The requirements of polarizing film coating machine are similar to other optical film coating production lines, which require precise manufacturing and accurate control. This paper briefly introduces the market situation and structure of polarizing film, expounds the main production process and structure composition of polarizing film coating, and puts forward relevant views on how to reduce the investment cost of polarizing film coater and the localization of equipment.

Summary
The production of polarizing film is divided into three processes: TAC surface treatment, PVA stretching and laminating after release film coating. This paper only describes the optical coating machine for release film coating and lamination.

Corona device
The use of corona device is to carry out surface shock treatment on the coated side according to the needs, so as to make it have higher adhesion. The principle of this method is to use high frequency and high voltage to corona discharge on the surface of the treated plastic to produce low-temperature plasma, which makes free radical reaction on the surface of the plastic, so as to cross link the polymer, roughen the surface, and increase its wettability and adhesion to polar solvents.

Coating head
The coating head is the core of the whole coating production line. At present, there are comma knife and slot die for polarizing film coating.
The suitable coating thickness of comma knife is 18-100 μ m, and the viscosity of coating solution is high. Its outstanding advantage is that it is easy to change the coating width, and the glue supply system is relatively simple. But there is a problem of large area exposure of coating solution, so the cleanliness of coating head must be ensured.
Slot die slit coating is a kind of coating method of estimated amount, that is to say, the coating amount depends on the ratio of input coating liquid amount and substrate running speed, which can be set accurately in advance. High precision non pulse metering pump is usually used to transport coating liquid. Slot die coating can be divided into two ways: back roller direct contact and substrate tension control. The polarizing film coating is mainly back roller direct contact. This kind of coating has a wide range of thickness, about 3 ~ 300 μ m, which can meet different application requirements, and is suitable for production speed from low to high. Its coating accuracy is affected by the flatness of the back roll itself and the beating of the bearing. Because the coating gap is very small, it is very sensitive to the change of substrate thickness and the influence of surface foreign matters. In the production process, it is difficult to clean the coating solution when changing the coating solution, so it needs to be cleaned repeatedly with solvent.
The thickness error of the two kinds of coating can be controlled within 1 μ M. Among them, slot die slit coater has higher precision, high cost, and needs to be equipped with a perfect glue supply system.