Packaging material having a water-based barrier layer

Abstract

To provide a method of producing a packaging material having a functional layer on a substrate using a casting process to coat the substrate.SOLUTION: A manufacture of a packaging material having at least one functional layer in which a water-based multilayer curtain is formed, the curtain to a substrate is applied, the outer layer of the curtain which comes into contact with air during casting includes surface activation additive, and the difference in a surface tension between the two outer layers of the curtain and the adjacent one or plurality of inner layers is at least 5 mN / m is described.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing packaging materials with functional layers on a substrate by using a casting process to coat the substrate. [Background technology]

[0002] In the field of web-type packaging, paper-based products are used for many applications. In many cases, and when the barrier properties of the packaging are low, they are used without further modification. Functional coatings are used to impart barrier properties against oxygen, water vapor, oils and fats, and other substances to packaging paper. The food industry, particularly for sensitive products, has very high requirements, which have until now usually been met by plastic or composite materials, such as aluminum or plastic films. Social developments over the past few years have led to a further shift in thinking in the field of packaging. Market and customer demands for packaging production are to use ecological materials based on paper and renewable resources whenever possible. In addition, legal requirements and societal demands to avoid or reduce hazardous substances further reduce the limit values ​​for substances hazardous to health to the lowest possible values. The challenge for food packaging manufacturers is then to meet high barrier properties and ecological requirements in an economically acceptable manner.

[0003] It is known to apply water-based functional materials, such as polymer dispersions, to fiber-based substrates such as paper. Depending on the application method, functional additives are necessary to achieve the subsequent quality requirements for the packaging material. A commonly used application method is curtain coating. In this case, surface-active or interfacially active substances are required to ensure a stable production process. These substances are used to reduce the surface tension of the layer in contact with air, thereby enabling a stable curtain and therefore a more stable application of the curtain to the substrate. Many of these substances can migrate through the barrier layer of the packaging material over time and come into contact with the packaged food.

[0004] When applying curtain coating, the first priority is the stability of the resulting curtain, which may consist of one or more material streams. Furthermore, manufacturers must economically minimize the amount of material applied, thereby casting the thinnest possible layer. Furthermore, factors such as the variety of products, production speed, and the viscosity and type of materials used also play a key role. This also requires high flexibility and adaptability when formulating formulations for curtain coating.

[0005] The simultaneous application of multiple layers by curtain coating is described, for example, in EP 1 416 087. Along with the individual layers, the aforementioned oxygen and water vapor barrier and sealing layers are also applied to the substrate. Table 1 lists the formulations and application weights for applying a curtain consisting of five individual layers by curtain coating. The two outer plies / layers of the curtain have a higher application weight and a similar amount of surfactant than the inner layers. All layers contain surfactant. Accordingly, in the case of the product described in this document, the amount of surfactant additive used throughout the product is very high to ensure sufficient quality during manufacturing.

[0006] EP 1 666 637 A1 largely dispenses with the use of surface-active additives by using solvents, which are, however, undesirable for ecological and occupational health reasons.

[0007] EP 1395705 describes a wrapping paper with barrier properties. Different layers are applied in various combinations by curtain coating. Again, emphasis is placed on functional curtain coating, which is ensured by using surface-active additives in all layers. Thus, again, process stability is achieved by using a large amount of surface-active additives.

[0008] EP 1 255 615 describes the curtain coating of substrates for producing packaging materials, where the use of surface-active substances for the curtain coating exceeds the required limit. Summary of the Invention

[0009] The present invention is based on the problem of providing a stable coating method for producing packaging materials using the principle of curtain coating, which results in packaging materials that better meet legal requirements regarding the content of harmful substances than known packaging materials produced by curtain coating. A stable coating method means that the coating of substrates by a casting process can be carried out on an industrial scale without jeopardizing the material flow barrier of the curtain.

[0010] According to the present invention, the above problem is solved by applying a functional layer to a substrate using a casting process, which includes forming an aqueous multi-layer curtain and applying the curtain to a substrate, wherein the outer layer of the curtain that comes into contact with air during casting contains a surface-active additive, and the difference in surface tension between the outer layer of the curtain and the adjacent inner layer(s) is at least 5 mN / m.

