WITH IMPROVED ADHESION CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to USSN 61/597252, filed February 10, 2012, which is incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention is related to metalized polypropylene films, and, in particular, to low molecular weight additives to films that improve adhesion of metal coatings to the film.

BACKGROUND

[0003] For metalized oriented polypropylene films, the base film should have stiff skin layers that will provide good metal adhesion. The metalized film should also have very good barrier properties. High crystallinity polypropylene can be used as skin resin material that would provide sufficient stiffness. Ideally, having a polypropylene homopolymer or copolymer skin would prevent a deposited metal layer to form cracks during handling, which would lead to reduced barrier properties. However, polypropylene homopolymer usually has low surface energy after treatment and usually has low metal adhesion after metalization. Frequently, to overcome the metal adhesion problem, ethylene-propylene copolymers were used as metalization skin. However, the softer EP copolymer may give other negative properties to the finished films.

[0004] This problem is solved by the inventor by adding a small amount of selected skin layer modifier that would not affect the mechanical properties of the homopolymer skin, but gives improved metal adhesion and barrier properties. Examples of modifiers are the low molecular weight acid-modified polypropylenes described in U.S. Patent No. 7, 183,359. The inventor has found that the acid-modified polypropylenes, when added to film skin layers, results in improved properties when added into coextruded oriented polypropylene films. SUMMARY

[0005] Disclosed herein is a multi-layer film (or "film") comprising a core layer comprising a polyolefin, a metalizable layer in surface contact with the core layer, the metalizable layer comprising 0.10 wt% to 2 wt% or 5 wt% or 10 wt% or 15.0 wt% of an acid- modified polypropylene having a number-average molecular weight (Mn) of from 300 or 500 or 800 g/mol to 10,000 or 20,000 or 50,000 or 80,000 g/mol and comprising at least one functional group selected from the group consisting of alkoxy, ester, anhydride, carboxylic acid, amine, nitrile, imine, silane, siloxane, sulfonate, alkane, aldehyde, epoxide, organoborane, ethoxylate, propoxylate, higher alkoxylate, halogen, and combinations thereof; and, optionally, a metal layer in surface contact with the metalizable layer.

[0006] Also disclosed herein is a multi-layer film comprising (or consisting essentially of, or consisting of) a core layer comprising a polypropylene, a metalizable layer in surface contact with the core layer, the metalizable layer comprising 0.10 wt% to 2 wt% or 5 wt% or 10 wt% or 15.0 wt% of an acid-modified polypropylene having a number-average molecular weight (Mn) of from 300 or 500 or 800 g/mol to 10,000 or 20,000 or 50,000 or 80,000 g/mol and comprising at least one functional group selected from the group consisting of alkoxy, ester, anhydride, carboxylic acid, aldehyde, and combinations thereof, and the remainder of the metalizable layer comprising polypropylene; and a metal layer in surface contact with the metalizable layer; wherein the modulus (MD or TD) of the film is within 5% or 10% of the value of the modulus for a similar film having from 10 wt% to 20 wt% of a propylene-a- olefin elastomer instead of the acid-modified polypropylene in the metalizable layer.

DETAILED DESCRIPTION

[0007] It is desirable to metalize polyolefin films to enhance their oxygen and water vapor impermeability. At the same time, the films must still be flexible and strong as reflected in their modulus and tensile strengths. Given that highly polar metal does not readily adhere to non-polar polyolefin, especially polypropylene, surfaces, it is desirable to also improve the bonding of the metal to the polymer film. The inventor has found that a low molecular weight polypropylene "wax" having been acid-modified, when added to a polyolefin or polyolefin blend, enhances the ability of a metal layer to adhere to the surface of the polyolefin film without destroying its desirable physical characteristics. The polyolefin blend with the "acid-modified polypropylene" is preferably a skin layer or "metalizable layer" adhered to at least the core layer making up a multi-layered film which is particularly useful for packaging various articles, especially food articles. Given its usefulness, the multi- layered films described herein have a high resistance to water vapor and oxygen penetration (low values).

[0008] Thus, the inventor provides a multi-layer film comprising at least a core layer comprising a polyolefin, preferably a polypropylene, and a metalizable layer in surface contact with the core layer, the metalizable layer comprising 0.10 wt% to 2 wt% or 5 wt% or 10 wt% or 15.0 wt% of the acid-modified polypropylene having a number-average molecular weight (Mn) of from 300 or 500 or 800 g/mol to 10,000 or 20,000 or 50,000 or 80,000 g/mol. The number average molecular weight Mn is determined by gel permeation chromatography (GPC) against a polypropylene standard or by NMR analysis. The acid-modified polypropylene is preferably modified with some polar functionality, especially functionality that includes oxygen, sulfur, nitrogen, phosphorous, or some combination thereof. Desirably, the acid-modified polypropylene comprises at least one functional group selected from the group consisting of alkoxy, ester, anhydride, carboxylic acid, amine, nitrile, imine, silane, siloxane, sulfonate, alkane, aldehyde, epoxide, organoborane, ethoxylate, propoxylate, higher alkoxylate, halogen, and combinations thereof. Most preferably, the functional group is selected from the group consisting of alkoxy, ester, anhydride, carboxylic acid, aldehyde, and combinations thereof.

[0009] Preferably, the multi-layered films of the invention have at least 3 layers, and more preferably at least 4 layers, and most preferably at least 5 layers. The films typically have one, more preferably at least two, skin layers that are bound to a core layer, and are unbound (face away from the multi-layer film) on the other face. One of the skin layers is the "metalizable layer" described herein. In other embodiments, there is a tie-layer between the core layer and each skin layer that are otherwise adjacent to one another in the structure. If each skin layer is labeled "S" (one of which may be metalizable, S ^m ), each core layer labeled "C", and each tie-layer labeled "T", then preferable film structures include, but are not limited to, S ^m C, S ^m CS, S ^m TC, S ^m TCT, S ^m TCS, S ^m TCTS, SS ^m TCTS, STS ^m CTSTS, SS ^m TCCTSS, etc. In particular, a metal layer "M" on the metalizable layer would make structures such as MS ^m C, MS ^m CS, MS ^m TCS, MS ^m TCTS, etc. An additional "first" skin layer, which may be sealable, would result in the structures S ¹ MS ^m C, S ¹ MS ^m CS, SlMSmfCS, etc. Finally, as described herein, S ² may be a "second" skin layer, preferably sealable, which results in MS ^m CS ² , SiMSmCS ² SiMSmTCS ² , SiMSmTCTS ² etc.

