EP1491680A1 - Method for smoothing a paper or board web and extended nip calender - Google Patents

Abstract

In a process to smooth the surface of a paper or carton web (2) the paper feeds to a wide-nip (5) that extends at least 30 mm in length. The nip has a lower drum (4) and an upper drum (3) with a surface temperature of 100C or more. The paper or carton is surrendered to a curl generator that cancels the curl generated in the nip. The curl generator has a steam dispenser or water jets discharging at a rate of 1 - 10 g/m paper. The moisture is dispensed towards that side of the web in contact with the top drum. Also claimed is a wide-nip calender.

Description

The invention relates to a method for smoothing a paper or cardboard web, in which the web is guided through a wide nip with a length of at least 30 mm and is in the wide nip on a heated roller with a surface temperature of at least 100 ° C and a pressure element. The invention further relates to a wide nip calender for smoothing a paper or cardboard web with a wide nip at least 30 mm long, which is formed by a heated roller with a surface temperature of at least 100 ° C. and a pressure element.

Paper or cardboard webs, which are briefly referred to below as "webs", are usually smoothed at least on one side in the course of their production. For this purpose, the web is passed through a nip which is formed between two rollers. One of the two rollers has a hard and smooth surface. The other of the rollers has an elastic surface that is more compliant than that of the smooth roller. In this nip, the web is subjected to increased pressure and, by heating one of the two rollers, also to an increased temperature. This treatment results in excellent smoothness on the side of the web that lies against the hard roller. However, it has the disadvantage that the web may be relatively heavily compacted, so that it suffers a loss of volume.

To avoid loss of volume, so-called wide nips are often used, i.e. nips that have a greater length in the running direction of the web than the nips that are formed between the two rollers described above. For the purposes of the present invention, a wide nip is considered to be a nip which has an extension of at least 30 mm in the running direction of the web. Such a nip can be formed in different ways. On the one hand, it can be formed by the roller and an encircling belt or an encircling jacket, the latter being in contact with the roller over a predetermined circumferential area. The band or jacket is pressed on using a pressure shoe. A roller with a very soft surface layer can also be used as a pressure element, into which the heated roller can be pressed so far that the desired length of the wide nip is produced. A wide nip is also referred to as an "extended nip" or "extended nip".

In the case of a Breitnip calender, the heated roll is designed as a hard, smooth roll, i. H. the smoothness of the heated roller is transferred to the surface of the web. The side of the web lying against the heated roller is thus smoothed to the desired extent.

However, it has been found that a web which has been smoothed in a wide nip with a heated roller and a pressure element tends to curl. Curl is a phenomenon in which the web no longer lies flat, but bulges. Curl is particularly reinforced by the long dwell time in the wide nip, the high temperatures and the humidification, which is advantageously applied to reinforce the smoothing effect on the side of the web to be smoothed. Curl can be observed, for example, in sheets that have been cut from the web. But even with a web that is processed from a roll, the curl has negative consequences for further processing, especially when printing.

The invention has for its object to improve the processability of the web.

This object is achieved in a method of the type mentioned at the outset by taking measures in the vicinity of the wide nip to produce a counter curl which is opposite to a curl produced by the wide nip.

One makes use of the knowledge that a curl and a counter curl, if they are coordinated accordingly, balance each other out again so that the web again reaches a sufficient flatness before further processing. So if the web curves concavely so that it follows the surface of the heated roller, then measures have to be taken by which the web bulges in the other direction. The two measures taken together then balance each other out and result in the web regaining the desired flatness. It is advantageous if the two measures are in a relatively close spatial proximity to one another. Accordingly, the measure for generating the counter curl is taken in the neighborhood of the Breitnip.

To generate the counter curl, the side of the web that is in contact with the pressure element is preferably moistened. The web is therefore moistened on one side, namely on the side that is not in contact with the heated roller. The moistening leads to a curl in the side facing the moisture application. For the purposes of the following explanation, it is assumed in a simplified manner that the top of the web rests on the heated roller and the bottom of the web rests on the pressure element. So you apply the moisture from below. As a result, the web bulges down. The top of the web lies against the heated roller. As a result, the path arches upwards. The curvature downwards and the curvature upwards, i.e. counter curl and curl, balance each other so that the desired flatness is achieved.

