Surface Finishing Coatings
Going Into Electrocoating Bath
Electrocoating, which is
also referred to as electrodeposition, electrophoretic
deposition, or electropainting, is an organic
finishing process that uniformly applies
thin-film primers and one-coat finishes
to metallic substrates. Electrocoating resembles
electroplating in that it utilizes an electrical
current to deposit a coating onto substrates.
However, electrocoating deposits waterborn
paint onto substrates rather than metal
ions. The overall process consists of four
main process steps: pretreating, electrocoating,
rinsing, and baking.
The electrocoating process
may be anodic or cathodic, depending on
the charge applied the substrate. Although
the processes are virtually the same, properties
of the resultant coating are dissimilar.
Anodic systems, which were the first to
be used for electrocoating, apply paint
to positively charged substrates. The negatively
charged pigment and resin particles deposit
onto the substrate (anode). One disadvantage
of this process is that substrate metals
dissolve and become incorporated into the
coating, which affects surface properties.
Cathodic electrocoating deposits paint onto
negatively charged substrates and offers
several advantages over anodic electrocoating.
For example, metal dissolution of the substrate
does not occur, cathodic electrocoating
has the ability to deposit over contaminants,
corrosion resistance is improved, and a
better color consistency occurs over welded
The electrocoat process
can be divided into four distinct steps:
- Electrocoat Bath
- Post Rinses
- cleaning and phosphating
The pretreatment zone
cleans and phosphates the metal to prepare
the surface for electrocoating. Cleaning
and phosphating are essential to achieving
the performance requirements desired by
today's end user of the product. A high
quality zinc phosphate system using the
immersion method is primarily used where
steel and iron parts are to be coated.
Bath - applying coating in
The electrocoat bath and
ancillary equipment zone is where the
coating is applied and the process control
equipment operates. The electrocoat bath
consists of 80-90% deionized water and
10-20% paint solids. The deionized water
acts as the carrier for the paint solids
which are under constant agitation. The
solids consist of resin and pigment. Resin
is the backbone of the final paint film
and provides corrosion protection, durability
and toughness. Pigments are used to provide
color and gloss.
Rinses - rinsing off excess
The post rinses provide
both quality and conservation. During
the electrocoat 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 a coating application efficiency
Oven - thermally
curing the paint film
The bake oven receives
the parts after they exit the post rinses.
The bake oven cross links and cures the
paint film to assure maximum performance
properties. The minimum bake schedule
is 20 minutes with the part temperature
at 375°F for most electrocoat technologies.
However, there is also a "low temperature
cure" electrocoat material. This
material has a minimum cure of 20 minutes
at a part temperature of 180°F so
that many assemblies containing seals,
bushings, bearings, or oil can use the
E-coat provides an excellent
base for a variety of topcoats. It provides
an incredible "dual application advantage,"
creating a more decorative and durable finish.
In addition, e-coat offers an "environomic"
solution - no heavy metals, no HAPS and low
It can be used on a wide
variety of substrates including -
- Cold Rolled/Hot Rolled
- Galvanized Steel
- Iron Castings
- Zinc Castings
- Conductive Composites
- Aluminum Extrusions
- Rare Earth Magnets
- NiZn Plated Steel
- Stainless Steel
- Chrome Plate.
Electrocoating readily conforms
to complex configurations and yet maintains
engineered tolerances on parts ensuring
intended operating functions. Some examples
include: Internal Surfaces, Deep Recesses,
Weldments, Fasteners, Small Parts, Large
Parts, Uniform Coating- No Sags or Runs.