NL8300616A - LINEAR POLYETHENE SHRINKLING FOILS. - Google Patents

Description

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Linear polyethylene shrink films

Summary of the invention

A multilayer thermoplastic film with improved physical properties is produced by using a low density linear polyethylene or medium density linear polyethylene resin as the core and / or intermediate layer component.

Field of the invention

The invention relates to heat-shrinkable, thermoplastic packaging films. In particular, the invention is directed to shrink films which utilize low density linear polyethylene or medium density linear polyethylene resins as constituents of a core and / or an interlayer in a multilayer film.

Background of the Invention The invention is directed to novel and effective heat shrinkable film compositions. A distinguishing feature of a shrink film is the ability of the film to shrink when exposed to a certain temperature or, when shrinkage is prevented, to develop shrink stress in the film.

The production of shrink films which is known can generally be accomplished by extrusion of the resinous materials, which have been heated to the flow or melting point, from a tubular or planar extrusion die.

After quenching after the extruding for cooling, the exudate persists are reheated to the orientation temperature range. The orientation temperature range for a given film differs for the different resinous polymers and mixtures thereof contained in the film. However, the orientation temperature range can generally be said to be above room temperature and below the melting point of the film.

The terms "u" oriented "or" orientation "are used herein to describe the process and resultant product properties obtained by stretching and directly cooling a resinous polymeric material which has been heated to the orientation temperature range to achieve molecular weight. configuration of the material by physically aligning the molecules to improve the mechanical properties of the film, for example, the shrinkage stress and orientation cancellation stress, both properties can be measured according to ASTM D 2838-69 (re-approved 1975) · When the stretch 10 force is applied in one direction, the result is uniaxial orientation. When the tensile force is applied in two directions, biaxial orientation results. Orientation is also used interchangeably here with "heat shrinkability", these terms denoting a material, which is provided 15 and put by cooling in the dimensions provided.A georia The deformed (i.e., heat shrinkable) material tends to return to the original non-stretched dimensions when heated to a suitable temperature below the melting point temperature range.

Returning to the basic process of manufacturing the film as described above, it is clear that once the film has been extruded and quenched for cooling, it is then heated to the orientation temperature range and oriented. The stretching for orientation can be accomplished in many ways, for example, by "bubble bubble" methods or "applying a stretcher". These terms are 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 length or processing direction (MD). After being stretched, the film is rapidly cooled and thus set or blocked in the oriented molecular configuration.

After blocking in the oriented molecular configuration, the film can then be stored in rolls and used for form-fitting packaging of a variety of 8300616% by weight of products. In this regard, the product to be packaged is first coated with the heat shrinkable material by sealing the shrink film on itself if necessary. Thereafter, the encapsulated product is subjected to higher temperatures by, for example, passing the product through a hot air or hot water tunnel. This causes the film to shrink around the product and forms a tight-fitting envelope that closely follows the outline of the product.

The above general sketch for making films is not intended to be comprehensive because this method is known to those skilled in the art. See, for example, U.S. Pat. Nos. 27¼,900. 4,229.2 ^ 1, 194,039, 4,188,443, 4,048,428, 3,821,182, and 3,022.5¾. The contents of these patents should be considered incorporated herein.

Many variations of the process discussed above are possible depending on the end application for which the film is intended and the properties desired for the film. For example, the molecules of the film can be cross-linked during treatment to improve the resistance of the films to abuse and other properties.

Cross-linking and cross-linking methods are known. Cross-linking can take place by irradiating the film or it can also take place chemically by the use of peroxides. Another possible process variant is the application of a fine mist of silicone spray to the interior of the freshly extruded material to improve the further processability of the material. A method of performing such an internal application is described in copending U.S. Application Serial No. 289,018, filed July 31, 19Ö1, the content of which is hereby incorporated by insertion.

