Barrier Films

Field of the Invention

The present invention relates to film materials for use in the packaging industry as barrier films. More particularly, the film materials of the present invention are multilayer composites containing a base layer of a polymeric material, such as polyester, a barrier layer comprising a carbon-rich material, and a heat sealable layer of a polymeric material containing ethylene monomeric units.

Background of the Invention

Many applications in packaging consumer items, such as food, pharmaceuticals, health care products, electronic products, and chemicals, require good barrier properties such that the packaging resists penetration by moisture and atmospheric gases. Such barrier properties are obtained by incorporating a barrier film into the packaging. Such films are widely used and are made of a variety of materials. Well-known examples of barrier films include waxed paper, aluminum foil, and Saran™ wrap. Multilayer composite structures are also known, such as laminates of: (1) a polymeric base film, e.g., polycarbonate, polyethylene, or polyethylene terephthalate; (2) a gas- and/or liquid-impermeable, moisture resistant barrier layer, such as ethylene vinyl alcohol, polyvinylidene chloride, or an inorganic material, e.g., SiO _x (wherein x = 1.5- 1.8), Siθ ₂ , amoφhous carbon, AI ₂ O ₃ , or Al, and a top coating of a polymeric material, e.g., polyethylene or polyvinyl chloride. See, for example, U.S. Patent Nos. 5,085,904 (Deak et al.), 4,756,964 (Kincaid et al ), 3,442,686 (Jones), and 5,112,673 (Sawada et al.). These barrier films, however, have limitations. For example, the barrier films containing polyvinylidine chloride or ethylene vinyl alcohol are moisture and/or temperature sensitive. The barrier films containing a thick layer of aluminum metal foil (>500 A) are opaque and environmentally unfriendly because they can't be recycled easily. The barrier films containing a thin layer of aluminum metal (<100 A), aluminum

oxides, and silicon oxides can be transparent, however, their barrier properties deteriorate significantly upon flexing, stretching, or abrading

Barrier films containing a layer of carbon, however, are more resistant to physical abuse than are inorganic barrier layers, particularly when the carbon layer has a protective topcoat Few top coating materials are known that adhere well to amoφhous carbon, however, particularly without the use of a tie layer Thus, few barrier films are available that contain an amoφhous carbon layer Those that are available generally contain migrating solvents in the adhesive tie layers that are undesirable for use in many applications, particularly food packaging applications Therefore, there is a need for barrier films that are transparent, environmentally friendly, and resistant to physical abuse

Summary of the Invention

The present invention provides a multiple-layer composite film containing a base layer of a polymeric material, a barrier layer containing a carbon-rich material adhered to the base layer, and a heat sealable layer of an active gas treated, heat sealable, polymeric material containing ethylene monomeric units adhered to the barrier layer As used herein, an "active gas-treated" material is one that has been subjected to an active gas surface treatment process Such processes include corona treatment, flame treatment, ozone treatment, and plasma treatment An "active gas" therefore refers to a gaseous material having therein reactive species capable of modifying the surface of the material

Preferably, this film has a peel strength between the heat sealable and barrier layers of at least about 15 ounces/inch (167 grams/cm), an oxygen permeability of less than about 2 0 cubic centimeters of oxygen per 1 square meter of film per day, and a moisture permeability of less than about 2 0 grams of water vapor per 1 square meter of film per day Thus, the multiple-layer composite films of the present invention are good barrier films

The heat sealable polymeric material includes one or more types of polymers containing ethylene monomeric units This heat sealable polymer is preferably

selected from the group consisting of an ethylene-α-olefin polymer; an acid or anhydride modified ethylene-α-olefin polymer; an ethylene-containing polymer having -C(O)OR groups, -OC(O)R groups; an acid or anhydride modified ethylene-containing polymer having -C(O)OR groups, -OC(O)R groups; an acid or anhydride modified polyethylene homopolymer; and mixtures thereof; wherein R represents a monovalent hydrocarbyl group. More preferably, the heat sealable polymer containing ethylene monomeric units is selected from the group consisting of a single-site, ethylene-α-olefin polymer; an ethylene-propylene elastomer; an ethylene-containing polymer having -C(O)OR groups, -OC(O)R groups; an acid or anhydride modified ethylene-containing polymer having -C(O)OR groups, -OC(O)R groups; an acid or anhydride modified low density polyethylene; an acid or anhydride modified linear low density polyethylene; and mixtures thereof; wherein R represents a monovalent aliphatic group having 1-10 carbon atoms.

The barrier films of the present invention, i.e., the multiple-layer composite films, are prepared by treating the heat sealable polymeric material with an active gas surface treatment process, e.g., corona, ozone, plasma, or flame, and heat laminating it to the barrier layer at a temperature of at least about 180°F (82°C).

Preferably, the heat sealable layer is corona treated, more preferably air corona treated.

The present invention also provides containers that incoφorate the barrier films either in lidding or sealing applications or within the body of the container itself For example, a container is provided that includes a body having an opening therein and a covering over the opening, the covering comprising the multiple-layer composite film of the present invention. Examples of such embodiments include containers with lidding films and innerseals, such as induction innerseals, one-piece and two-piece innerseals, and tabbed innerseals, for example. Also provided is a container that includes a body having therein a multiple-layer composite film of the present invention. Examples of such embodiments include pouches, gable-top cartons, brick packs, blister packs, blood bags, and medicine bags.

Brief Description of the Drawings

Figure 1 is a cross-sectional view of a multiple layer composite film of the present invention

Figure 2 is a schematic of the process of the present invention for preparing the film illustrated in Fig 1

Figure 3 is a cross-sectional view of a tray having a lidding film formed from the film illustrated in Fig 1

Figure 4 is a side view of a bottle having a lidding film formed from the film illustrated in Fig 1 Figure 5 is a cross-sectional view of an innerseal film formed from the film illustrated in Fig 1

Figure 6 is a cross-sectional view of a bottle cap having therein the innerseal film illustrated in Fig 5

Figure 7 is a perspective view of a container sealed with a top tabbed innerseal film formed from a multiple layer composite film of the present invention

Figure 8 is a cross-sectional view of the container assembly illustrated in Fig 7

Figure 9 is a perspective view of a pouch made from the film illustrated Fig 1 Figure 10 is a cross-sectional view of a gable-top carton incoφorating therein the film illustrated in Fig 1.

Figure 11 is a perspective view of a blister pack incoφorating therein the film illustrated in Fig 1

Detailed Description of the Invention

The present invention provides multiple-layer, i e , multilayer, composite packaging films made of a base layer of a polymeric material, a barrier layer of a carbon- rich material coated thereon, and a heat sealable layer of active gas-treated, heat sealable polymeric material that includes ethylene monomeric units coated on the barrier layer Each of these layers is adhered to the layer on which it is coated Preferably, the

co posite film displays a peel strength, i.e., peel adhesion, between the barrier layer and the heat sealable layer of at least about 15 ounces/inch (167 g/cm), more preferably at least about 20 ounces/inch (223 g/cm), and most preferably at least about 30 ounces inch (334 g/cm), using the 180° Peel Test described in detail below for a 1 mil (2.54 x 10 ^" cm) thick heat sealable layer.

Typically, the only treatment needed to adhere the heat sealable polymeric material to the barrier layer is an active gas surface treatment, preferably corona treatment. Thus, in preferred embodiments, each of these layers is directly adhered to the layer on which it is coated. By this it is meant that there are no intervening tie layers (other than the active gas treated surface layer, which can be considered a functional equivalent of a "tie layer") to provide adhesion between the base layer and barrier layer or between the barrier layer and the heat sealable layer. Thus, in the context of the present invention, when a layer is "directly" adhered to another layer, the only "intervening layer" allowed is that created by an active gas surface treatment. The multilayer composite barrier films of this invention are capable of forming a strong bond with a variety of substrates, e.g., polypropylene substrates. They can be used in a variety of packaging applications known in the art, such as lidding films, induction innerseals, one-piece and two-piece innerseals, tabbed innerseals, gable-top cartons, brick packs, blister packs, and pouches. Certain preferred embodiments of the films are capable of being substantially cleanly separated from the substrate such that little or no residue remains after removal of the film. A particularly preferred example of this is a barrier film containing a heat sealable, single-site, ethylene-α-olefin polymer used on a polypropylene substrate. Accordingly, such multilayer composite films of this invention can be used as lidding films or sealing films for containers made of polymers including a significant percentage, i.e., a majority, of propylene monomeric units. As used herein, these polymers are referred to as propylene polymers or simply polypropylene, although they may contain monomeric units other than propylene, such as ethylene, for example.

