Electrophoretic Coating

Green, white, red, yellow, purple, black, rose gold, blue, and gold electrophoresis processing

Electrophoretic Coating Process Introduction

Electrocoating is a painting method that utilizes an applied electric field to cause the directed migration and deposition of pigment and resin particles suspended in an electrocoating solution onto the surface of an electrode, typically a substrate. It is a chemical process that applies a layer of colored paint film to the workpiece.Black spot electrophoretic coating is the most widely used electrophoretic color and can be divided into high gloss, matte, and semi-matte finishes.

Electrophoretic coatings utilize water-soluble or water-dispersible ionic polymers as film-forming materials, and the workpiece to be coated can function as either the anode or the cathode.

Electrophoretic coatings can be classified into anodic electrophoretic coatings and cathodic electrophoretic coatings based on the electrode of the workpiece. They can also be categorized as anionic electrophoretic coatings and cationic electrophoretic coatings based on the ionic form in which the film-forming material exists in water.

Cathodic electrophoretic coatings can further be classified based on their water dispersibility into single-component electrophoretic coatings and two-component electrophoretic coatings. They can also be categorized based on film thickness as thin-film, medium-thickness, and thick-film cathodic electrophoretic coatings.

The principle of the process is that under the action of an external DC power supply, charged particles are used to achieve the purpose of separating different particles at different speeds in the electric field. The paint particles move directionally towards the cathode or anode in a dispersed medium, and this phenomenon is called electrophoresis. Depending on the direction in which the paint particles move directionally, electrophoresis can be divided into anode electrophoresis and cathode electrophoresis.

Anodic electrophoretic coating is a new type of coating introduced in industrial applications abroad in the 1970s. The film-forming material is a carboxyl-functionalized anionic polymer, which is rendered ionic by neutralization with alkaline substances and dispersed in water. Common neutralizing agents include organic amines and inorganic bases such as ethanolamine, triethanolamine, triethylamine, and KOH. These resins, along with pigments, fillers, and various additives, form stable aqueous dispersion systems. Under the influence of a direct current electric field, the negatively charged resin coats the pigments and migrates towards the anode, depositing on its surface. Therefore, this type of coating is referred to as anodic electrophoretic coating. The electrophoretic painting process involves electrophoresis, electrolysis, electrodeposition, and electroosmosis, resulting in the formation of a low moisture content, highly resistant, and dense film on the metal surface. The technical requirements are lower, but the corrosion resistance of the coating is poorer than that of cathode electrophoresis (about one-fourth of the lifespan of cathode electrophoresis).

Cathode electrophoresis: If the paint particles carry a positive charge and the workpiece is the cathode, the paint particles are deposited on the workpiece as a film, which is called cathode electrophoresis. The reason why the corrosion resistance of the cathode electrophoretic coating is high is that the workpiece is the cathode, and there is no anodic dissolution. The surface of the workpiece and the phosphating film are not destroyed. Two-component cathodic electrophoretic coatings consist of two components: one is a uniform white milky liquid, and the other is a gray (or black) pigment slurry. Their raw materials mainly include epoxy resin, ether-alcohol compounds, and isocyanates. Through the action of electric current and solution, the coating can adhere to the surface of the workpiece, forming a protective film. It offers a relatively high cost-effectiveness and is therefore favored in many industries.

Common Substrates Used in Electrophoretic Coating Processing:

Almost all conductive materials (not just metal materials) can be used as substrates for electrophoretic processing! Substrates that I have personally processed through electrophoresis include steel parts (A3 steel, 45 steel, 304 stainless steel, 316 stainless steel, etc.), copper parts (brass, bronze, tin bronze, phosphor bronze, etc.), aluminum parts (aluminum alloy 2A12, aluminum alloy 6061, aluminum alloy 6063, aluminum alloy 6082, aluminum alloy 7075, etc.), iron parts, zinc alloy, etc.;

Note 1

Not all electrophoresis factories can process all materials. I have encountered many electrophoresis factories that do not process iron parts and zinc alloy parts, especially cast iron parts, because impurities in these materials may contaminate the electrophoretic solution, leading to many electrophoresis factories not processing these materials.

Electrophoretic CoatingProcessing Film Thickness, Hardness, and Neutral Salt Spray Test Duration

The typical film thickness for normal electrophoretic surface treatment can range from a minimum of 5μm to a maximum of over 20μm. This depends on the application or purpose of the workpiece. For certain products, a thicker film may be detrimental as it can affect the assembly or lead to paint bursting during stamping. Additionally, thicker coatings result in higher paint consumption costs. On the other hand, reducing the film thickness lowers paint consumption costs but also compromises corrosion resistance.The film thickness for different types of products is generally as follows

For products with high corrosion resistance requirements, such as automotive parts, a film thickness of 20μm or more is generally used.

For ordinary hardware processing, a film thickness of about 15μm is generally sufficient, and this is also the most widely used electrophoretic paint film thickness.

In general, the film thickness of hardware components typically only needs to be 10μm, such as for the guide rails of stamped, bent, or deformed parts.Products with precision assembly requirements are often the same, otherwise, if it is too thick, it will affect the assembly.