It is preferred that moisture is applied to the web in an amount of 1 to 10 g / m ² . Such an application of moisture is sufficient to produce the desired counter curl.

Steam and / or water is preferably applied to the side of the web lying against the pressure element. The application of steam and / or water is a relatively simple measure to apply moisture to the underside of the web to a sufficient extent and with sufficient uniformity, i. H. to the side of the web that lies against the pressure element.

It is particularly preferred here that water is applied to the pressure element. First of all, you create a water film with the desired thickness the surface of the pressure element. The order can be placed at a position just before the wide nip. When the web then runs through the wide nip, the moisture is transferred from the surface of the pressure element to the web.

The web for producing the counter curl is preferably dried from the side abutting the pressure element. In this way, the conditions in the wide nip are simulated. The web is also dried in the Breitnip, but from the side adjacent to the heated roller. By drying, which is preferably combined with the application of moisture, you can achieve a counter curl that can be adjusted to the degree to which the curl in the wide nip results.

Steam or water is preferably applied to the side of the web which is in contact with the heated roller. Applying steam to the top of the web improves smoothness. However, it also leads to an increased curl. This reinforced curl is not critical, however, because the measures to generate the counter curl can at least largely compensate for the reinforced curl.

Steam or water with a mass of 1 to 5 g / m ^{2 is} preferably fed to the web. A certain proportion of this, usually between 25% and 100%, is absorbed by the railways. Such an amount of steam or water has proven to be sufficient to achieve good smoothness.

The humidification and / or the drying of the side of the web lying on the pressure element is preferably adjusted as a function of the steam application or water application of the side of the web lying on the heated roller and / or the temperature of the heated roller. Applying steam or water to the top reinforces the curl. Similarly, the curl is amplified when the temperature of the heated roller is raised. The temperature of the heated roller is above 100 ° C and can be up to about 300 ° C. You can now increase the formation of the counter curl if the temperature of the heated roller is higher and / or the steam application is greater. For this purpose, for example, the application of moisture to the underside of the web is increased and / or the drying is increased.

Measures for generating the counter curl in front of the wide nip are preferably taken. So you create a counter curl before the curl is created in the wide nip. Both measures together lead to a flat position of the railway.

Alternatively or in addition, measures can be taken to generate the counter curl behind the wide nip. It is therefore also possible to take part of the measures before the wide nip and some of the measures behind the wide nip. Overall, however, one will try to align the counter curl and the curl with one another in such a way that the end result is a path with sufficient flatness.

The task is solved in a wide nip calender of the type mentioned in that in the neighborhood of the wide nip, a counter curl generating device is arranged which generates a counter curl which is opposite to a curl generated by the wide nip.

As stated above in connection with the method, the curl and the counter curl overlap in such a way that the result is a web with sufficient flatness. Such a web can be processed much better than a web that still contains a curl.

The counter-curl generating device preferably has a moisture application device which acts on the side of the web which is in contact with the pressure element. With this moisture application device, moisture is thus applied to the underside of the web. This application of moisture creates a counter curl that is opposite to the curl created in the wide nip. Both measures together create the desired flatness of the train.
The moisture application device is preferably designed as a water application device directed onto the pressure element. The application of water to the pressure element is a relatively simple measure to transfer a sufficient amount of moisture to the underside. The transfer takes place when the web is passed through the wide nip together with the water film that has been formed on the pressure element.

The counter-curl generating device preferably has a drying device which acts on the side of the web which is in contact with the pressure element. Drying the underside of the web also creates the counter curl.

It is particularly preferred that the drying device is connected downstream of the moisture application device. Through this sequence, that is, first moisten and then dry, the conditions in the wide nip are at least approximately simulated, so that one can achieve similar conditions in the formation of the counter curl as in the formation of the curl in the wide nip.

A steam application device is preferably arranged on the side of the web lying against the heated roller. The steam application device applies steam to the top of the web. This application of steam leads on the one hand to an increase in the moisture on the top of the web and on the other hand to an increase in the web temperature. If the steam application device is located close enough in front of the wide nip, then only the upper layers of the web are moistened and heated, i. H. the middle of the sheet and also the underside are not plasticized as much as with continuous moistening. This achieves smoothing and at the same time protects the volume of the web.

