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    Home > Coatings News > Paints and Coatings Market > The causes and prevention methods of electrophoresis paint shrink holes.

    The causes and prevention methods of electrophoresis paint shrink holes.

    • Last Update: 2020-10-16
    • Source: Internet
    • Author: User
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    The problem of electrophoresis paint shrink hole is one of the most common paint film problems in the process of coating production, and it is also one of the most important problems to be paid attention to in the pre-treatment. For the film pre-treatment matching high-swimming permeable electrophoresis paint, high-swimming permeable electrophoretic lacquer tank liquid is more sensitive to oil and silicone-like substances, once the problem of shrinking holes, easy to form a batch of quality problems, and affect the appearance of the product paint film and anti-corrosion ability, has a great impact on product quality.
    the cause and classification of electrophoresis paint shrink hole formation
    Electrophoresis paint shrink hole formation is caused by surface stress gradient, electrophoresis paint shrink hole type according to its appearance and formation characteristics can be divided into four types .
    the principle of shrink hole formation
    . 1. Particles, fiber shrink holes
    this type of shrink hole is caused by the external low surface pressure or solid material, falling on the surface of the electrophoresis paint wet film. This shrink hole is characterized by the visible of fibers, particles and other foreign objects in the middle of the shrink hole.
    2. Oil-stained shrink hole
    oil-stained shrink hole is due to low surface pressure of oil glue, silicone-like substances fell on the paint film caused by this shrink hole in the middle position can not see the raised particles, normal conditions will not be exposed, the size is generally 0.5 to 3 mm. Such shrink holes generally occur before electrophoresis paint film curing, if after curing will generally only form oil spots or very shallow depressions, more convenient to deal with.
    3. Groove liquid shrink hole
    groove shrink hole refers to the groove fluid by equipment, environment or work pieces with the shrink material pollution, and after a long period of accumulation caused by the groove fluid itself shrink hole problem. Such shrink holes are bound to be accompanied by oil-stained shrink holes, its appearance is similar, the impact of the early stage is small, can be confirmed by the site tank liquid monthly inspection monitoring.
    4. Bubble shrink hole
    this shrink hole by solvent bubbles, small foam, etc. piled up on the surface of the electrophoresis paint wet film, into the oven before not completely washed defrosting, after baking film curing formation, this shrink hole is generally larger and easy to dew bottom.
    measures to solve the electrophoresis shrink hole
    to solve the electrophoresis shrink hole problem to control the source of impurities, reduce the source of oil pollution.
    1. The main source of oil pollution from electrophoresis coating line
    (1) when welding white body, anti-rust oil to prevent rust coating, as well as the pressure oil used in the body production process, etc. The surface of the work part, especially the rust-proof oil, pressure oil, oil and other oil stains present in the inner surface and seams, after long transport and storage, partially dried up to form stubborn oil stains, usually can not be effectively removed in the skimming tank. The solution is to remove stubborn oil stains from the white body with pre-scrubbing agent, which can greatly reduce the chance of stubborn oil stains entering the electrophoresis tank and directly eliminate the important source of oil contamination in the tank, thereby reducing the chance of shrink holes.
    (2) the lubricant dripping from the conveyor chain and sling. During the operation of the electrophoresis synchronous double-stranded and ground rollers, the power transfer mechanism needs to be lubricated regularly and oil applied. When the conveyor chain and sling are running over the electrophoresis tank, the lubricant may drip into the electrophoresis tank, causing the hole to shrink. The solution is to clean the conveyor chain and lifting gear on a regular basis, to set up an oil plate under the conveyor chain and the lifting gear to prevent oil from dripping into the electrophoresis tank, to ensure that the joint joints and welds are sealed, and to be cleaned regularly.
    (3) after long-term use of the oven, the smoke from the coating baking is attached to the inner wall of the oven in large quantities and is also a source of impurities. The shrink hole produced in the drying process is generally not exposed, commonly known as the "superficial shrink hole", the reason is that the workware in the oven by the influence of oil smoke. The solution is to clean the inner wall of the oven regularly, check whether the circulating wind used in the oven contains oil and pollutants, usually strengthen ventilation to discharge exhaust gas, to prevent the accumulation of fumes.