[0011] The subject of the invention is also a packaging material having a substrate and at least three layers of a coating arranged thereon and applied to the substrate by curtain coating, the coating comprising at least one functional layer, the layer of the coating in contact with the substrate and the layer of the coating in contact with air comprising a surface-active additive, and the difference in surface tension between the two outer layers of the coating and the inner layer adjacent to these outer layers is at least 5 mN / m.

[0012] The difference in surface tension of the layers is achieved by a higher concentration of surface-active additives in the coating for the outer layer of the curtain compared to the concentration in the inner layer(s) of the curtain, which may in particular be free of surface-active additives.

[0013] The procedure according to the present invention allows the amount of surface-active additive introduced into the two outer material streams of the curtain that are in contact with air to be limited to a range of 0.02% to 0.6% by weight, based on the weight of the composition of the two outer layers. Thus, the amount of surface-active additive in the resulting unprinted packaging material is limited to a range of 0.02% to 0.6% by weight. This significantly limits the total amount of surface-active additive relative to the weight of the curtain compared to the prior art. Surprisingly, this procedure nevertheless provides high stability of the curtain during casting coating. Therefore, the packaging material obtained according to the present invention has a much lower concentration of undesirable surface-active additives than packaging materials, particularly for food products, produced by known methods.

[0014] definition The two sides of the packaging material described herein are distinguished. The side on which the functional layer or layers are applied is called the "top side" of the packaging material. During subsequent use, this side will come into contact with the product to be packaged, e.g., food.

[0015] The surface opposite the top surface is the "bottom" surface of the packaging material. The bottom surface will later form the outer surface of the packaging in use and may optionally be printed on.

[0016] The coated material, which moves in free fall toward a substrate or substrate web as a composite of multiple layers, is called a curtain. Immediately after leaving the nozzle of the flow coater, the individual layers are combined and then flow toward the substrate as a curtain. This curtain has two surfaces that are in contact with the ambient air. In this case, the surface that is in direct contact with the substrate after being coated thereon is called the inner surface of the curtain. Correspondingly, the outer surface of the curtain is the surface located opposite, which will later come into contact with the packaged product.

[0017] A functional layer in the sense of the present invention is a layer on a substrate that improves the usability of the packaging material obtained according to the present invention for a particular packaged item or creates a desired functionality of the packaging material, for example, a functional layer can provide barrier properties against any substance. DETAILED DESCRIPTION OF THE INVENTION

[0018] The packaging material according to the invention or obtainable by the curtain coating method according to the invention can have one or more functional layers on the substrate and further layers such as a printed ink-receptive layer, a binder layer or a release layer (separation layer).

[0019] The functional layer and additional layers can be applied to the substrate in the form of a composite curtain. During coating, only the two outer layers of the curtain are in contact with the air. A free-flowing, aqueous, multi-layer curtain contains at least three individual material streams. Thus, in this case, the curtain is a composite, consisting of two outer material streams in contact with the air and at least one material stream located between the outer material streams. The number of material streams (layers) in the curtain between the two outer material streams in contact with the air can be from 1 to 7 or more, especially from 1 to 5. It is particularly preferred that the curtain, together with the outer material streams, contain a total of four or five material streams. Therefore, the curtain can have multiple functional layers with different properties or different functions for the packaging material. Furthermore, the curtain can contain two material streams with the same functionality for the packaging material. The material streams are miscible with water.

[0020] On top of the coating applied by the casting process, further layers can be applied by other coating methods. Other coating methods are known coating techniques for web-like substrates, such as melt extrusion, blade coating, roll coating, etc. By such techniques, for example, ink-receptive layers, binder layers, or separation layers can be applied.

[0021] In particular, a curtain with a wet coating layer is applied to the substrate using a so-called curtain coater.

