DK169579B1 - Oriented multilayer shrink film - Google Patents

Description

DK 169579 B1

The present invention relates to an oriented multilayer shrink film consisting of a core layer, two surface layers consisting essentially of an ethylene-propylene copolymer, and optionally two intermediate layers. A prominent feature of a shrink film is the ability of the film to shrink, when subjected to a particular temperature or, if kept from shrinking, to produce shrinkage stress within the film.

The preparation of shrink films well known in the art can usually be accomplished by extrusion of the resin materials which have been heated to their flow or melting point from an extrusion nozzle in tubular or planar form. After a quench after extrusion, the extrudate is again heated to its orientation temperature range. The orientation temperature range of a given film will vary with the various resin polymers and mixtures thereof which include the film. However, the orientation temperature is usually above room temperature and below the melting point of the foil.

The terms "oriented" or "orientation" are used herein to describe the characteristics of the process and the resulting product formed by stretching and instant cooling a polymeric resin material which has been heated to its orientation temperature range to change the molecular configuration of the material by physical aligning the molecules to improve the mechanical properties of the film, e.g. shrinkage stress and orientation release stress. Both of these properties can be measured in accordance with ASTM D 2838-69 (newly approved 1975). When the tensile force is applied in one direction, uniaxial orientation appears. When the pulling force is applied in two directions biaxial orientation appears. Orientation is also used here interchangeably with "heat shrinkage" where these designations denote a material which has been stretched and which, upon cooling, is made to stiffen in its stretched dimensions. An oriented (i.e. heat shrinkable) material will tend to DK 169579 B1 2

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to return to its original unstretched target when heated to a suitable temperature below its melt-temperature range.

With regard to the basic process for preparing the film as described above, it can be seen that after being extruded and initially quenched, it is again heated to its orientation temperature range and oriented. The orientation stretch can be accomplished in many ways, e.g. by "bubble blowing" or "frame clamping". These terms are well known to those skilled in the art and refer to orientation steps whereby the material is stretched in the cross or transverse direction (TD) and in the longitudinal or machine direction (MD). After being stretched, the film is quenched rapidly, thus causing the oriented molecular configuration to stiffen or lock.

After locking the oriented molecular configuration, the film can then be stored in rolls and used for tight packaging of a wide variety of products. For this purpose, the product to be packaged is first enclosed in the heat-shrinkable material by heat sealing the shrink wrap to itself where necessary. Then the enclosed product is subjected to elevated temperatures at e.g. to pass it through a hot air or hot water tunnel. This causes the film to shrink 25 around the product, providing a tight wrap that closely aligns with the shape of the product.

The aforementioned general outline of the production of films does not intend to be fully exhaustive, as this method is well known to those skilled in the art, cf.

U.S. Patent Nos. 4,274,900, 4,229,241, 4,194,039, 4,188,443, 4,048,428, 3,821,182 and 3,022,543.

Many variations of the general treatment described above are possible for those skilled in the art depending on the end use of the film and the properties it is desired for the film 35 to have. Eg. For example, the molecules of the film can be crosslinked during the treatment to improve the film's resistance to damage and other properties. Crosslinking and crosslinking methods are well known in the art. Crosslinking can be done by irradiating the foil or alternatively, chemically using peroxides.

Another possible treatment variation is the application of a fine mist of silicone spray liquid to the interior of the freshly extruded material to enhance the material's ability for further processing. Such an internal application method is described in U.S. Patent Application No.

289,018.

The polyolefin family and especially the polyethylene family of shrink films provide a wide variety of physical and performance properties such as shrinkage (the force exerted by a film per unit area of its cross-section during shrinkage), the degree of free shrinkage (the reduction in linear dimension , which a material undergoes when subjected to elevated temperatures without being maintained), tensile strength * (the highest force that can be applied to a foil unit area before it begins to tear), sealing ability, shrinkage temperature curve (shrinkage to temperature ratio), initial tearing and tearing strength (the force at which a film begins to tear and continue with it), optical properties (gloss, 25 veils, and transparency of the material) and dimensional stability (the film's ability to maintain its original dimensions under various types of storage conditions). Foil properties play an important role in the selection of a particular foil, and they vary for each type of packaging use and for each package. Account must be taken of the product size, weight, shape, stiffness, number of product components, other packaging materials that can be used with the foil, and the type of packaging equipment available.

