EA045734B1 - METHOD FOR PRODUCING MULTILAYER COMPOSITE FILM, MULTILAYER COMPOSITE FILM AND ITS APPLICATION - Google Patents

Description

Field of technology

The present application relates to a co-extruded and biaxially stretched multilayer film, which can be used, for example, as packaging materials, in particular for food products, as well as a method for its production and its use, preferably for the packaging of food products, delicacies or liquid or solid , in particular, powdered goods. In addition, the present application also relates to laminated multilayer films and corresponding production methods.

State of the art and problem statement

On the one hand, laminated multilayer films are known from the prior art, which are excellent packaging materials. Thus, laminates consisting of at least two or three or even more layers, manufactured independently of each other, are widespread in the packaging market. Basically, a distinction is made between so-called duplex laminated films and so-called triplex laminated films. Duplex laminated films are solution-extruded or blown films, including 5-, 7-, or 9-layer barrier films, that are laminated (bonded) together in a separate process with a dual-base polyethylene terephthalate (PET), polyamide (PA) film. or polypropylene (PP), also produced separately. Until now, the combination of desired and/or required properties could only be achieved with these films, which are manufactured and laminated in separate, sequential process steps. Thus, two of the required properties (tightness and impermeability to oxygen or aromatic substances) are achieved thanks to an extruded single or multi-layer film, while other properties such as printability, heat or heat resistance and mechanical strength are achieved thanks to a separate biaxially stretched film . In addition, the impermeability, in particular to oxygen, is usually achieved or increased also by applying a metal layer (metallization), carried out in an additional technological step.

Examples of duplex films widely available on the market.___________

film type oxygen tightness BORR/PE no/low VORA/RE no/low VORET/RE no/low V OPP/ metallization/PE due to metallization VORA/metallization/PE due to metallization VORET/metallization/PE due to metallization BOPET/PE-HV-EVOH-HV-PE due to a barrier layer, for example EVOH BOPET/PE-HV-PA-EVOH-PA-HV-PE due to a barrier layer, for example EVOH duplex film heat resistance / melting resistance of the outer layer printability shrinkage at 90°C BORR/met/PE 164°С 32 dynes/cm (32 10' ³ N/m) 1-2% VORET/met./RE 250°С 43 dynes/cm (43 10' ³ N/m) 0-1% BOPET/5-layer barrier film (PE/HV/EVOH/HV/PE) 250°С 43 dynes/cm (43 10' ³ N/m) 0-1% BOPET/7-layer barrier film (PE/HV/PA/EVOH/PA/HV/PE) 250°C 43 dynes/cm (43 10 ³ N/m) 1-2%

The situation is similar with triplex laminated films, and here the combination of desired and/or required properties is achieved with three separately produced films, which are later laminated (glued) to each other.

Here, a biaxially stretched film of PET, PA or PP is laminated to a separate aluminum foil, and this composite is in turn laminated to an extruded solution-cast or blown film.

Here, extruded cast or blown film takes on the task of sealing, aluminum foil takes on the task of barrier, and biaxially drawn film takes on the task of optimal printability, heat resistance and mechanical strength. The disadvantage of laminated films, however, is that their production is naturally complex, resource-intensive and expensive, and the composite film as a whole is often very thick, since a large number of films must first be manufactured individually, and then they have to be glued together over several successive process steps using hot melt adhesive or liquid adhesive to ultimately obtain a laminated multilayer film.

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Examples of triplex films widely available on the market.

film type oxygen tightness BOPP/Alu/PE due to aluminum foil BOPA/Alu/PE due to aluminum foil BOPET/Alu/PE due to aluminum Yulgi triplex film heat resistance / melting temperature of the outer layer printability shrinkage at 90°C BOPP/Alu/PE 164°С 32 dynes/cm (32 -10“ ³ N/m) 0% BOPA/Alu/PE 220°С 43 dynes/cm (43 10' ³ N/m) 0% BOPET/Alu/PE 250°C 43 dynes/cm (43 10 ³ N/m) 0%

Known duplex and triplex films are shown in FIG. 1-6.

On the other hand, multilayer films obtained by coextrusion and biaxial stretching are known from the prior art. The production processes used for this make it possible to obtain a multilayer film in just one technological operation by coextrusion, while subsequent gluing/lamination of individual film layers and the associated disadvantages are completely eliminated. At most, the coextruded raw multilayer film is stretched along two axes to impart the desired combination of properties (heat sealability, heat resistance, barrier properties, mechanical strength, printability). In addition to sealing, most of the required properties such as mechanical strength, heat resistance, printability and barrier properties (mainly impermeability to oxygen or gases) are achieved through the use of raw materials such as PET, PA, ethylene vinyl alcohol copolymer (EVOH). , polyvinyl alcohol (PVOH) or polylactic acid (PLA).

Thus, to achieve oxygen or gas impermeability, materials such as EVOH, PVOH, PVDC and PA are preferably used, in addition, materials such as PET or PLA also provide significantly better barrier protection than polyolefin-based starting materials such as PE or RR, especially after pulling, ideally even after biaxial pulling.

In addition, PET and PA are used in particular in the outer layer of films to achieve particularly good heat resistance and excellent printability, in particular after biaxial stretching.

PA and PET, in addition to their excellent heat resistance, printability and good gas and oxygen barrier properties, also make a decisive contribution to maintaining the desired mechanical strength, and here in particular after biaxial drawing.

In this regard, many composites are known from the prior art, for example, from the documents: DE 10/227580 Al, DE 10/254172 Al, DE 10/2006 046483 Al, DE 10/2006 036844 A1, EP 0476836 B2, EP 1190847 B1, EP 1084035 B1 and EP 1985444 A1.

However, what is common to the prior art embodiments and methods is that all of these coextruded multilayer barrier films typically have relatively high shrinkage, most often more than 20%, in any case always more than 5%, both in machine direction (MD ) and in the transverse direction (TD), which is advantageous or even desirable for many applications such as shrink bags/plates.

Examples of coextruded films widely available on the market.

film type application 1 EVA/PVDC/EVA A 2 PE/EVOH/PE A 3 PP/EVOH/PP b 4 PA/EVOH/PA/PE A. b 5 PE/PA/EVOH/PA/PE a, b 6 PA/PE/PA/EVOH/PA/PE a, b 7 PET/PE/PA/EVOH/PA/PE a, b 8 PET/PP/PA/EVOH/PA/PE a, b

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Application film type shrinkage MD+TD A shrink bags for meat or cheese 1, 2, 4, 5, 6, 7, 8 25-50% b plates for trays with meat or cheese 3.4, 5, 6, 7.8 5-20% co-extruded biaxially stretched film (no radiation cross-linking or coating) heat resistance / melting temperature of the outer layer printability shrinkage at 90°C shrink film EVA/PVDC/EVA 93°C 32 dynes/cm (32-10“ ³ N/m) 40-50% shrink film PE/EVOH/PE 118°C 32 dynes/cm (32 10' ³ N/m) 30-40% plate PP/EVOH/PP 164°С 32 dynes/cm (32 10' ³ N/m) 5-15% platinum PET/PE/EVOH/PE 250°C 43 dynes/cm (43 10' ³ N/m) 10-20% platinum PET/PE/PA/EVOH/PA 250°С 43 dynes/cm (43 10' ³ N/m) 5-15%

However, there are still no multilayer barrier films that are produced by coextrusion or lamination and biaxial stretching that have relatively little shrinkage (less than 5%, preferably less than 3%) or no shrinkage at all, as in machine direction (MD). ), and in the transverse direction (TD), and would also have sufficient barrier properties, airtightness, heat resistance, mechanical strength and printability.

In addition, the processability and/or recyclability of many conventional composite films leaves much to be desired.

Purpose of the invention

It is therefore an object of the present invention to develop a method for producing a coextruded and/or laminated and biaxially drawn composite film, preferably a coextruded and/or laminated and biaxially drawn multilayer barrier film, and to provide a multilayer film, preferably a multilayer barrier film, obtained by this method, having improved processing properties and/or improved recyclability. In addition, the composite film according to the invention should preferably have at least one of the following properties, and preferably all of the following properties: sufficient impermeability to oxygen and/or water vapor, sealability, heat resistance, printability and mechanical strength, even without an additional lamination process . It is particularly advantageous if the composite film according to the invention also has relatively low shrinkage (less than 5%, preferably less than 3%) or no shrinkage at all, both in the machine direction (MD) and in the transverse direction (TD).

Disclosure of the Invention

This goal is achieved through the objects listed below and defined in the claims. According to the invention, there is provided a co-extruded and/or laminated and double-drawn composite film, the outer layer (a) of which consists of or contains EVOH. In addition, an appropriate production method and use of the composite film are provided. With regard to the coextruded and biaxially stretched composite film according to the invention, it is preferably provided that it is not laminated. Accordingly, the method of producing a multilayer composite film according to the invention may provide that the method does not include a lamination step.

