MXPA01001899A - Liquid packages having improved leaker frequency performance - Google Patents

Abstract

A pouch for containing a flowable material, said pouch being made from a film in tubular form and having transversely heat-sealed ends, said film comprising at least one layer made from a material comprising from about 70 to about 100 parts of at least one interpolymer of ethylene and a C3-C20 alpha-olefin having a density of from 0.840 to 0.940 g/cm3 and a melt index of 0.01 to 2.0 dg/min, and from about 0 to about 30 parts by weight of at least one high-pressure polyethylene having a density of at least about 0.916 g/cm3 and a melt index of from about 0.01 to about 2 dg/min, said film having an overall melt strength of from about 10 toabout 15 centiNewtons as determined using a Goettfert Rheotens unit at 190°, and the transverse seal integrity of the pouch is such that leaker frequency rate for pouches, as measured in terms of 10,000 pouches produced, is substantially reduced as compared with the leaker frequency rate for pouches produced from films having a melt strength outside the specified range. Also described is a process for making such pouches.

Description

PACKINGS FOR LIQUIDS, WHICH HAVE IMPROVED CHARACTERISTICS OF THE LEAK POINT FREQUENCY FIELD OF THE INVENTION This invention is focused on the area of liquid packaging, especially the manufacture of bags containing liquids. In particular, this invention relates to bags for fluid materials made from films formed primarily of int erpels of the ethylene-to-fa-oleofin which have superior characteristics in food bags such as milk. The disposable bags containing the fluid can be manufactured in forming, filling and sealing equipment, preferably employing pulse sealing techniques. The screens are selected such that the film exhibits melt strengths in the range of about 10 to about 15 cent iNewtons. The packages manufactured from these films exhibit superior characteristics of the frequency of vanishing points, during use.

REF. : 127658 -A.afeaaE-i < MY ^^ -. ". J ^: Í¿ ^ & BACKGROUND OF THE INVENTION U.S. Patent No. 4521437 (Storms) (the descriptions of which are incorporated herein by reference) discloses a film to produce bags for containing liquids, containing a linear polymer of ethylene and α-olefin with at least one other polymer. selected from ethylene, linear, low density and α-olefin copolymers of 4 to 10 carbon atoms and low density, high pressure polyethylene. The film is selected based on its characteristics in the M-test whose results are superior to a known film standard. For many years this test has been a good indicator of the characteristics of films in a bag type packaging. In the past 20 years or more, the measurement of Re sist in the Adhesion in Ca li en te, using a method developed by DuPont, was considered the best predictor of the characteristics of film sealing in DuPont liquid packing machines. PrepacMR. Although several films have been evaluated for use in the manufacture of packaging for liquids, JM? Í? ^? ^^? K ^. The typical approach has been in films that have hot adhesion resistance curves, improved, versus temperature on the side, on the basis that this property was an indicator of 5 good characteristics. However, field leakage frequency tests have revealed that this property is not a good or consistent indicator of field behavior. Based on a superior curve of Re s i t t in Ad h e s t ion in Ca l i t e, a film was expected to demonstrate better board characteristics in milk bag packaging trials. In the field trials of hybrid film (see the patent application North American No. 09 / 135,187 filed August 17, 1998 (Climenhage and Chow) and based on United States Provisional Patent Application No. 60 / 056,900, filed on August 22, 1997, the descriptions of the which is incorporated herein by reference) against the industry standard film, SCLAIRFILMMR SM3, it was found that the hybrid film has approximately twice the frequency of horizontal joint faults compared with the SM3, despite its resistance to i m * ^ ¿* ** * * *** * ?? * .... *. .- ^ ........-, iWffftl.M¡ÍH ^ ^ ^ warm adhesion, improved. This result was very surprising and led to the theory that some other characteristic of the "fused", not understood at the moment, could be critical to obtain superior characteristics. The hybrid film is obtained from resin that is produced using a combination catalyst that includes metallocene catalysts and Zeigler-Nat catalysts. Processes for producing those films are described in U.S. Patent No. 5,844,045, issued December 1, 1998 to Kolthammer et al (the descriptions of which are incorporated herein by reference). SCLAIRFILMMR SM3 is a mixture of linear, low density ethylene-octene copolymer resin, and high pressure low density polyethylene resin and its use in bags is described in US Patent No. 4,521,437 issued to Storms. The North American Patent No. ,879,768, issued March 9, 1999 to Falla et al, discloses an environmentally non-damaging polymeric film bag, made from a polyethylene film structure for the packing of fluid materials for example, milk, including for example, a bag from a single-layer or multi-layer film structure, such as a two-layer or three-layer coextruded film, containing at least one layer of a substantially linear ethylene polymer blend or a polymer homogenously branched ethylene and a low density, high pressure polyethylene, as a sealing layer. Also disclosed is a process for producing the bag to pack fluid materials using a film structure described hereinabove. In this patent the bag is formed from a film structure having a sealing layer that includes a low density, high pressure polyethylene having a melt strength greater than 10 cN determined using a Gottfert Rheotens unit at 190 ° C. . The melt strength of the polymer composition is described as greater than 5 cN, ranging from 5 to 70 cN, 10 to 70 cN, preferably from about 15 to 70 cN and, most preferably, from 15 to 50 cN. In PCT Patent Application W097 / 12755, Falla et al. Describes a bag of & Sy, ¡-BSj .- * l ^ i ^ ft «-Mafe ^ afo;.« M ^. MlÜtííJSt. * • > .. ». Fr-3 non-environmentally harmful polymeric film, produced from a polyethylene film structure for the packing of fluid materials, for example, a bag produced from a single layer or multilayer film structure, such as a coextruded, two-layered or three-layered film, containing at least one layer of a mixture of a substantially linear ethylene polymer and a low-density, high-pressure polyethylene as a sealant layer. Also disclosed is a process for producing the bag to pack fluid materials, using the film structure described. In the PCT Patent Application WO 97/20693, Falla et al discloses an environmentally non-harmful polymeric film bag, made from a polyethylene film structure for the packaging of fluid materials, for example milk. The film may be a single layer or multilayer structure, such as a two layer or three layer coextruded film, containing at least one layer of a mixture of ultra low density polyethylene and high density low density polyethylene. Pressure .. ^^ j &. ^^^^^ ,, ^^^^. ^ &^ '' 'As a sealing layer that has a high melting strength. Also disclosed is a process for manufacturing the bag for packing fluid materials, using a film structure as described. In the PCT Patent Application of Failure W098 / 34844, there is disclosed an environmentally non-harmful polymeric film bag, produced from a polyethylene film-0 structure for the packaging of fluid materials, for example, milk, which includes, for example, example, a bag made from a single layer or multilayer film structure, such as a coextruded film 5 of two layers or of three layers, containing at least one layer of a mixture of an int erpo 1 imero of linear ethylene and a low density, high pressure polyethylene, as a sealing layer. A process for making a bag for packaging fluid materials is also described, using a film structure of a mixture of a linear ethylene interpolymer and a low density, high pressure polyethylene. All these references seem to describe that the resistance of the melt, of the polymer composition, is preferably greater than 5 cN and, most preferably, above 15 cN. Although Falla et al focused on reducing the high incidence of "vanishing points", it is 5 to say defects of the board, such as tiny holes that develop in the board or in it, through which it escapes from the bag the fluid material, for example milk, they emphasize more adhesion resistance in hot and lower temperatures of hot adhesion start and thermosel side, in order to improve the processability of the film and to improve the bags made from the films. Falla et al, in the references mentioned above, indicated that their film structures have improved melt strength and end-face resistance, particularly the strength of the end seal. Falla et al claim that the use of bag making films using forming, filling and sealing machines, leads to machine speeds that are greater than those that can be obtained commonly with the use of commercially available film and bags with fewer vanishing points. However, machines used in their examples, although they are commonly used are not the latest generation of machines that operate at significantly increased speeds. Falla et al seems to believe that the use of LDPE having high melt strength, in a film structure for bags, is the key ingredient responsible for the benefits associated with its proposed film structures. In the Patent and Requests, Falla et al discloses that LDPE can be combined with an extremely wide range of linear and substantially linear ethylene interpolymers to achieve high melt strength. In the examples of the Patent and Requests referred to above, a very small sample (20) of bags for "in-line vanishing points", "subjective resistance of the board" and "joints" was analyzed and / or examined. extreme. " This sample was quite small and did not involve any data of field leakage frequencies, real. It is important to appreciate that when bags for liquids are manufactured, the process involves sealing through the liquid that is g ^^ ¡ß ^ j ^^ ¿^^^^ ¡gf ^ ¡& ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡ Packs, which makes the seal itself problematic. However, since the bag is produced on a vertical filling machine, and the film is in a melted condition when it is sealed, obtaining an upper gasket is a challenge. To ensure that the melt strength of the film is at the levels established herein, produces a seal that not only satisfies the high-speed manufacturing requirements for new machines, but also meets the rigorous requirements of the field.

