EP2635741A1

EP2635741A1 - Process for producing multilayer fiber web

Info

Publication number: EP2635741A1
Application number: EP10792953.1A
Authority: EP
Inventors: Reijo PIETIKÄINEN
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2010-11-01
Filing date: 2010-11-01
Publication date: 2013-09-11
Also published as: WO2012059619A1; CN103189568A

Abstract

The invention relates to a process for producing multilayer fiber web (MLW) by joining two or more fiber webs (W1, W2, W3,...) together. The webs (W1, W2, W3,...) to be layers of the multilayer web (MLW) are joined in hot pressing zone of a joining unit (10) in which by pressing a moist fiber web together with another fiber web a tight bond between the webs that create layers of the multilayer fiber web is achieved.

Description

Process for producing multilayer fiber web

In general present invention relates to producing multilayer fiber web in a fiber web machine. More especially the present invention relates to a process according to preamble part of claim 1 . Multilayer fiber webs are known from prior art. By producing a fiber web as a multilayer web the purpose is usually to achieve better stiffness and better surface properties and great bulkiness and at the same time achieve savings in raw material. Typically and simplifying the savings in raw material are attempted to achieve by using in surface layers pulp with better grade and better properties and by using in middle layer / layers pulp that is of not so good grade and properties.

Different methods for producing multilayer fiber web are known from prior art. One way to produce multilayer fiber web is to use multilayer headbox in which the pulp suspension jets for each layer are prepared separately in layers of the head box and the streams are directed together to one and same forming part. Another way is to use several headboxes, one for each layer and then bond the layers in forming part or in press section of the fiber web machine. It is also known from prior art that a multilayer fiber web is produced by adhering fiber webs together by using an adhesive agent between the web layers to bond the layers together.

US patent 6,059,029 discloses a three layer headbox for producing a multilayer fi- ber web. This head box has top and bottom walls that are inclined toward each other toward the outlet of the headbox. Top and a bottom separating vanes in the headbox, the top vane defining a first chamber toward the top wall, the bottom vane being below defining a second chamber between the vanes and also defining a third chamber between the bottom vane and the bottom wall. A respective pulp inlet to each of the three chambers is provided. The pulp suspension layers passing through a head box are delivered to a paper machine forming section wire and the three streams from the headbox are combined directly before or upon stock feeding on the wire.

US patent 3,215,589, DE patent 1049224 and US patent 1 ,347,619 disclose ar- rangements in which the multilayer fiber web is achieved by bonding the layer webs together by an adhesive or corresponding clueing agent.

EP patent 1218592 and US patent 6699361 disclose further known methods for producing multilayer webs. A drying method called condebelt drying is known from prior art and disclosed for example in patent publication US 41 12586. By this method a one-sided web is produced. This process is very effective based on transferring water by high temperature difference to one direction and condensation to the porous wire of cool side. The wire on the cool side replicates the back side of the web to be rough which limits suitable uses of this kind of product significantly due to printing qualities.

From prior art also another one-sided concept is known called boostdryer. This method is disclosed in patent publication DE 102004017807. In this process there is also wire on the cooler side, which wire marks the surface of the web.

In some cases with one-sidedly dried fiber web products are not suitable due to the one-sidedness of the web in which marking on the back side of the web is usually very strong and permanent and usually not possible to remove by for example by calendaring without losing the bulkiness. Typically in these webs only one side is printable.

It is known from prior art to include functional or intelligent properties to a fiber product for example to a packing material by attaching functional or intelligent elements to the product. Packing made of fiber can include for example indication to inform about the surroundings in which the packing has been: temperature, hu- midity which relate to conditions of the goods inside, RFID-tag with information or safety indicators for genuine (holograms). From prior art it is known to locate these components on the top of the web by printing or by stamping (replicating), or as adhesive labels or by laminating with plastic foil.

An object of the present invention is to create a new process for producing multi- layer fiber webs.

Another object of the present invention is to create a process for producing multilayer fiber webs in which possible disadvantages and problems of known methods are eliminated or at least minimized.

