EP4101980A1 - Packaging paper and method for the production thereof - Google Patents

Abstract

Packaging paper consisting of an unbleached kraft paper with a kappa value according to ISO 302:2015 between 38 and 60, preferably between 40 and 58 as base paper, which is optionally coated at least on one side, the kraft paper being made of at least 90% primary cellulose, a basis weight according to ISO 536:2019 between 60 g/m² and 150 g/m² and an air resistance according to ISO 5636-5:2013 (Gurley) between 5 and 30 seconds , characterized in that the base paper has an elongation at break in the machine direction according to ISO 1924-3:2005 of between 2.5% and 8.5% and a Bendtsen roughness according to ISO 8791-2:2013 of between 70 ml/min and 600 ml/min min, preferably between 150 ml/min to 550 ml/min, particularly preferably 200 ml/min to 500 ml/min' and a method for its production.

Description

The present invention relates to a packaging paper consisting of an unbleached kraft paper with a kappa value according to ISO 302:2015 between 38 and 60, preferably between 40 and 58 as the base paper, which is optionally coated on at least one side, the kraft paper being at least 90% is made from primary pulp, has a basis weight according to ISO 536:2019 between 60 g/m ² and 150 g/m ² and an air resistance according to ISO 5636-5:2013 (Gurley) between 5 and 30 seconds, and to a method of manufacture a packaging paper, in which an unbleached kraft pulp consisting of at least 90% primary pulp with a kappa value according to ISO 302:2015 between 38 and 60, preferably between 40 and 58, which has an average length-weighted fiber length according to ISO 16065-2:2014 between 2.0 mm and 2.9 mm and less than 4.5%, preferably less than 4.2%, in particular less than 4.0% fillers and cationic starch and other processing aids is used as the base material.

Packaging papers are used in a wide variety of areas and must have certain properties depending on the goods to be packaged. What all packaging papers have in common is that they must not tear and must be stable against mechanical and, to a certain extent, chemical and moisture stress so that the goods packaged in them are neither damaged nor lost, for example if a bag or other container tears. These requirements are usually met particularly well by packaging made from kraft paper, which is the paper grade with the highest strength. Kraft paper can be used to make heavy-duty bags, for example for building materials, bags for sharp-edged materials such as gravel or screws, but also shopping bags, bags or bags for packaging food or containers for toys. Furthermore, kraft paper and kraft pulp are used for the production of corrugated board or cardboard, in which case, however, papers with basis weights of more than 120 g/m ² are usually used.

In addition to its high resilience, kraft paper or packaging paper must generally also be easy to print on and, moreover, have material properties that should be precisely adapted to the goods to be packaged or stored in them. For example, kraft paper can be (micro)creped in a Clupak system, which increases its elongation at break, in particular the elongation at break in the machine direction, as a result of which, for example, heavy materials such as sand can be packed in containers made of kraft paper without fear of tearing. not even if the filled and sealed packaging or containers fall to the ground from a height of more than one meter. However, in the case of kraft paper packaging for building materials, other important properties of the packaging are sufficient air permeability and moisture resistance or barrier property against moisture and printability for the packaging paper to ensure that the packaging, such as pouches, bags or sacks can be filled quickly on the one hand, are sufficiently stable during transport and storage and, on the other hand, important information quickly and permanently without e.g. fading or bleeding of the colors can be printed on the packaging.

It is known to the person skilled in the art that the improvement in one property of the packaging paper is usually accompanied by the deterioration in another property, such as the higher the elongation at break of a paper, which is achieved, for example, by (micro)creping in a Clupak system, the worse it becomes the printability of the paper due to the (micro)-creped surface and the resulting higher roughness of the same. Another well-known relationship is, for example, that the higher the basis weight of a paper, the lower its air permeability, unless this is counteracted by regulating the corresponding beating capacity during manufacture, which in turn usually has a negative effect on the strength properties of the paper.

It is known to the person skilled in the art that the properties of the kraft paper can be influenced by specifically selected additives or processing steps, just as the choice of wood from which the fibers forming the paper originate can influence the paper properties. For example, at least one side of a calendered kraft paper is very smooth and can therefore be printed well. Excessive calendering can thus produce a smooth surface on at least one side of the paper. On the other hand, such a measure usually degrades the elongation at break of the paper, especially in the machine direction, for example, as well as many other mechanical properties of the paper, which means that the packaging loses elasticity and threatens to tear under heavy loads. Another known measure to ensure that the paper properties can be kept as uniform as possible is, for example, that in order not to worsen the air permeability when the basis weight of the paper is increased, the freeness of the fiber suspension from which the paper is formed is changed and, for example is reduced so that the air permeability of the paper is kept as constant as possible despite the changing basis weight.

The use of unbleached pulp, which has relatively stiffer pulp fibers compared to bleached pulp, and the associated use of reduced amounts of process chemicals, in particular the chemicals required for bleaching, provides a packaging paper that, due to its extensibility, is in the middle area of achievable elongations at break for kraft papers, such as sack kraft papers, is particularly well suited as paper for packaging building materials, etc., but has significant defects in terms of surface smoothness and printability.

The present invention thus aims to provide a packaging paper which is made from unbleached kraft paper and which has both the strength properties of conventional kraft paper qualities and, in addition, a smooth surface that is excellently suitable for further processing steps such as surface coating and/or printing, in particular printing with mass printing processes has surface.

