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Revision Date: January 13, 2010
Updated On: January 19, 2010
A colorant sometimes fails to disperse completely in a base paint due to poor compatibility, which can be the fault of the colorant, the paint, or both. This will result in poor color development, which is readily manifested by the common procedure of applying the paint with a doctor blade and subjecting the drawdown to high shear stress by finger-rubbing a small area of the partially dry film. This tends to disperse undeveloped colorant, if any, and produces a color variation between the unsheared and sheared areas of the paint film. The variation can be measured colorimetrically to give a numerical color difference value that is a measure of the color development of the original paint, the smaller the difference the better the color development and vice versa. Color difference values obtained by finger-rubbing were found to vary widely for the same as well as among different operators. This test method establishes a controlled shear-stress procedure analogous to the finger rub-up test, but with far better reproducibility.
Poor color development can be a problem in the production of paints, and in their performance in the field. In production it causes a loss of colorant monetary value, and unpredictable tinting results. In field performance it results in color variations in the applied paint film due to the varying shear forces to which the paint is subjected at different stages or by different modes of application.
Although poor color development is primarily and most often related to the colorant portion of a tinted paint, the white pigment in the base paint can also be poorly developed due to flocculation or other causes. In the latter case, shear dispersion can make the paint film lighter and less colorful, rather than the reverse. Then too, the colorant and the white might both be poorly developed, and the color change due to shear stress would then be the combined effect of both.
In any case, color development is an important paint property, for the measurement of which this test method is intended to provide a generally accepted and reproducible test method.
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