Paper coating apparatus

A coating applicator for applying coating liquid to one side of a moving web of paper, comprising means for supporting the moving web in position located on the other side of the web, a beam carrying a front wall and a rear wall forming a chamber extending substantially across and parallel to the web, said chamber having a header with at least one coating liquid inlet and discharging between said front and rear walls, said chamber receiving the coating liquid from said header, said chamber defining a narrow outlet slot extending across the web and adjacent thereto, means for delivering coating liquid through said header, said chamber and said outlet slot and onto said web at a pressure of between 150 and 7 inches of water, a single doctor blade located at a rear edge of said outlet slot on the rear wall of said chamber for doctoring the coating liquid on the web, said doctor blade being spaced from a front edge of said front wall by a small dimension such that the blade doctors the coating liquid on the web within about 0.0004 to about 0.0100 second of the pressure application of the coating to the web, and end dam means for sealing the end spaces between said front and rear walls and said doctor blade with the web, the front edge of said front wall of said chamber being spaced less than one inch from the web, a liquid seal established between said front edge of said front wall and the web continuously across the web at the front edge of said outlet slot by flow of coating liquid under said pressure reversely of the direction of web travel through the space between said front edge of said front wall and the web, said liquid seal causing the coating liquid in said chamber and between said doctor blade and said seal to be held under said pressure while permitting reverse flow of coating liquid between said front edge and the moving web for establishing said liquid seal, for sealing off the forward edge of said chamber against entry of air and foreign matter, for continuously purging said chamber, and for causing said blade to doctor the coating liquid on the web while said coating liquid is held under said pressure, whereby said moving web may be coated with coating applied primarily to the surface of the web and doctored almost immediately so that there is a minimum penetration of coating liquid beyond the surface of the web into the paper;

• an orifice plate comprising said front edge of said front wall and adjustably mounted on said front wall for movement toward and away from the web for establishing a desired clearance between the front edge of said orifice plate and the web, and means for adjusting said orifice plate to establish a clearance of less than one inch which, in relation to the delivery of coating liquid, is such as to cause a reverse flow of coating liquid under said pressure between said front edge of said orifice plate and the moving web sufficient to maintain said liquid seal and said coating liquid pressure in said chamber;
• said adjusting means comprising an adjustable member slidable on said front wall in a direction transverse to the movement of said orifice plate and having inclined slots therein, said front wall having vertical slots therein intersecting said inclined slots, said orifice plate carrying first and second cam means engaged respectively in said inclined and vertical slots, the cam means engaging in said inclined slots comprising rotatable rollers eccentrically and adjustably mounted on said orifice plate to provide for uniform engagement thereof within said inclined slots, whereby movement of said adjustable member in a direction transverse to the movement of said orifice plate causes said orifice plate to move linearly toward or away from said web uniformly over its length.