Single-scratch tests

With this background several measuring methods are currently being discussed in the automotive and paint industry with the objective to obtain a clear characterization of the scratch resistance of clearcoats. Especially procedures that create a single scratch have recently been developed (micro or nano scratch method) [1-8], These methods are different from more practically oriented procedures that are based on relatively simple methods to fly to test or even come close to reality (e.g. car wash brush method). 

Tests with Progressive Load In this context a method was developed in the DuPont Marshall Lab. (Philadelphia) that generates and evaluates a single scratch on a surface (nanoscratch method). This method is used for tests along with development work for clearcoats and it is constantly being improved. 

ASTM C1624-05. (2010a) Standard Test Method for Adhesion Strength and Mechanical Failure Modes of Ceramic Coatings by Quantitative Single Point Scratch Testing, American Society for Testing Materials. 

The Japanese spent at least seven years trying to perfect an anthrax bomb. Over 2,000 Uji bombs were filled with anthrax and tested experimentally. It was a substantial programme the Uji bomb was one of nine types of aircraft bomb which had been tested at Pingfan by 1940. The deadliest munition developed was the Ha bomb, designed to shatter into thousands of pieces of shrapnel, spreading the anthrax spores to murderously good effect. A single scratch wound from a piece of contaminated shrapnel was estimated to cause illness and death in 90 per cent of its victims. The standard Japanese heavy bomber could carry twelve Ha bombs. 

Figure 9.6 The scratch resistances of the reference and hybrid system have been evaluated. The test has been performed in accordance to ISO 1518 standard (Paints and Varnishes - Scratch test) [62]. This standard specifies a test method for determining under defined conditions the resistance of a single coating or a multicoat system of paint, varnish or related product to penetration by scratching with a hemispherically tipped needle. Scratch resistance has been determined as the minimum load in grams required to cut through the film until the substrate. (Courtesy, Celine de Lame, CoRl).

Table 15.13. This specification follows good industrial practice, with additional safeguards in rinsing to remove residues to treatment solutions. Nonaccelerated treatments must be followed by a single rinse which may contain chromate accelerated treatments must be followed by three rinses—cold water, hot water and a final chromate rinse. Table 15.14 shows the salt-spray test requirements for phosphate coatings with various finishes without formation of rust the paints and lacquer have the additional requirement that no rust shall be visible beyond 0-2 in (5 mm) from the deliberate scratches and no blistering, lifting or flaking beyond 0-05 in (1-27 mm) from the original boundaries of the scratches.

---