Electrophoretic deposition

The cathodic electrodeposition (CED ), also called " cataphoresis ", is an electrochemical process in which the workpiece is coated by immersion. It is well suited for painting complicated structures and large quantities. CEC is a standard method for ensuring the corrosion protection for vehicle bodies.

The electrochemical dip-coating

A basic distinction between anodic ( ATL) and cathodic electrodeposition (CED ). Both dip coating are electrochemical painting. The object to be painted is immersed in an electrically conductive aqueous coating material and applying a direct voltage field between the object to be painted and a counter electrode. The basic principle of the electrodeposition coating, is to precipitate water-soluble binder on the surface of the electrode to be painted and connected so as to generate a closed, adhering paint film.

Cathodic dip painting

When cathodic dip coating, the coating deposition occurs as a result of chemical reactions ( coagulation ) of the binder. This is implemented by an electrical current flow from an external electrode (anode ) through the conductive paint to be painted (cathode).

The cathodic dip painting is well suited for automated coating. She is a very environmentally friendly way, since today mostly demineralized water is used as solvent. The paint yield is up to 98.5 %, thus 1.5% of the paint used are only discharged. The result of the KTL is a very uniform coating of metal surfaces and cavities with uniform layer thicknesses and good surface qualities. The assets of the coating material to coat well and cavities is called Umgriffsvermögen.

Technology

The essential components of the KTL basin are a rectifier to supply the plant with DC voltage, several dialysis cells, a circulating system for a constant, uniform mixing of the paint (avoidance of pigment sedimentation ), a temperature control, filtration systems for the removal of registered dirt and ultrafiltration systems for supplying the system with flushing medium for rinsing the adhering paint.

In CDL bath dialysis cells are used as anodes usually. They are mounted on both sides of the basin and form as an anode, the corresponding counterpart to the cathode body. The anodes are covered by special anion exchange membranes. Anolyte by an external system is pumped through the cells. While the painting form in the paint interfering anions that are transported out of the paint through the membrane into the anolyte and then disposed of. Through the anolyte so freely become one neutralizing agent is removed. This will keep the pH in the e-coat tank within the process parameters.

Chemicals

The pelvis of the KTL contains binder, pigment paste, water-miscible organic solvent and water. An essential component of the binder and pigment paste is often epoxy resin. Binder and pigment paste make up the majority of about 20 % solids content of the paint. The electrodeposition paint persists to about 80 % of deionized water. In addition, a small proportion of organic solvent ( 1-2 % ), acids (0.4%) and additives.

The epoxy resin is dissolved by adding a neutralizing agent in a water-dispersible form. For an organic acid (usually formic acid ) was used. Often only a part of the functional groups is reacted with a neutralizing agent. The molar ratio of acid to the functional group is called the degree of neutralization. A neutralization degree of about 30% is sufficient to achieve the desired water dispersibility. Also for setting the slightly acidic pH in the e-coat tank, an organic acid. During the process, forms on the surface of the components a 15-20 micron thick primer layer, which is used for corrosion protection and the protection against stones.

Curing

In the curing process after the cathodic form in the paint epoxidharzhaltigen linear chain molecules that are interconnected in three dimensions, forming a stable structure. Crosslinking occurs during the mixing of precursors with branching points and is activated either chemically or by high temperatures (approx. 185 ° C) at room temperature with the aid of catalysts.

• Coating
• Paint