© Copyright 1999/2004 Mario S Pennisi
Principal Consultant - Penlia & Co
What is electrocoating?
Electrocoating is another of the more recent coatings systems.
It was originally developed as an 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 friendly process.
Today, more than 98% of all car bodies produced globally
use an electrocoat primer. New end uses for electrocoat are
found annually, for example, automotive parts and accessories;
appliances; heat exchangers; decorative plated objects and
Surfaces have to be chemically clean prior to electrocoating.
A 7-stage phosphating sequence is usual.
How is it done?
The basic principle of electrocoat is that materials with
opposite electrical charges are attracted to each other. In
an electrocoat bath a specific charge is applied to the part
that is immersed in paint particles that have an opposite
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 the charge.
In anodic electrocoating, the part to be coated
is made the anode (a positive electrical charge) and
attracts the negatively charged paint particles in
the paint bath.
In cathodic electrocoating, the workpiece is made the cathode
(a negative charge) and attracts the positively charged paint
Today the electrocoat industry serves much more than the automotive
market. It is specified before wet coatings and powder coating
because of the tremendous advantages in application techniques,
efficiency, automation and environmental compliance.
Anodic type coatings are mainly used for products in interior
or moderate exterior environments. Anodic coatings are economical
systems that offer excellent colour and gloss control.
Low cure anodic epoxy coatings that have high corrosion
resistance in exterior applications are used for agricultural
implements, automotive parts and structural steel.
Anodic acrylic coatings provide good colour and gloss control.
They are economical and used for interior applications such
as metal office furniture, air diffusers, shelving, wire screens
Cathodic coatings are mainly high-performance coatings with
excellent corrosion resistance and can be formulated for exterior
Cathodic epoxy coatings provide good chemical and corrosion
resistance and are used for automotive parts, transformer
Cathodic acrylic electrocoatings have high UV durability,
corrosion resistance and good colour control. They are used
for lawn and garden furniture, agricultural implements, and
automotive wheels and trim appliances.
Advantages of Electrocoat
The major advantage of electrocoat over most other systems
is its covering ability. It provides total coverage of complex-shaped
parts with film uniformity. All recessed areas and sharp edges
can be covered and it provides excellent film uniformity and
precise film build control without sags, runs or drips. Thickness
is easily controlled using simple voltage adjustment. Also,
parts can be assembled prior to coating.
Electrocoating lines can be highly automated, closed-loop
systems with excellent productivity and low operating costs
so no direct labour is required. It allows for high productivity
with fast line speeds and high part-racking densities. Parts
pass very quickly through the production line, resulting in
lower unit costs. The process has high transfer efficiency,
approaching 100%, with low energy requirements since no drying
or flash-off time is required. Minimal exhaust and air make-up
is needed as well as reduced cure times and 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 health hazards.
There are a number of environmental advantages to electrocoating
as well. Electrocoating emits low or zero VOCs and HAPs. Operators
are not required to wear any special personal protection.
The system is totally enclosed and has low air and wastewater
emissions. The process produces minimal solid waste and since
it is a closed-loop system it minimises water loss. As a waterborne
system, fire hazards are reduced.
In general electrocoats can provide high gloss; good colour
control; weatherability; barrier, corrosion, chemical and
stain resistance; chip resistance; good edge coverage and
hardness. 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 acrylics are in the marketplace,
targeted at high-performance applications with improved environmental
A two-coat electrocoat process is available for extreme
performance environments. The first coat is a conductive epoxy
electrocoat, which, when baked, provides a surface that can
receive a second coat of acrylic electrocoat. The two-coat
system is capable of providing long-term exterior durability
and corrosion resistance in excess of 2,000 salt spray hours.
Wet coatings and powder coatings have a tendency to flow
away from sharp edges while still in the liquid phase so that
corrosion protection of objects such as body panel edges and
fins on radiators has proven difficult. Advances in cathodic
epoxy electrocoat formulations have resulted in the ability
to control film thickness over sharp objects, greatly enhancing