WO2006114343A1

WO2006114343A1 - Machine for the production of a fiber web

Info

Publication number: WO2006114343A1
Application number: PCT/EP2006/060135
Authority: WO
Inventors: Ingolf Cedra
Original assignee: Voith Patent Gmbh
Priority date: 2005-04-28
Filing date: 2006-02-21
Publication date: 2006-11-02
Also published as: DE102005000046A1

Abstract

Disclosed is a machine for producing a paper web or another fiber web (1). Said machine comprises a press section in which the fiber web (1) can be directed over a central roll (6) that forms two press nips (7, 10) along with first (5) and a second press roll (11). The inventive machine is characterized in that the fiber web (1) can be guided through the press nips (7, 10) formed between the central roll (6) and the press rolls (5, 12) together with a transfer belt (8).

Description

Machine for producing a fibrous web

The invention relates to a machine for producing a paper or another fibrous web having a press section, in which the fibrous web can be guided via a central roll forming two press nips with first and a second press roll

From DE 100 22 087 A1 a press section for a paper machine is known. The press section has two pressing points, which are each formed by a press roller cooperating with a shoe press roll. A first upper felt, the paper web coming from a forming wire, an underfelt and a press jacket of a first shoe press roll pass through the first press point. The underfelt continues with the paper web to the second press site. Together with a second top felt and a press jacket of a second press site, the paper web then passes through the second press site. The paper web follows the underfelt further up to a take-off roll, through which it is transferred to a first dryer wire which transfers the paper web to the dryer section. Guide rollers and suction rollers are provided for deflecting the upper felt and the lower felt. In press sections known from the prior art, support by a transfer belt is necessary due to the low strength of the paper web.

From WO 00/55423 a press section for a paper machine is known, in which a central roll (Fig. 1) is used, which cooperates in two press nips with a press roll and a shoe press roll. In each of the two press nips the fibrous web is guided on both sides: in the first press nip by a felt and a transfer belt, in the second press nip by the transfer belt and another band. As high-speed paper machines, the following configurations are currently used for the production of high-quality SC-A paper (SC = super calendered). These are called roll-blade shapers, ie screen formers with a forming roller and drainage strips, without flexible strips in conjunction with a downstream conventional one Press section built with three press nips. The press nips can also be formed by shoe press rolls. Subsequently, a free-standing press unit is preferably arranged for a fourth press nip. Outside the paper machine, the fibrous web is smoothed by at least two calenders with a plurality of nips (multinip calenders). The calenders follow the speed of calendering paper machine production.

To set the required inlet moisture and the most uniform possible moisture distribution over the entire web width, the fibrous web is usually dried in the dryer section to a residual moisture content of 2 to 3% and moistened before the reeling station still within the paper machine with the help of a water applicator, such as a nozzle moistener. The residence time of the wound with the paper web of the after winding in the paper machine to the calendering of the paper web in the calenders is between 0.5 and 2 hours. Thanks to the drying out and the long dwell time, a very good moisture distribution in all directions within the paper web can be assumed.

The integration of the multinip calender in the paper machine (on-line process) generally results in a significant speed increase of the calendering process. Due to the shorter residence time in the nip and due to other web running conditions, the online process has cost advantages compared to the classic offline process described above; At the same time, however, it leads to quality disadvantages, which manifest themselves in particular in the printability in the gravure printing process in the form of print unrest and a higher number of missing dots (missing dots). Such on-line processes are carried out in the following manner: A roll-blade former with or without flexible twin-mesh bars is used in conjunction with two freestanding shoe presses or a freestanding roller press and a subsequent shoe press in conjunction with a multi-pin calender.

Alternatively, a roll-blade former with or without flexible strips in the twin-wire area and a conventional three-nip press with or without Schuhnip used in conjunction with a multi-pin calender.

Or a roll-blade former without flexible strips in the twin-wire area and a conventional three-nip press with or without Schuhnip and a freestanding fourth press in conjunction with a multi-pin calender used.

