EP1397587B1 - Method and device for producing a fibre strip provided with a three-dimensional surface structure - Google Patents

Abstract

In a process to manufacture a tissue web with a three-dimensional embossed surface, the wet web (less than 35% dry matter content) is pressed by suction to the surface of a pre-embossing belt. The pre-dried web is then transferred to and pressed onto a second embossing belt where the three-dimensional structure is fixed. Also claimed is a commensurate tissue or hygiene material (12) drying and embossing assembly (10) with first (I) and second (II) de-watering and embossing zones. The web is embossed by an embossing sieve belt (14) moving around first (30) and second (24) embossing drums. The second embossing drum (22) squeezes the web (12) and embossing belt (14) against a drying cylinder (20).

Description

The invention relates to a method for producing a fibrous web provided with a three-dimensional surface structure, in particular tissue or hygiene web, according to the preamble of claim 1.

The embossing of a three-dimensional structure in the surface of a paper web, in particular a tissue web, in particular of hand-tissue, is known (see, for example, WO 99/47749, WO 01/18307). Furthermore, it is known that very good paper quality can be achieved by so-called through-air drying (TAD = Through Air Drying). The disadvantage, however, is that the use of TAD dryers is very expensive and correspondingly expensive.

The aim of the invention is to provide an improved method of the type mentioned, with which, in particular, even without the use of a larger TAD-drying device in an economical and correspondingly cost-effective manner, a high quality of the final product can be achieved. In this case, in particular with regard to the water retention capacity, the water absorption rate, the volume (bulk), etc., a corresponding quality can be achieved.

According to the invention, this object is achieved in that the fibrous web is pressed at a dry content <35% by means of the first pressure field on the embossing belt, e.g. sucked, and thereby is pre-embossed and that at least three in the web running direction successively arranged Durchströmeinrichtungen be used, in the region of which is located on the embossing belt fibrous web a respective flow, in particular air flow, exposed, wherein the related to the fibrous web flow-through at the various flow-through at least partially are opposite each other.

Due to this configuration, in the relevant fibrous web, i. in particular the paper, tissue or hygiene web in question, produces a sustainable three-dimensional surface structure which, even after the drying process in the desired manner in the web, i. in the paper, for example. The use of a complex and correspondingly expensive TAD method is no longer necessary. Even without such a TAD drying device, it is now possible in particular to produce a sustainable surface structure, for example a tissue or hygiene web, after the forming area or forming zone. Thus, in particular, a concept with at least three flow-through devices is conceivable, in which the throughflow direction of at least one flow-through device, relative to the web, deviates from the flow-through direction of the other flow-through device (web top / bottom side). For embossing and fixing the surface structure, the same embossing belt is used.

Although WO 93/00475 A already discloses a method for producing a fibrous web provided with a three-dimensional surface structure in which the fibrous web is pressed onto an embossing belt by means of a first pressure field and thereby pre-embossed and subsequently for further dewatering and drying by means of a further pressure field pressed once more on the embossing belt to fix the three-dimensional surface structure and strength. However, only one of the drying serving flow device is used. From WO 00/19014 A results in a comparable method. All flow devices are rectified. In addition, the embossing is carried out in the present case only by a nip formed between two rolls.

As an embossing or structured band ("imprinting fabric", "structured fabric"), preferably an embossing screen or an embossing membrane is used.

In general, the fibrous web is pre-stamped after the forming area.

In certain cases, it is advantageous if the fibrous web is formed on the embossing belt used for pre-embossing. However, the fibrous web can also be transferred to the embossing belt used for pre-embossing.

In the inventive concept, for example, all flow-through devices can each comprise a suction device. However, such a variant of the mentioned concept is also conceivable, in which at least one of the throughflow devices comprises a suction device and at least one air press. Thus, for example, considered in the web running direction, a first flow device, a suction device, a second throughflow device an air press and a third throughflow device again comprise a suction device.

A respective suction device may in particular each comprise a suction roll, a suction box and / or the like.

Advantageously, at least one suction device is used, in which the pressure difference .DELTA.p is in a range from about 0.2 to about 0.4 bar. The temperature is preferably ≦ 220 ° C, especially ≦ 180 ° C, and preferably ≦ 150 ° C. The air flow velocity through the fibrous web is preferably less than or equal to 15 m / s, in particular for very fine fabrics. As a result, this means a significantly lower energy requirement and a significantly lower investment outlay than in the conventional TAD method. The residence time of the fibrous web in the suction region is advantageously ≦ 0.5 s, in particular ≦ 0.4 s and preferably s 0.3 s.

According to a preferred embodiment, at least the first pressure field is generated by means of a arranged on the side facing away from the fibrous web side of the embossing belt Saugelements to suck the fibrous web in the surface structure of the embossing belt. In this case, in particular a so-called wet vacuum can be used as a suction element.

It is also advantageous if the fibrous web is pressed gently in the further pressure field, ie, preferably over a length which is extended in the web running direction.

