Painting and coating

Although parts can be made with molded-in color, painting and coating are nevertheless done for a number of reasons such as:

- Aesthetics: to hide irregularities in the substrate; free choice of color-gloss-structure; color matching with adjacent parts
- Improved chemical, abrasion or UV-resistance
- Electrical conductivity
- Electromagnetic shielding
- Styling versatility
- Manufacturing convenience

The use of paint can on the other hand have an important drawback. It is often observed that a paint and/or primer on a ductile plastic results in a brittle fracture during impact loading, whereas the unpainted part tested under the same conditions deforms in a ductile manner. The paint layer can result in a 40-fold reduction of the fracture energy, especially when too rigid a paint is used. On loading of the part, the brittle paint fractures first and this crack may propagate through the substrate. An extreme example of a big difference in modulus between substrate , paint and primer is shown below.

Additionally solvents in the paint might lead to environmental stress cracking. High internal stresses in the part near gates, weld lines or wall thickness transitions, but also stresses due to external load, in combination with aggressive solvents may cause cracks in the surface of the substrate.

Finishing and decorations home
Painting
•Pretreatment
•Process
• Testing
•Paint types
• Recommendations

Arnitel® is a registered trademark of Royal DSM.