Packaging material with at least one barrier layer for hydrophobic compounds

Abstract

The invention relates to a coated packaging material that has a substrate having a base material of cellulose, an outer side to be faced away from the packaging item as well as an inner side to be faced towards the packaging item. The inner side of the substrate carries at least one layer of an aqueous composition, which includes at least polyvinyl alcohol and/or at least one polyvinyl alcohol copolymer as well as a cross-linking agent, wherein the aqueous composition has at most 40% by wt. of polyvinyl alcohol and/or polyvinyl alcohol copolymer and a total solid content of at most 55% by wt. The layer and cross-linking the polyvinyl alcohol and/or the polyvinyl alcohol copolymer is dried with the aid of the cross-linking agent with formation of a barrier layer for hydrophobic compounds are performed.

Claims

1. A packaging material, comprising: a substrate having a base material of pulp, an outer side to be faced away from a packaging item as well as an inner side to be faced towards the packaging item, wherein the base material is coated or uncoated paper, coated or uncoated cardboard, or coated or uncoated paperboard; and a plurality of layers disposed on the inner side of the substrate with at least two barrier layers for hydrophobic compounds, wherein at least a first barrier layer is produced by coating at least the inner side of the substrate with at least one layer of an aqueous composition including at least polyvinyl alcohol and/or at least one polyvinyl alcohol copolymer as well as a cross-linking agent, wherein the aqueous composition has before drying at most 40% by wt. of polyvinyl alcohol and/or polyvinyl alcohol copolymer and a total solid content of at most 55% by wt., and by drying the at least two barrier layers and cross-linking the polyvinyl alcohol and/or the polyvinyl alcohol copolymer with the aid of the cross-linking agent with formation of said at least two barrier layers for hydrophobic compounds, and wherein the plurality of layers additionally include at least one additional layer, which contains one or more of a non-cross-linked polyvinyl alcohol and a non-cross-linked polyvinyl alcohol copolymer, wherein said at least one additional layer, which contains non-cross-linked polyvinyl alcohol and/or a non-cross-linked polyvinyl alcohol copolymer, is disposed on a side of a second barrier layer facing away from the base material; and wherein said second barrier layer of said at least two barrier layers is formed from one or more of said cross-linked polyvinyl alcohol and said cross-linked polyvinyl alcohol copolymer.

2. The packaging material according to claim 1, wherein at least one of the at least two barrier layers after drying is at least predominantly composed of cross-linked polyvinyl alcohol and/or cross-linked polyvinyl alcohol copolymer.

3. The packaging material according to claim 1, wherein the at least two barrier layers include cross-linked polyvinyl alcohol and/or cross-linked polyvinyl alcohol copolymer, wherein at least one barrier layer includes at least one filler and/or at least one pigment.

4. The packaging material according to claim 1, wherein the plurality of layers further includes at least one layer, which contains non-cross-linked polyvinyl alcohol and/or a non-cross-linked polyvinyl alcohol copolymer, wherein the layer containing the non-cross-linked polyvinyl alcohol and/or the non-cross-linked polyvinyl alcohol copolymer is disposed between two of the at least two barrier layers.

5. The packaging material according to claim 1, wherein the cross-linking agent, configured and arranged to cross-link the polyvinyl alcohol and/or the polyvinyl alcohol copolymer, provides a three-dimensional network by reaction with the polyvinyl alcohol and/or said polyvinyl alcohol copolymer.

6. The packaging material according to claim 5, wherein the cross-linking agent comprises at least one alkyl orthosilicate and/or at least one bi-, tri-, or multi-functional compound which contributes to the formation of a three-dimensional network by reaction with the hydroxyl groups of the polyvinyl alcohol and/or the polyvinyl alcohol copolymer and which comprises at least two functional groups selected from carboxylic acid and carboxylic acid anhydride.

7. The packaging material according to claim 6, wherein the cross-linking agent is one or more of tetraethylorthosilicate, malonic acid, glutaric acid, adipic acid, citric acid, butanetetracarboxylic acid and maleic acid.

8. The packaging material according to claim 1, wherein the aqueous composition has a pH value adjusted to a value between 1 and 6.5 before application to the substrate.

9. The packaging material according to claim 1, wherein the coated substrate has a residual humidity between 3% by wt. and 12% by wt.

10. The packaging material according to claim 1, the outer side of the substrate includes a conditioning layer and/or a cover layer thereon.

11. The packaging material according to claim 1, wherein said at least two barrier layers include one or more of polyvinyl alcohols and/or polyvinyl alcohol copolymers with different degrees of polymerization and/or polyvinyl alcohols and/or polyvinyl alcohol copolymers with different degrees of hydrolysis and/or polyvinyl alcohols and/or polyvinyl alcohol copolymers cross-linked by different cross-linking agents.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) Further features of the invention are apparent from the claims, the embodiments as well as based on the drawing. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the embodiments are usable not only in the respectively specified combination, but also in other combinations without departing from the scope of the invention. There show:

(2) FIG. 1 a schematic lateral sectional view of a packaging material according to the invention according to a first embodiment; and

(3) FIG. 2 a schematic lateral sectional view of a packaging material according to the invention according to a second embodiment.

DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows a schematic lateral sectional view of a packaging material 10 according to the invention according to a first embodiment. The packaging material 10 includes a substrate 12 consisting of a base material 14 and having an outer side 16 to be faced away from a packaging item as well as an inner side 18 to be faced towards the packaging item. In the present embodiment, the base material 14 is a cardboard with an area-related mass of 400 g/m.sup.2. On the inner side 18 of the substrate 12, a layer system 20 is formed, which is produced by generating a first barrier layer 22a, a second barrier layer 22b as well as a layer 24 functioning as a cover layer. The barrier layers 22a, 22b include cross-linked polyvinyl alcohol. Moreover, the barrier layer 22a includes platelet-shaped or spherical particles or mixtures thereof as a filler and/or pigment. Thereby, the barrier layers 22a, 22b at least largely impede or prevent the migration of hydrophobic compounds through the layer system 20. Therein, the transverse cross-linking of the polyvinyl alcohol described in more detail below provides for increased mechanical stability and prevents swelling of the barrier layers 22a, 22b if they come into contact with humidity.

(5) Generally, organic, inorganic as well as organic-inorganic modified particles provided with or without swelling capability in water are suitable as fillers and/or pigments. In the present embodiment, the barrier layer 22a includes kaolin. Therein, kaolin offers the advantage that it is acid-stable and does not swell in water. Moreover, the used kaolin is composed of platelet-shaped particles, which form a mechanical barrier and hereby additionally aggravate or prevent the migration of compounds through the barrier layer 22a. In contrast, the second barrier layer 22b is exclusively composed of cross-linked polyvinyl alcohol, wherein polyvinyl alcohols with different degrees of hydrolysis and polymerization are used for producing the two barrier layers 22a, 22b and have been cross-linked by different cross-linking agents. However, generally, the two barrier layers 22a, 22b can of course also include the same cross-linked polyvinyl alcohol. In contrast, the terminating layer 24, which is in contact with the packaging item in a subsequent packaging formed of the packaging material 10, is composed of non-cross-linked polyvinyl alcohol and in particular increases the flexibility and expansibility of the layer system 20. Alternatively or additionally, it can be provided that the layer 24 is formed directly on the substrate 12 and/or between the barrier layers 22a, 22b.

(6) In the shown embodiment, the outer side 16 of the substrate 12 is not coated. However, generally, one or more layers can also be provided on the outer side 16 to achieve certain characteristics of the packaging material 10, for example a better printability or a gas and/or humidity barrier effect. Similarly, the outer side 16 can be printed, embossed, satinized or otherwise treated.

(7) Generally, the substrate 12 can be pre- or post-treated before, during and/or after application of the layer system 20. For example, the substrate 12 or the packaging material 10 can be calandered, for example embossed, smoothed, densified and/or satinized. Hereto, for example, conventional calenders, shoe calenders, belt calenders (metal belt, plastic belt etc.), smoothing presses or smoothing cylinders can be used. However, other treating methods can generally also be provided.

(8) FIG. 2 shows a schematic lateral sectional view of a packaging material 10 according to the invention according to a second embodiment. The base material 14 is again a cardboard with an area-related mass of 400 g/m.sup.2. In contrast to the preceding embodiment, the layer system 20 does not include a layer 24 without cross-linked polyvinyl alcohol or without cross-linked polyvinyl alcohol copolymer. Instead, the layer system 20 has a first barrier layer 22a, which is obtained by coating the substrate 12 with an aqueous composition, which includes polyvinyl alcohol or a polyvinyl alcohol copolymer, pigments, fillers, additives as well as a cross-linker. Furthermore, the layer system 20 includes a second barrier layer 22b, which functions as a cover layer and is obtained by coating the first barrier layer 24a with an aqueous composition, which also includes polyvinyl alcohol or a polyvinyl alcohol copolymer, pigments, fillers, additives as well as a cross-linker.

(9) Generally, the barrier layers 22a, 22b in FIG. 1 and FIG. 2 can contain the same components. Differences between the barrier layers 22a, 22b arise by the different addition of pigments, fillers and/or additives, for example in the form of colloidal polymer dispersions. The second barrier layer 22b exhibits excellent flexibility despite of the addition of pigment and cross-linker, which positively effects on the further processing process of the packaging material 10. As a further additive, for example, microcrystalline cellulose can be employed, which positively effects on the water retention behavior. Due to the crystalline structure, an additional barrier efficiency is already given with addition of small amounts (e.g. ≤1% by wt.). If it is required, a further layer 24 of non-cross-linked PVOH or non-cross-linked polyvinyl alcohol copolymer can also be applied in the second embodiment to further improve the flexibility and expansibility of the packaging material 10 as needed.

(10) In the following, various further embodiments for producing the packaging material 10 according to the invention with barrier characteristics with respect to non-polar chemical compounds are listed.

1. Production of an Aqueous Polyvinyl Alcohol Solution

(11) If the polyvinyl alcohol or the water-soluble polyvinyl alcohol copolymer is not already present dissolved in water, the production of a polyvinyl alcohol (copolymer) solution is performed as follows:

(12) First, a defined amount of cold water is provided. Subsequently, a defined amount of an optionally finely ground polyvinyl alcohol powder (analogously: polyvinyl alcohol copolymer powder) with a degree of hydrolysis, which is preferably between 80% and 99.9%, is stirred in with severely stirring (2000 rpm) at a temperature of 75° C. to 80° C. within 30 to 45 minutes with an intensive or dissolver stirrer. The dissolving process is terminated as soon as the solution is clear. The still warm solution is cooled down to 25° C. Before the further use, the exact solid content of the solution is determined for example by means of a thermobalance and optionally adjusted to a value between 5% by wt. and 15% by wt. The determined or adjusted solid content serves as a basis for the further course of procedure and in particular for determining the layer thickness to be applied to the substrate as well as for amount determination of the cross-linking reagents to be added. The pH value of the obtained polyvinyl alcohol solution is neutral.

