In addition, vehicles, both solventborne or waterborne, are film-formers. If foots get into a paint, they can cause quality problems. These particles can make their way into a drum or tank car, often appearing as sediment on the bottom of the container or transportation vessel. These are small pieces of leftover hull or meal that occur during the grinding and oil-extraction process, even though oils are filtered to remove foots. linseed oil or soya oil) can contain "foots". To assume that the liquids used in coatings are pure and free from particulates is not a good assumption. Where Quality Begins While the focus of this article is on filtering the end-product-coating, one cannot overlook the importance of good filtration techniques that, in many cases, should be applied to incoming liquid raw materials such as resins, emulsions, liquid additives and even water. It is safe to say that proper filtration is key in producing a quality liquid coating, whether that coating be for homeowner architectural use or industrial or commercial applications including military specifications. Substrates may vary from a clean metal finish (automobile), to dirty steel (a bridge), to wood (home siding) and plastic. The type, shape, size and flexibility of the pigment varies widely, as do the percent solids, viscosity and rheological properties of the vehicle. EPA consists of the pigment particulates plus the non-volatile portion of the vehicle (the vehicle is the liquid component of a coating).įiltration requires a close look at the pigments used in a formulation. It is important to understand that "solids", as calculated by the U.S. In a 100%-solids coating, nothing in the can evaporates - everything ends up on the surface to be painted. The percent solids of a coating may vary from zero percent (when filtering solvents or water) to 100% solids, such as pure linseed oil. Paint filtration, or to be more accurate, "coatings" filtration, involves paints, oils, varnishes and lacquers that may be very thin and low-viscosity in nature, to very heavy, thixotropic liquids. Paint filtration can be one of the simplest or one of the most complicated liquid-particle separations encountered in the process industries.
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