CN106715794A - Method of producing boards - Google Patents

Abstract

The present invention relates to a process for the manufacture of paperboard wherein a foamed fiber layer is formed by contacting foam forming of a fiber slurry and drying said foamed fiber layer to form a paper web, wherein polyvinyl alcohol is used as a foaming agent in the foam forming agent. The invention also relates to a system for producing paperboard and a paperboard having at least one dry foamed fiber layer, wherein the foamed fiber layer is produced from a mixture of fiber slurry and foam formed from water and polyvinyl alcohol.

Description

Method of making cardboard

technical field

The present invention relates to a method of manufacturing paperboard (hereinafter also referred to as "fibrous web") by foam forming. The method is suitable for forming various products of paperboard material and is particularly suitable for the manufacture of high bulk cartonboard products such as folding box board or white pulp lined chipboard. The invention also relates to the paperboard thus obtained.

Background technique

Fibrous webs can be produced by foam forming, which has many advantages. In foam, the fibers do not flocculate. When the web is made from fibrous foam that has been dewatered, for example by applying suction to the foam through a wire, the fibers will retain their unflocculated state and form a web with good formation. The structural pressure that the foam exerts on the structure when water is removed by suction is much less than the pressure exerted by conventional water removal from fibrous slush. This technology provides high bulk in the product.

Foam formation on foraminous webs to produce nonwoven fibrous webs is disclosed in a number of patent documents including GB 1129757, GB 1329409, GB 1395757, GB 1397378, GB 1431603 and US4944843, all assigned Give Wiggins Teape (Radfoam).

Furthermore, US 3,326,745 teaches that the forming of the web can be carried out between a foraminous forming fabric and a felt carried by two adjacent turning rolls, an arrangement such that the forming The wires are in substantial contact with the felts along their web-forming regions unrolled along one or both of these rolls. After dewatering in the forming zone, the formed web follows and is carried by the felt, and subsequent dewatering and transfer to a steam-heated dryer occurs while the web runs with the felt.

US 6,413,368 B1 discloses an apparatus and method for producing a foam-formed fibrous web, wherein the furnish is produced by mixing a dilute aqueous slurry of fibers having a consistency in the range of about 0.5 to about 7% by weight fibers with a surface-active agent and have an air content in the range of about 55 to about 80% by volume with sufficient aqueous foam mixing to form a foamed fiber furnish containing about 0.1 to about 3% by weight fiber, which is supplied directly to the forming felt of a twin wire paper machine or net, adding additional surfactant and discarding excess aqueous foam from the process as necessary to maintain the desired volume of foaming liquid therein.

Furthermore, US 2005/0039870 A1 teaches a method and an apparatus for foam forming, in which a fiber foam suspension is introduced from the headbox of a production machine into its web forming section. At least one solid material is mixed into the foam in the headbox. The method and apparatus are suitable for the manufacture of various web-like products of cellulose, fiberglass, aramid, sisal or other corresponding fibrous materials.

Paperboard comprises multiple layers with high bulk. Although the formation of fibrous nonwoven layers by foam formation with high bulk is so taught in the prior art, the internal strength properties of such layers are important for applications where the strength in the z-direction of the layer is very important (such as paperboard) is still not satisfactory.

GB 1431603 discloses increasing internal strength by grinding, by using strengthening chemicals and by wet pressing, but although some improvement is obtained over the prior art, bulk is lost.

Other prior art is disclosed in US6419792.

The wallpaper base is usually manufactured using conventional hydroforming techniques. The wallpaper must be substantially dimensionally stable to avoid shrinkage when wet glue paste is applied, ie minimal wet expansion of the wallpaper substrate would be beneficial. Cellulosic fiber matrices themselves are usually not particularly dimensionally stable because moisture causes swelling of the fibers and disrupts the hydrogen bonds between the fibers. Therefore, synthetic fibers are often used to form a dimensionally stable structure within a matrix of cellulose fibers.

