Natural wax oxidation product emulsions with improved barrier properties

Abstract

The present invention relates to a natural wax oxidation product emulsion with improved barrier properties, to a method for producing such an emulsion, and to a cellulose fiber product or a biopolymer coated with such a natural wax oxidation product emulsion. The present invention further relates to the use of such an emulsion for coating a substrate containing cellulose fibers or a biopolymer.

Description

Background Art

[0002] In the food and consumer goods industry as well as for industrial products, many different types of packaging materials are required. With regard to the packaging of moisture-sensitive or water-containing items, the packaging must be protected from getting wet. For this purpose, water-impermeable films or coated cellulose-containing substrates, such as coated paper or coated paperboard, are used.

[0003] Suitable for coating cellulose-containing substrates are thin impermeable polymer layers or water-repellent waxy coatings. Another factor that plays a role here is the interaction between the coating and the object to be packaged. Therefore, for food packaging, packaging materials that do not contain any substances that have potential health problems, such as MOSH / MOAH from mineral oil fractions, phthalates and other plasticizers should preferably be used. Therefore, coatings of natural renewable waxes are particularly suitable and have been described many times in the literature.

[0004] For example, EP3781485 describes a composition for impregnating paper and paperboard, which contains vegetable waxes, such as sugar cane wax and / or rice bran wax. The composition is formed into pellets containing sugar cane wax and / or rice bran wax and can be applied as a barrier layer with a corresponding machine. It has been found that when they are applied to paper alone, both sugar cane wax and rice bran wax initially adhere, but detach from the paper substrate after prolonged exposure to hot water. In addition, it has been observed that a waterproof layer consisting of a mixture of sugar cane wax and rice bran wax adheres and remains waterproof for a long time when exposed to hot water.

[0005] Heinrich et al. describe the water vapor barrier properties of beeswax, candelilla wax, rice wax and sunflower wax in Powder Technology 357 (2019) 223-231. Rice wax exhibits the highest water vapor permeability of all the waxes studied, and therefore the worst barrier properties.

[0006] WO2006137274 describes a polymer composition comprising rice bran wax which is suitable for producing a biodegradable thin layer barrier and a laminate comprising the same. The coating composition is anhydrous.

[0007] The described barrier coatings containing natural waxes have in common that they are applied from the melt and therefore require special equipment for the coating operation. In addition, coating requires input of thermal energy to convert the composition into a melt, which makes the application of the barrier layer energy-intensive.

[0008] WO 2007 / 061592 describes a composition for producing an edible, biodegradable container comprising, inter alia, water, pregelatinized and native starches and a wax emulsion, wherein the composition consists essentially of food grade materials.

[0009] Preferred wax emulsions are stable aqueous emulsions usually consisting of carnauba wax, candelilla wax, rice bran wax, paraffin or another suitable food grade wax. The wax used is a bleached wax, but not further oxidized wax, i.e. the acid value of the bleached wax corresponds substantially to the acid value of the original wax. The emulsion is produced with the aid of an emulsifier. Preferred examples of wax emulsions suitable for formulations known from WO2007 / 061592 are emulsified carnauba wax and emulsified candelilla wax. Emulsifiers that may be mentioned are all emulsifiers approved for food applications, especially sorbitan monostearate, polysorbate 60, polysorbate 65, polysorbate 80, food grade gums (e.g. arabinogalactan, carrageenan, furcellaran, xanthan gum), citric acid stearyl monoglyceride, succinyl stearin and hydroxylated lecithin.

[0010] The wax emulsion is said to increase the water resistance of the composition but is not used to form a barrier layer.

[0011] DE102014001709A discloses an aqueous natural wax oxide emulsion with a cationic emulsifier. However, the document does not disclose an aqueous natural wax oxide emulsion with an anionic or nonionic emulsifier.

