WO2009049667A1

WO2009049667A1 - Multi-layer film and method for the production thereof

Info

Publication number: WO2009049667A1
Application number: PCT/EP2007/060984
Authority: WO
Inventors: Harald Schmidt; Christoph Hess; Johannes Mathar; Ralf Hackfort
Original assignee: Biotec Biologische Naturverpackungen Gmbh & Co. Kg
Priority date: 2007-10-15
Filing date: 2007-10-15
Publication date: 2009-04-23

Abstract

The invention relates to a multi-layer film, particularly for packaging purposes, comprising at least one first layer A and at least one second layer B, layer A comprising thermoplastic polyester and layer B comprising thermoplastic starch, and layer B does not contain any additional biologically degradable, thermoplastic polymers other than thermoplastic starch. The multi-layer film according to the invention is characterized by excellent barrier properties, a low sensitivity to moisture, and a good mechanical durability.

Description

October 15, 2007

Multilayer film and process for its production

The invention relates to a multilayer film, in particular for packaging purposes, comprising at least two layers A and B. The invention further relates to a process for the production of the multilayer film as well as packaging materials produced therefrom.

Multilayer films of the type mentioned above are well known and are used, for example, for the packaging of food and other goods. It is also necessary for the packaging of oxygen-sensitive foods that the films have a low oxygen permeability. Such films are also referred to as "barrier films". They are used, for example, in the packaging of fresh meat or fruit and vegetables, the durability of which can be considerably extended by targeted adjustment of the gas barrier, in particular the oxygen and / or water vapor barrier. The vast majority of barrier films used today in the packaging industry consist of plastics derived from petrochemicals.

For economic and environmental reasons, there is an increasing demand for suitable films made from renewable raw materials are produced and / or biodegradable.

The present invention is therefore based on the object to provide a multilayer film of the type mentioned, which has good barrier properties and which is made from renewable resources and / or biodegradable. Furthermore, the film should have sufficient mechanical strength and beyond moisture-insensitive and inexpensive and depending on the application have good transparency.

This object is achieved according to the invention by a multilayer film, in particular for packaging purposes, which comprises at least a first layer A and at least one second layer B, the layer A containing at least one thermoplastic polyester and the layer B thermoplastic starch.

Advantageous embodiments of the invention are described in the subclaims.

An essential feature of the multilayer film according to the invention is that its layer structure contains on the one hand thermoplastic polyester (layer A) and on the other hand thermoplastic starch (layer B). Surprisingly, it has been found that multilayer films containing this combination of materials have exceptionally good properties as packaging films.

The films of the invention are characterized by excellent barrier properties and have in particular a low oxygen and carbon dioxide permeability. The films also have excellent mechanical strength and low moisture sensitivity. If desired, thermoformable films with excellent transparency can also be produced with the layer structure according to the invention.

The multilayer film according to the invention is distinguished by excellent mechanical strength and can be excellently processed for the production of packaging. For example, tensile strength values according to DIN 53455 in the range 10 to 40 N / mm ² , in particular 15 to 30 N / mm ² , can be achieved with the layer structure according to the invention.

The multilayer films according to the invention are furthermore distinguished by excellent barrier properties. Thus, the multilayer film of the invention preferably has an oxygen permeability according to ASTM F 1927-98 at 23 ⁰ C, 50% rh and 400 microns film thickness of 1 to 50, especially 1.5 to 20 cm ³ / m ² d, more preferably 2 to 10 cm ³ / m ² d. Furthermore, the multilayer film according to the invention preferably has a water vapor permeability according to ASTM F 1249 at 23 ⁰ C, 75 rF and 400 microns film thickness of 1 to 100, especially 2 to 10 cm ³ / m ² d. Finally, the multilayer film according to the invention preferably has a carbon dioxide permeability according to ASTM D 1434 at 23 ^° C., 50 rF and 400 μm film thickness of 0.5 to 5, in particular 1 to 2.5 cm ³ / m ² d. Due to the above-mentioned barrier properties is the invention Multi-layer film ideal as a barrier film for packaging purposes.

The multilayer film of the invention may have any desired thickness, the thickness of the film significantly depending on the intended application and the desired film properties. For packaging purposes, the film preferably has a total thickness of 10 to 2000 .mu.m, in particular 100 to 2000 .mu.m, more preferably 200 to 800 .mu.m, wherein the individual layers preferably each have a thickness of 5 to 1000 .mu.m, in particular 10 to 1000 .mu.m preferred 20 to 700 microns, more preferably 10 to 700 microns possess. Multilayer-based blown films preferably have a total thickness of 30 to 100 μm.

The packaging produced from the multilayer films of the invention may have any thickness. From the multilayer films of the invention produced trays for the packaging of food preferably have a total thickness of 350 to 400 .mu.m, the corresponding lidding films preferably has a thickness of 30 to 100 microns.

