MXPA99006642A - Easy open tear film - Google Patents

Abstract

A film includes a core layer including a polyamide, two intermediate layers, disposed on opposite surfaces of the core layer, including an adhesive;and two outer layers, each disposed on a surface of the respective intermediate layer, comprising an ethylene/alpha olefin copolymer;wherein the two outer layers each constitute at least 27%of the total thickness of the film. The core layer can include either a single polyamide layer, or three layers wherein two layers of polyamide have therebetween a layer comprising a polymeric adhesive. The film is made preferably by a hot blown process at a blow up ratio of between 2.0:1 and 3.0:1. A process and package are also described.

Description

I EASY OPENING FILM Field of the invention. The present invention relates to a film that can be formed in a bag with an easy opening feature. This thermoplastic film can be used to make vertical / fill / seal (VFFS) packaging for a wide variety of foods and non-food items. BACKGROUND OF THE INVENTION Vertical / filler / seal (VFFS) packaging systems are very useful in packing a wide range of products that can flow. An example of systems of this type is the Onpack ® flowable food packaging system sold by W.R. Grace & Co.-Conn through its group Grace Packaging. The VFFS process is known to those skilled in the art and is described, for example, in U.S. Patent No. 4,589,247 (Tsuruta et al), which is incorporated herein by reference. A product that can flow is introduced through a central vertical filling tube to a formed tubular film that has been sealed transversely at its lower end, and longitudinally. The bag is then completed by the seal of the upper end of the tubular segment, and the bag of the tubular film is cut above it. The choice of packaging materials is important and should correspond to the intended use of the bag. Various ways have been proposed to provide the contents of said bags at their point of use, for example in a restaurant, curator or the like. One way is to use an internal abutment sealed on the inner surface of a bag wall such as, for example, the Asept® attachment distributed in the United States by the recipient of the present application and presented in U.S. Patent No. 4,603,793 (Stern). ). In use, a coupling device will be inserted into the bag material to communicate with the internal attachment, and a conventional delivery device would be connected to the coupling device to supply measured portions of the contents of the bag. An alternative technique and apparatus for dispensing the contents of a bag is the use of a pouring tube such as a Top-Tap ® pouring tube supplied by DuPont Canada, and described in various embodiments in its Canadian patent number 1,192,164 (Obidniak ) and in U.S. Patent No. 5,325,9995 (Harrison et al). This system includes punching the stuffed bag with a sharp tip (punching nozzle) of a pouring tube, and pushing the punching nozzle towards the inside of the bag until the laminated product that forms the wall of the bag Bag hook the shoulder of the piercing nozzle. When this happens, the plastic material that forms the bag will be supplied around the shoulder of the nozzle, to be fixed by a collar. The emptying tube can then be used to supply the contents of the bag. In some cases, a packaging manager may wish to avoid the use of internal or external attachments due to the additional packaging cost associated with such devices. An alternative is to simply open by cutting the bag with a knife at the time when it is desired to have access to the contents of the bag, for example, at the time at which the contents of the bag should be placed in a delivery device. However, this procedure, even when it is simple, exposes the user to the possibility of injuries 15 when the bag is opened by cutting. Even if the cutting / opening operation is carried out without injury, this procedure leaves the choice of where to cut the bag to the person opening the bag, which can cause spillage of the contained product. In addition, for insurance reasons, many 20 restaurants, such as fast food restaurants, do not allow knives or similar devices in the food preparation area of the restaurant. Therefore, it would often be desirable to avoid the need to use attachments, and the dangerous use of a knife or other type of sharp object to open the "» And ^? »L» j¡-U | lj.? _ I.Jl M - '»» - * J' »- '*» «? -Zí? ^ 2 m bag, and to allow the bag to open easily and easily at a preselected point in the bag, chosen to make the opening process easier and to reduce potential spillage, however, many VFFS and other packaging applications require the use of packaging materials, especially flexible packaging materials that can be used to pack food and other items and to protect these items during storage and distribution When packing foods that can flow, as in the case of many VFFS applications, the hydrostatic pressure of many foods based in oil and water they require a durable, impact-resistant and abuse-resistant packaging material that will maintain its structural integrity during the packaging process and during subsequent distribution and storage. to the point where many films offer a high degree of resistance to abuse. Unfortunately, the same abuse resistance and durability properties that are desirable for the performance of the packaging material to protect contained articles often make it difficult or impossible for the end user to manually open the package without the aid of a knife or the like. Several solutions to this problem have been proposed to overcome this problem and to make it easier to open packages of the type just described. One solution is the use of tearing notches, perforations, slits, etc., which guide the user to a particular location in the bag to initiate the break. However, the fact of providing the initiation of rupture and placement is often not enough. The packing material must have a rupture propagation sufficiently low so that the material continues to break easily beyond the end point of a rupture notch or the like. If the rupture propagation values for the material are too high, the material will stretch rather than break, and it will be very difficult to properly open the bag by breaking. It would therefore be of great benefit to the packaging industry to offer an easy breaking film compatible with current commercial packaging systems, that is, a film having good dimensional