According to the invention, there is provided a method for producing a multilayer composite film, the method comprising at least the following steps:

the step of coextruding and/or laminating at least three layers (a), (b) and (c), of which layer (a) forms the outer surface of the composite film, layer (c) forms the surface of the composite film facing the packaged product or contacting with it, and layer (b) is located between layer (a) and layer (c);

wherein layer (b) consists of a single layer or a plurality of layers (bl, b2, b3, b4, ...), preferably two, three or four layers;

a step of stretching the coextruded or laminated composite film and a step of relaxing the stretched composite film;

wherein the stretching is carried out along two axes;

wherein the drawing ratio in the machine direction, or longitudinal direction, (MD) is at least 2.0;

wherein the stretch ratio in the transverse, or transversal, direction (TD) is at least 2.0;

- 3 045734 wherein the sum of the drawing ratio in the machine direction (MD) and the drawing ratio in the transverse direction (TD) is at least 5.0;

wherein the composite film during stretching has a temperature of from 70°C to 130°C;

wherein the relaxation coefficient in the machine direction (MD) is more than 0.00;

wherein the relaxation coefficient in the transverse direction (TD) is more than 0.00;

wherein the sum of the relaxation coefficient in the machine direction (MD) and the relaxation coefficient in the transverse direction (TD) is at least 0.05 (=5%), preferably at least 0.1 (=10%), preferably at least 0.2 ( =20%), in particular, not less than 0.4 (=40%);

wherein the composite film during relaxation has a temperature of from 60°C to 180°C, preferably from 60°C to 150°C, especially preferably from 60°C to 120°C, especially preferably 80-100°C;

wherein the residence time in the relaxation process, preferably relaxation at an elevated temperature, is preferably at least 2 seconds, in particular more than 5 seconds, or the relaxation duration is preferably at least 2 seconds, in particular more than 5 seconds;

wherein the residence time in the relaxation process, preferably relaxation at an elevated temperature, is preferably no more than 30 s, preferably no more than 20 s, in particular no more than 10 s, or the relaxation duration is preferably no more than 30 s, preferably no more than 20 s, in particular, no more than 10 s;

wherein the residual draft ratio in the machine direction (MD) is no more than 5.0;

wherein the residual draw ratio in the transverse direction (TD) is no more than 5.0;

wherein layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH) with a density of at least 1.12 g/cm ³ ;

wherein layer (b) or multiple layers (b1, b2, ...) each contains or consists of a thermoplastic resin with a density of more than 1.00 g/cm ³ ; and wherein layer (c) contains or consists of a thermoplastic resin with a density of less than 0.95 g/cm ³ .

Until now, no composite film has been known in the prior art in which EVOH is used as a component of the outer layer (a) or in which layer (a) is composed of EVOH. Thus, it is known in the art to use EVOH as an excellent oxygen barrier material. However, use for this purpose requires EVOH to be the inner layer, as EVOH quickly loses its good oxygen barrier properties when exposed to moisture. Therefore, EVOH has always been used only as a component or layer material, surrounded on both sides by protective layers, such as polyolefin or polyamide, which have a high barrier to water vapor. However, the use of EVOH in conventional composite films for a different purpose and in a different way or in a different location, for example, as an outer or sealing layer (inner layer; the surface facing the packaged product) is not known to date.

On the contrary, according to the invention, EVOH is intentionally used in layer (a), that is, in the outer layer representing the outer surface of the composite film. The outer layer (a) contains or even consists of EVOH. However, when EVOH is present in the outer layer (a), the oxygen barrier property of EVOH does not play a role. Moreover, it has surprisingly been found that the use of EVOH in the outer layer significantly increases the recyclability of the film, for example, compared to conventional composite films that contain outer layers with PA or PET. This is because EVOH has a lower melting point than the PA and PET hitherto provided as outer layer materials, so that the difference between the melting temperatures of the outer layer and the sealing layer (inner layer) is reduced. By doing so, the melting temperature required for recycling can generally be lowered, thereby improving the recyclability of the composite film.

In addition, the inventors have found that the presence of EVOH in the outer layer can further improve the mechanical properties of the film, such as rigidity and printability, compared to polyolefins such as PE or PP. Thus, the higher melting point of EVOH compared to these polyolefins generally leads to improved recyclability of the composite film.

In the composite film according to the invention, the EVOH used in layer (a) has a density of 1.12 g/cm ³ or more, preferably 1.13 g/cm ³ or more, in particular 1.13 to 1.22 g/cm 3 cm ³ . The EVOH used in accordance with the invention has a content of ethylene monomer units of no more than 48 mol%, preferably from 24 to 44 mol%. As a result, the melting point of EVOH is 160°C or higher, preferably 180°C or higher, in particular 190°C or higher. According to the invention, EVOH has a higher melting point than the resin of layer (c).

Current state of the art and practical use have shown that materials such as PET and PA in the outer layer have proven effective in achieving the best printability and maintaining the highest possible heat resistance. However, materials such as PLA or

EVOH are also much better suited in terms of printability, heat resistance and further processing than polyolefin based raw materials such as PE or PP.

raw materials heat resistance/melting point no DSG (ISO 11357) homo-PET 250°C PA6 220°C PLA 210°C EVOH (32 mol%) 183°C HDPE 131°C homo-PP 164°C Raw materials EV A 28% EV A 18% EV A 12% LLD PE mLL DPE stat, coPP CoP P EV OH P.L. PA6. 66 PA 6 co- PET homo PET VST(°C) DIN 40 60 70 100 100 100 120 155 160 180 190 210 240 ΕΝ ISO 306 50 70 85 120 120 120 140 175 180 200 210 230 260

raw materials printability or polarity/surface tension (dynes/cm) (= KG N/m) P.E. 30-32 PP 30-32 PET 43 PA 43

To achieve a sufficient barrier against oxygen or gas, starting materials such as PET, PA, EVOH, PVOH and PVDC have proven themselves.

raw materials oxygen tightness rel.vl. 65% rel.vl. 80% cm ³ /(m ² D-bar) CM ³ /(M ² -d-6ap) EVOH (PE 32 mol%) 0.5 1.2 EVOH (PE 44 mol%) 1 2.3 PVDC (extrusion resin) 4 4 PVDC (dispersion resin) 10 10 PAN 8 10 RET 50 50 PA6 35 50 PVC 240 240 PE-HD 2500 2500 RR 3000 3000 PE-LD 10000 10000 EVA 18000 18000

Source: oxygen permeability at 20°C measured for different barrier plastics (from Kyoichiro; Joachim Nentwig, Kunstoff-Folien, 3. Auflage, 2006, Carl Hanser Verlag; table 26)

But as those skilled in the art know, the barrier properties of most of these raw materials are only sufficient if they are properly protected from moisture.

For this reason, these starting materials, if intended to provide a barrier, are always used in one of the middle or inner layers of the film.

As a matter of practice, to achieve the best sealing performance, polyolefin based raw materials such as PE or PP or the like should always be used, which have the lowest heat sealing or melting point possible.

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What's amazing is that raw materials that are ideally suited to achieve properties such as heat resistance, printability, and oxygen barrier also provide significantly higher strength, especially after biaxial drawing, which polyolefins can only approach despite biaxial drawing.

Thus, in an optimal multi-layer structure, the oxygen barrier layer should consist of EVOH, PVOH or PA and be located in one of the middle or intermediate layers, and the sealing layer, consisting of a heat-sealable polyolefin, would be located in the inner layer.

Therefore, the outer layer may also contain some amounts of heat-resistant and printable materials, such as PET or PA.

If you look more closely at materials that benefit from properties such as heat resistance, printability, oxygen resistance and strength, you will see that all materials have much in common: for example, they all have a density of more than 1.0 g/cm ³ , all of them are polar materials and almost all have a melting point above 160°C, in particular above 170°C.

Upon further analysis of the starting materials that are preferably used as the sealing layer, it is also seen that they all have a density of less than 0.95 g/cm ³ and a melting point of <120°C.

raw materials density (g/cm ³ ) RET 1.33-1.4 RA 1.12-1.14 PLA 0.124-0.125 EVOH 1.12-1.22 RE 0.89-0.96 RR 0.895-0.915

Not all of these raw materials with a density greater than 1.0 g/cm ³ are ideal for printing to the same extent as PA or PET, or are as heat resistant as PET or PA. Additionally, not all of them have the same high oxygen barrier properties as EVOH, PVOH or PA, and not all of them enhance strength to the same extent as PA or PET. But they all exhibit significantly better individual properties, especially when combined in a composite film, particularly after biaxial stretching, than any polyolefin based raw material.

Due to the different optimal characteristics of raw materials with densities greater than 1.0 g/cm ³ in terms of their heat resistance, printability and oxygen barrier, and the resulting ideal or preferred separation into at least two separate layers, such separation leads to another a very positive effect, namely sometimes a significant increase in the strength and rigidity of the film.

This effect is more pronounced the further apart the two layers containing raw materials with a density of more than 1.0 g/cm ³ are spaced in the multilayer composite structure as a whole.

Thus, it is possible to select a layered structure which, on the one hand, includes at least two independent layers with a density greater than 1.0 g/cm ³ , one of these layers being an outer layer and the other an intermediate layer. On the other hand, the composite film must contain a heat sealable layer, which is the innermost layer and consists of a material, preferably a polyolefin, with a density of less than 0.95 g/cm ³ and a melting point below 120°C.

Although such a layered structure can effectively achieve many desirable properties (in particular, sufficient oxygen and/or water vapor impermeability, sealability, heat resistance, printability and mechanical strength), especially after biaxial stretching, but achieving the desired low shrinkage in particular after biaxial pulling, this is not yet ensured.

This goal cannot be achieved with raw materials alone, at least not if the resulting film has been biaxial stretched. To achieve this goal, a suitable technological process and/or suitable processing is required.

