Page 54 - Handbook of Surface Improvement and Modification

3.4 Durability of gloss 49

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gloss above 190 GU measured at 60°. A UV-curable, metallic, decorative composition
contains metallic pigment particles, an acrylate oligomer and or monomer, initiator, and
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cure accelerator (tertiary amine).
Printable, radiation-curable barrier coating has high gloss because it is composed of
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high level of solids approaching 100% of non-volatile solids.
For coating having high gloss, the average particle size ranging from 1 to 200 nm is
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preferred in formulation of anti-fingerprint coating composition.
Nail enhancement is thought to date back to the Incas, who decorated their finger-
th
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nails with different tints, paints, and even pictures of animals. By the turn of the 19 cen-
tury, simple painting of the nail was not as desirable as having polished nails with a glossy
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varnish finish. This was achieved by tinting the nails with scented red oils and then buff-
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ing with chamois cloth to achieve the final polished and shiny appearance. In 1920, high
gloss lacquer automobile paint was created, which inspired the introduction of colored nail
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polish. The currently used nail coatings must have chipping resistance and high gloss.
For high gloss trim paints, the weight percent of binder is typically in the range of 30
to 40 wt%; for the semi-gloss 15 to 25 wt%; for satin and flat paints, the range is typically
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from 5 to 10 wt%, based on the weight of the formulation.
The above examples show that glossiness depends on several factors such as mor-
phological (smooth surface, low roughness, low pigment level, lack of pigment particles
protruding binder surface, relaxation of internal stress above glass transition temperature,
and lack of formation or releasing gaseous products), compositional (non-volatile compo-
nents, high percentage of binder, rheological properties of binder which improve levelling,
metallic pigments, addition of waxes and polymers which migrate to surface and form
smooth surface), or mechanical abrasion (polishing, sanding, or buffing). The mechanical
abrasion can only be effective for harder materials and it is not suitable for materials
which have thermoplastic properties at temperature of abrasion process. For thermoplastic
materials, thermoforming in contact with a glossy surface can be used as it helps to
smooth surface imperfections by equilibration.
The above information shows that gloss is a phenomenon related to the surface. It
can be easily changed if surface properties are changed. This is a subject of discussion in
the next section.

3.4 DURABILITY OF GLOSS
Full account of studies on material degradation can be found in the monographic source
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fully devoted to material weathering − Handbook of Material Weathering. Here, we
are to discuss only a few examples illustrating effects of abrasion, thermal energy, and
weathering on gloss.
Studies of the effect of toothbrush action on dentures and impact resistance of nail
polish were already mentioned in the previous section as actions which may affect glossy
surfaces. Polishing and buffing give best results on metals because they remove products
of metal oxidation which results in smoothing the surfaces and increasing their uniformity.
Scratch and mar resistance are well-recognized factors in the performance of automotive
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coatings. The scratch visibility is slightly increased for high gloss samples which likely
results from a stronger specular reflection by the glossy samples, which increases sensitiv-
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ity to defects of human eyes. Similar is the effect of gloss on mar visibility which