FR2521907A1 - RETRACTABLE FILMS OF LINEAR POLYETHYLENE - Google Patents

Abstract

THE INVENTION RELATES TO A MULTI-LAYER POLYOLEFIN FILM. ACCORDING TO THE INVENTION, IT CONSISTS OF A CORE LAYER 2 CONSISTING ESSENTIALLY OF A LINEAR POLYETHYLENE OF LOW DENSITY AND TWO SKIN LAYERS 1, 3 CONSISTING ESSENTIALLY OF A MIXTURE OF 80 BY WEIGHT OF A COPOLYMER OF ETHYLENE-PROPYLENE WITH 20 IN WEIGHT OF A PROPYLENE HOMOPOLYMER. THE INVENTION APPLIES IN PARTICULAR TO HEAT-SHRINK PACKAGING.

Description

The present invention relates to heat-shrinkable films and

  In particular, the present invention is directed to

  shrink films using poly-resins

  low density linear ethylene or medium density linear polyethylene resins as a constituent of a core and / or an intermediate layer in a

multilayer film.

  The present invention is directed to novel useful shrink film formulations. A feature that distinguishes a shrink film is the ability of the film, upon exposure to a certain temperature, to shrink or if it is

  prevented from shrinking, to produce a narrowing tension

in the film.

  The manufacture of shrink films, as is well known, can generally be accomplished by extruding the resinous materials which have been heated to their pour point or melting point from an extrusion die in tubular or planar form. post extrusion quench for cooling, the extrudate is then warmed to its orientation temperature range The orientation temperature range for a given film will vary with the different resinous polymers and their mixtures which form the film. However, the temperature range Andorientation can usually be indicated as being above room temperature and below the melting point of

film.

  The terms "oriented" or "orientation" are used herein to describe the characteristics of the resulting process and product obtained by immediately stretching and cooling a resinous polymeric material that has been heated to its orientation temperature range in order to revise the molecular configuration of the material by physically aligning the molecules to improve the mechanical properties of the film such as, for example, shrinkage stress and orientation release stress These two properties can be measured according to the American ASTM standard D 2838-69 (Reapproved in 1975) When the stretching force is applied in one direction, the result is a uniaxial orientation When the stretching force is

  applied in two directions, the result is an orienta-

  Biaxial orientation is also used here interchangeably with "heat shrinkability", a term that refers to a material that has been stretched and held, by cooling, to its stretched dimensions. Oriented (ie heat-shrinkable) material will tend to return to its original unstretched dimensions when it is heated to an appropriate temperature below

  its melting temperature range.

  By returning to the basic process for the manufacture

  of the film as described above,

  can see that the film once extruded and initial-

  The stretching for orientation is then warmed to its orientation temperature range and oriented. The stretching for orientation can be accomplished in many ways such as, for example, by "blown bubble" or "expanding frame" techniques. These terms are well known. and indicate orientation steps where the material is stretched crosswise or transversely (TD) and longitudinally or from the machine (MD). After being stretched, the film is rapidly cooled to soak it and thereby maintain or block at the

  oriented molecular configuration.

  After blocking the oriented molecular configuration, the film can be stored in roll and used for very tight packaging of a wide variety of articles. From this point of view, the product to be packaged is first enclosed in the heat-shrinkable material by heat-sealing the shrink wrap to itself when necessary Then the enclosed product is subjected to high temperatures, for example by passing the product through a hot air or hot water tunnel This forces the film to shrink around the produced to produce a tight wrap that will

  very precisely in line with the product outline.

  The general description above for the

  This process is well known to those skilled in the art. For example, reference may be made to patents.

  No. 4,274,900, 4,229,241, 4,194,039, 4,188,443, US Pat.

  4,048,428, 3,821,182 and 3,022,543 are all incorporated

here for reference.

  Many variations of the above-described general treatment scheme are available to those skilled in the art depending upon the end use for which the film is intended and the characteristics desired to be given to the film.

  of the film may be cross-linked during

  The crosslinking and crosslinking processes are well known. Crosslinking can be accomplished by irradiating the film or, alternatively, it can be accomplished chemically by the use of peroxides. Possible treatment is to apply a fine mist of a silicone jet inside the freshly extruded material to improve the subsequent processability of the material. A method for accomplishing this internal application is disclosed in the current US patent application.