Immediately after drawing, in particular after biaxial drawing, polymers or polymer films sometimes exhibit significant shrinkage. Depending on the polymer, it can be expressed to varying degrees and depends significantly on whether heat or heating is applied to the film, and if so, to what extent.

In other words, it is generally true that the higher the temperature and the longer the exposure time, the greater the shrinkage of the film.

Processes or treatments are known from the prior art which are used in the case of uniaxial but also, in particular, in the case of biaxially drawn films to reduce the shrinkage of the drawn films.

Thus, in particular in the case of uniaxially drawn films, but also for biaxially drawn films, post-processing is known, i.e. processing after the drawing process, in which the films are passed over heated rollers (so-called hardening rollers) with the greatest possible winding. As a result, heat or temperature is introduced into the film, i.e. it is thermally fixed, thereby reducing residual shrinkage.

In addition, in the field of flat film stretching, the so-called Tenter Frame process, post-processing (quenching), also called heat setting, is also known, in which the film, after stretching, is passed horizontally through a downstream heating oven and is treated with hot air, As a result, shrinkage is reduced.

The method according to the invention preferably uses the following drawing conditions in combination:

drawing temperature in the range from 70°C to 130°C, drawing ratio in the machine direction or longitudinal direction (MD): at least 2.0, drawing ratio in the transverse or transversal direction (TD): at least 2 ,0, and the sum of the machine direction drawing ratio (MD) and the transverse drawing ratio (TD): at least 5.0.

In addition, thermal post-treatment after stretching is also known from the so-called triple-blow or multiple-blow technology for tubular films. Here, the tube-shaped film is passed through an oven and treated with heat, in most cases hot air, as in the Tenter Frame process. Alternatively, the triple blown process also uses infrared or hot steam to treat the film to reduce shrinkage caused by stretching.

Thus, various technologies are known after biaxial drawing to reduce shrinkage by introducing heat. In addition to the level of the entered temperature, an important factor is also the time, or duration of exposure to heat.

However, treating film with heat/temperature alone to not only reduce film shrinkage, but even eliminate it completely, is effective and sufficient for only a small number of film types.

Thus, films produced in the Tenter Frame process, such as BoPET, BoPA or BoPP (Bo=biaxial oriented), are stabilized by very intensive heat treatment (heat setting) so that they have very little or no shrinkage. shrinkage.

A similar situation is with some types of film that have been biaxially stretched in a double blowing process and then heat set using quench rollers or a horizontal hot air oven. Here too, in particular, BoPP or BoPA films are often processed or fixed only by heat, after which they exhibit no or very low shrinkage.

This is mainly due to the fact that these types of films, regardless of the drawing process, are pure films in composition, which use only one type/grade of raw materials: BoPET (PET only), BoPA (PA only), BoPP (PP only).

In this case, a high heat setting temperature corresponding to the raw material, just below the softening point or melting point, can be selected for stabilization, and thus shrinkage can be significantly reduced or even eliminated solely by heat treatment.

However, until now this was considered impossible for film types consisting of different raw materials, e.g. different grades of raw materials, in particular raw materials with very different softening or melting points.

Thus, in practice, co-extruded and biaxially drawn films are unknown which contain a combination of different raw materials with very different softening or melting points and which, in addition, despite being stretched, have very little or no shrinkage.

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The exception here is individual multilayer films produced using the Tenter process.

Frame or double blowing method. Here we are talking mainly about the following layered structure (from the inside out; HV = adhesion promoter):

PP-HV-EVOH-HV-PP.

Since this uses almost exclusively HomoPP (homopolymer PP; melting point: 155-165°C) in combination with EVOH, with high ethylene EVOH grades having a lower melting point compared to low ethylene EVOH (temperature melting point: 170-180°C), these composites can be stabilized at similar temperatures almost exclusively by heat treatment, and shrinkage is reduced or eliminated.

True, these PP-based multilayer films, the vast majority of which consist of PP, do not have the required heat resistance, much less the required printability.

Since even the most heat-resistant types of HomoPP always melt at temperatures below 170°C and, in addition, PP is the most non-polar raw material, which is completely unsuitable for printing without additional post-processing, the choice of PP as the ideal raw material for the outer layer cannot be considered and speeches.

In addition, as is known on the market, these PP-based multilayer films, due to the types of polypropylene used and the generally poorer sealing properties, have very poor or mediocre heat sealability compared to the preferably used raw material, for example PE, i.e. have a relatively high heat sealing temperature. For this reason, these films are usually later laminated with PE-based films.

Thus, a multilayer, co-extruded and then biaxially stretched film, which has a low melting point seal layer that has not been subsequently laminated, also contains a heat-resistant and printable (polar) outer layer, as well as an oxygen barrier layer located in the middle layers, and which has no or minimal shrinkage is not currently produced.

This is because such multilayer composites cannot be produced stably or at all at the temperature required to eliminate or reduce shrinkage below 5%, or better yet below 3%, without additional processing measures.

Thus, even before reaching the temperature required to eliminate shrinkage, softening or even melting of individual layers of the multilayer composite occurs, which inevitably leads to interruption or at least significant deterioration of the film production process.

When or at what temperature disturbances or even process interruptions occur depends largely on whether and how many layers of the entire film composite are made from non-polyolefin based materials, i.e. from heat-resistant materials with a density >1.00 g/cm ³ and a melting point above 160°C, preferably above 170°C.

If the mass fraction of materials with a density of >1.00 g/cm ³ is more than 40% of the total mass of the multilayer film structure, then the composite film also allows processing (heat setting) at temperatures of 80-100°C, and with a mass fraction of 50% or more even at higher temperatures.

But even with a high, 40% or more, mass fraction of materials with a density of >1.00 g/cm ³ , if the composite film contains a sealing layer of polyolefin-based raw materials with a density of >0.95 g/cm ³ , even before reaching the residual shrinkage below 5%, both in the MD and TD directions, there are always disturbances or interruptions in the technological process, since the temperatures required for heat setting of films must not be lower than 120-150°C, even for materials with a density >1.00 g/cm ³ and a melting point above 160°C, preferably above 170°C, are no longer sufficient to ensure stability of the production process.

Therefore, to avoid negatively impacting the film production process, only temperatures that do not completely eliminate shrinkage can be selected for thermal post-processing.

In order, however, to reduce shrinkage to a minimum or even completely eliminate it, according to the invention an additional process step is required. In addition to treating the biaxially stretched film with heat to eliminate shrinkage, an additional technological step is widely used in the triple or multiple blowing process, namely the so-called relaxation. In this case, the film, after being stretched, is allowed to shrink again in a controlled manner, which is called relaxation and which occurs under the influence of temperature or heat.

Relaxation can occur in both directions, i.e. both in the direction of production, i.e. in the machine direction (MD) and in the direction perpendicular to production (TD).

Relaxation can occur equally in both directions (MD and TD) or to varying degrees (severity) in one direction or the other.

In addition, relaxation in only one direction is also possible, i.e. only in MD or TD. The direction of relaxation can always be chosen independently of each other. In the context of the present invention, the quantitative level of relaxation is expressed by the so-called relaxation coefficient, which is defined in more detail below.

Relaxation refers to the controlled or adjustable return shrinkage of the film in MD

- 8 045734 and/or TD. Controlled return shrinkage in the MD direction is achieved by different drawing speeds, i.e. film stretching during the relaxation process occurs at a lower number of revolutions than film stretching in the previous process. In the TD direction, controlled return shrinkage is achieved by reducing the film width between two film stretches. An example of the relaxation process of an extruded and stretched single- or multilayer film is known to specialists from the work of Savic, Z., Savic. I, Sausage Casings, VICTUS Lebensmittelindustriebedarf Vertriebsgesellschaft mbH., Wien, 1. Auflage, 2002, chapter 7, subsection 4.2, 267-270, in particular fig. 7-13a and 7-13b.

However, film relaxation alone does not sufficiently reduce shrinkage by itself, and under no circumstances can shrinkage be completely eliminated.

This is explained by the fact that films (shrink films/plates) during relaxation are usually processed or fixed only at temperatures of a maximum of 60-80°C, since these relatively low temperatures are already sufficient to achieve a controlled return shrinkage of the film and reduce the residual shrinkage to values of 10- 20% in both MD and TD, at best to values ranging from >5% to 10% in one of the two directions.

Lower shrinkage values have so far been unattainable because neither the relaxation achieved at these conditions (temperatures) nor the applied temperature is sufficient to reduce shrinkage to below 5% in both MD and TD.

The level of relaxation that can be achieved depends significantly on the level of temperature at which the film is processed or fixed.

Thus, the maximum possible relaxation, which has an additional positive effect on residual shrinkage, i.e. further reduces permanent shrinkage, can only be achieved at appropriately high temperatures during film processing (heat setting).

However, here again the same problem as described above arises, namely that when a film, in particular a film containing combinations of raw materials with very different melting points, is processed at the temperatures required to eliminate shrinkage, the individual layers soften or even melt , which inevitably interrupts or at least significantly impairs the film making process.

Further, when processing a film by a combination of heating and relaxation, the temperature range over which disturbances or interruptions in the production process occur depends on how high the mass fraction of materials with a density of >1.00 g/cm ³ is in the multilayer structure of the film.

However, it unexpectedly turned out that the proportion of materials contained with a density >1.00 g/cm ³ with appropriate relaxation can be significantly lower than in the case of heat treatment alone without relaxation.