35 From the above-mentioned prior art, the technique disclosed in US Patent Nos. 4,188,443 and 4,194,039 (which DK 169579 B1 4 corresponds to DE disclosure no. 2,914,914) is to be considered as closely related to the present invention. invention.

Specifically, U.S. Patent No. 4,188,443 discloses, as is well known in the art, a shrinkable five-layer film with a copolyester core layer, ethylene-vinyl acetate copolymer intermediate layer, and outer layer of ethylene-propylene copolymer. The sheets of this patent are oriented and stated to have good shrinkage stress, heat seal strength and sealability, and a wide shrinkage temperature range.

Specifically, U.S. Patent No. 4,194,039 discloses a shrinkable three-layer film having a core layer of a mixture of ethylene-vinyl acetate copolymer and ethylene-butylene copolymer and outer layers of ethylene-propylene copolymer. The sheets of this patent are oriented and stated to have good shrinkage stress, optical clarity, cutability and sealability, a wide shrinkage temperature range and good tear strength.

The present invention relates to an oriented multilayer shrink film consisting of a core layer, two surface layers consisting essentially of an ethylene-propylene copolymer, and optionally two intermediate layers, the film being characterized in that the core layer consists essentially of 25 linear low density polyethylene or linear medium density polyethylene.

Similar to the above, the multilayer shrink film according to the invention differs from the prior art, which is considered to be most obvious and is described in the above-mentioned U.S. Patent Nos. 4,194,039 and 4,188,443, in that the core layer of the known films is a material other than the core layer of the film of the invention, and the film of the invention consists in its basic embodiment of a core layer of a linear low density polyethylene or linear medium density polyethylene and two outer layers of ethylene-propylene copolymer.

DK 169579 B1 5

This particular combination of material layers, not disclosed or proposed in the prior art, provides, upon orientation, a film which, in particular, in relation to the films of the prior art, is particularly distinguished by a particularly high shrinkage stress (or equivalent free shrinkage).

In addition, the three-layer foil of the invention and - depending on the composition of the intermediate layers - also exhibit good five-layer foil according to the invention 10 (with respect to, for example, clarity, gloss and veil) and good mechanical properties (with regard to, for example, toughness). ).

Unless specifically mentioned and defined or limited, the terms "polymer" or "polymer resin" used herein usually include homopolymers, copolymers, terpolymers, block polymers, graft polymers, statistical and alternate polymers.

The terms used herein refer to the following: "Melt Flow" or "Melt Flow Index" is the amount in g of a thermoplastic resin which can be pressed through a given nozzle under a specified pressure and temperature over 10 minutes as described in ASTM D 1238.

"Core" or "core layer" refers to the middle layer of the three- or five-layer film.

"Surface" or "surface layer" refers to an outer (surface) layer of the three or five layer film.

"Intermediate" or "intermediate layer" means a layer of a five-layer film that lies between the core layer and a surface layer.

"Low density polyethylene" (LDPE) refers to homopolymers of ethylene having a density of 0.910-0.925.

"Linear Low Density Polyethylene" (LLDPE) refers to a copolymer of ethylene and 8% or less butene, octene or hexene having a density of 0.910-0.925 and wherein the molecules comprise long chains with few or no branches or crosslinked structures. .

GB 169579 B1 6 "Linear Medium Density Polyethylene" (LMDPE) refers to a copolymer of ethylene and less than 8% butene, octene or hexene having a density of 0.926-0.940 and wherein the molecules comprise long chains with few or no branches. or cross-linked structures.

"Ethylene vinyl acetate copolymer" (EVA) refers to a copolymer formed from ethylene and vinyl acetate monomers in which the ethylene-derived units are present in larger quantities and the vinyl acetate-derived units are present in smaller amounts.