[0022] Surfactants in the sense of the present invention are those that are commonly used when surface activity or surface-active effects are desired or when the material flow for curtain coating must be stabilized. Surface-active additives (surfactants) can be anionic, cationic, or amphoteric surfactants and reduce the surface tension of the aqueous system or water. It is particularly preferred that the two outer layers of the curtain, which come into contact with the air during casting, contain only 0.02 to 0.4% by weight of surface-active additives. The middle layer contains less surfactant than the outer layers. In particular, the middle layer of the curtain does not contain any surface-active additives.

[0023] The wet coating weight of the outer layer is 0.5 g / m 2 ~15g / m 2 , especially 1.0 g / m 2 ~6.0g / m 2 It could be.

[0024] The total coating weight of the layers applied to the substrate by curtain coating is 3 g / m 2 ~50g / m 2 (dry), especially 4g / m 2 ~30g / m 2 The coating weight of each individual layer of the total coating can be 0.3 g / m 2 ~20g / m 2 or more (dry), especially 0.5g / m 2 ~10g / m 2 or 15 g / m 2 The layer thickness or dry coating weight on the substrate of the individual material streams in the curtain may be the same or different. In particular, the coating weight of the outer layer of the curtain is less than the coating weight of the inner layer, and may be less than 0.3 g / m. 2 ~5g / m 2 ), especially 0.3 g / m 2 ~3g / m 2 This allows the surfactant content in the packaging material to be further reduced.

[0025] The static viscosity of the material flow in the curtain, measured at 25°C with a Brookfield RVT rotational viscometer at a spindle speed of 20-100 rpm, may be at most 3 Pa·s, in particular 50-500 mPa·s. The surface tension of the two outer layers may be at least 5 mN / m less than the surface tension of the inner layer of the curtain adjacent to each of them.

[0026] The solids content of the layer of the curtain can be 5 to 50% by weight, in particular 10 to 30% by weight, based on the mass of the layer.

[0027] The functional layers applied to the paper according to the invention are, for example, layers with a barrier effect against water vapor, air, fats, oils and gases, or heat-sealing layers. Each of the functional layers (substance streams) applied according to the invention, except for the heat-sealing layer, can be an outer or inner layer in the curtain. However, a second heat-sealing layer can also be arranged inside the curtain.

[0028] The functional layer having water vapor barrier properties may substantially comprise a hydrophobic polymer or a mixture of hydrophobic polymers, or may consist of a hydrophobic polymer or a mixture of hydrophobic polymers. Such polymers may be polyolefins. Preferred polyolefins are polyethylene (PE), polypropylene (PP), or a mixture of polyethylene and polypropylene. In particular, the barrier layer against water vapor may be such that the water vapor transmission rate of the packaging material is 50% or more at 1 atm (23°C, 50% RH) per 24 hours. g / m 2 The following restrictions apply: The curtain may also be provided with two or more layers having water vapor barrier properties for application to the substrate.

[0029] Another functional layer can have fat and / or oil barrier properties. Such layers can be made of polar polymers, in particular. Suitable polar polymers for this purpose are, for example, polyvinyl alcohol (PVOH) and ethylene vinyl alcohol (EVOH). The so-called KIT value of the fat-tight packaging material obtained according to the present invention is at least KIT5 (DIN 53116), in particular greater than KIT8.

[0030] Insofar as the packaging material obtained according to the present invention requires moisture barrier properties, a corresponding barrier layer can be applied to the substrate. The moisture barrier properties can be achieved by applying a layer containing polypropylene or polyamide. For this purpose, it is particularly preferred to use polypropylene.

[0031] Furthermore, a gas barrier layer can be applied to the substrate. For this purpose, conventional polymers known for this purpose can be used. In particular, the gas barrier layer of the packaging material according to the present invention is formed from at least one thermoplastic polymer. The thermoplastic polymer can be selected from ethylene-vinyl alcohol copolymer (EVOH), at least partially saponified polyvinyl acetate, polyvinylidene chloride (PVDC), in particular vinylidene chloride copolymers having a vinylidene chloride content of at least 80% by weight, based on the total weight of the vinylidene chloride copolymer, or a mixture of at least two of the aforementioned polymers. In a particularly preferred embodiment, an ethylene-nonyl alcohol copolymer is included.

