POUCHES FOR PACKAGING FLOWABLE MATERIALS

Abstract: An environmentally friendly polymer film pouch made from a polyethylene film structure for the packaging of flowable materials, for example milk, including, for example, a pouch made from a monolayer or multilayer film structure such as a two-layer or a three-layer coextruded film containing at least one layer of a blend of a linear ethylene interpolymer and a high pressure low density polyethylene as a seal layer. Also disclosed is a process for making a pouch for packaging flowable materials using a film structure of a blend of a linear ethylene interpolymer and a high pressure low density polyethylene.

Description: POUCHES FOR PACKAGING FLOWABLE MATERIALS This invention relates to a pouch used in consumer packaging made from certain film structures useful for packaging flowable materials, for example liquids such as milk. U.S. Patent Nos. 4,503,102, 4,521 ,437 and 5,288,531 disclose the preparation of a polyethylene film for use in the manufacture of a disposable pouch for packaging of liquids such as milk. U.S. Patent No. 4,503,102 discloses pouches made from a blend of a linear ethylene copoiymer copolymerized from ethylene and an alpha-oiefin at the C 4 to C 10 range and a ethylene-vinyl acetate polymer copolymerized from ethylene and vinyl acetate. The linear polyethylene copoiymer has a density of from 0.916 to 0.930 g/cm3 and a melt index of from 0.3 to 2.0 g/10 minutes. The ethylene-vinyl acetate polymer has a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10 g/10 minutes. The blend disclosed in U.S. Patent No. 4,503,102 has a weight ratio of linear low density polyethylene to ethylene- vinyl acetate polymer of from 1.2:1 to 4:1 U.S. Patent No. 4,503,102 also discloses laminates having as a sealant film the aforementioned blend. U.S. Patent No. 4,521,437 describes pouches made from a sealant film which is from 50 to 100 parts of a linear copoiymer of ethylene and octene-1 having a density of from 0.916 to 0.930 g/cm3 and a melt index of 0.3 to 2.0 g/10 minutes and from 0 to 50 parts by weight of at least one polymer selected from the group consisting of a linear copoiymer of ethylene and a C 4 -C 10 -alpha-olefin having a density of from 0.916 to 0.930 g/cm3 and a melt index of from 0.3 to 2.0 g/10 minutes, a high-pressure polyethylene having a density of from 0.916 to 0.924 g/cm3 and a melt index of from 1 to 10 g/10 minutes and blends thereof. The sealant film disclosed in the U.S. Patent No. 4,521,437 was selected on the basis of providing (a) pouches with a M-test value substantially smaller, at the same film thickness, than that obtained for pouches made with film of a blend of 85 parts of a linear ethylene/butene-1 copoiymer having a density of 0.919 g/cm3 and a melt index of 0.75 g/10 minutes and 15 parts of a high pressure polyethylene having a density of 0.918 g/cm3 and a melt index of 8.5 g/10 minutes, or (b) an M(2)-test value of less than 12%, for pouches having a volume of from greater than 1.3 to 5 liters, or (c) an M(1.3)-test value of less than 5% for pouches having a volume of from 0.1 to 1.3 liters. The M, M(2) and M(1.3)-tests are defined pouch drop tests in U.S. Patent No. 4,521,437. The pouches may also be made from composite films in which the sealant film forms at least the inner layer. U.S. Patent No. 5,288,531 discloses pouches made from a film structure having a blend of (a) from 10 to 100 percent by weight of at least one polymeric seal layer of an ultra low density linear ethylene copoiymer interpolymerized from ethylene and at least one aipha- olefin in the range of C 3 -C 10 with a density of from 0.89 g/cm3 to less than 0.915 g/cm3 and (b) from 0 to 90 percent by weight of at least one polymer selected from the group consisting of a linear copoiymer of ethylene and a C 3 -C 18 -alpha-olefin having a density of greater than 0.916 g/cm3 and a melt index of from 0.1 to 10 g 10 minutes, a high-pressure low density polyethylene having a density of from 0.916 to 0.930 g/cm3 and a melt index of from 0.1 to 10 g/10 minutes, or ethylene-vinyl acetate copoiymer having a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10 g/10 minutes. The heat seal layer in the U.S. Patent No. 5,288,531 provides improved hot tack strength and lower heat seal initiation temperature to a two-layer or three-layer coextruded multilayer film structure described therein. The polyethylene pouches known in the prior art have some deficiencies. The problems associated with films known in the prior art relate to the sealing properties and performance properties of the film for preparing pouches, In particular, prior art films made into pouches in general have a high incident of "leakers", i.e., seal defects such as pinholes which develop at or near the seal in which flowable material, for example milk escapes from the pouch. Although the seal and performance properties of the prior art films have been generally satisfactory, there is still a need in the industry for better seal and performance properties in films for manufacture of hermetically sealed pouches containing flowable materials. More particularly, there is a need for improved sealing properties of the film such as hot tack and melt strength in order to improve the processability of the film and to improve pouches made from the films. For example, the line speed of known packaging equipment used for manufacturing pouches such as form, fill and seal machines, is currently limited by the sealing properties of the film used in the machines. Prior art polyethylene films have low melt strength. Therefore, the speed at which a form, fill and seal machine can produce a pouch is limited and, thus, the number of pouches produced on a form, fill and seal machine is limited. If the melt strength is