WO1998006571A1

WO1998006571A1 - Easily compostable composite, multilayered foil, process for producing the same and its use

Info

Publication number: WO1998006571A1
Application number: PCT/EP1997/004389
Authority: WO
Inventors: Frank-Martin Neumann
Original assignee: Sengewald Verpackungen Gmbh
Priority date: 1996-08-14
Filing date: 1997-08-13
Publication date: 1998-02-19
Also published as: EP0918632A1; AU4454497A; DE19632799A1

Abstract

Easily compostable composite, multilayered foils (1) have at least one polyvinyl alcohol barrier layer (2) both sides of which are covered with one or several foils (3) made of a biodegradable polyester and/or polyester amide glued with an adhesive and/or bonding agent (4) or applied by coextrusion or hot-coating. All materials used to produce the composite foil are biodegradable, in particular capable of rotting and being composted, the composite being even more easily compostable than the individual materials. The composite, multilayered foil can replace as barrier foil the corresponding polyolefin foils for all purposes, such as packaging or in hygienic products.

Description

Well compostable multilayer film, process for its production and use thereof

The invention relates to a well compostable composite multilayer film comprising at least one barrier layer made of polyvinyl alcohol, to which one or more films are laminated on both sides by means of an adhesive or applied by means of coextrusion or by hot coating, a method for producing such multilayer films and their use.

Composites used in the prior art for packaging purposes, medical hygiene purposes or other special purposes are fundamentally not biodegradable. Thermoplastic processable and biodegradable materials for biodegradable (compostable) films are already known, for example from EP-0-641 817 A2. There, polyesteramides are disclosed, for example, from adipic acid, butanediol and aminocarboxylic acid with an ester content of 45% by weight, which in the biological degradation test show a large microbial growth of, for example, 102 mg in 14 days. According to the criteria disclosed in the cited patent application, a sample is also referred to as well compostable, which, under certain conditions, enables a biomass growth of at least 30 mg / l on the polymers within a maximum of two weeks.

The prior art also includes mixed polyurethane prepolymers which can be used as adhesives for laminating film materials, as they are made of EP 0 150 444 B1 are accessible. These polyurethane prepolymers have terminal isocyanate groups from diisocyanates of different reactivity and polyfunctional alcohols, and are suitable in bulk or in aqueous solution for bonding plastics, in particular for laminating plastic films. It is known that the products obtainable with such polyurethane prepolymers (manufactured film composites) show a high level of processing reliability when heat-sealing. This may be attributed to a reduced proportion of low molecular weight products capable of migration in the prepolymers.

So far, nothing is known about the biodegradability of such adhesives.

The invention has now set itself the task of providing a polyethylene or polyolefin film replacement in general, which contains a corresponding barrier layer, so that all the requirements for barrier films are met and which still fulfills all processing requirements for a film composite and at the same time is outstandingly biological is degradable (compostable). Furthermore, a method for producing such biodegradable multilayer films is to be specified. Finally, the present invention also relates to the use of the well rot and compostable films.

These and other tasks which are not mentioned individually are solved by a composite film of the type mentioned at the outset with the features of the characterizing part of claim 1. Preferred embodiments are protected in the dependent claims dependent on claim 1, while in procedural terms the subject matter of claim 5 is a Solution of the problems according to the invention presented. Finally, uses according to the invention are protected in the corresponding claims 9 and 10. Surprisingly, a multilayer film which has at least one polyvinyl alcohol film as the barrier layer and on both sides of the barrier layer has at least one film consisting of biodegradable aliphatic polyester amides and / or biodegradable polyesters which are connected to the polyvinyl alcohol layer by hot coating or laminated thereon by means of an adhesive to provide a multilayer film which has excellent biodegradability (compostability). What is particularly surprising here is that the compostability of the multi-layer film is better than the compostability of the materials involved in the construction of the multi-layer film, seen in isolation. That is, within the multilayer composite of the multilayer film, the most poorly compostable component (for example the layer made of polyester amide and / or polyester) rots faster than the comparable single layer under appropriate composting conditions. This quasi-synergistic effect was unpredictable and completely surprising.

