SCHOTT Technical Glasses

40
8.5 Anti-reflective glasses for technical
applications (CONTURAN ® /DARO)
8.5.1. CONTURAN ®
CONTURAN ® is an anti-reflective coating on both surfaces
based on optical interference coatings, which can be used
for technical applications i.e. front panels of visual display
units, televisions, display panels, public displays.
The multilayer coating is applied by way of a sol gel process
that uses dip coating technology. As shown in Fig. 32a, three
different layers are subsequently formed simultaneously on
both surfaces of the glass. The refractive index of the layers
is varied by the composition of the sol gel solution. SiO 2 is
used as a low index material and TiO 2 for the high refractive
index. In standard float glass, without an interference coating,
about 8 % of light is reflected backwards to the observer
(Fig. 32b, lower picture). The interference coating creates a
design, which reduces reflecting light waves significantly.
As shown in Fig. 32b, less than 1 % of light is now reflected.
This reduction of the reflection leads to an enhanced contrast
for pictures or displays behind CONTURAN ® cover plates.
The coating is designed to reduce the reflection in the visual
wavelength region of approximately 400 to 700 nm. Fig. 33
shows the reflection curve for two distinctive coating designs
used in the CONTURAN ® product portfolio. The “green
hue” coating is a design used in standard optics. The “blue
hue” coating yields a distinct residual blue reflection often
desired in technical, design-oriented applications.
Reflectance ρ in % ––>
10.0
8.0
6.0
4.0
2.0
0.0
425 450 475 500 525 550 575 600 625 650 675 700
Wavelength in nm ––>
Clear float glass (standard) Green anti-reflective coating
Blue-violet anti-reflective coating
Fig. 33. Reflection spectrum of CONTURAN ® : Comparison of “blue hue”
and “green hue” reflection
8.5.2. Applications of CONTURAN ®
Mineral-based cover plates are often used in display applications
to protect the display from mechanical damage.
However, the reflection of light on the glass reduces the
contrast of the display, especially when used outdoors. One
of the most obvious examples is the usage of smartphone
outdoors, where the excellent display performance often is
completely wiped out by the sunlight. CONTURAN ® with
its low reflection is exactly designed to maintain the contrast
of the display by reducing undesired reflections. Popular
examples for applications are automotive displays, public
displays and professional displays used for automatization.
CONTURAN ®
SiO
Absorptance in the glass
2
~ 1 %
TiO 2
Exposure
SiO 2 +
to light
TiO 2
100 %
Glass substrate
SiO 2 +
Transmittance
TiO 2
TiO 2
> 98 %
< 1 %
Reflectance
Standard float glass
Absorptance in the glass
~ 1 %
Exposure
to light
100 %
Transmittance
~ 91 %
~ 8 %
Reflectance
Fig. 32a. Three layer coating design
Fig. 32b. Effect of anti-reflective coatings on the reflection of light