(13) After the cooling operation is terminated, the pH value of the freshly prepared polyvinyl alcohol solution is adjusted as needed. The adjustment of the pH value is effected in a manner known per se by addition of a suitable acid or base. For example, mineral acids such as for instance concentrated hydrochloric acid or bases as sodium hydroxide are suitable.

(14) Alternatively, it can be provided that the polyvinyl alcohol (PVOH) or the polyvinyl alcohol copolymer is dissolved at temperatures between 75° C. and 95° C., wherein a content of the aqueous solution in terms of polyvinyl alcohol (copolymer) is adjusted to maximally 40% by wt., for example to 30% by wt.

2. Production of an Aqueous Composition

(15) 2.1 Glyoxal as the Cross-Linking Agent

(16) To the polyvinyl alcohol solution produced according to item 1., a 40% glyoxal solution is added at room temperature (25° C.) with severely stirring within about 15 minutes with simultaneous adjustment of the pH value of the solution to pH=3 to obtain an aqueous composition for coating the substrate 12. The amount of glyoxal to be added ranges between 5 and 40% by wt. related to 100% by wt. of polyvinyl alcohol.

(17) After 15 minutes, the aqueous composition is degassed at an initial negative pressure of −200 mbar, which is subsequently slowly increased to −500 mbar to −600 mbar. If the vacuum is further increased (e.g. to above −800 mbar, i.e. to a pressure of about 200 mbar), the water begins to boil and condensate deposits on the walls of the vacuum container. Finally, the aqueous composition is degassed at a pressure of about 100 mbar without further stirring.

(18) After termination of the degassing, the aqueous composition can be applied to the substrate 12, wherein the polyvinyl alcohol is cross-linked by the glyoxal.

(19) 2.2 Adipic Acid (AS), Glutaric Acid (GS) and/or Maleic Acid (MS) as the Cross-Linking Agent

(20) The addition of the mentioned dicarboxylic acids can be divided into two sub-categories:

(21) AS and GS belong to the group of the saturated dicarboxylic acids, wherein AS is poorly (24 g/l) and GS is easily (640 g/l) soluble in cold water (20° C.). The condensation reactions of both acids with polyvinyl alcohol are preferably catalytically assisted by addition of mineral acids (e.g. hydrochloric acid) by adjusting the pH value of the aqueous composition to pH=3.

(22) MS is an unsaturated dicarboxylic acid, which is very well water-soluble (788 g/l, 20° C.) and reacts severely acidic in aqueous solution. MS is present in cis form. By UV radiation and extended heating at 150° C., it transforms into the trans form (fumaric acid), which optionally can be taken into account in the transverse cross-linking reaction. In using the MS, therefore, additional pH adjustment of the aqueous composition is usually not required. According to used amount, the pH value is between 1.6 and 3.2 depending on the amount of MS dissolved in the aqueous polyvinyl alcohol solution. The added total amount of dicarboxylic acid generally ranges between 5 and 25% by wt. related to 100% by wt. of polyvinyl alcohol.

(23) The aqueous composition including polyvinyl alcohol and one or more of the mentioned dicarboxylic acids is subsequently heated to 70° C., intensively stirred at 70° C. for 15 minutes and then cooled down to 25° C. Now, the pH value can be adjusted as needed corresponding to the respectively employed dicarboxylic acid. After pH value adjustment of the aqueous composition, preferably, the above described degassing step is effected.

(24) 2.3 Iron Chloride (FeCl.sub.3) as the Cross-Linking Agent

(25) The addition of FeCl.sub.3 to the polyvinyl alcohol solution is preferably effected at 25° C. with severe stirring. FeCl.sub.3 can be present as a solid or already dissolved in water. The added amount of FeCl.sub.3 ranges between 1 and 15% by wt. related to 100% by wt. of polyvinyl alcohol. The mixing time is 15 minutes at 25° C. A pH value adjustment is not required if further cross-linking agents are not provided. Before applying to the substrate 12 to be coated, a degassing step is recommended here too.

(26) 2.4 Polyacrylates as the Cross-Linking Agent

(27) Within the scope of the present invention, by polyacrylates, derivatives of the polyacrylic acid having the general formula

(28) ##STR00003##
are understood, wherein R denotes hydrogen or unsubstituted or substituted alkyl group, in particular methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl and/or tert-butyl. Preferably, polyacrylic acids in the molecular weight range from 2000 to 1500000 g/mol, in particular from 50000 to 500000 g/mol, are used since this class is comparatively well soluble in cold water (20° C.). The added amount of polyacrylic acid ranges between 0.01 and 10% by wt. The mixing time is approximately 15 min. at 25° C. to 60° C. The pH value of the mixture can be increased as needed by addition of basic additives such as KOH, NaOH or the like. A degassing step is recommended before application.

(29) Alternatively to a dissolver stirrer, for dissolving PVOH or for producing an aqueous solution with pigments/fillers/additives and cross-linker, a special beaker stirrer (manufacturer Viscojet) with conically tapered nozzles can be used, which prevents the input of gas bubbles into the polymer solution or filled polymer dispersion. With this stirring organ, it is possible to dissolve PVOH or a copolymer thereof in gentle and fast manner and to gently and uniformly introduce other components such as pigments, additives, cross-linkers etc. The dispersion and dissolution of the ingredients is effected similar to the dissolver stirrer. The individual ingredients are added to the aqueous provision, well wetted and distributed with the aid of the beaker stirrer.

(30) As further additives, colloidal dispersions with high solid content (45-55%) are suitable. As the colloidal particles, for example, organic polymers can be used, which have a barrier effect with respect to hydrophobic compounds or do not impair the hydrophobic barrier effect.

(31) 2.5 Mixtures of Polyvinyl Alcohol with the Cross-Linking Agents Described Under 2.1. to 2.4.

