Shanghai Xinfan Bio: Electrophoresis principle and electrophoresis equipment requirements - Database & Sql Blog Articles

**Principle of Electrophoresis** Electrophoretic coating is a process that involves the deposition of paint onto a conductive surface using an electric current. The water-soluble resin used in anodic electrophoresis is a high acid value carboxylate, which dissolves in water and exists in a molecular and ionic equilibrium state under a DC electric field. When the system is energized, ions move in a directional manner due to the potential difference between the two electrodes. Anions are deposited on the anode, while cations are reduced at the cathode, forming a film through a complex electrochemical reaction involving four simultaneous processes: electrophoresis, electrolysis, electrodeposition, and electroosmosis. **1. Electrophoresis** This refers to the movement of charged colloidal particles in a medium under the influence of an electric field toward the electrode with the opposite charge. It is a fundamental mechanism driving the transport of paint particles during the coating process. **2. Electrodeposition** During this phase, anion resins emit electrons and deposit on the anode, forming a water-insoluble paint film. This step is critical for achieving a uniform and durable coating. **3. Electroosmosis** This is the reverse process of electrophoresis. As the anion resin accumulates on the anode, the surrounding medium is pulled through the deposited film, creating a flow from the anode back into the paint solution. **4. Electrolysis** When current passes through the paint bath, the electrolyte decomposes, releasing hydrogen gas at the cathode and oxygen at the anode. This process plays a role in maintaining the chemical balance within the system. **Electrophoretic Coating Overview** Electrophoretic coatings have evolved through three generations. The first generation used epoxy resins, primarily for automotive chassis. The second generation introduced acrylic resins, which are more commonly used today due to their better performance and versatility. The third generation includes polyurethane coatings, often used for cathodic electrophoretic paints applied to jewelry surfaces. Acrylic resins typically contain carboxyl groups trapped within the molecule and amine groups on the exterior. Approximately 70% of the carboxyl groups are substituted by amine groups, making the resin water-soluble via -COONHR groups. These resins are usually crosslinked with amine-based curing agents to achieve optimal adhesion and durability. **Painting Process** 1. **Degreasing**: Alkaline degreasing using Na₂CO₃ and NaOH is recommended when an acid recovery system is available. This ensures a clean, bright surface without causing side effects during subsequent steps. 2. **Washing**: Tap water is used to remove any residual acid or alkali from previous treatments. 3. **Etching**: Alkali etching can slightly reduce surface brightness but is essential for proper adhesion. Care must be taken to avoid excessive Al³⁺ content and high temperatures, which can cause spotting after drying. 4. **Two Washes**: A spray rinse or increased overflow is recommended to ensure thorough cleaning. 5. **Ash Removal**: Nitric acid (HNO₃) is effective, but it requires thorough rinsing (at least two washes plus a spray). 6. **Oxidation**: Sulfuric acid (H₂SO₄) is commonly used for 20 minutes to form a 9µm oxide layer. High-temperature oxidants may not yield optimal results in terms of color, hardness, or colorability. 7. **Coloring**: Tin or nickel salts can be used for coloring, ensuring no color differences to prevent discoloration after electrophoretic painting. 8. **Hot Pure Water Washing**: Required conductivity < 100 µS/cm, temperature 70–80°C, pH 4–6. For silver-white or high-voltage profiles, this step should be extended, and pH adjusted with triethylamine. 9. **Pure Water Washing**: Conductivity < 100 µS/cm, room temperature, pH 4–6, lasting 2–4 minutes. pH adjustment is also done with triethylamine. **Electrophoresis Coating Equipment** - **Electrophoresis Tank**: Typically lined with hard PVC or epoxy glass-reinforced plastic. - **Overflow Tank**: Controls paint level and removes foam, with a capacity of about 1/5 of the main tank. - **Stirring System**: Ensures even paint distribution. Circulation rate should allow full tank turnover 4–6 times per hour. Cooling or heating systems may be needed based on ambient conditions. - **Electrodes**: Cathode plates are usually made of 316 stainless steel. Anode area should not exceed twice the cathode area for safety. - **Power Supply**: Modern systems offer ripple factors below 6%, with options for constant voltage or current control. - **Deionized Water System**: Requires purity above 1 MΩ, using methods like electrodialysis or ion exchange. - **Paint Refining Equipment**: Cation and anion exchange towers are used for purification, with specific regeneration procedures for each. - **Paint Recovery**: Ultrafiltration (UF) and Reverse Osmosis (RO) are common, with UF focusing on polymer separation and RO on concentration. - **Oven**: Convection, infrared, or far-infrared heating methods are used, with convection being the most common. **ELISA and Related Products** - **ELISA Kit** - **SOD Kit** - **IgG Kit** - **IgM Kit** - **Western Blot (WB)** - **Immunohistochemistry** - **Free Test** - **GIBCO, AMRESCO** - **Shanghai Xinfan Biological**

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