increased, then the speed of a form, fill and seal machine can be increased and, thus, the number of pouches produced can be increased. Until the present invention, many have attempted to improve sealing properties of the polymeric composition used in pouch film without success. It is desired to provide a polyethylene film structure for a pouch container having improved melt strength with performance properties as good or better than the known prior art pouch films. It is also desired to provide a film structure for a pouch container which can be processed through a form fill and seal machine as a monolayer film. It is further desired to provide a pouch made from the aforementioned film structures such that the pouch has a reduced failure rate. The present invention provides a pouch containing a flowable material, said pouch being made from a film structure with at least one seal layer of a polymeric composition comprising: (a) from 10 to 100 percent, based on the total weight of said composition, of a mixture of (1) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of linear ethylene copoiymer interpolymerized from ethylene and at least one alpha-olefin in the range of C3-C18 and having a density from 0.916 to 0.940g/cm3 and a melt index of less than 10g/10 minutes, and a molecular weight distribution, Mw/Mn, ratio of greater than 4.0, and a peak melting point greater than 100°C as measured by a differential scanning colorimeter, and (2) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of high pressure low density polyethylene having a density from 0.916 to 0.930g/cm3, a melt index of less than 1g/10 minutes and melt strength greater than 10 cN as determined using a Gottfert Rheotens unit at 190°C; and (b) from 0 to 90 percent, based on the total weight of said composition, of at least one copoiymer selected from the group consisting of an ethylene-vinyl acetate copoiymer having a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10g/10 minutes. One embodiment of the present invention is a pouch made from a two-layer coextruded film containing an outer layer of linear low density polyethylene and an inner seal layer of the aforementioned polymeric composition. Another embodiment of the present invention is a pouch made from a three- layer coextruded film containing an outer layer and a core layer of linear low density polyethylene and an inner seal layer of the aforementioned polymeric composition. Another aspect of the present invention is a process for preparing the aforementioned pouch. Yet another embodiment of the present invention is a pouch made from a three- layer coextruded film containing an outer layer and a core layer of high pressure low density polyethylene and an inner seal layer of the aforementioned polymeric composition. It has been discovered that the film structures for the pouches of the present invention have an improved melt strength and heat seal strength, particularly the end-seal strength. Use of the films for making pouches of the present invention in form, fill and seal machines leads to machine speeds higher than currently obtainable with the use of commercially available film. Brief Description of the Drawings Fig. 1 shows a perspective view of a pouch package of the present invention. Fig. 2 shows a perspective view of another pouch package of the present invention. Fig. 3 shows a partial, enlarged cross-sectional view of the film structure of a pouch of the present invention. Fig. 4 shows another partial, enlarged cross-sectional view of the film structure of a pouch of the present invention. Fig. 5 shows yet another partial, enlarged cross-sectional view of the film structure of a pouch of the present invention. Fig. 6 is a graphical illustration of end seal strength versus melt strength. The pouch of the present invention, for example as shown in Figure 1 and 2, for packaging flowable materials is manufactured from a monolayer film structure of a polymeric seal layer which is a blend of a linear low density polyethylene and a high pressure low density polyethylene having a high melt strength. The blend can also contain an ethylene vinylacetate copoiymer. "Melt strength" which is also referred to in the relevant art as "melt tension" is defined and quantified herein to mean the stress or force (as applied by a wind-up drum equipped with a strain cell) required to draw a molten extrudate at some specified rate above its melting point as it passes through the die of a standard plastometer such as the one described in ASTM D1238-E. Melt strength values, which are reported herein in centi-Newtons (cN), are determined using a Gottfert Rheotens at 190°C. In general, for ethylene α-olefin interpoiymers and high pressure ethylene polymers, melt strength tends to increase with increased molecular weight, or with broadening of the molecular weight distribution and/or with increased melt flow ratios. The melt strength of the high pressure low density polyethylene of the present invention is greater than 10 cN as determined using a Gottfert Rheotens unit at 190°C, preferably from 13 to 40 cN, and most preferably 15 to 25cN. Further, the melt strength of the polymeric composition of the present invention is greater than 10 cN as determined using Gottfert Rheotens unit at 190X, preferably from 15 to 70 cN, and most preferably 15 to 50. One component of the polymer composition of the present invention is a polyethylene referred to hereinafter as "linear low density polyethylene" ("LLDPE"). An example of a commercially available LLDPE is DOWLEX™ 2045 (Trademark of and commercially available from The Dow Chemical Company). The LLDPE is generally a linear copoiymer of ethylene and a minor amount of an α-olefin having from 3 to 18 carbon atoms, preferably from 4 to 10 carbon atoms and most preferably 8 