AU2022261651A1

AU2022261651A1 - Printable, multi-layered paper for packaging and process for production thereof

Info

Publication number: AU2022261651A1
Application number: AU2022261651A
Authority: AU
Inventors: Marvin MÖHLE
Original assignee: Mondi AG
Current assignee: Mondi AG
Priority date: 2021-04-21
Filing date: 2022-04-19
Publication date: 2023-12-07
Also published as: AT524998B1; WO2022221897A1; EP4355949A1; AT524998A1; BR112023021532A2

Abstract

The invention relates to a process for producing a multi-layered paper for packaging which is printable/intended for printing and to a multi-layered paper for packaging which is printable/intended for printing. The process comprises providing or producing a cellulose fiber-comprising bleached first pulp and providing or producing a cellulose fiber-comprising second pulp. Here, the cellulose fiber-comprising second pulp provided or produced is a mixture consisting of 40% by weight to 80% by weight of unbleached pulp material and 20% by weight to 60% by weight of bleached pulp material, based on 100% by weight of total dry matter of the second pulp.

Description

PRINTABLE, MULTILAYER PAPER FOR PACKAGING AND METHOD FOR PRO DUCTION THEREOF

The invention relates to a method for producing a multilayer paper for packaging which is printable or is intended for printing, and a multilayer paper for packaging which is printable or is intended for printing.

Product manufacturers and/or sellers usually demand printable packaging for their products, for example to display graphic representations of the contained products and/or product infor mation for consumers. Such product packaging is common in practically all sectors nowa days, such as in food production and sales or device manufacturing and sales. Demand is hereby increasing for high quality printing, in particular high colour density, sharpness and contrast of the printed images applied to the packaging paper to represent the contained prod uct in as attractive and enticing manner as possible.

Printable papers for packaging can, on the one hand, be configured as separate packaging pa pers, such as outer packaging papers. On the other hand, a generic paper for packaging can also be a component, in particular a printable outer paper layer, of packaging as is frequently the case with carton packaging. Generic multilayer papers or paper plies are also referred to as liners, paper liners, or kraft liners. Accordingly, the present printable, multilayer paper for packaging can also be referred to as a liner, paper liner or kraft liner.

In order to provide as high a print quality as possible, in particular high colour density, colour sharpness and contrast, a surface intended for printing with a high brightness is desirable in the packaging papers according to the present invention. Bleached pulp is frequently used for this purpose when producing printable papers for packaging. On the one hand, printable pa pers for packaging are known which are produced entirely from bleached pulp, or which ex clusively comprise bleached cellulose fibre material. The disadvantages of such entirely bleached papers include a deterioration primarily of the mechanical properties of the resulting packaging due to the chemical treatment of the pulp and the increased amount of process chemicals required, and of course the corresponding increased production costs.

On the other hand, multilayer packaging papers or paper liners are known which have an outer top ply or top layer intended for printing made from bleached fibre material, with a car rier layer beneath made from unbleached cellulose fibre material, including unbleached recy cled fibre material. Depending on the type of unbleached pulp material used for the produc tion of the carrier layer, the surface of the top ply intended for printing of such multilayer pa pers for packaging does, however, often have a greyish or brownish appearance. That is be cause the unbleached fibre material of this lower carrier layer practically shines through the top layer made from bleached fibre material. This of course leads to disadvantages regarding printing quality, in particular because colours of printed images can appear distorted. In order to provide a high brightness of such multilayer packaging papers, it was thus far necessary or known to use a top layer with a very high grammage. This, however, is itself disadvantageous regarding resource efficiency and production costs.

A multilayer paper for packaging or a corresponding (paper) liner is known from EP 1392 923 BI, for example.

The problem to be solved by the present invention was to overcome the existing disad vantages in the prior art and, on the one hand, provide an economically and ecologically im proved method for producing a printable paper for packaging, the use of said method allowing for the production of a paper with good mechanical properties and at the same time good printability, in particular a high brightness. On the other hand, the problem to be solved by the invention was the provision of a paper for packaging with good mechanical properties and at the same time good printability, said paper being producible in an improved economical and ecological respect.

This problem is solved firstly by a method according to the claims.

The method according to the invention for producing a multilayer paper for packaging or packaging paper which is printable or intended for printing comprises the steps - the provision or production of a bleached first cellulose comprising cellulose fibres and pro duction of a first paper web comprising the first cellulose by forming afirst pulp comprising the first cellulose and dehydration/drying of this first pulp, - the provision or production of a second cellulose comprising cellulose fibres and production of a second paper web comprising the second cellulose by forming a second pulp comprising the second cellulose and dehydration/drying of this second pulp,

- the connection of the two paper webs into a multilayer paper web, such that the first paper web forms an uppermost or outer top layer and the second paper web forms a carrier layer, which is directly connected to this uppermost top layer, of the multilayer paper web, - the optional production of one or more further paper layers and the connection of at least one of these further paper layers with the carrier layer, - the optional further drying of the multilayer paper web, - the assembly of the multilayer paper web.

As a second cellulose comprising cellulose fibres, a mixture consisting of 40 wt. % to 80 wt. % unbleached cellulose material and 20 wt. % to 60 wt. % bleached cellulose material related to 100 wt. % total dry mass of the second cellulose is provided or produced.

Here and in the following, the term pulp is to be understood as an aqueous suspension of the respective cellulose. As usual, other terms such as fibrous material-water suspension, fibre suspension, cellulose suspension etc. can be used synonymously. An initial consistency of the first and the second pulp can, for example, be 0.5 % to 2 %. Standard adjuvants can also be optionally added to the first and/or second pulp in addition to the respective cellulose materi als. By way of example, these could include wet-end starch, PAC (polyaluminium chloride), ASA (alkyl succinic anhydride) or other sizing agents, wet strength agents, betonite etc.. As is known in the art, a percentage by weight of such adjuvant chemicals in the pulp can be low.