A control device is preferably provided, which on the one hand matches the moisture application device and / or the drying device and the steam application device and / or a heating device that heats the heated roller. The heating device can heat the heated roller to surface temperatures in the range from 100 ° C. to approximately 300 ° C. The hotter the surface of the heated roller, the stronger the curl that is produced in the wide nip becomes. Similarly, an increase in steam application by the steam application device also contributes to an increase in curl. Since the control device controls both the heating of the heated roller and the steam application (or only one of them), it can produce a corresponding dependency on the application of moisture to the underside and / or the drying of the underside, so that the counter curl can largely be designed in this way that he balances the curl.

The pressure element is preferably designed as a shoe roller. In one embodiment, a shoe roller can have a circumferential jacket which is pressed against the heated roller by a pressure element. In another embodiment, the shoe roller can also be designed as a belt, which is also pressed against the heated roller by a pressure shoe. Both configurations allow the length of the wide nip to be made quite large. As stated above, a nip is considered to be a nip that has a length in the web running direction of at least 30 mm. With the help of a shoe roller, significantly longer wide nips can be produced, i.e. wide nips with a length in the range from 30 to 300 or even 400 mm.

The counter curl generating device is preferably arranged in front of the wide nip. So you first create the counter curl and then let it compensate by the curl in the wide nip.

In an alternative or additional embodiment it can be provided that the counter curl generating device is arranged behind the wide nip. If the counter curl generating device is arranged only behind the wide nip, then it compensates for the curl created in the wide nip. Of course, it is possible to arrange parts of the counter curl generating device in front of and other parts of the counter curl generating device behind the wide nip.

Fig. 1

eine erste Ausgestaltung eines Breitnip-Kalanders,

Fig. 2

eine zweite Ausgestaltung eines Breitnip-Kalanders,

Fig. 3

eine dritte Ausgestaltung eines Breitnip-Kalanders,

Fig. 4

eine vierte Ausgestaltung eines Breitnip-Kalanders,

Fig. 5

eine fünfte Ausgestaltung eines Breitnip-Kalanders,

Fig. 6

eine sechste Ausgestaltung eines Breitnip-Kalanders und

Fig. 7

eine siebte Ausgestaltung eines Breitnip-Kalanders.

The invention is described below on the basis of preferred exemplary embodiments in conjunction with the drawing. Show here:

Fig. 1

a first embodiment of a wide nip calender,

Fig. 2

a second embodiment of a wide nip calender,

Fig. 3

a third embodiment of a wide nip calender,

Fig. 4

a fourth embodiment of a wide nip calender,

Fig. 5

a fifth embodiment of a wide nip calender,

Fig. 6

a sixth embodiment of a Breitnip calender and

Fig. 7

a seventh embodiment of a Breitnip calender.

1 shows a wide-nip calender 1 for smoothing the volume of a paper or cardboard web 2, which is also referred to below as "web". The Breitnip calender has a heated roller 3 and a pressure element 4 designed as a shoe roller. The roller 3 and the pressure element 4 form between them a wide nip 5, which has a length in the running direction 6 of the web 2 in the range from 30 to 300 mm.

The pressure element 4 has, in a manner known per se, a circumferential jacket 7 which is pressed against the roller 3 by a schematically illustrated pressure shoe 8 in order to apply increased pressure to the web 2 passing through the wide nip 5. As an alternative to this, the pressure element 4 can also be formed by a circumferential belt which is pressed against the roller 3 by a similar pressure shoe 8. Finally, it is also possible for the pressure element 4 to be formed by a roller with a relatively soft surface coating, into which the roller 3 can be immersed to such an extent that the required length of the wide nip 5 results. The shape and position of the pressure shoe 8 depends on the circumstances.

The roller 3 is designed as a hard roller with a smooth surface 9. The surface 9 of the roller 3 is generally much smoother than a surface 10 of the pressure element 4.

This leads to the fact that the surface 9 of the roller 3 is impressed on the surface of the web 2 which bears against the roller 3. To simplify the further explanation, the side of the web 2 resting on the roller 3 is referred to as the "top side" and the opposite side as the "bottom side". After passing through the wide nip 5, the web 2 has an increased smoothness on its surface. In order to further improve this smoothness, the roller 3 is heated. In order to illustrate this schematically, a heating device 11 is shown which acts on the surface 9 of the roller 3. As an alternative or in addition to this, the roller 3 can also have peripheral bores 12 through which a heat transfer medium can be passed, for example hot steam. It is thus possible to bring the surface 9 of the roller 3 to a temperature of at least 100 ° C. It is preferable to use even significantly higher temperatures, namely a surface temperature in the range from 150 ° C. to 300 ° C.