Thus, with appropriate relaxation, the treatment can be carried out at a significantly higher temperature, in any case above 60°C, preferably above 70°C, in particular above 80°C and up to a temperature of 180°C, preferably up to 150°C, in particular , up to 120°C, while simultaneously reducing the amount of materials (thermoplastic resin with a density of >1.00 g/cm ³ ) to a mass fraction in any case below 40%, preferably below 30%, in particular below 20%, and even up to to a mass fraction below 10% of the total mass of the multilayer film structure. In this case, the mass fraction of thermoplastic resin with a density of >1.00 g/cm ³ is at least 1%, preferably at least 5% of the total mass of the multilayer film structure.

Thus, in the method according to the invention, the temperature of the composite film during relaxation can preferably be set in the following ranges: 60-180°C, preferably 60-150°C, particularly preferably 60-120°C, highly preferably 80-100°C.

In the method according to the invention, the residence time (residence duration) during the relaxation process, preferably relaxation under heating, is preferably 2-30 s, preferably 2-20 s, preferably 5-30 s, preferably 5-20 s, preferably 2-10 s or preferably 5-10 s.

To achieve low shrinkage, it is important that the sum of the relaxation coefficient in the machine direction (MD) and the relaxation coefficient in the transverse direction (TD) is at least 0.05 (=5%), preferably at least 0.1 (=10%), preferably at least 0.2 (=20%), in particular at least 0.4 (=40%). In this case, both the relaxation coefficient in the machine direction and the relaxation coefficient in the transverse direction exceed 0.00.

Thus, along with the heat input for fixation (temperature of the composite film during relaxation), the relaxation coefficients are critical factors in reducing or eliminating the shrinkage that occurs during film stretching.

Thus, in the context of the present invention, in order to achieve low shrinkage, it has proven advantageous to controllably reduce or attenuate the stretch or elongation of the film introduced during film stretching.

If we consider the technological stages in total, including stretching and subsequent relaxation, then after both stages there is a residual stretch, or residual elongation, in the film. At

- 9 045734 In this case, it is possible to determine the residual stretch ratio, which is described in detail below and which is based on the ratio of the length of the section of the composite film after stretching and after relaxation to the length of the same section before stretching and before relaxation.

Since the residual draw factor is equally the result of both processes (drawing and relaxation), ideally it can also be influenced or modified by both processes to an equal extent.

A closer look at this dependence shows that even a decrease in stretching, all other things being equal, gives an effect similar to the effect of later relaxation of the film, i.e., with less stretching, you can also achieve very low shrinkage with less relaxation, and with greater stretching, in in turn, high relaxation is required to keep shrinkage low. However, it unexpectedly turned out that, in principle, the influence of the relaxation coefficient is significantly higher than the drawing ratio.

However, the decisive factor in both technological stages is not only relaxation, but the total or combinatorial influence of both of these stages.

Thus, the residual draw ratio and, of course, the temperature introduced during relaxation mainly determine whether and how much shrinkage will remain in the film.

Since the residual shrinkage is significantly influenced not only by the relaxation process and the temperature introduced into it, but also by the stretching process, and heat treatment is also implemented during the stretching process, it is also necessary to take into account the influence of this.

Indeed, here too one can see the influence, i.e. At low drawing temperatures, without simultaneous changes in other process parameters, higher residual shrinkage is observed than at higher drawing temperatures.

However, unlike relaxation, the stretching process is much more sensitive, i.e. the temperatures required to achieve a stable process are often within a narrow range of only ±(23)°C. Consequently, the range over which temperatures can vary is smaller or limited.

Moreover, to the best of the inventors' knowledge, the effect of the temperature of the composite film during stretching is quite small.

Thus, the temperature when drawing a composite film is an influencing factor, but is not as decisive as the temperature during relaxation or the drawing ratio, as well as the relaxation coefficient or the residual drawing ratio.

A more precise analysis of the process steps and their influence reveals another important factor, namely the time, or duration, during which the film is exposed to individual stages of the process and under the prevailing conditions there.

True, it turned out that the influence of the time factor during the drawing process can be neglected in comparison with the influence of temperature and the multiplicity of drawing.

On the contrary, it turns out that in the relaxation process, the relaxation time (duration) can be at least as important as the relaxation coefficient and the steady-state temperature.

It turns out that the combination of time (duration) and relaxation coefficient is less significant than time (duration) in combination with temperature, i.e. more precisely, the period during which the film is exposed to the relaxation temperature.

The longer the heat treatment, the greater this influence and, thus, the more the residual shrinkage decreases.

However, it also turned out that this effect cannot intensify indefinitely; on the contrary, after a certain period of time exposure to temperature, its further increase, i.e. shrinkage reduction cannot be realized and a kind of saturation occurs.

However, it is much more important how long the film is exposed to the temperature, so a duration or exposure time of at least 2 s is required to recognize the desired exposure.

Thus, the method of the invention may be limited in this respect in that the composite film, during relaxation, has a temperature in one of the above temperature ranges for a period of time defined above (the so-called temperature residence time). Thus, the duration of relaxation or the time spent in the relaxation process at temperature should preferably be at least 2 seconds, in particular more than 5 seconds. In this case, the duration of relaxation or the time spent in the relaxation process at temperature can be limited to a maximum of 30 s, preferably a maximum of 20 s, in particular a maximum of 10 s.

Just as temperature or relaxation alone cannot provide adequate low shrinkage, time at temperature alone cannot provide this. These influencing factors and the effect they achieve are interdependent and influence each other.

The residual shrinkage of the film (shrinkage after stretching and relaxation) is small during high-temperature processing and at the same time high relaxation, despite the short time at temperature.

- 10 045734

However, permanent film shrinkage is also low when processed at high temperature and longer residence time at temperature, despite low relaxation.

Likewise, permanent film shrinkage is low at long temperature exposure times and high relaxation times, despite moderate heat treatment.

Thus, only a combination of these influencing factors makes it possible to achieve the desired low residual shrinkage of the film.

In order to achieve low shrinkage of the multilayer structures according to the invention, in addition to the ideally suited layered structures with the raw materials preferably contained therein in combination with temperatures set in the individual process steps, process parameters, here in particular the drawing ratio, relaxation coefficient and residual drawing ratio, as well as residence time, at least the duration of heat fixation (relaxation) is decisive. Thanks to the combination of the features and parameters specified in the present description or defined in the claims, the goal of obtaining, in particular, the stable production of a standard composite film by lamination or by coextrusion, preferably coextrusion without lamination, which, in addition to improved processability and/or recyclability, is achieved for the first time , also has other useful properties such as heat resistance, printability, oxygen barrier and which has no shrinkage or has less than 5% shrinkage, preferably less than 3% in both the MD and TD directions.

It is particularly preferable that the thermoplastic resin contained in the layer (c) or of which the layer (c) is composed has a melting point below 120°C. Due to the increased difference with the melting temperature of the outer layer, the composite film can be sealed earlier, i.e., at a lower temperature. In addition, higher cycle times can be achieved by further processing the composite film.

Further, it is particularly preferable if the thermoplastic resin which is contained in the layer (a) or of which the layer (a) is composed has a melting point higher than 160°C, preferably higher than 170°C. Due to the higher temperature of the outer layer, higher temperatures can be used during further processing and thus higher cycle times can be achieved during further processing of the composite film.

Further, according to the invention, layer (a), that is, the outer layer, can preferably have a predetermined polarity, which is represented by surface tension expressed in units of dynes/cm (=10-3 N/m). This value may preferably be >40 dynes/cm (>40-10-3 N/m), in particular >42 dynes/cm (> ^42-10-3 N/m), in order to ensure the highest possible printability.

Moreover, according to the invention, in one preferred embodiment it can be provided that the outer layer (a) consists of or contains EVOH.

Until now, no standard composite films have been known in the art in which EVOH is used as a component of the outer layer (a) or in which layer (a) consists of EVOH. Thus, it is known from the prior art to use EVOH as a material with excellent oxygen barrier properties. However, use for this purpose requires EVOH to be the inner layer, as EVOH quickly loses its good oxygen barrier properties when exposed to moisture. Therefore, EVOH as a component or layer material has always been used, surrounded on both sides by protective layers, such as polyolefin or polyamide, which sometimes have a high impermeability to water vapor. However, the use of EVOH in standard composite films for a different purpose and in a different way or in a different location, for example, as an outer or sealing layer (inner layer; the surface facing the packaged product), has not been known until now.

On the contrary, according to the invention it is possible to intentionally use EVOH in layer (a), i.e. in the outer layer that forms the outer surface of the composite film. The outer layer(s) may contain or be composed of EVOH. However, when EVOH is present in the outer layer (a), the oxygen barrier property of EVOH is not important. But in accordance with the invention, it is important that the use of EVOH in the outer layer significantly increases the recyclability of the film compared to composite films that have outer layers with PA or PET. This is because EVOH has a lower melting point compared to the PA and PET materials previously used for the outer layer, so the difference in the melting temperatures of the outer layer and the sealing layer (inner layer) is reduced. In doing so, the temperature required for recycling to melt can generally be reduced, thereby improving the recyclability of the composite film.

In addition, the applicants have discovered that the presence of EVOH in the outer layer can improve the mechanical properties of the film, such as rigidity and printability, such as PET or PA, compared to polyolefins such as PE or PP. The higher melting point of EVOH than these polyolefins and the associated higher temperature resistance of the inner layer (seal layer) result in an overall better ability to further process the composite film (number of cycles).

