UV CURE SERIES
UV
Cure Epoxies
Epoxy Technology offers a complete line of high performance
Ultraviolet (UV) cure adhesives ranging in viscosity,
flexibility, refractive index and light transmission. Our UV
products differ from typical thermal cure adhesives which
have two parts (part A and part B) that when mixed and
heated, create a crosslinked product. In UV cure adhesive,
there are also two main components. One part is the adhesive
monomer and second part – already mixed in – is the
photoinitiator. UV cure epoxies are considered single
component adhesives. The photoinitiator will not react with
the monomer by itself; it must be activated by UV light and
undergo a chemical reaction that causes the adhesive to
cure/harden. For the photoinitiator to react correctly, it
must be exposed to light of the correct wavelength and of
sufficient intensity. Otherwise, crosslinking will not occur
or not occur completely, yielding inconsistent adhesive
performance.
Some UV cure epoxies when applied onto an opaque surface or
in a “shadowed area” are not exposed to the UV cure
radiation. In certain applications these “shadowed areas”
mean that the epoxy is applied under a component that is to
be adhered to a substrate. In this situation, the most
efficient means for complete
 cure
is to apply heat 80-150oC) which will completely cure the
epoxy to ensure consistent and uniform adhesive properties.
This is called a dual cure adhesive.
There are two fundamental mechanisms for the UV curing of
epoxy adhesives : free radical and cationic. Cationic cure
mechanisms generally provide less shrinkage, improved
adhesion, and better reliability. Epoxy Technology offers a
large selection of cationic options as well as some free
radical product offerings.
The energy sources for UV light cured epoxy adhesives are
typically medium pressure mercury lamps, electrode-less
vapor lamps, pulsed xenon lamps, LED’ or Lasers. These
generally emit electromagnetic radiation in the region of
200-760nm. They also produce a certain degree of infrared
radiation as heat which acts to anneal the cured epoxy
adhesive (to relieve internal stresses and strains) and to
enhance cure rate in cationic cure systems. Pigmentation and
fillers can block or diffuse the UV radiation. Thus, UV
epoxy adhesives are usually clear or transparent, although
Epoxy Technology, Inc. also offers thixotropic, opaque epoxy
adhesives are designed for minimum and certain screen
printing applications.
Epoxy Technology’s UV cure epoxies provide advantages such
as extremely fast curing rates, single component (no mixing)
chemistries, solventless, accurate alignment of components,
ease of automation, improved production rates and thermal
energy savings over conventional systems (little power
consumption) by the elimination of all or part of curing by
heat.
The selection of an adhesive for a specific application
depends on many factors such as viscosity, postcure strength
and hardness, shrinkage. Tg, the type of surface to be
bonded, surface transparency, bond area and design/geometry.
One must also consider the application method, such as
having the proper viscosity/rheology to accurately dispense
and apply the material. Another important criteria is
refractive index. The refractive index of a material is the
most important property of any optical system that transmits
light. It is also used to calculate the focusing power of
lenses, and the dispersive power of prisms.
 Common
Applications
EPO-TEK UV cure epoxy adhesives are commonly used in a
variety of applications such as encapsulation, glob-tops,
coatings, and bonding.
Specifically they are a fast way to bond fiber (fiber
optics) arrays in a waveguide module in passive alignment.
They are also used in fiber optic pigtailing to diodes where
the UV cure material is used for fiber alignment to the
diode. Some UV cure epoxies with low index of refraction can
be used to channel light down fiber optic cables so that no
light is lost. This is known as fiber cladding. OG197 is a
primary adhesive used in fiber cladding.
Many UV cure epoxy adhesives cure in a matter of seconds or
minutes, have good temperature resistance and excellent
chemical resistance, making them ideal for automotive and
hostile environments. These epoxies are dry to touch after
cure and exhibit low shrinkage resulting in low stress on
delicate surfaces. Low water absorption and very low
outgassing make them ideal for electronic applications.
Several UV cure epoxy adhesives are non-toxic (meeting USP
Class VI biocompatibility standards), making them especially
suitable for implantable medical devices. These UV cure
epoxy adhesives have a reliability record for use across a
wide spectrum of medical device applications. Medical device
fabrication includes assembling dental hand tools and
connecting the balloon to catheter in a balloon angioplasty.
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