WO2012113466A1

WO2012113466A1 - Press section of a machine for producing a fibrous web and method for producing a fibrous web

Info

Publication number: WO2012113466A1
Application number: PCT/EP2011/069516
Authority: WO
Inventors: Marc Erkelenz; Peter Mödl; Daniel Gronych
Original assignee: Voith Patent Gmbh
Priority date: 2011-02-23
Filing date: 2011-11-07
Publication date: 2012-08-30
Also published as: CN103384741A; CN103384741B; EP2678472A1; DE102011004568A1; EP2678472B1

Abstract

The invention relates to a press section (10) for drying a fibrous web (1), in particular a paper, cardboard, or tissue web, in a machine for producing same, in which only one press nip is provided, wherein the press nip is formed by a shoe press roll (2) and a counter roll (3), and the shoe press roll (2) has a circumferential flexible cylindrical surface (7) and a pressing element (4), which can be pressed onto the cylindrical surface (7) from inside and thus can press the cylindrical surface (7) against the counter roll (3), and wherein the press section (10) comprises a first felt (5, 5.1, 6) having a base structure (12), which has at least one layer (12.1, 12.2) made of only twisted monofilament threads (20, 20.1, 20.2, 20.3, 20.4) and at least one nonwoven layer (12.1, 12.2) comprising a multitude of threads, wherein the threads of the one layer are oriented substantially in the running direction of the web.

Description

Press section of a machine for producing a fiber web and method for producing a fiber web

The invention relates to a press section for dewatering a fibrous web, in particular a paper, board or tissue web, in a machine for producing the same, in which only a single press nip is provided, wherein the press nip is formed by a shoe press roll and a counter roll, and Shoe press roll to a running flexible jacket and a pressing element which can be pressed from the inside of the jacket and thus can press the jacket against the counter roll, and wherein the fibrous web can be performed together with at least one first felt through the press nip.

Furthermore, the invention relates to a method for producing a fibrous web, in particular a paper, board or tissue web m by means of such a press section.

The fibrous web is passed through the nip together with a felt or between two felts, which are themselves endlessly circumferential. Due to the pressing force with which the shoe press roll and the counter roll are pressed against each other, water is pressed out of the fibrous web into the felt and thus the fibrous web is dewatered.

Such a press section is known for example from the document EP 1072721 A1, which describes a press section with only a single shoe press nip. The shoe press nip has an extended compared to simple Walzenpressnips press zone. The nip length is synonymous with the length of the press zone, which is given by the pressing element, the so-called shoe. This results in the fibrous web when passing through the press a longer residence time in the nip, ie in the press zone. And thus more water can be squeezed out.

For woodfree paper pulp which is easily dewaterable, such press sections are successful in medium speed production machines used. An example of this are machines for the production of copy paper or writing paper. For other types of paper from not so easy to dehydrate fibers reach press sections with only a single press nip according to the prior art, however, no adequate drainage and therefore can not be used. Too little dry content after press leads to poor web travel and frequent breaks. For such types of paper press sections are used with several press nips and, accordingly, several press and counter rolls. The object of the invention is to develop a press section with only a single press nip so that it can be used for the dewatering of fibrous webs from difficult to dewater pulp and thereby a sufficient dry content is achieved, and a method for producing a fibrous web with such To provide press section.