Another non-mandatory object of the present invention is to create process for producing new (multilayer) products with functional or intelligent properties.

One object of the present invention is to solve at least part of the disadvantages and problems relating to one-sided drying processes. To achieve the objects mentioned above and later the process according to the invention is mainly characterized by the features of the characterizing part of claim 1 .

According to the present invention a multilayer fiber web is manufactured of two or more fiber webs by a process in which two webs are pressed together by belt zone in which heat is present. The pressing and heat create conditions in which either due to moisture difference or due to temperature difference moisture and heat begin to flow in order to even the difference. This creates conditions in which in the boundary area between the webs hydrogen bonds are formed thus joining the webs together. The inventive process has two major embodiments. In one embodiment two webs are pressed together in a metal belt zone and in another embodiment two webs are pressed together in a condebelt zone. The bonds formed are like bonds achieved by laminating but according to the invention no adhesive agent is needed. The bond formation in the joining process according to the inven- tions occurs and bonds are created without addition of adhesive agent. Within the scope of the invention are naturally those processes in which adhesive is added in some small amounts for other reasons than the actual bonding.

In the embodiment utilizing metal belt zone two fiber webs of different moisture level are joined to a multilayer fiber web. In the pressing zone heat and pressure create conditions in which the moisture from the moister web flows to the other web and hydrogen bonds begin to form. During the pressing zone due to heat and pressure moisture evens in the web materials and the dry solids content raises. The hydrogen bonds form to final state and stay permanent. When the pressure releases after the belt zone bonds remain, the moisture content in the webs has evened out and further drying is taking place.

In the embodiment utilizing condebelt the two webs are joined in a condebelt zone between two belts (wires), one of which is hot and one of which is dry. In this process the moisture and heat flow to the web that is on the side of the cooler belt and hydrogen bonds are forming. During the pressing zone due to heat and pres- sure moisture evens in the web materials and the dry solids content raises. The hydrogen bonds form to final state and stay permanent. When the pressure releases after the belt zone bonds remain. During this process drying is also taking place as moisture condensates into the wire on the cooler side.

In an advantageous example by pressing a (thin) moist fiber web f. ex. moist paper web together with another (thicker) fiber web f. ex. board web so that after press- ing the final moisture level of fiber web is close to the desired final moisture level so that no further drying is needed.

During the process according to the invention hot pressing heats one of the webs water and it evaporates and moisture and heath flow deeper into the web and reach the boundary between the webs. Moisture may move also over the boundary layer to the other web. In moist conditions the fibers and natural polymers in them create strong hydrogen bonds. In order to achieve strong bonding it is advantageous that the dry solids content of the boundary area is under 80%, preferably 30 - 75 %. During the process raised temperature softens the fibers and the pressing pressure in the zone compresses the structure and produces more fiber- fiber contacts thus providing for formation of new bonds to form to great extent. The moister web does not necessarily have so high moisture content in total as needed in the boundary. The moisture level needed can also be achieved by a moisture gradient in that the moisture level at the surface to be joined is greater. Hot pressing creates rapidly a moisture gradient inside to the web and provides for the moisture to flow inside of the web. The boundary area (and inside) will rapidly be provided with moisture as the surface dries.

In an advantageous embodiment of the invention the webs to be layers of the multilayer web are joined by pressing them together in a hot metal belt zone without using any adhesive agents or similar so that by the side of the moist web is a hot surface, suitably 100 - 300 degrees Celsius, preferably 120 -150 degrees Celsius, and by the side of the drier web is cooler surface, suitably about 25 - 50 degrees Celsius. Preferably, the pressing time in the zone is about 0,2 - 2 seconds, preferably 0,3 -1 seconds and the pressing pressure 0,1 - 2 MPa, advantageously 0,1 - 0,5 MPa.

According to an advantageous embodiment of the invention the moist web is thinner and the drier web is thicker. During the process the thinner web (f. ex. paper web) is smoothed and dried and attached the thicker web (board web) very tightly, even so well that the paper slits rather be the bond between the webs breaks if when trying to separate the web layers. During the process the hot pressing the moisture of the web creates hydrogen bonds to the boundary of the webs which hydrogen bonds results the joining of the layers of the multilayer web.

