FI20205490A1

FI20205490A1 - Method for forming a fiber web and a forming section for a fiber web

Info

Publication number: FI20205490A1
Application number: FI20205490A
Authority: FI
Inventors: Reijo Pietikäinen
Original assignee: Valmet Technologies Oy
Priority date: 2020-05-15
Filing date: 2020-05-15
Publication date: 2021-11-16
Also published as: DE102021112426A1

Abstract

The invention relates to a method for forming a fiber web, which has at least one layer, in a forming section of a fiber web production line, in which forming section the fiber web (W) is supported by a wire (10; 20; 30) and in which forming section at least part of the sizing of the fiber web (W) is provided by applying sizing agent by a curtain type application device (C10; C20; C30) onto at least one layer of the fiber web (W) in the forming section of the fiber web production line. The sizing agent is applied onto the at least one layer of the fiber web (W) during at least one run, wherein the running direction of the run of the wire (10; 20; 30) and the fiber web layer (W) is deviated substantially from horizontal and the running direction is downwards inclined. The invention also relates to a forming section of a fiber web production line for forming a fiber web, which has at least one layer, and which forming section comprises at least one wire (10; 20; 30) for supporting the at least one layer of the fiber web (W) and which forming section comprises at least a curtain type application device (C10; C20; C30) for applying at least part of the sizing of the fiber web onto the at least one layer of the fiber web (W) in the forming section of the fiber web production line. The sizing agent is configured to be applied onto the at least one layer of the fiber web during at least one run the fiber web layer (W), wherein running direction of the run of the wire and the fiber web layer is deviated substantially from horizontal and the running direction is downwards inclined during the at least one run.

Description

Method for forming a fiber web and a forming section for a fiber web Technical field The invention relates generally to producing fiber webs.

Particularly the invention relates to a method for forming a fiber web according to the preamble of the independent method claim and to a forming section for a fiber web according to the preamble of the independent forming section claim.

Background As known from the prior art in fiber web machines, especially in paper and board machines, the fiber web is produced and treated in an assembly formed by a number of apparatuses arranged consecutively in a process line.

A typical production and treatment line comprises a forming section comprising a headbox and a forming unit 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 sections for finishing the fiber web, for example, a size press, a calender, a coating section.

The production and treatment line also comprises typically at least one winder for forming customer rolls as well as a roll packaging apparatus.

In this description and the following claims by fiber webs are meant especially containerboard or cartonboard webs.

The task of a forming unit is to remove water from fiber suspension fed by the headbox.

When the web is manufactured of watery fiber stock, water in the N stock is removed on the forming section through a forming wire or forming N wires for starting the formation of the web.

Fibers remain on the forming wire 3 or between the forming wires moving together.

Depending on the grade of the 2 web being manufactured, different types of stocks are used.

The volume for z 30 which water can be removed from different stocks for achieving a web of good > quality is a function of many factors, such as e.g. a function of the desired basis S weight of the web, the design speed of the machine, and the desired level of S fines, fibers and fill materials in the finished product.

Many types of devices are known on the forming unit such as foil strips, suction boxes, turning rolls, suction rolls, and rolls provided with an open surface, which are used in many different arrangements and arrays when trying to optimize the volume, time and location of water being removed when forming the web. The manufacturing a high-quality end-product of desired grade is a function of the volume of dewatering, the dewatering method, the duration of dewatering, and the location of dewatering.

A commonly used method of making a multi-ply fiber web is based on the use of several separate web forming units in which the different layers of the fiber web are caused to be drained in a layer by layer fashion either onto one another or onto separate wires, in which case they are combined with one another after partial dewatering. Typically in multi-ply / multilayer fiber web production, i.e. when producing a fiber web having more than one layers, term *multi-ply” is used when the layers are formed separately in the forming section and term “multilayer” is used when a multilayer headbox is used for feeding suspension layers to the forming section even though these terms multi-ply / multilayer are used very often synonymously and thus the difference can be defined by the context only. A foam application system comprises typically a chemical dosing and mixing device, a pumping device, a foaming device, a piping system, and an application unit. The foaming is based on powerful mixing for adding air into the liquid-based substance with a surfactant additive, resulting substantial increase in the specific volume and thus making the handling and application of the substance much easier at small dry substance weights. The foam application device typically comprises an application head with a slot-type nozzle for extruding the foam onto the web. Very shortly after the application, N the foamy structure disintegrates, absorbs, and spreads into the surface N structure of the web, leaving a wetted substance layer.