[0012] Document US2007068642A1 discloses waxy emulsions for coating paper substrates or fruits. The waxes described are "palm wax" and "soy wax", which are partially and completely hardened oils obtained by hydrogenation of triglycerides forming soybean oil or palm oil. In this way, palm wax or soybean wax are obtained by reduction. This reduces the double bonds of unsaturated fatty acids. Therefore, "palm wax and soybean wax" are chemically completely different substances from natural wax oxides, which are made of authentic natural waxes and are therefore usually made of monovalent esters of long-chain fatty acids.

[0013] There is a continuing need for coatings containing natural waxes which can be applied to polysaccharide-containing substrates without heat input and which form a barrier to water and water vapor therein. Such coatings containing natural waxes are also suitable for water (vapor) permeable polymer substrates and can be used on water (vapor) permeable plastic films, such as biopolymer films, in particular polylactide (PLA) films. The barrier layer should require as little as possible no addition of polymers or film formers, exhibit good adhesion to the substrate, be able to be applied in a thin layer, and be sufficiently flexible so as not to become brittle or porous, since this would adversely affect the barrier properties. Summary of the invention

[0014] Subject matter of the invention

[0015] It has surprisingly been found that this object is achieved by an aqueous natural wax oxide emulsion comprising (a) at least one natural wax oxide having an acid number / OH number ratio of not less than 1 and (b) at least one anionic or nonionic emulsifier.

[0016] Such emulsions are stable and can therefore be applied without problems to polysaccharide- or biopolymer-containing substrates, preferably to cellulose-containing substrates, and form a correspondingly adherent, homogeneous layer thereon.

[0017] Emulsifier refers to an auxiliary agent for producing and stabilizing emulsions, which is used to blend and stabilize two immiscible liquids, such as oil and water, to obtain a finely dispersed mixture, i.e., a so-called emulsion. The situation is similar to that of solid insoluble substances mixed in a liquid to form a so-called suspension. Molecules with coordinated properties, such as surfactants, have this property. Surfactants contain both hydrophobic and hydrophilic molecular parts, so that micelles around finely distributed droplets or particles (such as wax particles) can be formed, and they are stabilized in a dispersion medium (such as water) to prevent agglomeration and sedimentation. Nonionic surfactants are distinguished from ionic surfactants here. The former includes partial charges, while in the case of ionic surfactants, the polar molecular part is represented by ions. Therefore, there are anionic, cationic and zwitterionic surfactants.

[0018] Suitable natural wax oxides can be emulsified in water by emulsifying them with water and a specially matched emulsifier system at a temperature above the melting point of the wax while stirring, and the emulsion thus formed can then be cooled while stirring. The wax suspension thus prepared is called a "wax emulsion" in industry terminology.

[0019] It is possible here to use nonionic, ionic emulsifier systems or a combination of both.Ionic emulsifiers can also be prepared in situ by hydrolysis of waxy or oleic acid, for example with alkaline media or amines.

[0020] Suitable emulsifiers for the natural wax oxide emulsions are especially anionic and nonionic emulsifiers, for example the Emulsifiers from Clariant International Ltd. or Emulsifier.

[0021] The invention further provides a process for producing such an emulsion and its use for producing coated polysaccharide-containing or biopolymer-containing substrates.

[0022] Application from an aqueous emulsion is advantageous because it does not require heating for application and makes it possible to apply thinner and therefore more flexible layers. This makes the process more energetically favorable compared to prior art coating methods, brings advantages in terms of resource utilization and facilitates paper recycling. The layer applied from this emulsion has a very low water vapor permeability and leads to a significant reduction in the water absorption of an otherwise hydrophilic substrate. In addition, the layer is very uniform and non-porous, which also leads to a good barrier effect. DETAILED DESCRIPTION OF THE INVENTION

[0024] The production of the natural wax oxide in the emulsion containing the natural wax oxide can be achieved, for example, using any known oxidation process which also oxidizes the natural wax itself and thus increases the acid number of the natural wax oxide measured in accordance with ISO 3681 by at least 5 mg KOH / g, preferably at least 10 mg KOH / g, compared to the starting material (generally natural wax or a bleached form of natural wax), and which does not only lead to bleaching of the wax by oxidation of impurities in the wax. These include oxidation with chromic acid, with chromosulfuric acid (chromium trioxide and sulfuric acid) and with dichromates, thermal oxidation with air oxygen (which can also be carried out with the aid of a catalyst) and all types of electrochemical oxidation.

