Car paint
From a technical point of view, the main task of car paint is to protect the sheet metal of vehicles from corrosion .
history
In the early days of the automobile , painting was a lengthy process in which a slowly drying liquid was applied to the body in several layers over several days or even weeks.
Originally, natural varnishes made from resin, linseed oil and turpentine oil were used as solvents. In 1910, Ludwig Berend developed the first oil-soluble synthetic varnish resin which, after the First World War, was considerably improved as a rosin resin (especially faster drying) by the Dr. Kurt Albert GmbH in Mainz-Amöneburg was produced under the name Albertol .
With the start of series production in the 1920s, chemistry also had to speed up, and the quick-drying nitrocellulose lacquers then revolutionized car painting worldwide in the mid-1920s. Although these dried quickly, they required an extensive high-gloss polish.
Therefore, the first alkyd resins were brought onto the market in the USA in 1929 . With these paints, there was no need to polish and they also offered good protection against chemical, mechanical and environmental influences. Large-scale use took place in the 1960s.
In the 1980s and 1990s, mainly 2-component acrylic resins were used as binders. When cross-linked with an isocyanate hardener, they have a long shelf life, good processing, excellent UV protection and high resistance, e.g. B. against fuels , acids , stone chips, etc.
At the same time, water-based paints were used in series production and now also in the repair of cars; Until now, the resins and pigments were always dissolved in solvents . When the organic solvents or water evaporate, resins and pigments are deposited; in two-component systems, these are crosslinked by adding hardeners (usually isocyanates ) and form a hard and resilient surface.
For some years now, powder resins have been used more and more here.
One-component systems such as nitro and alkyd resin paints dry in the air and harden in the process, two-component systems (e.g. acrylic resin-based) only by adding hardeners.
A further distinction is made between single and multi-layer systems. In the single-layer process, only a top coat is applied, which is mixed with a hardener. This is inexpensive, but offers little protection against UV radiation, mechanical stress, etc. Therefore, this method is practically no longer used in the automotive sector. Top coats are still used for painted metal parts in rooms.
In the multi-layer process, the coloring material, the basecoat, is an unprotected pigment layer that dries like water-based paint and also becomes matt. Several layers of basecoat are possible; they are essential for effect paints. Finally, an i. d. Usually two-component clear lacquer is applied, which forms a glossy and high-strength protective layer over the paint layer. Several clearcoat coats are possible for heavily used surfaces. The clear lacquer is clearly superior to the single-layer systems in terms of UV protection, scratch resistance and mechanical protection. Metallic paints are only possible in a multi-layer process.
Red car paint was more prone to fading than any other color.
As an alternative to expensive and thin-film coating is (z. B. with wheels, chassis parts, motorcycle frames) often the powder coating used.
Starting in 1999, the sale of paints with a high solvent content ( volatile organic compounds ) was restricted in the EU and Germany , see Decopaint Directive .
construction
The classic structure of the paint looks like this:
- Pretreatment : The body is sprayed or dipped in various phosphate salt solutions. A crystalline metal-phosphate layer forms .
- Primer : A corrosion protection primer is applied to the phosphated sheet metal, which leads to very good adhesion to the sheet metal and thus prevents or slows down corrosion. Electrolytic deposition can also be used to reliably prime inaccessible corners. (→ KTL coating )
- Filler: The filler has the task of "filling in" any unevenness in the substrate so that they are not subsequently visible in the very thin top coat. In addition to covering the roughness, the filler protects the underlying layer from UV radiation and provides flexibility for so-called stone chip protection.
- Basecoat : The coloring layer, today usually water-thinnable and often with effect pigments, e.g. B. Metallic , pearl effect, color changing effects depending on the incidence of light, etc. provided.
- Clear lacquer : Is applied as the last layer and protects the entire structure against mechanical, chemical and environmental loads. (→ acrylic resins )
Refinishing: For the coating, systems are used that cure at normal ambient temperature.
Manufacturer
Well-known manufacturers of automotive refinish paints include the brands Standox, Spies Hecker and Cromax (formerly DuPont Refinish), all of which belong to Axalta Coating Systems (formerly DuPont Performance Coatings), Glasurit and RM, which belong to the BASF Group, PPG, Nexa (formerly ICI) and Max-Meyer, which belong to the PPG group (also USA), Sikkens and Lesonal, both part of the Akzo Nobel group (Netherlands), Valspar and De Beer, which belong to the Valspar group, as well as that independent Lechler companies in Italy.
See also
literature
- Charles E. Oliver: The technique of car and coach painting . Stuttgart 1930
- Ernst Schwenk: A brilliant story. 100 years of automotive engineering, 100 years of automotive painting . Kunstharz Nachrichten, special issue, Frankfurt a. M. 1986
- Hans-Joachim Streitberger: BASF Handbook Painting Technology By Artur Goldschmidt
- Anselm: The automotive refinishing . Vogel Buchverlag, ISBN 3-8023-1768-8
- Pavel Svejda: Processes and application methods in industrial painting technology , 2003