The object is achieved in that the first felt of the claimed press section comprises a basic structure having at least one layer of exclusively twisted monofilament threads and at least one non-woven layer consisting of a group of threads, wherein the threads of a layer in the Essentially aligned in the direction of web travel. The first felt may be an upper felt or a lower felt in the press section. Due to pilot plant tests, it was recognized that the dewatering performance of a press nip can be significantly improved if a purpose optimized felt is used as described above. The basic structure with a layer of monofilament threads offers less inner surface and the non-woven layer has no cross points with transverse or diagonal threads, so that there is less moisture in the fabrics or dirt particles are deposited and the felt is less polluted as in felts having a basic structure of layers with multifilament threads or of woven layers. Since more difficult to dehydrate fibers, such as heavily ground pulps or wood pulp or waste paper-containing materials containing a large amount of fines or dirt particles, these are from the Fibrous web flushed during drainage in the felt. If they can not be deposited there, the felt retains its good drainage properties and a high dry content is achieved. This felt is less compacted in the shoe press nip as opposed to felts with a base structure of woven layers and therefore retains important in the nip its important for drainage permeability, which is particularly important for shoe press nips due to the longer residence time and the high load in the press zone. In addition, it retains the necessary permeability over a longer period, ie even with numerous rounds, and does not have to be changed so quickly. The pilot plant tests have also shown that other felts so heavily foul very quickly, sometimes within a few hours, in such an application that the drainage performance drops unacceptably. With some felts, the press section does not achieve satisfactory drainage from the beginning.

The basic structure of a felt serves to ensure the tensile strength in the web running direction and in the transverse direction. It consists of twisted threads, which are either processed into a woven layer or processed into a non-woven so-called layer of scrim. The basic structure can have several layers. The threads consist of several individual yarn threads, which are twisted together. The individual yarn threads can be monofilaments, ie in each case a single compact yarn thread, or multifilaments, that is, be twisted or spun from many individual very fine filament fibers. The monofilaments preferably have a diameter of 0, 1 to 0.5 mm. By monofilament yarn is meant when all yarn yarns are monofilaments. By multifilament yarns it is meant that one or more yarn yarns are multifilament yarns or a yarn yarn twisted in itself from individual fibers. In order to achieve the desired tensile strength, it is important in so-called scrim layers that at least one layer is arranged so that the threads do not deviate more than 10 °, preferably not more than 5 °, from the web running direction. A further advantage of the press section according to the invention is that drive energy can be saved in the press in comparison to the multiple-nip press section otherwise necessary for more difficultly dewaterable fibrous webs. Furthermore, there are less felting, operating and maintenance costs in a single-nip press.

It is advantageous if a second felt, and therefore all the felts of the single-nip press section, comprise a basic structure which has at least one ply of exclusively twisted monofilament threads and at least one non-woven ply consisting of a group of threads, wherein the threads of the one layer are aligned substantially in the web running direction. Again, the deviation to the web running direction should be at most 10 °, preferably the highest 5 °. The first and second felts thus formed improve the dewatering performance of the press section in both directions up and down.

The drainage performance is also improved if the first and / or second felt has a basic structure with at least three layers. This can make the felt more stable.

The fouling tendency of the felt is further reduced and thus the drainage is further improved if the first and / or the second felt has a basic structure in which all layers consist exclusively of twisted monofilament threads. This further reduces the internal surface that could deposit particles.

It is equally positive if the first and / or the second felt has a basic structure in which all layers are non-woven. This provides the felt with significant compaction resistance.

On the basic structure of a felt, one or more fleece layers of felted and needled fibers are applied in order to achieve a more uniform pressure distribution in the nip and no marking of the background fabric to produce in the fibrous web. It can also be targeted parts of the nonwoven layers integrated into the basic structure and located between the layers or even within the layers between the threads. As a result, the porosity of the basic structure can be selectively changed or adjusted. The nonwoven layers differ in the fineness of the fibers used for production. The common unit for specifying the fiber fineness is the indication of the fiber weight per length in dtex according to the standard ISO 1 144. 1 dtex corresponds to 1 gram per 10 000 m. It is advantageous if the first and / or the second felt has a coarse fleece layer, which is composed of coarse fibers having a fiber fineness between 67 and 200 dtex. As a result, even a certain pressure distribution in the felt is achieved without too much filtering and retention of fines and dirt particles takes place. The coarse fleece can be integrated into the basic structure, so that too large interstices in the basic structure are filled or it is arranged as an intermediate layer between two layers of the basic structure, so that there is already a pressure distribution. However, the coarse nonwoven layer can also be laid onto the basic structure, preferably on the side facing the fibrous web, or it even encloses the basic structure or individual layers of the basic structure so that they are embedded in the coarse nonwoven. The effect is particularly positive when the coarse nonwoven layer consists of one or more layers, each layer having a basis weight of at least 100 g / m ² , preferably of at least 150 g / m ² . The weight of the entire coarse nonwoven layer is preferably between 100 g / m ² and 600 g / m ² .