Compared to an offline process, the productivity in an online process can be significantly higher due to the loss of rewinding losses caused by winding, unwinding and rewinding the paper web after calendering.

A conventional press section, which is designed as a three-nip press without an additional free-standing fourth press generally shows a very strong structure two-sidedness of the paper due to asymmetric dewatering conditions in the press, as in the second and third press nip the dewatering takes place only to the top. When operating a shoe tip in the third position, the dry content may indeed be increased significantly, which generally leads to a higher speed and consequently also to a higher productivity. However, the heavier dewatering to the top further increases paper two-sidedness. Therefore, for high quality papers a free-standing fourth press with drainage reversal to the bottom is absolutely necessary. The disadvantage of this concept, however, is that the paper web must be conveyed over two areas in the open draw. It runs freely between the central roll after the third press and from the fourth press. This has a negative impact on the runnability of the paper web. The paper web overstretches. It can tears and transverse contractions occur, which significantly reduce the maximum speed potential.

It is the object of the invention to provide a machine in which the press section, in particular for high quality SC papers, in terms of runnability, d. H. runtime and material efficiency, and product quality, paper surface roughness and missing dots are improved.

According to the invention this object is achieved in a machine of the type mentioned in that the fibrous web can be passed together with a transfer belt through the press nips formed between the central roller and the press rollers.

Advantageous developments of the invention are contained in the subclaims, the description and the drawings.

For further mechanical dewatering after the wire section, the paper web, supported and guided by press felts or impermeable or permeable transfer belts, passes through several press nips formed by pairs of rolls. Due to the intensive contact of the paper web with the felt surface in the press nip, it is necessary for high quality papers to allow each paper side to be in final contact with a smooth roller or a smooth transfer belt. This smoothing takes place in a conventional press section with or without Schuhnip on the central roll and for the upper side in a subsequent press in which the paper web passes through a fourth press nip.

In the last two press nips a high pressure pulse is applied Macro smoothing of the surface of the paper web which leads to improved calenderability in the subsequent multinip calender. It can be seen that due to wet-smoothness in the press section, for a given PPS roughness after calendering, the required calendering line forces can be lower by up to 100 kN / m. This results in a significantly improved quality of the final product, since negative effects of the calendering, such. B. Schwarzsati nage or volume decrease, be significantly reduced.

In order to be able to achieve even higher production speeds according to this concept, maximum dry contents must after passing through the

Achieved and the required web tracks are minimized to a

Overstretching and thus avoiding tears in the dryer section. The operation of a shoe tip in the third press nip can increase the dry content compared to conventional roll nips by up to four percent. However, this positive effect is at the expense of the surface quality and thus the printability, in particular the felt-contacting surface of the paper web.

To produce high-quality uncoated magazine papers (SC papers), the use of a fourth press nip is essential, with the paper web being led through the press nip together with an underfelt for smoothing. This nip can also be used as a Schuhnip with extended residence time to enhance the smoothness effect.

Instead of the felt used according to the prior art in the third press nip an impermeable, smooth transfer belt is now used, thereby avoiding that the paper web must be continued in free train from the central roll. Rather, the paper web is about to reach the fourth

Pressnips, which is arranged in a free-standing press, removed using an evacuated transfer roller and transferred to another suction roller with the underfelt or a permeable, absorbable transfer belt.

The transfer suction roll advantageously has a rubberized one Sheath surface on. It can also be equipped with a drilling pattern in its roll shell. For safe removal of the paper web, the roller can be variably adjusted in its immersion depth with respect to the paper web and the transfer belt. For this purpose, an adjusting device is provided, by means of which the roller is movable.

In order to increase the positive smoothness effect of the press section, novel press felts can be used in all positions. An extremely fine surface of the press felts is due to the use of a certain amount of molten fiber material. By this measure, the negative appearing felt marks are drastically reduced.