S 2 In production of fiber webs, for example in production of paper or board webs, z 30 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 S and surface sizing. In internal sizing, sometimes called stock sizing, the sizing S agent is added to pulp in the wet end of the 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. Sizing is used in order to improve paper web properties, in particular water resistance, water absorption properties, strength, internal strength and bending stiffness. In addition, runnability as well as dusting tendency can be affected favorably. Sizing of a fiber web can also be cationic pulp sizing but as a disadvantages of this known method is low sizing response when large amounts of sizing agent is used, complicated chemistry of the short circulation system, poor retention and in large sizing agent dosages degradation of the formation. In pulp sizing by multilayer headbox of a forming section for middle layer additives are used for fixation of the sizing agent and thus compound achieved is firmer containing larger particles and fixation to the fiber web is increased. It is also known to apply spray sizing agent, for example so called spray starch, typically granular (uncooked) starch slurry, in between the layers of a multi-ply fiber web. Disadvantages of this known method are low sizing response and misting. It is also known to apply sizing agent onto surface of a single-layer fiber web by spray or foam application. Disadvantageous in this method is that the sizing agent remains on the surface of the fiber web and thus may easily be flushed away and also that sizing agent distribution in thickness direction of the fiber web is inclined as on the applied surface remains more sizing agent than reaches the other side and thus only minor strengthening is achieved, particularly with thick paper or board grades.

In FI patent publication 124556 is disclosed a method for the preparation of a hydrophobically sized layer of a fibrous web, comprising the steps of bringing water, microfibrillated cellulose (MFC), hydrophobic size, and a heat-sensitive surfactant into a foam; supplying the foam onto a forming fabric; dewatering the foam on the forming fabric by suction to form a web, subjecting the web to N drying, and heating the web to suppress the hydrophilic functionality of the N surfactant.

S 2 In US patent publication 7,892,613 is disclosed a method of making a multi- z 30 ply paper or paperboard while reducing weight basis of a top ply, the method > comprising the steps of: applying a mixture comprising starch and a filler to a 2 surface of a base ply to form an intermediate layer, the base ply includes a S preselected color; and applying the top ply to a surface of the intermediate layer wherein the intermediate layer is configured to obscure the color of the base ply when viewed through the top ply. In connection with this known method a sizer comprising a special applicator that is positioned over the

Fourdrinier machine is used and a liquid dispersion of additive is forced out of a narrow slot in the applicator and falls as a full-width curtain onto the wet stock.

In EP patent application publication 3640399 A1 is disclosed a method for sizing a multi-ply fiber web at least part of the forming is done in a twin-wire forming part formed between a wire for the bottom layer of the multi-ply fiber web and a wire for the top layer of the multi-ply fiber web, in which the layers for the multi-ply fiber web are joined and treated layers combined in the twin- wire part, whereby at least part of sizing of the multi-ply fiber web is provided by applying sizing agent in form of foam by a curtain type application device in between at least two layers of the multi-ply fiber web in forming section of a multi-ply fiber web production line. Also, in the EP publication is disclosed a forming section for a multi-ply fiber web comprises at least one twin-wire forming part formed between a wire for the bottom layer of the multi-ply fiber web and a wire for the top layer of the multi-ply fiber web, in which twin-wire part in the layers for the multi-ply fiber web are joined and treated layers combined, wherein the forming section comprises at least one curtain type application device for applying sizing agent in form of foam by in between at least two layers of the multi-ply fiber web in forming section of a multi-ply fiber web production line. In from prior art known methods and forming sections the sizing agent is applied on runs of the wires and the fiber web, during which the run is horizontal. This sometimes causes an effect called a back flow, during which N flow direction of the applied substance as whole does not follow running N direction of the wire and the fiber web but instead is at least part of the applied 3 substance flows to opposite direction than the running direction of the wire and 2 the fiber web and forms an accumulation of the substance behind the curtain. z 30 > An object of the invention is to create a method for sizing a fiber web and a S forming section for a fiber web, in which the disadvantages and problems of S prior art are eliminated or at least minimized.

O N

A particular object of the invention is to provide a method for sizing a fiber web and a forming section for a fiber web, by which the problems relating to sizing agent flow, especially relating to back flow, are solved. 5 Summary In order to achieve the abovementioned objects, the method for sizing a fiber web according to the invention is mainly characterized by the features of the characterizing clause of the independent method claim and the and a forming section for a fiber web according to the invention is mainly characterized by the features of the characterizing clause of the independent forming section claim. Advantageous embodiments and features are disclosed in the dependent claims.

According to the invention in the method for forming a fiber web, which has at least one layer, in a forming section of a fiber web production line, in which forming section the fiber web layer is supported by a wire and in which forming section at least part of sizing of the fiber web is provided by applying sizing agent by a curtain type application device onto the at least one layer of the fiber web in the forming section of a fiber web production line, wherein the sizing agent is applied onto the at least one layer of the fiber web during at least one run, wherein the running direction of the run of the wire and the fiber web layer is deviated substantially from horizontal and the running direction is downwards inclined.

