All types of holograms
(DOVIDs) are a collection of microscopic peaks and valleys (interference
patterns) on the plate surface. The holographic interference pattern can
be recorded in a photoresist that after development contains the pattern
as a microscopic surface relief. From this relief pattern a nickel
replica is derived by electroplating. Thin nickel replica is used to
press this surface pattern into a plastic foil at an elevated
temperature. This process is called hologram embossing. The embossed
pattern in the foil is provided with a very thin reflective layer of
aluminum or another metal, like gold or chromium, which transforms the
transmission hologram into a reflection hologram. In spite of the
thinness of the metal layer, such embossed reflection holograms are
completely opaque. Semitransparent alternatives can be achieved by the
application of high-refractive-index layer (ZnSe, TiO2) as
well as partially metallized layers, which render so-called
semitransparent overlays or see-through holograms.
Holograms can be
applied to a product as an adhesive label, hot-stamped onto an item,
used as a thread or tape, or used as an over-laminate of a product.
The production of
holograms gets through the following steps:
Origination
The first step is
making the original hologram image called Master hologram. This process
differs holography production from standard printing processes. The
process needs special optical equipment, which records original image
onto photo-resist. After developing glass plate with photo-resist, the
result is Master hologram.
Electroforming and
recombining
Electroforming - the
process converts image from photo-resist or plastic to metal (nickel).
Recombining - the process of multiplying a single image from nickel
original to plastic base.
Step by step:
Converting image
from photo-resist to nickel;
Multiplying a single image from a nickel original to a plastic base;
Converting multiple images from plastic to nickel. This product is
called a Master shim;
After that the Master shim is used as an original for the reproduction
of Work shims.
Work shims are used as
instruments for embossing holograms.
Electroforming and
recombining is a complete prepress process for mass production of
holograms.
Embossing and
finishing operations
Embossing is a kind of
printing process where by means of high pressure and temperature
micro-relief from Work nickel shim transforms to base materials (foils).
In security holography base materials are special multilayer foils.
After embossing, depending on the end product, embossed foil gets
through some additional operations: laminating, die cutting, coating,
slitting, and rewinding.
End products can be:
Self-adhesive
labels;
Hot stamping foil;
Laminate.
Special operations
For high security applications are known different additional steps like
numbering and selective demetallisation.
Short History
Applications