The problem of uneven printing and coating

Coating unevenness means that the raw paper is affected by certain factors during the coating process, resulting in sparse local paint coverage on the coating surface of the paper sheet, near missed coating in severe areas, and almost no color development or light coloration, resulting in finished paper. Lost copy function. This kind of paper disease is difficult to see in daylight or in ordinary light. It must use UV light, which increases the difficulty of searching. The main factors that cause this kind of paper disease are: hydrophilic properties of the applicator applicator roller; air cooling The performance of the device; paint contains impurities and air bubbles; poor film formation of the paint causes the material film formed on the coating roller to be easily broken and easily cracked; the process parameters of the coating head are not properly set, and the paint does not transfer between the rollers. Well, it affects the quality of the coating. For the above reasons, the following measures should be taken in actual production.

1. Add sifting system to the paint conveying pipeline

For the impurities and bubbles contained in the paint, the paint conveying process was reformed. A screening system was added between the working tank and the working disk. The impurities mixed in the paint and coarse particles of the spacer were screened to improve the quality of the paint. Improved film-forming properties of the paint.

2. Cancel metering roller scraper

Because the CB coating has a low degree of brilliance and the thixotropy is relatively large, the film thickness of the CB coating formed on the application roller is too small, and it is easily broken at high speed operation. When the metering roller is not used, the metering roller is The metering effect is weakened, so CB paint can form a relatively thick film on the surface of the application roller, and the material film will not be broken even at high speed operation.

3. Reasonably adjust the coating head process

Reasonable and appropriate roll gap, speed ratio and wiping ratio have a very important influence on the quality of carbonless paper. By adjusting the roller gap and speed ratio, the thickness and uniformity of the wet film layer on the applicator roller can be changed; adjusting the wipe ratio can change the thickness and uniformity of the transfer of the wet film layer on the applicator roller. Shanghai adhesive printing has selected the following process parameters after exploration and practice: the gap between the application roller and the impregnation roller is 0.2mm, the gap between the application roller and the metering roller is 0.2mm, and the gap between the application roller and the package is 0.16mm; The speed ratio of the roller to the impregnating roller was 2.1:1, the speed ratio of the applicator roller to the metering roller was 2.1:1; the wipe ratio of the web to the applicator roller was 1.9:1.

4. Select an application roller with excellent hydrophilicity

The hydrophilic properties of the applicator roller are very important for the coating process. Selecting the applicator roller material with excellent performance and replacing the applicator roller in time can greatly improve the film-forming properties of the applicator on the roller surface and improve the paper quality.

5. Inspect and replace air cooler traps and condensate drain lines in time

Since the condensed water in the compressed air is sprayed onto the paper, “coating unevenness” may also be formed. Upon inspection, there are indeed problems with the traps of the air cooler and the condensate drain lines. During the production, the traps have been adjusted and the condensate discharge lines have been cleared to allow the condensate in the air to be discharged smoothly.