WO2007133383A1

WO2007133383A1 - Multilayer adhesive polymer film

Info

Publication number: WO2007133383A1
Application number: PCT/US2007/009531
Authority: WO
Inventors: Robert L. Mcgee; James P. Maher
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2006-05-09
Filing date: 2007-04-19
Publication date: 2007-11-22
Anticipated expiration: 2008-11-09

Abstract

A multilayer adhesive polymer film structure that includes at least three layers, one of which forms an adhesive bond with, for example, electrolytically chrome coated steel, is useful for forming metal plastic laminates that may be converted via cold forming into products such as aerosol valve caps that resist delamination when immersed in methylene chloride, give clean edge cuts and evidence little, if any, tensile stress whitening.

Description

MULTILAYER ADHESIVE POLYMER FILM

This application claims the benefit of U.S. Provisional Application 60/798,991, filed May 9, 2006.

The present invention relates generally to a multilayer adhesive polymer film and more particularly to a multilayer film that includes at least three layers, one of which is an outer adhesive layer that forms an adhesive bond with a metal, preferably steel (for example, tin plate steel or electrolytically chrome coated steel (ECCS)) thereby forming a metal plastic laminate (MPL) that resists delamination when the laminate is immersed in methylene chloride (MeCl₂) for a period of at least forty-eight (48) hours. The present invention also relates to use of the multilayer adhesive polymer film as a gasket when the MPL is used to fabricate articles of manufacture such as an aerosol valve cap.

European Patent Application (EP) 0 417 380 Bl teaches food packaging containers formed from a deep-drawable laminate sheet that comprises aluminum foil and at least one thermoplastic resin layer joined to a surface of the aluminum foil. The thermoplastic resin layer may be made of a polyolefin such as polypropylene (PP) or polyethylene (PE), polyester, polyvinyl chloride (PVC), polycarbonate (PC), polystyrene (PS), copolymers of such resins, or a blend thereof. The thermoplastic resin layer may comprise a single thermoplastic resin, an unstretched co-extrudate of at least two layers or at least two thermoplastic resin layers separably joined by an adhesive layer. One such coextrudate is a layer of high density polyethylene (HDPE) and a layer of either PP or a mixture of PP and PE.

EP 0 828 609 B 1 discusses protective coatings for a metal (for example, steel) surface that comprise a two layer adhesive film (a first layer of a copolymer of ethylene and acrylic acid (EAA) and a second layer that consists essentially of a blend of LDPE and maleic anhydride (MAH)) that adheres the coating to the metal surface and an extrudate of low density polyethylene (LDPE) that overlays the second layer of the two layer adhesive film. While the EAA copolymer provides an acceptable delamination resistant bond for such end uses, EAA polymers tend to dissolve in MeCl₂. If used as the metal adhesive layer, dissolution of the polymer in MeCl₂ leads to delamination. United States Patent (USP) 4,945,008 teaches laminated metal sheets that comprise a metal sheet having adhered to one of its major surfaces a composite coextruded, polyolefin- containing film. The film comprises a plurality of sequential layers as follows: an inner layer of a bonding resin that is an acid modified polyolefin (for example, PP or PE) resin containing carboxyl or anhydride groups; a layer of polyolefin; a second layer of the bonding resin; and a layer of polyamide. Typical carboxyl group-containing resins include copolymers of ethylene and acrylic acid or methacrylic acid and an illustrative anhydride is maleic anhydride (MAH).

EP 0 659 552 relates to a PP laminated film with good low-temperature heat sealability. The film comprises a layer of crystalline PP and a layer of a random copolymer of propylene and at least one four to ten carbon atom (C₄-Ci o) alpha (α)-olefin on at least one side of the crystalline PE layer. The amount of α-olefin preferably ranges from 15 to 30 percent by weight (wt%), based on copolymer weight. The random copolymer must be obtainable by gas phase polymerization substantially in the absence of a liquid medium using a specific solid catalyst. The laminated film may be prepared by any of a variety of methods including coextrusion.

USP 4,449,014 teaches MPLs with improved high and/or low temperature adhesion to various substrates such as cable jacketing resins. The MPLs include a multiple layered thermoplastic adhesive system that comprises a first thermoplastic layer of a random copolymer of ethylene and an ethylenically unsaturated carboxylic acid monomer and a second thermoplastic layer comprising a polymer blend of a random copolymer of ethylene and an ethylenically unsaturated carboxylic acid monomer and at least one different olefin polymer resin that is not a random copolymer of ethylene and an ethylenically unsaturated carboxylic acid monomer. The metal contacting layer may comprise polymers such as normally solid random copolymers of a major proportion of ethylene and a minor proportion of an ethylenically unsaturated carboxylic acid monomer. The latter term includes carboxylic acids, acid anhydrides and partial esters of polybasic acids and their salts. USP 4,980,210 proposes laminated materials that comprise a polyolefin-based film bonded to a metal sheet. The polyolefin-based film is a multi-layer coextruded film comprising an inner layer of a bonding resin that is an acid modified polyolefin resin containing carboxyl or anhydride groups and an outer layer of a polyolefin or polyamide that contains an amount of low opacity synthetic silica. An aspect of the present invention is a coextruded multilayer film comprising: a. a first external film layer, the first external film layer comprising at least one anhydride-grafted olefin polymer; b. a second external film layer, the second external film layer comprising at least one propylene homopolymer; and c. an intermediate film layer that is interposed between, and in a delamination-resistant, adhesive-free bond with, both the first and second external film layers, the intermediate film layer comprising a blend of at least one polypropylene homopolymer, at least one anhydride-grafted linear olefin polymer; at least one random propylene-ethylene copolymer, and, at least one ethylene polymer having a density no more than 0.915 g/cm³; the multilayer film having a one percent secant modulus (1% SM) (machine direction (MD)) of at least 50,000 pounds per square inch (345 megapascals), a percent haze, determined in accordance with ASTM D- 1003, of no more than 30 percent, and a Rockwell/Wilson Superficial Hardness (RWSH) (applied load) of at least 20, but less than 40, preferably greater than 27 and less than 33.

