Specifications

Guide to Selecting and Using Dymax UV Light-Curing Systems
Page 6
Developing a successful light-curing process requires knowledge
of the following key concepts.
Higher Intensity = Faster Cures – Intensity is the light energy
reaching a surface per time and it is often measured in mW/cm
2
.
Higher intensity light (of the proper wavelengths) will generally
provide faster cure.
Shortwave and Longwave Bulbs – Dymax UV light-curing
systems can be outfitted with either shortwave bulbs (emphasizing
UVB and UVC) or longwave bulbs (emphasizing UVA and visible
light). Longwave bulbs are recommended for curing most Dymax
(and similar) light-curing materials due to their superior depth of
cure and substantial visible-light intensity. The chart at the bottom
of this page describes the portion of the electromagnetic spectrum
emitted by standard Dymax longwave bulbs.
Distance and Substrates Affect Intensity – Distance from a
light-curing lamp always affects intensity. Intensity decreases with
increasing distance from both spot lamps and flood-curing
systems, especially spot lamps. Intensity decreases with
increasing distance from the focal point for focused-beam
systems. Intensity is also reduced when curing through
substrates that transmit less than 100% of the light used for
curing. Advances in light-curable adhesive technology now allow
curing through most translucent substrates, even those that block
UV completely.
Limited Depth of Cure – Since light-curable materials
themselves absorb light, each has a maximum depth of cure. For
most Dymax products, this depth is between ¼" (6.35 mm) and ½"
(12.7 mm).
Determining Complete Cure – Changing from a liquid to a solid
is a simple definition of cure. A more complete definition is that
curing is complete when further light exposure no longer improves
product properties. Quantitative testing of cured specimens can
be used to determine the minimum exposure time and/or minimum
intensity required for complete cure. The graph on page 18 shows
how this method could be used in a bonding application.
Shadows – Light-curable materials will not cure unless exposed
to light of appropriate wavelength, intensity, and duration. Some
Dymax light-curable materials can be cured with heat in
“shadowed” areas.
Oxygen Inhibition – In some cases, UV adhesive surfaces
exposed to oxygen during curing may remain tacky after cure.
This is caused by oxygen inhibition. Oxygen in the air actually
slows the cure at the top-most layer of an air-exposed coating
surface. This tackiness does not necessarily indicate incomplete
cure and can be observed with some materials, even after
complete cure. In general, there are four ways to minimize or
eliminate the tackiness associated with oxygen inhibition:
■ Longer and/or Higher Intensity Cure – In many cases, curing longer
or with higher intensity will minimize or eliminate a tacky surface.
■ Use of “Shortwave” Bulb – Use of a UVB (shortwave) bulb instead
of a UVA (longwave) bulb may also help to eliminate surface tack.
A UVB bulb may, however, result in a limited depth of cure.
■ Choose an Alternate Dymax Material – An alternate formulation may
cure “tack free” more readily.
■ Blanket with Inert Gas – Blanketing exposed resin surfaces with
inert gas (like nitrogen or argon) during cure can often eliminate the
problem of oxygen inhibition completely.
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