The multilayer film according to the invention comprises at least one layer A and at least one layer B. In addition, the film according to the invention may comprise any further layers. According to a particularly preferred embodiment of the invention, the multilayer film according to the invention comprises at least two layers A and one layer B, the layer B preferably being arranged between the two layers A. is. Such a multilayer film has the following layer structure: Layer A - Layer B - Layer A.

With such a layer structure, the layer A can adjoin the layer B directly. However, it is also possible to provide one or more further layers as an intermediate layer, such as one or more adhesion promoter layers H. Such adhesion promoter layers H are known to the person skilled in the art and preferably consist of block copolymer. Adhesion promoter layer H preferably directly adjoins layer A on its one surface side and directly on layer B on its other surface side and serves to improve the adhesion between layers A and B. The following layer structure is given as an example of a multilayer film according to the invention containing adhesion promoter layers Layer A - Adhesive layer H - Layer B - Adhesive layer H - Layer A.

Depending on the intended application, the film may comprise further layers A and / or B. It is also possible, for example, a multilayer film with the following layer structure: Layer A - Layer B - Layer A - Layer B - Layer A. Due to the double-provided layer B, such a film has even better barrier properties. In addition, an adhesion promoter layer H can be arranged between the individual layers. Shoot A

According to the invention, it is provided that the layer A of the multilayer film contains at least one thermoplastic polyester. The selection of the thermoplastic polyester is not limited. Both aliphatic and aromatic polyesters and their copolymers and / or mixtures are suitable.

Thermoplastic polyesters are well known and described, for example, in Oberbach et al. "Saechtling plastic paperback", 29th ed., Hanser-Verlag, Munich (2004) described.

According to a preferred embodiment of the invention, the thermoplastic polyester contained in layer A is a biodegradable thermoplastic polyester according to EN 13432.

In particular, the thermoplastic polyester may be a biopolymer based on one or more hydroxycarboxylic acids.

Particularly suitable thermoplastic polyesters according to the invention are poly (hydroxyalkanoates) (PHA), polyalkylene succinates (PAS), e.g.

Polybutylene succinate (PBS), polyalkylene terephthalate (PAT) such as poly (ethylene terephthalate) (PET), aliphatic-aromatic copolyester and / or poly-[p-dioxanone] (PPDO), and copolymers and blends thereof. Also conceivable is the use of biopropanediol (Bio-PDO) - polyester alone or in combination with other thermoplastic polyesters. According to a particularly preferred embodiment of the invention, layer A contains at least one polyhydroxyalkanoate (PHA) as thermoplastic polyester. Examples of suitable polyhydroxy [hydroxyalkanoates] are poly (hydroxyethanoate) such as polyglycolic acid (PGA), poly (hydroxypropanoate) such as polylactic acid or polylactide (PLA), poly [hydroxybutanoate] such as polyhydroxybutyric acid (PHB), poly (hydroxypentanoate) such as Polyhydroxyvalerate (PHV) and / or poly (hydroxyhexanoate) such as polycaprolactone (PCL), as well as copolymers and mixtures thereof.

A thermoplastic polyester which is particularly suitable according to the invention is polylactic acid or polylactide (PLA). PLA is a biodegradable polyester that can be prepared by a multi-step synthesis of sugar. In this case, sugar is fermented to lactic acid and this polymerized usually via the intermediate of the dilactide to PLA. PLA is transparent, crystalline, rigid, has high mechanical strength and can be processed by conventional thermoplastic processes. Suitable polymers based on PLA are described, for example, in US Pat. Nos. 6,312,823, 5,142,023, 5,274,059, 5,274,073, 5,258,488, 5,357,035, 5,338,822 and 5,359 026. According to the invention PLA can be used both as a virgin material and in the form of recycled material.

A further particularly suitable thermoplastic polyester is polyhydroxybutyric acid (PHB). PHB is known in the nature of numerous bacteria as storage and Reservestoff be formed. Accordingly, the technical production of PHB can be carried out by bacteria. Suitable polymers based on PHB are described, for example, in US Pat. Nos. 4,393,167, 4,880,592 and 5,391,423.

Suitable materials for layer A of the present invention are, in particular, the "aliphatic polyester polymers" described in US Pat. No. 6,312,823, the description of which is incorporated herein by reference and which is the subject of the present disclosure.

Suitable copolymers or mixtures of said thermoplastic polyesters are, for example, polycaprolactone / polybutylene succinate mixtures or copolymers (PCL / PBS), polyhydroxybutyric acid / polyhydroxyvalerate copolymers (PHB / PHV),

Polyhydroxybutyrate valerate (PHBV), polybutylene succinate / polybutylene adipate blends or copolymers (PBS / PBA), polyethylene terephthalate / polyethylene succinate copolymers (PET / PES) and / or polybutylene terephthalate / polybutylene adipate copolymers (PBT / PBA).