[0025] Suitable natural wax oxides are in particular those produced from real natural waxes by oxidation. "Real natural waxes" are understood to mean those natural waxes which are already in wax form in the raw material source and do not need to undergo further chemical conversion in order to be considered as waxes.

[0026] Preferred are natural waxes formed from monovalent esters of long chain fatty acids.

[0027] Particularly preferred are oxides of rice bran wax, corn wax, sugar cane wax, sunflower wax and carnauba wax. Particularly preferred are oxides of rice bran wax and corn wax. Very particularly preferred are oxides of rice bran wax.

[0028] The natural wax oxides preferably have an acid number of between 1 and 140 mg KOH / g, preferably between 15 and 140 mg KOH / g, more preferably between 30 and 140 mg KOH / g, measured according to ISO 2114. Very particular preference is given to acid numbers of between 15 and 110 mg KOH / g or between 30 and 110 mg KOH / g. These acid number ranges are achieved by oxidation alone and no further esterification step is required. Such natural wax oxides have, on the one hand, sufficient polarity to be more easily emulsifiable in water, but, on the other hand, are not so polar that the barrier layer has defects in the microstructure of the barrier layer which are attributable to the polarity and which adversely affect the barrier effect.

[0029] In a preferred embodiment, the at least one natural wax oxide in the emulsion according to the invention has a saponification value of between 30 and 200 mg KOH / g, preferably between 50 and 180 mg KOH / g, more preferably between 80 and 170 mg KOH / g, measured according to ISO 3681. Very particular preference is given to saponification values ​​of between 80 and 140 mg KOH / g.

[0030] The at least one natural wax oxide in the emulsion of the invention preferably has a hydroxyl number measured according to DGF M-IV 6 of less than 8 mg KOH / g, preferably less than 5 mg KOH / g, which represents more homogeneous material properties and therefore leads to the formation of a more homogeneous barrier layer with fewer defects in the microstructure.

[0031] In a preferred embodiment, the natural wax oxide has an iodine color value of less than 20, preferably less than 15, more preferably less than 10, measured according to DIN 6162. A low iodine color value indicates that the wax is particularly light in color, so that the wax has no negative impact on the color of the substrate.

[0032] The at least one natural wax oxide in the emulsion of the invention preferably has a dropping point between 65 and 110° C. measured according to ISO 2176. This means that the resulting coating has good thermal stability without having to expend excessive energy in the production of the natural wax emulsion to melt the natural wax.

[0033] In order to ensure easy application of the aqueous natural wax emulsion and to make the barrier layer as thin and uniform as possible, the natural wax oxide is present in the emulsion to an extent of 5 to 50 wt. %, preferably to an extent of 10 to 45 wt. %, more preferably to an extent of 15 to 40 wt. %, most preferably to an extent of 20 to 35 wt. %, based on the total mass of the emulsion.

[0034] In a preferred embodiment, the at least one emulsifier is an anionic or nonionic emulsifier.Hydrophobic waxes can be emulsified particularly easily with the aid of anionic or nonionic emulsifiers.

[0035] Anionic emulsifiers have an ammonia smell, which may be unpleasant to the user. This can be avoided when using nonionic emulsifiers, preferably surfactants. In addition, anionic emulsifiers have a relatively high pH value, which has an adverse effect in some applications. Therefore, for some applications, such as pH-sensitive products or cosmetics, nonionic emulsifiers are preferred.