During the joining process by the pressing zone by pressing a dry web and a moist web together against each other the webs are joined by very strong bonding effect and simultaneously the surface on the side of the metal belt will smoothen. In one example of the process according to the invention for one-sided surfacing for one-sided products a first fiber web is produced by a board machine and is dried to a suitable dryness f. ex. dry solids content 70 - 95 % and a second web is produced by a paper machine and dried to a lower dry solids content f. ex dry sol- ids content 50 - 75 %. The second web is attached to the first web by pressing them together in a long pressing zone, preferably in between a metal belt and a roll. In this example of the invention the pressing is done so that the warmer surface of the pressing zone is on the side of the moister second web and the cooler surface of the pressing zone is on the side of the first web. By this manner the moisture from the second web transfers towards the first web and the moisture will finally even out in the webs. Thus separate drying is not necessarily needed. The side of the web that is in the pressing zone against the warmer surface will become smooth and the cooler side will likely stay rough but if needed the rough side can be calenderer to achieve smoothness. In one example of the process according to the invention for two sided surfacing for two sided products a fiber web is produced in a board machine for the middle layer of the multilayer web. This middle web is dried to suitable dry solids content f. ex. dry solids content 80 - 95 %. Two webs are produced in a fiber web machine and dried to lower dry solids content. The two moister webs are attached to the outer surfaces of drier web so that the surface webs are pressed onto the middle web in the pressing zone in which the surface side contacts hot pressing zone either simultaneously or in two different phases. In this example it is advantageous that the middle layer board web is preferably of lesser grade or produced of lower, cheaper quality pulp, for example of recycled pulp, and preferably drained in high consistency in the forming section. Middle layer can be also be manufactured by laying technique in which forming is done as air-fiber suspension instead of usually used water. This way the drying costs can be saved by using a web of lesser grade inside surface layer webs of better grade and/or produced of better quality pulp. In this example of the invention it is very advantageous that the web that will be the middle layer in the final product can be manufactured of poorer and/or cheaper raw material as f. ex coarser fibers can be accepted as well greater flog- giness and the manufacturing process can be simple and cost effective. For example in the manufacturing line only simple former and press part is needed, laying technique can be utilized as the surfaces of the web are created by joining to them a further layer. According to one aspect of the invention the first step of the process, the joining of two webs performed by a device of condebelt-type so that on the cooler side of the pressing zone a wire of felt is located to receive water from the webs. From this first step of the process result is a one-sided product because of wire marking. Af- terwards on the rougher side a thin, moist fiber web can be joined by using the metal belt process also for the second step or replacing the second step for example attaching the thin, moist web with the aid of an adhesive by using normal metal belt calendar. This way both surfaces of the multilayer fiber web are smooth.

Depending on the moisture level of the first and second web the third web is either moist or dry in examples where two sided web is manufactured.

According to one aspect of the invention the webs to be joined as a multilayer web can be produced by separate fiber web machines or same fiber web machine to parent rolls and web can be transported as rolls to be combined by using pressing in hot metal belt pressing zone. According to one further aspect of the invention a web for the invention is reeled and brought to second fiber web machine to be combined with second, online produced web and possibly further joined with third web produced online or offline.

According to one further embodiment of the invention to an one-sidedly dried, by condensate drying method, web on its rougher side another web layer is attached by the process of the invention. There after the multilayer fiber web can be calendared or pressed to be smooth. The joining and the surface smoothening are preferably done in a same process step where the fiber webs are pressed together in hot pressing zone for example in a metal belt pressing zone (by using a metal belt calendar). According to one aspect of the invention two webs dried by condensate drying are joined by attaching the rougher sides of the webs together. Also during joining process it is possible to join the moister surfaces together when the moisture level is distributed in z-direction of the webs.

