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UV Curable

 
 

Types of UV Curable Wood Coating - Industrial Wood Coat - Green Light Coatings Wood Coatings:

 

Fillers

 

Our exclusive ASAC™ Technology has enabled the development of Quality Wood Fillers that apply easily, cure rapidly, and sand well to permit smooth, uniform coverage of applied sealers and topcoats with excellent adhesion.

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Primers

 

Van Technologies innovated pigmented UV curable technologies during the 1990’s and today our exclusive ASAC™ Technology has introduced GreenLight Coatings™ UV curable primers that coat a variety of wood species, sands easily and permits smooth, uniform coverage of applied topcoats with excellent adhesion.

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Stains

 

Designed using our exclusive ASAC™ Technology, GreenLight Coatings™ UV curable stains have exceptional clarity, superb workability, and are offered in a variety of colors.  Custom color matching is also available.

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Sealers

 

The GreenLight Coatings™ UV curable sealers are designed to apply to wood surfaces uniformly, penetrate and seal the pore structure, and permit smooth, uniform coverage of applied topcoats with excellent adhesion.

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Paints

 

Van Technologies innovated pigmented UV curable technologies during the 1990’s and today our exclusive ASAC™ Technology has introduced GreenLight Coatings™ UV curable paints in either 100% UV curable or waterborne-UV curable compositions.

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Topcoats

 

Finish quality and beauty is a characteristic of our GreenLight Coatings™ UV curable topcoats.  Whether you select one of our self-sealing topcoats, or apply them over our UV curable sealer, GreenLight Coatings™ UV curable topcoats will always provide an exceptional finish appearance with excellent adhesion.

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Waterborne UV Sealers/Topcoats

 

Our exclusive ASAC™ Technology has enabled the development of high performance Waterborne UV Curable Self‐Sealing Topcoats that provide exceptional finish appearance with excellent adhesion. These coatings are available in clear or pigmented options and allow for close to the grain finishing for a very natural appearance.

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Waterborne UV Tiecoat

 

Our exclusive ASAC™ Technology has enabled the development of a unique waterborne-UV curable adhesion promoting tiecoat for use with sap wood species and exotic woods that contain oils.  Although lumber producers do their best to deliver quality wood substrate, there can occur in nature higher or lower content of free sap, pitch, and oils in these types of wood species.

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General Tech Tips

 

System Comments

 

GreenLight Coatings™ UV Curable Products are available in 100% (solids) or hybrid waterborne-UV curable compositions. There are significant differences from conventional coatings 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

 

GreenLight Coatings™ UV Curable Products are available in open or closed top drums (55 gallon; agitator heads are optionally available) 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

 

GreenLight Coatings™ 100% (solids) UV Curable Products are not susceptible to damage from freezing.  The waterborne-UV curable coatings, however, should be protected from freezing.  It is recommended to store products at room temperature or a cool holding area.  Keep all product away from excessively hot conditions, specifically do not store at temperatures above 110o F. Product temperature will affect viscosity, thereby effecting spray, roll coat, flow coat, etc. characteristics.  If product is below 60o 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.

 
 

Safety

 

REVIEW MATERIAL SAFETY DATA SHEET (SDS) BEFORE ANY USE AND POSSIBLE EXPOSURE! UV curable products contain ingredients that can be irritating to eyes, skin, respiratory, and digestive system. Follow all recommendations for personal and environmental protection.

 
 

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 products thoroughly before use with the use of an appropriate mixer. The preferable method 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.

 
 

Filtration

 

All GreenLight Coatings™ products are pre‐filtered for optimum performance, but it is advised to install in‐line filtration between the fluid reservoir or container and the coating applicator system.  Standard filters installed in many finishing lines are made of 100 mesh (150u mesh opening) stainless steel screen material.  It is highly recommended to perform pre‐mixing and continuous agitation when using any product containing flatting or gloss reduction aids and/or fillers.

 
 

Application Equipment

 

Use stainless steel or suitable non‐corrosive material for any wetted parts of the spray line or coating application equipment used.