The foregoing multilayer film or MLF preferably also meets several additional requirements. First, it should form a bond, when laminated to steel, especially ECCS and tin plate steel, to form a MPL, classified as "delamination-resistant". An MPL merits such a classification if, following immersion in MeCl₂ for a period of at least 48 hours (hrs), it is substantially free of visible signs of delamination either of the MLF as a whole from the steel or between any two layers of the MLF itself. Second, when used in a MPL, it should not separate or delaminate from the metal of the MPL during stamping or cold forming operations. In addition to resisting delamination during such operations, the MLF should show no visible signs of stress whitening. While some stress whitening may occur, it preferably occurs to such a small extent that is effectively masked or rendered visibly indistinguishable from the metal of the MPL following stamping. The MLF is preferably substantially free of stress whitening. Third, the MLF preferably passes a Die Cut Test (explained in detail below). Simply stated, when subjected to die cutting, the MLF preferably yields a clean, sharp-edged cut surface that is substantially free of tattered remnants from either that portion removed by die cutting or the MLF from which the die cut portion is removed. In addition, die cut portion segments proximate to the cut surface are preferably substantially free of residual indications of stretching (for example, stretch lines). Finally, the MLF has a 1 percent secant modulus in the machine direction (1% SM (MD)) of at least 50,000 psi (345 MPa), preferably at least 60,000 psi (414 MPa) and more preferably at least 75,000 psi (517 MPa). The 1% SM (MD) preferably does not exceed 125,000 psi (862 MPa). A 1% SM (MD) less than 50,000 psi (345 MPa) is undesirable because the film and MPL is too soft and causes irregularities during the stamping operation (ripples/creases in the plastic surface). A 1% SM (MD) greater than 125,000 psi (862 MPa) is undesirable because the film and MPL becomes too stiff to act as an effective gasket material( that is, needs to conform slightly to form a gasket ). A 1 % SM (MD) less than 50,000 psi (345 MPa) gives a MLF that deforms too easily for a MPL made with the MLF to be useful as a gasketing material, thereby meriting a failed or F rating. A 1 % SM (MD) in excess of 125,000 psi (862 MPa) yields a MLF that is too stiff to deform sufficiently for a MPL made with the MLF to be useful as a gasketing material, thereby warranting an F rating. A 1% SM (MD) of from 50,000 psi (345 MPa) to 125,000 psi (862 MPa) gives a MLF that, when converted to a MPL, provides satisfactory results when the MPL is used as a gasketing material.

All percentages, preferred amounts or measurements, ranges and endpoints thereof . herein are inclusive, that is, "less than about 10" includes about 10. "At least" is, thus, equivalent to "greater than or equal to," and "at most' is, thus, equivalent "to less than or equal to." Numbers herein have no more precision than stated. Thus, "105" includes at least from 104.5 to 105.49. Furthermore, all lists are inclusive of combinations of two or more members of the list. AU ranges from a parameters described as "at least," "greater than," "greater than or equal to" or similarly, to a parameter described as "at most," "up to,"' "less than," "less than or equal to" or similarly are preferred ranges regardless of the relative degree of preference indicated for each parameter. Thus a range that has an advantageous lower limit combined with a most preferred upper limit is preferred for the practice of this invention. AJl amounts, ratios, proportions and other measurements are by weight unless stated otherwise. All percentages refer to weight percent based on total composition according to the practice of the invention unless stated otherwise, except that percentages of monomers in a polymer are weight percentages unless stated otherwise. Unless stated otherwise or recognized by those skilled in the art as otherwise impossible, steps of processes described herein are optionally carried out in sequences different from the sequence in which the steps are discussed herein. Furthermore, steps optionally occur separately, simultaneously or with overlap in timing. For instance, such steps as heating and admixing are often separate, simultaneous, or partially overlapping in time in the art. Unless stated otherwise, when an element, material, or step capable of causing undesirable effects is present in amounts or in a form such that it does not cause the effect to an unacceptable degree it is considered substantially absent for the practice of this invention. Furthermore, the terms "unacceptable" and "unacceptably" are used to refer to deviation from that which can be commercially useful, otherwise useful in a given situation, or outside predetermined limits, which limits vary with specific situations and applications and may be set by predetermination, such as performance specifications. Those skilled in the art recognize that acceptable limits vary with equipment, conditions, applications, and other variables but can be determined without undue experimentation in each situation where they are applicable. In some instances, variation or deviation in one parameter may be acceptable to achieve another desirable end. The first external layer, which functions as an adhesive layer, comprises at least one anhydride grafted olefin polymer, preferably a maleic anhydride grafted (MAH-g-) olefin polymer. The olefin polymer is preferably MAH-g-LLDPE, such as PLEXAR™ PX3060 (Equistar Chemicals, LP) or AMPLIFY™ GR207 (The Dow Chemical Company). While MAH-g-LLDPE may be the sole polymeric component of the first external layer (for example, 100 percent by weight (wt%), based upon total olefin graft polymer weight), especially desirable results may be obtained with up to 50 wt%, based upon total olefin graft polymer weight, of a second MAH-g-olefin polymer such as MAH-g-HDPE (for example, PLEXAR™ PX2220, Equistar Chemicals, LP) or AMPLIFY™ GR205 (The Dow Chemical Company). More preferably, the amount of MAH-g-LLDPE exceeds that of MAH-g- HDPE. The first external layer optionally also contains processing aids to provide additional processability, such as to lubricate in extrusion. Such processing aids are exemplified by a lubricant believed to be a fluoroelastomer in LLDPE commercially available from Ampacet, Inc. under the trade designation Ampacet 102113. Preferred MAH-g-olefin polymers have a melting point, determined by Differential Scanning Calorimetry (DSC), in excess of 1 15 degrees centigrade (⁰C), more preferably at least about 120⁰C. The melting point of each anhydride grafted ethylene polymer or polymer in the first exterior layer, and more preferably also in the intermediate layer, are preferably less than about 140 ⁰C, more preferably less than about 135 ⁰C, and most preferably less than about 130⁰C. Sources of such graft polymers other than Equistar include E. I. du Pont de Nemours and Company and The Dow Chemical Company.

