Barrier paper

Abstract

The invention relates to a barrier paper comprising a base paper and at least one coating colour layer S1, which is applied directly or indirectly to the base paper, the coating colour layer S1 comprising at least one polymer binder and at least one wax. The invention also relates to a method for producing such a barrier paper, the use of such a barrier paper as packaging material, and a packaging material comprising such a barrier paper.

Description

[0001] Barrier paper

[0002] Description

[0003] The present invention relates to a barrier paper, a process for producing such a barrier paper, the use of the barrier paper as packaging material and a packaging comprising the barrier paper.

[0004] Packaging generally refers to the covering or (partial or complete) wrapping of an object, particularly for its protection or ease of handling. Consequently, packaging material includes the material that forms such a package.

[0005] Packaging materials can be based on paper, plastics, and / or metals, for example. The present invention relates to paper-based packaging materials.

[0006] The main requirements for packaging materials of any origin are to protect the packaged goods from external influences, to prevent leakage, and to function as an advertising and information medium. To achieve this, the packaging material must meet different criteria depending on the packaged goods and the packaging process. Suitable packaging materials should not only possess barrier properties against, for example, water, grease, oxygen, or mineral oil, but also meet mechanical and process-specific requirements. A packaging material, especially a flexible packaging material, should possess sufficient tear resistance, a suitable coefficient of friction, and flexibility depending on the packaging system. It should be heat-sealable and externally printable, and it should retain its protective effect throughout the entire conversion and packaging process.

[0007] Known paper-based, coated packaging materials often contain compounds such as polyvinylidene chloride (containing halogens) or are composites of paper and metal or plastic films, have a tear resistance that needs to be improved, which can lead to running problems on packaging lines, and / or are often not recyclable due to an excessive coating content of adhesive components or the formation of so-called stickies via the paper fiber stream.

[0008] Polyvinyl alcohols, especially cross-linked polyvinyl alcohols, are widely known as linear, water-soluble, biodegradable barrier coatings, including for paper. Such coatings exhibit good barriers against oil, grease, oxygen, solvents, and other non-polar gases, liquids, or solids. However, due to their hydrophilicity, polyvinyl alcohols exhibit very high permeability to polar compounds, such as water. This can also influence the barrier effect against non-polar migrants, as polyvinyl alcohols absorb moisture very well, swell, and thus create pathways through the barrier coating at the molecular level.

[0009] Mixtures of all types of polymer dispersions and wax emulsions are offered to solve this problem. However, during testing of papers produced in laboratory and pilot trials, it was observed that such known mixtures of polymer dispersions and wax emulsions have the disadvantage that grease can penetrate the coating, which in turn leads to an increase in water vapor permeability. This creates the risk that water vapor permeability increases upon direct contact with fatty foods. When transferring laboratory recipes to a pilot coating system, it was also observed that heat sealability deteriorates. Furthermore, during the production of such coatings on a pilot scale, a decrease in heat sealability was often observed with increasing storage time.This refers to the ability of the material to create a stable seal seam through heat sealing, and not the stability of an existing seal seam.

[0010] The object of the present invention is to overcome the disadvantages of the known materials and to provide a material that is suitable as a packaging material, especially for moisture-sensitive foods, and that maintains its water vapor permeability at a low level even when in contact with fat, or increases it as little as possible. Furthermore, it must be suitable for heat-sealing applications. In particular, a seal strength of greater than 4 N / 15 mm and a water vapor transmission rate (WVTR) with target values ​​of < 20 g / m 2 / d (38°C, 90% rH) or < 8 g / m 2 / d (23°C, 50% rH) is targeted.

[0011] Furthermore, the material according to the invention should be as easy to produce as possible, require the smallest possible application weights and, if possible, allow recycling via the paper fiber stream.

[0012] This object is achieved by a barrier paper according to claim 1, i.e. by a barrier paper comprising a base paper and at least one coating layer S1 applied directly or indirectly to the base paper, wherein the coating layer S1 comprises at least one polymeric binder and at least one wax, and wherein the coating layer S1 has at least one of the following features: a) change in the surface tension of not more than +10 mN / m, preferably of not more than +6 mN / m, b) change in the polar component of the surface tension of not more than -0.65 mN / m, preferably of not more than -0.60 mN / m, c) change in the polar component of the surface tension of not more than -3.0 percentage points, preferably of not more than -1.5 percentage points.The respective change is determined by measuring and comparing the measured values ​​of the surface tension of the polar portion of the surface tension before and after a temperature treatment of the barrier paper at 105 °C for 3 minutes. Preferred embodiments are defined in the dependent claims.

[0013] Such a coated paper is particularly suitable as a packaging material for moisture-sensitive and greasy objects, especially foodstuffs, and can be used for heat-sealing applications.

[0014] Furthermore, such a barrier paper can achieve the above-defined guideline values ​​regarding heat sealability and water vapor permeability.

[0015] Finally, the barrier paper according to the invention can be produced relatively easily and with low application weights and can be recycled via the waste paper cycle.

[0016] Numerous specific details are also discussed below to provide a thorough understanding of the subject matter. However, it will be apparent to one skilled in the art that the subject matter can be practiced and recreated without these specific details.

[0017] All features of one embodiment may be combined with features of another embodiment if the features of the different embodiments are not incompatible.

[0018] The terminology used in the description of the present disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the subject matter. As used in this description and the claims, the singular forms "a," "an," and "the" are intended to include the plural forms, unless the context clearly dictates otherwise. The reverse is also true, meaning that the plural forms are intended to include the singular forms. It is also understood that the term "and / or," as used herein, refers to and includes all possible combinations of one or more of the related listed elements.It is further understood that the terms "includes," "including," "comprises," and / or "comprising," when used in the present description and claims, specify the presence of the stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0019] In the present description and claims, the terms "includes", "comprises" and / or "comprising" may also mean "consisting of", that is, the presence or addition of one or more other features, steps, operations, elements, components and / or groups is excluded.

[0020] In this description and the claims, the term "including" may therefore also mean "exclusively".

[0021] Unless otherwise stated, information in "%" in the context of formulations and / or compositions refers to "% by weight", in particular based on the respective total weight of the respective formulations and / or compositions.

[0022] As mentioned above, the barrier paper according to the invention comprises a base paper and at least one coating layer S1 applied directly or indirectly to the base paper, wherein the coating layer S1 comprises at least one polymeric binder and at least one wax, and wherein the coating layer S1 has at least one of the following features: a) change in the surface tension of not more than +10 mN / m, preferably of not more than +6 mN / m, b) change in the polar portion of the surface tension of not more than -0.65 mN / m, preferably of not more than -0.60 mN / m, c) change in the polar and disperse portions of the surface tension of not more than -3.0 percentage points, preferably of not more than -1.5 percentage points,The respective change is determined by measuring and comparing the measured values ​​of the surface tension of the polar component of the surface tension before and after a temperature treatment of the barrier paper at 105 °C for 3 minutes. If the coating layer S1 is applied directly to the base paper, this means that no further coatings or substances are present between the base paper and the coating layer S1.

[0023] If the coating layer S1 is applied indirectly to the base paper, this means that there are further coatings or substances between the base paper and the coating layer S1.

[0024] Laboratory tests have shown that it is possible to apply the coating layer S1 directly onto base paper, especially on calendered base paper with a surface thickness and a low Cobb value. For better hold-out of the coating and to minimize the required coating application, the prior application of a base coat is preferred. Ultimately, economic and production-technical considerations also determine which approach is preferred in each individual case.

[0025] The surface tension (alternatively called surface energy) of solids can be determined by contact angle measurements with at least two different liquids. Manufacturers of measuring instruments based on this principle, such as DataPhysics Instruments GmbH (D-70794 Filderstadt), describe the relationship on their website as follows:

[0026] "The cohesion of atoms and molecules, which determines the surface tension of a substance, is due to different types of interactions. In particular, a distinction can be made between disperse and polar interactions. Interactions due to temporal fluctuations in the charge distribution of the atoms / molecules are referred to as disperse interactions (van der Waals interactions). Polar interactions include Coulomb interactions between permanent dipoles or between permanent and induced dipoles (e.g. hydrogen bonds). Accordingly, the surface tension is also composed of an additive disperse and a polar component. If the ratio of disperse to polar component of the surface tension is compared for two phases, predictions can be made about the adhesion of the two phases to one another.The more closely the disperse and polar components match, the more interaction possibilities there are between the phases and the stronger the adhesion can be expected."

