EP1626121A1 - 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 and an apparatus for producing a provided with a three-dimensional surface structure fibrous web, in particular tissue or sanitary membrane.

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 a very good paper quality can be achieved by a 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 and an improved Vo-direction of the type mentioned, with which, in particular, even without the use of a larger TAD drying device in an economical and cost-effective manner, a high quality of the final product can be achieved. In this case, in particular with regard to the Wasserrückhalteverm assets, the water absorption rate, the volume (bulk), etc., a corresponding quality can be achieved.

According to the invention, this object is achieved by a method for producing a fibrous web provided with a three-dimensional surface structure, in particular tissue or hygiene web, in which the fibrous web pressed at a dry content <35% by means of a first pressure field on a stamping tape, for example, sucked, and thus pre-stamped and then pressed for further dewatering and drying by means of another pressure field a further time on a stamping tape to fix the three-dimensional surface structure and strength.

Furthermore, the fibrous web for expelling water by means of gas pressure together with an embossing belt at least once, preferably twice, passed through a pressure chamber bounded by at least four parallel rollers and into which a compressed gas is introduced. The fibrous web is guided together with the embossing belt and a membrane through the pressure chamber.

The basic principle of such a displacement press, in which the water in the fibrous web is displaced by air, is described for example in DE 19946972.

Due to this configuration, a sustainable three-dimensional surface structure is produced in the relevant fibrous web, ie in particular the paper, tissue or hygiene web in question, which is still present after the drying process in the desired manner in the web, ie for example in the paper. 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.

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.

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 in the further pressure field is gentle, i. preferably over a lengthened in the web running direction distance, is pressed.

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 Preßnip 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 counteracting element cooperating with the drying cylinder, it is possible in particular to use a shoe press unit which comprises a flexible band guided in the region of the press nip via a press shoe.

In this case, a shoe press roll provided with a flexible roll shell is preferably used as the shoe press unit.

Advantageously, a provided within the loop of the embossing belt, preferably soft band, in particular felt, is guided by the Preßnip generating the further pressure field. The soft felt may, for example, be a felt with a foamed layer, which, as will be explained in more detail below, contributes to drainage of the fibrous web due to its capillary action (capillary fabric).

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-embossed, and / or the dry content at which the three-dimensional surface structure is fixed, in each case <35%, in particular <30% and preferably <25%. This will u.a. the water retention capacity and the volume increased sustainably, which means that even with the use of the final product, such as a respective tissue or tissue web, the desired embossment 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 is between the first pressure field generating suction element and the further pressure field generating Preßnip an evacuated device used and led the fibrous web together with an embossing belt both on the evacuated device and by the Preßnip. 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.

The embossing belt can be guided in particular in front of the evacuated device, ie for example the suction roller, via the suction element or the wet vacuum to suck the fibrous web into the three-dimensional surface structure of the embossing belt and thus to impart this structure to the belt.

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 works in comparison with a shoe press with a smaller and longer residence time pressure.

It is also advantageous if the length of the press nip of the drying cylinder and the shoe press unit considered in the web running direction greater than a value of about 80 mm selected and the shoe press is designed so that over the Preßniplänge results in a pressure profile with a maximum pressure, 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 are guided over a forming element such as in particular a forming roller, and as not coming into contact with the forming element outer band and / or as inner band a drainage 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-stamped by the wet embossing in 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 Preßnip an embossing belt, eg embossing screen or embossing membrane, led, 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 correspondingly in the Preßnip a smaller area fraction of the fibrous web is pressed. The smaller areal proportion of raised or closed zones provides the high density web areas for strength, while the larger areal fraction of recessed zones or holes remaining at least substantially unpressed will provide the desired water absorbency and volume as previously limited a complex and expensive Durchströmungs- or TAD drying were achieved.

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. result from crossing points of weft and warp threads, a screen mesh. 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. As a counter-element cooperating with the drying cylinder, a shoe press unit can in particular be used again. 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 inventive method, a 50% higher water absorption capacity (g H20 / g fibers) and a 100% higher volume (cm ³ / g) can be achieved with the same tensile strength when using a stamping tape instead of a conventional felt in Preßnip before creping.

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 corresponding dry content must be achieved in order to achieve wet stamping in a conventional machine, i. in particular a conventional tissue machine to perform.

