EP4144914B1 - Multi-layer paper containing recycled paper and additional fibres - Google Patents

Description

The invention relates to a multi-layer, in particular two-layer paper, in particular for use in the production of corrugated cardboard, according to the preamble of claim 1. The invention further relates to a method for producing such a paper.

Two different types of fibers have long been used in paper production to produce a fiber composition, known as pulp, which is then spread in a thin layer on a screen and subsequently dewatered, detached from the screen as a web and further dewatered and finally dried to form the finished paper. These fibers are so-called fresh fibers, which are obtained from fresh pulp, typically wood scraps or wood chips, and broken up to such an extent that they form fibrils with which they later form a firm bond in the paper. In addition, waste paper fibers are also used in paper production, i.e. fibers obtained from paper recovered from the recycling cycle, i.e. waste paper. The use of waste paper fibers is advantageous from an environmental point of view because it enables a second cycle or even several further cycles of the fiber material. On the one hand, the waste paper can be recycled as a valuable raw material, and on the other hand, fewer fresh fibers are needed for paper production, so less wood has to be taken from nature for this purpose.

The problem with waste paper fibres, however, is that they are usually smaller in size than fresh fibres and therefore, especially if they have already been through the recycling process several times, result in poorer bonding within the paper and thus a lower tear resistance of the paper.

For this reason, waste paper fibres were often mixed with fresh fibres in order to reuse the waste paper on the one hand and to ensure that the paper material produced had sufficient tear resistance on the other.

• recyceltem, zuvor aus Frischfasern hergestelltem Kraftkarton oder Kraftpapier, welches Material besonders lange Zellstofffasern enthält,
• herkömmlichem Papier oder Karton, das bzw. der aus gewerblichen Abfällen stammt,
• unbedrucktem weißen Papier (zum Beispiel aus Druckereien oder Buchbindereien stammende Abschnitte von unbedrucktem Papier aus dem Buchdruck),
• nur mit wenig Druckfarbe bedruckten Abschnitten weißen Papiers und
• gemischtem Altpapier aus Haus- oder Gewerbeabfällen.

Nowadays, waste paper is sorted very carefully into different qualities. For example, a distinction is made between:

• recycled kraft cardboard or kraft paper previously made from virgin fibres, which material contains particularly long pulp fibres,
• conventional paper or cardboard from commercial waste,
• unprinted white paper (for example, offcuts of unprinted paper from book printing or bookbinding),
• sections of white paper printed with only a little ink and
• mixed waste paper from household or commercial waste.

This fact has led in particular to the fact that nowadays paper can be made from pure waste paper, the properties of which not only meet the requirements placed on it, for example in terms of tear resistance, but which can also be technologically adjusted to such an extent that different qualities with special properties can be produced. Paper made from pure waste paper is, for example, used to later produce corrugated cardboard in a corrugated cardboard factory.

It is also known to produce paper, including paper made without the use of fresh fibres, in particular 100% recycled paper, in multiple layers, e.g. two layers, with two or more paper layers of different compositions and properties couched together. For example, a If the visible layer or top layer is made of white waste paper in order to produce a layer that is visually attractive and suitable for later printing on this layer, a rear layer on which the visible layer or top layer is applied, possibly with an intermediate layer or several intermediate layers in between, can consist of simple brown waste paper, which does not have to meet high optical requirements. This is advantageous, for example, because white waste paper is a high-priced raw material compared to brown waste paper, the consumption of which is reduced when the paper is produced in multiple layers, in particular two layers. An intermediate layer (or several intermediate layers) can be provided in particular to prevent the rear layer from showing through the top layer.

In principle, it is also known that, in addition to waste paper and fresh fibers, other fibers, in particular grass fibers, can be used in paper production, usually as an additive to fresh fibers and/or waste paper fibers. Grass fibers are fibers that are obtained by appropriate processing from dried, semi-dried or fresh sweet and/or sour grass and/or seaweed and/or algae. Since these fibers are significantly shorter than fresh fibers or waste paper fibers and bond much less firmly to one another in a paper layer, the production of paper from 100% of such fibers is not possible, at least not yet. However, as already mentioned, grass fibers are added to the fiber compositions in paper production. Compared to fresh fibers, grass fibers have two advantages: Firstly, they are cheaper than fresh fibers. According to the current price structure, the price for 1 ton of fresh fibers is around €800 to €1000 compared to a price for 1 ton of grass fibers of around €300-400. Furthermore, grass fibres are more environmentally friendly than fresh fibres, as they can be obtained from a much faster renewable raw material. Compared to waste paper fibres, the advantage is reduced to environmental friendliness alone. Here, grass fibres are superior to waste paper fibres in terms of environmental friendliness, as waste paper fibres often contain printing ink residues, and thus Paper production processes introduce chemicals, often mineral oil-based chemicals, from the printing process, which pollute the process, especially the waste water. However, there is no price advantage, since according to the current price structure, waste paper is significantly cheaper than grass fibers (the current average price for 1 tonne of waste paper is around €80-140).