Unbleached cellulose material is to be understood in very general terms as a cellulose material which is not bleached during the production process of the printable, multilayer paper.

A packaging paper with high brightness and at the same time good mechanical properties can be produced using the described method. This is achieved despite the high proportion of un bleached cellulose material. Surprisingly, a grammage or layer thickness of the top layer can be kept low without overly compromising the brightness of the surface of the top layer which is intended for printing, as shall be explained in more detail in the following using corre sponding values of the paper for packaging. Overall, a packaging paper or a paper for packag ing with good printability, in particular printable with print images of high quality and colour fidelity that also fulfils the mechanical robustness and strength requirements for packaging papers can be produced using the described method.

At the same time, compared to the production of fully bleached packaging papers, the amount of process chemicals used during the method can be reduced. Due to the lower amounts of bleached cellulose material used and the lower grammage of the top layer enabled, the amount of cellulose can be kept low overall. This and the reduced use of chemicals consequently also have a positive effect regarding the production costs of the packaging paper.

Preferably, as a second cellulose comprising cellulose fibres, a mixture consisting of 45 wt.

% to 75 wt. % unbleached cellulose material and 25 wt. % to 55 wt. % bleached cellulose mate rial related to 100 wt. % total dry mass of the second cellulose can be provided or produced.

The unbleached cellulose material of the second cellulose can preferably be selected from a group consisting of unbleached, virgin long-fibre pulp material, unbleached recycled fibre cel lulose material, or a mixture of unbleached cellulose material from this group.

The term recycled fibre cellulose material is to be understood in particular as a cellulose mate rial obtained by processing already used waste paper. The term recycled fibre cellulose mate rial is defined in ISO 4046-4:2016. The term recycled fibre cellulose material is not under stood as a cellulose material discarded or lost during a packaging paper production process as defined in ISO 4046-3 and commonly referred to as broke.

A mixture of 30 wt. % to 80 wt. % bleached short-fibre cellulose material and 20 wt. % to 70 wt. % bleached long-fibre cellulose material can preferably be used as the bleached cellulose material of the second cellulose.

In particular, 70 wt. % to 100 wt. % bleached short-fibre cellulose material can be used to form the bleached cellulose material of the first cellulose. Depending on requirements, how ever, up to 30 wt. % long-fibre cellulose material can be also used to form the bleached cellu lose material of the first cellulose.

The cellulose materials described herein have proven to be particularly well suited for the pro duction of a paper for packaging with the desired or sufficiently good properties, in particular for obtaining good mechanical properties and sufficient strength and at the same time good printability.

According to a further embodiment, it can be provided that directly prior to connecting the first paper web and the second paper web, a dry content of the first paper web is set to 3 % to 50 % and a dry content of the second paper web is set to 3 % to 50 %.

It has been found that a connection of the two paper webs within the two stated dry content ranges is particularly successful. As a further result, very good adhesion of the top layer and the carrier layer to one another in the paper for packaging can also be provided. In particular, a delamination of the two plies can be prevented effectively.

Furthermore, 100 kg to 150 kg of a white pigment filler material per tonne of total dry mass of the bleached first cellulose can be added to the first pulp or thefirst paper web.

This measure can further improve the printability of the surface of the top layer of the paper for packaging. The white pigment filler material thereby gives the top layer further opacity or covering effect over the carrier layer below. Surprisingly, the addition of such a large quan tity of filler material as described above has proven possible, without, in particular, excessive losses in the mechanical properties of the packaging paper, in particular its mechanical strength, having to be accepted. Moreover, the production costs for the paper for packaging can be further reduced in this manner.

Calcium carbonate or lime can preferably be added to the first pulp or first paper web as a white pigment filler material.

According to a preferred method, it can be provided that after complete drying to a final dry content the multilayer paper web is produced with a grammage of 75 g/m 2 to 120 g/m2 ,

wherein the top layer is produced with a grammage of 50 g/m 2 to 70 g/m 2 , and wherein a ratio of the grammage of the top layer to a grammage of the carrier layer is set to 1.2:1 to 2:1.

Corresponding grammages can, as is known in the art, be configured by adjusting various pro cess parameters such as consistencies in a constant part of a paper machine, the quantities of pulp fed into the headbox of a paper machine, and headbox consistency, throughput speeds in various areas of a paper machine, and so on. A paper with the disclosed grammages and grammage ratios has proven to be particularly well suited for combining good mechanical properties and good printability. Furthermore, the described measures can provide a paper for packaging with low material use overall, but nevertheless good properties.

According to a further method, the second cellulose can be provided or produced with a Schopper-Riegler value according to ISO 5267-1:2000 of 20 °SR to 35 °SR.

A corresponding cellulose material has proven to be particularly well suited for forming the second cellulose, and further for the formation of the carrier layer of the packaging paper. De pending on the feedstock cellulose materials, a cellulose within the aforementioned Schopper Riegler value range can be obtained through mechanical grinding and/or defibration as is known in the art, in particular in refiners.

Specifically, in a preferred method the second cellulose can be provided or produced with a Kappa number according to ISO 302:2015 of 20 to 65.

By using a second cellulose with corresponding Kappa number from the disclosed ranged, a well-suited colouration of the carrier layer of the packaging paper or paper for packaging can be configured without far-reaching losses in the mechanical strength of the packaging paper having to be accepted. A Kappa number within the disclosed range can, as is known in the art, be configured primarily through the selection and/or processing of the respective cellulose materials, predominantly during chemical pulping, and through the composition of cellulose materials for the formation of the second cellulose.

Furthermore, the first, bleached cellulose can be provided or produced with a Kappa number according to ISO 302:2015 of 12 or less, preferably 10 or less.

Furthermore, it can be expedient for a smoothing of a surface intended for printing of the top layer of the multilayer paper web to be provided for. Specifically, such a smoothing can be performed by calendering this surface using a calender such as hard-nip, soft-nip, long-nip, or shoe calenders or metal strip calenders.