According to one aspect of this embodiment of the invention a web dried by con- densate drying method (f. ex by condebelt or Boostdryer drying) and another web to be attached are brought into contact and in this contact the webs are pressed against each other by hot, long extended pressing zone so that webs bond together. Joining of another web can be done on either side of the first web but preferably on the rougher side. Preferably the first web is drier (dry solids content 75 - 95 % and is greater by grammage than the second web. During pressing temperature on the moister side (second web) is preferably greater than on the drier side (first web). This way moisture from the web (second web) transfers towards the boundary between the webs and over it to the other web (first web) and finally distri- butes to both webs and evens out. Advantageously by choosing the dry solids contents of the webs depending on the ratio of the grammages of the webs the moisture distribution content will be near the target final dry solids content and the need for further drying is small or not needed at all.

According to one embodiment of the invention a layered special paper is manufac- tured by utilizing the process according to the invention. In this embodiment already in production stage functional and/or intelligent elements are placed inside the structure (between the layers). The functional and/or intelligent elements will be located between the layers of the multilayer web at the latest during the joining process before the bonding and pressing. The elements can be adhered to the surface that in joining will be between the webs to be joined already in an earlier production stage. Advantageously one web is package board (SBS- or FBB-board) web but all different paper and board types can be used.

The functional and intelligent elements can be indicators of consumer non- durables indicating oxygen, hydrogen sulfide, temperature or humidity; different chemicals for anti-microbic substances or preservatives which can be in capsule or powder form; indicators indicating mechanical stress such as ink capsules; functional polymers such as light sensitive, light emitting or electrically conductive polymers; electronic circuits such as memory chips, smart labels and other wireless communicating or like miniature components and circuits, provided for exam- pie by printing technique produced electrically conductive printing inks; electro- magnetically readable or activated circuits and components provided by printing technique produced magnetic printing inks; optically readable or activated (active or passive) circuits and components, optically alterable polymers, pigments and like substances; authentication indicating safety components, such as safety wires, holograms readable by laser, colored fibers, magnetic patterns, structures visible only by transillumination; rolled batteries (a power source produced of paper fibers) etc.

By placing the elements inside fiber web in between the different layers already in production stage remarkable advantages are achieved by this embodiment of the invention: elements are not visible by final end user and protected for outer factors; elements cannot be removed without breaking the package; elements are be- tween the layers in exact depth which is important when indicating temperature, humidity or in optical solutions (diminishing and scattering of light while travelling inside the fiber structure); element inside the web do not effect printing of surface; simple and low cost elements can be placed to the web during production process in large scale effectively and economically thus providing for lower unit cost (one of major disadvantages of smart packages is high unit cost thus preventing mushrooming of this technology and its use).

In this embodiment functional and/or intelligent elements can be placed into the layer structure during the joining stage of layers in different ways: placing elements on inside surface of the web to be bonded such that in finally the location is in the boundary between the layered webs; producing structures and patterns by printing methods, specially by digital printing and digital printers (printing inks, inks); scattering, spraying or placing otherwise using mechanical or electrostatic methods; transferring with help of transfer surface (roll, belt, drum) or with help of transfer foils to provide controlled structures; application by coating methods by using suitable medium: water, paste, polymer or starch which also provides for adhesive; mixing elements into pulp suspension of one of the webs.

In the following the invention is discussed in more detail by reference to figures of accompanying drawings. Figure 1 shows schematically one example of the invention for producing multilayer fiber web in which a two layer web is produced.

Figure 2 shows schematically another example of the invention for producing multilayer fiber web in which a two layer web is produced.

Figure 3 shows schematically further example of the invention for producing multi- layer fiber web in which a three layer web is produced.

Figure 4 shows schematically another further example of the invention for producing multilayer fiber web in which a three layer web is produced.

Figure 5 shows schematically yet another further example of the invention for producing multilayer fiber web in which a three layer web is produced. Figure 6 shows schematically an example of the invention for producing multilayer fiber web in which a three layer web is produced.

Figures 7 A - 7B show schematically layered structure of web. Figures 8 - 10 show schematically further examples of the invention for producing multilayer fiber web in which two layer web is produced.