Synthetic fibers generally tend to be unevenly distributed in a matrix of cellulose fibers. First, cellulosic and synthetic fibers are oriented primarily in the machine direction of the paper machine. Second, synthetic fibers are longer, stiffer, more hydrophobic, and may have a different density than cellulose fibers. Consequently, synthetic fibers tend to bundle, flocculate, or form layers near the bottom side of the web. This can lead to sticking to the dryer cylinder, surface dusting and non-uniformity of the web (which can lead to uneven water absorption and gluing problems, as well as to uneven print densities). Synthetic fibers also do not form hydrogen bonds or other strong chemical bonds with each other or with cellulose fibers. The internal strength of the web is low, and adverse effects on forming further reduce the internal strength so that retention of the web may be poor, causing dusting.

Internal strength is also critical for wallpaper processing and application. Low internal strength may lead to web breaks during converting processes such as printing or lamination. During application to the wall, misalignment is usually not apparent until the paper is mostly glued to the wall. In this case, the wallpaper is pulled off while the paste is still wet, and the wallpaper is reapplied. It is beneficial to avoid delamination of the paper. Furthermore, the applied dry wallpaper should be removable from the wall without delamination. Internal bond strength is key to preventing delamination during use. Usually, agents are used to prevent loss of strength when wetting the wallpaper sheet.

Document WO 2008/040635 A1 discloses a wallpaper substrate for wallpaper that can be peeled off in a dry manner, has minimal wet expansion, and consists of a multilayer paper strip with an upper side and a lower side, between which There is a fibrous lower layer of a cellulose-based fiber mixture with synthetic fibers and a fibrous upper layer of a cellulose-based fiber mixture without synthetic fibers.

Summary of the invention

technical problem

The present invention relates to the production of paperboard products comprising layers with high bulk. In particular, the present invention solves the problem of manufacturing paperboard products where a high bulk ply is desired which simultaneously exhibits good internal strength properties (e.g. by at least one of improved Scott Bond and improved strength in the z-direction). as demonstrated).

It is an object of the present invention to provide for the production of multi-ply boards, such as folding boxboard and white pulp-lined chipboard, wherein the high bulk ply is arranged as an intermediate layer of the board product.

A third object of the invention is to produce fibrous layers with a surface weight of typically 110 to 750 ^g /m2, wherein at least a part of the product exhibits a combination of high bulk with good internal strength, in particular exhibiting a) Minimum target values for exemplary cartonboard interlayers with bulk > 1.8 g/ ^m3 and b) Scott Bond > 100 J/ ^m3 .

A fourth object of the present invention is to provide a method for manufacturing paperboard satisfying the aforementioned target values by foam forming on a mesh with pores.

Furthermore, the object of the invention is also a paperboard having one or more plies, at least one of which satisfies the aforementioned target values.

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

problem solution

In one aspect, the invention relates to a method of making paperboard, wherein at least one foamed fibrous layer is provided and said at least one foamed fibrous layer is dewatered on a board machine wire to form a paper web, wherein the water-soluble or water-dispersible polymer A foaming polymeric agent is used as a foaming agent. More specifically, the polymeric blowing agent is selected from water-soluble or water-dispersible polysaccharides, especially polysaccharides and their derivatives, and other hydrophilic polymers and copolymers, such as poly(vinyl alcohol) and poly( vinyl acetate) and its copolymers.

Such blowing agents have been found to be effective in bonding to fibers during foam formation to produce a web with good formation, which upon dewatering produces a fibrous matrix with high bulk and excellent internal strength properties.

Also disclosed herein is an arrangement for making cardboard. Included therein is preferably one or more of: at least one foam generator for generating fiber foam from fiber slurry, water and at least one hydrophilic polymer; for producing a paper web from said fiber foam A web former; a dewatering unit for a web; and a device for drying a dewatered fibrous web.

The invention also relates to a paperboard having at least one dry foamed fiber layer, wherein at least one foamed fiber layer is produced from a mixture of fiber slurry and foam formed from water and at least one hydrophilic polymer.

More specifically, the method according to the invention is characterized by what is stated in the characterizing part of claim 1 .

The board according to the invention is characterized by what is stated in the characterizing part of claim 12 .

Advantageous Effects of the Invention

Significant advantages are obtained by means of the invention. The use of a hydrophilic polymer as a blowing agent increases the internal strength of the foam forming layer. Hand sheet tests showed that folding boxboard made from chemithermomechanical pulp (CTMP) without starch or retention aids by using a hydrophilic polymer blowing agent such as poly(vinyl alcohol) The middle layer has a Scott Bond value of 123 J/m ³ and a bulk value of 3.71 g/m ³ . Furthermore, the layer maintains the high bulk provided by foam forming.