[0032] The ethylene / vinyl alcohol copolymers (EVOH) used to prepare the layers are obtained by complete or incomplete hydrolysis of the corresponding ethylene / vinyl acetate copolymers (EVAc). In particular, fully saponified ethylene / vinyl acetate copolymers are used, with a degree of saponification of 98% or more and an ethylene content of 0.01 to 80 mol %, in particular 1 to 50 mol %, based on the total weight of the ethylene / vinyl alcohol copolymer.

[0033] The at least partially saponified polyvinyl acetate for producing the gas barrier layer is obtained by complete or incomplete hydrolysis of the corresponding polyvinyl acetate. Particularly suitable at least partially saponified polyvinyl acetates for producing the layer are fully saponified polyvinyl acetate (polyvinyl alcohol, PVOH) with a saponification degree of 98% or more and partially saponified polyvinyl acetate with a saponification degree of 75% to 98%.

[0034] The gas barrier layer, in particular if the gas barrier layer is based at least in part on an ethylene vinyl alcohol copolymer, can in each case be combined with a polyamide layer as a further layer, in particular for protection against moisture.

[0035] In particular, the barrier layer of the packaging material produced according to the invention has a layer thickness of 1 μm to 30 μm, particularly preferably 1 μm to 20 μm, most particularly preferably 1 μm to 10 μm, in particular 1.5 to 7 μm. Insofar as the layer contributes to optimizing the mechanical properties of the packaging material according to the invention, the layer has a layer density of 5 μm to 500 μm, particularly preferably 20 μm to 150 μm when used as a tube bag or lid material, or 100 μm to 500 μm when used for containers such as pots. The barrier layer of the packaging material according to the invention can comprise a biopolymer, as described for the preparation of the heat-seal layer. Transparent mixtures of the biopolymer with another polymer or polyamide used to prepare the heat-seal layer can be used.

[0036] It is particularly preferred that an oxygen barrier layer and a water vapor barrier layer are provided on the substrate as barrier layers, each of which may be an outer layer in contact with the air in the curtain or an inner layer disposed between two outer layers.

[0037] In a preferred embodiment, one of the functional layers may be a multi-layer heat-seal layer, optionally consisting of a thermoplastic polymer, which is oriented toward the inside of the resulting packaging material. Thermoplastic polymers particularly suitable for the heat-seal layer include olefin homopolymers and olefin copolymers, homopolyesters and copolyesters, transparent mixtures of at least two of the aforementioned polymers, and mixtures of at least two of the aforementioned, but with limited compatibility. Furthermore, the heat-seal layer may in particular comprise up to 100% by weight of a biopolymer as a polymer component. The polymer may also be a copolymer of at least one olefin and at least one α-β-unsaturated non-olefinic monomer having a carboxy group, a salt or ester thereof, such as an ethylene / vinyl acetate copolymer, or a copolymer of ethylene and an ester of acrylic acid or methacrylic acid, a copolymer of ethylene and acrylic acid or methacrylic acid, and / or a salt thereof, preferably a sodium or zinc salt. Mixtures of at least two of the aforementioned polymers, or mixtures of at least two of the aforementioned, but with limited compatibility, polymers may also be used.

[0038] Each layer of the multilayer packaging material according to the present invention, particularly the heat-sealable layer, may be provided with at least one common additive, if necessary, selected from anti-sticking agents, lubricants, anti-static agents, dyes, inorganic fillers, antioxidants, UV stabilizers, UV absorbers, or oxygen scavengers, insofar as these do not belong to the above-mentioned surface-active substances (surfactants).

[0039] At least one of the functional layers can include a pigment, which can be kaolin, calcined clay, talc, calcium carbonate, layered nanoparticles, high aspect ratio clay, titanium dioxide, satin white, synthetic polymer pigments, zinc oxide, barium sulfate, gypsum, synthetic magadiite, silicon dioxide, aluminum oxide trihydrate, mica, and diatomaceous earth.