"Ethylene propylene copolymer" (EPC) refers to a copolymer formed from ethylene and propylene monomers in which the propylene-derived units are present as a major component and the ethylene-derived units are present as a minor component.

"Propylene homopolymer" (PP) refers to a thermoplastic resin having a density of approx. 0.90 and formed by polymerizing propylene with suitable catalysts well known in the art.

2Q The multilayer film can be combined with other polymeric materials for specific applications. Eg. For example, relatively thin layers may be applied to one or both sides of the preferred three-layer base structure to improve sealing strength or to reduce air and moisture permeability.

Another embodiment of the present invention comprises a five-layer foil structure. A preferred five layer structure comprises the same core and surface layers as the above three layer structure and comprises two further intermediate layers each comprising a blend of an ethylene vinyl acetate copolymer and either an ionomer resin or a linear low density polyethylene.

FIG. 1 is a cross-sectional view of a preferred three-layer foil.

FIG. 2 shows a cross-section of a preferred five-layer foil.

DK 169579 B1 7

Referring to FIG. 1, which is a cross-section of a preferred three-layer film according to the invention, it can be seen that this film comprises a core layer 2 and surface layers 1 and 3. The preferred thickness ratio for the three layers is 5 1/3/1 as shown in FIG. 1. A preferred core layer 2 comprises a linear low density polyethylene polymer. A linear medium density polyethylene polymer can replace the core layer without significantly altering the properties of the finished film product.

10 As defined above, LLDPE is used as an abbreviation for linear low density polyethylene, LMDPE for linear medium density polyethylene, EPC for an ethylene propylene copolymer and EVA for an ethylene vinyl acetate copolymer. The term ionomer resin refers to ethylene (meth) acrylic acid copolymers in which the acid functions are neutralized in the form of metal salts. One of the most significant of the ionomeric resins is marketed by du Pont under the name "Surlyn".

Tests have shown that a particularly preferred core layer formulation consists essentially of linear low density polyethylene. This material is available from the Dow Chemical Company and is marketed under the name "Dowlex 2045".

Referring to FIG. 1 and especially for surface layers 1 and 3, suitable surface layer formulations may be selected from the following groups: 25 (1) EPC or (2) 70-90% EPC mixed with 10-30% PP or 30 (3) 70-90% EPC mixed with 10-30% LLDPE or (4) 70-90% EPC mixed with 10-30% LMDPE.

All abbreviations are the same as stated above in connection with the core layer formulations. Furthermore, PP is used as an abbreviation for a propylene homopolymer such as

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8 DK 169579 B1 defined above. Experiments have also shown that a particularly preferred surface layer formulation consists essentially of a blend of 20% PP with 80% EPC.

The propylene homopolymer can be obtained from Hercules Chemical 5 Company under the trade name "PD064". The ethylene propylene copolymer can be obtained from Soltex Chemical Company under the trade name "42X01" or alternatively from Solvay Chemical Company under the trade name "KS400".

In the present specification and claims, all 10 percentages are by weight and all references to density 3 are in g / cm.

In summary, it has been found that a particularly preferred film according to the invention comprises a core layer consisting essentially of linear low-density polyethylene and surface layer consisting essentially of a mixture of 20% propylene homopolymer with 80% ethylene. propylene copolymer.

Although the above three-layer foils are usually preferred over structures having more than 20 three layers, as a result of the economics of manufacture, various five-layer foils which are also satisfactory in terms of physical properties can also be produced. However, the cost of producing a five-layer film is usually greater than that of producing a three-layer film.

FIG. 2, which is a cross-section of a preferred five-layer film according to the invention, shows the preferred layer thickness ratio of 2/2/1/2/2. A core layer 6 may comprise any of the core layer formulations described above with respect to core layer 2 of the three layer film.

Surface layers 4 and 8 of the five-layer foil may comprise any of the surface layer formulations described above in connection with the surface layers 1 and 3 of the three-layer foil of FIG. First

The five-layer foil of FIG. 2 also includes intermediate layers 5 and 7.

