Tech Tips for VanUltra UV Curable Wood Coatings
General
Tips for UV Wood Coatings
VanUltra Stain Application Tips
VanUltra Sealer Application Tips
VanUltra Topcoat Application Tips
Troubleshooting for UV Wood Coatings
TECH TIPS
For VanUltra UV Curable Wood Coatings The VanUltra UV Curable wood coatings consist of stains, sealers, and topcoats for the professional wood finisher. When used properly, these coatings will provide ultimate performance and quality. General VanUltra System Comments: UV Curable coatings are typically high non-volatile (solids) or solvent reduced compositions. Characteristically, they will behave similar to conventional coating systems. However, there are significant differences that will require an adjustment period to "come up to speed." Patience and practice will help achieve the full benefit of these high tech wood coatings. The topics below have been determined to be best through actual experience with UV curable coating compositions. Packaging: VanUltra UV Curable products are available in open top drums (55 gallon) and pails (5 gallon). It is highly recommended that adequate mixing be done to any product containing flatting, or gloss reduction additives, and fillers before application begins. Shipping and Storage Conditions: VanUltra UV Curable Products are not susceptible to damage from freezing. No special handling is required during the winter shipping season. It is recommended to store the product at room temperature or a cool holding area. Keep all product away from excessively hot conditions. Product temperature will effect viscosity, thereby effecting spray, roll coat, etc. characteristics. If product is below 60° F, let the product come to room temperature before applying. Note: Some product compositions may contain solvent reducers that will require special storage rooms to comply with local and state fire codes. Mixing: Like all coating materials that contain suspended solids (flatting or gloss reduction additives and/or fillers), there is a chance that the solids may settle to the bottom of the container. Always check the bottom of the container by scraping the bottom with an inspection stick or spatula. Settled solids will appear to be thick and paste-like when examined. It is recommended to mix all product thoroughly before use with the use of an appropriate mixer. The preferable methods of mixing will use a variable speed mixer having a propeller shaped agitator. The propeller or agitator should be approximately one third the diameter of the container and positioned off the bottom of the container by a distance approximately equal to the diameter of the propeller or agitator. When mixing, operate at a RPM sufficient to create a rapid flow of surface fluid material with the formation of a slight vortex. Avoid any aeration of the product that may cause bubbles in the final coated surface. Consistent, smooth, lump free fluid should be seen when the product is fully mixed. Agitation: Once material is adequately mixed, an agitator is recommended to maintain suspension of solids for the entire duration of application. Typical agitators have much larger "paddle" like blades that slowly and gently mix or stir the coating. Typical agitator blade diameters are between 1/2 and 1/3 the diameter of the fluid reservoir or container serving the application equipment and are positioned close to the bottom. Often, there may be more than one agitation blade assembly, one near the bottom and one approximately 1/2 of the distance to the top of the reservoir or container. With two agitator assemblies, it is essential to watch fluid height and agitator speed to avoid introducing air into the fluid. Application Equipment:
a. Use stainless steel or suitable non-corrosive material for any wetted parts of the spray line or coating application equipment used.
b. Fluid Transfer Pumps: By their nature, UV cured coating systems are highly susceptible to damage from fluid shear forces. We do not recommend the use of piston pumps, gear pumps, or any other pump that will apply high shear forces to the fluid. The following pumping methods are recommended:
i. Roll Coating and Flow Coating: Air pressure pots and diaphragm pumps
ii. HVLP Spray Guns: Air double diaphragm pumps
iii. Airless and Air Assisted Airless Spray Guns: Glutton style pumps c. Spray tips, tip pressure, and pot pressure will require adjustment to provide optimum performance and may not be the same as that used with other coatings used in the past. For example, the viscosity of available UV coating systems will vary and will, therefore, require different adjustment settings. For typical spray systems, we recommend the following for start-up:
i. HVLP guns are highly recommended for relatively low viscosity UV coatings. We suggest using a fluid tip and needle size of 0.035" - 0.040" and air pressure of 45 - 60 psi to the gun. Use a pressure pot of 9 - 12 psi to pressurize fluid.
ii. Conventional spray equipment will result in greater overspray and a lower transfer efficiency. When using this type of spray equipment, use a fluid tip and needle size of 0.035" - 0.055" and air pressure of 55 to 75 psi. Again, a pressure pot of 9 - 12 psi is adequate to pressurize fluid.
iii. For airless and air assisted airless systems, use a fluid tip and needle size of 0.009" - 0.015". For airless spray use pressure of 1000 - 1500 psi and for air assisted use 500 to 750 psi. Grain Raise: The grain raise is observed as very similar to that experienced with conventional coatings and does not typically present any problems. The VanUltra UV sealers and sealer topcoats will "lock in place" any raised fibers so that during the sanding process, a highly smooth, uniform surface is ready for topcoat application. After topcoating, no secondary grain raise is seen and a high quality finish results. Wood moisture content will influence the degree of grain raise seen, and therefore, the potential effort necessary to achieve the quality desired. Maintain a constant storage environment for wood stock to help eliminate any finish quality variations. Waste Disposal: Check with your local sanitary treatment facility and district! They will evaluate materials for you in their effort to help you properly dispose of waste. Do not discharge any waste to a septic system or storm water drain regardless on how harmless you believe it is! The EPA considers septic disposal as an underground injection and closely regulates discharges. Storm water drainage is also closely regulated. In the dry form, after UV curing, the waste from VanUltra UV curable products is not regulated and may be disposed of as normal solid waste. As a liquid it is quite common to find that VanUltra UV curable product waste material will require hazardous waste handling procedures - ALWAYS CHECK FIRST! General Application Tips: 1. Topcoats may be used as sealers. The cost will be higher, the sandablility will be more difficult, and there may be less of a "fill" effect. It is recommended to first try the sealer and then evaluate the use of a "topcoat" sealer if a single coating sealer/topcoat system is desired. 2. Coating Application: All of the VanUltra products have been designed to coat uniformly over most all wood species even when using standard tack cloths. Machine oils and other surface contaminants can interfere with coating application, so take care to prevent possible contact with these materials. 3. It has been observed, especially in spray lines, that the VanUltra products actually may remove residues of other types of coatings. During start-up, it may be possible to observe "chunks", "slugs", and other particulate deposits on the surface after drying. These are most likely to originate from residues in the fluid lines or tips from prior coatings used. It is recommended to flush the system with appropriate cleaning solvents prior to using a VanUltra product. For optimum performance, a final rinse or flush using acetone solvent is recommended. Sanding: This is a very critical step in finishing with any UV coating system. UV curable coating compositions exhibit high chemical resistance, even to the same un-cured UV coating composition. Sanding performs two functions with UV coating systems. First, sanding will remove unwanted rough regions for smooth topcoat application. Second, sanding will roughen the surface on a micro scale and increase the surface area for best topcoat adhesion. Take not that, the higher the grit used in pre-sanding, the better the smoothness of the final finish. It is advised to pre-sand up to a minimum of 150 grit and it is preferred to reach 220 grit. Apply stain and sealer, and re-sand to 220 grit when completely cured through action of UV light. It is recommended to always sand with the wood grain and, if using hand power sanders, to use a random orbit sander. The application of one topcoat, over a sanded seal coat layer, will be remarkably smooth and for many instances it will be sufficient as the final finish. A second application of topcoat, after light fine sanding, will further improve final finish quality. Automatic flat panel sanders perform remarkably well and it is highly recommended to use a segmented pressure belt sanding process. It is essential to apply even pressure over the entire surface area, leaving no regions untouched. Untouched areas may exhibit fish-eyes, crawling, and/or repel spots. Automatic sanders may also be too aggressive when not set up properly, sanding entirely through the applied seal coat. This will result in spots or craters where the topcoat absorbs into, and re-seals exposed wood. Silicon carbide sanding media is highly recommended. Since cured UV curable coatings exhibit a high degree of hardness it is recommended to use silicon carbide sanding media. This type of sanding media on paper will perform much more efficiently and will also last longer saving cost on replacement belts and paper. Drying and UV Curing: Most often, only a UV curing process is required for the VanUltra UV curable products. However, there are certain VanUltra UV curing products that contain reducing solvents and/or water that may require a preliminary drying step. When it is necessary to evaporate reducing solvents and/or water, it is essential to maintain a drying temperature no