  No. 289,018 filed July 31, 1981.

  The family of polyolefins and, in particular, the family of retractable film polyethylenes gives a wide range of physical characteristics and performance such as the shrink force (the amount of force a film exerts per unit area of its cross-section during the shrinkage), the degree of shrinkage or free shrinkage (linear dimension reduction in a specified direction, which a material undergoes when subjected to high temperatures while not retained), tensile strength (the highest force that can be applied to a unit area of the film before it begins to tear), the sealability, the shrinkage temperature curve (the relationship of shrinkage to temperature), the primer and the resistance

  tearing (the strength at which a film begins-

  will tear and continue to tear), the characteristics

  optical properties (gloss, haze and transparency of the material), and dimensional stability (the film's ability to maintain its original dimensions under

  different types of storage conditions) Characteristics

  The film properties play an important role in the choice of a particular film, and they differ for each type of packaging application and for each package. It is necessary to consider the size of the product, its weight, its shape, its rigidity, the number of its components, other packaging materials that can be used with the film and the type of equipment

packaging available.

  Given the many physical characteristics described above that are associated with polyethylene film and given the many applications to which these films have already been associated and those to which they can be applied in the future, it is easy to notice that the need for any improvement in the above physical characteristics of these dandruff is important

and of course is moving forward.

  Accordingly, the present invention

  general purpose heat-shrink polyolefin film

  table which represents an improvement over

  films already used in the prior art.

  Another object of the present invention is a polyolefin film having improved shrinkage stresses. Another object of the present invention is an improved shrink film of polyolefin having

better optical qualities.

  Another object of the present invention is a polyolefin shrink film having a wide range of

  shrinkage temperatures.

  Another object of the present invention is an improved shrink film of polyolefin having

  better sealability

  Another object of the present invention is a shrink film of polyolefin having a

  better resistance to the propagation of the tear.

  Another object of the present invention is a polyolefin shrink film having improved

machinability.

  Another object of the present invention is an improved shrink film of polyethylene using either linear low density or medium density polyethylene as a core component and / or

an intermediate layer.

  These objects and others are affected by

  the retractable polyolefin film disclosed herein.

  Unless otherwise indicated

  The terms "polymer" or "polymer resin" as used herein are defined or limited, and generally include homopolymers, copolymers, terpolymers, copolymers, and the like.

  sequences, grafted, statistics and alternate.

  The term "melt flow" as used herein or "melt flow index" is the amount, in grams, of a thermoplastic resin that can be forced through a given orifice under pressure and temperature. specified in ten minutes as this is

  described in US ASTM D 1238.

  The term "heart" or "heart layer" as used herein means a layer in a multilayer film that is

  locked on both sides in extra layers.

  The term "skin" or "skin layer" used here

2521907 4

  means an outer layer (i.e., surface)

a multilayer film.

  The term "intermediate" or "intermediate layers" as used herein means a layer of a multilayer film which is neither a core layer nor a skin layer. The term "low density polyethylene" (LDPE) as used herein indicates homopolymers of ethylene

  having a density of 0.910 to 0.925.

  The term "linear low density polyethylene" (LLDPE) as used herein denotes a copolymer of ethylene and 8% or less of butene, octene or hexene having

  a density of 0.910 to 0.925 and where the molecules comprise

  long chains with some ramifications or

  no ramifications or branched structures.

  The term "linear medium density polyethylene" (LMDPE) as used herein denotes a copolymer of ethylene and less than 8% butene, octene or hexene having a density of 0.926 to 0.940 and where the molecules include long-bodied cats with few branches or no branches or reticulate structures. The term "ethylene-vinyl acetate copolymer" (EVA) as used herein refers to a copolymer formed of ethylene-vinyl acetate monomers where units derived from ethylene are present in major amounts and units derived from vinyl acetate are present in

minor quantities.

