DE3305198C2 - - Google Patents

Description

The invention relates to a multilayer shrink film with a core layer, two outer layers comprising an ethylene-propylene Copolymer, and optionally two Interlayers.

A feature of a shrink film is the ability of the film to be present To shrink the action of a certain temperature or if shrinkage is not possible in the Foil to produce a shrinkage stress.

The production of shrink films from the state The technique is generally known by extrusion by means of an extrusion head one on his Flow or melting point of heated, resinous material take place, wherein the film as a hose or flat film accrues. Following a quench for cooling The extrudate is then returned to its orientation temperature range heated. The orientation temperature range for a particular slide changes depending on the different resinous polymers and mixtures thereof, which make up the film consists. In general, the orientation temperature range however, be defined to be above room temperature and below the melting point of the film.  

The terms "oriented" or "orientation" are used used in the context of the present invention to the Process and the resulting product properties to describe that by stretching and immediate Cooling of a resinous polymeric material obtained that's on its orientation temperature range has been heated to the molecular configuration of the material by physical alignment of the molecules to change the mechanical properties the film, such as the shrinkage stress and to improve the orientation release voltage. These two properties can be confirmed according to ASTM D 2838-69 (re-confirmed 1975). If the stretch in one direction takes place, results in a uniaxial orientation. If the stretching is done in two directions, results a biaxial orientation. Orientation becomes in the context of the present invention exchangeable with Used "heat shrinkability", these designations a material that stretched and through Cooling set to its stretched dimensions has been. An oriented, d. H. a heat shrinkable Material tends to be its original unstretched dimensions return when it to a suitable temperature below its melting temperature range is heated.

In the basic method of making the The film discussed above is thus the extruded and For the purpose of cooling quenched foil back on her Orientation temperature range heated and oriented. The orienting routes can be based on many Way, such as "inflated bladder Techniques "or" Spannrahmung "  respectively. These designations are known to the person skilled in the art and denote orientation levels in which the material in the transverse direction (TD) or in the longitudinal or machine direction (MD) is stretched. After stretching, the Film cooled quickly to the oriented molecular Quench the configuration and set it in this way or block.

After blocking the oriented molecular configuration the film can be stored in the form of rolls and for taut packaging of a variety of items be used. For this purpose, the product to be packaged initially wrapped in the heat-shrinkable material, what by heat sealing the shrink film, if required with yourself, done. Subsequently the coated product is exposed to elevated temperatures, for example, by a hot air or hot water tunnel is guided. This causes the film shrinks on the product and a firm Packaging that fits tightly to the contours of the Creates product.

The above general description of the production of Of course, slides are not complete because this method is well known to those skilled in the art. It was Therefore, for example, in US-PS 42 74 900, 42 29 241, 41 94 039, 41 88 443, 40 48 428, 38 21 182 and 3,022,543, the disclosures of which are hereby incorporated by reference should be explicitly included.  

For example, in the already mentioned US-PS 41 94 039 a multilayer film is described, which is a core layer made of thermoplastic material and two outer layers, which contain an ethylene-propylene copolymer, and which is shrinkable. The core layer consists of a Polymer blend of EVA and ethylene-butylene copolymer. Furthermore, from the on the same priority as the previously mentioned US-Patent going back DE-OS 29 14 912 a shrink film of three layers known in the the inner layer is substantially not oriented and is a homopolymer or copolymer of ethylene and at least one of the other layers (ie the Outer layers) and is made of a polyester or Copolyester exists. The aim of the teaching of this document is it, a multi-layer film with reduced shrinkage stress to create that due to this property with PVC films can compete.

As these examples show, the skilled person many Variations of the method generally described above in Dependence on the intended use and the desired properties of the film available. For example, the molecules can  the film are crosslinked during processing, to the resistance of the films against damage and to improve other properties. The Networking and networking techniques are general known. Thus, the crosslinking by irradiation of the Foil or alternatively chemically by use made of peroxides. Another possible process variant is the application of a fine spray a silicone spray on the inside of the fresh extruded material for further processability to improve the material.