The polyolefin group, and in particular, the polyethylene group of shrink films, provides a great range of physical and behavioral properties, such as shrink force (the force 35 exerted by a film per unit area of 8300 6 1 6 * I of the cross section during shrinkage ), the degree of free shrinkage (the reduction in linear dimensioning in a "certain direction, that a material undergoes it subject to higher temperatures, when it is not under tension), tensile strength (the 5 greatest force, which is on a surface unit film can be applied before it starts to tear), weldability, shrink temperature, (the relationship of shrinkage and temperature), initiation and tear resistance (the force at which a film starts to tear and continues to tear), optical properties ( gloss, haze and transparency of material), and dimensional stability (the ability of the film to maintain the original dimensions in different types o handling conditions). Film properties play an important role in the selection of a particular film and differ for each type of packaging application and for each packaging. Attention should be paid to the product size, weight, shape, stiffness, number of product components, Other packaging materials used together with the film, and the type of packaging equipment available.

In view of the many physical properties discussed above associated with polyethylene films, and further in view of the many applications with which these films are already associated and those for which they may be used in the future, it will be apparent that the need for ever improving one or all of the above-described physical properties of these films is great, and of course, still ongoing.

Objects of the invention

Accordingly, a general object of the invention is to provide a heat shrinkable polyolefin film which will be an improvement over those already used *, another object of the invention is to provide a polyolefin film having improved shrinkage stresses; Yet another object of the invention is to provide an 8300616 5 'improved polyolefin shrink film with improved optical properties; a further object of the invention is to provide a polyolefin shrink film with a high shrink temperature range; a still further object of the invention is to provide an improved polyolefin shrink film with improved weldability; yet another object of the invention is to provide a polyolefin shrink film with improved abrasion resistance;

Yet another object of the invention is to provide a polyolefin shrink film with improved processability; Yet another object of the invention is to provide an improved polyethylene shrink film for which a linear polyethylene of either low or medium density is used as a component of a core and / or an intermediate layer.

These and other objects are accomplished by the polyolefin shrink film described here.

Definitions

Unless otherwise stated and defined or limited, the terms "polymer" or "polymer resin" generally include homopolymers, copolymers, terpolymers, block, graft polymers, random and alternating polymers.

The term "melt flow" as used herein or "melt flow index" is the amount, in grams, of a thermoplastic resin that can be pressed through a given opening at a given pressure and temperature in 10 minutes, as described in 30 ASTM D 1238.

The term "core" or "kera layer" as used herein denotes a layer in a multilayer film enclosed on both sides by additional layers.

The term "skin" or "skin layer" as used herein means an outer "ie, surface" layer of an 8300616% 6 multilayer film.

The term "intermediate layer" 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 refers to ethylene homopolymers having a density of 0.910 to 0.925 ·

The term "low density linear polyethylene" (LLDPE) as used herein refers to a copolymer of 10 ethylene and 8% or less butene, octene or hexene with a density of 0.910 to 0.925 and in which the molecules have long chains with some or none contain branches or cross-linked structures.

The term "medium density linear polyethylene" (LMDPE) as used herein refers to a copolymer of ethylene and less than 8% butene, octene or hexene having a density of 0.926 to 0.9l | 0 and in which the molecules have long chains contain little or no branching or cross-linked structures.

The term "ethylene-vinyl acetate copolymer" (EVA) as used herein refers to a copolymer of ethylene and vinyl acetate monomers in which the ethylene-derived units are present in predominant amount and the vinyl acetate-derived units are in minor amounts.

The title, "ethylene-propylene copolymer" (EPC), as used herein, refers to a copolymer prepared from ethylene and propylene monomers, wherein the units derived from propylene are present as the main constituent and the units derived from ethylene as a minor constituent.

The term "propylene homopolymer" (PP) as used herein refers to a thermoplastic resin with a density of about 0.90 and has been prepared by polymerizing propylene with suitable catalysts, as known to those skilled in the art.

Summary of the invention It has been found that a flexible, heat shrinkable 8300616% ......

Thermoplastic packaging film with a desired combination of physical properties, such as shrinkage stress, optical properties, cutability, weldability, shrinkage temperature range, and tear resistance are obtained with the multilayer flexible thermoplastic packaging film according to the invention. This multilayer film has a "core" layer, which includes a low density linear polyethylene resin.

