Oriented film of high clarity and gloss

םרט מוצב עם בהירות גבוהה וברק

ORIENTED FILM OF HIGH CLARITY AND GLOSS

Oriented Film of High Clarity and Gloss

Background of the Invention

The present invention pertains to packaging film,and more particularly to a thin polymeric film suitable forreplacing polyvinyl chloride film especially in packaging andlabeling applications.

Polyvinyl chloride (PVC) has long been used in manyapplications in the packaging art. One particularly wide-spread application for PVC is the use of such material as anoverwrap' material for trayed retail cuts. of meat and otherfood products in a retail environment such as a supermarket. PVC has several desirable properties for this use.For example, it has excellent optics and good elasticity andstretch properties at use temperatures.

Unfortunately, PVC also has several disadvantages,including the production of hydrogen chloride gas during heatsealing and the generally corrosive effects of such gases inthe packaging room.

It would be of great benefit to the packaging indus-try, and particular to applications requiring an instore filmfor overwrapping trayed food products, to provide a film withmany of the advantages of PVC but without the disadvantages,described above. 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 1

I PVC is also used in producing labels for cans andbottles. It would also be of benefit to the label industryto provide a film which can be used as a label on a rigidcontainer such as bottles and cans, but without the disadvan-tages of PVC.

Films or laminates used as label material for thelabels of beverage bottles and the like are preferablymonoaxially oriented in order to permit a tight label to beproduced around the bottle or vessel, without undesirablewrinkling and shrinking of the label which can occur withsome biaxially oriented films. These label films can also beused to produce band type seals for tamper evidence. Suchlabel material ideally possesses several properties making itparticularly useful for this end use.

For example, the material should have the requiredstiffness (i.e. higher modulus) to permit the use of the filmor laminate in a roll stock form . in conjunction with labelmanufacturing apparatus. Printability of the label is alsodesirable, as well as excellent optical properties.

The inventor has discovered that a relatively thinpolymeric film, including a layer of a polyolefin, and morepreferably very low density polyethylene (VLDPE), combinedwith a layer of styrene butadiene copolymer (SBC), producedby hot blowing and then stretch orienting the extruded film,exhibits excellent elasticity, toughness, stretch and opticalproperties.

Processes for producing oriented films, and orient-ed films themselves are disclosed in many patents includingthe following patents of interest. U. S. Patent No. 3,456,044 (Pahlke) mentions thinfilms of thicknesses less than 1 mil such as 0.5 mils, anddiscloses a double bubble method for biaxially orientingthermoplastic films including the steps of producing a prima- 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 2 ry tubing which is inflated by introducing air into the inte־rior thereof, and a cooling ring 22, as well as squeeze rolls34 and 28, with rails 34 having a greater speed than rolls28. Between the two pairs of squeeze rolls is a reinflatedsecondary bubble. If annealing is desired, the tubing can bereinflated to form a bubble 70. U. S. Patent No. 3,555,604 (Pahlke) is a patentbased on a divisional application which was derived from thesame priority application as the ,.044 patent described above,and discloses the same information described above for the’044 patent. U. S. Patent No. 4,258,166 (Canterino et al) dis-closes a uniaxially oriented plastic film material with ira-proved strength and clarity in the direction of orientationpreferably comprising homopolymers and copolymers ofethylene. U. S. Patent No. 4,355,076 (Gash) disclosesmonoaxially oriented polypropylene film laminated to amonoaxially oriented high density polyethylene film, thefilms produced by for example tubular*blowing. U. S. Patent No. 4,440,824 (Bonis) discloses athermoformable coextruded multilayer structure useful forthermoforraing into containers, the structure havingpolyolefin coextruded with a high impact polystyrene layer.A five layer structure is shown. U. S. Patent No. 4,464,439 (Castelein) discloses acoextruded laminate having a sheet of polypropylene and asheet of a mixture of high impact polystyrene, crystallinepolypropylene, and styrene/dienic monomer block׳copolymer. U. S. Patent No. 4,626,455 (Karabedian) discloses amultilayer sheet and sleeve label for bottles, the sheet 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 3 f being a skin layer/brittle polystyrene foam layer structure,the skin layer comprising a polyolefin, a block copolymer ofbutadiene and styrene as comparability agent, and polysty-rene. U. S. Patent No. 4,879,177 (Boice) discloses amonoaxially oriented shrink film having a core layer of buta-diene styrene copolymer, outer layers of ethylene propylenecopolymer, and intermediate bonding layers of ethylenecopolymer.

