Electrophoresis anode system
Core Function
The electrophoresis anode system is an indispensable key component of the electrophoresis coating process. Its core function is to serve as the anode in the electrophoresis circuit, complete the current loop, and maintain the chemical balance of the electrophoresis tank solution (particularly neutralizing the excess acid ions generated by the electro-deposition reaction in the tank solution).
Why is an anode system needed?
In cathodic electrophoresis coating (the most widely used form today):
1.The workpiece is the cathode: positively charged paint resin particles move toward the cathode (workpiece) under the influence of an electric field and deposit and cure on its surface to form a paint film.
2.Electrochemical reactions: The primary reaction occurring at the cathode (workpiece) is the electrolysis of water to produce hydrogen gas and hydroxide ions.
3.Excess acid production: Resin particles in the coating typically contain carboxyl groups. During deposition on the cathode (workpiece), to maintain charge balance, the resin particles must bind with positively charged amine neutralizers (such as organic amines). After the resin is deposited on the workpiece, these amine neutralizers (positively charged cations) are released back into the bath solution. These free amines react with water in the bath solution to form ammonium ions and hydroxide ions, causing the pH of the bath solution to rise. More importantly, the carboxylate ions (negatively charged anions) inherent in the resin are “left behind” in the bath solution during the deposition process.
4.Maintaining balance: If left uncontrolled, negatively charged acid anions (such as acetate anions, formate anions, etc.) in the bath solution will continue to accumulate, leading to:
uAbnormal increase in conductivity: Affecting penetration and coating quality.
upH imbalance: Affecting the stability and solubility of resin particles.
uDeterioration of coating performance: Potentially causing issues such as pinholes, roughness, and poor flow.
uDestruction of bath stability: In severe cases, this may cause resin precipitation and sedimentation.
Composition and Function of the Anode System
A typical electrophoretic anode system primarily consists of the following components:
Anode:
uMaterial:Typically made of corrosion-resistant, highly conductive inert materials such as stainless steel (316L is common) or titanium (more corrosion-resistant, longer lifespan, but higher cost). Titanium anodes are sometimes coated with a layer of precious metal oxides (such as iridium-tantalum oxide) to further enhance conductivity and durability.
uShape: Common types include plate-shaped anodes and tubular(or box-shaped) anodes. Tubular/box-shaped anodes are more commonly used because they can accommodate anode solution internally.
uFunction: Directly connected to the positive terminal (+) of the power source, serving as part of the current circuit, where oxidation reactions occur on the anode surface.
Anode Cell/Anode Chamber:
uStructure: This is a compartment surrounding the anode, typically made of chemically resistant insulating materials such as PVC or PP. The anode is completely sealed within this cover.
uKey Components: The key component of the anode cover is the ion-selective permeable membrane (Ion-Selective
Membrane).
nMaterial: Typically a cation exchange membrane.
nFunction: This membrane allows positively charged ions (such as H⁺and ammonium ions NH₄⁺) to pass through while blocking negatively charged ions (such as paint resin particles, pigment particles, and acetate ions CH₃COO⁻) and larger molecules. This ensures that only the cations requiring neutralization enter the anode chamber to participate in the reaction, while protecting the anode from paint contamination and preventing paint deposition on the anode.
Anolyte Circulation System:
uComponents: Includes a circulation pump, pipes, flow meter, storage tank (if applicable), conductivity meter, pH meter (if applicable), and heat exchanger (if temperature control is required).
uFunctions:
nCirculation: Continuously pumps anolyte into the anode housing, flows over the anode surface, and recirculates out.
nConductivity: Provides a conductive medium to ensure current can pass through the anolyte to the anode.
nRemoval of reaction products: Removes acids and gases (primarily oxygen) generated on the anode surface from the anode chamber.
nConcentration control: Control discharge and replenishment by monitoring the conductivity of the anode solution (which reflects the acid concentration). When the conductivity of the anode solution is too high (acid concentration is too high), discharge a portion of the high-acid-concentration anode solution while replenishing with fresh ultrafiltration liquid or deionized water to maintain appropriate acid concentration and conductivity.
Power connection:
uConnect the positive terminal (+) of the DC power supply to each anode via a busbar or cable. Ensure that the connections are secure, conductive, and properly insulated.
Conductivity/Concentration Control System:
uReal-time monitoring of the anode solution's conductivity (directly reflecting the acid concentration) via an online conductivity sensor.
uBased on the set conductivity range, automatically control the drainage of anode solution and the addition of fresh ultrafiltration liquid/deionized water to maintain stable system operation.
Safety and Protection Devices:
uGrounding Protection: Ensure system safety.
uLeakage Protection: Prevent electrical accidents.
uLiquid Level Control: Prevent dry burning of the anode cover, which could damage the membrane and anode.
uFlow Monitoring/Alarm: Ensure normal circulation.
Applications
Electrophoresis anode systems are widely used in industries that employ cathodic electrophoresis coating processes, particularly in the following areas:
üAutomotive industry: Bodywork, chassis, and primer for components.
üHome appliance industry: Refrigerators, washing machines, air conditioners, and other housings.
üHardware and building materials: Aluminum profiles, steel furniture, door and window fittings, etc.
üAgricultural and construction machinery
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