At the end of this module, you will be able to:
- Identify the main purposes of paper and board coatings
- List the three main categories of coating ingredients
- Identify and describe the three most common coater designs
- List the three main objectives of coating equipment
- List the advantages and disadvantages of air-knife, blade and roll coaters
- Describe the three most common methods of drying paper coatings
The following key questions are answered in this module:
Why are there so many different coater designs?
The coater design used must take into account properties of the base sheet, properties of the coating mixture, number of sides to be coated, number of coats on each side, and the desired final coated sheet properties.
Why is some coating done on-machine and some off-machine?
There are advantages and disadvantages to each method. In general, on-machine coating is better suited to light to moderate coating applications with less stringent quality requirements. Most coaters can be used either way.
Which type of coater is best at filling in low spots in the sheet to create a smooth printing surface?
Because blades are quite rigid, blade coaters do a rather good job of filling in low spots on the sheet, at the expense of the uniformity of the coating layer thickness.
What is a ""contour coater""?
Air-knife and roll coaters are ""contour coaters."" This means that they create a coating layer with a relatively even thickness that follows the contour of the sheet surface.
Why are other types of dryer equipment, besides steam-heated dryer cans, used to dry paper coatings?
Dryer cans dry by contacting the sheet. The coated side of the sheet must be sufficiently dried before it contacts a dryer can to prevent sticking or picking of coating on the dryer surface.
Below is a transcript of the video sample provided for this module:
Air knife coaters operate on the principle of applying too much coating to the sheet and then removing the excess. A driven roll rotating in a coating solution filled pan applies a meter to the amount of coating solution to the sheet. Shortly after, the sheet travels around a backing roll and an air jet or air knife is directed onto the coated sheet surface to remove the excess. The excess coating is collected in an overflow pan so that it can be recirculated and reused. The air knife is set up to sheer off the excess coating near the sheet surface, where the water in the coating solution is beginning to absorb into the sheet. The velocity and energy of the air knife control the coat weight.
Use the additional resources and links below to learn more about this topic: