By Peter L. Phillipson
Scottsdale, Arizona — February 1, 2017 — In recent years, as the first of the ultraviolet curing products and the equipment to cure them landed in the marketplace, many questions were asked regarding the future use of this paint technology. In the following article I have tried to give a fair overview of what this product’s potential is, as well as some facts regarding health and safety that should be considered.
UV coatings are relatively new on the scene in automotive refinish. However, UV coatings have been used in industry for many years. Some of the main benefits that UV coatings offer are the potential increase in productivity, the environmental advantages of containing little or no solvent and a fully cured result (no post cure).
One of the problems experienced with UV when trying to perfect the curing process is adhesion faults. This is normally experienced when the paint has been exposed to insufficient energy/ultraviolet, incorrect wave lengths or shadowing.
Two pack or urethane paint systems that most body shops are familiar with include a hardener that contains isocyanate that kicks off the molecular cross-linking of the paint. In UV technology the coating contains photoinitiators that basically take over for the hardener used in conventional urethane products. When the photoinitiators contained in the UV coating are exposed to UV radiation they change, chemically triggering the cross-linking/curing process.
As with different hardeners that can be fast, medium or slow, various photoinitiators are available that respond to certain wavelengths. This is to get the right balance between fast curing and reasonable pot life. For example, you could produce a really quick cure, but the coating was so sensitive that natural UV light coming through a window started to harden the paint in the spray gun tip!
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Another variable is the matching of the equipment to the UV coating based on the photoinitiators used. This could be high discharge UV, fluorescent UV or even LED UV. For example, a coating that cured great using high discharge UV could remain wet if you tried using fluorescent or LED UV to trigger the photoinitiators.
Now bear in mind that the photoinitiators are dispersed throughout the coating and obviously next to the substrate. If you don’t get enough energy down to the substrate the paint will not cross-link and you will have an adhesion problem.
This problem was less common in the manufacturing industry. For example, the coatings over tables and other furnishings had a very low film-build, so it was much easier to zap with UV.
Automotive coatings have a higher film build and are therefore more susceptible to this type of problem. Most UV coatings in automotive, including primers, are clear or translucent. The reason for this is that the pigments could block the radiation from activating the photoinitiators, especially next to the substrate. Another factor that makes industrial application easier was that the coating did not have to be resilient to UV attack. Another significant factor is that the objects would be treated with UV in an enclosed environment, as opposed to shop floor conditions where other workers are exposed to UV radiation.
UV coatings themselves are not dangerous. However, the equipment needed to cure them should be used with caution. The aim of the manufacturer is to produce the equipment that gives off only “A” rays. UV radiation is split into three categories A, B and C:
• UVC – 100 to 290 nm
• UVB – 290 to 320 nm
• UVA – 320 to 400 nm
It’s the UVB and UVC rays that are best avoided, but it should be noted that prolonged exposure to UVA can also affect human DNA. UVB is commonly associated with skin cancer and UVC is a powerful and hazardous radiation which can be used as a method of purifying water and as a sterilisation ray. It’s not good for the human body. Accidental overexposure to UVC can cause corneal burns, commonly termed welder’s flash or snow blindness. Special filters can be used to filter out these rays. The alternative is to ensure that no UV can spill into the workplace by using a blocking shroud.
As a side note, most of the UVB and all of the UVC from the sun is blocked by our atmosphere. This is why some worry that depletion of the ozone could allow more UVB through, increasing the risk serious skin damage.
The most common UV lamp currently being used is sometimes referred to as a high discharge lamp. This type of unit is only good for spot repair and cannot be used inside a spray booth.
The lamp has quite a short life expectancy and sells for around $2,000 in the US. Similar lamps sell for around €2,500 in Europe.
This type of lamp is fitted with a filter to block the UVB and UVC rays. The operator is also required to wear skin protection, not just goggles. Long sleeves and gloves and full-face shield are suggested, as this protects more skin. When the lamp is operating, other unprotected workers should not be within several feet of the operation.
The potential for this type of coating is huge, not only in auto refinish but also at the OEM level.
Many conventional spot repairs are treated with very high temperatures to achieve a cure. This is normally around 140-degrees Celsius, which can cause problems with plastic parts. UV equipment produces very little temperature increase, so obviously this could be a great application for the car manufacturers.
Another great application is for repairing cloudy polycarbonate headlight lenses, instead of just polishing which is a temporary fix.
The two areas that could cause slower introduction of these products are the health and safety issues as well as the cost of the equipment. As you increase the curing area requirement you not only increase the cost of the equipment, but also increase the amount of radiation to be controlled and equipment to keep clean.
Costs increase further when you start curing UV clearcoat. The equipment has to be located inside the spray booth, therefore it has to be approved and safe. It is estimated that good quality UV in-booth systems for panel drying will cost around $30,000 to $50,000.
Much is being made of the UV clearcoats, but something is missing! As the clearcoat can only be cured in the booth you need a large, approved in-booth UV curing system. At the time of writing this article I have yet to see it. There has to be a good marriage between coatings technology and UV equipment if this application is to succeed.
In the longer term, I predict that UV will be commonly used in the refinish market but will be better suited to purpose built installations. For example, a drive-thru booth connected to a drying chamber. Once the vehicle is painted, it is pushed into the drying chamber freeing the booth for the next vehicle. This method would not be easily adopted in a retrofit market.
In the short term, the growth in UV will be for smaller panel applications and predominately for primers. In that area it will be competing against infrared equipment. There are some very good fast curing urethane primers available. We tested one recently that was ready to sand in five to six minutes after using short wave infrared. UV is currently producing results of three to four minutes, so it’s not a great amount of time saving.
The new kid on the automotive stage is getting some very good reviews but the ticket prices are high resulting in smaller audiences. My thoughts are that UV will be seen more often, but it will take much time and marketing before it becomes an established method of curing automotive refinish coatings on a large scale.
Peter L. Phillipson is the Technical Sales & Marketing Manager (IR) B-TEC Systems. He can reached via email to btecusaoffice@gmail.com.