In the context of the invention, "compostability" is understood to mean a property of the individual materials used and of the entire composite, that is to say the composite multilayer film, the compostability being in a specific connection to the biodegradability. In particular, compostability means biodegradability in the soil under composting conditions. Biodegradable polymers and plastics are materials that are quantitatively converted into either CO ₂ and H ₂ O or CH ₄ and H ₂ O by microorganisms under aerobic or anaerobic conditions.

There are a number of tests to investigate compostability, such as tests with isolated enzymes, film composting tests, in which films are buried in mature compost at 58 ° C and the biodegradation visually is rated or degradation tests in composting trials or digging trials.

In the sense of the invention, good compostability means that a material in the biodegradation test according to ASTM G22 produces> 30 mg / 1 biomass. In a preferred embodiment of the invention, this is met or exceeded both by the individual layers and by the composite as a whole. The measuring method is explained in more detail in the example section.

In addition, it is particularly noteworthy in the invention that if the barrier PVOH layer is laminated with the aliphatic polyester amide and / or polyester layer (s) by means of a polyurethane adhesive, the polyurethane adhesive used also has excellent biodegradability (compostability). This was previously unknown and cannot be expected based on the data available. The invention thus provides a film which can be used universally as a polyolefin film substitute for a variety of purposes.

The basic structure of the film according to the invention with a core of polyvinyl alcohol as a barrier layer and film layers of biodegradable goods surrounding this core from both sides, in particular of aliphatic polyester amides and / or polyesters, can be used universally and can be modified in many ways. Among other things, it is possible to apply a thin aluminum layer (a few nanometers) to the biodegradable goods by vapor deposition or sputtering, this thin aluminum layer acting as an aroma sealing layer. Even the most sensitive substances (vanillin) do not lose their aroma when wrapped in the appropriate foil. In addition, a thin aluminum layer in the range of a few nanometers is readily environmentally compatible, since it can be assumed that, for example, aluminum is converted to oxides or hydroxides, which do not stand in the way of compostability. A combination with paper goods, for example in the form of superabsorbers, is also conceivable. In this case, the film according to the invention can be used as a polyethylene or polypropylene substitute in hygiene goods, for example diapers, sanitary napkins, etc. Using appropriate superabsorbents made from completely biodegradable materials, for example based on graft copolymers which have a backbone made of starch or another biodegradable material and onto which backbones corresponding readily biodegradable side chains are grafted, for example from maleic anhydride, succinic anhydride etc., can be used in particular Create special composites with excellent biodegradability and rotability. Furthermore, the films and film composites according to the invention are outstandingly suitable for packaging in the food sector and also for all other purposes in which polyethylene or polypropylene films are primarily used today.

The films according to the invention have excellent processing properties, are extrudable, optionally coextrudable, and can be stretched not only individually but also in combination, for example a multilayer film according to the invention can be stretched biaxially.

The core of the material according to the invention is in any case a film layer made of polyvinyl alcohol. Such materials are familiar to the person skilled in the art and can be produced, for example, by saponification of polyvinyl acetate. It is known that such films made of polyvinyl alcohol are largely impenetrable for gases such as oxygen, nitrogen, carbon dioxide etc., but that they do allow water vapor to pass through. Various characteristics can be used to characterize polyvinyl alcohol, which is generally free of residual monomers as a commercial product Partial and full saponification. The fully hydrolyzed (fully hydrolyzed) vinyl acetate polymer corresponds to the basic building block of the PVOH. The partial saponification leads to a polymer of -CH ₂ -CH (OH) - and -CH ₂ -CH (OCOH ₃ ) - building blocks

the viscosity, measured in 4% aqueous solutions, expressed in m Pa s.

the molecular weight, expressed in Mw, which is 1.7 x 10 ⁵ to 2.5 x 10 ⁵ for highly viscous, fully saponified types and only 1 x 10 ⁴ - 6 x 10 ⁴ for low-viscosity types.