For some special products, such as seat springs, which do not require high corrosion resistance but have a large production volume, it can be a headache to use the conventional single-piece hanging electrophoresis method. Efficiency and benefits are extremely low. In this case, for mass-produced components, the thickness requirements for the electrophoretic film are not stringent and only require a thickness of 5-10μm.

Thin-film electrophoretic paint with a thickness of only 5μm can provide good coverage for the substrate, which effectively guarantees the increase of user productivity and cost control, creating more value!

The hardness of electrophoretic coating

Generally, the hardness of the electrophoretic coating film is 2H, 3H, and in some special scenarios, it can reach 4-5H. (Converted to HV (Vickers hardness) and HR (Rockwell hardness),

Electrophoretic coatings exhibit excellent corrosion resistance in salt spray environments. Compared to zinc plating coatings, electrophoretic coatings perform significantly better. It is known that the salt spray test duration for regular white zinc plating coatings is 24 hours, for blue zinc plating coatings is 72 hours, and the highest duration for color zinc plating coatings reaches only 96 hours. However, in electrophoretic coating processes, the salt spray test duration typically ranges from 24 to 1000 hours. For example, according to the Chinese automotive industry standard “Automotive Electrophoretic Coating,” the salt spray test duration for automotive electrophoretic coatings should be no less than 240 hours. The American ASTM D1654 standard also provides detailed specifications for the salt spray test duration and requirements for “corrosion-resistant coatings.” Additionally, in certain industries with specific requirements, the salt spray test duration can exceed 1000 hours.

Characteristics and Effects of Electrophoretic Coating

Detailed characteristics:

Electrophoretic coating can form a complete protective film even in highly concealed areas such as flanges, box structures, and tubular structures, resulting in high corrosion resistance.

Compared to spray painting, electrophoretic coating achieves a utilization rate of over 95%, reducing paint waste.

The electrophoretic process is stable and ensures a uniform coating on the workpiece.

The use of water as a carrier eliminates the risk of fire. It significantly reduces water and air pollution and reduces environmental equipment costs.

The bath solution has low viscosity (approximately equal to that of water), making it easy to pump and facilitating the draining of the coated body.

Uncured paint films are non-sticky and can even undergo certain treatments. Unlike sprayed coatings, electrophoretically deposited coatings do not run during drying.

Unlike immersion coatings, electrophoretic coatings deposited on internal surfaces are not washed off by hot steam during drying.

Due to fully automated production processes, labor costs are reduced, and coating production efficiency is greatly improved, making it highly suitable for mass production.

Electrophoretic Coating Colors

Clear (transparent), white, black, bright silver (rarely done by electrophoretic factories, as few can produce this color), gray, matte white, matte black, glossy black, red, purple, yellow, green, gold, rose gold, champagne gold, and partial electrophoresis (local electrophoresis) … almost all colors can be done!

Note 1

Due to technological limitations, not all electrophoretic coating factories can produce all colors. Generally, these factories produce some standard colors. However, if a custom color is needed, a significant order volume is required to support it; otherwise, the factory will not support custom colors.

Note 2

The most common electrophoretic color we see is black, which can be produced by almost every electrophoretic factory. The difference lies in the formulation ratio, resulting in slight color variations. Black colors typically include matte black, semi-matte black, glossy black, and others.

Note 3

If your order quantity is large enough and there is enough output value, the electrophoretic factory can also cooperate with you to achieve any color you want by adjusting the color.

Electrophoretic Process Flow

The process includes hanging the product, acid pickling, water rinsing, pre-degreasing, degreasing, water rinsing, phosphating, water rinsing, ultrasonic cleaning, pure water rinsing, electrophoresis, spray rinsing, water rinsing, pure water rinsing, air drying, baking, curing, quality inspection, packaging, and shipment.

Note 1

Different colors of electrophoretic coatings are achieved by adding different color pastes to the ED coating during the ED process.

Note 2

The ED (electrophoresis) process can be divided into four processes
electrolysis (decomposition), electrophoretic motion (swimming, migration), electrodeposition (precipitation), and electroosmosis (dehydration). These processes cause the charged coating ions to move to the cathode under the action of voltage and form insoluble substances on the cathode surface due to alkaline effects, which are deposited on the surface of the workpiece. By controlling the construction voltage and time and adjusting the bath temperature, the best electrophoresis effect can be achieved in combination with the proportion of various electrophoretic coatings.

Dacromet Processing Fee Explanation

As a process that specifically replaces the existing galvanizing (electroplating zinc/cold galvanizing) and hot-dip galvanizing technologies, Dacromet processing has a very clear target market. In most cases, customers are torn between whether to do galvanizing or Dacromet and are concerned about the comprehensive cost of both options. Therefore, based on the charging standard for galvanizing/cold galvanizing, I will examine whether Dacromet processing is expensive or not:

For small and medium-sized parts, the market processing price for electroplating zinc/cold galvanizing is calculated at 230 USD/Ton, and the cost of Dacromet processing is about 30%-50% higher, which is approximately 300-350 USD/Ton.