The films of the present invention are particularly useful in packaging materials that undergo processing conditions at elevated temperatures (e.g., up to about

100°C) and/or elevated pressures (e g , greater than 1 atmosphere) Such a material includes packages for foods (e.g , frozen vegetables, etc ), beverages, medical instruments, etc Advantageously, the films of the present invention have a heat seal window, i e., temperature range in which the films can be heat sealed to a substrate, of greater than about 30°F (16°C), and preferably greater than about 50°F (28°C) Certain preferred embodiments have a heat seal window of greater than about 80°F (44°C), and even greater than about 100°F (56°C) For example, the heat seal window can be between 100°C and 116°C Furthermore, certain preferred films of the present invention are not tacky at room temperature, and peel substantially cleanly from a variety of substrates, e g , polypropylene substrates, even after the sealed substrate is stored at a high relative humidity, i e , greater than about 95%, and low temperature, i e , less than about 32°F (0°C), for about one week

Referring to Figure 1, a representation of a multiple-layer composite film 10 is shown This film includes a base layer 12 of polymeric material, a barrier layer 13 of carbon-rich material adhered to base layer 12, and a heat sealable layer 14 of an active gas treated, heat sealable, polymeric material containing ethylene monomeric units adhered to carbon-rich barrier layer 13 The polymeric material used in the base layer 12 can include any polymer that is heat-resistant, i e , does not melt or deteriorate significantly at temperatures typically used in the packaging process (e g , the heat sealing process) Such processes can utilize temperatures of about 210°F (99°C) or above Preferred polymeric materials for the base layer do not melt or deteriorate significantly at temperatures up to about 350°F (177°C) The polymeric material of the base layer is preferably chosen such that its melting or softening point is at least about 50°F higher than that of the polymeric material of the heat sealable layer Furthermore, it is chosen such that the barrier layer preferably adheres to it without an intervening tie layer Thus, preferred films of the present invention eliminate the need for a tie layer or interdispersed anchor to bond the barrier layer to the base layer (or to bond the heat sealable layer to the barrier layer) In this way, additional solvents are not used nor are adhesives needed to tie the two layers together It is understood, however, that a tie

layer could be used if desired It is also understood that the heat sealable layer can be used as a tie layer itself to adhere another material, such as a shear activated adhesive, for example, to the composite film

The polymeric materials of the base layer should be able to form a film having strong internal bond, i e , an internal bond greater than the strength of the bonds between any of the layers It is preferred that such materials be oriented, i e , have a high degree of crystallinity Examples of polymeric materials for base layer 12 include polycarbonates, polyethylenes, polypropylenes, polybutylenes, polystyrenes, polyurethanes, polyvinylchlorides, polyesters, polybutadienes, polyamides, polyimides, polysulfones, fluoroplastics such as polytetrafluorethylene and polyvinylidenefluoride, cellulosic resins such as cellulose propionate, cellulose acetate, and cellulose nitrate, acrylics and copolymers such as acrylonitrile-butadiene-styrene, and other copolymers derived from any of the aforementioned polymers Polyesters, polyamides, polyethylenes, polycarbonates, polyimides, and polypropylenes are particularly preferred polymeric materials for the base layer Of these preferred materials, those having a relatively high tensile strength, i e , at least about 5,000 psi (3 45 x 10 kPa) as measured by ASTMD-882 (1991), are particularly preferred

A representative example of a preferred polymer suitable for use in base layer 12 is polyethylene terephthalate, i e , often referred to as simply "polyester," preferably biaxially oriented polyethylene terephthalate Other polyesters such as poly(l,4-cyclohexylenedimethylene terephthalate) and poly(ethylene naphthalate) can also be used as a material for base layer 12 Commercially available polymers suitable for base layer 12 include the polyesters "Melinex 850" commercially available from ICI Americas, Ine , Wilmington, DE, and "Mylar 48LB" commercially available from E I DuPont de Nemours and Co , Wilmington, DE Particularly preferred polymers for use in the base layer are high melting temperature polyesters, i e , those having a melting point of at least about 230°C

The polyester base layer can also be treated with an active gas surface treatment, e g , corona discharge, as can any of the polymers of the base layer For a discussion of corona treated polypropylene and polyethylene terephthalate films, see, for

example, M. Strobel et al., J. Adhesion Ses. Techno!.. 6, 429-443 (1992), and M. Strobel et al., J. Adhesion Ses. Techno!.. 2, 321-333 (1989). Typically, such active gas surface treating processes are used to improve the adhesion and wetting properties of the material. Base layer 12 can also include additives of a type and in an amount that do not substantially adversely affect its strength. For example, it can include: slip or antiblock agents such as silica, calcium carbonate, calcium fluoride, etc., or fatty acids (preferably in an amount no greater than about 1%); antifogging agents such as silicates (preferably in an amount no greater than about 1%); antioxidants or uv-stabilizers such as butylated hydroxy toluene (preferably in an amount no greater than about 1%); pigments such as titanium dioxide, zinc oxide, iron oxide, or carbon black (preferably in an amount no greater than about 5%); and fillers such as calcium carbonate (preferably in an amount no greater than about 30%). The total amount of additives in base layer 12 generally should not exceed about 40% of the total weight of the base layer polymer and additives.

Base layer 12 can be of any suitable thickness. It should be sufficiently thin, however, so that the final barrier film will have the desired flexibility. It preferably ranges from about 0.3 mil (0.0008 cm) to about 10 mils (0.0254 cm), and more preferably from about 0.4 mil (0.001 cm) to about 3.0 mils (0.008 cm). The choice of base layer thickness is determined by the intended use of the multiple-layer composite film.

The barrier layer 13 is an amoφhous carbon coating, i.e., carbon-rich coating. It is deposited on, and adheres to, the base layer 12, preferably without the use of a binder or tie layer. It is typically no less than about 50 A thick and no greater than about 2000 A thick. Thicker carbon coatings than about 2000 A generally have an undesirable degree of cracking, whereas thinner carbon coatings than 50 A do not generally have good barrier properties. Preferably, the carbon coating is about 100-800 A, and more preferably about 150-500 A, thick.

The resultant coatings are found to be hard, optically transparent, nonconducting and have excellent low oxygen and moisture permeability. The low

oxygen and moisture permeability properties of the coating makes the coated polymeric substrate especially useful as a barrier film. The oxygen permeability of these carbon- coated polymeric base films is less than about 5.0 cubic centimeters (cc) of oxygen per 1 square meter of film per day (per atmosphere), as measured by an Oxtran Permeability Tester manufactured by Modem Controls, Inc., Minneapolis, MN, using an aluminum foil standard. The moisture permeability of these carbon-coated polymeric base films is less than about 5.0 grams of water vapor per 1 square meter of film per day, as measured by a Permatran W-6 Permeability Tester manufactured by Modern Controls, Inc., Minneapolis, MN. The carbon-rich coatings can be applied using any of a variety of techniques, such as vapor deposition, sputter deposition, plasma deposition, and the like Examples of useful plasma deposition processes are described in U.S. Patent Nos. 5,232,791 (Kohler et al.) and 4,756,964 (Kincaid et al ). A particularly preferred plasma deposition process is described in Applicant's Assignee's copending application Serial No. entitled "Jet Plasma Process and Apparatus" (filed on even date herewith), which is incoφorated herein by reference.

The latter process involves depositing a carbon-rich coating by means of jet plasma deposition. In general, the process uses a carbon-rich plasma (i.e., expanded gaseous reactive ionized and neutral hydrocarbon fragments) that is directed in a jet stream toward the base film. Generally, the base film is negatively charged as a result of being exposed to a radio frequency bias. The carbon-rich plasma is generated from a plasma gas using a hollow cathode system, i.e., either a "hollow cathode tube" or a "hollow cathode slot," preferably a slot, and more preferably a tube in line with a slot, and then accelerated toward and past an anode onto the film. More specifically, the process involves providing a base film in a vacuum chamber; and generating a carbon- rich plasma in the vacuum chamber by injecting a plasma gas into a hollow cathode slot system containing a cathode comprising two electrode plates arranged parallel to each other, providing a sufficient voltage to create and maintain a carbon-rich plasma in the hollow cathode slot system, and maintaining a vacuum in the vacuum chamber sufficient for maintaining the plasma. The base film is then exposed to the plasma, preferably

while the base film is in close proximity to a radio frequency bias means, and a carbon- rich coating is deposited thereon

The hollow cathode slot system contains two plates in a parallel orientation, which create a "slot" in which a stable plasma is generated This slot is generally rectangular in shape and has a length to width ratio of less than 1 1 That is, the space between the plates is wider than it is long, as distinguished from a "tube" or an elongated hollow cathode in which the length to diameter ratio is at least 1 1 and generally greater than this In this context, the length of the cathode is the distance between the inlet for the gases and the outlet for the plasma The hollow cathode slot system used in this process preferably includes a first compartment having therein a hollow cathode tube, a second compartment connected to the first compartment, and a third compartment connected to the second compartment having therein the two parallel plates that function as a cathode Although the voltage can be applied using a nonpulsating filtered DC power supply or a pulsating DC power supply, in particularly preferred embodiments, the voltage is provided by a first pulsating DC power supply connected to the hollow cathode tube and a second pulsating DC power supply connected to the two electrode plates, i e the hollow cathode slot