Paper with added grass fibers is currently in high demand due to its environmental friendliness, for example in the packaging industry, where packaging made from paper with grass fibers, so-called grass paper, is used in particular in the secondary packaging of organic food. This type of paper, which has a greenish appearance on one side due to the added grass fibers, and the individual grass fibers can still be seen as particles, means that the customer recognizes the packaging made from this paper as environmentally friendly and sustainable, so that the overall concept of environmentally friendly food and environmentally friendly and sustainably produced packaging is consistent. This is especially true if the actual carrier fiber of the paper is not fresh fiber, but rather waste paper fiber, which supports the idea of recycling.

In order to meet the demands made by users of grass paper, particularly in the packaging industry, to paper manufacturers to increase the proportion of grass fibres in paper, especially in paper that is otherwise made from waste paper fibres, while also maintaining a visually appealing, easily printable visible surface with a high grass content that clearly shows the character of grass paper, a procedure has already been proposed in which the top layer of a multi-layer paper system is made up of at least two layers couched together, in any case a base layer and a cover layer, and the top layer is formed with a particularly high grass content. Such a procedure is described, for example, in the EP 3 683 357 A1 .

The addition of grass fibers, which further reduce the tear resistance of the resulting paper due to the even shorter fiber length and fibril density, has otherwise only been possible to a limited extent, particularly in the production of paper based on waste paper fibers, which have shorter fiber lengths and fibril density compared to fresh fibers and thus result in paper that is less resilient in terms of tear resistance. However, there are still limits here, which are determined by the requirements placed on the technological properties of the paper.

The inventors have therefore set themselves the task of developing a paper obtained using waste paper fibers and additional fibers obtained from environmentally friendly, rapidly renewable raw materials, which can contain a higher proportion of additional fibers obtained from renewable raw materials while retaining the technological properties of the paper, such as in particular the tear resistance, or which can maintain improved technological properties of the paper while retaining the proportion of additional fibers obtained from rapidly renewable raw materials. In the resulting paper, in particular, a visible surface should continue to have an attractive appearance and also show the high proportion of additional fibers obtained from environmentally friendly, rapidly renewable raw materials.

According to the invention, this object is achieved by a paper, in particular for use in the production of corrugated cardboard, which is formed from at least two layers of different compositions which are couched together. A first layer of the paper forms a base layer and a second layer of the paper forms a cover layer. Furthermore, the paper contains waste paper fibers and additional fibers in the form of fibers other than waste paper. The special feature of the paper according to the invention is that the additional fibers contain at least a proportion of fibers from the Silphium perfoliatum , fibers obtained from fruits and/or the bark of trees of the genus Adansonia , fibers obtained from plants of the genus Cannabis and/or from residues of Contain fibers originating from biogas plants. The base layer may not contain any additional fibers, but may contain a proportion of additional fibers of up to 60% by weight. The top layer always contains additional fibers, with a minimum proportion of 8% by weight. The maximum proportion of additional fibers in the top layer can be 80% by weight. The proportion of additional fibers in the top layer is always higher than the proportion of additional fibers in the base layer. It can, for example, be at least 5% by weight, in particular at least 10% by weight, particularly preferably at least 15% by weight higher than the proportion of additional fibers in the base layer. The proportion of additional fibers in the top layer can, for example, be at least 20% by weight, 30% by weight, 40% by weight, 50% by weight, 60% by weight or 70% by weight. The maximum proportion of additional fibres in the cover layer can be, for example, 70 wt.%, 60 wt.%, 50 wt.%, 40 wt.% or 30 wt.%.

It is similar to the EP 3 683 357 A1 a system with at least two layers is proposed, in which a first of the layers forms a base layer, which therefore ensures stability and essential technological properties, such as in particular tear resistance, and in which a second of the layers forms a cover layer, which can be formed with a correspondingly increased proportion of additional fibers. Since the cover layer itself does not have to form a stability that supports the system, but is supported by the base layer, additional fibers with inherently poor values in terms of fiber length and fibril density can also be used here, such as grass fibers obtained from sweet and/or sedge grass and/or seaweed and/or algae, so that the cover layer can also form a visually appealing visible side of the paper that emphasizes the proportion of additional fibers.

The inventive addition of fibres of the perennial Silphium ( Silphium perfoliatum ) , fibres obtained from fruits and/or the bark of trees of the genus Adansonia , fibres obtained from plants of the genus Cannabis and/or fibres originating from residues of biogas plants into the additional fibres, which can also be formed entirely by such fibres as mentioned above, has been achieved by Inventors discovered that this leads to a significant improvement in the technological properties of the paper obtained in this way. This means that either more additional fibers obtained from rapidly renewable raw materials, in particular plant-based raw materials that are harvested at least once a year, can be used without impairing the technological properties compared to a known grass paper, or improved properties can be obtained with the same amount used. It is also conceivable to work with lower material thicknesses, i.e. smaller paper surface weights, while retaining the technological properties compared to a known grass paper with a higher surface weight.

