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The Cholesteric liquid crystal (CLC) pigments are fabricated with CLC
films rather CLC polymers. The polymers are typically cross linked materials
which have their molecules "locked" during the cholesteric phase.
Now this enables the unique and brilliant optical properties of a liquid
crystal to be exploited to the hilt in a solid pigment. Each of the flake in
the pigment is a piece of microfilm in a platelet form. It has dimensions of
around 5 micron in thickness. Cholesteric liquid crystal or CLC polymer film
is kind of naturally reflective polarizer. If the center wavelength is set
in a way, to be within the visible spectra, then it is possible to create
color travel effects through a circular polarized reflection. A typical
structure of CLC structure is given below:
Key Properties of CLCs
For enabling a good special effect pigment, that
is to be derived from a CLC (cholesteric liquid crystal technology), some
sort of modification needs to be done to several properties of CLCs
Optical Properties of CLC Pigments
|Cholesteric Liquid Crystals
||Requirements for Pigment
|Periodic structure (facilitates color travel)
||Temperature Insensitive (Color Fixed)
|Thermochromic (change of color with temperature)
||Fairly Durable Properties wrt temperature, chemical resistance
|Alignment is needed
||Good processing i.e. ease in manufacture is needed
|Highly aromatic nature
A diagram can betterly describe the optical properties of CLC pigments,
such as :
It is to be understood here, that quite unlike the metal interference
systems, CLCs can develop their color reflection through a single layer
Color travelling properties of CLC Pigments
CLC pigments show very good blue-shifting color travel as illustrated in
this graphical representation.
Advantages of CLC Pigments
- As CLC pigments are manufactured using polymeric material, and their
optical properties mostly determined by CLC mixtures only. Features like
control of band width color fine-tuning, special wavelength design, etc.
becomes relatively easier as compared to those using traditional
- CLC pigments are basically circular polarized that can create a
secondary detection mechanism that is very simple.
- In the case of CLC based flakes, center wavelength can be adjusted
with ease thus enabling a vast set of custom products.
- CLC pigments are produced by using a continuous film based
polymerization, this allows for considerable cut in expenditure as
compared to vacuum deposition technologies.
- Every CLC pigment comes with circular polarization, that facilitates
simple detection mechanisms like opposite handedness extinction. This
features is unique to CLC pigments.
- Owing to the periodic structure of CLC films, CLC pigments has in it
a strong color travel effect.
Application of CLC pigments
CLC pigments are increasingly applied as a
deterrence for counterfeit in banknotes, securing documents, and in
authentication processes to protect brand and products. Light that is
reflected from a CLC is circularly polarized, this effect finds very popular
application in security and machine read applications.
Gen Next Developments:-
- A Multilayer CLC system
- Doping of the CLC pigment
- Very High process speeds of 100 ft/min
- Smart Pigments that has controlled shape
- Ultrathin CLC pigments