DE2914912A1 - MULTI-LAYER POLYESTER / POLYOLE SHRINK FILM - Google Patents

Description

£ 29U912

description

The invention relates to a multilayer flexible thermoplastic Packaging film.

A "shrink film", also called "heat shrinkable Film "is known, is a film that, when exposed to heat, shrinks, and not is stretched again. When the film is stretched again, shrinkage tension is created in it. One packs a product in a shrink film and heats it up, e.g. by passing it through a hot air tunnel or a hot water bath, like this the film shrinks around the product, forming a tightly fitting envelope that corresponds to the contour of the product. When using a transparent shrink film, an aesthetically pleasing packaging is created that the product prevents components from being lost, parts being removed, the product during handling and transport damaged or contaminated by dirt, bacteria, etc.

A "shrink film is made by having a The film is heated to an orientation temperature, i.e. a temperature at which the polymeric material of the film will orient will. The orientation temperature is below the melting temperature of the polymer and usually above room temperature. The film is then stretched, usually biaxially, i.e. in the longitudinal direction (LR) and in the transverse direction (QR). The stretching can

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between pairs of nip rollers or e.g. by tenter frames. The stretched film is quickly cooled, to freeze the molecules of the polymeric material in their oriented state. When rewarming the foil will be The tension forces of the polymer molecules are released in their oriented configuration and the film begins in its original shrink back non-oriented dimension.

Polyolefins and polyvinyl chlorides are the two main classes of synthetic resins that make up the bulk of the im Commercially available shrink films for packaging purposes will be produced. Other resins that make up shrink films Include ionomers, polyesters, polystyrenes and polyvinylidene chlorides. The ones currently on the market existing polyolefin shrink films are made of cross-linked! or uncrosslinked oriented polyethylene, oriented Polypropylene or oriented propylene-ethylene copolymers.

The polyvinyl chloride and polyolefin shrink films provide a wide range of physical and performance properties, such as the shrinkage force (the force that a film per unit area of its cross-section during shrinkage exerts), the degree of free shrinkage (the reduction in the surface area of the film if it is allowed to shrink without it to stretch), the tensile strength (the highest force on a unit area of the film can be applied before

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it tears), the weldability, the shrinkage-temperature curve (the relationship between shrinkage and temperature), the Onset of cracking and resistance (the Force at which a film begins to tear and continues to tear), optical appearance (gloss, lack of clarity and transparency of the Materials) and dimensional stability (the ability of the film to maintain its original dimensions under all types of Storage conditions). The optimal type of shrink film depends, among other things, on the size, weight and shape and the strength of the product to be packaged, the number of product components, other packaging materials, which can be used with the film and the type of packaging device available.

Polyolefins are best suited for applications where moderate to high shrink stresses are preferred, and on new automatic high-speed wrapping machines that have shrink and Welding temperatures can be controlled more closely. The polyolefins leave less deposits and residues behind, thereby extending the life of the device and reducing maintenance of the device. The PVC films have generally better optical properties and lower Shrinkage stresses, weld more firmly with increased Temperatures and shrink over a much wider temperature range than the polyolefins. Set the polyolefins

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usually not free of corrosive gases when welding like PVC foils and are also in this respect cleaner than the PVC films.

So far, polyolefins could not compete with packaging made from PVC film when it comes to the products to be packaged the low shrinkage tensions of the PVC films require, because the products for the application of polyolefins that Shrinkage tensions of up to 4 times the shrinkage tension of PVC films are too fragile. PVC films also represent the shrink films of choice for older, manual ones operated sealing devices and semi-automatic packaging devices in which the temperatures ötark can be varied. Older, poorly maintained packaging devices of all kinds usually operate better with PVC foils than with single-layer polyolefin foils, since the PVC films generally have wider shrinkage and sealing temperature ranges. Also require Products with sharp or dotted dimensions often use PVC foils due to the high resistance of PVC foils to initial cracking compared to the resilience of the Polyolefins, i.e. about 7 grams are required to cause PVC to crack, while a typical single-layer one Polyolefin shrink film is enough for this purpose as little as 2 to 3.5 g.

