Matte surfaces
Continuing with the subject of surface haze, we have the figure showing the impact of surface roughness to the affect of haze where the line separating no effect and an affect is shown as the Rayleigh Model for a wavelength of 550 nm, which is red light. Here the wavelength (lamda) is divided by 8sin(angle) which is where the approximate 1/6 of the wavelength of light rule of thumb comes from. Now if we want to make a low surface haze, we want a smooth surface, but if we want a hazy surface (matte surface) this allows us to estimate the size of the bumps we need to put in the film surface to make it hazy.
In general, matte films are produced by coextruding a thin layer onto a substrate where the outer skin is filled with mineral particles or by using an incompatible blend of polymers. In this case, the viscosity ratio of the various polymers can be used to control the particle diameter. Generally, for oriented PP films (OPP), the surface layer is a blend of PP, HDPE and perhaps copolymer PP. There are many patents for the matte-film blends, and it is hard to decipher what the real blends are, but generally they are three polymers as described here.
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