Analysis of Common Problems of Dry Coating in the Manufacturing Process of Waterborne Polyurethane Synthetic Leather
pinholes on the surface
The reasons for the occurrence of pinholes on the surface are: the viscosity of the surface layer is too high, the coating is too thick, the temperature of the first oven is too high, the drying time of the surface layer is too short, there are too many bubbles in the prepared material, and there is air in the coating tank Join etc. The situation of the slurry during drying is shown in the figure below. Since the release liner is much thicker than the stock, this structure is formed before the heat of heating arrives.
Analysis of Common Problems of Dry Coating in the Manufacturing Process of Waterborne Polyurethane Synthetic Leather
When the viscosity of the surface layer is too high, the water vapor generated during drying is not easy to escape from the coating, resulting in small air pockets and pinholes. Reducing the viscosity of the top layer mixture can solve the pinholes caused by this reason. If the coating is too thick, the water vapor will not be easily discharged, which will also cause pinholes. Coating thickness should be reduced when this problem is encountered. If the temperature of the first oven is too high, a large amount of water vapor will be generated instantaneously, and these water vapors cannot be effectively discharged, resulting in pinholes. Therefore, the temperature of the first oven should not be too high. When the drying time of the surface layer is short and the surface layer is not completely dried, the slurry of the second layer will affect the discharge of water vapor from the surface layer, and will also cause pinholes. This requires the surface layer slurry to be completely dried before the second layer can be applied. There are many bubbles in the prepared material, which is also one of the reasons for the pinholes on the surface. The prepared slurry needs to be left to stand for defoaming before use. The addition of air into the coating tank will also cause surface pinholes. At this time, it is necessary to add a baffle to the coating to fill the material tank.
jam
The reasons for paper jams are: too small gap, residues on the paper, too thick paper joints or tape roll, improper operation, the edge of the first coating scraper is covered by the second coating to accumulate the jammed paper, there are tapes and other debris on the back of the paper Wait.
When the knife gap is too small, the knife may come into contact with the release liner and cause paper jams. Therefore, it is necessary to operate according to the standard process gap. Residual debris on the paper will be caught between the paper and the knife, causing paper jams. In this case, the paper inspector should remove the debris on the paper in advance. Paper jams can also occur if the paper splices are too thick or if the tape is rolled up. Therefore, the paper joint must be straight, and the tape must be glued and flattened. Paper jams will also occur when there are debris such as tapes on the back of the paper. Before using the paper, in addition to checking the surface, pay attention to the back. If the edge of the first coating scraper is covered by the second coating material, the second coating should be used to cover the first coating, and the edge material should be removed at any time with a feeler gauge. Improper operation is also one of the causes of paper jams, so it is necessary to operate according to the operating procedures.
scratches on the surface
The reasons for the scratches on the surface are: the blade of the scraper is defective, there are debris in the material, the filter barrel is not clean, the coating equipment such as the scraper is not clean, the tools are not clean, the filter is not used properly, the mesh size is wrong, and people are careless. fall into debris, etc.
The defective blade of the scraper will lead to uneven feeding, too much or too little local material, resulting in scraping lines. In this case, the scraper should be repaired or replaced. If there are debris in the material and the filter barrel is not clean, these debris will be stuck in the gap between the coating knives, affecting the feeding and causing scraping. Therefore, the filtration should be strengthened, and the clean barrels can be used. Similarly, the coating equipment such as scraper is not clean, and the tools used are not clean, which will also cause scratches. The equipment should be hygienic, and the necessary tools should be cleaned. If the filter is used improperly and the mesh size is wrong, the large particles in the material may be stuck in the gap between the coating knives, resulting in scratches. Therefore, when filtering, it is necessary to clarify the scope of use of the filter and pay attention to the number of meshes. Of course, the accidental drop of debris is also one of the reasons for scratching the line. In this case, the responsibility should be strengthened. As soon as there is a drag line, it should be handled