Furthermore, polyvinyl alcohol generally has excellent biodegradability, which can be demonstrated for aqueous PVOH solutions in a test with adapted activated sludge, the PVOH elimination from water generally being determined by determining the chemical oxygen demand (COD). PVOH films are also biodegradable, measured in the Zahn-Wellens test. Both findings are therefore a clear indication of excellent compostability, although this depends to a certain extent on the degree of saponification of the polyvinyl acetate. For example, a certain residual concentration of acetate groups has proven to be beneficial for biodegradability, in particular compostability.

The thickness of the core layer made of polyvinyl alcohol is not particularly critical in the context of the multilayer film structure according to the invention. It can be varied beyond the usual values and is preferably in the range from about 3-20 .mu.m.

Thicknesses in the range between 5 and 12 μm are particularly preferred. Within the scope of the invention, particularly useful barrier layers result if the PVOH fulfills one or more of the following criteria:

Mw between 14,000 and 210,000, preferably between 14,000 and 175,000, particularly preferably between 18,000 and 175,000;

and or

Viscosity between 3 and 60 mPa.s, preferably between 3 and 40 mPa.s, particularly preferably between 5 and 40 mPa.s;

and or

Degree of seeding between 73 and 99 mol%, preferably between 82 and 99 mol%.

For use in this invention PVOH grades include the Mowiol® ^® from Hoechst.:

Mowiol ^® 15-79, Ilowiol ^® 30-92,

4-80, 3-98,

3 -83, 4- 92,

4-88, 6- 98,

5-88, 10-98,

18-88, 20-98,

23-88, 28-99,

26 - 88, 66 - 100,

40-88, 'GE 4-86. Polyesteramide materials which are suitable for films which are suitable in combination with polyvinyl alcohol films in the context of the invention generally have relatively high molecular weights with ester contents between 30 and 70% by weight, are easy and reproducible to produce and have good mechanical properties also for the production of transparent films and good biodegradability or compostability. Such materials are known for example from EP 0 641 817 A2. The aliphatic polyester amides have aliphatic ester and aliphatic amide structures and have melting points of at least 75 ° C. The weight fraction of the ester structures is between 30 and 70%, the proportion of the amide structures between 70 and 30%. The copolymers suitable for the production of the films have an average molecular weight (MW determined by gel chromatography in m-cresol against standard polystyrene) of 10,000 to 300,000, preferably 20 to 150,000.

Such polyester amides are preferably synthesized by mixing the amides or ester-forming starting components and polymerization at elevated temperature under autogenous pressure and then distilling off the water of reaction and excess monomers in vacuo and at elevated temperature. The arrangement of the ester or amide segments is carried out purely statistically by the synthesis conditions, ie these compounds are not to be referred to as thermoplastic elastomers but as thermoplastics. The structure of thermoplastic elastomers is described in the specialist literature with "the simultaneous presence of soft and elastic segments with high ductility and low glass transition temperature (to Tg value) as well as hard and crystallizable segments with low ductility, high Tg value and the tendency to form asociates". This segment arrangement is not given. However, block copolymers with ester and amide structures which have the composition according to the invention can also be composted. However, their synthesis is significantly more complex. The monomers used to prepare the copolymers can come from the following groups:

Dialcohols such as ethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,6-hexanediol, diethylene glycol and others, and / or dicarboxylic acids such as oxalic acid, succinic acid, adipic acid and others also in the form of their respective esters (methyl, ethyl, etc .) and / or hydroxycarboxylic acids and lactones such as caprolactone and others and / or amino alcohols such as ethanolamine, propanolamine etc. and / or cyclic lactams such as epsilon-captrolactam or laurolactam etc. and / or omega-aminocarboxylic acid such as aminocaproic acid etc. and / or mixtures ( 1: 1 salts) from dicarboxylic acid such as adipic acid, succinic acid etc. and diamines such as hexamethylene diamine, diaminobutane etc.

