On the paper machine, the size press is

used to apply surface size to dried paper.182,183 Starch is the most frequently used binder in surface sizing. Besides

raising surface strength, starch also imparts stiffness, lowers water sensitivity, reduces dimensional changes and raises air

leak density of the sheet. In conventional practice, the sheet passes through a pond of starch dispersion held above the nip

between two large rotating cylinders. In the nip a high, transient, hydrostatic pressure is developed. Excess starch

dispersion is drained from the ends of the nip. The surface size is transferred to paper by capillary penetration, pressure

penetration and by hydrodynamic force during nip passage.