MXPA98004440A - Novedos bags to pack fluible materials in bol - Google Patents

Abstract

The present invention relates to a bag containing a flowable material, said bag being made from a film structure with at least one seal layer of a polymer composition comprising: (A) from 10 to 100 percent, based on the total weight of the composition, of a mixture of: (1) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one ultra-low density polyethylene, which is an ethylene copolymer linear interpolymerized from ethylene, and when an α-olefin on the scale of 3 to 18 carbon atoms, and having: (a) a density of 0.89 grams / cm3 to less than 0.916 grams / cm3, (b) a melting index (I2) less than 20 grams / 10 minutes, (c) a melt flow ratio I10 / I2, greater than 5, (d) a proportion of molecular weight distribution, Mw / Mn, greater than 3, (e) at peak melting point greater than 100 ° C, measured by a differential scanning calorimeter, and (2) from 5 to 95 percent by weight, based on 100 parts by weight of the mixture, of at least one low density and high pressure polyethylene having (a) a density of 0.916 grams / cm3 to 0.93 grams / cm3, (b) an index of fusion (I2) less than 1 gram / 10 minutes, and (c) a melt strength greater than 10 cN, determined using a Gottfert Rheotens unit, at 190 ° C, and (B) from 0 to 90 percent, based on the total weight of the composition, of at least one polymer selected from the group consisting of a linear low density polyethylene, a low density and high pressure polyethylene, and an ethylene-vinyl acetate copolymer

Description

NOVEDOS BAGS TO PACK FLUENT MATERIALS IN BAGS This invention relates to a bag 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 describe the preparation of a polyethylene film to be used in the manufacture of a disposable bag for packaging liquids, such as milk. U.S. Patent No. 4,503,102 discloses bags made from a blend of a copolymer of linear ethylene copolymerized from ethylene and an α-olefin on the scale of 4 to 10 carbon atoms, and an ethylene polymer - copolymerized vinyl acetate from ethylene and vinyl acetate. The linear polyethylene copolymer has a density of 0.916 to 0.930 grams / cm3, and a melt index of 0.3 to 2.0 grams / 10 minutes. The ethylene-vinyl acetate polymer has a weight ratio of ethylene to vinyl acetate of 2.2: 1 to 24: 1, and a melt index of 0.2 to 10 grams / 10 minutes. The mixture described in U.S. Patent No. 4,503,102 has a weight ratio of linear low density polyethylene to ethylene vinyl acetate polymer, from 1.2: 1 to 4: 1. U.S. Patent No. 4,503,102 also discloses laminates having a sealing film of the aforementioned mixture. U.S. Patent No. 4,521,437 discloses bags made from a sealant film that is 50 to 100 parts of a linear polymer of ethylene and octene-1, having a density of 0.916 to 0.930 grams / cm 3, and a melt index of 0.3 to 2.0 grams / 10 minutes, and 0 to 50 parts by weight of at least one polymer selected from the group consisting of a linear copolymer of ethylene and an α-olefin of 4 to 10 carbon atoms; carbon, which has a density of 0.916 to 0.930 grams / cm3, and a melt index of 0.3 to 2.0 grams / 10 minutes, or a high pressure polyethylene that has a density of 0.916 to 0.924 grams / cm3 and a melt index of 1 grams / 10 minutes, and mixtures thereof. The sealing film described in U.S. Patent No. 4,521,437 is selected based on providing: (a) bags with a substantially smaller M-test value, with the same film thickness, as that obtained for bags made with a 85-part blend film of a linear ethylene / bu-teno-1 copolymer having a density of about 0.919 grams / cm and a melt index of about 0.75 grams / 10 minutes, and 15 parts of a polyethylene of high pressure that has a density of approximately 0.918 grams / cm3 and a melt index of 8.5 grams / 10 minutes, or (b) an M (2) test value of less than approximately 12 percent, for bags that have a volume from more than 1.3 to 5 liters, or (c) a test value M (1.3) less than about 5 percent for bags that have a volume of 0.1 to 1.3 liters. The M, M (2) and M (1.3) tests are defined as evidence of stock market crash in U.S. Patent Number 4,521,437. The bags can also be made from composite films, wherein the sealing film forms at least the inner layer. U.S. Patent No. 5,288,531 describes bags made from a film structure having a mixture of: (a) from 10 to 100 weight percent of at least one polymeric seal layer of an ethylene copolymer linear ultra-low density interpolymerized from ethylene, and at least one α-olefin on the scale of 3 to 10 carbon atoms, with a density of about 0.89 grams / cm 3 to less than 0.915 grams / cm 3, and (b) ) from 0 to 90 weight percent of at least one polymer selected from the group consisting of a linear copolymer of ethylene and an α-olefin of 3 to 18 carbon atoms, which has a density greater than 0.916 grams / cm3 and a melt index of 0.1 to 10 grams / 10 minutes, a low density and high pressure polyethylene, which has a density of 0.916 to 0.930 grams / cm3, and an index of melting from 0.1 to 10 grams / 10 minutes, or an ethylene-vinyl acetate copolymer having a weight ratio of ethylene to vinyl acetate of 2: 2: 1 to 24: 1, and a melt index of 0.2 to 10 grams / 10 minutes. The heat seal layer of U.S. Patent No. 5,288,531 provides improved hot-bond strength, and lower heat seal initiation temperature, for a two-layer co-extruded film structure layers or in three layers described in it. The polyethylene bags known in the prior art have some deficiencies. The problems associated with the bags known in the prior art relate to the sealing properties and operating properties of the film used to prepare the bags. In particular, the prior art films formed into bags generally have a high incidence of "leaks", ie, seal defects, such as pitting that develops on or near the seal from which the flowable material escapes, for example. example, milk, from the bag. Although the seal and performance properties of the prior art films have been generally satisfactory with respect to other desired properties, there is still a need in the industry for better sealing and performance properties in films for the manufacture of bags hermetically sealed that contain flowable materials. More particularly, there is a need for better film sealing properties, such as hot viscosity, and better melt strength, in order to improve the processability of the film, and to improve the bags made from the movies. For example, the line speed of the known packaging equipment used to make bags, such as forming machines, fillers and sealants, is often limited by the sealing properties of ordinary polyethylene films, due or substantially to their resistance to the fusion relatively low. Accordingly, the speed at which a forming, filling and sealing machine can produce a bag from ordinary polyethylene films is limited and, consequently, the number of bags produced per unit of time is also limited. Many have tried to improve the sealing properties of the polymeric composition used in the bag film, without success. It is desired to provide a polyethylene film structure for a bag container having a better melt strength, with performance properties as good or better than known prior art bag films.

