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Significance and Use
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
1.1.2 Test Method B
Note 1—The measured parameters follow powder coating industry practice by measuring hiding power in relation to film thickness, rather than the “Spreading Rate” function employed in Test Methods D344 and D2805 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 D16, D2805, and the Paint and Coatings Testing Manual.
Note 3—The contrast ratio 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 to determine in advance the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D16 Terminology for Paint, Related Coatings, Materials, and Applications
D344 Test Method for Relative Hiding Power of Paints by the Visual Evaluation of Brushouts
D2805 Test Method for Hiding Power of Paints by Reflectometry
D3451 Guide for Testing Coating Powders and Powder Coatings
E284 Terminology of Appearance
E1331 Test Method for Reflectance Factor and Color by Spectrophotometry Using Hemispherical Geometry
E1347 Test Method for Color and Color-Difference Measurement by Tristimulus Colorimetry
E1349 Test Method for Reflectance Factor and Color by Spectrophotometry Using Bidirectional (45:0 or 0:45) Geometry
Other Standard1-GP-71 Method 14.7, Hiding Power, Contrast Ratio Method, October 1982 Canadian General Standards Board, (CGSB), 222 Queen St., Ottawa, Ont., Canada K1A 1G6.
ICS Number Code 87.040 (Paints and varnishes)
UNSPSC Code 46181533(Protective coats)