EP1877251A1

EP1877251A1 - High-strength polypropylene-base barrier film for packing purposes, method for the production and the use thereof

Info

Publication number: EP1877251A1
Application number: EP06723090A
Authority: EP
Inventors: Helmut Enzinger; Lajos Edward Keller
Original assignee: Brueckner Maschinenbau GmbH and Co KG
Current assignee: Brueckner Maschinenbau GmbH and Co KG
Priority date: 2005-05-04
Filing date: 2006-02-23
Publication date: 2008-01-16
Also published as: WO2006117034A1; JP2008540156A; DE102005020913B3; US20090053513A1; EP2484520A1; US20110300363A1

Abstract

The invention relates to a high-strength and brilliant quality barrier film for packing purposes, in particular for food packaging embodied in the form of a multilayer film based on of at least one carrier layer consisting of a biaxially oriented polypropylene film (PP-film) and of a functional layer based on amorphous and partially-crystalline polyamide (PA) which is produced by simultaneously stretching a primary multilayer coextruded film, wherein said polyamide functional layer consists of an external film layer and a central internal layer placed between two carrier layers. Methods for the production of the inventive film and the uses thereof are also disclosed.

Description

High-strength barrier film for polypropylene-based packaging, process for its preparation and its use

The present invention relates to a high-strength barrier film for packaging purposes, in particular for the packaging of foodstuffs and other sensitive goods, in the form of a multilayer film whose mechanical properties are largely determined by a biaxially oriented film, for the film-forming polymer crystallizable Polypropylene is used, and also as a functional layer or barrier on its surface or optionally in an inner layer, a coextruded layer based on an amorphous or partially crystalline polyamide (PA) or a mixture of such a polyamide with ethylene-vinyl alcohol copolymers (EVOH) having.

The invention further relates to processes for producing such a film, as well as the use of this film for packaging purposes, in particular for the packaging of food and semi-luxury products, wherein the excellent optical properties, strength properties and barrier properties of the film are used. Plastic film-based packaging is an indispensable part of modern life. Depending on the goods to be packaged various demands are made on such plastic films. In the case of plastic films for the packaging of food and beverages, the focus is on properties that ensure the shelf life of the packaged food or beverage on the distribution channels and at the end consumer until consumption of the food. Additional requirements for the films result from the fact that the packaging usually has to be provided with information about the packaged goods, manufacturer information, etc., and is also an advertising medium, which should have an appealing, sales-promoting appearance.

Part of the quality assurance by the plastic film of the packaging is in many foods protection against loss of aroma and the prevention of the emission of odorous substances and, in many cases, a protection against atmospheric oxygen and / or humidity and / or moisture loss from the goods. Films having such properties are also referred to as barrier films or barrier films.

Around. To ensure the printability of the films, the film surface must have certain properties, which includes a suitable surface tension. Further, the appearance and feel of the film is also an important selling property, i. their surface quality and stiffness or their dimensional stability and stiffness or softness.

Since these various requirements are not normally met by a single sheet material at the same time, it is necessary to have a sheet material to undergo a special surface treatment and / or coating treatment and / or to ensure the desired properties by using multilayer films instead of simple films in which different layers perform different tasks.

As a rule, multilayer films comprise at least one major mechanical properties-determining support layer of a main film-forming polymer, external or internal barriers for achieving the desired barrier properties, as well as outer layers, the printability, the coatability or the sealability for the production closed packaging or laminates.

When high demands are placed on packaging films, in the foodstuffs and luxury foods sector today, polyester-based films (PET, polyethylene terephthalate) are frequently used which have good strength, good optical properties and good coatability for glossy metal films, in particular aluminum. or for transparent ceramic coatings, in particular SiOx or AlOx. The thin metal or ceramic films give the films high barrier properties, in particular with respect to the water vapor transmission rate (WVTR), measured in g / (m ² d) or g / (m ² 24 h). and for oxygen (Oxygen Transmission Rate, OTR, measured in cm ³ / (m ² dbar) or cm ³ / (m ² 24 h) at an atmospheric pressure of 1 bar). In order to ensure the required weldability or sealability of the films required for packaging, they usually also have an additional outer polyolefin layer, for example a polyethylene layer provided over the metallization or ceramic coating, for example made of HDPE or LDPE. Although these polyester films meet high quality requirements, they have the disadvantage, inter alia, that polyester polymers are relatively expensive and have a relatively high density.

It is therefore an attempt, instead of using polyester films, to resort to polyolefin films, in particular to polypropylene films, which are comparatively cheap to produce in particular as biaxially oriented polypropylene films (BOPP films) in large quantities and which are lighter in strength than polyester films. However, polypropylene films as such do not have the barrier properties required for demanding applications, and they are not readily coated with shiny aluminum or clear ceramic coatings without pretreatment. For this purpose, a surface treatment of the oriented polypropylene films is required, which takes place as corona, flame or plasma treatment and in which the surface tension or surface polarity important for the wettability is increased. These surface treatments, however, interfere with BOPP films, which is familiar to those skilled in the art as "maggot" odor. Metal- or ceramic-coated polypropylene films are also less suitable for applications in which consumers have clear, glossy and cellophane-like, i. crackling or wrinkling, packaging materials are used or expected.

