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Surface haze
December 6, 2007
The components of a substrate's haze, surface and internal haze, can be separated and measured to determine the source of the haze. Because surface haze is principally due to roughening of the surface, it can be measured by eliminating or replacing the surface with another surface. This can be done by coating the substrate surface with a liquid to cover the surface irregularities. The oil will fill in the surface irregularities and create a smooth surface which will not scatter the light, making the surface haze disappear. The liquid should match the refractive index of the film surface to remove any remaining light scattering between the surface and the oil. Most polyolefin polymers have a refractive index of about 1.5 and can be oiled with mineral oil. In a pinch, the oil on your face can be used to get a fast determination of surface haze. Spread the oil from beside your nose on the film surface and see if the film becomes clearer, and if so, then there is some surface haze.
Therefore, to determine the relative amount of surface and internal haze, you first measure the total film haze, then you place an oil layer on the film surface, either one surface at a time or both surfaces, and then measure the haze again. The difference in haze between the two measurements is the surface haze and the difference between the surface and total haze is the internal haze.
Sources of surface haze are due to processing conditions or additives to make the film surface matte, and we will explore the causes and troubleshooting of surface haze in the days ahead.
Posted by Eldridge M. Mount on December 6, 2007 | Comments (0)