  The term "ethylene-propylene copolymer" (EPC) used herein denotes a copolymer of ethylene-propylene monomers where units derived from propylene are present as the major component and units derived from ethylene are present as

minor constituent.

  The term "propylene homopolymer" (PP) used herein indicates a thermoplastic resin having a density of about 0.90 and made by propylene polymerization.

  with suitable catalysts as is well known.

2521907.

  It has been found that a flexible thermoplastic and shrink wrapping film having a desired combination of physical characteristics such as shrinkage tension, optical characteristics, cutability, sealability,

  shrinkage and shrinkage temperatures and

  This multi-layer film has a "core" layer which comprises a low density linear polyethylene resin. A linear density polyethylene resin is thought to be obtained by the multilayer flexible thermoplastic film of the invention. A preferred three-layer embodiment also includes, in addition to the above-identified "core" layer, two layers of skin each comprising a mixture of a

  homopolymer of propylene and a copolymer of ethylene

  propylene Preferably, the multilayer film is oriented so that it is heat-shrinkable in

least one direction.

  The multilayer film can be combined with other polymeric materials for specific applications. For example, relatively thin layers can be added on one or both sides of the preferred three-layer base structure to improve seal strength. or to lower

  permeability to gases and moisture.

  In another embodiment of the present invention, a five layer film structure is contemplated. A preferred five layer structure comprises the same core and skin layers as the above three layer structure and further comprises two layers. intermediates, each comprising a mixture of an ethylene-vinyl acetate copolymer and either an ionomeric resin or a linear low density polyethylene. It is currently believed that linear medium density polyethylene may also replace polyethylene linear low density of the intermediate layer. The invention will be better understood, and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory text which will follow with reference to the accompanying schematic drawings given by way of example only, illustrating several embodiments of the invention and in which: FIG. 1 is a cross-sectional view of a preferred three-layer embodiment according to the invention; and Fig. 2 is a cross-sectional view of a preferred five-layer embodiment according to

the invention.

  Referring to FIG. 1, which is a cross-sectional view of a preferred three-layer embodiment according to the invention, it can be seen that this embodiment comprises a core layer 2 and

  layers of skin 1 and 3 The preferred ratio of

  A preferred component of the core layer 2 comprises a low density linear polyethylene polymer. However, it is believed that it can be replaced by a linear polyethylene polymer. of medium density, as constituent of the core layer without substantial modification of the characteristics of the final produced film The core layer 2 comprises linear low density polyethylene (alternately linear of average density) or the core layer 2 may comprise a linear polyethylene copolymer blend of low density (alternately linear

  average density) with either (a) a copolymer of ethylene-

  propylene or (b) an ethylene-vinyl acetate copolymer or (c) an ethylene-vinyl acetate copolymer mixed with an ionomeric resin or (d) a low-density polyethylene. Thus, the various mixing formulas for the 2 heart layer can, according to this

  invention, be selected from the following groups.

  (1) 10-100% LLDPE blended at 0-90% EPC or (2) 10-100% LMDPE blend at 0-90% EPC or (3) 10-80% LLDPE blended at 20-90% EVA or (4) ) 10-80% LMDPE blended at 20-90% EVA or (5) 10-80% LLDPE blended at 10-80% EVA and -80% ionomeric resin or (6) 10-80% LMDPE blended at 10-80 % EVA and 10-80% ionomer resin or (7) 10-80% LLDPE mixed with 20-90% LDPE or

  (8) 10-80% LMDPE mixed with 20-90% LDPE.

  LLDPE is used here as an abbreviation for low density linear polyethylene as defined above. LMDPE is used as an abbreviation of linear medium density polyethylene as defined above. EPC is used herein as an abbreviation of a ethylenepropylene copolymer as defined above EVA is used herein as an abbreviation of an ethylene-vinyl acetate copolymer as defined above The term ionomeric resin is used herein

  to describe, in general, the group of ionomer resins.

  One of the most remarkable ionomer resins is sold under the trade name Surlyn

by Du Pont.

  Our experiments revealed that a particularly preferred core layer formulation consisted of

  essentially linear low density polyethylene.

  This material can be obtained by the Dow Chemical Company

  under the trademark Dowlex 2045.

