefit of automated painting is that it is much easier to transition from recirculating air systems in the paint booth to rotational air systems. This achieves energy savings of 60-70%. With well-designed logistics, it is possible to use less material. Unused paint can be recovered from the line or the exact amount of paint needed for special coatings can be used. This makes it possible to save paint even when coating small parts. In addition to dryers, overspray waste represents the highest energy loss in the painting process. In conventional paint drying, for example, an optimized ventilation system with tunnels, radiators, and even waste heat recovery systems can reduce expensive electricity bills. Another alternative is infrared drying. This technology can be used even on parts that are sensitive to heat. Infrared rays penetrate the material and dry the paint from the inside out. This allows for fast and clean drying without bubble formation. Since wet cleaning of overspray consumes considerable electricity and water, dry cleaning methods have been developed to achieve savings here. Dry cleaning systems coming with various solutions work with brushes, electrostatics, powder, or special cardboard structures.

Paint Systems for Every Need

Generally, quality and efficient plastic painting requires a specialized paint system that meets facility technology, paint, and other requirements. For solvent-based paints commonly used on plastics, systems designated as "very high solid" or "ultra high solid" make it possible to significantly reduce solvent emissions. The fact that water-based paint systems are being increasingly preferred is undeniable. Especially with the use of new raw materials, water-based paints have begun to replace solvent paints in both quality and durability. Entirely tailored to requirements, there are multi-layer systems with primer, paint and varnish, or single-coat paints with 1K and 2K systems also offering a wide range of colors and effects. These systems can be completely customized according to the processes and requirements to be used. One of the innovations in the coating field is a system made of carbon-fiber-reinforced plastics, especially for coating. This coating system, which performs very successfully according to automotive industry criteria in terms of paint adhesion, UV resistance, scratch and chemical resistance, is based on a highly durable transparent primer. Thanks to this primer, it is possible to apply thick layers in each paint process and thus economically conceal surface damage on parts. A varnish appropriate for the primer and the paint above it provides additional protection. PaintExpo – International Industrial Coating Technology Fair PaintExpo covers the entire process chain in painting technology and presents comprehensive and detailed information about the latest developments. PaintExpo International Industrial Coating Technology Fair addresses all sectors of the industry and attracts participation from all major leading companies in the sector. The fair also addresses post-processing steps such as printing technologies and packaging. Thanks to its comprehensive range of prestigious products and services, it enables direct comparison of various systems and applications at a single location and provides access to all types of detailed information. PaintExpo will take place 17-20 April 2018 at the Karlsruhe Exhibition Center (Germany). Prior to this, the 4th PaintExpo Eurasia Fair will be held in Istanbul 12-14 October 2017 by Artkim Fuarcılık, which specializes in paint and chemical fairs. www.paintexpo.com Doris Schulz / Journalist Author - Schulz. Presse. Text.