The second external layer, which functions as a barrier layer, comprises a) at least one homopolymer polypropylene or PP; and, optionally, b.) at least one propylene/ethylene (P/E) random copolymer (RCP). If one desires to use the MLF of the present in applications where the barrier layer will contact, for example, food products or beverages, the polymers and any other constituents of the second external layer should be selected from among polymers approved by the United States Food and Drug Administration (FDA) or comparable regulatory authority in any country where the multilayer film is to be used in such an application. ^••* ^"

The second external or barrier layer preferably has a PP content of at least about 20, more preferably at least about 30, most preferably at least about 40 weight percent and, when present, a P/E RCP content of at least about 35 wt%, more preferably at least about 40 wt%, and preferably at most about 80 wt% and more preferably at most about 75 wt% in each case based upon combined weight of PP, and optional P/E RCP

It is believed that PP, in the amounts stated above for the barrier layer, provide the MLF with sufficient temperature resistance to enable the MLF to be hot roll laminated to a metal substrate substantially without sticking to the hot rolls. It is also believed that composition of the barrier layer must have sufficient compatibility with composition of the intermediate or core layer to effectively eliminate interlayer delamination between the barrier layer and the core layer during metal stamping, for example, cold stamping, processes. Such compatibility follows from selection of components that are common between the two layers. The PP is preferably a "cast grade" homopolymer, more preferably with a melt flow rate (MFR), determined in accord with American Society for Testing and Materials (ASTM) D- 1238 (230°C, 2.16 kilogram (kg) weight) of at least 5 decigrams per minute (dg/min), still more preferably at least 8 dg/min. A variety of commercial grade PP resins may bemused including, but not limited to DX5E66 or H700-12, both available from The Dow Chemical Company. If the PP has a MI less than 5 dg/min, preparation of a cast film becomes increasingly difficult as extruder back pressure increases to a point where melt fracture, flow instability or both can occur. The MI preferably does not exceed 20 dg/min in order to avoid unacceptable layer profiles as evidenced by non-uniform layer thicknesses across a film layer width. The term "cast grade", as used herein, refers to a resin with a MFR greater than 3 dg/min, preferably greater than 5 dg/min.

The P/E RCP, when included in the second external layer, like PP, is preferably a cast grade copolymer, more preferably a cast grade copolymer with a MFR of at least 1.9 dg/min. The MFR is preferably less than 20 dg/min. The P/E RCP has a polymerized ethylene content that is preferably within a range of from 1 wt% to 10 wt%, more preferably • within a range of from 2 wt% to 5 wt%, in each case based upon RCP weight. If the P/E

RCP has a MFR less than 1.9 dg/min, preparation of a cast film becomes increasingly difficult as extruder back pressure increases to a point where melt fracture, flow instability or both can occur. Conversely, a MFR of more than 20 dg/rnin tends to make the second - external layer formulation have too much flow and makes the layers profile hard to control during coextrusion. Illustrative RCPs include 6D20 and DS6D21 propylene polymer resins commercially available from The Dow Chemical Company. The intermediate film layer, sometimes referred to as the "core" layer, preferably comprises at least four polymers. The three polymers are at least one PP, at least one P/E RCP; and, at least one ethylene polymer having a density no more than 0.915 g/cm³ and at least one anhydride-grafted linear olefin polymer, preferably a maleic anhydride-grafted linear ethylene polymer (MAH-g-PE) such as MAH-g-LLDPE with or without MAH-g- HDPE. Except for the ethylene polymer, each of such polymers is described above in connection with either the first external layer or the second external layer. The PP is preferably at least about 15, more preferably at least about 25, most preferably at least about 50 and preferably at most about 70, more preferably at most about 65, most preferably at most about 60 weight percent based on the combined weight of the components, or blend, of the intermediate layer. The P/E RCP is preferably at least about 10, more preferably at least about 12, most preferably at least about 15 and preferably at most about 60, more preferably at most about 40, most preferably at most about 20 weight percent. The MAH-g-PE, or combination thereof, is preferably at least about 3, more preferably at least about 5, most preferably at least about 7 and preferably at most about 15, more preferably at most about 13, most preferably at most about 12 weight percent. The ethylene polymer having a density no more than 0.915 g/cm³ is preferably at least about 4, more preferably at least about 10, most preferably at least about 15 and preferably at most about 25, more preferably at most about 23, most preferably at most about 22 weight percent. All weight percentages are based on the combined weight of the components of the blend making up the intermediate layer.

In addition to types of polymers previously described, the intermediate or core layer includes at least one ethylene polymer having a density no more than 0.915 g/cm³ as measured in accordance with ASTM D-792. The density is preferably at least about 0.85 g/cm ³ and especially at least about 0.86 g/cm ³ and advantageously up to about 0.915 g/cm ³ , preferably up to about 0.91 g/cm ³ , more preferably up to about 0.90 g/cm ³, most preferably 0.885 g/cm ³. Suitable ethylene polymers include, for example, heterogeneously branched ultra low density polyethylene (ULDPE), homogeneously branched linear ethylene polymers, homogeneously branched substantially linear ethylene polymers (SLEP) and combinations thereof. Homogeneously branched ethylene polymers are preferred with - substantially linear ethylene polymers are most preferred.

Preferred ethylene polymers in the core layer of this invention are ethylene copolymers with narrow molecular weight distribution (MWD), that is a Mw/Mn of less than about 3, more preferably less than about 3.0, most preferably less than about 2.5. These can be produced using at least one C₃-C₂₀ olefin comonomer, preferably C₃-C1₀. About 0.5-5 mole percent comonomer as determined by ASTM 5017 is preferred in the starting material. Commercially available polymers in this category include homogeneous polymers such as TAFMER polymer commercially available from Mitsui Petrochemical Industries, EXACT® polymer commercially available from Exxon Chemical Company, AFFINITY® polyolefin plastomers commercially available from The Dow Chemical Company, and the like. The ethylene polymers are preferably produced using a metallocene or constrained geometry catalyst, more preferably the latter.