Likewise, both hydroxyl- or acid-terminated polyesters with molecular weights between 200 and 10,000 can be used as the ester-forming component. The synthesis can be carried out either by the polyamide method by stoichiometric mixing of the starting components, optionally with the addition of water and subsequent removal of water from the reaction mixture, or by the polyester method by adding an excess of diol with esterification of the acid groups and subsequent transesterification or transamidation of these esters. In this second case, the excess glycol is distilled off in addition to water. Of the monomers mentioned, caprolactam, diol and dicarboxylic acid are preferably mixed in the desired stoichiometry for the production of polyester amides for biodegradable film components.

The polyester amides which can be used can furthermore contain 0.1 to 5% by weight, preferably 0.1 to 2% by weight, of branching agents. These branching agents can include, for example, alcohols such as trimethylolpropane or glycerol, tetrafunctional alcohols such as pentaerythritol, trifunctional carboxylic acids such as citric acid. The branching agents increase the melt viscosity of the polyester amides according to the invention to such an extent that extrusion blow molding of these polymers is possible. This does not hinder the biodegradation of these materials.

Aliphatic polyesteramides which can be used in the context of the invention have ester fractions between 35 and 80% by weight, containing aliphatic dialcohols with a chain length of C ₂ to C ₁₂ , preferably C ₂ to C ₅ , aliphatic dicarboxylic acids or their esters with a chain length of C-, to C ₁₂ , preferably C ₂ to C ₆ , omega-aminocarboxylic acids with a chain length of C, to C ₁₂ , preferably C ₄ to C ₆ , or cyclic lactams with a ring size of C ₅ to C ₁₂ , preferably C ₅ to C _π , or a 1: 1 salt of aliphatic dicarboxylic acid and aliphatic diamine with a chain length of C ₄ to C ₁₂ , preferably C ₄ to C ₆ , with optionally 0.01 to 5% by weight, preferably 0.01 to 3 % By weight of branching. They have a melting point of more than 75 ° C and a molecular weight MW> 30,000.

The aliphatic polyesteramides suitable for film production can contain 0 to 50% by weight of inorganic or organic fillers or reinforcing materials, mineral fillers, UV stabilizers, antioxidants, pigments, dyes, nucleating agents, crystallization accelerators or retarders, flow aids, lubricants, Mold release agents, flame retardants and modified or unmodified rubbers. In the case of the additives and auxiliaries mentioned, it should preferably be ensured that the compostability of the polyester amides is essentially not adversely affected.

In addition to these polyester amides, especially biodegradable copolyesters and their blends with starch are suitable as biodegradable goods. The basic framework of biodegradable Polyesters form copolyesters from well-known aliphatic diols, aliphatic and aromatic dicarboxylic acids. All monomers used are biodegradable and ecotoxicologically harmless. The statistical incorporation of the aromatic dicarboxylic acid units is important since, in the presence of longer aromatic blocks, complete degradability is no longer achieved.

The additional modifications to this basic structure are of crucial importance for practical use. This gave new copolyesters. For example, by incorporating hydrophilic components, branching monomers and / or compounds that lead to a chain extension and thus an increase in molecular weight, specifically biodegradable copolyesters for film applications can be obtained that are elastic and have a high tensile strength and elongation .

Copolyester and starch blends are also suitable. Thermoplastic starch is first produced from native wheat, maize or potato starch and a plasticizer such as glycerin in an extruder and then processed "on line" with the copolyester to form a blend. Important parameters are a complete digestion of the native starch in the extruder (i.e. destruction of the crystalline superstructures in the starch grain, but no reduction in molecular weight) and the setting of the desired blend morphology. The copolyester is present as a continuous phase in which the thermoplastic starch is finely dispersed. This targeted hydrophobicization of the starch achieves the water resistance of the starch blend required for many areas of application. Films made from them show good mechanical properties such as high tear resistance and -expansion, are antistatic, permeable to oxygen and water vapor, printable, sealable and are characterized by an extremely pleasant soft handle.

