MXPA97002832A - Multicapa films with better accession between ca - Google Patents

Abstract

The present invention relates to a multilayer film which generally includes: a) a first outer layer consisting of a homopolymer or copolymer of polypropylene, and b) a second layer adhered to the first layer, the second layer contains a homogeneous copolymer of ethylene / alpha olefin having a density less than or equal to 0.92 grams per cubic centimeter. This multilayer film is advantageously used in various applications for packaging food due to its excellent heat sealability, as well as the resistance to cracking and perforation.

Description

MULT1CAPA FILMS WITH BETTER ACCESSION BETWEEN LAYERS Cross-referencing with the related request this application is a continuation in part of the copending application Serial No. 08 / 408,667, filed on March 22, 1995, the description of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION This invention relates to multilayer films in which it is possible to make a heat seal to form a sack, such as a sack for introducing medicinal solutions or packaging food products. More particularly, the invention relates to the muiticapa films having better adhesion between, in this way the heat sealing can be improved and there will be a greater resistance to flex cracking and pinching. At present it is a common medical practice to provide medicinal solutions for parenteral administration (eg, intravenous) in the form of flexible, disposable bags. A class of these sacks is commonly known as an "I.V. bag". These sacks must comply with a series of operating criteria that include the folding, clarity and optical transparency, must be heat resistant at high temperatures and with sufficient mechanical strength to withstand the rigors of use in the environment. The sacks with medicinal solutions should also form a sufficient barrier to the passage of a wet steam and other gases to avoid contamination of the solution they contain. In general, medicinal sacks containing solution are sterilized by heat in an autoclave at about 120 ° C (250 ° F) for periods of 15 to 30 min. Usually, steam is used as a heat transfer medium. Thus, sacks with medicinal solutions must also withstand the high temperatures with which they face during thermosetting without deterioration, for example, by developing leaks in the thermal joint or other type of contaminant defect. The bags with medicinal solution must also have sufficient mechanical resistance to withstand the abuse to which they are usually subjected during use in an environment. For example, in some situations an air chamber or plastic or rubber blister is placed around the bag containing the medicinal solution and pressed at, for example, 300-400 mm / Hg, in order to force the exit of the solution of the bag to the patient. This blister is commonly referred to as a "pressure cuff" and is used, for example, when a patient bleeds profusely to quickly replace lost fluids or, for example, when a patient has high blood pressure, so that a greater amount of fluid should be generated. antagonist pressure in the sac to introduce the medicinal solution into the patient's veins. The bags with medicinal solution must be sufficiently durable to remain leak-free during these procedures. A drawback of the medicinal, multilayer bags containing polyolefins currently available is their inability to continuously resist the application of a pressure cuff over an extended period of time. In particular, these medicinal sacks usually contain one or more layers of polypropylene, for example, as a layer for heat sealing, which is attached to the rest of the film with an adhesive or "tie" layer, usually a homopolymer or anhydride-modified polyethylene copolymer, such as an ethylene / vinyl acetate copolymer or linear low density polyethylene. It has been determined that these bags fail prematurely with the application of a pressure sleeve due to poor adhesion between the polypropylene layer (s) and the adhesive layer (s). Due to poor adhesion, the layer (s) containing polypropylene does not have adequate support and strength with the rest of the film. As a result, the polypropylene layer (s) are very susceptible to breakage during the application of a pressure sleeve due to the increase in pressure in the fluid within the bag. Another consequence of bad adhesion is that, once the polypropylene layer has been broken, the medicinal solution can easily flow out of the bag between the polypropylene layer and the adjacent tie layer. It has also been determined that the adhesion between the layers containing polypropylene and the adjacent tie layers result in different forms of contaminating defects in the multilayer films, and particularly, in the coextruded multilayer films, which are used to form the bags to pack. food and other wrappers for packaging. In this sense, two main types of failure mechanisms have been identified, of which both are activated by the tension and flexion stress which is imparted in flexible films to pack in common food packaging applications. The first type is similar to the failure mechanism described above in relation to the bags for medical solutions, and is a result of the propagation of a stress crack or other imperfection in the film in the area of a thermal joint. When a material with a relatively high coefficient, such as polypropylene, is included in multilayer packaging films, these flaws can potentially be prevented from spreading further in leaks. However, due to the poor adhesion between the polypropylene materials and the traditional bonding layer, the fracture can continue to propagate between the polypropylene-containing layer and the adjacent bonding layer until it reaches the heat-sealed end of the bag, thus forming a hole through which the contents of the bag leave and / or air can enter the interior of the bag. When this happens, both the bag and its contents should be discarded. A second type of failure mechanism associated with poor adhesion between polypropylene materials and traditional binding potato is the development of cracks and / or perforations in the film due to the flexing of the film during food packaging operations. This problem is particularly important in vertical and horizontal "sealing-packing" operations for which a multilayer film wrap is continuously formed in a sack, filled with the food product and then closed with heat sealing. The inventors have found that the use of a polypropylene-containing layer in the multilayer film, which is used in these operations, improves the resistance of the film to flex cracking or the development of perforations, but only if the polypropylene is adequately bound to the polypropylene. rest of the structure of the movie. Accordingly, in the art, there is a need for a multilayer film containing polypropylene, which has better adhesion between the layers, between the polypropylene-containing layer (s) and the rest of the film structure, especially in coextruded multilayer films.

SUMMARY OF THE INVENTION This need is met by the present invention, which makes available a multilayer film consisting of: v a) a first layer consisting of a mixture of polypropylene homopolymer or copolymer and an elastomer; and b) a second layer adhered to the first layer, the second layer consists of a homogeneous ethylene / alpha olefin copolymer having a density less than or equal to 0.89 grams' per cubic centimeter. The first layer, preferably, contains a propylene / ethylene copolymer with from about 2 to about 10% by weight of ethylene and, most preferably, about 4 to about 6% of ethylene.

The elastomer may be selected from the group consisting of styrene-ethylene-butylene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, ethylene-propylene rubber and ethylene-propylene terpolymer- diene Preferably, the elastomer is present in the first layer at a percentage by weight in the range from about 5 to almost 50, and, most preferably from about 10 to about 40. The aforementioned multilayer film of the present invention it is particularly useful as material from which flexible sacks can be formed for packaging and administering medicinal solutions. As such, the first layer preferably functions as a layer for the thermal joint and forms the inner surface of the bag. The second layer preferably serves to join the first, the layer for the thermal joint, with the additional layers that provide the desirable properties when the multilayer film of the present invention is to be used to form a bag for medicinal solutions. These additional layers preferably include: a third layer or central layer adhered with the second, the adhesive layer; a fourth layer or adhesive layer adhered to the third, the central layer; and a fifth layer resistant to heat and abuse adhering to the fourth, the adhesive layer. It has been found that, when used to form bags for medicinal solution, the aforementioned multilayer film provides much better resistance to leakage during the application of a pressure sleeve than the multilayer films based on polyolefin, above. It is believed that this better resistance to leakage is the result of excellent adhesion between the first layer for heat sealing and the second adhesive layer. Surprisingly, the inventor has found that an adhesive layer containing homogeneous ethylene / alpha "olefin copolymer with a density of 0.89 g / cc or less adheres very well to the heat seal layer consisting of a mixture of a homopolymer or copolymer Polypropylene and an elastomer The good adhesion between these layers was unexpected due to their differences, the adhesive layer is mainly polyethylene and the layer for the heat sealing, mainly, is polypropylene.It is considered that, this good unexpected adhesion is the reason why that, the bags for medicinal solution of the present invention had much better performance before the pressure cuff compared to the conventional medicinal solution sacks, in which the adhesive layer which is attached to the layers for the heat-sealing and the central contain A mixture of the components from which the layers for the heat-sealing and the plant are formed. these requirements when the films of the present invention are used in food packaging applications. Thus, according to another aspect of the invention, the multilayer film that is most suitable for packaging food consists of: a) a first outer layer consisting of a polypropylene homopolymer or copolymer; and b) a second layer adhered to the first layer, the second layer consists of a homogeneous ethylene / alpha olefin copolymer having a density less than or equal to 0.92 grams per cubic centimeter. Preferably, the density range of the homogeneous ethylene / alpha plephine copolymer is from about 0.85 to about 0.91 grams per cubic centimeter, and more preferably, from about 0.89 to about 0.91 grams per cubic centimeter. More preferably, the multilayer film is co-extruded. It is possible to carry out various embodiments of the multilayer film for food packaging applications, for example, the film can be a two-layer film, in which case, the second layer serves as an outer layer for the heat-sealing, while that the first layer serves as an outer layer resistant to heat and abuse.