carbon atoms. The LLDPE for the polymeric composition of the present invention has a density of greater than 0.916 g/cm3, more preferably from 0.916 to 0.940 g/cm3, most preferably from 0.918 to 0.926 g/cm3; generally has a melt index of less than 10 g/10 minutes, preferably from 0.1 to 10 g/10 minutes, most preferably from 0.5 to 2g/10 minutes and generally has an I 10 /l 2 ratio of from 0.1 to 20, preferably from 5 to 20, and most preferably 7 to 20. The LLDPE can be prepared by the continuous, batch or semi-batch solution, slurry or gas phase polymerization of ethylene and one or more optional α-olefin comonomers in the presence of a Ziegler Natta catalyst, such as by the process disclosed in U.S. Patent No. 4,076,698 to Anderson et al., incorporated herein by reference. Suitable α-oief in for the LLDPE of the present invention are represented by the following formula: CH 2 = CHR where R is a hydrocarbyi radical having from one to twenty carbon atoms. The interpolymerization process can be a solution, slurry or gas phase technique or combinations thereof. Suitable α-olefin for use as comonomers include 1-propylene, 1-butene, 1-isobutyiene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene and 1-octene, as well as other monomer types such as styrene, halo- or alkyl-substituted styrenes, tetraf iuoro-ethyiene, vinyl benzocyclobutane, 1 ,4-hexadiene, 1 ,7-octadiene, and cycloalkenes, e.g., cyclopentene, cyclohexene and cyclooctene. Preferably, the α-olefin will be 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, or mixtures thereof. More preferably, the α- olefin will be 1-hexene, 1-heptene, 1-octene, or mixtures thereof, as coatings, profiles and films fabricated with the resultant extrusion composition will have especially improved abuse properties where such higher α-olef ins are utilized as comonomers. However, most preferably, the α-olefin will be 1-octene and the polymerization process will be a continuous solution process. The molecular weight distribution of the ethylene α-olefin interpolymer compositions and the high pressure ethylene polymer compositions are determined by gel permeation chromatography (GPC) on a Waters 150 high temperature chromatographic unit equipped with differential ref ractometer and three columns of mixed porosity. The columns are supplied by Polymer Laboratories and are commonly packed with pore sizes of 10 3 , ,10 4 , 10 s and 10 6 Λ. The solvent is 1 ,2,4-trichlorobenzene, from which 0.3 percent by weight solutions of the samples are prepared for injection. The flow rate is 1.0 milliliters/minute, unit operating temperature is 140°C and the injection size is 100 microliters. The molecular weight determination with respect to the polymer backbone is deduced by using narrow molecular weight distribution polystyrene standard (from Polymer Laboratories) in conjunction with their elution volumes. The equivalent polyethylene molecular weights are determined by using appropriate Mark-Houwink coefficients for polyethylene and polystyrene (as described by Williams and Ward in Journal of Polymer Science. Polymer Letters, Vol. 6, p. 621, 1968) to derive the following equation: "polyethylene = a * ("polystyrene) 15 . In this equation, a = 0.4316 and b = 1.0. Weight average molecular weight, M w , is calculated in the usual manner according to the following formula: M w = ∑ Wj x M ( , where w, and Mj are the weight fraction and molecular weight, respectively, of the i th fraction eluting from the GPC column. For LLDPE, the Mw/Mn is preferably 2 to 7, especially 4. It is believed that the use of LDPE having high melt strength in a film structure for pouches of the present invention (1) provided a pouch that can be fabricated at a fast rate through a form, fill and seal machine, and (2) provides a pouch package having few leakers, particularly when the pouch of the present invention is compared to pouches made with linear low density polyethylene, low density polyethylene or a combination thereof. With reference to Figures 3 to 5, the film structure of the pouch of the present invention also includes a multilayer or composite film structure 30, preferably containing the above-described polymer seal layer being the inner layer of the pouch. As will be understood by those skilled in the art, the multilayer film structure for the pouch of the present invention may contain various combination of film layers as long as the seal layer forms part of the ultimate film structure. The multilayer film structure for the pouch of the present invention may be a coextruded film, a coated film or a laminated film. The film structure also included the seal layer in combination with a barrier film such as polyester, nylon, EVOH, polyvinylidene dichloride (PVDC) such as SARAN™ (Trademark of The Dow Chemical Company) and metallized films. The end use for the pouch tends to dictate, in a large degree, the selection of the other material or materials used in combination with the seal layer film. The pouches described herein will refer to seal layers used at least on the inside of the pouch. One embodiment of the film structure 30 for the pouch of the present invention, shown in Figure 3, comprises seal layer 31 of a blend of LLDPE and high melt strength LDPE of this invention and at least one polymeric outer layer 32. The polymeric outer layer 32 is preferably a polyethylene film layer, more preferably a LLDPE. An example of a commercially available LLDPE is DOWLEX™ 2045 (Trademark of the commercially available from The Dow Chemical Company). The thickness of the outer layer 32 may be any thickness so long as the seal layer 31 has a minimum thickness of 0.1 mil (2.5 microns). Another embodiment of the film structure 30 for the pouch of the present invention, shown in Figure 4, comprises the polymeric layer 