Fluid Transfer Pumps:
-100% active UV curable coatings, by their nature, 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.
-Waterborne-UV curable coatings are robust and can be pumped using most all industrial pumps available in the market.

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.

 
 

Grain Raise

 

For 100% UV curable coatings, the grain raise observed is very similar to that experienced with conventional coatings and does not typically present any problems.  Waterborne-UV curable coatings, however, will exhibit grain raise consistent with non-UV curable waterborne coatings.  The GreenLight Coatings™ UV primers, 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 topcoat application, 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

 

Review the material safety data sheet (SDS) and always check with your local sanitary treatment facility and/or waste disposal 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 of 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 GreenLight Coatings™ 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 GreenLight Coatings™ 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 sandability 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 GreenLight Coatings™ products have been designed to coat uniformly over most 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.  Seal coat and topcoat applied wet thicknesses should not exceed 2.0 mil (0.002”).
  3.  It has been observed, especially in spray lines, that the GreenLight Coatings™ 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 GreenLight Coatings™ 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 note that, the higher the grit used in pre‐sanding, the better the smoothness of the final finish.  It is cautioned, however, that it is possible to sand with too high of a grit media and the surface may not possess enough microtexture for adhesion promotion.  Grit count higher than 300 should be avoided.

In general, 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 prime coat or 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 due to the high degree of hardness of cured UV curable coatings.  This type of sanding media on paper will perform much more efficiently and will also last longer, saving cost on replacement belts and paper.

For lineal mouldings and profile sanding it is recommended to employ the use of two initial brush sanding rolls that are constructed of 180 grit abrasive nylon bristles.  These brush rolls should rotate with and then against the direction of the part.  These should be followed by two additional Flex‐Trim type 150 grit sanding brushes, the first of which having ⅛” sanding strips and the second having ¼” sanding strips.  Again, the brush head rotations are with and then against the direction of the part.

 
 

Drying and UV Curing

 

Most often, only a UV curing process is required for 100% UV curable GreenLight Coatings™ products.  However, there are certain GreenLight Coatings™ UV curing products, including waterborne-UV curable coatings that contain water and/or reducing solvents that require a preliminary drying and/or flash off process.  When it is necessary to evaporate reducing solvents and/or water, it is essential to maintain a drying temperature no higher than 80o 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.  Quality problems associated with stray light or excessive heat include:

a.)  Gel formation in the liquid with potential to clog in‐line filters and spray gun tips,

b.)  Irregular shaped particulates, lumps, slugs, etc. in the surface finish, and

c.)  Fluid line plugging.

One commonly encountered phenomenon is the appearance of an irregular expression of gloss and/or the appearance of haze on a surface when curing low sheen UV curable coatings.  This is the result of unbalanced cure conditions across the coated surface and can be corrected by lamp position and intensity.  A radiometer is essential for troubleshooting and for quality control.

Most cure related problems are associated with under cure or situation where the UV coating does not receive enough UV light energy to cure completely.  Under cure will result in soft, easily deformed coating surface, loss of adhesion, and/or sanding difficulties (clogging of sanding media).  Excessive or long exposure to UV energy will not pose damage to the UV coating unless the surface temperature increases to the point where substrate discoloration and degradation occurs.  When UV curing, it is recommended to use standard medium pressure mercury arc lamps, iron and/or gallium doped medium pressure arc lamps, and/or microwave energized mercury lamps of type “H”, “Q”, “V”, or type “D”.  Please contact your technical representative for the specific lamp preference for the GreenLight Coatings™ product to be used.  The recommended wattage per inch ratings is 300 to 600 W/in and has proven to be quite effective.

CAUTION:  Protect all individuals from exposure to high intensity UV lamps.  Safety goggles or eyeglass protection is required that will prevent eye exposure to UV light.  Protect skin from possible exposure by wearing appropriate clothing.  Follow UV lamp manufacturers’ instructions and precautions.