This improvement in the technological properties is, as the inventors were able to recognize, due to the fact that the fibers mentioned above have significantly longer fibers and a higher fibril density compared to the grass fibers described above. In biogas plants, primarily fast-growing, energy-rich plants are used, such as corn. In particular, the cellulose-containing fibers are not converted into biogas in the fermentation process and remain in the fermentation residues. However, the fermentation residues also contain other components, e.g. proteins not metabolized by the bacteria in the biogas plant. Accordingly, these fermentation residues must also be processed further to separate the fiber material before this fiber material can then be used in the production of a paper according to the invention. The same applies to fibers from the perennial silphium ( Silphium perfoliatum ). These can also be obtained in particular from fermentation residues from biogas plants, since this plant is also used as an energy source in feeding biogas plants. However, it is also conceivable to obtain the fibers of this plant from other processes or to process the plant directly after harvest to obtain fibers for paper production. Since both the residues from biogas plants have to be processed to obtain the paper used in the invention and the fibers of the perennial Silphium ( Silphium perfoliatum ) are currently more expensive to obtain. than waste paper. Nevertheless, their use is advantageous because it represents an improvement from an ecological point of view.

Fibers obtained from the fruits and/or bark of trees of the baobab genus ( Adansonia ) have also proven to be advantageous additional fibers, as these also have a greater fiber length and greater fibril density than the grass fibers described in more detail above. Accordingly, these fibers can also improve the technological properties of the paper obtained in this way, or higher proportions of rapidly renewable raw materials can be used by using these fibers. The fruits of trees of the Adansonia genus, such as fruits of trees of the species Adansonia digitata (African baobab), have always been used for human consumption. The fibers contained in the fruits are separated from the actual pulp, which is used for consumption, and thus arise as a waste product. This can now - after appropriate processing - be used in paper production as disclosed here, thus helping to further improve the sustainability of the paper produced. The fibers from the bark of trees of the genus Adansonia can also be harvested sustainably, in particular without unduly weakening or even endangering the tree itself, and are therefore also suitable for the production of sustainable paper material. The above-mentioned species Adansonia digitata is not the only one that can be used to obtain fibers from fruit and/or bark. Other species of the genus Adansonia can also be considered, such as the species Adansonia grandidieri, Adansonia suarezensis, Adansonia gregorii, Adansonia madagascariensis, Adansonia perrieri, Adansonia rubrostipa and/or Adansonia za.

Fibers obtained from plants of the genus Cannabis also have similarly favorable properties in the form of comparatively long fiber lengths and high fibril density. These are types of hemp. Basically, the fibers from plants of all known types of hemp can be used, especially the species Cannabis sativa in all known variants or subspecies. as well as the species Cannabis indica in all known variants or subspecies.

The additional fibers used according to the invention, which in any case contain a proportion of fibers from the Silphium perfoliatum , fibers obtained from fruits and/or the bark of trees of the genus Adansonia , fibers obtained from plants of the genus Cannabis and/or fibers obtained from residues of biogas plants, can also contain proportions of other fibers, such as grass fibers obtained from sweet and/or sour grass and/or seaweed and/or algae. It is also possible that the additional fibers contain a proportion of fresh fibers. If grass fibers are used, they can be, for example, as in the EP 2 825 699 A1 described in order to be used in the fiber composition, whereby the grass material does not necessarily have to be pelletized, but can also be added as loose bulk material. The grass can also be processed to obtain grass fibers used in the invention in accordance with the EN 10 2013 114 386 A1 take place.

Advantageously, the proportion of fibres from the perennial silphium ( Silphium perfoliatum ), fibres obtained from fruits and/or the bark of trees of the baobab genus ( Adansonia ) , fibres obtained from plants of the genus Cannabis and/or fibres originating from residues from biogas plants in the fibre composition of the covering layer is at least 5% by weight, based on the dry weight of the total fibres incorporated in the covering layer.

In the paper disclosed here, the layer forming the cover layer with the high additional fiber content can not only be kept stable in a paper machine until couching with the layer forming the base layer, but this layer with the high additional fiber content can also be sufficiently firmly bonded to the layer forming the base layer by couching. As a result, and in particular through the use of the fibers By using fibres obtained from the fruit and/or bark of trees of the genus Adansonia , from fibres obtained from plants of the genus Cannabis and/or from fibres obtained from residues of biogas plants, which are additionally beneficial for bonding by couching, it is possible to achieve a splitting strength that is manageable for further processing and use of the paper.

Within the scope of the invention, the paper can also contain more than two layers, in particular one or more intermediate layers can be provided between the base layer and the cover layer. In this case, the couching of the cover layer with the base layer is to be understood as a couching of the cover layer with the intermediate layer(s), a couching of the intermediate layers with each other and a couching of the intermediate layer facing the base layer with the base layer. If intermediate layers are used, these can also contain additional fibers and preferably be based at least predominantly on fibers obtained from waste paper, at most have a small, preferably no, proportion of fresh fibers. The base layer does not necessarily have to be an external layer, it can also be covered on both sides with further layers and couched with these.

