Translate
What is the Electrophoretic Coating Process?
The Electrophoretic coating process is a method of depositing water based paint or clear coatings on to metal or conductive parts. The biggest use for this process is as a first coat primer for automotive cars, truck bodies, parts and components. 99% of mass produced cars, trucks and component parts are Electrophoretic primer coated. The most common resin types used are epoxy, acrylic, hybrid and polyurethane technologies. Epoxy type chemistry give excellent corrosion resistance whereas acrylic and polyurethane offer high UV resistance. Polyurethane type offer very good UV properties combined with excellent chemical resistance. Another big market is for decorative or protective finishes on electroplated door hardware, light fitting, jewellery and electronic devices such as mobile phones.Process Method
The Electrophoretic Process uses a stable emulsion of suspended organic resins in purified water (deionised). The Electrophoretic Process solution normally comprises of organic solvents, water, acid or alkali stabilisers, ionic components, wetting agents and if coloured pigments or dyes.
When a D.C. voltage is applied across two immersed electrodes, the passage of current is accompanied by electrolysis of water. This results in oxygen gas being liberated at the anode (positive electrode) and hydrogen gas liberated at the cathode (negative electrode). The liberation of these gases disturbs the hydrogen ion balance in the water nearby the electrodes. This results in a subsequent pH change and this in turn de-stabilises the resin emulsion components of the solution and they coagulate onto the appropriate electrode. It is often referred to as controlled precipitation of the paint or resin particles on to the electrode.
Electrolysis of water causes the cathode to become alkaline and the anodes to become acid. Cathodic Electrophoretic systems are stable except at high (alkaline) pH. Anodic are stable except at low (acid) pH.
It is very common to refer to Electropaint as "Electrophoretic"
How is it applied?
An unfinished pre-treated metal or conductive component part is immersed in a bath containing the Electrophoretic paint emulsion, and then an electric current is passed through both the part and the emulsion. The paint particles that are in contact with the part adhere to the surface, as described in the above mechanism, and build up an electrically insulating layer. This layer prevents any further electrical current passing through, resulting in a perfectly level coating even in the recessed parts of complex-shaped goods. The product is then removed from the paint bath and baked in an oven.Depending on the polarity of the charge, electrocoating is classified as either anodic or cathodic.
In anodic electrocoating, the part to be coated is the anode with a positive electrical charge, which attracts negatively charged paint particles in the paint bath. During the anodic process, small amounts of metal ions migrate into the paint film, which limit the performance properties of anodic systems. The main use for anodic products is interior or moderately exterior environments. Anodic coatings are economical systems that offer excellent colour and gloss control. In cathodic electrocoating, the product has a negative charge, attracting the positively charged paint particles. Cathodic electrocoat applies a negative electrical charge to the metal part, which attracts positively charged paint particles. Reversing the polarities used in the anodic process significantly reduces the amount of iron entering the cured paint film and improves the cathodic properties. Cathodic coatings are high-performance coatings with excellent corrosion resistance that can be formulated for exterior durability
Electrophoretic deposition (EPD), is a term for a broad range of industrial processes which includes electrocoating, e-coating, Cathodic electrodeposition, and Electrophoretic coating, or Electrophoretic painting. A characteristic feature of this process is that colloidal particles suspended in a liquid medium migrate under the influence of an electric field (electrophoresis) and are deposited onto an electrode. All colloidal particles that can be used to form stable suspensions and that can carry a charge can be used in Electrophoretic deposition. This includes material classes such as polymers, pigments, dyes, ceramics and metals.
The process is useful for applying materials to any electrically conductive surface. The materials, which are being deposited, are the major determining factor in the actual processing conditions and equipment, which may be used. Due to the wide utilization of Electrophoretic painting processes in many industries, aqueous EPD is the most common commercially used EPD process. However, non-aqueous Electrophoretic deposition applications are known. Applications of non-aqueous EPD are currently being explored for use in the fabrication of electronic components and the production of ceramic coatings. Non-aqueous processes have the advantage of avoiding the electrolysis of water and the gas evolution, which accompanies electrolysis.
