EP3012371A1

EP3012371A1 - Method of treating a fiber web and a calender for treating a fiber web

Info

Publication number: EP3012371A1
Application number: EP14189733.0A
Authority: EP
Inventors: Mika Viljanmaa; Jari Ilomäki
Original assignee: Valmet Technologies Oy
Current assignee: Valmet Technologies Oy
Priority date: 2014-10-21
Filing date: 2014-10-21
Publication date: 2016-04-27
Also published as: CN205152719U; DE202015105426U1

Abstract

The invention relates to a method of treating a fiber web, in which the fiber web (W) is calendered in at least one calender nip (N) formed between two calender rolls (15,16) or in a calender comprising a belt zone, which is formed by a belt guided along surface of a calender roll, in which method before the calender in running direction of the fiber web (W) at least one side of the fiber web is cooled by at least one spray cooler (11, 12; 21, 22) before calendering such that temperature of the fiber web (W) is below or at low level of the glass transition temperature range (T_gr). The invention also relates to a calender, which comprises at least one calender nip (N) formed be-tween two calender rolls (11, 12) or a belt calendering zone, which is formed by a belt guided along surface of a heated calender roll. The calender further comprises at least one spray cooler (11, 12; 21, 22) for cooling and moisturizing at least one side of the fiber web (W) before calendering such that temperature the fiber web (W) is below or at low level of the glass transition temperature range (T_gr).