BRIEF DESCRIPTION OF THE INVENTION In the present it has been found that by ensuring that the melt strength of the final film structure is in the range of about 10 to about 15. cent iNewtons, bags can be obtained to contain fluid, ie liquid, materials that exhibit significantly improved leak rate frequency ratios in actual use. 25 The Resistance of the Melt or the -y »&& * M tak¡ &xm Melt Tension, defined as effort or force (such as that applied by a winding drum, equipped with a stress cell) required to stretch an extruded, melted product, to a specified degree above its melting point, as it passes through the nozzle of a standard plastometer such as that described in ASTM D1238-E. The values of the melt strength are determined using a Gottfert Rheotens unit at 190 ° C. In general, for ethylene and α-olefin interpolymers and high-pressure ethylene polymers, melt strength tends to increase when molecular weight is increased, or when The molecular weight distribution is widened and / or with increased melt flow rates. The branching of long chains also contributes to the increase in the strength of the melt. All Patents and Fault Requests describe that the proportion of leak points in the bags is consistently reduced when the melt strength of the polymer composition increases. 25 Surprisingly the inventors have discovered that melt strengths greater than 15 cN are harmful to the vanishing point proportions of the bags. Operating the horizontal sealing jaws, in the VFFS equipment, at high speeds, presents certain problems. The latest generation of bagging machines (PrepacMR IS 7E) operates at a rate of 120 bags per minute (1 1/3 liters) compared to 90 bags per minute for Prepac ™ IS-6, which is used commonly in Canada. At a rate of 120 bags per minute, the impulse sealing element has difficulty in pressure and clean cutting. This results in a joint that remains partially joined when the jaws open. Subsequently the board will detach and remain attached to one of the bags, resulting in a missing section of the board bed or a "Disjoint Board". This can leak immediately or lead to a greater frequency of leakage points in the horizontal joint. For this reason, experience and data show that the maximum benefit of increasing the melt strength is between 10 and 15 cN and the increase in melt strength above 15 cN results in a high frequency of leak points unless the speed of the machine is reduced making the film / machine combination unfavorable. The above results were observed with a film composition having a melt strength of only 16 c. This is a surprising indication that the optimum value of the melt resistance is found in the narrow range of 10 to 15 cN for bags that are operated at speeds above 100 / minute, in particular 120 / minute. The effect of "Junction Board" was so pronounced that films above 15 cN not could be analyzed in the field safely. When the data were plotted in the field, they revealed that there is little benefit in additionally increasing the resistance of the melt, above 15 cN, because the curve of frequencies in horizontal joints approaches the vertical and ends at a frequency of zero. In this way, the present invention provides in one aspect, a bag for containing a fluid material, the bag is made of a tubular shaped film and having ends On the transverse side, the film comprises at least one layer made of a material comprising from about 30 to about 100 parts of at least one interpolymer of linear or substantially linear ethylene and an alpha-olefin of 3 to 20 carbon atoms. which has a density from about 0.840 to about 0.940 grams / cm3 and a melt index of About 0.01 to about 2.0 dg / minute, and from 0 to 70 parts by weight of at least one high pressure polyethylene having a density of at least about 0.916 grams / cm3 and a melt index of about 0.01 to about 2 dg / minute, the film has an overall melt strength of about 10 to about 15 cN determined using a Goettfert Rheotens unit at 190 ° C, so such that the integrity of the horizontal or transverse joint of the bag exhibits a leak rate frequency ratio, measured in terms of 10,000 bags produced, which is substantially reduced compared to the proportion frequency of vanishing points for bags produced from films with melt strengths outside the speci fi ed range. The substantial reduction in the 5 proportions of leakage point frequencies is, as has been found, in the range from about four to five times the reduction. This is very significant since this represents a result in the field, which is opposite to the theoretical measurements of the laboratory. Preferably, the interpolymer comprises from about 75 to about 90 parts by weight, most preferably 85 parts by weight, wherein the Low-density, high-pressure polyethylene comprises from about 10 to about 25 parts by weight, most preferably 15 parts by weight. In the case where multilayer films or films are desired, it is preferable that the melt strength of each polymer layer be greater than about 7 cN in order to produce a film for bags, with the required melt strength and to achieve the desired melt strength. the results in the field established in the ^ ¡^^^ & ^^ «s2¿ ^ j ^^ present. Most preferably, the individual layers should have a melt strength greater than 10 cN. The film preferably has a global density ranging from about 0.900 to about 0.930 grams / cc, more preferably from about 0.915 to about 0.925 grams / cc, in the ranges of the melt index from about 0.01 to about 2.0 dg / minute. More preferably, the overall density of the film varies from about 0.916 to 0.924 grams / cc and the melt index varies from about 0.1 to about 1.0 dg / minute. The melt index of the low density polyethylene and high pressure, preferably varies from about 0.1 to about 2 dg / minute. The interpolymer can be selected from a single-site catalyst, a multi-site catalyst or mixed catalyst polymers. There are many examples of such polymers known in the art and it is expected that any of these will be convenient as long as the melt strength values presented herein are met. Preferably the int erpolymer is selected from the following: 5 (a) from about 4 to about 100% of the total weight parts of the linear interpolymer of an ethylene α-olefin of 3 to 20 carbon atoms having a density from about 0.900 to about 0.940 grams / cc and a Melt Index from about 0.01 to about 2.0 dg / minute, and (b) from about 0 to about 96% by weight of the total parts by weight of the linear integer 1 e of an ethylene α-olefin having from 3 to 20 carbon atoms, having a density from about 0.840 to about 0.915 grams / cc and a melt index from about 0.01 to approximately 2.0 dg / minute. More preferably, the interpolymer is selected from the following: (a) from about 40 to about 100% by weight of the total parts by weight of the linear intemer of an ethylene a- olefin of 3 to 20 carbon atoms, having a density from about 0.915 to about 0.925 grams / cc and a melt index of from about 0.1 to about 1.0 dg / minute, and (b) from about 0 to about 60% by weight of the total weight parts of the linear interpolymer of an ethylene α-olefin of 3 to 20 carbon atoms having a density from about 0.900 to about 0.910 grams / cc and a melt index of from about 0.1 to about 1.0 dg / minute. Preferred amounts for the interpolymers (a) and (b) will vary depending on the individual polymers and can be selected according to known combinations, taking into account the strength requirements of the melt, the film, and the polymeric components as set forth at the moment. Subsequently, numerous patents and patent applications are referred to herein, which establish guidelines for selecting those polymers and a person skilled in the art can refer to them and make choices. easily. Reference may also be made to the references of Falla and