The results demonstrate that a hydrophilic polymer can be employed as a foam former to produce a high bulk interlayer of folding boxboard with favorable strength properties.

This also shows the possibility of forming the middle ply of folding boxboard from insufficiently refined CTMP pulp and using polyvinyl alcohol to achieve the desired strength properties.

In the tests referred to above, samples were wet pressed.

The present invention also enables the use of insufficiently refined fibrous material in high bulk fibrous webs.

The economical and ecological impact of the invention is, for example, savings in chemical consumption. No other strength chemicals such as starch or retention aids are required, and the use of coarser CTMP pulp saves refining energy.

The use of foam forming can often also significantly reduce production costs and at the same time improve the properties of existing products. The present invention will retain the benefits gained by foam shaping. For example, using foam can significantly improve forming consistency compared to water forming techniques. Foam forming technology requires much less water than conventional paper and board manufacturing, which results in a minimization of raw water inflow and waste water to be treated in the treatment plant. Pulp contains a lot of air, which provides a better opportunity to influence the properties of the final product. Foam forming technology reduces energy consumption while saving raw materials and also significantly expands the choice of raw materials.

Foam forming technology applied to paperboard manufacturing using hydrophilic polymers as blowing agents further introduces new opportunities for fibre-based products. Thus, it is possible to improve the properties of existing packaging, carton boards, as well as to manufacture different types of highly porous, lightweight and smooth products such as hygiene products, insulators and filters. Foam forming technology may also be a solution for printing smart and electronics applications (electronics) and microcrystalline cellulose applications.

The results show that the desired strength properties can be obtained with polyvinyl alcohol, for example in high bulk interlayers of folding boxboard. Especially good Scott Bond values are obtained when polyvinyl alcohol is used as blowing agent. In contrast, with sodium lauryl sulfate and a nonionic former, foaming could be achieved, but internal strength was not particularly improved.

The results also show that it is possible to use hydrophilic polymers as foam formers to produce high bulk wallpaper sheets with favorable strength properties. Due to the foam-forming manufacturing method, the synthetic fibers can be oriented uniformly in all directions of the wallpaper, thereby providing a favorable moisture expansion of the wallpaper substrate. In addition, sticking to the dryer drum can be minimized, surface dusting can be reduced, and web uniformity can be improved. Such wallpapers can furthermore provide better visual appearance and better functionality both in paper converting operations and end use.

Figure overview

For a more complete understanding of certain embodiments, reference is now made to the following description taken in conjunction with the accompanying drawings. In the attached picture,

Figure 1 shows a schematic diagram of a typical paper machine production line to explain the steps involved in producing carton board;

Figure 2 shows the various types of boards included in the "cardboard" concept;

Figure 3 shows a table with the values of the middle ply of folding boxboard obtained in the laboratory according to the tests of the present invention; and

Figure 4 schematically depicts the structure of a multi-layer product.

Implementation Description

As discussed above, the present technology basically relates to a method of manufacturing paperboard comprising the following steps:

- manufacture of fibrous foams from cellulosic or lignocellulosic fibers, water and blowing agents;

- shaping of fibrous foam into a foamed layer on a mesh with small holes;

- dewatering (e.g. by suction) the fibrous foam layer on the foraminous web to form a dewatered paper web; and

- drying the web thus obtained to obtain a foamed fibrous web.

Optionally, the fibrous web can be formed as a separate layer, or it can be formed as part of a multilayer product, for example by combining the web forming procedure described above with simultaneous forming of 2 to 5 webs.

The terms "paperboard" or "cartonboard" are used to denote the fibrous web or fibrous layer provided by the present invention. Figure 2 shows the various types of paperboard included in the general concept of "paperboard". Included, therefore, are cartonboard, other boards and containerboards. The terms "paperboard" or "cartonboard" also include wallpaper as will be discussed below.

Foam forming of at least one fibrous layer is preferably carried out by mixing a fiber slurry with a foam formed from water and a blowing agent to provide a foamed fiber slurry, which is fed onto a wire to form a fibrous layer. The preferred consistency of the fiber slurry is from 0.6% to 7% by weight.