It is an object of the present invention to providea thermoplastic film useful as an overwrap material for traderetail cuts of meat and other food products in a super marketor other retail environment.

It is also an object of the present invention toprovide a thermoplastic film useful in forming labels ortamper evident bands for vessels such as bottles, cans, andthe like.

It is also an object of the present invention toprovide a film having excellent optical properties, specifi-cally excellent gloss and clarity.

It is also an object of the present invention toprovide a film which can be either primarily monoaxiallyoriented, or biaxially oriented to substantially the sameextent in both its transverse and longitudinal directions.

Summary of the Invention

In one aspect of the present invention, a biaxiallyoriented multilayer film comprises a core layer comprising avery low density polyethylene; two outer layers each compris-ing a styrene butadiene copolymer; and two intermediate lay-ers each bonding the core layer to a respective outer layer,and comprising a polymeric adhesive. 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 4

In another aspect·· of the present, invention, a meth-od of making a thin biaxially oriented polymeric film compris-es coextruding a first melt stream of a very low densitypolyethylene, a second and third melt stream of a polymericadhesive, and a fourth and fifth melt stream of a styrenebutadiene copolymer; extruding the melt streams through atubular die such that the first melt stream forms the centrallayer of the coextrudate, and the fourth and fifth meltstreams form the outer surfaces of the coextrudate; hot blow-ing the extruded film; heating the hot blown film to a temper-ature above its orientation temperature; directing the heatedfilm through a first set of pinch rolls; reinflating the hotblown film by a blown bubble process wherein the bubble isexpanded in both its longitudinal and transverse directions;and collapsing the reinflated film through a second set ofpinch rolls.

In still another aspect of the present invention, amultilayer film oriented in primarily one direction, compris-es a core layer comprising a very law density polyethylene;two outer layers each comprising styrene butadiene copolymer;and two intermediate layers each bonding the core layer to arespective outer layer, and comprising a polymeric.adhesive.

In yet another aspect of the invention, a method ofmaking a thin, polymeric film oriented in primarily one direc-tion comprises extruding a first melt stream of very lowdensity polyethylene, second and third melt streams of apolymeric adhesive, and fourth and fifth melt streams ofstyrene butadiene copolymer through a tubular die wherein thefirst melt stream forms the central layer of the coextrudateand the fourth and fifth melt streams form the outer surfacesof the coextrudate.; hot blowing the caextruded film; heatingthe hot blown film to a temperature above its orientationtemperature; directing the heated film through a first set ofpinch rolls; inflating the hot blown film by a blown bubbleprocess wherein the bubble is stretched in the longitudinaldirection but substantially unstretched in the transverse 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 5 direction; and collapsing the reinflated film through a sec-ond set of pinch rolls.

In yet another aspect of the invention, an orientedmultilayer film comprises a first layer comprising very lowdensity polyethylene; and a second layer adhered to the firstlayer, said second layer comprising a styrene butadienecopolymer.

Definitions

The term "polyolefin” is used herein in its strict-er sense to mean a thermoplastic polymer derived from simpleolefins. Among these are polyethylene, polypropylene andcopolymers thereof with olefinic comonomers. For example,very low density polyethylene may be considered a linearethylene copolymer with a comonomer comprising such materialsas butene, hexene or octene. The term "polyolefin" is alsoused herein in a broader sense to include copolymers andterpolymers of ethylene with comonomers that are not them-selves olefins, such as vinyl acetate (e.g. ethylene vinylacetate copolymer or EVA). <·

The term "very low density polyethylene", or"VLDPE" is .used herein to describe linear ethylene alpha-olefin copolymer (flexomer) having densities, of generallybetween about 0.880 and 0.915 grams/cubic centimeter, andproduced by a catalytic, low pressure process. "Ultra lowdensity polyethylene" is also included in this term.