It is also desired to provide a film structure for a bag container, which can be processed through a forming, filling and sealing machine, such as a single layer or multilayer film. It is further desired to provide a bag made of the aforementioned film structures, such that the bag has a reduced failure rate. It has been found that as the melt strength of the film increases, the amount of thinning of the film occurring in the area of the seal is reduced, and as such, the speed of a forming machine can be increased, filler and sealer, and therefore, the number of bags produced per unit of time can be increased. One aspect of the present invention provides a bag containing a flowable material, this bag being made of a film structure with at least one seal layer of a polymer composition comprising: (A) from 10 to 100 percent, based on the total weight of the composition, of a mixture of: (1) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one ultra-low density polyethylene, which is an ethylene copolymer linear interpolymerized from ethylene, and at least one α-olefin on the scale of 3 to 18 carbon atoms, and having: (a) a density of 0.89 grams / cm 3 to less than 0.916 grams / cm 3, (b) a melt index (I2) less than 10 grams / 10 minutes; (c) a melt flow ratio I10 / l2 'greater than 5, (d) a molecular weight distribution ratio, Mw / Mn, greater than about 3, (e) a peak melting point greater than 100 ° C as measured by an exploratory calorimeter n differential; and (2) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of a low density and high pressure polyethylene having it; (a) a density of 0.916 grams / cm3 to 0.93 grams / cm3, (b) a melt index (I2) of less than 1 gram / 10 minutes, and (c) a melt strength greater than 10 cN, determined using a Gottfert Rheotens unit, at 190 ° C; and (B) from 0 to 90 percent, based on the total weight of the composition, of at least one polymer selected from the group consisting of linear low density polyethylene, low density polyethylene and high pressure polyethylene, and an ethylene-vinyl acetate copolymer. One embodiment of the present invention is a bag made from a two-layer coextruded film, which contains an outer layer of linear low density polyethylene, ultra-low density polyethylene, low density and high pressure polyethylene, copolymer ethylene-vinyl acetate, or mixtures thereof, and an inner seal layer of the aforementioned polymer composition. Another aspect of the present invention is a process for the preparation of the aforementioned bag. Still another embodiment of the present invention is a bag made from a film coextruded in three layers, which contains an outer layer and a core layer of ultra-low density polyethylene, linear low density polyethylene, low density polyethylene and high pressure, ethylene-vinyl acetate copolymer, or a mixture thereof, and an inner seal layer of the aforementioned polymer composition. It has been found that the film structures for the bags of the present invention have a better resistance to melting, and correspondingly better resistance to the heat seal, particularly the resistance of the end seal. The use of the bag making films of the present invention in forming, filling and sealing machines leads to higher machine speeds than can currently be obtained with the use of commercially available film. Figure 1 shows a perspective view of a bag pack of the present invention. Figure 2 shows a perspective view of another bag pack of the present invention. Figure 3 shows a partial amplified cross-sectional view of the film structure of a bag of the present invention.

Figure 4 shows another partial amplified cross-sectional view of the film structure of a bag of the present invention. Figure 5 shows yet another partial amplified cross-sectional view of the film structure of a bag of the present invention. Figure 6 is a graphic illustration of the resistance to the end seal of bags filled with two liters of milk against the melt strength of ATTANE111 * 4203 (ultra-low density polyethylene supplied by The Dow Chemical Company) in blends with polyethylene Low density and high pressure. The bag of the present invention, for example, as shown in Figures 1 and 2, for packaging flowable materials, is manufactured from a coextruded film structure in three layers having a polymeric seal layer comprised of a mixture of an ultra-low density polyethylene, and a low-density, high-pressure polyethylene that has a high melt strength. The mixture may also contain an ethylene-vinyl acetate copolymer, linear low density polyethylene, a substantially linear and homogeneously branched ethylene / α-olefin interpolymer, a homogenously branched linear ethylene polymer, low density polyethylene and high pressure polyethylene. , or mixtures thereof.

