Physical properties of paint and coatings play an important role in the quality control. Depending on the application a coating is supposed to be extremely hard and rigid such as for example the coating on the hull of an ice-breaker. Automotive coatings however require a certain flexibility since the thin sheet metal of a car body is not fully r...
Physical properties of paint and coatings play an important role in the quality control. Depending on the application a coating is supposed to be extremely hard and rigid such as for example the coating on the hull of an ice-breaker. Automotive coatings however require a certain flexibility since the thin sheet metal of a car body is not fully rigid and a slamming hood should not cause the paint to break. Coil coated steel that is to be formed into products such as white goods or cladding should have excellent forming properties.
Several empirical tests
There are a number of different empirical tests that are used to deform test panels and so assess the deformation resistance or flexibility. Coatings that fail such a test will crack and/or detach from the substrate. Also there is quite some overlap between different test systems and their results. Many tests provide information about similar parameters such as elasticity / forming resistance, adhesion, hardness, brittleness, stress resistance etc..
Although some tests overlap there is no cross-reference for their results.
More information can be found in the section hardness/scratch resistance
Commonly used tests
Common tests used in the paint and coatings industry are:
Hardness / Scratch Resistance
The property of a substance that is resistant to repeated rubbing or scratching. In general, it meant the resistance of a (coating) layer or surface against mechanical friction. Abrasion of products is a concept that can't be handled in general. One must explicitly specify the conditions under which the product must be durable.
Any change in wear conditions, the assessment of the wear thoroughly change. In general we distinguish wear as single or repetitive. In the former case, a small contamination in the long run leads to serious damage. By repeating is meant the resistance of a surface under prolonged load. The lowering of the coefficient of friction can give a significant improvement. For the determination of the abrasion resistance it should be practical to approach conditions as much as possible.
Forms of wear or scratch resistance are e.g. brush abrasion testing, rotating abrasion testing, rub testing, sand fall testing and or shear tests.
The determination of the reactive resistance, the hardness of a surface of which a coating or alternative protective layer is provided. As with abrasion and scratch resistance there should be an explicit reference given to the hardness meant. Under the hardness of the coatings is in general understood the impression value at which a deformation of the coating occurs. This is determined by pressing sharp or blunt stylus, depending on the material or coating, into the surface.
Another method to measure hardness is the determination of rolling resistance of a coated surface. The equipment required is using spheres that find resistance during the rolling movement on the test surface i.e. Pendulum hardness. The degree of hardness determines on the number of movements by a pendulum roller experiencing resistance during this process.
Other types of hardness tests are, Barcol Impression, Shore A-D, Sclerometer and Wolf-Wilburn pencil scratch resistance determination and Persoz or Konig pendulum hardness testers.
Commonly used tests used in the paint and coatings industry are: