Chitosan-based barrier coating on paper, for use as food packaging

Abstract

The invention relates to a coating color for coating papers, the coating color containing chitosan and / or the derivative thereof having an average molecular weight of not more than 50 kDa, and also containing at least one solvent. The invention also relates to paper coated with the coating color. The invention finally relates to a production method and to packaging produced using the coated paper.

Description

[0001]CHITOSAN-BASED BARRIER COATING ON PAPER FOR USE AS FOOD PACKAGING FIELD OF THE INVENTION This application relates to a coating color for coating paper containing chitosan and / or its derivative and at least one solvent. BACKGROUND OF THE INVENTION Packaging accounts for a large proportion of global plastic waste pollution, which is why the search for alternatives made of biodegradable materials is being driven forward. Food packaging, in particular, presents a challenge because good barrier properties against oxygen, water vapor, and microorganisms are required. Packaging materials for food are often made of plastics, for example, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP), since these not only have good barrier properties but also low weight and high mechanical stability.Paper-based packaging materials offer many advantages over plastic materials, such as renewability, recyclability, and compostability. However, their application is limited due to their often poor barrier properties against gases and high sensitivity to moisture. To improve barrier properties, the paper-based packaging material can be laminated with aluminum or petroleum-based polymers such as PE, EVOH, and PVC derivatives. However, these coatings complicate waste sorting and thus recycling and reduce compostability. Therefore, the use of barrier layers based on natural, bio-based polymers or replacing the conventional metal or plastic-based layer is highly desirable from an ecological perspective. Examples of natural polymers that have been tested for packaging applications include chitosan, hemicelluloses, lignin, microfibrillated cellulose, and starch.However, many natural polymers are hydrophilic, and films made from these materials are often hygroscopic, leading to a partial loss of their barrier properties at high humidity. Chitosan is a natural polysaccharide derived from chitin, a substance found in the shells of crustaceans and insects, and exists in a wide range of molecular weights and degrees of deacetylation. Commercially viable quantities are already being extracted from waste from the fishing industry, primarily from the processing of crabs and shrimp. The barrier properties of chitosan are well known in the art, as are its film-forming properties. However, many publications do not describe chitosan in detail but simply propose it based on its properties as a biodegradable polymer.However, the possible applications of chitosan are limited, as the maximum solubility is below 10 wt.% and frequently even below 5 wt.%. Even at 5 wt.%, the viscosities of chitosan paints are usually so high that they are unsuitable for large-scale paper coating processes. Above 10 wt.%, known chitosan paints are no longer processable. If chitosan paints are to be used as barrier layers on paper against gases such as water vapor or oxygen, several coating steps are necessary due to the low solids content in order to obtain defect-free coatings and achieve application weights that enable barrier performance against these gases. US 2013 / 0273353A1 describes multilayer films for use as book covers and packaging materials.The multilayer films contain at least one biodegradable polymer layer and one or more high-density moisture barrier layers bonded to it, either directly or via a primer layer. The films should be at least 90% biodegradable and simultaneously achieve the desired water vapor permeability properties. All (modified) naturally produced and synthetically produced biodegradable polymers can be used as biodegradable polymers. A long list of possible polymers includes PLA, PLA derivatives, polylactic acid / aliphatic polyester copolymer, polyglycolic acid polymers, polyethylene terephthalate copolymer, polyethylene terephthalate cosuccinate, poly(tetramethylene adipate / terephthalate), polyethylene sebacate, polyvinyl alcohol, chitosan, chitosan / cellulose polymers, cellulose acetate-based polymers, thermoplastic starch-based polymers, and denatured starch-based polymers.The moisture barrier layer is a thermoplastic polymer layer with a moisture vapor transmission rate (MVTR) of approximately 0.5 g / 100 in. 2 (645.2 cm 2 ) per day up to about 45 g / 100 in 2 per day. US 2017 / 0016182 A1 describes the composition of chitosan-coated paper and board products and the process for using chitosan as a surface coating or pulp additive to improve the properties of paper and board products. In particular, a chitosan layer is applied to a fibrous base sheet with a chitosan coating weight of approximately 1 g / m 2 up to about 10 g / m 2an air permeability of approximately 20 nm / Pa s to approximately 50 nm / Pa s is achieved. US 2017 / 0016182A also teaches methods for obtaining unique chitosan compositions from chitin and chitosan-containing fungal biomass. The compositions according to US 2017 / 0016182A are said to be characterized by a combination of high degrees of deacetylation and high molecular weights. Although US 2017 / 0016182A does not provide specific examples of the degrees of deacetylation and molecular weights, deacetylation degrees of more than approximately 50%, more than approximately 75%, or even more than approximately 95% are suggested. Similarly, number-average molecular weights of more than 50,000 g / mol, more than 100,000 g / mol, or even more than 175,000 g / mol are suggested for the chitosan compositions. In addition, ranges for the number-average molecular weights from 60,000 g / mol to 90,000 g / mol are defined. CN109112892A describes a degradable, environmentally friendly lining paper for cigarette packets.The lining paper comprises a base paper layer, a barrier layer, a chitosan layer, and a microcrystalline wax layer. The barrier layer is arranged on the upper surface of the base paper layer, the chitosan layer on the lower surface, and the microcrystalline wax layer is arranged between the base paper layer and the barrier layer. Chitosan is used for its good moisturizing, film-forming, and antibacterial properties, as well as its mechanical strength. However, the chitosan layer is not used as a barrier to gases or moisture. Instead, the paper contains an additional barrier layer, which is also made of biodegradable polymers such as polylactic acid, starch, polybutylene succinate, or polyhydroxyalkane.The object underlying the invention is to provide a chitosan-based coating color that can be used as a barrier layer for gases such as oxygen on paper and is suitable for the large-scale production of such coated papers. SUMMARY OF THE INVENTION The present invention is based, among other things, on the surprising finding that using low-molecular-weight chitosans, in particular chitosans with a number-average molecular weight below 50 kDa, high chitosan contents of over 10 wt. % in a coating color could be achieved for the first time in viscosity ranges that are suitable for large-scale application and thus, in principle, enable the production of papers with chitosan coatings as gas barriers.According to a first aspect, the application relates to a coating composition for coating paper containing chitosan and / or its derivative with a number-average molecular weight of at most 50 kDa and at least one solvent. By further optimizing the type and amount of acid used to dissolve the chitosan, as well as by adding certain surfactants, plasticizers, clays, or oligochitosans, defect-free individual coats of the chitosan coating composition could be generated with application weights that provide very good oxygen barrier performance on paper (OTR less than 10 cm³ m). -2 d -1). Furthermore, depending on the additive, additional barrier properties against fat and flavorings or hexane could be achieved. A coated paper produced with this coating layer has a sufficient barrier effect for use in the food industry and is nevertheless biodegradable and recyclable. According to a second aspect, the invention therefore relates to a coated paper comprising a base paper and at least one barrier layer applied directly or indirectly to the base paper, wherein the coating layer is based on a coating color according to the first aspect. The barrier effect of the coating layer in the coated paper, which is essential here, is achieved in particular with the process used according to the invention for producing the coated paper.Accordingly, according to a third aspect, the invention relates to a process for producing a coated paper according to the second aspect, comprising the steps: a) producing a coating color according to the first aspect, containing an acid and a surfactant, by initially introducing the acid and the surfactant into water and adding the chitosan in portions; b) providing a base paper; c) applying the coating color to the base paper, preferably by means of a curtain or doctor blade process; and d) curing the coating color to form the coating color layer. Due to its barrier properties against oxygen, fat, and flavorings, the coated paper according to the invention is suitable as packaging for foodstuffs. According to a fourth aspect, the present invention thus relates to packaging for foodstuffs comprising the coated paper according to the second aspect. FIGURES Figure 1 shows confocal microscope images of a CT1 coating with a basis weight of 5 g / m. 2from a 5 wt.% solution in water / acetic acid (Figure 1 A) or a 5 wt.% solution in water / formic acid (Figure 1 B) and a CT6 coating with a basis weight of 5 g / m 2 from a 5 wt.% solution in water / acetic acid (Figure 1 C) or a 5 wt.% solution in water / formic acid (Figure 1 D). Figure 2 shows confocal micrographs of a 5 g / m 2 CT6 single chitosan coating from a 7.5 wt.% solution in water / acetic acid, as well as magnifications of selected areas with and without defects. Figure 3 shows sequentially applied chitosan coating patterns after oxygen barrier measurement: A: 5 g / m 2 made of 2 layers (layers), B: 7.5 g / m 2 made of 3 layers; C: 10 g / m 2 with 4 layers. Figure 4 shows a diagram of the oxygen barrier performance (OTR) as a function of the total application weight of a coating composition containing CT8, lactic acid, and Tween20. ®Figure 5 shows the results of the optical evaluation of drops of coating color containing CT8, lactic acid, and various surfactants. The evaluation is performed by determining the area occupied by the air bubbles within the total surface area of ​​the drops. The surfactants are A) Span60 ® , B) Tween60 ® and C) Tween20 ®Figure 6 shows the results of defect tests using colored biodiesel (pinhole test) on a porous paper coated with a coating color according to the invention containing CT8, lactic acid and Tween20. A) Coating color containing CT8, lactic acid and Tween20. B) Coating color containing CT8, lactic acid, Tween20 and kaolin-based inorganic pigment. Figure 7 shows the development of the solids content and the viscosity of a coating color according to the invention as a function of the pigment content. DETAILED DESCRIPTION OF THE INVENTION Definitions According to the invention, the "degree of deacetylation" of the chitosan is the percentage of free amino groups, i.e. amino groups that do not carry an acetyl group, on the molecule: Degree of deacetylation % = 1-FA = 100 - degree of acetylation.In the context of the present invention and in accordance with the general understanding in the field of paper technology, the term "coating color" refers to coating materials containing or consisting of binders, additives and optionally pigments or matrix pigments, which are applied ("coated") to the paper surface using special coating devices for the surface finishing or modification of a base paper. Papers produced in this way are referred to as "coated papers." In the context of the present invention, a "coated paper" is understood to mean a base paper which comprises one or more layers applied by coating, i.e. coating color layers. Suitable layers of such a coated paper substrate include functional layers and structure-forming layers (such as leveling layers for smoothing the surface).The term “coating color” is used according to the invention as a generic term for all spreadable coating compositions, preparations and / or solutions in the paper industry for treating, modifying or refining a paper surface. “Coating color layer” is understood to mean the coating color applied to the base paper and cured. “Paper” is a flat material that essentially consists of fibers of plant origin and is formed by dewatering a fiber suspension on a sieve. The resulting fiber web is compacted and dried. For the purposes of this invention, the flat materials “cardboard” and “paperboard”, which are produced in the same way, are also subsumed under the term “paper”. A distinction is made between paper, cardboard and paperboard only on the basis of their basis weight, with cardboard having a square meter weight of more than 600 g / m. 2 cardboard has a square meter weight of greater than 150 and less than or equal to 600 g / m 2and paper has a square meter weight of less than or equal to 150 g / m 2The "molar mass" M, also "molar mass" or "molar weight" of a substance is the mass per amount of substance or, in other words, the proportionality factor between mass m and amount of substance n: m = M ⋅ n. The SI unit is kg / mol. The numerical value of the molar mass in g / mol is the "relative molecular mass", also molecular weight, and is equal to the numerical value of the molecular mass in the atomic mass unit (u or Dalton). According to the invention, the "molecular weight" usually refers to the relative molecular mass. The "molar mass distribution" (MWD, molecular weight distribution), also molecular weight distribution, describes in science and technology the frequency distribution of individual molecular masses in samples of polymeric substances. Various mean values ​​are defined to statistically describe the sample: the viscosity average, the mass average, and the number average of the molar mass. The molar mass Mi of the i-mer is weighted by the relative numerical fraction that this polymer has.The "number-average molar mass" or "number-average molecular weight" indicates the average molar mass of a molecule randomly taken from the sample. Ni corresponds to the number of macromolecules in the sample with exactly i repeating units. According to the first aspect, the invention relates to a coating composition for coating paper containing chitosan and / or its derivative with a low average molecular weight and at least one solvent. According to one embodiment, the average molecular weight is less than 50 kDa. Chitosan and chitin are naturally occurring biopolymers similar to cellulose. The difference from glucose is the group bonded to the C2 atom. Cellulose has a hydroxyl group at this position, while chitosan has an amino group or an acetamido group. Chitosan and chitin are therefore composed of β-1,4-glycosidically linked N-acetylglucosamine monomers (precisely 2-acetamido-2-deoxy-β-D-glucopyranose residues) and glucosamine monomers and are polyaminosaccharides. Chitosan and chitin can be obtained from the shells of crustaceans and some fungi.The ratio of acetamido groups to amino groups in the chain is an important characteristic and is referred to as the "degree of deacetylation." A degree of deacetylation of less than 50% is referred to as "chitin," and a degree of deacetylation of more than 50% is referred to as "chitosan." To produce chitosan, chitin is deacetylated. This occurs, for example, by enzymatic digestion of the chitin with appropriate deacetylases or by boiling with sodium hydroxide solution. According to one embodiment, the chitosan or its derivative has a degree of deacetylation of at least 50%. With the degree of deacetylation, the solubility of the chitosan generally increases, but so does its viscosity. The degree of deacetylation can be 50%, 53%, 56%, 59%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, or 100%. According to one embodiment, the chitosan has a degree of deacetylation of at least 70%.A degree of deacetylation of at least 70% has the advantage that these chitosans have a higher solubility than chitosans with the same number-average molecular weight but a lower degree of deacetylation. According to one embodiment, the chitosan has a degree of deacetylation of at least 90%. According to one embodiment, the chitosan has a degree of deacetylation of at least 93%. A degree of deacetylation of at least 93% has the advantage that the chitosans are soluble in a wider pH range, with particular solubility in acidic media being increased. The increased degree of deacetylation increases solubility in, for example, aqueous lactic acid. Furthermore, a higher degree of deacetylation allows the addition of larger amounts of acid, which also contributes significantly to the solids content and ultimately leads to better barrier properties.Chitosans with different combinations of average molecular weight and degree of deacetylation are commercially available. For example, Chitosan 90 / 10 / A1 from BioLog Heppe® GmbH, with a degree of deacetylation of 90% and a number-average molecular weight of approximately 50 kDa, or GP1318 Chitosan (5 cps), ultra-low molecular weight from Glentham LIFE SCIENCES, with an average number-average molecular weight of approximately 20 kDa and a degree of deacetylation of greater than or equal to 90%. Chitosan derivatives can also be used instead of chitosan if their physicochemical properties are similar to chitosan. Such chitosan derivatives can be obtained by a modification of the chitosan selected from esterification, etherification, carboxylation, alkylation, acylation, acetylation, Schiff base, alkanolylation, sulfonylation, and quaternization.According to one embodiment, the derivative is selected from hydroxypropyl chitosan, glycol chitosan, methyl glycol chitosan, carboxymethyl chitosan, chitosan hydrochloride, and trimethyl chitosan. During the manufacturing process, not only the degree of deacetylation of the chitosans can be influenced, but also the average (number-average) molecular weight. The chitosans have a number-average molecular weight of up to 1,000,000 g / mol or a number-average molecular weight of over 1,000 kDa, but chitosans with significantly lower average number-average molecular weights can also be produced. Alternatively, other hydrolysis processes that cause molecular degradation can be used, such as enzymatic hydrolysis, oxidative hydrolysis, microwave hydrolysis, or gamma radiation hydrolysis.Until now, the prior art has assumed that chitosans with a high number-average molecular weight in particular are well suited for layer formation and lead to layers with high barrier performance. As shown in the present application, however, the opposite is the case. Compared to chitosan with high number-average molecular weights, chitosans with low number-average molecular weights, in particular number-average molecular weights below 70 kDa, can be dissolved in a coating color in a significantly higher concentration. Chitosans with a high number-average molecular weight of 80 kDa (CT1) or in the range from 100 kDa to 250 kDa (CT7) already lead to good barrier performance at concentrations of 1 to 5 wt.-% leads to viscosities at which the coating colors can no longer be processed in an industrial-scale process, especially viscosities above 1000 mPas. In contrast, coating color solutions with a chitosan concentration of up to 7.5 wt.% could be produced using the inventive chitosan CT6 (50 kDa) (see Example 1). CT8, with a chitosan with an even lower average number-average molecular weight of only 20 kDa, led to even better results (see Example 4 ff.). Concentrations of up to 15 wt.% could be achieved. Consequently, the average number-average molecular weight of the chitosan can be a maximum of 70 kDa.For example, the number average molecular weight is 10 kDa, 12 kDa, 14 kDa, 16 kDa, 18 kDa, 20 kDa, 22 kDa, 24 kDa, 26 kDa, 28 kDa, 30 kDa, 32 kDa, 34 kDa, 36 kDa, 38 kDa, 40 kDa, 42 kDa, 44 kDa, 46 kDa, 48 kDa, 50 kDa, 52 kDa, 54 kDa, 56 kDa, 58 kDa, 60 kDa, 62 kDa, 64 kDa, 66 kDa, 68 kDa, or 70 kDa. According to one embodiment, the chitosan has a number average molecular weight of less than 50 kDa. According to one embodiment, the chitosan has an average number-average molecular weight of at most 40 kDa. According to one embodiment, the chitosan has an average number-average molecular weight of at most 30 kDa. According to one embodiment, the chitosan has an average number-average molecular weight of at most 20 kDa. These chitosans with such a low average number-average molecular weight or corresponding chitosan derivatives can be used at a concentration of up to 15 wt.-% are brought into solution. The chitosan and / or its derivative is present in the coating colour in a concentration of more than 5 wt.% based on the total weight of the coating colour. The chitosan and / or its derivative is present in the coating colour in a concentration of 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.% or 20 wt. According to one embodiment, the chitosan and / or its derivative is present in a concentration of more than 9 wt.% based on the total weight of the coating colour. According to one embodiment, the chitosan and / or its derivative is present in a concentration of more than 11 wt.% based on the total weight of the coating colour. According to one embodiment, the chitosan and / or its derivative is present in a concentration of more than 13 wt.% based on the total weight of the coating. Above 13 wt.%-% the chitosan can lead to viscosities at which the coating color is no longer easy to process. In addition to the chitosan or chitosan derivative, the coating color can also contain oligochitosans. The oligochitosans can have an average molecular weight in the range of 1 to 10 kDa. For example, the average number average molecular weight of the oligochitosan is 1 kDa, 2 kDa, 3 kDa, 4 kDa, 5 kDa, 6 kDa, 7 kDa, 8 kDa, 9 kDa, or 10 kDa. According to one embodiment, the average number average molecular weight of the oligochitosan is in the range of 2 to 8 kDa. According to one embodiment, the average number average molecular weight of the oligochitosan is in the range of 4 to 6 kDa.As shown in the examples, the addition of oligo-chitosan makes it possible to reduce the viscosity of the coating color by up to one-third without impairing the barrier effect of the chitosan coating layer. This is achieved by using oligo-chitosan in a ratio of 1:3 (25%:75%) to chitosan. A further increase in the ratio up to 1:1 results in an even greater reduction in viscosity. However, this is achieved at the expense of the barrier effect against oxygen. A pure oligo-chitosan layer has no barrier effect against oxygen at all. The oligo-chitosan can make up a proportion in the range of 5 wt.% to 30 wt.% based on the total weight of the chitosan, i.e. chitosan and / or chitosan derivative plus oligo-chitosan. High solids contents can be achieved - as shown in the examples - particularly when using an organic acid.According to one embodiment, the coating composition according to the invention contains at least one organic acid. Examples include alkanoic acids such as acetic acid or formic acid, hydroxycarboxylic acids such as lactic acid, dicarboxylic acids such as malic acid or tartaric acid, tricarboxylic acids such as citric acid, or vinylogous carboxylic acids such as ascorbic acid. Surprisingly, it was shown that the choice of acid not only has a significant influence on the solubility of the chitosan and thus on the chitosan content in the coating composition, but also on the viscosity of the coating composition. In particular, using the organic acids lactic acid, malic acid, and ascorbic acid, it was not only possible to dissolve high chitosan contents, but also to maintain the viscosity at a high solids content within a range suitable for large-scale paper production. According to one embodiment, the organic acid is selected from lactic acid, malic acid, and ascorbic acid.As shown in the examples, lactic acid, in particular, could be combined with a variety of different additives such as surfactants, plasticizers, or inorganic pigments to generate a chitosan coating that is easy to process and ensures a high oxygen barrier. According to one embodiment, the organic acid is lactic acid. In the prior art, 1% acetic acid is regularly used to dissolve chitosan. Other sources assume that the acid should be used in a molar ratio of 1:1 to chitosan. The inventors have determined that the optimal molar ratio of acid to chitosan corresponds at least to the degree of deacetylation. It is assumed that with this amount of acid, the amine functions of the chitosan are completely protonated, thus dissolving the chitosan. The resulting pH should be below the pKa value of chitosan of approximately 6.5.The pH can be less than 6.5, less than 6.3, or less than 6.0. According to one embodiment, the molar ratio of organic acid corresponds to the degree of deacetylation. Thus, with a degree of deacetylation of 50%, the molar ratio is preferably 0.5, with a degree of deacetylation of 70%, the molar ratio is preferably 0.7, and with a degree of deacetylation of 90%, the molar ratio is preferably 0.9. According to one embodiment of the coating composition, the organic acid is present in a molar ratio to the chitosan and / or the chitosan derivative of at least 0.5. For example, the molar ratio can be 0.50, 0.52, 0.54, 0.56, 0.58, 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, 0.72, 0.74, 0.76, 0.78, 0.80, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, 0.98, or 1.00.According to one embodiment of the coating color, the organic acid is present in a molar ratio to the chitosan and / or the chitosan derivative of at least 0.7. According to one embodiment of the coating color, the organic acid is present in a molar ratio to the chitosan and / or the chitosan derivative of particularly preferably at least 0.9. According to one embodiment of the coating color, the organic acid is present in a molar ratio to the chitosan and / or the chitosan derivative of at least 0.93. Apart from the presence of an organic acid in the solution, there are no special requirements for the solvent. The solvent should preferably be an aqueous solvent. According to one embodiment, the aqueous solvent is water.Further additives can contribute to the property of the coating slips according to the invention to serve as an oxygen barrier when applied to paper. For example, the use of a non-ionic surfactant leads to a reduction in the OTR. According to one embodiment, the coating slip contains at least one non-ionic surfactant. As shown in the examples, optionally ethoxylated sorbitan fatty acid esters are particularly suitable as surfactants in the chitosan coating slip. Particularly good results were achieved with the ethoxylated sorbitan fatty acid esters sorbitan monolaurate (Span20®), polyoxyethylene(20) sorbitan monostearate (Tween60). ® ), and polyoxyethylene(20) sorbitan monolaurate (Tween20 ® ). According to one embodiment, the coating color contains at least one surfactant selected from the group consisting of sorbitan monolaurate (Span20 ® ), polyoxyethylene(20) sorbitan monostearate (Tween60 ®), and polyoxyethylene(20) sorbitan monolaurate (Tween20 ®The concentration of the surfactant also influences the oxygen transmission rate (OTR) of the coating layer. The surfactant should be present in the coating layer at a concentration of at least 0.1 wt.%, based on the chitosan weight. For the purposes of the present invention, "chitosan weight" refers to the total weight of all chitosans and chitosan derivatives present in the coating layer. For example, the surfactant can be present in the coating color in a concentration based on the weight of the chitosan and / or the derivative of 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2.0 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 4.65.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, 10.0 wt%, 10.5 wt%, 11.0 wt%, 11.5 wt%, 12.0 wt%-%, 12.5 wt.%, 13.0 wt.%, 14.0 wt.%, 14.5 wt.%, 15.0 wt.%, 15.5 wt.% or 16.0 wt.%. According to one embodiment, the surfactant is present in the coating slip in a concentration based on the chitosan weight in the range of 0.4 to 15 wt.%. According to one embodiment, the surfactant is present in the coating slip in a concentration based on the weight of the chitosan and / or the derivative in the range of 0.8 to 12 wt.%. According to one embodiment, the surfactant is present in the coating slip in a concentration based on the chitosan weight in the range of 1 to 8 wt.%. Furthermore, the coating slip according to the invention can contain a plasticizer. As shown in the examples, hydrophilic plasticizers increase the creasing resistance of the coating slip coated on paper without increasing the oxygen transmission rate (OTR). According to one embodiment, the coating slip contains at least one hydrophilic plasticizer.Sugar alcohols such as sorbitol, glycerol, xylitol, and mannitol are particularly suitable. According to one embodiment, the coating color contains at least one sugar alcohol. According to one embodiment, the coating color contains a sugar alcohol selected from sorbitol, glycerol, xylitol, and mannitol. The plasticizer can be present in the coating color in a concentration based on the chitosan weight in the range of 1 to 40 wt.%. The plasticizer concentrations can, for example, be 1 wt.%, 3 wt.%, 5 wt.%, 7 wt.%, 10 wt.%, 11 wt.%, 13 wt.%, 15 wt.%, 17 wt.%, 20 wt.%, 21 wt.%, 23 wt.%, 25 wt.%, 27 wt.%, 30 wt.%, 31 wt.%, 33 wt.%, 35 wt.%, 37 wt.%, or 40 wt.% based on the chitosan weight. As the plasticizer concentration increases, so does the kink resistance. While, for example, slight cracks are still visible at the kink point at a concentration of 10 wt.%, these are no longer visible at 30 wt.-% can only be detected at higher magnification in the scanning electron microscope. While, depending on the choice of plasticizer, concentrations of up to 50 wt.% deliver even better results in terms of kink resistance, the OTR can increase significantly at such high plasticizer contents. According to one embodiment, the plasticizer concentration in the coating color is in the range of 5 to 35 wt.% based on the chitosan weight. According to one embodiment, the plasticizer concentration in the coating color is in the range of 8 to 32 wt.%. According to one embodiment, the plasticizer concentration in the coating color is in the range of 10 to 30 wt.% In addition, the coating color can contain other additives that impart additional functionalities to the coating color.As shown in the examples, it is possible to use inorganic pigments, for example kaolin-based ones, to produce coating colors with even higher solids contents that nevertheless remain within a viscosity range in which they are easy to process. Coating colors additived in this way also have the advantage that the coating can impart oxygen barrier properties even to highly porous papers. According to one embodiment, the coating color contains at least one inorganic pigment. This pigment can be selected from natural calcium carbonates, precipitated calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, in particular precipitated and pyrogenic silicas, diatomaceous earths, magnesium carbonates, titanium oxide, bentonite, and clays such as kaolinite, montmorillonite-smectite and illite, chlorite, vermiculite, talc, and pyrophyllite.The coating color may also contain several of these pigments, especially two, three, or four of these pigments. The clay is, in particular, talc or kaolin. According to one embodiment, the inorganic pigment is a platelet-shaped phyllosilicate. Commercially available silicates include ASP109 and Capim. TMNP. The inorganic pigment can be present in the coating color at a concentration based on the chitosan weight in the range of 1 to 30 wt.%. The concentration of inorganic pigment can be, for example, 1 wt.%, 3 wt.%, 5 wt.%, 7 wt.%, 9 wt.%, 11 wt.%, 13 wt.%, 15 wt.%, 17 wt.%, 20 wt.%, 21 wt.%, 23 wt.%, 25 wt.%, 27 wt.% or 30 wt.% based on the chitosan weight. According to one embodiment, the concentration of inorganic pigment in the coating color is in the range of 10 to 28 wt.% based on the weight of the chitosan or the derivative. According to one embodiment, the concentration of inorganic pigment in the coating color is in the range of 20 to 26 wt.%. According to one embodiment, the concentration of inorganic pigment in the coating color is in the range of 20 to 25 wt.%.By using the inorganic pigment, the solids content in the coating color, based on the total weight of the coating color, can be more than 9 wt.