The term "ethylene vinyl acetate copolymer" (EVA)as used herein refers to a copolymer formed from ethylene andvinyl acetate monomers wherein the ethylene derived units arepresent in major amounts and the vinyl acetate derived unitsare present in minor amounts, generally one to 30 percent byweight. 4/901010.5/SPECFLDR/04;03:18 PM/10/10/90 . 6

The term "styrene butadiene copolymer" (SBC) isused, herein to denote thermoplastic copolymers, especiallyblock copolymers containing a major portion (greater than50%) of styrene and a minor proportion (less than 50%) ofbutadiene comonomer.

The terms "melt flow" and "melt index" are usedherein to mean the amount, in grams, of a thermoplastic resinwhich is forced through an orifice of specified length anddiameter in ten minutes under prescribed conditions in accor-dance with ASTM D 1238.

The term "flow rate ratio" (FRR) is used to mean adimensionless number derived by dividing the flow rate (meltflow or melt index) at one Condition with the flow rate atanother Condition (ASTM D 1238). FUR is indicative of molecu-lar weight distribution. The higher the FRR, the broader themolecular weight distribution.

Brief Description of the Drawings

The invention may be further understood by refer-ence to the drawings herein, where: FIG. 1 is a schematic cross section of a preferredembodiment of a multilayer film in accordance with the inven-tion; and FIG. 2 is a schematic diagram indicating the appara-tus and process by which the films of the present inventionare made.

Description of the Preferred Embodiments

The preferred film structure is a multilayer compos־ite having a core layer 10 comprising a very low densitypolyethylene (VLDPE). 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 • 7 i

<img img-format="tif" img-content="drawing" file="IL97643AD00101.tif" id="idf0001" />

<img img-format="tif" img-content="drawing" file="IL97643AD00102.tif" id="idf0002" />

Preferred VLDPE resins are characterized by highmolecular weight (i.e. relatively low melt index), broadmolecular weight distribution (i.e. relatively high flow rateratio), and relatively low crystallinity at processing temper-atures.

For the VLDPE, a melt index (MI) of no more thanabout .15 grams/ 10 minutes (ASTM D 1238) .(Condition190/2.16) is preferred. A more preferred MI is .12 grams/ 10minutes.

Preferred VLDPE resins can also be characterized bya melt index of no more than about .50 grams/ 10 minutes,more preferably no more than about .45 grams/ 10 minutes(ASTM D 1238) (Condition 190/5.0);' no more than about 1.50grams/ 10 minutes, and more preferably no more than about1.35 grams/ 10 minutes (ASTM D 1238) (Condition 190/10.); orno more than about 10 grams/ 10 minutes, and more preferablyno more than about 6 grams/ 10 minutes (ASTM D 1238) (Condi-tion 190/21.601).

For the VLDPE, a molecular weight distribution(flow rate ratio) of at least about 10 (I21/Is) (ASTM D1238)' is preferred. This value is derived by dividing theflow rate at Condition 190/21.6 by the flow rate at Condition190/5.0. A more preferred FRR is 13.

Preferred VLDPE resins can also be characterized bya FFR of at least about 40, more preferably at least about 50(121/12.1) (ASTM D 1238). This value is derived by divid-ing the flow rate at Condition 190/21.6 by the flow rate atCondition 190/2.16.

An especially preferred VLDPE is a high molecularweight resin such as DEFD 1015 from Union Carbide. Thisresin, has a density of about .900 grams/cc, a melt flow rateof about 6 grams/ 10 minutes (ASTM D 1238, Condition190/21.601), and a FFR (Ial/Ia.!) of about 50. 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 3

Outer layers 12 comprise a styrene butadienecopolymer such as that commercially available from Phillipsunder the designation KR-10 having a butadiene content of 25%by weight of the copolymer; or KK 36 (for fatty food con-tact).

In the multilayer film of the invention, the outerlayers 12 are bonded to the core layer 10 by means of interne-diate layers 14 each comprising a polymeric adhesive and preferably a copolymer of ethylene, and more preferably an ethylene vinyl acetate copolymer (EVA). An even more pre-ferred EVA is one having a vinyl acetate content above about18% by weight of the copolymer, and more preferably about 28%by weight of the copolymer. Other polymeric materials may beused for layers 14 provided they process adequately in pro-cesses such as that disclosed in mare detail below. Blendsof polymeric materials and polymeric adhesives can also beused for intermediate layers 14.