[0027] If the comparison of the measured values ​​shows that a) no significant change in the surface tension, ie of not more than +10 mN / m, and / or b) or c) no significant change in the polar part of the surface tension, ie of not more than -0.65 mN / m or of not more than -3.0 percentage points, could be determined, the barrier paper has the advantageous properties.

[0028] The inventors assume that in a coating layer comprising or consisting of at least one polymeric binder and at least one wax, drying the coating layer also causes at least partial demixing and / or partial film formation of the coating layer, and possibly also an uneven distribution of wax within the coating layer. For one and the same coating layer composition, different properties of the coating layer and thus also of the barrier paper result, depending on the drying parameters selected.

[0029] The inventors have applied these findings to the coating layer S1, where at least one of the following characteristics of the dried coating layer S1 a) change in surface tension of not more than +10 mN / m, preferably of not more than +6 mN / m, b) change in the polar component of the surface tension of not more than -0.65 mN / m, preferably of not more than -0.60 mN / m, c) change in the polar component of the surface tension of not more than -3.0 percentage points, preferably of not more than -1.5 percentage points. can be regarded as an indicator of the quality of the coating layer S1 with regard to the properties stated in the task, in particular with regard to whether there is partial demixing and / or partial film formation of the coating layer S1 or whether there is an uneven distribution of wax within the coating layer S1.

[0030] In other words, the properties of a barrier paper mentioned in the task depend not only on the composition of a coating layer S1, but also on how this coating layer S1 was dried.In addition to the composition, the dried coating layer S1 must therefore have at least one of the following structural features: a) change in surface tension of not more than +10 mN / m, preferably not more than +6 mN / m, b) change in the polar portion of the surface tension of not more than -0.65 mN / m, preferably not more than -0.60 mN / m, c) change in the polar and disperse portions of the surface tension of not more than -3.0 percentage points, preferably not more than -1.5 percentage points, wherein the respective change is determined by measuring and comparing the measured values ​​of the surface tension of the polar portion of the surface tension before and after a temperature treatment of the barrier paper at 105 °C for 3 minutes.

[0031] The drying parameters (temperature, time) for a specific coating composition S1 should preferably be selected such that, after drying, the coating layer S1 exhibits at least one of the features a) to c), preferably at least two features, and particularly preferably all three features. A person skilled in the art can determine the drying parameters using simple drying experiments.

[0032] For successful drying, it is preferable that the web temperature of the coating in the drying process exceeds the melting range of the wax for a sufficiently long period of time.

[0033] As found in numerous laboratory tests with various polymer-wax mixtures, the surface tension of the coating layer S1 is preferably between 15 and 40 mN / m, in particular between 20 and 35 mN / m. The polar component of the surface tension of the coating layer S1 is preferably 0 to 12%, in particular 0 to 6%, preferably 0 to 3%, and particularly preferably 0 to 1%, with 0% being specifically excluded as the lower limit in a preferred embodiment.

[0034] The disperse portion of the surface tension of the coating layer S1 is preferably 88 to 100%, in particular 94 to 100%, preferably 97 to 100% and particularly preferably 99 to 100%

[0035] The surface tension and the determination of the polar and disperse components of the surface tension are determined according to DIN EN ISO 19403-2 (2020-04):

[0036] Contact angle measuring device OCA 20 (DataPhysics) with software SCA 20, measuring principle: OWRK method (Owens, Wendt, Rabel, Kaelble).

[0037] Measuring fluids used and origin of the entered material constants:

[0038] Water and diiodomethane (according to Buscher) and 1,5-pentanediol (according to Gebhardt). In contrast to DIN EN ISO 19403-2 (2020-04), 1,5-pentanediol is used as the third measuring fluid because, unlike other non-polar measuring fluids, it still allows measurable contact angles on paper surfaces before the fluid is absorbed by the paper.

[0039] The temperature treatment of the barrier paper at 105 °C for 3 minutes is preferably carried out in a hot air oven (drying oven), whereby it is particularly important to ensure that the paper is actually exposed to 105 °C for a period of 3 minutes. For this purpose, the oven should preferably be preheated and have a sufficient internal volume (e.g. > 100 dm 3(e.g., width x height x depth 60 cm x 48 cm x 37 cm) so that no significant temperature drop occurs when the front door is opened briefly (2-3 s) to insert the paper. The barrier paper is preferably placed on a metal grid located in the middle of the drying oven, preferably with a cardboard base. The metal grid and cardboard should have already reached the oven temperature and have been placed in the oven, which has already been preheated to 105°C, for at least 15 minutes before the start of the temperature treatment. It should be noted that the duration of the temperature treatment was preferably set at 3 minutes to ensure that the barrier paper has enough time to actually reach 105°C, and that the treatment of the paper does not last too long to prevent decomposition processes. After removing the barrier paper from the oven, it was left to dry for at least 12 hours at 23°C and 50% RH.stored (air-conditioned) before further measurements were taken.

[0040] The wax in the coating layer S1 is preferably a wax according to the following definition of the German Society for Fat Research (DGF).

[0041] "Waxes are substances defined today by their mechanical and physical properties. Their chemical composition and origin, however, vary greatly. A substance is referred to as a wax if it is malleable at 20 °C, solid to brittle, has a coarse to finely crystalline structure, is translucent to opaque in color but not glassy, ​​melts above 40 °C without decomposition, is slightly liquid (slightly viscous) slightly above the melting point, has a strongly temperature-dependent consistency and solubility, and is polishable under light pressure." If more than one of the properties listed above is not met, the substance is not a wax according to the DGF (DGF Standard Method MI 1 (75)).

[0042] As our own laboratory studies have shown, the chemical composition of the waxes used is not crucial. They should simply be selected so that they melt under the technically feasible drying conditions in the coating system. It has been shown that it is beneficial for the formation of the water vapor barrier if the melting temperature is below the boiling point of water (100°C), and even better, below 90°C.

[0043] The polymeric binder in the coating layer S1 is in principle not limited, but includes all polymeric binders known to the person skilled in the art for binding waxes in paper coatings.

[0044] In principle, hydrophobic polymers can be used. However, polar, water-soluble binders of synthetic or natural origin, or derivatives thereof, may also be suitable, provided the hydrophilic functional groups are shielded by the waxes also present in the coating and the water vapor barrier does not impair the coating.

[0045] Laboratory tests have shown the following correlations: The lower the wax content, the better the heat sealability, especially the hot tack. However, a lower wax content results in higher water vapor permeability and a comparatively high sensitivity of the water vapor barrier to grease contact. If minimal wax is required, the aqueous coating should be dried in such a way that wax migrates to the surface, thus achieving a good, less grease-sensitive water vapor barrier.

[0046] In one embodiment, the wax content of the coating layer S1 is selected such that the barrier paper has at least one of the following features: a) a seal seam strength (cold tack) coating layer S1 against coating layer S1 of > 4 N / 15 mm, produced with the heat sealing parameters T = 130 - 150°C, sealing time = 0.3 s, sealing pressure = 3.3 bar or with ultrasonic sealing parameters that produce a T of 130 - 150°C in the sealing medium and a sealing time of 0.3 s and a sealing pressure of 3.3 bar b) a water vapor transmission rate (WVTR) < 20 g / m 2 / d (38°C, 90% rH), c) a water vapor transmission rate (WVTR) < 8 g / m 2 / d (23°C, 50% rH), d) an increase in water vapor permeability (38°C, 90% rH) after carrying out the palm kernel fat test according to DIN 53116 2003-02 (under the test conditions 10 min exposure time and pressure load of 2000 N / m 2 ) to not exceed 70 g / m 2 / d, preferably not more than 60 g / m2 / d, e) an increase in water vapor permeability after carrying out the palm kernel fat test according to DIN 53116 2003-02 (under the test conditions 60 min exposure time and 2000 N / m 2 ) of not more than a factor of 6, f) a static friction coefficient (coating layer S1 against coating layer Sl) of < 0.9 g) a kinetic friction coefficient (coating layer Sl against coating layer Sl) of < 0.6, where the values ​​for a) to g) are for a basis weight of the coating layer Sl of < 12 g / m 2 be determined.

[0047] The basis weight of the coating layer Sl is not limited to values ​​of < 12 g / m 2 The above-mentioned parameters only need to be met for these basis weights. For higher basis weights, the parameters must be adjusted accordingly.