(32) Generally, the above mentioned cross-linking agents can be arbitrarily mixed, e.g. FeCl.sub.3 with di- and/or polycarboxylic acids and/or dialdehydes.

(33) As further additives, colloidal dispersions with high solid content (45-55%) are suitable. The colloidal particles can be organic polymers, which also have a barrier effect with respect to hydrophobic compounds or do not impair the hydrophobic barrier effect.

(34) 2.6 Introduction of Fillers and/or Pigments

(35) Fillers and/or pigments with preferably spherical and/or platelet-shaped particles are added to the aqueous composition in a percent by weight range of 5-60% related to 100% by wt. of polyvinyl alcohol (PVOH). As fillers and/or pigments, generally, organic, inorganic and/or organic-inorganic modified particles are suitable, which are provided with or without swelling capability in water.

(36) Spherical particles such as silica particles with specific surfaces of 200-500 g/m.sup.2 can be employed. The silica particles are in solid form or in aqueous dispersions. The size of the particles ranges between 5-60 nm. Unmodified as well as (hydrophilically) modified particles can be employed. Particles are added in the range of 10-60% related to 100% by wt. of PVOH.

(37) Alternatively, mixtures of spherical and platelet-shaped particles can be added. Platelet-shaped particles such as kaolins and sheet silicates (partially or completely exfoliated) can be employed in unmodified or modified manner. Sheet silicates can be functionalized with alkoxy silanes, which bear amino, epoxy or mercapto groups. Besides it, kaolin, montmorillonite, bentonite, vermiculite, hectorite, saponite, laponite etc. or mixtures thereof can be employed. In the employment of kaolin, a so-called “hyper-platy”, nano-scaled type with a form factor of at least 40 is used. A form factor between 60 and 100 and a size of max. 1 μm is preferred.

(38) Further fillers like natural and/or synthetic aluminosilicates with defined pore volumes of 3-10 Å, 8-13 Å and 10-15 Å or more Angstrom can be added alone or in combination with spherical or platelet-shaped fillers or be added as mixtures thereof.

(39) Furthermore, natural organic fillers such as cellulose fibers and/or cellulose regenerate fibers, in particular micro- and nano-fibrillated celluloses, can be used as the fillers. These fillers can be used alone or in combination with one or more other fillers.

(40) In a further configuration, it is provided that the aqueous composition is generally formed free of boron compounds such as for example borax, free of silicates swellable in water, in particular of swellable sheet silicates, and/or free of hydrogen sulfite adducts to ensure a high chemical and mechanical resistance with at the same time high food compatibility of the resulting barrier layer 22.

(41) Besides fillers and/or pigments, additives in the form of colloidal dispersions can be added, which increase the total solid content of the aqueous composition and do not or not significantly vary the viscosity besides a barrier effect with respect to hydrophobic substances.

3. Application of the Aqueous Composition

(42) An aqueous composition produced according to the above described recipes is applied to the coated or preferably uncoated substrate 12. The base material 14 of the substrate 12 is composed of cardboard and has a grammage between 200 g/m.sup.2 and 800 g/m.sup.2.

(43) 3.1 Possibilities of Application and Layer Arrangement

(44) 3.1.1 Single-Layer Wet Film Application

(45) The substrate 12 can be coated for producing a single barrier layer 22 with aqueous compositions consisting of: polyvinyl alcohol+glyoxal; polyvinyl alcohol+dicarboxylic acids; polyvinyl alcohol+polyacrylic acids; polyvinyl alcohol+dicarboxylic acids+fillers and/or pigments; polyvinyl alcohol+polyacrylic acids+dicarboxylic acids+fillers and/or pigments; polyvinyl alcohol+FeCl.sub.3; or polyvinyl alcohol+mixture of different cross-linking agents; polyvinyl alcohol+mixture of different cross-linking agents+fillers and/or pigments; wherein the wet film application can be 3 to 15 g/m.sup.2. Therein, it is to be emphasized that generally the substrate 12 alternatively can already be composed of a base material 14 coated with non-cross-linked polyvinyl alcohol, wherein fillers and/or pigments can be mixed to the non-cross-linked polyvinyl alcohol as required.

(46) Further embodiments for the aqueous composition used within the scope of the invention are indicated in table 1. Therein, it is again to be emphasized that the solid content of each aqueous composition is at most 25% by wt. including possibly present fillers and/or pigments. Preferably, the solid content of each aqueous composition is at most 15% if the aqueous composition is formed free of fillers and/or pigments. The amounts of polyvinyl alcohol indicated in table 1 are always to be regarded as 100 parts. The amount of the cross-linking agent is always related to the 100 parts of polyvinyl alcohol.

(47) TABLE-US-00001 TABLE 1 Ingredients of the aqueous composition Main component Parts Parts Parts PVOH Degree of hydrolysis: 80 -> 99% 100 100 100 Cross-linking Parts- Parts- agent/compound Chem. min. max. Parts class compound Structural formula number number preferred Dialdehydes, unsaturated aldehydes Glyoxal 1 50  10-30 Glutar- aldehyde 1 50   5-25 Acryl- aldehyde 1 50   5-20 Polycarboxylic acids, unsaturated carboxylic acids, carboxylic acid esters Malonic acid 1 50  10-30 Glutaric acid 1 50  10-30 Adipic acid 0 1 50  10-30 Citric acid 1 50   2-10 Butanetetra- carboxylic acid anhydride 0.1 25   1-10 Acrylic acid 0.1 25   1-10 Methacrylic acid 0.1 25   1-10 Maleic acid 0.1 25   1-10 Methacryl- methylester 0.1 25   5-20 Hydroxy- ethylmeth- acrylate 0.1 25   5-20 FeCl.sub.3 FeCl.sub.3 0.1 20   1-10 Silanes TEOS 0.1 10   1-10 Urea formaldehyde resin (e.g. Urecoll ®) 0.1 20   1-10 Polyacrylic acid 0.01 25 0.1-10