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However, for health reasons it would be desirable to have a substitute for some or all of these uses Finding PVC, especially to avoid its noxious fumes and corrosive by-products.

A film has now been developed that is heat-shrinkable can be equipped and has many of the desirable properties of PVC shrink films, but avoids many of their disadvantages, especially the noxious fumes and corrosive by-products. The films according to the invention have shrinkage tensions, which roughly correspond to those of PVC films, good optical properties, a wide shrink temperature range, have good weldability, good resistance to cracking and heat seal resistance which is larger than that of the widely used polyolefin films. The invention consists in the development of multilayer films with at least three layers, the differ from the well-known multilayer films, which are not used as a substitute for PVC.

The invention provides a multilayer, flexible, heat-shrinkable thermoplastic packaging film having at least three layers are available, namely at least one inner layer which is essentially non-oriented and consists of a homopolymer or copolymer of ethylene, the thickness of the inner layer or the total thickness of the

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inner layers 10 to 90% of the total thickness of the multilayer film constitutes an oriented layer of a polyester or copolyester and at least one third layer of a thermoplastic polymeric material.

The multilayer film according to the invention therefore comprises at least three layers, with the inner layer or at least one of the inner layers if the film has more has as three layers, of a homopolymer or copolymer, which may be a terpolymer of ethylene, consists, and at least one of the other layers is made of a polyester or copolyester, the following for the sake of simplicity it is referred to as a "polyester layer". The "third layer" according to the above Definition can consist of a polyester layer, i.e. an oriented layer of a polyester or copolyester exist.

The inner layer need not consist exclusively of an ethylene polymer. You can tolerate others Contain ingredients. A preferred material for the inner layer is a mixture, the majority of which Component made from an ethylene polymer and its minor component made from a homopolymer or copolymer of Butylene. The multilayer film is oriented as a whole, i.e. it has the properties of an oriented film

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and is heat-shrinkable in at least one direction. The orientation is given to the polyester layer, while the inner layer of ethylene polymer is essentially unoriented. Preferably the orientation is biaxial.

The invention includes multilayer films as indicated above
with three or more layers. A preferred embodiment consists of three layers with one essentially
unoriented central inner layer, as indicated above, the thickness of which makes up 10 to 90%, preferably 25 to 90% of the total thickness of the film and which is flanked by two outer layers. At least one of the two outer layers is oriented and consists of a polyester
or copolyester, the thickness of the two outer layers together making up 90 to 10%, preferably 75 to 10% of the total thickness of the film.

Another preferred film according to the invention consists
from five layers, namely:

(a) an oriented central layer of a polyester or copolyester or a homopolymer or copolymer of propylene.

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(b) two substantially unoriented inner layers on either side of the central layer with one Total thickness of 10 to 90% of the total thickness of the multilayer film, with each inner layer constructed as indicated above is and

(c) two outer layers, at least one of which consists of a polyester or copolyester.

Preferably the or each polyester outer layer is oriented.

Another embodiment comprises five layers, namely

(a) a central layer made of a polyester or copolyester

(b) two inner layers on each side of the central layer, each inner layer being made from an ethylene copolymer, preferably an ethylene-vinyl acetate copolymer, and

(c) two outer layers, one or both outer layers of a polyester, copolyester, polyethylene, crosslinking! Polyethylene or crosslinked ethylene-vinyl acetate copolymers or homopolymers or copolymers of propylene.

In their heat-shrinkable form is usually the central layer and optionally one or both of the outer layers oriented, while the inner layers (b) are normally not substantially oriented.

