Method For the Production of a Paper Web, Especially Rotogravure Paper
The invention relates to a method for producing a paper web or another fibrous web. According to said method, the fibrous web is impinged upon by pressure in the penultimate press nip and then in a last press nip of a press section. One face of the fibrous web is in contact with a smooth surface when penetrating the penultimate press nip while the other face of the fibrous web is in contact with a smooth surface the when penetrating the last press nip.
The invention relates to a method for the production of a paper or another fibrous web according to the preamble of patent claim 1.
At present, the following configurations are implemented as high-speed paper machines for the production of high-quality SC paper (SC—supercalendered): What are known as roll-blade formers, i.e. wire formers having a forming roll and dewatering foils, are constructed without flexible foils in conjunction with a conventional press section arranged downstream and having three press nips. The press nips can also be formed by shoe press rolls. Following these, there is preferably a free-standing press unit for a fourth press nip. Outside the paper machine, the fibrous web is calendered by at least two offline multi-nip calenders, which follow the paper machine production at a lower supercalendering speed.
In order to set the necessary inlet moisture and the most uniform moisture distribution possible over the entire web width, the fibrous web is normally dried out in the drying section down to a residual moisture of 2 to 3% and, before the reeling station, is moistened, still within the paper machine, with the aid of a water application unit, for example a nozzle moistener. The residence time of the spool wound with the paper web following the reeling in the paper machine until the supercalendering of the paper web into the calenders is between 0.5 and 2 hours. Thanks to the drying out and the long residence time, it is possible to assume that there is a very good moisture distribution in all directions within the paper web.
The integration of the multi-nip calender into the paper machine (online process) generally results in a considerable increase in the speed of the supercalendering process. On account of the shorter residence time in the nip and on account of other web running conditions, the online process has cost advantages as compared with the classical offline process described above; however, at the same time it leads to quality disadvantages which are expressed in particular in printability in the rotogravure process in the form of mottling and a higher number of missing dots.
Online processes of this type are implemented in the following way: use is made of a roll-blade former with or without flexible foils in the twin-wire region in conjunction with two free-standing shoe presses or one free-standing roll press and a following shoe press in conjunction with a multi-nip calender.
Alternatively, use is made of a roll-blade former with or without flexible foils in the twin-wire region and a conventional three-nip press with or without a shoe nip in conjunction with a multi-nip calender.
Alternatively, use is made of a roll-blade former without flexible foils in the twin-wire region and a conventional three-nip press with or without a shoe nip and a free-standing fourth press in conjunction with a multi-nip calender.
As compared with an offline process, the productivity in an online process can be considerably higher on account of the rewinding losses resulting from the reeling, the unwinding and the rewinding of the paper web following calendering, which are dispensed with.
A conventional press section which is constructed as a three-nip press without an additional free-standing fourth press normally exhibits very high structural two-sidedness of the paper on account of asymmetrical dewatering conditions in the press since, in the second and third press nip, the dewatering takes place only toward the top side. In the case of operating a shoe nip in the third position, although the dryness can be increased considerably, which in general leads to a higher speed and consequently also to higher productivity, the paper two-sidedness is increased further as a result of the more intense dewatering toward the top side.
The press configurations having two free-standing press nips are either felted four-fold or have an impermeable transfer belt in the second lower position. This permits a supported web run with low web draws. In the case of the four-fold-felted configuration, this results in an increased roughness of the machine-finished paper. In the case of the configuration with the transfer belt in the second lower position, the machine-finished paper exhibits increased two-sidedness.
It is the object of the invention to propose a method for the production of a fibrous web, in particular high-quality SC papers, in which improved results are achieved with regard to the runability, that is to say the running time and material efficiency, and the product quality, the roughness of the paper surface and the printability (missing dots).
According to the invention, this object is achieved by a method for the production of a paper or another fibrous web, in which the fibrous web has pressure applied to it in a press section in a plurality of press nips, one side of the fibrous web being led through the penultimate press nip of the press section in contact with a smooth surface, and the side of the fibrous web opposite the one side being led through the last press nip of the press section in contact with a smooth surface.
