SE1651631A1 - Method of producing boards - Google Patents

Abstract

The present invention concerns a method for producing a board, wherein a foamed fibrous layer is formed by contacting foam forming of a fibrous slush and said foamed fibrous layer is dried to form a web, wherein polyvinyl alcohol is used as a foaming agent in foam forming. The invention also concerns a system for producing a board and a board with at least one dried foamed fibrous layer, wherein the foamed fibrous layer is made from a mixture of fibrous slush with foam formed from water and polyvinyl alcohol.

Description

Method of Producing Boards Technical Field The present invention relates to a method of producing a paperboard (in the following also“fibrous web”) by foam forming. The method is suitable for forming various products of paperboard material, in particular it is suitable for the production of high bulk cartonboardproducts, such as fo lding box board or white lined chipboard. The invention also concerns paperboards thus obtained.

Background Fibrous webs can be produced by foam forrning which gives many advantages. In a foam,the fibres do not flocculate. When a web is made from such a fibrous foam is dewatered,for example by applying suction to the foam through a wire, the fibres will retain their non-flocculated state and form a web with good formation. The structural pressure that thefoam applies to the structure when water is removed by suction is much smaller than thepressure exerted by conventional removal of water from fiber slush. The technology gives rise to a high bulk in the products.

Foam forming on a foraminous wire to yield a non-woven fibrous web is disclosed in anumber of patent documents, including GB 1129757, GB 1329409, GB 1395757, GB1397378, GB 1431603 and US 4944843, all assigned to Wiggins Teape (Radfoam).

In addition, US 3,326,745 teaches that formation of a paper web can take place between aforaminous forrning fabric and a felt, with the forrning fabric and felt being carried by twoadjacent tuming rolls, the arrangement being such that the forrning fabric and felt arebrought substantially into contact along web formation areas thereof lying along one orboth of these rolls. After dewatering in the formation areas, the formed web follows and iscarried by the felt, and subsequent dewatering and transference to steam heated driers occurs as the web travels with the felt.

US 6,413,368 B1 discloses an apparatus and process for producing foam formed fibrous web in which the fumish is made up by mixing a thin water slurry of fibers at a consistency in the range of from about 0.5 to about 7 weight percent f1bers with sufficient aqueousfoam containing a surfactant and having an air content in the range of from about 55 toabout 80 percent by volume to forrn a foamed fiber fumish containing from about 0.1 toabout 3 weight percent fibers which is supplied directly to the forrning felt or wire of atwin wire paperrnaking machine, adding makeup surfactant and discarding excess aqueous foam from the process as required to maintain the desired volume of foamed liquid therein.

Furthermore US 2005/ 0039870 Al teaches a method and apparatus for foam forrning,wherein f1brous foam suspension is introduced from a head box of a production machine tothe web forrning section thereof. At least one solid material is mixed into the foam in thehead box. The method and the apparatus are suitable for manufacturing various web-like products of cellulose, glass fiber, aramide, sisal or other corresponding fiber material.

Paperboards comprise layers of high bulk. Although the formation of f1brous non-wovenlayers by foam formation having high bulk is, as such, taught in the art, the intemalstrength properties of such layers is still unsatisfactory for applications in which strength in the z-direction of the layer is of considerable importance, such as paperboards.

GB 1431603 discloses a method of increasing intemal strength by grinding, by use ofreinforcing chemicals and by wet pressing, but while some improvement has been obtained in the art, bulk has been lost simultaneously.

Further art is disclosed in US 6419792.

Wall paper base is typically produced with the conventional water forrning technology.The wall paper needs to be substantially dimension stable in order to avoid shrinking whenapplying wet glue paste, i.e. a minimum wet expansion of the wall paper substrate wouldbe benef1cial. A cellulo se f1bre matrix as such is norrnally not notably dimension stable,since moisture causes swelling of the f1bres and can break the hydrogen bonds between thef1bres. Therefore, synthetic f1bres are often used to form a dimension stable structure inside the cellulose f1bre matrix.