higher than 80° C. UV curable products will react only when exposed to UV light and extreme heat. Avoid any unwanted exposure to stray light or heat as these may cause serious coating quality problems to the UV curable product. When UV curing it is recommended to use standard medium pressure mercury arc lamps, iron doped medium pressure arc lamps, and/or microwave energized mercury lamps of type "H" or type "D". The recommended wattage per inch ratings are 300 to 600 W/in and have proven to be quite effective. Clean-Up: Since high non-volatile (solid) VanUltra UV curable products will not cure unless exposed to UV light or extreme heat, they will always remain in a liquid state. This makes cleaning quite easy by simply flushing the equipment and spray lines with clean acetone solvent. Under the circumstance that application shut down time is minimal (1 day or less), a black UV opaque cover or bag should be placed over exposed fluid and over spray gun tips to prevent premature cure of the UV curable product by stray light. Normal application process may then resume the next day. Longer shut down periods will require a system flush with acetone solvent. Cured UV product will be extremely difficult to remove. Caustic coating removers will be required using proper safety equipment and care for the surface cured product that is contaminated. Remember - SAFETY FIRST when using any cleaning solvent - use appropriate precautions and disposal procedures. VanUltra Stain Application Tips 1. Stain up-take will very by wood species and moisture content. Maintain a constant storage environment for wood stock to help eliminate any finish quality variations. 2. Apply stain to the desired color intensity. Multiple coats may be applied to develop darker shades. 3. Small parts and pieces are easily stained by a dip process followed by wiping, whereas larger pieces are more easily sprayed with stain followed by wiping. 4. Cracks and crevices are easily filled with stain during spray application, and when wiping the uses of a sponge or cotton swab may be of help. These work great for difficult to reach areas. 5. Always wipe stains using a lint free cloth. 6. Color variation: Should color variation occur, there are a few possible reasons.
a. All VanUltra UV curable wood stains should be mixed well before use to ensure uniform color.
b. Examine the color of the wood substrate. Since wood is a natural product, it is common to see color variations that will influence the final stained appearance. VanUltra Sealer Application Tips 1. Apply the sealer to a wet thickness between 1 mil to 4 mil (0.001" - 0.004"; 25u - 100u). When cured this will permit excellent sanding without burnishing through the stain coat. Therefore, if the stain color is burnished or sanded to lighter shades during seal coat sanding, it is very possible that the seal coat was not thick enough. 3. As a visual aid to correct wet sealer thickness, when applied correctly, the sealer will appear to provide a wet appearance over 90%+ of the surface area. Some areas may appear to be slightly dry due to increase pore size and greater absorption of sealer. This is normal if maintained to a minimum of 10% or less. There should not be any discernible pockets, dimples or fish-eyes. 4. If fish-eyes or repel spots occur, check for contamination on the wood surface. The VanUltra coatings have been specifically designed to be tolerant of certain wood rosins/resins but may not coat well over machine or other types of oils and certain other contaminants. 5. Do not be alarmed should some grain raise be observed. Grain raise is common with long fiber wood species such as white oak surfaces. The sealer will "lock" any raised grain in place and permit excellent sanding properties to remove any evidence of raised grain. 6. It is recommended to sand the dry sealed surface with 220 grit media or finer. This will provide the smoothness quality necessary for superior topcoat application. 7. If difficulty is experienced in sanding the sealer, due to poor dusting or it gums up in the sanding paper, the sealer is probably not sufficiently cured. UV lamps may not produce the same intensity as they age. Always check for UV lamp intensity daily, or at a minimum weekly, and replace when sufficiently low that productivity suffers. Product showing difficulty in curing may be cured by slowing the conveyor or passing product through the UV curing section once more to promote full cure. VanUltra Topcoat Application Tips 1. The VanUltra topcoats include epoxy acrylate and urethane acrylate based systems. Both provide excellent topcoat quality with the urethane system superior in abrasion and chemical resistance. 2. All systems meet the demands of the KCMA standards when cured appropriately. 3. It is recommended to apply the topcoats to a wet thickness between 1 mil to 4 mil (0.001" - 0.004"; 25u - 100u). 4. Again, if the final coating surface is not uniform, check for surface contaminants on the wood substrate and any possible contaminants from the application equipment. Spray hoses must have a minimum of compressor oil, and, as discussed above, it has been noted that residues in the fluid lines have been "cleaned" and removed with the use of the VanUltra coatings. 