Figures 1 1 -12 show schematically further examples of the invention for producing multilayer fiber web in which drying is combined to the process. Figures 13-15 show schematically further examples of the invention for producing multilayer fiber web in which functional elements are located between web layers.

In the following description same reference signs designate for similar components 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 the invention.

In the example according to figure 1 a multilayer fiber web MLW is produced from two webs W1 and W2. Each of the webs W1 , W2 are directed by a roll 9 to the joining unit 10 which comprises a hot roll or cylinder 15 and a metal belt 1 1 with its leading rolls 12. The metal belt 1 1 is pressed against the hot roll 15 thus forming a pressing zone trough which the webs W1 , W2 are guided. Hot pressing heats the web W2 and water in it evaporates and moisture and heath flows deeper into the web and reach the boundary surface of the webs. Moisture moves over the boundary layer to web W1 . In moist conditions the fibers and natural polymers are softened and create strong hydrogen bonds. This joins the webs W1 , W2 together and a multilayer (two layer) web MLW is achieved. If needed the multilayer web MLW will be lead to a coating unit 25 to achieve a coated multilayer web CMLW. The first web W1 in this example is a board or paper web and its dry solids content before bonding process is preferably 70 - 95 %. The second web W2 which in final product will be on the surface side is moist and its dry solids content is 50 - 75 %,. The pressure in the pressing zone between the hot roll 15 and the metal belt 1 1 is about 0,1 - 2 MPa, preferably 0,1 - 0,5 MPa. The multilayer web produced in the example of figure 1 has a rough back side, in the figure the top side, and a smooth front side, in the figure the bottom side but naturally it can also be vice versa. The optional coating in the coating unit 25 is done by utilizing a suitable coating method. In examples of the invention one side of the multilayer web will be rough if Condebelt-technique is used and by suing metal belt technique both sides will be smooth. In figure 2 an example of the invention is shown in which the pressing zone for joining the webs W1 , W2 to produce a multilayer fiber web MLW is constructed of two metal belts 1 1 and their guiding rolls 12.

In figure 3 an example of the invention is shown in which a three layer multilayer fiber web is produced by joining the webs W1 , W2 and W3 in a joining unit 10 similar to joining unit of figure 1 . In this example a double surfaced multilayer web MLW is achieved. The middle web W1 is drier and can be produced of lower quality pulp than the surface webs W2, W3. In the pressing zone heat is brought from both sides and the moisture is driven from the surface webs W2, W3 to the boun- dary and deeper into the middle web W1 . Heat and moisture activate the bonding and the moisture content evens out in all three layers at the latest just after the pressing zone. The applied pressing helps out to create enough bonding contacts. As shown in the layer detail partial figure in figure 3 the surface layers SL of the multilayer fiber web MLW are of good quality and the middle layer ML is of cheap- er quality.

In the example of the invention shown in figure 4 a multilayer fiber web MLW with three layers is produced. The first web W1 is the dryer web and the second web is moister and they are first joined in the joining unit 10 and a one-sided two layer web is produced. There after a third web W3, which is moist, is joined in a reverse joining unit 10 thus a three layer fiber web with two surfaces of good grade is achieved. In figure 4 the joining unit 10 comprises a hot roll or cylinder 15 and a cool metal belt with its guide rolls 12.

In the example of the invention shown in figure 5 also a three layer fiber web with both sides of good quality is produced in a compact layout solution suitable f. ex. for machines with limited length capacity. In this embodiment the joining unit 10 comprises means for two pressing zones. The roll 15 is cool and the metal belts 1 1 are hot. The first, dryer web W1 and the moister second web W2 are guided to the pressing zone for joining and the bonding to occur. There after the two layer web is guided around the roll to the second pressing zone together with third web W3 which is moist. Thus a multilayer fiber web with two surface layers L2, and a middle layer L1 is produced.