Synthetic f1bres typically tend to be unevenly distributed in the cellulose f1bre matrix.Firstly, cellulose f1bres and synthetic f1bres are mainly orientated along the machinedirection of the paper machine. Secondly, synthetic f1bres are longer, stiffer, morehydrophobic, and may have a different density than cellulose f1bres. Therefore, syntheticf1bres have a tendency to bundle, flocculate, or form a layer near the bottom side of theweb. This may cause adhesion to the dryer cylinders, surface dusting, and unevenness ofthe web which can lead to uneven water absorption and gluing problems as well as causeuneven print density. Synthetic f1bres also do not form hydrogen or other strong chemicalbond with each other or with the cellulo se f1bres. The intemal strength of the web is lowand the negative impact on the formation lowers the intemal strength further such that retention to the web can be poor causing dusting.

Intemal strength is also critical to wall paper processing and application. Low intemalstrength may result in web breaks during a converting process such as printing orlaminating. During application to the wall, a fault in alignment is often not apparent untilthe paper is mostly glued to the wall. In such cases the wall paper is pulled off while thepaste is still wet and then the wall paper is reapplied. It would be benef1cial to avoiddelamination of the paper. Additionally, applied dry wall paper should be removable fromthe wall without delamination. Intemal bond strength is the key to prevent delaminationduring use. Commonly, agents are used to prevent strength loss when wetting a wall paper sheet.

Document WO 2008/040635 Al discloses a wall paper substrate for a wall paper that canbe peeled in a dry manner, has a minimal wet expansion and consists of a multilayer stripwith an upper and lower side, between which are arranged a f1brous lower layer of a f1bremixture on cellulose basis and synthetic f1bres and a f1brous upper layer of a f1bre mixture on cellulose basis and free of synthetic f1bres.

Summary of Invention Technical Problem The present invention relates to the production of paperboard products Which containlayers having a high bulk. In particular, the present invention addresses the issue ofmanufacturing paperboard products Wherein layers of high bulk are needed Whichsimultaneously exhibit properties of good intemal strength, as evidenced by at least one of improved Scott Bond and improved strength in z-direction.

An aim of the present invention is to provide for the production of multilayeredpaperboards, such as fo lding box boards and White lined chipboards, Where high-bulk layer are arranged as middle layers of the paperboard product.

A third aim of the present invention is to manufacture f1brous layers having surfaceWeights of generally ll0 to 750 g/mz, Wherein at least a part of the products exhibit incombination high bulk and good intemal strength, in particular exhibiting minimum targetvalues of the exemplary middle layer of cartonboard of a) bulk > 1.8 g/m3 and b) ScottBond > 100 J/nf.

A fourth object of the present invention is to provide a method of producing, by foam forming on a foraminous Wire, paperboards Which meets the aforementioned target values.

Furthermore the present invention also aims at paperboards having one or a plurality of layers of Which at least one meets the afore-mentioned target values.

These and other objects are achieved by the present invention, as hereinafter described and claimed.

Solution to Problem In one aspect, the invention concems a method for producing a paperboard, Wherein at least one foamed f1brous layer is provided, and said at least one foamed f1brous layer is deWatered on the Wire of a paperboard machine to form a Web, Wherein a Water-soluble ordispersible foaming polymeric agent is used as a foaming agent. More specif1cally, thepolymeric foaming agent is selected from the group of Water-soluble or dispersibleglycans, in particular polysaccharides and derivatives thereof, and other hydrophilicpolymers and copolymers, such as poly(vinyl alcohol) and poly(vinyl acetate) and copolymers thereof.

Such foaming agent have been found to be capable of eff1ciently bonding to the f1bresduring foam formation to produce a Web With good formation, Which upon deWatering gives a f1brous matrix having high bulk and excellent intemal strength properties.

Disclosed herein is also an arrangement for producing a paperboard. Comprised therein arepreferably one or several of the fo llowing: At least one foam generator for production off1brous foam from f1brous slush, Water and at least one hydrophilic polymer; a Web formerfor producing a Web from the f1brous foam; a deWatering unit for the Web; and means for drying of the deWatered fibrous Web.

The invention also concems a paperboard With at least one dried foamed f1brous layer,Wherein the at least one foamed f1brous layer is made from a mixture of f1brous slush With foam formed from Water and at least one hydrophilic polymer.

More specif1cally, the method according to the present invention is characterized by What is stated in the characterizing part of claim 1.

A board according to the present invention is characterized by What is stated in the characterizing part of claim 12.

