Air quality impact of paints and surface coatings
Pinpointing the cause of poor air quality can be difficult at times – leading to unnecessarily prolonged exposure to hazardous pollutants for workers, neighbours and the environment. In this expert series, we take a closer look at specific industries and some of the more common contaminants that could affect the air in your workplace or home, as well as treatment strategies to deal with it.
Paints and material coatings are ubiquitous. We use them to protect and decorate almost every man-made structure. Paint keeps the rain out of wood and iron, protecting against rot and rust. Depending on the colour, it can change the mood of any space.
In the 21st century the paint industry has the social and legal responsibility to avoid damaging our environment, including the atmosphere. This article explores the emissions present in the use of paint, from its manufacture to its application, and provides information that can help you protect the environment as well as your house walls.
Synthesising a Rainbow
Manufacturing large amounts of paint involves a delicate balance of ingredients. Paints are made from a variety of solid pigments, which are ground up and suspended in a liquid solution. Once applied to a surface, part of the liquid evaporates. This leaves behind a thin film that provides a colourful and protective coating. The ratio between pigment, volatile solvent, non-volatile binding agent and any other additives must be scrutinised before each batch of paint is manufactured (Resene, 2020).
Pigments, the compounds that provide colour and opacity, are milled into a fine paste as an early step in the manufacturing process. There are many compounds used for pigment, with varying chemical and physical properties. However, just because a compound makes a delightful shade, doesn’t mean that it should be used as a pigment. Paints have an unfortunate history of toxic additives. In the eighteenth and nineteenth centuries, a poor choice of ingredients often poisoned communities. Painting homes with lead-based white pigments or the arsenic-based Scheele’s Green, would cause serious health issues to residents. Since those times, safer compounds have been employed. Now, manufacturers are legally obliged to limit the inclusion of known hazardous substances (Standards Australia, 2017).
Pigment milling techniques will vary depending on the compound selected. Usually, paint factories use a high-speed disk disperser for easy-to-disperse pigments like undercoats or primers. With this technique, the pigment is dispersed against itself and the walls of the rotor. More difficult ingredients are tackled with older technology. Cylindrical mills filled with a grinding media – metal, stone, or sand – help disperse the ingredients that clump together. To stop the breakdown of these compounds forming intrusive dust clouds, factories often wet the pigment, and keep the mills simulating a closed system (McMinn & Marsosudiro, 1992).
While the pigments are being milled, the liquid vehicle for the paint is premixed. This liquid vehicle is made up of resin, which forms a binding agent for the pigment, solvent, which should evaporate completely once the coat of paint is applied, and additives, that enhance the paint’s commercial or practical value. The premix is finally combined with the milled pigment in a process called letdown. This thins the paste into a more manageable consistency. Tinting, blending with additives, and other finishing touches during this process create the evenly distributed final product that we know as paint. This is filtered and canned before being distributed to commercial or industrial outlets (McMinn & Marsosudiro, 1992).
Smelling Paint Dry
The primary air emission concern with the paint industry is the release of volatile organic compounds (VOCs). Some of the compounds are familiar – such as acetone, toluene, and benzene – but there are hundreds more with names only common to experts. For example, isocyanates are a curing agent hazardous to humans and commonly used in varnishes, adhesives and paints (Safe Work Australia, 2015). Many of these compounds are used as paint solvents since their low boiling points help with quick evaporation once the paint is applied. Many of these compounds are known carcinogens (IARC Working Group on the Evaluation of Carcinogenic Risk to Humans, 2012) and some of them can photochemically react in the atmosphere with nitrogen oxides to form tropospheric ozone (CEPE Technical Committee, 2002).
In manufacturing, the addition of solvents to the paint mixture is the most likely culprit for emitting VOCs. Solvents are added to premix, used to wet the pigments for milling, and used to clean some drums and mills. This should be done in a well-ventilated room with airflow scrubbed by an odour control device before being emitted into the atmosphere. Every detection of a recognisable sharp chemical odour is an indication that solvent VOCs have evaporated out of the paint batch. With closed system millers, careful storage of ingredients and cleaning products, and appropriate occupational health and safety procedures, these occurrences can be limited.