[0010] In the films described herein, each individual skin layer may be the same or different, preferably different, in composition compared to other skin layers in the same film. Thus, for example, preferable film structures are represented by S ^l C, S ^l CS ² , S ¹ T ¹ CT ² S ² , S ¹ S ² T ¹ CT ² S ¹ , etc., wherein "S ¹ " and "S ² " are distinct from one another, meaning that they comprise different materials, and/or the same materials but in different ratios. The same is true for "T ¹ " and "T ² ". Each skin layer, tie-layer, and core layer that makes up a film may have a similar or identical identity, as this type of structure allows the use of only three extruders to melt blend and extrude the materials that form each layer of the film.

[0011] As used herein, the term "layer" refers to each of the one or more materials, the same or different, that are secured to one another in the form of a thin sheet or film by any appropriate means such as by an inherent tendency of the materials to adhere to one another or by inducing the materials to adhere as by a heating, radiative, chemical, or some other appropriate process. The term "layer" is not limited to detectable, discrete materials contacting one another such that a distinct boundary exists between the materials. Preferably, however, the materials used to make one layer of a film will be different (i.e., the weight percent of components, the properties of each component, and/or the identity of the components may differ) from the materials used to make an adjacent, and adhering, layer. The term "layer" includes a finished product having a continuum of materials throughout its thickness. The "films" described herein comprise three or more layers, and may comprise 3, 4, 5, 6, or more layers in preferred embodiments.

[0012] The 3, 4, 5, 6, or more layer film structures (films) of the invention may be any desirable thickness and preferably have an average thickness within the range of from 12 μιη or 20 μιη or 30 μιη or 40 μιη to an upper limit of 50 μιη or 60 μιη or 80 μιη or 100 μιη or 150 μιη or 200 μιη or 500 μιη. Thus, an exemplary average thickness is within the range of from 12 μιη ίο 80 μιη.

[0013] The acid-modified polypropylene useful in the films herein can be made by any suitable means to arrive at the desired properties. Preferably, the acid-modified polypropylene is made by the method described in U.S. Patent No. 7, 183,359. In any case, the acid-modified polypropylenes useful herein preferably have a melting point within the range from 20°C or 30°C to 80°C or 100°C or 120°C or 140°C. Also, the viscosity of the acid-modified polypropylene is preferably within the range from 10 or 20 or 30 cP to 500 or 800 or 1000 cP (149°C). Further, the average number of acid sites per polymer chain of the acid-modified polypropylenes is within the range from 5 or 10 or 15 to 50 or 80 or 100 or 150 or 200.

[0014] In a preferred embodiment, the multi-layer films of the invention comprise a core layer comprising a polypropylene, a metalizable layer in surface contact with the core layer, the metalizable layer comprising 0.10 wt% to 2 wt% or 5 wt% or 10 wt% or 15.0 wt% of an acid-modified polypropylene having a number-average molecular weight (Mn) of from 300 or 500 or 800 g/mol to 8,000 or 10,000 or 20,000 or 50,000 or 80,000 g/mol and comprising at least one functional group selected from the group consisting of alkoxy, ester, anhydride, carboxylic acid, aldehyde, and combinations thereof, and the remainder of the film comprising polypropylene; and a metal layer in surface contact with the metalizable layer; wherein the modulus (MD or TD) of the film is within less than 5% or 10% the value of the modulus for a similar film having from 10 wt% to 20 wt% of a propylene-a-olefin elastomer instead of the acid-modified polypropylene in the metalizable layer. That is, in comparing two films otherwise identical but one having a metalizable layer consisting of polypropylene and the acid-modified polypropylene (an amount within the disclosed range), and the other film having a metalizable layer consisting of polypropylene and a propylene-a-olefin elastomer (an amount within the disclosed range), the two should have a TD and/or MD modulus within less than 5% or 10% of one another.

[0015] In certain embodiments, a "propylene-a-olefin elastomer" may be present in an amount from 2 wt% or 3 wt% or 5 wt% or 10 wt% to 15 wt% or 20 wt% or 25 wt% or 30 wt% or 35 wt% in the metalizable skin layer of the inventive films in addition to the acid- modified polypropylene. In any case, whether present or not in the metalizable layer, the metalizable layer also comprises a polyolefin in the balance, preferably polypropylene, polyethylene, or a blend thereof, most preferably polypropylene. The additional elastomer, as well as the "polypropylene" and the "skin layer" that may also be part of the multi-layered films, are described further below.

[0016] In a most preferred embodiment of the invention, a layer, such as the core layer, may consist essentially of the named polymer components. Also, the multi-layered film can consist essentially of, or consist of, the named layers. By "consisting essentially of what is meant is that the film or layer referred to only includes as effective polymer components the named polymers but can also include up to 1 wt% or 2 wt% or 3 wt% or 4 wt% or 5 wt% of an "additive" as described further below, those additives not changing the properties of the film or layer as claimed.

[0017] Propylene-a-olefin Elastomers. As used herein, a "propylene-a-olefin elastomer" refers to a random copolymer that is elastomeric, has moderate crystallinity, and possesses propylene-derived units and one or more units derived from ethylene, higher a-olefins, and/or optionally diene-derived units. One or a mixture of different propylene-a-olefin elastomers may be present in the core compositions, preferably only one. The propylene-based elastomers are copolymers of propylene having an intermediate amount of a-olefin, such as within a range of from 6 wt% or 8 wt% or 10 wt% or 12 wt% or 14 wt% to 25 wt% or 30 wt% a-olefin derived units by weight of the polymer. The propylene-a-olefin elastomers may be described by any number of different parameters, and those parameters may comprise a numerical range made up of any desirable upper limit with any desirable lower limit as described herein.