[0036] The properties of nonionic emulsifiers can be described by the mass ratio between the polar and nonpolar parts of the surfactant and defined by the HLB value ("hydrophile-lipophile balance", the hydrophile-lipophile ratio of the molecule). As described by Griffin (see, for example, Journal of the Society of Cosmetic Chemists, 5(4), 249-256 (1954)), the level of this hydrophile-lipophile ratio can be determined by calculating the values ​​of different regions of the molecule. The Griffin method was developed primarily for nonionic surfactants; the HLB value is calculated by the following formula:

[0037] HLB=10*Mh / M

[0038] Where Mh is the molecular mass of the hydrophilic part of the molecule and M is the molecular mass of the entire molecule, this gives a value on a scale of 0 to 20.

[0039] An HLB value of 0 corresponds to a completely lipophilic molecule; an HLB value of 20 corresponds to a completely hydrophilic molecule.

[0040] Surfactants with low HLB values ​​have good oil solubilizing properties; high HLB values ​​lead to good wetting of hydrophilic surfaces. Based on different HLB values, it is possible to form stable emulsions in O / W to W / O systems.

[0041] Oil-in-water emulsifiers (O / W emulsifiers) are understood to mean emulsifiers whose HLB value is high enough to produce oil-in-water emulsions. Such emulsifiers generally have an HLB value greater than about 8 and generally in the range of 8 to 18.

[0042] The nonionic emulsifier for stabilizing the water-in-natural wax oxide emulsion of the present invention preferably has an HLB value between 11 and 19, since it is possible to stabilize the natural wax oxide emulsion particularly efficiently with such a nonionic emulsifier. The HLB value is more preferably between 13 and 18.

[0043] The nonionic emulsifier preferably has an EO value (the number of ethylene oxide units bonded to the functional group) of greater than 10-80.

[0044] Nonionic emulsifiers are preferably fatty alcohol polyglycol ethers, alcohol ethoxylates, such as fatty alcohol ethoxylates, and tributylphenol ethoxylate.

[0045] In an alternative embodiment, the emulsifier stabilizing the aqueous natural wax oxide emulsion is an anionic emulsifier system, since such a system surprisingly achieves very good results in terms of stabilization of the emulsion and formation, flexibility and stability of the barrier layer, and the barrier layer has very good water resistance and water vapor barrier effect. This means that these emulsifiers are particularly suitable for applications requiring high water resistance, for example in wood care products.

[0046] The anions of the anionic emulsifier systems can be obtained by adding water-soluble or water-dispersible alkali metal hydroxides and / or basic ammonium compounds to organic acids having a linear aliphatic hydrocarbon radical containing 12 to 24 carbon atoms. The anions are supplied as alkali metal salts, preferably sodium and / or potassium salts, or the corresponding ammonium salts or substituted ammonium salts of the corresponding organic acids.

[0047] The term "ammonium salt" refers to those neutralization products obtained by reaction of a surfactant acid in an aqueous medium with ammonia or an amine, such as a volatile base, for example morpholine, methylaminopropanol, diethylaminoethanol (DEAE), etc., or a non-volatile base, for example monoethanolamine, triethanolamine, isopropanolamine, α,ω- and α,γ-substituted diamines, such as ethylenediamine, propylene-1,2-diamine, propylene-1,3-diamine, butane-1,4-diamine, etc. Due to its basic properties, DEAE may form corresponding salts with organic acids.

[0048] The polar organic group of the salt or acid may be a carboxylate, sulfate or sulfonate ion, and the compound providing the anion may have more than one such polar group.

[0049] Examples of suitable organic acids providing anions are natural and synthetic aliphatic carboxylic acids having from 12 to 24 carbon atoms, for example myristic acid, palmitic acid, stearic acid, oleic acid and behenic acid, especially those of soaps as obtained by cleavage of triglyceride oils, for example tallow fatty acid, which is a mixture of fatty acids consisting mainly of palmitic acid, stearic acid and oleic acid.

[0050] The anion is preferably one in which an alkyl or alkenyl group having 16 to 24 carbon atoms is present.

[0051] Preferably, an oleic acid / ammonium hydroxide / KOH emulsifier system is used.

