CA2559180A1

CA2559180A1 - Multilayer film, article made therefrom, and packaged product utilizing same

Info

Publication number: CA2559180A1
Application number: CA002559180A
Authority: CA
Inventors: David Wayne Grams
Original assignee: Individual
Current assignee: Cryovac LLC
Priority date: 2004-03-09
Filing date: 2005-02-17
Publication date: 2005-10-06
Also published as: AU2005225383A1; WO2005092611A2; EP1722971A2; WO2005092611A3

Abstract

A multilayer film comprises six layers in the layer arrangement 1/5/4/3/6/2.
The first layer (1) serves as a heat sealing layer and comprises a homogeneous ethylene/alpha-olefin copolymer wherein the alpha-olefin has from 3 to 20 carbon atoms. The second layer (2) is a second outer layer and serves as an abuse layer. The third layer (3) is an O2-barrier layer and is between the first layer and the second layer. The fourth layer (4) is an inner layer comprising at least one member selected from the group consisting of polyamide and polyester. The fourth layer is between the fifth layer and the sixth layer. The fifth layer (5) is an inner layer serving as a first tie layer, the fifth layer being between the first layer and the third layer. The sixth layer is an inner layer serving as a second tie layer, the sixth layer being between the second layer and the third layer. The invention also pertains to a packaging article, such as a bag, pouch, casing, etc., which is made from or comprises the multilayer film as well as a packaged product comprising a product (e.g., food) surrounded by a package comprising the multilayer film.

Description

MULTILAYER FILM ARTICLE MADE THEREFROM, AND PACKAGED PRODUCT UTILIZING SAME
Field of the Invention The present invention relates to flexible packaging films, packaging articles made therefrom, and packaged products utilizing a flexible packaging film in the package. The present invention is particularly directed to high impact strength, multilayer shrink films suitable for the packaging of bone-in meat products.
1o Background of the Invention For many years patch bags have been utilized for the packaging of various bone-in meat products, particularly fresh meat products, especially beef, pork, poultry, and lamb. The patch is placed on the bag in order to lower the risk that a the bag will be punctured by exposed bone, particularly an exposed cut bone end.
15 Although exposed bone and particularly cut bone ends are abusive to the films from which the bags and patches are made, some meat cuts present higher risk of film puncture than do other meat cuts. It would be desirable to provide a patch-free bag which provides abuse and puncture resistance at a level comparable to a patch bag. It would also be desirable to provide such a patch-free bag which both provides ample abuse and puncture-resistance, 20 while at the same time being sealable on existing equipment to produce a strong heat seal.
Summary of the Invention The present invention is directed to a multilayer film which is suitable for conversion to a bag or pouch or casing or for use as a flat film lidstock to be adhered to a tray, preferably 25 the flange of a tray. The multilayer film has one or more inner layers comprising at least one member selected from the group consisting of polyamide and polyester, and the multilayer film has a seal layer comprising a homogeneous ethylene/alpha-olefin copolymer. The presence of the homogeneous ethylene/alpha-olefin copolymer improves sealability of the film to itself or another film, especially if the film has a thickness of at least 2.5 mils, as 30 sealing through a thick film containing layers of nylon or polyester is more difficult than sealing through a thinner film made up entirely of polyolefin based polymers.

As a first aspect, the present invention is directecL to a multilayer film, comprising: (A) a first layer which is a first outer layer and which serves as a heat seal layer, the first layer comprising a homogeneous ethylene/alpha-olefin copolymer, wherein the alpha-olefin has from 3 to 20 carbon atoms; (B) a second layer which ~s a second outer layer and which serves as an abuse layer; (C) a third layer which is an Oa-bax~ier layer, the third layer being between the first layer and the second layer; (D) a fourth layer which is an inner layer comprising at least one member selected from the group consisting of polyamide and polyester; (E) a fifth layer which is an inner layer serving as a first tie layer, the fifth layer being between the first layer and the third layer; and (F) a sixth layer which is an inner layer serving as a second tie to layer, the sixth layer being between the second layer and the third layer.
The fourth layer is between the fifth layer and the sixth layer.
Preferably, the homogeneous ethylene/alpha-olefin copolymer has a density of from about 0.88 g/cc to 0.95 g/cc; more preferably, from about 0.89 g/cc to 0.93g/cc; more preferably, from about 0.90 g/cc to 0.93 g/cc; more preferably, from about 0.91 g/cc to 0.93 g/cc; and more preferably, from about 0.92 g/cc to 0.93 g/cc.
Preferably, the alpha-olefin in the ethylene/alpha~-olefin copolymer of the first layer is an alpha-olefin having from 3 to 10 carbon atoms; more preferably, from 4 to 8 carbon atoms;
more preferably, from about 6 to 8 carbon atoms.
Preferably, the homogeneous ethylene/alpha-olefin copolymer in the seal layer 2o comprises metallocene-catalyzed copolymer.
Optionally, the homogeneous ethylene/alpha-olefin copolymer of the first layer is present in a blend with another polymer comprising a~.t least one member selected from the group consisting of linear low density polyethylene, very low, density polyethylene, high density polyethylene, low density polyethylene, ethylene/unsaturated ester copolymer, ethylene/unsaturated acid copolymer, and ionomer re=sin, with the homogeneous ethylene alpha-olefin. Preferably, the homogeneous ethylene/alpha-olefin copolymer comprises from about 20 to 99 weight percent of the blend; more preferably, the homogeneous ethylene/alpha-olefin copolymer comprises from about 40 to 95 weight percent of the blend;
more preferably, the homogeneous ethylene/alpha-olefin copolymer comprises from about 50 3o to 95 weight percent of the blend.