[0048] The parameter a) a seal seam strength (cold tack) coating layer Sl against coating layer Sl is preferably understood to mean that a sheet of barrier paper is folded in such a way that the coating layer Sl is covered with itself in the seal seam area or that two sheets of barrier paper are placed on top of each other in such a way that the coating layers Sl of the two sheets are covered in the seal seam area.

[0049] In one embodiment, the barrier paper according to the invention is preferably characterized in that the water vapor permeability (38°C, 90% RH) has a change of maximum -40%, preferably of < -30%, wherein the change is determined by measuring and comparing the measured values ​​of the water vapor permeability before and after a temperature treatment of the barrier paper at 105°C for 3 min (analogous to the above statements).

[0050] In one embodiment, the wax is a wax according to DGF (DGF Standard Method MI 1 (75)) as defined above.

[0051] In one embodiment, the barrier paper according to the invention is preferably characterized in that the at least one wax is a wax based on mixtures or pure substances of fossil or natural short- to medium-chain hydrocarbons, their acids, esters, amides and diamides, hydrogenated vegetable oils, waxes produced by hydrogenation or partial hydrogenation of vegetable oils and animal oils or fats and / or metal soaps, preferably heneicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, triacontane, hentriacontane, dotriacontane, tritriacontane, tetratriacontane, pentatriacontane, hexatriacontane, heptatriacontane, octatriacontane, nonatriacontane, montan waxes, carnauba wax, beeswax, candelilla wax, rice bran wax, sugar cane wax, wax obtained from sunflower seed press cake, particularly preferably beeswax and / or wax obtained by hydrogenation of soybean oil,and / or paraffin waxes with an average molecular weight of at least 500 Daltons and a viscosity of at least 11 cSt at 100°C,

[0052] Beeswax and / or paraffin wax are particularly preferred, as they are approved for direct food contact according to BfR XXVI of April 1, 2021, Chapter C, Section IV, Item 2, with reference to BfR XXV of June 1, 2019, Federal Institute for Risk Assessment of the Federal Ministry of Food and Agriculture, Germany.

[0053] When using paraffin waxes, those listed in FCM substance No. 94 of the EU Commission Regulation No. 10 / 2100 of 14 January 2011 "on plastic materials and articles intended to come into contact with food" are particularly preferred.

[0054] In one embodiment, the barrier paper according to the invention is preferably characterized in that the at least one wax is present in an amount of 0.01 to 10% by weight, preferably from 0.01 to <8.0% by weight, preferably from 0.01 <6.0% by weight, particularly preferably from 0.01 to <5.0% by weight, and very particularly preferably from 0.01 <2.0% by weight, the lower limit being preferably at least 0.1% by weight, particularly preferably at least 0.2% by weight, based on the total weight of the coating slip layer S1.

[0055] In one embodiment, the barrier paper according to the invention is preferably characterized in that the at least one polymeric binder in the coating layer S1 is selected from the group comprising polyacrylates and copolymers with unsaturated hydrocarbons, polyolefins, copolymers consisting of unsaturated hydrocarbons and acrylic acid or salts thereof, (partially carboxylated) styrene-butadiene copolymers, styrene-butadiene copolymers, styrene-butadienes, polyvinyl acetates, partially saponified polyvinyl acetates, polyesters, for example polylactides and (made from glucose) polyhydroxyalkanoates, polyamides, polyurethanes, polyethers, polyethyleneimines, and / or polyvinylamides, preferably selected from the group comprising polymethyl acrylates, polymethyl methacrylates, polyethyl arylates, polyethyl methacrylates, poly(n-, iso-, tert-)butyl acrylates, poly(n-, iso-, tert-)butyl acrylates,-) butyl methacrylates, polycyclohexyl methacrylates, polyethylhexyl acrylates and their copolymers, graft polymers, and copolymers thereof with styrene, acrylonitrile, methylstyrene and / or vinyltoluene, particularly preferably styrene acrylate / methyl acrylate / butyl acrylate / ethylhexyl acrylate copolymer, and / or natural polymers, such as (modified) polysaccharides, proteins, lignin (derivatives) and other natural macromolecules, such as shellac.

[0056] In one embodiment, the barrier paper according to the invention is preferably characterized in that the at least one polymeric binder is contained in the coating layer S1 in an amount of 99.9 to > 92% by weight, particularly preferably > 95% by weight and very particularly preferably > 98% by weight, based on the total weight of the coating layer S1.

[0057] In one embodiment, the coating layer S1 comprises only the wax and the polymeric binder.

[0058] In another embodiment, the coating layer S1 comprises, in addition to the wax and the polymeric binder, further components or additives.

[0059] Other possible components of the coating layer Sl include, for example, pigments, in particular inorganic pigments such as Ca carbonate (GCC or PCC), talc, kaolins, natural and / or synthetic silicates.

[0060] Such pigments are preferably present in an amount of 0 to 70 wt.%, based on the total weight of the dry coating layer S1. To avoid excessively impairing the heat-sealability of the coating layer S1, amounts of 0 to 50 wt.%, better 0 to 30 wt.%, and most preferably 0 to 10 wt.%, should be selected.

[0061] Preferably, the value of 0 wt.% is excluded as a lower limit. Platelet-shaped pigments are preferred, as they can contribute to improving the barrier when aligned laminarly parallel to the coating. The particle size should preferably be selected such that the particles are completely enclosed in the layer when aligned laminarly. The aspect ratio (ratio of average diameter to thickness, also called the form factor) should be greater than 10, preferably greater than 100, and particularly preferably greater than 1000.

[0062] Other possible additives include thickeners, surfactants, crosslinkers and / or rheology modifiers.

[0063] These additives are preferably present in an amount of 0 to 2 wt.%, preferably 0 to 1 wt.%, based on the total weight of the dry coating layer S1. Preferably, the value of 0 wt.% is excluded as a lower limit.

[0064] The smoothness of the coating layer Sl (according to Bekk (ISO 5627, 1995-03)) is preferably from 400 s to 2500 s, preferably from 500 to 2000 s.

[0065] The roughness of the coating layer Sl (according to Parker-Print-Surf (PPS) DIN ISO 8791-4, 2008-05) is preferably from 0.8 to 2.0 pm, preferably from 1.0 to 1.8 pm.

[0066] The application quantity (ISO 536, 2020-05) of the coating layer Sl is preferably 4 to 20 g / m 2 , preferably 6 to 15 g / m 2 and particularly preferably 8 to 12 g / m 2 . The quantity refers to the dried coating layer Sl in the final product.

[0067] In one embodiment, the barrier paper according to the invention is preferably characterized in that the at least one wax in the coating layer S1 is enriched on the side facing away from the base paper.

[0068] Enriched is understood here in particular to mean that the local concentration of wax in the coating layer Sl on the side facing away from the base paper is greater than the local concentration of wax in the coating layer Sl on the side facing the base paper, which is indirectly demonstrated by the fact that the polar component of the surface energy does not decrease significantly further during subsequent drying.

[0069] Further detection of wax enrichment can be performed using electron microscopy (ESCA, also abbreviated XPS). Wax enrichment in the coating layer S1 on the side facing away from the base paper was also detected by the following tests.

[0070] Coating tests on a pilot coating line failed to achieve the low water vapor permeability achievable with laboratory coatings of individual sheets. To determine whether the cause was poor coating quality (defects, air bubbles, wetting disturbances) or simply insufficient drying and film formation, individual sheets were post-dried gently but for a sufficiently long time (3 min, 105°C) in a drying oven. The water vapor permeability of the post-dried papers (Comparative Examples 1 and 2) improved, and the polar component of the surface tension decreased. Since no chemical reaction is expected in the coating, it can be concluded that the non-polar wax migrated to the interface during post-drying.

[0071] The base paper used in the barrier paper according to the invention is in principle not limited.

[0072] It is preferred that the base paper has a basis weight of 20 to 120 g / m 2 , preferably from 40 to 100 g / m 2 , has.

[0073] Furthermore, it is preferred that the base paper has a long fiber content of 10 to 80 wt.%, preferably 20 to 50 wt.%, and a short fiber content of 20 to 90 wt.%, preferably 50 to 80 wt.%, based on the total weight of the base paper, wherein a long fiber is a fiber with a fiber length of 2.6 to 4.4 mm and a short fiber is a fiber with a fiber length of 0.7 to 2.2 mm.