According to the invention, therefore, the fibrous web is calendered on both sides with low drynesses in the two last press nips of a press section, since each side of the fibrous web is led through a press nip in contact with a smooth side. Thus, two-sided macro calendering of the surface of the fibrous web takes place in the two last press nips, which leads to a considerably improved ability to be calendered in the following calender.
Trials by the applicant in this regard have shown that, on account of the two-sided wet calendering according to the invention in the press section, the supercalendering line forces required for a specific PPS roughness following supercalendering can be up to 100 kN/m lower.
This results in a considerably improved final product quality, since negative effects of the supercalendering, such as supercalender blackening or bulk reduction, can be reduced considerably by the reduction in the supercalendering line forces.
The smooth surface with which the fibrous web is brought into contact during the passage through a press nip can be formed both by a roll shell with a smooth cover or by a smooth transfer belt.
If it is a transfer belt with which the fibrous web is led through the press nip in contact, this can be permeable or impermeable, depending on the application.
One preferred refinement of the invention provides for the press section to comprise a three-nip press having a central roll and a free-standing press having a single nip, the third nip of the three-nip press being the penultimate press nip of the press section and the individual nip of the free-standing press being the last press nip of the press section.
A further embodiment of the invention provides for the fibrous web to be led together with a transfer belt through the second and third press nips formed between the central roll and the press rolls of the three-nip press.
In a further refinement of the invention, provision is made for one side of the fibrous web to be led through the penultimate press nip in contact with the transfer belt and for the other side of the fibrous web to be led through the penultimate press nip in contact with a press felt. Thus, dewatering takes place in the direction of the press felt, whereas the fibrous web is smoothed as a result of the contact with the smooth transfer belt in the wet state.
If the press, as described above, is formed for example by a three-nip press having a central roll and a downstream free-standing press having a single nip, then one side of the fibrous web is preferably led through the third press nip of the three-nip press in contact with the circumferential surface of the central roll and the other side of the fibrous web is led through the third press nip of the three-nip press in contact with a press felt, said last press nip forming the penultimate press nip of the press.
Furthermore, one side of the fibrous web is preferably led through the last press nip in contact with a press felt and the other side of the fibrous web is led through the last press nip in contact with the circumferential surface of the press roll, it being possible for the last press nip to be formed by the single press nip of the free-standing press.
In order to be able to reach higher production speeds, it is necessary to increase the dryness after the press section, in order thus, for example, to avoid overstretching and tearing of the fibrous web on account of web tension. By forming the penultimate press nip and/or the last press nip as a shoe press nip, the dryness of the fibrous web can be increased. For instance, by using a shoe press in the penultimate press nip, the dryness is increased by 4%. Furthermore, as a result of the longer residence time of the fibrous web in the shoe press nip, the calendering effect is intensified as compared with conventional press nips.
If the fibrous web is, for example, led through the three-nip press on the transport belt and then through the single press nip of the free-standing press, it is expedient if the fibrous web is transferred by a transfer suction roll from the transfer belt to the press felt, on which said fibrous web then passes through the single press nip of the free-standing press.
If, in the method according to the invention, for example in a following step, calendering of the fibrous web is carried out in an online process (online calendering), then this places very high requirements on the cross-machine profile quality of mass and moisture per unit area, because of the higher supercalendering speeds as compared with the offline process. One preferred embodiment of the method according to the invention accordingly provides that, in order to correct the cross-machine moisture profile of the fibrous web, a damping agent is applied selectively to the fibrous web at least once in the cross-machine direction at a moisture content of less than 50%, preferably after the press section.
Furthermore, in order to correct the cross-machine moisture profile, it may be expedient to apply a damping agent selectively at least once to the fibrous web in the cross-machine direction in the forming section and/or in the press section.
The fibrous web is preferably formed in a vertical gap former, in particular a twin-wire former.
In this case, the gap former has flexible formation foils. This improves the formation and the mottling in half-tones and full tones. Trials have shown that, by using flexible formation foils in a dewatering range between 2% and 8% dryness, preferably between 3% and 6% dryness, the formation index according to Ambertec can be reduced considerably.