The further pressure field is preferably generated by means of a press nip. In order to accomplish the most gentle pressing of the web, this press nip can be generated for example between a drying cylinder and a counter element, wherein the guided through the press nip fibrous web is in contact with the surface of the drying cylinder and rests with its other side on the embossing belt. As a drying cylinder, in particular a so-called Yankee cylinder can be used. As a counter-element cooperating with the drying cylinder, it is possible in particular to use a shoe press unit which comprises a flexible band guided over a press shoe in the region of the press nip. In this case, a shoe press roll provided with a flexible roll shell is preferably used as the shoe press unit.

Advantageously, provided within the loop of the embossing belt, preferably soft band or fine-pored covering with capillary effect, in particular felt, through which the further pressure field generating press nip out. The soft felt may be, for example, a felt with a foamed layer, which, as will be explained in more detail below, contributes to the dewatering of the fibrous web due to its capillary action.

A preferred practical embodiment of the method according to the invention is characterized in that the pre-embossed fibrous web is dried on the drying cylinder or Yankee cylinder, the fibrous web is creped and / or the fibrous web is subsequently wound up.

According to a preferred embodiment of the method according to the invention, the dry content at which the fibrous web is pre-stamped, and / or the dry content at which the three-dimensional surface structure is fixed, in each case <35%, in particular <30% and preferably <25%. Thus, inter alia, the water retention capacity and the volume is increased sustainably, which means that even with the use of the final product, such as a respective tissue or tissue web, the desired embossing is still present. In particular, the advantage of a higher water retention capacity for towel tissue (towel paper) also comes into play when using the end product in question.

According to a preferred practical embodiment of the method according to the invention, an evacuated device is used between the suction element producing the first pressure field and the press nip producing the further pressure field and the fibrous web is guided together with an embossing belt both via the evacuated device and through the press nip. It is advantageous if the evacuated device has a curved surface and the fibrous web and the embossing belt are guided over this curved surface. As a suctioned device, for example, a suction roll can be used.

The felt is conveniently passed between the embossing belt and the flexible belt of the shoe press unit through the press nip.

In certain cases, it is advantageous if the particular soft felt is also passed over the evacuated device. Here, since the suction of the evacuated device is reduced accordingly, this is preferably associated with a standing under pressure hood to support the negative pressure effect of the evacuated device.

Further advantages result from the relatively long common leadership of felt and embossing belt, as over a longer distance, the capillary action of the felt is used for dewatering the fibrous web.

The felt can be conditioned, for example, by means of a suction device, in particular by means of a suction box, before it is brought together with the embossing belt carrying the fibrous web. By appropriate conditioning, in particular, the dry content of the felt can be increased and the felt can be cleaned.

In particular, the embossing band can be placed in front of the evacuated device, i. For example, the suction roll, are guided over the suction element or the wet vacuum to suck the fibrous web in the three-dimensional surface structure of the embossing belt and thus impart this structure to the band. At the same time the relevant suction element brings a corresponding increase in dry content with it.

According to another advantageous embodiment of the method according to the invention, the felt is brought together only after the evacuated device with the embossing belt carrying the fibrous web. The evacuated device is therefore not wrapped in this case of the felt, whereby the suction effect of this device is increased and increased according to the dry content. The wet molding effect is maintained by the gentler dewatering by the so-called TissueFlex, which operates at a lower pressure and a longer residence time compared to a shoe press roll.

It is also advantageous if the length of the press nip of the press cylinder and the shoe press unit, which is considered in the web running direction, is greater than a value of about 80 mm and the shoe press is designed so that a pressure profile with a maximum pressing pressure results over the press nip length, which is less than or equal to a value of about 2.5 MPa. This ensures a gentle pressing, which avoids that the structure produced in the fibrous web, e.g. Tissue or Hygienebahn, is flattened out again.

As already mentioned, it is possible, for example, to insert a suction roll between the suction element producing the first pressure field and the press nip, which is preferably associated with a pressure hood.

According to a preferred practical embodiment of the method according to the invention, at least one dewatering screen with zonal different screen permeability is used in the forming area. The relevant drainage sieve can be provided in particular as an outer sieve. A corresponding embodiment of the method is particularly advantageous in the production of towel tissue. The screen produces a fine structure which increases the rate of water absorption and, in conjunction with the embossing of the present invention, brings with it increased water retention.

In certain cases, it is advantageous if a former with two circumferential dewatering belts is used, which converge to form a Stoffseinlaufspaltes and a forming element such as in particular, a forming roller are guided, and as a non-contact with the forming element in contact outer band and / or as an inner belt, a dewatering screen with zonal different Siebdurchlässigkeit is used. In this case, for example, an embossing belt and preferably as an outer belt, a dewatering screen with zonal different Siebdurchlässigkeit be used as an inner band. It is also possible, for example, that the fibrous web is preferably taken over by an embossing belt from the inner band.