The polyolefin group and in particular the polyolefin group the shrink films provides a wide range of physical and performance characteristics such as shrinkage force (Force a foil during shrinking per unit area of its cross-section), the degree free shrinkage (the reduction of the linear Dimension in a certain direction, the material subject when elevated in the unhampered state Exposed to temperatures), tensile strength (the greatest force acting on a unitary surface of the foil can be exercised before it starts to tear apart), Sealability, shrinkage temperature curve (the relationship between shrinkage and temperature), beginning of tearing and resistance (the force at which a foil begins to rip and continues to rip), optical Properties (gloss, haze and transparency of the Materials) and dimensional stability (the ability of the Foil, their original dimensions under different To maintain types of storage conditions). film properties play an important role in choosing one particular film and differ in each packaging process  and with every packaging. Considered must be the size, the weight, the shape and the hardness of the product as well as the number of Product components. Furthermore, other packaging materials, which used together with the foil can be, and the type of available To consider packaging devices.

Given the many physical ones mentioned above Properties of polyethylene films and given the numerous applications with which these slides already have been linked and for which they are in Future could still be used, it is without Further understand that the need for one always further improvement of any or all the physical properties described above This slides is large and exists continuously.

Accordingly, the invention is based on the object to provide a heat-shrinkable polyolefin film, the one improvement over the known films represents. In particular, the invention is a film with improved shrinkage stresses, improved optical Properties, a wide shrinkage temperature range, an improved sealability, a improved resistance to crack propagation and improved machinability.  

To solve this problem, a multi-layer shrink film of proposed in the opening paragraph, which is characterized that all layers are oriented and the core layer is linear Low density polyethylene or linear medium density polyethylene contains.

Unless specifically specified and defined or limited mean the terms "polymer" or "polymer resin" in the context of the present description, homopolymers, Copolymers, terpolymers, block and graft polymers, statistical and alternating polymers.

The term "melt flow" or "melt flow index" denotes the amount of a thermoplastic resin in Grams passing through a specific opening under one certain pressure and at a certain temperature can be pressed within 10 minutes, like it in ASTM D 1238.

The term "core" or "core layer" means a Layer in a multilayer film, of both Pages enclosed by additional layers.

The term "outer layer" means an outer one Layer (i.e., a surface layer) of a multilayered one Foil.

The term "interlayers" means a layer a multilayer film that neither has a core layer nor an outer layer is.

The term "low density polyethylene" (LDPE) relates to homopolymers of ethylene with a density of 0.910 to 0.925.

The term "linear low-density polyethylene" (LLDPE) refers to a copolymer of ethylene and 8% or  less butene, octene or hexene with a density of 0.910 to 0.925, where the molecules are long chains few or no branches or networked structures are.

The term "linear medium density polyethylene" (LMDPE) refers to a copolymer of ethylene and less as 8% butene, octene or hexene with a density of 0.926 to 0.940, with the molecules having long chains few or no branches or networked structures are.

The term "ethylene-vinyl acetate copolymer" (EVA) relates to a copolymer of ethylene and vinyl acetate monomers, wherein the units derived from ethylene in overwhelming quantities and differing from vinyl acetate are derived in minor amounts.

The term "ethylene-propylene copolymer" (EPC) a copolymer of ethylene and propylene monomers, wherein the propylene derived units as predominant component and those derived from ethylene Units exist as a subordinate component are.

The term "propylene homopolymer" (PP) refers to a thermoplastic resin having a density of about 0.90, by taking place in a known manner polymerization of propylene with suitable catalysts is made.

It has been found that a flexible, heat-shrinkable, thermoplastic packaging film with a favorable Combination of physical properties  like shrinkage stress, optical properties, cutting ability, Sealability, shrinkage temperature range and crack resistance by the multilayered, flexible, thermoplastic packaging film has been created. This multilayer film has a core layer which is a linear polyethylene resin lower Contains density. The linear polyethylene resin lower Density can be achieved by linear polyethylene resin medium Density be replaced. A preferred embodiment with three layers also includes next to the core layer two outer layers, each one a mixture of a propylene homopolymer and an ethylene-propylene Copolymer included. The multilayer film is oriented so that they are heat shrinkable in at least one direction is.