In order to obtain the desired dry content, according to a preferred embodiment of the method according to the invention for dewatering the web at least one felt with a foamed layer is used. In this case, the foam coating may in particular be selected so that pores in a range of about 3 to about 6 microns. For dewatering, therefore, the corresponding capillary action is utilized. The felt is provided with a special foam layer which gives the surface very narrow pores whose diameters are for example in the stated range of about 3 to about 6 microns can. The air permeability of this felt is very low. It uses the natural capillary action to drain the web while in contact with the felt.

Conveniently, a string, e.g. Sieve or felt, with foamed layer together with an embossing belt and intermediate fibrous web guided around a suction roll, wherein the fabric is preferably in contact with the suction roll.

For example, the foamed layer fabric may comprise a suction roll having a diameter of e.g. about 2 to 3 m or more suction rolls of smaller diameter, preferably two suction rolls with a diameter of, for example, in each case about 2 m, loop. The residence time of the web in the area of the suction roll or the suction rolls should expediently be greater than about 0.15 s and less than about 0.40 s.

The respective suction roll can be placed on its underside, e.g. be applied with vacuum, or it can be used a Saugsalze with associated Siphonabzug. In particular, with a smaller diameter, the water can be thrown off, for example by centrifugal force in a gutter.

Although drainage utilizing capillary action has already been described in US Pat. No. 5,701,682. However, the capillary element in question is part of the suction roll here.

Despite the utilization of the capillary action for dehydration, the evacuated device can, in particular, again be assigned a hood which is under overpressure to assist the vacuum effect of the evacuated device.

The device according to the invention for producing a fibrous web provided with a three-dimensional surface structure, in particular tissue or hygiene web, is correspondingly characterized in that the fibrous web at a dry content <35% by means of a first pressure field on an embossing belt, e.g. pressed by suction and thereby pre-stamped and then pressed for further dewatering and drying by means of another pressure field a further measure on a stamping tape to fix the three-dimensional surface structure and strength.

Preferred embodiments of the device according to the invention are specified in the subclaims.

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 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 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

1 is 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 dewatering device is additionally provided, in which the capillary action of a foamed-layer felt is utilized for dewatering;

Fig. 4

a schematic partial view of another embodiment of an apparatus for producing a provided with a three-dimensional surface structure fibrous web, in which a drainage device is additionally provided in which the capillary action of 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 Preßnip, 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 gently, ie in particular over a lengthened in the direction of web travel L distance pressed. In this case, the further pressure field II can be generated in particular by means of a press nips 18, which is formed between a drying cylinder 20 and a counter-element 22. The guided through the press nip 18 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 cooperating with the drying cylinder 20 counter element is preferably a Schuhpreßeinheit 22 is provided which comprises a guided in the region of the press nips 18 via a press shoe 24 flexible belt 26. In the present embodiment is provided as Schuhpreßeinheit 22 provided with a flexible roll shell 26 shoe press roll.

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

Within the loop of the embossing belt 14, a preferably soft band 28 (capillary fabric), in particular a soft felt or a soft foam felt, may be guided through the press nip 18. This soft band 28 thus runs between the embossing belt 14 and the flexible belt 26 of the shoe press unit 22.

The fibrous web 12 may be placed on the drying cylinder 20, i. For example, on a Yankee cylinder, dried. 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, a suctioned device 30 is provided, which in particular is a suction roll can. 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 felt 28 is guided 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 Preßnip 18, but also on the evacuated device 30. Since the Saugwi kung of the device 30 is reduced by the resistance of the felt 28, the evacuated means 30 may be associated with an over-standing hood to support 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 arranged in front of (shown in solid lines) a lower deflection roller 72. 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.

Before the evacuated device 30, the embossing belt 14 is guided over the suction element 16, which in addition to a dry content increase a pre-embossing of the fibrous web 12 causes. 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 shown in FIG. 1 essentially only in that the felt 28 is brought together after the suctioned egg n-direction 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. Thus, here too, the suction device 32 is preferably arranged again before (representation in solid lines) of the lower deflection roller 72, wherein in principle, however, an arrangement behind this lower deflection roller 72 is again possible (dashed representation 32 ').

3 shows, in a schematic partial representation, an embodiment in which a drainage device 34 is additionally provided, in which the capillary action of a felt 36 with foamed layer is utilized for dewatering. In this case, the foam coating may in particular be selected so that pores in a range of about 3 to about 6 microns.

