ES2982071T3 - Multi-ply paper containing waste paper fibers and additional fibers - Google Patents

Abstract

A paper (10) according to the invention is formed by at least two layers of different compositions which are bonded together. A first layer forms a base layer (11). A second layer forms a cover layer (12). The paper (10) always contains waste paper fibres and additional fibres in the form of fibres other than waste paper fibres. The paper is characterised in that the additional fibres always contain a proportion of fibres of the perennial species Silphium perfoliatum, fibres obtained from fruits and/or bark of trees of the baobab genus (Adansonia), fibres obtained from plants of the Cannabis genus and/or fibres from biogas plant residues. The base layer contains a proportion of additional fibres of 0 to 75% by weight and the cover layer contains a minimum proportion of additional fibres of 8% by weight and a maximum proportion of additional fibres of 80% by weight. The proportion of additional fibres in the top layer (12) is higher than the proportion of additional fibres in the base layer (11). (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Multi-ply paper containing waste paper fibers and additional fibers

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

In paper production, two different types of fibres have long been used to produce a fibrous composition, the so-called pulp, which is then applied in a thin layer onto a sieve and subsequently dehydrated, released from the sieve as a web and further dehydrated and finally dried to give the finished paper. These fibres are so-called virgin fibres, which are obtained from virgin pulp, usually wood cuttings or wood chips, and are broken down to such an extent that they form fibrils with which they are subsequently firmly bound together in paper. In addition, waste paper fibres, i.e. those fibres that are obtained from paper recovered from the recycling cycle, waste paper, are also used to produce paper. The use of waste paper fibres is advantageous from an environmental point of view because it enables a second cycle or even several more cycles of the fibre material. On the one hand, waste paper can be reused as a valuable raw material, on the other hand, less virgin fibres are needed for paper production, so less wood has to be extracted from nature for this.

The problem with waste paper fibres, however, is that they are generally smaller compared to virgin fibres and therefore, particularly if they have already been through the recycling process several times, result in poorer bonding within the paper and thus a lower tear strength of the paper.

Therefore, in the past, waste paper fibres were often mixed with virgin fibres in order to reuse the waste paper on the one hand and to obtain sufficient tear strength of the generated paper material on the other hand.

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

- kraft cardboard or recycled kraft paper, previously produced from virgin fibres, the material of which contains particularly long cellulose fibres,

- conventional paper or cardboard derived from commercial waste,

- unprinted white paper (e.g. scraps of unprinted typographical paper from printing shops or bookbinding workshops),

- just pieces of white paper printed with a small amount of ink and

- mixed waste paper from domestic or commercial waste.

This has led in particular to the fact that paper can now be produced from pure waste paper, the properties of which not only meet the requirements imposed on it, for example in terms of tear resistance, but can also be technologically controlled to the extent that different qualities with special properties can be produced. The paper produced from waste paper is used, for example, to subsequently produce corrugated cardboard in a corrugated cardboard factory.

It is also known to produce paper, including paper made without the use of virgin fibres, in particular 100 % from waste paper, in multiple layers, for example two layers, with two or more paper layers of different composition and properties pressed together. For example, a visible layer or cover layer can be produced from white waste paper in order to produce a layer that is visually attractive and suitable for subsequent printing on this layer. A back layer on which the visible layer or the cover layer is applied, optionally by interleaving an intermediate layer or several intermediate layers, 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 an expensive raw material compared to brown waste paper, the consumption of which is reduced when the paper is produced in multiple layers, in particular in two layers. In this respect, in particular, an intermediate layer (or also several intermediate layers) can be provided to prevent the back layer from being visible through the cover layer.

In principle, it is known that in addition to waste paper and virgin fibres, other fibres, in particular grass fibres, are also used in paper production, usually as a supplement to virgin fibres and/or waste paper fibres. Grass fibres are fibres obtained by suitable processing from dried, semi-dried or fresh sweet grass and/or bitter grass and/or sea grass and/or algae. Since these fibres are significantly shorter compared to virgin fibres or waste paper fibres and are much less tightly bound together in a paper layer, it is not possible to produce paper from 100 % of these fibres, at least not yet. However, as already mentioned, grass fibres are added to the fibre compositions in paper production. Compared to virgin fibres, grass fibres have two advantages: On the one hand, they are more cost-effective than virgin fibres. According to the current price structure, the price of 1 t of virgin fibres is around €800 to €1000, compared to a price of 1 t of grass fibres of around €300-400. In addition, grass fibres are more environmentally friendly than virgin fibres because they can be obtained from a raw material that grows much more quickly. Compared to recycled paper fibres, the advantage is only reduced to environmental friendliness. In this case, grass fibres are superior to waste paper fibres in terms of environmental friendliness, as waste paper fibres are often contaminated with printing ink residues and thus introduce chemicals into the papermaking process – often mineral oil-based chemicals from the printing process – which pollute the process, in particular waste water. However, there is no price advantage, as, according to the current price structure, waste paper is significantly cheaper than grass fibres (the current average price of 1 tonne of waste paper is around 80-140 Euro).