However, homogeneously branched substantially linear ethylene polymers are preferred for use in the core layer compositions disclosed herein. These polymers can be interpolymers of ethylene with at least one C₃-C₂₀ α- olefin. The term "interpolymer" and "ethylene polymer" used herein indicates that the polymer can be a polymer of more than two monomers. Monomers usefully copolymerized with ethylene to make the homogeneously branched linear or substantially linear ethylene polymers include the C₃ -C₂₀ α-olefins especially 1-pentene, 1-hexene, 4-methyl-l- pentene, and 1- octene. Especially preferred comonomers include I-pentene, 1-hexene and 1- octene. Copolymers of ethylene and a C₃-C ₂₀ α-olefin are especially preferred.

The substantially linear ethylene/α-olefin polymers are made by a continuous process using suitable constrained geometry catalysts, preferably constrained geometry catalysts as disclosed in U.S. Pat. Nos. 5,132,380, 5,703,187; and 6,013,819, the teachings of all of which are incorporated herein by reference. The monocyclopentadienyl transition metal olefin polymerization catalysts taught in U.S. Pat. No. 5,026,798, the teachings of which are incorporated herein by reference, and are also suitable for use in preparing the polymers of the present invention.

The term "substantially linear" means that, in addition to the short chain branches attributable to homogeneous comonomer incorporation, the ethylene polymer is further characterized as having long chain branches in that the polymer backbone is substituted with an average. of 0.01 to 3 long chain branches/ 1000 carbons. Preferred substantially linear polymers for use in the invention are substituted with from 0.01 long chain branch/1000 carbons to 1 long chain branch/1000 carbons, and more preferably from 0.05 long chain branch/1000 carbons to 1 long chain branch/1000 carbons. Long chain branching is defined herein as a branch having a chain length greater than that of any short chain branches which are a result of comonomer incorporation. The long chain branch can be as long as about the same length as the length of the polymer back- , bone. Long chain branching can be determined using methods within the skill in the art, for instance by using ¹³C nuclear magnetic resonance (NMR) spectroscopy measurements, with quantification using, for instance, the method of Randall (Rev. Macromol. Chem. Phvs., C29 (2&3), p. 275-287).

For the substantially linear ethylene/α-olefin polymers used in the compositions of the invention, the I₁₀/I₂ ratio indicates the degree of long chain branching, i.e., the higher the I10/I2 ratio, the more long chain branching in the polymer. Generally, the I₁₀/I₂ ratio of the substantially linear ethylene/α-olefin polymers is at least about 5.63, preferably at least about 7, especially at least about 8 or above, and as high as about 25. The melt index is measured according to ASTM D- 1238 condition 190 °C. /2.16 Kg (formerly known as Condition E).

Among the layers the first exterior layer or adhesive layer has a thickness at least sufficient to bond or adhere to an adjacent, preferably metal, more preferably steel surface. This thickness is advantageously at least about 5, preferably at least about 10, and preferably at most about 30, more preferably at most about 25, most preferably at most about 20 volume percent based on total volume of the three layers. The second exterior or barrier layer has a thickness at least sufficient to provide temperature resistance to enable the MLF to be hot roll laminated to a metal substrate substantially without sticking to the hot rolls. This thickness is advantageously at least about 5, preferably at least about 10, more preferably at least about 15 and preferably at most about 30, more preferably at most about 25 volume percent based on total volume of the three layers. The intermediate or core layer comprises the remainder of the layer volume. This volume is preferably maximized because it is desirable to be able to use as much edge trim and recycled material from this film in this layer to maximize resin use and minimize the cost of manufacturing this film. This thickness is preferably at least about 40, more preferably at least about 50, most preferably at least about 55 and preferably at most about 90, more preferably at most about 80, most preferably at most about 75 volume percent based on total volume of the three layers.

MLFs of the present invention preferably have a 1% secant modulus (ASTM D-882) greater than 50,000 pounds per square inch (psi) (345 megapascals (MPa)), more preferably greater than 65,000 psi (448 MPa), and a RWSH (also known as "applied load hardness") of more than 20, preferably from 28 to 35. The 1% secant modulus is preferably less than 125,000 psi (862 MPa).

MLFs of the present invention preferably exhibit very little stretching, more preferably no visible stretching, during forming.

When subjected to a tensile pull test, MLFs of the present invention show no visible signs of delamination and very little machine direction (MD) tensile stress whitening

(TSW), preferably no MD TSW. For MD TSW testing, cut test strips measuring 6 inches (in.) (15.24 centimeters (cm) in length by 1 in. (2.54 cm) in width from a MLF. Clamp each strip into the jaws of a tensile test apparatus (Instron Model 4202) with a 2 in. (5.08 cm) gap and pull the jaws apart at a rate of 20 in./minute for a distance of 2 in. (5.08 cm). Remove the pulled test strips from the apparatus and evaluate the strips for stress whitening. MD TSW is a visual assessment using a pass (P)/fail (F) rating. A sample receives a P rating if it exhibits little, if any, opacity and no visible signs of interlayer delamination and an F rating if it evidences significant opacity and/or interlayer delamination.

For edge sharpness (ES) testing, cut test pieces measuring 4 in. (10 cm) in length by 4 in. (10 cm) from a MLF. Clamp the test piece into the jaws of a test apparatus designed to hold the sample. Press a formed cylindrical metal piece 1 in. (2.54 cm) in diameter with a slightly beveled edge upward into the test sample using an Instron Model 4202 test instrument for a distance of 1 in. (2.54 cm) to deform and stretch the MLF, then remove the formed MLF and examine any resulting edges. As with MD TSW, ES is a visual assessment with a P/F rating. A sample receives a P rating if it shows little or no apparent edge stretching or an F rating if it shows moderate to severe edge stretching.