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The invention also encompasses a process for producing the multilayer film which consists in pulling together all of the polymer layers required for the film and stretching the multilayer film formed in order to orient it. For this purpose, the film is normally heated to a temperature of, for example, 80 to 200 ^° C. and then stretched while still hot. It is not desirable to orient the polymer molecules of each layer. In the preferred method, the or each inner layer is "blown hot", thereby stretching the film at a temperature which is above the orientation temperature of the polymeric material of that layer so that it is not substantially oriented. In other words, the orientation of the multilayer film is predominantly effected in the other layer (s).

Unless the context indicates otherwise, the term "polymer" used herein means homopolymer and copolymers, which can also be terpolymers. They can be present as graft polymers, also as polymers with in any order or with alternating monomer units. The naming of a monomer in the first place in the full, non-abbreviated name of a copolymer means that this monomer is usually in a larger proportion in the copolymer is present.

As used herein, the term "melt flow" is otherwise known as "melt index". It indicates the amount of thermoplastic resin that is pressed through a given opening under a given pressure, namely a load of 2160 g and a temperature of 190 ^° C., within 10 minutes

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can be as described in ASTM Test D 1238, Condition E. is.

The term "oriented" as used herein denotes the orientation of the molecules of a polymer in predominantly a direction sufficient to impart heat shrinkability to the sheet or film.

The "inner layer" referred to as the "core layer" in the priority US application means one Layer in a multilayer film that is flanked on both sides by adjacent layers. The inner layer is essentially not oriented, e.g. hot blown. It does not necessarily constitute a central layer of the foil For example, in the five-layer film identified above, there are inner layers on each side of a central one Layer.

As used herein, "blown hot" means that the specified material is at or above its orientation temperature range and therefore has generally been stretched above its melting temperature, so that the stretching process caused minimal stress and molecular orientation. Such a material is not considered to be heat-shrinkable considered because there is a very low shrinkage stress, usually

2
borrowed below about 7 kg / cm (100 psi).

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"Outer layers", also referred to as "skin layers" are the layers on the surface of the multilayer film, i.e. the top and bottom layers a flat sheet as well as the radial innermost and radial outermost layer of tubular film or sack, etc.

The term "polyester" as used herein means a thermoplastic, film-forming, saturated polyester, e.g. polyethylene terephthalate or polybutylene terephthalate. The term "polyester" also includes the film-forming Polycarbonates.

The term "copolyester" means thermoplastic, film-forming Copolyesters, e.g., ethylene terephthalate-glycol, terephthalic acid / isophthalic acid-cyclohexanedimethanol, and butylene terephthalate-tetramethylene ether terephthalate.

The term "crosslinked" means that bonds have been formed between the molecules of the individual polymers. A network some polymers can be introduced by exposing them to ionizing radiation, such as gamma or X-rays, or electrons or ß-particles. For networkable Polymers such as polyethylene or ethylene-vinyl acetate copolymers can relate the radiation dose to the degree of crosslinking by removing the insoluble gel, i.e. that portion of the polymer that is not in a solvent,

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like boiling toluene, dissolves, as a crosslinked portion of the irradiated polymers. Usually there is no measurable radiation dose below 0.5 megarads Determine gel. In the case of the polymers given above, a small increase in crosslinking is found for more than 12 megarad observed. Partial crosslinking at intermediate dosage levels can have beneficial effects e.g., improving the toughness and strength of the polymer without reducing the flowability to an undesirable level Reduce measure.

The term "butylene polymer" denotes from butene-1, normally referred to as butylene, synthesized high molecular weight isotactic polymers. They represent flexible are crystalline thermoplastic polyolefins with a density of about 0.91 g / cm. They are different from polymers from isobutene, usually called butene, widely used as oil additives, and from amorphous ones atactic poly (1-butene) polymers, which are viscous oils to rubbery polymers.

In the following, the "ethylene-vinyl acetate copolymer" is referred to as "EVA" and the "propylene-ethylene copolymer" are abbreviated as "EP".

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The essentially unoriented inner layer cushions or obviously moderates the relatively high shrinkage stress of the polyester layer and, if present, of the oriented EP layer. Without this moderating effect, the shrinkage tension of the film would be great enough to hold the packaged Deform product in many packaging applications. It enables the desired shrinkage stresses that are about those of PVC films can be achieved for these applications.

