Press arrangement and method for pressing a fibrous web

Abstract

A press arrangement for pressing a web of fibrous material includes at least two presses which are arranged one behind the other in a direction of travel of the web of fibrous material, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip, the second press being configured for being operated at a linear load of at least 500 kN/m, the second press being configured such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the second press being configured for applying the peak pressure of at least 12 MPa onto the web of fibrous material.

What is claimed is: 
     
         1 . A press arrangement for pressing a web of fibrous material, the press arrangement comprising:
 at least two presses which are arranged one behind the other in a direction of travel of the web of fibrous material, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip, the second press being configured for being operated at a linear load of at least 500 kN/m, the second press being configured such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the second press being configured for applying the peak pressure of at least 12 MPa onto the web of fibrous material.   
     
     
         2 . The press arrangement according to  claim 1 , wherein the quotient of the average pressure and the peak pressure is at least one of less than 0.46 and greater than 0.3. 
     
     
         3 . The press arrangement according to  claim 1 , wherein the second press is configured for being operated at the linear load of at least 1,000 kN/m. 
     
     
         4 . The press arrangement according to  claim 1 , wherein the first press is configured such that at least one of the following applies:
 a) a quotient of an average pressure and a peak pressure in the first press nip is greater than 0.5;   b) a maximum linear load with which the first press is configured for being operated is less than a maximum linear load with which the second press is configured for being operated; and   c) a peak pressure that can be applied to the web of fibrous material in the first press nip is less than the peak pressure that can be applied to the web of fibrous material in the second press nip.   
     
     
         5 . The press arrangement according to  claim 1 , wherein the second press is a shoe press, which includes a press shoe, with a concavely curved surface, and a shoe press shell rotatably mounted around the press shoe. 
     
     
         6 . The press arrangement according to  claim 5 , wherein the shoe press shell includes polyurethane, which is configured for being formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least one of at least one polyether polyol and at least one polycarbonate polyol, and wherein the crosslinking component contains a C 2-14  diol. 
     
     
         7 . The press arrangement according to  claim 6 , wherein the polyol component of the prepolymer includes a poly-tetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol. 
     
     
         8 . The press arrangement according to  claim 6 , wherein the crosslinking component includes at least one of poly-tetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol. 
     
     
         9 . A machine for producing of a web of fibrous material, the machine comprising:
 a press arrangement configured for pressing the web of fibrous material, the press arrangement including at least two presses which are arranged one behind the other in a direction of travel of the web of fibrous material, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip, the second press being configured for being operated at a linear load of at least 500 kN/m, the second press being configured such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the second press being configured for applying the peak pressure of at least 12 MPa onto the web of fibrous material.   
     
     
         10 . A method for pressing a web of fibrous material, the method comprising the steps of:
 guiding the web of fibrous material through at least two presses consecutively, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip; and   pressing the web of fibrous material in the second press with a linear load of at least 500 kN/m, the web of fibrous material being pressed in the second press such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the web of fibrous material being pressed in the second press with the peak pressure of at least 12 Mpa.   
     
     
         11 . The method according to  claim 10 , wherein the quotient of the average pressure and the peak pressure is at least one of less than 0.46 and greater than 0.3. 
     
     
         12 . The method according to  claim 10 , wherein the web of fibrous material is pressed in the second press with a linear load of at least 1,000 kN/m. 
     
     
         13 . The method according to  claim 10 , wherein the web of fibrous material is pressed in the second press with a linear load of at least 1,300 kN/m. 
     
     
         14 . The method according to  claim 10 , wherein the first press is operated such that at least one of the following applies:
 a) a quotient of an average pressure and a peak pressure in the first press nip is greater than 0.5;   b) a maximum linear load with which the first press is operated is less than a maximum linear load with which the second press is operated; and   c) a peak pressure that is applied to the web of fibrous material in the first press nip is less than the peak pressure that is applied to the web of fibrous material in the second press nip.   
     
     
         15 . The method according to  claim 10 , wherein the web of fibrous material includes at least 20 wt. % of OCC (old corrugated containers) fibers. 
     
     
         16 . The method according to  claim 10 , wherein the web of fibrous material includes at least 50 wt. % of OCC (old corrugated containers) fibers. 
     
     
         17 . The method according to  claim 10 , wherein the web of fibrous material is a packaging paper web. 
     
     
         18 . The method according to  claim 10 , wherein the method of pressing the web of fibrous material is carried out using a press arrangement, wherein the press arrangement includes the at least two presses which include the first press and the second press which is arranged behind the first press in the direction of travel of the web of fibrous material.