For outer layers 12, SBC resins having minor amounts of butadiene, ranging from about 1 to 50%, are mostpreferred and provide an optimum balance of stiffness and flexibility to the film.

The films of the present invention are preferablymade by coextrusion techniques well known in the art, com-bined with an apparatus and process depicted in Figure 2 anddescribed in more detail below.

Figure 2 shows schematically a device 10 for makingthe oriented films of the present invention.

Five melt streams, including a first melt stream ofVLDPE, second and third, melt streams of an ethylene copolymersuch as EVA, and fourth and fifth melt streams of SBC arecoextruded and exit as a coextrudate through an annular die12 in a conventional manner. The extruded film is hot blownby conventional techniques to form a blown bubble 14. 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 9

The' preferred process for carrying out the presentinvention permits the bubble to be reinflated into the secon-dary bubble 20 and then expanded to impart orientation of thematerial in primarily the transverse direction, primarily thelongitudinal direction, or in both the transverse and longitu-dinal directions. This ,,flexibility” in the process permitsfilms of the invention to be produced which are orientedprimarily in one direction (monoaxially oriented films) orfilms which are oriented in both the longitudinal and trans-verse directions (biaxially oriented films).

Air cooling ring 16 positioned circumferentiallyaround the blown bubble at the position shown cools thethermoplastic melt as it exits die 12.

An optional auxiliary chilling ring 17 may also bepositioned circumferentially around the blown bubble downstream from air cooling ring 16 to further chill the hotblown film.

The primary bubble 14 is melt oriented in both themachine and transverse directions. Various blow up ratiosmay be used, but preferably the primary bubble 14 is hotblown to a blow up ratio of between 1.5 and 3.0.

The primary bubble 14 is collapsed at pinch rolls 16.

To assist in this process, guide plates 18 arepositioned at the extremities of the blown bubble 14.

The collapsed bubble is then reinflated in a blownbubble process to stretch orient the blown and collapsedfilm. This is done in a conventional manner by trapping airor other hot gas within the secondary bubble 20 so that thematerial stretches at· its orientation temperature transverse-ly to impart further orientation of the material in the trans-verse direction. The secondary bubble 20 is collapsed at a 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 10 second set of pinch rolls 22. A second set of guide plates24 may be employed to assist in the collapsing process.

The second set of pinch rolls 22 is rotated at aspeed faster than the first set of pinch rolls 16 if it isdesired to impart stretch orientation in the machine or longi-tudinal direction to the thermoplastic material.

The recollapsed bubble 20 then passes from thesecond set of pinch rolls 22 to take up roll 26.

The take up roll 26 may be a mill log which can beimmediately stored or shipped to a distributor or customer,or may be stored for further processing such as slitting intosingle wound film, machine or natural center fold film.Thus, as used herein the take up roll 26 represents any fur-ther processing, storage, or further modification of thedouble wound, collapsed film once it exits the second set ofpinch rolls 22, and is used herein to denote any of thesepossible further processing steps.

It is preferred that a reservoir 28 of heated fluidbe disposed at the lower end of primary bubble 14 in such away that the collapsing material drawn through the primaryset of pinch rolls 16 will pass in communication with theheated fluid. In this manner, the film is more uniformlyheated and temperature control can be achieved. Thickenedtape edges can be substantially avoided by such means.

Although the heated, fluid of reservoir 28 is prefer-ably hot water, other media may be used if temperatures abovethe 212 °F limit of hot water are desired. For examplepropylene glycol (a food approved material), hot oil or hotemulsions may be used. One skilled in the art will under-stand that the exact nature of the heated fluid is not ascritical as its effectiveness in helping to uniformly heatthe collapsing bubble 14 as it is drawn through pinch rolls 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 11 16, and to uniformly heat the collapsing bubble 14 to a tem-perature above its orientation temperature.

The heated fluid may also be an "active" substancewhich not only reheats the surrounding film, but also actual-ly coats the interior of the bubble as . it passes over thereservoir. An example is a hot wax or other functional coat-ing.

The heated fluid may be recirculated from the reser-voir through a heating means 30 by means of conduits' 32 orother suitable transfer means. Using the reservoir 28 ofheated fluid, the types of materials which may be effectivelyused in the present process and device are increased.

