Page 50 - Handbook of Surface Improvement and Modification

3.1 Gloss perception 45

Majority of practical measurements and studies are done with the use of a method
4
based on the international standard. The method is suitable for the gloss measurement of
4
non-textured coatings on the plane, opaque substrates. The glossmeter measures the ratio
of the gloss of a coating and the gloss of a polished plane of glass plate with specified ref-
4
erence refractive index. Different angles are used for different surfaces, as follows 20° for
high-gloss surfaces; 60° for semigloss surfaces; 85° for matt surfaces. 4
It should be noted that many interferences caused by a sample condition can be
expected such as the effects of surface roughness, ghost marks, and humidity.
The effect of mesoscale (e.g., surface bumpiness) and microscale (roughness on the
sub-pixel level, which cannot be observed directly from the surface shape, but can only be
perceived from the reflections from surfaces) roughness on perceived gloss has been stud-
5
5
ied. Both roughness parameters significantly affected perceived gloss. Their additive
model did not adequately described their mutually interactive and nonlinear influence. 5
5
The perceived gloss was well predicted using a linear model.
The injection-molded automotive
parts have many surface defects, such as
black lines, flow marks, ghost marks, jet
lines, shrinkage, silver lines, sink marks,
6
yellowing, and weld lines. Ghost marks
are distinguishable because they refract
light from nearby surfaces differently than
6
other defects do. The ghost mark is visible
in Figure 3.2 (left) but invisible in Figure
Figure 3.2. Ghost marks as seen from different viewing 3.2 (right) because of differences in illumi-
6
angles. [Adapted, by permission, from Su, H-Y; Nian, nation. Ghost marks are caused by nonuni-
S-C; Huang, M-S, Int. Commun. Heat Mass Transfer, form shrinkage, which is particularly
66, 1-10, 2015.]
substantial under a high degree of pattern
6
orientation and large thickness.
The effect of the air temperature, relative humidity, and air velocity on the surface
7
gloss of one component waterborne wood top coating was studied. Surface gloss
increases as the air temperature and the relative humidity increase, whereas decreases as
7
the air velocity decreases. The relative humidity had the most pronounced effect of
7
gloss.