Layer A may contain other components besides thermoplastic polyester. In particular, the layer A may consist of a mixture of different polymers. Layer A may also contain conventional additives such as processing aids, plasticizers, stabilizers, antiflams and / or fillers. Further, the layer A, a bonding agent can be added, which serve in particular to improve the adhesion between layer A and B. can. Preferably, layer A contains thermoplastic polyester in an amount of at least 20% by weight, in particular at least 30% by weight or at least 40% by weight, more preferably at least 50% by weight or at least 60% by weight, even more preferably at least 80% by weight. %, and most preferably at least 90% by weight. or at least 95% by weight, based on the total weight of layer A. More preferably, layer A consists essentially of thermoplastic polyester.

Processing aids which can be used according to the invention are generally known to the person skilled in the art. In principle, all processing aids are suitable which are suitable for improving the processing behavior of the polymers used, in particular their flow behavior in the extruder.

Particularly suitable processing aids according to the invention are polymers which have a polymer backbone which is functionalized or modified with reactive groups. Such polymers are also referred to as "functionalized polymers". The processing aids used according to the invention preferably have a molecular weight of up to 200,000, in particular up to 100,000.

In principle, all polymers which are miscible with at least one polymer component (eg PLA) from at least one layer of the multilayer film (eg layer A) are suitable as the polymer backbone for the processing aid. Possible polymer scaffolds for the processing aid are, for example Ethylene vinyl acetate (EVA), polyethylene (PE), polypropylene (PP), ethylene acrylates, polyesters (eg, PLA), as well as blends and / or copolymers (eg, polyethylene-methyl acrylate copolymer or polyethylene-butyl acrylate copolymer) thereof.

Suitable reactive groups for the processing aids used according to the invention are, in principle, all reactive groups which are suitable for chemically reacting with at least one polymer component (for example TPS) from at least one layer of the multilayer film (for example layer B). Suitable reactive groups are, for example, maleic anhydride and / or other anhydrides of suitable carboxylic acids or dicarboxylic acids or other polybasic acids. Preferably, the backbone having reactive groups in an amount of 0.01 to 7 wt.%, Particularly 0.1 to 5 wt.%, More preferably 0.3 to 4 wt.%, Based on the total composition of the processing aid , modified. Preferably, the reactive groups are grafted onto the polymer backbone.

Such processing aids are commercially available, for example, under the trade names Lotader® and Orevac® (Arkema Inc., USA), Fusabond®, Biomax strong® and Bynel® (DuPont, USA) and Plexar® (Equistar Chemical Company, USA).

The processing aid is preferably used in an amount of up to 5% by weight, especially 0.01 to 2% by weight, more preferably 0.1 to 1.5% by weight, still more preferably 0.2 to 1% by weight, and most preferred in an amount of less than 1% by weight, based on the total composition of the respective layer. According to a particularly preferred embodiment of the invention, the processing aid used for layer A is a maleic anhydride-modified polymer based on ethylene, in particular a maleic anhydride-modified polyethylene-alkyl acrylate copolymer.

According to the invention, it has been found that not only the processability of the polymers used {flow behavior in the extruder, homogeneity of the melt) can be improved by the use of said processing aids, but also a significantly improved bond between the layers can be achieved.

Layer B

According to the invention, it is further provided that layer B of the multilayer film contains thermoplastic starch.

Thermoplastic starch or thermoplastically processable starch (TPS) is generally known and described in detail, for example, in the publications EP 0 397 819 B1, WO 91/16375 A1, EP 0 537 657 B1 and EP 0 702 698 B1. With a market share of about 80 percent, thermoplastic starch is the most important and common representative of bioplastics. Thermoplastic starch is generally made from native starch such as potato starch. To make native starch thermoplastically processable, their plasticizers such as sorbitol and / or Added glycerin. Thermoplastic starch is characterized by a low water content, which is preferably less than 6% by weight, based on the total weight of the thermoplastic starch. Furthermore, thermoplastic starch is characterized by its preferably substantially amorphous structure.

As the thermoplastic starch, it is preferable to use a polymeric material obtainable by homogenizing a mixture containing

From 40 to 85% by weight of starch and / or starch derivative,

- 15 to 55 wt.% Plasticizer

while supplying thermal and / or mechanical energy and adjusting the water content of the mixture to less than about 12% by weight.

