BMW April 2022

The curing process has traditionally been the “bottleneck” of the body shop – something the industry has put pressure on manufacturers to change. Well, they listened. Since the days of convection ovens being the industry’s only option, the likes of infrared drying systems have gained a lot of traction in the market.

Infrared is now the most common form of paint curing used by UK body shops, having overtaken convection oven use. Gone are the days where body shops would place whole cars into giant ovens for days at a time – a time consuming process made so by the slow warm up and cool down processes involved in convection drying. It’s not just drying time that infrared offers improvements on, either – efficiency and overall energy consumption levels have been improved, resulting in a greener, more efficient repair shop.

Most automotive paints are mixed with solvents that form the solution that is sprayed onto a vehicle using a spray gun. The solvent then evaporates to leave behind the paint only. How quickly this happens will depend on the solvent – the higher the solvent’s boiling point, the slower the evaporation.

Once the solvent has evaporated, it is deemed dry. However, dry paint must not be confused with cured paint. The act of polymerisation is required to “cure” – a process which uses heat to bond together the paint’s molecules making it hard and ultimately more durable.

During paint application, each layer is finished with a “flash”, which dries the paint enough to accept another coat until the vehicle is finished and ready for curing.

Whether it’s an infrared oven or lamp being used, infrared uses short or medium wavelength light to heat from the inside out, targeting a layer at a time, which drives out solvents and speeds up polymerisation for a quick and even dry. Infrared also negates the need for air circulation, which lowers the chance of paint flaws incurred during curing. Medium wavelength tends to be used for larger areas, such as resprayed panels, while short wavelength tends to be used more in spot repairs, with overall drying times ranging from 10 minutes to an hour.

Benefits of infrared include lower operating costs, thanks to quicker drying times and there being no need to pre-heat. There’s also no worry about the material you’re drying changing form because using infrared will not increase surface temperature. Wavelengths are also adaptable to each job, allowing for more flexibility.

Infrared ovens are one of the most expensive options on the market currently, with the highest level of servicing required. That said, there is a cheaper option available of portable infrared lamps that tend to work best on more targeted areas.

Despite the obvious and continued success of infrared, the industry is still looking to improve on drying times and the overall efficiency of their body shops and manufacturers are listening.

The next big trend in automotive paint curing looks to be UV. Tesla Cure’s managing director Hugh O’Neill said: “The revolution that is about to happen will be a full system UV product used in a body shop.

Like all new technology it will start slowly then at a certain point accelerate to become mainstream.” UV paints contain photo initiators that replace the hardening aspect of urethane paints. When those photo initiators are under UV light, the chemical structure changes to activate the curing process. The UV lamp being used needs to offer the same (or as close to as possible) wavelength requirement of the photo initiators contained in the UV paint being cured. Around 80mW/m2 of irradiance strength is required for a spot cure and more than 180mW/m2 for UV primers and fillers. Adhesion problems can occur with UV curing when using insufficient energy or incorrect wavelength.

The use of UV paint, requiring UV curing, has an environmental advantage on infrared as it contains little to no solvent. It can also be the more productive way of curing. That said, UV paint products are often more expensive than the likes of urethane.

It’s important to note that UV light can be dangerous to use if not used responsibly or without added care. There are special filters, as well as blocking shrouds available to ensure there is no overspill of those potentially harmful UV rays. UV rays are made up of UVA, UVB and UVC. B and C are the most dangerous, but A can cause changes in human DNA over time. UV lamps are fitted with filters to block the UVB and UVC rays and, when a UV lamp is in use, users are advised to wear long sleeves, gloves, and full-face protection.

The way in which paints are formulated is also key to the success of both infrared and UV curing, such as the inclusion of quick drying activators to enable curing at lower temperatures – particularly for UV curing.

Integration Technology has recently developed an LED-based UV portable device. Sales director David Johnson said: “Advances in UV devices have enabled a new wave of powerful yet portable solutions that bring flexibility to the workshop. Portable units compare favourably with gas or electric ovens that usually have a large footprint in the body shop, require the vehicle to be inside and, in these more environmentally aware times, have a poor conversion of energy to curing ratio.

“New UV units such as our AC-500 use LED that, unlike UV lamp technology, produce minimal heat and no harmful ozone. This makes them safer to use and less likely to cause damage to heat sensitive parts such as carbon composites and additive manufacturing materials.”

Stephen Healer, Symach UK sales manager, said: “As we move into the world of electric vehicles and carbon management plans, infrared along with UV will be at the forefront of curing technology.”

The journey to faster drying solutions is ongoing. The industry is constantly moving the goalposts and body shops must continue to keep up with industry pace and get those vehicles in and out as efficiently as possible.

Story Bodyshop Magazine 

Picture from PCII Magazine