ELECTROCOATING© Copyright 1999/2004 Mario S Pennisi Principal Consultant - Penlia & Co

mariopen@coatfab.com or mariopen@ worldconferencesystems.com

What is electrocoating?Electrocoating is another of the more recent coatings systems. It was originally developed asan automotive body primer in the early 1960's and used by Ford in Australia from that time.The technology has grown to become an economically efficient and environmentally friendlyprocess.

Today, more than 98% of all car bodies produced globally use an electrocoat primer. New enduses for electrocoat are found annually, for example, automotive parts and accessories;appliances; heat exchangers; decorative plated objects and heat-sensitive components.

PreparationSurfaces have to be chemically clean prior to electrocoating. A 7-stage phosphating sequenceis usual.

How is it done?The basic principle of electrocoat is that materials with opposite electrical charges areattracted to each other. In an electrocoat bath a specific charge is applied to the part that isimmersed in paint particles that have an opposite charge.

The paint particles are attracted to the part and are deposited on the part to form an even,continuous film over every surface until the coating reaches the desired thickness.Electrocoating is complete when attraction stops.

Electrocoating is classified as either anodic or cathodic depending on the polarity of thecharge.

CathodicIn cathodic electrocoating, the workpiece is made the cathode (a negative charge) and attractsthe positively charged paint particles

UsesToday the electrocoat industry serves much more than the automotive market. It is specifiedbefore wet coatings and powder coating because of the tremendous advantages in applicationtechniques, efficiency, automation and environmental compliance.

Anodic type coatings are mainly used for products in interior or moderate exteriorenvironments. Anodic coatings are economical systems that offer excellent colour and glosscontrol.

Low cure anodic epoxy coatings that have high corrosion resistance in exterior applicationsare used for agricultural implements, automotive parts and structural steel.

AnodicIn anodic electrocoating,the part to be coated ismade the anode (a positiveelectrical charge) andattracts the negativelycharged paint particles inthe paint bath.

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Anodic acrylic coatings provide good colour and gloss control. They are economical andused for interior applications such as metal office furniture, air diffusers, shelving, wirescreens and hangers.

Cathodic coatings are mainly high-performance coatings with excellent corrosionresistance and can be formulated for exterior durability.

Cathodic epoxy coatings provide good chemical and corrosion resistance and are used forautomotive parts, transformer and appliances.

Cathodic acrylic electrocoatings have high UV durability, corrosion resistance and goodcolour control. They are used for lawn and garden furniture, agricultural implements, andautomotive wheels and trim appliances.

Advantages of ElectrocoatThe major advantage of electrocoat over most other systems is its covering ability. Itprovides total coverage of complex-shaped parts with film uniformity. All recessed areasand sharp edges can be covered and it provides excellent film uniformity and precise filmbuild control without sags, runs or drips. Thickness is easily controlled using simplevoltage adjustment. Also, parts can be assembled prior to coating.

Electrocoating lines can be highly automated, closed-loop systems with excellentproductivity and low operating costs so no direct labour is required. It allows for highproductivity with fast line speeds and high part-racking densities. Parts pass very quicklythrough the production line, resulting in lower unit costs. The process has high transferefficiency, approaching 100%, with low energy requirements since no drying or flash-offtime is required. Minimal exhaust and air make-up is needed as well as reduced cure timesand temperatures.

Electrocoat systems are low maintenance with minimal hook cleaning and no "booth"maintenance. Insurance rates are minimal because there are no specific fire or healthhazards.

There are a number of environmental advantages to electrocoating as well. Electrocoatingemits low or zero VOCs and HAPs. Operators are not required to wear any specialpersonal protection. The system is totally enclosed and has low air and wastewateremissions. The process produces minimal solid waste and since it is a closed-loop systemit minimises water loss. As a waterborne system, fire hazards are reduced.

PropertiesIn general electrocoats can provide high gloss; good colour control; weatherability; barrier,corrosion, chemical and stain resistance; chip resistance; good edge coverage andhardness. They are FDA-Approved and have no effect on flavour.

Cathodic acrylic electrocoats can provide the best combination of corrosion resistance,exterior durability (high UV resistance) and colour control. In the appliance market single-coat white cathodic acrylic can replace previous applications of primer and topcoat,leading to economic advantages for the end user. New low-VOC and HAPS-free acrylicsare in the marketplace, targeted at high-performance applications with improvedenvironmental characteristics.

A two-coat electrocoat process is available for extreme performance environments. Thefirst coat is a conductive epoxy electrocoat, which, when baked, provides a surface thatcan receive a second coat of acrylic electrocoat. The two-coat system is capable ofproviding long-term exterior durability and corrosion resistance in excess of 2,000 saltspray hours.

Wet coatings and powder coatings have a tendency to flow away from sharp edges whilestill in the liquid phase so that corrosion protection of objects such as body panel edgesand fins on radiators has proven difficult. Advances in cathodic epoxy electrocoatformulations have resulted in the ability to control film thickness over sharp objects,greatly enhancing corrosion resistance.

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