The advantages of the invention are that highest production speeds due to the achievement of maximum dry contents after passing through the wire section and the press section and as a result of minimizing the free draws in the press section by the use of the transfer belt are possible. Due to the wet smoothness effect in the press section on both sides of the paper web also a gentle calendering is possible. By means of the press section constructed according to the invention, best printability properties, especially for gravure printing, are achieved on account of improved topography properties of the base paper.

Furthermore, it may be useful to selectively apply at least once a dampening solution to correct the moisture profile in the forming section and / or in the press section on the fibrous web in the cross machine direction.

Preferably, the fibrous web is formed in a vertical gap former, in particular twin-wire former.

The gap former has flexible formation strips. As a result, the formation and the pressure balance in half and full tones is improved. Experiments have shown that through the use of flexible formation strips in one Drainage range between 2% and 8% dry content, preferably between 3% and 6% dry content, the formation index according to Ambertec can be significantly reduced.

Experiments showed an average formation improvement of 20% as well as an improvement of moping of 10%. In the formation with flexible formation strips can be compared to the formation without formation strips a pulp with a significantly lower freeness used to obtain a fibrous web with the same quality properties. Due to the lower degree of grinding, the required specific grinding energy is significantly reduced. Assuming that the specific grinding energy, the Mahlgard and the formation / pressure rest are linearly linked together, this results in an energy cost advantage of up to 20% in the area of pulp processing.

It has been found that the best results in terms of the above properties are achieved when flexible formation strips are used. Preferably, 1 to 10, particularly preferably 3 to 5, flexible formation strips are used here.

Furthermore, the formation strips are advantageously pressed against the sandwich, consisting of the two forming fabrics with interposed fibrous web, with a contact pressure in the range between 5kPA and 3OkPa, preferably between 8kPa and 25kPa.

Furthermore, the flexible formation strips cause additional drainage in the twin-wire area.

For optimum drainage, the wrap angle of the forming roll through the two forming fabrics is between 30 ° and 60 °, preferably between 40 ° and 55 °. Thus, it is possible even at speeds of up to 2000m / min dry contents of 18% to 20% at the end of Formierpartie too achieve.

With increasing speed of the fibrous web, the properties of the forming fabrics used for the dewatering regime and the structure of the paper surface play an increasingly important role.

Here, the forming fabrics used should ensure a sufficiently high dewatering rate, have a low water storage volume and have a fine paper-side surface. Forming fabrics with a sieve thickness of less than 0.7 mm, preferably less than 0.65 mm and with a number of fiber support points of more than 1400 / cm ² , preferably more than 1500 / cm ² , more preferably more than 1600 / cm ² are for this purpose particularly suitable.

After the press section, the fibrous web passes through a drying section and is dried in this. There are different ways to dry the fibrous web, for example by drying on heated cylinders or by Impallströmtrocknung with hot air.

After drying the fibrous web in the dryer section, this is, if it is, for example, rotogravure paper, fed to a multinip calendering device. The multi-pin calendering device can have between 6 and 12 rollers.

To increase the productivity, it makes sense if the multinip calendering device is an on-line calendering device, since, for example, offline calenders permit significantly lower web speeds and a repeated rewinding of the paper web is necessary.

If lower requirements are placed on the production speed, an offline calendering device can also make sense. Especially for Offestdruck- applications has been found, for example, in experiments with fibers with a high fines content that over-drying of the fibrous web and subsequent humidifying between dryer section and online Multinip -Kalander is advantageous, whereby disturbances in dimensional stability such as cockling and fluting significantly reduced or be prevented. A preferred embodiment of the method according to the invention therefore provides that the moisture content of the fibrous web when leaving the dryer section is below the equilibrium moisture content at standard conditions. A further preferred embodiment of the method according to the invention further provides that the fibrous web before entering the

Calendering device is preferably selectively moistened in the cross machine direction. By selective moistening in the cross-machine direction, moisture transverse profile fluctuations can be compensated.

