DE3618775A1 - Multilayer composite film and process for the production of this film by the system of coextrusion - Google Patents

Abstract

The invention relates to a process and a film in which the water vapour-sensitive barrier layers for gases are enclosed in the centre of the film and bonded by melting. The gas barrier layers consist optionally of an ethylene-vinyl alkanoate (ethylene-vinyl alcohol), known as EVAL or EVOH, and a polyamide, and the water vapour-tight sealing layers consist of a polyolefin, preferably a polyethylene. By virtue of the capability of hot bonding one of the layers disposed in the centre with the other layer disposed in the centre of the film, an inseparable bond is formed, so that the gas barrier layers are doubled in comparison to other film designs and are thus more reliable. Depending on its construction, the film has 7 to 9 layers and is highly efficient in comparison to 3-layer films or 5-layer films known hitherto.

Description

The invention relates to a method for producing multilayered Foils, especially of gas and water vapor Barrier films made by the process of co-extrusion blown films are produced and the film produced thereafter itself.

Multi-layer films are usually produced in that various in a multi-layer ring nozzle of a film die Plastic melts are brought together and such layer by layer to a multilayer film through the nozzle of the Foil die are pressed so that immediately after Exit from the blow head or partially still in the blow head - also called molding tool - by layering the multilayer film of different plastics.

The minimum of layers are two in number, as a rule most manufactured product has 3 layers and in the last Years have passed to films using this system lay up to 5 layers on top of each other and so the multilayer film to build.

The cost of making this 5-layer film is very high due to the type of tools to be used, as well as the Investment for the remaining parts on the film production line.  

The three-layer foils have drawbacks that stand out Document reduced barrier properties.

The layer structure of the barrier films of the previous type is as follows:
Layer ( 1 ) barrier layer made of polyamide 6 or polyamide 6.6,
Layer ( 2 ) adhesion promoter, acting as a thermoplastic adhesive against layer ( 1 ) and against layer ( 3 ), without which the entire laminate cannot achieve a permanent bond,
Layer ( 3 ) sealing layer material, with which the finished films can later be "glued" to the side of layer ( 3 ) under contact pressure and heat.

The layer ( 1 ) made of polyamide is exposed and can absorb water due to its physical properties, this absorption of water vapor permanently reducing or reducing the barrier effect of the polyamide composition. Even the water vapor of normal air is sufficient to enrich the material with up to 2.6% moisture under the following condition: normal climate DIN 50014 23 / 50-2 saturation% DIN 53714, ISO 1110 value 2.6 ± 0.3.

The water absorption at 23 degrees C saturation% DIN 53495, ISO 62, ASTM D 570 = 8.0 ± 0.3% by weight water in polyamide. Water consists of 2 parts hydrogen and 1 part oxygen.

Because of the continuous absorption of water, it also penetrates Oxygen into the film and can thus pass through the barrier Diffuse polyamide material. This is a major disadvantage Kind for the user of the packaging film.

By developing new materials like ethylene vinyl alcohol, Also known as EVAL or EVOH, the number was necessary of the film layers and thus the highly hygroscopic Protect EVAL / EVOH from water vapor. EVOH / EVAL reached with a proportion of 44 parts by weight of ethylene still good value in terms of gas barrier, but that is necessary  Barrier material EVOH / EVAL also a first class for these types and safe protection against water vapor or water.

The blown film lines were therefore converted and the Molding tools - blow heads - with the possibility to to layer 5 or more layers of plastics and so to produce 5 or multilayer films. This was only possible with considerable investment.

The better the barrier material layers, the more effective a barrier film is the greater the number of individuals are protected Layers on top of each other. This has resulted in that for the Thermoforming of the film on the known thermoforming machines for vacuum packaging of meat, sausage, cheese, pharmaceutical Products and others increased the number of layers in the film has been with the aim of packaging safety and thereby improve the barrier ability. That was it necessary, the 3 or 5-layer films already produced to conceal in a subsequent process and so the original 3- or 5-layer films with one at room temperature acting and processable 1 or 2-component laminating adhesive based on polyurethane to a 6 or 10 layer Connect foil. There are still significant costs for the Processing, investment and waste (usually 3-5%) of Case. Such slides are then paid higher by the user and preferred for absolutely safe barriers.

The investment costs of a laminating or coating system are from currently 0.8 million DM to 6.0 million DM, each according to the type, capacity and design of the width.

The invention of the production of a 7- or 9-layer film after the blowing process is based on the surprising fact that it is possible to have a really permanent and firm, almost homogeneous connection of the two inner film layers (from the View of the center seen in the tubular bladder) if a highly adhesive thermoplastic mass is in the inner first layer of the bladder is pressed, which then is used as an adhesive to stack the film layers on top of each other  to press and so together with the high residual heat of the to connect tubular film together. The connection takes place through pressure, heat and ability the plastic mass, instantly a very high heat adhesive ability trigger. This is the 7 or more layered film initially made.