To solve this problem, the packaging paper is essentially characterized in that the base paper has an elongation at break in the machine direction according to ISO 1924-3:2005 of between 2.5% and 8.5% and that the packaging paper has a Bendtsen roughness according to ISO 8791-2 :2013 between 70 ml/min and 600 ml/min, preferably between 150 ml/min to 550 ml/min, particularly preferably 200 ml/min to 500 ml/min. Because the packaging paper has an elongation at break in the machine direction according to ISO 1924-3:2005 of between 2.5% and 8.5%, it is sufficiently flexible to withstand high elongation stresses, such as when filled packaging is dropped, and at the same time it is possible to provide a packaging paper which has a smooth surface with a low Bendtsen roughness according to ISO 8791-2:2013 between 70 ml/min and 600 ml/min. These properties can be achieved in particular by using unbleached kraft paper with a kappa value according to ISO 302:2015 between 38 and 60, preferably between 40 and 58, which compared to bleached paper has relatively stiffer fibers, but due to the lack of bleaching subjected to milder manufacturing conditions. By applying these milder manufacturing conditions, it is possible to retain much residual lignin in the paper, resulting in more negatively charged sites in the fiber network compared to bleached paper, which negatively charged sites subsequently allow the paper to be stronger in comparison can be loaded to bleached paper. Because the kraft paper is still made from at least 90% primary pulp, it is possible, in contrast to conventional kraft paper qualities on the market, to further increase the tear strength due to the extremely low content of possible recycled or waste paper fibers, which means that kraft papers with high TEA indices (Tensile Energy Absorption Index, according to ISO 1924-3:2005) can be achieved. High TEA indices are important for the mechanical stability of the paper, but on the other hand they are not optimal for the printability of the paper and it has surprisingly been shown that the use of unbleached pulp and the associated possibility of increased amounts of starch in the kraft paper to bring in, it succeeds, not only to keep the TEA index high and at the same time to use mild conditions in the production of the paper, but due to the use of relatively high amounts of starch, in particular corn starch, potato starch or the like, the open pores of the paper and thus its air permeability continue to be high receive. By using relatively high amounts of cationic starch compared to bleached kraft paper, it is possible to keep the air permeability high (Gurley according to ISO 5636-5:2013) through flocculation resulting from the interaction between the negatively charged fibers and the positively charged starch to keep the air resistance of the packaging paper produced in this way low, so that it is possible to calender the paper in order to achieve the surface smoothness necessary for good printing. The calendering causes compression and thus a reduction in the air permeability of the paper, but surprisingly a combination of using an unbleached, (micro)creped paper which has been subjected to calendering makes it possible to provide a packaging paper that has both good mechanical properties , such as an elongation at break in the machine direction between 2.5% and 8.5% and an excellent smoothness, in particular Bendtsen roughness according to ISO 8791-2:2013 in the range between 70 ml/min and 600 ml/min, preferably between 150 ml /min to 550 ml/min, particularly preferably 200 ml/min to 500 ml/min.

According to a development of the invention, the packaging paper is further characterized in that the base paper has at least one side with a coating material selected from the group of polyolefins, such as polyethylene, polypropylene, polyolefin-based copolymers and terpolymers and ionomers, or from the group of polyolefin-free coating materials, such as polylactic acid is coated. By the base paper being coated on at least one side with a coating material selected from the group of polyolefins such as polyethylene, polypropylene, polyolefin-based copolymers and terpolymers and ionomers or the group of polyolefin-free coating materials such as polylactic acid or other coating materials known in the art, it is possible to provide a flexible barrier coating which not only further reduces the surface roughness and thus improves the printability, but also does not have a negative effect on the elasticity or the elongation at break of the packaging paper. An open-pored base paper has proven to be particularly advantageous, for example, in the extrusion coating of polyethylene or other polyolefin-based copolymers, since this promotes the inflow of the polyethylene melt into the paper structure and thus mechanical interlocking and anchoring of the coating material on or in the paper.

A remaining small roughness of between 70 and 200 ml/min of the packaging paper has proven to be favorable for the mechanical interlocking of the packaging paper with e.g. a polymer melt. With Bendtsen roughnesses between 70 and 200 ml/min, such an interlocking succeeds surprisingly well, while at the same time a far improved and high-quality printability (for example in flexographic printing) is achieved. If the printability requirements are not so high, higher Bendtsen roughnesses can also be set without adversely affecting other properties of the packaging paper.

By, as corresponds to a development of the invention, the coating on each side of the base paper in an amount of between 1% by weight and 7% by weight, in particular between 2% by weight and 6% by weight, of the basis weight of the base paper is applied, it is also possible to apply extremely thin coatings to the base paper without adversely affecting the extensibility of the packaging paper, while at the same time significantly improving the printability and, in particular, the moisture resistance of the packaging paper. In particular, when the amount of the coating material is chosen at the lower end of the claimed amount, packaging papers are obtained whose mechanical properties are essentially the same as uncoated packaging papers, but with a significantly smoother surface and thus improved printability and moisture resistance. Such a coating can be present as a so-called smooth finish on the surface of the base paper, which also improves the optical properties of the base paper, in terms of a velvety sheen on the base paper and a beautiful smooth surface with an even significantly lower Bendtsen roughness in the range between 50 ml /min and 500 ml/min, can be positively influenced. By applying polyethylene, for example, the packaging paper is additionally equipped with a heat-sealable sealing layer, with the seal having sufficient sealing strength both in the case of a coating on one side at the paper-polymer interface and in the case of a coating on both sides at the polymer-polymer interface. Furthermore, for example, paper coated on one side can also be folded during further processing in such a way that contact is established between two coated areas, which, for example, when producing containers such as sacks, bags or pouches from the packaging paper, makes it possible to apply an additional adhesive component or adhesive layer unnecessary.

