DE202010008675U1 - Multilayer film - Google Patents

Abstract

Multi-layer composite film with:
an outer cover layer (A) and a thermally sealable peel layer (P), wherein
a) the cover layer (A) is a polar bonds polymer;
b) the heat-sealable peel layer (P) is sealable even without fusion against polar polymers and has a polar thermoplastic elastomer or a mixture thereof with polymers and conventional additives.

Description

The invention relates to a multilayer composite film comprising: an outer cover layer (A) and a thermally sealable peel layer (P).

Sealable, on the outside polar polymers having multilayer films are known. The packaging industry has a high demand for such films. Particularly sought after are transparent films which adhere to polar films, such as thermoformed polyester films, polystyrene trays or polylactide shells. If fresh, perishable foodstuffs are packed with film, it is desirable to be able to open the packaging easily without cutting tools - for example, by using a so-called peel film. In this case, the cover sheet of the pad on which it is sealed, be deducted. The peelability of the cover film is usually ensured by the fact that foreign molecules are introduced into an adhesive layer, which reduce the tack on the pad.

In the GB-A-1465973 describes a coextruded, two-layered polyester film, one layer of isophthalic and terephthalic acid containing copolyesters and their other layer of polyethylene terephthalate. About the sealing behavior of the film can be found in the document no usable information. The film is only partially windable and weiterverarbeitbar.

In the EP-A-0 035 835 describes a coextruded, sealable polyester film, which are added to improve the winding and the processing behavior in the sealing layer particles whose average particle size exceeds the layer thickness of the sealing layer. The particulate additives form surface protrusions which prevent unwanted blocking and sticking of the film to rollers or guides. About the other, non-sealable layer of the film are no further details for the incorporation of antiblocking agents made. It remains unclear whether this layer contains antiblocking agents. By choosing particles with a larger diameter than the thickness of the sealing layer and the concentrations specified in the examples, the sealing behavior of the film is deteriorated. The seal seam is made at 140 ° C and the seal seam strength is determined at 23 ° C, and is in a range of 63 to 120 N / m (corresponding to 0.97 to 1.8 N / 15 mm film width).

In the EP-A-0 515 096 describes a coextruded, multilayer, sealable polyester film which has an additional additive on the sealable layer. The additive may, for. As inorganic particles and is preferably applied as an aqueous layer to the film in their preparation. This should maintain the good sealing properties and be easy to process the film. The back side of the film contains only very few particles, which pass mainly through the regranulate into this layer. Information on the sealing temperature range of the film are not made in this document. The seal seam is produced at 140 ° C and the seal seam strength is determined at 23 ° C, and it is more than 200 N / m (corresponding to 3 N / 15 mm film width). For a 3 [mu] m thick sealing layer, a seal seam strength of 275 N / m (corresponding to 4.125 N / 15 mm film width) is specified.

In the EP 0 920 381 B1 describes a coextruded, multilayered polyester film having a sealable overcoat and a non-sealable basecoat. The base layer may be composed of one or more layers, wherein one of the layers is in contact with the sealable layer. The other (outer) layer then forms the second, non-sealable cover layer. The sealable topcoat may consist of isophthalic and terephthalic acid containing copolyesters. The film also contains a UV absorber, which is added to the base layer in an amount of 0.1 to 10 wt .-%. The base layer of this film is equipped with conventional antiblocking agents. The film is characterized by a good sealability, but does not have the desired processing behavior and has deficits in the optical properties. For example, the haze of the film is given as <75%.

In the EP-A-1 138 480 describes a biaxially oriented, sealable polyester film having a base layer (B), a sealable top layer (A) and another non-sealable top layer (C). The sealable outer layer (A) has a sealing temperature (also called minimum sealing temperature) of at most 110 ° C and a seal strength of at least 1.3 N / 15 mm film width. The topographies of the two outer layers (A) and (C) are characterized by certain features. This film is particularly suitable for use in flexible packaging, especially for use on high-speed packaging machines. The film still shows deficits regarding handling and processing behavior.

EP-A-1 471 096 . EP-A-1 471 097 . EP-A-1 475 228 . EP-A-1 475 229 . EP-A-1 471 094 and EP-A-1 471 098 describe heat-sealable and APET / CPET peelable polyester films with ABC structure, which to adjust the desired peel properties in the peelable and heat-sealable topcoat (A) either about 2-10 wt .-% inorganic or organic particles or a polyesterunverträgliches polymer such , As a norbornene / ethylene copolymer.