It is known from EP 0 546 709 A1 or the corresponding US Pat. No. 5,591,520 that the application of a thin coextruded layer based on an amorphous or possibly semicrystalline polyamide which is bonded to the polypropylene base film by means of a special adhesive layer , the wetting surface tension of a such coated polypropylene film greatly increased, so that very well adhering aluminum layers can be vapor-deposited. According to the illustrative example of EP 0 546 709 A1, a coextrusion of a three-layer multilayer film with a first layer of an amorphous polyamide (condensation product of hexamethylenediamine with isophthalic anhydride), a second layer which forms the actual supporting film layer and essentially consists of a polypropylene homopolymer to which a maleic anhydride-modified polypropylene is added to improve the adhesion of the polyamide layer, and a third layer serving as a sealability or sealability layer consisting of an ethylene-propylene-1-butene terpolymer known for the purpose.

The coextruded melt is solidified on a chill roll into a primary multilayer film and then sequentially stretched first in the machine direction (MD) to 3.5 times its original length and then laterally (TD) to 8 times its original width. Draw ratio of 28 or area increase to 28 times). The polyamide side of the resulting film had a wetting surface tension greater than 50 dynes / cm. The film was conventionally vacuum deposited to an optical density of 2.5 with an aluminum layer.

After the vapor deposition of aluminum, the film had a water vapor transmission rate (WVTR) of 0.02 g / 100inch ^2/24 h or - converted - of 0.31 g / m ² d, and an oxygen permeability (OTR) of 1.0 cm ³ / 100inch ² / 24h or 15.5 cm ³ / (m ² d). In particular, the oxygen permeability of the metallized film is significantly higher than that required for high-quality modern barrier films and, for example, is below 0.1 cm ³ / m ² / 24h in the case of metallized polyester-based films.

Any information on the strength and appearance of the film obtained according to EP 0 546 709 A1 is not made. However, it is well known to those skilled in the art of biaxially orienting polypropylene film that in the described sequential stretching, which is followed by a low stretching in the machine direction (MD), a stronger transverse direction stretching (TD), the strength properties of the obtained biaxially stretched Polypropylene film (tensile strength, modulus of elasticity) are lower in the MD direction than in the TD direction, and typical values for the tensile strength under the specified production conditions are about 140 N / mm ² in the MD direction and 280 N / mm ² in the TD direction are. Similarly, the elongation at break in such MD direction films is higher (typically 150 to 250%) than in the TD direction (50 to 60%). Similar conditions as for the tensile strength also apply to the elastic modulus.

It could not be established that aluminum-coated films according to EP 0 546 709 A1 were ever commercially tested or used to any appreciable extent. Information on the appearance, the other film properties and on the aroma and odor retention of the films are just as little to be found in the description of EP 0 546 709 A1 as any information on preferred uses of the disclosed oriented polypropylene films with polyamide coating and aluminum vaporization. Furthermore, it can not be ruled out that the procedural nical limitations of the stretching ratios lead to unacceptable poor thickness tolerances.

DE 699 16 111 T2 discloses a barrier film for packaging purposes in the form of a multilayer film based on at least one supporting core layer in the form of an ethylene-vinyl alcohol copolymer film having at least two outer layers of ethylene homo- or co-polymers simultaneous stretching of a coextruded multilayer primary film is made. Such a foil. may be used as an additional layer (s), e.g. to increase the total mass and / or to improve shrinkage and / or mechanical properties, etc., one or more intermediate layer (s) based on various other polymers, also called polyamides. A seven-layer film is described in which a polyamide compound layer is provided on both sides of a polyamide-added core layer which serves as a plasticizer for the ethylene-vinyl alcohol copolymer.

EP 0 311 293 B1 discloses a barrier film for packaging purposes, in particular as a barrier against oxygen, nitrogen and carbon dioxide, in the form of a multilayer film based on at least one support layer in the form of a polypropylene film (PP film) with at least one coextruded functional layer the basis of ethylene-vinyl alcohol copolymers (EVOH).

The present invention has for its object to provide high-quality brilliant, ie clear and glossy, high-strength packaging films with excellent impermeability to flavors and odors, which is additionally metallizable or clear ceramic coatings and then having barrier properties, especially with regard to oxygen permeability, which are on the order of modern barrier films based on coated polyethylene terephthalate, but which have the cost and weight advantages and production advantages of polypropylene films over polyester films.

Surprisingly, the inventors found that this object is achieved when a multilayer film from

Polypropylene and a polyamide layer simultaneously and without contact with a high stretching ratio, which increases the surface area of the primary film on the 40-

80 times, so that in the machine direction (MD) strength properties are obtained which are at least equal, but usually better than in the transverse direction

(TD), and overall a high-strength film is obtained.