It is believed that the medium density linear polyethylene resin may be used in place of the low density linear polyethylene resin. A preferred three-layer embodiment also includes, in addition to the "core" layer described above, two skin layers, each containing a mixture of a propylene homopolymer and an ethylene-propylene copolymer.

Preferably, the multilayer film is oriented such that it is heat shrinkable in at least one direction.

The multilayer film can be combined with other polymeric materials for certain applications. For example, relatively thin layers can be added to one or both sides of the preferred base three-layer structure 20 to improve weld strength or to decrease gas and moisture permeability.

Another embodiment of the invention includes a five-layer bubble structure. A preferred five-layer structure comprises the same core and skin layers as the three-layer structure discussed above, and additionally comprises two intermediate layers, each containing a mixture of an ethylene-vinyl acetate copolymer and either an ionomer resin or a linear low-density polyethylene.

It is currently believed that a medium density linear polyethylene may also be used in place of the low density linear polyethylene of the intermediate layer.

Brief description of the drawing

Fig. 1 is a sectional view of a preferred three-layer embodiment of the invention.

Fig. 2 is a cross-sectional view of a preferred five-layer embodiment of the invention.

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Description of the Preferred Embodiments

Fig. 1j, which is a cross-sectional view of a three-layer preferred embodiment of the invention, shows that this embodiment comprises core layer 2 and skin layers 5 1 and 3. The preferred thickness ratio of the three layers 1/3/1 is shown in Fig. 1. A preferred core layer 2 component comprises a linear low density polyethylene polymer. However, it is believed that linear medium density polyethylene polymer may be used in place of a core layer component without significantly altering the properties of the final film product. The core layer 2 comprises low density linear polyethylene (alternating, linear average density) or the core layer 2 may comprise a copolymer blend of low density linear polyethylene (alternating, linear average density) either an (a) ethylene-propylene copolymer or ( b) ethylene-vinyl acetate copolymer or (c) ethylene-vinyl acetate copolymer mixed with an ionomer resin or (d) low-density polyethylene. Thus, the different core layer 2 blend compositions can be selected according to the invention from the following groups: (1) 10-100 $ LLDPE mixed with 0-90% EPC or (2) 10-100% LMDPE mixed with 0-90% EPC or (3) 10-80% LLDPE mixed with 20-90% EVA or (4) 10-80% LMDPE mixed with 20-90% EVA or 25 (5) 10-80% LLDPE mixed with 10-80% EVA and 10-80% ionomer resin or (6) 10-80% LMDPE mixed with 10-80% EVA and 10-80% ionomer resin or (7) 10-80% LLDPE mixed with 20-90% LDPE or 30 (8) 10- 80% LMDPE mixed with 20-90% LDPE.

LLDPE is used here as an abbreviation for the previously defined low density linear polyethylene. LMDPE is used here as an abbreviation for medium density linear polyethylene as defined above. EPC is used herein as an abbreviation for an ethylene propylene copolymer 8300616 * 9 as defined above. EVA is used here as an abbreviation for an ethylene-vinyl acetate copolymer as defined above. The term ionomer resin is used here to broadly describe the group of ionomer resin. One of the most notable of the ionomer resin and is marketed under the trade name Surlyn by du Pont.

Applicant studies have shown that a particularly preferred keralayer composition consists essentially of linear low density polyethylene. This material can be obtained from the Dow Chemical Company under the tradename Dowlex 20 ^ 5,

With reference to Fig. 1 and, in particular to the skin layers 1 and 3, suitable skin layer compositions can be selected from the following groups: 15 O) 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 the same as stated for the 20 core layer compositions. Additionally, PP is used here as an abbreviation for a propylene homopolymer as defined above. Research has further shown that a particularly preferred skin layer composition essentially consists of a blend of 20% PP with 80% EPC.

The propylene homopolymer can be obtained from the

Hercules Chemical Company under the trade designation PD064.

The ethylene propylene copolymer can be obtained from the

Soltex Chemical Company under the trade designation ^ 2 X01 and also of the Solvay Chemical Company under the trade designation KS400.