[0052] The amount of emulsifier used has an influence on the stability of the suspension and the distribution and size of the wax particles. It has been found that particularly thin and uniform barrier layers can be formed when the emulsifier is present in the emulsion to an extent of 1 to 20% by weight, preferably to an extent of 2 to 15% by weight, based on the total mass of the emulsion.

[0053] The present invention further provides a method for producing an aqueous natural wax oxide emulsion, comprising the following steps:

[0054] a) providing a natural wax oxide and an anionic or nonionic emulsifier,

[0055] b) emulsifying the natural wax oxide in water at a temperature above the melting point of the natural wax oxide with the aid of an emulsifier,

[0056] Characterized in that the natural wax oxide has an acid value / OH value ratio of not less than 1. The natural wax oxide can be produced by the above oxidation method.

[0057] The present invention further provides the use of the aqueous natural wax oxide emulsion according to the invention for coating a polysaccharide-containing or biopolymer-containing substrate, preferably a cellulose-containing substrate, with a water vapor barrier. Also suitable are water vapor barriers for water-permeable polymer substrates, for example biopolymer substrates, in particular substrates composed of polylactide (PLA).

[0058] The present invention therefore further provides a polysaccharide-containing or biopolymer-containing substrate comprising a water vapour barrier layer made from the aqueous natural wax oxide emulsion according to the invention.

[0059] The polysaccharide-containing or biopolymer-containing substrate is preferably a cellulose-containing substrate, more preferably paper or paperboard.

[0060] These coated polysaccharide- or biopolymer-containing substrates can be used in any kind of packaging or casing, such as tobacco products, outer packaging of tobacco products, paper cups, packaging of frozen products, outer packaging of bread, sausages and cheese, and plants, as well as cardboard boxes, outer packaging of electronic products, etc.

[0061] The present invention further provides a method for producing a polysaccharide-containing or biopolymer-containing substrate, comprising the steps of:

[0062] a) applying the aqueous natural wax oxide emulsion of the present invention to the surface of a polysaccharide-containing or biopolymer-containing substrate;

[0063] b) drying the coated substrate to form a barrier layer. DETAILED DESCRIPTION

[0064] Experimental part:

[0065] Table 1: Methods for determining reported parameters

[0066]

[0067]

[0068] Preparation of corn wax oxides 1 to 3:

[0069] Since the corn wax oxide is not a commercially available product, the experimental description for preparing the corn wax oxide is described in detail below:

[0070] A 3-liter reaction vessel equipped with a stirrer, a temperature sensor, a dropping funnel and a reflux condenser is initially charged with the amount of chromium trioxide / sulfuric acid (concentration: 100 g CrO3 / l) specified in Table 4 and heated to 100°C. Then the molten (90°C) natural wax in the crude state is added portionwise. The temperature of the reaction mixture is adjusted to 110°C and the reaction mixture is stirred for 4 hours at about 200 rpm with a precision glass (KPG) stirrer. Heating and stirring are stopped. Once the phases have separated, the aqueous phase is separated. This operation is carried out twice to prepare corn wax oxides 1 and 2, and five times to prepare corn wax oxide 3, using the amounts specified in Table 3.

[0071] Table 3: Data on the amount of corn wax oxide used to prepare the

[0072]

[0073] The organic phase was freed from chromium residues by washing with an aqueous solution of oxalic acid and sulfuric acid and subsequently with water, discharged into a warmed centrifuge glass tube and centrifuged.

[0074] Table 4: Emulsifiers used to prepare emulsions

[0075]

[0076] A) Preparation of various water-based wax emulsions

[0077] A1) Preparation of formulations F1, F2, F9, F10 of Table 5 and formulations F12, F13, F14, F15 of Table 6:

[0078] The respective wax and the respective emulsifier were completely melted at 125° C. and stirred to obtain a homogeneous mass. Boiling distilled water was stirred into the hot wax melt at 125° C. The resulting emulsion was cooled while stirring vigorously (approximately 3 K / min).