Advantageous Effects of Invention Considerable advantages are obtained by means of the invention. The use of a hydrophilicpolymer as a foaming agent enhances the intemal strength of a foam formed layer. Handsheet tests have showed that by the use of a hydrophilic polymeric foaming agent, such as poly(vinyl alcohol), a fo lding boxboard middle layer produced from chemitherrno- mechanical pulp (CTMP) without starch or retention agents has a Scott Bond Value of 123J/m3 and bulk value of 3.71 g/m3. In addition, the layer retains the high bulk provided by fo am forming.

The results show that it is possible to produce a high bulk middle layer of fo lding boxboardhaving advantageous strength properties with hydrophilic polymers as foam forrning agents.

This also shows the possibility of forming the middle layer of fo lding boxboard from lessrefined CTMP pulp and with polyvinyl alcohol use to reach the needed strength properties.

In the tests referred to above, the samples were wet pressed.The present invention also enables the use of less ref1ned fiber material in high bulk fiber web.

The economical and the eco lo gical influences of the present invention are for examplesavings in chemical consumptions. No other strength chemicals, such as starch or retention aids, are needed and using coarser CTMP pulp enables savings in refining energy.

Using foam forrning it is also typically possible to remarkably reduce production costs andsimultaneously improve properties of current products. The present invention will retainthe benefits obtained by foam formation. For example, compared to water forrningtechnology the forrning consistency may be increased substantially with foam. Foamforming technology requires signif1cantly less water than conventional paper andpaperboard manufacturing which leads to minimization of the amount of raw water intakeand the amount of waste water to be treated in treatment plants. Pulp contains largeamounts of air, providing better opportunities for influencing the properties of the end-product. Foam forrning technology reduces energy consumption, while saving on raw materials, and also widens remarkably the raw material choice.

Foam forming technology applied to paperboard manufacture using hydrophilic polymersas foaming agents further introduces new opportunities for fiber based products. Thus, it is possible to improve the properties of existing packaging, cartonboard, and the manufacture of different types of highly porous, light-weight and smooth products, such as hygieneproducts, insulators and filters. Foam forrning technology may also be the solution for printed intelligence and electronics and microcellulose applications.

The results show that, for example in a high bulk middle layer of fo lding boxboard, therequired strength properties can be obtained with polyvinyl alcohol. When using polyvinylalcohol as a foaming agent especially good Scott Bond values are obtained. By contrast,with sodium lauryl sulfate and non-ionic forrning agents, foaming is achieved but no particular improvement of intemal strength.

The results also show that it is possible to produce high bulk wall paper sheets havingadvantageous strength properties with hydrophilic polymers as foam forrning agents.Synthetic f1bres can be evenly orientated in all directions of the wall paper due to the foamforming manufacturing process, thus providing an advantageous wet expansion of the wallpaper substrate. Additionally, adhesion to dryer cylinders can be minimized, surfacedusting can be reduced, and the evenness of the web can be improved. Such a wall paperfurther provides better visual appearance and better functionality both in converting operations and end use.

Brief Description of Drawings For a more complete understanding of particular embodiments, reference is now made tothe following descriptions, taken in conjunction with the accompanying drawings. In thedrawings, Figure l illustrates a schematic view of a typical paperrnaking machine line to explain thesteps of producing cartonboard; Figure 2 shows the various types of boards included in the concept of “paperboard”;Figure 3 shows a table with values of a middle layer of fo lding boxboard according to testsof the present invention in a laboratory; and Figure 4 depicts in a schematic fashion the structure of a multilayered product.

Description of Embodiments As discussed above, the present technology basically concerns a method for producing aboard, comprising the steps of- producing a f1brous foam from cellulosic or lignocellulosic f1bres, Water and afoaming agent;- forming the f1brous foam on a foraminous Wire into a foamed layer;- deWatering the f1brous foam layer on the foraminous Wire, for example by suction,to form a deWatered Web; and - drying the Web thus obtained is dried to give a foamed f1brous Web.

Optionally, the f1brous Web can be formed as a stand-alone layer or it can be formed as partof a multilayered product for example by combining the above Web forrning procedure With the simultaneous formation of 2 to 5 Webs.

The terms “paperboard” or “cartonboard” are used for designating f1brous Web or f1brouslayer Which is provided by the present invention. Figure 2 shows the various boards typesincluded in the general concept of “paperboard”. Thus, included are cartonboards, other paper boards and containerboards. The terms “paperboard” or “cartonboard” also contain Wallpapers as Will be discussed below.

