The different technologies of paint application
N.B.: The information contained in this sheet comes from reliable sources. Nevertheless, it is provided without any guarantee, express or implied, of its accuracy.
Principle:
Paints can be applied using different technologies.
Spraying by pneumatic projection with or without electrostatic effect:
- of a solvent-based paint mixture
- of a powder
Simple soaking
Electrophoretic dipping
Some of these technologies require special paint formulations. A spray formulation cannot be used for electrophoresis.
SPRAYING
SPRAYING A SOLVENT + POLYMER MIXTURE
This method is widely used. It consists of projecting the paint mixture through a nozzle using compressed air, which acts by spraying the mixture or "pushing" it through the orifice.
This method finds applications in all industrial sectors. The spraying methods used are relatively simple and affordable. On the other hand, the cabins used can be expensive because of the quality requirements (temperature and humidity control) and the increasingly stringent hygiene and safety requirements.
The paint formulations used are diverse:
Solvent-based paints
High solvent paints
Water-based, water-soluble or water-dilutable paints
A variant of this technology consists in using an electrostatic field, which will increase the overlap of the parts.
POWDER COATING
Another variant is to use powdered polymers instead of a solvent mixture.
Electrostatic powdering consists of charging the powder particles and placing them in an electric field, which they follow the lines of force to reach the part, on which they are fixed thanks to the Coulomb forces. The melting and cross-linking of the powder takes place only in the baking oven. The powder is fluidized by compressed air in the powder container and fed to the gun, where it is electrostatically charged and propelled by compressed air in the form of a cloud towards the surface to be coated.
This technology is widely used in the construction and railway sectors.
The main advantages of these processes are:
Improved recovery achieved
Reduction of product losses
Elimination of the health and safety issue related to solvents.
SIMPLE SOAKING
This technique consists of immersing the parts in a vat of liquid paint, then removing them and letting them drain before drying or baking the coating.
The process is very simple, requires little investment and is relatively well suited to special cases, such as hollow bodies with a single opening, like a metal bottle.
However, it has disadvantages in terms of the life of the mixture, control of the thickness of the paint lm, dripping effect...
The applications are therefore limited.
ELECTROPHORETIC DIPPING
There are two variants of this technology.
THE CATAPHORY
Cataphoresis is a painting technique that involves immersing the part in a water-soluble paint bath by placing the part in the cathode (hence the name cataphoresis) and causing positively charged paint particles to migrate from the anode to the cathode by means of an electric current of a certain voltage. The paint particles are then deposited uniformly and over virtually the entire surface of the immersed part. The part (or bath) is slightly agitated during the operation, which lasts only a few minutes. The deposit can be monitored by time or the amount of electricity passed. The parts are then drained, rinsed and polymerized in an oven at around 180 °C.
The great homogeneity of thickness of the lm, as well as the oxide coating produced by anodization of aluminum alloys, is due to the fact that the coating obtained is an electric insulator produced by a process managed by an electric field. There is thus a self-regulation of the thickness of the lm, even on parts of complex shape.
The benefits are:
The speed of the operation, whatever the surface to be treated, is of the order of a few minutes.
The coating of complex parts, resulting in a controlled and relatively constant thickness of the film.
The high level of corrosion protection achieved.
The major disadvantage is the cost of the installation, to which must be added the rigorous control of the numerous physicochemical parameters of the bath.
The automotive industry has been using this technology to apply a primer to car bodies since the 1980s. For the topcoat, the surface has become insulating and is applied by spraying.
Other industries use this technology, such as the manufacture of metal furniture, electric heaters, tractors, household appliances...
ANAPHORESIS
During anaphoresis, the part to be coated is not connected to the cathode but to the anode of the current generator.
This method is particularly suitable for the treatment of aluminum alloys. Indeed, in this case, parallel to the electrocoagulation of the paint, a layer of oxide is created on the surface of the metal, contributing to the adhesion of the paint and the corrosion resistance of the system.
The applications are less numerous than for cataphoresis, but seem promising for aluminum alloys, in particular since progress has made it possible to lower the polymerization temperature to a level compatible with the metallurgy of this material.
In addition to the technologies described briefly above, we should mention the touch-up techniques used, in particular, when it is necessary to repair damage to a paint layer, either during manufacture or in service. In this case, after cleaning the area to be repaired, the retouching can be done with a brush, a stick or an airbrush.
Implementation
If you are a company interested in being listed on this page, please contact us: a3ts@a3ts.org