When a proportion of the paper in % by weight or of the additional fibres is stated above and below, this proportion is to be understood as a proportion measured on a dry mass basis (after drying in the oven).

The additional fiber material can be pelletized or used as loose bulk material and added to the process.

As already mentioned, the base layer also provides the required stability of the paper in the paper according to the invention described here. It will therefore advantageously have a high proportion of waste paper fibres, in particular those of high fibre quality, and can also consist of 100% waste paper fibres. However, it can also have a proportion of additional fibres, whereby the The additional fibres added to the base layer can in turn have a high proportion of fibres from the perennial silphium ( Silphium perfoliatum ), fibres obtained from the fruit and/or bark of trees of the baobab genus ( Adansonia ) , fibres obtained from plants of the genus Cannabis and/or fibres originating from residues from biogas plants, which, as the inventors have discovered, result in better technological properties of the paper due to the greater fibre lengths and/or higher fibril density. In this respect, if additional fibres are added to both the base layer and the top layer, the composition of the additional fibres added can be different in the two layers. For example, a mixture of additional fibres added to the top layer may contain proportionately fewer fibres from the perennial Silphium ( Silphium perfoliatum ), fibres obtained from fruits and/or the bark of trees of the baobab genus ( Adansonia ) , fibres obtained from plants of the genus Cannabis and/or fibres originating from residues from biogas plants than a mixture of additional fibres added to the base layer.

The proportion of additional fibers in the base layer can be between 20% by weight and 50% by weight, for example, but also less. The maximum proportion of additional fibers in the base layer can also be further limited to 35% by weight or 30% by weight, for example. As already mentioned, it is also conceivable that no additional fibers are contained in the base layer at all, or only small proportions such as 5% by weight, 10% by weight or 15% by weight, or only a maximum of one proportion in the specified size. Accordingly, according to a possible embodiment of the invention, a minimum proportion of waste paper fibers in the base layer can be set at 20% by weight, in particular at 40% by weight, particularly preferably at 60% by weight, but also correspondingly higher, in particular also as a remaining balance of 100% by weight, in each case corresponding to the above-mentioned proportions of additional fibers. In one embodiment, the base layer and also the cover layer can be produced in particular without the addition of fresh fibers. The proportion of additional fibers and also the proportion of with these added fibres of the perennial silphium ( Silphium perfoliatum ), fibres obtained from the fruit and/or bark of trees of the baobab tree genus ( Adansonia ) , fibres obtained from plants of the genus Cannabis and/or fibres originating from residues from biogas plants in the base layer will generally be set according to the requirements for the mechanical properties, in particular the tear resistance, of the paper on the one hand and a total proportion of additional fibres to be set in the paper on the other hand. If inexpensive paper is required, the proportion of additional fibres in the base layer will currently be chosen to be low, preferably zero, since, as mentioned above, the price of waste paper is currently significantly lower than the price of the material of the additional fibres. If there is a change or even a reversal in the price trend, then a different prioritisation can of course prevail and, if necessary, from a cost perspective, a high proportion of additional fibres can also be aimed for in the base layer.

According to the invention, the cover layer should have as high a proportion as possible, or at least a clearly higher proportion, of additional fibers, particularly those obtained from rapidly renewable raw materials, in order to be able to increase the total proportion of additional fibers in the paper and/or to give the cover layer the appearance of paper with a high proportion of such additional fibers. However, the cover layer also usually requires a proportion of other fibers, preferably waste paper fibers, for a minimum strength, particularly in the manufacturing process. Accordingly, the maximum proportion of additional fibers, in particular the actual proportion of additional fibers, can be in a range between 20% by weight and 70% by weight. The minimum proportion of additional fibers in the cover layer can be, for example, 25% by weight, 30% by weight, 35% by weight or even 40% by weight, depending on the requirements that the later user places on the paper according to the invention. It is possible, for example, to incorporate 40% by weight, 50% by weight or even 60% by weight of additional fibers in the cover layer, or up to such proportions as a maximum proportion. The remaining portion is preferably filled with waste paper fibres.

Even if the additional fibers can also contain any proportion of fresh fibers, which can be incorporated in the base layer and/or the cover layer, according to a particular embodiment the paper according to the invention can have no fresh fibers or only a small proportion of fresh fibers, typically a maximum of 10% by weight, in particular a maximum of 5% by weight.

For further technological adjustment of the paper and also for obtaining different properties of the surface showing the base layer and the surface showing the cover layer, it can also be provided in particular that the above-mentioned layers contain different types of waste paper fibers. For example, the cover layer can contain waste paper fibers obtained from white waste paper; in order to obtain an easily printable appearance, the base layer can contain brown waste paper fibers obtained from a cheaper raw material. However, if a brown appearance is desired, the cover layer can also contain waste paper fibers from brown waste paper. The waste paper fibers of the base layer can also be fibers obtained from kraft cardboard or kraft paper, for example, which give the base layer particularly good strength. When choosing such waste paper fibers for the base layer, a particularly high proportion of additional fibers can then also be integrated into the base layer.

