Common problems and troubleshooting for micro concave coating unit

As we all known that, the coating unit is the coating machine’s key part. The coating quality and performance will be effected by the coating method. Shaanxi Beiren CL series precision coating equipment has become a top domestic brand in the field of high-end protective film and release film coating, and its market share in the high-end market has far exceeded the industry competitors. Currently, the CL series coating equipment usually use the following five kinds of coating method: micro concave coating, comma coating, Die coating, anilox coating and five-roll coating.

Micro concave coating is a reverse gravure coating, glue range 1-1000μps, coating thickness 1-80μm, mainly applicate for shading film, optical film, lithium battery materials, composite tape, protect film etc. The advantages of micro concave coating are thin coating layer, suitable for thin substrate, coating layer without glue, no wrinkles etc., and coating layer is uniform, easy to use which accepted by most of users. Here we summarize the common problems of micro concave coating and troubleshooting:  

Coating horizontal lines 

1、The precision of the micro-concave roller directly affects the uniformity of the coating layer and the quality of the product. The poor precision will cause horizontal stripes on the surface of the coating layer, and the horizontal stripes become dense with the increase of machine speed.

2、The precision of the front and back pressure roller of the concave roller directly affects the coating quality (horizontal and vertical lines), the runout of the back pressure guide roller to be less than 0.02mm. When the runout is bigger than 0.05mm, it should be replaced.

3、The micro concave roller’s bearing running situation should be checking in time, if the rotation is not flexible, should immediately replace.

4、Ensure the coaxiality of micro-concave roller, coupling, bearing and motor.

5、Ensure the film tension stable.

6、If the pressure of the doctor blade is too high or the blade is too soft, it is necessary to adjust the pressure and reinstall the blade.

7、The influence of other mechanical vibration on horizontal stripes cannot be ignored: ①It is suggested that the coating head and the motor should be fixed separately on the ground and connected with flexible part; ② The oven fan is separated from the oven bracket and a shock absorber is installed to reduce the vibration; ③All transmission reducer should use the famous brand with good quality

 Coating vertical lines, Mainly including two kinds, thin lines and thick.

Thin lines

1、Machine speed is high, micro concave roller running slowly, need adjust to the suitable speed ratio

2、Doctor blade pressure is big or blade installed inappropriately, need adjust the initial doctor pressure. Install the doctor blade and base plate properly.

3、Material tension is small, tension control accuracy is bad, wrap angle is small, need adjust the tension and film wrap angle accordingly.

Thick lines

1、Coating material including bubble, air etc, suggest to install plate to remove the bubbles.

2、High viscosity, high roll speed, high machine speed; Adjust to low viscosity, low machine speed, low roll speed

3、The ratio of gap to wet thickness of the coating is too large (Ho/t), and the coating layer is thin, which should be adjusted to a thicker wet cover thickness

4、There is dry glue below the blade or blade is worn, the blade should be cleaned or replaced in time

5、Micro concave roller net is blocked, need to be cleaned properly.

 

In addition: the small diameter rollers, such as micro-concave roller, back pressure roller need to be placed vertically. The micro-concave roller LPI, the viscosity of coating liquid, the surface tension and the solid content also will affect the product quality. The influence of coating liquid on micro concave coating is also very obvious, such as formula change may cause coating wetting difference, surface coating take off, etc. The mixing time, mixing ratio and addition time of curing agent will also affect the coating quality. Therefore, when coating, should be strictly according to the formula. Coating environment humidity and temperature have significant influence on coating quality. It is suggested that coating materials should be carried out under the condition of constant temperature. At the same time pay attention to the correct installation of micro-concave roller, doctor blade system. Eliminate the vibration caused by the motor and environment, maintain on time, clean, and improve the accuracy of the whole coating transmission system.