In the broadest sense, this can improve the quality of the surface intended for printing, whereby the quality of the print images applied to this surface can be further improved. The person of skill in the art is fundamentally familiar with various parameters such as pressure, temperature and dwell time during calendering to achieve respective desired surface proper ties, for example surface roughness.

The problem to be solved by the invention is also solved by a multilayer paper for packaging or a packaging paper which is printable or intended for printing, according to the Claims.

The paper for packaging or packaging paper comprises

- a first top layer, predominantly comprising a first, bleached cellulose fibre material or pre dominantly consisting of a first, bleached cellulose fibre material, - and a carrier layer which is directly connected with the upper top layer, predominantly com prising a second cellulose fibre material or predominantly consisting of a second, bleached cellulose fibre material.

The second cellulose fibre material is formed by a mixture consisting of 40 wt. % to 80 wt.

% unbleached fibre material and 20 wt. % to 60 wt. % bleached fibre material related to 100 wt. % total dry mass of the second cellulose fibre material.

These features allow for the provision of a highly printable paper for packaging, which in par ticular has a high brightness on the surface of the top layer to be printed, and thus also ensures a high colour sharpness or colour fidelity of print images printed thereupon. At the same time, a packaging paper with good mechanical properties can be provided. Surprisingly, a gram mage or layer thickness of the top layer can be kept low without overly compromising the brightness of the surface of the top layer which is intended to be printed upon. This shall be explained in more detail in the following using corresponding values of the paper for packag ing.

Furthermore, a corresponding packaging paper can be produced using the method as de scribed above, said method excelling through high efficiency in both an ecological and eco nomic respect. Preferably, the second cellulose fibre material can be formed by a mixture con sisting of 45 wt. % to 75 wt. % unbleached fibre material and 25 wt. % to 55 wt. % bleached fibre material related to 100 wt. % total dry mass of the second cellulose fibre material. Un bleached fibre material is to be understood as a fibre material which was not bleached during the production process of the printable, multilayer paper or results from an unbleached cellu lose material.

The top layer of the packaging paper or its outward-facing surface is intended for printing, and when the paper is used this top layer forms the outer layer of a packaging intended for printing. The paper for packaging can fundamentally be used on its own for packaging pur poses as primary packaging and is also suited as outer packaging paper to cover items or ob jects. A further, common use of the paper for packaging is an application on or connection with other primary packaging, such as a packaging carton. Specifically, use of the packaging paper as a printable top paper for cardboard or carton packaging etc. is therefore possible. Nevertheless, the paper according to the present invention is also suitable as a component of secondary packaging or as secondary packaging on its own, that is to say as packaging or a packaging component of packaging without direct contact with the packaged products.

According to a preferred embodiment of the paper for packaging, the unbleached fibre mate rial of the second cellulose fibre material can be selected from a group consisting of un bleached, virgin long-fibre material, unbleached recycled fibre material, or a mixture of un bleached fibre materials from this group.

As already determined above in connection with the term recycled fibre cellulose material, the term recycled fibre material is to be understood as a processed fibre material obtained by pro cessing already used waste paper into new paper, here the multilayer paper for packaging. As above, reference is also made to the terminological definition according to ISO 4046-4:2016 regarding the term recycled fibre material.

Furthermore, the bleached fibre material of the second cellulose fibre material can be formed from a mixture of 30 wt. % to 80 wt. % bleached short-fibre material and 20 wt. % to 70 wt. % bleached long-fibre material.

Moreover, it can also be provided that the bleached fibre material of the first cellulose fibre material comprises 70 wt. % to 100 wt. % bleached short-fibre material. The bleached fibre material of the first cellulose fibre material can thereby also comprise up to 30 wt. % bleached long-fibre material.

In particular, the bleached fibre material of the second cellulose fibre material can have a Kappa number according to ISO 302:2015 of 12 or less, preferably 10 or less, and in particu lar 5 or less.

The cellulose fibre materials described herein have proven to be particularly well suited for achieving desired or sufficiently good properties, in particular for obtaining good mechanical properties and sufficient strength and at the same time good printability.

According to a further embodiment of the paper for packaging, its top layer can have a white pigment filler material, wherein an ash residue according to ISO 1762:2015 of the top layer can be from 10 wt. % to 14 wt. %.

The printability of the surface of the top layer of the paper for packaging can thereby be fur ther improved. The white pigment filler material thereby gives the top layer further opacity or covering effect over the carrier layer below. Surprisingly, it has been found that such a high quantity of filler material does not lead to excessive losses in the mechanical properties of the packaging paper having to be accepted. As is known in the art, depending on the materials or additives used during production, the measurable ash residue is generally primarily consti tuted by mineral additives or inorganic aggregates. For the sake of completeness, it should be noted that regarding the method for producing the paper, during the dehydration or drying of the pulp of the paper web formed in the paper machine, unavoidable loss of inorganic aggre gates used can always occur, for example during dehydration on a wire section. This unavoid able loss thus leads to a reduction of the measurable ash residue in the paper compared to the quantities of inorganic aggregates added in the method.

Preferably, the white pigment filler material can be formed by calcium carbonate or lime.

According to a further embodiment of the paper for packaging, the paper can have a Cobb 60 value of 30 g/m 2 to 40 g/m 2 when the top layer is impacted with water according to ISO 535:2014.

This feature can improve the printability of the paper for packaging. Specifically, the absorp tion of standard, water-based inks and their drying on the paper can be improved, thus in par ticular preventing undesired penetration of the printing ink. As is known in the art, the Cobb 60 value can thereby be primarily influenced by the materials used, in particular also by the use of additives such as sizing agents, for instance alkenyl succinic anhydride (ASA).

The paper for packaging can have a grammage of 75 g/m 2 to 120 g/m 2 , wherein the top layer can have a grammage of 50 g/m 2 to 70 g/m 2 , and wherein a ratio of the grammage of the top layer to a grammage of the carrier layer can be 1.2:1 to 2:1.