    2. Enhanced skimming on the electrophoresis coating line
    1) pre-treatment of degreasing. Factors that affect the effect of skimming include the time of degreasing, the temperature of degreasing and the material of degreasing agent. Can appropriately extend the time of degreasing, improve the temperature of skimming 5 to 10 degrees C, improve alkalinity (generally improve 2 to 3 alkalinity) to strengthen the degreasing effect of the work piece;
    water flushing process before electrophoresis (2) electrophoresis. The body droplets after degreasing are still oily and require an increase in the pure water flushing process and monitoring the conductivity of the pure sink (usually required ≤ 30 s/cm) and the drop water and electricity conductivity (usually ≤ 20 s/cm) before the body enters the electrophoresis tank. Collecting high conductivity water droplets from these two parts of the process and adding them to the laboratory electrophoresis tank fluid for experiments showed that they were one of the reasons for the shrink hole. Increase the pure water flushing process, and monitor the conductivity of pure water tank, drop water and electricity conductivity before entering the tank, can effectively prevent this part of the oil into the electrophoresis tank, thereby reducing the production of shrink holes.
    (3) electrophoresis groove degreasing. The ordinary filter bag used in the filtration system is replaced with a strong oil-absorbing filter bag, and the frequency of the oil-absorbing filter bag is changed to strengthen the oil pollution in the adsorption tank fluid, which can also reduce the oil content and reduce the reduction of holes.
    (4) after the electrophoresis tank. After the end of the work part electrophoresis leaves the electrophoresis tank, there is still some groove fluid, even oily groove liquid will attach to the surface of the work piece. If you rinse only after coating according to the normal method, there is also a greater possibility of shrink holes after drying. In order to reduce the surface paint of the work piece, eliminate the factors of shrink holes, usually after electrophoresis set the groove spray, through ultrafiltration (UF) 1 / ultrafiltration (UF)2 and pure water 3 channels of immersion, can achieve good results.
    3. Strengthen the parameter control of electrophoresis tank
    Electrophoresis process, if the slot voltage, slot liquid face ratio, solvent content control is not proper, the same will produce shrink holes. The electrophoresis process allows the metal surface to release some heat, and the resulting temperature allows the cathode electrophoresis paint to begin to partially cure during deposition. This uneven curing, especially the air bubbles produced when the work piece is first slotted, is an important reason for shrinking holes in the surface of the paint film. Reducing the slot voltage can effectively avoid this problem without affecting the thickness of the film and the performance of the paint film.
    tank liquid pigment base ratio is too low, indicating that resin and pigments are not completely deposited in proportion, electrophoresis process knock-through voltage drop, poor electro-permeability, swimming permeability decline, coating film easy to produce shrink holes. The solution is to strengthen the parameter control, regularly add high concentration pigment slurry, and appropriately improve the tank liquid pigment base ratio.
    solvent content has a great influence on the stability of the slot solution, the smoothness of the paint film and the thickness of the paint film. Solvent content is too low, then the paint film is thin, poor smoothness, easy to shrink holes and pinhole defects. The solution is to regularly replenish the tank fluid with solvents.
    practical application shows that: alone to improve the face-based ratio or solvent content is not particularly effective for the elimination of shrink holes, improve the face-based ratio and keep the solvent content in sync, you can get better results.
    4. Improve the anti-shrinkability of electrophoresis paint
    by adjusting the surface stress gradient of the paint film and impurities, the same can be achieved to reduce the paint film shrink hole. The following measures can be taken:
    1) choose a lubricant with strong adaptability to electrophoretic paint resin
    The same concentration of different lubricant pollution caused by the tank liquid surface stress gradient is also different, the smaller the surface pressure gradient, indicating that the higher the tolerance of the tank fluid for this kind of lubricant contamination, the less likely to produce shrink holes. Selecting lubricants that can be immersed in each other with electrophoretic paint resin and have a small difference in the pressure gradient of the surface of the groove is beneficial to improve the anti-shrinking performance of electrophoresis tank fluid.
    2) Use a small amount of low-temperature unsealed crosslinker
    use a small amount of low-temperature unsealed crosslinker as a cathode electrophoresis paint fully enclosed crosslinker, in the paint film baking curing early can be quickly unsealed, so that the relative molecular quality of the resin to a certain extent rapidly increase, thereby adjusting the flow of the paint film, improve the oil-resistant oil shrinkage of the electrophoretic paint film.
    attention to cross-linking agent addition control, so as not to affect other properties of the paint film.
    3) the oven using gradient heating, through heat leveling to improve the shrink hole
    the initial heating of the oven too fast, the crosslinking agent in the wet film will quickly unseal to participate in cross-linking reaction, which will lead to poor surface leveling of the coating film. Under the premise of ensuring the coating film curing completely, the temperature of the first section of the oven is reduced appropriately, and the defects of partial paint film shrink hole can be concealed to a certain extent by heat leveling, forming a smoother dry film.
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