In the description and claims, all percentages are weight percentages.

In the description and claims, the density is given in grams / cm.

In summary, Applicant's investigation has shown that a particularly preferred embodiment of the invention comprises a core layer consisting essentially of linear low density polyethylene and skin layers consisting essentially of a mixture of 20. % propylene homopolymer and 80% ethylene propylene copolymer.

Although the three-layer compositions discussed above are generally preferred over hours of more than three-layer hours due to the more economical manufacturing, the Applicant has also produced several five-layer compositions which are also satisfactory from the point of view of physical properties. . However, the cost of manufacturing a five-layer film is generally higher than that of a three-layer film.

Fig. 2, which is a cross-sectional view of a preferred five-layer array according to the invention, shows the preferred layer thickness ratio of 2/2/1/2/2. The core layer 6 may comprise any of the core layer formulations discussed above with respect to the core layer 2 of the three-layer embodiment. In addition, the core layer may consist essentially of either (1) an ethylene propylene copolymer (EPC) or (2) an ethylene vinyl-20 acetate copolymer (EVA).

The skin layers 4 and 8 of the five layer embodiment may comprise any of the skin layer formulations discussed above with respect to the skin layers 1 and 3 of the three layer embodiment of Fig. 1.

The five-layer embodiment of Fig. 2 also includes between layers 5 and 7. These intermediate layers may comprise any of the compositions discussed above with respect to core layer 2 of the three-layer embodiment. Also, the composition of the intermediate layers 5 and 7 can be selected from the following additional groups.

(1) EVA or (2) 20-80% LLDPE mixed with 20-80% ionomer resin or (3) 20-80% IMDPE mixed with 20-80% ionomer resin.

Applicant's investigation has shown that a particularly preferred five-layer structure will comprise skin layers 8300616 ψ 11 1 * and 8 consisting essentially of an ethylene propylene copolymer (EPC), interlayers 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 a linear low density polyethylene 5. The EPC can be obtained from the Soltex

Chemical Company under the trade designation 1 * 2X01. The 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 Surlyn 10 trademark and has the trade designation Surlyn 1601. The LLDPE

can be obtained from the Dow Chemical Company under the trade designation Dowlex 20l * 5

It will be apparent to those skilled in the art that all the aforementioned weight percentages are subject to slight variation. In addition, these percentages may vary slightly due to the inclusion or use of additives such as the silicone mist discussed above or agents such as sludge and anti-blocking agents. A preferred anti-blocking agent is silicon dioxide, which is available from Johns Manville 20 under the trade name White Mist. Preferred sludges are Erucamide (available from Humko Chemical under the trade name Kemamide E), and Stearamide (available from the Humko Chemical Company under the trade name Kemamide S) and ΙΓ, N'-dioleoylethylenediamine (available from Glyco Chemical 25 under the trade name Acrawax C) . A preferred silicone spray is a liquid polyorganosiloxane manufactured by General Electric under the trade designation General Electric SF18 polydimethylsiloxane.

The general ranges for using these additives are the following:

(1) silica - 250-3000 DPM

(2) Acrawax C: 200 - 1 * 000 DPM

(3) Erucamide: 200-5000 DPM

(1 *) Stearamide: 200 - 5000 DPM

2 35 (5) Silicon spray: 0.5 mgft - and more.

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In the "description and claims, the term" essentially "consisting of" not "is intended to exclude slight percent variations of additives and agents of this kind.

Additional layers and / or small amounts of additives of the types described above can be added, as desired, and either the three-layer or five-layer structure of the invention, but care must be taken to ensure that the desired shrinkage stresses, shrinkage properties, optical properties and other properties of the multilayer film of the invention are not adversely affected.

In the preferred method of manufacturing the multilayer shrink film of low or medium density linear polyethylene, the basic steps are mixing the polymers for the different layers, extruding the 15 layers together to form a multilayer film, and then drawing the film for biaxial orientation thereof.

These steps and additional desired steps will be explained in detail in the following paragraphs.