stability and good resistance to abuse. SUMMARY OF THE INVENTION In one aspect of the present invention, a film comprises a core layer comprising a polyamide; two intermediate layers, placed on opposite surfaces of the core layer, comprising an adhesive; and two outer layers, each placed on a surface of the respective intermediate layer, comprising an ethylene / alpha-olefin copolymer, wherein the two outer layers each comprise at least 27% of the total thickness of the film. In a second aspect of the invention, a process for making a film comprises extruding a film comprising a core layer comprising a polyamide; two intermediate layers placed on opposite surfaces of the core layer, comprising an adhesive; and two outer layers, each placed on a surface of the respective intermediate layer 10 comprising an ethylene / alpha-olefin copolymer; and the expansion of the film by means of a hot expansion process to an expansion ratio of between 2.0: 1 and 3.0: 1. In a third aspect of the invention, a package comprises a food product that can flow; and a bag containing the food product, the bag is made of a film comprising a core layer comprising a polyamide; two intermediate layers, placed on opposite surfaces of the core layer, comprising an adhesive; Y two outer layers, each placed on a surface of the respective intermediate layer, comprising an ethylene / alpha-olefin copolymer; where the two outer layers each comprise at least 27% of the total thickness of the film. Definitions 25 The term "core layer" as used herein refers to < gglglft? fj ^ .M .t * l-l? - the central layer of a multi-layer movie. In the present invention, it may comprise either a single polyamide layer, or three layers where two layers of polyamide have a layer comprising an adhesive therebetween. The term "outer layer" as used herein refers to what is typically a usually extreme surface layer of a multilayer film, even though additional layers and / or films may adhere there.The term "intermediate" as used herein refers to a layer of a multilayer film that lies between an outer layer and a core layer of the film 'Polymer * here includes homopolymer, copolymer, terpolymer, etc. "Copolymer" includes copolymer, terpolymer, etc. "Polyamide" is used herein in the sense of polyamides and copolyamides, and refers to a polymer in which amide bonds (-CONH-) occur along the molecular chain. Examples are nylon 6, nylon 11, nylon 12, nylon 66, nylon 69, nylon 610, nylon 612, nylon / 66, and amorphous nylon. 'Adhesive' refers to adhesives, preferably polymeric adhesives, more preferably polyolefins having an anhydride functionality grafted therein and / or copolymerized and / or mixed 'Anhydride functionality' refers to any form of anhydride functionality, such as anhydride for example of maleic acid, fumaric acid, etc., either grafted onto a polymer, copolymerized with a polymer or mixed with one or more polymers, and also includes derivatives of such functionalities, such as, for example, acids, 5 esters, and metal salts derived from there. More generally, "adhesive" refers to any material that adheres a polyamide layer to another polyamide layer, or to an ethylene / alpha-olefin copolymer such as LLDPE, as used herein, the term 'ethylene copolymer / "alpha olefin" (EAO) refers to heterogeneous materials such as, for example, medium linear density polyethylene (I-MDPE), low linear density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); as well as homogeneous polymers (HEAO) such as TAFMER®, ethylene / alpha-olefin copolymers supplied by Mitsu Petrochemical Corporation and metallocene-catalyzed polymers, such as EXACT® materials supplied by Exxon. These materials generally include copolymers of ethylene with one or more comonomers selected from C4 to C14 alpha-olefins such as butene-1 (ie, 1-butene), hexene-1, octene-1, etc., wherein the molecules of the copolymers comprises long chains with relatively few side branches or cross-linked structures. This molecular structure must be contrasted with low density polyethylenes or Kgqg -wa. ' l * • »» •• • * •! '*, * • -y »-, - g» «t | u -" wj »t" »--- m» n? ja »conventional mean density that present a more developed branch than its respective counterparts. Other ethylene / alpha-olefin copolymers, such as the branched homogeneous long chain ethylene / alpha-olefin copolymers available from the Dow Chemical Company, known as AFFINITY® resins, are also included as another type of copolymer / alpha-olefin useful in the present invention. 'Linear Low Density Polyethylene (LLDPE)' as used herein is required to a polyethylene with a density within a range of about 0.916 to 0.924 grams per cubic centimeter. "Linear Medium Density Polyethylene" (LMDPE) as used herein , has a density of 0.930 grams per cubic centimeter at 0.939 grams per cubic centimeter. "A high density polyethylene" (HDPE), as defined herein, has a density of 0.94 grams per cubic centimeter or more. The term "ethylene / ester copolymer" (E / E) as used herein refers to a copolymer formed of ethylene and an ester such as, for example, vinyl acetate, alkyl acrylate., or else other monomers, where the units derived from ethylene in the copolymer are present in larger amounts and the units derived from ester in the copolymer are present in smaller amounts. The term 'heat shrinkable' is defined herein as a property of a saterial which, when heated to an appropriate temperature above room temperature (eg, 96 ° C), exhibits a free shrink of 5% or more in at least a linear direction 'Materials that can flow' indicate here food or non-food elements that can flow by gravity, or can be pumped according to the definition in the US patent number 4,521,437 (Storms), which is incorporated herein by reference In its entirety, all the compositional percentages used here are calculated on a basis * by weight ". BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a 5-layer embodiment of the present invention. Figure 2 is a cross-sectional view of a 7-layer embodiment of the present invention. Figure 3 illustrates a vertical and sealed form filling apparatus that can be employed in connection with the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to Figure 1, which is a cross-sectional view of a 5-layer embodiment of the present invention, it appears that this embodiment is a film 10 comprising a core layer 11, two interlayers 12 Y 13, and two outer layers 14 and 15. The outer layers 14 and 15 are preferably surface layers.