[0018] Preferably, the propylene-a-olefin elastomer comprises C2 or C ₄ to C\ a-olefin- derived units (or "comonomer-derived units") within the range of 6 wt% or 8 wt% or 10 wt% or 12 wt% or 14 wt% to 25 wt% or 30 wt%, by weight of the elastomer. The propylene-a- olefin elastomer may also comprise two different comonomer-derived units. Also, these copolymers and terpolymers may comprise diene-derived units as described below. Preferably, the propylene-a-olefin elastomer comprises propylene-derived units and comonomer units selected from ethylene, 1-butene, 1-hexene, and 1-octene. And, more preferably, the comonomer is ethylene and, thus, the propylene-a-olefin elastomer is a propylene-ethylene copolymer. When dienes are present, the propylene-a-olefin elastomer comprises less than 5 wt% or 3 wt%, by weight of the elastomer, of diene derived units, or within the range of from 0.1 wt% or 0.5 wt% or 1 wt% to 5 wt% in other embodiments. Suitable dienes include, for example: 1,4-hexadiene, 1,6-octadiene, 5-methyl-l,4-hexadiene, 3, 7-dimethyl- 1,6-octadiene, dicyclopentadiene (DCPD), ethylidiene norbornene (ENB), norbornadiene, 5 -viny 1-2 -norbornene (VNB), and combinations thereof.

[0019] These propylene-a-olefin elastomers may have some isotactic polypropylene sequences but they also have some amorphous regions in the polymer chains, thus imparting desirable qualities to them and the compositions in which they are blended. Preferably, the propylene-a-olefin elastomers have a melting point (DSC) of less than 1 15°C or 1 10°C or 100°C or 90°C or 80°C; or more preferably within the range of from 10°C or 15°C or 20°C or 25°C to 65°C or 75°C or 80°C or 95°C or 105°C or 1 10°C or 115°C. In certain embodiments, the propylene-a-olefin elastomers have no discernable melting point but are better described by their Vicat softening temperature. Whether the copolymers have a melting point or not, the propylene-a-olefin elastomers preferably have a Vicat softening temperature (ISO 306, or ASTM D1525) of less than 120°C or 110°C or 105°C or 100°C, or within a range of from 50°C or 60°C to 110°C or 120°C, or a very particular range of from 70°C or 80°C to 100°C or 1 10°C. Preferably, the softening point of the polypropylene is at least 5°C or 10°C or 15°C or 20°C higher than the softening point of the propylene-a-olefin elastomers used as an additive.

[0020] Preferably, the propylene-a-olefin elastomers have an Hf, determined according to DSC, within the range of from 0.5 J/g or 1 J/g or 5 J/g to 35 J/g or 40 J/g or 50 J/g or 65 J/g or 75 J/g. In certain embodiments, the H _f value is less than 75 J/g or 60 J/g or 50 J/g or 40 J/g. Preferably, the propylene-a-olefin elastomers have a percent crystallinity within the range of from 0.5% to 40%, and from 1% to 30% in another embodiment, and from 5% to 25% in yet another embodiment, wherein "percent crystallinity" is determined according to the DSC procedure described herein. The thermal energy for the highest order of polypropylene is estimated at 189 J/g (i.e., 100% crystallinity is equal to 189 J/g). Preferably, the propylene-a-olefin elastomers have a glass transition temperature (Tg) within the range of from -50°C or -40°C to -10°C or 0°C.

[0021] Preferably, the propylene-a-olefin elastomers have a melt flow rate ("MFR," ASTM D1238, 2.16 kg, 230°C), within the range of from 0.5 g/10 min or 1 g/10 min or 1.5 g/10 min or 2 g/10 min to 4 g/10 min or 6 g/10 min or 12 g/10 min or 16 g/10 min or 20 g/10 min in other embodiments.

[0022] Preferably, the molecular weight distribution (Mw/Mn, MWD) of the propylene- a-olefin elastomers is within the range of from 1.5 or 1.8 or 2.0 to 3.0 or 3.5 or 4.0 or 5.0. Techniques for determining the molecular weight (Mn, Mz, and Mw) and molecular weight distribution (MWD) are as follows and as in Verstate et al. in 21 MACROMOLECULES 3360 (1988). Conditions described herein govern over published test conditions. Molecular weight and molecular weight distribution are measured using a Waters 150 gel permeation chromatograph equipped with a Chromatix KMX-6 on-line light scattering photometer. The system was used at 135°C with 1,2,4-trichlorobenzene as the mobile phase. Showdex™ (Showa-Denko America, Inc.) polystyrene gel columns 802, 803, 804, and 805 are used. This technique is discussed in LIQUID CHROMATOGRAPHY OF POLYMERS AND RELATED MATERIALS III 207 (J. Cazes ed., Marcel Dekker, 1981).

[0023] The propylene-a-olefin elastomers described herein can be produced using any catalyst and/or process known for producing polypropylenes. Preferred methods for producing the propylene-a-olefin elastomers are found in U.S. Patent Application Publication 2004/0236042 and U.S. Patent No. 6,881,800. Preferred propylene-a-olefin elastomers are available commercially under the trade names Vistamaxx™ (ExxonMobil Chemical Company, Houston, TX, USA) and Versify™ (The Dow Chemical Company, Midland, Michigan, USA), certain grades of Tafmer™ XM or Notio™ (Mitsui Company, Japan), or certain grades of Clyrell™ and/or Softel™ (LyondellBasell Polyolefins of the Netherlands).