5. With a sealer pre-sanding to 220 grit one topcoat application is sufficient for quality results. Two topcoat applications will result in exceptional surface finish quality. Troubleshooting: 1. Plugged Filters: The most frequent cause is inadequate mixing prior to use. Over time heavier solids will settle out of suspension and form a thicker, paste-like consistency at the bottom of the container. Upon pumping and in-line filtration of this thick consistency concentrated solids are delivered to the filter choking off flow. Clean the filter with acetone, carefully inspecting for foreign matter and re-install. Fully mix fluid and agitate prior to pumping. 2. Rough Orange Peel Finish: This is typically due to insufficient sanding. Use silicon carbide media paper. Monitor board thickness variation and adjust accordingly. 3. Bumps: Smooth raised bumps are usually caused from drips of UV product on to coated surfaces during automatic spraying operations. Wipe down guns and internal spray booth surfaces and restart. When drips are observed there are typically two sources possible. One, loose fittings on hoses, air caps, tips, etc. Tighten all fittings Second, excessive overspray. Wipe down all surface area above the travel path of the work piece. If excessive dripping continues, inspect air flow in the spray booth or cabinet. Filters may need replacement, exhaust vents may be partially blocked, blower may not be working properly. 4. Seal Coat Too Thin: Wood materials will vary from board to board and how the seal coat will lay down. It may be necessary to apply more sealer on some lots of board than others. Variations exist between species of wood (i.e. pine, oak, maple, birch, mahogany, etc.). The seal coat need only be thick enough to provide a uniform light coat over the entire work piece. Excessive seal coat thickness is usually a waste of material. When using spray application equipment - To increase thickness, increase fluid pressure to spray guns, increase tip size on spray guns, and/or in the case of automatic systems, reduce the line speed of the conveyor. CAUTION: Some UV application systems have long conveyor lines with drying ovens to accommodate waterborne or solvent reduced UV coatings. These longer conveyor lines may create a situation where the UV material will have time to soak into the wood more than desired. Several adjustments of the conveyor line speed may be required to get optimum results. 5. Seal Coat Too Thick: Reduce fluid pressure to spray guns. Spray tips may be too large. increase line speed to reduce dwell time under spray guns. 6. Very Small Bumps or Rough Surface: This can be from a number of sources. Before attempting any corrective action, try to identify the imperfection with the aid of a magnifying glass.
a. Airborne Contaminants: Appearing as particles, usually the same color as the wood being processed. check filters and replace if needed. Clean entire coating application area. Check if dust collector is full. Check if vacuum on sander is working properly. When hand sanding, inform employees to take care on wiping dust or blow off operations.
b. Clear Specks or Tiny Bumps: This is likely to be a result of insufficient spray technique. Be sure fluid is properly mixed. Be sure filters are not clogging. Check spray tips for adequate spray pattern and uniformity. Look for guns that are "spitting" and not adequately atomizing fluid.
c. Raised Grain: Seal coat too thin. Inadequate sanding of seal coat, check board dimensions when using automatic sanders.
d. "Hair Like" Particles: Sanding problem where belt may be traveling too slow. The wrong type of sanding media may be used, install silicon carbide media. 7. Topcoat Shows Dry Spots: There are three most common causes for this:
a. Seal coat is too thin. Increase seal coat thickness
b. Sanding operation is too aggressive, removing seal coat in areas. Adjust sander to remove less seal coat.
c. Too light of a topcoat. Increase topcoat thickness. 8. Sanding Lines on Wood: Usually this is from the sanding belt loading. Inspect and/or replace sanding belt as needed. Check with the sanding belt manufacturer to be sure you have the proper grit for the application.
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Important: Technologies, Inc. makes no warranty, whether expressed or implied, including warranties of merchantability or of fitness for a particular purpose. Under no circumstances shall Van Technologies, Inc. be liable for incidental, consequential or other damages, alleged negligence, breach of warranty, strict liability, tort, contract, or any other theory, arising out of the use or handling of this product.
For information on typical properties, technical questions,
pricing, or to sample and purchase products, contact Van Technologies at:
5791 Bergquist Road
Duluth, MN 55804
218-525-9424
Fax: 218-525-5594
email: vantech@vtcoatings.com