The multilayer film can be used for specific applications be combined with other polymeric materials. For example, relatively thin layers on one or both sides of the preferred three-tier Basic structure can be added to the seal strength to improve or gas and moisture permeability to reduce.

Another embodiment of the invention relates a five-layer film structure. A preferred Five-layer structure includes the same core and Outer layers such as the above-described three-layer Structure and also has two intermediate layers each containing a mixture of an ethylene-vinyl acetate Copolymer and either an ionomer resin or a linear low density polyethylene. The low-density polyethylene of the intermediate layer can through a linear medium density polyethylene be replaced.  

In the following the invention with reference to the drawings be explained in more detail. It shows

Fig. 1 shows a cross section through a preferred three-layer structure and

Fig. 2 shows a cross section through a preferred five-layer structure.

From Fig. 1, which shows a cross section through a preferred three-layer structure, it can be seen that this embodiment has a core layer 2 and outer layers 1 and 3 . The preferred thickness ratio of the three layers of 1/3/1 is shown in FIG . A preferred core layer 2 component is a linear low density polyethylene. However, linear medium density polyethylene can also be used as the core layer component without significant change in the properties of the final film product. The core layer 2 comprises linear low density polyethylene (alternatively linear medium density polyethylene) or the core layer 2 may be a copolymer blend of linear low density polyethylene (alternatively linear medium density polyethylene) with either (a) an ethylene-propylene copolymer or (b) an ethylene-vinyl acetate copolymer or (c) an ethylene-vinyl acetate copolymer mixed with an ionomer resin or (d) low-density polyethylene. Accordingly, the various mixture formulations for the core layer 2 can be selected according to the invention from the following groups:

• (1) 10 to 100% LLDPE mixed with 0 to 90% EPC or
• (2) 10 to 100% LMDPE mixed with 0 to 90% EPC or
• (3) 10 to 80% LLDPE mixed with 20 to 90% EVA or
• (4) 10 to 80% LMDPE mixed with 20 to 90% EVA or
• (5) 10 to 80% LLDPE mixed with 10 to 80% EVA and 10 to 80% ionomer resin or
• (6) 10 to 80% LMDPE mixed with 10 to 80% EVA and 10 to 80% ionomer resin or
• (7) 10 to 80% LLDPE mixed with 20 to 90% LDPE or
• (8) 10 to 80% LMDPE mixed with 20 to 90% LDPE.

LLDPE is an abbreviation for the above defined linear Low density polyethylene used. LMDPE is called Abbreviation for the above-defined linear polyethylene medium density used. EPC is short for an ethylene-propylene copolymer as defined above has been used. EVA is the abbreviation for that above defined ethylene-vinyl acetate copolymer. The name Ionomer resin is commonly used to Group of ionomer resins and in particular the group of Ethylene / methacrylic acid copolymers dissipating resins that are ionic have been networked to describe.

It has been found that a particularly preferred core layer formulation essentially of linear polyethylene low density. This material possesses preferably a density of about 0.920 g / cc and a nominal Melt index of about 1.0.  

The formulations for the outer layers 1 and 3 in Fig. 1 can be selected from the following groups:

• (1) EPC or
• (2) 70 to 90% EPC mixed with 10 to 30% PP or
• (3) 70 to 90% EPC mixed with 10 to 30% LLDPE or
• (4) 70 to 90% EPC mixed with 10 to 30% LMDPE.

All abbreviations have the same meaning as above in connection with the core layer formulations. In addition, PP is the abbreviation for a propylene Homopolymer as defined above. investigations have shown that a particularly preferred outer layer formulation essentially a mixture of 20% PP and 80% EPC.

All percentages in the specification and claims are weight percentages.

All densities in the description and in the claims are given in g / cm³.

A preferred embodiment of the invention is from a core layer consisting essentially of a  linear low density polyethylene, and outer layers, which consists essentially of a mixture of 20% of a propylene homopolymer with 80% ethylene-propylene Copolymer exist.

Although the three-layer formulations described above basically with respect to structures with more preferred as three layers for reasons of manufacturing costs are, according to the invention, also different five- Layer formulations have been prepared under the point of view of physical properties as well are satisfactory. The cost of production However, a five-layer film are basically higher than that for the production of a Layer film.