The core layer 1 comprises a polyamide. Preferred polyamides include nylon 6, nylon 11, nylon 12, nylon 66, nylon 69, nylon 610, nylon 612, nylon 6/66, and amorphous nylon.

The intermediate layers 12 and 13 comprise a polymeric adhesive. The outer layers 14 and 15 comprise an ethylene / alpha-olefin copolymer. A preferred material is a linear low density polyethylene. Figure 2 shows a preferred film of 7 layers with a core layer 21, two intermediate layers 22 and 23, and two outer layers 24 and 25. The outer layers 24 and 25 are preferably surface layers. The core layer 21 in this embodiment includes in fact 3 layers where two layers 26 and 28 comprise polyamide, and have between them a layer 27 comprising a polymeric adhesive. The layers 26 and 28 may be selected from the elements presented above for the layer 11 of the 5-layer film. Layer 27, and intermediate layers 22 and 23, may comprise the same materials as those described above for layers 12 and 13 of the 5-ply film. Layers 24 and 25 may comprise the same materials as those described above for layers 14 and 15 of the 5-ply film. For any of the embodiments, other polymeric materials may optionally be included in the core layer, intermediate layers, or outer layers in addition to the polyamide, insofar as the rupture propagation values discussed above can be obtained, and in the extent to which the layer in which these materials are included, and the overall film, function adequately for their intended end use. Examples of these additional materials are ethylene polymer or copolymers such as LLDPE or VLDPE; ethylene / ester copolymers, such as for example ethylene / vinyl ester copolymer, for example, ethylene / vinyl acetate copolymer, or ethylene / alkyl acrylate copolymer, for example, ethylene / ethyl acrylate copolymer, copolymer of ethylene / methyl acrylate, or ethylene / butyl acrylate copolymer, or ethylene / acid copolymer, such as for example ethylene / acrylic acid copolymer, or ethylene / methacrylic acid copolymer. Mixtures of these materials in any suitable ratio can also be employed. The invention will be better understood with reference to the examples provided below. The final film thicknesses may vary, depending on the process, the end-use application, etc. the typical thicknesses are within a range of 0.1 to 20 mils, more preferably 1 to 10 mils, and especially 2 to 7 mils. Table 1 identifies the materials 25 used in the examples. The remaining tables describe the -asaftiMiMMt - ^^^^^ »* '*' - ^ - ^ * ^ • **" 'properties of films made with these materials Table 1 Material Trade name source PA1 Ultramid® KR-4047film BASF PEÍ Dowlex® KG 3347a Dow PE2 Dowlex® 2045.03 Dow PE3 Escorene LD-102.69 Exxon PE4 Dow 609 A Dow AD1 10853 Master batch of Ampacet Anti-blocking polyethylene Tiel Tymor® 1228B Morton International PA1 is a nylon 6 (polycaprolactam) PEI is a linear low polyethylene density (LLDPE) with a density of 0.917 grams / cubic centimeter PEI is an ethylene / 1-octene copolymer PE2 is a linear low density polyethylene (LLDPE) with a density of 0.20 grams / cubic centimeter. an ethylene / 1-octene copolymer with an octene content of 6.5% by weight of the overall polymer PE3 is a low density polyethylene with a density of 0.92 grams / cubic centimeter PE4 is a low density polyethylene with a density of 0.92 grams / cubic centimeter.AD1 is a master lot of additive that has approximately 80% LLDPE with a density of 0.918 grams / cubic centimeter and approximately 20% of diatomssea. Tiel is a polymeric adhesive comprising an ethylene copolymer grafted with anhydride / butene with a density of 0.9201 grams / cubic centimeter. In Tables 2 and 3, two 5-layer film structures according to the invention are presented. Example 1 is a 5-layer film; Example 2 is a 7-layer film. They were each made by a co-extrusion process where the co-extruded product was expanded hot at an expansion ratio of approximately 2.2: 1 to allow the production of a film having an average thickness (4 samples for each example) comprised between 5.0 and 5.3 thousandths of an inch. Example 1 presents the structure: A / B / C / B / A Where: A = 72% PE2 + 25% PE4 + 3% AD1; B = 100% tiel; and C = 100% PA1. Example 2 