Woodworker's Journal 2011-35-Winter, страница 69
ers, contains about 75% solvent, almost all of which is both a VOC and a HAR Several strategies have emerged to lower that number, sometimes to zero. You can now buy zero VOC lacquer, which oddly enough still contains about 75% solvent. The difference is that it is formulated with exempt VOCs, meaning those that are not ozone generators. Typically, the solvent package is a mixture of parachlorobenzotri-fluoride (PCBTF) and acetone, the latter of which appears less harmful to us than some of the solvents it replaces. Thus, zero VOC lacquer may actually be safer to use, not just less ozone generating. A totally different approach, and one that works particularly well with two-part cross-linking coatings (a specific chemical formulation), is to raise the solids and lower the solvent level. These so-called ultra-high solids coatings can range from 85% solids to almost 100% solids, the latter containing little or no solvent whatsoever. Typically, these are either chemically cured polyesters or UV cured acrylics and polyesters. Most are designed to be sprayed and are sold only to the industry, not to hobby woodworkers. Even at that, their safety is a bit of a mixed bag. While they contain almost no VOCs, they carry dangers to the workers indoors. That's because they often emit free monomers that are hazardous. Monomers are resins, not solvents, but the molecule is so small that it can become airborne, and thus can be breathed in. As a result, those who use such coatings generally suit up in hooded coveralls with clean air pumped in to the hood. Water-based Coatings Contrary to popular belief, water-based coatings are not water-soluble, nor do they con tain water-soluble resins. That's a good thing. If they did, you would be able to remove any evaporative water-based finish with water after it dried. Imagine wiping a counter with a wet sponge and having the finish wipe off. If not water-soluble, then what are they? Water-based coatings are those in which some of the solvents of a traditional coating have been replaced with water. Almost any type of coating can be made water-based; there are water-based lacquers, shellacs, polyurethanes, one and two-part cross-linking coatings, and even water-based UV cured coatings. Water-based does not mean that the coating contains no solvents. It merely means some of the solvent has been replaced by water. The majority of clear water-based finishes contain glycol ethers, all of which are considered VOCs. While some are quite harmless, others are hazardous to humans, including a very common one, Just because a finish is called "water-based" does not mean it is solvent free. Are water-based products greener than others? EB (sold under the trade name Butyl Cellosolve), which is believed to be a teratogen (a substance that can cause birth defects). Water-based polyurethanes typically contain n-methyl-2-pyrollidone (NMP) or gamma butyrolactone (BLO) as well as glycol ethers, both of which are also considered VOCs and HAPs. Still, water-based coatings contain far lower amounts of VOCs than their solvent-based counterparts. For example, a typical nitrocellulose lacquer will contain upwards of 75% solvent, most of which is VOCs, while its water-based counterpart will contain only 10% or less. There are even zero VOC water-based coatings. continues on page 70... Another chapter in the green finishing story is the new focus on nontoxic paints. There is an ever-expanding list of products available for both interior and exterior use. WINTER 2011 69 |
