TiO2 Impact on Paint Weather Resistance
TiO2. Secondly, one can increase the amount of energy per photon
by using more energetic light, such as UV-B light. A third method
is increasing the number of photons, or light intensity. This is
done using weatherometers with Xenon lamps (WOM).
Trying to accelerate the degradation is risky, since the different degradation reactions do have varying dependence on light
intensity. The photocatalysis reaction changes with the square
root of the light intensity, whereas the direct degradation of the
resin is directly proportional to the light intensity. This implies
that usage of high intensity UV light will increase the direct resin
degradation more than the photocatalysis. Based on this, we can
already assume that accelerated methods do not necessarily correlate well with true weather exposure.
The best way to accelerate the weather exposure is natural
accelerated exposure (EMMAQUA). In a typical exterior expo-
sure, panels are attached to racks with the painted portion fac-
ing the sun. In the natural accelerated test, panels are mounted
facing away from the sun and towards a bank of mirrors. The
mirrors reflect the sunlight onto the panels. This concentrates
the sunlight, increasing its intensity by a factor of 10 or more.
The advantage of this type of exposure is that the balance be-
tween the different types of UV light is maintained at the same
level as it is found in sunlight, and so we need not be concerned
with unnatural reaction pathways that are initiated by UV-B or
UV-C light. This accelerated test is however not yet well estab-
lished in international standards and will not be further includ-
ed in this study.
Now that we understand the different influences at play
when trying to accelerate weathering, let us look at some examples of weatherability testing, and how TiO2 plays a role.
Experimental Methods
Having a standard method for measuring/assessing durability is
one of the challenges in the coatings industry. Not every paint
application has weathering standards. This study uses two internationally recognized standards for the construction industry.
The first one is the GSB standard (GSB AL 631), using QUV-B as
accelerated method (DIN EN ISO 11507). The second one is the
Figure 1a. Correlation between QUV-B exposure and Florida exposure (
standard class GSB).
Figure 1b. Correlation between QUV-B exposure and Florida exposure (Master
class GSB).
Figure 2a. Correlation between WOM exposure and Florida exposure (class 1
Qualicoat).
Figure 2b. Correlation between WOM exposure and Florida exposure (class 2
Qualicoat).
