FI128040B

FI128040B - Method of treating a fiber web and a treatment system for treatment of a fiber web

Info

Publication number: FI128040B
Application number: FI20175659A
Authority: FI
Inventors: Jari Ilomäki
Original assignee: Valmet Technologies Oy
Priority date: 2017-07-06
Filing date: 2017-07-06
Publication date: 2019-08-15
Also published as: FI20175659A1; DE102018115923A1; FI20175659A

Abstract

The invention relates to a method of treating a fiber web, in which the fiber web (W) is calendered in at least one nip (N) of a calender (10), and before the calender (10) in running direction of the fiber web (W) one side of the fiber web or both sides of the fiber web is/are only surface dried in a surface drying zone (Z). The invention also relates to a treatment system for treatment of a fiber web comprising a calender (10) and before the calender (10) in running di-rection of the fiber web (W) located surface drying zone (Z), in which one side of the fiber web or both sides of the fiber web (W) is/are only surface dried.

Description

Method of treating a fiber web and a treatment system for treatment of a fiber web

In general present invention relates to treating of fiber webs in a fiber web production line. More especially the present invention relates to a method according to 5 preamble part of the independent method claim and to a treatment system according to preamble part of the independent treatment system claim.

As known from the prior art in fiber web producing processes typically comprise an assembly formed by a number of apparatus arranged consecutively in the process line. A typical production and treatment line comprises a head box, a wire section 10 and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and/or sections for finishing the fiber web, for example, a pre-calender, a sizer, a final-calender, a coating section. The production and treatment line also typically comprises at least one slitter-winder for forming customer rolls as well as a roll packaging apparatus. 15 In this description and the following claims by fiber webs are meant for example a paper and board webs.

Calendering can be pre-calendering or final-calendering depending on the type of the production line. Pre-calendering is typically used for creating required surface properties for further treatment for example for coating. Final-calendering is gen20 erally carried out in order to improve the properties, like smoothness and gloss, of a web-like material such as a paper or board web. In calendering the web is passed into a nip, i.e. calendering nip, formed between rolls that are pressed against each other, in which nip the web becomes deformed as by the action of temperature, moisture and nip pressure. In the calender the nips are typically 25 formed between a smooth-surfaced press roll such as a metal roll and a roll coated with resilient material such as a polymer roll or between two smooth-surfaced rolls. The nips can be formed also by using instead a calender roll a belt or a shoe as known from prior art. Many different kinds of calenders to be used as a precalender and/or as a final-calender are known, for example hard nip calenders, 30 soft nip calenders, supercalenders, metal belt calenders, shoe calenders, long nip calenders, multinip calenders etc.

It is known from prior art to moisturize the fiber web before calendering in order to achieve required surface properties and simultaneously achieve required bulkiness i.e. relation of thickness of the web to its grammage (basis weight) or to con35 trol the curl of the fiber web.

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In production of fiber webs, for example in production of paper or board webs, sizing is used to alter the properties of a fiber web by adding sizing agents, for example starch or other sizing agents. Sizing can be divided to internal sizing and surface sizing. In internal sizing the sizing agent is added to pulp in the wet end of the 5 fiber web machine before forming. In surface sizing the sizing agent is added onto the surface of the fiber web typically at the dry end of the fiber web machine. Surface sizing is used in production of many fiber web grades, for example of uncoated fine papers and of several board grades. In fiber web production when fiber web is surface sized with water soluble starch or other sizing agent and dried, the 10 dried starch film easily dissolves in connection with moisture addition and can stick to the contacting surfaces. Due to the high water solubility of the starch the moisture addition before calendering has been possible only in very small amounts. Sizing is used in order to improve paper web properties, in particular water resistance, water absorption properties, strength, internal strength and bending stiff15 ness. In addition, runnability as well as dusting tendency can be affected favorably.