The foam forming of the at least one f1brous layer is preferably carried out by mixing thef1brous slush With foam formed from Water and the foaming agent so as to provide afoamed f1brous slush Which is fed onto a Wire to form the f1brous layer. The preferred consistency of the f1brous slush is 0.6 % to 7 % by Weight.

The Water and foaming agent are preferably used for forrning the foam having an aircontent of 40 % to 80 %, e.g. 55 % to 75 %, by volume. The concentration of the foamingagents is preferably l00 to 5000 ppm, in particular l50 ppm - l000 ppm, calculated fromthe total Weight of the liquid.

The at least one foamed f1brous layer is preferably wet pressed. Then the at least one foamed f1brous layer is dried to form a dried Web or board, for example by cylinder drying.

Drying can also be carried out as air drying by suction air through the Web.

The Web is preferably cartonboard made up of multiple layers of pulp. The top and/orbottom layers are preferably of bleached chemical pulp and may be coated With pigments.Mechanical pulp, semi-chemical pulp, chemical pulp, therrnomechanical pulp orchemitherrnomechanical pulp or recycled pulp can be contained in the middle layer of the cartonboard.

In the present technology, foam formation, in particular on a paperboard machine, iscarried out With the use of a foaming agent capable of acting as a surface active agent While simultaneously acting as a binder in the formed structure.

Generally, the foaming agent is selected from anionic, cationic, non-ionic and amphotericsurface active agents and surfactants, including polyvinyl alcohol and foamable starches, proteins, and combinations thereof.

Optionally at least one additional binder is used in an amount of 0.005-10 % by Weight,preferably 0.05-0.5 % by Weight, particularly preferably 1-2 % by Weight.

In a preferred embodiment, the foaming agent is polymeric and selected from the group ofhydrophilic polymers of natural or synthetic origin Which are capable of achieving bothfoaming and binding. Typically, suitable polymers are of a kind Which are soluble or atleast readily dispersible in Water. The polymers contain suitable polar groups attached directly to the main chain of the polymer or via side groups to the main chain.

Suitable natural and seminatural polymers are exemplied by glycans, in particularpolysaccharides and physical and chemical derivatives thereof Examples include f1nely divided cellulose or cellulose derivatives, biopolymers such as binders based onstarch derivatives, natural gum latexes, alginates, guar gum, hemicellulose derivatives,chitin, chitosan, pectin, agar, xanthan, amylose, amylopectin, alteman, gellan, mutan,dextran, pullulan, fructan, locust bean gum, carrageenan, glycogen, glycosaminoglycans, murein, bacterial capsular polysaccharides, and the like.

Naturally, niixtures of polynieric con1pounds can also be used.

Other hydrophilic polyniers and copolyniers, are represented by hydroxyl-substitutedsynthetic polymers and copolyniers thereof, such as polyvinyl alcohols, polyvinyl acetatedispersions, ethyl vinyl alcohol dispersions, polyurethane dispersions, acrylic latexes, styrene butadiene dispersions.

One particularly preferred foan1ing agent is polyvinyl alcohol. The structure of partiallyhydrolyzed polyvinyl alcohol is given below: *ÉBE u wherein R = H or COCHg Polyvinyl alcohol used as a foan1ing agent according to the present invention haspreferably a degree of hydrolysis fron1 80 % up to 99 %, preferably between 85 % and 99%.

Polyvinyl alcohol used as foan1ing agent according to the present invention has an1olecular weight between 10000 g/niol and 50000 g/n1ol, in particular between 15000g/n1ol and 40000 g/n1ol, preferably between 20000 g/n1ol and 35000 g/niol.

Turning now to the en1bodin1ent illustrated in the drawings, Figure 1 depicts aconventional process of producing cartonboard with a board machine line can be sub-divided into the steps of pulping, stock preparation, short circulation, forrning, pressing,drying, coating, calendering, and reeling. Figure 1 illustrates a 3-ply cartonboard line, but the invention can be used in 1 to n1ultiply board n1achines.

Mechanical Pulping is for example used to n1anufacture f1brous products such as printing and writing papers, paperboard, newsprint or tissue. Mechanical pulp provides high bulk 11 and good opacity. Mechanical Pulp can be combined With chemical pulps to produce amixture of properties and characteristics. Chemical pulp is pulp Which is prepared fromcooked Wood chips. Hybrid pulping methods, e. g. chemitherrno-mechanical pulping(CTMP), use a combination of chemical and therrnal treatment. Chemotherrnomechanicalpulp is a preferred raW material in the process and products of the present inVention, inparticular less ref1ned CTMP. In multilayered products, one or more layer can be of this CTMP, While other layers may be produced from other types of pulp.

