Bog'liq Automotive Coatings Formulation Ulrich Poth - Chemistry, Physics und Practices (2008, Vincentz Network) - libgen.li
4 Repair coatings The task of repair coatings is to rectify application failures of the OEM coating process or to
reproduce the coating layers after damage to car body substrates. This means reproducing on
one hand the colour, effect, and appearance of the original coating layers and on the other the
resistance properties of the original OEM coating. Nevertheless, because the application condi-
tions under which repairs are performed are different, other paint materials must be chosen
for repair coatings. While the primary goal of OEM coatings is to throughput high numbers
of pieces in a given time and obtain high ‘first-run-OK’ rates, the goal of repair coatings is to
faithfully reproduce the colour and effect of original coating layers. In most cases, more time
is available for meeting this requirement. Unlike the OEM coating process, repair coating
involves many manual interventions for meeting this demand. With the exception of manual
application of repair putties, pneumatic spraying is used exclusively for all repair coating
materials. The second reason for choosing other coating systems over OEM coating systems is
that repair coating is performed on a fully accessorised car (fitted with interior parts, electronic
equipment, engine and tyres). Exceptions here are attached car body parts, which may be
coated separately. Since fully accessorised cars allow heating temperatures of 80 °C at most,
it is impossible to use stoving coatings for repair coatings. Repair coatings are therefore physi-
cally drying systems or oxidatively drying paints, or they contain a resin combination which
crosslinks at ambient temperatures. Currently the most important repair coating materials
are two-component systems that react at ambient temperatures to form films having optimum
resistance properties. The two components must be delivered separately and the pot life must
be taken into consideration.
Repair coatings are mainly used in properly equipped repair shops or paint shops (“after-
market repairs”). They also find application during car production (in-line repairs), whenever
it is necessary to rectify coating flaws after OEM coating. If the car body has not been further
accessorised, it can be returned to the application line and OEM-coated again with the same
materials. Alternatively, it is transported to a separate special repair line. It is possible in this
line to apply the OEM coating systems. However, since conventional stoving temperatures are
usually unavailable, they must be catalytically crosslinked at lower temperatures (e.g. 60 to
80 °C). They may also be cured with IR radiation. The second possibility is to use the same
materials that are used in the repair shops.
Repair coatings for the do-it-yourself market are also available. As home users do not have spray
equipment, the DIY repair paints are supplied in aerosol cans. Manufacturers of such repair
paints offer very large series of most automotive topcoat colour shades in use, ready mixed and
filled into aerosol cans. These kinds of repair paints mainly contain physically drying resin
systems, for example acrylic resins (TPA). Water-borne aerosol paints are now also available,
mostly containing aqueous polyurethane dispersions in combination with acrylic dispersions.
Some companies specialise in the production and supply of aerosol paints.
VOC regulations for repair coatings relate to the paint itself – in contrast to the regulation for
OEM coating, which is related to consumption per unit time. This means that the paints may
contain limited quantities of solvent in a paint system of application viscosity (grammes solvent
per volume). The limitation varies from region to region. For the EU, for example, new limits
came into force on 1 January 2007
[163]
which mainly affect the composition of solvent-borne
repair paints.
Repair coatings