(48) 3.1.2 Multi-Layered Application

(49) On demand, multi-layered layer systems 20 with two, three, four of five barrier layers 22 applied one after the other can be produced. An aqueous polyvinyl alcohol solution without cross-linking agent can also be used as a first conditioning coat or as a primer in this case. Alternatively or additionally, the non-cross-linked polyvinyl alcohol layer can be applied between two barrier layers 22 and/or as a terminating layer 24, as shown in FIG. 1. The non-cross-linked or cross-linked polyvinyl alcohol layer can be filled with fillers and/or pigments. The dry weight of each layer 24 and/or barrier layer 22 can again be 3 to 15 g/m.sup.2.

(50) 3.2 Application Systems

(51) The layer systems 20 described under 3.1.1. and 3.1.2. can be applied by application tools usual in the coating and paper industry by means of spraying, coating with doctor blade, casting or an equivalent contour coating method. Suitable parameter values are for example:

(52) Roll doctor blade: 10, 20, 40, 60, 80 μm wet film thickness

(53) Film drawing frame: variable gap setting, 0-1000 μm wet film thickness

(54) Film drawing frame: fixed gap: 20, 40 60, 70, 100, 120 μm wet film thickness

(55) These application tools are employed by means of a motor-controlled application system with a maximum speed of the substrate 12 of up to 1000 m/min, for example 80 mm/s or. 4.8-5 m/min for a uniform application.

(56) Alternatively or additionally, a nozzle application system is used, which applies at least one barrier layer 22 or layer 24 and maximally four layers to the cardboard substrate 12 movable in horizontal direction at the same time. The mixing of the aqueous compositions can be effected in the nozzle chamber, in the nozzle gap (gap width e.g. 0.1-1.0 mm) or outside of the nozzle on the substrate 12. Wet film layer thicknesses above 200 μm are possible with this application method. The required delivery amount of the aqueous composition results from the parameters of “layer thickness” and “maximum speed” of the linear drive.

4. Drying and Cross-Linking of the Wet Films by Means of IR Radiation (IR), Convection Drying (KV) and/or UV Radiation (UV)

(57) The solvent (water) of the aqueous composition applied to the substrate 12 is eliminated by infrared and/or convection dryers. Both dryer types can be used individually, collectively, consecutively or independently of each other. The dryer temperatures of both dryer types can for example be chosen between 60° C. and 200° C. Supply and exhaust air, respectively, and temperature settings of the dryers or the dryer combination are preferably selected such that a bubble-free layer system 20 arises. A residual humidity of 7-9% by wt. in the substrate 12 can be used as a criterion for the exact temperature setting.

(58) All of the barrier layers 22 or layers 24 are preferably first dried by IR and/or KV. In aqueous compositions, which contain dialdehydes and/or dicarboxylic acids, polyacids and/or mixtures thereof as cross-linking agents (see 2.1 to 2.5), the thus supplied heat is sufficient to virtually quantitatively perform the transverse cross-linking of the polyvinyl alcohol.

(59) The cross-linking reaction with FeCl.sub.3 is a two-stage process. After the at least predominant removal of the solvent, the at least largely dry coating is irradiated with UV light. Hereto, for example, a Hg vapor high-pressure lamp can be used. The exposure of the UV-active polyvinyl alcohol layer takes about 10 s at a power of about 0.4 W/cm.sup.2 with an intensity specification of 75%.

(60) Generally, it is advisable to irradiate all of the aqueous compositions containing UV-active cross-linking agents with UV light before, during and/or after thermally drying.

5. Test Method

(61) 5.1 Measurement of the Barrier Effect with Respect to Hydrophobic Hydrocarbons

(62) The packaging material 10 shown in FIG. 1 was subjected to a migration examination with the food simulant Tenax® based on the test standards DIN EN 1186-13 and DIN EN 14338, wherein the Tenax® was applied to the layer system 20 of the packaging material 10. After incubation of the migration formulation at defined temperature and time, the migrated substances were eluted from Tenax® by means of n-hexane and the mineral oil hydrocarbons were specifically separated by means of liquid chromatography into two different fractions, namely the fraction of the saturated (mineral oil saturated hydrocarbons, MOSH) and the fraction of the aromatic hydrocarbons (mineral oil aromatic hydrocarbons, MOAH). The two fractions thus obtained were analyzed by gas chromatography and captured as sum parameters, wherein deuterated n-nonadecane and diethylnaphthalene, respectively, were employed for the evaluation of the signal area sums. With respect to the extractable initial amount of mineral oil hydrocarbons from the raw packaging material, which defines the sum of all components capable of migrating, less than 1% of the substances capable of migrating were detected in the Tenax® eluate. Thus, the migration of the hydrophobic hydrocarbons is more than 99% prevented, and therefore is always below a value of 0.6 mg/kg of packaged food for mineral oils.

(63) For the maximum transition of MOSH, a temporary value of 0.6 mg/kg was set. Based thereon, for hydrocarbon compounds with a carbon number between 10 and 16 from BfR 2011, a temporary value of 12 mg/kg was set. For the MOAH components, according to draft of the 22.sup.nd regulation for altering the Foodstuffs and Consumer Goods Law (mineral oil regulation), a value of 0.15 mg/kg should not be detectable. The migration of hydrophobic compounds is thereby below the requested value of 0.12 mg/kg.

