Coating of a web surface directly or indirectly on one or both sides is applied while the web is still wet to prevent the escape of matter from the paper/cardboard into the water recirculation system

摘要

To spread a coating of a liquid or paste medium (18) directly or indirectly on one or both sides of a running web (14), especially of paper or cardboard, the first application of the coating medium (18) is applied to the web (14) before it is completely dry but after the end of the mechanical water extraction stage. When the first coating of the medium (18) is applied, the web (14) has a dry content of at least 50% and has not achieved 75%. The coating is applied in the drying section (12) of the paper/cardboard prodn. machine (10). The coating medium (18) is applied to the web (14) surface in one or more layers, with a coating weight in at least one layer and pref. all layers of 1.5-2.5 g/m2 and pref. 2.0 g/m2. The coating medium (18) is applied by a number of separate jets (30), in at least two rows offset against each other across (Q) the web (14). The jets (30) are structured to spray one or two coating materials. The coating medium (18) is also applied by a free-stream jet applicator (20), and by transfer rollers (16c,28), where one transfer unit is a drying cylinder (16c). The coating medium (18) is applied at a rate to give a surplus, and then it is scraped by a doctor, or the application has no surplus. The coating medium (18) has a different composition from application to application. The coating medium (18) is applied to the web (14) at a section where it is supported by a cylinder (16b-16d), which can be heated, unheated or cooled. The cylinders have a rubber mantle. Or the coating medium (18) is applied to the web (14) at a free section between two cylinders (16d,16e) in its path where it is not supported by a cylinder. The web (14) is dried after the application of the coating medium (18), and then dried further so that it can be rolled. An Independent claim is included for a web coating assembly with an initial applicator (20), in the direction (L) of web (14) travel, at a point where the mechanical water extraction has finished and the web (14) has a dry content of at least 50% but has not yet achieved a dry content of 75%.