In wet embossing in a tissue machine provided with an embossing belt, it is particularly important to achieve the desired dry content. The web can be wet embossed by means of the embossing belt, for example by means of a suction box in front of the press. In order to avoid that the three-dimensional surface structure, which was pre-embossed by wet embossing in the area of the wet suction box, is again destroyed by a brief high pressure in the press nip, as is the case with a conventional suction press roll, according to Advantageous practical embodiment of the method according to the invention by the press nip an embossing belt, such as embossing screen or embossed membrane, performed, which is structured so that results for this embossing belt compared to the area ratio of recessed zones or holes smaller area ratio of raised or closed zones, and Accordingly, in the press nip a smaller area fraction of the fibrous web is pressed. The smaller area percentage of raised or closed zones provides the high density web areas for strength, while the larger area percentage of recessed zones or holes remaining at least substantially unpressed will provide the desired water absorbency and volume provides, as they were previously achieved only by a complex and expensive Durchströmungs- or TAD drying.

In this case, an embossing belt can advantageously be used in which the areal proportion of raised or closed zones is ≦ 40% and is preferably in a range from about 25 to about 30%.

Conveniently, an embossing belt is used in which the raised zones and recessed zones are offset by cranks, i. resulting from crossing points of weft and warp threads, a mesh fabric. As already mentioned, for example, an embossing membrane can also be used, with which the raised and recessed zones result through the holes. In this case, it is advantageous that 100% of the surface is pressed around the holes and results in a higher strength.

The embossing belt in question can be guided together with the fibrous web, for example, again over a drying cylinder, in particular Yankee cylinder. In particular, a shoe press unit can again be used as the counter element interacting with the drying cylinder. The length of the press nip considered in the web running direction as well as the pressure profile resulting over the press nip length can in particular be selected again as stated above.

It has been found that with the method according to the invention a 50% higher water absorption capacity (g H ₂ O / g fibers) and a 100% higher volume (cm ³ / g) with the same tensile strength in one use an embossing belt can be achieved instead of a conventional felt in the press nip before crimping.

Creping the web can improve the water absorbency by 50%, and taking this into account, TAD towel quality water absorption can be achieved.

The quality of the paper is due to the lower pressure of the web due to the smaller surface area of raised zones, and not by a TAD dryer. The permeability of the web results from the stretching of the web into the fabric structure by means of the suction element, whereby so-called "pillows" are produced, which increase the water absorption capacity and the volume accordingly. A relatively expensive and correspondingly expensive TAD dryer is therefore no longer required.

The function of the TAD drum and the air flow system is to dry the web, and therefore, the appropriate dry content must be achieved in order to perform wet stamping in a conventional machine, ie, in particular a conventional tissue machine.

According to a preferred practical embodiment of the method according to the invention, a vacuum dewatering of the fibrous web takes place, in which the pressure difference (Δp) ≥ 0.1 bar, in particular ≥ 0.2 bar and preferably ≥ 0.3 bar. In this case, the pressure difference (Δp) can be in particular in a range from about 0.2 bar to about 0.4 bar. In contrast to the conventional TAD method, an open area of approximately 20% is advantageously provided.

For vacuum dewatering, a fine-pored fabric, e.g. Sieve or felt with foamed layer, used. In this case, for example, again prevail such a pressure difference as before. However, the open area here is preferably very small, so that results in a very small volume of air flow.

(bis nahezu Null $\frac{m^3}{m^2\cdot \min }$

) ergibt.According to a preferred practical embodiment of the method according to the invention, the vacuum dewatering takes place such that an air volume flow ≦ 50, in particular ≦ 20, in particular ≦ 5, and preferably $\le 1\frac{m^3}{m^2\cdot \min }$

(to almost zero $\frac{m^3}{m^2\cdot \min }$

).

For a corresponding "Spectra" membrane which can be used for vacuum dewatering, for example, 15 m / s were measured, so that a higher vacuum is required.

The invention is particularly applicable to Crescent Formers, Duo Formers, C-Wrap Formers, S-Wrap Formers, and to the manufacture of multi-layer and multi-ply tissue.

Fig. 1

eine schematische Teildarstellung einer Vorrichtung zur Herstellung einer mit einer dreidimensionalen Oberflächenstruktur versehenen Faserstoffbahn,

Fig. 2

eine schematische Teildarstellung einer abgewandelten Ausführungsform der Vorrichtung, bei der der Filz nicht über die besaugte Einrichtung geführt ist,

Fig. 3

eine schematische Teildarstellung einer Ausführungsform einer Vorrichtung zur Herstellung einer mit einer dreidimensionalen Oberflächenstruktur versehenen Faserstoffbahn, bei der zusätzlich eine Entwässerungsvorrichtung vorgesehen ist, in der zur Entwässerung die Kapillarwirkung einer feinporigen Bespannung wie z.B. eines Filzes mit geschäumter Schicht ausgenutzt wird,