RWSH testing requires conversion of the MLF to a MPL. Form a MPL by first preheating tin plate steel in a heated press at 350 degrees Fahrenheit (177°C) (from HIX Corporation Model HT-600 T-shirt press) followed by hand crank lamination (10 psi to 25 psi (68.9 kilopascals (KPa) to 172.4 KPa)) to the MLF between two spring loaded rubber rollers and finally followed by baking with a set temperature of 482 degrees Fahrenheit (⁰F) 250 degrees centigrade (⁰C) for 10 minutes. Remove the MPL from the oven and immediately quench it in an ambient temperature water bath (nominally 25°C). Using a Rockwell/Wilson Superficial Hardness Test apparatus (Model 40, USA Tester #418) equipped with a VA in. (0.64 cm) ball to press against the film side of the MPL and a flat anvil surface to support the metal side of the MPL. Place a MPL sample between the anvil surface and the ball, press the ball against the film side of the MPL using a 15 kilogram (kg) load for 60 seconds, release the load, read the apparatus dial and record the applied load measurement. A RWSH Applied Load of 23-40 merits a P rating whereas a RWSH Applied Load of less than 23 or more than 40 gains an F rating.

Measure 1% SM (MD) according to ASTM D882 using an Instron Model 4202 tensile test apparatus. The multilayer films of the present invention may be prepared using conventional coextrusion processes.

The following examples illustrate but do not limit, either expressly or by implication, the scope of the present invention. Arabic numerals identify Examples (Ex) of the present invention and capitalized letters of the alphabet denote Comparative Examples (Comp Ex). Unless otherwise indicated, all expressions of percentages and parts are based upon weight. Comp Ex A-C

Coextrude a three layer MLF using a coextrusion feedblock with feed lines or ports connected to three extruders, one for each layer. The MLF has an outer adhesive layer bonded to a first side of a central or core layer and an outer barrier layer bonded to a second side of the central or core layer, the first and second sides being spaced apart from, and generally parallel to, one another.

A first extruder, nominally "Extruder A", supplies a polymer melt to form the outer adhesive layer (100% MAH-g-LLDPE-1 (PLEXAR™ PX3060, Equistar Chemicals, LP)). Extruder A is a 1 inch (2.54 cm) extruder (Killion Model # KTS-100) heated to the following nominal set points; Zone 1 = 340⁰F (171°C), Zone 2 = 370⁰F (188°C), Zone 3 = 41O⁰F (210⁰C) with the transfer lines, feedblock, and die zones set to 410⁰F (210⁰C). A second extruder, nominally "Extruder B", supplies a polymer melt that forms the central or core layer. The core layer compositions are as follows: Comp Ex A = 66% P/E RCP (DS6D21, The Dow Chemical Company (hereinafter "RCP-l"))/28% PP homopolymer (H700-12, The Dow Chemical Company (hereinafter "PP-I")) and 6% of the same MAH-g-LLDPE-1; Comp Ex B = 100% PP-I; and Comp Ex C = 88% PP-I, 3%

MAH-g-LLDPE-1, and 9% LLDPE-I (DOWLEX™ 2247G, The Dow Chemical Company). Extruder B is a 1 inch (2.54 cm) extruder (Killion extruder Model # KL- 100) heated to the following nominal set points; Zone 1 = 340⁰F (171°C), Zone 2 = 370⁰F (188°C), Zone 3 = 410⁰F (210⁰C) with the transfer lines, feedblock, and die zones set to 410⁰F (210⁰C). A third extruder, nominally "Extruder C", provides a polymer melt that forms the outer barrier layer (100% PP-I. Extruder C is a 1 inch (2.54 cm) extruder (Killion extruder Model # KTS-100) heated to the following set points; Zone 1 = 340⁰F (171°C), Zone 2 = 370⁰F (188°C), Zone 3 = 410⁰F (210⁰C) with the transfer lines, feedblock, and die zones set to 410°F (210°C). For each of Comp Ex A, Comp Ex B and Comp Ex C, the adhesive layer, core layer and barrier layer represent, respectively, volume percentages, based upon total laminate structure volume, as follows: Comp Ex A = 24 vol%, 52 vol% and 24 vol%; Comp Ex B = 15 vol%, 70 vol% and 15 vol%; and Comp Ex C = 20 vol%, 70 vol% and 10 vol%.

Test the multilayer film and evaluate the film for performance in MD TSW, ES, RWSH (applied load) and 1 % SM (MD) using the procedures detailed above. Summarize performance evaluation results in Table I below.

Each of Comp Ex A, Comp Ex B and Comp Ex C have, as shown in Table I below, a P for SH, but a MD TSW grade of F. While Comp Ex A and Comp Ex B earn a P for ES, Comp Ex C has an ES grade of F. Although each of Comp Ex A, Comp Ex B and Comp Ex C have a desirable 1% SM (MD,) the MD TSW ratings for Comp Ex A and Comp Ex B and both the MD TSW and ES ratings for Comp Ex C mean that the multilayer films of these Comp Exs are not useful for desired end use applications. Comp Ex D

Replicate Comp Ex A, but change the core layer composition by increasing, the amount of RCP-I to 70%, eliminating PP-I, adding 20% of a polyolefin plastomer (POP-I) (AFFINITY™ PL1280, MI of 6.0 dg/min, and a density of 0.900 g/cc, The Dow Chemical Company), decreasing the amount of MAH-g-LLDPE-1 to 5% and adding 5% MAH-g- HDPE-I (PLEXAR™ PX2220, Equistar Chemicals, LP). In addition, change the adhesive layer by decreasing the level of MAH-g-LLDPE-1 to 50% and adding 50% of MAH-g- HDPE-I . In addition, the barrier layer now contains 75% of RCP-I and 25% of RCP-2 (6D20, The Dow Chemical Company) and no PP-L The adhesive layer, core layer and barrier layer represent, respectively, 23 vol%, 50 vol% and 27 vol%, in each case based upon total laminate structure volume. The multilayer film rates an F for MD TSW and a P for ES. The 1% SM (MD) is, however, unacceptably low. As the film does not merit an overall pass rate, do not measure SH. Comp Ex D has too much MD TSW and too little 1% SM (MD) to be useful for desired end use applications. Comp Ex E Replicate Comp Ex D but use larger scale equipment, change the composition of the core layer such that the core layer includes the same amounts of MAH-g-LLDPE-1 and MAH-g-HDPE-1 as in Comp Ex D, but 50% rather than 70% of RCP-I, 25% of a different POP rather than 20% POP-I and adding 15% of a second P/E RPC (6D20, The Dow Chemical Company). The different POP, hereinafter "POP-2", is AFFINITY™ PL 1880G (The Dow Chemical Company).