Otherwise, the film may have three or more layers, in which case, the second layer is an inner layer and at least a third outer layer that functions as a layer for heat sealing is included. In this way, the second layer is placed between the first and third layers. Preferably, the third layer consists of a polyethylene homopolymer or copolymer, but if desired, it may contain polypropylene homopolymer or copolymer (in which case preferably it must be bonded to the rest of the film with a homogeneous ethylene / alpha-olefin copolymer). ). In an alternative, the third layer adheres directly to the second layer, so as to form a three layer film. In another version, additional layers are included between the second and third layers. For example, the first and second layers can be repeated as fourth and fifth layers, which adhere directly to each other, with the fourth layer adhered to the second layer and the fifth layer adhered to any of the additional layers (so that the repeated pairs additional of the first and second layers, such as, for example, the sixth and seventh layers) or the third layer to form a film with five layers. An alternative or additional form may be included as an inner layer, an oxygen layer or barrier, such as a material selected from the group consisting of ethylene / vinyl alcohol copolymer, vinylidene chloride copolymer, polyamide, polyvinyl alcohol, polyhydroxyamino ether and polyalkylene carbonate, which is placed between the second and third layers. According to still another aspect of the present invention, a multilayer film as mentioned in the previous paragraph is described, except that one or more additional layers are joined to the first layer containing a homogeneous polypropylene copolymer. In this mode, the first layer is not an outer layer but an inner layer. These additional layers can adhere to provide certain properties to the multilayer film. For example, it may be desirable to increase the stiffness, resistance to high temperatures or resistance to abuse of the film, by including, as an outer layer, at least one material selected from the group consisting of polyamide, polypropylene, polyester. , cellophane, polycarbonate, polyvinylidene fluoride and mixtures of these. The first layer is then placed between the second inner layer and the additional outer layer. This additional outer layer is preferably oriented at least in one direction, and more preferably oriented in the biaxial direction, and is laminated to the first layer containing polypropylene with a suitable adhesive.

The aforementioned multi-layer films, according to the present invention, provide excellent inter-layer adhesion, between the first polypropylene-containing layer and the rest of the film structure due to the surprising good adhesion between the polypropylene-containing layer and the second layer. layer containing a homogeneous ethylene / alpha olefin copolymer. In this way, better heat sealability is obtained, as well as, greater resistance to flex cracking and perforation in a co-extruded film, without having to laminate additional layers to the co-extruded film to achieve these improvements. As such, in theory, the films "are suitable for different food packaging applications, such as, for example, fresh or frozen meat for horizontal or vertical sealing-packing operations.

Definitions As used herein, the terms "film", "multilayer film" and the like, refer to a thermoplastic material, generally in the form of a sheet or in a continuous form with one or more layers of polymeric materials, which they can be linked by any suitable means well known in the art.