Trials resulted in an improvement in formation of 20% on average and an improvement in the mottling of 10%. In the case of the formation with flexible formation foils, as compared with the formation without formation foils, it is possible to use a fibrous stock having a considerably lower level of refining in order to obtain a fibrous web with the same quality properties. As a result of the lower level of refining, the necessary specific refining energy is reduced considerably. Under the assumption that the specific refining energy, the level of refining and the formation/mottling are linked linearly with one another, the result is thus an energy cost advantage of up to 20% in the area of fibrous stock preparation.
It has transpired that the best results with regard to the abovementioned properties are achieved if preferably 1 to 10 flexible formation foils, particularly preferably 3 to 5 flexible formation foils, are used.
Furthermore, the formation foils are advantageously pressed against the sandwich, comprising the two forming fabrics with a fibrous web arranged between them, with a contact pressure in the range between 5 kPa and 30 kPa, preferably between 8 kPa and 25 kPa.
Furthermore, the flexible formation foils effect additional dewatering in the twin-wire area.
For optimal dewatering, the wrap angle of the forming roll by the two forming fabrics is preferably between 30° and 60°, preferably between 40° and 55°. Thus, even at speeds of up to 2000 m/min, it is possible to achieve drynesses of 18% to 20% at the end of the forming section.
As the speed of the fibrous web increases, the properties of the forming fabrics used for the dewatering regime and the structure of the paper surface play an ever more important role.
In this case, the forming fabrics used should ensure a sufficiently high dewatering rate, have a low water storage volume and exhibit a fine surface on the paper side. Forming fabrics having a fabric thickness of less than 0.7 mm, preferably less than 0.65 mm, and having a number of fiber supporting points of more than 1400/cm2, preferably of more than 1500/cm2, particularly preferably of more than 1600/cm2, are particularly suitable for this purpose.
After the press section, the fibrous web runs through drying section and is dried in the latter. There are different possibilities for drying the fibrous web, for example by drying on heated cylinders or by means of impingement drying with hot air.
In another variant of the invention, the press section merely comprises three press nips and an impingement drying device is additionally arranged between the press section and the actual drying section. With this arrangement, it is also possible to achieve good results, in particular good runability and good rotogravure printability. In particular, the two-sidedness of the paper web can be reduced considerably by this arrangement.
The three press nips are preferably formed by a three-nip press having a central roll and two press rolls. This results in a compact structure and therefore has advantages in the space required and in the production costs.
The first and/or the third press nip in this variant can be formed as a roll press or as a shoe press in each case. With shoe presses, the drying performance can be increased.
One preferred configuration of the impingement drying device or impingement device consists in a HighDryer, which in particular comprises two drying cylinders and impingement hoods. In this case, it is preferred for the drying cylinder to be evacuated slightly. For the purpose of the evacuation, stabilizers can advantageously be used. The drying cylinders of the impingement drying device preferably have a diameter of 3 meters or more in this case.
Following the drying of the fibrous web in the drying section, said web, if it is rotogravure paper, for example, is fed to a multi-nip calendering device. In this case, the multi-nip calendering device can have between 6 and 12 rolls.
In order to increase the productivity, it is expedient if the multi-nip calendering device is an online calendering device since, for example, offline calenders permit considerably lower web speeds and repeated rereeling of the paper web is necessary.
In particular for offset printing applications, for example during trials with fibrous stocks having a high proportion of fines, it has been shown that overdrying of the fibrous web and subsequently rewetting between drying section and online multi-nip calender is advantageous, by which means defects in the dimensional stability such as cockling and fluting are reduced considerably or prevented. One preferred embodiment of the method according to the invention accordingly provides for the moisture content of the fibrous web as it leaves the drying section to be below the equilibrium moisture content under standard climatic conditions. A further preferred embodiment of the method according to the invention provides, moreover, for the fibrous web to be moistened selectively, preferably in the cross-machine direction, before entering the calendering device. By means of the selective moistening in the cross-machine direction, cross-machine moisture profile fluctuations can be compensated.
In order to produce a paper surface that is the same on both sides, equal two-sided treatment of the paper web is advantageous. One preferred embodiment of the invention therefore provides for one of the two sides of the fibrous web in each case to be brought into contact with a heated roll in a first sequence of calender nips and for the other of the two sides of the fibrous web then in each case to be brought into contact with a heated roll in a second sequence of calender nips.
In order to achieve a smoothness that is the same on both sides, it is expedient if the fibrous web is moistened on both sides after leaving the drying section.
