The brush coater is the oldest coating equipment originally used in the 1950s to produce coated wall paper using china clay coatings. There are three different types of brush coating heads: a round brush coating head, a blanket roll coating head, and a blanket coating head. Figure 1 shows an early application of a brush coating head. 
The advent of air knife coaters in the 1930s marked the birth of the modern paper coating industry. The air knife coater overcomes the aforementioned shortcomings of the brush coater and is rapidly being promoted, resulting in a sharp increase in the production of coated paper.
The first scraper coater patent appeared in the 1950s. Since then, the blade coater technology has been rapidly developed. According to the feeding equipment, the type of scraper and the mounting position of the scraper, the scraper coating head is also divided into many types, such as hard blade scraper coating machine, drag knife scraper coating machine, soft blade scraper coating machine, fountain type. A blade coater, a short-residence blade coater, a billet coater, a scraper coater, and the like.