The preferred ethylene polymer for the inner layer (s) is EVA. The melt flow of the copolymer is believed to be more important than its vinyl acetate content. It is usually 0.1 to 6.0 g / 10 min. Melt flow is believed to be an important factor in handling and machine processability of the final multilayer film, i.e. its ability to fit into automatic packaging machines to let use. A vinyl acetate content of 4 to 18 weight percent and a melt flow index have usually been found to be most useful from 0.1 to 6.0 g / 10 min.

Contains the EVA in Example 1, the preferred embodiment 12% by weight vinyl acetate and has a melting index of 0.3 g / 10 min. For a 3-layer structure, it is a preferred EVA.

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The polymeric material of an inner layer of the film according to the invention can be composed of a mixture of ethylene polymers and butylene polymer, although this is less beneficial than EVA alone. Preferably there is a larger one Part of the mixture of the ethylene polymer and a smaller part of the butylene polymer.

Preferred polymers for the larger component are low density polyethylene and EVA in proportions from 70 to 90% by weight of the total mixture, preferred polymers for the smaller constituent polybutylene and butylene-ethylene copolymers in amounts of 30 to 10% by weight of the total mixture.

The butylene copolymer component is preferably a butylene-ethylene Copolymer in which the proportion of ethylene units is advantageously up to 5% by weight. It turned out to be the most suitable a polymer with an ethylene unit content of about 2% by weight. The melt flow of the butylene-ethylene copolymer or of polybutylene is preferably 1.0 to 3.0 g / 10 min.

The most advantageous blend for the inner layer consists of EVA and a butylene-ethylene copolymer with a preferred one Ratio of 80:20% by weight.

An inner layer made of a mixture of about 80% by weight of EVA with about 12% by weight of vinyl acetate is particularly advantageous

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and a melt flow rate of about 0.25 g / 10 min. and about 20% by weight of a butylene-ethylene copolymer with up to 5% by weight ethylene and a melt flow rate of about 2.0 g / 10 min.

Instead of the preferred EVA, a mixture of EP with polybutylene or a copolymer of butylene can be used with the EP component making up the larger portion and the butylene polymer making up the smaller portion of the mixture. Instead of the EVA dipolymer or for mixing with it, EVA terpolymer can also be used sold under the trade designation "Plexar 3" by Chemplex Co., or the commercially available terpolymer of ethylene with 28% by weight vinyl acetate and 4 to 8% by weight methacrylic acid.

The multilayer film can include, preferably a layer of a homopolymer or copolymer of propylene a propylene-ethylene copolymer (EP). Homopolymers of propylene can also be used. To achieve a The desired atactic / isotactic ratio can be mixtures of isotactic and atactic polypropylene be used. In the most preferred embodiment according to Example 1, the EP contains about 3.0% by weight of ethylene units in Any arrangement, but EP with 2 to 4% by weight of ethylene units and a melt flow rate of 0.5 to 6.0 was also found as very satisfactory.

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The total thickness of the multilayer film is usually about 2.5 to 50 µ (about 0.1 to 2.0 mils), preferably about 10 to 38 µ (about 0.4 to 1.5 mils).

The thickness of the inner layer (s) of ethylene polymer preferably makes up 25 to 90% and especially 47 to 90% of the thickness of the entire film. In a preferred embodiment of the 3-layer film, the inner layer consists of an ethylene-vinyl acetate copolymer with 4 to 18% by weight Vinyl acetate and a melt flow rate of 0.1 to 6.0 g / 10 min., A surface layer made of a homopolymer or copolymer of propylene, the thickness of this layer being 5 to 50% of the thickness of the entire film and the other surface layer of a polyester or copolyester, the thickness of which is 5 to 25% of the thickness of the entire film. In another preferred 3-layer film, in which the inner layer also consists of EVA, this inner layer has Layer has a thickness of 50 to 90% of the thickness of the entire film and each of the two surface layers consists of a polyester or copolyester, the thickness of the two surface layers together being about 50 to 10% of the thickness of the entire film amounts to. Both surface layers are preferably oriented in this preferred 3-layer film.