The mixture may contain, in addition to the main constituents starch or starch derivative, plasticizer and water, also suitable additives, fillers and / or processing aids, as described in more detail above in connection with layer A. According to a preferred embodiment of the invention, the mixture contains no synthetic, according to EN 13432 biodegradable thermoplastic polymer. According to another preferred embodiment, no additional thermoplastic polymeric material is added to the mixture at all. The total amount of the additives and processing aids contained in the mixture is preferably not more than 5% by weight, especially not more than 3% by weight, more preferably not more than 2% by weight. As fillers, inorganic fillers are preferably used. If a polymeric material is used as the additive, filler and / or processing agent, it is preferably non-thermoplastic and / or not biodegradable according to EN 13432.

According to a preferred embodiment of the invention, the mixture for producing the thermoplastic starch contains 45 to 80% by weight, in particular 50 to 75% by weight, preferably 55 to 72% by weight, more preferably 58 to 70% by weight, most preferably 59 up to 67% by weight of starch and / or starch derivative. Further, the mixture for producing the thermoplastic starch preferably contains 20 to 50% by weight, especially 25 to 45% by weight, preferably 28 to 42% by weight, more preferably 30 to 40% and most preferably 35 to 38% by weight of plasticizer.

The starch used for the production of thermoplastic starch or the starch derivative are preferably selected from native potato starch, tapioca starch, rice starch and corn starch.

The plasticizer or plasticizer for producing the thermoplastic starch is preferably selected from the group consisting of ethylene glycol, propylene glycol, glycerol, 1, 4-propanediol, 1, 2-butanediol, 1,3-butanediol, 1, 4-butanediol, 1 , 5-pentanediol, 1,5-hexanediol, 1,6-hexanediol, 1,2,6-hexanetriol, 1,3,5-hexanetriol, neopentyl glycol, sorbitol acetate, sorbitol diacetate, sorbitan monoethoxylate, sorbitol diethoxylate, sorbitol hexaethoxylate, sorbitol dipropoxylate, aminosorbitol, trihydroxymethylaminomethane , Glucose / PEG, the Reaction product of ethylene oxide with glucose, trimethylolpropane monoethoxylate, mannitol monoacetate, mannitol monoethoxylate, butylglucoside, glucose monoethoxylate, α-methylglucoside, the sodium salt of

Carboxymethyl sorbitol, polyglycerol monoethoxylate, erythritol, pentaerythritol, arabitol, adonite, xyitol, mannitol, iditol, galactitol, alite, sorbitol, polyhydric alcohols in general, glycerol esters, formamide, N-methylformamide, DMSO, mono- and diglycerides, alkylamides, polyols, trimethylolpropane, Polyvinyl alcohol having 3 to 20 recurring units, polyglycerols having 2 to 10 recurring units and derivatives and / or mixtures thereof. The plasticizer further preferably has a solubility parameter (HiIdebrand parameter) d (SI) of 30-50 MPa ¹ ^"2 within a temperature range of about 150 to 300 ^° C. Particularly suitable plasticizers are glycerol and / or sorbitol.

According to a preferred embodiment of the invention, layer B is obtained by adding at least partially of thermoplastically processable starch having a water content of less than 6% by weight, preferably less than 5% by weight, in particular less than 4.5% by weight _; more preferably less than 4% by weight, based on the total composition of the starch.

In the preparation of the thermoplastic starch, the water content of the mixture is preferably 0.5 to 12% by weight, more preferably 1 to 7% by weight, more preferably 1 to 6% by weight, still more preferably 1.5 to 4.5% by weight. %, based on the total composition of the thermoplastically processable starch adjusted. _ 1 ζ

It has been found that when thermoplastically processable starch with the stated water contents (in particular <6% by weight) is used, improved flow behavior in the extruder and reduced microbubble formation in the layer can be achieved.

However, the thermoplastically processable starch used preferably has a water content of at least 1% by weight, in particular at least 1.5% by weight, since otherwise thermally induced oxidation processes and, correspondingly, unwanted discoloration of the product can easily occur. Conversely, with a water content greater than about 6% by weight, increased microbubble formation can easily occur, which is also undesirable.

The homogenization of the starch-containing mixture in the production of the thermoplastic starch is preferably carried out by the action of shear forces on the mixture. Suitable homogenization methods are, for example, dispersing, stirring, kneading and / or extruding. According to a particularly preferred embodiment of the invention, the homogenization is carried out by extruding the mixture in an extruder. When homogenizing or extruding, the mixture is preferably heated to a temperature of 90 to 200 ⁰ C, in particular 120 to 180 ⁰ C, more preferably 130 to 160 ⁰ C, is heated. The water content of the mixture is preferably adjusted during homogenization or extrusion. The adjustment of the water content, for example, by degassing of the mixture, in particular by degassing of the melt, take place. The thermoplastic starch contained in layer B is preferably characterized in that a film produced from the thermoplastic starch has a tensile strength according to DIN 53455 of 2 to 10 N / mm ² , in particular from 4 to 8 N / mm ² 'and / or an elongation at break according to DIN 53455 from 80 to 200%, in particular from 120 to 180%.

