1. Purpose of coating
The purpose of coating is to evenly coat the prepared slurry on the surface of the current collector, dry it, and make the cathode and anode plates respectively. The current collectors of the cathode and anode are aluminum foil and copper foil, respectively.
Coating has the following requirements: the size of the coating film area and the metal area conform to the document specifications. The weight of the coating film area is within the document specification range. The adhesion between the diaphragm and the current collector is OK. The coating film area cannot appear metal leakage. The appearance of stripes, bubbles, large particles, tailing, etc. is not good. The quality of coating has a great influence on the subsequent good rate.
2. Coating principle
The coating roller rotates to drive the slurry, adjust the amount of slurry transfer by adjusting the blade gap, and use the rotation of the back roller or the coating roller to transfer the slurry to the substrate. According to the process requirements, the thickness of the coating layer is controlled to meet the weight requirements. At the same time, the solvent in the slurry spread on the substrate is removed by drying and heating, so that the solid substance is well bonded to the substrate.
3. Coating equipment
The coating machine mainly includes eight parts: unwinding system, front unwinding tension, rectifying system, coating head, Baking box, rear winding rectifying, tension system, winding system. Coating methods are divided into transfer coating and extrusion coating according to different coating principles. All the coating heads of these two coating methods are quite different. The coating head used in transfer coating includes three parts: coating roller, scraper and back roller. The coating roller rotates to drive the slurry. We can adjust the transfer amount of the slurry by adjusting the blade gap, and use the rotation of the back roller to transfer the slurry to the substrate to achieve uniform coating. The coating head used in extrusion coating includes three parts: pump, extrusion device and back roller. The slurry is pumped to the extrusion device, and then directly transferred from the extrusion port of the extrusion device to the substrate, and then we adjust the amount of slurry transfer by adjusting the gap of the extrusion port.
4. Coating weight detection
Before the official production of coating, it is necessary to do the first inspection. The first inspection includes weight, size and so on. The weight test is to take a whole piece of diaphragm, cut it into small circular pieces with a special die machine and weigh it. A total of 12 pieces are taken from each part, and the weight of each piece is required to be within the range of the document specification. Dimensional inspection is to use a soft ruler to measure the length of the film coating area and gap of the diaphragm, which is required to be within the scope of the document specification.
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