[0074] The long-fiber content, in particular, ensures the strength of the comparatively thin paper, while the short-fiber content makes the paper denser and more cohesive, giving it a uniform appearance. A further increase in the long-fiber content would make the paper too stiff. The lower price of short-fiber pulp compared to long-fiber pulp also plays a role.

[0075] In addition, 0 wt% to 20 wt%, preferably 0 wt% to 5 wt%, of fillers, preferably excluding 0 wt%, such as GCC (ground calcium carbonate), known for example under the trade name Hydrocarb 60 or Hydroplex 60, PCC (precipitated calcium carbonate), known for example under the trade name Precarb 105, natural kaolin and / or talc.

[0076] Furthermore, common auxiliary substances such as retention agents and / or sizing agents may be included.

[0077] The advantage of such a base paper is, on the one hand, its high flexibility and, on the other hand, its good processability on existing packaging lines for flexible materials such as plastic films, maintaining high machine availability and achieving the necessary puncture resistance.

[0078] Particularly for food contact, the base paper comprises at least 60 wt.%, preferably at least 75 wt.% fiber, at most 25 wt.%, preferably at most 10 wt.% fillers, and at most 15 wt.% additives. In addition, unavoidable or necessary traces of processing aids (e.g., reagents, dispersants, anti-mold agents, etc.) may be present in the base paper.

[0079] In one embodiment, the barrier paper is characterized in that it has at least one further coating layer S2 applied directly or indirectly between the base paper and the coating layer S1, in particular for forming a mineral oil and / or fat barrier layer and / or also an oxygen barrier layer comprising at least one hydrophilic polymer.

[0080] If the coating layer S2 is applied directly between the base paper and the coating layer S1, this means that the coating layer S2 is in contact with the base paper on one side and with the coating layer S1 on the other. If the coating layer S2 is applied indirectly between the base paper and the coating layer S1, this means that the coating layer must be present between the base paper and the coating layer S1, but does not necessarily have to be in direct contact with them; thus, additional intermediate layers are not excluded.

[0081] Preferably, the coating layer S2 serves to form a mineral oil and / or fat barrier layer and comprises at least one hydrophilic polymer.

[0082] Preferred target values ​​for the mineral oil barrier are n-hexane permeabilities of < 30 g / m 2 / d. The preferred target value for fat resistance for foods that are not consumed immediately is passing the palm kernel fat test according to DIN 53116 Cat. 1 (no penetration even after more than 24 hours of testing).

[0083] Hydrophilic polymers are often cross-linked and therefore less flexible. For coating flexible packaging, they should preferably be selected so that they can withstand bends of up to 180° inward (coating to coating) and, ideally, outward as well, without allowing grease to seep through.

[0084] The coating layer S2 should preferably be able to be painted over in the dry state with the (aqueous) coating mass of the coating layer S1.

[0085] For this purpose, it should preferably not absorb or swell any water during the coating process so that, on the one hand, its own barrier effect (mineral oil, grease and, in special cases, oxygen) is not impaired and, on the other hand, an optimal, defect-free coating of the coating layer S1 is possible.

[0086] Since a polymer-based oxygen barrier (which is always also a mineral oil and grease barrier) is generally hydrophilic, it can only be coated if at least some of the free hydrophilic groups are covalently crosslinked during the coating's drying process. Reactive additives such as bi- or multifunctional aldehydes, carboxylic acids, epoxides, or inorganic crosslinkers such as zirconates or borates are preferably used for this purpose. Another possible group of crosslinkers are PAE resins (polyamideamine epichlorohydrin), which are also commonly used as wet strength agents for base papers. The use of these additives is either prohibited or restricted for contact with food.

[0087] Therefore, when looking for raw materials for mineral oil and grease barriers, the choice usually does not fall on water-soluble polymers, but rather on polymer dispersions that are adjusted by the manufacturers through functionalization so that they have the corresponding barrier effect without being significantly water-soluble, or by adding a sub-saturation of water-soluble polymers that provide or enhance the overall oleophobic effect.

[0088] Examples of suitable polymers are copolymers of polyvinyl alcohol and polyvinyl acetate, acrylate (co)polymers, acrylonitrile copolymers.

[0089] Also suitable is the use of cross-linked or partially hydrophobized polyvinyl alcohols, ethylene vinyl alcohols, or other copolymers of vinyl alcohol (for example those described in EP 4041548 A1), carbohydrates and / or proteins.

[0090] Preferred polymers are (according to EP 4041548 A1) partially saponified polyvinyl alcohols and / or partially saponified polyvinyl alcohol copolymers, each having an onset temperature determined by DSC of less than 210°C and preferably an average molecular weight (M w ) of less than 100,000 g / mol, where the onset temperature is defined by DSC according to DIN EN ISO 11357-1:2010-03 as the intersection point of the extrapolated baseline and the inflection tangent at the beginning of the melting or crystallization peak

[0091] Due to their high surface tension (surface energy), polyvinyl alcohols are particularly suitable for applying additional thin metal layers, which have a much lower and predominantly disperse surface tension.

[0092] The barrier paper according to the invention can preferably comprise at least one further layer consisting of or comprising metals, in particular aluminum. This allows the barrier effect to be further improved. This further layer can be designed as an intermediate layer or as a cover layer. When designed as an intermediate layer, this layer is preferably located directly below or above a heat-sealable layer, for example, the coating color layer S1.

[0093] Particularly preferred are polyacrylates, which preferably contain a starch-based protective colloid. A suitable polyacrylate is known under the trade name Epotal SP 101 D.

[0094] Also suitable are polyacrylates or polyacrylonitriles, known, for example, under the trade name Rhobarr 214.

[0095] Such polymers have the advantage that they swell little when in contact with water, because if they swell, a layer applied on top of them does not achieve its optimal water vapor barrier.

[0096] In one embodiment, the hydrophilic polymer is contained in the coating layer S2 in an amount of 30 to 100 wt.%, or 50 to 100 wt.%, based on the total weight of the coating layer S2.

[0097] Other possible components of the coating layer S2 include, for example, pigments, in particular inorganic pigments such as Ca carbonate (GCC or PCC), talc, kaolins, natural and / or synthetic silicates.

[0098] Such pigments are preferably present in the coating layer S2 in an amount of 0 to 70 wt.%, particularly preferably 0 to 50 wt.%, based on the total weight of the coating layer S2. Preferably, the value of 0 wt.% is excluded as a lower limit.

[0099] Platelet-shaped pigments are preferably selected, as they can contribute to improving the barrier when aligned laminarly parallel to the coating. The particle size should preferably be selected such that the particles are completely enclosed in the layer when aligned laminarly. The aspect ratio (ratio of average diameter to thickness, also called form factor) should be greater than 10, preferably greater than 100, and particularly preferably greater than 1000. In one embodiment, the coating slip layer S2 further comprises other additives. Possible additives include, for example, thickeners, surfactants, crosslinkers, and / or rheology modifiers.

[0100] Such additives are preferably present in the coating layer S2 in an amount of 0 to 2 wt.%, particularly preferably 0 to 10 wt.%, based on the total weight of the coating layer S2. Preferably, the value of 0 wt.% is excluded as a lower limit.

[0101] Preferably, the coating layer S2 does not contain glyoxal.

[0102] The surface tension of the coating layer S2 is preferably 45 to 70 mN / m, in particular 50 to 65 mN / m and most particularly 57 to 61 mN / m.

[0103] The polar component of the surface tension of the coating layer S2 is preferably 60 to 95%, in particular 70 to 90% and particularly preferably 78 to 84%.

[0104] The disperse portion of the surface tension of the coating layer S2 is preferably from 5 to 40%, in particular 10 to 30% and particularly preferably from 16 to 22%.

[0105] The surface tension and the respective proportions are determined as defined above.

[0106] Preferably, the surface tension of the coating layer S2 is at least 5 mN / m, generally 20 to 30 mN / m greater than that of the coating layer S1, and preferably has a significantly higher polar content, since this can be a maximum of 12% due to the wax content in the coating layer S1, as measurements have shown.

[0107] The application quantity (ISO 536, 2020-05) of the coating layer S2 is preferably 3 to 12 g / m 2 and particularly preferably 8 to 10 g / m 2 . The quantity refers to the dried coating layer S2 in the final product.