Water and blowing agent are preferably used to form foams having an air content of 40% to 80%, eg 55% to 75%, by volume. The concentration of blowing agent is preferably from 100 to 5000 ppm, especially from 150 ppm to 1000 ppm, calculated on the total weight of the liquid.

At least one foamed fiber layer is preferably wet pressed. The at least one foamed fibrous layer is then dried to form a dried paper or board, for example by drum drying. Drying can also be carried out as air drying by drawing air through the web.

The paper web is preferably a cartonboard composed of multiple layers of pulp. The top and/or bottom layer preferably has bleached chemical pulp and may be coated with pigments.

Mechanical, semichemical, chemical, thermomechanical or chemithermomechanical pulp or recycled pulp may be contained in the middle layer of the cartonboard.

In the present technology, foam forming, especially on a board machine, is carried out with a blowing agent capable of acting as a surface active agent and simultaneously as a binder in the formed structure.

Typically, the blowing agent is selected from anionic, cationic, nonionic and amphoteric surfactants and surfactants, including polyvinyl alcohol and foamable starch, proteins and combinations thereof.

At least one further binder is optionally 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 blowing agent is a polymeric blowing agent and is selected from hydrophilic polymers of natural or synthetic origin, capable of both foaming and adhesion. In general, suitable polymers are of the type soluble or at least readily dispersible in water. The polymers contain suitable polar groups attached directly to the polymer backbone or via pendant groups to the backbone.

Suitable natural and semi-natural polymers are exemplified by polysaccharides, especially polysaccharides and their physical and chemical derivatives. Examples include finely divided cellulose or cellulose derivatives, biopolymers such as binders based on starch derivatives, natural rubber pulp, alginates, guar gum, hemicellulose derivatives, chitin, chitosan, Pectin, agar, xanthan gum, amylose, pullulan, alternan, gellan, mutan, dextran, pullulan, fructan, locust bean gum , carrageenan, glycogen, glycosaminoglycans, murein, bacterial capsular polysaccharides, etc.

Of course, mixtures of polymeric compounds may also be used.

Other hydrophilic polymers and copolymers are represented by hydroxyl-substituted synthetic polymers and their copolymers, such as polyvinyl alcohol, polyvinyl acetate dispersions, ethyl vinyl alcohol dispersions, polyurethane dispersions, acrylic latex, Styrene-butadiene dispersion.

A particularly preferred blowing agent is polyvinyl alcohol. The structure of partially hydrolyzed polyvinyl alcohol is given below:

,

where R = H or COCH ₃ .

The polyvinyl alcohol used according to the invention as blowing agent preferably has a degree of hydrolysis of 80% to at most 99%, preferably 85% to 99%.

The polyvinyl alcohols used according to the invention as blowing agents have a molecular weight of 10 000 g/mol to 50 000 g/mol, in particular 15 000 g/mol to 40 000 g/mol, preferably 20 000 g/mol to 35 000 g/mol.

Turning now to the embodiment shown in the drawings, Figure 1 depicts the general flow of the production of cartonboard with a board machine line, which can be subdivided into pulping, stock preparation, short cycle, forming, pressing, drying, coating, Steps of calendering and winding. Figure 1 shows a 3-ply cartonboard line, but the invention can be used on 1-ply board machines.

Mechanical pulping is used, for example, for the manufacture of fiber products such as printing and writing paper, cardboard, newsprint or tissue. Mechanical pulps provide high bulk and good opacity. Mechanical pulp can be combined with chemical pulp to create a mix of properties and characteristics. Chemical pulp is pulp made from cooked wood chips. Hybrid pulping processes, such as chemithermomechanical pulping (CTMP), use a combination of chemical and thermal treatments. Chemithermomechanical pulp is the preferred raw material in the process and product of the present invention, especially under-refined CTMP. In a multilayer product, one or more layers may have the CTMP, while other layers may be made from other types of pulp.

The pulp may for example be made from any broad-leaved tree, such as a tree from the family Betula, such as birch or aspen, from the family Salicaceae, from eucalyptus, mixed tropical hardwood or pine, or from any combination of the foregoing. The pulp can also be made, for example, from any coniferous tree, such as spruce or pine, or from any combination thereof. Pulp can also be made from a combination of deciduous and coniferous trees.