In order to further improve the smoothness of the surface on the top of the web 2, a steam application device 13 is arranged in front of the wide nip, which applies steam to the top of the web 2. The steam is applied with a mass in the range of 1 to 5 g / mm ² . It leads to a moistening of the surface of the web 2 at the top and at the same time to a temperature increase. The steam application further improves the smoothness. If one places the steam application device 13 close enough in front of the wide nip 5, then the moisture is increased only in the surface layer. Similarly, only the surface of the web 2 is heated.

However, heating the roller 3 and applying steam to the surface of the web 2 has the disadvantage that the web tends to roll. The web thus receives a "curl", which manifests itself in the fact that the web bulges in the untensioned state. The result is a curvature transversely to the running direction 6, the longitudinal edges of the web 2 projecting towards the roller 3. Such a curl interferes with further processing. If the web is cut into sheets, for example, then these sheets do not lie flat on a base, but the edges of the sheets, which result from cutting lines parallel to the running direction 6, stand out from the base. Even if the web 2 is wound onto a roll and is unwound from the roll before printing or further processing, such a curl interferes.

In order to improve the machinability of the web 2, a counter curl generating device 14 is provided in the web running direction 6 in front of the wide nip 5. In the present case, the counter curl generating device has a moisture application device 15, which applies moisture to the underside of the web 2, that is to say to the side of the web 2 which abuts the pressure element 4 in the wide nip. The moisture application is in a range from 1 to 10 g / m ² .

A drying device 16 is arranged in the web running direction 6 behind the moisture application device 15 and dries the underside of the web 2 again. The combination of moisture application device 15 and drying device 16 simulates the conditions in and just before the wide nip 5. Here, too, the web is first moistened on its upper side and then heated by the heated one on its upper side Dried roller 3. In a similar way as the web 2 receives a curl in the wide nip 5, the counter curl generating device 14 generates a counter curl, ie a curl in the opposite direction. The counter curl curves the web 2 so that it is directed in the untensioned state opposite to the curvature of the roller 3.

A control device 17 is provided in order to control both the heating device 11, 12 and the moisture application device 15 and the drying device 16. The control device "knows" how much steam is applied to the top of the web 2 by means of the steam application device and how hot the heated roller 3 is. From this information, the curl that forms in the Breitnip 5 can be estimated. In a corresponding manner, the control device 17 can apply moisture to the underside of the web 2 with the aid of the moisture application device 15 and dry the underside of the web 2 with the drying device 16 accordingly. This makes it possible to generate a counter curl in such a way that it is practically compensated for by the curl generated in the wide nip 5 and the web 2 is given an improved flatness.

The moisture application device 15 can have different configurations. For example, it is possible to apply the moisture in the form of steam to the underside of the web 2. You can also create a spray or apply a film of moisture using a brush or squeegee or applicator roller. The type of order depends on the circumstances.

The drying device 16 can also have different designs. It is possible, for example, to use a drying cylinder here, to apply hot air to the underside of the web 2 or to provide a heat ray, for example an IR radiator.

Fig. 2 shows an alternative embodiment, in which the same elements are provided with the same reference numerals. For reasons of clarity, the control device 17 and the heating device 11, 12 are not shown here. An application of steam and / or liquid is symbolized by an arrow.

In the embodiment according to FIG. 2, the moisture application device 15 is followed by a conventional nip 18, which is formed by two rollers 19, 20. The roller 20 resting on the underside of the web 2 is preferably at a higher temperature than the roller 19 resting on the upper side. It can also be provided that the roller 20 resting on the underside is designed as a hard, heated roller while the the upper side of the web 2 adjacent roller 19 is designed as a soft roller.

In the nip 18, the web 2 is dried on its underside.

In the embodiment according to FIG. 3, a further drying treatment upstream of the wide nip 5 is dispensed with, ie the water application device 15 has no intermediate connection another unit arranged on the underside of the web 2 in front of the Breitnip 5.

4, the moisture application device acts on the surface 10 of the jacket 7, i. H. water is applied directly to the pressure element 4, for example by spraying or by means of a water scraper or by means of a transfer roller immersed in a water supply.