%. The solids content, based on the total weight, can be, for example, 9 wt.%, 11 wt.%, 13 wt.%, 15 wt.%, 17 wt.%, 20 wt.%, 21 wt.%, 23 wt.%, 25 wt.%, 27 wt.%, or 30 wt. According to one embodiment, the solids content is more than 12 wt.% According to a further embodiment, the solids content is more than 15 wt.% According to a further embodiment, the solids content is approximately 20 wt.% The dynamic viscosity of the coating color can be in the range from 80 mPas to 2000 mPas. The dynamic viscosity can be influenced by the concentration and type of chitosan, by the organic acid, and by various additives.For example, the dynamic viscosity of the coating color is 80 mPas, 100 mPas, 120 mPas, 140 mPas, 160 mPas, 180 mPas, 200 mPas, 250 mPas, 300 mPas, 350 mPas, 400 mPas, 450 mPas, 500 mPas, 550 mPas, 600 mPas, 650 mPas, 700 mPas, 750 mPas, 800 mPas, 850 mPas, 900 mPas, 950 mPas, 1000 mPas, 1050 mPas, 1100 mPas, 1150 mPas, 1200 mPas, 1250 mPas, 1300 mPas, 1350 mPas, 1400 mPas, 1450 mPas, 1500 mPas, 1550 mPas, 1600 mPas, 1650 mPas, 1700 mPas, 1750 mPas, 1800 mPas, 1850 mPas, 1900 mPas, 1950 mPas, or 2000 mPas. According to one embodiment, the dynamic viscosity of the coating color is in the range from 150 mPas to 1000 mPas. According to one embodiment, the dynamic viscosity of the coating color is in the range from 200 mPas to 400 mPas.Coated paper According to a second aspect, the invention relates to a coated paper comprising a base paper and at least one barrier layer applied directly or indirectly to the base paper, wherein the coating color layer is based on a coating color according to the first aspect. In principle, all types of paper are suitable as the base paper for the coated paper according to the first or second aspect, i.e. both cardboard and board or normal paper. Preference is given to using papers made from hardwood and softwood pulp. The base paper can be kraft paper. Kraft paper is known in the art. Kraft paper is the type of paper with the highest strength. It consists of almost 100% cellulose fibers; only starch, alum, and size are added to achieve surface effects and increase strength.For food packaging, papers with a low basis weight are often in demand because of their flexibility and material savings. Especially for such papers, the coating layer according to the invention leads to a significant increase in barrier performance. According to one embodiment of the coated paper according to the first or second aspect, the base paper has a basis weight of no more than 150 g m². According to one embodiment of the coated paper according to the first or second aspect, the base paper has a basis weight of less than 150 g m². -2 . The basis weight can be, for example, 150 g·m -2 , 145 g·m -2 , 140 g·m -2 , 135 g·m -2 , 130 g·m -2 , 125 g·m -2 , 120 g·m -2 , 115 g·m -2 , 110 g·m -2 , 105 g·m -2 , 100 g·m -2 , 95 g·m -2 , 90 g ·m -2 , 85 g·m -2 , 80 g·m -2 , 75 g·m -2 , 70 g·m -2 , 65 g·m-2 , 60 g·m -2 , 55 g·m -2 , 50 g·m -2 , 45 g·m -2 , 40 g·m -2 , 35 g·m -2 , 30 g·m -2, 25 g m -2 or 20 g m -2 . According to one embodiment, the basis weight is below 100 g·m -2 . According to one embodiment, the basis weight is below 80 g·m -2 . According to one embodiment, the basis weight is in the range of 40 to 80 g·m -2It is preferred that the paper has a composition with a long fiber content of 10 to 80%, preferably 20 to 50%, and a short fiber content of 20 to 90% by weight, preferably 50 to 80% by weight. Long fiber is understood to mean a fiber with a fiber length of 2.6 to 4.4 mm, and short fiber is understood to mean a fiber with a fiber length of 0.7 to 2.2 mm. The base paper of the coated paper according to the second aspect can be a base paper coated on one or both sides or an uncoated base paper. However, uncoated base paper can also be surface-treated and contain up to 5 g / m² of pigments. For use as packaging in the food sector, the paper requires a certain tear resistance or breaking strength. According to one embodiment, the coated paper has a width-related breaking strength in the fiber direction in the range of 3.0 to 6.0 kN m. -1 The width-related breaking force in the fiber direction can, for example, be 3.0 kN·m-1 , 3.2 kN·m -1 , 3.4 kN m -1 , 3.5 kN·m -1 , 3.6 kN·m -1 , 3.8 kN·m -1 , 4.0 kN·m -1 , 4.2 kN·m -1 , 4.4 kN·m -1 , 4.5 kN·m -1 , 4.6 kN·m -1 , 4.8 kN·m -1 , 5.0 kN·m -1 , 5.2 kN·m -1 , 5.4 kN·m -1 , 5.5 kN·m -1 , 5.6 kN·m -1 , 5.8 kN m -1 , 6.0 kN·m -1 According to one embodiment, the broad-based breaking strength in the fiber direction is in the range of 3.5 to 5.5 kN m -1 According to one embodiment, the broad-based breaking strength in the fiber direction is in the range of 4.0 to 5.0 kN m -1The coating layer reduces the permeability of the coated paper to at least one gas compared to the base paper. This gas can be oxygen (O2), nitrogen (N2), carbon dioxide (CO2), methane (CH4), hydrogen (H2), water vapor, or mixtures thereof, such as air. In particular, the oxygen transmission rate (OTR) is reduced. The OTR can be determined according to ISO 15105-1. The base paper itself usually has such a high permeability that no value for an oxygen transfer rate can be determined. The base paper without the coating layer has an OTR of at least 100,000 cm³·m -2· d -1 . According to one embodiment, the OTR of the base paper is at least 50,000 cm³·m -2· d -1 . According to a further embodiment, the OTR of the base paper is at least 10,000 cm³·m -2· d -1. With the coating layer according to the invention, a coated paper with a high barrier performance, in particular a very low OTR, can be achieved. According to one embodiment, the OTR is 10 ± 1 g·m -2 not more than 50 cm³·m -2 d -1 The OTR of the coated paper according to the invention can be, for example, 50 cm³ m -2 d -1 , 48 cm³·m -2 d -1 , 46 cm³·m -2 d -1 , 44 cm³·m -2 d -1 , 42 cm³·m -2 d -1 , 40 cm³·m 2 d -1 , 38 cm³ m 2 d -1 , 36 cm³·m -2 d -1 , 34 cm³·m -2 d -1 , 32 cm³·m -2 d -1 , 30 cm³· m -2 d -1 , 28 cm³·m -2 d -1 , 26 cm³ m 2 d -1 , 24 cm³·m -2 d -1 , 22 cm³·m -2 d -1 , 20 cm³·m -2 d-1 , 18 cm³·m -2 d -1 , 16 cm³·m -2 d -1 , 14 cm³ m -2 d -1 , 12 cm³·m -2 d -1 , 10 cm³·m -2 d -1 , 8 cm³·m -2 d -1 , 6 cm³·m -2 d -1 , 4 cm³·m -2 d -1 , 2 cm³·m -2 d -1 , 1 cm³·m -2 d -1 By selecting suitable components of the coating colour, an OTR of not more than 20 cm³·m -2 d -1 , or even not more than 10 cm³·m -2 d -1 The coating layer in the coated paper can have a total coating weight in the range of 2 to 30 g·m -2 For example, the basis weight can be 2 g·m -2 , 4 g·m -2 , 5 g·m -2 , 6 g·m -2 , 8 g·m -2 , 10 g·m -2 , 12 g·m -2 , 14 g·m -2 , 15 g·m -2 , 16 g·m -2 , 18 g·m -2, 20 g·m -2 , 22 g·m -2 , 24 g·m -2 , 25 g·m -2 , 26 g·m -2 , 28 g·m -2 or 30 g m -2 According to one embodiment, the coating layer has a basis weight in the range of 2 to 15 g·m -2 . According to one embodiment, the coating layer has a basis weight in the range of 4 to 10 g·m -2.According to one embodiment, the coating layer has a basis weight in the range of 6 to 8 g / m². According to one embodiment of the coated paper, the coating layer is created by applying and curing the coating. As shown in the examples, the chitosan coating can also be applied multiple times, for example to reduce oxygen permeability and / or to remove any defects. According to one embodiment, the coating layer is created by applying and curing the coating at least twice. According to one embodiment, a primer is arranged in the coated paper between the base paper and the coating layer. This primer comprises at least one inorganic pigment and optionally a polymeric binder.Applying such a primer has the advantage of sealing the paper surface, allowing the additional barrier layer coated on top to migrate only slightly into the paper, thus creating sufficient interlayer adhesion. Furthermore, this primer reduces the average roughness of the base paper and provides a beneficial "holdout," characterized by a comprehensive application and a defined surface energy, allowing the coated barrier layer to optimally form. Furthermore, the primer promotes interlayer adhesion between the base paper and the barrier layer, which can be important for subsequent sealing applications. The term "CCK paper" refers to base papers in which the base paper is kraft paper and which are coated with a coating, usually consisting of fine clay (kaolin) or other mineral fillers.This coating improves the surface properties of the paper by giving it a smoother, whiter, and often glossier finish. "CCK" stands for "Coated Clay Kraft." The precoat can be a hydrophobic precoat overall. In another embodiment, the precoat is hydrophilic overall. The precoat preferably contains 1 to 70 wt.%, preferably 5 to 50 wt.%, particularly preferably 15 to 30 wt.% polymeric binder. This amount refers to the dried precoat in the final product. Examples of polymeric binders are styrene-butadiene latex (SBR), styrene-acrylate latex, polyvinyl alcohol (PVA), acrylate copolymers, and starch selected from native starch, oxidized starch, etherified starch, and esterified starch. According to one embodiment, the binder is SBR. According to one embodiment, the SBR is present in a concentration of 15 to 30 wt.%. The precoat preferably further contains 50 to 95 wt.%-%, preferably 65 to 90 wt.%, particularly preferably 70 to 80 wt.% inorganic pigment. The amount refers to the dried primer in the final product. The inorganic pigment can be selected from silicate, in particular layered silicate, kaolin (China clay), calcium carbonate, titanium dioxide (TiO2) and talc. According to one embodiment, the inorganic pigment is layered silicate. According to one embodiment, the layered silicate is present in a concentration of 70 to 80 wt.%. In addition, the primer can contain additives such as thickeners, e.g. acrylate-based thickeners, surfactants and / or rheology modifiers. The use of crosslinking agents is also conceivable. The primer preferably contains a zirconium-based crosslinker and is itself crosslinked with formaldehyde. These additives are preferably each present in an amount of 0 to 2 wt.%, preferably greater than 0 to 2 wt.%, wherein the value 0% is preferably excluded.The total amount of additives is preferably 0.5 to 3.0 wt.%, particularly preferably 0.8 to 2.0 wt.%, most preferably 1.0 to 1.5 wt.%. This amount is based on the dried precoat in the final product. According to one embodiment, the additives are an acrylate-based thickener and a zirconium-based crosslinker. According to one embodiment, the additives are an acrylate-based thickener and a zirconium-based crosslinker. According to one embodiment, the additives are an acrylate-based thickener and a zirconium-based crosslinker. According to one embodiment, the additives are present in a total amount of 1.0 to 1.5 wt.%. According to one embodiment, the precoat contains 70 to 80 wt.% layered silicate, 15 to 30 wt.% SBR, and the additives are an acrylate-based thickener and a zirconium-based crosslinker in a total amount of 1.0 to 1.5 wt.