Biaxially oriented films of the present inventionare useful in overwrap applications for overwrapping retail i cuts of meat and nan-food products.

Monoaxially oriented films are useful in shrinklabel applications for producing labels for vessels such asbottles and cans.

The term "monoaxially oriented" is used herein tomean films oriented primarily in the longitudinal direction.However, some incidental orientation can be present in thetransverse direction, and this.is sometimes desirable to helpthe film to grip a container or vessel after heat shrinkingand to reduce the incidence of wrinkles in the final label.The term can also be used to refer to films oriented primari-ly in the transverse direction, with or without some inciden-tal orientation in the longitudinal direction.

The invention may be further understood by refer-ence to the examples which follow.

The resins used in these examples are identified in

Table 1. 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 12 TABLE 1

RESIN COMMERCIAL NAME DESCRIPTION COMPANY SBCi KR-10 STYRENE BUTADIENECOPOLYMER PHILLIPS sbc2 KK-36 STYRENE BUTADIENECOPOLYMER WITHFATTY FOODCOMPLIANCE Phillips EVAX ELVAX 3182 EVA (28% VA)MELT INDEX =grams/ 10 min. DU PONT eva2 ELVAX 3165 EVA (18%VA)MELT INDEX =6 grams/ 10 min. DU PONT eva3 3170 EVA (18% VA)MELT INDEX =2.5 grams/ 10 min. DU PONT VLDPEx XU 61509.32 VERY LOW DENSITYPOLYETHYLENEDENSITY = .911grams/cc DOW VLDPEa DEED 1161 VERY LOW DENSITY־ POLYETHYLENE UNION CARBIDE vldpe3 TAFMER 0580 VERY LOW DENSITYPOLYETHYLENEDENSITY = .88grams/cc MITSUI VLDPE« 1015 VERY LOW DENSITYPOLYETHYLENEDENSITY = .900grams/cc UNION CARBIDE PLx 164־22 50% POLY-ISOBUTYLENEIN LLDPE . SANTECH 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 13

Example 1 A film having the construction SBC1/EVA;L/8G%VLDPE! + 20% EVAa/EVAi/SBC! was produced by the pro-cess described above. Tubular film was blown into pinchrolls and reinflated into a secondary bubble without losingwidth dimensions. The secondary bubble was stretched at aratio of 2.5:1 in the machine direction and substantiallyunstretched in the transverse direction to produce an ultra-clear and glossy 1-mil film. The temperature of the liquidinside the liquid reservoir was 210eF.

The outer layers of SBC! each formed about 13% ofthe final film gauge. The core layer of the blend of 80%VLDPE! and 20% EVA2 formed about 42% of the final filmgauge by thickness. The intermediate adhesive layers ofEVA! each comprised about 16% of the final film gauge.

The film of Example 1 was evaluated in bench toptests with soft drink cans. This film was formed into shrinklabels that were wrapped around the cans.' The material ap-peered to shrink adequately when shrunk at a temperature of300eF and a conveyor setting of 60% with a Weldotron 7141tunnel. The material shrank tightly around the surface andcontours of the can.

It was also noted that a drop of methylene chloridesolvent, when placed on the surface of the film with the filmpressed to it, resulted in immediate bonding to itself with-out film shrinkage.

The film of Example 1 was also used to overwrap atray. Hot plate seals were made without undue film shrink-age. The hot plate temperature was 220°F.

Trim seals were also made with the film of Example1 at 2.6 pounds with an L bar sealer. 0 4/901010.5/SPECFLDR/04:03:18 PM/10/10/90 14

When making the shrink labels for the bench toptest, 4 inch width sections of the material were applied to3-1/8 inch outside diameter cores and shrunk at 300״F, with aconveyor setting of 60% on the Weldotron 7141 tunnel. Theresults indicated a width loss of approximately 3% (1/8 inch).

Seal strength evaluations conducted with theWeldotron L-bar sealer yielded a mean transverse sealstrength of 2.6 pounds per linear inch with a standard devia-tion of 0.45 and a range of 2.0 to 3.3 pounds. Longitudinalevaluations resulted in material stretching until the filmbroke rather than the seal.

In producing the film of Example 1, the deflateroll speed in the primary bubble was about 30 feet per minuteand the deflate roll speed in the secondary bubble was about75 feet per minute.

