The rapid development of the packaging and printing industry requires that both the level of packaging and printing machinery manufacturing and the quality of packaging processes in China must be significantly improved. Although there are a large number of packaging and printing machinery manufacturers in China, there are fewer mechanical manufacturing companies with higher technological content. Many small companies do not even have real mechanical designers. However, the manufacture of some coating composite devices requires single-piece manufacturing, and it is particularly necessary for mechanical manufacturing companies with high mechanical design technology to produce. At present, the coating types and squeegee methods used by many companies for coating composite equipment are relatively simple. This article will introduce several coating methods and methods of using different squeegee scrapers for designers' reference.
Coating type
Coater coating is divided into light roller coating, anilox roller coating and hot melt spray coating.
1. Light roller coating
The use of high-precision light roller for sizing coating, the coating effect is good, the coating amount can be flexibly controlled by the micro-motion adjustment of the coating squeegee, and the coating accuracy is high. At present, light roller coating is most widely used in coating composite devices.
2. Anilox roller coating
Using an anilox roller for sizing, uniform coating, but the amount of coating is difficult to adjust. The amount of coating is mainly related to the depth of the cell of the anilox roller and the viscosity of the glue. The deeper the anilox roller is, the more amount of glue is transferred from the mesh hole to the substrate. Conversely, the shallower the anilox roller hole is, the less glue is transferred to the substrate. Adhesive viscosity is too large and too small are not conducive to the normal transfer of glue, glue is too easy to transfer, too thin is easy to flow, so that uneven glue, easy to produce vertical or horizontal flow patterns. Therefore, once the types of anilox roll and glue are set, it is difficult to adjust the coating amount, which is also the main reason for the limited application of anilox roll coating.
3. Hot melt adhesive spray coating
The coating device adopting this coating method mainly causes the solid glue to be heated and melted, and the glue is directly sprayed on the substrate by the hydraulic device through the coating die. This kind of coating method can use 100% solid state glue without the need of thinner, and has no pollution to the environment. It is a green environment-friendly coating method and is favored by more and more users.
Squeegee type and application
In the coating process, there is often a phenomenon of uneven sizing, which requires a certain squeegee mechanism to evenly squeegee the squeegee. Squeegee mechanisms include stainless steel scrapers, comma scrapers, scrapers, wire scrapers, and air scrapers.
Stainless steel blade
This scraper was cut with a stainless steel foil, pressed against a scraper seat and applied to a coating roller. The structure is shown in FIG. 1 . The stainless steel sheet is relatively soft, so the squeegee is not very uniform, and most of the squeegee used for the sizing coating of the anilox roller is also used for the pre-squeegee coated by the stencil roller.
2. Comma type scraper
Such scrapers are often made of steel with good strength and hardness, and the scraper does not rotate when scraping. See Figure 2. The scraper has high strength and hardness, small straightness error of the cutting edge, and uniform scraping glue, and is suitable for precise scraping of glue on the light roller.
3. Scraper
This type of scraper is usually made of a round bar with good strength and hardness. The round bar rotation is required for scraping the rubber. See Figure 3. Sometimes the scraper can also be scraped directly on the substrate. The full run-out error of the scraper bar is required to be small, and it is mostly used for the pre-squeegee coated by the light roller.
4. Wire scraper
This kind of scraper is made by meticulously winding stainless steel wire outside the high-precision cold drawn round steel, see Figure 4. If the wire scraper is driven by the micro motor during the squeegee, the effect is better. Wire scrapers usually act directly on the substrate when scraping.
5. Air Scraper
The air scraper mechanism acts on the glue roll by uniformly ejecting the gas (pressure) flow, which serves the purpose of scraping the glue, see FIG. 5 . It is required that the gas (pressure) flow be evenly distributed over the entire width of the light roller, and this type of scraper is mostly used for scraping a good fluidity.
As the coating process improves, some newer coating methods will follow. In addition, it is also possible to use a combination of several scrapers to scrape.
Author: Peng Wenhua
Reprinted from: Printing Technology