Standard Test Method for Measuring Mechanistic Aspects of Scratch/Mar Behavior of Paint Coatings by Nanoscratching

Importancia y uso:

4.1 This test addresses two limitations in existing mar tests such as Test Methods D1044, D3363, D5178, D6037, and D6279, namely:

4.1.1 Measured damage is caused by hundreds of contacts with differing contact geometries making it difficult or impossible for mechanical quantities (force, displacement) at the contact points to be reliably determined.

4.1.2 The damage is evaluated using subjective visual assessments, which provide only a qualitative sense of wear with little information about mar mechanisms.

4.2 This test provides a quantitative assessment of a paint coating’s mechanistic aspects of scratch/mar behavior in various conditions. The ability to control testing variables such as loading rate, speed, and temperature allow the study of the scratch/mar behavior in a variety of environments.

4.3 This test method is particularly suitable for measurement of paint coatings on laboratory test panels.

4.4 The accuracy and precision of scratch/mar performance may be significantly influenced by coating surface non-uniformity and irregularities.

4.5 A correlation has been observed between good mar resistance in field studies and a combination of high plastic resistance and high fracture resistance. When coatings have had either high plastic resistance and low fracture resistance, or low plastic resistance and high fracture resistance, there have been contradictory results in field studies.

4.6 Mar resistance characterizes the ability of the coating to resist light damage. The difference between mar and scratch resistance is that mar is related to only the relatively fine surface scratches which spoil the appearance of the coating. The mechanistic aspects of mar resistance depend on a complex interplay between visco-elastic and thermal recovery, yield or plastic flow, and micro-fracture. Polymers are challenging because they exhibit a range of mechanical properties from near liquid through rubber materials to brittle solids. The mechanical properties are rate and temperature dependent and visco-elastic recovery can cause scratches to change with time. One such test for evaluating polymeric coatings and plastics is Test Method D7027.

4.7 Since this method measures mechanical qualities, such as forces and displacements (deformations) during the damage making process, rate dependence, temperature dependence, and visco-elastic-plastic recovery can be further investigated and visual impacts of damage can be related to deformation mechanisms.

Subcomité:

D01.23

Referida por:

D6577-24A

Volúmen:

06.01

Número ICS:

87.040 (Paints and varnishes)

Palabras clave:

coatings; gloss; mar or organic coating mar resistance; scratch resistance;