Falla et al, mentioned above, for appropriate formulations. The description of all the patents and applications mentioned are incorporated herein by reference. In the present description three methods have been used to control the melt strength, but other methods known in the art may be employed. The melt strength of the film can be increased by increasing the molecular weight, either of the linear interpol component or the high pressure polyethylene component, by broadening the molecular weight distribution of the linear integer 1 component. , or by selecting a polymer with a higher frequency of long chain branching. Typical polymers with long chain branching are low density, high pressure polyethylenes, but substantially linear ethylene interpolers having a limited amount of long chain branching are also available. By increasing the molecular weight of linear or high pressure polyethylenes, will reduce the melt index. The molecular weight of a polymer is generally indicated by its melt index. In another aspect the invention provides a process for manufacturing a bag to contain a fluid material, using a vertical machine for forming, filling and sealing, a process in which each bag is made from a flat cloth or film, forming a tubular film from there, with a longitudinal joint and subsequently flattening the tubular film in a first position and we transversely laminating the tubular film in the flattened position, flattening the tubular film 5, above the predetermined amount of fluid material in a second position , wherein the improvement comprises using the film of the present disclosure. The preferred type of equipment of 0 formed, filled and sealed, is that which produces a fusion through the joint, and this joint is preferably provided by impulse sealing. More preferably, the invention provides a process for manufacturing a bag to contain a fluid material, using a vertical machine for forming, filling and sealing, a process in which each bag is made from a flat cloth or film, forming a tubular film therefrom, with a longitudinal joint and subsequently flattening the tubular film in a first position and cross-sealing the tubular film in the flattened position, flattening the film tubular over a predetermined amount of fluid material in a second position, the improvement comprises using the film as previously defined and carrying out the process at machine speeds above 100 bags per minute.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings which are used to illustrate the present invention, FIG. 1 graphically illustrates curves of the hot adhesion strength versus the temperature of the side, for typical films of the present invention, used to manufacture packaging for liquids; Y Figure 2 is a curve of the melt resistance versus the frequency of leak points in horizontal joint, for films and bags made from them, of according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Examples of polymers that can selected for the film used to produce the bags of the present invention are described hereinafter. In all cases the melt strength of these polymers can be modified as required for the The present invention is in accordance with known methods for producing films of the required strength of the melt. It is thought that the present invention can equally be applied to all copolymers of olefin commonly used to produce film for liquid bags; Especially int erpolymers of low density polyethylene, linear (LLDPE, for its acronym in English), int polymers of very low density polyethylene (VLDPE, for its acronym in English), interpolymers jg ^ »: ^?.: á ^ ¿S« faith; : »> -. ^., i --'.-.-.- of metallocene (single-site catalyst), multi-site catalyst interpolymers, and single-site catalyst hybrid (metallocene) -catalyst of multiple sites, for example, int erpolyers of Zeigler-Nat t a (Z-N). The interloymers of metallocene, of e t i leno-octene, e t i leno-hexene, e t i leno-but ene-hexene and e leno-but ene, are commercially available in the density range of 0.80 to 0.915 grams / cc. Films with these densities generally have a module too low to be used to make bags for fluid materials. The metallocene interpolymers can be mixed with Zegler-Nat interpolymers or coextrusions used to form bags for liquids. As noted, the development of single-site catalyst (SSC) or metallocene technology, has resulted in an improved class of ethylene interpolymers ranging from crystalline to elastomeric materials. These ethylene interpolymers have characteristics such as improved impact strength and hardness, better melting characteristics, due to control over the molecular structure, and better transparency. Exxon and Dow have developed SSC or metallocene ethylene interpol and each has the benefit of a number of patents related to these polymers. It is said that Exxon uses mono-cyclopentyl adieni lme t allocenes and bis-cyclopentadieni lmetalócenos, while Dow concentrates on the cyclopent adieni lmet alócenos of titanium which he calls "catalysts of restricted geometry". In practice, Exxon produces copolymers of ethylene butene, hexyne-hexene and terpolymers of etheno-butene-hexene, while Dow produces copolymers of etheno-octene of the metallocene type or SSC. Dow claims that their metallocene (or SSC) polymers are different in that they have uniformly introduced branching into the long chain, which improves the processability in otherwise linear polymers. Examples of Exxon polymers are found in the following patents and applications, the descriptions of which are incorporated herein by reference. U.S. Patent No. 5,382,630 issued January 17, 1995 to Stehling et al and WO 93/03093 published on 18 j »§j, x., ^ ... ^ .. ^^ ... mn February 1993, issued to Meka et al. These resins are commercially available from Exxon under the trade name EXACTMR. Examples of Dow polymers are found in the following North American patents: North American Patents Numbers: 5,508,051 issued April 16, 1996 to Falla et al, 5,360,648 issued November 1, 1994 to Falla et al, 5,278,272 issued on January 11, 1994 to Lai et al, and 5,272,236 issued on December 21, 1993 to Lai et al. These resins are commercially available under the trade name of AFFINITY ™. In the PCT International Publication of DuPont Canada Inc., WO 95/10566 published April 20, 1995, bags for fluid materials are described wherein the sealing film is made of a linear, ethylene copolymer of an SSC, and minus an alpha-olefin of 4 to 10 carbon atoms. Mixtures of these SSC interpolymers, with at least one polymer selected from linear ethylene interpolymers, from multi-site catalysts, and at least one alpha-olefin from 4 to 10 carbon atoms, a high pressure polyethylene and mixtures of the - ^ IES ^ Í = ^ .....- ^ ¿^ - ~ ^^: ^ & ^ - ^ same. In the PCT International Publication of DuPont Canada Inc., WO 95/21743 published August 17, 1995, an ethylene copolymer film of improved stiffness is disclosed, for use in the manufacture of bags that will contain fluids. Typically the structure comprises an interposed layer of polyethylene, having a thickness that is in the range of 5 to 20 microns, and a density of at least 0.93 grams / cc and a melt index of about 1 to 10 dg / minute, wherein the outer layer is an SSC or polyethylene film of such ocean / fine fiber, which may have a density in the range of 0.88 to 0.93 g / cc. The only requirement for the layer interposed for r i gidi ation, is that it be of a particular thickness and density. These properties are greater in the stiffening layer than in the metallocene or SSC layer (s). This application indicates that the stiffening layer is included so that the bag that is to contain the fluid is held vertically in an appropriate manner, so that the fluid can be emptied thereof when the bag is placed in a support container .

