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Primer surfacers
For the objects described here, primer surfacers must be applied where high film thickness is
required for obtaining optimum barrier effects to improve corrosion resistance, or if the entire
coating structure has to be especially smooth, which is mostly the case for decorative effects. In
all other cases, the topcoats are applied directly to the primer.
Suitable primer surfacers here are two-component systems; the compositions are comparable to
those of primer surfacers for repair coatings (see Chapter 4.4). The primer surfacers contain satu-
rated polyesters and specific quantities of epoxy resins while the crosslinkers are polyisocyanate
adducts. Since such primer surfacers are occasionally also applied to bare metal parts (e.g. on
through-sanded parts, joints, bolts and rivets), they must also provide some corrosion protection;
that is the reason for using specific quantities of epoxy resin. They also contain some passive
corrosion-protection pigments.
For some coating structures, the primer surfacers are recoated with topcoats after just a short
flash-off time (wet-on-wet application). For small vehicle parts, there are water-borne stoving
primer surfacers available that are based on polyesters and contain amino resins as binders (see
Chapter 3.5.6).
Topcoats
For the application of topcoats to heavy vehicles, the products used are comparable to topcoat
systems for repair coatings. These are two-component coating systems consisting of hydroxy-
lic acrylic resins (see Chapter 3.8.3.1), which are crosslinked by polyisocyanate adducts (see
Chapter 3.8.3.4). To comply with VOC regulations mainly in Europe, high-solids systems and
also water-borne two-component paints are available. For high-solids topcoats, low-molecular
weight, low-viscosity acrylic resins and also low-viscosity aliphatic polyisocyanate adducts
are chosen, mostly those with a small molecular weight distribution or oligomers containing
allophanates. Resins for water-borne topcoats are secondary acrylic dispersions while the
crosslinkers are low-viscosity polyisocyanate adducts or polyisocyanate adducts containing
hydrophilic modifications. Both must lend themselves readily to homogenisation into the entire
coating system. As already described, it is necessary in these cases to bear the side-reaction
of isocyanates with water in mind, by adding excess polyisocyanate (the hardener), in terms
of stoichiometric ratios.
Only a few of the objects described here are coated by two-layer topcoat systems comprising
basecoat and clearcoat. In those cases, water-borne basecoats and high-solid two-component
clearcoats are used. Effect basecoats and clearcoats can also be applied. Such decorative con-
siderations for heavy vehicles are needed where companies seek to identify their vehicles, for
example, in their own livery colours. There are also coloured topcoats available for inscriptions
and company logos. Such inscriptions are also prepared using adhesive foils. Only when large
areas of coloured or effect designs are required is it necessary to use coating materials. In
that event, application is carried out by spraying and masking those parts which are not to be
coated.
As already mentioned, the entire coating process is arranged such that the parts are primed
separately first. Then the vehicle is assembled as necessary, followed by application of putties to
those parts or areas that require them. This may be followed by application of the primer surfacer
and a sanding process. After that, the topcoats and, in special cases, other decorative elements
are applied. For topcoats and decorative elements, the vehicle producers follow the wishes and
requirements of the ordering customer. There are also vehicle parts which are coated completely
before full assembly, for example with electro deposition primers, and powder topcoats applied
by electrostatic powder spray equipment.
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Plastic parts on heavy vehicles, for example, driver’s cabs, are coated with the same paint prod-
ucts as are used for attached parts for passenger cars (see Chapter 5.2). In addition, it must be
pointed out that many other parts and building elements on vehicles have to be coated that have
not been mentioned so far.
Examples of other coatings on automobiles are those for engine housings, oil pans, axle suspen-
sion parts, carburettor lids, compressors, brake housings, battery housings, fuel tanks, exhaust
pipes, cooling equipment, condensers, and heating equipment. Where aluminium or plastic is
used for the construction of such parts, it is not usual to coat them. The coating of such parts is
the responsibility of the parts producers. There are many products which have been formulated
to meet the properties and intended usage of the parts. These coating materials are not classified
as automotive coatings, but rather as general industrial coatings.
Coatings for heavy loader
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Alternatives and outlook
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