By, as corresponds to a development of the invention, the packaging paper is designed such that the base paper contains at least 90% primary pulp, containing at least 80%, preferably at least 85%, in particular at least 88% pulp with a mean length-weighted fiber length according to ISO 16065-2:2014 between 2.0 mm and 2.9 mm and contains less than 4.5%, preferably less than 4.2%, in particular less than 4.0% fillers and cationic starch and other processing aids, it is possible to provide a kraft paper with an extremely tear-resistant structure and, in particular due to optimal utilization of the length distribution of the fiber lengths of the primary pulp used, to set the paper properties as precisely as possible both in the machine direction and in the transverse direction. Such paper can also be used safely and reliably for the packaging of sharp-edged objects or heavy materials such as gravel, due to its toughness and its ability to be (micro)creped in a Clupak line. By also containing less than 4.5%, preferably less than 4.2%, in particular less than 4.0% (in the context of the present invention, the stated percentages are always to be understood as percentages by weight) of fillers and cationic starch and processing aids at the same time obtaining a strong but not overly stiff base paper, in which high percentages of starch, especially cationic starch, can be used due to the lignin and hemicelluloses remaining in the base paper and the associated high number of negative charges.

According to a development of the invention, the packaging paper is designed in such a way that it has a starch content of 0.5% by weight to 1.5% by weight of the base paper, in particular from 0.6% by weight to 1.4% by weight. % of the base paper. Due to this high starch content, it is possible to provide the paper with excellent mechanical properties and at the same time to keep the open pores of the paper high, thus counteracting an overall compaction of the paper structure in a calendering step and, as a result, a well-structured and yet smooth surface for any subsequent coating of the paper To make available.

In particular, the possible negative effects of recycled pulp as well as pulp from waste paper on the properties of the end product, such as reduced strength, reduced TEA index, reduced elongation at break, and the like, all of which are due to the unknown origin of, for example, pulp cannot be predicted from waste paper, the packaging paper according to the invention is preferably further developed in such a way that the pulp used is 100% primary pulp. The advantages of using 100% virgin pulp for packaging materials in the food packaging materials sector are well known to those skilled in the art. The full use of packaging papers made from 100% primary cellulose for dry, moist and high-fat foods is only given here as an example referred to with little or no additional testing and analysis of the paper material. This also requires careful selection of the process additives and their reduced use, as is achieved in the present packaging paper according to the invention.

In particular, in order to positively influence not only the strength properties of the packaging paper but also its surface smoothness, according to a further development of the invention the packaging paper is designed in such a way that the primary pulp consists of a mixture consisting of at least 80% softwood pulp, more preferably at least 90% softwood pulp, in particular at least 95% softwood pulp an average length-weighted fiber length according to ISO 16065-2:2014 of at least 2.0 mm and the balance consists of hardwood pulp with an average length-weighted fiber length according to ISO 16065-2:2014 of at least 1.0 mm. The predominant amount of softwood pulp with a mean length-weighted fiber length according to ISO 16065-2:2014 of at least 2.0 mm and the rest hardwood pulp with a mean length-weighted fiber length according to ISO 16065-2:2015 of at least 1.0 mm can through the softwood pulp the strength properties and the smoothness are positively influenced by the hardwood pulp and a packaging paper with both excellent mechanical properties, in particular elongation at break and good smoothness, which provides the best printability, can be provided by a targeted choice of the pulp composition. Both types of pulp are preferably used as primary pulp and are particularly suitable for packaging food, but also, for example, in the area of packaging children's toys, due to their reduced content of process additives.

By, as corresponds to a development of the invention, the packaging paper is designed in such a way that the primary cellulose is contained as ground, in particular high-consistency ground cellulose with a Schopper-Riegler freeness according to ISO 5267-1:1999 between 13 °SR and 20 °SR , it is possible to even out the average fiber length of the pulp even further, as a result of which a particularly homogeneous paper can be formed in which an optimal setting of the paper properties can be achieved both in the longitudinal and in the transverse direction. With the high-consistency refining, the elongation at break of the packaging paper is preferably set in the transverse direction. In addition to high-consistency beating, the paper can also be low-consistency (LC) beating, with a Schopper-Riegler beating degree according to ISO 5267-1:1999 of between 15 and 27°SR. With such a low-consistency refining, the strength properties of the paper, such as the tensile strength in the longitudinal and transverse directions, are adjusted and thus the properties of the paper can be further adapted to the respective requirements by means of HC and LC refining.

High-consistency grinding is understood to mean grinding in which the overall consistency of solids is between 25% and 40%, and low-consistency grinding is understood to mean grinding in which the overall consistency of solids is between 2% and 7%.