The paper according to the invention can be produced in particular as a paper web in a paper machine. As already mentioned above, it is preferably produced as a paper which is used for further production of corrugated cardboard. For this purpose, but also for other purposes, it can in particular have a basis weight of 80 g/m ² to 200 g/m ² , preferably from 125 to 175 g/m ² .

Of this total grammage of the paper, which is reflected in the thickness of the paper in a known manner, the larger proportion, indeed often the significantly larger proportion, is typically made up of the base layer. In the case of the paper according to the invention, this can in particular have a basis weight of 60-170 g/m ² .

This ensures that the base layer can guarantee the sufficient technological properties of the multi-layer, in particular two-layer, paper. The cover layer in the paper according to the invention can typically have a basis weight of 30-50 g/m ² . In a typical multi-layer, in particular two-layer, paper according to the invention, the cover layer makes up about 1/4 to 1/3 of the total thickness of the paper, and the base layer contributes about 2/3 to 3/4 to the total thickness of the paper.

A strong bond between the couched layers is important for the paper according to the invention. In this respect, it is preferred for the paper according to the invention to have a splitting strength determined according to the International Scott Bond Test according to DIN ISO 16260 of 180 to 300 J/m ² , in particular of 220-300 J/m ² .

In order to achieve good printability of the cover layer, it is preferred that the paper according to the invention has a Cobbeo value determined in accordance with DIN EN ISO 535 of a maximum of 40 g/m ² , in particular of less than 35 g/m ² , preferably less than 30 g/m ² . The Cobbeo value, which is a measure of the water absorption of the paper, is set in the manner known in paper production by adding glue and/or starch to the still wet or moist paper web before drying, which is typically carried out in a continuous run over drying cylinders. For certain applications, a high absorbency of the paper is required, i.e. a high Cobb ₆₀ value. This is required, for example, for corrugating medium, i.e. the paper layer that forms the intermediate layer in corrugated cardboard. Higher Cobbeo values can then also be set for such a paper, and in particular it can be worked without any addition of glue or starch. A paper according to the invention can in particular be produced in a paper machine. To do this, the fiber materials used are first introduced in a known manner into separate pulpers, one for the material of the base layer and another for the material of the top layer, in this case waste paper fibers in the pulper for forming the base layer, possibly also additional fibers, and waste paper and additional fibers in the pulper for forming the top layer. Additional fibers can be further treated, in particular fibrillated, before they are fed into the pulper(s). In the paper machine, a first fiber composition that is taken from a first of the pulpers, which may have been sifted again in further separators, refiners and/or vats and which contains water, waste paper fibers and possibly additional fibers, but in a maximum proportion of 50% by weight, based on the dry mass, is then applied to a first screen. This fiber composition forms a first layer, the base layer. In this fiber composition, the proportion of waste paper fibers may in particular be at least 60% by weight, based on the dry mass.

In parallel, in the process, a second fiber composition, which is taken from a second of the pulpers, which has possibly been sifted again in further separators, refiners and/or vats and which contains the waste paper fibers in a maximum proportion of less than 80% by weight, based on the dry mass, and additional fibers in a minimum proportion of 20% by weight, based on the dry mass, but in any case a higher proportion of additional fibers than the first fiber composition, is applied to a second screen. The webs formed from the fiber masses on the two screens are brought together after initial dewatering, if necessary, and couched to form a two-layer paper web. It can also be provided within the scope of the invention that a fiber composition applied to a further screen forms a further web, for example as an intermediate layer, which is brought together with the two webs described above after initial dewatering, if necessary. Several such further webs can also be formed and brought together with the two webs described above. The resulting two- or multi-layer paper web is then further dewatered and finally dried in a manner known in the paper industry, in particular by drying in a passage through drying cylinders. The resulting web-shaped paper is then wound up into a roll and can then be transported and used for further processing. In the appropriately adjusted setting the weight proportions in the fiber compositions, a paper with the weight proportions of waste paper fibers or additional fibers specified above can then be achieved. In the production process, furthermore, a known processing of the reject and a return of the fibers obtained from the reject to the feed of the fiber composition can be carried out.

The proportions of additional fibres and/or waste paper fibres in the fibre compositions for the production of the two webs for the base layer and the cover layer can be selected according to the requirements and in particular with the weight proportions mentioned above in the description of the paper according to the invention.

For example, a two-ply paper according to the invention can contain a total of over 30% by weight of additional fibers and still show sufficient stability, in particular tear resistance, if the base layer contains 75% by weight of waste paper fibers and 25% by weight of additional fibers and the base layer accounts for 110 g/m ² of a total basis weight of the paper of 150 g/m ² , the cover layer contributes 40 g/m ² to basis weight and contains 50% by weight of additional fibers. In addition, the cover layer with the particularly high proportion of additional fibers makes the addition of this material particularly easy to recognize and has an appearance that emphasizes the properties of the paper as paper made with such additional fibers obtained from rapidly renewable raw materials.