The carbon-rich plasma is created from a feed gas or a mixture of a feed gas and a carrier gas This is referred to herein as the "plasma gas " Preferably, the carrier gas is injected into the first compartment of the hollow cathode slot system and the feed gas is injected into the second compartment for mixing with the carrier gas The carrier gas flow rate can be about 50-500 standard cubic centimeters (seem), preferably about 50-100 seem, and the feed gas flow rate can be about 100-60,000 seem, preferably about 300-2000 seem For example, for carbon deposition rates of about 20-800 A second, the feed gas flow rate is about 50-350 seem and the carrier gas flow rate is about 50-100 seem, with higher feed gas flow rates in combination with lower carrier gas flow rates (typically resulting in higher deposition rates) Generally, for harder coatings, the carrier gas flow rate is increased and the feed gas flow rate is decreased

The feed gas, i.e., the carbon source, can be any of a variety of saturated or unsaturated hydrocarbon gases. Such gases can also contain, for example, nitrogen, oxygen, halides, and silicon. Examples of suitable feed gases include, but are not limited to: saturated and unsaturated hydrocarbons such as methane, ethane, ethylene, acetylene, and butadiene; nitrogen-containing hydrocarbons such as methylamine and methylcyanide; oxygen-containing hydrocarbons such as methyl alcohol and acetone; halogen-containing hydrocarbons such as methyl iodide and methyl bromide; and silicon-containing hydrocarbons such as tetramethylsilane, chlorotrimethyl silane, and tetramethoxysϋane. The feed gas can be gaseous at the temperature and pressure of use, or it can be an easily volatilized liquid. A particularly preferred feed gas is acetylene.

The carrier gas can be any inert gas, i.e., a gas that is generally unreactive with the chosen feed gas under the conditions of pressure and temperature of the process of the present invention. Suitable carrier gases include, but are not limited to, helium, neon, argon, krypton, and nitrogen. Typically, higher molecular weight molecules, e.g., argon, are preferred. The terms "inert" and "carrier" are not meant to imply that such gases do not take part in the deposition process at all. Generally, it is believed that the generated carrier gas ions act as bombarding particles to remove the softer portions of the coatings, e.g., those portions containing a higher hydrogen atom content, and thereby improve the density and strength of the coatings.

This process can be used to prepare any of a variety of carbon-rich coatings. Typical coatings prepared by this process contain greater than about 50 atom- % carbon (preferably about 70-95 atom-%), along with minor amounts of oxygen (preferably about 0.1-15 atom-%), nitrogen (preferably about 0.1-20 atom-%), and hydrogen (preferably about 0.1-40 atom-%). The composition of the carbon-rich coating can be controlled by means of the pressure of the carrier gas, the composition of the feed gas, the configuration of the hollow cathode, and the electrical power supplied by the DC and radio frequency power supplies. For example, by increasing the concentration of the carrier gas or by increasing the bias voltage, a coating with a higher carbon content can be formed.

The oxygen and moisture permeability of the carbon-coated polymeric base films can be increased upon the addition of the heat sealable polymers described herein, in part because the heat sealable material protects the carbon coating from mechanical abuse. Thus, the barrier films of the present invention have an oxygen permeability of less than about 2.0 cubic centimeters of oxygen per 1 square meter of film per day, and a moisture permeability of less than about 2.0 grams of water vapor per 1 square meter of film per day. Preferred barrier films of the present invention have an oxygen permeability of about 0.001 to about 1.0 cubic centimeter of oxygen per 1 square meter of film per day, and a moisture permeability of about 0.015 gram to about 1.0 gram of water vapor per 1 square meter of film per day.

Once treated with an active gas surface treatment technique (preferably corona treated), the heat sealable polymeric material containing ethylene monomeric units (1 mil (2.54 x 10 ^" cm) thick layer) is capable of displaying a 180° Peel Strength of at least about 15 ounces/inch (167 g/cm), preferably at least about 20 ounces/inch (223 g/cm), and more preferably at least about 30 ounces/inch (334 g/cm), when laminated to a carbon-coated polymeric base film. Suitable polymers for use in this heat sealable layer include, but are not limited to, ethylene-α-olefin polymers, i.e., polyethylene polymers containing α-olefin monomers having at least three carbon atoms, (optionally acid or anhydride modified); ethylene-containing polymers having -C(O)OR (carboxyl) groups, -OC(O)R (acetate) groups, or mixtures thereof (optionally acid or anhydride modified); or acid or anhydride modified polyethylene homopolymers, e.g., low density polyethylene, high density polyethylene, and the like. All of these materials can be treated with an active gas surface treatment and adhered to another substrate, e.g., the carbon-rich layer of another polymer, upon application of thermal energy. Additionally, some of these materials are also capable of being adhered to another substrate, e g, a polypropylene container, upon application of pressure.

The ethylene-α-olefin polymers, which is a preferred class of materials, include, for example, single-site ethylene-α-olefin polymers, as described below, linear low density polyethylene polymers, and ethylene-α-olefin elastomers. Each of these

groups is generally characterized by a different amount of α-olefin monomers. For example, the single-site ethylene-α-olefin polymers contain less than about 30 wt-% α- olefin monomers, preferably about 10-30 wt-%. The linear low density polyethylene polymers contain less than about 15 wt-% α-olefin monomers. The ethylene-α-olefin elastomers, which are more appropriately referred to as thermoelastomers, contain about 30-60 wt-% α-olefin, preferably propylene. Of these, the single-site and elastomeric ethylene-α-olefin polymers are the more preferred.

The ethylene-α-olefin polymers are prepared from olefins having at least 3 carbon atoms, preferably 3-20 carbon atoms, and more preferably 3-12 carbon atoms. The ethylene-α-olefin polymers can include more than one type of α-olefin comonomer. For example, they can be copolymers, i.e., combinations of ethylene and one type of α- olefin monomer, or teφolymers, i.e., combinations of ethylene and two types of α-olefin monomers. The material used in the heat sealable layer can also include mixtures of different ethylene-α-olefin polymers, for example. For the carboxyl and acetate groups, R represents a monovalent hydrocarbyl group, preferably an aliphatic group having 1-10 carbon atoms. For particularly preferred polymers containing carboxyl or acetate groups, the R group is an alkyl group of a size such that a nontacky polymer is formed. Most preferably, R is a Cι-C ₆ alkyl group. As used herein, "acid modified" means that the polymer has acidic monomers grafted thereon or within the polymer backbone. Typically, this is done with less than about 10 wt-% methyl acrylic acid. Such polymers are commercially available. As used herein, "anhydride modified" means that the polymer has anhydride monomers grafted thereon or within the polymer backbone. Typically, this is done with less than about 10 wt-% maleic anhydride. Such polymers are commercially available.

As used herein, "high density polyethylene", "low density polyethylene", and "linear low density polyethylene" are generally used in the conventional sense, although "low density" polyethylene also includes within its scope what is sometimes referred to as "medium density" polyethylene. Low density polyethylene (LDPE) is

generally prepared at high pressure, although low pressures can be used, using free radical initiators. As used herein, LDPE homopolymers typically have a density of about 0.915-0.940 g/cm . LDPE is also often referred to as "branched" polyethylene because of the relatively large number of long chain branches extending from the main polymer backbone. High density polyethylene (HDPE) is generally prepared at low or moderate pressures, although high pressures can be used, using a coordination catalyst, e.g., Ziegler-Natta type catalysts. HDPE homopolymers typically have a density of about 0.940-0.960 g/cm . HDPE has a generally nonbranched structure and is therefore substantially crystalline. Linear low density polyethylene (LLDPE) is generally prepared at low to moderate pressures, although high pressures can be used, using a coordination catalyst, e.g., Ziegler-Natta type catalysts. The term refers to a number of solid ethylene-α-olefin polymers, produced by polymerization of ethylene with less than about 15 wt-% of at least one type of α-olefin having 3-12, preferably 3-8, carbon atoms per olefin molecule. Typically, LLDPE contains less than 10 wt-% α-olefin, and frequently only about 2-3 wt-% α-olefin. These short chain α-olefin molecules generally introduce enough short chain branches into the otherwise linear polymer to reduce the density of the resultant polymer to about 0.911-0.935 g/cm , although the procedure for making the polymer is generally the same as that used for high density polyethylene. Preferred α-olefin monomers that are used in LLDPE include, for example, propylene, 1-butene, 1-isobutene, 4-methyl-l-pentene, 1-pentene, 1-isopentene, 1-hexene, 1-isohexene, 1- heptene, 1-isoheptene, 1-octene, 1-isooctene, 1-nonene, 1-isononene, 1-decene, and 1- isodecene.