Further, as the inventors were able to determine from the test films having PA outer layers that they produced that the polyamide layer as such ensures high aromatic density and odor density of the film even without additional coating, and also provides a significant contribution to the overall strength and rigidity of the polypropylene stretched film Variation also developed a further related film having a polyamide layer in the film core between two layers of orientable polyolefins, for example, between two identical or different polypropylene layers or, for example, a polypropylene layer and a polypropylene Regener- atschicht has. The novel films according to the present invention are represented by claims 1 and 2 of the appended set of claims.

Advantageous embodiments of one or both films according to claims 1 and / or 2 can be found in the dependent claims 3 to 20.

Claims 21 to 26 describe advantageous embodiments of processes for producing such films, and claims 27 and 28 relate to the use of films according to claims 1 to 20 as packaging films for food and beverages.

The inventors have found that, when a primary film having a base layer of an orientable polypropylene and a layer of an amorphous or semi-crystalline polyamide deposited thereon by an adhesive layer or a polyamide and a barrier polymer such as ethylene-vinyl alcohol copolymer, a to obtain a clear film having excellent surface properties, strength values and high gloss (Gloss; ASTM 2457) above 100, especially in the range of about 101 to 107, and high clarity. If an aluminum coating or ceramic coating of SiOx or AlOx is applied to the outer polyamide layer in a manner known per se, excellent barrier properties are obtained even with very thin coatings. For example, the application of an aluminum layer at an optical density of 2.3 results in a film having an oxygen permeability (OTR) ranging from 0.05 to 0.5 cm ³ / m ³ d at 23 ^° C. and 75% relative Humidity is and is therefore 30 to 300 times better than that of the film described in EP 0 546 709 A1. The water vapor transmission rates (WVTR; ASTM E 96 relative at 38 ⁰ C, 90% humidity) the metallized in an optical density of 2.3 foil below 0.5 g / m ² 24h, wherein, depending on the surface treatment prior to metallization, values between 0.3 and 2.5 were obtained.

In particular, stretching ratios in the range from 40 to 80 (calculated as the product of stretching in MD and in TD direction) are chosen as the high drawing ratio.

In this case, the primary multilayer film in the machine direction

(MD) is stretched to at least δ times its length, wherein stretching of the primary multilayer film simultaneously in MD is at least 7 times and in transverse direction (TD) less than 7 times, preferably in MD more than 8 times, preferably at least that 9 times, and in TD less than 8 times.

The inventors attribute the drastic improvement eg of the oxygen barrier of the metallized film according to the invention to the fact that in the longitudinal sequential stretching described in EP 0 546 709 A1 the formation of a smooth surface of the polyamide layer is prevented using the usual roller arrangements and this layer is also prevented during subsequent stretching in the transverse direction no longer smoothes because polyamides have too high melting points and subsequent surface improvement by forming an intermediate molten surface layer is not possible. The surface defects of the polyamide layer produced during sequential stretching result in the fact that during the subsequent application of a metallization no defect-free dense metal layer can be formed, which is required for high barrier properties, in particular a high barrier effect to oxygen. In addition, the inventors found that at the high stretching ratios made possible by simultaneous stretching, a film of high strength is obtained, which in many of its properties resembles a cellophane film, for example, crackling / wrinkling and of brilliant clarity and high gloss , The strength values are at least equal to, but usually better than, the direction of the direction of the MD of manufacture, corresponding to TD.

Thus, the tensile strength (ASTM D 822) of the film in MD is in the range of 170-280 N / mm ² and in TD is in the range of 130-215 N / mm ² , and its elongation at break (ASTM D 82) in MD is in the range of 50-120% and in TD in the range of 100-220%. Values for modulus of elasticity (ASTM D 882) for the test films in MD were measured in the range of between about 2750 N / mm ² and about 3630 N / mm ² , while the corresponding values in TD were in the range of more than about 1900 N / mm ² to about 2600 N / mm ² .

Due to the inherent strength properties of the simultaneously stretched film according to the invention, in particular based on the ratio of the strengths in the two main directions of the film, and because of their gloss, the skilled artisan can immediately distinguish a simultaneously highly stretched film from a film whose preparation is described in EP 0 546 709 Al is described.

The preferred method of performing the simultaneous stretching is stretching on a simultaneous stretching machine with

Linear motor operation (LISIM®). The less advantageous

Method of simultaneous stretching with a mechanical simultaneous stretching machine (MSO; Mechanical Simultaneous

orienter; with chain operation) and the production as tubular film with stretching after the BUBBLE or DOUBLE However, BUBBLE processes are also intended to be included within the scope of the invention. When produced as a multilayer tubular film, the layer composite is preferably arranged so that the PA layer forms the inside of the tube stretched by inflation.

