Wet-End Control Improvements in Boardmaking Applications, 2000 Papermakers Conference Proceedings

Bertil Olsson, Sylvain Renaud--There is no clear demarcation between paper and board apart from some distinctions made in some countries regarding duty and customs fees. Board or paperboard is generally defined as paper with a basis weight above 250 g/m 2 . Not even board can be defined by its structure or by the type of machine used to produce it. Paperboard can be solid or multiplied and can be produced on a Fourdrinier single or multiple wire. Board is most often defined by the way it is used. Packaging, boxboard, liner, fluting are common names given to paper that is used to carry, protect and wrap different goods. Significant innovations have been made in the board machine technology including gap former technology. These new machines require much tighter control of the additives used at the wet end and also better control of the fiber furnish to the machine. Improving paper machine stability depends in part on accurate and reliable consistency control from the stock preparation area to the wet-end. Retention systems are more and more common in paperboard applications as a result of increased use of retention-aid chemicals. Retention-aid suppliers have developed better and more specific chemicals for enhancing not only retention, but also other important properties for boardmakers such as air resistance (Gurley), liquid absorption (Cobb number) and strength. In boxboard applications, air resistance is very important since the product is used to transport all kinds of material from sophisticated electronic equipment to daily products, e.g. fruits, vegetables and other foodstuffs. Overdoses of a retention-aid chemical results in sealing the sheet and creates a high air-resistance box which may lead to a molding and deteriorating board product. Automatic control of the retention-aid using on-line consistency measurement can provide better product uniformity.