As used herein, "single-site" ethylene-α-olefin polymers are prepared using single-site catalysts, i.e., catalysts that permit olefins such as ethylene and α-olefin to react only at single sites on the catalyst molecules. Suitable such ethylene-α-olefin polymers are described in U.S. Patent No. 5,206,075 (Hodgson, Jr. et al.) and International Publication No. WO 93/03093 (Meka et al ), which are incoφorated herein by reference. They are commercially available from Exxon Chemical Company,

Houston, TX, under the tradena e EXACT or from Dow Chemical, Midland, MI, under the tradename AFFINITY. These "single-site" polymers are distinguished from ethylene-α-olefin polymers made using Ziegler-Natta catalysts, which have multiple active sites, in that the single-site polymers typically have narrower molecular weight distributions and more desirable α-olefin short-chain branching distributions.

Examples of suitable materials containing ethylene monomeric units for use in the barrier films of the present invention include, but are not limited to: ethylene- vinyl acetate methacrylic acid teφolymer; ethylene-vinyl acetate copolymer; ethylene acrylic acid copolymer; ethylene methyl acrylate copolymer; anhydride modified ethylene acrylate teφolymer; acid modified ethylene acrylate teφolymer; ethylene propylene elastomer; ethylene octene copolymer; maleic acid grafted ethylene-vinyl acetate copolymer; anhydride modified low density polyethylene; linear low density polyethylene; anhydride modified linear low density polyethylene; anhydride modified high density polyethylene; and ethylene butene copolymer. A particularly preferred group of polymeric materials containing ethyene monomeric units for use in the barrier films of the present invention includes: ethylene-vinyl acetate methacrylic acid teφolymer; ethylene-vinyl acetate copolymer; ethylene acrylic acid copolymer; ethylene methyl acrylate copolymer; anhydride modified ethylene acrylate teφolymer; acid modified ethylene acrylate teφolymer; maleic acid grafted ethylene-vinyl acetate copolymer; ethylene propylene elastomer; ethylene octene copolymer; ethylene butene copolymer; anhydride modified linear low density polyethylene; and anhydride modified linear low density polyethylene.

As stated above, a preferred class of materials suitable for use in heat sealable layer 14 is a heat sealable material containing an ethylene-α-olefin polymer, particularly a single-site ethylene-α-olefin polymer. Preferred ethylene-α-olefin polymers are chosen such that the films of the present invention are heat sealable to polypropylene substrates at a temperature of about 200-350°F (93-177°C), preferably at as low a temperature as possible, e.g., 200-230°F (93-110°C). Furthermore, preferred ethylene-α-olefin polymers are chosen such that layer 14 does not delaminate from

layers 12 and 13, and that layer 14 readily forms a peelable bond to polypropylene substrates. Thus, preferred ethylene-α-olefin polymers are chosen such that the peel force, i.e., the amount of force required to peel a film of the present invention from a polypropylene substrate to which it is sealed, is less than the internal cohesive strength of the ethylene-α-olefin polymer itself and less than the adhesive strength between the ethylene-α-olefin polymer and the carbon-coated base layer. In this way, such preferred films can be peeled from polypropylene substrates leaving little or no residue.

For desired adhesion, peelability, and tack, the total α-olefin content of the preferred single-site ethylene-α-olefin polymer, is preferably about 10-30 wt-%. More preferably, the total α-olefin content of the polymer is within a range of about 10- 20 wt-%, based on the total weight of the polymer. Most preferably, the α-olefin content is about 10-19 wt-% for applications requiring food grade materials, although it is even more preferred if this is about 10-15 wt-%, particularly for food grade applications. Useful ethylene-α-olefin polymers are characterized as having a low degree of crystallinity and a low degree of elasticity such that the polymers readily flow in the molten state. Preferably, the density is less than about 0.940 g/cm , more preferably less than about 0.930 g/cm 3 , and most preferably less than about 0.915 g/cm 3

(as determined by ASTM Test Method D 792-91, Method A, 1991). The density of the single-site ethylene-α-olefin polymers is preferably about 0.880-0.915 g/cm and more preferably less that about 0.900 g/cm . These polymers are thus a type of very low density polyethylene (VLDPE).

The preferred single-site ethylene-α-olefin polymers are also characterized as having a relatively narrow molecular weight distribution and/or a relatively small number of carbons in the short side-chain branches of the otherwise linear ethylene polymer. Preferably, useful ethylene-α-olefin polymers have a polydispersity, i.e., a molecular weight distribution (Mw/Mr,), of less than about 3.5, more preferably less than about 3.0, and greater than about 1.5. Most preferably, the

preferred single-site ethylene-α-olefin polymers used in the heat sealable layers of the packaging films of the present invention have a polydispersity within a range of about 2.0-3.0.

The composition distribution of the preferred single-site ethylene-α- olefin polymers is preferably less than about 40 total carbons in the short chain branches (which result from the addition of the α-olefin monomers) per 1000 carbons in the polymer, and more preferably within a range of about 5-35 per 1000. Alternatively, the composition distribution of the preferred single-site ethylene-α-olefin polymers can be reported as the composition distribution breadth index (CDBI). Preferably the CDBI is at least about 50%, and more preferably at least about 70%. The CDBI is the weight percent of the polymer molecules having a comonomer content within 50% of the median molar comonomer content. Either way of reporting, the composition distribution can be determined by Temperature Rising Elution Fractionation as described by Wild et al, J. Polv. Sci.. Polv. Phvs. Ed.. 20, 441 (1982). The preferred single-site ethylene-α-olefin polymers should also have an essentially single melting point characteristic with a peak melting point (T _m ) of no greater than about 100°C, as determined by Differential Scanning Calorimetry (DSC). More preferably, the DSC peak T _m is about 50°C to about 100°C. "Essentially single melting point" as used herein means that at least about 80% by weight of the material corresponds to a single T _m peak. Preferably, the melt index of useful ethylene-α-olefin polymers for the films of the present invention is greater than about 1.0 gram/10 minutes, more preferably about 1-100 grams/ 10 minutes, as determined by ASTM Test Method D1238-90B, Method A, 1990.

Ethylene-α-olefin polymers that meet all the requirements of the polymers used in the heat sealable layers of the films of the present invention include those prepared using single-site catalysts as defined above. As indicated herein, however, not all single site ethylene-α-olefin polymers are suitable for use in the barrier films of the present invention if they are to be peelable without leaving a residue, particularly when used on a polypropylene substrate. For example, those having an α-

olefin content of 9.0% or less do not adhere well to polypropylene substrates Also, those having an α-olefin content of greater than about 30% are generally too tacky

In particularly preferred embodiments of the packaging films of the present invention, the heat sealable material of layer 14 contains a blend of an ethylene- containing polymer (i.e., polymer containing ethylene monomeric units), particularly an ethylene-α-olefin polymer, and a compatible elastomeric polymer, e.g , rubber, having a low degree of crystallinity and tack As used herein, the term "compatible" means that the elastomeric polymer does not bloom from the composition Preferably, the compatible elastomeric polymer has a glass transition temperature (Tg) of less than about 0°C, and a molecular weight (Staudinger) of greater than about 10,000, more preferably about 11,000-99,000 Most preferably, the elastomeric polymer is food grade, i.e , contains no toxic extracts Suitable such elastomeric polymers include polyisobutylene and ethylene propylene rubber The preferred elastomeric polymer is polyisobutylene. The addition of the elastomeric polymer increases the heat seal window of the films to ranges greater than about 80°F (44°C), preferably greater than about 100°F (56°C), thereby allowing the films to withstand inexact heat sealing processes Preferably this blend includes at least about 10%, more preferably about 10% to about 40%, and most preferably about 10% to about 30% elastomeric polymer, e.g, polyisobutylene, based on total weight of the blend If the compatible elastomeric polymer content of the blend is less than about 10% by weight, there is no significant increase in the heat seal operation temperature window. If it is greater than about 40% by weight, the composition, i e , blend, is too tacky, does not flow well, and causes blocking problems The blend containing the elastomeric polymer can be prepared by blending the rubber using a twin screw extruder designed for rubber, such as is available from the Bonnot Co, Creen, OH, with the ethylene-α-olefin polymer using a standard twin screw extruder The molten polymeric blend is then extruded as a rod form into a water bath The solid blend can then be pelletized using a standard chopper

Heat sealable layer 14 can also contain small amounts of other materials, such as the additives described above for the base layer 12, so long as these materials do not adversely affect the function of the polymers. The total amount of additives in heat sealable layer 14 generally should not exceed about 40% of the total weight of the composition; however, for food grade films, the total amount of additives in layer 14 should not exceed about 5%.

The thickness of heat sealable layer 14 is not necessarily critical, although there should be a sufficient amount of polymer containing ethylene monomeric units to provide sufficient adhesion to the carbon layer (i.e., at least about 15 ounces inch (167 g/cm) peel strength) once treated with an active gas surface treatment, e.g, corona. It preferably ranges from about 0.3 mil (0.0008 cm) to about 10.0 mils (0.0254 cm), more preferably from about 0.5 mil (0.00127 cm) to about 5.0 mils (0.0127 cm), and most preferably from about 1.0 mil (0.00254 cm) to about 5.0 mils (0.0127 cm). The choice of thickness is determined by intended use of the film. Heat sealable layer 14 is bonded to barrier layer 13 by treating the heat sealable polymeric material with an active gas surface treatment technique. Examples of such surface treatment techniques include corona, flame, ozone, and plasma treatment processes. Subsequently, the two layers are treated with heat. Preferably, the heat sealable ethylene-containing polymeric material is corona treated. Corona discharge treatment of polymeric films to impart certain surface characteristics, e.g, adhesive properties, generally involves electrostatically treating the surface of the film. If the carbon-coated surface is treated, however, the heat sealable polymers of the present invention do not adhere well to the active gas treated carbon- coated films. Rather, it has been discovered that the surface of the polymer containing ethylene monomeric units must be treated with an active gas surface treatment process (preferably corona-treated) for good adhesion to the carbon-coated film. This can be accomplished by coating the heat sealable polymer on a carrier film, i.e., any high temperature material, e.g, polyester or paper, and then subjecting the heat sealable polymer to an active gas surface treatment process. The treated surface is then placed in contact with the carbon surface of the carbon-coated base layer and the layers are

laminated together under the influence of heat at a temperature of at least about 180°F (82°C), preferably at least about 200°F (93°C), and more preferably at least about 250°F (121°C), up to the melting temperature of the base film If the heat sealable polymer has a sufficiently high tensile strength, it may be self supporting, in which case the carrier film is not required Although the carbon-coated film can be treated with an active gas surface treatment process as well, no particular advantage is obtained by doing so

Corona treating involves exposing the material to be treated to a gaseous electrical discharge in which the ionization regions are confined around the active electrodes The specific type of corona used to modify polymer surfaces is the alternating-current (bipolar) streamer corona, which is characterized by two metallic electrodes at least one of which is covered with a dielectric material The material to be treated is typically located on the grounded electrode Suitable corona treatment processes for use in the present invention can be any typical corona treatment process, e.g , nitrogen corona, air corona, oxygen corona, halogen corona, etc The preferred corona treatment process, however, involves air corona treatment Methods for standard corona treatment processes are described, for example, in U S Patent Nos 3,705,844 (Haas), 3,546,065 (Ostermeier), 3,503,859 (Goncarovs et al ), and 3,754,117 (Walter) Typically, at least about 0 1 Joule/cm of energy can be used, although 0 3- 1 0 Joule/cm is preferred Corona systems are commercially available from Pillar Technology Ltd Partnership (Hartland, WI)

Flame treatment of polymeric films is also well known in the art as a surface modification treatment Many of these processes have been used to increase adherence to the polymer surfaces Representative flame treatment processes are described in U S Patent Nos 2,746,084 (Kreidl), 2,704,382 (Kreidl), 2,684,097 (Kritchever), 2,683,394 (Kritchever), and 2,632,921 (Kreidl)

In a preferred manner, the material of heat sealable layer 14 is applied to a carrier film in a molten state by a conventional extrusion process The temperature of the material of layer 14, when in the extruder, typically ranges from about 280°F

(138°C) to about 560°F (293°C). A typical process temperature profile for a three-zone extruder is 410°F (210°C) (Zone 1), 470°F (243°C) (Zone 2), 510°F (266°C) (Zone 3), 510°F (266°C) (die). The temperature of the material of layer 14, as it exits the extruder, typically ranges from about 300°F (149°C) to about 560°F (293°C). Referring to Fig. 2, a polymeric material is used as the carrier film 20 for the heat sealable material 21 applied from an extruder 22. After the heat sealable material (layer 14, Fig. 1) is applied to the carrier film 20 by extrusion, the thus-formed composite structure 24 can be allowed to cool to a temperature below about 180°F (82°C). However, such cooling is not necessarily required. The heat sealable material (layer 14, Fig. 1) is then air corona treated in the corona treatment system 25, although flame treatment, plasma treatment, and ozone treatment are also possible. The corona-treated composite structure 26 (i.e, corona-treated heat sealable material on carrier film 20) is then placed in contact with a carbon-coated polymeric material 27 prepared as described above, such that the barrier layer of carbon-rich material (layer 13, Fig. 1) is placed in contact with the heat sealable material (layer 14, Fig. 1). The heat sealable material is then laminated to the barrier layer of carbon-rich material by exposing the thus formed composite structure 28 to a temperature of at least about 180°F (82°C) and no greater than about the melting temperature of either the base film on which the carbon is coated or the carrier film on which the heat sealable material is coated. If polyethylene terephthalate is used for the base film or the carrier film, this maximum temperature is about 480°F (249°C). Preferably, the lamination occurs at a temperature of about 240°F (116°C) to about 310°F (154°C). This composite structure 28 is then allowed to cool to a temperature below about 100°F (38°C). The carrier film 20 is then removed and can be rewound and reused if desired. The final product 29 contains a base layer (layer 12, Fig. 1), a barrier layer of carbon-rich material (layer 13, Fig. 1), and a corona- treated, heat sealable layer (layer 14, Fig. 1).

The multiple-layer composite films of the present invention can be used as barrier films inside milk or juice cartons or pouches, blood bags, medicine bags, or as lidding films, standard innerseals, one-piece or two-piece innerseals, tabbed innerseals,

blister packs, and the like. The films of the present invention can be used to advantage in place of barrier films containing polymeric or inorganic thin barrier films. Polymeric barrier films are not generally desirable because they are moisture and/or temperature sensitive. That is, as the humidity and temperature rise, the barrier properties decrease. The typical inorganic barrier films, e g, Al, AI ₂ O ₃ , SiO _x (x = 1.5-1.8), SiO ₂ , etc, are not generally desirable because of environmental concerns and/or flexibility problems.

Preferred embodiments of the multiple-layer composite film of this invention can be used as a peelable film. For example, it can be adhered to the lip of a polypropylene container, from which it can be peeled away when desired The film can also be used as a fusible film. For example, it can be adhered to the lip of a polyethylene container by means of fusing. Fused films are generally removed by penetrating the film, e.g, with a cutting tool, and tearing the penetrated film away from the container.

Preferred multiple-layer composite films of this invention can be used for lidding and sealing functions, particularly if the containers are made of polymers having a high concentration of propylene monomeric units, at least at the point where the lid or seal is attached to the container. Figure 3 illustrates a container 30 in the form of a tray 32 having a wide mouth 34. Surrounding mouth 34 is a lip 36. Lip 36 of tray 32 is preferably formed from a polymer containing propylene monomeric units, which can contain small amounts of other monomers such as ethylene. Multiple-layer composite film 10 is bonded to lip 36 of tray 32 by means of layer 14.

Figure 4 illustrates a container 40 in the form of a bottle 42 having a mouth 44. Surrounding mouth 44 is a lip 46. Lip 46 of bottle 42 is preferably formed from a propylene polymer. Multiple-layer composite film 10 is bonded to lip 44 of bottle 42 by means of layer 14. Container 40 can also have a cap 48. Cap 48 can be of conventional construction. It can be made of metal or a polymer, but is preferably a polymer, such as polyethylene or polypropylene. Cap 48 can be placed over mouth 44 and lip 46 of container 40 and secured to container 40 by tightening Multiple-layer composite film 10 can be sealed to lip 46 by means of heating the heat sealable polymer of layer 14. Alternatively, the multiple-layer composite film 10 can be sealed to lip 46 by means of applying pressure if the heat sealable ethylene-containing polymer of layer 14 is

also a pressure sealable adhesive, e g, a torque sealable adhesive A pressure sealable adhesive that is both heat and pressure sealable can be used with a container having a lip made of glass, metal, or a polymer. These constructions are considered to be one-piece innerseals These films could also be incoφorated into two-piece innerseals Lids and innerseals can be applied to the lip of a container manually by means of a heated platen, but it is economically advantageous to use heated rollers to kiss seal the multiple-layer composite film to the lip of a container Typical conditions for sealing layer 14 to a substrate containing a propylene polymer, for example, are the following: temperature = 230°F (110°C) up to the base film melting temperature, pressure = 40 lbs/in ² (2 76 x 10 ⁵ Pa), and dwell time of 0 5 to 2 seconds

Again, if the heat sealable polymer is also pressure sealable, such as any of the heat sealable ethylene-containing polymers, i e , polymers having ethylene monomeric units, disclosed in U.S Patent No 4,327,147 (Ou-Yang), lids and innerseals can be applied to the lip of a container by application of pressure Such pressure sealable, e g , torque or shear activatable or sealable, materials can also be used in a distinct layer on top of the heat sealable layer A layer of pressure sealable material can be adhered to the heat sealable layer by means of heating or by means of an adhesive tie layer. If a pressure sealable adhesive is used in addition to the heat sealable material, pressure sealable adhesives other than those disclosed in U S Patent No 4,327,147 (Ou-Yang) can be used For example, the acrylonitrile torque activatable materials disclosed in U S Patent Nos 4,935,273 (Ou-Yang) and 5,145,929 (Ou-Yang) can be used