In the present case, the foamed layer felt 36 together with an embossing belt 14 and intermediate fibrous web 12 is guided around a larger suction roll 38, the felt 36 preferably being in contact with the suction roll 38. The foamed by the felt 36 layer wrapped suction roll For example, 38 may have a diameter of about 2 to about 3 meters. 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, the inner belt 14 also serving as an embossing belt. The two dewatering belts 14, 42 converge to form a material inlet gap 44 and are guided over a forming element 46, in particular a forming roller.

In the present case, the embossing belt 14 is formed by the element 46 coming into contact with the inner band of the former. 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 member 46, a pickup or Tren n-element 50 is provided, through which the web is held at the separation of the dewatering belt 42 on the embossing belt 14. Preferably, in front of the egg n-direction 34 with capillary action again a suction element 16 (solid line) is 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, a soft belt or felt 28 is again guided through 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. For example, this soft band 28 may again be a capillary felt. 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 during the separation from 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 again comprises a forming element 46, in particular a forming roller, in the region thereof the inner band 48 provided as a membrane and the outer band 42 converge to form a material inlet gap 44, which is fed by means of a headbox 48 with pulp suspension.

Following the air press 56, the fibrous web 12 together with the embossing belt 14 again via an evacuated device 30, in particular a suction roll, and guided by the formed between a drying cylinder 20, in particular Yankee cylinder, and a shoe press 22 Preßnip 18. 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.

As can be seen, for example, with reference to FIGS. 6 and 7, the respective embossing belt 14 guided by the press nip 18, e.g. 6) or embossing membrane (cf., in particular, the left-hand part of FIG. 6), be structured such that a zone or recessed zones or holes 74 are provided for this embossing belt 14 in comparison to the surface portion smaller area fraction of raised or closed zones 68 results and accordingly in the Preßnip 18 a smaller area fraction of the fibrous web 12 is pressed.

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%.

The raised zones 68 and the recessed zones can be, for example, by offsets, ie by crossing points of weft and warp threads, of a mesh fabric. In the case of the illustrated in the right part of Fig. 6 Preßmembran results in a corresponding patterning through the holes 74th

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 Preßnip 18 through which the embossing belt 14 shown in FIG. 6 is passed together with the fibrous web 12 and a preferably soft band or felt 28. 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 nips 18 via a press shoe 24, via which the desired contact pressure 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, the embossing belt is in contact 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, soft felt

30

vacuumed device, suction roller

32

Suction device, suction roller

34

Drainage device with capillary action

36

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

56

air press

58

pressure chamber

60

roller

62

roller

64

roller

66

roller

68

raised zones

70

nips

72

deflecting

74

holes

d

thickness

L

Web direction

I

first pressure field

II

another pressure field

Claims (83)