A paper with the disclosed grammages and grammage ratios has proven to be particularly well suited for combining good mechanical properties and good printability. It is hereby sur prising that the grammage of the top layer can be kept so low and nevertheless good printabil ity can be provided.

According to a further embodiment of the paper for packaging, a burst index of the paper ac cording to ISO 2758:2014 can be from 3.5 kPa*m2 /g to 4.5 kPa*m 2/g.

The paper can thereby be provided with sufficiently good mechanical strength for packaging purposes.

Furthermore, a Scott bond value according to TAPPI/ANSI T 569 om-14 of the paper for packaging can be from 250 J/m2 bis 450 J/m 2 .

This feature allows for a packaging paper with good adhesion of the top layer and the carrier layer to one another to be provided, and a delamination of these two layers during use of the paper for packaging applications can be prevented.

Preferably, the top layer of the paper for packaging can have an opacity according to ISO 2471:2008 of over 75 %.

Furthermore, a surface of the top layer of the paper for packaging can preferably have a brightness according to ISO 2470-1:2016 of over 70 %.

Moreover, the surface of the top layer of the paper for packaging can have an L* value in the CIELab colour space according to ISO 5631-2:2015 of over 65.

These features allow for the print quality of the print images applied to the surface of the top layer of the paper to be further improved, and in particular the colour fidelity of such print im ages can be improved.

According to a further embodiment of the paper, it can also be provided that it has a short span compression strength index according to ISO 9895:2008 as a geometric mean of 15 Nm/g to 30 Nm/g. As is known in the art, when expressed as a geometric mean according to ISO 9895:2008, the short span compression strength index represents the square root of the product of the respective measurements in machine direction (MD) and cross direction (CD).

This mechanical value is particularly important in packaging papers because the short span compression strength index of a paper is suited to counteracting the strains to which packag ing is frequently exposed. The disclosed feature can therefore further improve the resilience of the paper and thus also of the packaging which is formed by the paper or comprises the pa per as a component.

A Bendtsen roughness according to ISO 8791-2:2013 of the surface of the top layer of the pa per intended for printing can be from 100 mL/min to 300 mL/min.

This can also further improve the printability of the paper. The configuration of a respective Bendtsen roughness can be performed as already described above, for instance using calen dering.

Furthermore, it can be advantageous if a Dennison wax pick strength of the paper according to TAPPI T459 OM-13 has at least 14 as a critical wax strength number.

Such an embodiment of the paper for packaging can be particularly advantageous when using certain printing methods, for example the printing of the packaging paper using offset printing can be improved.

To improve understanding of the invention, it is described in more detail in the following fig ures.

These show in significantly simplified, schematic representation:

Fig. 1 an example embodiment for a method step of connecting two paper webs using wet pressing;

Fig. 2 an example embodiment of a printable, multilayer paper for packaging.

It is worth noting here that the same parts have been given the same reference numerals or same component configurations in the embodiments described differently, yet the disclosures contained throughout the entire description can be applied analogously to the same parts with the same reference numerals or the same component configurations. The indications of posi tion selected in the description, such as above, below, on the side etc. refer to the figure di rectly described and shown, and these indications of position can be applied in the same way to the new position should the position change.

The method for producing the paper according to the present invention can fundamentally be performed using common method steps using a paper machine. The method relates to the pro duction of a printable, multilayer paper for packaging, that is to say a paper with at least two paper layers, which has at least one surface intended for printing. Since the person of average skill in the art is sufficiently familiar with the method and in particular the dehydration and drying steps performed on a paper machine, a detailed description of these fundamental method steps using figures here and in the following can be dispensed with, and said funda mental method steps performed on a paper machine shall simply be mentioned. The paper for packaging according to the present invention can be produced using common paper machine parameters as used in paper production.

Since the product of this production method has at least two paper layers, the method com prises, on the one hand, a provision or production of a bleached first cellulose comprising cel lulose fibres, and on the other hand, a provision or production of a second cellulose compris ing cellulose fibres. Accordingly, as is common during paper production on a paper machine, a production of a first paper web comprising the bleached first cellulose is followed by a pro duction of a second paper web comprising the second cellulose.

To do so, a production of a first pulp comprising the first cellulose and a production of a sec ond pulp comprising the second cellulose is first performed. To do so, the two celluloses can be suspended in an aqueous fluid as is known in the art. An initial consistency of the first and the second pulp can, for example, be 0.5 % to 2 %. As is also common in paper production, in addition to the respective celluloses, further adjuvants can be added to the first pulp, the sec ond pulp, or both pulps. By way of example, such adjuvants could be wet-end starch, PAC (polyaluminium chloride) or alum, ASA (alkyl succinic anhydride) or other sizing agents, bet onite or talcum, pH adjusting agents, retention agents etc.. The selection of the type and quan tity of such adjuvants can be performed by a person of average skill in the present technical field, for instance based on the desired detail properties of the multilayer packaging paper and/or also adjusted to a certain embodiment of a paper machine or a certain method.

As is known in the art, the first pulp and the second pulp can be fed into or applied to a paper machine on or using a headbox. For the sake of completeness, it is noted here that the term pulp is to be understood as an aqueous solution of the respective cellulose. As usual, other terms such as fibrous material-water suspension, fibre suspension, cellulose suspension etc. can be used synonymously.

As the person of average skill in the art is sufficiently aware, a paper web is usually formed in a paper machine by gradually dehydrating and drying a pulp fed into the machine via a head box. For example, a paper web can be formed and at least thickened in a first dehydration step using a wire section, wherein a further drying of a formed paper web in a paper machine can be performed in further drying steps.

Accordingly, the method according to the present invention provides for a production or for mation of a first paper web by dehydrating/drying the first pulp, and a production or for mation of a second web by dehydrating/drying the second pulp.