[0108] The smoothness of the coating layer S2 (according to Bekk (ISO 5627, 1995-03)) is preferably 80 to 500 s, preferably 100 to 200 s. The roughness of the coating layer S2 (according to Parker-Print-Surf (PPS) DIN ISO 8791-4, 2008-05) is preferably 2 to 4 pm, preferably 2.5 to 3.5 pm.

[0109] In one embodiment, the barrier paper according to the invention is characterized in that a further coating layer S3 is present directly on the base paper, in particular a coating layer which comprises or consists of at least one inorganic pigment and a polymeric binder.

[0110] The inorganic pigment is preferably platelet-shaped and comprises in particular a talc, precipitated calcium carbonate or silicate, preferably a layered silicate and most preferably a kaolin.

[0111] The aspect ratio (ratio of average diameter to thickness, also called form factor) should be about 7 to 40 to 1, preferably about 15 to 30 to 1.

[0112] The particle size of the platelet-shaped pigment is preferably adjusted so that at least about 70%, preferably at least about 85%, of the particles have a particle size of about <2 μm (Sedigraph). The pH of the platelet-shaped pigment in aqueous solution is preferably 6 to 8.

[0113] Suitable polymeric binders include, in particular, acrylate-based or styrene / butadiene-based binders. In principle, all polymers that can be used as binders for pigment coatings in the paper industry are suitable. The use of starch-based binders (solutions of modified starches, dispersions of cross-linked starches, so-called biolatices) and polymer-starch hybrid latices is also possible.

[0114] The polymeric binder preferably comprises a polymeric binder based on a polyacrylate.

[0115] The polymeric binder preferably comprises a styrene-acrylate copolymer, preferably a styrene-butyl acrylate copolymer, in particular a styrene-n-butyl acrylate copolymer. A suitable styrene-n-butyl acrylate copolymer is known, for example, under the trade name Acronal S 305 FD.

[0116] The coating layer S3 can be a hydrophobic primer.

[0117] In another embodiment, the coating layer S3 is hydrophilic overall.

[0118] The coating layer S3 preferably contains 5 to 50 wt.%, more preferably 10 to 30 wt.%, of polymeric binder. This amount refers to the dried coating layer in the final product.

[0119] The coating layer S3 further preferably contains 50 to 95 wt.%, more preferably 70 to 90 wt.%, of inorganic pigment. This amount refers to the dried coating layer in the final product.

[0120] In addition, the coating layer S3 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 coating layer preferably contains a zirconium-based crosslinking agent and is itself crosslinked with formaldehyde.

[0121] These additives are preferably present in an amount of 0 to 2 wt.%, preferably greater than 0 to 2 wt.%, with the value 0 wt.% preferably being excluded. This amount refers to the dried coating layer S3 in the final product.

[0122] The application quantity (ISO 436, 2020-05) of the coating layer S3 is preferably 1 to 10 g / m 2 and particularly preferably 2 to 6 g / m 2 . The quantity refers to the dried coating layer in the final product.

[0123] If such a coating layer S3, also called a precoat or primer, is applied, this has the advantage that the paper surface is sealed and the further coating layer applied on top only migrates slightly into the paper. Furthermore, this coating layer reduces the average roughness of the base paper and offers a beneficial coating holdout, which is characterized by a comprehensive application and a defined surface energy, so that a coated coating layer can form optimally and create an optimal barrier with as little application as possible, which has a beneficial effect on the cost structure. In addition, the precoat is designed in such a way that the layer adhesion between the base paper and the coating layer is not significantly reduced, which can be important for later sealing applications.

[0124] The surface tension of the coating layer S3 is preferably 15 to 40 mN / m, in particular 22 to 30 mN / m.

[0125] The polar component of the surface tension of the coating layer S3 is preferably 10 to 50%, in particular 15 to 30%.

[0126] The disperse portion of the surface tension of the coating layer S3 is preferably 50 to 90%, in particular 70 to 85%.

[0127] The surface tension and the respective proportions are determined as defined above.

[0128] For good wetting and layer adhesion, the surface tension of the primer should be higher or at least more polar than that of the layer on top.

[0129] If an embodiment with a layer S2 is present, this may not be guaranteed, as the coating layer S2 itself already has a high surface tension and a high polar content. A highly polar coating layer S3 would swell excessively when coated with an aqueous coating formulation, which could lead to cracks after drying. Therefore, the specified data on the surface tension of the coating layer S3, in particular, have proven to be a universal basis for the direct coating of the coating layer S1 or the coating layer S2.

[0130] The smoothness of the coating layer S3 (according to Bekk (ISO 5627, 1995-03)) is preferably 80 to 200 s, preferably 90 to 120 s

[0131] The roughness of the coating layer S3 (according to Parker Print Surf (PPS) DIN ISO 8791-4, 2008-05) is preferably 2.8 to 4.0 pm, preferably 3.2 to 3.6 pm. In one embodiment, the barrier paper according to the invention can comprise further layers in addition to the coating layers SI, S2, and S3 described above.

[0132] 50 For example, the non-coated side of the paper can be provided with one or more coatings that are more printable than the surface of the base paper which is only provided with a starch film.

[0133] To improve the overall barrier properties of a paper, smooth surfaces can be coated with metals or metal oxides (e.g. via vacuum vapor deposition).

[0134] The prerequisite for this is preferably smooth surfaces, such as in this case the coating layer S2 or the coating layer Sl, or a smooth printing line on the uncoated side of the barrier paper.

[0135] Barrier coatings are also known, which a processor can apply over the entire surface or only to specific areas.

[0136] One example would be the HYDRO-LAC GA oxygen barrier coating from Hubergroup Print Solutions. This coating can be applied to the coating layer (S1) or to the uncoated side of the barrier paper, or even better, to a smooth printing coating.

[0137] The barrier paper can be used as a heat-sealable barrier paper, but it is still possible to apply cold seal adhesive to one of the two sides, especially if the paper is to be used on a packaging machine designed for cold seal bonding.

[0138] Preferably, one of the two sides, preferably the print side, can be provided with an additional heat-sealing adhesive with the aim of sealing between the front and back (A / B sealing).

[0139] In one embodiment, the barrier paper comprises the coating layers

[0140] 51 and S3, as defined above. In one embodiment, the barrier paper comprises the coating layers SI, S2, and S3, as defined above.

[0141] Here too, the coating layer S3 can be applied in two or more coats as described above.

[0142] The barrier paper according to the invention can be obtained economically using all known papermaking and coating processes (film press with or without pre-dosing, roller application, doctor blade, blade, curtain coater, spray coater).

[0143] However, it is preferred to obtain the barrier paper according to the invention by a process in which an aqueous suspension or solution comprising the starting materials of the respective coating layer S1, or coating layers S2+S1, is applied to the base paper, preferably coated with a coating layer S3, wherein the aqueous application suspension or solution has a solids content of 15 to 55% by weight, preferably of 20 to 45% by weight, and by a curtain coating process. In the case of the coating layers S2 + S1, the two coatings can be applied one after the other with intermediate drying or preferably by a double curtain coating process (double curtain coating) at an operating speed of the coating system of at least 100 m / min, preferably > 200 m / min.

[0144] The barrier paper is then preferably dried. This drying process should be gentle, ensuring that the web temperature never exceeds 90°C, as otherwise bubbles can form, which can degrade or, in extreme cases, destroy the barriers. Contactless drying systems consisting of a group of infrared dryers, whose drying performance can be individually adjusted, followed by several hot air hoods, which can also be individually adjusted, have proven effective. Optionally, a second section with IR dryers can be installed downstream to achieve better film formation.

[0145] This process is particularly advantageous from an economic perspective and due to the uniform application across the paper web. If the solids content falls below approximately 15 wt.%, the economic efficiency decreases, as a large amount of water must be removed in a short time through gentle drying, which adversely affects the coating speed. On the other hand, if the value exceeds 55 wt.%, this simply leads to increased technical effort to ensure the stability of the coating curtain during the coating process and the drying of the applied film, as the machine must again run at very high speeds.

[0146] In the curtain coating process, a freely falling curtain of a coating dispersion is formed. The coating dispersion, in the form of a thin film (curtain), is "poured" onto a substrate by free fall to apply the coating dispersion to the substrate. DE 10 196 052 TI discloses the use of the curtain coating process in the production of information recording materials, whereby multilayer recording layers are realized by applying the curtain consisting of several coating dispersion films to substrates.