The US patents of DuPont Canada Inc., Nos. 4,503,102 (Mollison) and 4,521,437 (Storms), describe a polyethylene film for use in a forming, filling and sealing process, for the manufacture of a disposable bag, for liquids such as milk. U.S. Patent No. 4,503,102 discloses bags made from a mixture of a linear ethylene copolymer of ethylene and an alpha-olefin of 4 to 10 carbon atoms and an ethylene-vinyl acetate polymer, copolymerized from ethylene and vinyl acetate. The polyethylene copolymer, linear, has a density of 0.916 to 0.930 grams / cm3 and a Melt Index of 0.3 to 2.0 dg / minute. The ethylene-vinyl acetate polymer has a weight ratio of ethylene to vmyl acetate, from 2.2: 1 to 24: 1 and a melt index of 0.2 to 10 dg / minute. The mixture described in U.S. Patent No. 4,503,102, of Mollison, has a weight ratio of linear low density polyethylene, to ethylene vinyl acetate polymer, from 1.2: 1 to 24: 1. U.S. Patent No. 4,503,102 also discloses multilayer films having as sealing film, the aforementioned mixture previously . U.S. Patent No. 4,521,437 (Storms) discloses bags made from a sealant film composed of 50 to 100 5 parts of an ethylene, linear and octene-1 copolymer having a density of 0.916 to 0.930 g / cm3 and a Melt index of 0.3 to 2.0 dg / min and 0 to 50 parts by weight of at least one polymer selected from the group consisting of a linear ethylene copolymer, and an alpha-olefin of 4 to 10 carbon atoms, having a density of 0.916 to 0.930 g / cm3 and a melt index of 0.3 to 2.0 dg / minute, a high pressure polyethylene that It has a density of 0.916 a 0.924 grams / cm3 and a melt index of 1 to 10 grams / 10 minutes. The sealing film described in U.S. Patent No. 4,521,437 is selected based on providing (a) bags with an M-proof value, substantially smaller, with the same film thickness, which is obtained for bags made with film from a mixture of 85 parts of a linear ethylene / but ene-1 copolymer, having a density of about 0.919 grams / cm3 and an index of cast of approximately 0.75 dg / minute and 15 parts of a ; Sas £ ^^. ^^ -i high pressure polyethylene, having a density of about 0.918 g / cm3 and a melt index of 8.5 dg / min, or (b) a value of the M test (2) lower that approximately 12%, for bags having a volume from more than 1.3 to 5 liters, or (c) a value of the M-test (1.3) less than about 5% for bags having a volume of 0.1 to 1.3 liters. The M, M (2) and M (1.3) tests are defined as bag drop tests, in U.S. Patent No. 4,521,437. The bags can also be made of composite films, in which the sealing film forms at least the inner layer. In US Patent No. 5,288,531 to Falla et al, the use of polymers in the manufacture of films used to make bags that will contain fluids is described. These films are characterized as ultra low density linear polyethylene ("ULDPE") and are sold commercially by Dow as ATTANEMR. These are described as an ethylene, linear, with at least one alpha-olefin having 3 to 10 carbon atoms, for example, the ULDPE may be selected from ethylene-1-propylene, et i leño- 1 -buteno, et ileno- 1 -pent eno, ethileno-4-methyl- 1-penteno, et ileno- 1 -hexeno, ethileno-1-hepteno, et i leño- 1-octén en e ti leño - 1 -decene, preferably of the ethylene-1-octene copolymer. In WO 93/03093 to Meka et al, published on February 18, 1993, metallocene polymers useful for the manufacture of sealed articles, comprising ethylene interpolymers having a CDBI of at least 50% and a narrow distribution are described. of molecular weights or a polymer mixture comprising a plurality of those ethylene interpolymers as blending components. Hybrid interpolymers of ethylene, melaocene / Zeigler-Natta (ZN), and alpha-olefins of 4 to 10 carbon atoms are now commercially available, offering just the right combination of improvements in properties to enhance the characteristics of bags for liquids, compared to those manufactured with conventional interpolymers of LLDPE (ZN) or pure metallocene. The hybrid int erpoly can be obtained from polymerization processes with multiple catalysts. He * A * process may comprise at least two reactors in series, or in parallel, or both, wherein each reactor has at least one catalyst selected from metallocene catalysts or at least 5 catalyst selected from catalysts Zeigler-Natta, and The process uses both types of catalysts. Alternatively, both types of catalysts can be used in a single reactor. The process can be adjusted to produce the desired 10 polymer weight fractions, according to methods known in the art. In this case, the polymer produced reams may preferably comprise from about 20 to about 80% by weight polymer 15 derived from metallocene catalyst and from about 80 to about 20 wt% polymer derived from Zeigler-Natta catalyst. More preferably the mixture of the weight 20 fractions may comprise from about 40 to about 60 wt% polymer derived from metallocene catalyst, with an amount from about 60 to about 40% by weight of polymer derived from catalyst 25 Zeigler-Natta . Most preferably, the *** £ ??? t ^^ JL?!?. 1 *? M ^ »?? ** £. ^^^^ .. ^. I ^^^^^^^^^? ^ AM ^^. . ^^^^^^. ~ W ratio is approximately 50:50% by weight. An example of a commercially available resin, which can be modified to produce film for bags in accordance with this invention, is the resin series with the ELITEMR trademark of Dow. As already mentioned, the film used to produce the bag of this invention can be a single layer or multiple layer film. layers. In multilayer structures, the individual polymers preferably have melt strengths that are in the required range. The patents referred to above, provide many examples of appropriate multilayer structures that can be used to make the bags of the present invention. In a preferred form of the invention, a bag formed from a film material is provided comprising from about 70 to about 100, preferably from 80 to about 100, more preferably 85 or 90 parts by weight of the hybrid interpolymer, and from about 0 to about 30, Preferably from 0 to about 20, Ták more preferably 10 or 15 parts by weight of the high pressure polyethylene. In another preferred form of the invention, the alpha-olefin for the int erpolymer is selected from the group consisting of 1- propylene, 1-butene, 1-i-sobut-1-ene, 1-hexene, 4-methyl-1-pentene, 1-pentene, 1-heptene and 1-octene. Typical structures for the films of this invention are those known in the art and that fit the packaging application. The patents and applications referred to above describe the different processes that can be used for the manufacture of bags of this invention. Preferably, the vertical apparatus for forming, filling and sealing is used to manufacture the bags contemplated herein. A flat sheet of film, from a roll, is unrolled and gives the shape of a continuous tube, in a tube forming section, sealing the longitudinal edges together, either by an overlap joint or a fin seal. This tube is pulled vertically to a filling station and then squeezed through a section cross section of the tube, the position of which coincides with a sealing device that is located below the station. In the section, a heat seal, horizontal or transverse is made, providing a hermetic seal to air or liquids, through the tube. The material to be packed enters the tube above the horizontal joint, the tube falls a predetermined distance under the influence of gravity or its load. The sealing device is operated again, and a second horizontal joint is made along with a cut through the tube and then through the liquid or fluid that is packed in the bag. So, in this operation, the bag, which has the shape of an elongated pillow, is formed, filled and sealed in a rapid sequence of stages. Many variations of this process are possible and are obvious to those skilled in the art. Examples of typical devices for the packing of liquids, used for this type of manufacture, are exposed by Hayssen, Thimonnier and Prepac. The term "fluid materials", as used herein, encompasses materials that flow under gravity or they can be pumped. Gaseous materials are not included in this definition. The fluid materials include liquids, for example, milk, water, fruit juices and oil; emulsions, for example, mixture of ice cream and soft margarine; pasta, for example, meat pastes and peanut butter; preserves, for example hams, stuffed pies or pies, jam, jellies and pasta; Ground beef, for example, meat for sausages; powders, for example, gelatin powders and detergents; granular solids, for example, nuts, sugar and similar materials. The bag of the present invention is particularly useful for liquids, for example milk. The resins used to produce the film of this invention are preferably extruded in known forms, although other suitable methods can be used, such as those involving laminates, coatings and the like. When blends are used, these can be produced by mixing the components before or at the time of extrusion, just before re-melting in the extruder. A film extruder can be used and the film can be manufactured using techniques known. An example of a blown film process is found in Canadian Patent No. 460,963 issued November 8, 1949 to Fuller. Canadian Patent No. 893,216 issued February 15, 1972 to Bunga et al discloses a preferred method using a cooling mandrel, external or internal, in the blown film process. To the polymers from which When the bags of the invention are produced, additives known to those skilled in the art can be added, such as antiblocking agents, slip additives, antioxidants, UV stabilizers, pigments and process auxiliaries. Typically these may comprise up to about 5% by weight of the total components of the resin. As stated above, the film of this invention can be used in packaging applications, where the sealing properties, particularly the strength of the hot tack, are important. Reference can be made to the Wiley Encyclopedia of Packaging Technology, 1986, John Wiley & Sons, Inc., under the title of Termose 11, the i ^^^^ t ^ - = - r A s. ? * description of which is incorporated herein by reference. In it are references for all types of heat sealing, including sealing with bar, band, pulse, wire or blade, ultrasonic, friction, gas, contact, hot melt, pneumatic, dielectric, magnetic, induction, with radiant energy and with solvents. Any of these techniques, which involve packaging materials incorporating the film of this invention, fall within the scope of this description. The most preferred packages are those made by impulse sealing.