[0024] Core Layer. The "polypropylene" that is preferably used in the core and other layers is a homopolymer or copolymer comprising from 60 wt% or 70 wt% or 80 wt% or 85 wt% or 90 wt% or 95 wt% or 98 wt% or 99 wt% to 100 wt% propylene-derived units, and comprising within the range of from 0 wt% or 1 wt% or 5 wt% to 10 wt% or 15 wt% or 20 wt% or 30 wt% or 40 wt% C _j _ and/or C ₄ to CIQ a-olefin derived units, and can be made by any desirable process using any desirable catalyst as is known in the art, such as a Ziegler- Natta catalyst, a metallocene catalyst, or other single-site catalyst, using solution, slurry, high pressure, or gas phase processes. Polypropylene copolymers are useful polymers in certain embodiments, especially copolymers of propylene with ethylene and/or butene, and comprise propylene-derived units within the range of from 70 wt% or 80 wt% to 95 wt% or 98 wt% by weight of the polypropylene. In any case, useful polypropylenes have a DSC melting point (ASTM D3418) of at least 125°C or 130°C or 140°C or 150°C or 160°C, or within a range of from 125°C or 130°C to 140°C or 150°C or 160°C. A "highly crystalline" polypropylene is preferred in certain embodiments of the inventive films, and is typically isotactic and comprises 100 wt% propylene-derived units (propylene homopolymer) and has a relatively high melting point of from greater than (greater than or equal to) 140°C or 145°C or 150°C or 155°C or l60°C or 165°C.

[0025] The term "crystalline," as used herein, characterizes those polymers which possess high degrees of inter- and intra-molecular order. Preferably, the polypropylene has a heat of fusion (H _f ) greater than 60 J/g or 70 J/g or 80 J/g, as determined by DSC analysis. The heat of fusion is dependent on the composition of the polypropylene; the thermal energy for the highest order of polypropylene is estimated at 189 J/g that is, 100% crystallinity is equal to a heat of fusion of 189 J/g. A polypropylene homopolymer will have a higher heat of fusion than a copolymer or blend of homopolymer and copolymer. Also, the polypropylenes useful in the inventive films may have a glass transition temperature (ISO 11357-1, Tg) preferably between -20°C or -10°C or 0°C to 10°C or 20°C or 40°C or 50°C. Preferably, the polypropylenes have a Vicat softening temperature (ISO 306, or ASTM D 1525) of greater than 120°C or 1 10°C or 105°C or 100°C, or within a range of from 100°C or 105°C to 110°C or 120°C or 140°C or 150°C, or a particular range of from 110°C or 120°C to 150°C.

[0026] Preferably, the polypropylene has a melt flow rate ("MFR", 230°C, 2.16 kg, ASTM D1238) within the range of from 0.1 g/10 min or 0.5 g/10 min or 1 g/10 min to 4 g/10 min or 6 g/10 min or 8 g/10 min or 10 g/10 min or 12 g/10 min or 16 g/10 min or 20 g/10 min. Also, the polypropylene may have a molecular weight distribution (determined by GPC) of from 1.5 or 2.0 or 2.5 to 3.0 or 3.5 or 4.0 or 5.0 or 6.0 or 8.0 in certain embodiments. Suitable grades of polypropylene that are useful in the oriented films described herein include those made by ExxonMobil, LyondellBasell, Total, Borealis, Japan Polypropylene, Mitsui, and other sources. Some specific examples of suitable polypropylenes include ExxonMobil PP-4612, 4712, or 4912, or Total PP-3371. A suitable high crystallinity polypropylene ("HCPP") is Total-3270.

[0027] Skin Layer Materials. The multi-layer films of the invention may have one, two or more skin layers, at least one each on either side of the core layer. These layers may desirably be sealable, that is, comprise components that can effectuate a seal with another part of the same film, a different film, or some other substrate such as paper, etc. A "first" skin layer may reside on the metalizable layer, sandwiching the metal layer and metalizable layer between the first skin and the core layer. A "second" skin layer is a skin layer that is adjacent to the core layer but opposite the metalizable layer. Preferably, one or both skin layers in the films of the invention include (or consist essentially of, or consist of) a polymer that is suitable for heat-sealing or bonding to itself when crimped between heated crimp- sealer jaws, or solvent sealable. Most preferably, only the second skin layer is sealable. Desirable polymers that make up the skin layers have a DSC melting point of from 120°C or 125°C or 130°C to 150°C or 160°C, a Shore D Hardness within the range of from 55 or 56 to 65 or 70, and a Flexural Modulus (ISO 178) of at least 500 MPa or 600 MPa or 650 MPa, or in another embodiment within the range of from 400 MPa or 500 MPa or 600 MPa to 800 MPa or 900 MPa or 1000 MPa or 1500 MPa or 2000 MPa. Commonly, suitable skin layer polymers include copolymers or terpolymers of ethylene, propylene, and butylene (EPB terpolymer, or C2/C3/C4 terpolymer) and may have DSC melting points of less than 140°C or

135°C, or within a range of from 100°C to 135°C or 140°C. In some preferred embodiments, the skin layers may also comprise a polymer selected from propylene homopolymer, ethylene-propylene copolymer, butylene homopolymer and copolymer, ethylene vinyl acetate (EVA), metallocene-catalyzed propylene homopolymer, polyethylene (low, linear low, medium or high), and combinations thereof. An example of a suitable EPB terpolymer is Japan Polypropylene Corp. propylene-based terpolymer 7510. In a particular embodiment, the skin layers consist essentially of one or more propylene-ethylene copolymers or propylene-ethylene-butylene terpolymers. Other examples of preferred commercially available resins include: XPM-7794 and XPM-7510 both C ₂ /C ₃ /C ₄ terpolymers available from Japan Polypropylene Corp; EP-8573 a C3/C2 copolymer available from Total Petrochemical Company; PB0300M and Adsyl™ 3C30FHP available from LyondellBasell.

[0028] Heat sealable blends of polymers can be utilized in a first, second, or both skin layers in the inventive films. Thus, along with the skin layer polymers identified above there can be, for example, other polymers, such as polypropylene homopolymer, for example, one that is the same as, or different from, the polypropylene of the core layer. The first skin layer may additionally or alternatively include materials selected from the group consisting of ethylene-propylene random copolymers, low-density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), and combinations thereof.