The pulp may be for example made from any broad-leaved tree such as a tree from thebetulaceae family, e. g. birch or aspen, from the salicaceae family, from eucalyptus, mixedtropical hardWood or pines or from any combination of the aforementioned. The pulp maybe also for example made from any conifer such as spruce or pine or from any combination thereof The pulp may be also made from a combination of broad-leaved trees and conifers.

The percentage of conifers in the pulp may reach for example from 20 % to 100 %, in particular from 50 % to 100 % and preferably from 75 % to 100 %.

The pulp may be also for example made from any annual such as straW, common reed, reed canary grass, bamboo, sugarcane or any grass plant.

Stock preparation systems modify the raW materials in such a Way that the stock suppliedto the board machine line suits the requirements of the board machine line. The quality ofthe stock supplied to the board machine line influences the quality of the cartonboard.Additives such as binders, f1llers, sizing agents, retention agents or other chemicals may beadded to the stock. Binder may be starch, Which can be modified or unmodif1ed starch, preferably starch derived from Wheat, potato, rice, com or cassava.

According to the present inVention a board is produced by forrning at least one foamedf1brous layer, Wherein a hydrophilic polymer is used as a foaming agent in contacting foam forming, and drying said at least one foamed f1brous layer to form said Web.

The foam forming of the at least one f1brous layer is preferably carried out by mixing a f1brous slush With foam formed from Water and the foaming agent so as to provide a 12 foamed f1brous slush which is fed onto a wire and dewatered to form the web which is thendried to form the board. The preferred consistency of the f1brous slush is 0.6 % to 7 % byweight. The water and foaming agent are used for forrning the foam, preferably, having anair content of 40 % to 80 %, eg. 55 % to 75 %, by volume. The concentration of thefoaming agents is typically 150 ppm-1000 ppm, calculated from the total weight of theliquid, in particular the liquid phase of the slush. The size of the bubbles can vary.Typically, bubble diameters are typically between 10 um and 300 um, in particularbetween 20 um and 200 um and norrnally between 20 um and 80 um.

In the invention the hydrophilic polymer is mixed with pulp either in a stock preparation orshort circulation in one or several paperboard ply(s). Typically the hydrophilic polymercan be added into chests or directly to the approaching pipe in the short circulation. Afterthe addition or simultaneously therewith, air is mixed with the pulp. Air can be generatedfor example in a normal pulper with a mixing rotor or pumping high pressure air into approaching pipe before the headbox. A foamed fibrous slush is thus created.

The foamed f1brous slush is conducted from one or several headbox(es) 1 onto one orseveral wire section(s). On the wire section foamed f1brous slush is drained typically withfoils, foilboxes, vacuum boxes or vacuum rolls. As a result, a board web is formed. Afterthe wire section the dry content of the web is typically between 18 and 30 %, calculatedfrom the total weight of the web.

From the wire section the web is conducted to the press section, where dewatering is carried out in roll nips. The dry content is increased up to 40 to 50 % in the press section.

After the press section, the web is directed onto the drier section. On the drier section, typically hot cylinders are used for evaporating water from the web.

After the drier section the board machine typically has coating and calendaring units where the final surface of the paper board is made. 13 Examples The present invention has been tested at laboratory conditions. Figure 2 contains a tablewith bulk values and Scott Bond values of a middle layer of fo lding boxboard according to the tests.

According to preferred embodiments for manufacturing the board of the present invention,fiber material and nanocellulose mixture is mixed with prefabricated foam produced usingpolyvinyl alcohol. The foam generally has an air content of about 60 % to 70 %. The webis made from this fiber foam for example by suction of the foam through the wire. Anexcellent formation is reached because in stable foam the distances between particlesremain and no flocculation takes place. After the web forrning the fiber web is dried, for example by suction air through the web, e.g. using a suction slit.

Tests of different embodiments of the present invention using different polyvinyl alcoholgrades as foaming agents in order to maximize the benefits of polyvinyl alcohol haveshowed that in laboratory scale it is for example possible to produce a middle layer offolding boxboard with CTMP pulp containing 10 % nanofibrillated cellulose (NFC) havinga bulk value of 2.99 g/m3 and Scott Bond value of 153 J/mz when using a first polyvinyl alcohol grade and foam forrning.