The tubing width of the primary bubble at the de-flate roll, and the final film width at the deflate roll ofthe secondary bubble were 28 inches.

The invention may be further understood with refer-ence to the following additional examples listed in tabularform in Table 2. 4/901010.5/SPECFLDR/Q4:03:18 FM/10/10/90 15

Table 2

SOCK EXAMPLE1 FILM STRUCTURE PRIMARY SECONDARY THICKNESS TEMP( °F) T L (MILS) 2 SBCj/EVAj/801 VLDPE2/EVA2/SBC!1+20% VLDPE3 2.33:1. 2.9:1 3.1:1 .30 210 3 SKjmjm VLDPE2/EVA2/SBC!1+20¾ VLDPE3 2.33:1 2.9:1 3.1:1 .27 210 4 SKjmjm VLDPE2/EVA2/SBC!4+20¾ VLDPEj ' 3.1:1 1.0:1 2.0:1 .70 210 5 SBC1/EVA2/80% VLDPEj/EVAj/SBC!+20¾ VLDPE3 2.97:1 1.6:1 1.7:1 .40 210 6 SBCx/EVA2/80% VLDPE2/EVA2/SBC!5+20¾ VLDPE3 2.02:1 3.1:1 3.0:1 .60 210 1 SBC1/EVA2/80% VLDPE3/EVA2/SBC26+20¾ VLDPE3 2.02:1 3.1:1 3.1:1 .30 . 209 8 SKjmjm VLDPE3/EVA2/SBC37+20¾ VLDPE3 י 2.02:1 3.1:1 3.1:1 .30 209 9 SBCx/EVA2/80% VLDPE1/EVA2/SBC1b+20¾ VLDPE3 2.44:1 2.5:1 3.1:1 .30 210 10 SBC!/EVA2y80¾ VLDPE3/EVA2/SBC!9+20¾ VLDPE3 2.44:1 2.5:1 3.1:1 .30 210 11 SBC2/EVA2/80¾ VLDPE3/EVA2/SBC210+20¾ VLDPEj 2.33:1 2.77:1 3.1:1 .35 210 12 SKjmjm VLDPE2/EVA2/SBC!11 2.44:1 2.61:1 3.1:1 .35 210 +20¾ VLDPE3 1/901010,5׳/SPECFLDR/04:15:50 PM/10/10/90 16

PRIMARY

FILM STRUCTURE

SOCK SECONDARY THICKNESS TEMPI°F)T L (MILS) EXAMPLE1 13 SBC1/EVA2/80% VLDPE2/EVA2/SBC!12+20% VLDPE! 2.44:1 2.6:1 3.1:1 .35 210 14 SBC!/EVA2/80% VLDPE!/EVA2/SBC!13+20% EVa2 2.33:1 2.8:1 3.1:1 .35 210 15 smjmjm vldpe!/eva2/sbcx 14 +20% VLDPE! 2.33:1 2.8:1 3.1:1 .35 210 16 SBC!/EVA2/80% VLDPE!/EVA2/SBC!15+20% VI.DPE3 2.33:1 2.8:1 3.0:1 .25 210 17 SBC!/EVA2/80% vldpe1/eva2/sbc116+20% VLDPE4 2.33:1 2.8:1 3.1:1 .35 210 18 SBC!/EVA2/60% VLDPE1/EVA2/SBC117+40% VLDPE! 2.33:1 2.8:1 3.1:1 .35 210 19 SBC!/EVA2/60% VLDPE4/EVA2/SBC!le+40% VLDPE! 2.33:1 2.8:1 3.1:1 .35 210 20 SBC!/EVA2/80% VLDPE4/EVA2/SBC!19 ‘+20% VLDPE! 2.33:1 2.8:1 3.1:1 .35 210 21 SBC!/EVA2/VLDPE4/EVA2/SBC!30 2.33:1 2.8:1 3.1:1 .35 210 22 SBC!/EVA2/80% VLDPE4/EVA2/SBC!21+20% VLDPE! 2.33:1 2.8:1 3.1:1 .35 210 23 SBC!/EVA2/90% VLDPE4/EVA2/SBC!22+10% PI! 2.33:1 2.8:1 3.1:1 .35 210 4/901010.5/SPECFLDR/04:15:50 PM/10/10/90 17

Notes: 'in each of Examples 2 through 23, the intermedi-ate EVA layers were actually made up of a blend of 65% EVA-3 and 35% of a blend composition. The blend coraposi-tion consisted of 88% EVA,, 6% of an antifog material (Atmer 645 from ICI) and 6% of a glycerol raonoleate (Atiaer1010 from ICI).