[0029] The first, second, or both skin layers may comprise (or consist essentially of) at least one polymer selected from the group consisting of a polyethylene (PE) polymer or copolymer, a polypropylene polymer or copolymer, an ethylene-propylene copolymer, an EPB terpolymer, a propylene-butylene (PB) copolymer, and combinations thereof. Preferably, the PE polymer is high-density polyethylene (HDPE), such as HD-6704.67 (ExxonMobil Chemical Company), M-6211 or HDPE M-6030 (Equistar Chemical Company). A suitable ethylene-propylene copolymer is Fina 8573 (Total). Preferred EPB terpolymers include Japan Polypropylene 7510 and 7794 (Japan Polypropylene Corp.). For coating and printing functions, the first skin layer may preferably comprise a copolymer that has been surface treated.

[0030] The first and/or second skin layer can also comprise (or consists essentially of) a styrenic block copolymer. Desirable polymer will have a density within the range of from 0.850 g/cc or 0.860 g/cc or 0.870 g/cc to 0.930 g/cc or 0.940 g/cc or 0.960 g/cc or 1.000 g/cc or 1.050 g/cc (ISO 1183). Preferably, the styrenic block copolymers comprise from 15 wt% or 20 wt% or 25 wt% to 35 wt% or 40 wt% or 45 wt% or 50 wt% styrenic derived units, by weight of the copolymer. Preferably, the styrenic block copolymer is a styrene- ethylene/butylene-styrene terpolymer having a melt flow rate (MFR, ASTM D 1238, 230°C at 2.16 kg) of from 0.5 g/10 min or 1 g/10 min or 2 g/10 min or 3 g/10 min to 6 g/10 min or 8 g/10 min or 10 g/10 min or 12 g/10 min. Desirable styrenic block copolymers may be SEBS or SBBS Tuftec™ styrenic elastomers from Asahi Kasei Chemicals; Chevron Phillips K- Resins™; and Kraton™ D or G elastomers.

[0031] The styrenic block copolymer may comprise from 50 wt% or 60 wt% or 70 wt% to 90 wt% or 100 wt%, by weight of the skin layer materials, of the skin layer. The skin layer may consist essentially of, or consist of, the styrenic block copolymer, but when other materials are present, skin layer materials or core layer materials may make up a portion or all of the remainder. Preferably, the skin layer(s) is made from a blend of the styrenic block copolymer and the ethylene-based polymers described above, the latter being present in the skin layer within a range of from 5 wt% or 10 wt% or 20 wt% to 40 wt% or 50 wt%, by weight of the skin layer.

[0032] Additives. Additives may be present in one or more layers of the multi-layer films of the invention. Typically, the additives are present, if at all, at a level of from 0.1 wt% or 0.5 wt% to 1 wt% or 2 wt% or 3 wt% or 5 wt%, by weight of the materials in the given layer. In some cases, such as for cavitating or opacifying agents, the amounts can be within the range of from 5 wt% to 10 wt% or 15 wt% or 20 wt% or 30 wt%, by weight of the given layer. Examples of additives include, but are not limited to, opacifying agents, pigments, colorants, cavitating agents, slip agents, antioxidants, anti-fog agents, anti-static agents, anti- block agents, fillers, moisture barrier additives, gas barrier additives, and combinations thereof. Such additives may be used in effective amounts, which vary depending upon the application and the property desired.

[0033] Examples of suitable opacifying agents, pigments, or colorants include iron oxide, carbon black, aluminum, titanium dioxide (TiC^), calcium carbonate (CaCC^), polybutylene terephthalate (PBT), talc, beta nucleating agents, and combinations thereof.

[0034] Cavitating or void-initiating additives may include any suitable organic or inorganic material that is incompatible with the polymer material(s) of the layer(s) to which it is added, at the temperature of biaxial orientation, in order to create an opaque film. Examples of suitable void-initiating particles are PBT, nylon, solid or hollow pre-formed glass spheres, metal beads or spheres, ceramic spheres, calcium carbonate, talc, chalk, or combinations thereof. The average diameter of the void-initiating particles typically may be within the range of from 0.1 μιη to 2 μιη or 3 μιη or 5 μιη or 8 μιη or 10 μιη. Cavitation may also be introduced by beta-cavitation, which includes creating beta- form crystals of polypropylene and converting at least some of the beta-crystals to alpha- form polypropylene crystals and creating a small void remaining after the conversion. Preferred beta-cavitated embodiments of the core layer may also comprise a beta-crystalline nucleating agent. Substantially any beta-crystalline nucleating agent ("beta nucleating agent" or "beta nucleator") may be used.

[0035] Slip agents may include higher aliphatic acid amides, higher aliphatic acid esters, waxes, silicone oils, and metal soaps. Such slip agents may be used in amounts ranging from about 0.1 wt% to about 2 wt%, based on the total weight of the layer to which it is added. An example of a slip additive that may be useful is erucamide.

[0036] Non-migratory slip agents, used in one or more skin layers of the multi-layer films, may include polymethyl methacrylate (PMMA). The non-migratory slip agent may have a mean particle size in the range of from about 0.5 μιη to about 8 μιη, or about 1 μιη to about 5 μιη, or about 2 μιη to about 4 μιη, depending upon layer thickness and desired slip properties. Alternatively, the size of the particles in the non-migratory slip agent, such as PMMA, may be greater than about 20% of the thickness of the skin layer containing the slip agent, or greater than about 40% of the thickness of the skin layer, or greater than about 50% of the thickness of the skin layer. The size of the particles of such non-migratory slip agents may also be at least about 10% greater than the thickness of the skin layer, or at least about 20% greater than the thickness of the skin layer, or at least about 40% greater than the thickness of the skin layer. Generally, spherical, particulate non-migratory slip agents are contemplated, including PMMA resins, such as Epostar™ (commercially available from Nippon Shokubai Co., Ltd.). Other commercial sources of suitable materials are also known to exist. "Non- migratory" means that these particulates generally do not change location throughout the layers of the film in the manner of migratory slip agents. A conventional polydialkyl siloxane, such as silicone oil or gum additive having a viscosity within the range of from 10,000 or 20,000 or 50,000 to 500,000 or 800,000 or 1,000,000 or 2,000,000 centistokes (25°C) is also contemplated.