In the case of a multilayer film according to the invention, the film layers made of biodegradable goods such as polyester amides or polyesters of the type mentioned above are in the form of a composite with a polyvinyl alcohol film. They can be laminated with this, for example using an adhesive. In the context of the invention, a polyurethane prepolymer with isocyanate end groups based on diisocyanates of different reactivity can be used as the adhesive. Such compounds with isocyanate groups have been known for a long time and can be converted to high polymers in a simple manner with suitable hard materials - usually polyfunctional alcohols. So their use as a sealant, as a varnish or adhesive is known. Particularly suitable as adhesives in the context of the invention are polyurethane prepolymers with terminal isocyanate groups of different reactivity and polyfunctional alcohols, which can be obtained by reacting 2,4-tolylene diisocyanate with polyfunctional alcohols in the ratio OH: NCO between 4 and 0.55 in a first reaction step and after the reaction of virtually all fast NCO groups with some of the OH groups present, in a second reaction step compared to the less reactive NCO groups of the 2,4-toluylene diisocyanate from reaction step one, more reactive diisocyanate in equimolar amounts or in excess to still free OH groups, if desired using customary catalysts and / or elevated temperatures.

In the first stage of this process, after which the adhesive which can be used in the context of the invention is available, a large number of polyfunctional alcohols can be used. Aliphatic alcohols with 2 to 4 hydroxyl groups per molecule are suitable in this stage. Although primary like secondary alcohols can also be used, the secondary are preferred. In particular, the reaction products of low molecular weight polyfunctional alcohols with alkylene oxides with up to 4 carbon atoms can be used. For example, the reaction products of ethylene glycol, propylene glycol, of the isomeric butane ions or hexane ions with ethylene oxide, propylene oxide and / or butene oxide are suitable. The reaction products of trifunctional alcohols such as glycerol, trimethylolethane and / or trimethylpropane or higher functional alcohols such as, for example, pentaerythritol or sugar alcohols can also be used with the alkene oxides mentioned. Particularly suitable are polyether polyols with a molecular weight of 100 to 10,000, preferably 1,000 to 5,000 and in particular polypropylene glycol.

Depending on the desired molecular weight, addition products of a few moles of ethylene oxide and / or propylene oxide per mole or of more than 100 moles of ethylene oxide and / or propylene oxide per mole of low molecular weight polyfunctional alcohols can thus be used. Further polyether polyols can be produced by condensation of, for example, glycerol or pentaerythritol with elimination of water. Polyols commonly used in polyurethane chemistry continue to be formed by the polymerization of tetrahydrofuran. Among the polyether polyols mentioned, the reaction products of polyfunctional low molecular weight alcohols such as propylene oxide are particularly suitable under conditions in which secondary hydroxyl groups are at least partially formed. Other suitable polyether polyols are e.g. described in DE 2 559 759.

Furthermore, polyester polyols with a molecular weight of 200 to 10,000 can be used in the context of the invention for producing the adhesive that can be used. According to a first embodiment, polyester polyols can be used which are converted to 1 to by reacting low molecular weight alcohols, in particular ethylene glycol, propylene glycol, glycerol or trimethylolpropane 50 moles of caprolactone are formed. Other suitable polyester polyols can be produced by polycondensation. For example, difunctional and / or trifunctional alcohols with a deficit of dicarboxylic acids and / or tricarboxylic acids or their reactive derivatives can be condensed to give polyester polyols.

Suitable dicarboxylic acids here are succinic acid and its higher homologues with up to 12 carbon atoms, furthermore unsaturated dicarboxylic acids such as maleic acid or fumaric acid and aromatic dicarboxylic acids, in particular the isomeric phthalic acids. Citric acid or trimellitic acid are suitable as tricarboxylic acids. Polyester polyols from the cited dicarboxylic acids and glycerol which have a residual content of secondary OH groups are particularly suitable for the purposes of the invention.

In order to obtain reaction products of 2,4-tolylene diisocyanate with polyfunctional alcohols which can be used according to the invention in the second reaction stage as a solvent or reactive diluent, it is important to maintain a certain ratio between hydroxyl groups and isocyanate groups. This results in suitable products which, after the more reactive NCO groups have reacted, still contain OH groups if the number of OH groups divided by the number of isocyanate groups is between 4 and 0.55, preferably between 1 and 0.6.