In the embodiments according to FIGS. 1 to 4, the counter curl generating device 14 was arranged in front of the wide nip 5, i. H. a counter curl was created in the web 2 before the curl was generated in the wide nip 5.

In the exemplary embodiments in FIGS. 5 to 7, the counter curl generating device is arranged behind the wide nip 5 in the web running direction 6. The same elements are provided with the same reference symbols in all seven figures.

The embodiment according to FIG. 5 corresponds to the embodiment according to FIG. 3 with the difference that the moisture application device 15 is arranged in the web running direction 6 not in front of but behind the wide nip 5.

The configuration according to FIG. 6 corresponds to the configuration according to FIG. 2 with the difference that the counter curl generating device 14 with the moisture application device 15 and the nip 18 is arranged behind the wide nip 5 in the web running direction 6.

The configuration according to FIG. 7 corresponds to the configuration according to FIG. 1 with the difference that the counter curl generating device 14 is arranged behind the wide nip 5 in the web running direction 6.

Formations are shown in which the heated roller 3 and the pressure element 4 are arranged below. Of course, it is also possible to reverse the arrangement, i. H. the heated roller 3 below and the pressure element 4 above. In this case, of course, the counter curl generating device 14 and the steam application device 13 are also arranged on the other side.

Claims (21)

Process for smoothing a paper or cardboard web, in which the web is passed through a wide nip with a length of at least 30 mm and in the wide nip lies against a heated roller with a surface temperature of at least 100 ° C and a pressure element, characterized in that takes measures in the vicinity of the wide nip to produce a counter curl that is opposite to a curl generated by the wide nip. A method according to claim 1, characterized in that the side of the web abutting the pressure element is moistened to produce the counter curl. A method according to claim 2, characterized in that moisture is applied to the web in an amount of 1 to 10 g / m ² . Method according to one of claims 1 to 3, characterized in that steam and / or water is applied to the side of the web which is in contact with the pressure element. A method according to claim 4, characterized in that water is applied to the pressure element. Method according to one of claims 1 to 5, characterized in that the web for producing the counter curl is dried from the side lying against the pressure element. Process according to one of claims 1 to 6, characterized in that steam or water is applied to the side of the web which is in contact with the heated roller. Process according to Claim 7, characterized in that steam or water with a mass of 1 to 5 g / m ² is fed to the web. A method according to claim 8, characterized in that the moistening and / or drying of the side of the web adjacent to the pressure element is adjusted as a function of the steam or water application of the side of the web adjacent to the heated roller and / or the temperature of the heated roller , Method according to one of claims 1 to 9, characterized in that measures are taken to generate the counter curl in front of the wide nip. Method according to one of claims 1 to 10, characterized in that measures are taken to generate the counter curl behind the wide nip. Breitnip calender for smoothing a paper or cardboard web with an at least 30 mm long Breitnip, which is formed by a heated roller with a surface temperature of at least 100 ° C and a pressure element, characterized in that in the vicinity of the Breitnip (5) a Counter curl generating device (14) is arranged, which generates a counter curl directed opposite to a curl generated by the wide nip (5). Calender according to Claim 12, characterized in that the counter curl generating device (14) has a moisture application device (15) which acts on the side of the web (2) which bears against the pressure element (4). Calender according to claim 13, characterized in that the moisture application device (15) is designed as a water application device directed onto the pressure element (4). Calender according to one of Claims 12 to 14, characterized in that the counter-curl generating device (14) has a drying device (16, 18) which acts on the side of the web (2) which bears against the pressure element (4). Calender according to claim 15, characterized in that the drying device (16, 18) is connected downstream of the moisture application device. Calender according to one of Claims 12 to 16, characterized in that a steam application device (13) is arranged on the side of the web (2) which bears against the heated roller (3). Calender according to claim 17, characterized in that a control device (17) is provided which the moisture application device (15) and / or the drying device (16, 18) on the one hand and the steam application device (13) and / or one heated roller heating device (11, 12) on the other hand coordinated. Calender according to one of claims 12 to 18, characterized in that the pressure element (4) is designed as a shoe roller. Calender according to one of claims 12 to 19, characterized in that the counter curl generating device (14) is arranged in front of the wide nip (5). Calender according to one of claims 12 to 20, characterized in that the counter curl generating device (14) is arranged behind the wide nip (5).

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