Paper with added grass fibres is currently in high demand due to its environmental friendliness, for example in the packaging industry, where packaging made from paper containing grass fibres, so-called grass paper, is used in particular in the secondary packaging sector for organic foods. By means of this type of paper, which due to the added grass fibres has a greenish appearance on one of its visible sides and which sometimes allows individual grass fibres to be distinguished as particles, the customer recognises that packaging made from this paper is environmentally friendly and sustainable, so that the overall concept of environmentally friendly food production and environmentally friendly and sustainably produced packaging is consistent. This is particularly true if the actual carrier fibre of the paper is not virgin fibres, but waste paper fibres that support the idea of recycling.

In order to meet the requirements of users of grass paper, in particular of the packaging industry, for paper manufacturers to increase the proportion of grass fibres in paper, in particular otherwise made from waste paper fibres, while also maintaining a visually attractive, easily printable and visible surface that clearly recognises the character of a grass paper with a high proportion of grass, a method has already been proposed in which, in a multi-layer paper system consisting of at least two layers pressed together, in each case a support layer and a cover layer, the cover layer is formed with a particularly high proportion of grass. Such a method is described, for example, in EP 3683357 A1.

The addition of grass fibres, which further reduce the tear strength of the resulting paper due to even lower fibre length and fibril density, could already be increased, especially in the production of paper based on waste paper fibres, which have lower fibre lengths and fibril density than virgin fibres and thus already result in a less robust paper in terms of tear strength. However, there are still limitations in this case due to the requirements placed on the technological properties of the paper.

The inventors have set themselves the objective of developing a paper obtained by using waste paper fibres and additional fibres obtained from environmentally friendly and rapidly renewable raw materials, which, while maintaining the technological properties of the paper, such as in particular the tear strength, can contain a higher proportion of additional fibres obtained from renewable raw materials, or while maintaining the proportion of additional fibres obtained from rapidly renewable raw materials, improved technological properties of the paper can be obtained. In particular, in the paper obtained, a visible surface must additionally have an attractive optic and also an optic that shows the high proportion of additional fibres obtained from environmentally friendly and rapidly renewable raw materials.

According to the invention, this objective is achieved by a paper, in particular for use in the production of corrugated cardboard, which is made up of at least two layers pressed together with different compositions. A first paper layer forms a support layer and a second paper layer forms a cover layer. In addition, the paper contains waste paper fibres and additional fibres in the form of fibres other than waste paper. The special feature of the paper according to the invention is that the additional fibres contain in any case a proportion of sylph fibres (Silphium perfoliatum), fibres obtained from fruits and/or bark of trees of the baobab genus (Adansonia), fibres obtained from plants of the Cannabis genus and/or fibres from biogas plant residues. No additional fibres may be contained in the support layer, but a proportion of additional fibres of up to 60% by weight may also be contained. In any case, additional fibres are contained in the cover layer with a minimum proportion of 8% by weight. The proportion of additional fibres in the cover layer may be a maximum of 80% by weight. The proportion of additional fibres in the cover layer is in any case higher than the proportion of additional fibres in the support layer. For example, it may 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 fibres in the support layer. A proportion of additional fibres in the cover layer may be, for example, 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 may be, for example, 70% by weight, 60% by weight, 50% by weight, 40% by weight or 30% by weight.

Similar to EP 3683 357 A1, a system of at least two layers is proposed here, in which a first of the layers forms a support layer, which therefore guarantees 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 high proportion of additional fibers. Since the cover layer itself does not have to provide stability to the system, but is supported by the support layer, additional fibers with inherently poor values in terms of fiber length and fibril density, such as for example grass fibers obtained from sweet grass and/or bitter grass and/or sea grass and/or algae, can also be used in this case, so that the cover layer in particular can also form a visually attractive visible side of the paper and which highlights the proportion of additional fibers.