In this case it is possible in each case for the side of the fibrous web which is brought into contact with the heated rolls to be moistened before each sequence of calender nips.
On the other hand, another embodiment provides for the fibrous web to be moistened on both sides before entering the calendering device.
Furthermore, it is possible to provide further moistening devices between the above-mentioned locations, in order to apply the necessary quantity of moisture to the fibrous web.
The best smoothness of the calendered fibrous web is achieved if the fibrous web is moistened to a moisture content of 7% to 9%, preferably to a moisture content of 8%.
In this case, it is expedient if the fibrous web has a moisture content of 7% to 9%, preferably of 8%, before each sequence of calender nips.
The fibrous web is preferably moistened by means of steam moisteners and/or nozzle moisteners.
On account of the very short residence time between damping agent application and first calender nip, the droplets must be distributed finely for adequate moistening of the fibrous web. This can be achieved by means of a two-component nozzle moistener with air and damping agent.
The above-described method with its multifarious embodiments according to the invention is preferably used for the production of rotogravure paper or SC or SCA+ paper which preferably has a filler content of 25% or more, particularly preferably a filler content of 30% or more.
The invention will be described in more detail below by using two exemplary embodiments. In the drawings:
During the production of a fibrous web 2, the latter runs successively through the following sections of the paper machine 1: forming section 3, press section 4, drying section 5 and calendering device 6, before it is reeled in a winding device, not illustrated.
The fibrous web 2 is formed in a stock inlet gap 7 between an upper forming fabric 11 and a lower forming fabric 10 in the forming section 3 constructed as a vertical gap former. After the stock inlet gap 7, the sandwich comprising the upper forming fabric 11, fibrous web 2 and lower forming fabric 10 wraps around a forming roll 8 in the angular range between 30° and 60°, preferably between 40° and 55°, in order to dewater the fibrous web 2.
The fibrous web 2 is then dewatered further by means of three flexible formation foils 12 in a dewatering range between 2% and 8% dryness, preferably between 3% and 6% dryness. The flexible formation foils 12 are in this case pressed against the sandwich comprising upper forming fabric 11, fibrous web 2 and lower forming fabric 10 with a contact pressure in the range between 8 kPa and 25 kPa.
In this way, the formation and the mottling in half-tones and full tones are improved. Trials have shown that, by using flexible formation foils, the formation index according to Ambertec can be reduced considerably. Furthermore, an improvement in formation of 20% on average and an improvement in the mottling of 10% are observed. In the case of the formation with flexible formation foils, as compared with the formation without formation foils, a fibrous stock having a considerably lower level of refining can be used to obtain a fibrous web having the same quality properties. As a result of the lower level of refining, the necessary specific refining energy is reduced considerably. Under the assumption that the specific refining energy, the level of refining and the formation/mottling are linked linearly with one another, the result is thus an energy cost advantage of up to 20% in the area of fibrous stock preparation.
The fibrous web has a top side 27 and a bottom side 28 arranged opposite the top side 27.
The sandwich comprising upper forming fabric 11, fibrous web 2 and lower forming fabric 10 is then led over a wire suction roll 13 before the upper forming fabric 11 is lifted off the top side 27 of the fibrous web 2 and the latter is led to the press section 4 with the bottom side 28 on the bottom forming fabric 10.
By means of the above-described configuration of the forming section 3, optimum dewatering of the fibrous web 2 takes place, so that it is possible, even at speeds of up to 2000 m/min, to achieve drynesses of the fibrous web 2 of 18% to 20% at the end of the forming section 3.
In order to ensure a sufficiently high dewatering rate combined with a low water storage volume and a fine surface on the paper side, the upper forming fabric 11 and the lower forming fabric 10 have a fabric thickness of less than 0.7 mm and a number of fiber supporting points of more than 1500/cm2.
At the end of the forming section 2, the fibrous web 2 is transferred from the lower forming fabric 10 to a press felt 20 of the press section 4 by a pick-up roll 24.
By means of the press felt 20, the fibrous web 2 is led on its top side 27 to a first press nip 14 of a three-nip press 13 and is deflected through the first press nip 14 in the sandwich between the press felt 20 and a press felt 19.