A preferred 5-layer film according to the invention has an oriented central layer made of polyester or propylene polymer and oriented or non-oriented outer

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layers, at least one of which is made of a polyester. Preferably both are surface layers oriented and are both made of polyester. For films of this type, there are three sets of preferred aspect ratios the following:

(D (2) (3)

a) central layer: 5-25

b) two inner layers

together:

c) two surface layers together:

15-85% 10-75%

5 - 25%
10-65%

10-65%

5 - 80% 10 - 85%

5 - 25%

An alternative 5-layer film according to the invention has the following layers:

(a) an oriented central layer made of a polyester or copolyester,

(b) two substantially unoriented layers on either side of the central layer with a total thickness of 10 up to 90% of the thickness of the multilayer film, the inner

Layers are constructed as indicated above, and (c) -two outer layers, each of which is made from a homopolymer or copolymers of propylene.

The outer layers are usually oriented. In this film, the inner layers are preferably made of EVA and the Outer layers preferably made of EP. The thickness of the polyester layer here is preferably 5 to 25% of the total Foil. The EP layers preferably make up 10 to 50% of the

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Total film thickness and the EVA layers 25 to 85% of the total film thickness.

All thickness ratios of the layers were determined on the non-oriented film.

A valuable advantage is that according to the invention only proportionally Thin layers of polyester are needed, which are more costly than olefin polymers, to reduce shrinkage stress and / or heat seal resistance.

The polymeric material is preferably at least one layer of all films according to the invention by irradiation networked. Irradiation improves strength and toughness. The radiation doses range from 1.0 to 4.0 megarads usually result in the most beneficial combination of improved strength without significant reduction in Flowability that would inhibit welding.

The films according to the invention usually have "moderate"

2 shrinkage tension of about 7-28 kg / cm (about 100 to 400 p.s.i.) in contrast to "high" shrinkage tension of about 28 to

2
700 kg / cm (about 400 to 1000 psi). These shrinkage stresses relate to a temperature range of 93 to 149 ° C (200 to 300 ⁰ F).

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The following examples illustrate the invention. The layers containing EVA are essentially non-oriented ("Hot Blown") inner layers. All other layers are oriented.

example 1

A preferred multilayer film according to the invention has the following layer arrangement:

EP / EVA / Copolyester / EVA / EP.

This 5-layer structure is made using three extruders that form an annular injection mold charge for pulling out together so that each layer is pulled out in a ring. An extruder carries a melt made of EP with about 3 wt.% ethylene in the injection mold to form the inner and outer annular layers. A second extruder delivers molten EVA with a vinyl acetate content of about 12 wt.% and a melt index of about 0.3 to the extruder to adjoin the inner EP layer and the outer EP layer to form annular EVA layers. The central layer between the two EVA layers are supplied from a third extruder which feeds a molten copolyester, which in this embodiment consists of ethylene terephthalate glycol. This five-layer pipe will be just like the extruder

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leaves, often referred to as the "band". In this embodiment, the total thickness of the tubular band was 0.4 mm (16 mils) of which the copolyester was 20%, the EVA layers 47% and the EP layers 33%.

After leaving the extruder, the strip is quickly cooled in a water bath to room temperature and below, preferably to about 10 C, passed through guide rollers, inflated and to a temperature in the range of 110 to 135 ° C, which is above the melting temperature of the EVA and is in the orientation temperature range of the copolyester and EP. In general, the orientation temperatures for multilayer films according to the invention are Range from 80 to 200 ° C. When the inflated tube is heated to this temperature range, it expands into a bubble under the influence of the internal air pressure, whereby the tube is biaxially stretched. In this embodiment, the tube expands to a wall thickness of 19, u (0.75 mil) is reached. Then the bladder is cooled by blowing deep-frozen air on its surface to remove the polymer Quenching materials and freezing the molecular structure of these materials in their oriented state. then the bladder is collapsed and the expanded tube is slit open to form packaging films.