For large parts, the market processing price for hot-dip galvanizing is calculated at 300 USD/Ton, and the cost of Dacromet processing is about 20%-30% higher, which is approximately 360-390 USD/Ton.

Electrophoretic Processing Fee Description

Although electrophoretic processing is a relatively new surface coating technology, it has quickly become a widely used process due to its fast speed, high efficiency, obvious coating advantages, high automation level, and stable quality. In addition, because the upfront investment cost for electrophoretic coating is high, it is more suitable for large-scale workpieces. As a result, compared to other processes, the overall cost advantage of electrophoretic processing can be more apparent.

Minimum Charge

A sample fee is generally charged for electrophoretic coating samples, which is also the minimum charge, usually around $40 (charges may vary from each electrophoretic factory).

Charge by piece

this mainly depends on the size of the workpiece and specific process requirements, ranging from a few cents to several dollars or tens of dollars per piece.

Electrophoretic Processing Production Equipment Display

Electrophoretic coating processing production equipment typically includes several components that work together to produce high-quality coated products. Here are some common examples of the equipment used in electrophoretic processing:

The electrophoretic tank is an immersion tank used in the process of electrophoretic coating and electrodeposition coating. It consists of three basic parts: the main tank, the auxiliary tank, and the storage tank.The tank contains the electrocoating solution that is used to coat the product. The product is immersed in the solution, and an electric field is applied to deposit the coating material onto the product.

Power Supply:

The power supply provides the electric current that is used to deposit the coating material onto the product. The voltage and amperage of the power supply are carefully controlled to ensure consistent coating thickness and quality.

Anodes and Cathodes

Anodes and cathodes are used to generate the electric field that is used to deposit the coating material onto the product. The anodes are typically made of lead or graphite, while the cathodes are made of stainless steel or other materials.

Heat Exchanger

A heat exchanger is used to regulate the temperature of the electrocoating solution. The temperature must be carefully controlled to ensure consistent coating quality and thickness.

Filtration System

The electrocoating solution must be filtered to remove any impurities that may affect the quality of the coating. The filtration system is a filtering device used in the pre-treatment stage to separate the resin in the paint from water, solvents, and dissolved metal impurities. The ultrafiltration process is a separation process between the continuous phase (water + solution + dissolved impurities including dye salts) and the dispersed phase (resin and pigments). It can also be referred to as the separation process between the aqueous phase and the organic phase. The aqueous phase, which passes through the ultrafiltration membrane, is called the "permeate." The permeate contains solvents, all water-soluble ionic impurities, and some low molecular weight resins.

Conveyor System

A conveyor system is used to transport the product through the electrocoating tank. The speed and orientation of the conveyor system are carefully controlled to ensure even coating thickness.

Drying Oven

After the product has been coated, it must be dried to remove any excess moisture from the coating. A drying oven is used to heat the product and evaporate any remaining solvent.

These are some of the main components used in electrophoretic processing production equipment. Depending on the specific application, additional equipment may be required.

Electrophoretic Processing and Testing Equipment Display

Electrophoretic processing generally requires the following tests

Appearance inspection

After electrophoresis, the surface should be free of particles, lumps, pits, shrinkage holes, pinholes, water droplet marks, stains, foreign materials, hanging flow, unevenness, roughness, exposure, peeling, and other defects; detection method: naked eye observation;

Film thickness detection

Check whether the thickness of the electrophoretic paint layer meets the predetermined requirements; detection method: film thickness gauge;

Adhesion test of electrophoretic paint layer

(1) Scratch grid method: that is, conduct a scratch test with 100 grids at a 1mm distance, with the scratch depth reaching the base material, then stick with 3M tape and instantly pull it off with force, and it should not fall off more than 20/100; (2) Scratch test with circular rolling line: measure with an adhesion tester, not lower than level 5 in GB/T1720.

Hardness of electrophoretic paint layer

Measured by plowing method: use a 2H pencil to cut the tip, push the pencil at a 45-degree angle against the test material, and there should be no scratches on the surface.

Neutral salt spray test (NSS)

The electrophoretic parts require a neutral experiment of 24 hours or 48 hours. After the experiment, there should be no white, black, or brown corrosion points on the edges and outer surfaces of the samples, and the coverage layer should not be lower than level 5 according to GB/T6461.

Electrophoretic Processing Sample Case

Here are some examples of electrophoretic coating samples:

Automotive components

Electrophoretic coating can provide corrosion-resistant and wear-resistant protection for automotive components, such as wheels, grilles, and door handles.

Furniture accessories

Electrophoretic coating can provide a variety of colors and gloss for furniture accessories, while improving their corrosion resistance and durability, such as door handles, hardware fittings, and metal legs.

Electronic products:

Electrophoretic coating can provide an aesthetically pleasing protective layer for electronic products, while improving their corrosion resistance and electrical insulation properties, such as electronic shells, chassis, and panels.

Building decoration

Electrophoretic coating can provide a variety of colors and texture effects for building decoration materials, while improving their corrosion resistance and durability, such as aluminum alloy doors and windows, curtain walls, and aluminum plates.