As used herein, the phrase "inner layer" refers to any layer of a multilayer film having the two principal surfaces directly adhered to another layer of the film. When the phrase "outer layer" is used in the present, refers to any layer of a multilayer film having only one of its principal surfaces directly adhered to another layer of the film. A multilayer film has two outer layers, each of which has two major surfaces. A main surface adheres to another layer of the film. The other main surface forms one of the two main external surfaces of the film. When the terms "polymer", "polymeric" and the like are used herein, unless specifically defined, they generally include homopolymers, copolymers, terpolymers and mixtures and modifications thereof. When the term "homopolymer" is used herein, it is used with reference to a polymer that is the result of the polymerization of a monomer, that is, a polymer consisting essentially of a single type of repeating unit. When used herein the term "copolymer" refers to polymers that are formed by the copolymerization reaction of at least two different co-reactants, for example, comonomers, and includes all types of copolymers, such as random, block, segmented, grafts, and so on. When the terms identifying the polymers are used herein, such as "polypropylene", "pohylene", "polyamide", "poter", etc., they not only include polymers containing repeating units derived from the monomers known to polymerize a polymer form of the type mentioned, but also include comonomers, derivatives, etc., which can be copolymerized with known monomers to polymerize to produce the aforementioned polymer. The derivatives also include the ionomers of the polymer (s), such as, for example, the metal salts of the copolymers of ethylene and methacrylic acid. As another example, the term "polyamide" comprises both the polymers containing repeating units derived from the monomers, such as caprolactam, which is polymerized to form a polyamide, as well as the copolymers derived from the copolymerization of the caprolactam with a comonomer , which, when polymerized alone, does not result in the formation of a polyamide. In addition, the terms that identify the polymers also include "blends" of these polymers with other polymers of different type. When the term "ethylene / alpha olefin copolymer" is used herein, ethylene copolymers are generally defined with one or more comonomers selected from the alpha olefins of c3 to C20, such as 1-butene, 1- pentene, 1-hexene, 1-heptene, methyl pentene and the like, in which the polymer molecules consist of large chains with relatively few side chain branches. These polymers are obtained by low pressure polymerization processes, and the side branches that are present will be short compared to the non-linear pohylenes (e.g., LDPE, a pohylene homopolymer of density). The ethylene / alpha olefin copolymers usually have a density range of about 0.85 g / cc to about 0.96 g / cc. The term linear low density pohylene (LLDPE) is generally understood to include this group of ethylene / alpha olefin copolymers which falls within the range of from about 0.915 to about 0.94 g / cc. On some occasions, the linear pohylene that is in the density range from about 0.926 to about 0.94 is known as linear density pohylene (LMDPE). The low density ethylene / alpha olefin copolymers can be mentioned as very low density pohylene (VLDPE, usually used to mention the ethylene / butene copolymers available from Union Carbide when the density range is from about 0.88 to about 0.91 g / cc) and ultra-low density pohylene (ULDPE), it is commonly used to mention the ethylene / octene copolymers manufactured by Dow). The phrase "ethylene / alpha olefin copolymers" also includes homogeneous polymers such as homogeneous, linear, metallocene-catalyzed ethylene / alpha olefin copolymer resins marketed by Exxon Chemical Company of Bayton, Texas.; the resins of homogeneous, linear ethylene / alpha olefin copolymer obtained from Mitsui Petrochemical Corporation; and the homogeneous, long-chain, branched, metallocene-catalyzed ethylene / alpha olefin copolymers commercially available from the Dow Chemical Company, known as AFFINITY resins. "The phrase" homogeneous polymer "refers to the reaction products of Polymerization of relatively limited molecular weight distribution and relatively limited composition distribution: Homogeneous polymers are structurally different from heterogeneous polymers (eg, ULDPE, VLDPE, LLDPE and MMDPE) since homogeneous polymers exhibit a relatively uniformity of the comonomers within a chain, equalization in the sequence distribution in all the chains and a similarity in the length of all the chains, that is, a narrower distribution in molecular weight. homogeneous polymers are prepared using metallocene or other catalysts of the type for a single site, in Instead of using the catalysts as Ziegler-Natta. These single-site catalysts usually only have a single catalytic site, which is believed to be the basis for the homogeneity of the polymers resulting from the polymerization. In general, an ethylene / alpha olefin copolymer can be prepared by copolymerization of ethylene and any one or more alpha olefins. Preferably, the olefin lfa is an alpha-monoolefin of C3-C20, more preferably, an alpha-monoolefin of C4-C2, and still more preferably, an alpha-monoolefin of C.CR. It is still more preferable that the alpha olefin contains at least one member selected from the group consisting of 1-butene, 1-pentene, 1-hexene and 1-octene. Methods of preparation and use of homogeneous polymers are described in U.S. Patent Nos. 5,206,075, 5,241,031, 5,272,236 and 5,278,272; and in PCT International Publication Nos. WO 90/03414 and 93/03093, all of which are incorporated herein by reference in their respective fortunes. When the term "olefins" is used herein, it generally refers to any of a class of aliphatic monounsaturated hydrocarbons of the general formula Cr? H2p, such as ethylene, propylene and butene. The term may also include aliphatics that contain more than one double bond in the molecule, such as a diolefin or diene, for example, butadiene. When used herein the term "polyolefins" refers to polymers and copolymers of olefins, especially polymers and copolymers of ethylene and propylene, and to polymeric materials having at least one olefinic comonomer, such as copolymer and ionomer. ethylene / vinyl acetate. The polyolefins can be linear, branched, cyclic, aliphatic, aromatic, substituted or unsubstituted. The term "polyolefins" includes olefin homopolymers, olefin copolymers, copolymers of an olefin and a non-olefin comonomer copolymerizable with the olefin, such as vinyl monomers, polymers, modified polyolefins include modified polymers that are prepared by copolymerization of the homopolymer of the olefin or the copolymer thereof, with an unsaturated carboxylic acid, for example, maleic acid, fumaric acid or the like, or a derivative thereof such as the anhydride, the metal salt of the ester or the like. It can also be obtained by incorporating in the homopolymer or copolymer of olefins, an unsaturated carboxylic acid, for example, maleic acid, fumaric acid or the like, or a derivative thereof such as anhydride, metal salt of the ester or the like. As used herein, the term "oriented" refers to a material that contains a polymer which has been elongated at an elevated temperature (the orientation temperature), followed by "stabilization" in the elongated configuration by cooling the material while substantially maintaining the extended dimensions. A material can be elongated in a direction ^ uniaxial orientation), two directions (biaxial orientation), or in multiple directions. The biaxial orientation usually occurs in two directions which are perpendicular to each other, such as the longitudinal direction and the transverse direction. As used herein, the phrase polymer "modified by anhydride" refers to one or more of the following: (1) polymers obtained by copolymerization of a monomer, which contains an anhydride, with a second, different monomer, (2) copolymers in which the anhydride is inserted , and, (3) a mixture of a polymer and an anhydride-containing compound.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic section of a five layer film according to the present invention, which is particularly suitable for packaging medicinal solutions; Figure 2 is a schematic section of a three layer film according to the present invention, which is particularly suitable for packaging food; Figure 3 is a schematic section of a five layer film according to the present invention, which is particularly suitable for packaging food; Figure 4 is a schematic section of a five layer film according to the present invention, which is particularly suitable for packaging food; Figure 5 is a schematic section of a three layer film shown in Figure 2, to which additional layers have been laminated according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a five-layer film 10 according to the present invention, which is suitable for forming a flexible bag for packaging and administering medicinal solutions. Examples of the medicinal solutions that are packaged and administered in this manner include saline solutions, dextrose solutions and solutions for dialysis applications. When the film 10 is formed into a bag for medicinal solutions, the first heat-sealing layer 12 will form the inner surface of the bag, that is, the surface that will be in contact with the medicinal solution it contains. The main function of the layer 12 is to form a thermal joint when the film 10 is bent over itself, or is joined to another film so that two regions of the layer 12 come into contact with each other and sufficient heat is applied to the segments predetermined regions of the contact regions of the layer 12, so that the heated segments melt and mix with each other. With cooling, the heated segments of layer 12 essentially become a single inseparable layer. In this way, the heated segments of the layer 12 produce a liquid tight seal commonly referred to as heat sealing. In general, the thermosets thus formed have a fin shape and are joined to define the peripheral limits of the bag, so that a medicinal solution can be completely contained in it.