From the EP 0540 031 B1 For example, a thermoplastic bonded multilayer structure has become known in which a vinyl aromatic polymer layer is in admixture with a layer of a vinyl aromatic monomeric butadiene block copolymer and one or more further layers is of a vinyl aromatic polymer and is sealable. This film is acid resistant but not peelable.

The DE 3921677 A1 describes a sealable plastic film which is sealable against polystyrene, wherein the outer layer sealing against polystyrene consists of up to 50% heat-sealable impact-resistant polystyrene-butadiene and then any other layers can be applied thereto, including by means of an adhesion promoter or adhesive. There is no information about a peelability.

From the EP 1173 331 Films are known which have a thermoplastic elastomer in the sealing layer and a polypropylene film as a cover layer, which are suitable for relatively temperature-resistant packaging.

EP 0515096 teaches multilayer films of oriented PET which are coextruded with a copolyester resin which can then form a heat seal bond on itself or on the substrate or both. It is proposed to introduce foreign molecules into the copolyester in order to modify the sealed seams

In general, sealable and peelable multilayer films with TPEs in the sealing layer are thus known.

The previously known films were problematic insofar as their peelability could only be ensured by complex measures. For example, foreign molecules were mixed into the peel layer, such as SiO 2 or polymer particles which are incompatible with the main polymer of the peel layer, in order to weaken the tack of the sealing layer and to ensure peelability. The incorporation of such foreign molecules is laborious and leads to poor traceability or reusability of these polymers modified in this way.

The object of the present invention is to provide a sealable, peelable multilayer film which avoids the disadvantages of the prior art films and is distinguished, in particular, by an improved peel / sealability with respect to itself and to substrates made from polar polymers. A particular concern of the present invention was to provide a polyester film with good seal against other polyester (non-sealable) polyester films or trays.

The object is achieved by a multilayer film having the features of patent claim 1. Due to the fact that, surprisingly, the multi-layer film also has reclosability relative to the outer surface, an improved film having hitherto unknown properties, namely reclosability, is achieved.

The sealability to itself makes it possible to produce bags or tubes from the multilayer film, while the sealability to polar polymers allows sealing to polar polymers, such as polyesters, polystyrene, polylactide, starch polymers, etc.

As a result, the film is suitable - depending on the nature of the intermediate layers or the cover sheet as material for trays, which are closed with a cover sheet resealable. Typical examples are food packaging for cheese slices and the like. Like., But also cotton wool, cloths or other objects that are removed individually, while in the packaging remains a residue to be kept in the packaged state. The material can also be used as a cover sheet, even with the appropriate layer structure, with a resealable sealability against polar surfaces.

The polar outer cover layer (A) may be selected from common polar plastics such as polyethylene terephthalate, polyurethane, polylactide, polycarbonate, starch polymers, polystyrene, polyamide and mixtures thereof.

The peel layer (P) sealable to the cover layer and itself without a melt has a polar TPE or a mixture thereof, the TPE being selected from the group consisting of TPS (styrene-butadiene block copolymers), TPE-E (thermoplastic polyester elastomers) , Polylactic acid, TPA (thermoplastic polyamide), TPU (thermoplastic polyurethane).

The multilayer composite film is preferably clear and transparent.

Depending on the application, the multilayer composite film between the outer cover layer and the peel layer can have further layers selected from barrier layers for gases or anti-fog agents, adhesive layers, UV protection layers, layers for improving the mechanical stability.

The peel layer (P) preferably adheres to the outer cover layer according to Peel by pressing back on. This is due to the fact that the polar surfaces of the polar TPE can form a van der Waals bond with the polar surface groups of the cover film, which are responsible for the Reclosability ensures. So far, had to be used for reclosability of a package or bag piping or zippers that were consuming in the production and required larger amounts of material.

According to the invention, a satisfactory reclosability can now be achieved by the combination of the TPE component having polar groups in the peel layer and the surface having polar groups, to which it is sealed without melting seam.

In a preferred embodiment, the cover layer comprises predominantly oriented polyethylene terephthalate and the peel layer comprises predominantly styrene-butadiene block copolymer.

A method for producing a multilayer composite film according to the invention comprises laminating a multilayer film having a polar outer cover layer with a polar TPE peel layer.

The lamination can be done with or without glue or solvent, depending on the material. In a simple embodiment, a layer substantially comprising styrene-butadiene copolymer (SEBS) can be produced directly on oriented polyethylene terephthalate, whereby adhesives, adhesion promoters, etc. are saved by solvent or solvent-free lamination of e.g. B. a PET-O film against a mono / coextrudate with a TPE-E peel layer against A-PET possible. This film seals easily reclosable thermally against PET trays or polystyrene and is clear and transparent.