(64) 5.2 Layer Structure

(65) For characterizing the layer structure of the layer system 20, a semi-thin section was manufactured, based on which the individual layers 22a, 22b and 24 were spectroscopically identified by an optical and an IR or Raman microscope. The assessment of the closeness and uniformity of the applied layer is performed by means of FTIR microscopy.

6. Further Embodiments

(66) In the following, further embodiments for the packaging material 10 according to the invention are specified. Unless otherwise indicated, the production was effected in the above described manner.

6.1 Example 1

(67) In the following, first, the production of a coated substrate 12 is explained:

(68) Base material 14: Cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(69) Composition (not cross-linking) for coating: Aqueous polyvinyl alcohol solution (Elvanol 90-50 or Elvanol 85-82, Dupont or mixtures thereof) Solid content: 10.00% by wt.

(70) Coating the cardboard base material 14 with the composition (40-200 μm wet film layer thickness)

(71) Application method: Doctor blade, airbrush, nozzle

(72) Speed of the substrate 12: up to 1000 m/min

(73) Drying: IR & convection until achieving 5-7% of residual humidity in the base material 14.

(74) The substrate 12 thus produced can be used as a starting material for the application of one or more barrier layers 22.

6.2 Example 2

(75) Base material 14: cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(76) Aqueous composition (cross-linking): Aqueous polyvinyl alcohol solution (Elvanol 90-50 or Elvanol 85-82, Dupont or mixtures thereof), pigments (according to item 2.5) As the cross-linkers, the cross-linkers listed in item 3.1.1 or mixtures thereof are considered Solid content: up to 25.00% by wt.

(77) Coating the cardboard base material 14 with the aqueous composition (40-200 μm wet film layer thickness)

(78) Application method: doctor blade, airbrush, nozzle

(79) Speed of the substrate 12: up to 1000 m/min

(80) Drying: IR & convection until achieving 5-7% of residual humidity in the base material 14

6.3 Example 3

(81) Base material 14: Cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(82) Composition (not cross-linking): Aqueous polyvinyl alcohol solution (Elvanol 90-50 or Elvanol 85-82, Dupont or mixtures thereof), filled with pigments (cf. item 2.5) Solid content: up to 25.00% by wt.

(83) Coating the cardboard base material 14 or the substrate 12 with the composition (40-200 μm wet film layer thickness)

(84) Application method: doctor blade, airbrush, nozzle

(85) Speed of the substrate 12: up to 1000 m/min

(86) Drying: IR & convection until achieving 5-7% of residual humidity in the base material 14

6.4 Example 4

(87) Base material 14: Cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(88) Composition (physically cross-linking): Aqueous polyvinyl alcohol solution (Elvanol 90-50 or Elvanol 85-82, Dupont or mixtures thereof), filled with aluminosilicates and carboxymethylcellulose Solid content: 12% by wt.

(89) Coating the cardboard base material 14 with the composition (40-200 μm wet film layer thickness)

(90) Application method: nozzle, single-layer application

(91) Speed of the base material: up to 1000 m/min

(92) Drying: IR & convection until achieving 5-7% of residual humidity in the cardboard

6.5 Example 5

(93) Substrate 12: Cardboard with an area-related mass between 200-800 g/m.sup.2, coated or preferably uncoated

(94) Aqueous composition (thermally cross-linking or curing): Aqueous PVOH solution, solid content 10% by wt. (Elvanol 85-82 or Elvanol 90-50 and mixtures thereof, Dupont), 100 parts Maleic acid, p. a. (Sigma), 5 parts related to 100 parts of PVOH

(95) Coating the substrate with the aqueous composition (1-layer application, 40-200 μm wet film layer thickness)

(96) Application method: nozzle, single-layer application

(97) Speed of the substrate 12: up to 1000 m/min

(98) Drying: IR & convection until achieving 5-7% of residual humidity in the base material 14

6.6 Example 6

(99) Base material 14: Cardboard with an area-related mass between 200-800 g/m.sup.2, coated or preferably uncoated

(100) Aqueous composition (UV curing): Aqueous PVOH solution, solid content 10% by wt. (Elvanol 85-82 or Elvanol 90-50 and mixtures thereof, Dupont), 100 parts Aqueous FeCl.sub.3 solution (Donau Chemie), solid content 46.33% by wt., 6.7 parts related to 100 parts of PVOH

(101) Coating the substrate with the aqueous composition (1-layer application, 40-200 μm wet film layer thickness)

(102) Application method: nozzle, single-layer application

(103) Speed of the base material: up to 1000 m/min

(104) UV curing with Hg vapor high-pressure lamp, 10 s exposure, 0.4 W/cm.sup.2 power

6.7 Example 7

(105) Base material 14: Cardboard with an area-related mass between 200-800 g/m.sup.2, coated or preferably uncoate

(106) Aqueous composition (thermally curing): Aqueous PVOH solution, solid content 10% by wt. (PVOH-8582 or Elvanol 9050 and mixtures thereof, Dupont), 100 parts Glyoxal (40% aqueous solution, BASF), 12.6 parts related to 100 parts of PVOH

(107) Coating the substrate with the aqueous composition (1-layer application, 40-200 μm wet film layer thickness)

(108) Application method: nozzle, single-layer application

(109) Speed of the base material: up to 1000 m/min

(110) Drying: IR & convection until achieving 5-7% of residual humidity in the cardboard base material 14.