The addition according to the invention of sylph fibres (Silphium perfoliatum), of fibres obtained from fruits and/or from the bark of trees of the genus Baobab (Adansonia), of fibres obtained from plants of the genus Cannabis and/or of fibres originating from biogas plant residues to the additional fibres, which can also be made up entirely of the fibres mentioned above, has been found by the inventors to lead to a significant improvement in the technological properties of the paper thus obtained. This means that, compared to a known grass paper, more additional fibres obtained from rapidly renewable raw materials, i.e. in particular plant raw materials that must be harvested at least once a year, can be used without impairing the technological properties or improved properties can be obtained using the same quantity. It is also conceivable to work with smaller material thicknesses, i.e. smaller paper grammages, while maintaining the technological properties compared to a known grass paper with a higher grammage.

As the inventors were able to recognise, this improvement in the technological properties is due to the fact that the above-mentioned fibres have significantly longer fibres and a higher fibril density compared, in particular, to the grass fibres described above. In biogas plants, mainly fast-growing and energy-rich plants, such as maize, are used. In this respect, in particular, cellulose-containing fibres are not converted into biogas during the fermentation process and remain in the fermentation residues. However, the fermentation residues also contain other components, for example proteins, which are not metabolised by the bacteria in the biogas plant. Therefore, these fermentation residues must also be further processed to separate the fibrous material before this fibrous material can be subsequently used in the production of a paper according to the invention. The same applies to Silphium perfoliatum fibres. In particular, these can also be obtained from fermentation residues of biogas plants, since this plant is also used as an energy source for feeding biogas plants. However, it is also conceivable to obtain the fibres from this plant from other processes or to process the plant directly after harvesting to obtain fibres for paper production. Since both the biogas plant residues and the Silphium perfoliatum fibres must be processed for production to obtain the paper according to the invention, these fibrous materials are currently more expensive to purchase than waste paper. However, their use is advantageous because it represents an improvement from an ecological point of view.

Fibres obtained from fruits and/or bark of trees of the genus baobab (Adansonia) have also proven to be advantageous additional fibres, as they also have a longer fibre length and a higher fibril density than, in particular, the grass fibres described in more detail above. Accordingly, these fibres can also improve the technological properties of the paper thus obtained or, by using these fibres, larger proportions of rapidly renewable raw materials can be used. Fruits of trees of the genus Adansonia, such as fruits of trees of the species Adansonia digitata (African baobab), have always been used for human consumption. In this respect, the fibres contained in the fruits are separated from the actual pulp, which is used for consumption, and are thus produced as a waste product. This can now be used, after appropriate processing, in the production of paper as described here and thus helps to further improve the sustainability of the paper produced. Bark fibres from trees of the genus Adansonia can also be harvested sustainably, in particular without excessively 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 the only one that can be used to obtain fibres from the fruit and/or bark. Other species of the genus Adansonia are also considered, such as for example the species Adansonia grandidieri, Adansonia suarezensis, Adansonia gregorii, Adansonia madagascariensis, Adansonia perrieri, Adansonia rubrostipa and/or Adansonia za.

Fibres obtained from plants of the Cannabis genus also have similarly favourable properties in the form of comparatively long fibre lengths and a high fibril density. In this respect, these are hemp species. In principle, plant fibres from all known types of hemp can be used, in particular from the Cannabis sativa species in all known variants or subspecies, as well as from the Cannabis indica species in all known variants or subspecies.

The additional fibres used according to the invention, which in any case contain a proportion of sylph fibres (Silphium perfoliatum), of fibres obtained from fruits and/or bark of trees of the baobab genus (Adansonia), of fibres obtained from plants of the Cannabis genus and/or of fibres from biogas plant residues, may also have proportions of other fibres, such as, for example, in particular also grass fibres obtained from sweet grass and/or bitter grass and/or sea grass and/or algae. It is also possible for the additional fibres to contain a proportion of virgin fibres. If grass fibres are used, then they can be processed, for example, as described in EP 2825699 A1 for use in the fibrous composition, whereby the grass material does not necessarily have to be granulated, but can also be added as loose bulk material. Processing of the grass to obtain grass fibres used in the context of the invention can also be carried out in a manner corresponding to DE 10 201 3114386 A1.

Advantageously, the proportion of sylph fibres (Silphium perfoliatum), fibres obtained from fruits and/or bark of trees of the baobab genus (Adansonia), fibres obtained from plants of the Cannabis genus and/or fibres obtained from biogas plant residues in the fibrous composition of the cover layer amounts to at least 5% by weight, based on the dry weight of the fibres introduced in total into the cover layer.