A use of the multilayer composite film according to the invention is as a packaging material for food, luxury and pharmaceutical articles and medical auxiliary products.

• a) die Deckschicht (A) z. B. ein orientiertes PET-O, PP-O oder PA-O ist;
• b.) die gegen A-PET siegelfähige Peelschicht (P) ein Compound aus einem TPE-E und/oder Polymilchsäure ist. Bevorzugt ist die PET-Mehrschichtverbundfolie Folie klar und transparent. Eine derartige Peelschicht siegelt ab einer Siegelinitialtemperatur von 135°C gegen A-PET und weist nach der Erstöffnung der Verpackung eine Siegelnahtfestigkeit Wiederverschlußkraft für nicht verschmolzene Siegelnähte gegenüber einem A-PET-Substrat von größer als 0,2 N/15 mm auf. Typische Dicken der Peelschicht (P) sind eine Dicke von 5% bis 90% der Gesamtfolienstärke, vorzugsweise 10%–50%, Idealerweise 20% bis 30%

In a preferred embodiment, the multilayer composite film has z. Example, a PET-O cover layer (A) and a thermally sealable peel layer (P), and an adhesive layer for connecting the layers wherein

• a) the cover layer (A) z. An oriented PET-O, PP-O or PA-O;
• b.) the A-PET sealable peel layer (P) is a compound of a TPE-E and / or polylactic acid. Preferably, the PET multilayer composite film is clear and transparent. Such a peel layer seals against A-PET at a sealing initial temperature of 135 ° C. and, after the initial opening of the packaging, has a sealing seam resealing force for unmelted sealing seams compared to an A-PET substrate of greater than 0.2 N / 15 mm. Typical thicknesses of the peel layer (P) are a thickness of 5% to 90% of the total film thickness, preferably 10% -50%, ideally 20% to 30%

• – eine verbesserte Wicklung,
• – verbessertes Verarbeitungsverhalten (niedrige Reibung),
• – verbesserte optische Eigenschaften (weniger Trübung).

A particularly typical use of the multilayer composite film is as a lid film for food containers. The film according to the invention has, inter alia, the following advantages:

• An improved winding,
• - improved processing behavior (low friction),
• - improved optical properties (less haze).

A typical shell, which can be peelably closed by this film, has A / CPET = two-layer laminate z. For example, in a menu tray, inside APET, outside CPET (APET = amorphous polyethylene terephthalate (PET), CPET = crystalline PET;) on.

A film according to the invention can be used, for example, as a cover film for plastic containers having a polar surface selected from PET, styrene, polylactide, polycarbonate, polyamide and mixtures thereof.

In addition, the film of the invention is easy to wind and can be processed on high-speed machines. In embodiments in which the TPE adheres directly to other film layers due to its tack, a thinner composite can be achieved, which leads to film rolls with a greater run length and thus less handling costs by changing the films in the sealing machine. In the production of the film is also ensured that accumulated waste material can be recycled as regenerated back to the production process, without affecting the physical and optical properties of the film are adversely affected.

A typical sealable polyester film having a top layer, a sealable peel layer (P), comprises polystyrene butadiene and / or polylactide, without external particles, when the sealable top layer (A) contains a polar polymer. Preferably, the haze of the transparent film is less than 5%.

There are no bubbles between the sealing layer (P) and the substrate (A), and the seal is full-surface since no voids occur through the tips of the previously used fillers, which deteriorate the seal. Polyesters of the invention are available as commercial products.

The desired sealing properties of the outer layer (A) are selected from the combination of chemical composition of the copolyester used, the topcoat.

The sealable peel layer (P) has - relative to itself a seal initiation temperature of preferably less than 150 ° C and a seal seam strength (the seal seam is prepared at 180 ° C, the seal seam strength determined at 23 ° C) of preferably at least 1.0 N / 15 mm foil width; - With respect to a substrate made of APET a sealing temperature of preferably less than 160 ° C and a sealed seam strength (the seal is prepared at 180 ° C, the sealed seam strength at 23 ° C determined) of preferably at least 1.0 N / 15 mm film width.

The layers of the multi-layer composite may additionally contain customary additives, for example UV stabilizers, hydrolysis stabilizers, antiblocking agents (for example via the regenerate). These additives are expediently added to the polymer or the polymer mixture before melting. The invention also relates to a process for the preparation of the novel polyester film according to the known coextrusion process.