6.8 Example 8

(111) Base material 14: paper with an area-related mass between 50-150 g/m.sup.2, coated or preferably uncoated

(112) Aqueous composition (thermally curing): Aqueous PVOH solution, solid content 10% by wt. (PVOH-8582 or Elvanol 9050 or mixtures thereof, Dupont), 100 parts Polyacrylic acid, 0.01-5.0 parts related to 100 parts of PVOH

(113) Coating the substrate with the aqueous composition (1-layer application, 40-200 μm wet film layer thickness)

(114) Application method: nozzle, single-layer application

(115) Speed of the base material: up to 1000 m/min

(116) Drying: IR & convection until achieving 5-7% of residual humidity in the base material 14.

6.9 Example 9

(117) Base material 14: cardboard with an area-related mass between 200-800 g/m.sup.2, coated or preferably uncoated

(118) Compositions: combination of example 1 and example 2, example 1 and example 3, example 1 and example 4, example 1 and example 5, example 1 and example 6, example 1 and example 7 or example 1 and Example 8

(119) The coating of example 1 is applied to the base material as the bottommost layer, the coating according to the recipe of example 2, 3, 4, 5, 6, 7 or 8 and/or double or triple combinations of these examples is applied thereon.

(120) Multi-layer application, each 80-200 μm wet film layer thickness

(121) Speed of the base material: up to 1000 m/min

(122) Application method: doctor blade, nozzle

6.10 Example 10

(123) Base material: Cardboard with an area-related mass between 200-800 g/m.sup.2, coated or preferably uncoated

(124) Compositions:

(125) Combination of 2 coats (aqueous compositions) of example 1 and one coat of example 2 to example 8. The coat of example 1 is used as a conditioning and covering coat in this application, to act leveling on the inner side 18 of the substrate 12 and protecting with respect to tension and compression on the outer side 16 of the substrate 12 (forces occurring in corrugating and punching operations). The covering coat is easily printable and adhesive.

(126) Multi-layer application, each 80-200 μm wet film layer thickness

(127) Application method: doctor blade, nozzle

(128) Speed of the base material: up to 1000 m/min

(129) Drying: IR & convection until achieving 5-7% of residual humidity in the cardboard.

6.11 Example 11

(130) Base material: cardboard with an area-related mass between 200-800 g/m.sup.2, coated or preferably uncoated

(131) Compositions:

(132) Aqueous PVOH solution (Elvanol 9050 or Elvanol 8582, Selvol 103 or 107, Mowiol 15-99 or 9-98, Exceval Aq 4104 or mixtures thereof).

(133) Wet film thickness: 20-200 μm.

(134) Solid contents PVOH solutions: maximum 30% by wt.

(135) Total solid contents filled PVOH solutions including cross-linker: 35-45% by wt.

(136) Drying until achieving a residual humidity between 7 and 9% by wt. in the base material 14.

6.12 Example 12

(137) Aqueous composition: PVOH content maximum 30% by wt. filled with pigments, addition of a colloidal polyacrylate dispersion as an additive

(138) Total solid content of the aqueous composition: max. 45% by wt.

(139) Further processing as in the preceding embodiments.

6.13 Example 13

(140) Aqueous composition: PVOH content maximum 30% by wt., filled with pigments, addition of microcrystalline cellulose (max. 1%) and acrylate dispersion as additives; total solid content: max. 45% by wt.

(141) Further processing as in the preceding embodiments.

6.14 Example 14

(142) Combination of two different aqueous compositions (coats) of the preceding embodiments for producing two different barrier layers 22a, 22b.

(143) Further processing as in the preceding embodiments.

6.15 Example 15

(144) Base material 14: Cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(145) Composition (not cross-linking) for coating: Aqueous polyvinyl alcohol solution (Selvol 103 or Selvol 107, Sekisui, Exceval, Kuraray or mixtures thereof) Solid content PVOH (=total solid content): 30.00% by wt.

(146) Coating the cardboard base material 14 with the composition (10-200 μm wet film layer thickness)

(147) Application method: doctor blade, nozzle at 30 to 80° C.

(148) Speed of the substrate 12: up to 1000 m/min

(149) Drying: IR & convection until achieving 7-10% of residual humidity in the base material 14.

(150) The substrate 12 thus produced can be used as a starting material for the application of one or more barrier layers 22.

6.16 Example 16

(151) Base material 14: Cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(152) Aqueous composition (cross-linking): Aqueous polyvinyl alcohol solution (Selvol 103 or Selvol 107, Sekisui, Exceval, Kuraray or mixtures thereof), pigments The above listed cross-linkers or mixtures thereof are considered as cross-linkers Total solid content: up to 45.00% by wt.

(153) Coating the cardboard base material 14 with the aqueous composition (10-200 μm wet film layer thickness)

(154) Application method: doctor blade, nozzle at 30 to 80° C.

(155) Speed of the substrate 12: up to 1000 m/min

(156) Drying: IR & convection until reaching 7-10% of residual humidity in the base material 14

6.17 Example 17

(157) Base material 14: Cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(158) Aqueous composition, cross-linking, without filler: Aqueous polyvinyl alcohol solution (Selvol 103 or Selvol 107, Sekisui, Exceval, Kuraray or mixtures thereof) The above listed cross-linkers or mixtures thereof are considered as cross-linkers Total solid content: up to 30.00% by wt.

(159) Coating the cardboard base material 14 with the aqueous composition (10-200 μm wet film layer thickness)

(160) Application method: doctor blade, nozzle at 30 to 80° C.

(161) Speed of the substrate 12: up to 1000 m/min

(162) Drying: IR & convection until reaching 7-10% of residual humidity in the base material 14

6.18 Example 18

(163) Base material 14: cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(164) Aqueous composition (physically cross-linking): Aqueous polyvinyl alcohol solution (Selvol 103 or Selvol 107, Sekisui, Exceval, Kuraray or mixtures thereof), colloidal poly(meth)acrylate dispersion and carboxymethylcellulose Total solid content: 25-45% by wt.