MEASUREMENT OF THE RESISTANCE OF THE FUNDIDO Determinations of melt strength are made at 190 ° C using a Goettfert Rheotens unit and an Instron capillary rheometer. The capillary rheometer is aligned and positioned above the Rheotens unit and supplies, at a constant piston speed of 25.4 mm / minute, a fused polymer filament, to the Rheotens unit. The Instron is equipped with a standard 2.1 mm diameter capillary nozzle and ^? 42 mm long '^ L / D ratio of 20: 1). The Instron supplies the filament to the cogged pick-up wheels of the Rheotens unit, which rotate at 10 mm / s. The distance between the outlet of the Instron capillary and the contact point on the Rheotens pick-up wheels is 100 mm. The experiment to determine the resistance of the melt begins by accelerating the pickup wheels of the Rheotens unit, at 2.4 mm / s2, and the Rheotens unit is able to achieve acceleration proportions of 0.12 to 120 mm / s2. As the speed of the Rheotens pickup wheels increases over time, the downward pulling force is recorded in centiNe tons (cN) using the Linear Variable Displacement Transducer (LVDT) that is found in the Rheotens unit. The computerized data acquisition system of the Rheotens unit records the downward stretching force as a function of the speed of the pickup wheel. The actual value of the melt strength is taken from the plateau of the recorded downward drawing force. The breaking speed of the filament is also recorded, in mm / s as the speed Ib ^ a | g ^ g | ^ '^ t **. »***., ***** ^ for the resistance of the melt.

