Method, paper machine and base paper for the manufacture of lwc printing paper coated once

Abstract

A paper machine for the manufacture of LWC printing paper which is coated once has a headbox ( 100 ), a gap former ( 200 ), a press section ( 300 ) having at least one extended nip press, a pre-dryer section ( 400 ) in which a web (W) is dried applying at least cylinder drying (R 1 -R 7 ), a precalender ( 500 ) in which the web (W) is pre-calendered, at least one portion which is formed of a coating station ( 600 ) and an after-dryer section ( 700 ) and in which the web (W) is coated on both sides applying a film coating method or a non-contact coating method and dried applying at least contact-free drying ( 710 ), an end calender ( 800 ) in which the web (W) is calendered, and a reel-up ( 900 ) in which the web (W) is reeled. The pre-calender ( 500 ) is a calender which is provided with at least one nip (NE 1 , NE 2 ) and in which both surfaces of the web are in contact with a calendering backup surface having a surface temperature of at least 200° C., advantageously at least 250° C., the total length of the nip or nips of the pre-calender is in a range of 15-600 mm, advantageously in a range of 30-600 mm, the linear load of each nip is in a range of 50-500 kN/m, advantageously in a range of 100-400 kN/m, and the moisture content of the web before the first nip of the pre-calender ( 500 ) is in a range of 5-20%, advantageously in a range of 6-15%.

1 - 44 . (cancelled)  
     
     
         45 . A method for the manufacture of LWC printing paper coated once, comprising the following successive steps: 
 feeding stock from a headbox to a gap former, in which water is removed from a web in two directions;    passing the web to a press section which comprises at least one extended nip press and in which water is removed from the web by pressing;    passing the web to a pre-dryer section, in which the web is dried by applying at least cylinder drying;    regulating the web to a moisture content of 5-20% before a first nip of a pre-calender, having a nip or nips, the nip or nips of the pre-calender having a total length;    passing the web to the pre-calender and calendering a first side and a second side of the web in the pre-calender, the pre-calender having a first side backup surface for the web first side and a second side backup surface for the web second side, each of the first side backup surface and the second side backup surface being heated to at least 200° C., the pre-calender nip or nips total length being at least in a range of 15-600 mm at a nip load of 50-500 kN/m, in which the web is pre-calendered;    passing the web to at least one coating station and one after-dryer section, in which the web is coated on both sides by using a film coating method or a noncontact coating method;    drying the web at least by contact-free drying;    passing the web which is now LWC printing paper coated once, to an end calender, in which the web is calendered; and    passing the LWC printing paper coated once web, to a reel-up, in which the web is reeled into machine reels.    
     
     
         46 . The method of  claim 45  wherein each of the first side backup surface and the second side backup surface has a surface temperature of at least 250° C.  
     
     
         47 . The method of  claim 45  wherein the linear load of each nip is in a range of 100-400 kN/m.  
     
     
         48 . The method of  claim 45  wherein moisture content of the web is regulated to a range of 6-15% before the first nip.  
     
     
         49 . The method of  claim 45  wherein the pre-calender nip or nips total length is in a range of 30-600 mm.  
     
     
         50 . The method of  claim 45  wherein the web is precalendered in at least two soft nip calenders, each soft nip calender being formed between a thermo roll forming the backup surface and an elastic surface roll such that one of said thermo rolls is situated in the nips alternately on the first side and the second side of the web.  
     
     
         51 . The method of  claim 45  wherein the web is precalendered in at least a first shoe calender forming the first nip between a first shoe roll and a hard surface thermo roll forming the first side backup surface which engages the first side of the web and a second shoe calender forming a second nip between a second shoe roll and a hard surface thermo roll forming the second side backup surface which engages the second side of the web.  
     
     
         52 . The method of  claim 45  wherein the first side of the web is pressed against a thermo roll in the first nip, and is moisturized before the first nip, whereby the effect of the temperature of the thermo roll of the pre-calender on the first side of the web is enhanced.  
     
     
         53 . The method of  claim 45  wherein the second side of the web is pressed against a second thermo roll in a second nip, and is moisturized between the first and the second nip, whereby the effect of the temperature of the thermo roll of the second nip on the second side of the web is enhanced.  
     
     
         54 . The method of  claim 50  wherein asymmetry of porosity and roughness of the first side and the second side of the web is equalized in the pre-calender by two-sided calendering, in which one of said first side and said second side is a more porous surface of the web and is densified more than the other of said first side and second side, by regulating the moisture content of the web or the temperature of the thermo rolls of the nips.  
     
     
         55 . The method of  claim 45  wherein the precalender includes a belt calender having a nip which is formed between a thermo roll and a metal belt running over a roll having an elastic surface, in which connection the surface temperature of the thermo roll and the metal belt is at least 200° C., the length of the nip is in a range of 15-600 mm, the linear load of the nip is in a range of 50-500 kN/m, and the moisture content of the web before the pre-calender is in a range of 5-20%.  
     