In order to obtain optimum film properties, the inventors have found that when simultaneously stretching a flat film, e.g. According to the LISIMO technique, it is advantageous to coextrude the polymers in the production of the multilayer film in such a way that the polyamide layer, when it forms an outer layer, comes into direct contact with the cooling roll, since in this way surface defects that pass through it on the other side melted air knives are generated can be avoided, and also avoid problems of accumulation of polyamide melt at the extrusion die edge.

If the polyamide film forms an outer layer of the primary multilayer film produced, its thickness should not be too large and less than 5 microns, preferably less than 2.5 microns, otherwise the inherent, increased stretching of the polyamide layer in stretching causes the film in the Cooling rolls up or warps. On the other hand, however, the polyamide layer of the stretched film can also be kept extremely thin, for example, in the range of about 0.1 microns or even lower, when it comes to improving the printability or writability of the resulting film and strength and tightness properties of are of secondary importance. As a guide, layer thicknesses of the PA outer layer of less than 0.5 microns, down to 0.1 microns, are selected when it comes only to the printability and coatability; Values in the range of 0.5 to 1.0 microns provide in the vacuum coating, in particular metallization with Aluminum, excellent barriers; and values in the range of 1.0 to 2.0 microns give excellent results in odor and aroma protection and barrier effects.

A film which has as main structural elements a supporting layer of a simultaneously biaxially oriented polypropylene and a coextruded and at the same time stretched polyamide layer generally has further layers. Thus, an adhesion-improving layer is usually provided between the polypropylene layer and the polyamide layer, which may be, for example, a layer of a modified polypropylene, as described in EP 0 546 709 A1.

In addition, a thermoplastic weldable or sealable polyolefin layer is preferably arranged on the opposite side of the polyamide layer, which may consist of a known and customary for this purpose polymer, such as a polyethylene propylene-butene terpolymer or a similar polymer and optionally can be connected to the polypropylene layer by means of an intermediate adhesive layer or an intermediate layer facilitating the peelability of the base film.

The inventors have found that the polyamide outer layer is well suited for direct metallization or ceramic coating due to its high surface quality. However, it is additionally possible to subject this layer to conventional corona, plasma or flame treatment and thus to further modify the surface properties. Compared to a corresponding treatment of an oriented polypropylene film is found that no disturbing smell develops. However, it was also found that a flame The quality of a subsequent metallization rather deteriorates and therefore is generally less advantageous.

Since it was found that the polyamide layer as such, even without additional coating, a high aroma and odor density of the film causes, and that it also can significantly improve the stiffness and mechanical properties of the resulting barrier multilayer film, another film was created in according to claim 2, the polyamide layer is arranged in the core of a barrier multilayer film in which it is covered on both sides by the same or different polypropylene carrier layers. In this case, the adhesive layers are extruded on both sides of the polyamide layer, and usually on the outer layers of the polypropylene layers additional functional layers, usually of propylene-ethylene copolymers or propylene-ethylene-butylene terpolymers applied, which is an improvement Surface treatment and / or a weldability and sealability of the films allow. If the polyamide layer is placed in the core of a multilayer film, it may be significantly thicker than in the case of its outer layer arrangement, i. it may have a thickness of up to about 10 microns since it will not distort or cause the film to bulge or curl when placed in the center of the thicker film.

By the term polypropylene is meant herein, it is meant a high quality biaxially stretch orientable polypropylene, which is preferably a high isotacticity polypropylene homopolymer. However, other polypropylene grades used for comparable purposes may also be used, for example those which account for a minor proportion copolymerized other monomers. The definition of the term "polypropylene" in EP 0 546709 B1 is also referenced for the purposes of the present application.

The same applies with regard to the definition of the term "amorphous polyamide" or "semicrystalline polyamide" and / or with regard to the definition of the adhesion layer which is generally required between the polypropylene and the polyamide layer. Also with regard to these components, reference is made to the corresponding material data in EP 0 546 709 A1 for the purposes of the present invention in addition to the material information in the following examples. In addition, all layers, depending on the intended use of the film, may contain various conventional additives, among which are mineral or organic additives for forming microvoids, fillers, absorbents, UV and light stabilizers, dyes and opacifying pigments.

The invention will be explained in more detail on the basis of exemplary embodiments, wherein the person skilled in the art will take further details of the invention and its advantages from the described process conditions, materials and film properties.

In the examples, Examples 1 to 15 describe the preparation of a total of 5-layer multilayer film with a polyamide outer layer, the layer structure of Example 1 is explained in more detail in principle.

Examples 16 to 18 describe a 7-layer multilayer film with a central polyamide layer, the general structure of which is explained before Example 16. The properties of the barrier multilayer films obtained in all of Examples 1 to 18 are summarized in the attached test results table.