[0037] Suitable anti-oxidants may include phenolic anti-oxidants, such as Irganox™ 1010 (Ciba Specialty Chemicals). Such an anti-oxidant is generally used in amounts ranging from about 0.1 wt% to about 2 wt%, based on the total weight of the layer(s) to which it is added.

[0038] Anti-static agents may include alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, and tertiary amines. Such anti-static agents may be used in amounts ranging from about 0.05 wt% to about 3 wt%, based upon the total weight of the layer(s).

[0039] Examples of suitable anti-blocking agents may include silica-based products such as Sylobloc™ 44 (Grace Davison Products), PMMA particles such as Epostar (Nippon Shokubai Co., Ltd.), or polysiloxanes such as Tospearl™ (GE Bayer Silicones). Such an anti-blocking agent comprises an effective amount up to about 3000 ppm of the weight of the layer(s) to which it is added.

[0040] Fillers may include finely divided inorganic solid materials, such as silica, fumed silica, diatomaceous earth, calcium carbonate, calcium silicate, aluminum silicate, kaolin, talc, bentonite, clay, wollastonite, and pulp.

[0041] Suitable moisture and gas barrier additives may include effective amounts of low- molecular weight resins, hydrocarbon resins, particularly petroleum resins, styrene resins, cyclopentadiene resins, and terpene resins.

[0042] Optionally, one or more skin layers may be compounded with a wax or coated with a wax-containing coating, for lubricity, in amounts ranging from about 2 wt% to about 15 wt% based on the total weight of the skin layer. Any conventional wax, such as, but not limited to, Carnauba™ wax (commercially available from Michelman Corporation) and Be Square™ wax (commercially available from Baker Hughes Corporation) that is useful in thermoplastic films is contemplated.

[0043] The multi-layered film. The inventive films may be made by any desirable technique. Preferably, prior to metalizing the film, the films are biaxially oriented. The inventive films can be made and oriented by any suitable technique known in the art, such as a cast, tentered, blown process, LISIM™, and others. Further, the working conditions, temperature settings, line speeds, etc. will vary depending on the type and the size of the equipment used. Nonetheless, described generally here is one method of making the films described throughout this specification. In a particular embodiment, the films are formed and biaxially oriented using the "tentered" method. In the tentered process, line speeds of greater than 100 m/min to 400 m/min or more and outputs of greater than 2000 kg/hr to 4000 kg/hr or more are achievable. In the tenter process, sheets/films of the various materials are melt blended and coextruded, such as through a 3, 4, 5, 7-layer die head, into the desired film structure. Extruders ranging in diameters from 100 mm to 300 mm or 400 mm, and length to diameter ratios ranging from 10/1 to 50/1 can be used to melt blend the molten layer materials, the melt streams then metered to the die having a die gap(s) within the range of from 0.5 or 1 nm to an upper limit of 3 or 4 or 5 or 6 mm. The extruded film is then cooled using air, water, or both. Typically, a single, large diameter roll partially submerged in a water bath, or two large chill rolls set at 20°C or 30°C to 40°C or 50°C or 60°C or 70°C are suitable cooling means. As the film is extruded, an air knife and edge pinning are used to provide intimate contact between the melt and chill roll.

[0044] Downstream of the first cooling step in this embodiment of the tentered process, the unoriented film is reheated to a temperature of from 80°C to 100°C or 120°C or 150°C, in one embodiment by any suitable means such as heated S-wrap rolls, and then passed between closely spaced differential speed rolls to achieve machine direction orientation. It is understood by those skilled in the art that this temperature range can vary depending upon the equipment, and in particular, upon the identity and composition of the components making up the film. Ideally, the temperature will be below that which will melt the film, or cause it to become tacky and adhere to the equipment, but high enough to facilitate the machine direction orientation process. Such temperatures referred to herein refer to the film temperature itself. The film temperature can be measured by using, for example, Infrared spectroscopy, the source aimed at the film as it is being processed; those skilled in the art will understand that for transparent films, measuring the actual film temperature will not be as precise. In this case, those skilled in the art can estimate the temperature of the film by knowing the temperature of the air or roller immediately adjacent to the film measured by any suitable means. The heating means for the film line may be set at any appropriate level of heating, depending upon the instrument, to achieve the stated film temperatures.

[0045] The lengthened and thinned film is cooled and passed to the tenter section of the line for TD orientation. At this point, the edges of the sheet are grasped by mechanical clips on continuous chains and pulled into a long, precisely controlled hot air oven for a preheating step. The film temperatures range from 100°C or 110°C to 150°C or 170°C or 180°C in the pre-heating step. Again, the temperature will be below that which will melt the film, or cause it to become tacky and adhere to the equipment, but high enough to facilitate the step of transverse direction orientation. Next, the edges of the sheet are grasped by mechanical clips on continuous chains and pulled into a long, precisely controlled hot air oven for transverse stretching. As the tenter chains diverge, a desired amount to stretch the film in the transverse direction, the film temperature is lowered by at least 2°C but typically no more than 20°C relative to the pre-heat temperature to maintain the film temperature so that it will not melt the film. After stretching to achieve transverse orientation in the film, the film is then cooled from 5°C to 10°C or 15°C or 20°C or 30°C or 40°C below the stretching temperature, and the clips are released prior to edge trim, optional coronal, printing and/or other treatment can then take place, followed by winding.