%. The preferred proportion of the acrylate-based thickener is 0.05 to 0.4 wt.%, and the zirconium-based crosslinker is 0.9 to 1.3 wt.%. As an alternative to the above-mentioned primers, a pure starch primer can also be used.The starch precoat consists of starch selected from native starch, cationized starch, oxidized starch, etherified starch, and esterified starch. Cationized starch with a degree of cationization of 0.05 to 0.2 is preferred. The application rate of the precoat is preferably 1 to 10 g / m² and more preferably 2 to 6 g / m², particularly preferably 4 to 6 g / m². This amount refers to the dried precoat in the final product. Due to the materials present in the coating layer, the coated paper is biodegradable. "Biodegradability" refers to the ability of organic chemicals to be broken down biologically, i.e., by living organisms or their enzymes. Ideally, this chemical metabolism proceeds completely to mineralization, but can also stop in the case of transformation products that are stable to degradation.The OECD guidelines for testing chemicals, which are also used in the context of chemical approval, are generally recognized. The tests in the OECD 301 test series (A-F) demonstrate rapid and complete biological degradation (ready biodegradability) under aerobic conditions. Different test methods are available for readily or poorly soluble as well as for volatile substances. "Biodegradable" or "biodegradable" in the sense of this invention refers to papers that have a biodegradability of at least 40% as measured according to OECD 301 F or of at least 20% as measured according to OECD 302 C (MITI-II test) and thus demonstrate inherent or fundamental degradability. This corresponds to the limit value for OECD 302 C according to the "Revised Introduction to the OECD Guidelines for Testing of Chemicals, Section 3, Part 1, dated 23 March 2006".From a limit of at least 60% measured according to OECD 301 F, papers in this case are also referred to as rapidly biodegradable. According to one embodiment of the coated paper according to the second aspect, the coated paper exhibits ready biodegradability according to OECD 301. Furthermore, the coated paper is recyclable according to the second aspect. Paper recycling is the pulping and processing of waste paper, used cardboard and board in paper industry plants with the aim of producing new paper, cardboard and board from them. On a small scale, waste paper pulp is first produced from the recycled waste paper, which is only later used to manufacture new paper. Printing ink removal or deinking (from English ink = “printing ink”, “ink”) is the key process in paper recycling for removing the printing ink from printed waste paper.The recyclability assessment can be carried out, for example, using INGEDE Method 11. The coated paper according to the invention achieves a deinkability score of over 50 using INGEDE Method 11. The deinkability score is preferably over 70. With the components of the barrier layer used, the coated paper can be approved for direct or indirect food contact. In particular, it is suitable for approval in accordance with the guidelines of the European Food Safety Authority. The coated paper according to the second aspect can contain further layers in addition to the barrier layer. According to one embodiment, the coated paper contains a further layer selected from a coating color, an ink, a sealing medium, and an adhesive. The coated paper according to the invention can also be metallized in the nanometer range, for example with Al2O3 or Al.The coated paper according to the invention is further preferably characterized in that a further layer comprising metals, in particular aluminum, and / or metal oxides, in particular aluminum oxide and / or silicon oxide, is applied to the barrier layer. Further layers can in particular reduce the permeability of the coated paper for further gases or form barriers for liquids or viscous substances such as fats, oils, hydrocarbons. A further layer can in particular: a) comprise at least one hydrophobic polymer, e.g. based on a polyacrylate, a styrene / butadiene copolymer and / or a polyolefin; b) comprise at least one hydrophilic polymer, e.g.based on a polyvinyl alcohol; c) comprise at least one inorganic pigment and a binder; d) comprise amorphous and crystalline regions; e) contain or consist of substances selected from the group consisting of lipophilic substances, paraffins, in particular hard paraffins, waxes, in particular microcrystalline waxes, waxes based on vegetable oils or fats, waxes based on animal oils or fats, vegetable waxes, animal waxes, low molecular weight polyolefins, polyterpenes and mixtures thereof; f) reduce or prevent the transfer of substances, in particular hydrophobic substances, e.g.of substances according to point e above, for example to prevent or reduce the transfer of substances from underlying layers to a food, in particular a fatty food; g) be at least heat- or cold-sealable; h) comprise at least one adhesive; i) comprise or consist of at least one thermoplastic material, in particular as a heat-sealable material j) comprise at least one natural wax and / or at least one carboxylic acid component and at least one natural resin. Manufacturing process Various manufacturing processes are possible for producing the coated paper according to the invention. The OTR of the coating layer in the coated paper, which is essential here, is achieved in particular with the process for producing the coated paper shown in the examples.Consequently, according to a fourth aspect, the invention relates to a process for producing a coated paper with a base paper and a coating layer, comprising the steps: a) producing a coating layer according to the first aspect with an organic acid and a non-ionic surfactant by initially introducing the organic acid and the non-ionic surfactant into water and adding the chitosan in portions; b) providing a base paper; c) applying the coating layer to the base paper, preferably by means of a curtain or doctor blade process; and d) curing the coating layer to form the coating layer. According to one embodiment, steps c) and d) are repeated at least once. According to one embodiment, the steps are repeated two, three, or four times. The process according to the invention can be used to influence the properties of the coating layer.In addition, the curing temperature, curing time, and curing pressure influence homogeneity and barrier effect. According to one embodiment of the method, the curing temperature is in the range from 20 to 300°C. The curing temperature can be 20°C, 40°C, 60°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 220°C, 240°C, 260°C, 280°C, or 300°C. According to one embodiment of the method, the curing temperature is in the range from 90 to 140°C. According to one embodiment of the method, the curing temperature is in the range from 100 to 110°C. According to one embodiment of the method, the curing time is in the range from 10 s to 15 min. The curing time can be, for example, 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s, 150 s, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min.According to one embodiment of the method, the curing time is in the range from 1 to 3 minutes. According to one embodiment of the method, the curing pressure is in the range from 0.2 bar to 3 bar. According to one embodiment of the method, the curing pressure is in the range from 0.9 bar to 1.1 bar. Packaging According to a fourth aspect, the invention relates to packaging comprising the coated paper according to the second aspect. This can, for example, be packaging for use for foodstuffs, as an insert for electronic components such as silica packets, for medical products such as rapid tests, for washing and cleaning agents, in particular in powder or tablet form, for tobacco products or consumer goods.Furthermore, it can be packaging for dried foods, cold-sold foods that require further preparation, packaging containing food in portion sizes for more than one person, or packaging with food in portion sizes for one person where more than one unit is sold. Examples of packaging that can be considered are stand-up pouch packaging, flow pack packaging, or packaging paper. According to one embodiment, the packaging is flow pack packaging. EXAMPLES A. Raw materials used The raw materials used in the following examples, their production, and characterizing properties are shown in Tables 1 to 5 below.Table 1: Chitosan Abbreviation Supplier Details CT1 BioLog Heppe® GmbH Chitosan 90 / 30 / A1, ~ 80 kDa CT2 BioLog Heppe® GmbH 90 / 2000 / A1, ~ 500 – 1000 kDa CT6 BioLog Heppe® GmbH Chitosan 90 / 10 / A1, ~ 50 kDa CT7 BioLog Heppe® GmbH 90 / 200 / A1, ~ 100 - 250 kDa CT8 Glentham LIFE 5 cps, ~20 kDa SCIENCES O-CT Glentham LIFE Oligmer, water-soluble, ≤ 5 kDa SCIENCES Table 2: Acids Name Supplier Details L-Lactic acid, PURAC® Corbion 80 wt% aqueous FCC80 solution L-Ascorbic acid Alfa Aesar 99 wt% DL-Malic acid Sigma-Aldrich > 99% wt. Acetic acid Merck 100% wt. Table 3: Surfactants Name Supplier Details Tween20® Sigma-Aldrich Polyoxyethylene(20) sorbitan monolaurate Tween60® Sigma-Aldrich Polyoxyethylene(20) sorbitan monostearate Span20® Sigma-Aldrich Sorbitan monododecanate Table 4: Inorganic. Name Supplier Details ASP109 Slurry BASF Kaolin Capim TMNP Slurry IMERYS Kaolin Table 5: Plasticizers Name Supplier Details Glycerol VWR Chemicals D-Sorbitol Thermo Scientific 98 wt.% Xylitol Thermo Scientific 99 wt.% PEG 400 Merck Polyethylene glycol D-Mannitol Alfa Aesar 99 wt.