32 sandwiched between two polymeric seal layers 31. Still another embodiment of the film structure 30 for the pouch of the present invention, shown in Figure 5, comprises at least one polymeric core layer 33 between at least one polymeric outer layer 32 and at least one polymeric seal layer 31. The polymeric layer 33 may be the same LLDPE film layer as the outer layer 32 or preferably a different LLDPE, and more preferably an LLDPE, for example DOWLEX™ 204S (Trademark of and commercially available from The Dow Chemical Company) that has a higher density than the outer layer 32. The thickness of the core layer 33 may be any thickness so long as the seal layer 31 has a minimum thickness of 0.1 mil (2.5 microns). The ultimate film thickness of the final film product used for making the pouch of the present invention is from 0.5 mil (12.7 microns) to 10 mils (254 microns), preferably from 1 mil (25.4 microns) to 5 mils (127 microns); more preferably from 2 mils (50.8 microns) to 4 mils (100 microns). Additives, known to those skilled in the art, such as anti-block agents, slip additives, UV stabilizers, pigments and processing aids may be added to the polymers from which the pouches of the present invention are made. As can be seen from the different embodiments of the present invention shown in Figure 3-5, the film structure for the pouches of the present invention has design flexibility. Different LLDPE can be used in the outer and core layers to optimize specific film properties such as film stiffness. Thus, the film can be optimized for specific applications such as for a vertical form, film and seal machine. The polyethylene film structure used to make a pouch of the present invention is made by either the blown tube extrusion method or the cast extrusion method, methods well known in the art. The blown tube extrusion method is described, for example, in Modern Plastics Mid-October 1989 Encyclopedia Issue, Volume 66, Number 11, pages 264 to 266. The cast extrusion method is described, for example, in Modern Plastics Mid-October 1989 Encyclopedia Issue, Volume 66, Number 11, pages 256 to 257. Embodiments of the pouches of the present invention, shown in Figure 1 and 2 are hermetically sealed containers filled with "flowable materials". By "flowable materials" it is meant, materials which are flowable under gravity or which may be pumped. The term "flowable materials" does not include gaseous materials. The flowable materials include liquids for example milk, water, fruit juice, oil; emulsions for example ice cream mix, soft margarine; pastes for example meat pates, peanut butter; preservers for example jams, pie fillings marmalade; jellies; doughs; ground meat for example sausage meat; powders for example gelatin powders, detergents; granular solids for example nuts, sugar; and like materials. The pouch of the present invention is particularly useful for liquid foods for example milk. The flowable material may also include oleaginous liquids for example cooking oil or motor oil. Once the film structure for the pouch of the present invention is made, the film structure is cut to the desired width for use in conventional pouch-forming machines. The embodiments of the pouch of the present invention shown in Figures 1 and 2 are made in so- called form, fill and seal machines well known in the art. With regard to Figure 1, there is shown a pouch 10 being a tubular member 11 having a longitudinal lap seal 12 and transverse seals 13 such that, a "pillow-shaped" pouch is formed when the pouch is filled with flowable material. With regard to Figure 2, there is shown a pouch 20 being a tubular member 21 having a peripheral fin seal 22 along three sides of the tubular member 21, for example, the top seal 22a and the longitudinal side seals 22b and 22c, and having a bottom substantially concave or "bowl-shaped" member 23 sealed to the bottom portion of the tubular member 21 such that when viewed in cross-section, longitudinally, substantially a semi-circular or "bowed- shaped" bottom portion is formed when the pouch is filled with flowable material. The pouch shown in Figure 2 is an example of so-called "Enviro-Pak" pouch known in the art. The pouch manufactured according to the present invention is preferably the pouch shown in Figure 1 made on so-called vertical form, fill and seal (VFFS) machines well known in the art. Examples of commercially available VFFS machines include those manufactured by Hayssen, Thimonnier, Tetra Pak, or Prepac. A VFFS machine is described in the following reference: F. C. Lewis, "Form-Fill-Seal," Packaging Encyclopedia, page 180, 1980. In a VFFS packaging process, a sheet of the plastic film structure described herein is fed into a VFFS machine where the sheet is formed into a continuous tube in a tube- forming section. The tubular member is formed by sealing the longitudinal edges of the film together - either by lapping the plastic film and sealing the film using an inside/outside seal or by fin sealing the plastic film using an inside/inside seal. Next, a sealing bar seals the tube transversely at one end being the bottom of the "pouch", and then the fill material, for example milk, is added to the "pouch." The sealing bar then seals the top end of the pouch and either burns through the plastic film or cuts the film, thus, separating the formed completed pouch from the tube. The process of making a pouch with a VFFS machine is generally described in U.S. Patent Nos. 4,503,102 and 4,521,437 incorporated herein by reference. The capacity of the pouches of the present invention may vary. Generally, the pouches may contain from 5 milliiiters to 10 liters, preferably from 1 milliliter to 8 liters, and more preferably from 1 milliliter to 5 liters of flowable material. The film structure for the pouch of