- 11 045734

Further, the method according to the invention can be implemented as a method for producing a multilayer composite film, comprising at least the following steps:

the step of coextruding and/or laminating at least four layers (a), (b), (d) and (c), of which layer (a) forms the outer surface of the composite film, layer (c) forms the surface of the composite film facing the product being packaged or in contact with it, layer (b) is located between layer (a) and layer (c);

layer (d) is located between layer (a) and layer (c), preferably between layer (a) and layer (b);

wherein layer (b) consists of a single layer or a plurality of layers (bl, b2, b3, b4, ...), preferably two, three or four layers;

wherein layer (d) consists of a single layer or multiple layers (dl, d2, .), preferably two, three or four layers;

a step of stretching the coextruded or laminated composite film and a step of relaxing the stretched composite film;

wherein the stretching is carried out along two axes;

wherein the drawing ratio in the machine direction, or longitudinal direction, (MD) is at least 2.0;

wherein the stretch ratio in the transverse, or transversal, direction (TD) is at least 2.0;

wherein the sum of the machine direction drawing ratio (MD) and the transverse drawing ratio (TD) is at least 5.0;

wherein the composite film during stretching has a temperature of from 70°C to 130°C;

wherein the relaxation coefficient in the machine direction (MD) is more than 0.00;

wherein the relaxation coefficient in the transverse direction (TD) is more than 0.00;

wherein the sum of the relaxation coefficient in the machine direction (MD) and the relaxation coefficient in the transverse direction (TD) is at least 0.05 (=5%), preferably at least 0.1 (=10%), preferably at least 0.2 ( =20%), in particular, not less than 0.4 (=40%);

wherein the composite film during relaxation has a temperature of from 60°C to 180°C, preferably from 60°C to 150°C, especially preferably from 60°C to 120°C, especially preferably 80-100°C;

wherein the residence time in the relaxation process, preferably relaxation at an elevated temperature, is preferably at least 2 s, in particular more than 5 s, or the relaxation duration is preferably at least 2 s, in particular more than 5 s;

wherein the residence time in the relaxation process, preferably relaxation at an elevated temperature, is preferably no more than 30 s, preferably no more than 20 s, in particular no more than 10 s, or the relaxation duration is preferably no more than 30 s, preferably no more than 20 s, in particular, no more than 10 s;

wherein the residual draft ratio in the machine direction (MD) is no more than 5.0;

wherein the residual draw ratio in the transverse direction (TD) is no more than 5.0;

wherein layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH) with a density of at least 1.12 g/cm ³ ;

wherein layer (d) or multiple layers (d1, d2, .) each contains or consists of a thermoplastic resin, preferably a polyolefin, with a density of less than 1.00 g/cm ³ , preferably less than 0.98 g/cm ³ ;

wherein layer (b) or multiple layers (b1, b2, .) each contains or consists of a thermoplastic resin with a density of more than 1.00 g/cm ³ ; and wherein layer (c) contains or consists of a thermoplastic resin with a density of less than 0.95 g/cm ³ .

Further advantageous embodiments of the method according to the invention are the subject of the dependent claims.

The above-described method according to the invention and its preferred embodiments can also be characterized in that layer (b) does not contain EVOH; or none of the layers (b1, b2, .) contains EVOH; or layer (b) contains or consists of EVOH; or at least one of the layers (b1, b2, .) contains or consists of EVOH; or none of the layers of the composite film, except layer (a), contains EVOH.

The above-described method according to the invention and its preferred embodiments can also be characterized in that

The EVOH of layer (a) has a melting point of at least 160°C, preferably at least 170°C; and/or the thermoplastic resin of layer (c) is a polyolefin with a heat sealing temperature lower

- 12 045734 heat sealing temperature of thermoplastic resin layer (a); and/or the thermoplastic resin of layer (c) is a polyolefin with a melting point below 120°C;

and/or the thermoplastic resin of layer (b) has an oxygen permeability of less than 100 cm ³ /(m%-bar), or the oxygen permeability of each of the thermoplastic resins of layers (bl, b2, ...) or in total is less than 100 cm ³ /(m %-bar); and/or layer (b) has an oxygen permeability of less than 100 cm ³ /(m ² dbar), or layers (bl, b2, ...) have, each or in total, an oxygen permeability of less than 100 cm ³ /(m ² dbar); and/or the stretching is carried out simultaneously or in several successive stages; and/or the composite film after stretching and relaxation has a shrinkage of less than 0.05 (=5%), preferably less than 0.03 (=3%), in the machine direction (MD); and/or the composite film after stretching and relaxation has a shrinkage of less than 0.05 (=5%), preferably less than 0.03 (=3%), in the transverse direction (TD); and/or after stretching and relaxation, the sum of the composite film's machine direction (MD) and transverse direction (TD) shrinkage (=total shrinkage) is preferably less than 0.05 (=5%).

The expression and/or means that the method according to the invention may be characterized by one, all or any selection or combination of the above features. This definition is also valid by analogy for the use of the expression and/or in subsequent parts of the description and in the claims.

The above-described method according to the invention and its preferred embodiments can also be characterized in that the thickness of the layer (a) does not exceed 20%, preferably 10% of the thickness of the entire composite film; and/or the thickness of the layer (b) or the total thickness of the layers (b1, b2, ...) does not exceed 20%, preferably 10% of the thickness of the entire composite film; and/or the mass fraction of layer (a) does not exceed 10% of the total mass of the composite film; and/or the mass fraction of the layer (b) or the sum of the mass fractions of the layers (b1, b2, ...) does not exceed 10% of the total mass of the composite film; and/or the sum of the mass fractions of layer (a) and layer (b) or layer (a) and layers (b1, b2, .) does not exceed 10% of the total mass of the composite film.

The above-described method according to the invention and its preferred embodiments can also be characterized in that the layer (a) does not contain at least one of the following types of polymers: a polyester, preferably polyethylene terephthalate (PET), or polylactic acid or polylactide (PLA), or polyamide (PA); and/or the thermoplastic resin of layer (c) contains or consists of a polyolefin (PO), preferably polyethylene (PE) and/or polypropylene (PP), ethylene vinyl acetate copolymer (EVA), ionomer (IO), ethylene methyl methacrylate copolymer (EMMA ), ethylene methacrylic acid copolymer (EMA), or any mixture thereof.

The above-described method according to the invention and its preferred embodiments can also be characterized in that the mass fraction of the components of the layer with a density of >1.0 g/cm ³ , preferably the EVOH layer (a) with a density of > 1.12 g/cm ³ , is from 1% to <40%, preferably from 1% to <30%, preferably from 1% to <20%, in particular from 5% to <20% of the total weight of the composite film.

Further, the problem facing the invention is solved by means of a multilayer, co-extruded and/or laminated, biaxially stretched and relaxed composite film obtained by the method according to the invention, as described above and defined in the claims. Moreover, the composite film according to the invention has at least two layers (a) and (c), of which layer (a) forms the outer surface of the composite film, and layer (c) forms the surface of the composite film facing or in contact with the packaged product wherein layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH);

wherein layer (c) contains or consists of a thermoplastic resin.

The advantages discussed above in connection with the method according to the invention apply by analogy to the composite film according to the invention and its variants.

Further, according to the invention, the object is achieved by means of a multi-layer, co-extruded and/or laminated, biaxially drawn and relaxed composite film, which has preferably been or can be produced by the method according to the invention and which has at least three layers (a), (b ) and (c), of which layer (a) forms the outer surface of the composite film;

layer (c) forms the surface of the composite film facing the product to be packaged or

- 13 045734 in contact with it, layer (b) is located between layer (a) and layer (c);

wherein layer (b) consists of a single layer or a plurality of layers (b1, b2, b3, b4, ...), preferably two, three or four layers;

wherein the residual drawing ratio of the composite film in the machine direction (MD) is no more than 5.0;

wherein the residual stretch ratio of the composite film in the transverse direction (TD) is no more than 5.0;

wherein layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH) with a density of at least 1.12 g/cm ³ ;

wherein layer (b) or multiple layers (b1, b2, .) each contains or consists of a thermoplastic resin with a density of more than 1.00 g/cm ³ ; and wherein layer (c) contains or consists of a thermoplastic resin with a density of less than 0.95 g/cm ³ .

According to the invention, the object is also achieved by means of a multi-layer, co-extruded and/or laminated, biaxially drawn and relaxed composite film, which has preferably been or can be produced by the method according to the invention and which has at least four layers (a), (b), (d) and (c), of which layer (a) forms the outer surface of the composite film;

layer (c) forms the surface of the composite film facing or in contact with the packaged product, layer (b) is located between layer (a) and layer (c);

layer (d) is located between layer (a) and layer (c), preferably between layer (a) and layer (b);

wherein layer (b) consists of a single layer or a plurality of layers (b1, b2, .), preferably two, three or four layers;

wherein layer (d) consists of a single layer or multiple layers (d1, d2, .), preferably two, three or four layers;

wherein the residual drawing ratio of the composite film in the machine direction (MD) is no more than 5.0;

wherein the residual stretch ratio of the composite film in the transverse direction (TD) is no more than 5.0;

wherein layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH) with a density of at least 1.12 g/cm ³ ;

wherein layer (d) or multiple layers (d1, d2, .) each contains or consists of a thermoplastic resin, preferably a polyolefin, with a density of less than 1.00 g/cm ³ , preferably less than 0.98 g/cm ³ ;

wherein layer (b) or multiple layers (b1, b2, .) each contains or consists of a thermoplastic resin with a density of more than 1.00 g/cm ³ ; and wherein layer (c) contains or consists of a thermoplastic resin with a density of less than 0.95 g/cm ³ .

