Application device and method for coating a fibrous material web

Abstract

An application device and method for coating a fibrous material web, in particular a paper, packaging or board web. The application device has an application nozzle for applying a coating medium, in particular a starch solution, to a moving surface and the application nozzle has an outlet gap which extends in the width direction of the application nozzle for producing a film of coating medium or a curtain of coating medium. The application nozzle has a gap width across its width direction that may be varied by profiling devices.

1 . An application device for coating a fibrous material web, the application device comprising:
 an application nozzle for applying a coating medium to a moving surface, said application nozzle being formed with an outlet gap which extends in a width direction of said application nozzle and which is configured to produce a film of coating medium or a curtain of coating medium;   said application nozzle having profiling devices for varying a gap width of said outlet gap over the width of said application nozzle;   said application nozzle further having a blower head configured to generate a linear jet of gaseous medium, and wherein an impingement line is defined along which the linear jet of gaseous medium impinges on the film or the curtain of coating medium for forming a spray curtain, and wherein said blower head is arranged to direct the spray curtain in a direction of the moving surface.   
     
     
         2 . The application device according to  claim 1 , wherein the fibrous material web to be coated is a paper web, a web of packaging material, or a web of board material. 
     
     
         3 . The application device according to  claim 1 , wherein the coating medium is a starch solution. 
     
     
         4 . The application device according to  claim 1 , wherein said application nozzle is a curtain nozzle configured to cause the coating medium from said outlet gap to be deposited on the moving surface in a form of a curtain falling freely under an influence of gravity. 
     
     
         5 . The application device according to  claim 1 , wherein said profiling means comprise a baffle, which extends over an entire width of said application nozzle, and said profiling means further comprise a plurality of actuators which are distributed over the width of said application nozzle and which are configured to open said outlet gap locally more or less by moving or deforming said baffle. 
     
     
         6 . The application device according to  claim 5 , wherein said actuators are mechanical actuators configured for actuation selected from the group consisting of manual actuation, actuation by motors, hydraulic actuation, and electromagnetic actuation. 
     
     
         7 . The application device according to  claim 1 , wherein said profiling means comprise a plurality of electromagnetic actuators that are distributed over the width of said application nozzle and that are configured to vary the gap width of said outlet gap locally by varying a magnetic force acting of said electromagnetic actuators. 
     
     
         8 . The application device according to  claim 7 , wherein the electromagnetic force acts by attraction, with the gap width of said outlet gap being varied by more intense or weaker attraction. 
     
     
         9 . The application device according to  claim 7 , wherein the electromagnetic force acts by repulsion, with the gap width of said outlet gap being varied by more intense or weaker repulsion. 
     
     
         10 . The application device according to  claim 1 , which comprises a plurality of actuators configured for varying a gap width of said application nozzle, wherein said actuators are distributed non-uniformly over the width of said application nozzle, and wherein spacing distances between mutually adjacent actuators at marginal edges of said application nozzle are smaller that at a center of said application nozzle. 
     
     
         11 . The application device according to  claim 1 , wherein:
 said application nozzle is one of two application nozzles, including a first application nozzle for applying the coating medium to a first moving surface formed on a first transfer roll and a second application nozzle for applying the coating medium to a second moving surface formed on a second transfer roll; and   said first and second transfer rolls are disposed to form a transfer nip in which the coating medium is transferred from the first moving surface and from the second moving surface onto the fibrous material web.   
     
     
         12 . A method of coating a fibrous material web, the method comprising:
 providing an application device according to  claim 1 ; and   coating the fibrous material web with a coating medium by the application device.   
     
     
         13 . The method according to  claim 12 , wherein the fibrous material web is a paper web, a packaging web, or a board web. 
     
     
         14 . The method according to  claim 12 , which comprises coating the fibrous material web indirectly by first applying the coating medium to a moving surface on a transfer roll and transferring the coating medium from the transfer roll to the fibrous material web in a transfer nip. 
     
     
         15 . The method according to  claim 12 , which comprises:
 a. predefining a predefined profile for a quantity of coating medium to be applied over a width of the application nozzle of the application device; and   b. varying the gap width of the outlet gap over the width of the application nozzle to attain the predefined profile.   
     
     
         16 . The method according to  claim 15 , which comprises determining a current profile of a property of the fibrous material web, and determining the predefined profile for the coating medium from the current profile of the property. 
     
     
         17 . The method according to  claim 16 , wherein the property is a strength property of the fibrous material web. 
     
     
         18 . The method according to  claim 16 , which comprises determining the current profile of a property directly, by direct measurement, or indirectly.