The materials indicated in the examples with their trade names are materials of the following type:

HP 522 H: isotactic polypropylene homopolymer "Moplen®" HP 522 H from Basell; PA 3426: DuPont ™ Selar® PA 3426 amorphous polyamide resin;

Bynel® 21 E 781: anhydride-modified ethylene acrylate resin from DuPont ™; Bynel® 50 E 739: anhydride-modified polypropylene resin from DuPont ™; TD 110 BF: C2 / C4 terpolymer PP resin Borseal ™ TD110BF from Borealis A / S, Denmark;

TD 120 BF: C2 / C4 terpolymer PP resin Borseal ™ TD120BF from Borealis A / S, Denmark.

Examples

Before example 1,

In Examples 1 to 15, 5-layer barrier multilayer films were prepared with a polyamide layer as the outer layer, extrusion through a 5-layer slot die onto a chill roll, and the 5-layer primary film formed on the chill roll immediately on a chill roll Laboratory LISIM® stretching machine from Brückner was simultaneously stretched as indicated in the examples. The layer arrangement of the melts for producing the multilayer film was produced by means of the following nozzle arrangement with the specified conveying devices:

Layer A - outer layer, air knife side: 35 mm single-screw extruder; Layer B - intermediate layer: 50 mm single screw extruder with melt pump;

Layer C - core layer: 55 mm twin-screw extruder with melt pump;

Layer D - intermediate layer: 43 mm single-screw extruder with melt pump;

Layer E - outer layer, cooling roll side: 35 mm single-screw extruder

It should be noted that the designation of the layers A to E is determined by the arrangement of the slot dies for the melt extrusion or their position relative to the cooling roll and the opposing air knife.

In Examples 1 to 5, the polyamide layer is extruded as layer A, while in Examples 6 to 15, the polyamide layer is extruded as layer E on the cooling roll side, which is preferred.

example 1

Materials and operating conditions of the five extruders were as follows:

Layer A: PA 3426, extruder with a conveying speed of 30 rpm. Layer B: Bynel 21E781; Extruder with melt pump at a conveying speed of 30

U / min.

Layer C: HP 522H; Core extruder with melt pump with a conveying speed of 45.7

Rpm Layer D: HP 522 H: extruder with melt pump with a conveying speed of 8 rpm.

Layer E: TD 110 BF, extruder with a conveying speed of 26 rpm.

The primary film obtained after the coextrusion of the 5-layer melt was oriented under conditions optimized for the simultaneous orientation of biaxially oriented polypropylene films (S-BOPP films), with an 8-fold stretching in the machine direction (MD). and a 7-fold transverse stretching (TD), in accordance with enlargement of a grid printed on the base sheet before stretching. A film having a total thickness of 20 μm was obtained, and the thickness of the polyamide layer (layer A) was about 1.2 μm.

The film was subjected to corona treatment of the surface of the polyamide layer (A) under standard conditions for BOPP films.

The resulting film was brilliant in appearance and crackled. The wetting surface tension was measured to be greater than 55 dynes / cm without detecting the "maggial" odors common to corona-treated BOPP films.

Example 2 The film production was carried out as in Example 1, except that for the extrusion of the layer A, the conveying speed of the corresponding extruder was reduced to 15 U / min. The thickness of the polyamide outer layer (layer A) was about 0.6 μm. The obtained film had the same brilliant appearance and the same high surface tension as in Example 1.

Example 3

The film was produced as in Example 2, but in this case no corona treatment took place. The appearance of the film was as in the previous examples and the surface tension of the freshly prepared film was about 50 dynes / cm.

On a slicing machine, a composite roll was made with the samples of Examples 1, 2 and 3, and all three rolls of the roll were subjected to the same conditions as the standard conditions for metallization of a BOPP film in an Applied Films metal steamer metallized at an optical density of 2.3. It was found that metal adhesion was excellent for all three metallized samples under the same conditions.

Example 4

Film preparation was as in Example 1, except that the conveying speed of the extruder of layer A was increased to 64 rpm, resulting in a film having a layer thickness of the PA layer on the oriented S-BOPP film of about 2.5 μm led. The film had the same brilliant appearance as before, but showed a high curling tendency due to the high rigidity of the outer polyamide layer (layer A) having the high surface tension.

Example 5

Film preparation was essentially as in Example 1, except that for layer B (subbing layer) a mixture of 50% Bynel 21 E 781 and 50% HP 522 HPP was used.

The obtained film had an improved appearance, a very good structural integrity and excellent adhesion of the polyamide layer (layer A).

Since it was observed that polyamide accumulation occurred at the edge of the outer molten die for polyamide extrusion which, in conjunction with the air knife effect, resulted in discernible film surface streaking, the feed of the melt nozzles for Examples 6 to 15 below for the layers A to E, so that the polyamide layer now formed that side of the melt which came into direct contact with the cooling roll. In the following examples 6 to 15, the polyamide layer is thus the layer E.