S N According to an advantageous feature of the invention in the method a multi- 3 ply-fiber web, which has at least two layers, is sized and at least part of the 2 forming is done in a twin-wire forming part formed between a wire for the z 30 bottom layer of the multi-ply fiber web and a wire for the top layer of the multi- > ply fiber web, in which the layers for the multi-ply fiber web are joined and S treated layers combined in the twin-wire part, and in which at least part of sizing S of the multi-ply fiber web is provided by applying sizing agent by a curtain type application device in between at least two layers of the multi-ply fiber web in forming section of a multi-ply fiber web production line during at least one run, wherein the running direction of the run of the wire and the fiber web layer is deviated substantially from horizontal and the running direction is downwards inclined. According to an advantageous feature of the invention the run of the wire and the fiber web layer is deviated from horizontal downwards inclined in an angle of 5 — 60 degrees. According to an advantageous feature of the invention in the method the sizing agent is applied in form of foam.

According to an advantageous feature of the invention the sizing agent in form of foam is applied by a slot-type curtain application device. According to an advantageous feature of the invention suction and/or underpressure is created at the location of the curtain type application device a suction or an underpressure device on the opposite side of the fiber web layer and its support wire in relation to the curtain application device. Thus, absorption of the sizing agent into the fiber web layer is improved as well as application of the sizing agent foam is stabilized.

According to an advantageous feature of the invention conveyance and penetration of the sizing agent into the web layer and/or over a boundary between the joined web layers is guided by suction means and/or by a sleeve roll after the application of the sizing agent in form of foam by the curtain application device.

S N Advantageously the suction device is located on the opposite side of the fiber 3 web layer in relation to the curtain application device at least partly just before 2 the application location of the sizing agent in form of foam, whereby the suction z 30 effect eliminates or at least minimizes the disadvantages of the boundary air > flow on the side of the multi-ply fiber web layer, where the application is 3 provided.

S N According to an advantageous feature of the invention boundary air flow is turned off the running direction of the fiber web before curtain application of the sizing agent in form of foam by an air guide.

According to the invention the forming section of the fiber web production line is for forming a fiber web, which has at least one layer, and which forming section comprises at least one wire for supporting the at least one layer of the fiber web and which forming section comprises at least one curtain type application device for applying at least part of sizing of the fiber web onto the at least one layer of the fiber web in the forming section of the fiber web production line, wherein the sizing agent is configured to be applied onto the at least one layer of the fiber web during at least one run, wherein the running direction of the run of the wire and the fiber web layer is deviated substantially from horizontal and the running direction is downwards inclined during the at least one run. According to an advantageous feature of the invention the forming section is for forming a multi-ply fiber web, which has at least two layers, and which forming section comprises at least one twin-wire forming part formed between a wire for a bottom layer of the multi-ply fiber web and a wire for a top layer of the multi-ply fiber web, in which twin-wire part in the layers for the multi-ply fiber web are joined and treated layers combined, which the forming section comprises at least one curtain type application device for applying sizing agent in between at least two layers of the multi-ply fiber web in forming section of a multi-ply fiber web production line. According to an advantageous feature of the invention the run of the wire and the fiber web layer is deviated from horizontal downwards inclined in an angle N of 5 — 60 degrees.

N 3 According to an advantageous feature of the invention the at least one curtain 2 type application device is configured to apply the sizing agent in form of foam. z 30 > According to an advantageous feature of the invention the curtain type 3 application device is a slot-type application device.

S N According to an advantageous feature of the invention the forming section comprises a suction or an underpressure device on the opposite side of the fiber web and its support wire in relation to the curtain application device. Thus,

absorption of the sizing agent into the fiber web layer is improved as well as application of the sizing agent foam is stabilized.

According to an advantageous feature of the invention the forming section of the fiber web production line comprises suction means and/or a sleeve roll to guide conveyance and penetration of the sizing agent into the web layer and/or over a boundary between the joined web layers after the application of the sizing agent in form of foam by the curtain application device.

Advantageously the suction device is located at least partly just before the application location of the sizing agent in form of foam, whereby the suction effect eliminates or at least minimizes the disadvantages of the boundary air flow.

According to an advantageous feature of the invention the forming section of the fiber web production line comprises air guide, preferably an air curtain and/or a reversing blade before the curtain type application device for turning boundary air flow off the running direction of the fiber web before curtain application of the sizing agent.

According to an advantageous feature of the invention the foam of the sizing agent comprises at least 50 %-vol. gas, preferably air.

According to an advantageous feature of the invention the sizing agent is applied at least in between layers that are middle layers of the multi-ply fiber N web.

& 3 According to an advantageous feature of the invention the sizing agent is 2 applied at least in between the top layer and the layer next to it.

z 30 > According to an advantageous feature of the invention the sizing agent applied S in form of foam penetrates deep into the structure of the fiber web and S advantageously the conveyance and the penetration of the sizing agent in form of foam is guided to desired direction and depth by a water-removal means and by controlling amount and viscosity of the foam.