has the structure A / B / C / B / C / B / A Where A = 72% PEI + 25% PE3 + 3% AD1; B = 100% tiel; and C = 100% PA1. Table 2 (Example 1) Sample physical property sample2 sample3 sample4 Propagation of break (gms) to LD 284.1 324.5 292.8 296.8 TD 405.0 413.6 448.9 443.5 Table 3 (Example 2) Sample physical property sample2 sample3 sample4 Propagation of rupture (gms) to LD 239.6 297.3 * * TD 279.8 * 280.5 294 .3 LD = longitudinal direction TD = transverse direction a = ASTM of 1938 * = the sample was not broken. Example 3 had a film and formulation structure similar to the film of Example 2, but had an average thickness (4 samples) of approximately 4.7 mils. Table 4 (Example 3) Sample physical property sample2 sample3 sample4 Break propagation (gms) to LD 253.7 255.2 221.6 290.8 TD 338.3 307.2 348.5 314.0 Example 4 presented a film structure and formulation cc --- or example 2, but presented an average thickness (4 ours) of approximately 4.2 thousandths of an inch. Table 5 (example 4) Sample physical property sample 2 sample3 sample4 Break propagation (gms) at 5 LD 242.7 246.6 204.0 228.7 TD 245.5 229.6 235.4 280.8 Example 5 had a film structure and formulation as example 1, and had an average thickness (5 samples) of 5.0 thousandths of an inch. 10 Table 6 (Example 5) Sample property sample2 sample3 sample4 physical sample5 Propagation of rupture (gms) at 15 LD 235.6 315.4 242.0 454.5 ** 297.8 TD 457.3 431.4 470.7 486.7 ** = the doubtful data taking into account the values obtained for the address longitudinal of samples 1 to 3 and 5. Figure 3 illustrates an apparatus for filling vertical forms and seal to be used in a packaging process in accordance with the present invention. Vertical filling and sealing equipment is well known to those skilled in the art of packaging, as presented in US Pat. No. 4,506,494 to Shimoyama et al.

It is incorporated here in its entirety by reference. In Figure 3, a vertical shape filling and sealing apparatus 40 is illustrated schematically. Vertical filling and sealing equipment and processes are well known to those skilled in the art of packaging technology. The following documents present various equipment suitable for vertical filling and sealing: U.S. Patent No. 2,956,383; U.S. Patent 3,340,129 to J.J. Grevich; U.S. Patent No. 3,611,657 to Kyoshi Inoue et. to the.; U.S. Patent No. 3,703,396 to Inoue, et al; U.S. Patent No. 4,103,473 to Bast, et al .; U.S. Patent No. 4,589,247; U.S. Patent No. 4,532,752 to Taylor; U.S. Patent No. 4,532,753 to Kovacs; U.S. Patent No. 4,571,926, to Scully, and British Patent Specification No. 1 334 616, to Groot, et al. The apparatus 40 employs a multilayer film 41 in accordance with the present invention. The product 42 to pack this supplied to the apparatus 40 from a source (not shown) from which a predetermined amount of product 42 reaches the upper end portion of the forming tube 44 through a funnel 43, or through other conventional means. The packages are formed in a lower portion of the apparatus 40, and a flexible sheet material 41 from which the bags or packages are made is fed from a roll 51 onto some forming bars (not shown), wrapped around of the forming tube 44, and is provided with longitudinal seal 47 by a longitudinal thermal sealing device 46, which results in the formation of a vertically oriented tube 48. The end seal bars 45 operate to close and seal horizontally through of the lower end of a vertically sealed tube 48, to form a bag 50 that is immediately filled with the product 42. A device for advancing and / or nullifying a portion of the tube 48, such as for example film drive rollers 51, advances the tube 48 and bag 50 over a predetermined distance, after which end seal bars 45 are simultaneously closed and sealed horizontally through the lower end of the vertically sealed tube 48 as well as sealing simultaneously horizontally through the upper end of the sealed bag 49 to form a product packaged in a sealed bag 49. The next bag 50 is then filled with a measured quantity of product 42, advanced, etc. It is also conventional to incorporate with the end seal bars a cutting blade (not shown) that operates to cut a lower sealed bag 49 from the bottom of the upstream bag 50.