Example 6

A coextrusion of 5 different polymers was carried out by 5 slot dies in the following arrangement:

Layer A: TD 110 BF, extruder conveying speed

25 rpm; Layer B: HP 522 H, extruder with melt pump,

Conveying speed 35 rpm; Layer C: HP 522 H, core extruder with melt pump,

Conveying speed 46 rpm; Layer D: 50% Bynel 50 E 739 and 50% HP 522 H; Extruder with melt pump, conveying speed 8 rpm. Layer E: PA 3426; Extruder conveying speed 12

U / min.

The primary film obtained on the chill roll was stretched simultaneously in MD 8.6 times and in TD 7 times, whereby a film having a thickness of 20 μm was obtained and the thickness of the polyamide layer (layer E) was about 0.6 μm.

The S-BOPP film of Example 6 made in a width of 800 mm had a better overall appearance than the films prepared in the preceding Examples 1 to 5 in that no streaks were recognizable. The surface tension of the PA outer layer was found to be about 50 dynes / cm.

Example 7

Film preparation was as in Example 6, except that the LISIM® stretching equipment was adjusted to stretch 7.5 times in TD and the finished S-BOPP film had a width of 900 mm, and it became a 4000m long roll produced.

Example 8

Foil production was carried out as in Example 7, and an 8000m roll was made for metallization purposes with the surface of the polyamide outer layer (Layer E) of the last 2,000 film-meters were subjected to a flame treatment under conditions which are customary for BOPP films.

The flame-treated surface had a surface tension greater than 55 dynes / cm.

The film prepared in Example 8 was vacuum-coated with aluminum vapor in a conventional manner so that the optical density became 2.3. In this case, the polyamide surface of the film was pretreated before the metallization in different ways, namely were

Subjected to 1200m of a flame treatment and an in-vacuum plasma treatment;

800m subjected exclusively to a flame treatment;

4500m. were not treated additionally; and

1500m were subjected to only one in-vacuum plasma treatment.

The results of the metallization after the different pretreatments are listed separately in the attached table at the end according to Example 18.

Example 9

Film preparation was as in Example 8, except that the entire 2000m of the outer PA layer (Layer E) was subjected to flame treatment under the conditions usual for BOPP films.

Example 10 Film preparation was as in Example 7, except that the thickness of the PA layer (layer E) was increased to about 1.2 μm.

The films produced in Examples 7, 9 and 10 were combined on a cutting machine into a composite roll and subjected under identical conditions to a vacuum coating with a clear ceramic barrier coating (SiOx).

Example 11

The film preparation was carried out as in Example 7, except that the stretching ratio in MD 9 and TD was 7.5 in simultaneous stretching and the conveying speed of the extruder for the core layer was adjusted so that a total film thickness of 12 .mu.m was obtained the thickness of the polyamide layer (layer E) was about 0.75 μm.

Example 12

Sheeting was made as in Example 11, except that the line speed and feed rate of the core extruder were adjusted to give a film having a total thickness of 15 microns with the feed rate of the extruder for layer E set to 24 rpm. which gave a thickness of the PA layer of 0.65 μm.

Example 13

In this example, as well as the two following examples 14 and 15, the thickness of the polyamide layer (layer E) was varied in order to determine the influence of the thickness of the PA layer on the printability and coatability of the multilayer film. The film production took place in Example 13 as in

Example 12, except that the thickness of the polyamide layer

(Layer E) was increased to about 0.38 microns by the

The conveying speed of the extruder increased to 12 rpm.

Example 14

Sheeting was made as in Example 11, except that the thickness of the polyamide layer (layer E) was reduced to about 0.2 μm by reducing the feed speed of the extruder for layer E to 6 rpm.

Example 15

Film preparation was as in Example 11, except that the thickness of the polyamide layer was reduced more by reducing the feed speed of the E layer extruder to only 3 rpm.

The resulting S-BOPP films of 15 μm thickness showed a good, uniform surface coverage by the very thin layer of less than 0.1 μm from the low-crystalline polyamide.

All 5-layer films of Examples 1 to 15 had high surface tension and excellent optical properties and strength properties, which can be seen from the table.

Before example 16:

In the following examples, 7-layer films were prepared with a 400 mm wide slot die using the above 5 extruders as follows. Layer A: twin-screw co-extruder for extrusion of 1 μm TD 120 BF, corona treated; Layer B: twin-screw extruder: HP 522 H with additives; Layer C: 35 mm single-screw extruder: 1 μm thick adhesive layer of 50% HP 522 H / 50% Bynel 50 E 739;

Layer D: 35 mm single screw extruder: polyamide barrier; Layer E: same extruder and same material as layer C; Layer F: same extruder and same material as layer B; Layer G: 50 mm single-screw extruder with melt pump, extrusion of a layer of 1 μm TD 110 BF.

Example 16

A film having the 7-layer structure described above was extruded, and the primary film formed on the chill roller was stretched 8.5 times in MD and 5.5 times in TD to obtain a film of 20 μm in thickness, which had at its center a PA barrier (layer D) of 1.45 μm thickness.