For the production of the multilayer paper for packaging, a method step for connecting the first paper web and the second paper web is of course provided for. Such a connection can fundamentally be performed at different degrees of drying or consistencies of the two paper webs, such as, for example, at a different location in a paper machine or, for instance, after or during different dehydration or drying stages in a paper machine.

Accordingly, the method according to the present invention provides for a connection of the two paper webs, i.e. a connection of the first and the second paper web to form a multilayer paper web for the formation of a multilayer paper web. An example embodiment of such a connection process is shown in significantly simplified, schematic representation in Fig. 1.

The example embodiment represented in Fig. 1 shows a connection of the formed first paper web 1 with the formed second paper web 2 during drying using a press section 3 of a paper machine, as is preferably performed. The example embodiment according to Fig. 1 thereby only shows a portion of the press section by way of depicting the connection of paper webs 1, 2. As is known in the art, a press section 3 can form a drying stage of a paper machine that follows a wire section.

It is hereby noted again that a connection of the two paper webs 1, 2 can also fundamentally be performed elsewhere or at different times in the method. A connection of the two paper webs 1, 2 from two different headboxes is thus entirely possible during or on a wire section as is usually positioned upstream of a press section. Equally, a connection of the first and second paper webs 1, 2 can be performed following prior drying to a final dry content or at least an approximate final dry content of the paper webs using adhesion, lamination, etc..

In the example embodiment shown in Fig. 1, the connection of the two paper webs 1, 2 can be performed as shown by pressing the two paper webs 1, 2 together using press rolls 4, 5. As further shown by the example embodiment in Fig. 1, the paper webs 1, 2 are connected to a multilayer paper web 6 in such a way that the first paper web 1 forms an uppermost top layer 7 and the second paper web 2 forms a carrier layer 8 or support layer of the multilayer paper web 6 that is directly connected to this uppermost top layer 7.

Preferably, immediately before connecting the first paper web 1 and the second paper web 2, a dry content of the first paper web 1 can be set to 3 % to 50 % and a dry content of the sec ond paper web 2 can be set to 3 % to 50 %. A corresponding dry content is thereby in the range of a usual water content of paper webs in a press section.

In very fundamental terms, it is of course optionally possible to produce one or more further paper layers and connect them into the multilayer paper web 6, wherein it is possible to con nect at least one of these further paper layers with the carrier layer 8 to form a multilayer pa per web 6. For the sake of clarity, this option is not shown in Fig. 1, but it is self-explanatory for the person of average skill in the art of paper production. Depending on the use purpose or requirements, further paper layers for forming the multilayer packaging paper can be expedi ent. A simply two-layer packaging paper and thus the formation of a two-layer paper web 6 for its production as represented schematically in Fig. 1 can, however, be wholly sufficient in most cases and can also be desirable for reasons of material savings and having as simple a method as possible.

Irrespective of the number of paper layers connected to form the multilayer paper web 6, after connection a further drying of this paper web 6 can be performed, for instance in stages fol lowing the press section 3 shown only partially in Fig. 1. As is known in the art, final drying using a drying section to achieve the desired final moisture can be performed subsequently to the press section 3.

Assembly of the multilayer, dried paper web 6 is then performed as a final step. Common as sembly can, for example, be performed by rolling up the dried, multilayer paper web 6 onto a carrier roll. Alternatively, assembly can comprise cutting the multilayer paper web 6 to a re spective desired size of the multilayer packaging paper, for example, and stacking the corre spondingly cut packaging paper pieces.

In this method, it is provided that a mixture consisting of 40 wt. % to 80 wt. % unbleached cellulose material and 20 wt. % to 60 wt. % bleached cellulose material related to 100 wt.

% total dry mass of the second cellulose is provided or produced as a second cellulose compris ing cellulose fibres. Unbleached cellulose material is to be understood here as a cellulose ma terial which is not bleached during the production process of the printable, multilayer paper.

The term "consisting of' is to be understood in the above context in absolute terms in relation to 100 wt. % total dry mass of the second cellulose. The stated wt. %-ranges thereby do not comprise, for instance, additives and/or unavoidable small quantities of impurities. Preferably, as a second cellulose comprising cellulose fibres, a mixture consisting of 45 wt. % to 75 wt. % unbleached cellulose material and 25 wt. % to 55 wt. % bleached cellulose material related to 100 wt. % total dry mass of the second cellulose can be provided or produced.

The unbleached cellulose material of the second cellulose can preferably be selected from a group consisting of unbleached, virgin long-fibre cellulose material, unbleached recycled fi bre cellulose material, or a mixture of unbleached cellulose material from this group.

Preferably, at least 70 wt. % and up to 100 wt. % bleached short-fibre cellulose material can be used to form the bleached cellulose material. Furthermore, up to 30 wt. % long-fibre cellu lose material can be used to form the bleached cellulose material of the first cellulose.

The term short-fibre cellulose material can be understood in particular as cellulose material obtained from hard woods, characterized by short central fibre lengths of the cellulose fibres. The term long-fibre cellulose material can be understood in particular as cellulose material obtained from soft woods, characterized by longer central fibre lengths of the cellulosefibres. The related correlations are well known to the person of average skill in the art of paper pro duction. As is known in the art, a corresponding production of such cellulose materials can be performed by crushing respective woods and the mechanical and/or chemical pulping thereof to remove lignin fractions, hemicellulose fractions and other wood components, along with possible further processing methods such as mechanical post-processing, for instance wet grinding or wet pulping in refiners.

In particular, in this method it can be expedient for the second cellulose to be provided or pro duced with a Schopper-Riegler value according to ISO 5267-1:2000 of 20 °SR to 35 °SR. For instance, this can be achieved by processing the cellulose with mechanical grinding or pulping in refiners, as already mentioned above.

Preferably, what are known very generally as kraft cellulose materials can be provided or pro duced as short- and long-fibre cellulose materials, that is to say kraft cellulose materials pro duced using the kraft method or kraft pulping. Such kraft celluloses are often also referred to as sulphate cellulose materials. The term recycled cellulose material is self-explanatory.