% B. Carrier material Unless otherwise specified, a base paper with primer was used as the carrier material in all examples. This base paper with primer consists of 40% long fiber and 60% short fiber with a precoat / primer (coating application: 5 g / m 2 ) consisting of 75.9% pigment (layered silicate), 22.8% latex (styrene-butadiene latex) and 1.3% rheology modifiers (0.2% acrylate-based thickener, 1.1% zirconium-based crosslinker) and with a total basis weight of 63 g / m 2This base paper with primer is also known as Clay Coated Kraft (CCK) paper. C. Methods Used C.1 Coating Process After preparing the coating color, it was degassed using a Hauschild Speedmixer for 5 minutes at 30 mbar and 800 rpm. 3-5 ml of this coating color were applied to the pre-coated side of the base paper at room temperature using a film applicator with metering bars (Erichsen). The metering bar was selected to achieve the specified application weight. The specified basis weight refers to the dried film. Wet film application doctor rod in µm K303 rod No.2 / S2 12 K303 rod No.3 / S3 24 K303 rod No.4 / S4 40 K303 rod No.5 / S5 50 K303 rod No.6 / S6 60 K303 rod No.7 / S7 80 K303 rod No.8 / S8 100 After the ink was applied, the papers were directly attached to a standard cardboard box with magnets (to prevent curling) and dried in a convection oven (Memmert; setting: 50% flap, 50% fan) at 105°C for 3 minutes. The papers were then stored at room temperature under standard laboratory conditions. C.2 Determination of Oxygen Transmission Rate (OTR) The oxygen transmission rate (OTR) was measured using the Brugger Gas Transmission Tester. The quantitative determination of gas permeability was performed using a pressure sensor via the differential pressure method (manometric method, ISO 15105-1). Here, the coated papers were prepared so that they covered the entire measuring area of ​​78.4 cm² with the coated side. By sealing them with high-vacuum grease, the papers served as a barrier between two chambers, the low-pressure and the high-pressure chamber.After ensuring proper sample preparation (no leaks, wrinkles, or creases), the low-pressure chamber was evacuated under high vacuum for one hour. Oxygen was then introduced into the high-pressure chamber at room temperature (1 bar, 50 ml / min). The amount of oxygen permeating through the coated paper into the low-pressure chamber was recorded by a pressure sensor as a pressure increase. The oxygen transmission rate (OTR) was only determined by the device's internal software once the time-dependent pressure change in the low-pressure chamber was at equilibrium. C.3 Determination of Greaseproofness The greaseproofness of the coated papers was determined using the method according to DIN 53116 (palm kernel fat test). C.4 Determination of Viscosity The viscosity of the prepared coating colors was determined using a Brookfield DV II+ rotational viscometer at a speed of 10–200 revolutions per minute.For this purpose, 10 ml of the coating color and the S34 spindle were used at a temperature of 22 °C. The viscosity was determined over a period of 15 minutes. C.5 Determination of the application weight of the barrier coating: The application weight of the barrier coating in g / m². 2is determined by differential weighing between coated and uncoated papers. Example 1 – Production of Comparative Coating Colors and Coating Colors According to the Invention The chitosan with the highest molecular weight (CT2) exhibited viscosities of over 2000 mPas even at low concentrations of 1 to 2 wt.% (dissolved in 1 M acetic acid). Chitosans with lower molecular weights (CT1, CT7) also resulted in viscosities of over 2000 mPas at low concentrations of 5 wt.% (dissolved in 1 M acetic acid). The chitosan was suspended in water and the required amount of acid was added according to the degree of deacetylation (DAC). Example calculation: Production of a 7.5% (w / v) solution of CT6 in aqueous acetic acid (HAC): ^^^ ⋅ ^^ The average molar mass of the chitosan monomer unit used for the calculation is obtained by a weighted average taking into account the degree of deacetylation and the molar masses of the glucosamine or N-acetylglucosamine unit: ^(^^) = ^^^ ⋅ ^(^^^ cos ^ ^^^) + (1 − ^^^) ⋅ ^(^ − ^^^^^ lg ^ ^ cos ^ ^^^) With a degree of deacetylation of 0.9, the following calculation results: ^ ^ ^ ^(^^) = 0.9 ⋅ 161.15 ^^^ + 0.1 ⋅ 203.1925 ^^^ = 165.35 ^^^ 7.5 wt.% CT6 solution: 7.5 g of CT6 were dissolved in 59.18 ml of dist. water and 40.82 ml of 1 M acetic acid were added while stirring. The mixture was stirred overnight at room temperature to ensure complete dissolution. The prepared solutions were sieved using a sieve bag with a mesh size of 150 µm and then with 80 µm to remove impurities and undissolved chitosan / chitin particles. 5 wt% CT6 / CT1 solution: 6 g of CT6 were dissolved in 87.33 ml of distilled water.The solution was suspended in water and mixed with 32.67 ml of 1 M acetic acid while stirring. The mixture was stirred overnight at room temperature for complete dissolution. The prepared solutions were sieved using a sieve bag with a mesh size of 150 µm and then with an 80 µm to remove impurities and undissolved chitosan / chitin particles. 2.1 Production and measurement of barrier papers with Chitosan CT6 Before coating, the sieved solution was degassed using a Hauschild Speedmixer for 5 minutes at 30 mbar and 800 rpm. The coating color was applied to the CCK-coated side of the base papers at room temperature using a film applicator with doctor blades (Erichsen). For a dry application weight of approximately 5 g / m², a wet film of 80 µm was applied. The doctor blade speed was 3 m / min. After application, the papers were attached directly to commercially available cardboard with magnets (to prevent curling) and dried in a convection oven (Memmert; setting: 50% flap, 50% fan) at a temperature of 105°C for 3 minutes. The resulting papers showed defects in the form of doctor blade streaks due to the high wet film application at low concentration. Furthermore, confocal microscopy images show defects caused by spontaneous dewetting.Areas with a high number of defects showed little or no oxygen barrier effect. However, measurements of selected areas without defects (“sweet spots”; see Figure 3) showed very good oxygen barrier effects of approximately 60 cm³·m³ in some cases. -2 d -1 or even about 5 cm 3 / m 2*d. The prepared solutions were sieved using a sieve bag with a mesh width of 150 µm and then with 80 µm to remove impurities and undissolved chitosan / chitin particles. Before coating, the sieved solution was degassed for 5 minutes at 30 mbar and 800 rpm. A doctor blade with a wet film application of 80 µm was used for coating. The doctor blade speed was 3 m / min. The chitosan coating was then immediately dried at 105 °C. The required wet film application was 100 µm. Figure 1 shows confocal microscope images of the papers coated with the coating colors according to Table 1. However, the high wet film application resulted in water damage to the paper, which is clearly visible on the back of the paper. Large-area fluorescence images revealed not only doctor blade streaks but also defect areas. OTR measurements were then carried out using these papers.It was found that only the chitosan coating consisting of 5 wt.% CT6 in water and acetic acid achieved a measurable, albeit low, oxygen barrier effect. With CT1, the barrier effect was completely lacking. The lack of, or low, oxygen barrier effect is attributable to the defects (see Figure 2). After closer investigation, the visible defects were caused by various sources, such as undissolved chitosan / chitin particles, dust particles, and spontaneous dewetting. 2.2 Production and Measurement of Barrier Papers with CT6 in Higher Concentration Subsequently, tests were carried out to determine whether better coatings could be obtained with a higher concentration of CT6, namely 7.5 wt.% (in acetic acid). The coating was applied as described in 2.1. However, defects again formed here, resulting in very low or unmeasurable oxygen barrier performance.However, measurements of the “sweet spots”, i.e. areas without defects, showed very good oxygen barrier effects of about 60 cm. 3 / m 2 *d or even about 5 cm 3 / m 2 *d. Example 3 – Production of Barrier Papers in Multiple Applications and OTR Measurement In this example, multilayer chitosan coatings were produced and their oxygen barrier properties determined. The multiple application was carried out to minimize the defects evident in Example 1. For this purpose, a 5% (w / v) solution of CT6 in aqueous 1 M acetic acid was prepared as described in Example 1. Table 6: CT6 Batch (5 wt%) Concentration m (CT6) / g V (1 M, HAC) / ml V (distilled H2O) / ml 5% (w / v) 6 32.67 87.33 Barrier coatings with 2, 3, and 4 layers were produced by applying a CT6 coating two, three, or four times, respectively. The application rate was 2.5 g / m 2per application. The results of these multi-coated papers are summarized in Table 7 below. The test results show that sequential application improves the oxygen barrier properties. The reason for this is probably that the multiple applications cover the defect areas, thus creating a continuous chitosan film on the paper that provides good oxygen barriers. Table 7: Multiple Application Number of 2 3 4 Layers Coating Weight / 5 7.5 10 g / m 2 OTR / cm³·m -2 d -1830 0.83 0.22 Example 4 – Variation of the production parameters acid, amount of surfactant and application weight Production of the coating colors: Coating colors were produced using chitosan CT8 and the acids acetic acid, lactic acid, ascorbic acid and malic acid as described below according to variant A or B. Variant A: The chitosan (CT8) was pre-suspended in water together with the surfactant (5 min at 650 rpm, KPG stirrer (core-pulled precision device)). The acid was then added while the stirrer was running until the chitosan dissolved. As a result, a sudden increase in viscosity was observed. The solutions prepared were sieved using a sieve bag with a mesh width of 150 µm and then with 80 µm in order to remove impurities and undissolved chitosan / chitin particles. Variant B: After placing the acid and the surfactant in water (stirring for 5 min at 650 rpm, KPG stirrer), the chitosan was added in portions while continuing to stir.This addition sequence allows the chitosan to be dissolved without a sudden increase in viscosity or shock stiffening. The prepared solutions were sieved using a sieve bag with a mesh width of 150 µm and then with 80 µm to remove impurities and undissolved chitosan / chitin particles. The CT8 was dissolved in different aqueous acid solutions according to the degree of deacetylation (93%), and different amounts of the surfactant Tween20® were added. The CT8 concentration was 15 wt.%. The acids were each used as described in Example 1 according to the degree of deacetylation (93%) with a molar ratio of acid to CT8 of 0.93. The coating colors were then applied as described under C.1 with a CT8 application weight of 6 g / m² or 7.5 g / m². Several papers were produced for each coating composition. The resulting papers were first visually inspected. Then the OTR was carried out in accordance with C.2. Finally, a grease resistance test was carried out according to C.4. Table 8: Variation of application weight and surfactant concentration Acid Application weight Tween20 conc. OTR CT8 [g / m²] [% Otro] [cm³ m. -2 d -1 ] Acetic acid 6 0.2 1000 Acetic acid 7.5 0.2 6000 Acetic acid 6 1.0 150 Acetic acid 7.5 1.0 5000 Lactic acid 6 0.2 nm Lactic acid 7.5 0.2 < 10 Lactic acid 6 1.0 1400 Lactic acid 7.5 1.0 nm Ascorbic acid 6 0.2 < 10 Ascorbic acid 7.5 1.0 5500 Malic acid 6 0.2 10 Malic acid 7.5 0.2 <10 Malic acid 6 1.0 10 Malic acid 7.5 1.0 <10 *nm = not measurable Based on the OTR values, malic acid, lactic acid and ascorbic acid are particularly suitable for the coating colors according to the invention. Using all three acids, barriers with OTR values ​​of less than 10 cm³·m -2 d -1which are also fat-resistant (all pass the palm kernel fat test). Adequate dry contents were achieved by adjusting the molecular weight. Spreadability was also significantly improved by using CT8 (individual coats for barrier generation possible). Acid variation has shown that, in principle, very good oxygen barriers with OTR values ​​of less than 10 cm³·m can be achieved using acetic acid, ascorbic acid, lactic acid, and malic acid in combination with the low-molecular CT8 (15 wt%). -2 d -1can be produced on paper coated with a precoat, wherein the precoat comprises clay minerals, in particular platelet-shaped kaolin. The addition of a surfactant such as Tween20 is advantageous as it can prevent wetting defects, for example. Example 5 - Influence of the chitosan concentration on the viscosity and the OTR To realize a curtain application, a viscosity range of ~ 200 - 400 mPas should be achieved. However, the use of 15 wt.