Extruder A is a 3.5 inch (8.89 cm) extruder manufactured by Black-Clawson and heated to the following set points; Zone 1 = 347°F (175°C), Zone 2 = 392⁰F (200⁰C), Zone 3 through 5 = 392°F (200⁰C) with the transfer lines, feedblock, and die zones set to 446°F (230⁰C). The extruder is run at 50 rpm. Extruder B is a 6 inch (15.24cm) extruder manufactured by Black-Clawson and heated to the following set points; Zone 1 = 347°F (175°C), Zone 2 = 392°F (200⁰C), Zone 3 through 5 = 446°F (230⁰C) with the transfer lines, feedblock, and die zones set to 446°F (230⁰C). The extruder is run at 75 rpm.

. Extruder C is a 3.5 inch (8.89 cm) extruder manufactured by Black-Clawson and heated to the following set points; Zone 1 = 347°F (175°C), Zone 2 = 392°F (200⁰C), Zone 3 through 5 = 446°F (230⁰C) with the transfer lines, feedblock, and die zones set to 446°F (230⁰C). The extruder is run at 90 rpm.

The adhesive layer, core layer and barrier layer represent, respectively, 11 volume percent (vol%), 73 vol% and 16 vol%, in each case based upon total laminate structure volume.

Physical property evaluation results for Comp_. Ex E show F ratings for MD TSW, ES and RWSH thereby meriting an overall F rating notwithstanding an acceptable 1% SM (MD). Comp Ex F

Replicate Comp Ex E using the same equipment as in Comp Ex D, and change the barrier layer composition to a 50%/50% blend of RCP-I and PP-L Change the adhesive layer to 100% MAH-LLDPE-I eliminating the MAH-HDPE-I. In addition, modify the core layer by increasing the amount of RCP-I to 75%, decreasing the amount of POP to 15% and using POP-I rather than POP-2, increasing the amount of MAH-g-LLDPE-1 to 10% and eliminating MAH-g-HDPE-1. The adhesive layer, core layer and barrier layer represent, respectively, 24 vol%, 50 vol% and 26 vol%, in each case based upon total laminate structure volume. A visual examination of the formed part shows that it receives a P rating for both MD TSW and ES. Notwithstanding such ratings, the laminate has a 1% SM (MD) that is below a minimum desired modulus of at least 50,000 psi (345 MPa). As such, the laminate structure merits an overall F rating. Comp Ex G

Replicate Comp Ex F but use the equipment of Comp Ex E and modify the barrier layer so it contains 60% RCP-I and 40% PP-I. The adhesive layer, core layer and barrier layer represent, respectively, 20 vol%, 65 vol% and 15 vol%, in each case based upon total laminate structure volume. As compared to Comp Ex F, laminate structure of Comp Ex G maintains the P rating for both MD TSW and ES, but 1 % SM (MD) further decreases to a level far below the desired 1% SM (MD) of at least 50,000 psi (345 MPa). As such, the laminate structure merits an overall F rating. Comp Ex H

Replicate Comp Ex G, but modify both the core layer and the barrier layer. Modify the core layer by reducing the amount of RCP-I to 50% as in Comp Ex E, leaving the amount of MAH-g-LLDPE-1 at 10% as in Comp Ex F, adding 20% PP-I and increasing the amount of POP-I to 20% rather than 15% as in comp Ex G. Change the barrier layer to contain 75% RCP-I and 25% PP-I. The 1% SM (MD) of the laminate structure increases relative to that of Comp Ex G, but still remains below the minimum level of 50,000 psi (345 MPa). In addition, the RWSH rating is an F. As such, the laminate structure of Comp Ex H merits an overall F rating notwithstanding a P rating for both MD TSW and ES. Comp Ex I

Replicate Comp Ex H, but modify both the core layer and the barrier layer. Modify the core layer by increasing the amount of RCP-I to 55% and adding 20% of a different PP homopolymer (PP-2, DX5E66, The Dow Chemical Company) than that used in Comp Ex H (PP-I). Modify the barrier layer by decreasing the amount of RCP-I to 73% and substituting 27% of PP-2 for the PP-I used in Comp Ex H. The adhesive layer, core layer and barrier layer represent, respectively, 42 vol%, 50 vol% and 8 vol%, in each case based upon total laminate structure volume. The 1% SM (MD) of the laminate structure increases relative to that of Comp Ex H, but still remains below the minimum level of 50,000 psi (345 MPa). As such, the laminate structure of Comp Ex H merits an overall F rating notwithstanding a P rating for both TS and ES. Ex 1

Replicate Comp Ex I, but modify both the core layer and the barrier layer. Modify the core layer by changing the amounts of RCP-I, PP-2, POP-I and MAH-g-LLDPE-1, respectively, to 48%, 19%, 18% and 15%. Modify the barrier layer to 75% RCP-I and 25% PP-2. The adhesive layer, core layer and barrier layer represent, respectively, 20 vol%, 70 vol% and 10 vol%, in each case based upon total laminate structure volume. Relative to Comp Ex T, the laminate structure of Ex 1 maintains a P rating for both MD TSW and ES while attaining a 1 % SM (MD) in excess of the minimum level of 50,000 psi (345 MPa). As such, the laminate structure of Ex 1 achieves an overall P rating. Ex 2