Figure 2, which is a cross-section of a preferred five-layer film, demonstrates the preferred layer thickness ratio of 2/2/1/2/2. The core layer 6 may include any of the core layer formulations described above in connection with the core layer 2 of the three-layer embodiment. Moreover, the core layer may consist essentially of either (1) an ethylene-propylene copolymer (EPC) or (2) an ethylene-vinyl acetate copolymer (EVA).

The outer layers 4 and 8 of the five-layer embodiment may include any of the outer layer formulations described above in connection with the outer layers 1 and 3 of the three-layer embodiment of FIG .

The five-layer embodiment according to FIG. 2 additionally has intermediate layers 5 and 7 . These intermediate layers may contain any of the formulations described above in connection with the core layer 2 of the three-layer embodiment. In addition, the formulation of the intermediate layers 5 and 7 can be selected from the following additional groups:

• (1) EVA or
• (2) 20 to 80% LLDPE mixed with 20 to 80% ionomer resin or
• (3) 20 to 80% LMDPE mixed with 20 to 80% ionomer resin.

The investigations carried out have shown that a preferred five-layer structure consists of outer layers 4 and 8 consisting essentially of an ethylene-propylene copolymer (EPC), intermediate layers 5 and 7 , which consist essentially of a mixture of 90% ethylene-vinyl acetate. Copolymer with 10% ionomer resin, and having a core layer 6 , which consists essentially of a linear low-density polyethylene.

It will be clear to those skilled in the art that all of the above weight percentages minor changes can. In addition, these percentages may be slightly vary when additives like the one described above Silicone mist or lubricants and antiblocking agents used  become. A preferred antiblocking agent is silica.

Preferred lubricants are erucamide and stearamide and N, N'-dioleoylethylenediamine.

A preferred silicone spray is a liquid polyorganosiloxane and especially a polydimethylsiloxane.

The general areas for using these additives are the following:

(1) Silica: | 250-3000 ppm (2) N, N-Dioleoylethyldiamine: 200-4000 ppm (3) Erucamide: 200-5000 ppm (4) Stearamide: 200-5000 ppm (5) Silicone spray: 5 mg / m² and more.

With the expression "consisting essentially of" should be low in the description and claims Percentage deviations or additives or additives This species can not be excluded.

Additional layers and / or small amounts of additives The types described above can be found both in the three-layer and five-layer Layer structure are added. It is, however, on it to ensure that the desired shrinkage stresses, Shrink properties, optical properties and others  Properties of the multilayer film according to the invention are not negatively affected.

In the preferred manufacturing method for the inventive multilayer polyethylene film (polyethylene low density or medium density) are the Basic steps of mixing the polymers for the different ones Layers, coextruding the layers to form a multilayer film and the Stretching of the film for biaxial orientation. These Steps and additional desired levels become detailed explained in the following paragraphs.

The process starts with the mixing of the raw materials (i.e., the polymeric resins) in the desired proportions and amounts as indicated above. The resins will be usually from a supplier in the form of pellets and can in a known manner in a variety be mixed by known mixing devices. While mixing, the additives and / or additives, which are to be used are added.

The mixed resins and the applied additives and / or additives are then in the hopper of the Feed extruders that supply the spray heads. For the three-layer film are at least 3 extruders required if each layer has a different composition should have. Two extruders are using the materials for the inner and outer outer layers and the other extruder with the linear polyethylene material low or medium density, that for the core layer serves, feeds. If desired, additional Extruders are used. Preferably, the materials as a hose with a diameter of the  Stretch ratio and the desired final diameter depends, coextrudes. This coextruded tube is relatively thick and is called a "band" designated. Circular spray heads are known and can be sourced from a number of manufacturers. In addition to coextrusion in the form of hoses can Also slit spray heads are used to handle the material in planar form to coextrude. Known individual or multi-layer extrusion coating processes if desired, also be used.

