UV Powder Coating Roundup
RadTech International UV Powder Focus Group
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Ultraviolet (UV) powder coating is such a hot topic in the powder coating industry right now that we decided to offer you, our readers, a way to ask questions and get answers from leading experts in the field. The UV Powder Focus Group of RadTech International, an association focused on UV and electron-beam (EB) technology, has agreed to answer your questions through this roundup. The group includes raw materials producers, powder and application equipment manufacturers, and other industry experts who meet quarterly. Your question will get the utmost scrutiny from leaders in the field as it makes the rounds among group members. We publish the roundup three times a year to give you the latest information about the coatings and equipment necessary to coat heat-sensitive substrates, such as medium-density fiberboard (MDF) and plastic. The first roundup was published in April. Contact information to submit a question is at the end of the roundup.
UV curables can sometimes have objectionable odor: is this also the case for UV powder?
The odor of UV liquids typically comes from low-molecular-weight monomers that are used to modify the performance of the liquid coatings. These materials are not present in UV powders.
Thermoset and UV contamination
If I use a line with both thermoset and UV-curable powders, is there a major risk of contaminating one material with another?
Whenever powder coatings of different chemistries, compositions, and manufacturers are mixed together, some risk of contamination is present. However, a basic powder compatibility test can be conducted by blending off line different ratios of the powders in question and evaluating the basic appearance and performance properties.
Can I overcure a UV powder coating?
No. However, the coating and the substrate could potentially be damaged or even burnt if parts get stuck under the UV lamps for an extended period of time.
IR melt and flow
What is the best type of oven to use for melting and flowing the UV powder coatings?
Short-wave IR is the most powerful conventional IR heating technology; however, the rapid heating can be difficult to control and often leads to hot spots. This accounts for the increased popularity of the medium-wave IR ovens, which provide rapid heating with more uniform part temperatures. Traditional convection ovens can also be used to melt and flow UV powders; however, they require a longer process time. Recent research in oven technology has yielded a combination IR-convection oven, which combines the fast heating attributes of IR technology with improved temperature uniformity. These combination ovens are more expensive than traditional heating technologies, but they provide additional process capabilities and a more uniform part temperature than traditional heating technologies.
How long does it take for the output from the lamps to stabilize?
Lamp stabilization depends on the length of the bulb and whether the system uses microwave-powered or electrode-type bulbs. In general, microwave-powered lamps stabilize in a few seconds. Electrode (arc) lamps of 10 inches or less stabilize from a cold start in less than 30 seconds. Longer electrode (arc) lamps can take anywhere from 1 to 3 minutes.
We hear that outgassing of porous substrates such as MDF can cause significant pinholing. How do we ensure this does not happen?
Outgassing on wood substrates such as MDF is typically associated with rapid moisture evolution from the board during processing. This problem can be minimized by monitoring and controlling the quality of the MDF being processed as well as through the optimization of the total process including preheating, melt and flow, and UV curing stages.
UV powder waste disposal
How do I dispose of waste UV powder?
UV powder coatings are typically disposed of in the same manner as traditional powder coatings. In some cases the powder can be heat-treated in an oven to melt the powder and form a block. This makes the powder easier to control. Disposal guidelines are regional in nature; therefore, local regulations should be read and followed.
Can I recoat previously coated and cured UV powder surfaces?
In most cases, recoating is possible by scuff-sanding the first coat before the application of the second coat. Be sure to check intercoat adhesion by using the standard crosshatch test method to ensure that a good bond is formed. PC
For more information or to submit a question, contact Steve Couzens of the RadTech North America Powder Coating Group. Couzens, USA sales manager, Radex UV Powder Coating, can be contacted by telephone at 616/822-7842 or by e-mail at firstname.lastname@example.org. Also see www.radtech.org.
Chairman of the RadTech Europe Powder Coating Group is Olivier Andre, market manager powders for Europe, UCB Chemicals; from the US, dial 011-32-25599666; or e-mail [email@example.com]. See also [www. radtech-europe.com].
You can also submit a question to Peggy Koop, editor, at 651/287-5603; fax 651/287-5650; e-mail [pkoop@ cscpub.com]