Types of paint
15.1 General
One
of the most effective ways of protecting metals against the influence of
climate is the application of a coating or paint system. Various types of paint
can be used to realize this. In order to make an appropriate choice from the
various types of paint available, it is necessary to have some insight into the
characteristics of the various paint types. A great many different types of
paint are available, and only the most important types will be described here.
The various paints will be classified according to the type of binder used, as
the binding agent largely determines the characteristics of the paint.
15.2 Alkyd paint
This
group of paints is often referred to synthetic paint or alkyd paint. They are
one of the most popular types, and hardening of the paint film is the result of
oxygen absorption. Alkyd paints are used practically everywhere, as they are
extremely versatile. They are used in the house painting sector, construction
sector and for ship coatings.
Generally
speaking, alkyd paints have the following characteristics:
durable
good flow characteristics
fast drying
good gloss retention
good elasticity
reasonably good corrosion control
15.3 Baking finish
This
group consists of paints which are heated to accelerate the curing or hardening
process. Most baking finishes consist of a melamine resin together with an
alkyd resin or polyester. These products are very suitable for use in
industrial mass production processes. Generally speaking, they are hard and
wear-resistant.
The
combination of alkyd resin and melamine resin produces the following
characteristics:
scratch-resistant
durable
good hardness
water-resistant
good chemical resistance
15.4 Acrylic paint
A
solution of an acrylic resin is very suitable for serving as a binder whereby
the drying process is a physical one. Evaporation of the solvent simply leaves
a paint film behind. An important advantage of these so-called thermoplastic
acrylic resins is that they dry quickly at room temperature. As a result, these
products are suitable for applications in which a fast drying process is
desired but raising the temperature is not possible. These products are also
used for car repair paints and concrete paints.
15.5 Chlorinated rubber paint
Chlorinated
rubber paints are used whenever resistance to chemicals is important. These
paints are very popular in the shipbuilding sector, for above-water and
underwater components, power pylons and bridges.
Chlorinated
rubber paints have the following characteristics:
water-resistant
resistant to chemicals
easy to apply
single-component
elastic paint film
15.6 Vinyl paint
Vinyl
paints also have good chemical resistance. Their drying properties depend upon
evaporation, and they are suitable for use in single-layer systems.
Vinyl
paints have the following characteristics:
wear-resistant
water-resistant
good adhesion on metal surfaces
good chemical resistance
One
specific type of vinyl paint is a product made on the basis of polyvinylbutyral.
This type of paints shows excellent adhesion to many different kinds of
surfaces and is therefore also used in formulating glues. They are also well
known for their use in so-called washprimers.
15.7 Two-component epoxy paints
Two-component
paints are products which must be mixed together with a curing agent just
before use. After mixing, the paint is usable for a short period of time i.e.
the so-called pot life. Epoxy paints can react with various types of curing
agents. The type of curing agent used will affect the final characteristics of
the epoxy paint coating. Generally speaking, these paints provide coatings with
excellent characteristics.
Epoxy
paints have the following characteristics:
hardness
good adhesion on metals
very good chemical resistance
very good water resistance
A
disadvantage of epoxy paints for outdoor applications is that, over time, part
of the outer layer turns into powder, thereby losing its glossy finish. One
cause of this is that the polymer is broken down by sunlight over time. As a
result, epoxy paints are most suited for use in base primers and in finish
coatings in combination with micaceous iron oxide.
15.8 Polyurethane paint
Polyurethane
paints are mostly two-component products, whereby the primary component is
mixed together with a curing agent shortly before use. There are two important
types of polyurethane paints, the aliphatic and aromatic polyurethane paints.
The most important difference between these two types is that the aromatic type
is subject to yellowing over time whereas the aliphatic type is not. Besides
the two-component versions, there are also single-component polyurethane
paints, the so-called moisture-curing polyurethane paints which use moisture
for the curing or hardening process.
There
are many possibilities for formulating polyurethane paints, which is why there
are many types on the market, which can also differ markedly in characteristics.
Some
important characteristics of these paints are:
hardness and wear-resistance
resistance to water and chemicals
excellent overall adhesion
fast drying