Other means of sealing layer 14 to a substrate include induction heating, i e , when the multiple-layer composite film is a component of a seal, e g , an innerseal Thus, the film can also be used as the sealing component of an induction innerseal Induction innerseals are described in greater detail in U S Patent Nos 4,684,554 (August 4, 1987) and 4,778,698 (Ou-Yang), both of which are incoφorated by reference for the puφose of illustrating embodiments of induction innerseals In the area of induction innerseals, the innerseal can be peelable or tamper resistant Peelable innerseals operate in the same manner as the peelable films described previously

Tamper resistant innerseals operate in the same manner as the fusible films described previously In other words, penetration of the tamper resistant innerseal indicates that the innerseal has been subjected to tampering Whether the innerseal is of the peelable type or of the tamper resistant type, the multiple-layer composite film of this invention can be used in either a standard innerseal, i e , two-piece innerseal or a one-piece innerseal, for example

In addition to induction sealing methods used to create innerseals using the films of the present invention, microwave sealing methods can be used as well as heat-activated and torque-activated methods These constructions are similar, but differ primarily in the layer of material that initially absorbs the energy for puφoses of creating a seal For example, in Fig 5, an innerseal 50, such as an induction innerseal, using the barrier film of the present invention is shown It includes, from top to bottom, a pulp board backing 51 (typically less than about 1500 μm thick and preferably about 1000 μm thick), a wax layer 52 (e.g , microcrystalline wax, typically less than about 100 μm thick and preferably about 25 μm thick), an energy-absorbing layer 53, a base layer 12 of polymeric material, a barrier layer 13 of carbon-rich base layer material adhered to the base layer 12, and a heat sealable layer 14 of a heat sealable material adhered to the barrier layer 13

The energy absorbing layer 53 in Fig 5 can be a layer of aluminum foil for use in absorbing radio frequency energy to produce an induction innerseal Alternatively, energy absorbing layer 53 can be a layer of microwave interactive material, such as vapor coated aluminum, or a conductive polymer, such as polypyrrole, polyaniline, etc The latter examples of conductive polymers could be used to absorb thermal energy applied by a heated roller In these embodiments, an adhesive or tie layer is typically also used between the base layer 12 and the energy absorbing layer 53, although this is not shown in Fig 5 An example of a useful laminating adhesive is Adcote 503 urethane available from Morton Industries Such adhesives are particularly useful for containers made with materials having a high surface energy, such as polyester and polyvinyl chloride

As shown in Fig. 6, an induction innerseal 50 is mounted inside screw- on cap 60. Although not a requirement, the innerseal 50 can be mounted into the screw- on cap 60 with an adhesive between the pulp board backing 51 and the inner roof of the top. After container 61 has been filled, cap 60 is screwed over the mouth and lip of container 61. The capped container is then passed through a radio frequency field, whereby the resulting eddy currents inductively heat the aluminum foil layer 53 (tie layer between aluminum foil layer 53 and base layer 12 not shown) and simultaneously melt wax layer 52 and heat sealable adhesive layer 14. As wax 52 melts, it is absorbed by pulpboard backing 51. As the capped container cools to room temperature, heat- sealable adhesive 14 bonds firmly to the lip of container 61. Once sealed, when the cap 60 is unscrewed from the container 61, pulpboard backing 51 twists free from the barrier film, i.e., base layer 12, barrier layer 13, and heat sealable material 14, which remains firmly bonded to the lip of the container 61. The seal is strong and resistant to internal pressures which may build up within the container. The waxed pulpboard backing remains in the cap to permit resealing after the innerseal has been removed or punctured. An innerseal such as this is often referred to as a two-piece innerseal. In some instances, the pulpboard material and the wax layer of the innerseal may be omitted, particularly if resealability is unnecessary. An innerseal such as this is often referred to as a one-piece innerseal. The barrier films of the present invention can also be used in tabbed innerseals, e.g, ear tabbed or top tabbed innerseals. Top tabbed innerseals are described in greater detail in U.S. Patent Nos. 4,934,544 (Han et al.) and 5,004,111 (McCarthy), both of which are incoφorated by reference for the puφose of illustrating embodiments of top tabbed innerseals. Referring to Fig. 7, a container 70 having a neck portion 72 and a rim, i.e., lip 76, includes a raised helical thread 74 formed upon neck portion 72 over which an appropriate sealing cap with mating threads may be applied. An arrangement 78 is provided for sealing an orifice defined in container 70 by rim or lip 76. Sealing arrangement 78 includes a removable innerseal 80 having a circular body portion 82 which includes an upper surface facing away from container 70. Innerseal 80 further includes a tab portion 84 attached to the upper surface of the circular body portion 82.

Referring to Fig. 8, the top tabbed innerseal includes (from bottom to top) a layer of a heat sealable material 14, a barrier layer 13, a base layer 12, an adhesive layer 88 for bonding force transmitting layer 89 to the base polymeric layer 12 of the barrier film.

The barrier films of the present invention can also be used in pouches for packaging medical items, food, juice, and other perishable items. Referring to Fig. 9, the pouch 90 is formed from two panels 94 and 95 out of multilayer barrier film 10 (Fig. 1), wherein the heat sealable layers are facing each other. The two panels 94 and 95 are aligned and three of the four edges, 96, 97, and 98 are heat sealed, leaving one side 99 open to permit filling with the desired item. The films may be laminated together using conventional equipment and techniques. For example, form, fill, and seal machinery can be used. In this process, two superimposed layers of the multilayer film of the desired width with the heat sealable layers facing each other are fed into the packaging machine. Bar seals fuse three sides of the square or rectangular pouch and a jaw separates the pouch with one open end. Food is then introduced into the pouch through the open end. Finally, the machine heat seals the open end producing a fully closed pouch.

Another commonly used container in which the barrier films of the present invention can be used include gable-top cartons, e.g, milk cartons. As shown in Fig. 10, a gable-top brick milk carton 100 using the barrier film of the present invention includes, from outside to inside, a wax layer 102 (e.g, paraffin wax), paper board backing 104, a layer 14 of a heat sealable material, a barrier layer 13 of carbon-rich material, and a base layer 12 of polymeric material. It should be understood that the thickness of each of these layers relative to the overall dimensions of the gable-top carton is exaggerated. A similar order of layers would be used for brick packs. Gable- top cartons are described in greater detail in U.S. Patent No. 5,083,702 (January 28, 1992) and brick packs are described in greater detail in U.S. Reexamination No. 33,893 (Elias et al ). Both of these more detailed discussions are incoφorated by reference for the puφose of illustrating such embodiments.

Finally, Fig. 11 shows a blister pack container for medicaments, for example, in the form of capsules, pills, and the like. In this embodiment, the heat sealable layer 14 of the multiple-layer composite film 10 of the present invention is laid

against the flanges 120 of a transparent, multi-compartment blister 122, each compartment of which contains one capsule 124. Once layer 14 is sealed to flanges 120 of the blister, a medication card is formed.

In the examples which follow, multiple-layer composite films were prepared by extruding a layer of a heat sealable polymer having ethylene monomeric units, or a blend of a heat sealable polymer and a compatible rubber, onto a polyethylene terephthalate carrier film. The heat sealable layer was then air corona treated using 0.4 Joule/cm , unless otherwise stated This corona-treated, heat sealable layer on the carrier film was then combined with a carbon-coated base layer of polyethylene terephthalate such that the heat sealable layer and the carbon were in contact This construction was then laminated by heating at a temperature of about 180°F (82°C), and allowing the construction (PET/heat sealable layer/carbon/PET) to cool to less than about 100°F (38°C). The PET attached to the heat sealable layer was then removed.

The invention will be further described by reference to the following detailed examples. These examples are offered to further illustrate the various specific and preferred embodiments and techniques It should be understood, however, that many variations and modifications may be made while remaining within the scope of the present invention. All percentages in the Examples and throughout the discussion of the invention are in weight percentages, unless otherwise noted.