In each of Examples 2 through 23, .1% Irganox(TM) 1010 (a high molecular weight stabilizer available fromCiba Geigy) was present in the VLDPE layer.

In Examples 3 through 23, 2% by weight of the outer-most layers constituted Atmer 645 and 2% constituted Atmer1010.

In Examples 2 through 6, the VLDPE central ar corelayer actually was produced from two separate extruders with identical blend materials. 3The extruders feeding the outermost SBC layers(KR-10) were run §15 8PM. 3KR-10 010 8PM., 3KR-10 @20 RPM L. 0. Material. SBIAX films are weak. 6Film is stronger. 7Film is softer. 6Reduced KR-10 from 10 to 5 RPM. Primary becamewider with tail. 9Reduced KR-10 from 5 to 2.5 RPM. Film moreelastic. The total amount of SBC resin is reduced to 7% ofstructure or about 1 gauge on each skin. 10IOC-36 @3.0 RPM ran 12-1/2 hours. To produce130,000 ft. of film without bubble break. 23-52" 2 5000ft. mill logs. 11Not stable operation. Weaker film than Example 11.· 13Stable operation but strength is poorer thanDow resin blend. 13Couldn't maintain secondary bubble. 4/901010.5/SPECFLDR/03:41:39 AM/10/11/90 13 '*Had. to remove Irganox 1010 from core because offeed problems. 48*52" X 5000 ft. mill logs. 15Thiimer film. 18Secondary bubble breaks due to gels.' 17Secondary bubble breaks due to gels. 18Secondary bubble breaks due to gels. 19IMPS and shear temp, increased to 475°F. Gels reduced for stable secondary bubble. 30Shear temp. §500°F. No gel and very stablesecondary bubble. 31Secondary bubble very unstable. 33Secondary bubble vary stable.

It was found that as the thickness of the outermostlayers was downgauged (by reducing the speed of the extrud-ers feeding the SBC resin), the final film had better elas-ticity but more shrinkback as the film was aged. The addi-tives (Atmer 645 and Atmer 1010) made the coextrudate soft-er.

Especially preferred films are those.in which: thetotal film thickness is less than about 1 mil, more prefera-bly than about .5 mils; the two outer layers each includebetween about 0.1% and 6%, more preferably about 4% of aplasticizer which makes the film more elastic (such as theAtmer 645 and Atmer 1010 antifog materials discussedabove); the two outer layers each have a thickness of lessthan about .04 mils, more preferably less than about .02mils, and most preferably about .01 mils (1 gauge); and thetwo outer layers each comprise less than about 4% of thetotal film thickness, and more preferably between about 1%and 3.5% of the total film thickness.

Films of the present invention can optionally becross-linked. This can be done chemically or by the use ofirradiation. 4/901010.5/SPECFLDR/08:41:39 AM/10/11/90 19

Irradiation may be accomplished by the use of highenergy electrons, ultra violet radiation, X-rays, gammarays, beta particles, etc. Preferably, electrons are em-ployed up to about 20 megarads (MR) dosage level. Theirradiation source can be any electron beam generator oper-ating in a range of about 150 kilovolts to about 6 mega-volts with a power output capable of supplying the desireddosage. The voltage can be adjusted to appropriate levelswhich may be for example 1,000,000 or 2,000,000 or3,000,000 or 5.,000,000 or higher or lower. Many apparatusfor irradiating films are known to those of skill in theart. The irradiation is usually carried out at a dosage upto about 20 MR, typically between about 1 MR and about 20MR, with a preferred dosage range of about 2 MR to about 12MR. Irradiation can be carried out conveniently at roomtemperature, although higher and lower temperatures, forexample, OeC to 60®C may be employed.