In the second stage, to produce the adhesive in the OH and NCO-functional reaction products of the first reaction stage, symmetrical, dicyclic diisocyanates are reacted with the remaining OH groups as reactive diluents. The amount of the dicyclic diisocyanates, based on the total amount of the diisocyanates in stages 1 and 2, is 5 to 80% by weight, preferably 5 to 60% by weight and in particular 10 to 40% by weight. For the reaction of the second stage, the molar ratio of OH groups: NCO groups, expressed as the quotient of the OH groups, is divided by isocyanate groups, preferably 0.5 to 1.0, in particular 0.6 to 0.8, based on the remaining OH groups.

When selecting the dicyclic diisocyanates, it is important that the reactivity of their isocyanate groups towards hydroxyl groups is higher than that of the terminal isocyanate groups of the reactive diluent. The diaryl diisocyanates are therefore primarily suitable. 4,4'-Diphenylmethane diisocyanate and / or substituted 4,4'-diphenylmethane diisocyanates are preferred.

The products, which are preferably obtainable at temperatures between 40 and 100 ° C., have a substantially reduced proportion of free, monomeric tolylene diisocyanate but also of free, monomeric dicyclic diisocyanates. Thus, when the prepolymers are used over a large area at elevated temperatures, about 80 to 100 ° C., there is no nuisance caused by volatile tolylene diisocyanate. Another advantage of the process products is their relatively low viscosity, which they e.g. suitable for solvent-free adhesive applications.

Such prepolymers were known to be suitable in bulk or as a solution in organic solvents for bonding plastics, in particular for laminating plastic foils, whereby customary hardeners, such as polyfunctional higher molecular alcohols, can be added (2-component systems) or surfaces with a defined moisture content can be glued directly with such available products, whereby film composites with high processing reliability can be obtained during heat sealing. In view of the otherwise unsatisfactory biodegradability of polyurethane prepolymer adhesives, it is all the more surprising that the polyurethane prepolymer adhesives of a multilayer film composite according to the invention have an equally good and excellent biodegradability and compostability as this is the case for the biodegradable goods consisting of polyester amides and / or polyester and the barrier layer made of polyvinyl alcohol.

In a particular embodiment, the compostable composite multilayer film is characterized in that the films made of polyester and / or polyester amide are coextruded together with the barrier layer with the aid of an adhesion promoter based on polyether epoxides. Although the adhesion between the barrier layer and the polyester and / or polyester amide layers applied thereon may be sufficient for many applications, this can be increased significantly by an adhesion promoter. The adhesion promoters that can be used include: those based on polyether epoxides.

As well as the potential connectivity of the film structures according to the invention to form special composites with, for example, paper, superabsorbent materials or metal layers, the multilayer films according to the invention have an excellent spectrum of applicability and, at the same time, excellent biodegradability.

The invention also relates to a method for producing fully biodegradable and compostable multilayer films of the type mentioned at the beginning.

In the method for producing well compostable composite multilayer films, a barrier layer made of polyvinyl alcohol is provided according to the invention, to which one or more film layers or layers made of a biodegradable polyester and / or polyester amide are applied on both sides. In an expedient modification of this method, the films made of a biodegradable polyester and / or polyester amide are laminated with an adhesive based on a polyurethane prepolymer. This makes it possible to combine a very simple production with a product which can satisfy all the requirements placed on a commercially available polyolefin film and also has good biodegradability, in particular rotability and compostability.

In a modified, particularly expedient modification of the method of the invention, the films of polyester and / or polyester amide are coextruded with the barrier layer with the aid of an adhesion promoter based on polyether epoxides.

Here, the adhesion promoter is used only in very small amounts and, moreover, polyether epoxy compounds are biodegradable, rot and compostable, so that either the small amount of polyether epoxide is ecologically essentially harmless or can be composted without problems.

Finally, the simple heat sealing of films and barrier layer is still possible, provided that the application does not require any particular adhesion between the individual layers of the composite film according to the invention.