"Melt strength", which is also referred to in the relevant art as "melt tension", is defined and quantified herein to mean the tension or force (applied by a embobinator drum equipped with a voltage cell) required for stretching a molten extrudate at some specified rate above its melting point as it passes through the die of a conventional plastometer, such as that described in STM 3128-E. The values of resistance to fusion, which is reported in the present in centi-Newtons (cN), are determined using a Gottfert Rheotens at 190 ° C. In general, for ethylene-to-olefin interpolymers and high-pressure ethylene polymers, melt strength tends to increase when the molecular weight is increased, or by expanding the molecular weight distribution and / or increasing the molecular weight distribution. proportions of the fusion flow. The melt strength of the low density and high pressure polyethylene of the present invention is greater than 10 cN, determined using a Gottfert Rheotens unit at 190 ° C, preferably from about 13 to 40 cN, and more preferably from 15 to 40 cN. 25 cN. In addition, the melt strength of the polymer composition of the present invention is greater than 5 cN, determined using a Gottfert Rheotens unit at 190 ° C, preferably from about 15 to 70 cN, and more preferably from 15 to 50 cN. Another feature of the present invention is that ultra-low density polyethylene and linear low density polyethylene have a "peak melting point" greater than 100 ° C. The peak melting point is determined using a differential scanning calorimeter (DSC). A full description of the test method is found in Thermal Characterization of Polymeric Material. E.A. Turi (New York: Academic Press, 1981), pages 46 to 59. A component of the polymer composition of the present invention is a polyethylene of ultra or very low density (ULDPE or VLDPE). The heterogeneously branched ultra-low density polyethylene is well known among practitioners of the linear polyethylene technique. These are prepared by polymerization in solution, paste or gas phase, continuous, batch, or semi-batches, of ethylene and one or more optional α-olefin comonomers, using conventional Ziegler-Natta polymerization processes and coordinating metal catalysts, as described, for example, in Anderson et al., in United States Patent Number 4,076,698. These conventional linear Ziegler polyethylenes do not branch in a homogeneous way, and they do not have long chain branching. Also, these polymers do not exhibit substantial amorphism at lower densities, since they inherently possess a substantial high density polymer (crystalline) fraction. At a density less than 0.90 grams / cm3, these materials are very difficult to prepare using conventional Ziegler Natta catalysts, and are also very difficult to granulate. At densities less than 0.90 grams / cm3, the granules are sticky and tend to adhere to each other. The terms "heterogeneous" and "heterogeneously branched" are used herein in the conventional sense with reference to a linear ethylene interpolymer having a comparatively low short chain branching distribution index. The short chain branching distribution index (SCBDI) is defined as the weight percentage of the polymer molecules having a comon content within 50 percent of the average total molar comon content. The short chain branching distribution index of the polyolefins that can be crystallized from solutions can be determined by well-known elution fractionation techniques with elevated temperature, such as those described by Wild et al., Journal of Polymer Science , Poly. Phys. Ed .. Volume 20, page 441 (1982), L.D. Cady, "The Role of Comon Type and Distribution in LLDPE Product Performance," SPE Regional Technical Conference, Quaker Square Hilton, Akron, Ohio, 1-2 October, pages 107-119 (1985), or in the United States Patent United States of America Number 4,798,081.

The terms "ultra-low density polyethylene" (ULDPE), "very low density polyethylene" (VLDPE) and "very low density linear polyethylene" (LVLDPE) have been used interchangeably in the polyethylene technique, for Designate the subset of linear low density polyethylene polymers having a density less than or equal to about 0.916 grams / cm 3. Then, the term "linear low density polyethylene" (LLDPE) is applied to those linear polyethylene having a density greater than 0.916 grams / cm3. These terms, by themselves, do not indicate whether the polymer is homogeneously branched or heterogeneously branched, but does indicate that the polymer is characterized as having a linear polymer base structure in the conventional sense of the term "linear". Commercial examples of heterogeneously branched linear interpolymers suitable for use in the present invention include the ATTANE ultra-low density polyethylene polymers, supplied by The Dow Chemical Company, and the FLEOXMER very low density polyethylene polymers supplied by Union Carbide Corporation. The ultra-low density polyethylene is in general a linear copolymer of ethylene and a minor amount of an α-olefin having from 3 to about 18 carbon atoms, preferably from 4 to about 10 carbon atoms, and more preferably 8. carbon atoms. The ultra-low density polyethylene for the polymer composition of the present invention has a density less than, or equal to, 0.916 grams / cm 3, more preferably from 0.916 to 0.89 grams / cm 3, and most preferably from 0.90 to 0.916 grams / cm 3; in general it has a melt index (I2) of less than 10 grams / 10 minutes, preferably 0.1 to 10 grams / 10 minutes, more preferably 0.5 to 2 grams / 10 minutes, and in general it has a ratio of Iio / 1 ^ The preferred α-olefin for the ultra-low density polyethylene and the linear low density polyethylene of the present invention, is preferably from 5 to 20, and more preferably from 7 to 20. represented by the following formula: CH2 = CHR wherein R is a hydrocarbyl radical having from 1 to 20 carbon atoms. The interpolymerization process can be a solution, paste or gas phase technique, or combinations thereof. The α-olefin suitable for use as the comonomer includes: 1-propylene, 1-butene, 1-isobutylene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene and 1-octene, as well as corao other types of monomers, such as styrene, styrenes substituted by halogen or alkyl, tetrafluoroethylene, vinylbenzocyclobutane, 1, -hexadiene, 1,7-octadiene, and cycloalkenes, for example, 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, since the coatings, profiles and films made with the resulting extrusion composition will have especially better properties of abuse where these higher α-olefin are used as comonomers. However, more 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 is determined by gel permeation chromatography (GPC) in a Waters 150 high temperature chromatographic unit, with a differential refractometer and three columns of mixed porosity. Columns are supplied by Polymer Laboratories, and are commonly packaged with pore sizes of 103, 104, 105 and 106A. The solvent is 1,2,4-trichlorobenzene, from which 0.3 percent by weight solutions of the samples for injection are prepared. The flow rate is 1.0 milliliters per minute, the operating temperature unit is 140 ° C, and the injection size is 100 microliters.