Starch based sizes, among some other sizing agents, are known to be water soluble. This will pose a major problem in moisture gradient calendering when sized paper is first moistened and soon after that calendered. It has been observed, that 20 moistening of starch sized webs prior to hot calendering leads to problems like sticking, starch picking and deposit building on the calender roll surfaces. It is believed, that the applied water is dissolving the dried starch film in the web surface. The dissolved starch can be transported, particularly with water movement, into a direct contact with roll surface. The mechanism of sticking and picking is not well 25 known, but it can be assumed, that at hot roll surface the water is evaporated while the size (binder) remains at the surface contact. The binder is adhered to and possibly held by sticky bonds at the metal surface.

In calendering and corresponding web treatment processes of moistened or moist fiber web, which has been sized with water soluble sizing agent like starch, a dis30 advantage is that the starch and associated fibers tend to pick and stick on the heated calender rolls and corresponding heated surfaces contacting the fiber web. This tends to be aggravated at higher nip loads and temperatures required for achieving high smoothness levels. The sticking and fiber pulling are caused by dissolving of starch or other binders that are added in to the web and may lead to 35 runnability problems, roll contamination and calendered or treated quality reduction and even to breaks in production in severe contamination cases.

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Dried sizing agent types, such as starch, and some other chemicals used in fiber web production are soluble in water and thus stick to for example hot calender rolls, if water is applied before calendering such that the moisture content of the fiber web, especially in surface areas, is high. This is preventing the use of water 5 moisturizing in calendering of these fiber webs even though the moisturizing before calendering would be very advantageous particularly due to enhanced moisture gradient calendering effect.

The water solubility of these sizing agents and other chemical substance of this type can be decreased by modifying the agents or chemicals or by adding chemi10 cals that prevent solubility. It is known for example to decrease water solubility of a starch based binding agent of a coating medium in order to prevent starch dissolving due to water based printing colors in offset printing or to improve wet rub-off properties of fiber webs.

Sticking and picking problems at heated calender rolls may also occur with other 15 sizing agents than starch especially when moisturizing and/or high moisture content before calendering is used. In some cases the fiber web may contain other chemicals that cause sticking and picking problems in calendering.

The most obvious solution is to use as small amounts of water as possible, but this is diminishing the benefits of the moisture gradient calendering. Ultimately, the 20 starch dissolving and picking at the calender can be prevented when the process is arranged in such way that starch and water are not brought together in to a contact before calendering.

In some fiber web production line for producing sized grades its calendering concept comprises in pre-calendering position moisturizing and hot hard nip calender25 ing. Typically these are limited to use of moisturizing - moisturizing can be used only very small amounts such that moisture evaporates before the calendering nip.

This is due to the effect of moisture causing sticking of sizing agent onto surface of the hot calender roll of the calendering nip.

In patent application publication WO 9964671 A1 is disclosed an integrated paper 30 machine, in which a web is passed into a calendering nip between a drying cylinder and a roll 532m in which the drying cylinder and the roll 532 form a surface treatment device.

In patent application publication EP 2549013 A1 is disclosed an integrated process for producing a fiber web, in which according to one example impingement

20175659 prh 29 -03- 2019 drying units are provided above a metal belt, which impingement drying devices dry the fiber web as it passes supported by the metal belt and after drying the fiber web is calendered in a metal belt calender.

In patent publication US 5771603 A is disclosed drying section for the drying of a 5 paper web in a paper making machine consisting exclusively of single-felt drying groups and two calenders arranged downstream of the drying section and additional contact-less dryers are provided.

In patent application publication US 2007151689 A1 is disclosed a sheet making machine comprising a treatment system with an infrared moisture sensor.

In patent application publication WO 8803193 A1 is disclosed a procedure for drying a moving web material, in which infrared radiation dryers with wavelength range of medium long wave are used.

An object of the invention is to create a method of treating a fiber web and a treatment system for treatment of a fiber web, in which the above problems and 15 disadvantages are eliminated or at least minimized.

A particular object is to prevent chemicals, especially size, in particular starch, sticking from wet I moistened fiber web into a hot contacting surface, particularly a hot calendering surface.

To achieve the objects mentioned above and later the method according to the in20 vention is mainly characterized by the features of the characterizing part of claim 1.

The treatment system for treatment of a fiber web according to the invention is mainly characterized by the features of the characterizing part of claim 5.