     
         56 . The method of  claim 55 , wherein both sides of the web are moisturized before the pre-calender, whereby the effect of the temperature of the thermo roll and the hot metal belt of the nip on the web is enhanced.  
     
     
         57 . The method of  claim 55  wherein a dilution headbox is used as the headbox.  
     
     
         58 . The method of  claim 57  wherein the headbox used is a multilayer dilution headbox in which fibres. additives, or fillers are layered.  
     
     
         59 . The method of  claim 45  wherein a gap former provided with a forming roll and dewatering units is used as the gap former.  
     
     
         60 . The method of  claim 45  wherein the press section is a press section which is provided with first successive extended press nip and a second successive extended press nip, and wherein the first and second extended press nips are formed between a shoe roll provided with an elastic belt shell and a recessed surface counter roll, wherein the counter roll is in the first press nip on the first side of the web and in the second press nip on the second side of the web.  
     
     
         61 . The method of  claim 60  wherein the web runs in first and second press nips between two press felts.  
     
     
         62 . The method of  claim 45  wherein the web is dried in the pre-dryer section by cylinder drying groups which apply single wire draw and by impingement drying units which are disposed in connection with the cylinder drying groups.  
     
     
         63 . The method of  claim 45  wherein the web is passed after the pre-dryer section and before the pre-calender to a first measurement device, in which a profile of the web is measured.  
     
     
         64 . The method of  claim 45  wherein the web is passed after the pre-calender and before the coating station to a second measurement device, in which the profile of the web is measured.  
     
     
         65 . The method of  claim 45  wherein the web is passed in the after-dryer section after a portion applying contact-free drying and before a portion applying cylinder drying to a third measurement device, in which the profile of the web is measured.  
     
     
         66 . The method of  claim 45  wherein profiling of the properties of the paper web is controlled based on profile measurements of the paper web.  
     
     
         67 . The method of  claim 45  wherein in the pre-dryer section, the drying of the web is profiled by impingement units associated with impingement cylinders.  
     
     
         68 . The method of  claim 45  wherein the web is calendered in an end calender which is formed of a soft calender having 2-4 nips, the soft calender having 1-2 thermo rolls having a surface temperature of at least 150° C., the linear load of the end calender nips being in a range of 50-500 kN/m and the moisture content of the web before a first nip of the end calender is in a range of 5-11%.  
     
     
         69 . The method of  claim 45  wherein the web is calendered in an end calender which is formed of a multi nip calender having 4-7 nips, and having at least two thermo rolls, the thermo rolls having surface temperatures of at least 120° C., the linear load of the end calender nips being in a range of 150-600 kN/m and the moisture content of the web before a first nip of the end calender is in a range of 5-11%.  
     
     
         70 . A paper machine for the manufacture of LWC printing paper coated once, comprising arranged in the running direction of a web: 
 a headbox from which stock is fed to a former;    a gap former arranged to remove water from the web in two directions, the paper web being formed in the gap former, and the web having a first side and a second side, the web being comprised of at least 70% mechanical pulp;    a press section having at least one extended nip press, through which the web is passing;    a pre-dryer section in which the web is dried by applying at least cylinder drying;    a pre-calender having at least one nip having a total length of the nip or nips in a range of 15-600 mm, and a linear load of the pre-calendering nip or nips is in a range of 50-500 kN/m and two heatable backing backup surfaces having a temperature of least 200° C. which are engage with the first side and the second side of the web and in which the web is precalendered, the web positioned immediately before the at least one nip having a moisture content of 5-20%;    a coating station having a supply of coating in contact with the first side of the web forming a film coating coater or a noncontact coater, and the coating station further having a supply of coating in contact with the second side of the web forming a film coating coater or a noncontact coater;    a subsequent after-dryer section having a noncontact dryer through which the web passes;    an end calender in which the web is calendered; and    a reel-up in which the web is reeled.    
     
     
         71 . The paper machine of  claim 70 , wherein the pre-calender is formed of a soft calender in which there are at least two nips which are each formed by an elastic surface roll and a hard surface thermo roll, the hard surface thermo rolls forming the two heatable backing backup surfaces.  
     
     
         72 . The paper machine of  claim 70 , wherein the pre-calender is formed of a shoe calender in which there are at least two nips which are each formed by a shoe roll and a hard surface thermo roll, the hard surface thermo rolls having surfaces which form the two heatable backing backup surfaces.  
     
     
         73 . The paper machine of  claim 70  wherein the pre-calender has at least a first nip and a second nip, and wherein the paper machine comprises a first moisturizing device situated, in the running direction of the web, before the first nip of the pre-calender for moisturizing at least that side of the web which will be against the thermo roll in the first nip, whereby the effect of the temperature of the thermo roll of the first nip on that side of the web is enhanced.  
     
