Coatings consist of resins, pigments, additives and solvents. The purpose of the solvent is as a carrier for the coating to achieve an even film on the surface, and as a thinner to achieve right application viscosity. The solvent then evaporates leaving the solids on the surface. In a waterborne coating the water is the solvent, and evaporates leaving the solids.
VOCs may be detrimental to the health of the applicator, those in the vicinity of the VOCs, and the environment, for instance in adding to photochemical smog.
Solvent based coatings typically have much larger amounts of VOCs but waterborne coatings still have some VOCs for film forming or application purposes. These are normally high boiling point organic solvents.
The VOC debate must be kept in balance as some VOCs will help achieve a much longer lasting coating, thereby being more environmentally sustainable. However, where it is possible to use a waterborne coating that is as durable as a solvent based coating, this is a great advantage.
Voluntary VOC limits for a range of coating products have been established by the Australian Paint Approval Scheme (APAS). APAS Document D181 details the limits on VOCs which will apply for a range of APAS paint specifications. There are, however, no legislatively based or mandated standards that prescribe maximum VOC content of coatings in Australia.
The VOC content of a paint or coating is determined by one or more of the following method…
a. Using raw material supplier’s data that corresponds with the above definition of VOC, by calculation for each of the raw materials and individual ingredients in any intermediate raw materials. If the information is not all available the Method outlined below must be used.
b. Determine experimentally in accordance with ASTM D3960 By determining the weight percent non-volatile content (and hence the volatile content) by ASTM D2369 (60 minutes at 110 ± 5°C) and converting to g/L (as per ASTM D3960). This method is not suitable for ingredients that decompose at elevated temperature.
Note: the VOC shall be expresses to include any thinning solvent recommended as mandatory on the label or data sheet for the method of application proposed.
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