Process for producing a fibrous web provided with a three-dimensional surface structure, in particular tissue or hygiene web, in which the fibrous web is pressed at a dry content <35% by means of a first pressure field on an embossing belt and thereby pre-embossed and then for further dewatering and drying by means of another pressure field pressed again on an embossing belt to fix the three-dimensional surface structure and strength, and the fibrous web is driven to expel water by gas pressure together with an embossing belt at least once and preferably twice through a pressure chamber bounded by at least four parallel rollers and in which a compressed gas is introduced, and the fibrous web is guided together with the embossing belt and a membrane through the pressure chamber. Method according to claim 1,
characterized ,
in that an embossing screen is used as embossing belt. Method according to claim 1,
characterized ,
in that an embossing membrane is used as stamping tape. Method according to one of the preceding claims,
characterized ,
that the fibrous web is pre-embossed after the forming area. Method according to one of the preceding claims,
characterized ,
that the fibrous web is formed on the embossing band used for embossing. Method according to one of the preceding claims,
characterized ,
that the fibrous web is transferred to the embossing belt used for pre-embossing. Method according to one of the preceding claims,
characterized ,
in that the same embossing band is used for pre-embossing and fixing the surface structure. Method according to one of the preceding claims,
characterized ,
in that at least the first pressure field is generated by means of a suction element arranged on the side of the embossing belt remote from the fibrous web, in order to suck the fibrous web into the surface structure of the embossing belt. Method according to claim 8,
characterized ,
in that a wet vacuum is used as the suction element. Method according to one of the preceding claims,
characterized ,
in that the fibrous web is gently pressed in the further pressure field, ie preferably over a length extended in the web running direction. Method according to one of the preceding claims,
characterized ,
that the further pressure field is generated by means of a press nip. Method according to claim 11,
characterized ,
in that the press nip forming the further pressure field is produced between a drying cylinder and a counter element, wherein the fibrous web guided through the press nip is in contact with the surface of the drying cylinder and rests with its other side on the embossing belt. Method according to claim 12,
characterized ,
in that a Yankee cylinder is used as the drying cylinder. Method according to claim 12 or 13,
characterized ,
in that a shoe pressing unit is used as the counteracting element cooperating with the drying cylinder, which comprises a flexible band guided in the region of the press nip via a press shoe. Method according to claim 14,
characterized ,
in that a shoe press roll provided with a flexible roll shell is used as the shoe press unit. Method according to one of the preceding claims,
characterized ,
in that a preferably soft band (28), in particular felt, provided within the loop of the embossing band is guided through the press nip which generates the further pressure field. Method according to one of the preceding claims,
characterized ,
that the pre-embossed fibrous web is dried on the drying cylinder, that the fibrous web is creped and / or that the fibrous web is subsequently wound up. Method according to one of the preceding claims,
characterized ,
in that the dry content at which the fibrous web is pre-embossed and / or the dry content at which the three-dimensional surface structure is fixed is selected in each case <35%, in particular <30% and preferably <25%. Method according to one of the preceding claims,
characterized ,
in that between the suction element producing the first pressure field and the press nip producing the further pressure field, an evacuated device is used and that the fibrous web is guided together with an embossing belt both on the evacuated device and by the Preßnip. Method according to claim 19,
characterized ,
that the evacuated device has a curved surface and the fibrous web and the embossing belt are guided over this curved surface. Method according to claim 20,
characterized ,
in that a suction roll is used as the suctioned device. Method according to one of the preceding claims,
characterized ,
that the felt between the embossing belt and the flexible band of Schuhpreßeinheit is guided by the Preßnip. Method according to one of the preceding claims,
characterized ,
that the felt is also passed over the evacuated device. Method according to one of the preceding claims,
characterized ,
in that the evacuated device is assigned an overpressure hood in order to support the vacuum effect of the evacuated device. Method according to one of the preceding claims,
characterized ,
that the felt is conditioned 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. Method according to one of the preceding claims,
characterized ,
that the felt is brought together only after the evacuated device with the embossing belt carrying the fibrous web. Method according to one of the preceding claims,
characterized ,
that considered in the web running direction length of the press nips of the drying cylinder and the Schuhpreßeinheit comprehensive shoe press greater than a value of about 80 mm and the shoe press is designed so that over the Preßniplänge a pressure profile results with a maximum pressing pressure, which is less than or equal Value of about 2.5 MPa. Method according to one of the preceding claims,
characterized ,
in that at least one dewatering screen with zonal different screen permeability is used in the forming area. Method according to claim 28,
characterized ,
that a former with two circumferential dewatering belts is used, which converge to form a Stoffeinlaufspaltes and are guided over a forming element, in particular a forming roller, and in that a drainage sieve with zonal different sieve permeability is used as outer band not coming into contact with the forming element and / or as inner band. Method according to claim 29,