To produce a same two-sided paper surface, a same treatment on both sides of the paper web is advantageous. A preferred embodiment of the invention therefore provides that one of the two sides of the fibrous web is brought into contact in each case with a heated roller in a first sequence of Kalandemips and that the other of the two sides of the fibrous web in the following in a second sequence of Kalandemips each with a heated roller is brought into contact.

In order to achieve the same smoothness on both sides, it makes sense if the fibrous web is moistened on both sides after leaving the dryer section.

In this case, it is possible that before each succession of Kalandemips each side of the fibrous web is moistened, which is brought into contact with the heated rollers.

On the other hand, another embodiment provides that the fibrous web is moistened on both sides prior to entry into the calendering device. Furthermore, it is possible to provide additional humidifying devices between the above-mentioned locations in order to apply the required amount of moisture to the fibrous web.

Best smoothness of the calendered fibrous web is achieved when the

Fibrous web is moistened to a moisture content of 7% to 9%, preferably to a moisture content of 8%.

It makes sense here if the fibrous web has a moisture content of 7% to 9%, preferably 8%, before each succession of Kalander dips.

Preferably, the fibrous web is moistened by means of steam humidifier and / or nozzle moistener.

Due to the very short residence time between dampening solution application and first Kalandemip the droplets must be finely distributed for a sufficient humidification of the fibrous web. This can be achieved by a two-fluid humidifier with air and dampening solution.

The above-described method with its various embodiments according to the invention is preferably used for the production of intaglio paper or SC paper, which preferably has a filler content of 25% or more, more preferably a filler content of 30% or more.

The invention will be explained in more detail in an embodiment. The single figure shows a schematic view of a press section.

A fibrous web 1 (figure), coming from a wire section, passed through a press section. In this, it is supported by a lower felt 2 and a top felt 3, passed through a first press nip 4, which is formed by a Presssaugwalze 5 with a press roll 6. After the press nip 4, the underfelt 2 is again separated from the fibrous web 1, so that these, on the top felt 3rd lying, between the Presssaugwalze 5 and a central roller 6 is passed through a second press nip 7.

In order to ensure a good smoothing on the central roller 6 side facing 19 of the fibrous web 1, a transfer belt 8 is passed together with the fibrous web 1 through the press nip 7. Subsequently, the top felt 3 is led away from the press suction roll 5.

The fibrous web 1 is now passed together with the transfer belt 8 and another upper felt 9 through a press nip 10, which is of the

Central roller 6 and one equipped with a shoe press zone 11

Shoe press roll 12 is formed. Here is the one side 19 of the

Fiber web 1 in contact with the smooth transfer belt 8 and the other side

20 of the fibrous web 1 is guided in contact with the press felt 9 through the press nip 10, which forms the penultimate press nip of the press section.

Then, the fibrous web 1 is sucked off by a transfer suction roll 13 from the transfer belt 8 and transferred by means of another transfer suction roll 14 onto a lower felt 15. Thereafter, the fibrous web 1 together with the lower felt 15 by belonging to a free-standing press unit

Press rollers 16, 17 passed, which together form a fourth press nip 18. Here, the one side 19 of the fibrous web 1 is guided in contact with the lower felt 15 and the other side 20 of the fibrous web 1 in contact with the lateral surface of the press roll 17 through the last press nip 18 of the press section. Due to the two-sided treatment of the fibrous web with a smooth surface when passing through a press nip a two-sidedness of the fibrous web 1 is almost completely prevented.

For further features of the overall process, reference is made to the German patent application no. 10 2005 000 045.2, which is fully described in this application and which is hereby incorporated in full in this application.

Claims

claims

1. Machine for producing a paper or another fibrous web

(1) with a press section, in which the fibrous web (1) can be guided via a central roller (6) forming two press nips (7, 10) with first (5) and a second press roller (12), characterized in that the fibrous web ( 1) together with a smooth transfer belt (8) can be guided through the press nips (7, 10) formed between the central roller (6) and the press rollers (5, 12).