Example 17

The film preparation was carried out as in Example 16, except that the conveying speed of the extruder for the polyamide barrier (layer D) was increased, so that a layer thickness of 1.75 μm was obtained.

Example 18 Sheeting was made as in Example 17, except that the conveying speed of the extruder for the polyamide barrier (layer D) was further increased to give a barrier having a thickness of 2.15 μm.

Results:

The properties of the films produced in Examples 1 to 18, insofar as they were measured, are reproduced in the table below.

The results of the film-forming experiments described in the examples clearly show that according to the present invention BOPP films with excellent barrier properties and a combination of other excellent and desirable for packaging properties are obtained, with very good film strengths, stiffnesses, excellent optical properties with excellent properties Aroma and odor-tightness and excellent other barrier properties that can be taken from the table are obtained.

Values for the tensile strength of about 140 N / mm ² (MD) or 280 N / mm ² can be used as comparative values for typical BOPP films obtained by sequential stretching. (TD), for the elongation at break in the range of 150-250% (MD) and 50-60% (TD) and for the modulus of elasticity in the range of 2000-2200 N / mm ² (MD) and up to 3800 N. / mm ² (TD) are used.

It should be noted that the aroma and odor resistance is also observed for films that have neither a metallization nor a ceramic coating. The scope of the manufacturing process given in the examples Conditions are limited only by the equipment available during the tests, but the process conditions given do not represent the limits of the present invention or the method for producing the films of the invention. Depending on the intended uses of the films, for example, thicknesses of Barrier can be obtained up to 10 μrα, especially for the core arranged in the barrier, if that should be desirable.

It should also be noted that the simultaneous stretching conditions can be controlled so as to stabilize the obtained sheets so that they have a dimensional stability in which one or both of their main directions corresponding to MD and TD, respectively, are of manufacture. a shrinkage of 5% or less is obtained. However, the stretching conditions can also be chosen so that the shrinkage in one or both directions at 135 ° C up to 20%.

It should also be noted that in the case of the 7-ply structure as described by Examples 16 to 18, one of the polypropylene layers is also made using polypropylene regenerate or using polyolefins different from that for the other layer (Layer B), depending on the end use used, taking advantage of the fact that the central PA barrier ensures all purity requirements with respect to the other side of the film.

In addition to the film properties given in the table, it should be noted that some of the values given during the aging of the films It is particularly important to increase the elastic modulus values by about 30% within 60 days of manufacture. It is also important that the surface tension of the treated or untreated film of the invention, in which the PA barrier is an outer layer, remains substantially constant over time, which is a distinct advantage over standard BOPP films in which the Surface tension after a surface treatment (flame treatment, plasma treatment) changes relatively rapidly over time.

Therefore, films of the present invention need not be immediately coated (metallized, ceramic coated), and the coating may be done as needed using ready-made finished films.

Due to the excellent barrier properties, the films are suitable for all packaging purposes where it is important that the packaged goods do not suffer from loss of aroma and / or that no odor develops through the packaging. The oxygen permeability and water vapor permeability of the films of the present invention are such that they are suitable for most uses currently requiring the more expensive and, due to their higher density, heavier coated polyester films.

Particularly preferred uses are uses for food packaging, such as fresh ones

Food, confectionery and confectionery, and of

Stimulants, which may include, for example, coffee and tea or tobacco. Also for the packaging of other goods, such as pharmaceuticals, the films can be used. Due to the cellophane-like or With its glass-like appearance and handle, the films can also be used for all applications where the consumer expects cellophane-like materials. Due to the good printability, the films of the invention are also ideal for advertising-effective designed packaging of all kinds.

Claims

claims:

1. Barrier film for packaging, in particular for the packaging of food and semi-luxury products, in the form of a multilayer film based on at least one support layer in the form of a biaxially oriented polypropylene film (PP film) with at least one co-extruded functional layer based on an amorphous or semi-crystalline Polyamide (PA) or a mixture of such a polyamide with ethylene-vinyl alcohol copolymers (EVOH),

characterized in that it is prepared by simultaneously stretching a coextruded multilayer primary film, the functional PA layer forming an outer layer of the film.

2. High-strength brilliant barrier film for packaging, in particular for the packaging of food, in the form of a multilayer film based on at least one support layer in the form of a biaxially oriented polypropylene film (PP film) having at least one co-extruded functional layer based on an amorphous or partially crystalline polyamide (PA) or a mixture of such a polyamide with ethylene-vinyl alcohol copolymers (EVOH),

characterized in that it is produced by simultaneously stretching a coextruded multilayer primary film, the functional PA layer comprising a central inner layer of the film is formed, which is arranged between two carrier layers.

3. A film according to any one of claims 1 or 2, characterized in that the tensile strength of the film and its modulus of elasticity in the machine direction (MD) and their elongation at break in the transverse direction (TD) are equal to or higher than in TD or MD.