Fig. 4

eine schematische Teildarstellung einer weiteren Ausführungsform einer Vorrichtung zur Herstellung einer mit einer dreidimensionalen Oberflächenstruktur versehenen Faserstoffbahn, bei der zusätzlich eine Entwässerungsvorrichtung vorgesehen ist, in der zur Entwässerung die Kapillarwirkung einer feinporigen Bespannung wie z.B. eines Filzes mit geschäumter Schicht ausgenutzt wird,

Fig. 5

eine schematische Teildarstellung einer Ausführungsform einer Vorrichtung zur Herstellung einer mit einer dreidimensionalen Oberflächenstruktur versehenen Faserstoffbahn, bei der zusätzlich eine Verdrängungspresse vorgesehen ist,

Fig. 6

eine schematische Teildarstellung eines Prägebandes mit einem im Vergleich zum Flächenanteil an zurückgesetzten Zonen kleineren Flächenanteil an erhabenen Zonen und

Fig. 7

einen schematischen Schnitt durch einen Pressnip, durch den das in der Fig. 6 dargestellte Prägeband zusammen mit der Faserstoffbahn und einem vorzugsweise weichen Filz hindurchgeführt ist.

The invention is explained in more detail below with reference to embodiments with reference to the drawing; in this show:

Fig. 1

FIG. 2 a schematic partial representation of a device for producing a fibrous web provided with a three-dimensional surface structure; FIG.

Fig. 2

a schematic partial view of a modified embodiment of the device in which the felt is not passed over the evacuated device,

Fig. 3

a schematic partial view of an embodiment of an apparatus for producing a provided with a three-dimensional surface structure fibrous web at in addition, a drainage device is provided, in which the capillary action of a fine-pored fabric such as a felt with foamed layer is used for dewatering,

Fig. 4

a schematic partial view of a further embodiment of an apparatus for producing a provided with a three-dimensional surface structure fibrous web, in which additionally a dewatering device is provided, in which the capillary action of a fine-pored fabric such as a felt with foamed layer is used for dewatering,

Fig. 5

FIG. 2 a schematic partial representation of an embodiment of an apparatus for producing a fibrous web provided with a three-dimensional surface structure, in which a displacement press is additionally provided, FIG.

Fig. 6

a schematic partial view of an embossing belt with a smaller compared to the area ratio of recessed zones area ratio of raised zones and

Fig. 7

a schematic section through a press nip, through which the embossing belt shown in FIG. 6 is passed together with the fibrous web and a preferably soft felt.

1 shows, in a schematic partial representation, a device 10 for producing a fibrous web 12 provided with a three-dimensional surface structure (see also FIG. 7), which may in particular be a paper web and preferably a tissue or hygiene web.

The fibrous web 12 is pressed at a dry content <35% by means of a first pressure pad I on a stamping or structural band 14, e.g. sucked, and thereby pre-embossed and then pressed for further drainage and drying by means of another pressure pad II a further time on the embossing belt 14 to fix the three-dimensional surface structure and strength. In this case can be provided as embossing belt 14, in particular an embossing screen.

In the present embodiment, the same embossing belt 14 is provided for embossing and fixing the surface structure.

The first pressure field I is produced by means of a suction element 16 arranged on the side of the embossing belt 14 facing away from the fibrous web 12, whereby the fibrous web 12 is sucked into the surface structure of the embossing belt 14. The suction element 16 may be provided in particular as a suction box or wet vacuum.

In the further pressure field II, the fibrous web 12 is preferably pressed gently, ie in particular over an extended distance in the web running direction L route. In this case, the further pressure field II can be generated in particular by means of a press nip 18 which is formed between a drying cylinder 20 and a counter-element 22. The by the Press nip 18 guided fibrous web 12 is in this case in contact with the surface 20 'of the drying cylinder 20. With its other side it lies against the embossing belt 14.

As a drying cylinder 20 may be provided in particular a Yankee cylinder.

As a counter-element cooperating with the drying cylinder 20, a shoe press unit 22 is preferably provided which comprises a flexible band 26 guided in the area of the press nip 18 via a press shoe 24. In the present embodiment is provided as a shoe press unit 22 provided with a flexible roll shell 26 shoe press roll.

This results in a lengthened in the web direction L press nip 18, whereby a relatively gentle pressure of the fibrous web 12 is achieved.

Within the loop of the embossing belt 14, a preferably soft belt 28 or a fine-pored clothing with capillary effect, in particular a soft felt or a soft foam felt, can be guided through the press nip 18. This soft band 28 or fine-pored stringing thus runs between the embossing band 14 and the flexible band 26 of the shoe press unit 22.

The fibrous web 12 can be dried on the drying cylinder 20, ie for example on a Yankee cylinder. In addition, the fibrous web 12 can be creped. Finally, the web 12 can be wound up by appropriate means.

The dry content at which the fibrous web 12 is pre-stamped and / or the dry content at which the three-dimensional surface structure is fixed is, as already mentioned, <35%, and may in particular be <30% and preferably <25%.