Replicate Ex 1, but modify both the core layer and the barrier layer. Modify the core layer by changing the amounts of RCP-I, PP-2, POP-I and MAH-g-LLDPE-1, respectively, to 40%, 35%, 15% and 10%. Modify the barrier layer to 55% RCP-I and 45% PP-2. The adhesive layer, core layer and barrier layer represent, respectively, 42 vol%, 50 vol% and 8 vol%, in each case based upon total laminate structure volume. As compared to Ex 1, Ex 2 maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating. Ex 3

Replicate Ex 2, but modify the core layer and barrier layer compositions. Modify the core layer by increasing the level of RCP-I to 50% as in Comp Ex E, using the same combination of MAH-g-LLDPE-1 and MAH-g-HDPE-1 as in Comp Ex E, changing the PP from PP-2 to PP-I and decreasing the amount to 20% , and increasing the amount of POP-I to 20%. Change the barrier layer composition to that of Comp Ex H. The adhesive layer, core layer and barrier layer represent, respectively, 23 vol%, 50 vol% and 27 vol%, in each case based upon total laminate structure volume As compared to Ex 2, the laminate structure of Ex 3 maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating. Comp. Ex K

Replicate Ex 3, but modify the core layer to eliminate the POP-I and increase the amounts of RCP-I and PP-I, respectively to 60% and 30%. The adhesive layer, core layer and barriep-iayer represent, respectively, 23 vol%, 50 vol% and 27 vol%, in each case based upon total laminate structure volume. As compared to Ex 3, the laminate structure of Comp. Ex K maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating. However, Comp. Ex. K is observed to delaminate during stamping or testing. Comp. Ex L

Replicate Comp. Ex K, but modify both the core layer and barrier layer compositions. Decrease the amount of RCP-I to 22%, eliminating MAH-g-HDPE-1, reducing MAH-g-LLDPE-1 content to 3%, increasing the amount of PP-I to 66% and adding 9% LLDPE- 1. Modify the barrier layer by reversing the amounts of RCP- 1 and PP- 1 such that the former is 25% rather than 75% and the latter is 75% rather than 25%. As compared to Comp. Ex K, the laminate structure of Comp. Ex L maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating. However, Comp. Ex. K is observed to delaminate during stamping or testing. Ex 4

Replicate Comp. Ex L, but modify both the core layer and barrier layer compositions. Change the barrier layer to 100% PP-I. Modify the core layer by increasing the amount of RCP-I to 58% from 22%, increasing the amount of MAH-g-LLDPE-1 to 6% from 3%, reducing the amount of PP-I from 66% to 23% and substituting 13% POP-I for the LLDPE. The adhesive layer, core layer and barrier layer represent, respectively, 24 vol%, 52 vol% and 24 vol%, in each case based upon total laminate structure volume. As compared to Comp. Ex L, the laminate structure of Ex 4 maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating.

Comp. Ex M

Replicate Comp. Ex L but modify the core layer by decreasing the amount of RCP-I to 17%, decreasing the amount of PP-I to 53% and increasing the amount of LLDPE-I to 27%. The adhesive layer, core layer and barrier layer represent, respectively, 20 vol%, 70 vol% and 10 vol%, in each case based upon total laminate structure volume. As compared to Comp. Ex L, the laminate structure of Comp. Ex. M maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating. However, Comp. Ex. K is observed to delaminate during stamping or testing. Comp. Ex N

Replicate Comp. Ex L, but modify the composition of all three layers. The adhesive layer contains 75% MAH-g-LLDPE-1 and 25% of MAH-g-HDPE-1. The core layer contains 60% PP-I, 15% RCP-I, 15% LLDPE-I, 7% MAH-g-LLDPE-1 and 3% MAH-g- HDPE-I. The barrier layer contains 65% PP-I, 20% RCP-I, and 15% LLDPE-I. The adhesive layer, core layer and barrier layer represent, respectively, 15 vol%, 70 vol% and 15 vol%, in each case based upon total laminate structure^" volume. As compared to Comp. Ex L, the laminate structure of Comp. Ex N maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating. However, Comp. Ex. K is observed to delaminate during stamping or testing. Comp. Ex O

Replicate Comp. Ex L , but modify the compositions of both the core layer and the barrier layer. The core layer contains 75% PP-I, 15% LLDPE-I and 10% MAH-g-LLDPE- 1. The barrier layer contains 85% PP-I and 15% LLDPE-I . The adhesive layer, core layer and barrier layer represent, respectively, 15 vol%, 70 vol% and 15 vol%, in each case based upon total laminate structure volume. As compared to Comp. Ex L, the laminate structure of Comp. Ex O maintains a P rating for both MD TSW and ES while having a further increase in 1 % SM (MD), thereby meriting an overall P rating. However, Comp. Ex. K is observed to delaminate during stamping or testing. Comp. Ex P

Replicate Comp. Ex O, but modify all three layers. The adhesive layer has the same composition as Ex 8. The core layer contains 2% MAH-g-LLDPE-1, 1% MAH-g-HDPE-1, 88% PP-I and 9% LLDPE-I. The barrier layer is 100% PP-L As compared to Comp. Ex O, the laminate structure of Comp. Ex P maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating. However, Comp. Ex. K is observed to delaminate during stamping or testing. Comp. Ex O

Replicate Comp. Ex P, but modify the core layer and the barrier layer. Change the barrier layer to match that of Comp. Ex M. Modify the core layer by deleting the MAH-g- HDPE-I, adding 25% RCP-I , and increasing the amount of PP-I to 73% while maintaining the 2% MAH-LLDPE-L The adhesive layer, core layer and barrier layer represent, respectively, 15 vol%, 70 vol% and 15 vol%, in each case based upon total laminate structure volume. As compared to Ex 10, the laminate structure of Comp. Ex Q maintains a P rating for both MD TSW and ES while having a further increase in 1% SM (MD), thereby meriting an overall P rating. However, Comp. Ex. K is observed to delaminate during stamping or testing. Comp Ex J