  Referring again to Figure 1 and in particular to the skin layers 1 and 3, the appropriate skin layer formulations can be selected from the following groups: (1) EPC or (2) 70-90% EPC mixed with 10-30% PP or (3) 70-90% EPC mixed with 10-30% LLDPE or

  (4) 70-90% EPC mixed with 10-30% LMDPE.

  All abbreviations are as indicated above with respect to the formulas of the core layer. Further, PP is used herein as an abbreviation of a propylene homopolymer as defined above. Experiments also determined that a particularly preferred formula of the skin layer was

  essentially in a mixture of 20% PP to 80% EPC.

  Propylene homopolymer can be obtained at

  Hercules Chemical Company under the trade name

  PD 064 The ethylene-propylene copolymer can be obtained from Soltex Chemical Company under the trade designation 42 X 01 or alternatively from Solvay Chemical.

  Company under the trade designation K 5400.

  Throughout this description, all

percentages are "by weight".

  Throughout this description, all

  Density references are in g / cc.

  In summary, our experiments determined that a particularly preferred embodiment of the present invention comprised a core layer consisting essentially of low density linear polyethylene and skin layers consisting essentially of a 20% homopolymer blend. propylene with 80%

  an ethylene-propylene copolymer.

  Although the above-described three-layer formulas are generally preferred over structures having more than three layers as a result of manufacturing economy, various five-layer formulas have also been produced which are also safe from a point of use. However, the cost of manufacturing a five-layer film is generally higher than that of a film with three

layers.

  Figure 2, which is a cross-sectional view of

  A preferred five-layer film of the present invention demonstrates the preferred ratio of layer thicknesses of 2/2/1/2/2. The core layer 6 may comprise any core layer formulation described above for In addition, the core layer 2 may consist essentially of either (1) an ethylene-propylene copolymer (EPC) or (2) an ethylene-acetate copolymer.

vinyl (EVA).

  The skin layers 4 and 8 of the five-layer embodiment may comprise any of the skin layer formulations described above for the skin layers 1 and 3 of the present invention.

  three-layer embodiment of Figure 1.

  The five-layer embodiment of FIG. 2 also includes intermediate layers 5 and 7. These intermediate layers may comprise any of the above-disclosed formula for the core layer 2 of the three-layer embodiment. intermediate layers 5 and 7 can be chosen from

  additional groups that follow.

  (1) EVA or (2) 20-80% LLDPE mixed with 20-80% ionomeric resin or (3) 20-80% LMDPE mixed with 20-80% ionomeric resin. Our experiments have revealed that a particularly preferred five-layer structure would comprise skin layers 4 and 8 consisting essentially of an ethylene-propylene copolymer (EPC), intermediate layers 5 and 7 consisting essentially of a mixture of 90% of the vinyl ethyleneacetate copolymer with 10% ionomeric resin and a core layer 6 consisting essentially of low density linear polyethylene EPC can be obtained by Soltex

  Chemical Company under the trade designation 42 X 01.

  EVA can be obtained from the Du Pont Chemical Company under the trade designation Alathon 3137. The ionomer resin can be obtained from the Du Pont Chemical Company under the trade name Surlyn with the commercial designation Surlyn 1601. The LLDPE can be obtained from the Dow Chemical Company under the commercial designation

Dowlex 2045.

  Those who are competent in the field recognize

  It is easy to see that all the weight percentages disclosed above may be subject to slight variations. Moreover, these percentages may vary slightly as a result of the inclusion or application of additives such as the silicone mist described above.

  or agents such as slip and antiblocking agents.

  A preferred antiblocking agent is the silica available to Johns Manville under the trademark White Mist. The preferred slip agents are Erucamide (marketed by Humko Chemical under the trade name Kemamide E), and Stearamide.

  (available to Humko Chemical Company under the name

  Kemamide S) and N, N dioleoylethylenediamine (marketed by Glyco Chemical under the trade name Acrawax C). A preferred silicone spray is a liquid polyorganosiloxane manufactured by General Electric under the trade designation General Electric SF 18 polydimethylsiloxane. The general ranges for the application of these additives are as follows: (1) Silica 250-3000 ppm (2) Acrawax C: 200-4000 ppm (3) Erucamide: 200-5000 ppm (4) Stearamide: 200-5000 ppm

  (5) Silicone jet: 5.38 mg / m 2 and more.