The present invention also aims at a method for producing a packaging paper, with which method it is possible to provide a paper with excellent mechanical properties and a smooth surface. To solve this problem, the method according to the invention is carried out in such a way that the base material is creped in a Clupak system until an elongation at break in the machine direction according to ISO 1924-3:2005 of between 2.5% and 8.5% is achieved, and then to is dried to a moisture content of at most 14% and the base paper is finally subjected to a calendering step, whereby a packaging paper with a Bendtsen roughness according to ISO 8791-2:2013 between 70 ml/min and 600 ml/min, preferably 150 ml/min to 550 ml/min, particularly preferably 200 ml/min to 500 ml/min, a basis weight according to ISO 536:2019 between 60 g/m ² and 150 g/m ² and an air resistance according to ISO 5636-5:2013 (Gurley) between 5 and 30 seconds is formed and that optionally at least one-sided coating of the packaging paper is carried out. By creping the base material in the Clupak line, it is possible to achieve an elongation at break in the machine direction according to ISO 1924-3:2005 in the range between 2.5% and 8.5%, which is a sufficient value for the packaging material for the Packaging of, for example, building materials, sand, gravel or pellets, foodstuffs such as rice and the like. By being able to dry the paper to a maximum moisture content of 14%, it is ensured that the paper remains sufficiently flexible and formable despite the unbleached kraft pulp fibers it contains, which are altogether stiffer. By further subjecting the paper to a calendering step, it is ensured that at least one side of the paper is smoothed again after processing in the Clupak system and this process step is carried out in such a way that the smoothing is preferably only carried out on one side, with particular attention being paid to this that the (micro) creping introduced by the Clupak system is not destroyed by the calendering in order to keep the elongation at break of the paper high. Such a procedure makes it possible to produce a packaging paper with a Bendtsen roughness according to ISO 8791-2:2013 between 70 ml/min and 600 ml/min, preferably between 150 ml/min and 550 ml/min, particularly preferably 200 ml/min up to 500 ml/min and a basis weight according to ISO 536:2019 between 60 g/m ² and 150 g/m ² . A packaging paper produced in this way also shows an air resistance according to ISO 5636-5:2013 (Gurley) of between 5 and 30 seconds, which on the one hand is sufficiently permeable, for example when filling various types of containers, such as pouches, sacks or bags with filling materials, to allow air that has been introduced to escape through the pores of the packaging and, on the other hand, to be sufficiently tight that the stability of the packaging made of paper can be maintained under heavy loads, since the pores formed are large enough for use as wrapping paper and small enough not to adversely affect the stability of the paper. Optionally, these method steps can be followed by a step of coating the packaging paper on one side.

According to a further development of the invention, the method is carried out in such a way that the calendering step takes place in a shoe calender with a line load between 200 and 1000 kN/m and a shoe length of 50 mm to 270 mm or a soft nip calender with a line load of 18 to 80 kN/m, in particular 20 to 50 kN/m. Using a shoe calender with a line load between 200 and 1000 kN/m for the calendering step ensures that the paper is not pressed too hard and the (micro) creping introduced by the Clupak system is not destroyed again by the shoe calender. The same applies if a soft nip calender with a line load of 18 to 80 kN/m is used. By carrying out an additional coating step in which the base paper is coated with either an olefinic coating, such as polypropylene, polyethylene, polyolefin-based copolymers and terpolymers and ionomers, or a non-polyolefinic coating such as polylactic acid, it is possible on the one hand to further increase the smoothness of the paper, at least on one side and on the other hand to further increase properties such as the printability, moisture resistance and the like of the base paper or kraft paper and thus to produce a packaging paper which, due to its smoothness, is excellently printable and coatable, but at the same time also has mechanical properties that meet all the requirements of a modern packaging paper .

According to a development of the invention, the coating step is carried out in such a way that an amount of coating material between 2% and 7%, in particular 2.5% and 6% of the basis weight of the base paper is applied to each side to be coated of the kraft paper representing the base paper. By using such small amounts of coating material, it is ensured that not all the pores of the packaging paper are glued or closed by the coating material and the paper has a smooth, easily printable and, for example, also heat-sealable surface.

In that, as corresponds to a development of the invention, the method is carried out in such a way that the coating is applied at least to one side creped in the Clupak unit it is possible to ensure that the coating adheres well to the surface, but at the same time the packaging paper as a whole does not become too smooth and, moreover, also has excellent printability. This is reflected in particular by the low roughness values of the Bendtsen roughness according to ISO 8791-2:2013 in the range from 70 ml/min to 600 ml/min.

The invention is explained in more detail below using exemplary embodiments.

Example 1: Production of a packaging paper with a basis weight (grammage) of 60 g/m ² Process description:

An unbleached pulp consisting of 95% softwood (spruce) primary pulp with a kappa number of 42 and 5% hardwood (birch) primary pulp with a kappa number of 40, which is first subjected to high-consistency beating with a beating capacity of 190 to 210 kWh /t was subjected, with a freeness of the pulp after the high-consistency refining amounting to 17 °SR and then this pulp was subjected to a low-consistency refining with a refining capacity of 75 kWh/t, wherein the freeness of the pulp after the high-consistency refining and the low-consistency refining was 22 °SR, was used.

The additives (aluminium sulphate, cationic starch and a mixture of alkenyl succinic anhydride (ASA) and alkylated ketene dimers (AKD)) are metered into the approach flow of the paper machine. Here, the pH was adjusted to a pH of 6.8 to 7.1 with aluminum sulfate, cationic starch, with a degree of cationization DS of 0.03, in an amount of 10 kg/t paper atro and 1 kg/t a dry strength agent (glyoxylated polyacrylamide (G-PAM)) was metered in and a mixture of ASA and AKD was used as the sizing agent in an amount of 0.4 kg/t paper atro. The pulp contained no fillers. The consistency of the pulp at the headbox was 0.21%. Dewatering took place on a Fourdrinier wire section, and with a press section with three nips, the line pressure at the three nips being 55 kN/m, 80 kN/m and again 80 kN/m. Before the still moist paper was fed to the Clupak unit, it was pre-dried in a slalom dryer section and treated and micro-creped in a Clupak unit with a differential speed of -5.2%. The paper was dried to a residual moisture content of 9% before it was calendered in a soft nip calender with a line load of 45 kN/m and a temperature of 100 °C and finally wound up. The paper can be used as such.