EXAMPLE For a period of almost two years a series of test films was formulated, to have a melt strength, increased, and then tested in the field to determine the characteristics of the horizontal joint, to observe if the characteristics of the joint and the resistance of the melt, of the films, were related. To measure the frequency of failures in the horizontal joint, a dairy was selected that had two packing machines with bags, for milk, DuPont Prepac ™ IS6, which were identical and worked together, in the dairy. This allowed a line to work using a standard material SCLAIRFILMMR SM3 (85% ethylene-octene LLDPE copolymer and 15% high pressure polyethylene: the film contained slip, antiblock additive and an auxiliary for extrusion, as part of its formulation) and the parallel line worked using the test films designated as Film A, Film B, Film C and Film D. The dates of the code on the milk packaging consisted of color codes to allow the identification of the line of the which came from a package returned and from the date it was made. The dairy distributed much of its milk through its own milk shops, along with some regular supermarkets. Any leaky or damaged package was returned from the stores or supermarkets, to the dairy, to grant credits. For this reason, a high proportion of leaking packages were returned to the dairy. By examining all the returned packages, which coincided with the test days (identified with their code date and the color of the code date), the cause and frequency of vanishing points could be determined for each of the test films that were were to evaluate. The cause and location of each vanishing point was identified and classified into three categories; leakage points in the horizontal joint, vertical joint leakage points and physical damage caused by a puncture or rip. The frequency of vanishing points was calculated for category by 10,000 bags produced during the test period.