The percentage of coniferous trees in the pulp may amount to, for example, 20% to 100%, in particular 50% to 100% and preferably 75% to 100%.

Pulp may also be made, for example, from any annual plant such as straw, reed, grass reed, bamboo, sugar cane or any grass plant.

The stock preparation system modifies the raw material in such a way that the stock supplied to the board machine line matches the requirements of the board machine line. The quality of the stock supplied to the board machine line affects the quality of the carton board. Additives such as binders, fillers, sizing agents, retention aids or other chemicals may be added to the slurry. The binder may be starch, which may be modified or unmodified starch, preferably starch derived from wheat, potato, rice, corn or tapioca.

According to the invention, paperboard is produced by forming at least one foamed fiber layer, wherein a hydrophilic polymer is used as a blowing agent for contact foam formation, and drying said at least one foamed fiber layer to form said paper width.

Foam forming of at least one fibrous layer is preferably carried out by mixing the fiber slurry with foam formed from water and a blowing agent to provide a foamed fiber slurry, feeding it onto a wire and dewatering to form a paper web, The web is then dried to form paperboard. The preferred consistency of the fiber slurry is from 0.6% to 7% by weight. Water and blowing agent are used to form the foam, which preferably has an air content of 40% to 80%, eg 55% to 75%, by volume. The concentration of the blowing agent is generally from 150 ppm to 1000 ppm calculated on the total weight of the liquid (especially the liquid phase of the slurry). The size of the bubbles can vary. Usually, the bubble diameter is generally 10 microns to 300 microns, especially 20 microns to 200 microns, generally 20 microns to 80 microns.

In the present invention, the hydrophilic polymer is mixed with the pulp in one or several board plies in stock preparation or short circulation. Typically, hydrophilic polymers can be added to the chests, or directly to the approaching pipe in short circulation. After or simultaneously with the addition, the air is mixed with the pulp. Air can be generated in a conventional pulper, for example, with a mixing rotor or by pumping high-pressure air into the stock inlet pipe before the headbox. A foamed fiber slurry is thus produced.

The foamed fiber slurry is conducted from one or several headboxes 1 to one or several wire sections. On the wire section, the foamed fiber slurry is usually drained with chopping boards, foilboxes, vacuum boxes or vacuum rolls. Thus, a cardboard web is formed. After the wire section, the dry content of the web is typically 18 to 30%, calculated on the total weight of the web.

The web is conducted from the wire section to the press section where dewatering takes place in the nip. The dry content increases to 40 to 50% in the press section.

After the press section, the web is led onto a dryer section. On the dryer section, heated cylinders are generally used in order to evaporate water from the web.

After the dryer section, the board machine usually also has a coating and calendering unit in which the final surface of the board is produced.

Example

The invention has been tested under laboratory conditions. Figure 2 contains a table with bulk and Scott Bond values obtained from tests for the middle ply of folding boxboard.

According to a preferred embodiment for manufacturing the paperboard of the invention, the fibrous material and nanocellulose mixture are mixed with a prefabricated foam made using polyvinyl alcohol. The foam typically has an air content of about 60% to 70% from which the fibrous foam is made (for example by pumping the foam through a wire). Excellent formation is achieved because in a stable foam the particles are kept at a distance and flocculation does not occur. After the web is formed, the fibrous web is dried, eg by sucking air through the web (eg using a suction slit).

Tests of different embodiments of the invention using different polyvinyl alcohol grades as blowing agents to maximize the benefits of polyvinyl alcohol have shown that, on a laboratory scale, for example when using the first polyvinyl alcohol grade and the foam When forming, a folding boxboard midply with a bulk value of 2.99 g/m ³ and a Scott Bond value of 153 J/m ² could be produced from CTMP pulp containing 10% nanofibrillated cellulose (NFC).

Tests of the second embodiment of the present invention have shown that, at laboratory scale, when using a second polyvinyl alcohol grade and foam formation, it is possible to produce a bulk of 2.60 g/ ^m3 from CTMP pulp containing 10% NFC value and a Scott Bond value of 281 J/ ^m2 for folding boxboard interlayers.