The paper had the paper properties described in Table 1 below: Table 1: paper property standard Unit Direction result grammage ISO 536:2019 gsm ² 60 tensile strenght ISO1924-3:2005 kN/m md 4.9 Tensile Strength Index ISO1924-3:2005 Nm/g md 81.7 tensile strenght ISO1924-3:2005 kN/m CD 3.3 Tensile Strength Index ISO1924-3:2005 Nm/g CD 55 elongation at break ISO1924-3:2005 % md 6.7 elongation at break ISO1924-3:2005 % CD 7.3 Tensile Break Work Index ISO1924-3:2005 y/g md 3.4 Tensile Break Work Index ISO1924-3:2005 y/g CD 2.9 Air Permeability Gurley ISO 5636-5:2013 s 14.3 Cobb value 60s ISO 535:2014 gsm ² 32 Bendtsen roughness ISO8791-2:2013 ml/min smooth side 298 Bendtsen roughness ISO8791-2:2013 ml/min rough side 819

Needless to say, the paper is additionally subjected to a coating treatment, such as an extrusion coating with polyethylene (eg 4.0 g/m ² ) or, after a pigmenting primer with kaolin, a dispersion coating (1.8 g/m ² ). can, as a result of which the properties, in particular the roughness and the air permeability, can be changed even further.

Example 2: Production of a packaging paper with a basis weight of 81 g/m ² Process description:

An unbleached pulp consisting of 100% primary softwood pulp (mixture of spruce and pine) with a kappa number of 47, which was first subjected to high-consistency beating with a beating capacity of 210 to 220 kWh/t, with a freeness of the pulp after high-consistency beating 18 °SR and this pulp was then subjected to low-consistency beating with a beating capacity of 80 kWh/t, the freeness of the pulp being 24 °SR after high-consistency beating and low-consistency beating was used.

The additives are added in the approach flow of the paper machine. Here, the pH was adjusted to a value of 6.6 to 7.1 with aluminum sulphate, cationic starch with a degree of cationization DS of 0.03 was metered in in an amount of 13 kg/t paper dry and used as sizing agent Alkenylsuccinic anhydride used in an amount of 0.5 kg / t paper atro. There were dosed 2% filler in the form of talc. The consistency of the pulp at the headbox was 0.19%. Dewatering took place on a Fourdrinier wire section, and with a press section with three nips, the line pressure at the three nips being 60 kN/m, 80 kN/m and again 80 kN/m. Before the still moist paper was fed to the Clupak unit, it was predried in a slalom dryer section and treated and (micro)creped in a Clupak unit with a differential speed of -6.1%. The paper was dried to a residual moisture content of 10.5% before it was calendered in a soft nip calender with a line load of 57 kN/m and a temperature of 110 °C and finally wound up. The paper can be used as such.

The paper had the paper properties described in Table 2 below: Table 2: paper property standard Unit Direction result grammage ISO 536:2019 gsm ² 81 tensile strenght ISO1924-3:2005 kN/m md 6.5 Tensile Strength Index ISO1924-3:2005 Nm/g md 80.2 tensile strenght ISO1924-3:2005 kN/m CD 4.7 Tensile Strength Index ISO1924-3:2005 Nm/g CD 58.0 elongation at break ISO1924-3:2005 % md 8.0 elongation at break ISO1924-3:2005 % CD 7.1 Tensile Break Work Index ISO1924-3:2005 y/g md 3.4 Tensile Break Work Index ISO1924-3:2005 y/g CD 2.8 Air Permeability Gurley ISO 5636-5:2013 s 18.7 Cobb value 60s ISO 535:2014 gsm ² 30 Bendtsen roughness ISO8791-2:2013 ml/min smooth side 241 Bendtsen roughness ISO8791-2:2013 ml/min rough side 857

The paper can also be subjected to a coating treatment, such as an extrusion coating with polyethylene (e.g. 4.0 g/m ² on the smoothed side or 6.0 g/m ² on at least one side), whereby the properties, in particular the roughness and the air permeability can be changed.

Such a paper was printed with a multicolor print in a flexographic printing process. The colors showed a high level of brilliance and bleeding of the same could not be observed.

In two further trials, sample packages were made from the paper, one batch in which the coated side of the paper forms the inside of the package and one batch in which the coated side of the paper forms the outside of the package. Both batches of packaging were filled with 25 kg of sand, 25 kg of gravel, 15 kg of rice, children's toys, 10 kg of wood shavings and 2 kg of nails, sealed and subjected to load tests. The load tests consisted of drop tests from a constant drop height of 0.8 meters with a flat drop in accordance with ISO 7965-1:1984.

In the case of the packages where the coated side of the paper forms the inside of the package, Package I, the closure was formed by heat sealing and in cases where the coated side of the paper forms the outside of the package, Package II, the closure was by means of of a conventional adhesive.

These tests showed that the packaging I and II made from the packaging paper according to the present invention did not break even after 9 to 10 drops and the pointed or sharp-edged filling materials did not bore through the paper either.

Both groups of packaging, packaging I and II, were also printed in multiple colors on the outside using flexographic printing. The packaging I could be printed well, the colors did not run or flow together, and the color brilliance was adequate. The feel of the packaging I corresponded to that of, for example, natural brown paper bags. Significantly less ink was required for printing packaging II than for packaging I, the color brilliance was excellent and the colors did not flow into one another or run out. The drying time of the paints was slightly longer compared to packaging I. After drying and after the drop tests as described above, it was found that the color print had neither flaked off nor smeared or been damaged in any other way on either packaging I or packaging II.

From these tests it follows that, depending on the desired feel of the packaging and the brilliance of the print applied to it and, if applicable, that to be packaged in it Goods which packaging paper can be used with its coated side facing both inwards and outwards.