Advantageous features and embodiments of the invention are defined in the de25 pendent claims.

According to the invention in the method of treating a fiber web the fiber web is calendered in at least one nip of a calender and before the calender in running direction of the fiber web one side of the fiber web or both sides of the fiber web is/are only surface dried in a surface drying zone.

In the surface drying zone the surface/-s of the fiber web is/are according to the invention dried such that surface moisture content of the surface dried side/sides

20175659 prh 29 -03- 2019 of the fiber web in thickness direction of the fiber web in surface layer 5 - 15 pm measured from the outer surface of the fiber web is at most 10%.

According to the invention the treatment system for treatment of a fiber web comprising a calender and before the calender in running direction of the fiber web lo5 cated surface drying zone, in which surface drying zone one side of the fiber web or both sides of the fiber web is/are only surface dried.

According to the invention in the treatment system the fiber web is surface dried such that surface moisture content of the surface dried side/sides of the fiber web is at most 10% in thickness of 5 - 15 pm of the thickness of the fiber web meas10 ured from the outer surface of the fiber web.

According to an advantageous feature of the invention the fiber web is surface dried in the surface drying zone before calendering such that the fiber web enters the first of the calendering nips or the only calendering nip one or on both sides of the fiber web surface dried and the middle layers of the fiber web are moist.

According to an advantageous feature of the invention the surface/-s of the fiber web is/are dried by contact drying with low contact pressure in the surface drying zone, in which drying zone the drying time is 100 - 300 ms, advantageously about 200 ms, and the contact pressure i.e. tension caused by the fiber web is 1 - 5 kPa.

According to an advantageous feature of the invention the surface/-s of the fiber 20 web is/are dried by contactless drying zone by means of an infra-red dryer using long wave lengths about 3 pm or over 6 pm.

According to an advantageous feature of the invention moisture content of the surface/^ of the fiber web are measured by a moisture sensor between the surface drying zone and the calender and based on the moisture measurement results the 25 drying effect of the surface drying zone is controlled by adjusting drying temperature and/or drying time and/or in case of contact drying the contact pressure.

According to an advantageous feature of the invention the surface drying zone comprises a run of the fiber web on a heated roll.

According to an advantageous feature of the invention the heated roll is a calender 30 roll or a contact drying roll or a drying cylinder.

According to an advantageous feature of the invention the surface drying zone comprises infra-red dryer using long wave lengths about 3 pm or over 6 pm.

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According to an advantageous feature of the invention the treatment system comprises a moisture sensor, advantageously reflection based IR moisture sensor, between the surface drying zone and the calender.

In this description and the claims:

- By high moisture content is meant moisture content over 10%.

- By surface of the fiber web in thickness direction is meant 5 - 15 pm measured from the outer surface of the fiber web.

- By low contact pressure is meant a contact pressure 1 - 5 kPa.

The present invention relates to methods of treating a fiber web and treatment sys10 terns for treatment of a fiber web, in which either internal sizing or surface sizing is used.

In this description the invention is described mainly in view of the sizing agent being the chemical substance of the fiber web to cause the sticking and picking problems in calendering but it is to be understood that the invention is utilizable also 15 when the chemical substance is another type of chemical causing the sticking and picking problems when moisturized.

In the method and in the system according to the invention either one or both sides of the fiber web are treated.

According to one aspect of invention in order to prevent the sticking and picking 20 problems in the calendering nip the sized fiber web with high moisture content is surface dried before the calendering nip such that the in thickness direction of the fiber web the surface of the fiber web is dried to dryness of 90 % or over, i.e. the moisture content is at most 10%, by contact drying with low contact pressure in a contact zone, in which contact zone the fiber web advantageously remains at least 25 for the drying time of 100 - 300 ms, advantageously about 200 ms, and the drying effects in depth 5 - 15 pm measured from the outer surface of the fiber web.

The drying of the surface of the fiber web increases the diffusion, which causes the moisture to move from the surface and to centralize in the middle due to increased partial steam pressure in the surface layer and thus moisture is drawn to30 wards the middle layer of the fiber web.

