Dip coating
Dip and brush are the oldest application methods. In the dip coating method, the continuously coated web is immersed in the coating solution. Then pull out the fluid. Either single-sided or double-sided can be wetted. The liquid adhering to the web determines the coating thickness, but excess liquid can be removed by wiping webs or squeeze rolls in what is known as the doctoring process. The coating thickness before coating amount adjustment is determined by the viscosity, density, coating speed and pull-out angle of the liquid. This technique has been studied by a number of people, most notably John Tallmaddge, who published his studies from the mid 1960's to the early 1970's which provided the mathematics and theory of the main factors affecting the applied wet film thickness Base
Rod coating
In bar coating, a wire-wound rod is used to scrape excess liquid from a moving web. Usually, the scraping rod rotates in the same or opposite direction to the direction of movement of the web, so that the winding is worn evenly, or the particles brought between the web and the scraping rod can pass through. As for which direction of rotation force of the scraper rod is better for coating, it should be the direction (weiss, 1977, p236). If the coating thickness depends only on the space between the tops of the windings, the coating thickness is 0.2lr, where r is the winding diameter (Statas, 1984, p71). However, the rheological properties of the fluid, the speed and tension of the web, and the direction and speed of rotation all affect the average thickness.
The winding scraping rod will produce many fine and raised lines along the web direction corresponding to the outline of the winding rod. In order to obtain a smooth coating after coating , these channels need to be leveled in the drying zone or in the transition zone between coating and drying.