Another possible process step is to the band or the unexpanded tube or the unexpanded railway due to bombardment with high-energy To irradiate electrons from an accelerator, to network the materials of the band. The networking increases the structural strength of the film or the Force with which the material can be stretched before it ruptures, considerably if the foil materials predominantly Ethylene such as polyethylene or ethylene-vinyl acetate are. The irradiation also improves the optical Properties of the film and changes the properties the film at higher temperatures. If an irradiation stage is performed, is a preferred Radiation dosage in the range of 0.5 MR to 12.0 MR. MR is an abbreviation for Megarad. A megarad are 1 × 10⁶ wheel, one wheel being that amount of ionizing Radiation is responsible for absorbing 100 ergs of energy Irrespective of the material irradiated per gram Radiation source leads. In some cases it may be desirable be to stretch the multi-layer film first and then to irradiate them or, if one after another a successful coating can be carried out Layer or a group of layers to be irradiated and then you can make another or different layers  added to the final stretch and orientation step become.

As indicated above, there is a possible additional Process stage in the application of a fine silicone spray on the inside of the freshly extruded ribbon.

After co-extruding, quenching to cool and optionally the irradiation, the extruded Band reheated and continuously through an inner Air pressure inflated to a bubble. This will the tight band with thick walls in a wide foil transferred with thin walls of the desired thickness. This Procedure is sometimes called "technique of the Bubble "for orientation or as" stretching " designated. After stretching the bubble collapsed and the film is placed on semi-finished rolls, so-called "mill rolls" wound. The stretching process orients the film by in the transverse direction and to some extent, too is stretched longitudinally to rearrange the molecules and in this way the film's shrinkability to confer and the physical properties of Modify the film. An additional stretch in Longitudinal or machine direction can be achieved by the breather rollers that coincide support the inflated bladder, with a larger Speed as the rollers run for transport of the reheated band in the stretch or blister area serve. All of these orientation methods belong to the state of the art.

The following examples serve for further explanation and clarification of the invention.

Example 1

A five-layer structure with an approximate coating thickness ratio from 2/2/1/2/2 was by loading extruded from four extruders. Extruder no. 1, which the Spray heads for both intermediate layers supplied, was with a mixture of 90% ethylene-vinyl acetate copolymer (12% vinyl acetate; melt index 0.5) and 10% ionomer resin (density 0.940, melt index 1.4). The mixture contained also 1100 ppm erucamide and 1100 ppm stearamide extruder no. 2, the provided the spray head for the core layer was with 100% linear low density polyethylene (Density 0.920, melt index 1.0). The Extruders Nos. 3 and 4 each supplied a spray head for an outer layer and both were 100% Ethylene-propylene copolymer (3.5% ethylene, Melt flow 4.5) mixed with 1100 ppm erucamide, 1100 ppm stearamide and 1100 ppm Silica charged.

Extruder No. 1 was at a temperature in the range from 199 to 219 ° C. Extruder no. 2 was opened a temperature in the range of 210 to 243 ° C held. Extruder No. 3 was at a temperature in the range from 177 to 188 ° C and Extruder No. 4 was kept at a temperature in the range of 174 to 185 ° C. The circular spray head was at a temperature kept in the range of 199 to 224 ° C.

After extruding the layers through the circular 25.4 cm spray head opening was the tubular Extrudate, that has a band thickness of about 381 microns and a hose width of about 24.5 cm, in order  Cooling quenched by moving at a speed from 11.3 m / min. passed through a cold water bath has been. The tube was then returned for orientation heated by passing through a heating zone or an oven at a speed of 11.6 m / min. was led. The oven was powered by horizontal, vertical and steam heating elements heated. In this example, the horizontal Heating element maintained at 93.3 ° C. The vertical Heating elements were kept at a temperature of 149 ° C and the vapor element that provided heat by Steam through tubes or containers inside the oven was passed with steam at a pressure of 0.14 bar.

After the heating described became the tubular Extrudate inflated and approximately in the transverse direction in a ratio of 4.8: 1 and in the longitudinal direction stretched approximately at a ratio of 4.3: 1. After that the film was cooled by water quenching, to set the oriented structure. The thickness of the finished film was about 19 microns.

The experimental results obtained for this film formulation Data are given in Table I, which follow the Examples followed.

example 2

A five-layer structure with an approximate layer thickness ratio from 2/2/1/2/2 was by loading extruded from four extruders. Extruder no. 1, which the Spray head openings for both intermediate layers supplied, was mixed with a mixture of 50% ethylene-vinyl acetate Copolymer (12% vinyl acetate;  0.5) and 50% linear low density polyethylene (Density 0.920, melt index 1.0) and 1100 ppm erucamide loaded. Extruder no. 2, which provided the spray head opening for the core layer, was made with 100% linear low density polyethylene (Density 0.920, melt index 1.0).