Compared to the previous system, there is one extremely high investment, high processing costs and the not inconsiderable waste - the material is very expensive and contains about 1.0-2.0 kW of pure energy of the forming process granules in foil - also a very much better product emerged with much more certainty for the user, a larger application and the greater freedom in the choice of materials.

The layer structure is 4-layer in the blown film head. The 4th layer is structurally inexpensive to achieve, if it is applied to the inside of the hose base.

A layer structure could look like this, seen from the hose from the outside in:
Layer ( 2 ) Thermoplastic sealing layer with a Vicat softening point of 70 degrees C to 120 degrees C made of the ionomer materials from Du Pont de Nemours in Wilmington, a polyethylene of various types such as low-density (LD), ethylene vinyl acetate (EVA ), High-density (HD), linear (LLD, a co-polymer with added acrylate, a polypropylene or a co-polypropylene made of ethylene-propylene, a co-polyester,
Layer ( 3 ) Thermoplastic layer made of an EVOH / EVAL that sticks to the ionomer from Du Pont or an adhesion promoter based on an inonomer, an ethylene-vinyl acetate-copolyethylene (EVA) a vinylidene-chloride copolymer Poly-vinylidene chloride with proportions of EVA and VC parts from 3% to 30%,
a polyamide or a co-polyamide, an adhesion promoter based on synthetic waxes, EVA and polyethylenes, the ADMER as adhesion promoter of Mitsui Petrochemical, a co-polyester of Eastmann Kodak, the KODAR, which partly act as barrier substances and when used in the layer ( 2 ) stick against ionomers or EVA polyethylenes,
Layer ( 4 ) the barrier material, as partially described under layer ( 3 ). For example, barrier materials are polyamide 6 and polyamide 6.6 and other types, polyamide amorphous type from Du Pont Wilmington, known as "Selar", an EVOH from Solvay or from Du Pont (ethylene-vinyl alcohol), an EVAL (ethylene-vinyl alcohol) ) Kurraray Japan, a co-polyester from Eastmann-Kodak, KODAR, a PVDC co-polymer, vinylidene chloride with 50-90% by weight and a vinyl chloride from 50% to 10% by weight, a poly- Carbonate and other currently known but not listed thermoplastic barrier plastics,
Layer ( 5 ) an adhesion promoter, which ultimately enables the layers to be hot-bonded to one another under pressure and heat after the multilayer melt has emerged from the die, such as an ionomer from Du Pont, known as "Surlyn", an inonomer co-polymer, known as "Bynel" or "CXA" by Du Pont, an ADMER from Mitsui Petrochemical Japan, an ethylene-vinyl-acetate-copolyethylene of more than 5 to 30% by weight in the polyethylene of the EVA.

Another very advantageous variant is the addition of a further layer, here referred to as layer ( 1 ). If the layer ( 2 ) is made of a polyethylene, it is very useful to improve the hot-sticking ability for the subsequent welding process if materials with a very high heat sealability or a low softening point are used here. Furthermore, a film with really optimal properties can be created, in which it is possible to use the expensive and very advantageous plastic masses in a small amount and layer thickness, while the cheap materials for the production of the minimum layer thickness and the "mechanical buffer" against damage can be selected from the mass product polyethylenes. Layer ( 1 ) in this case consists of the ionomer from Du Pont, known as "Surlyn", with a softening point that is at least 15 degrees above that of layer ( 5 ).

Once the film is made and up to 45 degrees Celsius Cooled down to 90 degrees Celsius, the process of hot lamination can kick off.

The tube bladder is pressed between two rollers on a conventional squeezing mechanism, so that a flattened sheet is produced from the original tubular film with higher air pressure inside than outside. This web is free of wrinkles and comes into contact with the inner layers ( 5 ) of the adhesion promoter. The contact pressure of the roller, which may be heated and thus allows very precise temperature control for hot lamination, enables an almost homogeneous connection of the two layers of the adhesion promoter. The result is a multilayer film of the following type, seen from top to bottom:
Outer layer ( 1 ) ionomer, then inner layers,
Layer ( 2 ) Polyethylene
Layer ( 3 ) adhesion promoter or copolymer that sticks to layers ( 2 ) and ( 4 ),
Layer ( 4 ) polyamides as barrier materials, or EVOH / EVAL as barrier material here protected against moisture,
Layer ( 5 ) adhesion promoter
Layer ( 5 ) adhesion promoter from the other inside of the hose
Layer ( 4 ) barrier material, such as polyamides or EVOH / EVAL, (6th layer / layer),
Layer ( 3 ) as adhesion promoter (7th layer / layer),
Layer ( 2 ) Polyethylene (8th layer / layer),
Layer ( 1 ) inonomer "Surlyn" (9th layer / layer).

Is now by mechanical action z. B. damaged the film, the layers ( 5 ) of the coupling agent act as a significant resistant barrier. Masses are then introduced into this layer, which in particular can be very resistant to pointed and sharp-edged influences, so that if a barrier layer is lost, the second barrier layer is still fully present. In practice, this has also been a reason for laminating multilayer films in a subsequent process.