Yet another embodiment of the invention is shown in figure 6. In this embodiment the joining unit 10 uses a Condebelt-zone in which a hot metal belt and a cool roll create the zone for bonds between the layers to form. Firstly a two layer web is produce and if needed a third web W3 can be attached to it in a second joining unit, for example as shown in figure 1 . A felt or a wire 16 is arranged to go around the cool roll 15 and another roll 17 is arranged to arrange a felt or a wire loop. In the return run the cleaning means for the felt of wire can be arranged.

Figures 7 A and 7B show schematically the structure of layers in the pressing and in the Condebelt zones. In figure 7A between the hot H and cool C metal treatment zones the two web layers L1 an L2 are located. The moisture transfers from layer L2 to layer L1 and evens out in the layers during the pressing during which the bonds between the layers form activated by the heat and moisture. In figure 7B is shown a Condebelt zone in which between the hot, smooth metal belt and a felt / a wire with cool roll or belt two web layers L1 , L2 are located. In this embodiment the web layer L2 is moister and the web layer L1 is dryer and the moisture transfers from layer L2 to layer L1 and further to the felt or wire during which the bonds joining the layers form. In this embodiment layers L1 , L2 can also both be relatively moist. In the presentation of figure 8 an online process is provided. In this embodiment a multilayer fiber web with two layers is produced. The webs W1 and W2 are produced online and there after joined together in the joining unit 10 online.

In the embodiment of figure 9 the process joins a online produced web W1 to offline web W2 which is unwound from a parent reel 20 before the joining unit 10 in which the webs W1 , W2 are joined and a multilayer fiber web MLW is produced. Also both webs W1 , W2 can be unwound from a parent reel 20 as indicated with dashed line connected reel 20 for web W1 .

The inventive process can be constructed in all different online- / offline combinations: online-online, online-offline, offline-offline, online-online-online, online- offline- online, online-online-offline, offline-offline-online etc.

In the example of figure 10 a one-sided two layer web is produced by joining two webs W1 , W2 and afterwards the rougher side is coated by a coating unit 25 applying suitable coating method. Device 10 can be Condebelt or similar condensat- ing dryer or metal belt device. In the embodiments of invention illustrated in figures 1 1 and 12 in addition to the joining process according to the invention also drying with condensate drying method is used. In the example presented in figure 1 1 moist web W1 from press part is transferred to a condensate dryer, for example to a Condebelt or to a Boostdryer drying unit 40, and one-sided web W1 is achieved. The lower side R in the figure of the web is not printable and the upper side is printable smooth, roughness about 50 - 200 ml/min Bendtsen. Another web W2 is joined to the rougher lower side. This web is moist and the webs W1 , W2 are joined in joining unit 10 which consists of a hot pressings zone (metal belt press) and a symmetric web is produced, both sides of which are smooth. Top side of the multilayer web MLW has roughness of 50 - 200 ml/min Bendtsen and lower side has roughness also of 50 - 200 ml/min. In the example presented in figure 12 board web W1 is dried in a condensate dryer 40 and thus a one-sided web is produced. One (top) side of the web is smooth and the other (lower) is rough R. A moist web W2 is then attached to the rougher side of the first web W1 in a joining unit 10A consisting of a hot pressing zone (metal belt press and/or Condebelt). Yet another moist web W3 is joined to the upper side of the web W1 , W2 in a joining unit 10B and a both side printable multilayer web MLW is produced.

In the examples of figures 13 to 15 are presented some possibilities of using the invention in connection of producing "intellectual paper" i.e. fiber web with functional elements. Process of figure 13 is an online process. In figure 14 an of- fline/online process is presented and in figure 15 an offline process is presented.

The pulp from headbox 30A is transferred to a press 35A and dried in a drying unit 40 to produce a web W1 as shown in figure 13. Another web W2 produced from pulp from the headbox 30B and pressed in a press 35B but not dried will be joined to the web W1 by joining unit 10. Functional elements are applied to the web W1 to its lower side and / or to the upper side of the other web W2 by units 45 so that the functional elements will locate in the boundary area of the multilayer web to be reeled to a parent roll 20.