Between the suction element 16 and the press nip 18, an evacuated device 30 is provided, which may in particular be a suction roller. The fibrous web 12 is guided together with the embossing belt 14 both via the evacuated device 30 and through the press nip 18. The fine-pored fabric or in the present case e.g. the felt 28 is passed between the embossing belt 14 and the flexible belt 26 of the shoe press unit 22 through the press nip 18.

In the present embodiment, the felt 28 is guided not only by the press nip 18 but also by the evacuated means 30. Since the suction of the device 30 is reduced by the resistance of the felt 28, the evacuated device 30 may be associated with a positive-pressure hood to assist the vacuum effect of the evacuated device 30.

For conditioning the felt 28, a suction device 32, in particular a suction box or the like, may be provided. As can be seen with reference to FIG. 1, this felting device 32 serving for felt conditioning is arranged in front of the evacuated device 30, in the region of which the felt 28 is brought together with the embossing belt 14 carrying the fibrous web 12. In this case, the suction device 32 is preferably before (shown in solid lines) a lower Deflection roller 72 is arranged. In principle, however, an arrangement behind this lower guide roller 72 is possible (dashed line 32 ').

Due to the relatively long joint leadership of felt 28 and embossing belt 14 water is removed by the capillary action of the felt 28 of the fibrous web 12 over a longer distance. Beforehand, the felt 28 is conditioned via the suction device 32, whereby its dry content is increased and the felt is cleaned.

In front of the evacuated device 30, the embossing belt 14 is guided over the suction element 16, which causes a pre-embossing of the fibrous web 12 in addition to a dry content increase. This is sucked into the three-dimensional surface structure of the embossing belt or sieve 14, whereby the structure of the web is impressed.

The embodiment shown in FIG. 2 differs from that according to FIG. 1 essentially only in that the felt 28 is brought together only after the evacuated device 30 with the embossing belt 14 carrying the fibrous web 12. The evacuated device 30 is thus not wrapped in this case by the felt 28, whereby their suction effect is increased and the dry content is increased accordingly. The wet embossing effect is maintained by the relatively gentle dewatering of the TissueFlex, where the pressure is lower than that of a conventional shoe press.

Incidentally, this embodiment may be at least substantially as designed as shown in FIG. 1. So here is the suction device 32 preferably again before (shown in solid lines) of the lower guide roller 72, wherein in principle, however, again an arrangement behind this lower guide roller 72 is possible (dashed line 32 ').

Fig. 3 shows a schematic partial representation of an embodiment in which a drainage device 34 is additionally provided, in which for the dewatering a fine-pored fabric 36 with capillary effect is used, in which it is e.g. can act to a felt or a sieve with foamed layer. In this case, a particular foam coating may in particular be selected such that pores result in a range of about 3 to about 6 microns.

In the present case, the fine-pored fabric 36 is guided together with an embossing belt 14 and intermediate fibrous web 12 to a larger suction roll 38, wherein the fine-pored fabric 36 is preferably in contact with the suction roll 38. The suction roll 38 looped around by the fine-pored fabric 36 may, for example, have a diameter of about 2 to about 3 m. The suction roller 38 may be acted upon by vacuum on its underside. In principle, the suction roll 38 can also be assigned a siphon outlet. The respective means are designated in Fig.3 with "40".

In the forming region, at least one drainage sieve with zonal different sieve permeability can be provided.

In the present case, a former with two circumferential dewatering belts 14, 42 is provided, wherein the inner band 14 at the same time as Embossing band serves. The two dewatering belts 14, 42 converge to form a material inlet gap 44 and are guided over a forming element 46 such as in particular a forming roller.

In the present case, the embossing belt 14 is formed by the inner band of the former coming into contact with the forming element 46. The outer band 42, which does not come into contact with the forming element 46, can be provided in particular as a dewatering screen with zonal different screen permeability.

By means of a headbox 48, the pulp suspension is introduced into the stock inlet gap 44. Behind the forming element 46, a pickup or separating element 50 is provided, through which the web is held on the embossing belt 14 during the separation from the dewatering belt 42. Preferably, in front of the device 34 with capillary action, a suction element 16 (solid representation) is again provided, through which the fibrous web 12 is pressed onto the embossing belt 14. However, this suction element can also be arranged between the device 34 with capillary action and the evacuated device or suction roller 30 (dashed representation 16 ').

Together with the fibrous web 12 and the embossing belt 14 is again a soft band or a fine-pored covering with capillary effect here z. B. felt 28, guided by the press nip 18 formed between a drying cylinder 20 and a shoe press unit 22. In the present case, the soft belt according to the embodiment of FIG. 1 is again guided around the evacuated device 30. As already mentioned, it can also be in this soft band 28, for example again to a fine-pored covering with capillary effect, for example, a corresponding capillary effect felt (capillary felt) act. For example, the felt 28 can be conditioned again via a suction device or a so-called UHLE box. The drying cylinder 20 may in particular be a Yankee cylinder again. In this case, this drying cylinder 20 may be associated with a drying hood 52.

