SCRATCH RESISTANT CLEAR COATS - DEVELOPMENT OF NEW TESTING METHODS FOR IMPROVED COATINGS

More and more car manufacturers are now demanding clear coats with imp roved scratch resistance from their paint suppliers. Some motor compan ies have developed their own tests, some have chosen a test developed by a paint supplier and others are still looking for their optimum tes t. The opinion prevails that there should be one test which covers all aspects of realistic damage. However, microscopic photographs and ref low experiments show that two kinds of scratches occur in reality, abr asive as well as non-abrasive, reflowable ones. Different standard cle ar coat systems have different sensitivities to both scratch types. In the scratch tests the rating of the clear coats is divergent, because the ratio of both sorts of scratches differs. We have developed a set of two tests, where each test mainly generates one scratch type. Thes e tests, together with physico-chemical measurements (glass transition onset temperature T(g), laser optical profile scanning, indentation d epths) lead to a deeper insight into scratch phenomena. One way to dev elop a clear coat which is resistant against all kinds of scratching d amage is described.