VOCs are also a problem whenever a fresh coat of paint is applied to a surface. Depending on the base, a coat of paint takes up to eight hours to dry and days to cure (Kraudelt, 2020). In this time, the chemical change in the binder and the evaporation of the solvent releases VOCs into the surrounding airspace. Painters can limit their exposure to these hazardous chemicals though various means. Only purchasing the amount of paint that they intend to use can limit stockpiling of half-open cans. Painting outdoors or in a well-ventilated area is also necessary to avoid breathing in fumes for extended periods of time.
But the best method of reducing VOCs emitted in paint application is to find products that have low or no VOC content. Regulations on the paint and material coating industry have been developed to manage growing environmental and health concerns. The regulations minimise paint VOC content as well as other harmful ingredients like heavy metals. Manufacturers are also pushing for safer alternatives to solvents – water-based paints are a fine example – as well as considering alternatives to some common pigments that are energy intensive to produce.
VOCs will emit while paint coatings dry, but if the coating is applied using a spray-painting booth – like in many industrial contexts – then it can harm the local environment without needing to wait. Spray painting involves forming a fine mist of liquid aerosol paint droplets under pressure and applying the aerosol spray onto an object or surface. Besides the established impacts of VOCs in solvents, this method can cause local fallout problems, due to overspray or ‘carryover’. This is where droplets can escape and impact downwind communities, coating unwanted surfaces and reacting to create smog.
Breathing in the aerosol resins and solvents can also severely damage respiratory health. If spray-paint workers must wear protective face masks to help them breathe while they apply coatings, then they should limit emissions to surrounding community members who should not have to wear breathing aids to go about their day. Work should be done in a well-designed, well maintained spray booth to maximise the capture and containment of emissions. Yet even with efficient capture in a spray booth at the point of evaporation, emissions are not fully eliminated. Further filtration, adsorption or scrubbing devices, as well as implementing proper dispersion of evaporated solvents, are needed to help eliminate stray droplets of resin, and control odorous or toxic materials (NSW EPA, 2017)
A Coat to Last
We need coatings to protect our infrastructure and colour people’s homes, but we should not sacrifice the longevity of our atmosphere to do so. Thankfully, manufacturers are evolving their processes with new technology to create sustainable factories and perfecting the ingredient mixtures of their product to minimise its environmental impact (Dulux, 2020). Seeking out environmentally sustainable paint and coating products is an excellent way to minimise hazardous chemical exposure and help protect workers and hobbyists. Monitoring and measurement of the paint production process for hazards to air quality should be a regular part of every paint manufacturer’s health and safety procedures.
Being wary of unsafe airborne compounds that emit during manufacture and application is one simple way to help paint a brighter picture for the environment.
References and Further Reading
CEPE Technical Committee. (2002). A Guide to VOC Reduction In Decorative Coatings. Brussels.
Dulux. (2020). Sustainability. Retrieved from Dulux Services & Programs: https://www.dulux.com.au/specifier/services-and-programs/sustainability
IARC Working Group on the Evaluation of Carcinogenic Risk to Humans. (2012). Occupational Exposure as a Painter. Lyon: International Agency for Research on Cancer.
Kraudelt, L. (2020). How Long Does It Take Paint to Dry? Retrieved from Kraudelt Painting: https://kraudeltpainting.com.au/how-long-does-it-take-paint-to-dry/
McMinn, B., & Marsosudiro, P. (1992). Control of VOC Emissions from Ink and Paint Manufacturing Processes. Durham: U.S. Environmental Protection Agency.
National Pollutant Inventory. (1999). Emission Estimation Technique Manual for Surface Coating. Canberra: Australian Government.
National Pollutant Inventory. (2007). Emission estimation technique manual for Paint and ink manufacturing. Canberra: Australian Government.
NSW EPA. (2017, September 29). Air quality guidance note: Spray painting operations. Sydney, NSW, Australia.
Resene. (2020). What is paint and how is it made? Retrieved from Resene.com.au: https://www.resene.com.au/whatispaint.htm
Safe Work Australia. (2015, July). Guide to Handling Isocyanates. Retrieved from Safe Work Australia: https://www.safeworkaustralia.gov.au/system/files/documents/1702/guide-to-handling-isocyanates.pdf
Standards Australia. (2017, September 19). Guide to hazardous paint management, Part 1: Lead and other hazardous metallic pigments in industrial applications. AS/NZS 4361.1:2017. Australia: Standards Australia.