Description

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 preamble part of claim 1 and to a calender according to preamble part of claim 8.
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 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 comprises at least one slitter-winder for forming customer rolls as well as a roll packaging apparatus. 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 and final-calendering is generally 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 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 resilient-surfaced roll adjusts itself to the forms of the web surface and presses the opposite side of the web evenly against the smooth-surfaced press roll. The nips can be formed also by using instead one of roll a belt or a shoe as known from prior art. Many different kinds of calenders to be used as a pre-calender and/or as a final-calender are known, for example hard nip calenders, soft nip calenders, supercalenders, metal belt calenders, shoe calenders, long nip calenders, multinip calenders etc.
One of main focus points in recent times in developing calendering of fiber webs is to achieve required surface properties and simultaneously achieve required bulkiness i.e. relation of thickness of the web to its grammage (basis weight). When the fiber web has high bulkiness, the basis weight can be reduced, which results as considerable savings in raw material.
In EP patent application publication 2682520A1 is disclosed a method for producing a fiber web, in which method the fiber web is calendered in at least one calendering nip of at least one calender and reeled up in a reel-up. The fiber web is cooled by cooling means before calendering to temperatures of not higher than 40 °C, preferably to temperature in the range of 10 - 30 °C. As an object of this known method has been disclosed to create a method for producing fiber webs in which high bulkiness is received with less raw stock. According to this known arrangement the fiber web is calendered to bulk loss less than 4 %.
It is also known from prior art to calender fiber webs in a belt calender, typically in a metal belt calender, in which a calendering zone is formed between surface of a calender roll and a belt guided over the roll. The belt is formed as a loop guided by guide rolls located inside or outside the loop. In some known applications of the belt calendering a calendering zone is formed by the belt around a heated roll and used as a pre-heating zone into which the fiber web is first led and then calendered in a roll nip between the heated calender roll and another calender roll. Further in some known applications of the belt calendering the fiber web is first calendered in a roll nip between a heated calender roll and another calender roll and then heated in a calendering zone formed by a belt running around the heated roll. In these known calenders the fiber web is calendered in temperatures 50 - 130 °C.
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 control the curl of the fiber web.
One important factor influencing the properties of the surface of the fiber web achieved by calendering is the roughness volume of the surface of the fiber web. The roughness volume is the volume below an imaginary level set on top of the roughness peaks of the roughness level.
An object of the invention is to create a more effective method of treating a fiber web compared to methods known from prior art, especially in respect of roughness and bulk level; advantageously to bulk level of 0,8 - 2,5 cm³/g and/or to roughness level of PP_s10 0,4 - 10 µm and/or to roughness level of Bendtsen 0,01 - 2000 ml/min.
An object of the invention is to create a more effective calender compared to calenders known from prior art, especially in respect of roughness level.
Another non-limiting object of the invention is to create an improved method of treating and a calender for fiber webs in respect of bulk level.
To achieve the objects mentioned above and later the method according to the invention is mainly characterized by the features of the characterizing part of claim 1.
The calender according to the invention is mainly characterized by the features of the characterizing part of claim 8.
Advantageous features and embodiments of the invention are defined in the dependent claims.
According to an advantageous feature of the invention in the method at least one side of the fiber web is cooled by a spray cooler before calendering such that temperature of the fiber web is below or at low level of the glass transition temperature range (T_gr). Different fiber web grades have different glass transition temperature ranges (T_gr). Typically glass transition temperature range of dry pulp is 200 - 250 °C. Moisture, such as water addition decreases the glass transition temperature range of cellulose significantly, depending of crystallinity, typically down to 20 - 80 °C.
Advantageously by cooling the fiber web below or at low level of the glass transition temperature range elastic modulus of middle layers of the fiber is increased. When the elastic modulus of the middle layers is increased, in calendering to surface layers of the fiber web are under increased nip pressure, by which roughness volume is reduced and surface layers are compressed.
According to an advantageous feature of the invention in the method the fiber web is moisturized by applying moisturizing agent by means of the spray cooler such that a moisture film is provided onto at least one of the surfaces of the fiber web.
According to an advantageous feature of the invention in the method the fiber web is moisturized by applying moisturizing agent by means of the spray cooler such that moisture film is vaporized completely or partly from the surfaces of the fiber web by means of high velocity air blow.
According to an advantageous embodiment the spray cooler functions like an air source heat blower, ASHB, in which liquid from the moisturized fiber web surface is vaporized by high velocity impingement air jets and heat is absorbed into the air and released outdoors with outgoing air. According to advantageous feature water or other high volatile liquid, that is sprayed on to the fiber web, works as refrigerant.
According to advantageous feature moisturizing agent spray is located in a ventilated shield box such that no liquid drops can escape.
Advantageously the ventilated shield box comprises suction zone against the fiber web such a way that suction zone skirts round the whole shield box.
According the invention at least one cycle of cooling and/or moisturizing is used and advantageously more than one cycles are used, which have similar or different stages of cooling and/or moisturizing.
The elastic modulus of the middle layers is 100 - 10 000 MPa.
The temperatures of the glass transition temperature range are 10 - 120 °C.
According to an advantageous feature as cooling agent cool and dry outside or basement air is used.
Advantageously the cooling of the fiber web is started 1 ms - 10 s before the point when the fiber web enters calendering i.e. first calendering nip or the only calendering nip or beginning of belt calendering zone.
Advantageously in the method according to the invention the fiber web after drying is moisturized and again dried which results as improved properties of the fiber web as the micro size pore on the surface of the fiber web is minimized, thus effect of calendering and also of coating is improved and also bulk in coating is saved.
The method according to the invention advantageously utilizes the heat energy of the fiber web as the partial steam pressure of the liquid layer is increased as the liquid is heated by the web. Higher steam pressure increase vaporation and thus the cooling effect.
According to an advantageous feature in the method by moisturizing moisture profile is influenced temperature and moisture profile of the fiber web and then by calendering the thickness profile of the fiber web.
According to the invention as moisturizing agent a fluid or liquid, advantageously liquid or water-alcohol solution, in particular a water starch solution is used.
The calendering roll is advantageously a thermo shock resistant calendering roll, for example a forged steel shell roll.
According to an advantageous feature of the invention the calender comprises at least one spray cooler for cooling and moisturizing at least one side of the fiber web before calendering, which device advantageously comprises one set of moisturizing means under use and one set of moisturizing means stand-by and one set of moisturizing means as spare means. Each set has advantageously quick coupling means in order to provide fast changes, when needed.
According to an advantageous feature of the invention the calender comprises cooling means, for example pumps and nozzles for providing cooling agent for cooling the fiber web.
According to an advantageous feature the spray cooler is self-supporting.
According to an advantageous feature the spray cooler is constructed as one module.
Advantageously the spray cooler is located in the basement area of the fiber web production site or above the main running line of the fiber web.
One set of moisturizing means comprises advantageously at least three nozzles for moisture spraying in cross direction of the fiber web such that threefold moisture coverage is achieved on the surface of the fiber web.
According to an advantageous feature the spray cooler comprises means for controlling at least one of the following:

1) distance of the moisturizing nozzles from the surface of the fiber web, 50 - 200 mm, advantageously 80 - 160 mm
2) amount of moisturizing agent applied by one nozzle, 0,1 - 0,5 l/min, advantageously 0,15 - 0,25 l/min
3) pressure of the moisturizing agent, 1,5 - 5 bar
4) angle of the moisturizing agent spray in respect of level of the surface of the fiber web, 90 - 150 °, advantageously 100 - 20 °
5) spray angel in respect of the surface of the fiber web, +/- 45 °, advantageously +/- 15 ° - +/- 40 °
6) spray tip offset of nozzles, 7 - 10 °.

