Vinyl Resins

24
Formulation of Pigmented Coatings
Pigments are selected for hiding power, ultraviolet
protection, purity, and ease of wetting. Although most
commercially-available pigments are suitable for use
with UCAR® Solution Vinyl Resins, there are some general
constraints. Additionally, there are specific constraints that
apply to UCAR Carboxyl-Modified Solution Vinyl Resins.
Do not use natural iron oxide pigments with any
UCAR Solution Vinyl Resin. These pigments contain trace
impurities that can gel the coating or cause discoloration
or excessive chalking of the film. Do not use ironcontaining
pigments, such as Prussian blue or the socalled
“chrome greens” (blends of Prussian blue and lead
chromate). Chromium oxide green, however, performs
well with UCAR Solution Vinyl Resins.
When an iron oxide pigment is desired, use synthetic
iron oxides; they perform well with UCAR Solution Vinyl
Resins. With coatings containing synthetic iron oxides,
use a heat stabilizer, particularly when bake temperatures
may reach 248ºF (120ºC).
Gold bronze metallic pigments are powdered alloys
of copper and zinc. They tend to react with vinyl, causing
color development and gellation. When used to make
gold inks, the powder is stirred into the ink vehicle shortly
before use, and quantities sufficient for the job at hand
are prepared.
There is a minimum amount of pigment that must
be used to impart opacity to ultraviolet light. For example,
about 65 parts of titanium dioxide (TiO 2 ) per 100 parts of
vinyl resin is the minimum amount that should be used.
To obtain maximum hiding power in thin films, about
125 parts TiO 2 per 100 parts of vinyl resin is a practical
maximum concentration. Exceeding this level can cause
excessive chalking. If color pigments are desired, they
can generally be substituted for TiO 2 at an equal volume
replacement. There are exceptions; ultra-fine particle
size pigments, for example, are used at much lower
concentrations.
The use of extender pigments or fillers will help
improve the economics of the formulation. They will
also help prevent sagging of thick wet films on vertical
surfaces, will help control gloss (flatting) at low levels,
and will permit greater film thickness per coat. Talcs,
clays, barytes, and silicas may be used as extender
pigments. If they are used, they will contribute little to
ultraviolet absorption. A sufficient quantity of ultravioletlight-absorbing
prime pigment must be included in
the formulation.
Table 7 provides a listing of pigment types and
loadings typically recommended for UCAR Vinyl
Copolymer and Hydroxyl-Modified Vinyl Resins.
Formulation with UCAR Carboxyl-Modified
Vinyl Resins VMCH, VMCC, and VMCA involves special
considerations. The carboxyl groups of these products are
randomly spaced along the polymer chain and will react
with basic materials to form irreversible gels or increased
consistency of pigment-vinyl combinations. Do not use
basic pigments, extenders, or fillers with UCAR Carboxyl-
Modified Vinyl Resins. Particularly, avoid lead-containing
pigments (red lead, chrome yellow, chrome orange), zinc
dust or zinc oxide, strontium-containing pigments, and
calcium carbonate. Do not even use small amounts of
these basic materials in pigment blends. With minor
proportions of basic pigments, viscosity aberrations may
not be predictable; some batches may have a normal
viscosity and others will gel. Table 8 lists pigments typically
used with UCAR Carboxyl-Modified Vinyl Resins.