[0147] In a preferred embodiment of the process according to the invention, the aqueous deaerated coating suspension has a viscosity of approximately 100 to approximately 400 mPas (Brookfield, 100 rpm, 20 °C). If the viscosity falls below approximately 80 mPas or exceeds approximately 500 mPas, this leads to poor runnability of the coating slip on the coating unit. The viscosity of the aqueous deaerated coating suspension is particularly preferably approximately 150 to approximately 300 mPas.

[0148] In a preferred embodiment, in order to optimize the process, the dynamic surface tension of the aqueous application suspension can be adjusted to about 35 to about 55 mN / m, preferably to about 38 to about 52 mN / m (measured 50 ms after bubble formation) in accordance with the standard for bubble pressure tensiometry (ASTM D 3825-90), as described below. Better control over the coating process is achieved by determining the dynamic surface tension of the coating color and specifically adjusting it by selecting the appropriate surfactant and determining the required amount of surfactant. The individual coatings can be formed online on a paper machine with a coating unit or in a separate coating process offline on a coating machine. For development purposes and to produce prototypes, the paper can also be produced on a laboratory scale by hand doctoring followed by drying in a drying cabinet. The drying can, for example,The drying process can be carried out in a drying cabinet for 3 minutes at 90°C, similar to the previously described temperature treatment. Since the risk of bubble formation is lower during this slow drying process, a temperature of greater than 100°C, preferably 105°C, can also be set.

[0149] In further embodiments, the individual coating layers can also be applied to the base paper using the following methods:

[0150] A coating layer can be applied to the base paper and / or to existing coating layers using printing processes (e.g. flexographic printing and gravure printing).

[0151] The coating layer can be applied water-free as a melt by extrusion onto the base paper and / or onto existing coating layers.

[0152] This technology has the advantage that significantly more material can be applied, but this is only of interest if the overall product doesn't need to be recyclable as paper. Disadvantages include slower application speeds, higher energy consumption, and a higher minimum application weight.

[0153] The coating layer can be applied by lamination or covering of paper, e.g. in the form of plastic films, onto the base paper and / or onto existing coating layers.

[0154] The coating layers can also be applied successively over several application steps. The present invention further relates to a barrier paper obtainable by the processes described above.

[0155] Finally, the present invention also relates to the use of a barrier paper as described above as packaging material or as a component of packaging material, in particular heat-sealable packaging material but also by applying cold sealing varnish or other media for closing flexible packaging, preferably for foodstuffs, in particular for packaging fatty and moisture-sensitive foodstuffs, luxury items such as tobacco, coffee, tea, medicinal herbs, as well as household articles, cosmetic products, other moisture-sensitive consumer goods such as washing powder, coffee pods, sanitary towels, baby diapers and handkerchiefs and for protecting them from mineral oil vapors from the environment.

[0156] The barrier paper according to the invention can be used on all common packaging systems. Examples include vertical and horizontal form-fill-seal machines for producing, among other things, stand-up pouches, flow packs, or pillow packs; air cushion bags or pillows as a replacement for plastic air cushion bags or pillows; and machines that combine two webs of the same or different materials and join them by heat sealing, e.g., tray sealers, chamber belt machines (also with vacuum), bag filling and closing machines, thermoforming packaging machines, linear filling machines that apply lids by heat sealing, wrapping machines with a final heat sealing step, blister packaging machines, and X-fold packaging machines.

[0157] In a further preferred embodiment of the invention, the coated paper according to the invention is applied to cardboard or paperboard, in particular by lamination, laminating or gluing.

[0158] The present invention further relates to a packaging material, in particular a heat-sealable packaging material, consisting of or comprising a barrier paper as described above. The invention is explained in detail below using non-limiting examples.

[0159] Examples

[0160] For Comparative Examples 1 to 3 and Examples 1 to 5, base papers from one production line were used.

[0161] The pure base paper was produced on the associated paper machine (38 wt.% long fiber, 57 wt.% short fiber, 5 wt.% calcium carbonate as filler, fully sized with alkyl ketene dimer on water cobb 25 g / m 2), smoothed by means of a smoothing machine and with a film press on both sides enzymatically partially degraded cationically modified potato starch (approx. 1 g / m 2 ) is applied.

[0162] The paper machine is equipped with a Yankee cylinder and is therefore able to produce paper that is smooth on one side.

[0163] In a second step, this paper was coated on a production coating machine with a coating layer S3, which was applied by means of a blade coater to the less smooth side, which was on the side facing away from the Yankee cylinder during the calendering process (Comparative Examples 1 to 3 and Examples 1 to 3).

[0164] For examples 4 and 5, coating color S3 was applied in two steps. 4 g / m 2 were already applied online on the paper machine to the less smooth side, while a further 4 g / m 2as in the previous examples and comparative examples, were applied directly to it using a blade coater

[0165] For comparative examples 1, 2 and 3, the coating layer S2 and then directly onto the coating layer S2 the coating layer S1 were applied individually in separate coating tests on a pilot coating line, both using a curtain coater.

[0166] In comparative example 1a and examples 4 and 5, the coating layer S1 was applied directly onto the coating layer S3 in the same way.

[0167] The drying unit consists of a series of electric infrared dryers followed by a block of air hoods (hot air drying). The information on the length of the drying sections, the web temperature of the paper surface, and the residence time in each drying zone can be found in Tables 1 and 2a. The manufacturing parameters are given only for the application of the coating layer S1.

[0168] Examples 1, 2, and 3 were also produced on a production coating machine using a curtain coater. The drying unit also consists of a block of infrared dryers, but this time powered by natural gas, followed by a block of air hoods. Example 2 does not contain a coating layer S2. The coating layer S1 is applied directly onto the coating layer S3. While Examples 1 and 3 still contain a coating layer S2.

[0169] The information on the length of the drying sections, the web temperature of the paper surface, and the residence time in the respective drying zone can be found in Table 2. The production parameters are given only for the application of coating layer S1. The drying of coating layer S2 is less demanding, so there are no differences in the mineral oil and grease barrier between production on the pilot or production coating line.

[0170] Production of coating color S1 (Comparative Examples 1 to 3 and Examples 1 to 3) (Recipe from pilot plant, scaled up identically for production plant) Aqueous application suspension with a solids content of 20 to 60%:

[0171] 38.1 kg of water are introduced and mixed with 452.8 kg of styrene acrylate / methyl acrylate / butyl acrylate / ethylhexyl acrylate (97.8 wt.%) and beeswax (2.0 wt.%), or in the case of Comparative Example 3, styrene acrylate / methyl acrylate / butyl acrylate / ethylhexyl acrylate (91.82 wt.%) and beeswax (8.0 wt.%). Additives include 0.523 kg of the extensional rheology aid Sterocoll DF 4 (BASF SE, polyacrylamide, W / O emulsion) and 0.188 kg of the defoamer Genapol PF 10 (Clariant Produkte (Deutschland) GmbH, a polymerization product of propylene oxide and ethylene oxide). This results in a pH of approximately 8.5 and a viscosity (Brookfield) of approximately 160 mPas.

[0172] Production of coating color S 1 (Examples 4 and 5):

[0173] Aqueous application suspension with a solids content of 20 to 60%: 16 kg of water are added and mixed with 267 kg of an aqueous suspension consisting of 90 parts of a carboxylated styrene-butadiene polymer and 10 parts of a paraffin wax with chain lengths of C 21 - C 38. Solutions of 6.5 kg of polyvinyl alcohol type 8-88 and 15.6 kg of polyvinyl alcohol type 28-99 are added as thickeners. 0.2 kg of the extensional rheology aid Sterocoll DF 4 (BASF SE, polyacrylamide, W / O emulsion) and 0.7 kg of the defoamer Genapol PF 10 (Clariant Produkte (Deutschland) GmbH, polymerization product of propylene oxide and ethylene oxide) are added as additives. 1.7 kg of Dynawet 2050 (CTP GmbH), a non-ionic surfactant preparation with CAS # 160875-66-1 as the main active ingredient, is added as surfactant. This results in a viscosity of 230 mPas and a pH of 6.5.

[0174] Production of coating color S2: (Recipe from pilot plant, scaled up identically for production plant).