The films of the present invention preferably have "balanced" rupture propagation properties, ie, the preferred films have a propagation of rupture in the longitudinal direction that is substantially equal to the propagation of rupture of the film in the transverse direction Alternatively, the difference between the propagation of break in the longitudinal direction and the propagation of break in the transverse direction is less than 70% To better understand the present invention, and to compare its performance with a conventional film, as well as to determine The feasibility of using film structures in certain applications, a series of tests was carried out.These tests include dimensional stability test, compression test, individual bag drop test, frozen state abuse test, seal resistance analysis as well as analytical evaluation, each of these tests e comments in more detail below. The film of the present invention was either the film of example 5 (5 mils thick) or a film of example 5 but with a difference in thickness. Thus, example 6 is like example 5, but it is 3 mils thick; Example 7 is like Example 5, but has a thickness of 3.5 mils. The films of the invention have outer layers comprising linear low density polyethylene, and each outer layer represented 33% of the total thickness of the film. The comparative film was C-300, a commercial packaging material sold by .R. Grace & Co-Conn through its Grace Packaging group. This material is a 5 layer film made by means of a casting process, and has a core layer of nylon 6, and outer layers of a mixture of 90% linear low density polyethylene and 10% of a master batch of color that has a low density polyethylene vehicle. The outermost layers each comprised 26.6% of the total thickness of the film. An intermediate layer is present between the core layer and each of the outermost layers, and consists of a polymeric adhesive grafted with anhydride. In the tables presented below, it is shown in comparative material in two different calibers. 1. Dimensional stability During this test, a series of empty bags, each with a bottom seal and an open end, were placed in a quality of a bag tester, and an air hose with airtight fit was fixed over the opening of each of the bags in turn. This allowed the sealing of the bags. The bag tester was an LVRP (Linear Ramp, Variable Pressure Hot Hot Burst Tank) (LRVP hot expansion tank) The bag tester was made of stainless steel, and consisted mainly of a container that contained approximately 30 gallons of hot water The container had a width of 4 feet, a length of three and a half feet and a height of 4 feet. On the upper front of this unit was an articulated Plexiglas® shield that could be opened and closed for allow the placement of the samples inside as well as to see for the purpose of evaluating.At the top of the tester, behind the protector, was a raised stainless steel unit that housed the control panel and adjustments inside the Plexiglas protector ®, where the hot water was located, there was an arm that held the bag / sample to be tested on top of the water, for each approved bag, once the bag was found. In its place, the protector was closed, air was applied under pressure, and the bag was lowered into the heated water. Several hundred plastic balls floated on top of the water to suppress any spatter that might occur when the bag exploded (eventually). The machine was adjusted to a cycle for a predetermined time, or even the failure of the bag, when it automatically lifted the bag and opened the protector. Light-emitting diodes indicated the time or pressure at the time of the bursting of the bag. The bags were initially empty. When the test cycle was started, air was plugged into each of the bags through a staple on the top of the bag as it was lowered into a hot water tank (180 ° F) for a pre-set period of time ( 10 seconds) . This procedure simulated the hot filling operation of the Onpack VFFS equipment. In a commercial packaging environment, the air pressure, combined with a hot aqueous liquid food product, can cause the packaging film to become too elastic to stretch undesirably or form hernias. Under production conditions, this stretch contributes to packing price variation due to a volume variation in the different bags. That is, the more a bag is stretched, the more product it contains. If the amount of stretch varies from bag to bag, then the weights of the packages made from these bags will also vary. This phenomenon is undesirable in commercial operations. To measure differences in the film, 5 bags of each type and film size were tested under the same conditions. After the specified time in the hot water, each bag was removed and measured. One-inch bands of 2 places were cut in the bag. The first sample was taken from an area not subject to air pressure and hot water (control). The second sample was taken from the area subjected to air and hot water. The widest circumference for each bag was used to determine the maximum amount of stretch under these conditions. These one-inch bands were cut and placed in a flat, measured position. The difference of the two measurements indicates the amount of stretch observed in this type of film. Table 7 summarizes the observed results. Table 7 Dimensional stability evaluation results of expanded films and castings Film type control length (mm) Test length (mm) C300 (3 mils) # 1 507 748 # 2 stock failure # 3 failure of the Bag # 4 fails to bag # 5 512 955 C300. { 4.5 thousandths of an inch) # 1 511 750 # 2 511 681 # 3 511 641 # 4 510 704 # 5 513 717 t, '. w- 4w < ^ < W_μij. '| J | ^ jM'MSCT Example 6 (3 thousandths of an inch) # 1 473 489 # 2 478 491 # 3 475 489 # 4 475 492 # 5 475 489 (4 thousandths of an inch) # 1 475 480 # 2 475 482 # 3 474 480 # 4 472 483 # 5 473 480 Type of film Difference (mm) percentage increase C300 (3 thousandths of an inch) # 1 241 47.5 # 2 NA NA # 3 NA NA # 4 NA NA # 5 443 86.5 Average = 67 * C300 (4.5 thousandths of an inch) # 1 239 46. 