According to a further preferred embodiment of the invention, the thermoplastic starch is obtainable by: (a) mixing starch and / or a starch derivative with at least 15% by weight of a plasticizer such as glycerine and / or sorbitol, (b) supplying thermal and / or or mechanical energy and (c) at least partially removing the natural water content of the starch or starch derivative to a water content of less than 6% by weight.

Layer B may contain other components in addition to thermoplastic starch. In particular, layer B may contain conventional additives such as plasticizers, processing aids, stabilizers, antiflams and / or fillers as described above for layer A. In particular, layer B may contain suitable processing aids, as described in more detail above in connection with layer A. Further, the layer B, an adhesion promoter can be added, which can serve in particular to improve the adhesion between layer B and A. If the other components contained in layer B are polymeric materials, these are preferably not Thermoplastic and / or not biodegradable according to EN 13432.

Preferably, layer B contains thermoplastic starch in an amount of at least 80 weight percent and most preferably at least 90 weight percent, at least 90.5 weight percent or at least 95 weight percent, based on the total weight of layer B. More preferably layer B consists essentially of thermoplastic starch, ie it is not a starch blend of starch and one or more other polymers, but only thermoplastic starch. According to a preferred embodiment of the invention, therefore, layer B contains, in addition to thermoplastic starch, no further biodegradable thermoplastic polymers according to EN 13432. According to a further preferred embodiment, layer B contains, in addition to thermoplastic starch, no further thermoplastic polymers.

According to one embodiment of the invention, both layer A and layer B consist essentially of thermoplastic polyester or of thermoplastic starch.

A particularly preferred according to the invention

Multilayer film is a three-layer film of type A-B-A, wherein layer A consists of a polymer based on PHA (in particular PLA) and layer B consists of a polymer based on thermoplastic starch.

The production of the multilayer film according to the invention can be carried out by any desired production methods, for example calendering, extrusion or else by casting respectively. Such preparation methods are generally known to the person skilled in the art and are described, for example, in J. Nentwig "Kunststoff-Folien", 2nd ed., Hanser Verlag, Berlin (2000), pages 39 to 63.

The multilayer films according to the invention are preferably formed by extrusion, in particular by blown film extrusion, flat film extrusion, cast film extrusion and / or blow molding. These production methods are generally known to the person skilled in the art. A detailed description of these methods of preparation can be found, for example, in J. Nentwig "Kunststoff-Folien", 2nd Ed., Hanser Verlag, Berlin (2000), pp. 45 to 60, which are expressly incorporated by reference and made the subject of the present disclosure becomes. The preparation examples described therein can also be applied to the production of the multilayer film according to the invention. In this case, both individual and all layers of the film can be formed by extrusion. Preferably, all layers of the film are formed by extrusion.

According to a particularly preferred embodiment of the invention, the multilayer film according to the invention is formed by coextrusion. Such coextrusion or multilayer extrusion processes are well known to those skilled in the art. A description of the coextrusion process can be found, for example, in J. Nentwig "Kunststoff-Folien", 2nd Ed., Hanser Verlag, Berlin (2000), pp. 58 to 60, to which expressly incorporated and the subject of the present disclosure is done. The ones described there Production examples are also transferable to the production of the multilayer film according to the invention.

Accordingly, the present invention further relates to a method for producing a multilayer film, wherein the multilayer film comprises at least one layer A, at least one layer B and optionally further layers, in particular optionally at least one further layer A, characterized by the following steps:

(a) extruding a material containing at least one thermoplastic polyester into a film, thereby forming at least one layer A;

(b) extruding a material containing melt processable starch into a film to form at least one layer B; and

(c) at least partially laminating the individual layers, thereby forming a multilayer film.

The individual process steps (a) to Cc) are preferably carried out simultaneously in the coextrusion process, in particular by blown film extrusion, flat film extrusion, cast film extrusion and / or blow molding.

After production, the multilayer film can be cut into parts of the desired dimensions, depending on the intended use. The cut-to-cut cut remnants can at least partially the material for the extrusion of layer B in step (b) are fed and thus serve as a recyclate.

Finally, the invention relates to a packaging for foodstuffs, in particular for fresh meat, cheese, fresh fruit or vegetables, baked goods, drinks and / or coffee, which comprises the multilayer film according to the invention.

The invention will be described in more detail below with reference to exemplary embodiments.

The single figure shows an example of a sectional view of a multilayer film according to the invention with a layer structure of the type A-B-A.

example 1

Production of Thermoplastic Starch for the Middle Layer (Layer B)

A mixture of native potato starch (63% by weight), glycerin (23% by weight) and sorbitol (14% by weight) was charged to a twin-screw extruder. The mixture was intensively mixed in the extruder in a temperature range of 130 to 16O ⁰ C, wherein the melt was simultaneously degassed to remove the mixture of water. This results in a homogeneous melt which can be withdrawn and granulated. The water content of the homogenized in the manner described, melt processable mass is between 3 and 4 wt.%. By blending and homogenizing the native starch with glycerine and sorbitol, crystalline structures of the starch are broken up so that the resulting thermoplastic starch is largely amorphous. In contrast to this, destructured starch, which can be prepared from native starch, for example by heating in water, still has a certain crystallinity.

