Customers today demand higher quality and durability from the products they buy. Not only do they expect these products to perform well; they want finishes to look good and resist corrosion for longer periods of time. The processes offered by PPG Coatings Services, including electrocoating (e-coating), are designed to meet each of these mandates.
How does Electrocoating Work?
Electrocoats readily conform to complex configurations and yet maintain engineered tolerances on parts ensuring intended operating functions. Some examples include internal surfaces, deep recesses, weldments, fasteners, small parts, large parts, and uniform coating (with no sags or runs).
The fundamental physical principle of this technology is that materials with opposite electrical charges attract one another. An electrocoat system applies a DC charge to a metal part immersed in a bath of oppositely charged paint particles. The paint particles are drawn to the metal part and paint is deposited on its surface, forming an even, continuous film over every curve, crevice and corner, until the electrocoat reaches the desired thickness.
At the desired thickness, the film insulates the part enough that the electrical attraction stops, and the coating process is complete. Depending on the polarity of the charge, electrocoat is classified as either anodic or cathodic.
What is the process for Electrocoating?
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In the first step – pretreatment – metal is cleaned and a phosphate is applied to prepare the surface for application of the e-coat. This process is essential to achieving the performance requirements desired by product end users. PPG Coatings Services analyzes the metals to be processed and chooses the most appropriate chemicals for cleaning and phosphating. In our facilities, the most common pretreatment regimen for steel and iron parts is immersion in a high-quality zinc-phosphate system.
- During the next step, coatings are applied to the pretreated metal in an electrocoat bath using precisely calibrated process control equipment. The e-coat bath consists of 80-90% deionized water and 10-20% paint solids. The deionized water acts as a carrier for the paint solids, which are under constant agitation. The solids consist of resin – the backbone of the final paint film, which provides corrosion protection, durability and toughness – and pigments, which contribute color and gloss.
- Post-rinsing, which occurs next, enhances the quality of the coating and enables the recovery of excess paint. During the e-coat process, paint is applied to a part using a regulated amount of voltage to achieve the desired film thickness. Once the coating reaches the prescribed thickness, the part “insulates” and the coating process slows down. As the part exits the bath, paint solids that cling to the surface are rinsed off to maintain application efficiency and aesthetics. This residue material, which is called “drag out” or “cream coat,” is returned to the tank, enabling the e-coat process to achieve application efficiency rates above 95%.
- After the coated part exits the post-rinse phase, it is placed in a bake oven that cures and cross-links the paint film to maximize its performance properties. The minimum bake time is 20 minutes with a part temperature at 375°F for most e-coat technologies. PPG Coatings Services can also apply a supplemental “low temperature cure” e-coat material depended on volume.
The e-coat process is divided into four distinct steps:
- In the first step – pretreatment – metal is cleaned and a phosphate is applied to prepare the surface for application of the e-coat. This process is essential to achieving the performance requirements desired by product end users. PPG Coatings Services analyzes the metals to be processed and chooses the most appropriate chemicals for cleaning and phosphating. In our facilities, the most common pretreatment regimen for steel and iron parts is immersion in a high-quality zinc-phosphate system.
- During the next step, coatings are applied to the pretreated metal in an electrocoat bath using precisely calibrated process control equipment. The e-coat bath consists of 80-90% deionized water and 10-20% paint solids. The deionized water acts as a carrier for the paint solids, which are under constant agitation. The solids consist of resin – the backbone of the final paint film, which provides corrosion protection, durability and toughness – and pigments, which contribute color and gloss.
- Post-rinsing, which occurs next, enhances the quality of the coating and enables the recovery of excess paint. During the e-coat process, paint is applied to a part using a regulated amount of voltage to achieve the desired film thickness. Once the coating reaches the prescribed thickness, the part “insulates” and the coating process slows down. As the part exits the bath, paint solids that cling to the surface are rinsed off to maintain application efficiency and aesthetics. This residue material, which is called “drag out” or “cream coat,” is returned to the tank, enabling the e-coat process to achieve application efficiency rates above 95%.
- After the coated part exits the post-rinse phase, it is placed in a bake oven that cures and cross-links the paint film to maximize its performance properties. The minimum bake time is 20 minutes with a part temperature at 375°F for most e-coat technologies. PPG Coatings Services can also apply a supplemental “low temperature cure” e-coat material depended on volume.
Electrocoating Technologies
E-coat technologies are categorized according to their primary use. Generally they are either used as a primer or as a topcoat.
As a primer:
Cathodic epoxy electrocoat is a popular primer technology because of its superior adhesion and corrosion protection properties, as well as its compatibility with a wide range of liquid and powder topcoat materials. Since this technology has good appearance properties, it can also be used for single-coat applications where resistance to the ultraviolet (UV) rays from sunlight is not needed. Today’s cathodic epoxy e-coat materials are environmentally friendly and suited to parts with possible cure temperature above 380°F.
Anodic epoxy electrocoat materials also are commonly employed as primers because their adhesion and corrosion resistance properties are generally better than commonly used liquid paint primer materials. Anodic epoxy e-coat materials are well-suited to components, coated as assemblies, that contain heat-sensitive parts such as bearings and seals. The part temperature for curing can be as low as 180°F.
As a topcoat:
Cathodic acrylic electrocoat materials lend themselves to topcoat applications because they feature very good UV resistance. They also perform well in single-coat applications and are generally superior to popular liquid primer plus topcoat paint systems because they deliver better overall adhesion and corrosion resistance properties.
Electrocoat technologies are generally restricted to a given color. When additional color options are required for an application, PPG Coatings Services recommends using cathodic acrylic e-coat as the primer for liquid or powder topcoat, or as a one-coat system for a primary product color.
Why Outsource?
An e-coat system with the appropriate supporting equipment, such as the treatment system for process fluids represents a significant capital and staffing investment. For low-to-moderate production volumes, outsourcing can be a cost-effective way to obtain the advantages of professional e-coat application for a given part or product.
When production volumes reach the levels that could justify an in-house system, the decision to outsource electrocoating becomes more complex than a "make or buy" evaluation. At that point, it also becomes a “strategic” decision that requires answers to two fundamental questions: “What is our business?” and “Do we want to run a coatings operation?”
Here are a few of the advantages of outsourcing with PPG Coatings Services:
- Project Analysis: PPG Coatings Services will assist with development and then support the most effective process to meet and exceed the customer's goals.
- Equipment: PPG Coatings Services can design, build and manage the coating application equipment for maximum efficiency specific to the customer’s product.
- Coating Application: PPG Coatings Services will provide highly trained personnel for total custom coating system management.
- Parts Handling: PPG Coatings Services is experienced in packaging, logistics, assembly, inventory control, masking and specialized fixturing.
- Long-Term Management: PPG Coatings Services' unique "bundle" of skills related to painting technologies allows the customer to focus on the core business without the worries of operating a coating facility.
Learn more
PPG Coatings Services offers e-coat services in multiple U.S. states and other countries. Complementary technologies, such as liquid and powder coating, are available at certain locations as additional coating service options.
Well-known for the capabilities of its internal Technology Group, Equipment Division and experienced operating teams, PPG Coatings Services has earned a reputation for providing total, integrated, cost-effective coating solutions.
