Brushstrokes - October 2011 - Surface Coatings Association of New ...

Table 2. WB2K formulations.
Component Raw material Weight
Clear varnish White paint
Polyol
emulsion
51.41 36.37
Wetting
additives
0.52 0.36
Base
High shear
thickener
2.70 1.91
Defoamer variable variable
Hardener
Diluents
Properties
Demineralized
water
13.73 11.86
Mill base
HDI/IPDI
- 27.11
based
hydrophilic
isocyanate
HDI based
9.85 6.97
hydrophilic
isocyanate
8.66 6.12
Co-solvents* 5.82 4.12
Demineralized
water
7.31 5.18
Density (kg/l) 1.04 1.22
Volume solids
(%)
38.9 38.9
Weight solids
(%)
42.3 50.5
VOC ready to
use (g/l)
87 73
NCO/OH ratio 1.25 1.25
* co-solvent mixture consisting of butyl acetate:dipropylene glycol
dimethyl ether:butyldiglycol acetate in a ratio of 13/74/13.
In the base for the clear varnish formulation given in table 2,
a number of different defoamer types were added at different
concentration levels.
All varnish samples were subjected to a foam test that is
carried out as follows: the coating is applied with a pipette to
the white part of a black-white paper contrast chart. After that,
Table 3. Results for the foam test in a clear varnish.
14 SURFACE COATINGS ASSOCIATION OF NEW ZEALAND
coating is applied to half of the black part of the chart using a
brush. The varnish on the white chart is stipulated intensively
with the brush to incorporate a lot of air. This varnish is then
brushed over the second half of the black part of the chart. The
amount of foam in the two black parts of the chart is judged
after drying overnight according to a scale of one (bad) to five
(good). Also the clarity of the varnish applied onto glass was
judged after drying. The results are given in table 3.
In the foaming test the defoamers based on a mixture of
hydrophobic solids and polysiloxanes and the polyether siloxane
defoamer perform well both at high and low addition levels.
However the first type does introduce a strong orange peel
effect in the dried film, even at low concentrations. Also this
defoamer has a negative influence on the clarity of the film.
The polyether siloxane defoamer also introduces a slight orange
peel effect, but at low concentrations this is judged to be
acceptable. The defoamer based on the mixture of polymers
and hydrophobic solids is somewhat less effective but has
no effect on gloss and haze. At the lower addition level, no
negative effect on the leveling properties was observed.
In order to verify if these defoamers also worked in pigmented
systems, additional tests were performed using the defoamers
at the lowest addition level. Gloss and haze values were
measured for both brush and roller application and are given in
Defoamer Addition level Before After Orange peel Clarity on glass Gloss*
(20°)
None none 2 1 none OK 84 24
Mixture of hydrophobic solids
and polysiloxanes
Mixture of polymers and
hydrophobic solids
Polyether siloxane copolymer
* applied by brush low=0,17 wt%, high=0,34 wt%
Figure 4. Gloss and haze values for different defoamer types.
Haze*
low 5 5 yes NOK 76 93
high 5 5 yes NOK 82 39
low 4 4 none OK 84 20
high 5 4.5 none OK 83 28
low 5 5 slight OK 84 22
high 5 5 yes OK 84 24