Example 2

Production of a three-layer film (flat film)

A three-layer film (A-B-A) consisting of polylactic acid (PLA) / thermoplastic starch (TPS) / PLA was prepared. As the starch, the thermoplastic glycerol / sorbitol starch having a water content of 3 to 4% by weight prepared in Example 1 was used. The polylactic acid used (PLA granules, Nature Works) had a D content of 1.4%.

The two materials (PLA and TPS) were simultaneously driven to a three-layer film with a coextrusion line. For this purpose, the TPS was melted in a single-screw extruder with an L / D ratio of 33 in a temperature range of 140 to 19O ⁰ C. The extruder ran at a speed of 100 rpm and, at a throughput of 25 kg / h, produced a melt pressure of 130 bar. In parallel, a second single-screw extruder was (L / D = 30, temperature 200 ⁰ C, speed 20 rev / min, melt pressure 100 bar, throughput 10 kg / h) melted PLA (Melting temperature 177 ⁰ C). Both melts were combined in a coex-adapter, wherein the PLA melt stream was split and fed in half over and under the starch layer (-> outer layers A). The three-layer system thus produced was drawn off through a slot die (T = 190 ^° C.) by means of temperature-controllable rolls (T = 25 ^° C., V = 3 m / min), cut to width and wound into a roll.

The total thickness 400 .mu.m of the three-layer film thus produced was composed of 2 × 50 μm (outer layers A) and 300 μm (middle layer B).

The following gas permeabilities were determined for the three-layer film:

Oxygen (O ₂ ): 15.5 cπvVm ² d carbon dioxide (CO ₂ ): 2.1 cm ³ / m ² d

Example 3

Production of a Three-Layer Film According to Exemplary Embodiment 2 with Premixed Middle Layer (Layer B)

Analogously to the procedure described in Example 2, a three-layer film ABA with PLA was produced as outer layer (A). For the middle layer (B), a premix of the TPS granules prepared according to Example 1 (90% by weight) and PLA granules (10% by weight) was prepared, fed to the single-screw extruder and melted at 150 to 19O ⁰ C. The extruder for the middle class was running at 100 rpm at a throughput of 25 kg / h and a melt pressure of 120 bar. PLA melted (melt temperature 175 ⁰ C) - parallel to this was in the second single-screw extruder (flow rate 10 kg / h 200 ⁰ C, speed 20 rev / min, melt pressure 130 bar, temperature 185). Both melts were combined in the coex-adapter, wherein, as described in Example 2, the PLA melt stream was divided and each half over or under the layer of starch was performed (-> outer layers A). The three-layer system thus produced was drawn off through a slot die (T = 19O ⁰ C) by means of temperature-controllable rolls (T = 35 ° C., V = 2.7 m / min), cut to width and wound into a roll.

The three-layered film exhibited a more severe haze compared to Embodiment 2, but a more stable bond between the outer layers (A) and the middle layer (B) than that in Embodiment 2 was obtained.

Example 4

Preparation of a modified thermoplastic starch for the middle layer (layer B)

A mixture of native potato starch (56.5 wt.%), Glycerol (20.5%), sorbitol (13%) and PLA (10%) was charged to a twin-screw extruder. The mixture was in the extruder in a temperature range of 130 to 16O ⁰ C intensively mixed, wherein the melt was simultaneously degassed to remove the mixture of water. Similar to Embodiment 1, a homogeneous melt is formed which can be withdrawn and granulated. The water content of the homogenized in the manner described, melt processable mass is between 3 and 4% by weight.

Example 5

Production of a Three-Layer Film According to Application Example 2 with Modified Thermoplastic Starch in the Middle Layer (Layer B)

Analogously to the procedure described in Application Examples 2 and 3, a three-layer film ABA with PLA as outer layer (A) was produced. For the middle layer (B), the thermoplastically processable starch / PLA compound described in Example 4 was fed to the extruder and melted at 140 to 195 ^° C. The extruder for the middle layer ran at 90 rpm at a throughput of 25 kg / h and a pressure of 115 bar.

Parallel to this was in the second single-screw extruder (temperature 190 - 200 ⁰ C, speed 25 U / min, melt pressure

120 bar, throughput 10 kg / h) PLA melted (melt temperature 180 ^° C.).