As is known to the person of average skill in the art, the bleaching process for the production of bleached cellulose materials comprises a further chemical pulping to at least largely re move residual lignin and other colouring substances. A corresponding bleaching is thereby suited both for removing residual lignin, but also fundamentally for the removal of colouring substances such as from recycled cellulose material.

Furthermore, in this method the second cellulose can be provided or produced with a Kappa number according to ISO 302:2015 of 20 to 65. A Kappa number within the disclosed range can be configured primarily through the selection and/or processing of the respective cellulose materials, predominantly during chemical pulping, and through the composition of cellulose materials for the formation of the second cellulose, as is known to the person of average skill in the art of paper production.

According to a preferred method, 100 kg to 150 kg of white pigment filler material per tonne total dry mass of the bleached first cellulose can be added to the first pulp or the first paper web. A corresponding white pigment filler material can therefore be added to the first pulp before beginning the dehydration and formation of the first paper web 1 or also after an at least first dehydration step or a first dehydration stage of the formed, first paper web 1. Cal cium carbonate can preferably be added to the first pulp or first paper web 1 as a white pig ment filler material.

As already mentioned above, depending on requirements or intended use of the multilayer, printable packaging paper, other common adjuvants in paper production can be added or used during the production, such as modified or native starch, sizing agents, retention agents, fix ing agents, wet strength agents etc..

In this method, in particular the multilayer paper web 6 can be produced to have a final dry content with a grammage of 75 g/m2 to 120 g/m 2 after full drying. In this context, the top layer 7 of the multilayer paper web 6 can be produced with a grammage of 50 g/m2 to 70 g/m 2 , and a ratio of the grammage of the top layer 7 to a grammage of the carrier layer 8 of 1.2:1 to 2:1 can be configured.

Corresponding grammages can, as is known in the art, be configured by adjusting various pro cess parameters such as consistencies in the fibre material processing and in a constant part of a paper machine, the quantities of pulp fed into the headbox of a paper machine and its con sistency, throughput speeds in various areas of a paper machine, and so on.

Furthermore, a smoothing of a surface intended for printing of the top layer 7 of the multi layer paper web 6 can be provided for. Specifically, such a smoothing can be performed by calendering this surface using a calender such as hard-nip, soft-nip, long-nip, or shoe calen ders or metal strip calenders. The person of average skill in the art knows that various parame ters can be adjusted or varied during calendering, such as pressure, temperature and dwell time, to achieve desired surface properties such as a certain surface roughness.

An example embodiment for a printable, multilayer paper 9 for packaging according to the present invention is shown in Fig. 2.

As shown by Fig. 2, the multilayer, printable packaging paper 9 according to the present in vention comprises an uppermost top layer 10 and a carrier layer 11 directly connected to the uppermost top layer 10. The uppermost top layer 10 predominantly comprises a first, bleached cellulose fibre material and the carrier layer 11 predominantly comprises a second cellulose fibre material. This second cellulose fibre material of the carrier layer 11 is hereby formed by a mixture consisting of 40 wt. % to 80 wt. % unbleached fibre material and 20 wt. % to 60 wt. % bleached fibre material related to 100 wt. % total dry mass of the second cellulose fibre material.

The packaging paper 9 shown in Fig. 2 is ultimately formed or produced by connecting the paper webs 1, 2 shown in Fig. 1 into the multilayer paper web 6, where necessary with further drying of this multilayer paper web 6 and finally by assembling the multilayer paper web 6.

Preferably, the second cellulose fibre material can be formed by a mixture consisting of 45 wt. % to 75 wt. % unbleached fibre material and 25 wt. % to 55 wt. % bleached fibre material re lated to 100 wt. % total dry mass of the second cellulose fibre material.

The terms cellulose fibre material or fibre material used in reference to the packaging paper according to the present invention were selected because the terms cellulose or cellulose ma terial are not commonly used for finished papers, and rather the term cellulose is used to des ignate a feedstock for paper production. The selected different material designations are, how ever, to be understood in this sense and primarily in a formal nature, and this circumstance is not to be understood as any kind of material conversion during the production process, in par ticular not as a chemical conversion into a chemically different material. On the contrary, dur ing paper production on a paper machine with celluloses as feedstock, no significant material conversions, at least in a chemical sense, are to be expected, as the person of average skill in the art is sufficiently aware. As is known in the art, processes in a paper machine primarily comprise mechanical and physical processes, for instance an at least partial alignment of the cellulose fibres, and dehydration processes, etc.. These circumstances as explained above are applicable throughout the document. Furthermore, unbleached fibre material is to be under stood as a fibre material which was not bleached during the production process of the printa ble, multilayer paper or results from an unbleached cellulose material.

The packaging paper 9 shown in Fig. 2 can, for example, by all means be used as a separate outer packaging paper for products as a primary packaging, but also as a secondary packag ing. The paper 9 for packaging according to the present invention can, however, also be used simply as a component of a packaging, in particular an uppermost or outward-facing layer of a packaging, as is common in carton packaging, for instance.

Irrespective thereof, the packaging paper 9 according to the present invention has at least one surface which is intended for printing or is printable, said surface being formed by the out ward-facing surface 12 of the top layer 10 as shown in Fig. 2.

The unbleached fibre material of the second cellulose fibre material can be selected from a group consisting of unbleached, virgin long-fibre material, unbleached recycled fibre material, or a mixture of unbleached fibre materials from this group.

In this regard, it can be advantageous for certain applications if only virgin fibre material is used as fibre material in all layers 10, 11, 13 of the packaging paper. In this case, in compli ance with all legal requirements such as those concerning possible adjuvants, the packaging paper according to the present invention can by all means be suited as packaging with direct contact with foodstuffs for dry, moist and fatty foodstuffs. When using recycled fibre mate rial, restricted suitability together with additional cost can arise in this regard, whereby be sides the foodstuff primary packaging sector the use of recycled fibre material can be abso lutely expedient and advantageous.

