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Abstract

A method of applying a starch sizing to a forming web on a paper machine, such as in the form of a curtain on a fourdrinier machine, employs a suspension of uncooked particulate starch and water which is applied, as a suspension, to the inlet of a downwardly opening die positioned over the forming web and applied at a consistency of between about 2 to 10% onto the surface of the web as a free falling curtain, the impact velocity of which is controlled to a rate sufficiently low to prevent distortion of the web on impact. Improved drainage is achieved by heating the suspension to a temperature less than about 150.degree., to prevent the cooking of the starched particles. The curtain may be applied to the web at fourdrinier table consistencies as low as about 2% and still obtain starch retention rates of about 80%. An improved coater die for applying a curtain of finely divided material carried as a suspension, such as uncooked starch, on the surface of a newly formed web of paper material has an elongated die body formed as a pair of mating die body portions. The portions define opposed land surfaces which define an extrusion slot. A suspension feed passageway is formed through the die body in communication with the slot and is formed with ends which terminate exclusively at one of the die body portions thereby eliminating the need for a conventional die body end plate. The die lips are chilled to produce a sweating on the surface by moisture condensation for preventing a build up of coating particles at the die lips which would interrupt the integrity of the coating curtain. The feed-through passageway is tapered or reduced in cross section between the inlet and the outlet to maintain a turbulent flow condition therethrough to maintain the particulate material in suspension within the die body.

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