The three-nip press 13 has a central roll 21 which forms a second press nip 15 with a roll 25 and a third press nip 16 with a roll 26.
As it passes through the second press nip 15, the top side 27 of the fibrous web 2 is in contact with the press felt 20, and the bottom side 28 of the fibrous web 2 is in contact with the smooth circumferential surface of the central roll 21.
As it passes through the third press nip 16, the top side 27 of the fibrous web 2 is in contact with a press felt 22, and the bottom side 28 of the fibrous web 2 is in contact with the smooth circumferential surface of the central roll 21. The third press nip 16 constitutes the penultimate press nip of the press section 4.
The fibrous web 2 then passes through the single press nip 17 of a free-standing press 18. The press nip 17 forms the last press nip of the press section 4.
As it passes through the press nip 17, the top side 27 of the fibrous web 2 is in contact with the smooth circumferential surface of a press roll 29, and the bottom side 28 of the fibrous web 2 is in contact with a press felt 23.
Thus, the fibrous web 2 is calendered successively on both sides 27, 28 with a low dryness in the two last press nips 16, 17 of the press section 4, since each side 27, 28 of the fibrous web 2 is led through one of the press nips 16, 17 with a smooth side in contact. Thus, in the two last press nips 16, 17, macro-calendering of the surface of both sides of the fibrous web 2 takes place, which leads to a considerably improved ability to be calendered in the following calender.
In order to be able to reach higher production speeds, it is necessary to increase the dryness after the press section, in order thus, for example, to avoid overstretching and tearing of the fibrous web on account of web tension. Therefore, the penultimate press nip 16 and/or the last press nip 17 could optionally be constructed as a shoe press nip. Furthermore, as a result of the longer residence time of the fibrous web 2 in the shoe press nip, the calendering effect would be intensified as compared with conventional press nips.
On account of the calendering of the fibrous web 2 to be carried out in a following step in an online process (online calendering), very high requirements are placed on the quality of the cross-machine profile of mass per unit area and moisture, because of the higher supercalendering speeds as compared with the offline process. Accordingly, in order to correct the cross-machine moisture profile of the fibrous web 2, a damping agent can be applied to the fibrous web 2 selectively at least once in the cross-machine direction with a moisture content of less than 50% after the press section 4.
After the press section 4, the fibrous web 2 is transferred into the drying section 5 which, in the present embodiment, has a plurality of drying cylinders 30 arranged in one row and is not illustrated completely in its length.
Following the drying of the fibrous web 2 in the drying section 5, it is fed to an online multi-nip calendering device 6.
As it leaves the drying section 5, the fibrous web has a moisture content which is below the equilibrium moisture content under standard climatic conditions. The fibrous web 2 has a moisture content of about 2.5%. Before entering the calendering device 6, the fibrous web 2 is moistened selectively in the cross-machine direction, so that the fibrous web 2 has a uniform moisture content of about 8% over the web width.
The moistening is carried out on the bottom side 28 of the fibrous web 2 by means of a nozzle moistener 35, which is constructed as a two-component nozzle moistener, from which an air-damping agent mixture emerges.
The above-described method step of overdrying the fibrous web 2 with subsequent rewetting before the entry into the multi-nip calender 6 has proven to be advantageous in particular in trials with fibrous stocks having a high proportion of fines, since in this way defects in the dimensional stability, such as cockling and fluting, are reduced considerably or prevented. As a result of the selective moistening in the cross-machine direction, transverse moisture profile fluctuations can be compensated.
The online multi-nip calendering device 6 has six resilient rolls 31 and four heated rolls 32, which form eight calendering nips 33 and a calendering nip 34.
By means of the calendering device 6, identical treatment of both sides of the fibrous web 2 takes place. This is achieved in that, firstly, the bottom side 28 of the fibrous web 2 is brought into contact with one of the heated rolls 32 in each case in a first sequence 37 of four calender nips 33 and in that, subsequently, after passing through the calender nip 34, which is also designated a reversing nip, the top side 27 of the fibrous web 2 is brought into contact with one of the heated rolls 32 in each case in a second sequence 38 of four calender nips 33.
After leaving the first sequence 37 of calender nips 33 and before entering the second sequence 38 of calender nips 38, the top side 27 of the fibrous web 2 is moistened by means of a nozzle moistener 36, which is constructed as a two-component nozzle moistener. After this moistening, the fibrous web 2 has a moisture of about 8%.