[0079] A2) Preparation of formulation F4 of Table 5:

[0080] The wax was completely melted at 125°C and DEAE was slowly added dropwise. The melt was stirred for 2 minutes. Boiling water was stirred into the hot wax melt at 125°C. The resulting emulsion was cooled while stirring vigorously (approximately 3K / min).

[0081] A3) Preparation of formulations F3, F5 and F6 of Table 5 and formulations F16 and F17 of Table 6:

[0082] Wax, oleic acid, ammonia solution and KOH were admixed with the required amount of 50% distilled water in a pressure reactor. The admixture was heated to 135° C. in a pressure reactor and the remaining amount of water was added to the mixture at approximately 125° C. The mixture was stirred at 135° C. for 15 minutes. The emulsion was then cooled to 30° C. (approximately 3 K / min) while stirring.

[0083] A4) Preparation of Formulation F7:

[0084] The wax and emulsifier E 5 were completely melted at 125°C and stirred to obtain a homogeneous mass. The KOH / ethylene glycol mixture was added dropwise while stirring and mixed for another 2 minutes. The hot wax mixture was then stirred into boiling distilled water. The resulting emulsion was cooled while stirring vigorously (approximately 3K / min).

[0085] Table 5: Formulations used based on rice bran wax oxide

[0086]

[0087] Table 6: Formulations used based on corn wax oxide

[0088]

[0089] The inventive formulations F1-F6 and F12-F17 listed in Tables 5 and 6 all form stable emulsions. This is not the case with comparative example F10, where a stable emulsion is no longer formed at a wax content of 20%. Although comparative example F9 with 10% wax forms a stable emulsion, the lower wax content is detrimental to coating quality and drying time.

[0090] B) Preparation of coated paper substrate with wax emulsion.

[0091] The wax emulsion detailed in Table 7 was applied with a 50 μm doctor blade, a test area of ​​12.5 cm×12.5 cm was cut out and stored for 24 hours at a constant temperature of 23° C. and 30% relative air humidity. The sample was tared (Tara 1) and clamped in an aluminum Cobb cup.

[0092] Then 100 ml of distilled water was applied to the sample for 60 seconds and removed. The residual water was removed with absorbent paper and an absorbent roller, and the weight was measured again (Tara 2). The Cobb value was calculated by the following formula:

[0093] Cobb value 60s =(Tara2-Tara1)×115.48658

[0094] These values ​​were determined in triplicate and the median values ​​measured are listed in Table 7.

[0095] Table 7: Cobb Properties of Coated Paper Substrates 60 value

[0096]

[0097] All of the inventive examples F1-F6 and F12-F17 show significantly reduced water absorption compared to the uncoated paper and the comparative examples F7 and F9, which is reflected in the lower Cobb 60 value.

[0098] C) Preparation of coated carrier films for determining the barrier effect of wax coatings by means of water vapor transmission rate

[0099] The wax or wax oxide emulsion or dispersion is applied as a thin film onto glass paper (Cellophan). For this purpose, a semi-automatic coating system of the company Sumet Messtechnik, model CUF 5, is used to process the substrate with the largest surface area in the curved shape in the DIN A3 format (420×297 mm). The wet coating amount is 50 μm. The coating speed is 30 mm / s. The drying temperature is between 70° C. and 90° C., and the drying time is 1-5 minutes.

[0100] To eliminate the effect of the substrate, all barrier layers were applied to glassine paper with known water vapor permeability. The water vapor transmission rate Q of the cellophane film was 1084 g / (m 2 *d).

[0101] The water vapor barrier is determined as the water vapor transmission rate Q according to DIN 53122-1 at 23°C and a humidity gradient of 85% relative air humidity on one side of the barrier layer and 0% relative air humidity on the other side of the barrier layer. The measured Q value (unit: g / (m2*d)) describes how many grams of water will penetrate an area of ​​one square meter in one day. However, this value depends critically on the thickness of the wax layer. The thicker the wax layer, the lower the measured value. Therefore, in order to make various materials of different thicknesses comparable, the value normalized to a layer thickness of 100 μm is reported (Q100 [g*100 μm / (m2*d)]). This is determined by the following formula:

[0102]

[0103] In this way, it is possible to calculate the measured water vapor transmission rates of the individual barrier layers listed in the table as follows

[0104]

[0105] To determine the water vapor permeability Q100 normalized for the layer thickness, the layer thickness of the barrier layer was determined microscopically by means of microtome sections of the coated substrate.