The determination of the molecular weight with respect to the base structure of the polymer is deduced by using a polyethylene standard of a narrow molecular weight distribution (from Polymer Laboratories) in conjunction with its elution volumes. Equivalent polyethylene molecular weights are determined using the appropriate Mark-Houwink coefficients for polyethylene and polystyrene (as described by Williams and Wad in Journal of Polymer Science, Polymer Letters, Volume 6, page 621, 1968) to derive the following equation : ^ olietileno = a * (^ oliestireno) 13. In this equation, a = 0.4316 and b = 1.0. The weight average molecular weight, Mw, is calculated in the usual manner according to the following formula: i = S w x Hi (where w 1 and M 1 are the weight fraction and the molecular weight, respectively, of The fraction that is eluted from the gel permeation chromatography column For the ultra-low density polyethylene and the linear low density polyethylene, the Mw / Mn is from about 2 to 7, preferably greater than 3. , and especially of about 4. As used herein, the term "Interpolymer" includes copolymer and terpolymer. The density is measured according to ASTM D-792. The melt index (I2) is measured according to ASTM D-1238 (condition 190 / 2.16), less than 10 grams / 10 minutes, and a melt flow ratio (I10 / I2) greater than 5. I10 is measured in accordance with ASTM D-1238 (condition 190/10). Yet another component of the polymer composition of the present invention is a polyethylene referred to hereinbelow as "linear low density polyethylene" ("LLDPE"). An example of a commercially available linear low density polyethylene is DOWLEX111 * 2045 (registered trademark of, and commercially available from, The Dow Chemical Company). The linear low density polyethylene is in general a linear copolymer of ethylene and a minor amount of an α-olefin having from 3 to about 18 carbon atoms, preferably from 4 to about 10 carbon atoms, and more preferably 8 atoms of carbon. The linear low density polyethylene for the polymer composition of the present invention has a density greater than or equal to 0.916 grams / cm3, more preferably from 0.916 to 0.940 grams / cm3, and most preferably from 0.918 to 0.926 grams / cm3; in general, it has a melt index of less than 10 grams / 10 minutes, preferably from 0.1 to 10 grams / 10 minutes, more preferably from 0.5 to 2 grams / 10 minutes, and in general has an IK ratio of. -1 to 20 ', preferably from 5 to 20, and more preferably from 7 to 20. The linear low density polyethylene can be prepared by a solution, paste or gas phase polymerization, continuous, batchwise, or semi-batches of ethylene and one or more optional α-olefin comonomers in the presence of a conventional Ziegler-Natta catalyst, such as by the process described in United States Patent Number 4,076,698 to Anderson et al. The low density, high pressure polyethylene ("LDPE") useful for the polymeric compositions and blends of this invention is widely known and readily available. Low density polyethylene has a density of 0.916 grams / cm3 to 0.930 grams / cm3, and a melt index (I2) of 0.1 to 10 grams / 10 minutes. The low density polyethylene used to form a blend with ultra-low density polyethylene for use in the seal layer of this invention has a melt strength greater than lOcN, determined using a Gottfert Rheotens unit at 190 ° C. An additional description of low density and high pressure polyethylene is found in Modern Plastics Encvclopedia. mid-October 1992, volume 68, number 11, pages 61 to 63. The ethylene-vinyl acetate copolymer ("EVA") useful for the polymer compositions and blends of this invention, has a weight ratio of ethylene to vinyl acetate from 2.2: 1 to 24: 1, and a melt index of 0.2 to 10 grams / 10 minutes. A further description of the ethylene-vinyl acetate copolymer is found in Modern Plastics Encyclopedia, issue of mid-October 1992, volume 68, number ll, page 66. It is believed that the use of low density polyethylene having a high strength to fusion in a film structure for bags of the present invention: (1) provides a bag that can be manufactured at a rapid speed through a forming, filling and sealing machine, and (2) provides a bag packing that it has few leaks, particularly when the bag of the present invention is compared to bags made with linear low density polyethylene (LLDPE), low density polyethylene (LDPE), or a combination thereof. With reference to Figures 3 to 5, the film structure of the bag of the present invention also includes a multilayer or composite film structure 30, which preferably contains the above-described polymeric seal layer, which is the inner layer of the bag. As will be understood by those skilled in the art, the multilayer film structure for the bag of the present invention may contain different combinations of film layers, provided that the seal layer forms part of the final film structure. The multilayer film structure for the bag of the present invention can be a co-extruded film, a coated film, or a laminated film. The film structure also includes the seal layer in combination with a barrier film, such as polyester, nylon, EVOH, polyvinylidene dichloride (PVDC), such as SARAN1® (registered trademark of The Dow Chemical Company), metallized films and thin metal sheets. The final use for the bag tends to dictate, to a high degree, the selection of the other materials used in combination with the seal layer film. The bags described herein will refer to the seal layers used at least on the inside of the bag. One embodiment of the film structure 30 for the bag of the present invention, shown in Figure 3, comprises the seal layer 31 of an ultra-low density polyethylene blend, and a low density polyethylene and high resistance to polyethylene. the melt of this invention, and at least one outer polymeric layer 32. The outer polymeric layer 32 is preferably a layer of polyethylene film, more preferably a linear low density polyethylene. An example of a commercially available linear low density polyethylene is DOWLEXMR 2045 (commercially available from The Dow Chemical Company). The thickness of the outer layer 32 can be any thickness, as long as the seal layer 31 has a minimum thickness of approximately 0.1 thousandths (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 core polymer layer 33 between at least one outer polymer layer 32 and at least one polymer layer of seal 31. The polymer layer 33 may be the same polymer layer as the outer layer 32, or preferably of a different polymer, and more preferably a linear low density polyethylene, for example, DOWLEX * 11 * 2049 (registered trademark of, and commercially available from, The Dow Chemical Company), having a higher density high that of the outer layer 32. The thickness of the core layer 33 can be any thickness, as long as the seal layer 31 has a minimum thickness of about 0.1 m ilsimas (2.5 microns). The final film end thickness of the final film product used to make the bag of the present invention, is 0.5 thousandths (12.7 microns) to 10 thousandths (254 microns), preferably from 1 thousandth (25.4 microns) to 5 thousandths (127 microns); more preferably from about 2 thousandths (50.8 microns) to 4 thousandths (100 microns).