According to an advantageous feature of the invention the multi-ply fiber web is cartonboard, for example folding box board (FBB), white lined chipboard (WLC), solid bleached board (SBB), solid bleached sulphate (SBS) or liquid packaging board (LPB). In addition, the fiber web is advantageously containerboard, for example fluting or multi-ply board like kraftliner (KL), testliner (TL) or white top liner (WTL). Typically, these grade basis weights are between 100 to 400 g/m?. The fiber web can have single or multi-ply structure and it can be a coated or an uncoated fiber web.

By the forming section according to the invention many advantages are achieved: In the method and the forming section the problem of back flow is avoided as the contact angle of the curtain to the passing fiber web is inclined downwards and thus, the sizing substance flows in the running direction downstream. Better curtain guality and evenness is achieved. Curtain running window is larger, enabling higher speeds and larger application amounts. The bulkiness of the fiber web is increased when the sizing agent is applied in form of foam. Also, the strength properties, especially ply-bond strength, of the fiber web are improved due to the uniform sizing agent distribution achieved by applying the sizing agent in form of foam. In addition, internal strength is improved due to application to the inner structure (i.e. between the plies) and due to good movability and/or penetration of the sizing agent within the fiber web layer in thickness direction. Thus, grammage of the fiber web can be decreased as the critical strength properties are achieved by better effect of N the sizing agents. Further, good retention is achieved due beneficial N application to the inner structure and cost-savings are achieved as smaller 3 amounts of sizing agent are needed as it is applied by foam and thus the sizing 2 agent remains within the fiber web and does not flush away with following z 30 water removal steps. Additionally, good runnability properties of the fiber web > are achieved as misting and other spreading as well as adherence to rolls and S other components of the sizing agent is minimized due to foam application of S the sizing agent causing good distribution and stability of the sizing agent. Also, chemistry of short circulation is easier as handling of the sizing agent can be isolated from the pulp circulation. Foamed sizing agent can contain starch, native starch, modified starch, cationic starch, carboxy methyl cellulose CMC,

microfibrillated cellulose MFC, nanofibrillated cellulose NFC, highly refined cellulose, AKD, ASA, SAE, pigments (GCC, PCC, kaolin, talc), barrier chemicals (e.g. synthetic or bio-based polymer latexes, polyvinyl acetate PVA, polyvinyl alcohol PVOH) or mixture of those or other sizing agents, other natural or synthetic polymer based binders or strength agents. The curtain type application device can be any kind of applicator which creates a curtain-like sizing film, for example a slot-type or a slide-type curtain application device. The slot-type curtain application device is advantageous because dwell time is shortest from the nozzle to the fiber web and as an equipment it has compact size and simple design. Brief description of the drawings In the following the invention is explained in detail with reference to the accompanying drawing to which the invention is not to be narrowly limited. In figure 1 is shown schematically an advantageous example of a forming section according to the invention.

In figure 2 is shown schematically another advantageous example of a forming section according to the invention. In figure 3 is shown schematically a curtain application device and an air guide — steam box arrangement according to an advantageous example.

S N In figure 4 is shown schematically yet another advantageous example of a 3 forming section according to the invention.

LO E 30 In figure 5 is shown schematically further another advantageous example of a a o forming section according to the invention. 3 S In figure 6 is shown schematically further another advantageous example of a N forming section according to the invention.

Detailed description During the course of the following description like numbers and signs will be used to identify like elements according to the different views which illustrate the invention and its advantageous examples. In the figures some repetitive reference signs have been omitted for clarity reasons. In figure 1 is shown an example of a forming section for a multi-ply fiber web W, in this example for a two-ply fiber web W. The forming section comprises a headbox M10; M20 for each layer, from which the stock suspension is fed to the forming unit for each layer W beginning as single wire part comprising a wire 10 for the bottom layer of the multi-ply fiber web W and a wire 20 for the top layer W of the multi-ply fiber web W, each wire comprising rolls 12, 22 for guiding, tensioning and/or driving the wire 10; 20 as an endless loop. The headbox M10; M20 can be single layer or multilayer headbox. The stock suspension is first fed onto the wire 10; 20 and thereafter a fiber web layer W formed of the stock on the wire is guided past inside the loop of the wire 10; located water removal means 11; 21; 25. Inside of the loop of the upper wire 20 at least one suction means 25 are located. The run of the wire 10; 20 20 during this water removal on the single wire part is at least in the beginning substantially horizontal. An upper wire loop 60 located above the substantially horizontal run of the wire part 10 forming a short twin-wire part comprises at least one suction means 67 located inside the wire loop 60 for removing water upwards from the fiber web layer W. The upper wire loop 60 comprises rolls 62 for guiding, tensioning, and/or driving the wire as an endless loop.