Tests of a third embodiment of the present invention have shown that CTMP pulp with 10% NFC can be produced with a bulk of 2.68 g/ ^m3 when using a second polyvinyl alcohol grade and foam formation at laboratory scale value and a Scott Bond value of 314 J/ ^m2 for folding boxboard interlayers.

Testing of a fourth embodiment of the invention has shown that, at laboratory scale, when using a second polyvinyl alcohol grade and foam formation, it is possible to use coarser CTMP pulp without NFC, starch and retention aid additions ( 574 CSF) to make a folding boxboard interlayer with a bulk value of 3.71 g/m ³ and a Scott Bond value of 123 J/m ² .

Reference values for middle layers of folding boxboard containing 10% NFC using sodium dodecyl sulfate (SDS) as blowing agent instead of polyvinyl alcohol are eg 3.11 g/m ³ and 136 J/m ² , respectively.

Reference values (bulk value and Scott Bond value) for the middle layer of folding boxboard containing 10% NFC using non-ionic blowing agent instead of polyvinyl alcohol are eg 3.15 g/m ³ and 137 J/m ² , respectively.

As can be seen from this table, the use of polyvinyl alcohol as blowing agent offers the possibility of obtaining middle layers of folding boxboard with bulk values at least as high as 3.90 g/m ³ . Using sodium lauryl sulfate as blowing agent instead of polyvinyl alcohol, it was possible to obtain middle layers of folding boxboard with bulk values ranging from 2.45 g/m ³ to 3.11 g/m ³ . Using nonionic blowing agents instead of polyvinyl alcohol, it was possible to produce folding boxboard interlayers with bulk values of 3.15 g/m ³ to 3.45 g/m ³ .

As can be seen from the table, the use of polyvinyl alcohol as blowing agent offers the possibility of obtaining middle layers of folding boxboard with Scott Bond values of 105 J/m ² to 314 J/m ² . Using sodium lauryl sulfate as blowing agent instead of polyvinyl alcohol, it is possible to obtain folding boxboard interlayers with Scott Bond values ranging from 70 J/ ^m2 to 149 J/ ^m2 . Using a nonionic blowing agent instead of polyvinyl alcohol produced folding boxboard interlayers with Scott Bond values of 112 J/ ^m2 to 137 J/ ^m2 .

Tests of the fifth embodiment of the invention have shown that, on laboratory scale, when using polyvinyl alcohol with a degree of hydrolysis of 88.0%, it is possible to use coarser CTMP pulp without NFC, starch and retention aid additions (574 CSF) to make a folding boxboard interlayer that matched the aforementioned target values. The polyvinyl alcohol may have another degree of hydrolysis, for example a degree of hydrolysis of 87.0% or 89.0%.

Tests of the sixth embodiment of the invention have shown that, on laboratory scale, when using polyvinyl alcohol with a molecular weight of 27000 g/mole, it is possible to use coarser CTMP without NFC, starch and retention aid additions. Pulp (574CSF) was used to make the middle ply of folding boxboard, which matched the aforementioned targets. The polyvinyl alcohol may have another molecular weight, for example a molecular weight of 25000 g/mole or 35000 g/mole.

In Fig. 3, a multilayer product produced according to the invention is schematically shown. The product may for example be folding boxboard, consisting of an intermediate layer arranged between a top layer and a lower layer. The top and bottom layers may eg be from bleached or unbleached chemical pulp. On the other hand, the middle layer may have chemithermomechanical pulp. The top and/or bottom layer may be further coated with an optional pigment coating, which is not shown in FIG. 3 .

The paperboard typically exhibits a grammage (surface weight) of approximately 50 to 750 ^g /m2.

The folding boxboard intermediate layer according to the invention may have any weight, in particular the weight may be from 10 g/m ² to 300 g/m ² . Testing of a seventh embodiment of the present invention has shown that, at laboratory scale, a coarser CTMP pulp (574 CSF) without NFC, starch and retention aid additions can be used to make a folding boxboard midply that matches The above target values and have a weight of 200 g/m ² . The middle ply of folding boxboard may have another weight, for example a weight of 100 g/m ² or 300 g/m ² .