The material, from which the heat sealing layer is formed, must be able to preserve a liquid-tight heat seal in a wide variety of harsh conditions, which, in general, a bag with medicinal solution will face. For example, during thermosetting, bags with medicinal solution are exposed to elevated temperatures (eg, 120 ° C) for periods of 15 to 30 min. In this way, the heat-sealed material must have sufficient heat resistance to retain the seal under these conditions. In addition, the heat-sealed material must have sufficient resistance to deformation at the service temperature to maintain the heat seal when the bag is placed in a pressure sleeve. Without sufficient resistance to deformation, the relatively high pressure of the fluid from the medicinal solution inside the bag will cause the heat seal to separate. Additionally, the material for heat sealing must have sufficient shock resistance to maintain the seal when the bag containing the solution is dropped, or handled harshly. The aforementioned criteria are satisfied with the first layer for the heat seal 12 of the present invention, which contains a mixture of polypropylene and elastomer homopolymers and copolymers. It has been found that polypropylene imparts good thermal resistance to layer 12, while the elastomer provides resistance to thermal deformation and shock. When the elastomer is combined with the polypropylene in such a way that the percentage by weight of the elastomer is in a range from about 5 to about 50 (based on the total weight of layer 12), excellent heat sealing can be produced . The best heat sealing is achieved when the elastomer is present in a weight percentage in the range of about 10 to 40 and more preferably from about 10 to 30. These sealed thermometers are capable of withstanding all the aforementioned severity conditions that usually they will find the sacks with medicinal solutions, that is to say, the heat sterilization, the application of a pressure cuff and the rough handling in general. The polypropylene homopolymer or copolymer is preferably a propylene / ethylene copolymer having from about 2 to about 10 percent by weight of and, more preferably from about 4 to about 6 percent of ethylene. A suitable propylene / ethylene copolymer is commercially available from Fina Oil &; Chemical Company under the trade name Z9450, and has an ethylene content of about 6 percent by weight. Another commercially available propylene / ethylene copolymer includes, for example, PLTD 665 from Exxon. The polypropylene used in layer 12 may be any of the available types, ie, isotactic, syndiotactic and of less atactic preference. The elastomer can be selected from the group consisting of the styrene-ethylene-butylene-styrene block copolymer (SEBS), the styrene-butadiene-styrene block copolymer (SBS), the styrene-isoprene-styrene block copolymer (SIS) ), ethylene-propylene rubber (EPM) and ethylene-propylene-diene terpolymer (EPDM). The SEBS is commercially available, for example, from Shell Chemical Co., under the name Kraton G-1650, G-1652 and G-1657 X. The BSB available commercially, for example, from Shell, as Kraton D-1101, D-1102, D-1300C, D-4122, D-4141, D-4455X and D-4460X. The SIS is commercially available from, for example, Shell, such as Kraton D-1107, D-111, D-1112 and D-1117. EPM is available commercially by Exxon, such as Vistalon 719 or 503. EPDM is commercially available, for example, by Exxon as Vistalon 3708. Pre-prepared and suitable polypropylene and elastomer blends are also commercially available. For example, the Horizon Polymers Z-4650 is a blend of 80 percent by weight of Z-9450 (propylene / ethylene copolymer as described above) and 20 percent by weight of Kraton G-1652 (SEBS as described above). in the above). The second adhesive layer 14 adheres to the first layer for heat sealing 12. As already described, it has been found that this layer plays a crucial role in the operation of a bag for medicinal solution when a pressure sleeve is applied thereto. That is, the insufficient adhesion capacity between this layer and the layer for heat sealing 12 has been considered as the key reason for the failure (ie leaks) of the bags for medicinal solution during the application of a pressure cuff. The inventor has discovered that when the layer 14 contains a homogeneous ethylene / alpha olefin copolymer with a density less than or equal to about 0.89 grams per cubic centimeter, excellent adhesion is achieved between this layer and the heat seal layer 12. As As a result, operation with the pressure sleeve of the bag with medicinal solution made with multilayer films of the present invention is markedly superior to bags made with conventional multilayer films. That is, the period during which the bag with medical solution can be maintained in a pressure sleeve without failure was markedly increased using the multilayer films of the present invention.

