Canadian Finishing & Coatings Manufacturing Magazine - May/June 2023 - 38

PAINT AND COATINGS MANUFACTURING: WATERBORNE PIGMENTS
and disperse, as well as transparent oxide reds and yellows.
There are a variety of horizontal and vertical mills or basket
mills that have been optimised over the years to achieve faster
and more efficient dispersions and at the same time better
quality in terms of colour development and tint strength. On
the other hand, advances in the technology of the additives
used as surfactants, dispersants and anti-settling agents
have been crucial to significantly improve the stability of
the dispersions of the different pigments used in the paint
industry.
Can a pigment remain consistent or does it fade as the
pigment molecules deteriorate?
EM: There are many factors that can cause colour deterioration
in paints, and they are not only related to pigments. It is true
that not all pigments have the same durability. Some pigment
chemistries are more vulnerable to the effects of sunlight
than others. For example, when it comes to exterior paints,
there are pigments with excellent resistance to weathering
such as inorganic yellow and red iron oxides, and others with
limited resistance such as certain organic reds and yellows
whose use is not recommended outdoors. But there are other
components that can compromise the integrity of the colour,
such as the sunlight and water resistance of the resin used,
the PVC (pigment concentration by volume) of the paint, the
characteristics of the substrate, the use or not of ultraviolet
light absorbers, and others.
The degradation of pigments and resins in exterior paints
is caused mainly by the ultraviolet fraction of sunlight, which
is of high energy, and can break the bonds of both polymers
and pigments, producing discoloration, chalking, severe
loss of gloss, cracking and even delamination. The hiding
power of the pigments normally has a protective effect both
on the resin and on the substrate, blocking the penetration
of sunlight, but if the pigments used, such as some organic
reds and yellows already mentioned, are more chemically
vulnerable to ultraviolet rays, colour degradation will occur.
DL: Colour is determined by three elements-a light source,
a receptor (e.g., the eye) and an object that transmits a
wavelength. It is a misconception that colourants are
individual particles. Instead, they are agglomerates, albeit
quite small of discrete dispersed size. Applying the coating
that contains colourants is half of the chemistry of creating the
coating system. Depending on the chemistry, some pigments
naturally fade under direct sunlight without any protection
and OEM coating formulators know which combination of
specialty chemicals (e.g., UV absorbers, light stabilizers)
keep that colour looking new. BASF's rigorous pigment
qualification process ensures the pigments used have the
target durability that the automotive market demands.
How do pigments respond to certain forms of light?
EM: It is an intrinsic characteristic of pigments to produce
a different colour response depending on the type of light
they receive. All pigments have this characteristic. It is a very
important colour property in the colour matching process.
When a colour is to be matched to a particular standard, the
only way to guarantee that the two colours, the standard and
the match, will look the same as each other under different
lighting is to use the same pigments in the match (i.e., the
same pigment chemistry) that were used in the original
standard. If pigments of different chemistry are used in the
match, the two colours may look the same under one type of
light (say, morning sunlight) but different under another light
(afternoon light, or fluorescent, or other). It is the well-known
phenomenon of metamerism.
How long will the molecules take exposure to sunlight and
have there been recent advancements?
EM: The durability of the pigments outdoors will depend
on their chemistry, as previously stated. Inorganic pigments
(titanium dioxide, red and yellow iron oxides, titanates, and
others) are highly stable to sunlight, unlike many organic
pigments, which have chemical bonds that can be broken by
UV rays. Of course, even within the organic pigment family,
there are chemistries that are more resistant than others
and can be used in exterior paints. Pigment manufacturers
offer red, yellow, green, blue, magenta-and other-organic
pigment variants of high purity and tint strength that can
be used satisfactorily in exterior paints. Normally the most
resistant are also the most expensive.
DL: It is relative how much UV stabiliser is needed for OEM
paint. Vehicles are the second largest consumer purchase
besides a house, and consumers don't refresh car paint as
often as they might refresh their house paint. Fortunately,
the sunlight protection offerings on the market combined
with automotive paint chemistry know-how and advance
weathering and predictive methods overcome durability
issues.
" Colour is determined by three elements-a
light source, a receptor (e.g., the eye) and
an object that transmits a wavelength. It
is a misconception that colourants are
individual particles. Instead, they are
agglomerates, albeit quite small of discrete
dispersed size. "
- Diane Langer
38
www.cfcm.ca
http://www.cfcm.ca
Canadian Finishing & Coatings Manufacturing Magazine - May/June 2023

Table of Contents for the Digital Edition of Canadian Finishing & Coatings Manufacturing Magazine - May/June 2023