[0040] The packaging material according to the present invention can be packaging for any food product, whether solid, semi-solid or liquid, such as cheese, sausage, ham, meat, poultry or poultry parts, bakery products, baking ingredients, snack foods such as chips or peanut flips, confectionery such as nuts, seeds, chocolate, candy or chewing gum, fish, seafood, solid or liquid prepared foods such as pate, spreads such as butter or margarine, mayonnaise, mustard, ketchup, or spices or spice mixes.

[0041] A layer composite in the form of a curtain to be applied according to the invention to a substrate to obtain a packaging material according to the invention can be constructed, for example, as follows: / PE-DISP plus / PE-DISP / EVOH / PVAc / PVAc plus / / PE-DISP plus / PE-DISP / EVOH / EVOH plus / / PE-DISP plus / PE-DISP / PVAc / EVOH plus / / PE-DISP plus / PE-DISP / PE-DISP plus / / PVAc plus / PVAC / PVAc plus / / EVOH plus / EVOH / EVOH plus / 、 where EVOH is an oxygen barrier without surface active additives, PE-DISP is a water vapor barrier without surface-active additives. PVAC is a sealing layer without surface-active additives, PVAc plus is a sealing layer containing 0.02% to 0.4% by weight of a surface-active additive based on the mass of the layer; PE-DISP plus is a water vapor barrier containing 0.02% to 0.4% by weight of a surface-active additive relative to the mass of the layer; EVOH plus is an oxygen barrier containing 0.02% to 0.4% by weight of surface active additives relative to the mass of the layer.

[0042] These can be applied wet to the substrate in one operation as a curtain. Paper, cardboard, or plastic film can be used as the substrate or support for one or more functional layers and / or one or more additional layers. Preferably, cellulose-based paper, especially web-like paper, is used as the support material.

[0043] Paper within the meaning of the present invention is base paper or coated base paper. In this specification, the term base paper is understood to mean uncoated or surface-sized paper. In addition to cellulose fibers, base paper may contain sizing agents such as alkylketene dimers, fatty acids and / or fatty acid salts, epoxidized fatty acid amides, alkenyl succinic anhydrides or alkyl succinic anhydrides, wet strength additives such as polyamine-polyamide epichlorohydrins, dry strength additives such as anionic, cationic, or amphoteric polyamides or cationic starch, optical brighteners, fillers, pigments, dyes, defoamers, and other auxiliaries known in the papermaking industry. Base paper may be surface-sized. Suitable sizing agents for this purpose are, for example, polyvinyl alcohol or oxidized starch. Base paper may be produced on a Fourdrinier or Yankee (cylinder) paper machine. The basis weight of the base paper is, in particular, between 20 and 350 g / m². 2 The base paper can be used in uncompressed or compressed form (smoothed). 0.8-1.2 g / cm 3 , especially 0.90 to 1.1 g / cm 3 Base papers with a density of 1000 .mu.m are particularly well suited.