Additives, known to those skilled in the art, such as anti-blocking agents, anti-skid additives, ultraviolet stabilizers, pigments, and processing aids, can be added to the polymers, from which the bags are made. the present invention. As can be seen from the different embodiments of the present invention shown in Figures 3 to 5, the film structure for the bags of the present invention has design flexibility. Different polymers of linear low density polyethylene can be used in the outer and core layers, to utilize specific film properties, such as film stiffness. Accordingly, the film can be optimized for specific applications, such as for a vertical forming, filling and sealing machine. The polyethylene film structure used to make a bag of the present invention is made either by the blown tube extrusion method or the cast extrusion method, methods that are well known in the art. The blown tube extrusion method is described, for example, in Modern Plastics, Encyclopedia Issue of mid-October 1989, Volume 66, Number 11, pages 264 to 266. The cast extrusion method is described, for example, in Modern Plastics, Issue of Encyclopedia of mid-October 1989, Volume 66, Number 11, pages 256 to 257. The embodiments of the bags of the present invention, shown in Figures 1 and 2, are hermetically sealed containers that are filled with "flowable materials". "Flowable materials" means materials that are flowable under gravity or that can be pumped. The term "flowable materials" does not include gaseous materials. The flowable materials include liquids, for example, milk, water, fruit juice, oil; body fluids, chemical reagents and different liquids used for medical treatments and diagnostics, emulsions, for example, ice cream mix, soft margarine; pasta, for example, meat pates, peanut butter; conservatives, for example, jellies, cake filling jam; gelatins; masses; ground beef, for example, sausage meat; powders, for example, gelatin powders, detergents; granular solids, for example, nuts, sugar; and similar materials. The bag 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 bag of the present invention is made, the film structure is cut to the desired width for use in conventional bag forming machines. The embodiments of the bag of the present invention shown in Figures 1 and 2 are made in so-called forming, filling and sealing machines well known in the art. With respect to Figure 1, a bag 10 is shown which is a tubular member 11 having a longitudinal overlap seal 12 and transverse seals 13, so that a "pillow-shaped" bag is formed when the bag is filled with the flowable material Referring to Figure 2, there is shown a bag 20 which is a tubular member 21 having a peripheral flap seal 22 along three sides of the tubular member 21, i.e., the upper seal 22a and the longitudinal side seals 22b and 22c, and having a substantially concave bottom or "bowl-shaped" member 23 sealed to the bottom portion of the tubular member 21, such that when viewed in cross-section, longitudinally, a portion of the bottom is formed substantially semicircular or "bowl-shaped", when the bag is filled with the flowable material. The bag shown in Figure 2 is an example of the so-called "Enviro-Pak" bag known in the art. The bag made in accordance with the present invention, preferably it is the bag shown in Figure 1, made in a so-called vertical forming, filling and sealing machine (VFFS), well known in this field. Examples of commercially available vertical forming, filling and sealing machines include those manufactured by Hayssen, Thimonnier, Tetra Pak or Prepac. A vertical forming, filling and sealing machine is described in the following reference: F.C. Lewis, "Form-Fill-Seal", Packaging Encyclopedia, page 180, 1980. In a process of packaging a vertical forming, filling and sealing machine, a sheet of plastic film structure described herein is fed inwardly. of a vertical forming, filling and sealing machine, wherein the sheet is formed in a continuous tube, in a tube forming section. The tubular member is formed by sealing the longitudinal edges of the film together - either by overlapping the plastic film and sealing the film using an internal / external seal, or by sealing the fin of the plastic film using an internal / internal seal Next, a sealing bar seals the tube transversely at one end which is the bottom of the "bag", and then the filling material, for example, milk, is added to the "bag". Then the sealing bar seals the upper end of the bag, and burns through the plastic film, or cuts the film, thereby separating the finished formed bag from the tube. The process for making a bag with a vertical forming, filling and sealing machine is generally described in US Patents Nos. 4,503,102 and 4,521,437. The capacity of the bags of the present invention may vary. In general, the bags can contain from 5 milliliters to 10 liters, preferably from 1 liter to 8 liters, and more preferably from 1 milliliter to 5 liters of flowable material. The film structure for the bag of the present invention has a precisely controlled resistance. The use of the film structure described in the present invention to manufacture a bag results in a stronger bag and, therefore, more preferably, the bag contains fewer leaks related to use. The use of a mixture of ultra-low density polyethylene (ULDPE) and low density polyethylene in the seal layer of the present invention, in a film product coextruded in two or three layers, will provide a film structure that can be Use to make bags at a faster speed in the vertical forming, filling and sealing machine, and these bags produced will contain less leakage. With the trend in today's consumer packaging industry, which is moving towards providing the consumer with more environmentally friendly packages, the polyethylene bag of the present invention is a good alternative. The use of the polyethylene bag to pack consumer liquids, such as milk, has its advantages over the containers used in the past: the glass bottle, the cardboard box, and the high density polyethylene jar. Previously used vessels consumed large quantities of natural resources in their manufacture, required a significant amount of space in landfills, 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 bag of the present invention, made of a thin polyethylene film, used to pack flowable materials, offers many advantages over the containers used in the past. The polyethylene bag (1) consumes less natural resources, (2) it requires less land fill space, (3) it can be recycled, (4) it can be easily processed, (5) it requires less storage space, (6) uses less energy for storage (heat transfer properties of the package), (7) can be safely incinerated, and (8) can be reused, for example, the bag can be used for other applications , such as freezer bags, sandwich bags and storage bags for general purposes. The polymeric resins described in Table 1, hereinafter, were used to prepare samples of blown films shown in the Examples and Comparative Examples.

Table I: Resin Properties Erucamide, a skid agent, was added; sio-, an agent against the blockade; and a processing aid, to each of the resins described in Table i, in such a way that the final concentrations of the additives are as follows: 1200 ppm of erucamide; 2500 ppm of Sio ,. The composition of different mixtures of oligope-low-density and high-pressure and r-olyotilin-1 .. work density, and its resistance to melting, will go on in I. following Table 11.

Table II: Resistance to the Fusion of Resin Mixtures (*)% refers to the weight per cent d- j. ) 1 t i 1 r not low density (LDPC) in the mixture.

A 5 kilogram sample of each mixture shown in Table II was processed through a Leistritz twin screw extruder. The resistance fusion of the mixtures was determined using a Gottfert Rheotens unit.

Table III: Resin Mixtures for Multilayer Films (A / B / A) for the Physical Properties Test (*)% refers to the weight percent of low density polyethylene (LDPE) in the mixture.