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According to an advantageous feature of this aspect of the invention the contact drying zone is formed as a run of the fiber web on a heated roll. The contact time in the contact zone can be defined by the running speed of the fiber web and the wrap angle of the fiber web on the roll. The wrap angle is advantageously 90 - 230 ° and the temperature of the heated roll is 60- 100 °C. Instead of a heated roll also a heated belt formed as a loop guides by guide rolls can be used.

According to one aspect of invention in order to prevent the sticking problems in the calendering nip the sized fiber web with high moisture content is surface dried before the calendering nip such that the in thickness direction of the fiber web the surface of the fiber web is dried in a contactless drying zone by means of an infrared dryer using long wave lengths about 3 pm or over 6 pm such that the moisture content of the surface is at most 10% in depth 5 - 15 pm of the fiber web measured from the outer surface of the fiber web.

According to one aspect of invention in order to prevent the sticking problems in the calendering nip the sized fiber web is moisturized when the fiber web is dried on the second last drying cylinder of the last drying cylinder group and the surface of the fiber web is dried by the last drying cylinder of the fiber web adjusting the temperature of the last drying cylinder.

According to an advantageous feature of the invention a moisture sensor for example an infrared moisture sensor is located between the drying zone and the calender and based on the moisture measurement results the drying effect is controlled by adjusting drying temperature and/or drying time and/or in case of contact drying the contact pressure.

Advantageously the invention is utilized when treating fiber web grades in a wide variety of types and which can be divided according to basis weight in two grades: papers with a single ply and a basis weight of 25-300 g/m² and boards manufactured in multi-ply technology and having a basis weight of 150-600 m/m². It should be noted that the borderline between paper and board is flexible since board grades with lightest basis weights are lighter than the heaviest paper grades. Generally speaking, paper is used for printing and board for packaging.

The subsequent descriptions are examples of values presently applied for fiber webs, and there may be considerable fluctuations from the disclosed values. The descriptions are mainly based on the source publication Papermaking Science and

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Technology, section Papermaking Part 3, edited by Rautiainen, P., and published by Paper Engineers’ Association, Helsinki 2009, 404 pages.

Mechanical-pulp based, i.e. wood-containing printing papers include newsprint, uncoated magazine and coated magazine paper.

Today's newsprint furnishes mostly contain between 80 and 100 % deinked pulp (DIP). The rest of the furnish is mechanical pulp (typically TMP). However, there is also newsprint made of 100 % mechanical fiber furnishes. DIP based newsprint may contain up to 20 % filler. The filler content of a virgin-fiber based newsprint furnish is about 8 %.

General values for CSWO newsprint can be regarded as follows: basis weight 4048.8 g/m², PPS s10 roughness (SCAN-P 76-95) 4.0-4.5 pm, Bendtsen roughness (SCAN-P21:67) 150 ml/min, density 600-750 kg/m³, brightness (ISO 2470:1999) 58-59 %, and opacity (ISO 2470:1998) 92-95%.

Uncoated magazine paper (SC-supercalendered) grades usually contain 50 % 15 75 % mechanical pulp, 5 % - 25 % chemical pulp, and 10 % - 35 % filler. The paper may also contain DIP. Typical values for calendered SC paper (containing e.g. SC-C, SC-B, and SC-A/A+) include basis weight 40-60 g/m², ash content (SCAN-P 5:63) 0-35%, Hunter gloss (ISO/DIS 8254/1) <20-50%, PPS s10 roughness (SCAN-P 76:95) 1.0-2.5 pm, density 700-1250 kg/m³, brightness (ISO 2470:1999) 20 62-75%, and opacity (ISO 2470:1998) 90-95%.

Coated mechanical papers include for example MFC (machine finished coated), LWC (lightweight coated), MWC (medium weight coated), and HWC (heavy weight coated) grades. Coated mechanical papers usually contain 45 % -75 % mechanical or recycled fiber and 25 % - 55 % chemical pulp. Semi chemical pulps are typi25 cal in LWC paper grades made in the Far East. The filler content is about 5 % -10

%. The grammage is typically in the range 40-80 g/m2.

