Application device and method for coating a fibrous material web

Abstract

An application device and method for coating a fibrous material web, such as a paper web, a web of packaging material, or a web of cardboard. 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 that produces a film of coating medium or a curtain of coating medium. A device is provided for varying the application amount and the variation is based on a strength variable.

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;   a device for varying an application amount of coating medium by varying said application nozzle; and   a control unit configured to determine a variation in the application amount from at least one characteristic value provided for a strength of the fibrous material web.   
     
     
         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 the device for varying the application amount comprise a conveying system having a variable delivery rate. 
     
     
         5 . The application device according to  claim 1 , wherein said application nozzle is formed with an outlet gap having a gap width, and wherein the application amount is changed by varying the gap width of said outlet gap. 
     
     
         6 . The application device according to  claim 5 , which comprises an actuator for changing the gap width, said actuator including at least one of a cover or a movable wall element. 
     
     
         7 . The application device according to  claim 5 , which comprises an actuator for changing the gap width, said actuator having one or more individual actuators that are distributed along a width of said application nozzle. 
     
     
         8 . The application device according to  claim 7 , wherein said individual actuators are uniformly distributed over the width of said application nozzle. 
     
     
         9 . The application device according to  claim 6 , wherein the gap width is variable by one or more of motor actuation, hydraulic actuation, or pneumatic actuation. 
     
     
         10 . The application device according to  claim 1 , wherein said control unit is configured to automatically change the application amount. 
     
     
         11 . The application device according to  claim 1 , wherein said application nozzle is configured to allow the application amount to be varied between a minimum amount and a maximum amount, the maximum amount being at least 30% greater than the minimum amount. 
     
     
         12 . The application device according to  claim 11 , wherein the maximum amount is at least 50% greater than the minimum amount. 
     
     
         13 . The application device according to  claim 11 , wherein the maximum amount is at least 100% greater than the minimum amount. 
     
     
         14 . 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.   
     
     
         15 . The application device according to  claim 14 , wherein at least one of said first surface of said first transfer roll or said second surface of said second transfer roll has a hardness of more than 55 ShoreD or a hardness of more 90 ShoreD. 
     
     
         16 . A method of coating a fibrous material web, the method comprising:
 providing an application device according to  claim 1 ;   determining a value for a strength of the fibrous material web; and   coating the fibrous material web with a coating medium by the application device, and thereby varying the application amount depending on the characteristic value.   
     
     
         17 . The method according to  claim 16 , wherein the coating medium is a starch solution or a barrier medium. 
     
     
         18 . The method according to  claim 16 , which comprises coating the fibrous material web indirectly by first applying the coating medium to a moving surface on a transfer roll and then transferring the coating medium from the transfer roll to the fibrous material web in a transfer nip. 
     
     
         19 . The method according to  claim 16 , which comprises determining the characteristic value directly, by direct measurement, or indirectly. 
     
     
         20 . The method according to  claim 16 , which comprises, when the fibrous material web is changed from a first type of fibrous web to a second type of fibrous web, automatically changing the application amount from a first default value to a second default value by adapting the device for varying an application amount.