In the present embodiment, the dry content of the fibrous web before the capillary drainage device 34 is about 10 to about 25%, in the area downstream of this device 34 e.g. about 30 to about 40%.

The embodiment shown in FIG. 4 differs from that shown in FIG. 3 initially in that the fibrous web 12 is taken over by the embossing belt 14 from an inner band 54 of the former. In the present case, for example, this inner band 54 or the outer band 42 of the former can again be provided as a dewatering screen with zonal different Siebdurchlässigkeit. The two circulating dewatering belts 42, 54 converge again to form a material inlet gap 44, wherein they are guided again over a forming element 46 such as in particular a forming roller. By means of a headbox 48 of the material inlet gap 44 is fed again with pulp suspension. Unlike the embodiment according to FIG. 3, however, the pulp suspension in the present case is supplied from below. Within the loop of the embossing belt 14, a pickup or separating element is again provided, through which the fibrous web 12 is held on the embossing belt in the separation of the inner band 54 of the former.

The provided within the loop of the embossing belt 14 suction member 16 is arranged in front of the dewatering device 34 with capillary action, in principle, however, an arrangement according to this device 34 is possible.

In the present case, the felt 28 is missing.

The dry content of the fibrous web in the present embodiment is about 10 to about 25% in the region of the pickup element 50, about 15 to about 30% in the region upstream of the dewatering device 34 and about 35 to about 45% downstream of the device 34.

Moreover, this embodiment may have at least substantially the same structure as that shown in FIG. 3. Corresponding elements are assigned the same reference numerals.

5 shows a schematic partial representation of an embodiment of the device 10 in which a displacement press 56 is provided. The fibrous web 12 is guided to expel water by means of gas pressure with the embossing belt 14 at least once through a pressure chamber 58 which is bounded by at least four parallel rollers 60 - 66 and in which a compressed gas can be introduced. The fibrous web 12 is preferably guided together with the embossing belt 14 and a membrane 68 through the pressure chamber 58.

In the present case, the membrane 68 forms the inner band of the former, which in turn comprises a forming element 46, in particular a forming roller, in the region of which provided as a membrane inner band 68 and the outer band 42 converge to form a Stoffeinlaufspaltes 44, by means of a headbox 48 with pulp suspension is charged.

Following the air press 56, the fibrous web 12, together with the embossing belt 14, is guided again over an evacuated device 30, in particular a suction roller, and through the press nip 18 formed between a drying cylinder 20, in particular a Yankee cylinder, and a shoe press unit 22. In the illustrated embodiment, the drying cylinder or Yankee cylinder 20 is again associated with a drying hood 52.

In the present case, the first pressure field I, by which the fibrous web 12 is pressed at a dry content of <50% on the embossing belt 14 and pre-embossed, for example, be generated by the air press 56.

6 and 7, the respective embossing belt 14 guided by the press nip 18, eg embossing screen (cf., in particular, the left-hand part of FIG. 6) or embossing membrane (cf., in particular, the right-hand part of FIG. 6), be structured so that for this embossing belt 14 a smaller compared to the surface portion of recessed zones or holes 74 smaller proportion of raised or closed zones 68 results and according to a smaller area portion of the fibrous web 12 is pressed in the press nip 18.

In this case, the area fraction of raised or closed zones 68 can be in particular ≦ 40% and preferably in a range of about 25 to about 30%.

For example, the raised zones 68 and the recessed zones may be defined by cranks, i. resulting from crossing points of weft and warp threads, a mesh fabric. In the case of the press membrane shown in the right-hand part of FIG. 6, a corresponding structuring results through the holes 74.

Fig. 6 shows a partial schematic representation of a corresponding embossing belt 14, e.g. Embossing felt or embossing membrane, with a smaller surface portion of raised or closed zones 68 compared to the area proportion of recessed zones or holes 74.

The thickness d of the embossing membrane shown in the right part of Fig. 6 may e.g. be about 1 to about 3 mm. In particular, the open area may be greater than 50%, and more preferably greater than 60%, and preferably within a range of from about 70% to about 75%. The membrane expediently consists of a material which is resistant to pulp chemistry. It can for example consist of polyester.

FIG. 7 shows a schematic section through a press nip 18, through which the embossing belt 14 shown in FIG. 6 passes together with the fibrous web 12 and a preferably soft belt or felt 28 is. In this case, this soft band 28 is in contact with the flexible band 26 of the shoe press unit, which is guided in the region of the press nip 18 via a press shoe 24, via which the desired contact force can be applied.

The fibrous web 12 is applied to the drying cylinder 20, preferably a Yankee cylinder.

In FIG. 7, moreover, the pressing zones 70 resulting from the raised zones 68 can be seen.

The fibrous web 12 is already marked before the nip. As can be seen with reference to FIG. 7, it lies against the embossing belt even before the nip.

