Process for making high aspect ratio reflective metal flakes

摘要

A process for making high aspect ratio metal flakes comprises applying a multi-layer sandwich of vapor deposited metal and release coats in alternating layers to a rotating chilled drum or suitable carrier medium contained in a vapor deposition chamber. The alternating metallized layers are applied by vapor deposition and the intervening release layers are preferably solvent-soluble materials applied by suitable coating or vapor deposition sources contained in the vapor deposition chamber. The release coat materials can be a thermoplastic solvent-soluble polymer. The multi-layer sandwich built up in the vacuum chamber is removed from the drum or carrier and treated with a suitable solvent to dissolve the release coating from the metal in a stripping process that leaves the metal flakes essentially release coat free. The solvent and dissolved release material are then removed by centrifuging to produce a cake of concentrated flakes which can be air milled and let down in a preferred vehicle and further sized and homogenized for final use in inks, paints or coatings. In one embodiment the finished flakes comprise single-layer thin metal flakes and in another embodiment the flakes are coated on both sides with protective polymeric coatings that were applied from vacuum deposition sources contained in the vapor deposition chamber. In an alternative embodiment the release coat can be a thermoset material which is lightly cross-linked in the vacuum chamber and then later treated with a de-polymerizing solvent material that breaks the chemical bonds sufficiently to separate the layers.