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Analysis of Common Problems of Dry Coating in the Manufacturing Process of Waterborne Polyurethane Synthetic Leather

Analysis of Common Problems of Dry Coating in the Manufacturing Process of Waterborne Polyurethane Synthetic Leather

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  • Time of issue:2018-09-11 17:34

(Summary description)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

Analysis of Common Problems of Dry Coating in the Manufacturing Process of Waterborne Polyurethane Synthetic Leather

(Summary description)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

  • Categories:news
  • Author:
  • Origin:
  • Time of issue:2018-09-11 17:34
Information
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 with a feeler gauge smaller than the coating gap.
 
    color bar color difference
 
    The reasons for the color difference of the color bars are: quality problems of raw materials such as color paste and colorants, changes in coating amount or unstable vehicle speed, too low material level in the trough, no material stirring, poor compatibility between colorants and resins, and poor color matching. Strict lack of attendance, color difference of ingredients, layering of materials, etc.
 
    If the color bar color difference is caused by the quality problems of raw materials such as color chips or pigments, it is necessary to strictly control the materials. Changes in coating weight or unstable vehicle speeds can cause uneven coating thickness, resulting in color differences. Therefore, the coating gap and vehicle speed must be stable. The material level of the trough is too low, and if the material is not stirred, the slurry will be uneven and the color stripe will be different. It is very necessary to keep a certain material level during the tanning process, and it is very necessary for the coating personnel to keep stirring the material. Sometimes there is no problem with the quality of the colorant, but poor compatibility with the resin used can cause color banding. It is necessary to use matching pigments or resins. If the color bar color difference caused by the material layering, pay attention to the viscosity adjustment and strengthen the stirring and feeding. If the color is not strict and diligent, and the color of the color bar is caused by the color difference of the ingredients, the craftsman and the monitor should strengthen their responsibilities and strictly control.
 
    The hand feels wrong, the crease is too large
 
    The reasons for the wrong hand feel and the too large creases are: wrong resin modulus, too thick coating, too wet bonding, and improper bonding pressure.
 
    Modulus is one of the important indicators to measure the feel of resin, and the leather feel will be different if the modulus is not correct. Therefore, the appropriate resin modulus should be selected. When the modulus is too high, the hardness of the finished leather is large, and creases are easy to occur. At this time, the resin modulus should be reduced. If the coating is too thick, the finished leather is prone to creases due to extrusion. In this case, the coating amount should be reduced. If the lamination is too wet, a large amount of pulp will penetrate into the base material, resulting in the leather being too hard and prone to creases. In this case, the dry humidity of the fit should be adjusted. If the bonding pressure is too large, a large amount of slurry will also penetrate into the substrate, resulting in a hard feel.
 
    "Fish Eye", "Orange Peel"
 
    "Fish eye" is a small circular area in which there is no coating agent, and "orange peel" is a slight ripple on the surface of the coating film, both of which are caused by the failure of the coating agent to wet the The solution is to add a leveling aid or reduce the viscosity, reduce the surface tension and improve the wettability. If there are oily hydrophobic substances on the surface or material of the release paper, it will also cause "fish eyes" and "orange peel". When batching, choose additives that do not contain hydrophobic substances, and do not use batching buckets that have been in contact with oily hydrophobic substances. In the choice of release paper, do not use PVC release paper. In short, the choice of ingredients and release paper should be strictly checked.
 
    Pad wound or coating spot
 
    Bright spots or coating spots are caused by debris on the back of the paper or debris on the coating roll. These contaminants can affect the uniformity of the coating, resulting in pad scratches or coating spots. Therefore, the debris on the back should be removed when checking the paper, and the debris on the coating roller should be removed before feeding.
 
    Pre-peel and paper leather adhesion
 
    Both of these drawbacks are caused by the poor compatibility between the coating agent and the release paper. The adhesion between the coating agent and the paper is too small to cause pre-peeling, that is, the surface layer film has been separated from the paper during the drying process of the adhesive layer coating agent laminated base cloth (skin), and the corrective method is to mix it in the surface layer Sprinkle some sticky coating agent. The adhesion between the coating agent and the paper is too large, which will cause the peeling resin on the surface of the paper to fall off or tear the paper when peeling off. Choose a coating agent that is compatible with the release paper.
 
    In a word, the production process of dry coating is a relatively complex process of physical and chemical changes, and the problems that occur in actual production are also ever-changing. .
 
    Does not fit well
 
    In the dry production of water-based synthetic leather, there are often problems in lamination, especially the phenomenon of poor lamination, which is one of the most troublesome problems in the manufacture of synthetic leather.
 
    Insufficient fit generally has the following reasons: 1. Improper selection of resin. Generally, if the resin selected is too soft, it will cause more poor adhesion; ②The size of the sizing material of the laminating material or the serious damage of the release paper will cause the lack of local sizing and lead to the poor adhesion; Properly, the resin of the adhesive layer is too dry, and there is no adhesiveness, which leads to poor bonding; 4. After bonding, the pressure roller is too loose, resulting in poor bonding; 5. The base fabric has been treated with anti-adhesive or water repellent The material results in a non-adhesive fit.
 
    In addition, the water-based resin adhesive must be fully dried to have adhesive force, otherwise it will be degummed when exposed to water. In particular, the speed of the bass veneer is more than half slower than that of the oil-based resin under the same conditions. Otherwise, the bottom surface of the synthetic leather will be separated after being rubbed with water because the resin of the lamination layer is not dried.
 
    feel too hard
 
    When water-based resin is used as a lamination layer, especially for soft synthetic leather, it will feel too hard. This kind of phenomenon generally comes from two reasons: one is that the resin selection is too hard; On the one hand, if the viscosity of the primer resin is too thin, it will cause glue leakage. On the other hand, if the lamination is too high, it will also cause glue leakage or hardening.

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