General values for LWC paper can be regarded as follows: basis weight 40-70 g/m², Hunter gloss 50-65%, PPS S10 roughness 1.0-1.5 pm (offset) and 0.6-1.0 pm (roto), density 1100-1250 kg/m³, brightness 70-75%, and opacity 89-94%.

General values for MFC paper (machine finished coated) can be regarded as follows: basis weight 48-70 g/m², Hunter gloss 25-40%, PPS S10 roughness 2.2-2.8 pm, density 900-950 kg/ m³, brightness 70-75%, and opacity 91-95%.

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General values for MWC paper (medium weight coated) can be regarded as follows: basis weight 70-90 g/ m², Hunter gloss 65-70%, PPS S10 roughness 0.6-1.0 pm, density 1150-1250 kg/ m³, brightness 70-75%, and opacity 89-94%.

Wood free paper is divided into two segments: uncoated and coated. Convention5 ally, the furnish of wood free papers consists of bleached chemical pulp, with less than 10 % mechanical pulp.

Typical values are for uncoated WFU Copy paper: grammage 70-80 g/m², Bendtsen roughness 150-250 ml/min and bulk > 1.3 cm³/g; for uncoated offset paper: grammage 60-240 g/m², Bendtsen roughness 100-200 ml/min and bulk 1.210 1.3 cm³/g; and for color copy paper: grammage 100 g/m², Bendtsen roughness <

ml/min and bulk 1.1 cm³/g.

In coated pulp-based printing papers (WFC), the amounts of coating vary widely in accordance with requirements and intended application. The following are typical values for once- and twice-coated, pulp-based printing paper: once-coated basis 15 weight 90 g/ m², Hunter gloss 65-80%, PPS s10 roughness 0.75-1.1 pm, brightness 80-88%, and opacity 91-94%, and twice-coated basis weight 130 g/ m², Hunter gloss 70-80%, PPS S10 roughness 0.65-0.95 pm, brightness 83-90%, and opacity 95-97%.

Containerboard includes both linerboard and corrugating medium. Liners are di20 vided according to their furnish base into Kraft liner, recycled liner and white top liner. Liners are typically 1- to 3-ply boards with grammage varying in the range 100-300 g/m².

Linerboards are generally uncoated, but the production of coated white-top liner is increasing to meet higher demands for printability.

The main cartonboard grades are folding boxboard (FBB), white-lined chipboard (WLC), solid bleached board (SBS) and liquid packaging board (LPB). In general, these grades are typically used for different kinds of packaging of consumer goods. Carton board grades vary from one- up to five-ply boards (150-400 g/m²). The top side is usually coated with from one to three layers (20-40 g/m²); the back side has less coating or no coating at all. There is a wide range of different quality data for the same board grade. FBB has the highest bulk thanks to the mechanical or chemi mechanical pulp used in the middle layer of the base board. The middle layer of WLC consists mainly of recycled fiber, whereas SBS is made from chemical pulp, exclusively.

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FBB’s bulk typically is between 1.1-1.9 cm³/g whereas WLC is on range 1.1-1.6 cm³/g and SBS 0.95-1.3 cm³/g. The PPS-s10-smoothess is respectively for FBB between 0.8 - 2.1 pm, for WLC 1.3- 4.5 pm and for SBS 0.7 - 2.1 pm.

Release paper is used in label base paper in various end-use applications, such 5 as food packaging and office labels. The most common release paper in Europe is supercalendered glassine paper coated with silicone to provide good release properties.

Typical values for supercalendered release papers are basis weight 60 - 95 g/m², caliper 55-79 pm, IGT 12-15 cm, Cobb Unger for dense side 0.9-1.6 g/m² and for 10 open side 1.2-2.5 g/m².

Coated label paper is used as face paper for release, but also for coated backing paper and flexible packings. Coated label paper has a grammage of 60-120 g/m²and is typically sized or pre-coated with a sizer and single-blade coated on one side. Some typical paper properties for coated and calendered label paper are 15 basis weight 50-100 g/m², Hunter gloss 70-85%, PPS s10 roughness 0.6-1.0 pm,

Bekk smoothness 1500-2000 s and caliper 45-90 pm.