the present invention has precisely controlled strength. The use of the film structure described in the present invention for making a pouch results in a stronger pouch, and, therefore, more preferably, the pouch contains fewer use-related leakers. The use of a LLDPE and LDPE blend in the seal layer of the present invention in a two or three-layer coextruded film product will provide a film structure that can be used for making pouches at a faster rate in the VFFS and such pouches produced will contain fewer leakers. With the trend in today's consumer packaging industry moving toward providing the consumer with more environmentally friendly packages, the polyethylene pouch of the present invention is a good alternative. The use of the polyethylene pouch for packaging consumer liquids such as milk has its advantages over containers used in the past: the glass bottle, paper carton, and high density polyethylene jug. The previously used containers consumed large amounts of natural resources in their manufacture, required a significant amount of space in landfill, used a large amount of storage space and used more energy in temperature control of the product (due to the heat transfer properties of the container). The polyethylene pouch of the present invention made of thin polyethylene film, used for liquid packaging, offers many advantages over the containers used in the past. The polyethylene pouch (1) consumes less natural resources, (2) requires less space in a landfill, (3) can be recycled, (4) can be processed easily, (5) requires less storage space, (6) uses less energy for storage (heat transfer properties of package), (7) can be safely incinerated and (8) can be reused, for example, the empty pouch can be used for other applications such as freezer bags, sandwich bags, and general purpose storage bags. The polymeric resins described in Table I herein below were used to prepare samples of blown films shown in the Examples and Comparative Examples. Table I: Resin Properties The composition of various LDPE and LLDPE blends and their melt strength is shown in Table II herein below. Table II: Melt Strength of Resin Blends (*) % refers to percent by weight of LDPE in the blend A 5kg sample of each blend shown in Table II was processed through a Leistritz twin screw extruder. The melt strength of the blends were determined using a Gottfert Rheotoens unit. Erucamide, a slip agent; Si0 2 , an antiblock agent; and a processing aid were added to each of the resins described in Table I such that the final concentrations of the additives were as follows: 1200 ppr Erucamide; 2500 ppm Si0 2 . Film structures produced were subjected to physical testing to determine its various properties including: (1) Puncture, using method ASTM D3763; (2) Dart Impact, using ASTM D1709, Method A; (3) Elmendorf Tear, using ASTM D1922; (4) Tensiles, using ASTM D882; (5) 1% and 2% Secant Modulus, using ASTM D882; (6) Hot Tack Strength, using method described hereinbelow; and (7) Heat Seal Strength, using method described hereinbelow; The hot tack strength of sample films was measured using the "DTC Hot Tack Test Method," which measures the force required to separate a heat seal before the seal has had a chance to fully cool (crystallize). This simulates the filling of material into a pouch before the seal has had a chance to cool. The "DTC Hot Tack Test Method" is a test method using a DTC Hot Tack Tester Model #52D according to the following conditions: Specimen Width: 25.4 mm Sealing Time: 0.5 seconds Sealing Pressure: 0.27 N/mm/mm Delay Time: 0.5 seconds Peel Speed: 150 mm/seconds Number of Samples/Temperature 5 Temperature Increments: 5°C Temperature Range: 75 C C - 150°C The heat seal strength of sample films was measured using the "DTC Heat Seal Strength Test Method," which is measure designed to measure the force required to separate a seal after the material has cooled to 23°C temperature. The film samples were exposed to a relative humidity of 50 percent and a temperature of 23°C for a minimum of 24 hours prior to testing. The "DTC Heat Seal Strength Test Method" uses a DTC Hot Tack Tester Model #52D, wherein the heat seal portion of the tester is used, according to the following conditions: Specimen Width: 25.4 mm Sealing Time: 0.5 seconds Sealing Pressure: 0.27 N/mm/mm Number of Samples/Temperature 5 Temperature Increments: 5°C Temperature Range: 80°C - 150°C The seal strength of the film samples was determined using an Instron Tensile Tester Model #1122 according to the following test conditions: Direction of Pull: 90° to seal Crosshead Speed: 500 mm/minute Full Scale Load: 5 kg Number of Samples/Threshold: 1 percent of FSL Break Criterion: 80 percent Gauge Length: 2.0 inches (50.8 millimeters) Sample Width: 1.0 inch (25.4 millimeters) Table III: Multilayer (A/B/A) Films for Physical Property Testing (*) % refers to percent by weight of LDPE in the blend Physical properties of films show in Table III are reported in Table IV below, and the results of hottack and heat seal strength are reported in Table V. Table IV: Physical Properties of Multilayer Films AFF AFF AFF AFF AFF AFF AFFINITY 1880+2 1880+ 1880+ 1880 + 1880 1880 1880 0% 20% 20% 20% XU + + 1351 1351 1351 60021.6 20% 20% 80% Id 3MIL 2 5031 526I IN core) Gauge mil 2.49 3.18 2.46 2.50 2.50 2.10 2.54 Elmendorf f M253D Tear Table VI: Hottack/Heat Seal Strength Hot Tack Strength, N/in DOWLEX DOWLEX 2045 DOWLEX 2045 DOWLEX 2045 2045 + + + 20% LDPE 1351 20% LDPE 20% 609C XU60021.62 TEMPERATURE °C 90 0.23 0.14 0.22 0.19 95 0.17 0.21 0.15 0.19 100 0.64 0.62 0.66 0.68 105 1.91 1.91 1.85 1.79 110 2.47 2.86 2.55 2.83 115 3.28 3.47 3.30 3.59 120 2.64 3.04 2.73 3.17 125 2.51 2.96 2.63 3.16 130 2.38 2.86 2.56 3.13 135 2.35 2.73 2.32 2.89 140 2.27 2.48 2.16 2.62 145 2.17 2.35 2.14 2.39 150 