8 # 2 170 33. 3 # 3 130 25.4 # 4 194 38. 0 # 5 204 39. 8 Example 6 Average = 36. 7 (3 thousandths of an inch) # 1 16 3.4 # 2 13 2.7 # 3 14 2.9 # 4 17 3.6 # 5 14 2.9 Average = 3.1 (4 thousandths of puigaaa) # 1 5 1.1 # 2 7 1.5 # 3 6 1.3 # 4 11 2.3 # 5 7 1.5 Average = 1.5 The films of the present invention showed less distortion than the comparative films. Comparative films showed a tendency to acquire a 'pear shape *. 2. Compression test The compression test was carried out to help the amount of compression that an individual bag could withstand. This type of test can cause the failure either at the end of the body or in the body of the bag. To carry out this test, individual bags (100 ounces of ambient water in each bag) were placed in a compression device. This device has two metal plates, approximately 8 inches by 14 inches, hinged directly between them at one end. From the other end of the two plates, two arms extend about 18 inches. The device is placed on the floor, a bag is placed between the two plates and the two plates close together. To obtain the high pressure necessary to produce a fault, the operator must put on one of the arms. Frequently the pressure required is so high that the operator must jump to obtain the required pressure. A meter, placed on the top plate measures the highest force exerted on the bag at the time of failure. This pressure device is used by several commercial food processors. For the test, 5 bags of each structure were produced and said bags were hydrated for several days. The bags were tested until the failure of each of them, and the pressure exerted at the time of the failure was recorded. Table 8 summarizes the tests. Table 8 Compression Test Results C300 Film C300 RDX-3193 RDX-3193 (3 mil.in) (4.5 mil.in.) (3.5 mil.in.) (5 mil.in.) # 1 5.4 7.4 10.0 15.2 # 2 5.5 7.4 10.3 13.2 # # 33 5 5..55 8.4 10.3 13.0 # 4 5.5 7.9 9.0 13.5 # 5 5.0 7.9 9.9 13.3 Average 5.38 7.8 9.9 13.6 Diversion - 0.217 0.418 0.534 0.891 standard distribution PSI / mil- 1.79 1.73 2.8 2.7 Inch 3. individual bag drop test individual bag drop tests were carried out to determine the amount of abuse that an individual bag can withstand. In order to carry out this test, each bag was kept in a flat position (with the ends sealed) and dropped manually by increasing height. Each bag was dropped once from a height of 3 feet, then once from a height of 4 feet, and then up to 6 times from a height of 5 feet. The height and number of the fall was recorded and the average number of falls at which the bag survived was calculated by comparison. This test was performed with hydrated bags (filled with 500 milliliters of water and stored for at least 24 hours) as well as with non-hydrated bags (which were filled and tested within 15 minutes). Tables 9 and 10 summarize the results. Table 9 Individual bag drop test results (hydrated bags) Approved / failed high drop film Example 7 (3.5 Thousandths of an Inch # 1 Failed 5 '# 2 Approved 5' # 3 Approved 5 '# 4 Approved 5' # 5 Approved 5 'Example 5 (5 thousandths of an inch) # 1 Approved 5' # 2 Approved 5 '# 3 Failed 5' # 4 Failed 5 '# 5 Approved 5' C300 (3: piles in.) # 1 Failed 4 '# 2 Failed 5' # 3 Failed 5 '# 4 Failed 5' # 5 Approved 5 'C300 (4.5 mil. Simas de in.) # 1 Approved 5' # 2 Failed 5 '# 3 Failed 5' # 4 Approved 5 '# 5 Failed 5' Movie total number of No. of falls Comments 5-foot drop to which the bag survived Example 7 (3.5 Thousandths of an inch # 1 6 7 seal failure # 2 6 8 No leakage # 3 6 8 No leakage # 4 6 8 No leakage # 5 6 8 No leakage Average = 7.8 Example 5 (5 thousandths of an inch) # 1 6 8 No leakage # 2 6 8 No leakage # 3 3 4 seal failure # 4 4 5 seal failure # 5 6 8 No leakage Average = 6.6 C300 (3 mm in.:.}. # 1 1 1 seal failure # 2 3 4 sidewall rupture # 3 3 4 seal failure # 4 2 3 seal failure # 5 6 8 No leakage iic? = 4-0 C300 (4.5 miles in. # 1 6 8) No leakage # 2 3 4 seal failure # 3 1 2 seal failure # 4 6 8 No leakage # 5 1 2 seal failure Average = 4.8 Table 10 Individual bag drop test results (unhydrated bags) Approved / failed film Highest height of total fall No. of falls of 5 feet RDX3193 ( 3.5 mi-thirds-in.) # 1 Failed 5 '2 # 2 Approved 5' 6 # 3 Failed 5 '1 # 4 Approved 5' 6 # 5 Failed 5 '3 RDX-3193 (5 mils) # 1 Failed 5 '6 # 2 Failed 5 '3 # 3 Failed 5 '1 # 4 Failed 5' 2 # 5 Failed 5 '5 C300 (3 - thousandths of an inch) # 1 Failed 4 '1 # 2 Failed 4 '1 # 3 Failed 3 '1 # 4 Failed 4 '1 # 5 Failed 3 '1 C300 (4.5 thousandth of an inch) # 1 Failed 4' 1 # 2 Failed 3 '1 # 3 Failed 4' 1 # 4 Failed 4 '1 # 5 Failed 4 '1 Film Number of falls Comments To which the bowl survived RDX3193 (3.5 thousandths of an inch) # 1 3 Lateral wall rupture # 2 6 No leakage # 3 1 seal failure # 4 8 No leakage # 5 4 seal failure Average = 5.4 RDX-3193 (5 mils) # 1 7 seal failure # 2 4 seal failure # 3 2 failure seal # 4 3 seal failure # 5 6 seal failure]? rom = 4.4 C300 (3-thousandths of an inch) # 1 1 seal failure # 2 1 seal failure # 3 0 seal failure # 4 1 failure seal # 5 0 seal failure Average = 0.6 C300 (4.5 thousandth of an inch) # 1 1 seal failure # 2 0 seal failure # 3 1 seal failure # 4 1 seal failure # 5 1 seal failure Average = 0.8 4. Evidence of abuse in the frozen state Abuse tests were carried out in the frozen state to determine if the product packed in the film structures could survive transport and handling conditions under freezing conditions. To simulate this effect, four bags of each of the water-filled films were placed in appropriately sized boxes and subjected to freezing. To further exaggerate the abuse that the bags could suffer, the boxes were packed loosely to allow movement during the evaluation. This greatly increased the contact between the bags. A box of each type of film was placed on a Lansmont Vibration Table to simulate boarding abuses. The boxes were tested for one hour at 0.75 G and 5.0 Hz. After the vibration test, each box was removed and immediately dropped (flat, on the bottom) from a height of two feet. Then it was allowed to thaw overnight, to check for leaks. Table 11 contains the results of this test. Table 11 Abuse test results in frozen state Film Leaks Comments Example 7 4/4 (1005) Sidewall stress cracks Example 5 0/4 (0%) No leak C300 (3 milé-0 (0% ) No Leakage Gaps -Fully C300 (4.5 (25%) First Thousands of Inch Rupture) Even though the comparative films performed better than the films of the present invention in this particular test, the experience of commercial applications of the films of the present invention suggests that in fact these films perform well in terms of resistance to abuse when they contain a frozen product. 5. Seal resistance analysis Several bags of each sample were sealed in a Vertrod® sealer using a Scot® tester, which is similar in operation to an Instron® supplier, the seal resistances were evaluated. A one inch band of seal area was cut for each seal tested, and the results are reported in pounds per linear inch (pli). Table 12 summarizes the results. Table 12 Seal Strength Analysis Film Sample number Average (in pli) Standard deviation Example 7 10 11.85 0.428 Example 5 9 16.53 0.522 C300 (3 mil 10 10 0.83 0.646 gaps) C300 (4.5 - 10 16.63 0.827 Thousands of Inches) The data demonstrates that films of the present invention show high resistance to abuse in freezing and hot fill applications. This resistance to abuse includes a high resistance to impacts, and good dimensional stability. These attributes are important in VFFS systems. In systems of this type, the team fills a bag up to a certain level. If the film is stretched, too much product is put in the bag. This phenomenon makes it difficult to standardize the dimensions of the bags, which causes, for example, difficulty in packaging the bags in shipping boxes of predetermined size. Therefore, the dimensional stability is of great importance. Films of the present invention have a rupture propagation preferably less than 350 grams 8ASTM 1938) in the longitudinal direction, more preferably less than 325 grams, such as less than 300 grams, less than 275 grams, and less than 250 grams. Films of the present invention have a rupture propagation preferably of less than 500 grams (ASTM 1938) in the transverse direction, more preferably less than 450 grams, such as less than 400 grams, less than 350 grams, and less than 300 grams. The burst propagation values of the films of the present invention are preferably similar in both the longitudinal and transverse directions, and preferably differ by less than 70% between the longitudinal direction and the transverse direction, more preferably by less 60%, such as less than 50%, less than 40%, less than 30%, less than 20% and less than 10%. The films of the present invention are made by thermal expansion of a coextruded product at an expansion ratio of up to 2.0: 1 and 3.0: 1, such as between 2.1: 1 and 2.9: 1.; between 2.2: 1 and 2.8: 1; and between 2.3: 1 and 2.7: 2.1; as for example 2.5: 1. The films of the present invention are preferably not heat shrinkable, but may optionally be stretch oriented by conventional orientation processes well known in the art, such as for example the trapped bubble or hanging frame processes, in order to make The material becomes shrinkable. Films of the present invention may optionally be crosslinked by irradiation, or chemically. Preferred embodiments of five layer films of the present invention have a layer thickness ratio between layers A / B / C / B / A of 33/7/20/7/33. The films of the present invention have outer or seal layers each comprising at least 27%, more preferably at least 28%, and especially at least 30% of the total thickness of the film. The core layer of the films of the present invention is preferably between 15% and 25%, more preferably 20% of the total thickness of the film. Internal attachments such as, for example, the Asept ® attachment distributed in the United States of America by the beneficiary of the present application, and presented in the US patent number 4,603,793 (Stern), can optionally be sealed on the inner surface of a bag wall of a bag made from the film of the present invention.