Furthermore, steam moisteners 39 to 41 are provided, in order to apply the requisite amount of moisture to the fibrous web 2.
The variant illustrated in
Around the central roll 21 there wraps a transfer belt 47, which is led through the second and third press nip 15, 16 with the paper web 2. The fibrous web 2 is taken off the transfer belt 47 by means of a suction roll 48 and transferred to the first drying cylinder 43. Around the suction roll 48 there wraps a felt belt 49, which is additionally led over three web guide rolls 50.
From the first drying cylinder 43, the fibrous web 2 is transferred directly to the second drying cylinder 44. From the latter, the fibrous web 2 passes over a roll 51 and a suction roll 52 into the drying section 5. In this case, the dryer felt 53 of the drying section 5 wraps around the suction roll 52. Only the first two drying cylinders 30 of the drying section 5 are illustrated.
Finally, the two drying cylinders 43 and 44 are each evacuated via stabilizers 54, which are arranged outside the two drying cylinders 43, 44, in each case on the side facing away from the impingement hoods 45, 46. The stabilizers 54 are in each case located within the loops formed by the fabrics 55, 56 which wrap around a section of the first drying cylinder 43 and, respectively, the second drying cylinder 44 of the impingement drying device 42. In addition, web guide rolls 57, 58 are in each case provided for the loops.
Claims
1. A method for the production of a paper or another fibrous web, in which the fibrous web has pressure applied to it in a penultimate press nip and then in a last press nip of a press section,
- characterized in that
- one side of the fibrous web, when passing through the penultimate press nip, is in contact with a smooth surface, and in that the other side of the fibrous web, when passing through the last press nip, is in contact with a smooth surface.
2. The method as claimed in claim 1, characterized in that the smooth surface is formed by a roll shell with a smooth cover and/or by a smooth transfer belt.
3. The method as claimed in claim 2, characterized in that the transfer belt is permeable or impermeable.
4. The method as claimed in claim 1, characterized in that the press section comprises a three-nip press having a central roll and a free-standing press having a single nip, the third nip of the three-nip press being the penultimate press nip of the press section and the individual nip of the free-standing press being the last press nip of the press section.
5. The method as claimed in claim 4, characterized in that the fibrous web is led together with a transfer belt through the second and third press nips formed between the central roll and the press rolls of the three-nip press.
6. The method as claimed in claim 2, characterized in that one side of the fibrous web is led through the penultimate press nip in contact with the transfer belt and the other side of the fibrous web is led through the penultimate press nip in contact with a press felt.
7. The method as claimed in claim 2, characterized in that one side of the fibrous web is led through the penultimate press nip in contact with the circumferential surface of a roll, in particular the central roll, and the other side of the fibrous web is led through the penultimate press nip in contact with a press felt.
8. The method as claimed in claim 1, characterized in that one side of the fibrous web is led through the last press nip in contact with a press felt, and the other side of the fibrous web is led through the last press nip in contact with the circumferential surface of a press roll.
9. The method as claimed in claim 1, characterized in that the penultimate press nip and/or the last press nip is formed as a shoe press nip.
10. The method as claimed in claim 1, characterized in that the fibrous web is led through four press nips in the press section.
11. The method as claimed in claim 2, characterized in that the fibrous web is transferred by a transfer suction roll from the transfer belt to the press felt of the last press nip.
12. The method as claimed in claim 11, characterized in that the transfer suction roll has a rubber-covered circumferential surface and/or a hole pattern in the circumferential surface.
13. The method as claimed in claim 11, characterized in that the penetration depth of the transfer suction roll with respect to the transfer belt and the fibrous web can be adjusted.
14. The method as claimed in claim 1, characterized in that, in order to correct the cross-machine moisture profile of the fibrous web, a damping agent is applied selectively to the fibrous web at least once in the cross-machine direction at a moisture content of less than 50%, preferably after the press section.
15. The method as claimed in claim 1, characterized in that, in order to correct the cross-machine moisture profile, a damping agent is applied selectively to the fibrous web at least once in the cross-machine direction in the forming section and/or in the press section.