1.96 2.21 2.09 2.12 155 1.99 1.91 1.85 1.89 160 1.65 1.78 1.80 1.84 Table VII: Heat Seal Strength, lb/in DOWLEX 2045 DOWLEX 2045 DOWLEX 2045 DOWLEX 2045 20% LDPE 1351 20% LDPE 20% 609C XU60021.62 RATURE °C 100 0.26 0.20 0.19 0.26 105 0.51 0.72 0.51 0.71 110 4.28 4.88 4.10 4.95 115 4.71 5.76 5.15 6.14 120 5.52 7.09 6.00 7.83 125 5.71 7.01 6.50 7.79 130 6.02 7.07 6.60 7.82 135 5.33 7.37 5.90 7.70 140 6.11 7.50 6.75 8.00 145 5.56 7.01 6.06 7.75 150 5.27 7.53 6.33 7.70 155 4.86 7.74 6.48 8.25 160 5.68 7.75 6.50 8.69 The present invention is illustrated by the following examples but is not to be limited thereby. Examples 1-3 and Comparative Examples A The film samples described in Table III were made as a monolayer using a Macro blown film line. The extruder was 2-1/2 inches (6.4 cm) in diameter and had a 24:1 L/D ratio and a barrier screw with a Maddock mixing head. A 6 inch (15.2 cm) diameter die was used with a 60 mil (1 ,524 microns) die gap for the manufacture of the test films. The fabrication conditions for the blown film live were a blow-up ratio of 2.5 and a melt temperature of 220°C. Examples 4-6 and Comparative Example B The films described in Table III were slit to a width of 15 inches (38.1 cm)to produce 2-liter milk pouches using a Prepac IS6 Vertical, Form, Fill and Seal machine located at a commercial dairy. The unit packaged 2-liter milk filled pouches at the rate of 30 pouches per minute per filling head under normal operating conditions. For each film tested, approximately 16-20 milk-filled pouches were collected. They were inspected for initial seal integrity. 6-8 pouches were tested on site for heat seal strength and 10 pouches were drained, washed and dried for further evaluation. The seal strength was determined using an Instron Tensile Tester Model #1122. Sample were expose to a relative humidity of 50% and 23°C for 24-48 hours prior to testing. The Instron test conditions were as follows: Direction of pull: 90° to seal Crosshead speed: 500 mm/min. Full Scale Load: 5 kg Threshold: 1% of FSL Break Criterion 80% Gauge length: 2.0 in. (50.8 mm) Sample width: 1.0 in. (25.4 mm) The initial examination of end seal integrity involved three steps: i) Determination Of On-Line Leakers ii) Subjective Seal Strength Test iii) Visual Examination of End Seals On Line Leakers On line leakers were only seen with the pouches made form the DOWLEX 2045. No leakers were seen with the other films. Subjective Seal Strength Test The subjective seal strength test involved squeezing the pouch from one end until the pouch either yielded or the seal failed. Table VIII shows that no seal failures were seen with the pouches made with 20% 1351 or XU 60021.62. Visual Examination of End Seals The DOWLEX 2045 films were found to have significant seal thinning and end seal stringers as shown in Table IX. The pouches made with 20% 609C were found to have some seal thinning and some end seal stringers. No seal thinning or stringers were found with the 20% 1351 and XU 60021.62 films. End Seal Strength Ten 2-liter milk pouches were tested for end seal strength using an Instron Tensile Tester Model # 4206, under same conditions described in connection with the determination of heat seal strength hereinabove. The seal strengths are shown in Table X. Seal strength was found to increase as the melt strength of the blend increased. This finding is graphically illustrated in Fig. 6 using a blend of 80% by weight of LLDPE and 20% by weight of LDPE, except the first data point having melt strength of 6.4 cN did not contain any LDPE. No correlation was evident between LDPE melt index and seal strength. Microscopy Examination of End Seals The stringer regions and edge regions of the pouches were cryo-sectioned and examined using light microscopy techniques. Table XI summarizes the results. The films made with 20% 1351 and XU 60021.62 showed very little seal thinning and no end seal stringers (fine polymer filaments coming from the seal area), while the films made with 100% DOWLEX 2045 had significant seal thinning and stringers. Seal Region Film Thinning The weakest part of a good seal is typically the film just in front of the seal bead. Any thinning of this film results in lower seal strengths since this is the region that fails when the seal is stressed. Comparing the melt strength of the resin blends (Table II) with the amount of film thinning seen with the pouches made with a commercial VFFS unit (Table XI), it is seen that, as the melt strength of the resin blend increased, the amount of film thinning decreased. No correlation was seen between film thinning (Table XI) and melt index of LDPE in resin blends (Table I). Seal Bead Comparing seal bead thickness (Table XI) to resin blend melt strength (Table II) and LDPE melt index (Table I), it is seen that there is a strong correlation between melt strength and bead thickness, and no correlation between LDPE melt index and seal bead thickness. Higher melt strength blends resulted in thicker seal beads. Table VIII: Liconsa Dairy Prepac VFFS Evaluation Subjective Seal Strengths Table IX: Liconsa Dairy Prepac VFFS Evaluation Visual Examination of End Seals Table X: Prepac VFFS Pouch End Seal Strength Table XI: Prepac VFFS Microscopy Analysis Summary *measured 550μm from seal "measured cross section at thinnest part of film before the seal The following polymeric resin blends shown in Table XII were used to further illustrate the advantages of this invention: Table XII: Resin Blends (*) % refers to percent by weight of the amount of LDPE in various blends. The resin blends of Table XII were used to fabricate 2.8 mil (71 microns)thick films using a MACRO® blown film line having a barrier screw with a diameter of 2 1/2 inches (63.5 mm, 24:1 L/D ratio and Maddock mixing head. A six inch (15.2 cm) die with