Claims (9)

1. CLAIMS 1. A film comprising: a) a core layer comprising a polyamide; b) two intermediate layers placed on opposite surfaces of the core layer, comprising an adhesive, and c) two outer layers, each placed on a surface of the respective intermediate layer, comprising an ethylene / alpha-olefin copolymer; where the two outer layers each conform at least 27% of the total thickness of the film. The film of claim 1, wherein the core layer comprises a polyamide selected from the group consisting of nylon 6, nylon 11, nylon 12, nylon 66, nylon 69, nylon 610, nylon 612, nylon 6/66, and amorphous nylon. . The film of claim 1, wherein the intermediate layers each comprise a polymeric adhesive selected from the group consisting of ethylene copolymer grafted with anhydride / 1-butene, ethylene copolymer grafted with anhydride / 1-hexene, and ethylene copolymer grafted with anhydride / 1-octene. . The film of claim 1, wherein the outer layers each comprise an ethylene / alpha-olefin copolymer having a density comprised between 0.916 and 0.925 grams per cubic centimeter. 5. The film of claim 1, wherein the film is characterized by a rupture propagation (ASTMD-1938) less than 350 grams in the longitudinal direction and less than 500 grams in the transverse direction. 6. The film of claim 1, wherein the polyamide constitutes between 15% and 25% of the total film thickness. The film of claim 1, wherein the two outer layers each comprise at least 30% of the total thickness of the film. 8. The film of claim, wherein the core layer comprises: a) a first layer of polyamide. b) a second layer of polyamide, and c) a third layer, placed between the first layer and the second layer, comprising an adhesive. The film of claim 8, wherein the first polyamide layer and the second polyamide layer of the core layer each comprise selected polyamide within the group consisting of nylon 6, nylon 11, nylon 12, nylon 66, nylon 69, nylon 610, nylon 612, nylon 6/66, and amorphous nylon. The film of claim 8, wherein the intermediate layers and the third layer placed between the first polyamide layer and the second polyamide layer, each comprise a polymeric adhesive selected from the group consisting of anhydride-grafted ethylene copolymer. / 1-butene, ethylene copolymer grafted with anhydride / 1-hexene, and ethylene copolymer grafted with anhydride / octene. The film of claim 8, wherein the outer layers each comprise an ethylene / alpha-olefin copolymer having a density comprised between 0.916 and 0.925 grams per cubic centimeter. The film of claim 8, wherein the film is characterized by a rupture propagation (ATMD-1938) less than 350 grams in the longitudinal direction and less than 500 grams in the transverse direction. The film of claim 8, wherein the polyamide of the first layer of polyamide and the second layer of polyamide together constitutes between 18% and 25% of the total thickness of the film. 14. A process for making a film comprising: a) extruding a film comprising a core layer comprising a polyamide; two intermediate layers placed on opposite surfaces of the core layer, comprising an adhesive; and two outer layers, each placed on a surface of the respective intermediate layer comprising an ethylene / alpha-olefin copolymer; and b) the expansion of the film by means of a hot expansion process up to an expansion ratio between 2.0: 1 and 3.0: 1. 15. The process of claim 14, wherein the core layer comprises: a) a first layer of polyamide, b) a second layer of polyamide, and c) a third layer, placed between the first layer and the second layer, comprising a polymeric adhesive. 16. A package comprises: a) a food product that can flow; and b) a bag containing the food product, the bag is made of a film comprising: i) a core layer comprising a polyamide; ii) two intermediate layers, placed on opposite surfaces of the core layer comprising an adhesive; and iii) two outer layers, each placed on a surface of the respective intermediate layer, comprising an ethylene / alpha-olefin copolymer; where the two outer layers make up at least 27% of the total thickness of the film. The package of claim 16, wherein the bag includes a notch of rupture. 8. The package of claim 16, wherein the bag includes a longitudinal seal and two transverse thermal seals. The package of claim 16, wherein the polyamide constitutes between 15% and 25% of the total thickness of the film. The package of claim 16, wherein the film is characterized by a rupture propagation (ASTMD-1938) less than 350 grams in the longitudinal direction, and less than 500 grams in the transverse direction. The package of claim 16, wherein the bag comprises an internal attachment adhered on an inner wall of the bag.