Experimental Examples

Test Methods

180° Peel Test Adhesion strength between the heat sealable layer and the carbon-coated base layer was determined by means of a 180° Peel Test. The procedure is as follows: (1) from a roll of polyethylene terephthalate coated with a heat sealable layer and ethylene vinyl acetate tie layer (0.5 mil PET/0.3 mil EVA/1 mil heat sealable layer), samples 1 inch (2.54 cm) wide by 4 inches (10.16 cm) long were cut; (2) a sheet of

carbon-coated polyethylene-terephthalate (0 5 mil PET/200-300 A carbon) approximately 5 inches (12 7 cm) by 4 inches (10 16 cm) was cut, (3) three samples of composite film were placed on the carbon-coated PET sheet (surfaces to be sealed should be clean and dry) and sealed via the heat sealable layer using a Sentinel heat sealer [sealing conditions desired temperature - 350°F (177°C), 40 lbs/in ² (2 76 x 10 ⁵ Pa), 1 5 second dwell time with the PET/EVA/heat-sealable film located next to the upper sealer jaw and the PET/carbon film located next to the lower sealer jaw], (4) when the seals had cooled, the composite sheet was cut into three sections taking care not to cut into the composite film, (5) all sealed samples were conditioned at room temperature for 24 hours after sealing before the Instron 180° Peel Test was performed, (6) the peel strength was tested at room temperature (i e , 20-30°C) by placing the PET/EVA/heat-sealable film in the upper jaw of an Instron 180° peel testing apparatus and the PET/carbon film in the lower jaw of the Instron apparatus [the Instron apparatus was set at 100 ounces (2838 g) scale with crosshead speed of about 12 inches (30 48 cm) per minute and chart speed of about 5 inches (12 7 cm) per minute and jaw separation at 3 inches (7 62 cm)], (7) the entire seal was then pulled and the jaws pulled away from each other at a speed of about 12 inches (30 48 cm) per minute and the maximum force in ounces/inch necessary to separate the heat sealable layer from the carbon layer recorded Alternatively, this test can be used to determine adhesion between the heat sealable layer and the carbon-coated base layer of the films of the present invention by testing self-adhesion This was done by placing two portions of the film together (0 5 mil PET/200-300 A carbon/ 1 mil corona-treated heat sealable layer), heat sealable layers facing each other This was then heat sealed using a Sentinel heat sealer (temperature = 350°F (177°C), 40 lbs/in ² (2 76 x 10 ⁵ Pa), 1 5 second dwell time) The two portions of the film were then conditioned at room temperature for 24 hours, and subsequently placed in the jaws of the Instron apparatus and the maximum force required to separate the bond recorded Typically, self adhesion results for the films encompassed by the present invention were greater than about 150 ounces/inch (1 7 g cm)

O? Transmission Test — The barrier films were tested for oxygen permeability on an Oxtran 1000H Permeability Tester commercially available from Modern Controls, Inc., Minneapolis, MN. The test was performed according to ASTM D 3985-81 (1988) using an aluminum foil standard for calibration. A 10.16 cm x 10.16 cm film sample was conditioned for 24 hours at room temperature (about 21°C). The temperature in the tester was maintained at 26°C and the station dwell time was 15 minutes. The heat sealable side (or barrier layer side) of the barrier film was positioned downward over the cell and the test was conducted with dry oxygen. The test results are reported as cubic centimeters per square meter per day (cc/m day). These are all reported as per atmosphere.

H?O Transmission Test — The barrier films were tested for moisture permeability on a Permatran W-6 Permeability Tester manufactured by Modern Controls, Inc., Minneapolis, MN. The test was performed according to ASTM F 1249-90 using aluminum foil for calibration, and a 10.16 cm x 10.16 cm film sample. The sample was placed, with the heat sealable film side (or barrier layer side) positioned up, over a cell that had been filled about halfway with deionized water. The film was left in the tester overnight to condition it, and the test was conducted for 60 minutes with a gas pressure of 15 psi (1.0 x 10 Pa) before a result was recorded. Test results are reported in grams per square meter per day (g/m day).

Gelbo Flex Test — The test was performed on a Gelbo Flex Tester, manufactured by the United States Testing Company, Hoboken, NJ using the procedure outlined in ASTM F 392-74 (1 79), except that the film, clamped in the cylindrical shape described in the test procedure, was twisted 360°. In the test, one cycle consisted of one 360° rotation of the film cylinder and a reverse rotation of the film cylinder back to the starting point. After the designated number of cycles, the film was tested for oxygen and moisture permeability.

Abrasion Test

The abrasion resistance test is a measure of the ability of a film to maintain barrier properties when subjected to abrasion with a coated abrasive, i.e., sandpaper. The barrier films of the present invention were tested using a Sutherland Rub Tester, manufactured by James River Coφ. of Kalamazoo, MI. A 1200 grit coated abrasive (manufactured by Minnesota Mining & Manufacturing Co.) was adhered to a 908 gram test block with double coated adhesive tape. The test block was attached to an arm which was used to move the test block back and forth across a sample. A film sample, measuring 10.16 cm x 10.16 cm was mounted onto a Teflon™ coated rubber cushion located below the test block with the barrier surface (or heal sealable surface) facing the coated abrasive. One cycle consisted of one stroke forward and one stroke back across the film sample. A new sheet of coated abrasive was used for each sample. Samples were subjected to 5 or 10 cycles as indicated in the examples.

Extension Resistance Test

The extension resistance test is a measure of the ability of a film to maintain its barrier properties upon stretching and exposure to ambient and elevated temperatures. The apparatus used for this test included two clamps wide enough to secure a 16.5 cm wide film with uniform pressure across the width of the film. One of the clamps stayed in a fixed position, while the other clamp was moved away from the fixed clamp by a pair of adjustment screws located on each side of the clamps. A film measuring 16.5 cm x 33 cm was carefully mounted into the clamps such that the film was in a horizontal position and was free of wrinkles. The adjustment screws were then turned simultaneously and slowly to stretch the film the desired amount (3% or 4%), at an extension rate of about 1 to 2 cm per 10 seconds. For example, if the film distance between the clamps was 30 cm and a stretch of 3% was desired, the adjustment screws were turned to stretch the film between the clamps to a length of 30.9 cm. The stretched film, clamped in the apparatus, was then conditioned at either room temperature (about 21°C) or at 100°C for 10 minutes. The film was brought to room

te perature, and then removed and tested for oxygen and moisture permeability (about 10 minutes to cool) as described above.

Example I

Table 1 compares the barrier properties (O ₂ and H ₂ O transmission) of six conventional films (I- VI) and a film of the present invention (VII). The values for the six conventional films are literature values. For the following films, PET = polyethylene terephthalate, CPP = crystallized polypropylene, EVOH = ethylene vinyl alcohol, E-O = ethylene-α-olefin polymer, PVDC = polyvinylidine dichloride, LLDPE = linear low density polyethylene, AmC = amoφhous carbon. Film VII is a film of the present invention containing a layer of carbon (300 A thick) on a 0.56 mil (1.4 x 10 ^"3 cm) dual layer video grade polyethylene terephthalate film - only one layer of which contained less than about 1% by weight of an Siθ ₂ slip agent (OX-50 from Degussa of Germany) (previously wrapped for storage handling in a packaging film with moisture barrier characteristics, manufactured by Minnesota Mining and Manufacturing (St. Paul, MN)) using a layer of ethylene butene copolymer available as EXACT 3027 from Exxon Chemical Co, [about 1 mil (2.54 x 10 ^* cm) thick] coated on the carbon. The data in Table 1 demonstrates that the films of the present invention display good barrier properties, i.e., low O ₂ and H ₂ O transmission, and qualify as "ultrahigh" barrier films

Table 1 The Barrier Properties of Selected Composite Barrier Films

O ₂ H ₂ O

Construction Composite Barrier Transmission Transmission Film (c.cJm -day) (gm/m -day)

I PET/EVOH/LLDPE < 1.0 5.3

II PET/PVDC/CPP 1.6 1.1 in PET/AI ₂ O ₃ /LLDPE 1-2 1-2

IV PET/Al/CPP < 1.0 < 1.0

V PET/SiO _x /LLDPE < 1.0 < 1.0

VI PET/SiO ₂ /LLDPE < 1.0 < 1.0

VII PET/AmC/E-O < 1.0 < 1.0

Example II

Table 2 compares the barrier properties (O ₂ and H ₂ O transmission) of five conventional films (VHI-XJT) after physical abuse. The values for films Vm to XII are an average of three tests. Film VQI is a PET film coated with aluminum deposited from aluminum vapor. Film IX is a PET film coated with SiO _x , which was obtained from ULVAC Japan, Ltd, Kanagawa, Japan. Film X is a "QLF" film, which was obtained from ALRCO Coating Technology, Concord, CA. Film XI is a PET film coated with AI ₂ O ₃ , which was obtained from Flex Products, Inc., Santa Rosa, CA. Film XJT is a film made according to the present invention, but without the ethylene-containing polymer layer coated on the carbon-rich layer. All PET base layers were about 12 μm thick except for the PET base layer of film VHI, which was 50 μm thick. The PET base layer of films Vm and XII was a 0.56 mil (1.4 x 10 ^" cm) dual layer PET film described in Example I. All barrier layers (Al vapor, Siθ ₂ , AI ₂ O ₃ , AmC) were about 250 A thick, except for the SiO _x barrier layer of film IX, which was about 1,000 A thick.

