Development and Applications of the Metering Size Press, PaperCon '09 Conference

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The conventional two-roll pond size press has been a standard component of paper machines for over a century. It has been used not only for starch surface sizing but also for pigmented precoating and coating. It suffers a number of limitations. Pickup is dependent on internal sizing level and moisture content of the sheet, necessitating overdrying the sheet in the main dryer section to flatten the profile entering the size press. It saturates the sheet and has poor runnability on lightweight and other low wet tensile strength sheets. When used for pigmented coating, it requires high binder levels. It has speed limitations due to the hydrodynamics of the pond. As machine speeds increased, size press designers tried to the use of larger rolls, but the practical speed limit was about 800 m/min. The gate roll size press was introduced in the 1960's to overcome the speed limit, but there were problems with roll cover life, film split and coating rheology limitations. In the early 1980's, the metering size press was developed by using short dwell coaters as applicators of wet films to the roll surface. Today, several types of applicators are available, including short dwell coater, fountain and enclosed pond. Metering element choices include volumetric grooved rods or wire wound rolls and pressure controlled blades and smooth rods. Metering size presses are being used to apply 0.7-4.0 gsm/side surface size at 5-18% solids and 3-15 gsm/side pigmented coating at 30-65% solids. The metering size press is an important papermaking tool.