It is preferable that the density of the homogeneous ethylene / alpha olefin copolymer be less than 0.88 g / cc. The inventors have found that the strength of adhesion between a layer containing homogeneous ethylene / alpha olefin copolymer and a layer containing the polypropylene increases when the density of the homogeneous ethylene / alpha olefin copolymer is decreased. In view of the severe conditions to which the bag with medicinal solution will be exposed (for example, the heat sterilization, the elevated internal pressure in the thermal joint when a pressure cuff is applied, etc.), a high degree of adhesion is preferred. between the layers, that is, layers 12 and 14. At present, the lowest densities with which it is counted, for ethylene / alpha olefin, are around 0.86 g / cc. If lower densities for ethylene / alpha olefin were available in the future, they would also be included within the scope of the present invention. Preferred alpha olefin comonomers include 1-butene, 1-pentene, 1-hexene and 1-octene. The preferred ethylene / alpha olefin copolymers with densities of 0.89 g / cc or lower are those that are homogeneous, for example, those catalysed by metallocene. These copolymers are commercially available from resin manufacturers such as The Dow Chemical Company and Exxon Company. An example of an ethylene / alpha olefin copolymer is ENGAGE * EG 8150, an ethylene / octene copolymer DE available commercially from Dow. This material has a density of 0.868 g / cc (ASTM D-792), a melt index of 0.5 grade / min. (ASTM D-1238), and 25% octene (ASTM D-2238, Method B). Other suitable ethylene / alpha olefin copolymers of Dow include ENGAGE® EG 8100, an ethylene / octene copolymer with a density of 0.87 g / cc (ASTM D-792), a melt index of 1 degree / min. (ASTM D-1238), and 24% octene (ASTM D-2238, Method B); and ENGAGE® EG 8200 an ethylene / octene copolymer having a density of 0.87 g / cc (ASTM D-792), a melt index of 5 grade / min. (ASTM D-1238), and octene at 24 (ASTM D-2238, Method B). The third layer, which is the central 16, preferably imparts flexibility to the multilayer film 10 as well as the resistance and gas impermeability. Any material which gives the film 10 a desired level of fexibility, strength and gas impermeability, and which adheres well to the adhesive film 14 can be used to form the layer 16. In this sense, the layer 16 preferably contains a material selected from the group consisting of a very low density polyethylene, linear low density polyethylene, ethylene / vinyl acetate copolymer, ethylene / methyl acrylate copolymer, high density polyethylene, a homogeneous ethylene / alpha olefin copolymer and combinations of the aforementioned materials. All these materials are widely available in commerce. Preferably, the third central layer 16 consists of a homogeneous ethylene / alpha olefin copolymer or a combination of homogeneous ethylene / alpha olefin copolymers. It has been found that these copolymers result in a bag for medicinal solutions with better optical properties after the bag has been subjected to thermal sterilization. The homogeneous ethylene / alpha olefin copolymer or copolymer blends preferably have a density range from about 0.89 to about 0.92 grams per cubic centimeter and, most preferably, from about 0.90 to about 0.91 g / cc. Preferably, the melt index (ASTM D-1238) of the homogeneous ethylene / alpha olefin copolymer or combination of copolymers is less than 20, more preferably less than 10, even more preferred less than 2.2 and much more preferable between 0.1 and 1.5. the fourth adhesive layer 18 may contain a conventional material that is used to form a tie layer, such as a material selected from the group consisting of anhydride-modified ethylene / vinyl acetate copolymer, ethylene / methyl anhydride modified acrylate copolymer, ethylene / ethyl anhydride modified acrylate copolymer, linear modified low density polyethylene with anhydride and very low density polyethylene modified with anhydride. The particular choice of the material for the layer 18 will depend on the materials selected for the layers 16 and 20. When the multilayer film 10 is formed into a bag for medicinal solution, the heat and abuse resistant fifth layer 20 forms the outer surface of the bag. coat. The main functions of layer 20 are to provide thermal resistance to the bag during heat sealing and heat sterilization, and to provide resistance to abuse from handling and external abrasion. The layer 20 preferably consists of a material selected from the group consisting of polyamide, copolyamide and copolyester. Suitable polyamides and copolyamides include nylon 66, nylon 610, nylon 12 and copolymers thereof, nylon 12 and copolymers thereof, amorphous nylon and mixtures of the aforementioned polyamides and copolyamides. A preferred copolyamide is nylon 66/610. This material is commercially available from EMS-A erican Grilon, Inc. under the name XE 3303. Commercially available copolyesters are available from Eastman Chemical Products, Inc. Under the trademarks ECDEL® 9965, 9966 and 9967. The multilayer film 10 preferably has a total thickness in the range from about 3 to 14 mils (1 mil = 0.001 in. = 0.0254 mm) preferably from 5 to 10 mils and more preferably from 6.5 to 9.5 mils. Layers 12 and 20 may be in a thickness range from about 0.5 to about 8 mils, but preferably they are close to 0.75 mil thick. Layers 14 and 18 may be in a range of thickness from about 0.1 to about 0.75 mil, but more preferably they are close to 0.4 mil thick. The layer 16 can have a thickness range from about 1 to about 9 mils, but preferably about 5.2 mils in thickness. As can be appreciated by those with elementary skill in the art, the multilayer films of the present invention are not limited to the five layer structure described in the foregoing. Films having a lower number of layers or a greater number of layers than those shown are included within the scope of the present invention. For example, if it is desired to increase the moisture barrier capabilities of the film, additional layers may be included, such as high density polyethylene. Layers can also be included, if desired, as a barrier to oxygen. The multilayer films of the present invention have been described together with a bag for packaging medicinal solutions. However, it should be understood that other embodiments of the invention have also been envisaged. That is to say, the first layer for the heat seal 12 and the second adhesive layer 14 can be joined to different layers with different functional properties to those described in order to form films for other uses. Other embodiments of the multilayer films, according to the present invention, are illustrated in Figures 2-5. These films are particularly useful for packaging applications in which the relatively stringent conditions of heat sterilization and / or the application of a pressure cuff are not commonly found, for example, the packaging of food, medical devices, household articles, products industrial, etc. In this way, the structure of the films that are used to package food will be somewhat different from the structure of the films that are used in medical applications. For example, the heat seal layer used for packaging food need not possess the degree of thermal resistance and heat distortion as described above for the film 10 for medicinal use. In this way, the layers for heat sealing and the film for food packaging, in accordance with the present invention, should not necessarily contain polypropylene and elastomer. In contrast, a film for heat sealing containing a polyethylene homopolymer or copolymer is suitable for most food packaging applications. Furthermore, although it is desirable that the homogeneous layer of ethylene / alpha olefin (14) which binds with the polypropylene-containing layer (12) to the rest of the film have a density of 0.89 g / cc or less for medical applications, the layer homogenous ethylene / alpha olefin which is attached to the polypropylene-containing layer with the remainder of the film for food packaging, preferably has a density of 0.92 g / cc or less and, most preferably a density in the range from about 0.85 to about 0.91 g / cc. For food packaging applications, these higher densities are preferred over the lower densities that are used in the film for packaging medicinal solutions. Now, in relation to Figure 2, there is shown a three layer film 22, according to the present invention. The film 22 includes a first outer layer 24 consisting of a polypropylene homopolymer or copolymer, a second inner layer 26 adhered to the first layer 24 consisting of a homogeneous ethylene / alpha olefin copolymer with a density less than or equal to 0.92 grams per cubic centimeter, and a third outer layer adhered to the second layer 26. Alternatively, the film 22 may be a double layer film that includes only the layers 24 and 26, in which the layer 26 serves as a layer for the heat seal. The film 22 preferably has a thickness in the range from about 1 to 10 mils. The outer layer 28, which preferably consists of a polyethylene homopolymer or copolymer, provides heat sealing for the film to facilitate its formation in a container. When the film 22 is manufactured as a container, the layer 28 will be the inner surface of the container and will be in contact with the packaged product. This container can be a sack for, for example, cheese, t vegetables, liquid foods such as soups, etc. The bag can be formed by conventional vertical or horizontal sealing-packing techniques by folding a continuous form of film 22 on itself with layer 28 inside, by heat sealing where it is necessary to form an open bag, separating the bag from the bag. the film continues and filled with a food product, and then heat sealing the hole in the bag to form a closed container with the food product contained therein. Preferably, the heat seal that is formed will be of thermal joints of the fin type with the layer 28 sealed on itself unlike, for example, the thermal joints of the flap type in which the layer 28 would be sealed to the layer 24. another way, the container can be a package for meat products, such as fresh or frozen beef, pork or poultry, etc. These packages can be formed using conventional methods, for example, by matching a previously cut section of the film 22 with another section of film that is the same or different from the film 22, and then heat-sealing around the periphery of the structure resulting to form a package. One or both films can be thermoformed before heat sealing to form a bag in which the meat product can be placed. All of the aforementioned packaging techniques are well known in the packaging art. The layer 28 can be formed with any material that is heat-sealable, such as the polyethylene homopolymer or copolymer (such as low density polyethylene). Non-limiting examples of preferred polyethylene copolymers include homogeneous ethylene / alpha olefin copolymers; the heterogeneous ethylene / alpha olefin copolymers such as LLDPE, VLPE, etc .; the ionomers; and ethylene / unsaturated ester copolymers such as ethylene / vinyl acetate and ethylene / methyl acrylate. These materials are available commercially. When the film 22 is shaped as a container, the outer layer 24 forms the outer surface of the container. The main functions of the layer 24 are to provide the overall resistance for the container, for example, by stopping the propagation of a rip in the area of the heat seal; imparting heat resistance in the container, particularly during heat sealing, so that the heat sealing mechanism does not melt or burn the film, and to protect the package against abuse, such as abrasion or perforation during the packaging process, and when handling later. The polypropylene