Ulrich Schulz

The influence of weathering on scratches and on scratch and mar resistance of automotive coatings

Automotive coatings are expected to retain a good scratch resistance over years of service. On the other hand, scratches once arisen should disappear by reflow or should not become more visible during further use of the car. These expectations are a challenge to the paint manufacturer and are not easy to fulfil as our work will show. Seven car coatings were examined, each with different PU clearcoats. The coatings were treated under artificial weathering conditions before and after the scratch test. Scratching was carried out using laboratory car wash and Nano Scratch techniques. In comparison to other essential coating properties measured, the scratch and mar resistance was mainly affected by pre-weathering. Alterations in reflow behaviour, shape and size of single scratches were observed during post-weathering which included partly acid precipitation.

Stabilizers in automotive coatings under acid attack

To examine the action of acid atmospheric precipitation on the light stabilisers in automotive coatings two common clearcoat types (TSA and 2K-PU) blended with commercially available HALS and UVA were subjected to artificial weathering (Acid Dew and Fog test and Acid-free weathering test) and natural weathering outdoors in Jacksonville, FL. Tracing gloss and haze during weathering the test results showed that the influence of acid stress on the long-term performance of the clearcoats depended on the kind of the stabilisation system.

Predicting water spot and acid etch resistance of clearcoats by artificial weathering: Acid dew and fog test

The formation of water spots and acid etches at the surfaces of modern automotive basecoat/clearcoat systems occurs sporadically. This is caused by acid depositions and acid chemical attack during outdoor exposures. Currently used outdoor exposure tests in locations having a high incidence of acid rain, dew or fog, show often contradicting data of coating weatherability. This is because they depend on a large number of randomly occuring conditions like frequency, combination and acidity of the actual atmospheric precipitations. Current artificial weathering standardized test methods do not incorporate conditions such as controlled, introduced variables like acid depositions. The objective of our investigations was the development of an artificial weathering test for automotive finishes which includes the action of acid depositions, that will provide reproducibility and repeatability of test results. The conditions that result in environmental etch are examined and an improved artificial weathering test proposed.