The process begins by mixing the base materials (ie, polymeric resins) in the desired amounts and ranges discussed above. The resins are usually purchased from a pellet supplier and can be mixed in a commercially available mixer, as known to those skilled in the art. Other additives and / or agents which are desirable to be used may also be included during the mixing process.

The mixed resins and the additives and / or agents used are then placed in bunkers of extruders which feed the coextrusion die. At least three extruders must be used for the three-layer film when each layer has a different composition. Two extruders are fed with the materials desired for the inner and outer skin layers and the other extruder is fed with the low or medium density linear polyethylene material, which is desirably 8300616 »13 for use in the core layer . Additional extruders can be used if desired. Preferably, the materials are extruded together as a tube with a diameter depending on the stretch ratio and desired final diameter. This coextruded tube is relatively thick and is referred to as the "tape". Circular coextrusion dies are known and can be purchased from a number of manufacturers.

In addition to tubular coextrusion, slit dies can be used to co-extrude the material in flat form.

Known single and multi-layer extrusion coating processes can also be used if desired.

An additional process step that can be used is to irradiate the tape or unexpanded tube or filament by bombarding it with high energy electrons from an accelerator for cross-linking the materials of the tape. Cross-linking greatly enhances the structural strength of the film or the strength with which the material can be stretched before tearing when the film materials are mainly ethylene, such as polyethylene or ethylene-vinyl acetate. The radiation 20 also improves the optical properties of the film and changes the properties of the film at higher tender temperatures. When an irradiation stage is used, a preferred irradiation dose level is in a range from 0.5 MR to 12.0 MR. MR is short for megarad. A megarad is 1 x 10 rad and a 25 rad is the amount of ionizing radiation, which results in the absorption of 100 erg energy per gram of irradiated material, independent of the radiation source. In some instances, it may be desirable to first stretch and then irradiate the multilayer film, or, when successive coating is employed, one layer or group of layers may be irradiated and then another layer or layers may be added, for the end stage of stretching and orienting.

As noted above, an optional additional process step is to apply a fine silicone spray 35 to the interior of the freshly extruded tape. The details of 8300 6 1 6

1U

This process step is described in U.S. Patent Application Serial No. 289,018, filed July 31, 1981, which application is to be considered incorporated herein.

After co-extruding, quenching for cooling and optionally irradiating, the extruded tape is reheated and continuously inflated by internal air pressure into a bubble, converting the thick-walled narrow tape into a wide thin-walled film of the desired film thickness. This process stage is sometimes referred to as the "trapped calling method" of orienting 10 or as "stretching". After drawing, the air is then released and the film is wound onto semi-finished rolls called "mill rolls". The stretching process orients the film by drawing it transversely and, to some extent, longitudinally for rearranging the molecules and thus imparting shrinkage to the film and modifying the physical properties of the film. Additional longitudinal stretching or processing direction may be accomplished by rotating the venting rollers which support the "blown bubble" incidence at a speed greater than that of the rollers serving to transport the reheated tape to the dispenser or blow bubble area. All these methods are known.

The invention is illustrated in the following examples.

Example I

A five-layer jerk hour with a layer thickness ratio of about 2/2/1/2/2 was extruded by feeding four extruders. Extruder 1, which feeds the die openings for both interlayers, was fed with a mixture of 90% ethylene vinyl acetate copolymer (12% vinyl acetate) (Alathon β137 (melt index 0.5)) and 10% ionomer resin (Surlyn 1601 (density 0.9 ^ 0, melt index 1, ¾)). The mixture also contained 1100 ppm Erucamide (Kemamide E) and 1100 ppm Stearamide (Kemamide S). Extruder 2, which fed the die opening of the core layer 35, was fed with 100% linear polyethylene of low 8300616-15 density (Dowlex 201 + 5 (density 0.920, melt index 1.0)).

The extruders 3 and U each feed a dermal opening for a skin layer and heather were fed with 100% ethylene propylene copolymer (3S5% ethylene) (Soltex 1 + 2 X01 (melt flow 1 +, 5)) 5 mixed with 1100 ppm Erucamide (Kemamide E), 1100

Stearamide (Kemamide S), and 1100 ppm silicon dioxide (White Mist).