In the case of the paper disclosed here, too, the layer forming the cover layer with the high proportion of additional fibres can not only be kept stable on a paper machine until it is pressed with the layer forming the support layer, but this layer with the high proportion of additional fibres can still be sufficiently firmly bonded to the layer forming the support layer by pressing. By this, and in particular by using fibres from the sylph (Silphium perfoliatum), fibres obtained from fruits and/or bark of trees of the baobab (Adansonia) genus, fibres obtained from plants of the Cannabis genus and/or fibres from biogas plant residues, which additionally favours the bonding by pressing, a manageable layer separation strength can be achieved for further processing and use of the paper.

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

If a proportion of paper in % by weight or of additional fibres is indicated above and also below, it is understood that this proportion is a proportion measured with respect to a dry mass (after oven drying).

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

As already mentioned, in the paper according to the invention described here, the support layer also provides the necessary stability of the paper. 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 % of waste paper fibres. However, it can also have a proportion of additional fibres, whereby the additional fibres added to the support layer may in turn have a high proportion of fibres from the sylph (Silphium perfoliatum), of fibres obtained from fruits and/or bark of trees of the baobab genus (Adansonia), of fibres obtained from plants of the Cannabis genus and/or fibres from biogas plant residues which, as the inventors have discovered, result in better technological properties of the paper due to the longer fibre lengths and/or the higher fibril density. In this respect, if additional fibres are added to both the support layer and the cover layer, the composition of the added additional fibres can be designed differently in both layers. Thus, for example, in a mixture of additional fibres added to the cover layer, proportionally less sylph fibres (Silphium perfoliatum), fibres obtained from fruits and/or bark of baobab trees (Adansonia), fibres obtained from plants of the genus Cannabis and/or fibres from biogas plant residues can be contained than in a mixture of additional fibres added to the support layer.

The proportion of additional fibres in the support layer can be, for example, between 20% by weight and 50% by weight, but also less than this. The maximum proportion of additional fibres in the support layer can thus also be additionally limited to, for example, 35% by weight or 30% by weight.

As already mentioned, it is also conceivable that there are no additional fibres in the support layer or that there are only small proportions, such as for example 5% by weight, 10% by weight or 15% by weight or in each case only a maximum proportion of the specified size. Accordingly, according to a possible embodiment of the invention, a minimum proportion of waste paper fibres in the support layer can be set to 20% by weight, in particular 40% by weight, particularly preferably 60% by weight, but also correspondingly higher, in particular also as a remainder up to 100% by weight, in each case corresponding to the proportions of additional fibres mentioned above. In one embodiment, the support layer and also the cover layer can be produced in particular without the addition of virgin fibres. The proportion of additional fibres and also the proportion of fibres added to these from sylphium (Silphium perfoliatum), from fibres obtained from fruits and/or bark of baobab trees (Adansonia), from fibres obtained from plants of the genus Cannabis and/or from biogas plant residues in the support layer will generally be adjusted according to the requirements of the mechanical properties, in particular the tear resistance, of the paper on the one hand, and of an adjusted total proportion of additional fibres in the paper on the other hand. If an economical paper is required, the proportion of additional fibres in the support layer will currently be selected quite low, preferably zero, since, as mentioned above, the price of waste paper is currently significantly below the price of the additional fibre material. If a change or even a reversal of the price trend occurs in this case, a different prioritisation may of course prevail and, if necessary, from a cost perspective, a high proportion of additional fibres in the backing layer may also be desired.

According to the invention, the cover layer should have the highest possible proportion, in any case significantly higher, of additional fibers obtained, in particular, 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 a mixed paper with a high proportion of such additional fibers. However, the cover layer usually also requires a proportion of other fibers, preferably waste paper fibers, for minimum strength, in particular in the production 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 downstream user places on the paper according to the invention. In this case, it is possible, for example, to incorporate 40% by weight, 50% by weight or even 60% by weight or even a maximum proportion of additional fibres into the cover layer. The remaining proportion is preferably filled with waste paper fibres.

Although any proportion of virgin fibres may also be contained in the additional fibres, which may be incorporated into the support layer and/or the cover layer, in a special embodiment, the paper according to the invention may have no virgin fibres or only a small proportion of virgin fibres, typically at most 10% by weight, in particular at most 5% by weight.

For further technological adjustment of the paper and also to obtain different properties of the surface facing the support layer and the surface facing the cover layer, it can also be provided in particular that the layers mentioned contain different types of waste paper fibers. For example, waste paper fibers obtained from white waste paper can be contained in the cover layer to achieve an easily printable appearance, brown waste paper fibers obtained from a cheaper raw material can be contained in the support layer. 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 support layer can, for example, also be fibers obtained from kraft cardboard or kraft paper, which give the support layer a particularly good strength. When choosing such waste paper fibers for the support layer, for example, a particularly high proportion of additional fibers can also be integrated into the support layer.