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The multilayer film can be stretched to the desired thinness depending on the specific packaging purpose for which the film is to be used depends on. The practically lower limit on the films according to the invention usually stretchable is about 2.5 microns (0.1 mil), the upper useful limit is about 50 microns (2.0 mils).

The multilayer film made by the above procedure was designed to pack 20 25 χ 2.5 cm (8 "χ 10" χ 1 ") large gift boxes are used with a conventional "L" sealer with a sheet of film over the Can is folded and welded on the remaining three sides. With this type of welding device, the decisive factor is Closure of a pack The expiring closure of the pack immediately before the next pack. The pack will moved further by pushing against the film in the area of the still hot seal. The heat seal strength is therefore important to ensure the integrity of the package and the packaging speed.

After the gift boxes had been wrapped in the foil, they were passed through a "shrink tunnel". In In this tunnel they were heated to about the same temperature at which the film was oriented. After this The packs are "ready" when they leave the tunnel. All

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Packaging with the film according to this embodiment were excellent in appearance, did not exert excessive shrinkage force on the thin-walled gift boxes around them deform and showed good heat seal strength as well as good weldability and cuttability. In all In some cases, the films of this embodiment were found to be just as good as commercially available PVC films among the same conditions.

Example 2

A second multilayer film was produced as in Example 1 with the difference that the middle layer was made of copolyester 18%, the inner layers made of EVA together 52% and the outer layers made of EP 30% of the total thickness of the film made out. The film was also stretched to a thickness of about 19 microns (0.75 mils). The tensile strength and tear strength and the maximum shrinkage stress were lower than in the case of the film according to Example 1. The overall properties however, were very satisfactory and comparable to those of PVC.

Example 3

A 5-layer film was produced as in Example 1 with the exception manufactured that the central copolyester layer 9.5%, the EVA layers together 57%, one of the EP layers 19% and the other 14.5% of the total 25 microns (1.0 mil) thickness Make out multilayer film. Similar to those in packaging tests

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of Example 1, the film showed lower but satisfactory Heat seal resistance. Also their shrinkage tension was lower.

A comparison of the shrinkage properties of the films of Examples 1 to 3 with polyvinyl chloride (PVC), polypropylene (PP) and crosslinked polyethylene (PE) is in the below Table reproduced.

Table 1

Foil shrinkage tension range, kg / cm (p.s.i.)

from 93 to 149 ° C (200 - 300 ⁰ F)

PVC 1 11.2 - 18.3 (160 - 260) example 2 20.0 - 27.4 (285 - 390) example 3 20.7 - 23.2 (295 - 330) example 13.4 - 17.6 (190 - 250) PP ^b 30.9 - 49.9 (440 - 710) PE ^C 24.6 - 29.5 (350 - 420)

^a "Reynolon 4155" from Reynolds Metals Corporation

Film made from propylene-ethylene copolymer, which is predominantly propylene

contains and _c sold by WR Grace & Co. as "CP-900".

Crosslinked polyethylene sold by W.R. Grace & Co. under the trademark "D-Film".

It is noteworthy that the shrinkage tension ranges of the Films according to Example 1 to 3 were lower than that of

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simple films made from polyolefins such as polypropylene and Polyethylene and approached those of PVC. The films of Examples 1 to 3 also had adequate heat seal strength at high packaging speeds. The optical properties and the appearance of the packaging from the films of Examples 1 to 3 were excellent.

Example 4

In accordance with the previous examples a 5-layer film with the following layer arrangement pulled out:

Polyester / EVA / Polyester / EVA / EP.