Preferably, the multilayer film has a total free shrixik, at 185°F, of from 15 to 8o percent; more preferably, from 25 percent to 60 percent; more preferably, from 30 to 50 percent.
Preferably, the multilayer film has a total thickness of from about 0.5 to 10 mils; more preferably, from about 1 to 8 mils; more preferably, from about 1 to 6 mils;
more preferably, from about 1 to 5 mils; more preferably, from about 2 to 4 mils, and more preferably, from 3 to 4 mils.
Preferably, the multilayer film has a peak load impact strength of from about 300 to 2000 Newtons; more preferably, from about 400 to 1000 Newtons; more preferably, from about 425 to 800 Newtons; more preferably, from about 450 to 600 Newtons.
1o Preferably, the multilayer film further comprises a seventh layer which is an internal layer and which comprises at least one member selected from the group consisting of polyamide and polyester, with the seventh layer being between the fifth and sixth layers, and the third layer being between the seventh layer and the fourth layer.
Preferably, the fourth layer comprises polyamide and the seventh layer comprises 15 polyamide; more preferably, the fourth layer comprises polyamide having a melting point of from about 150°C to 270°C, and the seventh layer comprises polyamide having a melting point of from 150°C to 270°C. Preferably, the fourth layer comprises at least one member selected from the group consisting of polyamide 6, polyamide 11, polyamide 66, and polyamide 610, and the seventh layer comprises at least one member selected from the group 20 consisting of polyamide 6, polyamide 11, polyamide 66, and polyamide 610 more preferably, the fourth layer comprises polyamide 6 and the seventh layer comprises polyamide 6.
Preferably, the fourth layer and the fifth layer together make up from about 20 to 80 percent of the total thickness of the multilayer film more preferably, the fourth layer and the fifth layer together make up from about 30 to 70 percent of the total thickness of the 25 multilayer film more preferably, the fourth layer and the fifth layer together make up from about 30 to 60 percent of the total thickness of the multilayer film more preferably, the fourth layer and the fifth layer together make up from about 30 to 50 percent of the total thickness of the multilayer film more preferably, the fourth layer and the fifth layer together make up from about 35 to 45 percent of the total thickness of the multilayer film.
3o Preferably, the third layer comprises at least one member selected from the group consisting of polyvinylidene chloride (particularly vinylidene chloride/methyl acrylate copolymer and vinylidene chloride/vinyl chloride copolymer) and ethylene/vinyl alcohol copolymer. Preferably, the third layer make up from about 1 to 1 O percent of the total thickness of the multilayer film more preferably, the third layer m~lces up from about 2 to 5 percent of the total thickness of the multilayer film. Preferably, tl~e third layer comprises ethylene/vinyl alcohol copolymer.
Preferably, the second layer comprises at least one member selected from the group consisting of linear low density polyethylene, very low density porlyethylene, high density polyethylene, low density polyethylene, homogeneous ethylene/aLpha-olefin copolymer, polyester, and polyamide. Preferably, the second layer makes up from 10 to 30 percent of the l0 total thickness of the multilayer film; more preferably, the second layer makes up from 15 to 25 percent of the total thickness of the multilayer film.
Preferably, the fifth layer and the sixth layer each make up from 1 to 10 percent of the total thickness of the multilayer film; more preferably, the fifth layer and the sixth layer each make up from 2 to 6 percent of the total thickness of the multilayer film.
15 As a second aspect, the present invention is directed to a packaging article the multilayer film according to the first aspect of the present invention.
Preferably, the multilayer film is heat sealed to itself to form at least one member selected from the group consisting of a bag, a pouch, and a backseamed casing. Particularly preferred are end-seal bags and side-seal bags. In addition, the multilayer film can be present as a lidstock over a 2o tray, the film being heat sealed around a perimeter of a flange on -the tray.
As a third aspect, the present invention is directed to a packaged product comprising a product surrounded by a package, the package comprising the m~xltilayer film in accordance with the first aspect of the present invention. Preferably, the product comprises a bone-in meat product. Preferably, the bone-in meat product comprises at least one member selected 25 from the group consisting of beef, pork, poultry, and lamb. If beef, preferably the bone-in meat product comprises at least one member selected from the group consisting of beef short ribs, beef back ribs, beef rib subprimal, beef shank, beef chuck, aid beef short loin; more preferably, the bone-in meat product comprises at least one member selected from the group consisting of beef short ribs and beef back ribs. If pork, preferably the bone-in meat product 3o comprises at least one member selected from the group consisting of pork boston butt, pork spare ribs, pork picnics, pork back ribs, and bone-in pork loin; more preferably, at least one member selected from the group consisting of pork boston butt and pork spare ribs.