[0046] Thus, TD orientation is achieved by the steps of pre-heating the film having been machine oriented, followed by stretching it at a temperature below the pre-heat temperature of the film, and then followed by a cooling step at yet a lower temperature. In one embodiment, the films described herein are formed by imparting a transverse orientation by a process of first pre-heating the film, followed by a decrease in the temperature of the film within the range of from 2°C or 3°C to 5°C to 10°C or 15°C or 20°C relative to the preheating temperature while performing transverse orientation of the film, followed by a lowering of the temperature within the range of from 5°C to 10°C or 15°C or 20°C or 30°C or 40°C relative to the stretching temperature, holding or slightly decreasing (by no more than 5%) the amount of stretch, to allow the film to "anneal." The latter step imparts (reduces or minimizes) the high TD shrink characteristics of the films described herein, thus improving dimensional stability. In certain embodiments, the dimensional stability of the films described herein is within 15% or 10% or 8% at 135°C after 5-10 minutes in either the MD or TD as otherwise measured by ASTM D1204. Thus, for example, where the pre-heat temperature is 120°C, the stretch temperature may be 114°C, and the cooling step may be 98°C, or any temperature within the ranges disclosed. The steps are carried out for a sufficient time to affect the desired film properties as those skilled in the art will understand. After stretching, the films may be treated such as by flame, plasma, or coronal treatments as are well known in the art, and then have a layer of metal applied thereto. Preferably, the metalizable layer is treated prior to applying a metal layer. [0047] After the metalizable skin layer has been subjected to appropriate surface treatment, generally in accordance with the process of this invention, the multi-layer films herein will have deposited on the metalizable layer having the requisite composition as described herein a thin layer comprising an elemental metal component. The outer surface(s) of the metalizable layer may be metalized such as by vacuum deposition, or any other metalization technique, such as electroplating or sputtering. The metal is preferably aluminum, but may be any other metal capable of being vacuum deposited, electroplated, or sputtered, such as, for example, gold, zinc, copper, or silver. Techniques for polymeric film metalization are well known. For example, procedures for depositing a metal layer onto a polymeric film layer are described in greater detail in WO 2004/091884.

[0048] The inventive films preferably would have a 3 -layer structure with one side skin sealable (as copolymer or terpolymers). The other skin would be the metalizable skin with the acid-modified polypropylene additive in a polypropylene matrix. The metalizable skin should not be too soft. If too soft, the metal coating may crack easily (crazing) when the film is folded or handled. The polypropylene skin for metallization would be more resistant to metal cracking, but shows lower metal adhesion. Therefore adding small quantity of acid- modified polypropylene wax into a polypropylene skin is surprisingly found to not affect the metalizable skin's hardness, but improves its metal adhesion.

[0049] The resulting multi-layered films described herein have many desirable properties. Preferably, the films have a haze value of less than 10% or 8% or 5% or 4% or 3%. Further, prior to metalizing the film, the Young's Modulus (MD) of the film is preferably at least 200 or 220 kpsi, or more preferably within the range of from 200 or 250 to 320 or 350 kpsi. Also, the Young's Modulus (TD) of the film is preferably at least 500 or 520 kpsi, or more preferably within the range of from 500 or 520 to 560 or 600 kpsi. Also, prior to metalizing the film, the Ultimate Tensile Strength (MD) of the inventive films is preferably at least 15 or 16 or 17 kpsi, or more preferably within the range of from 15 or 16 to 25 or 30 kpsi. Finally, the Ultimate Tensile Strength (TD) of the film is preferably at least 30 or 32 or 35 kpsi, or more preferably within the range of from 30 or 32 to 40 or 45 kpsi.

[0050] In any case, the metalized films have a low water vapor and oxygen permeability. Preferably, the multi-layered films have a water vapor transmission rate ("WVTR") of less than 0.30 or 0.10 or 0.08 or 0.05 g/m ² at 100°F/90RH. The oxygen transmission rate ("OTR") of the multi-layered metalized films is preferably less than 20 or 15 or 12 or 10 70°F/0RH, cc/m ² /day. These features and the others described herein give the inventive films desirable qualities as packaging for many types of articles, especially packaging for food items.

[0051] Described below are non-limiting examples of the inventive films.

EXAMPLES

[0052] Acid-modified polypropylenes were obtained from Baker Petrolite Polymers Group and blended in various amounts with another base polymer to form a metalizable film layer. The acid-modified polypropylenes of Table 1 were blended at a level of 1 wt% with polypropylene homopolymers or copolymers and formed into 0.7 mil films. The films were coextruded into three-layer films (ExxonMobil PP-4712 core layer, Japan Polypropylene 7320 skin layer), biaxially oriented, and the acid-modified skin layer was corona treated and metalized. Samples of this film were then tested for water vapor transmission, haze, metal adhesion, surface tension, and coefficient of friction. The results of this testing is in Table 2. Tests are as follows:

• Metal adhesion test: In particular, a strip of Scotch™ 610 tape approximately 4 inches in length is smoothed out over the metalized surface layer in the transverse direction. The tape strip is then peeled off at an angle of approximately 150 degrees, and the percentage of metal picked off is visually inspected and estimated.

• Surface tension test: ASTM Standard D2578-84.

. Barrier Properties: ASTM F1249.

. Haze: ASTM D 1003.

· Coefficient of friction: The static coefficient of friction is measured with a 4-lb sled with a 45-second delay using a Monitor/Slip Friction™ tester Model No. 32-06 made by Testing Machines Inc., Amityville, N.Y.).

• The "Young's Modulus" is the equivalent of the Elastic Modulus or 1% Secant Modulus, measured per ASTM D 882.

· Ultimate tensile strength within the range of from 15 or 18 to 28 or 34 kpsi in the MD in other embodiments, measured according to ASTM D882.

Table 1. Materials

NiMH ¹ Diseripl idii Sfiiiri

acid-PPl C3/< 26 copolymer, Mn=2000, maleic anhydride Baker Petrolite Polymers Group

graf ted

acid-PP2 C3 1 lomopolymer, Mn=1000, maleic anhydride Baker Petrolite Polymers Group

graf ted

acid-PP3 C3 1 lomopolymer, Mn=2500, maleic anhydride Baker Petrolite Polymers Group

graf ted

acid-PP4 C3 1 lomopolymer, Mn=8000, maleic anhydride Baker Petrolite Polymers Group

graf ted

acid-PP5 C3/( 26 copolymer, Mn=8000 Baker Petrolite Polymers Group

PP-A ethy lene-propylene copolymer Total Petrochemical Co.