  When used in the present description,

  the term "consisting essentially of" is not intended to exclude slight percentage changes

  or additives and agents of this kind.

  Additional layers and / or minor amounts of additives of the types described above may be added to either the three-layer structure or the five-layer structure of the present invention, if desired, but care must be taken to not to adversely affect desirable withdrawal voltages,

  shrinkage or shrinkage properties,

  optical features and other features of the multilayer film according to the invention. In the preferred process for the production of the low density or medium density linear polyethylene multilayer shrink film according to the invention, the basic steps are the mixing of the polymers for the various layers, the coextrusion of the layers to form a multilayer film and then the Stretching the film for biaxial orientation These steps and additional desirable steps are explained in detail

in the following paragraphs.

  The process begins with mixing the raw materials (i.e., the polymeric resins) to the desired proportions and ranges as described above. The resins are usually purchased from a supplier in the form of pellets, and can

  mixed in one of the many commercial mixers

  As is well known during the mixing process, any additive and / or agent that is desired

  use are also incorporated.

  Mixed resins and additives and / or

  Applicable agents are then brought to the extrusion hoppers

  The three co-extrusion die feeds the coextrusion die For the three-layer film, at least three extruders must be used if each layer is to have a different composition. Two extruders receive the desired materials for the inner and outer layers of skin and the outer layer. Another extruder receives the low or medium density linear polyethylene material that is desired for use in the core layer. Additional extruders may be employed, if desired. Preferably, the materials are coextruded in the form of a tube. having a diameter which depends on the filling ratio and the

14 2521907

  desired final diameter This coextruded tube is relatively

  thick and is called the "ribbon"

  The coextrusion streams are well known and can be purchased from a number of manufacturers. In addition to tubular coextrusion, slot dies could be used to coextrude the material in a planar form. layer or multilayer could also

be used if you wish.

  An additional step of the method that can be used is to irradiate the unexpanded ribbon or sheet by bombarding high energy electrons from an accelerator to crosslink the ribbon materials. The crosslinking greatly increases the strength of the structure of the ribbon. film or the force to which the material can be stretched before tearing when the film materials are predominantly ethylene such as polyethylene or vinyl ethylene vinyl acetate Irradiation also improves the optical properties of the film and changes the properties of the film at higher temperatures. If an irradiation step is employed, the preferred dose of irradiation is between 0.5 billion and 12.0 billion Mrd is an abbreviation for megarad One megarad is equal at lx 106 rads, one rad being the amount of ionizing radiation resulting from the absorption of 100 ergs of energy per gram d Irradiated Material Regardless of the Source of the Radiation In some cases, it may be desirable to stretch the multilayer film first and then irradiate it, or if sequential coating is employed, a layer or group of layers may be used. irradiated then another layer or

  The layers can be irradiated before the final stage of stretching and orientation.

  As noted above, one step

  additional optional treatment is the application of

  cation of a thin silicone jet inside the newly extruded ribbon The details of this step are disclosed in US Patent Application No. NI 289,018 filed

July 31, 1981.

  Following coextrusion, quenching to cool, and if desired irradiation, the extruded ribbon is reheated and continuously inflated by internal air pressure into a bubble to thereby transform the narrow ribbon having Thick walls in a thin film having thin walls at the desired film thickness This process is sometimes called

  "trapped bubble technique" for orientation or "stretching".

  After stretching, the bubble is then deflated and the film is wound on semi-finished rolls. The stretching process directs the film, stretching it transversely and, at a certain point, longitudinally to rearrange the molecules and thus impart shrink capabilities to the film and modify

  its physical characteristics An additional stretching

  in the longitudinal direction or the machine can be accomplished by rotating the deflated rollers which facilitates the collapse of the "blown bubble" at a speed greater than that of the rollers which serve to transport the "ribbon" heated to the stretching area

  or blown bubble All these methods are well known.

