Coating technology: three common phenomena in cathodic electrophoresis and their solutions

The key points are as follows: cathodic electrophoretic coating is a special method of film formation, with the coating as the cathode, and the electrophoretic coating used is cation type (with positive charge) It is to dip the coating with conductivity into the electrophoretic coating tank diluted with full water and with relatively low concentration as the cathode, and set the anode corresponding to it in the tank, and apply direct current between the two poles A coating method in which a uniform, water-insoluble film is deposited on the coating Here are three common phenomena of cathodic electrophoresis and their solutions I particle (1) phenomenon The surface of the dried electrophoretic coating is rough and hard Paint knowledge | precautions for wall paint color selection Recommended introduction: when painting the wall, the owner sometimes has difficulty in choosing what color of the wall paint to paint In fact, there is no ugly color in the wall paint, only the disharmonious color matching The use of wall color contains the knowledge of health Too strong color will stimulate people's perception, make people have a sense of fidgety, affect people's mental health Grasp the basic principles of wall color and paint a colorful space 1、 Wall paint color selection notice 1 Light color is generally used for the top surface Light colors make people feel light, dark colors make people feel heavy Usually, the treatment of rooms is from top to bottom, from shallow to deep For example, the ceiling and walls of rooms are white and Home of coatings: cathodic electrophoretic coating is a special coating The formation method takes the coated object as the cathode, and the electrophoretic coating used is cationic type (with positive charge) It is a kind of coating that the conductive coated object is immersed in the electrophoretic coating tank diluted with full water and with relatively low concentration as the cathode, and the corresponding anode is additionally arranged in the tank, and the direct current is applied between the two poles to precipitate uniform and water-insoluble coating film on the coated object Method Here are three common phenomena of cathodic electrophoresis and their solutions 1、 Particles (1) there are rough and hard particles on the surface of the dried electrophoretic coating film, or small prickly heat particles visible to the naked eye The horizontal surface of the coating is often more serious than the vertical surface, which is called particles (2) The causes are as follows: ① the pH value of CED bath solution is too high, and alkaline substances are mixed in, resulting in unstable bath solution, resin precipitation or agglomeration ② There are precipitated "dead angle" and exposed metal in the tank ③ After electrophoresis, the cleaning solution is dirty, the paint content is too high, and the filtration is poor ④ The surface of the coating and the spreader are not clean, and the water washing after phosphating is poor ⑤ During the drying process, the granular dirt falls ⑥ The painting environment is dirty ⑦ The supply coating or resin is poorly dissolved and has particles (3) Prevention and control methods: ① control the pH value of CED tank liquid to the lower limit, forbid to bring alkaline substances, strengthen filtration, and accelerate the renewal of tank liquid ② Eliminate the "dead angle" that is easy to precipitate and the bare metal parts that produce deposition coating To enhance filtration, it is recommended to use a filter element with a precision of 25 m for foams ④ Ensure that the coated surface is clean and free of phosphating sediment to prevent secondary pollution ⑤ Clean the drying chamber and air filter ⑥ Keep the painting environment clean, check and eliminate the dust source of air ⑦ Ensure that the new paint dissolves well and the color paste fineness is within the standard range 2、 Shrinkage (cavity) (1) can't be seen on wet electrophoretic film After drying, crater like pits appear on the surface of the film, with a diameter of 0.5-3.0mm The ones without bottom exposure are called cavity, depression and bottom exposure are called shrinkage cavity, and the ones with particles in the middle are called fish eye The main reason for this defect is that there is dust in or on the surface of the electrophoresis wet film, and the particles that are insoluble between the oil and the electrophoresis coating become the center of the cave, which makes the flow development ability of the wet film at the early stage of drying unbalanced, and the film defects occur (2) The causes are as follows: (1) the degreasing is poor before the coating or the oil and dust fall after cleaning ② Oil is mixed in the tank liquid, floating on the liquid surface or emulsifying in the tank liquid ③ After electrophoresis, the washing solution is mixed with oil stain ④ The drying room is not clean, and the circulating air contains oil ⑤ The ratio of pigment to base of the bath solution is out of balance, and the pigment with low content is easy to produce shrinkage cavity ⑥ The coating environment is dirty, the air may contain oil mist, paint mist, organic silicon and other pollutants or wet coating ⑦ The supply coating has shrinkage cavity or the resin in it has poor dissolution and poor neutralization (3) Control methods: ① strengthen the degreasing process of the coating to ensure that the phosphating film is not polluted twice ② The tank liquid circulation system shall be equipped with oil removal filter bag, and the oil pollution source shall be checked at the same time It is strictly prohibited to bring oil into the tank ③ Improve the cleaning water quality and strengthen the filtration ④ Keep the drying room and circulating hot air clean ⑤ Adjust the ratio of pigment to base of the bath solution, and properly add the color paste to increase the pigment content ⑥ Keep the coating environment clean and remove the harmful material sources, especially the organic silicon material sources ⑦ Strengthen the management of replenishment coating Unqualified coating shall not be added to the tank to ensure that the replenishment coating is well dissolved, neutralized and filtered 3、 Pinhole (1) phenomenon: after drying, the electrophoretic coating will produce small pinhole or pinhole The defect of this coating is called pinhole The difference between pinhole and shrinkage (pockmark) is that the aperture is small, the center is free of foreign matters, and the surrounding area is free of film accumulation and bulge According to the causes of pinholes are as follows: ① the pinholes caused by wet film re dissolution resistance are called re dissolution pinholes ② In the process of electrophoresis, due to the intense electrolysis reaction, there are too many bubbles, bad defoaming or low temperature or insufficient stirring of the bath solution, resulting in the coating, and the pinhole produced by the bubble rupture in the drying process is called bubble pinhole 3 The step pin holes in the charged slot: when the level of defects in the charged slot is serious, the pin holes are exposed along the slant line of the slot In addition, due to the poor wetting of the liquid on the surface of the surface, some bubbles are sealed in the paint film or the surface of the liquid surface is attached to the surface of the workpiece to form bubble pinholes, which generally occur at the lower part of the coated material (2) Causes: ① after electrophoretic coating, the coating was not cleaned out of the tank in time, and the wet coating produced re dissolution ② The impurity ion content in the bath solution is too high, the electrolysis reaction is violent, and too much gas is produced on the surface of the coating ③ Phosphating film has high porosity and easy to contain bubbles ④ The temperature of the bath solution is too low or the agitation is not enough, which makes the wet film defoaming badly ⑤ The transport chain speed is too slow when the workpiece is charged into the slot The liquid flow velocity of the coated tank is low, and there is foam accumulation (3) Prevention and control method ① the coated material shall be washed with UF solution or pure water immediately after leaving the tank solution, and the time shall not exceed 1min ② Discharge UF liquid and add pure water to reduce the content of impurity ions ③ The phosphating formula and process were adjusted to make the phosphating film crystallized and densified ④ Strengthen the mixing of the tank liquid to ensure that the temperature of the tank liquid is 28 ~ 30 ℃ ⑤ When the chain speed is too slow, it is not suitable to select the electrophoresis coating process with the way of charging into the tank, instead, power on after entering the tank The flow velocity of the tank is greater than 0.2m/s, so as to eliminate the accumulated foam Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and 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