It is therefore apparent here that the invention provides a novel paper and a manufacturing process for such a paper, which in the combination of waste paper fibers and additional fibers in the use for the manufacture of such a paper due to the use of fibers of the perennial Silphium ( Silphium perfoliatum ), which are significantly more stable than grass fibers, of fibers obtained from fruits and/or the bark of trees of the genus of baobabs ( Adansonia ) , of fibers obtained from plants of the genus Cannabis and/or of residues of It is possible to use an even higher proportion of additional fibres in fibres originating from biogas plants than is possible with the state of the art according to the EP 3 683 357 A1 was known, without jeopardising the required technological properties, in particular the stability and tear resistance of the paper, and/or in which the side of the paper showing the top layer has an appearance which particularly clearly shows the character of the paper produced with fibres obtained from rapidly renewable raw materials.

Fig. 1

eine schematische Darstellung der Herstellung einer aus einer Tragschicht und einer einen hohen Anteil an Zusatzfasern enthaltenden Deckschicht zusammengefügten, zweilagigen Papierbahn gemäß der Erfindung; und

Fig. 2

in einer tabellarischen Darstellung mögliche Kombinationen von Zusammensetzungen des Papiers jeweils in der Tragschicht (auch als "Unterlage" bezeichnet) und in der Deckschicht (auch als "Decke" bezeichnet).

Further advantages and features of the invention emerge from the following description and from the figures referred to. They show:

Fig.1

a schematic representation of the production of a two-ply paper web according to the invention, composed of a base layer and a cover layer containing a high proportion of additional fibres; and

Fig.2

in a tabular representation possible combinations of compositions of the paper in the base layer (also called "base") and in the top layer (also called "cover").

In Figure 1 A procedure for producing a paper according to the invention is shown schematically.

There, a paper web 10 is produced in multiple layers, here in two layers. For this purpose, a first paper layer, a base layer 11, is formed by applying a first fiber composition to a first screen of a paper machine, e.g. to a lower screen. In parallel, a second paper layer, a cover layer 12, is formed by applying a second fiber composition to a second screen of a paper machine, e.g. to an upper screen. The base layer 11 contains a high proportion of waste paper fibers, e.g. waste paper fibers in a proportion of at least 60% by weight, based on the dry mass. The cover layer 12, on the other hand, is characterized by a high proportion of additional fibers, namely at least 20% by weight in the dry mass. The proportion of additional fibers in the top layer 12 can in particular be between 30 and 70% by weight. The base layer 11 can also contain additional fibers, but this is not mandatory. The proportion of additional fibers in the top layer should be limited to a maximum of 50% by weight, preferably to a maximum of 35% by weight, in particular a maximum of 30% by weight. In any case, the proportion of additional fibers in the top layer 12 is higher, in particular significantly higher, than the proportion of additional fibers in the base layer 11.

The additional fibers used in any case contain fibers from the perennial silphium ( Silphium perfoliatum ), from fibers obtained from the fruit and/or bark of trees of the baobab genus ( Adansonia ) , from fibers obtained from plants of the genus Cannabis and/or from residues from biogas plants. Furthermore, the additional fibers can also contain proportions of grass fibers in the form of fibers from sweet and/or sedge grass and/or seaweed and/or algae and/or fresh fibers. The fact that the additional fibers contain fibers from the perennial silphium ( Silphium perfoliatum ), from fibers obtained from the fruit and/or bark of trees of the baobab genus ( Adansonia ) , from fibers obtained from plants of the genus Cannabis and/or from residues from biogas plants leads to a clearly improved stability, in particular tear resistance, of the paper produced with these fibers compared to the addition of pure grass fibers. This is due to the longer fibers and the higher fibril density of these special fibers.

Preferably, if additional fibers are added to the base layer 11, the rest of the dry mass in the base layer 11 can be formed entirely by waste paper fibers. In this way, the base layer 11 is formed sufficiently stable to be able to meet the tear resistance and other properties required of the paper of the paper web 10.

In the cover layer 12, the proportion of fibers not formed by additional fibers is preferably also completely realized by waste paper fibers.

Fresh fibers are preferably avoided in both layers, the base layer and the cover layer. However, such fresh fibers can be contained in the layers, in particular as components of the additional fibers. In this case, however, the proportion of fresh fibers in the mass of the additional fibers is chosen to be low, in particular in this case it is at most 10% by weight or even significantly less, e.g. below 5% by weight, so that the proportion of such fresh fibers in the resulting paper is also correspondingly low.

Due to the high proportion of additional fibers, the cover layer 12 is not sufficiently stable in itself and as such does not meet the technological properties required of the paper in the paper web 10.