The paper according to the invention can be produced in particular as a paper web on a paper machine. As mentioned above, it is preferably produced as paper which is used for use in the subsequent production of corrugated cardboard. For this purpose, but also for other purposes, it can in particular have a grammage of 80 g/m2 to 200 g/m2, preferably 125 to 175 g/m2.

Of this total grammage of the paper, which is reflected in a known manner in the thickness of the paper, the support layer normally represents the largest proportion, often the significantly largest proportion. In the case of the paper according to the invention, this can in particular have a grammage of 60-170 g/m2.

This ensures that the support layer can guarantee sufficient technological properties of the multi-ply, in particular two-ply, paper. The cover layer in the paper according to the invention can typically have a grammage of 30-50 g/m2. In a typical multi-ply, in particular two-ply, paper according to the invention, the cover layer constitutes approximately 1/4 to 1/3 of the total thickness of the paper, and the support layer contributes approximately 2/3 to 3/4 to the total thickness of the paper.

The important thing for the paper according to the invention is a firm bond of the pressed layers. In this respect, it is preferred that the paper according to the invention has a layer separation resistance of 180 to 300 J/m2, in particular 220-300 J/m2 determined according to the international Scott-Bond test according to DIN ISO 16260.

In order to achieve good printability of the cover layer, it is preferred that the paper according to the invention has a Cobb<60> value determined in accordance with DIN EN ISO 535 of at most 40 g/m2, in particular less than 35 g/m2, preferably less than 30 g/m2. The Cobb<60> value, which is a measure of the water absorption of the paper, is adjusted in a manner known in paper production by adding glue and/or starch to the still wet or damp paper web before drying, which is usually carried out by passing over drying cylinders. For certain applications, a high absorbency of the paper, i.e. a high Cobb<60> value, is required. This is necessary, for example, for corrugated material, i.e. the paper layer forming the middle layer in corrugated cardboard. For such paper, higher Cobb<60> values can then also be set, in particular it can be processed without adding glue or starch. A paper according to the invention can be produced in particular on a paper machine. For this purpose, the fibrous materials used are first introduced in a manner known per se into separate pulpers, in each case one for the support layer material and one for the cover layer material, in this case therefore in each case waste paper fibers in the pulper for the formation of the support layer, if appropriate also additional fibers and waste paper, as well as additional fibers in the pulper for forming the cover layer. The additional fibers can be further treated, in particular crushed to fibrillation, before being introduced into the pulper or pulpers. In the paper machine, a first fibrous composition is then taken, which is extracted from a first of the pulpers, which may have been further sieved in further separators, refiners and/or vats and which contains water, waste paper fibers as well as if appropriate additional fibers, however this in a maximum proportion of 50% by weight, based on the dry matter, onto a first sieve. This fibrous composition forms a first layer, the support layer. In this fibrous composition, the proportion of waste paper fibres can in particular be at least 60% by weight, relative to the dry matter.

In parallel, a second fibrous composition is applied to a second screen in the process, which is taken from a second pulper and which may have been further screened in further separators, refiners and/or vats and which contains the waste paper fibres in a maximum proportion of less than 80% by weight, based on dry matter, and additional fibres in a minimum proportion of 20% by weight, based on dry matter, but in any case a higher proportion of additional fibres than the first fibrous composition. The webs formed from the fibre masses on the two screens are, if appropriate, joined together after a first dewatering and pressed to form a two-ply paper web. It can also be provided within the scope of the invention that a fibrous composition applied to another screen forms a further web, for example as an intermediate layer, which is joined to the two webs described above after a first dewatering, if appropriate. Several such additional webs can also be formed and can be joined together in a corresponding manner with the two webs described above. The two- or multi-ply paper web thus produced is then subsequently dewatered and finally dried in a manner known in paper production, in particular by drying by passing through drying cylinders. The resulting web-shaped paper is finally wound into a roll and can then be transported and used for further processing. By appropriately adjusting the weight proportions in the fibrous compositions, a paper with the aforementioned weight proportions of waste paper fibers or additional fibers can then be obtained. In particular, a known processing of the reject and a return of the fibers obtained from the reject to the feed of the fibrous composition can be carried out in the production process.