The extruders Nos. 3 and 4 each supplied a spray head opening for an outer layer and were both with 100% ethylene-propylene copolymer (2.7% ethylene; Melt flow 2.3) including 1100 ppm erucamide and 1100 ppm silicone.

Extruder No. 1 was at a temperature in the range held from 207 to 213 ° C. Extruder no. 2 was opened a temperature in the range of 204-246 ° C held. Extruder No. 3 was at a temperature in the range from 180 to 224 ° C, while extruder no. 4 was kept at a temperature of 180 ° C to 210 ° C. The circular spray head was at a temperature kept in the range of 199 to 219 ° C.

After extruding the layers through the circular 25.4 cm spray head opening was the tubular Extrudate with an approximate width of 22.2 cm and a thickness of 431.8 microns quenched for cooling, by moving it at a speed of about 11.7 m / min. was passed through a cold water bath. The tubular extrudate then became orientation reheated by heating at a speed of about 11.4 m / min. through a heating zone or a Oven was performed. The oven was heated by horizontal, heated vertical and steam elements. In this example the horizontal heating element was at a temperature kept at 100 ° C. The vertical heating element was maintained at a temperature of 173 ° C and the vapor element,  the heat supplied by steam through tubes or container was passed inside the furnace was charged with steam under a pressure of 0.48 bar.

After heating, the tubular extrudate became inflated and approximately in the transverse direction in proportion of 4.8: 1 and in the longitudinal direction in an approximate Ratio of 4.5: 1 stretched. After that, the film became to block the oriented molecular structure Quench cooled. The thickness of the finished film was about 19 μm.

The data obtained when testing this material is in Table I.

example 3

A three-layer structure with an approximate layer thickness ratio from 1/3/1 was under load from extruded four extruders. Extruders Nos. 1 and 2, which supplied the spray head opening for the core layer, became lower with 100% linear polyethylene Density (density 0.920, melt index 1.0) charged together with 3300 ppm erucamide. The extruders Nos. 3 and 4 each supplied a spray head opening for an outer layer and were both with a mixture of 80% ethylene-propylene copolymer (3.5%) ethylene; Melt flow 4.5) and 20% propylene Homopolymer (density 0.906, melt flow 3.5) along with 3300 ppm erucamide and 1100 ppm silica and 1650 ppm N, N-dioleoylethylenediamine charged.  

The temperature of extruder no. 1 was in the range kept from 202 to 252 ° C. The extruder no. 2 became maintained at a temperature in the range of 219 to 243 ° C. Extruder No. 3 was at a temperature of 188 to 191 ° C held. Extruder No. 4 was on a Temperature also maintained from 188 to 191 ° C. The circular spray head was at a temperature of 196 ° C held. The actual temperature ranges, on which the extruder and the spray heads are kept were not recorded in this example.

After extruding the layers through the circular 25.4 cm spray head opening was the tubular Quenched extrudate for cooling by using a speed of about 11,85 m / min. by a cold bath was passed. After extruding The tape was a fine silicone spray on the Inside the extruded tube in a crowd from 50 to 70 mg / m² applied. The cooled tubular Extrudate was then returned to orientation heated by moving it at a speed of about 11.3 m / min. passed through a heating zone or an oven has been. The stove was made by horizontal, vertical and Steam heating elements heated. In this example was the horizontal element at a temperature of 93.4 ° C held. The vertical element was at a temperature kept at 152 ° C while the vapor element, the heat supplied by steam through tubes or containers inside the stove was steamed a pressure of 0.25 bar was charged.

After reheating, the tubular extrudate became in the transverse direction in the ratio of approximately 4.8: 1 and in the longitudinal direction in the ratio of approximately 4.5: 1  stretched. Thereafter, the film was quenched cooled with water to the oriented structure too To block. The thickness of the finished film was approximately 19 μm.

The results obtained when testing this film are in Table I.  