2. Machine according to claim 1, characterized in that the fibrous web (1) can be guided by a transfer suction roll (13) from the transfer belt (8) to a felt, in particular an underfelt (15), and can be guided by a further press nip (18) ,

3. Machine according to claim 1 or 2, characterized in that the transfer belt (8) is permeable or impermeable.

4. Machine according to claim 2 or 3, characterized in that the transfer suction roll (13) has a rubberized mantle surface and / or a drilling pattern in the mantle surface and / or that the transfer suction roll (13) is evacuated.

5. Machine according to one of claims 1 to 4, characterized in that by the central roller (6) and the second press roller (12) formed press nip (10) forms the penultimate, in particular third press nip of the press section and that the further press nip (18 ) forms the last press nip, in particular the fourth press nip, the press section.

6. Machine according to one of claims 1 to 5, characterized in that the one side (19) of the fibrous web (1) in contact with the smooth

Transfer belt (8) and the other side (20) of the fibrous web (1) in contact with a press felt (9) through the penultimate press nip (10) is feasible.

7. Machine according to one of claims 2 to 6, characterized in that the one side (19) of the fibrous web (1) in contact with the lower felt (15) and the other side (20) of the fibrous web (1) in contact with the Jacket surface of a press roller (17) through the last press nip (18) is feasible.

8. Machine according to one of claims 1 to 7, characterized in that the penultimate press nip (10) and / or the last press nip (18) is designed as a shoe press nip.

9. Machine according to one of claims 1 to 8, characterized in that the transfer suction roll (13) in its immersion depth relative to the transfer belt (8) and the fibrous web (1) is adjustable.

10. Machine according to one of claims 1 to 9, characterized in that a vertical gap former, in particular a twin-wire former, is arranged in front of the press section.

11. Machine according to claim 10, characterized in that the gap former has flexible formation strips.

12. Machine according to one of claims 1 to 11, characterized in that a drying section is arranged after the press section.

13. Machine according to claim 12, characterized in that the drying section has a Impallströmtrocknungseinrichtung.

14. Machine according to one of claims 1 to 13, characterized in that after the drying section a multi-pin calendering device is arranged.

15. Machine according to claim 14, characterized in that the multi-pin calendering device is an online calendering device or an offline calendering device.

16. Machine according to one of claims 1 to 15, characterized in that the moisture content of the fibrous web (1) when leaving the dryer section below the equilibrium moisture content at standard climate.

17. Machine according to claim 16, characterized in that a moistening device for moistening the fibrous web (1) is provided before entering the calendering device.

18. Machine according to claim 17, characterized in that the fibrous web (1) can be selectively moistened in the cross machine direction.

19. Machine according to one of claims 14 to 18, characterized in that one of the two sides of the fibrous web (1) in a first sequence of nips in each case with a heated roller can be brought into contact and that the other of the two sides of the fibrous web (1 ) is subsequently in a second sequence of nips in each case with a heated roller in contact can be brought.

20. Machine according to claim 19, characterized in that before each sequence of nips in each case the side of the fibrous web (1), which is brought into contact with the heated roll, is moistened.

21. Machine according to claim 20, characterized in that the fibrous web (1) is preferably moistened to a moisture content of 7% to 9%, particularly preferably to a moisture content of 8%.

22. Machine according to one of claims 14 to 21, characterized in that the fibrous web (1) is moistened before entering the calendering, preferably to a moisture content of 7% to 9%, particularly preferably to a moisture content of 8%.

23. Machine according to claim 22, characterized in that the fibrous web (1) is moistened on both sides before entering the calendering device.

24. Machine according to one of claims 20 to 23, characterized in that the fibrous web (1) is moistened by means of steam humidifier and / or nozzle moistener.

25. Machine according to one of claims 1 to 24, characterized in that the fibrous web (1) produced is rotogravure paper (SC paper).

Machine according to claim 25, characterized in that the gravure paper has a filler content of 25% or more, preferably 30% or more.