With this multilayer film, the polyester or copolyester layers make 10 to 50%, the EVA layers 10 to 50% and the EP layer comprises 5 to 25% of the total thickness of the film. The 5-layer film is desirable when an additional polyester content is required for better heat seal strength and one of the surfaces of the film should have the hardness and scratch resistance conferred by the polyester.

Example 5

Another 5-layer film can be produced according to the preferred embodiment with the following layer arrangement will:

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Polyester / EVA / EP / EVA / Polyester.

The polyester or copolyester makes up 10 to 50 %, the EVA layers make up 10 to 85% and the EP layer makes up 5 to 80% of the total thickness of the film. This structure is advantageous if both surfaces of the film are to have the hardness and scratch resistance of polyester and an additional polyester content is required for better heat seal resistance.

Example 6

A 3-layer film was made in a manner similar to that of preferred embodiment pulled out. Three extruders and the annular injection mold were required for the three materials co-pulling was designed so that the EVA layer made the central or middle layer. the Structure was as follows:

EP / EVA / copolyester.

This 3-layer film was biaxially stretched to a thickness of 19 microns (0.75 mils) so that the two outer layers are one 4 microns (0.15 mil) thick and the middle layer was 11 microns (0.45 mil) thick. Gift boxes were like in the preferred embodiment packed in this 3-layer film. However, this slide was not balanced due to its nature

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1 .

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Consistency less satisfactory, i.e. the EP layer and the copolyester layer have different shrink properties so that the film puckered. The ripple appeared inside on the copolyester side so that the copolyester face is located on the inside of the vertebra. In some cases, such a crimp may be desirable, for example when Sacks are made from the film and a crimp on the eyelet sheet of the sack makes it easier to open the sack.

Example 7

A balanced 3-layer film can have the following structure getting produced:

Polyester / EVA / polyester.

A copolyester can of course also be used instead of the polyester can be used for this structure. The polyester layers make 10 to 50% and the EVA layer makes 50 to 90% of the total thickness of the film.

Example 8

According to the invention, another 5-layer film can be used as follows getting produced:

PE / EVA / polyester / EVA / PE.

The abbreviation "PE" refers to polyethylene, which, depending on your needs, can be of low, medium or high density. if

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If low or medium density polyethylene is used, it may be required by additional crosslinking To give strength. The middle layer can, as indicated, consist of polyesters or of a copolyester.

Example 9

A 5-layer film was preferred with the following Thickness ratio established for the individual layers: 1/2/1/2/1. The outer or skin layers consisted of the Propylene-ethylene copolymers "WO 7-1" from ARCO Polymers, Inc. with 3.5 to 4.0 wt.% ethylene and a melt flow of about 4.0. The central layer was made of polyethylene terephthalate. The remaining two layers consisted of the preferred one EVA / butylene-ethylene copolymer composition in the ratio 80% / 20%. The EVA consisted of "Alathon 3135" the du Pont with 12% by weight vinyl acetate and a melt flow rate of about 0.25 and the butylene-ethylene copolymer from "Witron-8240-2" from Witco Chemical Corporation with about 2 weight percent ethylene and a melt flow of 1.0 to 2.0. This slide has good shrink properties and good "heat seal resistance" .

Example 10

The same film as in Example 9 was produced, except that the central layer was made of a polycarbonate resin duration. Again, good shrink properties and "Heat seal resistance" achieved.

sch: cm / 15662 9Q98A3 / Ö842

Claims (13)