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DK 169579 B1 9

Tests have shown that a particularly preferred five-layer structure comprises surface layers 4 and 8 consisting essentially of an ethylene propylene copolymer (EPC), intermediate layers 5 and 7 consisting essentially of a mixture of 90% ethylene vinyl acetate copolymer with 10 % ionomer resin and a core layer 6 consisting essentially of linear low density polyethylene. EPC is available from Soltex Chemical Company under the trade name "42X01". EVA is available from du Pont Chemical Company under the trade name "Alathon 10 3137". The ionomer resin is available from du Pont Chemical Company under the trade name "Surlyn 1601". LLDPE is available from the Dow Chemical Company under the trade name "Dowlex 2045".

Those skilled in the art will quickly recognize that all of the above weight percentages are subject to less variation. Furthermore, these percentages may vary slightly as a result of the use of additives such as the silicone mist described above, or agents such as slip and anti-blocking agents. A preferred anti-blocking agent is silica which is available from Johns Manville * under the trade name 20 "White Mist". Preferred abrasives are erucamide (available from Humko Chemical Co. under the trade name "Kemamide E") and stearamide (available from Humko Chemical Co. under the trade name "KemamideS") and NiN3-diolecylethylenediamine (available from Glyco Chemical under the trade name "Acrawax C").

A preferred silicone spray liquid is a liquid polyorganosiloxane made by General Electric under the trade name General Electric wSF18 "polydimethylsiloxane.

The usual uses of these additives are as follows: 30 (1) Silica: 250-3000 ppm (2) "Acrawax C": 200-4000 ppm (3) Erucamide: 200-5000 ppm (4) Stearamide: 200-5000 ppm 2 (5) Silicone spray liquid: from 5 mg / m upwards.

O When the term "consisting essentially of" is used in this specification and claims, it shall not exclude minor percentage variations or additives and agents of the said type.

Additional layers and / or smaller amounts of additives of the types described above may be added to the three-layer or five-layer structure of this invention as desired, but care must be taken to ensure the desired shrinkage stresses, shrinkage properties, optical and other properties of the present invention. -10-lead multilayer foil does not change in an unfortunate direction.

In the preferred method of preparing the low or medium density linear polyethylene multi-layer shrink film of the present invention, the basic steps are mixing the polymers for the various layers, co-extruding the layers to form a multilayer film, and then stretching the film to biaxial orientation. These and further desirable steps will be explained in more detail in the following sections.

The process begins with mixing the raw materials (e.g. polymeric resins) in the above quantities and ratios. The resins are usually obtained from the supplier in pellet form and can be blended into any of the commercially available blending containers well known in the art. During the mixing process, any additives and / or agents which are desired to be used are also incorporated.

The mixed resins and useful additives and / or agents are then fed into the funnels of extruders which feed the coextrusion nozzle. For the three-layer film, it is necessary to use at least three extruders if each layer is to have a different composition. Two extruders are fed with the materials desired for the inner and outer surface layers and the other extruder is fed with the linear low or medium density polyethylene material which is desired to be used in the core layer. Additional extruders can be used if desired. Preferably, the material is co-extruded as a tube having a diameter which is dependent on the stretch ratio and the desired final diameter.

This coextruded tube is relatively thick and is referred to as "ribbon". Round coextruding nozzles are well known in the art and can be purchased from a variety of manufacturers. Methods of application may also be used if desired.

A further process step which can be used comprises irradiating the tape or unstretched tube or layer by bombarding it with high energy electrons from an accelerator for crosslinking the materials in the tape. Crosslinking greatly increases the structural strength of the foil or the force at which the material can be stretched before it is torn when the foil materials are predominantly ethylene such as polyethylene or ethylene-vinyl acetate. Radiation also improves the optical properties of the film and changes the film's properties at higher temperatures. If an irradiation step is used, a preferred radiation dose level is from 0.5Mr to 12, OMR. MRI is an abbreviation for. megarads. A megarad is 1 x 10 5 rad, with 1 rad being the amount of ionizing radiation resulting in absorption of 100 erg energy per day. g irradiated material 25 irrespective of the radiation source. In some cases, it may be desirable to first stretch the multilayer film and then irradiate it, or, if continuous coating is applied, one layer or group of layers may be irradiated, to which another or more layers may be added before the final coating. stretching and orientation steps.