Extruder 1 was maintained at a temperature range of 390 ~ 1 + 25 ° F. Extruder 2 was maintained at a temperature range of 1 + 10-1 + 70 ° F. Extruder 3 was maintained at a temperature range of 350-370 ° F and extruder 1+ was maintained at a temperature range of 3l + 5 + 365 ° F. The circular die was maintained at a temperature range of 390-1 + 35 ° F.

After extruding the layers through the 10 inch circular-15 die opening, the tubular extrudate, which had a tape thickness of about 15 mils and a tube width of about 9 5/8 inches, was quenched for cooling by passing it through a cold water bath at about 37 feet per min.

The tube was then reheated for orientation by passing it through a heating zone or oven at 38 feet per min.

The oven was heated by horizontal, vertical and steam heating elements. In this example, the horizontal heating element was kept at 200 ° F. The vertical heating elements were kept at 30 ° F.

25 and the steam element, which supplied heat by passing it through pipes or cans in the oven, was fed with steam of 2 pp. 1.

After heating as described above, the tubular extrudate was inflated and stretched about 30 to 1 +, 8 to 1 in the transverse direction and about 1 +, 3 to 1 in the longitudinal direction. Then the film was cooled by quenching with water to block the oriented structure . The final fpd size was about 75.

The experimental data obtained for this film composition is shown in Table A.

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Example II

A five-layer structure with a layer thickness ratio of about 2/2/1/2/2 was extruded by feeding four extruders. Extruder 1, which feeds the die 5 openings for both interlayers, was fed with a mixture containing 50 % ethylene-vinyl acetate copolymer (12% vinyl acetate) (alathon 3137 (melt index 0.5)) and 50% linear low density polyethylene (Dowlex 20U5 (density 0.929, melt index 1.0)) and also contained 1100 ppm Erucamide 10 (Kemamide E). Extruder 2, which fed the die opening for the kera layer, was fed with 100% linear low density polyethylene (Dowlex 20 ^ 5 (density 0.920, melt index 1.0)). The extruders 3 and each feeding a skin layer die opening and both fed 15 were fed 100% ethylene propylene copolymer (2.7% ethylene) (ARCO K-193 (melt flow 2.3)) at 1100 ppm Erucamide (Kemamide E) and 1100 ppm silicon (White Mist).

Extruder 1 was maintained at a temperature range of U05 - 15 ° F. Extruder 2 was maintained at a temperature range of U00-1 + 75 ° F. Extruder 3 was maintained at a temperature range of 355 ° -35 ° F and extruder b was maintained at a temperature of 355-150 + 100Ε.

The circular mold was maintained at a temperature range of 390 -25 ° P.

After extruding the layers through the 10 inch circular die opening, the tubular extrudate with a tape width of about 8 3A inches and a thickness of 17 mils was quenched for cooling by passing it through a cold water bath at about 39 feet per min. The tubular extrudate 30 was then heated for orientation by passing it through a heating zone or oven at about 38 feet per minute. The oven was heated by horizontal, vertical and steam elements.

In this example, the horizontal heating element was kept at 212 ° F. The vertical heating element was held at 3l * 3 ° F and the steam element, which supplied heat by passing it through 8300616 * - 17, was piped or furnace fed at 7 psi.

After heating, the tubular extrudate was inflated and stretched about 4.8 to 1 in the transverse direction and about 4.5 to 1 in the longitudinal direction. The film was then cooled by quenching with water to block the oriented molecular structure. The final film thickness was about 75

The data obtained from this material 10 on examination is given in Table A.

