|
Making
paints durable takes an understanding of chemistry
and additional cost.
Durability
against the suns UV radiation, against the weather
elements, against knocks and bumps, against
temperature fluctuations that cause surfaces to
expand and contract, against bacteria that feed on
and weaken paint, against mildew and other
biological activity and against the impact of a
number of air and rain born pollutants are all
essential.
Translated
into paint characteristics, the paint needs to have a
well formed (coalesced) film and high adhesion, must
be flexible, tough but not brittle, colour-fast,
water resistant, dirt resistant and must have
components that are not sensitive to UV-radiation as
well as agents that protect it from this radiation.
A good degree of alkali durability is required for
primers that are painted directly onto plasters or
cement.
Paints for
different applications require the various
properties to differing degrees. Exterior Paints
need high UV resistance and those that have this
cost more. Generally Interior Paints should either
have high scrub resistance (for cleaning and damage
resistance) and/or be stain resistant. Good matt
paints should be scrub resistant while good sheen
paints should be stain resistant.
Paint
chemistry is complex so the following are just a few
pointers:
-
More binder generally makes paint
more durable. This can be measured
by the PVC (pigment volume
concentration). A lower PVC % means
higher binder level.
-
Binder type is critical. Some
binders are sensitive to
UV-radiation. Binder selection also
influences toughness, hardness,
brittleness and flexibility.
-
More TiO2
(titanium dioxide) gives more UV
resistance to white and lightly
tinted paints. In deep colours the
colourant should perform the same
role.
-
The numerous minor paint additives
used can have a major impact on
properties such as water resistance
so their selection is important.
|
|