As indicated above, a further optional process step is to apply a fine silicone mist to the interior of the freshly extruded tape. The details of this process step are described in U.S. Patent Application No. 289,018.

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12 DK 169579 B1

After coextrusion, quenching and, if desired, irradiation, the extruded band is heated again and continuously inflated with an internal air pressure to a bubble, whereby the narrow band of thick walls is converted to a wide film of thin walls with it. desired foil thickness. This approach is sometimes referred to as "trapped bubble technique" for orientation or stretching.

After stretching, the air is then discharged from the bubble and the film is wound onto semi-finished rolls referred to as "machine-10 rolls". The stretching process orients the film by stretching it transversely and to some extent longitudinally to rearrange the molecules, thereby imparting shrinkage to the film and modifying its physical properties. Further stretching in the longitudinal or machine direction can be accomplished by rotating the air emptying rollers, which helps to cause the "blown bubble" to burst at a speed greater than the speed of the rollers which serve to transport the reheated belt to the stretching area or .bubble blowing area.

All of these stretching methods are well known in the art.

The following examples serve to illustrate and clarify the scope of the invention.

Example 1

A five-layer structure, which has a layer thickness ratio of approx. 2/2/1/2/2, extruded using four extruders. Extruder # 1, which supplies the nozzle openings to both intermediate layers, is fed a mixture of 90% ethylene vinyl acetate copolymer (12% vinyl acetate, "Alathon 3137", melt index 0.5) and 10% ionomer resin ("Surlyn 1601", density 0.940, melt index 1.4). The mixture also contains 1100 ppm erucamide ("Kemamide E") and 1100 ppm stearamide ("Kemamide S"). Extruder # 2, 35 which supplies the nozzle aperture to the core layer is fed 100% linear low density polyethylene ("Dowlex 2045"

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13 DK 169579 B1 site 0.920, melt index 1.0). Extruder # 3 and # 4 each provide a nozzle aperture for a surface layer, and both are supplied with 100% ethylene propylene copolymer (3.5% ethylene, "Soltex 42x01", melt flow 4.5), which is mixed with 5,100 ppm erucamide. ("IKemamide E"), 1100 ppm stearamide ("Chemamide S") and 1100 ppm silica ("White Mist"). '

Extruder # 1 is kept at a temperature of 199-218 ° C. Extruder # 2 is kept at a temperature of 210-243 ° C.

Extruder # 3 is maintained at a temperature of 177-188 ° C and 10 extruder # 4 is maintained at a temperature of 174-185 ° C.

The round nozzle is maintained at a temperature of 199-224 ° C.

After extruding the layers through the round 25.4 cm nozzle opening, the tubular extrudate is quenched, which has a strip thickness of approx. 0.38 mm and a pipe width 15 of approx. 24.4 cm by passing through a cold water bath at approx. 11.3 m per minute. The tube is then heated again for information by passing through a heating zone or furnace at 11.6 m / s. minute. The oven is heated by horizontal, vertical and steam heating elements. In this example, the horizontal heating element is maintained at 93 ° C. The vertical heating elements are maintained at 149 ° C and the steam element, which provides heat as it is passed through pipes or sheaths placed inside the furnace, is supplied with steam 2 at 0.14 kg / cm.

After being treated as described above, the tubular extrudate is inflated and stretched transversely to ca. 4.8: 1 and longitudinally approx.

4.3: 1st The film is then cooled by quenching with water to lock in the oriented structure. The finished film-30 target is approx. 75 gauge. The test results obtained for this material are given in Table I below.