Tests of a second embodiment of the present invention have showed that in laboratoryscale it is possible to produce a middle layer of folding boxboard with CTMP pulpcontaining 10 % NFC having a bulk value of 2.60 g/m3 and Scott Bond value of 281 J/mz when using a second polyvinyl alcohol grade and foam forrning.

The tests of a third embodiment of the present invention have showed that in laboratoryscale it is possible to produce a middle layer of folding boxboard with CTMP pulpcontaining 10 % NFC having a bulk value of 2.68 g/m3 and Scott Bond value of 3 14 J/mz when using the second polyvinyl alcohol grade and foam forming.

Tests of a fourth embodiment of the present invention have showed that in laboratory scale it is also possible to produce a middle layer of folding boxboard using coarser CTMP pulp 14 (5 74 CSF) without NFC, starch and retention aid additions having a bulk Value of 3.71g/m3 and Scott Bond value of 123 J/mz when using the second polyvinyl alcohol grade and fo am forming.

The reference values of a middle layer of fo lding boxboard containing 10 % NFC withsodium lauryl sulfate (SDS) as a foaming agent instead of polyvinyl alcohol are for example 3.11 g/m3 and 136 J/mz, respectively.

The reference values (bulk Value and Scott Bond Value) of a middle layer of foldingboxboard containing 10 % NFC with a non-ionic foaming agent instead of polyvinyl alcohol are for example 3.15 g/m3 and 137 J/mz, respectively.

As can be seen from the table, use of polyvinyl alcohol as a foaming agent offers thepossibility to achieve middle layers of fo lding boxboard with a bulk value of at least up to3.90 g/m3. Using sodium lauryl sulfate as a foaming agent instead of polyvinyl alcoholmiddle layers of folding boxboard with a bulk value between 2.45 g/m3 and 3.11 g/m3 canbe achieved. Use of a non-ionic foaming agent instead of polyvinyl alcohol can lead tomiddle layers of folding boxboard with a bulk value between 3.15 g/m3 and 3.45 g/m3 .

As can be also seen from the table, use of polyvinyl alcohol as a foaming agent offers thepossibility to achieve middle layers of fo lding boxboard with a Scott Bond value between105 J/mz and 314 J/mz. Using sodium lauryl sulfate as a foaming agent instead of polyvinylalcohol middle layers of folding boxboard with a Scott Bond value between 70 J/mz and149 J/mz can be achieved. Use of a non-ionic foaming agent instead of polyvinyl alcoholcan lead to middle layers of folding boxboard with a Scott Bond value between 112 J/mzand 137 J/mz.

Tests of a f1fth embodiment of the present invention have showed that in laboratory scale itis possible to produce a middle layer of folding boxboard using coarser CTMP pulp (574CSF) without NFC, starch and retention aid additions, which suits the aforementionedtarget values, when using a polyvinyl alcohol with a degree of hydrolysis of 88.0 %. Thepolyvinyl alcohol may have another degree of hydrolysis, e. g. a degree of hydrolysis of87.0 % or 89.0 %.

Tests of a sixth embodiment of the present invention have showed that in laboratory scaleit is possible to produce a middle layer of folding boxboard using coarser CTMP pulp (574CSF) without NFC, starch and retention aid additions, which suits the aforementionedtarget values, when using a polyvinyl alcohol with a molecular weight of 27000 g/mol. Thepolyvinyl alcohol may have another molecular weight, e. g. a molecular weight of 25000 g/mol or 35000 g/mol.

In Figure 3, a multilayered product produced according to the present invention is shownschematically. The product may be for example folding boxboard consisting of a middlelayer arranged between a top layer and a lower layer. The top layer and the lower layermay be for example from bleached or unbleached chemical pulp. The middle layer on theother hand may be of chemitherrnomechanical pulp. The top layer and/or the lower layer may be further coated with an optional pigment coating which is not shown in Fig. 3.

The board exhibits generally a grammage (surface weight) of about 50 to 750 g/ m2.

A middle layer of fo lding boxboard according to the present invention may be of anyweight, in particular the weight may be between 10 g/mz and 300 g/mz. Tests of a seventhembodiment of the present invention have showed that in laboratory scale it is possible toproduce a middle layer of folding boxboard using coarser CTMP pulp (574 CSF) withoutNFC, starch and retention aid additions, which suits the aforementioned target values andhas a weight of 200 g/mz. The middle layer of fo lding boxboard may have another weight,e.g. a weight of 100 g/mz or 300 g/mz.