  To better reveal and clarify the scope of the invention, to those who are competent in the field,

  the following examples are presented.

EXAMPLE I

  A five-ply structure having the approximate thickness ratio of the 2/2/1/2/2 layers was extruded feeding four extruders. The extruder NO 1 feeding the die orifices for the two intermediate layers received a mixture of 900% ethylene-vinyl acetate copolymer (12% vinyl acetate) Alathon 3137 (melt index 0.5) 3 and 10% Surlyn 1601 ionomer resin (density 0.940, melt index) 1.4) The mixture also contained 1100 ppm Erucamide L Kemamide E and 1100 ppm Stearamide Kemamide. The N 2 extruder fed the orifice

  of the die for a heart layer received poly-

  100% low density linear ethylene Dowlex 2045 (0.920 density, 1.0 melt index) The N 3 and 4 extruders each fed a die orifice for one skin layer and both received an ethylene-plastic copolymer. 100% propylene (3.5% ethylene) Soltex 42 X 01 (melt flow 4.5) J mixed with 1100 ppm Erucamide (Kemamide EJ, 1100 ppm Stearamide 1 Kemamide S and 1100 ppm of White Mistl silicone

  The extruder N I was kept at a temperature of

  between 199 and 218 ° C. The extruder N 2 was

  maintained at a temperature between 210 and 243 C.

  The extruder N 3 was maintained at a temperature of between 177 and 188 ° C. and the extruder N 4 was

  maintained at a temperature between 174 and 185 C.

  Circular die was kept at a temperature

between 199 and 224 C.

  After extrusion of the layers through the 25.4 cm circular die orifice, the tubular extrudate which had a tape thickness of about 0.38 mm and a tubular width of about 244.5 mm was quenched to cool it by passing through a bath of cold water at about 15.27 m / min The tube was then warmed to orient it by passing through a heating zone or an oven at 11.58 m / min The oven was heated by horizontal, vertical and steam heating elements In this example, the horizontal heating element was maintained at 93 ° C. The vertical elements were held at 149 ° C and the steam element, which supplied heat through a passage through tubes or boots in the oven,

received steam at 0.138 bar.

  After heating as described above, the tubular extrudate was swollen and stretched transversely about 4.8 to 1 and stretched longitudinally to about 4.3 to 1. The film was quenched at room temperature. water to block the oriented structure The thickness

  The final film was about 75 gauge.

  The experimental data obtained for this film formulation are given in

  Table I which follows the description of the remaining examples.

EXAMPLE II

  A five-layer structure having an approximate thickness ratio of the 2/2/1/2/2 layers was extruded by feeding four extruders. The No. 1 extruder which fed the die orifices for the two intermediate layers received a mixture containing 50% ethylene-vinyl acetate copolymer (12% vinyl acetate) Alathon 3137 (melt index 0.5) J and 50% linear low density polyethylene t Dowlex 2045 (density 0.920 , Melt Index 1,10) J also having 1100 ppm Erucamide t Kemamide E 3 The NI 2 extruder which fed the die orifice for the core layer received 100% linear low density polyethylene t Dowlex 2045 ( density 0.920, melt index 1.0) 3 The NOS extruders 3 and 4 each fed a die orifice for one skin layer and both received a 100% ethylene propylene copolymer (2.7% ethylene) t ARCO K-193 (melt flow 2.3) l ayan t 1100 ppm of Erucamide l Kemamide El and 1100 ppm of silicon lWhite Mistl

  The extruder NO 1 was maintained at a temperature of

  The extruder NI 2 was maintained at a temperature between 204 and 2460 C. The extruder NO 3 was maintained at a temperature between 180 and 2240 C and the extruder NO 4 was maintained at a temperature between 180 and 2100 C. The circular die was maintained at a temperature between 199 and 2180 C. After extrusion of the layers through the orifice of the 25.4 cm circular die, the tubular extrudate having an approximate ribbon width of 222 mm and a thickness of 0.432 mm was quenched to cool by passing through a cold water bath at about 11.88 m / min. The tubular extrudate was then reheated for The oven was heated by horizontal, vertical and steam elements. In this example, the horizontal heating element was maintained at 100 ° C. The element green heating ical was maintained at 1730 C and the steam element, which provided heat by passing through tubes or boxes in the

oven, was fed at 0.48 bar.

