EP1491680B1 - 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 board web, in which the web is passed through a nip with a length of at least 30 mm and rests in the nip on a heated roll with a surface temperature of at least 100 ° C and a pressure element. Furthermore, the invention relates to a flat-nip calender for smoothing a paper or board web with a 30 mm long nip, which is formed by a heated roller with a surface temperature of at least 100 ° C and a pressure element.

Paper or board webs, which are referred to below as "webs" in the following, 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 a resilient surface which 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 rolls also at elevated temperature. This treatment results in excellent smoothness on the side of the web which bears against the hard roller. But it has the disadvantage that the web is compressed under certain circumstances relatively strong, so suffers a loss of volume.

To avoid the loss of volume one often uses so-called broad nips, ie nips, which have a greater length in the direction of travel of the web than the nips formed between the above-described two rollers. For the purposes of the present invention, a nip is considered as 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. First, it can be formed by the roller and a circulating belt or a circumferential jacket, the latter rests against the roller over a predetermined circumferential area. The pressing of the tape or the jacket takes place via a pressure shoe. It is also possible to use as a pressure element a roller with a very soft surface layer into which the heated roller can be pushed in so far that the desired length of the extended nip is formed. A wide nip is also called an "extended nip" or "extended nip".

In a wide-nip calender, the heated roll is designed as a hard, smooth roll, d. H. the smoothness of the heated roll is transferred to the surface of the web. The voltage applied to the heated roller side of the web is thus smoothed to the desired extent.

Out US 2002/0060005 A1 A method for calendering paper and board is known, with which the smoothness of the paper or board web is to be increased, while the reduction of the paper thickness is reduced. In this case, the paper or board web is guided by a Multikalander following a printing or coating device, wherein they are between individual nips of the multicalander can be rehydrated by means of moistening. Subsequently, the paper or board web is further treated in a dry calender, which has at least one nip and wherein for wetting the web further vapor deposition means are provided. In order to control the occurrence of a curl during production, the vaporization of the material web should take place from both sides, so that finally a uniform moisture content is achieved. Already the occurrence of a curl should be prevented in general.

In WO 02/103109 A1 discloses a method and a paper machine with which LWC printing paper can be produced, which is coated only once. The paper web is guided in front of a coating station through a pre-calender, which has two nips, which may be formed by a shoe calender each. Before the respective shoe calender, a vapor deposition device can be arranged on one or both sides of the paper web in order to control the moisture content of the paper web. With the aid of a measuring device, the transverse profile of the web W can be detected, with irregularities in the transverse profile are compensated by profiled Vorkalandern.

In this case, additional facilities for controlling curling can be used. It is suggested to control and regulate curling of the paper web in the dry section by means of steam or humidifiers. The occurrence of curls should thus be prevented from the outset by an appropriate regulation of the moisture content of the paper web.

However, it has been found that a web that has been smoothed in a nip with a heated roller and a pressure element tends to curl. Curl is a phenomenon in which the web is no longer flat, but bulges. Curl is particularly enhanced by the long residence time in the nip, the high temperatures and the humidification, which is advantageously applied to reinforce the smoothness 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 ago, the curl has negative consequences in the further processing, especially in 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 in that in the vicinity of the broad nip measures for generating a generated by the broad nip curl opposite countercurl hits, which bulges the web.

One makes use of the knowledge that a curl and a counter curl, if they are correspondingly matched to one another, compensate again so that the web again reaches a sufficient flat position before further processing. Thus, if the web curves concavely so that it follows the surface of the heated roll, then one must take measures by which the web bulges in the other direction. Taken together, the two measures balance each other out and cause the web to regain the desired flatness. It is advantageous if the two measures are in a relatively close spatial proximity to each other. Accordingly, the measure for generating the countercurl in the vicinity of the nip is encountered.

Preferably, to generate the countercurl, the side of the web resting against the pressure element is moistened. The web is therefore moistened on one side and that on the side that is not applied to the heated roller. The moistening leads to a curl in the side facing the moisture application. For the purposes of the following explanation is simplified assuming that the upper side of the web on the heated roller and the underside of the web bears against the pressure element. So you wear the moisture from below. As a result, the web bulges down. The web lies with its top on the heated roller. As a result, the web bulges upwards. The curvature down and the curvature upward, so Gegencurl and curl, make up for each other, so that one reaches the desired flatness.

It is preferred that moisture is applied to the web at a rate of 1 to 10 g / m ² . Such a moisture application is sufficient to produce the desired countercurl.

It is preferable to apply steam and / or water to the side of the web resting against the pressure element. The application of steam and / or water is a relatively simple means of applying moisture to the underside of the web sufficiently and with sufficient uniformity, i. H. on the side of the web, which rests against the pressure element.