Any other layer, e.g. a first other layer, a second other layer, a lower layer or a top layer,may be produced using the method of the present invention or any other method. The firstother layer may be the lower layer and the second other layer may be the top layer. Thenumber of layers in a multilayered product according to the invention is at least two.Folding boxboard according to the invention can for example also consist of five layers, i.e. a middle layer, a first other layer, a second other layer, a top layer and a lower layer.

In case of multilayered products any other layer, e.g. a first other layer, a second otherlayer, a lower layer or a top layer, may be according to the invention of any weight. In particular the weight of any other layer may be between 10 g/mz and 100 g/mz. Tests of an 16 eighth embodiment of the present invention have showed that in laboratory scale it ispossible to produce a middle layer of folding boxboard using coarser CTMP pulp (574CSF) without NFC, starch and retention aid additions, which suits the aforementionedtarget values and is connected to a top layer which has a weight of 50 g/mz. The top layerof folding boxboard may have another weight, e. g. a weight of 20 g/mz or 80 g/mz. It isfurther possible to produce a middle layer of folding boxboard using coarser CTMP pulp(5 74 CSF) without NFC, starch and retention aid additions, which suits the aforementionedtarget values and is connected to a lower layer which has a weight of 50 g/mz. The lower layer of folding boxboard may have another weight, e. g. a weight of 20 g/mz or 80 g/mz.

In another embodiment of the present invention, wall paper is provided comprising af1brous layer exhibiting in combination a) bulk > 1.8 g/m3 and b) Scott Bond > 100 J/m3. Inother words, the terms “paperboard” and “board” in accordance with the disclo sure of thisdocument also comprise wall paper or other paper products within the meaning of theinvention. The grammage (surface weight) of the wall paper may be in the range between60 g/mz and 200 g/mz, for example 90 g/mz or 110 g/mz. The wall paper may comprise one layer or more than one layer. The wall paper may comprise two layers, for instance.

Additionally, the wall paper may include synthetic f1bers according to certainembodiments. The synthetic f1bers may be, for example, made of polyester. Use ofsynthetic fibers in the fibrous foam provides isotropy of the fibers, i.e. the f1bers areorientated evenly in all directions in order to withstand tension. The synthetic f1bres arecarried by the three dimensional structure of the foam before removal of the foam on theforming section. The foam separates the f1bres thereby reducing flocculation and poorformation. This more uniform three-dimensional orientation improves the retention of thesynthetic fibres, builds stronger networks because the synthetic f1bres are bound to eachother in all directions, and also results in a more even formation. The improved syntheticf1bre distribution and bond in the web provide better dimension stability, less dusting, better visual appearance and better functionality both in converting operations and end use.

Although the present invention has been described in detail for the purpose of illustration,various changes and modif1cations can be made within the scope of the claims. Different polyvinyl alcohol grades, different NFC percentages, starch and retention aid additions and 17 use of other pulp than (coarser) CTMP pulp can for example lead to other embodimentsWith other Characteristics. In addition, it is to be understood that the present disclosurecontemplates that, to the extent possible, one or more features of any embodiment may be combined With one or more features of any other embodiment.

Industrial Applicability The fiber Web according to the invention may be used in a broad range of paperboards.Within the scope of the inVention, the following paperboards may be mentioned:Wallpaper Base, Duplex Wallpaper Base, Gypsum liners and boards and Core board. Thecontainerbords include liners, such as kraftliners and testliners, and fluting and mediums, such as semi chemical fluting and recycled mediums.

In the present context, particularly interesting are, hoWeVer, the cartonboards, Whichinclude fo lding box boards, White lined chipboards, greyboards, liquid packaging boardsand food service boards, as Well as solid bleached boards and coated unbleached boardsand carrier boards. Thus, the fiber Web can be a middle layer of folding boxboard, a cardboard product, a packaging, a hygiene product, an insulator, or a filter.

The fiber Web according to the inVention can also be used in the preparation of Wall paper. 18 Citation List Patent DocumentsUS 3,326,745 US 6,413,368 US 2005/0039870GB 1129757 GB 1329409 GB 1395757 GB 1397378 GB 1431603 US 4944843 US 6419792 WO 2008/040635 A1

Claims (25)

19 Claims:

1. Method of producing a paperboard Which comprises at least one fibrous Web, Wherein afibrous foam is provided, said fibrous foam is formed into a foamed fibrous layer Which isdewatered and dried to form said Web, Wherein a hydrophilic polymer is used as a foaming agent for forming said fibrous foam.