4. A film according to any one of claims 1 or 2, characterized in that the sum of the E-modules in the longitudinal and transverse directions exceeds 3500 N / mm ² , preferably 4500 N / mm ² .

5. A film according to claim 3 or 4, characterized in that its tensile strength (ASTM D 822) in MD in the range of

170-280 N / mm ² , and in TD is in the range of 130-215 N / mm ² .

6. A film according to claim 3, 4 or 5, characterized in that its elongation at break (ASTM D 82) in MD in

Range of 50-120%, and in TD is in the range of 100-220%.

7. A film according to any one of claims 1 and 3 to 6, characterized in that it has a gloss (Gloss, ASTM 2457) over 100.

8. A film according to any one of claims 1 and 3 to 7, characterized in that it has on the PA barrier metallization or a clear SiOx or AlOx ceramic coating and its oxygen permeability (OTR) at 23 ° C and 75% relative humidity below 0.50 cm ³ / (m ² datm), in particular below 0.20 cm ³ / (m ² datm), and their water vapor permeability (WVTR, ASTM E 96) under tropical conditions. (38 ° C, 90% relative humidity) is less than 0.5 g / (m ² d).

9. A film according to any one of claims 1 and 3 to 8, characterized in that its layer structure is at least three layers and comprises a PP support layer, an adhesive layer disposed thereon and an overlying the adhesion layer outer PA barrier.

10. A film according to claim 9, characterized in that it is at least four layers and on the PA barrier side facing away from the PP support layer has at least one further layer which is heat-sealable.

11. A film according to claim 2, characterized in that its layer structure is at least five-layered and the sequence of layers comprises a first PP support layer, a first adhesion layer, a PA barrier, a second adhesion layer and a second PP support layer.

12. A film according to claim 11, characterized in that it additionally has a heat-sealable thermoplastic outer layer over the first PP supporting layer suitable for corona or plasma treatment thermoplastic outer layer, and / or on the second PP Tra-.

13. A film according to claim 12, characterized in that one of the PP supporting layers contains a regenerated PP.

14. A film according to any one of claims 9 to 13, characterized in that the adjacent to the PA barrier adhesive layers of PP are formed by mixing with an anhydride-modified PP, a polyethylene copolymer or an anhydride-modified acrylic resin modified, wherein the PP amount of the adhesive layer is up to 75 wt .-%.

15. A film according to claim 1 or 2, characterized in that the thickness of the PA barrier is in the range of 0.1 to 10 microns.

16. A film according to claim 1, characterized in that the thickness of the PA barrier is in the range of 0.1 to 5 microns.

17. A film according to claim 2, characterized in that the thickness of the PA barrier arranged in the interior of the multilayer film is in the range of 0.5 to 10 μm.

18. A film according to any one of claims 1 to 17, characterized in that the thickness of the film is in the range of 8 to 80 microns.

19. A film according to any one of claims 1 to 18, characterized in that one or more of the PP support layer (s), the adhesive layer (s) and / or the barrier contains additives which are selected from a group, which comprises mineral or organic additives for forming microvoids, fillers, absorbents, UV and light stabilizers, dyes and opacifying pigments.

20. A film according to any one of claims 1 to 19, characterized in that they according to a method according to the

Claims 21 to 26 is available.

21. A process for producing a barrier film for packaging according to one of claims 1 to 19, characterized in that the layers of the Multilayer film-forming polymers are coextruded as melts from the required number of slot dies onto a chill roll and the primary multilayer film formed is subjected to non-contact simultaneous stretching with a 40- to 80-fold increase in area on a simultaneous stretching machine with linear motor operation (LISIM®). or on a mechanical simultaneous stretching unit.

22. The method according to claim 21, characterized in that the primary multilayer film in the machine direction (MD) is stretched to at least βfache their length.

23. The method according to claim 22, characterized in that the primary multilayer film is stretched simultaneously in MD to at least 7 times and in the transverse direction (TD) to less than 7 times.

24. The method according to claim 22, characterized in that the primary multilayer film is stretched simultaneously in MD to more than 8 times, preferably at least 9 times, and in TD to less than times.

25. The method according to any one of claims 21 to 24, characterized in that the PA layer is coextruded as that outer layer of the primary film having direct contact with the cooling roller.

26. A process for producing a barrier film for packaging according to any one of claims 1 to 19, characterized in that the layers forming the multilayer film forming polymers coextruded as melts from an annular die and subjected to simultaneous stretching by the BUBBLE or DOUBLE BUBBLE process , wherein an area increase is effected to 40- to 80-fold.

27. Use of a barrier film according to one of claims 1 to 20 as a flavor, odor and oxygen-tight packaging film for food and beverage.

28. Use according to claim 26 of a barrier film with a clear SiOx or AlOx ceramic coating according to claim 8 for the production of aroma, odor and oxygen-tight blister packs for food and beverages.