Single layers from a roll of film having the con-struction SBC,/EVA3/VLDPE4/EVA2/SBCa&gt; were irradiat-ed in .5 MR increments from 1 through 7.0 MR using an elec-tron beam irradiation system. The roll was then placed ona heat seal hand-overwrap station using a 275 °F hot barcutter and a variable temperature seal, pad and subjectivelyevaluated for cutting ease while wrapping trayed product.All irradiated samples from 1 MR to approximately 5.0 MRcut satisfactorily for wrapping (Table 3). From 5.5 MR to7.0 MR, however, cuttability was marginal to unacceptable.It should be noted that as the irradiation doses increased,shrinkback in the film increased which may have reduced theperceived cuttability as well.

The burn through threshold at each dose level wasalso evaluated by wrapping a single layer of sample filmover the bottom of a 2OS foam tray containing a 1/2-lb.block. The wrapped tray was then placed on a hot pad forone second at varying temperatures, then removed and evalu-ated for burnouts. The results appear in Table 3 and demon- 4/901010.5/SPECFLDR/01:43:12 PM/10/11/90 20 strate the effect of the varying dosages on film burnoutresistance. Values in parentheses denote a 10-second dwelltime at 300eF without film burnout. The results also demon-strate an irradiation threshold, of 4.5 MR to achieve sealcharacteristics and heat tolerance characteristic similarto PVC.

Table 3

Electron Beam Irradiated Film

Approximate Film Burnout

Bosaqe (MR) Hot Bar Cuttinq Threshold (eF for 1 1 ' Acceptable 230°F - 240°F 2 Acceptable 250°F - 260°F 3 Acceptable 26Q°F - 270°F 3.5 . Acceptable 270°F - 280°F 4.0 Acceptable 280°F 290° יF 4.5 Acceptable (&gt;300°F) 5.0 Acceptable (&gt;300eF) 5.5 Marginal (&gt;300°F) 6.0 Slightly Unacceptable (&gt;300eF) 6.5 Unacceptable (&gt;300eF) 7.0 Unacceptable (&gt;300eF)

Four rolls of the film were also gamma irradiated,as finished rolls, for similar evaluation. The dosagecuttability, and film burnout threshold appear in Table 4.The response of these samples to gamma irradiation is dif-ferent from that of electron beam irradiated samples. On adose-for-dose basis, the gamma samples did not have theburnout resistance nor cuttability characteristics observedwith electron beam irradiated samples. 4/901010.5/SPECFLDR/01:53:25 PM/10/11/90 21

Table 4

Gamma Irradiated Film

Approximate Film BurnoutThreshold (°F for 1 Sec.)

Hot Bar Cutting

Dosage (MR)

230°F 240° ־F250eF - 260eF250°F 260 ־“F270°F - 28Q°F

Acceptable

Acceptable

Acceptable 2 4 6 8

Acceptable with lessedge curl than othersamples.

Single layers of film from the outside and the in-side portions of each of the four gamma irradiated rollswere then wrapped around foam trays containing a l־lb.block, placed on the hot pad sealer for up to 10 seconds atvarying temperatures, then checked for burn through. Re-suits of the. evaluation appear in Table 5. Two and 4 MRdosage results in little to no burn through resistanceregardless of location in the roll. Six and 8 MR dosageresults in appreciable burn through resistance towards theinside or core of the roll as compared to the outer layers; this equates to greater sealability of the film. 4/901010.5/SRECFLDR/01:58:52 PM/10/11/90 22

Table 5

Gamma Irradiation Analysis

Handwrapper, 4S Trays, 1-Lb. Blocks

Dosage Burnout Threshold, 10 Seconds Outside 2.0 230240°־F Inside 2.0 230-240°F Outside 4.0 240250'־eF Inside 4.0 260-270°F Outside 6.0 240250־eF Inside 6.0 230330°־F (340350־eF for 1 Second) Outside 8.0 290300°־F Inside 8.0 &gt;340°F

While the invention has been disclosed with refer־ence to illustrative examples, those skilled in the artwill understand that various modifications may be made tothe invention as disclosed without departing from thesphere and scope of the claims which follow.

For example, in an alternative embodiment, a singlelayer of VLDPE may be adhered, either directly or by meansof a polymeric adhesive layer, to a single layer of styrenebutadiene copolymer by one of the methods disclosed herein,to produce a film with a preferred thickness of less thanabout 1 mil. 4/901010.5/SPECFLDR/01:29:36 PM/10/11/90 23