(165) Coating the cardboard base material 14 with the composition (10-200 μm wet film layer thickness)

(166) Application method: nozzle, single-layer application at 30 to 80° C.

(167) Speed of the base material: up to 1000 m/min

(168) Drying: IR & convection until achieving 7-10% of residual humidity in the cardboard

6.19 Example 19

(169) Substrate 12 or base material 14: cardboard with an area-related mass between 200-800 g/m.sup.2, coated or preferably uncoated

(170) Aqueous composition (thermally cross-linking or curing): Aqueous PVOH solution, solid content 10-20% by wt. (Selvol 103 or Selvol 107, Sekisui, Exceval, Kuraray or mixtures thereof), 100 parts Pigments, 60 parts related to 100 parts of PVOH Maleic acid (DSM) as cross-linker, 5 parts related to 100 parts of PVOH Total solid content: 17-35% by wt.

(171) Coating the substrate 12 with the aqueous composition (1-layer application, 10-200 μm wet film layer thickness)

(172) Application method: nozzle, single-layer application at 30 to 80° C.

(173) Speed of the substrate 12: up to 1000 m/min

(174) Drying: IR & convection until achieving 7-10% of residual humidity in the base material 14

6.20 Example 20

(175) Substrate 12 or base material 14: cardboard with an area-related mass between 200-800 g/m.sup.2, coated or preferably uncoated

(176) Aqueous composition (thermally cross-linking): Aqueous PVOH solution, solid content 10-22% by wt. (Selvol 103 or Selvol 107, Sekisui, Exceval, Kuraray or mixtures thereof), 100 parts Pigments, 20-50 parts related to 100 parts of PVOH Maleic acid as cross-linker, 5-10 parts related to 100 parts of PVOH Total solid content: 18-35% by wt.

(177) Coating the substrate with the aqueous composition (1-layer application, 10-200 μm wet film layer thickness)

(178) Application method: nozzle, single-layer application at 30 to 80° C.

(179) Speed of the substrate 12: up to 1000 m/min

(180) Drying: IR & convection until achieving 7-10% of residual humidity in the base material 14

6.21 Example 21

(181) Base material 14: cardboard with an area-related mass between 200-800 g/m.sup.2, preferably uncoated

(182) Composition (physically cross-linking): Aqueous polyvinyl alcohol solution (Selvol 103 or Selvol 107, Sekisui, Exceval, Kuraray or mixtures thereof), 100 parts Colloidal polymer dispersion, 20-40 parts related to 100 parts of PVOH Pigments, 20-50 parts related to 100 parts of PVOH Cross-linker or mixtures thereof, 5-10 parts related to 100 parts of PVOH Total solid content: 25-45% by wt.

6.22 Example 22

(183) Application of one of the above embodiments with double slit.

(184) By the division of the aqueous composition into the two chambers and the subsequent combination in a container, excess aqueous composition is collected in varietal manner.

6.23 Further Examples

(185) Based on the above mentioned recipes, further variations and combinations are possible:

(186) Alternative cross-linkers: 6.7% FeCl.sub.3 related to 100% of PVOH (or PVOH copolymer) 12.6% glyoxal related to 100% of PVOH (or PVOH copolymer) 0.01 to 5% poly(meth)acrylic acid (dispersion) related to 100% of PVOH

(187) Application of single- and multi-layer coatings by means of doctor blade or nozzle, wherein the compositions of the examples 12, 13 and 17 can be used as a conditioning layer.

(188) Colloidal Dispersions/Suspensions

(189) Colloids are macroscopic particles distributed in a homogeneous dispersion medium with a size of 1-1000 nm. Colloidal dispersions appear colorless if the degree of fragmentation of the colloids is at 500 nm. Among other things, the stability of colloids is depending on the factors of pH value, dispersant, additives (surface active agents), propensity for micelle formation etc. One speaks of colloidal particles e.g. in aqueous system if the molecular weight is (Mr)>1000 g/mol. If the particles have Mr<1000 g/mol, thus, one often speaks of molecular solutions. Dispersions are composed of macromolecular molecules, which can be partially or completely cross-linked and which no longer dissolve due to their molecular weight. Examples for polymer, polar dispersions are: poly(meth)acrylates, polymethylmethacrylates polyethyleneglycolacrylates polyamides polyesters (for example acrylic acid esters, vinyl esters, biopolymers like polylactic acid ester, PHA, polyhydroxybutyrate, PHB) polyurethanes styrene-butadiene copolymers carbohydrate colloids such as cellulose, starch, dextrin, chitosan proteins polyvinylacrylate dispersions or copolymer dispersions thereof.

(190) Furthermore, there are still organic-inorganic hybrid polymer dispersions, which are present in colloidal manner. Examples for them are tetraorthosilicates (TEOS), which are modified with functional organic groups by means of sol-gel reaction. All of the inorganic pigments, fillers, additives, catalysts, which have particle sizes of few nm to several μm and can be dispersed in a liquid, solid or gaseous phase (applies to all of the colloids), come within the group of the inorganic colloids.

(191) The parameter values specified in the documents for defining process and measurement conditions for the characterization of specific properties of the inventive subject matter are to be considered as encompassed by the scope of the invention even within the scope of deviations—for example due to measurement errors, system errors, weighing errors, DIN tolerances and the like.

(192) It would be appreciated by those skilled in the art that various changes and modifications can be made to the illustrated embodiments without departing from the spirit of the present invention. All such modifications and changes are intended to be covered by the appended claims.