Optionally, the blend can fi~riher comprise up to about 15 percent, based on total blend weight, of one or more members selected from the group consisting of slip, filler, pigment, dye, radiation stabilizer, antioxidant, fluorescence additive, antistatic agent, elastomer, and viscosity-modifying agent.
Brief Description of the Drawings Figure 1 illustrates a lay-flat view of an end-seal bag.
Figure 2 illustrates a cross-sectional view of the bag of Figure 1, taken through section 2-2 thereof.
1o Figure 3 illustrates a lay-flat view of a side-seal bag of the present invention.
Figure 4 illustrates a cross-sectional view of the bag of Figure 3, taken through section 4-4 thereof.
Figure 5 illustrates a schematic view of a preferred process fog making a multilayer film in accordance with the present invention, for example, as described in Table I.
Detailed Description of the Invention As used herein, the term "bag" is inclusive of L-seal bags, side-seal bags, backseamed bags, and pouches. An L-seal bag has an open top, a bottom seal, one side-seal along a first side edge, and a seamless (i.e., folded, unsealed) second side edge. P~ side-seal bag has a an open top, a seamless bottom edge, with each of its two side edges having a seal therealong.
Although seals along the side and/or bottom edges can be at the very edge itself, (i.e., seals of a type commonly referred to as "trim seals"), preferably the seals are spaced inward (preferably 1/4 to 1/2 inch, more or less) from the bag side edges, and preferably are made using a impulse-type heat sealing apparatus, which utilizes a bar which is quickly heated and then quickly cooled. A backseamed bag is a bag having an open top, a seal running the length of the bag in which the bag film is either fin-sealed or lap-sealed, two seamless side edges, and a bottom seal along a bottom edge of the bag.
As used herein, the phrases "heat-shrinkable," "heat-shrink" ~.nd the like refer to the tendency of a film, generally an oriented film, to shrink upon the application of heat, i.e., to 3o contract upon being heated, such that the size (area) of the film decre=ases if the film is not restrained when heated. Likewise, the tension of a heat-shrinkable film increases upon the application of heat if the film is restrained from shrinking. As a corollary, the phrase "heat-contracted" refers to a heat-shrinkable film, or a portion thereof, which has been exposed to heat such that the film or portion thereof is in a heat-shrunken state, i.e., reduced in size (unrestrained) or under increased tension (restrained). Preferably, the heat shrinkable film has a total free shrink (i.e., machine direction plus transverse direction), as measured by ASTM D 2732, of at least as 5 percent at 185°C, more preferably at least 7 percent, still more preferably, at least 10 percent, and, yet still more preferably, at least 20 percent.
As used herein, the phrase "heterogeneous polymer" refers to polymerization reaction products of relatively wide variation in molecular weight and relatively wide variation in to composition distribution, i.e., typical polymers prepared, for example, using conventional Ziegler-Natta catalysts. Heterogeneous copolymers typically contain a relatively wide variety of chain lengths and comonomer percentages.
As used herein, the phrase "homogeneous polymer" refers to polymerization reaction products of relatively narrow molecular weight distribution and relatively narrow 15 composition distribution. Homogeneous polymers are useful in various layers of the multilayer film used in the present invention. Homogeneous polymers are structurally different from heterogeneous polymers, in that homogeneous polymers exhibit a relatively even sequencing of comonomers within a chain, a mirroring of sequence distribution in all chains, and a similarity of length of all chains, i.e., a narrower molecular weight distribution.
2o Furthermore, homogeneous polymers are typically prepared using metallocene, or other single-site type catalysis, rather than using Ziegler Natta catalysts.
More particularly, homogeneous ethylene/alpha-olefin copolymers may be characterized by one or more processes known to those of skill in the art, such as molecular weight distribution (Mw/Mn), Mz/Mn, composition distribution breadth index (CDBI), and 25 narrow melting point range and single melt point behavior. The molecular weight distribution (Mw/Mn), also known as polydispersity, may be determined by gel permeation chromatography. The homogeneous ethylene/alpha-olefin copolymers useful in this invention generally has (Mw/Mn) of less than 2.7; preferably from about 1.9 to 2.5; more preferably, from about 1.9 to 2.3. The composition distribution breadth index (CDBI) of such 3o homogeneous ethylene/alpha-olefin copolymers will generally be greater than about 70 percent. The CDBI is defined as the weight percent of the copolymer molecules having a comonomer content within 50 percent (i.e., plus or minus 50°10) of the median total molar comonomer content. The CDBI of linear polyethylene, which does not contain a comonomer, is defined to be 100%. The Composition Distribution Breadth Index (CDBI) is determined via the technique of Temperature Rising Elution Fractionation (TREF). CDBI
determination clearly distinguishes the homogeneous copolymers (narrow composition distribution as assessed by CDBI values generally above 70%) from VLDPEs available commercially which generally have a broad composition distribution as assessed by CDBI
values generally less than 55%. The CDBI of a copolymer is readily calculated from data obtained from techniques known in the art, such as, for example, temperature rising elution fractionation as described, for example, in Wild et. al., J. Poly. Sci. Poly.
Phys. Ed., Vol. 20, p.441 (1982). Preferably, homogeneous ethylene/alpha-olefin copolymers have a CDBI
to greater than about 70%, i.e., a CDBI of from about 70% to 99%. In general, the homogeneous ethylene/alpha-olefin copolymers in the patch bag of the present invention also exhibit a relatively narrow melting point range, in comparison with "heterogeneous copolymers", i.e., polymers~having a CDBI of less than 55%. Preferably, the homogeneous ethylene/alpha-olefin copolymers exhibit an essentially singular melting point characteristic, with a peak melting point (Tm), as determined by Differential Scanning Calorimetry (DSC), of from about 60°C to 110°C. Preferably the homogeneous copolymer has a DSC peak Tm of from about 80°C to 100°C. As used herein, the phrase "essentially single melting point" means that at least about 80%, by weight, of the material corresponds to a single Tm peak at a temperature within the range of from about 60°C to 110°C, and essentially no substantial 2o fraction of the material has a peak melting point in excess of about 115°C., as determined by DSC analysis. DSC measurements are made on a Perkin Elmer System 7 Thermal Analysis System. Melting information reported are second melting data, i.e., the sample is heated at a programmed rate of 10°C./min. to a temperature below its critical range. The sample is then reheated (2nd melting) at a programmed rate of 10°C/min. The presence of higher melting peaks is detrimental to film properties such as haze, and compromises the chances for meaningful reduction in the seal initiation temperature of the final film.
A homogeneous ethylene/alpha-olefin copolymer can, in general, be prepared by the copolymerization of ethylene and any one or more alpha-olefin. Preferably, the alpha-olefin is a C3-C2o alpha-monoolefin, more preferably, a C4-C12 alpha-monoolefin, still more preferably, a C4-C8 alpha-monoolefin. Still more preferably, the alpha-olefin comprises at least one member selected from the group consisting of butene-1, hexene-1, and octene-l, i.e., 1-butene, 1-hexene, and 1-octene, respectively. Most preferably, the alpha-olefin comprises octene-l, and/or a blend of hexene-1 and butene-1.