LIST OF REFERENCE NUMBERS

10

contraption

12

Fibrous web

14

embossing tape

16

suction

18

press nip

20

Drying cylinder, Yankee cylinder

20 '

surface

22

Counter element, shoe press unit

24

press shoe

26

flexible band, flexible roll jacket

28

soft band or fine-pored covering with capillary effect, soft felt

30

vacuumed device, suction roller

32

Suction device, suction roller

34

Drainage device with capillary action

36

fine-pored covering with capillary effect, felt with foamed layer

38

big suction roll

40

Vacuum, siphon outlet

42

dewatering belt

44

Stock inlet gap

46

Forming element, forming roller

48

headbox

50

Pickup or separating element

52

Trockenhaube

54

inner drainage sieve

Claims (46)

1. Method for producing a fibrous web (12) provided with a three-dimensional surface structure, in particular a tissue or hygiene web, in which the fibrous web (12) is pressed onto an embossing belt (14) by means of a first pressure area (I) and is pre-embossed as a result and subsequently, for the purpose of further dewatering and drying, is pressed onto the embossing belt (14) a further time by means of a further pressure area (II) in order to fix the three-dimensional surface structure and strength, characterized in that the fibrous web (12) is pressed onto the embossing belt (14) by means of the first pressure area (I) at a dryness of < 35% and is pre-embossed as a result, and in that at least three through-flow devices (16, 38, 30) arranged one after another in the web running direction (L) are used, in the region of which the fibrous web (12) located on the embossing belt (14) is subjected to a respective through flow, in particular a through air flow, the through-flow directions, referred to the fibrous web (12), being at least partly opposed to one another in the various through-flow devices (16, 38, 30).
2. Method according to Claim 1, characterized in that the embossing belt (14) used is an embossing fabric.
3. Method according to Claim 1 or 2, characterized in that the embossing belt (14) used is an embossing membrane.
4. Method according to one of the preceding claims, characterized in that the fibrous web (12) is pre-embossed after the forming region.
5. Method according to one of the preceding claims, characterized in that the fibrous web (12) is formed on the embossing belt (14) used for the embossing.
6. Method according to one of the preceding claims, characterized in that the fibrous web (12) is transferred to the embossing belt (14) used for the pre-embossing.
7. Method according to Claim 1, characterized in that all the through-flow devices (16, 38, 30) each comprise a suction device.
8. Method according to Claim 1, characterized in that, of the through-flow devices (16, 38, 30), at least one comprises a suction device and at least one an air press.
9. Method according to Claim 8, characterized in that, as viewed in the web running direction (L), a first through-flow device (16) comprises a suction device, a second through-flow device comprises an air press, and a third through-flow device (30) again comprises a suction device.
10. Method according to one of the preceding claims, characterized in that the respective suction device comprises a suction roll, a suction box and/or the like.
11. Method according to one of the preceding claims, characterized in that at least one suction device (38) is used in which the pressure difference (Δp) lies in a range from about 0.2 to about 0.4 bar.
12. Method according to one of the preceding claims, characterized in that at least one suction device (38) is used in the region of which the temperature is ≤ 220°C, in particular ≤ 180°C and preferably ≤ 150°C.
13. Method according to one of the preceding claims, characterized in that at least one suction device (38) is used in which the air flow velocity through the fibrous web is preferably ≤ 15 m/s in the case of very fine fabrics and in particular ≤ 8 m/s.
14. Method according to one of the preceding claims, characterized in that at least one suction device (38) is used in which the residence time of the fibrous web (12) in the suction region is ≤ 0.5 s, in particular ≤ 0.4 s and preferably ≤ 0.3 s.
15. Method according to one of the preceding claims, characterized in that at least the first pressure area (I) is produced by means of a suction element (16) arranged on the side of the embossing belt (14) facing away from the fibrous web (12), in order to suck the fibrous web (12) into the surface structure of the embossing belt (14).
16. Method according to Claim 15, characterized in that the suction element (14) used is a wet suction means.
17. Method according to one of the preceding claims, characterized in that the fibrous web (12) is pressed gently in the further pressure area (II), that is to say preferably over a section which is extended in the web running direction (L).
18. Method according to one of the preceding claims, characterized in that the further pressure area (II) is produced by means of a press nip (18).
19. Method according to Claim 18, characterized in that the press nip (18) forming the further pressure area (II) is produced between a drying cylinder (20) and an opposing element (22), the fibrous web (12) guided through the press nip (18) resting in contact with the surface (20') of the drying cylinder (20) and with its other side on the embossing belt (14).
20. Method according to Claim 19, characterized in that the drying cylinder (20) used is a Yankee cylinder.
21. Method according to Claim 19 or 20, characterized in that the opposing element (22) interacting with the drying cylinder (20) is a shoe press unit which comprises a flexible belt (26) guided over a press shoe (24) in the region of the press nip (18).
22. Method according to Claim 21, characterized in that the shoe press unit used is a shoe press roll provided with a flexible roll cover (26).
23. Method according to one of the preceding claims, characterized in that a belt (28), preferably a soft belt, provided within the loop of the embossing belt (14) or a fine-pore fabric with a capillary effect, in particular a felt, is guided through the press nip (18) producing the further pressure area (II).