The Gelbo Flex Test, the Abrasion Test, and the "Stretch" Test (i.e., Extension Resistance Test) were performed as described above. Water and oxygen permeability tests were then performed on samples subjected to each of these conditions, i.e., flexing, abrading, and stretching. These results indicate that carbon- coated films are much less susceptible to damage as a result of physical abuse than are films having Al- or Si-containing barrier layers

coated films are much less susceptible to damage as a result of physical abuse than are films having Al- or Si-containing barrier layers.

Table 2 The Barrier Properties After Physical Abuse For Barrier Film

H ₂ 0 Tran. After Physical O2 Tran. After Physical Abuse Abuse

(gm/m -day) (c.c./m -day)

Construction Composite Gelbo Gelbo Barrier Flex Abrasion Stretch Flex Abrasion Stretch Films 5 cycles 10 cycles 4% 5 cycles 5 cycles 3%

VIII PET/A1 4.55 2.65 5.12 — 5.96 2.84 vapor

IX PET/SiOx *~ 42.69 38.90 — Over 7.69 (2.5%) limit

X PET/Siθ2 9.39 7.15 35.86 14.3 9.25 18.20

XI PET/AI ₂ 0 ₃ 13.96 8.93 22.86 - - >50.0

XII PET/AmC 3.90 1.72 1.64 - 1.21 1.80

'Over limit" = machine shut down.

A sample of 0.56 mil (1.4 x 10 ^" cm) PET film (which had been corona treated, prepared with less than about 1% of a Siθ ₂ slip agent, and wrapped for storage/transport in a packaging film with moisture barrier characteristics) manufactured by Minnesota Mining and Manufacturing Company (St. Paul, MN) containing a carbon- rich coating about 100-200 A thick was determined to have water vapor permeability values of 1-2 g/m 2 -day. After lamination, i.e, overcoating with about 1 mil (2.54 x 10 3

cm) of ethylene butene copolymer available under the tradename EXACT 3027 from Exxon Chemical Company, Houston, T the water vapor permeability values were below 1 g/m ² -day. In a series of experiments, carbon coated and laminated samples

₇ although this value was still lower than the PET film alone (30 g/m -day) or the PET film with the polymer laminated onto it without the carbon coating (18 g/m -day). The laminated samples containing the carbon coating and ethylene butene copolymer as an overcoat, however, which were folded up to six times, revealed a high degree of flexibility which resulted in a slow deterioration of the barrier properties. That is, the water vapor permeability values increased slightly, but remained below about 2 g/m - day. Thus, the corona-treated, heated sealable, ethylene-containing polymer not only acts as a heat seal layer, but also improves the properties of the barrier film, and protects it from mechanical abuse.

Example HI

Tables 3 and 4 compares the 180° Peel Adhesion Strength between various heat sealable layers and carbon-coated polyethylene terephthalate (0.56 mil (1.4 x 10 ^" cm) film, (described in Example I) with and without air corona treating. The heat sealable layer was laminated onto an ethylene vinyl acetate-coated polyethylene terephthalate film, which was then heat sealed onto a carbon-coated polyethylene terephthalate film and tested according to the procedure outlined above in the description of the 180° Peel Test.

The product name and manufacturer of the materials listed in Tables 3 and 4 used in the heat-sealable layers are as follows: Film XHI, EL VAX 4260 obtained from E.I. DuPont deNemours Company, Wilmington, DE; Film XTV, BYNEL 2022 obtained from DuPont; Film XV, MODIC E-300K obtained from Mitsubishi Petrochemical Co, Ltd, Tokyo, Japan; Film XVI, EPM 306 obtained from Polysar Rubber Division, Mobay Coφoration, Akron, OH; Film XVII, ethylene octene copolymer with 20% 1 -octene obtained from Dow Chemical Company, USA, Midland, MI; Film XVEI, SURLYN 1702 obtained from DuPont, Film XIX, MODIC L-100F obtained from Mitsubishi Petrochemical Co, Ltd.; Film XX, MODIC P-300M obtained from Mitsubishi Petrochemical Co, Ltd.; Film XXI, NUCREL 3990 obtained from DuPont; Film XXII, MALINEX 850 obtained from ICI Company, Wilmington, DE;

Film XXm, ELVAX 250 obtained from DuPont; Film XXTV, BYNEL E-369 obtained from DuPont; Film XXV, BYNEL E-388 obtained from DuPont; Film XXVI, BYNEL 4105 obtained from DuPont; Film XXVH, BYNEL 4001 obtained from DuPont; Film XXVm, BYNEL E-379 obtained from DuPont; Film XXIX, ATTANE 4603 obtained from Dow Chemical; Film XXX, EXACT 3027 obtained from Exxon Chemical Company, Houston, TX; Film XXXI, SHELL DP-0300 obtained from Shell Chemical Company, Houston, TX; Film XXXΗ, EMAC SP-2205 obtained from Chevron Chemical Company, Houston, TX.

These results show that the classes of ethylene-containing materials useful for the heat sealable layer include ethylene-α-olefin polymers (optionally acid or anhydride modified); ethylene-containing polymers having -C(O)OR (carboxyl) groups, -OC(O)R (acetate) groups, or mixtures thereof (optionally acid or anhydride modified); or acid or anhydride modified polyethylene homopolymers, e.g., low density polyethylene, high density polyethylene, and the like. These results also show clearly the advantages of corona treating to enhance adhesion between the carbon-rich barrier layer and the heat-sealable, ethylene-containing polymer.

Table 3

180° Peel Adhesion Strength Between Heat Sealable Layer and Carbon-Rich Coating

180° Peel Adhesion (oz/in)

Air Corona at

Constructio Heat Sealable Layer No Air 7 watts-min n Corona square feet

XIII Ethylene-vinyl acetate methacrylic 12.3 72.0 acid teφolymer

XIV Acid modified ethylene acrylate 5.0 35.0 teφolymer

XV Maleic acid grafted ethylene-vinyl 0.0 52.0 acetate copolymer

XVI Ethylene propylene elastomer 5.0 45.5

XVII Ethylene octene copolymer 0.0 68.0 xvπi Methacrylic acid ionomer 0.8 2.0

XIX Maleic acid grafted polyethylene 0.0 10.0

XX Maleic acid grated polypropylene 0.0 0.0

XXI Ethylene acrylic acid copolymer 2.0 11.0 ¹

XXII Polyester 0.0 0.0

This value is believed to be low due to an insufficient amount of material in the heat sealable layer (i.e., 0.3 mil (7.6 x 10 cm) thick film).

Table 4

180° Peel Adhesion Strength Between Heat Sealable Layer and Carbon-Rich Coating

180° Peel Adhesion (oz/in)

Air Corona at

Construction Heat Sealable Layer No Air 4.5 watts-min Corona per square feet

XXIII Ethylene-vinyl acetate copolymer 3.5 63.0 xπi Ethylene-vinyl acetate methacrylic 15.7 48.0 acid teφolymer xrv Acid modified ethylene acrylate 5.0 71.0 teφolymer

XXIV Anhydride modified ethylene 6.6 72.0 acrylate teφolymer

XXV Anhydride modified low density 3.0 32.7 polyethylene

XXVI Anhydride modified LLDPE 0.5 29.0

XXVII Anhydride modified high density 0.5 15.7 polyethylene

XXVIII Anhydride modified polypropylene 0.5 6.6

XXIX Linear low density polyethylene 0.0 15.7

XIX Maleic acid grafted polyethylene 0.0 8.7

XX Maleic acid grated polypropylene 0.0 1.5

XVIII Methacrylic acid ionomer 1.0 5.0

XVI Ethylene propylene elastomer 1.0 55.3

XVII Ethylene octene copolymer 0.0 75.0

XXX Ethylene butene copolymer 0.0 84.3

XXXI Polybutene 0.0 0.2

XXI Ethylene acrylic acid copolymer 2.0 45.3

XXXII Ethylene methyl acrylate 2.0 63.7 copolymer

XV Maleic acid grafted ethylene-vinyl 6.5 92.0 acetate copolymer

Exa ple IV

A single screw extruder (2 inch screw extruder) from the Bonnet Co. of Cream, Ohio, in conjunction with a twin screw extruder from APV Chemical Machine, Inc. of Saginaw, MI, was used for compounding polyisobutylene rubber and ethylene-α- olefin polymer. The rubber was extruded with the Bonnot Co.'s single screw extruder at a temperature of 250°F (121°C) to 450°F (232°C), depending on the viscosity of the rubber. The molten rubber met the partially molten ethylene-α-olefin at port 3 of the APVs twin screw extruder, which then continuously blended these molten materials at a temperature of about 285°F (141°C). The blended material was extruded into a cool water trough in a rod shape before being cut into pellet form. This material could then be used for overcoating carbon-rich barrier layers on polymeric base layers.

The complete disclosure of all patents, patent documents and publications cited herein are incoφorated by reference. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for variations obvious to one of skill in the art will be included within the invention defined by the claims.