Example III

A three-layer structure with a layer thickness ratio of about 1/3/1 was extruded by feeding 4 extruders. Eccentricators 1 and 2, which feed the die core die opening 15, were fed with 100% linear low density polyethylene (Dowlex 2045 (density 0.920, melt index 1.0)) with 3300 ppm Erucamide (Kemamide E). Eccentricators 3 and 4, each feeding a die opening for a skin layer, were both fed a mixture of 80% ethylene-20 propylene copolymer (3.5% ethylene) (Soltex 42X01 (melt flow 4.5)) and 20% propylene homopolymer ( Hercules PD064 (density 0.906, melt flow 3.5)) and with 3300 ppm Erucamide (Kemamide E) and 1100 ppm silicon dioxide (White Mist) and 1650 ppm Acrawax C.

The temperature of extruder 1 was set in the temperature range of 395-485 ° C. Extruder 2 was set at a temperature range of 425 ° 470 ° C. Crusher 3 was set in a temperature range of 370-375 ° F. Crusher 4 was set in a temperature range of 370-375 ° F. The circular die was set at a temperature of 385 ° F. The actual temperatures in which the extrusion devices and dies were held are not Termeld for this example.

After extrusion of the layers through the 10 inch circular die opening, the tubular extrudate was quenched for cooling by passing it through a cold bath at about 8300616 - 18 - 39 5 feet per min. After extruding the time, a fine silicone mist applied to the interior of the extruded tube at a rate of 5 ~ 7 mg ft. The cooled tubular extrudate was then reheated for orientation by passing it through a heating zone or oven at about 377 feet per minute. The oven was heated by a horizontal, vertical and steam heating elements. In this example, the horizontal element was kept at 200 ° F. The vertical element was held at 305 ° F and the steam element, which supplied heat by passing it through pipes and cans in the oven, was fed at 3.5 p.s.i.

After heating the tubular extrudate, it was stretched about 1.8 to 1 in the transverse direction and about 1.5 ° P 1 in the longitudinal direction. The film was then cooled by quenching with water to block the oriented structure. The final foil size was approximately 75

The data obtained in b.e tests of this film are shown in Table A.

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Table A

Example_I_II_III

layer ratio 2/2/1/2/2 2/2/1/2/2 1/3/1 tensile strength x 100 (PSI) ^ MD 97.1 125.2 12U, 6 TD 110.5 105.1 130, 7 elongation (%) 2 MD 86 98 113 TD 65 107 102 modulus x 1000 (PSI) 3 MD 90.3 98.3 96.5 TD 101Λ 99, k 91.6 propagation tearing (gma) ^ MD ij-, 10 kt33 9.60 TD h, 01 5.53 9.83 tear resistance (lbs MD 0.70 0.61 0.60 TD 0.90 0.83 0.67 shrinkage properties at 200 ° F free shrinkage (%) ^ MD 16 1¾. 12 TD 18 20 17 7 shrinkage tension (PSI) MD 239 30U 288 TD 327 h51 509 at 260 ° F free shrinkage (%) ^ MD 52 b9 kd> TD 57 57 5 ^ * 7 shrinkage tension (PSI) MD 220 3 ^ 5 U31 * TD 365 U22 538

at 280 ° F

g free shrinkage {%) MD 71 66 62 TD 67 68 6k 8 300 616 f - 20 -

Table A (continued)

Example I II III

shrinkage stress (PSI) 7 MD 237 3 ^ 8 1 * 32 TD 30¾. 362 581 * optical properties ^ haze {%) 2.5 2.1 2.0 glass (1 + 5 °) 9 ** 88 88 total transmission 92.5 92.2 92.2

Footnote to Table A.

1ASRM D 882 2ASRM D 882 3ASTM D 882 ^ ASTM D 1938 5ASTM D 100l * 6ASTM D 2732 7ASTM D 2838 o ASTM D 1003

All data in Table A are averages obtained by methods according to the indicated ASTM standard.

It is to be noted that the detailed description and specific examples, which presently represent preferred embodiments of the invention, are given for illustration only, since various changes and modifications within the scope of the invention will be apparent to those skilled in the art.