16. The method as claimed in claim 1, characterized in that the fibrous web is formed in a gap former, in particular a twin-wire former.
17. The method as claimed in claim 16, characterized in that the gap former has flexible formation foils, preferably 1 to 10 formation foils, particularly preferably 3 to 5 formation foils.
18. The method as claimed in claim 17, characterized in that the gap former is a vertical gap former.
19. The method as claimed in claim 16, characterized in that the wrap angle of the forming roll by the two forming fabrics is in the range from 30° to 60°, preferably from 40° to 55°.
20. The method as claimed in claim 17, characterized in that the formation foils are pressed against the sandwich, comprising the two forming fabrics with a fibrous web arranged between them, with a contact pressure in the range between 5 kPa and 30 kPa, preferably between 8 kPa and 25 kPa.
21. The method as claimed in claim 16, characterized in that use is made of forming fabrics having a fabric thickness of less than 0.7 mm, preferably less than 0.65 mm, and having a number of fiber supporting points of more than 1400/cm2, preferably of more than 1500/cm2, particularly preferably of more than 1600/cm2.
22. The method as claimed in claim 1, characterized in that, after running through the press section, the fibrous web is dried in a drying section.
23. The method as claimed in claim 22, characterized in that, after running through the press section, the fibrous web is subjected to impingement drying.
24. The method as claimed in claim 23, characterized in that the press section (4) merely comprises three press nips (14, 15, 16), and in that an impingement drying device (42) is arranged between press section (4) and drying section (5).
25. The method as claimed in claim 24, characterized in that the three press nips (14, 15, 16) are formed by a three-nip press (13) having a central roll (21) and two press rolls (25, 26).
26. The method as claimed in claim 24, characterized in that the first and/or the third press nip (14, 16) is formed as a shoe press nip.
27. The method as claimed in one of claims 24 to 26 claim 24, characterized in that the impingement drying device (42) is constructed as a HighDryer.
28. The method as claimed in claim 24, characterized in that at least one drying cylinder (43, 44) of the impingement drying device (42) is evacuated slightly.
29. The method as claimed in claim 28, characterized in that stabilizers (54) are used for the evacuation of the drying cylinders (43, 44).
30. The method as claimed in claim 1, characterized in that, following its drying in the drying section, the fibrous web is fed to a multi-nip calendering device.
31. The method as claimed in claim 30, characterized in that the multi-nip calendering device is an online calendering device.
32. The method as claimed in claim 1, characterized in that the moisture content of the fibrous web as it leaves the drying section is below the equilibrium moisture content under standard climatic conditions.
33. The method as claimed in claimed 32, characterized in that the fibrous web is moistened before entering the calendering device.
34. The method as claimed in claims 33, characterized in that the fibrous web is moistened selectively in the cross-machine direction.
35. The method as claimed in claim 30, characterized in that one of the two sides of the fibrous web in each case is brought into contact with a heated roll in a first sequence of nips, and in that the other of the two sides of the fibrous web in each case is brought into contact with a heated roll in a second sequence of nips.
36. The method as claimed in claim 35, characterized in that, before each sequence of nips, in each case the side of the fibrous web which is brought into contact with the heated roll is moistened.
37. The method as claimed in claim 36, characterized in that the fibrous web is preferably moistened to a moisture content of 7% to 9%, particularly preferably to a moisture content of 8%.
38. The method as claimed in claim 30, characterized in that, before entering the calendering device, the fibrous web is moistened, preferably to a moisture content of 7% to 9%, particularly preferably to a moisture content of 8%.
39. The method as claimed in claim 38, characterized in that, before entering the calendering device, the fibrous web is moistened on both sides.
40. The method as claimed in claim 36, characterized in that the fibrous web is moistened by means of steam moisteners and/or nozzle moisteners.
41. The method as claimed in claim 1, characterized in that the fibrous web produced is rotogravure paper (SC or SCA+ paper).
42. The method as claimed in claim 41, characterized in that the rotogravure paper has a filler content of 25% or more, preferably of 30% or more.
Type: Application
Filed: Jun 20, 2006
Publication Date: Oct 2, 2008
Inventor: Ulrich Begemann (Heidenheim)
Application Number: 11/914,718
International Classification: D21F 3/08 (20060101);
