Every surface finishing process requires masking. Masks such as tapes, waxes and solvent-based lacquers protect components and surfaces, acting as a self-sacrificing barrier. But this relatively simple process can have hidden costs—including scrap and component rework. To minimize these costs and to gain a competitive edge, shops should consider a new masking option—ultraviolet (UV) curable masking resins.

Introduced in the mid-1990s, UV curable masks are non-flammable liquid resins that become solid in seconds when exposed to UV light energy. Meeting OSHA standards, these resins do not release strong odors and do not contain any solvents. They are urethane-based, free of heavy metals, silica and other compounds that can modify the properties of the part's surface or finish. These masks can be manipulated like any industrial plastic once they are cured.

Most importantly, these resins offer shops many savings opportunities. For starters, they cure instantly, allowing component processing to continue without interruption. In fact, overall processing time can be cut by 60-70% using these resins. Also, these masks come in several viscosities—from free-flowing water to non-flowing gels—so they can be applied just once, with good control over coating depth and coverage. Moreover, they can be conveniently dispensed in both manual and fully automated processing lines, reducing labor costs by as much as 50%.

These resins also display superior adhesion and resiliency, which help boost the quality of the component. Such desirable properties allow them to minimize post-processing rework and scrap. Additionally, because of the masks' durability, one application can be sufficient for multiple surface processing operations, removing the need for stripping and remasking between processes.

Additionally, uncured UV masking resins are highly stable, with a shelf life of up to one year when stored at temperatures between 50-90°F. Refrigeration is not necessary. Also not required are measuring and mixing before use, because these resins are single-component formulations. They can be applied to the part's surface using several methods, such as bead placement, dip, brush and spray. Next, they can be cured using ultraviolet energy sources, such as spot lamps, which are good for small areas, and flood lamps, which are suitable for larger surfaces.

UV curable masking resins do not leave any residue behind when they are removed using proper methods. The removal mechanism—burn-off, peelable and water-soluble—determines the resins' grade. Here are the three grades of UV masking resins:

· Burn-off masking resins: These grades generally provide the best surface adhesion and are most resistant to heat and harsh chemical solutions, such as acid/alkali baths. They are suitable for plating baths. UV light can cure these grades in 20-30 seconds under a flood lamp, though times can vary based on the mask volume and the component's size and configuration. To remove the burn-off grade mask, the component needs to be baked in an air-enriched furnace at temperatures ranging from 900-1,400°F. Bake times depend on factors such as temperature, mask volume and the part's thermal conductivity. These resins can be completely burned off in as little as 15 minutes for thinly coated surfaces.

· Peelable masking resins: Maybe the most flexible of the UV masking resins, these grades can be removed by simply peeling them off. They offer good adhesion to most clean metal surfaces and are durable enough to protect surfaces during processes such as acid cleaning, plating, anodized coating and grit blasting. The surface bond can also withstand multiple surface cleaning and processing operations, making stripping and remasking between processes unnecessary. UV light can cure these masks in a few seconds, and once cured, you can remove them by prying up an edge and pulling. Because they're elastic, they can be quickly taken out in one piece, rather than in segments. You can also heat the cured masking resin to 120-150°F in a warm water bath or oven to make the removal process even easier.

· Water-soluble masking resins: These grades protect surfaces during "dry" finishing processes, such as grit blasting, shot peening and plasma spraying. Unlike the burn-off and peelable grades, which are both urethane-based, these masks are composed of water-soluble polymers and thus completely dissolve in water. The recommended way to remove these masks is through heated water, from 140-180°F, and a spray wash or agitated/ultrasonic bath. A closed-loop aqueous cleaning system is ideal for the job. Such systems are already in place in many surface finishing operations; thus shops choosing this grade can remove the mask and clean parts in one single operation.

Indeed, even simple operations like masking cannot be overlooked now that companies are seeking out cost savings with greater urgency. And a fast-curing masking option, like UV curable masking resins, presents companies with various cost reduction opportunities—from labor to scrap and component rework. These masks may even help boost worker productivity. Because they are low-odor, solvent-free and OSHA-compliant materials, they eliminate health hazards and lower the risk of operator injury, thus improving the work environment as a whole. This can lead to bolstered worker morale and quite possibly, greater productivity.

Source: UV Masking Users See the Light
Richard Golebiewski and Doug Berkowitz
Finishers' Management, March 2003
http://www.finishers-management.com/march2003/uvmasking.htm