S N The top fiber web layer W of the multi-ply fiber web guided on the wire 20 is 3 after the single-wire part guided as a downwards inclined run towards the first 2 wire 10 and the runs of the wire 10 for the bottom layer and the wire 20 for the z 30 top layer are united by a combining roll 23 to form a twin-wire part and the > webs for the bottom layer and the top layer are guided into a gap formed S between the wires 10; 20 forming the twin-wire part of the forming unit. Web S layers W have been joined together by a combining roll 23 at the beginning of the twin-wire forming part. Combining roll 23 is situated in the top layer wire loop 20.

A curtain application device C20 is located at the downwards inclined run of upper wire loop 20 for applying sizing agent advantageously in form of foam by the curtain type application device onto the fiber web layer W and to be in between at the layers W of the multi-ply fiber web W in forming section. The curtain application device C20 is advantageously located such that the suction means 25 are located on the opposite side of the multi-ply fiber web inside of the loop of the wire 20. In that way the sizing agent contacts fiber web layer W on the suction means 25 area. Also, more than one application devices C20 can be used consecutively for one fiber web layer.

Thus, the sizing agent applied in form of foam by the curtain application device C20 onto the layer of the web is guided in between the layers. Advantageously, after applying the sizing agent in form of foam by the curtain application device C20 its conveyance and penetration into the web layer is assisted such that the sizing agent is forwarded deeper into the web layer on which the sizing agent is applied in form of foam by guiding the foam to desired direction. In the example of figure 1 the suction means 11 are provided inside the lower wire loop 10 also after the web layers W are joined by the combining roll 23 at the beginning of the twin-wire forming part in order to assist the conveyance and penetration of the sizing agent into the web layer. After the joining of the layers the multi-ply fiber web W is guided on the wire 10 supporting the bottom side of the multi-ply fiber web as a single wire part during which run support foils 16 located inside the wire 10 loop. The support foils 16 do not deviate the run of the wire 10 only remove water from the bottom N surface of the wire 10 and support the run of the wire 10 as the multi-ply fiber N web is guided via suction roll 13 towards a pick-up roll 41 for transferring the 3 multi-ply fiber web to a first press fabric 40 of a press section. The press section 2 also comprises a second press fabric 50 with a roll 51. The press fabrics 40, z 30 50 comprise rolls 42, 52 for guiding, tensioning, and/or driving the fabrics 40; > 50 as an endless loop. In the press section the multi-ply fiber web is guided S between the first press fabric 40 and the second press fabric 50 to a press nip S formed between a first press roll 45 and a second press roll 55. Press nip even improves conveyance and penetration of the sizing agent. After the press section the fiber web W is guided to a drying section (not shown).

In figure 2 is shown an example of a forming section for a multi-ply fiber web, in this example for a three-ply fiber web. The forming section comprises a headbox M10; M20; M30 for each layer, from which the stock suspension is fed to the forming unit for each fiber web layer of the stock beginning as single wire part comprising a wire 10 for the bottom layer of the multi-ply fiber web and a wire 20 for the top layer of the multi-ply fiber web and a wire 30 the middle layer of the multi-ply fiber web, each wire comprising rolls 12, 22; 32 for guiding and driving the wire 10; 20; 30 as an endless loop. The headbox M10; M20; M30 can be single layer or multilayer headbox. The stock suspension is first fed onto the wire 10; 20; 30 and thereafter the removal means 11; 21; 25; 31; 35, which can be for example forming shoes and/or suction devices. The upper wire loops 20, 30 comprise at least one suction device 25; 35. The run of the wire 10; 20; 30 during this water removal on the single wire part is at least in the beginning substantially horizontal. The upper wire loops 20; 30 comprise downwards inclined runs of the wire 20, 30 following the substantially horizontal beginning run. A curtain application device C20; C30; is located at the downwards inclined run of the fiber web layer W the single wire part for applying sizing agent, advantageously in form of foam, by a curtain type application device C20; C30 located at the downwards inclined run of the upper wire 20; 30 onto the fiber web layer W and to be in between at the layers of the multi-ply fiber web in forming section. The curtain application device C20; C30; is advantageously located such that the suction means 25; 35 are located on the opposite side of the multi-ply fiber web inside of the loop of the wires 20, 30. In that way the N sizing agent contacts fiber web layer on the suction means 25; 35 area.

