Page 55 - Handbook of Surface Improvement and Modification

50 Gloss Enhancement

increases for glossy materials. 23
Also, darker materials have higher
23
mar visibility. The fatty amide
slip agent improved both scratch
23
and mar visibility resistance.
Studies on marble may be
used as a good example of thermal
24
effects on gloss. It was found
that the thermal shock influenced
more the marble surface properties
than the thermal aging cycle. 24
The thermal shock cycles affected
Figure 3.3. Gloss loss (60°) versus exposure time of 4 mm thick material by heat but also the pres-
cured resin plaques exposed in different atmospheric conditions in
borosilicate glass vessels and in “direct exposure”. Atlas Weather- ence of water in the pores had an
Ometer Ci65A running according to ISO 4892-2/ASTM G155. effect on surface quality. L* and
24
[Adapted, by permission, from Sampers, J; Hutten, E; Gijsman, P, b* parameters of CIELAB system
Polym. Test., 44, 208-23, 2015.]
were strong indicators for predict-
24
ing gloss loss. L represents
whiteness, b represents yellow-
24
ness and blueness.
Accelerated weathering of
unsaturated polyester resins shows
that gloss loss occurs much later
than discoloration and it is almost
25
absent in inert atmosphere. The
presence of oxygen was found
25
necessary for gloss loss. Mois-
ture is irrelevant for the discolor-
ation process of unsaturated
polyesters but plays a crucial role
in the mechanism of gloss loss. 25
Extraction of photooxidation
products is the main reason for
Figure 3.4. Surface topography of samples weathered in the WOM. gloss loss under weathering condi-
2
The scan size is 10×10 µm . [Adapted, by permission, from Makki, 25
H; Adema, KNS; Hendrix, MMRM; Peters, EAJF; Laven, J; van tions. Increase in relative humid-
der Ven, LGJ; van Benthem, RATM; de With, G, Polym. Deg. Stab., ity from 50% to 100% caused an
122, 180-6, 2015.] increase in the rate of gloss loss. 25
25
Spraying with water significantly enhanced gloss loss rate (Figure 3.3).
The weathering study of a polyester-urethane clearcoat showed that the degradation
26
was a laterally inhomogeneous process. Water facilitates material removal and leads to
26
an increase in the surface roughness and consequently to a gloss loss. Oxidation reac-
26
tions are the main causes of lateral inhomogeneous degradation of coatings. Figure 3.4
26
shows the progress of lateral damage. Large gloss changes were recorded after exposure
for 3500 h but some smaller changes were already observed after 2750 h of exposure. 26
26
And this agrees with observations of the surface damage.