[0106]

[0107] The benchmark used was the water vapor transmission rate of Lupolen with a Q100 value of 1.

[0108] In addition, the water vapor permeability of a thin coarse RBW layer not applied to a glassine substrate was determined.

[0109] The measurements reported in Table 8 are the average of 4 measurements performed.

[0110] Table 8: Water vapor transmission rates of uncoated and coated film substrates (carrier films)

[0111]

[0112] All of the inventive examples exhibit significantly reduced water vapor permeability compared to the uncoated cellophane film, which is reflected in lower Q100 values. The Q100 values ​​of the inventive examples are in a comparable range to the Q100 values ​​of the Lupolen 100 reference film, which represents a commonly used polyethylene-based barrier material.

[0113] Although crude rice bran wax exhibits good barrier properties, it is not emulsifiable. Application from the melt requires a higher energy input and is associated with higher layer thicknesses compared to aqueous emulsions, which has a negative effect on material consumption. Higher layer thicknesses also have a negative effect on the adhesion and flexibility of the barrier layer.

Claims

1. An aqueous natural wax oxide emulsion for producing a water and / or water vapor barrier layer on a polysaccharide-containing or biopolymer-containing substrate, the emulsion comprising (a) at least one natural wax oxide having an acid number / OH number ratio of not less than 1; and (b) at least one anionic or nonionic emulsifier; The natural wax oxide is selected from rice bran wax oxide, corn wax oxide, sugar cane wax oxide, sunflower wax oxide and carnauba wax oxide.

2. The aqueous natural wax oxide emulsion as claimed in claim 1, characterized in that The natural wax oxide is produced by an oxidation process selected from chromic acid oxidation, chromium sulfate oxidation, dichromate oxidation, thermal oxidation using atmospheric oxygen, and electrochemical oxidation.

3. The aqueous natural wax oxide emulsion according to claim 1 or 2, characterized in that The natural wax oxide is selected from rice bran wax oxide and corn wax oxide.

4. The aqueous natural wax oxide emulsion as claimed in claim 1 or 2, characterized in that The natural wax oxides have an acid number, measured according to ISO 2114, between 1 and 140 mg KOH / g.

5. The aqueous natural wax oxide emulsion as claimed in claim 4, characterized in that The natural wax oxides have an acid number, measured according to ISO 2114, between 15 and 140 mg KOH / g.

6. The aqueous natural wax oxide emulsion as claimed in claim 4, characterized in that The natural wax oxides have an acid number, measured according to ISO 2114, between 30 and 140 mg KOH / g.

7. The aqueous natural wax oxide emulsion as claimed in claim 1 or 2, characterized in that The natural wax oxide has a hydroxyl number measured according to DGF M-IV 6 of less than 8 mg KOH / g.

8. The aqueous natural wax oxide emulsion as claimed in claim 7, characterized in that The natural wax oxides have a hydroxyl number measured according to DGF M-IV 6 of less than 5 mg KOH / g.

9. The aqueous natural wax oxide emulsion as claimed in claim 1 or 2, characterized in that The natural wax oxides have an iodine color value of less than 20 measured according to DIN 6162.

10. The aqueous natural wax oxide emulsion as claimed in claim 9, characterized in that The natural wax oxides have an iodine color value of less than 15 measured according to DIN 6162.

11. The aqueous natural wax oxide emulsion as claimed in claim 9, characterized in that The natural wax oxides have an iodine color value of less than 10 measured according to DIN 6162.

12. The aqueous natural wax oxide emulsion according to claim 1 or 2, characterized in that The natural wax oxides have a dropping point measured according to ISO 2176 between 65 and 110°C.

