Finishing - July-August 2022

38 FILMS
All on film
White films are used in many
applications including packaging,
pharmaceutical, solar reflectors and
farming. Furthermore, white films are also
used as back reflectors that are critical for
silicon thin film solar cells and as energy
efficient ‘cool roofing’ membranes to reflect at
least 85% of sunlight back into the sky to
keep the building cooled during summer
time. Opal frosted window white films are
used for added privacy to give a frosted
appearance to the glass.
White coloured flexible films are mainly
produced by using white pigments of titanium
dioxide (TiO2). Titanium Dioxide pigments are
used because it scatters visible light, thereby
imparting whiteness, brightness and opacity
when incorporated into a coating. Titanium
dioxide is commercially available in two crystal
structures—anatase and rutile. Rutile TiO2
pigments are preferred because they scatter
light more efficiently, are more stable and are
more durable than anatase pigments. Usually
spherically shaped non-absorbing, high
refractive index titanium dioxide powders are
used in the manufacturing of white films.
However the use of TiO2 carries a high
environmental burden, health concerns and
high carbon footprint. Furthermore, recent
studies have raised safety concerns on its
extensive use in formulations indicating the
need for more compatible alternatives.
Idvac Ltd., a UK vacuum R&D specialist, is
introducing a new innovative product of
bright, non- pigmented metallized white films
which can be used for many applications. No
TiO2 or other pigments are used. The bright
white metallized film has an excellent
scattering performance across the visible
electromagnetic spectrum.
Idvac new development process represents
a new approach to manufacture aesthetically
appealing bright white metallized films
without using pigments such as TiO2. The
process involved the utilisation of a special low
refractive index polymer which is transparent
when applied as a thin coating onto flexible
films. However, the polymer changes its colour
and opacity to white following the vacuum
metallizing of aluminium. The
Aluminium/Polymer reaction results in light
scattering from the film surface to give the
white colour. The aluminium can be applied
using thermal, sputtering or electron beam
evaporation techniques. Idvac special polymer
can be applied or printed on flexible films
using standard coating machine such as
gravure or flexo printing. Final product has a
bright white metallized finish on front and
back surfaces of the film. In this process no
pigments are used. Flexible films such as PET,
BOPP, Polycarbonate (PC), etc. can be coated
with this new white metallized finish. Idvac
white film can be hot stamped for some
applications to give white bright finish.
The main features of this new white
metallized coating are:
1. No pigments are used.
2. The polymer can be applied onto flexible
films using conventional printing machines
such as gravure, flexo, etc.
3. Aluminium metallization is done inside
standard vacuum R2R metallizers. No
modification is required.
4. The white coating is thin and has a
smooth bright finish.
5. UV reflection at 300nm from metallized
side is about 40-65% and can be adjusted to
lower or higher levels.
6. Visible light reflection in wavelength
range of 400-800nm from the metallized side
is about 94%.
7. When applied onto BOPP film, the white
metallized coating exhibit good oxygen (30-
40 cc/m 2 .day) and water (