Advantageously the means for controlling control at least the angle of the moisturizing agent spray in respect of the level of the surface of the fiber web and the amount of moisturizing agent applied by one nozzle, which is advantageously controlled by pressure of the moisturizing agent in relation to the running speed of the fiber web.
According to an advantageous feature of the invention the calender comprises at least one calender roll nip or a belt calendering zone, which is formed by a belt guided along surface of a heated calender roll, spray cooler located before the calender in the running direction of the fiber web and means to control the cooling effect of the cooling means.
Advantageously at least one roll nip is formed between a heated calender roll and another calender roll.
The calender according to the invention is according to one embodiment of the invention is a pre-calender and the method according to the invention is used to pre-calender the fiber web.
The calender according to the invention is according to one embodiment of the invention is a final-calender and the method according to the invention is used to final-calender the fiber web.
According to an advantageous feature the belt of the belt calender is a metal, polymer, coated metal or polymer belt.
Advantageously the fiber web is cooled-moisturized by spraying cooling moisture spray/sprays at least on one of the surfaces of the fiber web and then the sprayed agent is vaporized to the cool web.
According advantageous features of the invention the cooling means is/are device for blowing or creating a flow of cooled gas, for example air.
According to an advantageous feature of the invention the gas for cooling flow or blow is dry, cool, outside air of which especially in the Nordic and in corresponding climate zone located countries is available an unlimited supply in required temperatures during most times of the year and no further device is needed for cooling or drying the gas.
According to an advantageous feature of the invention a moisturizing device is located before the calender for providing moisture vaporization from the fiber web with latent thermal cooling effect. The moisture vaporization can be enhanced by the blow speed, for example 30 - 60 m/s, and low air humidity.
Advantageously the invention is utilized when treating fiber web grades such as:

Paper and board are available in a wide variety of types and 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 fibrous webs, and there may be considerable fluctuations from the disclosed values. The descriptions are mainly based on the source publication Papermaking Science and 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 40 - 48.8 g/m², PPS s10 roughness (SCAN-P 76-95) 4.0 - 4.5 µm, 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 - 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 µm, density 700 - 1250 kg/m³, brightness (ISO 2470:1999) 62 - 75 %, and opacity (ISO 2470:1998) 90 - 95 %.
Coated mechanical papers include for example MFC (machine finished coated), LWC (light weight 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. Semichemical pulps are typical 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 µm (offset) and 0.6 - 1.0 µm (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 µm, density 900 - 950 kg/ m³, brightness 70 - 75 %, and opacity 91 - 95%.
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 µm, density 1150 - 1250 kg/ m³, brightness 70 - 75 %, and opacity 89-94%.
Woodfree paper is divided into two segments: uncoated and coated. Conventionally, the furnish of woodfree 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 1.2 - 1.3 cm³/g; and for color copy paper: grammage 100 g/m², Bendtsen roughness < 50 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 weight 90 g/ m², Hunter gloss 65 - 80 %, PPS s10 roughness 0.75 - 1.1 µm, 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 µm, brightness 83 - 90 %, and opacity 95 - 97 %.
Containerboard includes both linerboard and corrugating medium. Liners are divided according to their furnish base into kraftliner, recycled liner and white top liner. Liners are typically 1- to 3-ply boards with grammages 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 chemimechanical 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.
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 µm, for WLC 1.3 - 4.5 µm and for SBS 0.7 - 2.1 µm.
Release paper is used in label base paper in various end-use applications, such 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 µm, IGT 12 - 15 cm, Cobb Unger for dense side 0.9 - 1.6 g/m² and for 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/m² and is typically sized or precoated with a sizer and single-blade coated on one side. Some typical paper properties for coated and calendered label paper are basis weight 50 - 100 g/m², Hunter gloss 70 - 85 %, PPS s10 roughness 0.6 - 1.0 µm, Bekk smoothness 1500 - 2000 s and caliper 45 - 90 µm.
In the following the invention is further explained in detail with reference to the accompanying drawing in which:

In figures 1A-1B is very schematically shown examples of the invention.
In figures 2A-2B is very schematically shown cooling examples of a fiber web.
In figure 3 is very schematically shown an example of an air turning device.
In figure 4 is a schematical example of a spray cooler.
In figure 5 is a schematical example of nozzle arrangement of a spray cooler.

