It was the middle of the 60s when an ever-growing demanding market called for a larger range of high performing coatings. Tired of mediocre alkyds, polyurethanes, acrylics, nitrocellulose and other polymer-based ones, constructors started to seek ways of having a new type of resin that could be used in solvent borne and powder coatings. The efforts paid off and solid epoxy resins, both with middle and high molecular weight, were born. Finally, these had all the desired properties: resistance to chemicals and corrosion as well as excellent adhesion and outstanding performance in home appliances. Later on, a combination of epoxies and polyesters or the other reactive hardeners proved to be the ideal technique for coating and, since then, various ways of applying and curing powder coatings have been developed over time.
Dry paint, just the beginning
Like in many other chemical procedures, epoxy-based powder coatings undergo a long manufacturing process before they are ready to be used. First, epoxy resins are applied in a molten form on a cooling steel belt where solidifies. Then, a crushing and grinding device transforms it into tiny flakes which are then packed and supplied to manufacturers, who mix in extruders at higher temperature and pressures epoxides with hardeners, additives, pigments and fillers according to the required formulations. After cooling down, the mixture is milled and classified to the desired particle size using a special mill. Et voilà, ready to coat!
Resilient and versatile
Epoxy coatings are extremely resistant to corrosion and other chemicals, hence they are amazing metal protectors. For example, epoxy-based powder coatings are used in pipelines, poles and pillars, as well as to reinforce bars in concrete structures. Similarly, ships and structures dug into the ground also enjoy the wide range of epoxies’ anti-corrosion benefits.
However, the most common applications of powder coatings are “white goods”: refrigerators, washing machines, stoves and microwaves, which come into frequent contact with water and cleaning chemicals. Most use a combination of epoxy, polyester, titanium dioxide and barium sulphate to ensure they stay white and well protected for a long, long time.
Similarly, some toolboxes and industrial furniture, frequently exposed to cooling, lubrication and cleaning fluids typically have an “ivory” colour, indicating a high epoxy content.
How are coatings applied?
Components are usually sprayed during production time. The powder coatings, which is electrically charged in the gun during spraying, is attracted by the opposite charge on the ‘earthed’ component being sprayed, acting like a magnet which ensures that the powder is uniformly distributed on the metal part and perfectly adhered to the surface. The metal part is then introduced into an oven where it melts at 140-220Cº, and once the epoxy has reacted with the hardener and cooled down, the surface will be perfectly adhered. The advantage of powder coating, compared to other systems, is that the powder which was not used in the surface can be reused.
Sustainability and market
Epoxy-based powder coatings are possible thanks to the high demand for environmentally friendly paints. These coatings do not produce any hazardous vapours, neither for the factory workers nor the users. On top of this, the long-term protection they provide extends the life expectancy of structures and thus reduces maintenance and replacement costs. And the industry is taking steps ahead by creating even more sustainable epoxy resins using bio-based components which can help producers comply with increasing consumer and regulatory demands.