[0175] 77 kg of water are added and mixed with 228.6 kg of Epotal SP 101 D (BASF SE, polyacrylate with starch-based protective colloid). Additives include 0.957 kg of the thickener Texturecel 100 GA (DDP Specialty Products Germany GmbH, carboxymethylcellulose), 0.081 kg of the extensional rheology aid Sterocoll DF 4, and 0.210 kg of the defoamer Genapol PF 10. A pH of 8.8 is adjusted by adding sodium hydroxide solution, resulting in a Brookfield viscosity of approximately 200 mPas.

[0176] Both coating colours are suitable for curtain coaters and are de-aerated by vacuum in the working container of the coating machines before coating.

[0177] Production of coating color S3:

[0178] The composition is shown in Table 1: For the expert, this information is sufficient to produce a spreadable coating compound.

[0179] The composition of the respective coating layers, the drying parameters, and the determined properties of the barrier papers are summarized in Table 1 below. Description of the measurement methods for which no standard is known or for which proprietary procedures have been developed:

[0180] Heat sealability: While testing the seal strength of an existing seal is clearly defined, for example, by DIN 55529: 2012-09, there is no standardized method for testing a material's suitability for heat sealability. This is evidently due to the fact that packers prefer to develop their own incoming inspections for heat sealable films or papers, tailored to their packaging systems.

[0181] Based on industry information, relatively critical sealing conditions were applied (sealing time 0.3 s, sealing pressure 3.33 bar, smooth sealing jaws). Sealability is tested by sealing the two sealable coatings of a paper against each other. To determine the optimal sealing temperature, test specimens are produced and sealed at various sealing jaw temperatures (100-200°C).

[0182] Hot-Tack (hot seam strength): This test is carried out according to DIN 55571-2 Method C. It should also be noted that the same sealing conditions apply as for the heat-sealability test. The cooling time between sealing and force measurement was chosen to be 80 ms. The force measurement is carried out over a tensile length of 80 mm.

[0183] Palm kernel fat test according to DIN 53116: Test condition I (pressure 2000 N / m 2and exposure time > 24 h (practice 25 h). The display paper used is the print side of a CIS paper of the brand NexCoat-Smart 60 g / m 2 (Koehler Paper SE) is used.

[0184] Testing the palm kernel fat test on a folded piece of paper: For folded samples, a bend of 180° is created using a roller that exerts a load of 330 g / cm on the resulting bend and where the coating can be on the inside (inner bend) or outside (outer bend).

[0185] Hexane vapor transmission rate (HVTR): n-hexane is poured into a solvent-resistant beaker, tightly sealed with the test specimen, and the weight loss is monitored over time. The test is conducted at 23°C and 50% humidity. The coated side faces inward, toward the hexane vapor atmosphere. Suitable beakers with PTFE seals are available from specialist retailers.

[0186] Determination of water vapor permeability according to ISO / FDIS 2528: Here, too, it should be noted that the coated side of the test specimen faces the desiccant.

[0187] Dependence of the coating's water vapor permeability on grease contact: The test specimen is first subjected to a palm kernel fat test in accordance with DIN 53116 2003-02. The corresponding test conditions are specified. At the end of the exposure time, after wiping off the grease, the water vapor transmission rate (WVTR) of the paper is determined according to ISO / FDIS 2528. After wiping off the grease (which normally contains a red dye), a certain amount remains in or on the water vapor barrier coating. However, this does not lead to any further change in the WVTR, as a constant water vapor permeability is established over the course of the measurement.

[0188] The determination of the dynamic surface tension of the dry paper coatings is explained in the description.

[0189] Regarding Tables 1, 2 and 2a:

[0190] The columns marked with * contain the measured values ​​of the paper indicated on the left after a 3-minute treatment in a hot air drying cabinet at 105°C. A Binder type E 115 drying oven with the following internal dimensions width x height x depth: 60 x 48 x 40 cm (internal volume 115 dm 3 ), drying oven temperature range: 0 - 250°C, natural convection, no fan). A metal grid is located at mid-height inside the oven, with a cardboard box approximately 2 mm thick resting on top. The oven is then preheated to 105°C for at least 30 minutes. While the door is briefly opened (< 2 seconds), the test specimen is placed on the cardboard box. After 3 minutes, the test specimen is removed and conditioned for at least 12 hours at 23°C and 50% RH before further measurements are taken. Table 1: Comparative examples

[0191]

[0192]

[0193]

[0194]

[0195]

[0196] * Post-drying: 105 °C, 3 min

[0197] ** no coating layer S2

[0198] Table 2: Examples

[0199]

[0200]

[0201]

[0202]

[0203]

[0204]

[0205] * Post-drying: 105 °C, 3 min

[0206] ** no 2nd coating layer

[0207] Table 2a: Examples

[0208]

[0209]

[0210]

[0211] * Post-drying: 105 °C, 3 min

[0212] Example 2: (Example 2 from Table 1)

[0213] Another heat-sealable paper with water vapor barrier for flexible packaging according to the invention was tested.

[0214] The paper is suitable for various applications as secondary packaging and primary packaging, especially for food and non-food products that require a water vapor barrier.

[0215] Advantages of the paper are:

[0216] - Without optical brighteners

[0217] - Water vapor barrier for optimal product protection

[0218] - Good sealability

[0219] - Excellent strength properties

[0220] - Suitable for direct food contact

[0221] - 100% virgin fiber pulp

[0222] - Very good running properties on converting and packaging machines

[0223] - Recyclable in the paper cycle

[0224] - Particularly suitable for flexo, gravure and digital printing

[0225] The properties of the paper are summarized in Table 3 below.

[0226] Table 3: Example 3: (Example 1 from Table 1)

[0227] Another heat-sealable paper made of virgin fiber pulp according to the invention with barriers against water vapor, grease and mineral oil residues was tested.

[0228] The paper is suitable for various applications in the tobacco industry for particularly demanding tobacco products.

[0229] Advantages of the paper are:

[0230] - High degree of whiteness

[0231] - Without optical brighteners

[0232] - Smooth surface

[0233] - Good sealability

[0234] - Very good aroma barrier

[0235] - High kink and break resistance

[0236] - Excellent strength properties

[0237] - Suitable for direct food contact

[0238] - 100% virgin fiber pulp

[0239] - Excellent print and varnish quality

[0240] - Very good running properties on converting and packaging machines

[0241] - Particularly suitable for flexo and gravure printing

[0242] The properties of the paper are summarized in Table 4 below.

[0243] Table 4:

[0244] Example 4: (Example 1 from Table 1)

[0245] Another heat-sealable paper with water vapor barrier for flexible packaging according to the invention was tested.

[0246] The paper is suitable for various applications as secondary packaging and primary packaging for tobacco products such as tobacco volume pouches, tobacco pouches and coated tobacco inner liners with barrier.

[0247] Advantages of the paper are:

[0248] - Without optical brighteners

[0249] - Water vapor barrier for optimal product protection

[0250] - Good sealability

[0251] - Excellent strength properties

[0252] - Suitable for direct food contact

[0253] - 100% virgin fiber pulp

[0254] - Very good running properties on converting and packaging machines

[0255] - Recyclable in the paper cycle

[0256] - Particularly suitable for flexo and gravure printing

[0257] The properties of the paper are summarized in Table 5 below.

[0258] Table 5: Example 5: (Example 1 from Table 1)

[0259] Another grease-resistant heat-sealable paper made of virgin fiber pulp with a water vapor barrier and a mineral oil barrier according to the invention was tested.

[0260] The paper is suitable for various applications in flexible packaging for dry and powdery filling materials in the food and non-food sectors.

[0261] Advantages of the paper are:

[0262] - High degree of whiteness

[0263] - Without optical brighteners

[0264] - Smooth surface

[0265] - Good sealability

[0266] - High kink and break resistance

[0267] - Excellent strength properties

[0268] - Suitable for direct food contact

[0269] - 100% virgin fiber pulp

[0270] - Excellent print and varnish quality

[0271] - Very good running properties on converting and packaging machines

[0272] - Particularly suitable for flexo, gravure and digital printing

[0273] The properties of the paper are summarized in Table 6 below.

