The comma blade coating method is widely used in various coating industries. It is characterized by accurate coating weight, wide adjustable range of coating thickness, good adaptability to the solid content of coating chemicals, simple structure and simple operation.

1 Two types of traditional comma blade coating machine

1.1 Structure 1 (Shown in Figure 1)

The flat plate and the rubber baffle plates on both sides form a glue groove with the coating rotating bottom roller. A layer of bottom film is applied to the flat plate to prevent glue from leaking from the bottom. The substrate material runs from bottom to top to form a coating surface. The coating surface is formed by the scraper roller and rotation. The gap between the bottom rollers controls the thickness of the coating. The excess glue scraped off by the scraper edge flows back to the glue tank. The barrier films on both sides are used to make the blank area on both sides.

Figure 1 Structure of traditional comma knife 1

This structure has the following disadvantages:

①Because the base film will contact the coating surface of the substrate under a certain pressure, it will cause scratches on some substrates.

②Since the baffles on both sides are set at the position of the rotating bottom roller, the rotation of the bottom roller and the adhesion of the adhesive will cause wrinkles, jamming, and fragmentation of the baffle film and the base paper. At the same time, the baffles on both sides are also prone to glue leakage.

③For glue containing powder and poor dispersion that is easy to settle, it will cause sedimentation at the bottom of the glue tank, resulting in uneven coating.

④There will be residual coating dye after each batch of production. Every time change the products and use different pigments, it must be replaced the base film, so that causing waste.

⑤The glue exposed area at the glue groove of the coating head is large, and the solvent volatilization is large, which causes the changes of the coating solid content.

1.2 Structure 2 (Shown in Figure 2)

The rubber roller brings the glue from the trough to the surface of the substrate. The substrate runs from bottom to top to form a coating surface. The thickness of the coating is controlled through the gap between the scraper roller and the rotating bottom roller. The excess glue scraped off by the scraper edge flows back to the material trough. The coater knife with a rubber roller to control the blank space on both sides of the coating.

Figure 2 Structure of traditional comma knife 2

Structure 2 solves some of the problems of structure 1, but there are still some shortcomings:

①Due to the inconsistent return flow of excess glue scraped off by the scraper blade, the glue's infiltration state on the entire substrate is inconsistent. In particular, colored glue and glue with higher viscosity cause longitudinal stripes, flow lines and color spots in the coating.

②The glue exposed area of the coating head is larger and the solvent volatilization is large, resulting in an increase in solid content during the process and inconsistent coating amounts before and after, so that causes the coating thickness changing.

③After one kind of products is produced, there is a lot of residual glue in the trough, and the clearing workload is heavy. If you switch to other colors of dye coating, it is easy to cause color cross-fertilization.

④The blank area edges on both sides are unclear and wavy.

2 New type comma blade coating machine

New comma scraper coating device: no glue trough , no bottom film, less exposed of dye coating surface, upgraded baffle structure on both sides. At the same time, coating is carried out through ultrasonic liquid level automatic control. The coating head does not need manual control during the production process, realizing automation.

Its structure is shown in Figure 3 and Figure 4

Figure 3 Structure of new type comma knife

Figure 4 Front view of new type comma knife

2.1 Illustration：

The components of the new comma doctor blade coater include a bottom roller, a comma doctor blade roller, a fixed film retaining shaft and a guide roller. There is a glue coating gap between the bottom roller and the comma doctor blade roller, and the two fixed film retaining shafts are used to fix the tangent. There are membranes on both sides of the bottom roller, and two guide rollers on the front and rear sides of the bottom roller are used to transport the substrate.The bottom roller includes: a rotating bottom roller with intermediate transmission and fixed bottom rollers on both sides; there are baffles at both ends between the comma scraper roller and the bottom roller, and the baffles are in contact with the comma scraper roller and the fixed bottom rollers fixed on both sides of the bottom roller. The baffle, the comma scraper roller and the fixed bottom rollers fixed on both sides form a glue storage area; the glue storage area is connected to the ultrasonic liquid level automatic control machine, realizing automatic control without manual labor.

2.2 Coating process:

① Unwind the substrate and transport it to the comma scraper coating device through the guide roller, and make the substrate pass through the glue coating gap between the comma scraper device and the fixed bottom roller;

② Set the barrier film on the fixed bottom roller and the substrate, and set both ends of the barrier film on the fixed shaft of the barrier film;

③ Add a certain amount of glue to the glue storage area formed by the scraper roller, the rotating bottom roller and the baffles on both sides, and control the coating thickness through the gap between the scraper roller and the rotating bottom roller;

④ Coat the glue on the substrate through the movement of the substrate in the coating device, and then enter the drying ovens.

2.3 Beneficial effect

① The coating head stores less glue and is self-stirring, so there will be no settling or uneven problems;

② Without a bottom film which will cause scratches to the substrate, and will not cause problems such as wrinkles, jamming, or fragmentation of the substrate;

③ Does not cause longitudinal stripes, flowing lines and color spots;

④ Clear and convenient to change pigment after production, saving costs;

⑤The exposed area of the glue on the coating head is small, and the glue is taken away by the substrate from top to bottom. No dry glue, glue strips and glue spots will be produced. The solid content of the glue is stable during the coating process;

⑥Realizing automatic control without manual labor.

3 Summary

The new comma blade coating device is designed and used in various coating industries to achieve the advantages of effectively improving production efficiency, improving the working environment, improving product quality, and reducing manual labor.