(1) Roller coating characteristics
Roller coating is suitable for the coating of flat metal plates, plywood, and paper, especially for high-speed coating of metal coils. Roller coating has the following characteristics:
(1) High-speed automatic coating operation, high production efficiency, and the line speed is generally above 100m/min;
(2) The paint utilization rate is close to 100%;
(3) Suitable for coatings of various viscosities, the coating film can be thick or thin, and the thickness is uniform;
(4) Both sides can be coated at the same time.
However, in the process of roller coating, the solvent volatilizes quickly, which easily causes the viscosity of the coating to change, and the process conditions are not properly controlled, and the coating film is prone to roll marks.
(2) Roller coating equipment
The roller coating equipment is composed of pretreatment, roller coating machine and baking equipment. The process is as follows: Coil unwinding→sewing→looper→paint pretreatment→drying→roller coating→baking→water cooling→looper→cutting→coiling.
The roller coater consists of a coating mechanism (feeding roller, coating roller and coating pan), a steering support mechanism and a drive motor. Roller coaters are available in the following types to suit various applications.
1. Same direction roller coater
It is suitable for thin coating of low-viscosity paint, the dry film thickness is 10~20µm, and the line speed does not exceed nearly 100m/min. The thickness of the coating film is adjusted by adjusting the gap between the rollers.
2. Reverse roller coater
High-viscosity coatings can be applied to obtain thick coatings, the wet film thickness is 50~100µm, and the coating viscosity can be above 120s. The thickness of the coating film is adjusted by the gap between the take-up roller and the applicator roller.
High-viscosity coatings are likely to cause insufficient material intake, and the top feeding method should be adopted to ensure sufficient material supply by the gravity of the coating itself.
The coating effect is adjusted by the speed ratio between the applicator roll and the back-up roll. For the same direction roller coating, the speed ratio of the coating roller and the backing roller should be less than 1 to improve the surface quality of the coating film; when the reverse roller coating is used, the speed ratio should be slightly greater than 1 so that the coating roller coating can be evenly transferred to the coil.