This method of evaluating films is very laborious and time consuming but it is the best way to determine the comparative characteristics of films since all failure modes were observed. A film may have good sealing or sealing characteristics, but may be more susceptible to physical damage or vice versa. A common goal in the industry is to develop films that have good characteristics in all categories. In the past, the proportion of flaws in stock market bags was used to predict the characteristics, and although it is a good general indicator, the actual performance in the field is more definitive because it evaluates the films under all the negative situations that can cause vanishing points, and not just severe impacts. For example, leak points in joints can be caused by a defective joint element, or during startup, when joint components are heating up, etc. Physical damage can be caused by abuse or mismanagement during distribution (transport, loading and unloading, etc.) or by packaging machinery used to place the milk bags in larger bags and then in milk boxes. In summary, this field trial was designed to evaluate the films under the actual conditions of use, observing the three main failure modes. The values for field trials appear in Table I below.

Table 1 10 EFFECT OF CAST RESISTANCE ON THE FREQUENCY OF LEAK POINTS IN HORIZONTAL JOINTS fifteen ¿^ .. ^^ ¿I Aa ^ ¿^^^ ¿^^^^ ¿^^^^ ¿^^^^ Table 1 (continued) EFFECT OF THE RESISTANCE OF THE FUNDIDO IN THE FREQUENCY OF LEAK POINTS IN HORIZONTAL JOINTS * Previously this Melt Strength value was estimated as 14 CN. The measured test results gave a value of 12 CN. The variation of the predicted is due to the variation in the accuracy of the mixture and in the accuracy of the measurement, but it does not change the conclusion that there is a correlation between the Melt Resistance and the Leak Points in the Board.

The results of field tests were plotted in Figure 2. Film A with a melt strength of approximately 4 cN produced a ratio of leakage points in the horizontal joint "of 11.6 per 10,000 bags produced It was found that a modified hybrid copolymer of Ethylene and Octene, film B in which the melt strength was increased to approximately 6 CentiNewtons (cN) produced a proportion of leakage points in the horizontal joint, 8.6 by 10,000.A further modification resulted in Test Film C with a melt strength, increased to approximately 11 CN.The proportion of leakage points in horizontal joint was reduced to 2.1 leak points in horizontal joint, per 10,000 bags produced.An additional increase in melt strength, up to about 12 CN was evaluated on a test film designated as Film D, exhibiting a horizontal joint leakage ratio of only 1.8 per 10,000 bags manufactured Figure 2 shows the resistance of the melt versus the ratio of failures by vanishing points in the horizontal joint 1. The surprisingly strong correlation between the melt strength, carried out in the Rheotens unit, and the horizontal joint failure ratio, has never before been observed or measured. The correlation confirmed that The resistance of the melt is a critical and previously unknown parameter in the formulation of films for application in bags for liquids, in which the joints and cuts are made through the liquid column. Three methods were used to control the melt strength, in Test films A through D. Melt strength can be increased by increasing the molecular weight of the film. int erpoly, broadening the molecular weight distribution of the int erpoly or selecting a high pressure polyethylene, with fractional melt index, in the mixture for the film. The molecular weight of a polymer is indicated generally by its Melt Index. The base resin used at approximately 85% in Film A had a Melt Index of 0.85 dg / minute. Test film B contained a hybrid copolymer of ethylene and octene, similar, at the 85% level, whereby the melt index was reduced to 0.5. The same low density and high pressure polyethylene (5.0 melt) was mixed in 10% in Film A and in Film B. In Test Film C high polyethylene pressure, with Melt Index 5.0, was replaced ^ »^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ by a high-pressure polyethylene, with Melt Index of 0.2, increasing its melt strength, up to Approximately 11. The Rheotens Unit Fade Resistance and the Horizontal Board Characteristics of the SCLAIRFILMMR SM3 were also plotted in Figure 2 and found to be close to the melt strength curve / joint characteristics, for the hybrid copolymers. It appears that the melt strength is independent of the polymer used and should be carefully controlled if conventional linear low density polyethylene or the linear, metallocene hybrid ethylene copolymer is used. The invention may be varied in a number of ways, which may be apparent to one skilled in the art, and it is intended that all obvious and similar equivalents are within the scope of this description and claims. It is intended that the description serve as a guide to interpret the claims and not limit them unnecessarily.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, the content in the following is claimed as property:

Claims (9)

RE IVIND ICATIONS

1. A bag for containing a fluid material, characterized in that it is made from a tubular shaped film and has thermosel sides transversely, wherein the film comprises at least one layer produced from a material comprising from about 70 to about 100 parts of at least one interpolymer of ethylene and an alpha-olefin of 3 to 20 carbon atoms, having a density of 0.840 g / cm3 to 0.940 g / cm3 and a melt index of 0.01 to 2.0 dg / minute, and from about 0 to about 30 parts by weight of at least one high pressure polyethylene having a density of at least about 0.916 g / cm 3 and a melt index of from about 0.01 to about 2 dg / minute, the film has a strength of global melt from about 10 to about 15 CentiNewtons, determined using a Goettfert Rheotens unit at 190 °, and the integrity of the transverse joint of the bag is such that the proportion of the frequency of vanishing points for the bags, measured in terms of Al & ^ Gg ^^^^ & g ^ ^^^^^^ .. ^., T ^^^^^ i ^^ 10,000 bags produced, is substantially reduced, compared to the proportion of the frequency of points leakage, for bags produced from films having a melt strength that is outside the specified range.

2. The bag according to claim 1, characterized in that the overall density of the film varies from about 0.915 to about 0.925 g / cc, and the melt index varies from about 0.01 to about 0.8 dg / minute.

3. The bag according to claim 1, characterized in that the melt index of the interpolar varies from about 0.1 to about 1.0 dg / minute, and the melt index for the 20 low density polyethylene and high pressure varies from about 0.1 to about 2 dg / minute.

4. The bag according to claim 1, characterized in that the Index 0 The linear copolymer melt varies from about 0.01 to 2 dg / minute.

5. The bag according to claim 1, characterized in that the linear int erpolymer is selected from polymers of a single-site catalyst, a multi-site catalyst or mixed catalysts.

6. The bag according to claim 1, characterized in that the linear or substantially linear interpolymer comprises: (a) from 4 to 100% by weight of the total parts by weight of the linear int erpoly, of an ethylene alpha- olefin of 3 to 20 carbon atoms, having a density from about 0.900 to about 0.940 g / cc and a melt index of from about 0.01 to about 2.0 dg / minute, and (b) from 0 to 96% by weight of the total parts by weight of the linear interpolymer of an ethylene alpha-olefin of 3 to 20 carbon atoms, having a density of about 0.840 25 up to about 0.915 g / cc and an index of £ tá. & ^ - s.fc? ^^ jj jH g ^^ á | ^^ fused from about 0.01 to about 2.0 dg / min.

7. The bag according to claim 5, characterized in that the film is a single layer film.

8. The bag according to claim 1, characterized in that the alpha-olefin used in the interpolymer is selected from the group consisting of 1-propylene, 1-butene, 1-i-sobut-1-ene, 1-hexene, 4 -methyl-l-pentene, 1-pentene, 1-heptene and 1-octene.

9. A process for manufacturing a bag to contain a fluid material using a vertical machine for forming, filling and sealing, a process in which each bag is produced from a flat cloth or film, forming a 20 tubular film therefrom, with a longitudinal joint, and subsequently flattening the tubular film in a first position and cross-sealing the tubular film in the flattened position, flattening the film 25 tubular, above the predetermined amount '^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^ of fluid material, in a second position, the process is characterized by the improvement comprising using the film claimed in claim 1 and operating the process at machine speeds Above 100 bags per minute. 10 fifteen twenty 25 = f a __________________ ^^^^^^^^^^^^^^^ j ^^^^^^^ ^ ^^^^^^^ G ^ M ^ feM ^^^^ M SUMMARY OF THE INVENTION A bag for containing a fluid material, the bag is made from a tubular shaped film and having thermosel sides transversely, wherein the film comprises at least one layer produced from a material comprising from about 70 to approximately 100 10 parts of at least one interpolymer of ethylene and an alpha-olefin of 3 to 20 carbon atoms, having a density of 0.840 g / cm3 to 0.940 g / cm3 and a melt index of 0.01 to 2.0 dg / minute, and from about 0 to about 30 15 parts by weight of at least one high pressure polyethylene having a density of at least about 0.916 g / cm 3 and a melt index of from about 0.01 to about 2 dg / mm, the film has a strength of 20 global melt from about 10 to about 15 CentiNewtons, determined using a Goettfert Rheotens unit at 190 °, and the integrity of the transverse joint of the bag is such that the proportion of the frequency of points 25 flight for the bags, measured in terms of 10,000 bags produced, is substantially reduced, compared to the leakage frequency ratio, for bags produced from films that have a melt strength that is outside the specified range. A process to manufacture these bags is also described.