By the invention many advantages are achieved for example sticking problems are eliminated, and thus dust problems are minimized, increased cleanliness and better runnability and higher production capacity is achieved. Also the lifetime of cal20 ender roll or belt, or their coatings is increased, since wearing and damaging pick due to sticking is decreased. The invention also makes it possible to use water moisturizing in increased amounts. The possibility of moisturizing also makes the calendering more efficient and thus quality results and production capacity improve. The fiber web treated by the method or in the system has dry, stiff surface 25 and cold middle layer with high moisture content and is thus optimal for calendering and sticking and picking problems are avoided.

In the following the invention is further explained in detail with reference to the accompanying drawing in which:

In figures 1 is very schematically shown an example of the treatment system ac30 cording to the invention,

In figure 2 is very schematically shown another example of the treatment system according to the invention,

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In figure 3 is very schematically shown yet another example of the treatment system according to the invention,

In figure 4 is very schematically shown yet another example of the treatment system according to the invention,

In figure 5 is a schematical example of graphs showing in thickness direction optimal moisture content and temperature of the fiber web and

In figure 6 is a schematical example showing moisture content in thickness direction of the fiber web after moisturizing and after surface drying zone.

In the following description same reference signs designate for respective compo10 nents etc. unless otherwise mentioned and it should be understood that the examples are susceptible of modification in order to adapt to different usages and conditions within the frames of a calender.

In the example of figure 1 the fiber web W is guided by a guide roll 13 towards a calender 10 comprising two calender rolls 11,12 and in between of which the cal15 endering nip N is formed. The calender roll 11 is a heated thermo roll. Another guide roll 14 is located before the calender 10 by which guide roll 14 the fiber web is guided onto the heated thermo roll 11 by which the surface drying zone Z is formed as a wrap angle A of the fiber web W on the thermo roll 11. Thus surface drying of the fiber web W is provided under low contact pressure during the run of 20 the fiber web W on the thermo roll. The wrap angle is 90 - 230 ° and the contact pressure in the surface drying zone Z is 1 - 5 kPa.

In the example of figure 2 the fiber web W is guided by guide rolls 13, 14 towards a calender 10 comprising two calender rolls 11, 12 and in between of which the calendering nip N is formed. The calender roll 11 is a heated thermo roll. Between 25 the guide rolls 13, 14a contact drying roll 15 is located by which the surface drying zone Z is formed as a wrap angle A of the fiber web W on the contact drying roll

15. Thus surface drying of the fiber web W is provided under low contact pressure during the run of the fiber web W on the contact drying roll 15. The wrap angle is 90 - 230 ° and the contact pressure in the surface drying zone Z is 1 - 5 kPa and 30 temperature of the contact drying roll 15 is 60 - 100 °C. Between the contact drying roll 15 and the calender 10 a moisture sensor 21 is located by which the surface moisture content of the fiber web W is measured and based on the measurement results the drying effect of the contact drying roll 15 is adjusted.

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In the example of figure 3 the fiber web W is guided by a guide roll 13 towards a calender 10 comprising two calender rolls 11,12 and in between of which the calendering nip N is formed. The calender roll 11 is a heated thermo roll. Before the guide roll 13 a drying cylinder group is located, of which last three drying cylinders 5 24, 25, 26 are shown. The fiber web W is moisturized by a moisturizing device 27 at the second last drying cylinder 25. By the last drying cylinder 26 the surface drying zone Z is formed as a wrap angle A of the fiber web W on the drying cylinder 26. Thus surface drying of the fiber web W is provided under low contact pressure during the run of the fiber web W on the drying cylinder 26. The wrap angle is 90 10 230 ° and the contact pressure in the surface drying zone Z is 1 - 5 kPa and temperature of the drying cylinder 26 is 60-100 °C.

In the example of figure 4 the fiber web W is guided towards a calender 10 comprising two calender rolls 11, 12 and in between of which the calendering nip N is formed. The calender roll 11 is a heated thermo roll. An infrared dryer 22 using 15 long wave lengths about 3 pm or over 6 pm is located to form the surface drying zone Z. Thus surface drying of the fiber web W is provided as contactless drying during the run of the fiber web W passing the infrared dryer 22 such that the dryness of the surface is over 90%, i.e. the moisture content is at most 10% in depth of 5 - 15 pm in the thickness of the fiber web measured from the outer surface of 20 the fiber web.