UEXKÜ'-L & SrOLefc ^ G professional representatives PATEN TAN- '. OLD BEFORE THE EUROPEAN PATENT OFFICE SESELERSTI-ASSE 4 D-2000 HAMSUF ^ G 52 OR JD FRHR by UEXKULL DR ULRICH GRAF STOLBERG DIPL ING JÜRGEN SUCHANTKE DIF1L ING ARNULF HUBER DR ALLARD by KAMEKE WRG) KARL-HEINZ Plaza Avenue of the Americas (Prio 17.4.78 US 896,963 New York, NY 1OO36 / V.St.A. 308.78 US 938,191 N 30820 - 15662) Hamburg, April 2, 1979 Multi-layer polyester / polyolefin shrink film patent claims 1. Heat-shrinkable, flexible multilayer film for packaging purposes made of at least three layers of thermoplastic polymeric materials, at least an inner layer is substantially non-oriented and is made from a homopolymer or copolymer of ethylene and at least one of the other layers is oriented, characterized in that the thickness of the inner layer or the total thickness of the inner layers is 10 to 90% of the total thickness of the multilayer film, and that the film comprises an oriented layer of a polyester or copolyester. 909843/0842 ORIGINAL INSPECTED 2. Film according to claim 1, characterized in that the or each inner layer consists of a mixture of a homopolymer or copolymers of ethylene with a homopolymer or copolymer of butylene. 3. Film according to claim 1 and 2, characterized in that the ethylene polymer of the inner layer consists of a copolymer of ethylene with vinyl acetate. 4. Film according to claim 3, characterized in that the ethylene-vinyl acetate copolymers are 4 to 18% by weight of vinyl acetate and a melt flow rate of 0.1 to 6.0 g / 10 min at a load of 2160 g and a temperature of 190 ° C according to ASTM No. D 1238, condition E. 5. Film according to claim 1 to 4, characterized in that the inner layer consists of a hot-blown layer. 6. Film according to claim 1 to 5, characterized in that it has at least one third layer made of a homopolymer or copolymers of propylene. 7. Film according to claim 1 to 6, characterized in that the thickness of the inner layer (s) is 25 to 90% of the thickness of the entire film. 909843/0842 8. Film according to claim 7 with three layers, characterized in that that one or both of the two outer layers is oriented and made of a polyester or copolyester consists, the thickness of the two outer layers together making up 75 to 10% of the thickness of the total film. 9. Film according to claim 8, characterized in that the inner layer made of an ethylene-vinyl acetate copolymer according to claim 4, an outer layer made of a homopolymer or copolymers of propylene, the thickness of this layer being 5 to 50% of the thickness of the total film and the other outer layer: consists of a polyester or copolyester, the thickness of which is 5 to 25% of the thickness of the total film matters. TO. Foil according to claim 8, characterized in that the inner layer of an ethylene-vinyl acetate copolymer according to claim 4 having a thickness of about 50 to 90% of the Thickness of the overall film and each of the two outer layers consists of a polyester or copolyester, the Thickness of the two outer layers together makes up about 50 to 10% of the thickness of the total film. 11. Heat-shrinkable multilayer flexible film for Packaging purposes with five layers of thermoplastic Materials, characterized in that they: 909843/0842 (a) an oriented central layer of a polyester or copolyester or a homopolymer or copolymer of propylene (b) two substantially unoriented inner layers on each side of the central layer of total thickness from 10 to 90% of the total thickness of the multilayer film, the composition of the inner Layers corresponds to that specified in claim 1, 2, 3 or 4 and (c) two outer layers, at least one of which consists of a polyester or copolyester, and each outer layer may or may not be oriented. 12. Film according to claim 11, characterized in that the thickness of the individual layers, based on the thickness of the overall film constitutes the following percentages: 12 3 a) Central layer: 5-25% 5-25% 5-80% b) · the two inner _{1 ς Rc} - _{a 1n} "^ _{1n Rc} -"",. ,, Ib - whether -6 OK - whether% OK - whether% Layers together: c) the two outside _ _ layer together: 13. Film according to claim 1, characterized in that it has five layers, namely: 909843/0842 (a) an oriented central layer made of a polyester or copolyester (b) two substantially unoriented layers on either side of the central layer with one Total thickness from 10 to 90% of the total thickness of the multilayer film, the composition of the inner Layers as specified in claim 1, 2, 3 or 4 corresponds and (c) two outer layers, each of which is a homopolymer or copolymers of propylene and is oriented or unoriented. 909843/0842