ASTM D6441-05

Contrast ratio at a specified film thickness is a useful hiding power parameter for production control and purchasing specifications.

The greater the hiding power, the less coating is required per unit area to obtain adequate hiding. Knowledge of hiding power is therefore important in regard to coating costs and for comparing coating value.

1.1 These test methods determine and report the hiding power of a powder coating with respect to two parameters:
1.1.1 Test Method A-Contrast Ratio at a given film thickness
1.1.2 Test Method B-Film thickness at 0.98 (98%) contrast ratio.

Note 1-The measured parameters conform to powder coating industry practice by measuring hiding power in relation to film thickness, rather than the more conventional "Spreading Rate" function employed in Test Methods D 344 and D 2805 and other hiding power test methods.
Note 2-Hiding power is photometrically defined as the spreading rate at 0.98 contrast ratio. See definitions of spreading rate and hiding power in Terminology D 16, D 2805, and the Paint and Coatings Testing Manual.
Note 3-The contrast ratio of 0.98 is conventionally accepted in the coatings industry as representing "complete" hiding for reflectometric hiding power measurements. But visually, as well as photometrically, it is slightly less than complete.

1.2 These test methods cover the determination of the hiding power of powder coatings applied by electrostatic spraying.

1.3 These test methods determine hiding power by means of reflectometric and thickness gage measurements. They are limited to coatings having a minimum CIE-Y reflectance of 15 %.

1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.