Method of applying a film of coating material to a paper web including successive doctoring steps

摘要

A method and apparatus for applying coating liquid to a web of paper traveling over a web supporting surface at speeds of 3,000 or more feet per minute to produce a coated web free of streaking and other imperfections includes the steps and structural elements for distributing coating liquid onto the supported web through a limited application zone within a short dwell time of the liquid on the web, the web moving through the application zone at a speed that is sufficiently high to create turbulence in the coating liquid being applied to the web, doctoring the coating liquid on the web by biasing a primary doctor against the coated web at the rear edge of the application zone so as to form a layer of coating liquid on the web as the web leaves the application zone, the turbulence in the coating liquid causing machine direction streaks in the layer of the coating liquid as the web leaves the application zone; and, at a location downstream and isolated from the application zone, performing a successive doctoring of excess coating liquid on the supported web by biasing a final doctor blade against the coated web to remove excess coating from the web and to level and smooth the coating retained on the web to a final wet film thickness and smoothness.