a 60 mil (1524 microns) die gap was used. A Macro dual lip air ring supplied with chilled air was used. Each resin was blended to a target of 1200 ppm erucamide slip and 2500 ppm Si0 2 antiblock. Each film was tested for hottack and heat seal strength, values reported in Table XIII and Table XIV, respectively. TABLE XIII HOTTACK STRENGTH N/IN OF DOWLEX 2045/LDPE XU 60021.62 BLENDS TABLE XIV HEAT SEAL STRENGTH (LB/IN) OF DOWLEX 2045/LDPE XU 60021.62 BLENDS The hottack strength was determined using a DTC Hottack Tester Model #D52D under the conditions described hereinabove. The test films were heat sealed using the DTC Hottack Tester Model #D52D under the conditions described hereinabove. The heat seal strength was determined using an Instron Tensile Tester Model #1122. Test samples were exposed to a relative humidity of 50 percent and 23°C for 24 to 48 hours prior to testing. The Instron test conditions were the same as described hereinabove. From the results of hottack and heat seal tests shown in Table XIII and Table XIV, it is seen that the maximum hottack strength was reached with the 50 percent DOWLEX 2045/50 percent XU 60021.62 blend. The highest hest seal strenght were also seen with the 50 percent DOWLEX 2045/50 percent XU 60021.62 blend. Expected hottack strength was calculated as per the following: TABLE XV: HOTTACK = (0.5 X LLDPE hottack) + (0.5 X LDPE hottack) Predicted DOWLEX LDPE 135I DOWLEX 2045 + 20% DOWLEX 2045 + 20% vs. Actual 2045 Hottack LDPE 135I - LDPE 135I - ACTUAL Strength EXPECTED Temp. (°C) 95 0.29 0.18 0.24 0.27 100 0.45 0.22 0.33 0.35 105 1.76 0.56 1.16 0.97 110 2.40 0.81 1.60 2.19 115 2.82 0.86 1.84 3.18 120 2.96 0.74 1.85 3.41 125 2.77 0.69 1.73 3.54 130 2.54 0.69 1.62 3.34 135 2.40 0.64 1.52 3.10 140 2.31 0.64 1.47 3.05 145 2.32 0.60 1.46 2.87 150 2.18 0.56 1.37 2.74 The results of predicted versus actual hottack strength are shown in Table XV. It can be seen that the actual hottack strength of the present invention is significantly higher than the predicted level, indicating a clearly synergistic effect.

Claims: WHAT IS CLAIMED IS: 1. A pouch containing a flowable material, said pouch being made from a film structure with at least one seal layer of a polymeric composition comprising: (a) from 10 to 100 percent, based on the total weight of said composition, of a mixture of (1) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of linear ethylene copoiymer interpolymerized from ethylene and at least one alpha-olefin in the range of C 3 -C 18 and having a density from 0.916 to 0.940g/cm 3 and a melt index of less than 10g/10 minutes, and a molecular weight distribution, Mw/Mn, ratio of greater than 4.0, and a peak melting point greater than 100°C as measured by a differential scanning colorimeter, and (2) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of high pressure low density polyethylene having a density from 0.916 to 0.930g/cm 3 , a melt index of less than 1g/10 minutes and melt strength greater than 10 cN as determined using a Gottfert Rheotens unit at 190°C; and 5 (b) from 0 to 90 percent, based on the total weight of said composition, of an ethylene-vinyl acetate copoiymer having a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10g/10 minutes. 2. A pouch containing a flowable material, said pouch being made from a o multilayer film structure comprising: (I) a layer of polymeric composition comprising: (a) from 10 to 100 percent, based on the total weight of said composition, of a mixture of (1 ) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of linear ethylene copoiymer interpolymerized from 5 ethylene and at least one alpha-olefin in the range of C3-C18 and having a density from 0.916 to 0.940g/cm3 and a melt index of less than 10g/10 minutes, and a molecular weight distribution, Mw/Mn, ratio of greater than 4.0, and a peak melting point greater than 100°C as measured by a differential scanning colorimeter, and (2) from 5 to 95 percent by weight, 0 based on 100 weight parts of said mixture, of high pressure low density polyethylene having a density from 0.916 to 0.930g/cm3, a melt index of less than 1g/10 minutes and melt strength greater than 10 cN as determined using a Gottfert Rheotens unit at 190°C; and (b) from 0 to 90 percent, based on the total weight of said composition, of 5 an ethylene-vinyl acetate copoiymer having a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10g/10 minutes; and (II) at least one layer of linear ethylene copoiymer interpolymerized from ethylene and at least one alpha-olefin in the range of C 3 -C 18 and having a density from 0.916 to 0.940g/cm 3 and a melt index of from 0.1 to 10g/10 minutes. 3. The pouch of Claim 1 wherein said film structure is in a tubular form and said pouch has transversely heat sealed ends. 4. The pouch of Claim 2 having (III) a layer of a high-pressure polyethylene having a density of from 0.916 to 0.930 g/cm3 and a melt index of from 0.1 to 10g/10 minutes. 5. The pouch of Claim 2 wherein layer (I) is a seal layer. 6. The pouch of Claim 2 wherein layer (II) is an outer layer and layer (I) is a seal layer. 7. The pouch of Claim 4 wherein layer (II) is an outer layer, layer (III) is a core layer and layer (I) is a seal layer. 8. The pouch of Claim 2 wherein the linear copoiymer of ethylene has a melt index less than 10g/10 minutes. 9. The pouch of Claim 1 wherein the pouch holds from 5 mL to 10,000 mL. 10. The pouch of Claim 1 wherein the flowable material is milk. 11. The pouch of Claim 1 wherein the copoiymer of ethylene has an indicator of molecular weight distribution ( o/\ 2 ) of from 0.1 to 20. 12. The pouch of Claim 1 wherein the film structure contains a slip agent, antiblock agent and, optionally, a processing aid. 13. The pouch of Claim 1 wherein the film structure contains a pigment to render the film structure opaque. 