In figure 14 the first web W1 is unwounded from a parent roll 20A and the second web W2 is produced as in figure 13. Functional elements are added by units 45 as in the embodiment of figure 13. Functional elements can also be added to the web in roll. The reel with functional elements is indicated by reference 20 C.

In the example of figure 15 both webs are unwounded from a parent roll 20A, 20B and then after addition of functional elements to the sides of the webs to be against each other by unit 45 the webs W1 , W2 are joined in a joining unit and then reeled to a parent roll 20C.

Above some preferred embodiments and examples of the invention have been described but many modifications are possible to those presented.

Claims

Process for producing multilayer fiber web by joining two or more fiber webs (W1 , W2, W3, ...) together, characterized by pressing at least two webs (W1 , W2, W3, ...) in hot pressing zone of a joining unit (10) in which by pressing a moist fiber web together with another fiber web a tight bond between the webs that create layers of a multilayer fiber web (MLW) is created.

Process according to claim 1 , characterized in that the webs to be joined as layers of a multilayer web are pressed in a metal belt pressing zone.

Process according to claim 1 , characterized in that the webs to be joined as layers of a multilayer web are pressed in a condebelt pressing zone.

Process according to claim 1 , characterized in that dry solids content of boundary area of webs to be joined is under 80 %, preferably 30-75 %

Process according to claim 1 , characterized in that the webs are pressed in joining unit (10) comprising a metal belt pressing zone consisting of a metal belt loop (1 1 ) guided by guide rolls (12) and a belt or a roll (15) or cylinder pressed against the metal belt (1 1 ).

Process according to claim 1 , characterized in that during the process the hot pressing heats one of the webs in which moisture evaporates and that during the process moisture and heat flow deeper into the web and reach the boundary between the webs and strong hydrogen bonds are created.

Process according to claim 1 , characterized in that in the process the webs (W1 , W2, W3,...) to be layers of the multilayer web (MLW) are joined by pressing them together in a hot metal belt zone of the joining unit (10) without using any adhesive agents or similar.

Process according to claim 1 , characterized in that in the process at least two webs (W1 , W2, W3, ...) are joined in the pressing zone by the side of the moist web is a hot surface, suitably 100 - 300 degrees Celsius, preferably 120 -150 degrees Celsius. Process according to claim 1 , characterized in that in the pressing zone the pressing time is about 0,2 - 2 seconds, preferably 0,3 - 1 seconds and the pressing pressure 0,05 - 0,2 MPa, preferably 0,1 - 0,5 MPa.

Process according to claim 1 , characterized in that a first fiber web (W1 ) is produced by a fiber machine and is dried to dry solids content 70 - 95% and a second web (W2) is produced by a fiber machine and dried to dry solids content 50 - 75 % and that the second web (W2) is attached to the first web (W1 ) by pressing them together in a long pressing zone.

Process according to claim 1 , characterized in that at least a three layer multilayer fiber web (W1 ) is produced for which a web is produced in a fiber machine for the middle layer of the multilayer web and the web is dried to dry solids content 80 - 95 % and that further two webs (W2, W3) are produced in a fiber web machine and dried to lower dry solids content and attached to the drier web (W1 ) so that the surface webs (W2, W3) are pressed onto the middle web (W1 ) in the pressing zone either simultaneously or in two different phases.

Process according to claim 1 , characterized in that at least one of the webs (W1 , W2, W3,...) for a multilayer web to be joined is dried by using a condensate drying method.

Process according to claim 1 , characterized in that the webs (W1 , W2, W3,...) to be joined as layers of a multilayer web (MLW) are produced by fiber web machine/s to parent rolls (25) which are unwounded before the joining process in the joining unit (10).

Process according to claim 1 , characterized in that functional and/or intelligent elements (45) are placed between the layers of the multilayer web (MLW) at the latest during the joining process before the bonding and pressing in the joining unit (10).

Process according to claim 13 or 14, characterized in that functional and/or intelligent elements (45) are placed on a surface of a web before reeling the web into a parent roll that will provide web for a layer of a multilayer web and that the elements (45) are located on the side of the web that will be in between the layers in the multilayer web.