Both melts were combined in the coex-adapter, wherein, as described in the embodiments 2 and 3, the Split PLA melt flow and half each was passed over or under the starch layer (-> outer layers A). The three-layer system thus produced was drawn off through a slot die (T = 185 ° C.) by means of temperature-controllable rolls (T = 35 ° C., V = 3.1 m / min), cut to width and wound into a roll.

The total thickness 400 μm of the three-layer film thus produced was composed of 2 × 50 μm (outer layers A) and 300 μm (middle layer B).

The three-layered film showed more haze in comparison with the patterns made in Embodiments 2 and 3, but a more stable bond between the outer layers A and the middle layer B was obtained in comparison with Embodiments 2 and 3.

Example 6

As in Example 2, however, the polylactic acid (PLA) for the outer layer became an ethylene / methyl acrylate polymer functionalized with about 3% by weight of maleic anhydride in an amount of about 1% by weight, based on

Total composition of the PLA layer, added. The three-layer film thus obtained had an increased bond between the individual layers compared to the product described in Example 2.

Example 7

Production of a three-layer film (blown film) A three-layer film (ABA) consisting of polylactic acid (PLA) / thermoplastic starch (TPS) / PLA was produced. As the starch, the thermoplastic glycerol / sorbitol starch having a water content of 3 to 4% by weight prepared in Example 1 was used. The polylactic acid used (PLA granules, Nature Works) had a D content of 1.4%.

The two materials (PLA and TPS) were simultaneously driven to a three-layer film with a coextrusion line. For this purpose, the TPS was melted in a single-screw extruder (Dr. Collin 0 45 × 25 D) in a temperature range from 140 to 160 ^° C. The extruder ran at a speed of 20 rpm and, at a throughput of about 7 kg / h, produced a melt pressure of 130 bar. In parallel, in a second single-shaft extruder (Dr. Collin 0 30 x 25 D, temperature 160-190 ⁰ C, speed 60 rev / min, melt pressure 140 bar, throughput 15 kg / h) was melted PLA. Both melts were combined in an annular nozzle (three-layer nozzle 0 80 mm, annular gap 1.1 mm), wherein the PLA melt stream was split and fed in half over and under the starch layer (-> outer layers A). The three-layer system thus produced was with a blow-up ratio of 3.5 and a speed of about 4.5 m / min as a hose with a total film thickness of about 50 microns and a lying width of 325 mm on each a chromed and rubberized roller (width each 400 mm) and wound into a roll. The percentage thickness ratio of the resulting multilayer film ABA was found to be 20-60-20. Example 8

As in Example 7, however, to the outer layer, an ethylene / methyl acrylate polymer functionalized with about 3 weight percent maleic anhydride in an amount of about 1 weight percent, based on the total composition of the PLA layer, was added to the polylactic acid (PLA) , The three-layer film thus obtained had an increased interconnection between the individual layers compared to the product described in Example 7.

Example 9

Like Example 8, however, the polylactic acid (PLA) for the outer layer was additionally added 5 wt.%, Based on the total composition of the PLA layer, of aliphatic / aromatic copolyester (ECOFLEX® from BASF AG). The system thus obtained had a better processability compared to the formulation according to Example 13.

Example 10

Procedure according to Example 7, but using a thermoplastic glycerol / sorbitol starch prepared according to Example 1 was used with a water content of about 2.5 wt.%. The system thus obtained had improved extrudability in the extruder and less bubbling in the middle layer than Example 7. The invention has been described above by way of exemplary embodiments by way of example. It is understood that the invention is not limited to the described embodiments. Rather, various modifications and modifications are possible for the person skilled in the art within the scope of the invention, and the scope of protection of the invention is defined in particular by the following claims.

Claims

October 15, 2007Patent claims

1. multilayer film, in particular for packaging purposes, comprising at least a first layer A and at least a second layer B, wherein the layer A thermoplastic polyester and the layer B contains thermoplastic starch, wherein the layer B in addition to thermoplastic starch contains no further biodegradable thermoplastic polymer.

2. Multilayer film according to claim 1, characterized in that the thermoplastic polyester contained in the layer A is a biodegradable according to EN 13432 thermoplastic polyester.

3. Multilayer film according to one of the preceding claims, characterized in that the thermoplastic polyester is a biopolymer based on one or more polyhydroxycarboxylic acids.

4. Multilayer film according to one of the preceding claims, characterized in that the thermoplastic polyester is selected from the group consisting of poly (hydroxyalkanoates) (PHA), poly (alkylene succinates) (PAS), such as e.g. Poly (butylene succinate) (PBS),

Poiy [alkylene terephthalate] (PAT) such as Poly (ethylene terephthalate (PET), aliphatic-aromatic copolyesters and poly (p-dioxanone) (PPDO), and copolymers and mixtures thereof.