Replicate Comp. Ex Q, but modify all three layers. Change the adhesive layer to comprise 90% MAH-g-LLDPE-1 and 10% of a developmental propylene/ethylene plastomer having an ethylene content of 5 wt%, based on plastomer weight (DP3000.01 , The Dow Chemical Company). Modify the core layer by increasing the amount of PP-I to 75%, increasing the MAH-g-LLDPE-1 content to 10%,using the same amount of LLDPE-I as in Comp. Ex O and eliminating the RCP-I. The barrier layer has the same composition as its counterpart layer in Comp. Ex O. While the multilayer film of Comp Ex J passes both the MD TSW and ES evaluations and has sufficient 1% SM (MD), it fails to have adequate RWSH and, as such, fails to be suitable for desired applications. Example 5

Replicate Comp Ex E, but modify the composition of all three layers. Change the composition of the adhesive layer by using 49 wt% MAH-g-LLDPE-2 (commercially available from The Dow Chemical Company under the trade designation AMPLIFY ™ GR- 207 MAH-g-LLDPE), 48 wt% MAH-g-HDPE-2 (commercially available from The Dow

Chemical Company under the trade designation AMPLIFY ™ GR-205 MAH-g-HDPE), and 3 wt% of Ampacet 102113 lubricating process aid in LLDPE from Ampacet, Inc generally recommended to improve surface quality of the film without effecting sealability or printability and may increase gloss and clarity and reduce haze in extruded plastic part. Change the composition of the barrier layer by using 60 wt% PP-I and 40 wt% RCP-I. Change the composition of the core layer by using 55 wt% PP-I, 15 wt% RCP-I, 20 wt% POP-1 , 5 wt% MAH-g-LLDPE-2, and 5 wt% MAH-g-HDPE-2. The adhesive layer, core layer, and barrier layer represent, respectively, 10 volume percent, 70 vol% and 20 vol%. The laminate structure of Example 5 maintains a P rating for MD TSW, ES, and RWSH, while attaining a 1% Secant Modulus (SM) in excess of the minimum level of 50,000 psi (345 MPa). As such, the laminate structure of Ex 12 achieves an overall P rating.

Table I

* "P" means "Pass", "F" means "Fail", "NM" means not measured and "MD" means "machine direction"

The data presented in Table I support several observations. First, a single P rating is not enough to award a multilayer film structure an overall P rating, but a single F rating causes a multilayer film structure to have an overall F rating. Second, by careful selection of layer composition for each of the layers, one can obtain a number of multilayer film structures that have a desired balance of MD TSW, ES, RWSH and MD TM. Such multilayer film structures have a number of commercially viable applications such as those disclosed hereinabove. Third, skilled artisans understand that consumer acceptance of a lower standard, for example, a moderate to high level of MD TSW or some stretching means that some of the MLF structures denoted as Comp Ex would be commercially viable. Finally, similar results are expected with other multilayer films structures prepared in accordance with the composition limits detailed hereinabove. Some that are rated P appear acceptable but some additional handling and down stream processing have proven that they have a tendency to delaminate when subjected to the high stress seen during stamping and forming operation on the MPL.

Claims

CLAIMS:

1. A coextruded multilayer _'film comprising: a. a first external film layer, the first external film layer comprising at least one anhydride-grafted olefin polymer; b. a second external film layer, the second external film layer comprising at least one propylene homopolymer; and c. an intermediate film layer that is interposed between, and in a delamination-resistant, adhesive-free bond with, both the first and second external film layers, the intermediate film layer comprising a blend of at least one polypropylene homopolymer, at least one anhydride-grafted linear olefin polymer, at least one random propylene-ethylene copolymer, and, at least one ethylene polymer having a density no more than 0.915 g/cm³; the multilayer film having a 1 percent secant modulus (machine direction) of at least 50,000 pounds per square inch (345 megapascals), a percent haze, determined in accordance with ASTM D-1003, of no more than 30 percent, and a Rockwell/Wilson Superficial Hardness (applied load) of at least 20, but less than 40.

2. The multilayer film of Claim 1, wherein the intermediate film layer comprises a blend of from 15 to 70 percent by weight polypropylene, from 3 to 15 percent by weight anhydride-grafted olefin polymer, from 10 to 60 percent by weight random propylene-ethylene copolymer, and from 4 to 25 percent by weight of the ethylene polymer, all percentages being based on blend weight and, when combined, totaling 100 percent by weight; and , wherein the second external film layer comprises a blend of at least 20 percent by weight of at least one propylene homopolymer and up to 80 percent by weight of at least one random propylene-ethylene copolymer, both percentages being based on blend weight.

3. The multilayer film of Claim 1 or 2 wherein the first exterior film layer comprises at least one anhydride-grafted linear low density ethylene polymer in an amount from 40 to 100 weight percent of the layer, and an anhydride-grafted high density ethylene polymer in an amount from 0 to 50 weight percent of the layer such that the layer has a melting temperature as determined by determined by Differential Scanning Calorimetry (DSC) between 1 15 and 140 ⁰C.

4. The multilayer film of Claim 3, wherein the anhydride is maleic anhydride.

5. The multilayer film of Claim 1, wherein the second external film layer meets criteria established by the United States Food and Drug Administration for designation as food compliant.

6. The multilayer film of any of Claims 1 through 5, wherein the first external film layer comprises from 5 to 30 volume percent, the second external film layer comprises from 5 to 30 volume percent and the intermediate film layer comprises from 40 volume percent to 90 volume percent, based upon total film volume.

7. The multilayer film of any of Claims 1 through 5, wherein the intermediate layer optionally comprises an amount of multilayer film regrind material.

8. The multilayer film of any of Claims 1 through 5, wherein the

Rockwell/Wilson Superficial Hardness (applied load) is from greater than 27 to less than 33.

9. The multilayer film of any of Claims 1 to 5, wherein the 1 percent secant modulus (machine direction) is greater than or equal to 50,000 pounds per square inch (345 megapascals), but less than or equal to 125,000 pounds per square inch (862 megapascals).

10. The multilayer film of any of Claims 1 to 5, wherein the film is bonded to a metal such that the metal is directly adjacent the first external film layer.