2. The method according to claim 1, Wherein foam forrning is carried out by mixing afibrous slush With foam formed from Water and the foaming agent so as to provide a foamed fibrous slush Which is fed onto a Wire to form the foamed fibrous layer.

3. The method according to claim 1 or 2, Wherein the consistency of the fibrous slush is 0.6 % to 7 % by Weight.

4. The method according to any of the preceding claims, Wherein foam having an air content of40 % to 80 %, e.g. 55 % to 75 %, by volume, is used.

5. The method according to any of the preceding claims, Wherein the concentration of the foaming agent is about 150 ppm-1000 ppm, calculated from the total Weight of the liquid.

6. The method according to any of the preceding claims, Wherein the at least one foamed fibrous layer is wet pressed after deWatering.

7. The method according to any of the preceding claims, Wherein the foaming agents isselected from Water-soluble and dispersible foaming polymeric agent, in particular Water- soluble or dispersible glycans, in particular polysaccharides and derivatives thereof.

8. The method according to any of the preceding claims, Wherein the foaming agents isselected from Water-soluble and dispersible foaming polymeric agent, in particular Water-soluble or dispersible hydrophilic polymers and copolymers, such as poly(vinyl alcohol) and poly(vinyl acetate) and copolymers thereof

9. The method according to any of the preceding claims, Wherein the hydrophilic polymer is used as a foaming agent in an efficient amount to provide a bulky fibrous layer Which exhibits properties of good internal strength, as evidenced by at least one of improved Scott Bond and improved strength in z-direction.

10. The method according to any of the preceding claims, comprising providing a f1brous layer exhibiting in combination a) bulk > 1.8 g/m3 and b) Scott Bond > 100 J/m3.

11. The method according to any of the preceding claims, Wherein synthetic f1bres are provided in the f1brous foam.

12. A board With at least one dried foamed f1brous layer containing non-flocculated f1bers, processed With foam formed from Water and a hydrophilic polymer as a foaming agent.

13. The board according to claim 12, Wherein the at least one dried foamed f1brous layer is arranged between a first other layer and a second other layer.

14. The board according to claim 12 or 13, Which contains mechanical pulp, semi-chemical pulp, chemical pulp, therrnomechanical pulp, chemitherrnomechanical or recycled pulp.

15. The board according to any of the claims 12 to14, Wherein the Web is cartonboard made up of multiple layers of pulp.

16. The board according to claim 15, Wherein a bottom and/or top layer is of bleached chemical pulp.

17. The board according to claim 16, Wherein the bottom and/or top layer is coated With pigments.

18. The board according to any of claims 12 to 17, Wherein the board is a cardboard product or a part thereof

19. The board according to any of claims 12 to 18, Wherein the board is a cartonboard, in particular a cartonboard selected from fo lding box boards, White lined chipboards, 21 greyboards, liquid packaging boards, food service boards, solid bleached boards, coated unbleached boards and carrier boards.

20. The board according to any of claims 12 to 19, Wherein the foaming agent is selectedfrom Water-soluble and dispersible foaming polymeric agent, in particular Water-soluble or dispersible glycans, in particular polysaccharides and derivatives thereof.

21. The board according to any of claims 12 to 19, Wherein the foaming agent is selectedfrom Water-soluble and dispersible foaming polymeric agent, in particular Water-soluble ordispersible hydrophilic polymers and copolymers, such as poly(vinyl alcohol) and poly(vinyl acetate) and copolymers thereof

22. The board according to any of claims 12 to 21, Wherein the f1brous layer exhibitsa combination of high bulk and good intemal strength, in particular a) bulk > 1.8 g/m3 and b) scott Bond > 100 J/nf.23. The board according to any of claims 12 to 22, Wherein the board has a Weight of 110to 750 g/mz and Wherein at least a part of the products exhibits in combination: a) bulk >

23. 1.8 g/m3 and b) Scott Bond > 100 J/m3.

24. The board according to any of claims 12 to 23, Wherein the at least one dried foamed f1brous layer comprises synthetic f1bres.

25. The board according to any of claims 12 to 14, comprising a Wallpaper.