Processes for preparing and using homogeneous polymers are disclosed in U.S.
Patent No. 5,206,075, U.S. Patent No. 5,241,031, and PCT International Application WO
93/03093, each of which is hereby incorporated by reference thereto, in its entirety.
Further details regarding the production and use of homogeneous ethylene/alpha-olefin copolymers are disclosed in PCT International Publication Number WO 90/03414, and PCT
International Publication Number WO 93/03093, both of which designate Exxon Chemical Patents, Inc. as the Applicant, and both of which are hereby incorporated by reference thereto, in their respective entireties.
Still another genus of homogeneous ethylene/alpha-olefin copolymers is disclosed in to U.S. Patent No. 5,272,236, to LAI, et. al., and U.S. Patent No. 5,278,272, to LAI, et. al., both of which are hereby incorporated by reference thereto, in their respective entireties. Each of these patents disclose substantially linear homogeneous long chain branched ethylene/alpha-olefin copolymers produced and marketed by The Dow Chemical Company.
As used herein, the phrase "ethylene/alpha-olefin copolymer", and "ethylene/alpha-15 olefin copolymer", refer to such materials as linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); and homogeneous polymers such as metallocene catalyzed polymers such as EXACT~ resins obtainable from the Exxon Chemical Company, and TAFMER~ resins obtainable from the Mitsui Petrochemical Corporation. All these materials generally include copolymers of ethylene 2o with one or more comonomers selected from C4 to Clo alpha-olefin such as butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures.
This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. The heterogeneous 25 ethylene/alpha-olefins commonly known as LLDPE have a density usually in the range of from about 0.91 grams per cubic centimeter to about 0.94 grams per cubic centimeter. Other ethylene/alpha-olefin copolymers, such as the long chain branched homogeneous ethylene/alpha-olefin copolymers available from the Dow Chemical Company, known as AFF1NITY~ resins, are also included as another type of homogeneous ethylene/alpha-olefin 3o copolymer useful in the present invention.
In general, the ethylene/alpha-olefin copolymer comprises a copolymer resulting from the copolymerization of from about 80 to 99 weight percent ethylene and from 1 to 20 weight percent alpha-olefin. Preferably, the ethylene/alpha-olefin copolymer comprises a copolymer resulting from the copolymerization of from about 85 to 95 weight percent ethylene and from to 15 weight percent alpha-olefin.
As used herein, the phrase "very low density polyethylene" refers to heterogeneous ethylene/alpha-olefin copolymers having a density of 0.915 g/cc and below, preferably from about 0.88 to 0.915 g/cc. As used herein, the phrase "linear low density polyethylene" refers to, and is inclusive of, both heterogeneous and homogeneous ethylene/alpha-olefin copolymers having a density of at least 0.915 g/cc, preferably from 0.916 to 0.94 g/cc.
As used herein, the phrases "inner layer" and "internal layer" refer to any layer, of a 1o multilayer film, having both of its principal surfaces directly adhered to another layer of the film.
As used herein, the phrase "outer layer" refers to any film layer of film having less than two of its principal surfaces directly adhered to another layer of the film. In multilayer films, there are two outer layers, each of which has a principal surface adhered to only one other layer of the multilayer film. In monolayer films, there is only one layer, which, of course, is an outer layer in that neither of its two principal surfaces are adhered to another layer of the film.
As used herein, the phrase "inside layer" refers to the outer layer of a multilayer film packaging a product, which is closest to the product, relative to the other layers of the 2o multilayer film.
As used herein, the phrase "outside layer" refers to the outer layer, of a multilayer film packaging a product, which is furthest from the product relative to the other layers of the multilayer film. Likewise, the "outside surface" of a bag is the surface away from the product being packaged within the bag.
As used herein, the term "adhered" is inclusive of films which are directly adhered to one another using a heat seal or other means, as well as films which are adhered to one another using an adhesive which is between the two films.
Figure 1 is a lay-flat view of a schematic of an end-seal bag 10, in a lay-flat position, this bag being in accord with the present invention; Figure 2 is a cross-sectional view of bag 10 3o taken through section 2-2 of Figure 1. Viewing Figures l and 2 together, bag 10 comprises bag film 12, top edge 14 defining an open top, first bag side edge 16, second bag side edge 18, bottom edge 20, and end seal 22.

