Notes on Bonding Holograms
with Norland Optical Adhesives
Bonding cover glasses to holographic plates
is easy with NOA 60 or NOA 61 and it is an excellent way to protect
them against moisture and scratches. The index matching qualities
of these adhesives greatly reduces surface noise.
Which adhesive to use?
Major criteria for deciding on either NOA 60
or NOA 61 is the temperatures you expect the plate to see. NOA
60 can withstand temperatures from -40°C to 60°C and is
suitable for most applications. NOA 61 has extra adhesion to glass
which allows it to withstand the stress of harsher environments.
It can withstand temperatures from -150°C to 125°C and
is recommended for military applications.
Gelatin plates should be completely free of
moisture before they are bonded. Suggested methods are to heat
plates in an oven at 60°C for 10 minutes or to use a hair
dryer and blow hot air on them for 1 to 2 minutes before bonding.
Any moisture that is in the gelatin can eventually rise to the
surface and cause separations.
One of the major advantages of NOA is its long
pot life. This is important when bonding large holographic plates
because it allows you to take as much time as you desire to spread
the adhesive and work out any bubbles.
For small plates a drop of adhesive is applied
to the center of the bottom plate. The top plate is lowered at
an angle and then pressure is applied to work the adhesive to
For large plates (4" x 5" and up)
it may be easier to apply a bead of adhesive from corner to corner
forming an X pattern. Also apply extra into the center of the
X. Now one edge of the top plate is lowered onto the bottom plate
and gradually lowered so the whole plate is in contact. The adhesive
in the corners will spread in the corner areas while the adhesive
in the center will spread out in a circular fashion to the sides.
If care is taken when applying the adhesive
and lowering the plate no bubble should form. Our one ounce bottles
are notorious for forming bubbles on applications from its dropper
tip. If these bottles are used for large plates we recommend removing
the dropper tip and pouring the adhesive out to prevent bubbles.
As preventive maintenance, when the top plate
is lowered, do not press the adhesive out but allow the weight
of the plate to initially spread the adhesive. Inspect for bubbles
at this time. With a thick layer of adhesive you can slide the
edge of the plate over to the air bubble to release it. This is
usually easier than pressing the air bubbles out with the adhesive.
Once the bubbles are removed slight pressure can be applied to
work adhesive to the edges.
Fluorescent black lights are the best light
sources for curing large plates because a group of them can be
arranged to give an even distribution of light. This is important
for even cure, to prevent strains from forming.
It has been noted that NOA may cause a slight
darkening of the silver halide emulsions (field effect) after
bonding. Although the exact mechanism for this is not known, it
has been shown that washing the plates copiously with water after
the bleach process makes a tremendous difference in reducing it.
NOA makes an excellent molding surface in thin layers. It may
have potential in replicating or embossing holograms.
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