Plastics, emulsion paints, paper, coatings, printing ink – many of the colored items we use every day contain titanium dioxide. Due to its photoelectronic properties and its high refractive index, the inorganic white pigment has high UV resistance and excellent opacity. Dr. Thomas Koch is Head of the analysis lab of the Research Services department of Kronos, which has been producing titanium dioxide ever since 1916. We interviewed him to find out why Kronos works with the confocal Leica DCM8 3D surface metrology system.
We use the Leica DCM8 to analyze titanium dioxide (TiO2) applications. For instance, we do surface roughness analysis to check coatings and plastics for corrosion, and we also determine how well the top layers of the titanium dioxide pigments are embedded in the coating matrix. For example, every coating is prone to sedimentation as it dries, that is to say, depending on the coating system the pigment particles sink more or less to a certain degree. That’s why special organics are added that make the coating as tough as to show rubber like behavior, thereby reducing the amount of sinking. One of the important measurements for us is the height between the top coating layer and the beginning of the first pigment layer. The Leica DCM8 is ideal for this job. If the coating is OK, we can only see the first pigment layer because it is impervious to light. But if we discover steps that go further into the coating layer, we know there are damages and flaws. On the basis of the height profiles which are easy to produce with the Leica DCM8 software, we can measure the roughness of surface and pigment layer and the distance from the pigment layer to the surface. The analysis delivers two reflections – one of the pigment layer and one of the surface of the coating.
Yes, we use the Leica DCM8 for plastics as well. Plastics contain little titanium dioxide. The pigment provides opacity and serves as light protection – e.g. UV light destroys the organic matter. The titanium dioxide reflects the sunlight, absorbs the UV portion and prevents the light from penetrating deeper into the matrix. With the Leica DCM8 we look at the plastic profile and take roughness measurements. Just as for coatings, we can thus measure the position of the titanium dioxide and the weathering of the surface.
We’ve been using the Leica DCM8 for a year and a half. Now we have worked out various standard routines for test methods, these processes run semi-automatically thanks to the software. The instrument increases our sample throughput, because conventional analysis is experimental and entails more effort and manpower. So the Leica DCM8 is an excellent tool both for characterizing the state of the new surface and the results of the weathering of coatings and plastic surfaces, and for analyzing damage.
The Leica DCM8 enables us to obtain precise measurements of the quality of the first TiO2 layer and the surface of the sample and the space between them – and all without lengthy sample preparation and multiple measurements or having to make polished and unpolished cross-sectional samples. However, the main advantage is that the measurement is so sensitive to the TiO2. Otherwise we can only achieve such high resolution with electron microscopy, which is expensive and time-consuming. Apart from that, the Leica DCM8 method is contactless and non-destructive, saves us sample preparation time and sometimes even allows us to view the customer’s sample in its original state.
Using a confocal surface metrology system for the analysis of plastics and coatings is new. As far as I know, we are the first to work on such applications with the Leica DCM8. I imagine that this type of analysis could also be used by plastics manufacturers and paint producers in future.
I would like to take this opportunity to thank Dr. Ralf Theissmann and Dr. Horst Purwin, who have developed these new methods so successfully at our company.