In the following description same reference signs designate for respective components 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 figures 1A - 1B a calender is shown, which in this example comprises two calender rolls 15, 16 between of which a calendering nip N is formed. In the calendering nip N the fiber web W is calendered under the calendering pressure formed by the calender rolls 15, 16. The calender can also be a belt calender, advantageously a metal, coated metal or polymer belt calender, in which the fiber web W is calendered in a calendering zone formed between the surface of a heated calender roll and a belt guided over the heated calender roll. Further the calender comprises a spray cooler 11, 12 located before the calender in the running direction of the fiber web W. The spray cooler 11, 12 is provided to moisturize the fiber web W by moisturizing agent such that a moisture film is provided onto the surface of the fiber web i.e. no separate droplets exists on the surface of the fiber web. As moisturizing agent aliquid, advantageously water or water-alcohol solution, in particular a water starch solution is used. The spray cooler 11, 12 is provided advantageously to apply cooling agent and dry cool outside or basement air. The spray cooler comprises control means for controlling at least one of the following: distance of the moisturizing nozzles from the surface of the fiber web, amount of moisturizing agent applied by one nozzle, pressure of the moisturizing agent, angle of the moisturizing agent spray in respect of level of the surface of the fiber web, coverage of the moisture sprays on the surface of the fiber web. The fiber web W is guided by means of guide rolls 13, 14 to and from the spray cooler 11, 12.
In the method the fiber web is cooled and moisturized by the spray cooler 11,12 located before the calender in running direction of the fiber web W is calendered in the calender formed by the calender rolls 15, 16 forming the calendering nip N. Typically in fiber web production the fiber web W is heated for example in drying section, typically preceding pre-calender and final-calender, when coated fiber web grades are produced, or preceding final-calender when uncoated fiber web grades are produced. The calender can be a pre-calender or a final-calender. In the method the fiber web W is cooled before calendering such that temperature of middle layers of the fiber web is below or at low level of the glass transition temperature range (T_gr) by which elastic modulus of middle layers of the fiber is increased. When the elastic modulus of the middle layers is increased, in calendering to surface layers of the fiber web are under increased nip pressure, by which roughness volume is reduced and surface layers are compressed. At least one cycle of cooling and/or moisturizing or moisturizing cooling is used and advantageously more than one cycles are used, which have similar or different stages of cooling and/or moisturizing.
As shown in the figures 1A-1B the spray cooler 11, 12 is arranged such that the fiber web W makes a U-shaped run upwards or downwards from its main running direction such that the spray cooler is advantageously located in the basement area of the fiber web production site or above the main running line of the fiber web. and the spray cooler is advantageously formed as two part construction; each part located at one arm of the U-shape. The spray cooler advantageously comprises one set of moisturizing means under use, one set of moisturizing means stand-by and one set of moisturizing means as spare means. Each set has advantageously quick coupling means in order to provide fast changes, when needed. The cooling means of the spray cooler is advantageously a blower for providing cooling agent for cooling the fiber web. One set of moisturizing means comprises advantageously at least three nozzles for moisture spraying in cross direction of the fiber web such that threefold moisture coverage is achieved on the surface of the fiber web.
In figures 2A-2B is shown cooling examples of a fiber web. On the Y-axis of the figures is indicated temperature of the fiber web in degrees Celsius and on the X-axis the cooling time of the fiber web in seconds. The base of the fiber web is indicated by line B and the surface of the fiber web by line S. In the example of figure 2A cooling-moisturizing is used and in the example of figure 2B no moisturizing is used i.e. only cooling with dry cooling agent is used. As can be seen from the figure 2A surface is cooled rapidly, but internal heat resistance first restricts cooling effect due to the influence of middle layers, i.e. base B of the fiber web but as the warmed moisture vaporizes the cooling effect speeds up and cooling is rapid. As can be seen from the figure 2B without the influence of moisture the cooling speeds of the surface S and the base B follow same pattern. Depending on the thickness of the fiber web the distance between the lines B, S in figure 2B varies; when the thickness decreases the distance decreases and vice versa.
In figure 3 is shown an example of an air turning device 21, 22 that can be used to turn the run of the fiber web W and simultaneously as spray cooler 11, 12 providing the same effect as explained in connection with the examples of figures 1A-1B.
In figure 4 is shown an example of a spray cooler 11, 12 comprising nozzles 31 for creating a spray 32, air suction 33 and drain lines 34. In the example of figure 4 one spray cooler 11, 12 is located on each side of the fiber web W for moisturizing the fiber web by double-faced air blowing unit in which temperature of the fiber web W is below or at low level of the glass transition temperature range. The spray cooler functions like an air source heat blower, in which liquid from the moisturized fiber web surface is vaporized by high velocity impingement air jets and heat is absorbed into the air and released outdoors with outgoing air. From the nozzles 31 of the device 11, 12 water or other high volatile liquid, that is sprayed as spays 32 on to the fiber web, works as refrigerant. The spray cooler 11, 12 is formed as a ventilated shield box inside of which moisturizing agent sprays 32 are located such that no liquid drops can escape but excess liquid is removed via the drain line 34. The air suctions 33 create a suction zone against the fiber web W such a way that suction zone skirts round the whole shield box i.e. the spray cooler on one side of the fiber web W. Suction air volume is at least 0,2 - 0,5 m³/s per fiber web width and suction under pressure is advantageously 500 - 1500 Pa.
In figure 5 is shown an advantageous example of a nozzle arrangement of a spray cooler 11, 12 comprising nozzles 31 for creating moisturizing sprays 32 for cooling the fiber web by a double-faced air blowing unit in which such that temperature of the fiber web W is cooled below or at low level of the glass transition temperature range. The spray tip offset A of the nozzles 31 is advantageously 7 - 10 °.