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

A paper according to the invention, formed in two layers, for example, if it contains 75% by weight of waste paper fibres and 25% by weight of additional fibres in the support layer and the support layer constitutes a proportion of 110 g/m2 with a total paper weight of 150 g/m2, the cover layer contributes 40 g/m2 of weight and contains a proportion of additional fibres of 50% by weight, can contain a total of more than 30% by weight of additional fibres and can additionally show sufficient stability, in particular tear resistance. In addition, the cover layer with the particularly high proportion of additional fibres makes the addition of this material particularly recognisable and has an appearance which correspondingly underlines the properties of the paper as paper made with such additional fibres obtained from rapidly renewable raw materials.

It can therefore be seen here that the invention provides a new type of paper and a production process for such paper which, in the combination of waste paper fibres and additional fibres in use for the production of such paper due to the use of sylph fibres (Silphium perfoliatum) which are clearly more favourable in terms of stability compared to grass fibres, 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 biogas plant residues, makes it possible to use an even higher proportion of additional fibres than is known from the prior art according to EP 3683 357 A1, in this respect without 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 cover layer has an appearance which particularly reveals the character of the paper produced with fibres obtained from rapidly renewable raw materials.

Other advantages and features of the invention are apparent from the following description and from the figures mentioned in this regard. In this respect, they show:

Figure 1 a schematic representation of the production of a two-ply paper web according to the invention, consisting of a support layer and a cover layer containing a high proportion of additional fibers; and

Figure 2 shows a tabular representation of possible combinations of paper compositions in each case in the support layer (also called "base layer") and in the cover layer (also called "cover").

A process for producing a paper according to the invention is shown schematically in Figure 1.

There, a paper web 10 is produced in several layers, in this case in two layers. For this purpose, a first paper layer, a support layer 11, is formed by applying a first fibrous composition to a first screen of a paper machine, for example to a lower screen. In parallel, a second paper layer, a cover layer 12, is formed by applying a second fibrous composition to a second screen of a paper machine, for example to an upper screen. The support layer 11 contains a high proportion of waste paper fibers, for example waste paper fibers in a proportion of at least 60% by weight, based on the dry mass. The cover layer 12 is characterized, in contrast, by a high proportion of additional fibers, specifically at least 20% by weight in the dry mass. The proportion of additional fibers in the cover layer 12 can be in particular between 30 and 70% by weight. The support layer 11 may also contain additional fibres, but this does not necessarily have to be the case. The proportion of additional fibres in the cover layer should be limited to a maximum of 50% by weight, preferably a maximum of 35% by weight, in particular a maximum of 30% by weight. In any case, the proportion of additional fibres in the cover layer 12 is higher, in particular significantly higher, than the proportion of additional fibres in the support layer 11.

The additional fibres used contain in any case sylph fibres (Silphium perfoliatum), fibres obtained from fruits and/or bark of trees of the baobab genus (Adansonia), fibres obtained from plants of the Cannabis genus and/or biogas plant residues. In addition, the additional fibres may also contain portions of grass fibres in the form of sweet grass fibres and/or bitter grass fibres and/or sea grass and/or algae and/or virgin fibres. The fact that the additional fibres contain sylph fibres (Silphium perfoliatum), fibres from fruits and/or bark of trees of the baobab genus (Adansonia), fibres obtained from plants of the Cannabis genus and/or biogas plant residues leads to a significantly improved stability, in particular tear resistance, of the paper produced with these fibres compared to the addition of pure grass fibres.

This is due to the longer fibers and higher fibril density of these special fibers.

Preferably, if additional fibers are added to the support layer 11, the remainder of the dry mass in the support layer 11 may be formed entirely of waste paper fibers. In this way, the support layer 11 is formed to be sufficiently stable to be able to meet the tear strength and also other required properties of the paper of the paper web 10.

In the cover layer 12, the proportion of fibres that is not made up of additional fibres is preferably also made up entirely of waste paper fibres.

Virgin fibres are preferably avoided in both the support layer and the cover layer. However, such virgin fibres may be present in the layers, in particular as components of the additional fibres. However, it is then selected that the proportion of virgin fibres in the mass of additional fibres is low, in particular this is already at most 10% by weight or even significantly below this, for example below 5% by weight, so that the proportion of such virgin fibres is also correspondingly low in the paper obtained.

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

By joining the two webs of the support layer 11 and the cover layer 12 in position 13 and by pressing the two webs there, the two-layer paper web 10 is obtained, which - primarily due to the properties of the support layer 11, but also due to the proportion of sylph fibres (Silphium perfoliatum), fibres obtained from fruits and/or bark of baobab trees (Adansonia), fibres obtained from plants of the genus Cannabis and/or residues of biogas plants in the additional fibres - has the required technological properties. This paper web 10 is usually wound onto a paper roll 14 after it has been dewatered and subsequently dried.

