Electrophoretic E-Coat Painting, Electrophoretic Paint Black E-Coat ED Paint
Electrophoretic paint (E Coat) is now the finish of choice within the automotive industry where high corrosion resistance is required on sub frame components. This is generally far more durable and offers a low cost alternative to powder coating and is becoming ever more popular is general industrial or retail applications where a high corrosion resistance and aesthetically pleasing finish is required.
E-coat Epoxy Type (electrophoretic painting) offers a high corrosion resistance, normally in excess of 1000 hours salt spray resistance as well as an excellent aesthetic appearance.
When applied to such coatings such as phosphate, zinc or zinc-nickel the corrosion properties can be increased even further. In addition, unlike sprayed or dipped coatings the E-coat finish gives a uniform density of coating over the whole part regardless of the complexity of the product. This surface finish provides a hard surface coupled with good chemical resistance giving excellent wear properties and is an excellent alternative to powder coating on many applications.
The major wordwide suppliers of automotive ecoat KTL are PPG Industries USA, BASF Germany, Hawking Electrotechnology UK, DuPont, FreiLacke Freiotherm and Henkel.
Electrophoretic e-coat customers today insist on high quality and durability from the products they pay money for. They demand these products must perform well, but they want the finish to look excellent and resist corrosion for a much longer period of time. The finishing processes offered by Electrophoretic coating are designed to do just that. A common name for those finishing processes is KTL Electrophoretic lacquer, Electrodeposition, electrocoating Cathodic dip-painting (CDP) processes
Ecoat Photo courtesy of Euro Quality Coatings Limited Cardiff Wales http://www.euroqualitycoatings.co.uk/e-coat/
E-coating is a method of painting which uses electrical current to deposit the paint. The process works on the principal of "Opposites Attract". This process is also known as electrodeposition or KTL (Kathodische Tauchlackierung)
cathodic dip painting
The e-coat process can be separated into four basic zones:
- Electrocoat Bath and Ancillary Equipment
- Post Rinses
- Bake Cure Dry Oven
Typical Ecoat Process Sequence
1. Spray degreasing
2. Immersion degreasing
3. Water rinse.
4. Surface activation
5. Zinc phosphate coating (chromium free).
6. Demineralised water rinse dip
7. Demineralised water rinse dip
8. Demineralised water rinse spray
9. E-coating coating thickness from 10 up to 40 µm
10. UF cascade spray rinse.
11. UF rinse.
12. Demineralised water rinse spray
13. Drying of the parts – compressed air blow.
14. Three stage electric or gas baking of coating with thermal, infrared stove drying oven
The pre-treatment zone cleans and phosphates the metal to prepare the surface for e-coating. With automotive ecoat or KTL cleaning and phosphating are fundamental to achieving the performance needs desired by today's end user of the product. Major e-coat sub contract finishing companies analyze the metals to be processed and choose the most appropriate chemicals and pre-treatment process. A high quality tricationic zinc phosphate system using the immersion method is primarily used in automotive ecoat, KTL systems where steel and iron parts are to be coated.
The electrocoat bath and ancillary equipment zone is where the coating is applied and the process control equipment operates. The e-coat bath consists of 80-90% deionised water and 10 -20% paint solids. The deionised water acts as the delivery system for the paint solids which are under constant agitation and movement. The ecoat solids content consist of resin, extender and pigment. Resin is the backbone of the final paint film and provides corrosion protection, durability and toughness. Pigments are used to provide colour and gloss.
Post rinses provide both quality and conservation. During the e-coat process, paint is applied to a part at a certain film thickness, regulated by the amount of voltage applied. Once the coating reaches the desired film thickness, the part insulates and the coating process slows down. As the part exits the bath, paint solids cling to the surface and have to be rinsed off to maintain efficiency and aesthetics. The excess paint solids are called "drag out" or "cream coat." These excess paint solids are returned to the tank to create e-coating application efficiency above 95%.
The bake oven receives the parts after they exit the post rinses. The bake oven crosslinks and cures the paint film to assure maximum performance properties. Depending on the resi n chemistry bake schedule is typically 15- 20 minutes metal temperature for most e-coat technologies. However, many new technologies offer low temperature cure of e-coat material. Low temperature ecoat or KTL cure helps many assemblies containing seals, bushings, bearings. Electrophoretic e-coat technologies tend to be most commonly used as a primer or as a topcoat.
Cathodic type epoxy electrocoat are the most popular automotive used technology because of their superior adhesion and salt spray corrosion protection properties. They are designed to be compatible with a wide range of liquid spraya paint and powder coating topcoat finishes. Since this technology has good appearance properties it can also be a single coat finish but only where resistance to the ultraviolet rays from sunlight is not needed. Cathodic epoxy e-coat materials available today are very environmentally friendly.
Cathodic acrylic and polyurethane electrocoat materials lend themselves to topcoat applications because of their very good resistance to the ultraviolet rays from sunlight. A big advantage is that only one coat is necessary. The overall adhesion and corrosion resistance properties are good when compared to popular liquid primer plus topcoat paint systems. Electrocoat technologies are generally restricted to a given dull yellow shade colour, however, with some applications additional colour options are required. A good solution is to use cathodic polyurethane or acrylic as a one coat system for the primary product colour. It can also be used as a primer to be top coated with a liquid spray or powder coat topcoat material for multiple colour options.
An e-coating system with the appropriate supporting equipment such as the treatment system for process fluids represents a significant capital and staffing investment. For low to moderate production volumes, outsourcing is an easy decision. It is the cost effective way to obtain the advantages of e-coating for a product. However, when production volumes reach the levels where it would seem to be justified to install a system in-house, the outsource decision for e-coating becomes more than a normal "make or buy" decision.
For Information on Autodeposition Autophoretic Coatings CLICK HERE