24. Method according to one of the preceding claims, characterized in that the pre-embossed fibrous web (12) is dried on the drying cylinder (20), in that the fibrous web is creped and/or in that the fibrous web (12) is subsequently wound up.
25. Method according to one of the preceding claims, characterized in that the dryness at which the fibrous web (12) is pre-embossed and/or the dryness at which the three-dimensional surface structure is fixed are in each case chosen to be < 35%, in particular < 30% and preferably < 25%.
26. Method according to one of the preceding claims, characterized in that, between the suction element (16) producing the first pressure area (I) and the press nip (18) producing the further pressure area (II), an evacuated device (30) is used, and in that the fibrous web (12), together with an embossing belt (14), is guided both over the evacuated device (30) and through the press nip (18).
27. Method according to Claim 26, characterized in that the evacuated device (30) has a curved surface, and the fibrous web (12) and the embossing belt (14) are guided over this curved surface.
28. Method according to Claim 27, characterized in that the evacuated device (30) used is a suction roll.
29. Method according to one of the preceding claims, characterized in that the felt (28) is guided through the press nip (18) between the embossing belt (14) and the flexible belt (26) of the shoe press unit (22).
30. Method according to one of the preceding claims, characterized in that the felt (28) is also guided over the evacuated device (30).
31. Method according to one of the preceding claims, characterized in that the evacuated device (30) is assigned a hood under a positive pressure in order to assist the negative pressure action of the evacuated device (30).
32. Method according to one of the preceding claims, characterized in that the felt (28) is conditioned by means of a suction device (32), in particular by means of a suction box, before it is led together with the embossing belt (14) carrying the fibrous web (12).
33. Method according to one of the preceding claims, characterized in that the felt (28) is led together with the embossing belt (14) carrying the fibrous web (12) only after the evacuated device (30).
34. Method according to one of the preceding claims, characterized in that the length, viewed in the web running direction (L), of the press nip (18) of the shoe press comprising the drying cylinder (20) and the shoe press unit (22) is chosen to be greater than a value of about 80 mm, and the shoe press is designed in such a way that the result over the press nip length is a pressure profile with a maximum pressing pressure which is less than or equal to a value of about 2.5 mPa.
35. Method according to one of the preceding claims, characterized in that, in the forming region, at least one dewatering fabric (42, 54) with a zonally different fabric permeability is used.
36. Method according to Claim 35, characterized in that a former having two circulating dewatering belts (14, 42) is used, which run together, forming a stock inlet gap (44), and are guided over a forming element (46), such as in particular a forming roll, and in that a dewatering fabric with a zonally different fabric permeability is used as the outer belt (42) not coming into contact with the forming element (46) and/or as the inner belt (54).
37. Method according to Claim 36, characterized in that the inner belt used is an embossing belt (14) and, preferably, the outer belt (42) used is a dewatering fabric with a zonally different fabric permeability.
38. Method according to Claim 37, characterized in that the fibrous web (12) is preferably picked up from the inner belt (54) by an embossing belt.
39. Method according to one of the preceding claims, characterized in that an embossing belt (14), for example an embossing fabric or embossing membrane, is guided through the press nip (18), which embossing belt (14) is structured in such a way that the result for this embossing belt (14) is a smaller proportion of the area of elevated or closed zones (68) as compared with the proportion of the area of recessed zones or holes and, accordingly, a smaller proportion of the area of the fibrous web (12) is pressed in the press nip (18).
40. Method according to Claim 39, characterized in that an embossing belt (14) is used in which the proportion of the area of elevated or closed zones (68) is ≤40% and preferably lies in a range from about 25% to about 30%.
41. Method according to Claim 39 or 40, characterized in that an embossing belt (14) is used in which the elevated zones (68) and the recessed zones result from shoulders, i.e. from crossing points of weft and warp fibres of a fabric weave.
42. Method according to one of the preceding claims, characterized in that the thickness of the embossing membrane is about 1 to about 3 mm and/or in that the open area of this embossing membrane is greater than 50% and expediently greater than 60% and preferably lies in a range from about 70% to about 75%.
43. Method according to one of the preceding claims, characterized in that vacuum dewatering of the fibrous web (12) is carried out, in which the pressure difference (Δp) is ≥ 0.1 bar, in particular ≥ 0.2 bar and preferably ≥ 0.3 bar.
44. Method according to Claim 43, characterized in that the pressure difference (Δp) lies in a range from about 0.2 bar to about 0.4 bar.
45. Method according to Claim 43 or 44, characterized in that, for the purpose of vacuum dewatering, fine-pored fabrics (36) are used, for example a fabric or felt with a foamed layer.
46. Method according to one of the preceding claims, characterized in that the vacuum dewatering is carried out in such a way that an air volume flow ≤ 50, in particular ≤ 20, in particular ≤ 5 and preferably $\le 1\frac{m^3}{m^2\cdot \min }$

    

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