  After being heated, the tubular extrudate was inflated and stretched transversely from about 4.8 to 1 and longitudinally from about 4.5 to 1. Then, the film was cooled by quenching with water to block the structure. oriented molecular The final thickness of

  the film was about 75 gauge.

  Data obtained by testing this material

can be found in Table I below.

EXAMPLE III

  A three layer structure having an approximate 1/3/1 layer thickness ratio was extruded feeding four extruders. The NOS extruders 1 and 3 which fed the die orifice for the core layer received linear polyethylene. 100% low density Dowlex 2045 (0.920 density, melt index 1.0) having 3300 ppm Erucamide Elamide NOS extruders 3 and 4 each fed a die orifice for one skin layer and both received a mixture of 80% of a copolymer of ethylene-propylene (3.5% ethylene) 1 Soltex 42 X 01 (melt flow 4.5) and 20% of a propylene homopolymer Hercules PD 064 ( density 0.906, melt flow 3.5) J and having 3300 ppm Erucamide C Kemamide E 3 and 1100 ppm silica Mistl lWhite and 1650 ppm Acrawax C The temperature of the extruder NI 1 was set between 202 and 2521 C The extruder NO 2 was established between 218 and 2430 C. NI 3 extruder was established between 188 and 1900 C. The extruder NO 4 was established between 188 and

  1900 C The circular sector was established at a temperature of

  The actual temperature ranges at which die extruders were maintained

  not recorded for this example.

  After extruding the layers through the 25.4 cm circular die orifice, the tubular extrudate was quenched to cool by passing through a cold bath at about 12 m / min. a fine silicon fog was applied inside the extruded tube at a rate of 53.82-75.35 mg / m 2. The cold tubular extrudate was then reheated to direct it by passage through a heating zone or oven at about 11.5 m / min The oven was heated by horizontal, vertical and steam heating elements In this example, the horizontal element was maintained at 930 C. The vertical element was maintained at 1520 C. and the steam element, which supplied heat by passing through tubes or boxes in the oven, was fed

at 0.24 bar.

  After being heated, the tubular extrudate was transversely stretched from about 4.8 to 1 and stretched longitudinally by about 4.5 to 1. Then, the film was cooled by quenching with water to block the oriented structure. The film was about

75 gauge.

  Data obtained by testing this film

  are shown in Table I below.

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  ## EQU1 ## where ## EQU1 ## ## EQU1 ## where ## EQU1 ## where ## EQU1 ## u: -. 3: 4 nx uu (31% cyl% l 0- at% \, O OD uu OO u NN "O \ DOO PQ u" \ o O 3 l, ÈD '(3) (D -11 ## EQU1 ## ## EQU1 ## ## where ## EQU1 ## where ## EQU1 ## OD OD N) D m Ln N) -.1 "O CD -.1

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  ro 1- F i H 1-1 ru N) 1-3 1 t: -, Table I notes 1 American Standard ASTM D 882 2 American Standard ASTM D 882 American Standard ASTM D 992 4 American Standard ASTM D 1938 American Standard ASTM D 1930 6 American Standard ASTM D 2732 US Standard ASTM D 2838 8 US Standard ASTM D 1003 All data shown in Table I above are averages obtained by processes as per

designated ASTM standard.

  It will be understood that the detailed description and

  the specific examples which indicate the presently preferred embodiments of the invention are given by way of example only, because various changes can be made to them, which will be apparent to those

  who are competent in this area.