Figures 3 and 4 illustrate a schematic of a side-seal bag 30, an alternative bag in accordance with the present invention. While Figure 3 illustrates side-seal bag 30 in lay-flat view, Figure 4 illustrates a cross-sectional view through section 4-4 of Figure 3. With reference to Figures 3 and 4 together, side-seal bag 30 is comprised of bag film 32, top edge 34 defining 5 an open top, first side seal 36, second side seal 38, and folded (seamless) bottom edge 40.
The bags illustrated in Figures l, 2, 3, and 4 are made from the film in accordance with the present invention, and preferred embodiments of the bags of Figures l, 2, 3, and 4 are made from preferred embodiments of the film of the present invention.
Figure 5 illustrates a preferred process for making the film of the present invention, to which film can be readily converted into the bags of Figures 1, 2, 3, and 4, described above.
A preferred embodiment of the film of the present invention is set forth following the description of Figure 5. The process of Figure 5 is a full coextrusion process, in which all of the film layers are extruded simultaneously.
In the process illustrated in Figure 5, solid polymer beads (not illustrated) are fed to a plurality of extruders (for simplicity, only extruder 88 is illustrated).
Inside extruders 88, the polymer beads are degassed, following which the resulting bubble-free melt is forwarded into die head 90, and extruded through an annular die, resulting in seamless tubing tape 92 which is preferably from about 15 to 30 mils thick, and preferably has a lay-flat width of from about 2 to 10 inches.
2o After cooling or quenching by water spray from cooling ring 94, tubing tape 92 is collapsed by pinch rolls 96, and is thereafter fed through irradiation vault 98 surrounded by shielding 100, where tubing 92 is irradiated with high energy electrons (i.e., ionizing radiation) from iron core transformer accelerator 102. Tubing tape 92 is guided through irradiation vault 98 on rolls 104. Preferably, tubing tape 92 is irradiated to a level of from about 40-100 kGy, resulting in irradiated tubing tape 106. Irradiated tubing tape 106 is wound upon windup roll 108 upon emergence from irradiation vault 98, forming irradiated seamless tubing tape coil 110.
After irradiation and windup, windup roll 108 and irradiated tubing tape coil 110 are removed and installed as unwind roll 112 and unwind tubing tape coil 114, on a second stage in the process of making the film as ultimately desired. Trradiated tubing 106, being unwound from unwind tubing tape coil 114, is then passed over guide roll 116, after which irradiated tubing 106 is passed through hot water bath tank 118 containing hot water 120. Irradiated tubing 106 is then immersed in hot water 120 (preferably having a temperature of about 185-210°F) for a period of about 20-60, i.e., for a time period long enough to bring the filin up to the desired s temperature for biaxial orientation. Thereafter, hot, irradiated tubular tape 122 is directed through nip rolls 124, and bubble 126 is blown, thereby transversely stretching hot, irradiated tubular tape 122 so that an oriented film tube 128 is formed. Furthermore, while being blown, i.e., transversely stretched while in the solid state, nip rolls 130 have a surface speed higher than the surface speed of nip rolls 124, thereby resulting in longitudinal orientation. As a result of to the transverse stretching and longitudinal drawing, oriented filin tubing 128 is produced, this blown tubing preferably having been both stretched in a ratio of from about 1:1.5 to 1:6, and drawn in a ratio of from about 1:1.5 to 1:6. More preferably, the stretching and drawing are each performed at a ratio of from about 1:2 to 1:4. The result is a biaxial orientation of from about 1:2.25 to 1:36, more preferably, 1:4 to 1:16. While bubble 126 is maintained between 15 pinch rolls 124 and 130, oriented filin tube 128 is collapsed by rollers 132, and thereafter conveyed through pinch rolls 130 and across guide r~11134, and then rolled onto wind-up roll 136. Idler roll 138 assures a good wind-up. The resulting multilayer film can be used to form backseamed casings, etc., which, in turn, can be used for the packaging of meat products, in accordance with the present invention.
2o Table I, below, illustrates in table form a cross-sectional view of preferred multilayer film for use as the tubing film stock from which the bags of Figures l, 2, 3, and 4 can be formed, which film can be prepared using the process illustrated in Figure 5, described above.
The multilayer film of Table 1 has a physical structure, in terms of number of layers, layer thickness, and layer arrangement and orientation in the patch bag, and a chemical 25 composition in terms of the various polymers, etc. present in each of the layers, as set forth in Table I, below.