By bringing together the two webs of base layer 11 and cover layer 12 at position 13 and by couching the two webs there, the two-ply paper web 10 is obtained which has the required technological properties - primarily due to the properties of the base layer 11, but also due to the proportion of fibers from the perennial silphium (Silphium perfoliatum ), fibers obtained from fruits and/or the bark of trees of the baobab tree genus ( Adansonia ) , fibers obtained from plants of the genus Cannabis and/or residues from biogas plants in the additional fibers. This paper web 10 is, after further dewatering and drying, typically wound up on a paper roll 14.

The paper web 10 can in particular have a basis weight of 80 to 200 g/m ^2. The paper can, for example, be one that is later used in the production of corrugated cardboard.

The base layer 11 can in particular have a basis weight of 60 to 170 g/m ² . The cover layer 12 can in particular have a basis weight of 30 to 50 g/m ² . By adjusting the ratio of the thicknesses, i.e. basis weights, of the base layer 11 and the cover layer 12, the required technological properties and also a Adjustment of the proportion of additional fibres in the two-layer paper web 10 (with preset proportions of additional fibres in the cover layer 12 and, if applicable, also the base layer 11).

The two-ply paper web 10 preferably has a splitting strength, determined according to the International Scott Bond Test according to DIN ISO 16260, of 180 to 300 J/m ² , in particular of 220 to 300 J/m ² .

For the cover layer 12, a Cobb ₆₀ value according to DIN EN ISO 535 of a maximum of 40 g/m ² , in particular less than 35 g/m ² , preferably less than 30 g/m ² , is preferably set. This is achieved by a known addition of glue and/or starch.

In order to obtain a certain appearance of the cover layer 12, it can be provided, for example, that the waste paper fibers used there are fibers obtained from white waste paper. Especially in a white-based cover layer, the usually greenish or green-brownish or brownish additional fibers can be easily recognized and are thus easily perceived by viewers of an end product made from the paper according to the invention, which has the cover layer 12 as a visible surface.

AP:

Altpapierfasern,

Sil o. Bio:

Fasern der Durchwachsenen Silphie, aus Rückständen von Biogasanlagen stammenden Fasern oder aus Früchten und/oder der Rinde von Bäumen der Gattung der Affenbrotbäume (Adansonia) gewonnene Fasern,

Hanf:

aus Pflanzen der Gattung Cannabis gewonnene Fasern,

Gras:

aus getrocknetem, halbgetrocknetem oder frischem Süß- und/oder Sauergras und/oder Seegras und/oder Algen gewonnene Grasfasern.

In the Figure 2 Possible combinations of the base layer, referred to as the "base" in the figure, and the covering layer, referred to as the "cover" in the figure, are shown in a matrix-like representation or in tabular form. The abbreviations used refer to the following fiber components in the layers:

AP:

Waste paper fibres,

Sil o. Bio:

Fibers from the perennial Silphium, fibers from residues of biogas plants or fibers obtained from fruits and/or the bark of trees of the genus Adansonia ,

Hemp:

fibres obtained from plants of the genus Cannabis ,

Grass:

Grass fibres obtained from dried, semi-dried or fresh sweet and/or sedge grass and/or seaweed and/or algae.

In the overview after Fig.2 Nine combination ranges of base layers and surface layers are shown, illustrated by the crosses in the respective cells. Three different possible composition ranges of base layers are listed, namely, starting from a base layer consisting of 100% waste paper, a base layer composed of waste paper and grass fibers (top row), a base layer composed of waste paper, grass and other fibers, including fibers obtained from plants of the genus Cannabis (middle row) and a base layer composed of waste paper, hemp and grass fibers (bottom row).

The respective proportions of fibres in the differently composed base layers are given in weight % of the composition in the layer and as proportions in the dry mass with possible ranges.

Furthermore, three possible composition ranges of the top layer are shown, in the left column with proportions of waste paper, grass and other fibers as well as possibly fibers obtained from plants of the genus Cannabis . In the middle column a top layer with a composition of waste paper, grass and other fibers is shown. In the right column a composition range of the top layer made of waste paper, grass and possibly fibers obtained from plants of the genus Cannabis is shown.

The respective proportions of fibres in the differently composed cover layers are given in % by weight of the composition in the layer and as proportions in the dry mass with possible ranges.

The above description once again shows the advantages of the paper according to the invention and the process for its production. In particular, it has become clear that by using fibers from the perennial Silphium ( Silphium perfoliatum ), fibers obtained from fruits and/or the bark of trees of the genus Adansonia , fibers obtained from plants of the genus Cannabis and/or from residues from biogas plants, on the one hand the total proportion of additional paper fibers in a paper based on waste paper fibers manufactured paper can be increased and adjusted in a very freely configurable manner, so that in particular a covering layer can be obtained, which can later serve in particular as a visible surface, in which an even higher proportion of additional fibres obtained from rapidly renewable raw materials is incorporated compared to known material, which has a corresponding appearance.