Example 2

A five-layer structure having a layer thickness ratio 35 of approx. 2/2/1/2/2, extruded using four extruders. Extruder # 1, which supplies the nozzle openings

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To both intermediate layers, a mixture comprising 50% ethylene vinyl acetate copolymer (12% vinyl acetate, "Alathon 3137", melt index 0.5) and 50% linear low density polyethylene ("Dowlex 2045", density 0.920, melt density) is added. 5 dex 1.0) and 1100 ppm erucamide ("Kemamide E"). Extruder # 2, which supplies the nozzle opening to the core layer; 100% linear low density polyethylene ("Dowlex 2045", density 0.920, melt index 1.0) is added. Extruder # 3 and # 4 each provide a nozzle aperture for a surface layer, 10 and both are fed 100% ethylene propylene copolymer (2.7% ethylene, "ARCO K-193", melt flow 2.3) containing 1100 ppm erucamide ( "Kemamide E") and 1100 ppm silicone ("White Mist").

Extruder # 1 is kept at a temperature of 207-213 ° C. Extruder # 2 is kept at a temperature of 204-246 ° C.

Extruder # 3 is maintained at a temperature of 179-224 ° C and extruder # 4 is maintained at a temperature of 179-210 ° C.

The round nozzle is maintained at a temperature of 199-218 ° C.

After extruding the layers through the 25.4 cm nozzle opening, the tubular * extrudate which has a bandwidth of approx. 22.2 cm and a thickness of 0.43 mm, passing through a cold water bath at approx. 11.9 m per minute. The tubular extrudate is then again heated for orientation by passing through a heating zone or furnace at approx. 11.6 m per minute. The oven is heated by horizontal, vertical and steam heating elements. IN

in this example, the horizontal heating element is maintained at 100 ° C. The vertical heating element is maintained at 173 ° C and the steam element, which provides heat as it is passed through pipes or casings inside the furnace, is supplied with steam 2 at 0.49 kg / cm.

After being heated, the tubular extrudate is inflated and stretched transversely in approx. 4.8: 1 and longitudinally approx. 4.5: 1st Thereafter, the film is cooled by quenching with water to lock in the oriented molecular structure. The finished film thickness is approx. 75 gauge.

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15 DK 169579 B1

The test results obtained for this material are given in Table I below.

Example 3 A three-layer structure having a layer thickness ratio of approx. 1/3/1, extruded using 4 extruders. Extruder # 1 and # 2, which supply the nozzle aperture to the core layer, are fed 100% linear low density polyethylene ("Dowlex 2045", density 0.920, melt index 1.0) containing 3300 ppm erucamide ("Kemamide E"). Extruder no.

3 and No. 4, each providing a nozzle aperture for a surface layer, both are fed a mixture of 80% ethylene-propylene copolymer (3.5% ethylene, "Soltex 42X01", melt flow 4.5) and 20% propylene homopolymer ("Hercules"). PD064 ", site 0.906, melt flow 3.5) containing 3300 ppm erucamide (" Kemamide E ") and 1100 ppm silica (" White Mist ") and 1650 ppm" Acrawax C ".

The temperature of extruder # 1 is set to a temperature of 202-252 ° C. Extruder # 2 is set to a temperature of 218-243 ° C. Extruder # 3 is set to a temperature of 188-191 ° C. Extruder # 4 is set to a temperature of 188-191 ° C. The round nozzle is set to a temperature of 196 ° C. The actual temperature ranges at which the extruders and nozzle are held are not recorded for this example.

After extrusion of the layers through the 25.4 cm round mouthpiece opening, the tubular extrudate is quenched by passing through a cold bath at ca. 12.04 m per minute. After extrusion of the tape, a fine 30 silicone mist is applied to the interior of the extruded tube in an amount of 50-70 mg / m 2. The cooled tubular extrudate is then again heated for information by passing through a heating zone or furnace at approx. 11.49 m per minute. The oven is heated by horizontal, vertical and steam heating elements. In this example, the horizontal 16 DK 169579 B1 is held

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element at 93 ° C. The vertical element is maintained at 152 ° C and the steam element, which provides heat by passing through pipes or sheaths placed inside the furnace, provides steam at 2 0.23 kg / cm.