Table I

All data given in Table I are averages, obtained according to the indicated ASTM standards have been.

Claims (6)

A multi-layer shrink film having a core layer, two outer layers containing an ethylene-propylene copolymer, and optionally two intermediate layers, characterized in that all layers are oriented and the core layer contains linear low density polyethylene or linear medium density polyethylene. 2. Multilayer shrink film according to claim 1, characterized characterized in that the two outer layers of a mixture of 70 to 90 wt .-% of an ethylene-propylene copolymer and 10 bis Contain 30 wt .-% of a propylene homopolymer. 3. shrink film according to claim 1 or 2, characterized that it has two intermediate layers which are a mixture from 20 to 90 wt .-% ethylene-vinyl acetate copolymer and 10 bis 80% by weight of a linear low density polyethylene contain. 4. shrink film according to one of claims 1 to 3, characterized in that the core layer contains a formulation selected from one of the following groups:

• a) 10 to 100 wt .-% of a linear low density polyethylene mixed with 0 to 90 wt .-% of an ethylene-propylene copolymer;
• b) 10 to 100% by weight of a linear medium density polyethylene blended with 0 to 90% by weight of an ethylene-propylene copolymer;
• c) from 10% to 80% by weight of a linear low density polyethylene blended with from 20% to 90% by weight of an ethylene-vinyl acetate copolymer;
• d) from 10% to 80% by weight of a linear medium density polyethylene blended with from 20% to 90% by weight of an ethylene-vinyl acetate copolymer;
• e) 10 to 80% by weight of a linear low density polyethylene blended with 10 to 80% by weight of an ethylene-vinyl acetate copolymer and 10 to 80% by weight of an ionomer resin;
• f) 10 to 80% by weight of a linear medium density polyethylene blended with 10 to 80% by weight of an ethylene-vinyl acetate copolymer and 10 to 80% by weight of an ionomer resin;
• g) from 10% to 80% by weight of a low density linear polyethylene blended with from 20% to 90% by weight of a low density polyethylene;
• h) 10 to 80% by weight of a linear medium density polyethylene blended with 20 to 90% by weight of a low density polyethylene.

Shrink wrap according to one of claims 1, 2 or 4, characterized in that it comprises two intermediate layers with formulations selected from the following groups:

• a) 10 to 100 wt .-% of a linear low density polyethylene mixed with 0 to 90 wt .-% of an ethylene-propylene copolymer;
• b) 10 to 100% by weight of a linear medium density polyethylene blended with 0 to 90% by weight of an ethylene-propylene copolymer;
• c) from 10% to 80% by weight of a linear low density polyethylene blended with from 20% to 90% by weight of an ethylene-vinyl acetate copolymer;
• d) from 10% to 80% by weight of a linear medium density polyethylene blended with from 20% to 90% by weight of an ethylene-vinyl acetate copolymer;
• e) 10 to 80% by weight of a linear low density polyethylene blended with 10 to 80% by weight of an ethylene-vinyl acetate copolymer and 10 to 80% by weight of an ionomer resin;
• f) 10 to 80% by weight of a linear medium density polyethylene blended with 10 to 80% by weight of an ethylene-vinyl acetate copolymer and 10 to 80% by weight of an ionomer resin;
• g) from 10% to 80% by weight of a low density linear polyethylene blended with from 20% to 90% by weight of a low density polyethylene;
• h) from 10% to 80% by weight of a linear medium density polyethylene blended with from 20% to 90% by weight of a low density polyethylene;
• i) an ethylene-vinyl acetate copolymer;
• j) from 20% to 80% by weight of a low density linear polyethylene blended with from 20% to 80% by weight of an ionomer resin;
• k) 20 to 80% by weight of a linear medium density polyethylene blended with 20 to 80% by weight of an ionomer resin.

6. shrink film according to any one of claims 1, 3, 4 or 5, characterized in that the outer layers contain a formulation:

• a) 70 to 90 wt .-% of an ethylene-propylene copolymer mixed with 10 to 30 wt .-% of a linear low-density polyethylene;
• b) 70 to 90 wt .-% of an ethylene-propylene copolymer mixed with 10 to 30 wt .-% of a linear polyethylene medium density.