N 3 Advantageously, only one application device C20; C30; for the foam is used. 2 Either one of the application devices C20, C30 for the foam can also be only E 30 applicating onto the fiber web on the wire 20, 30. & The top layer of the multi-ply fiber web guided on the wire 20 is after the single-

LO S wire part guided to the downwards inclined run towards the third wire 30 and N the layers W for the top and the middle layer are united by a combining roll 33 to form a short twin wire part and the layers for the middle and top layer are united to the layer for the bottom layer at a combining roll 23. Thus all layers

W are united by the combining roll 23 and the webs for the bottom layer and the middle layer and the top layer are guided into a gap formed between the wires 10; 20 forming the twin-wire part of the forming unit. The web layers have been joined together by a combining roll 23 at the beginning of the twin-wire forming part. Combining roll 23 is situated in the top layer wire loop 20. Thus, the sizing agent applied in form of foam by the curtain application devices C20; C30 onto the middle and the top layer of the web is guided in between the layers.

Advantageously, after applying the sizing agent in form of foam by the curtain application device C20; C30 and after the web layers have been joined by the combining roll 23 conveyance of the sizing agent is further enhanced by guiding the direction of conveyance of the sizing agent from the surface over the joining boundary towards the web layer on the other side of the boundary of the joining web layers. In the example of figure 2 the suction means 11 are provided inside the lower wire loop 10 and after the web layers have been joined by the combining roll 23 at the beginning of the twin-wire forming part in order to enhance the conveyance of the sizing agent over the boundary between the web layers joined.

After the joining of the layers the multi-ply fiber web is guided on the wire 10 supporting the bottom side of the multi-ply fiber web as a single wire part during which run support foils 16 located inside the wire 10 loop. The support foils 16 do not deviate the run of the wire 10 only remove water from the bottom surface of the wire 10 and support the run of the wire 10 as the multi-ply fiber web is N guided via suction roll 13 towards a pick-up roll 41 for transferring the multi-ply N fiber web to a first press fabric 40 of a press section. The press section also 3 comprises a second press fabric 50 with a roll 51. The press fabrics 40, 50 2 comprise rolls 42, 52 for guiding, tensioning, and/or driving the fabrics 40; 50 z 30 as an endless loop. In the press section the multi-ply fiber web is guided > between the first press fabric 40 and the second press fabric 50 to a press nip S formed between a first press roll 45 and a second press roll 55. Press nip even S improves conveyance and penetration of the sizing agent. After the press section the fiber web is guided to a drying section (not shown).

In figure 3 is shown a curtain application device C10; C20; C30 and an air guide 61 — steam box 62 arrangement 60. The curtain application device C10; C20; C30 is advantageously located such that the suction means 15; 25; 35 are located on the opposite side of the multi-ply fiber web W and the wire 10; 20; 30. In the example as the air guide a reversing blade or air foil 61 is used before the curtain application device C10; C20; C30; C40 for turning boundary air flow F off the running direction of the multi-ply fiber web W before curtain application of the sizing agent. An air curtain can also be used as the air guide. A steam-box 62 is provided just after the air guide 61. The curtain application device C10; C20; C30 is located at the downwards inclined run of the wire 10, 20, 30 and the inclination angle A is 5-60 degrees. In figure 4 is shown an example of a forming section for a multi-ply fiber web, which corresponds to the example of the figure 2 but additionally a sleeve roll 19 is provided inside the lower wire loop 10 after the web layers have been joined by the combining roll 23 at the beginning of the twin-wire forming part in order to enhance the conveyance of the sizing agent over the boundary between the web layers joined and deeper towards the top surface of the multi- ply fiber web. Alternatively, this can be provided by locating a suction means (now shown) inside the upper wire loop and thus causing the conveyance of the sizing agent towards the top surface of the multi-ply fiber web. A sleeve roll 19 is a roll that comprises a stationary support shaft, an belt loop, which is led to circle around the stationary support shaft, that the sleeve roll further comprises at least one curvilinear dewatering zone consisting of two partial curves such that the radius of curvature of a first partial curve is greater than N the radius of curvature of a second partial curve following the first partial curve N in the travel direction of belt loop. A sleeve roll configuration is disclosed for 3 example in EP patent application 17164069 of the applicant.

LO E 30 In the example of figure 5 is schematically shown a forming section for a single- > ply fiber web. The forming section comprises a headbox M10 the fiber layer S W. From the headbox M10 the stock suspension is fed to the forming unit for S the layer beginning as a twin-wire part between wires 10, 20. The headbox M10 can be single layer or multilayer headbox. The wire loops 10, 20 comprise rolls 12, 22 for guiding, tensioning and/or driving the wire 10; 20 as an endless loop. The stock suspension M10 is first fed between the wires 10; 20 and thereafter the fiber web layer W is guided past inside the loops of the wires 10; 20 located water removal means 11; 27. During the run of the stock on the twin-wire part the water removal is substantially vertical.

At a suction roll 13 the runs of the wire loops 10, 20 is turned to downwards inclined runs and after a short twin-wire part the upper wire is turned off the lower wire 10 and the fiber web layer W supported on the wire is running downwards inclined as a single wire part.