characterized ,
in that an embossing belt and preferably as an outer belt a dewatering screen with zonal different screen permeability is used as inner band. Method according to claim 30,
characterized ,
that the fibrous web is preferably taken over by an embossing belt of the inner band. Method according to one of the preceding claims,
characterized ,
in that an embossing band, for example embossing sieve or embossing membrane, is guided by the press nip, which is structured in such a way that, for this embossing band, a smaller area proportion of raised or closed zones results in recessed zones or holes and accordingly in the press nip a smaller area fraction of the fibrous web is pressed. Method according to claim 32,
characterized ,
in that an embossing belt is used in which the surface area of raised or closed zones is ≤40% and preferably in a range of about 25% to about 30%. A method according to claim 32 or 33,
characterized ,
in that an embossing belt is used in which the raised zones and the recessed zones result from offsets, ie through intersections of weft and warp threads, of a screening fabric. Method according to one of the preceding claims,
characterized ,
in that at least one felt with a foamed layer is used for dewatering the web. Method according to claim 35,
characterized ,
that the foam coating is selected so that pores in a range of about 3 to about 6 microns. A method according to claim 35 or 36,
characterized ,
in that a covering, for example wire or felt, with foamed layer is guided around at least one suction roll together with an embossing belt and intermediate fibrous web, the covering preferably being in contact with the suction roll. Method according to one of claims 35 to 37,
characterized ,
that the foamed layer covering a suction roll with a diameter of about 2 to about 3 m or more suction rolls with a smaller Diameter, preferably two suction rolls with a diameter of, for example, each about 2 m, wraps. Method according to one of claims 35 to 38,
characterized ,
that the suction roller is applied to the underside of vacuum. Method according to one of claims 35 to 38,
characterized ,
that a suction roll with associated Siphonabzug used or the water is thrown off by centrifugal force into a gutter. Method according to one of the preceding claims,
characterized ,
that the thickness of the embossing membrane is about 1 to about 3 mm and / or that the open area of this embossing membrane is greater than 50% and suitably greater than 60%, and preferably within a range of about 70% to about 75%. Device (10) for producing a provided with a three-dimensional surface structure fibrous web (12), in particular tissue or hygiene web, wherein the fibrous web (12) at a dry content <35% by means of a first pressure pad (I) pressed onto a stamping tape (14) and thereby pre-embossed and then for further dewatering and drying by means of a further pressure field (II) is pressed once more on an embossing belt (14) to fix the three-dimensional Oberflächenstru k-tur and strength, and the fibrous web (12) for expelling from Water by gas pressure together with an embossing belt (14) at least once and preferably twice through a pressure chamber (58) is guided, bounded by at least four parallel rollers (60-66) and in which a compressed gas can be introduced, and the fibrous web (12) is guided together with the embossing belt and a membrane (68) through the pressure chamber (58). Device according to claim 42,
characterized ,
in that an embossing sieve is provided as embossing band (14). Device according to claim 42,
characterized ,
in that an embossing membrane is provided as embossing band (14). Device according to claim 43 or 44,
characterized ,
that the fibrous web (12) is embossed after the forming region. Device according to one of the preceding claims,
characterized ,
in that the fibrous web (12) is formed on the embossing band (14) used for embossing. Device according to one of the preceding claims,
characterized ,
that the fibrous web (12) is transferred to the embossing belt (14) used for pre-embossing. Device according to one of the preceding claims,
characterized ,
that for embossing and fixing the surface structure the same embossing belt (14) is provided. Device according to one of the preceding claims,
characterized ,
in that at least 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) in order to suck the fibrous web (12) into the surface structure of the embossing belt (14). Device according to claim 49,
characterized ,
in that a wet vacuum is provided as the suction element (14). Device according to one of the preceding claims,
characterized ,
in that the fibrous web (12) in the further pressure field (II) is pressed gently, ie preferably over an extended distance in the web running direction (L). Device according to one of the preceding claims,
characterized ,
that the further pressure field (II) is produced by means of a press nip (18). Apparatus according to claim 52,
characterized ,
in that the press nip (18) forming the further pressure field (II) is provided between a drying cylinder (20) and a counter element (22), wherein the fibrous web (12) guided by the press nip (18) is in contact with the Surface (20 ') of the drying cylinder (20) and rests with its other side on the embossing belt. Device according to claim 53,
characterized ,
in that a Yankee cylinder is provided as the drying cylinder (20). Device according to claim 53 or 54,
characterized ,
in that a shoe pressing unit is provided as a counter-element (22) cooperating with the drying cylinder (20) and comprising a flexible band (26) guided in the region of the press nip (18) via a press shoe (24). Device according to claim 55,
characterized ,
in that a shoe press roll provided with a flexible roll shell (26) is provided as the shoe press unit. Device according to claim 53 or 54,
characterized ,
in that a suction press roll with a soft covering and / or a low contact pressure is provided as a counter element (22) cooperating with the drying cylinder (20). Device according to one of the preceding claims,