The bleached fibre material of the second cellulose fibre material can be formed from a mix ture of 30 wt. % to 80 wt. % bleached short-fibre material and 20 wt. % to 70 wt. % bleached long-fibre material.

The bleached fibre material of the first cellulose fibre material can preferably comprise 70 wt. % to 100 wt. % bleached short-fibre material, but can also comprise up to 30 % bleached long-fibre material.

As described above, corresponding fibre materials can be formed by using or producing corre sponding cellulose materials in the production method also described above.

A paper 9 for packaging can, depending on the intended purpose or requirements, by all means also comprise further paper layers, wherein at least one such optional further paper layer would have to be connected with carrier layer 11. Such an optional further paper layer 13 is represented by a dashed line in Fig. 2.

The top layer 10 of the packaging paper 9 according to the present invention can, in particu lar, have a white pigment filler material as an additive. In this regard, an ash residue according to ISO 1762:2015 of the top layer 10 can be from 10 wt. % to 14 wt. %. The white pigment filler material can preferably be formed by calcium carbonate.

As is known in the art, depending on the materials or additives used during production, the measurable ash residue is generally primarily constituted by mineral additives or inorganic aggregates. In addition, other celluloses can, however, contain a small amount of ash them selves, which can vary depending on cellulose type. For the sake of completeness, it should be noted that regarding the method for producing the paper, during the dehydration/drying of the pulp of the paper web formed in the paper machine, unavoidable loss of inorganic aggregates used can always occur, for example during dehydration on a wire section. This unavoidable loss can thus lead to a reduction of the measurable ash residue in the paper compared to the quantities of inorganic aggregates added in the method.

Furthermore, the paper for packaging can have a grammage of 75 g/m 2 to 120 g/m 2 , wherein the top layer can have a grammage of 50 g/m 2 to 70 g/m 2 , and wherein a ratio of the gram mage of the top layer to a grammage of the carrier layer can be 1.2:1 to 2:1.

In the following, a number of further particularly preferred properties of the paper 9 for pack aging according to the present invention are explained in more detail, primarily by way of characteristic values.

The paper for packaging 9 can have a Cobb 60 value of 30 g/m 2 to 40 g/m2 when the top layer 10 is impacted with water according to ISO 535:2014. A corresponding Cobb 60 value can thereby be primarily configured by the materials used, in particular also by the use of addi tives such as sizing agents.

Furthermore, a burst index according to ISO 2758:2014 of the paper 9 according to the pre sent invention can be from 3.5 kPa*m 2/g to 4.5 kPa*m 2/g.

A Scott bond value according to TAPPI/ANSI T 569 om-14 of the paper 9 for packaging can be from 250 J/m2 bis 450 J/m 2 . The Scott bond value denotes the delamination tendency of layers in papers, in the present case thus with regard to the top layer 10 and the carrier layer 11.

The packaging paper 9 per se can have a short span compression index according to ISO 9895:2008 as a geometric mean of 15 Nm/g to 30 Nm/g. As is known to the person of skill in the art, when expressed as a geometric mean according to ISO 9895:2008, the short span com pression strength index represents the square root of the product of the respective measure ments in machine direction (MD) and cross direction (CD).

Regarding characteristic values of the optical appearance and in this regard the printability of the packaging paper 9 according to the present invention, its top layer 10 can have an opacity according to ISO 2471:2008 of over 75 %.

Furthermore, the surface 12 of the top layer 10 of the packaging paper 9 intended for printing can have a brightness according to ISO 2470-1:2016 of over 70 %.

Moreover, the surface 12 of the top layer 10 of the paper for packaging 9 according to the pre sent invention can have an L* value in the CIELab colour space according to ISO 5631 2:2015 of over 65.

A packaging paper with these optical characteristic values is characterized by very good print ability, and in particular is suited to printing with coloured print images of high quality and high colour fidelity.

Furthermore, a Bendtsen roughness according to ISO 8791-2:2013 of the surface of the top layer of the paper intended for printing can be from 100 mL/min bis 300 m/min.

Moreover, a Dennison wax pick strength of the paper according to TAPPI T459 OM-13 has at least 14 as a critical wax strength number.

The example embodiments show possible embodiment variations, although it is to be noted here that the invention is not limited to the specifically represented embodiment variations of the same, but rather various combinations of the individual embodiment variations with one another are possible, and that given the technical teachings provided by the present invention this variation possibility is within the ability of the skilled person in this technical field.

The scope of protection is defined by the claims. The description and the drawings should, however, be consulted when construing the claims. Individual features or combinations of features from the various example embodiments as shown and described can constitute sepa rate inventive solutions. The problem to be solved by the individual inventive solutions can be derived from the description.

All value ranges specified in the current description are to be understood such that they in clude any and all sub-ranges, e.g., the specification 1 to 10 is to be understood such that all sub-ranges, starting from the lower limit 1 and the upper limit 10 are included, i.e., all sub- ranges begin with a lower limit of 1 or more and end at an upper limit of 10 or less, e.g., 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

As a matter of form and by way of conclusion, it is noted that, to improve understanding of the structure, elements have partially not been shown to scale and/or enlarged and/or shrunk.