% CT8 leads to viscosities above this range. To ensure runnability, the CT8 content was reduced and the viscosities of the resulting solutions were measured. Table 9: Dependence of viscosity on the CT8 concentration CT8 Acid Viscosity Conc. [mPas] [wt.-%] 15 Lactic acid ~ 800 15 Ascorbic acid >1000 15 Malic acid >1000 13.5 Malic acid ~ 400 11 Lactic acid ~ 215 11 Ascorbic acid ~ 250 11 Malic acid ~ 300 *Surfactant concentration 0.2% The results show that with a reduction of the chitosan concentration (CT8) to 11 wt.%, viscosities in the range for curtain application can be achieved. With malic acid, with an even smaller reduction, namely 13.5 wt.% (based on CT8), a viscosity in the range, namely 400 mPas, could be achieved. Table 10: OTR values ​​of coating colors with 11% CT8 CT8 Conc. Acid OTR performance [wt.%] 11 Lactic acid Consistently very good barrier values ​​of < 10 cm³·m. -2 d -1 for total application weights ≥ 7 g / m² 11 Ascorbic acid For ~ 10 g / m² total application ~ 40 cm³·m -2 d -1 . For ~ 12.5 g / m² total application < 10 cm³·m -2 d -1 11 Malic acid > 10000 cm³·m -2 d -1Direct barrier failure at total application weights < 11 g / m². Breakdown after several hours at ~ 11 g / m² * Drying for 3 min at 105°C. The results show that, especially when using lactic acid and ascorbic acid, good to very good OTR values ​​can be achieved even at low CT8 contents (11 wt%) to achieve the viscosity range (200 – 400 mPas). For OTR values ​​below 10 cm³·m -2 d -1 When using ascorbic acid, total coating weights of more than 10 g / m² are required. When using lactic acid, a total coating weight of about 7 g / m² is sufficient. The coated papers still showed OTR values ​​of less than 10 cm³·m even after 4 months of storage at room temperature. -2 d -1Example 6 - Characterization of an inventive coating system made from CT8 and lactic acid. Coating colors were prepared using the recipe shown in Table 11. Table 11: Composition of a CT8 / lactic acid coating color Designation Quantity / g TG / % Od / g Proportion / % Od Chitosan (CT8) 11 100 11 65.09 Water 81.7 0 0 0 Tween20 ® 0.3 98 0.294 1.77 Lactic acid 7 80 5.6 33.14 (80 wt%) 6.1 Oxygen barrier as a function of the coating weight The coating color was applied to the base paper at different coating weights. Table 12: Dependence of OTR on the coating weight Total coating weight CT8 Coating weight OTR [g / m²] [g / m²] [cm³ m -2 d -1] 3.1 2.0 > 10000 (no stable measurements) 5.1 3.3 922 ± 90 7.1 4.6 < 10 8.8 5.7 < 10 11 7.1 < 10 *Drying for 3 min at 105°C 6.2 Grease & Aroma Barrier Properties The grease and aroma barrier properties were then tested. The chitosan coatings are effective grease barriers. Palm kernel fat test on CCK-coated base paper as described in example 4.7. Single-sided coating using a doctor blade. The chitosan coatings are effective aroma barriers and hexane vapor barriers: Hexane Vapor Transmission Rate (HVTR) < 1 g / m²d (total coating weight ~ 8.8 g / m²). Example 9 – Addition of Oligochitosan. To further reduce viscosity and address problems related to drying and air entrapment, oligochitosans (O-CT) can be added. For this purpose, in the recipe described in Table 10 (100 g batch), parts of the CT8 were replaced with oligochitosan (O-CT): Table 13: Batches with CT8, O-CT, and lactic acid Recipe Dest.Tween20 Lactic acid O-CT / g CT8 / g H2O / g (20 wt.%) (80 wt.%) / ml / g 0% O-CT 80.5 1.5 7 0 11 12.5% ​​O-CT 80.5 1.5 7 1.375 9.625 25% O-CT 80.5 1.5 7 2.75 8.25 50% O-CT 80.5 1.5 7 5.5 5.5 100% O-CT 80.5 1.5 7 11 0 Table 14: Influence of the O-CT concentration on viscosity and OTR fraction O-CT [wt.%] Viscosity / mPas OTR / cm³·m. -2 d -10 ~ 250 < 10 12.5 ~ 150 < 10 25 ~ 80 < 10 50 ~ 40 >10000 Barrier breakdown 100 ~10 >10000 No barrier performance In the CT8-lactic acid formulation, parts of the CT8 were replaced with O-CT in order to lower the viscosity of the coating color. A lower viscosity allows for gentler drying and thus reduces the occurrence of drying defects. By adding O-CT, a significant reduction in viscosity was possible. However, if O-CT is used alone, continuous coatings cannot be formed. Therefore, there is no barrier performance. Example 10 Variation of surfactants A surfactant is used in the coating color to improve the coating pattern and the dewetting problem (reducing the surface tension). In combination with the CT8 lactic acid-based coating color, various non-ionic surfactants proved to be suitable for generating effective oxygen barriers.Table 15: Recipe of the coating colour for the surfactant test series Substance Content / g Proportion / %otro Water 82 (ref) / 81.18 (with surfactant) 0 CT8 11 63.15 Lactic acid (80 wt. 7 32.15%) Surfactant 0.82 4.7 Table 16: OTR values ​​of the coating colours with different surfactants Recipe OTR / cm³·m. -2 d -1CT8-Lactic Acid: Without surfactant > 10000 (dewetting) CT8-Lactic Acid: Span20 < 10 (homogeneous coating pattern) CT8-Lactic Acid: Tween60 < 10 (homogeneous coating pattern) CT8-Lactic Acid: Tween20 < 10 (homogeneous coating pattern) Example 11: Addition of phyllosilicates In the course of an investigation of different base papers, the addition of platelet-shaped phyllosilicates in the form of slurry was also investigated. These can, on the one hand, seal any porous structures present in a paper during drying and, on the other hand, increase the solids content and thus potentially reduce the required drying performance. The base paper with primer (see B.) or a starch-coated paper were used as the carrier materials. The starch-coated paper consists of 40% long fiber and 60% short fiber with a precoat / primer (coating application: 0.5 g / m 2) consisting of cationized starch with a cationization degree of 0.1 and with a total basis weight of 63 g / m 2. Preparation of the coating color: Preparation of the coating color according to variant B from Example 4, whereby the inorganic pigment was pre-suspended before adding the CT8. After placing the acid and surfactant in water, the inorganic pigment was added in the form of a slurry while the stirrer was running (650 rpm, KPG stirrer). To ensure homogeneous distribution of the pigment, the mixture was stirred for a further 10 minutes before the CT8 was added in portions. Coating of the base papers: Analogous to the previous examples. Preliminary evaluations for defects (pinhole test) (see Figure 6) show a significant reduction in open spots in the porous starch-coated paper by the addition of platelet-shaped layered silicates: Otro proportions: 56.78% CT8, 28.89% lactic acid, 14.19% kaolin-based layered silicate (ASP109), 0.16% Tween20 Different proportions of Capim NP slurry (TG = 68 wt.-%) were investigated in a CT8 lactic acid formulation and their influence on the viscosity and barrier properties on base papers precoated with a kaolin-based phyllosilicate was examined. The results are shown in Figure 7. Up to a phyllosilicate content of around 20 wt.% (otro), there was only a moderate increase in viscosity, so that the coating colors were still within the viscosity range for large-scale application. At contents greater than 20 wt.% (otro), a sudden increase in viscosity was observed. This suggests a possible gel effect that can be used for film stabilization. Up to a phyllosilicate content of around 20 wt.% (otro), OTR values ​​of less than 10 cm³·m were achieved after coating and drying the precoated papers. -2 d -1measured, with the precoat comprising in particular platelet-shaped kaolin. For the porous starch-coated paper, OTR values ​​above 20 wt.% (otro) were determined for the first time. With the further increase in the proportion of phyllosilicate, the OTR was also further reduced. This indicates an almost complete closure of the fibrous structures of the base paper, which makes stable OTR measurements possible. Example 12: Addition of plasticizers to improve kink resistance To address the brittleness of the natural chitosan polymer in the dried state, various plasticizers were added to the CT8 lactic acid formulation in varying proportions. The plasticizers reduce the interaction between the polymer chains, thereby lowering the glass transition temperature and making the material more flexible.Production of the coating color: Production of the coating color according to variant B as per example 4, whereby the plasticizer was pre-suspended before the CT8 was added. After the acid and the surfactant had been placed in water, the plasticizer was added while the stirrer was running (650 rpm, KPG stirrer). To ensure homogeneous distribution of the plasticizer, the mixture was stirred for a further 5 minutes before the CT8 was added in portions. Coating of the base papers: The coating was carried out as described in C.1. Table 17: Composition of the coating colors with different plasticizer concentrations Component Mass / g Chitosan 11 Tween (20 wt.%) 1.5 Lactic acid 7 Plasticizer 1.1-5.5 Water 79.4-75.5 Total 100 Glycerol, sorbitol, mannitol, xylitol and PEG400 were used as plasticizers in concentrations of 10 to 50 wt.% based on the chitosan mass.This resulted in the following proportions in the coating: Table 18: Proportion in the dry coating Plasticizer content 10% 20% 30% 40% 50% Chitosan / oven-dry% 61.1 57.6 54.47 51.7 49.1 H2O / oven-dry% 0 0 0 0 0 Tween20 / oven-dry% 1.63 1.54 1.46 1.38 1.31 Lactic acid / oven-dry% 31.2 29.3 27.7 26.3 25 Plasticizer / oven-dry% 6.11 11.56 16.37 20.62 24.59 The results are shown in Table 19: Table 19: OTR of coating colors with different plasticizers in different quantities before folding Plasticizer content Plasticizer Measured value 10 wt.% 30% by weight 50% by weight Mannitol OTR / cm³ m. -2 ·d- ~ 50 ~ 20 Not stable 1 Xylitol OTR / cm³·m -2 ·d- < 10 < 10 Not stable 1 Glycerol OTR / cm³·m -2 ·d- < 10 < 10 Not stable 1 sorbitol OTR / cm³ m -2·d- < 10 < 10 Not stable 1 The plasticizers sorbitol, glycerol, xylitol (and mannitol) can be added up to a proportion of about 30 to 40 wt.% based on CT8 in the formulation without impairing the oxygen barrier properties: OTR less than 10 cm³·m -2 d -1The addition of sugar alcohols as plasticizers (particularly xylitol, glycerol, sorbitol) reduces the interaction between the polymer chains with increasing amounts. This allows the generation of a barrier with improved flexibility. Regarding further advantageous embodiments of the device according to the invention, reference is made to the general part of the description and the appended claims to avoid repetition. Finally, it should be expressly noted that the exemplary embodiments of the device according to the invention described above serve merely to explain the claimed teaching, but do not limit it to the exemplary embodiments.

