Description
This unique drawdown blade applies a series of stripes with thicknesses in equal percentage steps, to permit single-drawdown exploration of the widest practical application range. The individual stripes are identified by “Index” numbers (20 – 48), engraved on the instrument and also printed on the Form 23B Logicator Chart designed for use with this applicator. The Index Numbers are in equal numerical steps corresponding to increments of approximately 20% in notch clearance, film thickness and spreading rate, as shown in the following table:
INDEX NUMBER
20 24 28 32 36 40 44 48
WET FILM THICKNESS (W.F.T.)*
mils 5.7 4.7 3.9 3.2 2.6 2.2 1.8 1.5
µm 145 120 98 81 67 55 45 37
NOTCH CLEARANCE
mils 10.40 8.56 7.04 5.79 4.76 3.92 3.23 2.65
µm 264 217 179 147 121 100 82 67
SPREADING RATE*
ft²/gal 208 341 414 504 612 744 904 1100
m²/L 6.9 8.4 10.2 12.4 15 18 22 27
* Based on W.F.T. = 55% of Notch Clearance
Test Procedure for Exploration of Dry Film Hiding Power: After the applied coating has dried, the operator locates the critical stripe, visually or photometrically, and encircles the parameter of interest. It is generally accepted that the hiding power endpoint is not total visual extinction but a degree of contrast just short of complete hiding, corresponding to a photometric contrast ratio of 0.98.
Test Procedure for Comparison of Wet-to-Dry Hiding Power Change: The TG19 conforms with ASTM Method D 5007 Wet-To-Dry Hiding Change. In this standard, the hiding power of the wet film and then of the dry film are observed visually and the percentage increase or decrease is reported. The complete method is available through the ASTM website.
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