Any other layer, such as a first further layer, a second further layer, a bottom layer or a top layer may be produced using the method of the present invention or any other method. The first other layer may be the bottom layer and the second other layer may be the top layer. The number of layers in the multilayer product according to the invention is at least two layers. A folding boxboard according to the invention may also consist of, for example, five layers, namely a middle layer, a first further layer, a second further layer, a top layer and a bottom layer.

In the case of a multilayer product, any other layer, eg a first further layer, a second further layer, a bottom layer or a top layer, may have any weight according to the invention. In particular, any other layer may have a weight of 10 g/m ² to 100 g/m ² . Testing of an eighth embodiment of the present invention has shown that a coarser CTMP pulp (574 CSF) without NFC, starch and retention aid additions can be used to make a folding boxboard midply at laboratory scale that matches The aforementioned target value and connected to the top layer with a weight of 50 g/m ² . The top ply of the folding boxboard may have another weight, for example a weight of 20 g/m ² or 80 g/m ² . Coarser CTMP pulp (574 CSF) without NFC, starch and retention aid additions was also used to make a folding boxboard midply matching the aforementioned target values and attached to a bottom layer with a weight of 50 ^g /m2. The bottom layer of the folding boxboard may have another weight, for example a weight of 20 g/m ² or 80 g/m ² .

In another embodiment of the present invention there is provided a wallpaper comprising a fiber layer exhibiting a combination of a) bulk > 1.8 g/m ³ and b) Scott Bond > 100 J/m ³ . In other words, the terms "paperboard" and "board" according to the disclosure herein also include wallpaper or other paper products within the meaning of the present invention. The grammage (surface weight) of the wallpaper can be from 60 g/m ² to 200 g/m ² , for example 90 g/m ² or 110 g/m ² . A wallpaper may comprise one layer or more than one layer. For example, a wallpaper may consist of two layers.

Furthermore, according to certain embodiments, the wallpaper may comprise synthetic fibers. Synthetic fibers may, for example, be made of polyester. The use of synthetic fibers in fibrous foam provides isotropy of the fibers, i.e. the fibers are oriented evenly in all directions to withstand tension. The synthetic fibers are carried by the three-dimensional structure of the foam before the foam is removed on the forming section. The foam separates the fibers thereby reducing flocculation and poor formation. This more uniform three-dimensional orientation improves retention of the synthetic fibers, builds a stronger network because the synthetic fibers bond to each other in all directions, and also results in a more uniform formation. Improved synthetic fiber distribution and bonding in the web provides better dimensional stability, less dusting, better visual appearance and better functionality both in paper converting operations and end use.

Although the invention has been described in detail for purposes of illustration, various changes and modifications may be made within the scope of the claims. Different polyvinyl alcohol grades, different NFC percentages, starch and retention aid additions and use of pulps other than (coarser) CTMP pulps, for example, can obtain other embodiments with other properties. Furthermore, it is to be understood that this disclosure contemplates, 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 fibrous web according to the invention can be used for a wide variety of paperboards. Within the scope of the present invention, mention may be made of the following paperboards: wallpaper substrates, double-sided wallpaper substrates, gypsum liners and gypsum paperboards, and coreboards. Containerboard includes liners, such as kraft board and testliners, as well as fluting and mediums, such as semi-chemical corrugating and recycled medium.

But in this context, of particular interest is cartonboard, which includes folding boxboard, white pulp lined chipboard, gray board, liquid packaging board and food board, as well as solid bleached board and coated unbleached board and carrier boards. Thus, the fibrous web may be an intermediate layer of folding boxboard, cardboard products, packaging, hygiene products, insulation or filters.

The fibrous webs according to the invention can also be used for producing wallpapers.

Citation list

patent documents

US 3,326,745

US 6,413,368

US 2005/0039870

GB1129757

GB1329409

GB1395757

GB1397378

GB1431603

US 4944843

US6419792

WO 2008/040635 A1.