List of reference symbols

10

Paper web

11

Base layer

12

Top layer

13

position

14

Paper roll

Claims (19)

1. A paper (10), in particular for use in the manufacture of corrugated cardboard, wherein the paper (10) is formed from at least two layers of different composition which are rubberised together, wherein a first layer of the paper (10) forms a base layer (11) and wherein a second layer of the paper (10) forms a top layer (12) and wherein the paper (10) in any case contains waste paper fibres and additional fibres in the form of fibres other than waste paper fibres,
   characterised in that the additional fibres contain in any case a proportion of fibres of the cup plant (Silphium perfoliatum), of fibres obtained from fruits and/or the bark of trees of the baobab genus (Adansonia), of fibres obtained from plants of the Cannabis genus and/or of fibres originating from residues of biogas plants, wherein the base layer contains a proportion of additional fibres of 0 to 75 % by weight, and wherein the top layer contains a minimum proportion of additional fibres of 8 % by weight and a maximum proportion of additional fibres of 80 % by weight, wherein furthermore the proportion of additional fibres in the top layer (12) is higher than the proportion of additional fibres in the base layer (11).
2. A paper (10) according to claim 1, characterised in that the proportion of additional fibres in the top layer (12) is at least 5% by weight, in particular at least 10% by weight, particularly preferably at least 15% by weight higher than the proportion of additional fibres in the base layer (11).
3. A paper (10) according to one of the preceding claims, characterised in that additional fibres are also contained in the base layer, in particular in a proportion of at least 5% by weight.
4. A paper (10) according to one of the preceding claims, characterised in that the proportion of additional fibres in the base layer (11) is at most 80% by weight, in particular at most 60% by weight.
5. A paper (10) according to one of the preceding claims, characterised in that the proportion of additional fibres in the top layer (12) is 20 to 70% by weight.
6. A paper (10) according to one of the preceding claims, characterised in that the minimum proportion of additional fibres in the top layer (12) is 25 % by weight, in particular 30 % by weight, preferably 35 % by weight, particularly preferably 40 % by weight.
7. A paper (10) according to one of the preceding claims, characterised in that the base layer has a minimum proportion of waste paper fibres of 20% by weight, in particular of 40% by weight, further preferably of 60% by weight.
8. A paper (10) according to one of the preceding claims, characterised in that the additional fibres also contain a proportion of fresh fibres and/or a proportion of grass fibres in the form of fibres of sweet and/or sour grass and/or seaweed and/or algae.
9. A paper (10) according to any one of the preceding claims, characterised in that the proportion of fibres of the cup plant ( Silphium perfoliatum ) , of fibres obtained from fruits and/or the bark of trees of the baobab genus ( Adansonia ), of fibres obtained from plants of the Cannabis genus and/or of fibres originating from residues of biogas plants in the fibre composition of the top layer is at least 5% by weight, based on the dry weight of the total fibres introduced into the top layer.
10. A paper (10) according to one of the preceding claims, characterised in that it contains no virgin fibres.
11. A paper (10) according to one of the preceding claims, characterised in that the base layer contains other types of recycled paper fibres than the top layer.
12. A paper (10) according to claim 11, characterised in that waste paper fibres obtained from white waste paper are contained in the top layer (12) and that brown waste paper fibres are contained in the base layer (12).
13. A paper (10) according to one of the preceding claims, characterised in that the base layer (11) contains waste paper fibres from kraft paper or kraft board.
14. A paper (10) according to one of the preceding claims, characterised in that it has a basis weight of 80 to 200 g/m², in particular of 125 to 175 g/m².
15. A paper (10) according to one of the preceding claims, characterised in that the base layer (11) has a basis weight of 60 to 170 g/m².
16. A paper (10) according to one of the preceding claims, characterised in that the cover sheet (1 2) has a basis weight of 30 to 50 g/m².
17. A paper (10) according to one of the preceding claims, characterised by a splitting strength determined according to the International Scott Bond Test according to DIN ISO 1 6260 of 180 to 300 J/m², in particular of 220 to 300 J/m².
18. A paper (10) according to one of the preceding claims, characterised by a Cobbeo value of the top layer (12) according to DIN EN ISO 535 of at most 40 g/m², in particular of less than 35 g/m², preferably less than 30 g/m².
19. A method of manufacturing a paper according to any one of the preceding claims, comprising the following steps carried out in a paper machine:

    - a web-shaped application of a first pulp composition comprising water, recycled paper fibres and, if desired, additional fibres in the form of fibres other than recycled paper fibres in a maximum proportion of 50% by weight or less, based on the dry mass, and on a first wire;

    • applying a second pulp composition containing water, waste paper fibres in a maximum proportion of 80% by weight, based on the dry mass, and additional fibres in the form of fibres other than waste paper fibres in a minimum proportion of 20% by weight, based on the dry mass, to a second wire in the form of a web, the second pulp composition having a higher proportion of additional fibres than the first pulp composition;

    • the webs formed on the sieves are smoothed to form a paper web with at least two layers;

    • drying the paper web,
    wherein the additional fibres in any case contain a proportion of fibres of the cup plant Silphium perfoliatum, of fibres obtained from fruits and/or the bark of trees of the genus Adansonia, of fibres obtained from plants of the genus Cannabis and/or of fibres originating from residues of biogas plants.

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