     
         74 . The paper machine of  claim 70  wherein the pre-calender has at least a first nip and a second nip, and wherein the paper machine comprises a second moisturizing device placed in connection with a run of the web between the first and the second nip of the pre-calender for moisturizing at least that side of the web which will be against the thermo roll in the second nip, whereby the effect of the temperature of the thermo roll of the second nip on that side of the web is enhanced.  
     
     
         75 . The paper machine of  claim 70 , wherein the pre-calender is formed of a belt calender having a nip which is formed between a thermo roll and a metal belt running over a backup roll having an elastic surface, and wherein the surface temperature of the thermo roll and the metal belt is at least 200° C.  
     
     
         76 . The paper machine of  claim 70 , wherein the paper machine comprises moisturizing devices which are situated, in the running direction of the web, before the pre-calender and by which the first and second sides of the web are moisturized, whereby the effect of the temperature of the two heatable backing backup surfaces on the web in the nip is enhanced.  
     
     
         77 . The paper machine of  claim 70 , wherein the headbox is a dilution headbox.  
     
     
         78 . The paper machine of  claim 70 , wherein the headbox is a multilayer headbox.  
     
     
         79 . The paper machine of  claim 70 , wherein the gap former is a gap former provided with a forming suction roll and with at least one blade loading unit.  
     
     
         80 . The paper machine of  claim 70  wherein the press section is a press section provided with two extended press nips, the extended press nips being formed between a shoe roll, which is provided with a belt shell and a loading shoe, and a recessed surface counter roll.  
     
     
         81 . The paper machine of  claim 80 , wherein each extended press nip of the press section is double-felted.  
     
     
         82 . The paper machine of  claim 70 , wherein the pre-dryer section comprises cylinder drying groups which apply single-wire draw and to which impingement drying cylinders provided with impingement units are connected.  
     
     
         83 . The paper machine of  claim 70 , wherein the coating station is a film coating station applying two-side roll application.  
     
     
         84 . The paper machine of  claim 70 , wherein the noncontact dryer is followed by a one cylinder drying group.  
     
     
         85 . The paper machine of  claim 70 , further comprising a first measurement device which is placed on a run of the web between the pre-dryer section and the pre-calender and in which the profile of the web is measured.  
     
     
         86 . The paper machine of  claim 70 , further comprising a second measurement device which is placed on a run of the web between the pre-calender and the coating station and in which the profile of the web is measured.  
     
     
         87 . The paper machine of  claim 70 , further comprising a third measurement device which is placed on a run of the web between the portion applying contact-free drying and the portion applying cylinder drying in the after-dryer section and in which the profile of the web is measured.  
     
     
         88 . The paper machine of  claim 70 , wherein the end calender is a soft calender having 2-4 nips.  
     
     
         89 . The paper machine of  claim 70 , wherein the end calender is a multi-nip calender having 4-7 nips.  
     
     
         90 . A base paper intended for LWC printing paper which is coated once, wherein the base paper comprises at least 70% mechanical pulp, and that the PPSs10 roughness of the base paper before coating is below 3.5 μm, that the Cobb-Unger oil absorption of the base paper before coating is below 15 g/m 2 , and that the bulk of the base paper before coating is over 1.0 cm 3 /g.  
     
     
         91 . A method for the manufacture of LWC printing paper coated once, comprising the following successive steps: 
 feeding stock from a headbox to a gap former, in which water is removed from a web which is being formed in two directions to form a web comprised of at least 70% mechanical pulp;    passing the web to a press section which comprises at least one extended nip press and in which water is removed from the web by pressing;    passing the web to a pre-dryer section, in which the web is dried by applying at least cylinder drying;    regulating the web to a moisture content of 5-20% before a first nip of a pre-calender, having a nip or nips, the nip or nips of the pre-calender having a total length;    passing the web to the precalender and calendering a first side and a second side of the web, the precalender having a first side backup surface for the web first side and a second side backup surface for the web second side, each of the first and second backup surfaces heated to at least 200° C., the pre-calender nip or nips having a total length in a range of 15-600 mm at a nip load of 50-500 kN/m, in which the web is precalendered to form a base web from the formed web having a PPSs10 roughness below 3.5 μm, a Cobb-Unger oil absorption below 15 g/m 2 , and a bulk of over 1.0 cm 3 /g;    passing the web to at least one coating station and one after-dryer section, in which the web is coated on both sides by using a film coating method or a non-contact coating method;    drying the web at least by contact-free drying;    passing the web which is now LWC printing paper coated once, to an end calender, in which the web is calendered; and    passing the LWC printing paper coated once web, to a reel-up, in which the web is reeled into machine reels.    
     
     
         92 . The method of  claim 91  wherein the web is pre-calendered to form a base web from the formed web having a PPSs10 roughness below 3.0 μm, a Cobb-Unger oil absorption below 12 g/m 2 , and a bulk of over 1.2 cm 3 /g.