14. The pouch of Claim 1 wherein the film structure contains an ultraviolet light absorbing additive. 15. The pouch of Claim 1 wherein the alpha-olefin of the film structure is 1- octene. 16. The pouch of Claim 1 wherein the melt strength of the high pressure low density polyethiene is in the range of from 10 to 40 cN. 17. The pouch of Claim 1 wherein the melt strength of the high pressure low density polyethlene is in the range of from 13 to 25 cN. 18. The pouch of Claim 1 wherein the melt strength of the polymeric composition is in the range of from 10 to 70 cN. 19. The pouch of Claim 1 wherein the thinning in edge region is reduced by less than 25 percent. 20. A film structure of a polymeric composition for a packaging application comprising: (a) from 10 to 100 percent, based on the total weight of said composition, of a mixture of (1 ) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of linear ethylene copoiymer interpolymerized from ethylene and at least one alpha-olefin in the range of C 3 -C 18 and having a density from 0.916 to 0.940g/cm 3 and a melt index of less than 10g/10 minutes, and a molecular weight distribution, Mw/Mn, ratio of greater than 4.0, and a peak melting point greater than 100°C as measured by a differential scanning colorimeter, and (2) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of high pressure low density polyethylene having a density from 0.916 to 0.930g/cm 3 , a melt index of less than 1g/10 minutes and melt strength greater than 10 cN as determined using a Gottfert Rheotens unit at 190°C; and (b) from 0 to 90 percent, based on the total weight of said composition, of an ethylene-vinyl acetate copoiymer having a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10g/10 minutes. 21. The film of Claim 20 wherein the density of the linear ethylene copoiymer is from 0.916 to 0.940 g/cm 3 . 22. The film of Claim 20 wherein the concentration of ethylene vinyl acetate copoiymer is 5 to 85 percent based on the total weight of said composition. 23. The film of Claim 20 wherein the concentration of ethylene vinyl acetate copoiymer is 5 to 25 percent based on the total weight of said composition. 24. The film of Claim 20 wherein the melt strength of the polymeric composition is in the range from 10 to 70 cN. 25. A process for preparing a pouch containing a flowable material comprising forming a film structure by either blown tube extrusion or cast extrusion, forming the film structure into a tubular member and transversely heat-sealing opposite ends of the tubular member, said tubular member comprising a film structure for a pouch container with at least one seal layer of a polymeric composition comprising: (a) from 10 to 100 percent, based on the total weight of said composition, of a mixture of (1) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of linear ethylene copoiymer interpolymerized from ethylene and at least one alpha-olefin in the range of C3-C18 and having a density from 0.916 to 0.940g/cm3 and a melt index of less than 10g 10 minutes, and a molecular weight distribution, Mw/Mn, ratio of greater than 4.0, and a peak melting point greater than 100°C as measured by a differential scanning colorimeter, and (2) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of high pressure low density polyethylene having a density from 0.916 to 0.930g/cm3, a melt index of less than 1g/10 minutes and melt strength greater than 10 cN as determined using a Gottfert Rheotens unit at 190°C; and (b) from 0 to 90 percent, based on the total weight of said composition, of at least one copoiymer selected from the group consisting of an ethylene- vinyl acetate copoiymer having a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10g/10 minutes. 26. A process for preparing a pouch containing a flowable material comprising forming a film structure by either blown tube extrusion or cast extrusion, forming the film structure into a tubular member and transversely heat-sealing opposite ends of the tubular member, said tubular member comprising: (I) a layer of polymeric composition comprising: (a) from 10 to 100 percent, based on the total weight of said composition, of a mixture of (1) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of linear ethylene copoiymer interpolymerized from ethylene and at least one alpha-olefin in the range of C 3 -C 18 and having a density from 0.916 to 0.940g/cm 3 and a melt index of less than 10g/10 minutes, and a molecular weight distribution, Mw/Mn, ratio of greater than 4.0, and a peak melting point greater than 100°C as measured by a differential scanning colorimeter, and (2) from 5 to 95 percent by weight, based on 100 weight parts of said mixture, of high pressure low density polyethylene having a density from 0.916 to 0.930g/cm3, a melt index of less than 1g/10 minutes and melt strength greater than 10 cN as determined using a Gottfert Rheotens unit at 190°C; and (b) from 0 to 90 percent, based on the total weight of said composition, of at least one copoiymer selected from the group consisting of an ethylene- vinyl acetate copoiymer having a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10g/10 minutes. (II) at least one layer of linear ethylene copoiymer interpolymerized from ethylene and at least one alpha-olefin in the range of C 3 -C 18 and having a density from 0.916 to 0.0940 g/cm 3 and a melt index of from 0.1 to 10g/10 minutes. 27. The process of Claim 26 wherein the film structure includes: (III) at least one layer of a high-pressure polyethylene having a density of from 0.916 to 0.930 g/cm3 and a melt index of from 0.1 to 10g 10 minutes.

Inventors: FALLA DANIEL JAMES, FALLA, DANIEL, JAMES
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1997
Main classification: B65D33
IPC codes: B32B27, B65D30, B65D65, C08L23