The paper web 10 may in particular have a grammage of 80 to 200 g/m2. The paper may, for example, be one that is used in a further use in the production of corrugated cardboard.

The support layer 11 can have in particular a grammage of 60 to 170 g/m². The cover layer 12 can have in particular a grammage of 30 to 50 g/m². By adjusting the ratio of the thicknesses, i.e. the grammages, of the support layer 11 and the cover layer 12, the required technological properties can be adjusted and also the proportion of additional fibers in the two-ply paper web 10 can be adjusted (with predetermined proportions of additional fibers in the cover layer 12 and, if appropriate, also in the support layer 11).

The two-ply paper web 10 preferably has a layer separation strength, determined according to the international Scott-Bond test according to DIN ISO 16260, of 180 to 300 J/m2, in particular 220 to 300 J/m2.

For the cover layer 12, a Cobb value<60> according to DIN EN ISO 535 of a maximum of 40 g/m2, in particular less than 35 g/m2, preferably less than 30 g/m2 is preferably set. This is achieved by a known addition of glue and/or starch.

In order to achieve a specific appearance of the cover layer 12, it can be provided, for example, that the waste paper fibres used there are fibres obtained from white waste paper. Particularly in a white base cover layer, the additional fibres, which are usually greenish or green-brown or brown, can be easily recognised and are therefore easily perceived by those who observe a final product produced from the paper according to the invention, which has the cover layer 12 as a visible surface.

In Figure 2, the possible combinations of support layer, referred to as "base layer" in the figure, as well as cover layer, referred to as "cover" in the figure, are illustrated in a matrix-like representation or in a table. In this respect, the abbreviations used refer to the following fiber components in the layers:

AP: used paper fibers,

Sil or Bio: sylph fibers, fibers from biogas plant waste or fibers obtained from Adansonia, Hemp: fibers obtained from plants of the Cannabis genus,

Grass: grass fibres obtained from dried, semi-dried or fresh sweet grass and/or bitter grass and/or sea grass and/or algae.

The summary according to Figure 2 shows nine combination ranges of support layers and cover layers, represented by crosses in the respective cells. Three different possible composition ranges of support layers are listed here, namely in each case starting from a support layer consisting of 100 % waste paper, such a support layer consisting of waste paper fibres and grass fibres (top row), a support layer consisting of waste paper fibres, grass fibres and other fibres, possibly also fibres obtained from plants of the genus Cannabis (middle row) and a support layer consisting of waste paper fibres, hemp fibres and grass fibres (bottom row).

The respective proportions of the fibres in the support layers of different composition are indicated in % by weight of the composition in the layer and as proportions in the dry mass with possible intervals.

In addition, three possible composition ranges of the cover layer are shown, with the left column showing proportions of waste paper fibres, grass fibres and other fibres, as well as fibres obtained from plants of the genus Cannabis, if applicable. The middle column shows a cover layer with a composition of waste paper fibres, grass fibres and other fibres. The right column shows a composition range of the cover layer consisting of waste paper fibres, grass fibres and fibres obtained from plants of the genus Cannabis, if applicable.

The respective proportions of the fibres in the cover layers of different composition are indicated in % by weight of the composition in the layer and as proportions in the dry mass with possible intervals.

From the above description it is clear once again what advantages the paper according to the invention and the process for its production have. In particular, it has become clear that by using sylph fibres (Silphium perfoliatum), fibres obtained from fruits and/or bark of trees of the genus baobab (Adansonia), fibres obtained from plants of the genus Cannabis and/or residues of biogas plants, on the one hand, the total proportion of additional paper fibres in a paper produced from waste paper fibres can be increased and adjusted in a very freely configurable manner, so that in this respect in particular a cover layer can also be obtained which can subsequently serve in particular as a visible surface, in which a higher proportion of additional fibres obtained from rapidly renewable raw materials has been introduced than of the known material, which has the corresponding appearance.