 
 

Clean‐Up

 

Since the GreenLight Coatings™ 100% 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 shutdown time is minimal (3 day or less), a black UV opaque cover or bag should be placed over exposed fluid and over application equipment to prevent premature cure of the UV curable product by stray light.  Normal application processes may then resume the next day.  Longer shut down periods will require a system flush with acetone solvent.

When using waterborne-UV curable products follow the procedure below for performing a system change over from solvent, or other UV curable compositions, and for general cleaning:

System contains conventional solvent or high solids UV curable coating:

  1.  Flush system with cleaning solvent required and/or acetone until clean.
  2.  Flush system with acetone or isopropyl alcohol (IPA) solvent.  NOTE:  These two solvents are solvent and water miscible and will act as an intermediate compatible solvent.
  3.  Flush system with water.
  4.  Begin introduction of waterborne UV product.

System contains waterborne UV product:

  1. Flush system with water.
  2.  Flush system with acetone or isopropyl alcohol (IPA) solvent.  NOTE:  These two solvents are solvent and water miscible and will act as an intermediate compatible solvent.
  3.  Allow the acetone or IPA to remain in the system until further use.
  4.  To go to further use of waterborne UV product:
  5.  Flush system with water
  6.  Begin introduction of waterborne UV product.
  7.  To go to the use of conventional solvent or high solids UV curable coating:
  8.   Begin introduction of conventional solvent or high solids UV curable coating.

Cured UV product will be extremely difficult to remove.  Caustic coating removers will be required using proper safety equipment and care for the surface the cured product is contaminating.  Remember‐ SAFETY FIRST when using any cleaning solvent ‐ use appropriate precautions and disposal procedures.

 
 

Miscellaneous Topics

 
  1. Clogged Fluid 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, 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. Certain in‐line fluid heaters may have “hot spots” that are present.  The use of these heaters with a fluid delivery system that has a stop and go cycle relative to pumping and coating delivery to the wood surface can result in overheating of the UV curable coating.   Under these circumstances, gels or partially cured coating can accumulate in the filters causing them to clog and restrict fluid flow.  Check to make sure the UV curable coating fluid has a return flow even when the coating is not actively being applied to the wood surface.
    Another cause of fluid filter plugging is related to the effect of stray UV light from the UV ovens striking the UV coating in the applicator station.  Stray UV light will “kick over” the UV curable coating over time and, again gels or partially cured coating may be recycled back to the fluid filters and result in filter plugging.  Attempts to reduce stray UV light exiting from the UV oven should be made to prolong run time and improve the quality of finish.
  3.  Rough Orange Peel Finish:  This is typically due to insufficient sanding.  Use silicon carbide media paper.  Monitor board thickness variation and adjust accordingly.
  4.  Bumps:  Smooth raised bumps are usually caused from drips of UV product onto 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.  First, 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 workpiece.  If excessive dripping continues, inspect air flow in the spray booth or cabinet.  Filters may need replacement, exhaust vents may be partially blocked, and the blower may not be working properly.
  5.  Seal Coat Too Thin:  Wood materials will vary from board to board and influence how the seal coat will lay down.  It may be necessary to apply more sealer on certain board supplies relative to 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 workpiece.  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 100% active UV materials 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.
  6.  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.
  7.  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.
  8.  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.
  9.  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.
  10.  Raised Grain:  Seal coat too thin.  Inadequate sanding of seal coat, check board dimensions when using automatic sanders.
  11.  “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.
  12.  Topcoat Shows Dry Spots:  There are three most common causes for this:
    1.  Seal coat is too thin.  Increase seal coat thickness.
    2.  Sanding operation is too aggressive, removing seal coat in areas.  Adjust sander to remove less seal coat.
    3.  Too light of a topcoat.  Increase topcoat thickness.
  13.  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.
  14.  Surface Cracking:  Topcoat is too thick and insufficiently cured through it entire thickness.   Thick layers often exhibit surface cure before depth cure.  This formation of a hard surface over a soft surface will result in surface cracks when deeper regions of the layer begin to cure.  Reduce topcoat applied thickness.

 

 
 
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