[0044] Examples of cellulose fibers that can be used include bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), bleached hardwood sulfite pulp (LBSP), and bleached softwood sulfite pulp (NBSP). Cellulose fibers obtained from wastepaper can also be used. The above-mentioned cellulose fibers can also be used as a mixture and, in some cases, can contain other fiber components, such as synthetic resin fibers. However, cellulose fibers made from 100% hardwood pulp are preferred. The medium fiber length of unbeaten cellulose is, in particular, 0.6 mm to 0.85 mm (Kajaani measurement). Furthermore, the cellulose has a lignin content of less than 0.05 wt. %, especially 0.01 to 0.03 wt. %, based on the mass of the cellulose. Fillers that can be used for the base paper include natural forms of calcium carbonate, such as kaolin, limestone, marble, or dolomite; precipitated calcium carbonate; calcium sulfate; barium sulfate; titanium dioxide; talcum; silica; aluminum oxide; and mixtures thereof. In yet another preferred embodiment, the paper layer may consist of a coated base paper. In the case of coated base paper, at least one pigment-containing layer is disposed on at least one side of the base paper. Metal oxides, silicates, carbonates, sulfides, or sulfates may be used as pigments. Pigments such as kaolin, talcum, calcium carbonate, and / or barium sulfate are particularly well suited. In another embodiment of the present invention, the pigment-containing layer may be a pigment mixture consisting of calcium carbonate and kaolin, as described above. The calcium carbonate / kaolin ratio is preferably 30:70 to 70:30. The binder / pigment ratio in the pigment-containing layer may be 0.1 to 2.5, preferably 0.2 to 1.5, but more preferably about 0.9 to 1.3. Any known water-soluble and / or water-dispersible binder may be used in the pigment-containing layer. For this purpose, in addition to latex binders, thermally modified starches, especially corn starch, or film-forming starches such as hydroxypropylated starch, are particularly suitable. The pigment-containing layer can be applied in-line or off-line using any coating machine common in papermaking, the coating amount being in particular such that after drying the coating weight is between 0.1 and 30 g / m 2 , especially 1 to 20 g / m 2or in a particularly preferred embodiment, 2 to 8 g / m 2 In a preferred embodiment, the pigment-containing layer is applied using a size press or film press integrated into the paper machine. The paper layer is based on substantially recycled raw materials such as cellulose and cellulose derivatives. The paper, and therefore the substrate, has a density of 20 g / m 2 ~350g / m 2 The sheet may have a basis weight of

[0045] The multi-layer packaging material according to the invention preferably has a total layer thickness of 40 μm to 1,000 μm, particularly preferably 40 μm to 150 μm. Three to ten layers can be arranged on the substrate of the packaging material. In particular, three to six functional layers and / or other layers as mentioned above can be arranged on the substrate. Particularly preferably, the packaging material according to the invention can have four, five, or six layers.

[0046] The present invention is further illustrated by the following examples.

[0047] Base paper manufacturing Base paper was produced from eucalyptus cellulose. For beating, the cellulose was prepared as an approximately 5% by weight aqueous suspension (thick stock) using a refiner to a beating degree of 36°SR. The medium fiber length was 0.64 mm. The concentration of cellulose fibers in the diluted stock was 1% by weight based on the mass of the cellulose suspension. Additives such as 0.4% by weight cationic starch, 0.48% by weight alkyl ketene dimer (AKD) as a neutral sizing agent, 0.36% by weight polyamine-polyamide epichlorohydrin resin (Kymene®) as a wet strength agent, and 10% by weight natural CaCO3 were added to the diluted stock. The amounts are based on the mass of cellulose. The diluted stock, with its pH adjusted to approximately 7.5, was conveyed from the headbox to the sieve of the paper machine, where paper formation took place under web dewatering in the sieve section of the paper machine. In the press section, the paper web was further dewatered until the moisture content was 60% by weight of the web. Further drying was carried out in the drying section of the paper machine using heated drying cylinders. The basis weight was 160 g / m2 This resulted in a base paper with a moisture content of approximately 7%.

[0048] Both sides of this base paper were coated with a coating material consisting of a styrene acrylate binder, starch, and a pigment mixture consisting of calcium carbonate and kaolin, each at 15 g / m 2 The coated base paper is then coated with a coating weight of 1000g, dried and subsequently smoothed using a calender. The material thus obtained is hereinafter referred to as coated base paper and is used for subsequent coating by a curtain coater.

[0049] The composition was applied to one side of the coated base paper using a curtain coater. The components and formulation of this composition are described below. In this case, the speed of the paper web to be coated was 120 m / min. The applicator for curtain coating was equipped with an edge guide coated with water droplets and a vacuum suction device to remove the edge lubricant water at the lower end of the edge guide just above the coated paper edge. The curtain height was 125 mm and the curtain width was 260 mm. The coated web was dried using a floating hot air dryer.