It is particularly preferred that one applies water to the pressure element. So you first created on a water film with a desired strength the surface of the pressure element. The job can be done at a position just before the nip. Then, when the web passes through the nip, moisture transfers from the surface of the nip to the web.

The web is preferably dried to produce the counter curl from the side adjacent to the pressure element. One thus recreates the conditions in the nip, so to speak. In broad nip the web is also dried, but from the adjacent to the heated roller side ago. The drying, which is preferably combined with the application of moisture, thus achieves a Gegencurl that can be set pretty much to the degree that results in the curl in the nip.

Preferably, applied to the heated roller adjacent side of the web with steam or water. Applying steam to the top of the web improves smoothness. However, it also leads to a stronger curl. However, this increased curl is not critical because the countercurl measures can at least largely compensate for the increased curl.

Preferably, steam or water having a mass of from 1 to 5 g / m ^{2 is added to} the web. Of this, a certain proportion, usually between 25% and 100%, is absorbed by the railway. Such a quantity of steam or water has proved to be sufficient to achieve a good smoothness.

Preferably, the moistening and / or the drying of the side of the web contacting the pressure element is adjusted depending on the vapor deposition or water application of the side of the web adjacent to the heated roll and / or the temperature of the heated roll. The steam or water spray on the top reinforces the curl. Similarly, the curl is increased as the temperature of the heated roll is increased. The temperature of the heated roll is above 100 ° C and can be up to about 300 ° C. It is now possible to increase the formation of the countercurl when the temperature of the heated roller is higher and / or the vapor deposition is greater. For this purpose, for example, the moisture application is increased to the underside of the web and / or increased drying.

One meets the measures for the production of the Gegencurl before the broad nip. So you create a counter curl before the curl arises in the nip. Both measures together then lead to a flatness of the web.

In addition, measures can be taken to create the countercurl behind the nip. It is therefore also possible to take part of the measures before the nip and part of the measures behind the nip. Overall, however, one will try to match the countercurl and the curl to each other in such a way that the result is a web with a sufficient flatness.

The problem is solved by a wide-nip calender of the type mentioned in that in the neighborhood a Gegencurl generating means is arranged in front of the nip, which generates a countercurl directed counter to a curl produced by the broad nip and which archs the web.

As indicated above in the context of the method, the curl and the counter curl overlap one another to ultimately yield a sheet 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 bears against the pressure element. With this moisture application device so moisture is applied to the underside of the web. This moisture application creates a countercurl that is opposite to the curl created in the nip. Both measures together thus produce the desired flatness of the web.
The moisture application device is preferably designed as a water applicator 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 bottom. The transfer takes place when the web, together with the water film which has been formed on the pressure element, is guided through the wide nip.

The counter curl generating device preferably has a drying device which acts on the side of the web resting against the pressure element. Drying the underside of the web also creates the countercurl.

It is particularly preferred that the drying device of the moisture application device is connected downstream. By this sequence, ie moisten first and then dry, the conditions in the nip are at least approximately replicated, so that you can achieve similar conditions in the formation of Gegencurl, as in the formation of curl in the nip.

Preferably, a steam application device is arranged on the side of the web adjacent to the heated roller. The steam applicator applies steam to the top of the web. This vapor deposition leads on the one hand to an increase in the humidity of the upper side of the web and on the other to an increase in the web temperature. If the steam applicator is placed close enough in front of the nip, then only the upper layers of the web are moistened and heated, i. H. the middle of the web and the bottom are not plasticized as much as in a continuous moistening. This achieves a smoothing and at the same time protects the volume of the web.

Preferably, a control device is provided, which tunes the moisture application device and / or the drying device on the one hand and the steam application device and / or a heated roller heating the heater on the other hand to each other. The heater may heat the heated roll to surface temperatures in the range of 100 ° C to about 300 ° C. The hotter the surface of the heated roll is, the stronger the curl produced in the nip becomes. Similarly, an increase in vapor deposition by the vapor deposition 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 dependence on the moisture application to the underside and / or the drying of the bottom, so that one can form the counter curl largely so that he balances the curl.

Preferably, the pressure element is designed as a shoe roll. In one embodiment, a shoe roll can have a circumferential jacket, which is pressed against the heated roll by a pressure element. In another embodiment, the shoe roll may also be formed as a band, which is also pressed by a Andruckschuh against the heated roller. Both embodiments allow to make the length of the wide nip quite large. As stated above, a nip is considered as a nip, which has a length in the web running direction of at least 30 mm. With the help of a shoe roll can also produce much longer long nipples, so long nipples with a length in the range of 30 to 300 or even 400 mm.