TABLEI
Layer Orderl Layer Function Layer Chemical Layer Thickness Layer Identity Designation (percent of total film thickness 1 I First Inside layer, 100% homogeneous 31 which serves as a sealethylenelalpha-olefin layer copol mer 2 I Fifth tie layer Anhydride-modified4 linear low density polyethylene 3 / 4ourth inner puncture-resistant100% polycaprolactam and abuse-resistant 20 high strength layer 4 / Third Oz-barrier layer100% ethylenelvinyl3 alcohol copolymer (EVOH) Inner puncture-resistant / Seventh and abuse-resistant100% polycaprolactam20 high stren th la er 6 I Sixth tie layer 100% Anhydride-modified4 linear low density polyethylene 7 / Second outside layer, 100% linear low 19 which density serves as an polyethylene abuse-resistant layer The polymer components used to fabricate multilayer films according to the present invention may also contain appropriate amounts of other additives normally included in such compositions. These include antiblocking agents (such as talc), slip agents (such as fatty acid amides), fillers, pigments and dyes, radiation stabilizers (including antioxidants), fluorescence additives (including a material which fluoresces under ultraviolet radiation), antistatic agents, elastomers, viscosity-modifying substances (such as fluoropolymer processing aids) and the like additives known to those of skill in the art of packaging films.
1o Preferred homogeneous ethylene/alpha-olefin in the first film layer include metallocene-catalyzed ethylene/alpha-olefin copolymers commercially available from Exxon (i.e., EXACT~ metallocene-catalyzed ethylene/hexene and ethylene/octene copolymers) and commercially available from The Dow Chemical Company (i.e., AFFINITY~
metallocene-catalyzed ethylene/octene copolymer). The homogeneous ethylene/alpha-olefin copolymer can have a melt flow index of from about 0.3 to about 50 grams per 10 minutes, as measured by ASTM D1238; the teaching of which is hereby incorporated, in its entirety, by reference thereto; more preferably from about 0.5 to about 20; more preferably from about 0.7 to about 10; even more preferably from about 1 to about 8; and, more preferably from about 1 to about Preferably, the first film according to the present invention comprises a total of from 6 1 o to 20 layers; more preferably, from 6 to 15 layers; more preferably, from 6 to 10 layers; more preferably, from 6 to 8 layers. Particularly preferred film structures have symmetry with respect to layer composition and thickness. More particularly, preferably the puncture-resistant high strength layers on each side of the barrier layer are symmetrical, and preferably there is symmetry with respect to the tie layers which are outwardly located from the puncture-resistant high strength layers. Although the outer heat seal layer and the outer abuse layer can also be symmetrical with respect to composition and thickness, the seal layer contains homogeneous ethylene/alpha-olefin copolymer while the outer abuse layer preferably comprises a heterogeneous ethylene/alpha-olefin copolymer.
The multilayer film of the present invention can (optionally) be irradiated to induce 2o crosslinking, as well as corona treated. In the irradiation process, the film is subjected to an energetic radiation treatment, such as corona discharge, plasma, flame, ultraviolet, X-ray, gamma ray, beta ray, and high energy electron treatment, which induce cross-linking between molecules of the irradiated material. The irradiation of polymeric films is disclosed in LT.S.
Patent NO. 4,064,296, to BORNSTEIN, et. al., which is hereby incorporated in its entirety, ' 25 by reference thereto. BORNSTEIN, et. al. discloses the use of ionizing radiation for crosslinking the polymer present in the film.
Radiation dosages are referred to herein in terms of the radiation unit "RAD", with one million RADS, also known as a megarad, being designated as "MR", or, in terms of the radiation unit kiloGray (kGy), with 10 kiloGray representing 1 MR, as is known to those of 3o skill in the art. A suitable radiation dosage of high energy electrons is in the range of up to about 16 to 166 kGy, more preferably about 40 to 90 kGy, and still more preferably, 55 to 75 kGy. Preferably, irradiation is carried out by an electron accelerator and the dosage level is determined by standard dosimetry processes. Other accelerators such as a van der Graaf or resonating transformer may be used. The radiation is not limited to electrons from an accelerator since any ionizing radiation may be used.
As used herein, the phrases "corona treatment" and "corona discharge treatment" refer to subjecting the surfaces of thermoplastic materials, such as polyolefins, to corona discharge, i.e., the ionization of a gas such as air in close proximity to a film surface, the ionization initiated by a high voltage passed through a nearby electrode, and causing oxidation and other changes to the film surface, such as surface roughness.
to Corona treatment of polymeric materials is disclosed in U.S. Patent No.
4,120,716, to BONET, issued October 17, 1978, herein incorporated in its entirety by reference thereto, discloses improved adherence characteristics of the surface of polyethylene by corona treatment, to oxidize the polyethylene surface. U.S. Patent No. 4,879,430, to HOFFMAN, also hereby incorporated in its entirety by reference thereto, discloses the use of corona 15 discharge for the treatment of plastic webs for use in meat cook-in packaging, with the corona treatment of the inside surface of the web to increase the adhesion of the meat to the adhesion of the meat to the proteinaceous material. Although corona treatment is a preferred treatment of the multilayer films used to make the patch bag of the present invention, plasma treatment of the film may also be used.
20 In addition, a patch can be laminated to a bag made from the film of the present invention. Laminating the patch to the bag can be accomplished by a variety of methods, including the use of an adhesive, corona treatment, or even heat sealing.
Adhesives are the preferred means for accomplishing the lamination. Examples of suitable types of adhesives include thermoplastic acrylic emulsions, solvent based adhesives and high solids adhesives, 25 ultraviolet-cured adhesive, and electron-beam cured adhesive, as known to those of skill in the art. A preferred adhesive is a thermoplastic acrylic emulsion known as RHOPLEX~
N619 thermoplastic acrylic emulsion, obtained from the Rohm & Haas Company, at Dominion Plaza Suite 545, 17304 Preston Rd., Dallas, Texas 75252, Rohm & Haas having headquarters at 7th floor, Independence Mall West, Philadelphia, Penn. 19105.

Although the present invention has been described in connection with the preferred embodiments, it is to be understood that modifications and variations may be utilized without departing from the principles and scope of the invention, as those skilled in the art will readily understand. Accordingly, such modifications may be practiced within the scope of the following claims.