[0050] The following formulations were prepared in a correspondingly equipped mixing vessel and have the properties set out in Table 1. Curtains were formed in the described examples according to the compositions listed in Table 2. The weight of the total packaging material and also the application amounts for the individual layers of the curtain are also given in Table 2. This table further includes parameters related to the quality of the packaging material produced.

[0051] Formulation 1 66.7 g of polyolefin dispersion is introduced and mixed with 33.3 g of water while stirring, followed by the addition of 0.5 g of a wetting agent of the sodium dioctyl sulfosuccinate type while continuing to stir.

[0052] Formulation 2 66.7 g of the polyolefin dispersion is added, and 33.3 g of water is mixed therein while stirring.

[0053] Formulation 3 63.5 g of water was added, and 17.5 g of polyvinyl alcohol was added with vigorous stirring. The mixture was heated to 95°C using a steam lance and maintained at this temperature for 60 minutes with continuous stirring. 19 g of condensed water was added to the mixture using the steam volume specified. The mixture was cooled to room temperature. 19 g of kaolin was added with stirring.

[0054] Formulation 4 Charge 63.5 g of water and, with stirring, add 0.5 g of a wetting agent of the sodium dioctyl sulfosuccinate type. Add 17.0 g of polyvinyl alcohol with vigorous stirring, and heat the mixture to 95°C using a steam lance and maintain it at this temperature for 60 minutes with continuous stirring. Add 19 g of condensed water to the mixture using the steam amount specified. Allow the mixture to cool to room temperature.

[0055] Formulation 5 84.4 g of styrene acrylic copolymer dispersion are introduced and, with continued stirring, 0.7 g of a wetting agent of the sodium dioctyl sulfosuccinate type is added, followed by adding 14.9 g of water to adjust the viscosity to 30 mPas.

[0056] [Table 1]

[0057] [Table 2]

[0058] Experimental results The results in Table 2 show that the examples according to the invention require a lower amount of surfactant, with the process-related parameters remaining within acceptable limits. The surface tension of the outer layer in contact with air used in this case is at least 5 mN / m lower than the surface tension of the adjacent inner layer. The lower surface tension ensures a stable curtain, which is the basis for high-quality packaging.

[0059] Furthermore, the wrapping paper according to the invention produced in the experiments meets all the market-standard quality standards set for packaging in the food sector, including, by way of example, the barrier properties against water vapor and oxygen, which can be significantly lower in the examples according to the invention.

[0060] Measurement method Surface tension of liquids The determination of the surface tension of the liquid is carried out in accordance with the standard DIN EN ISO 19403-3.

[0061] Oxygen permeation or oxygen transmission rate (Oxygen Transmission Rate, OTR) This test is used to determine the oxygen transmission rate (permeation of pure oxygen or oxygen gas mixtures, e.g. air) of plastic films and hollow plastic bodies (e.g. packaging containers, plastic tubes, etc.) and therefore their suitability for packaging purposes and technical applications. The test is carried out in accordance with DIN 53380-3 at a temperature of 23°C and a relative humidity of 50%.

[0062] Water Vapor Permeation or Water Vapor Transmission Rate (WDD) This test is used to determine the water vapor transmission rate of plastic films, plastic webs (plates), and multi-layer structures with plastic components using an electrolytic sensor. The test is carried out in accordance with EN ISO 15106-3.

[0063] Seal / weld seam strength, strip tensile test Seal seam strength or weld seam strength of mechanically created seal seams on bags, packages or seal specimens (peel, cold seal, zipper tape) according to DIN 55529.

[0064] Fat Tolerance Test or Kit Test The fat tolerance test, commonly known as the kit test, was carried out according to DIN 53116.

[0065] Curtain Stability Limit The curtain stability limit test is performed with the curtain holder in a vertical position and no suction, starting at a flow rate (D) that produces the desired dry application for a given casting width (B), machine speed, solids content, and density of the formulation. Formula: Flow rate (cm 3 / min) = width (m) * speed (m / min) * dry application (g / m 2 )*100% / (Solid content (%)*Density (g / cm 3 ))

[0066] The flow rate is then reduced in 5% increments relative to the mass of the flow until the curtain breaks without any other external action. The curtain stability limit is determined by dividing the last adjusted flow rate by the curtain width before curtain collapse.