5. Multilayer film according to claim 4, characterized in that the poly (hydroxyalkanoate) (PHA) is selected from the group consisting of

Poly (hydroxyethanoate) (eg polyglycolic acid, PGA), poly (hydroxypropanoate) (eg polylactic acid, polylactide, PLA), poly (hydroxybutanoate) (eg polyhydroxybutyric acid, PHB), polyhydroxypentanoate (eg polyhydroxyvalerate, PHV) and polyhydroxyhexanoate (eg polycaprolactone, PCL) as well as copolymers and mixtures thereof.

6. Multilayer film according to one of the preceding claims, characterized in that the layer B is obtained at least partially starting from thermoplastically processable starch having a water content of less than 6 wt.%, Preferably less than 3 wt.%, Based on the

Total composition of strength.

7. Multilayer film according to one of the preceding claims, characterized in that the layer B contains a thermoplastic starch which is characterized in that a film prepared from the thermoplastic starch has a tensile strength according to DIN 53455 of 2 to 10 N / mm ² , in particular of 4 to 8 N / mm ² 'and / or an elongation at break according to DIN 53455 of 80 to 200%, in particular from 120 to 180%.

8. Multilayer film according to one of the preceding claims, characterized in that the thermoplastic starch is obtainable by (a) mixing starch and / or a starch derivative with at least 15% by weight of a plasticizer, such as, for example, glycerol and / or sorbitol, (b) Supplying thermal and / or mechanical energy and

(c) at least partially removing the natural water content of the starch or starch derivative to a water content of less than 6% by weight.

9. Multilayer film according to one of the preceding claims, characterized in that the layer A consists essentially of thermoplastic polyester and / or the layer B consists essentially of thermoplastic starch.

10. multilayer film according to one of the preceding

Claims, characterized in that the film has a total thickness of 100 to 2000 .mu.m, in particular 200 to 800 .mu.m.

11. Multilayer film according to one of the preceding claims, characterized in that the individual layers each have a thickness of 10 to 1000 .mu.m, in particular 10 to 700 .mu.m.

12. Multilayer film according to one of the preceding claims, characterized in that the film is a three-layer film with the following layer structure: Layer A - Layer B - Layer A.

13. Multilayer film according to one of the preceding claims, characterized in that between the layer A and the layer B at least one adhesion promoter layer H, in particular a primer layer H of block copolymer, is provided.

14. Multilayer film according to one of the preceding claims, characterized in that the film is a three-layer film having the following layer structure: Layer A - Adhesive layer H - Layer B - Adhesive layer H - Layer A.

15. Multilayer film according to one of the preceding claims, characterized in that the film has a tensile strength according to DIN 53455 of 10 to 40, in particular 15 to 30 N / mm ² .

16. Multilayer film according to one of the preceding claims, characterized in that the film has an oxygen permeability according to ASTM F 1927-98 at 23 ° C, 50% RH and 400 microns film thickness of 1 to 50, especially 1.5 to 20 cm ³ / m ² d.

17. Multilayer film according to one of the preceding claims, characterized in that the film has a water vapor permeability according to ASTM F 1249 at 23 ° C, 75 rF and 400 microns film thickness of 1 to 100, in particular 2 to 10 cm ³ / m ² d.

18. Multilayer film according to one of the preceding claims, characterized in that the film has a carbon dioxide permeability according to ASTM D 1434 at 23 ° C, 50 rF and 400 microns film thickness of 0.5 to 5, in particular 1 to 2.5 cm ³ / m ² d.

19. Multilayer film according to one of the preceding claims, characterized in that at least one layer of the film is formed by extrusion, in particular by blown film extrusion, flat film extrusion, cast film extrusion and / or blow molding.

20. Multilayer film according to one of the preceding claims, characterized in that all layers of the film by extrusion, in particular by blown film extrusion, flat film extrusion and / or blow molding, is formed.

21. Multilayer film according to one of the preceding claims, characterized in that the film is formed by coextrusion.

22. A process for producing a multilayer film according to one of the preceding claims, wherein the multilayer film comprises at least one layer A, at least one layer B and optionally further layers, in particular optionally at least one further layer A, characterized by:

(a) extruding a material containing at least one thermoplastic polyester a film, whereby at least one layer A is formed;

23. The method according to claim 22, characterized in that the method steps (a) to (c) are carried out simultaneously in the coextrusion process, in particular by blown film extrusion,

Flat film extrusion, cast film extrusion and / or blow molding,

24. The method according to claim 22 or 23, characterized in that the multi-layer film is cut depending on the application after its production in parts with the desired dimensions.

25. The method according to claim 24, characterized in that the resulting cut at the cutting residues is at least partially supplied to the material for the extrusion of layer B in step (b).

26. Packaging for food, in particular for fresh meat, bakery products, cheese, fresh fruit or vegetables, drinks and / or coffee, comprising a multilayer film according to one of claims 1 to 24.