The term coated applied to any paper or board to which has been applied a coating of any character or substance. In the present case of coating the printing grades of paper and boards, the primary objects in the coating operation is to produce a sheet with an even, semi-absorbent surface for printing. This is effected by covering the fibers on the surface of the paper and filling the hollows between them with finely divided mineral matter, mixed with an adhesive or "size". When such paper is calendered, there results a smooth even surface, which reproduces the half tone dots of the printing plate much more faithfully than any plain paper.
Air Knife Coater : The lab coater is designed to make it possible to obtain small coated paper samples. Different types of coating mixtures can be used to obtain the coated paper samples. The coating result corresponds well to that obtained by production airknife coaters.
The coater consists of a welded squire shaped frame of the size length 24", width 14" and height 12". The frame contains a transformer , a blower with a manometer 8-800 mm water pressure and a reversible motor.
On the front are the controls. When the main switch is in position 1, the table can be moved. In position 2, the blower for the air knife will operate. Beside the main switch is the switch for the reversible motor that moves the table with the sample forward and backwards. A movement to the right moves the table to the right and the monometer is then visible. By switching on to the left the table goes back. On the right of the main switch is the regulating transformer for the blower. The air pressure is read, on the monometer. Across the table over the whole width is the air knife.
It is possible to adjust the opening of the slit by the screws along the length of the airknife and is generally kept at 0.04-0.05 cm.
Test the coated sheets and uncoated base paper sheets for the following and compare the results and report :