The invention also relates to the use and the films mentioned above for packaging purposes, preferably in the food industry or detergent industry, medical hygiene purposes and in special composites.

According to one use according to the invention, the compostable composite multilayer film, as described herein, is a replacement for Polyolefin films are ideal for packaging purposes in the food industry. Here, their food safety is to be emphasized, their positive properties such as high transparency and tear resistance, which can be enhanced by biaxial stretching. In addition, the compostable composite multilayer film according to the invention is outstandingly suitable for use in medical hygiene areas, applications in particular as an insert in diapers or sanitary napkins being considered. As a result, in particular by replacing polyolefin films, it is possible to create a product that is completely decomposable more quickly than is the case with the hygiene articles previously available on the market.

The following examples serve to explain the subject matter of the invention in detail. First, various embodiments of compostable composite films according to the invention are described in more detail with reference to the accompanying figures.

The figures show:

FIG. 1 shows a schematic cross section through a first embodiment of a compostable composite multilayer film according to the invention, the individual layers which are close to one another being shown at a distance to improve clarity; and

FIG. 2 shows a schematic cross section through a second embodiment of the compostable composite multilayer film according to the invention, the individual layers and layers firmly connected to one another in the finished film also being shown at a distance from one another here in order to simplify the illustration and improve clarity.

In FIG. 1, 1 denotes a compostable composite multilayer film. This has a core layer or middle layer Foil layer 2 made of polyvinyl alcohol material. In the structure shown, the polyvinyl alcohol film acts as a barrier layer. Layers 3 of biodegradable goods are arranged on both the front and the back of the polyvinyl alcohol film 2. In the present example, the layers 3 and the layers 2 are connected to one another by heat sealing.

FIG. 2 represents a modification of this first embodiment according to the invention. Here too, reference number 1 denotes a compostable multilayer composite film according to the invention, which, however, in addition to the barrier layer 2 and the film layers 3 made of biodegradable goods, also has two layers 4. The layers 4 denote adhesive materials based on polyurethane prepolymer, which are used to laminate the films 3 onto the barrier film 2.

The embodiments shown in the two Figures 1 and 2 each illustrate a symmetrical structure. However, modifications of this structure are possible within the scope of the invention. The invention also includes an asymmetrical structure in which, for example, only one layer 3 is laminated onto a barrier layer 2. Finally, depending on requirements, further layers 3 or 2 can also be laminated onto the embodiment of FIGS. 1 or 2 by gluing or applied by hot coating. It is also conceivable to provide more than one barrier layer made of a PVOH.

Finally, the vapor deposition of layers 3 with metals such as aluminum is also possible.

Test method

The property of biodegradability or

Compostability of a film is defined as follows: The polymers and films to be tested are incubated in a liquid medium according to ASTM G22 (composition Table 1) with a mixture of microorganisms from garden compost with swirling (220 rpm) and air admission at 37 ° C. For this purpose, about 1 g of the polymer is inoculated into several cm ² pieces in 250 ml of nutrient salt solution in 11 Erlenmeyer flasks with 2 ml of a suspension of 10 g of garden compost with 100 ml of nutrient salt solution. Coarse parts are separated from the compost suspension beforehand using a fine sieve. The dry matter (TS) content of the inoculated amount is then about 50 mg. As a control for measuring the abiotic weight loss of the polymer sample, HgCl ₂ (500 mg / 1) is added to a batch. Other control batches contain cellulose (4 g / 1 type DP 500, Wolff, Walsrode) to check the growth with a natural substrate or are used without the addition of a C source to determine the background growth and the TS decrease in the inoculum.

Table 1: Composition of the nutrient solution according to ASTMG 22

KH ₂ PO ₄ 0.7g

K ₂ HPO ₄ 0.7g

MgSO ₄ 7H ₂ O 0.7 g

NH ₄ NO ₃ 1.0 g

NaCl 0.005g

FeSO ₄ 7H ₂ O 0.002g

Z _n SO ₄ 7H ₂ O 0.002g

MnSO ₄ H ₂ O 0.001g

H ₂ Odest 1,000g To determine the TS content of the water-soluble components (polymers or polymer residues, biomass and inoculum), the entire contents of a flask are centrifuged off, washed once in 0.05 m phosphate buffer and the insoluble residue is dried at 80 ° C. for at least 48 hours. The biomass and the pure inoculum are determined in parallel flasks. The proportion of polymer residues can be calculated by subtracting these measured variables.

