Page 32 - CFCM Nov-Dec-2020 Final_Neat

industrial finishing: E-COATING

Opposites Attract

E-COATING – also known as electrodeposition coating, elec- coat,” is returned to the tank, enabling the e-coat process
trophoretic painting, electrocoating, and electropainting – to achieve application efficiency rates above 95 percent.
uses electrical current to deposit paint on a surface. It Baking: After rinsing, the part is placed in a bake oven
works according to the “opposites attract” principle. that cures and cross-links the paint film to maximize its
The process has been developed over the last 50 years, performance properties. The minimum bake time is 20
originally for applying an anti-corrosive coating over minutes with a part temperature at 375 deg. F for most e-
steel car bodies, says ClearClad Coatings, which offers coat technologies.
e-coat products. E-coating is also used for a wide range
of consumer goods including hardware, jewellery, giftware, ADvAnTAGES
and eyeglass frames. One of the main advantages of e-coat, says e-coat service
The benefit is the ability to paint high volumes of parts provider Valmont Coatings, is the ability to get into hard-
with a unique combination of decoration and protection. to-reach places. The process ensures that any small holes,
“Material utilization is close to 100 percent,” says ClearClad. deep recesses or other areas inaccessible with conventional
“This high production efficiency coupled with advanced sprayers are evenly covered. Even the most complicated
quality results in lower unit costs.” shapes can be completely coated and parts can be more
densely packed on the rack to increase production rate.
HOw IT wORkS “E-coat is so effective, it is often used as a primer prior
The e-coat process is divided into four main steps, says to powder or liquid coating parts,” Valmont says. Products
PPG Coating Services, which offers e-coat services. can also be coated after final assembly.
Pretreatment: The metal is cleaned and a phosphate is In fact, e-coat technologies are categorized according to
applied to prepare the surface for application of the their primary use which is generally either as a primer or
e-coat. This process is essential to achieving the perform- as a topcoat, both of which PPG offers.
ance requirements desired by product end users, PPG Cathodic epoxy electrocoat is a popular primer technol-
says. The most appropriate chemicals for cleaning and ogy because of its superior adhesion and corrosion protec-
phosphating must be chosen based on the type of metal tion properties, PPG says, as well as its compatibility with
to be processed. The most common pretreatment regimen a wide range of liquid and powder topcoat materials. It
for steel and iron parts is immersion in a high-quality can also be used for single-coat applications where resist-
zinc-phosphate system. ance to UV from sunlight is not a factor. The materials are
Coating application: Coatings are applied to the environmentally friendly and suited to parts with cure tem-
pretreated metal in an electrocoat bath using precisely peratures above 380 F, the company adds.
calibrated process control equipment. “The e-coat bath Anodic epoxy electrocoat materials also are commonly
consists of 80 to 90 percent deionized water and 10 to 20 used as primers because their adhesion and corrosion re-
percent paint solids,” PPG says. “The deionized water sistance properties are generally better than some liquid
acts as a carrier for the paint solids, which are under paint primer materials, PPG says. Anodic epoxy e-coat
constant agitation. The solids consist of resin – the back- materials are well-suited to components coated as assem-
bone of the final paint film, which provides corrosion blies that contain heat-sensitive parts such as bearings
protection, durability and toughness – and pigments, and seals. The part temperature for curing can be as low
which contribute color and gloss.” as 180 deg. F.
Post-rinsing: This enhances the quality of the coating Cathodic acrylic electrocoat materials are viable
and enables the recovery of excess paint. During the topcoat applications because they feature very good
e-coat process, paint is applied to a part using a regulated UV resistance, PPG says. They also perform well in
amount of voltage to achieve the desired film thickness. single-coat applications.
Once the coating reaches the prescribed thickness, the part Because e-coat technologies are typically restricted to
“insulates” and the coating process slows down. As the a single color, PPG recommends using cathodic acrylic
part exits the bath, paint solids that cling to the surface are e-coat as the primer for liquid or powder topcoat, or
rinsed off to maintain application efficiency and aesthetics. as a one-coat system for a primary product color when
This residue material, which is called “drag out” or “cream additional color options are required

32 CAnADIAn FInISHInG & COATInGS MAnuFACTuRInG nOvEMbER/DECEMbER 2020