characterized ,
in that a preferably soft band (28), in particular felt, provided within the loop of the embossing band (14) is guided through the press nip (18) which generates the further pressure field (II). Device according to one of the preceding claims,
characterized ,
in that means are provided in order to dry the pre-embossed fibrous web (12) on the drying cylinder (20), to crepe the fibrous web and / or subsequently to wind up the fibrous web (12). Device according to one of the preceding claims,
characterized ,
in that 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 in each case <35%, in particular <30% and preferably <25%. Device according to one of the preceding claims,
characterized ,
in that an evacuated device (30) is provided between the suction element (16) producing the first pressure field (I) and the press nip (18) generating the further pressure field (II) and in that the fibrous web (12) together with an embossing belt (14) both over the evacuated device as well as by the Preßnip (18) is guided. Device according to claim 61,
characterized ,
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. Device according to claim 62,
characterized ,
in that a suction roll is provided as the suctioned device (30). Device according to one of the preceding claims,
characterized ,
that the felt (28) of the shoe press unit is guided through the press nip (18) (22) between the embossing belt (14) and the flexible band (26). Device according to one of the preceding claims,
characterized ,
that the felt (28) is also passed over the evacuated device (30). Device according to one of the preceding claims,
characterized ,
in that the evacuated device (30) is associated with an overpressure hood in order to support the vacuum effect of the evacuated device (30). Device according to one of the preceding claims,
characterized ,
in that a suction device (32), in particular a suction box, is provided in order to condition the felt (28) before it is brought together with the embossing belt (14) carrying the fibrous web (12). Device according to one of the preceding claims,
characterized ,
that the felt (28) is brought together only after the evacuated device (30) with the embossing belt (14) carrying the fibrous web (12). Device according to one of the preceding claims,
characterized ,
that in the web running direction (L) considered length of the press nips (18) of the drying cylinder (20) and the shoe press unit (22) comprising shoe press is greater than a value of about 80 mm and the shoe press is designed so that over the Preßniplänge a Pressure profile results in a maximum pressure which is less than or equal to a value of about 2.5 MPa. Device according to one of the preceding claims,
characterized ,
in that at least one dewatering screen (42, 54) with zonal different screen permeability is provided in the forming area. Device according to claim 70,
characterized ,
in that a former with two circulating dewatering belts (14, 42) is provided, which converge to form a material inlet gap (44) and are passed over a forming element (46), in particular a forming roller, and than not in contact with the forming element (46) passing outer band (42) and / or as inner band (54) a drainage sieve with zonal different Siebdurchlässigkeit is provided. Device according to claim 70,
characterized ,
in that an embossing belt (14) and preferably as an outer belt (42) a drainage screen with zonal different screen permeability is provided as inner band. Device according to claim 71,
characterized ,
that the fibrous web (12) is preferably taken over by an embossing belt from the inner band (54). Device according to one of the preceding claims,
characterized ,
in that an embossing band (14), for example embossing sieve or embossing membrane, is guided by the press nip (18), which is structured in such a way that for this embossing band (14) a smaller or smaller surface area of raised or raised area compared to the area proportion of recessed zones or holes is obtained Closed zones (68) and accordingly in the Preßnip (18) a smaller area fraction of the fibrous web (12) is pressed. Apparatus according to claim 74,
characterized ,
in that an embossing belt (14) is provided in which the area ratio of raised or closed zones (68) is ≤ 40% and is preferably in a range of approximately 25 to approximately 30%. Apparatus according to claim 74 or 75,
characterized ,
in that an embossing band (14) is provided, in which the raised zones (68) and the recessed zones result from offsets, ie through intersections of weft and warp threads, of a screening fabric. Device according to one of the preceding claims,
characterized ,
in that at least one felt (36) with a foamed layer is provided for dewatering the web (12). Device according to claim 77,
characterized ,
that the foam coating is chosen so that pores in a range of about 3 to about 6 microns. Device according to claim 77 or 78,
characterized ,
that a covering (36), eg sieve or felt, with foamed layer together with an embossing belt (14) and intermediate fibrous web (12) is guided around at least one suction roller (38), wherein the clothing (36) is preferably connected to the suction roller (36). 36) is in contact. Device according to claims 77 to 79,
characterized ,
in that the foamed layer covering (36) wraps around a suction roll (38) with a diameter of about 2 to about 3 m or several suction rolls with a smaller diameter, preferably two suction rolls with a diameter of, for example, about 2 m each. Device according to claims 77 to 79,
characterized ,
that the suction roller (38) can be acted upon by vacuum on its underside. Device according to claims 77 to 80,
characterized ,
that a suction roll (38) is provided with associated Siphonabzug or the water is thrown off by centrifugal force into a gutter. Device according to one of the preceding claims,
characterized ,
that the thickness of the embossing membrane is about 1 to about 3 mm and / or that the open area of this embossing membrane is greater than 50% and suitably greater than 60%, and preferably within a range of about 70% to about 75%.

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