Examples 1-8? Comparative Examples A and B Blown films were made with the r: v- resin footings described in lane III, using a J &I. < coextrusion of three Egan layers, except for the. < • I Comparative B, which was made using a blown film line in a single Macro layer. The Egan line was operated under conventional extruder conditions, with a blowing ratio of 2.0, and a melting temperature of 221 ° C. The three layers of the coextruded film consisted of two identical skin layers (A) and a core layer (B) in an A / B / A configuration, which has the ratio of layers of A: B: A equal to 1: 3: 1 Comparative Example B, made with the Macro blown film line, was operated under conventional extruder conditions, with a blowing ratio of 2.0, and a melting temperature of 215 ° C. All films were formulated to contain the same level of skidding aid, blocking, and processing. In films containing low density polyethylene, each of the three layers contained 20 weight percent low density polyethylene, as indicated in Table III. The film structures produced were subjected to the physical test to determine the different properties of the same, including: (1) Drilling, using the ASTM method D3763; (2) Impact of Dart, using ASTM D1709, Method TO; (3) Tear The endorf, using ASTM D1922; (4) Fraction, using ASTM D882; (5) Secant module of 1 percent and 2 percent, using ASTM D882; (6) Resistance to Hot Viscosity, using the method described hereinafter; and (7) Heat Seal Resistance, using the method described hereinafter. The hot viscosity resistance of the sample films was measured using the "DTC Hot Viscosity Test Method", which measures the force required to separate a seal by heat before the seal has had a chance to completely cool ( crystallize). This simulates filling the material in a bag before the seal has had a chance to cool. The "DTC Hot Viscosity Test Method" is a test method that uses a DTC Hot Viscosity Tester Model # 52D, according to the following conditions: Sample Width 25.4 mm Sealing Time 0.5 seconds Pressure Sealing 0.27 N / mm / mm Delay Time 0.5 seconds Separation Speed 150 mm / second Number of Samples / Temperature 5 Temperature Increments 5 ° C Temperature Range 75 ° C - 150 ° C The heat seal resistance of the films sample was measured using the "Heat Seal Test Method DTC", which is designed to measure the force required to separate a seal after the material has cooled to a temperature of 23 ° C. The film samples were exposed to a relative humidity of 50 percent, and at a temperature of 23 ° C for a minimum of 24 hours, before the test. The "DTC Heat Seal Resistance Test Method" uses a DTC Model # 52D Hot Viscosity Tester, where the heat seal portion of the tester is used, in accordance with the following conditions: Sample Width 25.4 mm Sealing time 0.5 seconds Seal 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 Traction Tester Model # 1122 according to the following test conditions: Draw direction: 90 ° C to seal Crosshead Speed: 500 mm / minute Load to Full Scale 5 kg Number of Samples / Threshold 1 percent FSL. Breaking Criterion 80 percent Caliber Length 2.0 inches (50.8 mm). Sample Width 1.0 inches (25.4 mm).

The physical properties of the films in three layers (A / B / A) from the resin blends shown in Table III, are reported in Table IV below, and the results of hot viscosity resistance and to heat seal are reported in Table V and VI, respectively.

Table V: Hot Viscosity Resistance (N / 25 mm) of Pßlic in Three Layers (A / B / A) LO The present invention is illustrated by the following examples, but should not be limited by them.

Examples 9-11 and Comparative Examples C and D The films made from the resin blends described in Table III, were slit to a width of 15 inches (38.1 centimeters), to produce 2 liter milk bags, using a Prepac IS6 Vertical Formulator, Filler and Sealer, located in a commercial dairy. The unit packed bags filled with 2 liters of milk at the rate of 30 bags per minute per filling head under normal operating conditions. For each film tested, approximately 16 to 20 bags filled with milk were collected. They were inspected for the integrity of the initial seal. Ten (10) bags were drained, washed and dried for another evaluation. The initial examination of the integrity of the final seal involved three steps: i) Determination of Online Leaks ii) Subjective Test of Seal Resistance iii) Visual Examination of Final Seals Leaks were seen in line with bags made from 100 percent of ATTANE 4203 and DOWLEX 2045. No leaks were seen with the other films. The subjective test of resistance of the seal involved squeezing the bag from one end, until the bag gave of itself, or until the seal failed. Table VII shows that seal failures were not seen with bags made with films containing 20 percent by weight of 1351 or XU 60021.62. The bags made from a multilayer film containing ATTANE 4203 and DOWLEX 2045 in the seal layer, had a significant seal thinning and fraying of the end seal, as shown in Table VIII. Bags made with 20 percent low density polyethylene 5261 had some thinning of the seal and some fraying of the end seal in polymeric film filaments that came from the seal area. No slimming or fraying was found with 20 percent of bags containing 20 percent low density polyethylene 1351 or low density polyethylene XU 60021.62 in the seal layer of the film. 2 liter milk bags were tested by the end seal resistance, using an Instron Model Traction Tester # 1122, under the same conditions described in connection with the determination of heat seal resistance hereinbefore. The seal resistances are shown in Table IX. It was found that the resistance of the seal increases as the melt strength of the polymer mixture in the seal layer increases. There was no obvious correlation between the melt index of the low density polyethylene and the strength of the seal. The fraying regions and the bank regions of the bags were cryogenically sectioned, and examined using light microscopy techniques. Table X summarizes the results. The bags made from films containing 20 percent of 1351 and XU 60021.62 in the seal layer, showed very little thinning of the seal and no fraying of the end seal (fine polymer filaments that came from the seal area), while the bags containing 100 percent of ATTANE 4203 and DOWLEX 2045 had a thinning of the seal and significant fraying. The weakest part of a good seal is typically the film just in front of the stamp's projection. Any thinning of this film results in lower seal strengths, since this is the region that fails when the seal is tightened. Comparing the melting strength of the resin mixtures (Table II) with the amount of film thinning seen with the bags made with the commercial vertical forming, filling and sealing unit (Table X), it is seen that, as that the melting strength of the resin mixture increased, the amount of thinning of the film decreased. No correlation was found between the thinning of the film (Table X) and the melt index of the low density polyethylene in the resin mixtures (Table I).