In order to obtain even drainage and pressure distribution, the coarse nonwoven layer as a whole should have no preferential orientation. This can be achieved, for example, in that the coarse fleece consists of one or more layers, which are designed as random fleece. A random fleece is a fleece layer in which the fibers have no preferred orientation, that is, that they are confused in all directions. On the other hand, the coarse nonwoven layer can also consist of at least two layers, which, although a Preferred direction of the fibers have, but are superimposed so that the preferred directions differ by at least 5 °, preferably at least 20 ° from each other. In the case of more than two layers, it is particularly advantageous if the respectively adjacent layers deviate from one another by at least 5 °, preferably by at least 20 °.

Furthermore, it is advantageous if the first and / or the second felt has one or more nonwoven layers which are arranged on the side of the basic structure facing the fibrous web and which consist of fibers with a fiber fineness of 22 to 67 dtex. In particular, in combination with a coarse nonwoven layer, the drainage can be further improved. Only when the pressure distribution is as even as possible over the surface, the fibrous web can be well drained. Too coarse and only selective pressure not only leads to markings, but also to only moderate drainage.

In order to achieve a good fixation of the nonwoven layers or the coarse nonwoven layer on the basic structure, these layers may contain in addition to polyamide fibers and melt fibers. Melt fibers are partially or wholly of polymer which has a lower softening or melting temperature. They may also be formed as so-called BiCo or Bi-component fibers, in which case the core is formed of polyamide and the sheath of the lower-melting polymer. Preferably, the softening or melting temperature of the molten fiber is between 90 and 140 ° C. When thermofixing the felts, this temperature is reached, so that the melt fibers are soft and act as an adhesive.

A felt as described so far would not provide good drainage at the beginning, when newly installed in the machine. This would only be the case after some time, when the top fleece layers are compressed so that the pressure distribution on the fibrous web becomes very uniform. To avoid this disadvantage at the beginning after a change of felt, the first and / or the second felt may have a fine fleece layer on that of the fibrous web facing felt surface, which consists of fibers with a fiber fineness of at most 1 1 dtex. This fine nonwoven layer can be quite thin, for example less than 100 g / m ² , preferably less than 50 g / m ² and can be abraded during operation or removed by high-pressure cleaning spray pipes during operation. It is necessary only during the fairly short time of running in.

Due to the suitable combination of coarse nonwoven layer, nonwoven layer and thin fine nonwoven layer, the felt in the press section according to the invention can be adapted even better to the specific conditions, so that it has a good start-up behavior, good drainage even with difficultly dewaterable fibers and good long-term behavior even at high fines and has dirt particle load. The object is achieved for the method according to the invention in that a press section according to one of claims 1 to 14 is used, wherein the pulp, which is used to produce the fibrous web, at least 60% m, preferably at least 80% of waste paper was won. In such a pulp with high pollution load, the advantages of the invention are particularly strong. The pulp can be made directly from recyclable waste paper, ie it can be produced without any ink removal, or from a cleaned waste paper which has passed through a deinking plant with flotation or washing stage. Particularly advantageous is the use of the press according to the invention in the production of newsprint paper having a basis weight of 30 to 52 g / m ² or in packaging paper with a basis weight of 70 to 120 g / m ² . So far, press sections with two, three or even four press nips are required for these papers.

By way of embodiments, further advantageous features of the invention will be explained with reference to the drawings. they show in Figure 1 Schematic cross-section of a possible felt; how it could be used in a press section according to the invention

in Fig.2a, 2b, 2c Schematic cross sections of monofilament threads

with 9, 4 or 6 yarn threads

in Figure 3a monofilament

in Fig.3b multifilament

in Figure 3c multifilament yarn of six yarn yarns, one of which ein

Multifilament is

in Figure 4 embodiment of a press section according to the invention

The figures are described in more detail below.