Claims

1. A multilayer film, comprising:
(A) a first layer which is a first outer layer and which serves as a heat seal layer, the first layer comprising a homogeneous ethylene/alpha-olefin copolymer, wherein the alpha-olefin has from 3 to 20 carbon atoms;
(B) a second layer which is a second outer layer and which serves as an abuse layer;
(C) a third layer which is an O2-barrier layer, the third layer being between the first layer and the second layer;
(D) a fourth layer which is an inner layer comprising at least one member selected from the group consisting of polyamide and polyester;
(E) a fifth layer which is an inner layer serving as a first tie layer, the fifth layer being between the first layer and the third layer;
(F) a sixth layer which is an inner layer serving as a second tie layer, the sixth layer being between the second layer and the third layer; and wherein the fourth layer is between the fifth layer and the sixth layer.

2. The multilayer film according to Claim 1, wherein the multilayer film has a total free shrink, at 185°F, of from 15 to 80 percent.

3. The multilayer film according to Claim 1, wherein the homogeneous ethylene/alpha-olefin copolymer has a density of from about 0.88 g/cc to 0.95 g/cc.

4. The multilayer film according to Claim 1, wherein the homogeneous ethylene/alpha-olefin copolymer has a density of from about 0.89 g/cc to 0.93g/cc.

5. The multilayer film according to Claim 1, wherein the homogeneous ethylene/alpha-olefin copolymer has a density of from about 0.90 g/cc to 0.93 g/cc.

6. The multilayer film according to Claim 1, wherein the homogeneous ethylene/alpha-olefin copolymer has a density of from about 0.91 g/cc to 0.93 g/cc.

7. The multilayer film according to Claim 1, wherein the homogeneous ethylene/alpha-olefin copolymer has a density of from about 0.92 g/cc to 0.93 g/cc.

8. The multilayer film according to Claim 1, wherein the alpha-olefin has from 3 to 10 carbon atoms.

9. The multilayer film according to Claim 1, wherein the alpha-olefin has from 4 to 8 carbon atoms.

10. The multilayer film according to Claim 1, wherein the alpha-olefin has from 6 to 8 carbon atoms.

11. The multilayer film according to Claim 1, wherein the homogeneous ethylene/alpha-olefin copolymer in the seal layer comprises metallocene-catalyzed copolymer.

12. The multilayer film according to Claim 1, wherein the homogeneous ethylene/alpha-olefin copolymer of the first layer is present in a blend with another polymer comprising at least one member selected from the group consisting of linear low density polyethylene, very low density polyethylene, high density polyethylene, low density polyethylene, ethylene/unsaturated ester copolymer, ethylene/unsaturated acid copolymer, and ionomer resin, with the homogeneous ethylene alpha-olefin.

13. The multilayer film according to Claim 12, wherein the homogeneous ethylene/alpha-olefin copolymer comprises from about 20 to 99 weight percent of the blend.

14. The multilayer film according to Claim 13, wherein the homogeneous ethylene/alpha-olefin copolymer comprises from about 40 to 95 weight percent of the blend.

15. The multilayer film according to Claim 13, wherein the homogeneous ethylene/alpha-olefin copolymer comprises from about 50 to 95 weight percent of the blend.

16. The multilayer film according to Claim 1, wherein the multilayer film has a total free shrink, at 185°F, of from 25 percent to 60 percent.

17. The multilayer film according to Claim 1, wherein the multilayer film has a total free shrink, at 185°F, of from 30 to 50 percent.

18. The multilayer film according to Claim 1, wherein the multilayer film has a thickness of from about 0.5 to 10 mils.

19. The multilayer film according to Claim 1, wherein the multilayer film has a thickness of from about 1 to 8 mils.

20. The multilayer film according to Claim 1, wherein the multilayer film has a thickness of from about 1 to 6 mils.

21. The multilayer film according to Claim 1, wherein the multilayer film has a thickness of from about 1 to 5 mils.

22. The multilayer film according to Claim 1, wherein the multilayer film has a thickness of from about 2 to 4 mils.

23. The multilayer film according to Claim 1, wherein the multilayer film has a peak load impact strength of from about 300 to 2000 Newtons.

24. The multilayer film according to Claim 1, wherein the multilayer film has a peak load impact strength of from about 400 to 1000 Newtons.

25. The multilayer film according to Claim 1, wherein the multilayer film has a peak load impact strength of from about 425 to 800 Newtons.

26. The multilayer film according to Claim 1, wherein the multilayer film has a peak load impact strength of from about 450 to 600 Newtons.

27. The multilayer film according to Claim 1, wherein the film further comprises a seventh layer which is an internal layer and which comprises at least one member selected from the group consisting of polyamide and polyester, with the seventh layer being between the fifth and sixth layers, and the third layer being between the seventh layer and the fourth layer.

28. The multilayer film according to Claim 1, wherein the fourth layer comprises polyamide and the seventh layer comprises polyamide.

29. The multilayer film according to Claim 28, wherein the fourth layer comprises polyamide having a melting point of from about 150°C to 270°C, and the seventh layer comprises polyamide having a melting point of from 150°C to 270°C.

30. The multilayer film according to Claim 28, wherein the fourth layer comprises at least one member selected from the group consisting of polyamide 6, polyamide 11, polyamide 66, and polyamide 610, and the seventh layer comprises at least one member selected from the group consisting of polyamide 6, polyamide 11, polyamide 66, and polyamide 610.