Example 3: Production of a packaging paper with a basis weight (grammage) of 138 g/m ² Process description:

An unbleached pulp consisting of 80% softwood (spruce and pine) primary pulp with a kappa number of 45 and 15% hardwood (birch and beech) primary pulp with a kappa number of 40, which is first subjected to high-consistency beating with a refining capacity of 190 to 210 kWh/t, with a freeness of the pulp after high-consistency refining was 17 °SR and then this pulp was subjected to low-consistency refining with a refining capacity of 75 kWh/t, with the freeness of the pulp after high-consistency refining and low-consistency refining being 23 °SR was used. A 5% share of waste paper was also used, but this was only added to the material flow after grinding.

The auxiliary materials were added in the approach flow of the paper machine. Here, the pH was adjusted to a value of 7.0 to 7.2 with aluminum sulfate, cationic starch, with a degree of cationization DS of 0.04, was metered in in an amount of 13 kg/t paper atro and as a size alkenylsuccinic anhydrides were used in an amount of 0.7 kg/t paper atro (absolutely dry). Furthermore, no fillers were added. The consistency of the pulp at the headbox was 0.25%. Dewatering was carried out on a Foudrinier wire section and with a press section with three nips, one of which may be a shoe press, the line pressure on the three nips being 60 kN/m, 90 kN/m and 500 kN/m respectively (in the shoe press ) fraud.

Before the still moist paper was fed to the Clupak unit, it was predried in a slalom dryer section and treated and (micro)creped in a Clupak unit with a differential speed of -4.2%. The paper was dried to a residual moisture content of 9% before it was calendered in a soft nip calender with a line load of 37 kN/m and a temperature of 110 °C and finally wound up. The paper can be used as such.

The paper had the paper properties described in Table 3 below: Table 3: paper property standard Unit Direction result grammage ISO 536:2019 gsm ² 138 tensile strenght ISO1924-3:2005 kN/m md 11.5 Tensile Strength Index ISO1924-3:2005 Nm/g md 83.3 tensile strenght ISO1924-3:2005 kN/m CD 8.2 Tensile Strength Index ISO1924-3:2005 Nm/g CD 59.4 elongation at break ISO1924-3:2005 % md 5.9 elongation at break ISO1924-3:2005 % CD 6.1 Tensile Break Work Index ISO1924-3:2005 y/g md 3.0 Tensile Break Work Index ISO1924-3:2005 y/g CD 2.6 Air Permeability Gurley ISO 5636-5:2013 s 26.9 Cobb value 60s ISO 535:2014 gsm ² 28 Bendtsen roughness ISO8791-2:2013 ml/min smooth side 334 Bendtsen roughness ISO8791-2:2013 ml/min rough side 1264

The paper obtained in this way was extrusion-coated on one side on the smooth side (the side facing the calender roll) with 7 g/m ² of polyethylene. After coating, the Bendtsen roughness of the smooth side was 78 ml/min and the air permeability has dropped to 15400 seconds according to ISO 5636-5:2013 (Gurley).

Such paper was printed with a multicolor print using a flexographic printing process. The colors showed a high level of brilliance and bleeding of the same could not be observed.

In a further test, sample packaging such as pouches, sacks or pouches was made from the paper and these were filled with 25 kg of sand, 25 kg of gravel, 15 kg of rice, children's toys, 10 kg of wood chips and 2 kg of nails, heat-sealed and subjected to load tests subject. The load tests consisted of drop tests from a constant drop height of 0.8 meters with a flat drop in accordance with ISO 7965-1:1984

These tests showed that the packaging made from the packaging paper according to the present invention did not break even after 9 to 10 drops, the pointed or sharp-edged filling materials did not drill through the paper and finally the color print did not chip off or smudge been damaged or damaged in any way.

Example 4: Production of a packaging paper with a basis weight of 80 g/m ² Process description:

An unbleached pulp consisting of 100% primary softwood pulp (mixture of spruce and pine) with a kappa number of 52, which was first subjected to high-consistency beating with a beating capacity of 220 to 230 kWh/t, with a freeness of the pulp after the high-consistency beating 17 °SR and this pulp was then subjected to low-consistency beating with a beating capacity of 90 kWh/t, the freeness of the pulp being 22 °SR after high-consistency beating and low-consistency beating was used.

The additives are added in the approach flow of the paper machine. Here, the pH was adjusted to a value of 6.6 to 7.1 with aluminum sulphate, cationic starch with a degree of cationization DS of 0.03 was metered in in an amount of 13 kg/t paper dry and used as sizing agent Alkenylsuccinic anhydride used in an amount of 0.5 kg / t paper atro. There were dosed 2% filler in the form of talc. The consistency of the pulp at the headbox was 0.19%. Dewatering took place on a Fourdrinier wire section, and with a press section with three nips, the line pressure at the three nips being 60 kN/m, 80 kN/m and again 80 kN/m. Before the still moist paper was fed to the Clupak unit, it was predried in a slalom dryer section and treated and (micro)creped in a Clupak unit with a differential speed of -6.1%. The paper was dried to a residual moisture content of 10.5% before being calendered in a soft nip calender with a top roll with an Ra value of 0.03 μm with a line load of 65 kN/m and a temperature of 120.degree and finally wound up. The paper can be used as such.