Claims (25)

1. A method of manufacturing a paperboard comprising at least one fibrous web, wherein a fibrous foam is provided, the fibrous foam is shaped into a foamed fibrous layer, the foamed fibrous layer is dewatered and dried to form the paper web, wherein the hydrophilic Aqueous polymers are used as blowing agents to form the fibrous foam. 2. The method according to claim 1 , wherein foam forming is carried out by mixing a fiber slurry with a foam formed by water and a blowing agent to provide a foamed fiber slurry, said foamed fiber slurry Slurry is fed onto the wire to form the foamed fibrous layer. 3. The method according to claim 1 or 2, wherein the fiber slurry has a consistency of 0.6% to 7% by weight. 4. The method according to any one of the preceding claims, wherein a foam is used having an air content of 40% to 80%, for example 55% to 75%, by volume. 5. The method according to any one of the preceding claims, wherein the concentration of the blowing agent is about 150 ppm to 1000 ppm, calculated by the total weight of the liquid. 6. The method according to any one of the preceding claims, wherein at least one foamed fibrous layer is wet pressed after dewatering. 7. The method according to any one of the preceding claims, wherein the foaming agent is selected from water-soluble and water-dispersible polymeric foaming agents, especially water-soluble or water-dispersible polysaccharides, especially polysaccharides and its derivatives. 8. The method according to any one of the preceding claims, wherein the blowing agent is selected from water-soluble and water-dispersible polymer blowing agents, especially water-soluble or water-dispersible hydrophilic polymers and Copolymers such as poly(vinyl alcohol) and poly(vinyl acetate) and copolymers thereof. 9. The method according to any one of the preceding claims, wherein the hydrophilic polymer is used as a blowing agent in an effective amount so as to provide a bulky fibrous layer exhibiting good internal strength properties, As evidenced by at least one of improved Scott Bond and improved strength in the z-direction. 10. A method according to any one of the preceding claims, comprising providing a fibrous layer exhibiting a combination of a) bulk > 1.8 g/ ^m3 and b) Scott Bond > 100 J/ ^m3 . 11. The method according to any one of the preceding claims, wherein synthetic fibers are provided in the fibrous foam. 12. Paperboard having at least one dry foamed fiber layer containing unflocculated fibers treated with a foam formed from water and a hydrophilic polymer as blowing agent. 13. The paperboard of claim 12, wherein the at least one dry, foamed fiber layer is disposed between the first further layer and the second further layer. 14. Paperboard according to claim 12 or 13, comprising mechanical, semi-chemical, chemical, thermomechanical, chemithermomechanical or recycled pulp. 15. The paperboard of any one of claims 12 to 14, wherein the paper web is a cartonboard comprised of a plurality of pulp layers. 16. Paperboard according to claim 15, wherein the bottom and/or top ply has bleached chemical pulp. 17. Paperboard according to claim 16, wherein the bottom and/or top layer is coated with a pigment. 18. Paperboard according to any one of claims 12 to 17, wherein the paperboard is a cardboard product or a part thereof. 19. Paperboard according to any one of claims 12 to 18, wherein the paperboard is a containerboard, in particular selected from the group consisting of folding containerboard, white pulp-lined chipboard, gray board, liquid packaging board, food board , solid bleached board, coated unbleached board and carton board for carrier board. 20. Paperboard according to any one of claims 12 to 19, wherein the blowing agent is selected from water-soluble and water-dispersible polymeric blowing agents, especially water-soluble or water-dispersible polysaccharides, especially polysaccharides and their derivatives. 21. Paperboard according to any one of claims 12 to 19, wherein the blowing agent is selected from water-soluble and water-dispersible polymeric blowing agents, in particular water-soluble or water-dispersible hydrophilic polymeric blowing agents compounds and copolymers such as poly(vinyl alcohol) and poly(vinyl acetate) and their copolymers. 22. Paperboard according to any one of claims 12 to 21, wherein the fibrous layer exhibits a combination of high bulk and good internal strength, in particular a) bulk > 1.8 g/ ^m3 and b) Scott Bond > 100 J/m ³ . 23. Paperboard according to any one of claims 12 to 22, wherein the paperboard has a weight of 110 to 750 ^g /m2, and wherein at least a portion of the product exhibits the combination of: a) bulk > 1.8 g /m ³ and b) Scott Bond >100 J/m ³ . 24. The paperboard of any one of claims 12 to 23, wherein the at least one dry foamed fibrous layer comprises synthetic fibres. 25. Paperboard according to any one of claims 12 to 14, comprising wallpaper.