[0067] Curtain Defect / Curtain Opener For the determination of curtain defects / curtain openers, the flow rate is adjusted by 20% according to the determined curtain stability limit. The curtain is then visually inspected for curtain openers for 10 minutes and the number is recorded.

[0068] Brookfield Viscosity The viscosity is measured using a Brookfield RVT viscometer (available from Brookfield Engineering Laboratories, Inc., Stoughton, Massachusetts, USA). To determine the viscosity, 600 ml of the sample is poured into a 1000 ml beaker and the viscosity is measured at 25°C with a spindle speed of 20-100 rpm.

[0069] Basis weight The basis weight was determined according to DIN EN ISO 536.

Claims

1. 1. A method for producing a packaging material having at least one functional layer, comprising: forming an aqueous multi-layer curtain; and applying the curtain to a substrate, wherein an outer layer of the curtain that comes into contact with air during a casting process comprises a surface-active additive; and the difference in surface tension between the two outer layers of the curtain and the inner layers adjacent to each of the outer layers is at least 5 mN / m; the amount of the surface-active additive in the outer stream of the curtain that contacts the air is between 0.02% and 0.6% by weight relative to the mass of the two streams; and The method, wherein the inner layer is free of surface-active additives.

2. 2. The method of claim 1, wherein the surface tension of the two outer layers is at least 5 mN / m less than the surface tension of the inner layer adjacent to each of the outer layers of the curtain.

3. The method of claim 1 or 2, wherein the outer air-contacting layer of the curtain has a wet application weight in the range of 0.5 to 15 g / m 2 .

4. 4. The method according to claim 1, wherein at least one functional layer has oxygen barrier properties, said functional layer comprising a polymer with polar groups, polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), starch, and / or nanofibrillated cellulose (NFC).

5. The oxygen permeability of the packaging material is 15 cm per 24 hours at 1 atm. ３ / m ２ The method according to claim 4, characterized in that the temperature is 23°C, 50% RH or less.

6. The method according to any one of claims 1 to 5, characterized in that the packaging material has at least one functional layer with water vapor barrier properties, the functional layer comprising a non-polar polymer.

7. The method of claim 6, wherein the non-polar polymer is a polyolefin, polyethylene, polypropylene, or a mixture thereof.

8. The water vapor permeability of the packaging material is 50 g / m per 24 hours at 1 atm. ２ The method according to claim 6, characterized in that the temperature is 23°C, 50% RH or less.

9. 10. The method of claim 1, wherein the packaging material comprises at least one functional layer, a sealing layer, the sealing layer comprising a thermoplastic polymer.

10. The method of claim 9, wherein the thermoplastic polymer is selected from polyvinyl acetate (PVAc), polyethylene, polybutylene succinate (PBS), and mixtures thereof.

11. 10. The method of claim 1, wherein at least one functional layer has fat / oil barrier properties and comprises a polar polymer selected from PVOH, EVOH, mixtures thereof, and mixtures with other polymers.

12. The method according to any one of claims 1 to 11, characterized in that the substrate is paper, cardboard or a plastic film and already has one or more coating layers.

13. A method according to any one of claims 1 to 12, comprising forming a package or assembling a packaging film from the packaging material.

14. The method according to any one of claims 1 to 13, characterized in that the packaging material is a food packaging material.

15. 1. A packaging material comprising a substrate and at least three layers of a coating disposed thereon and applied to the substrate by curtain coating, the coating comprising at least one functional layer, wherein the layer of the coating in contact with the substrate and the layer of the coating in contact with air comprise a surface-active additive, the difference in surface tension between the two outer layers of the coating and the inner layer adjacent to the outer layers being at least 5 mN / m, the amount of surface-active additive in the packaging material being 0.02 to 0.6% by weight relative to the mass of the unprinted packaging material, and the inner layer does not contain a surface-active additive.

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