The paper had the paper properties described in Table 4 below: Table 4: paper property standard Unit Direction result grammage ISO 536:2019 gsm ² 80 tensile strenght ISO1924-3:2005 kN/m md 6.5 Tensile Strength Index ISO1924-3:2005 Nm/g md 80.2 tensile strenght ISO1924-3:2005 kN/m CD 4.7 Tensile Strength Index ISO1924-3:2005 Nm/g CD 58.0 elongation at break ISO1924-3:2005 % md 7.9 elongation at break ISO1924-3:2005 % CD 7.0 Tensile Break Work Index ISO1924-3:2005 y/g md 3.4 Tensile Break Work Index ISO1924-3:2005 y/g CD 2.8 Air Permeability Gurley ISO 5636-5:2013 s 20.2 Cobb value 60s ISO 535:2014 g/m2 28 Bendtsen roughness ISO8791-2:2013 ml/min smooth side 93 Bendtsen roughness ISO8791-2:2013 ml/min rough side 790

The paper can also be subjected to a coating treatment, such as an extrusion coating with polyethylene (e.g. 3.8 g/m ² on the smoothed side or 6.0 g/m ² on at least one side), whereby the properties, in particular the roughness and the air permeability can be changed.

Example 5: Production of a packaging paper with a basis weight of 100 g/m ² Process description:

An unbleached pulp consisting of 100% primary softwood pulp (mixture of spruce and pine) with a kappa number of 53, which was first subjected to high-consistency beating with a beating capacity of 220 to 230 kWh/t, with a freeness of the pulp after high-consistency beating of 17 °SR and this pulp was then subjected to low-consistency beating with a beating capacity of 90 kWh/t, the freeness of the pulp after high-consistency beating and low-consistency beating being 22 °SR was used.

The additives are added in the approach flow of the paper machine. Here, the pH was adjusted to a value of 6.6 to 7.1 with aluminum sulphate, cationic starch with a degree of cationization DS of 0.03 was metered in in an amount of 13 kg/t paper dry and used as sizing agent Alkenylsuccinic anhydride used in an amount of 0.5 kg / t paper atro. There were dosed 2% filler in the form of talc. The consistency of the pulp at the headbox was 0.2%. Dewatering took place on a Fourdrinier wire section, and with a press section with three nips, the line pressure at the three nips being 60 kN/m, 80 kN/m and again 80 kN/m. Before the still moist paper was fed to the Clupak unit, it was predried in a slalom dryer section and treated and (micro)creped in a Clupak unit with a differential speed of -6.1%. The paper was on one dried to a residual moisture content of 10.5% before it was calendered in a soft nip calender with an O top roll with an Ra value of 0.03 µm with a line load of 25 kN/m and a temperature of 120 °C and finally wound up. The paper can be used as such.

The paper had the paper properties described in Table 5 below: Table 5: paper property standard Unit Direction result grammage ISO 536:2019 gsm ² 100 tensile strenght ISO1924-3:2005 kN/m md 7.9 Tensile Strength Index ISO1924-3:2005 Nm/g md 79 tensile strenght ISO1924-3:2005 kN/m CD 5.9 Tensile Strength Index ISO1924-3:2005 Nm/g CD 59 elongation at break ISO1924-3:2005 % md 8.0 elongation at break ISO1924-3:2005 % CD 7.3 Tensile Break Work Index ISO1924-3:2005 y/g md 3.4 Tensile Break Work Index ISO1924-3:2005 y/g CD 2.8 Air Permeability Gurley ISO 5636-5:2013 s 18.9 Cobb value 60s ISO 535:2014 gsm ² 27 Bendtsen roughness ISO8791-2:2013 ml/min smooth side 421 Bendtsen roughness ISO8791-2:2013 ml/min rough side 898

The paper can also be subjected to a coating treatment, such as an extrusion coating with polyethylene (e.g. 5.0 g/m ² on the smoothed side or 7.0 g/m ² on at least one side), whereby the properties, in particular the roughness and the air permeability can be changed.

Example 6 Production of a packaging paper with a basis weight (grammage) of 140 g/m ² Process description:

An unbleached pulp consisting of 80% softwood (spruce and pine) primary pulp with a kappa number of 40 and 15% hardwood (birch and beech) primary pulp with a kappa number of 40, which is first subjected to high-consistency beating with a refining capacity of Was subjected to 180 to 200 kWh / t, with a freeness of the pulp after High-consistency beating was 17 °SR and this pulp was then subjected to low-consistency beating with a beating capacity of 70 kWh/t, the freeness of the pulp after high-consistency beating and low-consistency beating being 23 °SR was used.

The auxiliary materials were added in the approach flow of the paper machine. Here, the pH was adjusted to a value of 7.0 to 7.2 with aluminum sulfate, cationic starch, with a degree of cationization DS of 0.04, was metered in in an amount of 13 kg/t paper atro and as a size alkenylsuccinic anhydrides were used in an amount of 0.7 kg/t paper atro (absolutely dry). Furthermore, no fillers were added. The consistency of the pulp at the headbox was 0.25%. Dewatering was carried out on a Foudrinier wire section and with a press section with three nips, one of which may be a shoe press, the line pressure on the three nips being 60 kN/m, 90 kN/m and 500 kN/m respectively (in the shoe press ) fraud.

Before the still moist paper was fed to the Clupak unit, it was predried in a slalom dryer section and treated and (micro)creped in a Clupak unit with a differential speed of -4.2%. The paper was dried to a residual moisture content of 9.5% before it was calendered in a soft nip calender with a line load of 20 kN/m and a temperature of 110 °C and finally wound up. The paper can be used as such.