Claims

Claims 1. Coating composition for coating paper containing chitosan and / or a derivative thereof having an average number-average molecular weight of at most 50 kDa and at least one solvent.

2. Coating composition according to claim 1, wherein the chitosan and / or the chitosan derivative has an average number-average molecular weight of at most 40 kDa, preferably of at most 30 kDa, particularly preferably of at most 20 kDa.

3. The coating composition according to claim 1, wherein the chitosan derivative was obtained by a modification of the chitosan selected from esterification, etherification, carboxylation, alkylation, acylation, acetylation, Schiff base, alkanolylation, sulfonylation, and quaternization. Preferably, the derivative is selected from hydroxypropyl chitosan, glycol chitosan, methylglycol chitosan, carboxymethyl chitosan, chitosan hydrochloride, and trimethyl chitosan. 4.A coating according to any one of the preceding claims, wherein chitosan has a degree of deacetylation of at least 50%, preferably at least 70%, preferably at least 90%, in particular at least 93%.

5. A coating according to any one of the preceding claims, wherein the chitosan and / or its derivative is present in a concentration, based on the total weight of the coating, of more than 7% by weight, preferably more than 9% by weight, particularly preferably more than 11% by weight, in particular more than 13% by weight.

6. A coating according to any one of the preceding claims, additionally containing oligochitosan, preferably having a number-average molecular weight in the range from 1 to 10 kDa, particularly preferably in the range from 2 to 8 kDa, and in particular in the range from 4 to 6 kDa.Coating color according to one of the preceding claims, further comprising at least one organic acid, preferably selected from acetic acid, formic acid, citric acid, tartaric acid, lactic acid, malic acid and. Ascorbic acid, particularly preferably from lactic acid, malic acid, and ascorbic acid, in particular the acid is lactic acid.

8. The coating color according to claim 7, wherein the acid is present in a molar ratio to the chitosan and / or the chitosan derivative of at least 0.5, preferably at least 0.7, particularly preferably at least 0.9, in particular at least 0.

93.

9. The coating color according to any one of the preceding claims, further comprising at least one nonionic surfactant, preferably an optionally ethoxylated sorbitan fatty acid ester, particularly preferably selected from sorbitan monolaurate (Span20), polyoxyethylene(20) sorbitan monostearate (Tween60), and polyoxyethylene(20) sorbitan monolaurate (Tween20).

10. Coating colour according to claim 9, wherein the surfactant is present in a concentration based on the chitosan weight of at least 0.1 wt.%, preferably in the range from 0.4 to 15 wt.%, particularly preferably in the range from 0.8 to 12 wt.%, in particular in the range from 1 to 8 wt.-% in the coating slip.

11. Coating slip according to one of the preceding claims, further comprising at least one hydrophilic plasticizer, preferably a sugar alcohol, particularly preferably selected from sorbitol, glycerol, xylitol and mannitol.

12. Coating slip according to claim 11, wherein the plasticizer is present in a concentration based on the chitosan weight in the range from 1 to 40 wt.%, preferably in the range from 5 to 35 wt.%, particularly preferably in the range from 8 to 32 wt.%, in particular in the range from 10 to 30 wt.% in the coating slip.

13. Coating slip according to one of the preceding claims, further comprising at least one inorganic pigment, preferably selected from natural calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, in particular precipitated and pyrogenic silicas, diatomaceous earths, magnesium carbonates, titanium oxide, bentonite and clays, in particular talc or kaolin.

14. The coating slip according to claim 13, wherein the inorganic pigment is present in the coating slip at a concentration based on the chitosan weight in the range of 1 to 30 wt.%, preferably in a concentration in the range of 10 to 28 wt.%, particularly preferably in the range of 20 to 26 wt.%, in particular in the range of 20 to 25 wt.%.

15. The coating slip according to any one of the preceding claims, wherein the solvent is selected from an aqueous solvent, preferably the solvent is water.

16. The coating slip according to any one of the preceding claims, wherein the solids content, based on the total weight of the coating slip, is more than 9 wt.%, preferably more than 12 wt.%, particularly preferably more than 15 wt.%, in particular about 20 wt.%.Coating slip according to one of the preceding claims, wherein the coating slip has a dynamic viscosity in the range from 80 mPas to 2000 mPas, preferably in the range from 150 mPas to 1000 mPas, particularly preferably in the range from 200 mPas to 400 mPas.

18. Coated paper, comprising a base paper and at least one coating slip layer applied directly or indirectly to the base paper, wherein the coating slip layer is based on a coating slip according to one of claims 1 to 17.

19. Coated paper according to claim 17, wherein the total application weight of the coating slip layer is in the range from 2 to 15 g / m², preferably in the range from 4 to 10 g / m², particularly preferably in the range from 6 to 8 g / m².

20. Coated paper according to claim 17 or 18, wherein the coated paper has an oxygen transport rate (OTR) of at most 50 cm³·m. -2· d -1 , preferably in a volume of not more than 30 cm³·m -2· d -1, particularly preferably of at most 20 cm³·m -2· d -1 , in particular not more than 10 cm³·m -2· d -1 amounts.

21. Coated paper according to claim 20, wherein the base paper without coating layer has an OTR of at least 100,000 cm³·m -2· d -1 , preferably of at least 50,000 cm³·m -2· d -1 , particularly preferably 10,000 cm³·m -2· d -122. Coated paper according to one of the preceding claims, wherein the coating color layer is formed by applying and curing the coating color, preferably by applying and curing the coating color at least twice.

23. Coated paper according to one of the preceding claims, wherein a primer comprising at least one inorganic pigment and optionally a polymeric binder is arranged between the base paper and the coating color layer.

24. Coated paper according to one of claims 19 to 23, wherein the coated paper has at least one of the following features: ^ the coated paper is biodegradable, in particular it has ready biodegradability according to OECD 301; ^ the coated paper is recyclable; and ^ the coated paper can be approved for direct or indirect food contact, in particular according to the guidelines of the European Food Safety Authority.

25. A process for producing a coated paper according to any one of claims 18 to 24, comprising the steps of: a) producing a coating composition according to any one of claims 9 to 17, containing an organic acid and a non-ionic surfactant, by initially introducing the organic acid and the non-ionic surfactant into water and adding the chitosan in portions; b) providing a base paper; c) applying the coating composition to the base paper, preferably by means of a curtain or doctor blade process; and d) curing the coating composition to form the coating composition layer.

26. Packaging for consumer goods, food or tobacco products, comprising the coated paper according to any one of claims 18 to 24.

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