1 shows the structure of a possible Fi lese 5.1 in cross section. The basic structure 12 here consists of two layers 12.1 and 12.2, of which at one, namely at the position 12.1, the threads are aligned in the web running direction 1a and in which case both layers of monofilament threads (20 and 20. 1) exist. The coarse nonwoven layer 13 is arranged between the basic structure layers as an intermediate layer. In this case, the coarse nonwoven layer 13 can be constructed from one or more layers. Overall, the weight of the coarse nonwoven layer 13 is between 100 g / m ² and 600 g / m ² . On the side facing the fibrous web are two further nonwoven layers 14, 15 and a fine nonwoven layer 16. On the running side of the felt, a nonwoven layer 17 is applied. This combination achieves very good drainage over the entire life of the felt. The nonwoven layers 14, 15, 17 and / or the coarse nonwoven layer 13 may contain so-called melt fibers which serve to fix the layers to the base structure during the production of the felt.

The monofilament threads can be made of different numbers of individual yarn threads that are twisted together. FIG. 2a shows a monofilament thread 20.2 with 9 yarn threads, in FIG. 2b a monofilament thread 20.3 with 4 yarn threads and in Fig.2c a monofilament thread 20.4 with 6 yarn threads. All yarn threads are monofilaments 21 .1, 21 .2, 21 .3.

3a shows an example of a monofilament 21.4 how it can be used as a yarn thread. Fig. 3b shows in comparison to a multifilament 22.1, which is twisted or spun from numerous fine individual fibers.

4 shows a possible embodiment of a press section 10 according to the invention. The shoe press roll 2 forms with the counter roll 3 the press nip by the pressing member 4, the so-called shoe, is pressed from the inside of the jacket 7 and thus brings the jacket with the counter roll 3 in contact. The top felt 5 passes around the suction roll 8 and transports the fibrous web 1, which comes from a sheet forming unit, to the press nip, which passes through the fibrous web 1 in the sandwich between bottom flap 6 and top felt 5. Thereafter, the felts 5, 6 are separated on the suction roll 9 and the fibrous web 1 runs on with the underfelt 6 on. The fibrous web 1 is then continued to a drying section, not shown. Both felts 5, 6 run around endlessly, which is also not shown. The first felt may be the top felt 5 or the bottom felt 6.

In another embodiment of the invention, the shoe press roll may also be arranged as a lower roll and the counter roll as an upper roll.

LIST OF REFERENCE NUMBERS

I fibrous web

1a web running direction

2 shoe press roll

3 mating roll

4 pressing element

5, 5.1.6 felt

7 coat

8, 9 suction rolls

10 press section

I I the fibrous web facing felt surface 12 basic structure 1

12.1, 12.2 Layers of the basic structure

13 coarse fleece

14, 15, 17 nonwoven layers

16 fine fleece layer

20, 20.1, 20.2, 20.3, 20.4 Monofilament thread

21.1, 21.2, 21.2, 21.3, 21.4, 21.5 monofilament

22.1,22.2 multifilament

23 multifilament thread

Claims

claims

1 . Press section (10) for dewatering a fibrous web (1), in particular a paper, board or tissue web in a machine for producing the same, in which only a single press nip is provided, wherein the press nip is formed by a shoe press roll (2) and a Counter roller (3), and the shoe press roll (2) has a continuous flexible jacket (7) and a pressing element (4) which from the inside of the jacket (7) can be pressed and thus the jacket (7) against the counter roll (3 ), and wherein the fibrous web (1) together with at least one first felt (5, 5.1, 6) can be guided through the press nip,

characterized,

in that the first felt (5, 5.1, 6) comprises a basic structure (12) comprising at least one layer (12.1, 12.2) of exclusively twisted monofilament threads (20, 20.1, 20.2, 20.3, 20.4) and at least one nonwoven Layer (12.1, 12.2) consisting of a family of threads (20, 20.1, 20.2, 20.3, 20.4), wherein the threads of the one layer are aligned substantially in the web running direction.

