White pigments must have a consistent size of about 300 nm to minimize the difference in scatter of all wavelengths of light to maintain the highest scattering power. It’s obvious that the blue wavelength reaches the maximum relative scattering power when the particle size is around 150 nm, while the green and red are about 200 nm, and the maximum relative scattering power of blue wavelength is much larger than green and red. 1 Comparison of blue, green and red light for particle size vs relative scattering power 3įigure 1 shows the particle size vs relative scattering power of blue, green and red light by TiO 2 of different particle sizes. In that case, pigments that average 200-300 nm in diameter give the highest light scattering, since human eye is most sensitive to yellow-green light, which is around 550 nm 3.įig. If the pigment particle size is a little smaller than one-half the wavelength of the light, it will give the most light scattering. It is not always true that the larger pigment particle size gives less light scattering. Light scattering is dependent on the particle size and its refractive index difference from the continuous matrix at a specific wavelength. The Kubelka-Munk theory describes the propagation of light going through inhomogeneous materials, like paints 2. Diffuse reflectance was developed to study the common characteristic of internal inhomogeneities materials. Light going through homogeneous material is quite different from going through inhomogeneous medium.
It’s obvious that the thicker paint film, the better hiding ability, since there will be more pigment scattering or absorbing the light. This relationship also holds for reflectance which is what is observed in paint. It relates the attenuation of light to the material passing through the medium, also, the absorbance of a transparent sample is proportional to the thickness and the concentration. There are some factors that will affect the hiding, such as the thickness of the paint film as well as the light scattering and light absorption of all the pigments.īeer-Lambert law is the relationship used for transmittance calculations for transparent samples. The “hide” is film thickness dependent and any comparison must be at a set thickness 1. Take the ratio L b/L w times 100 is generally termed the hide. One easy way to measure the hide is to make a drawn down on a black/white card, and then measure the whiteness for the black and white areas of the card. It indicates the capacity of paint to hide the surface of an object. Hide is a very important optical property of paint. Peng Geng, Missouri S&T Coating Institute The highly practical approach of this course will greatly aid the personnel involved in the painting operation to reduce and systematically approach issues.
Several of the surface defects are discussed – from basic principles and real world automotive and aircraft examples. The course covers the defects caused by the coatings process, as well as human issues, including personal care product causes. This course addresses many of the issues in prevention and minimization of defects. We are offering "Surface Defects: Elimination from Human and Process Contaminants" online short course. The importance of surface preparation and other manufacturing criteria will show the system complexity and each step's importance. Color measurement, surface profile, and other evaluation criteria will be related to composition. The pigments, resin, solvents and additives will be discussed including their influence on the coatings performance. This self-paced seminar will cover the painting system from the composition of paints to the evaluation of the dry film. This course is targeted for automotive and aviation type OEM companies. We are offering "Introduction to the Coating Systems" online short course.
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