[0274] Table 6:

Claims

Claims 1. Barrier paper, comprising a base paper and at least one coating layer S1 applied directly or indirectly to the base paper, wherein the coating layer S1 comprises at least one polymeric binder and at least one wax, and wherein the coating layer S1 has at least one of the following features: a) change in surface tension of not more than +10 mN / m, preferably not more than +6 mN / m, b) change in the polar component of the surface tension of not more than -0.65 mN / m, preferably not more than -0.60 mN / m, c) change in the polar component of the surface tension of not more than -3.0 percentage points, preferably not more than -1.5 percentage points, wherein the respective change is determined by measuring and comparing the measured values ​​of the surface tension and the polar component of the surface tension before and after a temperature treatment of the barrier paper at 105 °C for 3 minutes.

2. Barrier paper according to claim 1, wherein the wax content of the coating layer S1 is selected such that the barrier paper has at least one of the following features: a) a seal seam strength (cold tack) after sealing the coating layer S1 against the coating layer S1 of > 4 N / 15 mm, with the heat sealing parameters sealing temperature of 130 to 150 °C, sealing time of 0.3 s, sealing pressure of 3.3 bar or with ultrasonic sealing parameters that result in a sealing temperature of 130 to 150 °C and a sealing time of 0.3 s and a sealing pressure of 3.3 bar, b) a water vapor transmission rate (WVTR) < 20 g / m 2 / d (38°C, 90% rH), c) a water vapor transmission rate (WVTR) < 8 g / m 2 / d (23°C, 50% rH), d) an increase in water vapor permeability (38°C, 90% rH) after carrying out the palm kernel fat test according to DIN 53116 under the test conditions (10 min exposure time and pressure load of 2000 N / m 2) to not exceed 70 g / m 2 / d, preferably not more than 60 g / m 2 / d, e) an increase in water vapor permeability after carrying out the palm kernel fat test according to DIN 53116 under the test conditions (60 min exposure time and 2000 N / m 2 ) of not more than a factor of 6, f) a static friction coefficient (coating layer S1 against coating layer Sl) of < 0.9, g) a kinetic friction coefficient (coating layer Sl against coating layer Sl) of < 0.6, where the values ​​for a) to g) are for a basis weight of the coating layer Sl of < 12 g / m 2 be determined.

3. Barrier paper according to claim 2, characterized in that the water vapor permeability (38°C, 90% RH) has a change of maximum - 40%, preferably of less than -30%, wherein the change is determined by measuring and comparing the measured values ​​of the water vapor permeability before and after a temperature treatment of the barrier paper at 105°C for 3 min.

4. Barrier paper according to any one of the preceding claims, wherein the wax is a wax as defined by DGF (DGF Standard Method MI 1 (75)).

5. Barrier paper according to any one of the preceding claims, wherein the at least one wax is a wax based on mixtures or pure substances of fossil or natural short to medium-chain hydrocarbons, their acids, esters, amides and diamides, hydrogenated vegetable oils, waxes produced by hydrogenation or partial hydrogenation of vegetable oils and animal oils or fats and / or metal soaps, preferably heneicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, Nonacosane, triacontane, hentriacontane, dotriacontane, tritriacontane, tetratriacontane, pentatriacontane, hexatriacontane, heptatriacontane, octatriacontane, nonatriacontane, montan waxes, carnauba wax, beeswax, candelilla wax, rice bran wax, sugar cane wax, wax obtained from sunflower seed presscake, particularly preferably beeswax and / or wax obtained by hydrogenating soybean oil, and / or paraffin waxes having an average molecular weight of at least 500 Daltons and a viscosity of at least 11 cSt at 100°C.

6. Barrier paper according to any one of the preceding claims, wherein the at least one wax is present in an amount of 0.01 to 10 wt.%, preferably from 0.01 to <8.0 wt.%, preferably from 0.01 <6.0 wt.%, particularly preferably from 0.01 to <5.0 wt.%, and very particularly preferably from 0.01 <2.0 wt.%, the lower limit being preferably at least 0.1 wt.%, particularly preferably at least 0.2 wt.%, based on the total weight of the coating slip layer S1.

7. Barrier paper according to any one of the preceding claims, wherein the at least one polymeric binder in the coating layer S1 is selected from the group comprising polyacrylates and copolymers with unsaturated hydrocarbons, polyolefins, copolymers consisting of unsaturated hydrocarbons and acrylic acid or salts thereof, (partially carboxylated) styrene-butadiene copolymers, styrene-butadiene copolymers, styrene-butadienes, polyvinyl acetates, partially saponified polyvinyl acetates, polyesters, such as polylactides, and polyhydroxyalkanoates made from glucose, polyamides, polyurethanes, polyethers, polyethyleneimines, and / or polyvinylamides, preferably selected from the group comprising polymethyl acrylates, polymethyl methacrylates, polyethyl arylates, polyethyl methacrylates, poly(n-, iso-, tert-)butyl acrylates, poly(n-, iso-, tert-)butyl acrylates, poly(n-, iso-, tert-)butyl acrylates,-) butyl methacrylates, polycyclohexyl methacrylates, polyethylhexyl acrylates and their copolymers, graft polymers, and copolymers thereof with styrene, acrylonitrile, methylstyrene and / or vinyltoluene, particularly preferably styrene acrylate / methyl acrylate / butyl acrylate / ethylhexyl acrylate copolymer and / or natural polymers, such as polysaccharides or modified polysaccharides, proteins, lignin or lignin derivatives and other natural macromolecules, such as shellac.

8. Barrier paper according to any one of the preceding claims, wherein the at least one polymeric binder is present in an amount of 99.9 to > 92 wt.%, preferably > 94 wt.%, particularly preferably > 95 wt.% and very particularly preferably > 98 wt.%, based on the total weight of the coating color layer S1.

9. Barrier paper according to any one of the preceding claims, wherein the at least one wax in the coating layer S1 is enriched on the side facing away from the base paper, which is indirectly demonstrated by the fact that the change in the polar portion of the surface tension is not more than -0.65 mN / m, and / or the change in the polar portion of the surface tension is not more than -3.0 percentage points, wherein the respective change is determined by measuring and comparing the measured values ​​of the polar portion of the surface tension before and after a temperature treatment of the barrier paper at 105 °C for 3 minutes.

10. Barrier paper according to any one of the preceding claims, wherein the base paper has a basis weight of 20 to 120 g / m 2 , preferably from 40 to 100 g / m 2 , has.

11. Barrier paper according to any one of the preceding claims, wherein the base paper has a long fiber content of 10 to 80 wt.%, preferably 20 to 50 wt.%, and a short fiber content of 20 to 90 wt.%, preferably 50 to 80 wt.%, wherein a long fiber is a fiber with a fiber length of 2.6 to 4.4 mm and a short fiber is a fiber with a fiber length of 0.7 to 2.2 mm.

12. Barrier paper according to one of the preceding claims, wherein the base paper contains a filler content of 0 wt.% to 20 wt.%, preferably 0 wt.% to 5 wt.%, of fillers, preferably excluding the value 0 wt.%, wherein the fillers comprise in particular ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), kaolin and / or talc.

13. Barrier paper according to any one of the preceding claims, wherein the barrier paper has at least one further coating layer S2 applied directly or indirectly between the base paper and the coating layer S1, in particular for forming a mineral oil and / or fat barrier layer and / or also an oxygen barrier layer comprising at least one hydrophilic polymer.

14. Barrier paper according to any one of the preceding claims, wherein a further coating layer S3 is present directly on the base paper, in particular a coating layer color layer which comprises or consists of at least one inorganic pigment and a polymeric binder.

15. A process for producing a barrier paper according to any one of the preceding claims, characterized in that an aqueous suspension comprising the starting materials of the coating color layer S1 is applied directly or indirectly to the base paper, the aqueous application suspension having a solids content of 15 to 55% by weight, preferably 20 to 45% by weight, and is applied using a curtain coating process at an operating speed of the coating system of at least 100 m / min and then dried, the drying preferably taking place by means of infrared or heat radiators and a subsequent air hood area, and the web temperature in the entire drying area remaining < 90°C.

16. Barrier paper obtainable by the process according to claim 15.

17. Use of a barrier paper according to any one of claims 1 to 14 or claim 16 as a packaging material or as a component of a packaging material, in particular heat-sealable packaging material, preferably for foodstuffs, in particular for packaging fatty and moisture-sensitive foodstuffs and for protecting them from mineral oil vapors from the environment.

18. A packaging material, in particular heat-sealable packaging material, consisting of a barrier paper or comprising a barrier paper according to any one of claims 1 to 14 or according to claim 16. * * *

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