After forming of the layer of the fiber web is guided on the wire towards a pick-up roll 41 for transferring the fiber web to a first press fabric 40 of a press section. 10 A curtain application device C10 is located at the run of the fiber web layer the single wire part for applying sizing agent, advantageously in form of foam, by the curtain type application device C10 onto the fiber web layer.

The curtain application device C10 is advantageously located such that the suction means 15 are located on the opposite side of the fiber web inside of the loop of the wire 10. In that way the sizing agent contacts stock layer on the suction means 15 area.

Advantageously, after applying the sizing agent in form of foam by the curtain application device C10 its conveyance and penetration into the web layer is assisted such that the sizing agent is forwarded deeper into the web layer on which the sizing agent is applied in form of foam by guiding the foam to desired direction.

In figure 6 is shown an example of a forming section for a multi-ply fiber web N W, in this example for a two-ply fiber web W.

The forming section comprises a N headbox M10; M20 for each layer, from which the stock suspension is fed to 3 the forming unit for each layer W beginning as single wire part comprising a 2 wire 10 for the bottom layer of the multi-ply fiber web W and a wire 20 for the z 30 top layer W of the multi-ply fiber web W, each wire comprising rolls 12, 22 for > guiding, tensioning and/or driving the wire 10; 20 as an endless loop.

The S headbox M10; M20 can be single layer or multilayer headbox.

The stock S suspension is first fed onto the wire 10; 20 and thereafter a fiber web layer W formed of the stock on the wire is guided past inside the loop of the wire 10; 20 located water removal means 11; 21; 25. Inside of the loop of the upper wire 20 at least one suction means 25 are located.

The run of the wire 10; 20 during this water removal on the single wire part is at least in the beginning substantially horizontal. The top fiber web layer W of the multi-ply fiber web guided on the wire 20 is after the single-wire part guided as a downwards inclined run towards the first wire 10 and the runs of the wire 10 for the bottom layer and the wire 20 for the top layer are united by a combining roll 23 to form a twin-wire part and the webs for the bottom layer and the top layer are guided into a gap formed between the wires 10; 20 forming the twin-wire part of the forming unit. Web layers W have been joined together by a combining roll 23 at the beginning of the twin-wire forming part. Combining roll 23 is situated in the top layer wire loop 20. A curtain application device C20 is located at the downwards inclined run of upper wire loop 20 for applying sizing agent advantageously in form of foam by the curtain type application device onto the fiber web layer W and to be in between at the layers W of the multi-ply fiber web W in forming section. The curtain application device C20 is advantageously located opposite to a inside the upper wire loop 20 located turning roll 22A, at which area the fiber web layer run is turned from horizontal into vertical run. In that way the sizing agent contacts fiber web layer W on the turning roll 22A at downwards inclined, turning, area. Also, more than one application devices C20 can be used consecutively for one fiber web layer. The curtain application device C20 is located at the downwards inclined run of the wire 20 and the inclination angle A is 5-60 degrees.

S N Thus, the sizing agent applied in form of foam by the curtain application device 3 C20 onto the layer of the web is guided in between the layers. Advantageously, 2 after applying the sizing agent in form of foam by the curtain application device z 30 C20 its conveyance and penetration into the web layer is assisted such that > the sizing agent is forwarded deeper into the web layer on which the sizing S agent is applied in form of foam by guiding the foam to desired direction. In the S example of figure 6 the suction means 11 are provided inside the lower wire loop 10 also after the web layers W are joined by the combining roll 23 at the beginning of the twin-wire forming part in order to assist the conveyance and penetration of the sizing agent into the web layer.

After the joining of the layers the multi-ply fiber web W is guided on the wire 10 supporting the bottom side of the multi-ply fiber web as a single wire part during which run support foils 16 located inside the wire 10 loop. The support foils 16 do not deviate the run of the wire 10 only remove water from the bottom surface of the wire 10 and support the run of the wire 10 as the multi-ply fiber web is guided via suction roll 13 towards a pick-up roll 41 for transferring the multi-ply fiber web to a first press fabric 40 of a press section. The press section also comprises a second press fabric 50 with a roll 51. The press fabrics 40, 50 comprise rolls 42, 52 for guiding, tensioning, and/or driving the fabrics 40; 50 as an endless loop. In the press section the multi-ply fiber web is guided between the first press fabric 40 and the second press fabric 50 to a press nip formed between a first press roll 45 and a second press roll 55. Press nip even improves conveyance and penetration of the sizing agent. After the press section the fiber web W is guided to a drying section (not shown). Above only some advantageous examples of the inventions have been described to which examples the invention is not to be narrowly limited and many modifications and alterations are possible within the invention.