Claims (9)

R E V E N D I C A T IO NS ___________________________   A polyethylenefin film, characterized in that it comprises linear polyethylene of low or medium density, irradiated as constituent of a   core layer and / or an intermediate layer.   2 mutilayer polyolefin film according to claim 1, characterized in that it comprises a core layer consisting essentially of a linear polyethylene low density.   3 Polyolefin polyurethane film according to claim   1, characterized in that it comprises a layer   heart (2) consisting essentially of linear polyethylene   low densities and two layers of skin (1, 3)   consisting essentially of a mixture of 80%, by weight, of an ethylene-propylene copolymer blended with 20% by weight of propylene homopolymer.   4 mutilayer polyolefin film according to claim   1, characterized in that it comprises a core layer (6) consisting essentially of linear low density polyethylene; two intermediate layers (5, 7) consisting essentially of a mixture of 90%, by weight, of an ethylene-vinyl acetate copolymer mixed with 10% by weight, an ionomeric resin and two layers of   skin (4, 8) consisting essentially of a copolymer of ethyl propylene.   Multilayer polyolefin film according to claim   1, characterized in that it comprises a layer   heart consisting essentially of linear polyethylene medium density nee.   6 multilayer polyolefin film according to claim   1, characterized in that it further comprises   two intermediate layers, said layers   mediums comprising linear polyethylene of low den- site.   7 Multilayer polyolefin film according to claim   1, characterized in that the core layer   comprises a mixture of copolymers selected from one of the following groups: a 10-100% by weight of a linear polyethylene of   low density mixed with 0-90% by weight of a copo-   ethylene-propylene monomer; b 10-100% by weight of a linear polyethylene of   average density mixed with 0-90% by weight of a copo-   ethylene-propylene monomer; c 10-80% by weight of a linear polyethylene of   low density mixed with 20-90% by weight of a copo-   ethylene-vinyl acetate polymer; d 10-80% by weight of a linear medium density polyethylene mixed with 20-90% by weight of an ethylene-vinyl acetate copolymer;   e 10-80% by weight of a linear polyethylene of   mixed density of 10-80% by weight of a copo-   ethylene-vinyl acetate and 10-80% by weight of an ionomeric resin;   10-80% by weight of a linear polyethylene of den-   medium density mixed with 10-80% by weight of a copo-   ethylene-vinyl acetate and 10-80% by weight of an ionomeric resin;   10-80% by weight of a linear polyethylene of   density mixed with 20-90% by weight of a polyethylene low density ethylene;   10-80% by weight of a linear polyethylene of   medium density mixed with 20-90% by weight of a poly- low density ethylene.   8 film according to claim 1, characterized   in that it further comprises two layers of skin, the   skin layers having formulas selected from the following groups: an ethylene-propylene copolymer;   b 70-90% by weight of an ethylene-propylene copolymer   mixed with 10-30% by weight of a propylene homopolymer;   70-90% by weight of a copolymer of ethylene-pro-   pylene mixed with 10-30% by weight of a polyethylene linear lenium of low density;   d 70-90% by weight of an ethylene-propylene copolymer   mixed with 10-30% by weight of a polyethylene Linear average density.   Film according to claim 1, characterized in that it further comprises intermediate layers having formulas selected from the following groups: a 10-100% by weight of a linear polyethylene of   low density mixed with 0-90% by weight of a   ethylene-propylene polymer; b 10-100% by weight of a linear polyethylene of   average density mixed with 0-90% by weight of a   ethylene-propylene polymer; c 10-80% by weight of linear low density polyethylene mixed with 20-90% by weight of an ethylene-acetated vinyl copolymer; d 10-80% by weight of a linear medium density polyethylene mixed with 20-90% by weight of an ethylene-vinyl acetate copolymer; e 10-80% by weight of linear low density polyethylene mixed with 10-80% by weight of ethylene copolymer (vinyl acetate and 10-80% by weight of an ionomeric resin; 80% by weight of a linear medium density polyethylene mixed with 10-80% by weight of an ethylene-vinyl acetate copolymer and 10-80% by weight of an ionomeric resin; 10-80% by weight weight of a linear low density polyethylene mixed with 20-90% by weight of a low density polyethylene, 10-80% by weight of a linear medium density polyethylene mixed with 20-90% by weight of low density polyethylene; ethylene-vinyl acetate copolymer; 20-80% by weight of a linear low density polyethylene mixed with 20-80% by weight of an ionomeric resin; % by weight of a linear medium density polyethylene mixed with 20-80% by weight of a ionomer resin.