Air knife coating is the most common and effective coating equipment among all coating machine manufacturers in China. The advantage of air knife coating is that it does not directly contact the paper surface but blows excess paint off the paper. Therefore, air knife coating is particularly suitable for in-machine coating and cardboard coating. Saving paint here means maintaining the specified coating amount while ensuring quality, preventing waste of paint and reducing costs.

1.Coating solid content:

The characteristic of air knife coating is that the coatingweightis relatively large (10-40g/m2) and the solid content of the coating is required to be low (20-50%). When the solid content of the coating reaches about 60%, not only the coating amount will increase significantly, but also uneven coating will occur, the coating will stick to the cylinder and powder will fall off, the coating will spray back, the air knife will be clogged, foam will increase, the overflow will be clogged, and the material trough will be blocked. The inner coating is easy to deposit or solidify, making it difficult to operate. When the vehicle speed is increased, the time for the coating to pass through the air knife airflow is short, and the amount of excess paint blown off is relatively small, and the coating amount will increase; as the temperature rises, the coating will lose water quickly, which will also cause the coating amount to increase. Therefore, as the vehicle speed and temperature increase, the solid content of the paint should be reduced to maintain an appropriate coating amount, which not only savesmaterialbut also reduces the drying load.

2.Supply ofcoating chemical:

Material pump leakage not only causes waste, but also pollutes environmental hygiene. The paint contains a lot of stone powder, which can easily cause the material pump to wear and leak. It is best to use an anti-wear and anti-seepage material pump. Because the solid content of the air knife coating is not high, it is not necessary to use a medium consistency slurry pump that is prone to leakage, but a general non-clogging sewage pump! Sewage pump, mud pump), which can not only save energy and maintenance costs, but also prevent leakage. If it leaks, it also leaks back into the material trough. Be careful not to place the trough next to heat sources such as ovens, drying cylinders and radiators, especially stainless steel troughs, to prevent the paint from losing water and solidifying due to heat and wastage.

3.Quality of base paper:

When the base paper enters the drying section, it should be dried strictly according to the appropriate drying curve. When the dryness of the paper exiting the dryer is controlled at about 90%, not only the calendering effectGood, and the water absorption of the base paper is moderate, the "filter cake" formed by the coating when meeting the base paper is moderate, and the coating is smooth and not easy to fall off. If the base paper is too dry, the water absorption will be strong, the "filter cake" will become thicker, and the coating will easily lose powder; if the base paper is too wet, the "filter cake" will become thin, resulting in uneven coating and insufficient whiteness. Holes, broken edges, and paper breaks in the base paper should also be minimized.

4.Air knife operation:

Knife angle refers to the inclination angle of the air knife, generally 0-15°. If the angle is small, the air flow will act on the coating at a nearly vertical angle. If the depth of the blow shovel is large, the paint will be blown off.

If the angle is too large, the coating amount will be reduced; if the angle is large, the airflow will act on the coating at a tangent angle, and the depth of the blow shovel will be shallow, and the coating amount will increase. The knife pitch refers to the distance between the knife edge and the lining roller surface, generally 2-8mm. To ensure that the knife edge does not scratch the original paper when the air knife is being raised or lowered, the knife distance should be as small as possible to increase the force of the air knife airflow. The knife gap is the width of the knife edge, which is generally 0.5-1.5mm. If the knife edge is too small, it will be easily blocked, and if the knife edge is too large, the wind pressure will be reduced. The general requirement for wind pressure is 10-60Kpa. The wind pressure is small and the coating amount increases. The speed of the belt roller (also called the feed roller) increases, the direction of rotation is opposite to that of the base paper, and the belt roller is immersed in the material tank, which will increase the coating amount. The pressure of the paper roller is low, the contact surface between the base paper and the belt roller is large, and the coating amount is increased. The leveling roller not only has the function of smoothing the paint, but also serves as a metering roller. The base paper is pulled tightly, the tension is high, the base paper is in close contact with the belt roller, and the coating is uniform. Of course, if you pull it too tight, it will easily lift the pressure roller or break the paper. The base paper is loose, the contact between the base paper and the belt roller is uneven, and the coating is uneven. In addition, the coating width should not be too wide. If it is too wide, there will be too much waste paper trimmed, whichalso causesa big waste.