2. Press section according to claim 1

characterized,

in that the press section (10) comprises a second felt (5, 5.1, 6) with a basic structure (12) which comprises at least one layer (12.1, 12.2) of exclusively twisted monofilament threads (20, 20.1, 20.2, 20.3, 20.4). and at least one nonwoven layer (12.1, 12.2) consisting of a group of threads (20, 20.1, 20.2, 20.3, 20.4), wherein the threads of the one layer are aligned substantially in the web running direction.

3. Press section according to one of the preceding claims

characterized,

in that the first and / or a second felt (5, 5.1, 6) has a basic structure (12) with at least three layers (12.1, 12.2).

4. Press section according to one of the preceding claims characterized,

in that the first and / or a second felt (5, 5, 1, 6) has a basic structure (12) in which all the layers (12.1, 12.2) exclusively of twisted monofilament threads (20, 20.1, 20.2, 20.3, 20.4 ) consist.

5. Press section according to one of the preceding claims

characterized,

the first and / or a second felt (5, 5.1, 6) has a basic structure (12) in which all the layers (12.1, 12.2) are non-woven.

6. Press section according to one of the preceding claims

characterized,

the first and / or a second felt (5, 5.1, 6) has a coarse nonwoven layer (13) which consists of fibers having a fiber fineness of between 67 dtex and 200 dtex.

7. Press section according to claim 6

characterized,

the coarse nonwoven layer (13) is integrated in the basic structure and is provided at least partially between two layers (12.1, 12.2) of the basic structure (12).

8. Press section according to claim 6

characterized,

in that for the present a layer (12.1, 12.2) of the basic structure (12) is embedded in the coarse nonwoven layer (13) or enclosed by the coarse nonwoven layer (13).

9. Press section according to claim 6

characterized,

the coarse nonwoven layer (13) consists of one or more layers and each layer has a basis weight of at least 100 g / m ² , preferably of at least 150 g / m ² .

10. Press section according to claim 6

characterized,

that the coarse nonwoven layer (13) consists of one or more layers, which are designed as a so-called random web, in which the fibers are arranged without a preferred direction.

1 1. Press section according to claim 6

characterized,

that the coarse nonwoven layer (13) consists of at least two layers each having a preferred direction, in which a majority of the fibers is aligned, wherein the preferred directions of the two layers differ by at least 5 °, preferably at least 20 ° from each other.

12. Press section according to one of the preceding claims

characterized,

in that the first and / or a second felt (5, 5.1, 6) has one or more nonwoven layers (14, 15, 17) which are provided on the side facing the fibrous web and which comprise fibers with respect to the basic structure (12) consist of a fiber fineness between 22 dtex and 67 dtex.

13. Press section according to one of the preceding claims

characterized,

in that a nonwoven layer (14, 15, 17) or coarse nonwoven layer (13) of the first and / or a second felt (5, 5. 1, 6) contains melt fibers and polyamide fibers, the melt fibers at least partially having a lower softening or melting temperature than the polyamide fibers.

14. Press section according to one of the preceding claims

characterized,

the first and / or a second felt (5, 5, 1, 6) has a fine fleece layer (16) which is provided on the felt surface (11) facing the fibrous web and consists of fiber with a fiber fineness of at most 11 dtex ,

15. A process for producing a fibrous web, in particular a paper, board or tissue web by means of a press section (10) according to one of the preceding claims

characterized,

that the pulp used for the production of the fibrous web (1) was obtained at least 60%, preferably at least 80%, from recovered paper.

16. The method according to claim 15

characterized,

in that the fibrous web (1) is a newsprint web having a basis weight of between 30 and 52 g / m ² , or a wrapping paper web having a basis weight of 70 to 120 g / m ² .