Table VII: Evaluation of Commercial Dairy Preparatory, Filler and Sealer Machine Subjective Resistances of the Seal Table VIII: Evaluation of Commercial Dairy Preparatory, Filler and Vertical Sealing Machine Visual Examination of the End Seals Table IX: Vertical Trainer, Filler and Sealer Prepac Resistance of Bag End Seal Table X: Summary of Microscope Analysis of the Vertical Formulator, Filler and Sealer Measured at 550 microns from the seal Cross section measured in the thinnest part of the film before the stamp.

Table XI shows the hot viscosity data for low density polyethylene 1351 and ATTANE 4203, as well as predicted and observed hot viscosity values for mixtures of 80 percent by weight of ATTANE 4203 and 20 percent by weight of low density polyethylene 1351. It can be seen that the observed hot viscosity resistance of the mixtures of ATTANE 4203 and low density polyethylene 1351 of the present invention is significantly higher than the predicted level for mixing, indicating a clearly synergistic effect.

Table XI: Hot Viscosity Resistance - ATTANE Predicted vs. Observed Values The resistance to hot viscosity prr-i? Cha was calculated according to the following: Viscosity in < v. ' 'Predicted entity = (0.8 x hot viscosity of ATTANl. A: "J (0.2 x hot viscosity of DPE).

Claims (29)

REVINDICATIONS

1. A bag containing a flowable material, said bag being made from a film structure with at least one seal layer of a polymer composition comprising: (A) from 10 to 100 percent, based on the total weight of the composition , of a mixture of: (1) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one ultra-low density polyethylene, which is a linear ethylene copolymer interpolymerized from ethylene, and at least one α-olefin on the scale of 3 to 18 carbon atoms, and that has: (a) a density of 0.89 qramos / cm3 to less than 0.916 grams / cm3, (b) a melt index ( I2) less than 10 grams / 10 minutes, (c) a melt flow ratio I10 / I2 'greater than 5, (d) a molecular weight distribution ratio, Mw / Mn, greater than 3, (e) a peak melting point greater than 100 ° C, measured by a differential scanning calorimeter; and (2) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one low density and high pressure polyethylene having; (a) a density of 0.916 grams / cm3 to 0.93 grams / cm3, (b) a melt index (I) less than 1 gram / 10 minutes, and (c) a melt strength greater than 10 cN, determined using a Gottfert Rheotens unit, at 190 ° C; and (B) from 0 to 90 percent, based on the total weight of the composition, of at least one polymer selected from the group consisting of linear low density polyethylene, low density polyethylene and high pressure polyethylene, and an ethylene-vinyl acetate copolymer.

2. A bag containing a flowable material, this bag being made from a multilayer film structure comprising: (I) A layer of a polymer composition comprising: (A) from 10 to 100 percent, based on the total weight of the composition, of a mixture of: (1) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one ultra-low density polyethylene, which is a copolymer of linear ethylene interpolymerized from ethylene, and at least one α-olefin on the scale of 3 to 18 carbon atoms, and having: (a) a density of 0.89 grams / cm 3 to less than 0.916 grams / cm 3, (b) ) a melt index (I2) less than 10 grams / 10 minutes, (c) a melt flow rate Iio / ^ 'greater than 5, (d) a molecular weight distribution ratio, Mw / Mn, greater than 3, (e) a peak melting point greater than 100 ° C, as measured by a differential scanning calorimeter; and (2) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one low density and high pressure polyethylene having a density of 0.916 grams / cm3 to 0.93 grams / cm3, a melt index (I2) of less than 1 gram / 10 minutes, and a melt strength greater than 10 cN, determined using a Gottfert Rheotens unit, at 190 ° C; and (B) from 0 to 90 percent, based on the total weight of the composition, of at least one polymer selected from the group consisting of linear low density polyethylene, low density polyethylene and high pressure polyethylene, and an ethylene-vinyl acetate copolymer; (II) at least one layer of linear ethylene copolymer interpolymerized from ethylene and at least one α-olefin on the scale of 3 to 18 carbon atoms, and having a density of 0.916 to 0.940 grams / cm3, and a melting index of 0.1 to 10 grams / 10 minutes.

3. The bag of claim 1, wherein the film structure is in a tubular shape, and the bag has transversely sealed ends by heat.

4. The bag of claim 2, having (III) a layer of a high pressure polyethylene having a density of 0.916 to 0.930 grams / cm3, and a melt index of 0.1 to 10 grams / 10 minutes.

The bag of claim 2, wherein the layer (I) is a seal layer.

6. The bag of claim 2, wherein the layer (II) is an outer layer, and the layer (I) is a seal layer.

The bag of claim 3, wherein the layer (II) is an outer layer, the layer (III) is a core layer, and the layer (I) is a seal layer.

8. The bag of claim 2, wherein the ultra-low density polyethylene has a melt index (I) less than 10 grams / 10 minutes.

9. The bag of claim 1, wherein the bag contains from 5 milliliters to 10,000 milliliters.

10. The bag of claim 1, wherein the flowable material is milk.

The bag of claim 1, wherein the ultra-low density polyethylene has a ° -1 to 20.

The bag of claim 1, wherein the film structure contains an anti-skid agent, an agent against blocking, and optionally, a processing aid.

13. The bag of claim 1, wherein the film structure contains a pigment to render the film structure opaque.

14. The bag of claim 1, wherein the film structure contains an ultraviolet light absorbing additive.

15. The bag of claim 1, wherein the α-olefin of the film structure is l-butene.

16. The bag of claim 1, wherein the α-olefin of the film structure is 1-hexene.

17. The bag of claim 1, wherein the α-olefin of the film structure is 1-octene.

18. The bag of claim 1, wherein the α-olefin of the film structure is a mixture of at least two α-olefins selected from the group consisting of l-butene, 1-hexene and 1-octene.

