To address the problem of soiling and fouling, there are several approaches that can provide guidelines for future development yielding tomorrow’s competitive solutions with improved
bio-fouling and soiling performance:
Scheme 1
• Paint surface hardening
• Prolonged effect of existing biocides
• Novel biocides
• Self-cleaning coating via superhydrophobic mechanism
• Paint erosion
• Weak dirt adhesion
• Minimize nitrogen content in coating
• Reduce oxygen level in water
• Block enzyme activity which enhances micro-organisms
glue production
• Introduce enzymes degrading bio-foulers glue
• Avoid surface recognition
• Use secondary metabolites
• Manipulate the microorganisms communication
• Add a cationic polymer at the surface
This paper elaborates and discusses experimental approaches
of the top three methods and presents results on how to improve
dirt pick-up and bio-fouling performance.
Anti-soiling
As mentioned above the value of a property can decrease if the
painted surface looks dirty. The consumer owning the property
might need to repaint more often which yields costs for material
and labor or is time consuming (if the consumer paints himself).
It is thus an interest from paint companies to make paints which
are more durable against dirt pick-up. The aim of this project
was to understand which factors are important for dirt pick-up;
or – in other words - increase dirt pick-up resistance. For this
purpose we have developed methods in the laboratory to evaluate dirt pick-up and tested several parameters which were expected to influence the soiling. Lab results were compared with
exterior testing.
The dirt pick-up test was based on our industrial experience,
spraying the test panels with an aqueous solution of a model-dirt mixed according to Scheme 1. The dry components were
mixed in a mortar and then the pitch was added and stirred in
manually. 1 g of the dirt was mixed with 1 g butyl glycol and
these 2 g were filled in a spray bottle and filled up with 998 g de-ionized water. The dirt solution was filled into a pressurized
aerosol bottle and sprayed on the samples, set up in a 45° angle,
as shown in Figure 1. The samples were sprayed with the dirt solution for 3 times with one minute between each spraying. The
distance between the spray bottle and the samples was 30-40 cm.
The maximal possible pressure (≈ 3 bar) of the bottle was used
to perform each spraying. After the contamination the samples
were left for 1 day for drying followed by rinsing with de-ionized
water. To evaluate the dirt pick-up of the surfaces, the L- value
(a brightness index) was measured before and after the contamination as well as after rinsing.
Several types of paints
were evaluated with this
setup with various binder
chemistries painted on
metal panels. The painted
panels were tested fresh
and weathered in a
weatherometer (
corresponding to 6 months of
ageing in southern Sweden). ΔL values for 22
samples are shown in Figure 2.
Figure 1
Setup of contamination procedure.
Figure 2: ΔL Values for 22 Paint Formulations after Three
Contamination Cycles.
Formulation 10 and formulation 15 missed on purpose a
cross-linker and were therefore expected to be very tacky with an
expected high dirt pickup. 10w and 15w have probably been
washed away during weathering. The “normal” formulations 20-
65 can roughly be divided into two groups:
(A) high dirt pick-up 55, 55w and 65
(B) moderate dirt pick-up 20, 20w, 25, 25w, 35, 35w, 40,
40w, 45, 45w, 65 w.
To measure the tackiness of the coatings after drying, the adhesion of a hydrophobic silica particle to the surface was measured with AFM colloidal adhesion technique. The probe used
was a silanized, hydrophobic silica particle. We measured the
force needed for the probe to detach from the coating surface.
Thus, it is a measure of the adhesion force and thus the tackiness
www.coatingsworld.com
April 2012