Preferred embodiments of the composite film according to the invention are the subject of dependent claims.

Thus, the composite film according to the invention can be characterized by the fact that the thermoplastic resin of layer (b) has an oxygen permeability of less than 100 cm ³ /(m ² dbar), or the thermoplastic resins of layers (b1, b2, .) have, each or in total, an oxygen permeability of less 100 cm ³ / (m ² dbar); and/or layer (b) has an oxygen permeability of less than 100 cm ³ /(m ² dbar), or layers (b1, b2, .) have, each or in total, an oxygen permeability of less than 100 cm ³ /(m ² dbar); and/or the thickness of the layer (b) or the total thickness of the layers (b1, b2, .) does not exceed 20%, preferably 10% of the thickness of the entire composite film; and/or the mass fraction of the layer (b) or the sum of the mass fractions of the layers (b1, b2, .) does not exceed 10% of the total mass of the composite film; and/or the sum of the mass fractions of layer (a) and layer (b) or layer (a) and layers (b1, b2, .) does not exceed 10% of the total mass of the composite film.

Further, the composite film according to the invention can be characterized in that

The EVOH of layer (a) has a melting point of at least 160°C, preferably at least 170°C; and/or the thermoplastic resin of layer (c) is a polyolefin whose heat sealing temperature is lower than the heat sealing temperature of EVOH layer (a); and/or the thermoplastic resin of layer (c) is a polyolefin with a melting point below 120°C.

- 14 045734

Further, the composite film according to the invention can be characterized in that, after stretching and relaxation of the composite film, the sum of the machine direction (MD) shrinkage and the transverse direction (TD) shrinkage (=total shrinkage) is less than 0.05 (=5%);

the thickness of layer (a) does not exceed 20%, preferably 10% of the thickness of the entire composite film;

layer (a) does not contain at least one of the following types of polymers: polyester, preferably polyethylene terephthalate (PET) or polylactic acid or polylactide (PLA), or polyamide (PA); and/or the thermoplastic resin of layer (c) contains or consists of a polyolefin (PO), preferably polyethylene (PE) and/or polypropylene (PP), ethylene vinyl acetate copolymer (EVA), ionomer (IO), ethylene methyl methacrylate copolymer (EMMA ), ethylene methacrylic acid copolymer (EMA), or any mixture thereof.

the mass fraction of the components of the layer with a density of >1.0 g/cm ³ , preferably the EVOH layer (a) with a density of >1.12 g/cm ³ , is from 1% to <40%, preferably from 1% to <30%, preferably from 1% to <20%, in particular from 5% to <20% of the total weight of the composite film.

According to the invention, the object is also achieved by using a composite film according to the invention, as defined in the claims or described above, or a shell made from it for packaging an object, preferably for packaging food products, delicacies or liquid or solid, in particular powdery goods.

In a preferred embodiment, the use according to the invention is characterized in that the mass fraction of the components of the layer with a density of >1.0 g/cm ³ , preferably the EVOH layer (a) with a density of > 1.12 g/cm ³ , is between 1% and <40 %, preferably from 1% to <30%, preferably from 1% to <20%, in particular from 5% to <20%, of the total weight of the composite film.

The advantages discussed above in connection with the method according to the invention are valid by analogy with respect to the use of the composite film according to the invention and its variants.

Additional Description

The method proposed by the invention and described here for producing a multilayer composite film can be characterized by the fact that it does not include a lamination step, i.e. gluing layers or layered systems.

Accordingly, the multilayer composite film of the invention described herein may be a non-laminated composite film.

Length definitions (each in relation to machine direction or transverse direction):

L0:= length of a given section of the composite film before stretching;

L1:= length of the same section of the composite film after stretching and before relaxation;

L2:= length of the same section of the composite film after stretching and before relaxation;

L3:= length of the same section of the composite film after stretching and after relaxation.

Determination of the stretch ratio: stretch ratio V=length L1 of a given section of the composite film after stretching and before relaxation, divided by the length L0 of the same section of the composite film before stretching (V=L1/L0).

Determination of the relaxation coefficient: relaxation coefficient RL=absolute value of the difference between the length L3 of a given section of the composite film after stretching and after relaxation and the length L2 of the same section of the composite film after stretching and before relaxation, divided by the length L2 of the same section of the composite film after stretching and before relaxation (RL=|(L3-L2)|/L2).

Determination of the residual stretch ratio: residual stretch ratio RV=length L3 of a given section of the composite film after stretching and after relaxation, divided by the length L0 of the same section of the composite film before stretching and before relaxation (RV=L3/L0).

The composite film of the invention is preferably a multilayer composite film with a barrier function, or a multilayer barrier film, wherein the barrier property relates to reduced oxygen permeability or reduced vapor permeability or both.

Shrinkage (or heat shrinkage): measured in water at 90°C, preferably within 1 s after immersion, but not later than 10 s after immersion.

According to the invention, the sample for determining shrinkage (or shrinkage when heating) is immersed for a certain time, in particular the time indicated above, in water at 90°C and, after removal, is immediately cooled with water to room temperature. The length of the pre-marked section after this treatment is measured and correlated with the length of the same section of the sample measured before treatment. The resulting ratio of lengths (shrink to unshrink), indicated as a percentage, determines the shrinkage. Depending on the direction of length measurement, shrinkage in the longitudinal direction (MD) and in the transverse direction (TD) is obtained. The total shrinkage is calculated by adding the shrinkage in the longitudinal and transverse directions. Repeated determinations, for example three or five determinations of length measurements and the formation of corresponding average values from them, advantageously increase the accuracy of the determination. According to the invention, shrinkage and total shrinkage can be determined, in particular, in accordance with the ASTM 2732 standard.

The measurement of oxygen permeability within the framework of the invention is carried out at 23°C and a relative humidity of 75% (AsTmD 1434).

The method according to the invention can preferably be carried out, and the composite film according to the invention can be produced using the so-called double blowing technology and, in particular, triple blowing, for which the authors propose suitable installations known to specialists in the field. In this case, the multilayer composite film can be co-extruded from appropriate resin melts, for example, using an extrusion head from the Applicant designed for the production of composite films with three or more layers, preferably with thermal separation of the individual layers, cooled by water cooling from the Applicant, heated again, stretched along two axes (machine direction (MD) and transverse direction (TD)) using a closed compressed air bubble, and finally relax (thermofix) in the next step at a given temperature. The composite film according to the invention may be a composite film forming a barrier to gas diffusion, in particular the diffusion of oxygen and/or water vapor. This method of production is also known to specialists from the textbook Sausage Casings, VICTUS Lebensmittelindustriebedarf Vertriebsgesellschaft mbH, Vienna, Austria, 1st edition, 2002, chapter 7, in particular subsection 4.2, 267-270.

Another possibility for producing the film according to the invention is to stretch the co-extruded flat film using Tenter Frame technology known in the art.

The composite film of the present invention can be successfully produced by a device or installation from the present Applicant for the production of tubular films for food packaging, for example, shrink films or shrink bags, by the jet blow molding method, if additionally using the device disclosed in the description patent DE 19916428 B4 from the same Applicant for rapid cooling of thin thermoplastic tubes after extrusion. In this connection, reference can also be made to the corresponding development according to patent DE 10048178 B4.

The tubular film obtained from the polymer melt is subjected to intensive cooling in the extrusion head, during which the amorphous structure of thermoplastics from the polymer melt is preserved. The tubular film, vertically extruded from the polymer melt through the extruder head, first passes into a cooling device for cooling without touching the walls, as described in detail in publications DE 19916428 B4 and DE 10048178 B4. To avoid repetition, full reference is made to the contents of publications DE 19916428 B4 and DE 10048178 B4 regarding the details of the procedures, design and operation of this cooling device, also called a calibration device.

The tubular film then passes through the supports in the cooling device, on which the film rests due to the pressure difference between the inside of the tubular film and the refrigerant, while a liquid film is maintained between the film and the supports, so that the tubular film does not stick. The diameter of the tubular film is influenced by the diameter of the supports, therefore the specified cooling device of the same Applicant is also called a calibration device.

According to the invention, the polyamide (PA) may be a substance selected from the group consisting of PA from ε-caprolactam, or poly(ε-caprolactam) (PA6), PA from hexamethylenediamine and adipic acid or polyhexamethylene adipamide (PA6.6), PA from ε-caprolactam and hexamethylenediamine/adipic acid (PA6.66), PA from hexamethylenediamine and dodecanoic acid, or polyhexamethylenedodecanamide (PA6.12), PA from 11-aminoundecanoic acid, or polyundecanamide (PA11), PA from 12-laurin lactam, or poly (ω-laurin lactam) (PA12), or a mixture of these PAs or a mixture of these PAs with amorphous PA or with other polymers. The general designation PAx.y is synonymous with PAx/y or PAxy.

