Analysis of Paint Craters
More than just aesthetics
Coatings in the form of lacquers or coatings are applied as powder coatings and as water- or solvent-based liquid coatings. The substrates are not only metallic surfaces, but can also be wood or plastics. In addition to improving the aesthetic of the object, paints and coatings also have extensive protective functions. For example, the multi-layer structure of an automotive coating made of cathodic dip coating (CDC), filler, basecoat and clear coat protects the body from corrosion and withstands the stresses of weather, UV radiation, stone chips, winter road salt or car washes for years. In the case of craters in the paint, or process disturbances (e.g. particle inclusions, formation of gas bubbles (cooker), or needle faults) or painting failures when applying the paints, the causes must be quickly identified and eliminated to prevent further coating failure from occurring.
Experienced employees in the painting process are often able to draw conclusions about the cause of a process disturbance or a paint crater based on the defect pattern. Especially in the area of series production, such as automotive engineering or plastics processing, a more detailed determination of the causes of a paint crater in a laboratory is necessary to ensure possible recourse claims. Such analyses on paint craters can be carried out in the Tascon laboratories. Depending on the particular fault pattern of the paint crater or process disorder, analytical methods such as light microscopy, infrared spectroscopy, SEM-EDX or ToF-SIMS analysis are used. If metal particles are found inside a paint crater during a light microscopic examination, an examination of the elemental composition of the particles using SEM-EDX is often very helpful to identify the origin of the particle. If, on the other hand, there is a fibrous disorder in the paint crater, infrared spectroscopy is a preferred method of analysis. If no obvious faults are observed in a paint crater, local organic contamination is suspected as the cause of the paint crater formation. The substances that can lead to such wetting flaws are diverse. In addition to media from the production process, polysiloxanes (silicone oils) are particularly common contaminations that lead to the formation of paint craters. In these cases, time-of-flight secondary ion mass spectrometry (ToF-SIMS) is routinely used to find the cause, as the following example shows:
Tracking paint defects
To avoid the formation of paint craters as much as possible, particular care is taken to ensure cleanliness and absence of particles when high-quality coatings are applied. If paint craters or process disorders nevertheless occur, ToF-SIMS is one of the established methods to investigate the cause. With a ToF-SIMS analysis it is possible to identify unknown quantities of inorganic or organic substances on surfaces with a diameter of less than 100 µm within a paint crater. Due to this screening property and the high sensitivity, the ToF-SIMS method in our laboratory can often determine the cause of a crater in the paint even when other analytical techniques have reached their limits. In the example shown, the color layer shows many clear craters of different sizes close together. Fluorine-containing hydrocarbons are detected with high intensity in the paint craters (see figure). By comparative investigations, the impurities found in the paint craters could be assigned to a high-performance lubricant based on a perfluorinated polyether (PFPE). This was used in the production plant to lubricate the conveyor systems and had dripped onto the surface before painting. In this case, the application of suitable shields prevented the further formation of paint craters.
Find existing paint craters with Tascon and prevent future paint craters
If you work in a manufacturing industry, where parts have to be coated with high precision, it is in your interest to find craters and their cause as quickly as possible. With a proper analysis of the cause paint craters can be prevented in the future. We at Tascon are the competent partner at your side and want to help you prevent paint craters in your production. If you want to use our service for the targeted removal of paint craters, please contact us. We look forward to your inquiry.