31. The multilayer film according to Claim 30, wherein the fourth layer comprises polyamide 6 and the seventh layer comprises polyamide 6.

32. The multilayer film according to Claim 27, wherein the fourth layer and the fifth layer together make up from about 20 to 80 percent of the total thickness of the multilayer film.

33. The multilayer film according to Claim 27, wherein the fourth layer and the fifth layer together make up from about 30 to 70 percent of the total thickness of the multilayer film.

34. The multilayer film according to Claim 27, wherein the fourth layer and the fifth layer together make up from about 30 to 60 percent of the total thickness of the multilayer film.

35. The multilayer film according to Claim 27, wherein the fourth layer and the fifth layer together make up from about 30 to 50 percent of the total thickness of the multilayer film.

36. The multilayer film according to Claim 27, wherein the fourth layer and the fifth layer together make up from about 35 to 45 percent of the total thickness of the multilayer film.

37. The multilayer film according to Claim 1, wherein the third layer comprises at least one member selected from the group consisting of polyvinylidene chloride and ethylene/vinyl alcohol copolymer.

38. The multilayer film according to Claim 1, wherein the third layer make up from about 1 to 10 percent of the total thickness of the multilayer film.

39. The multilayer film according to Claim 1, wherein the third layer makes up from about 2 to 5 percent of the total thickness of the multilayer film.

40. The multilayer film according to Claim 36, wherein the third layer comprises ethylene/vinyl alcohol copolymer.

41. The multilayer film according to Claim 1, wherein the second layer comprises at least one member selected from the group consisting of linear low density polyethylene, very low density polyethylene, high density polyethylene, low density polyethylene, homogeneous ethylene/alpha-olefin copolymer, polyester, and polyamide.

42. The multilayer film according to Claim 40, wherein the second layer makes up from to 30 percent of the total thickness of the multilayer film.

43. The multilayer film according to Claim 41, wherein the second layer makes up from to 25 percent of the total thickness of the multilayer film.

44. The multilayer film according to Claim 1, wherein the fifth layer and the sixth layer each make up from 1 to 10 percent of the total thickness of the multilayer film.

45. The multilayer film according to Claim 1, wherein the fifth layer and the sixth layer each make up from 2 to 6 percent of the total thickness of the multilayer film.

46. A packaging article comprising a multilayer film, wherein the multilayer film comprises:
(A) a first layer which is a first outer layer and which serves as a heat seal layer, the first layer comprising a homogeneous ethylene/alpha-olefin copolymer, wherein the alpha-olefin has from 3 to 20 carbon atoms;
(B) a second layer which is a second outer layer and which serves as an abuse layer;
(C) a third layer which is an O2-barrier layer, the third layer being between the first layer and the second layer;
(D) a fourth layer which is an inner layer comprising at least one member selected from the group consisting of polyamide and polyester;
(E) a fifth layer which is an inner layer serving as a first tie layer, the fifth layer being between the first layer and the third layer;
(F) a sixth layer which is an inner layer serving as a second tie layer, the sixth layer being between the second layer and the third layer; and wherein the fourth layer is between the fifth layer and the sixth layer.

47. The packaging article according to Claim 46, wherein the film is heat sealed to itself to form at least one member selected from the group consisting of a bag, a pouch, and a backseamed casing.

48. The packaging article according to Claim 47, wherein the film is sealed to itself to form an end-seal bag or a side-seal bag.

49. The packaging article according to Claim 46, wherein the film makes up a lidstock over a tray, the film being heat sealed around a perimeter of a flange on the tray.

50. A packaged product comprising a product surrounded by a package, the package comprising a multilayer film, comprising:
(A) a first layer which is a first outer layer and which serves as a heat seal layer, the first layer comprising a homogeneous ethylene/alpha-olefin copolymer, wherein the alpha-olefin has from 3 to 20 carbon atoms;
(B) a second layer which is a second outer layer and which serves as an abuse layer;
(C) a third layer which is an O2-barrier layer, the third layer being between the first layer and the second layer;
(D) a fourth layer which is an inner layer comprising at least one member selected from the group consisting of polyamide and polyester;
(E) a fifth layer which is an inner layer serving as a first tie layer, the fifth layer being between the first layer and the third layer;
(F) a sixth layer which is an inner layer serving as a second tie layer, the sixth layer being between the second layer and the third layer; and wherein the fourth layer is between the fifth layer and the sixth layer.

51. The packaged product according to Claim 50, wherein the product comprises a bone-in meat product.

52. The packaged product according to Claim 51, wherein the bone-in meat product comprises at least one member selected from the group consisting of beef, pork, poultry, and lamb.

53. The packaged product according to Claim 52, wherein the bone-in meat product comprises at least one member selected from the group consisting of beef short ribs, beef back ribs, beef rib subprimal, beef shank, beef chuck, and beef short loin.

54. The packaged product according to Claim 52, wherein the bone-in meat product comprises at least one member selected from the group consisting of beef short ribs and beef back ribs.

55. The packaged product according to Claim 52, wherein the bone-in meat product comprises at least one member selected from the group consisting of pork boston butt, pork spare ribs, pork picnics, pork back ribs, and bone-in pork loin.

56. The packaged product according to Claim 55, wherein the bone-in meat product comprises at least one member selected from the group consisting of pork boston butt and pork spare ribs.