First, as is customary in the coextrusion process, the polymer or the polymer mixtures for the individual layers are compressed and liquefied in an extruder, wherein the additives optionally provided as additives may already be present in the polymer or in the polymer mixture. The melts are then simultaneously pressed through a flat die (slot die) and the extruded multilayer melt is drawn off on one or more draw rolls, with the melt cooling and solidifying to an unoriented prefilm.

Biaxial stretching is generally performed sequentially. Preferably, the prefilm is stretched first in the longitudinal direction (i.e., in the machine direction = MD direction) and then in the transverse direction (i.e., perpendicular to the machine direction = TD direction). This leads to a spatial orientation (orientation) of the polymer chains. The stretching in the longitudinal direction can be carried out with the aid of two rolls rotating at different speeds according to the desired stretch ratio. For transverse stretching is generally used a corresponding clip frame in which the film is clamped on both edges and then pulled at elevated temperature to both sides.

The temperature at which the stretching is carried out may vary within a relatively wide range and depends on the desired properties of the film. In general, the longitudinal stretching is carried out at a temperature in the range of 80 to 130 ° C and the transverse extension in the range of 90 to 150 ° C. The longitudinal stretch ratio is generally in the range of 2.5: 1 to 6: 1, preferably 3.0: 1 to 5.5: 1. The transverse stretch ratio is generally in the range of 3.0: 1. to 5.0: 1, preferably from 3.5: 1 to 4.5: 1. In the subsequent thermosetting, the film is held for a period of about 0.1 to 10 s at a temperature of about 150 to 250 ° C. Subsequently, the film is wound in the usual manner.

Preferably, after the biaxial stretching, a non-sealable surface of the polar group-containing film is corona-treated or flame-treated by one of the known methods. The treatment intensity is generally in the range of over 50 mN / m.

The biaxially oriented polyester film of the present invention can also be coated in-line on the sealable layer, i. H. the coating is preferably applied during the film production process before the longitudinal and / or before the transverse extension. In order to achieve a good sealability of the polyester film with the polar TPE, the surface is preferably first corona treated.

It is also possible to produce the multilayer film by laminating a at least the polar outer cover layer having film with the peel layer.

The inventive film is characterized by an excellent sealability, a very good winding and appearance, a very good processing behavior. The sealable peel layer (P) seals against itself and against a sealable polar cover layer (A), which is also on substrates of z. APET, A / CPET and CPET. The film is thus used in many areas such. As a lidding film for (menu) dishes or bags or generally as packaging material for food and beverage. In addition, it is ensured in the production of the film that the blend material (regenerate) in an amount in the range of about 20 to 60 wt .-%, based on the total weight of the film, can be fed back to the extrusion without the physical and optical properties of the film are appreciably adversely affected, especially not their visual appearance.

Sealing seam strength (compared to APET)

To determine the seal seam strength, a film strip (100 mm long x 15 mm wide) is placed on the APET side of a corresponding strip of a menu dish and at the set temperature of 180 ° C, a sealing time of 0.5 s and a Sealing pressure of about 3 bar (sealing device HSG / ET Brugger, DE, sealed on both sides sealed sealing jaw) sealed. Corresponding 4 the sealed strips are clamped in the tensile testing machine (eg universal testing machine TC-FR1.0TH.D09 from Zwick, DE) and the 180 ° seal strength, ie the force required to separate the test strips, at a take-off speed of 200 mm / min and a test temperature of 23 ° C determined. The seal seam strength is given in N per 15 mm foil strip (eg 2 N / 15 mm).

Determination of the minimum sealing temperature (compared to APET)

With the sealing device HSG / ET from Brugger, heat-sealed samples (sealed seam 15 mm × 100 mm) are produced, as described above for the measurement of the seal seam strength, the film being heated at different temperatures with the aid of two heated sealing jaws at a sealing pressure of 3 bar and sealed for a period of 0.5 seconds. The seal seam strength was measured as in the determination of 180 ° C seal strength. The minimum sealing temperature is the temperature at which a seal seam strength of at least 0.5 N / 15 mm is achieved (= seal initiation temperature).

Sealing seam strength against itself (= FIN-seal)

To determine the seal seam strength, two 15 mm wide film strips were superimposed and sealed at 180 ° C., a sealing time of 0.5 s and a sealing pressure of 3 bar (device: Brugger type NDS, one-side heated sealing jaw). The seal strength was determined by the T-Peel method = 2 90.