The Gegencurl generating device is arranged in front of the broad nip. So first you create the countercurl and then let it balance through the curl in the nip again.

In an additional embodiment, it can be provided that the countercurl generating device is arranged behind the wide nip. If the Gegencurl generating device is located only behind the nip, then it compensates for the resulting in the nip Curl again. Of course, it is possible to place parts of the counter curl generator before and other parts of the counter curl generator behind the broad 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,

The invention will be described below with reference to preferred embodiments in conjunction with the drawings. Herein show:

Fig. 1

a first embodiment of a wide-nip calender,

Fig. 2

a second embodiment of a broad-nip calender,

Fig. 3

a third embodiment of a broad-nip calender,

Fig. 4

A fourth embodiment of a broad-nip calender,

Fig. 1 shows a broad-nip calender 1 for volume-smoothing a paper or board web 2, which is also referred to below as "web". The wide-nip 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 broad nip 5, which in a running direction 6 of the web 2 has a length in the range of 30 to 300 mm.

The pressure element 4 has in a conventional manner a circumferential jacket 7, which is pressed by a pressure shoe 8 shown schematically against the roller 3 in order to pressurize the web 2 passing through the broad nip 5 with increased pressure. Alternatively, the pressure element 4 may also be formed by a circulating belt which is pressed by a similar pressure shoe 8 against the roller 3. Finally, it is also possible that the pressure element 4 is formed by a roller with a relatively soft surface coating, in which the roller 3 can dip so far that the required length of the extended nip 5 results. The shape and position of the pressure shoe 8 depends on the circumstances.

The roller 3 is formed 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 results in that the surface 9 of the roller 3 impresses on the surface of the web 2, which bears against the roller 3. To simplify further explanation, For example, the side of the web 2 contacting the roller 3 is referred to as "top" and the opposite side as "bottom". After passing through the broad nip 5, the web 2 thus has on its surface an increased smoothness. To further improve this smoothness, the roller 3 is heated. To illustrate this schematically, a heater 11 is shown, which acts on the surface 9 of the roller 3. Alternatively or additionally, the roller 3 may also have peripheral holes 12, through which a heat transfer medium can be passed, for example, hot steam. This makes it possible to bring the surface 9 of the roller 3 to a temperature of at least 100 ° C. Preferably, even much higher temperatures will be used, namely a surface temperature in the range of 150 ° C to 300 ° C.

In order to further improve the smoothness of the surface at the top of the web 2, a steam applicator 13 is arranged in front of the nip, which applies steam to the top of the web 2. The steam is applied here 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 applicator 13 close enough in front of the nip 5, then the moisture is increased only in the surface layer. Similarly, only the surface of the web 2 is heated.

However, the heating of the roller 3 and the vapor deposition on the surface of the web 2 has the disadvantage that the track tends to roll. The orbit thus receives a "curl", which manifests itself in the fact that the web bulges in the untensioned state. The result is a curvature transverse to the direction 6, wherein the longitudinal edges of the web 2 protrude in the direction of the roller 3. Such a curl interferes with further processing. For example, if the web is cut into sheets, then these sheets will not lie flat on a backing but the edges of the sheets resulting from cut lines parallel to the direction 6 will lift off the backing. Even if the web 2 is wound onto a roll and unwound from the roll before being printed or processed, such a curl interferes.

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

In the web running direction 6 behind the moisture application device 15, a drying device 16 is arranged, which dries the underside of the web 2 again. With the combination of moisture applicator 15 and drying device 16 forms the conditions in and shortly before the nip 5 after. Again, the web is first moistened on its upper side and then on its upper side by the heated Roller 3 dried. Similarly, as web 2 in broad nip 5 is given a curl, countercurl generator 14 generates a countercurl, ie, a curl in the opposite direction. The Gegencurl buckles the web 2 so that it is directed in the untensioned state opposite to the curvature of the roller 3.

A controller 17 is provided to control both the heater 11, 12 and the moisture applicator 15 and the drying device 16. The control device thus "knows" how much steam is applied by means of the steam application device to the upper side of the web 2 and how hot the heated roll 3 is. From this information, the curl forming in the broad nip 5 can be estimated. The control device 17 can apply moisture to the underside of the web 2 in a corresponding manner with the aid of the moisture application device 15 and dry the underside of the web 2 with the drying device 16 accordingly. Thus, it is possible that one generates a Gegencurl so that it is virtually compensated by the curl produced in the nip 5 and the web 2 receives an improved flatness.