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Claims

1. Method for forming a fiber web, which has at least one layer, in a forming section of a fiber web production line, in which forming section the fiber web (W) is supported by a wire (10; 20; 30) and in which forming section at least part of the sizing of the fiber web (W) is provided by applying sizing agent by a curtain type application device (C10; C20; C30) onto at least one layer of the fiber web (W) in the forming section of the fiber web production line, characterized in that the sizing agent is applied onto the at least one layer of the fiber web (W) during at least one run, wherein the running direction of the run of the wire (10; 20; 30) and the fiber web layer (W) is deviated substantially from horizontal and the running direction is downwards inclined.

2. Method according to claim 1, characterized in that in the method a multi-ply fiber web, which has at least two layers, is sized and at least part of the forming is done in a twin-wire forming part formed between a wire (10) for the bottom layer of the multi-ply fiber web and a wire (20; 30) for the top layer of the multi-ply fiber web, in which the layers for the multi-ply fiber web are joined and treated layers combined in the twin- wire part, in which at least part of sizing of the multi-ply fiber web is provided by applying sizing agent by a curtain type application device (C20; C30), at least part of sizing of the multi-ply fiber web is provided by applying sizing agent by the curtain type application device (C20; C30) in between at least two layers of the multi-ply fiber web in forming section of a multi-ply fiber web production line during at least one run, o 25 wherein the running direction of the run of the wire and the fiber web a layer is deviated substantially from horizontal and the running direction ro is downwards inclined. -

3. Method according to claim 1 or 2, characterized in that the run of the E wire and the fiber web layer is deviated from horizontal downwards S 30 inclined in an angle of 5 — 60 degrees. 5 N

4. Method according to any of previous claims, characterized in that the N sizing agent is applied in form of foam.

5. Method according to any of previous claims, characterized in that the sizing agent in form of foam is applied by a slot-type curtain application device (C10; C20; C30).

6. Method according to any of previous claims, characterized in that suction and/or underpressure is created at the location of the curtain application device (C10; C20; C30) by a suction or an underpressure device (15; 25;35) on the opposite side of the multi-ply fiber web and its support wire (10; 20; 30) in relation to the curtain application device.

7. Method according to any of previous claims, characterized in that conveyance and penetration of the sizing agent into the web layer and/or over a boundary between the joined web layers is guided by suction means (11) and/or by a sleeve roll (19) after the application of the sizing agent in form of foam by the curtain application device (C10; C20; C30).

8. Method according to any of previous claims, characterized in that boundary air flow is turned off the running direction of the multi-ply fiber web before curtain application of the sizing agent in form of foam by an air guide (61).

9. Forming section of a fiber web production line for forming a fiber web, which has at least one layer, and which forming section comprises at least one wire (10; 20; 30) for supporting the at least one layer of the fiber web (W) and which forming section comprises at least a curtain o type application device (C10; C20; C30) for applying at least part of the a sizing of the fiber web onto the at least one layer of the fiber web (W) in ro 25 the forming section of the fiber web production line, characterized in LO that the sizing agent is configured to be applied onto the at least one > layer of the fiber web during at least one run, wherein running direction E of the run of the wire and the fiber web layer is deviated substantially > from horizontal and the running direction is downwards inclined during S 30 the at least one run. N

10. Forming section according to claim 9, characterized in that the forming section is for a multi-ply fiber web, which has at least two layers, and which forming section comprises at least one twin-wire forming part formed between a wire (10) for the bottom layer of the multi-ply fiber web and a wire (20; 30) for the top layer of the multi-ply fiber web, in which twin-wire part in the layers for the multi-ply fiber web are joined and treated layers combined, which forming section comprises at least a curtain type application device (C10; C20; C30) for applying sizing agent, the forming section comprises at least the curtain type application device (C10; C20; C30) for applying sizing agent in form of foam by in between at least two layers of the multi-ply fiber web in forming section of a multi-ply fiber web production line.

11. Forming section according to claim 9 or 10, characterized in that the run of the wire and the fiber web layer is deviated from horizontal downwards inclined in an angle of 5 — 60 decrees.

12. Forming section according to any of claims 9 - 11, characterized in that the at least one curtain type application device is configured to apply the sizing agent in form of foam.

13. Forming section according to any of claims 9 - 12, characterized in that the curtain type application device (C10; C20; C30) is a slot-type curtain application device (C10; C20; C30).

14.Forming section according to any of claims 9 - 13, characterized in that the forming section of the multi-ply fiber web production line comprises a suction or an underpressure device (15; 25; 35) on the o opposite side of the multi-ply fiber web and its support wire in relation a to the curtain type application device (C10; C20; C30).

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15.Forming section according to any of claims 9 - 14, characterized in T that the forming section of the multi-ply fiber web production line E comprises air guide (61), preferably an air curtain and/or a reversing S blade before the slot-type application device (C10; C20; C30) for turning > boundary air flow off the running direction of the multi-ply fiber web ä 30 before curtain application of the sizing agent.