
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. |