The moisture applicator 15 may have different configurations. For example, it is possible to apply the moisture in the form of vapor to the underside of the web 2. It is also possible to produce a spray or to apply a moisture film by means of a brush or a doctor blade or an applicator roll. The type of order depends on the circumstances.

The drying device 16 may also have different configurations. It is possible, for example, to use a drying cylinder here, to apply hot air to the web 2 on its underside or to provide a heat jet, for example an IR emitter.

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 order of vapor and / or liquid is symbolized by an arrow.

In the embodiment according to Fig. 2 Followed by the moisture applicator 15, a conventional nip 18, which is formed by two rollers 19, 20. The voltage applied to the underside of the web 2 roller 20 is preferably at a higher temperature than the voltage applied to the top roller 19. It can also be provided that the voltage applied to the bottom roller 20 is formed as a hard, heated roller, while at the top of the web 2 adjacent roller 19 is formed as a soft roll.

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

In the embodiment according to Fig. 3 one waives a further drying treatment before the nip 5, ie the water applicator 15 is without interposition a further unit at the bottom of the web 2 in front of the nip 5 arranged.

In the embodiment according to Fig. 4 the moisture application device acts on the surface 10 of the jacket 7, ie 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 the FIGS. 1 to 4 For example, the counter curl generator 14 was located in front of the nip 5, ie, a countercurl was created in the web 2 before the curl was produced in the nip 5.

Shown are embodiments in which the heated roller 3 above and the pressure element 4 are arranged below. Of course it is also possible to choose the arrangement in reverse, d. H. the heated roller 3 below and the pressure element 4 above. In this case, of course, the Gegencurl generating means 14 and the steam applicator 13 are arranged on the other side.

Claims (19)

1. Method for smoothing a paper or board web, in which the web is led through an extended nip having a length of at least 30 mm and, in the extended nip, lies against a heated roll having a surface temperature of at least 100°C and a pressure element, measures being taken in the vicinity before the extended nip to produce an opposing curl oriented oppositely to the curl produced by the extended nip, the opposing curl curving the web.
2. Method according to Claim 1, characterized in that, in order to produce the opposing curl, the side of the web lying against the pressure element is moistened.
3. Method according to Claim 2, characterized in that moisture is applied to the web in an amount from 1 to 10 g/m².
4. Method according to one of Claims 1 to 3, characterized in that steam and/or water is applied to the side of the web lying against the pressure element.
5. Method according to Claim 4, characterized in that water is applied to the pressure element.
6. Method according to one of Claims 1 to 5, characterized in that the web is dried from the side lying against the pressure element in order to produce the opposing curl.
7. Method according to one of Claims 1 to 6, characterized in that steam or water is applied to the side of the web lying against the heated roll.
8. Method according to Claim 7, characterized in that steam or water is supplied to the web with a mass from 1 to 5 g/m².
9. Method according to Claim 8, characterized in that the moistening and/or the drying of the side of the web lying against the pressure element is adjusted as a function of the application of steam or water to the side of the web lying against the heated roll and/or the temperature of the heated roll.
10. Method according to one of Claims 1 to 9, characterized in that measures for producing an opposing curl are also taken after the extended nip.
11. Extended nip calender (1) for smoothing a paper or board web (2), having an extended nip (5) which is at least 30 mm long and which is formed by a heated roll (3) having a surface temperature of at least 100°C and a pressure element (4), characterized in that in the vicinity before the extended nip (5) there is arranged an opposing curl producing device (14), which produces an opposing curl oriented oppositely to the curl produced by the extended nip (5) and which curves the web.
12. Calender according to Claim 11, characterized in that the opposing curl producing device (14) has a moisture application device (15) which acts on the side of the web (2) lying against the pressure element (4).
13. Calender according to Claim 12, characterized in that the moisture application device (15) is constructed as a water application device aimed at the pressure element (4).
14. Calender according to one of Claims 12 to 13, characterized in that the opposing curl producing device (14) has a drying device (16, 18) which acts on the side of the web (2) lying against the pressure element (4).
15. Calender according to Claim 14, characterized in that the drying device (16, 18) is connected downstream of the moisture application device.
16. Calender according to one of Claims 11 to 15, characterized in that a steam application device (13) is arranged on the side of the web (2) lying against the heated roll (3).
17. Calender according to Claim 16, characterized in that a control device (17) is provided which coordinates the moisture application device (15) and/or the drying device (16, 18), on the one hand, and the steam application device (13) and/or a heating device (11, 12) heating the heated roll, on the other hand, with one another.
18. Calender according to one of Claims 11 to 17, characterized in that the pressure element (4) is constructed as a shoe roll.
19. Calender according to one of Claims 11 to 18, characterized in that an opposing curl producing device (14) is also arranged after the extended nip (5).

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