Reference signs used in the drawing:

11: spray cooler
12: spray cooler
13: guide roll
14: guide roll
15: calender roll
16: calender roll
21: air turning device
22: air turning device
31: nozzle
32: spray
33: suction
34: drain line
W: fiber web
N: calender nip
B: base
S: surface
A: spray tip offset

Claims

Method of treating a fiber web, in which the fiber web (W) is calendered in at least one calender nip (N) formed between two calender rolls (15,16) or in a calender comprising a belt zone, which is formed by a belt guided along surface of a calender roll, characterized in that before the calender in running direction of the fiber web (W) at least one side of the fiber web is cooled by at least one spray cooler (11, 12; 21, 22) before calendering such that temperature of the fiber web (W) is below or at low level of the glass transition temperature range (T_gr).
Method according to claim 1, characterized in that the fiber web is moisturized by applying moisturizing agent by means of the spray cooler (11, 12; 21, 22) such that a moisture film is provided onto at least one of the surfaces of the fiber web.
Method according to claim 1 or 2, characterized in that the fiber web is moisturized by applying moisturizing agent by means of the spray cooler (11, 12; 21, 22) such that moisture film is vaporized completely or partly from the surfaces of the fiber web by means of high velocity air blow.
Method according to any of previous claims, characterized in that at least one cycle of cooling and/or moisturizing is used and advantageously more than one cycles are used, which have similar or different stages of cooling and/or moisturizing.
Method according to any of previous claims, characterized in that cooling of the fiber web is started 1 ms - 10 s before the point when the fiber web enters calendering i.e. first calendering nip or the only calendering nip or beginning of belt calendering zone.
Method according to any of previous claims, characterized in that as moisturizing agent a fluid, advantageously liquid, such as water or water-alcohol solution, in particular a water starch solution is used.
Method according to any of previous claims, characterized in that the fiber web is cooled-moisturized by spraying cooling moisture spray/sprays on the surface of the fiber web.
Calender, which comprises at least one calender nip (N) formed between two calender rolls (11, 12) or a belt calendering zone, which is formed by a belt guided along surface of a heated calender roll, characterized in that the calender further comprises at least one spray cooler (11, 12; 21, 22) for cooling and moisturizing at least one side of the fiber web (W) before calendering such that temperature the fiber web (W) is below or at low level of the glass transition temperature range (T_gr).
Calender according to claim 8, characterized in that the spray cooler (11, 12; 21, 22) is arranged such that the run of the fiber web (W) makes a U-shaped run upwards or downwards from its main running direction.
Calender according to claim 8 or 9, characterized in that the spray cooler (11, 12; 21, 22) is advantageously located in the basement area of the fiber web production site or above the main running line of the fiber web.
Calender according to any of claims 8-10, characterized in that the spray cooler comprises one set of moisturizing means under use and one set of moisturizing means stand-by and one set of moisturizing means as spare means.
Calender according to claim 11, characterized in that at least one set of moisturizing means comprises advantageously at least three nozzles for moisture spraying in cross direction of the fiber web such that threefold moisture coverage is achieved on the surface of the fiber web
Calender according to claim 8-12, characterized in that at least one calendering roll is a thermo shock resistant calendering roll.
Calender according to any of claims 8-13, characterized in that the spray cooler (11, 12; 21, 22) is self-supporting and that the spray cooler (11, 12; 21, 22) is constructed as one module.
Calender according to any of claims 8-14, characterized in that the spray cooler (11, 12; 21, 22) the fiber web before calendering comprises means for controlling at least one of the following: distance of the moisturizing nozzles from the surface of the fiber web, amount of moisturizing agent applied by one nozzle, pressure of the moisturizing agent, angle of the moisturizing agent spray in respect of level of the surface of the fiber web, coverage of the moisture sprays on the surface of the fiber web.