8300616

Claims (10)

1. Multilayer polyolefin film containing a core layer Idevat, which core layer contains a linear polyethylene of low density. 2. Multilayer polyolefin infusion film containing a core layer "consisting essentially of linear low density polyethylene. 3. Multilayer polyolefin infusion film containing a core layer consisting essentially of linear low density polyethylene and two skin layers consisting essentially of a mixture of 80% by weight of an ethylene propylene copolymer mixed with 20% by weight of a propylene homopolymer. U. Multi-layer polyolefin film containing a core layer consisting essentially of a linear low density polyethylene 15, two intermediate layers consisting essentially of a mixture of 90% by weight ethylene-vinyl acetate copolymer mixed with 10% by weight of an ionomer resin and two layers of skin consisting essentially of an ethylene-propylene copolymer. 4> ....... "" • Vt - 21 - Multilayer polyolefin infusion film containing a core layer 20 consisting essentially of linear medium density polyethylene. Multilayer polyolefin film containing a core layer and at least two intermediate layers, which intermediate layers contain a linear low density polyethylene. 25 Multi-layer polyolefin film according to claim 1, further comprising at least two intermediate layers, which intermediate layers contain a linear low density polyethylene. Multilayer polyolefin film according to claim 8, wherein the core layer contains a copolymer mixture selected from one of the following groups: a. 10-100 wt.% Of a linear low density polyethylene mixed with 0-90 wt. # of an ethylene propylene copolymer; b. 10-100 wt.% Of a medium density linear polyethylene, blended with 0-90 wt.% Of an ethylene-propylene-8300616-22 copolymer; c. 10-80% by weight of a linear low-density polyethylene mixed with 20-90% by weight of an ethylene-vinyl acetate copolymer; 5 d. 10-80% by weight of a medium density linear polyethylene, blended with 20-90% by weight of an ethylene-vinyl acetate copolymer; e. 10-80 wt.% Of a linear low density polyethylene, blended with 10-80 wt.% Of an ethylene-vinyl acetate copolymer and 10-80 wt.% Of an ionomer resin; f. 10-80% by weight of a medium density linear polyethylene, blended with 10-80% by weight of an ethylene-vinyl acetate copolymer and 10-80% by weight of an ionomer resin; g. 10-80% by weight of a linear low density polyethylene, blended with 20-90% by weight of a low density polyethylene; h. 10-80% by weight of a medium density linear polyethylene mixed with 20-90% by weight of a low density polyethylene. 20 Multilayer polyolefin film according to claim 1, further comprising two skin layers, which skin layer have compositions selected from the following groups: a. An ethylene propylene copolymer; b. JO-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 mixed with 10-30% by weight of a linear low density polyethylene; d. 7Ο-9Ο% by weight of an ethylene propylene copolymer, mixed with 10-30% by weight> of a medium density linear polyethylene. Multilayer polyolefin film according to claim 1, further comprising interlayers with compositions selected from the following groups: 35 a. 10-100% by weight of a linear low density polyethylene, mixed with 0-90% by weight of an ethylene propylene- 8300616-23 - copolymer; b. 10-100% by weight of a medium density linear polyethylene mixed with 0-90% by weight of an ethylene-propylene copolymer; 5 c. 10-80% by weight of a linear low density polyethylene, blended with 20-90% by weight of an ethylene-vinyl acetate copolymer; d. 10-80% by weight of a medium density linear polyethylene, blended with 20-90% by weight of an ethylene 10 vinyl acetate copolymer; e. 10-80% by weight of a linear low-density polyethylene, blended with 10-80% by weight of an ethylene-vinyl acetate copolymer and 10-80% by weight of an ionomer resin; f. 10-80% by weight of a medium density linear polyethylene, blended with 10-80% by weight of an ethylene-vinyl acetate copolymer and 10-80% by weight of an ionomer resin; g. 10-80% by weight of a linear low density polyethylene, blended with 20-90% by weight of a low density polyethylene; 20 h. 10-80% by weight of a medium density linear polyethylene mixed with 20-90% by weight of a low density polyethylene; i. an ethylene-vinyl acetate copolymer; j. 20-80% by weight of a linear low density polyethylene mixed with 20-80% by weight of an ionomer resin; k. 20-80% by weight of linear medium density polyethylene, blended with 20-80% by weight of an ionomer resin. 8300616