13. The aqueous natural wax oxide emulsion according to claim 1 or 2, characterized in that The natural wax oxide is present in the emulsion to an extent of 5 to 50% by weight, based on the total mass of the emulsion.

14. The aqueous natural wax oxide emulsion as claimed in claim 13, characterized in that The natural wax oxide is present in the emulsion to an extent of 10% to 45% by weight, based on the total mass of the emulsion.

15. The aqueous natural wax oxide emulsion as claimed in claim 13, characterized in that The natural wax oxide is present in the emulsion to an extent of 15% to 40% by weight, based on the total mass of the emulsion.

16. The aqueous natural wax oxide emulsion as claimed in claim 13, characterized in that The natural wax oxide is present in the emulsion to an extent of 20% to 35% by weight, based on the total mass of the emulsion.

17. The aqueous natural wax oxide emulsion according to claim 1 or 2, characterized in that The nonionic emulsifier has an HLB value between 11 and 19.

18. The aqueous natural wax oxide emulsion as claimed in claim 17, characterized in that The nonionic emulsifier has an HLB value between 13 and 18.

19. The aqueous natural wax oxide emulsion according to claim 1 or 2, characterized in that The at least one nonionic emulsifier is selected from fatty alcohol polyglycol ethers, alcohol ethoxylates and tributylphenol ethoxylate.

20. The aqueous natural wax oxide emulsion according to claim 1 or 2, characterized in that The emulsifier is an anionic emulsifier system.

21. The aqueous natural wax oxide emulsion as claimed in claim 20, characterized in that The emulsifier is an oleic acid / ammonium hydroxide / KOH and / or diethylaminoethanol emulsifier system.

22. The aqueous natural wax oxide emulsion according to claim 1 or 2, characterized in that The emulsifier is present in the emulsion in an amount of 1 to 20% by weight, based on the total mass of the emulsion.

23. The aqueous natural wax oxide emulsion as claimed in claim 22, characterized in that The emulsifier is present in the emulsion in an amount of 2 to 15% by weight, based on the total mass of the emulsion.

24. A method for producing an aqueous natural wax oxide emulsion as described in any one of claims 1 to 23, comprising the following steps a) Provide natural wax oxides and anionic or nonionic emulsifiers, b) emulsifying the natural wax oxide in water at a temperature above the melting point of the natural wax oxide with the aid of an emulsifier, It is characterized in that The natural wax oxide has an acid value / OH value ratio of not less than 1.

25. A method for producing an aqueous natural wax oxide emulsion as claimed in claim 24, characterized in that The natural wax oxide is produced by an oxidation method selected from chromic acid oxidation, chromium sulfate oxidation, dichromate oxidation, oxidation using atmospheric oxygen and electrochemical oxidation.

26. Use of an aqueous natural wax oxide emulsion as claimed in any one of claims 1 to 23 for coating polysaccharide-containing substrates with a water and / or water vapour barrier.

27. The use as claimed in claim 26, characterized in that The polysaccharide-containing substrate is a cellulose-containing substrate.

28. A polysaccharide-containing or biopolymer-containing substrate comprising a water and / or water vapor barrier formed from an aqueous natural wax oxide emulsion as claimed in any one of claims 1 to 23.

29. The polysaccharide- or biopolymer-containing substrate as claimed in claim 28, characterized in that The polysaccharide-containing or biopolymer-containing substrate is a cellulose-containing substrate.

30. The polysaccharide- or biopolymer-containing substrate as claimed in claim 29, characterized in that The cellulose-containing substrate is paper or paperboard.

31. A method for producing a polysaccharide-containing or biopolymer-containing substrate as claimed in any one of claims 28 to 30, comprising the following steps: a) applying an aqueous natural wax oxide emulsion as described in any one of claims 1 to 23 to the surface of a polysaccharide-containing or biopolymer-containing substrate; b) drying the coated substrate to form a barrier layer.

Images