Determining the minimum sealing temperature with respect to oneself

Heat-sealed samples (sealing seam 20 mm × 100 mm) are produced with the sealing device HSG / ET from Brugger, the film being sealed at different temperatures with the aid of two heated sealing jaws at a sealing pressure of 3 bar and a sealing time of 0.5 s. Test strips of 15 mm width were cut from the sealed samples. The T-seam strength was measured as in the determination of the seal strength. The minimum sealing temperature is the temperature at which a sealed seam strength of at least 0.5 N / 15 mm is achieved.

The invention will be explained in more detail by means of embodiments to which it is by no means limited, and the accompanying drawings. It shows:

1 a cover sheet according to the invention for PET trays

2 an inventive thermoforming film

3 a film according to the invention for resealable bags; and

4 a bag from the film according to 3

example 1

Resealable sealable cover sheet

A schematic in 1 Cover sheet (A) shown has a layer of 12 μm PET-O. This is provided with an adhesive-containing color layer (F), which may contain advertising for the contents of the package, laminated with a polyolefinic layer, on which then a barrier layer (B) of EVOH against oxygen, by means of adhesion promoter (H) on a Styrene butadiene TPE layer (P) is attached. This film seals against PET trays and is very well suited for resealable food packaging. ( 2 )

Example 2

Reclosable sealable thermoforming film

A coextruded multilayer film (A) of mono-A-Pet, C-Pet, G-PET, optionally with the addition of conventional additives and antiblocking agents - also for ease of further processing - is coated with a polylactide / SEBS mixture, resulting in a thermoplastic sealant layer (P) leads. The composite is deep-drawn into a dish with a rim so that the polylactide / SEBS mixture lies on the inside of the dish. The shell is resealable against PET-O film layers, polylactide film layers, polycarbonate film layers as covers or cover films.

Example 3

Foil for the production of resealable bags

Polyethylene terephthalate is coextruded as a topcoat (A) with SEBS (P). In the coextrusion film thus produced, the peeling layer of SEBS thermally seals itself permanently by selecting a sealing temperature at which melting of the SEBS layer partially takes place, so that a fusion seam is formed. However, it also seals thermally peelable and resealable against the PET cover layer. Thus, it is possible with a single film without further additives reclosable bags, as in 3 shown. In 4 is shown resealable bag according to the invention. Here are the permanent, indissoluble melt sealing seams 10 used to form the bag, while the peelable thermally sealed without melting openable closure seam ( 20 ) allows the bag to be opened.

Of course, the specific methods and systems described are only illustrative of an application of the principle of the invention. Various modifications can be made without departing from the gist of the invention and its scope.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• GB 1465973A [0003]
• EP 0035835 A [0004]
• EP 0515096 A [0005]
• EP 0920381 B1 [0006]
• EP 1138480A [0007]
• EP 1471096A [0008]
• EP 1471097 A [0008]
• EP 1475228 A [0008]
• EP 1475229A [0008]
• EP 1471094A [0008]
• EP 1471098A [0008]
• EP 0540031 B1 [0009]
• DE 3921677 A1 [0010]
• EP 1173331 [0011]
• EP 0515096 [0012]

Claims (7)

Multi-layer composite film with: an outer cover layer (A) and a thermally sealable peel layer (P), wherein a) the cover layer (A) is a polar bonds polymer; b) the heat-sealable peel layer (P) is sealable even without fusion against polar polymers and has a polar thermoplastic elastomer or a mixture thereof with polymers and conventional additives. Multi-layer composite film according to claim 1, characterized in that the polar outer layer (A) is selected from polyethylene terephthalate, polyurethane, polylactide, polycarbonate, starch polymers, polystyrene, polyamide and mixtures thereof. Multilayer composite film according to Claim 1 or 2, characterized in that the peel layer (P) sealable against the cover layer and itself without a melt has a TPE or a mixture thereof, the TPE being selected from the group consisting of TPS (styrene-butadiene block copolymers ), TPE-E (thermoplastic polyester elastomers), polylactic acid, TPA (thermoplastic polyamide), TPU (thermoplastic polyurethane). Multi-layer composite film according to one of the preceding claims, characterized in that the film is clear and transparent. Multilayer composite film according to one of the preceding claims, characterized in that it comprises, between the outer cover layer and the peel layer, further layers selected from barrier layers for gases or anti-fogging agents, adhesive layers, UV protection layers, layers for improving the mechanical stability. Multi-layer composite film according to one of the preceding claims, characterized in that the peel layer (P) adheres to the outer cover layer after Peel by pressing reclosable. Multi-layer composite film according to one of the preceding claims, characterized in that the cover layer comprises predominantly an oriented polyethylene terephthalate and the peel layer predominantly comprises a styrene block copolymer.

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