homopolymer or copolymer, such as the propylene / ethylene copolymer, is theoretically suitable to provide all of the aforementioned functions when the film 22 is used in common food packaging applications as previously described. Polypropylenes are readily available from various commercial sources. It has also been surprisingly found that polypropylene can be used to form the film 22, as well as the other films described below, with a high degree of resistance to the formation of perforations or cracks, commonly referred to as "flex cracking". , which may otherwise occur when films undergo the rigors of packaging operations. However, as noted above, it has also been found that polypropylene is largely ineffective in protecting the film from the development of cracks / perforations, as well as to prevent tearing and leakage in the area of the heat seal, when the layer containing Polypropylene is not well adhered to the rest of the film structure. According to the present invention, the polypropylene-containing layer adheres very well to the rest of the film structure using an adhesive layer containing a homogeneous ethylene / alpha-olefin copolymer with a density less than or equal to 0.92 grams per cubic centimeter . As a result, the multilayer films of the invention exhibit excellent resistance to the development of cracks / perforations and form resistant thermal joints. As shown in Figure 2, the layer 26 containing a homogeneous ethylene / alpha olefin copolymer with a density less than or equal to 0.92 grams per cubic centimeter, joins the polypropylene-containing layer 24 to the layer for heat-sealing 28. Preferably , the density of the homogeneous ethylene / alpha olefin copolymer ranges from about 0.85 to about 0.91 grams per cubic centimeter and more preferably, from about 0.89 to 0.91 grams per cubic centimeter. If desired, the second layer 26 may contain one or more other materials combined with the homogeneous ethylene / alpha olefin copolymer. However, preferably, the second layer consists essentially of homogeneous ethylene / alpha olefin copolymer. Suitable homogeneous ethylene / alpha olefin copolymers from which layer 26 is formed include any of those described above. Specific examples include the following from Exxon Chemical Company: EXACT ™ 4011 with a melt index of approximately 2.2 degrees / min. (ASTM D-1238 (E)), a density close to 0.89 g / cc (ASTM D-1505) and a maximum DSC melting point of approximately 70 ° C (Exxon Method); EXACT "'3030 with a melt index of approximately 2.2 degrees / min. (ASTM D-1238 (E)), a density close to 0.91 g / cc (ASTM D-792) and a maximum melting point DSC of approximately 101 ° C (Exxon Method) and EXACT® 3037 with a melting index of approximately 2.2 degrees / min. (ASTM D-1238 (E)), a density close to 0.90 g / cc (ASTM D-792) and a maximum DSC melting point of approximately 95 ° C (Exxon Method). Other suitable homogeneous ethylene / alpha olefin copolymers include the AFE'INITY'5 'resins from Dow Chemical Co., such as PL 1850 or PL 1880. Now, with reference to Figure 3, a five-layer film will be described. 30, according to the present invention. The film 30 is similar to the film 22 in that the first outer layer 32 corresponds to the first outer layer 24, as described above; the second inner layer 34 corresponds to the second inner layer 26 as described above; and the third outer layer 40 corresponds to the third outer layer 28, as also described. Film 30 is different from film 22 because additional interior layers 36 and 38 are present. Fourth inner layer 36 adheres to second layer 34, and consists of a polypropylene homopolymer or copolymer which may or may not have the same composition than the first layer 32. The fifth inner layer 38 adheres with the fourth layer 36 and consists of homogenous ethylene / alpha olefin copolymer with a density less than or equal to 0.92 grams per cubic centimeter and may or may not have the same composition as the second layer 34. If desired, additional internal layers may be included that have the same composition or similar to layers 36 and 38 between layers 38 and 40. preferably film 30 has a thickness in the range of about 2 to 15 mils Now, in relation to Figure 4, the seven layer film 42 according to the present invention will be described. The film 42 is similar to the film 22 because the first outer layer 44 corresponds to the first outer layer 24; the second inner layer 46 corresponds to the second inner layer 26; and the third outer layer 56 corresponds to the third outer layer 28. The film 42 is different from the film 22 because the additional inner layers 48, 50, 52 and 52 are present. The inner layer 50 is formed with a material that provides a barrier to the passage of oxygen through the film, as may be in material selected from the group consisting of ethylene / vinyl alcohol copolymer, vinylidene chloride copolymer, polyamide, polyvinyl alcohol, polyhydroaminic ether and polyalkylene carbonate. A preferred material is the ethylene / vinyl alcohol copolymer. The layers 48 and 52 are bonding layers and are preferably formed from a material having the ability to bond the layer 50 to the rest of the film structure. Layers 48 and 52 may contain a material that is conventionally used to form a tie layer, such as a material selected from the group consisting of ethylene / vinyl acetate-modified anhydride copolymer, modified ethylene / methyl-acrylate copolymer with anhydride, ethylene copolymer / anhydride modified ethyl acrylate, linear modified low density polyethylene with anhydride and very low density polyethylene modified with anhydride. The particular choice of material for layers 48 and 52 will depend on the materials selected for layers 50, 46 and 54. For example, when layer 50 contains ethylene / vinyl alcohol copolymer and layers 46 and 54 contain the homogenous ethylene / alpha olefin copolymer, layers 48 and 52 preferably should contain the ethylene / vinyl acetate modified anhydride copolymer or the linear low density polyethylene modified with anhydride. Layer 54 is an optional layer that is preferably included with the remainder of the film structure 42. Layer 54 may be formed from any desired material, but is preferably formed of an ethylene homopolymer or copolymer. More preferably, the layer 54 is formed from a homogeneous ethylene / alpha olefin copolymer. Now, with reference to Figure 5, another embodiment of the invention will be described. The film 58 is similar to the film 22 as described above, except that two additional layers are attached to the first layer 24 containing a polypropylene homopolymer or copolymer. The multilayer films 30 and 42 can be modified in the same way by joining the additional layers similar to the layers 32 and 44 respectively. In this embodiment, the first layer 24 is no longer an outer layer but is an inner layer. The outer layer 60 is added to increase stiffness, resistance to high temperature and / or abuse of the film. Preferably the layer 60 is formed with at least one material selected from the group consisting of polyamide, polypropylene, polyester, cellophane, polycarbonate, polyvinylidene fluoride and mixtures thereof. Preferably, the layer 60 is oriented in at least one direction and, of greater reference, is oriented in the biaxial direction. More preferably, layer 60 consists of nylon oriented in the biaxial direction, polypropylene oriented in the biaxial direction or polyethylene terephthalate oriented in the biaxial direction. From the functional point of view, an oxygen barrier can be imparted to the film including an oxygen barrier layer 62 placed between the layers 24 and 60. Suitable materials for the oxygen barrier include, for example, the ethylene / alcohol copolymer. vinyl, vinylidene chloride copolymer (saran), polyamide, polyvinyl alcohol, polyhydroxyamine ether and polyalkylene carbonate. Double layer films are commercially available, which combine a polymeric layer oriented in the biaxial direction with a layer of a material that serves as an oxygen barrier. Examples include polytanylene terephthalate coated with sarán, which is commercially available DuPont with the trade name 50M-44 MYLAR "and also available by SPC Films under the trade name KEG Polyester Film The film 58 can be formed by first coextruding layers 24, 26 and 28, and then joining layers 60 and 62 to the layer 24, for example, by lamination with the suitable adhesives 64. Suitable adhesives include urethane adhesives, acrylic adhesives or ethylene / vinyl acetate.An adhesive layer may be necessary or necessary to join the layers 60 and 62. These layers may be joined using any suitable technique, in which lamination, co-extrusion, etc. are included. Alternatively, layers 62 and / or 60 can be co-extruded with layers 24, 26 and 28 using a homogeneous ethylene / alpha olefin copolymer as material from which the layer 64 is formed. In this way, the film 58 would be co-extruded as a six layer film.The aforementioned description of the structures of the preferred films, as shown in FIG. In Figures 2-5, they are only proposed as examples, not as limiting scope. Other film structures containing additional layers, fewer layers or different layers are also within the scope of the invention. In any or all of the layers of the multilayer film of the present invention the different additives can be used. These additives include, without limitation, antiacking agents, antioxidants, processing aids such as calcium stearate, pigments, antistatic agents, lubricants, etc. When the multilayer film is to be used to make bags for medicinal solution, the amount of additive that is included in the film of preference is kept at a minimum to reduce the likelihood that these additives will be extracted to the medicinal solution during the heat sterilization. The multilayer film of the present invention is preferably formed by a coextruded or hot-blown melt process as a tubular or flat film. The containers for medical applications, for food packaging or other end uses can be manufactured directly from the coextruded, tubular film or otherwise from the rolled material that is obtained from the tube after it has been divided and separated into layers. Other processes, such as extrusion coating, conventional lamination, slotted nozzle extrusion, etc., can also be used to make the multilayer film of the present invention. The combinations of the aforementioned methods can also be used. For example, two or more groups of film layers can be formed separately by, for example, coextrusion, and these groups can subsequently be joined by, for example, adhesive lamination. If desired, the multilayer films according to the present invention can be crosslinked. Preferably crosslinking is done with irradiation, ie bombardment of the film with particle or non-particle radiation as with high-energy electrons in an accelerator or cobalt-60 gamma-ray, to crosslink the film materials. For medical applications, a preferred radiation dose level is in the range from about 2 megarads (MR) to about 8 MR. Any conventional crosslinking technique can be used, for example, electronic crosslinking can be carried out by beam irradiation of curtain. Chemical crosslinking techniques can also be employed, for example, by the use of peroxides or silanes. The bags made with multilayer films of the present invention can be sealed using the various means well known in the art, including impulse and hot-stick sealing. An example of a commercially available impulse type sealing device is a Vertrod '"heat sealer." Furthermore, the invention can be understood with reference to the following examples, which are provided for the purpose of representation and have not been proposed. as limiting the scope of the invention.