The paper had the paper properties described in Table 3 below: Table 6: paper property standard Unit Direction result grammage ISO 536:2019 gsm ² 140 tensile strenght ISO1924-3:2005 kN/m md 11.6 Tensile Strength Index ISO1924-3:2005 Nm/g md 82.9 tensile strenght ISO1924-3:2005 kN/m CD 8.1 Tensile Strength Index ISO1924-3:2005 Nm/g CD 57.9 elongation at break ISO1924-3:2005 % md 6.0 elongation at break ISO1924-3:2005 % CD 6.4 Tensile Break Work Index ISO1924-3:2005 y/g md 3.0 Tensile Break Work Index ISO1924-3:2005 y/g CD 2.7 Air Permeability Gurley ISO 5636-5:2013 s 25.2 Cobb value 60s ISO 535:2014 gsm ² 27 Bendtsen roughness ISO8791-2:2013 ml/min smooth side 561 Bendtsen roughness ISO8791-2:2013 ml/min rough side 1242

The paper obtained in this way was extrusion-coated on one side on the smooth side (the side facing the calender roll) with 7 g/m ² of polyethylene. After coating, the Bendtsen roughness of the smooth side was 112 ml/min and the air permeability has dropped to 14900 seconds according to ISO 5636-5:2013 (Gurley).

Such paper was printed with a multicolor print using a flexographic printing process. The colors showed a high level of brilliance and bleeding of the same could not be observed.

Claims (13)

Packaging paper consisting of an unbleached kraft paper with a kappa value according to ISO 302:2015 between 38 and 60, preferably between 40 and 58 as base paper, which is optionally coated at least on one side, the kraft paper being made of at least 90% primary cellulose, a basis weight according to ISO 536:2019 between 60 g/m ² and 150 g/m ² and an air resistance according to ISO 5636-5:2013 (Gurley) between 5 and 30 seconds, characterized in that the base paper has an elongation at break in the machine direction according to ISO 1924 -3:2005 between 2.5% and 8.5% and that the packaging paper has a Bendtsen roughness according to ISO 8791-2:2013 between 70 ml/min and 600 ml/min, preferably between 150 ml/min and 550 ml /min, particularly preferably 200 ml/min to 500 ml/min. Packaging paper according to claim 1, characterized in that the base paper is coated on at least one side with a coating material selected from the group of polyolefins such as polyethylene, polypropylene, polyolefin-based copolymers and terpolymers and ionomers or from the group of polyolefin-free coating materials such as polylactic acid . Packaging paper according to Claim 1 or 2, characterized in that the coating on each side of the base paper is present in an amount between 1% and 7% by weight, in particular between 2% and 6% by weight, of the basis weight of the Base paper is applied. Packaging paper according to Claim 1, 2 or 3, characterized in that the base paper contains at least 90% primary cellulose, containing at least 80%, preferably at least 85%, in particular at least 88% cellulose with an average length-weighted fiber length according to ISO 16065-2:2014 between 2 0 mm and 2.9 mm and less than 4.5%, preferably less than 4.2%, in particular less than 4.0% fillers and cationic starch and other processing aids. Packaging paper according to Claim 1, characterized in that it has a starch content of from 0.5% to 1.5% by weight of the base paper, in particular from 0.6% to 1.4% by weight of the base paper , having. Packaging paper according to Claim 4, characterized in that it contains 100% primary cellulose. Packaging paper according to claim 6, characterized in that the primary pulp consists of a mixture consisting of at least 80% softwood pulp, more preferably at least 90% softwood pulp, in particular at least 95% softwood pulp with an average length-weighted fiber length according to ISO 16065-2:2014 of at least 2.0 mm and balance hardwood pulp having a mean length-weighted fiber length according to ISO 16065-2:2014 of at least 1.0 mm. Packaging paper according to one of Claims 1 to 7, characterized in that the primary cellulose is contained as ground, in particular high-consistency ground cellulose with a Schopper-Riegler freeness according to ISO 5267-1:1999 of between 13°SR and 20°SR. Process for the production of a packaging paper, in which an unbleached kraft pulp consisting of at least 90% primary pulp with a kappa value according to ISO 302:2015 between 38 and 60, preferably between 40 and 58, which has a mean length-weighted fiber length according to ISO 16065- 2:2014 between 2.0 mm and 2.9 mm and less than 4.5%, preferably less than 4.2%, in particular less than 4.0% fillers and cationic starch and other processing aids is used as the base material, characterized in that the base material is creped in a Clupak unit until an elongation at break in the machine direction according to ISO 1924-3:2005 of between 2.5% and 8.5% is achieved, dried to a maximum moisture content of 14% and is subjected to a calendering step that a packaging paper with a Bendtsen roughness according to ISO 8791-2:2013 between 70 ml/min and 600 ml/min, preferably between 150 ml/min and 550 ml/min , particularly preferably 200 ml/min to 500 ml/min, a basis weight according to ISO 536:2019 between 60 g/m ² and 150 g/m ² and an air resistance according to ISO 5636-5:2013 (Gurley) between 5 and 30 seconds is formed, so that optionally at least one-sided coating of the packaging paper is carried out. Method according to claim 9, characterized in that the calendering step is carried out in a shoe calender with a line load between 200 and 1000 kN/m and a shoe length of 50 mm - 270 mm or a soft nip calender with a line load of 18 to 80 kN/m , in particular 20 to 50 kN/m. Method according to claim 9 or 10, characterized in that the calendered base paper is subjected to a coating step, in which at least one side of the base paper is coated with a coating material selected from the group of polyolefins, such as Polyethylene, polypropylene, polyolefin-based copolymers and terpolymers and ionomers or from the group of polyolefin-free coating materials such as polylactic acid is coated, in particular extrusion-coated. Method according to Claim 9, 10 or 11, characterized in that in the coating step an amount of between 2% and 7%, in particular 2.5% and 6% of the basis weight of the base paper is applied to each side of the base paper to be coated. Method according to one of Claims 9 to 12, characterized in that the coating is applied to at least one side creped in the Clupak unit.