In figure 5 is by graphs M, T are shown in thickness direction of the fiber web W optimal moisture content M and temperature T of the fiber web after the fiber web W has passed the surface drying zone Z before the calender 10. In the example of figure 5 both sides of the fiber web W have passed the surface drying zone Z. As 25 can be seen from the moisture content graph M the moisture content on the surface and near the surface of the fiber web W is very low increasing towards the middle of the fiber web W and then evening to a bit lower level in the middle of the fiber web W. As can be seen from the temperature graph T the temperature on the surface and near the surface of the fiber web W is high decreasing towards the 30 middle of the fiber web W and then evening in the middle of the fiber web W.

In figure 6 by graphs M1, M2 are shown moisture content in thickness direction of the fiber web W after moisturizing by a moisturizing device 28 by graph M1 and after drying in a surface drying zone Z by graph M2. As can be seen from the moisture content graph M1 the moisture content on the surface of the fiber web W after 35 moisturizing is high. And as can be seen from the moisture content graph M2 the moisture content on the surface and near the surface of the fiber web W after dry13 ing in the surface drying zone is very low increasing towards the middle of the fiber web W and then evening to a bit lower level in the middle of the fiber web W.

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Reference signs used in the drawing:

calender thermo roll counter roll

13 guide roll guide roll contact drying roll moisture sensor infrared drying device

24 drying cylinder drying cylinder drying cylinder moisturizing device moisturizing device

A wrap angle

M, M1, M2 moisture content

N calender nip

T temperature

W fiber web

Z drying zone

Claims

The claims

A method for treating a fibrous web, wherein the fibrous web (W) is calendered in at least one nip (N) of the calender (10) and in the direction of travel of the fibrous web (W) before the calender (10) on one side of the fibrous web or

A method according to claim 1, characterized in that the fiber web surface (s) are dried by contact drying at low contact pressure in the surface drying zone (Z), wherein in the drying zone (Z), the fiber web (W)

15 contact pressures are 1 to 5 kPa.

3. A method according to claim 1, characterized in that the surface (s) of the fibrous web are dried in a non-contact drying zone via an infrared dryer using long wavelengths of about 3 µm or

8pm to 6pm.

Method according to one of Claims 1 to 3, characterized in that the moisture content of the surface (s) of the fibrous web (W) is measured by a moisture sensor between the surface drying zone (Z) and the calender and the result of the moisture measurement.

Based on this, the drying effect of the surface drying zone (Z) is controlled by adjusting the drying temperature and / or drying time and / or contact pressure in the case of contact drying.

A processing system for treating a fibrous web comprising a calendar

30 (10) and a surface drying zone (Z) located in the direction of travel of the fibrous web (W) before the calender (10), wherein one side of the fibrous web or both sides of the fibrous web (W) are only surface dried. non-contact drying so that the surface moisture content of the surface-dried side (s) of the fibrous web (W) does not exceed 10% in the thickness direction of the fibrous web at a thickness of 5 to 15 µm, measured from the outer surface of the fibrous web.

5 only half surface dried in the surface drying zone (Z) characterized in that the fiber web surface (s) are dried by contact drying or non-contact drying so that the surface moisture of the fibrous web (W) .

Treatment system according to Claim 5, characterized in that the surface drying zone (Z) comprises the passage of the fibrous web (W) on a heated roll (11; 15; 25).

A treatment system according to claim 6, characterized in that the heated roll is a calender roll (11) or a contact drying roll (15) or a drying cylinder (25).

A processing system according to claim 5, characterized in that

The surface drying zone (Z) comprises an infrared dryer operating at long wavelengths of about 3 µm or more than 6 µm.

A treatment system according to any one of claims 5 to 8, characterized in that the treatment system comprises a moisture sensor (21), preferably a reflection-based IR moisture sensor, between a surface drying zone (Z) and a calender (10).