EXAMPLES The materials used in the examples are identified below: "PEC-1": ESCORENE'8 PD9012-E1; propylene / ethylene copolymer having an ethylene content of about 2.8 percent by weight, a density close to 0.90 g / cc (ASTM D-1505) and a melt index of 6; is available from Exxon Chemical Company, of Bayton, Texas. "PEC-2": ESCORENE'8 'PP9122; propylene / ethylene copolymer having a density close to 0.90 g / cc (ASTM D-1505) and a melt index of 2.1; it is obtained from Exxon Chemical Company, of Bayton, Texas. "PP": ESCORENE- PP 3445; polypropylene homopolymer that has a density close to 0.906 g / cc and a melting index close to 36; it is obtained from Exxon Chemical Company, of Bayton, Texas. "EAO-1": EXACT 3027'-; homogenous ethylene / butene copolymer having a density of 0.90 g / cc (ASTM D-792) and a melt index of 3.5 degrees / min. (ASTM D-1238); it is obtained from Exxon Chemical Company, of Bayton, Texas.

"EAO-2": ECD401A0; homogeneous ethylene / alpha olefin copolymer having a density of 0.92 g / cc (ASTM D-792) and a melt index of 4.9 degrees / min. (ASTM D-1238); it is obtained from Exxon Chemical Company, of Bayton, Texas. "EAO-3": AFFINITY-.1140; homogeneous ethylene / octene-1 copolymer having 14% octene, a density of 0.90 g / cc, melt index of 1.6 degrees / min .; it is obtained from Dow Chemical Company, of Midland, MI. "EAO-4": AFFINITY- PL 1880; homogeneous ethylene / octene-1 copolymer having octene 12. density of 0.90 g / cc and a melt index of 1.0 degrees / min .; it is obtained from Dow Chemical Company, of Midland, MI. "LLDPE": LD200-48; linear low density polyethylene with a density close to 0.98 g / cc and a melting index of about 7.5; it is obtained from Exxon Chemical Company, of Bayton, Texas. "LDPE": PE 1042CS15; linear low density polyethylene that has a density close to 0.92 g / cc and a melting index close to 2.0; It is obtained from Rexene Company. "ASH": polyurethane adhesive "BOPP": AET 75B523; polypropylene film oriented in the biaxial direction with a thickness of 0.75 mil; It is obtained from AET Packaging Films.

"T1E-1": TYMOR-1203; binder material of linear low density polyethylene grafted with anhydride having a density of 0.91 g / cc and a melt index of 1.6; It is obtained from Morton International. "TIE-2": PLEXING "PX TR040; ethylene / vinyl acetate-binder material grafted with anhydride having 8.5% vinyl acetate and a melt index of 2.0, obtained from Quantum Chemical." TIE-3": PLEXAR '107, polyolefin grafted with ethylene / vinyl acetate anhydride with melt index of 3.2, is obtained from Quantum Chemicals "EVOH": SOARNOL® ET; ethylene / vinyl alcohol copolymer having 38% ethylene, a density of 1.17 g / cc and a melting index close to 2.8, obtained from Nippon Gohsei, "PET-1": MELINEX® 800, polyethylene terephthalate film having a thickness of 0.48 mils, obtained from ICI. -2": 50M-44 MYLAR®, polyethylene terephthalate film coated with saran, with a thickness of 0.56 thousand, obtained from DuPont.

Example 1 A multilayer film, according to the present invention, had the following eight-layer structure: LAYER 1 (heat-sealed): 82% EAO-1 ^ 15% EAO-2 + 3% slipping agent (10% of the total thickness of the film).

LAYER 2: 90% EAO-2 + 10% LLDPE (23% of the total film thickness). LAYER 3 EAO-1 (7% of the total thickness of the film). LAYER 4 PEC-1 (13% of the total thickness of the film). LAYER 5 EAO-1 (7% of the total thickness of the film). LAYER 6 PEC-1 (13% of the total thickness of the film). LAYER 7 EAO-1 (15% of the total thickness of the film). LAYER 8 (heat resistant / abuse: PP (12% of total film thickness). The film was made by fusion-coextrusion and a total thickness of 5 mils was achieved.

Example 2 A multilayer film, in accordance with the present invention, had the following four-layer structure: LAYER 1 (heat-sealed): EAO-1 LAYER 2: PEC-2 LAYER 3: ADH CAPA 4: (heat resistant / mistreated) : BOPP The film was prepared by first coextruding layers 1 and 2 as a film blown in two layers, with a thickness close to 3 mils .; wherein layer 1 contained 65% of the total thickness of the film and layer 2 contained 35% of the total thickness of the film. Then, layer 4 was laminated with layer 2 by means of adhesive layer 3.

Example 3 The packages for frozen red meat are made with the films of example 1 and 2, thermoforming the film of example 1 in trays, to then place the pieces of frozen red meat in the trays, and making the heat-sealing of pieces of similar size of the Example 2 film to the trays. The heat sealing was carried out by contacting the layer for heat sealing the film of example 1 with the layer for heat sealing the film of example 2, aligning the two films and applying sufficient heat, pressure and vacuum at the periphery of the films for put them together, forming in this way a wrap for frozen meat. The packaging operations were carried out on a 16 * 1 vacuum packaging machine Multivac "R 7000.

Example 4 A multilayer film, according to the present invention, had the following structure of nine layers: LAYER 1 (heat-sealed): 97% EAO-3 + 3% slip agent (35% of the total thickness of the co-extruded film). LAYER 2: EAO-3 (10% of the total thickness of the co-extruded film). LAYER 3: TIE-1 (8% of the total thickness of the co-extruded film). LAYER 4: EVOH (10% of the total thickness of the co-extruded film). LAYER 5: TIE-1 (7% of the total thickness of the co-extruded film). , LAYER 6: EAO-3 (10% of the total thickness of the co-extruded film). LAYER 7: PEC-2 (20% of the total thickness of the co-extruded film). LAYER 7: ADH CAPA 9 (heat resistant / mistreated): PET-1 (12% of the total thickness of the co-extruded film). The film was prepared by first coextruding layers 1-7 as a seven layer blown film with a thickness of about 2.5 mils. The layer 9 was then laminated to the layer 7 by means of an adhesive layer 8.

Example 5 The film of example 4 was used to make packages for striped cheese in a Hayssen Ultima II vertical packaging-sealing machine.

Example 6 A multilayer film, according to the present invention, had the following four-layer structure CAPA 1 (heat-sealed): EAO-1 LAYER 2 PEC-2, LAYER 3 ADH CAPA 4 (heat resistant / mistreated): BOPP The film is prepared by first coextruding layers 1 and 2 as a bilayer, blown film. Then, layer 4 was laminated with layer 2 by means of adhesive layer 3.

Example 7 A multilayer film, according to the present invention, had the following four-layer structure: LAYER 1 (heat-sealed): EAO-1 LAYER 2: PEC-2 LAYER 3: ADH CAPA 4: (heat resistant / mistreatment) : PET-2 The film was prepared by first coextruding layers 1 and 2 as a bilayer film, blown. Then, layer 4 was laminated with layer 2 by means of adhesive layer 3.