19. The bag of claim 1, wherein the melt strength of low density and high pressure polyethylene is in the range of 10 to 40 cN.

20. The bag of claim 1, wherein the melt strength of low density and high pressure polyethylene is in the range of 13 to 25 cN.

21. The bag of claim 1, wherein the melt strength of the polymer composition is in the range of 5 to 70 cN.

22. A film structure of a polymeric composition for a packaging application, which comprises: (A) from 10 to 100 percent, based on the total weight of the composition, of a mixture of: (1) from 5 to 95 percent by weight, based on 100 parts by weight of the mixture, of at least one ultra-low density polyethylene, which is a linear ethylene copolymer interpolymerized from ethylene, and at least one α-olefin on the scale from 3 to 18 carbon atoms, and having: (a) a density of 0.89 grams / cm3 to less than 0.916 grams / cm3, (b) a melt index (I2) of less than 10 grams / 10 minutes, (c) ) a melt flow ratio I10 / I2 'greater than 5, (d) a molecular weight distribution ratio, Mw / Mn, greater than 3, (e) a peak melting point greater than 100 ° C, measured by a differential scanning calorimeter; and (2) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one low density and high pressure polyethylene having a density of 0.916 grams / cm3 to 0.93 grams / cm3, a melt index (I2) of less than 1 gram / 10 minutes, and a melt strength greater than 10 cN, determined using a Gottfert Rheotens unit, at 190 ° C; and (B) from 0 to 90 percent, based on the total weight of the composition, of at least one polymer selected from the group consisting of linear low density polyethylene, low density polyethylene and high pressure polyethylene, and an ethylene-vinyl acetate copolymer.

23. The film of claim 22, wherein the density of the linear ethylene copolymer is from 0.916 to 0.94 grams / cm3.

24. The film of claim 22, wherein the concentration of ethylene-vinyl acetate copolymer is from 5 to 85 percent, based on the total weight of the composition.

25. The film of claim 22, wherein the concentration of the ethylene-vinyl acetate copolymer is from 5 to 25 percent, based on the total weight of the composition.

26. The film of claim 22, wherein the melt strength of the polymer composition is in the range of 5 to 70 cN.

27. A process for the preparation of a bag containing a flowable material, which comprises forming a film structure, either by extrusion of blown tube or cast extrusion, forming the film structure in a tubular member, and sealing by heat transversely the opposite ends of the tubular member, said tubular member comprising a film structure for a bag container with at least one seal layer of a polymer composition comprising: (A) from 10 to 100 percent, based on the total weight of the composition, of a mixture of: (1) from 5 to 95 weight percent, based on 100 parts by weight of the blend, of at least one ultra-low density polyethylene, which is an interpolymerized linear ethylene copolymer from ethylene, and at least one α-olefin on the scale of 3 to 18 carbon atoms, and having: (a) a density of

0. 89 grams / cm3 to less than about 0.916 grams / cm3, (b) a melt index (I2) of less than 10 grams / 10 minutes, (c) a melt flow ratio of Iio / ^ 'maY ° r of 5, (d) a molecular weight distribution ratio, Mw / Mn, greater than 3, (e) a peak melting point greater than 100 ° C, as measured by a differential scanning calorimeter; and (2) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one low density and high pressure polyethylene having a density of 0.916 grams / cm3 to 0.93 grams / cm3, a melt index (I2) of less than 1 gram / 10 minutes, and a melt strength greater than 10 cN, determined using a Gottfert Rheotens unit, at 190 ° C; and (B) from 0 to 90 percent, based on the total weight of the composition, of at least one polymer selected from the group consisting of linear low density polyethylene, low density polyethylene and high pressure polyethylene, and an ethylene-vinyl acetate copolymer.

28. A process for the preparation of a bag containing a flowable material, which comprises forming a film structure, either by extrusion of blown tube or cast extrusion, forming the film structure in a tubular member, and heat sealing transversely the opposite ends of the tubular member, said tubular member comprising: (I) A layer of a polymer composition comprising: (A) from 10 to 100 percent, based on the total weight of the composition, of a mixture of: 1) from 5 to 95 weight percent, based on 100 parts by weight of the mixture, of at least one ultra-low density polyethylene, which is a linear ethylene copolymer interpolymerized from ethylene, and at least one -olefin on the scale of 3 to 18 carbon atoms, and having: (a) a density of 0.89 grams / cm3 to less than about 0.916 grams / cm3, (b) a melt index (I2) of less than 10 grams / 10 minutes, (c) a proportion n of melt flow I? o / I2 'ma ° r of 5, (d) a molecular weight distribution ratio, Mw / Mn, greater than 3, (e) a peak melting point greater than about 100 ° C , measured by a differential scanning calorimeter; and (2) from 5 to 95 percent by weight, based on 100 parts by weight of the mixture, of low density polyethylene and high pressure polyethylene having a density of about 0.916 grams / cm3 to 0.93 grams / cm3, an index of fusion (I2) less than 1 gram / 10 minutes, and a melt strength greater than about 10 cN, determined using a Gottfert Rheotens unit, at 190 ° C; and (B) from 0 to 90 percent, based on the total weight of the composition, of at least one polymer selected from the group consisting of linear low density polyethylene, low density polyethylene and high pressure polyethylene, and an ethylene-vinyl acetate copolymer; (II) at least one layer of linear ethylene copolymer interpolymerized from ethylene and at least one α-olefin on the scale of 3 to 18 carbon atoms, and having a density of 0.916 to 0.940 grams / cm3, and a melting index of 0.1 to 10 grams / 10 minutes. The process of claim 28, wherein the film structure includes: (III) at least one layer of a high pressure polyethylene having a density of 0.916 to

0. 93 grams / cm3, and a melt index (I2) of 0.1 to 10 grams / 10 minutes.