The entire contents of a flask are also processed to measure the biomass. A modification of the adenosine triphosphate (ATP) determination by Lumac-3M is used for this purpose: ten minutes after the addition of the reactive reagent (Lumac), 2.5 ml of a 33% tetrabutylammonium hydroxide solution are added. This leads to a complete release of ATP from the entire biomass within 30 seconds. After this time, the ATP content can be determined according to the usual luciferin / luciferase reaction according to Lumac. To correlate the ATP content with the dry matter, a 24-hour culture of Kl. Planticola is measured, the ATP / TS ratio of which is determined beforehand.

All samples which allow biomass growth on the polymer of at least 30 mg / l within a maximum of 2 weeks under the above-mentioned conditions are designated as well compostable in the sense according to the invention.

In the sense of the invention, samples are not compostable which, under the above-mentioned conditions, allow a biomass growth of at most 15 mg / l within a maximum of 2 weeks.

The individual materials of a multilayer film according to the invention in the individual test each have good compostability according to the criteria mentioned. Fe he can be seen that in the composite the compostability the individual materials are better in themselves than in individual examinations. The multilayer films according to the invention therefore have a quasi-synergistic biological compostability.

Comparative Example 1: Polyester amide from adipic acid, butanediol and aminocaproic acid with 45% by weight ester fraction 146 g (1 mol) of adipic acid, 90 g (1 mol) of 1,4-butanediol and 131 g (0.1 mol) of 6-aminocaproic acid are combined and heated up to 120 ° C within 30 minutes. After 2 hours at this temperature, the mixture is heated to 220 ° C. and a vacuum is applied. Finally, the mixture is polymerized with an oil pump vacuum at 220 ° C. for 4 h. A light yellow product is obtained which can be granulated. The melting point according to DSC is 125 ° C. The relative viscosity (1 g% in m-cresol at 25 ° C) is 2.2. In the biological degradation test, the material shows a microbial growth of 102 mg in 14 days.

Claims

claims

1. Well compostable composite multilayer film comprising at least one barrier layer made of polyvinyl alcohol, on which one or more films are laminated on both sides by means of an adhesive and / or adhesion promoter or applied by coextrusion or hot coating, characterized in that the one or more films made of a biodegradable polyester and / or polyesteramide exist.

2. Compostable composite multilayer film according to claim 1, characterized in that the one or more films> 30 mg / 1 biomass, determined in the biological degradation test according to ASTM G 22, produce.

3. Compostable composite multilayer film according to one of the preceding claims, characterized in that the films made of polyester and / or polyester amide are laminated onto the barrier layer with an adhesive based on polyurethane prepolymer.

4. Compostable composite multilayer film according to claim 1 or 2, characterized in that the films made of polyester and / or polyester amide are coextruded together with the barrier layer with the aid of an adhesion promoter based on polyether epoxides.

5. A method for producing well compostable composite multilayer films of claims 1-4, in which at least one barrier layer made of polyvinyl alcohol is provided, on which one or more films made of a biodegradable polyester and / or polyester amide are applied on both sides.

6. The method according to claim 5, characterized in that the films are laminated with an adhesive based on a polyurethane prepolymer.

7. The method according to claim 5, characterized in that the films made of polyester and / or polyester amide are coextruded together with the barrier layer with the aid of an adhesion promoter based on polyether epoxides.

8. The method according to claim 5, characterized in that the films are thermally welded to the barrier layer.

9. Use of a well compostable composite multilayer film according to claims 1-4 as a replacement for polyolefin films for packaging purposes in the detergent industry.

10. Use of a well compostable composite multilayer film according to claims 1-4 as a replacement for polyolefin films for medical hygiene purposes, in particular as an insert in diapers or sanitary napkins.