Example 8 A multilayer, co-extruded film according to the present invention had the following structure: LAYER 1 (heat-sealed): EAO-3 LAYER 2 EAO-4 LAYER 3 LAYER-2 LAYER 4 EVOH, LAYER 5 LAYER-2 LAYER 6 EAO- 4 CAPA 7 (heat resistant / abuse): PEC-2 Example 9 A multilayer, co-extruded film, according to the present invention, had the following structure: LAYER 1 (heat-sealed): EAO-3 LAYER 2: EAO-4 LAYER 3: LAID-1 LAYER 4: EVOH LAYER 5: LAYER-1 LAYER ß: EAO-4 CAPA 7: (heat resistant / mistreated): PEC-2 Example 10 (Comparative) A multilayer film, co-extruded, according to the present invention, had the following structure: LAYER 1 (heat-sealed): EAO-1 LAYER 2: LAYER 3: LAYER-1 LAYER 4: EVOH LAYER 5: LAID-1% LAYER 6: TIE-3 LAYER 7: (resistant to heat / abuse): LDPE Example 11 The films of Example 6-10 were tested for cracking / perforation resistance in accordance with ASTM F392-74 (condition B, 900 cycles) by wrapping a 21.5 X 28 centimeter film sample around two separate disks 21.5 cm apart. make a film sample in the form of a cylinder. One disc was turned continuously 440 degrees in relation to the other disc and it moved continuously 12.7 cm towards the other disc and then it was returned to its original position. These rotation / translation cycles were repeated 90 times for each film sample. The test was carried out at approximately 1.7 ° C. The film samples were then measured to determine the amount of cracks / perforations that developed.

Table 1 shows a summary of the cracking / perforation resistance test results, which were present in five tested film samples, of each of the films that were made according to Examples 6-10.

TABLE 1 as a footnote, the laminated films were manufactured by adhesively laminating the films prepared according to Examples 8-10 to a PET layer oriented in the biaxial direction. These films were then subjected to the cracking / perforation resistance test described in the above. For reasons that are not yet fully understood, the cracking / perforating performance of the laminated films of Examples 8 and 9 worsened compared to their unlaminated counterparts (an average of 7.6 and 6.4 perforations, respectively), while the operation of the laminated films of the comparative film 10 improved in comparison to its non-laminated counterpart (an average of 11 perforations). However, the results established in the Table 1 illustrate that the films of the present invention (Examples 6-9) exhibit superior cracking / puncture resistance. This superior performance arises as a result of the excellent adhesion between the heat resistance / abuse layer containing polypropylene with the rest of the coextruded film structure due to the unexpected high degree of bond between the polypropylene-containing layer and the adjacent copolymer layer homogeneous ethylene / alpha olefin.

Although the invention has been described with reference to the illustrative examples, those skilled in the art will understand that various modifications may be made to the invention as described, without departing from the scope of the following claims.

Claims (20)

1. A multilayer film consisting of: a) a first outer layer containing a polypropylene homopolymer or copolymer; and b) a second layer adhered to the first layer, the second layer consisting of a homogeneous ethylene / alpha olefin copolymer having a density less than or equal to 0.92 grams per cubic centimeter.

2. The multilayer film, in accordance with claim no. 1, characterized in that the density of the homogeneous ethylene / alpha olefin copolymer is in the range from about 0.85 to about 91 grams per cubic centimeter. (3.

The multilayer film, according to claim 2, is characterized in that the density range of the homogeneous ethylene / alpha olefin copolymer is from about 0.89 to about 0.91 grams per cubic centimeter.

According to claim 1, it is characterized in that the second layer consists essentially of a homogeneous ethylene / alpha olefin copolymer having a density less than or equal to 0.92 grams per cubic centimeter.

5. The multilayer film, in accordance with claim no. 1, characterized in that the second layer is an inner layer and the multilayer film also includes a third external layer, so that, the second layer is placed between the first and third layers, this third layer contains a homopolymer or polyethylene copolymer.

6. The multilayer film, in accordance with claim no. 5, characterized in that the third layer is adhered directly to the second layer.

7. The multilayer film, in accordance with claim no. 5, further includes: a) a fourth inner layer adhered to the second layer, the fourth layer consisting of a polypropylene homopolymer or copolymer; and, b) a fifth inner layer adhered to the fourth layer, this fifth layer contains a homogeneous ethylene / alpha olefin copolymer with a density less than or equal to 0.92 grams per cubic centimeter.

8. The multilayer film, in accordance with claim no. 5, further includes a fourth inner layer placed between the second and third layers, the fourth layer consists of at least one material selected from the group consisting of ethylene / vinyl alcohol copolymer, vinylidene fluoride copolymer, polyamide, polyvinyl alcohol, polyhydroxyamine ether and polyalkylene carbonate.

9. A multilayer film consisting of: a) a first inner layer containing polypropylene homopolymer or copolymer; b) a second layer adhered to the first layer, this second layer contains a homogeneous ethylene / alpha olefin copolymer having a density less than or equal to 0.92 grams per cubic centimeter; and c) a third outer layer containing at least one material selected from the group consisting of polyamide, polypropylene, polyester, cellophane, polycarbonate, polyvinylidene fluoride and combinations thereof, this first layer is placed between the second and third layers.

10. The multilayer film, in accordance with claim no. 9, characterized in that the third layer is oriented in at least one direction.

11. The multilayer film, in accordance with claim no. 9 further includes a fourth inner layer placed between the first and third layers, the fourth layer consists of at least one material selected from the group consisting of ethylene / vinyl alcohol copolymer, vinylidene chloride copolymer, polyamide, polyvinyl alcohol, ether polyhydroxyamino and polyalkylene carbonate.

12. The multilayer film, in accordance with claim no. 9, characterized in that the density of the homogeneous ethylene / alpha olefin copolymer is in the range from about 0.85 to about 0.91 grams per cubic centimeter.

13. The multilayer film, in accordance with claim no. 12, characterized in that the density of the homogeneous ethylene / alpha olefin copolymer is in the range from about 0.89 to about 0.91 grams per cubic centimeter.

14. The multilayer film, in accordance with claim no. 9, characterized in that the second layer consists essentially of a homogeneous ethylene / alpha olefin copolymer with a density less than or equal to 0.92 grams per cubic centimeter.

15. The multilayer film, in accordance with claim no. 9 is characterized in that the second layer is an inner layer and the multilayer film further includes a fourth outer layer, so that, the second layer is placed between the first and fourth layers, the fourth layer consists of a polyethylene homopolymer or copolymer.

16. The multilayer film, in accordance with claim no. 9 is characterized in that the fourth layer adheres directly to the second layer.

17. The multilayer film, in accordance with claim no. 15 further includes: a) a fifth inner layer adhered to the second layer, this fifth layer consists of a polypropylene homopolymer or copolymer; and b) a sixth inner layer adhered to the fifth layer, this sixth layer consists of a homogeneous ethylene / alpha olefin copolymer having a density less than or equal to 0.92 grams per cubic centimeter.

18. The multilayer film, in accordance with claim no. 15 further includes a fifth inner layer placed between the second and fourth layers, this fifth layer consists of at least one material selected from the group consisting of ethylene / vinyl alcohol copolymer, vinylidene chloride copolymer, polyamide, polyvinyl alcohol, polyhydroxyamine ether and polyalkylene carbonate.

19. A package that is manufactured with the multilayer film according to claim no. 1.

20. A container that is manufactured with the multilayer film according to claim no. 9.