In the context of the present application, polyolefin (PO) may be a substance selected from the group consisting of PP, PE, LDPE, LLDPE, polyolefin plastomer (POP), ethylene vinyl acetate copolymers (EVA), ethylene methyl methacrylate copolymers (EMMA), ethylene copolymers and methacrylic acid (EMA), copolymers of ethylene and acrylic acid (EAA), copolymers of cycloolefins/cycloalkenes and 1-alkenes, or cycloolefin copolymers (COC), ionomers (IO) or a mixture thereof. In addition, for the purposes of the present invention, PO also includes a mixture of the above PO with ionomers and/or adhesion promoters.

Within the scope of the present invention, a polyester can be used as a component of layer (a). Polyesters are polymers with ester groups in the main chain, they can be, in particular, aliphatic or aromatic polyesters. Polyesters can be prepared by polycondensation of the corresponding dicarboxylic acids with diols. For polyester synthesis, any dicarboxylic acid suitable for polyester formation can be used, in particular terephthalic acid and isophthalic acid, as well as dimers of unsaturated aliphatic acids. As another component for polyester synthesis, diols can be used, for example polyalkylene glycols such as ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, diethylene glycol, polyethylene glycol and polytetramethylene oxide glycol; 1,4-cyclohexanedimethanol and 2-alkyl-1,3-propanediol.

A particularly preferred polyester is polyethylene terephthalate, abbreviated PET. PET can be produced by the polycondensation of terephthalic acid (1,4-benzenedicarboxylic acid) and ethylene glycol (1,2-dihydroxyethane).

Other preferred polyesters are polylactides or polylactic acids (PLA), which may be contained as a layer component in layers for which polyester is provided as a layer component. These polymers are biocompatible/biodegradable and, in addition to low moisture absorption, have high melting points and good tensile strength.

For the purposes of the present invention, EVOH means either pure EVOH or a mixture of EVOH with other polymers, ionomers, EMA or EMMA. In particular, EVOH also includes a mixture of EVOH and PA or a mixture of EVOH and an ionomer.

Adhesion promoters (HV) can be provided in the composite film according to the invention as intermediate layers, they are adhesive layers that ensure good adhesion of the individual layers to each other. In this case, HVs can be based on a base material selected from the group consisting of PE, PP, EVA, EMA, EMMA, EAA and ionomer, as well as mixtures thereof. According to the invention, particularly suitable adhesion promoters (HV) are EVA, EMA or EMMA with a purity greater than 99%, preferably >99.9%.

According to a further preferred embodiment, layers containing HV as a layer component may also contain a mixture of PO and HV, or a mixture of EVA, EMA, EMMA and/or EAA and HV, or a mixture of ionomer and HV, or a mixture of several HVs.

For the purposes of the present invention, the melting point of the polymer is determined by dynamic differential calorimetry or differential thermal analysis according to DIN 51007:2019-04 or DIN EN ISO 11357-1:2017-02. Alternatively, the ASTM D3418 method is also known from the prior art.

For the purposes of the present invention, the softening temperature of the polymer is determined by the method for determining the Vicat softening temperature (VST=Vicat softening temperature) according to DIN EN ISO 306:2014-03.

For the purposes of the present invention, printability is determined in accordance with DIN 16500-2:2018-09.

In the context of the present invention, designation of a material as a component of a layer means that the layer of the composite film according to the invention at least partially contains this material. The term layer component in the context of the present invention covers in particular the case where the layer consists entirely, that is, exclusively of this material.

In the context of the present invention, the middle or intermediate layer means the composite film layer that is located between layer (a) and layer (c). According to the invention, layer (a) is a layer forming the outer surface of the composite film (outer layer). According to the invention, layer (c) is the layer that forms the surface of the composite film facing or in contact with the packaged product (inner layer). By definition, layers (a) and (c) of the composite film according to the invention cannot be a middle or intermediate layer.

The composite film according to the invention is preferably flat or tubular. Preferably, the composite film is a food grade film or casing. In addition, the composite film is preferably suitable for use as a non-shrink packaging material.

Examples of coextruded and biaxially stretched multilayer films with a barrier function according to the invention, containing at least three layers (a), (b) and (c):

3-layer structure

(A) (b) (With) EVOH RA RO

Examples of coextruded and biaxially stretched multilayer films with a barrier function according to the invention, containing at least four layers (a), (b), (d) and (c):

4-layer structures

(A) (d) (b) (With) EVOH RO EVOH RO

(A) (d) (b) (With) EVOH RO PVDC RO

(A) (d) (b) (With) EVOH RO RA RO

- 17 045734

5-layer structures

(A) (dl) (b) (d2) (With) EVOH RO EVOH H.V. RO

(A) (dl) (b) (d2) (With) EVOH RO PVDC H.V. RO (A) (dl) (b) (d2) (With) EVOH RO RA H.V. RO

7-layer structures

(A) (dl) (d2) (d3) (b) (d4) (c) EVOH H.V. RO H.V. EVOH H.V. P.O.

(a) (dl) (d2) (d3) (b) (d4) (c) EVOH H.V. P.O. H.V. PVDC H.V. P.O.

(a) (dl) (d2) (d3) (b) (d4) (c) EVOH H.V. P.O. H.V. PA H.V. P.O.

9-layer structures

(a) (dl) (d2) (d3) (bl) (b2) (b3) (d4) (c) EVOH H.V. P.O. H.V. PA EVOH PA H.V. P.O.

Claims (18)