5 After being heated, the tubular extrudate is stretched in a transverse direction approx. 4.8: 1 and longitudinally approx. 4.5: 1st Then, the film is cooled by quenching with water to lock the oriented structure. The finished film target is approx. 75 gauge.

The test results obtained for this film are given in Table I below.

15 20 25 1 35

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Table I

Example I II m

Layer Relations 2/2/1/2/2 2/2/1/2/2 1/3/1

Tensile strength x 100 (kg / cm 2) ^ 5 MD 6,827 8,802 8,760 TD 7,769 7,389 9,189 2

Extension (%) MD 86 98 113 TD 65 107 102 10 Modulus x 1000 (kg / cm 2) ^ MD 6,349 6,911 6,785 TD 7,129 6,988 6,862 4

Rift Expansion (g) MD 4.10 4.33 9.60 15 TD 4.01 5.53 9.83 5

Tear strength (kg) MD 0.32 0.28 0.27 TD 0.41 0.38 0.30

Shrinkage properties 20 at 93 ° C

Free shrinkage (%) 6 MD 16 14 12 TD 18 20 17 2 7

Shrinkage stress (kg / cm) 25 MD 16.8 21.4 20.2 TD 23.0 32.1 35.8

at 127 ° C

g

Free shrinkage (%) MD 52 49 48 30 TD 57 57 54 2 7

Shrinkage stress (kg / cm) MD 15.5 24.3 30.5 TD 25.7 29.7 37.8

at 138 ° C

C

35 Free shrinkage (%) MD 71 66 62 TD 67 68 64 DK 169579 B1 18 o

Table I (continued)

Example II III

Shrinkage stress (kg / cm2) 2 MD 16.7 24.5 30.4 5 TD 21.4 25.5 41.1

Optical properties

Veil (%) 2.5 2.1 2.0

Gloss (45 °) 94 88 88

Total transmission 92.5 92.2 92.2 10

Footnote to Table I

1ASTM D 882 2ASTM D 882 15 3ASTM D 882 4ASTM D 1938 5ASTM D 1004 6ASTM D 2732 7ASTM D 2838 20 8ASTM D 1003

All of the data listed in Table I are averages obtained by methods consistent with the stated ASTM standard.

25 1 35

Claims (6)

1. Oriented multilayer shrink film consisting of a core layer, two surface layers consisting essentially of an ethylene-propylene copolymer, and optionally two intermediate layers, characterized in that the core layer consists essentially of linear low-density polyethylene or linear medium density polyethylene. Multilayer shrink film according to claim 1, characterized in that it consists of a core layer consisting essentially of linear low density polyethylene and two surface layers consisting essentially of a mixture of 80 wt% of an ethylene propylene copolymer mixed with 20 wt. -% of a propylene homopolymer. Multilayer shrink film according to claim 1, characterized in that it consists of a core layer consisting essentially of linear low-density polyethylene, two intermediate layers consisting essentially of a mixture of 90 wt% ethylene vinyl acetate copolymer mixed with 10 % by weight of an ethylene (meth) acrylic acid copolymer wherein the acid functions are neutralized in the form of metal salts, and two surface layers consisting essentially of an ethylene-propylene copolymer. Multilayer shrink film according to claim 1, characterized in that the core layer consists essentially of linear medium density polyethylene. Multilayer shrink film according to claim 1, characterized in that it consists of a core layer consisting essentially of linear low-density polyethylene or linear medium density polyethylene, two intermediate layers consisting essentially of a mixture of 50% ethylene-vinyl acetate polymer and 50 % linear low density polyethylene, and two surface layers consisting essentially of an ethylene-propylene copolymer. Multilayer shrink film according to claim 1, characterized in that the surface layers have a composition selected from the following groups: (a) an ethylene propylene copolymer, (b) 70-90% by weight of an ethylene propylene copolymer mixed with 10-30% by weight of a propylene homopolymer, (c) 70-90% by weight of an ethylene propylene copolymer blended with 10-30% by weight linear low density polyethylene, (d) 70-90% by weight of an ethylene propylene copolymer mixed with 10% by weight. -30% by weight linear average density polyethylene. i 4.