List of reference numerals

1 Paper web 2 Paper web 3 Press section 4 Press roll Press roll 6 Paper web 7 Top layer 8 Carrier layer 9 Paper Top layer 11 Carrier layer 12 Surface 13 Paperlayer

Claims

Patent claims

1. A method for producing a printable, multilayer paper (9) for packaging, comprising - the provision or production of a bleached first cellulose comprising cellulose fibres and pro duction of a first paper web (1) comprising the first cellulose by forming a first pulp compris ing the first cellulose and dehydration/drying of this first pulp, - the provision or production of a second cellulose comprising cellulose fibres and production of a second paper web (2) comprising the second cellulose by forming a second pulp compris ing the second cellulose and dehydration/drying of this second pulp, - the connection of the two paper webs (1, 2) into a multilayer paper web (6), such that the first paper web (1) forms an uppermost top layer (7) and the second paper web (2) forms a carrier layer (8) directly connected to this uppermost top layer (7) of the multilayer paper web, - the optional production of one or more further paper layers and the connection of at least one of these further paper layers with the carrier layer (8), - the optional further drying of the multilayer paper web (6), - the assembly of the multilayer paper web,

characterized in that

a mixture consisting of 40 wt. % to 80 wt. % unbleached cellulose material and 20 wt. % to 60 wt. % bleached cellulose material is provided or produced as a second cellulose material comprising cellulose fibres.

2. The method according to Claim 1, characterized in that the unbleached cellulose material of the second cellulose is selected from a group consisting of unbleached, virgin long-fibre cellulose material, unbleached recycling fibre cellulose material, or a mixture of unbleached cellulose materials from this group.

3. The method according to Claim 1 or 2, characterized in that a mixture of 30 wt. % to 80 wt. % bleached short-fibre cellulose material and 20 wt. % to 70 wt. % bleached long-fibre cellulose material is used as the bleached cellulose material of the second cellulose.

4. The method according to one of Claims I to 3, characterized in that 70 wt. % 100 wt. % bleached short-fibre cellulose material is used to form the bleached cellulose mate rial of the first cellulose.

5. The method according to one of Claims 1 to 4, characterized in that directly prior to connecting the first paper web (1) and the second paper web (2), a dry content of the first paper web (1) is set to 3 % to 50 % and a dry content of the second paper web (2) is set to 3

% to 50 %.

6. The method according to one of Claims I to 5, characterized in that 100 kg to 150 kg of white pigment filler material per tonne total dry mass of the bleached first cellulose is added to the first pulp or the first paper web.

7. The method according to Claim 6, characterized in that calcium carbonate is added as the white pigment filler material.

8. The method according to one of Claims 1 to 7, characterized in that after complete drying to a final dry content the multilayer paper web (6) is produced with a grammage of 75 g/m2 to 120 g/m2 , wherein the top layer (7) is produced with a grammage of 50 g/m 2 to 70

g/m 2 , and wherein a ratio of the grammage of the top layer (7) to a grammage of the carrier layer (8) is set to 1.2:1 to 2:1.

9. The method according to one of Claims 1 to 8, characterized in that the second cellulose is provided or produced with a Schopper-Riegler value according to ISO 5267 1:2000 of 20 °SR to 35 °SR.

10. The method according to one of Claims 1 to 9, characterized in that the second cellulose is provided or produced with a Kappa number according to ISO 302:2015 of 20 to 65.

11. A printable, multilayer paper (9) for packaging comprising - an uppermost top layer (10) predominantly comprising a first, bleached cellulose fibre mate rial, - a carrier layer (11), directly connected with the uppermost top layer (10), predominantly comprising a second cellulose fibre material,

characterized in that the second cellulose fibre material is formed by a mixture consisting of 40 wt. % to 80 wt. % unbleached fibre material and 20 wt. % to 60 wt. % bleached fibre mate rial related to 100 wt. % total dry mass of the second cellulosefibre material.

12. The paper (9) according to Claim 11, characterized in that the unbleached fibre material of the second cellulose fibre material is selected from a group consisting of un bleached, virgin long-fibre material, unbleached recycled fibre material, or a mixture of un bleached fibre material from this group.

13. The paper (9) according to Claim 11 or 12, characterized in that the bleached fibre material of the second cellulose fibre material is formed from a mixture of 30 wt. % to 80 wt. % bleached short-fibre material and 20 wt. % to 70 wt. % bleached long-fibre material.

14. The paper (9) according to one of Claims 11 to 13, characterized in that the bleached fibre material of the first cellulose fibre material comprises 70 wt. % to 100 wt. %

bleached short-fibre material.

15. The paper (9) according to one of Claims 11 to 14, characterized in that the top layer (10) has a white pigment filler material, wherein an ash residue according to ISO 1762:2015 of the top layer (10) amounts to 10 wt. % to 14 wt. %.

16. The paper (9) according to Claim 15, characterized in that calcium carbonate forms the white pigment filler material.

17. The paper (9) according to one of Claims 11 to 16, characterized in that the paper (9) has a Cobb 60 value of 30 g/m 2 to 40 g/m 2 when the top layer (10) is impacted with water according to ISO 535:2014.

18. The paper (9) according to one of Claims 11 to 17, characterized in that it has a grammage of 75 g/m2 to 120 g/m 2 , wherein the top layer (10) has a grammage of 50 g/m2 to 70 g/m 2 , and wherein a ratio of the grammage of the top layer (10) to a grammage of the car rier layer (11) is 1.2:1 to 2:1.

19. The paper (9) according to one of Claims 11 to 18, characterized in that a burst index according to ISO 2758:2014 is from 3.5 kPa*m 2/g to 4.5 kPa*m 2/g.

20. The paper (9) according to one of Claims 11 to 19, characterized in that a Scott bond value according to TAPPI/ANSI T 569 om-14 is from 250 J/m 2 to 450 J/m 2

. 21. The paper (9) according to one of Claims 11 to 20, characterized in that the top layer (10) has an opacity according to ISO 2471:2008 of over 75 %.

22. The paper (9) according to one of Claims 11 to 21, characterized in that a surface (12) of the top layer (10) has a brightness according to ISO 2470-1:2016 of over 70 %.

23. The paper (9) according to one of Claims 11 to 22, characterized in that a surface (12) of the top layer (10) has an L* value in the CIELab colour space according to ISO 5631 2:2015 of over 65.

24. The paper (9) according to one of Claims 11 to 23, characterized in that it has a short span compression strength index according to ISO 9895:2008 as a geometric mean of 15 Nm/g to 30 Nm/g.