1. A method for producing a multilayer composite film, the method comprising at least the following steps: the step of coextruding and/or laminating at least three layers (a), (b) and (c), of which layer (a) forms the outer surface of the composite film, layer (c) forms the surface of the composite film facing or touching the packaged product with it, and layer (b) is located between layer (a) and layer (c); wherein layer (b) consists of a single layer or a plurality of layers (b1, b2, b3, b4, ...); a step of stretching the coextruded or laminated composite film and a step of relaxing the stretched composite film; wherein the stretching is carried out along two axes; the drawing ratio in the machine direction or longitudinal direction (MD) is at least 2.0; the draw ratio in the transverse or transversal direction (TD) is at least 2.0; the sum of the machine direction (MD) drawing ratio and the transverse direction (TD) drawing ratio is at least 5.0; the composite film during stretching has a temperature of 70 to 130°C; the relaxation coefficient in the machine direction (MD) is more than 0.00; the relaxation coefficient in the transverse direction (TD) is more than 0.00; the sum of the relaxation coefficient in the machine direction (MD) and the relaxation coefficient in the transverse direction (TD) is at least 0.05 (=5%); the composite film during relaxation has a temperature from 60 to 180°C; the time spent in the relaxation process is more than 2 s; the time spent in the relaxation process is no more than 30 s; the residual draft ratio in the machine direction (MD) is no more than 5.0; the residual draw ratio in the transverse direction (TD) is no more than 5.0; layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH) with a density of at least 1.12 g/cm ³ ; layer (b) or multiple layers (b1, b2, ...) each contains or consists of a thermoplastic resin with a density of more than 1.00 g/cm ³ ; and layer (c) contains or consists of a thermoplastic resin with a density of less than 0.95 g/cm ³ . 2. The method according to claim 1, characterized in that the method includes at least the following steps: a step of co-extrusion and/or lamination of at least four layers (a), (b), (d) and (c), from of which layer (a) forms the outer surface of the composite film; layer (c) forms a surface of the composite film facing or in contact with the product to be packaged; layer (b) is located between layer (a) and layer (c); - 18 045734 layer (d) is located between layer (a) and layer (c), preferably between layer (a) and layer (b); wherein layer (b) consists of a single layer or a plurality of layers (b1, b2, b3, b4, ...), preferably two, three or four layers; layer (d) consists of a single layer or a plurality of layers (d1, d2, ...), preferably two, three or four layers; a step of stretching the coextruded or laminated composite film and a step of relaxing the stretched composite film; wherein the stretching is carried out along two axes; the drawing ratio in the machine direction or longitudinal direction (MD) is at least 2.0; the draw ratio in the transverse or transversal direction (TD) is at least 2.0; the sum of the machine direction (MD) drawing ratio and the transverse direction (TD) drawing ratio is at least 5.0; the composite film during stretching has a temperature of 70 to 130°C; the relaxation coefficient in the machine direction (MD) is more than 0.00; the relaxation coefficient in the transverse direction (TD) is more than 0.00; the sum of the relaxation coefficient in the machine direction (MD) and the relaxation coefficient in the transverse direction (TD) is at least 0.05 (=5%), preferably at least 0.1 (=10%), preferably at least 0.2 (= 20%), in particular, not less than 0.4 (=40%); the composite film during relaxation has a temperature of 60 to 180°C, preferably 60 to 150°C, particularly preferably 60 to 120°C, particularly preferably 80 to 100°C; the residence time in the relaxation process, preferably relaxation at an elevated temperature, is preferably at least 2 s, in particular more than 5 s, or the relaxation duration is preferably at least 2 s, in particular more than 5 s; the residence time in the relaxation process, preferably relaxation at an elevated temperature, is preferably no more than 30 s, preferably no more than 20 s, in particular no more than 10 s, or the duration of relaxation is preferably no more than 30 s, preferably no more than 20 s, in particular no more than 10 s; the residual draft ratio in the machine direction (MD) is no more than 5.0; the residual draw ratio in the transverse direction (TD) is no more than 5.0; layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH) with a density of at least 1.12 g/cm ³ ; layer (d) or multiple layers (d1, d2, ...) each contains a thermoplastic resin, preferably a polyolefin, with a density of less than 1.00 g/cm ³ , preferably less than 0.98 g/cm ³ , or consists of her; layer (b) or multiple layers (b1, b2, ...) each contains or consists of a thermoplastic resin with a density of more than 1.00 g/cm ³ ; and layer (c) contains or consists of a thermoplastic resin with a density of less than 0.95 g/cm ³ . 3. Method according to claim 1 or 2, characterized in that layer (b) is free of EVOH; or layers (b1, b2, ...) are free of EVOH; or layer (b) contains or consists of EVOH; or at least one of the layers (b1, b2, ...) contains or consists of EVOH; or the layers of the composite film other than layer (a) are free of EVOH. 4. Method according to one of claims 1-3, characterized in that The EVOH of layer (a) has a melting point of at least 160°C, preferably at least 170°C; and/or the thermoplastic resin of layer (c) is a polyolefin with a heat sealing temperature lower than the heat sealing temperature of the thermoplastic resin of layer (a); and/or the thermoplastic resin of the layer (c) is a polyolefin with a melting point below 120°C; and/or the thermoplastic resin of layer (b) has an oxygen permeability of less than 100 cm ³ /(m ² dbar) or the oxygen permeability of each of the thermoplastic resins of layers (b1, b2, ...) or in total is less than 100 cm ³ /(m ² dbar ); and/or layer (b) has an oxygen permeability of less than 100 cm ³ /(m ² dbar) or layers (b1, b2, ...) have, each or in total, an oxygen permeability of less than 100 cm ³ /(m ² dbar); and/or the stretching is carried out simultaneously or in several successive stages; and/or the composite film after stretching and relaxation has a shrinkage of less than 0.05 (=5%), preferably less than 0.03 (=3%), in the machine direction (MD); and/or the composite film after stretching and relaxation has a shrinkage of less than 0.05 (=5%), preferably less than 0.03 (=3%), in the transverse direction (TD); and/or after stretching and relaxation, the sum of the composite film's machine direction (MD) and transverse direction (TD) shrinkage (=total shrinkage) is preferably less than 0.05 (=5%). 5. Method according to one of claims 1-4, characterized in that the thickness of layer (a) does not exceed 20%, preferably 10% of the thickness of the entire composite film; and/or the thickness of the layer (b) or the total thickness of the layers (b1, b2, ...) does not exceed 20%, preferably 10% of the thickness of the entire composite film; and/or the mass fraction of layer (a) does not exceed 10% of the total mass of the composite film; and/or the mass fraction of the layer (b) or the sum of the mass fractions of the layers (b1, b2, ...) does not exceed 10% of the total mass of the composite film; and/or the sum of the mass fractions of layer (a) and layer (b) or layer (a) and layers (b1, b2, ...) does not exceed 10% of the total mass of the composite film. 6. Method according to one of claims 1 to 5, characterized in that the layer (a) is free from polymers of at least one of the following types: polyester, preferably polyethylene terephthalate (PET), or polylactic acid or polylactide (PLA), or polyamide (PA); and/or the thermoplastic resin of the layer (c) contains or consists of a polyolefin (PO), preferably polyethylene (PE) and/or polypropylene (PP), ethylene vinyl acetate copolymer (EVA), ionomer (IO), ethylene methyl methacrylate copolymer (EMMA ), copolymer of ethylene with methacrylic acid (EMA) or any mixture thereof. 7. Method according to one of claims 1 to 6, characterized in that the mass fraction of components of the layer with a density of >1.0 g/cm ³ , preferably EVOH layer (a) with a density of > 1.12 g/cm ³ , is from 1 to <40%, preferably from 1 to <30%, preferably from 1 to <20%, in particular from 5 to <20% of the total weight of the composite film. 8. A multilayer coextruded and/or laminated, biaxially drawn and relaxed composite film comprising at least three layers (a), (b) and (c), of which layer (a) forms the outer surface of the composite film; layer (c) forms the surface of the composite film facing or in contact with the packaged product, layer (b) is located between layer (a) and layer (c); wherein layer (b) consists of a single layer or a plurality of layers (b1, b2, b3, b4, ...), preferably two, three or four layers; the residual drawing ratio of the composite film in the machine direction (MD) is no more than 5.0; the residual draw ratio of the composite film in the transverse direction (TD) is no more than 5.0; layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH) with a density of at least 1.12 g/cm ³ ; layer (b) or multiple layers (b1, b2, ...) each contains or consists of a thermoplastic resin with a density of more than 1.00 g/cm ³ ; layer (c) contains or consists of a thermoplastic resin with a density of less than 0.95 g/cm ³ ; the composite film has a shrinkage of less than 0.05 (=5%) in the machine direction (MD); The composite film has a shrinkage of less than 0.05 (=5%) in the transverse direction (TD). 9. Multilayer coextruded and/or laminated, biaxially stretched and relaxed composite film according to claim 8, containing at least four layers (a), (b), (d) and (c), of which layer (a) forms the outer surface of the composite film; layer (c) forms the surface of the composite film facing or in contact with the packaged product, layer (b) is located between layer (a) and layer (c); layer (d) is located between layer (a) and layer (c), preferably between layer (a) and layer (b); wherein layer (b) consists of a single layer or a plurality of layers (b1, b2, ...), preferably two, three or four layers; layer (d) consists of a single layer or a plurality of layers (d1, d2, ...), preferably two, three or four layers; the residual drawing ratio of the composite film in the machine direction (MD) is no more than 5.0; the residual draw ratio of the composite film in the transverse direction (TD) is no more than 5.0; wherein layer (a) contains or consists of an ethylene vinyl alcohol copolymer (EVOH) with a density of at least 1.12 g/cm ³ ; layer (d) or multiple layers (d1, d2, ...) each contains a thermoplastic resin, preferably a polyolefin, with a density of less than 1.00 g/cm ³ , preferably less than 0.98 g/cm ³ , or consists of her; - 20 045734 layer (b) or a plurality of layers (b1, b2, ...) each contains or consists of a thermoplastic resin with a density of more than 1.00 g/cm ³ ; and layer (c) contains or consists of a thermoplastic resin with a density of less than 0.95 g/cm ³ . 10. Composite film according to claim 8 or 9, characterized in that layer (b) is free of EVOH; or layers (b1, b2, ...) are free of EVOH; or layer (b) contains or consists of EVOH; or at least one of the layers (b1, b2, ...) contains or consists of EVOH; or the layers of the composite film other than layer (a) are free of EVOH. 11. Composite film according to one of claims 8 to 10, characterized in that the thermoplastic resin of layer (b) has an oxygen permeability of less than 100 cm ³ /(m ² dbar) or the thermoplastic resins of layers (b1, b2, ...) have, each or in total, oxygen permeability less than 100 cm ³ / (m ² dbar); and/or layer (b) has an oxygen permeability of less than 100 cm ³ /(m ² dbar) or layers (b1, b2, ...) have, each or in total, an oxygen permeability of less than 100 cm ³ /(m ² dbar); and/or the thickness of the layer (b) or the total thickness of the layers (b1, b2, ...) does not exceed 20%, preferably 10% of the thickness of the entire composite film; and/or the mass fraction of the layer (b) or the sum of the mass fractions of the layers (b1, b2, ...) does not exceed 10% of the total mass of the composite film; and/or the sum of the mass fractions of layer (a) and layer (b) or layer (a) and layers (b1, b2, ...) does not exceed 10% of the total mass of the composite film. 12. Composite film according to one of claims 8-11, characterized in that The EVOH of layer (a) has a melting point of at least 160°C, preferably at least 170°C; and/or the thermoplastic resin of the layer (c) is a polyolefin whose heat sealing temperature is lower than the heat sealing temperature of the EVOH layer (a); and/or the thermoplastic resin of layer (c) is a polyolefin with a melting point below 120°C. 13. Composite film according to one of claims 8 to 12, characterized in that after stretching and relaxation of the composite film, the sum of shrinkage in the machine direction (MD) and shrinkage in the transverse direction (TD) (= total shrinkage) is less than 0.05 ( =5%). 14. Composite film according to one of claims 8 to 13, characterized in that the thickness of layer (a) does not exceed 20%, preferably 10% of the thickness of the entire composite film. 15. Composite film according to one of claims 8 to 14, characterized in that layer (a) is free from at least one of the following types of polymers: polyester, preferably polyethylene terephthalate (PET), or polylactic acid or polylactide (PLA), or polyamide (PA); and/or the thermoplastic resin of the layer (c) contains or consists of a polyolefin (PO), preferably polyethylene (PE) and/or polypropylene (PP), ethylene vinyl acetate copolymer (EVA), ionomer (IO), ethylene methyl methacrylate copolymer (EMMA ), copolymer of ethylene with methacrylic acid (EMA) or any mixture thereof. 16. Composite film according to one of claims 8 to 15, characterized in that the mass fraction of the components of the layer with a density of >1.0 g/cm ³ , preferably the EVOH layer (a) with a density of >1.12 g/cm ³ , is from 1 to <40%, preferably from 1 to <30%, preferably from 1 to <20%, in particular from 5 to <20% of the total weight of the composite film. 17. Use of a multilayer composite film according to one of claims 8 to 16 or a shell obtained from it for packaging an item. 18. Application according to claim 17, characterized in that the mass fraction of the components of the layer with a density of >1.0 g/cm ³ , preferably the EVOH layer (a) with a density of >1.12 g/cm ³ , is from 1 to <40 %, preferably from 1 to <30%, preferably from 1 to <20%, in particular from 5 to <20%, of the total weight of the composite film.