There are three coating methods: immersion coating, slide extrusion coating and free-fall curtain coating:

Immersion coating A method commonly used before the 1960s. The coating roller is immersed in the coating tank containing the coating liquid to a certain depth, and the support is wrapped tightly on the coating roller and runs forward at a constant speed. The coating liquid is evenly distributed on the surface of the support. Obviously only one coat can be applied per pass through the coating tank. The coating quality mainly depends on the liquid/solid wetting and spreading characteristics between the coating liquid and the coated support surface. The coating speed is generally limited to below 20m/min.

Each layer of coating liquid to be coated in slope flow extrusion coating enters the inner cavity of the extrusion nozzle from the feeding port, and then flows out from the opening gap located in the upper part of the inner cavity, overlaps each other on the inclined slope flow surface, and is flow downward under the force of gravity. The coating liquid contacts the coated support with a certain distance at the lip edge of the extrusion nozzle, and forms a specific liquid bridge. Through the action of the liquid bridge, the running support is uniformly coated with the desired coating. As long as the superimposed coating liquid layers can maintain a laminar flow state, and measures are taken to stabilize the liquid bridge, the smooth progress of a multi-layer high-speed coating can be ensured; when the total coating amount is kept constant, due to the realization of multiple Layer coating, the coating amount of each layer, that is, the coating thickness can be greatly reduced. Therefore, compared with traditional immersion coating, slide extrusion coating has the remarkable characteristics of multi-layer, thin-layer and high-speed. The advanced slide extrusion can coat more than 6 layers at the same time, and the coating speed can reach more than 100m/min.

Free-fall curtain coating is a new technology developed on the basis of slope flow extrusion coating process. The coating liquid flows out of the coating gap, passes through a special pouring slope, forms a free vertical curtain, and is transferred to the running support. This method avoids the influence of the coating gap and the liquid bridge, and is suitable for High-speed coating over several hundred meters.

Condensation and drying There is a lot of water in the photosensitive emulsion. The emulsion applied to the support will flow during the movement. Therefore, the coating should be condensed and shaped with cold air to make it no longer fluid, and then dried. Due to the requirements of the coating characteristics of photosensitive materials, air with low temperature (not exceeding 40°C), high wind speed (20~30m/s) and low water content is generally used for drying. The drying air must be specially air-conditioned and purified.