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Blog
Keeping large particles in the film surface
August 15, 2008
In the posting on large particles in thin films, it was explained how a particle thicker than the layer can be extruded. Of course, this begs the question of why they don’t fall out of the film surface!
Well, sometimes they do. But particles which come out of the film surface can still function as antiblock particles as they roll around the film surface, but they can leave scratches in some cases. Other times the particles are coated with an additive to aid in wetting by the polymer so that they are adhered to the film, like sand in epoxy for stair paint. Key examples of this is range of behavior: Sipernat and Syloid silica antiblock particles. In copolymer PP, Sipernat is uncoated and does not adhere well to the PP skin, it therefore falls out onto the surface (and rollers, etc.) and is a very effective antiblock. But it easily scratches the film surface if the roll is poorly wound. In contrast, Syloid is coated with citric acid and will be covered by the polymer of the film surface. This makes it a little less effective as an antiblock particle but prevents scratching of the film surface when rubbed together.
In the case of spherical particles, if the particle is less than ½ exposed, then it is held in place by the polymer surrounding it above the mid height of the particle, it is mechanically held in place.
Posted by Eldridge M. Mount on August 15, 2008 | Comments (0)