Furthermore, the barrier layers can be made extremely thin and therefore inexpensive. In the case of the EVOH / EVAL barrier material, the adhesion promoter ( 5 ) is thus a further water vapor barrier, so that, depending on the height of the side from which the water vapor effect comes, an effective barrier against the EVOH / EVAL falling off due to the action of water vapor as a gas barrier layer. With EVOH, 3 my layer thickness is already sufficient for a good gas barrier. The addition of two independently effective layers results in better and higher usage values for the film. So when thermoforming the film for the production of vacuum packaging.

The feared water absorption of the polyamide and that the following swelling of the material may occur with the new Material can be avoided in an optimal manner and inexpensively.

The solution leaves considerable advantages in terms of manufacturing costs the film, in the function of the film for the user and the amount of the investment, further with the process engineering to. It is therefore an interesting, easy to manufacture Material created with excellent properties.

Claims (11)

1. Multi-layer composite film produced by the blowing process, characterized in that shortly after the extrusion process, the layers consisting of an adhesion promoter ( 5 ) are hot-laminated to one another, so that an almost homogeneous and very permanent connection of the two layers to one another is created and a tubular film Has become flat film. 2. The multilayer film according to claim 1, which is a Gas and water vapor barrier film acts on both outer Sides is heat sealable. 3. Multi-layer film according to claim 1 + 2, characterized in that the layer ( 1 ) is an ionomer known as "Surlyn" and manufactured by Du Pont Wilmington, which forms the heat seal layer and has a Vicat softening point which is at least 15 degrees Celsius the softening point of layer ( 5 ) of the adhesion promoter is Vicat Norm ASTM D-1525-70. 4. According to claim 3, wherein as a layer ( 1 ) a copolymer based on an ethylene-vinyl acetate-polyethylene with parts by weight of 70-98% polyethylene and 30 to 2 parts of ethylene-vinyl acetate = EVA is used, 5. According to claim 3, wherein a CO-polymer is used as layer (1), which is used in the market as ADMER of Mitsui Petrochemical Japan, 6. According to claim 1 + 2, wherein a thermoplastic layer ( 2 ) with a softening point according to Vicat standard ASTM D-1525-70 from 70 degrees Celsius to 120 degrees Celsius is used. 7. According to claim 6, wherein thermoplastic compositions optionally Polyethylenes of the types LD, HD, LLD or Copolyethylenes with proportions of ethylene vinyl acetate or Co-polyethylene with proportions of ethylene acrylates or an ionomer known as "Surlyn" by Du Pont or a co-polypropylene based on ethylene propylene or a co-polyester extrudable is used.   8. According to claims 1 to 7, wherein a thermoplastic layer ( 3 ) is used, which is made of an EVOH / EVAL and adheres to an ionomer of the layer ( 2 ), or an adhesion promoter based on an ionomer from Du Pont, or an adhesion promoter based on a "Bynel" or "CXA" from Du Pont, or a co-polymer consisting of parts by weight of 2 to 30 ethylene-vinyl acetate and 98 to 70 parts of polyethylene, or an "ADMER" from Mitsui Chemical Japan exists 9. According to claims 1-8, wherein a thermoplastic barrier material is used as the barrier layer ( 4 ), which optionally consists of one of the following materials, such as polyamide 6, polyamide 6.6, amorphous polyamide, a co-polyamide, ethylene-vinyl alcohol, as EVOH from Solvay Brussels or EVOH from Du Pont, an EVAL from Duraray Japan, each known as a co-polymer, a polyvinylidene chloride co-polymer = PVDC, a co-polyester from Eastmann-Kodak Rochester NY State USA, one Polycarbonate, 10. According to claims 1-9, wherein is used as an adhesion promoter for the following hot gluing in the squeezing mechanism of the film winder, which optionally consists of a material of the following type:
Copolymers by Du Pont known as "Bynel" or "CXA", ionomer known as "Surlyn" by Du Pont, copolymers based on synthetic waxes, ethylene-vinyl acetate and polyethylene, known as XBR by Rousselot Paris, a copolymer based on a polyethylene, known as "ADMER" from Mitsui Petrochemical Japan, an ethylene-vinyl acetate copolymer based on polyethylene with 5-30 parts by weight of ethylene-vinyl acetate and 98 to 70 parts by weight of polyethylene, 11. According to claim 1 to 10, wherein as the layer ( 1 ) a material is used, the Vicat softening point according to ASTM D-1525-70 is at least 15 degrees Celsius higher than that of the layer ( 5 ), optionally made from the materials of the following type:
Ionomer "Surlyn" the Du Pont,
Co-polyethylene "ADMER" from Mitsui Petrochemical Japan,
Co-polymer based on ethylene-vinyl acetate with 2 to 25 parts by weight and a polyethylene with 98 to 75 parts by weight,
a co-polypropylene based on ethylene-propylene copolymers,
a "Bynel" or "CXA" from Du Pont Wilmington