List of references

10 Paper band

11 Support layer

12 Cover layer

13 Position

14 Roll of paper

Claims (19)

1. Paper (10), in particular for use in the production of corrugated cardboard, wherein the paper (10) is formed by at least two layers pressed together with different compositions, wherein a first layer of the paper (10) forms a support layer (11) and wherein a second layer of the paper (10) forms a cover layer (12) and wherein the paper (10) contains in any case used paper fibres and additional fibres in the form of fibres other than used paper, characterised in that the additional fibres in any case contain a proportion of sylph fibres (Silphium perfoliatum), of fibres obtained from fruits and/or bark of trees of the genus baobab (Adansonia), of fibres obtained from plants of the genus Cannabis and/or of fibres from biogas plant residues, wherein a proportion of additional fibres of 0 to 75% by weight is contained in the support layer, and wherein a minimum proportion of additional fibres of 8% by weight is contained in the cover layer. by weight and a maximum proportion of additional fibres of 80% by weight, wherein the proportion of additional fibres in the cover layer (12) is greater than the proportion of additional fibres in the support layer (11). 2. Paper (10) according to claim 1, characterized in that the proportion of additional fibres in the cover 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 support layer (11). 3. Paper (10) according to one of the preceding claims, characterized in that additional fibers are also contained in the support layer, in particular in a proportion of at least 5% by weight. 4. Paper (10) according to one of the preceding claims, characterized in that the proportion of additional fibres in the support layer (11) is at most 80% by weight, in particular at most 60% by weight. 5. Paper (10) according to one of the preceding claims, characterized in that the proportion of additional fibers in the cover layer (12) is 20 to 70% by weight. 6. Paper (10) according to one of the preceding claims, characterized in that the minimum proportion of additional fibres in the cover layer (12) is 25% by weight, in particular 30% by weight, preferably 35% by weight, particularly preferably 40% by weight. 7. Paper (10) according to one of the preceding claims, characterized in that the support layer has a minimum proportion of used paper fibres of 20% by weight, in particular 40% by weight, more preferably 60% by weight. 8. Paper (10) according to one of the preceding claims, characterized in that the additional fibers also contain a proportion of virgin fibers and/or a proportion of grass fibers in the form of sweet grass and/or bitter grass and/or sea grass fibers and/or algae. 9. Paper (10) according to one of the preceding claims, characterized in that the proportion of sylph fibres (Silphium perfoliatum), of fibres obtained from fruits and/or from the bark of trees of the genus baobab (Adansonia), of fibres obtained from plants of the genus Cannabis and/or of fibres from biogas plant residues constitutes at least 5% by weight of the fibre composition of the cover layer, based on the dry weight of the fibres introduced in total into the cover layer. 10. Paper (10) according to one of the preceding claims, characterized in that it does not contain virgin fibers. 11. Paper (10) according to one of the preceding claims, characterized in that the support layer contains other types of used paper fibers than the cover layer. 12. Paper (10) according to claim 11, characterized in that the cover layer (12) contains waste paper fibers obtained from white waste paper and the support layer (12) contains brown waste paper fibers. 13. Paper (10) according to one of the preceding claims, characterized in that used paper fibers made of kraft paper or kraft cardboard are contained in the support layer (11). 14. Paper (10) according to one of the preceding claims, characterized in that it has a weight of 80 to 200 g/m2, in particular 125 to 175 g/m2. 15. Paper (10) according to one of the preceding claims, characterized in that the support layer (11) has a weight of 60 to 170 g/m2. 16. Paper (10) according to one of the preceding claims, characterized in that the cover layer (12) has a weight of 30 to 50 g/m2. 17. Paper (10) according to one of the preceding claims, characterized by a layer separation resistance determined according to the international Scott-Bond test according to DIN ISO 16260 of 180 to 300 J/m2, in particular 220 to 300 J/m2. 18. Paper (10) according to one of the preceding claims, characterized by a Cobb value<60> of the cover layer (12) according to DIN EN ISO 535 of at most 40 g/m2, in particular less than 35 g/m2, preferably less than 30 g/m2. 19. Process for producing a paper according to one of the preceding claims, with the following steps performed on a paper machine: • applying in the form of a band onto a first sieve a first fibrous composition containing water, used paper fibres and, if appropriate, additional fibres in the form of fibres other than used paper in a proportion of not more than 50% by weight or less, relative to the dry mass; • applying in the form of a band on a second sieve a second fibrous composition containing water, used paper fibres in a maximum proportion of 80% by weight, relative to the dry mass, as well as additional fibres in the form of fibres other than used paper in a minimum proportion of 20% by weight, relative to the dry mass, where the second fibrous composition has a higher proportion of additional fibres than the first fibrous composition; • press the formed bands on the sieves to give a paper band of at least two layers; • dry the paper web, where the additional fibres contain in any case a proportion of sylph fibres (Silphium perfoliatum), of fibres obtained from fruits and/or bark of trees of the genus baobab (Adansonia), of fibres obtained from plants of the genus Cannabis and/or of fibres from biogas plant residues.