MF] I 6.8 g/10 min, MP = 135°C

PP-B Min i random C2/C3 polypropylene copolymer, ExxonMobil Chemical Co.

MP = 158°C-159°C , MFR= 2.8 g/10 min; FM

= 8C O MPa

PP-C Higl l crystallinity polypropylene homopolymer Total Petrochemical

EP Proj )ylene-a-olefm elastomer, 9 wt% C2, MP = ExxonMobil Chemical Co.,

79° ₍ AH _f = 33.5 J/g, MFR= 8 g/10 min Vistamaxx™

Table 2. Formulations, acid-modified PP properties, and Test Results

[0053] In a second set of examples as set forth in Table 3, film samples were produced on "semiworks" line with 3-layer film structure. The gauge ratios for the film layers are typically 3/72/3, where the total thickness is about 50 μιη. The line includes a 3.5 inch (8.89 cm) extruder with L/D ratio of 32: 1, single flight, double compression screw with a Maddock mixing head, smooth bore. Unless otherwise specified, the temperatures of the three zones in the TD tenter stretching unit are 355°F/320°F/315°F (±5°F), or 179°C/160°C/157°C (±3°C). The non-metalized side has a skin of EPB terpolymer (XPM-7320 from JPC), the core layer was ExxonMobil PP-4712E2. The metalization side skin materials are listed in the table below. Three of the samples contain HCPP 3270 from Total Petrochemical. The last sample had ExxonMobil PP-4712 E2 as the main resin in the skin. The modulus and tensile strength were measured prior to metalization. Units of WVTR are 100°F/90RH, g/m ² /day. Units of OTR are 70°F/0RH, cc/m ² /day. The Coefficient of Friction is determined as above, only a 200 g sled is used.

Table 3. Second set of experimental films with acid-modified PP additive

[0054] Now, having described the various features of the inventive films, described herein in numbered embodiments are:

1. A multi-layer film comprising:

a core layer comprising a polyolefin;

a metalizable layer in surface contact with the core layer, the metalizable layer comprising 0.10 wt% to 2 wt% or 5 wt% or 10 wt% or 15.0 wt% of an acid- modified polypropylene having a number-average molecular weight (Mn) of from 300 or 500 or 800 g/mol to 10,000 or 20,000 or 50,000 or 80,000 g/mol and comprising at least one functional group selected from the group consisting of alkoxy, ester, anhydride, carboxylic acid, amine, nitrile, imine, silane, siloxane, sulfonate, alkane, aldehyde, epoxide, organoborane, ethoxylate, propoxylate, higher alkoxylate, halogen, and combinations thereof; and

optionally, a metal layer in surface contact with the metalizable layer.

2. A multi-layer film comprising:

a core layer comprising a polypropylene;

a metalizable layer in surface contact with the core layer, the metalizable layer comprising 0.10 wt% to 2 wt% or 5 wt% or 10 wt% or 15.0 wt% of an acid- modified polypropylene having a number-average molecular weight (Mn) of from 300 or 500 or 800 g/mol to 10,000 or 20,000 or 50,000 or 80,000 g/mol and comprising at least one functional group selected from the group consisting of alkoxy, ester, anhydride, carboxylic acid, aldehyde, and combinations thereof, and the remainder of the metalizable layer comprising polypropylene; and

a metal layer in surface contact with the metalizable layer;

wherein the modulus (MD or TD) of the film is within less than 5% or 10% the value of the modulus for a similar film having from 10 wt% to 20 wt% of a propylene-a-olefin elastomer instead of the acid-modified polypropylene in the metalizable layer.

3. The film of either one of embodiments 1 or 2, wherein the functional group is selected from the group consisting of alkoxy, ester, anhydride, carboxylic acid, aldehyde, and combinations thereof.

4. The film of any one of the previous numbered embodiments, wherein the acid-modified polypropylene has a melting point within the range from 20°C or 30°C to 100°C or 120°C or 140°C.

5. The film of any one of the previous numbered embodiments, wherein the viscosity of the acid-modified polypropylene is within the range from 10 or 20 or 30 cP to 500 or 800 or 1000 cP (149°C).

6. The film of any one of the previous numbered embodiments, wherein the average number of acid sites per polymer chain of the acid-modified polypropylene is within the range from 5 or 10 or 15 to 50 or 80 or 100 or 150 or 200.

7. The film of any one of the previous numbered embodiments, having a haze value of less than 10% or 8% or 5% or 4% or 3%.

8. The film of any one of the previous numbered embodiments, wherein the Young's Modulus (MD) of the film is at least 200 or 220 kpsi, or within the range of from 200 or 250 to 320 or 350 kpsi.

9. The film of any one of the previous numbered embodiments, wherein the Young's Modulus (TD) of the film is at least 500 or 520, or within the range of from 500 or 520 to 560 or 600 kpsi.

10. The film of any one of the previous numbered embodiments, wherein the Ultimate Tensile Strength (MD) of the film is at least 15 or 16 or 17 kpsi, or within the range of from 15 or 16 to 25 or 30 kpsi.

1 1. The film of any one of the previous numbered embodiments, wherein the Ultimate Tensile Strength (TD) of the film is at least 30 or 32 or 35 kpsi, or within the range of from 30 or 32 to 40 or 45 kpsi.

12. The film of any one of the previous numbered embodiments, further comprising the metal layer in surface contact with the metalizable layer.

13. The film of any one of numbered embodiments 2-12, having a water vapor transmission rate ("WVTR") of less than 0.10 or 0.30 or 0.08 or 0.05 g/m ² at 100°F/90RH.

14. The film of any one of the previous numbered embodiments, wherein the metalizable layer is flame, plasma, or corona treated on the side which makes contact with the metal layer.

15. The film of any one of the previous numbered embodiments, further comprising a second skin layer in contact with the core layer opposite the metalizable layer.

16. The film of any one of the previous numbered embodiments, wherein the film is biaxially oriented.

17. A sealed bag containing articles comprising the film of any one of the previous numbered embodiments. The invention described herein also includes the use of a film for producing a package for containing articles, especially food articles, the film of any one of the previous numbered embodiments.